Prefeeding of aldose reductase inhibitor and galactose cataractogenesis

Topical aldose reductase inhibitor formulations for effective lens drug delivery in a rat model for sugar cataracts

PURPOSE

In the topical delivery of drugs to the lens, drug retention on the eye surface is considered to be important because increased retention on the ocular surface should lead to increased ocular absorption of a drug through the cornea into the aqueous humor and subsequently the lens. The aim of this study was to investigate whether increasing the viscosity of a topical aldose reductase inhibitor suspension increases the lenticular bioavailability of the inhibitor and whether such a formulation can arrest sugar cataract formation.

METHODS

Five topical suspensions of 3% 2-methylsorbinil (2-MS) were prepared using (1) hydroxypropyl methylcellulose (HPMC, 0.5% w/v), (2) xanthan gum (0.5% w/v), (3) gellan gum (0.5% w/v), (4) carbopol (0.25% w/v), and (5) carbopol (0.25% w/v)--hydroxypropyl methylcellulose (HPMC) (0.25% w/v). Viscosity measurements were conducted with a viscometer. Lenticular levels of 2-MS were determined in the lenses from young Sprague Dawley rats receiving 1 drop of selected topical suspension twice-daily for 7 days. The efficacy of the suspensions to arrest sugar cataract formation was evaluated by administering the suspensions for 21 days to similar rats fed a diet containing 50% galactose. Lens changes were examined by portable slit lamp following mydriasis.

RESULTS

Lenticular levels of 2-MS was highest in rats administered suspensions containing 0.25% carbopol + 0.25% HPMC as vehicles followed by 0.5% gellan gum, 0.5% HPMC, 0.25% carbopol, and 0.5% xanthan gum. All untreated rats fed a 50% galactose diet developed hypermature cataracts within 15 days; however, none of the topical treated rats demonstrated cortical vacuole formation after 21 days of galactose feeding.

CONCLUSIONS

In the suspensions examined, no direct relationship between the lenticular drug levels of 2-MS and either viscosity or pH of the vehicles were observed. The observed arrest of sugar cataract formation indicated that therapeutically adequate lenticular levels of 2-MS were provided by all topical suspensions.

Effect of germanium-132 on galactose cataracts and glycation in rats

Germanium compounds have been shown to be effective in preventing the formation of advanced glycation end-products and for reversible solubilization of glycated proteins. As protein glycation has been proposed to play a role in lens opacification, we initiated studies to evaluate the effects of 2-carboxyethyl germanium sesquioxide (germanium compound 132 or Ge-132) on galactose-induced cataractogenesis. For this study young Sprague-Dawley rats were fed a 50% galactose diet. One group of rats received topical saline and another group was administered Ge-132 in saline four times a day. The lenses were periodically examined with an ophthalmoscope and at desired intervals processed for light and scanning electron microscopy. Our observations, beginning at 3 days and continuing to 21 days of galactose feeding, exhibited the characteristic galactose-induced morphological alterations, which include the formation of vacuoles, cysts, membrane disruption and swelling of fibers and epithelial cells as well as disorganization of the bow in lenses of rats in both groups. However, in the majority of rats administered Ge-132 these alterations were delayed as compared to the lenses of rats administered saline. Our findings show that, although the initiation, progression and pattern of lens opacification in rats receiving saline and Ge-132 were similar, in the majority of lenses the progression and establishment of mature cataracts in the Ge-132 group of rats were delayed. Analysis of the water-soluble and water-insoluble lens-protein fractions for glycated proteins showed increased levels of the Amadori products and advanced glycation related fluorescent products in galactosemic rats treated with saline eye drops. In rats receiving the topical Ge-132 treatment the levels of these glycation products were substantially reduced to levels lower than control values. Prevention of glycation seems to be a mechanism by which cataract progression is delayed.

The role of polyols in the pathophysiology of hypergalactosemia

Cellular accumulation of galactitol has been suggested to cause the apparent dietary-independent, long-term complications in classic galactosemia. Experimental animals rendered hypergalactosemic by galactose feeding accumulate tissue galactitol, as well as millimolar quantities of galactose, and manifest biochemical, physiological and pathological abnormalities which are generally eliminated or curtailed by the concomitant administration of an aldose reductase inhibitor. This includes reduced cellular content of the cyclic polyol, myo-inositol, which like galactitol may function as an alternate intracellular osmolyte. However, the abnormalities detected in experimental galactosemic animals are more compatible with findings in experimental diabetes mellitus than in human galactosemia. Because patients with galactokinase deficiency fail to manifest the CNS and ovarian complications which characterize classic galactosemia, yet during long-term lactose restriction excrete comparable urinary quantities of galactitol, this polyol alone is not likely to play an important role during postnatal life in the pathogenesis of long-term complications. Notwithstanding, a role for either galactitol or myo-inositol in an intrauterine toxicity cannot be dismissed.

Effect of aldose reductase inhibitors on lenticular dulcitol level in galactose fed rats

We have shown that galactose cataract development is delayed or inhibited with the administration of aldose reductase inhibitors (ARIs). Dulcitol forms and accumulates in the lens of rats fed galactose. We undertook investigations to study the effectiveness of ARIs in preventing the formation and accumulation of dulcitol in the lens. Young Sprague Dawley rats were fed Purina Rat Chow with 50% galactose either with or without 15 mg sorbinil, 0.15, 0.5, or 1.0 mg E-0722/day/Kg body weight. At desired intervals following the initiation of diets, the lenses were processed for the determination of galactose and dulcitol levels. The lenticular dulcitol increased significantly in all animals fed galactose reaching a maximum level by approximately 15 days with comparatively lower levels in the groups fed ARIs with galactose; this increase was dose dependent in the groups fed E-0722. There was a subsequent, rapid drop in lenticular dulcitol by 18 days in all dietary groups. Interestingly, a second peak of increased lenticular dulcitol was observed in all groups. The correlation between dulcitol accumulation and cataract development is discussed.

In utero and milk-mediated effect of aldose reductase inhibitor on galactose cataracts

Our previously reported investigations showed that cataracts could be induced in fetal lenses through the maternal feeding of galactose during pregnancy. We also reported that the lens opacity present at birth reverses completely by 30 days of age if there is no further post-natal exposure to galactose. This investigation was designed to investigate if an aldose reductase inhibitor (ARI) has any cross-placental effect in preventing galactose-induced cataracts in fetuses. We have also evaluated if there are any milk-mediated effects of galactose on cataract induction and of galactose and ARI on the maintenance or reversal of opacities induced in utero. Pregnant Sprague-Dawley rats were fed either 50% galactose or rat chow with or without the ARI, (2R,4S)-6-fluoro-2-methyl spirochroman-4,4'-imidazolidine-2',5'-dione (Eisai compound E-0722). Following parturition, pups of mothers from the different dietary groups were either fed by their own mothers or foster fed by lactating females fed either rat chow or 50% galactose with or without the ARI. Lenses of the pups were examined at desired intervals with light and scanning electron microscopes. We observed that: (a) both galactose and the ARI had a cross-placental effect on the fetal lenses in the development and inhibition of cataracts, respectively; (b) galactose had very little, if any, milk-mediated effect on either the induction of cataracts in newborn pups that were born with transparent lenses or the maintenance of cataracts induced in utero; (c) the ARI appeared to have a milk-mediated effect, which accelerates the reversal of cataract associated alterations in lenses of pups with cataracts induced in utero, leading to further reinstatement of lens transparency; and (d) the presence of ARI in the diet of rats during pregnancy and/or post-parturition provided continued protection to the lenses of pups that were exposed to a galactose diet following birth.