© 2002 by the American Diabetes Association, Inc. Effects of Treatment With Sulfonylurea Drugs or Insulin on Ischemia-Induced Myocardial Dysfunction in Type 2 Diabetes
1 Division of Cardiology, Department of Clinical and Experimental Medicine, University of Padua Medical School, Padua, Italy
In patients with diabetes and coronary artery disease, the potential negative role of sulfonylurea drugs is under intensive investigation. We assessed the effects of treatment with glibenclamide or insulin on the extension of left ventricular myocardial dysfunction induced by acute ischemia. Nineteen consecutive patients with type 2 diabetes and coronary artery disease entered the study. Each patient was randomly assigned to either insulin or glibenclamide therapy. Treatment was crossed over after 12 weeks and maintained for another 12 weeks. At the end of each treatment, left ventricular myocardial function at rest and during dipyridamole infusion was studied by two-dimensional echocardiography under the same conditions of metabolic control. Glibenclamide or insulin treatment did not influence the rest values of left ventricular dimensions, left ventricular ejection fraction (LVEF), or wall motion score index (WMSI). Dipyridamole infusion, in patients receiving glibenclamide treatment, decreased LVEF (43 ± 7 vs. 37 ± 12%, P < 0.005) and increased WMSI (1.4 ± 0.28 vs. 1.98 ± 0.24, P < 0.001) compared with baseline values; during insulin treatment, LVEF (46 ± 8 vs. 45 ± 11%, NS) and WMSI (1.4 ± 0.29 vs. 1.6 ± 0.4, NS) did not change significantly. Peak stress LVEF was higher (45 ± 11 vs. 37 ± 12%, P < 0.001) and WMSI lower (1.6 ± 0.4 vs. 1.98 ± 0.24, P < 0.001) in patients receiving insulin. The results indicate that in patients with type 2 diabetes and coronary artery disease, ischemic myocardial dysfunction induced by dipyridamole infusion is less severe during treatment with insulin than with glibenclamide. Restitution of a preconditioning mechanism in insulin-treated patients may be the potential beneficial mechanism.
Patients with diabetes have a more than threefold increased risk of coronary ischemic events and congestive heart failure (1,2), as well as an increased incidence of late complications and increased mortality after acute myocardial infarction and coronary angioplasty (36). In patients with type 2 diabetes and myocardial ischemia, the use of sulfonylurea drugs may be harmful by preventing endogenous cardioprotective mechanisms to act. Ischemic preconditioning is a powerful, endogenous mechanism by which the myocardium may protect itself from ischemic insult, markedly reducing the impact of prolonged ischemia (7,8). In particular, in the human heart, preconditioning is able to reduce the severity of myocardial dysfunction associated with ischemia induced by coronary angioplasty, intermittent aortic cross-clamping during coronary artery bypass graft surgery, and exercise testing (911). In contrast, loss of preconditioning response has consistently been observed in the presence of sulfonylurea drugs (12,13). Inhibition of a metabolism-sensitive channel (ATP-sensitive K+ channel [KATP channel]) present in both pancreatic ß-cells (14) and cardiac myocytes (15) is the mechanism by which the sulfonylurea drugs cause ischemic preconditioning loss. In this study, we assessed the effects of treatment with sulfonylurea drugs or insulin on sensitivity to ischemia and on the extension of ischemia-induced contractile dysfunction during dipyridamole stress echocardiography in patients with type 2 diabetes associated with ischemic heart disease.
Study patients. We studied 19 consecutive type 2 diabetic patients (15 men, 4 women, aged 61 ± 2 years [mean ± SD]) treated with diet plus oral sulfonylurea drugs. The main demographic and clinical characteristics of the study population during glibenclamide or insulin therapy are summarized in Table 1.
All patients had a clinical history of stable angina pectoris (Canadian Cardiovascular Society class 1 or 2) and evidence of significant coronary vessel obstruction ( 70% lumenal diameter narrowing) by coronary angiography (12 patients had two-vessel and 7 had three-vessel disease). Five patients had histories and electrocardiogram (ECG) evidence of previous myocardial infarction (four anterior and one inferior). Patients were excluded for any of the following reasons: 1) previous or ongoing insulin therapy; 2) severe diabetes; 3) diabetic proliferative retinopathy assessed by an experienced ophthalmologist; 4) diabetic neuropathy assessed by autonomic neuropathy tests or diabetic nephropathy (creatinine >1.4 mg/dl); 5) potential sources of gastrointestinal bleeding, anemias, and other endocrine or major organ diseases; 6) arterial systemic hypertension; and 7) inadequate echocardiogram to assess wall motion and thickening in every left ventricular (LV) myocardial segment. Nitrates were the only drugs permitted to control ischemic symptoms in study patients and were withdrawn 12 h before stress echocardiographic studies. The study protocol was approved by the local ethics committee of the University of Padua School of Medicine, and written informed consent was obtained from all participants after the nature of the procedure was explained.
Study design.
Biochemical assays.
Echocardiographic analysis. LV volumes were calculated by an ellipsoid biplane area-length method (17). LV ejection fraction (LVEF) was derived as end-diastolic volume minus end-systolic volume divided by the end-diastolic volume. LV endocardial echocardiograms in the apical four- and two-chamber views, for a minimum of two to four cardiac cycles, were digitized at end-diastole (R wave peak) and end-systole (time of smallest cavity area) by two independent observers. A discrepancy of >10 ml for LV volume required the analysis of the echocardiographic tracing by a third observer. Agreement was achieved by consensus. Interobserver and intraobserver variability for LV area (r = 0.96 and r = 0.98, respectively) and for LV length (r = 0.95 and r = 0.95, respectively) was acceptable. The interstudy variability of LVEF was assessed by echocardiographic examination twice within a half-hour and calculated by averaging the absolute differences between the two measurements. Changes in LVEF were considered significant if they were outside the 95% confidence limit of interstudy variability.
Dipyridamole echocardiography.
Statistical analysis.
Baseline LV function. Baseline characteristics of study patients are shown in Table 1. Measurements of LV end-diastolic volume index (LVEDVI) (64 ± 9 ml/m2, range 5474) and LVEF (60 ± 9%, range 5770) in the control group were used to determine the means and 95% confidence limits of normal values. Resting values of LV dimensions and function are listed in Table 2. In diabetic patients, no differences were detected in baseline LVEDVI (glibenclamide, 109 ± 20 ml/m2; insulin, 109 ± 19 ml/m2; NS) and LVEF (glibenclamide, 43 ± 7%; insulin, 46 ± 8%; NS) during both treatments; the baseline LVEDVI values were higher (P < 0.005) and LVEF lower (P < 0.005) than those of control subjects, regardless of treatment group. Heart rate and systolic and diastolic blood pressures did not differ between diabetic patients and control subjects, regardless of treatment group. Regional impairment of myocardial contractility in diabetic patients did not differ during treatment with glibenclamide or insulin; in fact, baseline LV WMSI was similar in diabetic patients during both treatment strategies (glibenclamide, 1.40 ± 0.29; insulin, 1.40 ± 0.28; NS).
Dipyridamole echocardiography. Changes in heart rate and systolic blood pressure during dipyridamole infusion were similar in both treatment groups of diabetic patients (Table 2). During glibenclamide treatment, peak stress LVEF decreased (43 ± 7 vs. 37 ± 12%; P < 0.005) (Fig. 1) and WMSI increased significantly (1.4 ± 0.28 vs. 1.98 ± 0.24; P < 0.001) (Fig. 2) in comparison to the baseline values; in patients treated with insulin, peak stress LVEF (46 ± 8 vs. 45 ± 11%; NS) (Fig. 1) and WMSI (1.4 ± 0.29 vs. 1.6 ± 0.4; NS) (Fig. 2) did not differ from baseline values. It was noted that during insulin treatment, patients had significant changes in peak stress LV function compared with values obtained during glibenclamide therapy: LVEF was higher (45 ± 11 vs. 37 ± 12%; P < 0.001) and WMSI lower (1.6 ± 0.4 vs. 1.98 ± 0.24; P < 0.001).
Metabolic parameters. As shown in Table 2, no changes were observed in short- or long-term metabolic control between the two treatments; furthermore, no changes were observed in intermediary metabolites or plasma lipid levels. Only FFAs were slightly higher during glibenclamide treatment, although the difference was not statistically significant.
The major aim of this study was to assess the effects of either insulin or glibenclamide therapy on susceptibility to ischemia, in terms of extension of left ventricular myocardial dysfunction, during dipyridamole infusion in type 2 diabetic patients with coronary artery disease. Because metabolic control per se may deeply affect several variables of cardiac function such as substrate utilization (18), coronary blood flow reserve (19), and myocardial contractility (20), we meticulously ensured the same metabolic control under the two different treatments. This control was maintained weekly by modifying therapies according to each patients home blood glucose monitoring (Table 1). This result allowed us to assess the effect of each treatment on cardiac function without the confounding consequences of different metabolic control levels. In patients with type 2 diabetes, many factors contribute to increased morbidity and mortality by ischemic heart disease. One contributor may be the use of sulfonylurea drugs. Such a possibility, which first arose several years ago, has recently resurfaced after the discovery that sulfonylureas act by inhibiting KATP channels. In the heart, inhibition of these channels prevents ischemic preconditioning, an endogenous mechanism that protects the heart from ischemic injury. Furthermore, experimental data (21) suggest that the myocardium in streptozotocin-induced diabetic rat hearts may benefit more from preconditioning than normal myocardium, possibly as a result of the reduced production of glycolytic metabolites during sustained ischemia and the concomitant attenuation of intracellular acidosis. The difficulty of translating these findings to the outcome of patients is demonstrated by some U.K. Prospective Diabetes Study data (22) that showed no increase in cardiovascular events with sulfonylurea drug use. On the other hand, in a recent prospective study (23), it has been shown that sulfonylurea drugs increased early mortality in patients with diabetes after direct angioplasty for acute myocardial infarction. However, the outcome of these patients may be influenced by several factors that could explain the controversies regarding long-term results; for example, angiotensin II type 1 receptor antagonists and ACE inhibitors are beneficial not only for suppressing ventricular remodeling (24) but also for preserving the preconditioning mechanism (25). Our results reflect different effects of insulin and glibenclamide treatment on myocardial contractile function in patients with type 2 diabetes during acute ischemia provoked by dipyridamole infusion, and they should not be translated to other sulfonylurea drugs without further evidence. The diversities of sulfonylurea drugs relate to their potency and half-lives. However, there is increasing data to support that they may differ in their cardiovascular effects, possibly because of a distinct affinity for cardiac and vascular KATP channels. For example, the half-maximal inhibitory concentration (IC50) of glimepiride in blood vessels has been reported to be 31.6 nmol compared with an IC50 of 6.8 nmol for glibenclamide. It should be noted, however, that these IC50 values are several orders of magnitude greater than the IC50 values for KATP channels in pancreatic islet cells. Plasma levels of glibenclamide in patients treated for type 2 diabetes range between 0 and 1.5 mmol/l. Because glibenclamide concentrations as low as 0.01 mmol/l have been shown to inhibit vascular relaxation induced by KATP channelopening drugs, it is quite possible that significant vascular effects occur during glibenclamide treatment in type 2 diabetic patients (26). Moreover, in experimental and pharmacological studies, glibenclamide is used as a classical KATP channel inhibitor (27), and its deleterious effect on ischemic preconditioning has been widely investigated, suggesting a possible negative role in myocardial function in diabetic patients with coronary artery disease (27,28). Furthermore, glibenclamide is by far the most commonly used sulfonylurea drug for type 2 diabetes in Italy. For these reasons, and because of a more homogeneous effect using exclusively one instead of several different oral hypoglycemic agents, we decided to compare insulin versus glibenclamide. Further studies are needed to assess possible differences on the in vivo cardiac effects of other sulfonylurea drugs. The results of this study show that ischemic myocardial dysfunction induced by dipyridamole infusion is more severe during treatment with sulfonylurea drugs than during insulin treatment of type 2 diabetic patients with documented ischemic heart disease. In fact, during glibenclamide treatment, peak stress LV global pump function (evaluated as ejection fraction) decreases and is significantly less than during insulin treatment. This impairment in LV systolic function is the result of an extension in ischemic myocardial dysfunction induced by dipyridamole, as demonstrated by the increase of LV WMSI. On the other hand, patients treated with insulin do not show a worsening of myocardial function during dipyridamole stress, as demonstrated by the absence of a significant increase in LV WMSI. It is reasonable to suggest that the restitution of a preconditioning mechanism in insulin-treated patients is able to reduce the severity of myocardial dysfunction associated with ischemia induced by dipyridamole stress. Other possible mechanisms may be a locally higher plasma insulin concentration during insulin treatment causing 1) an increase in coronary blood flow by a primary reduction in coronary tone secondary to insulin-mediated elaboration of vasoactive and/or paracrine factors within the coronary circulation (29) and 2) a direct positive inotropic effect on postischemic heart, reducing the extension of myocardial dysfunction (30). In this study, dipyridamole stress has been chosen for induction of myocardial ischemia on the basis of several considerations. It has been shown that dipyridamole is more effective, or at least no less effective, than dobutamine at producing flow disparity between myocardial regions supplied by normal and stenotic arteries (3134). Moreover, minor and major complications appear more frequently during dobutamine than dipyridamole tests (33,34). On the other hand, the mechanism of action of dipyridamole renders this pharmacological stress particularly useful in the diabetic heart characterized by severe abnormalities in the coronary microcirculation and flow reserve along with the atherosclerotic occlusion of epicardial vessels. In fact, the standard dose of dipyridamole can induce maximal or near-maximal coronary vasodilatation in most patients (35), whereas dobutamine produces a significantly smaller increase in myocardial blood flow (36,37). Finally, the mechanism of action of dobutamine involves stimulation of cardiac adrenergic receptors. In the diabetic heart, a defective cardiac response to catecholamines occurs. This has been explained by an impairment of the cardiac adrenergic signaling system mainly due to the decrease in ß-adrenergic receptor concentration (3840). Thus, this randomized crossover design study may help to define the potential negative action of glibenclamide in type 2 diabetic patients with coronary artery disease. The results demonstrate that ischemic myocardial dysfunction is easily inducible by dipyridamole in type 2 diabetic patients with ischemic heart disease. Insulin treatment instead of glibenclamide therapy significantly prevents this phenomenon. Although the precise underlying pathophysiological mechanism is not completely known, these data may eventually be important in designing optimal therapy for patients with type 2 diabetes.
Address correspondence and reprint requests to Roldano Scognamiglio, MD, Divisione di Cardiologia, Policlinico Universitario, via Giustiniani 2, 35128 Padua, Italy. E-mail: rscognamiglio{at}unipd.it. Received for publication 4 June 2001 and accepted in revised form 29 November 2001. 3-BOH, 3-hydroxybutyrate; AcAc, acetoacetate; ECG, electrocardiogram; FFA, free fatty acid; IC50, half-maximal inhibitory concentration; KATP, ATP-sensitive K+ channel; LV, left ventricular; LVEDVI, left ventricular end-diastolic volume index; LVEF, left ventricular ejection fraction; WMSI, wall motion score index.
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