The metabolic effect of α-ketoisocaproic acid: in vivo and in vitro studies

In Vivo Intracerebral Administration of α-Ketoisocaproic Acid to Neonate Rats Disrupts Brain Redox Homeostasis and Promotes Neuronal Death, Glial Reactivity, and Myelination Injury

Maple syrup urine disease (MSUD) is caused by severe deficiency of branched-chain α-keto acid dehydrogenase complex activity, resulting in tissue accumulation of branched-chain α-keto acids and amino acids, particularly α-ketoisocaproic acid (KIC) and leucine. Affected patients regularly manifest with acute episodes of encephalopathy including seizures, coma, and potentially fatal brain edema during the newborn period. The present work investigated the ex vivo effects of a single intracerebroventricular injection of KIC to neonate rats on redox homeostasis and neurochemical markers of neuronal viability (neuronal nuclear protein (NeuN)), astrogliosis (glial fibrillary acidic protein (GFAP)), and myelination (myelin basic protein (MBP) and 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase)) in the cerebral cortex and striatum. KIC significantly disturbed redox homeostasis in these brain structures 6 h after injection, as observed by increased 2',7'-dichlorofluorescein oxidation (reactive oxygen species generation), malondialdehyde levels (lipid oxidative damage), and carbonyl formation (protein oxidative damage), besides impairing the antioxidant defenses (diminished levels of reduced glutathione and altered glutathione peroxidase, glutathione reductase, and superoxide dismutase activities) in both cerebral structures. Noteworthy, the antioxidants N-acetylcysteine and melatonin attenuated or normalized most of the KIC-induced effects on redox homeostasis. Furthermore, a reduction of NeuN, MBP, and CNPase, and an increase of GFAP levels were observed at postnatal day 15, suggesting neuronal loss, myelination injury, and astrocyte reactivity, respectively. Our data indicate that disruption of redox homeostasis, associated with neural damage caused by acute intracerebral accumulation of KIC in the neonatal period may contribute to the neuropathology characteristic of MSUD patients.

Definition of the Neurotoxicity-Associated Metabolic Signature Triggered by Berberine and Other Respiratory Chain Inhibitors

To characterize the hits from a phenotypic neurotoxicity screen, we obtained transcriptomics data for valinomycin, diethylstilbestrol, colchicine, rotenone, 1-methyl-4-phenylpyridinium (MPP), carbaryl and berberine (Ber). For all compounds, the concentration triggering neurite degeneration correlated with the onset of gene expression changes. The mechanistically diverse toxicants caused similar patterns of gene regulation: the responses were dominated by cell de-differentiation and a triggering of canonical stress response pathways driven by ATF4 and NRF2. To obtain more detailed and specific information on the modes-of-action, the effects on energy metabolism (respiration and glycolysis) were measured. Ber, rotenone and MPP inhibited the mitochondrial respiratory chain and they shared complex I as the target. This group of toxicants was further evaluated by metabolomics under experimental conditions that did not deplete ATP. Ber (204 changed metabolites) showed similar effects as MPP and rotenone. The overall metabolic situation was characterized by oxidative stress, an over-abundance of NADH (>1000% increase) and a re-routing of metabolism in order to dispose of the nitrogen resulting from increased amino acid turnover. This unique overall pattern led to the accumulation of metabolites known as biomarkers of neurodegeneration (saccharopine, aminoadipate and branched-chain ketoacids). These findings suggest that neurotoxicity of mitochondrial inhibitors may result from an ensemble of metabolic changes rather than from a simple ATP depletion. The combi-omics approach used here provided richer and more specific MoA data than the more common transcriptomics analysis alone. As Ber, a human drug and food supplement, mimicked closely the mode-of-action of known neurotoxicants, its potential hazard requires further investigation.

Comprehensive Metabolic Fingerprints Characterize Neuromyelitis Optica Spectrum Disorder by Nanoparticle-Enhanced Laser Desorption/Ionization Mass Spectrometry

Timely screening of neuromyelitis optica spectrum disorder (NMOSD) and differential diagnosis from myelin oligodendrocyte glycoprotein associated disorder (MOGAD) are the keys to improving the quality of life of patients. Metabolic disturbance occurs with the development of NMOSD. Still, advanced tools are required to probe the metabolic phenotype of NMOSD. Here, we developed a fast nanoparticle-enhanced laser desorption/ionization mass spectrometry assay for multiplexing metabolic fingerprints (MFs) from trace plasma and cerebrospinal fluid (CSF) samples in 30 s. Machine learning of the plasma MFs achieved the timely screening of NMOSD from healthy donors with an area under receiver operator characteristic curve (AUROC) of 0.998, and it comprehensively revealed the dysregulated neurotransmitter and energy metabolisms. Combining comprehensive MFs from both plasma and CSF, we constructed an integrated panel for differential diagnosis of NMOSD versus MOGAD with an AUROC of 0.923. This approach demonstrated performance superior to that of human experts in classifying two diseases, especially in antibody assay-limited regions. Together, this approach provides an advanced nanomaterial-based tool for identifying vulnerable populations below the antibody threshold of aquaporin-4 positivity.

Nontargeted metabolomics analysis of follicular fluid in patients with endometriosis provides a new direction for the study of oocyte quality

Endometriosis is a common, estrogen-dependent chronic gynecological disease that endangers the reproductive system and systemic metabolism of patients. We aimed to investigate the differences in metabolic profiles in the follicular fluid between infertile patients with endometriosis and controls. A total of 25 infertile patients with endometriosis and 25 infertile controls who were similar in age, BMI, fertilization method and ovulation induction treatment were recruited in this study. Metabolomics analysis of follicular fluid was performed by two methods of high-performance liquid chromatography tandem mass spectrometry. There were 36 upregulated and 17 downregulated metabolites in the follicular fluid of patients in the endometriosis group. KEGG pathway analysis revealed that these metabolites were enriched in phenylalanine, tyrosine and tryptophan biosynthesis, aminoacyl-tRNA biosynthesis, phenylalanine metabolism and pyrimidine metabolism pathways. A biomarker panel consisting of 20 metabolites was constructed by random forest, with an accuracy of 0.946 and an AUC of 0.988. This study characterizes differences in follicular fluid metabolites and associated pathway profiles in infertile patients with endometriosis. These findings can provide a better comprehensive understanding of the disease and a new direction for the study of oocyte quality, as well as potential metabolic markers for the prognosis of endometriosis.

Acute effects of intracerebroventricular administration of α-ketoisocaproic acid in young rats on inflammatory parameters

Maple Syrup Urine Disease (MSUD) is an autosomal recessive inborn error of metabolism (IEM), responsible for the accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine, and valine, in addition to their α-keto acids α-ketoisocaproic acid (KIC), α-keto-β-methylvaleric acid (KMV), and α-ketoisovaleric acid (KIV) in the plasma and urine of patients. This process occurs due to a partial or total blockage of the dehydrogenase enzyme activity of branched-chain α-keto acids. Oxidative stress and inflammation are conditions commonly observed on IEM, and the inflammatory response may play an essential role in the pathophysiology of MSUD. We aimed to investigate the acute effect of intracerebroventricular (ICV) administration of KIC on inflammatory parameters in young Wistar rats. For this, sixteen 30-day-old male Wistar rats receive ICV microinjection with 8 µmol KIC. Sixty minutes later, the animals were euthanized, and the cerebral cortex, hippocampus, and striatum structures were collected to assess the levels of pro-inflammatory cytokines (INF-γ; TNF-α, IL-1β). The acute ICV administration of KIC increased INF-γ levels in the cerebral cortex and reduced the levels of INF-γ and TNF-α in the hippocampus. There was no difference in IL-1β levels. KIC was related to changes in the levels of pro-inflammatory cytokines in the brain of rats. However, the inflammatory mechanisms involved in MSUD are poorly understood. Thus, studies that aim to unravel the neuroinflammation in this pathology are essential to understand the pathophysiology of this IEM.

Branched-chain amino acids (BCAA) administration increases autophagy and the autophagic pathway in brain tissue of rats submitted to a Maple Syrup Urine Disease (MSUD) protocol

Maple Syrup Urine Disease (MSUD) is an inborn error of metabolism (EIM) biochemically characterized by the tissue accumulation of branched-chain amino acids (BCAA) and their branched-chain alpha-keto acids. The mechanisms by which BCAA and their branched-chain alpha-keto acids lead to the neurological damage observed in MSUD are poorly understood. Mounting evidence has demonstrated that BCAA induce the overproduction of reactive oxygen species, which may modulate several important signaling pathways necessary for cellular homeostasis maintenance, such as autophagy. Taking this into account, we evaluated the effects of BCAA on the autophagic pathway in brain structures of rats submitted to the administration of these amino acids (animal model of MSUD). Our findings showed that BCAA significantly increased the levels of Beclin-1, ATG7, and ATG5 in the cerebral cortex of rats. In addition, BCAA augmented ATG12 levels in the striatum and ATG5 and LC3 I-II in the hippocampus. Therefore, our work demonstrates that the administration of BCAA increases autophagy and autophagic cell death, possibly mediated by the elevated levels of reactive species generated by BCAA.

Real-world management of maple syrup urine disease (MSUD) metabolic decompensations with branched chain amino acid-free formulas in France and Germany: A retrospective observational study

Maple syrup urine disease (MSUD) is a rare inborn metabolic disorder, managed with a strict protein-restricted diet. At any time or age patients may still experience metabolic decompensations, requiring administration of branched chain amino acid (BCAA)-free formula to reduce leucine levels. This retrospective observational study of 126 decompensation episodes from 54 MSUD patients treated at five centers in France and Germany from 2010 to 2016, describes episodes and outcomes for patients stratified into groups who received enteral/oral or intravenous (IV) BCAA-free formula, and by pediatric or adult age categories. IV administration of BCAA-free formula was required in cases of gastric intolerance (33%), refusal to undergo nasogastric tubing (31%), "emergency" (14%) or coma patients (8%), and as prophylaxis before surgery (6%). Overall, mean duration of hospitalization was 6.6 days with oral/enteral BCAA-free formula and 5.4 days with IV formula. Leucine levels at discharge decreased by a mean of 548.5 μmol/L (69.3%) in the oral/enteral group and 657.2 μmol/L (71.3%) in the IV group. In the pediatric subgroup, there were no marked differences between administration groups on any outcome. In the adult subgroup, mean time to episode resolution was 15.8 days in the oral/enteral group and 7.7 days in the IV group (P = .008); mean duration of hospitalization was 6 days in the oral/enteral group and 4.6 days in the IV group (P = NS). Overall, seven serious adverse events in two patients were reported, of which only nausea and vomiting were treatment related.