Vitamin C supplementation to pregnant smokers alters asthma- and allergy-associated CpGs in child buccal DNA at 5 years of age

Abstract

Background: We previously reported improved respiratory outcomes in babies born to pregnant smokers supplemented with vitamin C (500 mg/day) versus placebo in a randomized clinical trial. Improved respiratory outcomes persisted to 5 years of age and were associated with buccal DNA methylation (DNAm) measured using the InfiniumMethylationEPIC array. The objective of this study was to examine associations of vitamin C treatment and lung function with buccal DNAm using a custom-content Asthma&Allergy array enriched for asthma and allergy loci likely to have a functional impact on gene expression. Results: We profiled DNAm at 36,999 CpGs in loci previously associated with asthma or allergic diseases using custom-content Asthma&Allergy arrays in 137 subjects (65 placebo; 72 vitamin C) with pulmonary function testing (PFT) at the 5-year visit in the “Vitamin C to Decrease the Effects of Smoking in Pregnancy on Infant Lung Function” (VCSIP) double-blind, placebo-controlled randomized clinical trial. We examined the association of buccal DNAm with (1) vitamin C treatment vs placebo, (2) forced expiratory flow between 25 and 75% of expired volume (FEF25-75) and (3) wheeze at 4–6 years of age. We identified 9 genome-wide differentially methylated CpGs (DMCs; FDR < 0.05) and 2 differentially methylated regions (DMRs) between vitamin C and placebo subjects and one CpG associated with FEF25-75 at FDR significance. DNAm at 5 CpGs mediated a significant proportion of the vitamin C treatment effect on lung function, including 2 CpGs annotated to the SLC25A37 gene involved in mitochondrial iron transport. Conclusions: Our study revealed association of in utero vitamin C supplementation and childhood lung function with DNAm at novel loci, providing additional insight toward potential mechanisms for the persistent effects of vitamin C supplementation to pregnant smokers. Clinical trial registration: ClinicalTrials.gov, NCT01723696 (Registered on November 6, 2011) and NCT03203603 (Registered on March 28, 2017).