Inhibitory effects on phospholipase A2 and antivenin activity of melanin extracted from Thea sinensis Linn

Antivenin activity of melanin extracted from black tea (MEBT) was reported for the first time. The antagonistic effect of MEBT was evaluated for Agkistrodon contortrix laticinctus (broadbanded copperhead), Agkistrodon halys blomhoffii (Japanese mamushi), and Crotalus atrox (western diamondback rattlesnake) snake venoms administered i.p. to ICR mice. MEBT was injected i.p. immediately after the venom administration in dose of 3 mg per mouse in the same place of venom injection. MEBT demonstrated neutralization effect against all venoms tested. The greatest antivenin effect of MEBT was found against Japanese mamushi snake venom. In this case, half the mice died within 2.5 +/- 0.7 h after injection of 0.9 mg/kg of venom. An immediate injection of MEBT substantially reduced the toxic effect of venom and extended time at the 50% level of survival up to 52.3 +/- 2.3 h. The antivenin activity of MEBT is due to chelating of Ca++ and non-specific binding of phospholipase A2. The inhibitory effect of MEBT on phospholipase A2 assessed for different venoms was similar to that obtained with pure enzyme. Low toxicity of MEBT in combination with its antagonistic activity against different venoms may allow effective life-saving treatment against snakebites. Such application of MEBT is important when identification of the snake is impossible or if specific treatment is unavailable.