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G C Farrell

Publications and source records attributed to G C Farrell.

At least 19 recordsLinked to original sources
PubMed2001

Specific involvement of G(alphai2) with epidermal growth factor receptor signaling in rat hepatocytes, and the inhibitory effect of chronic ethanol.

We have previously shown that chronic alcohol consumption inhibits liver regeneration by impairing epidermal growth factor receptor (EGFR)-operated phospholipase C-(gamma1) (PLC-(gamma1)) activation and the resultant rise in intracellular [Ca(2+)](i). In hepatocytes, activation of PLC-(gamma1) by EGFR requires involvement of a pertussis toxin-sensitive inhibitory guanine nucleotide-binding regulatory protein (G(alphai)) as an intermediate. In the present study, we first identified the G(alphai) protein isoform associated with the activated EGFR, and then examined whether the toxic effect of alcohol on EGFR signaling and liver cell proliferation was exerted on this association. In cultured hepatocytes from control rats, EGF rapidly induced association between EGFR and G(alphai2) but not other G(alphai) isoforms. In hepatocytes from rats fed alcohol for 16 weeks, EGF failed to stimulate this association of G(alphai2) with the EGFR. The impairment of EGFR-G(alphai2) complex formation caused by alcohol was associated with a decreased level of G(alphai2) in the plasma membrane fraction (approximately 50% control). Pertussis toxin, an inhibitor of G(alphai) function, produced an analogous disruption of the association between G(alphai2) and the EGFR, as well as inhibiting EGF-induced DNA synthesis. It is concluded that, in hepatocytes, G(alphai2) is specific among G(alphai) isoforms in coupling activation of the EGFR to other signaling pathways that control cell proliferation. Impaired coupling of G(alphai2) of EGFR could contribute to the mechanism by which chronic alcohol exposure inhibits liver regeneration.

Adenosine Diphosphate↗
PubMed2001

Mechanism of azathioprine-induced injury to hepatocytes: roles of glutathione depletion and mitochondrial injury.

BACKGROUND/AIMS: We sought evidence that azathioprine causes cell death through reduced glutathione (GSH) depletion and mitochondrial injury. METHODS: Studies were conducted in primary cultures of rat hepatocytes and cultured Hep G2 cells. RESULTS: Azathioprine toxicity to rat hepatocytes was preceded by depletion of GSH. Prior GSH depletion (by treatment with buthionine sulfoximine) enhanced toxicity whilst supplemental GSH or N-acetylcysteine was protective. In hepatocytes, GSH is consumed during metabolism of azathioprine to 6-mercaptopurine. 6-Mercaptopurine was not toxic to hepatocytes, suggesting that the later steps in azathioprine metabolism were not related to the pathogenic mechanism. In Hep G2 cells, azathioprine did not alter levels of GSH and was not toxic. Ultrastructural studies showed hepatocyte mitochondrial lesions after exposure to azathioprine, but no features of apoptosis. Azathioprine produced rapid and profound depletion of adenosine 5'-triphosphate (ATP). Cyclosporin A and glycine afforded protection against azathioprine toxicity, and Trolox and high-dose allopurinol also attenuated injury. CONCLUSIONS: The mechanism of azathioprine toxicity to hepatocytes involves depletion of GSH leading to mitochondrial injury with profound depletion of ATP and cell death by necrosis. Cell death was prevented by potent antioxidants, glycine and blocking the mitochondrial permeability transition pore.

Adenosine Triphosphate↗
PubMed2001

Etiopathogenesis of nonalcoholic steatohepatitis.

The definable causes of nonalcoholic steatohepatitis (NASH) include jejunoileal bypass surgery (JIB), other causes of rapid and profound weight loss in obese subjects, total parenteral nutrition, drugs, industrial toxins, copper toxicity, and disorders characterized by extreme insulin resistance. However, the etiopathogenesis in most cases of NASH appears multifactorial. Obesity, type 2 diabetes, and hypertriglyceridemia are often associated with hepatic steatosis, and although this does not invariably lead to NASH, the fatty liver is vulnerable to hepatocellular injury initiated by reactive oxygen species (ROS). It is critical to understand not only the triggers for hepatitis (injury and inflammation) in NASH but also how this is perpetuated as chronic liver disease. The present focus is on whether the biochemical processes that generate oxidative stress lead to hepatocyte injury and secondary recruitment of inflammation or whether inflammation is the primary mediator of liver cell injury. Insulin resistance is a reproducible pathogenic factor in NASH. It favors accumulation of free fatty acids in the liver and predisposes to oxidative stress by stimulating microsomal lipid peroxidases and by the direct effects of high insulin levels in decreasing mitochondrial beta-oxidation. CYP2E1 is normally suppressed by insulin but is invariably increased in the livers of patients with NASH. In rodent dietary models of steatohepatitis, CYP2E1 is the catalyst of microsomal lipid peroxidation, while in Cyp 2e1 nullizygous mice, CYP4A proteins are induced and function as alternative microsomal lipid peroxidases. Other studies implicate activation of peroxisome proliferator-activated receptor-alpha (PPAR alpha) as leading to NASH; PPAR alpha is a transcription factor that governs both microsomal (via CYP4A) and peroxisomal (beta-oxidation) pathways of lipid oxidation and ultimately production of ROS. Increased lipid peroxidation is a crucial difference between the livers of rodents with experimental NASH and those of ob/ob genetically obese mice that have uncomplicated steatosis. Administration of endotoxin, through the release of tumor necrosis factor-alpha (TNF-alpha), provokes liver inflammation with hepatocyte injury in the steatotic liver. This may be particularly relevant in JIB and has been suggested as a pathogenic mechanism in primary NASH. It has been proposed that inheriting one or more copies of the hemochromatosis gene, C282Y, promotes fibrotic progression in NASH because of increased hepatic iron deposition, but recent studies have failed to confirm this. The relationship between the severity of hepatitis in NASH and progression to cirrhosis implies that products of the inflammatory infiltrate play a role in fibrogenesis. In summary, NASH can be regarded as the hepatic consequence of the metabolic syndrome (or syndrome X). Attention should now shift from steatosis, a generally benign process that is less evident in the advanced stages of cirrhosis, to the mechanisms for hepatocellular injury, inflammation, and hepatic fibrosis. In particular, the genetic, molecular, and cellular factors that ordain and moderate fibrosis in the context of steatohepatitis will be of greatest relevance to effective therapy and clinical outcome.

Chronic Disease↗
PubMed2001

Nonalcoholic steatosis and steatohepatitis. II. Cytochrome P-450 enzymes and oxidative stress.

Oxidative stress is present in the liver of humans with steatosis and nonalcoholic steatohepatitis (NASH) and is a plausible mediator of cellular injury, inflammatory recruitment, and fibrogenesis. CYPs 2E1 and 4A are the microsomal oxidases involved with fatty acid oxidation. Both enzymes can reduce molecular oxygen to produce prooxidant species, which, if not countered efficiently by antioxidants, create oxidative stress. In this theme article, we present the evidence that, in the context of hepatic steatosis, CYPs 2E1 and 4A could generate the "second hit" of cellular injury, particularly when antioxidant reserves are depleted, and propose ways in which this could contribute to the pathogenesis of NASH.

Animals↗
PubMed2001

Drug-induced cholestasis.

The spectrum of drug-induced cholestasis ranges from 'bland' reversible cholestasis to chronic forms due to the vanishing bile duct syndrome. Agents known for many years to cause cholestasis include estrogens and anabolic steroids, chlorpromazine, erythromycin, and the oxypenicillins; structurally similar congeners of these drugs (tamoxifen, newer macrolides) may also cause cholestasis. Contemporary drugs linked to cholestastic liver injury include ticlopidine, terfenadine, terbinafine, nimesulide, irbesartan, fluoroquinolones, cholesterol-lowering 'statins,' and some herbal remedies (greater celandine, glycyrrhizin, chaparral). Amoxillin-clavulanate, ibuprofen, and pediatric cases of the vanishing bile duct syndrome are recent additions to a long list of drugs associated with the vanishing bile duct syndrome. Particular human leukocyte antigen profiles have recently been identified among those who have developed cholestasis with specific drugs (tiopronin and amoxicillin-clavulanate), and the mechanistic relevance of these genetic associations is being explored. The treatment of drug-induced cholestasis is largely supportive. The offending drug should be withdrawn immediately. Cholestyramine or ursodeoxycholic acid are used to alleviate pruritus, with rifampicin and opioid antagonists being reserved for those who fail first line therapy. Nutritional support is essential for those with prolonged cholestasis, a subgroup who are at risk of developing biliary cirrhosis and liver failure. Timely referral for liver transplant assessment is crucial in these patients.

Aged↗
PubMed2000

Constitutive and inducible expression of hepatic CYP2E1 in leptin-deficient ob/ob mice.

In this study we have analyzed the inducible as well as constitutive hepatic expression of Cyp2e1 in a genetic model of obesity and non-insulin dependent (type II) diabetes, the leptin-deficient ob/ob mouse. In obese mice, Cyp2e1 levels were decreased compared to lean littermates. Treatment with leptin increased hepatic Cyp2e1 in obese mice to the levels observed in lean animals, but failed to alter Cyp2e1 expression in lean animals. As expected, leptin also reduced food intake in treated mice compared to saline-treated controls. In obese mice pair-fed the reduced amount of food, there was a significant increase in Cyp2e1 mRNA but no increase in Cyp2e1 protein or enzyme activity. Fasting and administration of acetone and 4-methylpyrazole increased Cyp2e1 mRNA as well as protein and activity in both obese and lean mice. The present data indicate that while Cyp2e1 is still inducible in obese mice by xenobiotics and fasting, full constitutive expression of Cyp2e1 requires leptin to be present. This effect of leptin appears to be at least partly independent of the hypothalamic control of food intake.

Acetone↗
PubMed2000

Role of oxidative stress in hypoxia-reoxygenation injury to cultured rat hepatic sinusoidal endothelial cells.

To characterize the role of oxidative stress in cultured rat sinusoidal endothelial cells, we studied the production of superoxide after reoxygenation, the relationship of reduced glutathione (GSH) levels to cell injury, and the protective efficacy of antioxidants. Hypoxia (pO(2) 1-2 mm Hg) was achieved by culturing cells under 95% N(2)5% CO(2) for 4 hours. Reoxygenation was then reestablished, and viability was determined at 24 hours by trypan blue exclusion; putative protective agents were added at the time of reoxygenation (4 hours). As previously reported, reoxygenation after 4 hours hypoxia accentuated sinusoidal cell death fourfold compared with hypoxic or normoxic controls (P <.0001). Superoxide was not produced on reoxygenation, and superoxide dismutase provided no protection against reoxygenation injury. Cellular levels of GSH fell to 37 +/- 4% of normoxic controls (P <.0001) following reoxygenation. These changes were essentially abrogated by Trolox (Aldrich Chemical Co., Milwaukee, WI) and dimethyl sulfoxide, both of which also completely protected against reoxygenation injury. When cellular GSH levels were lowered by addition of diethylmaleate (which conjugates GSH), this reduced the viability of endothelial cells cultured under normoxic conditions and greatly augmented reoxygenation injury. Conversely, addition of exogenous GSH partially protected endothelial cells against hypoxia-reoxygenation injury. Desferrioxamine also protected against reoxygenation injury, but catalase was only partly protective. It is concluded that sinusoidal endothelial cells undergo significant intracellular oxidative stress following reoxygenation, and their viability is critically dependent on GSH levels. Reactive oxygen species are likely mediators of oxidative stress in hepatic sinusoidal endothelial cells.

Animals↗
PubMed2000

Which patients with hepatitis C develop liver complications?

To identify variables that are independent predictors of adverse outcomes in chronic hepatitis C, we analyzed a cohort of 455 patients followed for a median of 4.7 years. Associations were sought between demographic and behavioral factors, hepatitis C virus (HCV) genotype, liver histology and liver tests at entry, and development of liver complications, hepatocellular carcinoma (HCC), hepatic transplantation and liver-related death. Independent predictors were identified by multivariate analysis. The following were associated with a significantly higher rate of liver complications: age; birth in Asia, Europe, Mediterranean region, or Egypt; transmission by blood transfusion or sporadic cases; HCV genotypes 1b and 4 (compared with 1/1a); fibrosis stage 3 or 4 (cirrhosis); serum albumin; bilirubin; prothrombin time; and alpha-fetoprotein. However, the only independent predictors of liver-related complications were sporadic transmission (P <.001), advanced fibrosis (P =.004), and low albumin (P <.001). The corresponding independent risk factors for HCC were male gender (P =. 07), sporadic transmission (P <.001), and albumin (P <.001); bilirubin (P =.02) was an additional predictor of transplantation or liver-related death. It is concluded that only patients with advanced hepatic fibrosis or cirrhosis, are at risk of developing hepatic complications of chronic hepatitis C during 5-year follow-up. Among such patients, abnormalities in serum albumin, bilirubin, or prothrombin time indicate a high probability of complications. Patients without definite risk factors for HCV (sporadic cases) are at higher risk of complications, possibly because of interaction between older age, duration of infection, country of birth, and HCV genotypes 1b and 4.

Adult↗
PubMed2000

Herbal hepatotoxicity: an expanding but poorly defined problem.

Alternative therapies, including herbal remedies, are popular in the general population and even more so among patients with liver disease. The use of such products is now well established in western society and is no longer confined to traditional medicine practitioners in Asia, Africa and the Middle-East. Their perceived benefits remain generally unproven and concern about adverse effects is leading to closer scrutiny of these products. Herbal hepatotoxicity has been recognized for many years, but new agents are constantly being identified. The varied manifestations of liver injury include steatosis, acute and chronic hepatitis, hepatic fibrosis, zonal or diffuse hepatic necrosis, bile duct injury, veno-occlusive disease, acute liver failure requiring liver transplantation and carcinogenesis. Potential interactions between herbal medicines and conventional drugs may interfere with patient management. Concurrent use of such products is not often disclosed unless specifically sought after and can lead to perpetuation of the liver injury. The present review focuses on emerging herbal hepatotoxins, newer patterns of liver injury among the older agents and provides an updated tabulation of the adverse effects of major herbal hepatotoxins. Key issues of diagnosis and prevention of this growing problem are addressed. Continued public education, physician awareness and more stringent licensing are required to tackle this growing problem.

Adult↗
PubMed2000

CYP2E1 and CYP4A as microsomal catalysts of lipid peroxides in murine nonalcoholic steatohepatitis.

Nonalcoholic steatohepatitis (NASH) and alcoholic liver disease have similar pathological features. Because CYP2E1 plays a key role in alcoholic liver disease with its ability to stimulate lipid peroxidation, we tested the proposal that CYP2E1 could also be a factor in the development of NASH. In a dietary model - mice fed a methionine- and choline-deficient (MCD) diet - liver injury was associated with both induction of CYP2E1 and a 100-fold increase in hepatic content of lipid peroxides. Microsomal NADPH-dependent lipid oxidases contributed to the formation of these lipid peroxides, and in vitro inhibition studies demonstrated that CYP2E1 was the major catalyst. To further define the role of CYP2E1 as an initiator of oxidative stress in NASH, Cyp2e1(-/-)mice were administered the MCD diet. CYP2E1 deficiency neither prevented the development of NASH nor abrogated the increased microsomal NADPH-dependent lipid peroxidation, indicating the operation of a non-CYP2E1 peroxidase pathway. In Cyp2e1(-/-) mice with NASH (but not in wild-type mice), CYP4A10 and CYP4A14 were upregulated. Furthermore, hepatic microsomal lipid peroxidation was substantially inhibited by anti-mouse CYP4A10 antibody in vitro. These results show that experimental NASH is strongly associated with hepatic microsomal lipid peroxidation. CYP2E1, the main enzyme associated with that process in wild-type mice, is not unique among P450 proteins in catalyzing peroxidation of endogenous lipids. We have now identified CYP4A enzymes as alternative initiators of oxidative stress in the liver.

Animals↗
PubMed2000

Clinical potential of emerging new agents in hepatitis B.

Treatment of chronic hepatitis B is directed at interrupting the natural history and clinical outcomes of the disease. It needs to take into account the virology and replication cycle of the hepatitis B virus (HBV), and the host immune response to HBV. Long term follow-up of patients treated with interferon supports the paradigm that a sustained, major suppression of HBV replication, particularly that associated with hepatitis B e antigen (HBeAg) seroconversion, interrupts the natural history of hepatitis B. The availability of potent but well tolerated and orally available HBV antivirals, of which lamivudine is the prototype, has allowed clearer treatment objectives to be formulated. These are: temporary or permanent reduction of hepatitis (necroinflammatory) activity, arrest of fibrotic progression, prevention of cirrhosis and liver failure, and prevention of recurrent HBV infection after liver transplantation. Lamivudine has good medium term efficacy in achieving each of these objectives. The only significant problem for the longer term is emergence of antiviral resistance conferred by mutations in the YMDD (tyrosine-methionine-aspartic acid-aspartic acid) motif of the HBV reverse transcriptase. As a result, contentious issues remain about defining when antiviral therapy is indicated, whether to treat for a defined interval or indefinitely, and when to stop treatment if HBeAg seroconversion is not achieved. Some personal views are expressed in this review. Among newer HBV antivirals in clinical studies, adefovir dipivoxil, entecavir and emtricitabine appear to be at least as potent as lamivudine in suppressing HBV replication. Famciclovir appears less potent. In vitro studies show that YMDD mutations confer cross-resistance between lamivudine, emtricitabine and beta-L-Fd4C (L-2',3'-didehydro-dideoxy-5-fluorocytidine). However, adefovir dipivoxil, lobucavir, entecavir, DAPD (beta-D-2,6-diaminopurine dioxolane) and possibly clevudine (L-FMAU) suppress replication of YMDD mutant HBV, as well as wildtype. Preliminary studies indicate clinical efficacy of adefovir dipivoxil once resistance to lamivudine has developed. Immunomodulatory approaches to treatment of chronic hepatitis B are conceptually attractive, but newer agents used to date (thymalfasin, interleukin-12, therapeutic vaccines) have not demonstrated sufficient efficacy for widespread use. The next challenge for HBV treatment is to use antivirals in combination and/or in cyclical therapy to reduce the emergence of drug resistance and increase efficacy, particularly to achieve sustainable post-treatment suppression of hepatitis B.

Antiviral Agents↗
PubMed1999

Hepatitis C: an economic evaluation of extended treatment with interferon.

OBJECTIVES: To re-evaluate the cost effectiveness of treating hepatitis C virus (HCV) infection with interferon alfa (IF alpha) in Australia, taking into account changes in clinical practice. DESIGN: A decision-analytic method (Markov model) was used to simulate the costs and effects of 6 months and 12 months of treatment with IF alpha versus no treatment (conventional management). Both costs and effects were modelled over 30 years. DATA SOURCES: Published meta-analysis of the effectiveness of treatment, professional judgement about treatment protocols, scheduled medical fees, diagnosis-related costs for hospital admission, and a literature search for quality-of-life weights. PATIENTS: A hypothetical cohort of 1000 patients with chronic HCV infection aged 40 years at the start of treatment. MAIN OUTCOME MEASURES: Incremental costs per life-year gained and per quality-adjusted life-year (QALY) gained. RESULTS: Compared with no treatment, IF alpha treatment for 6 months results in an extra 94.2 life-years or 320.1 QALYs at an extra cost of $1.8 million (after discounting at 3%) in a cohort of 1000 patients. Discounted cost per life-year gained is $19,110, which is about a quarter of the cost reported in 1994. The discounted cost per QALY gained is $5625. Extended treatment for another 6 months results in an additional 89.0 life-years saved or 170.8 QALYs gained at an incremental discounted cost of $15,835 per life-year gained and $8250 per QALY gained. CONCLUSIONS: The cost effectiveness of IF alpha treatment for HCV infection has improved as a result of better patient selection, cost reductions and enhanced effectiveness of extended treatment. The results are sensitive to assumptions made about quality of life and the discount rate.

Antiviral Agents↗
PubMed1999

Chronic ethanol consumption disrupts complexation between EGF receptor and phospholipase C-gamma1: relevance to impaired hepatocyte proliferation.

We have previously shown that chronic ethanol consumption inhibits liver regeneration by impairing EGF receptor (EGFR)-operated phospholipase C-gamma1 (PLC-gamma1) activation and resultant intracellular Ca2+ signalling. Activation of PLC-gamma1 by EGFR requires the EGFR to bind to PLC-gamma1 after its translocation from cytosol to cytoskeleton. In order to understand the mechanism by which ethanol impairs PLC-gamma1 activation, we examined the effect of alcohol on interactions between EGFR and PLC-gamma1. In cultured hepatocytes from control rats, EGF rapidly induced tyrosine phosphorylation of both the EGFR and of PLC-gamma1. EGF also stimulated PLC-gamma1 translocation from cytosol to a cytoskeletal compartment where PLC-gamma1 interacted with EGFR. In hepatocytes from rats fed ethanol for 16 weeks, the above reactions were substantially inhibited. Tyrphostin AG1478, an EGFR-specific tyrosine kinase inhibitor, mimicked the effects of chronic ethanol on EGFR phosphorylation, PLC-gamma1 translocation and interactions between EGFR and PLC-gamma1 in the cytoskeleton. Further, tyrphostin AG1478 also inhibited EGF-induced DNA synthesis. These results indicate that ethanol impairs EGFR-operated [Ca2+]i signaling by disrupting the interactions between EGFR and PLC-gamma1.

Animals↗
PubMed1999

Altered expression of hepatic CYP2E1 and CYP4A in obese, diabetic ob/ob mice, and fa/fa Zucker rats.

Hepatic levels of the cytochrome P450 (CYP) proteins 2E1 and 4A are often increased in obesity, diabetes and fasting. In such states of nutritional imbalance, CYPs 2E1 and 4A may play a more significant role in fatty acid oxidation. In order to more fully characterize the regulation of CYP2E1 and CYP4A in obesity and obesity-related (type II) diabetes, we analyzed the hepatic expression of CYP2E1 and CYP4A in ob/ob mice which are leptin deficient, and fa/fa Zucker rats which have defective leptin receptor function. CYP2E1 protein and mRNA were either unchanged or reduced in both models. Conversely, expression of murine Cyp4a10 and 4a14 in the obese mice, and 4A2 in the male fatty Zucker rat, were greatly increased. The levels of other CYP4As were either unchanged or reduced. These results show that CYP2E1 is not inevitably increased by obesity and diabetes and indicate differential regulation of CYP4A subfamily genes in rodent models. Further, they implicate leptin receptor signaling as a factor that may modulate expression of CYP gene products involved in fatty acid oxidation.

Animals↗