A method for quantitative acylcarnitine profiling in human skin fibroblasts using unlabelled palmitic acid: diagnosis of fatty acid oxidation disorders and differentiation between biochemical phenotypes of MCAD deficiency

Hydroxymethylglutaryl-CoA reductase activity is essential for mitochondrial β-oxidation of fatty acids to prevent lethal accumulation of long-chain acylcarnitines in the mouse liver

BACKGROUND AND PURPOSE

Statins are competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMGCR), and exert adverse effects on mitochondrial function, although the mechanisms underlying these effects remain unclear. We used a tamoxifen-induced Hmgcr-knockout (KO) mouse model, a multi-omics approach and mitochondrial function assessments to investigate whether decreased HMGCR activity impacts key liver energy metabolism pathways.

EXPERIMENTAL APPROACH

We established a new mouse strain using the Cre/loxP system, which enabled whole-body deletion of Hmgcr expression. These mice were crossed with Rosa26Cre mice and treated with tamoxifen to delete Hmgcr in all cells. We performed transcriptomic and metabolomic analyses and thus evaluated time-dependent changes in metabolic functions to identify the pathways leading to cell death in Hmgcr-KO mice.

KEY RESULTS

Lack of Hmgcr expression resulted in lethality, due to acute liver damage caused by rapid disruption of mitochondrial fatty acid β-oxidation and very high accumulation of long-chain (LC) acylcarnitines in both male and female mice. Gene expression and KO-related phenotype changes were not observed in other tissues. The progression to liver failure was driven by diminished peroxisome formation, which resulted in impaired mitochondrial and peroxisomal fatty acid metabolism, enhanced glucose utilization and whole-body hypoglycaemia.

CONCLUSION AND IMPLICATIONS

Our findings suggest that HMGCR is crucial for maintaining energy metabolism balance, and its activity is necessary for functional mitochondrial β-oxidation. Moreover, statin-induced adverse reactions might be rescued by the prevention of LC acylcarnitine accumulation.

Messenger RNA rescues medium-chain acyl-CoA dehydrogenase deficiency in fibroblasts from patients and a murine model

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the most common inherited disorder of mitochondrial fatty acid β-oxidation (FAO) in humans. Patients exhibit clinical episodes often associated with fasting. Symptoms include hypoketotic hypoglycemia and Reye-like episodes. With limited treatment options, we explored the use of human MCAD (hMCAD) mRNA in fibroblasts from patients with MCAD deficiency to provide functional MCAD protein and reverse the metabolic block. Transfection of hMCAD mRNA into MCAD- deficient patient cells resulted in an increased MCAD protein that localized to mitochondria, concomitant with increased enzyme activity in cell extracts. The therapeutic hMCAD mRNA-lipid nanoparticle (LNP) formulation was also tested in vivo in Acadm-/- mice. Administration of multiple intravenous doses of the hMCAD mRNA-LNP complex (LNP-MCAD) into Acadm-/- mice produced a significant level of MCAD protein with increased enzyme activity in liver, heart and skeletal muscle homogenates. Treated Acadm-/- mice were more resistant to cold stress and had decreased plasma levels of medium-chain acylcarnitines compared to untreated animals. Furthermore, hepatic steatosis in the liver from treated Acadm-/- mice was reduced compared to untreated ones. Results from this study support the potential therapeutic value of hMCAD mRNA-LNP complex treatment for MCAD deficiency.

Complex metabolic disharmony in PMM2-CDG paves the way to new therapeutic approaches

PMM2-CDG is the most common defect among the congenital disorders of glycosylation. In order to investigate the effect of hypoglycosylation on important cellular pathways, we performed extensive biochemical studies on skin fibroblasts of PMM2-CDG patients. Among others, acylcarnitines, amino acids, lysosomal proteins, organic acids and lipids were measured, which all revealed significant abnormalities. There was an increased expression of acylcarnitines and amino acids associated with increased amounts of calnexin, calreticulin and protein-disulfid-isomerase in combination with intensified amounts of ubiquitinylated proteins. Lysosomal enzyme activities were widely decreased as well as citrate and pyruvate levels indicating mitochondrial dysfunction. Main lipid classes such as phosphatidylethanolamine, cholesterol or alkyl-phosphatidylcholine, as well as minor lipid species like hexosylceramide, lysophosphatidylcholines or phosphatidylglycerol, were abnormal. Biotinidase and catalase activities were severely reduced. In this study we discuss the impact of metabolite abnormalities on the phenotype of PMM2-CDG. In addition, based on our data we propose new and easy-to-implement therapeutic approaches for PMM2-CDG patients.

Treatment of VLCAD-Deficient Patient Fibroblasts with Peroxisome Proliferator-Activated Receptor δ Agonist Improves Cellular Bioenergetics

Background: Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is an autosomal recessive disease that prevents the body from utilizing long-chain fatty acids for energy, most needed during stress and fasting. Symptoms can appear from infancy through childhood and adolescence or early adulthood, and include hypoglycemia, recurrent rhabdomyolysis, myopathy, hepatopathy, and cardiomyopathy. REN001 is a peroxisome-proliferator-activated receptor delta (PPARδ) agonist that modulates the expression of the genes coding for fatty acid β-oxidation enzymes and proteins involved in oxidative phosphorylation. Here, we assessed the effect of REN001 on VLCAD-deficient patient fibroblasts. Methods: VLCAD-deficient patient and control fibroblasts were treated with REN001. Cells were harvested for gene expression analysis, protein content, VLCAD enzyme activity, cellular bioenergetics, and ATP production. Results: VLCAD-deficient cell lines responded differently to REN001 based on genotype. All cells had statistically significant increases in ACADVL gene expression. Small increases in VLCAD protein and enzyme activity were observed and were cell-line- and dose-dependent. Even with these small increases, cellular bioenergetics improved in all cell lines in the presence of REN001, as demonstrated by the oxygen consumption rate and ATP production. VLCAD-deficient cell lines containing missense mutations responded better to REN001 treatment than one containing a duplication mutation in ACADVL. Discussion: Treating VLCAD-deficient fibroblasts with the REN001 PPARδ agonist results in an increase in VLCAD protein and enzyme activity, and a decrease in cellular stress. These results establish REN001 as a potential therapy for VLCADD as enhanced expression may provide a therapeutic increase in total VLCAD activity, but suggest the need for mutation-specific treatment augmented by other treatment measures.

Effects of mechanical stimulation on metabolomic profiles of SW1353 chondrocytes: shear and compression

Mechanotransduction is a biological phenomenon where mechanical stimuli are converted to biochemical responses. A model system for studying mechanotransduction are the chondrocytes of articular cartilage. Breakdown of this tissue results in decreased mobility, increased pain, and reduced quality of life. Either disuse or overloading can disrupt cartilage homeostasis, but physiological cyclical loading promotes cartilage homeostasis. To model this, we exposed SW1353 cells to cyclical mechanical stimuli, shear and compression, for different durations of time (15 and 30 min). By utilizing liquid chromatography-mass spectroscopy (LC-MS), metabolomic profiles were generated detailing metabolite features and biological pathways that are altered in response to mechanical stimulation. In total, 1457 metabolite features were detected. Statistical analyses identified several pathways of interest. Taken together, differences between experimental groups were associated with inflammatory pathways, lipid metabolism, beta-oxidation, central energy metabolism, and amino acid production. These findings expand our understanding of chondrocyte mechanotransduction under varying loading conditions and time periods. This article has an associated First Person interview with the first author of the paper.

Very long chain fatty acid metabolism is required in acute myeloid leukemia

Acute myeloid leukemia (AML) cells have an atypical metabolic phenotype characterized by increased mitochondrial mass, as well as a greater reliance on oxidative phosphorylation and fatty acid oxidation (FAO) for survival. To exploit this altered metabolism, we assessed publicly available databases to identify FAO enzyme overexpression. Very long chain acyl-CoA dehydrogenase (VLCAD; ACADVL) was found to be overexpressed and critical to leukemia cell mitochondrial metabolism. Genetic attenuation or pharmacological inhibition of VLCAD hindered mitochondrial respiration and FAO contribution to the tricarboxylic acid cycle, resulting in decreased viability, proliferation, clonogenic growth, and AML cell engraftment. Suppression of FAO at VLCAD triggered an increase in pyruvate dehydrogenase activity that was insufficient to increase glycolysis but resulted in adenosine triphosphate depletion and AML cell death, with no effect on normal hematopoietic cells. Together, these results demonstrate the importance of VLCAD in AML cell biology and highlight a novel metabolic vulnerability for this devastating disease.

Comprehensive Metabolomic Analysis Reveals Dynamic Metabolic Reprogramming in Hep3B Cells with Aflatoxin B1 Exposure

Hepatitis B virus (HBV) infection and aflatoxin B1 (AFB1) exposure have been recognized as independent risk factors for the occurrence and development of hepatocellular carcinoma (HCC), but their combined impacts and the potential metabolic mechanisms remain poorly characterized. Here, a comprehensive non-targeted metabolomic study was performed following AFB1 exposed to Hep3B cells at two different doses: 16 μM and 32 μM. The metabolites were identified and quantified by an ultra-performance liquid chromatography-mass spectrometry (UPLC-MS)-based strategy. A total of 2679 metabolites were identified, and 392 differential metabolites were quantified among three groups. Pathway analysis indicated that dynamic metabolic reprogramming was induced by AFB1 and various pathways changed significantly, including purine and pyrimidine metabolism, hexosamine pathway and sialylation, fatty acid synthesis and oxidation, glycerophospholipid metabolism, tricarboxylic acid (TCA) cycle, glycolysis, and amino acid metabolism. To the best of our knowledge, the alteration of purine and pyrimidine metabolism and decrease of hexosamine pathways and sialylation with AFB1 exposure have not been reported. The results indicated that our metabolomic strategy is powerful to investigate the metabolome change of any stimulates due to its high sensitivity, high resolution, rapid separation, and good metabolome coverage. Besides, these findings provide an overview of the metabolic mechanisms of the AFB1 combined with HBV and new insight into the toxicological mechanism of AFB1. Thus, targeting these metabolic pathways may be an approach to prevent carcinogen-induced cancer, and these findings may provide potential drug targets for therapeutic intervention.

UPLC-Q-TOF/MS based Untargeted Metabolite and Lipid Analysis on Premature Ovarian Insufficiency Plasma Samples

Background:

Metabolomics is one of the main areas to understand cellular process at molecular level by analyzing metabolites. In recent years metabolomics has emerged as a key tool to understand molecular basis of diseases, to find diagnostic and prognostic biomarkers and develop new treatment opportunities and drug molecules.

Objective:

In this study, untargeted metabolite and lipid analysis were performed to identify potential biomarkers on premature ovarian insufficiency plasma samples. 43 POI subject plasma samples were compared with 32 healthy subject plasma samples.

Methods:

Plasma samples were pooled and extracted using chloroform:methanol:water (3:3:1 v/v/v) mixture. Agilent 6530 LC/MS Q-TOF instrument equipped with ESI source was used for analysis. A C18 column (Agilent Zorbax 1.8 μM, 50 x 2.1 mm) was used for separation of the metabolites and lipids. XCMS, an “R software” based freeware program, was used for peak picking, grouping and comparing the findings. Isotopologue Parameter Optimization (IPO) software was used to optimize XCMS parameters. The analytical methodology and data mining process were validated according to the literature.

Results:

83 metabolite peaks and 213 lipid peaks were found to be in semi-quantitatively and statistically different (fold change >1.5, p <0.05) between the POI plasma samples and control subjects.

Conclusion:

According to the results, two groups were successfully separated through principal component analysis. Among the peaks, phenyl alanine, decanoyl-L-carnitine, 1-palmitoyl lysophosphatidylcholine and PC(O-16:0/2:0) were identified through auto MS/MS and matched with human metabolome database and proposed as plasma biomarker for POI and monitoring the patients in treatment period.

Metabolic and Nutritional Issues Associated with Spinal Muscular Atrophy

Spinal muscular atrophy (SMA), the main genetic cause of infant death, is a neurodegenerative disease characterized by the selective loss of motor neurons in the anterior horn of the spinal cord, accompanied by muscle wasting. Pathomechanically, SMA is caused by low levels of the survival motor neuron protein (SMN) resulting from the loss of the SMN1 gene. However, emerging research extends the pathogenic effect of SMN deficiency beyond motor neurons. A variety of metabolic abnormalities, especially altered fatty acid metabolism and impaired glucose tolerance, has been described in isolated cases of SMA; therefore, the impact of SMN deficiency in metabolic abnormalities has been speculated. Although the life expectancy of these patients has increased due to novel disease-modifying therapies and standardization of care, understanding of the involvement of metabolism and nutrition in SMA is still limited. Optimal nutrition support and metabolic monitoring are essential for patients with SMA, and a comprehensive nutritional assessment can guide personalized nutritional therapy for this vulnerable population. It has recently been suggested that metabolomics studies before and after the onset of SMA in patients can provide valuable information about the direct or indirect effects of SMN deficiency on metabolic abnormalities. Furthermore, identifying and quantifying the specific metabolites in SMA patients may serve as an authentic biomarker or therapeutic target for SMA. Here, we review the main epidemiological and mechanistic findings that link metabolic changes to SMA and further discuss the principles of metabolomics as a novel approach to seek biomarkers and therapeutic insights in SMA.

Current Progress of Lipid Analysis in Metabolic Diseases by Mass Spectrometry Methods

BACKGROUND

Obesity, insulin resistance, diabetes, and metabolic syndrome are associated with lipid alterations, and they affect the risk of long-term cardiovascular disease. A reliable analytical instrument to detect changes in the composition or structures of lipids and the tools allowing to connect changes in a specific group of lipids with a specific disease and its progress, is constantly lacking. Lipidomics is a new field of medicine based on the research and identification of lipids and lipid metabolites present in human organism. The primary aim of lipidomics is to search for new biomarkers of different diseases, mainly civilization diseases.

OBJECTIVE

We aimed to review studies reporting the application of mass spectrometry for lipid analysis in metabolic diseases.

METHOD

Following an extensive search of peer-reviewed articles on the mass spectrometry analysis of lipids the literature has been discussed in this review article.

RESULTS

The lipid group contains around 1.7 million species; they are totally different, in terms of the length of aliphatic chain, amount of rings, additional functional groups. Some of them are so complex that their complex analyses are a challenge for analysts. Their qualitative and quantitative analysis of is based mainly on mass spectrometry.

CONCLUSION

Mass spectrometry techniques are excellent tools for lipid profiling in complex biological samples and the combination with multivariate statistical analysis enables the identification of potential diagnostic biomarkers.

Evaluation of Metabolic Defects in Fatty Acid Oxidation Using Peripheral Blood Mononuclear Cells Loaded with Deuterium-Labeled Fatty Acids

Because tandem mass spectrometry- (MS/MS-) based newborn screening identifies many suspicious cases of fatty acid oxidation and carnitine cycle disorders, a simple, noninvasive test is required to confirm the diagnosis. We have developed a novel method to evaluate the metabolic defects in peripheral blood mononuclear cells loaded with deuterium-labeled fatty acids directly using the ratios of acylcarnitines determined by flow injection MS/MS. We have identified diagnostic indices for the disorders as follows: decreased ratios of d₂₇-C14-acylcarnitine/d₃₁-C16-acylcarnitine and d₂₃-C12-acylcarnitine/d₃₁-C16-acylcarnitine for carnitine palmitoyltransferase-II (CPT-II) deficiency, decreased ratios of d₂₃-C12-acylcarnitine/d₂₇-C14-acylcarnitine for very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, and increased ratios of d₂₉-C16-OH-acylcarnitine/d₃₁-C16-acylcarnitine for trifunctional protein (TFP) deficiency, together with increased ratios of d₇-C4-acylcarnitine/d₃₁-C16-acylcarnitine for carnitine palmitoyltransferase-I deficiency. The decreased ratios of d₁-acetylcarnitine/d₃₁-C16-acylcarnitine could be indicative of β-oxidation ability in patients with CPT-II, VLCAD, and TFP deficiencies. Overall, our data showed that the present method was valuable for establishing a rapid diagnosis of fatty acid oxidation disorders and carnitine cycle disorders and for complementing gene analysis because our diagnostic indices may overcome the weaknesses of conventional enzyme activity measurements using fibroblasts or mononuclear cells with assumedly uncertain viability.

Management and diagnosis of mitochondrial fatty acid oxidation disorders: focus on very-long-chain acyl-CoA dehydrogenase deficiency

Mitochondrial fatty acid oxidation disorders (FAODs) are caused by defects in β-oxidation enzymes, including very long-chain acyl-CoA dehydrogenase (VLCAD), trifunctional protein (TFP), carnitine palmitoyltransferase-2 (CPT2), carnitine-acylcarnitine translocase (CACT) and others. During prolonged fasting, infection, or exercise, patients with FAODs present with hypoglycemia, rhabdomyolysis, cardiomyopathy, liver dysfunction, and occasionally sudden death. This article describes the diagnosis, newborn screening, and treatment of long-chain FAODs with a focus on VLCAD deficiency. VLCAD deficiency is generally classified into three phenotypes based on onset time, but the classification should be comprehensively determined based on genotype, residual enzyme activity, and clinical course, due to a lack of apparent genotype-phenotype correlation. With the expansion of newborn screening for FAODs, several issues have arisen, such as missed detection, overdiagnosis (including detection of benign/asymptomatic type), and poor prognosis of the neonatal-onset form. Meanwhile, dietary management and restriction of exercise have been unnecessary for patients with the benign/asymptomatic type of VLCAD deficiency with a high fatty acid oxidation flux score. Although L-carnitine therapy for VLCAD/TFP deficiency has been controversial, supplementation with L-carnitine may be accepted for CPT2/CACT and multiple acyl-CoA dehydrogenase deficiencies. Recently, a double-blind, randomized controlled trial of triheptanoin (seven-carbon fatty acid triglyceride) versus trioctanoin (regular medium-chain triglyceride) was conducted and demonstrated improvement of cardiac functions on triheptanoin. Additionally, although the clinical efficacy of bezafibrate remains controversial, a recent open-label clinical trial showed efficacy of this drug in improving quality of life. These drugs may be promising for the treatment of FAODs, though further studies are required.

Angiocrine Wnt signaling controls liver growth and metabolic maturation in mice

Postnatal liver development is characterized by hepatocyte growth, proliferation, and functional maturation. Notably, canonical Wnt signaling in hepatocytes has been identified as an important regulator of final adult liver size and metabolic liver zonation. The cellular origin of Wnt ligands responsible for homeostatic liver/body weight ratio (LW/BW) remained unclear, which was also attributable to a lack of suitable endothelial Cre driver mice. To comprehensively analyze the effects of hepatic angiocrine Wnt signaling on liver development and metabolic functions, we used endothelial subtype-specific Stab2-Cre driver mice to delete Wls from hepatic endothelial cells (HECs). The resultant Stab2-Cre^tg/wt ;Wls^fl/fl (Wls-HECKO) mice were viable, but showed a significantly reduced LW/BW. Specifically, ablation of angiocrine Wnt signaling impaired metabolic zonation in the liver, as shown by loss of pericentral, β-catenin-dependent target genes such as glutamine synthase (Glul), RhBg, Axin2, and cytochrome P450 2E1, as well as by extended expression of periportal genes such as arginase 1. Furthermore, endothelial subtype-specific expression of a c-terminally YFP-tagged Wls fusion protein in Wls-HECKO mice (Stab2-Cre^tg/wt ;Wls^fl/fl ;Rosa26:Wls-YFP^fl/wt [Wls-rescue]) restored metabolic liver zonation. Interestingly, lipid metabolism was altered in Wls-HECKO mice exhibiting significantly reduced plasma cholesterol levels, while maintaining normal plasma triglyceride and blood glucose concentrations. On the contrary, zonal expression of Endomucin, LYVE1, and other markers of HEC heterogeneity were not altered in Wls-HECKO livers.

CONCLUSION

Angiocrine Wnt signaling controls liver growth as well as development of metabolic liver zonation in mice, whereas intrahepatic HEC zonation is not affected. (Hepatology 2017).

Effect of Toxicants on Fatty Acid Metabolism in HepG2 Cells

Impairment of hepatic fatty acid metabolism can lead to liver steatosis and injury. Testing drugs for interference with hepatic fatty acid metabolism is therefore important. To find out whether HepG2 cells are suitable for this purpose, we investigated the effect of three established fatty acid metabolism inhibitors and of three test compounds on triglyceride accumulation, palmitate metabolism, the acylcarnitine pool and dicarboxylic acid accumulation in the cell supernatant and on ApoB-100 excretion in HepG2 cells. The three established inhibitors [etomoxir, methylenecyclopropylacetic acid (MCPA), and 4-bromocrotonic acid (4-BCA)] depleted mitochondrial ATP at lower concentrations than cytotoxicity occurred, suggesting mitochondrial toxicity. They inhibited palmitate metabolism at similar or lower concentrations than ATP depletion, and 4-BCA was associated with cellular fat accumulation. They caused specific changes in the acylcarnitine pattern and etomoxir an increase of thapsic (C18 dicarboxylic) acid in the cell supernatant, and did not interfere with ApoB-100 excretion (marker of VLDL export). The three test compounds (amiodarone, tamoxifen, and the cannabinoid WIN 55,212-2) depleted the cellular ATP content at lower concentrations than cytotoxicity occurred. They all caused cellular fat accumulation and inhibited palmitate metabolism at similar or higher concentrations than ATP depletion. They suppressed medium-chain acylcarnitines in the cell supernatant and amiodarone and tamoxifen impaired thapsic acid production. Tamoxifen and WIN 55,212-2 decreased cellular ApoB-100 excretion. In conclusion, the established inhibitors of fatty acid metabolism caused the expected effects in HepG2 cells. HepG cells proved to be useful for the detection of drug-associated toxicities on hepatocellular fatty acid metabolism.

Open-label clinical trial of bezafibrate treatment in patients with fatty acid oxidation disorders in Japan

Introduction

Fatty acid oxidation disorders (FAODs) are rare diseases caused by defects in mitochondrial fatty acid oxidation (FAO) enzymes. While the efficacy of bezafibrate, a peroxisome proliferator-activated receptor agonist, on the in vitro FAO capacity has been reported, the in vivo efficacy remains controversial. Therefore, we conducted a clinical trial of bezafibrate in Japanese patients with FAODs.

Materials and methods

This trial was an open-label, non-randomized, and multicenter study of bezafibrate treatment in 6 patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency and 2 patients with carnitine palmitoyltransferase-II (CPT-2) deficiency (median age, 8.2 years; ranging from 5.8 to 26.4 years). Bezafibrate was administered for 6 months following a 6-month observation period. The primary endpoint was the frequency of myopathic attacks, and the secondary endpoints were serum acylcarnitines (ACs, C14:1 or C16 + C18:1), creatine kinase (CK) levels, degree of muscle pain (VAS; visual analog scale) during myopathic attacks, and quality of life (QOL; evaluated using validated questionnaires).

Results

The frequency of myopathic attacks after bezafibrate administration decreased in 3 patients, increased in 3, and did not change in 2. The CK, AC, and VAS values during attacks could be estimated in only three or four patients, but a half of the patients did not experience attacks before or after treatment. Changes in CK, AC, and VAS values varied across individuals. In contrast, three components of QOL, namely, physical functioning, role limitation due to physical problems (role physical), and social functioning, were significantly elevated. No adverse drug reactions were observed.

Conclusion

In this study, the frequency of myopathic attacks and CK, AC, and VAS values during the attacks could not be evaluated due to several limitations, such as a small trial population. Our findings indicate that bezafibrate improves the QOL of patients with FAODs, but its efficacy must be examined in future investigations.

L-Carnitine and Acetyl-L-carnitine Roles and Neuroprotection in Developing Brain

L-Carnitine functions to transport long chain fatty acyl-CoAs into the mitochondria for degradation by β-oxidation. Treatment with L-carnitine can ameliorate metabolic imbalances in many inborn errors of metabolism. In recent years there has been considerable interest in the therapeutic potential of L-carnitine and its acetylated derivative acetyl-L-carnitine (ALCAR) for neuroprotection in a number of disorders including hypoxia-ischemia, traumatic brain injury, Alzheimer's disease and in conditions leading to central or peripheral nervous system injury. There is compelling evidence from preclinical studies that L-carnitine and ALCAR can improve energy status, decrease oxidative stress and prevent subsequent cell death in models of adult, neonatal and pediatric brain injury. ALCAR can provide an acetyl moiety that can be oxidized for energy, used as a precursor for acetylcholine, or incorporated into glutamate, glutamine and GABA, or into lipids for myelination and cell growth. Administration of ALCAR after brain injury in rat pups improved long-term functional outcomes, including memory. Additional studies are needed to better explore the potential of L-carnitine and ALCAR for protection of developing brain as there is an urgent need for therapies that can improve outcome after neonatal and pediatric brain injury.

Efficacy of bezafibrate on fibroblasts of glutaric acidemia type II patients evaluated using an in vitro probe acylcarnitine assay

INTRODUCTION

We evaluated the effects of bezafibrate (BEZ) on β-oxidation in fibroblasts obtained from patients with glutaric acidemia type II (GA2) of various clinical severities using an in vitro probe (IVP) assay.

METHODS

Cultured fibroblasts from 12 patients with GA2, including cases of the neonatal-onset type both with and without congenital anomalies (the prenatal- and neonatal-onset forms, respectively), the infantile-onset, and the myopathic forms, were studied. The IVP assay was performed by measuring acylcarnitines (ACs) in the cell culture medium of fibroblasts incubated with palmitic acid for 96h in the presence of 0-800μM BEZ using tandem mass spectrometry.

RESULTS

The IVP assay showed that 100μM BEZ markedly reduced the level of palmitoylcarnitine (C16) in the neonatal-onset, infantile-onset, and myopathic forms of GA2, either increasing or maintaining a high level of acetylcarnitine (C2), which serves as an index of energy production via β-oxidation. In the prenatal-onset form, although a small reduction of C16 was also observed in the presence of 100μM BEZ, the level of C2 remained low. At concentrations higher than 100μM, BEZ further decreased the level of ACs including C16, but a concentration over 400μM decreased the level of C2 in most cases.

DISCUSSION

BEZ at 100μM was effective for all GA2 phenotypes except for the prenatal-onset form, as a reduction of C16 without deterioration of C2 is considered to indicate improvement of β-oxidation. The effects of higher doses BEZ could not be estimated by the IVP assay but might be small or nonexistent.

Sodium Valproate Exacerbating an Underlying Disorder of Fatty Acid Metabolism

We describe a 29-year-old female who presented with rhabdomyolysis shortly after starting a course of sodium valproate. A thorough investigation revealed a likely mitochondrial origin inducing this susceptibility. An underlying mitochondrial disorder should be considered in all patients who present with undifferentiated disease whilst taking sodium valproate.

Metabolic analysis of osteoarthritis subchondral bone based on UPLC/Q-TOF-MS

Osteoarthritis (OA), one of the most widespread musculoskeletal joint diseases among the aged, is characterized by the progressive loss of articular cartilage and continuous changes in subchondral bone. The exact pathogenesis of osteoarthritis is not completely clear. In this work, ultra-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UPLC/Q-TOF-MS) in combination with multivariate statistical analysis was applied to analyze the metabolic profiling of subchondral bone from 42 primary osteoarthritis patients. This paper described a modified two-step method for extracting the metabolites of subchondral bone from primary osteoarthritis patients. Finally, 68 metabolites were identified to be significantly changed in the sclerotic subchondral bone compared with the non-sclerotic subchondral bone. Taurine and hypotaurine metabolism and beta-alanine metabolism were probably relevant to the sclerosis of subchondral bone. Taurine, L-carnitine, and glycerophospholipids played a vital regulation role in the pathological process of sclerotic subchondral bone. In the sclerotic process, beta-alanine and L-carnitine might be related to the increase of energy consumption. In addition, our findings suggested that the intra-cellular environment of sclerotic subchondral bone might be more acidotic and hypoxic compared with the non-sclerotic subchondral bone. In conclusion, this study provided a new insight into the pathogenesis of subchondral bone sclerosis. Our results indicated that metabolomics could serve as a promising approach for elucidating the pathogenesis of subchondral bone sclerosis in primary osteoarthritis. Graphical Abstract Metabolic analysis of osteoarthritis subchondral bone.

Carnitine-acylcarnitine translocase deficiency: Two neonatal cases with common splicing mutation and in vitro bezafibrate response

BACKGROUND

Mitochondrial fatty acid oxidation (FAO) disorders are among the causes of acute encephalopathy- or myopathy-like illness. Carnitine-acylcarnitine translocase (CACT) deficiency is a rare FAO disorder, which represent an energy production insufficiency during prolonged fasting, febrile illness, or increased muscular activity. CACT deficiency is caused by mutations of the SLC25A20 gene. Most patients developed severe metabolic decompensation in the neonatal period and died in infancy despite aggressive treatment.

PATIENTS AND METHODS

We herein report the clinical findings of two unrelated cases of CACT deficiency with mutation confirmation, and in vitro bezafibrate responses using in vitro probe acylcarnitine (IVP) assay. Patients 1 and 2 are products of nonconsanguineous parents. Both patients developed cardiac arrest at day 3 of life but survived the initial events. Their blood chemistry revealed hypoglycemia and metabolic acidosis. The acylcarnitine profiles in both patients demonstrated increased long-chain acylcarnitines, suggesting CACT or carnitine palmitoyltransferase-2 (CPT2) deficiency.

RESULTS

The mutation analysis identified homozygous IVS2-10T>G in the SLC25A20 gene in both patients, confirming the diagnosis of CACT deficiency. The IVP assay revealed increased C16, C16:1, but decreased C2 with improvement by bezafibrate in the cultured fibroblasts. The short-term clinical trial of bezafibrate in Patient 1 did not show clinical improvement, and died after starting the trial for 6 months.

CONCLUSION

This splicing mutation has been identified in other Asian populations indicating a possible founder effect. IVP assay of cultured fibroblasts could determine a response to bezafibrate treatment. A long-term clinical trial of more enrolled patients is required for evaluation of this therapy.

Metabolic disease in 10 patients with sudden unexpected death in infancy or acute life-threatening events

In order to determine the associations between sudden unexpected death in infancy (SUDI) or acute life-threatening events (ALTE) and inborn errors of metabolism, particularly organic acidemia and fatty acid oxidation disorders, we evaluated clinical features in patients with SUDI or ALTE. The subjects were infants between the ages of 7 days and 3 years who developed SUDI or ALTE between January 2004 and December 2013. They were then diagnosed as having inborn errors of metabolism on gas chromatography-mass spectrometry (GC/MS) and/or tandem mass spectrometry (MS/MS). The age distribution, onset forms, and clinical findings were evaluated during the acute phase. Inborn errors of metabolism were detected in three of 196 patients with SUDI, and in seven of 167 patients with ALTE. Of these 10 patients, nine had a history of poor feeding and somnolence during the neonatal period, and symptoms of infection such as cough, fever or vomiting during infancy. Routine laboratory tests during an acute phase indicated hyperammonemia, liver dysfunction, increased blood creatine kinase, acidosis, positive ketone bodies in urine or blood, or hypoglycemia. When SUDI or ALTE are encountered in the emergency unit, it is essential that a detailed medical history is taken, particularly with regard to the neonatal period, and that specific abnormalities are investigated on routine laboratory tests. Moreover, samples such as urine, serum, and filter paper blood specimens should be collected for GC/MS and/or MS/MS of organic acids and acylcarnitines, to identify inborn metabolic disorders.

Deficiency of ECHS1 causes mitochondrial encephalopathy with cardiac involvement

Objective

Short-chain enoyl-CoA hydratase (ECHS1) is a multifunctional mitochondrial matrix enzyme that is involved in the oxidation of fatty acids and essential amino acids such as valine. Here, we describe the broad phenotypic spectrum and pathobiochemistry of individuals with autosomal-recessive ECHS1 deficiency.

Methods

Using exome sequencing, we identified ten unrelated individuals carrying compound heterozygous or homozygous mutations in ECHS1. Functional investigations in patient-derived fibroblast cell lines included immunoblotting, enzyme activity measurement, and a palmitate loading assay.

Results

Patients showed a heterogeneous phenotype with disease onset in the first year of life and course ranging from neonatal death to survival into adulthood. The most prominent clinical features were encephalopathy (10/10), deafness (9/9), epilepsy (6/9), optic atrophy (6/10), and cardiomyopathy (4/10). Serum lactate was elevated and brain magnetic resonance imaging showed white matter changes or a Leigh-like pattern resembling disorders of mitochondrial energy metabolism. Analysis of patients’ fibroblast cell lines (6/10) provided further evidence for the pathogenicity of the respective mutations by showing reduced ECHS1 protein levels and reduced 2-enoyl-CoA hydratase activity. While serum acylcarnitine profiles were largely normal, in vitro palmitate loading of patient fibroblasts revealed increased butyrylcarnitine, unmasking the functional defect in mitochondrial β-oxidation of short-chain fatty acids. Urinary excretion of 2-methyl-2,3-dihydroxybutyrate – a potential derivative of acryloyl-CoA in the valine catabolic pathway – was significantly increased, indicating impaired valine oxidation.

Interpretation

In conclusion, we define the phenotypic spectrum of a new syndrome caused by ECHS1 deficiency. We speculate that both the β-oxidation defect and the block in l-valine metabolism, with accumulation of toxic methacrylyl-CoA and acryloyl-CoA, contribute to the disorder that may be amenable to metabolic treatment approaches.

Metabolomic profiling of emodin-induced cytotoxicity in human liver cells and mechanistic study

A metabolomics approach was used to explore emodin-induced liver cells toxicology and a new mechanism was tentatively proposed.

Functional analysis of iPSC-derived myocytes from a patient with carnitine palmitoyltransferase II deficiency

INTRODUCTION

Carnitine palmitoyltransferase II (CPT II) deficiency is an inherited disorder involving β-oxidation of long-chain fatty acids (FAO), which leads to rhabdomyolysis and subsequent acute renal failure. The detailed mechanisms of disease pathogenesis remain unknown; however, the availability of relevant human cell types for investigation, such as skeletal muscle cells, is limited, and the development of novel disease models is required.

METHODS

We generated human induced pluripotent stem cells (hiPSCs) from skin fibroblasts of a Japanese patient with CPT II deficiency. Mature myocytes were differentiated from the patient-derived hiPSCs by introducing myogenic differentiation 1 (MYOD1), the master transcriptional regulator of myocyte differentiation. Using an in vitro acylcarnitine profiling assay, we investigated the effects of a hypolipidemic drug, bezafibrate, and heat stress on mitochondrial FAO in CPT II-deficient myocytes and controls.

RESULTS

CPT II-deficient myocytes accumulated more palmitoylcarnitine (C16) than did control myocytes. Heat stress, induced by incubation at 38°C, leads to a robust increase of C16 in CPT II-deficient myocytes, but not in controls. Bezafibrate reduced the amount of C16 in control and CPT II-deficient myocytes.

DISCUSSION

In this study, we induced differentiation of CPT II-deficient hiPSCs into mature myocytes in a highly efficient and reproducible manner and recapitulated some aspects of the disease phenotypes of CPT II deficiency in the myocyte disease models. This approach addresses the challenges of modeling the abnormality of FAO in CPT II deficiency using iPSC technology and has the potential to revolutionize translational research in this field.

Development of a metabolomic radiation signature in urine from patients undergoing total body irradiation

The emergence of the threat of radiological terrorism and other radiological incidents has led to the need for development of fast, accurate and noninvasive methods for detection of radiation exposure. The purpose of this study was to extend radiation metabolomic biomarker discovery to humans, as previous studies have focused on mice. Urine was collected from patients undergoing total body irradiation at Memorial Sloan-Kettering Cancer Center prior to hematopoietic stem cell transplantation at 4-6 h postirradiation (a single dose of 1.25 Gy) and 24 h (three fractions of 1.25 Gy each). Global metabolomic profiling was obtained through analysis with ultra performance liquid chromatography coupled to time-of-flight mass spectrometry (TOFMS). Prior to further analyses, each sample was normalized to its respective creatinine level. Statistical analysis was conducted by the nonparametric Kolmogorov-Smirnov test and the Fisher's exact test and markers were validated against pure standards. Seven markers showed distinct differences between pre- and post-exposure samples. Of those, trimethyl-l-lysine and the carnitine conjugates acetylcarnitine, decanoylcarnitine and octanoylcarnitine play an important role in the transportation of fatty acids across mitochondria for subsequent fatty acid β-oxidation. The remaining metabolites, hypoxanthine, xanthine and uric acid are the final products of the purine catabolism pathway, and high levels of excretion have been associated with increased oxidative stress and radiation induced DNA damage. Further analysis revealed sex differences in the patterns of excretion of the markers, demonstrating that generation of a sex-specific metabolomic signature will be informative and can provide a quick and reliable assessment of individuals in a radiological scenario. This is the first radiation metabolomics study in human urine laying the foundation for the use of metabolomics in biodosimetry and providing confidence in biomarker identification based on the overlap between animal models and humans.

The effect of valinomycin in fibroblasts from patients with fatty acid oxidation disorders

Disorders of the carnitine cycle and of the beta oxidation spiral impair the ability to obtain energy from fats at time of fasting and stress. This can result in hypoketotic hypoglycemia, cardiomyopathy, cardiac arrhythmia and other chronic medical problems. The in vitro study of fibroblasts from patients with these conditions is impaired by their limited oxidative capacity. Here we evaluate the capacity of valinomycin, a potassium ionophore that increases mitochondrial respiration, to increase the oxidation of fatty acids in cells from patients with inherited fatty acid oxidation defects. The addition of valinomycin to fibroblasts decreased the accumulation of the lipophilic cation tetraphenylphosphonium (TPP(+)) at low concentrations due to the dissipation of the mitochondrial membrane potential. At higher doses, valinomycin increased TPP(+) accumulation due to the increased potassium permeability of the plasma membrane and subsequent cellular hyperpolarization. The incubation of normal fibroblasts with valinomycin increased [(14)C]-palmitate oxidation (measured as [(14)C]O2 release) in a dose-dependent manner. By contrast, valinomycin failed to increase palmitate oxidation in fibroblasts from patients with very long chain acyl CoA dehydrogenase (VLCAD) deficiency. This was not observed in fibroblasts from patients heterozygous for this condition. These results indicate that valinomycin can increase fatty acid oxidation in normal fibroblasts and could be useful to differentiate heterozygotes from patients affected with VLCAD deficiency.

Production and release of acylcarnitines by primary myotubes reflect the differences in fasting fat oxidation of the donors

CONTEXT

Acylcarnitines are biomarkers of incomplete β-oxidation and mitochondrial lipid overload but indicate also high rates of mitochondrial fatty acid oxidation. It is unknown whether the production of acylcarnitines in primary human myotubes obtained from lean, metabolically healthy subjects reflects the fat oxidation in vivo.

OBJECTIVE

Our objective was to quantify the acylcarnitine production in myotubes obtained from subjects with low and high fasting respiratory quotient (RQ).

METHODS

Fasting RQ was determined by indirect calorimetry. Muscle biopsies from the vastus lateralis muscle were taken from 6 subjects with low fasting RQ (mean 0.79 ± 0.03) and 6 with high fasting RQ (0.90 ± 0.03), and satellite cells were isolated, cultured, and differentiated to myotubes. Myotubes were cultivated with 125 μM (13)C-labeled palmitate for 30 minutes and 4 and 24 hours. Quantitative profiling of 42 intracellular and 31 extracellular acylcarnitines was performed by stable isotope dilution-based metabolomics analysis by liquid chromatography coupled to mass spectrometry.

RESULTS

Myotubes from donors with high fasting RQ produced and released significant higher amounts of medium-chain acylcarnitines. High (13)C8 and (13)C10 acylcarnitine levels in the extracellular compartment correlated with high fasting RQ. The decreased expression of medium-chain acyl-coenzyme A dehydrogenase (MCAD) in these myotubes can explain the higher rate of incomplete fatty acid oxidation. A lower intracellular [(13)C]acetylcarnitine to carnitine and lower intracellular (13)C16/(13)C18 acylcarnitine to carnitine ratio indicate reduced fatty acid oxidation capacity in these myotubes. Mitochondrial DNA content was not different.

CONCLUSION

Acylcarnitine production and release from primary human myotubes of donors with high fasting RQ indicate a reduced fatty acid oxidation capacity and a higher rate of incomplete fatty acid oxidation. Thus, quantitative profiling of acylcarnitine production in human myotubes can be a suitable tool to identify muscular determinants of fat oxidation in vivo.

Bezafibrate can be a new treatment option for mitochondrial fatty acid oxidation disorders: evaluation by in vitro probe acylcarnitine assay

BACKGROUND

The number of patients with mitochondrial fatty acid oxidation (FAO) disorders is recently becoming larger with the spread of newborn mass screening. Despite the advances in metabolic and molecular characterization of FAO disorders, the therapeutic studies are still limited. It was reported recently that bezafibrate (BEZ), an agonist of peroxisome proliferating activator receptor (PPAR), can restore FAO activity in cells from carnitine palmitoyltransferase-2 (CPT2) and very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies as well as clinical symptoms in the adult patients.

METHODS

In this study, the therapeutic effect of BEZ was determined by in vitro probe acylcarnitine (IVP) assay using cultured fibroblasts and tandem mass spectrometry on various FAO disorders. The clinical trial of BEZ treatment for a boy with the intermediate form of glutaric acidemia type 2 (GA2) was also performed.

RESULTS

The effect of BEZ was proven in cells from various FAO disorders including GA2, deficiencies of VLCAD, medium-chain acyl-CoA dehydrogenase, CPT2, carnitine acylcarnitine translocase and trifunctional protein, by the IVP assay. The aberrantly elevated long- or medium-chain acylcarnitines that are characteristic for each FAO disorder were clearly corrected by the presence of BEZ (0.4 mmol/L) in culture medium. Moreover, daily administration of BEZ in a 2-year-old boy with GA2 dramatically improved his motor and cognitive skills, accompanied by sustained reduction of C4, C8, C10 and C12 acylcarnitines in blood, and normalized the urinary organic acid profile. No major adverse effects have been observed.

CONCLUSION

These results indicate that BEZ could be a new treatment option for FAO disorders.

In situ assay of fatty acid β-oxidation by metabolite profiling following permeabilization of cell membranes

Quantitative analysis of mitochondrial FA β-oxidation (FAO) has drawn increasing interest for defining lipid-induced metabolic dysfunctions, such as in obesity-induced insulin resistance, and evaluating pharmacologic strategies to improve β-oxidation function. The aim was to develop a new assay to quantify β-oxidation function in intact mitochondria and with a low amount of cell material. Cell membranes of primary human fibroblasts were permeabilized with digitonin prior to a load with FFA substrate. Following 120 min of incubation, the various generated acylcarnitines were extracted from both cells and incubation medium by protein precipitation/desalting and subjected to solid-phase extraction. A panel of 30 acylcarnitines per well was quantified by MS/MS and normalized to citrate synthase activity to analyze mitochondrial metabolite flux. Pretreatment with bezafibrate and etomoxir revealed stimulating and inhibiting regulatory effects on β-oxidation function, respectively. In addition to the advantage of a much shorter assay time due to in situ permeabilization compared with whole-cell incubation systems, the method allows the detection of multiple acylcarnitines from an only limited amount of intact cells, particularly relevant to the use of primary cells. This novel approach facilitates highly sensitive, simple, and fast monitoring of pharmacological effects on FAO.

Newborn screening for medium chain acyl-CoA dehydrogenase deficiency in England: prevalence, predictive value and test validity based on 1.5 million screened babies

BACKGROUND

Medium chain acyl-CoA dehydrogenase deficiency (MCADD) is a rare, life-threatening condition. Early diagnosis by screening asymptomatic newborns may improve outcome, but the benefit to newborns identified with variants not encountered clinically is uncertain.

OBJECTIVE

To estimate, overall and by ethnic group: screen-positive prevalence and predictive value (PPV); MCADD prevalence; proportion MCADD variants detected of predicted definite or uncertain clinical importance.

SETTING

All births in areas of high ethnic minority prevalence in England.

METHODS

Prospective multicentre pilot screening service; testing at age five to eight days; standardized screening, diagnostic and management protocols; independent expert review of screen-positive cases to assign MCADD diagnosis and predicted clinical importance (definite or uncertain).

RESULTS

Approximately 1.5 million babies (79% white; 10% Asian) were screened. MCADD was confirmed in 147 of 190 babies with a positive screening result (screen-positive prevalence: 1.20 per 10,000; MCADD prevalence: 0.94 per 10,000; PPV 77% [95% CI 71-83]), comprising 103 (70%) with MCADD variants of definite clinical importance (95 white [95%]; 2 Asian [2%]) and 44 (30%) with variants of uncertain clinical importance (29 white [67%]; 12 Asian [28%]).

CONCLUSION

One baby in every 10,000 born in England is diagnosed with MCADD by newborn screening; around 60 babies each year. While the majority of MCADD variants detected are predicted to be of definite clinical importance, this varies according to ethnic group, with variants of uncertain importance most commonly found in Asian babies. These findings provide support for MCADD screening but highlight the need to take account of the ethnic diversity of the population tested at implementation.

Data mining methods for classification of Medium-Chain Acyl-CoA dehydrogenase deficiency (MCADD) using non-derivatized tandem MS neonatal screening data

Newborn screening programs for severe metabolic disorders using tandem mass spectrometry are widely used. Medium-Chain Acyl-CoA dehydrogenase deficiency (MCADD) is the most prevalent mitochondrial fatty acid oxidation defect (1:15,000 newborns) and it has been proven that early detection of this metabolic disease decreases mortality and improves the outcome. In previous studies, data mining methods on derivatized tandem MS datasets have shown high classification accuracies. However, no machine learning methods currently have been applied to datasets based on non-derivatized screening methods. A dataset with 44,159 blood samples was collected using a non-derivatized screening method as part of a systematic newborn screening by the PCMA screening center (Belgium). Twelve MCADD cases were present in this partially MCADD-enriched dataset. We extended three data mining methods, namely C4.5 decision trees, logistic regression and ridge logistic regression, with a parameter and threshold optimization method and evaluated their applicability as a diagnostic support tool. Within a stratified cross-validation setting, a grid search was performed for each model for a wide range of model parameters, included variables and classification thresholds. The best performing model used ridge logistic regression and achieved a sensitivity of 100%, a specificity of 99.987% and a positive predictive value of 32% (recalibrated for a real population), obtained in a stratified cross-validation setting. These results were further validated on an independent test set. Using a method that combines ridge logistic regression with variable selection and threshold optimization, a significantly improved performance was achieved compared to the current state-of-the-art for derivatized data, while retaining more interpretability and requiring less variables. The results indicate the potential value of data mining methods as a diagnostic support tool.

Effect of heat stress and bezafibrate on mitochondrial beta-oxidation: comparison between cultured cells from normal and mitochondrial fatty acid oxidation disorder children using in vitro probe acylcarnitine profiling assay

Hyperpyrexia occasionally triggers acute life-threatening encephalopathy-like illnesses, including influenza-associated encephalopathy (IAE) in childhood, and can be responsible for impaired fatty acid beta-oxidation (FAO). In this regard, patients with impaired FAO may be more susceptible to febrile episodes. The effects of heat stress and a hypolipidemic drug, bezafibrate, on mitochondrial FAO were investigated using cultured cells from children with FAO disorders and from normal controls, using an in vitro probe acylcarnitine (AC) profiling assay. Fibroblasts were incubated in medium loaded with unlabelled palmitic acid for 96 h at 37 and 41 degrees C, with or without bezafibrate. AC profiles in culture medium were analyzed by electrospray ionization tandem mass spectrometry. Heat stress, introduced by 41 degrees C, significantly increased acetylcarnitine (C2) but slightly decreased the other acylcarnitines (ACs) in controls and medium-chain acyl-CoA dehydrogenase (MCAD)-deficient cells. On the other hand, in very long-chain acyl-CoA dehydrogenase (VLCAD)-deficient cells, accumulation of long-chain ACs were enhanced at 41 degrees C, compared with that at 37 degrees C. In contrast, bezafibrate decreased long-chain ACs with significant increase of C2 in both control and VLCAD-deficient cells at 37 degrees C. These data suggest that heat stress specifically inhibits long-chain FAO, whereas bezafibrate recovers the impaired FAO. Our approach is a simple and promising strategy to evaluate the effects of heat stress or therapeutic drugs on mitochondrial FAO.

Enzymatic evaluation of glutaric acidemia type 1 by an in vitro probe assay of acylcarnitine profiling using fibroblasts and electrospray ionization/tandem mass spectrometry (MS/MS)

Glutaric acidemia type 1 (GA1) is usually diagnosed with an accumulation of glutaric acid (GA) or 3-hydroxyglutaric acid by GC/MS. In some cases, however, excretion of GA is low. We investigated enzymatic evaluation of GA1 using fibroblasts and MS/MS. After loading substrates, lysine, 2-aminoadipate (2AA), or GA, in fibroblasts, and incubating for 96 h, glutarylcarnitine (C5DC) levels in the media were measured. A significant increase of C5DC was observed in GA1 patients, irrespective of substrates added. 2AA showed the largest difference between patients and controls (p = 0.0004). Results suggested enzymatic evaluation of GA1 is useful under appropriate culture conditions.

Deuterated palmitate-driven acylcarnitine formation by whole-blood samples for a rapid diagnostic exploration of mitochondrial fatty acid oxidation disorders

BACKGROUND

The biochemical diagnosis of mitochondrial fatty acid oxidation defects (FAOD) currently rests on enzyme assays. A dynamic ex vivo exploration consisting of incubations of whole-blood samples with stable-labeled palmitate and determining leukocyte capacities to produce deuterated acylcarnitines was developed on healthy controls (n=52) and patients with very-long- (VLCADD) (n=2), medium- (MCADD) (n=6), or short- (SCADD) (n=1) chain acyl-CoA dehydrogenase deficiencies.

METHODS

Incubations were optimized with L-carnitine and [16-(2)H(3), 15-(2)H(2)]-palmitate at 37 degrees C for various time periods on MCADD and control whole-blood samples. Labeled acylcarnitines were quantified by electrospray-ionization tandem mass spectrometry after thawing, extraction and derivatization to their butyl esters and the method was applied to patients with defects mentioned above.

RESULTS

The production of acylcarnitines was linear until 6 h of incubation and optimal on 50 to 200 nmol deuterated substrate. A good discrimination between MCADD patient and control data was found, with median C8/C4 acylcarnitine production rate ratios of 81.0 (5th-95th percentile range: 16.6-209.9) and 0.21 (5th-95th percentile range: 0.06-0.79), respectively. The method also discriminated from controls the VLCADD and SCADD patients. Preliminary studies on a healthy control indicated that the storage at 4 degrees C does little or not alter capacities of whole-blood samples to generate labeled acylcarnitines over a period of 48 h.

CONCLUSION

The rapid management afforded by the method, its abilities to characterize patients and to work on whole-blood samples after a stay of 24-48 h at 4 degrees C make it promising for the diagnostic exploration of FAOD.

Mitochondrial fatty acid oxidation defects--remaining challenges

Mitochondrial fatty acid oxidation defects have been recognized since the early 1970s. The discovery rate has been rather constant, with 3-4 'new' disorders identified every decade and with the most recent example, ACAD9 deficiency, reported in 2007. In this presentation we will focus on three of the 'old' defects: medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, riboflavin responsive multiple acyl-CoA dehydrogenation (RR-MAD) deficiency, and short-chain acyl-CoA dehydrogenase (SCAD) deficiency. These disorders have been discussed in many publications and at countless conference presentations, and many questions relating to them have been answered. However, continuing clinical and pathophysiological research has raised many further questions, and new ideas and methodologies may be required to answer these. We will discuss these challenges. For MCAD deficiency the key question is why 80% of symptomatic patients are homozygous for the prevalent ACADM gene variation c.985A > G whereas this is found in only approximately 50% of newborns with a positive screen. For RR-MAD deficiency, the challenge is to find the connection between variations in the ETFDH gene and the observed deficiency of a number of different mitochondrial dehydrogenases as well as deficiency of FAD and coenzyme Q(10). With SCAD deficiency, the challenge is to elucidate whether ACADS gene variations are disease-associated, especially when combined with other genetic/cellular/environmental factors, which may act synergistically.

Setting the stage: possible mechanisms by which acute contraction restores insulin sensitivity in muscle

It has long been known that acute exercise can dramatically improve insulin sensitivity in previously insulin-resistant muscle; however, the precise mechanisms underlying this clinically significant interaction remain unknown. Using hindlimb perfusions in obese Zucker rats, our group found that acute muscle contraction synergistically improved insulin-stimulated glucose transport in skeletal muscle, but contrary to our hypothesis, these findings were not associated with either improved insulin signaling or decreased intramuscular lipid metabolites. A further analysis revealed that the improved insulin sensitivity was associated with a robust increase in mitochondrial energy flux. These findings and reports from other labs suggest that mitochondrial energy flux and mitochondrial oxidative capacity may govern insulin sensitivity and override insulin signaling defects associated with obesity. This review will discuss the effects of acute exercise to enhance insulin sensitivity in previously insulin-resistant muscle and present possible novel mechanisms by which alterations in mitochondrial energy metabolism may play a regulatory role.

Spectrum of medium-chain acyl-CoA dehydrogenase deficiency detected by newborn screening

OBJECTIVE

Our goal was to describe the clinical spectrum of medium-chain acyl-CoA dehydrogenase deficiency detected by routine newborn screening and assess factors associated with elevations of octanoylcarnitine in newborns and characteristics associated with adverse clinical consequences of medium-chain acyl-CoA dehydrogenase deficiency.

METHODS

The first 47 medium-chain acyl-CoA dehydrogenase deficiency cases detected by the New England Newborn Screening Program were classified according to initial and follow-up octanoylcarnitine values, octanoylcarnitine-decanoylcarnitine ratios, medium-chain acyl-CoA dehydrogenase genotype, follow-up biochemical parameters, and feeding by breast milk or formula.

RESULTS

All 20 patients who were homozygous for 985A-->G had high initial octanoylcarnitine values (7.0-36.8 microM) and octanoylcarnitine-decanoylcarnitine ratios (7.0-14.5), whereas the 27 patients with 0 to 1 copy of 985A-->G exhibited a wide range of octanoylcarnitine values (0.5-28.6 microM) and octanoylcarnitine-decanoylcarnitine ratios (0.8-12.7). Initial newborn octanoylcarnitine values decreased by days 5 to 8, but the octanoylcarnitine-decanoylcarnitine ratio generally remained stable. Among 985A-->G homozygotes, breastfed newborns had higher initial octanoylcarnitine values than newborns who received formula. Adverse events occurred in 5 children, 4 985A-->G homozygotes and 1 compound heterozygote with a very high initial octanoylcarnitine: 2 survived severe neonatal hypoglycemia, 1 survived a severe hypoglycemic episode at 15 months of age, and 2 died as a result of medium-chain acyl-CoA dehydrogenase deficiency at ages 11 and 33 months.

CONCLUSION

Newborn screening for medium-chain acyl-CoA dehydrogenase deficiency has detected cases with a wide range of genotypes and biochemical abnormalities. Although most children do well, adverse outcomes have not been entirely avoided. Assessment of potential risk and determination of appropriate treatment remain a challenge.

Feature construction can improve diagnostic criteria for high-dimensional metabolic data in newborn screening for medium-chain acyl-CoA dehydrogenase deficiency

BACKGROUND

In newborn screening with tandem mass spectrometry, multiple intermediary metabolites are quantified in a single analytical run for the diagnosis of fatty-acid oxidation disorders, organic acidurias, and aminoacidurias. Published diagnostic criteria for these disorders normally incorporate a primary metabolic marker combined with secondary markers, often analyte ratios, for which the markers have been chosen to reflect metabolic pathway deviations.

METHODS

We applied a procedure to extract new markers and diagnostic criteria for newborn screening to the data of newborns with confirmed medium-chain acyl-CoA dehydrogenase deficiency (MCADD) and a control group from the newborn screening program, Heidelberg, Germany. We validated the results with external data of the screening center in Hamburg, Germany. We extracted new markers by performing a systematic search for analyte combinations (features) with high discriminatory performance for MCADD. To select feature thresholds, we applied automated procedures to separate controls and cases on the basis of the feature values. Finally, we built classifiers from these new markers to serve as diagnostic criteria in screening for MCADD.

RESULTS

On the basis of chi(2) scores, we identified approximately 800 of >628,000 new analyte combinations with superior discriminatory performance compared with the best published combinations. Classifiers built with the new features achieved diagnostic sensitivities and specificities approaching 100%.

CONCLUSION

Feature construction methods provide ways to disclose information hidden in the set of measured analytes. Other diagnostic tasks based on high-dimensional metabolic data might also profit from this approach.

A novel functional assay for simultaneous determination of total fatty acid beta-oxidation flux and acylcarnitine profiling in human skin fibroblasts using (2)H(31)-palmitate by isotope ratio mass spectrometry and electrospray tandem mass spectrometry

BACKGROUND

Two separate and complementary assays, total mitochondrial fatty acid beta-oxidation (FAO) flux rate and acylcarnitine profiling, have been used to establish a definitive diagnosis of FAO defects (FAOD) in cultured cells. We developed a novel functional assay for total FAO rate assay by measurement of deuterated water enrichment and to combine it with the conventional acylcarnitine profiling method into a single tracer incubation experiment.

METHODS

Skin fibroblasts were incubated in a medium containing universal deuterium-labeled palmitate ((2)H(31)-palmitate) and l-carnitine without glucose supplementation for 96 h. The culture medium was assayed for deuterated water enrichment using isotope ratio mass spectrometry (IRMS) and acylcarnitine profiling by electrospray-ionization tandem mass spectrometry (ESI/MS/MS).

RESULTS

The medians of (2)H(2)O enrichment after 96 h of incubation of (2)H(31)-palmitate of the control, other inherited metabolic diseases and FAOD cell lines were 109.9, 102 and 23.1 ppm/mg protein/96 h, respectively. All fibroblasts with FAOD except carnitine uptake defective, multiple acyl-CoA dehydrogenase and short-chain 3-hydroxyacyl-CoA dehydrogenase deficient cells were well separated from the control (<60% control median, p<0.05) and could be identified by IRMS assay. Accumulations of disease-specific acylcarnitines due to blockage in the carnitine cycle and FAO spiral were also demonstrated by acylcarnitine profiling.

CONCLUSIONS

This novel functional assay is less time consuming and relatively simple by comparison to other published methods and can be used to investigate patients suspected to have FAO defects.

Contraction of insulin-resistant muscle normalizes insulin action in association with increased mitochondrial activity and fatty acid catabolism

Acute exercise can reverse muscle insulin resistance, but the mechanism(s) of action are unknown. With the use of a hindlimb perfusion model, we have found that acute contraction restores insulin-stimulated glucose uptake in muscle of obese Zucker rats to levels witnessed in lean controls. Previous reports have suggested that obesity-related insulin resistance stems from lipid oversupply and tissue accumulation of toxic lipid intermediates that impair insulin signaling. We reasoned that contraction might activate hydrolysis and oxidation of intramuscular lipids, thus alleviating "lipotoxicity" and priming the muscle for enhanced insulin action. Indeed, analysis of mitochondrial-derived acyl-carnitine esters suggested that contraction caused robust increases in beta-oxidative flux and mitochondrial oxidation. As predicted, contraction decreased intramuscular triacylglycerol content; however, diacylglycerol and long chain acyl-CoAs, lipid intermediates presumed to trigger insulin resistance, were either unchanged or increased. In muscles from obese animals, insulin-stimulated tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 remained impaired after contraction, whereas phosphorylation of the downstream signaling protein, AS160, was partially restored. These results suggest that acute exercise enables diabetic muscle to circumvent upstream defects in insulin signal transduction via mechanisms that are more tightly coupled to increased mitochondrial energy metabolism than the lowering of diacylglycerol and long chain acyl-CoA.

Quantitative acylcarnitine profiling in peripheral blood mononuclear cells using in vitro loading with palmitic and 2-oxoadipic acids: biochemical confirmation of fatty acid oxidation and organic acid disorders

Organic acid (OAD) and fatty acid oxidation disorders (FAOD) are inborn errors of metabolism often presenting with life-threatening metabolic decompensation followed by (irreversible) organ failure, and even death during catabolic state. Most of these diseases are considered as treatable, and metabolic decompensations can be avoided by early diagnosis and start of therapy. Confirmation of suspected diagnosis currently relies on enzymatic and mutation analyses and in vitro loading of palmitic acid in human skin fibroblast cultures. Furthermore, in some cases potentially life-threatening in vivo loading or fasting tests are still performed. In this study, we established a standardized in vitro loading test in peripheral blood mononuclear cells (PBMC) that allows reliable biochemical confirmation of a suspected diagnosis within 1 week. Patients with confirmed diagnosis of short-, medium-, very-long-chain, and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiencies, methylmalonic, propionic, isovaleric acidurias, and glutaric aciduria type I were included in the study. PBMC, isolated from heparinized venous blood samples of these individuals were incubated for 5 days with palmitic acid or 2-oxoadipic acid (glutaric aciduria type I), respectively, and quantitative acylcarnitine profiling was subsequently performed in supernatants using electrospray ionization tandem mass spectrometry. All patients were clearly identified, including those with mild biochemical phenotypes who, in particular, are at risk to be missed under balanced metabolic conditions. In glutaric aciduria type I, the same results were also obtained using lymphoblasts. In conclusion, our assay allows biochemical confirmation of a number of FAOD and OAD and could easily be implemented into the confirmatory diagnostic work-up.

Screening of newborns and high-risk group of children for inborn metabolic disorders using tandem mass spectrometry in South Korea: a three-year report

BACKGROUND

Mass screening using tandem mass spectrometry(MS/MS) was initiated to determine if the incidence of metabolic disorder is sufficiently high to meet the criteria for newborn screening, and whether or not early medical intervention might be beneficial to the patients.

METHODS

Newborns and children in a high-risk group were screened using MS/MS from April 2001 to March 2004. Blood spots of newborns were collected between 48 and 72 h after birth. The dried blood spots was extracted with 150 microl of methanol, and analyzed by MS/MS.

RESULTS

From April 2001 to March 2004, 79,179 newborns were screened for organic, amino and fatty acid metabolism disorders, which account for approximately 5.4% of annual births in South Korea. Twenty-eight newborns were diagnosed with one of the metabolic disorders and the collective estimated prevalence amounted to 1 in 2800 with a sensitivity of 97.67%, a specificity of 99.28%, a recall rate of 0.05%, and a positive predictive value of 6.38%. 6795 infants/children at high risk were screened and 20 were confirmed to have metabolic disorders.

CONCLUSION

The collective total prevalence of 1:2800 in newborns indicates an underestimation of the incidence of metabolic disorders prior to implementing MS/MS screening in South Korea.

Bioenergetics in glutaryl-coenzyme A dehydrogenase deficiency: a role for glutaryl-coenzyme A

Inherited deficiency of glutaryl-CoA dehydrogenase results in an accumulation of glutaryl-CoA, glutaric, and 3-hydroxyglutaric acids. If untreated, most patients suffer an acute encephalopathic crisis and, subsequently, acute striatal damage being precipitated by febrile infectious diseases during a vulnerable period of brain development (age 3 and 36 months). It has been suggested before that some of these organic acids may induce excitotoxic cell damage, however, the relevance of bioenergetic impairment is not yet understood. The major aim of our study was to investigate respiratory chain, tricarboxylic acid cycle, and fatty acid oxidation in this disease using purified single enzymes and tissue homogenates from Gcdh-deficient and wild-type mice. In purified enzymes, glutaryl-CoA but not glutaric or 3-hydroxyglutaric induced an uncompetitive inhibition of alpha-ketoglutarate dehydrogenase complex activity. Notably, reduced activity of alpha-ketoglutarate dehydrogenase activity has recently been demonstrated in other neurodegenerative diseases, such as Alzheimer, Parkinson, and Huntington diseases. In contrast to alpha-ketoglutarate dehydrogenase complex, no direct inhibition of glutaryl-CoA, glutaric acid, and 3-hydroxyglutaric acid was found in other enzymes tested. In Gcdh-deficient mice, respiratory chain and tricarboxylic acid activities remained widely unaffected, virtually excluding regulatory changes in these enzymes. However, hepatic activity of very long-chain acyl-CoA dehydrogenase was decreased and concentrations of long-chain acylcarnitines increased in the bile of these mice, which suggested disturbed oxidation of long-chain fatty acids. In conclusion, our results demonstrate that bioenergetic impairment may play an important role in the pathomechanisms underlying neurodegenerative changes in glutaryl-CoA dehydrogenase deficiency.