Effect of R-(+)-?-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-(+)-α-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-(+)-α-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-(+)-α-lipoic acid i.p. for 30 weeks. Quantitative retinal morphometry included acellular occluded capillaries and pericyte numbers. The effects of R-(+)-α-lipoic acid on parameters of oxidative and nitrative stress, AGE and its receptor and nuclear factor kappa B (NFκB) were assessed by immunoblotting, and NFκB 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]/mm2 of retinal area) compared with non-diabetic (19.8±5.1 ac/mm2; p<0.001). Results with 60 mg/kg R-(+)-α-lipoic acid reduced the numbers by 88% (p<0.001 vs diabetic). Pericyte loss was also significantly inhibited in diabetic rats treated with R-(+)-α-lipoic acid (non-diabetic: 1,940±137 pericytes/mm2capillary area; untreated diabetic: 1,294±94 pericytes/mm2capillary area vs treated diabetic: 1,656±134 pericytes/mm2; p<0.01). R-(+)-α-lipoic acid results reduced oxidative stress, normalised NFκB activation and angiopoietin-2 expression, and reduced vascular endothelial growth factor in the diabetic retina by 43% (p<0.0001).
Conclusions/interpretation  R-(+)-α-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.

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