Effect of R-(+)-α-lipoic acid on experimental diabetic retinopathy

Aims/hypothesis: Hyperglycaemia-induced mitochondrial overproduction of reactive oxygen species (ROS) is central to the pathogenesis of endothelial damage in diabetes. R-(+)-alpha-lipoic acid has advantages over classic antioxidants, as it distributes to the mitochondria, is regenerated by glycolytic flux, and has a low redox potential. Methods: To assess the effect of R-(+)-alpha-lipoic acid on experimental diabetic retinopathy, three groups of male Wistar rats were studied: non-diabetic controls, untreated diabetic controls, and diabetic rats treated with 60 mg/kg bodyweight R-(+)-alpha-lipoic acid i.p. for 30 weeks. Quantitative retinal morphometry included acellular occluded capillaries and pericyte numbers. The effects of R-(+)-alpha-lipoic acid on parameters of oxidative and nitrative stress, AGE and its receptor and nuclear factor kappa B (NF kappa B) were assessed by immunoblotting, and NF kappa B activation by electrophoretic mobility shift assay. Angiopoietin-2 and vascular endothelial growth factors were also determined by immunoblotting. Results: After 30 weeks of diabetes, the number of acellular capillaries was significantly elevated in diabetic rats (57.1 +/- 10.6 acellular capillary segments [ac]/mm(2) of retinal area) compared with non-diabetic (19.8 +/- 5.1 ac/mm(2); p < 0.001). Treatment with 60 mg/kg R-(+)-alpha-lipoic acid reduced the numbers by 88% (p < 0.001 vs diabetic). Pericyte loss was also significantly inhibited in diabetic rats treated with R-(+)-alpha-lipoic acid (non-diabetic: 1,940 +/- 137 pericytes/mm(2) area; untreated diabetic: 1,294 +/- 94 pericytes/mm(2) stopcapillary area vs treated diabetic: 1,656 +/- 134 pericytes/mm(2); p < 0.01). R-(+)-alpha-lipoic acid treatment reduced oxidative stress, normalised NF kappa B activation and angiopoietin-2 expression, and reduced vascular endothelial growth factor in the diabetic retina by 43% (p < 0.0001). Conclusions/interpretations: R-(+)-alpha-lipoic acid prevents microvascular damage through normalised pathways downstream of mitochondrial overproduction of ROS, and preserves pericyte coverage of retinal capillaries, which may provide additional endothelial protection.