DOI: 10.2337/diacare.29.01.06.dc05-0955 © 2006 by the American Diabetes Association
Effects of Different Insulin Regimes on Postprandial Myocardial Perfusion Defects in Type 2 Diabetic PatientsMetabolic Cardiology, Division of Metabolic Diseases, Department of Clinical and Experimental Medicine, University of Padova Medical School, Padua, Italy Address correspondence and reprint requests to Roldano Scognamiglio, MD, Cardiologia Metabolica, Divisione di Malattie del Metabolismo, Policlinico Universitario, via Giustiniani 2, 35128 Padova, Italy. E-mail address: r.scognamiglio{at}unipd.it
OBJECTIVEPostprandial glycemia is an independent risk factor for cardiovascular disease that is more powerful than fasting glycemia and determines myocardial perfusion defects in type 2 diabetes. We examined the efficacy of two different insulin regimes (regular insulin and insulin analog) in controlling postprandial hyperglycemia and in preventing myocardial perfusion abnormalities. RESEARCH DESIGN AND METHODSA total of 20 consecutive type 2 diabetic patients and 20 control subjects were enrolled in this randomized, three-way, cross-over, placebo-controlled study. Myocardial perfusion was assessed by myocardial contrast echocardiography (MCE) in fasting and postprandial (120 min) state. RESULTSInsulin analog was associated with lower, but not statistically significant, postprandial glycemia than regular insulin (glucose increase: 116 ± 8 vs. 136 ± 5%, P = NS). However, the area under the curve following insulin analog was significantly lower than regular insulin (18,354 ± 702 vs. 20,757 ± 738 mg per 120 min, P = 0.032). Fasting myocardial flow velocity (ß), myocardial blood volume (MBV), and myocardial blood flow (MBF) did not differ between control and type 2 diabetic subjects. Postprandial ß (0.67 ± 0.24 vs. 0.92 ± 0.25, P < 0.01), MBV (8.4 ± 2 vs. 10.9 ± 1.2, P < 0.01), and MBF (5.6 ± 2 vs. 9.9 ± 2.8, P < 0.01) increased significantly in control subjects. In type 2 diabetes, during placebo in the postprandial state, ß increased (0.65 ± 0.27 vs. 0.89 ± 0.24, P < 0.01), while MBV (8.34 ± 1.2 vs. 4.3 ± 1.3, P < 0.01) and MBF (5.4 ± 1.5 vs. 3.4 ± 0.9, P < 0.01) decreased. Similar changes in MCE variables were observed after regular insulin: ß increased (0.65 ± 0.22 vs. 0.92 ± 0.12, P < 0.01) and MBV (8.2 ± 2 vs. 5.2 ± 1.16, P < 0.01) and MBF (5.4 ± 1.9 vs. 4.2 ± 0.86, P < 0.01) were reduced. After insulin analog, postprandial ß (0.66 ± 0.18 vs. 0.9 ± 0.18, P < 0.01), MBV (8.2 ± 1.6 vs. 9.6 ± 1.2, P < 0.01), and MBF (5.4 ± 2 vs. 7.2 ± 1.9, P < 0.01) increased. Values of postprandial MBV and MBF were higher after insulin analog than regular insulin treatment. CONCLUSIONSInsulin analog partially reversed myocardial perfusion abnormalities observed in postprandial state by improving glucose control.
Abbreviations: AUC, area under the curve CVD, cardiovascular disesase FFA, free fatty acid MBF, myocardial blood flow MBV, myocardial blood volume MCE, myocardial contrast echocardiography
Diabetes is associated with a markedly increased risk of cardiovascular disease (CVD), and this excess risk is not explained by the increase of conventional cardiovascular risk factors (1). Several studies confirmed that tight glycemic control reduces and delays late diabetes and microvascular complications (2, 3). Considerable data indicate that postprandial plasma glucose level might be an independent risk factor of CVD that is more powerful than fasting hyperglycemia, and the presence of postprandial hyperglycemia is a significant predictor of myocardial infarction and death (4). Recently, the Diabetes Epidemiology: Collaborative Analysis of Diagnostic Criteria in Europe (DECODE) study confirmed that postload hyperglycemia increases mortality and that postload glucose is a better predictor of mortality than fasting glucose (5). Postprandial hyperglycemia could result in labile nonenzymatic glycation, promotion of thrombosis, and production of free radicals that could generate tissue damage and favor the development of micro- and macrovascular complications (6). In a recent study including type 2 diabetic patients, postprandial hyperglycemia determined myocardial perfusion defects secondary to deterioration in microvascular function (7). Thus, clinically it seems reasonable to avoid excessive postprandial hyperglycemia in the management of diabetes (8). The present study was conducted to compare the efficacy of two different insulin regimes (regular insulin or insulin analog) in controlling postprandial hyperglycemia and preventing myocardial perfusion defects in type 2 diabetic patients.
Among type 2 diabetic patients regularly attending the Diabetes Clinic of University of Padua, we enrolled 20 consecutive patients with a diagnosis of type 2 diabetes for 6 months but 10 years, aged 60 years, with a BMI of 26.4 ± 1.4 and HbA1c (A1C) of 7.2 ± 1%. All patients were managed by dietary therapy. Exclusion criteria included any hepatic disease, renal disease (plasma creatinine >1.5 mg/dl), cigarette smoking, alcohol intake, arterial hypertension (blood pressure >130/85 mmHg), hypercholesterolemia (total cholesterol >250 mg/dl), hypertrgliceridemia (triglyceride >200 mg/dl), or the presence of micro- or macrovascular complications. Microangiopathy was excluded by an ophtalmologic exam of the retina and by at least three determinations of albuminuria excretion rate. Macroangiopathy was excluded by the palpation of peripheral pulses, ankle brachial pressure ratio, and echocolordoppler ultrasound of the carotid arteries. Diabetic patients were not taking any drugs. They were on a standard diet containing at least 50% of calories as carbohydrates. Before, to include a patient in this study, he or she underwent (in chronological order) stress perfusion imaging with technetium during exercise and dipyridamole echocardiography. The negativity of these diagnostic procedures allowed exclusion of subjects with the presence of obstructive coronary artery disease. Twenty healthy subjects were recruited as the control group. They were nonsmokers and had no evidence of present or past hypertension, hyperlipidemia, diabetes, coronary artery disease, or any systemic conditions. All control subjects were following ad libitum diets, had no recent change in body weight, and were taking no medication. The study protocol was approved by the ethics committee of the University of Padua. Both healthy subjects and diabetic patients gave informed consent before being tested. The clinical characteristics of the study populations are reported in Table 1.
Study design This study was conducted according to a randomized, three-way, cross-over design. There were 3 study days (separated by a 5- to 10-day interval). Patients were on their own diet regimen, and no medication for glycemic control was used between visits. During these 3 study days, the following three therapeutic regimens were adopted in a random order: 1) regular insulin (Actrapid; Novo Nordisk, Bagsvaerd, Denmark) injected subcutaneously in the periumbelical region 25 min before the standard meal, 2) insulin analog (Novorapid; Novo Nordisk) injected subcutaneously in the periumbelical region immediately before the standard meal, and 3) saline (placebo) injected subcutaneously. Both physicians and patients were blinded to active medications. Blood samples were drawn for obtaining 0-, 1-, and 2-h postprandial glucose, free fatty acids (FFAs), insulin, and lipid levels. Diabetic patients and control subjects assumed a mixed standardized meal (460 kcal; 54% carbohydrates, 31% lipids, and 25% proteins) (Novasource Novartis). The meals were consumed over a 5-min period under supervision of a nurse. Myocardial perfusion by contrast echocardiography was performed before and 2 h after eating.
Myocardial contrast echocardiography
Analytical methods
Statistical analysis
Hemodynamic variables, serum glucose, lipids, FFAs, and insulin Heart rate and systolic and diastolic blood pressure in fasting state did not differ between diabetic patients and control subjects. Two hours after eating, heart rate and systolic and diastolic blood pressure did not change significantly in either treatment group of diabetic patients (regular insulin, insulin analog, or placebo) or in control subjects. Hence, in type 2 diabetic patients, fasting rate-pressure product was similar to postprandial value independent of experimental conditions (placebo 8,050 ± 1,596, regular insulin 8,020 ± 1,650, insulin analog 8,065 ± 1,674; P = NS for all comparison). In fasting state, type 2 diabetic patients showed higher plasma glucose concentration and A1C content than control subjects. Moreover, total cholesterol, LDL cholesterol, and triglyceride serum levels were higher, while HDL cholesterol levels were lower in diabetic patients than in control subjects (Table 1).
In the placebo study, the postprandial glucose concentrations in type 2 diabetic patients were significantly higher than those in control subjects (223 ± 11 vs. 124 ± 18 mg/dl, P < 0.002). In the studies in which regular insulin or insulin analog were injected, postprandial plasma glucose increased significantly from baseline values, but the peak values were significantly lower than those observed during the placebo study. Percentage changes in glucose values during insulin analog were not statistically different from those observed following regular insulin (116 ± 8 vs. 136 ± 5%, P = NS) (Fig. 1). However, the value of AUC for glucose after regular insulin (20,757 ± 738 mg · dl1 · 120 min1) was significantly higher than that observed following insulin analog (18,354 ± 702 mg · dl1 · 120 min1, P = 0.032) (Fig. 2). Furthermore, a postprandial plasma glucose concentration
Myocardial perfusion MCE studies showed that fasting ß, MBV, and MBF did not differ between control subjects and type 2 diabetic patients in the three treatment groups (Table 2). Changes in MBV expression of the capillary cross-sectional area following the mixed meal are shown in Fig. 3. In the postprandial state, ß (0.67 ± 0.24 vs. 0.92 ± 0.25, P < 0.01) and MBV (8.4 ± 2.0 vs. 10.9 ± 1.2, P < 0.01) increased significantly from fasting values in control subjects. As a consequence, postprandial MBF also increased in nondiabetic subjects (5.6 ± 2.0 vs. 9.9 ± 2.8, P < 0.01). In type 2 diabetic patients, during placebo in the postprandial state, ß increased (0.65 ± 0.27 vs. 0.89 ± 0.24, P < 0.01), while MBV (8.34 ± 1.2 vs. 4.3 ± 1.3, P < 0.01) and MBF (5.4 ± 1.5 vs. 3.4 ± 0.9, P < 0.01) reduced significantly in comparison to fasting values. This pattern of postprandial changes in MCE variables did not change significantly after injection of regular insulin before the meal: postprandial ß increased (0.65 ± 0.22 vs. 0.9 ± 0.12, P < 0.01) but MBV (8.2 ± 2 vs. 5.2 ± 1.16, P < 0.01) and MBF (5.4 ± 1.9 vs. 4.2 ± 0.86, P < 0.01) decreased significantly. In type 2 diabetic patients, in whom insulin analog was injected before eating, all MCE variables increased significantly in comparison to fasting values: ß from 0.66 ± 0.18 to 0.9 ± 0.18 (P < 0.01), MBV from 8.2 ± 1.6 to 9.6 ± 1.2 (P < 0.01), and MBV from 5.4 ± 2 to 7.2 ± 1.9 (P < 0.01). Comparisons between type 2 diabetic patients and control subjects show that postprandial ß does not differ, while postprandial MBV and MBF are lower irrespective of treatment. Comparisons between diabetic patients treated with placebo or with different insulin regimens show that the highest postprandial MBV and MBF are obtained after insulin analog injection. Values of postprandial MBV and MBF are higher in diabetic patients after regular insulin injection than those of patients treated with placebo.
This study demonstrated that insulin analog rather than regular insulin, when administered to type 2 diabetic patients in a controlled mixed meal test setting, improved postprandial glycemic control and has the potential to partially reverse myocardial perfusion abnormalities observed in this metabolic state. In type 2 diabetic patients, a significant decrease in myocardial perfusion, which correlated with hyperglycemia during the postprandial state, has been recently demonstrated (7). This postprandial reduction in myocardial perfusion was determined by a deterioration in function of coronary microvascular circulation as demonstrated by the reduction in myocardial blood volume assessed by MCE. This parameter is related to microvascular indexes (total microvascular density, capillary density, and capillary area) in biopsied myocardial segments (10). The present study confirmed that myocardial perfusion defects due to a microvascular coronary dysfunction occur in the postprandial state in type 2 diabetic patients treated with diet. Similar postprandial myocardial perfusion defects occurred in patients in whom regular insulin was injected but were prevented, together with a better glycemic control, by the injection of insulin analog before the meal. The occurrence and reversion of myocardial perfusion defects in the postprandial state may recognize a multifactorial pathogenesis. Information from in vitro and in vivo studies have provided biochemical mechanisms by which increases in plasma glucose levels may produce cardiovascular damage. It is accepted that glucose and mixed meals induce oxidative stress with a parallel decreased bioavailability of nitric oxide and an impaired ability to respond to nitric oxidedependent vasodilatory stimuli (1113). Besides the production of free radical species, hyperglycemia activates the polyol and glucosamine pathways, increases advanced glycation end product synthesis, and activates protein kinase C (14). A better control of hyperglycemia may reverse this complex metabolic derangement. Moreover, in addition to this action on myocardial substrate metabolism, insulin has a physiological role in vasodilating arterial (15) and venous (16) beds through an increase in nitric oxide synthesis and release. It has been also shown that insulin induces a dose-dependent expression of endothelial nitric oxide synthase in human aortic endothelial cells (17) and stimulates a dose-dependent production of nitric oxide in human umbilical vein endothelial cell (18). Moreover, in human skeletal muscle, it has been shown that insulin induces vasodilation and increases perfusion by a rapid capillary recruitment that is blunted in insulin-resistant states (19). In addition to this vasoactive action in the peripheral vasculature, insulin directly affects myocardial perfusion by enhancing hyperemic myocardial blood flow in a dose-dependent manner (20). Insulin also has other positive effects, most notably the capability to inhibit platelet aggregation by increasing cGMP (21) and an anti-inflammatory and profibrinolytic effect at least in patients with acute myocardial infarction (22). Postprandial glucose peak (4, 23, 24) is an independent risk factor, especially with respect to CVD. Prevention and delay of late diabetes complications has been shown to be dependent on glycemic control as measured by level of A1C (2, 3). The Diabetes Control and Complications Trial (2) showed that at equivalent levels of A1C, patients on intensive basal-bolus therapy had a reduced risk of complications compared with patients on conventional insulin therapy. This may imply that features of glycemic control not reflected by A1C such as postprandial glycemia may add to or modify the risk of complications. The glycemic control in type 2 diabetic patients occurred only if postprandial glucose control is part of the therapeutic regimen (25), as convincingly shown by Bastyr et al. (26) in the IOEZ study group, in which insulin lispro was used to focus on postprandial blood glucose, resulting in greater impact on overall metabolic control. These observations suggest that control of excessive postprandial glycemia may give clinical benefits in type 2 diabetic patients.
Postprandial abnormalities in myocardial perfusion have been related to peak glucose values (7). In the present study, although insulin analog treatment was associated with peak glucose values not statistically different from those observed following regular insulin, it provided a significant amelioration of postprandial plasma glucose (as indicated by the AUCs) without substantial differences in insulin concentrations. Moreover, a postprandial plasma glucose concentration It should be noted that the small differences in plasma glucose levels may lead to significant changes in vascular response to insulin. This hypothesis stems from the observations made by Capes et al. (27) who showed that small difference in admission plasma glucose levels in patients with acute myocardial infarction but without previously known diabetes are associated with tremendously different outcomes. Furthermore, differences in plasma glucose levels of 20 mg/dl are associated with a twofold increase in cardiogenic shock in patients with acute myocardial infarction (28). In conclusion, myocardial perfusion defects induced by postprandial hyperglycemia may have relevant clinical implications because, as suggested by the response-to-injury hypothesis (29), they represent an early marker of atherogenic process in the coronary circulation, and their recognition may offer new hope for the early identification of subgroups of patients at increased risk of coronary vessels obstructive disease. Moreover, it may constitute an important goal in the treatment of the disease. The present study offers a practical clinical approach to this relevant problem showing that treatment with insulin analog immediately before eating, by allowing better postprandial glycemic control, either attenuates or reverses the myocardial perfusion defects and coronary microvascular dysfunction in the postprandial state.
A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. Received for publication May 25, 2005. Accepted for publication October 14, 2005.
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