Quantitative proteomic analysis and antivenom study revealing that neurotoxic phospholipase A enzymes, the major toxin class of Russell's viper venom from southern India, shows the least immuno-recognition and neutralization by commercial polyvalent antivenom.

The proteome composition of Russell's viper venom (RVV) from southern India (SI) was investigated by 1D-SDS-PAGE of venom followed by tandem mass spectrometry analysis of protein bands. A total of 66 proteins belonging to 14 snake venom protein families were identified by LC-MS/MS analysis against Viperidae (taxid 8689) protein entries from the non-redundant NCBI database. Phospholipase A (43.25%) and snaclec (14.57%) represented the most abundant enzymatic and non-enzymatic proteins, respectively. SI RVV was characterized as containing a higher quantity of PLA and a lower amount of Kunitz-type serine protease inhibitors, in comparison to RVV from other regions of the Indian subcontinent. The enzymatic activities, pharmacological properties, and clinical manifestations of RV envenomation in SI were well correlated with its proteome composition; however, ATPase, ADPase, and hyaluronidase enzymes were not identified by LC-MS/MS analysis, owing to paucity of the existing database. Neurological symptoms exhibited by RV-bite patients in SI were correlated to the presence of abundant neurotoxic phospholipase A enzymes (15.66%) in SI RVV. Neutralization studies, immunological cross-reactivity, and antivenomics studies unequivocally demonstrated the poor recognition and lowest neutralization of PLA enzymes by commercial polyvalent antivenom, which is a major concern for the treatment of RV-envenomed patients in SI.