Plasma remnant-like particle lipid and apolipoprotein levels in normolipidemic and hyperlipidemic subjects

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.

Combination of Scutellaria baicalensis and Metformin Ameliorates Diet-Induced Metabolic Dysregulation in Mice via the Gut-Liver-Brain Axis

Scutellaria baicalensis (SB), a herbal medicine, is commonly used to treat metabolic diseases, while Metformin (MF) is a widely used drug for type 2 diabetes. The purpose of this study was to investigate whether co-treatment of SB with MF could produce a potential therapeutic effect on high-fat and high-fructose diet (HFFD)-induced metabolic dysregulation. First, we optimized the dose of SB (100, 200, 400, and 800[Formula: see text]mg/kg) with MF (200[Formula: see text]mg/kg) in HFFD-induced C57BL6J mice. Next, the optimized dose of SB (400[Formula: see text]mg/kg) was co-administered with MF (50, 100, and 200[Formula: see text]mg/kg) in a similar animal model to find the effective combinations of SB and MF. Metabolic markers were determined in serum and tissues using different assays, histology, gene expression, and gut microbial population. The SB and MF co-treatment significantly decreased the body, liver, and VAT weights. The outcome of OGTT was improved, and the fasting insulin, HbA1c, TG, TC, LDL-c, AST, and ALT were decreased, while HDL-c was significantly increased. Histological analyses revealed maintained the integrity of liver, adipose tissue, and intestine prevented lipid accumulation in the liver and intestine and combated neuronal damage in the brain. Importantly, controlled the expression of PPAR[Formula: see text], and IL-6 genes in the liver, and expression of BDNF, Glut1, Glut3, and Glut4 genes in the brain. Treatment-specific gut microbial segregation was observed in the PCA chart. Our findings indicate that SB and MF co-treatment is an effective therapeutic approach for HFFD-induced metabolic dysregulation which is operated through the gut-liver-brain axis.

Familial hypercholesterolemia with extensive coronary artery disease and tuberous and tendinous xanthomas: A case report and mutation analysis

This is a case report of a 38-year-old Syrian refugee male with early-onset extensive atherosclerosis. The physical and laboratory examination were remarkable with severe xanthomas in the upper and lower extremities and with low-density lipoprotein cholesterol (LDL-C) 417 mg/dL, total cholesterol 495 mg/dL, high-density lipoprotein cholesterol 30 mg/dL, and triglycerides 242 mg/dL. LDL-C level responded poorly to the high-dose statin treatment. The genetic analysis indicated that the patient had a large homozygous deletion in LDL receptor gene including the exons 7-14. A 12-kb deletion had occurred between the 2 Alu repetitive sequences that were oriented in opposite directions, one in intron 6 and the other in intron 14. This deletion eliminated exons 7-14, which exactly corresponded to the entire exon sequence coding the epidermal growth factor precursor homology domain. This deletion in LDL receptor was previously reported. This rare case of homozygous familial hypercholesterolemia presenting with multiple large and widely distributed xanthomas implicates the need for novel treatment options in familial hypercholesterolemia patients. The case is a Syrian refugee and emphasizes the urgent need to address orphan disease in refugee populations throughout the world.

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.

A novel posttranscriptional mechanism for dietary cholesterol-mediated suppression of liver LDL receptor expression

It is well-established that over-accumulation of dietary cholesterol in the liver inhibits sterol-regulatory element binding protein (SREBP)-mediated LDL receptor (LDLR) gene transcription leading to a reduced hepatic LDLR mRNA level in hypercholesterolemic animals. However, it is unknown whether elevated cholesterol levels can elicit a cellular response to increase LDLR mRNA turnover to further repress LDLR expression in liver tissue. In the current study, we examined the effect of a high cholesterol diet on the hepatic expression of LDLR mRNA binding proteins in three different animal models and in cultured hepatic cells. Our results demonstrate that high cholesterol feeding specifically elevates the hepatic expression of LDLR mRNA decay promoting factor heterogeneous nuclear ribonucleoprotein (HNRNP)D without affecting expressions of other LDLR mRNA binding proteins in vivo and in vitro. Employing the approach of adenovirus-mediated gene knockdown, we further show that depletion of HNRNPD in the liver results in a marked reduction of serum LDL-cholesterol and a substantial increase in liver LDLR expression in hyperlipidemic mice. Additional studies of gene knockdown in albumin-luciferase-untranslated region (UTR) transgenic mice provide strong evidence supporting the essential role of 3'UTR in HNRNPD-mediated LDLR mRNA degradation in liver tissue. Altogether, this work identifies a novel posttranscriptional regulatory mechanism by which dietary cholesterol inhibits liver LDLR expression via inducing HNRNPD to accelerate LDLR mRNA degradation.

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.

Consuming fructose-sweetened, not glucose-sweetened, beverages increases visceral adiposity and lipids and decreases insulin sensitivity in overweight/obese humans

Studies in animals have documented that, compared with glucose, dietary fructose induces dyslipidemia and insulin resistance. To assess the relative effects of these dietary sugars during sustained consumption in humans, overweight and obese subjects consumed glucose- or fructose-sweetened beverages providing 25% of energy requirements for 10 weeks. Although both groups exhibited similar weight gain during the intervention, visceral adipose volume was significantly increased only in subjects consuming fructose. Fasting plasma triglyceride concentrations increased by approximately 10% during 10 weeks of glucose consumption but not after fructose consumption. In contrast, hepatic de novo lipogenesis (DNL) and the 23-hour postprandial triglyceride AUC were increased specifically during fructose consumption. Similarly, markers of altered lipid metabolism and lipoprotein remodeling, including fasting apoB, LDL, small dense LDL, oxidized LDL, and postprandial concentrations of remnant-like particle-triglyceride and -cholesterol significantly increased during fructose but not glucose consumption. In addition, fasting plasma glucose and insulin levels increased and insulin sensitivity decreased in subjects consuming fructose but not in those consuming glucose. These data suggest that dietary fructose specifically increases DNL, promotes dyslipidemia, decreases insulin sensitivity, and increases visceral adiposity in overweight/obese adults.

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.

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.

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.

Dietary intake of n-6 fatty acids modulates effect of apolipoprotein A5 gene on plasma fasting triglycerides, remnant lipoprotein concentrations, and lipoprotein particle size: the Framingham Heart Study

BACKGROUND

Apolipoprotein A5 gene (APOA5) variation is associated with plasma triglycerides (TGs). However, little is known about whether dietary fat modulates this association.

METHODS AND RESULTS

We investigated the interaction between APOA5 gene variation and dietary fat in determining plasma fasting TGs, remnant-like particle (RLP) concentrations, and lipoprotein particle size in 1001 men and 1147 women who were Framingham Heart Study participants. Polymorphisms -1131T>C and 56C>G, representing 2 independent haplotypes, were analyzed. Significant gene-diet interactions between the -1131T>C polymorphism and polyunsaturated fatty acid (PUFA) intake were found (P<0.001) in determining fasting TGs, RLP concentrations, and particle size, but these interactions were not found for the 56C>G polymorphism. The -1131C allele was associated with higher fasting TGs and RLP concentrations (P<0.01) in only the subjects consuming a high-PUFA diet (>6% of total energy). No heterogeneity by sex was found. These interactions showed a dose-response effect when PUFA intake was considered as a continuous variable (P<0.01). Similar interactions were found for the sizes of VLDL and LDL particles. Only in carriers of the -1131C allele did the size of these particles increase (VLDL) or decrease (LDL) as PUFA intake increased (P<0.01). We further analyzed the effects of n-6 and n-3 fatty acids and found that the PUFA-APOA5 interactions were specific for dietary n-6 fatty acids.

CONCLUSIONS

Higher n-6 (but not n-3) PUFA intake increased fasting TGs, RLP concentrations, and VLDL size and decreased LDL size in APOA5 -1131C carriers, suggesting that n-6 PUFA-rich diets are related to a more atherogenic lipid profile in these subjects.

The adipocyte life cycle hypothesis

The adipocyte life cycle hypothesis states that the metabolic properties of an adipocyte vary predictably during its life cycle: that as an adipocyte matures, it accumulates triacylglycerol (triglyceride) and becomes larger; that the rates of triacylglycerol synthesis and lipolysis are matched within adipocytes and that larger adipocytes, in general, have greater rates of triacylglycerol synthesis and, concurrently, greater rates of lipolysis and, therefore, larger adipocytes have greater rates of transmembrane fatty acid flux; and that the secretion of cytokines can also be related to adipocyte size with larger adipocytes having a more unfavourable profile of cytokine secretion than smaller adipocytes. Adipocyte location is an important modifier of this relationship and the favoured sites of adipocyte proliferation are a function of gender and the position within the life cycle of the organism at which proliferation occurs. The adipocyte life cycle hypothesis posits that the metabolic consequences of obesity depend on whether expansion of adipose tissue is achieved primarily by an increase in adipocyte number or adipocyte size. This hypothesis may explain a variety of previously unanswered clinical puzzles such as the vulnerability of many peoples from South East Asia to the adverse metabolic consequences of obesity.

Remnant lipoproteins and atherosclerosis

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

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.

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.

Biochemical aspects of overtraining in endurance sports : the metabolism alteration process syndrome

Recent studies have shown that endurance overtraining could result from successive and cumulative alterations in metabolism, which become chronic during training. The onset of this process is a biochemical alteration in carbohydrate (saccharide) metabolism. During endurance exercises, the amount of saccharide chains from two blood glycoproteins (alpha(2)-macroglobulin and alpha(1)-acid glycoprotein) was found to have decreased, i.e. concentrations of these proteins remained unchanged but their quality changed. These saccharide chains were probably used for burning liver glycogen stores during exercise. This step was followed by alterations in lipid metabolism. The most relevant aspect of this step was that the mean chain length of blood fatty acids decreased, i.e. the same amount of fatty acids were found within the blood, but overtrained individuals presented shorter fatty acids than well-trained individuals. This suggests that alterations appeared in the liver synthesis of long-chain fatty acids or that higher peroxidation of blood lipoparticles occurred. For the final step of this overtraining process, it was found that these dysfunctions in carbohydrate/lipid metabolism led to the higher use of amino acids, which probably resulted from protein catabolism. The evolution of three protein concentrations (alpha(1)-acid glycoprotein, alpha(2)-macroglobulin and IgG(3)) correlated with this amino acid concentration increase, suggesting a specific catabolism of these proteins. At this time only, overtraining was clinically diagnosed through conventional symptoms. Therefore, this process described successive alterations in exercise metabolism that shifted from the main energetic stores of exercise (carbohydrates and lipids) towards molecular pools (proteins) normally not substantially used for the energetic supply of skeletal muscles. Now, a general biochemical model of the overtraining process may be proposed which includes most of the previously identified metabolic hypotheses.

Structural and functional properties of human plasma high density-sized lipoprotein containing only apoE particles

To investigate the metabolism of HDL-apolipoprotein E (apoE) particles in human plasma, we isolated a fraction of plasma HDL-apoEs that lack apoA-I (HDL-LpE) from subjects with apoE3/3 phenotype by immunoaffinity. Plasma HDL-LpE had a particle size ranging from 9 nm to 18.5 nm in diameter and was characterized by two-dimensional nondenaturing gradient gel electrophoresis as having either gamma-, prebeta1-, prebeta2-, or alpha-electrophoretic mobility. HDL-LpE was also present in the medium of cultured human hepatoma cell lines and monocyte-derived macrophages. The majority of apoE3 was found as a monomeric form in HDL-LpE and floated at density d > 1.21 g/ml. Plasma levels of HDL-LpE in normolipidemic, CETP-deficient, and ABCA1-deficient subjects were 0.72 +/- 0.15 mg/dl (n = 12), 1.77 +/- 0.75 mg/dl (n = 3), and 0.55 +/- 0.11 mg/dl (n = 3), respectively. The ratio of HDL-apoE containing apoA-I to HDL-LpE was significantly higher 4 h after a fat load, representing a 35 +/- 9% increase (n = 3). Isolated plasma HDL-LpE3 was as effective as apoE3, reconstituted HDL particles, or apoA-I in promoting cellular cholesterol efflux. These results demonstrate that 1) plasma HDL-LpE may have hepatogenous and macrophagic origins; 2) HDL-LpE was preserved even with large reductions in apoA-I-containing lipoproteins; 3) HDL-LpE was active in the transfer of apoE to triglyceride-rich lipoproteins, and 4) HDL-LpEs efficiently take up cell-derived cholesterol.

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

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

Postprandial lipemia--effect of lipid-lowering drugs

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

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

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

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

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

The atherogenic plasma remnant-like particle cholesterol concentration is increased in the fasting and postprandial state in active acromegalic patients

BACKGROUND

Premature atherosclerosis is a clinical feature in untreated acromegaly. Increased postprandial lipoprotein remnant levels are associated with premature atherosclerosis. In most studies, remnants have been measured indirectly using retinyl esters (RE) as a chylomicron core label. Remnants can also be directly quantified by immunoseparation using monoclonal antibodies to apolipoprotein (apo) AI and apo B100 to remove nonremnant lipoproteins. Cholesterol is quantified in the remaining apo E-rich remnant fraction (RLP-C).

OBJECTIVE

The aim of the present study was to investigate the role of postprandial lipaemia in patients with acromegaly to further define abnormalities leading to increased susceptibility for atherosclerosis.

PATIENTS

In a case-control study, the plasma postprandial lipoprotein remnant fraction (RLP-C and RE) were analysed in six patients with active acromegaly [two females, four males; aged 53 +/- 9 years; body mass index (BMI), 29 +/- 4 kg/m2] and in six normolipidaemic control subjects (matched for age, gender, BMI and apo E genotype). They underwent an oral vitamin A fat loading test.

RESULTS

Baseline plasma triglycerides (TG) were not significantly different in patients (1.75 +/- 0.71 mM) and controls (1.15 +/- 0.46 mM). Lipoprotein lipase activity was significantly lower in patients than in controls (108 +/- 21 vs. 141 +/- 19 U/l, respectively; P < 0.05). Baseline plasma apo E levels were higher in patients (60.8 +/- 7.9 mg/l) than in controls (48.3 +/- 5.9 mg/l; P < 0.05). No differences were found in the area under the postprandial TG curve (AUC-TG), the incremental AUC-TG (DeltaAUC-TG) and AUC-RE in the Sf < 1000 remnant fraction. However, fasting plasma RLP-C concentrations, isolated by immunoseparation, were increased in patients with active acromegaly (0.41 +/- 0.13 mM) compared to control subjects (0.20 +/- 0.07 mM; P < 0.05). Incremental postprandial RLP-C response (corrected for fasting values) was also significantly elevated in patients (2.14 +/- 1.19 mM/h/l) compared to controls (0.86 +/- 0.34 mM/h/l; P < 0.05). In both groups, the maximal RLP-C concentration was reached between 2 and 4 h.

CONCLUSIONS

In conclusion, the atherogenic postprandial remnants, represented by RLP-C, were significantly elevated at baseline and in the postprandial period, whereas the larger-sized remnants, represented by retinyl esters (Sf < 1000), were not different from controls. The disturbances in the postprandial RLP-C response increased the susceptibility for premature atherosclerosis as observed in patients with acromegaly.

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.

Comparative effects of cerivastatin and fenofibrate on the atherogenic lipoprotein phenotype in proteinuric renal disease

Patients with nephrotic-range proteinuria have impaired clearance of triglyceride-rich lipoproteins. This results in the atherogenic lipoprotein phenotype (mild hypertriglyceridemia, low high-density lipoproteins [HDL], and excess small, dense low-density lipoproteins [LDLIII]). Excess remnant lipoproteins (RLP) are linked to hypertriglyceridemia and may contribute to the atherogenicity of nephrotic dyslipidemia. A randomized crossover study compared the effects of a statin (cerivastatin) and a fibrate (fenofibrate) on LDLIII and RLP in 12 patients with nephrotic-range proteinuria. Cerivastatin reduced cholesterol (21%, P: < 0.01), triglyceride (14%, P: < 0.05), LDL cholesterol (LDL-C; 23%, P: < 0.01), total LDL (18%, P: < 0.01), and LDLIII concentration (27% P: < 0.01). %LDLIII, RLP-C, and RLP triglyceride (RLP-TG) were unchanged. Plasma LDLIII reduction with cerivastatin treatment correlated with LDL-C reduction (r(2) = 34%, P: < 0.05). Fenofibrate lowered cholesterol (19%), triglyceride (41%), very low-density lipoprotein cholesterol (52%), LDLIII concentration (49%), RLP-C (35%), and RLP-TG (44%; all P: < 0.01). Fenofibrate also reduced %LDLIII from 60 to 33% (P: < 0.01). HDL-C (19%, P: < 0.01) increased with fenofibrate treatment; LDL-C and total LDL were unchanged. The reduction in LDLIII concentration and RLP-C with fenofibrate treatment correlated with plasma triglyceride reduction (LDLIII r(2) = 67%, P: < 0.001; RLP cholesterol r(2) = 58%, P: < 0.005). Serum creatinine increased with fenofibrate treatment (14%, P: < 0.01); however, creatinine clearance was unchanged. LDLIII concentration was 187 +/- 85 mg/dl after cerivastatin treatment and 133 +/- 95 mg/dl after fenofibrate treatment. Cerivastatin and fenofibrate reduce LDLIII concentration in nephrotic-range proteinuria. However, atherogenic concentrations of LDLIII remain prevalent after either treatment. Fenofibrate but not cerivastatin reduces remnant lipoproteins. The two treatments seem to reduce LDLIII by different mechanisms, suggesting a potential role for combination therapy to optimize lowering of LDLIII and RLP.

Remnant lipoproteins as therapeutic targets

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

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.

Dyslipidemia and vascular dysfunction in diabetic pigs fed an atherogenic diet

Diabetic patients typically have not only hyperglycemia but also dyslipidemia. Study of the pathogenic components of the diabetic milieu and mechanisms of accelerated atherosclerosis is hindered by inadequate animal models. A potentially suitable animal model for human diabetic dyslipidemia is the pig, because it carries a large fraction of total cholesterol in low-density lipoprotein (LDL), similar to humans. In this study, male Sinclair miniature pigs were made diabetic by destroying the insulin-producing cells of the pancreas with alloxan and then were fed a high fat and high cholesterol diet for comparison with pigs fed a nondiabetic high fat and high cholesterol diet and control pigs. Diabetic pigs exhibited hyperglycemia, but plasma urea nitrogen, creatinine, and transaminase levels were in the normal range, indicating no adverse effects on kidney and liver function. The lipoprotein profile in diabetic pigs was similar to that found in human diabetic patients and was characterized by hypertriglyceridemia (2.8-fold increase versus control and high fat-fed pigs) and a profound shift of cholesterol distribution into the LDL fraction (81%) versus the distribution in high fat-fed (64%) and control (57%) pigs. LDL particles were lipid-enriched and more heterogeneous in diabetic pigs. Apolipoprotein B was distributed among a much broader spectrum of LDL particles, and apolipoprotein E was partially redistributed from high-density lipoprotein to apolipoprotein B-containing lipoproteins in diabetic pigs. There was little change in apolipoprotein A-I distribution. Diabetic pigs showed several early signs of excess vascular disease. In diabetic pigs, 75% of the coronary artery segments showed contractile oscillations in response to prostaglandin F(2alpha) compared with 25% in high fat-fed pigs and 10% in control pigs. Endothelium-dependent relaxation of brachial arteries was nearly abolished in diabetic pigs but unchanged in high fat-fed versus control pigs. Carotid artery Sudan IV staining for fatty streaks was significantly increased only in diabetic pigs. This porcine model should provide insights into the etiology of human diabetic dyslipidemia and facilitate study of peripheral vascular and coronary artery disease in diabetic 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.

Postprandial lipoprotein metabolism and atherosclerosis

Postprandial lipids and lipoproteins have been associated with the presence of cardiovascular disease in a large number of case-control studies. Because the metabolic perturbations around the postprandial situation is a key driving force for cholesterol flux between lipoproteins and tissues, together with the augmented generation of potentially atherogenic cholesterol-rich remnant lipoproteins, several hypotheses have been formulated to link excessive lipoproteinaemic response to fat intake with cardiovascular disease. Recent information on the regulation of lipoprotein remnant formation and its relation to atherosclerosis will enable us to test a pertinent clinical question: is there a direct relationship between repeated elevations of postprandial lipoproteins and development of atherosclerosis?

Evaluation of an immunoseparation method for quantitative measurement of remnant-like particle-cholesterol in serum and plasma

Substantial evidence indicates that triglyceride-rich lipoprotein remnants are atherogenic. Additional research has, however, been limited by available methods for separation and quantification of remnants. We have evaluated an immunoseparation assay developed to measure cholesterol in remnant-like particles (RLP-C). This method uses monoclonal antibodies to human apolipoproteins B-100 and A-I to remove most of the apolipoprotein B-100-containing lipoproteins (namely LDL and nascent VLDL) and apolipoprotein A-I-containing lipoproteins (namely chylomicrons and HDL), leaving behind a fraction of triglyceride-rich lipoproteins, including chylomicron and VLDL remnants, both of which are enriched in apolipoprotein E. Cholesterol in the unbound fraction is measured with a sensitive enzymatic assay. The RLP-C concentration was highly correlated with total triglyceride-rich lipoproteins (sum of VLDL-cholesterol and IDL-cholesterol) separated by ultracentrifugation and by polyacrylamide gel electrophoresis (r = 0.86 and 0.76, respectively). The within-run and run-to-run imprecision (CV) of the assay was ∼6% and 10%, respectively. The assay was not affected by hemoglobin up to 5000 mg/L (500 mg/dL), bilirubin up to 342 mmol/L (20 mg/dL), glucose up to 67 mmol/L (1200 mg/dL), or ascorbic acid up to 170 mmol/L (3.0 mg/dL). In 726 subjects (men, n = 364; women, n = 362) in the US, the 75th percentiles of RLP-C concentration were 0.17 mmol/L (6.6 mg/dL) and 0.23 mmol/L (8.8 mg/dL) in sera obtained after overnight fasting or randomly, respectively. A group of 151 patients from nine US centers and one Canadian center with coronary artery atherosclerosis established by angiography had higher median RLP-C concentrations than 302 gender- and age-matched controls (P &lt;0.05). We conclude that the RLP-C assay compares favorably to ultracentrifugation and electrophoresis and provides a convenient and economical approach to measure triglyceride-rich lipoprotein remnants in routine clinical laboratories.