Previous studies have shown that large doses of diethyldithiocarbamate (DDC) cause liver injury in rats and the pathogenesis of this injury involves, in part, release of superoxide anion by Kupffer cells. The purpose of this study was to evaluate if DDC was able to stimulate other potentially toxic mediators such as nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) using isolated rat Kupffer cells. DDC alone did not stimulate the release of NO and TNF-alpha by Kupffer cells. Interestingly, when Kupffer cells were stimulated by lipopolysaccharide (LPS), DDC (0-30 microM) enhanced the production of both NO and TNF-alpha in a concentration-dependent manner. Therefore, we further studied how DDC modulated the response of Kupffer cells to LPS. Immunocytochemical studies revealed that DDC increased the amount of inducible NO synthase and TNF-alpha protein in Kupffer cells after their exposure to LPS. The enhanced effects of DDC on the release of NO and TNF-alpha from Kupffer cells was inhibited by N-acetyl-L-cysteine (an inhibitor of transcription factor NF-kappaB activation). By using a specific antibody for NF-kappaBp65, it was found that DDC enhanced the LPS-activated nuclear translocation of NF-kappaB. There was no evidence of intracellular oxidative stress following either LPS alone or DDC + LPS exposure. The stimulatory effect of DDC on both NO and TNF-alpha release was inhibited by H-7 (an inhibitor of protein kinase C) but not H-8 (an inhibitor of cAMP-dependent protein kinase). These findings demonstrate that DDC enhances the production of NO and TNF-alpha by LPS-stimulated Kupffer cells and suggest that protein kinase C plays a critical role in mediating these effects of DDC.