Cytotoxic activities of [Ser49]phospholipase A2 from the venom of the saw-scaled vipers Echis ocellatus, Echis pyramidum leakeyi, Echis carinatus sochureki, and Echis coloratus

Abstract

Fractionation by reversed-phase HPLC of venom from four species of saw-scaled viper: Echis ocellatus, Echis pyramidum leakeyi, Echis carinatus sochureki, and Echis coloratus led to identification in each sample of an abundant protein with cytotoxic activity against human non-small cell lung adenocarcinoma A549 cells. The active component in each case was identified by MALDI-TOF mass fingerprinting of tryptic digests as [Ser49]phospholipase A2 ([Ser49]PLA2). An isoform of [Ser49]PLA2 containing the single Ala18 → Val substitution and a partially characterized [Asp49]PLA2 were also present in the E. coloratus venom. LC50 values against A549 cells for the purified [Ser49]PLA2 proteins from the four species are in the range 2.9–8.5 μM. This range is not significantly different from the range of LC50 values against human umbilical vein endothelial HUVEC cells (2.5–12.2 μM) indicating that the [Ser49]PLA2 proteins show no differential anti-tumor activity. The LC50 value for [Ser49]PLA2 from E. ocellatus against human erythrocytes is >100 μM and the MIC values against Escherichia coli and Staphylococcus aureus are >100 μM. It is suggested that the [Ser49]PLA2 proteins play a major role in producing local tissue necrosis and hemorrhage at the site of envenomation.