Aims: Macrophage-related oxidative stress plays an important role in the inflammatory process in atherosclerosis. Recently, dextromethorphan (DXM), a common cough-suppressing ingredient with a high safety profile, was found to inhibit the activation of microglia, the resident macrophage in the nervous system. We investigated whether DXM could reduce macrophage production of cytokines and superoxide and the resultant influence on atherosclerosis formation in mice.
Methods and results: We used in vitro and in vivo studies to evaluate the DXM inhibitory effect on oxidative stress. Dextromethorphan pretreatment significantly suppressed the production of tumour necrosis factor-alpha, monocyte chemoattractant protein-1, interleukin-6, interleukin-10, and superoxide in macrophage cell culture after stimulation. Indeed, DXM reduced macrophage nicotinamide adenine dinucleotide phosphate oxidase activity by decreasing membrane translocation of p47(phox) and p67(phox) through the inhibition of protein kinase C and extracellular signal-regulated kinase activation. The anti-atherosclerosis effect of DXM was tested using two animal models, apolipoprotein E (apoE)-deficient mice and a mouse carotid ligation model. Dextromethorphan treatment (10-40 mg/kg/day) for 10 weeks in apoE-deficient mice significantly reduced superoxide production in their polymorphonuclear leukocytes and aortas. It significantly decreased the severity of aortic atherosclerosis in the apoE-deficient mice and decreased carotid neointima formation after ligation in C57BL/6 mice.
Conclusion: Our data show that DXM, with its novel effect in reducing oxidative stress, significantly reduces atherosclerosis and neointima formation in mice.