ABSTRACT
Preliminary evidence suggests adenosine, a neuromodulator, has neuroprotective properties during cerebral ischemia. It is unclear, however, if adenosine has glioprotective effects. We studied the effect of adenosine on cellular injury in astroglial cultures subjected to combined glucose-oxygen deprivation. Adenosine (100-1,000 microM)dramatically reduced astroglial injury, whereas the adenosine agonists 2-chloroadenosine (10 nM-100 microM), N6-cyclopentyladenosine (1 nM-10 microM), 5'-N-ethylcarboxamidoadenosine (10 nM-100 microM), and N6-2-(4-aminophenyl)ethyladenosine (10 nM-100 microM) had no effect. Furthermore, the adenosine antagonists 8-cyclopentyl-1,3-dipropylxanthine (1 nM-1 microM), xanthine amine congener (10 nM-10 microM), and 8-(p-sulfophenyl)-theophylline (10-300 microM) failed to reverse the protective effect of 200 microM adenosine. Next, adenosine degradation products were studied. Inosine proved to be glioprotective at concentrations nearly identical to those of adenosine, but hypoxanthine and ribose had no effect. The protective effect of 200 microM inosine was not reversed by 8-(p-sulfophenyl)theophylline (10-300 microM). Adenosine deaminase (1 unit/ml) had no effect on protection produced by adenosine, whereas erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride (10 microM) reversed the protective effect of adenosine. Dipyridamole (4 microM) inhibited the protective effect of both adenosine and inosine. We conclude that adenosine dramatically decreases astroglial injury during combined glucose-oxygen deprivation and that this protective effect appears to be mediated by inosine.
Subject(s)
Adenosine/analogs & derivatives , Adenosine/pharmacology , Astrocytes/drug effects , Cerebral Cortex/cytology , Glucose/metabolism , Inosine/pharmacology , 2-Chloroadenosine/pharmacology , Adenosine-5'-(N-ethylcarboxamide) , Animals , Animals, Newborn , Astrocytes/cytology , Astrocytes/metabolism , Cell Hypoxia , Cell Survival/drug effects , Cells, Cultured , Cerebral Cortex/metabolism , Kinetics , L-Lactate Dehydrogenase/analysis , Purines/metabolism , Rats , Rats, Sprague-DawleyABSTRACT
Phosphatidylinositol bisphosphate hydrolysis, leading to the production of myo-inositol trisphosphate and diacylglycerol, may play a significant role in the pathogenesis of hypoxic-ischemic brain injury. We used tritiated myo-inositol phosphate (3H-IP) accumulation as a means to quantitate phosphoinositide hydrolysis in pre-labeled astroglial cultures subjected to combined glucose-oxygen deprivation. Astroglial cultures exposed to combined glucose-oxygen deprivation had significantly greater 3H-IP accumulation compared with cultures exposed to control conditions. To delineate the role of the metabotropic glutamate receptor in astroglial phosphoinositide hydrolysis during combined glucose-oxygen deprivation, we studied the effects of two metabotropic glutamate receptor antagonists, 2-amino-3-phosphonopropionic acid and (+)-methyl-4-carboxyphenylglycine. 2-Amino-3-phosphonopropionic acid attenuated the accumulation of 3H-IP during combined glucose-oxygen deprivation but acted as an agonist under control conditions. (+)-Methyl-4-carboxyphenylglycine had no effect on 3H-IP accumulation during combined glucose-oxygen deprivation or under control conditions. These results suggest that activation of astroglial phosphoinositide hydrolysis during combined glucose-oxygen deprivation may be mediated, at least in part, by the metabotropic glutamate receptor.
Subject(s)
Astrocytes/metabolism , Glucose/administration & dosage , Oxygen/administration & dosage , Phosphatidylinositols/metabolism , Receptors, Metabotropic Glutamate/physiology , Alanine/analogs & derivatives , Alanine/pharmacology , Animals , Animals, Newborn , Benzoates/pharmacology , Cells, Cultured , Glutamic Acid/pharmacology , Glycine/analogs & derivatives , Glycine/pharmacology , Hydrolysis , Inositol Phosphates/metabolism , L-Lactate Dehydrogenase/metabolism , Lithium Chloride/pharmacology , Rats , Rats, Sprague-Dawley , Receptors, Metabotropic Glutamate/antagonists & inhibitors , TritiumABSTRACT
Membrane phospholipid degradation has been proposed to play a key role in hypoxic-ischemic brain injury. We tested the hypotheses that both nordihydroguaiaretic acid, a phospholipase A2 and lipoxygenase inhibitor, and RHC 80267, a diacylglycerol lipase inhibitor, would decrease the release of [3H]arachidonic acid metabolites from prelabeled cultures of astroglia subjected to combined glucose-oxygen deprivation and that these inhibitors would also decrease astroglial injury during combined glucose-oxygen deprivation. Both nordihydroguaiaretic acid and RHC 80267 significantly inhibited the release of [3H]arachidonic acid metabolites during combined glucose-oxygen deprivation. This suggests that two separate enzymic pathways, the phospholipase A2 pathway and the phospholipase C/diacylglycerol lipase pathway, contribute to the release of astroglial [3H]arachidonic acid metabolites during combined glucose-oxygen deprivation. However, both of these lipase inhibitors increased astroglial cell death during combined glucose-oxygen deprivation, probably due to inhibition of arachidonic acid release. We speculate that arachidonic acid release may be a mechanism of astroglial self-preservation during combined glucose-oxygen deprivation.
Subject(s)
Antioxidants/pharmacology , Astrocytes/drug effects , Cell Hypoxia/drug effects , Cyclohexanones/pharmacology , Glucose/deficiency , Lipoprotein Lipase/antagonists & inhibitors , Masoprocol/pharmacology , Protease Inhibitors/pharmacology , Animals , Animals, Newborn , Arachidonic Acids/metabolism , Astrocytes/enzymology , Astrocytes/metabolism , Cell Death/drug effects , Cells, Cultured , Immunohistochemistry , L-Lactate Dehydrogenase/metabolism , Rats , Rats, Sprague-DawleyABSTRACT
Hypothermia provides significant protection when initiated during or after cerebral ischemia in vivo. However, the mechanisms producing this protective effect are not known. Astroglial cultures were prelabeled with [3H]arachidonic acid. Hypothermia reduced both cellular injury and release of [3H]-labeled arachidonic acid metabolites during combined glucose-oxygen deprivation. Inhibition of phospholipid degradation may be one of the mechanisms that contributes to the protective effect of hypothermia.
