Effect of diabetes on lipoprotein size

Maternal pea fiber supplementation to a high calorie diet in obese pregnancies protects male offspring from metabolic dysfunction in adulthood

We investigated the influence of maternal yellow-pea fiber supplementation in obese pregnancies on offspring metabolic health in adulthood. Sixty newly-weaned female Sprague-Dawley rats were randomized to either a low-calorie control diet (CON) or high calorie obesogenic diet (HC) for 6-weeks. Obese animals were then fed either the HC diet alone or the HC diet supplemented with yellow-pea fiber (HC + FBR) for an additional 4-weeks prior to breeding and throughout gestation and lactation. On postnatal day (PND) 21, 1 male and 1 female offspring from each dam were weaned onto the CON diet until adulthood (PND 120) for metabolic phenotyping. Adult male, but not female, HC offspring demonstrated increased body weight and feed intake vs CON offspring, however no protection was offered by maternal FBR supplementation. HC male and female adult offspring demonstrated increased serum glucose and insulin resistance (HOMA-IR) compared with CON offspring. Maternal FBR supplementation improved glycemic control in male, but not female offspring. Compared with CON offspring, male offspring from HC dams demonstrated marked dyslipidemia (higher serum cholesterol, increased number of TG-rich lipoproteins, and smaller LDL particles) which was largely normalized in offspring from HC + FBR mothers. Male offspring born to obese mothers (HC) had higher hepatic TG, which tended to be lowered (p = 0.07) by maternal FBR supplementation.Supplementation of a maternal high calorie diet with yellow-pea fiber in prepregnancy and throughout gestation and lactation protects male offspring from metabolic dysfunction in the absence of any change in body weight status in adulthood.

A single 1-h session of moderate-intensity aerobic exercise does not modify lipids and lipoproteins in normolipidemic obese women

The purpose of this study was to quantify the effects of a single session of aerobic exercise on lipids and lipoproteins in women who were sedentary and obese. Women (n = 12) who were premenopausal, sedentary, and obese (body mass index, 30–40 kg·m–2; waist circumference > 88 cm) completed exercise and control trials in a randomly assigned order. Exercise consisted of a single session of treadmill walking at 70% maximum oxygen uptake until 500 kcal were expended, and the control protocol consisted of 60 min of seated rest. Fasting blood samples were collected immediately prior to, 24 h, and 48 h following the exercise and control sessions and analyzed for triglyceride, total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), HDL2-C, and HDL3-C concentrations, and mean LDL, HDL2, and HDL3particle size and cholesterol distributions. A 2 × 3 (trial × time) ANOVA with repeated measures revealed no significant (p > 0.05) changes in the lipid and lipoprotein variables 24 and 48 h following exercise. In contrast to previously published data in lean men and women, a single session of treadmill exercise at 70% maximum oxygen uptake that expended 500 kcal was insufficient to modify lipids and lipoproteins in women who were sedentary, normolipidemic, and obese.

The association of the Clock 3111 T/C SNP with lipids and lipoproteins including small dense low-density lipoprotein: results from the Mima study

BACKGROUND

The clock molecule plays major roles in circadian rhythmicity and regulating lipid and glucose metabolism in peripheral organs. Disruption of the circadian rhythm can lead to cardiometabolic disorders. The existence of small dense low-density lipoprotein (sdLDL) in the circulation, an abnormality of lipid metabolism, in part associated with lifestyle, is also one of risk parameters for cardiometabolic disorders. The 3111 T/C single nucleotide polymorphism (SNP) of the Clock gene has been reported to be associated with lifestyle including morning/evening preference. We investigated whether the Clock 3111 T/C SNP may affect lipids and lipoproteins including sdLDL.

METHODS

In 365 community-dwelling subjects (170 men and 195 women, mean age 63 ± 14 years), the 3111 T/C SNP was genotyped using a fluorescent allele-specific DNA primer assay system. The levels of sdLDL were measured with the electrophoretic separation of lipoproteins employing the Lipoprint system.

RESULTS

The frequency of the Clock 3111 C allele was 0.14. The area of sdLDL did not differ between the subjects with obesity and those without. In carriers of T/T homozygotes, the area of sdLDL was significantly higher compared with carriers of the C allele (T/C or C/C) (1.7 ± 3.4 vs. 0.8 ± 1.9%; p < 0.05). A multiple regression analysis showed that the area of sdLDL was significantly and negatively correlated with the Clock 3111 T/C SNP (β = -0.114, p < 0.05), independently of age, sex, body mass index, and exercise habits.

CONCLUSION

Our findings indicated that the Clock 3111 T/C SNP might be associated with the existence of sdLDL.

Assessment of the validity of the frequently used lipid indices for predicting LDL peak particle diameter in a large cohort of 1955 normal and dyslipidemic subjects

OBJECTIVES

To assess the relationship between commonly used lipid indices and LDL peak particle diameter (LDL-PPD) in a large cohort of 1955 subjects.

DESIGN AND METHODS

Four statistical methods were used for comparison: correlation, concordance analysis, kappa statistics and receiver operating characteristic curve (ROC) analysis.

RESULTS

Plasma triglyceride (TG) levels, TG/HDL-C, LDL-C/apoB, total cholesterol (TC)/TG, LDL-C/TG, and TG/apoB ratios were best correlated with LDL-PPD but none of these ratios accounted for more than 45% of the variation in LDL-PPD. Moreover, across the range of the lipid indices and LDL-PPD quintiles, just under 40% of the values were concordant, with kappas varying between 0.20 and 0.25. Finally, plasma TG levels and the lipid ratios yielded areas under the ROC curve between 0.78 and 0.80.

CONCLUSIONS

The present study does not support the concept that plasma TG levels and the commonly used lipid indices may be considered as adequate surrogates for the small dense LDL phenotype. Our data also indicate that various lipid indices are not superior to plasma TG levels alone as a clinical tool for prediction of the small dense LDL phenotype.

Responses of LDL and HDL particle size and distribution to omega-3 fatty acid supplementation and aerobic exercise

The purpose of this investigation was to determine the independent and combined effects of aerobic exercise and omega-3 fatty acid (n-3fa) supplementation on lipid and lipoproteins. Sedentary, normoglycemic, nonsmoking men (n = 11) were assigned to perform rest and exercise before and during n-3fa supplementation. Exercise consisted of 3 consecutive days of treadmill walking at 65% maximum O(2) consumption for 60 min. Supplementation consisted of 42 days of 4.55 g/day of n-3fa. A two-way factorial ANOVA with repeated measures revealed significant reductions in total cholesterol (P = 0.001, -9.2%) and triglyceride (P = 0.007, -32.4%) concentrations postexercise. In addition, exercise increased LDL peak particle size (P = 0.001) from 26.2 to 26.4 nm, but not HDL size. The n-3fa supplementation resulted in a significant shift in the distribution of HDL-cholesterol (HDL-C) carried by HDL(2b+2a) (P = 0.001, 14.2%) and HDL(3a+3b) (P = 0.001, -22.8%), despite no significant changes in lipid and lipoprotein-cholesterol concentrations. The majority of the shift in HDL-C was noted in HDL(2b) (P = 0.001, 20.9%) and HDL(3a) (P < 0.001, -31.0%) particles. There were no combined effects of exercise and n-3fa supplementation on lipids and lipoproteins. Three consecutive days of aerobic exercise reduced triglyceride and total cholesterol concentrations with a concomitant increase in LDL peak particle size. In contrast, n-3fa supplementation shifted HDL-C from HDL(3) particles to HDL(2) particles, despite no significant changes in HDL(2)-C and HDL(3)-C concentrations. Exercise and n-3fa supplementation do not synergistically improve serum lipids and lipoproteins, but rather independently affect the metabolism of lipids and lipoproteins.

Atorvastatin effect on the distribution of high-density lipoprotein subfractions and human paraoxonase activity

Human serum paraoxonase-1 (PON1) protects lipoproteins against oxidation by hydrolyzing lipid peroxides in oxidized low-density lipoprotein (LDL); therefore, it may protect against atherosclerosis. Changes in the ratio of high-density lipoprotein (HDL) subfractions may alter the stability and the antioxidant capacity of PON1. The aim of the study was to examine the effect of atorvastatin treatment on the distribution of HDL subfractions, LDL size, cholesteryl ester transfer protein (CETP), lecithin-cholesterol acyltransferase (LCAT), and PON1 activity. In all, 33 patients with type IIa and IIb hypercholesterolemia were involved in the study. LDL sizes and HDL subfractions were determined by gradient gel electrophoresis. CETP, LCAT, and PON1 activities were measured spectrophotometrically. Three months of treatment with atorvastatin 20 mg daily significantly increased the HDL3 (+8.13%) and decreased the HDL2a and HDL2b subfractions (-1.57% and -6.55%, respectively). The mean LDL size was significantly increased (+3.29%). The level of oxidized LDL was significantly decreased (-46.0%). The PON1 activity was augmented by the atorvastatin treatment (+5.0%). The CETP activity positively correlated with the HDL2b level and negatively correlated with the HDL3 and HDL2a levels. Atorvastatin alters the HDL subfractions, which may improve its antiatherogenic effect via enhancement of the PON1 activity.

Cardiometabolic risk management in type 2 diabetes and obesity

Type 2 diabetes has become an epidemic in the United States, mainly due to an increase in obesity and sedentary lifestyle. Diabetes is considered a cardiovascular risk equivalent, and cardiovascular death remains the most common cause of death in this population. The cardiovascular complications of diabetes, beginning as early as 10 years before the development of frank hyperglycemia, are strongly linked to the development of insulin resistance and the ensuing metabolic disarray often referred to as the metabolic syndrome. To provide proper therapy for cardiovascular prevention, the downstream effects of insulin resistance must be understood. The most important aspect of treating patients with the metabolic syndrome is the realization that treatment must begin before the development of frank hyperglycemia, particularly if cardiovascular events are to be avoided. Thus, in addition to managing the hyperglycemia that develops with the onset of diabetes, insulin resistance, dyslipidemia, and hypertension must also be properly addressed.

The Trp64Arg polymorphism of the beta3-adrenergic receptor gene is associated with increased small dense low-density lipoprotein in a rural Japanese population: the Mima study

The presence of small dense low-density lipoprotein (sdLDL) is closely associated with an increased risk of developing coronary artery disease. The Trp64Arg polymorphism of the beta(3)-adrenergic receptor (beta(3)-AR) gene is a genetic marker for obesity-related traits. However, any possible association between this polymorphism and sdLDL profiles is unclear. The objective of this study is to investigate the effects of the polymorphism of the beta(3)-AR gene on LDL particle size and sdLDL in a rural Japanese population. Among 277 subjects, body mass index, blood pressure, fasting serum insulin levels, and insulin resistance index (fasting glucose x fasting insulin/405) were determined. The polymorphism of the beta(3)-AR gene was assessed by polymerase chain reaction-restriction fragment length polymorphism using buccal samples. Low-density lipoprotein particle size and sdLDL were measured with the electrophoretic separation of lipoproteins on the LipoPrint System (Quantimetrix, Redondo Beach, CA). The frequency of the beta(3)-AR allele was 0.19. In Arg carriers (Trp/Arg or Arg/Arg), the mean value of LDL particle size was smaller than that of non-Arg carriers (Trp/Trp) (P < .05). The area percentage of sdLDL was higher in Arg carriers (P < .05) than in non-Arg carriers. A multiple regression analysis showed that the area percentage of sdLDL was correlated with the polymorphism of the beta(3)-AR gene (P < .05), independently of age, sex, body mass index, smoking, and insulin resistance index. The present findings suggest that the beta(3)-AR gene polymorphism plays a role in the genetic predisposition to increased sdLDL, independently of insulin resistance.

Impact of low-density lipoprotein particle size on carotid intima-media thickness in patients with type 2 diabetes mellitus

Small low-density lipoprotein (LDL) particles and modifications to LDL such as glycation and oxidation have been linked to the pathogenesis of atherosclerosis in patients with diabetes. We investigated whether LDL particle size, or the levels of glycated LDL or malondialdehyde-modified LDL (MDA-LDL) are associated with carotid intima-media thickness (IMT) in patients with type 2 diabetes mellitus. One hundred seventy-two patients with type 2 diabetes mellitus were enrolled. Carotid IMT was measured by high-resolution ultrasound, and LDL particle size and serum glycated LDL and MDA-LDL levels were determined. The 3 variables were significantly correlated with one another. Univariate analyses defined statistically significant correlations of carotid IMT with LDL size, hemoglobin A(1c), glycated LDL, MDA-LDL, high-density lipoprotein (HDL) cholesterol, and age. The strongest association of IMT was with LDL size (r = -0.406, P < .0001), followed by that with HDL cholesterol (r = -0.225, P = .004). A stepwise multiple regression analysis revealed that LDL size and HDL cholesterol are independent predictors of carotid IMT. Neither glycated LDL nor MDA-LDL had a significant independent contribution to the severity of carotid IMT in the multivariate model. Low-density lipoprotein particle size, but not the glycated LDL or MDA-LDL level, was independently associated with carotid IMT in patients with type 2 diabetes mellitus regardless of antidiabetic and lipid-lowering medications. These results suggest that the measurement of LDL size may be more useful than quantification of modified LDLs for assessing atherosclerosis in patients with type 2 diabetes mellitus. Small LDL particles may be the most important predictor for the risk of cardiovascular disease in diabetic patients.

Polyacrylamide gradient gel electrophoresis of lipoprotein subclasses

High-density (HDL), low-density (LDL), and very-low-density (VLDL) lipoproteins are heterogeneous cholesterol-containing particles that differ in their metabolism, environmental interactions, and association with disease. Several protocols use polyacrylamide gradient gel electrophoresis (GGE) to separate these major lipoproteins into known subclasses. This article provides a brief history of the discovery of lipoprotein heterogeneity and an overview of relevant lipoprotein metabolism, highlighting the importance of the subclasses in the context of their metabolic origins, fates, and clinical implications. Various techniques using polyacrylamide GGE to assess HDL and LDL heterogeneity are described, and how the genetic and environmental determinations of HDL and LDL affect lipoprotein size heterogeneity and the implications for cardiovascular disease are outlined.

Clinical significance of the physicochemical properties of LDL in type 2 diabetes

Atherosclerosis is the leading cause of death in type 2 diabetes. LDL cholesterol and atherosclerosis are related, both in healthy people and those with diabetes; however, people with diabetes are more prone to atheroma, even though their LDL cholesterol levels are similar to those in their non-diabetic peers. This is because LDL particles are modified in the presence of diabetes to become more atherogenic. These modifications include glycation in response to high plasma glucose levels; oxidative reactions mediated by increased oxidative stress; and transfer of cholesterol ester, which makes the particles smaller and denser. The latter modification is strongly associated with hypertriglyceridaemia. Oxidatively and non-oxidatively modified LDL is involved in plaque formation, and may thus contribute to the accelerated atherosclerosis. This review discusses the techniques currently used to determine the physicochemical properties of LDL, and examines the evidence that modification of these properties plays a role in the accelerated atherosclerosis associated with type 2 diabetes.

Mechanisms, Significance and Treatment of Vascular Dysfunction in Type 2 Diabetes Mellitus

Endothelial dysfunction and increased arterial stiffness occur early in the pathogenesis of diabetic vasculopathy. They are both powerful independent predictors of cardiovascular risk. Advances in non-invasive methodologies have led to widespread clinical investigation of these abnormalities in diabetes mellitus, generating a wealth of new knowledge concerning the mechanisms of vascular dysfunction, risk factor associations and potential treatment targets. Endothelial dysfunction primarily reflects decreased availability of nitric oxide (NO), a critical endothelium-derived vasoactive factor with vasodilatory and anti-atherosclerotic properties. Techniques for assessing endothelial dysfunction include ultrasonographic measurement of flow-mediated vasodilatation of the brachial artery and plethysmography measurement of forearm blood flow responses to vasoactive agents. Arterial stiffness may be assessed using pulse wave analysis to generate measures of pulse wave velocity, arterial compliance and wave reflection. The pathogenesis of endothelial dysfunction in type 2 diabetes is multifactorial, with principal contributors being oxidative stress, dyslipidaemia and hyperglycaemia. Elevated blood glucose levels drive production of reactive oxidant species (ROS) via multiple pathways, resulting in uncoupling of mitochondrial oxidative phosphorylation and endothelial NO synthase (eNOS) activity, reducing NO availability and generating further ROS. Hyperglycaemia also contributes to accelerated arterial stiffening by increasing formation of advanced glycation end-products (AGEs), which alter vessel wall structure and function. Diabetic dyslipidaemia is characterised by accumulation of triglyceride-rich lipoproteins, small dense low-density lipoprotein (LDL) particles, reduced high-density lipoprotein (HDL)-cholesterol and increased postprandial free fatty acid flux. These lipid abnormalities contribute to increasing oxidative stress and may directly inhibit eNOS activity. Although lipid-regulating agents such as HMG-CoA reductase inhibitors (statins), fibric acid derivatives (fibrates) and fish oils are used to treat diabetic dyslipidaemia, their impact on vascular function is less clear. Studies in type 2 diabetes have yielded inconsistent results, but this may reflect sampling variation and the potential over-riding influence of oxidative stress, dysglycaemia and insulin resistance on endothelial dysfunction. Results of positive intervention trials suggest that improvement in vascular function is mediated by both lipid and non-lipid mechanisms, including anti-inflammatory, anti-oxidative and direct effects on the arterial wall. Other treatments, such as renin-angiotensin-aldosterone system antagonists, insulin sensitisers and lifestyle-based interventions, have shown beneficial effects on vascular function in type 2 diabetes. Novel approaches, targeting eNOS and AGEs, are under development, as are new lipid-regulating therapies that more effectively lower LDL-cholesterol and raise HDL-cholesterol. Combination therapy may potentially increase therapeutic efficacy and permit use of lower doses, thereby reducing the risk of adverse drug effects and interactions. Concomitant treatments that specifically target oxidative stress may also improve endothelial dysfunction in diabetes. Vascular function studies can be used to explore the therapeutic potential and mechanisms of action of new and established interventions, and provide useful surrogate measures for cardiovascular endpoints in clinical trials.

Combined data from LDL composition and size measurement are compatible with a discoid particle shape

The size of LDL is usually reported as particle diameter, with the implicit assumption that it is a spherical particle. On the other hand, data obtained by cryoelectron microscopy and crystallographic analysis suggest that LDL shape may be discoid. We have investigated LDL particle geometry by combining data on LDL lipid composition with size measurement. The mean LDL diameter of 160 samples was measured by high-performance gel-filtration chromatography (HPGC), and particle volume was calculated from its lipid composition. Assuming a spherical shape, diameters calculated from volume correlated poorly with values obtained by HPGC (R(2) = 0.36). Assuming a discoid shape, particle height was calculated from volume and HPGC diameter. Diameter (20.9 +/- 0.5 nm) and height (12.1 +/- 0.8 nm) were not significantly related to each other (r = 0.14, P = 0.09) and accounted for 23% and 77%, respectively, of the variation in particle volume. In multivariate regression models, LDL core lipids were the main determinants of height (R(2) = 0.83), whereas free cholesterol in the shell, which contributes only 5-9% to LDL mass, was the main determinant of diameter (R(2) = 0.54). We conclude that combined data from composition and size measurements are compatible with a discoid particle shape and propose a structural model for LDL in which free cholesterol plays a major role in determining particle shape and diameter.

Pioglitazone plus a sulphonylurea or metformin is associated with increased lipoprotein particle size in patients with type 2 diabetes

OBJECTIVE

To determine the effect of pioglitazone plus metformin or a sulphonylurea on lipoprotein particle size and subclass distribution in patients with type 2 diabetes.

METHODS

Lipid profiles were determined for blood samples from patients participating in two randomised, double-blind, 24-week studies of pioglitazone 30 mg or 45 mg daily plus either metformin or a sulphonylurea.

RESULTS

Samples from 177 patients were evaluated; 96 of these patients received a sulphonylurea, and 81 received metformin. Pioglitazone combination treatment produced significant increases from baseline for average and peak low-density lipoprotein (LDL) particle size at weeks 12 and 24 (p<0.0001 for each; range 0.29-0.39 nm for average and 0.36-0.55 nm for peak particle size, respectively). Significant shifts in high-density lipoprotein (HDL) and LDL distribution showed an increase in large particles and a decrease in small particles. For pioglitazone plus metformin, significant increases in levels of apolipoprotein (Apo) Al, Apo Al/All-containing HDL, and lipoprotein(a) also were noted, whereas Apo B levels decreased.

CONCLUSIONS

These observed changes are thought to affect the atherogenic profile positively. Therefore, pioglitazone combination treatment may lead to decreased cardiovascular risk in patients with type 2 diabetes.

Improved method for making nondenaturing composite gradient gels for the electrophoretic separation of lipoproteins

Nondenaturing gradient gel electrophoresis continues to be used widely for resolution and characterization of lipoprotein subclasses. Methods for making such gels in the laboratory have been published, but occasionally samples do not display uniform mobilities for all lanes in a laboratory-made gel. To help overcome this limitation, we recommend a modification

Lipid Analyses for the Management of Vascular Diseases

Despite a long history of studies on lipid abnormalities, numerous problems in laboratory technologies and techniques remain unresolved. One of the most commonly tested molecules is low-density lipoprotein (LDL) cholesterol, and a homogenous assay technique for measurement of this molecule has recently been introduced. Although the method represents remarkable technological breakthroughs with great potential for improving lipoprotein analysis, some discrepancies exist among assay protocols. Even for direct measurement of high-density lipoprotein (HDL) cholesterol, which has widely been accepted, there are still large discrepancies among data obtained by different protocols. Oxidatively modified LDL is an independent factor that is considered to directly contribute to the pathogenesis of early atherosclerosis. Lipid peroxidation products, surface charge, and spectrophotometric patterns are all applicable to the evaluation of in vitro oxidation. Only enzyme-linked immunosorbent assays using monoclonal antibodies have a potential for clinical use, but such methods are not yet standardized. There is also increasing evidence for the presence of anti-oxidized LDL autoantibodies in human sera, but the diagnostic utility remains controversial. In addition, small dense LDL has recently attracted much attention as an independent risk factor. Although this is a potential target of oxidization, a robust and simple analytical method does not yet exist. This review presents the current state of laboratory technologies for testing lipid abnormalities.

Low-density lipoprotein subclass and its correlating factors in diabetics

OBJECTIVES

Small dense LDL, low density lipoprotein (LDL) particles with small size and high density, is regarded as a significant risk factor for cardiovascular diseases. Diabetes mellitus is one of the conditions accompanied by increased small dense LDL. We analyzed LDL subclass in type 2 diabetics and normal controls with LipoPrint LDL System to investigate the LDL heterogeneity in diabetics and factors affecting it.

DESIGN AND METHODS

We selected 40 normal controls and 40 type 2 diabetics with fasting blood glucose level over 7.0 mmol/L and HbA1c level over 7%. LDL subclass was determined with LipoPrint LDL System. LipoPrint LDL System fractionates LDL into seven parts (LDL1-7) by size and LDL3 to LDL7 are defined as small-sized LDL. In addition we estimated 'the percent of small-sized LDL over whole LDL' and defined it as 'small-sized LDL proportion'.

RESULTS

Mean small-sized LDL proportion was significantly higher in diabetics (23.4%) than in controls (11.8%) (p<0.001) and small-sized LDL proportion showed positive correlation with blood levels of glucose, HbA1c, total cholesterol, triglyceride, and oxidized LDL and negative correlation with HDL cholesterol level in univariate analysis (p<0.001). Of these parameters, triglyceride, HbA1c, oxidized LDL were statistically significant variables contributing to the small-sized LDL proportion in stepwise multiple regression analysis.

CONCLUSIONS

We analyzed small-sized LDL proportion in type 2 diabetics and found that it was significantly increased in diabetics than control subjects and it was independently correlated with triglyceride, HbA1c, oxidized LDL in descending order, which are reflecting lipid metabolism, glycation, and oxidative stress, respectively.

Localization of genes that control LDL size fractions in baboons

LDL phenotypes are strongly associated with risk of cardiovascular disease and are heritable, although little is known about individual genes that influence them. We investigated genetic control of LDL size-related phenotypes in 634 pedigreed baboons fed three diets contrasting in levels of fat and cholesterol. On a high-cholesterol high-fat diet, we obtained significant evidence for a quantitative trait locus (QTL) for cholesterol concentrations of lipoproteins between 27 and 28 nm (LOD=4.22, genomic P=0.0047) on the baboon homologue of human chromosome 22. For baboons fed a low-cholesterol high-fat diet, we obtained suggestive evidence for a QTL for cholesterol concentrations between 26 and 27 nm (LOD=2.67) on the baboon homologue of human chromosome 5. We speculate that this QTL influences LDL size distributions because LDL median diameters and other LDL fractions also showed peak LOD scores in this same chromosomal region. On a low-cholesterol low-fat basal diet we obtained suggestive evidence for a QTL for cholesterol concentrations of lipoproteins between 26 and 27 nm in diameter (LOD=2.15) on the baboon homologue of human chromosome 16. Thus, we have evidence for three putative QTLs that influence variation in baboon LDL size phenotypes on different diets.

The polymorphism of the beta3-adrenergic receptor gene is associated with reduced low-density lipoprotein particle size

People with a predominance of small, dense low-density lipoprotein (LDL) particles appear to be at increased risk for coronary disease, independent of LDL cholesterol levels. The Trp64Arg variant of the beta3-adrenergic receptor gene is reported to be associated with abdominal obesity and resistance to insulin, and as a consequence, this variant may be a genetic factor in the development of atherosclerosis. Therefore, we investigated whether the beta3-adrenergic receptor polymorphism contributes to the distribution of LDL particle size in 136 Japanese subjects, aged 33 to 59 years, who visited for a routine annual checkup. None of these subjects were taking any medication. The diameter of LDL particles was determined at their peak size using nondenaturing 2% to 16% polyacrylamide gradient gels using fresh plasma samples. The genotype frequencies were: Trp/Trp, 71.3%; Try/Arg, 22.1%; and Arg/Arg, 6.6%, with allele frequencies of 0.82 for Trp64 and 0.18 for Arg64. The subjects with the Arg/Arg genotype had significantly higher levels of fasting plasma insulin and triglycerides and an insulin resistance index of homeostasis model assessment (HOMA-R), and significantly smaller LDL particle size than did the subjects with the Trp/Trp genotype. After adjusting for fasting insulin, body mass index (BMI), and HOMA-R index, there was no longer an observed difference in LDL particle size. The number of the Arg64 allele in individuals was significantly related with fasting insulin, BMI, triglycerides, glycosylated hemoglobin (HbA1c), and fasting glucose, and it was inversely related with LDL particle size. After adjusting for triglyceride, fasting insulin levels, and HOMA-R index, LDL particle size was no longer inversely correlated with the Arg allele. These findings suggest that the Trp64Arg variant in the beta3-adrenergic receptor gene may be associated with reducing LDL particle size, probably due to insulin resistance.

NAD (P) H oxidase p22 phox C242T polymorphism affects LDL particle size and insulin resistance in Japanese subjects

Elevated cardiovascular risk is associated with an increased number of small, dense low-density lipoprotein (LDL) particles, which exhibit increased susceptibility to lipid oxidation, however, the mechanism determining LDL particle size has never been fully elucidated. We have examined the association between the C242T polymorphism of the p22 phox gene, which is a small subunit of vascular NAD(P)H oxidase, and both LDL particle size and clinical characteristics in 260 healthy subjects. Peak LDL particle diameter (LDL-PPD) was measured by continuous disk polyacrylamide gel electrophoresis. Twenty-one of the 217 subjects with the CC genotype showed pattern B (median LDL-PPD under 25.5 nm), whereas, none of the 43 subjects with TC + TT genotypes showed pattern B. The pattern B fraction was significantly larger in the CC group than in the TC + TT group (p = 0.030). The subjects with the CC genotype also showed a significantly higher fasting glucose level, plasma insulin level, and insulin resistance index of homeostasis model assessment (HOMA-R) than those with the TC + TT genotype. Our data demonstrate that variation in the small NAD(P)H oxidase subunit p22 phox gene substantially influences LDL particle size and may also reflect differences in the insulin sensitivity of non-diabetic subjects.

Low-density-lipoprotein peak particle size in a Mediterranean population

BACKGROUND

The predominance of small, dense low-density lipoprotein (LDL) particles ('LDL phenotype B') has been associated with a three-fold increased risk of myocardial infarction, but the feasibility of the identification of small, dense LDL as independent predictors of coronary artery disease risk in population studies remains questioned. Design We evaluated the LDL peak particle size and its relation with other established risk factors for coronary heart disease in a group of 156 randomized subjects living on the Mediterranean island of Ustica (71 males and 85 women, range of age 20-69 years), representing approximately 30% of the total population.

RESULTS

The prevalence of LDL phenotype B subjects was low (approximately 15% in both men and women) and there was a clear trend for both genders in reducing the LDL peak particle size with age. Moreover, LDL phenotype B subjects had higher BMI values, prevalence of diabetes and plasma triglyceride (TG) levels and lower plasma HDL-C concentrations in comparison with LDL phenotype A individuals; in a multivariate analysis, plasma TG levels were the only variable independently associated with LDL peak particle size.

CONCLUSIONS

In this population, which appears to be somewhat protected by premature coronary artery disease, a low prevalence of the LDL pattern B was found in both men and women, and plasma TG could have a key role in regulating the LDL peak particle size. The follow up, still ongoing, will provide useful information on the predictive role of LDL peak particle size on cardiovascular risk, at least in a low-risk population.

Assay methods of modified lipoproteins in plasma

Modified lipoproteins, especially oxidatively modified low-density lipoprotein (Ox-LDL), are present in the plasma of patients with atherosclerosis and related diseases. The modification of LDL is believed to play an important role in the development of atherosclerosis. Thus, measurement of plasma Ox-LDL is essential not only for investigating its relevance to atherosclerotic diseases, but also for diagnosis. Chromatographic methods are effective for indirectly measuring the oxidatively modified state of LDL or directly measuring the modified LDL. Indirect determination can be done by estimating the LDL subfraction, LDL particle size, oxidized amino acids in apolipoprotein B, lipid hydroperoxide or F(2)-isoprostane in LDL. Direct determination of the modified LDL in plasma can be done with chromatographic methods such as anion-exchange chromatography and size-exclusion chromatography. Other methods for estimating the modified state of LDL include electromigration methods such as agarose gel, polyacrylamide gradient gel and capillary electrophoresis. Recently, enzyme-linked immunosorbent assay methods of malondialdehyde (MDA)-LDL and autoantibodies against Ox-LDL have been developed to assess Ox-LDL in plasma. This review article summarizes the detection and assay methods of modified lipoproteins in plasma.

Effects of the ApoE polymorphism on plasma lipoproteins in Mexican Americans

PURPOSE

To evaluate the impact of apolipoprotein E (apoE) genotypes on lipoprotein measurements relative to that of other known cardiovascular risk factors in participants of a large population-based family study.

METHODS

We measured concentrations of apoE, the major constituents of HDL (cholesterol, apoAI), LDL-C (cholesterol and apoB), and fraction of apoE in lipoprotein size classes in 859 participants of the San Antonio Family Heart Study, and then tested the association between the three common apoE genotypes (epsilon2epsilon3, epsilon3epsilon3, and epsilon3epsilon4) and lipoprotein traits using the measured genotype approach to account for residual familial correlations.

RESULTS

Allele frequencies in this population for epsilon2, epsilon3, and epsilon4 were 3.5%, 89.6%, and 6.9%, respectively. As expected, adjusted apoE concentrations were highest in those with epsilon2epsilon3, intermediate in those with epsilon3epsilon3, and lowest in those with epsilon3epsilon4. The concentrations of total cholesterol, LDL-C and apoB were lowest in those with epsilon2epsilon3, intermediate in those with epsilon3epsilon3, and highest in those with epsilon3epsilon4. There was no significant effect of apoE genotypes on triglycerides, HDL-C, or apoAI levels. Compared to subjects with epsilon3epsilon4, subjects with epsilon2epsilon3 had relatively less apoE in LDL and HDL(1), and relatively more in HDL(2) and HDL(3) size fractions. The effect of apoE genotypes was significantly greater on apoB in women than in men. ApoE genotypes accounted for 4.5%, 12.3%, and 4.7% of the total genetic variation in apoB, apoE, and LDL-C, respectively.

CONCLUSION

ApoE genotypes account for a modest, albeit significant, proportion of phenotypic variation in concentrations of LDL-C, apoB, and apoE, and distributions of apoE among lipoproteins in this population; these genotypes have a greater effect on apoB levels in women than in men.

Levels and correlates of LDL and VLDL particle sizes among children: the Bogalusa heart study

Levels of lipids and lipoproteins among children vary by sex and race/ethnicity, and are correlated with age, obesity, and other characteristics. There is, however, little information on the distribution and correlates of low-density lipoprotein (LDL) and very-low-density lipoprotein (VLDL) subclasses in early life. We used nuclear magnetic resonance (NMR) spectroscopy to determine mean LDL and VLDL particle sizes among 10- to 17-year-olds (n=918) who participated in the 1992-94 examination of the Bogalusa heart study. As compared with girls, boys had a smaller (0.1 nm) mean LDL particle size and a larger (0.9 nm) mean VLDL size; furthermore, the average size of VLDL particles increased with age among white boys but not among other children. Although there were also black/white differences in particle sizes, with black children having larger LDL and smaller VLDL particles, these racial contrasts could be attributed to differences in lipid levels. Levels of triglycerides, insulin, and relative weight were associated with the size of VLDL (positive) and LDL (negative) particles. These results suggest that the analysis of lipoprotein subclasses may provide a better understanding of the role of various risk factors in the development of coronary heart disease

LDL particle size in relation to intima-media thickness and plaque occurrence in the carotid and femoral arteries in patients with hypercholesterolaemia

OBJECTIVES

Small LDL particle size has been shown to be associated with coronary artery disease. However, no previous study has been performed relating LDL particle size to ultrasound measurement of atherosclerosis in hypercholesterolaemic subjects. The main aims of the present study were therefore: (i) to investigate the relationship between intima-media thickness (IMT) of the carotid bulb and LDL particle size in patients with primary hypercholesterolaemia (n = 102) and in matched normocholesterolaemic controls (n = 102); and (ii) to investigate the relationship between plaque occurrence in the carotid and femoral arteries and LDL particle size. LDL particle size was determined by subjecting serum to 2-16% polyacrylamide gradient gel electrophoresis.

RESULTS

The results showed that patients with primary hypercholesterolaemia had smaller LDL peak particle size compared with healthy control subjects (P < 0.001 for men, P = 0.006 for women). However, the difference in LDL peak particle size between patients with hypercholesterolaemia and controls disappeared when adjusting for serum triglycerides. There was no association between increasing IMT of the carotid bulb and decreasing LDL peak particle size or between the occurrence of moderate to large plaques in the carotid and femoral arteries and small LDL peak particle size. However, metabolic variables such as serum triglycerides, HDL, blood glucose, body mass index, and also systolic blood pressure were associated with LDL peak particle size.

CONCLUSION

The lack of an association between atherosclerosis, as measured by ultrasound, and small LDL particle size in patients with hypercholesterolaemia implies that other risk factors, such as hypercholesterolaemia and high blood pressure, may overshadow any importance of small LDL particle size.

Genomic searches for genes that influence atherosclerosis and its risk factors

We are performing genomic searches in randomly ascertained families to identify new quantitative trait loci (QTLs) that influence atherosclerosis and its risk factors. The genetic markers used for genomic searches are random microsatellite markers distributed throughout the human chromosomes. These markers are used for linkage analysis with variance component methods to identify QTLs for measured phenotypes related to lipid metabolism and atherosclerosis. We conducted such a genomic search in 477 participants of the San Antonio Family Heart Study. This genomic search identified QTLs on chromosomes 3 and 4 that influence LDL size class, an important risk factor of atherosclerosis. In addition to lipid risk factors, we measured a variety of gene products involved in atherogenesis in the arterial wall (such as adhesion molecules and components of hemostasis). We found QTLs for serum levels of soluble P-selectin on chromosome 15 (LOD = 3.8) and chromosome 12 (LOD = 2.6).

Lipoprotein correlates of LDL particle size

Correlations of low-density lipoprotein (LDL) predominant particle diameters (PPD) were investigated in samples taken from the San Antonio Family Heart Study. A frequency histogram showed LDL PPD occurs in at least two distinct modes, at about 25.5 and 26.9 nm, with the nadir at about 26.2 nm. Triglyceride (TG) concentrations were strongly correlated with LDL PPD, accounting for nearly 50% of the variation. However, examination of the relationship between TG concentrations and LDL PPD showed considerable overlap of the two LDL size categories for samples having intermediate levels of TG (1-3 mmol/l). In order to examine the factors associated with particle size variation within this region of overlap, 163 pairs of samples, which contrasted peak particle diameters, were matched for TG concentrations and for sex and age. In this matched set, LDL-related measures (i.e. LDL-C, apoB, apoE, and TG concentrations) did not differ. However, several high-density lipoprotein (HDL) measures were significantly related to the LDL particle size category. This category predicted a substantial proportion of variation in HDL-C (9.7%) and apoAI (7.5%) concentrations, and in HDL size distributions of cholesterol (13.6%) and apoAI (10.3%). Other traits related to insulin resistance syndrome (IRS) (glucose and insulin concentrations, blood pressure, and adiposity measures) were tested for association with the LDL size category. None of these traits were related to LDL size after adjusting for TG, except fasting and postchallenge glucose concentrations which showed modest correlations (P-values were 0.02 and 0.05, respectively). The data suggest that in addition to the strong effects of TG, there is also an aspect of LDL particle size variation that is strongly associated with variation in HDL concentration and particle size distribution, perhaps reflecting common metabolic determinants of lipoprotein size.

Computerized measurement of LDL particle size in human serum. Reproducibility studies and evaluation of LDL particle size in relation to metabolic variables and the occurrence of atherosclerosis

OBJECTIVES

The main aims of the present research project were to develop and evaluate a new software program for evaluation of LDL particle size applied to the gradient gel electrophoresis methodology without the use of previous ultracentrifugation, and to investigate the relationships among LDL particle size, metabolic variables and atherosclerosis, as measured by ultrasound, in subjects with different degrees of insulin resistance.

METHODS

LDL particle size was determined by polyacrylamide gradient gel electrophoresis.

RESULTS

Coefficient of variation for between-assay experiments was 0.3% (r = 0.99) for measurement of LDL peak particle size. LDL peak particle size was negatively correlated to serum triglycerides, apolipoprotein B, fasting insulin, BMI and diastolic blood pressure and positively correlated to HDL. Furthermore, subjects with moderate to large plaques in the carotid artery had smaller LDL particles compared to subjects without plaques.

CONCLUSIONS

This project resulted in a highly reproducible, computerized method for the analysis of LDL particle size. The data suggest that it is possible to assess LDL particle size in serum without the use of previous ultra-centrifugation. LDL particle size was associated with metabolic variables and the occurrence of moderate to large plaques in the carotid artery.

Dynamic Reaction in a Homogeneous HDL-Cholesterol Assay Visualized by Electron Microscopy

Background: Measurement of HDL-cholesterol (HDL-C) by homogeneous assays with automated analyzers is replacing precipitation methods. However, in this reaction-type assay, interactions between the reagents and lipoproteins remain unknown.

Methods: Electron microscopy was used to investigate the reactions in a homogeneous HDL-C assay. Negative staining with 10 g/L uranyl acetate was performed for lipoprotein visualization by electron microscopy. Observations of the interactions between lipoproteins and the reagents of a polyanion-polymer/detergent assay were achieved by cooling the reaction mixture in ice water. This treatment also allowed observation of the time course of the reaction.

Results: In the first-reagent reaction (polyanion-polymer), every lipoprotein aggregated almost completely. In the second-reagent reaction (enzymes and detergent), only HDL in the lipoprotein aggregates was selectively resolved and reacted enzymatically. Reagent 1 contains two important substances: polyanion and synthetic polymer. Using x-ray microanalysis, we confirmed that aggregation of lipoproteins in the first reaction occurred through interaction with the phosphotungstate of the polyanion.

Conclusion: Electron microscopy morphologically revealed the dynamic reaction in a homogeneous HDL-C assay.

Long-term effects of fish oil on lipoprotein subfractions and low density lipoprotein size in non-insulin-dependent diabetic patients with hypertriglyceridemia

The effects of fish oil on lipoprotein subfractions and low density lipoprotein (LDL) size in non-insulin-dependent diabetes mellitus (NIDDM) patients with hypertriglyceridemia are unknown. To elucidate this, 16 NIDDM hypertriglyceridemic patients (plasma triglyceride 2.25- 5.65 mmol/l, plasma cholesterol < or = 7.75 mmol/l) were randomly assigned to a 6-month period with either moderate amounts of fish oil (n = 8) or placebo (n = 8) after 4 weeks of wash-out and 3 weeks of run-in. Diet and hypoglycemic treatment were unchanged throughout the experiment. LDL size were evaluated at baseline and after 6 months. Three VLDL and LDL subfractions were measured at the end of the two periods. The total lipid concentration of all very low density lipoprotein (VLDL) subfractions was lower at the end of fish oil treatment compared with placebo (large VLDL 124.3 +/- 19.7 mg/dl vs 156.7 +/- 45.5 mg/dl; intermediate VLDL 88.5 +/- 9.5 mg/dl vs 113.9 +/- 23.2 mg/dl; small VLDL 105.9 +/- 9.7 mg/dl vs 128.9 +/- 40.7 mg/dl) (mean +/- SEM), although the difference was not statistically significant. Moreover, at the end of the two treatments, the percentage distribution of VLDL subfractions was very similar (large 37.5 +/- 3.3% vs 37.6 +/- 2.6%, intermediate 27.6 +/- 0.9% vs 31.0 +/- 2.4%; small 34.9 +/- 3.7% vs 31.4 +/- 2.1%). Concerning LDL, no significant change in LDL size was observed after the two treatments (255.4 +/- 2.2 A vs 254.2 +/- 1.7 A, fish oil; 253.7 +/- 2.0 A vs 253.3 +/- 1.7 A, placebo). LDL subfraction distribution was also very similar (large 17 +/- 3% vs 17 +/- 2%; intermediate 62 +/- 3% vs 65 +/- 3%; small 21 +/- 3% vs 18 +/- 2%), at the end of the two periods, confirming the lack of effects on LDL size. In conclusion, our study indicates that in NIDDM patients with hypertriglyceridemia, fish oil does not induce any improvement in LDL distribution and LDL size despite its positive effects on plasma triglycerides.

Increased Ability of LDL from Normolipidemic Type 2 Diabetic Women to Generate Peroxides

Background: We assessed the ability of LDL from 30 type 1 diabetic patients (18 men, 12 women), 65 type 2 diabetic patients (35 men, 30 women), and 35 controls (19 men, 16 women) to generate peroxides. The men and women in the diabetic groups were studied separately and matched for age, body mass index, duration of diabetes, glycohemoglobin, and conventional lipid characteristics according to the presence or absence of hyperlipidemia.

Methods: The ability of LDL to form peroxides was assessed by measuring the thiobarbituric acid-reactive substances corrected for LDL-cholesterol [ratio of malondialdehyde (MDA) to LDL-cholesterol]. LDL particle size was expressed as the ratio of LDL-cholesterol to apolipoprotein B (LDL-cholesterol/apoB).

Results: The MDA/LDL-cholesterol ratio was higher in type 1 and type 2 diabetic patients with hyperlipidemia than in controls. The MDA/LDL-cholesterol ratio was also higher in type 2 normolipidemic women than in controls (P &lt;0.01). The LDL-cholesterol/apoB ratio was lower in type 2 diabetic women than in type 2 diabetic men (P &lt;0.05). The MDA/LDL-cholesterol ratio was negatively correlated with the LDL-cholesterol/apoB ratio (r = −0.78, P &lt;0.001) in hyperlipidemic type 1 (not type 2) diabetic patients. In normolipidemic type 2 diabetic patients, the MDA/LDL-cholesterol ratio was also negatively correlated with the LDL-cholesterol/apoB ratio (r = −0.75, P &lt;0.001) because of the highly significant negative correlation in type 2 diabetic women (r = −0.89, P &lt;0.01).

Conclusions: LDL from well-controlled type 2 diabetic women is smaller and more prone to form peroxides. This could explain why diabetic women are at greater risk of cardiovascular disease.

The fatty acid distribution in low density lipoprotein in diabetes

Atherosclerosis is commonly found in diabetes. There is an association between small dense low density lipoprotein (LDL) phenotype, which is more prevalent in the diabetic state, and atherosclerosis. Small dense LDL is more easily oxidised and it is possible that fatty acid compositional changes, particularly an increase in polyunsaturated fatty acids, could underlie this association. However, there is little information about fatty acids in the different LDL phenotypes in the literature. This study examined LDL subfraction composition in 18 non-insulin-dependent diabetic (NIDDM) patients and 11 control subjects. LDL was isolated and fractionated into LDL 1, 2 and 3 by density gradient ultracentrifugation. NIDDM patients had significantly more fatty acids in all LDL subfractions than control subjects (P<0.01). Palmitic and linoleic acid were significantly greater in all subfractions in the diabetic patients compared to control subjects (P<0.01) and palmitoleic and oleic acids were also greater in LDL1 and LDL2 in diabetic patients (P<0.01). We conclude that in NIDDM fatty acids are increased in all LDL subfractions and this may be the reason for the increased atherosclerosis in diabetes irrespective of phenotype.

Relationship between the apolipoprotein E and angiotensin-converting enzyme genotypes and LDL particle size in Japanese subjects

We investigated whether the apolipoprotein E (apoE) and the angiotensin-converting enzyme (ACE) genotypes contribute to the variance in low-density lipoprotein (LDL) particle size in Japanese subjects (n = 136; M/F= 106/30). ACE polymorphism was associated with neither LDL size nor individual lipid levels. In contrast, the subjects with the epsilon2 allele of the apoE genotype had significantly lower levels of total cholesterol (P = 0.002) and LDL cholesterol (P = 0.004) compared with those without the epsilon2 allele. The subjects with the epsilon4 allele had a significantly smaller LDL particle size than those without the epsilon4 allele (P = 0.012). Separate analyses of the male subjects showed similar associations. A stepwise regression analysis revealed the epsilon4 allele to be an independent contributing variable that could affect LDL particle size. Our results suggest that the apoE genotype is associated with the development of atherosclerotic disease, since the epsilon2 and epsilon4 alleles relate to a decrease in LDL cholesterol levels and a decrease in LDL particle size, respectively.

Is leptin concentration associated with the insulin resistance syndrome in nondiabetic men?

OBJECTIVE

Insulin resistance has been strongly associated with cardiovascular risk. Recently, leptin, a hormone that regulates appetite, has been associated with both obesity and insulin resistance. However, the possible relation of leptin to the insulin resistance syndrome has been controversial.

RESEARCH METHODS AND PROCEDURES

To explore this issue, we examined the relation of leptin to blood pressure, lipid levels, low density lipoprotein (LDL) size, and glucose levels in 87 normoglycemic men.

RESULTS

Leptin levels were significantly correlated with body mass index (BMI) (r = 0.494), fasting insulin (r = 0.576), whole-body glucose disposal rate (GDR) (r = -0.566), fasting glucose (r = 0.510) total triglycerides (r = 0.294), apolipoprotein B (r = 0.223), systolic blood pressure (r = 0.223), and LDL size (r = -0.244). After adjustment for BMI and GDR, leptin levels remained significantly correlated with fasting insulin, fasting glucose, triglyceride, apolipoprotein B, and systolic blood pressure. Leptin levels were also correlated with the number of metabolic risk factors (dyslipidemia, systolic blood pressure, and fasting glucose).

DISCUSSION

We conclude that leptin concentrations may be associated with several cardiovascular risk factors related to insulin resistance syndrome. These associations are only partly explained by leptin's relationship with BMI and GDR.

Dyslipoproteinaemia and hyperoxidative stress in the pathogenesis of endothelial dysfunction in non-insulin dependent diabetes mellitus: an hypothesis

Endothelial dysfunction in non-insulin dependent (Type 2) diabetes mellitus (NIDDM) has implications for the pathogenesis of the two major complications, macrovascular disease and microangiopathy. Endothelial dysfunction is a consequence of a disturbance in the L-arginine/nitric oxide pathway. Its occurrence in NIDDM is well supported by both in vitro and in vivo studies. NIDDM results in diverse abnormalities in lipoprotein metabolism, the most significant being hypertriglyceridaemia which is associated with increased plasma concentrations of small dense LDL and low levels of HDL. Dysglycaemia results in hyperoxidative stress and increased formation of advanced-glycosylation endproducts, both of which enhance the oxidative modification of lipoprotein particles. Based on extensive in vitro studies and on human data, we generate the hypothesis that the development of endothelial dysfunction in NIDDM is a consequence of the effect of dyslipoproteinaemia, in particular increased circulatory concentrations of modified small dense LDL and of hyperoxidative stress on the formation, action and disposal of nitric oxide, by diverse molecular mechanisms; HDL is proposed to have a protective effect on these processes through its enzymic antioxidant properties. The hypothesis proposed is simple, testable and consistent with wide sources of evidence. The practical implications of the hypothesis and the existing opportunities for the prevention and reversal of endothelial dysfunction in NIDDM are also reviewed and discussed.

Measurement of LDL particle size in whole plasma and serum by high performance gel-filtration chromatography using a fluorescent lipid probe

We have recently described a technique for measuring LDL size by high performance gel-filtration chromatography (HPGC) with UV detection (Scheffer et al., Clin Chem 1997;43:1904–12). A drawback of this method is the necessity of LDL isolation before chromatography. We now describe a modification of this method based on selective detection of lipoproteins by postcolumn labeling with parinaric acid, a fluorescent lipid probe. Measuring the size of isolated LDL by HPGC in 56 subjects, we obtained diameters of 25.72 ± 0.60 nm with UV detection and of 25.74 ± 0.58 nm with fluorescence detection. The modified method is suitable for LDL size measurement in whole plasma or serum. LDL sizes measured in whole plasma correlated strongly with the respective values in isolated LDL (r = 0.976) but were on average 0.18 nm larger (P &lt; 0.001). CVs for within- and between-series imprecision were &lt;0.25%. The present method requires only 5 μL plasma or serum without sample preparation and is suitable for the unattended analysis of large series of samples.

Smaller, denser LDL particles are not a risk factor for cardiovascular disease in healthy nonagenarian women of the Cremona Population Study

We evaluated LDL particle size and its relation with other established risk factors for cardiovascular disease in a group of healthy nonagenarian ( > or = 90 years) women participating in the Cremona Population Study. A group of younger healthy postmenopausal women (45-75 years) was used as control group. Nonagenarian women had significantly lower body mass index, systolic and diastolic blood pressure, and fasting insulin concentrations. Plasma total, LDL and HDL cholesterol, apo AI and apo B concentrations, and LpAI and LpAI:AII particles were significantly lower in the nonagenarian group as well. LDL particle size (262.7+/-0.9 vs. 270.1+/-1.1 A) was also lower in the nonagenarian group. The presence of the E4 isoform of apo E in the nonagenarian group resulted in significantly higher levels of plasma apo AI and LpAI:AII particles, and a trend toward larger LDL particles, and a lower diastolic blood pressure. In conclusion, smaller and denser LDL particles might not represent an important risk factor for cardiovascular disease in healthy nonagenarian women of the Cremona Population Study, characterised by a reduced number of LDL particles and other protective factors, like low systolic and diastolic blood pressure, body mass index, and plasma insulin levels.

Modulation of LDL particle size after an oral glucose load is associated with insulin levels

Individuals with a predominance of small low-density lipoprotein (LDL) particles appear to be at increased risk for coronary artery disease. The purpose of this study was to determine whether the LDL particle size was modulated in response to a 75-g oral glucose load. Overall, there were no significant changes in the LDL particle size after glucose load. However, the difference in LDL particle size (deltaLDL size) between the fasting and 2-h post-load states was inversely correlated with the fasting LDL particle size. Also, deltaLDL size was positively correlated with BMI and the post-load glucose levels. Forward stepwise regression analysis revealed three parameters as independent factors capable of modulating LDL particle size: BMI, fasting insulin, and post-load glucose levels. After adjustment for BMI and glucose levels, the levels of fasting and 2-h post-load insulin remain independent determinants of deltaLDL size. These results suggest that plasma insulin levels during glucose load modulate LDL particle size.

Serum leptin levels are independently correlated with two measures of HDL

Leptin is the peptide product of the OB gene, which is associated with obesity in some strains of mice. Because dyslipidemias are frequently associated with obesity, we have begun to characterize the pathways connecting these related traits. In this investigation we tested for correlation of HDL phenotype measures with leptin concentrations using data from 1159 participants in the San Antonio Family Heart Study, a study of risk factors for cardiovascular disease in Mexican Americans living in and around San Antonio, Texas. In a subset of 288 unrelated individuals, we tested for correlation of leptin with nine different measures of HDL phenotype and found that only three were significantly related. However, stepwise regression analysis suggested that only two measures, HDL triglyceride concentrations (HDL-TG) and the proportion of apo A-I on HDL particles larger than HDL3 (Large HDL-apo A-I), were independently correlated with leptin. Because obesity and HDL phenotypes are both under strong genetic control, we conducted a trivariate genetic analysis, using the entire data set, to test the hypothesis that the phenotypic correlations were due to the effects of shared genes (i.e., pleiotropy). Heritabilities for the three traits were estimated to be 0.47 for leptin, 0.46 for HDL-TG, and 0.46 for Large HDL-apo A-I. Results from the genetic analyses revealed that the phenotypic correlation of leptin with HDL-TG was nongenetic (i.e., shared environment), while the phenotypic correlation with Large HDL-apo A-I was due to pleiotropy (i.e., shared genes). These results confirmed the result derived from the subset of unrelated individuals that the two measures of HDL are independently correlated with leptin. To our knowledge, this is the first report of a relationship between leptin and any aspect of lipoprotein phenotype. A better understanding of the genes responsible for this relationship may provide a molecular explanation for the aggregation of atherogenic phenotypes, such as diabetes, obesity, and dyslipoproteinemia.