SUPPRESSION OF PENTOSIDINE FORMATION IN GALACTOSEMIC RAT LENS BY AN INHIBITOR OF ALDOSE REDUCTASE

Recent work from our laboratory revealed a correlation between the deg ree of protein pigmentation in human cataractous lens and the advanced Maillard reaction as reflected by pentosidine formation. Although the data suggested a role for ascorbate in pentosidine formation in senil e cataractous lenses, elevated pentosidine levels in diabetic cataract s suggested that glucosylation may be involved directly in pentosidine biosynthesis. To clarify this issue, we quantified pentosidine in len ses from rats with experimental galactosemia with and without aldose r eductase inhibitor treatment. At 12 months, pentosidine-like fluoresce nce (335/385 nm) was three to six times higher (P < 0.0001) in water s oluble and insoluble crystallins of galactosemic compared with nongala ctosemic rats. Actual pentosidine levels increased shortly after onset of galactosemia. Contents in water-insoluble crystallins were 6.32 +/ - 2.2 and 1.40 +/- 0.66 pmol/mg protein in galactosemic and control le nses, respectively (P < 0.001). Fluorescence and pentosidine were supp ressed to almost control levels upon treatment with sorbinil. Incubati on experiments showed that pentosidine could form slowly from galactos e, but much more rapidly from ascorbate and its oxidation products. It s formation could be inhibited partly by both reduced and oxidized glu tathione or epsilon-aminocaproic acid. The requirement of oxygen for p entosidine formation suggests that oxidative stress associated with gl utathione depletion and ascorbate oxidation are plausible mechanisms f or rapid pentosidine formation upon onset of galactosemia. In contrast , Maillard reaction by glycoxidation products may account for the sust ained increase in pentosidine. Both these events may be linked to the newly recognized pseudohypoxic state of cells exposed to high sugar co ncentrations.