Selective accumulation of alpha-tocopherol in Drosophila is associated with cytochrome P450 tocopherol-omega-hydroxylase activity but not alpha-tocopherol transfer protein

Abstract

Humans and other mammals actively discriminate among the various forms of vitamin E to selectively retain alpha-tocopherol, but the phylogenetic breadth of this trait is unknown. We sought to determine if the fruit fly, Drosophila melanogaster, similarly discriminates and if so by what mechanism. Larvae and adult flies fed diets containing predominantly gamma- and delta-tocopherols were enriched in alpha-tocopherol. Inclusion in the diet of piperonyl butoxide (PBO), an insect cytochrome P450 inhibitor and inhibitor of tocopherol-omega-hydroxylase activity, greatly elevated tissue levels of delta-tocopherol but not alpha-tocopherol. Drosophila microsomes exhibited tocopherol-omega-hydroxylase activity in the order of delta-T > gamma-T >> alpha-T, a pattern consistent with the effect of PBO in vivo. To determine if selectivity involved alpha-tocopherol transfer protein (alpha-TTP), adult flies were fed an equimolar mixture of d3-RRR- and d6-all-racemic alpha-tocopherol. Flies exhibited a d3/d6 ratio of 1.03, demonstrating an inability to discriminate on the basis of phytyl tail stereochemistry, a hallmark of alpha-TTP activity. We conclude that Drosophila preferentially accumulates alpha-tocopherol via a mechanism involving cytochrome P450 tocopherol-omega-hydroxylase-mediated catabolism of other tocopherols, but not a mammalian-like alpha-TTP. The selective pressure favoring this trait and its remarkable conservation from insects to humans requires elucidation.