The effect of aging on acetaminophen pharmacokinetics, toxicity and Nrf2 in Fischer 344 rats.

We investigated the effect of aging on hepatic pharmacokinetics and the degree of hepatotoxicity following a toxic dose of acetaminophen. Young and old male Fischer 344 rats were treated with 800 mg/kg acetaminophen (young n = 8, old n = 5) or saline (young n = 9, old n = 9). Serum measurements showed old rats treated with acetaminophen had significantly lower serum alanine aminotransferase and higher acetaminophen and acetaminophen glucuronide levels and creatinine, compared with acetaminophen treated young rats (p < .05). Immunoblotting and activity assays showed old saline-treated rats had twofold lower cytochrome P450 2E1 activity and threefold higher NAD(P)H quinone oxireductase 1 protein expression and activity than young saline-treated rats (p < .05), although Nrf2, glutathione cysteine ligase-modulatory subunit, glutathione cysteine ligase-catalytic subunit, and cytochrome P450 2E1 protein expressions were unchanged. Primary hepatocytes isolated from young rats treated with 10 mM acetaminophen had lower survival than those from old rats (52.4% ± 5.8%, young; 83.6% ± 1.7%, old, p < .05). The pharmacokinetic changes described may decrease susceptibility to acetaminophen-induced hepatotoxicity but may increase risk of nephrotoxicity in old age.

Entecavir versus lamivudine for hepatitis B prophylaxis in patients with haematological disease.

BACKGROUND: Hepatitis B reactivation in patients receiving immunosuppressive therapy or chemotherapy may be associated with acute hepatitis, liver failure and/or death. AIM: To audit the efficacy of entecavir as compared to lamivudine for the prophylaxis of HBV reactivation in patients with haematological disease receiving immunosuppression or chemotherapy. METHODS: Patients treated for haematological disease with pretreatment serological evidence of chronic hepatitis B (CHB) (HBV surface antigen, HBsAg positive) or resolved HBV infection (HBsAg negative but HBV core antibody positive) are included in this study. Patients received lamivudine 100 mg or entecavir 0.5 mg daily. Hepatitis B serology, HBV DNA and ALT were audited at baseline, 6 months, year 1, 2 and 3. HBV reactivation was defined as a 1 log increase in HBV DNA from baseline or reversion to sAg positivity. The occurrence of jaundice, symptomatic hepatitis, liver failure or death were audited. RESULTS: Of the 40 patients included in the study, 65% (4 CHB and 22 resolved HBV) received entecavir and 35% (11 CHB and 3 resolved HBV) received lamivudine. One patient with resolved HBV experienced HBV seroreversion related to premature cessation of entecavir. Eight patients with CHB (two from entecavir group and six from lamivudine group) had detectable HBVDNA levels at baseline; one case of HBV reactivation related to probable lamivudine resistance was identified. No HBV related deaths occurred. CONCLUSION: Lamivudine and entecavir are both efficacious in the prophylaxis of hepatitis B reactivation. Entecavir should be used in preference to lamivudine in patients CHB with detectable baseline HBV DNA levels.

Toxicity of low dose azathioprine and 6-mercaptopurine in rat hepatocytes. Roles of xanthine oxidase and mitochondrial injury.

BACKGROUND/AIMS: To study effects of pharmacologic concentrations of azathioprine and 6-mercaptopurine (6-MP) on rat hepatocytes. METHODS: Hepatocytes cultured on matrigel were incubated with azathioprine or 6-MP; effects of putative protective agents were studied. Viability (LDH leakage), reduced (GSH) and oxidized glutathione (GSSG), mitochondrial (mt) GSH, ATP and ultrastructural changes were determined. RESULTS: Azathioprine and 6-MP (0.5-5 micromol/l) reduced viability 5-34% at day 1 and 42-92% by day 4. Allopurinol (20 microM) (xanthine oxidase inhibitor) and 2 mM Trolox (vitamin E analog) together provided near complete protection. During culture with azathioprine, GSSG increased before cell death and there was a disproportionate reduction of mtGSH and ATP, together with ultrastructural abnormalities in mitochondria. All changes were prevented by allopurinol and trolox. Discontinuation of 1 micromol/l azathioprine restored ATP levels and arrested cell injury, while culture in glucose-enriched media augmented ATP levels and ameliorated cell death. CONCLUSIONS: Clinically relevant concentrations of azathioprine and 6-MP are toxic to rat hepatocyte cultures by a mechanism that involves oxidative stress, mitochondrial injury and ATP depletion. This can lead to irreversible de-energization and cell death by oncosis (necrosis).

Cytochrome P450 2E1 expression induces hepatocyte resistance to cell death from oxidative stress.

Increased expression of cytochrome P450 2E1 (CYP2E1) occurs in alcoholic liver disease, and leads to the hepatocellular generation of toxic reactive oxygen intermediates (ROI). Oxidative stress created by CYP2E1 overexpression may promote liver cell injury by sensitizing hepatocytes to oxidant-induced damage from Kupffer cell-produced ROI or cytokines. To determine the effect of CYP2E1 expression on the hepatocellular response to injury, stably transfected hepatocytes expressing increased (S-CYP15) and decreased (AN-CYP10) levels of CYP2E1 were generated from the rat hepatocyte line RALA255-10G. S-CYP15 cells had increased levels of CYP2E1 as demonstrated by Northern blot analysis, immunoblotting, catalytic activity, and increased cell sensitivity to death from acetaminophen. Death in S-CYP15 cells was significantly decreased relative to that in AN-CYP10 cells following treatment with hydrogen peroxide and the superoxide generator menadione. S-CYP15 cells underwent apoptosis in response to these ROI, whereas AN-CYP10 cells died by necrosis. This differential sensitivity to ROI-induced cell death was partly explained by markedly decreased levels of glutathione (GSH) in AN-CYP10 cells. However, chemically induced GSH depletion triggered cell death in S-CYP15 but not AN-CYP10 cells. Increased expression of CYP2E1 conferred hepatocyte resistance to ROI-induced cytotoxicity, which was mediated in part by GSH. However, CYP2E1 overexpression left cells vulnerable to death from GSH depletion.

Increased cytochrome P-450 2E1 expression sensitizes hepatocytes to c-Jun-mediated cell death from TNF-alpha.

The mechanisms underlying hepatocyte sensitization to tumor necrosis factor-alpha (TNF-alpha)-mediated cell death remain unclear. Increases in hepatocellular oxidant stress such as those that occur with hepatic overexpression of cytochrome P-450 2E1 (CYP2E1) may promote TNF-alpha death. TNF-alpha treatment of hepatocyte cell lines with differential CYP2E1 expression demonstrated that overexpression of CYP2E1 converted the hepatocyte TNF-alpha response from proliferation to apoptotic and necrotic cell death. Death occurred despite the presence of increased levels of nuclear factor-kappaB transcriptional activity and was associated with increased lipid peroxidation and GSH depletion. CYP2E1-overexpressing hepatocytes had increased basal and TNF-alpha-induced levels of c-Jun NH(2)-terminal kinase (JNK) activity, as well as prolonged JNK activation after TNF-alpha stimulation. Sensitization to TNF-alpha-induced cell death by CYP2E1 overexpression was inhibited by antioxidants or adenoviral expression of a dominant-negative c-Jun. Increased CYP2E1 expression sensitized hepatocytes to TNF-alpha toxicity mediated by c-Jun and overwhelming oxidative stress. The chronic increase in intracellular oxidant stress created by CYP2E1 overexpression may serve as a mechanism by which hepatocytes are sensitized to TNF-alpha toxicity in liver disease.