Hepatic mitochondrial DNA deletion in alcoholics: association with microvesicular steatosis

The interleukin-2 receptor down-regulates the expression of cytochrome P450 in cultured rat hepatocytes

BACKGROUND & AIMS

Interleukin (IL) 2 is used in advanced cancers, but its effects on cytochrome P450 remain unknown. Other cytokines down-regulate hepatic cytochrome P450, but it is not known whether this involves cytokine receptors. The aim of this study was to determine whether the IL-2 receptor is expressed on hepatocytes and whether its activation by IL-2 depresses cytochrome P450 in cultured rat hepatocytes.

METHODS

A monoclonal antibody specific for the rat IL-2 receptor alpha chain was used to label the receptor, whereas effects on cytochrome P450 were determined after 24 hours of culture with human recombinant IL-2 (5000 U/mL).

RESULTS

The presence of the IL-2 receptor in hepatocytes was shown by immunoblots, flow cytometry, and scanning confocal microscopy. IL-2 caused a 46% decrease in total cytochrome P450; a 35%, 35%, 36%, 26%, and 56% decrease in immunoreactive cytochrome P4501A1, 2B, 2C11, 2D1, and 3A, respectively; and a marked decrease in cytochrome P4503A2 and 2C11 messenger RNAs. Addition to the culture medium of the anti-receptor antibody or the tyrosine kinase inhibitor genistein prevented the IL-2-mediated decrease in cytochrome P450.

CONCLUSIONS

IL-2 down-regulates the expression of cytochrome P450 genes in cultured rat hepatocytes by interacting with its receptor expressed on hepatocytes.

Determinants of progression to cirrhosis or fibrosis in pure alcoholic fatty liver

"Pure" alcoholic fatty liver has been widely assumed to be "benign" with very low risk of progression to cirrhosis. Studies thus far have included either patients with coexisting recognised precursor lesions of cirrhosis or have been restricted to short-term histological follow-up. We have followed 88 patients, first seen between 1978 and 1985, with a histological diagnosis of pure alcoholic fatty liver and no evidence of fibrosis or alcoholic hepatitis, for a median of 10.5 years, to determine any factors predictive of disease progression. Of the 88, at follow-up nine had developed cirrhosis and a further seven fibrosis. Eight of nine patients with cirrhosis had continuing alcohol consumption of more than 40 units per week at follow-up; in the other patients, consumption was unknown. Independent histological predictors of progression on index biopsy were: presence of mixed macro/microvesicular fat, and presence of giant mitochondria. We can no longer regard alcoholic fatty liver as benign. In the presence of continuing high alcohol consumption the above histological features identified those at high risk (47-61%) of disease progression. Therefore, patients with these features should be counselled intensively regarding their alcohol consumption.

Inhibition of mitochondrial beta-oxidation as a mechanism of hepatotoxicity

Severe and prolonged impairment of mitochondrial beta-oxidation leads to microvesicular steatosis, and, in severe forms, to liver failure, coma and death. Impairment of mitochondrial beta-oxidation may be either genetic or acquired, and different causes may add their effects to inhibit beta-oxidation severely and trigger the syndrome. Drugs and some endogenous compounds can sequester coenzyme A and/or inhibit mitochondrial beta-oxidation enzymes (aspirin, valproic acid, tetracyclines, several 2-arylpropionate anti-inflammatory drugs, amineptine and tianeptine); they may inhibit both mitochondrial beta-oxidation and oxidative phosphorylation (endogenous bile acids, amiodarone, perhexiline and diethylaminoethoxyhexestrol), or they may impair mitochondrial DNA transcription (interferon-alpha), or decrease mitochondrial DNA replication (dideoxynucleoside analogues), while other compounds (ethanol, female sex hormones) act through a combination of different mechanisms. Any investigational molecule should be screened for such effects.