EDITORIAL

Hippokratia 2015, 19(3):195-199

Papagianni M, Tziomalos K
1st Propedeutic Department of Internal Medicine, Medical School, Aristotle University of Thessaloniki, AHEPA Hospital, Thessaloniki, Greece

Abstract

Dipeptidyl peptidase-4 (DPP-4) inhibitors are effective glucose-lowering agents that do not increase body weight and are associated with a low risk for hypoglycemia. Also, they appear to exert beneficial effects on other established cardiovascular risk factors, including dyslipidemia and hypertension. Moreover, DPP-4 inhibitors exert antiinflammatory and antioxidant actions, improve endothelial function and reduce urinary albumin excretion. In contrast to these favorable cardiovascular effects, three recent large, randomized, placebo-controlled trials in patients with type 2 diabetes mellitus (T2DM) and established cardiovascular disease or multiple cardiovascular risk factors showed that DPP-4 inhibitors do not affect the risk of myocardial infarction or ischemic stroke and might increase the risk of heart failure.  The findings of the former randomized studies highlight the limitations of surrogate markers and show that beneficial effects on cardiovascular risk factors do not necessarily translate into reductions in hard clinical endpoints. Ongoing trials will shed more light on the safety profile of DPP-4 inhibitors and will clarify whether they will improve the cardiovascular outcomes of patients with T2DM. Hippokratia 2015; 19 (3): 195-199.

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Key words: Type 2 diabetes mellitus, dipeptidyl peptidase-4 inhibitors, heart failure, cardiovascular disease, safety

Corresponding author: Konstantinos Tziomalos, 1st Propedeutic Department of Internal Medicine, AHEPA Hospital, Thessaloniki 54636, Greece, tel: +302310994621, fax: +302310994773, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Type 2 diabetes mellitus (T2DM) is a major public health problem and currently affects 382 million people worldwide1. The aging of the population, urbanization and the rising prevalence of obesity are estimated to lead to a 55% increase in the worldwide prevalence of T2DM by 20351. Even though the highest prevalence of T2DM is currently observed in North America, most patients with T2DM live in low- and middle-income countries and these areas are expected to exhibit the largest increase in T2DM prevalence1. In low- and middle-income countries, the increase in life expectancy and the process of urbanization, followed by unhealthy lifestyle changes, are important factors contributing to the rising prevalence of T2DM2.

It is well-established that T2DM is independently associated with increased cardiovascular risk3,4. Both antihypertensive treatment and lipid-lowering treatment – primarily with statins – substantially reduce cardiovascular morbidity in patients with T2DM5,6. In contrast, it is unclear whether antidiabetic treatment decreases cardiovascular risk. In the UK Prospective Diabetes Study (UKPDS), metformin reduced cardiovascular morbidity in overweight patients with newly diagnosed T2DM7 and thus metformin currently represents the first-line antidiabetic treatment8. Among the other classes of antidiabetic agents, pioglitazone reduced cardiovascular events in patients with long-standing T2DM and established cardiovascular disease in the PROspective pioglitAzone Clinical Trial In macroVascular Events (PROACTIVE)9. However, pioglitazone has several adverse effects, including edema, heart failure and hip fractures that limit its use9,10. Very recently, empagliflozin, an inhibitor of sodium-glucose co-transporter 2, reduced cardiovascular and all-cause mortality in patients with T2DM and established cardiovascular disease in the EMPA-REG OUTCOME trial11. However, the incidence of non-fatal myocardial infarction and stroke was not reduced by empagliflozin, suggesting that mechanisms other than the prevention or delay of progression of atherosclerosis might underpin these benefits11. Moreover, rates of genital infections were considerably higher in patients treated with empagliflozin11. Accordingly, current guidelines recommend that the choice of the antidiabetic agent in patients who do not achieve HbA1c targets despite treatment with metformin should be individualized based on safety, efficacy and patient’s preferences8.

Dipeptidyl peptidase-4 (DPP-4) inhibitors, also known as gliptins, were initially introduced in the therapeutics of T2DM in 2006. They lower blood glucose levels through their ability to inhibit the degradation of the incretins glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP), which results in reduced secretion of glucagon, increased secretion of insulin and delayed gastric emptying12. In head-to-head comparisons, DPP-4 inhibitors were as effective as sulfonylureas and pioglitazone in reducing HbA1c levels13. However, DPP-4 inhibitors also appear to have beneficial effects on other cardiovascular risk factors. Indeed, these agents do not increase body weight, in contrast to sulfonylureas, pioglitazone, and insulin, which are associated with weight gain13. The effects of DPP-4 inhibitors on serum low- and high-density lipoprotein levels are neutral, but there is a trend for a reduction in triglyceride levels and in the more atherogenic, small-dense low-density lipoprotein particles14-17. In some studies, DPP-4 inhibitors reduced blood pressure18-20 but in others they had no effect21. The risk of hypoglycemia is also lower during treatment with DPP-4 inhibitors compared with sulfonylureas and insulin13. In turn, hypoglycemia has been associated with increased cardiovascular risk in patients with T2DM22,23.

Small and mostly uncontrolled studies also suggested that DPP-4 inhibitors exert beneficial effects on emerging cardiovascular risk factors. Indeed, these agents appear to exert antiinflammatory effects18,24-27, mitigate oxidative stress26,28, improve endothelial function18,25,29,30 and reduce urinary albumin excretion16,18,21,28. A beneficial effect on nonalcoholic fatty liver disease, which is independently associated with increased cardiovascular risk, has also been reported in patients treated with these agents31-33. It was also reported that treatment with DPP-4 inhibitors improves left ventricular function and reduces postischemic stunning in patients with T2DM and coronary heart disease (CHD)34,35. A recent study in 96 patients with T2DM and stable CHD also reported that vildagliptin maintains ischemic preconditioning whereas repaglinide abolishes this protective mechanism36. In this context, animal studies suggested that DPP-4 inhibitors reduce infarct size and mortality after experimental myocardial infarction37,38. Moreover, small studies also reported a decrease in carotid intima-media thickness, a marker of subclinical atherosclerosis, during treatment with DPP-4 inhibitors39,40.

The promise of a cardioprotective effect of DPP-4 inhibitors was further supported by early meta-analyses of phase 2b-3 studies, which suggested that DPP-4 inhibitors might reduce cardiovascular morbidity41-43. However, these results were based on very few events since the studies included in these meta-analyses were short-term and not designed to evaluate the effects of DPP-4 inhibitors on cardiovascular events and the ascertainment of these events was non-uniform and incomplete41-43. In a recent randomized study in 1,551 patients with T2DM, linagliptin reduced cardiovascular events more than glimepiride during the 2-year follow-up despite similar reductions in HbA1c44. However, this benefit was again based on very few cardiovascular events (n =38)44.

In contrast with the beneficial effects of DPP-4 inhibitors on multiple cardiovascular risk factors and the promising results of these preliminary meta-analyses of small studies, three recent large studies showed a neutral or even potentially adverse effect of these agents on cardiovascular events45-47. In the first trial, the Examination of Cardiovascular Outcomes with Alogliptin versus Standard of Care (EXAMINE) study, 5,380 patients with T2DM and recent hospitalization for an acute coronary syndrome were randomized to receive alogliptin 25 mg/day or placebo for a median of 18 months45. The primary end point included death from cardiovascular causes, nonfatal myocardial infarction or nonfatal stroke45. At the end of the study, HbA1c levels were an absolute 0.36% lower in patients treated with alogliptin than in those who received placebo whereas body weight and lipid levels did not differ between the two groups45. Despite this reduction in HbA1c levels with alogliptin treatment, the incidence of the primary end point was similar in patients treated with alogliptin and placebo (11.3 and 11.8%, respectively; hazard ratio (HR) 0.96, upper boundary of the one-sided repeated confidence interval (CI) 1.16, p <0.001 for non-inferiority and p =0.32 for superiority)45. Nevertheless, this trial was designed to evaluate the cardiovascular safety of alogliptin and had limited power (< 20%) to identify a reduction in cardiovascular events with this DPP-4 inhibitor45. Interestingly, subgroup analyses suggested a trend for reduction in cardiovascular events with alogliptin treatment in current smokers and patients with T2DM duration < 10 years, with normal kidney function, who were treated with metformin and who were not treated with insulin45. Conversely, former smokers and patients with T2DM duration ≥ 10 years, with impaired kidney function, who were not treated with metformin and who were treated with insulin showed a trend for greater cardiovascular risk when treated with alogliptin45. Nevertheless, these results should be considered preliminary and exploratory given the large number of subgroup analyses that were performed in the EXAMINE trial45.

The second study, the Saxagliptin Assessment of Vascular Outcomes Recorded in Patients with Diabetes Mellitus – Thrombolysis in Myocardial Infarction (SAVOR-TIMI 53) trial, included 16,492 patients with T2DM and either established cardiovascular disease or multiple cardiovascular risk factors (age > 55 years (men) or > 60 years (women) and at least one of the following: dyslipidemia, hypertension or smoking)46. Patients were randomly allocated to treatment with saxagliptin 5 mg/day or placebo for a median of 2.1 years46. At study completion, HbA1c levels were an absolute 0.2% lower in the saxagliptin group whereas body weight was similar in saxagliptin- and placebo-treated patients46. The incidence of the primary endpoint (cardiovascular death, nonfatal myocardial infarction and nonfatal ischemic stroke) did not differ between patients treated with saxagliptin and placebo (7.3 and 7.2%, respectively; HR 1.00, 95% CI 0.89-1.12, p = 0.99 for superiority and p < 0.001 for non-inferiority)46. It should be mentioned that SAVOR-TIMI 53 was designed as a superiority trial and had 85% power to show a 17% reduction in cardiovascular events with saxagliptin46.

In the third study, the Trial Evaluating Cardiovascular Outcomes with Sitagliptin (TECOS), 14,671 patients with T2DM and established cardiovascular disease were randomized to receive sitagliptin 100 mg/day (or 50 mg/day if the baseline estimated glomerular filtration rate was 30-50 ml/min/1.73m2) or placebo47. After a median follow-up of 3.0 years, HbA1c levels were 0.29% lower in patients treated with sitagliptin47. Again, the incidence of the primary endpoint (cardiovascular death, nonfatal myocardial infarction, nonfatal ischemic stroke or hospitalization for unstable angina) did not differ between patients treated with sitagliptin and placebo (11.4 and 11.6%, respectively; HR 0.98, 95% CI 0.88-1.09, p < 0.001 for non-inferiority)47.

An unexpected finding of the SAVOR-TIMI 53 trial was that the incidence of hospitalization for heart failure was higher in patients who received saxagliptin compared with the placebo group (3.5 and 2.8%, respectively; HR 1.27, 95% CI 1.07-1.51, p = 0.007)46. Importantly, 26.5% of patients hospitalized for heart failure were readmitted for heart failure and 26.1% died during follow-up48. Patients with established heart failure, estimated glomerular filtration rate ≤ 60 ml/min or elevated levels of N-terminal pro B-type natriuretic peptide had higher absolute risk for hospitalization for heart failure48. However, the relative increase in the risk for hospitalization for heart failure induced by saxagliptin was independent of the clinical characteristics of the patients, including the history of heart failure and chronic kidney disease48.

This increased risk of heart failure in patients treated with saxagliptin is difficult to explain, given the apparently beneficial effects of DPP-4 inhibitors on cardiovascular risk factors and potentially on heart function. The increased risk for hospitalization for heart failure was observed mostly during the first year of treatment with saxagliptin, suggesting an acute adverse effect48. However, there was no evidence of fluid retention or myocardial toxicity in patients treated with this agent48. In the EXAMINE trial, alogliptin did not increase the risk for hospitalization for heart failure49,50. Even though observational studies suggested that sitagliptin increases the risk for hospitalization for heart failure in patients with T2DM and pre-existing heart failure51, sitagliptin did not increase the risk for hospitalization for heart failure in the TECOS trial47. On the other hand, DPP-4 inhibitors appear to attenuate the antihypertensive effect of angiotensin converting enzyme inhibitors (ACE-Is)52, which are first-line agents for the management of hypertension in patients with T2DM and the management of heart failure53,54. Therefore, treatment with DPP-4 inhibitors might reduce the protective effects of ACE-Is against new-onset or worsening heart failure52. Notably, 54% of patients in the SAVOR-TIMI 53 were treated with ACE-Is46. DPP-4 also inactivates several vasoactive peptides, including neuropeptide Y, substance P, brain natriuretic peptide and peptide YY30. Therefore, DPP-4 inhibitors might increase the levels of these peptides, which in turn might have a detrimental effect on heart function30.

Other safety concerns were also noticed in the SAVOR-TIMI 53 trial. A trend for an increase in non-cardiovascular mortality was observed in the saxagliptin group (1.7 versus 1.3% in the placebo group, HR 1.27, 95% CI 1.00-1.62, p = 0.051)46. Somehow surprisingly, hypoglycemic events (both minor and major) were also more frequent in patients treated with saxagliptin than in those given placebo even though insulin was used less frequently in the former and the use of other antidiabetic agents was similar in the two groups46. On the other hand, saxagliptin was associated with a reduction in urinary albumin excretion46. Moreover, saxagliptin had comparable safety in patients < 65 years and in elderly (≥ 65 years) and very elderly patients (≥ 75 years)55.

The findings of the EXAMINE, SAVOR-TIMI 53 and TECOS trials highlight the limitations of surrogate markers and show that beneficial effects on cardiovascular risk factors do not necessarily translate into reductions in hard clinical endpoints. Ongoing trials will shed more light on the safety profile of DPP-4 inhibitors and will clarify whether they will improve the cardiovascular outcomes of patients with T2DM56.

Conflict of interest

Authors declare no conflict of interest.

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