A normotriglyceridemic, low HDL-cholesterol phenotype is characterised by elevated oxidative stress and HDL particles with attenuated antioxidative activity

OBJECTIVE: Low levels of high density lipoprotein-cholesterol (HDL-C) are highly prevalent in subjects presenting premature atherosclerosis. It is indeterminate as to whether high cardiovascular risk in low HDL-C subjects occurs concomitantly with elevated oxidative stress and/or with biologically dysfunctional HDL particles. METHODS AND RESULTS: Systemic oxidative stress (as plasma 8-isoprostanes) was 2.3-fold elevated (p<0.05) in normocholesterolemic, normotriglyceridemic, normoglycemic low HDL-C subjects (plasma HDL-C, <40 mg/dL; n=8) as compared to normolipidemic controls (n=15). HDL subfractions (HDL2b, 2a, 3a, 3b and 3c) isolated by density gradient ultracentrifugation from low HDL-C subjects displayed significantly lower (-21 to -43%, p<0.05) specific antioxidative activity (sAA; capacity to protect LDL from oxidation on a unit particle mass or on a particle number basis) as compared to controls. Altered chemical composition (core triglyceride enrichment, cholesteryl ester depletion) paralleled antioxidative dysfunction of HDL subfractions. Plasma 8-isoprostane levels negatively correlated with sAA of HDL subfractions and positively correlated with the total cholesterol/HDL-C ratio, which was significantly elevated in the low HDL-C phenotype. CONCLUSIONS: Low HDL-C subjects display elevated oxidative stress and possess HDL particle subspecies with attenuated intrinsic antioxidative activity which is intimately related to their altered chemical composition.     

Metabolic syndrome is associated with elevated oxidative stress and dysfunctional dense high-density lipoprotein particles displaying impaired antioxidative activity

A metabolic syndrome (MetS) phenotype is characterized by insulin-resistance, atherogenic dyslipidemia, oxidative stress, and elevated cardiovascular risk and frequently involves subnormal levels of high-density lipoprotein (HDL) cholesterol. We evaluated the capacity of physicochemically distinct HDL subfractions from MetS subjects to protect low-density lipoprotein against oxidative stress.MetS subjects presented an insulin-resistant phenotype, with central obesity and elevation in systolic blood pressure and plasma triglyceride, LDL-cholesterol, apolipoprotein B, glucose, and insulin levels. Systemic oxidative stress, assessed as plasma 8-isoprostanes, was significantly higher (3.7-fold) in MetS subjects (n = 10) compared with nonobese normolipidemic controls (n = 11). In MetS, small, dense HDL3a, 3b, and 3c subfractions possessed significantly lower specific antioxidative activity (up to -23%, on a unit particle mass basis) than their counterparts in controls. In addition, HDL2a and 3a subfractions from MetS patients possessed lower total antioxidative activity (up to -41%, at equivalent plasma concentrations). The attenuated antioxidative activity of small, dense HDL subfractions correlated with systemic oxidative stress and insulin resistance and was associated with HDL particles exhibiting altered physicochemical properties (core triglyceride enrichment and cholesteryl ester depletion).We conclude that antioxidative activity of small, dense HDL subfractions of altered chemical composition is impaired in MetS and associated with elevated oxidative stress and insulin resistance. Induction of selective increase in the circulating concentrations of dense HDL subfractions may represent an innovative therapeutic approach for the attenuation of high cardiovascular risk in MetS.     

Metabolic syndrome features small, apolipoprotein A-I-poor, triglyceride-rich HDL3 particles with defective anti-apoptotic activity

The metabolic syndrome (MetS) phenotype is typically characterized by visceral obesity, insulin resistance, atherogenic dyslipidemia involving hypertriglyceridemia and subnormal levels of high density lipoprotein-cholesterol (HDL-C), oxidative stress and elevated cardiovascular risk. The potent antioxidative activity of small HDL3 is defective in MetS [Hansel B, et al. J Clin Endocrinol Metab 2004;89:4963-71]. We evaluated the functional capacity of small HDL3 particles from MetS subjects to protect endothelial cells from apoptosis induced by mildly oxidized low-density lipoprotein (oxLDL). MetS subjects presented an insulin-resistant obese phenotype, with hypertriglyceridemia, elevated apolipoprotein B and insulin levels, but subnormal HDL-C concentrations and chronic low grade inflammation (threefold elevation of C-reactive protein). When human microvascular endothelial cells (HMEC-1) were incubated with oxLDL (200 microg apolipoprotein B/ml) in the presence or absence of control HDL subfractions (25 microg protein/ml), small, dense HDL3b and 3c significantly inhibited cellular annexin V binding and intracellular generation of reactive oxygen species. The potent anti-apoptotic activity of small HDL3c particles was reduced (-35%; p<0.05) in MetS subjects (n=16) relative to normolipidemic controls (n=7). The attenuated anti-apoptotic activity of HDL3c correlated with abdominal obesity, atherogenic dyslipidemia and systemic oxidative stress (p<0.05), and was intimately associated with altered physicochemical properties of apolipoprotein A-I (apoA-I)-poor HDL3c, involving core cholesteryl ester depletion and triglyceride enrichment. We conclude that in MetS, apoA-I-poor, small, dense HDL3c exert defective protection of endothelial cells from oxLDL-induced apoptosis, potentially reflecting functional anomalies intimately associated with abnormal neutral lipid core content.     

Atherogenic role of elevated CE transfer from HDL to VLDL(1) and dense LDL in type 2 diabetes : impact of the degree of triglyceridemia

Plasma cholesteryl ester transfer protein (CETP) facilitates intravascular lipoprotein remodeling by promoting the heteroexchange of neutral lipids. To determine whether the degree of triglyceridemia may influence the CETP-mediated redistribution of HDL CE between atherogenic plasma lipoprotein particles in type 2 diabetes, we evaluated CE mass transfer from HDL to apoB-containing lipoprotein acceptors in the plasma of type 2 diabetes subjects (n=38). In parallel, we investigated the potential relationship between CE transfer and the appearance of an atherogenic dense LDL profile. The diabetic population was divided into 3 subgroups according to fasting plasma triglyceride (TG) levels: group 1 (G1), TG<100 mg/dL; group 2 (G2), 100200 mg/dL. Type 2 diabetes patients displayed an asymmetrical LDL profile in which the dense LDL subfractions predominated. Plasma levels of dense LDL subfractions were strongly positively correlated with those of plasma triglyceride (TG) (r=0.471; P:=0.0003). The rate of CE mass transfer from HDL to apoB-containing lipoproteins was significantly enhanced in G3 compared with G2 or G1 (46.2+/-8.1, 33.6+/-5.3, and 28.2+/-2.7 microg CE transferred. h(-1). mL(-1) in G3, G2, and G1, respectively; P:<0.0001 G3 versus G1, P:=0.0001 G2 versus G1, and P:=0.02 G2 versus G3). The relative capacities of VLDL and LDL to act as acceptors of CE from HDL were distinct between type 2 diabetes subgroups. LDL particles represented the preferential CE acceptor in G1 and accounted for 74% of total CE transferred from HDL. By contrast, in G2 and G3, TG-rich lipoprotein subfractions accounted for 47% and 72% of total CE transferred from HDL, respectively. Moreover, the relative proportion of CE transferred from HDL to VLDL(1) in type 2 diabetes patients increased progressively with increase in plasma TG levels. The VLDL(1) subfraction accounted for 34%, 43%, and 52% of total CE transferred from HDL to TG-rich lipoproteins in patients from G1, G2, and G3, respectively. Finally, dense LDL acquired an average of 45% of total CE transferred from HDL to LDL in type 2 diabetes patients. In conclusion, CETP contributes significantly to the formation of small dense LDL particles in type 2 diabetes by a preferential CE transfer from HDL to small dense LDL, as well as through an indirect mechanism involving an enhanced CE transfer from HDL to VLDL(1), the specific precursors of small dense LDL particles in plasma.     

Decreased basal activity of HDL associated enzyme: Paraoxonase (PON) during uncompensated oxidative stress among type 2 diabetes mellitus patients

The inverse relationship between serum levels of High Density Lipoprotein (HDL) and the development of Cardio Vascular Disease (CVD) risk among diabetic patients was known for several decades. Besides the decreasing quantity of HDL, the qualitative functions of HDL are adversely affected during uncompensated oxidative stress among diabetics and leads to implication of several complications such as dyslipidemia, lipid peroxidation, endothelial dysfunction and atherosclerosis. Therefore we have undertaken this study to determine anti-atherogenic property of HDL by measuring it's one of the associated enzymes; paraoxonase (PON) among type 2 diabetes patients, along with the serum activity of superoxide dismutase (SOD) as an index of antioxidant status and lipid peroxidation end product, i.e malondialdehyde (MDA) as a marker for oxidative stress. This study included a total of 56 untreated type 2 diabetic patients and 29 healthy volunteers as controls. FBS, PPBS, HbA_1C and fasting lipid profile were measured in both the study groups. Activity of basal PON, SOD and plasma MDA levels was determined in both the study groups according to standard clinical laboratory procedures. All the diabetic patients were under poor glycemic control. Serum levels of HDL between the two study groups are not significantly differed. But, serum basal PON and SOD activity were significantly decreased, whereas MDA levels were highly elevated (284 ± 59 nM/mL/min, 111 ± 35 μmol/L, 10.38 ± 4.17 IU/mL respectively) when compared with healthy controls (371 ± 46 nM/mL/min, 63 ± 12 μmol/L, 16.91 ± 2.89 IU/mL respectively). Although there is no significant reduction in concentrations of HDL in diabetics when compared with controls, but there was a significant decrease in anti-atherogenic property i.e. activity of paraoxonase enzyme. Moreover the serum activity of paraoxonase was significant and negatively correlated with MDA levels (r = - 0.53, P < 0.001) as well as with FBS (r = - 0.30, P < 0.05). Therefore the qualitative functions of HDL are significantly affected by hyperglycemia induced oxidative stress. Hence, we concluded that the quality of HDL is most important in order to determine oxidative stress related complications in diabetes mellitus than its concentration.

     

Decreased protection by HDL from poorly controlled type 2 diabetic subjects against LDL oxidation may Be due to the abnormal composition of HDL.

High plasma triglyceride concentrations in diabetic subjects increase their risk for developing coronary heart disease. Numerous studies have shown that the high density lipoprotein (HDL) composition is abnormal in type 2 diabetic subjects. One study has shown that HDL (lipoprotein A-I) isolated from subjects with non-insulin-dependent diabetes mellitus exhibits a decreased capacity to induce cholesterol efflux. The current study examined the effect of HDL(2) and HDL(3) subfractions from poorly controlled type 2 diabetic and control subjects on THP-1 macrophage-mediated low density lipoprotein (LDL) oxidation. The composition and protective effects of HDL(2), but not of HDL(3), differed significantly between control and diabetic subjects. HDL(2) from diabetics were triglyceride enriched and cholesterol depleted compared with those from controls. Control HDL(2) inhibited LDL oxidation, as assessed by lipid peroxides and electrophoretic mobility, significantly (P<0.05) more than did diabetic HDL(2) in both the fasting and postprandial state. In addition, HDL(2) from diabetics did not protect against apolipoprotein B-100 fragmentation in LDL. Cross-linking in apolipoprotein A-I, oxidized in the presence of LDL, was extensive in HDL(2) from diabetics compared with that from controls. Serum triglyceride concentrations were negatively correlated with protection by HDL(2) (r=-0.673, P<0.05) in diabetic but not in control subjects. HDL(2)-associated platelet-activating factor acetylhydrolase activity was positively correlated with protection by HDL(2) in control (r=0.872, P<0.002) but not in diabetic subjects. In conclusion, compositional alterations in HDL(2) from poorly controlled type 2 diabetic subjects may reduce its antiatherogenic properties.     

HDL particles from type 1 diabetic patients are unable to reverse the inhibitory effect of oxidised LDL on endothelium-dependent vasorelaxation

Aims/hypothesis In healthy individuals, HDL can counteract the inhibition of vasorelaxation induced by oxidised LDL. Several abnormalities such as increased size, glycation and decreased paraoxonase activity have been reported for HDL from type 1 diabetic patients. Thus, we hypothesised that the ability of HDL to protect vessels against impairments of vasorelaxation would be decreased in these patients. Methods We compared the ability of HDL from 18 type 1 diabetic patients and 12 control participants to counteract the inhibition of endothelium-dependent relaxation induced by oxidised LDL on rabbit aorta rings. Results Serum triacylglycerol and total cholesterol, LDL- and HDL-cholesterol were similar in type 1 diabetic and control participants. Fasting glycaemia and the HDL-fructosamine level were higher in diabetic patients than in controls (9.06 ± 3.55 vs 5.27 ± 0.23 mmol/l, p < 0.005; and 10.2 ± 3.2 vs 7.7 ± 2.5 μmol/g protein, p < 0.05, respectively). HDL composition, size and paraoxonase activity were similar in both groups. HDL from controls reduced the inhibitory effect of oxidised LDL on maximal relaxation (E _max; 79.3 ± 11.8 vs 66.4 ± 11.7%, p < 0.05), whereas HDL from type 1 diabetic patients had no effect (E _max = 70.6 ± 17.4 vs 63.9 ± 17.2%, NS). In type 1 diabetic patients, E _max was not correlated with glycaemia or the HDL-fructosamine level. Conclusions/interpretation HDL particles from type 1 diabetic patients do not protect against inhibition of endothelium-dependent vasorelaxation induced by oxidised LDL, in contrast to HDL particles from healthy individuals. This defect cannot be explained by abnormalities in HDL composition, size or paraoxonase activity, and may contribute to the early development of atherosclerotic lesions in type 1 diabetic patients. L. Perségol and M. Foissac contributed equally to this study.     

Protective effect of paraoxonase activity in high-density lipoproteins against erythrocyte membranes peroxidation: a comparison between healthy subjects and type 1 diabetic patients

High-density lipoproteins (HDL) plays a key role in the protection against oxidative damage of lipoprotein and biological membranes. The aim of the present study was to investigate the relationship between the antioxidant role of HDL and the HDL-paraoxonase (PON) activity in healthy subjects and in type 1 diabetic patients. Moreover, the ability of HDL of controls and diabetic patients to protect and/or repair biological membranes from oxidative damage was studied. HDL were isolated from 31 type 1 diabetic patients and 31 sex- and age-matched healthy subjects and immediately used to evaluate lipid hydroperoxides and HDL-PON activity. Erythrocyte membranes obtained from healthy subjects were oxidized with 2,2-azo-bis(2-aminidinopropane)dihydrochloride and then incubated in the presence of HDL isolated from healthy or type 1 diabetic subjects, with measurements of membrane lipid hydroperoxides before and after the incubation. HDL from type 1 diabetic patients showed higher levels of lipid hydroperoxides and a lower activity of HDL-PON than healthy subjects. Moreover, HDL of type 1 diabetic patients protected less efficiently erythrocyte membranes against oxidative damage compared with HDL from healthy subjects. A negative correlation was found between HDL-PON activity and the levels of hydroperoxides of HDL, confirming the relationship between PON and lipid peroxidation and suggesting that subjects with low PON activity are more exposed to oxidative damage than subjects with high PON activity. The ability of HDL to protect erythrocyte membranes was positively correlated with HDL-PON activity and negatively correlated with the levels of lipid hydroperoxides of HDL of healthy subjects. These results confirm a linkage between PON activity and lipid peroxidation of lipoproteins and suggest that the ability of HDL to protect erythrocyte membranes might be related to the PON activity. It might be hypothesized that the decrease of PON activity in diabetic patients and the lower HDL protective action against membrane peroxidation could contribute to acceleration of arteriosclerosis in type 1 diabetes mellitus.     

Changes in high-density lipoprotein subfraction distribution and increased cholesteryl ester transfer after probucol

The effects of probucol (500 mg twice daily) on high-density lipoprotein (HDL) subfractions and cholesteryl ester transfer from HDL to lower density lipoproteins were tested in a series of patients with Type II hypercholesterolemia. In this placebo-controlled crossover trial, patients received probucol or placebo for 8 weeks, then switched to the other agent for another 8 weeks. Probucol significantly lowered total, low-density lipoprotein and HDL cholesterol levels. HDL subfractions, separated by rate zonal ultracentrifugation, showed a dramatic reduction in HDL2, whereas changes in HDL3 were not significant. Both subfractions eluted at a characteristically lower volume, indicating a reduced flotation rate. These findings were confirmed by gradient gel electrophoretic separation, which showed a typical reduction or disappearance of HDL2b particles and the prevalence of particles in the HDL3a-HDL3b electrophoretic range in almost all patients. After treatment, cholesteryl ester transfer from HDL to lower density lipoproteins was significantly increased in all patients. These data suggest that probucol may accelerate HDL particle conversion, leading to improvement in reverse cholesterol transport from the periphery to the liver, through HDL and very low density lipoprotein.     

2型糖尿病患者脂蛋白亚组分与冠心病的相关性分析

目的探讨2型糖尿病(T2DM)患者脂蛋白亚组分与冠心病(CHD)的关系。方法采用超速离心及高效液相色谱法测定84例(T2DM)患者的血清脂蛋白亚型。结果(1)CHD组年龄、高血压患病率升高(P<0.05)。(2)CHD与HDL和HDL2呈负相关;TG与LDLb呈正相关,与HDL、HDL2、HDL3和LDLa呈负相关(P均<0.05)。回归分析显示,年龄和HDL2是T2DM合并CHD的独立危险因素。结论HDL的抗动脉粥样硬化作用可能由HDL2完成,HDL2是比总HDL更好的糖尿病合并CHD的预测因子。     

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

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

Myeloperoxidase and paraoxonase-1 in type 2 diabetic patients

Background and aimsReduced high density lipoproteins (HDL) and increased oxidative stress are features of type 2 diabetes. Myeloperoxidase is an oxidative enzyme partly associated with HDL and causing HDL dysfunction. It is an independent risk factor for cardiovascular disease. Paraoxonase-1 is an HDL-associated enzyme that protects against cardiovascular disease and is reduced in diabetes. The present study examined if serum myeloperoxidase was (i) increased in type 2 diabetes, (ii) correlated with paraoxonase-1 activity.Methods and resultsThe study was based on cross-sectional analyses of serum myeloperoxidase and paraoxonase-1 in type 2 diabetic patients and non-diabetic participants, with and without cardiovascular disease.Serum myeloperoxidase concentrations were not increased in type 2 diabetic patients without cardiovascular disease compared to non-diabetic controls. They were significantly higher in type 2 patients and non-diabetic patients with angiographically confirmed coronary disease. HDL-associated myeloperoxidase was correlated with serum myeloperoxidase (r = 0.80, p < 0.001) but not HDL-cholesterol (r = 0.08) or apolipoprotein AI (r = 0.08). Multivariate analyses showed serum myeloperoxidase to be an independent determinant of paraoxonase activities (arylesterase, p = 0.024; paraoxonase, p = 0.026).ConclusionsMyeloperoxidase is an independent, negative determinant of paraoxonase-1 activity, which may be one mechanism by which it promotes HDL dysfunction and increases cardiovascular risk. Increased serum myeloperoxidase is not a feature of type 2 diabetes in the absence of overt cardiovascular disease. The level of HDL-associated myeloperoxidase is determined by the serum concentration of the enzyme suggesting that, in the context of reduced HDL concentrations in diabetic patients, myeloperoxidase may have a greater impact on HDL function.     

Antiatherogenic small, dense HDL--guardian angel of the arterial wall?

Our understanding of the relationship between the atheroprotective activities of HDL and heterogeneity of HDL particles has advanced greatly. HDL particles are highly heterogeneous in structure, intravascular metabolism and antiatherogenic activity. In this review, we discuss new findings on the antiatherogenic properties of HDL particles. Small, dense HDL possesses potent antioxidative activity but this is compromised under conditions of atherogenic dyslipidemia. HDL functional deficiency frequently coincides with reductions in HDL-cholesterol concentration and alterations in HDL metabolism and structure. Formation of small, dense HDL particles with attenuated antiatherogenic activity can be mechanistically related to HDL enrichment in triglycerides and in serum amyloid A, depletion of cholesteryl esters, covalent modification of HDL apolipoproteins and attenuated antiatherogenic function of apolipoprotein AI. Low circulating levels of HDL cholesterol might, therefore, be associated with the defective functionality of small HDL particles of abnormal structure and composition. In common metabolic diseases, such as type 2 diabetes and metabolic syndrome, deficiency of HDL particle number and function favor accelerated atherosclerosis. Therapeutic normalization of the quantity, quality and biological activities of HDL particles thus represents a novel approach to attenuating atherosclerosis in dyslipidemic individuals with metabolic disease. Cholesteryl ester transfer protein inhibitors, nicotinic acid, reconstituted HDL and other HDL-raising agents are being investigated. Induction of selective increase in the circulating concentrations of small, dense HDL3 particles with increased antiatherogenic activity seems especially promising, particularly for therapy of atherogenic dyslipidemia.     

Antiatherogenic properties of high-density lipoproteins from arterial plasma are attenuated as compared to their counterparts of venous origin

Background and aimsHigh-density lipoprotein (HDL) particles play atheroprotective roles by their ability to efflux cholesterol from foam cells and to protect low-density lipoproteins (LDLs) from oxidative damage in the arterial intima. We hypothesized that antioxidative properties of HDLs can be attenuated in the oxygen-rich prooxidative arterial environment, contributing to the development of atherosclerosis. To evaluate this hypothesis, we compared antioxidative activity of HDLs from arterial and venous plasmas.Methods and resultsArterial and venous blood samples were simultaneously obtained from 16 patients (age 68 ± 10 years; 75% males) presenting with ischemic or valvular heart disease. Major HDL subfractions and total HDLs were isolated by density gradient ultracentrifugation and their chemical composition and the capacity to protect LDLs from in vitro oxidation were evaluated. HDL-cholesterol, triglycerides and apolipoprotein (apo) B-100 levels were slightly but significantly reduced by −4 to −8% (p < 0.01) in the arterial vs. venous samples. Total mass of HDL subpopulations was similar and HDL subpopulations did not reveal marked compositional differences between the arterial and venous circulation. Potent antioxidative activity of the small, dense HDL3c subpopulation was significantly reduced in the particles of arterial origin vs. their counterparts from venous plasma (increase of +21% in the propagation rate of LDL oxidation, p < 0.05). Interestingly, antioxidative properties of venous HDLs were enhanced in statin-treated patients relative to untreated subjects.ConclusionAntioxidative properties of small, dense HDLs from arterial plasma are attenuated as compared to the particles of venous origin, consistent with the development of atherosclerosis in the arterial wall.     

High density lipoprotein changes during treatment of diabetic ketoacidosis

Serum concentration of apoprotein A, high density lipoprotein (HDL)-cholesterol and HDL-phospholipids has been studied in thirteen consecutive episodes of diabetic ketoacidosis. In three patients with type I diabetes mellitus HDL2 and HDL3 subfractions were also measured. Patients with type I diabetes showed greatly decreased HDL-cholesterol concentration on admission which increased into the normal range after insulin treatment, while HDL-phospholipids decreased during treatment and apoprotein A remained almost unmodified. In three patients with type I diabetes a virtual absence of HDL2-cholesterol subfraction was observed, which rose to normal values during recovery. Conversely, in type II diabetes mellitus HDL-cholesterol was slightly reduced on admission, and tended to decrease during recovery. These findings imply the existence of abnormalities in the qualitative composition of HDL, and indicate that HDL-cholesterol can fluctuate much more rapidly than previously thought.     

Treatment of diabetic dyslipoproteinemia.

Diabetes mellitus, specifically type 2, is often associated with disorders in lipid metabolism. Elevated levels of plasma free fatty acids play a pivotal role by contributing significantly to insulin resistance. In addition free fatty acids promote diabetic dyslipidemia through increasing VLDL synthesis in the liver, and by virtue of cholesterylester transfer protein, modifying LDL to increase small-dense LDL subfractions and to decrease HDL cholesterol. This atherogenic lipoprotein profile (elevated triglycerides, increased small-dense low-density lipoproteins, and decreased high-density lipoproteins), contributes to the development of atherosclerosis and increases the risk of experiencing cardiovascular events, the most common cause of death in type 2 diabetes. To decrease the risk of cardiovascular disease events in diabetics, dyslipidemia needs to be treated, as evidenced from epidemiology, from intervention trials, and from subgroup analyses of large intervention trials initiated to evaluate effects of lipid lowering treatment that also included patients with type 2 diabetes. Most measures used to counteract hyperglycemia, are also prone to ameliorate dyslipidemia: dietary intervention (medical nutrition) including omega-3 fatty acids as part of lifestyle changes that also comprise cessation of smoking, increases in physical activity and reduction in body weight. In addition insulin, biguanides, acarbose and glitazones applied for glycemic control also improve diabetic dyslipidemia. Additional pharmacological treatment of dyslipidemia if persisting after glycemic control relies on different drug classes. Fibrates effectively reduce free fatty acids, fasting and postprandial lipemia, shift the distribution of LDL particles towards less dense subfractions and increase HDL cholesterol, thus particularly addressing key components of diabetic dyslipidemia. For LDL cholesterol lowering statins are mainly used that decrease LDL cholesterol levels by competitive inhibition of the HMG-CoA reductase. As type 2 diabetes is found to be associated with a two- to fourfold increase in coronary heart disease risk and as the degree of glycemia is more related to microvascular complications, correcting dyslipidemia appears to be a major task in order to reduce macrovascular events in patients with type 2 diabetes.     

Altered high-density lipoprotein composition is associated with risk for complications in type 2 diabetes mellitus in South Asian descendants: A cross-sectional,case-control study on lipoprotein subclass profiling

Background

Composition of high-density lipoproteins (HDL) is emerging as an important determinant in the development of microvascular complications in type 2 diabetes mellitus (T2DM). Dutch South Asian (DSA) individuals with T2DM display an increased risk of microvascular complications compared with Dutch white Caucasian (DwC) individuals with T2DM. In this study, we aimed to investigate whether changes in HDL composition associate with increased microvascular risk in this ethnic group and lead to new lipoprotein biomarkers.

Materials and Methods

Using ¹H nuclear magnetic resonance spectroscopy and Bruker IVDr Lipoprotein Subclass Analysis (B.I.LISA) software, plasma lipoprotein changes were determined in 51 healthy individuals (30 DwC, 21 DSA) and 92 individuals with T2DM (45 DwC, 47 DSA) in a cross-sectional, case-control study. Differential HDL subfractions were investigated using multinomial logistic regression analyses, adjusting for possible confounders including BMI and diabetes duration.

Results

We identified HDL compositional differences between healthy and diabetic individuals in both ethnic groups. Specifically, levels of apolipoprotein A2 and HDL-4 subfractions were lower in DSA compared with DwC with T2DM. Apolipoprotein A2 and HDL-4 subfractions also negatively correlated with waist circumference, waist-to-hip ratio, haemoglobin A1c, glucose levels and disease duration in DSA with T2DM, and associated with increased incidence of microvascular complications.

Conclusion

While HDL composition differed between controls and T2DM in both ethnic groups, the lower levels of lipid content in the smallest HDL subclass (HDL-4) in DSA with T2DM appeared to be more clinically relevant, with higher odds of having diabetes-related pan-microvascular complications such as retinopathy and neuropathy. These typical differences in HDL could be used as ethnicity-specific T2DM biomarkers.     

Effect of type 2 diabetes on various electrophoretic characteristics of low-density lipoprotein particles in women

Aims/hypothesis Coronary heart disease represents the leading cause of death in type 2 diabetic patients. As the small, dense LDL phenotype is a typical feature of the dyslipidaemic state found in type 2 diabetes, this characteristic could be an important mediator of the elevated coronary heart disease risk in this condition. We have therefore studied the effect of type 2 diabetes on various electrophoretic characteristics of LDL particles.Methods Potential differences in LDL peak particle size and in concentration of LDL cholesterol in small (<255 Å) and large (>260 Å) LDL particles were assessed by polyacrylamide gradient gel electrophoresis among 183 non-diabetic and 56 type 2 diabetic women.Results LDL peak particle size was significantly smaller in type 2 diabetic women than in non-diabetic women (p<0.0001). In addition, the proportion of small LDL particles (<255 Å) was higher in type 2 diabetic women, whereas the proportion of large LDL particles (>260 Å) was lower than in non-diabetic women (p<0.0002). Type 2 diabetic women also had the highest waist circumference and triglyceride levels (p<0.03). When subgroups of non-diabetic and type 2 diabetic women were individually matched (n=41) for similar waist circumference and triglyceride levels, the differences initially found in LDL peak particle size and in the proportion of small and large LDL particles remained significantly different between the two groups (p<0.01).Conclusions/interpretation These results provide evidence that type 2 diabetes may have an independent effect on LDL peak particle size and on the proportion of small and large LDL particles.     

Inability of HDL from type 2 diabetic patients to counteract the inhibitory effect of oxidised LDL on endothelium-dependent vasorelaxation

Aims/hypothesis In healthy normolipidaemic and normoglycaemic control subjects, HDL are able to reverse the inhibition of vasodilation that is induced by oxidised LDL. In type 2 diabetic patients, HDL are glycated and more triglyceride-rich than in control subjects. These alterations are likely to modify the capacity of HDL to reverse the inhibition of vasodilation induced by oxidised LDL.Subjects and methods Using rabbit aorta rings, we compared the ability of HDL from 16 type 2 diabetic patients and 13 control subjects to suppress the inhibition of vasodilation that is induced by oxidised LDL.Results Oxidised LDL inhibited endothelium-dependent vasodilation (maximal relaxation [Emax]=58.2±14.6 vs 99.3±5.2% for incubation without any lipoprotein, p<0.0001). HDL from control subjects significantly reduced the inhibitory effect of oxidised LDL on vasodilatation (Emax=77.6±12.9 vs 59.5±7.7%, p<0.001), whereas HDL from type 2 diabetic patients had no effect (Emax=52.4±20.4 vs 57.2±18.7%, NS). HDL triglyceride content was significantly higher in type 2 diabetic patients than in control subjects (5.3±2.2 vs 3.1±1.4%, p<0.01) and was highly inversely correlated to Emax for oxidised LDL+HDL in type 2 diabetic patients (r=−0.71, p<0.005).Conclusions/interpretation In type 2 diabetes mellitus, the ability of HDL to counteract the inhibition of endothelium-dependent vasorelaxation induced by oxidised LDL is impaired and is inversely correlated with HDL triglyceride content. These findings suggest that HDL are less atheroprotective in type 2 diabetic patients than in control subjects.     

Pathogenesis of diabetic nephropathy: the role of oxidative stress and protein kinase C

Hyperglycemia, a well recognized pathogenetic factor of long-term complications in diabetes mellitus, not only generates more reactive oxygen species but also attenuates antioxidative mechanisms through glycation of the scavenging enzymes. Therefore, oxidative stress has been considered to be a common pathogenetic factor of the diabetic complications including nephropathy. A causal relationship between oxidative stress and diabetic nephropathy has been established by observations that (1) lipid peroxides and 8-hydroxydeoxyguanosine, indices of oxidative tissue injury, were increased in the kidneys of diabetic rats with albuminuria; (2) high glucose directly increases oxidative stress in glomerular mesangial cells, a target cell of diabetic nephropathy; (3) oxidative stress induces mRNA expression of TGF-beta1 and fibronectin which are the genes implicated in diabetic glomerular injury, and (4) inhibition of oxidative stress ameliorates all the manifestations associated with diabetic nephropathy. Proposed mechanisms involved in oxidative stress associated with hyperglycemia are glucose autooxidation, the formation of advanced glycosylation end products, and metabolic stress resulting from hyperglycemia. Since the inhibition of protein kinase C (PKC) effectively blocks not only phorbol ester-induced but also high glucose- and H2O2-induced fibronectin production, the activation of PKC under diabetic conditions may also have a modulatory role in oxidative stress-induced renal injury in diabetes mellitus.