Sorbinil prevents the hypergalactosemic-induced reduction in [³H]-myo-inositol uptake and decreased [³H]-myo-inositol incorporation into the phosphoinositide cycle in bovine lens epithelial cells in vitro

Abstract

The synthesis of phosphatidylinositol, phospha-tidylinositol-4-phosphate and phosphatidylinositol-4-5-bisphosphate was studied using ³H-myo-inositol (³H-MI) as precursor in cultured bovine lens epithelial cells (BLECs) maintained in galactose-free, physiological medium or 40 mM galactose (Gal) ± sorbinil for six days. The formation of inositol polyphosphates from phosphoinositides was also shown. Galactitol did not exceed 2mM in Gal-incubated cells after six days of exposure; no galactitol was observed in BLECs maintained in galactose-free, physiological medium or Gal supplemented with sorbinil. Uptake of ³H-myo-inositol(³H-MI) into BLECs was significantly reduced in cells exposed to Gal. A concomitant reduction in ³H-MI incorporation was observed in the phos-phoinositides, as well as with the released inositol phosphates. The simultaneous addition of sorbinil to the Gal medium corrected the drop in ³H-MI uptake and normalized ³H-MI incorporation into the phos-phoinositides and inositol phosphates. While an apparent decrease in the three inositol-containing lipids was observed with the Gal-incubated cells, based on ³H-MI incorporation, there was no change in total membrane phosphatidylinositol content when compared to cells maintained in physiological medium as determined by the μg PI PO₄ per μgj total membrane PO₄. The apparent loss of radiolabeled phosphoinositides was attributed to the decreased specific activity resulting from the lower internal pool of ³H-MI in the Gal-exposed cells available for incorporation into the phosophoinositides. Our observations support the contention that the net cellular content of inositol-con-taining lipids does not vary significantly between control cells and those exposed to hypergalactosemic conditions for six days. These studies demonstrate that activation of the polyol pathway interferes with lens myo-inositol uptake and that the co-administration of sorbinil to the Gal medium protects against the attendant decrease.