LDL particle size in familial combined hyperlipidemia: effects of serum lipids, lipoprotein-modifying enzymes, and lipid transfer proteins

Interaction Between Primary Hyperlipidemias and Type 2 Diabetes: Therapeutic Implications

There is a gap of knowledge about the clinical and pathophysiological implications resulting from the interaction between primary hyperlipidemias and type 2 diabetes (T2D). Most of the existing evidence comes from sub-analyses of cohorts; scant information derives from randomized clinical trials. The expected clinical implications of T2D in patients with primary hyperlipidemias is an escalation of their already high cardiovascular risk. There is a need to accurately identify patients with this dual burden and to adequately prescribe lipid-lowering therapies, with the current advancements in newer therapeutic options. This review provides an update on the interactions of primary hyperlipidemias, such as familial combined hyperlipidemia, familial hypercholesterolemia, multifactorial chylomicronemia, lipoprotein (a), and type 2 diabetes.

Small dense low-density lipoprotein-cholesterol (sdLDL-C): Analysis, effects on cardiovascular endpoints and dietary strategies

Lipid profile screening is crucial for the prevention, evaluation and treatment of cardiovascular (CV) disease (CVD). Small dense low-density lipoprotein-cholesterol (sdLDL-C) is an emerging biomarker associated with CVD and several comorbidities. The aim of this literature review is to discuss the potential importance of sdLDL-C as a surrogate biomarker for managing CVD by explaining its pathophysiology and promising treatments. The current synthesis demonstrates the impact of sdLDL-C on CV ailments, which are related to arterial pathologies and dysregulated lipid profiles. Several drug classes used for the treatment of dyslipidemia decrease the sdLDL-C concentrations. For instance, statins, fibrates, ezetimibe, nicotinic acid, resin and orlistat are pharmacological sdLDL-C-lowering agents. Regarding nutritional strategies, simple carbohydrate types, such as fructose, are common in Western diets and should be reduced or avoided due to their potential in increasing synthesis of sdLDL-C subclasses. Dairy products, avocado, pistachios, soy-based diet (except for hydrogenated soybean oil) and corn oil seem to be suitable food choices for a therapeutic diet aiming to control sdLDL-C concentrations. However, thus far dietary supplementation with omega-3 fatty acids is unsubstantiated for decreasing sdLDL-C concentration. In conclusion, coupled with the traditional lipid profile, measurement or even the estimation of sdLDL-C as a routine screening should be encouraged, whereas more insights into the control of sdLDL-C are imperative. Appropriate clinical reference ranges for sdLDL-C are also needed.

Small dense LDL cholesterol measured by homogeneous assay in Japanese healthy controls, metabolic syndrome and diabetes patients with or without a fatty liver

BACKGROUND

Serum small dense LDL-cholesterol (sdLDL-C) levels in healthy controls and the cases with diabetes (T2DM) and metabolic syndrome (MetS) with or without a fatty liver in a large, typical Japanese population was determined.

METHODS

The plasma lipids and lipoproteins, including sdLDL-C by homogeneous assay, were determined in controls, MetS and T2DM patients (n=5255). The cases with MetS and preliminary MetS (pre-MetS) as well as T2DM and preliminary T2DM (pre-DM) were selected based on the Japanese criteria for MetS and T2DM. Fatty liver was diagnosed using the ultrasonography.

RESULTS

The 75th percentile values for sdLDL-C were 27.5mg/dl for men and 23.3mg/dl for women and increased with age. The concentrations of sdLDL-C and sdLDL-C/LDL-C were significantly higher in pre-MetS and pre-T2DM patients than healthy controls as well as in MetS and T2DM patients. Significantly higher sdLDL-C was found in cases with a fatty liver than without a fatty liver in all five groups.

CONCLUSIONS

Significantly elevated sdLDL-C levels were found in pre-MetS, MetS and pre-T2DM, T2DM patients compared to the healthy controls. Fatty liver significantly enhanced serum sdLDL-C levels and the multiple regression analyses ascertained that fatty liver was an independent determinant for sdLDL-C.

Acquired liver fat is a key determinant of serum lipid alterations in healthy monozygotic twins

OBJECTIVE

The effects of acquired obesity on lipid profile and lipoprotein composition in rare BMI-discordant monozygotic (MZ) twin pairs were studied.

DESIGN AND METHODS

Abdominal fat distribution, liver fat (magnetic resonance imaging and spectroscopy), fasting serum lipid profile (ultracentrifugation, gradient gel-electrophoresis, and colorimetric enzymatic methods), and lifestyle factors (questionnaires and diaries) were assessed in 15 BMI-discordant (within-pair difference [Δ] in BMI >3 kg/m2) and nin concordant (ΔBMI <3 kg/m2) MZ twin pairs, identified from two nationwide cohorts of Finnish twins.

RESULTS

Despite a strong similarity of MZ twins in lipid parameters (intra-class correlations 0.42-0.90, P < 0.05), concentrations of apolipoprotein B (ApoB), intermediate-density lipoprotein cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein 3a% (HDL3a%), and HDL3c% were higher (P < 0.05) and those of HDL cholesterol, HDL2-C, and HDL2b% were lower (P < 0.01) in the heavier co-twins of BMI-discordant pairs. The composition of lipoprotein particles was similar in the co-twins. When BMI-discordant pairs were further divided into liver fat-discordant and concordant (based on median for Δliver fat, 2.6%), the adverse lipid profile was only seen in those heavy co-twins who also had high liver fat. Conversely, BMI-discordant pairs concordant for liver fat did not differ significantly in lipid parameters. In multivariate analyses controlling for Δsubcutaneous, Δintra-abdominal fat, sex, Δsmoking and Δphysical activity, Δliver fat was the only independent variable explaining the variation in ΔApoB, Δtotal cholesterol, and ΔLDL-C concentration.

CONCLUSIONS

Several pro-atherogenic changes in the amounts of lipids but not in the composition of lipoprotein particles were observed in acquired obesity. In particular, accumulation of liver fat was associated with lipid disturbances, independent of genetic effects.

Dietary omega-3 polyunsaturated fatty acid intake is related to a protective high-density lipoprotein subspecies profile independent of genetic effects: a monozygotic twin pair study

BACKGROUND

Studies on diet and high-density lipoprotein (HDL) subspecies distribution are limited.

OBJECTIVE

We examined the relationship between macronutrient composition and lipoprotein particle size and HDL subspecies independent of genetic effects by studying monozygotic (MZ) twins.

METHODS

24 healthy MZ twin pairs aged 23-33 years were identified from two longitudinal population-based studies, FinnTwin16 and FinnTwin12. Total energy and nutrient intake were assessed with 3-day food records and physical activity was measured by the Baecke index. HDL subspecies distribution was determined by non-denaturing gradient gel electrophoresis. Associations between diet composition and HDL mean particle size were determined by multivariate nutrient density models adjusted for confounding variables.

RESULTS

Substituting one energy percentage from omega-3 polyunsaturated fatty acids (n-3 PUFAs) for a corresponding amount of energy from other type of fats was related to changes in the relative proportions of the HDL subspecies 2b, 3a and 3b toward a larger mean particle size in men (β ± SE: 1.00 ± 0.26 nm, p = 0.004) and women (β ± SE: 0.90 ± 0.21 nm, p = 0.001). This association remained significant in analyses controlling for genetic and shared environmental influences using within-pair differences of the measures in MZ twin pairs (β ± SE: 0.37 ± 0.14 nm, p = 0.019). Twins with the higher n-3 PUFA intake had significantly higher proportions of large HDL(2b) particles and lower proportions of smaller-sized HDL(3a) and HDL(3b) particles as compared to their co-twins with lower intakes (p < 0.05).

CONCLUSIONS

Our data suggest that n-3 PUFA intake is associated with a favorable change in the distribution of HDL subspecies towards larger particles independent of genetic and shared environmental factors.

Novel drugs in familial combined hyperlipidemia: lessons from type 2 diabetes mellitus

PURPOSE OF REVIEW

Familial combined hyperlipidemia (FCHL) and type 2 diabetes mellitus (T2DM) are prevalent entities that share many features of the metabolic syndrome. Recent findings suggest that FCHL and T2DM are less distinct than initially anticipated, which could offer new insights for their therapeutic approach.

RECENT FINDINGS

Genetic association studies have provided evidence for a common genetic background (upstream transcription factor 1, activating transcription factor 6, transcription factor 7-like 2 and hepatocyte nuclear factor 4 alpha) between FCHL and T2DM. The metabolic overlap can be illustrated by the presence of ectopic fat accumulation and insulin resistance (muscle, adipose tissue and liver). We have shown that FCHL patients are at increased risk to develop T2DM. This indicates that both entities are not static, but instead the former is able to migrate to the latter as insulin resistance progresses. Given these new findings, it can be anticipated that FCHL patients could also benefit from insulin-sensitizing therapy such as pioglitazone and metformin. Indeed, pilot studies have demonstrated that pioglitazone might be advantageous in FCHL patients.

SUMMARY

Recent studies suggest that FCHL patients have an increased risk to develop T2DM, which has important clinical implications. Further studies are necessary to evaluate whether FCHL patients can be protected from new-onset T2DM and premature cardiovascular events with insulin-sensitizing therapy.

Increased apolipoprotein E level and reduced high-density lipoprotein mean particle size associate with low high-density lipoprotein cholesterol and features of metabolic syndrome

The metabolic syndrome (MetS) pandemic predisposes patients to low high-density lipoprotein cholesterol (HDL-C). To successfully treat low HDL-C, there is an urgent need for a better understanding of the changes in HDL particles in the low-HDL-C state. Especially, apolipoprotein (apo) E metabolism in HDL particles is an emerging and important issue. Therefore, we determined HDL subspecies, apo E distribution, and the impact of the MetS in subjects with low and high HDL-C. We studied 246 subjects derived from the Finnish Health 2000 Health Examination Survey. The 2 groups included 113 low-HDL-C (≤10th percentile) and 133 high-HDL-C (≥90th percentile) subjects. The low-HDL-C subjects had higher apo E concentration (39.4 ± 19.4 vs 25.6 ± 8.0 μg/mL, P < .001) and smaller HDL mean particle size (9.0 ± 0.2 vs 9.8 ± 0.3 nm, P < .001). The distribution of apo E genetic isoforms could not explain the difference. Apolipoprotein E content of very low-density lipoprotein particles was comparable between the study groups. In the low-HDL-C subjects, apo E level in large HDL particles was lower (P < .001) compared with that in the high-HDL-C subjects. The subjects with MetS had smaller HDL mean particle size and higher serum apo E concentration. Serum apo E concentration associated positively with different MetS markers (waist circumference, triglycerides, and glucose), whereas HDL mean particle size associated with those negatively. Our results highlight that, in the low-HDL-C state, there are changes in the size and composition of HDL particles associating with MetS. Apolipoprotein E, although generally considered antiatherogenic, associates with MetS and low HDL-C. Our results emphasize the need for a better understanding of apo E metabolism in HDL particles.

Composition and lipid spatial distribution of HDL particles in subjects with low and high HDL-cholesterol

A low level of high density lipoprotein cholesterol (HDL-C) is a powerful risk factor for cardiovascular disease. However, despite the reported key role of apolipo-proteins, specifically, apoA-I, in HDL metabolism, lipid molecular composition of HDL particles in subjects with high and low HDL-C levels is currently unknown. Here lipidomics was used to study HDL derived from well-characterized high and low HDL-C subjects. Low HDL-C subjects had elevated triacylglycerols and diminished lysophosphatidylcholines and sphingomyelins. Using information about the lipid composition of HDL particles in these two groups, we reconstituted HDL particles in silico by performing large-scale molecular dynamics simulations. In addition to confirming the measured change in particle size, we found that the changes in lipid composition also induced specific spatial distributions of lipids within the HDL particles, including a higher amount of triacylglycerols at the surface of HDL particles in low HDL-C subjects. Our findings have important implications for understanding HDL metabolism and function. For the first time we demonstrate the power of combining molecular profiling of lipoproteins with dynamic modeling of lipoprotein structure.

Familial combined hyperlipidemia is associated with alterations in the cholesterol synthesis pathway

OBJECTIVE

Familial combined hyperlipidemia (FCH) is a common familial lipid disorder characterized by increases in plasma total cholesterol, triglyceride, and apolipoprotein B-100 levels. In light of prior metabolic and genetic research, our purpose was to ascertain whether FCH cases had significant abnormalities of plasma markers of cholesterol synthesis and absorption as compared to unaffected kindred members.

METHODS AND RESULTS

Plasma levels of squalene, desmosterol, and lathosterol (cholesterol synthesis markers) and campesterol, sitosterol, and cholestanol (cholesterol absorption markers) were measured by gas-liquid chromatography in 103 FCH patients and 240 normolipidemic relatives (NLR). Squalene, desmosterol, and lathosterol levels were 6% (0.078), 31%, (P<0.001) and 51% (P<0.001) higher in FCH as compared to NLR, and these differences were especially pronounced in women. An interaction with obesity was also noted for a subset of these markers. We did not observe any apparent differences for the cholesterol absorption markers among FCH patients and NLR.

CONCLUSIONS

Our data indicate that both men and women with FCH have alterations in the cholesterol synthesis pathway, resulting in 51% higher levels of lathosterol (and additionally desmosterol in women). Plasma levels of the cholesterol precursor sterol squalene were only slightly increased (6%), suggesting enhanced conversion of squalene to lathosterol in this disorder.

HDL subspecies in young adult twins: heritability and impact of overweight

The association between abdominal obesity and atherogenic lipid profile emerges from complex interactions of genes and environment. We aimed to explore the heritability and effects of overweight on serum lipid profile (high-density lipoprotein-cholesterol (HDL-C), HDL mean particle size, percentages of HDL(2b, 2a, 3a, 3b, and 3c,) low-density lipoprotein-cholesterol (LDL-C), LDL peak particle size and triglycerides (TGs)) in healthy, young adults. HDL-C, LDL-C, and TG were measured in 52 monozygotic (MZ) and 89 dizygotic (DZ) twin pairs, aged 23-32 years, chosen to represent a wide range of BMIs (17.6-42.9 kg/m2). Of them, 24 MZ and 26 DZ pairs were chosen at random for measurements of HDL mean and LDL peak particle sizes and percentages of HDL subspecies. The heritabilities of the lipid parameters adjusted for BMI were HDL-C 73%, HDL mean particle size 56%, HDL subspecies 46-63%, LDL-C 79%, LDL peak particle size 49%, and TG 64%. Genetic and environmental correlations between BMI and HDL-C, LDL-C, and TG were modest (0.3-0.4). Abdominal overweight (waist circumference>or=94 cm for males and >or=80 cm for females) associated with decreased HDL-C, increased LDL-C, and TG concentrations, smaller HDL mean particle size, lower HDL2b, and higher HDL3c percentages in both genders. Within MZ twins, controlling for genetic influences, within-pair differences in HDL3c percentage were associated with those in waist (r=0.46, P=0.032) and BMI (r=0.51, P=0.013). In conclusion, serum lipid parameters, including LDL peak and HDL mean particle sizes and HDL subspecies distribution are under strong genetic control. Overweight associated with significant lipid profile changes, particularly, small HDL3c increased in overweight independent of genetic influences.

Reconstruction and functional analysis of altered molecular pathways in human atherosclerotic arteries

Background

Atherosclerosis affects aorta, coronary, carotid, and iliac arteries most frequently than any other body vessel. There may be common molecular pathways sustaining this process. Plaque presence and diffusion is revealed by circulating factors that can mediate systemic reaction leading to plaque rupture and thrombosis.

Results

We used DNA microarrays and meta-analysis to study how the presence of calcified plaque modifies human coronary and carotid gene expression. We identified a series of potential human atherogenic genes that are integrated in functional networks involved in atherosclerosis. Caveolae and JAK/STAT pathways, and S100A9/S100A8 interacting proteins are certainly involved in the development of vascular disease. We found that the system of caveolae is directly connected with genes that respond to hormone receptors, and indirectly with the apoptosis pathway.

Cytokines, chemokines and growth factors released in the blood flux were investigated in parallel. High levels of RANTES, IL-1ra, MIP-1alpha, MIP-1beta, IL-2, IL-4, IL-5, IL-6, IL-7, IL-17, PDGF-BB, VEGF and IFN-gamma were found in plasma of atherosclerotic patients and might also be integrated in the molecular networks underlying atherosclerotic modifications of these vessels.

Conclusion

The pattern of cytokine and S100A9/S100A8 up-regulation characterizes atherosclerosis as a proinflammatory disorder. Activation of the JAK/STAT pathway is confirmed by the up-regulation of IL-6, STAT1, ISGF3G and IL10RA genes in coronary and carotid plaques. The functional network constructed in our research is an evidence of the central role of STAT protein and the caveolae system to contribute to preserve the plaque. Moreover, Cav-1 is involved in SMC differentiation and dyslipidemia confirming the importance of lipid homeostasis in the atherosclerotic phenotype.

Apolipoprotein E polymorphism is associated with both carotid and coronary atherosclerosis in patients with coronary artery disease

BACKGROUND AND AIMS

Apolipoprotein E (apoE) polymorphism plays a significant role in the development of atherosclerosis and cardiovascular disease. Therefore, the aim of the present study was to examine the association between apoE polymorphism and carotid intima-media thickness (IMT), and severity and extent of coronary artery disease (CAD).

METHODS AND RESULTS

B-mode ultrasound and quantitative coronary angiography (QCA) were used to assess carotid, and coronary artery atherosclerosis in 91 patients with clinically suspected CAD referred for cardiac catheterization. Two apoE phenotype groups were defined: apoE3 (E3/E3) and apoE4 (including E4/E3, E4/E4 phenotypes). Maximum IMT was higher in the apoE4 group than in the apoE3 group (p=0.022). The global atheroma burden index was similarly higher in the apoE4 group than in the apoE3 group (p=0.033). ApoE4 subjects had higher levels of apolipoprotein B (apoB) (p=0.008), triglycerides (p=0.006), remnant lipoprotein-cholesterol (RLP-C) (p=0.023), and lipoprotein(a) [(Lp(a)] (p=0.041) than apoE3 subjects. The mean LDL particle size was smaller in the apoE4 group than in the apoE3 group (p=0.041).

CONCLUSIONS

ApoE polymorphism was associated with both carotid and coronary atherosclerosis. Patients with the apoE4 isoform had an increased carotid IMT and a more severe and extensive CAD than patients with the apoE3 isoform.

The role of CETP inhibition in dyslipidemia

Cholesteryl ester transfer protein (CETP) inhibitors are currently being investigated because of their ability to increase high-density lipoprotein cholesterol levels. In various metabolic settings, the relationship between CETP and lipoprotein metabolism is complex and may depend largely on the concentration of triglyceride-rich lipoproteins. Two CETP inhibitors, JTT-705 and torcetrapib, are in an advanced phase of development. Following hopeful intermediate results, a large endpoint study using torcetrapib has just been discontinued due to increased mortality in torcetrapib-treated subjects. In this review we summarize clinical data on the use of CETP inhibitors.

Long-term effects of fenofibrate on VLDL and HDL subspecies in participants with type 2 diabetes mellitus

AIMS/HYPOTHESIS

Low HDL-cholesterol (HDL-C) is frequently accompanied by high triacylglycerol levels in diabetic dyslipidaemia, increasing the risk of CHD. In the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study, fenofibrate treatment lowered triacylglycerol levels, but the initial 5% increase in HDL-C attenuated over 5 years. We explored the changes in VLDL and HDL subspecies during fenofibrate treatment in a statin-free FIELD cohort.

METHODS

We randomised 171 participants with type 2 diabetes mellitus, who had been recruited to the FIELD study in Helsinki, to micronised fenofibrate (200 mg/day) or placebo in double-blind study design. VLDL and HDL subspecies were separated by ultracentrifugation at baseline and at the second and fifth year. Apolipoprotein (apo)A-I and apoA-II were measured by immunoturbidometric methods and lipoprotein (Lp)A-I and LpAI-AII particles by differential immunoassay.

RESULTS

Fenofibrate reduced plasma triacylglycerol levels by 26%, resulting from a marked reduction in VLDL1 triacylglycerol (0.62 vs 0.29 mmol/l, p < 0.001). Fenofibrate caused an increase in LDL size (Delta 0.80 nm, p < 0.001). HDL-C was similar between the groups. HDL2-C was decreased by fenofibrate (-27.5% at 5th year, p < 0.001) and HDL3-C increased (13.0% at 5th year, p < 0.001). Fenofibrate had no effect on apoA-I, whereas apoA-II increased. Thus, LpA-I decreased while LpAI-AII increased. Activities of cholesteryl ester transfer protein, phospholipids transfer protein and lecithin:cholesterylacyl transferase were unchanged by fenofibrate. High homocysteine levels were associated with a slight decrease in HDL-C and apoA-I.

CONCLUSIONS/INTERPRETATION

Fenofibrate markedly reduced large VLDL particles and produced a clear shift in HDL subspecies towards smaller particles. The HDL3-C increase in conjunction with unchanged apoA-I [corrected] levels is a dilemma with regard to cardiovascular disease.

CETP and oxidized LDL levels increase in dyslipidemic subjects

OBJECTIVES

To explore the possible associations among cholesteryl ester transfer protein (CETP), contents of lipids in low-density lipoprotein (LDL), and in vivo oxidized LDL (Ox-LDL).

DESIGN AND METHODS

CETP and Ox-LDL were both detected by ELISA. Their levels and the lipid contents of LDL were investigated in 200 subjects with various dyslipidaemias.

RESULTS

Compared to the control, CETP levels were significantly increased in subjects with mixed hyperlipidaemia and hypercholesterolaemic. Ox-LDL levels were only significantly increased in mixed hyperlipidaemia subjects. Triacyglycerols to cholesterol ratio in LDL was significantly increased in various dyslipidaemias subjects, of which, hypertriglyceridaemic subjects exhibited the most significant change, while hypercholesterolaemic subjects the least. Multiple linear regression analysis showed that total cholesterol and triacyglycerols levels in very low-density lipoprotein were significantly related with CETP (R(2)=0.066), and triacyglycerols and total cholesterol levels were significantly related with Ox-LDL (R(2)=0.094), respectively.

CONCLUSIONS

High CETP promotes the transport of lipids among lipoproteins, which changed the lipid composition of LDL, resulting in the increase of in vivo Ox-LDL level, and subsequently contributing to the atherogenic process in dyslipidaemias subjects.

Insulin resistance as predictor of the angiographic severity and extent of coronary artery disease

BACKGROUND

Insulin resistance (IR) is frequently observed in patients with coronary artery disease (CAD). Aim. To examine the association between IR and severity and extent of CAD.

METHODS

Quantitative coronary angiography (QCA) was used to assess coronary atherosclerosis in 107 patients with clinically suspected CAD. QCA-derived indexes reflecting CAD severity, extent, and overall atheroma burden were calculated for the entire coronary tree, and separately for different coronary segments. IR was quantified using the homeostasis model assessment insulin resistance index (HOMA IR). Nondiabetic subjects (n = 83) were divided into group 1 (n = 41) with HOMA IR <1.8 (the median value), and group 2 (n = 42) with HOMA IR >or=1.8. Group 3 comprised diabetic subjects (n = 24).

RESULTS

Global age- and gender-adjusted indexes for severity (P = 0.007), extent (P = 0.038), and atheroma burden (P = 0.035) of CAD were higher in group 2 than in group 1. Similarly, the global severity (P = 0.027), extent (P = 0.090), and global atheroma burden (P = 0.024) indexes were higher in group 3 compared with group 1. IR was correlated with quantitative angiographic indexes for distal segments only, but not for proximal or mid segments of coronary vessels.

CONCLUSIONS

Patients with more severe degree of IR have a more severe, extensive, and distal type of CAD than patients with lower degree of IR.

Clinical importance and therapeutic modulation of small dense low-density lipoprotein particles

The National Cholesterol Education Programme Adult Treatment Panel III accepted the predominance of small dense low-density lipoprotein (sdLDL) as an emerging cardiovascular disease (CVD) risk factor. Most studies suggest that measuring low-density lipoprotein (LDL) particle size, sdLDL cholesterol content and LDL particle number provides additional assessment of CVD risk. Therapeutic modulation of small LDL size, number and distribution may decrease CVD risk; however, no definitive causal relationship is established, probably due to the close association between sdLDL and triglycerides and other risk factors (e.g., high-density lipoprotein, insulin resistance and diabetes). This review addresses the formation and measurement of sdLDL, as well as the relationship between sdLDL particles and CVD. The effect of hypolipidaemic (statins, fibrates and ezetimibe) and hypoglycaemic (glitazones) agents on LDL size and distribution is also discussed.

Impact of postprandial lipaemia on low-density lipoprotein (LDL) size and oxidized LDL in patients with coronary artery disease

BACKGROUND

Remnant lipoprotein particles (RLPs) and oxidative stress are components of postprandial state. We investigated the concentrations of triglyceride-rich lipoproteins (TRLs), RLPs, low-density lipoprotein (LDL) size, and oxidized LDL (oxLDL) during alimentary lipaemia, and evaluated whether changes among these variables could be associated with the severity and extent of coronary artery disease (CAD).

MATERIALS AND METHODS

Eighty men and 27 women with clinically suspected CAD underwent quantitative coronary angiography (QCA). TRLs were isolated by density gradient ultracentrifugation before and 6 h after an oral fat load. RLPs were measured by an immunoseparation method, oxLDL by ELISA, and LDL size by gradient gel electrophoresis.

RESULTS

Triglycerides, apolipoprotein (apo) B-48, and apoB-100 concentration in Swedberg flotation units (Sf) > 400 and in Sf 12-400 fractions were markedly increased at 6 h. Postprandial cholesterol content of RLPs (RLP-C) correlated with respective triglycerides in Sf > 400 (r = 0.737) and Sf 12-400 (r = 0.857), apoB-48 in Sf > 400 (r = 0.710) and Sf 12-400 (r = 0.664), apoB-100 in Sf > 400 (r = 0.812) and Sf 12-400 (r = 0.533). RLP-C correlated with oxLDL both in fasting and in fed state (r = 0.482 and r = 0.543, respectively) and inversely with LDL size (r = -0.459 and r = -0.442, respectively). (P < 0.001 for all). OxLDL was elevated postprandially (P < 0.001). In multivariate analysis, oxLDL was a determinant of severity and extent of CAD.

CONCLUSION

Postprandial state is associated with oxidative stress. The magnitude of oxLDL increases during alimentary lipaemia and is associated with coronary atherosclerosis.

Overproduction of large VLDL particles is driven by increased liver fat content in man

AIMS/HYPOTHESIS

We determined whether hepatic fat content and plasma adiponectin concentration regulate VLDL(1) production.

METHODS

A multicompartment model was used to simultaneously determine the kinetic parameters of triglycerides (TGs) and apolipoprotein B (ApoB) in VLDL(1) and VLDL(2) after a bolus of [(2)H(3)]leucine and [(2)H(5)]glycerol in ten men with type 2 diabetes and in 18 non-diabetic men. Liver fat content was determined by proton spectroscopy and intra-abdominal fat content by MRI.

RESULTS

Univariate regression analysis showed that liver fat content, intra-abdominal fat volume, plasma glucose, insulin and HOMA-IR (homeostasis model assessment of insulin resistance) correlated with VLDL(1) TG and ApoB production. However, only liver fat and plasma glucose were significant in multiple regression models, emphasising the critical role of substrate fluxes and lipid availability in the liver as the driving force for overproduction of VLDL(1) in subjects with type 2 diabetes. Despite negative correlations with fasting TG levels, liver fat content, and VLDL(1) TG and ApoB pool sizes, adiponectin was not linked to VLDL(1) TG or ApoB production and thus was not a predictor of VLDL(1) production. However, adiponectin correlated negatively with the removal rates of VLDL(1) TG and ApoB.

CONCLUSIONS/INTERPRETATION

We propose that the metabolic effect of insulin resistance, partly mediated by depressed plasma adiponectin levels, increases fatty acid flux from adipose tissue to the liver and induces the accumulation of fat in the liver. Elevated plasma glucose can further increase hepatic fat content through multiple pathways, resulting in overproduction of VLDL(1) particles and leading to the characteristic dyslipidaemia associated with type 2 diabetes.

Elevated plasma phospholipid transfer protein activity is a determinant of carotid intima-media thickness in type 2 diabetes mellitus

AIM/HYPOTHESIS

The plasma activity of phospholipid transfer protein (PLTP), which has putative pro- and anti-atherogenic roles in lipoprotein metabolism, is increased in type 2 diabetes mellitus. We analysed the relationship between carotid artery intima-media thickness (IMT), an established marker of atherosclerosis, and PLTP activity in diabetic patients and control subjects.

METHODS

The IMT (mean of three segments in both carotid arteries by ultrasonography), clinical variables, plasma PLTP activity (phospholipid vesicle-HDL system), lipoproteins, C-reactive protein and insulin were measured in 87 non-smoking men and women, who had type 2 diabetes mellitus, no cardiovascular disease, and were not on insulin or lipid-lowering medication, and in 83 age-matched control subjects.

RESULTS

In diabetic patients, carotid IMT (p=0.02), pulse pressure (p=0.003), plasma PLTP activity (p<0.001), triglycerides (p=0.01), C-reactive protein (p<0.01) and insulin (p<0.001) were higher, whereas HDL cholesterol was lower (p<0.001) than in control subjects. Multiple stepwise linear regression analysis demonstrated that in type 2 diabetic patients IMT was independently associated with age (p<0.001), sex (p=0.001), pulse pressure (p=0.003), plasma PLTP activity (p=0.03) and HDL cholesterol (p=0.03), but not with very low density lipoprotein+LDL cholesterol, triglycerides, C-reactive protein and insulin (all p>0.20). The relationship between plasma PLTP activity and IMT was not significant in control subjects.

CONCLUSIONS/INTERPRETATION

Plasma PLTP activity is a positive determinant of IMT in type 2 diabetes mellitus, suggesting that high PLTP activity is involved in accelerated atherosclerosis in this disease.

Fluoxetine-resistance genes in Caenorhabditis elegans function in the intestine and may act in drug transport

Fluoxetine (Prozac) is one of the most widely prescribed pharmaceuticals, yet important aspects of its mechanism of action remain unknown. We previously reported that fluoxetine and related antidepressants induce nose muscle contraction of C. elegans. We also reported the identification and initial characterization of mutations in seven C. elegans genes that cause defects in this response (Nrf, nose resistant to fluoxetine). Here we present genetic evidence that the known nrf genes can be divided into two subgroups that confer sensitivity to fluoxetine-induced nose contraction by distinct pathways. Using both tissue-specific promoters and genetic mosaic analysis, we show that a gene from one of these classes, nrf-6, functions in the intestine to confer fluoxetine sensitivity. Finally, we molecularly identify nrf-5, another gene in the same class. The NRF-5 protein is homologous to a family of secreted lipid-binding proteins with broad ligand specificity. NRF-5 is expressed in the intestine and is likely secreted into the pseudocoelomic fluid, where it could function to transport fluoxetine. One model that explains these findings is that NRF-5 binds fluoxetine and influences its presentation or availability to in vivo targets.

Cholesteryl ester transfer protein TaqIB polymorphism and its relation to parameters of the insulin resistance syndrome in an Austrian cohort

The cholesteryl ester transfer protein (CETP) is responsible for the exchange of triglycerides and cholesteryl esters between lipoprotein particles leading to an increased hepatic clearance of HDL-cholesteryl esters. A high CETP activity reduces serum HDL levels, whereas persons without CETP activity have high HDL levels. We investigated the association of the TaqIB CETP polymorphism and various parameters of the insulin resistance syndrome in a cross sectional population based study. We included 1029 persons without known cardiovascular disease or diabetes mellitus consecutively enrolled in our SAPHIR program (Salzburg Atherosclerosis Prevention program in persons with a High Infarction Risk). Numerous clinical and laboratory data were accomplished. Insulin sensitivity was measured by a short insulin tolerance test. The TaqIB CETP polymorphism was determined by PCR, TaqI restriction and electrophoresis. 35.2% were homozygous for the prevalence (B1B1), 46.7% were heterozygous (B1B2), and 18.1% homozygous for the absence (B2B2) of the restriction site. HDL cholesterol and apolipoprotein A1 were lower and small dense low-density lipoproteins (sdLDL) higher in B1B1 compared to B2B1 and B2B2 persons. In women, we found a significant interaction effect between CETP genotype and adiposity for HDL cholesterol. B1B1 women with a BMI and a waist circumference above the median had 9.7 mg/dl lower HDL than B1B2 and 9.1 mg/dl lower HDL than B2B2 women (P < 0.001). In men, no interaction effect but a marked genotype to HDL correlation was found. There was a high CETP effect on sdLDL detected in men (P = 0.001). B1B1 men had sdLDL in 36%, B1B2 in 24.6%, and B2B2 in only 14.5%. Men with adiposity and insulin resistance had twice as many sdLDL as insulin sensitive men. We found a significant sex specific effect of the TaqIB CETP polymorphism on the insulin resistance parameters HDL-cholesterol and sdLDL in an Austrian population based study.

Lifestyle modification improves risk factors in type 2 diabetes relatives

AIMS

To investigate the short-term (16 weeks) effect of lifestyle intervention on insulin sensitivity, anthropometric and metabolic variables in non-diabetic first-degree relatives of type 2 diabetic patients (FDR).

METHODS

Seventy-seven (49 male, 28 female) FDR were allocated to one of three groups, diet (D-group; n = 25), diet and exercise (DE-group; n = 30) or control group (C-group; n = 22). Lifestyle counselling was based on current nutrition recommendations, including increased intake of fatty fish and low glycaemic index foods. Group counselling was given on two occasions with follow-up through telephone interviews every 10 days. Assessments included insulin sensitivity index (Si), anthropometry, lipid parameters, circulating leptin and adiponectin levels.

RESULTS

The D-group reduced total cholesterol (-0.31 mmol/l, P = 0.024), LDL cholesterol (-0.22 mmol/l, P = 0.021) and apolipoprotein B (-9.5 mg/dl, P = 0.009) levels, whereas the DE-group decreased body weight (-2.1%, P = 0.030) and waist circumference (-3.0 cm, P < 0.001) versus controls. A 13% reduction in fasting insulin was observed in the DE-group, but no significant improvement in Si in D-group or DE-group was observed. A subgroup, adherent to diet and who increased exercise, significantly improved Si and lipid profile.

CONCLUSIONS

The improved metabolic risk profile in FDR suggests that lifestyle changes can be effective in individuals at high risk to develop type 2 diabetes and cardiovascular disease.

Locus for quantitative HDL-cholesterol on chromosome 10q in Finnish families with dyslipidemia

Decreased HDL-cholesterol (HDL-C) and familial combined hyperlipidemia (FCHL) are the two most common familial dyslipidemias predisposing to premature coronary heart disease (CHD). These dyslipidemias share many phenotypic features, suggesting a partially overlapping molecular pathogenesis. This was supported by our previous pooled data analysis of the genome scans for low HDL-C and FCHL, which identified three shared chromosomal regions for a qualitative HDL-C trait on 8q23.1, 16q23.3, and 20q13.32. This study further investigates these regions as well as two other loci we identified earlier for premature CHD on 2q31 and Xq24 and a locus for high serum triglycerides (TGs) on 10q11. We analyzed 67 microsatellite markers in an extended study sample of 1,109 individuals from 92 low HDL-C or FCHL families using both qualitative and quantitative lipid phenotypes. These analyses provided evidence for linkage (a logarithm of odds score of 3.2) on 10q11 using a quantitative HDL-C trait. Importantly, this region, previously linked to TGs, body mass index, and obesity, provided evidence for association for quantitative TGs (P = 0.0006) and for a combined trait of HDL-C and TGs (P = 0.008) with marker D10S546. Suggestive evidence for linkage also emerged for HDL-C on 2q31 and for TGs on 20q13.32. Finnish families ascertained for dyslipidemias thus suggest that 10q11, 2q31, and 20q13.32 harbor loci for HDL-C and TGs.

Circulating Oxidized Low-Density Lipoprotein and Its Association With Carotid Intima-Media Thickness in Asymptomatic Members of Familial Combined Hyperlipidemia Families

OBJECTIVE

Oxidized low-density lipoprotein (Ox-LDL)is implicated in the pathogenesis of atherosclerosis. Circulating oxidation-specific epitopes on plasma Ox-LDL has been linked with coronary artery disease, but its determinants and its association with early development of atherosclerosis in familial combined hyperlipidemia (FCHL) has not been very well studied. This study aimed to investigate the determinants of the circulating Ox-LDL and the association between Ox-LDL and carotid intima-media thickness (IMT) in asymptomatic members of FCHL families.

METHODS AND RESULTS

Ox-LDL, susceptibility of LDL to oxidation in vitro, plasma 8-isoprostane and antioxidants, lipids and lipoproteins, LDL particle size, and carotid IMT were measured in 150 asymptomatic FCHL family members. Affected FCHL family members had reduced LDL particle size and lag time for LDL oxidation, increased plasma levels of Ox-LDL, increased plasma urate and alpha-tocopherol, and a trend for the increase of 8-isoprostane as compared with nonaffected FCHL. Ox-LDL was independently associated with serum LDL cholesterol, apoB, and 8-isoprostane in multivariate analysis but only univariately correlated with LDL particle size and lag time for LDL oxidation. In addition, Ox-LDL was significantly associated with carotid mean IMT independently of other clinical and biochemical variables in a multivariate model.

CONCLUSIONS

Serum LDL cholesterol, apoB levels, and 8-isoprostane were the most important determinants of Ox-LDL. Ox-LDL is independently associated with carotid IMT in asymptomatic FCHL family members and can be used as a marker of early atherosclerosis in FCHL.

Low-grade inflammation, endothelial activation and carotid intima-media thickness in type 2 diabetes

OBJECTIVES

The objective of this study was to assess the relationship between inflammation, endothelial activation and incipient atherosclerosis in type 2 diabetes.

DESIGN

Cross-sectional study. Setting and subjects. We studied 239 type 2 diabetic patients [71 with clinical cardiovascular disease (CVD)] and 78 healthy control subjects, aged 50-75 in a single research centre.

METHODS

Carotid intima-media thickness (IMT) was determined by ultrasound. Circulating intracellular adhesion molecule-1, vascular cell adhesion molecule-1, E-selectin, ultra-sensitive C-reactive protein, human serum amyloid A, interleukin-6, monocyte colony-stimulating factor, secretory nonpancreatic phospholipase A(2) type IIA, glucose, HbA1c, and lipid/lipoprotein variables were measured.

RESULTS

Carotid IMT was significantly thicker in diabetic patients than healthy controls across the whole age range. IMT was also thicker in diabetic patients with, than without, CVD, but this difference disappeared after controlling for confounding factors. Concentrations of the inflammatory and endothelial markers except IL-6 were significantly higher in the diabetic patients than in healthy controls, but comparable in diabetic patients with and without CVD. The main determinants of IMT in the diabetic patients were blood pressure, age and diabetes duration.

CONCLUSIONS

Low-grade inflammation and endothelial activation are increased in diabetic patients but do not associate with IMT or clinical CVD. The inflammatory reaction seems to be rather a feature of the metabolic syndrome than a direct determinant of atherosclerosis.

Nomogram to Diagnose Familial Combined Hyperlipidemia on the Basis of Results of a 5-Year Follow-Up Study

Background— Familial combined hyperlipidemia (FCH) is traditionally diagnosed by total plasma cholesterol and/or triglyceride levels above the 90th percentile adjusted for age and gender. In a recent study, we showed that the diagnosis of FCH on the basis of these diagnostic criteria was inconsistent in 26% of the subjects over a 5-year period. This result emphasizes the need for reevaluation of the diagnostic criteria for FCH.

Methods and Results— A total of 32 families (299 subjects) were studied in 1994 and 1999. A subject was defined “truly” FCH when diagnosed FCH in 1994 and/or 1999 on the basis of traditional plasma lipid criteria. Additional lipid and lipoprotein parameters, including apolipoprotein B (apoB) and small, dense LDL, were measured at both time points. In total, 121 subjects (40%) were defined as truly FCH. Multivariate analysis revealed that absolute apoB values combined with triglyceride and total cholesterol levels adjusted for age and gender best predicted truly FCH. A nomogram including these parameters is provided to simply and accurately calculate the probability to be affected by FCH. Furthermore, it is shown that when percentiles of triglyceride and total cholesterol adjusted for age and gender are not available in a population, the definition of FCH can be established on the basis of hypertriglyceridemia (>1.5 mmol/L) and hyper-apoB (>1200 mg/L).

Conclusions— The diagnosis of FCH is best predicted by absolute apoB levels combined with triglyceride and total cholesterol levels adjusted for age and gender and can accurately be calculated by a nomogram. This definition is also a good predictor of cardiovascular risk in FCH.

Study of agreement between LDL size as measured by nuclear magnetic resonance and gradient gel electrophoresis

LDL particle size can be measured by gradient gel electrophoresis (GGE) and NMR. The agreement between the two methods has not been extensively evaluated. Therefore, we measured LDL size by NMR and GGE in 324 individuals (152 with type 1 diabetes and 172 controls). The Spearman correlation between both methods was 0.39 [95% confidence interval (CI) = 0.29, 0.48]. The average difference was 5.38 nm (NMR being smaller), but it increased with increasing LDL size. Less than 50% of people classified as pattern B on GGE were classified as pattern B on NMR (kappa = 0.31; 95% CI = 0.17, 0.45). Agreement was lower for diabetic subjects compared with controls, for women compared with men, and for subjects with triglycerides less than 1.30 mmol/l compared with subjects with triglycerides greater than 1.30 mmol/l. External validation showed that cholesteryl ester transfer rate was related to LDL size on GGE in all subgroups and to LDL size on NMR only in men and nondiabetic subjects. Our findings show that agreement between NMR- and GGE-based LDL size is far from perfect and is not consistent across subgroups of patients. In particular, the two methods should not be assumed to be interchangeable in women and diabetic subjects. Whether NMR or GGE predicts cardiovascular disease risk better has not yet been evaluated.

Subclasses of Low-Density Lipoprotein and Very Low-Density Lipoprotein in Familial Combined Hyperlipidemia: Relationship to Multiple Lipoprotein Phenotype

Objective— The present study addresses the presence of distinct metabolic phenotypes in familial combined hyperlipidemia (FCHL) in relation to small dense low-density lipoprotein (sd LDL) and very low-density lipoprotein (VLDL) subclasses.

Methods and Results— Hyperlipidemic FCHL relatives (n=72) were analyzed for LDL size by gradient gel electrophoresis. Pattern B LDL (sd LDL, particle size <258 Å) and pattern A LDL (buoyant LDL, particle size ≥258 Å) were defined. Analyses showed bimodal distribution of LDL size associated with distinct phenotypes. Subjects with predominantly large, buoyant LDL showed a hypercholesterolemic phenotype and the highest apo B levels. Subjects with predominantly sd LDL showed a hypertriglyceridemic, low high-density lipoprotein (HDL) cholesterol phenotype, with moderately elevated apoB, total cholesterol level, and LDL cholesterol level. Subjects with both buoyant LDL and sd LDL (pattern AB, n=7) showed an intermediate phenotype, with high normal plasma triglycerides. VLDL subfraction analysis showed that the sd LDL phenotype was associated with a 10-times higher number of VLDL1 particles of relatively lower apo AI and apo E content, as well as smaller VLDL2 particles, in combination with increased plasma insulin concentration in comparison to pattern A.

Conclusions— The present observations underscore the importance of the VLDL triglyceride metabolic pathway in FCHL as an important determinant of the phenotypic heterogeneity of the disorder.

Familial combined hyperlipidemia is associated with upstream transcription factor 1 (USF1)

Familial combined hyperlipidemia (FCHL), characterized by elevated levels of serum total cholesterol, triglycerides or both, is observed in about 20% of individuals with premature coronary heart disease. We previously identified a locus linked to FCHL on 1q21-q23 in Finnish families with the disease. This region has also been linked to FCHL in families from other populations as well as to type 2 diabetes mellitus. These clinical entities have several overlapping phenotypic features, raising the possibility that the same gene may underlie the obtained linkage results. Here, we show that the human gene encoding thioredoxin interacting protein (TXNIP) on 1q, which underlies combined hyperlipidemia in mice, is not associated with FCHL. We show that FCHL is linked and associated with the gene encoding upstream transcription factor 1 (USF1) in 60 extended families with FCHL, including 721 genotyped individuals (P = 0.00002), especially in males with high triglycerides (P = 0.0000009). Expression profiles in fat biopsy samples from individuals with FCHL seemed to differ depending on their carrier status for the associated USF1 haplotype. USF1 encodes a transcription factor known to regulate several genes of glucose and lipid metabolism.

Postprandial lipidemia is normal in non-obese type 2 diabetic patients with relatively preserved insulin secretion

To assess postprandial lipidemia in normotriglyceridaemic type 2 diabetic patients treated with diet only, 12 non-obese patients (8 males, hemoglobin A(1c) [HbA(1c)] 6.80 +/- 0.67%) and 14 controls of similar age, body mass index (BMI), and fasting triglyceride (Tg) were given a test meal (58 g fat, 100,000 IU vitamin A). Fasting low-density lipoprotein (LDL) cholesterol (LDLc), high-density lipoprotein (HDL) cholesterol (HDLc), free fatty acids, and apolipoprotein B (apoB), and fasting and postprandial Tg, retinylpalmitate (RP), LDL size, glucose, and insulin were measured. The homeostasis assessment model (HOMA) index and lipoprotein (Lpl) and hepatic (HL) lipase activities were estimated. Patients showed lower fasting HDLc (1.12 +/- 0.26 v 1.40 +/- 0.28 mmol/L, P =.02) and a trend towards smaller LDL particles, which was significant 4 hours postprandially (25.86 +/- 0.40 v 26.16 +/- 0.30 nm, P =.04). The area under the curve of Tg (AUC-Tg) and RP, and Lpl were similar, but HL was higher in patients (156.63 +/- 23.89 v 118 +/- 43.27 U/L, P =.011). HL correlated inversely with LDL size and directly with the HOMA index. In conclusion, normotriglyceridemic type 2 diabetic patients with insulin resistance but relatively preserved insulin secretion show low fasting HDLc and increased HL, but normal postprandial lipidemia.

Determinants of low HDL levels in familial combined hyperlipidemia

In familial combined hyperlipidemia (FCHL), affected family members frequently have reduced levels of HDL cholesterol, in addition to elevated levels of total cholesterol and/or triglycerides (TGs). In the present study, we focused on those determinants that are important regulators of HDL cholesterol levels in FCHL, and measured postheparin plasma activities of hepatic lipase (HL), lipoprotein lipase, cholesterol ester transfer protein, and phospholipid transfer protein (PLTP) in 228 subjects from 49 FCHL families. In affected family members (n = 88), the levels of HDL cholesterol, HDL2 cholesterol, HDL3 cholesterol, and apolipoprotein A-I were lower than in unaffected family members (n = 88) or spouses (n = 52). The main change was the reduction of HDL2 cholesterol by 25.4% in affected family members (P < 0.001 vs. unaffected family members; P = 0.003 vs. spouses). Affected family members had higher HL activity than unaffected family members (P = 0.001) or spouses (P = 0.013). PLTP activity was higher in affected than unaffected family members (P = 0.025). In univariate correlation analysis, a strong negative correlation was observed between HL activity and HDL2 cholesterol (r = -0.339, P < 0.001). Multivariate regression analysis demonstrated that gender, HL activity, TG, and body mass index have independent contributions to HDL2 cholesterol levels. We suggest that in FCHL, TG enrichment of HDL particles and enhanced HL activity lead to the reduction of HDL cholesterol and HDL2 cholesterol.

Circulating adiponectin levels are reduced in nonobese but insulin-resistant first-degree relatives of type 2 diabetic patients

Adiponectin, one of the most abundant gene transcript proteins in human fat cells, has been shown to improve insulin action and is also suggested to exert antiatherogenic effects. We measured circulating adiponectin levels and risk factors for atherosclerosis in 45 healthy first-degree relatives of type 2 diabetic subjects (FDR) as well as 40 healthy control subjects (CON) without a known family history of diabetes. Insulin sensitivity (S(i)) was studied with the minimal model, and measurements of adiponectin, metabolic variables, inflammatory markers, and endothelial injury markers, as well as lipoprotein concentrations, were performed. FDR were insulin resistant (3.3 +/- 2.4 vs. 4.5 +/- 2.6 x 10(-4) x min(-1) per microU/ml [mean +/- SD], P < 0.01), and their circulating plasma adiponectin levels (6.6 +/- 1.8 vs. 8.1 +/- 3.0 microg/ml, P < 0.03) were decreased. After adjustments for age in FDR, adiponectin levels were negatively correlated with fasting proinsulin (r -0.64, P < 0.001), plasminogen activator inhibitor (PAI)-1 activity (r -0.56, P < 0.001), fasting insulin (r -0.55, P < 0.001), and acute insulin response (r -0.40, P < 0.05); they were positively related to HDL cholesterol (r 0.48, P < 0.01) and S(i) (r 0.41, P < 0.01). Furthermore, when adjusted for age, waist, and S(i), adiponectin was associated with HDL cholesterol and proinsulin, which explained 51% of the variation in adiponectin in multiple regression analyses in that group. In conclusion, circulating plasma adiponectin levels were decreased in nonobese but insulin-resistant FDR and, in addition, related to several facets of the insulin resistance syndrome (IRS). Thus, hypoadiponectinemia may be an important component of the association between cardiovascular disease and IRS.

Relationships between low-density lipoprotein particle size, plasma lipoproteins, and progression of coronary artery disease: the Diabetes Atherosclerosis Intervention Study (DAIS)

BACKGROUND

The Diabetes Atherosclerosis Intervention Study showed that treatment with fenofibrate decreases progression of coronary atherosclerosis in subjects with type 2 diabetes. We determined whether on-treatment plasma lipid concentrations and LDL particle size contribute to the favorable effect of fenofibrate on the progression of coronary artery disease (CAD).

METHODS AND RESULTS

A total of 418 subjects with type 2 diabetes were randomly assigned to 200 mg micronized fenofibrate daily or placebo. The mean follow-up time was 39.6 months. LDL peak particle diameter (LDL size) was determined by polyacrylamide gradient gel electrophoresis from 405 subjects at baseline and at the end of the study. Progression of CAD was measured with quantitative coronary angiography. LDL size increased significantly more in the fenofibrate group than in the placebo group (0.98+/-1.04 versus 0.32+/-0.92 nm, P<0.001). In the combined group, small LDL size was significantly associated with progression of CAD measured as the increase of percentage diameter stenosis (r=-0.16, P=0.002) and decreases in minimum (r=-0.11, P=0.030) and mean (r=-0.10, P=0.045) lumen diameter. High on-treatment LDL cholesterol, apolipoprotein B, and triglyceride concentrations were also associated with the progression of CAD. In regression analyses, small LDL size added to the effect of LDL cholesterol and apolipoprotein B on the progression of CAD. Similar associations were observed in the fenofibrate group, whereas in the placebo group, lipoprotein variables were not significantly correlated with the progression of CAD.

CONCLUSIONS

Changes in LDL size and plasma lipid levels account for part of the antiatherogenic effect of fenofibrate in type 2 diabetes.

Plasma phospholipid transfer protein activity and small, dense LDL in type 2 diabetes mellitus

BACKGROUND

Phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP) remodel circulating lipoproteins and play a role in the antiatherogenic reverse cholesterol transport pathway. The present study determined whether abnormalities in the LDL subfraction pattern in type 2 diabetic patients were related to changes in lipid transfer proteins.

METHODS

Low-density lipoprotein (LDL) subfractions were measured by density gradient ultracentrifugation and plasma PLTP and CETP activities by radiometric assays in 240 diabetic patients and 136 controls.

RESULTS

The diabetic patients had lower LDL-I (P < 0.001) and higher LDL-III concentrations than the controls (P < 0.001). Plasma PLTP activity was increased (P < 0.001) whereas no significant differences were seen in CETP activity. In the diabetic patients, small, dense LDL-III correlated with plasma triglyceride (r = 0.18, P < 0.01), HDL (r = -0.14, P < 0.05), PLTP (r = 0.29, P < 0.001) and CETP activity (r = 0.15, P < 0.05). Linear regression analysis showed that plasma PLTP activity, triglyceride and age were the major determinants of LDL-III concentration (r2 = 28%, P < 0.001). The univariate relationship between CETP and LDL-III was no longer significant after adjusting for PLTP activity.

CONCLUSIONS

The increase in plasma PLTP activity was independently associated with small, dense LDL concentrations in type 2 diabetes. Hence, elevated PLTP activity might have both antiatherogenic and pro-atherogenic potential in these patients.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Genetic influences contributing to LDL particle size in familial combined hyperlipidaemia

The nature of the genetic and environmental factors influencing low density lipoprotein (LDL) particle size in patients with familial combined hyperlipidaemia (FCHL) is under debate. We measured LDL peak particle size in 553 subjects belonging to 48 Finnish FCHL families. Individuals with high triglyceride (TG) concentrations (phenotype IV) or combined hyperlipidaemia (phenotype IIB) had significantly smaller LDL particles than those with hypercholesterolaemia (phenotype IIA) or unaffected subjects (P<0.001). In stepwise regression analyses, serum TGs (r(2)=43%, P<0.001) and high density lipoprotein cholesterol (HDL-C) (r(2)=4.5%, P<0.001) were the only significant predictors of LDL peak particle size. Familial correlations support the conclusion that LDL peak particle size is familial, and most probably influenced by genes in these families. Segregation analysis of LDL peak particle size, a quantitative trait, was performed to model this genetic influence. Our results suggest a polygenic background for LDL size with a recessive major gene that may contribute to large LDL peak particle size in women. Serum TG and HDL-C concentrations predict the majority of variations in LDL particle size.

Metabolic origins and clinical significance of LDL heterogeneity

LDLs in humans comprise multiple distinct subspecies that differ in their metabolic behavior and pathologic roles. Metabolic turnover studies suggest that this heterogeneity results from multiple pathways, including catabolism of different VLDL and IDL precursors, metabolic remodeling, and direct production. A common lipoprotein profile designated atherogenic lipoprotein phenotype is characterized by a predominance of small dense LDL particles. Multiple features of this phenotype, including increased levels of triglyceride rich lipoprotein remnants and IDLs, reduced levels of HDL and an association with insulin resistance, contribute to increased risk for coronary heart disease compared with individuals with a predominance of larger LDL. Increased atherogenic potential of small dense LDL is suggested by greater propensity for transport into the subendothelial space, increased binding to arterial proteoglycans, and susceptibility to oxidative modification. Large LDL particles also can be associated with increased coronary disease risk, particularly in the setting of normal or low triglyceride levels. Like small LDL, large LDL exhibits reduced LDL receptor affinity compared with intermediate sized LDL. Future delineation of the determinants of heterogeneity of LDL and other apoB-containing lipoproteins may contribute to improved identification and management of patients at high risk for atherosclerotic disease.