Hypoxic Injury to Developing Glial Cells: Protective Effect of High Glucose

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Abstract
Hypoxic injury to differentiating glial cells is a critical event in the development of periventricular leukomalacia, the major hypoxic-ischemic lesion of the premature infant. This study has addressed the effects of hypoxia on differentiating glial cells, primarily astrocytes. Primary cultures of dissociated newborn rat brain, which are composed predominantly of differentiating astroglia, were used. Efflux of lactate dehydrogenase, an enzyme enriched in astroglia, was used to quantitate cellular injury. Three major findings are reported. First, differentiating astrocytes were resistant to hypoxic injury for many hours, although by 24 h of hypoxia severe cellular injury (lactate dehydrogenase efflux of 86% of total and morphologic changes) was obvious. Second, increase of glucose in the culture medium from the approximately physiological concentration of 5.6 to 15 mM had a marked protective effect versus hypoxia, i.e. lactate dehydrogenase efflux was totally prevented during 24 h of hypoxia in 15 mM glucose. Third, the protective effect of high glucose appeared to be related to increased utilization by glycolysis, because there was a direct correlation between the resistance to hypoxic cellular injury and the amount of lactate generated and of glucose consumed by the cells. Thus, the cells with the lowest lactate dehydrogenase efflux (and highest glucose supplementations) had medium lactate concentrations as high as 32-36 mM. These concentrations of lactate are approximately double the reported threshold concentration of lactate considered to produce cellular necrosis in in vivo models of hypoxic injury, primarily in mature animals. The data raise the possibility that hypoxic injury to differentiating glia can be prevented or ameliorated by increase in glucose availability.