Ethanol-mediated promotion of oesophageal carcinogenesis: association with lipid peroxidation and changes in phospholipid fatty acid profile of the target tissue.

Abstract

Ethanol consumption is a high risk factor for oesophageal carcinoma and studies indicate that it acts as a promoter of N-nitrosomethylbenzylamine (NMBzA)-induced oesophageal carcinogenesis. The studies described here indicate that ethanol-induced promotion was related with an increase in indices of lipid peroxidation in the target oesophageal tissue and that such an increase was associated with significant changes in the fatty acid profile of phospholipids. Young Sprague-Dawley rats were treated with NMBzA, 2.5 mg/kg body weight, three times a week for 3 weeks, and a week afterwards fed a 7% ethanolic diet that was continued until their death at 10 months. Cumulative ethane exhaled by rats was measured a week before their death and was found to increase significantly with NMBzA treatment but more so when followed by ethanol consumption. Cholesterol, phospholipids, and some indices of lipid peroxidation were measured in the oesophagus and liver. Whereas the levels of cholesterol and phospholipids were not affected in control-fed rats with or without the NMBzA treatment, ethanol consumption by either the untreated or NMBzA-treated rats caused a significant increase in the targeted oesophagus as well as the liver, the major site of ethanol and carcinogen metabolism. Ethanol consumption also increased all the indices of lipid peroxidation, i.e. malondialdehyde, lipid fluorescence, diene- and triene-conjugates; the largest increases were observed in rats that received both NMBzA and ethanol. A comparison of the fatty acid profile of phospholipids from the oesophagus and liver indicated significant alterations both with the NMBzA treatment and ethanol consumption. However, the fatty acid profile with regard to its peroxidability was significantly modified only with ethanol consumption and only in the oesophagus of the NMBzA-treated or untreated rats. Also, hepatic phospholipids showed a substantial increase in linolenate and no change in arachidonate, but the oesophageal phospholipids exhibited a pronounced increase in the levels of C18:3, C20:2, C20:3, C20:3' and C22:6 with a significant increase in arachidonate when use of ethanol followed the NMBzA treatment, suggesting a disorder in lipid and eicosanoid metabolism. We propose that ethanol may promote carcinogenesis through excessive cell proliferation induced by disordered lipid and eicosanoid metabolism that may cause a selective outgrowth of the initiated cells.