Elevated levels of DNA methylation at the OPRM1 promoter in blood and sperm from male opioid addicts

Abstract

Objective: The OPRM1 gene was studied for DNA methylation in opioid dependence and possible paternal contribution to epigenetic inheritance of altered methylation profiles.

Participants and methods: DNA was extracted from blood and sperm from 13 male opioid addicts and 21 male control subjects. DNA methylation was determined by pyrosequencing in 24 CpG sites at the OPRM1 promoter region.

Results: The authors found significantly increased overall methylation in blood DNA from addicted subjects (Kruskal-Wallis [K-W] p = 0.013). Seven CpG sites showed significantly hypermethylated blood DNA from cases when compared with blood DNA from controls (p < 0.05 at CpGs 5, 9, 10, 11, 18, 23, and 24). In sperm-derived DNA from addicts, the methylation was significantly increased at CpG 2 (p = 0.012), and overall methylation did not reach significant difference (K-W p = 0.523).

Conclusions: Increased DNA methylation in the OPRM1 gene is associated with opioid dependence. Hypermethylated CpG sites located in OPRM1 promoter may potentially block the binding of Sp1 and other transcription activators, thus leading to OPRM1 silencing. The increased DNA methylation in sperm may suggest a way of epigenetic heritability of opioid abuse or dependence phenotypes.

Figures

Figure 1

Average methylation levels of 24 CpG sites at the OPRM1 promoter region in blood and sperm DNA from opioid addicts and control subjects. Sp1, potential binding site for the Sp1 transcription activator;(*) p<0.05, Kruskal-Wallis rank test.

Figure 2

Methylation patterns of OPRM1 CpG island and distribution between blood and sperm DNA from opioid addicts and control subjects. (•) denotes single CpG sites and their respective location on chromosome 6.