The delicate balance of disease management versus off-target effects of treatment continues to be a vital concern to both patients and physicians. This article offers a brief overview of heart failure in diabetes and comments on the recent outcome trials of dipeptidyl peptidase-4 (DPP-4) inhibitors, with a closer look at a few pathobiological concerns.

The importance of safe antidiabetic treatments becomes apparent when one considers the increasing obesity and diabetes pandemics. Approximately 150,000 patients with moderate-high cardiovascular (CV) risk factor profiles are currently enrolled in trials of antidiabetic agents. Establishing the CV safety of newer antidiabetic agents, especially with respect to heart failure, remains crucial.

Heart failure syndrome is a symptom complex composed of worsening shortness of breath, orthopnea, paroxysmal nocturnal dyspnea, fatigue, and the well-known manifestation of ankle edema. The syndrome is characterized by physical findings of fluid retention (dependent edema), a third heart sound, rales sounds, and distension of the neck veins. In addition, heart failure is associated with chronic inflammation and a prothrombotic state. Endothelial dysfunction and proteomic and neurohormonal activation occur many months before development of the syndrome complex.1,2 

Newer areas of basic science research have identified potential prognostic indicators in chronic heart failure (miR126 and miR508-5p) that might be used as novel markers leading to earlier diagnosis and treatment of heart failure.3,4  Heart failure has several etiologies ranging from mechanical and electrical dysfunction to structural and valvular abnormities. Moreover, the consequences of heart failure are multi-systemic and adversely affect the liver, kidneys, bone marrow, and muscle.

Recent data from the Olmstead County population study5  showed that patients with diabetes had equal amounts of systolic and diastolic dysfunction. Patients with diabetes frequently have preserved left-ventricular function (a normal ejection fraction) but with a poorly compliant left ventricle that is very sensitive to volume changes. For example, people with type 2 diabetes who are exposed to an extra salt and fluid load could experience enough of an increase in circulating blood volume to place them into symptomatic heart failure. Autonomic dysfunction, glucose toxicity, and oxidative stress are believed to play a role in the development of heart failure in people with diabetes (Figure 1).

The occurrence of CV events and mortality in patients with diabetes is frequently underestimated when considering heart failure in diabetes. Notably, myocardial infarction (MI), non-ST elevation MI, and stroke are the leading primary endpoints of most current antidiabetic drug trials. However, heart failure may need to be added or considered as a principal secondary endpoint. Recently, Juhaeri et al.6  reported in a retrospective study encompassing > 50 million lives from Medicaid, Medicare, and 60 health maintenance organizations the incidence of heart failure, MI, and stroke in type 2 diabetes patients on insulin. The highest incidence was for heart failure (Figure 2). In addition, Bertoni et al.7  evaluated 151,738 Medicare beneficiaries with diabetes with practically a 10-fold increase in heart failure mortality versus patients with diabetes who were free of heart failure at 60 months.

In summary, the heart failure syndrome in diabetes carries an ominous outlook, and, with an increasing number of antidiabetic drugs to reduce blood glucose levels, newer trials should consider heart failure as one of the major clinical endpoints. In addition to an increasing BMI, which is frequently associated with diabetes, waist circumference should also be evaluated, even for patients with a normal weight (Figure 3).8 

Despite advances in medical and surgical therapy for the management of patients with diabetes, lifestyle modification leading to weight loss alone affords improvement in the CV risk profile, as shown in Table 1. It is possible that interventional procedures such as endobarrier or gastric bypass surgery may carry less risk for markedly obese patients who are at high risk for diabetes or who have diabetes, but these procedures also carry some degree of surgical risk.

Two recent DPP-4 inhibitor trials have increased discussion about hospitalizations for heart failure even though basic science studies have not noted significant heart failure concerns.

The SAVOR (Saxagliptin Assessment of Vascular Outcomes Recorded in Patients With Diabetes Mellitus [TIMI-53]) trial9  evaluated the safety and efficacy of saxagliptin on CV outcomes in patients with diabetes who are at risk for CV events. The trial was designed as a superiority trial. However, a closed testing hierarchy prespecified that a test for noninferiority of the primary composite endpoint should be completed first to preserve the alpha level, followed by a test for superiority. A total of 16,492 diabetes patients were prospectively randomized to saxagliptin 5 mg daily (2.5 mg if glomerular filtration rate [GFR] was < 50 ml/min/1.73 m2) or placebo, with a mean follow-up of 2.1 years. Demographic data are shown in Table 2. The primary endpoint was a composite of CV death, MI, or ischemic stroke.

The primary endpoint occurred in 613 patients in the saxagliptin group and 609 patients in the placebo group (7.3 and 7.2%, NS). The 2-year Kaplan-Meier estimate for superiority was not achieved (hazard ratio [HR] with saxagliptin 1.00, 95% CI 0.89–1.12, P = 0.99). However, noninferiority was significant at P < 0.001. The major composite secondary endpoints of CV death, MI, stroke, hospitalization for unstable angina, coronary revascularization, and heart failure was 12.8% in the treatment arm and 12.4% in the placebo arm (2-year Kaplan-Meier estimate HR 1.02, 95% CI 0.94–1.11, P = 0.66, NS). Unfortunately, hospitalization for heart failure was significantly increased in the saxagliptin arm by 27% (HR 1.27, 95% CI 1.07–1.51, P < 0.007). The risk for primary and secondary endpoints among patients who received saxagliptin was comparable to that among patients without a history of heart failure (primary endpoint HR in the saxagliptin group 1.13, 95% CI 0.89–1.43, vs. 0.97, 95% CI 0.85–1.10, in the comparison group; secondary endpoint HR in the saxagliptin group 1.06, 95% CI 0.89–1.27, vs. 1.01, 95% CI 0.91–1.11, in the comparison group). The rate of acute and chronic pancreatitis was similar in the saxagliptin and placebo groups: 0.3 vs. 0.2% for acute pancreatitis and < 0.1 vs. 0.1% for chronic pancreatitis.

The absolute risk for hospitalization for heart failure was highest among patients with a history of heart failure. However, the relative risk among patients assigned to saxagliptin was similar regardless of baseline history of heart failure (HR 1.21, 95% CI 0.93–1.58, vs. 1.32, 95% CI 1.04–1.65). In summary, the DPP-4 inhibitor saxagliptin did not reduce CV events in diabetes patients. The apparent off-target effect of increased risk for hospitalization for heart failure (best predicted by history of heart failure) will remain a question for future trials to answer in patients with stable CV disease and diabetes (Figures 4 and 5).

The EXAMINE (Examination of Cardiovascular Outcomes With Alogliptin Versus Standard of Care) trial10  was a double-blinded noninferiority trial comparing placebo to alogliptin and evaluating the impact of treatment on major CV events in patients with type 2 diabetes and acute coronary syndrome within 15–90 days before randomization. Demographic data are shown in Table 2. The primary CV endpoint was a composite of death from CV causes, nonfatal MI, and nonfatal stroke. A total of 5,380 patients underwent randomization with a follow-up of up to 40 months (median 18 months).

The primary endpoint occurred in 305 patients (11.3%) assigned to alogliptin and in 316 patients (11.8%) assigned to placebo (HR 0.96, upper boundary of the one-sided repeated confidence interval 1.16, P < 0.001 for noninferiority, P = 0.32 for superiority) at 36 months of follow-up. Table 3 shows the components of the primary endpoint and additional exploratory adjudicated components. The EXAMINE trial did not find significantly increased hospitalizations for heart failure. However, there were more patient hospitalizations for heart failure in the alogliptin arm than in the placebo arm. The principal secondary endpoints of death from CV causes, nonfatal MI, nonfatal stroke, and urgent revascularization because of unstable angina were not significant between placebo and alogliptin (13.4% [n = 359] vs. 12.7% [n = 344], P < 0.26). Hospitalization for heart failure in the alogliptin treatment arm was 106 of 2,701 events compared to 89 of 2,679 events in the placebo arm (odds ratio 1.19, 95% CI 0.89–1.58).

Figure 6 provides a comparison of the rates of hospitalization for heart failure between the SAVOR and EXAMINE trials. However, comparing these two trials in terms of heart failure may be misleading. The first concern is whether the patients in these studies had preserved left-ventricular function (low or high ejection fractions). Many patients with type 2 diabetes have preserved left-ventricular function but diastolic dysfunction. Other patients have ischemic heart disease with reduced left-ventricular function or a combination of both conditions. Understanding of heart failure in these two studies remains obscure; more data are required to fully understand the relationship between DPP-4 inhibitor therapy and heart failure.

Both of the SAVOR9  and EXAMINE10  trials failed to find CV event reduction in patients with diabetes using DPP-4 inhibitor therapy. Moreover, there was a significant increase in hospitalizations for heart failure with saxagliptin, but not with alogliptin. The reason for increased heart failure admissions with saxagliptin remains unclear, and it is possible this finding could be by play of chance rather than the result of other unknown off-target effects. Resolution of this issue awaits future studies to determine whether this is a problem with the DPP-4 inhibitor class, the characteristics of the specific drug within the class, or play of chance.

Pending large trials such as TECOS (Trial Evaluating Cardiovascular Outcomes with Sitagliptin) and CAROLINA (Cardiovascular Outcome Study of Linagliptin Versus Glimepiride in Patients With Type 2 Diabetes)12,13  will help to answer some questions related to the possible link between hospitalization for heart failure and DPP-4 inhibitor therapy. Unfortunately, these trials have not included heart failure as a primary or principal secondary endpoint (Table 4).

Potential beneficial pleotropic effects of DPP-4 inhibitors on the CV system are outlined in Figure 7. Translational consideration findings have ranged from improvement in cardiac function to increased circulating blood volume caused by neuropeptide Y–mediated vasoconstriction of the microcirculation.14  The optimal management of patients with diabetes who remain at risk for heart failure in addition to a plethora of other CV problems deserves due attention. Additional research will be required to clarify the role of novel agents such as DPP-4 inhibitors.

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