Anti-inflammatory and immunomodulatory activities of rifamycin SV

There have been several reports showing convincing evidence for non-bactericidal activities of the rifamycin antibiotics. In particular, the parent compound rifamycin SV has been employed in a limited number of cases to treat rheumatoid arthritis. Moreover, rifamycin SV and its derivative rifaximin have been found to be effective in experimental animal models of gut inflammation. The efficacy of rifamycin SV and rifaximin in these settings has been attributed partially to indirect non-bactericidal activities. To better clarify the mechanisms by which these two antibiotics exert their non-bactericidal effects, their activities were compared in in vitro cellular models of immunomodulation and inflammation. Both antibiotics were found to inhibit cytokine and chemokine synthesis from lipopolysaccharide-activated THP-1 monocytes and macrophages. It was also demonstrated, for the first time, that rifamycin SV exerts anti-inflammatory activities in HT-29 colonic epithelial cells. Moreover, rifamycin SV is also very effective in downregulating secretion of inflammatory cytokines from human CD4 T-cells. In general, both antibiotics show similar activities on all four cell types tested. However, rifamycin SV is less cytotoxic than rifaximin when tested in these cells.