Progression of mouse buthionine sulfoximine cataracts in vitro is inhibited by thiols or ascorbate

Mouse lens cultures were employed to study the progression of cataracts initiated by injection of buthionine sulfoximine, an inhibitor of glutathione (GSH) biosynthesis. Culture of lenses removed from untreated mice on postnatal day 7, for 48 hr in the presence of 4 mm BSO, resulted in only limited cataractous changes. To enable substantial progression of cataracts in vitro, it was therefore necessary to pretreat the mice with BSO prior to lens culture. A single injection of BSO (4 nmol mg-1 lens), administered on day 7, resulted in >90% depletion of lens GSH within 3 days, but no visible cataractous changes. The clear lenses were incubated for 29+/-1 hr at 37 degrees C in Medium HL-1, supplemented with EGF, insulin and Ca2+, in the presence or absence of BSO, and were scored for cataract development by previously described criteria. In the absence of BSO, only 4 of 10 lenses developed large opacities. However, in the presence of 4 mm BSO, 40 out of 45 experimental lenses developed opacities affecting at least 50% of the lens visual field and were scored as stages 1C-4, depending upon the extent and density of the cataracts. In addition, three lenses had opacities involving 20-50% of the field (stage 1B). By contrast, less than 10% of lenses from untreated mice incubated in the absence of BSO developed opacities. The cataracts developed in 4 mm BSO were accompanied by reduction of lens glutathione levels to <0.010 nmol mg-1 lens. They were almost completely prevented by 1 mm ascorbate, 2 mm GSH, 2 mm GSH monoethyl ester and 2 mm cysteamine. GSH and GSH ester maintained lens glutathione content between 0.1 and 0.2 nmol mg-1 in the presence of BSO, whereas ascorbate did not prevent near-total GSH depletion. The prevention of cataracts by thiols and ascorbate was confirmed by lens Na/K ratios not significantly different from those in control lenses. The above combination of GSH depletion in vivo by a single injection of BSO, followed 3 days later with lens culture in the presence of BSO, may yield a useful system to elucidate and control the biochemical mechanisms involved in oxidative cataract induction by this GSH-depleting agent.