Fuel utilization in patients with very long-chain acyl-coa dehydrogenase deficiency

Exercise testing and prescription in patients with inborn errors of muscle energy metabolism

Skeletal muscle is a dynamic organ requiring tight regulation of energy metabolism in order to provide bursts of energy for effective function. Several inborn errors of muscle energy metabolism (IEMEM) affect skeletal muscle function and therefore the ability to initiate and sustain physical activity. Exercise testing can be valuable in supporting diagnosis, however its use remains limited due to the inconsistency in data to inform its application in IEMEM populations. While exercise testing is often used in adults with IEMEM, its use in children is far more limited. Once a physiological limitation has been identified and the aetiology defined, habitual exercise can assist with improving functional capacity, with reports supporting favourable adaptations in adult patients with IEMEM. Despite the potential benefits of structured exercise programs, data in paediatric populations remain limited. This review will focus on the utilisation and limitations of exercise testing and prescription for both adults and children, in the management of McArdle Disease, long chain fatty acid oxidation disorders, and primary mitochondrial myopathies.

No effect of resveratrol on fatty acid oxidation or exercise capacity in patients with fatty acid oxidation disorders: A randomized clinical cross-over trial

The objective was to investigate whether resveratrol (RSV) can improve exercise capacity in patients with fatty acid oxidation (FAO) disorders. The study was a randomized, double-blind, cross-over trial. Nine patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency or carnitine palmitoyl transferase (CPT) II deficiency were randomized to receive either 8 weeks of 1000 mg day^-1 RSV or placebo (P) followed by a 4-weeks wash-out period and subsequently 8 weeks of the opposite treatment. Primary outcome measures were heart rate and FAO as measured via stable isotope technique during constant workload exercise. Secondary outcome measures included fat and glucose metabolism; perceived exertion; as well as subjective measures of energy expenditure, fatigue, and daily function. Eight participants completed the trial. Heart rate did not differ at the end of exercise after treatment with RSV vs placebo (P = .063). Rate of oxidation of palmitate at end of exercise was not different with 1.5 ± 0.8 (RSV) vs 1.3 ± 0.6 (P) μmol kg^-1  min^-1 (P = .109). Secondary outcomes did not change except for increased plasma glycerol and decreased plasma glucose levels at the end of exercise after treatment with RSV vs placebo. A daily dose of 1000 mg resveratrol does not improve exercise capacity or FAO during exercise in patients with CPTII or VLCAD deficiencies.

Prolonged fasting-induced hyperketosis, hypoglycaemia and impaired fat oxidation in child and adult patients with spinal muscular atrophy type II

AIM

This study explored hypoglycaemia and metabolic crises, including hyperketosis, in patients with spinal muscular atrophy (SMA).

METHODS

The study comprised four adolescents aged 15-17 and six adults aged 19-37 with SMA type II and eight adult controls aged 21-41, who were recruited by the Rigshospitalet, Denmark, from May 1st to October 30th 2017. We used stable isotope technique and indirect calorimetry to investigate fat and glucose metabolism during a 24-h fast or until hypoglycaemia occurred.

RESULTS

All patients with SMA II developed moderate to severe hyperketosis and 60% had symptoms of hypoglycaemia or blood glucose levels below 3 mmol/L. None of the controls developed hyperketosis or hypoglycaemia. Plasma bicarbonate decreased, in line with increased ketone bodies, indicating the start of metabolic acidosis in patients with SMA II. Increased fat production and utilisation were seen in healthy controls during the fasting period, but were absent in patients with SMA II, indicating blunted fat oxidation.

CONCLUSION

Low skeletal muscle mass was the best explanation for why patients with SMA II had an increased risk of hypoglycaemia, hyperketosis, metabolic acidosis and disturbed fat and glucose metabolism during fasting. These risks have implications for children facing surgery and those with severe illnesses.

Mitochondrial morphology, bioenergetics and proteomic responses in fatty acid oxidation disorders

Mutations in nuclear genes encoding for mitochondrial proteins very long-chain acyl-CoA dehydrogenase (VLCAD) and trifunctional protein (TFP) cause rare autosomal recessive disorders. Studies in fibroblasts derived from patients with mutations in VLCAD and TFP exhibit mitochondrial defects. To gain insights on pathological changes that account for the mitochondrial deficits we performed quantitative proteomic, biochemical, and morphometric analyses in fibroblasts derived from subjects with three different VLCAD and three different TFP mutations. Proteomic data that was corroborated by antibody-based detection, indicated reduced levels of VLCAD and TFP protein in cells with VLCAD and TFP mutations respectively, which in part accounted for the diminished fatty acid oxidation capacity. Decreased mitochondrial respiratory capacity in cells with VLCAD and TFP mutations was quantified after glucose removal and cells with TFP mutations had lower levels of glycogen. Despite these energetic deficiencies, the cells with VLCAD and TFP mutations did not exhibit changes in mitochondria morphology, distribution, fusion and fission, quantified by either confocal or transmission electron microscopy and corroborated by proteomic and antibody-based protein analysis. Fibroblasts with VLCAD and to a lesser extend cells with TFP mutations had increased levels of mitochondrial respiratory chain proteins and proteins that facilitate the assembly of respiratory complexes. With the exception of reduced levels of catalase and glutathione S-transferase theta-1 in cells with TFP mutations, the levels of 45 proteins across all major intracellular antioxidant networks were similar between cells with VLCAD and TFP mutations and non-disease controls. Collectively the data indicate that despite the metabolic deficits, cells with VLCAD and TFP mutations maintain their proteomic integrity to preserve cellular and mitochondria architecture, support energy production and protect against oxidative stress.

Nutrition management guideline for very-long chain acyl-CoA dehydrogenase deficiency (VLCAD): An evidence- and consensus-based approach

The nutrition management guideline for very-long chain acyl-CoA dehydrogenase deficiency (VLCAD) is the fourth in a series of web-based guidelines focusing on the diet treatment for inherited metabolic disorders and follows previous publication of guidelines for maple syrup urine disease (2014), phenylketonuria (2016) and propionic acidemia (2019). The purpose of this guideline is to establish harmonization in the treatment and monitoring of individuals with VLCAD of all ages in order to improve clinical outcomes. Six research questions were identified to support guideline development on: nutrition recommendations for the healthy individual, illness management, supplementation, monitoring, physical activity and management during pregnancy. This report describes the methodology used in its development including review, critical appraisal and abstraction of peer-reviewed studies and unpublished practice literature; expert input through two Delphi surveys and a nominal group process; and external review from metabolic physicians and dietitians. It includes the summary statements of the nutrition management recommendations for each research question, followed by a standardized rating based on the strength of the evidence. Online, open access of the full published guideline allows utilization by health care providers, researchers and collaborators who advise, advocate and care for individuals with VLCAD and their families and can be accessed from the Genetic Metabolic Dietitians International (https://GMDI.org) and Southeast Regional Genetics Network (https://southeastgenetics.org/ngp) websites.

Fat oxidation is impaired during exercise in lipin-1 deficiency

OBJECTIVE

To investigate substrate metabolism during exercise in an adult with lipin-1 deficiency, an inherited defect in lipid homeostasis, and to study the effect of glucose supplementation on his exercise tolerance.

METHODS

We studied a 48-year-old man with lipin-1 deficiency and 2 healthy men. The patient has exercise intolerance and monthly episodes of rhabdomyolysis. All participants performed a submaximal exercise test while total fatty acid oxidation (FAO) and palmitate oxidation rate were assessed by stable isotope technique and indirect calorimetry. On another day, the patient was infused with 10% glucose (410 mL/h) and repeated the exercise. On the third and fourth visits, he was randomized in a double-blind manner to drink a supplement of glucose (soft drink 2% concentration) or placebo (soft drink: aspartame, acesulfame-K) before and during exercise.

RESULTS

Mean FAO and palmitate oxidation rate during exercise were lower in the patient vs controls: 431 vs 1,271 and 1912 μmol/min and 122 vs 191 and 212 μmol/min. Plasma fatty acid concentration was lower in the patient during exercise than in controls: 477 vs 643 and 630 μmol/L. The patient's exercise duration increased from 36 to 60 minutes with IV glucose and 46 minutes with oral glucose, and his rating of exertion dropped from 15 to 9 on average (Borg scale).

CONCLUSION

In this adult lipin-1-deficient patient, FAO was reduced, which was associated with no increase in plasma free fatty acids during submaximal exercise, and his exercise capacity improved with continuous ingestion of high-dose glucose.

CLINICALTRIALSGOV IDENTIFIER

NCT02635269.

Blunted fat oxidation upon submaximal exercise is partially compensated by enhanced glucose metabolism in children, adolescents, and young adults with Barth syndrome

Barth syndrome (BTHS) is a rare X-linked condition resulting in abnormal mitochondria, cardioskeletal myopathy, and growth delay; however, the effects of BTHS on substrate metabolism regulation and their relationships with tissue function in humans are unknown. We sought to characterize glucose and fat metabolism during rest, submaximal exercise, and postexercise rest in children, adolescents, and young adults with BTHS and unaffected controls and examine their relationships with cardioskeletal energetics and function. Children/adolescents and young adults with BTHS (n = 29) and children/adolescent and young adult control participants (n = 28, total n = 57) underwent an infusion of 6'6'H2 glucose and U-¹³ C palmitate and indirect calorimetry during rest, 30-minutes of moderate exercise (50% V˙O2peak ), and recovery. Cardiac function, cardioskeletal mitochondrial energetics, and exercise capacity were examined via echocardiography, ³¹ P magnetic resonance spectroscopy, and peak exercise testing, respectively. The glucose turnover rate was significantly higher in individuals with BTHS during rest (33.2 ± 9.8 vs 27.2 ± 8.1 μmol/kgFFM/min, P < .01) and exercise (34.7 ± 11.2 vs 29.5 ± 8.8 μmol/kgFFM/min, P < .05) and tended to be higher postexercise (33.7 ± 10.2 vs 28.8 ± 8.0 μmol/kgFFM/min, P < .06) compared to controls. Increases in total fat (-3.9 ± 7.5 vs 10.5 ± 8.4 μmol/kgFFM/min, P < .0001) and plasma fatty acid oxidation rates (0.0 ± 1.8 vs 5.1 ± 3.9 μmol/kgFFM/min, P < .0001) from rest to exercise were severely blunted in BTHS compared to controls. Conclusion: An inability to upregulate fat metabolism during moderate intensity exercise appears to be partially compensated by elevations in glucose metabolism. Derangements in fat and glucose metabolism are characteristic of the pathophysiology of BTHS. A severely blunted ability to upregulate fat metabolism during a modest level of physical activity is a defining pathophysiologic characteristic in children, adolescents, and young adults with BTHS.

Translational Metabolism: A multidisciplinary approach towards precision diagnosis of inborn errors of metabolism in the omics era

The laboratory diagnosis of inborn errors of metabolism has been revolutionized in recent years, thanks to the amazing developments in the field of DNA sequencing including whole exome and whole genome sequencing (WES and WGS). Interpretation of the results coming from WES and/or WGS analysis is definitely not trivial especially since the biological relevance of many of the variants identified by WES and/or WGS, have not been tested experimentally and prediction programs like POLYPHEN-2 and SIFT are far from perfect. Correct interpretation of WES and/or WGS results can only be achieved by performing functional studies at multiple levels (different metabolomics platforms, enzymology, in vitro and in vivo flux analysis), often requires studies in model organisms like zebra fish, Caenorhabditis elegans, Saccharomyces cerevisiae, mutant mice and others, and also requires the input of many different disciplines to make this Translational Metabolism approach effective.

L-Carnitine Improves Skeletal Muscle Fat Oxidation in Primary Carnitine Deficiency

CONTEXT

Primary carnitine deficiency (PCD) is an inborn error of fatty acid metabolism. Patients with PCD are risk for sudden heart failure upon fasting or illness if they are not treated with daily l-carnitine.

OBJECTIVE

To investigate energy metabolism during exercise in patients with PCD with and without l-carnitine treatment.

DESIGN

Interventional study.

SETTING

Hospital exercise laboratories and department of cardiology.

PARTICIPANTS

Eight adults with PCD who were homozygous for the c.95A>G (p.N32S) mutation and 10 healthy age- and sex-matched controls.

INTERVENTION

Four-day pause in l-carnitine treatment.

MAIN OUTCOME MEASURES

Total fatty acid and palmitate oxidation rates during 1-hour submaximal cycle ergometer exercise assessed with stable isotope method (U13C-palmitate and 2H2-d-glucose) and indirect calorimetry with and without l-carnitine.

RESULTS

Total fatty acid oxidation rate was higher in patients with l-carnitine treatment during exercise than without treatment [12.3 (SD, 3.7) vs 8.5 (SD, 4.6) µmol × kg-1 × min-1; P = 0.008]. However, the fatty acid oxidation rate was still lower in patients treated with l-carnitine than in the healthy controls [29.5 (SD, 10.1) µmol × kg-1 × min-1; P < 0.001] and in the l-carnitine group without treatment it was less than one third of that in the healthy controls (P < 0.001). In line with this, the palmitate oxidation rates during exercise were lower in the no-treatment period [144 (SD, 66) µmol × kg-1 × min-1] than during treatment [204 (SD, 84) µmol × kg-1 × min-1; P = 0.004) .

CONCLUSIONS

The results indicate that patients with PCD have limited fat oxidation during exercise. l-Carnitine treatment in asymptomatic patients with PCD may not only prevent cardiac complications but also boost skeletal muscle fat metabolism during exercise.

An Introduction to Pharmacotherapy for Inborn Errors of Metabolism

Inborn errors of metabolism comprise a wide array of diseases and complications in the pediatric patient. The rarity of these disorders limits the ability to conduct and review robust literature regarding the disease states, mechanisms of dysfunction, treatments, and outcomes. Often, treatment plans will be based on the pathophysiology associated with the disorder and theoretical agents that may be involved in the metabolic process. Medication therapies usually consist of natural or herbal products. Established efficacious pediatric doses for these products are difficult to find in tertiary resources, and adverse effects are routinely limited to single case reports. This review article attempts to summarize some of the more common inborn errors of metabolism in a manner that is applicable to pharmacists who will provide care for these patients.

Metabolite accumulation in VLCAD deficiency markedly disrupts mitochondrial bioenergetics and Ca2+ homeostasis in the heart

We studied the effects of the major long-chain fatty acids accumulating in very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, namely cis-5-tetradecenoic acid (Cis-5) and myristic acid (Myr), on important mitochondrial functions in isolated mitochondria from cardiac fibers and cardiomyocytes of juvenile rats. Cis-5 and Myr at pathological concentrations markedly reduced mitochondrial membrane potential (ΔΨ_m ), matrix NAD(P)H pool, Ca²⁺ retention capacity, ADP- (state 3) and carbonyl cyanide 3-chlorophenyl hydrazine-stimulated (uncoupled) respiration, and ATP generation. By contrast, these fatty acids increased resting (state 4) respiration (uncoupling effect) with the involvement of the adenine nucleotide translocator because carboxyatractyloside significantly attenuated the increased state 4 respiration provoked by Cis-5 and Myr. Furthermore, the classical inhibitors of mitochondrial permeability transition (MPT) pore cyclosporin A plus ADP, as well as the Ca²⁺ uptake blocker ruthenium red, fully prevented the Cis-5- and Myr-induced decrease in ΔΨ_m in Ca²⁺ -loaded mitochondria, suggesting, respectively, the induction of MPT pore opening and the contribution of Ca²⁺ toward these effects. The findings of the present study indicate that the major long-chain fatty acids that accumulate in VLCAD deficiency disrupt mitochondrial bioenergetics and Ca²⁺ homeostasis, acting as uncouplers and metabolic inhibitors of oxidative phosphorylation, as well as inducers of MPT pore opening, in the heart at pathological relevant concentrations. It is therefore presumed that a disturbance of bioenergetics and Ca²⁺ homeostasis may contribute to the cardiac manifestations observed in VLCAD deficiency.

Mitochondrial β-oxidation of saturated fatty acids in humans

Mitochondrial β-oxidation of fatty acids generates acetyl-coA, NADH and FADH₂. Acyl-coA synthetases catalyze the binding of fatty acids to coenzyme A to form fatty acyl-coA thioesters, the first step in the intracellular metabolism of fatty acids. l-carnitine system facilitates the transport of fatty acyl-coA esters across the mitochondrial membrane. Carnitine palmitoyltransferase-1 transfers acyl groups from coenzyme A to l-carnitine, forming acyl-carnitine esters at the outer mitochondrial membrane. Carnitine acyl-carnitine translocase exchanges acyl-carnitine esters that enter the mitochondria, by free l-carnitine. Carnitine palmitoyltransferase-2 converts acyl-carnitine esters back to acyl-coA esters at the inner mitochondrial membrane. The β-oxidation pathway of fatty acyl-coA esters includes four reactions. Fatty acyl-coA dehydrogenases catalyze the introduction of a double bond at the C2 position, producing 2-enoyl-coA esters and reducing equivalents that are transferred to the respiratory chain via electron transferring flavoprotein. Enoyl-coA hydratase catalyzes the hydration of the double bond to generate a 3-l-hydroxyacyl-coA derivative. 3-l-hydroxyacyl-coA dehydrogenase catalyzes the formation of a 3-ketoacyl-coA intermediate. Finally, 3-ketoacyl-coA thiolase catalyzes the cleavage of the chain, generating acetyl-coA and a fatty acyl-coA ester two carbons shorter. Mitochondrial trifunctional protein catalyzes the three last steps in the β-oxidation of long-chain and medium-chain fatty acyl-coA esters while individual enzymes catalyze the β-oxidation of short-chain fatty acyl-coA esters. Clinical phenotype of fatty acid oxidation disorders usually includes hypoketotic hypoglycemia triggered by fasting or infections, skeletal muscle weakness, cardiomyopathy, hepatopathy, and neurological manifestations. Accumulation of non-oxidized fatty acids promotes their conjugation with glycine and l-carnitine and alternate ways of oxidation, such as ω-oxidation.

Very long-/ and long Chain-3-Hydroxy Acyl CoA Dehydrogenase Deficiency correlates with deregulation of the mitochondrial fusion/fission machinery

Children diagnosed with Long-Chain-3-Hydroxy-Acyl-CoA-Dehydrogenase-Deficiency (LCHADD) or Very-Long-Chain-3-Hydroxy-Acyl-CoA-Dehydrogenase-Deficiency (VLCADD) frequently present with hypertrophic cardiomyopathy or muscle weakness which is caused by the accumulation of fatty acid metabolites due to inactivating mutations in the mitochondrial trifunctional protein. By analyzing mitochondrial morphology we uncovered that mutations within the HADHA or the ACADVL gene not only affect fatty acid oxidation, but also cause significant changes in the DNM1L/MFN2 ratio leading to the significant accumulation of truncated and punctate mitochondria in contrast to network-like mitochondrial morphology in controls. These striking morphological abnormalities correlate with changes in OXPHOS, an imbalance in ROS levels, reduced mitochondrial respiration, reduced growth rates and significantly increased glucose uptake per cell, suggesting that HADHA and ACADVL mutations shift cellular energy household into glycolysis. Experiments using the NOX2-specific inhibitor Phox-I2 suggest that NOX2 is activated by accumulating long-chain fatty acids and generates ROS, which in turn changes mitochondrial morphology and activity. We thereby provide novel insights into the cellular energy household of cells from LCHADD/VLCADD patients and demonstrate for the first time a connection between fatty acid metabolism, mitochondrial morphology and ROS in patients with these rare genetic disorders.

Disruption of Slc52a3 gene causes neonatal lethality with riboflavin deficiency in mice

Homeostasis of riboflavin should be maintained by transporters. Previous in vitro studies have elucidated basic information about riboflavin transporter RFVT3 encoded by SLC52A3 gene. However, the contribution of RFVT3 to the maintenance of riboflavin homeostasis and the significance in vivo remain unclear. Here, we investigated the physiological role of RFVT3 using Slc52a3 knockout (Slc52a3−/−) mice. Most Slc52a3−/− mice died with hyperlipidemia and hypoglycemia within 48 hr after birth. The plasma and tissue riboflavin concentrations in Slc52a3−/− mice at postnatal day 0 were dramatically lower than those in wild-type (WT) littermates. Slc52a3−/− fetuses showed a lower capacity of placental riboflavin transport compared with WT fetuses. Riboflavin supplement during pregnancy and after birth reduced neonatal death and metabolic disorders. To our knowledge, this is the first report to indicate that Rfvt3 contributes to placental riboflavin transport, and that disruption of Slc52a3 gene caused neonatal mortality with hyperlipidemia and hypoglycemia owing to riboflavin deficiency.

The Biochemistry and Physiology of Mitochondrial Fatty Acid β-Oxidation and Its Genetic Disorders

Mitochondrial fatty acid β-oxidation (FAO) is the major pathway for the degradation of fatty acids and is essential for maintaining energy homeostasis in the human body. Fatty acids are a crucial energy source in the postabsorptive and fasted states when glucose supply is limiting. But even when glucose is abundantly available, FAO is a main energy source for the heart, skeletal muscle, and kidney. A series of enzymes, transporters, and other facilitating proteins are involved in FAO. Recessively inherited defects are known for most of the genes encoding these proteins. The clinical presentation of these disorders may include hypoketotic hypoglycemia, (cardio)myopathy, arrhythmia, and rhabdomyolysis and illustrates the importance of FAO during fasting and in hepatic and (cardio)muscular function. In this review, we present the current state of knowledge on the biochemistry and physiological functions of FAO and discuss the pathophysiological processes associated with FAO disorders.

Clinical outcome, biochemical and therapeutic follow-up in 14 Austrian patients with Long-Chain 3-Hydroxy Acyl CoA Dehydrogenase Deficiency (LCHADD)

Background

LCHADD is a long-fatty acid oxidation disorder with immediate symptoms and long-term complications. We evaluated data on clinical status, biochemical parameters, therapeutic regimens and outcome of Austrian LCHADD patients.

Study design

Clinical and outcome data including history, diagnosis, short- and long-term manifestations, growth, psychomotor development, hospitalizations, therapy of 14 Austrian patients with LCHADD were evaluated. Biochemically, we evaluated creatine kinase (CK) and acyl carnitine profiles.

Results

All LCHADD patients are homozygous for the common mutation. Three are siblings. Diagnosis was first established biochemically. Nine/14 (64%) were prematures, with IRDS occurring in six. In nine (64%), diagnosis was established through newborn screening, the remaining five (36%) were diagnosed clinically. Four pregnancies were complicated by HELLP syndrome, one by preeclampsia. In two, intrauterine growth retardation and placental insufficiency were reported. Five were diagnosed with hepatopathy at some point, seven with cardiomyopathy and eight with retinopathy, clinically relevant only in one patient. Polyneuropathy is only present in one. Three patients have a PEG, one is regularly fed via NG-tube. Growth is normal in all, as well as psychomotor development, except for two extremely premature girls. In 11 patients, 165 episodes with elevated creatine kinase concentrations were observed with 6-31 (median 14) per patient; three have shown no elevated CK concentrations. Median total carnitine on therapy was 19 μmol/l (range 11-61). For 14 patients, there have been 181 hospitalizations (median 9 per patient), comprising 1337 in-patient-days. All centres adhere to treatment with a fat-defined diet; patients have between 15% and 40% of their energy intake from fat (median 29%), out of which between 20% and 80% are medium-chain triglycerides (MCT) (median 62%). Four patients have been treated with heptanoate (C7).

Conclusion

Our data show LCHADD outcome can be favourable. Growth and psychomotor development is normal, except in two prematures. Frequency of CK measurements decreases with age, correlating with a decreasing number of hospitalizations. About 50% develop complications affecting different organ systems. There is no relevant difference between the patients treated in the respective centers. Concluding from single case reports, anaplerotic therapy with heptanoate should be further evaluated.

Bezafibrate in skeletal muscle fatty acid oxidation disorders: a randomized clinical trial

OBJECTIVE

To assess whether bezafibrate increases fatty acid oxidation (FAO) and lowers heart rate (HR) during exercise in patients with carnitine palmitoyltransferase (CPT) II and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies.

METHODS

This was a 3-month, randomized, double-blind, crossover study of bezafibrate in patients with CPT II (n = 5) and VLCAD (n = 5) deficiencies. Primary outcome measures were changes in FAO, measured with stable-isotope methodology and indirect calorimetry, and changes in HR during exercise.

RESULTS

Bezafibrate lowered low-density lipoprotein, triglyceride, and free fatty acid concentrations; however, there were no changes in palmitate oxidation, FAO, or HR during exercise.

CONCLUSION

Bezafibrate does not improve clinical symptoms or FAO during exercise in patients with CPT II and VLCAD deficiencies. These findings indicate that previous in vitro studies suggesting a therapeutic potential for fibrates in disorders of FAO do not translate into clinically meaningful effects in vivo.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that bezafibrate 200 mg 3 times daily is ineffective in improving changes in FAO and HR during exercise in adults with CPT II and VLCAD deficiencies.

Normal rates of whole-body fat oxidation and gluconeogenesis after overnight fasting and moderate-intensity exercise in patients with medium-chain acyl-CoA dehydrogenase deficiency

BACKGROUND

Impairments in gluconeogenesis have been implicated in the pathophysiology of fasting hypoglycemia in medium-chain acyl-CoA dehydrogenase deficiency. However, whole body glucose and fat metabolism have never been studied in vivo.

METHODS

Stable isotope methodology was applied to compare fat and glucose metabolism between four adult patients with MCADD and four matched controls both at rest and during 1.5 h of moderate-intensity exercise. Additionally, intramyocellular lipid and glycogen content and intramyocellular acylcarnitines were assessed in muscle biopsies collected prior to and immediately after cessation of exercise.

RESULTS

At rest, plasma FFA turnover was significantly higher in patients with MCADD, whereas the plasma FFA concentrations did not differ between patients and controls. Blood glucose kinetics did not differ between groups both at rest and during exercise. Palmitate and FFA turnover, total fat and carbohydrate oxidation rates, the use of muscle glycogen and muscle derived triglycerides during exercise did not differ between patients and controls. Plasma FFA oxidation rates were significantly lower in patients at the latter stages of exercise. Free carnitine levels in muscle were lower in patients, whereas no differences were detected in muscle acetylcarnitine levels.

CONCLUSIONS

Whole-body or skeletal muscle glucose and fat metabolism were not impaired in adult patients with MCADD. This implies that MCADD is not rate limiting for energy production under the conditions studied. In addition, patients with MCADD have a higher FFA turnover rate after overnight fasting, which may stimulate ectopic lipid deposition and, as such, make them more susceptible for developing insulin resistance.

Impaired amino acid metabolism contributes to fasting-induced hypoglycemia in fatty acid oxidation defects

The importance of mitochondrial fatty acid β-oxidation (FAO) as a glucose-sparing process is illustrated by patients with inherited defects in FAO, who may present with life-threatening fasting-induced hypoketotic hypoglycemia. It is unknown why peripheral glucose demand outpaces hepatic gluconeogenesis in these patients. In this study, we have systematically addressed the fasting response in long-chain acyl-CoA dehydrogenase-deficient (LCAD KO) mice. We demonstrate that the fasting-induced hypoglycemia in LCAD KO mice was initiated by an increased glucose requirement in peripheral tissues, leading to rapid hepatic glycogen depletion. Gluconeogenesis did not compensate for the increased glucose demand, which was not due to insufficient hepatic glucogenic capacity but rather caused by a shortage in the supply of glucogenic precursors. This shortage in supply was explained by a suppressed glucose-alanine cycle, decreased branched-chain amino acid metabolism and ultimately impaired protein mobilization. We conclude that during fasting, FAO not only serves to spare glucose but is also indispensable for amino acid metabolism, which is essential for the maintenance of adequate glucose production.

Pathophysiology of fatty acid oxidation disorders and resultant phenotypic variability

Fatty acids are a major fuel for the body and fatty acid oxidation is particularly important during fasting, sustained aerobic exercise and stress. The myocardium and resting skeletal muscle utilise long-chain fatty acids as a major source of energy. Inherited disorders affecting fatty acid oxidation seriously compromise the function of muscle and other highly energy-dependent tissues such as brain, nerve, heart, kidney and liver. Such defects encompass a wide spectrum of clinical disease, presenting in the neonatal period or infancy with recurrent hypoketotic hypoglycaemic encephalopathy, liver dysfunction, hyperammonaemia and often cardiac dysfunction. In older children, adolescence or adults there is often exercise intolerance with episodic myalgia or rhabdomyolysis in association with prolonged aerobic exercise or other exacerbating factors. Some disorders are particularly associated with toxic metabolites that may contribute to encephalopathy, polyneuropathy, axonopathy and pigmentary retinopathy. The phenotypic diversity encountered in defects of fat oxidation is partly explained by genotype/phenotype correlation and certain identifiable environmental factors but there remain many unresolved questions regarding the complex interaction of genetic, epigenetic and environmental influences that dictate phenotypic expression. It is becoming increasingly clear that the view that most inherited disorders are purely monogenic diseases is a naive concept. In the future our approach to understanding the phenotypic diversity and management of patients will be more realistically achieved from a polygenic perspective.

Patients with medium-chain acyl-coenzyme a dehydrogenase deficiency have impaired oxidation of fat during exercise but no effect of L-carnitine supplementation

BACKGROUND

It is not clear to what extent skeletal muscle is affected in patients with medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD). l-Carnitine is commonly used as a supplement in patients with MCADD, although its beneficial effect has not been verified.

DESIGN

We investigated (1) fuel utilization during prolonged low-intensity exercise in patients with MCADD and (2) the influence of 4 weeks of oral l-carnitine supplementation on fuel utilization during exercise.

METHODS

Four asymptomatic patients with MCADD and 11 untrained, healthy, age- and sex-matched control subjects were included. The subjects performed a 1-hour cycling test at a constant workload corresponding to 55% of Vo2max, while fat and carbohydrate metabolism was assessed, using the stable isotope technique and indirect calorimetry. The patients ingested 100 mg/kg/d of l-carnitine for 4 weeks, after which the cycling tests were repeated.

RESULTS

At rest, palmitate oxidation and total fatty acid oxidation (FAO) rates were similar in patients and healthy control subjects. During constant workload cycling, palmitate oxidation and FAO rates increased in both groups, but increased 2 times as much in healthy control subjects as in patients (P = .007). Palmitate oxidation and FAO rates were unchanged by the l-carnitine supplementation.

CONCLUSION

Our results indicate that patients with MCADD have an impaired ability to increase FAO during exercise but less so than that observed in patients with a number of other disorders of fat oxidation, which explains the milder skeletal muscle phenotype in MCADD. The use of carnitine supplementation in MCADD cannot be supported by the present findings.

Disrupted fat distribution and composition due to medium-chain triglycerides in mice with a β-oxidation defect

BACKGROUND

Because of the enhanced recognition of inherited long-chain fatty acid oxidation disorders by worldwide newborn screening programs, an increasing number of asymptomatic patients receive medium-chain triglyceride (MCT) supplements to prevent the development of cardiomyopathy and myopathy.

OBJECTIVE

MCT supplementation has been recognized as a safe dietary intervention, but long-term observations into later adulthood are still not available. We investigated the consequences of a prolonged MCT diet on abdominal fat distribution and composition and on liver fat.

DESIGN

Mice with very-long-chain acyl-coenzyme A dehydrogenase deficiency (VLCAD(-/-)) were supplemented for 1 y with a diet in which MCTs replaced long-chain triglycerides without increasing the total fat content. The dietary effects on abdominal fat accumulation and composition were analyzed by in vivo (1)H- and (13)C-magnetic resonance spectroscopy (9.4 Tesla).

RESULTS

After 1 y of MCT supplementation, VLCAD(-/-) mice accumulated massive visceral fat and had a dramatic increase in the concentration of serum free fatty acids. Furthermore, we observed a profound shift in body triglyceride composition, ie, concentrations of physiologically important polyunsaturated fatty acids dramatically decreased. (1)H-Magnetic resonance spectroscopy analysis and histologic evaluation of the liver also showed pronounced fat accumulation and marked oxidative stress.

CONCLUSION

Although the MCT-supplemented diet has been reported to prevent the development of cardiomyopathy and skeletal myopathy in fatty acid oxidation disorders, our data show that long-term MCT supplementation results in a severe clinical phenotype similar to that of nonalcoholic steatohepatitis and the metabolic syndrome.

A general introduction to the biochemistry of mitochondrial fatty acid β-oxidation

Over the years, the mitochondrial fatty acid β-oxidation (FAO) pathway has been characterised at the biochemical level as well as the molecular biological level. FAO plays a pivotal role in energy homoeostasis, but it competes with glucose as the primary oxidative substrate. The mechanisms behind this so-called glucose-fatty acid cycle operate at the hormonal, transcriptional and biochemical levels. Inherited defects for most of the FAO enzymes have been identified and characterised and are currently included in neonatal screening programmes. Symptoms range from hypoketotic hypoglycaemia to skeletal and cardiac myopathies. The pathophysiology of these diseases is still not completely understood, hampering optimal treatment. Studies of patients and mouse models will contribute to our understanding of the pathogenesis and will ultimately lead to better treatment.

Mitochondrial function and insulin resistance in overweight and normal-weight children

BACKGROUND

Obesity has become an epidemic in children, associated with an increase in insulin resistance and metabolic dysfunction. Mitochondrial function is known to be an important determinant of glucose metabolism in adults. However, little is known about the relationship between mitochondrial function and obesity, insulin resistance, energy expenditure, and pubertal development in children.

METHODS

Seventy-four participants, 37 overweight (> or = 85th percentile body mass index for age and sex) and 37 normal-weight (< 85th percentile) without personal or family history of diabetes mellitus were enrolled. Subjects were evaluated with an oral glucose tolerance test, metabolic markers, resting energy expenditure, Tanner staging, and (31)P magnetic resonance spectroscopy of skeletal muscle for mitochondrial function.

RESULTS

Overweight and normal-weight children showed no difference in muscle ATP synthesis [phosphocreatine (PCr) recovery after exercise] (32.4 +/- 2.3 vs. 34.1 +/- 2.1, P = 0.58). However, insulin-resistant children had significantly prolonged PCr recovery when compared with insulin-sensitive children, by homeostasis model assessment for insulin resistance quartile (ANOVA, P = 0.04). Similarly, insulin-resistant overweight children had PCr recovery that was prolonged compared with insulin-sensitive overweight children (P = 0.01). PCr recovery was negatively correlated with resting energy expenditure in multivariate modeling (P = 0.03). Mitochondrial function worsened during mid-puberty in association with insulin resistance.

CONCLUSION

Reduced skeletal muscle mitochondrial oxidative phosphorylation, assessed by PCr recovery, is associated with insulin resistance and an altered metabolic phenotype in children. Normal mitochondrial function may be associated with a healthier metabolic phenotype in overweight children. Further studies are needed to investigate the long-term physiological consequences and potential treatment strategies targeting children with reduced mitochondrial function.

Treatment recommendations in long-chain fatty acid oxidation defects: consensus from a workshop

Published data on treatment of fatty acid oxidation defects are scarce. Treatment recommendations have been developed on the basis of observations in 75 patients with long-chain fatty acid oxidation defects from 18 metabolic centres in Central Europe. Recommendations are based on expert practice and are suggested to be the basis for further multicentre prospective studies and the development of approved treatment guidelines. Considering that disease complications and prognosis differ between different disorders of long-chain fatty acid oxidation and also depend on the severity of the underlying enzyme deficiency, treatment recommendations have to be disease-specific and depend on individual disease severity. Disorders of the mitochondrial trifunctional protein are associated with the most severe clinical picture and require a strict fat-reduced and fat-modified (medium-chain triglyceride-supplemented) diet. Many patients still suffer acute life-threatening events or long-term neuropathic symptoms despite adequate treatment, and newborn screening has not significantly changed the prognosis for these severe phenotypes. Very long-chain acyl-CoA dehydrogenase deficiency recognized in neonatal screening, in contrast, frequently has a less severe disease course and dietary restrictions in many patients may be loosened. On the basis of the collected data, recommendations are given with regard to the fat and carbohydrate content of the diet, the maximal length of fasting periods and the use of l-carnitine in long-chain fatty acid oxidation defects.

Management and outcome in 75 individuals with long-chain fatty acid oxidation defects: results from a workshop

At present, long-chain fatty acid oxidation (FAO) defects are diagnosed in a number of countries by newborn screening using tandem mass spectrometry. In the majority of cases, affected newborns are asymptomatic at time of diagnosis and acute clinical presentations can be avoided by early preventive measures. Because evidence-based studies on management of long-chain FAO defects are lacking, we carried out a retrospective analysis of 75 patients from 18 metabolic centres in Germany, Switzerland, Austria and the Netherlands with special regard to treatment and disease outcome. Dietary treatment is effective in many patients and can prevent acute metabolic derangements and prevent or reverse severe long-term complications such as cardiomyopathy. However, 38% of patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency had intermittent muscle weakness and pain despite adhering to therapy. Seventy-six per cent of patients with disorders of the mitochondrial trifunctional protein (TFP)-complex including long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, had long-term myopathic symptoms. Of these, 21% had irreversible peripheral neuropathy and 43% had retinopathy. The main principle of treatment was a fat-reduced and fat-modified diet. Fat restriction differed among patients with different enzyme defects and was strictest in disorders of the TFP-complex. Patients with a medium-chain fat-based diet received supplementation of essential long-chain fatty acids. l-Carnitine was supplemented in about half of the patients, but in none of the patients with VLCAD deficiency identified by newborn screening. In summary, in this cohort the treatment regimen was adapted to the severity of the underlying enzyme defect and thus differed among the group of long-chain FAO defects.

Atypical presentation of VLCAD deficiency associated with a novel ACADVL splicing mutation

Very long chain acyl-CoA dehydrogenase (VLCAD) deficiency is an autosomal recessive inborn error of metabolism characterized by impaired mitochondrial beta-oxidation of fatty acids with a chain length between 14 and 18 carbons. While expansion of newborn screening has improved our ability to detect VLCAD deficiency in early childhood, the late-onset form of the disease still presents a significant diagnostic challenge. We report a 20-year-old female with VLCAD deficiency who first presented in infancy with hypoketotic hypoglycemia. In childhood the patient developed complex partial seizures that were aggravated by Lamotrigine treatment. The clinical course in early adulthood was complicated by recurrent, often unprovoked, episodes of rhabdomyolysis and myoglobinuria. In addition, she suffered from chronic myalgia, muscle weakness, and diffuse abdominal tenderness. A muscle biopsy revealed accumulation of fat droplets. Her acylcarnitine profile showed significantly elevated C14, C14:1, C16, and C18-carnitines. Sequence analysis of ACADVL revealed a heterozygous recurrent mutation c.848T>C (p.V283A) and a heterozygous novel splice mutation c.879-8T>A that results in the inclusion of six nucleotides from intron 9 into the transcript sequence. The molecular characterization of this novel mutation and its correlation with the clinical phenotype are discussed.

Task force guidelines handbook: EFNS guidelines on diagnosis and management of fatty acid mitochondrial disorders

Guidelines in the diagnosis and current dietary treatment of long-chain fatty acid (LCFA) defects have been collected according to evidence-based medicine. Since the identification of carnitine and carnitine palmitoyltransferase deficiency more than 25 years ago, nearly every enzymatic step required for beta-oxidation has been associated with an inherited metabolic disorder. These disorders effectively preclude the use of body fat as an energy source. Clinical consequences can range from no symptoms to severe manifestations including cardiomyopathy, hypoglycaemia, peripheral neuropathy and sudden death. A diet high in carbohydrates, diet with medium-chain triglycerides and reduced amount of LCFA has a beneficial effect (class IV evidence) and in appropriate deficiency states carnitine and riboflavin are used (good practice points).

The effect of dantrolene sodium in Very Long Chain Acyl-CoA Dehydrogenase Deficiency

We present a patient, who experienced recurrent episodes of rhabdomyolysis. Her beneficial response to treatment with dantrolene sodium was previously reported. Adult onset Very Long Chain Acyl-CoA Dehydrogenase (VLCAD) deficiency has been diagnosed only recently. In adults, VLCAD deficiency results in recurrent fasting-, exercise-, or infection-induced muscle stiffness, muscle pain and myoglobinuria caused by rhabdomyolysis. This case illustrates for the first time the beneficial effect of dantrolene in VLCAD deficiency. We discuss the therapeutic mechanism of dantrolene sodium and its possible role as additional treatment modality for patients with VLCAD deficiency.

Prolonged exercise testing in two children with a mild Multiple Acyl-CoA-Dehydrogenase deficiency

BACKGROUND: Multiple Acyl-CoA-Dehydrogenase deficiency (MADD) is an inherited metabolic disorder characterized by impaired oxidation of fatty acids and some amino acids. METHODS: We were interested whether children with MADD could tolerate a prolonged low-intensity exercise test and if this test could have any additional diagnostic value. Therefore, we performed a maximal exercise test and a low-intensity prolonged exercise test in 2 patients with MADD and in 5 control subjects. During a prolonged exercise test the subjects exercised on a cycle ergometer at a constant workload of 30% of their maximum for 90 minutes and heart rate, oxygen uptake, fuel utilization and changes in relevant blood and urinary parameters were monitored. RESULTS: The tests were tolerated well. During the prolonged exercise test the fatty acid oxidation (FAO) was quite low compared to 5 control subjects, while characteristic metabolites of MADD appeared in plasma and urine. CONCLUSION: We suggest that the prolonged exercise test could be of diagnostic importance and might replace the fasting test as a diagnostic procedure in some cases, particularly in patients with anamnestic signs of intolerance for prolonged exercise.

Fuel utilization in subjects with carnitine palmitoyltransferase 2 gene mutations

Patients with the myopathic form of carnitine palmitoyltransferase II (CPT II) deficiency typically experience muscle pain, cramps, and myoglobinuria during prolonged exercise. It has been suggested that carriers of CPT2 gene mutations also may have milder clinical symptoms, but fatty acid oxidation (FAO) has never been investigated in vivo in this group. We studied fuel utilization by indirect calorimetry and stable isotope methodology in four patients with CPT II deficiency, three subjects who carried one CPT2 gene mutation, and five healthy control subjects. Cycle exercise at a constant workload of 50% of maximal oxygen uptake capacity was used to facilitate FAO. We found that in vivo oxidation of long-chain fatty acids was normal at rest but severely impaired during prolonged, low-intensity exercise in patients with CPT II deficiency, and that two of the single CPT2 gene mutation carriers, who displayed symptoms of CPT II deficiency, had an FAO comparable with the patients. These results indicate that residual CPT II activity is sufficient to maintain long-chain FAO at rest in CPT II deficiency but not to increase FAO during exercise. The findings also suggest that single CPT2 gene mutations may exert a dominant-negative effect on the tetrameric CPT II protein.