Genistein, a potent inhibitor of secretory phospholipase A₂: A new insight in down regulation of inflammation

Objectives: Some of the legumes, spices and medicinal herbs rich in genistein are known for their anti-inflammatory properties. Anti-inflammatory property of these herbs is determined by subjecting secretory phospholipase A₂ (sPLA₂) inhibition, a key enzyme in the inflammatory reactions by genistein. Materials and methods: Genistein was assessed for inhibition of sPLA₂ activity using ¹⁴C-oleate radiolabelled Escherichia coli membrane as substrate. The enzyme-inhibitor interaction was established by intrinsic fluorescence and circular dichroism studies. The in vivo anti-inflammatory activity was tested by injecting sPLA₂, Vipera russelli venom phospholipase-V (VRV-PL-V) with different concentrations of genistein in the range of 3-21 μM into intra plantar surface of right hind footpad of mice. Systemic effect was tested by administering the genistein (21 μM) i.p. 30 min before and immediately after sPLA₂ injection. Result: Genistein inhibited sPLA₂ enzymes of inflammatory exudates (human synovial fluid and human pleural fluid) and snake venoms (VRV-PL-V and Naja naja phospholipase-I) in a concentration dependent manner with IC₅₀ values ranging from 5.75 to 11.75 μM. Increasing the calcium (Ca²⁺) concentration from 2.5 to 15 mM and substrate concentration up to 120 nM did not alter the level of inhibition. Genistein alters the intrinsic fluorescence intensity and shown apparent shift in far ultra violet-circular dichroism spectra of VRV-PL-V, indicating the direct interaction with enzyme. Genistein also inhibited the VRV-PL-V induced mouse paw oedema in a concentration dependent manner. The genistein at 21 μM concentration administered immediately after the VRV-PL-V injection, effectively neutralized the oedema inducing activity. Conclusion: Genistein inhibited sPLA₂ activity of both inflammatory exudates and snake venoms in a concentration dependent manner and sPLA₂ induced mouse paw oedema. The study partially explains the observed anti-inflammatory property of several medicinal herbs which containing genistein.