Impaired microvascular reactivity and endothelial function in patients with Cushing's syndrome: influence of arterial hypertension

The aim of the study was to evaluate skin microvascular reactivity (MVR) and possible influencing factors (fibrinolysis, oxidative stress, and endothelial function) in patients with Cushing's syndrome. Twenty-nine patients with active Cushing's syndrome (ten of them also examined after a successful operation) and 16 control subjects were studied. Skin MVR was measured by laser Doppler flowmetry during post-occlusive (PORH) and thermal hyperemia (TH). Malondialdehyde and Cu,Zn-superoxide dismutase were used as markers of oxidative stress. Fibrinolysis was estimated by tissue plasminogen activator (tPA) and its inhibitor (PAI-1). N-acetyl-beta-glucosaminidase, E-selectin, P-selectin, and ICAM-1 were used as markers of endothelial function. Oxidative stress and endothelial dysfunction was present in patients with hypercortisolism, however, increased concentration of ICAM-1 was also found in patients after the operation as compared to controls (290.8+/-74.2 vs. 210.9+/-56.3 ng.ml(-1), p<0.05). Maximal perfusion was significantly lower in patients with arterial hypertension during PORH and TH (36.3+/-13.0 vs. 63.3+/-32.4 PU, p<0.01, and 90.4+/-36.6 vs. 159.2+/-95.3 PU, p<0.05, respectively) and similarly the velocity of perfusion increase during PORH and TH was lower (3.2+/-1.5 vs. 5.2+/-3.4 PU.s(-1), p<0.05, and 0.95+/-0.6 vs. 1.8+/-1.1 PU.s(-1), p<0.05, respectively). The most pronounced impairment of microvascular reactivity was present in patients with combination of arterial hypertension and diabetes mellitus.     

Microalbuminuria in Type 2 diabetes indicates impaired microvascular vasomotion and perfusion

Vascular oscillation (vasomotion) occurs in the microcirculation and is thought to be a significant contributor to tissue perfusion. Our aims were to assess the relationship of vasomotion to perfusion in the cutaneous microcirculation of diabetic patients, to determine the influence on it of endothelium-dependent and nonendothelium-dependent vasodilatory stimuli, and to assess the relationship to perfusion and vasomotion of various biochemical markers of vascular function (HbA1c, LDL- and HDL-cholesterol, triglycerides, insulin resistance, high sensitive C-reactive protein, L- and E-selectin, soluble ICAM, von Willebrand factor) and microalbuminuria. Perfusion and vasomotion (spectral density at low and very low frequencies) were measured by laser-Doppler flowmetry after local heat and iontophoresis of ACh and sodium nitroprusside. Perfusion responses to all stimuli were impaired in patients with Type 2 diabetes (heat: F = 28.0, P < 0.001; ACh: F = 7.11, P = 0.003; sodium nitroprusside: F = 4.0, P = 0.028). Responses to endothelium-dependent stimuli were further impaired in microalbuminuric patients (heat: P = 0.035; ACh: P = 0.034). Vasomotion responses at low frequencies after endothelium-dependent stimuli were impaired in diabetic patients compared with that shown in controls (heat: F = 5.62, P = 0.002; ACh: F = 4.32, P = 0.015). Multivariate modeling showed microalbuminuria to be the only consistent predictor of perfusion and vasomotion responses. The results suggest that microalbuminuria in Type 2 diabetes reflects a generalized disturbance of microvascular function related to endothelium-dependent mechanisms.     

Microvascular reactivity in patients with hypercholesterolemia: effect of lipid lowering treatment

Impaired NO-dependent vasodilation of resistance vessels is an early marker of an increased risk of atherosclerosis; utility of the examination of microcirculation, however, is far less established. We have therefore tested the hypothesis that hypercholesterolemia is associated with an impaired microvascular reactivity and that this defect is at least partially reversible by lipid-lowering treatment. Twenty-seven otherwise healthy patients with severe hypercholesterolemia (HLP) were examined at rest and then after 10 weeks of atorvastatin treatment (20 mg/day). Skin microvascular reactivity (MVR) was examined by laser-Doppler flowmetry. Baseline MVR values of the studied group were compared to healthy control subjects, HLP patients with coronary artery disease (CAD) and diabetic patients with and without diabetic retinopathy. MVR was normal in HLP subjects without CAD. On the contrary, MVR was impaired in HLP patients with CAD. There was no effect of atorvastatin on MVR, despite the profound reduction of serum lipids. MVR values did not correlate with cholesterol levels. In diabetic subjects, the MVR was substantially impaired only in patients with retinopathy. In the subjects without retinopathy, MVR was either normal (type I diabetes) or moderately impaired (type II diabetes). MVR was thus normal in HLP patients without manifest vascular disease and was not influenced by lipid lowering therapy. Impairment in the MVR was only evident in subjects with HLP and severe CAD. These results suggest that microcirculation is not involved in the early vascular dysfunction induced by HLP and that MVR rather reflects changes which appear later in the course of the atherosclerotic disease.     

Microvascular permeability is increased in both types of diabetes and correlates differentially with serum levels of insulin-like growth factor I (IGF-I) and vascular endothelial growth factor (VEGF).

Vascular endothelial growth factor (VEGF) and insulin-like growth factor-I (IGF-I) both play a pivotal role in diabetic microangiopathy. This study assessed the relationship between capillary permeability as a marker of endothelial dysfunction and serum VEGF and IGF-I levels in normotensive diabetics. Subjects were 10 Type 1 (6/4, male/female, age: 30 [mean] +/- 5 [SD] years, HbA1c: 7.5 +/- 1.1 %), 13 Type 2 diabetics (9/4, m/f; 63 +/- 7 years, 8.3 +/- 1.8 %), and 24 age- and sex-matched control subjects. We determined nailfold capillary permeability by intravital fluorescence videomicroscopy after intravenous injection of sodium-fluorescein. Serum VEGF, free and total IGF-I, IGF binding protein (IGFBP)-1, IGFBP-3, and insulin levels were measured by specific immunoassays. Capillary permeability was increased in both types of diabetes patients compared to age- and sex-matched controls. In Type 1 diabetics, fluorescence light intensities increased over time, reaching significance 30 minutes after dye injection. Type 2 diabetics already revealed an early onset of elevated fluorescence light intensities after one minute. Capillary permeability showed a significant positive correlation with VEGF levels in Type 1 diabetics, (r = 0.76, p < 0.05; 20 min after dye injection) but with free IGF-I levels in type 2 diabetics (r = 0.65, p < 0.05; 5 min after dye injection). IGFBP-3 correlated negatively with capillary permeability in both diabetes types, whereas IGFBP-1 levels correlated positively in Type 2 patients. In conclusion, capillary permeability is increased in both types of diabetes mellitus. However, VEGF and IGF-I may differentially affect microvascular permeability depending on the diabetes type.     

Reduced nitric oxide bioavailability contributes to skeletal muscle microvessel rarefaction in the metabolic syndrome

This study tested the hypothesis that chronically elevated oxidant stress contributes to impaired active hyperemia in skeletal muscle of obese Zucker rats (OZR) vs. lean Zucker rats (LZR) through progressive deteriorations in microvascular structure. Twelve-week-old LZR and OZR were given 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (tempol) in the drinking water for approximately 4 wk. Subsequently, perfusion of in situ gastrocnemius muscle was determined during incremental elevations in metabolic demand, while a contralateral skeletal muscle arteriole and the gastrocnemius muscle was removed to determine dilator reactivity, vessel wall mechanics, and microvessel density. Under control conditions, active hyperemia was impaired at all levels of metabolic demand in OZR, and this was correlated with a reduced microvessel density, increased arteriolar stiffness, and impaired dilator reactivity. Chronic tempol ingestion improved perfusion during moderate to high metabolic demand only and was associated with improved arteriolar reactivity and microvessel density; passive vessel mechanics were unaltered. Combined antioxidant therapy and nitric oxide synthase inhibition in OZR prevented much of the restored perfusion and microvessel density. In LZR, treatment with N(omega)-nitro-L-arginine methyl ester (L-NAME) hydrochloride and hydralazine (to prevent hypertension) impaired active hyperemia, dilator reactivity, and microvessel density, although arteriolar distensibility was not altered. These results suggest that with the development of the metabolic syndrome, chronic reductions in nitric oxide bioavailability, in part via the scavenging actions of oxidative free radicals, contribute to a loss of skeletal muscle microvessels, leading to impaired muscle perfusion with elevated metabolic demand.     

Improved myocardial perfusion in chronic diabetic mice by the up‐regulation of pLKB1 and AMPK signaling

Previous studies related impaired myocardial microcirculation in diabetes to oxidative stress and endothelial dysfunction. Thus, this study was aimed to determine the effect of up‐regulating pAMPK‐pAKT signaling on coronary microvascular reactivity in the isolated heart of diabetic mice. We measured coronary resistance in wild‐type and streptozotocin (STZ)‐treated mice, during perfusion pressure changes. Glucose, insulin, and adiponectin levels in plasma and superoxide formation, NOx levels and heme oxygenase (HO) activity in myocardial tissue were determined. In addition, the expression of HO‐1, 3‐nitrotyrosine, pLKB1, pAMPK, pAKT, and peNOS proteins in control and diabetic hearts were measured. Coronary response to changes in perfusion pressure diverged from control in a time‐dependent manner following STZ administration. The responses observed at 28 weeks of diabetes (the maximum time examined) were mimicked by L‐NAME administration to control animals and were associated with a decrease in serum adiponectin and myocardial pLKB1, pAMPK, pAKT, and pGSK‐3 expression. Cobalt protoporphyrin treatment to induce HO‐1 expression reversed the microvascular reactivity seen in diabetes towards that of controls. Up‐regulation of HO‐1 was associated with an increase in adiponectin, pLKB1, pAKT, pAMPK, pGSK‐3, and peNOS levels and a decrease in myocardial superoxide and 3‐nitrotyrosine levels. In the present study we describe the time course of microvascular functional changes during the development of diabetes and the existence of a unique relationship between the levels of serum adiponectin, pLKB1, pAKT, and pAMPK activation in diabetic hearts. The restoration of microvascular function suggests a new therapeutic approach to even advanced cardiac microvascular derangement in diabetes. J. Cell. Biochem. 109: 1033–1044, 2010. © 2010 Wiley‐Liss, Inc.     

Association of obesity,diabetes, serum lipids and blood pressure regulates insulin action

Insulin resistance is present in patients with Type 2 diabetes mellitus as well as in obese patients without diabetes. The aim of our study was to compare insulin action in diabetic and control persons with or without obesity and to evaluate the influence of serum cholesterol, serum triglyceride and blood pressure on metabolic variables of insulin action. We examined 42 Type 2 diabetic patients and 41 control persons with body mass index (BMI) from 21.1 to 64.5 kg x m(-2), and 33 to 71 years old. The isoglycemic hyperinsulinemic clamp technique was performed at an insulin infusion rate of 1 mU x kg(-1) x min(-1) during 120 min. We evaluated the metabolic clearance rate of glucose (MCR(G), ml x kg(-1) x min(-1)) as the most important indicator of insulin action by isoglycemic clamp. The Pearson's correlation and multiple regression models were used to compare studied factors with the insulin action. We found following predictors of insulin resistance expressed in the relationship with MCR(G): BMI (r = -0.68, p<0.001), plasma glucose concentration (r = -0.66, p<0.001), cholesterol (r=-0.55, p<0.001), triglycerides (r = -0.54, p<0.001) and mean blood pressure (r = -0.38, p<0.01). From the multiple regression analysis we conclude that obesity may have even greater influence on the insulin action than diabetes mellitus itself.     

Impairments in microvascular reactivity are related to organ failure in human sepsis

Severe sepsis is a systemic inflammatory response to infection resulting in acute organ dysfunction. Vascular perfusion abnormalities are implicated in the pathology of organ failure, but studies of microvascular function in human sepsis are limited. We hypothesized that impaired microvascular responses to reactive hyperemia lead to impaired oxygen delivery relative to the needs of tissue and that these impairments would be associated with organ failure in sepsis. We studied 24 severe sepsis subjects 24 h after recognition of organ dysfunction; 15 healthy subjects served as controls. Near-infrared spectroscopy (NIRS) was used to measure tissue 1) microvascular hemoglobin signal strength and 2) oxygen saturation of microvascular hemoglobin (StO2). Both values were measured in thenar skeletal muscle before and after 5 min of forearm stagnant ischemia. At baseline, skeletal muscle microvascular hemoglobin was lower in septic than control subjects. Microvascular hemoglobin increased during reactive hyperemia in both groups, but less so in sepsis. StO2 at baseline and throughout ischemia was similar between the two groups; however, the rate of tissue oxygen consumption was significantly slower in septic subjects than in controls. The rate of increase in StO2 during reactive hyperemia was significantly slower in septic subjects than in controls; this impairment was accentuated in those with more organ failure. We conclude that organ dysfunction in severe sepsis is associated with dysregulation of microvascular oxygen balance. NIRS measurements of skeletal muscle microvascular perfusion and reactivity may provide important information about sepsis and serve as endpoints in future therapeutic interventions aimed at improving the microcirculation.     

Screening for vascular complications in children and adolescents with type 1 diabetes mellitus

Type 1 diabetes mellitus poses a significant health burden, particularly as a result of its microvascular complications. Clinically evident diabetes-related microvascular complications are extremely rare in childhood and adolescence. However, early functional and structural abnormalities may be present a few years after the onset of the disease. Therefore, regular screening for diabetic microvascular disease, particularly retinopathy and nephropathy, are of foremost importance in paediatric diabetes care. Early detection of diabetic microangiopathy and timely treatment of early signs of these complications have a pivotal role in prevention of blindness and end-stage renal failure in children and adolescents with diabetes.     

Effects of C-peptide on Microvascular Blood Flow and Blood Hemorheology

Beside functional and structural changes in vascular biology, alterations in the rheologic properties of blood cells mainly determines to an impaired microvascular blood flow in patients suffering from diabetes mellitus. Recent investigations provide increasing evidence that impaired C-peptide secretion in type 1 diabetic patients might contribute to the development of microvascular complications. C-peptide has been shown to stimulate endothelial NO secretion by activation of the Ca²⁺ calmodolin regulated enzyme eNOS. NO himself has the potency to increase cGMP levels in smooth muscle cells and to activate Na⁺ K⁺ ATPase activity and therefore evolves numerous effects in microvascular regulation. In type 1 diabetic patients, supplementation of C-peptide was shown to improve endothelium dependent vasodilatation in an NO-dependent pathway in different vascular compartments. In addition, it could be shown that C-peptide administration in type 1 diabetic patients, results in a redistribution of skin blood flow by increasing nutritive capillary blood flow in favour to subpapillary blood flow. Impaired Na⁺ K⁺ ATPase in another feature of diabetes mellitus in many cell types and is believed to be a pivotal regulator of various cell functions. C-peptide supplementation has been shown to restore Na⁺ K⁺ATPase activity in different cell types during in vitro and in vivo investigations. In type 1 diabetic patients, C-peptide supplementation was shown to increase erythrocyte Na⁺ K⁺ATPase activity by about 100%. There was found a linear relationship between plasma C-peptide levels and erythrocyte Na⁺ K⁺ATPase activity. In small capillaries, microvascular blood flow is increasingly determined by the rheologic properties of erythrocytes. Using laser-diffractoscopie a huge improvement in erythrocyte deformability could be observed after C-peptide administration in erythrocytes of type 1 diabetic patients. Inhibition of the Na⁺ K⁺ATPase by Obain completely abolished the effect of C-peptide on erythrocyte deformability. In conclusion, C-peptide improves microvascular function and blood flow in type 1 diabetic patients by interfering with vascular and rheological components of microvascular blood flow.     

Effect of IGF-I on FFA and glucose metabolism in control and type 2 diabetic subjects

The effects of insulin-like growth factor I (IGF-I) and insulin on free fatty acid (FFA) and glucose metabolism were compared in eight control and eight type 2 diabetic subjects, who received a two-step euglycemic hyperinsulinemic (0.25 and 0.5 mU x kg(-1) x min(-1)) clamp and a two-step euglycemic IGF-I (26 and 52 pmol x kg(-1) x min(-1)) clamp with [3-(3)H]glucose, [1-(14)C]palmitate, and indirect calorimetry. The insulin and IGF-I infusion rates were chosen to augment glucose disposal (R(d)) to a similar extent in control subjects. In type 2 diabetic subjects, stimulation of R(d) (second clamp step) in response to both insulin and IGF-I was reduced by approximately 40-50% compared with control subjects. In control subjects, insulin was more effective than IGF-I in suppressing endogenous glucose production (EGP) during both clamp steps. In type 2 diabetic subjects, insulin-mediated suppression of EGP was impaired, whereas EGP suppression by IGF-I was similar to that of controls. In both control and diabetic subjects, IGF-I-mediated suppression of plasma FFA concentration and inhibition of FFA turnover were markedly impaired compared with insulin (P < 0.01-0.001). During the second IGF-I clamp step, suppression of plasma FFA concentration and FFA turnover was impaired in diabetic vs. control subjects (P < 0.05-0.01). CONCLUSIONS: 1) IGF-I is less effective than insulin in suppressing EGP and FFA turnover; 2) insulin-resistant type 2 diabetic subjects also exhibit IGF-I resistance in skeletal muscle. However, suppression of EGP by IGF-I is not impaired in diabetic individuals, indicating normal hepatic sensitivity to IGF-I.     

Influence of exercise on dilatation of the basilar artery during diabetes mellitus.

Our goal was to examine whether exercise training alleviates impaired nitric oxide synthase (NOS)-dependent dilatation of the basilar artery in Type 1 diabetic rats. To test this hypothesis, we measured in vivo diameter of the basilar artery in sedentary and exercised nondiabetic and diabetic rats in response to NOS-dependent (acetylcholine) and -independent (nitroglycerin) agonists. To determine the potential role for nitric oxide in vasodilatation in sedentary and exercised nondiabetic and diabetic rats, we examined responses after NG-monomethyl-l-arginine (l-NMMA). We found that acetylcholine produced dilatation of the basilar artery that was similar in sedentary and exercised nondiabetic rats. Acetylcholine produced only minimal vasodilatation in sedentary diabetic rats. However, exercise alleviated impaired acetylcholine-induced vasodilatation in diabetic rats. Nitroglycerin produced dilatation of the basilar artery that was similar in sedentary and exercised nondiabetic and diabetic rats. l-NMMA produced similar inhibition of acetylcholine-induced dilatation of the basilar artery in sedentary and exercised nondiabetic and diabetic rats. Finally, we found that endothelial NOS (eNOS) protein in the basilar artery was higher in diabetic compared with nondiabetic rats and that exercise increased eNOS protein in the basilar artery of nondiabetic and diabetic rats. We conclude that 1) exercise can alleviate impaired NOS-dependent dilatation of the basilar artery during diabetes mellitus, 2) the synthesis and release of nitric oxide accounts for dilatation of the basilar artery to acetylcholine in sedentary and exercised nondiabetic and diabetic rats, and 3) exercise may exert its affect on cerebrovascular reactivity during diabetes by altering levels of eNOS protein in the basilar artery.     

Peripheral microvascular response to muscle contraction is unaltered by early diabetes but decreases with age

Long-term or untreated diabetes leads to micro- and macrovascular complications. However, there are few tests to evaluate microvascular function. A postcontraction blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) technique was exploited to measure peripheral microvascular function in diabetics and healthy controls matched with respect to age, body mass index, and physical activity. Postcontraction BOLD microvascular response was measured following 1-s maximal isometric ankle dorsiflexion in individuals with diabetes mellitus type I [DMI, n = 15, age 33 ± 3 yr (means ± SE), median diabetes duration = 5.5 yr] and type II (DMII, n = 16, age 45 ± 2 yr, median duration = 2.4 yr); responses were compared with controls (CONI and CONII). Peripheral macrovascular function of the popliteal and tibial arteries was assessed during exercise hyperemia with phase contrast magnetic resonance angiography following repetitive exercise. There were no group differences as a result of diabetes in peripheral microvascular function (peak BOLD response: DMI = 2.04 ± 0.38% vs. CONI = 2.08 ± 0.48%; DMII = 0.93 ± 0.24% vs. CONII = 1.13 ± 0.24%; mean ± SE), but the BOLD response was significantly influenced by age (partial r = -0.384, P = 0.003), supporting its sensitivity as a measure of microvascular function. Eleven individuals had no microvascular BOLD response, including three diabetics with neuropathy and four controls with a family history of diabetes. There were no differences in peripheral macrovascular function between groups when assessing exercise hyperemia or the pulsitility and resistive indexes. Although the BOLD microvascular response was not impaired in early diabetes, these results encourage further investigation of muscle BOLD as it relates to peripheral microvascular health.     

Mechanism of Protection by Soluble Epoxide Hydrolase Inhibition in Type 2 Diabetic Stroke

Inhibition of soluble epoxide hydrolase (sEH) is a potential target of therapy for ischemic injury. sEH metabolizes neuroprotective epoxyeicosatrienoic acids (EETs). We recently demonstrated that sEH inhibition reduces infarct size after middle cerebral artery occlusion (MCAO) in type 1 diabetic mice. We hypothesized that inhibition of sEH would protect against ischemic injury in type 2 diabetic mice. Type 2 diabetes was produced by combined high-fat diet, nicotinamide and streptozotocin in male mice. Diabetic and control mice were treated with vehicle or the sEH inhibitor t-AUCB then subjected to 60-min MCAO. Compared to chow-fed mice, high fat diet-fed mice exhibited an upregulation of sEH mRNA and protein in brain, but no differences in brain EETs levels were observed between groups. Type 2 diabetic mice had increased blood glucose levels at baseline and throughout ischemia, decreased laser-Doppler perfusion of the MCA territory after reperfusion, and sustained larger cortical infarcts compared to control mice. t-AUCB decreased fasting glucose levels at baseline and throughout ischemia, improved cortical perfusion after MCAO and significantly reduced infarct size in diabetic mice. We conclude that sEH inhibition, as a preventative treatment, improves glycemic status, post-ischemic reperfusion in the ischemic territory, and stroke outcome in type 2 diabetic mice.     

Differential expression of insulin-like growth factor-I and insulin-like growth factor binding protein-1 in the diabetic rat

Summary Multiple factors contribute to the growth retardation which is a characteristic feature of uncontrolled diabetes. In this report we have examined the effects of streptozotocin-induced (STZ) diabetes on expression of insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-1 (IGFBP-1) in various tissues. As early as 7 days after STZ administration there was a modest reduction in IGF-I mRNA abundance. The reduction (10–30%) was of similar magnitude in each of the 7 tissues examined; liver, kidney, lung, diaphragm, quadraceps, heart and adipose tissue. However, the reduction achieved statistical significance only in the lung (p < 0.05) and diaphragm (p < 0.01). A further reduction in IGF-I mRNA abundance was seen in many tissues, 32 and 91 days after STZ administration. In contrast to the decrease in IGF-I mRNA, IGFBP-1 mRNA was significantly increased in the liver and kidney of diabetic rats. IGFBP-1 mRNA was detectable at only very low levels in other tissues but was increased in diabetic rats compared non-diabetic rats. In diabetic rats, a highly significant correlation (R = 0.75, p < 0.001) between hepatic IGFBP-1 mRNA and glucose was observed whereas there was no significant correlation between serum glucose and hepatic IGF-I mRNA abundance (R = 0.24, p = NS). Treatment of diabetic rats with insulin resulted in a small, non significant increase in hepatic and renal IGF-I mRNA and a significant decrease in renal IGFBP-1 mRNA abundance. The observations reported here are consistent with the hypothesis that diminished IGF-I expression and inhibition of available IGF-1 by increased levels of IGFBP-1 may explain the impaired growth seen in diabetic animals.     

Paraoxonase 1 gene polymorphisms and enzyme activities in diabetes mellitus

Paraoxonase 1 (PON1), an antioxidant enzyme closely associated with HDL (high-density lipoproteins), preserves LDL (low-density lipoproteins) against oxidation. Less protection may be therefore supposed by decreased PON1 activity. This study was undertaken to investigate the association of PON1 gene polymorphisms with diabetic angiopathy and to evaluate the relationship of these polymorphisms with PON1 activity. Total of 86 Type 1 (T1DM) and 246 Type 2 (T2DM) diabetic patients together with 110 healthy subjects were examined. DNA isolated from leukocytes was amplified with polymerase chain reaction (PCR) followed by restriction enzyme digestion. The products were analyzed for L55M and Q192R polymorphisms in coding region and for -107 C/T and -907 G/C in promotor sequence of PON1. Serum enzyme activity was measured spectrophotometrically. Significant differences were found between T1DM or T2DM and control persons in L55M polymorphism (allele M more frequent in T1DM and T2DM vs. controls, p<0.05) and Q192R polymorphism (R allele less frequent in T1DM and T2DM vs. controls, p<0.01) of the PON1 gene. Serum PON1 activity was significantly decreased in T1DM (110+/-68 nmol/ml/min) and T2DM patients (118+/-69 nmol/ml/min) compared to the control persons (203+/-58 nmol/ml/min), both p<0.01. The presence of MM and QQ genotypes was accompanied by lower PON1 activity than of LL and RR genotypes (p<0.05), respectively. Better diabetes control was found in patients with LL than with MM genotypes and similarly in RR genotype than QQ genotype with p<0.05. Significantly different allele frequencies were found in diabetic patients with macroangiopathy than in those without it (M: 0.59 vs. 0.44. R: 0.12 vs. 0.19, p<0.01). The association of PON1 polymorphisms, lower PON1 activity and poorer diabetes control found in patients with macroangiopathy further support the idea of genetic factors contributing to the development of vascular disorders in diabetes.     

Advanced glycation end-products and advanced oxidation protein products in patients with diabetes mellitus

Accelerated glycoxidation takes part in the development of diabetic complications. We determined advanced glycation end-products (AGEs) and advanced oxidation protein products (AOPP) in the sera of 52 patients with diabetes mellitus (DM) - 18 with DM Type 1 and 34 with DM Type 2 and examined their relationship to the compensation of the disease. AGEs were estimated spectrofluorimetrically (350 nm/440 nm) whereas AOPP were determined spectro-photometrically (340 nm). AGEs were elevated only in DM Type 2 (DM2 5.11+/-1.15 x 10(3) AU/g vs controls 4.08+/-0.71 x 10(3) AU/g, p<0.001, vs DM1 4.14+/-0.86 x 10(3) AU/g, p<0.005, DM1 vs controls were not significant). AOPP were elevated significantly in both types of DM with higher levels in DM Type 2 (DM2 157.50+/-75.15 micromol/l vs healthy subjects 79.80+/-23.72 micromol/l, p<0.001, vs DM1 97.50+/-30.91 micromol/l, p<0.005, DM1 vs controls p<0.05). There was a tight correlation between AGEs and AOPP in both types of DM (DM1 r=0.75, DM2 r=0.47 (p<0.05)) and both AGEs and AOPP correlated with triglycerides. In DM Type 1 only, AGEs correlated with HbA1c r=0.47 (p<0.05) and with blood glucose. Slight but not significant differences in AGEs and AOPP levels were observed in patients with or without diabetic complications. Oxidative stress is increased in both types of DM, more in Type 2 where it contributes to the formation of glycoxidation products.     

Type 2 diabetes in non-obese Indian subjects is associated with reduced leptin levels: Study from Mumbai, Western India

Objective: Asian Indian subjects have a high tendency to develop Type 2 diabetes even though obesity is relatively uncommon. We evaluated the serum leptin levels in a group of non-obese Type 2 diabetic patients from Mumbai, Western India.Design: Cross sectional study.Methods: A total of 104 subjects consisting of 28 with Type 2 diabetes, 16 with impaired glucose tolerance and 60 age and sex-matched control subjects were given 75 g oral glucose tolerance test. Fasting serum leptin (IRMA), insulin and C-peptide were measured along with fasting and 2 h plasma glucose. The relation between these variables was studied by univariate and multiple regression analysis.Results: Type 2 diabetes was associated with marked (50–60%) reduction in serum leptin levels, in both men and women. Women, but not men, with impaired glucose tolerance exhibited 60% lower leptin. Serum leptin levels were positively correlated to body mass index (BMI; r = 0.501, p = 0.001) and calculated body fat percent (r = 0.525, p = 0.001) in all the study subjects with a better correlation in the normal subjects (r = 0.562 for BMI and 0.735 for body fat). On the other hand, serum leptin showed significant correlation to serum insulin (r = 0.362, p = 0.008) only in subjects with diabetes or IGT. In the multiple regression model, BMI was the only independent predictor of leptin, in all the subjects. However, in subjects with diabetes or impaired glucose tolerance, waist circumference (p = 0.003), gender (p = 0.007) and body fat (p = 0.009) were significant predictors of leptin, besides BMI. Gender-specific multiple regression revealed serum insulin as an independent predictor of leptin in men (p = 0.026). Therefore, lower serum leptin levels in diabetes is partly due to increased waist circumference, decreased BMI and male sex. These observations are consistent with the view that leptin levels in this cohort of non-obese Indians from Mumbai exhibit gender-specific relationship partly attributed to changes in serum insulin and waist circumference in men and to changes in BMI, in women.     

Reversibility of autonomic nerve function in relation to rapid improvement of glycemic control.

To determine the reversibility of autonomic nerve function in relation to the rapid improvement of glycemic control, we studied 54 patients with type 2 diabetes mellitus (33 men and 21 women; mean age, 49+/-8 years; mean duration of diabetes, 10+/-7 years). For 4 weeks of admission, the subjects were placed on strict dietary therapy, and 10 of them were under dietary therapy, 16 initially continued treatment with oral hypoglycemic agents, while 28 were treated with insulin. We measured the dark-adapted pupillary area (DAPA) by infrared photography, an indicator of diabetic autonomic neuropathy, on the second and 28th day after hospitalization. The change in FPG (delta FPG = - 111+/-49 mg/dl; mean +/- SD, p<0.001) and the change in HbA1c (delta HbA1c = -1.3+/-0.3%, p<0.001) were significantly improved. We observed significant improvements in the change in DAPA (delta DAPA) of all patients (25.1+/-11.0 vs. 25.7+/-11.6 mm2, delta DAPA = 0.6+/-1.4 mm2, p<0.01) and in those of patients without retinopathy (delta DAPA = 1.0+/-0.6 mm2, p<0.01). No change was observed in those of patients with retinopathy (delta DAPA= -0.02+/-0.3 mm2, NS). The delta DAPA was related to the delta HbA1c (r = -0.479, p<0.001) and also to the diabetic duration (years, r = -0.517, p<0.001). These findings suggest that a rapid improvement of glycemic control improves autonomic nerve function observed in type 2 diabetes with shorter duration. Particular attention should be paid to maintaining strict glycemic control at the stage of diabetic patients without retinopathy and those with shorter duration.     

Insulin signaling and glucose transport in insulin resistant human skeletal muscle

Insulin increases glucose uptake and metabolism in skeletal muscle by signal transduction via protein phosphorylation cascades. Insulin action on signal transduction is impaired in skeletal muscle from Type 2 diabetic subjects, underscoring the contribution of molecular defects to the insulin resistant phenotype. This review summarizes recent work to identify downstream intermediates in the insulin signaling pathways governing glucose homeostasis, in an attempt to characterize the molecular mechanism accounting for skeletal muscle insulin resistance in Type 2 diabetes. Furthermore, the effects of pharmaceutical treatment of Type 2 diabetic patients on insulin signaling and glucose uptake are discussed. The identification and characterization of pathways governing insulin action on glucose metabolism will facilitate the development of strategies to improve insulin sensitivity in an effort to prevent and treat Type 2 diabetes mellitus.