WY-14,643–Induced Cell Proliferation and Oxidative Stress in Mouse Liver are Independent of NADPH Oxidase

Long-term exposure of rodents to peroxisome proliferators leads to increases in peroxisomes, hepatocellular proliferation, oxidative damage, suppressed apoptosis, and ultimately results in the development of hepatic adenomas and carcinomas. Peroxisome proliferators–activated receptor (PPAR)a was shown to be required for these pleiotropic responses; however, Kupffer cells, resident liver macrophages, were also identified as playing a role in peroxisome proliferators–induced effects, independently of PPARa. Previous studies showed that oxidants from NADPH (nicotinamide adenine dinucleotide phosphate, reduced) oxidase mediate acute effects of peroxisome proliferators in rodent liver. To determine if Kupffer cell oxidants are also involved in chronic effects, NADPH oxidase– deficient (p47 phox -null) mice were fed 4-chloro-6-(2,3-xylidino)-2pyrimidinylthio acetic acid (WY-14,643)–containing diet (0.1% wt/ wt) for 1 week, 5 weeks, or 5 months along with Ppar-null and wild type mice. As expected, no change in liver size, cell replication rates, or other phenotypic effects of peroxisome proliferators were observed in Ppara-null mice. Through 5 months of treatment, the p47 phox -null and wild type mice exhibited peroxisome proliferators–induced adverse liver effects, along with increased oxidative DNA damage and increased cell proliferation, a response that is potentially mediated through nuclear factor kappa B (NFkB). Suppressed apoptosis caused by WY-14,643 was dependent on both NADPH oxidase and PPARa. Collectively, these findings suggest that involvement of Kupffer cells in WY-14,643–induced parenchymal cell proliferation and oxidative stress in rodent liver is an acute phenomenon that is not relevant to long-term exposure, but they are still involved in chronic apoptotic responses. These results provide new insight for understanding the mode of hepatocarcinogenic action of peroxisome proliferators.