747 Reduction of Glutamate Uptake into Cerebral Cortex of Developing Rats by the Branched-Chain Alpha-Keto Acids Accumulating in Maple Syrup Urine Disease Cláudia Funchal, 1 Aline Meyer Rosa, 1 Moacir Wajner, 1,2 Susana Wofchuk, 1,3 and Regina Pessoa Pureur 1,4 (Accepted October 2, 2003) In the current study we investigated the effect of the branched-chain alpha-keto acids (BCKA) -ketoisocaproic (KIC), -keto--methylvaleric (KMV), and -ketoisovaleric (KIV) acids, which accumulate in maple syrup urine disease (MSUD), on the in vitro uptake of [ 3 H]glutamate by cere- bral cortical slices from rats aged 9, 21, and 60 days of life. We initially observed that glutamate uptake into cerebral cortex of 9- and 21-day-old rats was significantly higher, as compared to that of 60-day-old rats. Furthermore, KIC inhibited this uptake by tissue slices at all ages studied, whereas KMV and KIV produced the same effect only in cortical slices of 21- and 60-day-old rats. Kinetic assays showed that KIC significantly inhibited glutamate uptake in the presence of high glutamate concentrations (50 M and greater). We also verified that the reduction of glutamate uptake was not due to cellular death, as evidenced by tetrazolium salt and lactate dehydrogenase viability tests of cortical slices in the presence of the BCKA. It is therefore presumed that the reduced glutamate uptake caused by the BCKA accumulating in MSUD may lead to higher extracellular glutamate levels and potentially to excitotoxicity, which may contribute to the neurological dysfunction of the affected individuals. KEY WORDS: Maple syrup urine disease; glutamate uptake; cerebral cortex; -ketoisocaproic acid; -keto--methylvaleric acid; -ketoisovaleric acid. INTRODUCTION Maple syrup urine disease (MSUD) is an autosomal recessive disorder of the metabolism caused by severe deficiency in the activity of the branched-chain -keto acid dehydrogenase complex (1,2). As a consequence of the defect, the branched-chain keto acids (BCKA) -ketoisocaproic acid (KIC), -keto--methylvaleric acid (KMV), and -ketoisovaleric acid (KIV) and their corre- sponding amino acids leucine, isoleucine, and valine accumulate in tissues of the affected patients. The charac- teristic features of MSUD include ketoacidosis, poor feed- ing, vomiting, apnea, seizures, coma, psychomotor delay, mental retardation, cerebral edema, and atrophy (3). Although neurological deterioration and convulsions are common symptoms, the mechanisms underlying the brain damage of this disorder remain unclear and have been poorly studied. However, leucine and its keto acid KIC, the metabolites that most accumulate in MSUD, 0364-3190/04/0400–0747/0 © 2004 Plenum Publishing Corporation Neurochemical Research, Vol. 29, No. 4, April 2004 (© 2004), pp. 747–753 1 Universidade Federal do Rio Grande do Sul, Instituto de Ciências Básicas da Saúde, Departamento de Bioquímica, Porto Alegre, RS, Brasil. 2 Serviço de Genética Médica, Hospital de Clínicas de Porto Alegre, Porto Alegre, RS, Brasil. 3 Instituto de Geriatria e Faculdade de Farmácia, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, RS, Brasil. 4 Address reprint requests to: Dr. Regina Pessoa-Pureur, Universidade Federal do Rio Grande do Sul, Instituto de Ciências Básicas da Saúde, Departamento de Bioquímica, Rua Ramiro Barcelos 2600 anexo, 90035-003 Porto Alegre RS Brasil. Tel: 5551-3316-5565; Fax: 5551-3316-5535.