Role of mitochondrial superoxide dismutase in the development of diabetic retinopathy

PURPOSE: Apoptosis of retinal capillary cells is an early event in the pathogenesis of retinopathy in diabetes, and oxidative stress has been linked to accelerated apoptosis of retinal capillary cells. Mitochondria are the major endogenous source of superoxide, and superoxide is considered to be a causal link between elevated glucose and the major biochemical pathways postulated to be involved in the development of vascular complications in diabetes. The purpose of the present study is to determine the role of mitochondrial superoxide dismutase (MnSOD) in the development of diabetic retinopathy. METHODS: The effect of overexpression of MnSOD on glucose-induced endothelial cell oxidative stress, nitrosative stress, and apoptosis was determined by using bovine retinal endothelial cells. Furthermore, the effect of diabetes in rats (11 months' duration) on the activity and the mRNA expression of retinal MnSOD were also determined. RESULTS: MnSOD activity in the nontransfected control retinal endothelial cells was 20% compared with the total SOD activity and was increased to 60% in the MnSOD-transfected cells. MnSOD overexpression prevented a glucose-induced increase in oxidative stress (8-hydroxy guanosine levels), nitrosative stress (nitrotyrosine formation), and apoptosis of retinal endothelial cells. MnSOD enzyme activity and its mRNA were decreased significantly in the retina obtained from the diabetic rats, and these abnormalities were prevented by long-term lipoic acid therapy. CONCLUSIONS: The results of this study suggest a protective role for MnSOD in retinal capillary cell death and, ultimately, in the pathogenesis of retinopathy in diabetes. Understanding the role of MnSOD to modify the course of retinopathy could elucidate important molecular targets for future pharmacological interventions.     

The role of lipid peroxidation products and oxidative stress in activation of the canonical wingless-type MMTV integration site (WNT) pathway in a rat model of diabetic retinopathy

Aims/hypothesis  

Our recent studies suggest that activation of the wingless-type MMTV integration site (WNT) pathway plays pathogenic roles in diabetic retinopathy and age-related macular degeneration. Here we investigated the causative role of oxidative stress in retinal WNT pathway activation in an experimental model of diabetes.     

Oxidative Stress Induced by Diclofenac Alone and under the Influence of Certain Variables in Broilers

Diclofenac toxicity was studied in male broiler chicks (Cobb strain) of a day old age. The chicks were randomly divided into eight groups consisting of 10 in each group. Group 1 was kept as basal diet control (1-32 days), group 2 on basal diet for 32 days + diclofenac (0.8 mg/kg body weight I/M) on day 24, 26, 28, 30, and 32, group 3 on basal diet for 32 days + cyclophosphamide (50 mg/kg body weight I/M once daily) from day 20 to 23, group 4 on high-protein, high-calcium, low vitamin A (HPHC) diet (1-32 days), group 5 on basal diet + diclofenac + cyclophosphamide (as per the schedule), group 6 on HPHC + diclofenac (as per the schedule), group 7 on HPHC + cyclophosphamide (as per the schedule), and group 8 on HPHC + diclofenac + cyclophosphamide (as per the schedule). The activity of TBARS, SOD, and catalase revealed a significant (P< 0.05) increase, while there was a significant (P < 0.05) decrease in the concentration of GSH in liver in the groups given diclofenac either alone or in combination with other variables. There was no significant difference in the diclofenac residue levels. The electron microscopy of liver revealed lesions of mild to marked severity in different combinations. It can be concluded that diclofenac has the toxic potential in poultry at subtherapeutic doses and further the toxic effects were more pronounced under the influence of immunosuppressants and HPHC diet.     

Oxidative stress induced by lead and antioxidant potential of certain adaptogens in poultry

Effect of lead was studied for its action on antioxidant defense in broilers. A total of 225 one-day-old male broiler chicks (Vencobb strain) were divided randomly into 15 groups consisting of 15 chicks in each group. Group 1 was maintained on basal diet, group 2 on polyherbal formulation (PHF; stressroak), group 3 on shilajit, group 4 on amla, and group 5 on vitamin E + selenium (Se). Group 6 was maintained on lead for 42 days (6 weeks) and group 7 on lead for 28 days and subsequently on basal diet without lead for the remaining two weeks. Groups 8, 9, 10, and 11 were given lead along with PHF, shilajit, amla, and vitamin E + Se, respectively throughout the experiment for 6 weeks. Groups 12, 13, 14, and 15 were given lead containing diet for the first four weeks (28 days) and subsequently treated with PHF, shilajit, amla, and vitamin E + Se, respectively for the remaining two weeks. Antioxidant status of the birds was analyzed by assaying blood samples for glutathione (GSH) peroxidase, GSH reductase, and catalase at the end of fourth and sixth weeks, whereas Thiobarbituric acid reacting substances (TBARS) and GSH concentrations were estimated in liver homogenate at the end of the sixth week. The antioxidant defense parameters were significantly altered in toxic control groups indicating the possible oxidative damage caused by lead, whereas the parameters were normal in control groups 1 to 5 and other groups that were given the drugs in test, indicating their good ameliorating activity in oxidative stress.     

Editorial Commentary: Dermal Allograft: A Viable Allograft for Salvage Procedures in Treating Irreparable Rotator Cuff Tears

Our experience with superior capsule reconstruction (SCR) has been successful in patients with isolated, irreparable, supraspinatus tears; however, we have found that bridging reconstruction may have a better role in treating patients with some cuff remnant. Our results are promising, and, although there is new evidence to show that dermal allografts can heal in the setting of rotator cuff deficiency, the basic principle of restoring anatomy should not be ignored. SCR has been accepted as a salvage procedure for irreparable cuff tears, with the precise indications being elucidated. Reconnecting viable cuff muscle to tuberosity directly or through a graft should be considered before SCR.     

Arf nucleotide binding site opener [ARNO] promotes sequential activation of Arf6, Cdc42 and Rac1 and insulin secretion in INS 832/13 β-cells and rat islets

Glucose-stimulated insulin secretion [GSIS] involves interplay between small G-proteins and their regulatory factors. Herein, we tested the hypothesis that Arf nucleotide binding site opener [ARNO], a guanine nucleotide-exchange factor [GEF] for the small G-protein Arf6, mediates the functional activation of Arf6, and that ARNO/Arf6 signaling axis, in turn, controls the activation of Cdc42 and Rac1, which have been implicated in GSIS. Molecular biological [i.e., expression of inactive mutants or siRNA] and pharmacological approaches were employed to assess the roles for ARNO/Arf6 signaling pathway in insulin secretion in normal rat islets and INS 832/13 cells. Degrees of activation of Arf6 and Cdc42/Rac1 were quantitated by GST-GGA3 and PAK-1 kinase pull-down assays, respectively. ARNO is expressed in INS 832/13 cells, rat islets and human islets. Expression of inactive mutants of Arf6 [Arf6-T27N] or ARNO [ARNO-E156K] or siRNA-ARNO markedly reduced GSIS in isolated β-cells. SecinH3, a selective inhibitor of ARNO/Arf6 signaling axis, also inhibited GSIS in INS 832/13 cells and rat islets. Stimulatory concentrations of glucose promoted Arf6 activation, which was inhibited by secinH3 or siRNA-ARNO, suggesting that ARNO/Arf6 signaling cascade is necessary for GSIS. SecinH3 or siRNA-ARNO also inhibited glucose-induced activation of Cdc42 and Rac1 suggesting that ARNO/Arf6 might be upstream to Cdc42 and Rac1 activation steps, which are necessary for GSIS. Lastly, co-immunoprecipitation and confocal microscopic studies suggested increased association between Arf6 and ARNO in glucose-stimulated β-cells. These findings provide the first evidence to implicate ARNO in the sequential activation of Arf6, Cdc42 and Rac1 culminating in GSIS.     

Protein histidine [de]phosphorylation in insulin secretion: abnormalities in models of impaired insulin secretion

In the majority of cell types, including the islet β-cell, transduction of extracellular signals involves ligand binding to a receptor, often followed by the activation G proteins and their effector modules. The islet β-cell is unusual in that glucose lacks an extracellular receptor. Instead, events consequent to glucose metabolism promote insulin secretion via the generation of diffusible second messengers and mobilization of calcium. A selective increase in intracellular calcium has been shown to regulate the phosphorylation status key islet proteins thereby facilitating insulin secretion. In addition to classical protein kinases [e.g., protein kinases A and C], recent studies from our laboratory have focused on the expression and function of various forms of NDPK/nm23-like histidine kinases in clonal β-cells, normal rodent, and human islets. Further, we recently reported localization of a cytosolic protein histidine phosphatase [PHP] in INS 832/13 cells, normal rat islets, and human islets. siRNA-mediated knock down of nm23-H1 and PHP in insulin-secreting INS 832/13 cells significantly attenuated glucose-induced insulin secretion. We also observed significant alterations in the expression and function of nm23-H1/PHP in β-cells chronically exposed to elevated levels of glucose and saturated fatty acids, such as palmitate (i.e., glucolipotoxicity). Similar changes were also noted in islets from the Goto-Kakizaki and Zucker Diabetic Fatty rats, two known models for type 2 diabetes. It is concluded that protein histidine phosphorylation-dephosphorylation cycles play novel regulatory roles in G protein-mediated physiological insulin secretion and that abnormalities in this signaling axis lead to impaired insulin secretion in glucolipotoxicity and type 2 diabetes.     

Photodegradation of selected PCBs in the presence of Nano-TiO2 as catalyst and H2O2 as an oxidant

Photodegradation of five strategically selected PCBs was carried out in acetonitrile/water 80:20. Quantum chemical calculations reveal that PCBs without any chlorine on ortho-positions are closer to be planar, while PCBs with at least one chlorine atoms at the ortho-positions causes the two benzene rings to be nearly perpendicular. Light-induced degradation of planar PCBs is much slower than the perpendicular ones. The use of nano-TiO(2) speeds up the degradation of the planar PCBs, but slows down the degradation of the non-planar ones. The use of H(2)O(2) speeds up the degradation of planar PCBs greatly (by >20 times), but has little effect on non-planar ones except 2,3,5,6-TCB. The relative photodegradation rate is: 2,2',4,4'-TCB > 2,3,5,6-TCB > 2,6-DCB ≈ 3,3',4,4'-TCB > 3,4',5-TCB. The use of H(2)O(2) in combination with sunlight irradiation could be an efficient and "green" technology for PCB remediation.