Structure-function relationships among neurotoxic phospholipases: NN-XIII-PLA2 from Indian cobra (Naja naja naja) and VRV PL-V from Russell's viper (Vipera russelli) venoms

Comparison of proteomic profiles of the venoms of two of the 'Big Four' snakes of India, the Indian cobra (Naja naja) and the common krait (Bungarus caeruleus), and analyses of their toxins

Snake venoms are mixtures of biologically-active proteins and peptides, and several studies have described the characteristics of some of these toxins. However, complete proteomic profiling of the venoms of many snake species has not yet been done. The Indian cobra (Naja naja) and common krait (Bungarus caeruleus) are elapid snake species that are among the 'Big Four' responsible for the majority of human snake envenomation cases in India. As understanding the composition and complexity of venoms is necessary for successful treatment of envenomation in humans, we utilized three different proteomic profiling approaches to characterize these venoms: i) one-dimensional SDS-PAGE coupled with in-gel tryptic digestion and electrospray tandem mass spectrometry (ESI-LC-MS/MS) of individual protein bands; ii) in-solution tryptic digestion of crude venoms coupled with ESI-LC-MS/MS; and iii) separation by gel-filtration chromatography coupled with tryptic digestion and ESI-LC-MS/MS of separated fractions. From the generated data, 81 and 46 different proteins were identified from N. naja and B. caeruleus venoms, respectively, belonging to fifteen different protein families. Venoms from both species were found to contain a variety of phospholipases A₂ and three-finger toxins, whereas relatively higher numbers of snake venom metalloproteinases were found in N. naja compared to B. caeruleus venom. The analyses also identified less represented venom proteins including L-amino acid oxidases, cysteine-rich secretory proteins, 5'-nucleotidases and venom nerve growth factors. Further, Kunitz-type serine protease inhibitors, cobra venom factors, phosphodiesterases, vespryns and aminopeptidases were identified in the N. naja venom, while acetylcholinesterases and hyaluronidases were found in the B. caeruleus venom. We further analyzed protein coverage (Lys/Arg rich and poor regions as well as potential glycosylation sites) using in-house software. These studies expand our understanding of the proteomes of the venoms of these two medically-important species.

Blood chemistry of rats pretreated with Mucuna pruriens seed aqueous extract MP101UJ after Echis carinatus venom challenge

The effect of a lethal Echis carinatus venom on serum enzyme levels and blood plasma coagulation parameters in rats pretreated with Mucuna pruriens seed aqueous extract MP101UJ (21 mg/kg body wt) 24 h and 3 wk before i.p venom injection (0.50 mg/kg rat) and rats injected with venom alone (0.50 mg/kg body wt) was investigated. The enzyme levels and coagulation parameter levels were measured 4 h after venom administration. The results showed that the increased enzymes lactate dehydrogenase (LDH), glutamic pyruvic transaminase (SGPT), creatinine kinase (CK) and changed coagulation parameters D-Dimer and Quick levels due to the venom effect were inhibited by M. pruriens seed aqueous extract MP101UJ in pretreated rats. Rats pretreated with a single dose (21 mg/kg and multiple doses 21 mg/kg rat) of extract MP101UJ maintained the normal enzyme levels and showed an anticoagulant effect as evidenced by the high PTT level which was also observed in venom treated animals. D-Dimer and Quick values were normal. However, the extract MP101UJ appeared to significantly inhibit the lethal venom induced myotoxic, cytotoxic and coagulation activities in experimental animals.

In vitro snake venom detoxifying action of the leaf extract of Guiera senegalensis

The extract of the leaves of Guiera senegalensis was found to detoxify (in vitro) venom from two common northern Nigerian snake species, Echis carinatus and Naja nigricollis, in separate experiments. There was a remarkable reduction in the mortality of albino mice after intra-peritoneal (i.p.) administration of reconstituted venom incubated with the extract, when compared to those challenged with the venom only. The survival of the animals exposed to the venom incubated with the different concentrations of the extract was used as the in vitro detoxification parameter.

Synaptosomal binding of 125I-labelled daboiatoxin, a new PLA2 neurotoxin from the venom of Daboia russelli siamensis

Daboiatoxin (DbTx), the PLA2 neurotoxin from Daboia russelli siamensis venom, was shown to bind specifically and saturably to rat cerebrocortical synaptosomes and synaptic membrane fragments. Two families of binding sites were detected by equilibrium binding analysis in the presence and absence of Ca2+. Scatchard analysis of biphasic plateaus revealed Kdl 5 nM and Bmax1, 6 pmoles/mg protein, and Kd2 80 nM and Bmax2 20 pmoles/mg protein, respectively, for the high- and low-affinity binding sites. The binding of 125I-DbTx to synaptosomes did not show marked dependence on Ca2+, Mg2+, Co2+ and Sr2+. Native DbTx was the only strong competitor to 125I-DbTx synaptosomal binding (IC50 12.5 nM, KI 5.5 nM). Two other crotalid PLA2 neurotoxins, crotoxin CB and mojave toxin basic subunit, and nontoxic C. Atrox PLA2 enzyme, were relatively weaker inhibitors, while two viperid PLA2 neurotoxins, ammodytoxin A and VRV PL V, were very weak inhibitors. Crotoxin CA was a poor inhibitor even at microM concentrations, whereas no inhibitory effect at all was observed with crotoxin CACB, ammodytoxin C, VRV PL VIIIa, taipoxin, beta-bungarotoxin, or with PLA2 enzymes from N. naja venom, E. schistosa venom, bee venom and porcine pancreas. All other pharmacologically active ligands examined (epinephrine, norepinephrine, histamine, choline, dopamine, serotonin, GABA, naloxone, WB-4101, atropine, hexamethonium and alpha-bun-garotoxin) also failed to interfere with 125I-DbTx binding. As those competitors that showed partial inhibition were effective only at microM concentration range compared to the Kd (5 nM) of 125I-DbTx synaptosomal binding, DbTx could well recognize a different neuronal binding site. Rabbit anti-DbTx polyclonal antisera completely blocked the specific binding. When a range of Ca2+ and K+ channels modulators were examined, Ca2+ channel blockers (omega-conotoxins GVIA and MVIIC, taicatoxin, calciseptine and nitrendiprene) did not affect the binding even at high concentrations, while charybdotoxin was the only K+ channel effector that could partially displace 125I-DbTx synaptosomal binding amongst the K+ channel blockers tested (apamin, dendrotoxin-I, iberiotoxin, MCD-peptide, 4-aminopyridine and tetraethylammonium), suggesting that neither K+ nor Ca2+ channels are associated with DbTx binding sites.

Purification of a basic phospholipase A2 from Indian saw-scaled viper (Echis carinatus) venom: characterization of antigenic, catalytic and pharmacological properties

A major basic phospholipase A2 was purified from the Indian saw-scaled viper (Echis carinatus) venom by the combination of column chromatography and electrophoresis. The purified phospholipase A2 (EC-IV-PLA2) has a mol. wt of 14,000 by SDS-PAGE. It is a basic protein with a pI value between 7.2 and 7.6, and has a fluorescence emission maxima at 340 nm. It induces neurotoxicity and oedema in mice with an i.p. LD50 of 5 mg/kg body weight. It is devoid of direct haemolytic, myotoxic, cytotoxic and anticoagulant activities. Rabbit polyclonal antibodies prepared against EC-IV-PLA2 inhibited the in vitro enzymatic activity dose dependently, but did not neutralize the toxic effects of EC-IV-PLA2 in experimental animals.

Immunochemical cross-reactivity of neurotoxic phospholipase A2 enzymes from Indian cobra (Naja naja naja) venom using polyclonal antibodies

Rabbit antibodies were prepared against purified phospholipase A2 (NN-XIa-PLA2) from Indian cobra (Naja naja naja) venom. The PLA2 has haemolytic, neurotoxic, myotoxic, cytotoxic and oedema-inducing activities apart from the catalytic activity. The immunological cross-reactivity of structurally similar neurotoxic PLA2s was investigated using enzyme-linked immunosorbent assay (ELISA) and immunodiffusion. Anti-NN-XIa-PLA2 IgG cross-reacted with other purified neurotoxic PLA2s from the same venom. Immunochemical cross-reactions of anti-NN-XIa-PLA2 IgG with NN-XIa-PLA2, NN-XIb-PLA2, NN-XIII-PLA2, NN-IVb1-PLA2 and NN-Vb-PLA2 were shown by a very high ELISA titre and a single precipitin band on double immunodiffusion agarose plates. The catalytic activity of these PLA2s was inhibited dose-dependently by anti-NN-XIa-PLA2 IgG but was unable to neutralize lethality and neurotoxic symptoms in experimental animals injected with neurotoxic PLA2. Anti-NN-XIa-PLA2 IgG fails to neutralize myotoxicity and oedema-inducing activities of NN-XIa-PLA2 and NN-XIII-PLA2. Anti-NN-XIa-PLA2 IgG inhibited cytotoxic effects of NN-XIa-PLA2 dose-dependently, but failed to inhibit NN-XIII-PLA2-induced cytotoxicity. Direct haemolytic activity of NN-XIa-PLA2 and NN-XIII-PLA2 was inhibited dose-dependently by these antibodies. The results indicate the presence of separate catalytic and pharmacologic site(s).