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

Assessing the quality and value of metabolic chart data for capturing core outcomes for pediatric medium-chain acyl-CoA dehydrogenase (MCAD) deficiency

BACKGROUND

Generating rigorous evidence to inform care for rare diseases requires reliable, sustainable, and longitudinal measurement of priority outcomes. Having developed a core outcome set for pediatric medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, we aimed to assess the feasibility of prospective measurement of these core outcomes during routine metabolic clinic visits.

METHODS

We used existing cohort data abstracted from charts of 124 children diagnosed with MCAD deficiency who participated in a Canadian study which collected data from birth to a maximum of 11 years of age to investigate the frequency of clinic visits and quality of metabolic chart data for selected outcomes. We recorded all opportunities to collect outcomes from the medical chart as a function of visit rate to the metabolic clinic, by treatment centre and by child age. We applied a data quality framework to evaluate data based on completeness, conformance, and plausibility for four core MCAD outcomes: emergency department use, fasting time, metabolic decompensation, and death.

RESULTS

The frequency of metabolic clinic visits decreased with increasing age, from a rate of 2.8 visits per child per year (95% confidence interval, 2.3-3.3) among infants 2 to 6 months, to 1.0 visit per child per year (95% confidence interval, 0.9-1.2) among those ≥ 5 years of age. Rates of emergency department visits followed anticipated trends by child age. Supplemental findings suggested that some emergency visits occur outside of the metabolic care treatment centre but are not captured. Recommended fasting times were updated relatively infrequently in patients' metabolic charts. Episodes of metabolic decompensation were identifiable but required an operational definition based on acute manifestations most commonly recorded in the metabolic chart. Deaths occurred rarely in these patients and quality of mortality data was not evaluated.

CONCLUSIONS

Opportunities to record core outcomes at the metabolic clinic occur at least annually for children with MCAD deficiency. Methods to comprehensively capture emergency care received at outside institutions are needed. To reduce substantial heterogeneous recording of core outcome across treatment centres, improved documentation standards are required for recording of recommended fasting times and a consensus definition for metabolic decompensations needs to be developed and implemented.

Medium-chain Acyl-COA dehydrogenase deficiency: Pathogenesis, diagnosis, and treatment

INTRODUCTION

Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCADD) is the most common inherited metabolic disorder of β-oxidation. Patients with MCADD present with hypoketotic hypoglycemia, which may quickly progress to lethargy, coma, and death. Prognosis for MCADD patients is highly promising once a diagnosis has been established, though management strategies may vary depending on the severity of illness and the presence of comorbidities.

METHODS AND RESULTS

Given the rapid developments in the world of gene therapy and implementation of newborn screening for inherited metabolic disorders, the provision of concise and contemporary knowledge of MCADD is essential for clinicians to effectively manage patients. Thus, this review aims to consolidate current information for physicians on the pathogenesis, diagnostic tools, and treatment options for MCADD patients.

CONCLUSION

MCADD is a commonly inherited metabolic disease with serious implications for health outcomes, particularly in children, that may be successfully managed with proper intervention.

Energy metabolism during exercise in patients with β-enolase deficiency (GSDXIII)

AIM

To investigate the in vivo skeletal muscle metabolism in patients with β-enolase deficiency (GSDXIII) during exercise, and the effect of glucose infusion.

METHODS

Three patients with GSDXIII and 10 healthy controls performed a nonischemic handgrip test as well as an incremental cycle ergometer test measuring maximal oxidative consumption (VO2max) and a 1-hour submaximal cycle test at an intensity of 65% to 75% of VO2max. The patients repeated the submaximal exercise after 2 days, where they received a 10% iv-glucose supplementation.

RESULTS

Patients had lower VO2max than healthy controls, and two of three patients had to stop prematurely during the intended 1-hour submaximal exercise test. During nonischemic forearm test, all patients were able to produce lactate in normal amounts. Glucose infusion had no effect on patients' exercise capacity.

CONCLUSIONS

Patients with GSDXIII experience exercise intolerance and episodes of myoglobinuria, even to the point of needing renal dialysis, but still retain an almost normal anaerobic metabolic response to submaximal intensity exercise. In accordance with this, glucose supplementation did not improve exercise capacity. The findings show that GSDXIII, although causing episodic rhabdomyolysis, is one of the mildest metabolic myopathies affecting glycolysis.

Management Principles for Acute Illness in Patients With Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency

Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) is a fatty acid oxidation disorder in which the patient is unable to break down fats to produce energy. This disorder places children at risk for metabolic decompensation during periods of stress, such as routine childhood illnesses. The intent of this clinical report is to provide pediatricians with additional information regarding the acute clinical care of patients with MCADD. Although each patient with MCADD will still be expected to have a primary metabolic physician, the involvement of the primary care provider is crucial as well. Appropriate treatment of children with MCADD can lead to avoidance of morbidity and mortality.

Diagnostic challenges in metabolic myopathies

INTRODUCTION

Metabolic myopathies comprise a clinically etiological diverse group of disorders caused by defects in cellular energy metabolism including the breakdown of carbohydrates and fatty acids, which include glycogen storage diseases and fatty acid oxidation disorders. Their wide clinical spectrum ranges from infantile severe multisystemic disorders to adult-onset myopathies. To suspect in adults these disorders, clinical features such as exercise intolerance and recurrent myoglobinuria need investigation while another group presents fixed weakness and cardiomyopathy as a clinical pattern.

AREAS COVERED

In metabolic myopathies, clinical manifestations are important to guide diagnostic tests used in order to lead to the correct diagnosis. The authors searched in literature the most recent techniques developed. The authors present an overview of the most common phenotypes of Pompe disease and what is currently known about the mechanism of ERT treatment. The most common disorders of lipid metabolism are overviewed, with their possible dietary or supplementary treatments.

EXPERT COMMENTARY

The clinical suspicion is the clue to conduct in-depth investigations in suspected cases of metabolic myopathies that lead to the final diagnosis with biochemical molecular studies and often nowadays by the use of Next Generation Sequencing (NGS) to determine gene mutations.

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.

Impaired Fat Oxidation During Exercise in Long-Chain Acyl-CoA Dehydrogenase Deficiency Patients and Effect of IV-Glucose

CONTEXT

Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency (LCHADD) affects oxidation of long-chain fatty acids (FAO) and is associated with risk of metabolic crises and episodic rhabdomyolysis.

CASE DESCRIPTION

We present the cases of two patients with LCHADD. Patient 1 (male, 26 years old) was severely affected by muscle weakness and neuropathy. He was diagnosed at age 20 years and was nonadherent to standard dietary management. MRI revealed significant fat replacement of muscle in both calves. Patient 2 (female, 15 years old) was diagnosed at age 1 year. She had no muscle weakness and was compliant with the recommended diet. Compared with healthy persons, both patients had reduced FAO and palmitate oxidation, measured with indirect calorimetry and stable isotope technique during a submaximal cycle ergometer test. Patient 2 had some residual capacity to increase FAO and a compensatory higher carbohydrate oxidation, which ensured a near-normal exercise capacity. Patient 1 was unable to increase FAO and could only complete 23 minutes of exercise, vs 60 minutes by patient 2 and healthy persons. In both, 10% IV infusion of glucose (IV-glucose) during exercise increased carbohydrate oxidation slightly, but endurance was not improved, which likely relates to the fixed weakness in patient 1 and because the residual FAO was suppressed by the glucose infusion in both.

CONCLUSION

The two patients illustrate that FAO is impaired and carbohydrate oxidation is elevated during exercise in patients affected by LCHADD, compared with healthy persons, but IV-glucose has no beneficial effect on exercise tolerance in LCHADD.

Metabolic lipid muscle disorders: biomarkers and treatment

Lipid storage myopathies (LSMs) are metabolic disorders of the utilization of fat in muscles due to several different defects. In this review, a molecular update of LSMs is presented and recent attempts of finding treatment options are discussed. The main topics discussed are: primary carnitine deficiency, riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency, neutral lipid storage disorders and carnitine palmitoyl transferase deficiency. The most frequent presentations and genetic abnormalities are summarized. We present their diagnosis utilizing biomedical and morphological biomarkers and possible therapeutic interventions. The treatment of these metabolic disorders is a subject of active translational research but appears, in some cases, still elusive.

Impaired fat oxidation during exercise in multiple acyl-CoA dehydrogenase deficiency

We investigated the in vivo skeletal muscle metabolism in patients with multiple acyl-CoA dehydrogenase deficiency (MADD) during exercise, and the effect of a glucose infusion. Two adults with MADD on riboflavin and l-carnitine treatment and 10 healthy controls performed an incremental exercise test measuring maximal oxidative capacity (VO2max) and a submaximal exercise test (≤1 hour) on a cycle ergometer. During submaximal exercise, we studied fat and carbohydrate oxidation, using stable isotope tracer methodology and indirect calorimetry. On another day, the patients repeated the submaximal exercise receiving a 10% glucose infusion. The patients had a lower VO2max than controls and stopped the submaximal exercise test at 51 and 58 minutes due to muscle pain and exhaustion. The exercise-induced increase in total fatty acid oxidation was blunted in the patients (7.1 and 1.1 vs 12 ± 4 μmol × kg-1 × min-1 in the healthy controls), but total carbohydrate oxidation was higher (67 and 63 vs 25 ± 11 μmol × kg-1 × min-1 in controls). With glucose infusion, muscle pain decreased and average heart rate during exercise dropped in both patients from 124 to 119 bpm and 138 to 119 bpm. We demonstrate that exercise intolerance in MADD-patients relates to an inability to increase fat oxidation appropriately during exercise, which is compensated partially by an increase in carbohydrate metabolism.

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.

Consequences of Late-Stage Non-Small-Cell Lung Cancer Cachexia on Muscle Metabolic Processes

INTRODUCTION

The loss of muscle is common in patients with advanced non-small-cell lung cancer (NSCLC) and contributes to the high morbidity and mortality of this group. The exact mechanisms behind the muscle loss are unclear.

PATIENTS AND METHODS

To investigate this, 4 patients with stage IV NSCLC who met the clinical definitions for sarcopenia and cachexia were recruited, along with 4 age-matched healthy volunteers. After an overnight fast, biopsy specimens were obtained from the vastus lateralis, and the key components associated with inflammation and the control of muscle protein, carbohydrate, and fat metabolism were assessed.

RESULTS

Compared with the healthy volunteers, significant increases in mRNA levels for interleukin-6 and NF-κB signaling and lower intramyocellular lipid content in slow-twitch fibers were observed in NSCLC patients. Although a significant decrease in phosphorylation of the mechanistic target of rapamycin (mTOR) signaling protein 4E-BP1 (Ser⁶⁵) was observed, along with a trend toward reduced p70 S6K (Thr³⁸⁹) phosphorylation (P = .06), no difference was found between groups for the mRNA levels of MAFbx (muscle atrophy F box) and MuRF1 (muscle ring finger protein 1), chymotrypsin-like activity of the proteasome, or protein levels of multiple proteasome subunits. Moreover, despite decreases in intramyocellular lipid content, no robust changes in mRNA levels for key proteins involved in insulin signaling, glycolysis, oxidative metabolism, or fat metabolism were observed.

CONCLUSION

These findings suggest that examining the contribution of suppressed mTOR signaling in the loss of muscle mass in late-stage NSCLC patients is warranted and reinforces our need to understand the potential contribution of impaired fat metabolism and muscle protein synthesis in the etiology of cancer cachexia.

Is L-Carnitine Supplementation Beneficial in 3-Methylcrotonyl-CoA Carboxylase Deficiency?

BACKGROUND

3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCd) is an autosomal recessive disorder in the catabolism of leucine. In the present study, we investigated the current and prior medical condition of patients with 3-MCCd in the Faroe Islands and their carnitine levels in blood, urine and muscle tissue with and without L-carnitine supplementation to evaluate the current treatment strategy of not recommending L-carnitine supplementation to Faroese 3-MCCd patients.

METHODS

Blood and urine samples and muscle biopsies were collected from patients at inclusion and at 3 months. Eight patients received L-carnitine supplementation when recruited; five did not. Included patients who received supplementation were asked to stop L-carnitine, the others were asked to initiate L-carnitine supplementation during the study. Symptoms were determined by review of hospital medical records and questionnaires answered at baseline and after the intervention.

RESULTS

The prevalence of 3-MCCd in the Faroe Islands was 1:2,400, the highest reported worldwide. All patients were homozygous for the MCCC1 mutation c.1526delG. When not administered L-carnitine, the 3-MCCd patients (n = 13) had low plasma and muscle free carnitine levels, 6.9 (SD 1.4) μmol/L and 785 (SD 301) nmol/g wet weight, respectively. L-Carnitine supplementation increased muscle and plasma carnitine levels to a low-normal range, 25.5 (SD 10.9) μmol/L and 1,827 (SD 523) nmol/g wet weight, p < 0.01, respectively. Seven of the thirteen 3-MCCd subjects suffered from self-reported fatigue with some alleviation after L-carnitine supplementation.

CONCLUSION

3-MCCd is common in the Faroe Islands. Some symptomatic 3-MCCd patients may benefit biochemically and clinically from L-carnitine supplementation, a more general recommendation cannot be given.

Carnitine levels in skeletal muscle, blood, and urine in patients with primary carnitine deficiency during intermission of L-carnitine supplementation

BACKGROUND

Primary carnitine deficiency (PCD) is a disorder of fatty acid oxidation with a high prevalence in the Faroe Islands. Only patients homozygous for the c.95A>G (p.N32S) mutation have displayed severe symptoms in the Faroese patient cohort. In this study, we investigated carnitine levels in skeletal muscle, plasma, and urine as well as renal elimination kinetics before and after intermission with L-carnitine in patients homozygous for c.95A>G.

METHODS

Five male patients homozygous for c.95A>G were included. Regular L-carnitine supplementation was stopped and the patients were observed during five days. Blood and urine were collected throughout the study. Skeletal muscle biopsies were obtained at 0, 48, and 96 h.

RESULTS

Mean skeletal muscle free carnitine before discontinuation of L-carnitine was low, 158 nmol/g (SD 47.4) or 5.4% of normal. Mean free carnitine in plasma (fC0) dropped from 38.7 (SD 20.4) to 6.3 (SD 1.7) μmol/L within 96 h (p < 0.05). Mean T 1/2 following oral supplementation was approximately 9 h. Renal reabsorption of filtered carnitine following oral supplementation was 23%. The level of mean free carnitine excreted in urine correlated (R (2) = 0.78, p < 0.01) with fC0 in plasma.

CONCLUSION

Patients homozygous for the c.95A>G mutation demonstrated limited skeletal muscle carnitine stores despite long-term high-dosage L-carnitine supplementation. Exacerbated renal excretion resulted in a short T 1/2 in plasma carnitine following the last oral dose of L-carnitine. Thus a treatment strategy of minimum three daily separate doses of L-carnitine is recommended, while intermission with L-carnitine treatment might prove detrimental.

Genetics of type 2 diabetes: insights into the pathogenesis and its clinical application

With rapidly increasing prevalence, diabetes has become one of the major causes of mortality worldwide. According to the latest studies, genetic information makes substantial contributions towards the prediction of diabetes risk and individualized antidiabetic treatment. To date, approximately 70 susceptibility genes have been identified as being associated with type 2 diabetes (T2D) at a genome-wide significant level (P < 5 × 10⁻⁸). However, all the genetic loci identified so far account for only about 10% of the overall heritability of T2D. In addition, how these novel susceptibility loci correlate with the pathophysiology of the disease remains largely unknown. This review covers the major genetic studies on the risk of T2D based on ethnicity and briefly discusses the potential mechanisms and clinical utility of the genetic information underlying T2D.

Skeletal muscle-specific CPT1 deficiency elevates lipotoxic intermediates but preserves insulin sensitivity

OBJECTIVE

By specific knockout of carnitine palmitoyl transferase 1b (CPT1b) in skeletal muscles, we explored the effect of CPT1b deficiency on lipids and insulin sensitivity.

METHODS

Mice with specific knockout of CPT1b in skeletal muscles (CPT1b M-/-) were used for the experiment group, with littermate C57BL/6 as controls (CPT1b). General and metabolic profiles were measured and compared between groups. mRNA expression and CPT1 activity were measured in skeletal muscle tissues and compared between groups. Mitochondrial fatty acid oxidation (FAO), triglycerides (TAGs), diglycerides (DAGs), and ceramides were examined in skeletal muscles in two groups. Phosphorylated AKT (pAkt) and glucose transporter 4 (Glut4) were determined with real-time polymerase chain reaction (RT-PCR). Insulin tolerance test, glucose tolerance test, and pyruvate oxidation were performed in both groups.

RESULTS

CPT1b M-/- model was successfully established, with impaired muscle CPT1 activity. Compared with CPT1b mice, CPT1b M-/- mice had similar food intake but lower body weight or fat mass and higher lipids but similar glucose or insulin levels. Their mitochondrial FAO of skeletal muscles was impaired. There were lipids accumulations (TAGs, DAGs, and ceramides) in skeletal muscle. However, pAkt and Glut4, insulin sensitivity, glucose tolerance, and pyruvate oxidation were preserved.

CONCLUSION

Skeletal muscle-specific CPT1 deficiency elevates lipotoxic intermediates but preserves insulin sensitivity.