Improvement of insulin resistance by removal of systemic hydrogen peroxide by PEGylated catalase in obese mice.
ABSTRACT Insulin resistance, a condition in which insulin action is impaired, is one of the characteristic features of type 2 diabetes. Excessive amounts of reactive oxygen species (ROS) interfere with the insulin signaling pathway, which leads to the progression of insulin resistance. To examine whether removal of systemic hydrogen peroxide is effective in improving insulin resistance, polyethylene glycol-conjugated catalase (PEG-catalase), a derivative with a long circulation half-life, was repeatedly injected into leptin-deficient ob/ob or high fat diet-induced obese mice for 16 or 10 consecutive weeks, respectively. Although ob/ob mice gradually gained weight with time irrespective of the treatment, repeated intraperitoneal injections of PEG-catalase significantly reduced glucose levels in the fed state. Glucose and insulin tolerance tests also showed PEG-catalase significantly improved glucose tolerance and insulin sensitivity in ob/ob mice, respectively. Similar but less marked results were obtained in the diet-induced obese mice. Treatment of 3T3-L1 adipocytes with glucose oxidase (GO) increased lipid hydroperoxide formation and reduced insulin-stimulated Akt phosphorylation. Addition of catalase or PEG-catalase significantly inhibited the GO-induced changes in adipocytes. These findings indicate that systemic removal of hydrogen peroxide by PEG-catalase activates the insulin signaling pathway and improves insulin resistance in obese mice.
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ABSTRACT: Diabetic patients are reported to have a high incidence and mortality of cancer, but little is known about the linkage. In this study, we investigated whether high oxidative stress is involved in the acceleration of tumor metastasis in diabetic mice. Murine melanoma B16-BL6 cells stably labeled with firefly luciferase (B16-BL6/Luc) were inoculated into the tail vein of streptozotocin (STZ)-treated or untreated mice. A luciferase assay demonstrated that tumor cells were present largely in the lung of untreated mice, whereas large numbers of tumor cells were detected in both the lung and liver of STZ-treated mice. Repeated injections of polyethylene glycol-conjugated catalase (PEG-catalase), a long-circulating derivative, reduced the elevated fasting blood glucose levels and plasma lipoperoxide levels of STZ-treated mice, but had no significant effects on these parameters in untreated mice. In addition, the injections significantly reduced the number of tumor cells in the lung and liver in both untreated and STZ-treated mice. Culture of B16-BL6/Luc cells in medium containing over 45 mg/dl glucose hardly affected the proliferation of the cells, whereas the addition of plasma of STZ-treated mice to the medium significantly increased the number of cells. Plasma samples of STZ-treated mice receiving PEG-catalase exhibited no such effect on proliferation. These findings indicate that a hyperglycemia-induced increase in oxidative stress is involved in the acceleration of tumor metastasis, and removal of systemic hydrogen peroxide by PEG-catalase can inhibit the progression of diabetic conditions and tumor metastasis in diabetes.Journal of Controlled Release 06/2013; · 7.63 Impact Factor
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ABSTRACT: Progressive accumulation of defective mitochondria is a common feature of aged cells. SIRT3 is a NAD(+)-dependent protein deacetylase that regulates mitochondrial function and metabolism in response to caloric restriction and stress. FOXO3 is a direct target of SIRT3 and functions as a forkhead transcription factor to govern diverse cellular responses to stress. Here we showed that hydrogen peroxide induces SIRT3 to deacetylate FOXO3 at K271 and K290, followed by the upregulation of a set of genes that are essential for mitochondrial homeostasis (mitochondrial biogenesis, fission/fusion and mitophagy). Consequently, SIRT3-mediated deacetylation of FOXO3 modulates mitochondrial mass, ATP production and clearance of defective mitochondria. Thus, mitochondrial quantity and quality are ensured to maintain mitochondrial reserve capacity in response to oxidative damage. Maladaptation to oxidative stress is a major risk factor underlying aging and many aging-related diseases. Hence, our finding that SIRT3 deacetylates FOXO3 to protect mitochondria against oxidative stress provides a possible direction for aging-delaying therapies and disease intervention.Free Radical Biology and Medicine 05/2013; · 5.27 Impact Factor
- Zeitschrift Fur Gastroenterologie - Z GASTROENTEROL. 01/2008; 46(01).