Attenuation of alcohol-induced apoptosis of hepatocytes in rat livers by polyenylphosphatidylcholine (PPC).

BACKGROUND

Alcohol consumption increases apoptosis of hepatocytes. This effect appears to be mediated by the induction of hepatic cytochrome P-4502E1(CYP2E1) and its generation of free radicals, which results in an enhanced lipid peroxidation that initiates apoptosis. Because polyenylphosphatidylcholine (PPC), a soybean extract rich in polyunsaturated phosphatidylcholines, decreases the induction of ethanol-specific CYP2E1 and opposes oxidative stress, we hypothesized that PPC supplementation may attenuate hepatocyte apoptosis caused by ethanol ingestion.

METHODS

Twenty-eight male Sprague Dawley rats were pair-fed Lieber-DeCarli liquid diets containing 36% of energy as alcohol or an isocaloric amount of carbohydrate for 28 days. Half of the rats were given PPC (3 g/liter), whereas the other half received the same amount of linoleate (as safflower oil) and of choline as the bitartrate. An additional dose of alcohol (3 g/kg) was given intragastrically 90 min before the livers were removed. We assessed apoptosis in formalin-fixed, paraffin-embedded liver sections by using the TUNEL (terminal transferase dUTP nick end labeling) assay. Apoptotic hepatocytes were identified by positive TUNEL staining in conjunction with condensation of nucleoplasm or margination of chromatin. In each rat, 20,000 to 60,000 hepatocytes were counted by light microscopy by using Image-Pro Plus computer software, and the incidence of apoptosis was expressed as the percentage of total hepatocytes.

RESULTS

Alcohol feeding resulted in a 4.5-fold increase in apoptosis of hepatocytes compared to pair-fed control rats; PPC supplementation decreased the alcohol-induced apoptosis to less than half. No difference in the incidence of apoptosis between the control and PPC-supplemented rats was found in the absence of alcohol. Apoptosis was distributed randomly in the liver lobules of the rats fed the control diet, whereas the alcohol-induced apoptosis was significantly increased in the perivenular area. PPC supplementation strikingly reduced this effect.

CONCLUSIONS

PPC attenuates alcohol-induced apoptosis of hepatocytes; this effect may provide a mechanism for PPC's protection against liver injury, possibly in association with its antioxidative action via the down-regulation of ethanol-mediated CYP2E1 induction.