Tissue specific metabolic abnormalities resulting form insulin deficiency and hyperglycemia are thought to contribute heavily to the development of diabetic neuropathy and other chronic complications of diabetes, although independent genetic and environmental variables are probably also operative. As the most common clinical complication of diabetes and the cause of most amputations in diabetic patients, diabetic neuropathy represents a major public health problem that has no generally accepted method of prevention of treatment. Over the last decade, animal, in vitro, and human studies emanating from this laboratory have defined biochemical likes between hyperglycemia, polyol pathway activation, myo-inositol (Ml) depletion, abnormalities in phosphoinositide (PPl) metabolism, protein kinase C (PKC), Na/K-ATPase, impaired impulse conduction, and the development of subtle structural defects in peripheral nerve from diabetic animals and patients. Recent studies with aldose reductase inhibitors (ARl's) that inhibit the rate-limiting enzyme in the polyol pathway, have tentatively implicated elements of this same metabolic pathway in the blunted regenerative response to injury and a putative decrease in """"""""neurotrophic tone"""""""" that may contribute to this """"""""dying back"""""""" distal symmetric peripheral polyneuropathy. A full understanding of these polyol- pathway-and Mi-linked metabolic factors and their role in nerve fiver damage, repair and regeneration should facilitate the rational development of new forms of intervention. Insight into this pathogenetic cascade is presently limited by (1) the increasingly recognized complexity of PPl metabolism and its role and regulation in cell function and growth; and (2) the cellular heterogeneity of the multicellular tissues involved in diabetic complications. This competing renewal application proposes detailed study of the mechanisms and implications of glucose-induced alterations in PPl metabolism in 2 newly developed human cell culture models that exhibit biochemical and functional abnormalities similar to those of diabetic nerve: non-transformed human retinal pigment epithelial (hRPE) cells, and a cloned, well-differentiated and genetically stable human neuroblastoma SH-SY5Y. Glucose-induced defects in cell function and growth such as decreased retinal rod outer segment (ROS) phagocytosis, and impaired ouabain-sensitive 86Rb-uptake and serum-and growth-factor-induced ornithine decarboxylase (ODC) induction in hRPE and Sy5Y cells respectively will be compared with abnormalities in basal and stimulated PPl metabolism under carefully defined experimental conditions simulating hyperglycemia and insulin deficiency. These studies should identify the locus or loci of glucose-sensitivity in the PPl cascade, and characterize the mechanism(s) by which glucose-induced defects in basal or stimulated PPl metabolism interfere with Na/K-ATPase regulation and growth-factor signal transduction that may be relevant to the pathogenesis of diabetic neuropathy.
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