Journal of Neurochemistry, 2001, 77, 408±415 N-Acetylaspartate, a marker of both cellular dysfunction and neuronal loss: its relevance to studies of acute brain injury Ce Âline Demougeot,* , ² Philippe Garnier,* Claude Mossiat,* Nathalie Bertrand,* Maurice Giroud,² Alain Beley* and Christine Marie* *Unite  de Biochimie-Pharmacologie-Toxicologie, Laboratoire de Pharmacodynamie, Faculte  de Pharmacie, Dijon, France ²Service de Neurologie, Centre Hospitalier Universitaire, Dijon, France Abstract To evaluate the contribution of cellular dysfunction and neuronal loss to brain N-acetylaspartate (NAA) depletion, NAA was measured in brain tissue by HPLC and UV detection in rats subjected to cerebral injury, associated or not with cell death. When lesion was induced by intracarotid injection of microspheres, the fall in NAA was related to the degree of embolization and to the severity of brain oedema. When striatal lesion was induced by local injection of malonate, the larger the lesion volume, the higher the NAA depletion. However, reduction of brain oedema and striatal lesion by treatment with the lipophilic iron chelator dipyridyl (20 mg/kg, 1 h before and every 8 h after embolization) and the inducible nitric oxide synthase inhibitor aminoguanidine (100 mg/kg given 1 h before malonate and then every 9 h), respectively, failed to ameliorate the fall in NAA. Moreover, after systemic administration of 3-nitropropionic acid, a marked reversible fall in NAA striatal content was observed despite the lack of tissue necrosis. Overall results show that cellular dysfunction can cause higher reductions in NAA level than neuronal loss, thus making of NAA quanti®cation a potential tool for visualizing the penumbra area in stroke patients. Keywords: aminoguanidine, brain ischaemia, dipyridyl, mito- chondrial poisoning, N-acetylaspartate. J. Neurochem. (2001) 77, 408±415. N-Acetylaspartate (NAA) is present at a very high con- centration in the CNS and is believed to be almost exclusively located in neurons in the adult brain (Birken and Oldendorf 1989; Moffett et al. 1991). Because this compound can be non-invasively measured in human by proton magnetic resonance spectroscopy ( 1 H-MRS), 1 H-MRS measurements of NAA have become of great interest to evaluate neuronal loss in patients with cerebral infarction. Indeed, in a number of reports, the fall in NAA signal was found to have a prognostic signi®cance regarding the clinical outcome of stroke (Ford et al. 1992; Graham et al. 1995; Federico et al. 1998; Pereira et al. 1999; Lemesle et al. 2000). However, reversible decreases in NAA levels have also been reported in patients with various kinds of brain injury (Davie et al. 1994; De Stefano et al. 1995; Hugg et al. 1996; Kalra et al. 1998; Pavlakis et al. 1998), thus questioning NAA as a speci®c marker of neuronal loss and the signi®cance of NAA measurements in stroke. Therefore, in order to better understand the changes in NAA obtained in acute human brain injury, NAA was measured by HPLC in rats submitted to ischaemic stroke and to mitochondrial poisoning. Ischaemic stroke was obtained by means of intracarotid injection of calibrated microspheres (Bralet et al. 1979), which allows the modulation of the severity of the insult by varying the amount of injected microspheres. Mitochondrial poisoning was performed either by local striatal microinjec- tion of different concentrations of malonate or by systemic administration of 3-nitropropionic acid (3NP). Malonate is a reversible inhibitor of the succinate dehydrogenase that does not pass through the blood±brain barrier, whereas 3NP, which irreversibly inhibits succinate dehydrogenase, is known to cause preferential striatal toxicity (Green et al. 1993; Wullner et al. 1994) after entering the brain. In order to 408 q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 77, 408±415 Received June 30, 2000; revised manuscript received November 17, 2000; accepted December 11, 2000. Address correspondence and reprints requests to Professor Alain Beley, Unite  de Biochimie-Pharmacologie-Toxicologie, Laboratoire de Pharmacodynamie, Faculte  de Pharmacie, BP 87900, 21079 Dijon CEDEX, France. E-mail: albeley@u-bourgogne.fr Abbreviations used: NAA, N-acetylaspartate; 1 H-MRS, proton magnetic resonance spectroscopy; 3NP, 3-nitropropionic acid; PVP, polyvinylpyrrolidone; SDH, succinate dehydrogenase.