Urinary excretion of l-carnitine and acylcarnitines by patients with disorders of organic acid metabolism: evidence for secondary insufficiency of l-carnitine

Liver transplantation in two cases of propionic acidaemia

Orthotopic liver transplantation (OLT) was performed in two patients with propionic acidaemia, a 7-year-old boy and a 9-year-old girl, diagnosed with a severe neonatal form with high risk of metabolic decompensation. In both cases the metabolic liver functions recovered within the 12 postoperative hours; no clinical symptoms of propionic acid toxicity, metabolic acidosis, severe hyperammonaemia, hyperglycinaemia or haematological abnormalities were observed. In both cases insulin-dependent diabetes mellitus occurred early after OLT (persisting in the boy's case). Severe post-transplantation complications were observed (acute rejection and CMV infection in both patients) which did not trigger metabolic decompensation. The boy developed chronic rejection and vanishing bile duct syndrome due to incomplete hepatic arterial thrombosis. He required permanent in-patient care with chronic hyperammonaemia and neurological sequelae involving the basal ganglia and died 15 months after OLT. The girl left hospital after 2 months and is presently leading a normal life with almost no dietary protein restriction (40 g protein per day). Urinary urea excretion and daily protein intake increased after liver transplantation. Propionyl- and tiglylglycine disappeared immediately after OLT. Urinary methylcitrate and 3-hydroxypropionate remained at concentrations corresponding to those before OLT. However, the total of all characteristic metabolites of organic acid analysis was reduced to 50-60% of the values before OLT in both patients. Propionylcarnitine was still detected at significant concentrations. Plasma odd-chain fatty acid concentrations decreased continuously after OLT only in the girl's case. Tissue of both transplanted livers showed increased odd-chain fatty acid concentrations 9 and 15 months after OLT, respectively, in both patients. We consider that at present OLT should only be performed in severe forms of propionic acidaemia.

Gas chromatographic profiling and determination of urinary acylcarnitines

A method is described for the routine profiling and determination in urine of most of the acylcarnitines clinically relevant for the diagnosis of organic acidurias. The procedure, which does not require expensive apparatus, involves extraction of the acylcarnitines on strong cation-exchange disposable columns, mild alkaline hydrolysis and gas chromatography of the liberated monocarboxylic acids. The different steps were optimized in order to increase the analytical performance. No significant interferences were encountered, the limit of detection (signal-to-noise ratio = 3:1) ranged from 0.1 to 4 mg/l and the between-day coefficient of variation from 3.6 to 17.7%, depending on the acyl species. The rapidity of the method results from the application of a single solid-phase extraction on disposable columns. The acyl moieties are chromatographed underivatized in order to permit the identification of short-, medium- and long-chain acylcarnitines. The method was assessed by analysing fourteen urine specimens from patients presenting an organic aciduria.

Primary defect of juvenile visceral steatosis (jvs) mouse with systemic carnitine deficiency is probably in renal carnitine transport system

We investigated the reabsorptional system for carnitine in the kidney to elucidate the mechanism of carnitine deficiency in juvenile visceral steatosis (jvs) mice. Jvs mice had a higher rate of carnitine excretion at 10 days after birth than the controls, in spite of having no pathological acylcarnitine excretion in the urine. In an experiment to assay the uptake of carnitine using kidney slices, homozygous mutants showed significantly lower rates of Na-dependent carnitine uptake than controls. Heterozygous mice showed values of transport activity intermediate between homozygous mutants and homozygous controls. Scatchard plots (transport activity versus transport activity/carnitine concentration) revealed that the homozygous mutants had a defect in the high affinity site (Km = 58 microM) in the Na-dependent carnitine transport system in the kidney. These results indicate that the primary defect of jvs mice is most probably related to the system for reabsorption of carnitine in the kidney.

Zidovudine-induced mitochondrial myopathy is associated with muscle carnitine deficiency and lipid storage

The use of zidovudine (AZT) for the treatment of acquired immunodeficiency syndrome (AIDS) induces a DNA-depleting mitochondrial myopathy, which is histologically characterized by the presence of muscle fibers with "ragged-red"-like features, red-rimmed or empty cracks, granular degeneration, and rods (AZT fibers). Because dysfunctioning muscle mitochondria may lead to defects of beta-oxidation of fatty acids, we examined the degree of neutral fat accumulation and muscle carnitine levels in the muscle biopsy specimens from 21 patients with AZT-induced myopathic symptoms of varying severity. Six patients with no AZT fibers had normal endomyofibrillar lipid deposits and muscle carnitine levels; 7 patients with fewer than 5 AZT fibers per field had a mild (+) to moderate (++) increase in lipid droplets, and reduced muscle carnitine levels (3 patients); and 8 patients with more than 5 AZT fibers had severe muscle changes, a ++ to marked ( ) increase in lipid droplets, and reduced muscle carnitine levels (6 patients). Serial sections showed lipid globules often within "cracks" or vacuoles of the abnormal muscle fibers. We conclude that the muscle mitochondrial impairment caused by AZT results in (1) accumulation of lipid within the muscle fibers owing to poor utilization of long-chain fatty acids, (2) reduction of muscle carnitine levels probably due to decreased carnitine uptake by the muscle, and (3) depletion of energy stores within the muscle fibers. The findings may have potential therapeutic implications in the treatment of AZT-induced myopathic symptoms using oral carnitine supplementation.

Propionic acidaemia: clinical, biochemical and therapeutic aspects. Experience in 30 patients

Comprehensive data on 30 patients with propionic acidaemia, diagnosed by selective screening for inborn errors of metabolism, are presented. The most valuable diagnostic metabolites found were methylcitric-, 3-hydroxypropionic-, and 2-methyl-3-oxovaleric acids. Hyperlysinaemia and hyperlysinuria are also characteristic findings in this disease. The metabolic pattern found in propionic acidaemia is discussed extensively as are enzymatic findings. Residual activity of propionyl-CoA carboxylase is neither a predictive marker for severity nor for outcome of the disease. Propionate fixation assays were less reliable for confirmation of propionic acidaemia and of no prognostic value. Clinical presentation of the disease is discussed in detail. Besides the well-known unspecific findings (poor appetite, feeding difficulties, vomiting, dehydration, weight loss, muscular hypotonia, dyspnoea, somnolence, apathy, convulsion, coma, severe metabolic acidosis, hyperammonaemia) various skin abnormalities have been detected in about 50% of all patients. In 27% "dermatitis acidemica" was found.

Acylcarnitine profile in tissues and body fluids of biotin-deficient rats with and without L-carnitine supplementation

Since biotin-deficient (BD) rats are a good animal model for human multiple carboxylase deficiency and have low plasma free carnitine levels, short-chain acylcarnitine profiles in biotin-deficient rats with L-carnitine supplementation (BDC rats) and BD rats were investigated by fast-atom bombardment and tandem mass spectrometry and gas chromatography/mass spectrometry. By the latter method, 3-hydroxyisovalerylcarnitine was identified in BD rats, and showed the greatest accumulation among short-chain acylcarnitines in tissues of BD rats, while the tissue levels of propionic acid were more markedly elevated than those of 3-hydroxyisovaleric acid. The tissue levels of 3-hydroxyisovaleryl-carnitine were significantly lower and those of propionyl-carnitine were somewhat higher in BDC rats than in BD rats, while the tissue levels of propionic acid and 3-hydroxyisovaleric acid in BDC rats were lower than those in BD rats. These changes were more apparent in kidney than in other tissues. The amounts of urinary excretion of acylcarnitines were markedly larger, and those of 3-hydroxyisovaleric acid were somewhat smaller in BDC rats than in BD rats, while those of propionic acid were very low in BD and BDC rats as compared with those of 3-hydroxyisovaleric acid. It seems that the relationship between the concentrations of 3-hydroxyisovalerylcarnitine and those of propionylcarnitine reflects the unique metabolism of the related metabolites in tissues, especially in kidney, which may be influenced by their urinary excretion and the availability of free carnitine. These data in biotin deficiency suggest that carnitine supplementation is possibly beneficial for patients with holocarboxylase synthetase deficiency who respond incompletely to biotin therapy.

Dystonia and dyskinesia in glutaric aciduria type I: clinical heterogeneity and therapeutic considerations

Glutaric aciduria type I (GA-I) is an inborn error in the degradation of lysine, hydroxylysine, and tryptophan due to a deficiency of glutaryl-CoA dehydrogenase. Glutaric, 3-OH-glutaric, and glutaconic acids are excreted in the urine, particularly during intercurrent illness. The enzyme may be assayed in leukocytes, cultured fibroblasts and chorionic villi. Twelve new cases, 9 months-16 years of age, are reported, comprising all known cases of GA-I in Sweden and Norway. Ten had a severe dystonic-dyskinetic disorder, one had a mild hyperkinetic disorder, and one was asymptomatic. Two children died in a state of hyperthermia. Carnitine deficiency and malnutrition developed in patients with severe dystonia and dysphagia, which necessitated substitution and gastrostomy. A slowly progressive dyskinetic disorder developed in spite of adequate early dietary treatment in one subject. Macrocephaly was found in three. Computed tomography and magnetic resonance investigations in 10 showed deep bitemporal spaces in 7. Neuropsychological testing of 8 of 12 subjects demonstrated receptive language function to be superior to expressive language and motor function. Cognitive functions were obviously less affected than motor functions. A review of 57 pooled cases showed that a severe dystonic syndrome developed in 77%, a mild extrapyramidal syndrome in 10%, and 12% were asymptomatic. This disorder may pass undetected in the cerebral palsy and mentally retarded child and adult populations. Repeated urine examinations of organic acids in the urine and enzyme assay may be necessary to confirm GA-I.

Determination of acylcarnitines in urine of patients with inborn errors of metabolism using high-performance liquid chromatography after derivatization with 4'-bromophenacylbromide

A high-performance liquid chromatographic method is presented for the determination of urinary acylcarnitines. After solid phase extraction on silica columns the acylcarnitines are converted to 4'-bromophenacyl esters with 4'-bromophenacylbromide in the presence of N,N-diisopropylethylamine. Complete derivatization was achieved at 37 degrees C within 30 min. The 4'-bromophenacyl esters were separated by high-performance liquid chromatography on a Hypersil BDS C8 reversed-phase column with a binary gradient containing varying proportions of acetonitrile, water and 0.1 M triethylamine phosphate buffer. Essentially baseline separation was obtained with a standard mixture containing 4'-bromophenacyl esters of carnitine and synthetic acylcarnitines of increasing chain length ranging from acetyl- to palmitoylcarnitine. The method was used to obtain urinary acylcarnitine profiles from patients with propionic, methylmalonic and isovaleric acidemia and with medium-chain and multiple acyl-CoA dehydrogenase deficiency. Quantification of the acylcarnitines was achieved using undecanoylcarnitine as internal standard.

Cardiomyopathy in propionic acidaemia

Following the death of a patient with propionic acidaemia with a cardiomyopathy we reviewed 19 patients with the same disorder for evidence of cardiomyopathy. Six patients were found to meet the diagnostic criteria. Three patients died and in the other three the cardiac disease resolved completely. All patients were treated with standard therapy and some received L-carnitine but this did not seem to influence the eventual outcome. Cardiomyopathy is an important complication of propionic acidaemia and may be rapidly fatal.

Quantification of carnitine and specific acylcarnitines by high-performance liquid chromatography: application to normal human urine and urine from patients with methylmalonic aciduria, isovaleric acidemia or medium-chain acyl-CoA dehydrogenase deficiency

This paper describes the development of a high-performance liquid chromatographic method for the quantitation of free carnitine, total carnitine, acetylcarnitine, propionylcarnitine, isovalerylcarnitine, hexanoylcarnitine and octanoylcarnitine in human urine. Carnitine and acylcarnitines were isolated from 10 or 25 microliters of urine using 0.5-ml columns of silica gel, derivatized with 4'-bromophenacyl trifluoromethanesulfonate and separated by high-performance liquid chromatography. Using 4-(N,N-dimethyl-N-ethylammonio)-3-hydroxybutanoate ("e-carnitine") as the internal standard, standard curves (10-300 nmol/ml) were generated. Carnitine and acylcarnitines were quantified (when they were present) in normal human urine and the urine of patients diagnosed with one of three different disorders of organic acid metabolism: methylmalonic aciduria, isovaleric aciduria, isovaleric acidemia, and medium-chain acyl-CoA dehydrogenase deficiency.

Plasma carnitine insufficiency and effectiveness of L-carnitine therapy in patients with mitochondrial myopathy

Plasma carnitine "insufficiency," (plasma esterified carnitine to free carnitine ratio above 0.25) was found in 21 of 48 (43.8%) patients with mitochondrial myopathy, of whom 4 also showed both total and free carnitine deficiencies in plasma. In addition, plasma levels of SCAC and LCAC were higher in patients with mitochondrial myopathy than in controls (P < 0.001 and P < 0.01, respectively). Patients diagnosed as having plasma carnitine insufficiency or deficiency were treated with L-carnitine (50-200 mg/kg per day in four daily doses). Muscle weakness improved in 19 of 20 patients, failure to thrive in 4 of 8, encephalopathy in 1 of 9, and cardiomyopathy in 8 of 8 patients. Plasma carnitine "insufficiency" provides an additional clue to the diagnosis of mitochondrial myopathy and an indication for L-carnitine therapy.

Infantile idiopathic myopathic carnitine deficiency: treatment with L-carnitine

A series of 9 infants, ranging in age from 3 months to 5 years (average: 2 years), suffered from idiopathic myopathic carnitine deficiency presenting as hypotonia and motor delay. Secondary carnitine deficiency was eliminated by appropriate tests. Muscle carnitine concentration ranged from 2.3-7.1 nmol/mg non-collagen protein (NCP; average: 4.87 nmol/mg NCP; normal: 22 +/- 6 nmol/mg NCP). Lipid accumulation in muscle was observed in 2 of 8 patients. Therapy with L-carnitine (100 mg/kg/day in most patients) was given with clinical and laboratory follow-up 6 months later. In 7 of 9 patients, muscle tone and motor function improved. Muscle carnitine concentration increased to a range of 2.7-23.4 nmol/mg (average: 12.27 nmol/mg). In some patients the muscle carnitine content multiplied by a factor of 3-4, but carnitine concentration reached the normal range in only 2 patients. Most infants with idiopathic carnitine deficiency did benefit from 6 months of therapy; however, in order to achieve full recovery the duration of therapy should probably continue for longer periods, with a dose of not less than 100 mg/kg/day.

Acylcarnitines in amniotic fluid: application to the prenatal diagnosis of propionic acidaemia

Acylcarnitines were assayed in amniotic fluid by isotope dilution tandem mass spectrometry. Control values for propionylcarnitine, C4 and C5 acylcarnitines were established. Propionylcarnitine was elevated by a factor of 5 relative to controls in the amniotic fluid of three pregnancies affected with propionic acidaemia. This may provide a convenient new method for prenatal diagnosis of propionic acidaemia. One pregnancy at risk for propionic acidaemia but unaffected according to methylcitrate analysis had an intermediate level of propionylcarnitine, indicating the need for further studies to determine the range of concentration in probable heterozygotes.

Case reports of successful pregnancy in women with maple syrup urine disease and propionic acidemia

We report on 2 women with organic acidemias, one with classical maple syrup urine disease and another with mild propionic acidemia in which protein restricted diets and carnitine supplementation were successfully employed to manage pregnancies. Healthy infants were delivered without maternal metabolic decompensation.

Neuropsychiatric manifestations of defect in mitochondrial beta oxidation response to riboflavin

A 29 year old woman is described with severe hyperemesis gravidarum, atypical migraine, numerous admissions to hospital for psychiatric illness, non-epileptic seizures, and valproate-induced coma. Metabolic studies and measurement of [9,10(n)-3H]palmitate oxidation by cultured fibroblasts suggested a multiple acyl-CoA dehydrogenation disorder. Treatment with riboflavin abolished headaches and abnormal behaviour and normalised the plasma free carnitine level. Subtle defects in mitochondrial beta oxidation may be a treatable cause of disordered behaviour in adults.

Effect of carnitine loading on long-chain fatty acid oxidation, maximal exercise capacity, and nitrogen balance

Carnitine has a potential effect on exercise capacity due to its role in the transport of long-chain fatty acids into the mitochondria for beta-oxidation, the export of acyl-coenzyme A compounds from mitochondria and the activation of branched-chain amino acid oxidation in the muscle. We studied the effect of carnitine supplementation on palmitate oxidation, maximal exercise capacity and nitrogen balance in rats. Daily carnitine supplementation (500 mg.kg-1 body mass for 6 weeks) was given to 30 rats, 15 of which were on an otherwise carnitine-free diet (group I) and 15 pair-fed with a conventional pellet diet (group II). A control group (group III, n = 6) was fed ad libitum the pellet diet. Palmitate oxidation was measured by collecting 14CO2 after an intraperitoneal injection of [1-14C]palmitate and exercise capacity by swimming to exhaustion. After carnitine supplementation carnitine concentrations in serum were supranormal [group I, total 150.8 (SD 48.5), free 78.9 (SD 18.4); group II, total 170.9 (SD 27.9), free 115.8 (SD 24.6) mumol.l-1] and liver carnitine concentrations were normal in both groups [group I, total 1.6 (SD 0.3), free 1.2 (SD 0.2); group II, total 1.3 (SD 0.3), free 0.9 (SD 0.2) mumol.g-1 dry mass]. In muscle carnitine concentrations were normal in group I [total 3.8 (SD 1.2), free 3.2 (SD 1.0) mumol.g-1 dry mass] and increased in group II [total 6.6 (SD 0.5), free 4.9 (SD 0.9) mumol.g-1 dry mass].(ABSTRACT TRUNCATED AT 250 WORDS)

Carnitine therapy and metabolism in the disorders of propionyl-CoA metabolism studied using 1H-NMR spectroscopy

1H-NMR spectroscopy has been used to study metabolic perturbations in patients with disorders of propionyl-CoA metabolism during the administration of oral and intravenous L-carnitine. The administration of L-carnitine either in the form of a challenge or as a therapeutic measure resulted in an increased excretion of propionylcarnitine, consistent with the removal of accumulated intramitochondrial propionyl-CoA esters. Additionally, during the therapeutic administration of L-carnitine excretion of acetylcarnitine occurred, coincident with an improvement in clinical condition and confirming the intracellular propionyl-CoA depletion. An additional benefit from the formation of acylcarnitines may be an accompanying intracellular alkalinisation.

Muscle carnitine deficiency in patients with severe peripheral vascular disease

BACKGROUND

This study was designed to evaluate the effect of severe peripheral arterial insufficiency on carnitine concentrations and carnitine acetyltransferase and palmitoyltransferase activities in the ischemic skeletal muscles of patients with severe peripheral vascular disease.

METHODS AND RESULTS

Nine biopsy specimens of ischemic muscles were obtained from five patients undergoing reconstructive vascular surgery. Biopsies from 35 normal subjects served as controls. Ischemic muscles showed a significant reduction in total carnitine from the control value of 20.9 +/- 5.2 to 11.6 +/- 6.2 nmol/mg noncollagen protein (p less than 0.01). A significantly lower free carnitine and acylcarnitine content contributed to this reduction. Similarly, carnitine acetyltransferase activity was reduced in the ischemic muscles from the control value of 102.1 +/- 41.2 to 52.9 +/- 22.1 nmol/min/mg noncollagen protein (p less than 0.01). On the contrary, carnitine palmitoyltransferase activity did not show any change (0.29 +/- 0.05 nmol/min/mg noncollagen protein in the ischemic muscles and 0.28 +/- 0.07 nmol/min/mg noncollagen protein in controls). Carnitine, acylcarnitines, and enzyme activities were also measured in the ischemic muscles in four additional patients 2 days after intravenous administration of L-propionylcarnitine (1.5 g as a single bolus followed by an infusion of 1 mg/kg/min for 30 minutes). Treatment restored normal levels of carnitine and its esters in the ischemic muscles but did not affect enzyme activities.

CONCLUSIONS

Demonstration of carnitine deficiency in severe peripheral vascular disease substantiates previous findings showing the efficacy of carnitine supplementation to ischemic muscles. Furthermore, the feasibility of restoring carnitine homeostasis with L-propionylcarnitine provides the basis for clinical trials aimed at assessing the efficacy of this carnitine ester in the treatment of peripheral vascular disease.

Detection of hereditary metabolic disorders involving amino acids and organic acids

Inherited disorders in the metabolism of amino acids and organic acids may cause neurological dysfunction and acute metabolic crises. For many of these disorders, early diagnosis and early treatment can greatly improve the outcome. A general description of the clinical manifestations and a discussion of selected techniques and approaches for the laboratory diagnosis are reviewed.

Carnitine in muscle, serum, and urine of nonprofessional athletes: effects of physical exercise, training, and L-carnitine administration

Efficient utilization of fatty acids to sustain prolonged physical efforts is thought to be dependent on the carnitine shuttle of muscle. A study has been carried out in 24 athletes (13 long-distance runners and 11 sprinters). These subjects received placebo or L-carnitine (1 g/orally b.i.d.) during a 6-month period of training. In endurance athletes, training induced lowering of total and free muscle carnitine. Increase of esterified muscle carnitine was also observed. Post-exertional overflow of acetylcarnitine and long-chain acylcarnitine, as well as reduction of the free fraction was also noticed in the blood. Fasting plasma carnitine levels, however, were not affected in carnitine-treated athletes at rest. These changes were likely related with the significantly increased urinary excretion of esterified and total carnitine which occurred after physical exercise. In the sprinters only, a decrease in free and total carnitine of muscle was detected after training. Both these potentially unfavorable effects were prevented by oral administration of L-carnitine. Our data suggest that training in endurance athletes, and to a lesser extent, in sprinters, is associated with a decrease in free and total carnitine of muscle, due to an increased overflow of short-chain carnitine esters in urine.

Inadequate iron availability as a possible cause of low serum carnitine concentrations in patients with phenylketonuria

A previous observation of decreased serum carnitine concentrations in phenylketonuria (PKU) was investigated in 169 patients either on a strict diet (n = 107; median: 8.1 years) or off diet (n = 62; median: 15.0 years). Fifty-seven metabolically healthy children (median: 8.5 years) served as controls. PKU patients on a strict diet and older than 2 years had significantly lower serum carnitine concentrations (19.4 +/- 5.4 mumol/l) than those off diet (29.6 +/- 6.7 mumol/l). PKU patients on diet also had significantly lower concentrations of haemoglobin and serum ferritin than those off diet. A linear correlation existed between total serum carnitine and ferritin concentrations up to 40 micrograms/l (r = 0.52; P less than 0.01). As iron is an essential cofactor of carnitine synthesis we conclude that reduced endogenous carnitine synthesis due to an inadequate availability of iron may be a major cause of low serum carnitine concentrations. The low carnitine content of the strict and highly protein-reduced diet additionally contributes to a decrease in the serum carnitine concentration. Our results show that a further optimization of the PKU diet increasing either iron availability or carnitine intake should be considered.

Is carnitine essential in children?

Carnitine has a fundamental biological role as a long-chain fatty acid carrier across the mitochondrial membrane and in ketone body formation. Although the body normally synthesizes carnitine, in certain circumstances such as total parenteral nutrition and haemodialysis a dietary supplement may be needed to maintain adequate levels. Several considerations suggest that carnitine is a truly essential nutrient in infancy and in other situations where the energy requirement is particularly high, e.g. pregnancy and breast feeding. There are, for example, congenital deficit syndromes due to enzymatic inadequacies. There is also the possible role of carnitine in serious metabolic disorders such as organic acidaemias and, above all, it has multiple physiological functions in major metabolic pathways which are essential for development and growth.

Long-term L-carnitine treatment in isovaleric acidemia

A 5-year-old girl with isovaleric acidemia was treated with long-term L-carnitine and no supplemental glycine. Clinical and laboratory data are presented. Following diagnosis and treatment at age 2 years, the frequency of acute exacerbations of metabolic acidosis was reduced and she resumed normal growth and development. L-carnitine supplementation and protein restriction may be sufficient for effective therapy of isovaleric acidemia.

Carnitine in dried blood spots: a method suitable for neonatal screening

A method is described which enables the quantitative determination of both free and total carnitine levels in dried blood spots. This method is suitable for neonatal screening for either primary or secondary carnitine deficiency. The 95% confidence interval for free carnitine was 26-76 mumol/l (median = 44) and for total carnitine was 35-102 mumol/l (median = 60).

Effects of propionate on mechanical and metabolic performance in aerobic rat hearts

The purpose of this report is to describe the contribution of propionate as an adjunct source of oxidative metabolism in aerobic myocardium. In the first series of studies, six groups of isolated working rat hearts (n = 6-8 per group) were perfused for 40 minutes with Krebs-Henseleit media containing 11 mM glucose. Propionate treatment was provided to the media at a constant dose per heart group and extended over a range of dosages, including: 0 (placebo control), 0.1, 0.5, 1.0, 5.0, and 10.0 mM, buffered to pH 7.4. Average aerobic coronary blood flow for all groups was 21.5 +/- 0.6 ml/min; average left ventricular peak systolic pressure was 123.7 +/- 1.4 mmHg. There were no significant differences among groups compared with placebo hearts for aortic flow, heart rate x aortic pressure product, or myocardial oxygen consumption, although performance tended to decline in the 10 mM group. A clear dose-response relationship was observed in 14CO2 production from labeled propionate, with a 12-fold increase between the 0.1 and 10 mM groups. Most of the increase occurred at the lower dosages, with a relative leveling off at the 1.0, 5.0, and 10.0 mM doses. In part 2, propionate was examined as a sole substrate. At 1.0 mM without glucose, propionate per se was unable to support mechanical function over the course of the perfusions, but still maintained high rates of oxidation, comparable to that of the 1.0 mM group with glucose in part 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Propionyl-L-carnitine: biochemical significance and possible role in cardiac metabolism

Propionyl-CoA is formed principally during amino acid catabolism. It is then converted chiefly to succinate in a described three-step sequence. Free propionate is formed from propionyl-CoA to a very limited extent, but this anion can participate in a futile cycle of activation and hydrolysis, which can significantly deplete mitochondrial ATP. Free CoA and propionyl-CoA cannot enter or leave mitochondria, but propionyl groups are transferred between separate CoA pools by prior conversion to propionyl-L-carnitine. This reaction requires carnitine and carnitine acetyl transferase, an enzyme abundant in heart tissue. Propionyl-L-carnitine traverses both mitochondrial and cell membranes. Within the cell, this mobility helps to maintain the mitochondrial acyl-CoA/CoA ratio. When this ratio is increased, as in carnitine deficiency states, deleterious consequences ensue, which include deficient metabolism of fatty acids and urea synthesis. From outside the cell (in blood plasma), propionyl-L-carnitine can either be excreted in the urine or redistributed by entering other tissues. This process apparently occurs-without prior hydrolysis and reformation. It is suggested that heart tissue utilizes such exogenous propionyl-L-carnitine to stimulate the tricarboxylic acid cycle (via succinate synthesis) and that this may explain its known protective effect against ischemia.

Creatine metabolism during metabolic perturbations in patients with organic acidurias

Creatine excretion was measured in two patients with methylmalonic aciduria and two patients with 3-hydroxy-3-methylglutaric aciduria. During periods of metabolic decompensation the creatine/creatinine ratio increased and fell during recovery. Prolonged periods of metabolic decompensation may result in the loss of a large proportion of the creatine pool. In one study, measurements of total daily urinary output of metabolites demonstrated that the absolute creatine excretion followed a similar qualitative pattern to the creatine/creatinine ratio. However, apparent fluctuations in methylmalonate excretion when expressed as methylmalonate/creatinine ratio were absent when absolute methylmalonate excretion was calculated. The increased creatine excretion during metabolic perturbations may result from loss from creatine containing tissues such as muscle and may represent an underlying defect in energy metabolism. Alternatively creatine transport may be disrupted by accompanying acidosis. The use of metabolite/creatinine ratios as a measure of metabolite excretion rates during metabolic decompensation whilst qualitatively sound may need a re-appraisal.

Rapid diagnosis of 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency via enzyme activity measurements in leukocytes or platelets using a simple spectrophotometric method

Patients with 3-hydroxy-3-methylglutaric aciduria due to a deficiency of 3-hydroxy-3-methylglutaryl Coenzyme A lyase usually present with a life-threatening crisis of hypoglycemia, metabolic acidosis and hyperammonemia. Diagnosis of this inborn error of leucine degradation is usually based upon gas-chromatographic analysis of organic acids in a patient's urine. In this paper we describe a simple spectrophotometric method allowing the activity of HMG-CoA lyase to be measured in leukocytes or platelets within a few hours, thus contributing to a rapid, unequivocal diagnosis and subsequent treatment. The validity of the method was established by demonstrating a deficient activity of HMG-CoA lyase in two patients with 3-hydroxy-3-methylglutaric aciduria. Furthermore, using this method, heterozygote detection can be done with great reliability.

Early diagnosis and treatment of neonatal medium-chain acyl-CoA dehydrogenase deficiency: report of two siblings

Two siblings are reported who were symptomatic in the neonatal period. The first died suddenly at 4 days of age after regurgitating a meal. The postmortem examination showed steatosis of the liver, kidney and muscle. In the second, medium-chain acyl-CoA dehydrogenase (MCAD) deficiency was diagnosed at 3 days of age with muscular hypotonia, vomiting, hyperammonaemia and mild acidosis. Thus disorders of fatty acid oxidation should also be considered in newborns. The biochemical work up indicates that in neonates, analysis of serum medium-chain fatty acids and of acyl and free carnitine are more likely to lead to a diagnosis than determining dicarboxylic acids alone in urine. Long-term treatment was effective and monitored by the acyl/free carnitine ratio.

Measurement of L-carnitine and acylcarnitines in body fluids and tissues in children and in adults

We have developed a reliable and validated radio-enzymatic method for the assay of L-carnitine and acylcarnitines, using a modification of existing methods. The sensitivity of the assay is 10 mumol/l using 10 microliters of plasma or urine. It is also suitable for measurements of carnitine in a 10 mg sample of liver or muscle obtained by percutaneous biopsy. The use of N-ethylmaleimide in the reaction mixture together with an excess of [1-14C]acetyl CoA ensures that the reaction proceeds to completion and a linear response is obtained. Using this method control ranges have been established for plasma and urine carnitine concentrations in healthy children and adults, and for the carnitine content of liver and muscle in adults. No significant difference was found between fasting and post-prandial plasma carnitine levels. An age-related increase was found in urinary total carnitine and acylcarnitine concentration throughout childhood. These data provide a reliable basis for studies of patients with abnormal carnitine and acylcarnitine metabolism, distribution and excretion.

High-performance liquid chromatographic separation of acylcarnitines following derivatization with 4'-bromophenacyl trifluoromethanesulfonate

A high-performance liquid chromatographic method for the separation of acylcarnitines after derivatization with 4'-bromophenacyl trifluoromethanesulfonate is presented. Derivatization of acylcarnitines was achieved at room temperature within 10 min. Separation of the acylcarnitine 4'-bromophenacyl esters was accomplished by high-performance liquid chromatography using as the analytical column a Resolve-PAK 5-microns C18 radially compressed cartridge eluted with a tertiary gradient containing varying proportions of water, acetonitrile, tetrahydrofuran, triethylamine, potassium phosphate, and phosphoric acid. Acylcarnitine 4'-bromophenacyl esters were detected spectrophotometrically at 254 nm. Baseline separation was obtained for a standard mixture (5 nmol of each injected) containing carnitine, acetyl-, propionyl-, butyryl-, valeryl-, hexanoyl-, heptanoyl-, octanoyl-, nonanoyl-, decanoyl-, lauroyl-, myristroyl-, palmitoyl-, and stearoylcarnitine. Nearly complete separation was obtained for a standard mixture containing butyryl-, isobutyryl-, isovaleryl-, and 2-methylbutyrylcarnitine. The method was applied to a normal human urine and then to this same urine spiked with the acylcarnitine standards. Urinary acylcarnitine profiles from patients having propionic acidemia, isovaleric acidemia, and medium-chain acyl-CoA dehydrogenase deficiency were performed. Urinary isovalerylcarnitine was quantified in the patient with isovaleric acidemia using heptanoylcarnitine as an internal standard.

Differential excretion of xenobiotic acyl-esters of carnitine due to administration of pivampicillin and valproate

The fate of supplemental carnitine was studied in human subjects treated with drugs known to cause carnitine deficiency. Six children were treated with pivampicillin and equimolar L-carnitine for 7 days. On the last day of treatment, the plasma levels of total and free carnitine were decreased, but acylcarnitine levels were increased. A 12-fold increase in urinary excretion of acylcarnitines was found; it increased from 188.5 +/- 82.7 to 2218.4 +/- 484.1 mumole/day, and 84% was pivaloylcarnitine. Free carnitine excretion was reduced. Ten epileptic children on chronic valproate treatment received equimolar carnitine for a 2-week period. Plasma carnitine levels were elevated on the last day of treatment. A 3.4-fold increase in urinary acylcarnitines was found, but most of the excreted carnitines were free (64.5-fold increases). These data show that pivalate is readily converted to carnitine esters, in contrast to the limited conversion of valproate to acylcarnitines in humans.

Medium-chain acyl-CoA dehydrogenase deficiency: metabolic effects and therapeutic efficacy of long-term L-carnitine supplementation

Medium-chain acyl-CoA dehydrogenase deficiency is a recently described inborn error of metabolism characterized by episodes of coma and hypoketotic hypoglycaemia in response to prolonged fasting. Secondary carnitine deficiency has been documented in these patients as well as the excretion in the urine of medium-chain-length acyl carnitine esters, such as octanoylcarnitine. Based on the potential toxicity of medium-chain fatty acid metabolites and the beneficial responses of patients with other inborn errors of metabolism and secondary carnitine deficiency, oral carnitine has been proposed as treatment for children with medium-chain acyl-CoA dehydrogenase deficiency. We report the results of carefully monitored fasting challenges of an infant with this deficiency both before and after 3 months of oral carnitine therapy. Carnitine supplementation failed to prevent lethargy, vomiting, hypoglycaemia and accumulation of free fatty acids in response to fasting despite normalization of plasma carnitine levels and a marked increase in urinary excretion of acyl-carnitine esters. Potentially toxic medium-chain fatty acids accumulated in the plasma in spite of therapy. Based on this study of one patient, we stress that avoidance of fasting and prompt institution of glucose supplementation in situations when oral intake is interrupted remain the mainstays of therapy for medium-chain acyl-CoA dehydrogenase deficient patients.

Measurement of urinary free and acylcarnitines: quantitative acylcarnitine profiling in normal humans and in several patients with metabolic errors

A method for determining urinary concentrations of carnitine and acylcarnitine esters is described that employs fast atom bombardment mass spectrometry, stable isotope dilution techniques, and a novel deutero-methyl esterification that permits unambiguous identification and quantitation of free carnitine and acylcarnitines. It is rapid, does not require chromatographic or other isolation procedures, and is immune to analyte losses in sample preparation. Urinary concentrations are reported for adult control subjects and for others with various metabolic disorders.

Effect of L-carnitine on ethanol and acetate plasma levels after oral administration of ethanol in humans

In a randomized double-blind, cross-over experiment, 0.5 g/kg of ethanol in the form of white wine and 3 g of L-carnitine by intravenous infusion were administered to 15 healthy volunteers. Ethanol and acetate plasma levels and the urine concentrations of acetylcarnitine were determined. Administration of ethanol induced a significant increase of both plasma ethanol and acetate, lasting 6-8 hr. The concomitant administration of carnitine resulted in a significant decrease of plasma acetate, whereas plasma ethanol levels remained unmodified. Urinary acetylcarnitine content significantly increased following administration of ethanol plus carnitine, but not when L-carnitine alone was administered. The resulting conclusion is that administered L-carnitine might trap excess acetyls derived both from free acetate, formed by ethanol oxidation, and from acetyl coenzyme A, accumulated as a result of the ethanol-induced decrease in the Krebs cycle flux.

Uptake, metabolism and release of carnitine and acylcarnitines in the perfused rat liver

The uptake and release of carnitine and isovalerylcarnitine have been studied in the perfused rat liver. Labelled carnitine accumulates in rat livers perfused with 50 or 500 microM [3H]carnitine. When alpha-ketoisocaproate (5 mM) is added to the perfusate after 30 min of perfusion, the net uptake of carnitine in the liver stops, and there is even a decrease in liver radioactivity. The decrease in liver carnitine can be attributed to an enhanced formation and efflux to the perfusate of short-chain acylcarnitines. Thin-layer chromatography of liver and perfusate extracts showed that efflux rates for branched-chain acylcarnitines (isovalerylcarnitine) formed are at least 2.5-fold the efflux rate for carnitine. Acetylcarnitine is released about twice as fast as carnitine from the liver. Perfusion with 50 microM [3H]isovalerylcarnitine showed that the influx rate of isovalerylcarnitine exceeds that of carnitine 1.5-fold. Since the efflux rate is still higher, a net loss of carnitine from the liver to the perfusate will result when branched-chain acylcarnitines are formed in the perfused liver. The addition of 500 microM unlabelled carnitine to the perfusate does not influence the release of labelled carnitine or acylcarnitines from the liver, showing that uptake and release are independent processes. Isovalerylcarnitine accumulates faster than carnitine does, also in the perfused rat heart. A mechanism for the development of secondary carnitine deficiencies associated with organic acidemia is proposed.

Formation and excretion of branched-chain acylcarnitines and branched-chain hydroxy acids in the perfused rat kidney

alpha-Keto[U-14C]isovalerate, alpha-keto[U-14C]isocaproate and alpha-keto[U-14C]beta-methylvalerate are metabolized in the perfused kidney. Labelled 3-hydroxyisobutyrate, 3-hydroxyisovalerate, 2-methyl-3-hydroxybutyrate, branched-chain amino acids, branched-chain acylcarnitines and lactate are formed. Hydroxy acids and acylcarnitines are excreted preferentially in the urine, whereas the branched-chain amino acids are preferentially excreted in the perfusate. There is no accumulation of (U-14C)-labelled alpha-keto acids or labelled metabolites in the kidney during perfusion. (-)-Carnitine accumulates rapidly in the kidney when it is added to the perfusate. A high kidney carnitine level enhances the excretion of carnitine esters in the urine.

Isovaleric acidemia: medical and neurodevelopmental effects of long-term therapy

Nine patients with isovaleric acidemia were treated with a low-protein diet and supplemental glycine for up to 10 years. Carnitine was added to the therapy in four patients. Overall, the treatment was well tolerated, resulting in no significant side effects other than persistent hyperglycinemia. Normal growth was observed in all patients. Of four patients with the chronic phenotype, three, whose treatment was delayed beyond the first year of life, are mentally retarded. Two of five patients with the acute phenotype are retarded. The outcome in these two was complicated in one by neonatal intraventricular hemorrhage and in the other by therapeutic noncompliance. In our patients, only those who were treated successfully from early infancy and had no complications did not develop mental retardation. After initiation of therapy, there was a significant decrease in ketoacidotic attacks requiring hospitalization. Glycine is indicated for the treatment of acute ketoacidosis in these patients; none of the catastrophically ill newborn who received glycine died. The aim of treatment is to reduce the isovaleric acid burden to a minimum. Therapy consisting of leucine restriction with supplemental glycine and carniline should be started as soon as possible after birth.