The proliferative ability of the lens epithelium in rat galactose cataracts. Examination using whole-mount preparations.

Abstract

We gave three-weeks-old rats a diet which included galactose in three different concentrations (15%, 25%, 50%) producing sugar cataracts of three different degrees.Combining the 3H-thymidine autoradiographic method with the whole-mount preparations of total lens epithelial cells of one lens, we examined the proliferative activity of the lens epithelium in the early stages of cataract crisis (for 14 days). In the lenses of three-weeks-old normal rats, 3H-thymidine labelled cells were observed mainly in the proliferative zone at the lens equator, and at the same time a few were detected in other parts. On the first day after we started feeding the rats galactose-included diets, the very early stages of cataract formation and an increase in the number of labelled cells were observed in the proliferative zone when compared with the control group on a normal diet. On the fourth day, we found an increase in the number of labelled cells in the proliferative zone and a remarkable ectopic proliferation in other parts. However, in contrast to this, as the cataract progressed from the seventh day to the fourteenth day, we noticed a decrease in the number of labelled cells in the proliferative zone and in the other epithelial layers when compared with the control group. The peak in the number of labelled cells on the fourth day was observed regardless of the galactose concentrations in the diet, and was not proportional to the degree of the cataracts.In rat galactose cataracts, the cure phenomenon (Diet-Reversal), in which the lens opacity is removed by altering the galactose-including diet to the normal diet, was observed. This Diet-Reversal was proved through light microscopy (17). Moreover, we also reported that aldose reductase inhibitors (ART) had curative effects and preventive effects on galactose cataracts (1-3, 11, 12). On the basis of the above-mentioned results, we think it is essential that the cataract lens is repaired by the regenerated fibers at the lens equator. That is to say, the examination of the proliferative ability and the kinetics of the regenerated lens epithelium seems to be very important in order to develop the cataract therapeutic agents for the future, though it is impossible at present.We used the 3H-thymidine autoradiographic method on thin sections embedded with methacrylate, and proved that, in the developmental process of rat galactose cataracts, the lens epithelium will repeat the ectopic proliferation even in other parts than the lens equator, and play an important role in the repair of the regenerated lens fibers (13,14). In particular, on the fourth day after we started feeding rats the 50% galactose-including diet, a remarkable increase in the amount of ectopic proliferation was observed. But to give a conjecture on the whole layer of lens epithelium from only one thin section seemed to be unreasonable. Therefore, in this investigation we used the whole-mount preparations of the lens epithelial layer. In this study, we examined the ability of the rat lens epithelium to proliferate dur...

Cell Growth of Rat Lens Epithelium in Galactose-induced Cataracts.

“…The appearance of cataracts depends on the concentration of the galactose feeding [11], and thus the appearance of the peak in growth of lens epithelial cells in the galactose-fed rats may also depend on the amount of galactitol accumulation. Although growth at the central part of lens epithelial cells in rats fed galactose supplementeddiets is thought to be induced by swelling and liquefaction of the lens fiber directly below the epithelial cells, and to be related to regeneration of the lens fiber [14], light microscopy performed in the present study clearly demonstrated that growth of lens epithelial cells precedes changes in lens fiber. The rise, peak and fall in epithelial cell growth, while changes in fiber continued unabated, suggests that growth of lens epithelial cells is facilitated by biochemical changes such as galactitol accumulation and water absorption in lens fiber above a certain threshold level.…”

“…The rise, peak and fall in epithelial cell growth, while changes in fiber continued unabated, suggests that growth of lens epithelial cells is facilitated by biochemical changes such as galactitol accumulation and water absorption in lens fiber above a certain threshold level. The peak in epithelial cell growth may be the same among high dose (25% to 50%) galactose-fed rats due to the rapidity of biochemical and morphological changes such as rapid galactitol accumulation and membrane permeability change in the lens [14]. This finding corresponds to the fact that in hypergalactosemia mice which had one tenth lower aldose reductase activity in the lenses than hypergalactosemia rats, no galactitol accumulation, changes in lens fiber or epithelial cell growth occurred [14].…”

“…Cataracts that develop in rats fed a galactose supplemented diet are thought to be useful as an animal model of diabetic cataracts [7,13,15]. We believe that the proliferation potency at the central part of the lens is strongly related to maturity onset cataracts or diabetic cataracts, because this proliferation potency decreases with aging [5,6,12,16] and increases in some types of human cataracts or galactose induced cataract in rats [4,14], while lens epithelial cells in normal rats grow vigorously at the equator. In the present study, the proliferation potency of lens epithelial cells at the central part of the lens was studied in rats fed 5%-25% galactose supplemented diets in order to examine the relationship between cataract development and epithelial cells.…”

“…The peak in epithelial cell growth may be the same among high dose (25% to 50%) galactose-fed rats due to the rapidity of biochemical and morphological changes such as rapid galactitol accumulation and membrane permeability change in the lens [14]. This finding corresponds to the fact that in hypergalactosemia mice which had one tenth lower aldose reductase activity in the lenses than hypergalactosemia rats, no galactitol accumulation, changes in lens fiber or epithelial cell growth occurred [14]. The cell growth induced by galactose-feeding decreased to the same level as that at day 0 in the present study.…”

“…In general, while senile cataracts are caused by cortical changes such as swelling and liquefaction of lens fiber, subcapsular cataracts display abnormal growth and stratification of lens epithelial cells from the early stages of the disease, suggesting that the development of cataracts is profoundly influenced by epithelial cell growth. In previous studies [4,14] that attempted to elucidate the cause of abnormal growth of lens epithelial cells, we reported that, in rat galactose cataracts, which is an animal model of diabetic cataracts, repeated ectopic growth of the lens epithelial cells was observed in areas other than the equator in the early stage of cataract development [14]. In the present study, two different methods, fluorescence cytophotometry of 4',6-diamidino-2-phenylindole (DAPI) staining and immunohistochemical staining of proliferating cell nuclear antigen (PCNA), were used to study the growth kinetics of epithelial cells of the anterior pole of lenses in rats fed low concentration galactose diets that are unable to induce diabetic cataracts in the early stages.…”