Acetylcholinesterase Inhibition of Marine Fish (Rastrelliger kanagurta) by Organophosphorus Pesticides as Biomarker of Neurotoxicants

Abstract

This paper evaluated the inhibitory effects of various phosphorothioates (Ethyl parathion and Chlorpyriphos) and phosphates (DDVP, Monocrotophos and Phosphamidon) on acetylcholinesterase (AChE) of marine Mackerel fish (Rastrelliger kanagurta) from the Goa coast. The characteristics of the AChE enzymes isolated from different tissues of the fishes for their affinity towards the substrate were determined by the Michaelis Menten constants. The pseudocholinesterase activity was also measured in the muscle tissues in terms of Butyryl-cholinesterase (BChE) activity of the fish. The AChE activity was found to be predominant in the Brain, gills, liver and muscle tissues. However, no significant BChE activity was observed in the muscle tissue. Among the five organophosphorus pesticides, DDVP was found to be most toxic with least I50 values (0.99±0.04nM) followed by Chlorpyriphos (I50, 24.59±2.86 nM), Ethyl Parathion (I50, 183.21±11.68 nM), Monocrotophos (I50, 13536.93±1292.94 nM) and Phosphamidon (I50, 21433.1±2651.96 nM) in the decreasing order. The I50 values of all other pesticides decreased considerably with respect to DDVP. The relative neurotoxicity of the pesticides decreased by an order of magnitude in the case of Chlorpyriphos followed by Ethyl Parathion by an order of magnitude whereas in the case of Monocrotophos and Phosphamidon the toxicity decreased significantly by an order of magnitude. The variation in the muscle AChE inhibition by the organophosphorus pesticides can be attributed to the sensitivity of the enzyme for each of the pesticides as observed by the bimolecular inhibition constants (KII). The muscle AChE inhibition of Rastrelliger kanagurta can be used as biomarker for bio- monitoring of neurotoxic contaminants in the marine environment.