Properties of an apolipoprotein E-enriched fraction of triglyceride-rich lipoproteins isolated from human blood plasma with a monoclonal antibody to apolipoprotein B-100

Postprandial Hyperlipidemia: Its Pathophysiology, Diagnosis, Atherogenesis, and Treatments

Postprandial hyperlipidemia showing postprandial increases in serum triglyceride (TG) is associated with the development of atherosclerotic cardiovascular disease (ASCVD). To diagnose postprandial hyperlipidemia, the oral fat loading test (OFLT) should be performed; however, this test is very time-consuming and is difficult to perform. Elevated serum TG levels reflect an increase in TG-rich lipoproteins (TRLs), such as chylomicrons (CM), very low-density lipoproteins (VLDL), and their remnants (CM remnants [CMRs] and VLDL remnants [VLDLRs]). Understanding of elevation in CMR and/or VLDLR can lead us to understand the existence of postprandial hyperlipidemia. The measurement of apo B48, which is a constituent of CM and CMR; non-fasting TG, which includes TG content in all lipoproteins including CM and CMR; non-high-density lipoprotein cholesterol (non-HDL-C), which includes TRLs and low-density lipoprotein; and remnant cholesterol are useful to reveal the existence of postprandial hyperlipidemia. Postprandial hyperlipidemia is observed in patients with familial type III hyperlipoproteinemia, familial combined hyperlipidemia, chronic kidney disease, metabolic syndrome and type 2 diabetes. Postprandial hyperlipidemia is closely related to postprandial hyperglycemia, and insulin resistance may be an inducing and enhancing factor for both postprandial hyperlipidemia and postprandial hyperglycemia. Remnant lipoproteins and metabolic disorders associated with postprandial hyperlipidemia have various atherogenic properties such as induction of inflammation and endothelial dysfunction. A healthy diet, calorie restriction, weight loss, and exercise positively impact postprandial hyperlipidemia. Anti-hyperlipidemic drugs such pemafibrate, fenofibrate, bezafibrate, ezetimibe, and eicosapentaenoic acid have been shown to improve postprandial hyperlipidemia. Anti-diabetic drugs including metformin, alpha-glucosidase inhibitors, pioglitazone, dipeptidyl-peptidase-4 inhibitors and glucagon-like peptide 1 analogues have been shown to ameliorate postprandial hyperlipidemia. Although sodium glucose cotransporter-2 inhibitors have not been proven to reduce postprandial hyperlipidemia, they reduced fasting apo B48 and remnant lipoprotein cholesterol. In conclusion, it is important to appropriately understand the existence of postprandial hyperlipidemia and to connect it to optimal treatments. However, there are some problems with the diagnosis for postprandial hyperlipidemia. Postprandial hyperlipidemia cannot be specifically defined by measures such as TG levels 2 h after a meal. To study interventions for postprandial hyperlipidemia with the outcome of preventing the onset of ASCVD, it is necessary to define postprandial hyperlipidemia using reference values such as IGT.

Peripheral metabolism of lipoprotein-amyloid beta as a risk factor for Alzheimer's disease: potential interactive effects of APOE genotype with dietary fats

Alzheimer's disease (AD) is a progressive neurodegenerative disorder pathologically characterized by brain parenchymal abundance of amyloid-beta (Aβ) and the accumulation of lipofuscin material that is rich in neutral lipids. However, the mechanisms for aetiology of AD are presently not established. There is increasing evidence that metabolism of lipoprotein-Aβ in blood is associated with AD risk, via a microvascular axis that features breakdown of the blood-brain barrier, extravasation of lipoprotein-Aβ to brain parenchyme and thereafter heightened inflammation. A peripheral lipoprotein-Aβ/capillary axis for AD reconciles alternate hypotheses for a vascular, or amyloid origin of disease, with amyloidosis being probably consequential. Dietary fats may markedly influence the plasma abundance of lipoprotein-Aβ and by extension AD risk. Similarly, apolipoprotein E (Apo E) serves as the primary ligand by which lipoproteins are cleared from plasma via high-affinity receptors, for binding to extracellular matrices and thereafter for uptake of lipoprotein-Aβ via resident inflammatory cells. The epsilon APOE ε4 isoform, a major risk factor for AD, is associated with delayed catabolism of lipoproteins and by extension may increase AD risk due to increased exposure to circulating lipoprotein-Aβ and microvascular corruption.

Sugar-Sweetened Beverage Consumption and Plasma Lipoprotein Cholesterol, Apolipoprotein, and Lipoprotein Particle Size Concentrations in US Adults

BACKGROUND

Prospective cohort studies have found a relation between sugar-sweetened beverage (SSB) consumption (sodas and fruit drinks) and dyslipidemia. There is limited evidence linking SSB consumption to emerging features of dyslipidemia, which can be characterized by variation in lipoprotein particle size, remnant-like particle (RLP), and apolipoprotein concentrations.

OBJECTIVES

To examine the association between SSB consumption and plasma lipoprotein cholesterol, apolipoprotein, and lipoprotein particle size concentrations among US adults.

METHODS

We examined participants from the Framingham Offspring Study (FOS; 1987-1995, n = 3047) and the Women's Health Study (1992, n = 26,218). Concentrations of plasma LDL cholesterol, apolipoprotein B (apoB), HDL cholesterol, apolipoprotein A1 (apoA1), triglyceride (TG), and non-HDL cholesterol, as well as total cholesterol:HDL cholesterol ratio and apoB:apoA1 ratio, were quantified in both cohorts; concentrations of apolipoprotein E, apolipoprotein C3, RLP-TG, and RLP cholesterol (RLP-C) were measured in the FOS only. Lipoprotein particle sizes were calculated from nuclear magnetic resonance signals for lipoprotein particle subclass concentrations (TG-rich lipoprotein particles [TRL-Ps]: very large, large, medium, small, and very small; LDL particles [LDL-Ps]: large, medium, and small; HDL particles [HDL-Ps]: large, medium, and small). SSB consumption was estimated from food frequency questionnaire data. We examined the associations between SSB consumption and all lipoprotein and apoprotein measures in linear regression models, adjusting for confounding factors such as lifestyle, diet, and traditional lipoprotein risk factors.

RESULTS

SSB consumption was positively associated with LDL cholesterol, apoB, TG, RLP-TG, RLP-C, and non-HDL cholesterol concentrations and total cholesterol:HDL cholesterol and apoB:apoA1 ratios; and negatively associated with HDL cholesterol and apoA1 concentrations (P-trend range: <0.0001 to 0.008). After adjustment for traditional lipoprotein risk factors, SSB consumers had smaller LDL-P and HDL-P sizes; lower concentrations of large LDL-Ps and medium HDL-Ps; and higher concentrations of small LDL-Ps, small HDL-Ps, and large TRL-Ps (P-trend range: <0.0001 to 0.001).

CONCLUSIONS

Higher SSB consumption was associated with multiple emerging features of dyslipidemia that have been linked to higher cardiometabolic risk in US adults.

Remnants of the Triglyceride-Rich Lipoproteins, Diabetes, and Cardiovascular Disease

Diabetes is now a pandemic disease. Moreover, a large number of people with prediabetes are at risk for developing frank diabetes worldwide. Both type 1 and type 2 diabetes increase the risk of atherosclerotic cardiovascular disease (CVD). Even with statin treatment to lower LDL cholesterol, patients with diabetes have a high residual CVD risk. Factors mediating the residual risk are incompletely characterized. An attractive hypothesis is that remnant lipoprotein particles (RLPs), derived by lipolysis from VLDL and chylomicrons, contribute to this residual risk. RLPs constitute a heterogeneous population of lipoprotein particles, varying markedly in size and composition. Although a universally accepted definition is lacking, for the purpose of this review we define RLPs as postlipolytic partially triglyceride-depleted particles derived from chylomicrons and VLDL that are relatively enriched in cholesteryl esters and apolipoprotein (apo)E. RLPs derived from chylomicrons contain apoB48, while those derived from VLDL contain apoB100. Clarity as to the role of RLPs in CVD risk is hampered by lack of a widely accepted definition and a paucity of adequate methods for their accurate and precise quantification. New specific methods for RLP quantification would greatly improve our understanding of their biology and role in promoting atherosclerosis in diabetes and other disorders.

The VLDL receptor plays a key role in the metabolism of postprandial remnant lipoproteins

A new concept to account for the process of postprandial remnant lipoprotein metabolism is proposed based on the characteristics of lipoprotein particles and their receptors. The characteristics of remnant lipoprotein (RLP) were investigated using an immuno-separation method. The majority of the postprandial lipoproteins increased after fat intake was shown to be VLDL remnants, not chylomicron (CM) remnants, based on the significantly high ratio of apoB100/apoB48 in the RLP and the high degree of similarity in the particle size of the apoB48 and apoB100 carrying lipoproteins, which fluctuate in parallel during a 6 h period after fat intake. The VLDL receptor was discovered as a receptor for TG-rich lipoprotein metabolism and is located in peripheral tissues such as skeletal muscle, adipose tissue, etc., but not in the liver. Postprandial VLDL particles are strongly bound and internalized into cells expressing the VLDL receptor. Ligands that bind to VLDL receptor, such as LPL and Lp(a), present in RLP. The presence of various specific ligands in VLDL remnants may enhance the capacity for binding to the VLDL receptor, which play the role primarily for energy delivery to the peripheral tissues, but is also a causal factor in atherogenic diseases when excessively and/or continuously remained in plasma.

Hypothesis: Postprandial remnant lipoproteins are the causal factors that induce the insulin resistance associated with obesity

We have long thought that remnant lipoproteins (RLP) in plasma are significantly increased as the result of disturbed lipoprotein metabolism followed by obesity and insulin resistance. Therefore, it was believed that insulin resistance causes and enhances RLP formation. In contrast, this hypothesis states that RLP induces insulin resistance as the result of obesity associated with the excessive fat intake. The majority of plasma TG increased after fat intake is TG in RLP (RLP-TG) and the majority of postprandial RLP is VLDL remnants, not CM remnants. RLP is newly formed lipoproteins primarily for energy supply against starvation, like blood sugar after carbohydrate intake. Since RLP bearing apoE, LPL and Lp(a) function as ligands for the VLDL receptor, RLP interacts with the VLDL receptor in visceral fat adipocytes and stored as TG similar to excessive blood sugar. However, the excessive VLDL remnants induces obesity and its associated insulin resistance, which plays a major role as the initiator of metabolic domino effects, similar to blood sugar primarily serving as an energy supply to protect against starvation.

A Dipeptidyl Peptidase-4 Inhibitor, Teneligliptin, Decreases Plasma Triglyceride-Rich Lipoprotein Remnants in Diabetic Patients with Chronic Kidney Disease Undergoing Hemodialysis

Objective

A high plasma level of remnant-like particle cholesterol (RLP-C), which is equivalent to triglyceride-rich lipoprotein remnant, is an important coronary risk marker. RLP-C level is high, independent of other plasma lipids, in patients with chronic kidney disease (CKD) undergoing hemodialysis. The effect of teneligliptin, a dipeptidyl peptidase (DPP)-4 inhibitor, on plasma levels of RLP-C in patients with diabetes mellitus and CKD under hemodialysis was studied.

Methods

Teneligliptin 20 mg/day was administered to 15 patients with diabetes and CKD undergoing hemodialysis for 12 weeks. Ten patients with diabetes and CKD undergoing hemodialysis were allocated to the control group. Blood was sampled following a 12-h fast. Fasting plasma glucose (FPG), C-peptide, triglyceride, low-density lipoprotein (LDL)-cholesterol (C), high-density lipoprotein (HDL)-C, RLP-C, apolipoprotein (apo) B, oxidized LDL, lipoprotein lipase, and glycated hemoglobin (HbA1c) were measured.

Results

HbA1c decreased in the teneligliptin group but significantly increased in the control group. FPG and RLP-C significantly decreased in the teneligliptin group. Plasma lipoprotein-related parameters except RLP-C were not affected by teneligliptin treatment.

Conclusion

Teneligliptin treatment significantly reduced plasma levels of RLP-C, FPG, and HbA1c in patients with diabetes with CKD who are undergoing hemodialysis.

Postprandial remnant lipoproteins as targets for the prevention of atherosclerosis

PURPOSE OF REVIEW

Oxidized low-density lipoprotein (Ox-LDL) and chylomicron remnants were previously proposed as the most atherogenic lipoproteins for the causal lipoproteins of atherosclerosis. However, there are still controversies on these hypothesizes. Therefore, we have proposed a new hypothesis based on our recent findings of remnant lipoproteins (RLPs) in postprandial plasma.

RECENT FINDINGS

Plasma RLP-C and RLP-TG increased significantly after fat load. More than 80% of the increased triglycerides after fat load consisted of the triglycerides in RLP, which contained greater amount of apoB100 than apoB48 particles as mostly very low density lipoproteins (VLDL) remnants. The majority of lipoprotein lipase (LPL) in plasma was found in RLP as RLP-LPL complex, which is released into circulation after hydrolysis. LPL activity and concentration in plasma did not increase after food intake associated with the insufficient hydrolysis of chylomicrons and VLDL and resulted in the significant increase of RLP-TG. Plasma LPL was inversely correlated with RLP particle size and number.

SUMMARY

VLDL remnants have been shown as the major atherogenic lipoproteins in postprandial plasma associated with LPL activity as the targets for prevention of atherosclerosis. We also proposed a new definition of RLPs, 'LPL bound TG-rich lipoproteins' based on the findings of RLP-LPL complex.

Update on the laboratory investigation of dyslipidemias

The role of the clinical laboratory is evolving to provide more information to clinicians to assess cardiovascular disease (CVD) risk and target therapy more effectively. Current routine methods to measure LDL-cholesterol (LDL-C), the Friedewald calculation, ultracentrifugation, electrophoresis and homogeneous direct methods have established limitations. Studies suggest that LDL and HDL size or particle concentration are alternative methods to predict future CVD risk. At this time there is no consensus role for lipoprotein particle or subclasses in CVD risk assessment. LDL and HDL particle concentration are measured by several methods, namely gradient gel electrophoresis, ultracentrifugation-vertical auto profile, nuclear magnetic resonance and ion mobility. It has been suggested that HDL functional assays may be better predictors of CVD risk. To assess the issue of lipoprotein subclasses/particles and HDL function as potential CVD risk markers robust, simple, validated analytical methods are required. In patients with small dense LDL particles, even a perfect measure of LDL-C will not reflect LDL particle concentration. Non-HDL-C is an alternative measurement and includes VLDL and CM remnant cholesterol and LDL-C. However, apolipoprotein B measurement may more accurately reflect LDL particle numbers. Non-fasting lipid measurements have many practical advantages. Defining thresholds for treatment with new measurements of CVD risk remain a challenge. In families with genetic variants, ApoCIII and lipoprotein (a) may be additional risk factors. Recognition of familial causes of dyslipidemias and diagnosis in childhood will result in early treatment. This review discusses the limitations in current laboratory technologies to predict CVD risk and reviews the evidence for emergent approaches using newer biomarkers in clinical practice.

Atherogenic postprandial remnant lipoproteins; VLDL remnants as a causal factor in atherosclerosis

Oxidized LDL (Ox-LDL) and chylomicron (CM) remnants have been suggested to be the most atherogenic lipoproteins that initiate and exacerbate coronary atherosclerosis. In this review, we propose a hypothesis of the causal lipoproteins in atherosclerosis based on our recent findings on postprandial remnant lipoproteins (RLP). Plasma RLP-C and RLP-TG increased significantly after food intake, especially a fat load. More than 80% of the TG increase after the fat load consisted of the TG in RLP, which contained significantly greater apoB100 than apoB48 particles as VLDL remnants. The majority of the LPL in non-heparin plasma was found in RLP as an RLP-LPL complex and released into the circulation after hydrolysis. Plasma LPL did not increase after food intake, which may have caused the partial hydrolysis of CM and VLDL as well as the significant increase of RLP-TG in the postprandial plasma. LPL was inversely correlated with the RLP particle size after food intake. We showed that VLDL remnants are the major atherogenic lipoproteins in the postprandial plasma associated with insufficient LPL activity and a causal factor in the initiation and progression of atherosclerosis. We also propose "LPL bound TG-rich lipoproteins" as a new definition of remnant lipoproteins based on the findings of the RLP-LPL complex in the non-heparin plasma.

Postprandial Hyperlipidemia and Remnant Lipoproteins

Fasting hypertriglyceridemia is positively associated with the morbidity of coronary heart disease (CHD), and postprandial (non-fasting) hypertriglyceridemia is also correlated with the risk status for CHD, which is related to the increase in chylomicron (CM) remnant lipoproteins produced from the intestine. CM remnant particles, as well as oxidized low density lipoprotein (LDL) or very low density lipoprotein (VLDL) remnants, are highly atherogenic and act by enhancing systemic inflammation, platelet activation, coagulation, thrombus formation, and macrophage foam cell formation. The cholesterol levels of remnant lipoproteins significantly correlate with small, dense LDL; impaired glucose tolerance (IGT) and CHD prevalence. We have developed an assay of apolipoprotein (apo)B-48 levels to evaluate the accumulation of CM remnants. Fasting apoB-48 levels correlate with the morbidity of postprandial hypertriglyceridemia, obesity, type III hyperlipoproteinemia, the metabolic syndrome, hypothyroidism, chronic kidney disease, and IGT. Fasting apoB-48 levels also correlate with carotid intima-media thickening and CHD prevalence, and a high apoB-48 level is a significant predictor of CHD risk, independent of the fasting TG level. Diet interventions, such as dietary fibers, polyphenols, medium-chain fatty acids, diacylglycerol, and long-chain n-3 polyunsaturated fatty acids (PUFA), ameliorate postprandial hypertriglyceridemia, moreover, drugs for dyslipidemia (n-3 PUFA, statins, fibrates or ezetimibe) and diabetes concerning incretins (dipeptidyl-peptidase IV inhibitor or glucagon like peptide-1 analogue) may improve postprandial hypertriglyceridemia. Since the accumulation of CM remnants correlates to impaired lipid and glucose metabolism and atherosclerotic cardiovascular events, further studies are required to investigate the characteristics, physiological activities, and functions of CM remnants for the development of new interventions to reduce atherogenicity.

High level of plasma remnant-like particle cholesterol may predispose to development of hypertension in normotensive subjects

BACKGROUND

Remnant-like lipoprotein particle cholesterol (RLP-C) is a highly atherogenic factor. RLP-C induces endothelial dysfunction and is associated with hyperinsulinemia. This study was designed to determine whether high plasma RLP-C levels predispose to the development of hypertension in subjects with normal blood pressure (BP).

METHODS

A total of 1,485 subjects aged >40 years in a Japanese Cohort of the Seven Countries Study received health examinations. We examined BP, anthropometric parameters, and blood chemistries, including fasting RLP-C levels. RLP-C levels were measured by an immune-separation method. We excluded from the analysis 676 subjects who had hypertension (BP ≥ 140/90mm Hg), or were on antihypertensive medication, and/or were on antihyperlipidemic medication at baseline. Ten years later, 681 subjects were re-examined.

RESULTS

Of 681 normotensive subjects at baseline, 303 subjects had developed hypertension 10 years later. Baseline RLP-C level was significantly higher (P < 0.01) in the subjects who developed hypertension than in those who remained normotensive (3.7±1.9 vs. 3.3±1.6mg/dl). Multivariable logistic regression analysis demonstrated that baseline RLP-C was a significant factor for incident hypertension after adjustments for homeostasis model assessment index and other hypertension-related factors (odds ratio = 1.05, 95% CI = 1.00-1.10; P = 0.04).

CONCLUSIONS

A high level of plasma RLP-C in normotensive subjects may predispose to the development of hypertension in a population of community-dwelling Japanese.

Effect of L-thyroxine replacement on apolipoprotein B-48 in overt and subclinical hypothyroid patients

Apolipoprotein B-48 (ApoB-48) is a constituent of chylomicrons and chylomicron remnants, and is thought to be one of the risk factors for atherosclerosis. We evaluated the effect of L-thyroxine (L-T(4)) replacement on serum ApoB-48 levels in patients with primary hypothyroidism. Eighteen patients with overt hypothyroidism (OH) and 18 patients with subclinical hypothyroidism (SH) participated in the study. The lipid profiles, including ApoB-48, were measured in patients with hypothyroidism before and 3 months after L-T(4) replacement. After L-T(4) replacement, the serum concentrations of all lipoproteins, exclusive of lipoprotein(a) (Lp(a)), were significantly decreased in patients with OH. In patents with SH, the serum levels of total cholesterol (TC), non-high-density lipoprotein cholesterol (non-HDL-C), remnant-like particle cholesterol (RLP-C), apolipoprotein B (ApoB), and ApoB-48 decreased significantly after L-T(4) replacement. The serum levels of triglycerides (TG), HDL-C, low-density lipoprotein cholesterol (LDL-C), apolipoprotein A1 (ApoA-1), and Lp(a) did not change significantly. In all 36 patients, the reduction in the ApoB-48 levels correlated significantly with the reduction in TSH levels (r = 0.39, P<0.05). This study showed clearly that L-T(4) replacement might reduce serum levels of ApoB-48 in both OH and SH patients. Such altered serum levels of ApoB-48 in patients with OH and SH may be related to the disturbed metabolism of chylomicron remnants in patients with hypothyroidism.

Triglyceride-rich lipoproteins in chronic kidney disease patients undergoing maintenance haemodialysis treatment

OBJECTIVE

Plasma triglyceride (TG) levels were reported to be high in chronic kidney disease (CKD) patients undergoing haemodialysis (HD) treatment. One of the atherogenic causes of hypertriglyceridemia is the increase in TG-rich lipoprotein remnants, which are equivalent to remnant-like particle cholesterol (RLP-C). Here, we compared the plasma levels of TG, a representative indicator of TG-rich lipoproteins and RLP-C, as well as the TG/RLP-C ratio between CKD patients undergoing HD and controls, in an effort to elucidate the atherogenicity of TG-rich lipoproteins in CKD patients on HD.

MATERIALS AND METHODS

Plasma lipid and apo(lipo)protein levels and the TG/RLP-C ratio were compared between 49 CKD patients undergoing HD and 627 controls. Blood sampling for lipid and apoprotein analysis was performed in a 12-h fasting state. Controls were divided into four subgroups according to TG level (from highest to lowest). RLP-C and apo(lipo)proteins were measured using the immunoprecipitation method and turbidimetric immunoassay, respectively. In addition, a comparison between HD patients and age-, gender-, and plasma TG level-matched controls was performed.

RESULTS

Plasma TG levels were 107 ± 70 (mean ± SD) mg/dl in HD patients and 115 ± 72 mg/dl in controls. Plasma RLP-C levels were 6.7 ± 4.5 mg/dl in HD patients and 4.6 ± 3.5 mg/dl in the controls (p < 0.0001). RLP-C levels decreased in descending order from the highest to the lowest TG group in controls. RLP-C levels were higher in HD patients than in controls with plasma TG levels of < 150 mg/dl (p < 0.0001). TG/RLP-C ratios were 19.0 ± 12.0 in HD patients and 25.9 ± 9.5 in controls (p < 0.0001). This ratio was significantly lower in HD patients than in all four TG subgroups. The comparison between HD patients and age-, gender-, plasma TG-matched controls revealed identical results.

CONCLUSION

Plasma RLP-C levels were high, and the TG/RLP-C ratio was low in CKD patients undergoing HD treatment. These findings indicate that total plasma TG-rich lipoprotein levels were not increased, but the distribution of plasma TG-rich lipoproteins were skewed towards remnant fractions in CKD patients undergoing HD treatment; these plasma TG-rich lipoproteins appear to be more atherogenic than those in controls.

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.

Particle size of apoB-48 carrying lipoproteins in remnant lipoproteins isolated from postprandial plasma

BACKGROUND

Particle size of apoB-48 carrying lipoproteins in remnant-like lipoprotein particles (RLP) in postprandial plasma has not been well characterized.

METHODS

Plasma lipids, lipoproteins and apolipoproteins in 12 healthy subjects were analysed after an oral fat load. RLP isolated by immunoaffinity gel from plasma of a normolipidaemic and a hyperlipidaemic subject in four hours after an oral fat load was fractionated by high-performance liquid chromatography (HPLC) and monitored by total cholesterol (TC), triglycerides (TG), apoB-48 and apoB-100.

RESULTS

TC, low-density lipoprotein (LDL)-C and apoB did not change after an oral fat load, while TG, RLP-C, RLP-TG and apoB-48 increased significantly in postprandial plasma. HPLC profiles monitored by TC and TG revealed that major lipoproteins increased in RLP after an oral fat load was VLDL size particles. The percentage of RLP-TG in total TG and the ratio of RLP-TG/RLP-C were significantly increased in four hours after an oral fat load compared with the fasting state (P < 0.01). RLP in four hours after an oral fat load fractionated by HPLC and monitored by TC, TG, apoB-48 and apoB-100 revealed that VLDL size or smaller particles were the major lipoproteins.

CONCLUSIONS

ApoB-48 carrying lipoproteins in RLP isolated from a normolipidaemic and a hyperlipidaemic subject after an oral fat load showed a similar particle size with apoB-100 carrying VLDL remnants. Therefore, the most apoB-48 carrying particles found in postprandial RLP can be classified as CM remnants. The majority of remnants in the postprandial state were not CM remnants, but VLDL remnants.

Nuclear Magnetic Resonance Lipoprotein Subclasses and the APOE Genotype Influence Carotid Atherosclerosis in Patients with Systemic Lupus Erythematosus

Objective.

Patients with systemic lupus erythematosus (SLE) have accelerated atherosclerosis. Since the conventional lipid profile (total plasma cholesterol, triglycerides, low and high density lipoprotein cholesterol) is not consistently altered in SLE, we hypothesized that investigation of lipoprotein subclasses would improve prediction of risk of atherosclerosis in these patients.

Methods.

As a quantitative index of atherosclerosis, we measured the carotid intima-media thickness (IMT) in 68 patients with SLE and related the atherosclerosis to a detailed lipoprotein profile generated using nuclear magnetic resonance (NMR). We measured the cholesterol transported by the pool of remnant lipoproteins (RLPc) and evaluated the modulatory effect of the APOE genotype on the lipoprotein subclass profile and atherosclerosis associated with SLE.

Results.

Circulating lipoprotein remnant particles [RLPc and intermediate density lipoprotein (IDL)] were positively correlated with IMT, and among them, the indicator that explained 20.2% of the variability in carotid atherosclerosis measured in these patients was IDL, as assessed by NMR. Carriers of the APOE2 allele were at increased risk due to a significant accumulation of IDL particles.

Conclusion.

Lipoprotein subclasses are more associated with subclinical atherosclerosis in patients with SLE than the lipid variables that are routinely measured. The IDL fraction, which is significantly modulated by the APOE genotype, is the most strongly, significantly, and positively correlated with IMT.

Comparative study of bezafibrate and pravastatin in patients with coronary artery disease and high levels of remnant lipoprotein

BACKGROUND

Remnant lipoproteinemia is a strong risk factor for cardiovascular (CV) diseases. This study examined which of 2 common lipid-lowering drugs (fibrates and statins) is more effective in patients with remnant lipoproteinemia and if lowering remnant lipoprotein levels can reduce CV risk.

METHODS AND RESULTS

Remnant lipoprotein levels were measured by an immunoseparation method (remnant-like lipoprotein particles cholesterol: RLP-C) in 274 patients with coronary artery disease and high RLP-C levels (>or=5.0 mg/dl). They were randomly assigned to receive bezafibrate (200-400 mg/day) or pravastatin (10-20 mg/day), and were prospectively followed-up for 1 year or until the occurrence of CV events. Complete follow-up data were obtained in 180 patients. RLP-C levels at 1 year of treatment were reduced more by bezafibrate than pravastatin (37% and 25% from baseline, respectively). During follow-up, bezafibrate-treated patients had 3 CV events, compared with 12 events in pravastatin-treated patients (P<0.01). In multivariate logistic regression analysis, a decrease in RLP-C level was significantly associated with a reduction in CV events after adjustment for treatment group and changes in levels of other lipids.

CONCLUSIONS

Bezafibrate therapy decreased RLP-C levels to a greater extent than pravastatin and a decrease in RLP-C level may be associated with a reduction in CV events in patients with high RLP-C levels.

Triglyceride-rich lipoproteins and plasma lipid transport

This memoir provides a history of the triglyceride-rich lipoproteins of blood plasma over the last half-century. As precursors of low-density lipoproteins and in their own right, triglyceride-rich lipoproteins are essential to the formation of atherosclerotic plaques and to consequent ischemic vascular disease. The author recounts research at the National Heart Institute during 1953 to 1956 and continuing thereafter at the University of California San Francisco. Emphasis is placed on key insights arising from investigations of human disease, the interplay of fatty acid and triglyceride-transport involving the liver, small intestine, adipose tissue and muscle, and the role of the liver in the synthesis and catabolism of atherogenic lipoproteins.

Dietary fats, cerebrovasculature integrity and Alzheimer's disease risk

An emerging body of evidence is consistent with the hypothesis that dietary fats influence Alzheimer's disease (AD) risk, but less clear is the mechanisms by which this occurs. Alzheimer's is an inflammatory disorder, many consider in response to fibrillar formation and extracellular deposition of amyloid-beta (Abeta). Alternatively, amyloidosis could notionally be a secondary phenomenon to inflammation, because some studies suggest that cerebrovascular disturbances precede amyloid plaque formation. Hence, dietary fats may influence AD risk by either modulating Abeta metabolism, or via Abeta independent pathways. This review explores these two possibilities taking into consideration; (i) the substantial affinity of Abeta for lipids and its ordinary metabolism as an apolipoprotein; (ii) evidence that Abeta has potent vasoactive properties and (iii) studies which show that dietary fats modulate Abeta biogenesis and secretion. We discuss accumulating evidence that dietary fats significantly influence cerebrovascular integrity and as a consequence altered Abeta kinetics across the blood-brain barrier (BBB). Specifically, chronic ingestion of saturated fats or cholesterol appears to results in BBB dysfunction and exaggerated delivery from blood-to-brain of peripheral Abeta associated with lipoproteins of intestinal and hepatic origin. Interestingly, the pattern of saturated fat/cholesterol induced cerebrovascular disturbances in otherwise normal wild-type animal strains is analogous to established models of AD genetically modified to overproduce Abeta, consistent with a causal association. Saturated fats and cholesterol may exacerbate Abeta induced cerebrovascular disturbances by enhancing exposure of vessels of circulating Abeta. However, presently there is no evidence to support this contention. Rather, SFA and cholesterol appear to more broadly compromise BBB integrity with the consequence of plasma protein leakage into brain, including lipoprotein associated Abeta. The latter findings are consistent with the concept that AD is a dietary-fat induced phenotype of vascular dementia, reflecting the extraordinary entrapment of peripherally derived lipoproteins endogenously enriched in Abeta. Rather than being the initiating trigger for inflammation in AD, accumulation of extracellular lipoprotein-Abeta may be a secondary amplifier of dietary induced inflammation, or possibly, simply be consequential. Clearly, delineating the mechanisms by which dietary fats increase AD risk may be informative in developing new strategies for prevention and treatment of AD.

Remnant lipoproteins as strong key particles to atherogenesis

Recent epidemiologic studies have revealed that hypertriglyceridemia is associated with atherosclerosis independent of other coronary risk factors. However, it is difficult to select patients at high risk for coronary artery disease using only serum triglyceride levels compared with low-density lipoprotein cholesterol levels since multiple factors are associated with elevating triglycerides. Atherosclerotic diseases with high triglyceride levels can be found in patients with familial combined hyperlipidemia, diabetes mellitus, and metabolic syndrome, in which remnant lipoproteins accumulate in the circulating blood. Recent researches have paid attention to remnant lipoproteins as atherogenic particles with the development of methods for measuring remnant cholesterol levels and apolipoprotein B-48 levels directly from human serum. Measurement of these parameters in addition to serum triglycerides may help to distinguish high-risk patients and enable us to prevent or suppress the progression of atherosclerotic diseases in those patients. However, questions remain to be answered to evaluate the significance of remnant lipoproteins. Here, we focus on three issues: the underlying problems in measuring remnant lipoprotein cholesterol, the assessment of postprandial hyperlipidemia as an atherogenic condition, and finally a review of our experimental and clinical findings about the mechanisms by which remnant lipoproteins induce atherosclerosis.

Remnant lipoproteins induced proliferation of human prostate cancer cell, PC-3 but not LNCaP, via low density lipoprotein receptor

BACKGROUND

Hypertriglyceridemia has been shown to be one of the risk factors for prostate cancer. In this study, we investigated the effect of remnant lipoproteins on cell growth in prostate cancer cell lines.

METHODS

Remnant lipoproteins were isolated as remnant like particles (RLP) from human plasma. We used RLP for TG-rich lipoproteins and low density lipoproteins (LDL) for cholesterol-rich lipoproteins respectively and examined the effect of lipoproteins on proliferation of PC-3 and LNCaP cells using MTS assays. Moreover, we studied the effect of RLP and LDL treatment on the regulation of lipoprotein receptors in prostate cancer cells to investigate the relationship between lipoprotein-induced cell proliferation and lipoprotein receptor expression using real-time PCR, Western blotting assays and siRNA.

RESULTS

RLP effectively induced PC-3 cell proliferation more than LDL, whereas both RLP and LDL could not induce LNCaP cell proliferation except at a higher concentration of RLP. LDL receptor (LDLr) was expressed in both prostate cancer cells but there was a sharp difference of sterol regulation between two cells. In PC-3 cells, LDL decreased the LDLr expression in some degree, but RLP did not. Meanwhile LDLr expression in LNCaP was easily downregulated by RLP and LDL. Blocking LDLr function significantly inhibited both RLP- and LDL-induced PC-3 cell proliferation.

CONCLUSIONS

This study demonstrated that RLP-induced PC-3 cell proliferation more than LDL; however, both RLP and LDL hardly induced LNCaP cell proliferation. The differences of proliferation by lipoproteins might be involved in the regulation of LDLr expression.

Therapeutic effects of fibrates in postprandial lipemia

Hypertriglyceridemia is observed in many metabolic diseases such as the metabolic syndrome, diabetes mellitus, or mixed dyslipidemia frequently leading to premature coronary heart disease (CHD). Additionally, several studies have shown that postprandial hypertriglyceridemia is pronounced in patients with CHD, metabolic syndrome, hypertension, and other pathologic conditions. The triglyceride-rich lipoprotein remnants accumulating in the postprandial state seem to be involved in atherogenesis and in events leading to thrombosis. Since abnormal postprandial lipemia is associated with pathologic conditions, its treatment is of clinical importance.Fibrates are of significant help in managing hypertriglyceridemia. This review summarizes the effect of fibric acid derivatives on postprandial lipemia. Fibrates decrease the production of and enhance the catabolism of triglyceride-rich lipoproteins through the activation of peroxisome proliferator-activated receptor-alpha. Results of clinical studies with fibrates have confirmed their action in decreasing postprandial triglyceride levels by increasing lipoprotein lipase activity, decreasing apolipoprotein CIII production, and by increasing fatty acid oxidation in the liver.It is concluded that fibrates are effective agents in lowering the postprandial increase in remnant lipoprotein particles and retinyl palmitate. Furthermore, fibrates can also affect the postprandial lipid profile by increasing hepatic lipase levels and in some cases, by reducing cholesterol ester transfer protein activity. The main target of fibrate therapy is to improve fasting hypertriglyceridemia, which is an essential component associated with improving postprandial lipemia. Fibrates are well tolerated by patients and adverse effects have been reported rarely after their administration.

Effects of statin on small dense low-density lipoprotein cholesterol and remnant-like particle cholesterol in heterozygous familial hypercholesterolemia

AIM

The effects of statin on small dense low-density lipoprotein cholesterol (sd-LDL-C) and remnant-like particle cholesterol (RLP-C) levels in heterozygous familial hypercholesterolemia (FH) have not been examined. This study aimed to clarify the effects of statin on sd-LDL-C and RLP-C levels in heterozygous FH.

METHODS

Seventeen patients with heterozygous FH were randomly assigned to 2 mg/day pitavastatin or 10 mg/day atorvastatin. At baseline and 12 weeks after treatment with statin, we measured sd-LDL-C and RLP-C levels.

RESULTS

Sd-LDL-C levels significantly decreased from 43 +/- 24 to 16 +/- 10 mg/dL (-63%, p=0.001) in the pitavastatin group, and from 44 +/- 17 to 19 +/- 10 mg/dL (-55%, p<0.001) in the atorvastatin group. RLP-C levels decreased from 8.4 +/- 2.8 to 6.6 +/- 2.7 mg/dL (-16%, p=0.156) in the pitava-statin group, and from 9.8 +/- 4.7 to 5.9 +/- 5.4 mg/dL (-45%, p=0.044) in the atorvastatin group. There were no significant differences in percent changes of sd-LDL-C (p=0.370) and RLP-C levels (p=0.097) between the two groups.

CONCLUSIONS

Sd-LDL-C measured by the heparin-magnesium precipitation method and RLP-C levels in heterozygous FH were decreased by 12 weeks of statin therapy. Statin might have additional anti-atherogenic effects by reducing not only LDL-C but also sd-LDL-C and RLP-C.

Possible relationship between insulin resistance and remnant-like lipoprotein particles in coronary endothelial dysfunction

BACKGROUND

High insulin resistance and elevated remnant lipoprotein levels both correlate with impaired coronary vascular endothelial function. Hyperinsulinemia induces abnormalities of lipid metabolism. However, the correlation among insulin resistance, remnant lipoproteins, and endothelial function has not been clinically elucidated.

HYPOTHESIS

This study was designed to elucidate the correlation among insulin resistance, remnant lipoproteins, and acetylcholine (ACh)-induced coronary artery response.

METHODS

Forty-nine patients suspected of having ischemic heart disease, but without angiographically significant atherosclerotic coronary artery disease, underwent an ACh provocation test. Fasting venous blood was taken early in the morning on the day coronary angiography was performed. The insulin resistance index (IR) was determined from fasting plasma glucose and insulin concentrations, using the homeostasis model assessment (HOMA). Serum levels of remnant-like lipoprotein particle cholesterol (RLP-C) were measured.

RESULTS

Homeostasis model assessment IR was significantly higher (3.65 +/- 1.38 vs. 0.75 +/- 0.14, p < 0.05) and log-transformed HOMA (Log HOMA) was even more significantly higher (0.20 +/- 0.12 vs. -0.29 +/- 0.08, p < 0.001) in the ACh-positive group (n = 23) than in the ACh-negative group (n = 26). The serum RLP-C level was also higher in the ACh-positive group than in the ACh-negative group (4.37 +/- 0.63 vs. 2.52 +/- 0.18 mg/dl, p < 0.01). Log HOMA and RLP-C levels correlated with each other (R = 0.54, p < 0.001). Multiple regression analysis indicated that only the RLP-C level was a dependent predictor of Log HOMA in various lipid profiles.

CONCLUSIONS

Both high insulin resistance and elevated remnant lipoprotein levels correlated and might have a crucial role in the impairment of coronary vascular endothelial function, even in patients without angiographically significant coronary artery disease.

Remnant lipoprotein density profiling by CsBiEDTA density gradient ultracentrifugation

Remnant lipoproteins (RLPs) are now considered a strong marker of the triglyceride-rich lipoprotein (TRL) class for cardiovascular heart disease. The purpose of this research is to demonstrate the efficacy of a novel method that combines an established immunoseparation assay used to measure the RLP class in human serum with ultracentrifugal density gradient separation. These two methods are combined to obtain an RLP density profile. The immunoseparation effectively removes the non-RLP lipoproteins from serum. The RLPs obtained from the immunoseparation are separated into two density-distinct fractions by ultracentrifugal density gradient separation in CsBiEDTA. It is now clear that IDL is distinct in density and immunoreactivity from the two RLP classes isolated by the immunoseparation and ultracentrifugation. This methodology defines the RLP by density and measures their relative prevalence in the TRL class. When applied to clinical samples, variations in the RLP subclasses in different patients are examined. The differences in the RLP density profile are also examined in fasting and postprandial samples. The RLP density profile significantly increases in the postprandial state versus the fasting state. However, the overall quantity of TRL does not appreciably increase in the postprandial state. This work demonstrates the feasibility of measuring the postprandial state in clinical samples to provide insight into the clearance of RLP by the liver as well as the general atherogenicity of these particles. The major outcome of this research is a novel analytical method that couples immunoseparation and density gradient ultracentrifugation to separate and differentially profile the RLP subclass against its nascent counterparts in the TRL class.

High plasma level of remnant-like particles cholesterol in familial combined hyperlipidemia

CONTEXT

The traditional lipid and lipoprotein levels in patients with familial combined hyperlipidemia (FCH) are relatively mildly elevated and do not fully explain the increased risk of cardiovascular disease (CVD). In other populations, high remnant-like particles cholesterol (RLP-C) levels are an independent risk factor for CVD.

OBJECTIVE

The objective of the study was to investigate whether plasma RLP-C concentrations are elevated in patients with FCH and contribute to the increased prevalence of CVD.

DESIGN, SETTING, PARTICIPANTS

In this cross-sectional study, we studied RLP-C levels in 37 FCH families comprising 582 subjects, of whom 134 subjects were diagnosed FCH based on total cholesterol, triglyceride, and apolipoprotein-B levels. Plasma RLP-C concentrations were determined using an immune-separation technique.

RESULTS

For both men and women, the mean plasma RLP-C concentration (mmol/liter) was 2-fold elevated in FCH patients [0.59 (0.54-0.66) and 0.40 (0.37-0.43), respectively] compared with both normolipidemic relatives [0.27 (0.26-0.29) in male and 0.22 (0.21-0.23) in female, all P<0.000]; and spouses [0.27 (0.23-0.31) in male and 0.24 (0.21-0.27) in female, all P<0.000]. Plasma RLP-C levels above the 90th percentile predicted prevalent CVD, independently of nonlipid cardiovascular risk factors [odds ratio 2.18 (1.02-4.66)] and triglyceride levels [odds ratio 2.35 (1.15-4.83)]. However, in both FCH patients and controls, RLP-C did not provide additional information about prevalent CVD over and above non-high-density lipoprotein cholesterol levels.

CONCLUSIONS

Patients with FCH have 2-fold elevated plasma RLP-C levels, which add to the atherogenic lipid profile and contribute to the increased risk for CVD. However, for clinical practice, non-high-density lipoprotein cholesterol is the best predictor of prevalent CVD.

Effect of weight loss on the postprandial response to high-fat and high-carbohydrate meals in obese women

OBJECTIVE

To assess the effect of weight loss on the plasma lipid and remnant-like lipoprotein cholesterol (RLPc) response to a high-fat or a high-carbohydrate meal in a population of obese women.

DESIGN

Nutritional intervention study.

SUBJECTS

Sixteen obese women (mean body mass index (BMI): 37.6+/-5 kg/m(2)).

METHODS

Subjects were asked to follow an energy-restricted diet (800 kcal/day) for 7 weeks, followed by a 1-week maintenance diet. Before and after weight loss, each participant was given (in random order) two iso-energetic meals containing either 80% fat and 20% protein (the high-fat meal) or 80% carbohydrate and 20% protein (the high-carbohydrate meal). Blood samples were collected over the following 10-h period. A two-way analysis of variance with repeated measures was used to assess the effect of the meal and postprandial time on biological variables and postprandial responses (notably RLPc levels).

RESULTS

Weight loss was associated with a significant decrease in fasting triglyceride (P=0.0102), cholesterol (P<0.0001), low-density lipoprotein cholesterol (P=0.0003), high-density lipoprotein-cholesterol (P=0.0009) and RLPc (P=0.0015) levels. The triglyceride response to the high-fat meal was less intense after weight reduction than before (interaction P<0.002). This effect persisted after adjustment on baseline triglyceride levels. The triglyceride response to the high-carbohydrate meal was biphasic (i.e. with two peaks, 1 and 6 h after carbohydrate intake). After adjustment on baseline values, weight reduction was associated with a trend towards a reduction in the magnitude of the second triglyceride peak (interaction P<0.054). In contrast, there was no difference in postprandial RLPc responses before and after weight loss, again after adjustment on baseline levels.

CONCLUSION

Our data suggest that weight loss preferentially affects postprandial triglyceride metabolism.

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.

Apolipoprotein E enrichment of immuno-separated chylomicron and chylomicron remnants following saturated fatty acids

AIM

We examined the effect of meal fatty acids on lipid and apolipoprotein concentrations of very low density lipoprotein (VLDL) and chylomicron/chylomicron remnants in lipid fractions with a Svedberg flotation rate (Sf) 60-400 and Sf 20-60.

METHODS AND RESULTS

Six healthy middle-aged men received in random order mixed meals enriched with saturated (SFA), polyunsaturated (PUFA) or monounsaturated (MUFA) fatty acids on 3 occasions. VLDL and chylomicron/chylomicron remnants in the lipid fractions were separated by immunoaffinity chromatography against apo B-100. In the Sf 60-400 chylomicron/chylomicron remnants, triacylglycerol and cholesterol concentrations were significantly lower following PUFA compared with SFA and MUFA (P < or = 0.05). Apolipoprotein (apo) E responses were significantly higher after SFA in chylomicron/chylomicron remnants and VLDL compared with PUFA and MUFA (P < 0.007). However, apo B responses (particle number) were higher following MUFA than SFA (P = 0.039 for chylomicron/chylomicron remnants). Composition of the chylomicron/chylomicron remnants (expressed per particle) revealed differences in their triacylglycerol and apo E contents; in the Sf 60-400 fraction, SFA-rich chylomicron/chylomicron remnants contained significantly more triacylglycerol than MUFA (P = 0.028), more apo E than PUFA- and MUFA-rich particles (P < 0.05) and in the Sf 20-60 fraction, more apo E than MUFA (P = 0.009).

CONCLUSION

There are specific differences in the composition of chylomicron/chylomicron remnants formed after saturated compared with unsaturated fatty acid-rich meals which could determine their metabolic fate in the circulation and subsequent atherogenicity.

The oxidative modification hypothesis of atherosclerosis: The comparison of atherogenic effects on oxidized LDL and remnant lipoproteins in plasma

A tremendous number of articles on oxidized LDL (Ox-LDL) and scavenger receptor in macrophage have been published since Steinberg proposed Ox-LDL hypothesis as the major cause of atherosclerosis. This hypothesis has provided strong support for the efficacy of LDL lowering drugs, indicating that lowering LDL means lowering Ox-LDL in vivo. This manuscript proposed a new oxidative modification hypothesis that remnant lipoproteins determined as remnant-like lipoprotein particles (RLP), not LDL are the major oxidized lipoproteins in plasma, resulting from the plasma concentration of these oxidized lipoproteins. Remnant lipoproteins may play a pivotal role for the initiation of atherosclerosis via lectin-like oxidized LDL receptor-1 (LOX-1) in endothelial cells. Isolated remnant lipoproteins were found to be oxidized or susceptible to be oxidized in plasma, not necessary to be further oxidized in vitro as Ox-LDL. High similarity of proatherogenic and proinflammatory properties of isolated Ox-LDL and remnant lipoporteins have been reported and predicted the presence of similar oxidized phospholipids in both lipoproteins as bioactive components. These results suggest the possibility that reducing plasma remnant lipoproteins rather than LDL should be the target for hyperlipidemic therapy especially in patients with metabolic syndrome for the prevention of endothelial dysfunction in the initiation of atherosclerosis.

Accumulation of apoE-enriched triglyceride-rich lipoproteins in patients with coronary artery disease

Triglycerides (TGs) are vehicled by multiple particles with different abilities to promote atherosclerosis. Among plasma TG-rich lipoproteins (TRLs), subspecies may or may not contain apolipoprotein E (apoE) molecules: in this study, we evaluated the relative contribution of apoE-rich and apoE-poor TRLs to coronary atherosclerosis. We selected a group of males with premature coronary artery disease (CAD) without any of the classical nonlipid risk factors and/or high plasma lipid levels and evaluated the plasma concentration of TRL subspecies in comparison with healthy controls. Patients with CAD and controls had total cholesterol and TG levels within the normal range (despite slightly, even if significantly, higher TG levels in patients with CAD) and low-density lipoprotein cholesterol levels near optimal values. Nevertheless, patients with CAD had significantly lower high-density lipoprotein cholesterol, smaller low-density lipoprotein peak particle size, and a reduced HDL2b subfraction than controls. In addition, we observed higher concentrations of total TRL in patients with CAD together with a selective increase in apoE-rich particles. All these data were confirmed after correction for TG levels. We also investigated which parameters were associated with the spread of coronary atherosclerosis. Subjects with a single-vessel disease had selectively lower levels of apoE-rich fractions than patients with a multivessel disease. This was confirmed by multivariate analysis. Patients with a premature CAD free of nonlipid conventional risk factors, despite not having elevated lipid levels, show several lipoprotein abnormalities. Besides known atherogenic alterations, the accumulation of apoE-rich TRL subfractions may represent an additive factor that can potentially promote and initiate the atherosclerotic process.

Relation between charge-based apolipoprotein B-containing lipoprotein subfractions and remnant-like particle cholesterol levels

OBJECTIVE

Both mildly modified LDL subfraction that carries a more-negative electric charge and remnant-like particles (RLP) are closely related to triglyceride (TG) levels. We examined the relation between the RLP-cholesterol (C) level and charge-based apolipoprotein (apo) B-containing lipoprotein subfractions as determined by capillary isotachophoresis (cITP) in patients with hypercholesterolemia.

METHODS AND RESULTS

cITP apo B lipoprotein subfractions were identified by analyzing plasma depleted of the related lipoproteins. While fast-migrating triglyceride-rich lipoprotein (fTRL) subfraction contained both chylomicrons and VLDL fraction, slow TRL (sTRL) only contained VLDL. cITP fLDL also contained VLDL fraction, i.e., beta-VLDL. Levels of cITP fTRL and sTRL were significantly correlated with serum levels of TG, RLP-C, apo C-II, and C-III. Levels of cITP sTRL were also correlated with apo E. Levels of cITP fLDL were positively correlated with not only LDL-C levels but also levels of TG, RLP-C, apo C-II, C-III, and E.

CONCLUSION

cITP fast LDL correlated with RLP-C levels and modified the relation between RLP-C and TG levels.

A brief history of lipid and lipoprotein measurements and their contribution to clinical chemistry

The study of modern lipid chemistry began in the 17th and 18th centuries with early observations by Robert Boyle, Poulletier de la Salle, Antoine François de Fourcroy and others. The 19th century chemist, Chevreul, identified several fatty acids, suggested the name 'cholesterine' for the fatty substance in gallstones, coined the word 'glycerine', and showed that fats were comprised of glycerol and fatty acids. The 20th century brought many advances in the understanding of lipoprotein structure and function, and explored relationships between lipoproteins and disease states. The development of the ultracentrifuge and other lipoprotein separation techniques, and reagents for accurate, standardized quantitative measurement have steadily increased our understanding of the important role of lipoprotein metabolism in both healthy and disease states.

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.

Effect of remnant-like particle on shear-induced platelet activation and its inhibition by antiplatelet agents

Remnant-like particles (RLPs) have been reported to promote atherosclerosis and to have effects on platelet function. We studied the effects of RLP on shear-induced platelet activation and their inhibition by antiplatelet agents in vitro. RLP were separated using two monoclonal antibodies, anti apo B-100 and anti apo A-I. These RLP fractions were added to whole blood (WB) or platelet-rich plasma (PRP) in serial dilution of 1, 10 or 100 microg RLP triglyceride (TG) per ml of total sample volume. These samples were incubated, and then stimulated with a high shear stress of 108 dyn/cm(2). Shear-induced platelet aggregation (SIPA) was calculated from the percentage of single platelet loss. P-selectin expression on platelet surface and platelet-derived microparticle (PMP) generation were measured before and after stimulation with shear stress using flow cytometer. SIPA was significantly enhanced by RLP in WB but not in PRP. This enhancing effect was not dose-dependent and was greatest at 10 microg TG/ml. P-selectin expression induced by shear stress was only enhanced by RLP at a concentration of 100 microg TG/ml in both WB and PRP, while generation of PMP induced by shear stress was only enhanced by RLP at a concentration of 100 microg TG/ml in WB. Aspirin inhibited only the enhancement of SIPA by RLPs, while cilostazol inhibited the enhancement of not only SIPA but also p-selectin expression and PMP generation by RLPs.

Postprandial changes in LDL phenotypes in patients with myocardial infarction

BACKGROUND

Low-density lipoprotein (LDL) particle size is strongly affected by both fasting and postprandial triglyceride levels. We report here that the LDL phenotype shifts toward the smaller phenotype during oral fat tolerance tests (OFTTs) in some patients with myocardial infarction (MI); a condition closely associated with postprandial increases of triglyceride and remnant-like particles (RLPs).

METHODS

Oral fat tolerance tests were performed on 63 MI patients with fasting serum triglyceride levels of less than 2.25 mmol L-1 (= 200 mg dL-1). Remnant-like particles and other serum lipids were compared among patients characterized by three LDL phenotypes based on nondenaturing gradient gel electrophoresis: pattern A (large LDLs, peak LDL particle size > or = 260 A), pattern I (intermediate-sized LDLs, LDL size > 255 A, < 260 A), and pattern B (small, dense LDLs, LDL size < or = 255 A).

RESULTS

The LDL size decreased significantly in patients with the highest tertile of areas under the incremental curves (AUICs) of triglycerides above the fasting levels. The LDL phenotype shifted toward the smaller phenotype after a fat load in three of eight patients with pattern A and in seven of 35 patients with pattern I. The AUICs of triglyceride-rich lipoproteins were significantly higher in these patients than in the patients exhibiting little change in LDL size, whereas the fasting metabolic parameters were similar among the patients of the same LDL phenotype in the fasting state.

CONCLUSION

These results suggest that alimentary lipaemia plays an important role in the remodeling of LDL particles into the more atherogenic small, dense LDLs in patients with MI.

Comparative effects of rosuvastatin and gemfibrozil on glucose, insulin, and lipid metabolism in insulin-resistant, nondiabetic patients with combined dyslipidemia

To evaluate the pharmacologic intervention most likely to decrease cardiovascular disease risk in insulin-resistant patients with combined dyslipidemia, 39 patients with this abnormality were assessed before and after 3 months of treatment with gemfibrozil (1,200 mg/day) or rosuvastatin (40 mg/day) with regard to: (1) steady-state plasma glucose concentration at the end of a 180-minute infusion of octreotide, insulin, and glucose; (2) fasting lipid, lipoprotein, and apolipoprotein concentrations; and (3) daylong glucose, insulin, triglyceride, and remnant lipoprotein cholesterol concentrations in response to breakfast and lunch. The 2 groups were similar at baseline in age, gender, body mass index and in measurements of carbohydrate and lipoprotein metabolism. Neither gemfibrozil nor rosuvastatin enhanced insulin sensitivity or lowered daylong glucose and insulin concentrations in insulin-resistant patients with combined dyslipidemia, but both drugs significantly decreased fasting triglyceride concentrations. However, only rosuvastatin treatment significantly (p <0.05 to <0.001) reduced fasting low-density lipoprotein cholesterol, apolipoprotein B-100, apolipoprotein C-III, apolipoprotein C-III:B particles, the apolipoprotein B-100:apolipoprotein A-I ratio, and increased apolipoprotein A-I (p <0.05). The degree of improvement in fasting and postprandial remnant lipoprotein cholesterol concentrations was significantly greater (p <0.05) in rosuvastatin-treated patients, and this difference in the relative effectiveness of the drugs was also true of the decrease in non-high-density lipoprotein cholesterol concentrations.

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.

Influence of the APOA5 locus on plasma triglyceride, lipoprotein subclasses, and CVD risk in the Framingham Heart Study

Several polymorphisms in the APOA5 gene have been associated with increased plasma triglyceride (TG) concentrations. However, associations between APOA5 and lipoprotein subclasses, remnant-like particles (RLPs), and cardiovascular disease (CVD) risk have been less explored. We investigated associations of five APOA5 single-nucleotide polymorphisms (SNPs; -1131T>C, -3A>G, 56C>G IVS3+ 476G>A, and 1259T>C) with lipoprotein subfractions and CVD risk in 1,129 men and 1,262 women participating in the Framingham Heart Study. Except for the 56C>G SNP, the other SNPs were in significant linkage disequilibria, resulting in three haplotypes (11111, 22122, and 11211) representing 98% of the population. SNP analyses revealed that the -1131T>C and 56C>G SNPs were significantly associated with higher plasma TG concentrations in both men and women. For RLP and lipoprotein subclasses, we observed gender-specific association for the -1131T>C and 56C>G SNPs. Female carriers of the -1131C allele had higher RLP concentrations, whereas in males, significant associations for RLPs were observed for the 56G allele. Moreover, haplotype analyses confirmed these findings and revealed that the 22122 and 11211 haplotypes exhibited different associations with HDL cholesterol concentrations. In women, the -1131C allele was associated with a higher hazard ratio for CVD (1.85; 95% confidence interval, 1.03-3.34; P = 0.04), in agreement with the association of this SNP with higher RLPs.

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.

Remnant Lipoproteins from Patients with Sudden Cardiac Death Enhance Coronary Vasospastic Activity Through Upregulation of Rho-Kinase

OBJECTIVE

Sudden cardiac death (SCD) still remains a serious problem. We have previously shown that remnant-like particles (RLP) are the major risk factor for SCD and that Rho-kinase plays a central role in the molecular mechanism of coronary vasospasm. In this study, we examined whether RLP from patients with SCD upregulate Rho-kinase associated with an enhanced coronary vasospastic activity.

METHODS AND RESULTS

We isolated RLP and non-RLP in very-low-density lipoprotein (VLDL) fraction from SCD patients without coronary stenosis. We performed in vivo study in which we treated the coronary artery with RLP or non-RLP fraction at the adventitia in pigs. After 1 week, intracoronary serotonin caused marked coronary hyperconstriction at the segment treated with RLP fraction but not with non-RLP fraction (P<0.001, n=6), and hydroxyfasudil, a selective Rho-kinase inhibitor, dose-dependently inhibited the spasm in vivo. In organ chamber experiments, serotonin caused hypercontraction of vascular smooth muscle cells (VSMC) from RLP-treated segment, which was significantly inhibited by hydroxyfasudil (P<0.001, n=6). In cultured human coronary VSMC, the treatment with RLP significantly enhanced the expression and activity of Rho-kinase (P<0.05, n=6).

CONCLUSIONS

These results indicate that RLP from SCD patients upregulate Rho-kinase in coronary VSMC and markedly enhance coronary vasospastic activity.