Immunomodulatory effects of drug metaboites: an unexpected role of sulfamethoxazole in the regulation of inflammation

Abstract

Sulphonamides together with trimethoprim are effective antimicrobial agents against specific bacterial and protozoan infections. During bacterial infection, monocytes/macrophages of healthy individuals mount effective innate immune responses including induction of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) following TLR4 recognition of bacterial lipopolysaccharide (LPS). Here, we investigated whether sulfamethoxazole and its metabolites can regulate cytokine production in primary human differentiated blood macrophages (PBMac). PBMac were incubated with the drug metabolites for 30 min and followed by the addition of LPS for another 15 min to 3 h. The results from Real time Quantitative RT-PCR assays showed that the mRNA expressions of IL-6 and IL-10 in metabolites-treated cells were downregulated, compared to the cells with LPS treatment alone. We also demonstrated that the protein levels of IL-6, IL-10 and TNF-alpha were suppressed. To delineate the molecular mechanisms involved in the metabolites-induced effects, we measured the activity levels of mitogen-activated protein kinases (MAPK), which are known to be the key signaling modulators in cytokine induction. The results illustrated that sulfamethoxazole metabolites abrogated the LPS-induced MAPK phosphorylation, concomitant with their effects on cytokine downregulation. Furthermore, sulfamethoxazole metabolites could inhibit the LPS-activated nuclear factor-kappa B (NF-kappa B) activation. In conclusion, our data demonstrated that in addition to their antimicrobial effects, sulfamethoxazole metabolites may play a role in limiting the propagation of uncontrolled inflammation, via the suppression of MAPK and NF-kappa B activities, in microbial infections. (The project was funded by a grant to ASY Lau from the HKU foundation and Dean’s Fund, Li Ka Shing Faculty of Medicine and by a CRCG grant to Dr. J.C.B. Li from the University of Hong Kong).