Compelling experimental and epidemiological evidence indicates that environmental factors can play a crucial role in the critical depletion of an essential mass of pancreatic beta cells in insulin-dependent diabetes mellitus. Also, functional alterations in beta cells, similar to those seen in noninsulin-dependent diabetes mellitus, have been produced in laboratory animals following exposure to the naturally occurring N-nitroso compound streptozotocin. This competitive renewal application will continue to focus on the study of the mechanisms by which xenobiotics interact with beta cells to either directly destroy these cells, elicit an autoimmune reaction against them, or cause their functional impairment. The objective of this proposal is to define the types of lesions that specific N-nitroso compounds and active oxygen radical generating chemicals cause in both nuclear and mitochondrial DNA, and to evaluate the ability of the beta cell to repair this damage. This objective will be pursued through the following specific aims: 1) An examination of the repair of alkylation lesions that are removed by either base or nucleotide excision. These studies will focus on factors that affect sequence specific repair. Parameters to be examined are the effects of transcription, hyper- and hypomethylation, caffeine and metabolic modulation. 2) Study of the repair of O6-alkylguanine. These experiments will be directed toward two areas. The first is to develop methodology to determine whether there is heterogeneity across the genome for the repair of O6-alkylguanine. The second is the evaluation of repair of O6-alkylguanine in insulin-secreting cells. Specifically, the effects of metabolic modulation of the cells on the repair of this lesion, and the induction of methylguanine-DNA methyltransferase will be scrutinized. 3) An evaluation of the production and repair of damage in the DNA of normal and neoplastic beta cells induced by active oxygen radicals. These studies will examine the formation and repair of lesions induced by a variety of oxygen radical generators, as well as explore the effects of metabolic alterations and transcription on the repair of this type of damage. 4) An examination of the repair of alkylation and oxidative damage in the mitochondrial DNA of beta cells. These studies will use new methodology developed in the previous funding period to examine the repair of these types of lesions in mitochondrial DNA. When successfully completed, these studies will provide a more complete understanding of the mechanisms by which xenobiotics can selectively interact with normal beta cells to cause functional impairment and/or the death of these cells. This work also will contribute new insights into the etiologies of some forms of cancer and the progression of the natural phenomenon of aging.
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