Oxidative stress and diabetes: what can we learn about insulin resistance from antioxidant mutant mouse models?

Developmental Programming: Impact of Gestational Steroid and Metabolic Milieus on Mediators of Insulin Sensitivity in Prenatal Testosterone-Treated Female Sheep

Prenatal testosterone (T) excess in sheep leads to peripheral insulin resistance (IR), reduced adipocyte size, and tissue-specific changes, with liver and muscle but not adipose tissue being insulin resistant. To determine the basis for the tissue-specific differences in insulin sensitivity, we assessed changes in negative (inflammation, oxidative stress, and lipotoxicity) and positive mediators (adiponectin and antioxidants) of insulin sensitivity in the liver, muscle, and adipose tissues of control and prenatal T-treated sheep. Because T excess leads to maternal hyperinsulinemia, fetal hyperandrogenism, and functional hyperandrogenism and IR in their female offspring, prenatal and postnatal interventions with antiandrogen, flutamide, and the insulin sensitizer rosiglitazone were used to parse out the contribution of androgenic and metabolic pathways in programming and maintaining these defects. Results showed that (1) peripheral IR in prenatal T-treated female sheep is related to increases in triglycerides and 3-nitrotyrosine, which appear to override the increase in high-molecular-weight adiponectin; (2) liver IR is a function of the increase in oxidative stress (3-nitrotyrosine) and lipotoxicity; (3) muscle IR is related to lipotoxicity; and (4) the insulin-sensitive status of visceral adipose tissue appears to be a function of the increase in antioxidants that likely overrides the increase in proinflammatory cytokines, macrophages, and oxidative stress. Prenatal and postnatal intervention with either antiandrogen or insulin sensitizer had partial effects in preventing or ameliorating the prenatal T-induced changes in mediators of insulin sensitivity, suggesting that both pathways are critical for the programming and maintenance of the prenatal T-induced changes and point to potential involvement of estrogenic pathways.

Inhibition of NF-κB activation improves insulin resistance of L6 cells

To explore the role of NF-κB activation in the development of insulin resistance and investigate whether or not that the inhibition of NF-κB activation by PDTC will improve the insulin resistance of L6 cells exposed to H₂O₂. L6 cells were treated with H₂O₂, PDTC or both H₂O₂ and PDTC for 4 hours. The uptake of glucose with stimulation of insulin, the expression of P38-MAPK, p- P38-MAPK, NF-κBp65, p- NF-κBp65, IRS-1, IRS-2, p-IRS-2, PI3K, IκBα, p- IκBα, caspase-8 and GLUT4, the production of ROS, TNF-α, IL-6 and IL-1β as well as the apoptosis rate of L6 cells were determined and compared in L6 treated with H₂O₂ alone or both H₂O₂ and PDTC. Compared with the L6 cells treated with H₂O₂ alone, the L6 cells treated with both H₂O₂ and PDTC showed (1) significantly lower production of ROS, TNF-α, IL-6 and IL-1β; (2) significantly decreased expression of P38-MAPK, p- P38-MAPK and NF-κBp65, p- NF-κBp65, p- IκBα and caspase-8; (3) significantly lower rate of apoptosis; (4) significantly higher expression of IRS-2, p-IRS-2 (Tyr 612), PI3K and GLUT4; (5) significantly higher uptake of glucose with stimulation of insulin; (6) significantly increased expression of Bcl2 and decreased ratio of Bax to Bcl2. Based on the findings of the present study, inhibition of NF-κB activation by PDTC would improve the insulin resistance of L6 cells exposed to H₂O₂.

HMGCS2 is a key ketogenic enzyme potentially involved in type 1 diabetes with high cardiovascular risk

Diabetes increases the risk of Cardio-vascular disease (CVD). CVD is more prevalent in type 2 diabetes (T2D) than type 1 diabetes (T1D), but the mortality risk is higher in T1D than in T2D. The pathophysiology of CVD in T1D is poorly defined. To learn more about biological pathways that are potentially involved in T1D with cardiac dysfunction, we sought to identify differentially expressed genes in the T1D heart. Our study used T1D mice with severe hyperglycemia along with significant deficits in echocardiographic measurements. Microarray analysis of heart tissue RNA revealed that the T1D mice differentially expressed 10 genes compared to control. Using Ingenuity Pathway Analysis (IPA), we showed that these genes were significantly involved in ketogenesis, cardiovascular disease, apoptosis and other toxicology functions. Of these 10 genes, the 3-Hydroxy-3-Methylglutaryl-CoA Synthase 2 (HMGCS2) was the highest upregulated gene in T1D heart. IPA analysis showed that HMGCS2 was center to many biological networks and pathways. Our data also suggested that apart from heart, the expression of HMGCS2 was also different in kidney and spleen between control and STZ treated mice. In conclusion, The HMGCS2 molecule may potentially be involved in T1D induced cardiac dysfunction.

Mitochondrial respiration and ROS emission during β-oxidation in the heart: An experimental-computational study

Lipids are main fuels for cellular energy and mitochondria their major oxidation site. Yet unknown is to what extent the fuel role of lipids is influenced by their uncoupling effects, and how this affects mitochondrial energetics, redox balance and the emission of reactive oxygen species (ROS). Employing a combined experimental-computational approach, we comparatively analyze β-oxidation of palmitoyl CoA (PCoA) in isolated heart mitochondria from Sham and streptozotocin (STZ)-induced type 1 diabetic (T1DM) guinea pigs (GPs). Parallel high throughput measurements of the rates of oxygen consumption (VO2) and hydrogen peroxide (H2O2) emission as a function of PCoA concentration, in the presence of L-carnitine and malate, were performed. We found that PCoA concentration < 200 nmol/mg mito protein resulted in low H2O2 emission flux, increasing thereafter in Sham and T1DM GPs under both states 4 and 3 respiration with diabetic mitochondria releasing higher amounts of ROS. Respiratory uncoupling and ROS excess occurred at PCoA > 600 nmol/mg mito prot, in both control and diabetic animals. Also, for the first time, we show that an integrated two compartment mitochondrial model of β-oxidation of long-chain fatty acids and main energy-redox processes is able to simulate the relationship between VO2 and H2O2 emission as a function of lipid concentration. Model and experimental results indicate that PCoA oxidation and its concentration-dependent uncoupling effect, together with a partial lipid-dependent decrease in the rate of superoxide generation, modulate H2O2 emission as a function of VO2. Results indicate that keeping low levels of intracellular lipid is crucial for mitochondria and cells to maintain ROS within physiological levels compatible with signaling and reliable energy supply.

Targeting Select Cellular Stress Pathways to Prevent Hyperglycemia-Related Complications: Shifting the Paradigm

Despite the advances made in preventing complications of diabetes, there is still substantial residual risk. Hence the need for developing new therapeutic agents that target the various facets of the pathogenesis of complications in people with diabetes. Traditionally four general biochemical pathways had been recognized as major contributors to glucotoxicity. These include the polyol pathway, the protein kinase C (PKC) pathway, glycosylation pathway, and oxidative stress. The latter has been proposed as a common impetus of the other pathways of glucotoxicity. More recently, the cross talk between oxidative stress and other recognized cellular stresses such as endoplasmic reticulum (ER), inflammatory, and mitochondrial stresses has emerged as an important additional mechanism of glucotoxicity. The observation that targeting oxidative stress with antioxidants has been associated with unfavorable clinical outcomes and the recognition that in cell cultures antioxidants may aggravate ER stress, suggests that selective targeting of individual cellular stresses may not be sufficient for preventing glucotoxicity. Future efforts should focus on developing therapeutic agents that can ameliorate cellular stress globally by simultaneously targeting the oxidative, ER, mitochondrial, and inflammatory stresses.

Hyperglycemia- and hyperinsulinemia-induced insulin resistance causes alterations in cellular bioenergetics and activation of inflammatory signaling in lymphatic muscle

Insulin resistance is a well-known risk factor for obesity, metabolic syndrome (MetSyn) and associated cardiovascular diseases, but its mechanisms are undefined in the lymphatics. Mesenteric lymphatic vessels from MetSyn or LPS-injected rats exhibited impaired intrinsic contractile activity and associated inflammatory changes. Hence, we hypothesized that insulin resistance in lymphatic muscle cells (LMCs) affects cell bioenergetics and signaling pathways that consequently alter contractility. LMCs were treated with different concentrations of insulin or glucose or both at various time points to determine insulin resistance. Onset of insulin resistance significantly impaired glucose uptake, mitochondrial function, oxygen consumption rates, glycolysis, lactic acid, and ATP production in LMCs. Hyperglycemia and hyperinsulinemia also impaired the PI3K/Akt while enhancing the ERK/p38MAPK/JNK pathways in LMCs. Increased NF-κB nuclear translocation and macrophage chemoattractant protein-1 and VCAM-1 levels in insulin-resistant LMCs indicated activation of inflammatory mechanisms. In addition, increased phosphorylation of myosin light chain-20, a key regulator of lymphatic muscle contraction, was observed in insulin-resistant LMCs. Therefore, our data elucidate the mechanisms of insulin resistance in LMCs and provide the first evidence that hyperglycemia and hyperinsulinemia promote insulin resistance and impair lymphatic contractile status by reducing glucose uptake, altering cellular metabolic pathways, and activating inflammatory signaling cascades.-Lee, Y., Fluckey, J. D., Chakraborty, S., Muthuchamy, M. Hyperglycemia- and hyperinsulinemia-induced insulin resistance causes alterations in cellular bioenergetics and activation of inflammatory signaling in lymphatic muscle.

Effects of vitamin C supplementation on glycaemic control: a systematic review and meta-analysis of randomised controlled trials

Randomised controlled trials (RCTs) have observed contrasting results on the effects of vitamin C on circulating biomarkers of glycaemic and insulin regulation. We conducted a systematic review and meta-analysis of RCTs testing the effect of vitamin C administration on glucose, HbA1c and insulin concentrations. Four databases (PubMed, Embase, Scopus and Cochrane Library) were used to retrieve RCTs published from inception until April 2016 and testing the effects of vitamin C in adult participants. The screening of 2008 articles yielded 22 eligible studies (937 participants). Overall, vitamin C did not modify glucose, HbA1c and insulin concentrations. However, subgroup analyses showed that vitamin C significantly reduced glucose concentrations (-0.44 mmol/l, 95% CI: -0.81, -0.07, P=0.01) in patients with type 2 diabetes and in interventions with a duration greater than 30 days (-0.53%, 95% CI: -0.79, -0.10, P=0.02). Vitamin C administration had greater effects on fasting (-13.63 pmol/l, 95% CI: -22.73, -4.54, P<0.01) compared to postprandial insulin concentration. Meta-regression analyses showed that age was a modifier of the effect of vitamin C on insulin concentration. Furthermore, the effect size was associated with baseline BMI and plasma glucose levels, and with the duration of the intervention. In conclusion, greater reduction in glucose concentrations observed in patients with diabetes, older individuals and with more prolonged supplementation. Personalised interventions with vitamin C may represent a feasible future strategy to enhance benefits and efficacy of interventions. Nevertheless, results need to be interpreted cautiously due to limitations in the primary studies analysed.

Excessive consumption of fructose causes cardiometabolic dysfunctions through oxidative stress and inflammation

A rapid rise in obesity, as well as physical inactivity, in industrialized countries is associated with fructose-consumption-mediated metabolic syndrome having a strong association with cardiovascular disease. Although insulin resistance is thought to be at the core, visceral obesity, hypertension, and hypertriglyceridemia are also considered important components of this metabolic disorder. In addition, various other abnormalities such as inflammation, oxidative stress, and elevated levels of uric acid are also part of this syndrome. Lifestyle changes through improved physical activity, as well as nutrition, are important approaches to minimize metabolic syndrome and its deleterious effects.

Vitamin C decreases the obesogenic and hyperglycemic effect of invert sugar in prediabetic rats

ABSTRACT Objective: To evaluate whether vitamin C can help to prevent obesity and hyperglycemia in Wistar rats treated with excess invert sugar to induce prediabetes. Methods: One hundred-day-old Male Wistar rats with a mean weight of 336.58±23.43g were randomly assigned to the following groups: (1) control, receiving water (C); (2) invert sugar control, receiving a 32% watery solution of invert sugar; (3) vitamin C control, receiving a watery solution of vitamin C (60mg/L), and (4) vitamin C plus invert sugar, receiving a watery solution of vitamin C and invert sugar. All animals had access to chow and water ad libitum and were treated for 17 weeks. Prediabetes was assessed according to two criteria: obesity (based on body mass indexand peritoneal fat content) and impaired glucose tolerance (assessed by the intraperitoneal glucose tolerance test and expressed as area under the curve) . Results: Group invert sugar control gained significantly more weight (p=0.035) and visceral fat (p<0.001) than groups vitamin C control and vitamin C plus invert sugar. Consequently, groups vitamin C control and vitamin C plus invert sugar had gained as little body mass index as group C by the end of the experiment. Vitamin C decreased the fasting glycemia of both groups supplemented with vitamin C and normalized the glucose tolerance of group vitamin C plus invert sugar, whose area under the curve matched that of group C. Conclusion: Vitamin C has anti-obesogenic and glycemia-lowering effects in Wistar rats, which might be promising to prediabetics. Future studies are needed to understand the anti-obesogenic and anti-hyperglycemic mechanisms of vitamin C in prediabetes.

The regulatory roles of O-GlcNAcylation in mitochondrial homeostasis and metabolic syndrome

Nutrients excess is one of the leading causes of metabolic syndrome globally. Protein post-translational O-GlcNAc modification has been recognized as an essential nutrient sensor of the cell. Emerging studies suggest that O-GlcNAcylation lies at the core linking nutritional stress to insulin resistance. Mitochondria are the major site for ATP production in most eukaryotes. Mitochondrial dysfunction and oxidative stress have long been considered as an important mechanism underlying insulin resistance. The metabolic process is under the influence of environmental and nutritional factors, thus sensing and transducing nutritional signals sit at the pivot of metabolism control. For a long time little was known about O-GlcNAcylation within mitochondria since mitochondrial O-GlcNAcylation was regarded rare. Recent findings have demonstrated that O-GlcNAcylation is widely spread among mitochondrial proteins, and that mitochondrial function and oxidative stress both can be regulated by O-GlcNAcylation, particularly under diabetic circumstances.

Healing effects of sumac (Rhus coriaria) in streptozotocin-induced diabetic rats

Context Sumac [Rhus coriaria L. (RC) (Anacardiaceae)] is used as a folk medicine in the treatment of diabetes in Turkey. Objective This study investigates the in vivo healing and protective effects of lyophilized extract sumac against streptozotocin (STZ)-induced diabetic complications. Materials and methods Toxicity test was conducted in three different dosages (250, 500 and 1000 mg/kg of plant extracts, respectively). Six groups of seven rats each were used in experiments. Groups were designed as Normal control, Diabetic (DM), DM + AC-20 mg/kg, DM + Extract-100 mg/kg, DM + Extract 250 mg/kg and DM + Extract 500 mg/kg group. Experimental diabetes [50 mg/kg, intraperitoneal (i.p.)] was induced by STZ. The effects of oral administration of the extract for 21 d on the level of serum glucose, insulin, C-peptide, lipid profile (LP), hepatic and renal damage biomarkers (HRDB), diabetic serum biomarkers (DSB), glycosylated haemoglobin (HbA1c), antioxidant defence system constituents (ADSCs), malondialdehyde (MDA) and α-glucosidase activity in small intestine tissue were evaluated. Results The extract decreased the levels of blood glucose in diabetic groups (an average of 31%). Triglyceride, total cholesterol, high-density lipoprotein and low-density lipoprotein levels were balanced by plant extract (500 mg/kg) supplementation in the diabetic group. Decreased levels of aspartate aminotransferase (89%), alanine aminotransferase (91%), lactate dehydrogenase (35%), alkaline phosphatase (47%), creatinine (25%) and urea (29%) were detected in plant extract (500 mg/kg) supplemented diabetic group. Additionally, a considerable increase in the HRDB, DSB, LP, MDA and fluctuated ADSC levels were restored in RC-extract supplemented groups. Conclusion RC lyophilized extract has a healing effect on diabetes and diabetes-related complications.

Cumulative Exposure to Ideal Cardiovascular Health and Incident Diabetes in a Chinese Population: The Kailuan Study

Background

It is unclear whether ideal cardiovascular health (CVH), and particularly cumulative exposure to ideal CVH (cumCVH), is associated with incident diabetes. We aimed to fill this research gap.

Methods and Results

The Kailuan Study is a prospective cohort of 101 510 adults aged 18 to 98 years recruited in 2006–2007 and who were subsequently followed up at 2‐ (Exam 2), 4‐ (Exam 3), and 6 (Exam 4)‐year intervals after baseline. The main analysis is restricted to those individuals with complete follow‐up at all 4 examinations and who had no history of diabetes until Exam 3. Cumulative exposure to ideal CVH (cumCVH) was calculated as the summed CVH score for each examination multiplied by the time between the 2 examinations (score×year). Logistic regression models were used to assess the association between cumCVH and incident diabetes. In fully adjusted models, compared with the lowest quintile of cumCVH, individuals in the highest quintile had ~68% (95% confidence interval [CI] 60‐75) lower risk for incident diabetes (compared with 61% [95% CI 52‐69] lower risk when using baseline CVH). Every additional year lived with a 1‐unit increase in ideal CVH was associated with a 24% (95% CI 21‐28) reduction in incident diabetes.

Conclusions

Ideal CVH is associated with a reduced incidence of diabetes, but the association is likely to be underestimated if baseline measures of CVH exposure are used. Measures of cumulative exposure to ideal CVH are more likely to reflect lifetime risk of diabetes and possibly other health outcomes.

Clinical Trial Registration

URL: https://www.chictr.org. Unique identifier: ChiCTRTNC‐11001489.

Curcumin improves the metabolic syndrome in high-fructose-diet-fed rats: role of TNF-α, NF-κB, and oxidative stress

This study aimed to investigate effects of curcumin on high fructose diet (HFD)-induced metabolic syndrome (MetS) in rats and the possible mechanisms involved. MetS was induced in male albino rats (n = 20), over 8 weeks, by 65% HFD. For 8-week experiment period, rats were assigned to 2 equal groups: curcumin-treated rats received curcumin (200 mg/kg, p.o, once daily) along with HFD, and untreated rats were fed with HFD only. We evaluated body mass (BM), systolic blood pressure (SBP), homeostasis model assessment of insulin resistance (HOMA-IR), and serum levels of glucose, insulin, leptin, total cholesterol (TC), triglycerides (TGs), uric acid, malondialdehyde (MDA; lipid peroxidation product), and tumor necrosis factor-α (TNF-α; inflammatory cytokine), and serum catalase (endogenous antioxidant) activity and immunohistochemical expression of nuclear factor κB (NF-κB; inflammation-related transcription factor) in hepatocytes. HFD produced increases in BM, SBP, HOMA-IR, and serum levels of glucose, insulin, leptin, TC, TGs, uric acid, MDA, and TNF-α, a decrease in catalase activity, and strong positive expression of NF-κB in hepatocytes. Curcumin, in presence of HFD, produced significant improvements in all glucose and fat metabolism parameters, and in oxidative stress and inflammation biomarkers. Curcumin may potentially be useful in the treatment of MetS through its ability to modulate oxidation stress status and inflammation cascades.

Antiglycation and Antioxidant Properties of Momordica charantia

The accumulation of advanced glycation endproducts (AGEs) and oxidative stress underlie the pathogenesis of diabetic complications. In many developing countries, diabetes treatment is unaffordable, and plants such as bitter gourd (or bitter melon; Momordica charantia) are used as traditional remedies because they exhibit hypoglycaemic properties. This study compared the antiglycation and antioxidant properties of aqueous extracts of M. charantia pulp (MCP), flesh (MCF) and charantin in vitro. Lysozyme was mixed with methylglyoxal and 0–15 mg/ml of M. charantia extracts in a pH 7.4 buffer and incubated at 37°C for 3 days. Crosslinked AGEs were assessed using gel electrophoresis, and the carboxymethyllysine (CML) content was analyzed by enzyme-linked immunosorbent assays. The antioxidant activities of the extracts were evaluated using assays to assess DPPH (1,1-diphenyl-2-picryl-hydrazyl) and hydroxyl radical scavenging activities, metal-chelating activity and reducing power of the extracts. The phenolic, flavonol and flavonoid content of the extracts were also determined. All extracts inhibited the formation of crosslinked AGEs and CML in a dose-dependent manner, with MCF being the most potent. The antioxidant activity of MCF was higher than that of MCP, but MCP showed the highest metal-chelating activity. MCF had the highest phenolic and flavonoid contents, whereas MCP had the highest flavonol content. M. charantia has hypoglycaemic effects, but this study shows that M. charantia extracts are also capable of preventing AGE formation in vitro. This activity may be due to the antioxidant properties, particularly the total phenolic content of the extracts. Thus, the use of M. charantia deserves more attention, as it may not only reduce hyperglycaemia but also protect against the build-up of tissue AGEs and reduce oxidative stress in patients with diabetes.

Beyond Diabetes: Does Obesity-Induced Oxidative Stress Drive the Aging Process?

Despite numerous correlative data, a causative role for oxidative stress in mammalian longevity has remained elusive. However, there is strong evidence that increased oxidative stress is associated with exacerbation of many diseases and pathologies that are also strongly related to advanced age. Obesity, or increased fat accumulation, is one of the most common chronic conditions worldwide and is associated with not only metabolic dysfunction but also increased levels of oxidative stress in vivo. Moreover, obesity is also associated with significantly increased risks of cardiovascular disease, neurological decline and cancer among many other diseases as well as a significantly increased risk of mortality. In this review, we investigate the possible interpretation that the increased incidence of these diseases in obesity may be due to chronic oxidative stress mediating segmental acceleration of the aging process. Understanding how obesity can alter cellular physiology beyond that directly related to metabolic function could open new therapeutic areas of approach to extend the period of healthy aging among people of all body composition.

Mitochondrial quality control in insulin resistance and diabetes

Diabetes is increasingly prevalent and a primary contributor to the major causes of disability and death. Despite the central role of mitochondria in metabolism, the relationship between mitochondrial quality and insulin action remains unclear. An increasing number of genetically-engineered and aging rodent models are shedding additional light on the mitochondrion's role in regulating glucose metabolism and insulin sensitivity by modulating mitochondrial morphology, function and quality control pathways. Clarification of the role of mitochondria in regulating key cellular processes including metabolic flux, autophagy, and apoptosis will drive the development of novel therapeutic strategies for maintaining mitochondrial quality and improving human health.

Excessive caloric intake acutely causes oxidative stress, GLUT4 carbonylation, and insulin resistance in healthy men

Obesity-linked insulin resistance greatly increases the risk for type 2 diabetes, hypertension, dyslipidemia, and non-alcoholic fatty liver disease, together known as the metabolic or insulin resistance syndrome. How obesity promotes insulin resistance remains incompletely understood. Plasma concentrations of free fatty acids and proinflammatory cytokines, endoplasmic reticulum ( ER) stress, and oxidative stress are all elevated in obesity and have been shown to induce insulin resistance. However, they may be late events that only develop after chronic excessive nutrient intake. The nature of the initial event that produces insulin resistance at the beginning of excess caloric intake and weight gain remains unknown. We show that feeding healthy men with ~6000 kcal/day of the common U.S. diet [~50% carbohydrate (CHO), ~ 35% fat, and ~15% protein] for 1 week produced a rapid weight gain of 3.5 kg and the rapid onset (after 2 to 3 days) of systemic and adipose tissue insulin resistance and oxidative stress but no inflammatory or ER stress. In adipose tissue, the oxidative stress resulted in extensive oxidation and carbonylation of numerous proteins, including carbonylation of GLUT4 near the glucose transport channel, which likely resulted in loss of GLUT4 activity. These results suggest that the initial event caused by overnutrition may be oxidative stress, which produces insulin resistance, at least in part, via carbonylation and oxidation-induced inactivation of GLUT4.

Association of Interleukin-6 and Myeloperoxidase with Insulin Resistance in Impaired Fasting Glucose Subjects

Impaired fasting glucose (IFG) is a high risk subclinical condition for the progression of type 2 diabetes mellitus and the hyperglycemia seen in this condition is because of the development of insulin resistance (IR). Obesity, inflammation, oxidative stress and many other factors have been implicated in development of IR in type 2 diabetes mellitus and its successive complications. Current study was aimed to ascertain the correlation of inflammation and oxidative stress markers [interleukin-6 (IL-6) and myeloperoxidase (MPO)] with IR in subjects with IFG. In this study, 80 subjects (40 IFG, 40 healthy controls) aged 25-45 years were selected based on their fasting plasma glucose (FPG) values and clinical history. Serum insulin, IL-6 and MPO were estimated by ELISA method and IR was calculated using Homeostatic Model Assessment Index 2 (HOMA 2) calculator. Pearson's correlation coefficient and independent sample 't' test were used for statistical analysis. IL-6 and MPO were found to be significantly elevated in IFG group and both correlates significantly with IR (r 0.413, r 0.645). Only MPO had significant correlation with FPG (r 0.388). In conclusion, the association of altered levels of IL-6 and MPO with IR are suggestive of a role of inflammation and oxidative stress in the initiation and progression of IR in individuals with IFG.

Expression of cardiac insulin signalling genes and proteins in rats fed a high-sucrose diet: effect of bilberry anthocyanin extract

Scope

Insulin resistance is associated with impaired cardiac function, but the underlying molecular abnormalities are largely unexplained. Bilberry anthocyanin (BAcn) may be protective, as it appears to potentiate insulin action.

Methods

Rats were randomly allocated to control, sucrose-fed (SF) or sucrose-fed + BAcn diets (SF-A) for 15 weeks. Cardiac insulin signalling genes and proteins were quantified using reverse transcription quantitative real-time polymerase chain reaction and western blots.

Results

Glucose tolerance was not different with treatment. SF showed lower (p < 0.05) ferric reducing antioxidant power, which increased with BAcn. SF resulted in significantly decreased (p < 0.05) expression of 10 genes: acetyl-coenzyme A carboxylase alpha; V-Akt murine thymoma viral oncogene homolog 1; Bcl2-like 1; cytosine-cytosine-adenosine-adenosine-thymidine/enhancer binding protein; FK506 binding protein 12-rapamycin associated; glycerol-3-phosphate dehydrogenase 1 (soluble); solute carrier family 2 (facilitated glucose transporter), member 1, 4; hexokinase 2; and thyroglobulin. SF-A prevented these changes. Compared to SF-A, SF up-regulated (p < 0.05) complement factor D and phosphoinositide-3-kinase, regulatory subunit1 (α); sterol regulatory element binding transcription factor 1 was down-regulated (p < 0.05). SF increased (p < 0.05) cardiac phospholamban and decreased phosphorylated troponin I, which were not attenuated by BAcn. Compared to control or SF, SF-A resulted in significantly lower (p < 0.05) 5′-AMP-activated protein kinase.

Conclusions

SF lowered antioxidant capacity and changed the expression of insulin signalling genes, which were modulated by BAcn.

Effect of Cosmos caudatus (Ulam raja) supplementation in patients with type 2 diabetes: Study protocol for a randomized controlled trial

BACKGROUND

Type 2 diabetes mellitus is a major health threat worldwide. Cosmos caudatus is one of the medicinal plants used to treat type 2 diabetes. Therefore, this study aims to determine the effectiveness and safety of C. caudatus in patients with type 2 diabetes. Metabolomic approach will be carried out to compare the metabolite profiles between C. Caudatus treated diabetic patients and diabetic controls.

METHODS AND DESIGN

This is a single-center, randomized, controlled, two-arm parallel design clinical trial that will be carried out in a tertiary hospital in Malaysia. In this study, 100 patients diagnosed with type 2 diabetes will be enrolled. Diabetic patients who meet the eligibility criteria will be randomly allocated to two groups, which are diabetic C. caudatus treated(U) group and diabetic control (C) group. Primary and secondary outcomes will be measured at baseline, 4, 8, and 12 weeks. The serum and urine metabolome of both groups will be examined using proton NMR spectroscopy.

DISCUSSION

The study will be the first randomized controlled trial to assess whether C. caudatus can confer beneficial effect in patients with type 2 diabetes. The results of this trial will provide clinical evidence on the effectiveness and safety of C. caudatus in patients with type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02322268.

Effects of Melatonin on Oxidative Stress Index and Alveolar Bone Loss in Diabetic Rats With Periodontitis

BACKGROUND

The aim of this study is to evaluate the effects of systemic melatonin treatment on serum oxidative stress index (OSI) and alveolar bone loss (ABL) in rats with diabetes mellitus (DM) and periodontitis.

METHODS

Seventy Sprague Dawley rats were divided into control, experimentally induced periodontitis (EP), DM, EP-DM, EP and melatonin treatment (EP-MEL), DM and melatonin treatment (DMMEL), and EP-DM-MEL groups. DM was induced by alloxan, after which periodontitis was induced by ligature for 4 weeks. After removal of the ligature, the rats in the melatonin groups (EP-MEL, DM-MEL, and EP-DM-MEL) were treated with a single dose of melatonin (10 mg/body weight) every day for 14 consecutive days. At the end of the study, all of the rats were euthanized, and intracardiac blood samples and mandible tissues were obtained for biochemical and histologic analyses. Serum levels of total oxidant status/total antioxidant status and OSI were measured. In addition, neutrophil and osteoclast densities and myeloperoxidase activities were determined in gingival tissue homogenates, and ABL was evaluated with histometric measurements.

RESULTS

Melatonin treatment significantly reduced fasting plasma glucose levels in the rats with DM. In addition, reduced OSI and ABL levels were detected in the EP-MEL and DM-MEL groups; the reductions in the EP-DM-MEL group were found to be more prominent. Melatonin also significantly decreased the increased myeloperoxidase activities and osteoclast and neutrophil densities in the EP, DM, and EP-DM groups.

CONCLUSION

It is revealed in this experimental study that melatonin significantly inhibited hyperglycemia-induced oxidative stress and ABL through antiDM and antioxidant effects in rats with DM and periodontitis.

Mitochondrial-generated ROS down regulates insulin signaling via activation of the p38MAPK stress response pathway

Impairment of insulin signaling and hepatic insulin resistance has been attributed to ROS-mediated activation of p38MAPK stress response signaling. Our research focused on whether (a) ROS generated by mitochondrial electron transport chain complex I (ETC-CI) dysfunction, via the use of Rotenone, inactivates insulin signaling; and (b) the p38MAPK pathway is involved in the ROS-induced impairment of insulin signaling. Our results show that in primary mouse hepatocytes the CI inhibitor, Rotenone, (a) induces IRS-1 Ser(307) phosphorylation that is blocked by the anti-oxidant NAC or by the p38MAPK inhibitors, SB203580 and SB202190; (b) inhibits insulin-stimulated AKT-Ser(473) and GSK3β-Ser(9) phosphorylations, in a manner that is not responsive to reversal by the anti-oxidant NAC or by the p38MAPK inhibitors, SB203580 and SB202190. We conclude that rotenone-induced insulin resistance involves a p38MAPK-dependent mechanism for the inhibition of the proximal end of insulin signaling (IRS1), and a p38MAPK-independent mechanism for the inhibition of the distal end (AKT and GSK3β). Our study suggests that ROS generated by inhibition of ETC CI, promotes hepatic insulin resistance partly via activation of the p38MAPK stress-response pathway.

Antidiabetic Effects of Resveratrol: The Way Forward in Its Clinical Utility

Despite recent advances in the understanding and management of diabetes mellitus, the prevalence of the disease is increasing unabatedly with resulting disabling and life-reducing consequences to the global human population. The limitations and side effects associated with current antidiabetic therapies have necessitated the search for novel therapeutic agents. Due to the multipathogenicity of diabetes mellitus, plant-derived compounds with proven multiple pharmacological actions have been postulated to "hold the key" in the search for an affordable, efficacious, and safer therapeutic agent in the treatment of the disease and associated complications. Resveratrol, a phytoalexin present in few plant species, has demonstrated beneficial antidiabetic effects in animals and humans through diverse mechanisms and multiple molecular targets. However, despite the enthusiasm and widespread successes achieved with the use of resveratrol in animal models of diabetes mellitus, there are extremely limited clinical data to confirm the antidiabetic qualities of resveratrol. This review presents an update on the mechanisms of action and protection of resveratrol in diabetes mellitus, highlights challenges in its clinical utility, and suggests the way forward in translating the promising preclinical data to a possible antidiabetic drug in the near future.

Role of Superoxide Dismutase 2 Gene Ala16Val Polymorphism and Total Antioxidant Capacity in Diabetes and its Complications

Diabetes Mellitus (DM) is a chronic heterogeneous disorder and oxidative stress is a key participant in the development and progression of it and its complications. Anti-oxidant status can affect vulnerability to oxidative damage, onset and progression of diabetes and diabetes complications. Superoxide dismutase 2 (SOD2) is one of the major antioxidant defense systems against free radicals. SOD2 is encoded by the nuclear SOD2 gene located on the human chromosome 6q25 and the Ala16Val polymorphism has been identified in exon 2 of the human SOD2 gene. Ala16Val (rs4880) is the most commonly studied SOD2 single nucleotide polymorphism (SNP) in SOD2 gene. This SNP changes the amino acid at position 16 from valine (Val) to alanine (Ala), which has been shown to cause a conformational change in the target sequence of manganese superoxide dismutase (MnSOD) and also affects MnSOD activity in mitochondria. Ala16Val SNP and changes in the activity of the SOD2 antioxidant enzyme have been associated with altered progression and risk of different diseases. Association of this SNP with diabetes and some of its complications have been studied in numerous studies. This review evaluated how rs4880, oxidative stress and antioxidant status are associated with diabetes and its complications although some aspects of this line still remain unclear.

Cichoric Acid Reverses Insulin Resistance and Suppresses Inflammatory Responses in the Glucosamine-Induced HepG2 Cells

Cichoric acid, a caffeic acid derivative found in Echinacea purpurea, basil, and chicory, has been reported to have bioactive effects, such as anti-inflammatory, antioxidant, and preventing insulin resistance. In this study, to explore the effects of CA on regulating insulin resistance and chronic inflammatory responses, the insulin resistance model was constructed by glucosamine in HepG2 cells. CA stimulated glucosamine-mediated glucose uptake by stimulating translocation of the glucose transporter 2. Moreover, the production of reactive oxygen, the expression of COX-2 and iNOS, and the mRNA levels of TNF-α and IL-6 were attenuated. Furthermore, CA was verified to promote glucosamine-mediated glucose uptake and inhibited inflammation through PI3K/Akt, NF-κB, and MAPK signaling pathways in HepG2 cells. These results implied that CA could increase glucose uptake, improve insulin resistance, and attenuate glucosamine-induced inflammation, suggesting that CA is a potential natural nutraceutical with antidiabetic properties and anti-inflammatory effects.

Eight Weeks of Cosmos caudatus (Ulam Raja) Supplementation Improves Glycemic Status in Patients with Type 2 Diabetes: A Randomized Controlled Trial

Objectives. Optimizing glycemic control is crucial to prevent type 2 diabetes related complications. Cosmos caudatus is reported to have promising effect in improving plasma blood glucose in an animal model. However, its impact on human remains ambiguous. This study was carried out to evaluate the effectiveness of C. caudatus on glycemic status in patients with type 2 diabetes. Materials and Methods. In this randomized controlled trial with two-arm parallel-group design, a total of 101 subjects with type 2 diabetes were randomly allocated to diabetic-ulam or diabetic controls for eight weeks. Subjects in diabetic-ulam group consumed 15 g of C. caudatus daily for eight weeks while diabetic controls abstained from taking C. caudatus. Both groups received the standard lifestyle advice. Results. After 8 weeks of supplementation, C. caudatus significantly reduced serum insulin (-1.16 versus +3.91), reduced HOMA-IR (-1.09 versus +1.34), and increased QUICKI (+0.05 versus -0.03) in diabetic-ulam group compared with the diabetic controls. HbA1C level was improved although it is not statistically significant (-0.76% versus -0.37%). C. caudatus was safe to consume. Conclusions. C. caudatus supplementation significantly improves insulin resistance and insulin sensitivity in patients with type 2 diabetes.

Exogenous spermine ameliorates high glucose-induced cardiomyocytic apoptosis via decreasing reactive oxygen species accumulation through inhibiting p38/JNK and JAK2 pathways

Reactive oxygen species (ROS) generation has been suggested to play a vital role in the initiation and progression of diabetic cardiomyopathy, a major complication of diabetes mellitus. Recent studies reveal that spermine possesses proliferative, antiaging and antioxidative properties. Thus, we hypothesized that spermine could decrease apoptosis via suppressing ROS accumulation induced by high glucose (HG) in cardiomyocytes. Cultured neonatal rat ventricle cardiomyocytes were treated with normal glucose (NG) (5 mM) or HG (25 mM) in the presence or absence of spermine for 48 h. The cell activity, apoptosis, ROS production, T-SOD and GSH activities, MDA content and GSSG level were assessed. The results showed that HG induced lipid peroxidation and the increase of intracellular ROS formation and apoptosis in primary cardiomyocytes. Spermine could obviously improve the above-mentioned changes. Western blot analysis revealed that spermine markedly inhibited HG-induced the phosphorylation of p38/JNK MAPKs and JAK2. Moreover, spermine had better antioxidative and anti-apoptotic effects than N-acetyl-L-cysteine (NAC). Taken together, the present data suggested that spermine could suppress ROS accumulation to decrease cardiomyocytes apoptosis in HG condition, which may be attributed to the inhibition of p38/JNK and JAK2 activation and its natural antioxidative property. Our findings may highlight a new therapeutic intervention for the prevention of diabetic cardiomyopathy.

Impact of morbid obesity and bariatric surgery on antioxidant/oxidant balance of the unstimulated and stimulated human saliva

OBJECTIVE

There is no study evaluating the influence of morbid obesity and bariatric surgery on antioxidant/oxidant homeostasis of the unstimulated and stimulated human saliva.

MATERIALS AND METHODS

Salivary flow rate, total antioxidant status (TAS), total oxidant status (TOS), oxidative status index (OSI), the total amount of uric acid (UA), polyphenols (pPh), catalase (CAT), superoxide dismutase 2 (SOD2), specific activity of peroxidase (Px), as well as malondialdehyde (MDA), and advanced glycation end products (AGE) concentrations were determined in the unstimulated (UWS) and stimulated (SWS) whole saliva of patients with morbid obesity before and after bariatric surgery.

RESULTS

In both UWS and SWS, the total amount of TOS, OSI, SOD2, and MDA was statistically higher in patients with morbid obesity as compared to the healthy controls, as well as significantly lower in the patients treated surgically as compared to the obese patients. The median values of the total amount of TAS, CAT, UA, pPh, and specific activity of Px were significantly reduced in UWS and SWS in patients with morbid obesity as compared to the control group and also statistically elevated in patients after bariatric surgery as compared to the patients with morbid obesity.

CONCLUSIONS

In morbid obesity, reduced unstimulated and stimulated salivary flow can be observed. Bariatric surgery restored only unstimulated salivary flow to normal values. Disturbances in oxidant/antioxidant homeostasis may be observed in UWS and SWS of obese patients before and after treatment.

Dynamic differences in oxidative stress and the regulation of metabolism with age in visceral versus subcutaneous adipose

Once thought only as storage for excess nutrients, adipose tissue has been shown to be a dynamic organ implicated in the regulation of many physiological processes. There is emerging evidence supporting differential roles for visceral and subcutaneous white adipose tissue in maintaining health, although how these roles are modulated by the aging process is not clear. However, the proposed beneficial effects of subcutaneous fat suggest that targeting maintenance of this tissue could lead to healthier aging. In this study, we tested whether alterations in adipose function with age might be associated with changes in oxidative stress. Using visceral and subcutaneous adipose from C57BL/6 mice, we discovered effects of both age and depot location on markers of lipolysis and adipogenesis. Conversely, accumulation of oxidative damage and changes in enzymatic antioxidant expression with age were largely similar between these two depots. The activation of each of the stress signaling pathways JNK and MAPK/ERK was relatively suppressed in subcutaneous adipose tissue suggesting reduced sensitivity to oxidative stress. Similarly, pre-adipocytes from subcutaneous adipose were significantly more resistant than visceral-derived cells to cell death caused by oxidative stress. Cellular respiration in visceral-derived cells was dramatically higher than in cells derived from subcutaneous adipose despite little evidence for differences in mitochondrial density. Together, our data identify molecular mechanisms by which visceral and subcutaneous adipose differ with age and suggest potential targetable means to preserve healthy adipose aging.

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Aging alters metabolism differently in C57BL/6 visceral and subcutaneous fat.

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Oxidative stress and antioxidants show little difference between these fat depots.

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Age-induced activation of JNK and ERK/MAPK is elevated in visceral fat.

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Preadipocytes from visceral fat have relatively higher metabolic rate.

Pristanic acid provokes lipid, protein, and DNA oxidative damage and reduces the antioxidant defenses in cerebellum of young rats

Zellweger syndrome (ZS) and some peroxisomal diseases are severe inherited disorders mainly characterized by neurological symptoms and cerebellum abnormalities, whose pathogenesis is poorly understood. Biochemically, these diseases are mainly characterized by accumulation of pristanic acid (Prist) and other fatty acids in the brain and other tissues. In this work, we evaluated the in vitro influence of Prist on redox homeostasis by measuring lipid, protein, and DNA damage, as well as the antioxidant defenses and the activities of aconitase and α-ketoglutarate dehydrogenase in cerebellum of 30-day-old rats. The effect of Prist on DNA damage was also evaluated in blood of these animals. Some parameters were also evaluated in cerebellum from neonatal rats and in cerebellum neuronal cultures. Prist significantly increased malondialdehyde (MDA) levels and carbonyl formation and reduced sulfhydryl content and glutathione (GSH) concentrations in cerebellum of young rats. It also caused DNA strand damage in cerebellum and induced a high micronuclei frequency in blood. On the other hand, this fatty acid significantly reduced α-ketoglutarate dehydrogenase and aconitase activities in rat cerebellum. We also verified that Prist-induced increase of MDA levels was totally prevented by melatonin and attenuated by α-tocopherol but not by the nitric oxide synthase inhibitor N(ω)-nitro-L-arginine methyl ester, indicating the involvement of reactive oxygen species in this effect. Cerebellum from neonate rats also showed marked alterations of redox homeostasis, including an increase of MDA levels and a decrease of sulfhydryl content and GSH concentrations elicited by Prist. Finally, Prist provoked an increase of dichlorofluorescein (DCFH) oxidation in cerebellum-cultivated neurons. Our present data indicate that Prist compromises redox homeostasis in rat cerebellum and blood and inhibits critical enzymes of the citric acid cycle that are susceptible to free radical attack. The present findings may contribute to clarify the pathogenesis of the cerebellar alterations observed in patients affected by ZS and some peroxisomal disorders in which Prist is accumulated.

The mitochondria in diabetic heart failure: from pathogenesis to therapeutic promise

SIGNIFICANCE

Diabetes is an important risk factor for the development of heart failure (HF). Given the increasing prevalence of diabetes in the population, strategies are needed to reduce the burden of HF in these patients.

RECENT ADVANCES

Diabetes is associated with several pathologic findings in the heart including dysregulated metabolism, lipid accumulation, oxidative stress, and inflammation. Emerging evidence suggests that mitochondrial dysfunction may be a central mediator of these pathologic responses. The development of therapeutic approaches targeting mitochondrial biology holds promise for the management of HF in diabetic patients.

CRITICAL ISSUES

Despite significant data implicating mitochondrial pathology in diabetic cardiomyopathy, the optimal pharmacologic approach to improve mitochondrial function remains undefined.

FUTURE DIRECTIONS

Detailed mechanistic studies coupled with more robust clinical phenotyping will be necessary to develop novel approaches to improve cardiac function in diabetes. Moreover, understanding the interplay between diabetes and other cardiac stressors (hypertension, ischemia, and valvular disease) will be of the utmost importance for clinical translation of scientific discoveries made in this field.

Protective mechanisms of mitochondria and heart function in diabetes

SIGNIFICANCE

The heart depends on continuous mitochondrial ATP supply and maintained redox balance to properly develop force, particularly under increased workload. During diabetes, however, myocardial energetic-redox balance is perturbed, contributing to the systolic and diastolic dysfunction known as diabetic cardiomyopathy (DC).

CRITICAL ISSUES

How these energetic and redox alterations intertwine to influence the DC progression is still poorly understood. Excessive bioavailability of both glucose and fatty acids (FAs) play a central role, leading, among other effects, to mitochondrial dysfunction. However, where and how this nutrient excess affects mitochondrial and cytoplasmic energetic/redox crossroads remains to be defined in greater detail.

RECENT ADVANCES

We review how high glucose alters cellular redox balance and affects mitochondrial DNA. Next, we address how lipid excess, either stored in lipid droplets or utilized by mitochondria, affects performance in diabetic hearts by influencing cardiac energetic and redox assets. Finally, we examine how the reciprocal energetic/redox influence between mitochondrial and cytoplasmic compartments shapes myocardial mechanical activity during the course of DC, focusing especially on the glutathione and thioredoxin systems.

FUTURE DIRECTIONS

Protecting mitochondria from losing their ability to generate energy, and to control their own reactive oxygen species emission is essential to prevent the onset and/or to slow down DC progression. We highlight mechanisms enforced by the diabetic heart to counteract glucose/FAs surplus-induced damage, such as lipid storage, enhanced mitochondria-lipid droplet interaction, and upregulation of key antioxidant enzymes. Learning more on the nature and location of mechanisms sheltering mitochondrial functions would certainly help in further optimizing therapies for human DC.

Obesity and Insulin Resistance Are the Central Issues in Prevention of and Care for Comorbidities

For a long time the assumption has been that, although weight reduction was necessary and desirable, comorbidities were far more important and needed treatment even if weight loss was not a treatment goal, preferably with medication. This controversy leads to postponement of treatment, and later on causes very intensive medical treatment, thus, raising the health care costs to unacceptable levels, leading to the medicalization of individuals, and a declining of the responsibility of patients for their health, leaving the question of when to regard their own weight as a problem that should be dealt with up to individuals. The central problem is insulin resistance, which leads to a cascade of health problems. This condition should be diagnosed in primary practice and obesity clinics to ensure a better, tailor-made treatment for patients. Treatment should start at the earliest stage possible, when comorbidities are still reversible and includes a personalized dietary advice and counseling, preferably by a dietitian, to tackle insulin resistance. An exercise program is part of the treatment.

The Labile Side of Iron Supplementation in CKD

The practice of intravenous iron supplementation has grown as nephrologists have gradually moved away from the liberal use of erythropoiesis-stimulating agents as the main treatment for the anemia of CKD. This approach, together with the introduction of large-dose iron preparations, raises the future specter of inadvertent iatrogenic iron toxicity. Concerns have been raised in original studies and reviews about cardiac complications and severe infections that result from long-term intravenous iron supplementation. Regarding the iron preparations specifically, even though all the currently available preparations appear to be relatively safe in the short term, little is known regarding their long-term safety. In this review we summarize current knowledge of iron metabolism with an emphasis on the sources and potentially harmful effects of labile iron, highlight the approaches to identifying labile iron in pharmaceutical preparations and body fluids and its potential toxic role as a pathogenic factor in the complications of CKD, and propose methods for its early detection in at-risk patients.

Neutrophil functions in morbidly obese subjects

The present study aimed to determine different peripheral blood neutrophil functions in 18 morbidly obese subjects with body mass index (BMI) ranging between 35 and 69 kg/m(2) in parallel with age- and gender-matched lean controls. Peripheral blood neutrophil functions of obese subjects and matched lean controls were determined. Neutrophils of obese subjects showed significant elevation of the release of basal superoxides (P < 0.0001), formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated superoxides (P < 0.0001) and opsonized zymosan (OZ)-stimulated superoxides (P < 0.045) compared with lean controls. Interestingly, there were no differences in phorbol myristate acetate (PMA)-stimulated superoxide production by neutrophils of the obese subjects and controls. There was also a significant elevation of chemotactic (P < 0.0003) and random (P < 0.0001) migration of neutrophils from obese subjects compared with lean controls. Phagocytosis, CD11b surface expression and adherence of neutrophils from obese subjects were not significantly different from those of the lean controls. The elevated superoxide production and chemotactic activity, together with the normal phagocytosis and adherence, suggest that neutrophils from obese subjects are primed and have the capability to combat infections. However, neutrophils in the priming state may participate in the pathogenesis of obesity-related diseases.

Assessment of benzene induced oxidative impairment in rat isolated pancreatic islets and effect on insulin secretion

Benzene (C6H6) is an organic compound used in petrochemicals and numerous other industries. It is abundantly released to our environment as a chemical pollutant causing widespread human exposure. This study mainly focused on benzene induced toxicity on rat pancreatic islets with respect to oxidative damage, insulin secretion and glucokinase (GK) activity. Benzene was dissolved in corn oil and administered orally at doses 200, 400 and 800mg/kg/day, for 4 weeks. In rats, benzene significantly raised the concentration of plasma insulin. Also the effect of benzene on the release of glucose-induced insulin was pronounced in isolated islets. Benzene caused oxidative DNA damage and lipid peroxidation, and also reduced the cell viability and total thiols groups, in the islets of exposed rats. In conclusion, the current study revealed that pancreatic glucose metabolism is susceptible to benzene toxicity and the resultant oxidative stress could lead to functional abnormalities in the pancreas.

Resveratrol protects PC12 cells from high glucose-induced neurotoxicity via PI3K/Akt/FoxO3a pathway

Diabetes is known to be associated with neurodegenerative diseases. Resveratrol, a plant-derived polyphenolic compound found in red wine, possesses antioxidant properties. In this study, we aimed to investigate the effects of resveratrol on the phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt)/FoxO3a pathway in mediating high glucose (HG)-induced injuries in neuronal PC12 cells. PC12 cells were exposed to HG to establish a model of HG neurotoxicity. Results showed that pre-treating PC12 cells with resveratrol before exposure to HG led to increased cell viability, decreased apoptotic cells, and reactive oxygen species generation. Western blot analysis showed that HG decreased the phosphorylation of Akt and FoxO3a and led to the nuclear localization of FoxO3a. These effects were significantly alleviated by resveratrol co-treatment. Furthermore, the protective effects of resveratrol were abolished by PI3K/Akt inhibitor LY294002. All these results demonstrate that resveratrol protected the PC12 cells from HG-induced oxidative stress and apoptosis via the activation of PI3K/Akt/FoxO3a signaling pathway.

SR-135, a peroxynitrite decomposing catalyst, enhances β-cell function and survival in B6D2F1 mice fed a high fat diet

Peroxynitrite has been implicated in β-cell dysfunction and insulin resistance in obesity. Chemical catalysts that destroy peroxynitrite, therefore, may have therapeutic value for treating type 2 diabetes. To this end, we have recently demonstrated that Mn(III) bis(hydroxyphenyl)-dipyrromethene complexes, SR-135 and its analogs, can effectively catalyze the decomposition of peroxynitrite in vitro and in vivo through a 2-electron mechanism (Rausaria et al., 2011). To study the effects of SR-135 on glucose homeostasis in obesity, B6D2F1 mice were fed with a high fat-diet (HFD) for 12 weeks and treated with vehicle, SR-135 (5mg/kg), or a control drug SRB for 2 weeks. SR-135 significantly reduced fasting blood glucose and insulin levels, and enhanced glucose tolerance as compared to HFD control, vehicle or SRB. SR-135 also enhanced glucose-stimulated insulin secretion based on ex vivo studies. Moreover, SR-135 increased insulin content, restored islet architecture, decreased islet size, and reduced tyrosine nitration and apoptosis. These results suggest that a peroxynitrite decomposing catalyst enhances β-cell function and survival under nutrient overload.

Endoplasmic reticulum stress and Nrf2 repression in circulating cells of type 2 diabetic patients without the recommended glycemic goals

Endoplasmic reticulum (ER) stress plays a role in the pathogenesis of type 2 diabetes mellitus (T2DM), with activation of the unfolded protein response (UPR) and ER apoptosis in β-cells. The aim of the study is investigating the role of the prolonged glycemic, inflammatory, and oxidative impairment as possible UPR and ER apoptosis inductors in triggering the ER stress response and the protective nuclear erythroid-related factor 2 (Nrf2)/antioxidant-related element (ARE) activation in peripheral blood mononuclear cells (PBMC) of T2DM patients without glycemic target. Oxidative stress markers (oxidation product of phospholipid 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine [oxPAPC], and malondialdehyde [MDA]), the UPR and ER apoptosis, the activation of the pro-inflammatory nuclear factor-kappa B (NF-kB) with its inhibitory protein inhibitor-kBα, and the expression of the protective Nrf2 and heme oxygenase-1 (HO-1) were evaluated in PBMC of 15 T2DM patients and 15 healthy controls (C). OxPAPC concentrations (in PBMC and plasma), MDA levels (in plasma), the expressions of the glucose-regulated protein 78 kDa (or BiP) as representative of UPR, and of the CCAAT/enhancer-binding protein homologous protein as representative of ER apoptosis were significantly higher (p < 0.01) in T2DM with respect to C. IkBα expression was significantly lower (p < 0.01) in T2DM as well as Nrf2 and HO-1. In vitro experiments demonstrated that hyperglycemic conditions, if prolonged, were NF-kB inductors, without a corresponding Nrf2/ARE response. In PBMC of T2DM without glycemic target achievement, there is an activation of the UPR and of the ER apoptosis, which may be related to the chronic exposure to hyperglycemia, to the augmented inflammation, and to the augmented oxidative stress, without a corresponding Nrf2/ARE defense activation.

Potent effects of the total saponins from Dioscorea nipponica Makino against streptozotocin-induced type 2 diabetes mellitus in rats

The aim of the present paper was to investigate the effects and possible mechanisms of the total saponins from Dioscorea nipponica Makino (TSDN) against type 2 diabetes mellitus. Streptozotocin (STZ) with high-fat diet induced type 2 diabetes mellitus (T2DM) rats were treated with TSDN. Some biochemical parameters, target proteins and genes were investigated. The results showed that TSDN decreased the levels of food/water intake, fasting blood glucose and serum lipid parameters, ameliorated oral glucose and insulin tolerance test levels, markedly increased body weight and serum insulin, reduced excess free radicals and affected ossification and renal protection. Histopathological examination indicated that TSDN increased liver glycogen, decreased the production of lipid vacuoles and lightened liver damage. Further investigation showed that TSDN down-regulated the protein expressions of NF-κB, GRP78, ATF6, eIF2 and the levels of MAPK phosphorylation and up-regulated the protein expressions of IRS-1, GLUT-4, p-Akt and p-AMPK. In addition, TSDN obviously decreased the gene expressions of TNF-a, IL-6, PEPCK, G6Pase, GSK-3β and GSK-3β activity, and increased the gene expressions of PFK, PK and GK activity. These findings show the anti-diabetic activity of total saponins from D. nipponica Makino, which should be developed as a new potent drug for treatment of diabetes mellitus in future.

Adaptive phylogeography: functional divergence between haemoglobins derived from different glacial refugia in the bank vole

Over the years, researchers have used presumptively neutral molecular variation to infer the origins of current species' distributions in northern latitudes (especially Europe). However, several reported examples of genic and chromosomal replacements suggest that end-glacial colonizations of particular northern areas may have involved genetic input from different source populations at different times, coupled with competition and selection. We investigate the functional consequences of differences between two bank vole (Clethrionomys glareolus) haemoglobins deriving from different glacial refugia, one of which partially replaced the other in Britain during end-glacial climate warming. This allows us to examine their adaptive divergence and hence a possible role of selection in the replacement. We determine the amino acid substitution Ser52Cys in the major expressed β-globin gene as the allelic difference. We use structural modelling to reveal that the protein environment renders the 52Cys thiol a highly reactive functional group and we show its reactivity in vitro. We demonstrate that possessing the reactive thiol in haemoglobin increases the resistance of bank vole erythrocytes to oxidative stress. Our study thus provides striking evidence for physiological differences between products of genic variants that spread at the expense of one another during colonization of an area from different glacial refugia.