Aims/hypothesis  

Considering that increased oxidative stress induced by hyperglycaemia plays a possible role in the pathogenesis of diabetic complications and that mitochondrial DNA (mDNA) is thought to be more vulnerable than nuclear DNA, we investigated what somatic mutations actually occur in the mDNA of diabetic patients. We also studied the relations between those mutations and urinary 8-hydroxy-2-deoxyguanosine (8-OHdG) which is known to increase considerably in people with diabetes.

Methods  

We identified somatic mutations by subcloning and sequencing two segments of mDNA [control region (nt 15996–16401) and the segment encompassing t-RNA ^Leu(UUR) (nt 3149–3404)] in the peripheral blood cells of six diabetic women and control subjects matched for age and sex. This was done in 20 colonies each. In each case we also assayed urinary 8-OHdG.

Results  

No difference in the aggregate somatic mutational burden of mDNA was found between patients and control subjects. However, the incidence of somatic transversion mutations in mDNA was significantly higher in diabetic patients than in control subjects (13.93±4.57×10^–5 vs 1.27±1.27×10^–5 mutations per base pair; p=0.031, according to Mann-Whitney U-test). There was no significant difference in transition mutations. A correlation was found between the transversion mutational burden and HbA₁c values, but not between it and 8-OHdG content in the urine.

Conclusions/interpretation  

We showed that somatic transversion point mutations of mDNA increase in diabetic patients. Such transversion mutations can become a new biomarker for mDNA damage associated with hyperglycaemia and possibly caused by oxidative stress but not reflected by urinary 8-OHdG.