Glutathione infusion potentiates glucose-induced insulin secretion in aged patients with impaired glucose tolerance

Randomized Clinical Trial of How Long-Term Glutathione Supplementation Offers Protection from Oxidative Damage and Improves HbA1c in Elderly Type 2 Diabetic Patients

Complications in type 2 diabetes (T2D) arise from hyperglycemia-induced oxidative stress. Here, we examined the effectiveness of supplementation with the endogenous antioxidant glutathione (GSH) during anti-diabetic treatment. A total of 104 non-diabetic and 250 diabetic individuals on anti-diabetic therapy, of either sex and aged between 30 and 78 years, were recruited. A total of 125 diabetic patients were additionally given 500 mg oral GSH supplementation daily for a period of six months. Fasting and PP glucose, insulin, HbA1c, GSH, oxidized glutathione (GSSG), and 8-hydroxy-2-deoxy guanosine (8-OHdG) were measured upon recruitment and after three and six months of supplementation. Statistical significance and effect size were assessed longitudinally across all arms. Blood GSH increased (Cohen’s d = 1.01) and 8-OHdG decreased (Cohen’s d = −1.07) significantly within three months (p < 0.001) in diabetic individuals. A post hoc sub-group analysis showed that HbA1c (Cohen’s d = −0.41; p < 0.05) and fasting insulin levels (Cohen’s d = 0.56; p < 0.05) changed significantly in diabetic individuals above 55 years. GSH supplementation caused a significant increase in blood GSH and helped maintain the baseline HbA1c overall. These results suggest GSH supplementation is of considerable benefit to patients above 55 years, not only supporting decreased glycated hemoglobin (HbA1c) and 8-OHdG but also increasing fasting insulin. The clinical implication of our study is that the oral administration of GSH potentially complements anti-diabetic therapy in achieving better glycemic targets, especially in the elderly population.

Production performance, egg quality and some blood parameters of heat-stressed laying hens as affected by dietary supplemental Vit B6, Mg and Zn

OBJECTIVES

The effects of dietary supplements, including magnesium sulfate (Mg), zinc oxide (Zn) and vitamin B6 (Vit B6), on the performance of laying hens reared under normal (NC) and heat-stress (HSC) conditions were investigated.

MATERIAL AND METHODS

A total of 288 30-week-old Lohmann LSL-Lite laying hens were randomly divided into 48 cages and assigned to receive one of the eight diets with six replicates and six hens per replicate, based on a 2 × 2 × 2 factorial arrangement of treatments. Dietary supplements, including two levels (0 & 600 mg/kg) of Mg, two levels (0 & 30 mg/kg) of Zn and two levels (0 & 8 mg/kg) of Vit B6, in normal and heat-stress conditions, were tested at 30-40 and 41-45 weeks of age, respectively.

RESULTS

In the Vit B6 group, a decrease in feed intake (FI), egg production (EP), albumin, Zn, Fe and Mg, and an increase in triglyceride and insulin in HSC were observed, in addition to a decrease in cholesterol and an increase in egg weight (EW) in NC. Supplemental Mg decreased EP, blood triglycerides and copper in NC, and Zn, Fe and Mg in HSC as well. Feeding Zn, increased egg shape index, total protein and copper in addition to yolk index in NC and Fe in HSC. EWs were higher in hens supplemented with Vit B6+Mg in HSC. Increased insulin and decreased glutathione peroxidase activity were detected with the Vit B6+Zn compared to feeding either Vit B6 or Zn in HSC.

CONCLUSIONS

The results indicated Vit B6 could improve EWs and suppress blood cholesterol in NC. Zn improved the egg shape index in NC.

Revisiting the contribution of mitochondrial biology to the pathophysiology of skeletal muscle insulin resistance

While the etiology of type 2 diabetes is multifaceted, the induction of insulin resistance in skeletal muscle is a key phenomenon, and impairments in insulin signaling in this tissue directly contribute to hyperglycemia. Despite the lack of clarity regarding the specific mechanisms whereby insulin signaling is impaired, the key role of a high lipid environment within skeletal muscle has been recognized for decades. Many of the proposed mechanisms leading to the attenuation of insulin signaling - namely the accumulation of reactive lipids and the pathological production of reactive oxygen species (ROS), appear to rely on this high lipid environment. Mitochondrial biology is a central component to these processes, as these organelles are almost exclusively responsible for the oxidation and metabolism of lipids within skeletal muscle and are a primary source of ROS production. Classic studies have suggested that reductions in skeletal muscle mitochondrial content and/or function contribute to lipid-induced insulin resistance; however, in recent years the role of mitochondria in the pathophysiology of insulin resistance has been gradually re-evaluated to consider the biological effects of alterations in mitochondrial content. In this respect, while reductions in mitochondrial content are not required for the induction of insulin resistance, mechanisms that increase mitochondrial content are thought to enhance mitochondrial substrate sensitivity and submaximal adenosine diphosphate (ADP) kinetics. Thus, this review will describe the central role of a high lipid environment in the pathophysiology of insulin resistance, and present both classic and contemporary views of how mitochondrial biology contributes to insulin resistance in skeletal muscle.

The effects of 3 weeks of oral glutathione supplementation on whole body insulin sensitivity in obese males with and without type 2 diabetes: a randomized trial

The effect of oral glutathione (GSH) supplementation was studied in obese subjects with and without type 2 diabetes (T2DM) on measures of glucose homeostasis and markers of oxidative stress. Twenty subjects (10 patients with T2DM and 10 obese subjects) were recruited for the study, and randomized in a double-blinded placebo-controlled manner to consume either 1000 mg GSH per day or placebo for 3 weeks. Before and after the 3 weeks insulin sensitivity was measured with the hyperinsulinemic-euglycemic clamp and a muscle biopsy was obtained to measure GSH and skeletal muscle mitochondrial hydrogen peroxide (H₂O₂) emission rate. Whole body insulin sensitivity increased significantly in the GSH group. Skeletal muscle GSH was numerically increased (∼19%) in the GSH group; no change was seen in GSH to glutathione disulfide ratio. Skeletal muscle mitochondrial H₂O₂ emission rate did not change in response to the intervention and neither did the urinary excretion of the RNA oxidation product 8-oxo-7,8-dihydroguanosine or the DNA oxidation product 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), although 8-oxodG decreased as a main effect of time. Oral GSH supplementation improves insulin sensitivity in obese subjects with and without T2DM, although it does not alter markers of oxidative stress. The study has been registered in clinicaltrials.gov (NCT02948673). Novelty: Reduced glutathione supplementation increases insulin sensitivity in obese subjects with and without T2DM. H₂O₂ emission rate from skeletal muscle mitochondria was not affected by GSH supplementation.

Carbonyl Stress in Red Blood Cells and Hemoglobin

The paper overviews the peculiarities of carbonyl stress in nucleus-free mammal red blood cells (RBCs). Some functional features of RBCs make them exceptionally susceptible to reactive carbonyl compounds (RCC) from both blood plasma and the intracellular environment. In the first case, these compounds arise from the increased concentrations of glucose or ketone bodies in blood plasma, and in the second-from a misbalance in the glycolysis regulation. RBCs are normally exposed to RCC-methylglyoxal (MG), triglycerides-in blood plasma of diabetes patients. MG modifies lipoproteins and membrane proteins of RBCs and endothelial cells both on its own and with reactive oxygen species (ROS). Together, these phenomena may lead to arterial hypertension, atherosclerosis, hemolytic anemia, vascular occlusion, local ischemia, and hypercoagulation phenotype formation. ROS, reactive nitrogen species (RNS), and RCC might also damage hemoglobin (Hb), the most common protein in the RBC cytoplasm. It was Hb with which non-enzymatic glycation was first shown in living systems under physiological conditions. Glycated HbA1c is used as a very reliable and useful diagnostic marker. Studying the impacts of MG, ROS, and RNS on the physiological state of RBCs and Hb is of undisputed importance for basic and applied science.

The relationship between glucose variability and insulin sensitivity and oxidative stress in subjects with prediabetes

AIM

The present study assessed the relationship between glucose variability (GV) and insulin levels, insulin resistance and oxidative stress at early stages of glucose intolerance.

MATERIAL AND METHODS

A total of 50 subjects - 12 males and 38 females, mean age 55.6 ± 9.7 years, mean BMI 28.4 ± 6.4 kg/m², divided into 2 groups according to glucose tolerance: 32 with prediabetes and 18 with normal glucose tolerance were included. Glucose tolerance was assessed by OGTT according to WHO 2006 criteria. Plasma glucose and serum insulin were measured at fasting, 120-minute and 180-minute during the test; and oxLDL and 3-Nitrotyrosine - at fasting and 120-minute. HOMA-IR and OGIS indexes were calculated. HbA1c and lipid levels was assessed. Continuous glucose monitoring was performed with a blind sensor (FreeStyle Libre Pro) for a mean period of 13.6 ± 2.3 days.

RESULTS

Our results demonstrate significantly increased insulin resistance in subjects with prediabetes, whereas there is no difference in oxidative stress markers between the two groups. OxLDL and 3-NT correlate positively with insulin levels and HOMA-IR and negatively with OGIS in both groups. There is a positive association between oxidative stress markers and 120-minute glucose in the prediabetes group. Insulin levels and HOMA-IR are positively related to plasma glucose and reciprocally to CV and M-Value in prediabetes, since the latter association is with borderline significance after adjustment for hypertension and smoking.

CONCLUSIONS

Our results demonstrate a significant correlation between oxidative stress and insulin resistance at early stages of glucose intolerance. Both chronic hyperglycemia and GV seem to be related to insulin levels and insulin resistance, and just postload glycaemia to oxidative stress in prediabetes.

Thresholds of oxidative stress in newly diagnosed diabetic patients on intensive glucose-control therapy

Cellular and animal studies suggest that oxidative stress could be the central defect underlying both beta-cell dysfunction and insulin resistance in type 2 diabetes mellitus. A reduction of glycemic stress in diabetic patients on therapy alleviates systemic oxidative stress and improves insulin resistance and beta-cell secretion. Monitoring oxidative stress systematically with glucose can potentially identify an individual's recovery trajectory. To determine a quantitative model of serial changes in oxidative stress, as measured via the antioxidant glutathione, we followed patients newly diagnosed with diabetes over 8 weeks of starting anti-diabetic treatment. We developed a mathematical model which shows recovery is marked with a quantal response. For each individual the model predicts three theoretical quantities: an estimate of maximal glutathione at low stress, a glucose threshold for half-maximal glutathione, and a rate at which recovery progresses. Individual patients are seen to vary considerably in their response to glucose control. Thus, model estimates can potentially be used to determine whether an individual patient's response is better or worse than average in terms of each of these indices; they can therefore be useful in reassessing treatment strategy. We hypothesize that this method can aid the personalization of effective targets of glucose control in anti-diabetic therapy.

Genetic variants associated with glycine metabolism and their role in insulin sensitivity and type 2 diabetes

Circulating metabolites associated with insulin sensitivity may represent useful biomarkers, but their causal role in insulin sensitivity and diabetes is less certain. We previously identified novel metabolites correlated with insulin sensitivity measured by the hyperinsulinemic-euglycemic clamp. The top-ranking metabolites were in the glutathione and glycine biosynthesis pathways. We aimed to identify common genetic variants associated with metabolites in these pathways and test their role in insulin sensitivity and type 2 diabetes. With 1,004 nondiabetic individuals from the RISC study, we performed a genome-wide association study (GWAS) of 14 insulin sensitivity-related metabolites and one metabolite ratio. We replicated our results in the Botnia study (n = 342). We assessed the association of these variants with diabetes-related traits in GWAS meta-analyses (GENESIS [including RISC, EUGENE2, and Stanford], MAGIC, and DIAGRAM). We identified four associations with three metabolites-glycine (rs715 at CPS1), serine (rs478093 at PHGDH), and betaine (rs499368 at SLC6A12; rs17823642 at BHMT)-and one association signal with glycine-to-serine ratio (rs1107366 at ALDH1L1). There was no robust evidence for association between these variants and insulin resistance or diabetes. Genetic variants associated with genes in the glycine biosynthesis pathways do not provide consistent evidence for a role of glycine in diabetes-related traits.

Redox-regulating role of insulin: the essence of insulin effect

It is well-known that insulin acts as an important hormone, controlling energy metabolism, cellular proliferation and biosynthesis of functional molecules to maintain a biological homeostasis. Over the past few years, intensive insulin therapy has been believed to be benefit for the outcome of diabetic patients, in which the suppression of oxidative stress plays a role. Moreover, insulin is accepted as a key component of glucose-insulin-potassium, a treatment which has been believed to exert significant cardiovascular protective effect via the reduction of oxidative stress. Furthermore, accumulating evidence has suggested that insulin exerts important redox-regulating actions in various insulin-sensitive target organs, implying the systematic antioxidative role of insulin as a hormone. It is time for us to revisit insulin effects, through summarizing and evaluating the novel functions of insulin and their mechanisms. This review focuses on the antioxidative effect of insulin and highlights insulin-induced regulation of various antioxidant enzymes via insulin signaling pathways and the cross talk between key transcription factors, including nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor κB (NF-κB) which are responsible for the transcription of antioxidant enzymes, leading to reduced generation of reactive oxygen species (ROS) and the enhancement of the elimination of ROS.

alpha-hydroxybutyrate is an early biomarker of insulin resistance and glucose intolerance in a nondiabetic population

BACKGROUND

Insulin resistance is a risk factor for type 2 diabetes and cardiovascular disease progression. Current diagnostic tests, such as glycemic indicators, have limitations in the early detection of insulin resistant individuals. We searched for novel biomarkers identifying these at-risk subjects.

METHODS

Using mass spectrometry, non-targeted biochemical profiling was conducted in a cohort of 399 nondiabetic subjects representing a broad spectrum of insulin sensitivity and glucose tolerance (based on the hyperinsulinemic euglycemic clamp and oral glucose tolerance testing, respectively).

RESULTS

Random forest statistical analysis selected alpha-hydroxybutyrate (alpha-HB) as the top-ranked biochemical for separating insulin resistant (lower third of the clamp-derived M(FFM) = 33 [12] micromol x min(-1) x kg(FFM) (-1), median [interquartile range], n = 140) from insulin sensitive subjects (M(FFM) = 66 [23] micromol x min(-1) x kg(FFM) (-1)) with a 76% accuracy. By targeted isotope dilution assay, plasma alpha-HB concentrations were reciprocally related to M(FFM); and by partition analysis, an alpha-HB value of 5 microg/ml was found to best separate insulin resistant from insulin sensitive subjects. alpha-HB also separated subjects with normal glucose tolerance from those with impaired fasting glycemia or impaired glucose tolerance independently of, and in an additive fashion to, insulin resistance. These associations were also independent of sex, age and BMI. Other metabolites from this global analysis that significantly correlated to insulin sensitivity included certain organic acid, amino acid, lysophospholipid, acylcarnitine and fatty acid species. Several metabolites are intermediates related to alpha-HB metabolism and biosynthesis.

CONCLUSIONS

alpha-hydroxybutyrate is an early marker for both insulin resistance and impaired glucose regulation. The underlying biochemical mechanisms may involve increased lipid oxidation and oxidative stress.

Antioxidant supplemention in the treatment of skeletal muscle insulin resistance: potential mechanisms and clinical relevance

The incidence of type 2 diabetes has increased dramatically over the past several decades and this trend is projected to continue into the foreseeable future. Skeletal muscle insulin resistance is thought to be a key development in the pathogenesis of type 2 diabetes. Given this fact, interventions that prevent or reverse impairments in skeletal muscle action can have profound effects on whole-body glucose homeostasis. Traditional approaches used in this regard include exercise, weight loss, and insulin-sensitizing drugs such as thiazolidinediones (TZDs). Although these interventions have proven effective in improving glucose homeostasis, there are adherence issues seen with lifestyle interventions and undesirable side effects have been reported with TZDs. With these points in mind, the development of alternative strategies to maintain or improve skeletal muscle insulin sensitivity is warranted. In this context, the purpose of the present review is to highlight the role of antioxidant compounds in the prevention and treatment of skeletal muscle insulin resistance. Specifically, we will briefly describe the mechanisms of insulin-stimulated skeletal muscle glucose uptake and the potential mediators of oxidative stress induced insulin resistance, highlight data suggesting that antioxidant compounds can have beneficial effects on skeletal muscle insulin action, and discuss potential mechanisms mediating this effect.

Co-administration of glutathione and nitric oxide enhances insulin sensitivity in Wistar rats

The liver modulates insulin sensitivity through a prandial-dependent mechanism that requires activation of the hepatic parasympathetic nerves, hepatic nitric oxide (NO) and hepatic glutathione (GSH). We tested the hypothesis that co-administration of GSH and NO to the liver enhances insulin sensitivity in a GSH and NO dose-dependent manner. 24 h fasted Wistar rats were used. Hepatic GSH was supplemented by administration of glutathione monoethylester (GSH-E; 0.1/0.25/0.5/1/2 mmol kg(-1)) and 3-morpholinosidnonimine (SIN-1; 5/10 mg kg(-1)) was used as a NO donor. The drugs were administered either systemically (i.v.) or intraportally (i.p.v.). Insulin sensitivity was assessed using a transient euglycemic clamp. Neither GSH-E nor SIN-1 increased insulin sensitivity when administered alone, both i.v. and i.p.v. Moreover, changes in insulin sensitivity were not observed when GSH-E was administered i.v. followed by either i.v. or i.p.v. SIN-1 at any of the doses tested. However, i.p.v. administration of GSH-E followed by i.p.v. SIN-1 10 mg kg(-1) significantly increased insulin sensitivity in a GSH-E dose-dependent manner: 26.1+/-9.4% after 0.1 mmol kg(-1) GSH-E; 44.6+/-7.9% after 0.25 mmol kg(-1) GSH-E; 59.4+/-15.1% after 0.5 mmol kg(-1) GSH-E; 138.9+/-12.7% after 1 mmol kg(-1) GSH-E and 117.3+/-29.2% after a dose of 2 mmol kg(-1) (n = 23, P<0.005). Our results confirm that insulin sensitivity is enhanced in a dose-dependent manner by co-administration of NO and GSH donors to the liver.

Functional and molecular defects of pancreatic islets in human type 2 diabetes

To shed further light on the primary alterations of insulin secretion in type 2 diabetes and the possible mechanisms involved, we studied several functional and molecular properties of islets isolated from the pancreata of 13 type 2 diabetic and 13 matched nondiabetic cadaveric organ donors. Glucose-stimulated insulin secretion from type 2 diabetic islets was significantly lower than from control islets, whereas arginine- and glibenclamide-stimulated insulin release was less markedly affected. The defects were accompanied by reduced mRNA expression of GLUT1 and -2 and glucokinase and by diminished glucose oxidation. In addition, AMP-activated protein kinase activation was reduced. Furthermore, the expression of insulin was decreased, and that of pancreatic duodenal homeobox-1 (PDX-1) and forkhead box O1 (Foxo-1) was increased. Nitrotyrosine and 8-hydroxy-2'-deoxyguanosine concentrations, markers of oxidative stress, were significantly higher in type 2 diabetic than control islets, and they were correlated with the degree of glucose-stimulated insulin release impairment. Accordingly, 24-h exposure to glutathione significantly improved glucose-stimulated insulin release and decreased nitrotyrosine concentration, with partial recovery of insulin mRNA expression. These results provide direct evidence that the defects of insulin secretion in type 2 diabetic islets are associated with multiple islet cell alterations. Most importantly, the current study shows that the functional impairment of type 2 diabetic islets can be, at least in part, reversible. In this regard, it is suggested that reducing islet cell oxidative stress is a potential target of human type 2 diabetes therapy.

Prevention of fructose-induced hypertension by dietary vitamins

Essential hypertension in humans may develop through a combination of genetic and environmental factors. Diet has long been under investigation as a potential effector of blood pressure. A diet high in sucrose or fructose can give rise to hyperlipidemia, insulin resistance and hypertension. Insulin resistance, glucose intolerance and oxidative stress are common features of hypertension. If glucose metabolism through the glycolytic pathway is impaired, as in insulin resistance, there will be a build-up of glyceraldehyde, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate with further metabolism to methylglyoxal, a highly reactive ketoaldehyde. Excess aldehydes can bind sulfhydryl groups of membrane proteins, altering membrane calcium channels, increasing cytosolic free calcium, peripheral vascular resistance and blood pressure. The presence of reactive aldehydes can also lead to oxidative stress. Dietary management through lower sucrose or fructose intake and increased consumption of vitamins improves glucose metabolism, lowers tissue aldehydes, increases anti-oxidant capacity and may also prevent hypertension.

Beta-cell glucose toxicity, lipotoxicity, and chronic oxidative stress in type 2 diabetes

The relentless decline in beta-cell function frequently observed in type 2 diabetic patients, despite optimal drug management, has variously been attributed to glucose toxicity and lipotoxicity. The former theory posits hyperglycemia, an outcome of the disease, as a secondary force that further damages beta-cells. The latter theory suggests that the often-associated defect of hyperlipidemia is a primary cause of beta-cell dysfunction. We review evidence that patients with type 2 diabetes continually undergo oxidative stress, that elevated glucose concentrations increase levels of reactive oxygen species in beta-cells, that islets have intrinsically low antioxidant enzyme defenses, that antioxidant drugs and overexpression of antioxidant enzymes protect beta-cells from glucose toxicity, and that lipotoxicity, to the extent it can be attributable to hyperlipidemia, occurs only in the context of preexisting hyperglycemia, whereas glucose toxicity can occur in the absence of hyperlipidemia.

Role of Oxidative Stress in the Etiology of Type 2 Diabetes and the Effect of Antioxidant Supplementation on Glycemic Control

Oxidative stress is a situation in which the amount of reactive oxygen species (ROS) exceeds the levels of neutralizing substances referred to as antioxidants. Numerous studies have shown that oxidative stress is associated with type 2 diabetes, and there is compelling biochemical evidence that suggests that ROS may even play a role, if only secondary, in the pathogenesis of type 2 diabetes. These observations have provided sufficient impetus for the use of antioxidant supplements as adjunct therapy for control of blood sugar in diabetic patients. However, there is currently no optimum regimen of antioxidant supplementation for diabetic patients. Studies are required to determine appropriate doses of relevant individual micronutrients that perhaps should be used in combination to diminish oxidative stress and improve glycemic control in individuals afflicted with type 2 diabetes.

Glycemic index in chronic disease: a review

AIM

The intent of this review is to critically analyze the scientific evidence on the role of the glycemic index in chronic Western disease and to discuss the utility of the glycemic index in the prevention and management of these disease states.

BACKGROUND

The glycemic index ranks foods based on their postprandial blood glucose response. Hyperinsulinemia and insulin resistance, as well as their determinants (eg high energy intake, obesity, lack of physical activity) have been implicated in the etiology of diabetes, coronary heart disease and cancer. Recently, among dietary factors, carbohydrates have attracted much attention as a significant culprit, however, different types of carbohydrate produce varying glycemic and insulinemic responses. Low glycemic index foods, characterized by slowly absorbed carbohydrates, have been shown in some studies to produce beneficial effects on glucose control, hyperinsulinemia, insulin resistance, blood lipids and satiety.

METHOD

Studies on the short and long-term metabolic effects of diets with different glycemic indices will be presented and discussed. The review will focus primarily on clinical and epidemiological data, and will briefly discuss in vitro and animal studies related to possible mechanisms by which the glycemic index may influence chronic disease.

Attenuation of expression of gamma-glutamylcysteine synthetase by ribozyme transfection enhance insulin secretion by pancreatic beta cell line, MIN6

Low levels of intracellular antioxidant enzyme activities as well as glutathione (GSH) concentrations have been described in pancreatic beta cells. We examined the effects of intracellular GSH depletion on insulin secretion and the role of intracellular GSH in signal transduction in beta cell line, MIN6 cells. Anti-gamma-glutamylcysteine synthetase (gamma-GCS) heavy subunit ribozyme was stably transfected to MIN6 cells to reduce intracellular GSH concentration. In the presence of 10 mM glucose, ribozyme-transfected cells (RTC) increased insulin secretion from 0.58 microg/10(6) cells/h in control cells (CC) to 1.48 microg/10(6) cells/h. This was associated with increased intracellular Ca(2+) concentration in RTC, detected by fluo-3 staining. Our results demonstrated that intracellular GSH concentration might influence insulin secretion by MIN6 cells, and suggest that enhanced insulin secretion by beta cells conditioned by chronic depletion of GSH is mediated by increased intracellular Ca(2+) concentration.

Depletion of total antioxidant capacity in type 2 diabetes

The purpose of the study was to examine the relationship between antioxidant depletion, glycemic control, and development of chronic complications in a controlled population of type 2 diabetic patients. Fifty age-matched type 2 diabetic patients receiving sulfonylureas but not insulin treatment were screened and assigned to two groups based on the presence or absence of proteinuria. A third group of normal subjects without diabetes were also enrolled in the study. All subjects in the three groups were Egyptians who were matched for body weight, and the two diabetic groups were also age-matched. Plasma glucose and fructosamine levels were higher in the two groups of diabetic patients versus the control group, but lipid peroxide levels were higher only in the patients with proteinuria. Compared with the control group, the total antioxidant capacity was depleted in the two diabetic groups, but the depletion was more severe in patients with proteinuria. Thus, the mean Trolox equivalent antioxidant capacity (TEAC) of the control group was 2.7+/-0.45, versus 1.7+/-0.5 (P < .001) in the patients without proteinuria. Furthermore, the TEAC measured in patients with proteinuria, who also had more diabetic complications, was lower (1.4+/-0.5, P < .001) than the TEAC in patients without urinary protein. In conclusion, a depletion of the total antioxidant capacity is associated with a higher incidence of diabetic complications.

Reoxygenation injury affects isolated islet response to fatty acid stimulation

Hyperlipidemia is frequently associated with hyperinsulinemia, but because the effects of fatty acids on insulin secretion in in vitro studies using isolated perifused islets have mostly been described with supraphysiological concentrations of fatty acids, it has remained uncertain whether elevated lipid levels contribute to hyperinsulinemia by their direct stimulation of insulin secretion. In the present study, we have identified reoxygenation injury in isolated islet function as a contributing factor in the failure of physiological concentrations of free fatty acids to stimulate insulin secretion in isolated perifused islets. Reoxygenation of isolated islets is associated with the production of reactive oxygen species, which impair islet function. We have found that pretreatment of freshly isolated islets with the antioxidant glutathione (GSH), as well as a 24-hour preculture of isolated islets under appropriate conditions, enhanced their sensitivity to fatty acid stimulation.

Diabetics do not have increased Alzheimer-type pathology compared with age-matched control subjects. A retrospective postmortem immunocytochemical and histofluorescent study

Diabetics have impaired cognitive performance relative to age-matched control subjects, but the pathologic basis for this impairment is unknown. Because Alzheimer-type lesions, including both senile plaques and neurofibrillary tangles, contain glycated proteins and glycation is known to be increased in diabetes, we hypothesized that cognitive impairment in diabetes may be due in part to increased Alzheimer-type pathology. We measured the amount of Alzheimer-type pathology in postmortem brains of diabetic and age-matched control subjects with sensitive and specific histofluorescent and immunocytochemical methods. As expected, there were strong correlations between severity of senile plaques and neurofibrillary degeneration and age and also a strong correlation between severity of senile plaques and neurofibrillary degeneration and age and also a strong correlation between the pathologic measures. On the other hand, there was no significant difference between diabetics and control subjects with respect to severity of Alzheimer-type pathology, on average, or with respect to age. This finding was true for diabetics with and without insulin dependence. The results confirm reports showing that diabetes is not a risk factor for Alzheimer-type pathology and suggest that factors other than Alzheimer's disease are responsible for cognitive impairment in diabetics.

The erythrocyte glutathione levels during oral glucose tolerance test

Erythrocytes glutathione (GSH) levels were measured in erythrocytes from 33 subjects, at baseline and after 2-hour glucose loading in order to investigate the effect of glucose ingestion on the erythrocyte GSH. According to the World Health Organisation criteria 18 subjects had normal glucose tolerance (NGT)(mean age 48 +/- 10 years, 10 women, 8 men), 15 subjects had impaired glucose tolerance (IGT)(mean age 52 +/- 8 years, 9 women, 6 men). After 12-hour fasting, erythrocyte GSH levels were 40.5 +/- 8.06 and 39.27 +/- 10.26 mg/dl hemolisate in subjects with NGT and IGT, respectively (p = N.S). After 2-hour glucose loading, erythrocyte GSH levels decreased to 36.01 +/- 9.4 (p < 0.05) and 32.36 +/- 5.7 (p < 0.005) in subjects with NGT and IGT, respectively. The decrease in erythrocyte GSH levels in subjects with IGT was greater than in NGT individuals (p < 0.001). There was negative correlation between glucose, insulin, C-peptide, and erythrocyte GSH levels after glucose loading (p < 0.005). Our results suggest that glucose loading induce an oxidative stress in all subjects but this oxidative stress is greater in subjects with IGT than with NGT.

Effect of glycemic control, race (white versus black), and duration of diabetes on reduced glutathione content in erythrocytes of diabetic patients

We designed this study to examine whether uncontrolled hyperglycemia, duration of diabetes, or race (black v white) have any effect on glutathione levels in erythrocytes of type I diabetic patients. Hyperglycemia was assessed by measuring the level of hemoglobin A1c (HbA1c). Results show that erythrocytes of diabetic patients have a significantly lower glutathione level compared with those of age-matched normal subjects (P < .004). We found a significant negative correlation (r = -.59, P < .001) between the degree of hyperglycemia and the level of reduced glutathione (GSH) in erythrocytes of diabetic patients. There was no significant relationship (r = -.29, P > .12) between the level of GSH in erythrocytes and the duration of diabetes. Erythrocytes of black diabetic patients had significantly lower levels of GSH (P < .05) than those of white diabetic patients. Using erythrocytes as a model, this study suggests that a lower level of GSH may have a role in the cellular damage and impaired insulin secretion in uncontrolled diabetic patients.

Evidence for a relationship between free radicals and insulin action in the elderly

In forty healthy subjects with normal glucose tolerance divided by age into four groups (group A, subjects with mean age < 25 years [n = 10]; group B, subjects with mean age < 40 years [n = 9]; group C, subjects with mean age < 60 years [n = 11]; group D, subjects with mean age > 75 years [n = 10]) and were matched for body mass index (BMI), lean body mass (LBM), mean arterial blood pressure, and sedentary life style, we determined the plasma O2- production, reduced to oxidized glutathione level ratio (GSH/GSSG), and plasma membrane microviscosity. Euglycemic hyperinsulinemic (1 mU/kg.min-1 for 120 minutes) glucose clamp with simultaneous D-3-H glucose infusion and indirect calorimetry allowed determination of glucose turnover parameters and substrate oxidation. In the oldest group of subjects, a significant increase in plasma O2-production and membrane microviscosity associated with a significative reduction in glucose disappearance rate (Rd), total body glucose disposal (TBGD), and nonoxidative glucose metabolism was found. In group D subjects (n = 10), all of these changes were correlated with one another. In a multiple regression analysis of the pooled data from all study subjects (n = 40), only plasma O2- production levels displayed a statistically significant relation with TBGD and nonoxidative glucose metabolism. In conclusion, in aged patients a significant relationship between free radical production and insulin action seems to exist.