Vance G Nielsen
- Professor, Anesthesiology
- University of Southern California College of Medicine, Los Angeles, California, United States
- Loyola Marymount University, Los Angeles, California, United States
- University of Arizona College of Medicine, Tucson, Arizona (2012 - Ongoing)
Licensure & Certification
- License, Arizona State Medical Board (2011)
- Certification, American Board of Anesthesiology (1992)
- Certification, National Board of Medical Examiners (1988)
- License, Pennsylvania State Medical Board (2008)
- License, Alabama State Medical Board (1988)
Cardiothoracic Anesthesiology; Coagulation; Fibrinolysis
Heme oxygenase mediated hypercoagulability; snake venom effects on coagulation; effects of iron and carbon monoxide on coagulation.
No activities entered.
- Johnson, T. E., Wells, R. J., Bell, A., Nielsen, V. G., & Olver, C. S. (2019). Carbon monoxide releasing molecule enhances coagulation and decreases fibrinolysis in canine plasma exposed to Crotalus viridis venom in vitro and in vivo. Basic & clinical pharmacology & toxicology, 125(4), 328-336.More infoCarbon monoxide releasing molecule-2 (CORM-2), an emerging therapeutic in human medicine, enhances plasmatic coagulation and attenuates fibrinolysis in vitro in human, rabbit and horse plasma and ameliorates hypocoagulation and hyperfibrinolysis secondary to venom exposure in human plasma in vitro. Fibrinogenases in rattlesnake venom cause decreased clot strength, and in the presence of tissue plasminogen activator (tPA) in vitro, a markedly increased rate of clot lysis. CO interacts with a haem group on fibrinogen, changing its configuration so that the fibrin clot is strengthened and more resistant to fibrinolysis. We hypothesized that CORM-2 enhances coagulation and attenuates fibrinolysis in canine plasma exposed to C viridis venom. We measured the effects of C viridis venom on clot strength, rates of coagulation and fibrinolysis in both pooled canine plasma and plasma from individual naturally envenomed dogs, with and without CORM-2, using thromboelastography (TEG). We tested venom effects on coagulation using tissue factor (TF) activated TEG and on both coagulation and fibrinolysis using TF-activated TEG with added tPA. We found that 17.9 µg/mL of venom causes a mean 26.4% decrease in clot strength, a 61.8% decrease in maximum rate of thrombus generation, 75% faster clot lysis, a 226% increase in maximum rate of lysis and a 92% decrease in total clot life span (CLS). CORM-2 ameliorated these effects, increasing CLS in the presence of venom by 603%. Additionally, we showed that CORM-2 has similar effects in vitro on plasma from naturally envenomed dogs, showing promise as an adjunct therapy for snake envenomation.
- Nielsen, V. G. (2019). Carbon monoxide inhibits the anticoagulant activity of Mojave rattlesnake venoms type A and B. Journal of thrombosis and thrombolysis, 48(2), 256-262.More infoThe Mojave rattlesnake is a unique species of pit viper that expresses either a highly potent phospholipase A (PLA)-dependent neurotoxin containing venom nearly devoid of fibrinogenolytic metalloproteinases (venom type A) or a hemotoxic venom with a high percentage of metalloproteinases and PLA without any neurotoxin present (venom type B) depending on its geographical location in the Southwestern United States and Mexico. Given that PLA have been demonstrated to affect coagulation, it was hypothesized that the anticoagulant effects of both type A and B venoms could be assessed by thrombelastography, and determination made if these venoms were heme modulated. Both venom types were exposed to carbon monoxide releasing molecule-2 or its inactivated molecule (0 or 100 µM) in isolation and then placed in human plasma with consequent coagulation kinetics assessed by thrombelastography. It was determined that type A venom was twice as potent as an anticoagulant compared to type B venom, and that both venoms were inhibited by carbon monoxide releasing molecule-2 but not its inactivated molecule. Given the lack of proteolytic activity of type A venom and the dependence of neurotoxicity on PLA activity, it may be possible that carbon monoxide could inhibit neurotoxicity based on inhibition of PLA anticoagulant activity. These data may serve as the rationale for extension of these observations into animal models to determine if CO may inhibit not just hemotoxic venom, but also PLA-dependent neurotoxic venom.
- Nielsen, V. G. (2019). Characterization of L-amino Acid Oxidase Derived from Venom: Procoagulant and Anticoagulant Activities. International journal of molecular sciences, 20(19).More infoSnake venom enzymes of the L-amino acid oxidase (LAAO) class are responsible for tissue hemorrhage, edema, and derangement of platelet function. However, what role, if any, these flavoenzymes play in altering plasmatic coagulation have not been well defined. Using coagulation kinetomic analyses (thrombelastograph-based), it was determined that the LAAO derived from venom displayed a procoagulant activity associated with weak clot strength (no factor XIII activation) similar to thrombin-like enzymes. The procoagulant activity was not modified in the presence of reduced glutathione, demonstrating that the procoagulant activity was likely due to deamination, and not hydrogen peroxide generation by the LAAO. Further, unlike the raw venom of the same species, the purified LAAO was not inhibited by carbon monoxide releasing molecule-2 (CORM-2). Lastly, exposure of the enzyme to phenylmethylsulfonyl fluoride (PMSF) resulted in the LAAO expressing anticoagulant activity, preventing contact activation generated thrombin from forming a clot. In sum, this investigation for the first time characterized the LAAO of a snake venom as both a fibrinogen polymerizing and an anticoagulant enzyme acting via oxidative deamination and not proteolysis as is the case with thrombin-like enzymes (e.g., serine proteases). Using this thrombelastographic approach, future investigation of purified enzymes can define their biochemical nature.
- Nielsen, V. G. (2019). Lethal concentrations of mercury or lead do not affect coagulation kinetics in human plasma. Journal of thrombosis and thrombolysis, 48(4), 697-698.
- Nielsen, V. G. (2019). The anticoagulant effect of Apis mellifera phospholipase A is inhibited by CORM-2 via a carbon monoxide-independent mechanism. Journal of thrombosis and thrombolysis.More infoBee venom phospholipase A (PLA) has potential for significant morbidity. Ruthenium (Ru)-based carbon monoxide releasing molecules (CORM) inhibit snake venoms that are anticoagulant and contain PLA. In addition to modulating heme-bearing proteins with carbon monoxide, these CORM generate reactive Ru species that form adducts with histamine residues resulting in changes in protein function. This study sought to identify anticoagulant properties of bee venom PLA via catalysis of plasma phospholipids required for thrombin generation. Another goal was to determine if Ru-based CORM inhibit bee venom PLA via carbon monoxide release or via potential binding of reactive Ru species to a key histidine residue in the catalytic site of the enzyme. Anticoagulant activity of bee venom PLA was assessed via thrombelastography with normal plasma. Bee venom PLA was then exposed to different CORM and a metheme forming agent and anticoagulant activity was reassessed. Using Ru, boron and manganese-based CORM and a metheme forming agent, it was demonstrated that it was unlikely that carbon monoxide interaction with a heme group attached to PLA was responsible for inhibition of anticoagulant activity by Ru-based CORM. Exposure of PLA to a Ru-based CORM in the presence of histidine-rich human albumin resulted in loss of inhibition of PLA. Ru-based CORM likely inhibit bee venom PLA anticoagulant activity via formation of reactive Ru species that bind to histidine residues of the enzyme.
- Nielsen, V. G., & Frank, N. (2019). The kallikrein-like activity of Heloderma venom is inhibited by carbon monoxide. Journal of thrombosis and thrombolysis, 47(4), 533-539.More infoLizards in the genus Heloderma are the most ancient venomous reptiles, with a traceable lineage nearly 100 million years old. The proteome of the venom of three of the remaining species (Heloderma suspectum, H. exasperatum, H. horridum) are very conserved, with kallikrein-like activity present to cause critical hypotension to immobilize and outright kill prey. Kallikrein-like activity would be expected to activate the contact protein pathway of coagulation, which would be detectable with thrombelastography in human plasma. Thus, it was proposed to determine if kallikrein-like activity could be detected with thrombelastography, and if this activity could be inhibited by carbon monoxide (CO) via a putative heme-based mechanism. Procoagulant activity of each venom was assessed via thrombelastography with normal plasma, and kallikrein-like activity confirmed with FX-depleted plasma. Venom was then exposed to carbon monoxide releasing molecule-2 (CORM-2) or its inactive releasing molecule to assess CO inhibition. All three venoms demonstrated kallikrein-like activity with the same potency and inhibition of activity by CO. In conclusion, the present work documented that procoagulant, kallikrein-like activity containing venoms of the oldest species of venomous reptiles was inhibited by CO, potentially via heme modulation. This is also the first identification and characterization of a kallikrein-like enzyme utilizing coagulation factor-depleted plasma to assess venom that inflicts hypotension. Future investigations will continue to define the vulnerability of venom enzymatic activities to CO.
- Nielsen, V. G., Frank, N., & Afshar, S. (2019). De Novo Assessment and Review of Pan-American Pit Viper Anticoagulant and Procoagulant Venom Activities via Kinetomic Analyses. Toxins, 11(2).More infoSnakebite with hemotoxic venom continues to be a major source of morbidity and mortality worldwide. Our laboratory has characterized the coagulopathy that occurs in vitro in human plasma via specialized thrombelastographic methods to determine if venoms are predominantly anticoagulant or procoagulant in nature. Further, the exposure of venoms to carbon monoxide (CO) or -phenylhydroxylamine (PHA) modulate putative heme groups attached to key enzymes has also provided mechanistic insight into the multiple different activities contained in one venom. The present investigation used these techniques to characterize fourteen different venoms obtained from snakes from North, Central, and South America. Further, we review and present previous thrombelastographic-based analyses of eighteen other species from the Americas. Venoms were found to be anticoagulant and procoagulant (thrombin-like activity, thrombin-generating activity). All prospectively assessed venom activities were determined to be heme-modulated except two, wherein both CO and its carrier molecule were found to inhibit activity, while PHA did not affect activity ( and ). When divided by continent, North and Central America contained venoms with mostly anticoagulant activities, several thrombin-like activities, with only two thrombin-generating activity containing venoms. In contrast, most venoms with thrombin-generating activity were located in South America, derived from species. In conclusion, the kinetomic profiles of venoms obtained from thirty-two Pan-American Pit Viper species are presented. It is anticipated that this approach will be utilized to identify clinically relevant hemotoxic venom enzymatic activity and assess the efficacy of locally delivered CO or systemically administered antivenoms.
- Nielsen, V. G., Frank, N., & Turchioe, B. J. (2019). Anticoagulant activity of krait, coral snake, and cobra neurotoxic venoms with diverse proteomes are inhibited by carbon monoxide. Blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis, 30(8), 379-384.More infoA phenomena of interest is the in vitro anticoagulant effects of neurotoxins found in elapid venoms that kill by paralysis. These enzymes include phospholipase A2 (PLA2), and it has recently been demonstrated that carbon monoxide inhibits the PLA2-dependent neurotoxin contained in Mojave rattlesnake type A venom. The purpose of this investigation was to assess if the anticoagulant activity of elapid venoms containing PLA2 and/or three finger toxins could be inhibited by carbon monoxide.
- Donaghy, D., Yoo, S., Johnson, T., Nielsen, V., & Olver, C. (2018). Carbon Monoxide-Releasing Molecule Enhances Coagulation and Decreases Fibrinolysis in Normal Canine Plasma. Basic & clinical pharmacology & toxicology, 123(3), 257-262.More infoThe dog is an important companion animal and also purpose-bred for research studies. Coagulopathies in dogs are common, although the availability of blood products for therapy is inconsistent throughout the profession. A pro-coagulant therapeutic that is readily available and easily stored would be useful for the treatment of coagulopathies. Tricarbonyldichlororuthenium (II) dimer [Carbon monoxide-releasing molecule-2 (CORM-2)] acts as a prothrombotic agent in plasma by increasing the velocity of clot formation and clot strength, and by decreasing the clot's vulnerability to fibrinolysis. We sought to test CORM-2's effect on coagulation and fibrinolysis in vitro in canine plasma using thromboelastography. Measures of the rate of clot formation and clot strength in plasma without CORM-2 were highly correlated with fibrinogen concentration. We found that CORM-2 significantly enhanced the rate of clot formation and clot strength and significantly reduced the rate of fibrinolysis and the clot lysis time. The per cent change in rate of clot formation and clot strength was not significantly correlated with fibrinogen concentration, indicating that CORM-2's pro-coagulant effect is not dependent on fibrinogen concentration. This study corroborates studies in other species that show that CORM-2 is pro-coagulant in plasma, and lays the groundwork for developing CORM-2 as a therapeutic agent for canine coagulopathies. Future studies will evaluate the effect of CORM-2 on whole blood both in vitro and in vivo.
- Nielsen, V. G. (2018). Carbon monoxide inhibits the anticoagulant activity of phospholipase A purified from Crotalus adamanteus venom. Journal of thrombosis and thrombolysis.More infoSnake venom contains a myriad of classes of enzyme which have been investigated for medicinal and toxinological purposes, including phospholipase A (PLA), which is responsible for anticoagulant, myotoxic and neurotoxic effects. Given the importance of PLA, the purposes of the present investigation were to characterize the coagulation kinetic behavior of a PLA purified from Crotalus adamanteus venom (Ca-PLA) in human plasma with thrombelastography and determine if carbon monoxide could inhibit its activity. Coagulation kinetics were determined in human plasma with a range of Ca-PLA activity (0-2 U/ml) via thrombelastography. Then, using carbon monoxide releasing molecule-2 or its inactivated molecule (0 or 100 µM), the vulnerability of Ca-PLA activity to carbon monoxide mediated inhibition was assessed. Lastly, the inhibitory response of Ca-PLA activity to exposure to carbon monoxide releasing molecule-2 (0-100 µM) was determined. Ca-PLA activity degraded the velocity of clot growth and clot strength in an activity dependent, exponential manner. Carbon monoxide inhibited Ca-PLA activity in a concentration dependent fashion, with loss of detectable activity at 100 µM of carbon monoxide releasing molecule-2. These findings, while preliminary, open the possibility that other PLA contained in snake venom with multiple toxicities (e.g., myotoxin, neurotoxin) may be heme bearing and CO-inhibitable, which have profound potential basic and clinical science implications.
- Nielsen, V. G. (2018). Crotalus atrox Venom Exposed to Carbon Monoxide Has Decreased Fibrinogenolytic Activity In Vivo in Rabbits. Basic & clinical pharmacology & toxicology, 122(1), 82-86.More infoEnvenomation by haemotoxic enzymes remains a significant source of human morbidity and mortality worldwide, with administration of long-acting or multiple doses of antivenom first-line therapy. However, coagulopathy can still occur and recur. Of interest, it has been recently demonstrated that direct, isolated exposure of snake venom enzymes with fibrinogenolytic activity to carbon monoxide (CO) abrogates venom-mediated loss of coagulation in human plasma. These observations of CO inhibition of venom fibrinogenolytic activity were subsequently repeated in rabbit whole blood. This study sought to translate these findings in an in vivo rabbit model of envenomation with fibrinogenolytic Crotalus atrox venom. Sedated rabbits were intravenously administered C. atrox venom (400 μg/kg) pre-exposed to 0 or 1000 μM carbon monoxide-releasing molecule-2 (CORM-2) in vitro. Arterial whole-blood samples demonstrated that compared to pre-envenomation values, the CORM-2-naïve venom significantly prolonged the onset of coagulation, decreased the velocity of clot growth and decreased clot strength as determined by thromboelastography an hour after venom injection. In contrast, CORM-2 pre-exposure prevented or attenuated C. atrox venom effects on coagulation kinetics. Future studies to determine whether rabbits injected with such venom subcutaneously/intramuscularly can have consequent coagulopathy abrogated by injection of carbon monoxide-releasing molecules into the 'bite site' are justified.
- Nielsen, V. G., & Ford, P. M. (2018). The ratio of concentrations of aminocaproic acid and tranexamic acid that prevent plasmin activation of platelets does not provide equivalent inhibition of plasmatic fibrinolysis. Journal of thrombosis and thrombolysis.More infoAminocaproic acid (EACA) availability has recently been decreased whereas tranexamic acid (TXA) is still available as an antifibrinolytic agent to decrease blood loss associated with procedures involving cardiopulmonary bypass (CPB) by inhibiting plasmin mediated platelet activation. Given that the clinical inclination is to substitute TXA for EACA, we sought to compare the antifibrinolytic efficacy of the two agents using the clinically accepted molar ratio of EACA:TXA (7.9:1) that prevents platelet activation in a viscoelastic based system under a variety of conditions in human plasma; 25-50% therapeutic concentration (EACA 32.5-65 µg/ml, TXA 5-10 µg/ml) in the presence of 1500-3000 IU tissue-type plasminogen activator, with 0-50% dilution of plasma with buffer. In all equipotent concentrations, TXA provided superior antifibrinolytic action compared to EACA. It is hoped that this work will serve as a rationale to further investigate these and other similar agents, especially now in a time of unpredictable unavailability of key medications needed to optimize patient care. It is also our wish that these data assist perfusionists, anesthesiologists and cardiothoracic surgeons with their consideration of using an antifibrinolytic agent when managing complex patients with hypercoagulable states (e.g., ventricular assist device explant, infective endocarditis) undergoing CPB.
- Nielsen, V. G., & Frank, N. (2018). Differential heme-mediated modulation of Deinagkistrodon, Dispholidus, Protobothrops and Pseudonaja hemotoxic venom activity in human plasma. Biometals : an international journal on the role of metal ions in biology, biochemistry, and medicine, 31(6), 951-959.More infoEnvenomation by vipers with hemotoxic enzymes continues to be a worldwide source of morbidity and mortality. The present work examined the effects of exposure of venom enzymes to carbon monoxide and O-phenylhydroxylamine, agents that modulate the biometal heme, by forming carboxyheme and metheme, respectively. Four venoms obtained from medically important, diverse snake venom found in Africa, Asia and Australia were analyzed. The species that had venom tested in human plasma with thrombelastography and heme modulating agents were Deinagkistrodon acutus, Protobothrops mucrosquamatus, Dispholidus typus and Pseudonaja textilis. These venoms varied four hundred-fold in potency (ng-µg/ml) to exert procoagulant effects on human plasma; further, there was species specific variability in venom inhibition after exposure to carboxyheme or metheme agents. Lastly, using a wide range of carbon monoxide concentrations, it was determined that the factor V component of P. textilis venom was likely inhibited before the factor X component. Further investigation using this thrombelastograph-based, venom "kinetomic" methodology involving heme modulation will demonstrate in time its laboratory and clinical utility.
- Nielsen, V. G., & Frank, N. (2018). Role of heme modulation in inhibition of Atheris, Atractaspis, Causus, Cerastes, Echis, and Macrovipera hemotoxic venom activity. Human & experimental toxicology, 960327118793186.More infoVenomous snake bite and subsequent coagulopathy is a significant source of morbidity and mortality worldwide. The gold standard to treat coagulopathy caused by these venoms is the administration of antivenom; however, despite this therapy, coagulopathy still occurs and recurs. Of interest, our laboratory has demonstrated in vitro and in vivo that coagulopathy-inducing venom exposed to carbon monoxide (CO) is inhibited, potentially by an attached heme. The present investigation sought to determine if venoms derived from snakes of the African genera Atheris, Atractaspis, Causus, Cerastes, Echis, and Macrovipera that have no or limited antivenoms available could be inhibited with CO or with the metheme-inducing agent, O-phenylhydroxylamine (PHA). Assessing changes in coagulation kinetics of human plasma with thrombelastography, venoms were exposed in isolation to CO or PHA. Eight species were found to have procoagulant activity consistent with the generation of human thrombin, while one was likely fibrinogenolytic. All venoms were significantly inhibited by CO/PHA with species-specific variation noted. These data demonstrate indirectly that the heme is likely bound to these disparate venoms as an intermediary modulatory molecule. In conclusion, future investigation is warranted to determine if heme could serve as a potential therapeutic target to be modulated during treatment of envenomation by hemotoxic enzymes.
- Nielsen, V. G., Frank, N., & Matika, R. W. (2018). Carbon monoxide inhibits hemotoxic activity of Elapidae venoms: potential role of heme. Biometals : an international journal on the role of metal ions in biology, biochemistry, and medicine, 31(1), 51-59.More infoEnvenomation by hemotoxic enzymes continues to be a major cause of morbidity and mortality throughout the world. With regard to treatment, the gold standard to abrogate coagulopathy caused by these venoms is still the administration of antivenom; however, despite antivenom therapy, coagulopathy still occurs and recurs. Of interest, this laboratory has demonstrated in vitro and in vivo that coagulopathy inducing venom derived from snakes of the family Viperidae exposed to carbon monoxide (CO) is inhibited, potentially by an attached heme. The present investigation sought to determine if venoms derived from snakes of the Elapidae family (taipans and cobras) could also be inhibited with CO or with the metheme inducing agent, O-phenylhydroxylamine (PHA). Assessing changes in coagulation kinetics of human plasma with thrombelastography, venoms from Elapidae snakes were exposed in isolation to CO (five species) or PHA (one specie) and placed in human plasma to assess changes in procoagulant or anticoagulant activity. The procoagulant activity of two taipan venoms and anticoagulant activity of three cobra venoms were significantly inhibited by CO. The venom of the inland taipan was also inhibited by PHA. In sum, these data demonstrate indirectly that the biometal heme is likely bound to these disparate venoms as an intermediary modulatory molecule. In conclusion, CO may not just be a potential therapeutic agent to treat envenomation but also may be a potential modulator of heme as a protective mechanism for venomous snakes against injury from their own proteolytic venoms.
- Nielsen, V. G., Frank, N., & Matika, R. W. (2018). Effects of Heme Modulation on and Venom Activity in Human Plasma. Toxins, 10(8).More infoGeographic isolation and other factors result in evolution-driven diversity of the enzymatic composition of venom of pit vipers in the same genus. The present investigation sought to characterize venoms obtained from such genetically diverse and pit vipers utilizing thrombelastographic coagulation kinetic analyses. The coagulation kinetics of human plasma were assessed after exposure to venom obtained from two and three species. The potency of each venom was defined (µg/mL required to equivalently change coagulation); additionally, venoms were exposed to carbon monoxide (CO) or a metheme-inducing agent to modulate any enzyme-associated heme. All venoms had fibrinogenolytic activity, with four being CO-inhibitable. While venoms had similar potency, one demonstrated the presence of a thrombin-like activity, whereas the other demonstrated a thrombin-generating activity. There was a 10-fold difference in potency and 10-fold different vulnerability to CO inhibition between the species. Metheme formation enhanced fibrinogenolytic-like activity in both species venoms, whereas the three species venoms had fibrinogenolytic-like activity enhanced, inhibited, or not changed. This novel "venom kinetomic" approach has potential to identify clinically relevant enzymatic activity and assess efficacy of antivenoms between genetically and geographically diverse species.
- Nielsen, V. G., Sanchez, E. E., Langlais, P. R., & Suntravat, M. (2018). CatroxMP-II: a heme-modulated fibrinogenolytic metalloproteinase isolated from Crotalus atrox venom.. Biometals.
- Nielsen, V. G., Sánchez, E. E., & Redford, D. T. (2018). Characterization of the Rabbit as an In Vitro and In Vivo Model to Assess the Effects of Fibrinogenolytic Activity of Snake Venom on Coagulation. Basic & clinical pharmacology & toxicology, 122(1), 157-164.More infoSeveral in vitro investigations have demonstrated that anticoagulant effects of fibrinogenolytic snake venom metalloproteinases have been abrogated in human plasma by modifying fibrinogen with iron (Fe) and carbon monoxide (CO) to prevent catalysis or by directly inhibiting these enzymes with CO. To translate these findings, we chose to assess the rabbit as a model of envenomation with Crotalus atrox venom. It was determined with thrombelastography that 15 times the concentration of venom noted to compromise coagulation in plasma in vitro was required to cause coagulopathy in vivo, likely secondary to venom binding to blood cells and being cleared from the circulation rapidly. Unlike human plasma, rabbit plasma pre-treated with Fe/CO was not protected from fibrinogenolysis by venom. Consequently, the administration of purified human fibrinogen (with or without Fe/CO) would be required before venom administration to rabbits. Of greater interest, venom exposed to CO had complete loss of fibrinogenolytic effect in rabbit plasma and partial loss of activity in whole blood, indicative of unbinding of CO from venom and binding to haemoglobin. Thus, venom exposed to CO could remain partially or completely inhibited in whole blood long enough for clearance from the circulation, allowing rabbits to be a useful model to test the efficacy of regional CO administration to the bite site. Future investigations are planned to test these novel approaches to attenuate venom-mediated coagulopathy in the rabbit.
- Nielsen, V. G., Ward, T. D., & Ford, P. M. (2018). Effects of cupric chloride on coagulation in human plasma: role of fibrinogen. Journal of thrombosis and thrombolysis.More infoCopper poisoning is associated with severe multiorgan injury and potentially death if chelation therapy is not administered. Of interest, while important gastrointestinal and urinary tract hemorrhage is associated with copper poisoning, very little is known concerning the nature of copper induced coagulopathy.
- Suntravat, M., Langlais, P. R., Sánchez, E. E., & Nielsen, V. G. (2018). CatroxMP-II: a heme-modulated fibrinogenolytic metalloproteinase isolated from Crotalus atrox venom. Biometals : an international journal on the role of metal ions in biology, biochemistry, and medicine.More infoIt has been recently demonstrated that the hemotoxic venom activity of several species of snakes can be inhibited by carbon monoxide (CO) or a metheme forming agent. These and other data suggest that the biometal, heme, may be attached to venom enzymes and may be modulated by CO. A novel fibrinogenolytic metalloproteinase, named CatroxMP-II, was isolated and purified from the venom of a Crotalus atrox viper, and subjected to proteolysis and mass spectroscopy. An ion similar to the predicted singly charged m/z of heme at 617.18 was identified. Lastly, CORM-2 (tricarbonyldichlororuthenium (II) dimer, a CO releasing molecule) inhibited the fibrinogenolytic effects of CatroxMP-II on coagulation kinetics in human plasma. In conclusion, we present the first example of a snake venom metalloproteinase that is heme-bound and CO-inhibited.
- Yu, S., Khalpey, Z. I., Wong, R. K., Huynh, T., & Nielsen, V. G. (2018). Complete antithrombin replacement for anticoagulation for cardiopulmonary bypass to repair severe infective mitral valve endocarditis. Blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis, 29(1), 123-125.More info: We present a case of a 26-year-old patient with severe infective endocarditis complicated with cerebral septic emboli that required essentially complete replacement of his circulating antithrombin activity to achieve an activated coagulation time near 480 s. The need for this degree of antithrombin administration may have been secondary to ongoing systemic inflammation and consequent thrombin generation despite blood culture results demonstrating no bacteremia. In sum, ongoing loss of endogenous antithrombin activity secondary to inflammation and the need for more than 80% normal activity to conduct safe cardiopulmonary bypass may require extraordinary administration of exogenous antithrombin in similar settings.
- Acevedo, F. A., Kim, E. J., Chyatte, D. A., & Nielsen, V. G. (2017). Rare cause of delirium and hypoxemia after coronary bypass surgery: transdermal lidocaine patch-associated methemoglobinemia. International journal of legal medicine.More infoWe present a case of a patient administered parasternal transdermal lidocaine patch therapy as part of a multimodal analgesic regime designed to diminish opioid-associated delirium after coronary bypass surgery. The patient presented with delirium and severe methemoglobinemia (41%) that responded to discontinuation of lidocaine therapy, oxygen administration, and methylene blue administration. The clinical contributors and medicolegal implications of this degree of lidocaine-associated methemoglobin-mediated delirium are presented in the hope of avoiding similar complications in the postoperative setting after coronary bypass surgery.
- Nielsen, V. G. (2017). Effects of purified human fibrinogen modified with carbon monoxide and iron on coagulation in rabbits injected with Crotalus atrox venom. Journal of thrombosis and thrombolysis, 44(4), 481-488.More infoWhile snake venom derived enzymes, such as the thrombin-like activity possessing ancrod, have been used to treat thrombotic disease by defibrinogenating patients, the therapeutic potential of fibrinogenolytic snake venom enzymes, such as those derived from Crotalus atrox, have not been fully explored. However, one of the potential risks of administering fibrinogenolytic enzymes to effect defibrinogenation is hemorrhage secondary to hypofibrinogenemia. The present investigation sought to determine if human fibrinogen modified with carbon monoxide (CO) and iron (Fe) could resist degradation by C. atrox venom as has been seen in vitro in a recently developed rabbit model of envenomation. Compared with unmodified human fibrinogen, CO/Fe modified fibrinogen administered prior to envenomation had significantly shorter onset of coagulation and greater strength; however, when administered after envenomation, there was no differences between the two types of fibrinogen. Of interest, when administered after envenomation, both types of fibrinogen delayed the onset of coagulation while increasing plasma clot strength, a mixed effect likely secondary to formation of fibrinogen degradation products. Further preclinical investigations are needed to further define the benefits and risks of the use of fibrinogenolytic enzymes as defibrinogenating agents, as well as the risks of the "biochemical brakes" used to modulate the activity or substrate of the fibrinogenolytic enzyme.
- Nielsen, V. G., & Bazzell, C. M. (2017). Carbon monoxide releasing molecule-2 inhibition of snake venom thrombin-like activity: novel biochemical "brake"?. Journal of thrombosis and thrombolysis, 43(2), 203-208.More infoA complication of defibrinogenation therapy with snake venom enzymes such as ancrod is hypofibrinogenemia associated bleeding secondary to no human-derived inhibitor being available to inactivate or diminish the activity of such enzymes. Of interest, ancrod contains a critical histidine residue without which enzymatic activity is inhibited, and carbon monoxide has been demonstrated to inhibit biomolecular function by interacting with histidine moieties in ion channels. We tested the hypothesis that exposure of three different snake venoms containing serine proteases with thrombin-like activity (which included ancrod) to carbon monoxide derived from carbon monoxide releasing molecule-2 would diminish their effects on plasmatic coagulation as assessed by thrombelastography. In the case of the Malayan pit viper and Eastern diamondback rattlesnake venoms, carbon monoxide diminished the effects of thrombin-like activity. In contrast, timber rattlesnake venom demonstrated enhancement of "thrombin-generating" activity with simultaneous loss of thrombin-like activity in response to carbon monoxide exposure. These findings may serve as the rational basis for not just continuing to investigate the potential of snake venom enzymes as clinical defibrinogenating agents, but to also to assess the potential to stop such agents from becoming a catalytic "runaway train" by judicious application of a biochemical "brake" such as carbon monoxide.
- Nielsen, V. G., & Losada, P. A. (2017). Direct Inhibitory Effects of Carbon Monoxide on Six Venoms Containing Fibrinogenolytic Metalloproteinases. Basic & clinical pharmacology & toxicology, 120(2), 207-212.More infoSince the introduction of antivenom administration over a century ago to treat venomous snake bite, it has been the most effective therapy for saving life and limb. However, this treatment is not always effective and not without potential life-threatening side effects. We tested a new paradigm to abrogate the plasmatic anticoagulant effects of fibrinogenolytic snake venom metalloproteinases (SVMP) by inhibiting these Zn+2 -dependent enzymes directly with carbon monoxide (CO) exposure. Assessment of the fibrinogenolytic effects of venoms collected from the Arizona black rattlesnake, Northern Pacific rattlesnake, Western cottonmouth, Eastern cottonmouth, Broad-banded copperhead and Southern copperhead on human plasmatic coagulation kinetics was performed with thrombelastography in vitro. Isolated exposure of all but one venom (Southern copperhead) to CO significantly decreased the ability of the venoms to compromise coagulation. These results demonstrated that direct inhibition of transition metal-containing venom enzymes by yet to be elucidated mechanisms (e.g. CO, binding to Zn+2 or displacing Zn+2 from the catalytic site, CO binding to histidine residues) can in many instances significantly decrease fibrinogenolytic activity. This new paradigm of CO-based inhibition of the anticoagulant effects of SVMP could potentially diminish haemostatic compromise in envenomed patients until antivenom can be administered.
- Nielsen, V. G., & Matika, R. W. (2017). Effects of iron and carbon monoxide on Lachesis muta muta venom-mediated degradation of plasmatic coagulation. Human & experimental toxicology, 36(7), 727-733.More infoHypofibrinogenemia is an important clinical consequence following envenomation by Lachesis muta muta, usually attenuated or prevented by administration of antivenom. The venom of L. m. muta contains both a metalloproteinase fibrinogenase and a serine protease thrombin-like enzyme, and exposure of fibrinogen to iron (Fe) and carbon monoxide (CO) has been demonstrated to decrease its catalysis by such enzymes. Using thrombelastographic analytical techniques, it was determined that this venom displayed weak procoagulant effects combined with fibrinogenolytic effects, and pretreatment of plasma with Fe and CO markedly attenuated venom-mediated effects. Additional experiments involving heparin exposure and varying calcium concentrations demonstrated that modification of fibrinogen with Fe and CO in human plasma rendered fibrinogen not recognizable to the fibrinogenolytic metalloproteinase but did not prevent polymerization by the thrombin-like serine protease. Lastly, when venom was exposed to CO in isolation and then placed in plasma, the fibrinogenase was inhibited but the thrombin-like enzyme was not inhibited. In sum, utilizing relatively facile modifications, we demonstrated with thrombelastography that Fe and/or CO addition can protect human plasmatic coagulation from fibrinogenase activity but not the effects of the thrombin-like activity of L. m. muta venom.
- Nielsen, V. G., Paidy, S. R., McLeod, W., Fox, A., & Nfonsam, V. N. (2017). Treatment of accidental perianal injection of topical thrombin with intravenous antithrombin. Journal of thrombosis and thrombolysis, 43(3), 423-425.More infoWhile topical thrombin application can markedly improve surgical hemostasis, rapid absorption of thrombin can result in pulmonary embolism and death. We report a case of accidental interstitial infiltration of topical thrombin after hemorrhoidectomy that was treated with administration of human antithrombin and heparin anticoagulation. Except for a marked decrease in antithrombin activity from super normal to normal values, the patient exhibited no laboratory or clinical signs of pulmonary embolism, thrombin mediated consumptive loss of procoagulants, or regional thrombosis. The patient had an uncomplicated recovery without sign of thrombotic morbidity. While it is hoped that such a medical misadventure should not occur, our case may serve as a reference to guide anticoagulant therapy if such a clinical scenario arises.
- Nielsen, V. G., Paidy, S. R., Meek, C. A., Thornton, T. K., & Lick, S. D. (2017). Survival after intravenous thrombin prior to cardiopulmonary bypass. International journal of legal medicine, 131(2), 485-487.More infoWe present a case of a patient undergoing aortic valve replacement being inadvertently administered 5000 U of bovine thrombin instead of heparin for anticoagulation for cardiopulmonary bypass. The labeling error was made within the operating room pharmacy. The key to survival of this patient was a rapid diagnosis, administration of antithrombin and heparin, and removal of cardiac and great vessel thrombi. It is recommended that point of care anesthesia providers `prepare heparin for cardiopulmonary bypass anticoagulation, as thrombin is not used in anesthetic practice and is not contained within anesthesia cabinet medication drawers.
- Olver, C. S., & Nielsen, V. G. (2017). Iron protects porcine plasma coagulation kinetics from degradation by Crotalus atrox venom. Biometals : an international journal on the role of metal ions in biology, biochemistry, and medicine, 30(5), 677-683.More infoWhile the administration of antivenom to treat hemotoxic snake bite injury remains the gold standard of therapy, we have demonstrated that modifying human fibrinogen with iron and carbon monoxide renders it resistant to fibrinogenolytic snake venom enzymes. In order to translate these findings into a possible biometal-based therapy complementary to antivenom administration, a preclinical model that possesses fibrinogen that closely mimics the human molecule in response to iron and carbon monoxide needed to be identified. The goal of this investigation was to determine if a swine model could serve in this capacity by assessing the thrombelastographic response of porcine plasma to iron and carbon monoxide exposure, without or with further exposure to the fibrinogenolytic venom of the viper Crotalus atrox. Using plasma obtained from eight swine, it was determined that their plasma responded to iron and carbon monoxide in a manner similar to that of human plasma by displaying enhanced coagulation kinetics. However, in sharp contrast to the response seen with human plasma, only iron significantly protected porcine plasma coagulation kinetics from C. atrox venom degradation. Therefore the pig is an animal beyond humans that could derive benefit from the biometal-focused therapy of iron infusion to protect against venom mediated compromise of coagulation. Thus, future investigation to assess the effects of iron administration to attenuate the effects of fibrinogenolytic envenomation with a pig model is justified.
- Swanepoel, A. C., Naidoo, P., Nielsen, V. G., & Pretorius, E. (2017). Clinical relevance of hypercoagulability and possible hypofibrinolysis associated with estrone and estriol. Microscopy research and technique, 80(7), 697-703.More infoEstrone (E1 ) and Estriol (E3 ) are endogenous female hormones, present in increased concentrations during female specific physiological processes (menopause and pregnancy respectively) that are associated with increased venous thrombotic risk. These hormones are also used as hormone therapies that are also associated with increased thromboembolism risk. Viscoelastic analysis revealed no significant difference to clot formation after hormone addition, however morphological analysis showed that the addition of both E1 and E3 result in fibrin clots composed of thinner fibrin fibers arranged in dense matted networks. These changes to the fibrin network ultrastructure are indicative of a prothrombotic state but may also indicate hypofibrinolysis. We therefore conclude that the increased risk of venous thrombosis during pregnancy and menopause may originate from a combination of hypercoagulation and a possible hypofibrinolytic mechanism of these hormones. Therefore females with a hypercoagulable tendency that fall pregnant or enter menopause need to be monitored to prevent venous thrombotic events. The decision to use hormone therapies during and after menopause should not be taken lightly and the risk-reward scale should be closely examined to ensure it does not tip towards thrombosis and subsequent thrombotic events that ultimately could have been prevented.
- Nielsen, V. (2016). The Contribution of Pin End-Cup Interactions to Clot Strength Assessed with Thrombelastography. Anesthesia and analgesia, 122(1), 43-5.More infoViscoelastic methods have been developed to assess the contribution of plasma proteins and platelets to coagulation in vitro to guide clinical transfusion therapy. One of the cardinal precepts of determining clot strength is making sure that the viscoelastic technique includes complete exposure of the plastic pin in the testing chamber with the fluid analyzed so as to assure maximal interaction of the cup wall with the pin surface. However, the various contributions of the pin surface area to final clot strength have not been investigated. That is, it is not clear what is more important in the in vitro determination of clot strength, the surface area shared between the cup and pin filled with fluid or the final viscoelastic resistance of the gel matrix formed. Thus, the purpose of this investigation was to determine the clot strength when only the tip of the pin was engaged with plasma thrombus and to compare these values with clot strength values obtained when the pin was completely in plasma. After determining the minimal amount of plasma required to cover a pin tip in a thrombelastographic system (30 μL), clot strength (elastic modulus, G) was determined in plasma samples of 30 or 360 μL final volume (n = 12 per condition) after tissue factor activation. The G value with 30 μL volume was 1057 ± 601 dynes/cm (mean ± SD; 95% confidence interval, 675-1439 dynes/cm), which was (P = 0.0015) smaller than the G value associated with 360-μL sample volumes, that was 1712 ± 48 dynes/cm (confidence interval, 1681-1742 dynes/cm). In conclusion, these data demonstrate that clot strength is not determined by a simple ratio of surface area of pin and cup to volume of sample, but rather strength is importantly influenced by the viscoelastic resistance of the fluid assessed.
- Nielsen, V. G., Boyer, L. V., Redford, D. T., & Ford, P. (2016). Thrombelastographic characterization of the thrombin-like activity of Crotalus simus and Bothrops asper venoms. Blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis.More infoAnnually, thousands suffer venomous snake-bite from Crotalus simus and Bothrops asper vipers in central and South America. The goals of the present study were to generally characterize the thrombin-like effects of venom from these snakes in human plasma with viscoelastic methods. Human plasma was exposed to the venom of three different C. simus subspecies and venoms obtained from B. asper vipers located in three different locations in Mexico. To characterize the factor X-activating and thrombin-like activity of these venoms, plasma (normal or factor XIII deficient) was pretreated with a variety of additives (e.g., heparin) in the absence or presence of calcium prior to exposure to 2.0 μg/ml of each viper's venom. These profiles were compared with plasma without venom that had contact activation of coagulation. Coagulation kinetics were determined with thrombelastography. All venoms had thrombin-like activity, with C. s. simus creating a slow growing, weak clot that was likely mediated by metalloproteinases. In contrast, B. asper venoms had rapid onset of coagulation and a high velocity of thrombus growth. Further, B. asper venom activity was calcium-independent, activated prothrombin, activated factor XIII, and independently polymerized fibrinogen. The viscoelastic methods used were able to differentiate subspecies of C. simus and specimens of B. asper, and provide insight into the mechanisms by which the venoms acted on plasma. These methods may be useful in the profiling of similar venoms and perhaps can assist in the assessment of interventions designed to treat envenomation (e.g., antivenom).
- Nielsen, V., & Jacobsen, W. (2016). Iron modulates the alpha chain of fibrinogen. Biometals : an international journal on the role of metal ions in biology, biochemistry, and medicine.More infoIron-bound fibrinogen has been noted to accelerate plasmatic coagulation in patients with divergent conditions involving upregulation of heme oxygenase activity, including hemodialysis, Alzheimer's disease, sickle cell anemia, and chronic migraine. Our goal was to determine if a site of iron-fibrinogen interaction was on the alpha chain. Using thrombelastography, we compared the coagulation kinetic profiles of plasma exposed to 0-10 µM ferric chloride after activation of coagulation with thrombin generated by contact activation of plasma with the plastic sample cup or by exposure to 1 µg/ml of Calloselasma rhodostoma venom (rich in ancrod activity), which causes coagulation via polymerization of alpha chain monomers. Venom mediated coagulation always occurred before thrombin activated thrombus formation, and ferric chloride always diminished the time of onset of coagulation and increased the velocity of clot growth. Iron enhances plasmatic coagulation kinetics by modulating the alpha chain of fibrinogen.
- Nielsen, V., Redford, D., & Boyle, P. (2016). Effect of iron and carbon monoxide on fibrinogenase-like degradation of plasmatic coagulation by venoms of four Crotalus species. Blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis.More infoAnnually, thousands suffer poisonous snake bite, often from defibrinogenating species. Iron and carbon monoxide (CO) improve coagulation kinetics by modulation of fibrinogen as demonstrated in various Agkistrodon species and Crotalus atrox. Thus, we sought to determine whether pretreatment of plasma with iron and CO could attenuate venom-mediated catalysis of fibrinogen obtained from four common Crotalus species with known fibrinogenase activity. Human plasma was pretreated with ferric chloride (0-10 μmol/l) and CO-releasing molecule-2 (0-100 μmol/l) prior to exposure to venom from a Northern Pacific rattlesnake, Arizona black rattlesnake, prairie rattlesnake, or red diamond rattlesnake. The concentration of venom used decreased coagulation function of one or more kinetic parameters by at least 50% of normal values. Coagulation kinetics were determined with thrombelastography.Three snake venoms significantly degraded plasmatic coagulation kinetics, prolonging the onset to clot formation, diminishing velocity of clot growth and decreasing clot strength. However, red diamond rattlesnake venom exposure resulted in mixed coagulation kinetics, significantly decreasing the time to onset of coagulation without decreasing the velocity of clot growth. Iron and CO attenuated these coagulation kinetic changes in a species-specific manner. Further in vitro investigation of other fibrinogenolytic venoms is indicated to determine if iron and CO can attenuate venom compromised coagulation.
- Faraoni, D., Van der Linden, P., Ducloy-Bouthors, A. S., Goobie, S. M., DiNardo, J. A., & Nielsen, V. G. (2015). Quantification of Fibrinolysis Using Velocity Curves Measured with Thromboelastometry in Children with Congenital Heart Disease. Anesthesia and analgesia, 121(2), 486-91.More infoIn this pilot study, we hypothesized that velocity parameters obtained from changes in clot amplitude (A) and clot elasticity (E) measured with thromboelastometry (ROTEM, Tem International GmbH, Munich, Germany) could improve detection of fibrinolysis in whole blood obtained from children undergoing surgery for congenital heart disease.
- N, S., Welsby, I. J., Fielder, M. A., Jacobsen, W. K., & Nielsen, V. G. (2015). Sickle cell disease is associated with iron mediated hypercoagulability. Journal of thrombosis and thrombolysis, 40(2), 182-5.More infoSickle cell disease (SCD) is associated with a significant hypercoagulable state and several hemostatic anomalies have been identified in this disease state. Of interest, SCD patients can become iron overloaded after transfusion, and iron can enhance fibrinogen as a substrate for thrombin, resulting in thrombi that commence coagulation quickly and form rapidly. We hypothesized that SCD patients would display hypercoagulable plasma coagulation kinetics and an iron enhancement of coagulation. After obtaining IRB approval, we assessed coagulation kinetics and iron enhancement with viscoelastic methods in archived, citrated plasma obtained from ambulatory or hospitalized SCD patients (n = 20). All SCD patients had plasmatic hypercoagulability, and 65 % were positive for iron enhancement of coagulation. In conclusion, continuing investigation correlating such viscoelastic data with clinical symptoms may provide insight into the role played by iron in the setting of SCD, including complications such as vaso-occlusive crisis.
- Nielsen, V. G. (2015). Iron and carbon monoxide prevent degradation of plasmatic coagulation by thrombin-like activity in rattlesnake venom. Human & experimental toxicology.More infoThousands suffer poisonous snake bite, often from defibrinogenating species annually. Three rattlesnake species in particular, the timber rattlesnake, Eastern diamondback rattlesnake, and Southern Pacific rattlesnake, cause clinically relevant hypofibrinogenemia via thrombin-like activity in their venom. It has been demonstrated that iron (Fe) and carbon monoxide (CO) change the ultrastructure of plasma thrombi and improve coagulation kinetics. Thus, the present investigation sought to determine if pretreatment of plasma with Fe and CO could attenuate venom-mediated catalysis of fibrinogen via thrombin-like activity. Human plasma was pretreated with ferric chloride (0-10 μM) and CO-releasing molecule-2 (0-100 μM) prior to exposure to 2.5-10 μg/ml of venom obtained from the aforementioned three species of rattlesnake. Coagulation kinetics were determined with thrombelastography. All three snake venoms degraded plasmatic coagulation kinetics to a significant extent, especially diminishing the speed of clot growth and strength. Pretreatment of plasma with Fe and CO completely abrogated the effects of all three venoms on coagulation kinetics. Further in vitro investigation of other pit viper venoms that possess thrombin-like activity is indicated to see if there is significant conservation of venom enzymatic target recognition of specific amino acid sequences such that Fe and CO can reliably attenuate venom-mediated catalysis of fibrinogen. These data also serve as a rationale for future preclinical investigation.
- Nielsen, V. G. (2015). Southern copperhead venom enhances tissue-type plasminogen activator induced fibrinolysis but does not directly lyse human plasma thrombi. Journal of thrombosis and thrombolysis.More infoIn addition to degrading fibrinogen as a source of consumptive coagulopathy, purified fractions of southern copperhead (Agkistrodon contortrix contortrix; A. c. contortrix) venom has been demonstrated to enhance fibrinolysis. The goal of this investigation was to characterize the kinetic fibrinolytic profile of A. c. contortrix venom in the absence and presence of tissue-type plasminogen activator (tPA) to determine if intact venom had tPA independent fibrinolytic properties. Utilizing thrombelastographic methods, the coagulation and fibrinolytic kinetic profiles of human plasma exposed to A. c. contortrix venom (0-6 μg/ml) were determined in the absence or presence of tPA (0-100 IU/ml). Then, plasma was exposed to 0-6 μg/ml of venom without tPA added and coagulation observed for 3 h. Venom significantly prolonged the onset of coagulation, decreased the velocity of thrombus growth but did not significantly decrease clot strength. In the presence of tPA, venom significantly decreased clot strength, shortened the time of onset of fibrinolysis, decreased clot lysis time but did not significantly affect the maximum rate of lysis. Lastly, while venom exposure in the absence of tPA significantly prolonged the onset of coagulation and decreased the velocity of clot growth, venom exposure did not result in detectable fibrinolysis over the 3 h observation period. A. c. contortrix venom enhances tPA mediated fibrinolysis by degrading plasma coagulation kinetics. Intact A. c. contortrix venom does not possess sufficient fibrinolytic activity to cause fibrinolysis in human plasma at the concentration tested.
- Nielsen, V. G., & Boyer, L. V. (2015). Iron and carbon monoxide attenuate degradation of plasmatic coagulation by Crotalus atrox venom. Blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis.More infoHypofibrinogenemia is an important clinical consequence following envenomation by Crotalus species, usually attenuated or prevented by administration of antivenom. It has been determined that iron and carbon monoxide (CO) enhance fibrinogen as a thrombin substrate, likely secondary to conformational changes in molecular structure. We tested the hypothesis that pretreatment of plasma with iron and CO could attenuate the effects of exposure to Crotalus atrox venom. Human plasma was exposed to 0 to 10 μmol/l ferric chloride (iron source) and 0 to 100 μmol/l CO-releasing molecule-2 (CO source) followed by exposure to 0 to 0.5 μg/ml venom for 5 to 20 min. Changes in coagulation kinetics were determined with thrombelastography. Iron and CO significantly attenuated venom-mediated degradation of plasmatic coagulation in terms of onset time, velocity of clot growth and final clot strength. Further preclinical investigation of iron and CO administration as a 'bridge-to-antivenom' to preserve plasmatic coagulation is justified.
- Nielsen, V. G., & Henderson, J. (2015). Sonoclot(®)-based method to detect iron enhanced coagulation. Journal of thrombosis and thrombolysis.More infoThrombelastographic methods have been recently introduced to detect iron mediated hypercoagulability in settings such as sickle cell disease, hemodialysis, mechanical circulatory support, and neuroinflammation. However, these inflammatory situations may have heme oxygenase-derived, coexistent carbon monoxide present, which also enhances coagulation as assessed by the same thrombelastographic variables that are affected by iron. This brief report presents a novel, Sonoclot-based method to detect iron enhanced coagulation that is independent of carbon monoxide influence. Future investigation will be required to assess the sensitivity of this new method to detect iron mediated hypercoagulability in clinical settings compared to results obtained with thrombelastographic techniques.
- Nielsen, V. G., Boyer, L. V., Matika, R. W., Amos, Q., & Redford, D. T. (2015). Iron and carbon monoxide attenuate Crotalus atrox venom-enhanced tissue-type plasminogen activator-initiated fibrinolysis. Blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis.More infoIn addition to degrading fibrinogen as a source of consumptive coagulopathy, rattlesnake venom has also been demonstrated to enhance fibrinolysis and degrade alpha-2-antiplasmin. The goals of this investigation was to characterize the kinetic fibrinolytic profile of Crotalus atrox venom in the absence and presence of tissue-type plasminogen activator (tPA), and to also ascertain if iron and carbon monoxide (CO, a positive modulator of alpha-2-antiplasmin) could attenuate venom-enhanced fibrinolysis. Utilizing thrombelastographic methods, the coagulation and fibrinolytic kinetic profiles of human plasma exposed to C. atrox venom (0-2 μg/ml) were determined in the absence or presence of tPA (0-100 IU/ml). Then, either separately or in combination, plasma was exposed to iron (ferric chloride, 10 μmol/l) or CO (carbon monoxide-releasing molecule-2, 100 μmol/l) prior to incubation with venom; the plasma sample was subsequently subjected to thrombelastographic analysis with addition of tPA. Venom exposure in the absence of tPA did not result in detectable fibrinolysis. In the presence of tPA, venom markedly enhanced fibrinolysis. Iron and CO, markedly attenuated venom enhancement of fibrinolysis. C. atrox venom enhances tPA-mediated fibrinolysis, and interventions that enhance/protect alpha-2-antiplasmin activity significantly attenuate venom-enhanced fibrinolysis. Future preclinical investigation is required to determine if iron and CO can attenuate venom-mediated degradation of alpha-2-antiplasmin-dependent fibrinolytic resistance.
- Nielsen, V. G., Galvani, C. A., Boyle, P. K., Steinbrenner, E. B., & Matika, R. W. (2015). Bariatric patients have plasmatic hypercoagulability and systemic upregulation of heme oxygenase activity. Blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis, 26(2), 200-4.More infoMorbid obesity is associated with significant thrombophilia. Of interest, adipocytes obtained from obese patients have increased heme oxygenase (Hmox) activity, the endogenous enzyme responsible for carbon monoxide (CO) production. Given that CO enhances plasmatic coagulation, we determined whether morbidly obese patients undergoing bariatric surgery had an increase in endogenous CO and plasmatic hypercoagulability. CO was determined by noninvasive pulse oximetry measurement of carboxyhemoglobin (COHb). A thrombelastographic method to assess plasma coagulation kinetics and formation of carboxyhemefibrinogen (COHF) was utilized. Nonsmoking bariatric patients (n = 20, BMI 47 ± 8 kg/m, mean ± SD) had abnormally increased COHb concentrations of 2.7 ± 1.9%, indicative of Hmox upregulation. When coagulation kinetics of these bariatric patients were compared with values obtained from normal individuals' (n = 30) plasma, 70% (95% confidence interval 45.7-88.1%) had abnormally great velocity of clot formation, abnormally large clot strength, and COHF formation. Future investigation of Hmox-derived CO in the pathogenesis of obesity-related thrombophilia is warranted.
- Nielsen, V. G., Kulin, W., LaWall, J. S., MacFarland, F. N., Chen, A., Hadley, H. A., DaDeppo, A. J., Steinbrenner, E. B., & Matika, R. W. (2015). Chronic Migraineurs Form Carboxyhemefibrinogen and Iron-Bound Fibrinogen. CNS & neurological disorders drug targets, 14(8), 1079-85.More infoChronic migraine (CM) is a disabling painful condition that is associated with dementia and thrombotic disease. It has been proposed that carbon monoxide (CO) and iron may play a role in CM, and CO and iron are products of the heme oxygenase system which is widespread within the brain. Further, CO and iron enhance plasmatic coagulation in part via a fibrinogen-dependent mechanism. Thus, our goal was to determine whether patients with CM had experienced carboxyhemefibrinogen formation, iron bound fibrinogen formation and plasmatic hypercoagulability. Nonsmokers with CM were recruited after informed, written consent. Blood was collected, anticoagulated with sodium citrate, and then centrifuged with plasma stored at -80ºC. Carboxyhemefibrinogen formation, iron bound fibrinogen formation and coagulation kinetics were determined via thrombelastographic methods. Patient results were compared with laboratory values generated from normal control plasmas. Incidence (95% confidence intervals) of the various parameters was determined using the Clopper-Pearson method. Twenty-six CM patients (24 female) were recruited; they were 46±12 years old. With regard to fibrinogen modification, 88.5% (69.8%-97.6%) of CM patients had formation of carboxyhemefibrinogen, iron bound fibrinogen, or both. With regard to coagulation, 42.3% (23.4%-63.1%) of patients had abnormally decreased time to clot initiation, 80.8% (60.6%-93.4%) had abnormally large velocity of clot formation, and 46.2% (26.6%-66.7%) had abnormally strong clot strength. Patients with CM have a large incidence of carboxyhemefibrinogen and iron bound fibrinogen formation and hypercoagulability. Confirmatory and potential therapeutic clinical trials targeting CO and iron modified hypercoagulation as a source of pain and vascular disease in CM patients are indicated.
- Nielsen, V. G., Pretorius, E., Bester, J., Jacobsen, W. K., Boyle, P. K., & Reinhard, J. P. (2015). Carbon monoxide and iron modulate plasmatic coagulation in Alzheimer's disease. Current neurovascular research, 12(1), 31-9.More infoAlzheimer's disease (AD) is a significant source of morbidity and mortality for millions of people worldwide, and multiple potential etiologies have been postulated to contribute to AD. Among these, spontaneous cerebral emboli and increased cerebral and circulating heme oxygenase (Hmox) activity in AD patients are of particular interest, as two of the products of Hmox activity, carbon monoxide (CO) and iron enhance plasmatic coagulation and modify the ultrastructure of thrombi. We hypothesized that patients afflicted with AD would have coagulation kinetics modulated by CO and iron. Using viscoelastic assessments of coagulation, it was determined with a small cohort (n=11) of AD patients that all had enhancement of coagulation by CO, iron, or both. In a complementary fashion, it was determined that a separate cohort (n=12) of AD patients had thrombi with ultrastructural features consistent with iron and CO exposure as assessed with scanning electron microscopy. Further, when stratified by normal or abnormally increased serum ferritin concentrations (which can be increased by Hmox), the AD patients with abnormal ferritin concentrations had significantly thinner fibrin fiber diameters, not unlike that noted when normal plasma is mixed with iron or CO. In sum, AD patients were noted to have plasmatic coagulation kinetic and thrombus ultrastructural changes consistent with exposure to CO and iron. Future investigation of CO and iron in the pathogenesis of Alzheimer's disease is warranted.
- Nielsen, V. G., Redford, D. T., & Boyle, P. K. (2015). Effect of Iron and Carbon Monoxide on Fibrinogenase-like Degradation of Plasmatic Coagulation by Venoms of Six Agkistrodon Species. Basic & clinical pharmacology & toxicology.More infoAnnually, thousands suffer poisonous snake bite, often from defibrinogenating species. It has been demonstrated that iron and carbon monoxide change the ultrastructure of plasma thrombi and improve coagulation kinetics. Thus, the present investigation sought to determine if pre-treatment of plasma with iron and carbon monoxide could attenuate venom-mediated catalysis of fibrinogen obtained from Agkistrodon species with fibrinogenase activity. Human plasma was pre-treated with ferric chloride (0-10 μM) and carbon monoxide releasing molecule-2 (CORM-2, 0-100 μM) prior to exposure to 0.5-11 μg/ml of six different Agkistrodon species' venom. The amount of venom used for experimentation needed to decrease coagulation function of one or more kinetic parameters by at least 50% of normal values for (e.g., half the normal speed of clot formation). Coagulation kinetics were determined with thrombelastography. All six snake venoms degraded plasmatic coagulation kinetics to a significant extent, especially prolonging the onset to clot formation and diminishing the speed of clot growth. Pre-treatment of plasma with iron and carbon monoxide attenuated these venom-mediated coagulation kinetic changes in a species-specific manner, with some venom effects markedly abrogated while others were only mildly decreased. Further in vitro investigation of other pit viper venoms that possess fibrinogenolytic activity is indicated to identify species amenable to or resistant to iron and carbon monoxide-mediated attenuation of venom-mediated catalysis of fibrinogen. Lastly, future preclinical investigation with animal models (e.g., rabbit ear bleed model) is planned to determine if iron and carbon monoxide can be used therapeutically after envenomation. This article is protected by copyright. All rights reserved.
- Nielsen, V. G., Sobieski II, M. A., & Slaughter, M. S. (2015). Left Ventricular Assist Device-Associated Carbon Monoxide and Iron-Enhanced Hypercoagulation: Impact of Concurrent Disease. ASAIO journal (American Society for Artificial Internal Organs : 1992), 61(4), 417-23.More infoLeft ventricular assist device (LVAD) therapy is associated with thrombophilia despite anticoagulation. Of interest, LVAD patients have increased carboxyhemoglobin, a measure of upregulated heme oxygenase (Hmox) activity that releases carbon monoxide (CO) and iron. Given that CO and iron enhance plasmatic coagulation, we determined if LVAD patients had hypercoagulability and decreased fibrinolytic vulnerability with measurable CO and iron-mediated effects. Blood samples were obtained a month or more after implantation of the LVAD. Thrombelastographic methods to assess coagulation kinetics, fibrinolytic kinetics, formation of carboxyhemefibrinogen, and iron-mediated enhancement of clot growth were utilized. Coagulation and fibrinolytic parameter normal individual (n = 30) plasma values were determined. Sixteen LVAD patients were studied. CO and iron enhancement of coagulation were observed in the majority of LVAD patients, contributing to hypercoagulation. However, most patients demonstrated abnormally increased rates of clot lysis. Critically, hemolysis as assessed by circulating lactate dehydrogenase activity was small in this cohort, and only four patients without comorbid states (e.g., obesity, diabetes, sleep apnea) were hypercoagulable with evidence of Hmox upregulation. However, seven patients with comorbidities were hypercoagulable with Hmox upregulation. Future investigation of CO and iron-related thrombophilia and comorbid disease is warranted to define its role in LVAD-related thrombosis.
- Redford, D. T., Paidy, S. R., Steinbrenner, E. B., & Nielsen, V. G. (2015). Effects of profound hypoxemia on coagulation & fibrinolysis in normal individuals. Blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis.More infoHypoxia has been proposed to enhance, diminish, or have no effect on laboratory measures of coagulation or clinical thrombosis. Further, there usually are significant pathological or environmental factors concurrently present with hypoxia. Thus, the goal of the present investigation was to determine whether whole blood or plasmatic coagulation and fibrinolytic kinetics would change in response to progressive hypoxia to a systemic oxygenation (SpO2) of 70%. Healthy, conscious volunteers (n = 9) breathing a hypoxic mixture of gases during an in-vivo validation of noninvasive cerebral oximetry had blood samples collected and assessed with thrombelastography at normoxia and after SpO2 of 70%. A mild release of endogenous heparin-like activity occurred that diminished plasmatic coagulation, and a mild increase in clot lysis time also was noted. Further investigation to determine whether these phenomena occur in more chronic, less hypoxic states as sources of hypocoagulation or thrombophilia is needed.
- Swanepoel, A. C., Nielsen, V. G., & Pretorius, E. (2015). Viscoelasticity and Ultrastructure in Coagulation and Inflammation: Two Diverse Techniques, One Conclusion. Inflammation, 38(4), 1707-26.More infoThe process of blood clotting has been studied for centuries. A synopsis of current knowledge pertaining to haemostasis and the blood components, including platelets and fibrin networks which are closely involved in coagulation, are discussed. Special emphasis is placed on tissue factor (TF), calcium and thrombin since these components have been implicated in both the coagulation process and inflammation. Analysis of platelets and fibrin morphology indicate that calcium, tissue factor and thrombin at concentrations used during viscoelastic analysis (with thromboelastography or TEG) bring about alterations in platelet and fibrin network ultrastructure, which is similar to that seen in inflammation. Scanning electron microscopy indicated that, when investigating platelet structure in disease, addition of TF, calcium or thrombin will mask disease-induced alterations associated with platelet activation. Therefore, washed platelets without any additives is preferred for morphological analysis. Furthermore, morphological and viscoelastic analysis confirmed that thrombin activation is the preferred method of fibrin activation when investigating fibrin network ultrastructure.
- Thompson III, J. L., Nielsen, V. G., Castro, A., & Chen, A. (2015). Heme oxygenase derived carbon monoxide and iron mediated plasmatic hypercoagulability in a patient with calcific mitral valve disease. Journal of thrombosis and thrombolysis, 39(4), 532-5.More infoWe present a case of a patient with calcific mitral valve stenosis and plasmatic hypercoagulability. Using thrombelastography, the patient was determined to have an abnormally large velocity of plasma thrombus growth and strength with reduced vulnerability to lysis. Critically, increased carboxyhemoglobin concentration (2.4 %) was present, likely secondary to hemolysis from mitral stenosis and engagement of systemic heme oxygenase. It was determined that the patient's plasmatic hypercoagulability was in part due to carboxyhemefibrinogen formation and iron-enhancement of coagulation via two thrombelastographic methods. In conclusion, future investigation of the involvement of both carbon monoxide and iron mediated hypercoagulability in the setting of stenotic valve disease is warranted.
- DaDeppo, A. J., Hadley, H. A., CHen, A., Matika, R. W., & Nielsen, V. G. (2015, May). Chronic Migraineurs Form Carboxyhemeifrinogen and Iron-Bound Fibrinogen. Western Anesthesia Residents Conference. Seattle, WA.
- Nielsen, V. G., Galvani, C. A., Boyle, P. K., Nielsen, V. G., Galvani, C. A., & Boyle, P. K. (2013, December 3). Obesity-Mediated Hypercoagulability: Role of Hemeoxygenase-1. IRB 13-0745.