Alpha-ketoisocaproic acid and leucine provoke mitochondrial bioenergetic dysfunction in rat brain.
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.
Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal de Rio Grande do Sul, Rua Ramiro Barcelos 2600, Porto Alegre-RS, Brazil.
Alexandre Umpierrez
AU
Amaral
Guilhian
G
Leipnitz
Carolina Gonçalves
CG
Fernandes
Bianca
B
Seminotti
Patrícia Fernanda
PF
Schuck
Moacir
M
Wajner
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000503:physiopathology; D002491:Central Nervous System Agents / Q000633:toxicity*; D004579:Electron Transport / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D007651:Keto Acids / Q000633:toxicity*; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism; D007930:Leucine / Q000633:toxicity*; D008375:Maple Syrup Urine Disease; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D028361:Mitochondrial Diseases / Q000139:chemically induced* / Q000503:physiopathology; D008933:Mitochondrial Swelling / Q000187:drug effects; D009249:NADP / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D016548:Prosencephalon / Q000187:drug effects / Q000503:physiopathology; D051381:Rats; D017208:Rats, Wistar; D014631:Valerates / Q000633:toxicity
D002491:Central Nervous System Agents; D007651:Keto Acids; D014631:Valerates; C035864:2-hydroxyisovaleric acid; D009249:NADP; C013082:alpha-ketoisocaproic acid; D007655:Ketoglutarate Dehydrogenase Complex; D007930:Leucine