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 necrosis factor-α (TNF-α). The purpose of this work was to characterize the mechanism of cloricromene-induced inhibition of TNF-α in rat macrophages. Cloricromene inhibited lipopolysaccharide-induced TNF-α release in a dose-dependent manner (IC 50 = 5.9 ± 0.8 μM). This was not due to cytotoxicity, as cloricromene was well tolerated up to 500 μM. Cloricromene inhibited lipopolysaccharide-induced expression of TNF-α 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-κB (NF-κB). Cloricromene inhibited NF-κB 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-κB activation. Our results show that cloricromene interferes with the early signal transduction pathway triggered by lipopolysaccharide.