The possible role of remnant-like particles as a risk factor for sudden cardiac death

Correlation between estimated plasma remnant-like particle cholesterol and vegetable fat intake in Uku town, Japan

Background

Remnant-like particle cholesterol (RLP-C) is highly atherogenic, which is associated with atherosclerosis. However, RLP-C has not been routinely measured in the clinical practice. We estimated RLP-C levels using conventional lipid profiles and examined the association between estimated RLP-C and related factors including nutrient intake.

Methods

This study was performed in Uku town, Nagasaki prefecture, Japan in 2019. A total of 225 subjects were enrolled and directly measured RLP-C levels. Estimated RLP-C levels were defined as the following formula [total cholesterol − (LDL-cholesterol) − (HDL-cholesterol)]. Multivariate analyses were used to assess the relationship between estimated RLP-C and atherogenic factors. We calculated cut-off values on dichotomized RLP-C (< 7.5 mg/dL vs. ≥ 7.5 mg/dL) by receiver operating characteristic (ROC) curve.

Results

The mean values of directly measured RLP-C levels and estimated RLP-C were 4.0 mg/dL and 16.4 mg/dL, respectively. In the multiple stepwise linear regression analysis, directly measured and estimated RLP-C levels were independently and commonly associated with apolipoprotein E, triglycerides, and vegetable fat intake (inversely). Using ROC curves, we found the cut-off value of estimated RLP-C was 22.0 mg/dL.

Conclusion

We demonstrated that the estimated RLP-C levels using conventional lipid profiles may substitute for directly measured RLP-C and these levels were independently and inversely associated with vegetable fat intake in the community-dwelling Japanese population.

Association of Intima-Media Thickness of Carotid Arteries With Remnant Lipoproteins in Men and Women

The subclass of triglyceride-rich lipoproteins – remnant-like particles (RLP) seems to be strong and independent risk factor for cardiovascular disease. We evaluated the role of RLP and other risk factors (RF) with sonographically measured intima-media thickness of carotid arteries (IMT CCA) in a cohort of Czech population including women defined according to the time after menopause. We investigated relation of IMT CCA to age, weight, central obesity, plasma lipids including remnant-like particles cholesterol (RLP-C) and triglycerides (RLP-TG) in 136 men and 160 women. Using multiple linear regression analysis, significant association between IMT CCA and RLP-C was found in women 1-7 years after menopause. In the whole group of women, only age and fasting blood glucose were independently associated with IMT CCA. In men only age significantly correlated with IMT CCA. Significant decrease of all plasma lipids between 1988 and 1996 in men was detected, while in women significant increase in triglycerides and no change in non-HDL cholesterol was observed. RLP-C was the strongest independent RF for atherosclerosis in postmenopausal women but its association with IMT CCA was limited to several years after menopause. In conclusion, women changing reproductive status could be more sensitive to atherogenic impact of remnant lipoproteins.

Postprandial lipoprotein metabolism: VLDL vs chylomicrons

Since Zilversmit first proposed postprandial lipemia as the most common risk of cardiovascular disease, chylomicrons (CM) and CM remnants have been thought to be the major lipoproteins which are increased in the postprandial hyperlipidemia. However, it has been shown over the last two decades that the major increase in the postprandial lipoproteins after food intake occurs in the very low density lipoprotein (VLDL) remnants (apoB-100 particles), not CM or CM remnants (apoB-48 particles). This finding was obtained using the following three analytical methods; isolation of remnant-like lipoprotein particles (RLP) with specific antibodies, separation and detection of lipoprotein subclasses by gel permeation HPLC and determination of apoB-48 in fractionated lipoproteins by a specific ELISA. The amount of the apoB-48 particles in the postprandial RLP is significantly less than the apoB-100 particles, and the particle sizes of apoB-48 and apoB-100 in RLP are very similar when analyzed by HPLC. Moreover, CM or CM remnants having a large amount of TG were not found in the postprandial RLP. Therefore, the major portion of the TG which is increased in the postprandial state is composed of VLDL remnants, which have been recognized as a significant risk for cardiovascular disease.

Pokkuri Death Syndrome; sudden cardiac death cases without coronary atherosclerosis in South Asian young males

Sudden death is one of the major concerns in forensic medicine. Especially when the deceased is a young subject without significant history, the case will be of major interest to the authorities. Sudden unexplained cardiac death has been known as "Pokkuri Death Syndrome" (PDS) in Japan, "Lai Tai" in Thailand, "Bangungut" in the Philippines, "Dream Disease" in Hawaii, and "Sudden Unexpected Nocturnal Death Syndrome" among South Asian immigrants in the USA. However, the clinical and pathological features of these sudden death cases, especially the characteristics of no coronary atherosclerosis, are surprisingly similar and mainly occur among Southeast Asian young males during sleep in the midnight. In this manuscript, we have reviewed the pathological characteristics and the possible mechanism of death in PDS cases, which were associated with significantly elevated remnant lipoproteins in plasma as revealed from our studies during the past 15 years in Japan. Although elevated plasma remnant lipoproteins have been known to be strongly atherogenic, coronary atherosclerosis was not observed in PDS cases. PDS cases were shown to be an interesting cardiovascular disease death discovered in forensic medicine research, which may suggest the difference between the occurrence of cardiovascular events and the severity of coronary atherosclerosis as separate factors. These observations in PDS cases suggest the possibility that the intervention could be more targeted to suppress the cardiovascular events rather than to slow down the progression of atherosclerosis, which is now most extensively targeted for the therapy of cardiovascular disease in Western countries.

Detection of apolipoproteins B-48 and B-100 carrying particles in lipoprotein fractions extracted from human aortic atherosclerotic plaques in sudden cardiac death cases

BACKGROUND

ApoB-48 is a major apolipoprotein secreted by the small intestine and is the main constitutive apolipoprotein in chylomicrons (CM). In the past, presence of apoB-48 in human aortic atherosclerotic plaques has not been detected.

METHODS

A newly developed apoB-48 ELISA together with an HPLC fractionation technique, were applied to investigate the presence of apoB-48 (CM) in aortic atherosclerotic plaques. The atherosclerotic plaques were obtained from aortae of sudden cardiac death cases. Total cholesterol, triglycerides (TG), apoB-100 and apoB-48 were measured in the aortic plaques extracts.

RESULTS

HPLC analysis of plaques extracts monitored by cholesterol revealed mainly particle sizes of CM and very low density lipoproteins (VLDL) in the d>1.006 fractions. The plaques extracts were monitored by apoB-48 and apoB-100 ELISA. There were no TG peaks in any lipoprotein fraction extracted from the plaques except as free glycerol. ApoB-100 was detected in VLDL particles and in LDL sizes. In contrast, apoB-48 was detected in particles of CM, VLDL and LDL sizes. Further, in postmortem plasma, apo B-48 was detected in particles sizes of HDL or smaller and the Western blot analysis could not show any 250 kDa molecular weight (MW) protein in the plaque extracts, but smaller and broader MW staining were observed at 20-150 kDa.

CONCLUSION

Hitherto there has been lack of an appropriate assay to measure apoB-48 in plaques. Our investigations show that apoB-48 is present in atherosclerotic plaques with denatured or degraded structure. This is the first report describing presence of apoB-48 in human atherosclerotic plaques.

ApoB-100 carrying lipoprotein, but not apoB-48, is the major subset of proatherogenic remnant-like lipoprotein particles detected in plasma of sudden cardiac death cases

We have previously reported that plasma levels of remnant-like lipoprotein particles (RLP) significantly increased in sudden cardiac death cases with and without coronary atherosclerosis. In this study we have elucidated the major subset of proatherogenic RLP, containing both apoB-48 and apoB-100-carrying remnants, in plasma of SCD and control death cases. One hundred and sixty seven Japanese cases of sudden cardiac death and 78 cases of control death underwent autopsy within 12h after death were studied. Heart weight was 9.2% higher in SCD cases than controls (P<0.05). Moreover 57.5% or 96/167 of the cases had more than grade (2+) coronary atherosclerosis versus 21.8% or 17 of 78 controls (P<0.01). Approximately 2/3 of the cases had full stomach, reflecting the postprandial state at the time of death. Plasma TC, TG, VLDL-C, LDL-C were significantly elevated (P<0.001) together with RLP-C (P<0.01), RLP-TG (P<0.005) in SCD cases. Plasma RLP-apoB-100 levels were significantly elevated in SCD (P<-0.001), but apoB-48 levels were not. The median ratio of apoB-100/apoB-48 in RLP was 7.1 in SCD. The median RLP-TG/RLP-C ratio was 4.7, which suggested a large VLDL size. When apoB-48 and apoB-100 in RLP were divided into two groups, above and below the median level, respectively, apoB-48 inversely correlated with RLP-C (P<0.05) and RLP-TG (P<0.01), while apoB-100 in RLP positively correlated with RLP-C (P<0.01) in SCD cases. In conclusion, these results indicated that apoB-100 carrying lipoproteins, not apoB-48 carrying lipoproteins, were the major subset of RLP associated with sudden cardiac death in the postprandial state, regardless to the severity of coronary atherosclerosis.

Age-dependent association between hepatic lipase gene C-480T polymorphism and the risk of pre-hospital sudden cardiac death: the Helsinki Sudden Death Study

OBJECTIVE

We investigated the association between hepatic lipase (HL) C-480T polymorphism and the risk of acute myocardial infarction (AMI) as well as pre-hospital sudden cardiac death (SCD).

METHODS

Seven hundred sudden or unnatural pre-hospital deaths of middle-aged (33-70 years, mean 53 years) Caucasian Finnish men were subjected to detailed autopsy (Helsinki Sudden Death Study). Genotype data were obtained for 682 men.

RESULTS

In logistic regression analysis with age, body mass index, hypertension, diabetes, smoking and alcohol consumption as covariates, men with the TT genotype had an increased risk for SCD and AMI compared to CC carriers (OR=3.0, P=0.011; and OR=3.7, P=0.003). There was a significant age-by-genotype interaction (P<0.05) on the risk of SCD. Compared to CC genotype carriers, the association between the TT genotype and SCD was particularly strong (P=0.001) among men <53 years of age, but this association was non-significant among older men. This was mainly due to a strong association between the TT genotype and AMI due to severe coronary disease in the absence of thrombosis. Carriers of the TT genotype were more likely to have severe coronary stenoses (> or =50%) than men with the CT or CC genotype (P=0.019).

CONCLUSIONS

The results suggest that HL C-480T polymorphism is a strong age-dependent risk factor of SCD in early middle-aged men.

Are Remnant-Like Particles Independent Predictors of Coronary Heart Disease Incidence?

Background— Remnant-like particles have been proposed as a new risk factor for coronary heart disease (CHD). This is the first long-term prospective investigation of the relationship between remnant-like particles and a cardiovascular disease outcome in healthy men.

Methods and Results— A cohort of 1156 Japanese-American men aged 60 to 82 from the Honolulu Heart Program was followed for 17 years. During that period 164 incident cases of CHD were identified. In multivariate Cox regression analyses, baseline remnant-like particle cholesterol (RLP-C) and triglyceride (RLP-TG) levels were significantly related to CHD incidence independently of nonlipid cardiovascular risk factors and of total cholesterol or high-density and low-density lipoprotein cholesterol levels. Total triglyceride levels were an independent predictor of CHD incidence. However, in models including RLP and triglyceride level simultaneously, neither variable was significant when adjusted for the other. This finding can be attributed to the strong correlation between RLP-C and RLP-TG levels and total triglycerides. When individuals with normal triglyceride levels (n=894) were separated from those with elevated triglycerides (n=260), the association between RLPs and CHD relative risk was only significant for the group with elevated triglyceride levels.

Conclusions— RLP levels predicted CHD incidence independently of nonlipid risk factors and of total cholesterol or high-density and low-density lipoprotein cholesterol levels. However, RLP levels did not provide additional information about CHD incidence over and above total triglyceride levels. Therefore, this study does not support the need for testing of remnants in men if measures of fasting triglycerides are available.

Validity of plasma remnant lipoproteins as surrogate markers of antemortem level in cases of sudden coronary death

Hitherto triglycerides (TG) and TG-rich lipoproteins were been of limited value as surrogates for antemortem levels. We measured TG levels in postmortem plasma from sudden coronary death cases (SCD, n=91) by using two TG assays, Dry Chem TG (free glycerol was added) and the Determiner L-TG (without added free glycerol) that measured net TG. TG levels were markedly higher by the Dry Chem TG (y) vs. Determiner L-TG (x), y = 1.03x + 229 mg/dl. HPLC showed large amounts of free glycerol in postmortem plasma and in TG-rich lipoprotein remnants (RLP). These results were verified in a rabbit model of SCD. Further, RLP from SCD were found to be biophysically similar to those from living patients with coronary artery disease (CAD). In conclusion, postmortem plasma sampled up to 12 h after death is appropriate for measuring lipid and lipoproteins, TG and RLP-TG as surrogates for antemortem levels when a TG assay without added free glycerol is used.

Remnant Lipoprotein Particles Induce Apoptosis in Endothelial Cells by NAD(P)H Oxidase–Mediated Production of Superoxide and Cytokines via Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1 Activation

Background— Remnant lipoprotein particles (RLPs), products of lipolytic degradation of triglyceride-rich lipoprotein derived from VLDL, exert atherogenesis. In this study, we observed how RLPs induced cytotoxicity in human umbilical vein endothelial cells (HUVECs) and cilostazol prevented cell death.

Methods and Results— RLPs were isolated from the plasma of hyperlipidemic patients by use of an immunoaffinity gel mixture of anti–apolipoprotein A-1 and anti–apolipoprotein B-100 monoclonal antibodies. RLPs (50 μg/mL) significantly increased superoxide formation in HUVECs associated with elevated gp91phox mRNA and protein expression and Rac1 translocation, accompanied by increased production of tumor necrosis factor (TNF)-α and interleukin-1β, DNA fragmentation, and cell death. Cilostazol (1 to 100 μmol/L) significantly suppressed not only NAD(P)H oxidase–dependent superoxide production but also TNF-α and interleukin-1β release and restored viability. RLPs activated a lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), which was not inhibited by cilostazol. Treatment of HUVECs with monoclonal antibody for LOX-1 attenuated RLP-mediated production of superoxide, TNF-α, and interleukin-1β and DNA fragmentation.

Conclusions— RLPs stimulated NAD(P)H oxidase–dependent superoxide formation and induction of cytokines in HUVECs via activation of LOX-1, consequently leading to reduction in cell viability with DNA fragmentation, and cilostazol exerts a cell-protective effect by suppressing these variables.

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.

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.

Effects of bezafibrate and pravastatin on remnant-like lipoprotein particles and lipoprotein subclasses in type 2 diabetes

The effects of bezafibrate and pravastatin on remnant-like lipoprotein particles (RLPs) and lipoprotein subclasses were compared in type 2 diabetes. Bezafibrate (400 mg/day) and pravastatin (10 mg/day) were given to 27 Japanese diabetics in a randomized crossover design. RLP cholesterol (RLP-C) and RLP triglyceride (RLP-TG) were measured by an immunoseparation technique. LDL and HDL were separated each into three subclasses (large, medium, small) and their cholesterol (C) contents were measured by an HPLC method. RLP-C was reduced more effectively by pravastatin (bezafibrate -16.0% vs. pravastatin -40.6%, P < 0.05), whereas RLP-TG was reduced more effectively by bezafibrate (-55.2% vs. -35.0%, P < 0.05). Further, pravastatin decreased large and small LDL-C levels equally (large; -23.6%; medium; -17.2%, small; -21.0%), while bezafibrate produced a relatively larger reduction in small LDL-C (-12.1; -16.9; -21.5%). Whereas bezafibrate significantly decreased large HDL-C and increased medium and small HDL-C (-49.6; 34.1; 35.8%), pravastatin significantly increased only medium HDL-C (5.2; 9.4; 5.9%). Bezafibrate reduced RLP-C and RLP-TG more effectively in patients with high TG levels, whereas pravastatin's effect was not markedly influenced by the initial TG level. Thus measurements of RLP-C, RLP-TG, and HPLC subclasses revealed that bezafibrate and pravastatin differently influence the lipoprotein status in type 2 diabetes.

Estrogen treatment of prostate cancer increases triglycerides in lipoproteins as demonstrated by HPLC and immunoseparation techniques

BACKGROUND

Estrogen administration is known to increase serum triglyceride concentrations. This study measured changes in lipoproteins of patients with prostate cancer treated with estrogen to determine whether the increased triglyceride concentrations are associated with atherogenic lipoprotein patterns.

METHODS

Fifteen patients (52-87 years) with histologically diagnosed prostate cancer received diethylstilbestrol diphosphate (250 mg/day). Serum samples were collected before and after 1 and 2 weeks of treatment. Cholesterol and triglyceride profiles of major lipoproteins were determined by HPLC, remnant-like particle cholesterol and triglyceride concentrations by an immunoseparation technique, and apolipoproteins by immunologic methods.

RESULTS

Estrogen treatment induced a 63.3% increase in total triglyceride concentrations, which occurred in all major lipoprotein classes with significant increases in HDL-triglycerides (130.4%), LDL-triglycerides (60.7%) and VLDL-triglycerides (56.2%). HDL-cholesterol increased significantly by 26.8%, while LDL-cholesterol decreased (15.6%). Remnant-like particle triglyceride concentrations also increased significantly by 77%, whereas remnant-like particle cholesterol concentrations remained unchanged. Apolipoproteins A-I and A-II increased; apolipoprotein E and Lp(a) decreased.

CONCLUSIONS

The techniques used here conveniently demonstrated that short-term estrogen treatment in prostate cancer patients resulted in triglyceride enrichment of all major lipoprotein classes but did not induce changes in the lipoprotein profiles generally recognized as increasing risk for cardiovascular disease, except for the elevation of plasma triglyceride and remnant-like particle triglyceride.

The atherogenic lipoprotein phenotype: small dense LDL and lipoprotein remnants in nephrotic range proteinuria

The dyslipidaemia in nephrotic-range proteinuria is believed to contribute to the increased atherogenesis associated with the condition. Excess small dense low density lipoprotein (LDLIII) contributes to this risk. Lipoprotein remnants (RLP) may also be implicated but have not been studied in this population. We measured the plasma concentration of low density lipoprotein (LDL) subfractions (by density gradient ultracentrifugation), RLP (by immunoaffinity gel), very low density lipoprotein (VLDL) subfractions, post heparin lipases and cholesteryl ester transfer protein (CETP) activity in 27 patients with glomerular disease and albuminuria >2.0g. These were compared with 27 age and sex matched controls. Proteinuric patients had increased LDLIII concentration (patients 182 (84:267) vs. controls 31 (27:62); P<0.0001) with reduced lighter LDLI (36 (24:43) vs 69 (46:101); P<0.0005) and LDLII (124 (79:220) vs 178 (129:236); P<0.04, all mg/dl, median+interquartile range). RLP-cholesterol (RLP-C) and triglyceride (RLP-TG) were increased in proteinuric patients (RLP-C 18.9 (11.0:26.9) vs 7.7 (6.0:8.8); P<0.0001, RLP-TG 35.8 (11.8:54.7) vs. 7.2 (4.3:10.0); P<0.0001, all mg/dl). Increased LDLIII and RLP were independent of renal function. VLDL(1) and VLDL(2) concentrations were increased by 258 and 260% (both P<0.0001). CETP activity was increased by 46% (P<0.005). Lipoprotein and hepatic lipase activities did not differ from control values. LDLIII concentration (r(2)=45.7%, P<0.001), RLP-C (r(2)=85.2%, P<0.001) and RLP-TG (r(2)=87.5%, P<0.001) all correlated positively with plasma triglyceride. Moreover, increased LDLIII was associated with both RLP-C (r(2)=31.3%, P<0.002) and RLP-TG (r(2)=33.6%, P<0.002). Excess LDLIII and RLP are present in nephrotic-range proteinuria and add to the spectrum of cardiovascular risk factors present in proteinuric patients. Increases in LDLIII and RLP are closely related to plasma triglyceride. The association between excess RLP and LDLIII suggests that RLP contribute to the increased atherogenicity attributed to the atherogenic lipoprotein phenotype.

Plasma triglyceride-rich lipoprotein remnants as a risk factor of 'Pokkuri disease'

In our recent report, it remained unclear whether or not triglyceride-rich lipoprotein remnants (RLP) were associated with the risk of sudden coronary death in younger cases without coronary atherosclerosis that were detected in about 10% of all sudden coronary death cases in Japan. These cases were categorized as 'origin unknown, but suspected to be due to coronary spasm', the so called 'pokkuri disease' in Japan. The present study population consisted of 108 sudden death cases without coronary atherosclerosis [(pokkuri disease n=57) and non-cardiac sudden death (control n=51)] aged 20-69 years from Kanagawa prefecture in Japan. All individuals had died suddenly and unexpectedly, most had no significant history of medical conditions including cardiac symptoms and had not taken medications prior to death according to their medical records. All the autopsies were performed within 12 h after death. Plasma total cholesterol (TC), triglycerides (TG), phospholipids, RLP-C and RLP-TG, VLDL-C, LDL-C, HDL-C, apolipoproteins A-I, A-II, B, C-II, C-III, E, Lp (a) and homocysteine were measured in postmortem plasma samples. The TG-rich lipoprotein remnants measured as RLP-C and RLP-TG were significantly higher in pokkuri disease compared with controls both in fasting and postprandial states (P<0.05 and P<0.001), indicating that RLP-C and RLP-TG were the most significant risk factor in pokkuri disease among the parameters tested in this study. In conclusion the TG level in RLP (RLP-TG) appeared to be strongly associated with the risk of sudden death in the absence of coronary atherosclerosis (pokkuri disease).

Association between triglyceride-rich lipoprotein remnant receptor polymorphisms and lipid traits

OBJECTIVES

The metabolism of triglyceride-rich lipoproteins (TRL) is, in part, mediated by lipoprotein receptors (such as low density lipoprotein receptor-related protein [LRP] and very low density lipoprotein [VLDL] receptors), which recognize TRL remnants after specific binding with apolipoprotein E. The purpose of this study was to explore the association of the genetic polymorphisms of remnant receptors with lipid, lipoprotein, and apolipoprotein levels including remnant-like particle-cholesterol (RLP-C).

DESIGN AND METHODS

Using polymerase chain reaction-amplified DNA, VLDL receptor tetranucleotide repeat polymorphism, LRP trinucleotide repeat polymorphism, and LRP exon 3 polymorphism were analyzed in normal adults (control group: n = 161) and in patients with coronary artery disease (CAD group: n = 102).

RESULTS

The allelic distributions of VLDL receptor triple repeat polymorphism, LRP tetranucleotide repeat polymorphism, and LRP exon 3 polymorphism in Koreans were similar to those of Japanese but were significantly different from those of other ethnic groups. There were no significant differences in the allele frequencies of the polymorphisms between the control and CAD groups. VLDL receptor polymorphism in the control group (p = 0.0403) and LRP exon 3 polymorphism in the CAD group (p = 0.0459) showed significant associations with lipoprotein (a) [Lp(a)] levels.

CONCLUSIONS

The results of the present study demonstrated significant interracial distribution of remnant receptor polymorphisms. There was no association between the remnant receptor polymorphisms and the RLP-C levels. However, the polymorphisms showed a significant association with Lp(a), which may suggest that the Lp(a) metabolism is in part mediated by the uptake through the remnant receptors.

Relation between RLP-triglyceride to RLP-cholesterol ratio and particle size distribution in RLP-cholesterol profiles by HPLC

Remnant-Like Particles (RLP) isolated by an immunoseparation method are heterogeneous in their physical and biochemical properties. The objective of this study was to examine the relation between RLP-triglyceride (RLP-TG) to RLP-cholesterol (RLP-C) ratio and particle size distribution in RLP-C profiles from patients with hyperlipoproteinemia by HPLC. RLP were isolated from serum samples from 147 subjects. RLP-C and RLP-TG were quantified by respective enzymatic methods. Particle sizes of the RLP were measured using HPLC with 4 connected TSKgel LipopropakXL columns. Based on HPLC profiles of RLP-C from individual subjects, three different types were classified: predominantly LDL, predominantly VLDL, and mostly VLDL types. All patients with type III hyperlipidemia were mostly VLDL type but with smaller particle size of VLDL (32 nm) than other subjects. Severe hypertriglyceridemic (TG>4.52 mmoll(-1)) subjects were mostly VLDL type with large particle size (41 nm). As for all subjects (n=105) without predominantly LDL type, a significant correlation between RLP particle size and RLP-TG to RLP-C ratio (r=0. 432, P<0.001) was obtained, but not in case of serum TG to RLP-C ratio (r=0.062). It suggests that RLP-TG to RLP-C ratio might be used for discrimination of atherogenic smaller-sized lipoprotein from larger-sized TG-rich lipoprotein remnants.

Remnant-like particle cholesterol levels in Korean patients with coronary artery disease and non-insulin dependent diabetes mellitus

Several studies have provided evidence that the remnants of lipoproteins may be the atherogenic components of triglyceride-rich lipoproteins. The purpose of this study was to investigate whether the remnant-like particle cholesterol (RLP-C) is an independent risk factor for coronary artery disease (CAD) and non-insulin dependent diabetes mellitus (NIDDM) in the Korean population and to explore the relationship between RLP-C and other biochemical markers as well as the apolipoprotein (apo) E genotypes. Lipid and lipoproteins including RLP-C and apo E genotypes were analyzed in 98 normal adults (control group), 68 patients with CAD (CAD group), 88 patients with NIDDM (DM group), and 19 patients with both CAD and NDDM (CAD + DM group). RLP-C levels were significantly higher in the DM (p < 0.0001), CAD (p = 0.0012) and the CAD + DM groups (p = 0.0184) than in the controls. To determine which variable could discriminate most effectively and independently among the different groups, stepwise linear discriminant analysis was performed for all the variables that showed p < 0.15 by univariate analysis. RLP-C was selected as an independent discriminator between the control and patient groups. RLP-C levels showed a strong positive correlation with trigylceride levels in the control, CAD and DM groups (r = 0.783, r = 0.610 and r = 0.746, respectively). In overall groups, apo epsilon4 and epsilon2 carrier genotypes showed a significant increase in RLP-C levels compared with epsilon3/3 wild-type (p = 0.0085). After adjusting for the effect of apo E genotypes, a significant increase of the RLP-C levels in the disease groups remained. In conclusion, RLP-C was determined to be an independent risk factor in Korean patients with CAD and NIDDM and showed a strong correlation with triglyceride levels. We suggest that the increased cardiovascular risk associated with the epsilon4 and epsilon2 allele may be mediated by more atherogenic RLP-C.

Eicosapentanoic acid reduces plasma levels of remnant lipoproteins and prevents in vivo peroxidation of LDL in dialysis patients

Causative factors of uremia-associated atherosclerosis are complex. However, it is likely that atherogenic lipoproteins accumulated in plasma are involved. Remnant lipoproteins are atherogenic and are frequently observed in uremic plasma. LDL from uremic patients has been shown to be susceptible to in vitro peroxidation, suggesting that oxidized LDL (ox-LDL) could be excessively generated in those patients. No effective treatments to prevent accumulation of both atherogenic lipoproteins in dialysis patients have been published. Eicosapentanoic acid (EPA) may change synthesis and/or catabolism of remnant lipoproteins and increase stability of LDL to peroxidation by altering the fatty acid composition of lipoproteins. A prospective comparative study was conducted to assess the efficacy of EPA on metabolism of remnant lipoproteins and ox-LDL in dialysis patients using two new methods: an immunoaffinity gel separation for quantifying plasma remnant lipoproteins and an enzyme-linked immunosorbent assay for measuring plasma ox-LDL levels, a marker for in vivo LDL peroxidation. Twenty-two hemodialysis and 16 continuous ambulatory peritoneal dialysis patients with relatively high plasma levels of remnant lipoproteins and ox-LDL were randomized to either EPA or placebo. Highly purified EPA, in an ethyl-ester form (ethyl all-cis-5,8,11,14,17-icosapentanoate) with a purity greater than 91%, was administered at a dose of 1800 mg daily. Overall, 3 mo of treatment with EPA significantly reduced the levels of both remnant lipoproteins (52% reduction) and ox-LDL (38% reduction). Additionally, gel filtration chromatography of lipoproteins showed that EPA treatment concomitantly normalized other potential abnormalities in lipoproteins. Treatment compliance was good and no critical adverse effects were observed. In conclusion, EPA administration proved to be effective and safe treatment to decrease plasma remnant lipoproteins and prevent in vivo peroxidation of LDL in dialysis patients.

Detection, quantification, and characterization of potentially atherogenic triglyceride-rich remnant lipoproteins

Triglyceride-rich lipoprotein (TRL) remnants are formed in the circulation when apolipoprotein (apo) B-48-containing chylomicrons of intestinal origin or apoB-100-containing VLDL of hepatic origin are converted by lipoprotein lipase, and to a lesser extent by hepatic lipase, into smaller and more dense particles. Compared with their nascent precursors, TRL remnants are depleted of triglyceride, phospholipid, and C apolipoproteins and are enriched in cholesteryl esters and apoE. They can thus be identified, separated, and/or quantified in plasma according to their density, charge, size, specific lipid components, apolipoprotein composition, and/or apolipoprotein immunospecificity. Each of these approaches has contributed to our current understanding of the compositional characteristics of TRL remnants and their potential to promote atherosclerosis. An ongoing search is nevertheless under way for more accurate and clinically applicable remnant lipoprotein assays that will be able to better define coronary artery disease risk in patients with hypertriglyceridemia.

Lipoprotein(a), homocysteine, and remnantlike particles: emerging risk factors

Although lipoprotein(a) [Lp(a)] was first described more than 35 years ago, adequate prospective data have only recently supported Lp(a) as an independent risk factor for coronary heart disease (CHD). In vitro studies suggest that Lp(a) contributes to atherogenesis directly by cholesterol uptake and indirectly by the inhibition of fibrinolysis. In patients with CHD or a significant risk for CHD, Lp(a) should be measured and treated with either niacin or estrogen if the patient has Lp(a) cholesterol levels of more than 10 mg/dL or an Lp(a) mass of more than 30 mg/dL. In addition, homocysteine and remnantlike lipoprotein cholesterol are strongly supported by prospective or population-based prevalence data as independent risk factors for CHD. Homocysteine levels of more than 14 mumol/L should be treated with vitamin supplements of folate, B6, and B12. Remnantlike lipoprotein cholesterol is the product of a novel immunoassay that separates the partially hydrolyzed triglyceride-rich remnant particles. The association of these particles with CHD risk in women may explain the small independent CHD risk that triglycerides have in women in the Framingham Heart Study. A clear therapeutic intervention has not been documented but may include diet, fibric acid derivatives, or hydroxymethylglutamyl coenzyme A reductase inhibitors.

Association of plasma triglyceride-rich lipoprotein remnants with coronary atherosclerosis in cases of sudden cardiac death

Among the risk factors for coronary atherosclerosis, elevated LDL-C level is best known. The action of lipoprotein lipase on triglyceride-rich lipoproteins produces remnant lipoprotein particles enriched in cholesterol and apolipoprotein E (apo E). Apo E serves as the ligand for uptake of remnant lipoproteins via the LDL-receptor or the remnant receptor. In this study, postmortem plasma total cholesterol, triglycerides (TG), VLDL-C, HDL-C, lipoprotein (a) [Lp(a)] and remnant-like lipoprotein particles (RLP)-cholesterol, RLP-TG, apolipoproteins B, C III and E were measured, together with LDL-C to assess their potential contribution to the severity of coronary and aortic atherosclerosis of the 197 cases of sudden death (132 cardiac death and 65 non-cardiac death). In all cases, the severity of coronary atherosclerosis was determined at postmortem pathological examination. RLP-cholesterol (RLP-C) and LDL-C concentrations were significantly higher in cases with advanced coronary atherosclerosis compared with those without coronary atherosclerosis; respective median values were 13.5 vs 8.4 mg/dl (P < 0.001) and 140 vs 115 mg/dl (P < 0.05). RLP-C levels were more strongly correlated with the severity score of coronary atherosclerosis than LDL-C.

Remnant lipoprotein cholesterol and triglyceride reference ranges from the Framingham Heart Study

Remnants of triglyceride-rich lipoproteins of both intestinal and liver origin are considered atherogenic, but they have been difficult to isolate and measure. An assay has been developed that allows the measurement of remnant-like particle cholesterol (RLP-C) and triglyceride (RLP-TG). RLP-C and RLP-TG concentrations were measured in &gt;3000 fasting plasma samples obtained from participants in exam cycle 4 of the Framingham Offspring Study and stored at −80 °C. After exclusions, comparisons were made for 2821 samples (1385 women, 1436 men; mean age, 52 years). For women, the mean RLP-C and RLP-TG values were 0.176 ± 0.058 mmol/L (6.8 ± 2.3 mg/dL) and 0.204 ± 0.159 mmol/L (18.1 ± 14.1 mg/dL), respectively; for men, the mean values were 0.208 ± 0.096 mmol/L (8.0 ± 3.7 mg/dL) and 0.301 ± 0.261 mmol/L (26.7 ± 23.1 mg/dL), respectively. Women had significantly lower RLP-C and RLP-TG values (P &lt;0.0001) than men; premenopausal women had significantly lower values than postmenopausal women (P &lt;0.0001); and younger subjects (&lt;50 years) had significantly lower values than older individuals (P &lt;0.0001). The 75th percentile values for RLP-C and RLP-TG were 0.186 mmol/L (7.2 mg/dL) and 0.225 mmol/L (19.9 mg/dL), respectively, for women, and 0.225 mmol/L (8.7 mg/dL) and 0.346 mmol/L (30.6 mg/dL) for men. These data provide reference ranges for use in the evaluation of RLP-C and RLP-TG as potential indicators of risk for coronary heart disease.