Effects of venom proteases on peptide chromogenic substrates and bovine prothrombin

A Clot Twist: Extreme Variation in Coagulotoxicity Mechanisms in Mexican Neotropical Rattlesnake Venoms

Rattlesnakes are a diverse clade of pit vipers (snake family Viperidae, subfamily Crotalinae) that consists of numerous medically significant species. We used validated in vitro assays measuring venom-induced clotting time and strength of any clots formed in human plasma and fibrinogen to assess the coagulotoxic activity of the four medically relevant Mexican rattlesnake species Crotalus culminatus, C. mictlantecuhtli, C. molossus, and C. tzabcan. We report the first evidence of true procoagulant activity by Neotropical rattlesnake venom in Crotalus culminatus. This species presented a strong ontogenetic coagulotoxicity dichotomy: neonates were strongly procoagulant via Factor X activation, whereas adults were pseudo-procoagulant in that they converted fibrinogen into weak, unstable fibrin clots that rapidly broke down, thereby likely contributing to net anticoagulation through fibrinogen depletion. The other species did not activate clotting factors or display an ontogenetic dichotomy, but depleted fibrinogen levels by cleaving fibrinogen either in a destructive (non-clotting) manner or via a pseudo-procoagulant mechanism. We also assessed the neutralization of these venoms by available antivenom and enzyme-inhibitors to provide knowledge for the design of evidence-based treatment strategies for envenomated patients. One of the most frequently used Mexican antivenoms (Bioclon Antivipmyn®) failed to neutralize the potent procoagulant toxic action of neonate C. culminatus venom, highlighting limitations in snakebite treatment for this species. However, the metalloprotease inhibitor Prinomastat substantially thwarted the procoagulant venom activity, while 2,3-dimercapto-1-propanesulfonic acid (DMPS) was much less effective. These results confirm that venom-induced Factor X activation (a procoagulant action) is driven by metalloproteases, while also suggesting Prinomastat as a more promising potential adjunct treatment than DMPS for this species (with the caveat that in vivo studies are necessary to confirm this potential clinical use). Conversely, the serine protease inhibitor 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride (AEBSF) inhibited the direct fibrinogen cleaving actions of C. mictlantecuhtli venom, thereby revealing that the pseudo-procoagulant action is driven by kallikrein-type serine proteases. Thus, this differential ontogenetic variation in coagulotoxicity patterns poses intriguing questions. Our results underscore the need for further research into Mexican rattlesnake venom activity, and also highlights potential limitations of current antivenom treatments.

Effects of Mucuna pruriens protease inhibitors on Echis carinatus venom

The medicinal plant Mucuna pruriens, with reputed anti-snake venom properties has been reported to contain a kunitz-type trypsin inhibitor. This study was undertaken to further evaluate the protease inhibitory potential of gpMuc, a multiform glycoprotein, and other protein fractions from M. pruriens seeds against trypsin, chymotrypsin, Echis carinatus snake venom, ecarin and thrombin. The results showed that gpMuc inhibited both trypsin and chymotrypsin activities and was thermally stable, maintaining its trypsin inhibitory activity at temperatures of up to 50°C. Its structural conformation was also maintained at pH ranges of 4-7. Immunoreactivity study confirms that it contains protease-recognizing epitope on one of its isoforms. The whole protein extract of M. pruriens seeds inhibited prothrombin activation by ecarin and whole E. carinatus venom, and also thrombin-like activity using chromogenic assay.

Ophidian envenomation strategies and the role of purines

Snake envenomation employs three well integrated strategies: prey immobilization via hypotension, prey immobilization via paralysis, and prey digestion. Purines (adenosine, guanosine and inosine) evidently play a central role in the envenomation strategies of most advanced snakes. Purines constitute the perfect multifunctional toxins, participating simultaneously in all three envenomation strategies. Because they are endogenous regulatory compounds in all vertebrates, it is impossible for any prey organism to develop resistance to them. Purine generation from endogenous precursors in the prey explains the presence of many hitherto unexplained enzyme activities in snake venoms: 5'-nucleotidase, endonucleases (including ribonuclease), phosphodiesterase, ATPase, ADPase, phosphomonoesterase, and NADase. Phospholipases A(2), cytotoxins, myotoxins, and heparinase also participate in purine liberation, in addition to their better known functions. Adenosine contributes to prey immobilization by activation of neuronal adenosine A(1) receptors, suppressing acetylcholine release from motor neurons and excitatory neurotransmitters from central sites. It also exacerbates venom-induced hypotension by activating A(2) receptors in the vasculature. Adenosine and inosine both activate mast cell A(3) receptors, liberating vasoactive substances and increasing vascular permeability. Guanosine probably contributes to hypotension, by augmenting vascular endothelial cGMP levels via an unknown mechanism. Novel functions are suggested for toxins that act upon blood coagulation factors, including nitric oxide production, using the prey's carboxypeptidases. Leucine aminopeptidase may link venom hemorrhagic metalloproteases and endogenous chymotrypsin-like proteases with venom L-amino acid oxidase (LAO), accelerating the latter. The primary function of LAO is probably to promote prey hypotension by activating soluble guanylate cyclase in the presence of superoxide dismutase. LAO's apoptotic activity, too slow to be relevant to prey capture, is undoubtedly secondary and probably serves principally a digestive function. It is concluded that the principal function of L-type Ca(2+) channel antagonists and muscarinic toxins, in Dendroaspis venoms, and acetylcholinesterase in other elapid venoms, is to promote hypotension. Venom dipeptidyl peptidase IV-like enzymes probably also contribute to hypotension by destroying vasoconstrictive peptides such as Peptide YY, neuropeptide Y and substance P. Purines apparently bind to other toxins which then serve as molecular chaperones to deposit the bound purines at specific subsets of purine receptors. The assignment of pharmacological activities such as transient neurotransmitter suppression, histamine release and antinociception, to a variety of proteinaceous toxins, is probably erroneous. Such effects are probably due instead to purines bound to these toxins, and/or to free venom purines.

Purification from Bothrops lanceolatus (fer de lance) venom of a fibrino(geno)lytic enzyme with esterolytic activity

Bothrops lanceolatus venom has high caseinolytic, phospholipasic, esterolytic and hemorrhagic activities. In spite of having no coagulant effect on plasma, this venom contains a thrombin-like enzyme. Using gel filtration and ion-exchange chromatographies, we have purified an esterolytic fraction (F-II-1a) from this venom with a protein yield of 4% and a 58% recovery in enzyme activity. SDS-PAGE in the presence of beta-mercaptoethanol showed that the enzyme is a single chain polypeptide with a MW=38,100. Immunodiffusion and immunoelectrophoresis of fraction F-II-1a against serum from horses immunized with B. lanceolatus venom and against rabbit antiserum prepared using fraction F-II-1a both showed a single immunoprecipitin line. The Km and Vmax values for TAME hydrolysis were 0.85 mM and 38.6 micromol/min/mg, respectively. The esterolytic activity was completely inhibited by PMSF (10 mM) but not by EDTA (20 mM). Fraction F-II-1a hydrolyzed the alpha and beta chains of fibrinogen. Degradation of the alpha chain occurred within 10 min while that of the beta-chain was slower. The enzyme had no effect on the gamma-chain even after 4 h of hydrolysis.

Purification and partial characterization of a thrombin-like/gyroxin enzyme from bushmaster (Lachesis muta rhombeata) venom

The acidic coagulating enzyme of the L. m. rhombeata venom was purified to homogeneity using one step on preparative isoelectric focusing followed by gel permeation on a high performance liquid chromatography system. The enzyme focused with pIs 3.1-5.0 and had a molecular mass of 47,000 mol. wt as determined by high performance liquid gel-filtration chromatography and about 45,000 mol. wt as judged by sodium dodecyl sulfate-polyacrylamide-gel electrophoresis. The enzyme is a glycoprotein containing sialic acid and 12.4% of neutral carbohydrates. The 30 N-terminal amino acid sequence of the L. m. rhombeata protein shows 100% identity with L. m. muta gyroxin and considerable sequence homology with gyroxin and thrombin-related proteins. The enzyme exhibits strong N-p-tosyl-L-arginine methyl esterase activity, hydrolyses tripeptide nitroanilide derivatives weakly or not at all, and cleaves specifically the fibropeptide A (alpha-chain).

Fibrinogenolytic proteases from the venoms of juvenile and adult northern Pacific rattlesnakes (Crotalus viridis oreganus)

1. Venoms of Crotalus viridis oreganus show marked ontogenetic variation in protease activity. Adult venoms are approximately five-fold higher in protease (caseinolytic) activity. 2. Of seven potential protease inhibitors, only EDTA and 1,10-phenanthroline caused a significant decrease in protease activity. Responses of juvenile and adult venoms were essentially equivalent, and attempts at recovery of protease activity of EDTA-treated venoms by the addition of Ca2+ or Zn2+ were unsuccessful. 3. Gel filtration resolved two proteases from juvenile and subadult venoms with approximate M(r) of 100,000 and 78,000. Four proteases were resolved from adult venom, and M(r) estimates were 78,000, 61,000, 35,000 and 19,000. 4. Proteases from juvenile and adult venoms showed fibrinogenolytic activity, each producing some unique degradation products. 5. The occurrence of three "new" proteases in adult venom produced the ontogenetic increase in activity seen in the crude venoms.

Basic proteinases from Bothrops moojeni (caissaca) venom--I. Isolation and activity of two serine proteinases, MSP 1 and MSP 2, on synthetic substrates and on platelet aggregation

Two serine proteinases, MSP 1 and MSP 2, were isolated from Bothrops moojeni venom by chromatographies on Sephadex G-100, DEAE-Sephacel (pH 7.5) and SP-Sephadex C-50 (pH 7.5). Both enzymes are basic glycoproteins. On sodium dodecyl sulfate-polyacrylamide electrophoresis, MSP 1 presented two close protein bands corresponding to the mol. wts of 34,000 and 32,500. MSP 2 behaved as a single-chain protein with a mol. wt of 38,000. Specific esterolytic activities of MSP 1 and MSP 2 on alpha-N-tosyl-L-arginine methyl ester (TAME) are 33 mumol min-1 mg-1 and 184 mumol min-1 mg-1, respectively. The most sensitive substrates for the amidolytic activity of both proteinases were the thrombin substrate D-Phe-pipecolyl(Pip)-Arg-4-nitroanilide(Nan) and the glandular kallikrein substrate D-Val-Leu-Arg-Nan. MSP 1, in a concentration of 10(-8) M, causes platelet aggregation in platelet-rich plasma and washed platelets. It also enhances the ADP-induced platelet aggregation. Prostaglandin E1 (PGE1), phenylmethylsulfonyl fluoride (PMSF) and ethylenediamine tetracetic acid (EDTA) abolished completely the aggregation induced by MSP 1. Torresea cearensis trypsin inhibitor (TCTI) inhibited both amidolytic (Ki = 1.96 x 10(-7) M) and platelet-aggregating (Ki = 1.66 x 10(-7) M) activities of MSP 1. The esterolytic activity of MSP 1 and MSP 2 was completely abolished by PMSF, only partially by soybean trypsin inhibitor (SBTI) and benzamidine and not affected by Trasylol. MSP 2 was also inhibited by TCTI (Ki = 0.7 x 10(-7) M).

Age changes of Vipera berus venom amidolytic activity

The study of age changes of amidolytic activity of Vipera berus venom is investigated using mixtures of chromogenic peptide substrates differing by detected groups. Quantities of venom (total protein content) and its proteolytic activity from snakes of different ages were compared. The venom composition of newly born adders was shown to be considerably different from the venom composition of young (12-month) adders of the same population. The next evolution of protease activity is weakly expressed.

Purification and properties of a kininogenin from the venom of Lachesis muta (bushmaster)

An acidic kininogenin from Lachesis muta snake venom was purified to apparent homogeneity by a combination of gel filtration, isoelectric focusing and preparative gel electrophoresis. It was shown to be a highly stable serine protease (mol. wt 27,900; pI 5.4) capable of releasing bradykinin from low mol. wt bovine kininogen and of cleaving some synthetic chromogenic peptides with the following catalytic efficiencies (Kcat/Km, M-1.sec-1): N-benzoyl-Phe-Val-Arg-p-nitroanilide (1.92 x 10(4)); H-D-Val-Leu-Arg-p-nitroanilide (1.55 x 10(4)); N-acetyl-Phe-Arg-p-nitroanilide (3.98 x 10(2)); no hydrolysis was observed with N-benzoyl-Arg-p-nitroanilide. A marked and sustained hypotensive effect was recorded following i.v. injection of purified kininogenin into rats. Tachyphylaxis was observed after repeated i.v. injection of the enzyme, a phenomenon accompanied by a decrease of only 15% in the total circulating rat kininogen. Both the in vivo action and the enzymatic properties of the L. muta kininogenin indicate that this enzyme might be helpful for understanding the kinin-kininogen system.