Arterial hypertension exacerbates oxidative stress in early diabetic retinopathy

The present study was undertaken to investigate the redox status in the retina of an experimental model that combines hypertension and diabetes. Spontaneously hypertensive rats (SHR) and their control Wystar Kyoto (WKY) rats were rendered diabetic and, after 20 days, the rats were sacrificed and the retinas collected. The superoxide production was higher in diabetic than in control WKY (p < 0.03) and SHR rats showed elevated superoxide production compared with WKY groups (p < 0.009). The glutathione antioxidant system was diminished only in diabetic SHR (p < 0.04). Tirosyne nitration was higher in diabetic WKY and control SHR compared with control WKY (p < 0.03), and further increment was observed in diabetic SHR (p < 0.02). The DNA damage estimated by immunohystochemistry for 8-OHdG was higher in control SHR than in WKY, mainly in diabetic SHR (p < 0.0001). Hypertension aggravates oxidative-induced cytotoxicity in diabetic retina due to increasing of superoxide production and impairment of antioxidative system.

Hypertension increases retinal inflammation in experimental diabetes: a possible mechanism for aggravation of diabetic retinopathy by hypertension

Inflammation is pivotal to the pathogenesis of diabetic retinopathy (DR). Hypertension is the main secondary risk factor associated with DR. The mechanisms by which hypertension increases the risk for DR are poorly understood. The aim of the current study was to investigate the contribution of genetic hypertension to early retinal inflammation in experimental diabetes. Diabetes was induced in 4-week-old (developing hypertension) and 12-week-old (fully hypertensive) spontaneously hypertensive rats (SHR) and age-matched control normotensive Wistar Kyoto (WKY) rats by administration of streptozotocin (50 mg/kg, i.v); after 20 days the rats were sacrificed and the retinas were collected. ED1 positive cells, ICAM-1 and VEGF levels were significantly higher in diabetic SHR in both prehypertensive and hypertensive ages (p < 0.005). NF-kappaB p65 levels were higher in prehypertensive SHR and in hypertensive diabetic SHR (p < 0.05). Induction of diabetes in normotensive WKY rats did not show any alteration in retinal expression of inflammatory parameters. Therefore, we conclude that the developing hypertension and also the fully developed hypertension lead to earlier development of inflammation in diabetic retina. Aggravation of the inflammatory process may be involved in the mechanism by which essential hypertension exacerbates retinopathy in the presence of diabetes.

Prevention of hypertension abrogates early inflammatory events in the retina of diabetic hypertensive rats

Hypertension is an important risk factor associated with development and progression of diabetic retinopathy (DR). The mechanisms by which hypertension increases the risk for DR are poorly understood. As the inflammatory mechanisms play a pivotal role in the pathogenesis of DR, in the present study, we investigated the effects of diabetes, hypertension, and combination of diabetes and hypertension on early inflammatory phenomena in the retina, and the effects of blood pressure control on retinal inflammation. Four-week-old spontaneously hypertensive rats (SHR) and their normotensive counterpart Wistar Kyoto (WKY) rats were rendered diabetic by intravenous injection of streptozotocin. Diabetic SHR rats were randomized to receive no antihypertensive drug (Sd), an antihypertensive drug that acts on renin-angiotensin system (losartan, Sd+Los), or antihypertensive drug that do not affect renin-angiotensin system (triple therapy, Sd+Tri). After 20 days, rats were sacrificed and the retinas were collected. The number of immunohistochemically detected ED1/microglial positive cells and the expression of ICAM-1 in the retina were significantly higher in diabetic SHR than in control SHR (p=0.003). The NF-kappaB p65 levels were higher in SHR compared with WKY groups (p=0.001) and its increment in diabetic SHR was not significant. These abnormalities in diabetic SHR rats were completely prevented by both types of antihypertensive drugs. The concomitance of diabetes and hypertension leads to exuberant inflammatory response in the retina, and the prevention of hypertension abrogates these abnormalities. It is suggested that the inflammatory events may be involved in the mechanism by which hypertension exacerbates retinopathy in patients with diabetes.