Inhibition of lipopolysaccharide-induced I-kappaB degradation and tumor necrosis factor-alpha expression by dimethyl-4,4'-dimethoxy-5,6,5',6'-dimethylene dioxybiphenyl-2,2'-dicarboxylate (DDB): minor role in hepatic detoxifying enzyme expression.

Abstract

Dimethyl-4,4'-dimethoxy-5,6,5',6'-dimethylene dioxybiphenyl-2,2'-dicarboxylate (DDB) is active against a variety of hepatotoxins and has been used as a curative agent for patients with acute and chronic viral hepatitis. Effects of DDB on the expression of xenobiotic-metabolizing enzymes and on nuclear factor-kappaB (NF-kappaB) activation and tumor necrosis factor-alpha (TNF-alpha) production by lipopolysaccharide (LPS), an endotoxin involved in inflammatory responses, were examined in rats and in RAW264.7 cells to investigate mechanistic aspects. Expression of hepatic cytochrome P450s, microsomal epoxide hydrolase and glutathione S-transferases was determined by immunoblot and Northern blot analyses. Activation of hepatic NF-kappaB and I-kappaBalpha degradation was assessed by gel mobility shift and immunoblot analyses, respectively. LPS-induced TNF-alpha expression was monitored in rats and in RAW264.7 cells by enzyme-linked immunosorbent assay and/or reverse transcription-polymerase chain reaction analysis. DDB failed to alter the expression of hepatic cytochrome P450 1A and 2C11, microsomal epoxide hydrolase and glutathione S-transferases in rats with slight inhibition of P450 2E1 expression, but induced P450 2B1/2. Pretreatment of rats with DDB prevented LPS-induced hepatic I-kappaBalpha degradation and the resultant NF-kappaB activation, and inhibited the LPS-induced plasma TNF-alpha protein and hepatic TNF-alpha mRNA expression in a dose-dependent manner. LPS-induced I-kappaBalpha degradation and TNF-alpha production were also inhibited by DDB in RAW264.7 cells, which was consistent with the results in rats. The present study demonstrated that DDB may inhibit inflammatory responses in association with reduction of NF-kappaB activation through prevention of I-kappaBalpha degradation and subsequent TNF-alpha production, but not with modulation of the detoxifying enzyme expression.