The overall goal of this proposal is to examine the hypothesis that the adverse effects of prolonged exposure of pancreatic islets to supraphysiologic glucose concentrations (i.e. glucose toxicity) is mediated at least in part by glucose oxidation and the subsequent generation of reactive oxygen species (ROS) that can impair insulin gene expression and beta cell function. The four specific aims are:
Specific Aim #1 : To determine whether intervention with antioxidants after establishment of hyperglycemia in ZDF rats is successful in decreasing plasma markers for oxidative stress, and, if so, also in decreasing plasma glucose levels and restoring islet PDX-1 and insulin mRNA, insulin content, and glucose-induced insulin secretion. We will also determine whether discontinuation of antioxidant treatment is followed by reversion to the pretreatment level of hyperglycemia and defects in beta cell function.
Specific Aim #2 : To determine whether progression of type 2 diabetes mellitus in db/db mice is accompanied by disruption of the balance between reactive oxygen species and islet antioxidant enzyme gene expression, enzyme levels, and enzyme activity and defects in PDX-1 and insulin gene expression, and to determine whether db/db mice transgenically modified to overexpress intraislet antioxidant enzymes as a preventive measure are protected from glucose toxicity-induced progression of type 2 diabetes.
Specific Aim #3 : To determine whether prolonged exposure of pancreatic islets to supraphysiologic glucose concentrations disrupts the intracellular balance between reactive oxygen species (ROS) and anti-oxidant enzyme gene expression, enzyme levels, and enzyme activity, thereby causing defective insulin gene expression and to determine whether in vitro overexpression of antioxidant enzymes islets prevents adverse effects of supraphysiologic glucose concentrations on PDX-1 and insulin gene expression, insulin content, and glucose-induced insulin secretion.
Specific Aim #4 : To ascertain whether measures of oxidative stress correlate positively with the level of hyperglycemia and negatively with residual beta cell function in type 2 diabetic patients; whether the intervention of improving glycemic control in type 2 diabetic patients leads to decreases in markers of oxidative stress and improvements in beta cell function; and whether interventional treatment with an antioxidant drug without changing current conventional drugs used for glycemic control diminishes hyperglycemia and improves beta cell function in poorly controlled type 2 diabetic patients. The methods used to achieve these specific aims will involve studies of insulin secretion, insulin content, PDX-1 and insulin mRNA levels, antioxidant enzyme levels and activity, and blood and islet markers for oxidative stress. We will conduct experiments using ZDF rats and antioxidant drugs, rat and human islets with adenoviral infection of cells to overexpress antioxidant enzymes, and db/db mice made transgenic to overexpress antioxidant enzymes, both singly and in combination. At the conclusion of these studies, we hope to have determined whether chronic oxidative stress is a mechanism of action for glucose toxicity in islets.
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