Lorenzo O. Merola

Aldose reductase in diabetic complications of the eye

Aldose reductase (AR) appears to initiate the cataractous process in galactosemic and diabetic animals. Sugars in excess are converted to polyols by lens AR. In sugar cataracts, polyols accumulate to levels substantial enough to cause a hypertonicity leading to lens fiber swelling. All other changes appear secondary to polyol accumulation and lens swelling. The development of sugar cataracts can be duplicated in organ culture. In culture, the various changes that occur were minimized or did not occur when inhibitors of AR were included in the medium. Moreover, AR inhibitors were shown to effectively delay the onset of sugar cataract development in animals. A defect in the corneal epithelium of diabetics became apparent in vitrectomy. One manifestation of this problem was the delay in the reepithelialization of denuded corneas. In examining this problem experimentally, the epithelium was removed from the corneas of diabetic and normal rats. The regeneration of epithelium in corneas of diabetic rats required a longer period than in the normal. The possibility that AR, active in the epithelium, was involved in this phenomenon was investigated. The corneal epithelium was removed from both eyes of a diabetic rat. One eye was treated topically with the AR inhibitor CP-45,634 while the other served as control. The eye treated with CP-45,635 regenerated epithelium much more quickly than the untreated eye. Other AR inhibitors had similar beneficial effects.

A possible cataractogenic factor in the Nakano mouse lens

Abstract A factor present in the Nakano mouse lens is an inhibitor of NaK ATPase. This inhibitor is not found in the normal mouse lens. It is not associated with any of the major crystallins but is found with the low molecular weight components. It is resistant to high temperatures and to acid and alkaline pHs. It appears to be a polypeptide since its activity is abolished by treatment with carboxy-peptidase A and leucine amino peptidase. Other properties of the inhibitor indicate that this factor appears quite different from other substances which inhibit NaK ATPase.

Induction of the enzyme aldose reductase in a lens epithelial cell line from a transgenic mouse

A lens epithelial cell line established from a transgenic mouse synthesizes high levels of the enzyme aldose reductase which converts sugars to polyols. This enzyme has been implicated in the formation of sugar cataracts in animals and with diabetic complications in man. The mouse aldose reductase has been characterized and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis has an apparent molecular mass of 38,000, similar to the enzyme in rat and man. The cellular enzyme is inhibited by two aldose reductase inhibitors: Sorbinil (IC50 = 1.8 X 10(-7) M) and Alcon 1576 (IC50 = 7.8 X 10(-8) M). The amount and the specific activity of the aldose reductase can be further increased in the cells by raising the osmolarity of the medium to 500 mOSM. Although the amount of aldose reductase is increased approximately sevenfold under these conditions, alpha-crystallin, one of the main lens specific proteins, remained at about the same concentration. No detectable increase in sorbitol was found within the cells, in contrast to published reports on renal cells in which this polyol increases under similar hyperosmotic conditions; however, in the lens cells there was a five-fold increase in the inositol content, suggesting that this polyol rather than sorbitol may be used to compensate for some of the changes in the osmolarity. The induction of the enzyme aldose reductase without the apparent accumulation of its product suggests a complex mechanism for osmoregulation in the lens cells.

Aldose reductase activity in a cultured human retinal cell line

Abstract The action of the enzyme aldose reductase has been shown to initiate cataract formation in diabetic animals. This enzyme may also play a role in other complications of diabetes such as retinopathy. In order to investigate aldose reductase from a human retinal source, the retinoblastoma cell line Y-79 was studied. Using a variety of substrates, these cells have enzyme activity consistent with aldose reductase. Immunologically, the aldose reductase from these cells cross-react with antibody to human placental aldose reductase. By immunohistochemistry, the enzyme is present in the cytoplasm of the Y-79 cells. Incubation of these cells with 30 m m -galactose resulted in considerable accumulation of dolcitol. This accumulation could be reduced when sorbinil, an aldose reductase inhibitor, was present in the culture medium. This report is the first to demonstrate the presence of human aldose reductase in a continuous cell line.

Effect of Prolactin on Galactose Cataractogenesis

Prolactin has been known to affect the water and electrolyte balance. Because increased lens hydration has been shown to be a common phenomenon in most, if not all types of cataracts, we have been interested in investigating a possible role of prolactin in sugar cataract induction and progression. For this study, we have used morphological and biochemical approaches. The prolactin delivery method involved intraperitoneal implantation of one or more pellets in Sprague-Dawley female rats. Following implantation of the desired number of prolactin or control (nonprolactin) pellets, animals were either fed galactose and lab chow, or lab chow diet. Gross morphological observations of whole lenses, slit-lamp examination of lenses and light microscopic analysis of lens sections showed that in the galactose-fed prolactin group, galactose associated alteration progressed faster and total opacification (mature cataract development) was achieved earlier than in the nonprolactin group. The levels of galactose and dulcitol were higher in the lenses of galactose-fed prolactin treated rats as compared to lenses from nonprolactin (control) rats. No significant difference in lens Na+-K+ ATPase activity between the prolactin and nonprolactin group was observed. Our results indicate that prolactin accelerates galactose-induced cataractogenesis in rats.

Inositol-1-Phosphatase in the Lens

The ocular lens has high concentrations of free myoinositol. The ability of the lens to actively concentrate inositol may explain the high levels of the cyclic polyol. However, no detectable amounts of inositol are present in the aqueous humor. The biosynthesis of inositol may contribute to the inositol stores in the lens. This paper describes a study on the various factors involved in explaining the presence of inositol in the lens. During the course of this study an active phosphatase of inositol-1-phosphate was uncovered. Consequently, this paper deals primarily with the phosphatase and also gives some features of the biosynthesis of inositol from glucose-6-phosphate in the lens.