Inhibition of phospholipase A₂ from Naja haje and Naja nigricollis venoms by active fraction of Moringa oleifera leaves: in vitro and in silico methods

Phospholipases are one of the principal toxic enzymes in snake venoms inducing a wide variety of pharmacological effects after envenomation. Natural inhibitors from plants are known to inhibit the toxic enzyme activities of snake venoms. In this study, ethanol crude extract of M. oleifera leaves was partitioned using n-hexane and ethyl acetate after which fractionation was done using column and thin layer chromatography. Subsequently, the inhibitory activities of the crude extract and sub-fractions of M. oleifera were investigated against phospholipases A(2) isolated from Naja haje and Naja nigricollis venoms using in vitro and in-silico approaches while EchiTab-PLUS polyvalent antivenom was used as the standard drug. The molecular weight of isolated N. haje phospholipase A(2) (NH-PL) and N. nigricollis phospholipase A(2) (NN-PL) were 24.11 and 35.22 kDa respectively. NH-PL enzyme had a specific activity of 2.70 mu M/min/mg substrate while NN-PL activity was 2.10 mu M/min/mg substrate. The K-m of NH-PL was 0.330 mu M with V-max of 0.085 mu M/mL min while NN-PL had V-max of 0.198 mu M/mL.min and K-m of 0.670 mu M. M. oleifera n-hexane sub-fraction 5 (MOLH5) exhibited a total inhibition of NN-PL and NH-PL enzyme activities at all concentrations used. Molecular docking of the phytoconstituents of MOLH5 against the catalytic site of phospholipase A(2) revealed 2-Hydrazino-8-hydroxy-4-phenylquinoline as the lead compound and a potential drug candidate with a docking score of -6.789 kcal/mol. Findings indicated that MOLH5 possesses phospholipase A(2) natural inhibitors that could be explored as a therapy for snake envenoming.