Endothelial dysfunction, insulin resistance and diabetes: exploring the web of causality

Effect of Dapagliflozin on Myocardial Insulin Sensitivity and Perfusion: Rationale and Design of The DAPAHEART Trial

INTRODUCTION

Sodium-glucose co-transporter-2 (SGLT-2) inhibitors have been shown to have beneficial effects on various cardiovascular (CV) outcomes in patients with type 2 diabetes (T2D) in primary prevention and in those with a high CV risk profile. However, the mechanism(s) responsible for these CV benefits remain elusive and unexplained. The aim of the DAPAHEART study will be to demonstrate that treatment with SGLT-2 inhibitors is associated with greater myocardial insulin sensitivity in patients with T2D, and to determine whether this improvement can be attributed to a decrease in whole-body (and tissue-specific) insulin resistance and to increased myocardial perfusion and/or glucose uptake. We will also determine whether there is an appreciable degree of improvement in myocardial-wall conditions subtended by affected and non-affected coronary vessels, and if this relates to changes in left ventricular function.

METHODS

The DAPAHEART trial will be a phase III, single-center, randomized, two-arm, parallel-group, double-blind, placebo-controlled study. A cohort of 52 T2D patients with stable coronary artery disease (without any previous history of myocardial infarction, with or without previous percutaneous coronary intervention), with suboptimal glycemic control (glycated hemoglobin [HbA1c] 7-8.5%) on their current standard of care anti-hyperglycemic regimen, will be randomized in a 1:1 ratio to dapagliflozin or placebo. The primary outcome is to detect changes in myocardial glucose uptake from baseline to 4 weeks after treatment initiation. The main secondary outcome will be changes in myocardial blood flow, as measured by 13N-ammonia positron emission tomography/computed tomography (PET/CT). Other outcomes include cardiac function, glucose uptake in skeletal muscle, adipose tissue, liver, brain and kidney, as assessed by fluorodeoxyglucose (FDG) PET-CT imaging during hyperinsulinemic-euglycemic clamp; pericardial, subcutaneous and visceral fat, and browning as observed on CT images during FDG PET-CT studies; systemic insulin sensitivity, as assessed by hyperinsulinemic-euglycemic clamp, glycemic control, urinary glucose output; and microbiota modification.

DISCUSSION

SGLT-2 inhibitors, in addition to their insulin-independent plasma glucose-lowering effect, are able to directly (substrate availability, fuel utilization, insulin sensitivity) as well as indirectly (cardiac after-load reduction, decreased risk factors for heart failure) affect myocardial functions. Our study will provide novel insights into how these drugs exert CV protection in a diabetic population.

TRIAL REGISTRATION

EudraCT No. 2016-003614-27; ClinicalTrials.gov Identifier: NCT03313752.

Diastolic dysfunction and abnormalities of the microcirculation in type 2 diabetes

AIM

Diabetic cardiomyopathy is an increasingly recognized entity. The pathogenic factors that may contribute to its development, especially the earliest changes of diastolic dysfunction (DD), have not been clearly defined. Microvessel dysfunction and upregulation of profibrotic growth factors have been described as possible causes. The aim of this study was therefore to determine whether microvascular dysfunction and/or upregulation of the profibrotic connective tissue growth factor (CTGF) are associated with subclinical DD in subjects with type 2 diabetes.

METHODS

Forty subjects with type 2 diabetes and 20 age-matched non-diabetic controls, all of whom had no clinical evidence of ischaemic heart disease, cardiac failure or echo evidence of systolic ventricular dysfunction, were recruited. Microvascular function was measured by laser Doppler velocimetry, with examination of endothelium-dependent increase in blood flow following iontophoresis of acetylcholine (ACh) and endothelium-independent increase in blood flow in response to the nitric oxide donor sodium nitroprusside (SNP). CTGF levels were determined by Western immunoblotting.

RESULTS

DD determined on the basis of traditional echocardiographic criteria was similar in diabetic subjects compared with controls (28 vs. 20%, p = 0.5). Using left ventricular myocardial tissue Doppler-based indices for DD, the E/E' and the E'/A' ratios (where E is the flow related to early ventricular filling and E' and A' are early and late diastolic velocities, respectively) in diabetic subjects revealed evidence of more DD than controls (p = 0.046 and p = 0.007 respectively) . Comparing controls with no DD by conventional echocardiographic criteria (Group I), diabetes and no DD (Group II) and diabetes with DD (Group III), there was a significant trend in reduction of both endothelium-dependent (ACh fold change; p = 0.04) and endothelium-independent (SNP fold change; p = 0.0004) blood flow across the groups. The ACh and SNP responses, however, were not correlated significantly with quartiles of the E/E' ratio or the E'/A' ratio. CTGF plasma levels did not differ across the groups and CTGF did not correlate with parameters of microvascular function.

CONCLUSIONS

This study indicates that while there is a significant association between DD and measures of microvascular function, the relationship between endothelial dysfunction, CTGF and subtle measures of DD is not strong. Other factors are therefore likely to play an important role in the early pathogenesis of subclinical cardiac DD in type 2 diabetes.

Oral infection, hyperglycemia, and endothelial dysfunction

Metabolic syndrome and type 2 diabetes (T2DM) resulting from sustained hyperglycemia are considered as risk factors for cardiovascular disease (CVD) but the mechanism for their contribution to cardiopathogenesis is not well understood. Hyperglycemia induces nonenzymatic glycation of protein-yielding advanced glycation end products (AGE), which are postulated to stimulate interleukin-6 (IL-6) expression, triggering the liver to secrete tissue necrosis factor alpha (TNF-alpha) and C-reactive protein (CRP) that contribute to CVD pathogenesis. Although the high prevalence of periodontitis among individuals with diabetes is well known by dental researchers, it is relatively unrecognized in the medical community. The expression of the same proinflammatory mediators implicated in hyperglycemia (i.e., IL-6, TNF-alpha, and CRP) have been reported to be associated with periodontal disease and increased risk for CVD. We will review published evidence related to these 2 pathways and offer a consensus.

Insulin Resistance, Inflammation, and Blood Pressure Determine Vascular Dysfunction in CKD

BACKGROUND

Conventional cardiovascular risk equations underestimate the risk for cardiovascular disease (CVD) in patients with chronic kidney disease (CKD), implying a role for novel risk factors. Our aim was to compare vascular function and arterial compliance, known markers of CVD, between patients with CKD and healthy controls and examine their association with traditional and novel CVD risk factors.

METHODS

Vascular function was determined by using high-resolution ultrasonography to measure brachial artery endothelial-dependent flow-mediated dilatation (FMD) and endothelial-independent glyceryl trinitrate (GTN)-mediated dilatation. Arterial compliance was measured by using pulse contour analysis to generate large-artery (C1) and small-artery (C2) compliance. We also examined the relationship between vascular function, arterial compliance and blood pressure, lipid and lipoprotein levels, insulin resistance, inflammation, oxidative stress, and calcium and phosphate levels in 105 patients with CKD and 40 healthy controls.

RESULTS

Vascular function and arterial compliance were significantly impaired in patients with CKD compared with healthy controls: mean FMD, 3.8% +/- 0.3% (SE) versus 5.7% +/- 0.6%; GTN-mediated dilatation, 15.7% +/- 0.9% versus 19.6% +/- 1.0%; C1, geometric mean, 12.1 mL/mm Hg; 95% confidence interval (CI), 11.2 to 13.1 versus 15.1 mL/mm Hg; 95% CI, 13.7 to 16.5; and C2, 3.8 mL/mm Hg; 95% CI, 3.4 to 4.3 versus 5.0 mL/mm Hg; 95% CI, 4.2 to 6.0; all P < 0.05. Patients with CKD had greater waist-hip ratios, systolic blood pressures (SBPs), pulse pressures, triglyceride levels, oxidized low-density lipoprotein levels, high-sensitivity interleukin 6 levels, and Homeostasis Model Assessment (HOMA) scores (all P < 0.05) and lower high-density lipoprotein levels (P < 0.001). In patients with CKD, HOMA score and SBP were associated negatively with FMD (model R(2) = 0.28; P < 0.001), and SBP and waist-hip ratio were associated negatively with GTN-mediated dilatation (model R(2) = 0.25; P < 0.001). Pulse pressure was associated negatively with C1 (R(2) = 0.37; P < 0.001), and pulse pressure and high-sensitivity interleukin 6 level were associated negatively with C2 (model R(2) = 0.36; P < 0.001).

CONCLUSION

Insulin resistance, inflammation, systolic hypertension, and increased pulse pressure, but not dyslipidemia, were associated with vascular dysfunction and may be targets for future interventional strategies to reduce CVD risk in patients with CKD.

The vascular endothelium in diabetes: a practical target for drug treatment?

Vascular disease remains a major cause of morbidity and mortality in diabetes mellitus, in spite of recent improvements in outcome, some of which may be modulated by improved endothelial function. Therapeutic strategies aimed directly at preventing, or minimising the extent of, these sequelae are required as an adjunct to treatments directed at normalising the metabolic milieu. The microvasculature, and the endothelium in particular, are early contributors to vascular dysfunction, thus raising the question as to how best to specifically target the endothelium. However, the expansive nature of the microvasculature, the varying demands that tissues have in terms of blood flow, and the heterogeneity that exists amongst cell types in different sites raises potential problems as to the practicality of such an approach. Further-more, temporal and genetic factors in the genesis of diabetic microvascular dysfunction may impact on therapeutic strategies. It is suggested that a systematic approach is required to understand the heterogeneity of the microvasculature, with particular emphasis on relating differences in gene and protein expression with functional properties. Such an approach may then provide the necessary information to allow exploitation of endothelial cell heterogeneity for unique targeted interventions, as well as providing the necessary rationale for pharmacological interventions (both prophylactic and corrective) aimed at the endothelium as a whole.

Statin therapy improves brachial artery vasodilator function in patients with Type 1 diabetes and microalbuminuria

AIMS

Type 1 diabetes mellitus patients with microalbuminuria have endothelial dysfunction associated with the degree of albuminuria but not with LDL-cholesterol levels. Lipid-lowering agents such as statins may still be of benefit as they can correct endothelial dysfunction by both lipid and non-lipid mechanisms. We therefore examined the effects of atorvastatin on brachial artery endothelial dysfunction in these patients.

METHODS

In a double-blind, randomized crossover study, 16 Type 1 diabetes mellitus patients with microalbuminuria received 6 weeks of atorvastatin 40 mg/day or placebo, separated by a 4-week washout. Brachial artery, endothelium-dependent, flow-mediated dilatation (FMD) and endothelium-independent, glyceryl trinitrate-mediated dilatation (GTNMD) were measured.

RESULTS

Compared with placebo, atorvastatin produced a significant decrease in apolipoprotein B (34.2%), LDL-cholesterol (44.1%) (all P < 0.001), and oxidized-LDL (35.7%, P = 0.03). There was a non-significant increase in plasma cGMP (P = 0.13) on atorvastatin. FMD and GTNMD increased significantly on atorvastatin (FMD: atorvastatin +1.8 +/- 0.4%; placebo +0.2 +/- 0.4%, P = 0.007); (GTNMD: atorvastatin +1.3 +/- 0.9%; placebo -1.2 +/- 0.6%, P = 0.04). An increase in cGMP was independently correlated with an increase in FMD on atorvastatin (adjusted (R2) 0.41, P = 0.02).

CONCLUSION

Atorvastatin improves endothelium-dependent and independent vasodilator function of the brachial artery in Type 1 diabetes mellitus patients with microalbuminuria. This may relate to pleiotropic effects of statins, in particular reduced oxidative stress and increased availability of nitric oxide.

Blood pressure in young adulthood and the risk of type 2 diabetes in middle age

OBJECTIVE

Hypertension is known to accompany type 2 diabetes in middle age, but it is unknown how early in life blood pressure (BP) begins to rise among individuals who later develop diabetes. The objective of this study was to evaluate elevated BP as a long-term predictor of type 2 diabetes.

RESEARCH DESIGN AND METHODS

We conducted a prospective cohort study of 1,152 white male medical students in The Johns Hopkins Precursors Study to longitudinally assess systolic BP (SBP) and diastolic BP (DBP) from young adulthood through middle age in men who went on to develop diabetes. Incident diabetes was identified by self-report through mailed questionnaires verified by medical record review.

RESULTS

During a median follow-up of 38 years, 77 cases of incident diabetes occurred. The mean age of diabetes diagnosis was 58 years. As early as age 30 years, mean SBP and DBP were significantly higher in men who developed diabetes during follow-up than in those who remained nondiabetic (SBP 122 vs. 119 mmHg, P = 0.009; DBP 78 vs. 75 mmHg, P = 0.0005). The rate of increase in SBP and DBP over time in men who developed diabetes was greater than the rate of increase in men who did not develop diabetes (SBP 0.49 vs. 0.27 mmHg/year, P < 0.00003; DBP 0.24 vs. 0.17 mmHg/year; P = 0.09). After adjustment for BMI and other risk factors for diabetes, SBP and DBP at age 30 years remained significantly higher in individuals who developed diabetes than in their nondiabetic counterparts; however, the difference in the rate of increase in SBP was no longer significant following multivariate adjustment.

CONCLUSIONS

BP elevations precede the development of type 2 diabetes in middle age by 20-25 years. Higher BP in the prediabetic state might contribute to the presence of vascular disease at the time of diagnosis of type 2 diabetes.