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Sugar cataracts rapidly develop in dogs fed a diet containing 30% galactose. While studies on the formation and progression of these sugar cataracts suggest that they are osmotic in nature and are linked to aldose reductase, sugar cataract formation in the dog to date has not been completely prevented by the administration of aldose reductase inhibitors sorbinil and M79175. To demonstrate that the formation and progression of sugar cataracts in galactose-fed dogs can be dose-dependently inhibited by the administration of aldose reductase inhibitors, 9-month old male beagles were placed on diet containing 30% galactose with/without 10 or 16 mg kg-1 day-1 of M79175 for up to 39 months. Cataract progression in all dogs was followed by periodic slit lamp examination and documented by retroillumination photography. Although large variations in cataract formation and progression were observed, all dogs fed a 30% galactose diet for 39 months developed cataracts. Lens changes were significantly less in galactose-fed dogs treated with either 10 or 16 mg kg-1 M79175 and no cataract formation was observed in 3 of 6 galactose-fed dogs treated with 16 mg kg-1 M79175. These observations confirm that aldose reductase plays a key role in initiating cataract formation in galactose-fed dogs and that cataract formation can be prevented by adequate inhibition of aldose reductase., (Copyright 1998 Academic Press Limited.)

Cataracts were produced in rat lenses by either feeding a diet containing 50% galactose or by inducing diabetic condition by intravenous injection of streptozotocin. Proteolysis of crystallins, protease activity of calpain II enzyme (EC 3.4.22.17), and presence of calpain molecule (antigen) were determined at four cataract stages--I, cortical vacuoles, II, vacuoles plus hazy cortex, III, nuclear cataract, and IV, mature cataracts. Calpain activity was normal or moderately elevated at early stages of galactose and diabetic cataracts. Later stages III and IV showed proteolysis of lens crystallins, increased proportion of insoluble proteins, loss of calpain enzyme activity and calpain molecule from the soluble fraction, and reduced amounts of calpain associated with insoluble pellet. In galactose cataract, the largest increase in lens calcium were found when proteolysis was present. These results provide evidence for calpain-induced proteolysis of lens crystallins in two in vivo models of sugar cataracts in rodents.

Soluble lens crystallins from 6-10-week-old, galactose-fed, male Sprague-Dawley rats were analyzed by two-dimensional polyacrylamide gel electrophoresis at each of the five Sippel stages of cataractogenesis. Electrophoretograms were compared with similarly analyzed crystallins from comparably aged, chow-fed controls. Polypeptides were assigned to crystallin families and subfamilies on the basis of chromatographic fractionations with Sephadex G-200, superfine. Staining intensities of polypeptides from control lenses remained essentially unchanged throughout the experimental period, while those of the polypeptides from cataractous lenses showed non-uniform changes. Staining of the genomic gamma-crystallins increases up to at least stage 3; by stage 4, staining of gamma-chains, with perhaps those of gamma 5 and gamma 6 excepted, diminishes and in the total cataract, staining of all chains is further reduced. With possibly the addition of one chain, the total number of postsynthetically modified gamma-crystallins in cataractous lenses does not exceed that in the comparably aged normal lens. The genomic alpha- and beta-crystallin polypeptides are sustained close to normal levels up to stages 3 or 2, respectively, after which their gradually falling levels are accompanied by the generation of new species or elevated levels of existing post-translational species. An exception to this behavior is the rapid and total loss of beta B1a, a genomic subunit implicated in the aggregation of beta H-crystallins. Charge heterogeneity and variable pI displayed by beta B1a and other highly cationic beta- and gamma-crystallin polypeptides can be induced during isoelectric focusing and may be due to thiol group oxidation.

Previous evidence has shown clearly that sugar cataract formation results from unusually high intracellular levels of polyol. Documentation of polyol-related histological changes in the cortical fiber cells of the equatorial zone has been extensive. However, little attention has been given to the early changes in the lens epithelial cells, in spite of the fact that the highest level of aldose reductase is found in this layer of the lens. Also, cultured lens epithelial cells exposed to high sugar levels exhibit rapid accumulation of polyol and show ultrastructural alterations. Therefore, a study was designed to evaluate the role of the lens epithelium in sugar cataract formation. Specifically, an attempt was made to localize the earliest fine structural lesions in intact lenses of galactose-fed rats and to test their relation to aldose reductase. Rats were fed either a normal diet or a 50% galactose diet with or without sorbinil, an aldose reductase inhibitor. Rats were killed at varying periods of time ranging from 6 to 96 hr, and the eyes were processed for light and electron microscopy. The first detectable abnormalities occurred after 36 hr of galactose feeding, and were limited to the central lens epithelium. Cell edema, apparent dilution of cytoplasm, rounding of nuclei, aberrant intracellular vacuoles, and loss of normal tortuosity of cell boundaries were the salient lesions. No changes were detectable in the equatorial zone until 48 hr, and no deviation from the control structure was found in any of the rats treated with an aldose reductase inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

The onset and progression of diabetic-like retinopathy has been investigated in age-matched male beagle dogs fed a 30% galactose diet. Examination of the intact retinal vessels, isolated by gentle trypsin digestion, reveals that the destruction of pericytes to form pericyte ghosts is the earliest observable retinal vessel change. This results in an irregular distribution of endothelial cell nuclei near pericyte ghosts and the subsequent formation of acellular capillaries containing neither endothelial cells or pericytes. This was followed by the histological appearance of microaneurysms and later, by the funduscopic appearance of intraretinal hemorrhages. Studies in similar galactose-fed dogs treated with aldose reductase inhibitors indicate that all of these changes are linked to the initial aldose reductase associated destruction of pericytes.

Whole mounts of lens epithelia from rats fed on a galactose-rich diet for one, two, three or seven days were examined for morphological alterations. The meridional rows of epithelia from lenses of animals fed on galactose for seven days were found to be grossly disorganized or abnormally elongated. There was some indication that the cells were edematous and that the epithelium had become multilayered. These abnormalities apparently extended into the transitional zone. Evidence of the cytoarchitectural changes was present as early as one day after institution of the 30% galactose diet and progressed steadily over the period of observation. The findings provide support for the hypothesis that loss of meridional row integrity is a phenomenon common to development of most types of cortical cataracts.

Weanling male Sprague-Dawley rats were given a 50% galactose diet with or without an aldose reductase inhibitor (0.04% tolrestat, Ayerst) for 88 weeks. Quantitative computer planimetry on electron micrographs of perpendicularly transected retinal capillaries showed mean basement membrane thicknesses to be 263 +/- 50 nm in galactose-fed rats, 153 +/- 10 nm in galactose-fed rats given tolrestat, and 114 +/- 16 nm in rats given control feed. The retinal capillary basement membrane thickening in galactose-fed rats was accompanied by other ultrastructural alterations mimicking changes observed in diabetic microangiopathy, such as multi-lamination and the formation of vacuoles and dense inclusions. The results extended previously reported (44-week) findings, showed greater galactose-induced changes in capillary basement membranes, and demonstrated the preventative effect of an aldose reductase inhibitor.