Pharmaceutical compositions are provided that are useful in treating diabetes. The compositions comprise a pharmaceutically acceptable carrier, and an effective therapeutic or prophylactic amount of a nitroxide antioxidant that alters the expression of genes related to diabetes. Methods are also provided for the use of the pharmaceutical compositions in the treatment or prevention of diabetes. In a preferred embodiment, the nitroxide antioxidant is Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl).