Association of air pollution and homocysteine with global DNA methylation: A population-based study from North India

Background
Anthropogenic air pollution has been implicated in aberrant changes of DNA methylation and homocysteine increase (>15μM/L). Folate (<3 ng/mL) and vitamin B12 (<220 pg/mL) deficiencies also reduce global DNA methylation via homocysteine increase. Although B-vitamin supplements can attenuate epigenetic effects of air pollution but such understanding in population-specific studies are lacking. Hence, the present study aims to understand the role of air pollution, homocysteine, and nutritional deficiencies on methylation.

Methods
We examined cross-sectionally, homocysteine, folate, vitamin B12 (chemiluminescence) and global DNA methylation (colorimetric ELISA Assay) among 274 and 270 individuals from low- and high- polluted areas, respectively, from a single Mendelian population. Global DNA methylation results were obtained on 254 and 258 samples from low- and high- polluted areas, respectively.

Results
Significant decline in median global DNA methylation was seen as a result of air pollution [high-0.84 (0.37–1.97) vs. low-0.96 (0.45–2.75), p = 0.01]. High homocysteine in combination with air pollution significantly reduced global DNA methylation [high-0.71 (0.34–1.90) vs. low-0.93 (0.45–3.00), p = 0.003]. Folate deficient individuals in high polluted areas [high-0.70 (0.37–1.29) vs. low-1.21 (0.45–3.65)] showed significantly reduced global methylation levels (p = 0.007). In low polluted areas, despite folate deficiency, if normal vitamin B12 levels were maintained, global DNA methylation levels improved significantly [2.03 (0.60–5.24), p = 0.007]. Conversely, in high polluted areas despite vitamin B12 deficiency, if normal folate status was maintained, global DNA methylation status improved significantly [0.91 (0.36–1.63)] compared to vitamin B12 normal individuals [0.54 (0.26–1.13), p = 0.04].

Conclusions
High homocysteine may aggravate the effects of air pollution on DNA methylation. Vitamin B12 in low-polluted and folate in high-polluted areas may be strong determinants for changes in DNA methylation levels. The effect of air pollution on methylation levels may be reduced through inclusion of dietary or supplemented B-vitamins. This may serve as public level approach in natural settings to prevent metabolic adversities at community level.