Detection of oxidative damage to DNA in diabetes mellitus by comet assay

Diabetic patients, both insulin-dependent (IDDM) and non-insulin dependent (NIDDM), exhibit abnormal antioxidant status, auto-oxidation of glucose and excess glycosylated proteins. Oxidative stress in diabetes leads to tissue damage, with lipid peroxidation and inactivation of proteins. Reduced anti oxidant defenses in diabetic patients are associated with an increased risk of free radical mediated diseases. Dietary antioxidant compounds, includin g ascorbic acid, tocopherol offer some protection against these complicatio ns through their roles as inhibitors of glycation and as free radical scave ngers. It has been reported that reactive oxygen generation in long standin g diabetes may also result in oxidative damage to DNA. Also there is eviden ce to suggest that reactive oxygen is involved in the pathogenicity and com plications arising from IDDM, but there is little to suggest a role of oxid ative stress in the pathogenesis of NIDDM. In order to investigate this hyp othesis further, peripheral blood samples were taken from 30 control indivi duals and 63 IDDM and NIDDM patients and examined by comet assay for DNA st rand breakage. Statistically significant differences (p<0.05) were detected between control and diabetic patient groups. DNA damage in the comet assay was at higher level in NIDDM patients and slightly lower level in IDDM pat ients which may indicate that these cells are handling more oxidative damag e on a regular basis. Also, a synergistic effect of smoking on DNA damage ( with high levels of tailed nuclei) was observed in smoking diabetic patient s in comparison with smoking non-diabetic controls.