bq-123 and Diabetic-Retinopathy

Hypertension is an independent risk factor for diabetic retinopathy, yet anti-hypertensive medications such as blockade of angiotensin II do not completely protect against vision-threatening vascular disease. We hypothesized that the potent vasoactive factor, endothelin (ET), is up-regulated in diabetic retinopathy and antagonism of the ET type A receptor (ETRA) or ET type B receptor (ETRB) ameliorates retinal vascular leakage independently of any blood pressure lowering effects. Spontaneously hypertensive rats (SHR) and their normotensive and genetic controls, Wistar Kyoto rats, were randomized to become diabetic or non-diabetic and studied for 8 weeks. Rats were further randomized to receive by intravitreal injection the ETRA antagonist, BQ123, the ETRB antagonist, BQ788, or vehicle, 5 days after the induction of streptozotocin diabetes and 4 weeks later. The treatments had no effect on systolic blood pressure which remained elevated in SHR. ET-1, ET-2, ETRA and ETRB were expressed in retina and retinal pigment epithelium (RPE)/choroid and increased by hypertension or diabetes. BQ123 reduced ET-1 and ET-2 expression in retina and RPE/choroid, while BQ788 had a similar effect but did not influence the mRNA levels of ET-1 in retina. Retinal vascular leakage and Müller cell stress as well as vascular endothelial growth factor (VEGF) expression in retina and RPE/choroid, were increased by hypertension or diabetes and there was an additive effect of these conditions. Treatment with BQ123 or BQ788 effectively reduced these events as well as the elevated levels of inflammatory factors in the retina. Our findings indicate that local ET systems exist in the retina and RPE/choroid that are up-regulated by hypertension and diabetes. The ability of locally delivered ET receptor antagonists to supress these overactive ET systems and reduce retinal vascular leakage and VEGF in the presence of hypertension indicate the potential of these approaches for the treatment of diabetic retinopathy.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Blood-Retinal Barrier; Choroid; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Endothelin A Receptor Antagonists; Endothelin B Receptor Antagonists; Endothelin-1; Endothelin-2; Enzyme-Linked Immunosorbent Assay; Fluorescent Antibody Technique, Indirect; Intravitreal Injections; Ocular Hypertension; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Real-Time Polymerase Chain Reaction; Retina; Retinal Pigment Epithelium; Streptozocin

To investigate the role of endogenous endothelin-1 (ET-1) expression and its interaction with the ETA receptor in the physiologic regulation of vascular tone as well as in the development of abnormal retinal hemodynamics in diabetes.. Retinal blood flow, using digitized video fluorescein angiography recordings, was quantitated after intravitreous injections of ET-1; BQ-123, an ETA receptor antagonist; and phosporamindon, an endothelin converting enzyme inhibitor in the eyes of diabetic and nondiabetic rats. A total of 154 rats were used for these experiments. Message levels of preproendothelin-1 (preproET-1) were measured from the retina of diabetic and nondiabetic rats using competitive polymerase chain reaction (PCR) techniques.. Retinal blood flow was reduced (33%, P < 0.001) in diabetic rats compared to nondiabetic rats. BQ-123, an ETA receptor antagonist, but not saralasin, an angiotensin receptor antagonist, increased retinal blood flow in a dose-dependent manner in diabetic (EC50 of 8 x 10(-7) M) and in nondiabetic rats (EC50 of 8 x 10(-8) M). Besides being resistant to BQ-123, the maximal response in diabetic animals occurred 20 minutes later than in nondiabetic animals. Decreasing ET-1 levels by inhibiting endothelin-converting enzyme with phosphoramidon normalized retinal blood flow in diabetic rats. In nondiabetic rats, the intravitreous injection of exogenous ET-1 (10(-8) M) resulted in retinal blood flow decreases comparable to those measured in diabetic animals, and the subsequent injection of 10(-4) M BQ-123 produced retinal blood flow changes comparable to those measured in BQ-123 injected diabetic rats. Comparison of preproET-1 messenger RNA expression in the retina, brain and lung of control and diabetic rats using quantitative PCR and Northern blot analysis showed 2.0- and 1.7-fold increases in the retina and the brain, respectively, without changes in the lung.. These data suggest that ET-1 is involved in the regulation of retinal blood flow in normal physiologic outcome, and an increase in the endogenous expression of ET-1 contributes to the reduction of retinal blood flow reported in the early stages of diabetes mellitus.

Topics: Animals; Brain; Diabetes Mellitus, Experimental; Diabetic Retinopathy; DNA Primers; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelin-1; Endothelins; Fluorescein Angiography; Glycopeptides; Hemodynamics; Male; Metalloendopeptidases; Peptides, Cyclic; Polymerase Chain Reaction; Protease Inhibitors; Protein Precursors; Rats; Rats, Inbred BN; Rats, Sprague-Dawley; Receptors, Endothelin; Retina; Retinal Vessels; RNA, Messenger