Non-tryptophan fluorescence and high molecular weight protein formation in lens crystallins of rats with chronic galactosemia: Prevention by the aldose reductase inhibitor sorbinil

Abstract

Crystallin-bound non-tryptophan fluorescence and protein cross-linking were studied in chronic galactosemia. Fluorescence (excitation/emission— 370 440 nm) was significantly higher in galactosemic rats compared to controls ( P < 0·001). Accumulation of fluorescence was significantly reduced both in water soluble ( P < 0·001) and insoluble ( P < 0·005) lens fractions in galactosemic rats receiving the aldose reductase inhibitor sorbinil. High performance liquid chromatography of water soluble lens crystallins showed an increase in the content of high molecular weight proteins and the fluorescence associated with it. Sorbinil partly prevented the formation of such fluorescent high molecular weight proteins. Under reducing conditions, sodium dodecyl sulfate polyacrylamide gel electrophoresis of water soluble proteins revealed a distinct high molecular weight protein of 60 kDa in galactosemia. Sorbinil treatment completely abolished the formation of this protein. Western blotting using rabbit antiserum to bovine α-, β- and γ-crystallins revealed the presence of gamma, but not α- and β-crystallins in the 60-kDa protein. Formation of this protein may result from trimerization of γ-crystallins or from an association of γ-crystallin with a non-crystallin cytosolic protein or mixed protein cross-linking of γ-crystallins with membrane protein(s). The present study shows that polyol pathway in cataractogenesis also extends to protein cross-linking and formation of fluorescent compounds, the nature of which remains to be elucidated.