In vivo binding of retinol to chromatin. The binding is mediated by a lipoprotein

Nutritive vitamins as epidrugs

Epigenetic modifications play an important role in disease pathogenesis and therefore are a focus of intense investigation. Epigenetic changes include DNA, RNA, and histone modifications along with expression of non-coding RNAs. Various factors such as environment, diet, and lifestyle can influence the epigenome. Dietary nutrients like vitamins can regulate both physiological and pathological processes through their direct impact on epigenome. Vitamin A acts as a major regulator of above-mentioned epigenetic mechanisms. B group vitamins including biotin, niacin, and pantothenic acid also participate in modulation of various epigenome. Further, vitamin C has shown to modulate both DNA methylation and histone modifications while few reports have also supported its role in miRNA-mediated pathways. Similarly, vitamin D also influences various epigenetic modifications of both DNA and histone by controlling the regulatory mechanisms. Despite the information that vitamins can modulate the epigenome, the detailed mechanisms of vitamin-mediated epigenetic regulations have not been explored fully and hence further detailed studies are required to decipher their role at epigenome level in both normal and disease pathogenesis. The current review summarizes the available literature on the role of vitamins as epigenetic modifier and highlights the key evidences for developing vitamins as potential epidrugs.

Vitamin A intake and in vivo expression of the genes involved in retinol transport

Two different metabolic alterations in vitamin A status are known to cause changes in the amount of circulating retinol-binding protein (RBP) and cellular retinol-binding protein (CRBP) in experimental animals; namely vitamin A deficiency, characterized by depleted retinol-liver stores and hypervitaminosis A, characterized by hepatic accumulation of retinyl esters. We have induced vitamin A deficiency and hypervitaminosis A in two groups of rats with the aim of determining whether the expression of the genes coding for these two proteins might be directly regulated by retinol. Using human RBP and CRBP cDNAs as probes, we measured the rate of transcription of the two genes in liver nuclei from control and treated rats by run-on transcription assays, and the steady-state level of the mRNAs by Northern blot analysis of total liver RNA. The distribution profile of RBP and CRBP mRNAs on fractionated liver polysomes was also examined. We have found a threefold decrease in the hepatic level of CRBP mRNA in vitamin-A-deficient animals, while the RBP mRNA is not affected by this nutritional deprivation. The decreases does not correspond to a lower transcription rate of the gene and therefore it is likely to result from lower stability of the CRBP mRNA. In hypervitaminosis A, we do not observe any differences in both the steady-state level of the mRNAs and in the rate of transcription of the two genes. The results are discussed in terms of retinol-dependent stabilization of the mRNA coding for CRBP.

New approaches and concepts in the study of differentiation of oral epithelia

Epithelial structural proteins, the keratins and keratin-associated proteins, are useful as markers of differentiation because their expression is both region-specific and differentiation-specific. In general, basal cells in all stratified oral epithelia express similar keratins, while the suprabasal cells express a specific set of markers indicating commitment to a distinct program of differentiation. Critical factors in the regulation of epithelial protein expression are now under investigation. The promoter regions of keratin genes are being characterized to determine what sequences within the genes are responsible for differential expression. One important extracellular factor that influences epithelial protein expression is retinol (vitamin A), which exerts its effects via a group of nuclear receptor proteins that may also be expressed in a region-specific manner. These molecular biological approaches enhance our understanding of the mechanisms regulating differentiation of oral epithelia and its regional complexity.

Interaction retinol-chromatin: an analysis of DNA from vitamin A-treated V79 Chinese hamster cells

When V79 cells are incubated in the presence of radiolabeled retinol, a small but consistent amount of radioactivity remains associated with nuclear DNA. Chromatographic analysis of enzymatic hydrolysates of DNA shows that no irreversible changes, such as adducts, have taken place on DNA. We present evidence that this radioactive incorporation may occur via a metabolic conversion of retinol, leading mainly to the formation of radiolabeled thymidine, which is then incorporated into newly made DNA. Mutagenic effects by retinol, given at concentrations well above physiological levels, have been also excluded.

Effect of retinyl acetate on nuclear proteins in rabbit liver

1. Retinyl acetate injected intraperitoneally to adult rabbits fed on standard diet caused detectable changes in the polyacrylamide gel patterns of liver nucleoplasmic and 0.35 M NaCl-soluble chromatin proteins. 2. Both histones and non-histone proteins soluble in 5 M urea were not affected in vitamin A-treated animals. 3. It seems that variations in liver nuclear proteins from retinyl acetate-administered rabbits may reflect retinol-dependent alterations in structure and function of their chromatins.