DNA methylation, an essential epigenetic feature of DNA that modulates gene expression and genomic integrity, is catalyzed by methyltransferases that use the universal methyl donor S-adenosyl-L-methionine. Methylenetetrahydrofolate reductase (MTHFR) catalyzes the synthesis of 5-methyltetrahydrofolate (5-methyl-THF), the methyl donor for synthesis of methionine from homocysteine and precursor of S-adenosyl-L-methionine. In the present study we sought to determine the effect of folate status on genomic DNA methylation with an emphasis on the interaction with the common C677T mutation in the MTHFR gene. A liquid chromatography͞MS method for the analysis of nucleotide bases was used to assess genomic DNA methylation in peripheral blood mononuclear cell DNA from 105 subjects homozygous for this mutation (T͞T) and 187 homozygous for the wild-type (C͞C) MTHFR genotype. The results show that genomic DNA methylation directly correlates with folate status and inversely with plasma homocysteine (tHcy) levels (P < 0.01). T͞T genotypes had a diminished level of DNA methylation compared with those with the C͞C wild-type (32.23 vs.62.24 ng 5-methylcytosine͞g DNA, P < 0.0001). When analyzed according to folate status, however, only the T͞T subjects with low levels of folate accounted for the diminished DNA methylation (P < 0.0001). Moreover, in T͞T subjects DNA methylation status correlated with the methylated proportion of red blood cell folate and was inversely related to the formylated proportion of red blood cell folates (P < 0.03) that is known to be solely represented in those individuals. These results indicate that the MTHFR C677T polymorphism influences DNA methylation status through an interaction with folate status.

The metabolism of vitamin A and the diverse effects of its metabolites are tightly controlled by distinct retinoid-generating enzymes, retinoid-binding proteins and retinoid-activated nuclear receptors. Retinoic acid regulates differentiation and metabolism by activating the retinoic acid receptor and retinoid X receptor (RXR), indirectly influencing RXR heterodimeric partners. Retinoic acid is formed solely from retinaldehyde (Rald), which in turn is derived from vitamin A. Rald currently has no defined biologic role outside the eye. Here we show that Rald is present in rodent fat, binds retinol-binding proteins (CRBP1, RBP4), inhibits adipogenesis and suppresses peroxisome proliferator-activated receptor-c and RXR responses. In vivo, mice lacking the Rald-catabolizing enzyme retinaldehyde dehydrogenase 1 (Raldh1) resisted diet-induced obesity and insulin resistance and showed increased energy dissipation. In ob/ob mice, administrating Rald or a Raldh inhibitor reduced fat and increased insulin sensitivity. These results identify Rald as a distinct transcriptional regulator of the metabolic responses to a high-fat diet.Although vitamin A and its metabolite retinoic acid have therapeutic applications, frequent side effects limit their use 1-3 . In clinical trials involving β-carotene supplementation, worrisome increases in cardiovascular events and mortality have been noted, despite evidence suggesting possible beneficial vascular effects of this treatment 3 . These variable responses to retinoids probably derive from the fact that β-carotene and vitamin A (retinol) and their major metabolites-retinaldehyde (Rald) and retinoic acid-regulate diverse cellular responses, including development, immune function and vision 4,5 . The tight control of retinoid biology is evident in the elaborate system that governs the absorption, formation, transportation and action of these structurally and functionally distinct retinoid metabolites. Despite this, retinoids

The literature describing vitamin D content of fat tissue is extremely limited. We conducted a pilot study that measured the concentrations of vitamin D(3) in the fat tissue and serum of obese adults. These measurements were performed using a new liquid chromatography mass spectrometry (LC/MS) method. The objectives of this study were: to measure and report the vitamin D(3) concentration in serum and subcutaneous fat samples from obese individuals and to examine the association of vitamin D(3) in fat with vitamin D(3) in serum. This cross-sectional study was conducted in 17 obese men and women who were scheduled to undergo gastric bypass surgery. The mean vitamin D(3) concentration in subjects' subcutaneous fat tissue samples was 102.8 +/- 42.0 nmol/kg. The mean vitamin D(3) concentration in serum was 7.78 +/- 3.99 nmol/l. Vitamin D(3) concentrations of fat tissue and serum were positively correlated (r = 0.68, P = 0.003). Consistent with previous findings in obese subjects, subjects in this study had suboptimal vitamin D status as demonstrated by a mean 25-hydroxyvitamin D concentration of 43.3 +/- 15.4 nmol/l. In conclusion, fat tissue vitamin D(3) can be measured by LC/MS and is detectable in obese subjects with suboptimal vitamin D status. Compatible with the long-standing concept that fat tissue is a storage site for vitamin D, fat tissue and serum vitamin D(3) concentrations were positively correlated.