Disorders of mitochondrial long-chain fatty acid oxidation

Pathophysiological roles of the serum acylcarnitine level and acylcarnitine/free carnitine ratio in patients with cardiovascular diseases

Introduction

L-carnitine exerts protective effects, such as maintaining mitochondrial functions and decreasing reactive oxygen species, while acylcarnitine (AC) is linked to the development of heart failure and atherosclerosis.

Hypothesis

Serum carnitines play important pathophysiological roles in cardiovascular diseases.

Methods

Pre-operative biochemical data were obtained from 117 patients (71 men, average age 69.9 years) who underwent surgery for cardiovascular diseases. Measurements included pre-operative biochemical data including estimated glomerular filtration rate (eGFR), physical functions, skeletal muscle mass index (SMI) measured by bioelectrical impedance analysis, anterior thigh muscle thickness (MTh) measured by ultrasound, and routine echocardiography. Carnitine components were measured with the enzyme cycling method. Muscle wasting was diagnosed based on the Asian Working Group for Sarcopenia criteria.

Results

Plasma brain natriuretic peptide (BNP) level was correlated with serum free carnitine (FC) and AC level, and the acylcarnitine/free carnitine ratio (AC/FC). AC/FC was elevated with stage of chronic kidney disease. In multivariate analysis, log (eGFR) and log (BNP) were extracted as independent factors to define log (serum AC) (eGFR: β = 0.258, p = 0.008; BNP: β = 0.273, p = 0.011), even if corrected for age, sex and body mass index. AC/FC was negatively correlated with hand-grip strength (r = -0.387, p = 0.006), SMI (r = -0.314, p = 0.012), and anterior thigh MTh (r = -0.340, p = 0.014) in men.

Conclusions

A significant association between serum AC level and AC/FC, and chronic kidney disease and heart failure exists in patients with cardiovascular diseases who have undergone cardiovascular surgery. Skeletal muscle loss and muscle wasting are also linked to the elevation of serum AC level and AC/FC.

Circulating long chain acylcarnitines and outcomes in diabetic heart failure: an HF-ACTION clinical trial substudy

BACKGROUND

Whether differences in circulating long chain acylcarnitines (LCAC) are seen in heart failure (HF) patients with and without diabetes mellitus (DM), and whether these biomarkers report on exercise capacity and clinical outcomes, remains unknown. The objective of the current study was to use metabolomic profiling to identify biomarkers that report on exercise capacity, clinical outcomes, and differential response to exercise in HF patients with and without DM.

METHODS

Targeted mass spectrometry was used to quantify metabolites in plasma from participants in the heart failure: a controlled trial investigating outcomes of exercise training (HF-ACTION) trial. Principal components analysis was used to identify 12 uncorrelated factors. The association between metabolite factors, diabetes status, exercise capacity, and time to the primary clinical outcome of all-cause mortality or all-cause hospitalization was assessed.

RESULTS

A total of 664 participants were included: 359 (54%) with DM. LCAC factor levels were associated with baseline exercise capacity as measured by peak oxygen consumption (beta 0.86, p  =  2 × 10-7, and were differentially associated in participants with and without DM (beta 1.58, p  =  8  ×  10-8 vs. 0.67, p  =  9  ×  10-4, respectively; p value for interaction  =  0.012). LCAC levels changed to a lesser extent in participants with DM after exercise (mean ∆ 0.09, p  =  0.24) than in those without DM (mean ∆ 0.16, p  =  0.08). In univariate and multivariate modeling, LCAC factor levels were associated with time to the primary outcome (multivariate HR 0.80, p  =  2.74  ×  10-8), and were more strongly linked to outcomes in diabetic participants (HR 0.64, p  =  3.21  ×  10-9 v. HR 0.90, p  =  0.104, p value for interaction  =  0.001). When analysis was performed at the level of individual metabolites, C16, C16:1, C18, and C18:1 had the greatest associations with both exercise capacity and outcomes, with higher levels associated with worse outcomes. Similar associations with time to the primary clinical outcome were not found in a control group of patients without HF from the CATHeterization GENetics (CATHGEN) study.

CONCLUSIONS

LCAC biomarkers are associated with exercise status and clinical outcomes differentially in HF patients with and without DM. Impaired fatty acid substrate utilization and mitochondrial dysfunction both at the level of the skeletal muscle and the myocardium may explain the decreased exercise capacity, attenuated response to exercise training, and poor clinical outcomes seen in patients with HF and DM. Trial Registration clinicaltrials.gov Identifier: NCT00047437.

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.

Comparative proteomic analyses of Duchenne muscular dystrophy and Becker muscular dystrophy muscles: changes contributing to preserve muscle function in Becker muscular dystrophy patients

BACKGROUND

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are characterized by muscle wasting leading to loss of ambulation in the first or third decade, respectively. In DMD, the lack of dystrophin hampers connections between intracellular cytoskeleton and cell membrane leading to repeated cycles of necrosis and regeneration associated with inflammation and loss of muscle ordered structure. BMD has a similar muscle phenotype but milder. Here, we address the question whether proteins at variance in BMD compared with DMD contribute to the milder phenotype in BMD, thus identifying a specific signature to be targeted for DMD treatment.

METHODS

Proteins extracted from skeletal muscle from DMD/BMD patients and young healthy subjects were either reduced and solubilized prior two-dimensional difference in gel electrophoresis/mass spectrometry differential analysis or tryptic digested prior label-free liquid chromatography with tandem mass spectrometry. Statistical analyses of proteins and peptides were performed by DeCyder and Perseus software and protein validation and verification by immunoblotting.

RESULTS

Proteomic results indicate minor changes in the extracellular matrix (ECM) protein composition in BMD muscles with retention of mechanotransduction signalling, reduced changes in cytoskeletal and contractile proteins. Conversely, in DMD patients, increased levels of several ECM cytoskeletal and contractile proteins were observed whereas some proteins of fast fibres and of Z-disc decreased. Detyrosinated alpha-tubulin was unchanged in BMD and increased in DMD although neuronal nitric oxide synthase was unchanged in BMD and greatly reduced in DMD. Metabolically, the tissue is characterized by a decrement of anaerobic metabolism both in DMD and BMD compared with controls, with increased levels of the glycogen metabolic pathway in BMD. Oxidative metabolism is severely compromised in DMD with impairment of malate shuttle; conversely, it is active in BMD supporting the tricarboxylic acid cycle and respiratory chain. Adipogenesis characterizes DMD, whereas proteins involved in fatty acids beta-oxidation are increased in BMD. Proteins involved in protein/amino acid metabolism, cell development, calcium handling, endoplasmic reticulum/sarcoplasmic reticulum stress response, and inflammation/immune response were increased in DMD. Both disorders are characterized by the impairment of N-linked protein glycosylation in the endoplasmic reticulum. Authophagy was decreased in DMD whereas it was retained in BMD.

CONCLUSIONS

The mechanosensing and metabolic disruption are central nodes of DMD/BMD phenotypes. The ECM proteome composition and the metabolic rewiring in BMD lead to preservation of energy levels supporting autophagy and cell renewal, thus promoting the retention of muscle function. Conversely, DMD patients are characterized by extracellular and cytoskeletal protein dysregulation and by metabolic restriction at the level of α-ketoglutarate leading to shortage of glutamate-derived molecules that over time triggers lipogenesis and lipotoxicity.

Hepatic lipid accumulation: cause and consequence of dysregulated glucoregulatory hormones

Fatty liver can be diet, endocrine, drug, virus or genetically induced. Independent of cause, hepatic lipid accumulation promotes systemic metabolic dysfunction. By acting as peroxisome proliferator-activated receptor (PPAR) ligands, hepatic non-esterified fatty acids upregulate expression of gluconeogenic, beta-oxidative, lipogenic and ketogenic genes, promoting hyperglycemia, hyperlipidemia and ketosis. The typical hormonal environment in fatty liver disease consists of hyperinsulinemia, hyperglucagonemia, hypercortisolemia, growth hormone deficiency and elevated sympathetic tone. These endocrine and metabolic changes further encourage hepatic steatosis by regulating adipose tissue lipolysis, liver lipid uptake, de novo lipogenesis (DNL), beta-oxidation, ketogenesis and lipid export. Hepatic lipid accumulation may be induced by 4 separate mechanisms: (1) increased hepatic uptake of circulating fatty acids, (2) increased hepatic de novo fatty acid synthesis, (3) decreased hepatic beta-oxidation and (4) decreased hepatic lipid export. This review will discuss the hormonal regulation of each mechanism comparing multiple physiological models of hepatic lipid accumulation. Nonalcoholic fatty liver disease (NAFLD) is typified by increased hepatic lipid uptake, synthesis, oxidation and export. Chronic hepatic lipid signaling through PPARgamma results in gene expression changes that allow concurrent activity of DNL and beta-oxidation. The importance of hepatic steatosis in driving systemic metabolic dysfunction is highlighted by the common endocrine and metabolic disturbances across many conditions that result in fatty liver. Understanding the mechanisms underlying the metabolic dysfunction that develops as a consequence of hepatic lipid accumulation is critical to identifying points of intervention in this increasingly prevalent disease state.

Metabolomic Profiling Identifies Novel Circulating Biomarkers of Mitochondrial Dysfunction Differentially Elevated in Heart Failure With Preserved Versus Reduced Ejection Fraction: Evidence for Shared Metabolic Impairments in Clinical Heart Failure

BACKGROUND

Metabolic impairment is an important contributor to heart failure (HF) pathogenesis and progression. Dysregulated metabolic pathways remain poorly characterized in patients with HF and preserved ejection fraction (HFpEF). We sought to determine metabolic abnormalities in HFpEF and identify pathways differentially altered in HFpEF versus HF with reduced ejection fraction (HFrEF).

METHODS AND RESULTS

We identified HFpEF cases, HFrEF controls, and no-HF controls from the CATHGEN study of sequential patients undergoing cardiac catheterization. HFpEF cases (N=282) were defined by left ventricular ejection fraction (LVEF) ≥45%, diastolic dysfunction grade ≥1, and history of HF; HFrEF controls (N=279) were defined similarly, except for having LVEF <45%. No-HF controls (N=191) had LVEF ≥45%, normal diastolic function, and no HF diagnosis. Targeted mass spectrometry and enzymatic assays were used to quantify 63 metabolites in fasting plasma. Principal components analysis reduced the 63 metabolites to uncorrelated factors, which were compared across groups using ANCOVA. In basic and fully adjusted models, long-chain acylcarnitine factor levels differed significantly across groups (P<0.0001) and were greater in HFrEF than HFpEF (P=0.0004), both of which were greater than no-HF controls. We confirmed these findings in sensitivity analyses using stricter inclusion criteria, alternative LVEF thresholds, and adjustment for insulin resistance.

CONCLUSIONS

We identified novel circulating metabolites reflecting impaired or dysregulated fatty acid oxidation that are independently associated with HF and differentially elevated in HFpEF and HFrEF. These results elucidate a specific metabolic pathway in HF and suggest a shared metabolic mechanism in HF along the LVEF spectrum.

Acylcarnitines--old actors auditioning for new roles in metabolic physiology

Perturbations in metabolic pathways can cause substantial increases in plasma and tissue concentrations of long-chain acylcarnitines (LCACs). For example, the levels of LCACs and other acylcarnitines rise in the blood and muscle during exercise, as changes in tissue pools of acyl-coenzyme A reflect accelerated fuel flux that is incompletely coupled to mitochondrial energy demand and capacity of the tricarboxylic acid cycle. This natural ebb and flow of acylcarnitine generation and accumulation contrasts with that of inherited fatty acid oxidation disorders (FAODs), cardiac ischaemia or type 2 diabetes mellitus. These conditions are characterized by very high (FAODs, ischaemia) or modestly increased (type 2 diabetes mellitus) tissue and blood levels of LCACs. Although specific plasma concentrations of LCACs and chain-lengths are widely used as diagnostic markers of FAODs, research into the potential effects of excessive LCAC accumulation or the roles of acylcarnitines as physiological modulators of cell metabolism is lacking. Nevertheless, a growing body of evidence has highlighted possible effects of LCACs on disparate aspects of pathophysiology, such as cardiac ischaemia outcomes, insulin sensitivity and inflammation. This Review, therefore, aims to provide a theoretical framework for the potential consequences of tissue build-up of LCACs among individuals with metabolic disorders.

Carnitine therapy for the treatment of metabolic syndrome and cardiovascular disease: evidence and controversies

As the incidence of metabolic syndrome increases, there is also a growing interest in finding safe and inexpensive treatments to help lower associated risk factors. L-carntine, a natural dietary supplement with the potential to ameliorate atherosclerosis, has been the subject of recent investigation and controversy. A majority of studies have shown benefit of L-C supplementation in the metabolic syndrome or cardiovascular risk factors. However, recent work has suggested that dietary L-C may accelerate atherosclerosis via gut microbiota metabolites, complicating the role of L-C supplementation in health.

Neuropsychological outcomes in fatty acid oxidation disorders: 85 cases detected by newborn screening

Mitochondrial fatty acid oxidation disorders include conditions in which the transport of activated acyl-Coenzyme A (CoA) into the mitochondria or utilization of these substrates is disrupted or blocked. This results in a deficit in the conversion of fat into energy. Most patients with fatty acid oxidation defects are now identified through newborn screening by tandem mass spectrometry. With earlier identification and preventative treatments, mortality and morbidity rates have improved. However, in the absence of severe health and neurological effects from these disorders, subtle developmental delays or neuropsychological deficits have been noted. Medical records were reviewed to identify outcomes in 85 children with FAOD's diagnosed through newborn screening and followed at one metabolic center. Overall, 54% of these children identified through newborn screening experienced developmental challenges. Speech delay or relative weakness in language was noted in 26 children (31%) and motor delays were noted in 24 children (29%). The majority of the 46 children receiving psychological evaluations performed well within the average range, with only 11% scoring <85 on developmental or intelligence tests. These results highlight the importance of screening children with fatty acid oxidation disorders to identify those with language, motor, or cognitive delay. Although expanded newborn screening dramatically changes the health and developmental outcomes in many children with fatty acid oxidation disorders, it also complicates the interpretation of biochemical and molecular findings and raises questions about the effectiveness or necessity of treatment in a large number of cases. Only by systematically evaluating developmental and neuropsychological outcomes using standardized methods will the true implications of newborn screening, laboratory results, and treatments for neurocognitive outcome in these disorders become clear.

Regulation of energy metabolism by long-chain fatty acids

In mammals, excess energy is stored primarily as triglycerides, which are mobilized when energy demands arise. This review mainly focuses on the role of long chain fatty acids (LCFAs) in regulating energy metabolism as ligands of peroxisome proliferator-activated receptors (PPARs). PPAR-alpha expressed primarily in liver is essential for metabolic adaptation to starvation by inducing genes for beta-oxidation and ketogenesis and by downregulating energy expenditure through fibroblast growth factor 21. PPAR-delta is highly expressed in skeletal muscle and induces genes for LCFA oxidation during fasting and endurance exercise. PPAR-delta also regulates glucose metabolism and mitochondrial biogenesis by inducing FOXO1 and PGC1-alpha. Genes targeted by PPAR-gamma in adipocytes suggest that PPAR-gamma senses incoming non-esterified LCFAs and induces the pathways to store LCFAs as triglycerides. Adiponectin, another important target of PPAR-gamma may act as a spacer between adipocytes to maintain their metabolic activity and insulin sensitivity. Another topic of this review is effects of skin LCFAs on energy metabolism. Specific LCFAs are required for the synthesis of skin lipids, which are essential for water barrier and thermal insulation functions of the skin. Disturbance of skin lipid metabolism often causes apparent resistance to developing obesity at the expense of normal skin function.

Clinical and biochemical aspects of primary and secondary hyperammonemic disorders

An increased concentration of ammonia is a non-specific laboratory sign indicating the presence of potentially toxic free ammonia that is not normally removed. This does occur in many different conditions for which hyperammonemia is a surrogate marker. Hyperammonemia can occur due to increased production or impaired detoxification of ammonia and should, if associated with clinical symptoms, be regarded as an emergency. The conditions can be classified into primary or secondary hyperammonemias depending on the underlying pathophysiology. If the urea cycle is directly affected by a defect of any of the involved enzymes or transporters, this results in primary hyperammonemia. If however the function of the urea cycle is inhibited by toxic metabolites or by substrate deficiencies, the situation is described as secondary hyperammonemia. For removal of ammonia, mammals require the action of glutamine synthetase in addition to the urea cycle, in order to ensure lowering of plasma ammonia concentrations to the normal range. Independent of its etiology, hyperammonemia may result in irreversible brain damage if not treated early and thoroughly. Thus, early recognition of a hyperammonemic state and immediate initiation of the specific management are of utmost importance. The main prognostic factors are, irrespective of the underlying cause, the duration of the hyperammonemic coma and the extent of ammonia accumulation. This paper will discuss the biochemical background of primary and secondary hyperammonemia and will give an overview of the various underlying conditions including a brief clinical outline and information on the genetic backgrounds.

Persistent neonatal hypoglycemia: Diagnosis and management

Maintenance of plasma glucose depends on a normal endocrine system, functional enzyme levels for glycogenolysis, gluconeogenesis and other processes, and there must be an adequate supply of endogenous fat, glycogen and substrates of gluconeogenesis. Neonatal hypoglycemia should be defined as serum glucose less than 2.2 mmol/L in the first 72 h of life and less than 2.5 mmol/L thereafter. The purpose of this paper is to review the more uncommon causes of hypoglycemia in the full term, apparently healthy neonate. Most of these conditions are inborn errors of metabolism. A protocol for investigation of these conditions and some of the more common diseases, such as hyperinsulinism, is provided, with a rationale explaining why these tests may be helpful.

Fasting-induced reduction in locomotor activity and reduced response of orexin neurons in carnitine-deficient mice

We found reduced locomotor activity (LA) under fasting in systemic carnitine-deficient juvenile visceral steatosis (jvs(-/-)) mice. When food was withdrawn at 8:00 a.m. (lights-off at 7:00 p.m., 12h/cycle), the nocturnal LA of jvs(-/-) mice was much less than the control (jvs(+/+) and jvs(+/-)) mice. LA recovered under carnitine or sucrose administration, but not under medium-chain triglyceride. In addition, fasted jvs(-/-) mice, without any energy supply, were activated by modafinil, a stimulator of the dopamine pathway. These results suggest that the reduced LA is not adequately explained by energy deficit. As the fasted jvs(-/-) mice showed lower body core temperature (BT), we examined the central nervous system regulating LA and BT. We found lower percentage of c-Fos positive orexin neurons in the lateral hypothalamus and reduced orexin-A concentration in the cerebrospinal fluid of fasted jvs(-/-) mice. Sleep analysis revealed that fasted jvs(-/-) mice had disruption of prolonged wakefulness, with a higher frequency of brief episodes of non-REM sleep during the dark period than fasted jvs(+/+) mice. These results strongly suggest that the reduced LA in fasted jvs(-/-) mice is related to the inhibition of orexin neuronal activity.

Differential inhibitory effect of long-chain acyl-CoA esters on succinate and glutamate transport into rat liver mitochondria and its possible implications for long-chain fatty acid oxidation defects

Long-chain fatty acid beta-oxidation defects are associated with a series of clinical and biochemical abnormalities, including accumulation of long-chain acyl-CoA esters which have been shown to inhibit several enzymes and transport systems that may disturb energy metabolism. Using isolated rat liver mitochondria incubated under state 3 conditions, we observed that long-chain acyl-CoA esters and their beta-oxidation intermediates inhibit ATP synthesis and oxygen consumption, both with succinate (plus rotenone) and l-glutamate as respiratory substrates. When an uncoupler (2,4-dinitrophenol) was used instead of ADP, to stimulate respiration maximally, the various CoA esters showed differential effects on the oxidation of succinate and l-glutamate, respectively. With succinate as substrate, there was a strong inhibition of oxygen consumption by palmitoyl-CoA, 2,3-unsaturated, 3-hydroxy, and 3-keto-palmitoyl-CoA, in coupled as well as uncoupled mitochondria. On the other hand, with l-glutamate as substrate, inhibition was only observed under coupled conditions. The finding that acyl-CoA esters inhibit the uncoupler-induced respiration with succinate as substrate but not with glutamate, indicates that the observed inhibitory effect is most probably at the level of the transport of succinate across the mitochondrial membrane as mediated by the mitochondrial dicarboxylate carrier. This conclusion was substantiated by mitochondrial swelling studies, which showed inhibition of succinate transport by the different CoA esters whereas no effect was observed on the phosphate/hydroxyl and glutamate/hydroxyl carriers. Furthermore, long-chain acyl-CoA esters were found to potentiate the inhibitory effect of N-butylmalonate, a known inhibitor of the dicarboxylate carrier, upon oxygen consumption driven by succinate (plus rotenone). We conclude that the inhibitory effects of long-chain acyl-CoA esters on oxidative phosphorylation are dependent on the type of substrate used with the ATP/ADP carrier and the dicarboxylate carrier as targets for inhibition.

Disrupted blastocoele formation reveals a critical developmental role for long-chain acyl-CoA dehydrogenase

Long-chain acyl-CoA dehydrogenase (LCAD) deficiency has not been found in human patients. There has been an LCAD deficient (LCAD-/-) mouse model developed via gene targeting strategies that has gestational loss as a part of its phenotype. We tested the hypothesis that LCAD deficiency disrupts normal embryonic development and explains at least in part the gestational loss in the mouse and may suggest a mechanism to explain the lack of any human patients with this inherited enzyme deficiency. We cultured and evaluated embryos with three different genotypes: LCAD+/+, LCAD+/-, and LCAD-/-. We found a significantly increased rate of death (P<0.012) in LCAD-/- embryos at the morula-to-blastocyst conversion indicating a deficient ability to complete the development of a blastocoele and formation of a blastocyst. Furthermore, we hypothesized that we could rescue LCAD-/- embryos in culture by supplying excess fatty acids of chain-lengths that could be readily oxidized by them despite their inherited enzyme deficiency. We were unable, however, to demonstrate any rescue by supplementing the culture medium with fatty acids of a wide-range of chain-lengths. Therefore, overall we demonstrated a severely deficient capacity for LCAD-/- embryos to develop past the morula stage with intermediate rates of development found in the LCAD+/- embryos as compared to the LCAD+/+ embryos. Furthermore, we were unable to rescue the LCAD-/- embryos with any fatty acid supplementation.

Heart mitochondria signaling pathways: appraisal of an emerging field

The contribution that mitochondria make to cardiac function extends well beyond their critical bioenergetic role as a supplier of ATP. The organelle plays an integral part in the regulatory and signaling events that occur in response to physiological stresses, including but not limited to myocardial ischemia and reperfusion, hypoxia, oxidative stress, and hormonal and cytokine stimuli. Research on both intact cardiac muscle tissue and cultured cardiomyocytes has just begun to probe the nature and the extent of mitochondrial involvement in interorganelle communication, hypertropic growth, and cell death. This review covers particular aspects of the newly emerging field of mitochondrial medicine offering a critical guide in the assessment of mitochondrial participation at the molecular and biochemical levels in the multiple and interrelated signaling pathways, gauging the effect that mitochondria have as a receiver, integrator, and transmitter of signals on cardiac phenotype. We also discuss future directions that may impact on the treatment of cardiac diseases.

[The mitochondrial organelle and the heart]

The heart is highly dependent for its function on oxidative energy generated in mitochondria, primarily by fatty acid beta-oxidation, respiratory electron chain and oxidative phosphorylation. Defects in mitochondrial structure and function have been found in association with cardiovascular diseases such as dilated and hypertrophy cardiomyopathy, cardiac conduction defects and sudden death, ischemic and alcoholic cardiomyopathy, as well as myocarditis. While a subset of these mitochondrial abnormalities have a defined genetic basis (e.g. mitochondrial DNA changes leading to oxidative phosphorylation dysfunction,fatty acid beta-oxidation defects due to specific nuclear DNA mutations), other abnormalities appear to be due to a more sporadic or environmental cardiotoxic insult or have not yet been characterized.This review focuses on abnormalities in mitochondrial bioenergetic function and mitochondrial DNA defects associated with cardiovascular diseases, their significance in cardiac pathogenesis as well as on the available diagnostic and therapeutic options. A concise background concerning mitochondrial biogenesis and bioenergetic pathways during cardiac growth,development and aging will also be provided.

Management of fatty acid oxidation disorders: a survey of current treatment strategies

Standardization of the nutritional care for patients with fatty-acid oxidation disorders is lacking. A literature review and national survey of metabolic dietitians describes the range of therapeutic strategies currently employed in the U.S. to treat patients with fatty-acid oxidation disorders. Questionnaire responses provided by dietitians specializing in metabolic disorders evaluated practices used for treatment of fatty acid oxidation disorders, medium-chain acyl-CoA dehydrogenase deficiency (MCAD), very-long-chain acyl-CoA dehydrogenase deficiency (VLCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHAD), long-chain acyl-CoA dehydrogenase deficiency (LCAD), and Trifunctional Protein deficiency (TFP). This survey reveals a significant lack of evidence supporting the protocols in use. Recent advances in tandem mass spectrometry technology promises an increase in the number of identified patients with fatty-acid oxidation disorders, which reinforces the need for comprehensive, clinical research studies to determine optimal care for patients with these genetic disorders.

Diagnosis and management of defects of mitochondrial beta-oxidation

PURPOSE OF REVIEW

At least 22 different inborn errors of metabolism affecting beta-oxidation in skeletal muscle and other tissues have been identified in the past 30 years. Early diagnosis and therapeutic diets offer the best chance for normal growth and development in most patients.

RECENT FINDINGS

Clinical heterogeneity has become the hallmark of defects in beta-oxidation. In many cases a correct diagnosis will only be made if these disorders are specifically considered and appropriate studies are obtained, since screening tests which detect other inborn errors of metabolism are often normal in patients with beta-oxidation defects. Dietary management provides the only opportunity for therapy in many cases, including carbohydrate supplements intended to provide more extended delivery of glucose to the bloodstream. Use of a novel odd chain fat supplement as an alternative fuel source in long chain fat metabolism defects offers promise of alleviating muscular symptoms not well controlled by diet. The introduction of expanded newborn screening will lead to the recognition of an increasing number of individuals with these disorders, placing greater demand for services on practitioners knowledgeable in their therapy. Study of the clinical outcome in these patients will provide a better understanding of defects of beta-oxidation.

SUMMARY

Clinical symptoms, diagnostic testing, and issues of newborn screening for this important group of disorders are discussed.

Understanding the impact of mitochondrial defects in cardiovascular disease: a review

OBJECTIVE

Defects in mitochondrial structure and function have been found in association with cardiovascular diseases such as dilated and hypertrophic cardiomyopathy, cardiac conduction defects and sudden death, ischemic and alcoholic cardiomyopathy, and myocarditis. A genetic basis has been established for some mitochondrial abnormalities (eg, mitochondrial DNA changes leading to oxidative phosphorylation dysfunction, fatty acid beta-oxidation (FAO) defects resulting from specific nuclear mutations) whereas other abnormalities appear to be due to a more sporadic or environmental cardiotoxic insult or have not yet been characterized.

METHODS

This article reviews mitochondrial abnormalities in structure or function reported in cardiac diseases highlighting information about their potential etiology, significance in cardiac pathogenesis, and diagnostic and therapeutic options available to the clinician. We also provide a brief background concerning mitochondrial biogenesis and bioenergetic pathways in cardiac growth, development, and aging.

CONCLUSIONS

Although aberrations in bioenergetic functioning of mitochondria appear to be most often related to cardiac dysfunction, the primary defect(s) causing bioenergetic dysfunction may reside in a nonbioenergetic pathway (eg, signaling between mitochondria and nucleus) or in overall mitochondrial biogenesis or degradation pathways.

Strategies for the diagnosis of mitochondrial fatty acid beta-oxidation disorders

Mitochondrial fatty acid beta-oxidation disorders (FAOD) are a group of clinically and biochemically heterogeneous inherited metabolic defects. The spectrum of phenotypes has expanded from hepatic encephalopathy to encompass myopathy, cardiomyopathy, peripheral neuropathy, sudden death and pregnancy complicated by fetal FAOD. Pre-symptomatic diagnosis is important to prevent morbidity and this is now achievable through newborn screening using tandem mass spectrometry (MS/MS). Moreover, most of the diagnosed defects are treatable and the prognosis is generally favourable. This article reviews the features of FAOD, critically evaluates methods of investigation including metabolite analyses in body fluids, in vitro oxidation rates and acylcarnitine profiling studies, enzymatic and mutational tests, and discusses genotype-phenotype correlation, treatment and monitoring options. Based on this knowledge, strategies for the biochemical investigation and differential diagnosis of patients presenting clinically, asymptomatic neonates detected by newborn screening, infants born after complications during late pregnancy, and cases of sudden death with suspected FAOD are presented. Laboratory investigation commonly begins with a search for diagnostic metabolites in physiological fluids, followed by in vitro functional studies if the initial findings are inconclusive, and confirmation by enzymology and molecular analyses. Occasionally a stress test in vivo may be required. At other times there may be no firm diagnosis achieved.

Long-chain L-3-hydroxyacyl-coenzyme a dehydrogenase deficiency: a molecular and biochemical review

Since the first report of long-chain L-3-hydroxyacyl-coenzyme A dehydrogenase deficiency a little more than a decade ago, its phenotypic and genotypic heterogeneity in individuals homozygous for the enzyme defect has become more and more evident. Even more interesting is its association with pregnancy-specific disorders, including preeclampsia, HELLP syndrome (hemolysis, elevated liver enzymes, low platelets), hyperemesis gravidarum, acute fatty liver of pregnancy, and maternal floor infarct of the placenta. In this review we discuss the biochemical and molecular basis, clinical features, diagnosis, and management of long-chain L-3-hydroxyacyl-coenzyme A dehydrogenase deficiency.

Evidence for fatty acid oxidation in human placenta, and the relationship of fatty acid oxidation enzyme activities with gestational age

Fetal disorders of mitochondrial fatty acid oxidation have recently been associated with obstetric complications including pre-eclampsia, Hemolysis, Elevated Liver enzymes, Low Platelets (HELLP) syndrome, placental floor infarct, and Acute Fatty Liver of Pregnancy (AFLP). These diseases occur in about a third of the mothers who are heterozygous for a defect in long chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) enzyme and who bear a fetus homozygous for the defect. The mechanism of this association is not clearly understood. In this study, we provide evidence that the placenta may be the site of production of toxic intermediates of fatty acid metabolism, which accumulate to cause liver damage in the mother. We show that two critical enzymes of long chain fatty acid metabolism, long chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and short chain 3-hydroxyacyl-CoA dehydrogenase (SCHAD), are active in the normal human placenta. There is an inverse correlation between the enzyme activity of both the enzymes and maternal gestational age during the second and third trimesters. We believe that the demonstration of fatty acid oxidation enzyme activity by the placenta is the first step towards assessing a possible role for fetal/placental fatty acid oxidation defects in the pathogenesis of a subset of pregnancy complications.

Differential effect of valproate and its Delta2- and Delta4-unsaturated metabolites, on the beta-oxidation rate of long-chain and medium-chain fatty acids

Overall fatty acid oxidation rates were investigated in rat hepatocytes using [9,10-3H]-palmitic, [9,10-3H]-oleic, [9,10-3H]-myristic and [2,3-3H]-phenylpropionic acids. The effect of both valproate (VPA) (0-10 mM) and two of its unsaturated metabolites, Delta2(E)-VPA and Delta4-VPA (0-10 mM), on the overall 3H2O production rate was studied. The results give evidence of a general inhibitory effect of VPA on the beta-oxidation rate of all the tested substrates. Similar effects were observed with both VPA metabolites but these effects appeared to be dependent on the chain length of the substrate. When the effect on the oxidation of the medium-chain fatty acid 3-phenylpropionate (PPA) was studied, Delta2(E)-VPA at 0.5 mM caused a 94% inhibition of the overall beta-oxidation rate. However, with long-chain substrates, 0.5 mM Delta(4)-VPA was a more potent inhibitor (20-30% of control activity) than 0.5 mM Delta(2E)-VPA (60-80% of control activity). Our results suggest that VPA and/or its metabolites inhibit fatty acyl-CoA metabolism within the mitochondrion by two different mechanisms. The first mechanism involves CoASH sequestration, which affects the oxidation rate of all fatty acids with different chain length. The second mechanism is more specific in nature and involves selective inhibition of particular enzymes implicated in fatty acid beta-oxidation.

Liver disease in pregnancy and fetal fatty acid oxidation defects

Acute fatty liver of pregnancy (AFLP) and the syndrome of hemolysis, elevated liver enzymes, and low platelets (the HELLP syndrome) are serious disorders of the third trimester with high maternal and perinatal morbidity and mortality. Over the past decade, several clinical observations have demonstrated an association between these maternal syndromes and a recessively inherited fatty acid oxidation disorder, long chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency. Many women who carried LCHAD-deficient fetuses developed maternal liver disease. Over the past few years, we and others have made significant progress in understanding the molecular basis for this fetal-maternal interaction. Here, we review the studies in literature that led to the establishment of this causative association with particular emphasis on the molecular analysis that delineated the molecular basis of this association. The likely mechanisms for the genotype-phenotype correlations in pediatric LCHAD deficiency and the fetal-maternal interaction are discussed. Finally, the potential implications of our current knowledge for families with pediatric LCHAD deficiency and for women who develop AFLP and HELLP syndrome are discussed.

Secondary carnitine deficiency and impaired docosahexaenoic (22:6n-3) acid synthesis: a common denominator in the pathophysiology of diseases of oxidative phosphorylation and beta-oxidation

A critical analysis of the literature of mitochondrial disorders reveals that genetic diseases of oxidative phosphorylation are often associated with impaired beta-oxidation, and vice versa, and preferentially affect brain, retina, heart and skeletal muscle, tissues which depend on docosahexaenoic (22:6n-3)-containing phospholipids for functionality. Evidence suggests that an increased NADH/NAD(+) ratio generated by reduced flux through the respiratory chain inhibits beta-oxidation, producing secondary carnitine deficiency while increasing reactive oxygen species and depleting alpha-tocopherol (alpha-TOC). These events result in impairment of the recently elucidated mitochondrial pathway for synthesis of 22:6n-3-containing phospholipids, since carnitine and alpha-TOC are involved in their biosynthesis. Therapeutic supplementation with 22:6n-3 and alpha-TOC is suggested.

Clinical and molecular heterogeneity in very-long-chain acyl-coenzyme A dehydrogenase deficiency

Very-long-chain acyl-coenzyme A dehydrogenase (VLCAD) deficiency is an increasingly recognized defect of mitochondrial fatty acid beta-oxidation manifesting with episodes of metabolic decompensation or isolated recurrent myoglobinuria. In this report the clinical, biochemical, and molecular studies in a series of five patients (four Italian and one Spanish) with this disorder are discussed. Biochemical studies included the determination of fibroblast substrate oxidation rates and enzyme activity and Western blot analysis of VLCAD protein. Molecular analysis was performed by sequencing the VLCAD gene from the genomic DNA. Clinical features were within the spectrum previously reported. Four patients presented in infancy or childhood with episodes of severe metabolic decompensation and dicarboxylic aciduria. Two exhibited cardiomyopathy. The fifth patient presented with isolated recurrent rhabdomyolysis, with no cardiomyopathy or dicarboxylic aciduria. In all patients a significant loss of VLCAD activity associated with a marked reduction of VLCAD protein levels occurred. Molecular analysis disclosed one novel missense mutation (Cys437Tyr) and four previously reported mutations, including two missense substitutions (Phe418Leu and Arg419Trp), a single amino acid deletion (Lys258del), and one splice site mutation (IVS8-C(-2)), which was present in all four Italian patients. All patients exhibited compound heterozygosity. The phenotypic variability and the high genotypic heterogeneity of this hereditary metabolic disorder is reported.

Arrhythmias and conduction defects as presenting symptoms of fatty acid oxidation disorders in children

BACKGROUND

The clinical manifestations of inherited disorders of fatty acid oxidation vary according to the enzymatic defect. They may present as isolated cardiomyopathy, sudden death, progressive skeletal myopathy, or hepatic failure. Arrhythmia is an unusual presenting symptom of fatty acid oxidation deficiencies.

METHODS AND RESULTS

Over a period of 25 years, 107 patients were diagnosed with an inherited fatty acid oxidation disorder. Arrhythmia was the predominant presenting symptom in 24 cases. These 24 cases included 15 ventricular tachycardias, 4 atrial tachycardias, 4 sinus node dysfunctions with episodes of atrial tachycardia, 6 atrioventricular blocks, and 4 left bundle-branch blocks in newborn infants. Conduction disorders and atrial tachycardias were observed in patients with defects of long-chain fatty acid transport across the inner mitochondrial membrane (carnitine palmitoyl transferase type II deficiency and carnitine acylcarnitine translocase deficiency) and in patients with trifunctional protein deficiency. Ventricular tachycardias were observed in patients with any type of fatty acid oxidation deficiency. Arrhythmias were absent in patients with primary carnitine carrier, carnitine palmitoyl transferase I, and medium chain acyl coenzyme A dehydrogenase deficiencies.

CONCLUSIONS

The accumulation of arrhythmogenic intermediary metabolites of fatty acids, such as long-chain acylcarnitines, may be responsible for arrhythmias. Inborn errors of fatty acid oxidation should be considered in unexplained sudden death or near-miss in infants and in infants with conduction defects or ventricular tachycardia. Diagnosis can be easily ascertained by an acylcarnitine profile from blood spots on filter paper.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: variable expressivity of maternal illness during pregnancy and unusual presentation with infantile cholestasis and hypocalcaemia

Patients with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency present with a Reye-like syndrome, cardiomyopathy, or sudden unexpected death. We describe an unusual presentation in a patient with unsuspected LCHAD deficiency. The proband presented at 2 months of age with an acute infantile hypocalcaemia and vitamin D deficiency associated with occult, unexplained cholestatic liver disease. Sudden, unexpected death occurred at 8 months. Molecular analysis revealed homozygosity for the prevalent LCHAD (1528G > C, E474Q) mutation. The mother had pre-eclampsia during the third trimester of her pregnancy. In a subsequent pregnancy, she developed severe acute fatty liver of pregnancy (AFLP) and intrauterine fetal death at 33 weeks of gestation. In conclusion, infantile hypocalcaemia is an unusual phenotype associated with LCHAD deficiency. The maternal pregnancy history documents that fetal LCHAD deficiency is associated with a spectrum of maternal illnesses ranging from pre-eclampsia to life-threatening AFLP.

A simple screening test for fatty acid oxidation defects using whole-blood palmitate oxidation

We report that measurement of whole-blood palmitate oxidation is a rapid and inexpensive screening test for fatty acid oxidation defects. The assay has been adapted from published assays using cultured fibroblasts or isolated white blood cells. Micro whole-blood samples are incubated with tritiated palmitic acid as substrate. The tritiated water produced is proportional to the mitochondrial beta-oxidation of palmitic acid. Patients with confirmed beta-oxidation defects show low whole-blood palmitate oxidation.

Carnitine-acylcarnitine translocase deficiency

Carnitine-acylcarnitine translocase deficiency, like other defects of mitochondrial fatty acid oxidation, is an autosomal, recessively inherited disorder. When the deficiency is near total, it is usually fatal, affects life soon after birth, and constitutes one of the causes of skeletal muscle myopathy, cardiac and liver abnormalities, and childhood sudden death. The presenting features have included neonatal distress, convulsions, hypoglycemia, hyperammonemia, hypoketonemia, intermittent dicarboxyluria, hypothermia, apnea, neurological deterioration, and hypocarnitinemia with grossly elevated acylcarnitines. Two cases of partial translocase deficiency (4-6% residual activity) with milder symptoms and without cardiac involvement have also been identified. Evidence so far indicates that the translocase protein is the product of a single gene. In two cases of translocase deficiency, the accompanying mutations have been identified. The benefits of prenatal diagnosis have been provided to the affected families by assays of the translocase and/or fatty acid oxidation in cultured amniotic/villous cells. In one such case genetic counseling was made possible even when the only specimen available from a deceased sibling was the Guthrie card.

Inherited long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency and a fetal-maternal interaction cause maternal liver disease and other pregnancy complications

Fetal-maternal interactions are critical determinants of maternal health during pregnancy and perinatal outcome. This review explores the causative relationship of a fetal disorder of mitochondrial fatty acid oxidation, long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, and the serious maternal liver diseases of pregnancy-preeclampsia, the HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet counts), and acute fatty liver of pregnancy. Features of the metabolic adaptation necessitated during the fetal-neonatal transition; common phenotypes of pediatric fatty acid oxidation disorders, including neonatal hypoketotic, hypoglycemia and hepatic crisis; and clinical abnormalities of HELLP and acute fatty liver of pregnancy are presented. Evidence that a common mutation in the alpha-subunit (LCHAD) of trifunctional protein, E474Q, is always one of the mutant alleles in fetal isolated LCHAD deficiency associated with these disorders of pregnancy that cause high maternal, fetal, and newborn morbidity and mortality is reviewed. Recommendations for molecular testing for LCHAD deficiency in families with life-threatening maternal liver disease are given.

Application of electrospray tandem mass spectrometry to neonatal screening

For the past 30 years, neonatal screening programs have been performed largely by using the bacterial inhibition assays developed by Dr Robert Guthrie. These programs focused on a small number of diseases such as phenylketonuria and maple syrup urine disease and involved one test for each disease. During the same period many new diseases were discovered, such as organic acidemias and fatty acid oxidation defects, and they presented a diagnostic challenge to biochemical laboratories. Different mass spectrometric approaches have been the main tools for the diagnosis; however, each has its own limitation. Recently, electrospray tandem mass spectrometry (MS/MS) has provided an alternative automated high throughput, specific, and broad-spectrum approach to screening for a relatively large number of disorders, including those covered by bacterial inhibition assays tests. By using specific scan functions, a large number of amino acids and acylcarnitines in blood spots are quantified in 2 minutes analytical time. A new scan function is described here for quantification and screening for argininosuccinic acid in blood spots, which is a key metabolite in the diagnosis of argininosuccinase deficiency. We describe the results of a 3-year tandem MS/MS-based neonatal study that was performed in our newborn population. We screened 27,624 blood spots and identified 20 cases yielding a frequency of 1:1,381. No false-negative cases were identified, but several false-positive cases were eliminated by repeat analysis by MS/MS of blood or by other means. We also used MS/MS analysis of urine or blood either for confirmation of initial positive results or for follow-up of treatment, such as in glutaric acidemia, citrullinemia, argininosuccinase deficiency, and biopterin-dependent phenylketonuria.

Fatty acid beta-oxidation deficiency masquerading as fulminant myocarditis

We present a 9-month-old child presenting with acute cardiomyopathy and fever following a viral illness. He was diagnosed to have acute myocarditis, was proposed for an external hemodynamic assistance but died of ventricular tachycardia. Post-mortem data revealed a very-long-chain acylcoenzyme A dehydrogenase deficiency. Our report raises awareness on the interest for preserving tissue samples and for performing a metabolic screening in acute childhood cardiomyopathy.

Cloning of the human carnitine-acylcarnitine carrier cDNA and identification of the molecular defect in a patient

The carnitine-acylcarnitine carrier (CAC) catalyzes the translocation of long-chain fatty acids across the inner mitochondrial membrane. We cloned and sequenced the human CAC cDNA, which has an open reading frame of 903 nucleotides. Northern blot studies revealed different expression levels of CAC in various human tissues. Furthermore, mutation analysis was performed for a CAC-deficient infant. Direct sequencing of the patient's cDNA revealed a homozygous cytosine nucleotide insertion. This insertion provokes a frameshift and an extension of the open reading frame with 23 novel codons. This is the first report documenting a mutation, in the CAC cDNA, responsible for mitochondrial beta-oxidation impairment.

[Cardiac involvement in neuromuscular diseases]

Many neuromuscular disorders involve the heart, occasionally with overt clinical disease. Muscular dystrophies (dystrophinopathies, limb girdle muscular dystrophy, Emery-Dreifuss muscular dystrophy, Steinert's myotonic dystrophy), congenital myopathies, inflammatory myopathies and metabolic diseases (glycogenosis, periodic paralysis, mitochondrial diseases) may produce dilated or hypertrophic cardiomyopathy and heart rhythm or conduction disturbances. Furthermore the heart is commonly involved in some hereditary and degenerative diseases (Friedreich's ataxia and Kugelberg-Welander syndrome) and acquired (Guillain-Barré syndrome) or inherited (Refsum's disease and Charcot-Marie-Tooth syndrome) polyneuropathies. A cardiologist's high clinical suspicion and a simple but systematic skeletal muscle and peripheral nerve investigation, including muscle enzymes quantification, neurophysiological study and muscle biopsy, are necessary for an accurate diagnosis. In selected patients, more sophisticated biochemical and genetic analysis will be necessary. In most cases, endomyocardial biopsy is not essential for the diagnosis.

Plasma free fatty acids in mitochondrial fatty acid oxidation defects

Plasma free fatty acid profiles from patients suffering from various mitochondrial beta-oxidation deficiencies were analyzed by gas chromatography-mass spectrometry. cis-4-Decenoic acid (10:1n-6) in medium-chain acyl-CoA dehydrogenase deficiency and cis-5-tetradecenoic acid (14:1n-9) in very-long-chain and 3-hydroxy-long chain acyl-CoA dehydrogenase deficiencies are characteristic of these diseases. In addition, patients with 3-hydroxy-long chain acyl-CoA dehydrogenase deficiency showed a specific increase of 3-hydroxy-long chain fatty acids. The study of plasma free fatty acids is an easy and useful methodology for the diagnostic approach of some mitochondrial beta-oxidation deficiencies, allowing us to establish a quick differentiation between medium- and long-chain defects.

Common missense mutation G1528C in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Characterization and expression of the mutant protein, mutation analysis on genomic DNA and chromosomal localization of the mitochondrial trifunctional protein alpha subunit gene

Mitochondrial trifunctional protein (MTP) is a recently identified enzyme involved in mitochondrial beta-oxidation, harboring long-chain enoyl-CoA hydratase, long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and long-chain 3-ketothiolase activity. A deficiency of this protein is associated with impaired oxidation of long-chain fatty acids which can lead to sudden infant death. Furthermore, it is clear that this inborn error of fatty acid oxidation is very frequent, second to medium chain acyl-CoA dehydrogenase deficiency. In most patients only the LCHAD activity of MTP is deficient with near normal activity of the two other enzyme activities of the complex. We recently described the occurrence of a frequent G1528C mutation in the cDNA coding for the a subunit of MTP. Using S. cerevisiae for expression of wild type and mutant protein we show that the G1528C mutation is directly responsible for the loss of LCHAD activity. Furthermore, we describe a newly developed method allowing identification of the G1528C mutation in genomic DNA. The finding of an 87% allele frequency of the G1528C mutation in 34 LCHAD deficient patients makes this a valuable test for prenatal diagnosis. Finally, we show that the gene encoding the alpha subunit of MTP is located on chromosome 2p24.1-23.3.