Date on Master's Thesis/Doctoral Dissertation

12-2003

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Pharmacology and Toxicology

Committee Chair

Epstein, Paul N.

Author's Keywords

Pancreatic beta cell; Antioxidant; Transgenes; Diabetes

Subject

Pancreatic beta cells; Diabetes--Pathophysiology

Abstract

Pancreatic beta cells are extremely vulnerable to the destruction of Reactive Oxygen Species (ROS). In both type 1 and type 2 diabetes ROS are involved in the loss of U+000DF-cells. We hypothesized that the deficiency in ROS detoxifying system of U+000DF-cells resulted in U+000DF-cell vulnerability and enhanced ROS protection would protect from diabetes. To test this hypothesis, transgenic mice with overexpression of U+000DF-cell antioxidant protein metallothionein (MT), manganese superoxide dismutase (MnSOD) and catalase were produced on an FVB background. Initial studies demonstrated that these transgenes did not affect U+000DF-cell normal function and morphology. But those transgenes significantly protected pancreatic islets or mice from ROS induced U+000DF-cell damage and diabetes. The transgenic islet cells had high efficacy in scavenging most forms of ROS, and generally survived and functioned better than control cells when exposed to various ROS insults. The transgenic mice were highly resistant to STZ induced diabetes. However, inconsistent with studies on insulin secreting tumor cell lines in which antioxidants were shown to be protective, all these antioxidant transgenes failed to prevent cytokine toxicities in the cultured islets. We employed a speed congenic strategy to produce two lines of congenic NOD mice containing U+000DF-cell specific expression of MT and catalase. NOD mice spontaneously develop type 1 diabetes, and cyclophosphamide (CYP) injection accelerates NOD diabetes onset. But very unexpectedly, either transgene MT or catalase dramatically hastened diabetes onset in NOD mice. In addition, no antioxidant transgene was found to be able to protect from type 2 diabetes in an Agouti obese diabetic model. But the MT transgene also unexpectedly caused severe diabetes on a normal C57BL/KsJ mouse which can be made to develop type 2 diabetes by producing obesity and insulin resistance. The data from this project indicate that the overexpression of antioxidant transgenes protects U+000DF-cells from ROS damaging stimuli but sensitizes U+000DF-cells to some other insults. Some of these data are at odds with the long term favored concept that antioxidant treatment is always beneficial for treatment of diabetes. These results imply that oxidative stress may not only be harmful, but it may also be necessary to activate self-protective mechanisms in the U+000DF-cells.

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