In vitro human metabolism of permethrin: the role of human alcohol and aldehyde dehydrogenases

Abstract

Permethrin is a pyrethroid insecticide widely used in agriculture and public health. It has been suggested that permethrin may interact with other chemicals used during military deployments and, as a result, be a potential cause of Gulf War Related Illness. To determine the causal relationship between permethrin and human health effects, the basic enzymatic pathway of permethrin metabolism in humans should be understood. In the present study we report that trans-permethrin is metabolized in human liver fractions, producing phenoxybenzyl alcohol (PBOH) and phenoxybenzoic acid (PBCOOH). We identified human alcohol (ADH) and aldehyde dehydrogenases (ALDH) as the enzymes involved in the oxidation of phenoxybenzyl alcohol, the permethrin hydrolysis product, to phenoxybenzoic acid by way of phenoxybenzaldehyde (PBCHO). Cis-permethrin was not significantly metabolized in human liver fractions. Cytochrome P450 isoforms were not involved either in the hydrolysis of trans-permethrin or in the oxidation of PBOH to PBCOOH. Purified ADH isozymes oxidized PBOH to PBCHO and PBOH was a preferred substrate to ethyl alcohol. Purified ALDH was responsible for PBCHO oxidation to PBCOOH with similar substrate affinity to a previously known substrate, benzyl alcohol. Based on these observations, it appears that PBOH is oxidized to PBCHO by ADH and subsequently to PBCOOH by ALDH, although PBCHO does not accumulate during microsomal incubation. In order to analyze permethrin and its metabolites, previous HPLC-UV methods had to be re-validated and modified. The resulting refined HPLC-UV method is described in detail.