Oxidative stress: A cause and therapeutic target of diabetic complications

Oxidative stress is defined as excessive production of reactive oxygen species (ROS) in the presence of diminished anti‐oxidant substances. Increased oxidative stress could be one of the common pathogenic factors of diabetic complications. However, the mechanisms by which hyperglycemia increases oxidative stress are not fully understood. In this review, we focus on the impact of mitochondrial derived ROS (mtROS) on diabetic complications and suggest potential therapeutic approaches to suppress mtROS. It has been shown that hyperglycemia increases ROS production from mitochondrial electron transport chain and normalizing mitochondrial ROS ameliorates major pathways of hyperglycemic damage, such as activation of polyol pathway, activation of PKC and accumulation of advanced glycation end‐products (AGE). Additionally, in subjects with type 2 diabetes, we found a positive correlation between HbA1c and urinary excretion of 8‐hydroxydeoxyguanosine (8‐OHdG), which reflects mitochondrial oxidative damage, and further reported that 8‐OHdG was elevated in subjects with diabetic micro‐ and macro‐ vascular complications. We recently created vascular endothelial cell‐specific manganese superoxide dismutase (MnSOD) transgenic mice, and clarified that overexpression of MnSOD in endothelium could prevent diabetic retinopathy in vivo. Furthermore, we found that metformin and pioglitazone, both of which have the ability to reduce diabetic vascular complications, could ameliorate hyperglycemia‐induced mtROS production by the induction of PPARγ coactivator‐1α (PGC‐1α) and MnSOD and/or activation of adenosine monophosphate (AMP)‐activated protein kinase (AMPK). We also found that metformin and pioglitazone promote mitochondrial biogenesis through the same AMPK–PGC‐1α pathway. Taking these results, mtROS could be the key initiator of and a therapeutic target for diabetic vascular complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00013.x, 2010)