Jill P. Crandall

Advanced glycation endproducts interacting with their endothelial receptor induce expression of vascular cell adhesion molecule-1 (VCAM-1) in cultured human endothelial cells and in mice. A potential mechanism for the accelerated vasculopathy of diabetes.

Vascular cell adhesion molecule-1 (VCAM-1), an inducible cell-cell recognition protein on the endothelial cell surface (EC), has been associated with early stages of atherosclerosis. In view of the accelerated vascular disease observed in patients with diabetes, and the enhanced expression of VCAM-1 in diabetic rabbits, we examined whether irreversible advanced glycation endproducts (AGEs), could mediate VCAM-1 expression by interacting with their endothelial cell receptor (receptor for AGE, RAGE). Exposure of cultured human ECs to AGEs induced expression of VCAM-1, increased adhesivity of the monolayer for Molt-4 cells, and was associated with increased levels of VCAM-1 transcripts. The inhibitory effect of anti-RAGE IgG, a truncated form of the receptor (soluble RAGE) or N-acetylcysteine on VCAM-1 expression indicated that AGE-RAGE-induced oxidant stress was central to VCAM-1 induction. Electrophoretic mobility shift assays on nuclear extracts from AGE-treated ECs showed induction of specific DNA binding activity for NF-kB in the VCAM-1 promoter, which was blocked by anti-RAGE IgG or N-acetylcysteine. Soluble VCAM-1 antigen was elevated in human diabetic plasma. These data are consistent with the hypothesis that AGE-RAGE interaction induces expression of VCAM-1 which can prime diabetic vasculature for enhanced interaction with circulating monocytes.

Inflammatory mediators are induced by dietary glycotoxins, a major risk factor for diabetic angiopathy

Diet is a major environmental source of proinflammatory AGEs (heat-generated advanced glycation end products); its impact in humans remains unclear. We explored the effects of two equivalent diets, one regular (high AGE, H-AGE) and the other with 5-fold lower AGE (L-AGE) content on inflammatory mediators of 24 diabetic subjects: 11 in a 2-week crossover and 13 in a 6-week study. After 2 weeks on H-AGE, serum AGEs increased by 64.5% (P = 0.02) and on L-AGE decreased by 30% (P = 0.02). The mononuclear cell tumor necrosis factor-α/β-actin mRNA ratio was 1.4 ± 0.5 on H-AGE and 0.9 ± 0.5 on L-AGE (P = 0.05), whereas serum vascular adhesion molecule-1 was 1,108 ± 429 and 698 ± 347 ng/ml (P = 0.01) on L- and H-AGE, respectively. After 6 weeks, peripheral blood mononuclear cell tumor necrosis factor-α rose by 86.3% (P = 0.006) and declined by 20% (P, not significant) on H- or L-AGE diet, respectively; C-reactive protein increased by 35% on H-AGE and decreased by 20% on L-AGE (P = 0.014), and vascular adhesion molecule-1 declined by 20% on L-AGE (P < 0.01) and increased by 4% on H-AGE. Serum AGEs were increased by 28.2% on H-AGE (P = 0.06) and reduced by 40% on L-AGE (P = 0.02), whereas AGE low density lipoprotein was increased by 32% on H-AGE and reduced by 33% on L-AGE diet (P < 0.05). Thus in diabetes, environmental (dietary) AGEs promote inflammatory mediators, leading to tissue injury. Restriction of dietary AGEs suppresses these effects.

Statin Therapy and Risk of Developing Type 2 Diabetes: A Meta-Analysis

OBJECTIVE Although statin therapy reduces cardiovascular risk, its relationship with the development of diabetes is controversial. The first study (West of Scotland Coronary Prevention Study [WOSCOPS]) that evaluated this association reported a small protective effect but used nonstandardized criteria for diabetes diagnosis. However, results from subsequent hypothesis-testing trials have been inconsistent. The aim of this meta-analysis is to evaluate the possible effect of statin therapy on incident diabetes. RESEARCH DESIGN AND METHODS A systematic literature search for randomized statin trials that reported data on diabetes through February 2009 was conducted using specific search terms. In addition to the hypothesis-generating data from WOSCOPS, hypothesis-testing data were available from the Heart Protection Study (HPS), the Long-Term Intervention with Pravastatin in Ischemic Disease (LIPID) Study, the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT), the Justification for the Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin (JUPITER), and the Controlled Rosuvastatin Multinational Study in Heart Failure (CORONA), together including 57,593 patients with mean follow-up of 3.9 years during which 2,082 incident diabetes cases accrued. Weighted averages were reported as risk ratios (RRs) with 95% CIs using a random-effects model. Statistical heterogeneity scores were assessed with the Q and I2 statistic. RESULTS In the meta-analysis of the hypothesis-testing trials, we observed a small increase in diabetes risk (RR 1.13 [95% CI 1.03–1.23]) with no evidence of heterogeneity across trials. However, this estimate was attenuated and no longer significant when the hypothesis-generating trial WOSCOPS was included (1.06 [0.93–1.25]) and also resulted in significant heterogeneity (Q 11.8 [5 d.f.], P = 0.03, I2 = 57.7%). CONCLUSIONS Although statin therapy greatly lowers vascular risk, including among those with and at risk for diabetes, the relationship of statin therapy to incident diabetes remains uncertain. Future statin trials should be designed to formally address this issue.

Role of Risk Factors in the Modulation of Tissue Factor Activity and Blood Thrombogenicity

Background—Several studies suggest a role for an increased circulating pool of tissue factor (TF) in atherothrombotic diseases. Furthermore, certain cardiovascular risk factors, such as diabetes, hyperlipemia, and smoking, are associated with a higher incidence of thrombotic complications. We hypothesized that the observed increased blood thrombogenicity (BT) observed in patients with type 2 diabetes mellitus may be mediated via an increased circulating tissue factor activity. We have extended our study to smokers and hyperlipidemic subjects. Methods and Results—Poorly controlled patients with type 2 diabetes mellitus (n=36), smokers (n=10), and untreated hyperlipidemic subjects (n=10) were studied. Circulating TF was immunocaptured from plasma, relipidated, and quantified by factor Xa (FXa) generation in the presence of factor VIIa. BT was assessed as thrombus formation on the Badimon perfusion chamber. Patients with improvement in glycemic control showed a reduction in circulating TF (362±135 versus 243±74 pmol/L per min FXa, P =0.0001). A similar effect was observed in BT (15 445±1130 versus 12 072±596 &mgr;m/mm2, P =0.01). Two hours after smoking 2 cigarettes, TF was increased (217±72 versus 283±106 pmol/L per min FXa, P =0.003). Hyperlipidemic subjects showed higher TF (237±63 versus 195±44 pmol/L per min FXa, P =0.035) than healthy volunteers. Conclusions—These findings suggest that high levels of circulating TF may be the mechanism of action responsible for the increased thrombotic complications associated with the presence of these cardiovascular risk factors. These observations strongly emphasize the usefulness of the management of the patients based on their global risk assessment.

Effects of Testosterone Treatment in Older Men

BACKGROUND Serum testosterone concentrations decrease as men age, but benefits of raising testosterone levels in older men have not been established. METHODS We assigned 790 men 65 years of age or older with a serum testosterone concentration of less than 275 ng per deciliter and symptoms suggesting hypoandrogenism to receive either testosterone gel or placebo gel for 1 year. Each man participated in one or more of three trials--the Sexual Function Trial, the Physical Function Trial, and the Vitality Trial. The primary outcome of each of the individual trials was also evaluated in all participants. RESULTS Testosterone treatment increased serum testosterone levels to the mid-normal range for men 19 to 40 years of age. The increase in testosterone levels was associated with significantly increased sexual activity, as assessed by the Psychosexual Daily Questionnaire (P<0.001), as well as significantly increased sexual desire and erectile function. The percentage of men who had an increase of at least 50 m in the 6-minute walking distance did not differ significantly between the two study groups in the Physical Function Trial but did differ significantly when men in all three trials were included (20.5% of men who received testosterone vs. 12.6% of men who received placebo, P=0.003). Testosterone had no significant benefit with respect to vitality, as assessed by the Functional Assessment of Chronic Illness Therapy-Fatigue scale, but men who received testosterone reported slightly better mood and lower severity of depressive symptoms than those who received placebo. The rates of adverse events were similar in the two groups. CONCLUSIONS In symptomatic men 65 years of age or older, raising testosterone concentrations for 1 year from moderately low to the mid-normal range for men 19 to 40 years of age had a moderate benefit with respect to sexual function and some benefit with respect to mood and depressive symptoms but no benefit with respect to vitality or walking distance. The number of participants was too few to draw conclusions about the risks of testosterone treatment. (Funded by the National Institutes of Health and others; ClinicalTrials.gov number, NCT00799617.).

The role of iron in type 2 diabetes in humans

The role of micronutrients in the etiology of type 2 diabetes is not well established. Several lines of evidence suggest that iron play may a role in the pathogenesis of type 2 diabetes. Iron is a strong pro-oxidant and high body iron levels are associated with increased level of oxidative stress that may elevate the risk of type 2 diabetes. Several epidemiological studies have reported a positive association between high body iron stores, as measured by circulating ferritin level, and the risk of type 2 diabetes and of other insulin resistant states such as the metabolic syndrome, gestational diabetes and polycystic ovarian syndrome. In addition, increased dietary intake of iron, especially that of heme iron, is associated with risk of type 2 diabetes in apparently healthy populations. Results from studies that have evaluated the association between genetic mutations related to iron metabolism have been inconsistent. Further, several clinical trials have suggested that phlebotomy induced reduction in body iron levels may improve insulin sensitivity in humans. However, no interventional studies have yet directly evaluated the effect of reducing iron intake or body iron levels on the risk of developing type 2 diabetes. Such studies are required to prove the causal relationship between moderate iron overload and diabetes risk.

Pilot Study of Resveratrol in Older Adults With Impaired Glucose Tolerance

BACKGROUND Resveratrol, a plant-derived polyphenol, has shown promising effects on insulin sensitivity and glucose tolerance in animal models and is also reported to have cardioprotective properties, but human studies are limited. In a pilot study, we tested the hypothesis that resveratrol improves glucose metabolism and vascular function in older adults with impaired glucose tolerance (IGT). METHODS Ten subjects aged 72 ± 3 years (M ± SD) with IGT were enrolled in a 4-week open-label study of resveratrol (daily dose 1, 1.5, or 2 g). Following a standard mixed meal (110 g carbohydrate, 20 g protein, 20 g fat), we measured 3-hour glucose and insulin area under the curve (AUC), insulin sensitivity (Matsuda index), and secretion (corrected insulin response at 30 minutes). Endothelial function was assessed by reactive hyperemia peripheral arterial tonometry (reactive hyperemia index) before and 90 minutes postmeal. Results did not differ by dose, so data were combined for analysis. RESULTS At baseline, body mass index was 29 ± 5 kg/m(2), fasting plasma glucose 110 ± 13 mg/dL, and 2-hour glucose 183 ± 33 mg/dL. After 4 weeks of resveratrol, fasting plasma glucose was unchanged, but peak postmeal (185 ± 10 vs 166 ± 9 mg/dL, p = .003) and 3-hour glucose AUC (469 ± 23 vs 428 ± 19, p = .001) declined. Matsuda index improved (3.1 ± 0.5 vs 3.8 ± 0.5, p = .03), and corrected insulin response at 30 minutes was unchanged (0.6 ± 0.1 vs 0.5 ± 0.5, p = .49). There was a trend toward improved postmeal reactive hyperemia index (baseline vs resveratrol postmeal delta -0.4 ± 0.2 vs 0.2 ± 0.3, p = .06). Weight, blood pressure, and lipids were unchanged. CONCLUSIONS At doses between 1 and 2 g/day, resveratrol improves insulin sensitivity and postmeal plasma glucose in subjects with IGT. These preliminary findings support the conduct of larger studies to further investigate the effects of resveratrol on metabolism and vascular function.

The prevention of type 2 diabetes

Type 2 diabetes mellitus (T2DM) affects more than 7% of adults in the US and leads to substantial personal and economic burden. In prediabetic states insulin secretion and action—potential targets of preventive interventions—are impaired. In trials lifestyle modification (i.e. weight loss and exercise) has proven effective in preventing incident T2DM in high-risk groups, although weight loss has the greatest effect. Various medications (e.g. metformin, thiazolidinediones and acarbose) can also prevent or delay T2DM. Whether diabetes-prevention strategies also ultimately prevent the development of diabetic vascular complications is unknown, but cardiovascular risk factors are favorably affected. Preventive strategies that can be implemented in routine clinical settings have been developed and evaluated. Widespread application has, however, been limited by local financial considerations, even though cost-effectiveness might be achieved at the population level.

Blood thrombogenicity in type 2 diabetes mellitus patients is associated with glycemic control

OBJECTIVES This study was designed to determine whether blood thrombogenicity is related to chronic glycemic control in type 2 diabetes mellitus (T2DM). BACKGROUND Type 2 diabetes mellitus is associated with accelerated atherosclerosis and a high rate of arterial thrombotic complications. Whether increased blood thrombogenicity is associated with glycemic control has not been properly tested. METHODS Forty patients with T2DM with hemoglobin A1c (HbA1c) > or =7.5% were selected. Maintaining their current hypoglycemic therapies, patients were randomized into a conservative (diet modification plus placebo) or intensive (diet modification plus troglitazone) hypoglycemic regimen for three months. Blood thrombogenicity was measured at baseline and after three months with the Badimon ex vivo perfusion chamber and assessed as platelet-thrombus formation. The repeated measurements allowed every patient to be his/her own control. RESULTS Patients in both groups (48% and 74% of the conservative and intensive groups, respectively) improved glucose control (HbA1c reduction > or =0.5%), showing a significant decrease in blood thrombogenicity. A significant positive correlation was observed between the reduction in thrombus formation and the reduction in HbA1c (r = 0.47, p < 0.01). The reduction in HbA1c achieved by both treatments was comparable. Patients without glycemic improvement showed no change in blood thrombogenicity. Improved glycemic control was the only significant predictor of a decrease in blood thrombogenicity. CONCLUSIONS In T2DM, there is an association between improved glycemic control and blood thrombogenicity reduction. The effect of glycemic control on the thrombotic complications of T2DM patients deserves further investigation.

Adiponectin, change in adiponectin, and progression to diabetes in the diabetes prevention program

OBJECTIVE— To determine whether baseline adiponectin levels or intervention-associated change in adiponectin levels were independently associated with progression to diabetes in the Diabetes Prevention Program (DPP). RESEARCH DESIGN AND METHODS— Cox proportional hazards analysis was used to evaluate the contribution of adiponectin and treatment-related change in adiponectin to risk of progression to diabetes. RESULTS— Baseline adiponectin was a strong independent predictor of incident diabetes in all treatment groups (hazard ratio per ∼3 μg/ml higher level; 0.61 in the lifestyle, 0.76 in the metformin, and the 0.79 in placebo groups; all P < 0.001, P = 0.13 comparing groups). Baseline differences in adiponectin between sexes and race/ethnicity groups were not reflected in differences in diabetes risk. DPP interventions increased adiponectin levels ([means ± SE] 0.83 ± 0.05 μg/ml in the lifestyle group, 0.23 ± 0.05 μg/ml in the metformin group, and 0.10 ± 0.05 μg/ml in the placebo group; P < 0.001 for increases versus baseline, P < 0.01 comparing groups). These increases were associated with reductions in diabetes incidence independent of baseline adiponectin levels in the lifestyle and placebo groups but not in the metformin subjects (hazard ratio 0.72 in the lifestyle group (P < 0.001), 0.92 in the metformin group (P = 0.18), and 0.89 in the placebo group; P = 0.02 per ∼1 μg/ml increase, P = 0.02 comparing groups). In the lifestyle group, adjusting for change in weight reduced, but did not remove, the effect of increased adiponectin. CONCLUSIONS— Adiponectin is a powerful marker of diabetes risk in subjects at high risk for diabetes, even after adjustment for weight. An increase in adiponectin in the lifestyle and placebo groups was associated with a reduction in diabetes risk. However, these changes in adiponectin were comparatively small and less strongly related to diabetes outcome than baseline adiponectin levels.