Protective effect of a radical scavenger, MCI-186 on islet cell damages induced by oxidative stress

Exendin-4 protects hypoxic islets from oxidative stress and improves islet transplantation outcome

Oxidative stress produced during pancreatic islet isolation leads to significant β-cell damage. Homeostatic cytokines secreted subsequently to islet transplantation damage β-cells by generating oxygen free radicals. In this study, exendin-4, a glucagon-like peptide-1 analog improved islet transplantation outcome by increasing the survival of diabetic recipient mice from 58% to 100%. We hypothesized that this beneficial effect was due to the ability of exendin-4 to reduce oxidative stress. Further experiments showed that it significantly reduced the apoptotic rate of cultured β-cells subjected to hypoxia or to IL-1β. Reduction of apoptotic events was confirmed in pancreatic islet grafts of exendin-4-treated mice. Exendin-4 enhanced Akt phosphorylation of β-cells and insulin released from them. It even augmented insulin secretion from islets cultivated at hypoxic conditions. Exposure to hypoxia led to a decrease in the activation of Akt, which was reversed when β-cells were pretreated with exendin-4. Moreover, exendin-4 increased the activity of redox enzymes in a hypoxia-treated β-cell line and reduced reactive oxygen species production in isolated pancreatic islets. Recovery from diabetes in mice transplanted with hypoxic islets was more efficient when they received exendin-4. In conclusion, exendin-4 rescued islets from oxidative stress caused by hypoxia or due to cytokine exposure. It improved the outcome of syngenic and xenogenic islet transplantation.

Poly(ethylene glycol) cross-linked hemoglobin with antioxidant enzymes protects pancreatic islets from hypoxic and free radical stress and extends islet functionality

The objective of this study was to investigate the efficiency of multifunctional poly(ethylene glycol)-based hemoglobin conjugates crosslinked with antioxidant enzymes for their ability to protect an oxygen carrier (hemoglobin) and insulin secreting islets from the combination of hypoxic and free radical stress under simulated transplantation conditions. In this study, RINm5F cells and isolated pancreatic islets were challenged with oxidants (H(2)O(2) or xanthine and xanthine oxidase) and incubated with conjugates (hemoglobin-hemoglobin or superoxide dismutase-catalase-hemoglobin) in normoxia (21% oxygen) or hypoxia (6% or 1% oxygen). Hemoglobin protection, intracellular free radical activity and cell viability in RINm5F cells measured by methemoglobin, dichlorofluorescein-diacetate, and (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay, respectively, showed that cells were better protected by conjugates containing antioxidant enzymes. Insulin secretion from islets and qualitative confocal evaluation of viability showed beta cells were protected by conjugates containing antioxidant enzymes when exposed to induced stress. Our study suggested that antioxidant enzymes play a significant role in hemoglobin protection and thus extended cell protection.

Edaravone, a free radical scavenger, promotes engraftment of intraportally transplanted islet cells

OBJECTIVES

Pancreatic islet transplantation requires multiple transplants to achieve insulin independence. Only one third of the islet mass is stably engrafted; one of the causes of which is ascribed to oxidative stress. We confirmed the hypothesis that administration of edaravone, a free radical scavenger, in the early posttransplantation period promotes islet cell engraftment.

METHODS

Islet isograft from a single donor was intraportally transplanted into streptozotocin-diabetic F344 rats, and intravenous edaravone (3 mg/kg) was administered immediately and 24 hours after the transplantation. Plasma glucose concentrations were monitored for 28 days. Serum insulin levels were obtained on the second week. Morphologic studies were performed on insulin-immunostained and TUNEL-stained sections of the recipient liver.

RESULTS

In the edaravone-treated group, hyperglycemia was ameliorated, and 50% of rats achieved normoglycemia (<200 mg/dL). All rats in the control group remained hyperglycemic (>400 mg/dL). Insulin secretion of the edaravone-treated group was superior to the controls. Morphologically, the number and size of the islet β cells of the edaravone-treated group were larger than those of the controls. The number of TUNEL-positive cells in each islet of the edaravone-treated group were fewer than those of the controls.

CONCLUSIONS

In streptozotocin-diabetic rats, edaravone administration in the early posttransplantation period promotes engraftment of intraportally transplanted islet cells.

Isoprostanes as markers of oxidative stress-induced cell damage in porcine islet cell isolation

INTRODUCTION

Mechanical stress and reagents used during the isolation and purification process as well as digestion time and temperature can alter the success of porcine islet cell (PIC) isolation. This study aimed to characterize the occurrence of isoprostanes during PIC isolation using a modified automated Ricordi method and to evaluate their influence on PIC isolation outcome.

METHODS

Porcine pancreatic tissue was harvested at the local slaughter house, and 10 PIC isolations were performed using a modified automated Ricordi method. As positive controls for tissue damage-associated oxidative stress, six consecutive PIC isolations were performed in the presence of 1 mug lipopolysaccharide (LPS). PIC were purified by density gradient centrifugation using the Lymphoprep density gradient. Isoprostane measurement was performed using enzyme-linked immunosorbent assay.

RESULTS

The final yield of viable and pure PICs in the experimental group was 3479 +/- 542 IEQ/g pancreas, and the LPS group yielded lower cell numbers compared to the experimental group. Isoprostane levels were significantly elevated in the LPS group as compared to the experimental group at all time points during the isolation from the beginning of the digestion process.

DISCUSSION

PIC isolation and purification results significantly differed in the two experimental groups, underlining the negative effects of oxidative stress on PIC viability and purity, which impact negatively on PIC transplantation success.

Edaravone inhibits DNA peroxidation and neuronal cell death in neonatal hypoxic-ischemic encephalopathy model rat

Neonatal hypoxic-ischemic encephalopathy (HIE) is the most frequent neurologic disease in the perinatal period. Its major cause is oxidative stress, which induces DNA peroxidation and apoptotic neuronal death. We examined 8-hydroxy-2'-deoxyguanosine (8-OHdG) expression to evaluate brain damage in neonatal HIE and the therapeutic effect of edaravone, a free radical scavenger. Using HPLC and immunohistochemistry, the 8-OHdG levels of neonatal HIE model Sprague-Dawley rats that were subjected to left common carotid artery ligation and 2-h hypoxia significantly increased after 24-48 h of hypoxic-ischemic (HI) insult, but decreased after 72 h. Moreover, the number of apoptotic cells with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and karyorrhexis significantly increased after 24-72 h of HI insult. In a therapeutic experiment, edaravone was administered i.p. (9 mg/kg) after HI insult every 24 h. Edaravone reduced both the apoptotic neuronal cell number and 8-OHdG expression after 24-48 h of HI. From a double immunofluorescent study, DNA peroxidation occurred in apoptotic neuronal cells with 8-OHdG expression. Edaravone may inhibit the number of apoptotic neuronal cells and 8-OHdG expression within 48 h after HI insult.

Islet transplantation and antioxidant management: A comprehensive review

Islet transplantation as a promising treatment for type 1 diabetes has received widespread attention. Oxidative stress plays an essential role in cell injury during islet isolation and transplantation procedures. Antioxidants have been used in various studies to improve islet transplantation procedures. The present study reviews the role of oxidative stress and the benefits of antioxidants in islet transplantation procedures. The bibliographical databases Pubmed and Scopus were searched up to November 2008. All relevant human and animal in-vivo and in-vitro studies, which investigated antioxidants on islets, were included. Almost all the tested antioxidants used in the in-vitro studies enhanced islet viability and insulin secretion. Better control of blood glucose after transplantation was the major outcome of antioxidant therapy in all in-vivo studies. The data also indicated that antioxidants improved islet transplantation procedures. Although there is still insufficient evidence to draw definitive conclusions about the efficacy of individual supplements, the benefits of antioxidants in islet isolation procedures cannot be ignored.

Protective effects of edaravone on rats with severe acute pancreatitis

AIM: To investigate the therapeutic effects and mechanism of edaravone on rats with severe acute pancreatitis (SAP) induced by L-arginine.

METHODS: A total of 60 rats were randomly and equally divided into three groups, namely control group, SAP model group and edaravone treatment group (n = 20). A SAP model was established by injecting intraperitoneally with L-arginine at a dose of 2.5 g/kg twice at an interval of 1 h, and injecting intravenously with edaravone 3 mg/kg, bid × 3 d (edaravone treatment group). The characteristics and volume of ascites, the pathological changes of pancreatic tissue and the serum levels of amylase (AMY), tumor necrosis factor-α (TNF-α), interleukin (IL)-6 and the contents of malonaldehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) in pancreatic tissue of rats and prognosis were compared after 72 h following administration of L-arginine.

RESULTS: Compared with control group, 72 h after administration of L-arginine, SAP model group showed typical histopathological changes of SAP, elevated the volume of ascites (5.16 ± 1.52 vs 0.50 ± 0.10, P < 0.01), and significantly higher serum levels of AMY, TNF-α, IL-6 and content of MDA of pancreatic tissue (8967.5 ± 298.4 vs 720.1 ± 119.7I; 103.98 ± 10.56 vs 41.59 ± 3.79; 548.57 ± 10.45 vs 198.34 ± 2.10; 35.6 ± 3.8 vs 7.9 ± 2.2, all P < 0.01), and lower GSH and SOD in pancreatic tissue (7.2 ± 0.6 vs 17.1 ± 2.1; 7300 ± 1800 vs 28 400 ± 2700, both P < 0.01). Compared with SAP model group, 72 h after administration of L-arginine, significantly alleviated pathological lesions of SAP, decreased volume of ascites (4.05 ± 1.22 vs 53.16 ± 1.52, P < 0.05), lower pathological scores (P < 0.05), lower serum levels of AMY, TNF-α, IL-6 and MDA in pancreatic tissue (7809.5 ± 158.3 vs 8967.5 ± 298.4; 79.80 ± 14.23 vs 103.98 ± 10.56; 467 ± 6.64 vs548.57 ± 10.45; 29.1 ± 2.6 vs 35.6 ± 3.8, all P < 0.05), and higher GSH and SOD in pancreatic tissue were observed in edaravone treatment group (8.7 ± 1.3 vs 7.2 ± 0.6; 114 000 ± 27 000 vs 7300 ± 1800, both P < 0.05).

CONCLUSION: Edaravone can scavenge oxygen-derived free radicals, upgrade the contents of SOD and GSH in pancreatic tissue, decrease the serum levels of proinflammatory cytokines and, ameliorate the pathological lesions of pancreatic tissue in rats, and has a possibility of decreasing death rate.

Beneficial Effect of the Nonpeptidyl Low Molecular Weight Radical Scavenger IAC on Cultured Human Islet Function

We examined a possible protective effect of the nonpeptidyl low molecular weight radical scavenger IAC [bis(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl)decanedioate di-hydrochloride] on isolated human islet cells against isolation and culture oxidative stress. Islets isolated from pancreases of nondiabetic multiorgan donors by collagenase digestion were purified by density gradient centrifugation. After the isolation, islets were either exposed or not exposed for 7 days to 10 μmol/L IAC. We found that IAC markedly reduced oxidative stress and ameliorated islets function. These results suggest that the use of IAC could be an interesting pharmacological approach for the treatment of the islets before transplantation.