ORIGINAL ARTICLE Effect of morphine on Mycobacterium smegmatis infection in mice and macrophages

Abstract The immunomodulatory effects of opioids are known in various infections. However, little is known about the effects of opioids in tuberculosis (TB). In the present study, we report the effects of morphine in Mycobacterium smegmatis infection in mice and macrophages. Morphine exerted a dose-dependent suppression of infection in vivo: 50 and 100 mg/kg morphine exerted signifi cant (P<0.05) suppression whereas 5 mg/kg morphine showed no effect. Analogous to the in vivo effects, incubation of M. smegmatis-infected mouse peritoneal macrophages with morphine (100 μM) showed signifi cant reduction in intramacrophage CFU counts. However, morphine did not show any direct antimycobacterial activity in broth dilution assay upto 100 μM concentration. Further, morphine-induced intramacro-phage killing of M. smegmatis was abrogated by naloxone and aminoguanidine indicating the involvement of opioid-receptor activation and nitric oxide production in protective effects of morphine. In conclusion, morphine suppressed the progression of experimental TB in both mice and mac-rophage models