3-fluoro-3-deoxy-D-galactose: A new probe for studies on sugar cataract

Purpose. Aldose reductase (AR) activity and flux through the polyol pathway can conveniently be monitored in dog lenses by measuring the metabolism of 3-fluoro-3-deoxy-D-glucose by F-19 nuclear magnetic resonance (NMR) spectr oscopy. Since AR has broad substrate specificity and preferentially utilize s galactose over glucose as substrate, the ability of AR to utilize 3-fluor o-3-deoxy-D-galactose (3-FDGal) as substrate as well as the metabolism of 3 -FDGal in intact dog lens and cultured lens epithelial cells has been inves tigated. Methods. The suitableness of 3FDGal as a substrate was examined by incubati ng 3FDGal with purified dog lens aldose reductase in the presence of an NAD PH generating system or with galactitol dehydrogenase in the presence of NA D(+). Dog lenses and dog lens epithelial cells were cultured in 3-FDGal med ium with and without the AR inhibitor AL 1576. Metabolism was studied using F-19 NMR. Results. AR activity with 3-FDGal as substrate is higher than that with D-g alactose and its Km of 4.2 mM is ca 10-fold higher than that of D-galactose . Purified dog lens AR incubated with 3-FDGal resulted in the formation of 3-fluoro-3 -deoxy-D-galactitol. Galactitol formation was prevented by the a ddition of AL 1576. Incubation of 3-FDGal with galactitol dehydrogenase res ulted in the formation of 3-fluoro-3-deoxy-D-galactonic acid. Dog lenses cu ltured in 3-FDGal medium formed NMR peaks corresponding to 3-fluoro-3-deoxy -D-galactitol and 3-fluoro-3-deoxy-D-galactonic acid. The presence of AL 15 76 inhibited the formation of galactitol but not galactonic acid. Lens epit helial cells cultured in 3-FDGal medium formed only 3-fluoro-3-deoxy-D-gala ctitol. These cells developed multiple cytoplasmic vacuoles which was preve nted by the aldose reductase inhibitor AL 1576. Conclusions. The high affinity of this fluorinated sugar for aldose reducta se makes this an excellent probe for investigating aldose reductase activit y in dog lens tissues.