Alpha-ketoisocaproic acid and leucine provoke mitochondrial bioenergetic dysfunction in rat brain. 2010

Alexandre Umpierrez Amaral, and Guilhian Leipnitz, and Carolina Gonçalves Fernandes, and Bianca Seminotti, and Patrícia Fernanda Schuck, and Moacir Wajner
Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal de Rio Grande do Sul, Rua Ramiro Barcelos 2600, Porto Alegre-RS, Brazil.

Patients affected by maple syrup urine disease (MSUD) present severe neurological symptoms and brain abnormalities, whose pathophysiology is poorly known. In the present study we investigated the in vitro effects of leucine (Leu), alpha-ketoisocaproic acid (KIC) and alpha-hydroxyisovaleric acid (HIV), respectively, the branched-chain amino, keto and hydroxy acids that most accumulate in MSUD, on brain bioenergetic homeostasis, evaluating respiratory parameters obtained by oxygen consumption, membrane potential (Psim), NAD(P)H content, swelling and citric acid cycle enzyme activities in mitochondrial preparations from rat forebrain using glutamate plus malate, succinate or alpha-ketoglutarate as respiratory substrates. KIC increased state 4 and decreased the respiratory control ratio with all substrates, in contrast with Leu and HIV. Furthermore, KIC and Leu, but not HIV, decreased state 3 using alpha-ketoglutarate. A KIC-induced selective inhibition of alpha-ketoglutarate dehydrogenase activity was also verified, with no alteration of the other citric acid cycle activities. The ADP/O ratio and the mitochondrial NAD(P)H levels were also reduced by KIC using glutamate/malate and alpha-ketoglutarate. In addition, KIC caused a reduction in the Psim when alpha-ketoglutarate was the substrate. Finally, KIC was not able to induce mitochondrial swelling. The present data indicate that KIC acts as an uncoupler of oxidative phosphorylation and as a metabolic inhibitor possibly through its inhibitory effect on alpha-ketoglutarate dehydrogenase activity, while Leu acts as a metabolic inhibitor. It is suggested that impairment of mitochondrial homeostasis caused by the major metabolites accumulating in MSUD may be involved in the neuropathology of this disease.

UI MeSH Term Description Entries
D007651 Keto Acids Carboxylic acids that contain a KETONE group. Oxo Acids,Oxoacids,Acids, Keto,Acids, Oxo
D007655 Ketoglutarate Dehydrogenase Complex 2-Keto-4-Hydroxyglutarate Dehydrogenase,2-Oxoglutarate Dehydrogenase,2-Oxoglutarate Dehydrogenase Complex,Oxoglutarate Dehydrogenase,alpha-Ketoglutarate Dehydrogenase,alpha-Ketoglutarate Dehydrogenase Complex,2 Keto 4 Hydroxyglutarate Dehydrogenase,2 Oxoglutarate Dehydrogenase,2 Oxoglutarate Dehydrogenase Complex,Complex, 2-Oxoglutarate Dehydrogenase,Complex, Ketoglutarate Dehydrogenase,Complex, alpha-Ketoglutarate Dehydrogenase,Dehydrogenase Complex, 2-Oxoglutarate,Dehydrogenase Complex, Ketoglutarate,Dehydrogenase Complex, alpha-Ketoglutarate,Dehydrogenase, 2-Keto-4-Hydroxyglutarate,Dehydrogenase, 2-Oxoglutarate,Dehydrogenase, Oxoglutarate,Dehydrogenase, alpha-Ketoglutarate,alpha Ketoglutarate Dehydrogenase,alpha Ketoglutarate Dehydrogenase Complex
D007930 Leucine An essential branched-chain amino acid important for hemoglobin formation. L-Leucine,Leucine, L-Isomer,L-Isomer Leucine,Leucine, L Isomer
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
D008933 Mitochondrial Swelling An increase in MITOCHONDRIAL VOLUME due to an influx of fluid; it occurs in hypotonic solutions due to osmotic pressure and in isotonic solutions as a result of altered permeability of the membranes of respiring mitochondria. Giant Mitochondria,Megamitochondria,Mitochondrial Hypertrophy,Giant Mitochondrias,Hypertrophy, Mitochondrial,Megamitochondrias,Mitochondria, Giant,Mitochondrial Hypertrophies,Swelling, Mitochondrial
D009249 NADP Nicotinamide adenine dinucleotide phosphate. A coenzyme composed of ribosylnicotinamide 5'-phosphate (NMN) coupled by pyrophosphate linkage to the 5'-phosphate adenosine 2',5'-bisphosphate. It serves as an electron carrier in a number of reactions, being alternately oxidized (NADP+) and reduced (NADPH). (Dorland, 27th ed) Coenzyme II,Nicotinamide-Adenine Dinucleotide Phosphate,Triphosphopyridine Nucleotide,NADPH,Dinucleotide Phosphate, Nicotinamide-Adenine,Nicotinamide Adenine Dinucleotide Phosphate,Nucleotide, Triphosphopyridine,Phosphate, Nicotinamide-Adenine Dinucleotide
D010101 Oxygen Consumption The rate at which oxygen is used by a tissue; microliters of oxygen STPD used per milligram of tissue per hour; the rate at which oxygen enters the blood from alveolar gas, equal in the steady state to the consumption of oxygen by tissue metabolism throughout the body. (Stedman, 25th ed, p346) Consumption, Oxygen,Consumptions, Oxygen,Oxygen Consumptions
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
D002491 Central Nervous System Agents A class of drugs producing both physiological and psychological effects through a variety of mechanisms. They can be divided into "specific" agents, e.g., affecting an identifiable molecular mechanism unique to target cells bearing receptors for that agent, and "nonspecific" agents, those producing effects on different target cells and acting by diverse molecular mechanisms. Those with nonspecific mechanisms are generally further classed according to whether they produce behavioral depression or stimulation. Those with specific mechanisms are classed by locus of action or specific therapeutic use. (From Gilman AG, et al., Goodman and Gilman's The Pharmacological Basis of Therapeutics, 8th ed, p252) Central Nervous System Drugs
D004579 Electron Transport The process by which ELECTRONS are transported from a reduced substrate to molecular OXYGEN. (From Bennington, Saunders Dictionary and Encyclopedia of Laboratory Medicine and Technology, 1984, p270) Respiratory Chain,Chain, Respiratory,Chains, Respiratory,Respiratory Chains,Transport, Electron

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