EFFECTS OF DIETARY POLYUNSATURATED FAT ON ETHANOL-INDUCED ITO CELL ACTIVATION

Ito cells, vitamin A-storing perisinusoidal cells, are believed to und ergo myofibroblastic transformation in liver fibrogenesis. Our previou s studies have shown that a diet high in polyunsaturated fat was key f or induction of experimental alcoholic liver fibrosis. To investigate the cellular basis for this fibrogenic effect of a high-fat diet, we a nalyzed the content of vitamin A and cellular retinol binding protein (CRBP), the steady-state mRNA levels of procollagen-alpha 1(I), transf orming growth factor-beta 1 (TGF-beta 1), interleukin-6 (IL-6), and sm ooth muscle alpha-actin (alpha-SM) in freshly isolated Ito cells from rats given isocaloric amounts of ethanol and a low- or high-fat diet. After 10 wk, the Ito cell content of retinyl palmitate was severely re duced in both the high- and low-fat diet-ethanol-fed animals to 13-17% of those measured in respective pair-fed controls. On the other hand, the content of CRBP was reduced in the high-fat-ethanol rats but not in the low-fat-ethanol group. The cells from the high-fat-ethanol but not low-fat-ethanol rats showed an 18-fold increase in procollagen-alp ha 1(I) mRNA at 17 wk, which was accompanied by 2.8- and 2.3-fold enha ncement of TGF-beta 1 and alpha-SM transcripts. IL-6 mRNA was not dete cted in the cells from any groups. These results demonstrate 1) myofib roblastic activation of Ito cells is evident in rats given a high-fat diet and ethanol but not in the low-fat-ethanol animals; 2) vitamin A depletion of Ito cells is the early and general effect of chronic etha nol intake but does not necessarily predict subsequent myofibroblastic activation; 3) reduced CRBP level is more closely associated with the subsequent cellular activation seen under the high-fat-ethanol regime n; and 4) IL-6 is not expressed in vivo by Ito cells from either norma l livers or livers with alcoholic Liver fibrosis.