WY-14 643 rapidly activates nuclear factor kappaB in Kupffer cells before hepatocytes

Stimulation of cell proliferation caused by peroxisome proliferators was blocked by antibodies against TNF alpha and agents that inactivate Kupffer cells, a rich source of TNF alpha, which supports the hypothesis that Kupffer cells play a pivotal role in peroxisome proliferator-induced hyperplasia. Here, the ability of the very potent peroxisome proliferator WY-14 643 to activate the transcription factor NF-kappaB in rat liver was examined since it is involved in TNF alpha production. Female Sprague-Dawley rats were treated by gavage with WY-14 643 (100 mg/kg) while control animals were given equivalent doses of vehicle (olive oil). Activation of NF-kappaB in both whole liver, non-parenchymal cells, Kupffer cells and hepatocytes was assessed for up to 36 h using an electrophoretic mobility shift assay. In whole liver, WY-14 643 transiently increased NF-kappaB binding maximally 3.5-fold in 2-8 h followed by a steady decline to near control levels at 36 h. As early as 2 h after WY-14 643 treatment, the active form of NF-kappaB was localized predominantly in Kupffer cells with values 20- to 25-times greater than in hepatocytes. In hepatocytes, a small increase in NF-kappaB binding was observed but only 8 h after WY-14 643 administration. Pre-treatment with allopurinol, a xanthine oxidase inhibitor and free radical scavenger, suppressed NF-kappaB activation by WY-14 643 almost completely. It is concluded that NF-kappaB is activated by reactive oxygen species and plays a central role in the mechanism of action of peroxisome proliferators. Moreover, these findings support the hypothesis that Kupffer cells play a pivotal role in peroxisome proliferator-induced hepatocyte proliferation through rapid NF-kappaB activation and subsequent induction of TNF alpha production. TNF alpha from Kupffer cells stimulates growth in parenchymal cells later via mechanisms that also involve NF-kappaB.