Inhibition of phosphatidylinositol synthase by glucose in human retinal pigment epithelial cells.
A series of interrelated biochemical and functional defects, induced by hyperglycemia, associated with intracellular depletion of D-myo-inositol, and corrected by aldose reductase inhibitors, have been ascribed to abnormal phosphoinositide metabolism in several tissues prone to diabetic complications. However, reductions in tissue D-myo-inositol content are not universally found in complications-prone diabetic tissues, and direct mass-action effects of cellular D-myo-inositol depletion on the critical CDPdiacylglycerol-inositol 3-phosphatidyltransferase (PI synthase; EC 2.7.8.11) step have never been shown conclusively in relevant cells. The studies reported here simultaneously estimated the chemical mass of CDP diglyceride by equilibrium labeling with 5-[3H]cytidine and phosphoinositide biosynthesis by the incorporation of [32P]orthophosphate into phosphoinositide. This was done to assess the degree of inhibition of PI synthase under various degrees of D-myo-inositol depletion and sorbitol accumulation induced by glucose and other metabolic manipulations in cultured human retinal pigment epithelial cells, a new in vitro model for diabetic complications. The results suggest that sorbitol accumulation limits the PI synthase reaction in these cells by selectively depleting specific intracellular pools of D-myo-inositol and/or by possible independent effects of sorbitol on PI synthase.
Nakamura
J
J
Department of Internal Medicine, University of Michigan, Ann Arbor 48109.
Del Monte
M A
MA
Shewach
D
D
Lattimer
S A
SA
Greene
D A
DA
D000449:Aldehyde Reductase / Q000037:antagonists & inhibitors; D051607:CDP-Diacylglycerol-Inositol 3-Phosphatidyltransferase; D003470:Culture Media; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007294:Inositol / Q000378:metabolism / Q000494:pharmacology; D008565:Membrane Proteins; D009994:Osmolar Concentration; D010716:Phosphatidylinositols / Q000378:metabolism; D010758:Phosphorus / Q000493:pharmacokinetics; D010770:Phosphotransferases / Q000037:antagonists & inhibitors*; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000201:enzymology*; D013012:Sorbitol / Q000378:metabolism / Q000494:pharmacology; D017855:Transferases (Other Substituted Phosphate Groups)
D003470:Culture Media; D008565:Membrane Proteins; D010716:Phosphatidylinositols; C009217:scyllitol; D010758:Phosphorus; D007294:Inositol; D013012:Sorbitol; D000449:Aldehyde Reductase; D010770:Phosphotransferases; D017855:Transferases (Other Substituted Phosphate Groups); C496766:CDIPT protein, human; D051607:CDP-Diacylglycerol-Inositol 3-Phosphatidyltransferase; D005947:Glucose