Atherosclerosis in type 2 diabetes mellitus and insulin resistance: mechanistic links and therapeutic targets

Effect of 6 Months of Meditation on Blood Sugar, Glycosylated Hemoglobin, and Insulin Levels in Patients of Coronary Artery Disease

Background and Objectives:

Coronary artery disease (CAD) is the leading cause of morbidity and mortality worldwide. It has been recognized that stress, diabetes, and hypertension are important in etiology and progression of CAD. This study is to evaluate the role of meditation in improving biochemical parameters such as blood glucose, glycosylated hemoglobin, and serum insulin levels in known CAD patients.

Material and Methods:

Sixty CAD patients are divided into two groups of which one group did meditation and other did not. Blood glucose, glycosylated hemoglobin, and fasting serum insulin levels were measured before and at the end of 6 months of study in both the groups.

Results:

At the end of the study, significant decrease was seen in patients who practiced meditation as compared to other group.

Conclusion:

Meditation may modulate the physiological response to stress through neurohumoral activation, which may be a novel therapeutic target for the treatment of CAD.

Fructose-Fed Rat Hearts are Protected Against Ischemia-Reperfusion Injury

High fructose-fed (HFF) rat model is known to develop the insulin-resistant syndrome with a very similar metabolic profile to the human X syndrome. Such metabolic modifications have been associated with a high incidence of cardiovascular disease. The role of free radical attack in diabetes mellitus and its cardiovascular complications have been abundantly documented. The present study examined the susceptibility to myocardial ischemic injury and the involvement of free radical attack and/or protection in the metabolic disorders of high FF rats. Rats were divided into two experimental groups that received diet for 4 weeks: a control group (C, n = 28) receiving a standard diet and a HFF group (FF, n = 28), in which 58% of the total carbohydrate was fructose. The euglycemic clamp technique was performed to assess insulin resistance. For the ischemia-reperfusion procedure, rat hearts were isolated and perfused at constant pressure before they were subjected to a 30-min occlusion of the left coronary artery followed by 120 mins of reperfusion. Hemodynamic parameters were measured throughout the protocol. Infarct-to-risk ratio (I/R) was assessed at the end of the protocol by 2,3,4-triphenyltetrazolium chloride staining and planimetric analysis. Lipid peroxidation, antioxidant enzyme activity, level of vitamin E, and trace element status were measured in blood samples from both groups. Rats of the FF group developed an insulin resistance indicated by the glucose infusion rate, which was decreased by 47%. Infarct size was significantly reduced in rats from the FF group (19.9% ± 6.6%) compared to rats from the control group (34.6% ± 4.9%), and cardiac functional recovery at reperfusion was improved in the FF group. Lipid peroxidation and oxidative stress were higher in the FF group, as indicated by higher malonedialdehyde level, whereas plasma vitamin E/triacylglycerol ratio was also enhanced in this group. This study indicates that fructose feeding affords protection against in vitro ischemia-reperfusion injury, potentially implicating vitamin E.

Cellular function and signaling pathways of vascular smooth muscle cells modulated by sphingosine 1-phosphate

Sphingosine 1-phosphate (S1P) plays important roles in cardiovascular pathophysiology. S1P₁ and/or S1P₃, rather than S1P₂ receptors, seem to be predominantly expressed in vascular endothelial cells, while S1P₂ and/or S1P₃, rather than S1P₁ receptors, seem to be predominantly expressed in vascular smooth muscle cells (VSMCs). S1P has multiple actions, such as proliferation, inhibition or stimulation of migration, and vasoconstriction or release of vasoactive mediators. S1P induces an increase of the intracellular Ca²⁺ concentration in many cell types, including VSMCs. Activation of S1P₃ seems to play an important role in Ca²⁺ mobilization. S1P induces cyclooxygenase-2 expression in VSMCs via both S1P₂ and S1P₃ receptors. S1P₂ receptor activation in VSMCs inhibits inducible nitric oxide synthase (iNOS) expression. At the local site of vascular injury, vasoactive mediators such as prostaglandins and NO produced by VSMCs are considered primarily as a defensive and compensatory mechanism for the lack of endothelial function to prevent further pathology. Therefore, selective S1P₂ receptor antagonists may have the potential to be therapeutic agents, in view of their antagonism of iNOS inhibition by S1P. Further progress in studies of the precise mechanisms of S1P may provide useful knowledge for the development of new S1P-related drugs for the treatment of cardiovascular diseases.

QSAR studies in the discovery of novel type-II diabetic therapies

INTRODUCTION

Type-II diabetes mellitus (T2DM) is a complex chronic disease that represents a major therapeutic challenge. Despite extensive efforts in T2DM drug development, therapies remain unsatisfactory. Currently, there are many novel and important antidiabetic drug targets under investigation by many research groups worldwide. One of the main challenges to develop effective orally active hypoglycemic agents is off-target effects. Computational tools have impacted drug discovery at many levels. One of the earliest methods is quantitative structure-activity relationship (QSAR) studies. QSAR strategies help medicinal chemists understand the relationship between hypoglycemic activity and molecular properties. Hence, QSAR may hold promise in guiding the synthesis of specifically designed novel ligands that demonstrate high potency and target selectivity.

AREAS COVERED

This review aims to provide an overview of the QSAR strategies used to model antidiabetic agents. In particular, this review focuses on drug targets that raised recent scientific interest and/or led to successful antidiabetic agents in the market. Special emphasis has been made on studies that led to the identification of novel antidiabetic scaffolds.

EXPERT OPINION

Computer-aided molecular design and discovery techniques like QSAR have a great potential in designing leads against complex diseases such as T2DM. Combined with other in silico techniques, QSAR can provide more useful and rational insights to facilitate the discovery of novel compounds. However, since T2DM is a complex disease that includes several faulty biological targets, multi-target QSAR studies are recommended in the future to achieve efficient antidiabetic therapies.

Antiatherothrombotic effects of dipeptidyl peptidase inhibitors

Atherothrombotic cardiovascular events are a leading cause of morbidity and mortality in patients with type 2 diabetes (T2D). A number of factors beyond hyperglycemia contribute to this increased risk of cardiovascular events in T2D, including elevated blood pressure, dyslipidemia, inflammation, endothelial dysfunction, and enhanced platelet activation. Importantly, most currently available antihyperglycemic treatments for T2D do not address these additional mechanisms. Indeed, we posit that this may explain why more intensive treatment of hyperglycemia has not contributed to a reduced incidence of cardiovascular events in subjects with T2D. Incretin-targeted therapies, such as dipeptidyl peptidase 4 inhibitors, are a relatively new class of antidiabetic treatments, and preclinical as well as small mechanistic clinical studies suggest that they exert beneficial cardiovascular effects. This review focuses specifically on the potential antiatherothrombotic effects of dipeptidyl peptidase 4 inhibitors.

The compensatory enrichment of sphingosine -1- phosphate harbored on glycated high-density lipoprotein restores endothelial protective function in type 2 diabetes mellitus

Background

Glycation of high-density lipoprotein (HDL) decreases its ability to induce cyclooxygenase-2 (COX-2) expression and prostacyclin I-2 (PGI-2) release in endothelial cells. Whether lipid content of HDL, especially sphingosine-1-phosphate (S1P), plays any specific role in restoring the protective function of HDL in type 2 diabetes mellitus (T2DM) is still unknown.

Methods and results

Immunochemical techniques demonstrated that glycated HDL loses its protective function of regulating COX-2 expression compared with diabetic HDL. We proved that the lipid content, especially phospholipid content differed between diabetic HDL and glycated HDL. Levels of HDL-c-bound S1P were increased in T2DM compared with control subjects as detected by UPLC-MS/MS (HDL-c-bound S1P in control subjects vs. T2DM: 309.1 ± 13.71 pmol/mg vs. 382.1 ± 24.45 pmol/mg, P < 0.05). Additionally, mRNA levels of S1P lyase enzymes and S1P phosphatase 1/2 were decreased in peripheral blood by real-time PCR. Antagonist of S1P receptor 1 and 3 (S1PR1/3) diminished the functional difference between apoHDL&PL (HDL containing the protein components and phospholipids) and diabetic apoHDL&PL (diabetic HDL containing the protein components and phospholipids). With different doses of S1P reconstituted on glycated HDL, its function in inducing the COX-2 expression was restored to the same level as diabetic HDL. The mechanism of S1P reconstituted HDL (rHDL) in the process of regulating COX-2 expression involved the phosphorylation of ERK/MAPK-CREB signal pathway.

Conclusion/Significance

S1P harbored on HDL is the main factor which restores its protective function in endothelial cells in T2DM. S1P and its receptors are potential therapeutic targets in ameliorating the vascular dysfunction in T2DM.

Study on the action of resistin-induced human umbilical vein endothelial cell dysfunction

The aim of this paper was to investigate the effects of resistin on human umbilical vein endothelial cells (HUVECs), and to explore its role and mechanism of action in atherosclerosis. HUVECs were incubated with recombinant human resistin (0, 50, 100 ng/mL) for 24 h. ICAM-1, VCAM-1 and reactive oxygen species (ROS) were assayed by flow cytometer. ET-1, eNOS and iNOS mRNA expression were measured by semi-quantitative RT-PCR. Incubation of HUVECs with resistin resulted in an increase in ICAM-1 expression and ET-1 mRNA expression. However, resistin had no effect on VCAM-1 expression and ROS release. eNOS and iNOS mRNA expression were not altered by resistin stimulation. Adipokine resistin exerted a direct effect in promoting HUVEC dysfunction by promoting ICAM-1 and ET-1 expression. These data suggest that adipocyte-endothelium cross-talk might play an important role in the pathogenesis of cardiovascular disease in diabetes mellitus.

High-density lipoprotein of patients with type 2 diabetes mellitus upregulates cyclooxgenase-2 expression and prostacyclin I-2 release in endothelial cells: relationship with HDL-associated sphingosine-1-phosphate

Background

Dysfunctional high-density lipoprotein (HDL) may have pro-inflammatory effects on the endothelial cells,which causes atherosclerosis in type 2 diabetes mellitus (T2DM). HDL is a major carrier of sphingosine-1-phosphate (S1P) in plasma while S1P exhibits multiple biological activities. However, potential role of HDL and S1P in T2DM remains unexplored. We hypothesized that diabetic HDL with higher contents of S1P exerts beneficial effects on the vascular system.

Methods

Subjects with T2DM with or without proved large arteries atherosclerosis and normal controls (n=15 for each group) were recruited in the present study. HDL was isolated from the subjects by ultracentrifugation. The levels of HDL-associated S1P were determined by UPLC-MS/MS. The protective function of diabetic HDL and S1P was evaluated by measuring cyclooxygenase-2 (COX-2) expression and prostacyclin I-2 (PGI-2) release by human umbilical vein endothelial cells (HUVECs) using western blot and enzyme-linked immunosorbent assay (ELISA), respectively.

Results

The S1P levels in isolated HDL were significantly increased in T2DM subjects compared with controls (235.6 ± 13.4 vs 195.0 ± 6.4 ng/mg, P< 0.05). The diabetic HDL exerted greater protective effects on inducing COX-2 expression and PGI-2 release by HUVECs than those of control HDL (p < 0.05, p < 0.01, respectively). Pertussis toxin, a common inhibitor of G-couple protein receptors, and VPC 23019, an antagonist of S1P receptor 1 and 3 significantly attenuated HDL-induced COX-2 expression and PGI-2 release.

Conclusions

Diabetic HDL carries higher level of S1P compared with normal HDL, which has the potential to contribute to protective effects on endothelial cells by inducing COX-2 expression and PGI-2 release. These findings provide a new insight of S1P function in T2DM patients, possibly leading to a new therapeutic target.

Interleukin-1-beta and dyslipidemic syndrome as major risk factors for thrombotic complications in type 2 diabetes mellitus

Diabetes mellitus (DM) is a complex disease characterized by chronic hyperglycemia, a known risk factor for accelerated atherosclerosis and vascular disease. The aim of this study was to show that the connection between DM and other risk factors, such as dyslipidemia, inflammatory phenomena, or the development of certain vascular injuries, leads to a high frequency of thrombotic events in diabetic patients compared to the nondiabetic population. The study included one hundred eighty patients divided in the following groups: diabetic without ischemic cardiopathy-related disorders (DM), diabetic with clinical or off-clinical (electrocardiogram, cardiac ultrasound) ischemic cardiopathy-related disorders (DM + IC), and nondiabetic with ischemic cardiopathy-related disorders (IC). We investigated the following parameters: von Willebrand Factor, HDL-cholesterol, LDL-cholesterol, interleukin-1-beta, protein C, and plasminogen activator inhibitor type 1. The results achieved in our study have revealed the highest thrombotic risk among the groups of diabetic patients, which is in direct correlation with the high values of interleukin-1-beta and the modifications of lipid parameters, acknowledging the data in the literature, according to which hyperglycemia alters endothelial functions directly and indirectly by synthesis of growth factors and cytokines and generates metabolic disorders which would explain the high risk for thrombotic events.

Insulin promotes macrophage foam cell formation: potential implications in diabetes-related atherosclerosis

The prevalence of atherosclerotic cardiovascular disease is higher in patients with type 2 diabetes, a disorder characterized by hyperinsulinemia and insulin resistance. The role of hyperinsulinemia as an independent participant in the atherogenic process has been controversial. In the current study, we tested the effect of insulin and the insulin sensitizer, adiponectin, on human macrophage foam cell formation. We found that both insulin and adiponectin increased the expression of the type 2 scavenger receptor CD36 by approximately twofold and decreased the expression of the ATP-binding cassette transporter ABCA1 by >80%. In both cases regulation was post-transcriptional. As a consequence of these changes, we found that oxidized LDL (oxLDL) uptake was increased by 80% and cholesterol efflux to apolipoprotein A1 (apoA1) was decreased by ∼25%. This led to two- to threefold more cholesterol accumulation over a 16-h period. As reported previously in studies of murine systems, scavenger receptor-A (SR-A) expression on human macrophages was downregulated by insulin and adiponectin. Insulin and adiponectin did not affect oxLDL-induced secretion of monocyte attractant protein-1 (MCP-1) and interleukin-6 (IL-6). These studies suggest that hyperinsulinemia could promote macrophage foam cell formation and thus may contribute to atherosclerosis in patients with type 2 diabetes.

CD36 inhibitors reduce postprandial hypertriglyceridemia and protect against diabetic dyslipidemia and atherosclerosis

CD36 is recognized as a lipid and fatty acid receptor and plays an important role in the metabolic syndrome and associated cardiac events. The pleiotropic activity and the multiple molecular associations of this scavenger receptor with membrane associated molecules in different cells and tissues have however questioned its potential as a therapeutic target. The present study shows that it is possible to identify low molecular weight chemicals that can block the CD36 binding and uptake functions. These inhibitors were able to reduce arterial lipid deposition, fatty acid intestinal transit, plasma concentration of triglycerides and glucose, to improve insulin sensitivity, glucose tolerance and to reduce the plasma concentration of HbAc1 in different and independent rodent models. Correlation between the anti-CD36 activity of these inhibitors and the known pathophysiological activity of this scavenger receptor in the development of atherosclerosis and diabetes were observed at pharmacological doses. Thus, CD36 might represent an attractive therapeutic target.

A study of the natural history of diabetic kidney disease (DKD)

BACKGROUND

In view of the alarming increase in the number of people with diabetes mellitus (DM), a rising number of patients with diabetic kidney disease (DKD), end-stage renal disease (ESRD) and cardiovascular disease (CVD) is forecasted. It is therefore imperative to re-visit the natural history of DKD and to identify potential risk factors, which may enhance the progression of the disease and its complications.

METHODS

The medical records of 270 Type 2 diabetic chronic kidney disease patients followed up at the Sheffield Kidney Institute between 2000 and 2008 were reviewed. Various socio-demographic, clinical and biochemical parameters (baseline and follow-up parameters) were retrospectively collected from the patients' database. Progression of DKD was evaluated by evaluation of the rate of decline of estimated glomerular filtration rate (eGFR) as calculated from the simplified Modification of Diet in Renal Disease formula [progressors: loss of glomerular filtration rate (GFR) >2 mL/min/1.73m(2)/year] as well as by the progression pattern based on the slope of GFR changes. Variables associated with progression in univariate analysis were examined by multivariate analysis to determine the factors independently associated with DKD progression.

RESULTS

The majority of the study populations were males (66.7%) and Caucasians (88%). Ninety-four patients (34.8%) had progressive, whereas 176 (65.2%) had non-progressive DKD. The rate of eGFR decline in progressors was -3.57 ± 1.45 mL/min/1.73m(2)/year compared to -1.31 ± 0.23 mL/min/1.73m(2)/year in non-progressors. The following parameters discriminated progressors from non-progressors by univariate analysis: baseline-blood pressure (BP) parameters, eGFR and proteinuria as well as serum uric acid. We also observed that area under the curve for follow-up systolic blood pressure (SBP), glycosylated haemoglobin (HbA1c) and proteinuria were significantly higher among the progressors (P = 0.043, P = 0.02 and P = 0.001, respectively). Independent determinants of DKD progression in this study in an adjusted logistic regression model were baseline HbA1c [odds ratio (OR), 2.27; 95% confidence interval (CI), 1.14-4.54], baseline SBP (OR, 1.23; 95% CI, 1.06-1.41), baseline proteinuria (OR, 3.24; 95% CI, 2.1-5.38), baseline serum uric acid (OR, 1.16; 95% CI, 1.09-1.39) and vascular co-morbidities (OR, 1.61; 95% CI, 1.02-2.54). Percentage changes in the key parameters (BP, HbA1c and proteinuria) during the first year of the study did not affect the rate of eGFR decline.

CONCLUSIONS

Baseline HbA1c, SBP, proteinuria and serum uric acid together with the presence of vascular co-morbidities are strongly and independently associated with faster DKD progression. A further prospective observational study is currently undertaken to evaluate these findings and to determine the predictive value of other biochemical peptides and cellular markers on DKD outcome.

Characteristics of coronary artery disease in symptomatic type 2 diabetic patients: evaluation with CT angiography

BACKGROUND

Coronary artery disease (CAD) is a common and severe complication of type 2 diabetes mellitus (DM). The aim of this study is to identify the features of CAD in diabetic patients using coronary CT angiography (CTA).

METHODS

From 1 July 2009 to 20 March 2010, 113 consecutive patients (70 men, 43 women; mean age, 68 ± 10 years) with type 2 DM were found to have coronary plaques on coronary CTA. Their CTA data were reviewed, and extent, distribution and types of plaques and luminal narrowing were evaluated and compared between different sexes.

RESULTS

In total, 287 coronary vessels (2.5 ± 1.1 per patient) and 470 segments (4.2 ± 2.8 per patient) were found to have plaques, respectively. Multi-vessel disease was more common than single vessel disease (p < 0.001), and the left anterior descending (LAD) artery (35.8%) and its proximal segment (19.1%) were most frequently involved (all p < 0.001). Calcified plaques (48.8%) were the most common type (p < 0.001) followed by mixed plaques (38.1%). Regarding the different degrees of stenosis, mild narrowing (36.9%) was most common (p < 0.001); however, a significant difference was not observed between non-obstructive and obstructive stenosis (50.4% vs. 49.6%, p = 0.855). Extent of CAD, types of plaques and luminal narrowing were not significantly different between male and female diabetic patients.

CONCLUSIONS

Coronary CTA depicted a high plaque burden in patients with type 2 DM. Plaques, which were mainly calcified, were more frequently detected in the proximal segment of the LAD artery, and increased attention should be paid to the significant prevalence of obstructive stenosis. In addition, DM reduced the sex differential in CT findings of CAD.

Tauroursodeoxycholic acid attenuates lipid accumulation in endoplasmic reticulum-stressed macrophages

BACKGROUND/AIM

Recent evidence suggests that endoplasmic reticulum (ER) stress provoked under diabetic conditions augments the expression of scavenger receptors on macrophages, promoting the uptake of oxidized low-density lipoprotein uptake and atherogenesis. The aim of the present study was to test the hypothesis that the chemical chaperone tauroursodeoxycholic acid (TUDCA) attenuates lipid accumulation in macrophages subjected to ER stress.

METHODS

Cultured human macrophages were subjected to ER stress by treating them with tunicamycin. Lipid uptake by macrophages subjected to ER stress in the presence or absence of TUDCA was assessed by oil red O staining and by assessing the cellular uptake of Dil-oxidized low-density lipoprotein by fluorescence measurement. Protein levels and phosphorylation status of ER stress markers, insulin-signaling molecules, and scavenger receptor were assessed by Western blotting.

RESULTS

Treatment of cultured human macrophages with the ER stressor tunicamycin caused an increase in the protein levels of cluster of differentiation 36 (CD-36) and augmentation of lipid uptake both of which were inhibited by TUDCA. TUDCA treatment inhibited tunicamycin-induced ER stress as evidenced by the attenuation of phosphorylation of eukaryotic translation initiation factor-2a and glucose reactive protein-78. In addition, TUDCA improved insulin signaling in macrophages by augmenting Akt phosphorylation and blunting c-Jun N-terminal kinase activity.

CONCLUSIONS

Inhibition of macrophage ER stress may represent a potential strategy in preventing atherogenesis under diabetic conditions.

Metabolic effects of various antidiabetic and hypolipidaemic agents on a high-fat diet and multiple low-dose streptozocin (MLDS) mouse model of diabetes

Insulin resistance and subsequent insulin secretory defect are two main features of type 2 diabetes and associated metabolic disorders. The animal models of type 2 diabetes are very complex and are as heterogeneous as the disease. We have evaluated the effect of various antidiabetic and lipid lowering agents (fenofibrate, rosiglitazone, glimepiride, metformin and simvastatin) on the metabolic abnormalities induced by combining a high-fat diet and multiple low-dose streptozocin (MLDS) in mice. Male Swiss albino mice were orally treated with the above agents and fed with a diet containing high fat for 28 days. On day 15 the animals were injected intraperitoneally with low-dose streptozocin (40 mg kg−1), which was administered for five consecutive days. At the end of the 28-day treatment plasma metabolic parameters (glucose, triglyceride and immunoreactive insulin) were estimated. The antidiabetic and hypolipidaemic agents exhibited differential effects on these metabolic parameters. With the exception of fenofibrate all these agents reduced the plasma glucose levels, and the effects of metformin and rosiglitazone on glucose were found to be statistically significant. Although the effect of the test drugs on cholesterol was modest, a significant decrease in triglyceride levels was observed with sub-chronic treatment with these agents. Interestingly, glimepiride mildly elevated the insulin levels while the other antidiabetics and hypolipidaemics reduced the insulin levels, with metformin and rosiglitazone exhibiting statistically significant effects on insulin. To our knowledge this is the first report on the effect of various peroxisome proliferator-activated receptor modulators and newer antidiabetics on the metabolic effects induced by the combined high-fat diet and MLDS model of type 2 diabetes in Swiss albino mice. The results suggested the complexity of the hyperglycaemia, hyperinsulinaemia and hypertriglyceridaemia induced by the high-fat diet and MLDS mouse model, and their correction by various antidiabetics and antihyperlipidaemics may have involved diverse mechanisms.

The impact of macrophage insulin resistance on advanced atherosclerotic plaque progression

Atherothrombotic vascular disease is the major cause of death and disability in obese and diabetic subjects with insulin resistance. Although increased systemic risk factors in the setting of insulin resistance contribute to this problem, it is likely exacerbated by direct effects of insulin resistance on the arterial wall cells that participate in atherosclerosis. A critical process in the progression of subclinical atherosclerotic lesions to clinically relevant lesions is necrotic breakdown of plaques. Plaque necrosis, which is particularly prominent in the lesions of diabetics, is caused by the combination of macrophage apoptosis and defective phagocytic clearance, or efferocytosis, of the apoptotic macrophages. One cause of macrophage apoptosis in advanced plaques is activation of a proapoptotic branch of the unfolded protein response, which is an endoplasmic reticulum stress pathway. Macrophages have a functional insulin receptor signaling pathway, and downregulation of this pathway in the setting insulin resistance enhances unfolded protein response-induced apoptosis. Moreover, other aspects of the obesity/insulin-resistance syndrome may adversely affect efferocytosis. These processes may therefore provide an important mechanistic link among insulin resistance, plaque necrosis, and atherothrombotic vascular disease and suggest novel therapeutic approaches to this expanding health problem.

Proinflammatory and atherogenic activity of monocytes in type 2 diabetes

Cytokines secreted by the monocyte-macrophage system play a key role in the progression of atherosclerotic lesions in Type 2 diabetes. The objectives of this study were to assess the influence of cytokine gene expression in monocytes from patients with Type 2 diabetes on direct markers of endothelial injury with regard to clinically manifest atherosclerosis.

METHODS

Monocytes from 58 patients with Type 2 diabetes and from 22 age-matched healthy volunteers of a control group were isolated in order to assess expression of tumor necrosis factor alpha (TNFalpha), interleukin (IL)-6, IL-8 and IL-10 cytokines (RTPCR, Applied Biosystems). Thrombomodulin concentration was determined using a Diagnostica Stago Immunoenzymatic assay, and circulating endothelial cell numbers were assayed using immunofluorescence studies with CLB-HEC19 antibodies.

RESULTS

In 28 patients, TNFalpha expression in monocytes was observed. In these patients, as compared to those with undetectable levels of this cytokine's expression, higher hemoglobin A(1c) (P=.012) and thrombomodulin (P=.005) concentrations were found. IL-8 expression was determined in 36 patients. Higher expression of TNFalpha (P=.048) and IL-8 (P=.049) was detected in patients with peripheral arterial disease in contrast to those free from this complication.

CONCLUSION

TNFalpha and IL-8 play a significant role in the proatherogenic activity of monocytes in Type 2 diabetes. The TNFalpha-connected activity of monocytes may directly determine endothelial dysfunction and injury. The location of atherosclerosis should be taken into account in the assessment of the proinflammatory activity of peripheral blood monocytes.

Homocysteine promotes vascular smooth muscle cell migration by induction of the adipokine resistin

Adipokines may represent a mechanism linking insulin resistance to cardiovascular disease. We showed previously that homocysteine (Hcy), an independent risk factor for cardiovascular disease, can induce the expression and secretion of resistin, a novel adipokine, in vivo and in vitro. Since vascular smooth muscle cell (VSMC) migration is a key event in vascular disease, we hypothesized that adipocyte-derived resistin is involved in Hcy-induced VSMC migration. To confirm our hypothesis, Sprague-Dawley rat aortic SMCs were cocultured with Hcy-stimulated primary rat epididymal adipocytes or treated directly with increasing concentrations of resistin for up to 24 h. Migration of VSMCs was investigated. Cytoskeletal structure and cytoskeleton-related proteins were also detected. The results showed that Hcy (300-500 microM) increased migration significantly in VSMCs cocultured with adipocytes but not in VSMC cultured alone. Resistin alone also significantly increased VSMC migration in a time- and concentration-dependent manner. Resistin small interfering RNA (siRNA) significantly attenuated VSMC migration in the coculture system, which indicated that adipocyte-derived resistin mediates Hcy-induced VSMC migration. On cell spreading assay, resistin induced the formation of focal adhesions near the plasma membrane, which suggests cytoskeletal rearrangement via an alpha(5)beta(1)-integrin-focal adhesion kinase/paxillin-Ras-related C3 botulinum toxin substrate 1 (Rac1) pathway. Our data demonstrate that Hcy promotes VSMC migration through a paracrine or endocrine effect of adipocyte-derived resistin, which provides further evidence of the adipose-vascular interaction in metabolic disorders. The migratory action exerted by resistin on VSMCs may account in part for the increased incidence of restenosis in diabetic patients.

Silent myocardial ischemia in middle-aged asymptomatic patients with type 2 diabetes in Turkish population

The authors investigated silent myocardial ischemia in unselected consecutive middle-aged asymptomatic patients with type 2 diabetes without any evidence of coronary heart disease documented by treadmill exercise test. Ninety asymptomatic patients with type 2 diabetes (48 men; mean age: 49 +/-6 years) were included in the study. Mean duration of diabetes in the study group was 4 +/-4.2 years (range 1 to 21 years); 38% of the study population, diabetes duration was only 1 year). All patients were subjected to treadmill exercise test with Bruce protocol. A positive test was noted in 4 of 90 (4%) study patients. Two male patients (4%) and 2 (4%) women patients developed exercise-induced ST-segment depression, but none had concomitant chest pain. Diabetics with silent myocardial ischemia were older (55 +/-3 years vs 49 +/-6 years, p = 0.04) than those without silent myocardial ischemia. Also, diabetics with silent myocardial ischemia had higher fibrinogen level (372 +/-51 vs 307 +/-71 mg/dL, p = 0.04) than diabetics without silent myocardial ischemia. In treadmill exercise test, diabetics with silent myocardial ischemia had lower total exercise time and peak workload (375 +/-30 vs 474 +/-115 seconds, p = 0.04; 7.3 +/-0.5 vs 8.9 +/-1.9, p = 0.04, respectively) than without silent myocardial ischemia. Insulin resistance is associated with a variety of atherosclerosis risk factors. Exercise test findings show increased cardiac sympathetic activity and parasympathetic withdrawal in increased insulin resistance.

Pioglitazone increases macrophage apoptosis and plaque necrosis in advanced atherosclerotic lesions of nondiabetic low-density lipoprotein receptor-null mice

BACKGROUND

Thiazolidinediones (TZDs), which have actions that involve both peroxisome proliferator-activated receptor (PPAR)-gamma-dependent and -independent effects, improve insulin sensitivity in type II diabetes and inhibit early atherogenesis in mice. However, the effects of TZDs on advanced lesion progression are unknown.

METHODS AND RESULTS

Pioglitazone and rosiglitazone enhanced macrophage apoptosis by a number of stimuli, including those thought to be important in advanced atherosclerosis. Macrophage death was not enhanced by non-TZD PPARgamma activators, and TZD-induced apoptosis was still observed in PPARgamma-deficient macrophages. In wild-type macrophages, death enhancement was associated with reduced activation of the cell-survival mediator nuclear factor-kappaB. TZDs also increased the ability of macrophages to phagocytically clear apoptotic cells, which is proposed to protect against plaque necrosis in advanced lesions. The mechanism of this effect was complex, involving both PPARgamma-dependent and -independent mechanisms. To explore the net effect on advanced atherosclerosis in vivo, Ldlr-/- mice were fed a nondiabetogenic cholesterol-enriched diet to promote midstage lesions. Then, pioglitazone was administered with the diet for an additional 10 weeks. Aortic root lesions from the pioglitazone-treated mice showed a substantial increase in apoptotic cells and plaque necrosis compared with lesions from non-drug-treated mice.

CONCLUSIONS

The potential atheroprotective effects of TZDs conferred by insulin sensitization may be partially offset by adverse effects on advanced atherosclerosis. Because the mechanisms of the beneficial and proposed adverse effects may differ, these findings have potentially important implications for drug optimization.

Stimulation of the peroxisome proliferator-activated receptor γ (PPARγ) and the expression of selected blood monocyte cytokine genes in diabetic macroangiopathy

Monocytes and macrophages play a key role in the progression of atheromatous changes. The peroxisome proliferator-activated receptor gamma (PPAR gamma) can limit macroangiopathy through the control of cytokine transcription. The objectives of this study were to examine the influence of PPAR gamma and its agonist (rosiglitazone) on the TNFalpha, IL-6, IL-8 and IL-10 gene expression in monocytes of patients with diabetic macroangiopathy and to analyse obtained results in context of selected atherogenic factors ant direct indicators of endothelial lesion. TNFalpha, IL-6, IL-8, IL-10 and PPAR gamma gene expression was assessed in peripheral blood monocytes in 45 patients with type 2 diabetes before and following 22 weeks of rosiglitazone therapy (real-time PCR [Applied Biosystems]). As indicators of endothelial lesion, concentration of thrombomodulin (immunoassay [Diagnostica Stago]) and amount of circulating blood endothelial cells (immunofluorescence method with MoAb CLB-HEC19) were determined. Following rosiglitazone therapy, a statistically significant downward tendency of TNFalpha (p=0.026) and IL-8 (p=0.008) gene expression was noted. Before and following rosiglitazone treatment, PPAR gamma, IL-6 and IL-10 gene expression was undetectable in studied monocytes in vivo. In conclusion, TNFalpha and IL-8 play an important role in monocyte atherogenic activity. Rosiglitazone reduces monocyte proinflammatory readiness by influencing the expression of selected atherogenic cytokines (PPAR gamma-independent pathway).

The macrophage at the crossroads of insulin resistance and atherosclerosis

The macrophage has emerged as an important player in the pathogenesis of both atherosclerosis and insulin resistance. Cross-talk between inflammatory macrophages and adipocytes may be involved in insulin resistance in peripheral tissues. Defective insulin signaling in cells of the arterial wall including macrophages may promote the development of atherosclerosis. Insulin resistant macrophages are more susceptible to endoplasmic reticulum stress and apoptosis in response to various stimuli such as nutrient deprivation, free cholesterol loading, and oxidized LDL. Increased apoptosis of insulin resistant macrophages and impaired phagocytic clearance of apoptotic cells by insulin resistant macrophages in atherosclerotic lesions may lead to enhanced postapoptotic necrosis, larger lipid-rich cores, increased inflammation, and more complex vulnerable plaques.

Calpains and their multiple roles in diabetes mellitus

Type 2 diabetes mellitus (T2DM) can lead to death without treatment and it has been predicted that the condition will affect 215 million people worldwide by 2010. T2DM is a multifactorial disorder whose precise genetic causes and biochemical defects have not been fully elucidated, but at both levels, calpains appear to play a role. Positional cloning studies mapped T2DM susceptibility to CAPN10, the gene encoding the intracellular cysteine protease, calpain 10. Further studies have shown a number of noncoding polymorphisms in CAPN10 to be functionally associated with T2DM while the identification of coding polymorphisms, suggested that mutant calpain 10 proteins may also contribute to the disease. Here we review recent studies, which in addition to the latter enzyme, have linked calpain 5, calpain 3, and its splice variants, calpain 2 and calpain 1 to T2DM-related metabolic pathways along with T2DM-associated phenotypes, such as obesity and impaired insulin secretion, and T2DM-related complications, such as epithelial dysfunction and diabetic cataract.

Platelet aggregation is not enhanced in patients with prediabetes

Prediabetes [impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG)] is a major risk factor for T2DM as well as for cardiovascular disease and mortality. In the present study, the platelet aggregation and fibrinogen levels were investigated in prediabetic subjects who had no confounding factors such as hypertension, obesity or dyslipidemia. Thirty-nine subjects with prediabetes (24 IFG and 15 IGT) and age, sex and BMI matched 36 healthy controls were enrolled. Platelet aggregation, fibrinogen and hsCRP levels, HOMA-IR and HOMA-beta indexes were determined. Platelet aggregation induced by collagen, epinephrine or ADP was not different (p=0.93, p=0.90 and p=0.29, respectively) between two groups, whereas fibrinogen levels were significantly higher (p=0.006) in the prediabetics when compared to controls. hsCRP levels, HOMA-IR and HOMA-beta indexes in the two groups were not different. The power of the study was calculated according to the results and established as 0.97 for collagen, 0.95 for epinephrine and 0.83 for ADP. Despite the high plasma fibrinogen levels, the platelet aggregation in prediabetics was not different when compared to healthy controls. These data suggest that platelet aggregation may not be involved in the mechanism of prothrombotic state in prediabetic state.

S-Glutathiolation of p21ras by Peroxynitrite Mediates Endothelial Insulin Resistance Caused by Oxidized Low-Density Lipoprotein

OBJECTIVE

To understand the mechanism by which oxidants are linked to insulin resistance, bovine aortic endothelial cells were exposed to oxidized low-density lipoproteins (oxLDL) or peroxynitrite.

METHODS AND RESULTS

OxLDL transiently increased phosphorylation of Erk and Akt within 5 minutes, but 60 minutes later, resulted in decreased insulin-induced Akt phosphorylation. OxLDL promoted a 2- to 5-fold increase in oxidant generation as measured by dihydrorhodamine or dihydroethidium oxidation that was ascribed to peroxynitrite. Exogenous peroxynitrite (25 to 100 micromol/L) or oxidized glutathione mimicked the effects of oxLDL. OxLDL increased the S-glutathiolation of p21ras, and adenoviral transfection with either a mutant p21ras (C118S) lacking the predominant site of S-glutathiolation or a dominant-negative mutant restored insulin-induced Akt phosphorylation. The requirement for oxidant-mediated S-glutathiolation and activation of p21ras in mediating insulin resistance was further implicated by showing that insulin signaling was restored by Mek inhibitors or by overexpression of glutaredoxin-1. Furthermore, oxLDL increased Erk-dependent phosphorylation of insulin receptor substrate-1 serine-616 that was prevented by inhibiting oxidant generation, Erk activation, or by the p21ras C118S mutant.

CONCLUSIONS

This study provides direct evidence for a novel molecular mechanism by which oxidants can induce insulin resistance via S-glutathiolation of p21ras and Erk-dependent inhibition of insulin signaling.

Myocardial preconditioning against ischemia-reperfusion injury is abolished in Zucker obese rats with insulin resistance

Insulin resistance (IR) precedes the onset of Type 2 diabetes, but its impact on preconditioning against myocardial ischemia-reperfusion injury is unexplored. We examined the effects of diazoxide and ischemic preconditioning (IPC; 5-min ischemia and 5-min reperfusion) on ischemia (30 min)-reperfusion (240 min) injury in young IR Zucker obese (ZO) and lean (ZL) rats. ZO hearts developed larger infarcts than ZL hearts (infarct size: 57.3 +/- 3% in ZO vs. 39.2 +/- 3.2% in ZL; P < 0.05) and also failed to respond to cardioprotection by IPC or diazoxide (47.2 +/- 4.3% and 52.5 +/- 5.8%, respectively; P = not significant). In contrast, IPC and diazoxide treatment reduced the infarct size in ZL hearts (12.7 +/- 2% and 16.3 +/- 6.7%, respectively; P < 0.05). The mitochondrial ATP-activated potassium channel (K(ATP)) antagonist 5-hydroxydecanoic acid inhibited IPC and diazoxide-induced preconditioning in ZL hearts, whereas it had no effect on ZO hearts. Diazoxide elicited reduced depolarization of isolated mitochondria from ZO hearts compared with ZL (73 +/- 9% in ZL vs. 39 +/- 9% in ZO; P < 0.05). Diazoxide also failed to enhance superoxide generation in isolated mitochondria from ZO compared with ZL hearts. Electron micrographs of ZO hearts revealed a decreased number of mitochondria accompanied by swelling, disorganized cristae, and vacuolation. Immunoblots of mitochondrial protein showed a modest increase in manganese superoxide dismutase in ZO hearts. Thus obesity accompanied by IR is associated with the inability to precondition against ischemic cardiac injury, which is mediated by enhanced mitochondrial oxidative stress and impaired activation of mitochondrial K(ATP).

Changes in liver tests during 1-year treatment of patients with Type 2 diabetes with pioglitazone, metformin or gliclazide

AIMS

Patients with Type 2 diabetes are at increased risk of liver damage. Therefore, it is of particular importance to investigate the hepatic effects of drugs used to treat such patients.

METHODS

Liver testing results performed in four 1-year, randomized, double-blind studies comparing effects of pioglitazone, metformin or a sulphonylurea, gliclazide, in the treatment of over 3700 patients with Type 2 diabetes have been analysed.

RESULTS

Pioglitazone caused reductions in mean levels of hepatic enzymes of between 3 and 18%, whilst gliclazide caused small increases of between 3 and 13%. Metformin treatment showed either small mean increases or decreases. More patients receiving pioglitazone had liver tests within the normal range at the end of treatment (> or = 87%) compared with patients receiving metformin (> or= 80%) or gliclazide (> or = 75%). Slightly fewer patients with pioglitazone than with comparators showed a large increase (> 3 upper limit of normal) in alanine aminotransferase levels at any time during treatment (pioglitazone 0.9%, metformin 1.9%, gliclazide 1.9%).

CONCLUSIONS

During pioglitazone treatment there is a reduction in liver enzyme levels. Although the mechanism of this effect is not clear, the results demonstrate potential beneficial effects on the liver during treatment of patients with Type 2 diabetes with pioglitazone.

The relationship between insulin resistance assessed by HOMA-IR and serum osteoprotegerin levels in obesity

AIM

We investigated the relationship between insulin resistance and serum osteoprotegerin (OPG) levels in healthy obese subjects and healthy lean controls.

METHODS

Fifty obese subjects (age: 31+/-8 years) and 24 lean controls (age: 30+/-7 years) were included in the study. We used the homeostasis model assessment for insulin resistance (HOMA-IR) index as the index of insulin resistance. OPG levels were measured with the commercial ELISA kit. Obese subjects were studied in three groups: Group I (n = 25) HOMA-IR index < 2.24, Group II (n = 13) index 2.24-3.59, Group III (n = 12) index > 3.59. Group IV (n = 24) was the lean controls with HOMA-IR index < 2.24.

RESULTS

Obese subjects with increased insulin resistance (Group III) had lower OPG values than other groups (11.88+/-7.43 pg/ml, 16.39+/-6.39 pg/ml, 17.37+/-9.61 pg/ml, and 18.1+/-6.65 pg/ml, respectively; Group I versus Group III p = 0.036; Group III versus Group IV p = 0.012). We also found significant inverse correlations between OPGc (corrected for BMI) and fasting glucose (r = -0.325, p = 0.005), fasting insulin (r = -0.404, p = 0.0001) as well as HOMA-IR (r = -0.428, p = 0.0001). Increased fibrinogen level was found in Group III than Group IV (9.32+/-1.97 micromol/l versus 7.47+/-1.65 micromol/l, respectively; p = 0.005). In conclusion, insulin resistance in obesity is associated with decreased serum OPG levels and increased fibrinogen levels. The relationship between serum OPG levels and HOMA-IR may provide an insight into vascular endothelial dysfunction in obesity.

Adipocyte-derived cytokine resistin causes endothelial dysfunction of porcine coronary arteries

OBJECTIVE

Resistin, a novel adipocyte-derived cytokine, is involved in the development of insulin resistance and diabetes mellitus. In this study, we determined whether resistin could affect vasomotor function, oxidative stress, and endothelial nitric oxide synthase (eNOS) expression in porcine coronary arteries.

METHODS

Porcine coronary arteries were treated with resistin or antioxidant seleno-L-methionine (SeMet). Vasomotor function was studied by using a myograph system. Levels of superoxide anion (O 2 - ) were detected by the lucigenin-enhanced chemiluminescence method. The eNOS mRNA and protein levels were determined by real-time polymerase chain reaction and immunohistochemistry, respectively. Culture of isolated porcine coronary artery endothelial cells (PCAECs) was also included.

RESULTS

Endothelium-dependent relaxation in response to bradykinin was reduced by 15% and 30% for the rings treated with 10 and 40 ng/mL of resistin, respectively, as compared with controls ( P < .05). Endothelium-independent relaxation in response to sodium nitroprusside (SNP) was also reduced by 11% after treatment with 40 ng/mL of resistin ( P < .05). The O 2 - level was increased in the 40 ng/mL resistin-treated vessels by 88% as compared with controls ( P < .05). SeMet reversed these effects. The eNOS mRNA levels in PCAEC cultures treated with resistin (10 and 40 ng/mL) were decreased by 27% and 55%, respectively ( P < .05) and by 39% in the endothelial cells purified from porcine coronary artery rings after treatment with 40 ng/mL of resistin ( P < .05). Immunoreactivity of eNOS in the resistin-treated vessel rings was also substantially reduced.

CONCLUSIONS

Resistin reduces the endothelium-dependent and endothelium-independent vasorelaxation. This effect is associated with increased superoxide radical production, decreased eNOS expression, and is effectively reversed by the antioxidant SeMet.

CLINICAL RELEVANCE

Obesity has been considered to be an independent risk factor for coronary artery disease and other vascular lesions. Resistin is a newly discovered adipocyte-derived cytokine, and its plasma levels are increased in obese individuals. However, it is not clear whether resistin could directly contribute to vascular disease formation. This study showed that resistin can cause endothelial dysfunction in porcine coronary arteries through oxidative stress and down-regulation of eNOS. Thus, this study may suggest a new mechanism of obesity-associated vascular disease and that antioxidants may effectively prevent vascular disease in obese individuals.

Insulin sensitivity at diagnosis of Type 2 diabetes is not associated with subsequent cardiovascular disease (UKPDS 67)

AIMS

Insulin resistance is common in Type 2 diabetes which, in turn, is associated with a markedly increased risk of cardiovascular disease. Whether insulin sensitivity measured after diagnosis of diabetes is associated with incident cardiovascular disease was evaluated in this prospective study.

METHODS

Three thousand five hundred and eighty-two subjects with newly diagnosed diabetes, recruited to the UK Prospective Diabetes Study (UKPDS), free of cardiovascular disease, and with complete information on insulin sensitivity and potential confounders, were followed prospectively to the first occurrence of (i) fatal or non-fatal myocardial infarction, MI (ii) fatal or non-fatal stroke, and (iii) coronary heart disease, CHD (fatal or non-fatal MI, sudden death or ischaemic heart disease). Insulin sensitivity was measured by Homeostatic Model Assessment (HOMA).

RESULTS

Insulin sensitivity as measured by HOMA was not associated with subsequent MI, stroke, or CHD in univariate or multivariate models controlling for age, sex, ethnicity, HbA(1c), body mass index, plasma triglycerides, cholesterol and smoking. The hazard ratio associated with a doubling of insulin sensitivity with fatal or non-fatal MI in a multivariate model was 0.92 (95% confidence interval, CI, 0.80-1.05). These results were not changed by the exclusion of overweight patients randomized to metformin.

DISCUSSION

Estimation of insulin sensitivity provides no additional useful information with respect to the risk of the first occurrence of cardiovascular disease in patients with newly diagnosed Type 2 diabetes. Among patients with Type 2 diabetes, insulin resistance is not a risk factor for cardiovascular disease.

Factors related to exercise capacity in asymptomatic middle-aged type 2 diabetic patients

AIM

We aimed to look at the relationship between exercise capacity and metabolic variables in unselected consecutive asymptomatic middle-aged type 2 diabetic patients as a potential marker for undiagnosed coronary heart disease.

METHOD

Ninety patients (49 +/- 6 years) were included in the study. All patients performed a treadmill exercise test using the Bruce protocol. According to achieved EC, patients were separated into three groups; Group I (n, 24) 8 > metabolic equivalents (METs) > or = 5, Group II (n, 54) 11 > METs > or = 8 and Group III (n, 12) METs > or = 11.

RESULTS

Patients in group I are more likely to be of female gender and to have a family history of coronary heart disease (CHD) than in group III (P = 0.015, P = 0.009, respectively). When compared to group III, patients in group I had higher fasting insulin and fibrinogen levels (P = 0.049 and P = 0.01, respectively). Homeostasis model assessment for insulin resistance (HOMA-IR) index (P = 0.03) was also higher in group I than in group III. We found a significant negative correlation between achieved exercise capacity and age (r = -0.204, P = 0.048), fasting insulin (r = -0.209, P = 0.048), HOMA-IR (r = -0.204, P = 0.048) as well as fibrinogen (r = -0.301, P = 0.007).

CONCLUSION

Reduced exercise capacity was associated with increased insulin resistance as assessed by HOMA-IR index in asymptomatic middle-aged type 2 diabetic patients.

Cellular mechanisms of insulin resistance, lipodystrophy and atherosclerosis induced by HIV protease inhibitors

Accumulating clinical evidence now links HIV protease inhibitors (HPIs) to the pathogenesis of insulin resistance, dyslipidaemia, lipodystrophy and atherosclerosis associated with highly active anti-retroviral therapy. Here we briefly describe the evidence for a distinct causative role for HPIs, and explore the cellular mechanisms proposed to underlie these side-effects. Acute inhibition of GLUT4-mediated glucose transport, and defective insulin signalling induced by chronic exposure to nelfinavir, are described as cellular mechanisms of insulin resistance. Interference with adipogenesis and adipocyte apoptosis and nelfinavir-induced activation of lipolysis are discussed as potential mechanisms of HPI-induced lipodystrophy. HPI-induced free radical production, apoptosis and increased glucose utilization in vascular smooth muscle cells are presented as possible novel mechanisms for atherosclerosis. Common pathways and cause-effect relationships between the various cellular mechanisms presented are then discussed, with emphasis on the role of insulin resistance, free radical production and enhanced lipolysis. Understanding the cellular mechanisms of HPI-induced side-effects will enhance the search for improved anti-retroviral therapy, and may also shed light on the pathogenesis of common forms of insulin resistance, dyslipidaemia and atherosclerosis.

Targeting insulin resistance and beta-cell dysfunction: the role of thiazolidinediones

Insulin resistance and beta-cell dysfunction are fundamental defects that contribute to the development of type 2 diabetes, and as such are targets for primary prevention of disease progression. The two parameters are linked by several factors, including glucotoxicity and lipotoxicity, and recent research has enlightened understanding of the molecular mechanisms underlying the development and progression of the disease. Historically, type 2 diabetes has been managed by controlling hyperglycemia, using agents that increase insulin levels or reduce hepatic glucose production, as exemplified by the United Kingdom Prospective Diabetes Study. The thiazolidinediones control hyperglycemia by targeting the fundamental defects of the disease, and have shown well-documented improvements in insulin sensitivity and beta-cell function, both in monotherapy and in combination with other oral antidiabetic agents. TRoglitazone In the Prevention Of Diabetes (TRIPOD) has demonstrated the potential for thiazolidinediones to delay progression to type 2 diabetes. Prospective studies such as Diabetes REduction Approaches with ramipril and rosiglitazone Medications (DREAM) are currently evaluating the long-term effects of thiazolidinediones on metabolic status and disease progression.

Cardiovascular effects of treatment of type 2 diabetes with pioglitazone, metformin and gliclazide

Cardiovascular mortality and morbidity are increased in patients with type 2 diabetes. However, there are few data from clinical trials comparing cardiovascular effects of alternative oral anti-diabetic agents. Major cardiovascular outcomes during four one-year, double-blind trials in over 3700 patients with type 2 diabetes randomised to either a thiazolidinedione, pioglitazone, metformin or a sulphonylurea, gliclazide treatment have been combined. Mean blood pressure was slightly reduced by all treatments, with pioglitazone treatment resulting in the largest falls (approximately 1.5 mmHg). Hospitalisations for cardiac or cerebrovascular events were similar with the different treatments. Overall mortality was seven of 1857 for pioglitazone and 10 of 1856 for non-pioglitazone treatments, of which three and six were cardiac deaths, respectively. The incidence of congestive cardiac failure was similar with pioglitazone (12/1857) and non-pioglitazone (10/1856) treatments. The results show similar cardiovascular outcome for the three different treatments over a one-year period, but demonstrate interesting differences, which will require longer-term formal outcome studies to determine their significance.

C-reactive protein, its role in inflammation, Type 2 diabetes and cardiovascular disease, and the effects of insulin-sensitizing treatment with thiazolidinediones

Increased concentrations of the marker of inflammation, C-reactive protein (CRP), are associated with insulin resistance, Type 2 diabetes and the development of cardiovascular disease. In particular, inflammation is closely associated with endothelial dysfunction and is recognized as one of the cardiovascular risk factors clustering in the Insulin Resistance Syndrome or Metabolic Syndrome. The exact mechanisms linking insulin resistance and inflammation remain unclear. However, the close association between insulin resistance and inflammation in atherogenesis suggests that therapies that address both parameters may have benefits in reducing diabetes-related macrovascular complications. The thiazolidinedione class of oral anti-diabetic agents are powerful insulin sensitizers that also have anti-inflammatory properties. Treatment with these agents has a range of anti-atherogenic effects, including reduced levels of CRP, plasminogen activator inhibitor-1 (PAI-1), TNF-alpha and reactive oxygen species. Additionally, the insulin-sensitizing effect of thiazolidinediones improves other factors of the Insulin Resistance Syndrome, including dyslipidaemia and hypertension. Outcome studies are underway to determine if the effects of improving insulin sensitivity and reducing inflammation will translate into clinical benefits and reduce the cardiovascular morbidity and mortality associated with insulin resistance and Type 2 diabetes.

Relationship between insulin resistance assessed by HOMA-IR and exercise test variables in asymptomatic middle-aged patients with type 2 diabetes

We investigated the relationship between index of insulin resistance (IR) and exercise test variables in middle-aged asymptomatic patients with Type 2 diabetes.

METHODS

90 patients (48 men, 42 women; age: 49 +/- 6 yr) were included in the study. We used homeostasis model assessment for IR (HOMA-IR) index as index of IR. All patients were subjected to treadmill exercise test. Four subjects were tested positive (4.4%). Study patients were separated into three groups: group I (no.=26) HOMA-IR index <2.24; group II (no.=26) index 2.24-3.59; group III (no.=38) index >3.59.

RESULTS

group I had less frequency of cardiovascular risk factors than group II and III (p=0.001). Systolic blood pressure baseline as well as peak exercise values, were higher in group III than in group I and II (p=0.048 vs p=0.01, respectively). Higher total exercise time and peak workload were found in group I than group II and III (p=0.04). The recovery of heart rate (delta HR(pr)) was similar among the study groups. We found significant negative correlations between HOMA-IR and total exercise time and peak workload. In addition we found significant negative correlations between age vs chronotrophic index (CI), delta HR(pr), and peak workload. There were also similar negative correlations between duration of diabetes vs CI and delta HR(pr).

CONCLUSIONS

IR is associated with a variety of cardiovascular risk factors. Some exercise test variables point out changes of autonomic tone during exercise in elevated IR group. Negative correlation between HOMA-IR and peak exercise capacity (METs) may well confirm increased mortality in hyperinsulinemia.

Insulin receptor substrate-2-dependent interleukin-4 signaling in macrophages is impaired in two models of type 2 diabetes mellitus

We have shown previously that hyperinsulinemia inhibits interferon-alpha-dependent activation of phosphatidylinositol 3-kinase (PI3-kinase) through mammalian target of rapamycin (mTOR)-induced serine phosphorylation of insulin receptor substrate (IRS)-1. Here we report that chronic insulin and high glucose synergistically inhibit interleukin (IL)-4-dependent activation of PI3-kinase in macrophages via the mTOR pathway. Resident peritoneal macrophages (PerMPhis) from diabetic (db/db) mice showed a 44% reduction in IRS-2-associated PI3-kinase activity stimulated by IL-4 compared with PerMPhis from heterozygote (db/+) control mice. IRS-2 from db/db mouse PerMPhis also showed a 78% increase in Ser/Thr-Pro motif phosphorylation without a difference in IRS-2 mass. To investigate the mechanism of this PI3-kinase inhibition, 12-O-tetradecanoylphorbol-13-acetate-matured U937 cells were treated chronically with insulin (1 nm, 18 h) and high glucose (4.5 g/liter, 48 h). In these cells, IL-4-stimulated IRS-2-associated PI3-kinase activity was reduced by 37.5%. Importantly, chronic insulin or high glucose alone did not impact IL-4-activated IRS-2-associated PI3-kinase. Chronic insulin + high glucose did reduce IL-4-dependent IRS-2 tyrosine phosphorylation and p85 association by 54 and 37%, respectively, but did not effect IL-4-activated JAK/STAT signaling. When IRS-2 Ser/Thr-Pro motif phosphorylation was examined, chronic insulin + high glucose resulted in a 92% increase in IRS-2 Ser/Thr-Pro motif phosphorylation without a change in IRS-2 mass. Pretreatment of matured U937 cells with rapamycin blocked chronic insulin + high glucose-dependent IRS-2 Ser/Thr-Pro motif phosphorylation and restored IL-4-dependent IRS-2-associated PI3-kinase activity. Taken together these results indicate that IRS-2-dependent IL-4 signaling in macrophages is impaired in models of type 2 diabetes mellitus through a mechanism that relies on insulin/glucose-dependent Ser/Thr-Pro motif serine phosphorylation mediated by the mTOR pathway.

Hypofibrinolysis in the insulin resistance syndrome: implication in cardiovascular diseases

Insulin resistance syndrome (IRS) is associated with increased cardiovascular morbidity and mortality. IRS is becoming one of the major health problems as its prevalence grows rapidly. Accelerated atherothrombotic process in the IRS is attributed to metabolic abnormalities, inflammation and to impaired fibrinolysis due to increased plasma plasminogen activator inhibitor type 1 (PAI-1) levels. Proinflammatory cytokines may have an important role in PAI-1 overexpression, particularly in the adipose tissue. Studies in genetically modified mice indicate that PAI-1 might be involved in the aetiopathogenesis of obesity. Modifying PAI-1 expression by PAI-1 inhibitors may open a new field of research and may reveal the true role of PAI-1 in atherosclerotic and insulin resistance processes.

Peroxisome proliferator-activated receptor gamma: implications for cardiovascular disease

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor belonging to the nuclear hormone receptor superfamily. PPARgamma is expressed by macrophages, endothelial cells, and vascular smooth muscle cells. It regulates gene expression of key proteins involved in lipid metabolism, vascular inflammation, and proliferation contributing to atherogenesis and postangioplasty restenosis. The discovery of synthetic ligands for PPARgamma has led to significant enhancement of our understanding of the mechanism of their ligand-dependent activation and subsequent biological effects, particularly with respect to the role of PPARgamma in vascular pathophysiology. The thiazolidinedione PPARgamma agonists not only improve insulin resistance in patients with type II diabetes but also exert a broad spectrum of antiatherogenic effects in vitro and in animal models of atherosclerosis. In this review, we summarize the important role of PPARgamma as a molecular target for thiazolidinediones and its implications for the control of vascular inflammation and proliferation for the cardiovascular system.

Angiotensin II-accelerated atherosclerosis and aneurysm formation is attenuated in osteopontin-deficient mice

Osteopontin (OPN) is expressed in atherosclerotic lesions, particularly in diabetic patients. To determine the role of OPN in atherogenesis, ApoE-/-OPN+/+, ApoE-/-OPN+/-, and ApoE-/-OPN-/- mice were infused with Ang II, inducing vascular OPN expression and accelerating atherosclerosis. Compared with ApoE-/-OPN+/+ mice, ApoE-/-OPN+/- and ApoE-/-OPN-/- mice developed less Ang II-accelerated atherosclerosis. ApoE-/- mice transplanted with bone marrow derived from ApoE-/-OPN-/- mice had less Ang II-induced atherosclerosis compared with animals receiving ApoE-/-OPN+/+ cells. Aortae from Ang II-infused ApoE-/-OPN-/- mice expressed less CD68, C-C-chemokine receptor 2, and VCAM-1. In response to intraperitoneal thioglycollate, recruitment of leukocytes in OPN-/- mice was impaired, and OPN-/- leukocytes exhibited decreased basal and MCP-1-directed migration. Furthermore, macrophage viability in atherosclerotic lesions from Ang II-infused ApoE-/-OPN-/- mice was decreased. Finally, Ang II-induced abdominal aortic aneurysm formation in ApoE-/-OPN-/- mice was reduced and associated with decreased MMP-2 and MMP-9 activity. These data suggest an important role for leukocyte-derived OPN in mediating Ang II-accelerated atherosclerosis and aneurysm formation.

Metformin and vascular protection: a diabetologist's view

The diabetologist's short-term priority is often to gain rapid control of severe and symptomatic hyperglycaemia, with the longer term objective of preventing or delaying the onset of the debilitating and life-threatening complications that result from continued poor glycaemic control. Indeed, guidelines for the management of type 2 diabetes are centred firmly on measures of glycaemic control, based on evidence from the landmark UK Prospective Diabetes Study and Diabetes Control and Complications Trial. Nevertheless, we must remember that most type 2 diabetic patients ultimately die from a cardiovascular cause. A comprehensive approach is needed, where effective control of blood glucose takes place alongside aggressive management of cardiovascular risk factors. A substantial database of clinical evidence, including the ground-breaking UK Prospective Diabetes Study, underpins the place of metformin both as an effective oral antihyperglycaemic agent and for reducing the risk of morbid cardiovascular events.

Fructose-fed rats are protected against ischemia/reperfusion injury

This study examines the relationship between insulin resistance (IR) induced by fructose feeding (FF) and susceptibility to myocardial ischemia/reperfusion injury (MI/R). Six-week-old male Sprague-Dawley rats were randomized into control (CON; n = 59) or FF (n = 58) groups. After 4 weeks, rats were further randomized into one of the following groups: placebo, ischemic preconditioning (IPC), 5-hydroxydecanoic acid (5-HD) (10 mg/kg), or 5-HD + IPC. Moreover, to determine the role of fructose, a second model of IR (Zucker obese) and rats fed fructose diet for 3 days (FF-3) were also subjected to MI/R. In all experiments, rats were subjected to 30 min of myocardial ischemia and 4 h of reperfusion. In rats randomized to placebo, infarct size was significantly reduced by FF (24 +/- 5%) compared with CON (54 +/- 1%, p < 0.05). Pretreatment with 5-HD did not alter the infarct size in CON (45 +/- 5%) but inhibited the protection afforded by FF (53 +/- 7%). IPC reduced the infarct size to an equivalent level in both groups, whereas 5-HD administration prior to IPC blunted the IPC effect. In Zucker obese rats, infarct size was significantly larger (57 +/- 4%) compared with lean controls (37 +/- 4%, p < 0.05). In FF-3 rats, infarct size was also decreased (20 +/- 2%, p < 0.01) compared with CON. This study suggests that fructose feeding affords protection against MI/R that is related to or mimics preconditioning. This protection is not consistent with other models of IR and is likely related to the fructose diet itself.