Oxidants from nicotinamide adenine dinucleotide phosphate oxidase are involved in triggering cell proliferation in the liver due to peroxisome proliferators

It was shown that 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio acetic acid ( Wy-14,643), a potent peroxisome proliferator, caused rapid oxidant-dependen t activation of nuclear factor kappa B (NF-kappa B) in Kupffer cells in viv o and activated superoxide production by isolated Kupffer cells, Here, we t ested the hypothesis that NADPH oxidase (NADPH OX) is the source of oxidant s increased by Wy-14,643. Indeed, both activation of NF-kappa B and increas es in cell proliferation due to a single dose of Wy-14,643 (100 mg/kg) were prevented completely when rats were pretreated with diphenyleneiodonium (1 mg/kg), an inhibitor of NADPH OX. p47(phox) is a critical subunit of NADPH OX: therefore, p47(phox) knockout mice were used to specifically address t he hypothesis of NADPH OX involvement. In livers of wild-type mice, Wy-14,6 43 activated NF-kappa B, followed by an increase in mRNA for tumor necrosis factor alpha. Importantly, these changes did not occur in p47(phox) knocko uts, Moreover, when Kupffer cells were treated with Wy-14,643 in vitro, sup eroxide production was increased in cells from wild-type but not p47(phox)- null mice. Finally, when mice were fed a Wy-14,643-containing (0.1%) diet f or 7 days, the increase in liver weight and cell proliferation caused by Wy -14,643 in wild-type mice was blocked in p47(phox)-null mice. Combined, the se results are consistent with the hypothesis that Wy-14,643 activates NADP H OX, which Leads to NF-kappa B-mediated production of mitogens that causes hepatocellular proliferation characteristic of this class of nongenotoxic carcinogens.