Anti-inflammatory Effect of d-(+)-Cycloserine Through Inhibition of NF-κB and MAPK Signaling Pathways in LPS-Induced RAW 264.7 Macrophages

Recently, additional therapeutic potentials of classical antibiotics are gaining considerable attention. The discovery of penicillin in the 1920s had a major impact on the history of human health. Penicillin has been used for the treatment for fatal microbial infections in humans and has led to the discovery of several new antibiotics. d-(+)-Cycloserine (DCS) is an antibiotic isolated from Streptomyces orchidaceous and is used in conjunction with other drugs in the treatment of tuberculosis. However, there have been no studies on the anti-inflammatory effects of DCS in RAW 264.7 macrophage cell line. To investigate the anti-inflammatory effects of DCS, we examined the ability of DCS to inhibit the inflammatory responses in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages in this study. Cell viability was analyzed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The cells were pretreated with various concentrations (2, 4, and 6 mM) of DCS, then treated with 1 μg/mL LPS to detect its anti-inflammatory effects. d-(+)-Cycloserine inhibited the production of nitric oxide (NO) in a concentration-dependent manner, and to some extent, inhibited the production of prostaglandin E2. Consistent with these findings, DCS suppressed the expression of pro-inflammatory cytokines such as interleukin (IL)-1β and IL-6. However, it had no effect on the expression of tumor necrosis factor-α. Western blot analysis demonstrated that DCS inhibited inducible nitric oxide synthase and suppressed cyclooxygenase type-2 (COX-2) expression. In addition, investigation of its effects on nuclear factor kappa B signaling showed that DCS inhibited phosphorylation of inhibitory kappa B-α (IκB-α) and increased intracellular IκB-α in a concentration-dependent manner. Furthermore, DCS inhibited the phosphorylation of LPS-induced extracellular signal-regulated kinase, however it did not affect phosphorylation of c-jun N-terminal kinase and p38. Further studies confirmed that the inhibition of phosphorylation of IκB-α was mediated through the inhibition of phosphoinositide 3-kinase/Akt (PI3K/Akt) pathway. To determine the applicability of DCS to the skin, cytotoxicity on HaCaT keratinocytes was measured following treatment with various concentrations (2, 4, 6, 8, and 10 mM) of DCS using MTT assay. These results suggest that DCS may be used as a potential drug for the treatment of inflammatory diseases.