Effect of alpha-ketoisocaproate and leucine on the in vivo oxidation of glutamate and glutamine in the rat brain. 1997

H R Zielke, and Y Huang, and P J Baab, and R M Collins, and C L Zielke, and J T Tildon
Department of Pediatrics, University of Maryland at Baltimore 21201-1559, USA. rzielke@umabnet.ab.umd.edu

Leucine and alpha-ketoisocaproate (alpha-KIC) were perfused at increasing concentrations into rat brain hippocampus by microdialysis to mimic the conditions of maple syrup urine disease. The effects of elevated leucine or alpha-KIC on the oxidation of L-[U-14C]glutamate and L-[U-14C]glutamine in the brain were determined in the non-anesthetized rat. 14CO2 generated by the metabolic oxidation of [14C]glutamate and [14C]glutamine in brain was measured following its diffusion into the eluant during the microdialysis. Leucine and alpha-KIC exhibited differential effects on 14CO2 generation from radioactive glutamate on glutamine. Infusion of 0.5 mM alpha-KIC increased [14C]glutamate oxidation approximately 2-fold; higher concentrations of alpha-KIC did not further stimulate [14C]glutamate oxidation. The enhanced oxidation of [14C]glutamate may be attributed to the function of alpha-KIC as a nitrogen acceptor from [14C]glutamate yielding [14C]alpha-ketoglutarate, an intermediate of the tricarboxylic acid cycle. [14C]glutamine oxidation was not stimulated as much as [14C]glutamate oxidation and only increased at 10 mM alpha-KIC reflecting the extra metabolic step required for its oxidative metabolism. In contrast, leucine had no effect on the oxidation of either [14C]glutamate or [14C]glutamine. In maple syrup urine disease elevated alpha-KIC may play a significant role in altered energy metabolism in brain while leucine may contribute to clinical manifestations of this disease in other ways.

UI MeSH Term Description Entries
D007651 Keto Acids Carboxylic acids that contain a KETONE group. Oxo Acids,Oxoacids,Acids, Keto,Acids, Oxo
D007930 Leucine An essential branched-chain amino acid important for hemoglobin formation. L-Leucine,Leucine, L-Isomer,L-Isomer Leucine,Leucine, L Isomer
D008297 Male Males
D008375 Maple Syrup Urine Disease An autosomal recessive inherited disorder with multiple forms of phenotypic expression, caused by a defect in the oxidative decarboxylation of branched-chain amino acids (AMINO ACIDS, BRANCHED-CHAIN). These metabolites accumulate in body fluids and render a "maple syrup" odor. The disease is divided into classic, intermediate, intermittent, and thiamine responsive subtypes. The classic form presents in the first week of life with ketoacidosis, hypoglycemia, emesis, neonatal seizures, and hypertonia. The intermediate and intermittent forms present in childhood or later with acute episodes of ataxia and vomiting. (From Adams et al., Principles of Neurology, 6th ed, p936) Branched-Chain Ketoaciduria,Thiamine Responsive Maple Syrup Urine Disease,BCKD Deficiency,Branched-Chain alpha-Keto Acid Dehydrogenase Deficiency,Classic Maple Syrup Urine Disease,Classical Maple Syrup Urine Disease,Intermediate Maple Syrup Urine Disease,Intermittent Maple Syrup Urine Disease,Keto Acid Decarboxylase Deficiency,MSUD (Maple Syrup Urine Disease),Maple Syrup Urine Disease, Classic,Maple Syrup Urine Disease, Classical,Maple Syrup Urine Disease, Intermediate,Maple Syrup Urine Disease, Intermittent,Maple Syrup Urine Disease, Thiamine Responsive,Maple Syrup Urine Disease, Thiamine-Responsive,Branched Chain Ketoaciduria,Branched Chain alpha Keto Acid Dehydrogenase Deficiency,Branched-Chain Ketoacidurias,Ketoaciduria, Branched-Chain,Ketoacidurias, Branched-Chain
D010084 Oxidation-Reduction A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471). Redox,Oxidation Reduction
D001921 Brain The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM. Encephalon
D002208 Caproates Derivatives of caproic acid. Included under this heading are a broad variety of acid forms, salts, esters, and amides that contain a carboxy terminated six carbon aliphatic structure. Hexanoates,Caproic Acid Derivatives,Caproic Acids,Hexanoic Acid Derivatives,Hexanoic Acids,Acid Derivatives, Caproic,Acid Derivatives, Hexanoic,Acids, Caproic,Acids, Hexanoic,Derivatives, Caproic Acid,Derivatives, Hexanoic Acid
D005973 Glutamine A non-essential amino acid present abundantly throughout the body and is involved in many metabolic processes. It is synthesized from GLUTAMIC ACID and AMMONIA. It is the principal carrier of NITROGEN in the body and is an important energy source for many cells. D-Glutamine,L-Glutamine,D Glutamine,L Glutamine
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D017551 Microdialysis A technique for measuring extracellular concentrations of substances in tissues, usually in vivo, by means of a small probe equipped with a semipermeable membrane. Substances may also be introduced into the extracellular space through the membrane.

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