Antioxidants attenuate early up regulation of retinal vascular endothelial growth factor in streptozotocin-diabetic rats

Abstract

Aims/hypothesis. A strong positive correlation has been found between lipid peroxidation product and vascular endothelial growth factor concentrations in the vitreous of patients with proliferative diabetic retinopathy. To establish a causal relation between diabetes-associated enhanced oxidative stress and vascular endothelial growth factor production, we evaluated two antioxidants, dl-a-lipoic acid and taurine, on retinal vascular endothelial growth factor protein and mRNA expression and on parameters of oxidative stress in streptozotocin-diabetic rats. Methods. Our experiments were on control rats and streptozotocin-diabetic rats with a 6-week duration of diabetes, treated with or without dl-a-lipoic acid (100 mg´kg ±1´d±1 , i. p.) or taurine (1 % in the diet) starting from induction of diabetes. Vascular endothelial growth factor protein in retinal homogenates was assessed by sandwich ELISA with an affinity-purified polyclonal antibody and vascular endothelial growth factor mRNA by ribonuclease protection assay. Retinal lipid peroxidation products i. e. malondialdehyde plus 4-hydroxyalkenals were quantified with n-methyl-2-phenylindole. Retinal reduced and oxidized glutathione, ascorbate, dehydroascorbate, and sorbitol pathway intermediates were measured spectrofluorometrically, and taurine by reverse-phase HPLC.Results. Vascular endothelial growth factor protein concentration (means SD) was increased in diabetic rats compared with control rats (33 7 vs 19 5 pg/mg total protein, p < 0.01) This increase was attenuated by taurine (26 8, p < 0.05) and prevented by dla-lipoic acid (21 4, p < 0.01). Vascular endothelial growth factor mRNA abundance was reduced by 1.4-fold in diabetic rats compared with control rats and this decrease was attenuated but not completely prevented by both antioxidants. Malondialdehyde plus 4-hydroxyalkenal concentration was increased in diabetic rats compared with control rats, and both antioxidants arrested accumulation of lipid peroxidation products. Taurine, reduced glutathione, oxidized glutathione, ascorbate, dehydroascorbate and sorbitol pathway intermediate concentrations as well as oxidized glutathione/reduced glutathione and dehydroascorbate/ascorbate ratios were similar in control and diabetic rats treated with or without taurine. Conclusion/interpretation. Oxidative stress is directly involved in up regulation of vascular endothelial growth factor protein in the retina during early diabetes. [Diabetologia (2001

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

“…in the absence of neovascularisation [30][31][32][33][34][35]. Interestingly, other formulations of α-lipoic acid, given for shorter periods, produced complete inhibition of VEGF in the diabetic retina [10]. It remains to be seen whether this discrepancy is due to differences in rat strains, relative concentrations of compounds, or other characteristics.…”

“…Another is the use of antioxidants. There is evidence for increased oxidative stress in the diabetic retina [8][9][10]. However, classic antioxidants are unsuitable, because they act stoichiometrically.…”

Vascular endothelial growth factor in eye disease

“…Increased levels of oxidative stress have been linked to increased production of VEGF upon high glucose treatment in vitro and in the diabetic retina (El-Remessy, 2003b;Ellis et al, 1998;Ellis et al, 2000;Kuroki et al, 1996;Obrosova et al, 2001). The mechanisms by which oxidative stress contributes to VEGF overexpression are not fully understood.…”

Microvascular lesions of diabetic retinopathy: clues towards understanding pathogenesis?

“…37 Accumulation of sorbitol in retinal cells is dependant on the activity of aldose reductase and this may impinge on a range of pathways and contribute to diabetic retinopathy. 38 Also de novo synthesis of diacylglycerol (DAG) leading to the over-activation of several isoforms of protein kinase C (PKC), 39 excessive production of free radicals leading to oxidative stress, 40,41 changes in blood rheology and haemodynamics, 42,43 and over-activation of the renin-angiotensin system 44 contribute significantly to retinopathy as diabetes progresses. Accumulation of advanced glycation end products (AGEs) and activation of receptors for AGEs are also important pathogenic mechanisms with clear links to diabetic retinopathy.…”