Disruption of Mouse Cytochrome P450 4f14 (Cyp4f14 Gene) Causes Severe Perturbations in Vitamin E Metabolism

Vitamin E is a family of naturally occurring and structurally related lipophilic antioxidants, one of which, alpha-tocopherol (alpha-TOH), selectively accumulates in vertebrate tissues. The omega-hydroxylase cytochrome P450-4F2 (CYP4F2) is the only human enzyme shown to metabolize vitamin E. Using cDNA cloning, cell culture expression, and activity assays, we identified Cyp4f14 as a functional murine ortholog of CYP4F2. We then investigated the effect of Cyp4f14 deletion on vitamin E metabolism and status in vivo. Cyp4f14-null mice exhibited substrate-specific reductions in liver microsomal vitamin E-omega-hydroxylase activity ranging from 93% (gamma-TOH) to 48% (gamma-tocotrienol). In vivo data obtained from metabolic cage studies showed whole-body reductions in metabolism of gamma-TOH of 90% and of 68% for delta- and alpha-TOH. This metabolic deficit in Cyp4f14(-/-) mice was partially offset by increased fecal excretion of nonmetabolized tocopherols and of novel omega-1- and omega-2-hydroxytocopherols. 12'-OH-gamma-TOH represented 41% of whole-body production of gamma-TOH metabolites in Cyp4f14(-/-) mice fed a soybean oil diet. Despite these counterbalancing mechanisms, Cyp4f14-null mice fed this diet for 6 weeks hyper-accumulated gamma-TOH (2-fold increase over wild-type litter-mates) in all tissues and appeared normal. We conclude that CYP4F14 is the major but not the only vitamin E-omega-hydroxylase in mice. Its disruption significantly impairs whole-body vitamin E metabolism and alters the widely conserved phenotype of preferential tissue deposition of alpha-TOH. This model animal and its derivatives will be valuable in determining the biological actions of specific tocopherols and tocotrienols in vivo.