The Effects of Alcohol on the Protein Profile of Rat Lingual Epithelium

[摘要] A large volume of epidemiological evidence suggests a strong correlation between chronic alcohol abuse and the development of intra oral squamous cell carcinoma (Rothman & Keller, 1972; Kissin, 1975; Tuyns, 1982). Despite this evidence linking alcohol abuse and oral cancer, there are few properly controlled studies of the effect of alcohol alone on the oral epithelium. Those that have been properly controlled have demonstrated histological effects of alcohol on the epithelium. Structural or morphological changes in the oral epithelium may have a biochemical basis and thus the aim of this study was to investigate any biochemical abnormalities in the oral epithelium of alcoholic animals. The specific approach to the study involved an assessment of the effects of alcohol on the protein profile of rat lingual epithelium. A suitable animal model was required for the study and that chosen was the Isocalorific Matched Pair Feeding Technique of Lieber and DeCarli (1973). This involved maintaining one group of experimental animals on a nutritionally adequate liquid diet with ethanol substituted to provide 36 percent of the daily calorific intake. A second group was maintained on the same liquid diet, but with sucrose substituted to provide 36 percent of the animals' calories. By measuring the volume of diet consumed, each pair of animals had their calorific intake closely monitored and matched exactly. A control group maintained on standard laboratory chow was included in both of the animal studies presented and, in the second study, an additional control group maintained on liquid diet alone was also included. The usefulness of this animal model as a representation of chronic alcohol consumption was demonstrated by assessing liver damage in the alcoholic animals. Liver damage was demonstrated both enzymically, with Gamma-Glutamyl Transferase being of particular use in this respect, and histologically, with centrilobular fatty infiltration being observed in the livers of the alcoholic animals. Unfortunately, two of the liver enzymes that were measured, Aspartate Transaminase and Alanine Transaminase, appeared to be affected by the liquid diet and as a result were of limited use in assessing liver damage. It was as a means of investigating the effects of the liquid diet on these enzymes that the extra control group was included in the second animal study. The initial animal study ran for 102 days at the end of which, the animals were sacrificed and the lingual epithelium was removed and prepared for sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis. Results from this protein study revealed, in the alcoholic animals, a reduction in the levels of a high molecular weight (MW) glycoprotein with a molecular weight of c. 160 Kilodaltons (K), and an accompanying increase in the levels of two lower MW proteins (30K and 28K). Visual and densitometric analysis revealed that these protein levels were significantly altered in the alcoholic animals with respect to both the sucrose pair-fed control animals and the animals maintained on standard laboratory chow. A second animal study was set up to investigate the alterations in the levels of these three proteins, in the alcoholic animals, over fractions of the original 102 day study. The results demonstrated that chronic alcohol consumption was required before alterations could be detected in the levels of these proteins. It was postulated that the two lower MW proteins may be breakdown products of the high MW glycoprotein although there was no evidence of such a relationship in this time-course study, with each of the proteins being capable of expressing themselves at altered levels independently of the other two. An alternative approach to investigating a possible relationship between the high MW glycoprotein and the two lower MW proteins involved the use of peptide mapping. Results from these studies were inconclusive as the high MW glycoprotein appeared to be resistant to proteolytic digestion. Characterisation of the two lower MW proteins proved to be difficult as little was known about them, short of their molecular weights. Subcellular localisation studies revealed the 30K protein to be present in the epithelial cells associated with the membrane/microsomal fraction. Unfortunately, the 28K protein was more difficult to study in this respect, as it banded on SDS gels alongside a protein of very similar molecular weight as a closely associated doublet. One member of this doublet was seen to be associated with the membrane/microsomal fraction and the other with the cytoplasmic fraction of the cell. It is not yet clear which member of this doublet is enhanced in the alcoholic animals. Investigation of the solubility of these two proteins showed them to be maximally soluble in distilled water. Given the lack of information on these two proteins, it has not been possible to accurately identify them. It is suggested, however, that they may be members of the heat shock family of proteins.(Abstract shortened by ProQuest.).

[发布机构] University:University of Glasgow

[关键词] Medicine