A new case of short-chain acyl-CoA dehydrogenase deficiency: clinical, biochemical, genetic and 1H-NMR spectroscopic studies

Acylcarnitines: Nomenclature, Biomarkers, Therapeutic Potential, Drug Targets, and Clinical Trials

Acylcarnitines are fatty acid metabolites that play important roles in many cellular energy metabolism pathways. They have historically been used as important diagnostic markers for inborn errors of fatty acid oxidation and are being intensively studied as markers of energy metabolism, deficits in mitochondrial and peroxisomal β -oxidation activity, insulin resistance, and physical activity. Acylcarnitines are increasingly being identified as important indicators in metabolic studies of many diseases, including metabolic disorders, cardiovascular diseases, diabetes, depression, neurologic disorders, and certain cancers. The US Food and Drug Administration-approved drug L-carnitine, along with short-chain acylcarnitines (acetylcarnitine and propionylcarnitine), is now widely used as a dietary supplement. In light of their growing importance, we have undertaken an extensive review of acylcarnitines and provided a detailed description of their identity, nomenclature, classification, biochemistry, pathophysiology, supplementary use, potential drug targets, and clinical trials. We also summarize these updates in the Human Metabolome Database, which now includes information on the structures, chemical formulae, chemical/spectral properties, descriptions, and pathways for 1240 acylcarnitines. This work lays a solid foundation for identifying, characterizing, and understanding acylcarnitines in human biosamples. We also discuss the emerging opportunities for using acylcarnitines as biomarkers and as dietary interventions or supplements for many wide-ranging indications. The opportunity to identify new drug targets involved in controlling acylcarnitine levels is also discussed. SIGNIFICANCE STATEMENT: This review provides a comprehensive overview of acylcarnitines, including their nomenclature, structure and biochemistry, and use as disease biomarkers and pharmaceutical agents. We present updated information contained in the Human Metabolome Database website as well as substantial mapping of the known biochemical pathways associated with acylcarnitines, thereby providing a strong foundation for further clarification of their physiological roles.

A pilot study on machine learning approach to delineate metabolic signatures in intellectual disability

Intellectual disability (ID) is a neurodevelopmental disorder characterized by cognitive delays. Inborn errors of metabolism constitute an important subgroup of ID for which various treatments options are available. We aimed to identify potential biomarkers of inherited metabolic disorders from the children with ID using tandem mass spectrometry and develop a novel machine learning algorithm to differentiate between the cases and the controls. All of the cases were having IQ score <70, gross motor delay, speech disorder and no recognizable symptoms of the condition. Metabolite profiling of ID individuals exhibited low tyrosine/large neutral amino acids, high citrulline/arginine ratios; elevated proline, alanine, phenylalanine, and ornithine, while a significant decrease in the level of amino acid arginine, and elevated C4 (butyrylcarnitine) and C4OH/C3DC (3-hydroxybutyrylcarnitine/malonylcarnitine). Machine learning algorithm differentiated cases and controls efficiently using specific thresholds of ornithine, arginine and C4OH/C3DC. Furthermore, ID cases were distinguished into mild, moderate, and severe based on specific thresholds of methionine, arginine, and C5OH/C4DC (3-hydroxyisovalerylcarnitine/methylmalonylcarnitine). The machine learning algorithm could successfully identify specific metabolite markers in ID and correlate the same with neurological features.

Neurochemical evidence that lysine inhibits synaptic Na+,K+-ATPase activity and provokes oxidative damage in striatum of young rats in vivo

Lysine (Lys) accumulation in tissues and biological fluids is the biochemical hallmark of patients affected by familial hyperlysinemia (FH) and other inherited metabolic disorders. In the present study we investigated the effects of acute administration of Lys on relevant parameters of energy metabolism and oxidative stress in striatum of young rats. We verified that Lys in vivo intrastriatal injection did not change the citric acid cycle function and creatine kinase activity, but, in contrast, significantly inhibited synaptic Na(+),K(+)-ATPase activity in striatum prepared 2 and 12 h after injection. Moreover, Lys induced lipid peroxidation and diminished the concentrations of glutathione 2 h after injection. These effects were prevented by the antioxidant scavengers melatonin and the combination of α-tocopherol and ascorbic acid. Lys also inhibited glutathione peroxidase activity 12 h after injection. Therefore it is assumed that inhibition of synaptic Na(+),K(+)-ATPase and oxidative damage caused by brain Lys accumulation may possibly contribute to the neurological manifestations of FH and other neurometabolic conditions with high concentrations of this amino acid.

Inhibition of creatine kinase activity by lysine in rat cerebral cortex

Accumulation of lysine (Lys) in tissues and biochemical fluids is the biochemical hallmark of patients affected by familial hyperlysinemia (FH) and also by other inherited neurometabolic disorders. In the present study, we investigated the in vitro effect of Lys on various parameters of energy metabolism in cerebral cortex of 30-day-old Wistar rats. We verified that total (tCK) and cytosolic creatine kinase activities were significantly inhibited by Lys, in contrast to the mitochondrial isoform which was not affected by this amino acid. Furthermore, the inhibitory effect of Lys on tCK activity was totally prevented by reduced glutathione, suggesting a possible role of reactive species oxidizing critical thiol groups of the enzyme. In contrast, Lys did not affect (14)CO(2) production from [U-(14)C] glucose (aerobic glycolytic pathway) and [1-(14)C] acetic acid (citric acid cycle activity) neither the various activities of the electron transfer chain and synaptic Na(+)K(+)-ATPase at concentrations as high as 5.0 mM. Considering the importance of creatine kinase (CK) activity for brain energy metabolism homeostasis and especially ATP transfer and buffering, our results suggest that inhibition of this enzyme by Lys may contribute to the neurological signs presented by symptomatic patients affected by FH and other neurodegenerative disorders in which Lys accumulates.