Increase in liver cytosolic lipases activities and VLDL-TAG secretion rate do not prevent the non-alcoholic fatty liver disease in cafeteria diet-fed rats

Abstract

We have previously shown that the cafeteria diet increases body fat mass, plasma triacylglycerol (TAG) and insulin levels, glucose uptake by white and brown adipose tissues, as well as the sympathetic activity to both adipose tissues in Wistar rats. The metabolic pathways responsible for the development of non-alcoholic fatty liver disease (NAFLD) were examined in cafeteria diet-fed rats. After 3 weeks offering cafeteria diet, we evaluated: (i) activity of the sympathetic nervous system by norepinephrine turnover rates; (ii) de novo fatty acid synthesis in vivo using ³H₂O; (iii) secretion of very low density lipoprotein (VLDL)-TAG secretion measuring serum TAG levels after administration of lipase lipoprotein inhibitor, (iv) liver cytosolic lipases activities and (v) liver mRNA expression of enzymes involved in lipids secretion and oxidation by RT-PCR. The cafeteria diet induced an increase in TAG (120%) and cholesterol (30%) liver contents. Cafeteria diet did not change the sympathetic nervous system activity to liver, but induced a marked increase in the lipogenesis (approximately four-fold) and significant increase in cytosolic lipases activities (46%) and VLDL-TAG secretion (22%) compared to control diet-fed rats. The cafeteria diet also increased the microsomal triglyceride transfer protein (30%) and carnitine palmitoyltransferase I (130%) mRNA expression but decreased the apolipoprotein B100 (26%) mRNA expression. Our findings demonstrate that the increase in the cytosolic lipases activities and VLDL-TAG secretion rates were not able to compensate for the increased lipogenesis rates induced by the cafeteria diet, resulting in NAFLD.

Keywords: Cytosolic lipases activities; Fatty acid synthesis; Lipid metabolism; Nonalcoholic fatty liver; Obesity.