Diabetes, Hypertension, and Cardiovascular Disease: Clinical Insights and Vascular Mechanisms

Cardiovascular and metabolic effects of metformin in patients with type 1 diabetes (REMOVAL): a double-blind, randomised, placebo-controlled trial

People with elevated, non-diabetic, levels of blood glucose are at risk of progressing to clinical type 2 diabetes and are commonly termed ‘prediabetic’. The term prediabetes usually refers to high–normal fasting plasma glucose (impaired fasting glucose) and/or plasma glucose 2 h following a 75 g oral glucose tolerance test (impaired glucose tolerance). Current US guidelines consider high–normal HbA1c to also represent a prediabetic state. Individuals with prediabetic levels of dysglycaemia are already at elevated risk of damage to the microvasculature and macrovasculature, resembling the long-term complications of diabetes. Halting or reversing the progressive decline in insulin sensitivity and β-cell function holds the key to achieving prevention of type 2 diabetes in at-risk subjects. Lifestyle interventions aimed at inducing weight loss, pharmacologic treatments (metformin, thiazolidinediones, acarbose, basal insulin and drugs for weight loss) and bariatric surgery have all been shown to reduce the risk of progression to type 2 diabetes in prediabetic subjects. However, lifestyle interventions are difficult for patients to maintain and the weight loss achieved tends to be regained over time. Metformin enhances the action of insulin in liver and skeletal muscle, and its efficacy for delaying or preventing the onset of diabetes has been proven in large, well-designed, randomised trials, such as the Diabetes Prevention Program and other studies. Decades of clinical use have demonstrated that metformin is generally well-tolerated and safe. We have reviewed in detail the evidence base supporting the therapeutic use of metformin for diabetes prevention.

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Therapeutic Use of Metformin in Prediabetes and Diabetes Prevention

Microvascular and metabolic physiology are tightly linked. This Perspective reviews evidence that 1) the relationship between hyperglycemia and microvascular dysfunction (MVD) is bidirectional and constitutes a vicious cycle; 2) MVD in diabetes affects many, if not all, organs, which may play a role in diabetes-associated comorbidities such as depression and cognitive impairment; and 3) MVD precedes, and contributes to, hyperglycemia in type 2 diabetes (T2D) through impairment of insulin-mediated glucose disposal and, possibly, insulin secretion. Obesity and adverse early-life exposures are important drivers of MVD. MVD can be improved through weight loss (in obesity) and through exercise. Pharmacological interventions to improve MVD are an active area of investigation.

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Microvascular Dysfunction and Hyperglycemia: A Vicious Cycle With Widespread Consequences.

Background Metformin, the eldest and most widely used glucose lowering drug, is likely to be effective also on cardiac and vascular disease prevention. Nonetheless, uncertainty still exists with regard to its effects on the cardiovascular system as a whole and specifically on the myocardium, both at the organ and cellular levels. Methods We reviewed the available data on the cardiac and vascular effects of metformin, encompassing both in vitro, either tissue or isolated organ, and in vivo studies in experimental animals and humans, as well as the evidence generated by major clinical trials. Results At the cellular level metformin’s produces both AMP-activated kinase (AMPK) dependent and independent effects. At the systemic level, possibly also through other pathways, this drug improves endothelial function, protects from oxidative stress and inflammation, and from the negative effects of angiotensin II. On the myocardium it attenuates ischemia-reperfusion injury and prevents adverse remodeling induced by humoral and hemodynamic factors. The effects on myocardial cell metabolism and contractile function being not evident at rest or in more advanced stages of cardiac dysfunction, could be relevant during transient ischemia, during an acute increase in workload and in the early stages of diabetic/hypertensive cardiomyopathy as confirmed by few small clinical trials and some observational studies. The overall evidence emerging from both clinical trials and real world registry is in favor of a protective effect of metformin with respect to both coronary events and progression to heart failure. Conclusions Given this potential, its efficacy and its safety (and also its low cost) metformin remains the central pillar of the therapy of diabetes.

Metformin effects on the heart and the cardiovascular system: A review of experimental and clinical data.

Objectives
We investigated whether metformin can improve endothelial function and decrease inflammatory activity, and thereby decrease the risk of atherothrombotic disease.

Subjects and design
A randomized, placebo-controlled trial with a follow-up period of 4.3 years set in the outpatient clinics of three nonacademic hospitals (Hoogeveen, Meppel and Coevorden Hospitals, the Netherlands). A total of 390 patients with type 2 diabetes treated with insulin were included. Either metformin 850 mg or placebo (one to three times daily) was added to insulin therapy. Urinary albumin excretion and plasma levels of von Willebrand factor (vWf), soluble vascular adhesion molecule-1 (sVCAM-1), soluble E-selectin (sE-selectin), tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1), C-reactive protein (CRP) and soluble intercellular adhesion molecule-1 (sICAM-1) were measured at baseline and after 4, 17, 30, 43 and 52 months.

Results
Metformin significantly reduced levels of vWF, sVCAM-1, t-PA, PAI-1, CRP and sICAM-1, which, except for CRP, remained significant after adjustment for baseline differences in age, sex, smoking and severity of previous cardiovascular (CV) disease. No effects on urinary albumin excretion or sE-selectin were observed. The improvements in vWf and sVCAM-1 statistically explained about 34% of the reduction in the risk of CV morbidity and mortality associated with metformin treatment in this study.

Conclusions
Metformin is associated with improvement in some (vWF and sVCAM-1) but not all markers of endothelial function, which may explain why it is associated with a decreased risk of CV disease in type 2 diabetes.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/joim.12128

J. van der Kolk

Papers

Long-term effects of metformin on endothelial function in type 2 diabetes: a randomized controlled trial