Reducing sugars trigger oxidative modification and apoptosis in pancreatic beta-cells by provoking oxidative stress through the glycation reaction

Qualitative and Quantitative Profiling of Fructose Degradation Products Revealed the Formation of Thirteen Reactive Carbonyl Compounds and Higher Reactivity Compared to Glucose

Fructose occurs in foods and as a metabolite in vivo. It can be degraded, leading to the formation of reactive carbonyl compounds, which may influence food properties and have an impact on health. The present study performed an in-depth qualitative and quantitative profiling of fructose degradation products. Thus, the α-dicarbonyl compounds 3-deoxyglucosone, glucosone, methylglyoxal, glyoxal, hydroxypyruvaldehyde, threosone, 3-deoxythreosone, and 1-desoxypentosone and the monocarbonyl compounds formaldehyde, acetaldehyde, glycolaldehyde, glyceraldehyde, and dihydroxyacetone were detected in fructose solutions incubated at 37 °C. Quantitative profiling after 7 days revealed 4.6-271.6-fold higher yields of all degradation products from fructose compared to glucose. Except for 3-deoxyglucosone, the product formation appeared to be metal dependent, indicating oxidative pathways. CaCl2 and MgCl2 partially reduced fructose degradation. Due to its high reactivity compared to glucose, particularly toward metal-catalyzed pathways, fructose may be a strong contributor to sugar degradation and Maillard reaction in foods and in vivo.

Metabolic Syndrome: A Narrative Review from the Oxidative Stress to the Management of Related Diseases

Metabolic syndrome (MS) is a growing disorder affecting thousands of people worldwide, especially in industrialised countries, increasing mortality. Oxidative stress, hyperglycaemia, insulin resistance, inflammation, dysbiosis, abdominal obesity, atherogenic dyslipidaemia and hypertension are important factors linked to MS clusters of different pathologies, such as diabesity, cardiovascular diseases and neurological disorders. All biochemical changes observed in MS, such as dysregulation in the glucose and lipid metabolism, immune response, endothelial cell function and intestinal microbiota, promote pathological bridges between metabolic syndrome, diabesity and cardiovascular and neurodegenerative disorders. This review aims to summarise metabolic syndrome's involvement in diabesity and highlight the link between MS and cardiovascular and neurological diseases. A better understanding of MS could promote a novel strategic approach to reduce MS comorbidities.

2-Deoxy-d-ribose induces ferroptosis in renal tubular epithelial cells via ubiquitin-proteasome system-mediated xCT protein degradation

Ferroptosis is a novel form of cell death triggered by iron-dependent lipid peroxidation. Recent findings suggest that inhibiting system χc-induces ferroptosis by reducing intracellular cystine levels, and that ferroptosis in renal tubular epithelial cells (RTECs) contributes to acute kidney injury (AKI) and diabetic nephropathy. Moreover, 2-deoxy-d-ribose (dRib) has been shown to inhibit cystine uptake through xCT, the functional unit of system χc-, in β-cells. This study aimed to investigate if dRib induces ferroptosis in RTECs and identify the underlying mechanisms. dRib treatment reduced cystine uptake and glutathione (GSH) content, and increased intracellular levels of malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), lipid reactive oxygen species (ROS), and cell death in both NRK-52E cells and primary cultured RTECs. However, treatment with inhibitors of ferroptosis, such as deferoxamine (DFO), ferrostatin-1 (Fer-1), and liproxstatin-1 (Lip-1), counteracted the effects of dRib on GSH, MDA, 4-HNE, and lipid ROS levels, as well as cell death. Additionally, 2-mercaptoethanol (2-ME) treatment or xCT gene overexpression protected against dRib-induced changes. Moreover, transmission electron microscopy revealed dRib-induced mitochondrial shrinkage, decrease in cristae number, and outer membrane rupture. Furthermore, dRib treatment upregulated the expression of genes associated with ferroptosis, and downregulated xCT protein expression. The decrease in xCT protein caused by dRib was consistently observed even when treated with the protein synthesis inhibitor cycloheximide. However, treatment with the proteasome inhibitor MG132 reversed the dRib-induced decrease in xCT protein expression. Additionally, dRib increased xCT protein ubiquitination. Overall, dRib induces ferroptosis in RTECs by degrading xCT protein through ubiquitin-proteasome system (UPS), resulting in reduced intracellular cystine uptake. Therefore, targeting the regulation of system χc-through UPS could be a potential therapeutic approach for AKI and diabetic nephropathy.

Protective Effect of Hawthorn Fruit Extract against High Fructose-Induced Oxidative Stress and Endoplasmic Reticulum Stress in Pancreatic β-Cells

Hyperglycemia has deleterious effects on pancreatic β-cells, causing dysfunction and insulin resistance that lead to diabetes mellitus (DM). The possible causes of injury can be caused by glucose- or fructose-induced oxidative and endoplasmic reticulum (ER) stress. Hawthorn (Crataegus pinnatifida) fruit has been widely used as a hypolipidemic agent in traditional herbal medicine. The study aimed to investigate whether high fructose-induced pancreatic β-cell dysfunction could be reversed through amelioration of ER stress by the treatment of polyphenol-enriched extract (PEHE) from hawthorn fruit. The extract was partitioned using ethyl acetate as a solvent from crude water extract (WE) of hawthorn fruits, followed by column fractionation. The results showed that the contents of total polyphenols, flavonoids and triterpenoids in PEHE could be enhanced by 2.2-, 7.7- and 1.1-fold, respectively, in comparison to the original obtained WE from hawthorn fruit. In ER stress studies, a sharp increase in the inhibitory activity on the gene expression levels of GRP79, ATF6, IRE1α and CHOP involved in ER stress was evident when dosages of PEHE at 50–100 μg/mL were used against high-fructose (150 mM)-treated cells. HPLC–MS/MS analysis showed that polyphenols and flavonoids collectively accounted for 87.03% of the total content of PEHE.

Protective Effects of Rifampicin and Its Analog Rifampicin Quinone in a Mouse Model of Obesity-Induced Type 2 Diabetes

Advanced glycation end-products (AGEs) form when glucose reacts non-enzymatically with proteins, leading to abnormal protein function, oxidative stress, and inflammation. AGEs are associated with aging and age-related diseases; their formation is aggravated during diabetes. Therefore, drugs preventing AGE formation can potentially treat diabetic complications, positively affecting health. Earlier, we demonstrated that rifampicin and its analogs have potent anti-glycating activities and increase the life span of Caenorhabditis elegans. This study aimed to investigate the effects of rifampicin during hyperglycemia in C. elegans and in a mouse model of obesity-induced type 2 diabetes. The effects of rifampicin were assessed by determining the life span of C. elegans cultured in the presence of glucose and by measuring HbA1c, AGE levels, and glucose excursions in the diabetic mouse model. Our results show that rifampicin protects C. elegans from glucose-induced toxicity and increases life span. In mice, rifampicin reduces HbA1c and AGEs, improves insulin sensitivity, and reduces indications of diabetic nephropathy without inducing hepatotoxicity. Rifampicin quinone, an analog with lower anti-microbial activity, also reduces HbA1c levels, improves glucose homeostasis and insulin sensitivity, and lowers indications of diabetic nephropathy, without adversely affecting the liver of the diabetic mice. Altogether, our results indicate that rifampicin and its analog have protective roles during diabetes without inflicting hepatic damage and may potentially be considered for repositioning to treat hyperglycemia-related complications in patients.

Dysregulation of nitric oxide synthases during early and late pathophysiological conditions of diabetes mellitus leads to amassing of microvascular impedement

Diabetes is a major killer worldwide and its unprecedented rise poses a serious threat to mankind. According to recent estimation, 387 million people worldwide are affected from the disease with a prevalence rate of 8.3 and 46.3 % still remains undiagnosed. Important characteristics of diabetes are abnormalities of the physiological signalling functions of reactive oxygen species and reactive nitrogen species. Increased oxidative stress contributes to the activation of stress-sensitive intracellular signalling pathways and the development of gene products that trigger cellular damage and contribute to the vascular complications of diabetes. Growing evidence from studies into many diseases suggests that the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure are correlated with oxidative stress. This leads to cell metabolism and cell-cell homeostasis to be complexly dysregulated. This review focuses to investigate the status of oxidative stress, nitric oxide and reactive species in early and diabetes. Significance of nitric oxide synthases Evidences has accumulated indicating that the generation of reactive oxygen species (oxidative stress) may play an important role in the etiology of diabetic complications thus attention was given on the reactive oxygen and reactive nitrogen species and their potential role in pathogenesis. Additionally, the therapeutic advances in diabetes management are included. Nanotechnology, statins and stem cell technology are some techniques which can be considered to have a possible future in the treatment sector of diabetes.

Protection of Polyphenols against Glyco-Oxidative Stress: Involvement of Glyoxalase Pathway

Chronic high glucose (HG) exposure increases methylglyoxal (MGO)-derived advanced glycation end-products (AGEs) and is involved in the onset of pathological conditions, such as diabetes, atherosclerosis and chronic-degenerative diseases. Under physiologic conditions the harmful effects of MGO are contrasted by glyoxalase system that is implicated in the detoxification of Reactive Carbonyl Species (RCS) and maintain the homeostasis of the redox environment of the cell. Polyphenols are the most abundant antioxidants in the diet and present various health benefits. Aims of the study were to investigate the effects of HG-chronic exposure on glyco-oxidation and glyoxalase system in intestinal cells, using CaCo-2 cells. Moreover, we studied the effect of apple polyphenols on glyco-oxidative stress. Our data demonstrated that HG-treatment triggers glyco-oxidation stress with a significant increase in intracellular Reactive Oxygen Species (ROS), lipid peroxidation, AGEs, and increase of Glyoxalase I (GlxI) activity. On the contrary, Glyoxalase II (GlxII) activity was lower in HG-treated cells. We demonstrate that apple polyphenols exert a protective effect against oxidative stress and dicarbonyl stress. The increase of total antioxidant capacity and glutathione (GSH) levels in HG-treated cells in the presence of apple polyphenols was associated with a decrease of GlxI activity.

Dacryodes edulis (G. Don) H.J. Lam modulates glucose metabolism, cholinergic activities and Nrf2 expression, while suppressing oxidative stress and dyslipidemia in diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Dacryodes edulis L. is an evergreen tree indigenous to western and eastern Africa which is utilized for nutritional and medicinal purposes. Folklorically, different parts of the tree are used in treating and managing diabetes and its complications.

AIMS

The antidiabetic effect of the butanol fraction of D. edulis ethanol extract (BFDE) was studied in fructose-streptozotocin induced type 2 diabetic rats.

METHODS

The ethanol extract was fractionated to yield the hexane, dichloromethane, ethyl acetate, butanol and aqueous fractions. The in vitro antidiabetic activities of the fractions were determined by their ability to inhibit α-glucosidase activity. BDFE was the most active and showed no cytotoxic effect while stimulating glucose uptake in 3T3-L1 adipocytes. Thus, selected for in vivo study. Diabetic rats were grouped into 4. The negative control group was administered water only, another group was treated with metformin (200 mg/kg bodyweight), while the other groups were administered BDFE at 150 and 300 mg/kg bodyweight respectively. Two other groups consisting of normal rats were given water and BFDE (300 mg/kg bodyweight) respectively, with the former serving as normal control. After 6 weeks of intervention, the rats were humanely sacrificed using appropriate anaesthesia.

RESULTS

Treatment with the fraction significantly (p < 0.05) reduced the blood glucose level of the diabetic rats, with concomitant increase in serum insulin secretion. It also caused significant (p < 0.05) elevation of reduced glutathione level, superoxide dismutase, catalase, α-amylase, and ATPase activities, with concomitant depletion in myeloperoxidase activity, NO and MDA levels of the serum and pancreas. The pancreatic morphology and β-cell function were significantly improved in BFDE-treated rats, with restoration of the pancreatic capillary networks. Treatment with BFDE significantly (p < 0.05) inhibited the activities of glycogen phosphorylase, fructose 1,6 biphosphatase, glucose 6 phosphatase, and acetylcholinesterase, while suppressing the expression of Nrf2. HPLC analysis revealed the presence of gallic acid, vanillic acid, vanillin, and (-)-epicatechin in the fraction.

CONCLUSION

These results portray the antidiabetic and antioxidative properties of BFDE, which may be a synergistic consequence of the identified phenolics.

Autophagy Induced by ROS Aggravates Testis Oxidative Damage in Diabetes via Breaking the Feedforward Loop Linking p62 and Nrf2

Testicular dysfunction due to hyperglycemia is the main cause of infertility in diabetic men. Over the years, in order to solve this growing problem, a lot of research has been done and a variety of treatments have been created, but so far, there is no safe, effective, and practical method to prevent male infertility caused by diabetes. In this review, we emphasize the male infertility mechanism caused by diabetes from the effects of oxidative stress and autophagy on the function of testes via the PI3K/Akt/mTOR signaling pathway, and we highlight that oxidative stress-induced autophagy breaks the feedforward loop linking Nrf2 and p62 and promotes oxidative damage in diabetic testes.

Compromised DNA repair is responsible for diabetes-associated fibrosis

Diabetes-associated organ fibrosis, marked by elevated cellular senescence, is a growing health concern. Intriguingly, the mechanism underlying this association remained unknown. Moreover, insulin alone can neither reverse organ fibrosis nor the associated secretory phenotype, favoring the exciting notion that thus far unknown mechanisms must be operative. Here, we show that experimental type 1 and type 2 diabetes impairs DNA repair, leading to senescence, inflammatory phenotypes, and ultimately fibrosis. Carbohydrates were found to trigger this cascade by decreasing the NAD⁺ /NADH ratio and NHEJ-repair in vitro and in diabetes mouse models. Restoring DNA repair by nuclear over-expression of phosphomimetic RAGE reduces DNA damage, inflammation, and fibrosis, thereby restoring organ function. Our study provides a novel conceptual framework for understanding diabetic fibrosis on the basis of persistent DNA damage signaling and points to unprecedented approaches to restore DNA repair capacity for resolution of fibrosis in patients with diabetes.

Chemical and Immunological Characterization of Oxidative Nonenzymatic Protein Modifications in Dialysis Fluids

← Background

Glucose degradation products (GDP) in dialysis fluids may induce nonenzymatic protein modifications, the chemical nature and biological properties of which should be better defined.

← Aims

To characterize nonenzymatic protein modifications present in glucose-based peritoneal dialysis fluids (PDF) and to evaluate the relationship between concentrations of GDP and the derived nonenzymatic modifications, and the potential of PDF for generating these modifications in vitro.

← Methods

The presence, distribution, and content of several nonenzymatic protein modifications in PDF were evaluated by immunological methods, by HPLC, and by gas chromatography-mass spectrometry (GC/MS). Peritoneal dialysis fluid-induced oxidative stress in cells was evaluated by flow cytometry. The potential of PDF for generating oxidative and glycoxidative modifications was examined by immunological and cross-linking analyses.

← Results

The albumin present in PDF is modified by carboxymethyllysine (CML). GC/MS analyses of PDF proteins confirmed the presence of CML and demonstrated the occurrence of carboxyethyllysine, malondialdehyde lysine, and oxidation-derived semialdehydes. Furthermore, their concentrations in PDF proteins were significantly higher than those in plasma proteins (in all cases, p < 0.02). The concentration of pyrraline, a non-oxidative advanced glycation end-product, increased with dwell time up to 6 hours ( p < 0.03). The PDF induced cellular free-radical production, which was partially inhibited by the Maillard reaction inhibitor aminoguanidine ( p < 0.001). The potential to generate oxidative and glycoxidative modifications demonstrated an inverse relationship with dwell time ( p < 0.05). The PDF was able to induce collagen cross-linking in a close relationship with GDP concentration.

← Conclusions

( 1 ) PDF contains non-oxidative and several oxidative nonenzymatic protein modifications in higher concentrations than plasma. ( 2 ) Peritoneal dialysis fluid induces oxidative stress in vitro, which can be partially inhibited by aminoguanidine. ( 3 ) These properties are directly related to GDP concentration. ( 4 ) Peritoneal dialysis fluid is able to generate glycoxidative and oxidative damage to proteins in vitro in a dwell-time dependent fashion.

Glycation With Fructose: The Bitter Side of Nature's Own Sweetener

Fructose is a ketohexose and sweetest among all the natural sugars. Like other reducing sugars, it reacts readily with the amino- and nucleophilic groups of proteins, nucleic acids and other biomolecules resulting in glycation reactions. The non-enzymatic glycation reactions comprise Schiff base formation, their Amadori rearrangement followed by complex and partly incompletely understood reactions culminating in the formation of Advance Glycation End products (AGEs). The AGEs are implicated in complications associated with diabetes, cardiovascular disorders, Parkinson's disease, etc. Fructose is highly reactive and forms glycation products that differ both in structure and reactivity as compared to those formed from glucose. Nearly all tissues of higher organisms utilize fructose but only a few like the ocular lens, peripheral nerves erythrocytes and testis have polyol pathway active for the synthesis of fructose. Fructose levels rarely exceed those of glucose but, in tissues that operate the polyol pathway, its concentration may rise remarkably during diabetes and related disorders. Diet contributes significantly to the body fructose levels however, availability of technologies for the large scale and inexpensive production of fructose, popularity of high fructose syrups as well as the promotion of vegetarianism have resulted in a remarkable increase in the consumption of fructose. In vivo glycation reactions by fructose, therefore, assume remarkable significance. The review, therefore, aims to highlight the uniqueness of glycation reactions with fructose and its role in some pathophysiological situations.

Effect of High Glucose-Induced Oxidative Stress on Paraoxonase 2 Expression and Activity in Caco-2 Cells

(1) Background: Hyperglycemia leads to several biochemical and physiological consequences, such as the generation of advanced glycation end products (AGEs) and reactive oxygen species (ROS), which are involved in the development of several human diseases. Intestinal cells are continuously exposed to pro-oxidants and lipid peroxidation products from ingested foods, and also to glyco-oxidative damage. It has been reported that free radical generation may be linked to the development of inflammation-related gastrointestinal diseases. (2) Methods: The effects of high glucose (HG) treatment (50 mM) were assessed in terms of free radical production, lipid peroxidation, and AGEs formation. Furthermore, the expression and the antiapoptotic and antioxidant activity of the paraoxonase-2 (PON2) enzyme in intestinal cells has been investigated. (3) Results: Caco-2 cells treated with media supplied with high glucose (HG) (50 mM) showed, with respect to physiological glucose concentration (25 mM), an increase in ROS production, lipid peroxidation, and AGEs formation. Moreover, a lower PON2 expression and activity in HG-treated cells was related to activation of the apoptotic pathways. (4) Conclusions: Our results demonstrated that high glucose concentrations triggered glyco-oxidative stress in intestinal cells; the downregulation of PON2 could result in a higher oxidative stress and might contribute to intestinal dysfunction.

Influence of Tacrolimus on Depressive-Like Behavior in Diabetic Rats Through Brain-Derived Neurotrophic Factor Regulation in the Hippocampus

The neurotoxicity of immunosuppressive agents and diabetes mellitus are known risk factors of neurological complications in kidney transplant recipients. The aim of the present study was to investigate the influence of tacrolimus on brain-derived neurotrophic factor (BDNF), the critical protein for maintenance of neuronal functions, in the hippocampus in a diabetic condition. A diabetic rat model was established by a single streptozotocin injection (60 mg/kg). Control and diabetic rats then received daily tacrolimus (1.5 mg/kg per day) injections for 6 weeks. BDNF expression in the hippocampus was examined in the dentate gyrus (DG) and CA3 region using immunohistochemistry. There was a significant decrease of BDNF expression in the DG and CA3 region in tacrolimus-treated and diabetic rats compared with that of the control group injected with vehicle only. However, there was no difference in BDNF expression between the two experimental groups. Tacrolimus treatment in diabetic rats further decreased the BDNF expression level in the DG and CA3 region. Interestingly, mossy fiber sprouting, demonstrated by prominent punctate immunolabeling of BDNF with synaptoporin, was observed in the diabetic group treated with tacrolimus, which localized at the stratum oriens of the CA3 region. These data suggest that tacrolimus treatment or a diabetic condition decreases BDNF expression in the hippocampus, and that tacrolimus treatment in the diabetic condition further injures the CA3 region of the hippocampus. In addition to BDNF expression, decreased locomotor activity and evident depressive behavior were observed in tacrolimus-treated diabetic rats. Moreover, there were significant decreases of the mRNA levels of γ-aminobutyric acid and serotonin receptors in the diabetic hippocampus with tacrolimus treatment. This finding suggests that tacrolimus treatment may cause further psychiatric and neurological complications for patients with diabetes, and should thus be used with caution.

Raffia palm (Raphia hookeri G. Mann & H. Wendl) wine modulates glucose homeostasis by enhancing insulin secretion and inhibiting redox imbalance in a rat model of diabetes induced by high fructose diet and streptozotocin

ETHNOPHARMACOLOGICAL RELEVANCE

Raffia palm (Raphia hookeri) wine (RPW) is amongst the natural products from plants, utilized singly or in combination with other medicinal plants for the treatment of several ailments including Diabetes Mellitus (DM). However, there is a scientific dearth on its antidiabetic activity.

AIM

The antidiabetic effect of RPW and its possible mechanism of actions were investigated in diabetic rats.

METHODS

Four groups of male SD rats were first supplied with 10% fructose solution ad libitum for 2 weeks instead of drinking water followed by an intraperitonial injection of streptozotocin (40 mg/kg) to induce diabetes. Two diabetic groups were administered RPW at 150 and 300 mg/kg bodyweight (BW) respectively; a group was administered with metformin, while the other one was served as a negative control. Two groups of normal rats were administered with water and RPW (300 mg/kg BW) and served as normal control and normal toxicology group, respectively.

RESULTS

Five weeks treatment of RPW led to significant (p < 0.05) increase in serum insulin and HDL-c levels with concomitant reduction in blood glucose, fructosamine, ALT, uric acid, triglycerides and LDL-c levels in diabetic rats. Rats treated with RPW had elevated levels of GSH, SOD, catalase, ATPase and α-amylase activities, while reduced NO level and myeloperoxidase activity was observed in their serum and pancreatic tissues. RPW also improved pancreatic β-cell function and restored β- and acinar cells morphology, and capillary networks. The activities of glycogen phosphorylase, fructose 1,6 biphosphatase, glucose-6-phosphatase, and acetylcholinesterase were also inhibited in RPW-treated diabetic rats, with concomitant down regulation of Nrf2 gene expression.

CONCLUSION

The data of this study suggest that RPW modulates glucose homeostasis by enhancing insulin secretion as well as inhibiting redox imbalance in diabetic rats, which may be attributed to the synergetic effects of its phytochemical constituents as identified by GC-MS analysis.

Propolis nanoparticles prevent structural changes in human hemoglobin during glycation and fructation

Nowadays diabetes, as a metabolic disorder, is increasing at an alarming rate. Glycation and production of advanced glycation end products (AGEs) is the most important factor involved in diabetic complications. Due to the side effects of synthetic drugs, the demand for natural anti-diabetic herbal medicines has increased. Propolis is a natural and resinous material, which iscollected by honeybees. Due to the impact of nanotechnology in medicine and the advantageous role of nanoparticles in treatment, nano-propolis particles (PNP) were prepared. The anti-glycation effect of PNP at various concentrations was investigated on human hemoglobin (Hb) glycation and fructation and compared with aspirin as a common anti-glycation agent using glycation specific AGE fluorescence, AGE-specific absorbance and circular dichroism (CD) methods. Fluorescence spectroscopy results showed that PNP inhibited the formation of AGEs in Hb glycation and fructation by glucose and fructose, respectively. CD results revealed that PNP caused an increase in Hb beta-sheet content while decreasing the alpha helical content. Additionally, the results of UV-Vis spectroscopy and fluorescence emission of heme degradation products revealed the protective effect of PNP on heme during glycation and fructation of human Hb. It is notable that the synergistic effects of combined propolis nanoparticles and aspirin is more than either of them alone. However, having said that, PNP as a natural product has a potential to be an effective drug in the treatment of diabetes.

Metabolic Syndrome and Neuroprotection

Introduction: Over the years the prevalence of metabolic syndrome (MetS) has drastically increased in developing countries as a major byproduct of industrialization. Many factors, such as the consumption of high-calorie diets and a sedentary lifestyle, bolster the spread of this disorder. Undoubtedly, the massive and still increasing incidence of MetS places this epidemic as an important public health issue. Hereon we revisit another outlook of MetS beyond its classical association with cardiovascular disease (CVD) and Diabetes Mellitus Type 2 (DM2), for MetS also poses a risk factor for the nervous tissue and threatens neuronal function. First, we revise a few essential concepts of MetS pathophysiology. Second, we explore some neuroprotective approaches in MetS pertaining brain hypoxia. The articles chosen for this review range from the years 1989 until 2017; the selection criteria was based on those providing data and exploratory information on MetS as well as those that studied innovative therapeutic approaches.

Pathophysiology: The characteristically impaired metabolic pathways of MetS lead to hyperglycemia, insulin resistance (IR), inflammation, and hypoxia, all closely associated with an overall pro-oxidative status. Oxidative stress is well-known to cause the wreckage of cellular structures and tissue architecture. Alteration of the redox homeostasis and oxidative stress alter the macromolecular array of DNA, lipids, and proteins, in turn disrupting the biochemical pathways necessary for normal cell function.

Neuroprotection: Different neuroprotective strategies are discussed involving lifestyle changes, medication aimed to mitigate MetS cardinal symptoms, and treatments targeted toward reducing oxidative stress. It is well-known that the routine practice of physical exercise, aerobic activity in particular, and a complete and well-balanced nutrition are key factors to prevent MetS. Nevertheless, pharmacological control of MetS as a whole and pertaining hypertension, dyslipidemia, and endothelial injury contribute to neuronal health improvement.

Conclusion: The development of MetS has risen as a risk factor for neurological disorders. The therapeutic strategies include multidisciplinary approaches directed to address different pathological pathways all in concert.

Extracts of Chrysanthemum zawadskii attenuate oxidative damage to vascular endothelial cells caused by a highly reducing sugar

Endothelial cells are considered candidates for involvement in the pathogenesis of diabetic vascular complications, and prevention of endothelial cell damage may be important in pharmacological attempts to prevent such complications. In the present study, I explored whether extracts of Chrysanthemum zawadskii (CZE) could prevent oxidative damage and dysfunction of a vascular endothelial cell line caused by the highly reducing sugar, 2-deoxy-D-ribose (dRib), and dysfunction of a vascular endothelial cell line. Vascular endothelial cells were treated with dRib in the presence or absence of CZE. Cell viability was monitored using a cell counting kit, and the induction of apoptosis was evaluated with a cell death kit. Prostaglandin E2 and cyclooxygenase-2 levels were measured using enzyme-linked immunosorbent assay kits. Mitochondrial membrane potential [ΔΨ(m)] was determined using a JC-1 kit. Intracellular oxidative stress was measured by fluorometric analysis of dichlorofluorescin oxidation using 2',7'-dichlorofluorescin diacetate as the probe. The expression levels of genes encoding antioxidant enzymes were analyzed by real-time polymerase chain reaction. dRib reduced cell survival and the ΔΨ(m) and markedly increased intracellular levels of reactive oxygen species and apoptosis. However, pretreatment of cells with CZE attenuated all these dRib-induced effects. The anti-oxidant N-acetyl-L-cysteine (NAC) also prevented dRib-induced oxidative cell damage. CZE attenuated the dRib-induced production of the inflammatory mediators cyclooxygenase-2 and Prostaglandin E2. NAC also exhibited anti-inflammatory effects and treatment with CZE caused transcriptional elevation of genes encoding antioxidant enzymes. Taken together, the results suggest that CZE may exert an antioxidant action that reduces dRib-induced cell damage to vascular endothelial cells and may thus aid in preventing diabetes-associated microvascular complications.

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.

Regulatory landscape of AGE-RAGE-oxidative stress axis and its modulation by PPARγ activation in high fructose diet-induced metabolic syndrome

Background

The AGE-RAGE-oxidative stress (AROS) axis is involved in the onset and progression of metabolic syndrome induced by a high-fructose diet (HFD). PPARγ activation is known to modulate metabolic syndrome; however a systems-level investigation looking at the protective effects of PPARγ activation as related to the AROS axis has not been performed.

The aim of this work is to simultaneously characterize multiple molecular parameters within the AROS axis, using samples taken from different body fluids and tissues of a rat model of HFD-induced metabolic syndrome, in the presence or absence of a PPARγ agonist, Rosiglitazone (RGZ).

Methods

Rats were fed with 60% HFD for the first half of the treatment duration (21 days) then continued with either HFD alone or HFD plus RGZ for the second half.

Results

Rats receiving HFD alone showed metabolic syndrome manifestations including hypertension, dyslipidemia, increased glucose levels and insulin resistance, as well as abnormal kidney and inflammatory parameters. Systolic blood pressure, plasma triglyceride and glucose levels, plasma creatinine, and albuminuria were significantly improved in the presence of RGZ. The following molecular parameters of the AROS axis were significantly upregulated in our rat model: carboxymethyl lysine (CML) in urine and liver; carboxyethyl lysine (CEL) in urine; advanced glycation end products (AGEs) in plasma; receptor for advanced glycation end products (RAGE) in liver and kidney; advanced oxidation protein products (AOPP) in plasma; and 4-hydroxynonenal (HNE) in plasma, liver, and kidney. Conversely, with RGZ administration, the upregulation of AOPP and AGEs in plasma, CML and CEL in urine, RAGE in liver as well as HNE in plasma and liver was significantly counteracted/prevented.

Conclusions

Our data demonstrate (i) the systems-level regulatory landscape of HFD-induced metabolic syndrome involving multiple molecular parameters, including HNE, AGEs and their receptor RAGE, and (ii) attenuation of metabolic syndrome by PPARγ modulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0149-z) contains supplementary material, which is available to authorized users.

Investigating the effects of Citrullus colocynthis pulp on oxidative stress in testes and epididymis in streptozotocin-induced diabetic male rats

BACKGROUND

Diabetes mellitus is one of the most common metabolic diseases in humans, affecting 100 million people around the world.

OBJECTIVE

Investigating the effects of Citrullus colocynthis pulp on oxidant and antioxidant factors of testes and epididymis in streptozotocin-induced diabetic male rats.

MATERIALS AND METHODS

Thirty two male rats were divided into four groups (n=8) 1) N (normal) group, 2) N+C group, 3) D (diabetic) group and 4) D+C group. Groups N and D received normal saline 2 ml orally for two weeks and groups N+C and D+C received 10 mg/kg.bw Citrullus colocynthis pulp orally for two weeks. Diabetes was induced by single intraperitoneal injection of streptozotocin (STZ) at 65 mg/kg.

RESULTS

D group had a significant increase in H₂O₂ (Hydrogen peroxide) and MDA (malondialdehyde) concentrations, and CAT (catalase) activity, and also a significant decrease in Peroxidase (POD) activity compared to N group. D+C group had a significant decrease in H₂O₂ and MDA concentrations and, CAT activity and significant increase in POD activity compared to D group.

CONCLUSION

Citrullus colocynthis pulp in two weeks had beneficial effects on oxidants and antioxidants changes in reproductive system in streptozotocin-induced diabetic rats.

Glyco-redox, a link between oxidative stress and changes of glycans: Lessons from research on glutathione, reactive oxygen and nitrogen species to glycobiology

Reduction-oxidation (redox) response is one of the most important biological phenomena. The concept introduced by Helmut Sies encouraged many researchers to examine oxidative stress under pathophysiological conditions. Our group has been interested in redox regulation under oxidative stress as well as glycobiology in relation to disease. Current studies by our group and other groups indicate that functional and structural changes of glycans are regulated by redox responses resulting from the generation of reactive oxygen species (ROS) or reactive nitrogen species (RNS) in various diseases including cancer, diabetes, neurodegenerative disease such as Parkinson disease, Alzheimer's disease and amyotrophic lateral sclerosis (ALS), and chronic obstructive pulmonary disease (COPD), even though very few investigators appear to be aware of these facts. Here we propose that the field "glyco-redox" will open the door to a more comprehensive understanding of the mechanism associated with diseases in relation to glycan changes under oxidative stress. A tight link between structural and functional changes of glycans and redox system under oxidative stress will lead to the recognition and interest of these aspects by many scientists. Helmut's contribution in this field facilitated our future perspectives in glycobiology.

Glycation vs. glycosylation: a tale of two different chemistries and biology in Alzheimer's disease

In our previous studies, we reported that the activity of an anti-oxidant enzyme, Cu,Zn-superoxide dismutase (Cu,Zn-SOD) became decreased as the result of glycation in vitro and in vivo. Glycated Cu,Zn-SOD produces hydroxyl radicals in the presence of transition metals due to the formation of a Schiff base adduct and a subsequent Amadori product. This results in the site-specific cleavage of the molecule, followed by random fragmentation. The glycation of other anti-oxidant enzymes such as glutathione peroxidase and thioredoxin reductase results in a loss or decrease in enzyme activity under pathological conditions, resulting in oxidative stress. The inactivation of anti-oxidant enzymes induces oxidative stress in aging, diabetes and neurodegenerative disorders. It is well known that the levels of Amadori products and N(e)-(carboxylmethyl)lysine (CML) and other carbonyl compounds are increased in diabetes, a situation that will be discussed by the other authors in this special issue. We and others, reported that the glycation products accumulate in the brains of patients with Alzheimer's disease (AD) patients as well as in cerebrospinal fluid (CSF), suggesting that glycation plays a pivotal role in the development of AD. We also showed that enzymatic glycosylation is implicated in the pathogenesis of AD and that oxidative stress is also important in this process. Specific types of glycosylation reactions were found to be up- or downregulated in AD patients, and key AD-related molecules including the amyloid-precursor protein (APP), tau, and APP-cleaving enzymes were shown to be functionally modified as the result of glycosylation. These results suggest that glycation as well as glycosylation are involved in oxidative stress that is associated with aging, diabetes and neurodegenerative diseases such as AD.

Fructose induces mitochondrial dysfunction and triggers apoptosis in skeletal muscle cells by provoking oxidative stress

Mitochondrial dysfunction in skeletal muscle has been implicated in the development of insulin resistance, a major characteristic of type 2 diabetes. There is evidence that oxidative stress results from the increased production of reactive oxygen species and reactive nitrogen species leads to mitochondrial dysfunction, tissue damage, insulin resistance, and other complications observed in type 2 diabetes. It has been suggested that intake of high fructose contributes to insulin resistance and other metabolic disturbances. However, there is limited information about the direct effect of fructose on the mitochondrial function of skeletal muscle, the major metabolic determinant of whole body insulin activity. Here, we assessed the effect of fructose exposure on mitochondria-mediated mechanisms in skeletal muscle cells. Exposure of L6 myotubes to high fructose stimulated the production of mitochondrial reactive oxygen species and nitric oxide (NO), and the expression of inducible NO synthase. Fructose-induced oxidative stress was associated with increased translocation of nuclear factor erythroid 2-related factor-2 to the nucleus, decreases in mitochondrial DNA content and mitochondrial dysfunctions, as evidenced by decreased activities of citrate synthase and mitochondrial dehydrogenases, loss of mitochondrial membrane potential, decreased activity of the mitochondrial respiratory complexes, and impaired mitochondrial energy metabolism. Furthermore, positive Annexin-propidium iodide staining and altered expression of Bcl-2 family members and caspases in L6 myotubes indicated that the cells progressively became apoptotic upon fructose exposure. Taken together, these findings suggest that exposure of skeletal muscle cells to fructose induced oxidative stress that decreased mitochondrial DNA content and triggered mitochondrial dysfunction, which caused apoptosis.

Dietary supplementation with fermented legumes modulate hyperglycemia and acetylcholinesterase activities in Streptozotocin-induced diabetes

The study investigated the hypoglycemic and anticholinesterase activities of some fermented legumes (bambara groundnut and locust bean) in Streptozotocin (STZ)-induced diabetic rats. The rats were made diabetic by intraperitoneal administration of STZ (35mg/kg b.w.) and were fed diets containing fermented legumes (10% inclusion) for 14 days. The effect of the diets on blood glucose, pancreatic glutathione peroxidase (GPx) activity, reduced glutathione (GSH) and malondialdehyde (MDA) contents, α-amylase, intestinal α-glucosidase and acetylcholinesterase activities were studied. Significant (P<0.05) increase in blood glucose, pancreatic MDA, α-amylase, intestinal α-glucosidase and acetylcholinesterase activities with concomitant decrease in pancreatic GPx and GSH contents were observed in diabetic rats. However, this trend was reversed in rats fed fermented legumes supplemented diets for 14 days. The HPLC-DAD finger printing revealed the presence of gallic acid, catechin, caffeic acid, epicatechin, rutin, isoquercitrin, quercitrin, quercetin and kaempferol as the dominant phenolic compounds of the fermented legumes. However, possible contributing role of some bioactive peptides could not be ruled out. Hence, the hypoglycemic and antiacetylcholinesterase activities of the fermented legume condiments could be attributed to their constituent phytochemicals.

Dietary Advanced Glycation End Products Consumption as a Direct Modulator of Insulin Sensitivity in Overweight Humans: A Study Protocol for a Double-Blind, Randomized, Two Period Cross-Over Trial

BACKGROUND

Advanced glycation end products (AGEs) are formed during the processing, storage, and cooking of foods. As part of a western diet, AGEs are consumed in excess and impair glucose metabolism in patients with type 2 diabetes. In the absence of diabetes, AGE-mediated decreases in insulin sensitivity and signaling have been postulated. However, randomized studies to test this relationship in humans are limited.

OBJECTIVE

The primary aim of this trial is to determine whether dietary consumption of AGEs will decrease insulin sensitivity in healthy overweight adults. A secondary aim is to determine the effects of dietary AGEs on insulin secretion, circulating soluble receptor for AGEs (sRAGE), and inflammation markers.

METHODS

Overweight, but otherwise healthy, non-diabetic adults (N=20) aged 18-50 years old will complete a randomized cross-over design intervention study alternating low and high (4-fold increase) AGE diets (2-week duration). At baseline, participants will undergo a medical review including an intravenous glucose tolerance test (IVGTT), a hyperinsulinemic-euglycemic clamp, and anthropometric measures and questionnaires assessing diet, physical activity, and general wellness. Each test diet will be followed for 14 days, followed by a 4-week washout period before commencement of the second alternate dietary period. Energy, macronutrient, and AGE intake will be calculated for each dietary period. Additionally, the AGE content of foods used in the study will be measured by ultra performance liquid chromatography mass spectrometry. All measurements will be repeated at the beginning and end of each dietary period. Primary and secondary outcomes will be expressed as a change over the dietary period for insulin sensitivity, secretion, anthropometric parameters, sRAGE, and inflammation markers and compared by paired t test and analysis of variance (ANOVA).

RESULTS

The study will be completed in early 2016.

CONCLUSION

The proposed trial will provide much needed clinical evidence on the impact of excess dietary AGE consumption on insulin sensitivity and will indicate whether lowering dietary AGE intake can improve insulin sensitivity and/or secretion, thereby decreasing risk for type 2 diabetes.

TRIAL REGISTRATION

Clinicaltrials.gov NCT00422253; https://clinicaltrials.gov/ct2/show/NCT00422253 (Archived by Webcite at http://www.webcitation.org/6ZXLhT89c).

Phloroglucinol Protects INS-1 Pancreatic β-cells Against Glucotoxicity-Induced Apoptosis

Decreasing numbers, and impaired function, of pancreatic β-cells are key factors in the development of type 2 diabetes. This study was designed to investigate whether phloroglucinol protected pancreatic β-cells against glucotoxicity-induced apoptosis using a rat insulinoma cell line (INS-1). High glucose treatment (30 mM) induced INS-1 cell death; however, the level of glucose-induced apoptosis was significantly reduced in cells treated with 100-μM phloroglucinol. Treatment with 10-100-μM phloroglucinol increased cell viability and decreased intracellular levels of reactive oxygen species, nitric oxide, and lipid peroxidation dose-dependently in INS-1 cells pretreated with high glucose. Furthermore, phloroglucinol treatment markedly reduced the protein expression of Bax, cytochrome c, and caspase 9, while increasing anti-apoptotic Bcl-2 protein expression. Cell death type was examined using annexin V/propidium iodide staining, revealing that phloroglucinol markedly reduced high glucose-induced apoptosis. These results demonstrated that phloroglucinol could be useful as a potential therapeutic agent for the protection of pancreatic β-cells against glucose-induced apoptosis.

Liraglutide improves pancreatic Beta cell mass and function in alloxan-induced diabetic mice

Glucagon-like peptide-1 (GLP-1) receptor agonists potentiate glucose-induced insulin secretion. In addition, they have been reported to increase pancreatic beta cell mass in diabetic rodents. However, the precise mode of action of GLP-1 receptor agonists still needs to be elucidated. Here we clarify the effects of the human GLP-1 analog liraglutide on beta cell fate and function by using an inducible Cre/loxP-based pancreatic beta cell tracing system and alloxan-induced diabetic mice. Liraglutide was subcutaneously administered once daily for 30 days. The changes in beta cell mass were examined as well as glucose tolerance and insulin secretion. We found that chronic liraglutide treatment improved glucose tolerance and insulin response to oral glucose load. Thirty-day treatment with liraglutide resulted in a 2-fold higher mass of pancreatic beta cells than that in vehicle group. Liraglutide increased proliferation rate of pancreatic beta cells and prevented beta cells from apoptotic cells death. However, the relative abundance of YFP-labeled beta cells to total beta cells was no different before and after liraglutide treatment, suggesting no or little contribution of neogenesis to the increase in beta cell mass. Liraglutide reduced oxidative stress in pancreatic islet cells of alloxan-induced diabetic mice. Furthermore, the beneficial effects of liraglutide in these mice were maintained two weeks after drug withdrawal. In conclusion, chronic liraglutide treatment improves hyperglycemia by ameliorating beta cell mass and function in alloxan-induced diabetic mice.

The production of cross-reactive autoantibodies that bind to bovine serum albumin in mice administered reducing sugars by subcutaneous injection

INTRODUCTION

In a previous study, we identified the formation of cross-reactive autoantibodies that bound to bovine serum albumin (BSA) in a D-galactose-induced aging mouse model.

AIM OF THE STUDY

In this study, we investigated the effect of other reducing sugars (namely, glucose and fructose) on the formation of autoantibodies. The effects of concentration and route of administration on the formation of autoantibodies were examined in detail.

MATERIAL AND METHODS

Three concentrations (100, 500, and 1,000 mg/kg) of reducing sugars were tested. The effects of different routes of administration (subcutaneous, oral, and intraperitoneal) on the formation of autoantibodies were also analysed. The immunoreactivities of serum samples from mice treated with reducing sugars were analysed by an enzyme-linked immunosorbent assay (ELISA) using BSA or mouse serum albumin antigens (MSA).

RESULTS

Repeated subcutaneous administration of all reducing sugars lead to autoantibody formation in a concentration-dependent manner. However, these autoantibodies did not cross-react with MSA, and simultaneous treatment of aminoguanidine with reducing sugars did not show any inhibitory effects on the formation of autoantibodies. No autoantibodies were detected after oral or intraperitoneal administration of reducing sugars. Immunohistochemistry data showed that the target antigen(s) of the autoantibodies were present only in the skin tissue of mice treated with reducing sugars.

CONCLUSIONS

Our results show that administration of reducing sugars by subcutaneous injection leads to the formation of autoantibodies that cross-react with BSA; the formation and target antigen(s) of the autoantibodies may originate from within the skin tissue treated with the reducing sugars.

Inhibitor of differentiation proteins protect against oxidative stress by regulating the antioxidant-mitochondrial response in mouse beta cells

AIMS/HYPOTHESIS

Oxidative stress is implicated in beta cell glucotoxicity in type 2 diabetes. Inhibitor of differentiation (ID) proteins are transcriptional regulators induced by hyperglycaemia in islets, but the mechanisms involved and their role in beta cells are not clear. Here we investigated whether or not oxidative stress regulates ID levels in beta cells and the role of ID proteins in beta cells during oxidative stress.

METHODS

MIN6 cells were cultured in H2O2 or ribose to induce oxidative stress. ID1, ID3 and small MAF proteins (MAFF, MAFG and MAFK) were inhibited using small interfering RNA. Isolated islets from Id1(-/-), Id3(-/-) and diabetic db/db mice were used.

RESULTS

ID1-4 expression was upregulated in vivo in the islets of diabetic db/db mice and stimulated in vitro by ribose and H2O2. Id1/3 inhibition reduced the expression of multiple antioxidant genes and potentiated oxidative stress-induced apoptosis. This finding was associated with increased levels of intracellular reactive oxygen species, altered mitochondrial morphology and reduced expression of Tfam, which encodes a mitochondrial transcription factor, and respiratory chain components. Id1/3 inhibition also reduced the expression of small MAF transcription factors (MafF, MafG and MafK), interacting partners of nuclear factor, erythroid 2-like 2 (NFE2L2), master regulator of the antioxidant response. Inhibition of small MAFs reduced the expression of antioxidant genes and potentiated oxidative stress-induced apoptosis, thus recapitulating the effects of Id1/3 inhibition.

CONCLUSIONS/INTERPRETATION

Our study identifies IDs as a novel family of oxidative stress-responsive proteins in beta cells. IDs are crucial regulators of the adaptive antioxidant-mitochondrial response that promotes beta cell survival during oxidative stress through a novel link to the NFE2L2-small MAF pathway.

Role of pancreatic transcription factors in maintenance of mature β-cell function

A variety of pancreatic transcription factors including PDX-1 and MafA play crucial roles in the pancreas and function for the maintenance of mature β-cell function. However, when β-cells are chronically exposed to hyperglycemia, expression and/or activities of such transcription factors are reduced, which leads to deterioration of β-cell function. These phenomena are well known as β-cell glucose toxicity in practical medicine as well as in the islet biology research area. Here we describe the possible mechanism for β-cell glucose toxicity found in type 2 diabetes. It is likely that reduced expression levels of PDX-1 and MafA lead to suppression of insulin biosynthesis and secretion. In addition, expression levels of incretin receptors (GLP-1 and GIP receptors) in β-cells are decreased, which likely contributes to the impaired incretin effects found in diabetes. Taken together, down-regulation of insulin gene transcription factors and incretin receptors explains, at least in part, the molecular mechanism for β-cell glucose toxicity.

Relationship of Soluble RAGE with Insulin Resistance and Beta Cell Function during Development of Type 2 Diabetes Mellitus

This study examined whether circulating levels of soluble receptor for advanced glycation end products (sRAGE) alter in prediabetes and correlate with insulin resistance (IR) and beta cell function in prediabetes and newly diagnosed type 2 diabetes mellitus (T2DM). Subjects without previous history of diabetes were recruited and grouped as control, prediabetes, and newly diagnosed T2DM. The control subjects (n = 40) and people with prediabetes (n = 52) and diabetes (n = 66) were similar in terms of age, sex, BMI, systolic and diastolic BP, and fasting insulin level. HOMA-IR was found significantly higher in people with diabetes than control subjects (p < 0.001) and people with prediabetes (p = 0.005); and HOMA-%B was found significantly deteriorated in people with diabetes (p < 0.001) compared to control subjects and people with prediabetes. However, serum sRAGE levels did not show any significant alteration in people with prediabetes compared to control subjects. Moreover, univariate and multivariate analyses did not identify any significant correlation and statistical association of sRAGE with HOMA-IR and HOMA-%B in people with prediabetes and newly diagnosed T2DM. Our data suggest that serum sRAGE levels do not alter in people with prediabetes compared to control subjects and do not correlate or associate with IR and beta cell function during development of T2DM.

Circulating concentrations of soluble receptor for AGE are associated with age and AGER gene polymorphisms in children with newly diagnosed type 1 diabetes

OBJECTIVE

We analyzed the relationship among soluble receptor for advanced glycation end products (sRAGEs), the clinical phenotype, HLA genotype, and risk-associated single nucleotide polymorphisms (SNPs) in the AGER gene in a large population of Finnish children with newly diagnosed type 1 diabetes.

RESEARCH DESIGN AND METHODS

Samples from 2,115 clinically phenotyped children <15 years of age in whom type 1 diabetes was diagnosed and 316 control subjects were analyzed for sRAGEs. Three SNPs of AGER, previously associated with HLA-DR/DQ haplotype independent diabetes risk (rs2070600, rs9469089, and rs17493811), were analyzed in 1,390 affected subjects.

RESULTS

Children with type 1 diabetes and control subjects had similar sRAGE concentrations (1,171 vs. 1,153 pg/mL, P = 0.48). There was a correlation between age at diagnosis and serum sRAGE concentrations (r = 0.10, P < 0.001) among the patients but not among the control subjects. Children <2 years of age had the lowest concentrations in the diabetic population (1,027 vs. 1,181 pg/mL, P < 0.001) and the highest among the control subjects (1,329 vs. 1,140 pg/mL, P = 0.04). Ketoacidosis at diagnosis was associated with reduced concentrations (1,086 vs. 1,190 pg/mL, P < 0.001). HLA DR3/DR4 heterozygosity and the DR3 allele were associated with reduced sRAGE concentrations. The predisposing AA genotype of rs2070600 was associated with decreased sRAGE concentrations, while the protective CC genotype of rs9469089 was linked to increased concentrations.

CONCLUSIONS

Age and AGER polymorphisms are associated with the circulating sRAGE concentration among children with type 1 diabetes. The observations of reduced sRAGE concentrations in young children, in those with ketoacidosis, and in carriers of the high-risk HLA DR3/DR4 genotype suggest that decreased sRAGE concentration reflects a more aggressive disease phenotype.

Padina arborescens extract protects high glucose-induced apoptosis in pancreatic β cells by reducing oxidative stress

BACKGROUND/OBJECTIVES

This study investigated whether Padina arborescens extract (PAE) protects INS-1 pancreatic β cells against glucotoxicity-induced apoptosis.

MATERIALS/METHODS

Assays, including cell viability, lipid peroxidation, generation of intracellular ROS, NO production, antioxidant enzyme activity and insulin secretion, were conducted. The expressions of Bax, Bcl-2, and caspase-3 proteins in INS-1 cells were evaluated by western blot analysis, and apoptosis/necrosis induced by high glucose was determined by analysis of FITC-Annexin V/PI staining.

RESULTS

Treatment with high concentrations of glucose induced INS-1 cell death, but PAE at concentrations of 25, 50 or 100 µg/ml significantly increased cell viability. The treatment with PAE dose dependently reduced the lipid peroxidation and increased the activities of antioxidant enzymes reduced by 30 mM glucose, while intracellular ROS levels increased under conditions of 30 mM glucose. PAE treatment improved the secretory responsiveness following stimulation with glucose. The results also demonstrated that glucotoxicity-induced apoptosis is associated with modulation of the Bax/Bcl-2 ratio. When INS-1 cells were stained with Annexin V/PI, we found that PAE reduced apoptosis by glucotoxicity.

CONCLUSIONS

In conclusion, the present study indicates that PAE protects against high glucose-induced apoptosis in pancreatic β cells by reducing oxidative stress.

Nucleotide pyrophosphatase/phosphodiesterase 1 exerts a negative effect on starch accumulation and growth in rice seedlings under high temperature and CO2 concentration conditions

Nucleotide pyrophosphatase/phosphodiesterase (NPP) is a widely distributed enzymatic activity occurring in both plants and mammals that catalyzes the hydrolytic breakdown of the pyrophosphate and phosphodiester bonds of a number of nucleotides. Unlike mammalian NPPs, the physiological function of plant NPPs remains largely unknown. Using a complete rice NPP1-encoding cDNA as a probe, in this work we have screened a rice shoot cDNA library and obtained complete cDNAs corresponding to six NPP genes (NPP1-NPP6). As a first step to clarify the role of NPPs, recombinant NPP1, NPP2 and NPP6 were purified from transgenic rice cells constitutively expressing NPP1, NPP2 and NPP6, respectively, and their enzymatic properties were characterized. NPP1 and NPP6 exhibited hydrolytic activities toward ATP, UDP-glucose and the starch precursor molecule, ADP-glucose, whereas NPP2 did not recognize nucleotide sugars as substrates, but hydrolyzed UDP, ADP and adenosine 5'-phosphosulfate. To gain insight into the physiological function of rice NPP1, an npp1 knockout mutant was characterized. The ADP-glucose hydrolytic activities in shoots of npp1 rice seedlings were 8% of those of the wild type (WT), thus indicating that NPP1 is a major determinant of ADP-glucose hydrolytic activity in rice shoots. Importantly, when seedlings were cultured at 160 Pa CO2 under a 28°C/23°C (12 h light/12 h dark) regime, npp1 shoots and roots were larger than those of wild-type (WT) seedlings. Furthermore, the starch content in the npp1 shoots was higher than that of WT shoots. Growth and starch accumulation were also enhanced under an atmospheric CO2 concentration (40 Pa) when plants were cultured under a 33°C/28°C regime. The overall data strongly indicate that NPP1 exerts a negative effect on plant growth and starch accumulation in shoots, especially under high CO2 concentration and high temperature conditions.

Anti-hyperglycemic and hypolipidemic effects of Cistanche tubulosa in type 2 diabetic db/db mice

ETHNOPHARMACOLOGICAL RELEVANCE

The dried succulent stem of Cistanche tubulosa (Schenk) R. Wight is one component of traditional Chinese medicine prescriptions for diabetes. However, there have been no modern scientific reports to confirm this traditional claim for the Cistanche species until now. Thus, we investigated the effects of Cistanche tubulosa on glucose homeostasis and serum lipids in male BKS.Cg-Dock7(m) +/+ Lepr(db)/J (db/db) mice, a model of type 2 diabetes.

MATERIALS AND METHODS

The verbascoside and echinacoside contents of Cistanche tubulosa powder were evaluated using HPLC. The total phenolic content, polysaccharide content and antioxidant activity of Cistanche tubulosa powder were also evaluated. Then, different doses of Cistanche tubulosa (equivalent to 120.9, 72.6 or 24.2mg verbascoside/kg) were administered orally once daily for 45 days to male db/db mice. Age matched db/+ mice were used as normal controls. Body weight, fasting blood glucose, postprandial blood glucose and insulin tolerance test were measured during the experiment. At the time of sacrifice, blood was collected for measurement of insulin level, the homeostatic model assessment of insulin resistance (HOMA-IR), and total cholesterol, triglyceride, HDL-c, LDL-c and VLDL-c levels; liver and muscle were harvested for measurement of glycogen levels.

RESULTS

Cistanche tubulosa significantly suppressed the elevated fasting blood glucose and postprandial blood glucose levels, improved insulin resistance and dyslipidemia, and suppressed body weight loss in db/db mice. However, Cistanche tubulosa did not significantly affect serum insulin levels or hepatic and muscle glycogen levels.

CONCLUSION

This study provides scientific evidence for the traditional use of Cistanche tubulosa to treat diabetes, suggesting that Cistanche tubulosa has the potential for development into a functional food ingredient or drug to prevent hyperglycemia and treat hyperlipidemia.

Genetic disruption of SOD1 gene causes glucose intolerance and impairs β-cell function

Oxidative stress has been associated with insulin resistance and type 2 diabetes. However, it is not clear whether oxidative damage is a cause or a consequence of the metabolic abnormalities present in diabetic subjects. The goal of this study was to determine whether inducing oxidative damage through genetic ablation of superoxide dismutase 1 (SOD1) leads to abnormalities in glucose homeostasis. We studied SOD1-null mice and wild-type (WT) littermates. Glucose tolerance was evaluated with intraperitoneal glucose tolerance tests. Peripheral and hepatic insulin sensitivity was quantitated with the euglycemic-hyperinsulinemic clamp. β-Cell function was determined with the hyperglycemic clamp and morphometric analysis of pancreatic islets. Genetic ablation of SOD1 caused glucose intolerance, which was associated with reduced in vivo β-cell insulin secretion and decreased β-cell volume. Peripheral and hepatic insulin sensitivity were not significantly altered in SOD1-null mice. High-fat diet caused glucose intolerance in WT mice but did not further worsen the glucose intolerance observed in standard chow-fed SOD1-null mice. Our findings suggest that oxidative stress per se does not play a major role in the pathogenesis of insulin resistance and demonstrate that oxidative stress caused by SOD1 ablation leads to glucose intolerance secondary to β-cell dysfunction.

Thioredoxins, glutaredoxins, and peroxiredoxins--molecular mechanisms and health significance: from cofactors to antioxidants to redox signaling

Thioredoxins (Trxs), glutaredoxins (Grxs), and peroxiredoxins (Prxs) have been characterized as electron donors, guards of the intracellular redox state, and "antioxidants". Today, these redox catalysts are increasingly recognized for their specific role in redox signaling. The number of publications published on the functions of these proteins continues to increase exponentially. The field is experiencing an exciting transformation, from looking at a general redox homeostasis and the pathological oxidative stress model to realizing redox changes as a part of localized, rapid, specific, and reversible redox-regulated signaling events. This review summarizes the almost 50 years of research on these proteins, focusing primarily on data from vertebrates and mammals. The role of Trx fold proteins in redox signaling is discussed by looking at reaction mechanisms, reversible oxidative post-translational modifications of proteins, and characterized interaction partners. On the basis of this analysis, the specific regulatory functions are exemplified for the cellular processes of apoptosis, proliferation, and iron metabolism. The importance of Trxs, Grxs, and Prxs for human health is addressed in the second part of this review, that is, their potential impact and functions in different cell types, tissues, and various pathological conditions.

Antioxidant N-acetylcysteine protects pancreatic β-cells against aldosterone-induced oxidative stress and apoptosis in female db/db mice and insulin-producing MIN6 cells

Previous studies have shown that primary aldosteronism is associated with glucose-related metabolic disorders. However, the mechanisms by which aldosterone (ALDO) triggers β-cell dysfunction remains unclear. This study aimed to investigate whether oxidative stress is involved in and whether the antioxidant N-acetylcysteine (NAC) or the mineralocorticoid receptor antagonist spironolactone (SPL) could prevent or delay β-cell damage in vivo and in vitro. As expected, 8 weeks after ALDO treatment, 12-week-old female diabetic db/db mice exhibited impaired oral glucose tolerance, decreased β-cell mass, and heightened levels of oxidative stress marker (urinary 8-hydroxy-2'-deoxyguanosine). NAC reversed these symptoms completely, whereas SPL treatment did so only partially. After exposure to ALDO, the mouse pancreatic β-cell line MIN6 exhibited decreased viability and increased caspase-3 activity, as well as reduced expression of Bcl-2/Bax and p-AKT, even if mineralocorticoid receptor was completely suppressed with small interfering RNA. NAC, but not SPL, suppressed oxidative stress in MIN6 cells, as revealed by the decrease in inducible NOS levels and expression of the proteins p22-phox and p67-phox. These findings suggest that oxidative stress may be involved in ALDO-induced β-cell dysfunction and that NAC, but not SPL, may protect pancreatic β-cells of mice from ALDO-induced oxidative stress and apoptosis in a manner independent of its receptor.

Oxidative stress in diabetes: implications for vascular and other complications

In recent decades, oxidative stress has become a focus of interest in most biomedical disciplines and many types of clinical research. Increasing evidence shows that oxidative stress is associated with the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure. Based on these studies, an emerging concept is that oxidative stress is the “final common pathway” through which the risk factors for several diseases exert their deleterious effects. Oxidative stress causes a complex dysregulation of cell metabolism and cell–cell homeostasis; in particular, oxidative stress plays a key role in the pathogenesis of insulin resistance and β-cell dysfunction. These are the two most relevant mechanisms in the pathophysiology of type 2 diabetes and its vascular complications, the leading cause of death in diabetic patients.

Small-molecule inhibition of inflammatory β-cell death

With the worldwide increase in diabetes prevalence there is a pressing unmet need for novel antidiabetic therapies. Insufficient insulin production due to impaired β-cell function and apoptotic reduction of β-cell mass is a common denominator in the pathogenesis of diabetes. Current treatments are directed at improving insulin sensitivity, and stimulating insulin secretion or replacing the hormone, but do not target progressive apoptotic β-cell loss. Here we review the current development of small-molecule inhibitors designed to rescue β-cells from apoptosis. Several distinct classes of small molecules have been identified that protect β-cells from inflammatory, oxidative and/or metabolically induced apoptosis. Although none of these have yet reached the clinic, β-cell protective small molecules alone or in combination with current therapies provide exciting opportunities for the development of novel treatments for diabetes.

Oral administration of ginseng ameliorates cyclosporine-induced pancreatic injury in an experimental mouse model

Background

This study was performed to investigate whether ginseng has a protective effect in an experimental mouse model of cyclosporine-induced pancreatic injury.

Methods

Mice were treated with cyclosporine (30 mg/kg/day, subcutaneously) and Korean red ginseng extract (0.2 or 0.4 g/kg/day, oral gavage) for 4 weeks while on a 0.01% salt diet. The effect of ginseng on cyclosporine-induced pancreatic islet dysfunction was investigated by an intraperitoneal glucose tolerance test and measurements of serum insulin level, β cell area, macrophage infiltration, and apoptosis. Using an in vitro model, we further examined the effect of ginseng on a cyclosporine-treated insulin-secreting cell line. Oxidative stress was measured by the concentration of 8-hydroxy-2′-deoxyguanosine in serum, tissue sections, and culture media.

Results

Four weeks of cyclosporine treatment increased blood glucose levels and decreased insulin levels, but cotreatment with ginseng ameliorated the cyclosporine-induced glucose intolerance and hyperglycemia. Pancreatic β cell area was also greater with ginseng cotreatment compared with cyclosporine monotherapy. The production of proinflammatory molecules, such as induced nitric oxide synthase and cytokines, and the level of apoptotic cell death also decreased in pancreatic β cell with ginseng treatment. Consistent with the in vivo results, the in vitro study showed that the addition of ginseng protected against cyclosporine-induced cytotoxicity, inflammation, and apoptotic cell death. These in vivo and in vitro changes were accompanied by decreases in the levels of 8-hydroxy-2′-deoxyguanosine in pancreatic β cell in tissue section, serum, and culture media during cotreatment of ginseng with cyclosporine.

Conclusions

The results of our in vivo and in vitro studies demonstrate that ginseng has a protective effect against cyclosporine-induced pancreatic β cell injury via reducing oxidative stress.