Remnant lipoprotein levels in fasting serum predict coronary events in patients with coronary artery disease

Remnant lipoproteins and atherosclerosis

A recently developed assay for quantification of remnant-like particle cholesterol has provided considerable evidence that reinforces the concept that elevated levels of plasma remnants are associated with increased cardiovascular disease in different populations and distinct patient groups. In this review, we provide a brief summary of the most recently published studies, emphasizing the clinical relevance of remnant analysis. We discuss recent evidence that sheds light on the mechanisms that may underlie the atherogenicity of remnant lipoproteins. Taken together, these data provide new insight into the significance of remnant lipoproteins in the onset and development of premature atherosclerosis.

Remnant lipoproteinemia is a risk factor for endothelial vasomotor dysfunction and coronary artery disease in metabolic syndrome

This study aimed to determine whether elevated levels of remnant lipoprotein, an atherogenic triglyceride-rich lipoprotein, might be associated with coronary artery disease (CAD) and endothelial vasomotor dysfunction in metabolic syndrome. The fasting serum levels of remnant lipoproteins (remnant-like lipoprotein particles cholesterol; RLP-C) were measured by an immunoseparation method in 210 patients with metabolic syndrome meeting ATP III criteria. Flow-mediated endothelium-dependent dilatation (FMD) in the brachial artery during reactive hyperemia was examined by high-resolution ultrasound technique. This study found that elevated RLP-C levels were a significant and independent risk factor for impaired FMD and angiographically proven coronary artery disease (CAD). Treatment with bezafibrate (n = 20) or atorvastatin (n = 20) for 4 weeks significantly reduced RLP-C levels, with a concomitant improvement in FMD. The % reduction in RLP-C levels from baseline after the treatment was independently correlated with the magnitude of improvement in FMD after adjustment for the % changes in levels of triglyceride, hsCRP, and IL-6, and HOMA index. Thus, elevated levels of RLP-C are a risk factor for CAD and endothelial vasomotor dysfunction, a predictor of coronary events, in metabolic syndrome. Measurement of RLP-C is useful for assessment of CAD risk and therapeutic effects in metabolic syndrome.

Effect of diacylglycerol on postprandial lipid metabolism in non-diabetic subjects with and without insulin resistance

The effects of diacylglycerol ingestion on postprandial lipid metabolism in non-diabetic subjects with and without insulin resistance were investigated. This was single dose ingestion study, in a double blind cross over manner and postprandial lipid concentrations were compared between diacylglycerol oil (DAG) and triacylglycerol oil (TAG) ingestion. The subjects were 18 male volunteers and homeostasis model assessment (HOMA-R) was used to classify them into insulin sensitive (IS, n=10, HOMA-R<2.0) and insulin resistant (IR, n=8, HOMA-R> or =2.0) groups. Fasting serum triglycerides (TG) and remnant-like particle cholesterol (RLP-C) correlated with HOMA-R and were significantly higher in the IR as compared to the IS group. Postprandial increments of TG and RLP-C after DAG ingestion were significantly lower as compared to those after TAG ingestion. In a case of TAG ingestion, their increments positively correlated with HOMA-R and were significantly higher in the IR as compared with the IS group. In contrast, their increments remained constant after DAG ingestion in both groups. In the IR group, the postprandial lipidemia were reduced after DAG ingestion to about half of those after TAG ingestion. In conclusion, DAG reduced postprandial lipidemia especially in subjects with insulin resistance and may be beneficial in preventing atherosclerosis and related diseases.

Association between LDL particle size and postprandial increase of remnant-like particles in Japanese type 2 diabetic patients

Small, dense LDL, as well as chylomicron- and VLDL-remnant lipoproteins, are known to be important risk factors for coronary heart disease in patients with type 2 diabetes mellitus. The aim of this study was to clarify the relationship between LDL particle size and postprandial remnant lipoprotein levels in Japanese type 2 diabetic patients. Forty-six patients with type 2 diabetes mellitus were divided into tertiles according to LDL particle size. The peak LDL particle diameter was <26.30 nm in tertile 1, 26.30-26.85 nm in tertile 2, and >26.85 nm in tertile 3. After a test meal, tertile 1 had a significantly greater increment of triglycerides (TG), remnant-like particle (RLP)-TG, and RLP-cholesterol (RLP-C) than tertiles 2 and 3. There was a negative correlation between LDL particle size and the postprandial increases of TG, RLP-TG, and RLP-C. These results indicate that smaller sized LDL particles may be a marker of fasting state for an exaggerated postprandial increase of remnant lipoproteins as well as an increase of TG-rich lipoproteins.

Intestinal lipoprotein production is stimulated by an acute elevation of plasma free fatty acids in the fasting state: studies in insulin-resistant and insulin-sensitized Syrian golden hamsters

It is not known whether intestinal lipoprotein production is stimulated by an acute elevation of plasma free fatty acids (FFA). We examined the effect of an intralipid and heparin infusion on the intestinal lipoprotein production rate (PR) in insulin-sensitive [chow-fed (CHOW)], insulin-resistant [60% fructose (FRUC) or 60% fat-fed (FAT)], and insulin-sensitized [FRUC or FAT plus rosiglitazone (RSG)-treated] Syrian Golden hamsters. After 5 wk of treatment, overnight-fasted hamsters underwent in vivo Triton WR-1339 studies for measurement of apolipoprotein B48 (apoB48) PR in large (Svedberg unit, >400) and small (Svedberg unit, 100-400) lipoprotein fractions, with an antecedent 90-min infusion of 20% intralipid and heparin (IH) to raise plasma FFA levels approximately 5- to 8-fold vs. those in the saline control study. IH markedly increased apoB48 PR in CHOW by 3- to 5-fold, which was confirmed ex vivo in pulse-chase experiments in primary cultured hamster enterocytes. Oleate, but not glycerol, infusion was associated with a similar elevation of apoB48 PR as IH. In FRUC and FAT, basal (saline control) apoB48 PR was approximately 4-fold greater than that in CHOW; there was no additional stimulation with IH in vivo and only minimal additional stimulation ex vivo. RSG partially normalized basal apoB48 PR in FAT and FRUC, and PR was markedly stimulated with IH. We conclude that intestinal lipoprotein production is markedly stimulated by an acute elevation of plasma FFAs in insulin-sensitive hamsters, in which basal production is low, but minimally in insulin-resistant hamsters, in which basal production is already elevated. With RSG treatment, basal PR is partially normalized, and they become more susceptible to the acute FFA stimulatory effect.

Genetic analysis of APOAV polymorphisms (T-1131/C, Ser19/Trp and Val153/Met): no effect on plasma remnant particles concentrations

BACKGROUND

APOAV is newly described protein, which plays a crucial role in the determination of plasma triglyceride (TG) levels. Remnant lipoproteins (RLPs) result from partial catabolised TG-rich particles. Elevated levels of RLP are associated with atherosclerosis, and they are a predictor of coronary events in patients with coronary artery disease.

METHODS

We have evaluated the influence of APOAV polymorphisms (T-1131/C, Ser19/Trp and Val153/Met were measured by PCR and restriction analysis) on plasma levels of RLP-cholesterol and RLP-TG in 285 unrelated representative selected individuals (131 men and 154 women) aged 33-72 years.

RESULTS

RLP-cholesterol and RLP-TG levels were not significantly influenced by the APOAV variants either in whole population or in males and females, if analyzed separately.

CONCLUSIONS

We conclude that variations T-1131/C, Ser19/Trp and Val153/Met in the APOAV gene have no effect on plasma levels of remnant particles.

Effects of atorvastatin on triglyceride-rich lipoproteins, low-density lipoprotein subclass, and C-reactive protein in hemodialysis patients

Dyslipidemia is an important risk factor for cardiovascular disease in patients with chronic renal failure (CRF). We evaluated the safety and efficacy of atorvastatin in patients with dyslipidemia associated with CRF who were undergoing hemodialysis (HD). Thirty-five patients who were receiving HD were given atorvastatin (10 mg/d) for 3 months. Chylomicron (CM), light and dense very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and light and dense low-density lipoprotein (LDL) were separated by ultracentrifugation. Apolipoprotein (apo) B was measured by electroimmunoassay. Mean LDL particle diameter was measured by gradient gel electrophoresis. Atorvastatin therapy reduced LDL-cholesterol (C) by 36% and remnant-like particle (RLP)-C by 58%. Atorvastatin significantly reduced apo B, apo CIII, and apo E in VLDL by 40% to 46% and IDL-apo B by 66%. Atorvastatin also significantly reduced cholesterol in CM, light VLDL, and dense VLDL without consistently affecting triglyceride (TG) in these lipoproteins. Atorvastatin similarly reduced both light and dense LDL-apo B by 38%. LDL particle size in the HD patients significantly increased during atorvastatin treatment from 25.7 +/- 0.4 to 26.2 +/- 0.6 nm. High sensitive C-reactive protein (HS-CRP) was halved by atorvastatin decreasing from 0.08 +/- 0.05 to 0.04 +/- 0.03 mg/dL. Atorvastatin treatment did not affect the creatinine kinase level, and no classical adverse effects were observed during the study. These results suggest that atorvastatin is safe and effective for the management of dyslipidemia in patients with CFR who are receiving HD, which may help to suppress the development of atherosclerosis.

Remnant-like lipoproteins, hormone therapy, and angiographic and clinical outcomes: the Women's Angiographic Vitamin & Estrogen Trial

BACKGROUND

Little is known about the impact of post-menopausal hormone therapy on remnant-like particle (RLP) concentrations and about the relationship between RLP concentration and angiographic progression of coronary artery disease and clinical events in women.

METHODS

RLP cholesterol and triglyceride levels were measured at baseline and 3 months after randomization in 397 post-menopausal women enrolled in The Women's Angiographic Vitamin & Estrogen (WAVE) trial. Correlates of baseline RLP levels and changes in levels with post-menopausal hormone therapy were determined with multiple linear regression. Coronary angiography was performed at baseline and after a mean of 2.9 years. Changes in minimal and average luminal diameter were modeled with multivariate linear regression, clinical outcomes (non-fatal myocardial infarction, stroke, or cardiovascular death) with multiple logistic regression.

RESULTS

The mean subject age was 65 years, 66% of subjects were white, 18% of subjects smoked, most subjects were overweight or obese, and 35% of subjects had diabetes mellitus. RLP cholesterol (0.277 +/- 0.254 mmol/L) and triglyceride (0.386 +/- 0.552 mmol/L) levels corresponded approximately to the 90th percentile in women in the Framingham study. RLP levels did not change significantly with hormone therapy. RLP levels at baseline, changes in RLP levels, and on treatment RLP levels did not relate to angiographic changes or clinical outcomes (non-fatal myocardial infarction, stroke, or cardiovascular death).

CONCLUSIONS

RLP levels were high among post-menopausal women enrolled in the WAVE study, were not affected by hormone therapy, and did not relate to angiographic progression of coronary artery disease or clinical outcomes.

Prognostic value of remnant-like lipoprotein particle levels in patients with coronary artery disease and type II diabetes mellitus

OBJECTIVES

This study prospectively examined whether the levels of high remnant-like lipoprotein particles (RLP) cholesterol have a significant risk and influence prognosis in patients with coronary artery disease (CAD) and type II diabetes mellitus (DM).

BACKGROUND

Several studies have shown that triglyceride-rich lipoproteins contribute to atherosclerotic complications in type II DM. However, it remains to be established which triglyceride-rich lipoproteins contribute to this risk.

METHODS

Levels of RLP cholesterol in fasting serum were measured by an immunoseparation method in 240 type II DM patients with (n = 120) or without (n = 120) CAD. The patients with CAD were followed up for a period of < or =24 months until the occurrence of one of the following clinical coronary events: re-admission or coronary revascularization due to recurrent or refractory angina pectoris, nonfatal myocardial infarction, or cardiac death.

RESULTS

Patients with CAD had higher RLP levels than patients without CAD. Multivariate logistic regression analysis showed that high RLP cholesterol levels (>4.7 mg cholesterol/dl, representing the 75th percentile of the distribution of RLP cholesterol levels in control subjects) were a significant risk factor for the presence of CAD, independent of traditional risk factors. Kaplan-Meier analysis demonstrated that higher RLP cholesterol levels in patients with CAD resulted in a significantly higher probability for the development of coronary events. Multivariate Cox hazards analysis showed that high RLP cholesterol levels in patients with CAD were a significant predictor of future coronary events, independent of other risk factors.

CONCLUSIONS

Increased levels of RLP cholesterol are a significant and independent risk factor of CAD and predict future coronary events in patients with CAD and type II DM.

Postprandial Increase in Plasma Concentrations of Remnant-Like Particles: An Independent Risk Factor for Restenosis after Percutaneous Coronary Intervention

Postprandial increase in remnant lipoprotein concentrations has been suggested as an important atherogenic factor. However, the influence of these remnants on the development of restenosis after percutaneous coronary intervention (PCI) remains to be examined. The present study was designed to address this point. In 60 consecutive patients with successful PCI, the influences of possible risk factors on the development of restenosis, including remnant-like particles (RLP) cholesterol (RLP-C) and triglyceride (RLP-TG), were examined. While mean concentrations of RLP-C and RLP-TG were normal in fasting state, postprandial change in RLP-C concentrations was a significant and independent risk factor for restenosis after PCI. The calculated cut-off index (COI) for the change was +64%. When the patients were divided into 2 groups according to this COI, minimal lumen diameter (MLD) and reference coronary diameter were comparable before and immediately after PCI between the high- (COI < 64%) and the low- (COI < 64%) responders. However, follow-up coronary angiography 3 to 6 months after PCI demonstrated that MLD, late loss, and loss index were all worse in the high responders compared with the low responders. These results indicate that post-prandial increase in RLP-C concentrations is an independent risk factor for restenosis after successful PCI, even in patients with normal fasting RLP-C levels.

The close relationship between postprandial remnant metabolism and insulin resistance

The aim of this study was to investigate the relationship between postprandial remnant-like particle (RLP) metabolism and insulin resistance (IR). The study group consisted of 52 randomly selected subjects. To evaluate postprandial hyperlipidemia, serum lipid and lipoprotein concentrations during fasting and 4h after the fat-loading test were measured in each subject. IR was assessed using the index of homeostasis model assessment (HOMA-R). The subjects were divided into two groups according to the value of HOMA-R: an IR group (n=17) with a HOMA-R value >/=1.73, and a normal (NR) group (n=35) with a HOMA-R value <1.73. Both fasting and postprandial RLP-cholesterol (RLP-C) concentrations were higher in the IR group than in the NR group (6.2+/-2.6 versus 4.1+/-1.7mg/dl fasting value, and 9.7+/-4.0 versus 5.8+/-2.9mg/dl postprandial value). The changes in RLP-C concentration during the fat-loading test were twice as high in the IR group compared with the NR group (3.5+/-2.4 versus 1.6+/-1.6mg/dl, P=0.0022). The HOMA-R correlated significantly with both fasting and postprandial triglyceride (r=0.41 and 0.43, respectively) and RLP-C (r=0.36 and 0.50, respectively) in all subjects. Multiple regression analysis indicate that postprandial RLP-C concentration was an independent predictor of HOMA-R regardless of age, BMI, and other lipid profiles. Thus, postprandial RLP metabolism is closely related to IR. Atherosclerotic proliferation in IR syndrome may be caused by the accumulation of postprandial remnant lipoproteins after the daily fat intake.

Influence of the −514C/T polymorphism in the promoter of the hepatic lipase gene on postprandial lipoprotein metabolism

The -514C/T polymorphism located in the promoter region of the hepatic lipase gene mediates changes in the plasma levels of the enzyme. The aim of this study was to determine whether the presence of this polymorphism modifies the postprandial clearance of lipoproteins of intestinal origin. 51 normolipemic volunteers, homozygotes for the allele E3 of the apo E were selected (26 homozygotes for the C allele and 25 carriers of the T allele in both homozygote and heterozygote form). The subjects underwent a Vitamin A fat-loading test. Blood was drawn every hour until the 6th hour and every 2 h and 30 min until the 11th hour to determine cholesterol and plasma triglycerides as well as cholesterol, triglycerides (TG) and retinyl palmitate in triacylglycerol-rich lipoproteins (chylomicrons and chylomicron remnants). Carriers of the T allele showed significantly lower postprandial levels of apolipoprotein B (P < 0.01), total TG in plasma (P < 0.05), small TRL-TG (P < 0.04), large TRL-TG (P < 0.04) and small TRL-cholesterol (P < 0.04) when compared to subjects homozygous for the C allele. Our data suggest that the T allele of the -514C/T polymorphism in the promoter region of the hepatic lipase gene is associated with a lower postprandial lipemic response.

Measurement of the serum lipoprotein lipase concentration is useful for studying triglyceride metabolism: Comparison with postheparin plasma

The catalytically inactive form of lipoprotein lipase (LPL) is detectable at high levels in serum, although its physiologic role remains unknown. The aim of this study was to elucidate the clinical significance of serum LPL compared with postheparin LPL or the net increment (Delta) of LPL (postheparin - preheparin LPL). We measured the LPL mass before and 15 minutes after the injection of heparin in 164 subjects with hyperlipidemia. LPL mass was measured by a sensitive sandwich enzyme-linked immunosorbent assay (ELISA). Serum LPL was one fifth of the postheparin LPL concentration. There was a weak correlation between the serum LPL and postheparin LPL concentrations (r =.225, P </=.005). The Delta LPL concentration was strongly related to the postheparin LPL concentration (r =.965, P </=.0001), but not to the preheparin LPL mass, suggesting that the weak correlation between serum LPL and postheparin LPL levels was attributable to contamination of postheparin plasma by pre-existing LPL (preheparin LPL). Both serum and postheparin LPL were significantly lower in diabetic patients and in subjects with high levels of triglyceride or low levels of high-density lipoprotein (HDL). Serum LPL was correlated negatively with triglyceride, remnants, and insulin resistance and was positively correlated with HDL cholesterol and low-density lipoprotein (LDL) size. Postheparin LPL was strongly correlated with HDL cholesterol, but not with other parameters, as was serum LPL. Delta LPL mass did not show a closer association with triglyceride metabolism than postheparin LPL or preheparin LPL. In conclusion, serum LPL measurement is simple and seems to be useful for studying triglyceride metabolism.

Postprandial Hyperlipidemia and Atherosclerosis

The development of the remnant like particle (RLP) method for conveniently measuring serum remnant lipoprotein levels in 1993 promoted much research on atherogenic significance and metabolism of remnant lipoproteins. This research brought about many results as the following. A novel apolipoprotein B48 receptor incorporating remnant lipoproteins into macrophages in arterial wall was discovered and the structure of the gene of the receptor was clarified. The expression of apolipoprotein B100 was recognized in the human small intestine, suggesting that dietary very low density lipoproteins (VLDL) might be synthesized in the human small intestine and converted into VLDL remnants and low density lipoproteins (LDL). It is recognized that the atherosclerotic risk of postprandial hyperlipidemia is derived from an increase of remnant lipoproteins and that measurement of serum RLP levels in postprandial state is more sensitive and necessary for evaluating an atherosclerotic risk because serum RLP levels remain high all day in patients with diabetes mellitus or coronary heart disease. The relation between postprandial hyperlipidemia and insulin resistance was clarified.

Time-dependent lipid response on fluvastatin therapy of patients with hypercholesterolemia sensitive to apoE phenotype

Sixty-seven male patients with hypercholesterolemia, divided into three groups according to apolipoprotein E phenotype (33 with apoE3/ 3 phenotype, E3 group; 23 with 2/2 or 2/3, E2+ group; 11 with 4/4 or 4/3, E4+ group), received daily 20-40 mg of fluvastatin for 12 weeks. The levels of triglyceride (TG), cholesterol (Chol), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) were measured after 0, 4, 8 and 12 weeks on fluvastatin and after 4 weeks washout period. Lipid percentage changes (delta) were not associated with apoE phenotype for any treatment time. Cholesterol decreased by 14% after 12 weeks and HDL-C increased by 14-16% after 12 weeks for three phenotype groups. deltaTG, deltaChol, deltaLDL-C were associated positively, while negatively for deltaHDL-C, with the corresponding basal lipid values for the three groups. The positive deltaTG values occurred at a low basal TG0 level and became negative at TG0 > 1.6-1.9 mM. For E3 and E4+ groups, only a single parameter contributed significantly into a variation of lipid percentage changes. For the E2+ group, TG0 and Chol0 contributed in a reciprocal manner into deltaTG12/0, both positively into deltaChol8/0; Chol0 and HDL-C0 both negatively contributed into deltaHDL-C12/0. HDL-C0 contributed reciprocally into LDL-C variability for E2+ and E4+ groups. Three effects seem to contribute differently into lipid response among patients with different apoE phenotype: the inhibition of hepatic and lipoprotein lipase activities, the competition between TG-rich and low-density lipoproteins for LDL-receptor and the accumulation of intermediate-density lipoproteins in patients bearing E2 isoform.

Remnant-like particles from subjects who died of coronary artery disease suppress NO synthase activity and attenuate endothelium-dependent vasorelaxation

BACKGROUND

Plasma levels of remnant-like particles (RLP) is one of the predictive markers for coronary artery disease (CAD), and the inhibition by RLP of endothelium-dependent vasorelaxation has been reported. We attempted to clarify whether or not RLP, which inhibits endothelium-dependent vasorelaxation, affects nitric oxide (NO) production and NO synthase (eNOS) levels in cultured endothelial cells.

METHODS

RLP were obtained from postmortem blood of subjects who died of CAD. Modification by RLP of acetylcholine-induced relaxation of rabbit aorta, and changes in NO production and (eNOS) in cultured bovine endothelial cells were examined.

RESULTS

RLP at 750 and 1500 microg triglyceride/ml inhibited vasorelaxation, and at 5-160 microg triglyceride/ml, concentration-dependently inhibited NO production. However, (eNOS) did not decrease after incubation with RLP.

CONCLUSION

Postmortem RLP from subjects who died of CAD do not change the amount of (eNOS), but rather, inhibits its activity and attenuates endothelium-dependent vasorelaxation.

Chylomicron remnants induce monocyte chemoattractant protein-1 expression via p38 MAPK activation in vascular smooth muscle cells

Chylomicron remnants, major lipoproteins at postprandial hyperlipidemia, have been considered to be proatherogenic lipoproteins. However, the mechanisms by which chylomicron remnants enhance atherosclerosis have not been fully understood. Monocyte chemoattractant protein-1 (MCP-1) is a chemokine which stimulates migration of monocytes and plays a critical role in the development of atherosclerosis. In this study, we investigated the effect of chylomicron remnants on MCP-1 expression in cultured vascular smooth muscle cells (VSMCs). We prepared chylomicrons from the lymph of gastrostomized rats fed with egg solution and obtained chylomicron remnants from the plasma of hepatectomized rats which were injected with chylomicrons. Treatment of VSMC with chylomicron remnants resulted in a significant increase of the expression of MCP-1 mRNA and protein in a time-and a dose-dependent manner. Further, chylomicron remnants activated p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK1/2). Pretreatment of VSMCs with p38 MAPK inhibitors, SB203580 and SB202190, resulted in a dose-dependent inhibition of chylomicron remnants-induced MCP-1 mRNA and protein expression, whereas a MAPK kinase inhibitor, PD98059, had no effect on these responses. MCP-1 secretion by chylomicron remnants was much more pronounced than those by chylomicrons, oxidized low-density lipoproteins, or lysophosphatidylcholine. These results indicated that chylomicron remnants stimulated MCP-1 expression in VSMCs, and suggested that chylomicron remnants might contribute to the formation of atherosclerosis through this proinflammatory effect.

Effects of treatment with Sandostatin LAR on small dense LDL and remnant-like lipoproteins in patients with acromegaly

OBJECTIVE

Acromegalic patients have been shown to have an increase in the concentrations of small dense low-density lipoprotein (LDL) and remnant-like lipoprotein particles (RLP). These lipoproteins are atherogenic and may contribute to the cardiovascular risk of these patients. The aim of this study was to determine whether treatment of acromegaly using Sandostatin LAR could lower these atherogenic lipoproteins.

METHODS

Fourteen patients with active acromegaly were recruited and Sandostatin LAR, a long-acting somatostatin analogue, was given every 4 weeks by intramuscular injection for 6 months. Fasting lipids, lipoproteins, lipolytic enzymes were determined at baseline, 12 and 24 weeks after treatment. Small dense LDL was measured using density gradient ultracentrifugation and RLP-cholesterol (RLP-C) by an immunoseparation assay.

RESULTS

There was already a marked reduction in GH and IGF-1 by week 8 and, in all subjects, IGF-1 levels within their respective age-specific normal range were achieved. At week 12, plasma triglyceride significantly decreased (P < 0.01) and both HDL2 (P < 0.01) and HDL3 (P < 0.01) subfractions increased. A reduction was seen in small dense LDL concentration (P < 0.05) and RLP-C (P < 0.05). Lipoprotein lipase (LPL) activity increased (P < 0.01) and the magnitude of the increase in LPL activity correlated with the increase in HDL at 3 months (r = 0.55, P < 0.05) but not with the changes in plasma triglyceride, small dense LDL or RLP-C. The improvement in plasma lipids and lipoproteins persisted until the end of the study.

CONCLUSION

Sandostatin LAR is effective in the treatment of acromegaly and is associated with favourable changes in plasma lipids and a reduction in small dense LDL and RLP-C.

The influence of the apolipoprotein E gene promoter (-219G/ T) polymorphism on postprandial lipoprotein metabolism in young normolipemic males

The apolipoprotein E (apoE) gene promoter (-219G/T) polymorphism has been associated with increased risk of myocardial infarction, premature coronary heart disease, and decreased plasma apoE concentrations. We examined whether the -219G/T polymorphism could modify the postprandial response of triacylglycerol-rich lipoproteins (TRLs). Fifty-one healthy apoE 3/3 male volunteers (14GG, 29GT, and 8TT) were given a vitamin A fat-loading test consisting of 1 g of fat/kg body weight and 60,000 IU of vitamin A per m2 of body surface area. Blood samples were taken at time 0 and every hour until the sixth hour, and every 2 hours and 30 minutes until the eleventh hour. Cholesterol, triacylglycerols (TGs), and apoE were determined in plasma; and cholesterol, TG, apoB-100, apoB-48, and retinyl palmitate (RP) were analyzed in lipoprotein fractions. Postprandial lipemia data revealed that subjects with the -219TT genotype had a higher postprandial response of large TRL-cholesterol (P < 0.03), large TRL-triacylglycerols (P < 0.001), large TRL-RP (P < 0.004), and small TRL-apoB-48 (P < 0.03) than carriers of the -219G allele. Moreover, the -219TT subjects had the lowest postprandial levels of serum apoE (P < 0.05). In conclusion, the -219G/T polymorphism may influence TRL metabolism during the postprandial period, thus prolonging postprandial lipemia in subjects with the TT genotype.

Effect of atorvastatin on apolipoprotein B48 metabolism and low-density lipoprotein receptor activity in normolipidemic patients with coronary artery disease

We aimed to examine postprandial dyslipidemia in normolipidemic patients with coronary artery disease (CAD) and the effects of treatment with an hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase inhibitor (atorvastatin). Subjects with angiographicaly established CAD were randomized to treatment for 12 weeks with 80 mg/d atorvastatin or placebo and the effects on markers of postprandial lipoproteins and low-density lipoprotein (LDL)-receptor binding determined. LDL-receptor binding was determined in mononuclear cells, as a surrogate for hepatic activity. Fasting levels of cholesterol (P <.001), LDL-cholesterol (P <.001), apolipoprotein (apo)B(48) (P =.019), remnant-like particle-cholesterol (RLP-C) (P =.032), and total postprandial apoB(48) area under the curve (AUC) (P =.013) significantly decreased with atorvastatin compared with placebo. Atorvastatin also significantly increased LDL-receptor binding activity (P <.001), and this was correlated with changes in fasting apoB(48) (r =.80, P =.01). We report that aberrations in chylomicron metabolism in normolipidemic CAD subjects are correctable with atorvastatin by a mechanism involving increased LDL-receptor activity. This effect may, in part, explain the cardiovascular benefit of statins used in clinical trials of CAD patients with normal lipid levels.

Effect of atorvastatin on postprandial lipoprotein metabolism in hypertriglyceridemic patients

Postprandial lipoprotein metabolism is impaired in hypertriglyceridemia. It is unknown how and to what extent atorvastatin affects postprandial lipoprotein metabolism in hypertriglyceridemic patients. We evaluated the effect of 4 weeks of atorvastatin therapy (10 mg/day) on postprandial lipoprotein metabolism in 10 hypertriglyceridemic patients (age, 40 +/- 3 years; body mass index, 27 +/- 1 kg/m2; cholesterol, 5.74 +/- 0.34 mmol/l; triglycerides, 3.90 +/- 0.66 mmol/l; HDL-cholesterol, 0.85 +/- 0.05 mmol/l; and LDL-cholesterol, 3.18 +/- 0.23 mmol/l). Patients were randomized to be studied with or without atorvastatin therapy. Postprandial lipoprotein metabolism was evaluated with a standardized oral fat load. Plasma was obtained every 2 h for 14 h. Large triglyceride-rich lipoproteins (TRLs) (containing chylomicrons) and small TRLs (containing chylomicron remnants) were isolated by ultracentrifugation, and cholesterol, triglyceride, apolipoprotein B-100 (apoB-100), apoB-48, apoC-III, and retinyl-palmitate concentrations were determined. Atorvastatin significantly (P < 0.01) decreased fasting cholesterol (-27%), triglycerides (-43%), LDL-cholesterol (-28%), and apoB-100 (-31%), and increased HDL-cholesterol (+19%). Incremental area under the curve (AUC) significantly (P < 0.05) decreased for large TRL-cholesterol, -triglycerides, and -retinyl-palmitate, while none of the small TRL parameters changed. These findings contrast with the results in normolipidemic subjects, in which atorvastatin decreased the AUC for chylomicron remnants (small TRLs) but not for chylomicrons (large TRLs). We conclude that atorvastatin improves postprandial lipoprotein metabolism in addition to decreasing fasting lipid levels in hypertriglyceridemia. Such changes would be expected to improve the atherogenic profile.

Atorvastatin markedly improves type III hyperlipoproteinemia in association with reduction of both exogenous and endogenous apolipoprotein B-containing lipoproteins

Remnant lipoproteins are known to promote atherosclerosis especially in patients with type III hyperlipoproteinemia (HLP). In the current study, the effects of atorvastatin were investigated with special reference to the exogenous and endogenous apolipoprotein (apo) B-containing lipoprotein metabolism in type III HLP. Four Japanese male patients with type III HLP associated with homozygous apoE2 were studied. One-month administration of atorvastatin (20 mg once daily), after a 4-week dietary run-in, strikingly reduced serum total cholesterol and triglyceride (TG) levels by 52 (P<0.01) and 56% (P<0.05), respectively. Atorvastatin further decreased remnant-like particle (RLP)-cholesterol by 73% and RLP-TG by 65% (P<0.05), respectively. Distribution analysis by polyacrylamide gel disc electrophoresis clearly showed that atorvastatin diminished very low-, intermediate- and low-density lipoprotein particles. The relative particle diameter of intermediate-density lipoprotein became smaller after atorvastatin treatment (P<0.01). Furthermore, ultracentrifugal analysis demonstrated that atorvastatin significantly decreased cholesterol, TG and phospholipid concentrations in all apoB-containing lipoprotein fractions and very low-density lipoprotein (VLDL)-cholesterol/serum TG ratio (P<0.05), implying atorvastatin-induced reduction of beta-VLDL. Finally, newly developed assays of apoB-48 and apoB-100 revealed that atorvastatin markedly reduced these apolipoproteins by 43 and 52%, respectively (P<0.01), suggesting that atorvastatin decreased the number of both exogenous and endogenous apoB-containing lipoproteins. Taken together, atorvastatin improves remnant lipoprotein metabolism in type III HLP both in quality and in quantity. Atorvastatin can be one of the optimal options for the treatment of patients with type III HLP.

Serum concentrations of remnant-like particles in hypothyroid patients before and after thyroxine replacement

OBJECTIVES

Remnant-like particles (RLPs) reflect chylomicron remnants and very-low-density lipoprotein remnants, which are most likely to be atherogenic particles. To investigate the effect of thyroxine replacement on the metabolism of RLPs in hypothyroidism, we measured serum concentrations of RLPs during an oral fat-loading test in patients with hypothyroidism before and after thyroxine replacement.

PATIENTS AND METHODS

Thirteen patients with hypothyroidism, having serum-free thyroxine (FT4) of 4.25 +/- 2.23 pmol/l (mean +/- SD) and TSH of 72.5 +/- 27.7 mU/l, participated in the study. Two-hundred grams of cream containing 32.9% of fat were given to each patient followed by blood draws every 2 h for 8 h. The patients became euthyroid after 3 months of T4 replacement, and the fat-loading tests were then repeated.

RESULTS

Fasting levels of serum total cholesterol and low-density lipoprotein cholesterol were remarkably decreased after T4 therapy (P < 0.0005). Serum high-density lipoprotein cholesterol and triglyceride were also decreased by T4 therapy, not so remarkably but significantly (P < 0.05). Activities of lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) increased 52% and 85%, respectively, from the pretreatment values. Serum concentrations of remnant-like particle cholesterol (RLP-C) and remnant-like particle triglyceride (RLP-TG), measured by immunoseparation assays, significantly decreased from 0.14 +/- 0.03 to 0.09 +/- 0.03 mmol/l (P < 0.0005) and from 0.19 +/- 0.11-0.11 +/- 0.07 mmol/l (P < 0.01), respectively. In the fat-loading test, serum low-density lipoprotein cholesterol concentrations were not changed, while serum RLPs concentrations were increased and remained high throughout the test, with the peak value at 6 h in a hypothyroid condition. In an euthyroid condition after T4 therapy, the peak values of RLPs were obtained at 4 h, and the concentrations were decreased rapidly. As the result, areas under the curve of serum RLPs were decreased remarkably after T4 therapy.

CONCLUSIONS

Hypothyroidism seems to be associated with a decrease in metabolism of serum RLPs. Such altered metabolism of RLPs may be related to the decreased activities of LPL and HTGL and can be corrected by T4 replacement therapy.

n-3 long-chain FA decrease serum levels of TG and remnant-like particle-cholesterol in humans

A large number of papers have reported that administration of n-3 FA reduced serum TG concentrations in hypertriglyceridemic patients. However, few studies have examined the effect of n-3 FA on serum concentrations of remnant-like particle (RLP) cholesterol. Volunteers (n = 41) whose serum TG concentrations were 100-300 mg/dL were recruited and randomly assigned to either an n-3 FA group or a control group with stratification by sex, age, and serum TG level in a double-blind manner. The subjects in the n-3 FA group were administered 125 mL of fermented soybean milk with fish oil containing 600 mg of EPA and 260 mg of DHA/d for 12 wk. The controls consumed control soybean milk with olive oil. Fasting blood samples were obtained before the start of administration and at 4, 8, and 12 wk. EPA concentrations in red blood cells increased significantly in all but one subject in the n-3 FA group, with no significant changes in the control group. TG levels decreased more in the n-3 FA group than in the control group at weeks 4 (P < 0.05), 8 (P < 0.01), and 12 (P < 0.05) with their baseline as covariate. RLP cholesterol levels decreased more in the n-3 FA group than in the control at weeks 8 (P < 0.01) and 12 (P < 0.05) with their baseline as covariate. The groups did not differ in the other lipid levels. It is likely that n-3 long-chain FA may exert anti-atherosclerotic effects by lowering serum TG and RLP-cholesterol levels even at the dose of 860 mg/d.

The renin-angiotensin system is involved in the production of plasminogen activator inhibitor type 1 by cultured endothelial cells in response to chylomicron remnants

Triglyceride-rich lipoproteins have been suggested to promote atherosclerosis. Plasminogen activator inhibitor type 1 (PAI-1) plays an important role in the events of cardiovascular pathophysiology. The renin-angiotensin system influences various vascular functions, including PAI-1 production. We examined whether or not chylomicron remnants increased PAI-1 mRNA and protein production in endothelial cells and whether or not an inhibition of the renin-angiotensin system interfered with this effect. Chylomicron remnants were isolated from functionally hepatectomized rats injected with chylomicrons. Human umbilical vein endothelial cell cultures (HUVECs) were incubated with chylomicron remnants with or without an angiotensin-converting enzyme inhibitor (temocaprilat), an angiotensin II receptor type 1 antagonist (RNH-6270), or an angiotensin II receptor type 2 antagonist (PD123319). Chylomicron remnants increased PAI-1 secretion in HUVECs (0.5 microg/ml; 128.3 +/- 6.1%, the mean +/- SEM) as well as angiotensin II (10 nmol/l; 130.7 +/- 9.5%) in 18 h, as compared with the controls, as well as stimulated PAI-1 mRNA expression to a maximum level at 4 h. Temocaprilat and RNH-6270, but not PD123319, attenuated all of these effects. Chylomicron remnants enhanced nuclear extract binding to a very low-density lipoprotein response element in the PAI-1 promoter region and activated nuclear factor-kappaB. Extracellular signal-regulated kinase (ERK 1/2) was phosphorylated in response to chylomicron remnants. These effects were inhibited by temocaprilat or RNH-6270. In conclusion, chylomicron remnants increased protein secretion and mRNA expression of PAI-1 in HUVECs. Inhibition of the renin-angiotensin system reduced this stimulation.

The apo A-I gene promoter region polymorphism determines the severity of hyperlipidemia after heart transplantation

BACKGROUND

To study whether the Apolipoprotein A-I (apo A-I) promoter region gene polymorphism produces changes in the lipid profile of heart transplant recipients.

METHODS

One hundred and three heart transplant recipients (93 men and 10 women, with a mean age of 47 +/- 13 yr) receiving triple immunosuppressive therapy were submitted to a genetic study of the apo A-I gene promoter region. Anthropometric and analytical data, including lipid profile, arterial blood pressure, were collected prior to transplantation and 3, 6, 12, and 24 months after transplantation.

RESULTS

Sixty-three subjects had the GG genotype and 40 the GA genotype. Carriers of the GA genotype had higher triglyceride levels at 6 months and 2 yr (2.50 +/- 1.20 versus 1.93 +/- 0.98 mmol/L and 2.46 +/- 1.58 versus 1.60 +/- 0.68 mmol/L, respectively, p < 0.001), and a greater rise in LDL-cholesterol at 1 yr than the GG subjects (4.57 +/- 1.16 versus 4.16 +/- 1.18 mmol/L, p < 0.05). Multiple regression analyses showed that genetic variants at the apo A-I promoter region are responsible for 11% of the variability in triglyceride levels at 6 months (p = 0.005).

CONCLUSIONS

The GA genotype of the apo A-I promoter region produces a greater rise in plasma triglyceride and LDL-cholesterol levels in heart transplant patients.

HDL and triglyceride as therapeutic targets

PURPOSE OF REVIEW

Epidemiological studies have shown that plasma HDL-cholesterol is inversely related to coronary artery disease and that there is an inverse relationship between HDL-cholesterol and triglyceride levels, but it is now demonstrated that hypertriglyceridemia is an independent risk factor for coronary heart disease (CHD). The goal of this review is to discuss if triglycerides and HDL-cholesterol could be therapeutic targets to reduce cardiovascular risk.

RECENT FINDINGS

Triglyceride measurement is not informative on the specificity of the triglyceride-rich lipoproteins present in the plasma because some of these are not atherogenic (chylomicrons, large VLDLs) while others are highly atherogenic (small VLDLs, remnants, IDL...). Statins, in addition to reducing LDL-cholesterol, significantly reduced atherogenic remnant lipoprotein cholesterol levels. 4S, CARE+LIPID, and AFCAPS/TexCAPS studies, suggested enhanced therapeutic potential of statins for improving triglyceride and HDL-cholesterol levels in patients with CHD. A fibrate (gemfibrozil) was shown to reduce death from CHD and non-fatal myocardial infarction in secondary prevention of CHD in men with low levels of HDL-cholesterol (VA-HIT); during the treatment these levels predicted the magnitude of reduction in risk for CHD events.

SUMMARY

ATP III recommendations state, on triglycerides and HDL-cholesterol as targets to reduce cardiovascular risk: (1) that lowering LDL-cholesterol levels is the primary target of therapy, (2) a secondary target is to achieve a triglyceride level < 150 mg/dL and (3) clinical trial data are considered to be insufficient to support recommended a specific HDL-cholesterol goal even if HDL-cholesterol < 40 mg/dL is considered to be a major risk factor of CHD.

Acute effect of orlistat on post-prandial lipaemia and free fatty acids in overweight patients with Type 2 diabetes mellitus

AIMS

Post-prandial lipaemia is prolonged and exaggerated in patients with Type 2 diabetes mellitus, with an accumulation of atherogenic triglyceride-rich lipoprotein remnants. We postulate that orlistat, a gastrointestinal lipase inhibitor, may cause changes in post-prandial lipoprotein metabolism by reducing dietary triglyceride absorption.

METHODS

The acute effect of a single dose of 120 mg orlistat on post-prandial glucose, lipids, remnant lipoproteins and free fatty acids (FFA) was evaluated in a randomized, double-blind, placebo-controlled cross-over study of 63 overweight patients with Type 2 diabetes mellitus (body mass index 30.4 +/- 3.8 kg/m2). Either a single dose of orlistat or placebo was given before a standard mixed meal containing 70 g of fat and plasma triglyceride (TG), remnant-like particles cholesterol (RLP-C) and FFA were sampled at 2-h intervals for 8 h. RLP-C was measured by an immunoseparation assay and FFA by an enzymatic colorimetric method.

RESULTS

The concentrations of plasma TG (P < 0.0001), RLP-C (P = 0.003), and FFA (P < 0.0001) were significantly lower at 2 h after orlistat compared with placebo. Both plasma RLP-C (P = 0.04) and FFA (P < 0.0001) remained lower after orlistat than placebo at 4 h. The incremental area under the curve (iAUC) above baseline fasting level for both TG and RLP-C was significantly more reduced after orlistat than placebo (iAUC-TG 5.8 (3.7-8.2) mmol/l x h-1 vs. 5.7 (4.1-10.9), respectively, P = 0.04; iAUC-RLP-C: 0.53 (0.23-1.04) mmol/l x h-1 vs. 0.56 (0.35-1.40), respectively, P = 0.02). The test meal was well tolerated by all subjects, with only three subjects reporting faecal urgency after orlistat.

CONCLUSIONS

Orlistat has a beneficial effect on post-prandial lipaemia in overweight Type 2 diabetic patients and lowers plasma TG, RLP-C and FFA in the early post-prandial period.

Effects of nateglinide and glibenclamide on postprandial lipid and glucose metabolism in type 2 diabetes

BACKGROUND

Postprandial hyperlipemia and small, dense LDL particles are features of dyslipidemia in type 2 diabetes. The purpose of this study was (1) to determine whether the oral insulinotropic drugs, nateglinide and glibenclamide, can overcome the defect of insulin action to suppress the hepatic VLDL release after a meal and decrease the postprandial lipemia and (2) to evaluate the acute effect of postprandial hypertriglyceridemia on LDL particle size in subjects with type 2 diabetes.

METHODS

Forty-three subjects with type 2 diabetes and mean baseline HbA(1c) 7.6% (95% CI 7.3 to 7.9) were treated with nateglinide 120 mg three times daily or glibenclamide 5 mg once or twice daily for 12 weeks in a double-blind randomised trial. Insulin, glucose, and lipoprotein responses to a mixed fat-rich meal were determined for 8 h postprandially at baseline and at 12 weeks on-trial.

RESULTS

Nateglinide and glibenclamide significantly augmented the maximal response in serum insulin at 60 min postprandially compared with the response without the drug [additional increase 25.0 mU/l (95% CI 11.2-38.8) p = 0.001 and 12.5 mU/l (95% CI 4.6-20.3) p = 0.003, respectively] and reduced hyperglycemia. Neither drug affected fasting or postprandial lipid or lipoprotein levels. LDL size did not significantly change in the 8-h postprandial period.

CONCLUSIONS

Although nateglinide and glibenclamide increase postprandial insulin secretion and attenuate hyperglycemia, they do not alleviate postprandial lipemia in subjects with type 2 diabetes and good glycemic control. Although small LDL particle size is associated with chronic hypertriglyceridemia, LDL size does not change during acute postprandial hypertriglyceridemia.

HMG-CoA reductase inhibitor decreases small dense low-density lipoprotein and remnant-like particle cholesterol in patients with type-2 diabetes

Patients with type 2 diabetes are known to have abnormalities in their remnant metabolism and low density lipoprotein (LDL) subfraction pattern, with a preponderance of small dense LDL. The effects of pitavastatin, a newly synthesized 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, on lipoprotein profiles in patients with type 2 diabetes were determined. Thirty-three patients were treated with pitavastatin with a daily dose of 2 mg for 8 weeks. After treatment, triglyceride, total and LDL cholesterol were significantly reduced by 28.7 +/- 36.7%, 25.2 +/- 14.3% and 36.1 +/- 14.3%, respectively. Remnant-like particle cholesterol (RLP-C), an independent risk factor for CAD which is known to be elevated in diabetic patients, was also significantly reduced (-30.9 +/- 30.5%) by the treatment and this decrease correlated well with the decrease in triglyceride level. The proportion of small dense LDL, which is known for its atherogenisity, decreased from 29.9 +/- 26.2% to 19.7 +/- 22.7% and the mean LDL particle size significantly increased from 26.36 +/- 1.13 nm to 27.10 +/- 1.36 nm. Pitavastatin, which is known to improve triglyceride levels and cholesterol levels, also improves RLP-C level and LDL subfraction profiles, and this in turn may reduce the cardiovascular risk in patients with type 2 diabetes and dyslipidemia.

Effects of atorvastatin on fasting and postprandial lipoprotein subclasses in coronary heart disease patients versus control subjects

The effects of atorvastatin at 20, 40, and 80 mg/day on plasma lipoprotein subclasses were examined in a randomized, placebo-controlled fashion over 24 weeks in 103 patients in the fasting state who had coronary heart disease (CHD) with low-density lipoprotein (LDL) cholesterol levels >130 mg/dl. The effects of placebo and atorvastatin 40 mg/day were examined in 88 subjects with CHD in the fasting state and 4 hours after a meal rich in saturated fat and cholesterol. These findings were compared with results in 88 age- and gender-matched control subjects. Treatment at the 20, 40, and 80 mg/day dose levels resulted in LDL cholesterol reductions of 38%, 46%, and 52% (all p <0.0001), triglyceride reductions of 22%, 26%, and 30% (all p <0.0001), and high-density lipoprotein (HDL) cholesterol increases of 6%, 5%, and 3%, respectively (all p <0.05 at the 20- and 40-mg doses). The lowest total cholesterol/HDL cholesterol ratio was observed with the 80 mg/day dose of atorvastatin (p <0.0001 vs placebo). Remnant-like particle (RLP) cholesterol decreased 33%, 34%, and 32%, respectively (all p <0.0001). Lipoprotein(a) [Lp(a)] cholesterol decreased 9%, 16%, and 21% (all p <0.0001), although Lp(a) mass increased 9%, 8%, and 10%, respectively (all p <0.01). In the fed state, atorvastatin 40 mg/day normalized direct LDL cholesterol (29% below controls), triglycerides (8% above controls), and RLP cholesterol (10% below controls), with similar reductions in the fasting state. At this same dose level, atorvastatin treatment resulted in 39%, 35%, and 59% decreases in fasting triglyceride in large, medium, and small very LDLs, as well as 45%, 33%, and 47% reductions in cholesterol in large, medium, and small LDL, respectively, as assessed by nuclear magnetic resonance (all significant, p <0.05), normalizing these particles versus controls (77 cases vs 77 controls). Moreover, cholesterol in large HDL was increased 37% (p <0.001) by this treatment. Our data indicate that atorvastatin treatment normalizes levels of all classes of triglyceride-rich lipoproteins and LDL in both the fasting and fed states in patients with CHD compared with control subjects.

ApoC-III gene polymorphisms and risk of coronary artery disease

Several polymorphisms in the apolipoprotein C-III (apoC-III) gene have been associated with hypertriglyceridemia, but the link with coronary artery disease risk is still controversial. In particular, apoC-III promoter sequence variants in the insulin responsive element (IRE), constitutively resistant to downregulation by insulin, have never been investigated in this connection. We studied a total of 800 patients, 549 of whom had angiographically documented coronary atherosclerosis, whereas 251 had normal coronary arteriograms. We measured plasma lipids, insulin, apoA-I, apoB, and apoC-III and assessed three polymorphisms in the apoC-III gene, namely, T-455C in the IRE promoter region, C1100T in exon 3, and Sst1 polymorphic site (S1/S2) in the 3' untranslated region. Each variant influenced triglyceride levels, but only the T-455C (in homozygosity) and S2 alleles influenced apoC-III levels. In coronary artery disease (CAD) patients, 18.6% were homozygous for the -455C variant compared with only 9.2% in CAD-free group (P < 0.001). In logistic regression models, homozygosity for -455C variant was associated with a significantly increased risk of CAD (OR = 2.5 and 2.18 for unadjusted and adjusted models, respectively) suggesting that it represents an independent genetic susceptibility factor for CAD.

Relationship between insulin-resistance and remnant-like particle cholesterol

We investigated the relationship between insulin-resistance (IR) and remnant-like particle cholesterol (RLP-C) using 472 subjects (174 men and 298 women) randomly selected from inhabitants of two rural communities in Japan, Tanno and Sobetsu. The level of fasting immunoreactive insulin (FIRI), fasting blood glucose (FBS), total cholesterol (TC), triglyceride (TG), HDL cholesterol, LDL cholesterol, and RLP-C were measured in each subject. Homeostasis model assessment (HOMA-R) was used as an indicator of IR. The subjects were divided into two groups according to the value of HOMA-R: an IR group of subjects with HOMA-R > approximately equal to 1.73 and a normal (NR) group of subjects with HOMA-R <1.73. There was a significant positive correlation between HOMA-R and RLP-C. The value of RLP-C was higher in the IR group than in the NR group (7.1 vs. 3.9 mg/dl in men and 5.3 vs. 3.6 mg/dl in women). The frequency of hyper RLP cholesterolemia (RLP-C > approximately equal to 7.5 mg/dl) was higher in the IR than in the NR group (23.7 vs. 6.6% in men and 20.3 vs. 6.6% in women). The results of multiple regression analysis showed that HOMA-R was closely related to RLP-C. The results of this study suggest that RLP-C is closely associated with IR syndrome.

Single LDL apheresis improves serum remnant-like particle-cholesterol, C-reactive protein, and malondialdehyde-modified-low-density lipoprotein concentrations in Japanese hypercholesterolemic subjects

BACKGROUND

Single low-density lipoprotein (LDL)-apheresis may affect serum remnant-like particle-cholesterol (RLP-C), C-reactive protein (CRP) and malondialdehyde-modified (MDA)-LDL concentrations.

SUBJECTS AND METHODS

Six subjects with hypercholesterolemia (five men, one woman) were involved in this study. Mean age and body mass index of the study subjects were 58+/-3.1 years and 23.6+/-2.07 kg/m(2), respectively. Five of the subjects were diagnosed as heterozygous familial hypercholesterolemia (FH) because of having both marked hypercholesterolemia and Achilles tendon xanthomas. LDL apheresis was introduced and continued using a dextran sulfate cellulose adsorption column technique every 2 weeks. Serum RLP-C was measured using an immunoaffinity mixed gel containing anti-apolipoprotein A-I and anti-apolipoprotein B monoclonal antibody. Serum CRP was measured by latex-enhanced assay. Serum MDA-LDL was measured using monoclonal antibody against MDA-LDL (ML25).

RESULTS

Combined treatment in the steady state pre-treatment yielded a total, LDL- and HDL-cholesterol, and TG concentrations of 5.39+/-0.81, 3.82+/-1.03, 1.24+/-0.29 and 0.92+/-0.43 mmol/l, respectively, and a post-treatment total, LDL- and HDL-cholesterol and TG concentrations of 2.79+/-0.37 (-48%, p<0.001), 1.63+/-0.29 (-57%, p<0.001), 1.18+/-0.26 (-5%, NS) and 0.23+/-0.11 mmol/l (-75%, p<0.001), respectively. Serum RLP-C and CRP concentrations showed a substantial reduction [-73%, p<0.05 for RLP-C; -56%, p<0.05 for CRP] during this procedure. In addition, LDL apheresis was found to also cause a marked reduction in serum MDA-LDL concentration (-61%, p<0.05).

CONCLUSION

LDL-apheresis is an effective treatment for removing atherogenic factors RLP-C, CRP and MDA-LDL from sera.

Elevated remnant-like particle cholesterol and triglyceride levels in diabetic men and women in the Framingham Offspring Study

OBJECTIVE

Remnants of triglyceride-rich lipoproteins are thought to be atherogenic. A new antibody-based assay allows for the isolation of remnant-like particles (RLPs) from plasma or serum, and the subsequent measurement of RLP cholesterol (RLPC) and triglycerides (RLPTGs). We hypothesized that diabetic patients would have higher remnant levels than nondiabetic patients.

DESIGN AND METHODS

We compared RLPC and RLPTG levels of diabetic subjects (68 women, 121 men) participating in the Framingham Heart Study with those of nondiabetic subjects (1,499 women, 1,357 men).

RESULTS

Mean RLPC values for diabetic women were 106% higher than those for nondiabetic women (0.367 +/- 0.546 mmol/l [14.2 +/- 21.1 mg/dl] vs. 0.179 +/- 0.109 mmol/l [6.9 +/- 4.2 mg/dl]; P < 0.0001), and RLPTG values for diabetic women were 385% higher than those for nondiabetic women (1.089 +/- 2.775 mmol/l [93.1 +/- 245.6 mg/dl] vs. 0.217 +/- 0.235 mmol/l [19.2 +/- 20.8 mg/dl]; P < 0.0001). Similar but less striking differences were observed in diabetic men, who had mean RLPC values 28% higher than those seen in nondiabetic men (0.285 +/- 0.261 mmol/l [11.0 +/- 10.1 mg/dl] vs. 0.223 +/- 0.163 mmol/l [8.6 +/- 6.3 mg/dl]; P < 0.001) and mean RLPTG values 70% higher than those seen in nondiabetic men (0.606 +/- 1.019 mmol/l [53.6 +/- 90.2 mg/dl] vs. 0.357 +/- 0.546 mmol/l [31.6 +/- 48.3 mg/dl]; P < 0.001). Moreover, diabetic men and women had significantly higher total triglycerides and lower HDL cholesterol levels than nondiabetic subjects.

CONCLUSIONS

The data indicate that RLP particles are elevated in diabetic subjects. To achieve optimal reduction of risk for cardiovascular disease, treatment of elevated RLP values, along with the control of LDL cholesterol levels, should be considered.

Postprandial lipemia--effect of lipid-lowering drugs

Exaggerated postprandial hyperlipidemia has been associated with cardiovascular disease. The mechanisms underlying this association are likely to depend on a multitude of effects. Potentially atherogenic remnants of triglyceride-rich lipoproteins (TRL) accumulate in the postprandial state. In addition, TRL may promote the formation of small dense LDL. There are some indications that the postprandial period is a hypercoagulable state and endothelial function seems to be hampered after acute fat intake. Conventional lipid lowering drugs such as statins and fibrates have the potency of reducing postprandial hyperlipidemia, but the fibrates seem to be more effective in this respect. There is a complete lack of prospective studies linking inefficient postprandial lipid metabolism with clinical endpoints and there is also a need to include investigations of postprandial lipid metabolism in the evaluation of novel drugs affecting lipid metabolism and insulin resistance.

Effects of atorvastatin on oxidized low-density lipoprotein, low-density lipoprotein subfraction distribution, and remnant lipoprotein in patients with mixed hyperlipoproteinemia

Atorvastatin (10 to 20 mg/day) was administered for 3 months to 15 outpatients (average age 58 +/- 4 years) with hypercholesterolemia accompanied by hypertriglyceridemia without hypolipemic treatment. Changes in lipid profile, particularly oxidized low-density lipoprotein (LDL) (malondialdehyde LDL), subfractions of LDL, and remnant lipoprotein (RLP) cholesterol, were examined before and after administration. In addition, the influence of atorvastatin on lipoprotein(a) (known to be an independent risk factor for atherosclerosis), asymmetric dimethylarginine (known to be an endogenous inhibitor of nitric oxide synthase), and homocysteine (methionine metabolite) was also investigated. Administration of atorvastatin significantly decreased serum total cholesterol, LDL cholesterol, and triglycerides. Conversely, a significant increase in high-density lipoprotein cholesterol was shown. In LDL subfractions, large, buoyant LDL fractions were not influenced by treatment with atorvastatin (before administration, 99 +/- 14 mg/dl; after administration, 91 +/- 6 mg/dl, shown as a cholesterol content in each subfraction), but a marked decrease in small, dense LDL fractions (p <0.001) (before administration, 119 +/- 17 mg/dl; after administration, 43 +/- 10 mg/dl) was shown. Moreover, oxidized LDL was significantly decreased (p < 0.01) (before administration, 169 +/- 13 U/L; after administration, 119 +/- 10 U/L) and RLP cholesterol also was significantly decreased (p <0.01) (before administration, 11.9 +/- 2.0 mg/dl; after administration, 6.0 +/- 0.9 mg/dl) with atorvastatin treatment. No significant change was observed in fasting plasma glucose, hemoglobin A1c, lipoprotein(a), asymmetric dimethylarginine, homocysteine, and so on. These data suggest that administration of relatively low doses of atorvastatin to patients with hypercholesterolemia accompanied with hypertriglyceridemia results in a decrease not only in LDL cholesterol and triglycerides, but also in oxidized LDL and RLP cholesterol, with an increase in high-density lipoprotein cholesterol. Furthermore, small, dense LDL decreased with a shift in LDL subfractions to large, buoyant fractions, and these changes are considered to be involved in the inhibition of the onset and progression of atherosclerosis.

Microsomal triglyceride transfer protein: does insulin resistance play a role in the regulation of chylomicron assembly?

We have previously demonstrated that diabetes is associated with an increase in intestinal microsomal triglyceride transfer protein (MTP) mRNA in both the rat and rabbit models. The present study was designed to investigate the relationship between MTP expression and chylomicron assembly in an insulin resistant non-diabetic animal model. Ten insulin resistant Zucker obese fa/fa rats and ten lean fa/minus sign rats were examined at 8-10 weeks of age. The lymph duct was cannulated and lymph collected for 4 h. Lymph chylomicrons were isolated by ultracentrifugation and their composition determined. RNA was extracted from intestinal mucosa and from the liver. MTP mRNA was measured using the RNase protection assay. Blood sugar in the fatty rats was significantly higher (6.3 +/-1.2 vs. 5.4 +/-0.4 P<0.05) and plasma insulin was almost six times that of the lean rats (P<0.001). Plasma cholesterol and phospholipid but not triglyceride were significantly increased in the obese animals (P<0.01). Obese animals secreted significantly more lymph chylomicron apo B48 (0.05 +/-0.02 vs. 0.02 +/-0.01 mg/h P<0.005), triglyceride (9.7 +/-5.3 vs. 3.8+/-1.9 mg/h P<0.005) and phospholipid (1.5 +/-0.7 vs. 0.4 +/-0.3 mg/h P<0.001). The only difference in the chylomicron particle composition between the two groups was a significant increase in phospholipid (P<0.01). Intestinal MTP mRNA expression was significantly higher in the fatty compared to the lean rats (22.1 +/-9.5 vs. 7.8+/-5.6 amol MTP mRNA/microg total RNA P<0.001) as was hepatic MTP mRNA expression (6.9 +/-3.5 vs. 3.4 +/-1.5 amol MTP mRNA/microg total RNA, P<0.01). Thus in this animal model of insulin resistance, increased MTP, which was associated with increased chylomicron particle number, may play a crucial role in the development of atherosclerosis.

Postprandial elevation of remnant lipoprotein leads to endothelial dysfunction

Recent studies have demonstrated that elevated levels of cholesterol in the form of remnant-like particles (RLP-C) induce deterioration of endothelial function during the fasting state, but it is not known whether postprandial RLP-C elevation has the same effect. The objective of this study was to assess the effect of postprandial RLP-C elevation on endothelial function in 24 fasting normolipidemic subjects. Flow-mediated dilatation (FMD) during reactive hyperemia in the brachial artery was investigated. Serum lipids and lipoproteins during fasting and 4h after regular fat-loading were measured. Subjects were divided into 2 groups: the high responders (postprandial RLP-C level >7.5mg/dl, n=8) and the normal responders (postprandial RLP-C level < or =7.5mg/dl, n=16). Significant increases in the level of both triglycerides and RLP-C were observed in the high responders. Basal FMD in the high responders (4.3+/-3.0%) was significantly lower than that in the normal responders (8.3+/-2.4%) (p<0.01), but FMD after the fat-loading in both groups did not change significantly. The change in RLP-C levels during the fat-loading test correlated significantly with basal FMD (r=-0.588, p<0.01). Multiple regression analysis showed a significant correlation between basal FMD and the change in RLP-C levels (r=-0.488, p<0.02). The results of this study suggest that postprandial RLP-C elevation could be associated with atherosclerotic progression even in normolipidemic subjects.

Comparison of remnant-like lipoprotein particles in postmenopausal women with and without coronary artery disease and in men with coronary artery disease

It is known that hypertriglyceridemia is a risk factor of coronary artery disease (CAD) in postmenopausal women. This study prospectively examined whether remnant lipoprotein, an atherogenic triglyceride-rich lipoprotein, may have a significant risk and prognostic values in postmenopausal women with angiographically verified CAD. Remnant-like lipoprotein particles cholesterol (RLP cholesterol) levels in fasting serum were measured in 134 consecutive postmenopausal women with (n = 56) or without (n = 78) CAD by an immunoseparation method. The women with CAD were followed for < or =24 months until occurrence of the following clinical coronary events: readmission or coronary revascularization due to recurrent or refractory angina pectoris, nonfatal myocardial infarction, and cardiac death. Multivariate logistic regression analysis showed that high RLP cholesterol levels (>5.7 mg/dl cholesterol; 90th percentile of the distribution of RLP cholesterol levels in controls) were a significant risk factor for the presence of CAD independent of low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, and other traditional risk factors. Kaplan-Meier analysis demonstrated that women with CAD and higher RLP cholesterol levels had a significantly higher probability of developing coronary events (p <0.001). In multivariate Cox hazard analysis, high RLP cholesterol levels as well as diabetes and hypercholesterolemia were a significant predictor of future coronary events independent of other risk factors in women with CAD (odds ratio 9.7, 95% confidence intervals 1.3 to 20.3, p = 0.02). In conclusion, increased levels of RLP cholesterol are a significant and independent risk factor of CAD and predict future coronary events in postmenopausal women with CAD.

Comparison of fasting and postprandial plasma lipoproteins in subjects with and without coronary heart disease

Plasma lipoprotein levels, including remnant-like particle (RLP) cholesterol and RLP triglycerides, were assessed in fasting (12 hours) and postprandial (PP) (4 hours after a fat-rich meal) states in 88 patients with coronary heart disease (CHD) and 88 controls. All lipoproteins were assessed by direct methods. We hypothesized that patients with CHD would have greater percent increases in their triglyceride levels, RLP cholesterol, and RLP triglycerides, in response to a fat-rich meal. In the fasting state, triglycerides, RLP cholesterol, RLP triglycerides, and low-density lipoprotein (LDL) cholesterol levels were all significantly higher in cases versus controls by 51%, 35%, 39%, and 40%, respectively. These levels were 57%, 37%, 64%, and 37% higher in the PP state, respectively. Mean high-density lipoprotein (HDL) cholesterol values were 27% lower in cases in both the fasting and PP states. After eating, triglycerides, RLP cholesterol, and RLP triglycerides increased 64%, 71%, and 290% in controls, respectively, whereas in cases these levels increased by 71%, 94%, and 340%, respectively (all p <0.0001). Percent increases in the PP state were not significantly different in cases versus controls. Following the fat-rich meal, LDL and HDL cholesterol decreased by 5% and 4% in controls, and by 7% and 6% in patients, with no significant difference in percent changes between groups. Fasting values correlated very highly with PP values for all parameters (all p <0.0001). Our data indicate that although patients with CHD have higher fasting and PP levels of triglycerides, RLP cholesterol, and RLP triglycerides than controls, the response (percent increase) to a fat-rich meal is comparable in both groups. Thus, a feeding challenge is not essential for assessment of these lipoproteins. Moreover, it is not necessary to obtain a fasting sample to assess direct LDL and HDL cholesterol.

Remnant lipoproteins induce endothelial plasminogen activator inhibitor-1

Remnant lipoproteins (RLPs) accumulate in type III hyperlipoproteinemia, a condition associated with significant cardiovascular morbidity. The effect of RLPs on fibrinolysis is unknown. Our aim was to study the effect of RLPs on endothelial expression of plasminogen activator inhibitor-1 (PAI-1). After 24-h culture of human aortic endothelial cells with RLPs at concentrations of 0 (control), 0.038, or 0.076 mg triglyceride/mL, postculture PAI-1 antigen concentrations were: 870 +/- 80, 1963 +/- 183 (P = 0.005), and 3551 +/- 177 ng/mL (P < 0.001), respectively. Furthermore, after 24-h incubation of endothelial cells with RLPs (0 or 0.076 mg triglyceride/mL), PAI-1 activity increased from 0.667 +/- 0.144 to 1.268 +/- 0.198 U/mL, respectively (P = 0.008) and endothelial PAI-1 mRNA increased to 2.7 +/- 0.66 that of control (P = 0.048). In conclusion, RLPs from patients with type III hyperlipoproteinemia induce endothelial cell PAI-1 expression, which may contribute to a prothrombotic state.

Remnant-like lipoprotein particle cholesterol concentration and progression of coronary and vein-graft atherosclerosis in response to gemfibrozil treatment

Remnant lipoproteins such as chylomicron and very low density lipoprotein (VLDL) remnants have been implicated in the progression of coronary atherosclerosis. Recently, a novel method for the determination of the remnant-like lipoprotein particle cholesterol (RLP-C) concentration was developed based on immunoaffinity-separation of plasma. The compositional characteristics of RLP are strikingly similar to those of postprandially modified VLDL. In addition, the method also detects chylomicron remnants. We investigated the relationship between the plasma RLP-C concentration and the angiographic outcome of the 2-year, randomised, placebo-controlled Lipid Coronary Angiography Trial (LOCAT), which used gemfibrozil as lipid lowering agent. The RLP-C response to gemfibrozil treatment has not been described before. Gemfibrozil reduced the median RLP-C concentration by 34%. The on-treatment RLP-C concentration was significantly associated with the progression of the minimum lumen diameter (MLD) (P<0.004). The plasma levels of RLP-C as well as the change in response to treatment was closely associated with plasma triglycerides and the association between on-treatment RLP-C concentration and progression of MLD was not independent of plasma triglycerides. A significant relation was seen between RLP-C and the occurrence of new lesions in vein grafts. Subjects with one new lesion had an approximately 25% higher on-treatment RLP-C concentration and the four patients showing two new lesions had a 100% higher RLP-C concentration than patients without vein graft stenosis. A total of 19 out of 23 subjects having one new lesion, and all four patients showing two new lesions, were assigned to the placebo group. We conclude that the RLP-C concentration, which is likely to reflect the plasma cholesterol contained in postprandially modified VLDL and chylomicron remnants, is strongly associated with angiographically verified progression of focal coronary atherosclerosis, and that lowering of RLPs prevents vein graft stenosis.

Post-prandial remnant lipids impair arterial compliance

OBJECTIVES

We sought to examine the effects of plasma lipids, especially in remnants after a fat meal, on systemic arterial compliance (SAC), a newly recognized cardiovascular risk factor.

BACKGROUND

Post-prandial remnants correlate with coronary heart disease events through mechanisms that may include vascular dysfunction, although the effect on SAC has not been studied.

METHODS

Systemic arterial compliance was measured non-invasively over 6 h after a fat meal in 16 subjects with varying plasma triglyceride levels. Changes were related to rises in plasma lipids and remnant lipids. Systemic arterial compliance was measured in 20 subjects after a control low-fat meal.

RESULTS

The fat meal induced increments in plasma triglyceride and remnant cholesterol and triglyceride (respectively +54%, 50% and 290% at 3 h, analysis of variance <0.001). Systemic arterial compliance fell at 3 h and 6 h by 25% and 27% (analysis of variance <0.001). Baseline SAC correlated significantly with all lipid concentrations at 0, 3 h and 6 h, but only with triglyceride on stepwise regression analysis. The SAC response to the low-fat meal was very small and not significant.

CONCLUSIONS

This is the first demonstration of SAC becoming impaired after a fat meal. Remnant lipids and plasma total triglyceride appeared to contribute to the fall in SAC.

Effect of a low-fat diet enriched with oleic acid on postprandial lipemia in patients with type 2 diabetes mellitus

The aim of the present study was to compare the effects of a low-fat diet enriched with oleic acid to those of a low-fat diet enriched with linoleic acid on fasting lipids, postprandial lipemia, and oxidative susceptibility of low-density lipoprotein (LDL) in patients with type 2 diabetes mellitus (DM). In a 3-wk randomized crossover study, eight patients with type 2 DM were given an experimental low-fat diet enriched with either oleic acid or linoleic acid. The oleic-acid-enriched diet contained 5, 15, and 5%, energy from saturated, monounsaturated, and polyunsaturated fatty acids, and the linoleic-acid-enriched diet contained 5, 5, and 15% energy from saturated, monounsaturated, and polyunsaturated fatty acids, respectively. In addition to evaluating the fasting lipids and oxidative susceptibility of LDL, we evaluated postprandial lipemia using an oral fat load at the end of each 3-wk dietary phase. There were no significant differences in fasting lipid profile or lag time of LDL oxidation between the two experimental dietary phases. The average and maximal increments of remnant-like particle (RLP) cholesterol levels during oral fat load were significantly higher after the oleic-acid-enriched dietary phase than after the linoleic-acid-enriched dietary phase. The area under the curve of RLP cholesterol was also significantly larger after the oleic-acid-enriched dietary phase than after the linoleic-acid-enriched dietary phase. These results suggest that the oleic-acid-enriched diet was associated with increased formation of postprandial chylomicron remnants compared with the linoleic-acid-enriched diet.

Remnant lipoproteins as therapeutic targets

Increasing evidence suggests that subsets of triglyceride-rich lipoproteins are particularly atherogenic. These include particles with some, but not necessarily all the properties classically attributed to remnants. Cholesteryl ester-enrichment seems to be a common feature of these particles, some of which can be taken up by macrophages by a novel receptor that recognizes species of apolipoprotein B but not apolipoprotein E. These characteristics seem to be common to postprandial and hypertriglyceridemic very low density lipoproteins as well as chylomicron remnants. Remnant-like triglyceride-rich lipoproteins that exhibit several potentially atherogenic properties can be quantified by a simple test that shows promise for identifying individuals at high risk for lesion formation and clinical events. Available hygienic and pharmaceutical measures that effectively lower the concentration of atherogenic triglyceride-rich lipoproteins deserve wider use.