Ultrastructural localization of blood-retinal barrier breakdown in diabetic and galactosemic rats.

Abstract

Breakdown of the blood-retinal barrier (BRB) is an early event in diabetic and galactosemic rats, but the location and nature of the specific defect(s) are controversial. Using an electron microscopic immunocytochemical technique, the retinas of normal, diabetic, and galactosemic rats were immunostained for endogenous albumin. Normal rats showed little evidence of BRB breakdown at either the inner barrier (retinal vasculature) or the outer barrier (retinal pigment epithelium) (RPE). In diabetic and galactosemic rats, as was true in human diabetics, BRB breakdown occurred predominantly at the inner BRB, but in some cases at the outer barrier as well. Treatment with the aldose reductase inhibitor sorbinil largely prevented BRB failure in galactosemic rats. In the inner retina of diabetic and galactosemic rats, albumin was frequently demonstrated on the abluminal side of the retinal capillary endothelium (RCE) in intercellular spaces, basal laminae, pericytes, ganglion cells, astrocytes, and the perinuclear cytoplasm of cells in the inner nuclear layer. Albumin did not appear to cross RCE cell junctions; however, it was occasionally seen in RCE cytoplasm of galactosemic rats. In the outer retina, albumin was frequently detected in the subretinal space, in the intercellular space between photoreceptors, and in the perinuclear cytoplasm of photoreceptor cells, but was only infrequently found in the RPE cells constituting the barrier. Albumin derived from the choroidal vasculature did not appear to cross the tight junctions of the RPE. These findings suggest that specific sites of BRB compromise are infrequent but that once albumin has crossed the RCE or RPE it freely permeates the retinal tissue by filling intercellular spaces and permeating the membranes of cells not implicated in BRB formation. The diffuse cytoplasmic staining of some RCE and RPE cells suggests that the predominant means of BRB breakdown in diabetes and galactosemia involves increased focal permeability of the surface membranes of the RCE and RPE cells rather than defective tight junctions or vesicular transport.

Vascular Expression of Endothelial Antigen PAL-E Indicates Absence of Blood-Ocular Barriers in the Normal Eye

“…In respect of this observation it is inter esting to note that in a previous study leakage of tracers was observed in the peripapillary retina in some but not all of a series of normal rabbits and monkeys studied [15]. Further more, in a study of retinal permeability in rats using albumin as an endogenous tracer in creased permeability was found in the ani mals over 2 years of age, suggesting that aging may also lead to local barrier loss in the retinal microvasculature [22],…”

“…In the study of eye diseases where these barrier functions arc lost or altered, such as uveitis and retinal vascular disease [22,23,29], this marker may be very useful.…”

Vascular Endothelial Growth Factor Plays a Role in Hyperpermeability of Diabetic Retinal Vessels

“…Streptozotocin-treated diabetic rats have been widely used to investigate the mecha nisms of hyperpermeability of diabetic retinal vessels by detecting extravasation of intrave nously injected tracers [5,6] or by immunohistochemically detecting extravasation of plasma proteins [4,7], The aim of the present study was to look for VEGF, a potent perme ability factor, in retinas of streptozotocintreated diabetic rats using immunohisto chemistry. To identify the cells which produce VEGF, we also performed immunohisto chemistry for a-smooth muscle actin which is a marker for smooth muscle cells of arteries and veins as well as pericytes of capillaries [ 8],…”

Prognostic MRI biomarkers of treatment efficacy for retinopathy

“…Using a variety of non-MRI but physiologically relevant methods and tracers in diabetic or galactose-fed rats, investigators have reported little or no change in BRB permeability in early diabetes (34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44). In contrast, in a study using a nonquantitative histological detection method with an endogenous tracer (extravasation of albumin), only a subset of diabetic rats is reported to develop some leakage (45)(46)(47). In further contrast, there are many reports (47-51) of studies using non-physiologically relevant tracers and methods, such as fluorescein, albumin, or Evans blue dye, in which BRB damage occurs as early as 2 weeks after diabetes induction in rats.…”