Neutral and polar lipid metabolism in liver microsomes of growing rats fed a calcium-deficient diet

We studied the incorporation of 14C-labeled fatty acids and glycerol into different classes of glycerolipids in an in vitro system containing liver microsomes from growing Wistar rats fed a calcium-deficient (CaD; 0.5 g/kg) diet for a 60-day period. Desaturase activities and incorporation of the elongation-desaturation metabolites into specific neutral and polar glycerolipids were also studied and correlated with the activities of various enzymes involved in complex lipid metabolism (acyl-CoA synthase, acyl-CoA hydrolase, DAG-acyltransferase, DAG-kinase, lysophospatidate-acyl-CoA transferase, phosphatidate-phosphohydrolase and phospholipase A2). Low calcium condition led to a significant increase in the incorporation (relative amounts and specific activities) of both labeled fatty acids and glycerol with a preferential increase of labeling in neutral lipids rather than in phospholipids. Acyl-CoA synthetase, diacylglycerol acyltransferase and diacylglycerol-3-P acyltransferase activities were increased in low calcium microsomes while diacylglycerol kinase, phospholipase A2 and palmitoyl-, stearoyl-, linoleyl-, α-linolenyl, and eicosatrienoyl-desaturases were decreased. The modifications observed in the interlipid and lipid/protein relationships, enzyme activities, and pattern of incorporation of labeled precursors into each glycerolipid class, suggest that decreased intake of calcium should be considered as a harmful risk factor for the development of cardiovascular diseases.