Epigenetics refers to modifications in chromatin structure that result in altered gene expression without any changes in DNA sequence. Chromatin comprises of a DNA sequence wrapped around an octamer of histone proteins called nucleosomes. The extent of the packing of DNA over the nucleosomes determines its accessibility to enzymes involved in various processes. While genes present in regions of DNA that are wound around relatively spaced nucleosomes are easily available for transcription, genes that are located in DNA wrapped over tightly packed nucleosomes are not readily accessed by the transcription machinery. The latter group of genes are consequently transcriptionally inactive or silenced. However, the arrangement of nucleosomes can undergo alteration catalysed by different enzymes and this in turn can result in changes in gene transcription or expression.
Acetylation and methylation of histone proteins can modify the way these proteins interact with DNA wound over them. Enzymes such as- histone acetyltransferases that add acetyl group and histone deacetylases (HDACs) that reverse the process, histone methyltransferases ( HMTs) that catalyse histone methylation and histone demethylases (HDMs) that remove it can change gene expression patterns in a cell without any changes in DNA sequence.
In addition to this, methylation of cytosine residues in DNA brought about by methyltransferases can block the ability of transcription factors to bind to specific regions in DNA, resulting in loss of gene expression. All such processes that can control gene expression without any changes in the DNA sequence are means of epigenetic regulation of gene expression.
A number of environmental factors can regulate gene expression via epigenetic modifications. Nutrition and our dietary choices can modify a number of physiological and pathological processes by altering critical genes involved in them at an epigenetic level. Bioactive components present in food can change the level of methylation and acetylation in chromatin, either by directly inhibiting the enzymes catalysing these modifications or changing the availability of metabolites required for these reactions.
Vitamin B-12, methionine, choline, and betaine are food ingredients that can alter the methylation pattern in DNA. These food components can alter metabolic reactions, resulting in changes in levels of metabolites like adenosylmethionine (AdoMet) and S-adenosylhomocysteine (AdoHcy). While AdoMet acts as a methyl donor for methylation reactions, AdoHcy can inhibit methyltransferases. Thus, changes in their level can result in epigentic changes in cells.
Nutritionally derived cofactors like nicotinamide adenonucleotide (NAD), Zn2+, ascorbate, Fe2+, oxygen have been reported to modify histones. Additionally, water-soluble vitamins such as biotin, niacin, and pantothenic acid too have been reported to mediate certain epigenetic modifications on histones. Compounds such as curcumin, diallyl sulphide, sulforaphane, butyrate, and resveratrol can change the acetylation levels of histones by inhibiting enzymes involved in their acetylation and deacetylation.
Understandably, fortified foods containing vitamins and mineral supplements can alter gene expression by interacting with chromatin at the epigenome level. Some reports propose the role of folic acid supplementation in mothers to result in an increased risk of neurological disorders in their offspring. Similarly, vitamin B fortification in grains can result in unpredictable alterations in methylation patterns in different cells. Phytochemical constituents present in spices, herbs, and other medicinal plants have also been reported to modulate the epigenome.
According to Umaima U, a clinical nutritionist, "Nutrients play fundamental role in human health and development. They are a source of energy that helps in the synthesis and regulation of cells. Certain nutrients like vitamin A and D can have dramatic effects on gene expression as well. "
Processes such as aging, carcinogenesis, and the development of diseases can be regulated by diet-mediated epigenetic alterations. With studies showing the role of epigenetics in lifestyle diseases like diabetes and obesity, immunity and inflammation, and some neurological ailments, an important role of nutritional epigenetics in the management of these diseases has emerged.
Including certain components in food or taking specific nutrients has the possibility of preventing certain diseases and promoting health. An advantage of this approach is that it’s fast and reversible. However, this effect is not so straightforward as these ingredients can interact with each other as well as the lifestyle factors to produce epigentic alterations, making it complex.
Furthermore, the delivery of nutrients to a specific tissue or organ also presents a challenge. It is important to remember that the expression of the genome depends on the environment and diet. Thus, personalised epigentic modulation through nutrition and diet can prove to be an effective way to manage and prevent diseases. Conversely, there should be a cautionary approach to food supplementation as it may lead to irregular changes at the epigenetic level.
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