myo‐Inositol Metabolism in 41 A3 Neuroblastoma Cells: Effects of High Glucose and Sorbitol Levels

Abstract

Neuroblastoma cells were used to determine the effect of high carbohydrate and polyol levels on myo-inositol metabolism. The presence of elevated concentrations of glucose or sorbitol caused a significant decrease in both inositol accumulation and incorporation into phospholipid. These conditions, however, did not alter the accumulation of the other phospholipid head groups or the growth rate and water content of the cells. Two weeks of growth in either of the modified conditions was necessary to obtain a maximal effect on inositol incorporation. In contrast, growth in elevated concentrations of fructose, mannitol, or dulcitol had no effect on inositol metabolism. The reduced inositol accumulation and incorporation into lipids seen with glucose or sorbitol supplementation resulted in a decrease in the total phosphatidylinositol content of the cell without changing the levels of the other phospholipids. Kinetic analysis of cells grown in the presence of elevated glucose indicated that V'max for inositol uptake was significantly decreased with little change in the K'm. These data suggest that glucose decreases myo-inositol uptake in this system by noncompetitive inhibition. Cells grown in the presence of increased glucose also had elevated levels of intracellular sorbitol and decreased levels of myo-inositol. These results suggest that the high levels of glucose and sorbitol which exist in poorly regulated diabetes may be at least partially responsible for diabetic neuropathy via a reduction in the cellular content of myo-inositol and phosphatidylinositol. This system may be a useful model to determine the effect of reduced inositol phospholipid levels on neural cell function.

Human Na+-myo-inositol cotransporter gene: alternate splicing generates diverse transcripts

“…The maximal velocity of Na ϩ -myo-inositol cotransport activity has been reported to be increased by experimental diabetes or hyperglycemic concentrations of glucose in renal (6) and endothelial (20) cells. The same manipulations have been reported to diminish Na ϩ -myo-inositol cotransport activity in a variety of experimental systems including incubated endoneural preparations from streptozotocin-diabetic rats (10) and various cell culture models (3,4,14,18,32). AR inhibitors that block the formation of the intracellular osmolyte sorbitol prevent both the reported increases (6) and decreases (3,10,18,32) in Na ϩ -myo-inositol cotransport activity produced by glucose, suggesting that the regulation of Na ϩ -myo-inositol cotransport by alternative intracellular osmolytes may be complex.…”

Cultured Adult Animal Neurons and Schwann Cells Give Us New Insights into Diabetic Neuropathy

“…Lined cells rapidly proliferate to increase the cell number, and are suitable for molecular and biochemical analyses. In fact, several lines of neuroblastoma cells [4,5] and Schwann cells [6][7][8] have been employed for *Address correspondence to this author at the Division of Neural Development and Regeneration, Tokyo Metropolitan Institute for Neuroscience, 2-6 Musashidai, Fuchu, Tokyo 183-8526, Japan; Tel: 81-42-325-3881; Fax: 81-42-321-8678; E-mail: kazsango@tmin.ac.jp the study of diabetic neuropathy. However, the characteristics of these cells are far different from those of neurons and Schwann cells in mature animals.…”

Histopathological heterogeneity of neuropathy in insulin-dependent and non-insulin-dependent diabetes, and demonstration of axo-glial dysjunction in human diabetic neuropathy.

“…Aldose reductase is primarily confined to paranodal Schwann cell cytoplasm and vascular endothelial cells in nerve (7), whereas elevated ambient glucose levels appear to depress myo-inositol and (Na,K)-ATPase in peripheral neurons (6,(8)(9)(10)(11)(12) as well as vascular smooth muscle and perhaps endothelial cells ( 13,14).…”