No abstract

Pretreatment of mice with a low hepatotoxic dose of acetaminophen (APAP) results in resistance to a subsequent, higher dose of APAP. This mouse model, termed APAP autoprotection was used here to identify differentially expressed genes and cellular pathways that could contribute to this development of resistance to hepatotoxicity. Male C57BL/6J mice were pretreated with APAP (400 mg/kg) and then challenged 48 hr later with 600 mg APAP/kg. Livers were obtained 4 or 24 hr later and total hepatic RNA was isolated and hybridized to Affymetrix Mouse Genome MU430_2 GeneChip. Statistically significant genes were determined and gene expression changes were also interrogated using the Causal Reasoning Engine (CRE). Extensive literature review narrowed our focus to methionine adenosyl transferase-1 alpha (MAT1A), nuclear factor (erythroid-derived 2)-like 2 (Nrf2), flavin-containing monooxygenase 3 (Fmo3) and galectin-3 (Lgals3). Down-regulation of MAT1A could lead to decreases in S-adenosylmethionine (SAMe), which is known to protect against APAP toxicity. Nrf2 activation is expected to play a role in protective adaptation. Up-regulation of Lgals3, one of the genes supporting the Nrf2 hypothesis, can lead to suppression of apoptosis and reduced mitochondrial dysfunction. Fmo3 induction suggests the involvement of an enzyme not known to metabolize APAP in the development of tolerance to APAP toxicity. Subsequent quantitative RT-PCR and immunochemical analysis confirmed the differential expression of some of these genes in the APAP autoprotection model. In conclusion, our genomics strategy identified cellular pathways that might further explain the molecular basis for APAP autoprotection.

Steatotic livers are vulnerable to oxidative insults that lead to hepatic lipid peroxidation and injury. Based on our finding that green tea extract (GTE) protected against hepatic steatosis and injury, we hypothesized that GTE would decrease hepatic lipid peroxidation and inflammation. Obese (ob/ob) mice (n = 38) were fed a diet containing GTE at 0, 0.5, or 1%, and lean mice (n = 12) were fed 0% GTE for 6‐wk. Then, hepatic lipid and malondialdehyde (MDA), serum alanine aminotransferase (ALT), and inducible nitric oxide synthase (iNOS) and tumor necrosis factor (TNF)‐α were measured. Body weight was 33% greater (p<0.05) in obese compared to lean controls and was 18% lower in obese mice fed GTE at 1%. Hepatic lipid was 2.3‐times higher in obese mice and GTE at 1% reduced it by 13%. Hepatic MDA was 40% higher in obese compared to lean mice and GTE reduced it 16‐22%. Serum ALT was 7.3‐fold higher in obese controls and GTE at 1% decreased it 25%. MDA was correlated (p < 0.05) to ALT (r = 0.358) and total lipid (r = 0.383). Immunohistochemical evidence suggested that obese mice had greater hepatic iNOS expression and may be decreased with GTE at 1%. TNF‐α expression was unaffected by GTE. These data suggest that GTE protects against hepatic injury by decreasing hepatic lipid accumulation, peroxidation, and potentially obesity‐induced inflammation. Supported by a USDA‐NRI grant (2007‐02303) to RSB.Grant Funding SourceUSDA