Characterization of Trypsin-Like Serine Protease from Lethocerus indicus Salivary Venom and its Cytotoxic Effect against Human Epidermoid Carcinoma Cell, A431

Objective: Lethocerus indicus salivary venom characterization and evaluation of extracellular degradation activity and cytotoxic effect against native human collagen type 1 and epidermoid carcinoma cell, A431.

Method: Salivary venom extract was collected from adult insects by injecting 2% pilocarpine of 50 µml. Enzyme presence was detected by the apiZYM assay. The proteolytic activity was tested by the photometric and zymogram methods using specific fluorescent substrates and inhibitors. The cytotoxic activity was determined by the MTT assay and Trypan blue exclusion method. Apoptosis induction was observed using AO/EB staining solution. Digestion of extracellular matrix protein was detected against native human type I collagen.

Result: L. indicus salivary venom presents amylases, proteases, carbohydrases, phosphatases and lipases. Among them, protease enzyme showed highest composition. The highest rate of proteolytic activity observed at pH 8 in 35ºC (100 %). Serine proteases present predominantly in salivary venom. Cysteine and metalloproteases are also detected. The activation energy of salivary venom is 49.86 kJ. Use of serine inhibitor, PMSF inhibited 92.77% which indicated that the maximum activity was due to serine protease. Detection of trypsin-like protease was confirmed by using PMSF and TLCK with specific substrate, BApNA. It shows significant inhibitions, 82% and 78% respectively suggesting maximum influence in salivary venom. Degradation of the fibrillar native state collagen Type I into 8 smaller peptide bands showed it importance in medical application. IC50 concentration of venom that induces cytotoxicity in epidermoid carcinoma cells, A431was 2.3 µg/ml only. It gives prominent apoptotic features such as cytoplasmic membrane blebbing, nuclear contraction, nuclear fragmentation and contact inhibition.

Conclusion: We suggest that further investigation of the venom will lead to identification of active compound in L. indicus salivary venom for its potential use in therapeutic application.