Suppression of NADPH oxidase 2 substantially restores glucose-induced dysfunction of pancreatic NIT-1 cells

NMDA receptors - regulatory function and pathophysiological significance for pancreatic beta cells

Due to its unique features amongst ionotropic glutamate receptors, the NMDA receptor is of special interest in the physiological context but even more as a drug target. In the pathophysiology of metabolic disorders, particularly type 2 diabetes mellitus, there is evidence that NMDA receptor activation contributes to disease progression by impairing beta cell function. Consequently, channel inhibitors are suggested for treatment, but up to now there are many unanswered questions about the signaling pathways NMDA receptors are interfering with in the islets of Langerhans. In this review we give an overview about channel structure and function with special regard to the pancreatic beta cells and the regulation of insulin secretion. We sum up which signaling pathways from brain research have already been transferred to the beta cell, and what still needs to be proven. The main focus is on the relationship between an over-stimulated NMDA receptor and the production of reactive oxygen species, the amount of which is crucial for beta cell function. Finally, pilot studies using NMDA receptor blockers to protect the islet from dysfunction are reviewed and future perspectives for the use of such compounds in the context of impaired glucose homeostasis are discussed.

MiR-190 ameliorates glucotoxicity-induced dysfunction and apoptosis of pancreatic β-cells by inhibiting NOX2-mediated reactive oxygen species production

Glucotoxicity-induced pancreatic β-cell failure contributes to the development of type 2 diabetes mellitus (T2DM). Accumulating evidence reveals that miRNAs play a critical role in regulating pancreatic β-cell function and survival. In this study, we employed a self-assembled cell microarray (SAMcell)-based functional screening assay to identify miRNAs that are capable of regulating the dysfunction of β-cells induced by glucotoxicity. Among 62 conserved miRNAs we tested, miR-190 was identified as a candidate regulator that could effectively restore insulin expression in NIT-1 cells under high-glucose (HG) stimulation. Further analyses demonstrated that miR-190 was significantly down-regulated in HG-treated NIT-1 cells, as well as in the pancreas of diabetic mice. Mechanistic studies showed that Cybb is the direct target gene of miR-190, which encodes the gp91phox protein, a subunit of the NOX2 complex. Furthermore, both miR-190 overexpression and Cybb knockdown inhibited apoptosis and improved glucose-stimulated insulin secretion (GSIS) in HG-stimulated NIT-1 cells by attenuating the excessive production of reactive oxygen species (ROS). More importantly, a targeted delivery of mPEG-PCL-g-PDMAEMA nanoparticles/miR-190 complexes (PECgD NPs/miR-190) to the pancreas significantly ameliorated hyperglycemia, decreased fasting serum insulin levels, and improved glucose tolerance in diabetic mice. Taken together, our findings suggest that the miR-190/Cybb axis plays an important role in glucotoxicity-induced pancreatic β-cell failure. Restoring miR-190 expression levels may be a possible therapeutic strategy to protect β-cells in T2DM.

New Advances on Pathophysiology of Diabetes Neuropathy and Pain Management: Potential Role of Melatonin and DPP-4 Inhibitors

Pre-diabetes and diabetes are growing threats to the modern world. Diabetes mellitus (DM) is associated with comorbidities such as hypertension (83.40%), obesity (90.49%), and dyslipidemia (93.43%), creating a substantial burden on patients and society. Reductive and oxidative (Redox) stress level imbalance and inflammation play an important role in DM progression. Various therapeutics have been investigated to treat these neuronal complications. Melatonin and dipeptidyl peptidase IV inhibitors (DPP-4i) are known to possess powerful antioxidant and anti-inflammatory properties and have garnered significant attention in the recent years. In this present review article, we have reviewed the recently published reports on the therapeutic efficiency of melatonin and DPP-4i in the treatment of DM. We summarized the efficacy of melatonin and DPP-4i in DM and associated complications of diabetic neuropathy (DNP) and neuropathic pain. Furthermore, we discussed the mechanisms of action and their efficacy in the alleviation of oxidative stress in DM.

Lipotoxicity and β-Cell Failure in Type 2 Diabetes: Oxidative Stress Linked to NADPH Oxidase and ER Stress

A high caloric intake, rich in saturated fats, greatly contributes to the development of obesity, which is the leading risk factor for type 2 diabetes (T2D). A persistent caloric surplus increases plasma levels of fatty acids (FAs), especially saturated ones, which were shown to negatively impact pancreatic β-cell function and survival in a process called lipotoxicity. Lipotoxicity in β-cells activates different stress pathways, culminating in β-cells dysfunction and death. Among all stresses, endoplasmic reticulum (ER) stress and oxidative stress have been shown to be strongly correlated. One main source of oxidative stress in pancreatic β-cells appears to be the reactive oxygen species producer NADPH oxidase (NOX) enzyme, which has a role in the glucose-stimulated insulin secretion and in the β-cell demise during both T1 and T2D. In this review, we focus on the acute and chronic effects of FAs and the lipotoxicity-induced β-cell failure during T2D development, with special emphasis on the oxidative stress induced by NOX, the ER stress, and the crosstalk between NOX and ER stress.

Effects of Propolis Extract and Propolis-Derived Compounds on Obesity and Diabetes: Knowledge from Cellular and Animal Models

Propolis is a natural product resulting from the mixing of bee secretions with botanical exudates. Since propolis is rich in flavonoids and cinnamic acid derivatives, the application of propolis extracts has been tried in therapies against cancer, inflammation, and metabolic diseases. As metabolic diseases develop relatively slowly in patients, the therapeutic effects of propolis in humans should be evaluated over long periods of time. Moreover, several factors such as medical history, genetic inheritance, and living environment should be taken into consideration in human studies. Animal models, especially mice and rats, have some advantages, as genetic and microbiological variables can be controlled. On the other hand, cellular models allow the investigation of detailed molecular events evoked by propolis and derivative compounds. Taking advantage of animal and cellular models, accumulating evidence suggests that propolis extracts have therapeutic effects on obesity by controlling adipogenesis, adipokine secretion, food intake, and energy expenditure. Studies in animal and cellular models have also indicated that propolis modulates oxidative stress, the accumulation of advanced glycation end products (AGEs), and adipose tissue inflammation, all of which contribute to insulin resistance or defects in insulin secretion. Consequently, propolis treatment may mitigate diabetic complications such as nephropathy, retinopathy, foot ulcers, and non-alcoholic fatty liver disease. This review describes the beneficial effects of propolis on metabolic disorders.

Calcium Ion Induced Structural Changes Promote Dimerization of Secretagogin, Which Is Required for Its Insulin Secretory Function

Secretagogin (SCGN), a hexa EF-hand calcium binding protein, plays key roles in insulin secretion in pancreatic β-cells. It is not yet understood how the binding of Ca²⁺ to human SCGN (hSCGN) promotes secretion. Here we have addressed this question, using mass spectrometry combined with a disulfide searching algorithm DBond. We found that the binding of Ca²⁺ to hSCGN promotes the dimerization of hSCGN via the formation of a Cys193-Cys193 disulfide bond. Hydrogen/deuterium exchange mass spectrometry (HDX-MS) and molecular dynamics studies revealed that Ca²⁺ binding to the EF-hands of hSCGN induces significant structural changes that affect the solvent exposure of N-terminal region, and hence the redox sensitivity of the Cys193 residue. These redox sensitivity changes were confirmed using biotinylated methyl-3-nitro-4-(piperidin-1-ylsulfonyl) benzoate (NPSB-B), a chemical probe that specifically labels reactive cysteine sulfhydryls. Furthermore, we found that wild type hSCGN overexpression promotes insulin secretion in pancreatic β cells, while C193S-hSCGN inhibits it. These findings suggest that insulin secretion in pancreatic cells is regulated by Ca²⁺ and ROS signaling through Ca²⁺-induced structural changes promoting dimerization of hSCGN.

Decreased paraoxonase 2 enzymatic activity in monocyte/macrophages cells. A comparative in vivo and in vitro study for diabetes

AIM

To investigate peripheral blood monocytes/macrophages (Mo/Mᴓ) paraoxonase 2 (PON2) in diabetes and the factors modulating its activity.

METHODS

One hundred and eighteen patients with newly diagnosed uncomplicated type 2 diabetes mellitus were compared regarding clinical, biochemical and oxidative stress parameters with 80 healthy subjects. The capacity of the peripheral blood mononuclear cells (PBMNC) to release pro-oxidants and to neutralise them was determined by measuring the respiratory burst (RB) and the intracellular antioxidant enzyme PON2. In vitro experiments were conducted on a differentiated monocytes cell line (dU937) that was exposed to serum deprivation followed by addition of isolated lipoproteins (VLDL or LDL).

RESULTS

Paraoxonase 2 activity in Mo/Mᴓ was significantly lower in type 2 diabetes patients (0.042 ± 0.044 vs 0.165 ± 0.133U lactonase activity/mg protein in controls, p < .0005) and decreased in the obese in all groups. It was inversely correlated to parameters of adiposity (BMI and Waist Circumference), of glucose control (blood glucose, fructosamine and HbA_1c) and insulin resistance (HOMA-IR). In multivariate regression models, 15-34% of the PON2 variance was explained by diabetes. The in vitro addition of VLDL normalised the RB of serum deprived dU937 cells, S- (to 82 ± 18% of the cells incubated with serum, S+) and PON2 activity (from 0.524 ± 0.061 in S - to 0.298 ± 0.048 U/mg protein). In contrast, when LDL was added, the RB remained lower (61 ± 12% of S+, p = .03) and PON2 higher (0.580 ± 0.030 U/mg protein, p = .003).

CONCLUSIONS

The decrease in monocyte/macrophage PON2 enzymatic activity observed in type 2 diabetes cannot be totally explained by abdominal obesity and insulin resistance. The underlying molecular mechanisms need to be identified.

Supplementation with Phycocyanobilin, Citrulline, Taurine, and Supranutritional Doses of Folic Acid and Biotin-Potential for Preventing or Slowing the Progression of Diabetic Complications

Oxidative stress, the resulting uncoupling of endothelial nitric oxide synthase (eNOS), and loss of nitric oxide (NO) bioactivity, are key mediators of the vascular and microvascular complications of diabetes. Much of this oxidative stress arises from up-regulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. Phycocyanobilin (PhyCB), the light-harvesting chromophore in edible cyanobacteria such as spirulina, is a biliverdin derivative that shares the ability of free bilirubin to inhibit certain isoforms of NADPH oxidase. Epidemiological studies reveal that diabetics with relatively elevated serum bilirubin are less likely to develop coronary disease or microvascular complications; this may reflect the ability of bilirubin to ward off these complications via inhibition of NADPH oxidase. Oral PhyCB may likewise have potential in this regard, and has been shown to protect diabetic mice from glomerulosclerosis. With respect to oxidant-mediated uncoupling of eNOS, high-dose folate can help to reverse this by modulating the oxidation status of the eNOS cofactor tetrahydrobiopterin (BH4). Oxidation of BH4 yields dihydrobiopterin (BH2), which competes with BH4 for binding to eNOS and promotes its uncoupling. The reduced intracellular metabolites of folate have versatile oxidant-scavenging activity that can prevent oxidation of BH4; concurrently, these metabolites promote induction of dihydrofolate reductase, which functions to reconvert BH2 to BH4, and hence alleviate the uncoupling of eNOS. The arginine metabolite asymmetric dimethylarginine (ADMA), typically elevated in diabetics, also uncouples eNOS by competitively inhibiting binding of arginine to eNOS; this effect is exacerbated by the increased expression of arginase that accompanies diabetes. These effects can be countered via supplementation with citrulline, which efficiently enhances tissue levels of arginine. With respect to the loss of NO bioactivity that contributes to diabetic complications, high dose biotin has the potential to "pinch hit" for diminished NO by direct activation of soluble guanylate cyclase (sGC). High-dose biotin also may aid glycemic control via modulatory effects on enzyme induction in hepatocytes and pancreatic beta cells. Taurine, which suppresses diabetic complications in rodents, has the potential to reverse the inactivating impact of oxidative stress on sGC by boosting synthesis of hydrogen sulfide. Hence, it is proposed that concurrent administration of PhyCB, citrulline, taurine, and supranutritional doses of folate and biotin may have considerable potential for prevention and control of diabetic complications. Such a regimen could also be complemented with antioxidants such as lipoic acid, N-acetylcysteine, and melatonin-that boost cellular expression of antioxidant enzymes and glutathione-as well as astaxanthin, zinc, and glycine. The development of appropriate functional foods might make it feasible for patients to use complex nutraceutical regimens of the sort suggested here.

NADPH oxidase: its potential role in promotion of pulmonary arterial hypertension

NADPH oxidases (NOXs) are a group of enzymes for superoxide anion (O₂^·- ) generation through transferring electrons from NADPH to molecular oxygen, which is rapidly converted into hydrogen peroxide (H₂O₂). There are seven members in NOX family, including NOX1 to NOX5, dual oxidase1, and dual oxidase 2. Recent studies have demonstrated that NOX subtypes may have different functions in different types of pulmonary arterial hypertension (PAH). The NOX-derived reactive oxygen species (ROS) are key factors that are involved in promoting the processes of pulmonary vascular remodeling, such as endothelial dysfunction, proliferation of pulmonary arterial smooth muscle cells (PASMCs), and cellular trans-differentiation, which are the basic pathologic characteristics of PAH. Inhibition of NOX shows beneficial effect on prevention of PAH development. Thus, NOX might be a potential target for PAH therapy. The main purpose of this review is to summarize recent findings on the role of NOX, particularly the NOX subtypes, in promotion of PAH development and to list recent progress regarding the NOX-based intervention for PAH.

Suppression of pancreatic beta cell apoptosis by Danzhi Jiangtang capsule contributes to the attenuation of type 1 diabetes in rats

BACKGROUND

Danzhi Jiangtang Capsule (DJC), a Chinese medicinal formula, has been clinically used for treatment of diabetes for many years. Previous studies have demonstrated that DJC was able to improve pancreatic islet function in diabetes, but the underlying mechanisms remained unclear.

METHODS

Streptozotocin (STZ) induced type 1 diabetic rats were treated with DJC for 6 weeks. Fasting plasma insulin and fasting plasma glucose were determined at the end of experiment. Antioxidant status was evaluated by measuring total antioxidant capacity, superoxide dismutase activity and malondialdehyde content in plasma and pancreas. Paraffin sections of pancreas were subjected to H&E staining, TUNEL staining and immunohistochemical examination. Protein levels of Bcl-2, Bax and pancreatic duodenal homeobox-1 (PDX-1) were measured by western blot analysis. Activities of Caspase-3 and Caspase-9 were determined with commercially available kits.

RESULTS

Supplementation with DJC resulted in a significant amelioration of type 1 diabetes as manifested by reduced blood glucose, increased fasting plasma insulin and improved body weight gains. The atrophy and reduction of pancreatic islets were also alleviated in DJC supplemented groups. DJC markedly reduced pancreatic beta cell apoptosis, with Bax protein down-regulated and Bcl-2 protein up-regulated significantly. The activities of caspase-3 and caspase-9 in pancreas were decreased evidently by DJC treatment. DJC effectively ameliorated oxidative stress in type 1 diabetic rats, with the expression of PDX-1 protein increased markedly.

CONCLUSIONS

DJC was capable of attenuating STZ induced type 1 diabetes in rats, which might be attributed to the suppression of pancreatic beta cell apoptosis. This study would provide further evidence for clinical use of DJC in the management of diabetes.

The Different Effects of Atorvastatin and Pravastatin on Cell Death and PARP Activity in Pancreatic NIT-1 Cells

Statins have been widely used drugs for lowering low-density lipoprotein and for preventing heart attack and stroke. However, the increased risk for developing diabetes during extended stain use and the molecular mechanisms remain unclear. The objective of this study was to elucidate the signaling pathway and biological function between necrosis and autophagy induced by atorvastatin (AS) and pravastatin (PS). Here we observed that atorvastatin (AS) can increase intracellular reactive oxygen species (ROS) and induce necrotic cell death and autophagy in NIT-1 cells, whereas pravastatin (PS) does not cause ROS and cell death but also induces autophagy. PARP1 exhibited a dual role in modulating necrosis and autophagy in AS- and PS-treated NIT-1 cells through RIP1-RIP3-MLKL pathway and PARP1-AMPK-mTOR pathway. Lastly, AS treatment induced mitochondrial morphology injury significantly more than PS treatment did. Thus, the PARP1 activation should be considered in the development of effective statin therapies for diabetes. Future studies may examine specific mechanisms and pathways in mitochondria, autophagy, and oxidative stress in vivo.

Phagocyte-like NADPH oxidase (Nox2) promotes activation of p38MAPK in pancreatic β-cells under glucotoxic conditions: Evidence for a requisite role of Ras-related C3 botulinum toxin substrate 1 (Rac1)

It is well established that glucotoxicity (caused by high glucose concentrations; HG) underlies pathogenesis of islet dysfunction in diabetes. We have recently demonstrated that Nox2 plays a requisite role in the generation of reactive oxygen species (ROS) under HG conditions, resulting in mitochondrial dysregulation and loss of islet β-cell function. Herein, we investigated roles of Nox2 in the regulation of downstream stress kinase (p38MAPK) activation under HG conditions (20mM; 24h) in normal rodent islets and INS-1 832/13 cells. We observed that gp91-ds-tat, a specific inhibitor of Nox2, but not its inactive analog, significantly attenuated HG-induced Nox2 activation, ROS generation and p38MAPK activation, thus suggesting that Nox2 activation couples with p38MAPK activation. Since Rac1, is an integral member of the Nox2 holoenzyme, we also assessed the effects of Rac1 inhibitors (EHT 1864, NSC23766 and Ehop-016) on HG-induced p38MAPK activation in isolated β-cells. We report a significant inhibition of p38MAPK phosphorylation by Rac1 inhibitors, implying a regulatory role for Rac1 in promoting the Nox2-p38MAPK signaling axis in the β-cell under the duress of HG. 2-Bromopalmitate, a known inhibitor of protein (Rac1) palmitoylation, significantly reduced HG-induced p38MAPK phosphorylation. However, GGTI-2147, a specific inhibitor of geranylgeranylation of Rac1, failed to exert any significant effects on HG-induced p38MAPK activation. In conclusion, we present the first evidence that the Rac1-Nox2 signaling module plays novel regulatory roles in HG-induced p38MAPK activation and loss in glucose-stimulated insulin secretion (GSIS) culminating in metabolic dysfunction and the onset of diabetes.

The regulatory roles of NADPH oxidase, intra- and extra-cellular HSP70 in pancreatic islet function, dysfunction and diabetes

The 70 kDa heat-shock protein (HSP70) family is important for a dynamic range of cellular processes that include protection against cell stress, modulation of cell signalling, gene expression, protein synthesis, protein folding and inflammation. Within this family, the inducible 72 kDa and the cognate 73 kDa forms are found at the highest level. HSP70 has dual functions depending on location. For example, intracellular HSP70 (iHSP70) is anti-inflammatory whereas extracellular HSP70 (eHSP70) has a pro-inflammatory function, resulting in local and systemic inflammation. We have recently identified a divergence in the levels of eHSP70 and iHSP70 in subjects with diabetes compared with healthy subjects and also reported that eHSP70 was correlated with insulin resistance and pancreatic β-cell dysfunction/death. In the present review, we describe possible mechanisms by which HSP70 participates in cell function/dysfunction, including the activation of NADPH oxidase isoforms leading to oxidative stress, focusing on the possible role of HSPs and signalling in pancreatic islet α- and β-cell physiological function in health and Type 2 diabetes mellitus.

Certain Diet and Lifestyle May Contribute to Islet β-cells Protection in Type-2 Diabetes via the Modulation of Cellular PI3K/AKT Pathway

PI3K/AKT pathway has been shown to play a pivotal role on islet β-cell protection, enhancing β-cell survival by stimulating cell proliferation and inhibiting cell apoptosis. Accordingly, this pathway appears to be crucial in type-2 diabetes. Understanding the regulations of this pathway may provide a better efficacy of new therapeutic approaches. In this review, we summarize advances on the involvement of the PI3K/AKT pathway in hypothetical intra-cellular signaling of islet β-cells. As recent findings may show the nutritional regulation of the survival pathway in the islet β-cells through activation of the PI3K/AKT pathway, we also review studies on the features of several diets, correlated lifestyle, and its signaling pathway involved in type-2 diabetes. The molecular mechanisms contributing to the disease are the subject of considerable investigation, as a better understanding of the pathogenesis will lead to novel therapies against a condition of the disease.

Crucial roles of Nox2-derived oxidative stress in deteriorating the function of insulin receptors and endothelium in dietary obesity of middle-aged mice

BACKGROUND AND PURPOSE

Systemic oxidative stress associated with dietary calorie overload plays an important role in the deterioration of vascular function in middle-aged patients suffering from obesity and insulin resistance. However, effective therapy is still lacking.

EXPERIMENTAL APPROACH

In this study, we used a mouse model of middle-aged obesity to investigate the therapeutic potential of pharmaceutical inhibition (apocynin, 5 mM supplied in the drinking water) or knockout of Nox2, an enzyme generating reactive oxygen species (ROS), in high-fat diet (HFD)-induced obesity, oxidative stress, insulin resistance and endothelial dysfunction. Littermates of C57BL/6J wild-type (WT) and Nox2 knockout (KO) mice (7 months old) were fed with a HFD (45% kcal fat) or normal chow diet (NCD, 12% kcal fat) for 16 weeks and used at 11 months of age.

KEY RESULTS

Compared to NCD WT mice, HFD WT mice developed obesity, insulin resistance, dyslipidaemia and hypertension. Aortic vessels from these mice showed significantly increased Nox2 expression and ROS production, accompanied by significantly increased ERK1/2 activation, reduced insulin receptor expression, decreased Akt and eNOS phosphorylation and impaired endothelium-dependent vessel relaxation to acetylcholine. All these HFD-induced abnormalities (except the hyperinsulinaemia) were absent in apocynin-treated WT or Nox2 KO mice given the same HFD.

CONCLUSIONS AND IMPLICATIONS

In conclusion, Nox2-derived ROS played a key role in damaging insulin receptor and endothelial function in dietary obesity after middle-age. Targeting Nox2 could represent a valuable therapeutic strategy in the metabolic syndrome.

Link between PI3K/AKT/PTEN Pathway and NOX Proteinin Diseases

Accumulating evidence has revealed that thePI3K/AKT/PTENpathway acts as a pivotal determinant of cell fate regarding senescence and apoptosis, which is mediated by intracellular reactive oxygen species (ROS) generation. NADPH oxidase (NOX) family of enzymes generates the ROS. The regulation of NOX enzymes is complex, with many members of this family exhibiting complexity in terms of subunit composition, cellular location, and tissue-specific expression. Cells are continuously exposed to the ROS, which represent mutagens and are thought to be a major contributor to several diseases including cancer and aging process. Therefore, cellular ROS sensing and metabolism are firmly regulated by a variety of proteins involved in the redox mechanism. In this review, the roles of oxidative stress in PI3K/AKT/PTEN signaling are summarized with a focus on the links between the pathways and NOX protein in several diseases including cancer and aging.

A matter of life, death and diseases: mitochondria from a proteomic perspective

Mitochondria are highly ordered, integrated organelles that energize cellular activities and contribute to programmed death by initiating disciplined apoptotic cascades. This review seeks to clarify our understanding of mitochondrial structural-functional integrity beyond the resolved nuclear genome by unraveling the dynamic mitochondrial proteome and elucidating proteome/genome interplay. The roles of mechanochemical coupling between mitoskeleton and cytoskeleton and crosstalk with other organelles in orchestrating cellular outcomes are explained. The authors also review the modulation of mitochondrial-related oxidative stress on apoptosis and cancer development and the context is applied to interpret pathogenetic events in neurodegenerative disorders and cardiovascular diseases. The accumulated proteomics evidence is used to describe the integral role that mitochondria play and how they influence other intracellular organelles. Possible mitochondrial-targeted therapeutic interventions are also discussed.

NADPH oxidase 2 plays a critical role in dysfunction and apoptosis of pancreatic β-cells induced by very low-density lipoprotein

In type 2 diabetes, pancreatic β-cells cannot secret enough insulin compensate for insulin resistance, which are often accompanied by abnormality in lipid metabolism such as hypertriglyceridemia. It is reported that oxidative stress is involved in pancreatic β-cell dysfunction. However, molecular mechanisms linking between excessive generations of reactive oxygen species (ROS) and β-cell dysfunction and apoptosis induced by high levels of very low-density lipoprotein (VLDL) are poorly understood. In this study, we test the hypothesis that NADPH oxidase 2 (NOX2)-derived ROS may play a key role in dysfunction and apoptosis of pancreatic β-cell induced by VLDL. Our results show that the ApoCIII transgenic mice displayed increased serum TG levels, enhanced generation of ROS and impaired insulin content in pancreatic β-cells. In vitro, the treatment of pancreatic NIT-1 cells with 1 mg/ml VLDL for 12 h stimulated NOX2-derived ROS generation, decreased expression and secretion of insulin. Furthermore, we found that VLDL induced dysfunction and apoptosis of pancreatic β-cells through JNK and p53 pathways, which were rescued by siRNA-mediated NOX2 reduction. In conclusion, our data demonstrate a critical role of NOX2-derived ROS in dysfunction and apoptosis through JNK and p53 pathways in pancreatic β-cells induced by VLDL.

Expression of NADPH oxidase in human pancreatic islets

AIMS

NADPH oxidase (NOX) is a known source of superoxide anions in phagocytic and non-phagocytic cells. In this study, the presence of this enzyme in human pancreatic islets and the importance of NADPH oxidase in human β-cell function were investigated.

MAIN METHODS AND KEY FINDINGS

In isolated human pancreatic islets, the expression of NADPH oxidase components was evidenced by real-time PCR (p22(PHOX), p47(PHOX) and p67(PHOX)), Western blotting (p47(PHOX) and p67(PHOX)) and immunohistochemistry (p47(PHOX), p67(PHOX) and gp91(PHOX)). Immunohistochemistry experiments showed co-localization of p47(PHOX), p67(PHOX) and gp91(PHOX) (isoform 2 of NADPH oxidase-NOX2) with insulin secreting cells. Inhibition of NADPH oxidase activity impaired glucose metabolism and glucose-stimulated insulin secretion.

SIGNIFICANCE

These findings demonstrate the presence of the main intrinsic components of NADPH oxidase comprising the NOX2 isoform in human pancreatic islets, whose activity also contributes to human β-cell function.

Reactive oxygen and nitrogen species generation, antioxidant defenses, and β-cell function: a critical role for amino acids

Growing evidence indicates that the regulation of intracellular reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels is essential for maintaining normal β-cell glucose responsiveness. While long-term exposure to high glucose induces oxidative stress in β cells, conflicting results have been published regarding the impact of ROS on acute glucose exposure and their role in glucose stimulated insulin secretion (GSIS). Although β cells are considered to be particularly vulnerable to oxidative damage, as they express relatively low levels of some peroxide-metabolizing enzymes such as catalase and glutathione (GSH) peroxidase, other less known GSH-based antioxidant systems are expressed in β cells at higher levels. Herein, we discuss the key mechanisms of ROS/RNS production and their physiological function in pancreatic β cells. We also hypothesize that specific interactions between RNS and ROS may be the cause of the vulnerability of pancreatic β cells to oxidative damage. In addition, using a hypothetical metabolic model based on the data available in the literature, we emphasize the importance of amino acid availability for GSH synthesis and for the maintenance of β-cell function and viability during periods of metabolic disturbance before the clinical onset of diabetes.

C-reactive protein promotes adhesion of monocytes to endothelial cells via NADPH oxidase-mediated oxidative stress

Enhanced monocyte adhesion to endothelial cells is an early event in atherogenesis. It has been shown that C-reactive protein (CRP) plays a key role in atherogenesis. Here, we investigated the effects of CRP on monocyte-endothelial cell adhesion and tested the hypothesis that NADPH oxidase (NOX)-mediated oxidative stress might play a key role in CRP-induced monocyte-endothelial cell adhesion. Firstly, 36 patients with carotid intima-media thickness (IMT) incrassation and 34 controls were enrolled in this study. The levels of glucose, lipids, CRP, monocyte chemotractant protein (MCP-1), malondialdehyde (MDA), and protein carbonylation were analyzed. The results showed that carotid IMT was associated with abnormal lipid metabolism, including elevated CRP, triglycerides (TG) (P < 0.01) and decreased high density lipoprotein (HDL) level (P < 0.05). The levels of CRP and MCP-1 in patients with carotid IMT incrassation were increased compared with the controls (P < 0.01). Moreover, patients with carotid IMT incrassation displayed enhanced MDA and protein carbonylation levels (P < 0.01), accompanied by activation and up-regulation of NOX in monocytes (P < 0.05) compared with the controls. The monocytes isolated from five healthy donors were used for in vitro experiments. Reactive oxygen species (ROS) production and NOX expression in monocytes were examined. The results also indicated that CRP could promote the adhesion of monocyte-endothelial cell by up-regulation of MCP-1 expression (P < 0.05). Importantly, NFκ B and p38 MAPK signaling pathways, which were activated by NOX-derived ROS, were involved in CRP-induced monocyte-endothelial cell adhesion and up-regulation of MCP-1 expression. These data suggested that CRP could promote the adhesion of monocytes to endothelial cells via NOX-mediated oxidative stress. J. Cell. Biochem. 113: 857-867, 2012. © 2011 Wiley Periodicals, Inc.

Differential roles of NADPH oxidases in vascular physiology and pathophysiology

Reactive oxygen species (ROS) are produced by all vascular cells and regulate the major physiological functions of the vasculature. Production and removal of ROS are tightly controlled and occur in discrete subcellular locations, allowing for specific, compartmentalized signaling. Among the many sources of ROS in the vessel wall, NADPH oxidases are implicated in physiological functions such as control of vasomotor tone, regulation of extracellular matrix and phenotypic modulation of vascular smooth muscle cells. They are involved in the response to injury, whether as an oxygen sensor during hypoxia, as a regulator of protein processing, as an angiogenic stimulus, or as a mechanism of wound healing. These enzymes have also been linked to processes leading to disease development, including migration, proliferation, hypertrophy, apoptosis and autophagy. As a result, NADPH oxidases participate in atherogenesis, systemic and pulmonary hypertension and diabetic vascular disease. The role of ROS in each of these processes and diseases is complex, and a more full understanding of the sources, targets, cell-specific responses and counterbalancing mechanisms is critical for the rational development of future therapeutics.