WY-14-643 RAPIDLY ACTIVATES NUCLEAR FACTOR KAPPA-B IN KUPFFER CELLS BEFORE HEPATOCYTES

Stimulation of cell proliferation caused by peroxisome proliferators w as blocked by antibodies against TNF alpha and agents that inactivate Kupffer cells, a rich source of TNF alpha, which supports the hypothes is that Kupffer cells play a pivotal role in peroxisome proliferator-i nduced hyperplasia, Here, the ability of the very potent peroxisome pr oliferator WY-14 643 to activate the transcription factor NF-kappa B i n 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-kappa B in both whole liver, non-parenchy mal cells, Kupffer cells and hepatocytes was assessed for up to 36 h u sing an electrophoretic mobility shift assay. In whole liver, WY-14 64 3 transiently increased NF-kappa B 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-kappa B was l ocalized predominantly in Kupffer cells with values 20- to 25-times gr eater than in hepatocytes. In hepatocytes, a small increase in NF-kapp a B 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-kappa B activation by WY-14 643 almos t completely. It is concluded that NF-kappa B is activated by reactive oxygen species and plays a central role in the mechanism of action of peroxisome proliferators. Moreover, these findings support the hypoth esis that Kupffer cells play a pivotal role in peroxisome proliferator -induced hepatocyte proliferation through rapid NF-kappa B activation and subsequent induction of TNF alpha production. TNF alpha from Kupff er cells stimulates growth in parenchymal cells later via mechanisms t hat also involve NF-kappa B.