Association of polymorphism in the human μ-opioid receptor OPRM1 gene with proinflammatory cytokine levels and health perception

Recent studies in psychoneuroimmunology have indicated that proinflammatory cytokines cause several diseases and behaviors that overlap symptomatically with depression. It is known that the endogenous opioid peptide β-endorphin regulates proinflammatory cytokine secretion from peripheral immune cells via μ-opioid receptor-dependent mechanisms. Therefore, it is possible that the functional polymorphism of the μ-opioid receptor gene (OPRM1, SNP: A118G) influences peripheral circulating proinflammatory cytokine levels and the health-related quality of life (QOL) even in healthy populations. In this study, we compared the serum concentrations of several proinflammatory cytokines (interleukin-2 (IL-2), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ)) and the health-related QOL between OPRM1 genotypes. Interestingly, serum concentrations of IL-6, TNF-α, and IFN-γ were significantly lower and the general health score was significantly higher in carriers of the G allele, who show a strong binding of β-endorphin to the μ-opioid receptor as compared to individuals without the G allele. Correlation analysis indicated that the general health score was negatively correlated with the IL-6 serum concentration. These results suggest that the sensitive endogenous opioid system in carriers of the G allele may suppress proinflammatory cytokine secretion from peripheral immune cells; consequently, it may influence the health perception.