Carbon monoxide-releasing molecule-2 enhances coagulation in rabbit plasma and decreases bleeding time in clopidogrel/aspirin-treated rabbits

Carbon Monoxide or Ruthenium: Will the Real Modulator of Coagulation and Fibrinolysis Please Stand Up!

The discovery of carbon monoxide releasing molecules (CORMs) was one of the most impactful innovations in biochemistry, affecting multiple disciplines for the past few decades. Sixteen years ago, a ruthenium dimer-containing CORM, CORM-2, enhanced coagulation and diminished fibrinolysis in human plasma by modulation of fibrinogen, plasmin, and α2-antiplasmin via CO binding to putative heme groups attached to these proteins. This finding linked CO exposure in settings involving heme oxygenase-1 upregulation during inflammation or environmental exposure to thromboembolic disease in hundreds of subsequent manuscripts. However, CO-independent effects of CORM-2 involving a putative ruthenium radical (Ru•) formed during CO release was found to be responsible for many of effects by CORM-2 in other works. Using a novel approach with human plasmatic coagulation kinetic methods, Ru• was posited to bind to critical histidines and other amino acids to modulate function, and excess histidine to quench CORM-2-mediated effects. This paradigm of histidine addition would definitively address if CO or Ru• was responsible for CORM-2-mediated effects. Thus, plasma coagulation/fibrinolytic kinetic data were assessed via thrombelastography ±CORM-2, ±histidine added. Histidine nearly completely abrogated CORM-2-mediated hypercoagulation in a concentration-dependent fashion; further, histidine also nearly eliminated all kinetic effects on fibrinolysis. In conclusion, CORM-2 Ru• formation, not CO release, is the true molecular mechanism modulating coagulation and fibrinolysis.

Novel Toxicodynamic Model of Subcutaneous Envenomation to Characterize Snake Venom Coagulopathies and Assess the Efficacy of Site-Directed Inorganic Antivenoms

Venomous snake bite adversely affects millions of people yearly, but few animal models allow for the determination of toxicodynamic timelines with hemotoxic venoms to characterize the onset and severity of coagulopathy or assess novel, site-directed antivenom strategies. Thus, the goals of this investigation were to create a rabbit model of subcutaneous envenomation to assess venom toxicodynamics and efficacy of ruthenium-based antivenom administration. New Zealand White rabbits were sedated with midazolam via the ear vein and had viscoelastic measurements of whole blood and/or plasmatic coagulation kinetics obtained from ear artery samples. Venoms derived from Crotalus scutulatus scutulatus, Bothrops moojeni, or Calloselasma rhodostoma were injected subcutaneously, and changes in coagulation were determined over three hours and compared to samples obtained prior to envenomation. Other rabbits had ruthenium-based antivenoms injected five minutes after venom injection. Viscoelastic analyses demonstrated diverse toxicodynamic patterns of coagulopathy consistent with the molecular composition of the proteomes of the venoms tested. The antivenoms tested attenuated venom-mediated coagulopathy. A novel rabbit model can be used to characterize the onset and severity of envenomation by diverse proteomes and to assess site-directed antivenoms. Future investigation is planned involving other medically important venoms and antivenom development.

Modulation of Diverse Procoagulant Venom Activities by Combinations of Platinoid Compounds

Procoagulant snake venoms have been inhibited by the ruthenium containing compounds CORM-2 and RuCl₃ separately, presumably by interacting with critical histidine or other sulfur-containing amino acids on key venom enzymes. However, combinations of these and other platinoid containing compounds could potentially increase, decrease or not affect the procoagulant enzyme function of venom. Thus, the purpose of this investigation was to determine if formulations of platinoid compounds could inhibit venom procoagulant activity and if the formulated compounds interacted to enhance inhibition. Using a human plasma coagulation kinetic model to assess venom activity, six diverse venoms were exposed to various combinations and concentrations of CORM-2, CORM-3, RuCl₃ and carboplatin (a platinum containing compound), with changes in venom activity determined with thrombelastography. The combinations of CORM-2 or CORM-3 with RuCl₃ were found to enhance inhibition significantly, but not in all venoms nor to the same extent. In sharp contrast, carboplatin-antagonized CORM-2 mediated the inhibition of venom activity. These preliminary results support the concept that platinoid compounds may inhibit venom enzymatic activity at the same or different molecular sites and may antagonize inhibition at the same or different sites. Further investigation is warranted to determine if platinoid formulations may serve as potential antivenoms.

CO-Releasing Materials: An Emphasis on Therapeutic Implications, as Release and Subsequent Cytotoxicity Are the Part of Therapy

The CO-releasing materials (CORMats) are used as substances for producing CO molecules for therapeutic purposes. Carbon monoxide (CO) imparts toxic effects to biological organisms at higher concentration. If this characteristic is utilized in a controlled manner, it can act as a cell-signaling agent for important pathological and pharmacokinetic functions; hence offering many new applications and treatments. Recently, research on therapeutic applications using the CO treatment has gained much attention due to its nontoxic nature, and its injection into the human body using several conjugate systems. Mainly, there are two types of CO insertion techniques into the human body, i.e., direct and indirect CO insertion. Indirect CO insertion offers an advantage of avoiding toxicity as compared to direct CO insertion. For the indirect CO inhalation method, developers are facing certain problems, such as its inability to achieve the specific cellular targets and how to control the dosage of CO. To address these issues, researchers have adopted alternative strategies regarded as CO-releasing molecules (CORMs). CO is covalently attached with metal carbonyl complexes (MCCs), which generate various CORMs such as CORM-1, CORM-2, CORM-3, ALF492, CORM-A1 and ALF186. When these molecules are inserted into the human body, CO is released from these compounds at a controlled rate under certain conditions or/and triggers. Such reactions are helpful in achieving cellular level targets with a controlled release of the CO amount. However on the other hand, CORMs also produce a metal residue (termed as i-CORMs) upon degradation that can initiate harmful toxic activity inside the body. To improve the performance of the CO precursor with the restricted development of i-CORMs, several new CORMats have been developed such as micellization, peptide, vitamins, MOFs, polymerization, nanoparticles, protein, metallodendrimer, nanosheet and nanodiamond, etc. In this review article, we shall describe modern ways of CO administration; focusing primarily on exclusive features of CORM's tissue accumulations and their toxicities. This report also elaborates on the kinetic profile of the CO gas. The comprehension of developmental phases of CORMats shall be useful for exploring the ideal CO therapeutic drugs in the future of medical sciences.

An Overview of the Potential Therapeutic Applications of CO-Releasing Molecules

Carbon monoxide (CO) has long been known as the “silent killer” owing to its ability to form carboxyhemoglobin—the main cause of CO poisoning in humans. Its role as an endogenous neurotransmitter, however, was suggested in the early 1990s. Since then, the biological activity of CO has been widely examined via both the direct administration of CO and in the form of so-called “carbon monoxide releasing molecules (CORMs).” This overview will explore the general physiological effects and potential therapeutic applications of CO when delivered in the form of CORMs.

Carbon Monoxide and Its Controlled Release: Therapeutic Application, Detection, and Development of Carbon Monoxide Releasing Molecules (CORMs)

Carbon monoxide (CO) is attracting increasing attention because of its role as a gasotransmitter with cytoprotective and homeostatic properties. Carbon monoxide releasing molecules (CORMs) are spatially and temporally controlled CO releasers that exhibit superior and more effective pharmaceutical traits than gaseous CO because of their chemistry and structure. Experimental and preclinical research in animal models has shown the therapeutic potential of inhaled CO and CORMs, and the biological effects of CO and CORMs have also been observed in preclinical trials via the genetic modulation of heme oxygenase-1 (HO-1). In this review, we describe the pharmaceutical use of CO and CORMs, methods of detecting CO release, and developments in CORM design and synthesis. Many valuable clinical CORMs formulated using macromolecules and nanomaterials are also described.

Characterization of the Rabbit as an In Vitro and In Vivo Model to Assess the Effects of Fibrinogenolytic Activity of Snake Venom on Coagulation

Several 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.

Iron and carbon monoxide attenuate degradation of plasmatic coagulation by Crotalus atrox venom

Hypofibrinogenemia 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.

Left Ventricular Assist Device-Associated Carbon Monoxide and Iron-Enhanced Hypercoagulation: Impact of Concurrent Disease

Left 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.

Carbon monoxide attenuates the effects of snake venoms containing metalloproteinases with fibrinogenase or thrombin-like activity on plasmatic coagulation

Carbon monoxide released from CORM-2 inhibitsCrotalus atroxsnake venom metalloproteinase mediated decreases in human plasma velocity of coagulation.

Bariatric patients have plasmatic hypercoagulability and systemic upregulation of heme oxygenase activity

Morbid 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.

Hemodialysis patients have plasmatic hypercoagulability and decreased fibrinolytic vulnerability: role of carbon monoxide

Chronic hemodialysis is associated with significant thrombophilia. Of interest, hemodialysis patients have increased carboxyhemoglobin (COHb) and exhaled carbon monoxide (CO), signs of upregulated heme oxygenase (Hmox) activity. Given that CO enhances plasmatic coagulation, we determined whether patients requiring chronic hemodialysis had an increase in endogenous CO, plasmatic hypercoagulability and decreased fibrinolytic vulnerability. Carbon monoxide was determined by noninvasive pulse oximetry measurement of COHb. Blood samples were obtained just before hemodialysis. Thrombelastographic methods to assess plasma coagulation kinetics, fibrinolytic kinetics, and formation of carboxyhemefibrinogen (COHF) were used. Hemodialysis patients (n = 45) had abnormally increased COHb concentrations of 2.2 ± 1.9%, indicative of Hmox upregulation. Coagulation and fibrinolytic parameter normal values were determined with normal individual (n = 30) plasma. Thirty-seven patients of the hemodialysis cohort had COHF formation (82.2%, [67.9%-92.0%]; mean, [95% confidence interval]), and many of this group of patients had abnormally great velocity of clot growth (73.3%, [58.1%-85.4%]) and strength (75.6%, [60.5%-87.1%]). Furthermore, over half of COHF positive patients had a hypofibrinolytic state, evidenced by an abnormally prolonged time to maximum rate of lysis (53.3%, [37.9%-68.6%]) and clot lysis time (64.4%, [48.8%-78.1%]). Carbon monoxide enhanced coagulation and diminished fibrinolytic vulnerability in hemodialysis patients. Future investigation of hemodialysis, CO-related thrombophilia is warranted.

Colon and pancreas tumors enhance coagulation: role of hemeoxygenase-1

Colon and pancreatic cancer are associated with significant thrombophilia. Colon and pancreas tumor cells have an increase in hemeoxygenase-1 (HO-1) activity, the endogenous enzyme responsible for carbon monoxide production. Given that carbon monoxide enhances plasmatic coagulation, we determined if patients undergoing resection of colon and pancreatic tumors had an increase in endogenous carbon monoxide and plasmatic hypercoagulability. Patients with colon (n = 17) and pancreatic (n = 10) tumors were studied. Carbon monoxide was determined by the measurement of carboxyhemoglobin (COHb). A thrombelastographic method to assess plasma coagulation kinetics and formation of carboxyhemefibrinogen (COHF) was utilized. Nonsmoking patients with colon and pancreatic tumors had abnormally increased COHb concentrations of 1.4 ± 0.9 and 1.9 ± 0.7%, respectively, indicative of HO-1 upregulation. Coagulation analyses comparing both tumor groups demonstrated no significant differences in any parameter; thus the data were combined for the tumor groups for comparison with 95% confidence interval values obtained from normal individuals (n = 30) plasma. Seventy percent of tumor patients had a velocity of clot formation greater than the 95% confidence interval value of normal individuals, with 53% of this hypercoagulable group also having COHF formation. Further, 67% of tumor patients had clot strength that exceeded the normal 95% confidence interval value, and 56% of this subgroup had COHF formation. Finally, 63% of all tumor patients had COHF formation. Future investigation of HO-1-derived carbon monoxide in the pathogenesis of colon and pancreatic tumor-related thrombophilia is warranted.

Iron and carbon monoxide enhance coagulation and attenuate fibrinolysis by different mechanisms

Two parallel lines of investigation elucidating novel mechanisms by which iron (scanning electron microscopy-based) and carbon monoxide (viscoelastic-based) enhance coagulation and diminish fibrinolysis have emerged over the past few years. However, a multimodal approach to ascertain the effects of iron and carbon monoxide remained to be performed. Such investigation could be important, as iron and carbon monoxide are two of the products of heme catabolism via heme oxygenase-1, an enzyme upregulated in a variety of disease states associated with thrombophilia. Human plasma was exposed to ferric chloride, carbon monoxide derived from carbon monoxide-releasing molecule-2, or their combination. Viscoelastic studies demonstrated ferric chloride and carbon monoxide mediated enhancement of velocity of growth, and final clot strength, with the combination of the two molecules noted to have all the prothrombotic kinetic effects of either separately. Parallel ultrastructural studies demonstrated separate types of fibrin polymer cross-linking and matting in plasma exposed to ferric chloride and carbon monoxide, with the combination sharing features of each molecule. In conclusion, we present the first evidence that iron and carbon monoxide interact with key coagulation and fibrinolytic processes, resulting in thrombi that begin to form more quickly, grow faster, become stronger, and are more resistant to lysis.

Brain tumors enhance plasmatic coagulation: the role of hemeoxygenase-1

BACKGROUND

Patients with brain tumors suffer significant thrombotic morbidity and mortality. In addition to increased thrombin generation via tumor release of tissue factor-bearing microparticles and hyperfibrinogenemia, brain tumors and surrounding normal brain likely generate endogenous carbon monoxide (CO) via the hemeoxygenase-1 (HO-1) system. CO has been shown to enhance plasmatic coagulation via formation of carboxyhemefibrinogen (COHF). Thus, our goals in this study were to determine whether patients with brain tumors had increased HO-1 upregulation/CO production, plasmatic hypercoagulability, and formation of COHF.

METHODS

Patients with brain tumors (N = 20) undergoing craniotomy had blood collected for determination of carboxyhemoglobin as a marker of HO-1 activity, plasmatic hypercoagulability (defined as clot strength > 95% confidence interval value of normal subject plasma), and COHF formation (determined with a thrombelastograph-based assay). Plasma obtained from commercially available normal subjects (N = 30) was used for comparison with brain tumor patient samples.

RESULTS

Brain tumor patients had carboxyhemoglobin concentrations of 1.5% ± 0.5% (mean ± SD), indicative of HO-1 upregulation. Compared with normal subject plasma, brain tumor patient plasma had significantly (P < 0.0001) greater clot formation velocity (5.2 ± 1.5 vs 9.5 ± 2.3 dynes/cm/s, respectively) and significantly (P = 0.00016) stronger final clot strength (166 ± 28 vs 230 ± 78 dynes/cm, respectively). Ten of the brain tumor patients had plasma clot strength that exceeded the 95% confidence interval value observed in normal subjects, and 12 of the brain tumor patients had COHF formation. Five of the brain tumor patients in the hypercoagulable subgroup had COHF formation. Last, 5 of the hypercoagulable patients had primary brain tumors, whereas the other 5 patients had metastatic tumors or an inflammatory mass lesion.

CONCLUSIONS

A subset of patients with brain tumors has increased endogenous CO production, plasmatic hypercoagulability, and COHF formation. Future investigation of the role played by HO-1 derived CO in the pathogenesis of brain tumor-associated thrombophilia is warranted.

Carbon monoxide: Anticoagulant or procoagulant?

Within the past decade there have been several investigations attempting to define the impact of exogenous and endogenous carbon monoxide exposure on hemostasis. Critically, two bodies of literature have emerged, with carbon monoxide mediated platelet inhibition cited as a cause of in vitro human and in vitro/in vivo rodent anticoagulation. In contrast, interaction with heme groups associated with fibrinogen, α₂-antiplasmin and plasmin by carbon monoxide has resulted in enhanced coagulation and decreased fibrinolysis in vitro in human and other species, and in vivo in rabbits. Of interest, the ultrastructure of platelet rich plasma thrombi demonstrates an abnormal increase in fine fiber formation and matting that are obtained from humans exposed to carbon monoxide. Further, thrombi obtained from humans and rabbits have very similar ultrastructures, whereas mice and rats have more fine fibers and matting present. In sum, there may be species specific differences with regard to hemostatic response to carbon monoxide. Carbon monoxide may be a Janus-faced molecule, with potential to attenuate or exacerbate thrombophilic disease.