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Keywords:

  • biomarkers;
  • coenzyme Q10;
  • diabetes;
  • oxidative stress;
  • tocopherol

Abstract

Aim  Individuals with diabetes and prediabetes are at risk of vascular injury. However, the exact mechanisms are unclear. The mitochondria mobile electron carrier coenzyme Q10 (CoQ10) is a potent lipophilic antioxidant. We hypothesize that oxidative stress, detectable as changes in plasma CoQ10 concentrations and composition, plays an important role in vascular disease in diabetes.

Methods  We measured plasma CoQ10 concentrations (including reduced ubiquinol and oxidized ubiquinone subfractions) in 60 subjects with normal glucose tolerance [NGT; fasting plasma glucose (FPG) < 5.5 mmol/l], 63 with impaired fasting glucose (IFG; FPG 5.6–6.9 mmol/l) and 69 with Type 2 diabetes (DM; FPG > 6.9 mmol/l).

Results  In men and women, the total CoQ10/total cholesterol ratio was reduced in DM (mean ±sd) [male (M) 0.09 ± 0.04; female (F) 0.07 ± 0.04] compared with NGT (0.29 ± 0.08; 0.21 ± 0.07) and IFG (0.27 ± 0.07; 0.23 ± 0.07) (DM vs. NGT and IFG P = 0.001). A stepwise reduction in the plasma ubiquinol fraction (ubiquinol/total CoQ10) was observed from NGT (M 0.93 ± 0.06; F 0.95 ± 0.06) compared with IFG (0.43 ± 0.25; 0.41 ± 0.15) and DM (0.24 ± 0.11; F 0.29 ± 0.16) (DM vs. IFG vs. NGT P = 0.001). In contrast, the plasma ubiquinone/ubiquinol ratio increased from NGT (M 0.08 ± 0.07, F 0.06 ± 0.08) to IFG (2.14 ± 1.84, 1.75 ± 1.04) to DM (4.77 ± 4.88, 3.81 ± 3.71) (DM vs. IFG vs. NGT P = 0.001). These differences remained after adjusting for age, body mass index and FPG.

Conclusions  The change in CoQ10 with increasing FPG concentration suggests an increase in oxidative burden, already evident in the prediabetic IFG individuals. This increase in oxidative stress might contribute to the increased risk of vascular disease.