The cardiovascular effects of metformin: lost in translation?

Metformin use in type 2 diabetic patients is not associated with lower arterial stiffness: the Maastricht Study

INTRODUCTION

Type 2 diabetes (T2D) is associated with cardiovascular disease complications such as myocardial infarction and stroke. These complications are at least partially the consequence of diabetes-associated increased arterial stiffness. Metformin, a first choice oral glucose-lowering drug, has been associated with potential cardio-protective effects. However, there are no data on the association between real-life metformin use and arterial stiffness. The objective of the current study is to investigate in a population-based sample of individuals with T2D the association between metformin use and aortic stiffness (i.e. carotid-femoral pulse wave velocity, cfPWV) and carotid stiffness [i.e. carotid distensibility coefficient and Young's elastic modulus (YEM)].

METHODS

We used data from The Maastricht Study, an ongoing observational prospective population-based cohort study (current N = 3451). All participants with T2D, based on pharmacy records (N = 672, 31.3% women, mean age 62.6 ± 7.7), were included in the current study. Linear regression analyses were used to study the association between current metformin use and cfPWV, distensibility coefficient and YEM, as compared with no metformin use. Furthermore, metformin use was stratified by cumulative dose (in grams), continuous duration of use (in days), average daily dose (in grams) and time since first prescription (in years). Regression coefficients of distensibility coefficient were multiplied by -1, consequently, for all arterial stiffness indices, a positive regression coefficient signifies increasing arterial stiffness.

RESULTS

Linear regression showed that neither current metformin use was associated with cfPWV [adjusted B: -0.04 (-0.11 to 0.02)] nor metformin use was as stratified by cumulative dose, by continuous duration of use, by average daily dose or by time since first prescription. Metformin use was statistically significantly associated with higher carotid stiffness as assessed by distensibility coefficient [0.12 (0.01 to 0.23)], but not with YEM [0.10 (-0.03 to 0.22)]. However, there was no consistent pattern with the different stratifications of metformin use when further investigating the association with distensibility coefficient.

CONCLUSION

We showed that there is no significant association between current metformin use and aortic stiffness, regardless of how metformin use in itself was defined. In addition, metformin use was not associated with a lower carotid stiffness. The present results showed no beneficial effect of metformin use, dosage or duration on arterial stiffness in middle-aged patients with T2D. Alternatively, metformin may exerts its cardio-protective effects via other pathways.

Pre, peri and posttransplant diabetes mellitus

PURPOSE OF REVIEW

The leading cause of death in both chronic kidney disease (CKD) and renal transplant patients is cardiovascular events. Post-transplant diabetes mellitus (PTx-DM), which is a major cardiovascular risk factor, is a metabolic disorder that affects 5.5-60.2% of renal allograft recipients by 1-year posttransplant (PTx). PTx-DM has been associated with a negative impact on patient and graft outcomes and survival.

RECENT FINDINGS

Individuals who develop PTx-DM are usually prone to this condition prior to and/or after developing CKD. Genetic factors, obesity, inflammation, medications and CKD all are risk factors for PTx-diabetes mellitus. The path to development of disease continues PTx frequently augmented by the use of diabetogenic maintenance immunosuppressive and some nonimmunosuppressive medications. These risk factors are usually associated with an increase in insulin resistance, a decrease in insulin gene expression and/or β-cell dysfunction and apoptosis.

SUMMARY

Some new anti-diabetes mellitus medications may help to improve the overall outcome; however, there is a real need for developing a preventive strategy. Identifying and targeting PTx-DM risk factors may help to guide the development of an effective programme. This could include the adoption of nondiabetogenic immunosuppressive protocols for high-risk patients.

Trained immunity as a novel therapeutic strategy

Recent studies have shown that upon certain vaccinations or infections human innate immune cells can undergo extensive metabolic and epigenetic reprogramming, which results in enhanced immune responses upon heterologous re-infection, a process termed trained immunity. Trained immunity has also been shown to be inappropriately activated in inflammatory diseases. This provides the potential for identifying novel therapeutic targets: potentiation of trained immunity could protect from secondary infections and reverse immunotolerant states, while inhibition of trained immunity might reduce excessive immune activation in chronic inflammatory conditions. By targeting specific mechanisms of trained immunity on either immunologic, metabolic or epigenetic level, novel therapeutic approaches could be developed.

Functional interplay between liver X receptor and AMP-activated protein kinase α inhibits atherosclerosis in apolipoprotein E-deficient mice - a new anti-atherogenic strategy

BACKGROUND AND PURPOSE

The liver X receptor (LXR) agonist T317 reduces atherosclerosis but induces fatty liver. Metformin activates energy metabolism by activating AMPKα. In this study, we determined if interactions between metformin and T317 could inhibit atherosclerosis without activation of hepatic lipogenesis.

EXPERIMENTAL APPROACH

Apolipoprotein E-deficient mice were treated with T317, metformin or both agents, in a high-fat diet for 16 weeks. Then, samples of aorta, liver, macrophage and serum were collected to determine atherosclerotic lesions, fatty liver, lipid profiles and expression of related proteins. Techniques used included immunohistochemistry, histology, qRT-PCR and Western blot.

KEY RESULTS

T317 inhibited en face and aortic root sinus lesions, and the inhibition was further enhanced by addition of metformin. Co-treatment with metformin and T317 increased lesion stability, by increasing collagen content, and reducing necrotic cores and calcification. Formation of macrophages/foam cells and their accumulation in arterial wall were inhibited by the co-treatment, which was accompanied by increased ABCA1/ABCG1 expression, reduced monocyte adhesion and apparent local proliferation of macrophages. Metformin blocked T317-induced fatty liver by inhibiting T317-induced hepatic LXRα nuclear translocation and expression of lipogenic genes and by activating AMPKα. Moreover, co-treatment with T317 and metformin improved triglyceride metabolism by inducing expression of adipose triglyceride lipase, hormone-sensitive lipase, PPARα and carnitine acetyltransferase and by inhibiting acyl-CoA:diacylglycerol acyltransferase 1 expression.

CONCLUSIONS AND IMPLICATIONS

Co-treatment with T317 and metformin inhibited the development of atherosclerosis without activation of lipogenesis, suggesting that combined treatment with T317 and metformin may be a novel approach to inhibition of atherosclerosis.

A systematic review and meta-analysis of the protective effects of metformin in experimental myocardial infarction

Metformin improves cardiovascular prognosis in patients with diabetes mellitus, compared to alternative glucose-lowering drugs, despite similar glycemic control. Direct cardiovascular protective properties have therefore been proposed, and studied in preclinical models of myocardial infarction. We now aim to critically assess the quality and outcome of these studies. We present a systematic review, quality assessment and meta-analysis of the effect of metformin in animal studies of experimental myocardial infarction. Through a comprehensive search in Pubmed and EMBASE, we identified 27 studies, 11 reporting on ex vivo experiments and 18 reporting on in vivo experiments. The primary endpoint infarct size as percentage of area at risk was significantly reduced by metformin in vivo (MD -18.11[-24.09,-12.14]) and ex vivo (MD -18.70[-25.39, -12.02]). Metformin improved the secondary endpoints left ventricular ejection fraction (LVEF) and left ventricular end systolic diameter. A borderline significant effect on mortality was observed, and there was no overall effect on cardiac hypertrophy. Subgroup analyses could be performed for comorbidity and timing of treatment (infarct size and mortality) and species and duration of ischemia (LVEF), but none of these variables accounted for significant amounts of heterogeneity. Reporting of possible sources of bias was extremely poor, including randomization (reported in 63%), blinding (33%), and sample size calculation (0%). As a result, risk of bias (assessed using SYRCLE’s risk of bias tool) was unclear in the vast majority of studies. We conclude that metformin limits infarct-size and improves cardiac function in animal models of myocardial infarction, but our confidence in the evidence is lowered by the unclear risk of bias and residual unexplained heterogeneity. We recommend an adequately powered, high quality confirmatory animal study to precede a randomized controlled trial of acute administration of metformin in patients undergoing reperfusion for acute myocardial infarction.

Long-term activation of the innate immune system in atherosclerosis

Efforts to reverse the pathologic consequences of vulnerable plaques are often stymied by the complex treatment resistant pro-inflammatory environment within the plaque. This suggests that pro-atherogenic stimuli, such as LDL cholesterol and high fat diets may impart longer lived signals on (innate) immune cells that persist even after reversing the pro-atherogenic stimuli. Recently, a series of studies challenged the traditional immunological paradigm that innate immune cells cannot display memory characteristics. Epigenetic reprogramming in these myeloid cell subsets, after exposure to certain stimuli, has been shown to alter the expression of genes upon re-exposure. This phenomenon has been termed trained innate immunity or innate immune memory. The changed responses of 'trained' innate immune cells can confer nonspecific protection against secondary infections, suggesting that innate immune memory has likely evolved as an ancient mechanism to protect against pathogens. However, dysregulated processes of immunological imprinting mediated by trained innate immunity may also be detrimental under certain conditions as the resulting exaggerated immune responses could contribute to autoimmune and inflammatory diseases, such as atherosclerosis. Pro-atherogenic stimuli most likely cause epigenetic modifications that persist for prolonged time periods even after the initial stimulus has been removed. In this review we discuss the concept of trained innate immunity in the context of a hyperlipidemic environment and atherosclerosis. According to this idea the epigenome of myeloid (progenitor) cells is presumably modified for prolonged periods of time, which, in turn, could evoke a condition of continuous immune cell over-activation.

The effect of dipyridamole on the pharmacokinetics of metformin: a randomized crossover study in healthy volunteers

PURPOSE

Concomitant treatment with the glucose-lowering drug metformin and the platelet aggregation inhibitor dipyridamole often occurs in patients with type 2 diabetes mellitus who have suffered a cerebrovascular event. The gastrointestinal uptake of metformin is mediated by the human equilibrative nucleoside transporter 4 (ENT4), which is inhibited by dipyridamole in preclinical studies. We hypothesized that dipyridamole lowers the plasma exposure to metformin.

METHODS

Eighteen healthy volunteers (mean age 23 years; 9 male) were randomized in an open-label crossover study. Subjects were allocated to treatment with metformin 500 mg twice daily in combination with dipyridamole slow-release 200 mg twice daily or to metformin alone for 4 days. After a washout period of 10 days, the volunteers were crossed over to the alternative treatment arm. Blood samples were collected during a 10-h period after intake of the last metformin dose. The primary endpoint was the area under the plasma concentration-time curve (AUC0-12h) and the maximum plasma metformin concentration (C max).

RESULTS

In healthy subjects, dipyridamole did not significantly affect Cmax nor AUC0-12h of metformin under steady-state conditions.

CONCLUSIONS

Previous in vitro studies report that dipyridamole inhibits the ENT4 transporter that mediates gastrointestinal uptake of metformin. In contrast, co-administration of dipyridamole at therapeutic dosages to healthy volunteers does not have a clinically relevant effect on metformin plasma steady-state exposure. This observation is reassuring for patients who are treated with this combination of drugs.

Uncomplicating the Macrovascular Complications of Diabetes: The 2014 Edwin Bierman Award Lecture

The risk of cardiovascular events in humans increases in the presence of type 1 or type 2 diabetes mellitus, in large part due to exacerbated atherosclerosis. Genetically engineered mouse models have begun to elucidate cellular and molecular mechanisms responsible for diabetes-exacerbated atherosclerosis. Research on these mouse models has revealed that diabetes independently accelerates initiation and progression of lesions of atherosclerosis and also impairs the regression of lesions following aggressive lipid lowering. Myeloid cell activation in combination with proatherogenic changes allowing for increased monocyte recruitment into arteries of diabetic mice has emerged as an important mediator of the effects of diabetes on the three stages of atherosclerosis. The effects of diabetes on atherosclerosis appear to be dependent on an interplay between glucose and lipids, as well as other factors, and result in increased recruitment of monocytes into both progressing and regressing lesions of atherosclerosis. Importantly, some of the mechanisms revealed by mouse models are now being studied in human subjects. This Perspective highlights new mechanistic findings based on mouse models of diabetes-exacerbated atherosclerosis and discusses the relevance to humans and areas in which more research is urgently needed in order to lessen the burden of macrovascular complications of type 1 and type 2 diabetes mellitus.