Changes of retinal neurons and glial fibrillary acid protein immunoreactive astrocytes in spontaneously hypertensive rats

Finerenone, a Non-Steroidal Mineralocorticoid Receptor Antagonist, Reduces Vascular Injury and Increases Regulatory T-Cells: Studies in Rodents with Diabetic and Neovascular Retinopathy

Vision loss in diabetic retinopathy features damage to the blood-retinal barrier and neovascularization, with hypertension and the renin-angiotensin system (RAS) having causal roles. We evaluated if finerenone, a non-steroidal mineralocorticoid receptor (MR) antagonist, reduced vascular pathology and inflammation in diabetic and neovascular retinopathy. Diabetic and hypertensive transgenic (mRen-2)27 rats overexpressing the RAS received the MR antagonist finerenone (10 mg/kg/day, oral gavage) or the angiotensin-converting enzyme inhibitor perindopril (10 mg/kg/day, drinking water) for 12 weeks. As retinal neovascularization does not develop in diabetic rodents, finerenone (5 mg/kg/day, i.p.) was evaluated in murine oxygen-induced retinopathy (OIR). Retinal vasculopathy was assessed by measuring gliosis, vascular leakage, neovascularization, and VEGF. Inflammation was investigated by quantitating retinal microglia/macrophages, pro-inflammatory mediators, and anti-inflammatory regulatory T-cells (Tregs). In diabetes, both treatments reduced systolic blood pressure, gliosis, vascular leakage, and microglial/macrophage density, but only finerenone lowered VEGF, ICAM-1, and IL-1ß. In OIR, finerenone reduced neovascularization, vascular leakage, and microglial density, and increased Tregs in the blood, spleen, and retina. Our findings, in the context of the FIDELIO-DKD and FIGARO-DKD trials reporting the benefits of finerenone on renal and cardiovascular outcomes in diabetic kidney disease, indicate the potential of finerenone as an effective oral treatment for diabetic retinopathy.

Mechanistic links between systemic hypertension and open angle glaucoma

Systemic hypertension or hypertension is a very common chronic age-related disease worldwide. It is typically characterised by a sustained elevation of blood pressure, particularly when the systolic blood pressure and/or diastolic blood pressure are of more than 140 mmHg and 90 mmHg, respectively. If hypertension is not well controlled, it may lead to an increased risk of stroke and heart attack. It has been shown that hypertension is linked to various ocular diseases, including cataract, diabetic retinopathy, age-related macular degeneration, and glaucoma. Glaucoma is the leading cause of irreversible blindness worldwide. Primary open angle glaucoma is the most common form of the disease and is usually characterised by an increase in intraocular pressure. This condition, together with normal tension glaucoma, constitutes open angle glaucoma. Systemic hypertension has been identified as a risk factor for open angle glaucoma. It is speculated that blood pressure is involved in the pathogenesis of open angle glaucoma by altering intraocular pressure or ocular blood flow, or both. Recent evidence has shown that both extremely high and low blood pressure are associated with increased risk of open angle glaucoma. Additional pathogenic mechanisms, including increased inflammation likely to be involved in the development and progression of these two diseases, are discussed.

Eye Drop Instillation of the Rac1 Modulator CNF1 Attenuates Retinal Gliosis and Ameliorates Visual Performance in a Rat Model of Hypertensive Retinopathy

In hypertensive retinopathy, the retinal damage due to high blood pressure is accompanied by increased expression of Glial Fibrillary Acidic Protein (GFAP), which indicates a role of neuroinflammatory processes in such a retinopathy. Proteins belonging to the Rho GTPase family, particularly Rac1, are involved in the activation of Müller glia and in the progression of photoreceptor degeneration, and may thus represent a novel candidate for therapeutic intervention following central nervous system inflammation. In this paper, we have observed that topical administration as eye drops of Cytotoxic Necrotizing Factor 1 (CNF1), a Rho GTPase modulator, surprisingly improves electrophysiological and behavioral visual performances in aged spontaneously hypertensive rats. Furthermore, such functional improvement is accompanied by a reduction of Rac1 activity and retinal GFAP expression. Our results suggest that Rac1 inhibition through CNF1 topical administration may represent a new strategy to target retinal gliosis.

Effects of Dietary Supplementation with Sea Buckthorn (Hippophae rhamnoides L.) Seed Oil on an Experimental Model of Hypertensive Retinopathy in Wistar Rats

Background/Aims

Sea buckthorn (Hippophae rhamnoides L.) oil is a rich source of phytosterols, flavonoids, unsaturated fatty acids, and carotenoids, known for their antioxidant and neuroprotective activity. In this study, we investigated the neuroprotective and antioxidant effect of sea buckthorn oil on rat retina in hypertensive retinopathy.

Methods

Twenty-eight male 6-month-old Wistar rats were separated into 3 groups: (1) controls, (2) unilateral nephrectomized rats receiving drinking water with 1% NaCl, (3) unilateral nephrectomized rats receiving 0.5 mL sea buckthorn oil and drinking water with 1% NaCl. Systemic pressures were being measured with the tail-cuff method. The antiapoptotic effect of sea buckthorn was determined by measuring glial fibrillary acidic protein (GFAP), cleaved caspase-3, and glutamine synthetase levels with immunohistochemistry and Western blot.

Results

Nephrectomy and salt intake caused increases in both systolic and diastolic pressures. Both types of analysis showed that group 2 had statistically significant increases in the expression of GFAP and cleaved caspase-3, while group 3 showed no significant differences compared with the control group. The expression of glutamine synthetase showed no significant differences between the 3 groups.

Conclusions

Our findings suggest that sea buckthorn could notably protect the retina from damage induced by hypertensive retinopathy.

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.