title: Evidence that 3-hydroxyisobutyric acid inhibits key enzymes of energy metabolism in cerebral cortex of young rats.
abstract: 3-Hydroxyisobutyric aciduria is an inherited metabolic disease caused by 3-hydroxyisobutyryl-CoA dehydrogenase deficiency. Tissue accumulation and high urinary excretion of 3-hydroxyisobutyric acid is the biochemical hallmark of this disorder. Clinical phenotype is heterogeneous and generally includes dysmorphic features, delayed motor development, profound mental impairment, and acute encephalopathy. Lactic acidemia is also found in the affected patients, indicating that mitochondrial dysfunction may be involved in the pathophysiology of this disorder. Therefore, the aim of the present work was to investigate the in vitro effect of 3-hydroxyisobutyric acid (0.1, 0.5 and 1mM) on essential enzymes of energy metabolism, namely the activities of the respiratory chain complexes I-V, total, cytosolic and mitochondrial creatine kinase and Na(+), K(+)-ATPase in cerebral cortex homogenates of 30-day-old rats. We also measured the rate of oxygen consumption in brain mitochondrial preparations in the presence of 3-hydroxyisobutyric acid. 3-Hydroxyisobutyric acid significantly reduced complex I-III (20%), without affecting the other activities of the electron transport chain. Furthermore, 3-hydroxyisobutyric acid did not change state III, state IV and the respiratory control ratio in the presence of glutamate/malate or succinate, suggesting that its effect on cellular respiration was weak. On the other hand, the activities of total and mitochondrial creatine kinase, but not cytosolic creatine kinase, were inhibited (30%) by 3-hydroxyisobutyric acid. We also observed that 3-hydroxyisobutyric acid-induced inhibition of mitochondrial creatine kinase activity was fully prevented by pre-incubation of the homogenates with reduced glutathione, alpha-tocopherol or the combination of superoxide dismutase plus catalase, suggesting that this inhibition was mediated by oxidation of essential thiol groups of the enzyme probably by superoxide, hydrogen peroxide and/or peroxyl radicals. It was also demonstrated that Na(+), K(+)-ATPase activity from synaptic plasma membranes was markedly suppressed (37%) by 3-hydroxyisobutyric acid and that this effect was prevented by alpha-tocopherol co-incubation implying that peroxyl radicals were probably involved in this action. Considering the importance of the affected enzyme activities for brain metabolism homeostasis and neurotransmision, it is suggested that increased tissue levels of 3-hydroxyisobutyric acid may contribute to the neurodegeneration of patients affected by 3-hydroxyisobutyric aciduria and possibly explain previous reports describing elevated production and excretion of lactate.
authors.affiliation: Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, UFRGS, Porto Alegre, RS, Brazil.
authors.forename: Carolina Maso
authors.initials: CM
authors.lastname: Viegas
authors.forename: Gustavo
authors.initials: G
authors.lastname: da Costa Ferreira
authors.forename: Patrícia Fernanda
authors.initials: PF
authors.lastname: Schuck
authors.forename: Anelise Miotti
authors.initials: AM
authors.lastname: Tonin
authors.forename: Angela
authors.initials: A
authors.lastname: Zanatta
authors.forename: Angela Terezinha
authors.initials: AT
authors.lastname: de Souza Wyse
authors.forename: Carlos Severo
authors.initials: CS
authors.lastname: Dutra-Filho
authors.forename: Clóvis Milton Duval
authors.initials: CM
authors.lastname: Wannmacher
authors.forename: Moacir
authors.initials: M
authors.lastname: Wajner
mesh_terms: D020155:3-Hydroxybutyric Acid / Q000378:metabolism* / Q000494:pharmacology; D000375:Aging / Q000378:metabolism; D000818:Animals; D000975:Antioxidants / Q000378:metabolism / Q000494:pharmacology; D001923:Brain Chemistry / Q000187:drug effects; D020739:Brain Diseases, Metabolic, Inborn / Q000201:enzymology* / Q000235:genetics; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D019069:Cell Respiration / Q000187:drug effects / Q000502:physiology; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology*; D003402:Creatine Kinase / Q000187:drug effects / Q000378:metabolism; D042967:Electron Transport Complex I / Q000187:drug effects / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology*; D008928:Mitochondria / Q000201:enzymology / Q000648:ultrastructure; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000378:metabolism; D013347:Subcellular Fractions; D013570:Synaptic Membranes / Q000187:drug effects / Q000201:enzymology
chemical_list: D000975:Antioxidants; D003402:Creatine Kinase; D042967:Electron Transport Complex I; D000254:Sodium-Potassium-Exchanging ATPase; D020155:3-Hydroxybutyric Acid