EFFECTS OF XYLOSE ON MONKEY LENSES IN ORGAN-CULTURE - A MODEL FOR STUDY OF SUGAR CATARACTS IN A PRIMATE

Lenses exposed to high concentrations of xylose in organ culture produ ce xylitol, and they lose transparency and exhibit other changes chara cteristic of cataracts. Most previous studies of this model system for cataractogenesis have employed rat or rabbit lenses, where the activi ty of the enzyme aldose reductase has been definitely implicated as th e initiating factor. Since lenses from this species have much higher a ldose reductase activity and have other differences relative to human lenses, the relevance of these findings to the human lens is uncertain . To determine the effects of xylose on the lenses of a primate, lense s from the rhesus monkey (Macaca mulatta) were incubated 24-48 hr in c ontrol medium or in TC-199 medium containing 30 mM xylose. Xylose caus ed a general haziness, focal swelling of epithelial cells, and swollen peripheral fiber cells, but the changes were much less pronounced tha n in rat lenses under similar conditions. Monkey lenses exposed to 30 mM glucose, galactose or xylose accumulated measurable sorbitol, dulci tol or xylitol, respectively, but the amounts were much lower than in rat lenses, perhaps reflecting the lower aldose reductase and higher s orbitol dehydrogenase activities in monkey lenses. The damage to monke y lenses appeared to be limited to the outer layers. In monkey lenses, xylose caused little, if any, change in membrane transport of choline or alpha-aminoisobutyrate, but severely depressed synthesis of phosph orylcholine (P-choline), and increased leakage of P-choline into the c ulture medium, leading to a decrease in the P-choline concentration wi thin 24-48 hr. In summary, xylose-induced damage to monkey lenses in o rgan culture Is qualitatively similar to that seen in rat lenses, but the changes are much less rapid and severe. Culture of monkey lenses w ith xylose provides a model system to extend previous studies of sugar cataractogenesis in rats to a species more closely related to humans. (C) 1998 Academic Press.