Time course investigation of PPARα- and Kupffer cell-dependent effects of WY-14,643 in mouse liver using microarray gene expression

Abstract

Administration of peroxisome proliferators to rodents causes proliferation of peroxisomes, induction of β-oxidation enzymes, hepatocelluar hypertrophy and hyperplasia, with chronic exposure ultimately leading to hepatocellular carcinomas. Many responses associated with peroxisome proliferators are nuclear receptor-mediated events involving peroxisome proliferators-activated receptor alpha (PPARα). A role for nuclear receptor-independent events has also been shown, with evidence of Kupffer cell-mediated free radical production, presumably through NAPDH oxidase, induction of redox-sensitive transcription factors involved in cytokine production and cytokinemediated cell replication following acute treatment with peroxisome proliferators in rodents. Recent studies have demonstrated, by using p47 phox -null mice which are deficient in NADPH oxidase, that this enzyme is not related to the phenotypic events caused by prolonged administration of peroxisome proliferators. In an effort to determine the timing of the transition from Kupffer cell-to PPARα-dependent modulation of peroxisome proliferator effects, gene expression was assessed in liver from Pparα-null, p47 phox -null and corresponding wild-type mice following treatment with 4-chloro-6-(2,3-xylidino)-pyrimidynylthioacetic acid (WY-14,643) for 8 h, 24 h, 72 h, 1 wk, or 4 wks. WY-14,643-induced gene expression in p47 phox -null mouse liver differed substantially from wildtype mice at acute doses and striking differences in baseline expression of immune related genes were evident. Pathway mapping of genes that respond to WY-14,643 in a time-and dose-dependent manner demonstrates suppression of immune response, cell death and signal transduction and promotion of lipid metabolism, cell cycle and DNA repair. Furthermore, these pathways were largely dependent on PPARα, not NADPH oxidase demonstrating a temporal shift in response to peroxisome proliferators. Overall, this study shows that NADPH oxidase-dependent events, while detectable following acute treatment, are transient and short-lived. To the contrary, a strong PPARα-specific gene signature was evident in mice that were continually exposed to WY-14,643.

Time-course comparison of xenobiotic activators of CAR and PPARα in mouse liver

“…However, there is limited data comparing time-course sensitive changes in liver gene expression between classes of chemicals which may be important to understand the timing of key events in the mode of action. We have recently reported on the time-course investigation of PPARα- and Kupffer cell-dependent effects of a model peroxisome proliferator compound WY-14,643 in mouse liver (Woods et al, 2007b). Here, we sought to compare responses to phenobarbital and WY-14,643 by closely matching the strain of mice, timing, and doses of exposure.…”

“…Studies with WY-14,643 were described in a previously published report (Woods et al, 2007b) where C57BL/6J mice were administered an acute dose by a single oral gavage of 0 (control) or 50 mg/kg of WY-14,643 in olive oil and sacrificed at 1 day post-dosing. Sub-chronic doses of WY-14,643 were administered in the diet ad libitum .…”

“…Indeed, many studies conducted with phenobarbital and like compounds confirm the key role of CAR in activating various xenobiotic metabolism genes (Wei et al, 2000; Ueda et al, 2002; Maglich et al, 2002). In this study we compared global transcriptional changes in response to activation of CAR and PPARα (Woods et al, 2007b) pathways in mouse liver over a time-course. We hypothesized that the initial transcriptional responses to the prototypical xenobiotic activators phenobarbital and WY-14,643 will exhibit distinct patterns of expression changes reflective of activation of CAR and PPARα, respectively; but at later time-points, these biological pathways will converge due to similar phenotypic responses observed in the mouse liver after sub-chronic treatment with the two chemicals.…”

Time-course Comparison of Gene Expression Profiles Induced by the Genotoxic Hepatocarcinogen, Chrysene, in the Mouse Liver

“…Although the number of published studies is limited, gene expression proˆling of the eŠects of hepatocarcino-gens in the experimental animal liver has been performed using DNA microarray and qPCR with diŠerent time courses (38)(39)(40)(41). Ellinger-Ziegelbauer et al examined the eŠects of four genotoxic hepatocarcinogens, namely dimethylnitrosamine, 2-nitro‰uorene, a‰atoxin B1 and 4-(methylnitrosamino)1-(3-pyridyl)-1-butanone, in the rat liver 1, 3, 7 and 14 days after administration using an AŠymetrix RG_U34 microarray (38).…”

“…Kang et al examined the eŠects of the genotoxic hepatocarcinogen MeIQx at weeks 4, 16 and 102 in the rat liver using an A‹metrix GeneChip Rat Genome 230 2.0 Array, observed no major diŠerences after 4 and 16 weeks administration, and found a few diŠerentially expressed genes in tumors at 102 weeks (40). Woods et al examined the eŠects of a non-genotoxic carcinogen, namely the peroxisome proliferator Wy-14,643, at 8, 24 and 72 h and 1 and 4 weeks in the mouse liver using an Agilent Mouse Oligo Microarray (41). Each of these researchers performed diŠerential gene expression proˆling at diŠerent time points in the mouse or rat liver.…”