Biochemical and pharmacological characterization of three toxic phospholipase A2s from Daboia russelii snake venom.

Three isoenzymes of phospholipase A2 (PLA2), VRV-PL-IIIc, VRV-PL-VII, and VRV-PL-IX were isolated from Daboia russelii snake venom. The venom, upon gel filtration on Sephadex G-75 column, resolved into six peaks (DRG75 I-VI). The VRV-PL-IIIc was purified by subjecting DRG75II to homogeneity by rechromatography in the presence of 8M urea on Sephadex G-75 column. The other two isoenzymes VRV-PL-VII and VRV-PL-IX were purified by subjecting DRG75III to ion exchange chromatography on CM-Sephadex C-25 column. Mol wt. for the three PLA2s, VRV-PL-IIIc, VRV-PL-VII, and VRV-PL-IX are 13.003kDa, 13.100kDa and 12.531kDa respectively. The VRV-PL-IIIc is not lethal to mice up to 14mg/kg body weight but it affects blood sinusoids and causes necrosis of the hepatocytes in liver. It causes hemorrhage in kidney and shrinkage of renal corpuscles and renal tubules. The LD50s for VRV-PL-VII and VRV-PL-IX are 7 and 7.5mg/kg body weight respectively. They induced neurotoxic symptoms similar to VRV-PL-V. All the three PLA2s are anticoagulant and induced varying degree of edema in the foot pads of mice. VRV-PL-V and VRV-PL-VII are shown to act as pre and post synaptic toxins, while VRV-PL-IX acts as presynaptic toxin. This is evident from experiments conducted on cultured hippocampal neurons by patch clamp electrophysiology.

INN-toxin, a highly lethal peptide from the venom of Indian cobra (Naja naja) venom-Isolation, characterization and pharmacological actions.

A novel toxic polypeptide, INN-toxin, is purified from the venom of Naja naja using combination of gel-permeation and ion-exchange chromatography. It has a molecular mass of 6951.6Da as determined by MALDI-TOF/MS and the N-terminal sequence of LKXNKLVPLF. It showed both neurotoxic as well as cytotoxic activities. INN-toxin is lethal to mice with a LD(50) of 1.2mg/kg body weight. IgY raised in chicks against basic peptide pool neutralized the toxicity of INN-toxin. INN-toxin did not inhibit cholinesterase activity. It is toxic to Ehrlich ascites tumor (EAT) cells, but it is not toxic to leukocyte culture. The toxin appears to be specific in its mode of action. Interaction of N-bromosuccinamide (NBS) with the peptide resulted in the modification of tryptophan residues and loss of lethal toxicity of INN-toxin.

Isolation and characterization of "Reprotoxin", a novel protein complex from Daboia russelii snake venom.

In snake venoms, non-covalent protein-protein interaction leads to protein complexes with synergistic and, at times, distinct pharmacological activities. Here we describe a new protein complex containing phospholipaseA(2) (PLA(2)), protease, and a trypsin inhibitor. It is isolated from the venom of Daboia russelii by gel permeation chromatography, on a Sephadex G-75 column. This 44.6 kDa complex exhibits only phospholipase A(2) activity. In the presence of 8M urea it is well resolved into protease (29.1 kDa), PLA(2) (13 kDa), and trypsin inhibitor (6.5 kDa) peaks. The complex showed an LD(50) of 5.06 mg/kg body weight in mice. It inhibited the frequency of spontaneous release of neurotransmitter in hippocampal neurons. It also caused peritoneal bleeding, and edema in the mouse foot pads. Interestingly, the complex caused degeneration of both the germ cells and the mouse Leydig cells of mouse testis. A significant reduction in both the diameter of the seminiferous tubules and height of the seminiferous epithelia were observed following intraperitoneal injection of the sub-lethal dose (3 mg/kg body weight). This effect of the toxin is supported by the increase in the activities of acid and alkaline phosphatases and the nitric oxide content in the testes, and a decrease in the ATPase activity. Because of its potent organ atrophic effects on the reproductive organs, the toxin is named "Reprotoxin". This is the first report demonstrating toxicity to the reproductive system by a toxin isolated from snake venom.

Chemistry and structural evaluation of different phospholipase A2 inhibitors in arachidonic acid pathway mediated inflammation and snake venom toxicity.

PLA2 inhibitors specific to Group I and II PLA2 isoforms are therapeutically important as anti-inflammatory molecules and against venom toxicity. From various natural sources diversified molecules with PLA2 inhibition and concomitant neutralization of inflammatory reactions and venom toxicity were characterized. Using these molecules, lead compounds are generated in several laboratories. Analogues of lead molecules were generated by substituting different types of functional groups in order to obtain a molecule with optimal PLA2 inhibition. The lead molecules characterized as PLA2 inhibitors are indoles, azetidinones, piperazines, isoxazolidines, isoxazolines, diazepinones, acenaphthenes and several substrate analogues. The lead optimization involves relative hydrophobicity and substitution of functional groups, such as electron withdrawing or donating. Many such groups are placed on hydrophobic moiety and their positional bioisosters are characterized. Among these analogue piperazine derivatives on optimization with respect to hydrophobicity and electronegativity showed inhibition at nanomolar levels. Structural analysis of many lead molecules indicated that a PLA2 inhibitor should have both hydrophobic moiety and polar functional groups. Each lead molecule requires optimization in this regard for effective inhibition.

A glycoprotein from a folk medicinal plant, Withania somnifera, inhibits hyaluronidase activity of snake venoms.

Venom hyaluronidases help in rapid spreading of the toxins by destroying the integrity of the extra-cellular matrix of the tissues in the victims. A hyaluronidase inhibitor (WSG) is purified from a folk medicinal plant, Withania somnifera. The glycoprotein inhibited the hyaluronidase activity of cobra (Naja naja) and viper (Daboia russelii) venoms, which was demonstrated by zymogram assay and staining of the skin tissues for differential activity. WSG completely inhibited the activity of the enzyme at a concentration of 1:1 w/w of venom to WSG. Thus we are able to demonstrate that the glycoprotein inhibits hyaluronidase activity of the venoms. External application of the plant extract as an antidote in rural parts of India to snakebite victims appears to have a scientific basis.

Purification of a post-synaptic neurotoxic phospholipase A2 from Naja naja venom and its inhibition by a glycoprotein from Withania somnifera.

A post-synaptic neurotoxic phospholipase A(2) (PLA(2)) has been purified from Indian cobra Naja naja venom. It was associated with a peptide in the venom. The association was disrupted using 8 M urea. It is denoted to be a basic protein by its behavior on both ion exchange chromatography and electrophoresis. It is toxic to mice, LD(50) 1.9 mg/kg body weight (ip). It is proved to be post-synaptic PLA(2) by chymographic experiment using frog nerve-muscle preparation. A glycoprotein, (WSG) was isolated from a folk medicinal plant Withania somnifera. The WSG inhibited the phospholipase A(2) activity of NN-XIa-PLA(2,) isolated from the cobra venom, completely at a mole-to-mole ratio of 1:2 (NN-XIa-PLA(2): WSG) but failed to neutralize the toxicity of the molecule. However, it reduced the toxicity as well as prolonged the death time of the experimental mice approximately 10 times when compared to venom alone. The WSG also inhibited several other PLA(2) isoforms from the venom to varying extent. The interaction of the WSG with the PLA(2) is confirmed by fluorescence quenching and gel-permeation chromatography. Chemical modification of the active histidine residue of PLA(2) using p-brophenacyl bromide resulted in the loss of both catalytic activity as well as neurotoxicity of the molecule. These findings suggest that the venom PLA(2) has multiple sites on it; perhaps some of them are overlapping. Application of the plant extract on snakebite wound confirms the medicinal value associated with the plant.

Novel non-enzymatic toxic peptide of Daboia russelii (Eastern region) venom renders commercial polyvalent antivenom ineffective.

The snake venoms are typically complex mixtures of enzymes and non-enzymatic peptides. Regional variation in the non-enzymatic fraction of Russell's viper venom from three regions of India studied. The eastern, western and southern regional venom upon gel permeation chromatography on sephadex-G-75 column resolved into three peaks. All the three overlapping peaks differ in their lethality and enzymatic potency. Peak III of all the regional venom found to be non-enzymatic, Western and southern regional venom has trypsin inhibitory activity with varying potencies. Interestingly, the peak III of eastern region is devoid of trypsin inhibitory activity. But it is highly lethal with a LD50 0.7 mg/kg body weight and also it exhibited post-synaptic neurotoxicity. On the other hand southern and western regional venom's non-enzymatic peak is non-lethal and did not induce neurotoxic symptoms in experimental model. The antibodies developed against the eastern regional venom cross-reacted with the peaks I and II of other regional venom, but failed to cross-react with the peak III of western and southern regional Russell's viper venom. Commercial anti-venom prepared to neutralize the toxic effects of common poisonous snakes of India, showed positive cross-reaction against peaks I, II and III of all three regional venom tested, except peak III of eastern regional venom. Commercial anti-venom neutralized the lethal toxicity of both western and southern regional Russell's viper venom, and failed to neutralize the lethal effects of eastern regional Russell's viper venom.

Inhibition of secretory phospholipase A(2) enzyme by bilirubin: a new role as endogenous anti-inflammatory molecule.

Bilirubin is a powerful antioxidant that suppresses the inflammatory process. However its interaction with proinflammatory PLA(2) enzyme is not known. Inhibition of several secretory phospholipase A(2) (sPLA(2)) enzyme activities by bilirubin was studied using (14)C-oleate labeled Escherichia coli as substrate. Bilirubin inhibits purified sPLA(2) enzyme from Vipera russellii and Naja naja venom and partially purified sPLA(2) enzymes from human ascitic fluid, pleural fluid and normal serum in a dose dependent manner. IC(50) values calculated for these enzymes ranges from 1.75 to 10.5 microM. Inflammatory human sPLA(2) enzymes are more sensitive to inhibition by bilirubin than snake venom sPLA(2)s. Inhibition of sPLA(2) activity by bilirubin is independent of calcium concentration. Increasing substrate concentration (upto 180 nmol) did not relieve the inhibition of sPLA(2) by bilirubin and it is irreversible. Bilirubin quenched the relative fluorescence intensity of sPLA(2) in a dose dependent manner in the same concentration range at which in vitro sPLA(2) inhibition was observed. In the presence of bilirubin, apparent shift in the far UV-CD spectra of sPLA(2) was observed, indicating a direct interaction with the enzyme. Inhibition of sPLA(2) induced mouse paw edema by bilirubin confirms its sPLA(2) inhibitory activity in vivo also. These findings indicate that inhibition of sPLA(2) by bilirubin is mediated by direct interaction with the enzyme and bilirubin may act as an endogenous regulator of sPLA(2) enzyme activity.

Purification of a Class B1 platelet aggregation inhibitor phospholipase A2 from Indian cobra (Naja Naja) venom.

A platelet aggregation inhibitor phospholipase A(2) (NND-IV-PLA(2)) was isolated from Naja naja (Eastern India) venom by a combination of cation and anion exchange chromatography. NND-IV-PLA(2) is the most catalytically active enzyme isolated from the Indian cobra venom. The acidic PLA(2) profile of Eastern regional Indian cobra venom is distinctly different from that of the western regional venom. However the acidic PLA(2)s from both the regions follow the pattern of increasing catalytic activity with increase in acidic nature of the PLA(2) isoform. NND-IV-PLA(2) is a Class B1 platelet aggregation inhibitor and inhibits platelet aggregation induced by ADP, collagen and epinephrine. Modification of active site histidine abolishes both catalytic activity and platelet aggregation inhibition activities while aristolochic acid, a phospholipase A(2) inhibitor has only partial effect on the two activities.