This laboratory has developed a novel procedure which permits, in both animals and humans, isolation of the entire vasculature network of the retina in an intact and essentially undistorted arrangement. Although a trypsin digestion procedure was developed 30 years ago for isolation of human retinal vessels, it has many limitations and has not been as dependable in animals. Systematic tests with rat retinas revealed that elastase, a """"""""contaminant"""""""" of the crude trypsin mixture traditionally used, is much more effective than trypsin for the selective preservation of retinal vessels. Digestion with purified elastase permits clear identification of the degeneration of pericytes ('ghosts'), the first lesion of diabetic retinopathy. Elastase-based procedures should apply directly to retinopathy of prematurity and provide new approaches in tissues, such as brain and inner ear. This procedure was the key to obtaining success in our studies on an animal model for the very distinct group of lesions characteristic of human background diabetic retinopathy. The galactose-fed rat model, first developed in our laboratory, takes advantage of the fact that aldose reductase has a higher affinity for galactose than for glucose, which results in more intracellular polyol accumulation in galactosemia. We fed rats galactose for extended periods in an effort to produce diabetic-like retinal lesions. Galactosemia did indeed induce diabetic-like microangiopathies that were more advanced and more like human diabetic lesions than those which develop in long-term diabetic rats. The galactose-fed rat model has distinct advantages over genetic or chemically induced models of diabetes for intervention studies. Intervention studies are under way to determine appropriate times for intervention via different aldose reductase inhibitors. We plan to attempt, by dietary manipulation, to produce rat models that develop the diabetic-like retinal angiopathies sooner. Also, using cell culture, we will investigate possible mechanisms of endothelial cell proliferation and subsequent pathologies.
