Methylsulfonylmethane modulates apoptosis of LPS/IFN-γ-activated RAW 264.7 macrophage-like cells by targeting p53, Bax, Bcl-2, cytochrome c and PARP proteins

Methylsulfonylmethane (MSM) is a non-toxic, natural organosulfur compound, which is known to possess antioxidant and anti-inflammatory activities. In recent years, MSM has been widely used as a dietary supplement for its beneficial effects against various diseases, especially arthritis. Despite being a popular supplement product, the mechanism of action of MSM is not well known. This study was designed to investigate the effects of MSM on cytotoxic signals induced by lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) in RAW 264.7 macrophage-like cells. The results showed that MSM reversed apoptosis of RAW 264.7 macrophage-like cells at non-cytotoxic concentrations probably through the modulation of apoptotic proteins. After pre-treatment of cells with non-toxic doses of MSM; caspase-3 activation, p53 accumulation, cytochrome c release and Bax/Bcl-2 ratio were significantly decreased and full length poly ADP-ribose polymerase (PARP) was significantly increased. In addition, the loss of mitochondrial membrane potential was decreased with MSM pretreatment in activated macrophages. Since excess nitric oxide production causes apoptosis of macrophages, anti-apoptotic effects of MSM are thought to be mediated by its inhibitor effects on inducible nitric oxide synthase (iNOS) protein and nitric oxide levels. More interestingly, higher doses of MSM exhibited biphasic effects, inhibited cell viability, induced apoptosis of macrophages, increased caspase-3 activity and PARP cleavage. Thus, our results reveal the molecular mechanism of of MSM indicating that MSM supplementation may be beneficial for complications related to nitric oxide-dependent apoptosis in inflammatory conditions. However, the optimum concentration of MSM must be chosen carefully to elicit the desired effect.