Antonio Tiengo

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.

The Oral Dipeptidyl Peptidase-4 Inhibitor Sitagliptin Increases Circulating Endothelial Progenitor Cells in Patients With Type 2 Diabetes: Possible role of stromal-derived factor-1α

OBJECTIVE Vasculoprotective endothelial progenitor cells (EPCs) are regulated by stromal-derived factor-1α (SDF-1α) and are reduced in type 2 diabetes. Because SDF-1α is a substrate of dipeptidyl-peptidase-4 (DPP-4), we investigated whether the DPP-4 inhibitor sitagliptin modulates EPC levels in type 2 diabetic patients. RESEARCH DESIGN AND METHODS This was a controlled, nonrandomized clinical trial comparing 4-week sitagliptin (n = 16) versus no additional treatment (n = 16) in addition to metformin and/or secretagogues in type 2 diabetic patients. We determined circulating EPC levels and plasma concentrations of SDF-1α, monocyte chemoattractant protein-1 (MCP-1), vascular endothelial growth factor (VEGF), and nitrites/nitrates. RESULTS There was no difference in clinical baseline data between the sitagliptin and control arms. After 4 weeks, as compared with control subjects, patients receiving sitagliptin showed a significant increase in EPCs and SDF-1α and a decrease in MCP-1. CONCLUSIONS Sitagliptin increases circulating EPCs in type 2 diabetic patients with concomitant upregulation of SDF-1α. This ancillary effect of DPP-4 inhibition might have potential favorable cardiovascular implications.

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.

Differential effects of hyperinsulinemia and hyperaminoacidemia on leucine-carbon metabolism in vivo. Evidence for distinct mechanisms in regulation of net amino acid deposition.

The effects of physiologic hyperinsulinemia and hyperaminoacidemia, alone or in combination, on leucine kinetics in vivo were studied in postabsorptive healthy subjects with primed-constant infusions of L-[4,5-3H]leucine and [1-14C]alpha-ketoisocaproate (KIC) under euglycemic conditions. Hyperinsulinemia (approximately 100 microU/ml) decreased (P less than 0.05 vs. baseline) steady state Leucine + KIC rates of appearance (Ra) from proteolysis, KIC (approximately leucine-carbon) oxidation, and nonoxidized leucine-carbon flux (leucine----protein). Hyperaminoacidemia (plasma leucine, 210 mumol/liter), with either basal hormone replacement or combined to hyperinsulinemia, resulted in comparable increases in leucine + KIC Ra, KIC oxidation, and leucine----protein (P less than 0.05 vs. baseline). However, endogenous leucine + KIC Ra was suppressed only with the combined infusion. Therefore, on the basis of leucine kinetic data, hyperinsulinemia and hyperaminoacidemia stimulated net protein anabolism in vivo by different mechanisms. Hyperinsulinemia decreased proteolysis but did not stimulate leucine----protein. Hyperaminoacidemia per se stimulated leucine----protein but did not suppress endogenous proteolysis. When combined, they had a cumulative effect on net leucine deposition into body protein.

The importance of first-phase insulin secretion: implications for the therapy of type 2 diabetes mellitus.

Type 2 diabetes is a heterogeneous disorder characterized by defects in insulin secretion and action. Insulin resistance is a key feature of type 2 diabetes. However, insulin resistance alone does not appear to be sufficient to cause diabetes. Longitudinal studies have shown that the development of overt hyperglycemia is associated with a decline in β‐cell secretion. In patients with impaired glucose tolerance or in the early stages of type 2 diabetes, first‐phase insulin release is almost invariably lost despite the enhancement of second‐phase secretion. Both animal and human studies support the critical physiologic role of the first‐phase of insulin secretion in the maintenance of postmeal glucose homeostasis. This effect is primarily mediated at the level of the liver, allowing prompt inhibition of endogenous glucose production (EGP) and thereby restraining the mealtime rise in plasma glucose. In type 2 diabetes, the loss of the early surge of insulin release is a precocious and quite common defect that plays a pathogenic role in postmeal hyperglycemia and one that may require specific therapeutic intervention. This becomes even more apparent if the negative impact of prandial glucose spikes is taken into consideration. Epidemiological evidence exists to indicate that 2‐h postload plasma glucose levels are strongly associated with all‐cause and cardiovascular mortality relative risk. Indeed the acute elevation of plasma glucose concentration triggers an array of tissue responses that may contribute to the development of diabetic complications. Considering that type 2 diabetes begins with meal‐related hyperglycemia in many patients, it becomes apparent that normalization of postmeal plasma glucose levels should be the target for rational therapy and the goal in the early stages of the disease. If a primary goal of diabetes therapy is control of postmeal glucose excursion, then the regulation of glucose absorption from the gut and entry into the circulation is an important mechanism to consider. The restoration of the rapid increase in plasma insulin concentration may be quite an efficient therapeutic approach. Copyright

Postprandial Myocardial Perfusion in Healthy Subjects and in Type 2 Diabetic Patients

Background—In diabetic patients, postprandial hyperglycemia is a more powerful risk factor for cardiovascular disease than fasting hyperglycemia itself. A negative influence of acute hyperglycemia on systemic endothelial function (brachial artery) has been shown. However, myocardial perfusion during postprandial hyperglycemia has not been investigated. Methods and Results—We evaluated the effects of a standardized mixed meal on myocardial perfusion in 20 healthy subjects and 20 consecutive patients with type 2 diabetes mellitus without macrovascular or microvascular complications. Myocardial perfusion was assessed in fasting and postprandial states by myocardial contrast echocardiography. Fasting myocardial flow velocity (&bgr;, 0.65±0.27 versus 0.67±0.24; P=NS), myocardial blood volume (MBV; 8.3±1.2 versus 8.4±2; P=NS), and myocardial blood flow (5.4±1.5 versus 5.6±2; P=NS) did not differ between control subjects and diabetic patients. In the postprandial state, &bgr; (0.67±0.24 versus 0.92±0.35; P<0.01), MBV (8.4±2 versus 10.9±2.7; P<0.01), and myocardial blood flow (5.6±2 versus 9.9±2.8; P<0.01) increased significantly in control subjects. In diabetic patients, &bgr; increased (0.65±0.27 versus 0.8±0.24; P<0.01) but MBV (8.3±1.2 versus 4.3±1.3; P<0.01) and myocardial blood flow (5.4±1.5 versus 3.4±0.9; P<0.01) decreased significantly. Changes in MBV (expressed as [(MBVpostprandial−MBVfasting)/MBVfasting]×100) were significantly correlated with postprandial glycemia levels in diabetic patients. Conclusions—Postprandial hyperglycemia determines myocardial perfusion defects in type 2 diabetic patients. They are secondary to deterioration in microvascular function causing a decrease in MBV. In diabetic patients without microvascular or macrovascular complications, postprandial myocardial perfusion defects may represent an early marker of the atherogenic process in the coronary circulation; hence, its reversal constitutes a potential goal of treatment.

Time Course and Mechanisms of Circulating Progenitor Cell Reduction in the Natural History of Type 2 Diabetes

OBJECTIVE Reduction of bone marrow–derived circulating progenitor cells has been proposed as a novel mechanism of cardiovascular disease in type 2 diabetes. The present study was designed to describe the extent and potential mechanisms of progenitor cell reduction during the natural history of type 2 diabetes. RESEARCH DESIGN AND METHODS We identified 425 individuals, divided into seven categories according to carbohydrate metabolism status (normal glucose tolerance [NGT], impaired fasting glucose, impaired glucose tolerance [IGT], and newly diagnosed type 2 diabetes) and diabetes duration (0–9, 10–19, and ≥20 years). These categories were examined as ideally describing the natural history of type 2 diabetes development and progression. We measured CD34+ and CD34+KDR+ progenitor cells by flow cytometry. We also evaluated progenitor cells in 20 coupled bone marrow and peripheral blood samples and examined progenitor cell apoptosis in 34 subjects. RESULTS In comparison to NGT, CD34+ cells were significantly reduced in IGT and had a first nadir in newly diagnosed type 2 diabetes and a second nadir after 20 years of diabetes. Statistical adjustment for possible confounders confirmed that CD34+ cell counts are deeply reduced at time of diagnosis, that they partially recover during the subsequent 0–19 years, and that they dip again after ≥20 years. A similar, but less consistent, trend was detected for CD34+KDR+ cells. Peripheral blood CD34+ cells were directly correlated with bone marrow CD34+ cells and inversely correlated with CD34+ cell apoptosis. CONCLUSIONS Circulating progenitor cell reduction marks the clinical onset of type 2 diabetes. Both defective mobilization and increased apoptosis may account for this phenomenon. While a partial recovery occurs during subsequent years, bone marrow reserve seems exhausted in the long term.

The metabolic syndrome is a risk indicator of microvascular and macrovascular complications in diabetes: results from Metascreen, a multicenter diabetes clinic-based survey.

OBJECTIVE—We aimed at assessing the degree of association and the predictive power of the metabolic syndrome with regard to clinically detectable complications in patients with diabetes. RESEARCH DESIGN AND METHODS—Metascreen is a cross-sectional survey of metabolic syndrome and clinically detected diabetes complications performed in 8,497 patients (7,859 with type 2 diabetes and 638 with type 1 diabetes) randomly chosen in 176 diabetes outpatient clinics throughout Italy. The metabolic syndrome was defined according to either the American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI) or the International Diabetes Federation (IDF) diagnostic criteria. Multivariate analyses of the association(s) between either AHA/NHLBI or IDF metabolic syndrome and clinical complications were performed. Receiver-operator characteristic (ROC) curves were constructed to compare the predictive power of the two sets of diagnostic criteria of the metabolic syndrome. RESULTS—Either definition of the metabolic syndrome was an independent statistical indicator of the presence of nephropathy and neuropathy (P < 0.02–0.01) in type 1 diabetes and of all complications (P < 0.0001), including cardiovascular disease and retinopathy, in type 2 diabetes. For each complication, the ROC curves based on either AHA/NHLBI or IDF metabolic syndrome were similar to each other and to the ROC curves constructed with all continuous traits compounding the metabolic syndrome. CONCLUSIONS—The metabolic syndrome, defined according to AHA/NHLBI or IDF diagnostic criteria, is an independent clinical indicator and may be involved in the pathogenesis of both macro- and microvascular complications of diabetes.

Insulin Resistance and Microalbuminuria: A Cross-Sectional, Case-Control Study of 158 Patients With Type 2 Diabetes and Different Degrees of Urinary Albumin Excretion

Microalbuminuria is a risk factor for renal and cardiovascular disease. A role for insulin resistance in the pathogenesis of microalbuminuria has been suggested but is still unproven. In this case-control, cross-sectional study, we compared glucose disposal rate (GDR), measured by hyperinsulinemic-euglycemic clamp, in 50 pairs of matched type 2 diabetic patients with micro- or normoalbuminuria (main study) and in 29 matched pairs of diabetic patients with macro- or microalbuminuria (substudy). In the main study, GDR was ∼25% lower in micro- than in normoalbuminuric patients (5.20 ± 1.91 vs. 6.86 ± 2.88 mg · kg−1 · min−1, P < 0.05) and was independently associated with microalbuminuria (P = 0.002), with each 1 mg · kg−1 · min−1 decrease predicting ∼40% increased prevalence (odds ratio 1.37 [95% CI 1.14–1.70]). Microalbuminuria was threefold more frequent in patients with GDR ≤7.50 ± 2.56 mg · kg−1 · min−1 than in those with higher GDR (60% vs. 20%, P < 0.005). In the substudy, GDR in macro- and microalbuminuric patients was comparable (5.52 ± 2.56 vs. 5.16 ± 1.61 mg · kg−1 · min−1) and independent of macroalbuminuria. GDR was significantly correlated with urinary albumin excretion rate in the main study (P = 0.004) but not in the substudy (P = 0.60). In type 2 diabetes, more severe insulin resistance is independently associated with microalbuminuria. Longitudinal studies are needed to clarify the role of insulin resistance in the pathogenesis of microalbuminuria and related complications.

Closed-Loop Artificial Pancreas Using Subcutaneous Glucose Sensing and Insulin Delivery and a Model Predictive Control Algorithm: Preliminary Studies in Padova and Montpellier

New effort has been made to develop closed-loop glucose control, using subcutaneous (SC) glucose sensing and continuous subcutaneous insulin infusion (CSII) from a pump, and a control algorithm. An approach based on a model predictive control (MPC) algorithm has been utilized during closed-loop control in type 1 diabetes patients. Here we describe the preliminary clinical experience with this approach. In Padova, two out of three subjects showed better performance with the closed-loop system compared to open loop. Altogether, mean overnight plasma glucose (PG) levels were 134 versus 111 mg/dl during open loop versus closed loop, respectively. The percentage of time spent at PG > 140 mg/dl was 45% versus 12%, while postbreakfast mean PG was 165 versus 156 mg/dl during open loop versus closed loop, respectively. Also, in Montpellier, two patients out of three showed a better glucose control during closed-loop trials. Avoidance of nocturnal hypoglycemic excursions was a clear benefit during algorithm-guided insulin delivery in all cases. This preliminary set of studies demonstrates that closed-loop control based entirely on SC glucose sensing and insulin delivery is feasible and can be applied to improve glucose control in patients with type 1 diabetes, although the algorithm needs to be further improved to achieve better glycemic control. Six type 1 diabetes patients (three in each of two clinical investigation centers in Padova and Montpellier), using CSII, aged 36 ± 8 and 48 ± 6 years, duration of diabetes 12 ± 8 and 29 ± 4 years, hemoglobin A1c 7.4% ± 0.1% and 7.3% ± 0.3%, body mass index 23.2 ± 0.3 and 28.4 ± 2.2 kg/m2, respectively, were studied on two occasions during 22 h overnight hospital admissions 2–4 weeks apart. A Freestyle Navigator® continuous glucose monitor and an OmniPod® insulin pump were applied in each trial. Admission 1 used open-loop control, while admission 2 employed closed-loop control using our MPC algorithm.