Heme oxygenase-1 participates in the anti-inflammatory activity of taurine chloramine

Interleukin-6 (IL-6) and interleukin-8 (IL-8) are implicated in the pathogenesis of rheumatic diseases. In affected joints fibroblast-like synoviocytes (FLS) are the major source of these pro-inflammatory cytokines. We have previously found that production of both cytokines is inhibited in vitro by taurine chloramine (Tau-Cl). Heme oxygenase (HO-1) activity was also reported to restrict synthesis of various inflammatory mediators, including IL-6 and IL-8. The aim of present study was to investigate whether this enzyme activity is implicated in the mechanism of Tau-Cl suppressive effect. We have shown that in rheumatoid FLS both hemin (known HO-1 inducer) and Tau-Cl significantly up-regulate HO-1 expression at the mRNA and protein levels and simultaneously inhibit IL-1 beta-triggered production of pro-inflammatory cytokines. However, the inhibitory potency of these compounds differs, because hemin is more potent inhibitor of IL-8 than IL-6 production, while Tau-Cl exerts opposite effect. Importantly, pretreatment of the cells with HO-1 inhibitor completely reverses the inhibitory effect of hemin on both cytokines production. However, in Tau-Cl treated cells this inhibitor fully restores only IL-8 secretion but has weaker effect on IL-6 response. Thus, the present results: (i) support HO-1 activity to be relevant to negatively control production of pro-inflammatory cytokines, and (ii) underline implication of HO-1 in mediating Tau-Cl inhibitory action.