Why is HDL functionally deficient in type 2 diabetes?

Elevated serum uric acid in nondiabetic people mark pro-inflammatory state and HDL dysfunction and independently predicts coronary disease

We explored the association of serum uric acid (UA) concentrations with pro-inflammatory state and high-density lipoprotein (HDL) dysfunction. UA tertiles in tracked 1,508 nondiabetic participants were analyzed cross-sectionally for associations with inflammation biomarkers and protective proteins over a mean follow-up of 4.9 years for incident coronary heart disease (CHD) using Cox proportional hazards regression. In the absence of metabolic syndrome (MetS), UA tertiles significantly distinguished, in each sex, increasing categories of three MetS components (inflammation/oxidation markers, apolipoprotein (apo)B) and (inversely) current smoking (but not protective proteins such as HDL, apoA-I, and adiponectin). Distinctions attenuated in the presence of MetS. Linear regression model revealed fasting triglycerides (1.86 mg/dl variance), male sex, and gamma-glutamyl transferase and age as covariates of UA levels in women. In Cox analysis, incident CHD (n = 137) was predicted by mid and upper UA tertile in men alone at significant hazard ratios of 2.7, additively to conventional risk factors. Elevated serum UA levels, linked to triglycerides, mark in nondiabetic people pro-inflammatory state, and, notably, HDL dysfunction. CHD risk is independently predicted by elevated UA levels in nondiabetic men and is modulated by MetS and gender.

Dyslipidemia, but not hyperglycemia and insulin resistance, is associated with marked alterations in the HDL lipidome in type 2 diabetic subjects in the DIWA cohort: impact on small HDL particles

In this study we have used mass spectrometry in order to characterize the HDL lipidome in three groups of women from the DIWA cohort; one control group, plus two groups with type 2 diabetes with insulin resistance; one dyslipidemic and one normolipidemic. The aim was to investigate whether dyslipidemia is required in addition to insulin resistance for the occurrence of an altered HDL lipidome, which in turn might impact HDL functionality. The dyslipidemic type 2 diabetic subjects were distinguished by obesity, hypertriglyceridemia with elevated apoC3, low HDL-cholesterol and chronic low grade inflammation. In a stepwise multivariate linear regression analysis, including biomarkers of dyslipidemia and insulin resistance as independent variables, only dyslipidemia showed a significant correlation with HDL lipid classes. Small HDL-particles predominated in dyslipidemic subjects in contrast to the normolipidemic diabetic and control groups, and were enriched in lysophosphatidylcholine (+13%), a product of proinflammatory phospholipases, and equally in two core lipids, palmitate-rich triacylglycerols and diacylglycerols (+77 %), thereby reflecting elevated CETP activity. Dyslipidemic small HDL particles were further distinguished not only as the primary carrier of ceramides, which promote inflammation and insulin resistance, but also by a subnormal plasmalogen/apoAI ratio, consistent with elevated oxidative stress typical of type 2 diabetes. From these data we conclude that in type 2 diabetes, dyslipidemia predominates relative to hyperglycemia for the occurrence of an altered HDL lipidome. Furthermore, dyslipidemia alters the cargo of bioactive lipids, with implications for HDL function.

Mass spectrometric immunoassay and MRM as targeted MS-based quantitative approaches in biomarker development: potential applications to cardiovascular disease and diabetes

Type 2 diabetes mellitus (T2DM) is an important risk factor for cardiovascular disease (CVD)--the leading cause of death in the United States. Yet not all subjects with T2DM are at equal risk for CVD complications; the challenge lies in identifying those at greatest risk. Therapies directed toward treating conventional risk factors have failed to significantly reduce this residual risk in T2DM patients. Thus newer targets and markers are needed for the development and testing of novel therapies. Herein we review two complementary MS-based approaches--mass spectrometric immunoassay (MSIA) and MS/MS as MRM--for the analysis of plasma proteins and PTMs of relevance to T2DM and CVD. Together, these complementary approaches allow for high-throughput monitoring of many PTMs and the absolute quantification of proteins near the low picomolar range. In this review article, we discuss the clinical relevance of the high density lipoprotein (HDL) proteome and Apolipoprotein A-I PTMs to T2DM and CVD as well as provide illustrative MSIA and MRM data on HDL proteins from T2DM patients to provide examples of how these MS approaches can be applied to gain new insight regarding cardiovascular risk factors. Also discussed are the reproducibility, interpretation, and limitations of each technique with an emphasis on their capacities to facilitate the translation of new biomarkers into clinical practice.

Obesity, adiposity, and dyslipidemia: a consensus statement from the National Lipid Association

The term "fat" may refer to lipids as well as the cells and tissue that store lipid (ie, adipocytes and adipose tissue). "Lipid" is derived from "lipos," which refers to animal fat or vegetable oil. Adiposity refers to body fat and is derived from "adipo," referring to fat. Adipocytes and adipose tissue store the greatest amount of body lipids, including triglycerides and free cholesterol. Adipocytes and adipose tissue are active from an endocrine and immune standpoint. Adipocyte hypertrophy and excessive adipose tissue accumulation can promote pathogenic adipocyte and adipose tissue effects (adiposopathy), resulting in abnormal levels of circulating lipids, with dyslipidemia being a major atherosclerotic coronary heart disease risk factor. It is therefore incumbent upon lipidologists to be among the most knowledgeable in the understanding of the relationship between excessive body fat and dyslipidemia. On September 16, 2012, the National Lipid Association held a Consensus Conference with the goal of better defining the effect of adiposity on lipoproteins, how the pathos of excessive body fat (adiposopathy) contributes to dyslipidemia, and how therapies such as appropriate nutrition, increased physical activity, weight-management drugs, and bariatric surgery might be expected to impact dyslipidemia. It is hoped that the information derived from these proceedings will promote a greater appreciation among clinicians of the impact of excess adiposity and its treatment on dyslipidemia and prompt more research on the effects of interventions for improving dyslipidemia and reducing cardiovascular disease risk in overweight and obese patients.

Low prevalence of type 2 diabetes mellitus among patients with high levels of high-density lipoprotein cholesterol

BACKGROUND

Diabetes mellitus and low levels of high-density lipoprotein cholesterol (HDL-C) are among several known risk factors for coronary artery disease. Recent research has shown potential mechanistic links between these two diseases.

OBJECTIVES

The aim of our study was to characterize, by examining particular coronary artery disease risk factors, patients with extremely high and low levels of HDL-C who were referred to a prevention clinic.

METHODS

We compared the phenotypes of 113 patients with HDL-C levels greater than the 90th percentile with 212 patients with levels less than the 10th percentile by using a retrospective chart review.

RESULTS

The cohort with high HDL-C had a remarkable difference in the incidence of type 2 diabetes (1.8% vs 21.7%). The high HDL-C cohort also had a greater age (52.1 years vs 46.7 years), more light or moderate alcohol consumption (70.8% vs 49.4%), more healthy diet (30.1% vs 22.4%), more light or moderate exercise (90.8% vs 52.2%), and a lower body mass index (25.2 kg/m² vs 28.1 kg/m²).

CONCLUSIONS

Compared with the low HDL-C group--and also the general population--the high HDL-C cohort had a remarkably low prevalence of diabetes mellitus.

High Density Lipoprotein and it's Dysfunction

Plasma high-density lipoprotein cholesterol(HDL-C) levels do not predict functionality and composition of high-density lipoprotein(HDL). Traditionally, keeping levels of low-density lipoprotein cholesterol(LDL-C) down and HDL-C up have been the goal of patients to prevent atherosclerosis that can lead to coronary vascular disease(CVD). People think about the HDL present in their cholesterol test, but not about its functional capability. Up to 65% of cardiovascular death cannot be prevented by putative LDL-C lowering agents. It well explains the strong interest in HDL increasing strategies. However, recent studies have questioned the good in using drugs to increase level of HDL. While raising HDL is a theoretically attractive target, the optimal approach remains uncertain. The attention has turned to the quality, rather than the quantity, of HDL-C. An alternative to elevations in HDL involves strategies to enhance HDL functionality. The situation poses an opportunity for clinical chemists to take the lead in the development and validation of such biomarkers. The best known function of HDL is the capacity to promote cellular cholesterol efflux from peripheral cells and deliver cholesterol to the liver for excretion, thereby playing a key role in reverse cholesterol transport (RCT). The functions of HDL that have recently attracted attention include anti-inflammatory and anti-oxidant activities. High antioxidant and anti-inflammatory activities of HDL are associated with protection from CVD.This review addresses the current state of knowledge regarding assays of HDL functions and their relationship to CVD. HDL as a therapeutic target is the new frontier with huge potential for positive public health implications.

High-density lipoprotein cholesterol and particle concentrations, carotid atherosclerosis, and coronary events: MESA (multi-ethnic study of atherosclerosis)

OBJECTIVES

The purpose of this study was to evaluate independent associations of high-density lipoprotein cholesterol (HDL-C) and particle (HDL-P) concentrations with carotid intima-media thickness (cIMT) and incident coronary heart disease (CHD).

BACKGROUND

HDL-C is inversely related to CHD, and also to triglycerides, low-density lipoprotein particles (LDL-P), and related metabolic risk. HDL-P associations with CHD may be partially independent of these factors.

METHODS

In a multiethnic study of 5,598 men and women ages 45 to 84 years old, without baseline CHD, excluding subjects on lipid-lowering medications, triglycerides >400 mg/dl, or missing values, we evaluated associations of HDL-C and nuclear magnetic resonance spectroscopy-measured HDL-P with cIMT and incident CHD (myocardial infarction, CHD death, and angina, n = 227 events; mean 6.0 years follow-up). All models were adjusted for age, sex, ethnicity, hypertension, and smoking.

RESULTS

HDL-C and HDL-P correlated with each other (ρ = 0.69) and LDL-P (ρ = -0.38, -0.25, respectively, p < 0.05 for all). For (1 SD) higher HDL-C (15 mg/dl) or HDL-P (6.64 μmol/l), cIMT differences were - 26.1 (95% confidence interval [CI]: -34.7 to -17.4) μm and -30.1 (95% CI: -38.8 to - 21.4) μm, and CHD hazard ratios were 0.74 (95% CI: 0.63 to 0.88) and 0.70 (95% CI: 0.59 to 0.82), respectively. Adjusted for each other and LDL-P, HDL-C was no longer associated with cIMT (2.3; 95% CI: - 9.5 to 14.2 μm) or CHD (0.97; 95% CI: 0.77 to 1.22), but HDL-P remained independently associated with cIMT (-22.2; 95% CI: - 33.8 to -10.6 μm) and CHD (0.75; 95% CI: 0.61 to 0.93). Interactions by sex, ethnicity, diabetes, and high-sensitivity C-reactive protein were not significant.

CONCLUSIONS

Adjusting for each other and LDL-P substantially attenuated associations of HDL-C, but not HDL-P, with cIMT and CHD. Potential confounding by related lipids or lipoproteins should be carefully considered when evaluating HDL-related risk.

Increased LCAT activity and hyperglycaemia decrease the antioxidative functionality of HDL

BACKGROUND

Type 2 diabetes mellitus increases the risk of atherosclerotic cardiovascular disease. Antioxidative properties of high density lipoprotein (HDL) are important for atheroprotection. This study investigated whether the antioxidative functionality of HDL is altered in type 2 diabetes mellitus and aimed to identify potential determinants of this parameter.

MATERIALS AND METHODS

In a cross-sectional study, we investigated 74 patients with type 2 diabetes and 75 control subjects. Antioxidative properties of HDL were measured and expressed as either (i) HDL antioxidative capacity or (ii) HDL antioxidation index after multiplying HDL antioxidative capacity results with individual plasma HDL cholesterol concentrations. Lecithin:cholesterol acyltransferase (LCAT) and paraoxonase-1 (PON-1) activities were determined.

RESULTS

HDL antioxidative capacity was similar in patients with diabetes and controls, while the HDL antioxidation index was decreased in patients with diabetes (P = 0.005) owing to lower plasma HDL cholesterol (P < 0.001). LCAT activity was higher and PON-1 activity lower in type 2 diabetes mellitus (each P < 0.001). In the combined subjects, HDL antioxidative capacity was inversely related to LCAT activity (P < 0.01). The HDL antioxidation index correlated negatively with blood glucose (P < 0.001), HbA1c and LCAT activity (each P < 0.01), and positively with PON-1 activity (P < 0.01). Multiple linear regression analysis demonstrated that high LCAT activity was associated with both decreased HDL antioxidation capacity (P < 0.05) and index (P < 0.001) independent of diabetes status, glycaemic control and PON-1.

CONCLUSIONS

Overall, the antioxidative functionality of HDL is impaired in type 2 diabetes mellitus mostly because of lower HDL cholesterol. Hyperglycaemia, increased LCAT activity and lower PON-1 activity likely contribute to impaired antioxidative functionality of HDL.

HDL of patients with type 2 diabetes mellitus elevates the capability of promoting breast cancer metastasis

PURPOSE

Epidemiologic studies suggested complicated associations between type 2 diabetes mellitus and breast cancer. High-density lipoprotein (HDL) is inversely associated with the risk and mortality of breast cancer. Our study is to determine the different effects of normal and diabetic HDL on breast cancer cell metastasis.

EXPERIMENTAL DESIGN

MDA-MB-231 and MCF7 cells were treated with N-HDL, D-HDL, G-HDL, and Ox-HDL. Cell metastasis potency was examined using a tail-vein injection model, and cell adhesion abilities to human umbilical vein endothelial cells (HUVEC) and extracellular matrix (ECM) were determined in vitro. Integrin expression and protein kinase C (PKC) activity were evaluated, and PKC inhibitor was applied.

RESULTS

D-HDL dramatically promoted cell pulmonary metastasis (103.6% increase at P < 0.001 for MDA-MB-231 with 1 × 10(5) cell injection; 157.1% increase at P < 0.05 for MCF7 with 4 × 10(5) cell injection) and hepatic metastasis (18.1-fold increase at P < 0.001 for MCF7 with 4 × 10(5) cell injection), and stimulated higher TC-HUVECs adhesion (21.9% increase at P < 0.001 for MDA-MB-231; 23.6% increase at P < 0.05 for MCF7) and TC-ECM attachment (59.9% and 47.9% increase, respectively, for MDA-MB-231 and MCF7, both at P < 0.01) compared with N-HDL. D-HDL stimulated higher integrin (β1, β2, β3, and αν) expression on cell surface and induced higher PKC activity. Increased TC-HUVECs and TC-ECM adhesion induced by D-HDL, G-HDL, and Ox-HDL could be inhibited by staurosporine.

CONCLUSIONS

Our study showed that glycation and oxidation of HDL in diabetic patients could lead to abnormal actions on breast cancer cell adhesion to HUVECs and ECM, thereby promoting metastasis progression of breast cancer. This will largely draw the attention of HDL-based treatments in the diabetes patients with breast cancer.

HOMA-IR and non-HDL-C as predictors of high cholesteryl ester transfer protein activity in patients at risk for type 2 diabetes

BACKGROUND AND AIMS

Metabolic syndrome (MS) and type 2 diabetes are highly associated with an abnormal lipoprotein profile, which may be generated and accentuated by high cholesteryl ester transfer protein (CETP) activity. Given the difficulty in measuring CETP activity, the aim was to identify simple biochemical predictors of high CETP activity.

DESIGN AND METHODS

Eighty five subjects at risk for type 2 diabetes were classified according to the presence of MS. Lipoprotein profile, HOMA-IR and endogenous CETP activity were evaluated.

RESULTS

As expected, MS patients presented higher concentration of glucose, insulin, triglycerides and non-HDL-C and lower HDL-C levels. Moreover, MS patients exhibited increased HOMA-IR and CETP activity. Employing a ROC curve for MS, high CETP activity was defined as >250%ml⁻¹ h⁻¹. The predictive variables of high CETP were non-HDL-C≥160mg/dl (OR=11.1;95%IC=3.3-38.2;p<0.001) and HOMA-IR>2.1 (OR=4.4;95%IC=1.3-14.8;p<0.05).

CONCLUSIONS

High non-HDL-C and insulin resistance were predictors for increased CETP activity which measurement is not accessible for clinical laboratories.

Nonenzymatic glycation of high-density lipoprotein impairs its anti-inflammatory effects in innate immunity

AIMS/HYPOTHESIS

In type 2 diabetes mellitus (T2DM), the abnormal protein and lipid composition of diabetic high-density lipoprotein (HDL) could impair its anti-inflammatory functions. Whether nonenzymatic glycation directly impaired the anti-inflammatory effects of HDL in innate immunity remained unclear.

METHODS

Human acute monocytic leukemia cell line (THP-1) cells, mouse RAW 264.7 macrophages and primary human monocytes derived macrophages were pre-incubated with native HDL, diabetic HDL isolated from T2DM patients or HDL glycated with different doses of d-glucose in vitro and then challenged with lipopolysaccharide (LPS). The release of tumor necrosis factor (TNF)-α and IL-1β was assayed by enzyme-linked immunosorbent assay (ELISA). Phosphorylation of Iκ-Bα in cytoplasm and nuclear translocation of NF-κB were detected by western blot. Glycation levels of native HDL, glycated HDL and diabetic HDL were determined using LC-MS/MS.

RESULTS

The potency of diabetic HDL to inhibit the release of TNF-α (p < 0.05) and IL-1β (p < 0.001) was dramatically attenuated compared with that of native HDL. Similarly, glycation of HDL in vitro impaired its ability to inhibit TNF-α and IL-1β release in a glucose dose-dependent manner. Moreover, apoHDL still effectively inhibited the release of TNF-α and IL-1β induced by LPS, but glycated apoHDL partly lost such abilities. Nonenzymatic glycation levels of glycated HDL and diabetic HDL increased 28 fold (p < 0.001) and 4 fold (p < 0.001), respectively compared with that of native HDL.

CONCLUSIONS

In this study, we observed that diabetic HDL and HDL glycated in vitro both partly lose their protective effects to inhibit cytokines release induced by LPS in macrophages, and nonenzymatic glycation of the protein components of HDL plays key roles in these impairments.

Hyperglycemia in apolipoprotein E-deficient mouse strains with different atherosclerosis susceptibility

Background

Type 2 diabetes mellitus (T2DM) is associated with an increased risk of atherosclerotic vascular disease, but it is unknown whether the other way around is true too. C57BL/6 (B6) and BALB/cJ (BALB) are two mouse strains that differ markedly in their susceptibility to atherosclerosis. In this study we investigated the development of diet-induced T2DM in these two strains.

Methods and Results

When deficient in apolipoprotein E (apoE^-/-) and fed a Western diet for 12 weeks, atherosclerosis-susceptible B6 mice developed significant hyperglycemia. In contrast, atherosclerosis-resistant BALB apoE^-/- mice had much lower plasma glucose levels than B6.apoE^-/- mice on either chow or Western diet and during an intraperitoneal glucose tolerance test. In response to glucose BALB.apoE^-/- mice displayed both the first and second phases of insulin secretion but the second phase of insulin secretion was absent in B6.apoE^-/- mice. In response to insulin B6.apoE^-/- mice showed a deeper and longer-lasting fall in blood glucose levels while BALB.apoE^-/- mice showed little reduction in glucose levels. Pancreatic islet area of BALB.apoE^-/- mice on light microscopy nearly doubled the area of B6.apoE^-/- mice. Most circulating proinflammatory cytokines were lower in BALB.apoE^-/- than in B6.apoE^-/- mice on the Western diet, as determined by protein arrays. Increased macrophage infiltration in islets was observed in B6.apoE^-/- mice by immunostaining for Mac2 and also by flow cytometry.

Conclusion

This study demonstrates that defects in insulin secretion rather than defects in insulin resistance explain the marketed difference in susceptibility to T2DM in the B6.apoE^-/- and BALB.apoE^-/- mouse model. A smaller islet mass and more prominent islet inflammation may explain the vulnerability of B6.apoE^-/- mice to diet-induced diabetes.

The Cholesterol Content of Western Diets Plays a Major Role in the Paradoxical Increase in High-Density Lipoprotein Cholesterol and Upregulates the Macrophage Reverse Cholesterol Transport Pathway

Objective—

A high–saturated fatty acid– and cholesterol-containing (HFHC) diet is considered to be a major risk factor for cardiovascular disease. The present study aimed to determine the effects of this Western-type diet on high-density lipoprotein (HDL) metabolism and reverse cholesterol transport (RCT) from macrophages to feces.

Methods and Results—

Experiments were carried out in mice fed a low-fat, low-cholesterol diet, an HFHC diet, or an HFHC diet without added cholesterol (high–saturated fatty acid and low-cholesterol [HFLC]). The HFHC diet caused a significant increase in plasma cholesterol, HDL cholesterol, and liver cholesterol and enhanced macrophage-derived [ 3 H]cholesterol flux to feces by 3- to 4-fold. These effects were greatly reduced in mice fed the HFLC diet. This HFHC diet–mediated induction of RCT was sex independent and was not associated with obesity or insulin resistance. The HFHC diet caused 1.4- and 3-fold increases in [ 3 H]cholesterol efflux to plasma and HDL-derived [ 3 H]tracer fecal excretion, respectively. Unlike a low-fat, low-cholesterol and HFLC diets, the HFHC diet increased liver ABCG5/G8 expression. The effect of the HFHC diet on fecal macrophage-derived [ 3 H]cholesterol excretion was totally blunted in ABCG5/G8-deficient mice.

Conclusion—

Despite its deleterious effects on atherosclerosis, the HFHC diet promoted a sustained compensatory macrophage-to-feces RCT. Our data provide direct evidence of the crucial role of dietary cholesterol signaling through liver ABCG5/G8 upregulation in the HFHC diet–mediated induction of macrophage-specific RCT.

High-density lipoprotein of patients with type 2 diabetes mellitus elevates the capability of promoting migration and invasion of breast cancer cells

Epidemiological studies suggested complicated associations between type 2 diabetes mellitus and breast cancer. There is a significant inverse association between high-density lipoprotein (HDL) and the risk and mortality of breast cancer. However, HDL could be modified in various ways in diabetes patients, and this may lead to the altered effects on many different types of cells. In our study, we found that glycation and oxidation levels are significantly higher in HDL from type 2 diabetes mellitus patients compared to that from healthy subjects. Diabetic HDL dramatically had a stronger capability to promote cell proliferation, migration and invasion of breast cancer (as examined both on hormone-independent cells and on hormone-dependent cells). In addition, glycated and oxidized HDL, which were produced in vitro, acted in similar way as diabetic HDL. Diabetic HDL, glycated HDL and oxidized HDL also induced higher synthesis and secretion of VEGF-C, MMP-2 and MMP-9 from malondialdehyde (MDA)-MB-231 cells. It was indicated that diabetic, glycated and oxidized HDL promote MDA-MB-231 cell migration and invasion through ERK and p38 MAPK pathways, and Akt pathway plays an important role as well in MDA-MB-231 cell invasion. The Akt, ERK and p38 MAPK pathways are also involved in VEGF-C and MMP-9 secretion induced by diabetic, glycated and oxidized HDL. Our study demonstrated that glycation and oxidation of HDL in diabetic patients could lead to abnormal actions on MDA-MB-231 cell proliferation, migration and invasion, thereby promoting the progression of breast cancer. This will largely draw the attention of HDL-based treatments in diabetic patients especially those with breast cancer.

Reverse cholesterol transport revisited: contribution of biliary versus intestinal cholesterol excretion

Reverse cholesterol transport (RCT) is usually defined as high-density lipoprotein-mediated transport of excess cholesterol from peripheral tissues, including cholesterol-laden macrophages in vessel walls, to the liver. From the liver, cholesterol can then be removed from the body via secretion into the bile for eventual disposal via the feces. According to this paradigm, high plasma high-density lipoprotein levels accelerate RCT and hence are atheroprotective. New insights in individual steps of the RCT pathway, in part derived from innovative mouse models, indicate that the classical concept of RCT may require modification.

Lipid-Free Apolipoprotein A-I and Discoidal Reconstituted High-Density Lipoproteins Differentially Inhibit Glucose-Induced Oxidative Stress in Human Macrophages

Objective—

The goal of this study was to investigate the mechanisms by which apolipoprotein (apo) A-I, in the lipid-free form or as a constituent of discoidal reconstituted high-density lipoproteins ([A-I]rHDL), inhibits high-glucose–induced redox signaling in human monocyte-derived macrophages (HMDM).

Methods and Results—

HMDM were incubated under normal (5.8 mmol/L) or high-glucose (25 mmol/L) conditions with native high-density lipoproteins (HDL) lipid-free apoA-I from normal subjects and from subjects with type 2 diabetes (T2D) or (A-I)rHDL. Superoxide (O 2 − ) production was measured using dihydroethidium fluorescence. NADPH oxidase activity was assessed using lucigenin-derived chemiluminescence and a cyotochrome c assay. p47phox translocation to the plasma membrane, Nox2, superoxide dismutase 1 (SOD1), and SOD2 mRNA and protein levels were determined by real-time polymerase chain reaction and Western blotting. Native HDL induced a time-dependent inhibition of O 2 − generation in HMDM incubated with 25 mmol/L glucose. Lipid-free apoA-I and (A-I)rHDL increased SOD1 and SOD2 levels and attenuated 25 mmol/L glucose-mediated increases in cellular O 2 − , NADPH oxidase activity, p47 translocation, and Nox2 expression. Lipid-free apoA-I mediated its effects on Nox2, SOD1, and SOD2 via ABCA1. (A-I)rHDL-mediated effects were via ABCG1 and scavenger receptor BI. Lipid-free apoA-I from subjects with T2D inhibited reactive oxygen species generation less efficiently than normal apoA-I.

Conclusion—

Native HDL, lipid-free apoA-I and (A-I)rHDL inhibit high-glucose–induced redox signaling in HMDM. The antioxidant properties of apoA-I are attenuated in T2D.

Low-grade inflammation, and dysfunction of high-density lipoprotein and its apolipoproteins as a major driver of cardiometabolic risk

Dysfunction of high-density lipoprotein (HDL) particles that even become proinflammatory or lose atheroprotective properties is known through analyses of HDL isolated from diabetic subjects. Recently, high concentrations of HDL or apolipoprotein (apo) A-I in individuals with diabetes or coronary heart disease were found to reveal dysfunction in some population-based studies. Such dysfunction of HDL and its apos A-I, A-II, and C-III has been observed in a general population for the first time among Turkish adults. Functional defectiveness manifested itself by unexpected correlations with inflammatory biomarkers and, in long-term follow-up, by lack of protection against diabetes and coronary heart disease, accounting for the excess incidences in Turks. Female sex was more pronouncedly affected by this process that presumably exists in other ethnicities in South Asia, East Europe, and the Middle East. In contradistinction, in Western and East Asian population, only individuals with glucose intolerance or those at risk for cardiometabolic disease are considered to be or were documented in a review of clinical trials to have been affected by impaired function of HDL. High-density lipoprotein dysfunctionality is closely linked to obesity and low-grade inflammation yet seems to act partly independently of them. Cigarette smoking in overweight women with low-grade inflammation appears to offer limited protection against cardiometabolic risk. The great impact in public health of the dysfunction of protective serum proteins requires individual clinical recognition, appropriate preventive measures, and delineation of management, including with anti-inflammatory drugs.

The differentiating effect of glimepiride and glibenclamide on paraoxonase 1 and platelet-activating factor acetylohydrolase activity

AIMS

The present study was designed to examine the effect of sulphonylureas, glimepiride (GM) and glibenclamide (GB), on paraoxonase 1 (PON1) and platelet activating factor acetylohydrolase (PAF-AH) activity in normal and streptozotocin (STZ)-induced (50 mg/kg) diabetic rats.

MAIN METHODS

In treated groups, glimepiride (0.1 mg/kg) or glibenclamide (2 mg/kg) was given orally for 4 weeks. A PON1 and PAF-AH activity were estimated by spectrophotometric method.

KEY FINDINGS

Hyperglycemia was accompanied by a significant decrease in plasma PON1 activity toward paraoxon (P < 0.001) and phenyl acetate (P < 0.01) and increase in plasma PAF-AH activity (P < 0.01). In STZ-induced diabetic rats the administration of both GM and GB had no effect on plasma PON1 activity but reversed elevated plasma PAF-AH activity (GM: P < 0.05, GB: P < 0.01). In non-diabetic rats after either GM or GB administration the decreased PON1 activity in the plasma was observed (GM: P < 0.001, GB: P < 0.05), but plasma PAF-AH activity remained unchanged. Both GM and GB had no effect on total plasma antioxidant capacity in diabetic and control treated groups. Additionally, both drugs increased PON1 activity toward phenyl acetate in the liver, in diabetic rats (GM: P < 0.05, GB:ns) as well as in non-diabetic rats (GM: P < 0.001, GB: P < 0.001), and reduced lipid peroxidation in the liver.

SIGNIFICANCE

These results demonstrate that in streptozotocin-induced diabetic rats as well as in normal rats glimepiride and glibenclamide have no beneficial effects on circulating PON1 and PAF-AH activities, but both drugs increase PON1 activity in the liver.

HDL and LDL cholesterol significantly influence beta-cell function in type 2 diabetes mellitus

PURPOSE OF REVIEW

Patients with type 2 diabetes mellitus (T2DM) display significant abnormalities in both LDL and HDL particles. Recent data suggest that these changes in lipoprotein particles could contribute to the pathogenesis of T2DM. In this review, we focus on these abnormalities and discuss their possible impact on beta-cell function and beta-cell mass.

RECENT FINDINGS

Infusion of reconstituted HDL in T2DM patients improves beta-cell function, whereas carriers of loss-of-function mutations in the cholesterol transporter ABCA1, who have decreased HDL levels, have impaired beta-cell function. In addition, recent studies show that HDL protects against stress-induced beta-cell apoptosis in vitro. Finally, increasing evidence points to a role for islet inflammation in the pathogenesis of T2DM. ABCA1 and ABCG1 may also modulate these inflammatory responses, suggesting an additional pathway by which HDL may impact T2DM.

SUMMARY

Recent findings indicate that HDL protects beta-cells from cholesterol-induced beta-cell dysfunction, stress-induced apoptosis and islet inflammation. As the protective properties of HDL are compromised in patients with metabolic syndrome and T2DM, dysfunctional HDL metabolism could contribute to the pathogenesis of T2DM. Therapeutic normalization of both the quantity and quality of HDL particles may be a novel approach to prevent or treat T2DM.

Nonenzymatic glycation impairs the antiinflammatory properties of apolipoprotein A-I

OBJECTIVE

The goal of this study was to investigate the effects of nonenzymatic glycation on the antiinflammatory properties of apolipoprotein (apo) A-I.

METHODS AND RESULTS

Rabbits were infused with saline, lipid-free apoA-I from normal subjects (apoA-I(N)), lipid-free apoA-I nonenzymatically glycated by incubation with methylglyoxal (apoA-I(Glyc in vitro)), nonenzymatically glycated lipid-free apoA-I from subjects with diabetes (apoA-I(Glyc in vivo)), discoidal reconstituted high-density lipoproteins (rHDL) containing phosphatidylcholine and apoA-I(N), (A-I(N))rHDL, or apoA-I(Glyc in vitro), (A-I(Glyc in vitro))rHDL. At 24 hours postinfusion, acute vascular inflammation was induced by inserting a nonocclusive, periarterial carotid collar. The animals were euthanized 24 hours after the insertion of the collar. The collars caused intima/media neutrophil infiltration and increased endothelial expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). ApoA-I(N) infusion decreased neutrophil infiltration and VCAM-1 and ICAM-1 expression by 89%, 90%, and 66%, respectively. The apoA-I(Glyc in vitro) infusion decreased neutrophil infiltration by 53% but did not reduce VCAM-1 or ICAM-1 expression. ApoA-I(Glyc in vivo) did not inhibit neutrophil infiltration or adhesion molecule expression. (A-I(Glyc in vitro))rHDL also inhibited vascular inflammation less effectively than (A-I(N))rHDL. The reduced antiinflammatory properties of nonenzymatically glycated apoA-I were attributed to a reduced ability to inhibit nuclear factor-kappaB activation and reactive oxygen species formation.

CONCLUSIONS

Nonenzymatic glycation impairs the antiinflammatory properties of apoA-I.

Lipid measures for prediction of incident cardiovascular disease in diabetic and non-diabetic adults: results of the 8.6 years follow-up of a population based cohort study

BACKGROUND

Diabetes is a strong risk factor for cardiovascular disease (CVD).The relative role of various lipid measures in determining CVD risk in diabetic patients is still a subject of debate. We aimed to compare performance of different lipid measures as predictors of CVD using discrimination and fitting characteristics in individuals with and without diabetes mellitus from a Middle East Caucasian population.

METHODS

The study population consisted of 1021 diabetic (men = 413, women = 608) and 5310 non-diabetic (men = 2317, women = 2993) subjects, aged > or = 30 years, free of CVD at baseline. The adjusted hazard ratios (HRs) for CVD were calculated for a 1 standard deviation (SD) change in total cholesterol (TC), log-transformed triglyceride (TG), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), non-HDL-C, TC/HDL-C and log-transformed TG/HDL-C using Cox proportional regression analysis. Incident CVD was ascertained over a median of 8.6 years of follow-up.

RESULTS

A total of 189 (men = 91, women = 98) and 263(men = 169, women = 94) CVD events occurred, in diabetic and non-diabetic population, respectively. The risk factor adjusted HRs to predict CVD, except for HDL-C, TG and TG/HDL-C, were significant for all lipid measures in diabetic males and were 1.39, 1.45, 1.36 and 1.16 for TC, LDL-C, non- HDL-C and TC/HDL-C respectively. In diabetic women, using multivariate analysis, only TC/HDL-C had significant risk [adjusted HR1.31(1.10-1.57)].Among non-diabetic men, all lipid measures, except for TG, were independent predictors for CVD however; a 1 SD increase in HDL-C significantly decreased the risk of CVD [adjusted HR 0.83(0.70-0.97)].In non-diabetic women, TC, LDL-C, non-HDL-C and TG were independent predictors.There was no difference in the discriminatory power of different lipid measures to predict incident CVD in the risk factor adjusted models, in either sex of diabetic and non-diabetic population.

CONCLUSION

Our data according to important test performance characteristics provided evidence based support for WHO recommendation that along with other CVD risk factors serum TC vs. LDL-C, non-HDL-C and TC/HDL-C is a reasonable lipid measure to predict incident CVD among diabetic men. Importantly, HDL-C did not have a protective effect for incident CVD among diabetic population; given that the HDL-C had a protective effect only among non- diabetic men.

Hyperglycemia and glycation in diabetic complications

Diabetes mellitus is a multifactorial disease, classically influenced by genetic determinants of individual susceptibility and by environmental accelerating factors, such as lifestyle. It is considered a major health concern,as its incidence is increasing at an alarming rate, and the high invalidating effects of its long-term complications affect macro- and microvasculature, heart, kidney, eye, and nerves. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage occurring in diabetes, either through repeated acute changes in cellular glucose metabolism, or through the long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs represent a heterogeneous group of chemical products resulting from a nonenzymatic reaction between reducing sugars and proteins, lipids, nucleic acids, or a combination of these.The glycation process (glucose fixation) affects circulating proteins (serum albumin, lipoprotein, insulin, hemoglobin),whereas the formation of AGEs implicates reactive intermediates such as methylglyoxal. AGEs form cross-links on long-lived extracellular matrix proteins or react with their specific receptor RAGE, resulting inoxidative stress and proinflammatory signaling implicated in endothelium dysfunction, arterial stiffening, and microvascular complications. This review summarizes the mechanism of glycation and of AGEs formation and the role of hyperglycemia, AGEs, and oxidative stress in the pathophysiology of diabetic complications.

Impaired protection against diabetes and coronary heart disease by high-density lipoproteins in Turks

The issue of whether or not incident type 2 diabetes mellitus and coronary heart disease (CHD) can be predicted by high-density lipoprotein (HDL) cholesterol in both sexes needs investigation. A representative sample of 3035 middle-aged Turkish adults free of CHD at baseline was studied with this purpose prospectively over a mean of 7.8 years. High-density lipoprotein cholesterol levels were found to be correlated in women positively with plasma fibrinogen and weakly with waist girth and C-reactive protein, and to be not correlated with fasting insulin. High-density lipoprotein cholesterol protected men against future CHD risk (for a 12-mg/dL increment: relative risk = 0.80 [95% confidence interval, 0.69-0.95]) after multivariable adjustment in logistic regression analyses for age, smoking status, physical activity grade, hypertension, abdominal obesity, diabetes, and lipid-lowering drugs. However, men were not protected against risk of diabetes. In women, HDL cholesterol was not associated with risk for CHD, whereas intermediate (40-60 mg/dL) compared with lower HDL cholesterol levels proved protective against risk of diabetes (relative risk = 0.57 [95% confidence interval, 0.36-0.90]) after adjustments that included apolipoprotein A-I tertiles. Yet higher serum concentrations failed to yield protection against diabetes. It was concluded that HDL particles confer partially lacking protection against cardiometabolic risk among Turks, and this impairment is modulated by sex. This highly important observation may result from a setting of prevailing chronic subclinical inflammation.

Dysfunctional HDL as a diagnostic and therapeutic target

The atheroprotective effects of HDL are mediated by several mechanisms, including its role in reverse cholesterol transport and via its antiinflammatory properties. However, not all HDL is functionally similar. HDL and apolipoprotein A-I may become dysfunctional or even proinflammatory and thus promote atherosclerosis. ApoAI posttranslational modification can have a large impact on its function. Myeloperoxidase modification of apoAI impairs its function as a cholesterol acceptor, and the molecular changes induced by myeloperoxidase have been studied in detail. These studies provide the basis for the development of an oxidant-resistant form of apoAI and clinical measures of HDL modification and dysfunction, which may be useful as a treatment criterion.

High-density lipoprotein: why all the fuss?

The current search for new treatments to combat coronary heart disease (CHD) is centred on increasing HDL-cholesterol. The failure of the CETP inhibitor torcetrapib may force a rethink. This perspective briefly reviews the antiatherosclerotic properties of HDL and ways HDL-cholesterol concentration can be raised, but argues – in light of the fact that HDL-cholesterol concentration does not reflect the protective properties of HDL particles – that this approach is flawed and a different approach, targeting know antiatherosclerotic components of HDL, is required.

Acute hypertriglyceridaemia in humans increases the triglyceride content and decreases the anti-inflammatory capacity of high density lipoproteins

INTRODUCTION

Post-prandial hypertriglyceridaemia is a risk factor for cardiovascular disease, although the underlying mechanisms remain unclear. High density lipoproteins (HDL) have been shown to be atheroprotective, in part through attenuation of vascular inflammation. In this study, the influence of acute hypertriglyceridaemia on the composition and anti-inflammatory properties of HDL was investigated.

METHODS

Eight fasting healthy male subjects (34+/-2 years) received 20% Intralipid (15 mg/kg/h) or saline, on separate occasions in random order. At baseline and 60 min post-infusion, the total HDL fraction was isolated and its chemical composition determined. HDL were added to TNF-alpha stimulated human coronary artery endothelial cells and VCAM-1 and ICAM-1 expression was determined by flow cytometry.

RESULTS

Serum triglyceride (97.4+/-8.5mg/dL baseline, 283.2+/-35.4 mg/dL post-infusion, p<0.001) and HDL triglyceride content (3.8+/-0.5% HDL mass baseline, 5.3+/-0.9% HDL mass post-infusion, p<0.05) increased significantly after Intralipid infusion. HDL post-Intralipid were significantly less anti-inflammatory compared with control (e.g. at 8 microM apoA-I, %VCAM-1 expression 54+/-5 post-saline, 73+/-4 post-Intralipid, p=0.01; %ICAM-1 expression 94+/-1 post-saline, 99.4+/-0.6 post-Intralipid, p<0.01). There was also a significant correlation between HDL triglyceride content and VCAM-1 expression (R=0.70, p=0.005); as well as between plasma triglyceride levels and both VCAM-1 (R=0.71, p<0.005) and ICAM-1 expression (R=0.80, p<0.005).

CONCLUSION

Acute hypertriglyceridaemia, simulating the post-prandial state, results in triglyceride-rich HDL with impaired anti-inflammatory capacity.

In vitro nonenzymatic glycation of guanosine 5'-triphosphate by dihydroxyacetone phosphate

Dihydroxyacetone phosphate (DHAP) is a glycolytic intermediate that has been found to be significantly elevated in the erythrocytes of diabetic patients and patients with triosephosphate isomerase deficiency. DHAP spontaneously breaks down to methylglyoxal, a potent glycating agent that reacts with proteins and nucleic acids in vivo to form advanced glycation endproducts (AGEs). Like methylglyoxal, DHAP itself is also a glycating metabolite, capable of condensing with proteins and altering their structure or function. The objective of this investigation was to evaluate the susceptibility of nucleotides to nonenzymatic attack by DHAP, and to determine the factors influencing the rate and extent of nucleotide glycation by this sugar. Of the four nucleotide triphosphates (ATP, CTP, GTP and UTP) that were studied, only GTP was reactive, forming a wide range of UV and fluorescent products with DHAP. Increases in temperature and nucleotide concentration enhanced the rate and extent of GTP glycation by DHAP and promoted the heterogeneity of AGEs. Capillary electrophoresis, HPLC, and mass spectrometry allowed for a thorough analysis of the glycated products and demonstrated that the reaction of DHAP with GTP occurred via the classical Amadori pathway.

Spotlight on HDL-raising therapies: insights from the torcetrapib trials

Subnormal levels of HDL cholesterol constitute a major cardiovascular risk factor. Inhibitors of cholesteryl ester transfer protein (CETP) are presently the most potent HDL-raising agents. Torcetrapib was the first CETP inhibitor to enter a large-scale, prospective, placebo-controlled interventional trial, which was prematurely terminated in December 2006 because of excess cardiovascular and noncardiovascular mortality in the active treatment group. Therapy with torcetrapib was associated with considerable increases in aldosterone level and blood pressure and changes in serum electrolytes indicative of mineralocorticoid excess. These findings indicate that torcetrapib has off-target toxic effects unrelated to HDL raising that involve the activation of mineralocorticoid receptors by aldosterone and result in the induction of hypertension. In contrast with torcetrapib, other CETP inhibitors such as JTT-705 and MK-825 do not increase blood pressure in humans, an observation which discounts a class effect. The available data do not, however, exclude potential adverse effects of CETP inhibition such as the generation of HDL particles that have deficient biological activities and a deleterious impact on reverse cholesterol transport and steroid metabolism. Normalization of both defective HDL function and diminished HDL levels should, therefore, be the focus of pharmacological HDL raising in future studies.