Acetylcholinesterase inhibition as relevant biomarker in environmental biomonitoring: new insights and perspectives

Acetylcholinesterase (AChE) is a key enzyme in the nervous system, terminating nerve impulses by catalyzing the hydrolysis of neurotransmitter acetylcholine. AChE is the target site of inhibition by organophosphorus and carbamate pesticides. In particular, organophosphorous pesticides inhibit the enzyme activity by covalently phosphorylating the serine residue within the active site group. They irreversibly inhibit AChE, resulting in excessive accumulation of acetylcholine, leading to the hyperactivities and consequently paralysis of the neural and muscle system. Therefore, monitoring of AChE inhibition is widely used as a biomarker of organophosphorous and carbamate exposure either in aquatic or terrestrial environments. Recently, new insights are emerging in the use of AChE as biomarker in environmental biomonitoring. A number of important contaminants other than carbamate and organophosphorus pesticides have recently been shown to have anticholinesterase properties, including heavy metals, detergents, hydrocarbons, and herbicides. It is also worth noting that not only different compounds may reach levels of significance in terms of anticholinesterase effect, but, moreover, combinations of different chemical classes were shown to be highly synergistic in their ability to inhibit AChE activity. Moreover, evidence for additional function of AChE is recently emerging. Apart from its catalytic function in hydrolyzing acetylcholine, different forms of AChE have been shown to affect cell proliferation, differentiation, and responses to various stresses. In addition, the relationship among the antioxidant defence systems and the AChE inhibition is now emerging. These recent insights open a new future in biological monitoring and environmental assessment to this “old” biomarker. Furthermore, its use in different phyla, either vertebrates or invertebrates, makes AChE a particularly versatile biomarker that can be used to investigate pollutant effects in many trophic levels and in many different environments.