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ABSTRACT: The widely conserved preferential accumulation of α-tocopherol (α-TOH) in tissues occurs, in part, from selective post-absorptive catabolism of non-α-TOH forms via the vitamin E-ω-oxidation pathway. We previously showed that global disruption of CYP4F14, the major but not the only mouse TOH-ω-hydroxylase, resulted in hyper-accumulation of γ-TOH in mice fed a soybean oil diet. In the current study, supplementation of Cyp4f14-/- mice with high levels of δ- and γ-TOH exacerbated tissue enrichment of these forms of vitamin E. However, at high dietary levels of TOHs, mechanisms other than ω-hydroxylation dominate in resisting diet-induced accumulation of non-α-TOHs. These include TOH metabolism via ω-1/ω-2 oxidation and fecal elimination of unmetabolized TOHs. The ω-1 and ω-2 fecal metabolites of γ- and α-TOH were observed in human fecal material. Mice lacking all liver microsomal CYP activity due to disruption of cytochrome P450 reductase revealed the presence of extra-hepatic ω-, ω-1, and ω-2 TOH hydroxylase activities. TOH-ω-hydroxylase activity was exhibited by microsomes from mouse and human small intestine; murine activity was entirely due to CYP4F14. These findings shed new light on the role of TOH-ω-hydroxylase activity and other mechanisms in resisting diet-induced accumulation of tissue TOHs and further characterizes vitamin E metabolism in mice and humans.
The Journal of Lipid Research 09/2012; · 5.56 Impact Factor
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ABSTRACT: Vitamin E is a family of naturally occurring and structurally related lipophilic antioxidants, one of which, α-tocopherol (α-TOH), selectively accumulates in vertebrate tissues. The ω-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-ω-hydroxylase activity ranging from 93% (γ-TOH) to 48% (γ-tocotrienol). In vivo data obtained from metabolic cage studies showed whole-body reductions in metabolism of γ-TOH of 90% and of 68% for δ- and α-TOH. This metabolic deficit in Cyp4f14(-/-) mice was partially offset by increased fecal excretion of nonmetabolized tocopherols and of novel ω-1- and ω-2-hydroxytocopherols. 12'-OH-γ-TOH represented 41% of whole-body production of γ-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 γ-TOH (2-fold increase over wild-type littermates) in all tissues and appeared normal. We conclude that CYP4F14 is the major but not the only vitamin E-ω-hydroxylase in mice. Its disruption significantly impairs whole-body vitamin E metabolism and alters the widely conserved phenotype of preferential tissue deposition of α-TOH. This model animal and its derivatives will be valuable in determining the biological actions of specific tocopherols and tocotrienols in vivo.
Journal of Biological Chemistry 06/2012; 287(31):26077-86. · 4.77 Impact Factor
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ABSTRACT: Human cytochrome P450 4F2 (CYP4F2) catalyzes the ω-hydroxylation of the side chain of tocopherols (TOH) and tocotrienols (T3), the first step in their catabolism to polar metabolites excreted in urine. CYP4F2, in conjunction with α-TOH transfer protein, results in the conserved phenotype of selective retention of α-TOH. The purpose of this work was to determine the functional consequences of 2 common genetic variants in the human CYP4F2 gene on vitamin E-ω-hydroxylase specific activity using the 6 major dietary TOH and T3 as substrate. CYP4F2-mediated ω-hydroxylase specific activity was measured in microsomal preparations from insect cells that express wild-type or polymorphic variants of the human CYP4F2 protein. The W12G variant exhibited a greater enzyme specific activity (pmol product · min(-1) · pmol CYP4F2(-1)) compared with wild-type enzyme for both TOH and T3, 230-275% of wild-type toward α, γ, and δ-TOH and 350% of wild-type toward α, γ, and δ-T3. In contrast, the V433M variant had lower enzyme specific activity toward TOH (42-66% of wild type) but was without a significant effect on the metabolism of T3. Because CYP4F2 is the only enzyme currently shown to metabolize vitamin E in humans, the observed substrate-dependent alterations in enzyme activity associated with these genetic variants may result in alterations in vitamin E status in individuals carrying these mutations and constitute a source of variability in vitamin E status.
Journal of Nutrition 11/2010; 140(11):1901-6. · 3.92 Impact Factor
