Cloricromene, a semi-synthetic coumarin derivative, inhibits tumor necrosis factor-α production at a pre-transcriptional level

Cloricromene decreases myocardial infarct size after ischemic-reperfusion injury in vivo, and it has been suggested that this is due to inhibition of tumor neurosis factor-alpha (TNF-alpha). The purpose of this work was to characterize the mechanism of cloricromene-induced inhibition of TNF-alpha in rat macrophages. Cloricromene inhibited lipopolysaccharide-induced TNF-alpha release in a dose-dependent manner (IC50 = 5.9 +/- 0.8 muM) This was not due to cytotoxicity, as cloricromene was well tolerated up to 500 muM. Cloricromene inhibited lipopolysaccharide-induced expression of TNF-alpha mRNA, which suggests a pre-transcriptional effect. We then investigated the early signal transduction pathway triggered by lipopolysaccharide. The binding of lipopolysaccharide to its receptor CD14 activates protein kinase C and nuclear Factor-kappaB (NF-kappaB). Cloricromene inhibited NF-kappaB` activation in a dose-dependent manner, but affected protein kinase C translocation only slightly. We then established that cloricromene inhibited lipopolysaccharide-induced cellular oxidative activity, which is important for NF-kappaB activation. Our results show that cloricromene interferes with the early signal transduction pathway triggered by lipopolysaccharide. (C) 2001 Elsevier Science B.V. All rights reserved.