Effect of Galactose and Glucose Levels and Sorbinil Treatment on myo-Inositol Metabolism and Na⁺-K⁺ Pump Activity in Cultured Neuroblastoma Cells

Abstract

Neuroblastoma cells were used to analyze the effect of galactose supplementation on myo-inositol metabolism, polyol accumulation, and Na^+-K⁺ pump activity. Culturing cells in 30 mM galactose for a minimum of 1 wk led to a large accumulation of intracellular galactitol and a >50% decrease in myo-inositol content. The effect of galactose on the intracellular content of galactitol and myo-inositol was concentration dependent. Extracellular myo-inositol accumulation and incorporation into phospholipid decreased by 20–30% in cells grown in 30 mM galactose. The decrease in myo-inositol accumulation is apparently due to a noncompetitive inhibition of high-affinity myo-inositol uptake. Treatment of the galactose-containing media with 0.4 mM sorbinil partially prevented the galactose-mediated decreases in myo-inositol metabolism and content. The galactitol content of the sorbinil-treated cells was significantly reduced compared with the galactitol levels in cells cultured in 30 mM galactose; however, galactitol levels remained significantly elevated over control cells. Exposing neuroblastoma cells to 30 mM galactose causes a decrease in the levels of phosphatidylinositol that is partially restored by the addition of sorbinil. The activity of the Na^+-K⁺ pump was decreased by 20% in cells cultured in 30 mM galactose and was partially protected by sorbinil treatment. The effects of long-term galactose supplementation on myo-inositol metabolism, polyol accumulation, and Na^+-K⁺-ATPase transport activity in cultured neuroblastoma cells are similar to the effects of high concentrations of glucose. These results provide additional evidence that the accumulation of polyol by neuroblastoma cells is partially responsible for alterations in myo-inositol metabolism and decreases in Na^+-K⁺-ATPase transport activity