Diabetes, Vol 35, Issue 8 866-872, Copyright © 1986 by American Diabetes Association

ARTICLES

Mechanisms of nitrosourea-induced beta-cell damage. Alterations in DNA

SP LeDoux, SE Woodley, NJ Patton and GL Wilson

The initial step in streptozocin (STZ)-induced beta-cell toxicity has been hypothesized to be the alkylation of specific sites on DNA bases. The enzymatic removal of these lesions results in single-strand breaks that over-activate the nuclear enzyme poly(ADP-ribose) synthetase and critically deplete the cell of NAD. Our studies were performed to quantitatively evaluate the extent of DNA damage in beta-cells and correlate this damage with toxicity. Monolayer cultures of neonatal rat beta-cells were used to determine cytotoxicity and DNA damage after exposure to STZ or the aglycone N-methyl-N-nitrosourea (MNU). Toxicity in beta-cells was determined by correlating morphological alterations observed by phase-contrast microscopy with decrements in immunoreactive insulin release. The extent of DNA damage was determined by alterations in nucleoid density and quantitation of N7-methylguanine formation. Toxicity tests revealed that STZ and MNU were not toxic at equimolar concentrations. Streptozocin was toxic at 10(-3) M, whereas only mild toxicity was observed with MNU at 10(-2) M. Surprisingly, however, at equimolar concentrations the two drugs caused comparable DNA-strand breaks as evidenced by their ability to shift the nucleoid migration ratio in neutral sucrose gradients. Additionally, quantitation of N7-methylguanine formation after exposure to equimolar concentrations of the drugs demonstrated that the two alkylated DNA to the same extent. These findings suggest that factors in addition to the activation of poly(ADP-ribose) synthetase must be responsible for the toxicity seen with STZ, because MNU at a nonlethal concentration is capable of causing comparable DNA damage.
CiteULike    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				H.-C. Su, L.-M. Hung, and J.-K. Chen Resveratrol, a red wine antioxidant, possesses an insulin-like effect in streptozotocin-induced diabetic rats Am J Physiol Endocrinol Metab, June 1, 2006; 290(6): E1339 - E1346. [Abstract] [Full Text] [PDF]

				Y. Song, J. E. Manson, J. E. Buring, and S. Liu A Prospective Study of Red Meat Consumption and Type 2 Diabetes in Middle-Aged and Elderly Women: The Women's Health Study Diabetes Care, September 1, 2004; 27(9): 2108 - 2115. [Abstract] [Full Text] [PDF]