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Binit Kumar, Renu A Kowluru; Interplay between lipotoxicity and glucotoxicity in the development of diabetic retinopathy . Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5194.
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© ARVO (1962-2015); The Authors (2016-present)
Hyperglycemia and dyslipidemia are considered as major metabolic insults in the development of diabetic retinopathy. Diabetes increases oxidative stress, and excessive reactive oxygen species (ROS) are implicated in the pathogenesis of retinopathy. Although mitochondria are the main source of ROS, NADPH oxidase (Nox) produces ROS in the cytosol, and Nox-2 activation is seen before mitochondrial damage. The aim of this study is to investigate the interplay between lipotoxicity and glucotoxicity in the development of diabetic retinopathy.
Retina from Zucker diabetic fatty (ZDF) rats were isolated at 6 weeks (mild hyperlipidemia and normal glycemia), 12 weeks (hyperlipidemia and hyperglycemia), 20-40 weeks (overt hyperlipidemia and hyperglycemia) of age. Age-matched lean rats served as controls. Activities of Nox2 and Rac1 (a small molecular weight G-protein important in Nox2 activation) were estimated by lucigenin based method and GLISA respectively, and ROS were quantified using 2’,7’-dichlorofluorescin diacetate. Mitochondrial DNA (mtDNA) damage was evaluated by extended length PCR and by quantifying mRNA levels of the mtDNA-encoded Cytochrome b. Capillary cell apoptosis was determined in the retinal vasculature by TUNEL staining, and degenerative capillaries were counted after PAS-hematoxylin staining.
Retina from ZDF rats at 6 and 12 weeks of age had significantly increased activities of Nox2 and Rac1, and ROS levels were elevated, but, their mitochondria remained intact. At 20 weeks of age, a stage where both hyperlipidemia and hyperglycemia are present in ZDF rats, in addition to increase in Nox2, mtDNA was also damaged and Cytochrome b transcripts were decreased. The numbers of TUNEL positive capillary cells and degenerative capillaries were significantly higher compared to the values obtained from age-matched lean rats. Similar retinal abnormalities were observed in ZDF rats at 40 weeks of age.
Although Rac1-mediated Nox2 activation is observed in the lipotoxic conditions, coinciding effect of hyperglycemia appears to be essential for mitochondrial damage to initiate the apoptotic machinery. Therefore, pharmacological modulation of Nox2 may prevent progression of retinopathy in pre-diabetic obese patients before their hyperglycemia becomes overt.
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