α-Ketoisocaproic acid and leucine provoke mitochondrial bioenergetic dysfunction in rat brain

Abstract

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.

The Intra-Hippocampal Leucine Administration Impairs Memory Consolidation and LTP Generation in Rats

“…creatine kinase or the malateaspartate shuttle-related enzymes, and by accelerating the Krebs cycle turnover, which could in turn induce free radical generation thought a-ketoglutarate dehydrogenase, as previously reported (Starkov et al 2004;Tretter and Adam-Vizi 2004;Amaral et al 2010). Thus, the LEUelicited oxidative stress could induce further energy adaptations by increasing the concentration of the respiratory chain mitochondrial enzymes (increased complex IV activity) and augmenting the mitochondrial oxygen consumption with concomitant free radical generation.…”

“…In this context, a large body of in vitro and in vivo studies has pointed out LEU accumulation as the main toxic condition in MSUD. In this context, it has been demonstrated that high LEU concentrations alter brain energy metabolism (Howell and Lee 1963;Halestrap et al 1974;Pilla et al 2003a, b;Sgaravatti et al 2003;Ribeiro et al, 2008;Zinnati et al 2009;Amaral et al 2010), glutamatergic neurotransmission system (Tashian 1961;Tavares et al 2000;Zinnanti et al 2009), brain uptake of essential amino acids (Araujo et al 2001), and induces oxidative stress and apoptosis (Jouvet et al, 2000;Fontella et al, 2002;Bridi et al, 2003;Bridi et al 2006). In addition, behavioral deficits induced by LEU administration or its cognate a-ketoacid and a-hydroxyisocaproate, have also been reported (Mello et al 1999;Vasques et al 2005;Zinnanti et al 2009).…”

Branched Chain Amino Acids and Maple Syrup Urine Disease

“…This suggests increased intracellular and decreased extracellular fl uid resulting from sodium pump failure. There is evidence that KIC acts as an uncoupler of oxidative phosphorylation and as a metabolic inhibitor possibly through its inhibitory effect on α-ketoglutarate dehydrogenase activity, while leucine acts as a metabolic inhibitor [ 35 ]. Branched chain amino acids and corresponding keto acids signifi cantly inhibited Na(+), K(+)-ATPase activity in synaptic plasma membranes in rat cerebral cortex [ 36 ].…”

Phenylketonuria Pathophysiology: on the Role of Metabolic Alterations

“…Brain energy metabolism alterations play an important role in the pathophysiology of many inborn errors of metabolism [80][81][82][83]. In this context, energy metabolism impairment was reported in HPA animal models and patients.…”