Intermediate-density Lipoprotein Cholesterol Research Articles

Rationale for Use of Non–High-Density Lipoprotein Cholesterol Rather Than Low-Density Lipoprotein Cholesterol as a Tool for Lipoprotein Cholesterol Screening and Assessment of Risk and Therapy

The plasma level of low-density lipoprotein (LDL) cholesterol is the “gold standard” for estimating the lipoprotein-related risk for complications of atherosclerotic vascular disease. LDL cholesterol concentrations are commonly estimated by the Friedewald formula that requires only the measurement (after overnight fasting) of plasma cholesterol and triglycerides along with high-density lipoprotein (HDL) cholesterol. This value, however, is not in fact a true estimate of LDL cholesterol but rather of LDL cholesterol along with variable, usually smaller, amounts of intermediate-density lipoprotein (IDL) cholesterol and lipoprotein(a). Estimation of LDL cholesterol levels by the Friedewald formula becomes progressively less accurate as plasma triglyceride concentrations increase, and the formula is generally considered inapplicable when triglyceride levels exceed 400 mg/dL. We believe that a very simple measurement—non–HDL cholesterol (serum cholesterol minus HDL cholesterol)—has considerable potential as a screening tool for identifying dyslipoproteinemias, for risk assessment, and for assessing the results of hypolipidemic therapy. Unlike the estimation of LDL cholesterol levels by the Friedewald formula, the estimation of non–HDL cholesterol concentrations requires no assumptions about the relation of very-low-density (VLDL) cholesterol levels to plasma triglyceride concentrations. This method includes all of the cholesterol present in lipoprotein particles now considered to be potentially atherogenic [VLDL, IDL, LDL, and lipoprotein(a)]. This article provides examples of the utility of non–HDL cholesterol concentrations in clinical medicine.

Effect of renin gene transfer on blood pressure in the spontaneously hypertensive rat.

To investigate whether molecular variation in the renin gene contributes to the greater blood pressure of spontaneously hypertensive rats (SHR) versus normotensive Brown Norway (BN) rats, we measured blood pressure in an SHR progenitor strain and an SHR congenic strain that are genetically identical except at the renin gene and an associated segment of chromosome 13 transferred from the BN strain. Backcross breeding and molecular selection at the renin locus were used to create the SHR congenic strain (designated SHR.BN-Ren) that carries the renin gene transferred from the normotensive BN strain. We found that transfer of the renin gene from the BN strain onto the genetic background of the SHR did not decrease blood pressure in rats fed either a normal or high-salt diet. In fact, the systolic blood pressures of the SHR congenic rats tended to be slightly greater than the systolic blood pressures of the SHR progenitor rats. However, the congenic strain exhibited lower serum high-density lipoprotein cholesterol, and greater levels of total cholesterol, very-low-density lipoprotein, and intermediate-density lipoprotein cholesterol during administration of a high-fat, high-cholesterol diet. These findings demonstrate that (1) under the environmental circumstances of the current study, the greater blood pressure of SHR versus BN rats cannot be explained by strain differences in the renin gene and (2) a quantitative trait locus affecting lipid metabolism exists on chromosome 13 within the transferred chromosome segment. The SHR.BN-Ren congenic strain may provide a useful new animal model for studying the interaction between high blood pressure and dyslipidemia in cardiovascular disease.

Hepatic Lipase Deficiency

Hepatic lipase (HL) is an enzyme that is made primarily by hepatocytes (and also found in adrenal gland and ovary) and hydrolyzes phospholipids and triglyc-erides of plasma lipoproteins. It is secreted and bound to the hepatocyte surface and readily released by heparin. It is a member of the lipase superfamily and is homologous to lipoprotein lipase and pancreatic lipase. The enzyme can be divided into an NH2-terminal domain containing the catalytic site joined by a short spanning region to a smaller COOH-terminal domain. The NH2-terminal portion contains an active site serine in a pentapeptide consensus sequence, Gly-Xaa-Ser-Xaa-Gly, as part of a classic Ser-Asp-His catalytic triad, and a putative hinged loop structure covering the active site. The COOH-terminal domain contains a putative lipoprotein-binding site. The heparin-binding sites may be distributed throughout the molecule, with the characteristic elution pattern from heparin-sepharose determined by the COOH-terminal domain. Of the three N-linked glycosylation sites, Asn-56 is required for efficient secretion and enzymatic activity.HL is hypothesized to directly couple HDL lipid metabolism to tissue/cellular lipid metabolism. The potential significance of the HL pathway is that it provides the hepatocyte with a mechanism for the uptake of a subset of phospholipids enriched in unsaturated fatty acids and may allow the uptake of cholesteryl ester, free cholesterol, and phospholipid without catabolism of HDL apolipoproteins.HL can hydrolyze triglyceride and phospholipid in all lipoproteins, but is predominant in the conversion of intermediate density lipoproteins to LDL and the conversion of post-prandial triglyceride-rich HDL into the postabsorptive triglyceride-poor HDL.HL plays a secondary role in the clearance of chylomicron remnants by the liver. Human post-heparin HL activity is inversely correlated with intermediate density lipoprotein cholesterol concentration only in subjects with a hyperlipidemia involving VLDL. This is consistent with intermediate-density lipoproteins being a substrate for HL. HDL cholesterol has been reported to be inversely correlated to HL activity, and on this basis it has been suggested that lowering HL would increase HDL cholesterol. However, the correlation could also be due to a common hormonal factor such as estrogen, which has been shown to up-regulate apoAI and HDL cholesterol and lower HL. A striking feature of severe deficiency of HL is the increase in HDL cholesterol and apolipoprotein AI and an approximately 10-fold increase in HDL triglyceride. Hyper-alpha-triglyceridemia is not a feature of antiatherogenic HDL.HL binds not only to heparan, but also to the LDL receptor-related protein. It has been suggested that enzymatically inactive HL can play a role in hepatic lipoprotein uptake, forming a “bridge” by binding to the lipoprotein and to the cell surface. This raises the interesting possibility that production and secretion of mutant inactive HL could promote clearance of VLDL remnants.We have described a rare family with HL deficiency. Affected patients are compound heterozygotes for a mutation of Ser267 to Phe that results in an inactive enzyme and a mutation of Thr3 83 to Met that results in impaired secretion and reduced specific activity. Human HL deficiency in the context of a second factor causing hyperlipi-demia is strongly associated with premature coronary artery disease. Recently, it has been reported that mutations affecting the structure of HL (e.g., T383M) are relatively frequent in the Finnish population. A C-to-T polymorphism in the promotor region of the HL gene is associated with lowered HL activity and less strongly with increased HDL cholesterol.In summary, there is a good understanding of what HL does in lipoprotein metabolism; however, there is little understanding of its physiological importance, that is, why HL does what it does. All of the current evidence consistently suggests that HL deficiency is in a state of increased susceptibility to heart disease that requires the coexistence of an independent cause of hyperlipidemia for the development of premature CAD. Any detrimental effects of high levels of HL are speculative at this time.

Insulin resistance is not a major determinant of low-density lipoprotein particle size

The relationship between low-density lipoprotein (LDL) peak particle diameter and insulin sensitivity, very—low-density lipoprotein (VLDL) + intermediate-density lipoprotein (LDL) triglyceride, cholesterol, and apoprotein B, postprandial lipemia, and LDL + high-density lipoprotein (HDL) triglyceride was assessed. The subjects were 101 healthy males aged 15 to 45 years. Sixty-one subjects (60.4%) were offspring of a parent with coronary artery disease before age 60, and 40 subjects (39.6%) had no parental history of coronary artery disease. LDL peak particle diameter was measured following polyacrylamide gradient gel electrophoresis. An insulin sensitivity index (S i) was determined from a frequently sampled intravenous glucose tolerance test using a minimal modeling method. A fat tolerance test was performed with a test meal containing 70 g/m 2 fat, with triglyceride concentrations measured hourly for 12 hours. LDL peak particle diameter was significantly correlated with body mass index (BMI) ( r = −.282, P < .01), waist to hip ratio ( r = −.291, P < .01), fasting triglyceride (logarithmically [log] transformed) ( r = −.556, P < .001), area under the postprandial triglyceride (log transformed) ( r = −.562, P < .001), VLDL + IDLL triglyceride (log transformed) ( r = −.321, P < .001), LDL + HDLL triglyceride (log transformed) ( r = .583, P < .001), and HDL cholesterol ( r = .347, P < .001), but there was no significant correlation with S i. Using stepwise regression analysis, LDL + HDL triglyceride showed the strongest relationship to LDL peak particle diameter, accounting for 34% of the variation in size. S I was not an independent predictor of LDL particle size. In conclusion, insulin sensitivity appears to have little influence on LDL particle size. The importance of LDL + HDL triglyceride should be ocnsidered a preliminary finding warranting varification in this and other populations.

Characteristics of coronary artery disease and lipoprotein abnormalities in patients with heterozygous familial hypercholesterolemia associated with diabetes mellitus or impaired glucose tolerance

Familial hypercholesterolemia (FH) is a genetic disorder characterized by high levels of serum low density lipoprotein (LDL) cholesterol and premature coronary atherosclerosis. In order to elucidate the influence of abnormal glucose metabolism on the development of coronary artery disease (CAD) in FH patients, we examined the prevalence of CAD and characteristics of lipoprotein abnormalities in patients with heterozygous FH who were accompanied by diabetes mellitus (DM) or impaired glucose tolerance (IGT). The subjects of the present study were 150 patients with heterozygous FH, all over 40 years of age. Oral glucose tolerance tests demonstrated that 15 patients had DM and 27 had IGT. The combination of DM or IGT with FH was associated with a further increase in the prevalence of CAD (DM:IGT:normal glucose tolerance (N), 87:59:43%). Furthermore, the prevalence of the stenoses in the distal coronary arteries was significantly higher in the DM group than in the N group, while there was no significant difference in the prevalence of proximal and middle lesions. Serum triglyceride levels were significantly higher in the DM and IGT groups than in the N group (P<0.01, DM versus N group; P<0.01, IGT versus N group), while total cholesterol levels were not significantly different. When lipoproteins were analyzed by polyacrylamide gel electrophoresis, the frequency of midband appearance, which implies an increase in remnant lipoproteins, was significantly higher in the DM and IGT groups than in the N group (DM:IGT:N, 87:72:29%, P<0.01, DM versus N group; P<0.01, IGT versus N group). Ultracentrifugation analysis of lipoproteins revealed that intermediate density lipoprotein cholesterol was increased in DM and IGT groups compared with the N group. These data suggest that abnormal glucose metabolism may accelerate the development of CAD in FH patients due to an increase in atherogenic remnant lipoproteins in addition to high concentration of LDL. Special attention should be paid in the treatment of FH patients with impaired glucose metabolism, to avoid the advancement of coronary atherosclerosis.

Intermediate density lipoprotein cholesterol as the best lipoprotein predictor of atherosclerosis severity in the Watanabe Heritable Hyperlipidemic rabbit

a Department of Clinical Biochemistry, Rigshospitalet, Uni6ersity of Copenhagen, Copenhagen, Denmark b Department of Clinical Biochemistry, Herle6 Hospital, Uni6ersity of Copenhagen, Herle6 Ring6ej 75, DK-2730 Herle6, Denmark c Department of Pathology, H6ido6re Hospital, Uni6ersity of Copenhagen, Copenhagen, Denmark d Department of Cardiology, H6ido6re Hospital, Uni6ersity of Copenhagen, Copenhagen, Denmark e Institute of Toxicology, National Food Agency of Denmark, Denmark

Atherogenic lipoprotein changes in the absence of hyperlipidemia in patients with chronic renal failure treated by hemodialysis

We compared plasma lipid and lipoprotein parameters between 210 chronic renal failure patients treated by hemodialysis and 223 age- and sex-matched healthy control subjects to examine whether atherogenic lipoprotein changes were present in hemodialysis patients in the absence of hyperlipidemia. The hemodialysis group showed higher levels of plasma triglycerides, very low density lipoprotein (VLDL) cholesterol, and intermediate density lipoprotein (IDL) cholesterol and a lower level of high density lipoprotein (HDL) cholesterol. Low density lipoprotein (LDL) cholesterol of the hemodialysis group was not elevated but their LDL was significantly more triglyceride-enriched than that of controls. Subjects were then divided into five categories according to their plasma triglyceride levels at an interval of 50 mg/dl, and comparison was made between the two groups in the same range of plasma triglycerides. Hemodialysis patients again showed higher levels of VLDL- and IDL-cholesterol, and lower levels of HDL-cholesterol than the control group even in the plasma triglycerides-matched comparisons. Similarly, higher VLDL- and IDL-cholesterol levels in hemodialysis patients were significant in plasma total cholesterol-matched subgroup comparisons. Multiple regression analysis indicated that the relationship between plasma lipid concentrations and individual lipoprotein levels were substantially altered in uremic state. The 95th percentile level of IDL-cholesterol in the nonuremic controls was 15 mg/dl, and 45% of hemodialysis patients exceeded this level. Decreased HDL-cholesterol levels ≤35 mg/dl were seen in 6% of the control and 38% of the hemodialysis group. Elevated IDL-cholesterol and decreased HDL-cholesterol were persistently found in hemodialysis patients with normal lipid levels. It is concluded that hemodialysis patients exhibited more atherogenic lipoprotein profile than nonuremic subjects with comparable levels of plasma triglycerides and total cholesterol. Especially, increased IDL- and decreased HDL-cholesterol levels in hemodialysis patients persisted even at very low levels of plasma lipids. Since elevated IDL and decreased HDL-cholesterol are implicated in the progression of atherosclerosis, these findings are of clinical importance in the diagnosis of lipoprotein disorder in chronic renal failure.

Increased serum remnant lipoproteins in patients with apolipoprotein E7 (apo E Suita)

Apolipoprotein (apo) E7 was originally identified by Yamamura et al. in subjects with atherosclerotic cardiovascular diseases (J. Clin. Invest. 1984;74:1229). However, the lipoprotein abnormalities associated with apo E7 phenotype have not been elucidated. In the current study, to clarify the physiological roles of apo E7, lipoprotein abnormalities were studied in 12 apo E7 heterozygotes. A total of seven subjects were hyperlipidemic and five subjects were normolipidemic. The apo E phenotype was apo E7/3 in 11 subjects and apo E7/4 in one subject. Polymerase chain reaction revealed that all of the subjects with apo E7 phenotype had the same mutation as that of apo E Suita as reported previously (J. Biochem. 1989;105:249). All the hyperlipidemic subjects were over 40 years of age and two of them also had and severe coronary heart disease. Ultracentrifugal analysis revealed that the cholesterol level both in very low density lipoprotein and in intermediate density lipoprotein (IDL) was substantially higher in hyperlipidemic apo E7 heterozygotes, compared with control subjects and that the IDL cholesterol was also increased even in normolipidemic apo E7 heterozygotes. Polyacrylamide gel electrophoresis of lipoproteins showed a midband, which implies the increase of remnant lipoproteins, in 11 subjects out of 12, irrespective of the presence or absence of hyperlipoproteinemia. In two cases, a broad β pattern was observed similar to that seen in type III hyperlipoproteinemia. Dietary therapy was dramatically effective for the treatment of hyperlipidemia in patients with apo E7. These findings confirm that apo E is crucial for remnant lipoprotein metabolism and that apo E7 is related to the increase in serum remnant lipoproteins, which leads to hyperlipoproteinemia in association with obesity, aging and impaired glucose metabolism.

Effect of exogenous hyperinsulinaemia on atherogenesis in cholesterol-fed rabbits

To examine the hypothesis that hyperinsulinaemia promotes atherosclerosis, cholesterol-fed rabbits were injected subcutaneously with 6 i.u. of human insulin (n = 16) or placebo (n = 20) daily for 24 weeks; injection of insulin resulted in hyperinsulinaemia for up to 16 h after injection. Compared to placebo rabbits, insulin-treated rabbits had higher levels of insulin antibodies in plasma, similar levels of intermediate density, low density and high density lipoprotein cholesterol and similar activities of hepatic and lipoprotein lipase in post-heparin plasma, but lower levels of plasma C-peptide, blood glucose, postprandial plasma triglycerides, plasma cholesterol and very low density lipoprotein cholesterol. On univariate analysis, with and without adjustment for differences in plasma cholesterol levels between the two groups, there were no significant differences in extent or severity of atherosclerosis between insulin and placebo rabbits. Furthermore, after combining the results from all the rabbits to examine plasma insulin levels and the other variables mentioned above as predictors of atherosclerosis severity, plasma insulin level was not a predictor, on univariate or multiple linear regression analysis; the first ranked independent predictors were postprandial intermediate density lipoprotein cholesterol in the arch, and postprandial plasma triglyceride in both the thoracic and abdominal aorta. These results suggest that exogenous hyperinsulinaemia does not promote atherogenesis in cholesterol-fed rabbits, but that postprandial levels of intermediate density lipoprotein cholesterol or plasma triglycerides may be involved in atherogenesis.

Adenoviral delivery of low-density lipoprotein receptors to hyperlipidemic rabbits: Receptor expression modulates high-density lipoproteins

Plasma concentrations of low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs) are inversely related in several dyslipoproteinemias. To elucidate the interactions between these lipoproteins, we used a recombinant adenovirus (hLDLR-rAdV) to express human LDL receptors (hLDLRs) in LDL receptor-deficient rabbits. hLDLR-rAdV administration resulted in hepatocyte expression and a reduction of total, intermediate-density lipoprotein (IDL), and LDL cholesterol. In addition, we found that hLDLR-rAdV treatment induced (1) increased very-low-density lipoprotein (VLDL) cholesterol, (2) increased VLDL, IDL and LDL triglycerides, (3) decreased α- and pre-β-migrating apolipoprotein E (apo E) and decreased pre-β-migrating apo A-I at 2 to 4 days posttreatment, and (4) increased total plasma apo A-I and pre-β-migrating apo A-I beginning 8 to 10 days posttreatment. Virtually all plasma apo A-I was present on α- and pre-β-HDL. Pre-β-HDL particles with size and electrophoretic properties consistent with nascent HDL demonstrated the greatest relative apo A-I enrichment following hLDLR-rAdV treatment. In summary, enhanced expression of hepatocyte LDLRs by hLDLR-rAdV treatment markedly altered apo A-I-containing lipoproteins and IDL and LDL. The use of recombinant viruses to express physiologically relevant genes in intact animals, analogous to transfection of cells in culture, provides a new strategy for the evaluation of effects of specific gene products on metabolic systems in vivo.

Alterations in plasma lipoproteins and apolipoproteins before the age of 40 in heterozygotes for lipoprotein lipase deficiency

We have assessed the expression of heterozygosity for lipoprotein lipase (LPL) deficiency by studying a single large French Canadian family comprising 92 persons including 21 carriers of the catalytically defective P207L mutation. Phenotypic changes distinguishing heterozygotes from controls were seen early, before the age of 40 and often before 20 years of age. In the total cohort these changes included an elevation in the mean very low density (VLDL) and intermediate density lipoprotein (IDL) triglyceride (+69%; P = 0.01 and +40%; P = 0.001) and cholesterol (+51%; P = 0.03 and +67%; P = 0.007) and apoB levels but decreased HDL2 and HDL3 cholesterol, (-32%; P = 0.01 and -15%; P = 0.002 respectively). While the lipid compositions of VLDL and IDL were similar between heterozygotes and controls, the low density (LDL) and high density lipoproteins (HDL) of carriers were triglyceride enriched. Heterozygotes also had a markedly lower apoC-III ratio (apoC-III in supernatant/apoC-III in heparin precipitate) (1.46 vs. 3.86 P = 1 x 10(-4)) indicating a substantial enrichment of VLDL and IDL with apoC-III and depletion of HDL apoC-III supporting this ratio as an effective index for efficiency of lipolysis. LpA-I was markedly reduced (0.34 vs. 0.43 P = 1 x 10(-5)) showing that levels of this particle are partly dependent on LPL catalytic activity. Heterozygotes manifest from an early age with a markedly reduced HDL, LpA-I, apoC-III ratio and an increased TC/HDLc ratio which would predict a relatively increased risk of premature coronary artery disease, compared to their normal siblings.

Relationship between obesity and concentration and composition of low-density lipoprotein subfractions in normoinsulinemic men

Obesity, insulin resistance (IR) with hyperinsulinemia, and a dyslipoproteinemia characterized by reduced high-density lipoprotein 2 (HDL 2) cholesterol and elevated levels of small, dense low-density lipoprotein (LDL) particles are risk factors for coronary artery disease (CAD). The impact of obesity independent of hyperinsulinemia on the concentration and composition of small, dense LDL subfractions is uncertain. The aim of this study was to investigate the relationship between obesity indices, namely body mass index (BMI), skinfold measurements (SF), and waist to hip ratio (WHR), and LDL-subfraction particle concentration and composition in 200 healthy men without evidence of IR. A precise analysis of the concentration of lipids and apolipoproteins and the composition of very—low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and two HDL- and six LDL-subfraction particles was obtained using the technique of density-gradient ultracentrifugation. Dividing the individuals according to BMI showed that those with a BMI greater than 27 kg/m 2 had significantly lower HDL 2 cholesterol and apolipoprotein (apo) A-I and higher VLDL and IDL cholesterol and apo B concentrations than those with a BMI less than 25 kg/m 2. Regarding LDL particles, we found that men with a BMI above 25 kg/m 2 had significantly more small, dense LDL particles (d 1.044 to 1.063 g/mL) and correspondingly fewer medium, dense LDL particles (d 1.031 to 1.037 g/mL) than leaner men; those with a BMI above 27 kg/m 2 had the highest concentration of circulating small, dense LDL particles. These findings were not influenced by fasting insulin concentrations, IR, or WHR. This study showed that obesity (BMI > 25 kg/m 2 associated with significantly higher SF, percent body fat, and waist circumference) is an important factor for the expression of a more atherogenic LDL-subclass phenotype even in normoinsulinemia. Characteristic differences in composition of LDL-subfraction particles between lean and obese men underlie the role of body weight in the metabolism of LDL-subfraction particles.

Sitostanol ester margarine in dietary treatment of children with familial hypercholesterolemia.

In familial hypercholesterolemia (FH) the lowering of serum cholesterol levels should be started in childhood in order to prevent coronary artery disease later in life. However, treatment of children is problematic. We studied the effects of sitostanol (3 g/day) ester dissolved in rapeseed oil margarine as a hypocholesterolemic agent in one homozygous and 14 heterozygous children with FH maintained on a low cholesterol diet for 6 weeks, using a double-blind crossover design. Absorption and synthesis of cholesterol were evaluated by measuring serum plant sterol and cholesterol precursor proportions to cholesterol by gas-liquid chromatography. The compliance was good, and the children could not distinguish by taste the two margarines without and with sitostanol ester. Sitostanol margarine significantly reduced serum total, intermediate density (IDL), and low density lipoprotein (LDL) cholesterol by 11, 26, and 15%, respectively, and increased HDL/LDL cholesterol ratio by 27%. The proportions of serum delta 8-cholestenol, lathosterol, and desmosterol were significantly increased by 36, 19, and 18%, and those of serum cholestanol, campesterol, and sitosterol were significantly decreased by 9, 42 and 29%, respectively, suggesting that cholesterol absorption was decreased and synthesis was compensatorily increased. High basal precursor sterol proportions predicted a high decrease in LDL cholesterol levels. In conclusion, partial replacement of normal dietary fat consumption by sitostanol ester margarine appears to be an effective and safe hypocholesterolemic treatment in children with FH.

Effect of fluvastatin on intermediate density lipoprotein (remnants) and other lipoprotein levels in hypercholesterolemia

The accelerated atherosclerosis in diseases associatedwith elevated remnant lipoprotein levels has directed interest toward the response of this lipoprotein species to lipid-lowering treatment. The effect of fluvastatin—a synthetic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor—was compared with that of placebo on parameters of remnant metabolism in 57 patients with moderate hypercholesterolemia, but not heterozygous familial hypercholesterolemia, type III hyperlipidemia, or endogenous hypertriglyceridemia. Fluvastatin therapy resulted in decreases versus baseline in plasma total cholesterol, low density lipoprotein cholesterol (LDL-C) and LDL apolipoprotein (apo) B levels of 18%, 20%, and 18%, respectively (p < 0.01). Plasma parameters related to remnant metabolism were also significantly decreased: intermediate density lipoprotein by 43% and apo E by 22% (p < 0.01). The percent decrease in plasma intermediate density lipoprotein cholesterol level was twice that of LDL-C and 50% greater than the decrease seen in very low density lipoprotein cholesterol (VLDL-C), which was decreased by 28%. Total triglycerides were reduced by 11% and VLDL apo B by 24%, whereas high density lipoprotein cholesterol (HDL-C) rose significantly by 8%, HDL2-C by 24%, and HDL3-C by 3%. There were no increases in apo A-I levels compared with placebo nor any significant change in plasma lipoprotein(a) levels. The composition of LDL and VLDL particles did not appear to be altered by therapy, as assessed by the LDL-C:LDL-B, VLDL-C:VLDL-B, ortriglyceride:VLDL-B ratios. Further, there was no correlation between baseline triglycende levels and percent changes in remnant parameters. In conclusion, the HMG-CoA reductase inhibitor fluvastatin induced major reductions in indices of remnant lipoprotein concentrations, including intermediate density lipoprotein cholesterol and apo E. The total plasma apo E levels fell despite the increased HDL-C level, where more than half of the total apo E resides. The marked reduction in remnant lipoprotein, in addition to LDL-C with fluvastatin, may contribute to the antiatherosclerotic effect associated with this class of agents.

Effect of fluvastatin on intermediatedensity Lipoprotein (remnants) and other lipoprotein levels in hypercholestarolemia

The accelerated atherosclerosis in diseases associatedwith elevated remnant lipoprotein levels has directed interest toward the response of this lipoprotein species to lipid-lowering treatment. The effect of fluvastatin—a synthetic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor—was compared with that of placebo on parameters of remnant metabolism in 57 patients with moderate hypercholesterolemia, but not heterozygous familial hypercholesterolemia, type III hyperlipidemia, or endogenous hypertriglyceridemia. Fluvastatin therapy resulted in decreases versus baseline in plasma total cholesterol, low density lipoprotein cholesterol (LDL-C) and LDL apolipoprotein (apo) B levels of 18%, 20%, and 18%, respectively (p < 0.01). Plasma parameters related to remnant metabolism were also significantly decreased: intermediate density lipoprotein by 43% and apo E by 22% (p < 0.01). The percent decrease in plasma intermediate density lipoprotein cholesterol level was twice that of LDL-C and 50% greater than the decrease seen in very low density lipoprotein cholesterol (VLDL-C), which was decreased by 28%. Total triglycerides were reduced by 11% and VLDL apo B by 24%, whereas high density lipoprotein cholesterol (HDL-C) rose significantly by 8%, HDL 2-C by 24%, and HDL 3-C by 3%. There were no increases in apo A-I levels compared with placebo nor any significant change in plasma lipoprotein(a) levels. The composition of LDL and VLDL particles did not appear to be altered by therapy, as assessed by the LDL-C:LDL-B, VLDL-C:VLDL-B, ortriglyceride:VLDL-B ratios. Further, there was no correlation between baseline triglycende levels and percent changes in remnant parameters. In conclusion, the HMG-CoA reductase inhibitor fluvastatin induced major reductions in indices of remnant lipoprotein concentrations, including intermediate density lipoprotein cholesterol and apo E. The total plasma apo E levels fell despite the increased HDL-C level, where more than half of the total apo E resides. The marked reduction in remnant lipoprotein, in addition to LDL-C with fluvastatin, may contribute to the antiatherosclerotic effect associated with this class of agents.

ACAT inhibitors CL 283,546 and CL 283,796 reduce LDL cholesterol without affecting cholesterol absorption in African green monkeys.

Previous studies with a number of selective acylcoenzyme A:cholesterol acyltransferase (ACAT) inhibitors in several animal models have demonstrated significant reductions in plasma cholesterol and, in some studies, triglyceride levels. This study was conducted to examine the effects of two ACAT inhibitors, CL 283,546 and CL 283,796, in cholesterol-high fat diet fed African green monkeys, a relevant primate model of hyperlipidemia and coronary artery atherosclerosis. Treatment with CL 283,546 or CL 283,796 resulted in significant reductions (ca. 25-30%) in total plasma cholesterol at both 10 and 30 mg/kg per day doses. This reduction in plasma cholesterol was due almost entirely to reduction in low density lipoprotein (LDL) cholesterol (ca. 45%) without significantly affecting high density lipoprotein (HDL) cholesterol, very low density lipoprotein + intermediate density lipoprotein (VLDL + IDL) cholesterol, or triglyceride concentrations. There were no significant effects on plasma concentrations of apolipoproteins A-I, E, or B and, thus, the reduction seen in LDL cholesterol appears to be due to a diminished cholesterol content of LDL particles. Our studies revealed that treatment with these compounds did not reduce cholesterol absorption, which was somewhat surprising as ACAT inhibitors are generally thought to exert their hypolipidemic effects, at least in part, by inhibition of intestinal cholesterol absorption. Our data are consistent with a principal activity of these drugs on the liver to reduce cholesteryl ester secretion in VLDL, leading to a diminished LDL-cholesterol content, and, presumably, enhanced biliary cholesterol-bile acid excretion.

Triglyceride-rich lipoprotein abnormalities in CAPD-treated patients.

In the present study intermediate-density lipoproteins (IDL) and very-low-density lipoproteins (VLDL) composition, structure, and mass were analysed in fasting uraemic patients on continuous ambulatory peritoneal dialysis (CAPD) (n = 12) and on haemodialysis (HD) (n = 15), and in 15 healthy volunteers. All the groups were matched for sex, age, and time on dialysis. Both groups of patients had elevated very-low-density lipoprotein levels, CAPD patients four and HD group three times that of control. We found a fourfold and a twofold increase in the concentration of IDL cholesterol in the CAPD and HD group respectively when they were compared with the control group. Both groups of patients present an increased VLDL mass. The CAPD group showed a four-fold increase in IDL mass compared with the control group, which indicated a preponderance of large size and suggested that defective IDL clearance was involved. The IDL composition of the CAPD patients was significantly different from that of the HD patients: a twofold increase in IDL mass was observed in the CAPD patients if compared with HD patients. We report new data concerning the metabolism of triglyceride-rich lipoproteins in CAPD treated patients, which confirm the adverse effect of CAPD on serum lipids.

Plasma lipoproteins in familial dysbetalipoproteinemia associated with apolipoproteins E2(Arg158--&gt;Cys), E3-Leiden, and E2(Lys146--&gt;Gln), and effects of treatment with simvastatin.

Using a density-gradient ultracentrifugation technique, we analyzed in detail the plasma lipoprotein profiles of 18 patients with familial dysbetalipoproteinemia (FD) who had apolipoprotein (apo) E2(Arg158-->Cys) homozygosity (the E2-158 variant, n = 6), apoE3-Leiden heterozygosity (the E3-Leiden variant, n = 6), or apoE2(Lys146-->Gln) heterozygosity (the E2-146 variant, n = 6), with average plasma cholesterol concentrations of 8.99 +/- 1.34 mmol/L, 9.29 +/- 1.55 mmol/L, and 8.46 +/- 1.10 mmol/L, respectively. No significant differences in sex, age, body mass index, dietary habits, and standard laboratory tests between the three groups were observed. The lipoprotein profiles of all FD patients were characterized by higher concentrations of very-low-density lipoprotein (VLDL) 1, VLDL2, and intermediate-density lipoprotein (IDL) and a higher cholesteryl ester content of VLDL1 and VLDL2 than in 6 normolipidemic control subjects with an average plasma cholesterol concentration of 5.90 +/- 0.53 mmol/L. Major differences between the plasma lipoprotein profiles of patients with the E2-158 variant, the E3-Leiden variant, and the E2-146 variant and the normolipidemic control subjects were in IDL cholesterol concentration (1.70 +/- 0.26, 1.50 +/- 0.26, 1.05 +/- 0.36, and 0.47 +/- 0.14 mmol/L, respectively), LDL cholesterol concentration (1.83 +/- 0.50, 3.09 +/- 0.32, 3.79 +/- 0.76, and 3.77 +/- 0.56 mmol/L, respectively), and the molar ratio of IDL cholesterol to LDL cholesterol (0.98 +/- 0.28, 0.48 +/- 0.04, 0.28 +/- 0.09, and 0.12 +/- 0.03, respectively). After 10 weeks of simvastatin treatment the concentrations of plasma cholesterol, VLDL2 cholesterol, IDL cholesterol, and LDL cholesterol in 3 patients with the E2-158 variant fell significantly, by 46%, 56%, 53%, and 48%, respectively; they also fell in 3 patients with the E3-Leiden variant, by 48%, 54%, 57%, and 52%, respectively, and in 3 patients with the E2-146 variant, by 38%, 55%, 46%, and 35%, respectively. Simvastatin therapy lowered plasma activity of cholesteryl ester transfer protein but had no significant effect on plasma activity of lecithin:cholesterol acyltransferase. It is concluded that patients with FD due to various apoE variants have different lipoprotein profiles, mainly with regard to IDL and LDL levels, although they have a number of similar features of dysbetalipoproteinemia. Simvastatin therapy effectively reduced the plasma concentrations of total cholesterol, VLDL2 cholesterol, IDL cholesterol, and LDL cholesterol in the three groups of patients studied. It is proposed that apoE-dependent defects of the conversion of IDL to LDL may be an important mechanism in the pathophysiology of FD.

Preferential uptake of intermediate-density lipoproteins from nephrotic patients by human mesangial and liver cells.

Hyperlipidemia of nephrotic origin could potentially cause glomerular injury as well as increase the risk of atherosclerosis. The precise interaction of human lipoproteins abnormal in lipid and protein composition, with lipoprotein receptors has not been clearly defined. This study examines receptor-mediated uptake and intracellular cholesterol metabolism of apolipoprotein (apo)B,E containing intermediate-density lipoprotein (IDL) and apoB-100 containing low-density lipoprotein (LDL), isolated from patients with the nephrotic syndrome (N = 6), in human glomerular mesangial and HepG2 cells. In the patients, serum IDL and LDL cholesterol levels were significantly increased as compared with those of healthy subjects. The IDL of nephrotic patients contained 80% more cholesterol than the IDL of healthy controls. No differences in lipid/protein composition were found in the LDL density range. Therefore, nephrotic and control LDL showed identical affinities for receptor-mediated uptake. In contrast, the IDL of nephrotic patients was taken up by mesangial cells and HepG2 with higher affinity than the LDL. Intracellular sterol synthesis was suppressed more effectively and cholesterol esterification rate was enhanced 2.2-fold by nephrotic IDL as compared with control IDL. These data indicate that hypercholesterolemia of nephrotic origin cannot be explained by reduced ligand binding for LDL. ApoE-containing IDL of patients with the nephrotic syndrome were avidly taken up by glomerular mesangial cells and could therefore play the predominant role in the development of glomerulosclerosis and atherosclerosis associated with this disorder.

Triglyceride-rich lipoproteins of subjects heterozygous for apolipoprotein E2(Lysl46→Gln) are inefficiently converted to cholesterol-rich lipoproteins

The APOE ∗2(Lys146→Gln) allele behaves like a dominant trait in the expression of familial dysbetalipoproteinemia (FD) (Smit et al., J. Lipid Res. 1990; 31: 42–53). FD patients carrying the APOE ∗2(Lysl46→Gln) allele exhibit less elevated cholesterol to triglyceride ratios in the d < 1.019 g/ml lipoprotein density fraction as compared to classical FD patients displaying homozygosity for the APOE ∗2(Arg158→Cys) allele (0.8 vs. 1.4). Upon treatment of complete serum with lipoprotein lipase (LPL), the mean cholesterol to triglyceride molar ratio of the d < 1.019 g/ml lipoprotein fraction in these FD patients increased only marginally (from 0.8 to 1.1), as compared with that of classical FD subjects (from 1.4 to 2.6) and non-FD control subjects (from 0.7 to 1.5). In order to obtain further evidence for an inefficient lipolysis of the d < 1.019 g/ml lipoprotein fraction in APOE ∗2(Lys146→Gln) carriers, possibly in combination with a less efficient cholesteryl ester transfer protein (CETP) activity, blood samples of APOE ∗2(Lys146→Gln) allele carrying FD patients were analysed and compared with classical FD patients and controls. In the APOE ∗2(Lysl46→Gln) FD patients, the increase in plasma cholesterol was mainly confined to the very low density lipoprotein (VLDL) fraction, whereas in classical FD patients, the levels of cholesterol in the intermediate density lipoprotein (IDL) fraction was also dramatically increased (ratios of VLDL to IDL cholesterol are 4.7 and 2.6, respectively). Family analyses of the APOE ∗2(Lysl46→Gln) FD subjects showed that the apo E to apo B ratio in the d < 1.019 g/ml lipoprotein fraction of allele carriers is 3.5 times as high as that found in non-carriers (2.8 vs. 0.8, by wt.). Also, in the APOE ∗2(Lysl46→Gln) allele carrying family members, the ratio of cholesterol to triglyceride of the d < 1.019 g/ml lipoprotein fraction is less markedly elevated upon addition of LPL when compared to that in non-carrying controls (from 1.1 to 1.8 vs 0.7 to 1.6). The efficiency of the d < 1.019 g/ml lipoprotein fraction of APOE ∗2(Lys146→Gln) FD patients to compete with low density lipoprotein (LDL) for binding to the LDL receptor is intermediate to that of controls and classical APOE ∗2(Arg158→Cys) homozygous FD patients. These findings suggest that in APOE ∗2(Lys146→Gln) allele carriers, the conversion of VLDL into IDL is impaired due to an inefficient lipolysis, possibly in combination with a retarded CETP activity. As a consequence, this might result in a less efficient cellular processing of these lipoproteins via the LDL receptor and in this way explain the dominant behaviour of the APO ∗2(Lys146→Gln) allele in the expression in FD.