The initial step in streptozocin (STZ)-induced β-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 β-cells and correlate this damage with toxicity. Monolayer cultures of neonatal rat β-cells were used to determine cytotoxicity and DNA damage after exposure to STZ or the aglycone N-methyl-N-nitrosourea (MNU). Toxicity in β-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.
Skip Nav Destination
Article navigation
Original Contributions|
August 01 1986
Mechanisms of Nitrosourea-Induced β-Cell Damage: Alterations in DNA
S P LeDoux;
S P LeDoux
Department of Anatomy, University of South Alabama, College of Medicine
Mobile, Alabama 36688
Search for other works by this author on:
S E Woodley;
S E Woodley
Department of Anatomy, University of South Alabama, College of Medicine
Mobile, Alabama 36688
Search for other works by this author on:
N J Patton;
N J Patton
Department of Anatomy, University of South Alabama, College of Medicine
Mobile, Alabama 36688
Search for other works by this author on:
G L Wilson
G L Wilson
Department of Anatomy, University of South Alabama, College of Medicine
Mobile, Alabama 36688
Search for other works by this author on:
Send reprint requests to Dr. Glenn L Wilson at the above address.
Diabetes 1986;35(8):866–872
Article history
Received:
November 12 1985
Revision Received:
February 03 1986
PubMed:
2942432
Citation
S P LeDoux, S E Woodley, N J Patton, G L Wilson; Mechanisms of Nitrosourea-Induced β-Cell Damage: Alterations in DNA. Diabetes 1 August 1986; 35 (8): 866–872. https://doi.org/10.2337/diab.35.8.866
Download citation file:
51
Views