Intermediate-density lipoprotein and cholesterol-rich very low density lipoprotein in angiographically determined coronary artery disease

Postchallenge plasma lipoprotein retinoids: chylomicron remnants in endogenous hypertriglyceridemia

This study was conducted to determine whether chylomicron remnants accumulate in the plasma of patients with "endogenous" hypertriglyceridemia. Retinyl esters were used as markers of chylomicrons and chylomicron remnants since they are carried mainly if not exclusively by lipoproteins of intestinal origin. Seventy-six fasting normotriglyceridemic and hypertriglyceridemic patients were studied 12 to 15 hours after ingesting 25,000 IU of vitamin A. Plasma retinol and retinyl esters were measured by reversed-phase high-performance liquid chromatography. Chylomicronemia was assessed by flotation at unit gravity and by chylomicron flocculation in 3% polyvinylpyrrolidone. Plasma lipids, retinoids, lipoprotein cholesterol, and the electrophoretic mobility of very-low density lipoproteins were determined in a subset of 36 subjects. Progressively elevated plasma retinyl ester concentrations were observed among patients with mild, moderate, and severe hypertriglyceridemia. All subjects with fasting chylomicronemia had retinyl ester retention. The majority of subjects with mild or moderate hypertriglyceridemia (predominantly type IV hyperlipoproteinemia) also had elevated plasma concentrations of retinyl esters. Total plasma retinyl ester and plasma triglyceride concentrations correlated significantly (rs = 0.721, P less than 0.001) in nonchylomicronemic subjects. In addition, total plasma retinol concentrations were mildly elevated among hypertriglyceridemic subjects because retinol, as well as retinyl esters, is transported by triglyceride-rich lipoproteins. If lipoprotein remnants are atherogenic in man, then chylomicron remnant retention may accelerate atherogenesis in hypertriglyceridemic individuals.

Influence of polyunsaturated fats and fat restriction on serum lipoproteins in humans

This study was designed to determine the effects of polyunsaturated fats and of reducing intake of total fat on serum lipids, lipoproteins, and apolipoproteins. Twenty-two normolipidemic women living in a nunnery were given a reference diet (fat/carbohydrate 42/46% of energy, P/S ratio 0.16), a polyunsaturated diet (42/46%, P/S 1,0), and a low-fat, polyunsaturated diet (32/56%, P/S 1.0) for 6 weeks each. Serum and lipoprotein lipids were determined by standard procedures, apolipoproteins either by laser immunonephelometry or by rocket immunoelectrophoresis. Consumption of the polyunsaturated diet decreased cholesterol and apolipoprotein B levels in VLDL (-33.1% and -23.8%) and in LDL (-13.5% and -8.8%) without affecting HDL. Consumption of the low-fat, polyunsaturated diet resulted in a reincrease of VLDL triglycerides, but not of VLDL cholesterol. Concentration of VLDL apolipoprotein B further fell (-41.6%) and that of apolipoprotein E decreased (-25.9%), resulting in an increased VLDL lipid/apolipoprotein mass ratio. This study indicates that responses to therapeutic polyunsaturated diet are lowered levels of VLDL and LDL, but unchanged levels of HDL. Additional restriction of dietary fat intake alters the VLDL composition with a decrement in apolipoprotein E enriched VLDL particles.

Relationship between lipids and angiographically defined coronary artery disease in Japanese patients

The relationship between the severity and extent of coronary artery disease (CAD) and the lipid profiles was evaluated in 120 Japanese male patients, who underwent coronary angiography. Analysis of the lipid quartile distribution showed that the percentage of patients with significant CAD increased as the total cholesterol (TC) increased and high-density lipoprotein cholesterol (HDL-C) decreased. In addition, as the number of vessels with marked coronary artery stenosis increased, TC and TC/HDL-C increased while HDL-C decreased. However, within this population, triglyceride level, high blood pressure, and smoking were not significantly associated with coronary angiographic findings.

Changes in very low and low density lipoproteins with dietary fat modification

Since VLDL and LDL are involved in atherogenesis, their response to dietary modification was studied in 15 normal male prisoners. A 3-month reference diet (P/S ratio 0.3, daily cholesterol intake 370 mg) was compared with a modified fat diet (P/S 1.0, 250 mg) given for further 3 months. The decrement in serum cholesterol by 32 mg/dl reflected a decrease in VLDL and LDL. It was associated with a decrease in serum apolipoprotein B by 16 mg/dl and in serum apolipoprotein E by 1.2 mg/dl. The decrement in VLDL cholesterol was paralleled by a lowered VLDL apolipoprotein E content. Serum and VLDL triglycerides, HDL cholesterol and the serum apolipoproteins A-I and A-II did not change significantly. One beneficial result of a conventional dietary regimen is lowered LDL with unaffected HDL. Another effect is the apparent modification of VLDL with a decrement of cholesterol and apolipoprotein E-enriched particles.

New concepts about the pathogenesis of atherosclerosis in diabetes mellitus

New concepts about the pathogenesis of atherosclerosis in diabetes mellitus are presented. Emphasis is given to alterations of endothelial function, as indicated by von Willebrand factor activity, prostacyclin release, and fibrinolytic activity in diabetes mellitus. Previous work on platelet aggregation and arachidonic acid metabolism is updated and recent findings are emphasized. The atherogenic mix of elevated low-density lipoprotein cholesterol and low high-density lipoprotein cholesterol levels in uncontrolled diabetes mellitus is noted. The lipid hypothesis is extended by consideration of very low-density lipoprotein and intermediate-density lipoprotein metabolism in diabetes. Lipoprotein-cell interactions that may contribute to atherosclerosis are reviewed and suggestions are made for future research in order to clarify the pathogenesis of atherosclerosis in diabetes mellitus.

Heterogeneity of very-low-density lipoprotein metabolism in hyperlipidemic subjects

Very-low-density lipoproteins (VLDL) are triglyceride-rich lipoproteins that have been shown, by physicochemical means, to comprise more than one group of particles. Because of the potential atherogenicity of catabolized VLDL, we used the technique of heparin-affinity chromatography to separate VLDL into two classes of particles, one of which appears to contain partly catabolized VLDL. This observation is based on the higher cholesterol/triglyceride and higher apoprotein E/apoprotein C ratios in VLDL particles that are bound to heparin, resembling in this way intermediate-density lipoproteins (IDL), which are certainly derived in the main through VLDL catabolism. Further studies showed separate metabolic characteristics for the unbound and heparin-bound VLDL particles. Radiolabeled whole VLDL or unbound particles were reinjected into seven hypertriglyceridemic subjects and the kinetics studied in serial samples of plasma over the next 18-48 hours. The specific radioactivity-time curves of apoprotein B in the unbound and bound particles showed that the bound particles were derived wholly or partly from the unbound particles and in turn, were the precursors of IDL. This confirmed that heparin-bound VLDL particles represented VLDL undergoing catabolism, although in one subject about one-half of the bound particles appeared to have an origin other than through VLDL catabolism. These studies show that VLDL metabolism is heterogeneous, that the kinetics of total VLDL must be interpreted accordingly, and that the technique of heparin-affinity chromatography can be used for more detailed studies of VLDL.

Preliminary report increased transport of intermediate density lipoprotein (LDL) with cholesterol loading

Although cholesterol loading in man generally leads to an increase in plasma cholesterol and low density lipoprotein cholesterol in particular, the mechanism for this is unknown. Because IDL formation rises in cholesterol-fed rats we have measured the transport of IDL apoprotein B in 8 men during two dietary periods containing either 200 mg or 1700 mg cholesterol per day. Radioiodinated IDL (Sf 12-20 or Sf 12-60) were reinjected and transport calculated from 48 hr specific radioactivity-time curves of apoprotein B in reisolated IDL. With cholesterol loading the IDL cholesterol and apoprotein B concentrations rose in 7 of 8 subjects (substantially in only 2). However IDL transport was stimulated more consistently and significantly (p less than 0.01), rising by at least 50% in 5 subjects. Furthermore the change in plasma total cholesterol concentration was significantly correlated with the change in IDL transport (r = +0.70, p less than 0.05). Since LDL are derived from IDL, the cholesterol-induced rise in IDL formation may explain the increase in LDL concentration with dietary cholesterol.

Increased lipoprotein-remnant formation in chronic renal failure

Since accelerated atherosclerosis may be induced by excess circulating remnants of triglyceride-rich lipoprotein catabolism, we looked for evidence of remnant particle accumulation in the lipoproteins of 11 patients on long-term dialysis. We found several abnormalities in lipoprotein protein and lipids: enrichment of intermediate-density lipoproteins (ILD) and low-density lipoproteins (LDL) with triglyceride; the presence of apoprotein B48 (a "marker" for intestinal lipoproteins) in very-low-density lipoproteins (VLDL); an increased concentration of apoprotein AIV (a protein related to chylomicron transport); the presence of AIV in VLDL, IDL, and LDL; and the presence in LDL of apoproteins C and E (proteins not normally found in LDL). These findings strongly suggest accumulation of remnants of triglyceride-rich lipoproteins in patients with chronic renal failure who are undergoing peritoneal dialysis or hemodialysis, and may explain in part the increased incidence of coronary deaths among these patients.