Blood cholinesterase activity: Inhibition as an indicator of adverse effect

Organophosphate and carbamate insecticides are designed to inhibit cholinesterase (ChE), the serine protease which hydrolyses the neurotransmitter acetylcholine. Inhibition of ChE activity may lead to central and peripheral nervous system dysfunction in both humans and laboratory animals. Although blood ChE does not participate in neurotransmission, depression of blood ChE activity has been traditionally used as a convenient biomarker for exposure to ChE-inhibiting insecticides. Our laboratory has been engaged in numerous studies to explore the possibility that blood ChE inhibition might also be utilized as a biomarker of adverse effect (in addition to a biomarker of exposure). Our results to date indicate that the degree of depression of blood ChE activity usually correlates well with the amount of ChE inhibition in the target tissues or the degree of clinical impairment; the exact numerical relationship, however, is dependent upon time after dosing, choice of tissue or clinical endpoint, and the insecticide tested.