Complementation analysis of fatty acid oxidation disorders.

We assayed [9,10(n)-3H]palmitate oxidation by fibroblast monolayers from patients with fatty acid oxidation disorders. Activities in the different disorders were (percent control): short-chain acyl-coenzyme A (CoA) dehydrogenase deficiency (115%), medium chain acyl-CoA dehydrogenase deficiency (18%), long-chain acyl-CoA dehydrogenase deficiency (28%), multiple acyl-CoA dehydrogenation disorder, mild and severe variants (49% and 7%), and palmityl-carnitine transferase deficiency (4%). Multiple acyl-CoA dehydrogenation disorder, medium chain acyl-CoA dehydrogenase-deficient lines, and long-chain acyl-CoA dehydrogenase-deficient lines all complemented one another after polyethylene glycol fusion, with average activity increases of 31-83%. We detected two complementation groups in the severe multiple acyl-CoA dehydrogenation disorder lines, consistent with deficiencies of either electron transfer flavoprotein or electron transfer flavoprotein:ubiquinone oxidoreductase. The metabolic block in the latter cell lines is threefold more severe than in the former (P less than 0.001). No intragenic complementation was observed within either group. We assigned two patients with previously unreported severe multiple acyl-CoA dehydrogenation disorder to the electron transfer flavoprotein:ubiquinone oxido-reductase-deficient group.     

Abnormal nonshivering thermogenesis in mice with inherited defects of fatty acid oxidation.

When placed in the cold (4 degreesC), BALB/cByJ mice of both genders rapidly lose body temperature as compared with the control strain, C57BL/6J. This sensitivity to cold resembles that previously described for mice with a defect in nonshivering thermogenesis due to the targeted inactivation of the brown adipocyte-specific mitochondrial uncoupling protein gene, Ucp1. Genetic mapping of the trait placed the gene on chromosome 5 near Acads, a gene encoding the short chain acyl CoA dehydrogenase, which is mutated in BALB/cByJ mice. The analysis of candidate genes in the region indicated a defect only in the expression of Acads. Confirmation of the importance of fatty acid oxidation to thermogenesis came from our finding that mice carrying the targeted inactivation of the long chain acyl CoA dehydrogenase gene (Acadl) are also sensitive to the cold. Both of these mutations attenuate the induction of genes normally responsive to adrenergic signaling in brown adipocytes. These results suggest that the action of fatty acids as regulators of gene expression has been perturbed in the mutant mice. From a clinical perspective, it is important to determine whether defects in thermogenesis may be a phenotype in human neonates with inherited deficiencies in fatty acid beta-oxidation.     

Combined enzyme defect of mitochondrial fatty acid oxidation.

A young girl presented with recurrent episodes of muscle weakness culminating in a severe attack of generalized muscle weakness. In the muscle mitochondria from the patient there was an abnormal pattern of intermediates of beta-oxidation with an accumulation of 3-hydroxyacyl- and 2-enoyl-CoA and carnitine esters, and 3-oxoacylcarnitines. There was low activity of long-chain 3-hydroxyacyl-CoA dehydrogenase in mitochondria from all tissues. The activity of long-chain 2-enoyl-CoA hydratase was low in muscle mitochondria and 3-oxoacyl-CoA thiolase activity measured with 3-oxohexadecanoyl-CoA as substrate was low in fibroblast, muscle, and cardiac mitochondria but only partial deficiency was present when the activity was measured with 3-oxooctanoyl-CoA. The activity of the long-chain 3-hydroxyacyl-CoA dehydrogenase and long-chain 3-oxoacyl-CoA thiolase in fibroblasts from the patient's parents was intermediate between those of controls and the patient. The patient has a combined defect of the long-chain 3-hydroxyacyl-CoA dehydrogenase, long-chain 3-oxoacyl-CoA thiolase, and long-chain 2-enoyl-CoA hydratase which appears to be inherited in an autosomal recessive manner. This suggests there is a multifunctional enzyme catalyzing these activities in human mitochondria and that this enzyme is deficient in our patient.     

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.     

Serum carnitine concentrations in patients with idiopathic hypertrophic cardiomyopathy: relationship with impaired myocardial fatty acid metabolism.

We evaluated the clinical significance of serum carnitine concentrations in determining the severity of impaired myocardial fatty acid metabolism in idiopathic hypertrophic cardiomyopathy (HCM). We studied 56 asymptomatic or mildly symptomatic patients with HCM. Serum levels of free carnitine and acylcarnitine were measured by the enzymic cycling method. Myocardial scintigraphy with (123)I-labelled 15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP) was performed, and the images were analysed quantitatively and semi-quantitatively. Serum free carnitine levels were significantly higher in HCM patients than in normal subjects (52. 5+/-9.5 and 42.3+/-5.5 nmol/ml respectively; P<0.0001). On the other hand, serum acylcarnitine levels and acyl/free carnitine ratios were lower in HCM patients than in normal subjects (10.2+/-4.0 nmol/ml and 0.19+/-0.08, compared with 13.2+/-3.9 nmol/ml and 0.32+/-0.11 respectively; P<0.0001). Clinical characteristics were not significantly different between the patients showing high and normal free carnitine levels, although female patients with high free carnitine levels were few (P=0.02). Both quantitative and semi-quantitative analyses revealed that the severity of decreased myocardial BMIPP uptake was significantly correlated with serum free carnitine levels (quantitative analysis: r=-0.422, P<0.0012; semi-quantitative analysis: r=0.633, P<0.0001). In the presence of reduced carnitine uptake into the myocardium in HCM, there may also be reduced transport of acylcarnitines out of the myocardium into the plasma. Although inborn errors of fatty acid metabolism and carnitine deficiencies are reported to provoke secondary HCM and are associated with low serum carnitine concentrations, this study has revealed that the levels of carnitine are, in contrast, increased in idiopathic HCM. Moreover, serum carnitine concentrations are a sensitive indicator of the severity of impaired myocardial fatty acid metabolism even in asymptomatic patients with HCM.     

Cell imaging and morphology: application to studies of inherited purine metabolic disorders

A number of inherited or drug-induced metabolic disorders involving dysfunctions in purines and pyrimidines are strongly associated with neurological dysfunction, e.g., Lesch Nyhan syndrome. Such disorders have been studied extensively using biochemical and molecular techniques in order to examine how such defects occur, sometimes using in vitro models based upon cultured neuroblastoma cell lines. However, these metabolic dysfunctions may manifest their effects in other ways, such as impaired synaptic transmission and gross abnormalities in neuronal growth and differentiation. This review outlines the latter novel facet of purine research. It is proposed that by employing cell imaging techniques and cultured neuroblastoma cell lines, believed to model the nervous system, significant insights into how inherited disorders of purine metabolism affect neuronal development can be obtained. This review provides an example of the application of these techniques to understand the etiology of Lesch Nyhan syndrome, and encourages further study of the role of purines and pyrimidines in the development of the nervous system.     

Rationale and application of fatty acid oxidation inhibitors in treatment of diabetes mellitus.

There are elevated fatty acid levels in non-insulin-dependent diabetes mellitus that are due to diminished insulin action in inhibiting fatty acid release from adipocytes. Insulin therapy and other inhibitors of fatty acid release from adipocytes (e.g., nicotinic acid) suppress these elevated fatty acid levels and bring about a reduction in hyperglycemia. One mechanism by which fatty acids may be causal in hyperglycemia is in stimulating gluconeogenesis in the liver in the postabsorptive state. Another mechanism is in attenuating glucose disposal in skeletal muscle in the fed state. Potential nonglycemia-related effects of fatty acids are in substrate utilization in the heart and lipid synthesis in the liver. Inhibition of fatty acid oxidation is useful in reducing hyperglycemia by inhibiting glucose production in humans. However, there is less evidence that such inhibition can be useful in increasing glucose utilization in muscle, as predicted by the Randle hypothesis. This, coupled with potential adverse effects on heart muscle, make liver targeting of fatty acid oxidation inhibitors an important factor in their potential for development. Although such agents have advantageous effects on lipid metabolism, overdosing can lead to adverse liver lipid effects via the same mechanism. These adverse liver lipid effects could be minimized by development of reversible inhibitors that allow fatty acid oxidation to occur only during the overnight fast. The potential usefulness of such agents is evident; however, no drug that meets these objectives has been developed.     

Malonyl-CoA: the regulator of fatty acid synthesis and oxidation

In the catabolic state with no food intake, the liver generates ketones by breaking down fatty acids. During the nocturnal fast or longer starvation periods, this protects the brain, which cannot oxidize fatty acids. In 1977, we published a study in the JCI noting the surprising realization that malonyl-CoA, the substrate of fatty acid synthesis, was also an inhibitor of fatty acid oxidation. Subsequent experiments have borne out this finding and furthered our understanding of molecular metabolism.     

Effect of stavudine on mitochondrial genome and fatty acid oxidation in lean and obese mice

Like other antihuman immunodeficiency virus dideoxynucleosides, stavudine may occasionally induce lactic acidosis and perhaps lipodystrophy in metabolically or genetically susceptible patients. We studied the effects of stavudine on mitochondrial DNA (mtDNA), fatty acid oxidation, and blood metabolites in lean and genetically obese (ob/ob) mice. In lean mice, mtDNA was depleted in liver and skeletal muscle, but not heart and brain, after 6 weeks of stavudine treatment (500 mg/kg/day). With 100 mg/kg/day, mtDNA transiently decreased in liver, but was unchanged at 6 weeks in all organs, including white adipose tissue (WAT). Despite unchanged mtDNA levels, lack of significant oxidative mtDNA lesions (as assessed by long polymerase chain reaction experiments), and normal blood lactate/pyruvate ratios, lean mice treated with stavudine for 6 weeks had increased fasting blood ketone bodies, due to both increased hepatic fatty acid beta-oxidation and decreased peripheral ketolysis. In obese mice, basal WAT mtDNA was low and was further decreased by stavudine. In conclusion, stavudine can decrease hepatic and muscle mtDNA in lean mice and can also cause ketoacidosis during fasting without altering mtDNA. Stavudine depletes WAT mtDNA only in obese mice. Fasting and ketoacidosis could trigger decompensation in patients with incipient lactic acidosis, whereas WAT mtDNA depletion could cause lipodystrophy in genetically susceptible patients.     

The effect of carnitine on the metabolism of valproic acid in epileptic patients.

The half-life of valproic acid (VPA) was studied in 8 epileptic and severely mental retarded patients before and after one month of carnitine supplementation. Serum carnitine concentration was significantly decreased and VPA half-life was prolonged especially in adult patients before carnitine supplementation. After the treatment with carnitine, serum carnitine concentration was increased, and prolonged half-lives of VPA were corrected near to the normal range (from 12.2 +/- 4.2 hr to 9.7 +/- 2.2 hr; p < 0.05). Controlled state of epilepsy was unchanged during the short period of observation.     

A sensitive and simplified method to analyze free fatty acids in children with mitochondrial beta oxidation disorders using gas chromatography/mass spectrometry and dried blood spots.

BACKGROUND: A precise diagnosis of mitochondrial fatty acid beta-oxidation (FAO) disorders can be difficult as several enzymatic reactions are involved. METHODS: Using 5 blood spots on filter paper, each 3 mm in diameter, octanoate, decanoate, cis-4-decenoic acid (C10:1) and cis-5-tetradecenoic acid (C14:1) were measured by one step transmethylation and gas chromatography-mass spectrometry (GC/MS). RESULTS: In subjects with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency C10:1 was increased. C14:1 was increased in very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, and both were increased in multiple acyl CoA dehydrogenase (MAD) deficiency. CONCLUSIONS: Free fatty acids (FFAs) can be measured with a small amount of blood sample if selective ion monitoring (SIM) in GC/MS analysis is used. A single microtube was sufficient throughout the procedure prior to injection onto GC/MS.     

The natural history of childhood-acquired hepatitis C infection in patients with inherited bleeding disorders

BACKGROUND: Although many patients with inherited bleeding disorders have been infected with hepatitis C in early childhood, the natural history of infection in this patient group remains poorly defined. STUDY DESIGN AND METHODS: A total of 212 patients with inherited bleeding disorders born between 1976 and 1992 were evaluated for hepatitis C virus (HCV) infection, spontaneous clearance, and (by noninvasive tests) progressive liver disease. RESULTS: A total of 120 of 212 patients had been exposed to non-HCV-inactivated clotting products, and 68 of these 120 patients (57%) were anti-HCV-positive. Of these patients, 44 (65%) had chronic hepatitis C (HCV RNA-positive) and 24 (35%) showed spontaneous clearance (HCV RNA-negative). Five patients with hepatitis C were coinfected with hepatitis B virus and/or human immunodeficiency virus (HIV). Multivariate analysis indicated that hepatitis C infection was independently associated with longer treatment period (odds ratio [OR], 1.6; 95% confidence interval [CI], 1.3-1.9) and exposure to a larger number of donors (OR, 2.1; 95% CI, 1.1-3.9). Spontaneous HCV clearance was associated with a younger age at first exposure to clotting product (p = 0.02). After a mean infection period of 21 years, evidence of cirrhosis was present in 2 patients (5%), both of whom were coinfected with HIV. CONCLUSION: Spontaneous HCV clearance is associated with young age at infection. Despite frequent childhood-acquired hepatitis C infection among patients with inherited bleeding disorders, progression to cirrhosis after 21 years of infection is rare. The diagnosis of cirrhosis without biopsy, however, remains challenging in this population, and new, noninvasive means must be developed to accurately identify cirrhotic patients.     

Interleukin-2-dependent T lymphocytes for the diagnosis and investigation of inherited metabolic disorders

Interleukin-2-dependent T cell lines can be started from as little as 1 ml of peripheral blood and expanded to 50 x 10(6) cells within 12 days. These cells represent an easily obtainable source of nucleated tissue with certain advantages over skin fibroblasts or transformed B lymphoblastoid cells for the rapid diagnosis and study of inherited metabolic disorders. A panel of 19 enzymes were assayed in IL-2-dependent T lymphocytes and the diagnosis of four enzyme deficiencies is demonstrated using T lymphocytes.     

Peroxisomal fatty acid beta-oxidation in relation to the accumulation of very long chain fatty acids in cultured skin fibroblasts from patients with Zellweger syndrome and other peroxisomal disorders.

The peroxisomal oxidation of the long chain fatty acid palmitate (C16:0) and the very long chain fatty acids lignocerate (C24:0) and cerotate (C26:0) was studied in freshly prepared homogenates of cultured skin fibroblasts from control individuals and patients with peroxisomal disorders. The peroxisomal oxidation of the fatty acids is almost completely dependent on the addition of ATP, coenzyme A (CoA), Mg2+ and NAD+. However, the dependency of the oxidation of palmitate on the concentration of the cofactors differs markedly from that of the oxidation of lignocerate and cerotate. The peroxisomal oxidation of all three fatty acid substrates is markedly deficient in fibroblasts from patients with the Zellweger syndrome, the neonatal form of adrenoleukodystrophy and the infantile form of Refsum disease, in accordance with the deficiency of peroxisomes in these patients. In fibroblasts from patients with X-linked adrenoleukodystrophy the peroxisomal oxidation of lignocerate and cerotate is impaired, but not that of palmitate. Competition experiments indicate that in fibroblasts, as in rat liver, distinct enzyme systems are responsible for the oxidation of palmitate on the one hand and lignocerate and cerotate on the other hand. Fractionation studies indicate that in rat liver activation of cerotate and lignocerate to cerotoyl-CoA and lignoceroyl-CoA, respectively, occurs in two subcellular fractions, the endoplasmic reticulum and the peroxisomes but not in the mitochondria. In homogenates of fibroblasts from patients lacking peroxisomes there is a small (25%) but significant deficiency of the ability to activate very long chain fatty acids. This deficient activity of very long chain fatty acyl-CoA synthetase is also observed in fibroblast homogenates from patients with X-linked adrenoleukodystrophy. We conclude that X-linked adrenoleukodystrophy is caused by a deficiency of peroxisomal very long chain fatty acyl-CoA synthetase.     

Inverse relationship of leucine flux and oxidation to free fatty acid availability in vivo.

To determine the effect of fatty acid availability on leucine metabolism, 14-h fasted dogs were infused with either glycerol or triglyceride plus heparin, and 46-h fasted dogs were infused with either nicotinic acid or nicotinic acid plus triglyceride and heparin. Leucine metabolism was assessed using a simultaneous infusion of L-[4,5-3H]leucine and alpha-[1-14C]ketoisocaproate. Leucine, alpha-ketoisocaproate (KIC), and totalleucine carbon (leucine plus KIC) flux and oxidation rates were calculated at steady state. In 14-h fasted animals, infusion of triglyceride and heparin increased plasma free fatty acids (FFA) by 0.7 mM (P less than 0.01) and decreased leucine (P less than 0.01), total leucine carbon flux (P less than 0.02), and oxidation (P less than 0.05). The estimated rate of leucine utilization not accounted for by oxidation and KIC flux decreased, but the changes were not significant. During glycerol infusion, leucine and KIC flux and oxidation did not change. In 46-h fasted dogs, nicotinic acid decreased FFA by 1.0 mM (P less than 0.01) and increased (P less than 0.05) the rate of leucine and total leucine carbon flux, but did not affect KIC flux. Leucine oxidation increased (P less than 0.01) by nearly threefold, whereas nonoxidized leucine utilization decreased. Infusion of triglyceride plus heparin together with nicotinic acid blunted some of the responses observed with nicotinic acid alone. In that changes in oxidation under steady state condition reflect changes in net leucine balance, these data suggest that FFA availability may positively affect the sparing of at least one essential amino acid and may influence whole body protein metabolism.     

脂肪酸酯在治疗PICC术后机械性静脉炎中应用的护理

[目的]探讨脂肪酸酯在治疗经外周静脉穿刺置入中心静脉导管(PICC)术后机械性静脉炎中的作用.[方法]前瞻性的把PICC术后机械性静脉炎的病人随机分为治疗组及对照组,对照组给予硫酸镁外敷,治疗组在对照组的基础上外用脂肪酸酯,比较两组病人的临床表现及治愈率.[结果]机械性静脉炎的总发生率为35.1%,治疗组的治愈率为85.7%,显著高于对照组的50%(P=0.014).[结论]脂肪酸酯是一种治疗PICC术后机械性静脉炎的理想方法.     

4-hydroxycyclohexane-1-carboxylic acid: an unusual compound isolated from the urine of children with suspected disorders of metabolism.

1. An unknown compound has been isolated in the acidic fraction of urine samples taken from several children suspected of having metabolic disorders. 2. This unknown has been characterized using a gas chromatograph/mass spectrometer/computer system. Both the high and low resolution mass spectra have been determined and a structure proposed. 3. Authentic samples were synthesized and compared to the unknown and a final proof of structure is presented. The compound, 4-hydroxycyclohexane-1-carboxylic acid, is suspected to come from a dietary source but the actual genesis will be determined in future work.