Increased J774 macrophage cytotoxicity of late postprandial triglyceride-rich lipoproteins from normolipidemic young men expressing an apolipoprotein epsilon 4 allele

Abnormalities in apo B-containing lipoproteins in diabetes and atherosclerosis

Atherosclerosis is the major cause of death in patients with diabetes. Low-density lipoprotein (LDL) being the most important cholesterol-carrying lipoprotein has been studied extensively in both diabetes and non-diabetes. This paper reviews the literature but also focuses on the precursors of LDL and in particular the postprandial apo B-containing lipoproteins. Abnormalities in the postprandial lipoproteins and alteration in chylomicron assembly and clearance are discussed and the evidence presented suggesting the importance of dysregulation of these lipoproteins in atherosclerotic progression. The relationship between chylomicron production in the intestine and hepatic release of very low-density lipoproteins (VLDL) is explored, as is the interrelationship between clearance rates of these lipoproteins. The size of LDL influences its atherogenicity. VLDL composition and size in relation to its influence on LDL is discussed. The effect of diet on the composition of lipoproteins and the relationship between fatty acid composition and clearance is reviewed. Evidence that diabetic control beneficially alters lipoprotein composition is presented suggesting how improved diabetic control may reduce atherosclerosis. The review concludes with a discussion on the effect of the apo B-containing lipoproteins and their modification through glycation and oxidation on macrophage and endothelial function.

Effect of the fat composition of a single meal on the composition and cytotoxic potencies of lipolytically-releasable free fatty acids in postprandial plasma

Ingestion of a meal increases plasma levels of triglyceride (TG)-rich lipoproteins through the secretion of intestine-derived chylomcirons and liver-derived very low density lipoproteins (VLDL). We have determined the effects of the fat composition of a single meal on the composition of TG in TG-rich lipoproteins (VLDL + chylomicrons) and circulating and lipolytically-releasable free fatty acids (FFA) in postprandial (PP) plasma and on the cytotoxic potencies of the lipolytically-released FFA to cultured arterial wall cells. PP lipemia was induced by feeding fasted normolipidemic human subjects with a meal rich in saturated fat (SF) and another meal rich in polyunsaturated fat (PUF), or vice versa; each meal provided 65% of energy as fat, and polyunsaturated to saturated fatty acid ratios (P/S) of the SF and PUF in the meals were 0.40 and 2.49, respectively. The mean P/S of TG in TG-rich lipoproteins (1.43) and circulating FFA (1.46) in 4 h PP plasma of PUF were significantly higher than those in PP plasma of SF (0.44 and 0.59, respectively) in fasting plasma (0.52 and 0.53, respectively). In vitro lipolysis of fasting and PP serum by purified bovine milk lipoprotein lipase (LpL) resulted in a marked (8.8-12.3-fold) increase in the serum FFA level. The P/S of serum FFA in postlipolysis fasting and PP serum were consistently higher than that of FFA or that of TG associated with TG-rich lipoproteins in prelipolysis fasting and PP serum, indicating that polyunsaturated TG in VLDL and/or chylomicrons is more susceptible than saturated TG to lipolysis. When postlipolysis serum was interacted with cultured endothelial cells and mouse peritoneal macrophages (MPM), the lipolytically-released FFA in PP serum of SF and PUF disrupted the barrier function of endothelial cells and were cytotoxic to cultured MPM; FFA in postlipolysis fasting serum was not cytotoxic. FFA in postlipolysis PP serum of PUF were consistently more potent than that in postlipolysis PP serum of SF. Further study showed that all long-chain monounsaturated FFA and polyunsaturated FFA, but not saturated FFA, incorporated into lipoproteins (LDL) were cytotoxic to cultured MPM. In conclusion, despite the generally well-accepted belief that SF is more atherogenic than PUF, the present study provides in vitro evidence that the lipolytic remnant products of TG-rich lipoproteins produced after a meal rich in PUF are more injurious to arterial wall cells than those produced after a meal rich in SF.