Alterations in methylation and SNPs of OPRM1 gene show lack of association with heroin (nyaope) consumption in South African males of African ancestry

Nyaope is a highly addictive heroin derivative that elicits its effects via the -opioid receptor. Gene mutations and (cytosine-phospho-guanosine) CpG methylation, alter the function of the -opioid receptor gene (OPRM1) and protein. The single nucleotide polymorphisms (SNPs) rs1799971 (118 A>G) and intronic rs3778150 (T>C) in the OPRM1 have previously been associated with heroin use. The SNP rs1799971 can influence methylation levels of OPRM1 and alter mRNA and protein expression. This study compared the degree of OPRM1 methylation and allele frequency of SNPs rs1799971 and rs3778150 in black South African male nyaope users (n=200) to age-and gender-matched controls (n=55).DNA was extracted from whole blood samples, and analysed by methylation-specific PCR and sequencing to determine methylation frequencies across 29 CpGs within the OPRM1promoter gene region. SNPsrs1799971 (118 A>G) and rs3778150 (T>C) were assessed using SNP genotyping Taqman assays.Using a positive methylation assignment method, most CpGs were significantly more unmethylated in nyaope users than in controls. Using a partial methylation assignment method, most CpGs displayed significantly higher percentages of partial methylation in nyaope users than in controls. The AG genotype frequency for SNP (118 A>G), was higher in controls than in nyaope users while other genotypes (AA & GG) for SNP rs1799971 and (TT, CT, CC) SNP rs3778150 were broadly similar in both groups. There was no correlation observed between nyaope consumption and the presence of SNP rs1799971 and/or rs3778150 in the study populations.This study provided evidence that methylation may not be associated with the intake of nyaope and that SNPs rs1799971 and rs3778150 did not alter the methylation status of the OPRM1 promoter gene or contribute to nyaope addiction in a black South African male population.