Fatty acid oxidation disorders: a new class of metabolic diseases

Effects of Fat and Carnitine on the Expression of Carnitine Acetyltransferase and Enoyl-CoA Hydratase Short-Chain 1 in the Liver of Juvenile GIFT (Oreochromis niloticus)

Carnitine acetyltransferase (CAT) and Enoyl-CoA hydratase short-chain 1 (ECHS1) are considered key enzymes that regulate the β-oxidation of fatty acids. However, very few studies have investigated their full length and expression in genetically improved farmed tilapia (GIFT, Oreochromis niloticus), an important aquaculture species in China. Here, we cloned CAT and ECHS1 full-length cDNA via the rapid amplification of cDNA ends, and the expressions of CAT and ECHS1 in the liver of juvenile GIFT were detected in different fat and carnitine diets, as were the changes in the lipometabolic enzymes and serum biochemical indexes of juvenile GIFT in diets with different fat and carnitine levels. CAT cDNA possesses an open reading frame (ORF) of 2167 bp and encodes 461 amino acids, and the ECHS1 cDNA sequence is 1354 bp in full length, the ORF of which encodes a peptide of 391 amino acids. We found that juvenile GIFT had higher lipometabolic enzyme activity and lower blood CHOL, TG, HDL-C, and LDL-C contents when the dietary fat level was 2% or 6% and when the carnitine level was 500 mg/kg. We also found that the expression of ECHS1 and CAT genes in the liver of juvenile GIFT can be promoted by a 500 mg/kg carnitine level and 6% fat level feeding. These results suggested that CAT and ECHS1 may participate in regulating lipid metabolism, and when 2% or 6% fat and 500 mg/kg carnitine are added to the feed, it is the most beneficial to the liver and lipid metabolism of juvenile GIFT. Our results may provide a theoretical basis for GIFT feeding and treating fatty liver disease.

Optical Metabolic Imaging of Mitochondrial Dysfunction on HADH Mutant Newborn Rat Hearts

BACKGROUND

Mitochondrial [Formula: see text]-oxidation of fatty acids is the primary energy source for the heart and carried out by Hydroxy Acyl-CoA Dehydrogenase (HADH) encoded trifunctional protein. Mutations in the genes encoding mitochondrial proteins result in functionally defective protein complexes that contribute to energy deficiencies, excessive reactive oxygen species (ROS) production, and accumulation of damaged mitochondria. We hypothesize that a dramatic alternation in redox state and associated mitochondrial dysfunction is the underlying cause of Fatty Acid Oxidation (FAO) deficiency mutant, resulting in heart failure. Mitochondrial co-enzymes, NADH and FAD, are autofluorescent metabolic indices of cells when imaged, yield a quantitative assessment of the cells' redox status and, in turn, that of the tissue and organ.

METHOD

We utilized an optical cryo-imager to quantitively evaluate the three-dimensional distribution of mitochondrial redox state in newborn rats' hearts and kidneys. Redox ratio (RR) assessment shows that mitochondrial dysfunction is extreme and could contribute to severe heart problems and eventual heart failure in the mutants.

RESULTS

Three-dimensional redox ratio (NADH/FAD) rendering, and the volumetric mean value calculations confirmed significantly decreased cardiac RR in mutants by 31.90% and 12.32%, in renal mitochondrial RR compared to wild-type control. Further, histological assessment of newborn heart myocardial tissue indicated no significant difference in myocardial tissue architecture in both control and severe (HADHAe4-/-) conditions.

CONCLUSION

These results demonstrate that optical imaging can accurately estimate the redox state changes in newborn rat organs. It is also apparent that the FAO mutant's heart tissue with a low redox ratio is probably more vulnerable to cumulative damages than kidneys and fails prematurely, contributing to sudden death.

Metabolic enzymes dysregulation in heart failure: the prospective therapy

The heart failure accounts for the highest mortality rate all over the world. The development of preventive therapeutic approaches is still in their infancy. Owing to the extremely high energy demand of the heart, the bioenergetics pathways need to respond efficiently based on substrate availability. The metabolic regulation of such heart bioenergetics is mediated by various rate limiting enzymes involved in energy metabolism. Although all the pertinent mechanisms are not clearly understood, the progressive decline in the activity of metabolic enzymes leading to diminished ATP production is known to cause progression of the heart failure. Therefore, metabolic therapy that can maintain the appropriate activities of metabolic enzymes can be a promising approach for the prevention and treatment of the heart failure. The flavonoids that constitute various human dietary ingredients also effectively offer a variety of health benefits. The flavonoids target a variety of metabolic enzymes and facilitate effective management of the equilibrium between production and utilization of energy in the heart. This review discusses the broad impact of metabolic enzymes in the heart functions and explains how the dysregulated enzyme activity causes the heart failure. In addition, the prospects of targeting dysregulated metabolic enzymes by developing flavonoid-based metabolic approaches are discussed.

Kruppel-like factor 15 is required for the cardiac adaptive response to fasting

Cardiac metabolism is highly adaptive in response to changes in substrate availability, as occur during fasting. This metabolic flexibility is essential to the maintenance of contractile function and is under the control of a group of select transcriptional regulators, notably the nuclear receptor family of factors member PPARα. However, the diversity of physiologic and pathologic states through which the heart must sustain function suggests the possible existence of additional transcriptional regulators that play a role in matching cardiac metabolism to energetic demand. Here we show that cardiac KLF15 is required for the normal cardiac response to fasting. Specifically, we find that cardiac function is impaired upon fasting in systemic and cardiac specific Klf15-null mice. Further, cardiac specific Klf15-null mice display a fasting-dependent accumulation of long chain acylcarnitine species along with a decrease in expression of the carnitine translocase Slc25a20. Treatment with a diet high in short chain fatty acids relieves the KLF15-dependent long chain acylcarnitine accumulation and impaired cardiac function in response to fasting. Our observations establish KLF15 as a critical mediator of the cardiac adaptive response to fasting through its regulation of myocardial lipid utilization.

Very long-chain acyl-CoA dehydrogenase (VLCAD-) deficiency-studies on treatment effects and long-term outcomes in mouse models

Very-long-chain-acyl-CoA-dehydrogenase deficiency is the most common disorder of mitochondrial long-chain fatty acid (LCFA) oxidation, with an incidence of 1:50,000-1:100,000 in newborns. Catabolic situations contribute to the aggravation of symptoms and induce severe metabolic derangement. Treatment for VLCAD-deficiency includes avoidance of fasting and a long-chain fat-restricted and fat-modified diet in which LCFAs are fully or partially replaced by medium-chain triglycerides (MCT). The aim of this work was to investigate the outcome and the effects of long-term treatment in a mouse model of VLCAD-deficiency. The application of a single MCT bolus in a mouse model of VLCAD-deficiency (VLCAD^-/- mice) immediately prior to exercise protected the muscles from the accumulation of acylcarnitines providing the required energy and it did not affect hepatic lipid metabolism. However, when MCT was applied over the course of a year as a regular part of the diet, female VLCAD^-/- mice developed a severe clinical phenotype comparable to the human metabolic syndrome. Indeed, they were characterized by massive visceral fat infiltration, hepatosteatosis, disturbed fatty acid composition, hyperlipidemia, and systemic oxidative stress. In contrast, male VLCAD^-/- mice seemed to be protected and displayed only signs of insulin resistance. Besides the sex-specific response to MCT supplementation with regard to the lipid metabolism, all VLCAD^-/- mice developed progressive cardiac dysfunction over time which worsened when they were treated with regular MCT resulting in severe dilated cardiomyopathy. While long term use of MCT oil in mice has adverse effects, no such effects have been demonstrated in humans, likely reflecting the differences in long chain fatty acid oxidation between the two species.

UX007 for the treatment of long chain-fatty acid oxidation disorders: Safety and efficacy in children and adults following 24weeks of treatment

BACKGROUND

Long-chain fatty acid oxidation disorders (LC-FAOD) lead to accumulation of high concentrations of potentially toxic fatty acid intermediates. Newborn screening and early intervention have reduced mortality, but most patients continue to experience frequent hospitalizations and significant morbidity despite treatment. The deficient energy state can cause serious liver, muscle, and heart disease, and may be associated with an increased risk of sudden death. Triheptanoin is a medium odd-chain fatty acid. Anaplerotic metabolites of triheptanoin have the potential to replace deficient tricarboxylic acid (TCA) cycle intermediates, resulting in net glucose production as a novel energy source for the treatment of LC-FAOD.

STUDY DESIGN

A single-arm, open-label, multicenter Phase 2 safety and efficacy study evaluated patients with severe LC-FAOD evidenced by ongoing related musculoskeletal, cardiac, and/or hepatic events despite treatment. After a four-week run-in on current regimen, investigational triheptanoin (UX007) was titrated to a target dose of 25-35% of total daily caloric intake. Patients were evaluated on several age/condition-eligible endpoints, including submaximal exercise tests to assess muscle function/endurance (12-minute walk test; 12MWT) and exercise tolerance (cycle ergometry), and health related quality of life (HR-QoL). Results through 24weeks of treatment are presented; total study duration is 78weeks.

RESULTS

Twenty-nine patients (0.8 to 58years) were enrolled; most qualified based on severe musculoskeletal disease. Twenty-five patients (86%) completed the 24-week treatment period. At Week 18, eligible patients (n=8) demonstrated a 28% increase (LS mean=+181.9 meters; p=0.087) from baseline (673.4meters) in 12MWT distance. At Week 24, eligible patients (n=7) showed a 60% increase in watts generated (LS mean=+409.3W; p=0.149) over baseline (744.6W) for the exercise tolerance test. Improvements in exercise tests were supported by significant improvements from baseline in the adult (n=5) self-reported SF-12v2 physical component summary score (LS mean=+8.9; p<0.001). No difference from baseline was seen in pediatric parent-reported (n=5) scores (SF-10) at Week 24. Eighteen patients (62%) had treatment-related adverse events, predominantly gastrointestinal (55%), mild-to-moderate in severity, similar to that seen with prior treatment with medium chain triglyceride (MCT) oil. One patient experienced a treatment-related serious adverse event of gastroenteritis. One patient discontinued from study due to diarrhea of moderate severity; the majority of patients (25/29; 86%) elected to continue treatment in the extension period.

CONCLUSIONS

In patients with severe LC-FAOD, UX007 interim study results demonstrated improved exercise endurance and tolerance, and were associated with positive changes in self-reported HR-QoL.

Levocarnitine and Dialysis: A Review

Among the various metabolic abnormalities documented in dialysis patients are abnormalities related to the metabolism of fatty acids. Aberrant fatty-acid metabolism has been associated with the promotion of free-radical production, insulin resistance, and cellular apoptosis. These processes have been identified as important contributors to the morbidity experienced by dialysis patients. There is evidence that levocarnitine supplementation can modify the deleterious effects of defective fatty-acid metabolism. Patients receiving hemodialysis and, to a lesser degree, peritoneal dialysis have been shown to be carnitine deficient, as manifested by reduced levels of plasma free carnitine and an increase in the acyl:free carnitine ratio. Cardiac and skeletal muscles are particularly dependent on fatty-acid metabolism for the generation of energy. A number of clinical abnormalities have been correlated with a low plasma carnitine status in dialysis patients. Clinical trials have examined the efficacy of levocarnitine therapy in a number of conditions common in dialysis patients, including skeletal-muscle weakness and fatigue, cardiomyopathy, dialysis-related hypotension, hyperlipidemia, and anemia poorly responsive to recombinant human erythropoietin therapy (rHuEPO). This review examines the evidence for carnitine deficiency in patients requiring dialysis, and documents the results of relevant clinical trials of levocarnitine therapy in this population. Consensus recommendations by expert panels are summarized and contrasted with present guidelines for access to levocarnitine therapy by dialysis patients.

A lethal neonatal phenotype of mitochondrial short-chain enoyl-CoA hydratase-1 deficiency

Short-chain enoyl-CoA hydratase (SCEH) is a mitochondrial enzyme involved in the oxidation of fatty acids and the catabolic pathway of valine and, to a lesser extent, isoleucine. Deficiency of this enzyme was recently shown to cause an early childhood Leigh syndrome phenotype. The few reported patients were compound heterozygotes for two missense or missense with truncating variants in ECHS1 that encodes SCEH. We describe two siblings with severe refractory lactic acidosis and death within the first 2 days of life. Following negative clinical whole-exome and whole-genome sequencing, we resorted to autozygome/exome analysis on research basis and identified a homozygous splice site mutation (c.88+5G>A) in the two cases. Analysis of cDNA confirmed complete replacement of the normal transcript with an aberrant transcript (r.88_89ins 88+1_88+11) predicting premature truncation of the protein [p.(Ala31Glufs*23)]. Furthermore, quantitative reverse transcriptase polymerase chain reaction (RTPCR) showed marked reduction in ECHS1, most likely nonsense-mediated decay (NMD)-mediated. This is the first report of homozygosity for a truncating mutation in ECHS1, which may explain the severe phenotype. Our report highlights the need to consider SCEH deficiency in patients with lethal neonatal lactic acidosis, and the potentially limited sensitivity of untargeted genomic sequencing towards non-canonical splicing mutations, which may explain at least some of the 'negative' cases on clinical exome/genome sequencing.

Triheptanoin treatment in patients with pediatric cardiomyopathy associated with long chain-fatty acid oxidation disorders

Long-chain fatty acid oxidation disorders (LC-FAOD) can cause cardiac hypertrophy and cardiomyopathy, often presenting in infancy, typically leading to death or heart transplant despite ongoing treatment. Previous data on triheptanoin treatment of cardiomyopathy in LC-FAOD suggested a clinical benefit on heart function during acute failure. An additional series of LC-FAOD patients with critical emergencies associated with cardiomyopathy was treated with triheptanoin under emergency treatment or compassionate use protocols. Case reports from 10 patients (8 infants) with moderate or severe cardiomyopathy associated with LC-FAOD are summarized. The majority of these patients were detected by newborn screening, with follow up confirmatory testing, including mutation analysis; all patients were managed with standard treatment, including medium chain triglyceride (MCT) oil. While on this regimen, they presented with acute heart failure requiring hospitalization and cardiac support (ventilation, ECMO, vasopressors) and, in some cases, resuscitation. The patients discontinued MCT oil and began treatment with triheptanoin, an investigational drug. Triheptanoin is expected to provide anaplerotic metabolites, to replace deficient TCA cycle intermediates and improve effective energy metabolism. Cardiac function was measured by echocardiography and ejection fraction (EF) was assessed. EF was moderately to severely impaired prior to triheptanoin treatment, ranging from 12-45%. Improvements in EF began between 2 and 21days following initiation of triheptanoin, and peaked at 33-71%, with 9 of 10 patients achieving EF in the normal range. Continued treatment was associated with longer-term stabilization of clinical signs of cardiomyopathy. The most common adverse event observed was gastrointestinal distress. Of the 10 patients, 7 have continued on treatment, 1 elected to discontinue due to tolerability issues, and 2 patients died from other causes. Two of the case histories illustrate that cardiomyopathy may also develop later in childhood and/or persist into adulthood. Overall, the presented cases suggest a therapeutic effect of triheptanoin in the management of acute cardiomyopathy associated with LC-FAOD.

Disorders of fatty acid oxidation

Recognition of fatty acid oxidation (FAO) disorders is important for the pediatric neurologist as they present with a spectrum of clinical disorders, including progressive lipid storage myopathy, recurrent myoglobinuria, neuropathy, progressive cardiomyopathy, recurrent hypoglycemic hypoketotic encephalopathy or Reye-like syndrome, seizures, and mental retardation. They constitute a critical group of diseases because they are potentially rapidly fatal and a source of major morbidity. There is frequently a family history of sudden infant death syndrome in siblings. Early recognition and prompt institution of therapy and appropriate preventive measures, and in certain cases specific therapy, may be life-saving and may significantly decrease long-term morbidity, particularly with respect to CNS sequelae. All currently known conditions are inherited as autosomal recessive traits. There are now at least 25 enzymes and specific transport proteins in the β-oxidation pathway and 18 have been associated with human disease. The most common defect is medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, which had an incidence of 1 in 8930 live births in one series. The identification of serum acylcarnitines by electrospray ionization-tandem mass spectrometry of dried blood spots on filter paper in newborn screening programs has significantly enhanced the early recognition of these disorders.

Cardiac-specific VLCAD deficiency induces dilated cardiomyopathy and cold intolerance

The very long-chain acyl-CoA dehydrogenase (VLCAD) enzyme catalyzes the first step of mitochondrial β-oxidation. Patients with VLCAD deficiency present with hypoketotic hypoglycemia and cardiomyopathy, which can be exacerbated by fasting and/or cold stress. Global VLCAD knockout mice recapitulate these phenotypes: mice develop cardiomyopathy, and cold exposure leads to rapid hypothermia and death. However, the contribution of different tissues to development of these phenotypes has not been studied. We generated cardiac-specific VLCAD-deficient (cVLCAD(-/-)) mice by Cre-mediated ablation of the VLCAD in cardiomyocytes. By 6 mo of age, cVLCAD(-/-) mice demonstrated increased end-diastolic and end-systolic left ventricular dimensions and decreased fractional shortening. Surprisingly, selective VLCAD gene ablation in cardiomyocytes was sufficient to evoke severe cold intolerance in mice who rapidly developed severe hypothermia, bradycardia, and markedly depressed cardiac function in response to fasting and cold exposure (+5°C). We conclude that cardiac-specific VLCAD deficiency is sufficient to induce cold intolerance and cardiomyopathy and is associated with reduced ATP production. These results provide strong evidence that fatty acid oxidation in myocardium is essential for maintaining normal cardiac function under these stress conditions.

Successful Treatment of Cardiomyopathy due to Very Long-Chain Acyl-CoA Dehydrogenase Deficiency: First Case Report from Oman with Literature Review

Very long-chain acyl-CoA dehydrogenase deficiency (MIM 201475) is a severe defect of mitochondrial energy production from oxidation of very long-chain fatty acids. This inherited metabolic disorder often presents in early neonatal period with episodes of symptomatic hypoglycemia usually responding well to intravenous glucose infusion. These babies are often discharged without establishment of diagnosis but return by 2-5 months of age with severe and progressive cardiac failure due to hypertrophic cardiomyopathy with or without hepatic failure and steatosis. An early diagnosis and treatment with high concentration medium chain triglycerides based feeding formula can be life saving in such patients. Here, we report the first diagnosed and treated case of Very long-chain acyl-CoA dehydrogenase deficiency in Oman. This infant developed heart failure with left ventricular dilation, hypertrophy and pericardial effusion at the age of 7 weeks. Prompt diagnosis and subsequent intervention with medium chain triglycerides-based formula resulted in a reversal of severe clinical symptoms with significant improvement of cardiac status. This treatment also ensured normal growth and neurodevelopment. It is stressed that the disease must be recognized by the pediatricians and cardiologists since the disease can be identified by Tandem Mass Spectrometry; therefore, it should be considered to be included in expanded newborn screening program, allowing early diagnosis and intervention in order to ensure better outcome and prevent complications.

ECHS1 acts as a novel HBsAg-binding protein enhancing apoptosis through the mitochondrial pathway in HepG2 cells

We aimed to confirm the role of ECHS1 as a binding protein of HBsAg (HBs) and investigate its function during the development of hepatocellular carcinoma (HCC). Our results show that both exogenous and endogenous ECHS1 proteins bind to HBs and co-localize in the cytoplasm in vitro. The coexistence of HBs and ECHS1 enhances HepG2 cell apoptosis, affects ECHS1 localization in the mitochondria and induces apoptosis by decreasing the mitochondrial membrane potential (MMP). These findings suggest that ECHS1 may be applied as a potential therapeutic target during the treatment of HBV-related hepatitis or HCC.

Connexin- and pannexin-based channels in normal skeletal muscles and their possible role in muscle atrophy

Precursor cells of skeletal muscles express connexins 39, 43 and 45 and pannexin1. In these cells, most connexins form two types of membrane channels, gap junction channels and hemichannels, whereas pannexin1 forms only hemichannels. All these channels are low-resistance pathways permeable to ions and small molecules that coordinate developmental events. During late stages of skeletal muscle differentiation, myofibers become innervated and stop expressing connexins but still express pannexin1 hemichannels that are potential pathways for the ATP release required for potentiation of the contraction response. Adult injured muscles undergo regeneration, and connexins are reexpressed and form membrane channels. In vivo, connexin reexpression occurs in undifferentiated cells that form new myofibers, favoring the healing process of injured muscle. However, differentiated myofibers maintained in culture for 48 h or treated with proinflammatory cytokines for less than 3 h also reexpress connexins and only form functional hemichannels at the cell surface. We propose that opening of these hemichannels contributes to drastic changes in electrochemical gradients, including reduction of membrane potential, increases in intracellular free Ca(2+) concentration and release of diverse metabolites (e.g., NAD(+) and ATP) to the extracellular milieu, contributing to multiple metabolic and physiologic alterations that characterize muscles undergoing atrophy in several acquired and genetic human diseases. Consequently, inhibition of connexin hemichannels expressed by injured or denervated skeletal muscles might reduce or prevent deleterious changes triggered by conditions that promote muscle atrophy.

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.

A method for comprehensive analysis of urinary acylglycines by using ultra-performance liquid chromatography quadrupole linear ion trap mass spectrometry

Acylglycines are an important class of metabolites that have been used in the diagnosis of several inborn errors of metabolism (IEM). However, current analytical methods detect only a few acylglycines. There is a need to profile these metabolites in a comprehensive manner for studying their functions and improving their diagnostic values for different IEM and potentially other diseases. We describe a sensitive method that combines the chromatographic resolving power of ultra-performance liquid chromatography (UPLC) to separate closely related metabolites including isomers with tandem mass spectrometry (MS/MS). Acylglycines were extracted from urine using an anion exchange solid-phase extraction (SPE) cartridge. After UPLC separation, the acylglycines were detected on a hybrid triple quadrupole linear ion trap mass spectrometer. A set of standards were used for the development of an optimal MS acquisition method. Several acquisition modes using information derived from collision-induced dissociation breakdown curves were used to detect acylglycines. Using this method, 18 acylglycines were detected in the urine of healthy individuals and confirmed using standards, while 47 additional acylglycines were detected and tentatively identified, based on their retention and fragmentation pattern. Among the 65 acylglycines detected, only 18 of them have been previously reported in biofluids of healthy individuals. These results will be deposited in a public human metabolome database. This example illustrates that by developing a method tailored to the analysis of a class of metabolites sharing similar structural moieties, we can potentially identify many more new metabolites, thereby expanding the overall metabolome coverage.

A novel mouse model of X-linked cardiac hypertrophy

We recovered a novel mouse mutant exhibiting neonatal lethality associated with severe fetal cardiac hypertrophy and with some adult mice dying suddenly with left ventricular hypertrophic cardiomyopathy. Using Doppler echocardiography, we screened surviving adult mice in this mutant line for cardiac hypertrophy. Cardiac dimensions were obtained either from two-dimensional images collected using a novel ECG-gated ultra-high-frequency ultrasound system or by traditional M-mode imaging on a clinical ultrasound system. These analyses identified, among the littermates, two populations of mice: those with apparent cardiac hypertrophy with hypercontractile function characterized by ejection fraction of 75–80%, and normal littermates with ejection fraction of 53–55%. Analysis of the ECG-gated two-dimensional cines indicated that the hypertrophy was of the nonobstructive type. Further analysis of heart-to-body weight ratio confirmed the ultrasound diagnosis of left ventricular hypertrophic cardiomyopathy. Histopathology showed increased ventricular wall thickness, enlarged myocyte size, and mild myofiber disarray. Ultrastructural analysis by electron microscopy revealed mitochondria hyperproliferation and dilated sarcoplasmic reticulum. Genome scanning using microsatellite DNA markers mapped the mutation to the X chromosome. DNA sequencing showed no mutations in the coding regions of several candidate genes on the X chromosome, including several known to be associated with left ventricular hypertrophic cardiomyopathy. These findings suggest that this mouse line may harbor a mutation in a novel gene causing X-linked cardiomyopathy.

Polymorphic ventricular tachycardia and abnormal Ca2+ handling in very-long-chain acyl-CoA dehydrogenase null mice

Patients with mutations in the mitochondrial very-long-chain acyl-CoA dehydrogenase (VLCAD) gene are at risk for cardiomyopathy, myocardial dysfunction, ventricular tachycardia (VT), and sudden cardiac death. The mechanism is not known. Here we report a novel mechanism of VT in mice lacking VLCAD (VLCAD(-/-)). These mice exhibited polymorphic VT and increased incidence of VT after isoproterenol infusion. Polymorphic VT was induced in 10 out of 12 VLCAD(-/-) mice (83%) when isoproterenol was used. One out of 10 VLCAD(-/-) mice with polymorphic VT had VT with the typical bidirectional morphology. At the molecular level, VLCAD(-/-) cardiomyocytes showed increased levels of cardiac ryanodine receptor 2, phospholamban, and calsequestrin with increased [(3)H]ryanodine binding in heart microsomes. At the single cardiomyocyte level, VLCAD(-/-) cardiomyocytes showed significant increase in diastolic indo 1 and fura 2 fluorescence, with increased Ca(2+) transient amplitude. These changes were associated with altered Ca(2+) dynamics, to include: faster sarcomere contraction, larger time derivative of the upstroke, and shorter time-to-minimum sarcomere length compared with VLCAD(+/+) control cells. The L-type Ca(2+) current characteristics were not different under voltage-clamp conditions in the two VLCAD genotypes. Sarcoplasmic reticulum Ca(2+) load measured as normalized integrated Na(+)/Ca(2+) exchange current after rapid caffeine application was increased by 48% in VLCAD(-/-) cells. We conclude that intracellular Ca(2+) handling represents a possible molecular mechanism of arrhythmias in mice and perhaps in VLCAD-deficient humans.

Oxygenation by COX-2 (cyclo-oxygenase-2) of 3-HETE (3-hydroxyeicosatetraenoic acid), a fungal mimetic of arachidonic acid, produces a cascade of novel bioactive 3-hydroxyeicosanoids

Cyclo-oxygenases-1/2 (COX-1/2) catalyse the oxygenation of AA (arachidonic acid) and related polyunsaturated fatty acids to endoperoxide precursors of prostanoids. COX-1 is referred to as a constitutive enzyme involved in haemostasis, whereas COX-2 is an inducible enzyme expressed in inflammatory diseases and cancer. The fungus Dipodascopsis uninucleata has been shown by us to convert exogenous AA into 3(R)-HETE [3(R)-hydroxy-5Z,8Z,11Z,14Z-eicosatetraenoic acid]. 3R-HETE is stereochemically identical with AA, except that a hydroxy group is attached at its C-3 position. Molecular modelling studies with 3-HETE and COX-1/2 revealed a similar enzyme-substrate structure as reported for AA and COX-1/2. Here, we report that 3-HETE is an appropriate substrate for COX-1 and -2, albeit with a lower activity of oxygenation than AA. Oxygenation of 3-HETE by COX-2 produced a novel cascade of 3-hydroxyeicosanoids, as identified with EI (electron impact)-GC-MS, LC-MS-ES (electrospray) and LC-MS-API (atmospheric pressure ionization) methods. Evidence for in vitro production of 3-hydroxy-PGE2 (3-hydroxy-prostaglandin E2) was obtained upon infection of HeLa cells with Candida albicans at an MOI (multiplicity of infection) of 100. Analogous to interaction of AA and aspirin-treated COX-2, 3-HETE was transformed by acetylated COX-2 to 3,15-di-HETE (3,15-dihydroxy-HETE), whereby C-15 showed the (R)-stereochemistry. 3-Hydroxy-PGs are potent biologically active compounds. Thus 3-hydroxy-PGE2 induced interleukin-6 gene expression via the EP3 receptor (PGE2 receptor 3) in A549 cells, and raised cAMP levels via the EP4 receptor in Jurkat cells. Moreover, 3R,15S-di-HETE triggered the opening of the K+ channel in HTM (human trabecular meshwork) cells, as measured by the patch-clamp technique. Since many fatty acid disorders are associated with an 'escape' of 3-hydroxy fatty acids from the b-oxidation cycle, the production of 3-hydroxyeicosanoids may be critical in modulation of effects of endogenously produced eicosanoids.

Debate Forum: Levocarnitine Therapy Is Rational and Justified in Selected Dialysis Patients

Carnitine is a metabolic cofactor which is essential for normal fatty acid metabolism. Patients with chronic kidney disease on dialysis have been shown both to suffer from disordered fatty acid metabolism and to have a significant deficiency in plasma and tissue carnitine. Aberrant fatty acid metabolism has been associated with a number of cellular abnormalities such as increased mitochondrial permeability (a promoter of apoptosis), insulin resistance, and enhanced generation of free radicals. These cellular abnormalities have, in turn, been correlated with pathological clinical conditions common in dialysis patients including cardiomyopathy with attendant hypotension and resistance to the therapeutic effect of recombinant human erythropoietin (EPO). In 1999, the Food and Drug Administration approved levocarnitine injection for the prevention and treatment of carnitine deficiency in patients on dialysis based on documentation of free plasma carnitine levels in dialysis patients similar to other serious carnitine deficiency states for which treatment was required. Data analysis performed by expert panels convened by both the American Association of Kidney Patients and, subsequently, the National Kidney Foundation recommended a trial of levocarnitine therapy for specific subsets of dialysis patients including those with EPO resistance, dialysis-related hypotension, cardiomyopathy and muscle weakness. In 2003, the Centers for Medicare and Medicaid services convened a Medical Advisory Committee which established reimbursement on a national level for carnitine-deficient dialysis patients who had either dialysis-related hypotension or EPO resistance. Recently, a correlation between reductions in hospitalization rates of dialysis patients receiving levocarnitine therapy has been demonstrated in a large retrospective study. Despite data-based recommendations and national reimbursement, only a small minority of dialysis patients have been prescribed a therapeutic trial of levocarnitine. Whereas the reasons for the reluctance of nephrologists to prescribe this therapeutic trial are unclear, possible explanations include a lack of appreciation of the pivotal role played by carnitine in cellular metabolism and the strength of evidence for a substantial deficiency of carnitine in dialysis patients, an underestimation of the prognostic import of EPO resistance and dialysis-related hypotension, inadequate dissemination of the clinical trial data supporting the use of levocarnitine in dialysis patients, and the heterogeneous clinical response of dialysis patients to levocarnitine therapy. Difficulties in documenting both initial eligibility and evidence of improvement as a result of therapy may also be a contributing factor. This paper discusses the biological role of carnitine and its particular relevance to dialysis patients. Clinical trial data concerning an effect of therapy on EPO resistance and dialysis-related hypotension are summarized along with a discussion of the logic behind the use of levocarnitine in dialysis. Finally, the difficulties posed by a reimbursement policy based on clinical as opposed to laboratory endpoints and a heterogeneous response to therapy are addressed.

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.

Abnormal mitochondrial bioenergetics and heart rate dysfunction in mice lacking very-long-chain acyl-CoA dehydrogenase

Mitochondrial very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is associated with severe hypoglycemia, cardiac dysfunction, and sudden death in neonates and children. Sudden death is common, but the underlying mechanisms are not fully understood. We report on a mouse model of VLCAD deficiency with a phenotype induced by the stresses of fasting and cold, which includes hypoglycemia, hypothermia, and severe bradycardia. The administration of glucose did not rescue the mice under stress conditions, but rewarming alone consistently led to heart rate recovery. Brown adipose tissue (BAT) from the VLCAD-/- mice showed elevated levels of the uncoupling protein isoforms and peroxisome proliferator-activated receptor-alpha. Biochemical assessment of the VLCAD(/- mice BAT showed increased oxygen consumption, attributed to uncoupled respiration in the absence of stress. ADP-stimulated respiration was 23.05 (SD 4.17) and 68.24 (SD 6.3) nmol O2.min(-1).mg mitochondrial protein(-1) for VLCAD+/+ and VLCAD-/- mice, respectively (P < 0.001), and carbonyl cyanide p-trifluoromethoxyphenylhydrazone-stimulated respiration was 35.9 (SD 3.6) and 49.3 (SD 9) nmol O2.min(-1).mg mitochondrial protein(-1) for VLCAD+/+ and VLCAD-/- mice, respectively (P < 0.20), but these rates were insufficient to protect them in the cold. We conclude that disturbed mitochondrial bioenergetics in BAT is a critical contributing factor for the cold sensitivity in VLCAD deficiency. Our observations provide insights into the possible mechanisms of stress-induced death in human newborns with abnormal fat metabolism and elucidate targeting of specific substrates for particular metabolic needs.

Endocrine disorders in the neonate

There is a significant amount of knowledge that has been gained in recent years in the study of endocrine disorders in the newborn. The explosion of genetic data shedding light on the origins of endocrine disease has expanded the level of diagnostic evaluation and management of these infants. This article provides a general review of endocrine disorders as they present in a newborn.

A novel mitochondrial carnitine-acylcarnitine translocase induced by partial hepatectomy and fasting

The carnitine-dependent transport of long-chain fatty acids is essential for fatty acid catabolism. In this system, the fatty acid moiety of acyl-CoA is transferred enzymatically to carnitine, and the resultant product, acylcarnitine, is imported into the mitochondrial matrix through a transporter named carnitine-acylcarnitine translocase (CACT). Here we report a novel mammalian protein homologous to CACT. The protein, designated as CACL (CACT-like), is localized to the mitochondria and has palmitoylcarnitine transporting activity. The tissue distribution of CACL is similar to that of CACT; both are expressed at a higher level in tissues using fatty acids as fuels, except in the brain, where only CACL is expressed. In addition, CACL is induced by partial hepatectomy or fasting. Thus, CACL may play an important role cooperatively with its homologue CACT in a stress-induced change of lipid metabolism, and may be specialized for the metabolism of a distinct class of fatty acids involved in brain function.

Very-long-chain acyl-coenzyme a dehydrogenase deficiency in mice

Fatty acid oxidation (FAO) defects are inborn errors of metabolism clinically associated with cardiomyopathy and sudden infant death syndrome (SIDS). FAO disorders often present in infancy with myocardial dysfunction and arrhythmias after exposure to stresses such as fasting, exercise, or intercurrent viral illness. It is uncertain whether the heart, in the absence of stress, is normal. We generated very-long-chain acyl-coenzyme A dehydrogenase (VLCAD)-deficient mice by homologous recombination to define the onset and molecular mechanism of myocardial disease. We found that VLCAD-deficient hearts have microvesicular lipid accumulation, marked mitochondrial proliferation, and demonstrated facilitated induction of polymorphic ventricular tachycardia, without antecedent stress. The expression of acyl-CoA synthase (ACS1), adipophilin, activator protein 2, cytochrome c, and the peroxisome proliferator activated receptor gamma coactivator-1 were increased immediately after birth, preceding overt histological lipidosis, whereas ACS1 expression was markedly downregulated in the adult heart. We conclude that mice with VLCAD deficiency have altered expression of a variety of genes in the fatty acid metabolic pathway from birth, reflecting metabolic feedback circuits, with progression to ultrastructural and physiological correlates of the associated human disease in the absence of stress.

Accumulation of 3-hydroxy-fatty acids in the culture medium of long-chain L-3-hydroxyacyl CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein-deficient skin fibroblasts: implications for medium chain triglyceride dietary treatment of LCHAD deficiency

Dietary management of long-chain l-3-hydroxyacyl CoA dehydrogenase (LCHAD) deficiency involves a regimen that contains adequate carbohydrate, protein, and essential lipids, and supplementation with medium-chain fatty acids in the form of medium-chain triglycerides, providing energy from fats that bypasses the long-chain metabolic block. This study analyzes the effects of dietary treatment of LCHAD deficiency in an in vitro model. Cultured skin fibroblasts from LCHAD-deficient and normal individuals were grown in media supplemented with physiologic combinations of medium-chain fatty acids octanoate and decanoate, and the long-chain palmitate. Medium was removed from the cells after various incubation times, and assayed for 3-hydroxy-intermediates of fatty acid oxidation. The 3-hydroxy-fatty acids were measured by stable-isotope dilution gas chromatography/mass spectrometry. We found that the addition of medium-chain fatty acids caused a decrease in the accumulation of long-chain fatty acid oxidation intermediates in LCHAD-deficient cells when the cells were incubated in untreated medium, and also when they were incubated in this medium with palmitate added. Medium with decanoate alone was better at achieving this effect than medium with only octanoate added. A 1:3 ratio of octanoate to decanoate worked best over an extended time period in LCHAD-deficient cells in untreated medium, whereas a 1:1 ratio of octanoate to decanoate worked best in the same cells incubated in medium containing palmitate. In all dietary medium-chain triglyceride preparations, the ratio of octanoate was greater than that of decanoate. Our results suggest that a medium-chain triglyceride preparation that is higher in decanoate may be more effective in reducing the accumulation of potentially toxic long-chain 3-hydroxy-fatty acids in LCHAD deficiency.

Clinical effects of L-carnitine supplementation on apnea and growth in very low birth weight infants

OBJECTIVE

Systemic carnitine deficiency may present with apnea, hypotonia, and poor growth. Premature infants often manifest these symptoms and are at risk of developing carnitine deficiency because of immaturity of the biosynthetic pathway, lack of sufficient predelivery transplacental transport, and lack of sufficient exogenous supplementation. This study was undertaken to examine the effect of carnitine supplementation in premature infants.

METHODS

Eighty preterm infants <1500 g were enrolled in a prospective, double-blind, placebo-controlled study of carnitine supplementation within 96 hours of delivery. Growth, length of hospital stay, and frequency and severity of apnea were the primary outcome measures.

RESULTS

Weight gain and change in length, fronto-occipital head circumference, mid arm circumference, and triceps skinfold thickness were similar between the carnitine-supplemented and placebo groups. The amount and severity of apnea and the overall length of hospitalization were also similar between the 2 groups. The carnitine levels in the supplemented group were significantly higher than in the placebo group at 4 and 8 weeks after study entry.

CONCLUSION

Although preterm infants <1500 g have low carnitine levels, routine supplementation with carnitine has no demonstrable effect on growth, apnea, or length of hospitalization and thus seems to be unnecessary.

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.

Characterization of altered myocardial fatty acid metabolism in patients with inherited cardiomyopathy

Inherited defects in myocardial long-chain fatty acid metabolism are increasingly recognized as a cause of cardiomyopathy and sudden death in children. To evaluate whether the phenotypic expression of these genetic diseases could be delineated using positron emission tomography (PET), 11 patients with inherited defects in fatty acid metabolism were evaluated and results were compared with those of 6 nonaffected siblings. Myocardial perfusion, myocardial oxygen consumption (MVO2), and long-chain fatty acid metabolism were determined noninvasively with PET using quantitative mathematical models. There were no differences in haemodynamics, perfusion, MVO2 or plasma substrate levels between groups. Patients with defects in enzymes of fatty acid beta-oxidation (acyl-CoA dehydrogenase and 3-hydroxyacyl-CoA dehydrogenase deficiencies) (n = 5) had diminished myocardial palmitate oxidation compared with healthy siblings (3.2 +/- 3.0 vs. 13.0 +/- 5.6 nmol/g per min, p < 0.03) and a decrease in the percentage of MVO2 accounted for by palmitate (2% +/- 3% vs. 9% +/- 5%, p < 0.04). In these patients, extracted palmitate was shunted into a slow-turnover compartment (predominantly reflecting esterification to triglycerides) with expansion of palmitate in that pool (185 +/- 246 compared with 27 +/- 67 nmol/g in healthy siblings,p < 0.02). In contrast, myocardium of patients with carnitine deficiency (n = 6) (all on oral carnitine therapy) had normal palmitate extraction but expansion of the interstitial/cytosolic fatty acid pool (617 +/- 399 vs. 261 +/- 73 nmol/g in healthy siblings, p < 0.04), suggesting different mechanisms for handling upstream fatty acyl intermediates. Thus, PET can be used to noninvasively assess abnormal myocardial handling of fatty acids in patients with inherited defects of metabolism. This approach should be useful in the assessment of altered myocardial fatty acid metabolism associated with cardiomyopathy as well as for evaluating the efficacy of therapeutic interventions in affected patients.

The molecular basis of congenital cardiac disease

Today, congenital cardiovascular disease is virtually always amenable to corrective or palliative surgical interventions. However, the mechanisms causing developmental anomalies of the heart and vessels have remained obscure until recently. This review presents genetic defects causing the pediatric vasculopathies; Marfan's syndrome, inherited supravalvar aortic stenosis, and Williams' syndrome. A synopsis of known mutations causing human cardiomyopathies in nuclear genes encoding contractile proteins, cardiomyocyte structural proteins, and mitochondrial proteins essential for cardiac energy production is provided. The molecular genetic evidence implicating single gene mutations in the pathogenesis of conotruncal anomalies (the 22q11 monosomy or "cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, and hypocalcemia with deletions on chromosome 22" [CATCH-22] syndrome), heterotaxy syndromes, trisomies and atrioventricular canal defects, and secundum atrial septal defects is presented. The consequences of these genetic causes for diagnostic evaluation and perioperative care are emphasized. Single gene defects are a common cause of congenital cardiac disease. Copyright 1998 by W.B. Saunders Company

Multiple acyl-CoA dehydrogenase deficiency: a rare cause of acidosis with an increased anion gap

Metabolic acidosis is encountered frequently in intensive care and common causes include lactic acidosis, ketoacidosis, or renal failure. We describe a patient presenting to intensive care with a rare cause of metabolic acidosis associated with an increased anion gap: multiple acyl-CoA dehydrogenase deficiency. The pathophysiology of this condition is discussed along with potential treatment options.

Quantitative measurement of total and free 3-hydroxy fatty acids in serum or plasma samples: short-chain 3-hydroxy fatty acids are not esterified

Diagnostic protocols for disorders of mitochondrial fatty acid oxidation (FAO) generally include the measurement of plasma acylcarnitines. Many biochemical intermediates of FAO resulting from a metabolic block require carnitine conjugation for transport out of the mitochondria, and so occur as fatty acid carnitine conjugates in the blood. Both short- and long-chain acylcarnitines are generally determined, and this procedure has a critical role to play in the diagnosis of disorders of the very long-chain, medium-chain and short-chain acyl-CoA dehydrogenase defects. Less is known about the utility of acylcarnitines for the measurement of the various chain length intermediates of the 3-hydroxyacyl-CoA dehydrogenase steps of beta-oxidation. This study utilizes stable-isotope dilution gas chromatography-mass spectrometry to determine the serum or plasma concentrations of free 3-hydroxy fatty acids (3-OHFAs) of chain lengths C6 to C16. The 3-OHFA concentrations are determined in samples from normal individuals, hyperketotic individuals and patients with long-chain L-3-hydroxyacyl-CoA dehydrogenase and short-chain L-3-hydroxyacyl-CoA dehydrogenase deficiencies, both before and after hydrolysis. The results of the study indicate the relative amounts of conjugated intermediates of all chain lengths. Long-chain 3-OHFAs (C14 and C16) are found in elevated concentrations after hydrolysis, whereas short-chain and medium-chain 3-OHFAs (C6 to C12) show no difference in concentrations between the two samples in all subjects tested, suggesting that only long-chain 3-hydroxy species form conjugates. This finding has important implications for the use of the acylcarnitine assay for the diagnosis of defects involving short-chain and medium-chain 3-hydroxy fatty acids.

Evaluation of urinary acylglycines by electrospray tandem mass spectrometry in mitochondrial energy metabolism defects and organic acidurias

We analyzed the urinary acylglycine excretion in 26 patients with mitochondrial energy metabolism disorders and in 55 patients with organic acidurias by electrospray tandem mass spectrometry (ESI-MS/MS), monitoring precursor ions of m/z 90. Urinary concentrations of the different acylglycines were quantified using deuterated internal standards. Normal values for the most important acylglycines were established. In MCAD and MAD (neonatal form) deficiencies, typical excretion patterns of urinary acylglycines were found in all the samples. In isovaleric aciduria, propionic aciduria, and 3-methylcrotonylglycinuria typical glycine conjugates were always found. Methylmalonic aciduria (mutase deficiency), multiple carboxylase deficiency, and 3-hydroxy-3-methylglutaric aciduria revealed pathological acylglycine profiles, even if not specific for the disease. In all these diseases acylglycine excretion seems to be less influenced by the clinical status than organic acid excretion. This method is a useful diagnostic tool for these metabolic disorders, complementary to organic acids and acylcarnitine profiles.

Synthesis and preliminary evaluation of (18)F-labeled 4-thia palmitate as a PET tracer of myocardial fatty acid oxidation

Interest remains strong for the development of a noninvasive technique for assessment of regional fatty acid oxidation rate in the myocardium. (18)F-labeled 4-thia palmitate (FTP, 16-[(18)F]fluoro-4-thia-hexadecanoic acid) has been synthesized and preliminarily evaluated as a metabolically trapped probe of myocardial fatty acid oxidation for positron emission tomography (PET). The radiotracer is synthesized by Kryptofix 2.2.2/K(2)CO(3) assisted nucleophilic radiofluorination of an iodo-ester precursor, followed by alkaline hydrolysis and by purification by reverse phase high performance liquid chromatography. Biodistribution studies in rats showed high uptake and long retention of FTP in heart, liver, and kidneys consistent with relatively high fatty acid oxidation rates in these tissues. Inhibition of carnitine palmitoyl-transferase-I caused an 80% reduction in myocardial uptake, suggesting the dependence of trapping on the transport of tracer into the mitochondrion. Experiments with perfused rat hearts showed that the estimates of the fractional metabolic trapping rate (FR) of FTP tracked inhibition of oxidation rate of palmitate with hypoxia, whereas the FR of the 6-thia analog 17-[(18)F]fluoro-6-thia-heptadecanoic acid was insensitive to hypoxia. In vivo defluorination of FTP in the rat was evidenced by bone uptake of radioactivity. A PET imaging study with FTP in normal swine showed excellent myocardial images, prolonged myocardial retention, and no bone uptake of radioactivity up to 3 h, the last finding suggesting a species dependence for defluorination of the omega-labeled fatty acid. The results support further investigation of FTP as a potential PET tracer for assessing regional fatty acid oxidation rate in the human myocardium.

Metabolic myopathies: a clinical approach; part I

Children and adults with metabolic myopathies have underlying deficiencies of energy production, which may result in dysfunction of muscle or other energy-dependent tissues, or both. Patients with disorders of glycogen, lipid, or mitochondrial metabolism in muscle may present with dynamic findings (i.e., exercise intolerance, reversible weakness, and myoglobinuria) or progressive muscle weakness, or both. In this first part of the review, we present a brief description of energy metabolism in muscle, a simplified overview of the clinical and laboratory evaluation of the patient with suspected metabolic myopathy, and a diagnostic algorithm aimed at predicting the nature of the underlying biochemical abnormality. The goal is to simplify a complex field of neuromuscular disease and thus lead to early recognition and treatment of these disorders.

Improved Stable Isotope Dilution-Gas Chromatography-Mass Spectrometry Method for Serum or Plasma Free 3-Hydroxy-Fatty Acids and Its Utility for the Study of Disorders of Mitochondrial Fatty Acid β-Oxidation

Background: Disorders of fatty acid oxidation (FAO) are difficult to diagnose, primarily because in many of the FAO disorders measurable biochemical intermediates accumulate in body fluids only during acute illness. Increased concentrations of 3-hydroxy-fatty acids (3-OH-FAs) in the blood are indicative of FAO disorders of the long- and short-chain 3-hydroxy-acyl-CoA dehydrogenases, LCHAD and SCHAD. We describe a serum/plasma assay for the measurement of 3-OH-FAs with carbon chain lengths from C6 to C16.

Methods: We used stable isotope dilution gas chromatography-mass spectrometry (GC-MS) with electron impact ionization and selected ion monitoring. Natural and isotope-labeled compounds were synthesized for the assay.

Results: The assay was linear from 0.2 to 50 μmol/L for all six 3-OH-FAs. CVs were 5–15% at concentrations near the upper limits seen in healthy subjects. In 43 subjects, the medians (and ranges) in μmol/L were as follows: 3-OH-C6, 0.8 (0.3–2.2); 3-OH-C8, 0.4 (0.2–1.0); 3-OH-C10, 0.3 (0.2–0.6); 3-OH-C12, 0.3 (0.2–0.6); 3-OH-C14, 0.2 (0.0–0.4); and 3-OH-C16, 0.2 (0.0–0.5). 3-OH-FAs were increased in infants receiving formula containing medium chain triglycerides. Two patients diagnosed with LCHAD deficiency showed marked increases in 3-OH-C14 and 3-OH-C16 concentrations. Two patients diagnosed with SCHAD deficiency showed increased shorter chain 3-OH-FAs but no increases in 3-OH-C14 to 3-OH-C16.

Conclusion: Measuring blood concentrations of the 3-OH-FAs with this assay may be a valuable tool for helping to rapidly identify deficiencies in LCHAD and SCHAD and may also provide useful information about the status of the FAO pathway.

Inborn errors of mitochondrial fatty acid oxidation

Inborn errors of the mitochondrial beta-oxidation of long-chain fatty acids represent an evolving field of inherited metabolic disease. Fatty acid oxidation defects demonstrate an abnormal response to the process of fasting adaptation and affect those tissues that utilize fatty acids as an energy source. These tissues include cardiac and skeletal muscle and liver. Muscle directly uses fatty acids as an energy source whilst hepatic metabolism of fatty acids is mostly directed toward the synthesis of ketone bodies for energy utilization by tissues such as brain. The clinical phenotypes of fatty acid oxidation disorders include disease of one or more of these fatty acid-metabolizing tissues. In this review, we provide an overview of the pathway, discuss the disorders that are well established, and describe recent advances in the field. Currently available diagnostic procedures are critically evaluated.

Hepatic carnitine palmitoyltransferase I deficiency presenting as maternal illness in pregnancy

The spectrum of clinical presentation of fatty acid oxidation defects (FAOD) continues to expand. One FAOD, L-3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency has been associated with liver disease in pregnancies involving a heterozygous mother carrying an affected fetus. Hepatic carnitine palmitoyltransferase (CPT I) deficiency typically presents as a Reyelike syndrome in children between 8 and 18 mo. of age. We have investigated a family in which the mother developed liver disease consistent with acute fatty liver of pregnancy (AFLP) and hyperemesis gravidarum in her two successive pregnancies. Neither child nor their mother was found to carry the common LCHAD G1528C mutation. Both children were subsequently shown to have absent activity of CPT I. This is the first report of CPT I deficiency presenting as maternal illness in pregnancy.

Fatal hepatic short-chain L-3-hydroxyacyl-coenzyme A dehydrogenase deficiency: clinical, biochemical, and pathological studies on three subjects with this recently identified disorder of mitochondrial beta-oxidation

This report describes the clinical, biochemical, and pathological findings in three infants with hepatic short-chain L-3-hydroxyacyl-coenzyme A dehydrogenase (SCHAD) deficiency, a recently recognized disorder of the mitochondrial oxidation of straight-chain fatty acids. Candidate subjects were identified from an ongoing study of infant deaths. SCHAD analysis was performed on previously frozen liver and skeletal muscle on subjects with a characteristic urine organic acid profile. Autopsy findings were correlated with the biochemical abnormalities. Enzyme analysis in liver revealed marked deficiency in SCHAD with residual activities of 3-11%. All subjects had normal activity in skeletal muscle. However, Western blot analysis of SCHAD revealed an identical truncated protein in both liver and muscle from one patient, suggesting that SCHAD is similar in liver and muscle and that the normal activity in muscle may be due to other enzymes with C4 activity. Autopsy findings revealed marked steatosis and a muscle pattern consistent with spinal muscular atrophy in one patient. Lipid storage was less pronounced in one patient and not detected in the third patient who had a well-documented history of recurrent hypoglycemia. This is the initial pathological characterization of this enzyme defect, and our observations suggest that SCHAD deficiency is a very severe disorder contributing to early infant death.