Effects of glucose on sorbitol pathway activation, cellular redox, and metabolism of myo-inositol, phosphoinositide, and diacylglycerol in cultured human retinal pigment epithelial cells.
Sorbitol (aldose reductase) pathway flux in diabetes perturbs intracellular metabolism by two putative mechanisms: reciprocal osmoregulatory depletion of other organic osmolytes e.g., myo-inositol, and alterations in NADPH/NADP+ and/or NADH/NAD+. The "osmolyte" and "redox" hypotheses predict secondary elevations in CDP-diglyceride, the rate-limiting precursor for phosphatidylinositol synthesis, but through different mechanisms: the "osmolyte" hypothesis via depletion of intracellular myo-inositol (the cosubstrate for phosphatidylinositol-synthase) and the "redox" hypothesis through enhanced de novo synthesis from triose phosphates. The osmolyte hypothesis predicts diminished phosphoinositide-derived arachidonyl-diacylglycerol, while the redox hypothesis predicts increased total diacylglycerol and phosphatidic acid. In high aldose reductase expressing retinal pigment epithelial cells, glucose-induced, aldose reductase inhibitor-sensitive CDP-diglyceride accumulation and inhibition of 32P-incorporation into phosphatidylinositol paralleled myo-inositol depletion (but not cytoplasmic redox, that was unaffected by glucose) and depletion of arachidonyl-diacylglycerol. 3 mM pyruvate added to the culture medium left cellular redox unaltered, but stimulated Na(+)-dependent myo-inositol uptake, accumulation, and incorporation into phosphatidylinositol. These results favor myo-inositol depletion rather than altered redox as the primary cause of glucose-induced aldose reductase-related defects in phospholipid metabolism in cultured retinal pigment epithelial cells.
Thomas
T P
TP
Department of Internal Medicine, University of Michigan, Ann Arbor 48109.
Porcellati
F
F
Kato
K
K
Stevens
M J
MJ
Sherman
W R
WR
Greene
D A
DA
D000449:Aldehyde Reductase / Q000502:physiology; D002478:Cells, Cultured; D004075:Diglycerides / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007294:Inositol / Q000378:metabolism*; D010084:Oxidation-Reduction; D010716:Phosphatidylinositols / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D011773:Pyruvates / Q000494:pharmacology; D019289:Pyruvic Acid; D013012:Sorbitol / Q000378:metabolism*
D004075:Diglycerides; D010716:Phosphatidylinositols; D011773:Pyruvates; D007294:Inositol; D013012:Sorbitol; D019289:Pyruvic Acid; D000449:Aldehyde Reductase; D005947:Glucose