Peroxynitrite-induced protein nitration contributes to liver mitochondrial damage in diabetic rats

Differential Impact of Flavonoids on Redox Modulation, Bioenergetics, and Cell Signaling in Normal and Tumor Cells: A Comprehensive Review

SIGNIFICANCE

Flavonoids can interact with multiple molecular targets to elicit their cellular effects, leading to changes in signal transduction, gene expression, and/or metabolism, which can, subsequently, affect the entire cell and organism. Immortalized cell lines, derived from tumors, are routinely employed as a surrogate for mechanistic studies, with the results extrapolated to tissues in vivo. Recent Advances: We review the activities of selected flavonoids on cultured tumor cells derived from various tissues in comparison to corresponding primary cells or tissues in vivo, mainly using quercetin and flavanols (epicatechin and (-)-epigallocatechin gallate) as exemplars. Several studies have indicated that flavonoids could retard cancer progression in vivo in animal models as well as in tumor cell models.

CRITICAL ISSUES

Extrapolation from in vitro and animal models to humans is not straightforward given both the extensive conjugation and complex microbiota-dependent metabolism of flavonoids after consumption, as well as the heterogeneous metabolism of different tumors.

FUTURE DIRECTIONS

Comparison of data from studies on primary cells or in vivo are essential not only to validate results obtained from cultured cell models, but also to highlight whether any differences may be further exploited in the clinical setting for chemoprevention. Tumor cell models can provide a useful mechanistic tool to study the effects of flavonoids, provided that the limitations of each model are understood and taken into account in interpretation of the data.

The protective effect of beta-casomorphin-7 via promoting Foxo1 activity and nuclear translocation in human lens epithelial cells

PURPOSE

To investigate the protective effect of beta-casomorphin-7 (β-CM-7) in oxidative stressed human lens epithelial cells (HLECs) and to explore the possible mechanism for oxidative stress in HLECs induced by high glucose.

METHODS

We used HLECs to determine the effect of different concentrations of β-CM-7 on cell viability by 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolimol/L bromide (MTT) assay. We used flow cytometry to determine the content of reactive oxygen species (ROS) induced by oxidative stress and a bioassay kit to determine the oxidant malondialdehyde (MDA) and antioxidant enzyme superoxide dismutase (SOD) levels. We used Western blotting and an immunofluorescence assay to determine the expression of Forkhead box o1 (Foxo1), SP1, and the related protein glutathione peroxidase (GSH-px) at the molecular biology level as well as their intracellular localization.

RESULTS

The expression of Foxo1 and SP1 was weakly expressed when the glucose concentration was 40 mM/L, but was highly expressed when cells were pre-treated with an appropriate concentration of β-CM-7. After pre-treatment with β-CM-7, the cells treated with 40 mM/L glucose for 48 h showed Foxo1 was transferred to the nucleus, and the expression of SP1 was increased. The content of ROS and MDA in the HLECs that were pre-treated with β-CM-7 was lower than in those that was not pre-treated (p <0.05). Accordingly, SOD was elevated in the cells pre-treated with β-CM-7. The relative expression of GSH-px increased with increases of Foxo1 and SP1.

CONCLUSION

β-CM-7 protects HLECs from oxidative damage by upregulating the relative expression of Foxo1 and promoting Foxo1 nuclear translocation.

Proteomic Analysis of Peroxynitrite-Induced Protein Nitration in Isolated Beef Heart Mitochondria

Mitochondria are exposed to reactive nitrogen species under physiological conditions and even more under several pathologic states. In order to reveal the mechanism of these processes we studied the effects of peroxynitrite on isolated beef heart mitochondria in vitro. Peroxynitrite has the potential to nitrate protein tyrosine moieties, break the peptide bond, and eventually release the membrane proteins into the solution. All these effects were found in our experiments. Mitochondrial proteins were resolved by 2D electrophoresis and the protein nitration was detected by immunochemical methods and by nano LC-MS/MS. Mass spectrometry confirmed nitration of ATP synthase subunit beta, pyruvate dehydrogenase E1 component subunit beta, citrate synthase and acetyl-CoA acetyltransferase. Immunoblot detection using chemiluminiscence showed possible nitration of other proteins such as cytochrome b-c1 complex subunit 1, NADH dehydrogenase [ubiquinone] iron-sulfur protein 2, elongation factor Tu, NADH dehydrogenase [ubiquinone] flavoprotein 2, heat shock protein beta-1 and NADH dehydrogenase [ubiquinone] iron-sulfur protein 8. ATP synthase beta subunit was nitrated both in membrane and in fraction prepared by osmotic lysis. The high sensitivity of proteins to nitration by peroxynitrite is of potential biological importance, as these enzymes are involved in various pathways associated with energy production in the heart.

Proteomic analysis of peroxynitrite-induced protein nitration in isolated beef heart mitochondria

Mitochondria are exposed to reactive nitrogen species under physiological conditions and even more under several pathologic states. In order to reveal the mechanism of these processes we studied the effects of peroxynitrite on isolated beef heart mitochondria in vitro. Peroxynitrite has the potential to nitrate protein tyrosine moieties, break the peptide bond, and eventually release the membrane proteins into the solution. All these effects were found in our experiments. Mitochondrial proteins were resolved by 2D electrophoresis and the protein nitration was detected by immunochemical methods and by nano LC-MS/MS. Mass spectrometry confirmed nitration of ATP synthase subunit beta, pyruvate dehydrogenase E1 component subunit beta, citrate synthase and acetyl-CoA acetyltransferase. Immunoblot detection using chemiluminiscence showed possible nitration of other proteins such as cytochrome b-c1 complex subunit 1, NADH dehydrogenase [ubiquinone] iron-sulfur protein 2, elongation factor Tu, NADH dehydrogenase [ubiquinone] flavoprotein 2, heat shock protein beta-1 and NADH dehydrogenase [ubiquinone] iron-sulfur protein 8. ATP synthase beta subunit was nitrated both in membrane and in fraction prepared by osmotic lysis. The high sensitivity of proteins to nitration by peroxynitrite is of potential biological importance, as these enzymes are involved in various pathways associated with energy production in the heart.

A Si-rhodamine-based near-infrared fluorescent probe for visualizing endogenous peroxynitrite in living cells, tissues, and animals

An aromatic tertiary amine-functionalized Si-rhodamine dye has been exploited as a near-infrared fluorescent probe for visualizing endogenous peroxynitrite in living cells, tissues, and mice.

Polysaccharides from Laminaria japonica show hypoglycemic and hypolipidemic activities in mice with experimentally induced diabetes

Diabetes mellitus (DM) is a chronic metabolic disorder of the endocrine system. The rapid increase in the incidence of DM is a serious public health concern worldwide. The treatment of DM and its complications mainly involves the use of chemically or biochemically synthesized drugs, but these drugs also have adverse side effects. Therefore, there is an urgent need to search for drugs from natural sources that would cause fewer side effects. This study aimed to determine whether polysaccharides from Laminaria japonica (LJP) exert hypoglycemic and hypolipidemic effects in mice with alloxan-induced diabetes. To this end, diabetes was induced by alloxan injection (200 mg/kg body weight [bw], intraperitoneal [ip]). After induction of diabetes, diabetic mice were randomly divided into five groups: diabetic control (DC) group, glibenclamide-treated (DG) group, low-dose LJP-treated (DLL) group, moderate-dose LJP-treated (DML) group, and high-dose LJP-treated (DHL) group, with normal mice used as the control group (NC group). After treatment for 28 days, body weight, fasting blood glucose (FBG), serum insulin, total cholesterol (TC), triglyceride (TG), high-density lipoprotein-cholesterol (HDL-C), and low-density lipoprotein-cholesterol (LDL-C) levels were measured. The results revealed that LJP administration prevented body-weight loss, decreased FBG levels, and increased serum insulin levels in diabetic mice. Furthermore, it decreased TC, TG, and LDL-C levels, and increased HDL-C levels in these mice. Thus, the results indicate that LJP possesses hypoglycemic and hypolipidemic activities and polysaccharides from LJP may hold promise for the development of a drug of natural origin for the treatment of DM.

A PPARγ, NF-κB and AMPK-dependent mechanism may be involved in the beneficial effects of curcumin in the diabetic db/db mice liver

Turmeric (Curcuma longa) is a rhizomatous herbaceous perennial plant of the ginger family which has been used to treat biliary disorders, anorexia, cough, rheumatism, cancer, sinusitis, hepatic disorders, hyperglycemia, obesity, and diabetes in both Ayurvedic and Traditional Chinese Medicine. Suggested mechanisms of action include the modulation of signal transduction cascades and effects on gene expression, however they remain to be elucidated. In this study, the expression of some proteins responsible for transcription factors, inflammation, and metabolic control were evaluated by western blot in 15-week-old db/db mice livers treated with curcumin 0.75% mixed in their diet for 8 weeks. In addition, nitrosative stress was evaluated. Curcumin increased the expression of AMPK and PPARγ, and diminished NF-κB protein in db/db mice. However, it did not modify the expression of PGC-1α or SIRT1. Nitrosative stress present in db/db mice livers was determined by a unique nitrotyrosylated protein band (75 kDa) and was not reverted with curcumin. In conclusion, curcumin regulates the expression of AMPK, PPARγ, and NF-κB; suggesting a beneficial effect for treatment of T2DM complications. In order to observe best beneficial effects it is desirable to administer curcumin in the earlier states of T2DM.

Beneficial effects of silibinin against the progression of metabolic syndrome, increased oxidative stress, and liver steatosis in Psammomys obesus, a relevant animal model of human obesity and diabetes

BACKGROUND

Insulin resistance and oxidative stress are major pathogenic mechanisms leading to chronic liver diseases in diabetic subjects. The gerbil Psammomys obesus is a unique model of nutritional diabetes resembling the disease in humans. This study investigated whether the natural ingredient silibinin, known as hepatoprotective, could decrease oxidative stress and reduce liver damage in obese gerbils.

METHODS

Control animals were fed their vegetable-based low caloric diet while two other rat groups ingested a high calorie diet for 14 weeks. Silibinin, or its vehicle, was administrated by gastric intubation (100 mg/kg per day) from the 7th week of treatment, which corresponds to an established insulin resistance state. At the end of the experiments, the hepatic biochemical profile, markers of oxidative stress in either plasma or liver tissue, and histological alterations were examined.

RESULTS

Diabetic P. obesus displayed many metabolic disturbances (hyperinsulinemia, hyperglycemia, dyslipidemia), which were aggravated for the last 8 weeks. These events were coupled with greater oxidative stress (decline in glutathione, rise in lipoperoxidation). In addition, glutathione peroxidase activity was reduced while the level of superoxide dismutase was elevated. Interestingly, treatment with silibinin alleviated most of the metabolic defects, especially high triglyceride levels, reduced insulin resistance and largely restored antioxidant status. Also, Masson's trichrome staining revealed distinct steatosis, yet silibinin partially reversed this manifestation.

CONCLUSION

Silibinin affords substantial protection against the progression of insulin resistance in Type 2 diabetes mellitus for P. obesus by hampering the oxidative process and improving hepatic metabolism.

Mitochondrial dysfunction in brain cortex mitochondria of STZ-diabetic rats: effect of l-Arginine

Mitochondrial dysfunction has been implicated in many diseases, including diabetes. It is well known that oxygen free radical species are produced endogenously by mitochondria, and also nitric oxide (NO) by nitric oxide synthases (NOS) associated to mitochondrial membranes, in consequence these organelles constitute main targets for oxidative damage. The aim of this study was to analyze mitochondrial physiology and NO production in brain cortex mitochondria of streptozotocin (STZ) diabetic rats in an early stage of diabetes and the potential effect of L-arginine administration. The diabetic condition was characterized by a clear hyperglycaemic state with loose of body weight after 4 days of STZ injection. This hyperglycaemic state was associated with mitochondrial dysfunction that was evident by an impairment of the respiratory activity, increased production of superoxide anion and a clear mitochondrial depolarization. In addition, the alteration in mitochondrial physiology was associated with a significant decrease in both NO production and nitric oxide synthase type I (NOS I) expression associated to the mitochondrial membranes. An increased level of thiobarbituric acid-reactive substances (TBARS) in brain cortex homogenates from STZ-diabetic rats indicated the presence of lipid peroxidation. L-arginine treatment to diabetic rats did not change blood glucose levels but significantly ameliorated the oxidative stress evidenced by lower TBARS and a lower level of superoxide anion. This effect was paralleled by improvement of mitochondrial respiratory function and a partial mitochondrial repolarization.In addition, the administration of L-arginine to diabetic rats prevented the decrease in NO production and NOSI expression. These results could indicate that exogenously administered L-arginine may have beneficial effects on mitochondrial function, oxidative stress and NO production in brain cortex mitochondria of STZ-diabetic rats.

Exercise in obese female rats has beneficial effects on maternal and male and female offspring metabolism

BACKGROUND

Maternal obesity (MO) impairs maternal and offspring health. Mechanisms and interventions to prevent adverse maternal and offspring outcomes need to be determined. Human studies are confounded by socio-economic status providing the rationale for controlled animal data on effects of maternal exercise (MEx) intervention on maternal (F0) and offspring (F1) outcomes in MO.

HYPOTHESIS

MO produces metabolic and endocrine dysfunction, increases maternal and offspring glucocorticoid exposure, oxidative stress and adverse offspring outcomes by postnatal day (PND) 36. MEx prevents these outcomes.

METHODS

F0 female rats ate either control or obesogenic diet from weaning through lactation. Half of each group wheel ran (from day ninety of life through pregnancy beginning day 120) providing four groups (n=8/group) – i) controls, ii) obese, iii) exercised controls and iv) exercised obese. After weaning, PND 21, F1 offspring ate a control diet. Metabolic parameters of F0 prepregnancy and end of lactation and F1 offspring at PND 36 were analyzed.

RESULTS

Exercise did not change maternal weight. Before breeding, MO elevated F0 glucose, insulin, triglycerides, cholesterol, leptin, fat and oxidative stress. Exercise completely prevented the triglyceride rise and partially glucose, insulin, cholesterol and oxidative stress increases. MO decreased fertility, recovered by exercise. At the end of lactation, exercise returned all metabolic variables except leptin to control levels. Exercise partially prevented MO elevated corticosterone. F1 Offspring weights were similar at birth. At PND 36 MO increased F1 male but not female offspring leptin, triglycerides and fat mass. In controls exercise reduced male and female offspring glucose, prevented the offspring leptin increase and partially the triglyceride rise.

CONCLUSIONS

MEx before and during pregnancy has beneficial effects on maternal and offspring metabolism and endocrine function occurring with no weight change in mothers and offspring indicating the importance of body composition rather than weight in evaluations of metabolic status.

Beneficial effects of the synthetic antioxidant tert-butyl bisphenol on the hepatic microcirculation in a rat model of diabetes mellitus

Diabetes mellitus is associated with oxidative injury to the vasculature. Here, the link between oxidative stress and ultrastructural changes in the hepatic microcirculation was investigated as well as the effects of a synthetic antioxidant, tert-butyl bisphenol (tBP). The study focused on the impact of experimental diabetes on liver sinusoidal endothelial cell (LSEC) fenestrations, which are pores in the liver endothelium that facilitate substrate transfer between blood and hepatocytes. Adult male rats were rendered diabetic using streptozotocin (60 mg/kg) and administered 1-2 IU insulin daily. After 8 weeks, animals received either 100 mg/kg tBP or vehicle alone, on 2 consecutive days. Livers were harvested 24 h later under isofluorane anaesthesia (5% v/v in O2(g) by inhalation) and fixed for scanning electron microscopy to evaluate fenestrations or for immuno-histochemical assessment of nitrotyrosine, a marker of nitrosative stress. Median fenestration diameter increased significantly following 8 weeks of diabetes (80 nm vs. 70 nm controls; P < 0.001). LSEC porosity increased by ~50% (P < 0.001). Treatment with tBP reversed these changes completely. Periportal nitrotyrosine staining was increased in diabetic livers, and this was abrogated by tBP, indicating that tBP reduced nitrosative stress in the liver. Early diabetes caused an increase in fenestration diameter and porosity. This was reversed by acute treatment with tBP, suggesting a link between nitrosative stress and regulation of liver endothelial fenestrations, and indicates that antioxidant therapy may protect the liver microvasculature against the effects of diabetes mellitus.

The association effect of insulin and clonazepam on oxidative stress in liver of an experimental animal model of diabetes and depression

CONTEXT

It is known that oxidative stress occurs in peripheral blood in an experimental animal model of diabetes and depression, and acute treatment with insulin and clonazepam (CNZ) has a protective effect on oxidative stress in this model.

OBJECTIVE

This study evaluated the effect of insulin plus CNZ on oxidative stress parameters in the liver of diabetic male rats induced with streptozotocin (STZ) and subjected to forced swimming test (FST).

MATERIALS AND METHODS

Diabetes was induced by a single intraperitoneal (i.p.) dose of STZ 60 mg/kg in male Wistar rats. Insulin (4 IU/kg) plus CNZ acute i.p. treatment (0.25 mg/kg) was administered 24, 5 and 1 h before the FST. Nondiabetic control rats received i.p. injections of saline (1 mL/kg). Protein oxidative damage was evaluated by carbonyl formation and the antioxidant redox parameters were analyzed by the measurements of enzymatic activities of the superoxide dismutase (SOD), catalase and glyoxalase I (GLO). Glycemia levels also were determined.

RESULTS

Our present study has shown an increase in carbonyl content from diabetic rats subjected to FST (2.04 ± 0.55), while the activity of catalase (51.83 ± 19.02) and SOD (2.30 ± 1.23) were significantly decreased in liver from these animals, which were reverted by the treatment. Also, the activity of GLO (0.15 ± 0.02) in the liver of the animals was decreased.

DISCUSSION AND CONCLUSION

Our findings showed that insulin plus CNZ acute treatment ameliorate the antioxidant redox parameters and protect against protein oxidative damage in the liver of diabetic rats subjected to FST.

The alternative crosstalk between RAGE and nitrative thioredoxin inactivation during diabetic myocardial ischemia-reperfusion injury

The receptor for advanced glycation end products (RAGE) and thioredoxin (Trx) play opposing roles in diabetic myocardial ischemia-reperfusion (MI/R) injury. We recently demonstrated nitrative modification of Trx leads to its inactivation and loss of cardioprotection. The present study is to determine the relationship between augmented RAGE expression and diminished Trx activity pertaining to exacerbated MI/R injury in the diabetic heart. The diabetic state was induced in mice by multiple intraperitoneal low-dose streptozotocin injections. RAGE small-interfering RNA (siRNA) or soluble RAGE (sRAGE, a RAGE decoy) was via intramyocardial and intraperitoneal injection before MI/R, respectively. Mice were subjected to 30 min of myocardial infarction followed by 3 or 24 h of reperfusion. At 10 min before reperfusion, diabetic mice were randomized to receive EUK134 (peroxynitrite scavenger), recombinant hTrx-1, nitrated Trx-1, apocynin (a NADPH oxidase inhibitor), or 1400W [an inducible nitric oxide synthase (iNOS) inhibitor] administration. The diabetic heart manifested increased RAGE expression and N(ε)-(carboxymethyl)lysine (CML, major advanced glycation end product subtype) content, reduced Trx-1 activity, and increased Trx nitration after MI/R. RAGE siRNA or administration of sRAGE in diabetic mice decreased MI/R-induced iNOS and gp91(phox) expression, reduced Trx nitration, preserved Trx activity, and decreased infarct size. Apocynin or 1400W significantly decreased nitrotyrosine production and restored Trx activity. Conversely, administration of either EUK134 or reduced hTrx, but not nitrated hTrx, attenuated MI/R-induced superoxide production, RAGE expression, and CML content and decreased cardiomyocyte apoptosis in diabetic mice. Collectively, we demonstrate that RAGE modulates the MI/R injury in a Trx nitrative inactivation fashion. Conversely, nitrative modification of Trx blocked its inhibitory effect upon RAGE expression in the diabetic heart. This is the first direct evidence demonstrating the alternative cross talk between RAGE overexpression and nitrative Trx inactivation, suggesting that interventions interfering with their interaction may be novel means of mitigating diabetic MI/R injury.

Hepatic nitrosative stress in experimental diabetes

AIM

The effects of the inhibition of nitrosative stress by aminoguanidine in an experimental model of diabetes mellitus (DM) were investigated.

METHODS

Twenty-one male Wistar rats were divided into three groups: control (CO), diabetic (DM), and diabetic treated with aminoguanidine (DM+AG). Aminoguanidine (aminoguanidine hemisulfate salt, Sigma Chemical Co., St. Louis, MO, USA) was used at a dose of 50 mg/kg (i.p.) during the last 30 days of the experiment. The expression levels of liver lipoperoxidation (TBARS - nmol/mg protein), inducible oxide nitric synthase (iNOS), nitrotyrosine and the NFκB nuclear transcription factor p65 were examined using western blot analysis.

RESULTS

The DM group demonstrated an increase in lipoperoxidation and in the expression of iNOS, nitrotyrosine and p65. Aminoguanidine reduced hepatic lipid peroxidation and protein expression levels of iNOS, nitrotyrosine and p65.

CONCLUSION

Aminoguanidine treatment reduces liver oxidative and nitrosative stress in diabetic animals. In addition, aminoguanidine reduced the expression of p65 in the liver.

Role of inducible nitric oxide synthase in mitochondrial depolarization and graft injury after transplantation of fatty livers

This study investigated the role of inducible nitric oxide synthase (iNOS) in failure of ethanol-induced fatty liver grafts. Rat livers were explanted 20 h after gavaging with ethanol (5 g/kg) and storing in UW solution for 24h before implantation. Hepatic oil red O staining-positive areas increased from ∼2 to ∼33% after ethanol treatment, indicating steatosis. iNOS expression increased ∼8-fold after transplantation of lean grafts (LG) and 25-fold in fatty grafts (FG). Alanine aminotransferase release, total bilirubin, hepatic necrosis, TUNEL-positive cells, and cleaved caspase-3 were higher in FG than LG. A specific iNOS inhibitor 1400W (5 μM in the cold-storage solution) blunted these alterations by >42% and increased survival of fatty grafts from 25 to 88%. Serum nitrite/nitrate and hepatic nitrotyrosine adducts increased to a greater extent after transplantation of FG than LG, indicating reactive nitrogen species (RNS) overproduction. Phospho-c-Jun and phospho-c-Jun N-terminal kinase-1/2 (JNK1/2) were higher in FG than in LG, indicating more JNK activation in fatty grafts. RNS formation and JNK activation were blunted by 1400W. Mitochondrial polarization and cell death were visualized by intravital multiphoton microscopy of rhodamine 123 and propidium iodide, respectively. After implantation, viable cells with depolarized mitochondria were 3-fold higher in FG than in LG and 1400W decreased mitochondrial depolarization in FG to the levels of LG. Taken together, iNOS is upregulated after transplantation of FG, leading to excessive RNS formation, JNK activation, mitochondrial dysfunction, and severe graft injury. The iNOS inhibitor 1400W could be an effective therapy for primary nonfunction of fatty liver grafts.

Ferric citrate CYP2E1-independently promotes alcohol-induced apoptosis in HepG2 cells via oxidative/nitrative stress which is attenuated by pretreatment with baicalin

In the case of alcoholic liver injury, an iron overload is always present. Both alcohol and iron can individually induce oxidative stress in liver. However, the combined effect of physiological concentrations of alcohol and iron on oxidative stress in hepatocytes remains unknown. Baicalin has been demonstrated to be an antioxidant or iron chelator in animal experiments. In this study, we investigated the injury to hepatocytes CYP2E1-independently induced by the combination of alcohol and iron and the protective effect of baicalin. Compared with cells treated with ethanol alone, ferric citrate enhanced the accumulation of reactive oxygen and nitrogen species, increased the occurrence of protein carbonylation/nitration and the levels of 4-hydroxy-2-nonenal, changed the distribution of iNOS, and eventually resulted in apoptosis. However, pretreatment with baicalin inhibited the oxidative stress induced by the combination of alcohol and iron, mainly by chelating iron. Our findings therefore suggest that iron could CPY2E1-independently enhance the oxidative stress induced by alcohol, which probably contributes to the pathogenesis of alcoholic liver disease. Baicalin is a promising phytomedicine for preventing alcoholic liver disease.

Diabetes-related adduct formation and retinopathy

The pathogenesis of diabetic retinopathy is complex, reflecting the array of systemic and tissue-specific metabolic abnormalities. A range of pathogenic pathways are directly linked to hyperglycaemia and dyslipidaemia, and the retina appears to be exquisitely sensitive to damage. Establishing the biochemical and molecular basis for this pathology remains an important research focus. This review concentrates on the formation of a range of protein adducts that form after exposure to modifying intermediates known to be elevated during diabetes. These so-called advanced glycation end products (AGEs) and advanced lipoxidation end products (ALEs) are thought to play an important role in the initiation and progression of diabetic retinopathy, and mechanisms leading to dysfunction and death of various retinal cells are becoming understood. Perspective is provided on AGE/ALE formation in the retina and the impact that such adducts have on retinal cell function. There will be emphasis placed on the role of the receptor for AGEs and how this may modulate retinal pathology, especially in relation to oxidative stress and inflammation. The review will conclude by discussion of strategies to inhibit AGE/ALE formation or harmful receptor interactions in order to prevent disease progression from the point of diabetes diagnosis to sight-threatening proliferative diabetic retinopathy and diabetic macular oedema.

Prebiotics and oxidative stress in constipated rats

OBJECTIVES

Constipation can adversely affect children's health, with disorders of host immunity and enhanced oxidative stress. As nondigestible carbohydrates, prebiotics can affect the host with constipation; however, whether the prebiotics have effects on the content of intestinal secretory immunoglobulin A (sIgA) and the contents of superoxide dismutase (SOD) and malondialdehyde (MDA) in constipation has not been fully clarified.

METHODS

In the present study, constipation was induced in female Sprague-Dawley rats by diphenoxylate, and the prebiotics dissolved in milk were used as an intervention. The indicators of intestinal peristalsis, including the time of passing black stool initially, the grains of black stool in 24 hours, and the advance rate of ponceau, were measured. The content of intestinal sIgA was detected by enzyme-linked immunosorbent assay. The contents of SOD and MDA in serum and intestinal tissue were analyzed by their detection kits.

RESULTS

The changes in intestinal peristalsis show obvious constipation. The content of intestinal sIgA decreases, the content of SOD decreases, but the content of MDA increases in constipated rats. Prebiotics can attenuate the constipation-caused abnormal indicators significantly.

CONCLUSIONS

Prebiotics can attenuate decreased intestinal immunity and enhanced oxidative stress, in addition to reduced intestinal peristalsis and of the constipated rats.

Advanced glycation end products accelerate ischemia/reperfusion injury through receptor of advanced end product/nitrative thioredoxin inactivation in cardiac microvascular endothelial cells

The advanced glycation end products (AGEs) are associated with increased cardiac endothelial injury. However, no causative link has been established between increased AGEs and enhanced endothelial injury after ischemia/reperfusion. More importantly, the molecular mechanisms by which AGEs may increase endothelial injury remain unknown. Adult rat cardiac microvascular endothelial cells (CMECs) were isolated and incubated with AGE-modified bovine serum albumin (BSA) or BSA. After AGE-BSA or BSA preculture, CMECs were subjected to simulated ischemia (SI)/reperfusion (R). AGE-BSA increased SI/R injury as evidenced by enhanced lactate dehydrogenase release and caspase-3 activity. Moreover, AGE-BSA significantly increased SI/R-induced oxidative/nitrative stress in CMECs (as measured by increased inducible nitric oxide synthase expression, total nitric oxide production, superoxide generation, and peroxynitrite formation) and increased SI/R-induced nitrative inactivation of thioredoxin-1 (Trx-1), an essential cytoprotective molecule. Supplementation of EUK134 (peroxynitrite decomposition catalyst), human Trx-1, or soluble receptor of advanced end product (sRAGE) (a RAGE decoy) in AGE-BSA precultured cells attenuated SI/R-induced oxidative/nitrative stress, reduced SI/R-induced Trx-1 nitration, preserved Trx-1 activity, and reduced SI/R injury. Our results demonstrated that AGEs may increase SI/R-induced endothelial injury by increasing oxidative/nitrative injury and subsequent nitrative inactivation of Trx-1. Interventions blocking RAGE signaling or restoring Trx activity may be novel therapies to mitigate endothelial ischemia/reperfusion injury in the diabetic population.

Exogenous superoxide dismutase: action on liver oxidative stress in animals with streptozotocin-induced diabetes

Aim. To investigate the effects of exogenous antioxidant copper zinc superoxide dismutase (Cu/Zn SOD) on oxidative stress in the experimental model of diabetes mellitus (DM). Methods. Twenty eight male Wistar rats divided in four groups were used: control (CO), controls treated with SOD (CO + SOD), diabetics (DM), and diabetics treated with SOD (DM + SOD). SOD (orgotein, 13 mg/Kg body weight was administered. DM was induced by a single streptozotocin injection (i.p., 70 mg/kg), and 60 days later, we evaluated liver oxidative stress. Results. Liver lipoperoxidation was increased in the DM group and significantly decreased in the DM + SOD group. Nitrite and nitrate measures were reduced in the DM and increased in the DM + SOD group, while iNOS expression in the DM group was 32% greater than in the CO and 53% greater in the DM + SOD group than in the DM group (P < .01). P65 expression was 37% higher in the DM (P < .05), and there was no significant difference between the DM and DM + SOD groups. Conclusion. SOD treatment reduced liver oxidative stress in diabetic animals, even though it did not change NFκB. SOD also increased NO, probably by the increased dismutation of the superoxide radical. The iNOS expression increase, which became even more evident after SOD administration.

Peroxynitrite-induced nitration of cyclooxygenase-2 and inducible nitric oxide synthase promotes their binding in diabetic angiopathy

Cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) play crucial roles in diabetic angiopathy. In vivo, however, the following facts remain unknown: whether COX-2 and iNOS bind, how peroxynitrite-induced nitration of COX-2 and iNOS affects their binding if they do bind and what effects of this mechanism contribute to diabetic angiopathy. This study focused on the issues above. Diabetes was induced in Wistar male rats by intraperitoneal injection of streptozotocin. As a specific scavenger of peroxynitrite, urate was used. After 13 wks of diabetes, the morphological and biochemical changes of the rats showed obvious diabetic angiopathy. There exists in vivo colocalization and binding of COX-2 and iNOS in diabetic angiopathy. The nitration level of total and co-immunoprecipitated COX-2 and iNOS increased significantly, and, simultaneously, their binding and activity increased in the diabetes group. In the diabetes + urate group, the nitration level of COX-2 and iNOS decreased and their binding reduced, consistent with their decreased activity and the attenuated pathological changes in the rat aorta and glomerulus. The results provide in vivo evidence that COX-2 and iNOS can bind in diabetic angiopathy and that peroxynitrite-induced nitration of COX-2 and iNOS promotes their binding, contributing to diabetic angiopathy.

Inhibition of inducible nitric oxide synthase prevents mitochondrial damage and improves survival of steatotic partial liver grafts

BACKGROUND

Steatotic liver grafts are excluded for partial liver transplantation because of increased risk of primary nonfunction. Mechanisms underlying the failure of fatty partial liver grafts (FPG) remain unknown. This study investigated whether inducible nitric oxide synthase (iNOS) plays a role in failure of FPG.

METHODS

Fatty livers were induced by feeding rats a high-fat high-fructose diet for 2 weeks. Hepatic triglyceride was approximately 9-fold higher in rats fed the high-fat high-fructose diet than those fed a low-fat low-fructose diet. Lean and fatty liver explants were reduced in size ex vivo to approximately one third, stored in the University of Wisconsin cold storage solution for 2 hr, and implanted.

RESULTS

Posttransplantational hepatic iNOS expression and reactive nitrogen species (RNS) formation (nitrite and nitrate levels and 3-nitrotyrosine adducts) increased more profoundly in FPG than in lean partial grafts (LPG). Serum alanine aminotransferase and bilirubin were 2- and 5.5-fold higher after transplantation of FPG than LPG. 5-Bromo-2'-deoxyuridine incorporation was 25% in LPG but only 5% in FPG, and graft weight increased by 64% in LPG while remaining unchanged in FPG. All rats that received FPG died, whereas all those receiving LPG survived. N-(1-naphtyl)ethylendiamine dihydrochloride (5 microM), a specific iNOS inhibitor, largely blunted the production of RNS, prevented the increase of alanine aminotransferase and bilirubin, restored liver regeneration, and improved survival of FPG. Mitochondrial cytochrome c oxidase-IV, ATP synthase-beta, and NADH dehydrogenase-3 decreased markedly in FPG, and these effects were blocked by N-(1-naphtyl)ethylendiamine dihydrochloride.

CONCLUSION

Thus, hepatic steatosis causes failure of partial liver grafts, most likely by increasing RNS that leads to mitochondrial damage and dysfunction.

Peroxynitrite-induced protein nitration is responsible for renal mitochondrial damage in diabetic rat

Oxidative stress, especially mediated by peroxynitrite (ONOO-), plays a key role in diabetes. Mitochondria, as the generating source of ONOO-, may also be the major damaging target of ONOO-. Whether ONOO--induced protein nitration is responsible for renal mitochondrial damage in diabetes is not fully known. This study was aimed to clarify the relationship between nitration of entire mitochondrial proteins induced by ONOO- and the renal mitochondrial damage in diabetes. Sprague-Dawley male rats were injected ip with streptozotocin to induce diabetes. After 10 weeks, inducible nitric oxide synthase (iNOS) mRNA expression and protein content in renal cortex were detected. Distribution of nitrotyrosine (NT), a specific marker of ONOO-, in renal cortex and NT content in mitochondrial proteins were detected. The ultrastructure of glomerulus was observed. Aminoguanidine was used as a selective inhibitor of iNOS to reduce the derivation of ONOO-. In diabetic rat, increasing levels of iNOS mRNA and protein content, and NT content were observed, in accord with the pathological alterations of glomerulus. In aminoguanidine group, these alterations were attenuated significantly. In conclusion, ONOO- could induce entire mitochondrial proteins nitration, responsible for the damage of renal mitochondria in diabetes.

Fasting induces a high level of 3-nitrotyrosine in the brain of rats

Although the relationship between hyperglycemia (using diabetic animal model) and plasma nitrotyrosine level has been studied, the effect of hypoglycemia on nitrotyrosine level in the brain has not been addressed. Here, we evaluated nitration of protein, the colocalization of nitration with alpha-synuclein, activity of inducible nitric oxide synthase, and nitric oxide content using fasting and diabetic animal models. The results showed that signals of alpha-synuclein were widely distributed in most parts of the pallium, midbrain, hippocampus and cerebellum, as indicated by immunohistochemistry. Most signals of the 3-nitrotyrosine were colocalized with those of alpha-synuclein in the midbrain of fasting rats. The level of proteins containing 3-nitrotyrosine was significantly increased in the brain of fasting rats in Western blotting, especially in the midbrain, compared with control rats. In addition, the 3-nitrotyrosine signals increased in hippocampus of diabetic rats. Immunoprecipitation showed that alpha-synuclein was nitrated in the fasting rats. The iNOS activity and nitric oxide levels were significantly increased in both fasting and diabetic animals. The enhanced 3-nitrotyrosine level in the brain of fasting rats suggests that nitration of protein including alpha-synuclein in the midbrain is more affected by hypoglycemia in fasting than hyperglycemia in diabetic rats.

Dysregulation of corticosterone secretion in streptozotocin-diabetic rats: modulatory role of the adrenocortical nitrergic system

An increased activity of the hypothalamo-pituitary-adrenal axis resulting in exaggerated glucocorticoid secretion has been repeatedly described in patients with diabetes mellitus and in animal models of this disease. However, it has been pointed out that experimental diabetes is accompanied by a decreased glucocorticoid response to ACTH stimulation. Because previous studies from our laboratory demonstrate the involvement of nitric oxide (NO) in the modulation of corticosterone production, present investigations were designed to evaluate 1) the impact of streptozotocin (STZ)-induced diabetes on the adrenocortical nitrergic system and 2) the role of NO in the modulation of adrenal steroidogenesis in STZ-diabetic rats. Four weeks after STZ injection, increased activity and expression levels of proteins involved in L-arginine transport and in NO synthesis were detected, and increased levels of thiobarbituric acid reactive species, carbonyl adducts, and nitrotyrosine-modified proteins were measured in the adrenocortical tissue of hyperglycemic rats. An impaired corticosterone response to ACTH was evident both in vivo and in adrenocortical cells isolated from STZ-treated animals. Inhibition of NO synthase activity resulted in higher corticosterone generation in adrenal tissue from STZ-treated rats. Moreover, a stronger inhibition of steroid output from adrenal cells by a NO donor was observed in adrenocortical Y1 cells previously subjected to high glucose (30 mM) treatment. In summary, results presented herein indicate an inhibitory effect of endogenously generated NO on steroid production, probably potentiated by hyperglycemia-induced oxidative stress, in the adrenal cortex of STZ-treated rats.

Peroxynitrite mediates glomerular lesion of diabetic rat via JAK/STAT signaling pathway

BACKGROUND

Peroxynitrite, a highly reactive oxidant produced by the reaction of nitric oxide with free radicals superoxide, has been indicated to be involved in many diseases. However, the contributions of peroxynitrite to diabetic nephropathy and the underlying mechanism have not been fully explored.

AIM

The present study was designed to evaluate the role and the underlying mechanism of peroxynitrite in glomerular lesion of diabetic rat.

METHODS

Diabetes was induced in male Wistar rats by i.p. injection of streptozotocin, and urate was used as a specific scavenger of peroxynitrite; the pathological changes of rat glomerulus were evaluated by hematoxylin and eosin, periodic acid-Schiff staining and transmission electron microscopy observation; immunohistochemistry and Western blot were used to detect the content of nitrotyrosine (the marker of peroxynitrite) in renal cortex; the expression levels of tyrosine phosphorylation of JAK2, STAT1, and STAT3 were assessed by Western blot assay; RT-PCR and Western blot were used to assay expression levels of transforming growth factor (TGF)-beta1 and fibronectin; biochemical indicators of renal function were also detected.

RESULTS

The content of nitrotyrosine was increased, consistent with the pathological changes of glomerulus and renal dysfunction in the diabetes group. Urate prevented the formation of nitrotyrosine in rat glomerulus and attenuated the pathological alterations. Furthermore, urate inhibited the activation of JAK2, STAT1, and STAT3. Finally, homogenates from renal cortices demonstrated reduced expression of TGF- beta1 and fibronectin under urate treatment.

CONCLUSIONS

Our findings thus provides in vivo evidence that exaggerated peroxynitrite formation mediates the glomerular lesion in, at least, Type 1 diabetes, which may function through JAK/STAT signaling pathway.

Protein tyrosine nitration: selectivity, physicochemical and biological consequences, denitration, and proteomics methods for the identification of tyrosine-nitrated proteins

Protein tyrosine nitration (PTN) is a post-translational modification occurring under the action of a nitrating agent. Tyrosine is modified in the 3-position of the phenolic ring through the addition of a nitro group (NO2). In the present article, we review the main nitration reactions and elucidate why nitration is not a random chemical process. The particular physical and chemical properties of 3-nitrotyrosine (e.g., pKa, spectrophotometric properties, reduction to aminotyrosine) will be discussed, and the biological consequences of PTN (e.g., modification of enzymatic activity, sensitivity to proteolytic degradation, impact on protein phosphorylation, immunogenicity and implication in disease) will be reviewed. Recent data indicate the possibility of an in vivo denitration process, which will be discussed with respect to the different reaction mechanisms that have been proposed. The second part of this review article focuses on analytical methods to determine this post-translational modification in complex proteomes, which remains a major challenge.

Superoxide dismutase analog (Tempol: 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine 1-oxyl) treatment restores erectile function in diabetes-induced impotence

We hypothesized that administration of the superoxide dismutase (SOD) mimetic Tempol (4-hydroxy-2, 2, 6, 6-tetramethylpiperidine 1-oxyl) may reverse diabetes induced ED(erectile dysfunction). To test this hypothesis, ROS related genes (SOD1, SOD2, GPx1, CAT, NOS2, NOS3), erectile functional studies, and immunohistochemical analysis were performed in diabetic rats treated with or without Tempol. Thirty Sprague-Dawley (3–4 months old) rats were divided into 3 groups (n=10 each), 20 with diabetes (diabetic control and Tempol treatment) and 10 healthy controls. Twelve weeks after induction of diabetes by streptozotocin and Tempol treatment, all groups underwent in vivo cavernous nerve stimulation. Rat crura were harvested and expression of antioxidative defense enzymes examined by semi-quantitative RT-PCR. To confirm the RT-PCR results, we performed immunohistochemistry (IHC) for catalase (CAT) and iNOS (NOS2). Nitration of tyrosine groups in proteins was also examined by IHC. Mean intracavernous pressure in the diabetic group was significantly lower than in healthy controls (p<0.001) and was reversed by Tempol treatment (p<0.0108). NOS2 protein expression was significantly increased in diabetic animals compared to healthy controls and Tempol restored NOS2 protein level. Nitrotyrosine was also higher in diabetic animals and though Tempol treatment decreased its formation, it remained higher than that found in healthy controls. This study suggests that Tempol treatment increased erectile function through modulating oxidative stress related genes in diabetic rats. This is the first report about the relationship between diabetes induced erectile dysfunction and oxidative stress, and anti-oxidative therapy using the superoxide dismutase mimetic, Tempol to restore erectile function.

Nitrosative stress, protein tyrosine nitration, PARP activation and NAD depletion in the kidneys of rats after single dose of cyclophosphamide

OBJECTIVES

Cyclophosphamide (CP) and its structural analogue ifosfamide are highly effective cytostatic drugs. While both cyclophosphamide and ifosfamide have severe urotoxic side effects, only ifosfamide is thought to be nephrotoxic. The nephrotoxicity of CP in generally overlooked because of normal plasma creatinine levels. Therefore, little information is available regarding the pathogenic mechanism of renal damage by CP. In the present study, we investigated the role of nitrosative stress in CP-induced renal damage.

METHODS

The experimental rats received a single i.p. of 150 mg/kg body weight CP in saline and were killed 6 h or 16 h later. The control rats received saline. The kidneys were used for histological and biochemical analysis. Nitrotyrosine and poly (ADP-ribose) polymerase (PARP) were localized immunohistochemically as indicators of protein nitration and DNA damage, respectively. Nitrite, NAD and superoxide dismutase (SOD) activity were assayed in the kidney homogenates.

RESULTS

The nitrite level in the kidneys of CP-treated rats was elevated twofold. The kidneys of CP-treated rats stained strongly for nitrotyrosine as well as for PARP. Significant decrease in oxidized NAD levels was also observed in the kidneys of CP-treated rats. The activity of the peroxynitrite sensitive enzyme SOD was significantly reduced in the kidneys of CP-treated rats.

CONCLUSION

The results of the present study reveal that nitrosative stress may play an important role in CP-induced renal damage. It is suggested that protein nitration, PARP activation and NAD +/- depletion may play a critical role in the pathogenesis of cyclophosphamide induced renal damage.

Cerulein pancreatitis: oxidative stress, inflammation, and apoptosis

Cerulein pancreatitis is similar to human edematous pancreatitis, manifesting with dysregulation of digestive enzyme production and cytoplasmic vacuolization, the death of acinar cells, edema formation, and infiltration of inflammatory cells into the pancreas. Reactive oxygen species are involved in nuclear factor-kappaB activation, cytokine expression, apoptosis and pathogenesis of pancreatitis. There is recent evidence that cerulein activates NADPH oxidase, which is a major source of reactive oxygen species during inflammation and apoptosis in pancreatic acinar cells. In addition, the Janus kinase/signal transducer and activator of transcription pathway has been suggested as being involved in inflammatory signaling in the pancreas. This review discusses the involvement of oxidative stress in inflammation and apoptosis in pancreatic acinar cells stimulated with cerulein as an in vitro model of pancreatitis.