Exposure to leucine induces oxidative stress in the brain of zebrafish.

Maple Syrup Urine Disease (MSUD) is an autosomal recessive inherited disorder caused by a deficiency in the activity of the branched-chain alpha-ketoacid dehydrogenase complex leading to the accumulation of branched-chain amino acids (BCAA) leucine, isoleucine, and valine and their respective branched-chain α-ketoacids and corresponding hydroxy acids. Considering that Danio rerio, known as zebrafish, has been widely used as an experimental model in several research areas because it has favorable characteristics that complement other experimental models, this study aimed to evaluate oxidative stress parameters in zebrafish exposed to high levels of leucine (2 mM and 5 mM), in a model similar of MSUD. Twenty-four hours after exposure, the animals were euthanized, and the brain content dissected for analysis of oxidative stress parameters: thiobarbituric acid reactive substances (TBARS), 2',7'-dichlorofluorescein oxidation assay (DCF); content of sulfhydryl, and superoxide dismutase (SOD) and catalase (CAT) activities. Animals exposed to 2 mM and 5 mM leucine showed an increase in the measurement of TBARS and decreased sulfhydryl content. There were no significant changes in DCF oxidation. In addition, animals exposed to 2 mM and 5 mM leucine were found to have decreased SOD activity and increased CAT activity. Based on these results, exposure of zebrafish to high doses of leucine can act as a promising animal model for MSUD, providing a better understanding of the toxicity profile of leucine exposure and its use in future investigations and strategies related to the pathophysiology of MSUD.

Acute exposure to leucine modifies behavioral parameters and cholinergic activity in zebrafish.

Maple Syrup Urine Disease (MSUD) is an autosomal recessive inherited disorder, caused by a deficiency on branched chain α-ketoacid dehydrogenase complex activity, resulting in accumulation of branched-chain amino acids (BCAA) (e.g. leucine). The treatment of MSDU patients increases survival time and quality of life. Thus, nowadays there are a crescent number of adolescents and adults with MSUD. Relevant studies have been reported behavioral alterations in these patients, i.e. high risk of chronic neuropsychiatric problems, such as attention deficit disorder, depression and anxiety. Moreover, MSUD is associated to neurotransmitters deficiency. Herein, we aimed to investigate whether the toxicity of leucine is associated to anxiety-like behavioral, using zebrafish acutely exposed to leucine as experimental model of MSUD. In addition, we evaluated the effects of high levels of leucine in the acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) activities, components of cholinergic neurotransmission system. Young zebrafish were exposed to 2 mM and 5 mM concentration of leucine for 24 h. After that, the animals were submitted to the Novel Tank test, having the brain collected to enzymatic determination. The exposure to both concentrations of leucine caused behavioral and brain cholinergic activity alterations in young zebrafish, indicating an anxiety-like behavior and cholinergic dysfunction. Therefore, this animal could be considered a promising organism to study the BCAA neurotoxic effects, which could help to a better comprehension of the behavioral and neurochemical alterations present in patients with MSUD.