Downregulation of the longevity-associated protein sirtuin 1 in insulin resistance and metabolic syndrome: potential biochemical mechanisms

OBJECTIVE

Sirtuins (SIRTs) are NAD(+)-dependent deacetylases that regulate metabolism and life span. We used peripheral blood mononuclear cells (PBMCs) to determine ex vivo whether insulin resistance/metabolic syndrome influences SIRTs. We also assessed the potential mechanisms linking metabolic alterations to SIRTs in human monocytes (THP-1) in vitro.

RESEARCH DESIGN AND METHODS

SIRT1-SIRT7 gene and protein expression was determined in PBMCs of 54 subjects (41 with normal glucose tolerance and 13 with metabolic syndrome). Insulin sensitivity was assessed by the minimal model analysis. Subclinical atherosclerosis was assessed by carotid intima-media thickness (IMT). In THP-1 cells exposed to high glucose or fatty acids in vitro, we explored SIRT1 expression, p53 acetylation, Jun NH(2)-terminal kinase (JNK) activation, NAD(+) levels, and nicotinamide phosphoribosyltransferase (NAMPT) expression. The effects of SIRT1 induction by resveratrol and of SIRT1 gene silencing were also assessed.

RESULTS

In vivo, insulin resistance and metabolic syndrome were associated with low PBMC SIRT1 gene and protein expression. SIRT1 gene expression was negatively correlated with carotid IMT. In THP-1 cells, high glucose and palmitate reduced SIRT1 and NAMPT expression and reduced the levels of intracellular NAD(+) through oxidative stress. No effect was observed in cells exposed to linoleate or insulin. High glucose and palmitate increased p53 acetylation and JNK phosphorylation; these effects were abolished in siRNA SIRT1-treated cells. Glucose- and palmitate-mediated effects on NAMPT and SIRT1 were prevented by resveratrol in vitro.

CONCLUSIONS

Insulin resistance and subclinical atherosclerosis are associated with SIRT1 downregulation in monocytes. Glucotoxicity and lypotoxicity play a relevant role in quenching SIRT1 expression.

Endothelial dysfunction: causes and consequences in patients with diabetes mellitus

Vascular endothelium plays a major role in maintaining cardiovascular homeostasis. Nitric oxide is the most powerful vasodilating compound. Diabetes disrupts endothelial integrity through an increased oxidative stress. Recent evidence indicates that there is a strong interaction between diabetes, the secretory proteins of adipocytes, called adipokines, and endothelium. Endothelial dysfunction may precede the development of overt DM, and a prolonged and repeated exposure to postprandial hyperglycemia may play an important role in the development of atherosclerosis, even in those who have normal fasting plasma glucose levels.

Why to screen heart disease in diabetes

The expanding diabetic epidemic and the high risk of cardiovascular events in diabetic patients suggest that screening heart disease in this population is an important issue. Nonetheless, the advisability of large-scale screening in asymptomatic individuals with diabetes is debated, because available techniques are expensive and have suboptimal diagnostic accuracy. Moreover, all diabetic patients should be treated aggressively as if they all had a positive screening test, because diabetes could be considered a coronary risk equivalent. In this article, we underline the importance of an early diagnosis of coronary artery disease and heart failure in diabetic patients, suggesting that positive screening tests have significant implications in clinical management.

Oxidative stress and vascular disease in diabetes: is the dichotomization of insulin signaling still valid?

The current wisdom indicates that insulin's positive effects, normoglycemia, vasodilation, and anti-inflammation, are mediated by the canonical phosphoinositide 3-kinase (PI3K)/Akt pathway whereas the negative effects are mediated by the mitogen-activated protein kinase (MAPK)/extracellular regulated kinase (ERK) pathway. Much of the intracellular oxidant stress is mediated by the MAPK/ERK pathway which is a downstream signal also for other proatherogenic hormones such as angiotensin II. However, recent evidence links MAPK activation to antioxidant activity and vascular protection. We argue against a dichotomization of insulin signaling also in light of the concept that ERK-MAPK represents a critical node in the intracellular insulin network responsible for several positive effects related not only to vascular function but also to life span.

Oral 17beta-estradiol and sequential progesterone in menopause: effects on insulin-like growth factors and their binding proteins

OBJECTIVE

We evaluated the acute effects of low-dose oral estradiol and sequential progesterone on the insulin-like growth factor (IGF)/growth hormone (GH) axis, IGF-binding proteins (IGFBPs) 1 and 3, and plasma levels of sex hormone-binding globulin (SHBG) in postmenopausal subjects.

STUDY DESIGN

Thirty healthy normal-weight women (mean age: 54.2 +/- 5.7 years) spontaneously postmenopausal for at least 6 months were enrolled. None had used hormone replacement therapy (HRT). Appropriate investigations excluded renal, glucose, lipid and coagulation abnormalities. Breast X-ray and endometrial ultrasound examinations excluded organic pathologies. They received oral cyclical HRT for 1 year, based on the administration of oral estradiol (1 mg/day) for 28 consecutive days plus progesterone (200 mg/day) from day 15 to day 28; out of the whole group, 15 subjects received progesterone orally (group A), while in 15 progesterone was administered transvaginally (group B). On the day before treatment (T0), on day 14 (T14) and on day 28 (T28) of the first cycle, plasma levels of estradiol, progesterone, SHBG, GH, IGF-I and -II, IGFBP-1 and -3, insulin and C-peptide were assayed in all patients. The same parameters were evaluated at T14 and T28 during the 12th month of treatment.

RESULTS

At T14, we observed significant increases in the levels of estradiol (from 20 +/- 16 to 115 +/- 71 pg/ml, p < 0.001), SHBG (from 132 +/- 42 to 182 +/- 55 nmol/l, p < 0.001) and IGFBP-1 (from 92 +/- 57 to 127 +/- 87 ng/ml, p < 0.004), while the level of IGF-I decreased (from 197 +/- 138 to 129 +/- 85 ng/ml, p < 0.003). At T28, progesterone levels were significantly higher in the women receiving it orally than transvaginally (8.4 +/- 6.1 vs. 3.7 +/- 3.2 ng/ml, p < 0.025). However, while oral progesterone did not affect the estrogen-induced variations, transvaginal progesterone abrogated the increase in the levels of IGFBP-1. The levels of IGF-II, IGFBP-3, GH, glucose, C-peptide and insulin did not change at any time. At 1 year, the values maintained the same trends. The estrogen-induced variations of SHBG were correlated directly with those of estradiol (r = 0.48) and inversely with those of IGF-I (r = -0.424).

CONCLUSIONS

Low-dose oral estradiol reduces plasma levels of IGF-I and increases IGFBP-1 and SHBG concentrations, while GH is unchanged. These effects, significant and immediate, lead us to hypothesize a direct action of estradiol on hepatocytes.

Circulating CD34+ cells, metabolic syndrome, and cardiovascular risk

AIMS

Circulating progenitor cells are believed to participate in cardiovascular (CV) homeostasis and their exhaustion has been linked to CV damage. As general agreement on their characterization is lacking, this work was carried out to assess the relationships between different antigenic profiles of progenitor cells and CV risk, with special regard to metabolic syndrome (MetSyn).

METHODS AND RESULTS

CD34, CD133, and KDR were used to quantify circulating progenitors in 214 subjects at different levels of CV risk. In a cross-analysis of six different cell subtypes (CD34(+), CD133(+), CD34(+)CD133(+), CD34(+)KDR(+), CD133(+)KDR(+), and CD34(+)CD133(+)KDR(+)), CD34(+) progenitors showed the best correlation with CV parameters and risk estimates. Components of the MetSyn were all characterized by reduction of CD34(+) cells and acted synergistically in decreasing CD34(+) cell count. Moreover, CD34(+) cell count demonstrated a high performance in detecting high CV risk.

CONCLUSION

These data demonstrate that CD34 identifies progenitor cells linked to CV risk, showing a close negative correlation between CD34(+) cells and CV risk, as well as a synergic detrimental effect of clustered metabolic components. Progenitor cell count may be used as a surrogate marker of CV risk, whereas extensive antigenic characterization may not be useful for this purpose.

Insulin generates free radicals in human fibroblasts ex vivo by a protein kinase C-dependent mechanism, which is inhibited by pravastatin

Insulin can generate oxygen free radicals. Statins, 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors, exert a powerful antioxidant effect. The present study aimed to clarify the mechanisms through which insulin generates free radicals and to assess whether pravastatin modulates such effects. In cultured skin fibroblasts from human volunteers exposed to high insulin concentration, either in the presence or in the absence of pravastatin, insulin induced translocation of the p47(phox) subunit of NAD(P)H oxidase from the cytosol to the membrane and generation of radical oxygen species through a PKC delta-dependent mechanism. The insulin-induced translocation of p47(phox) was PKC delta dependent and attenuated by pravastatin, but independent of the activation of Akt and Rac1. Insulin-induced Akt phosphorylation was increased by pravastatin and ERK1/2 phosphorylation attenuated. The present study demonstrates a novel mechanism by which insulin stimulates the generation of free radicals in human fibroblasts, ex vivo. It involves phosphatidylinositol 3-kinase, PKC delta, and p47(phox) translocation and promotes ERK1/2 phosphorylation. Pravastatin inhibited radical oxygen species production by inhibiting PKC delta. These observations offer a robust explanation for the positive effects of pravastatin treatment in patients with insulin resistance syndrome.

Peripheral blood CD34+KDR+ endothelial progenitor cells are determinants of subclinical atherosclerosis in a middle-aged general population

BACKGROUND AND PURPOSE

Disruption of the endothelial layer is the first step in the atherogenic process. Experimental studies have shown that endothelial progenitor cells (EPCs) are involved in endothelial homeostasis and repair. Conversely, EPC depletion has been demonstrated in the setting of established atherosclerotic diseases. With this background, we evaluated whether variations in the number of EPCs are associated with subclinical atherosclerosis in healthy subjects.

METHODS

Carotid intima-media thickness (IMT), high-sensitive C-reactive protein (hsCRP), levels of circulating EPCs, and cardiovascular risk were compared in 137 healthy subjects. Six subpopulations of progenitor cells were determined by flow cytometry on the basis of the surface expression of CD34, CD133, and KDR antigens: CD34(+), CD133(+), CD34(+)CD133(+), CD34(+)KDR(+), CD133(+)KDR(+), and CD34(+)CD133(+)KDR(+).

RESULTS

Among different antigenic profiles of EPCs, only CD34(+)KDR(+) cells were significantly reduced in subjects with increased IMT. Specifically, CD34(+)KDR(+) cells were inversely correlated with IMT, even after adjustment for hsCRP and 10-year Framingham risk and independently of other cardiovascular parameters.

CONCLUSIONS

Depletion of CD34(+)KDR(+) EPCs is an independent predictor of early subclinical atherosclerosis in healthy subjects and may provide additional information beyond classic risk factors and inflammatory markers.

Number and function of endothelial progenitor cells as a marker of severity for diabetic vasculopathy

OBJECTIVE

Peripheral arterial disease (PAD) is a threatening complication of diabetes. As endothelial progenitor cells (EPCs) are involved in neovasculogenesis and maintenance of vascular homeostasis, their impairment may have a role in the pathogenesis of diabetic vasculopathy. This study aimed to establish whether number and function of EPCs correlate with PAD severity in type 2 diabetic patients.

METHODS AND RESULTS

EPCs were defined by the expression of CD34, CD133 and KDR, and quantified by flow cytometry in 127 diabetic patients with and without PAD. PAD severity has been assessed as carotid atherosclerosis and clinical stage of leg atherosclerosis obliterans. Diabetic patients with PAD displayed a significant 53% reduction in circulating EPCs versus non-PAD patients, and EPC levels were negatively correlated with the degree of carotid stenosis and the stage of leg claudication. Moreover, the clonogenic and adhesion capacity of cultured EPCs were significantly lower in diabetic patients with PAD versus patients without.

CONCLUSIONS

This study demonstrates that EPC decrease is related to PAD severity and that EPC function is altered in diabetic subjects with PAD, strengthening the pathogenetic role of EPC dysregulation in diabetic vasculopathy. EPC count may be considered a novel biological marker of peripheral atherosclerosis in diabetes.

Circulating progenitor cells are reduced in patients with severe lung disease

Patients with chronic severe lung disease are prone to develop pulmonary vascular remodeling, possibly through pulmonary endothelial dysfunction. Circulating endothelial progenitor cells (EPCs) are involved in maintenance of endothelial homeostasis. The aim of this study was to assess whether obstructive and restrictive lung diseases are associated with modification of EPC number in peripheral blood. The study was cross-sectional and involved patients with obstructive (n = 15) and restrictive (n = 15) lung disease on oxygen therapy and 15 control subjects. Circulating EPCs were defined by the surface expression of CD34, CD133, and kinase-insert domain receptor. Results from spirometric tests, blood gas analyses, and blood cell counts have been related to EPC numbers. Patients with chronic hypoxia and severe lung disease showed lower levels of all progenitors than do control subjects. A consensual further reduction of EPC was found in restrictive patients in comparison with obstructive patients. Among restrictive patients, EPC reduction was related to reduced lung volumes and impaired alveolo-arterial diffusion, whereas progenitor cell levels were directly related to erythrocyte number. Considering obstructive patients, significant correlations were found between progenitor cell levels and bronchial obstruction and between progenitor cell levels and arterial oxygen tension. These findings demonstrate a reduction of EPCs in patients with chronic lung disease and long-lasting hypoxia. This alteration was more evident in restrictive patients and correlated to disease severity. Depletion of circulating EPCs may be involved in altered endothelial homeostasis of pulmonary circulation in these disorders.

Effects of different insulin regimes on postprandial myocardial perfusion defects in type 2 diabetic patients

OBJECTIVE

Postprandial 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 METHODS

A 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.

RESULTS

Insulin 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 (beta), myocardial blood volume (MBV), and myocardial blood flow (MBF) did not differ between control and type 2 diabetic subjects. Postprandial beta (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, beta 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: beta 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 beta (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.

CONCLUSIONS

Insulin analog partially reversed myocardial perfusion abnormalities observed in postprandial state by improving glucose control.

Mechanisms of endothelial dysfunction in obesity

Obesity is a chronic disease, whose incidence is alarmingly growing, affecting not only adults but also children and adolescents. It is associated with severe metabolic abnormalities and increased cardiovascular morbidity and mortality. Adipose tissue secretes a great number of hormones and cytokines that not only regulate substrate metabolism but may deeply and negatively influence endothelial physiology, a condition which may lead to the formation of the atherosclerotic plaque. In this review, the physiology of the endothelium is summarised and the mechanisms by which obesity, through the secretory products of adipose tissue, influences endothelial function are explained. A short description of methodological approaches to diagnose endothelial dysfunction is presented. The possible pathogenetic links between obesity and cardiovascular disease, mediated by oxidative stress, inflammation and endothelial dysfunction are described as well.

Circulating endothelial progenitor cells are reduced in peripheral vascular complications of type 2 diabetes mellitus

OBJECTIVES

We sought to establish whether a reduction in endothelial progenitor cells (EPCs) has a putative role in peripheral vascular disease (PVD) of type 2 diabetic patients.

BACKGROUND

Peripheral vascular disease is a common and severe complication of diabetes mellitus. Impaired collateralization of diabetic vasculopathy has been extensively shown, but causes leading to its pathogenesis are not fully understood. Recently, EPCs have been found to contribute to vascular repair and angiogenesis. Diabetes has been associated with low levels of circulating EPCs, but no data are available in the literature on the relationship between EPCs and PVD in diabetes.

METHODS

Flow cytometric analysis was used to quantify circulating progenitor cells (CPCs, CD34+) and EPCs (CD34+KDR+) in 51 patients and 17 control subjects.

RESULTS

The CPCs and EPCs from diabetic patients were reduced by 33% and 40%, respectively, compared with healthy subjects (p < 0.001). An inverse correlation was found between the number of EPCs and the values of fasting glucose (r = -0.49, p = 0.006). Peripheral vascular disease was associated with a 47% reduction in EPCs (p < 0.0001) and EPC levels directly correlated with the ankle-brachial index (r = 0.70, p = 0.01). The subgroup of diabetic patients with PVD also had reduced CPCs by 32% (p = 0.037), whereas patients with ischemic foot lesions had the lowest levels of both EPCs and CPCs (p = 0.02).

CONCLUSIONS

Our data demonstrate decreased EPC levels in diabetic patients and, for the first time, show that PVD is associated with an extensively low number of EPCs. Depletion of circulating EPCs in diabetic patients may be involved in the pathogenesis of peripheral vascular complications.

The effects of oral amino acid intake on ambulatory capacity in elderly subjects

BACKGROUND AND AIMS

The combination of high prevalence of inactivity in the older population, and high risk of ill-health and disability associated with inactivity, suggests that interventions that are successful in increasing levels of activity may have a great impact on population health in later life. With advancing age, the risk of developing serious nutritional deficiencies also increases. This study was designed to assess the effects of dietary amino acid supplementation on effort tolerance in healthy elderly subjects with reduced physical activity.

METHODS

Forty-four subjects (age > 65 years) with sedentary life-style and lower health-related quality of life were studied. Subjects, in an open-label fashion, received an oral amino acid mixture (AAM, 12 g/day) containing essential and non-essential amino acids for a 3-month period. Ambulatory dysfunction resulting in sedentary life-style was assessed by a 6-min walk test. A walking impairment questionnaire (WIQ) was used to evaluate self-perceived ambulatory dysfunction. Maximal isometric muscular strength of the right hand was measured during isometric exercise by a handgrip dynamometer.

RESULTS

The 6-min walk distance increased from 214.5 +/- 32 to 262.8 +/- 34.8 m (p < 0.001) after AAM treatment. The baseline scores on the three subscales of WIQ changed significantly during treatment: WIQ distance increased from 56.2 +/- 12.9 to 66.3 +/- 12.8% (p < 0.001); WIQ speed from 52 +/- 12.6 to 69.2 +/- 14.8% (p < 0.001) and WIQ stairs from 74.4 +/- 22.6 to 94.2 +/- 25% (p < 0.001), as did maximal isometric muscular strength (16.6 +/- 2.4 vs 19.2 +/- 2.2 kg, p < 0.001). Changes in plasma glucose (+11 +/- 11 mg/dL), total cholesterol (0 +/- 39 mg/dL), HDL cholesterol (0 +/- 17 mg/dL), and triglycerides (-11 +/- 58 mg/dL) were not significant between baseline and AAM.

CONCLUSIONS

An oral amino acid supplement, as used in this pilot study, improves ambulatory capacity and maximal isometric muscle strength in elderly subjects without affecting the main metabolic parameters. Amino acid supplementation may thus represent useful non-pharmacological intervention to maintain physical fitness in these subjects.

Diabetic cardiomyopathy: a metabolic perspective

Patients with diabetes mellitus have a >3-fold increased risk of coronary ischemic events and congestive heart failure. Several hypotheses have been provided to explain the increased cardiac vulnerability in individuals with diabetes; among these are the metabolic abnormalities. Diabetes is associated with profound changes in cardiac metabolism, characterized by diminished glucose utilization, diminished rates of lactate oxidation, and increased use of fatty acids. Very few investigations have focused on amino acid disturbances at the level of the heart. This area of research is potentially relevant because cardiac amino acid alterations may not only result in a reduced energy reserve but could also lead to quantitative and qualitative abnormalities of contractile protein present in the diabetic heart.

Early myocardial dysfunction in the diabetic heart: current research and clinical applications

Patients with diabetes mellitus have a high incidence of heart failure, which contributes significantly to their increased cardiovascular morbidity and mortality. One of the major complications of diabetes is the development of cardiomyopathy, a condition characterized by defects of contractile function in the absence of significant coronary artery disease or systemic hypertension. Experimental data in animal models show that contractile depression begins as early as 1 week after induction of diabetes, and the dysfunction is related to an isomyosin distribution shift from V(1) with high adenosine triphosphatase (ATPase) to V(3) with low ATPase activity. Moreover, diabetes is associated with an increased or poorly regulated rate of amino acid catabolism at the cardiac level. Abnormal responses to acute left ventricular (LV) overload induced by exercise (isometric or isotonic) have been demonstrated in patients with diabetes. Impaired augmentation of LV ejection fraction occurs in up to 40% of patients with diabetes. Analysis of the LV afterload-pump function (LV circumferential wall stress-ejection fraction) relationship shows that defective contractile recruitment is the main cause of this anomaly. Exercise-induced LV dysfunction may be the first manifestation of cardiac involvement in patients with diabetes. Increasing the supply of amino acids in addition to conventional therapy significantly attenuates this phenomenon. Although the precise underlying pathophysiologic mechanism is not completely known, these observations may eventually be important in designing an optimal dietary or supplemental approach for patients with diabetes in order to prevent progressive myocardial dysfunction.

Elevated non-esterified fatty acids impair nitric oxide independent vasodilation, in humans: evidence for a role of inwardly rectifying potassium channels

To evaluate the role of elevation of non-esterified fatty acids on forearm nitric oxide (NO) dependent and independent relaxation, four studies were performed in the forearms of 14 normals: (1). endothelium-dependent and -independent vasodilations were assessed during acetylcholine (Ach) and sodium nitroprusside (SNP) infusions; (2). flow-mediated vasodilation (FMD) was assessed; (3) .bradykinin (BK) was infused during NO and prostaglandin inhibition (NO clamp); (4). blood flow (FBF) was measured during Ouabain, a Na(+)/K(+) ATPase, and BaCl(2), rectifying potassium channel (K(IR)) blockers, respectively. All studies were performed before and after 120 min. Intralipid+heparin (high-NEFA) infusion. Ach-mediated FBF increase was lower at high-NEFA (332+/-34 vs. 436+/-44% at 45 microg l forearm(-1) min(-1); % of ratio infused: control arm P<0.05), while SNP response was similar. FMD did not differ before and during high-NEFA, which induced a blunted response of FBF during BK with or without NO clamp. Ouabain and BaCl(2)-mediated FBF inhibition was lower (P<0.01) at high-NEFA. During ouabain alone FBF decreased slightly.

IN CONCLUSION

High-NEFA exerts a negative role on both NO-dependent and independent vasodilations. The decrease in FBF, mediated by K(IR) inhibition, is blunted by high-NEFA: these substrates interfere with hemodynamic/metabolism coupling, possibly through the inhibition of these channels.

L-arginine-nitric oxide kinetics in normal and type 2 diabetic subjects: a stable-labelled 15N arginine approach

Defective endothelium is a key event in the development of atherosclerosis in diabetes: alteration of the L-arginine-nitric oxide (NO) pathway has been suggested. We propose a modeling approach of the L-arginine-NO pathway in vivo in both control and type 2 diabetic subjects based on the intravenous bolus injection of L-[(15)N]arginine and subsequent noncompartmental and compartmental model analysis of L-[(15)N] arginine in plasma and [(15)N]nitrate in the urine. No differences in arginine kinetics were observed between normal subjects and diabetic patients. [(15)N]nitrates were detectable up to 48 h from the L-(15)[N]arginine administration; no differences were found in the tracer-to-tracee ratio in each urine collection. However, the NO synthesis in plasma from arginine was lower (P = 0.05 for the noncompartmental and 0.1208 for the compartmental analysis, by Mann-Whitney test) in diabetic patients than in control subjects when expressed both in absolute terms (50% decrease) and as percentage of NO turnover (30% decrease). This new modeling approach of L-arginine-NO pathway provides a detailed picture of arginine kinetics and nitrate metabolism. From our data, it appears that noncomplicated type 2 diabetic patients have a decreased conversion of arginine to NO.

Effects of treatment with sulfonylurea drugs or insulin on ischemia-induced myocardial dysfunction in type 2 diabetes

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.