Skeletal muscle mitochondrial beta-oxidation. A study of the products of oxidation of [U-14C]hexadecanoate by h.p.l.c. using continuous on-line radiochemical detection

Fatty acid trafficking in starved cells: regulation by lipid droplet lipolysis, autophagy, and mitochondrial fusion dynamics

Fatty acids (FAs) provide cellular energy under starvation, yet how they mobilize and move into mitochondria in starved cells, driving oxidative respiration, is unclear. Here, we clarify this process by visualizing FA trafficking with a fluorescent FA probe. The labeled FA accumulated in lipid droplets (LDs) in well-fed cells but moved from LDs into mitochondria when cells were starved. Autophagy in starved cells replenished LDs with FAs, increasing LD number over time. Cytoplasmic lipases removed FAs from LDs, enabling their transfer into mitochondria. This required mitochondria to be highly fused and localized near LDs. When mitochondrial fusion was prevented in starved cells, FAs neither homogeneously distributed within mitochondria nor became efficiently metabolized. Instead, FAs reassociated with LDs and fluxed into neighboring cells. Thus, FAs engage in complex trafficking itineraries regulated by cytoplasmic lipases, autophagy, and mitochondrial fusion dynamics, ensuring maximum oxidative metabolism and avoidance of FA toxicity in starved cells.

The enzymology of mitochondrial fatty acid beta-oxidation and its application to follow-up analysis of positive neonatal screening results

Oxidation of fatty acids in mitochondria is a key physiological process in higher eukaryotes including humans. The importance of the mitochondrial beta-oxidation system in humans is exemplified by the existence of a group of genetic diseases in man caused by an impairment in the mitochondrial oxidation of fatty acids. Identification of patients with a defect in mitochondrial beta-oxidation has long remained notoriously difficult, but the introduction of tandem-mass spectrometry in laboratories for genetic metabolic diseases has revolutionalized the field by allowing the rapid and sensitive analysis of acylcarnitines. Equally important is that much progress has been made with respect to the development of specific enzyme assays to identify the enzyme defect in patients subsequently followed by genetic analysis. In this review, we will describe the current state of knowledge in the field of fatty acid oxidation enzymology and its application to the follow-up analysis of positive neonatal screening results.

Minocycline inhibits caspase activation and reactivation, increases the ratio of XIAP to smac/DIABLO, and reduces the mitochondrial leakage of cytochrome C and smac/DIABLO

OBJECTIVES

This study is aimed at investigating the novel use of minocycline for cardiac protection during ischemia/reperfusion (I/R) injury, as well as its mechanism of action.

BACKGROUND

Minocycline is a tetracycline with anti-inflammatory properties, which is used clinically for the treatment of diseases such as urethritis and rheumatoid arthritis. Experimentally, minocycline has also been shown to be neuroprotective in animal models of cerebral ischemia and to delay progression and improve survival in mouse models of neurodegenerative diseases.

METHODS

We studied 62 rat intact hearts exposed to I/R and cell cultures of neonatal and adult rat ventricular myocytes.

RESULTS

Minocycline significantly reduced necrotic and apoptotic cell death, both in neonatal and adult myocytes, not only when given prior to hypoxia (p < 0.001), but also at reoxygenation (p < 0.05). Moreover, in the intact heart exposed to I/R, in vivo treatment with minocycline promoted hemodynamic recovery (p < 0.001) and cell survival, with reduction of infarct size (p < 0.001), cardiac release of creatine phosphokinase (p < 0.001), and apoptotic cell death (p < 0.001). In regard to its antiapoptotic mechanism of action, minocycline significantly reduced the expression level of initiator caspases, increased the ratio of XIAP to Smac/DIABLO at both the messenger RNA and protein level, and prevented mitochondrial release of cytochrome c and Smac/DIABLO (all, p < 0.05). These synergistic actions dramatically prevent the post-ischemic induction of caspase activity associated with cardiac I/R injury.

CONCLUSIONS

Because of its safety record and multiple novel mechanisms of action, minocycline may be a valuable cardioprotective agent to ameliorate cardiac dysfunction and cell loss associated with I/R injury.

Control of mitochondrial beta-oxidation flux

The control of mitochondrial beta-oxidation, including the delivery of acyl moieties from the plasma membrane to the mitochondrion, is reviewed. Control of beta-oxidation flux appears to be largely at the level of entry of acyl groups to mitochondria, but is also dependent on substrate supply. CPTI has much of the control of hepatic beta-oxidation flux, and probably exerts high control in intact muscle because of the high concentration of malonyl-CoA in vivo. beta-Oxidation flux can also be controlled by the redox state of NAD/NADH and ETF/ETFH(2). Control by [acetyl-CoA]/[CoASH] may also be significant, but it is probably via export of acyl groups by carnitine acylcarnitine translocase and CPT II rather than via accumulation of 3-ketoacyl-CoA esters. The sharing of control between CPTI and other enzymes allows for flexible regulation of metabolism and the ability to rapidly adapt beta-oxidation flux to differing requirements in different tissues.

Accumulation of medium chain acyl-CoAs during beta-oxidation of long chain fatty acid by isolated peroxisomes from rat liver

We have reported fatty alcohol synthesis accompanied by chain elongation in liver peroxisomes (Biochim. Biophys. Acta, 1346, 38 (1997)). In the present experiment, we studied what kind of acyl-CoA(s) destined to be utilized as primer for fatty alcohol synthesis accumulate(s) during peroxisomal beta-oxidation. Peroxisomes were prepared from rat liver treated with clofibrate, a peroxisome proliferator, and incubated with [U-14C]palmitate, in order to investigate acyl-CoAs after beta-oxidation. At 1 mM concentration, MgATP activated beta-oxidation, but inhibited beta-oxidation at concentrations higher than 1 mM. After incubation of peroxisomes with palmitate, various acyl-CoAs were formed. Among medium-chain labelled acyl-CoAs, octanoyl-CoA was mainly detected. These results suggest that octanoyl-CoA accumulates during beta-oxidation of palmitate. When peroxisomes were incubated with [9,10-(3)H]palmitate and [9,10-(3)H]stearate, among medium-chain acyl-CoAs, octanoyl-CoA and decanoyl-CoA were primarily detected, respectively, suggesting the occurrence of at least 4 cycles of beta-oxidation of both fatty acids by peroxisomes.

Fatty acid import into mitochondria

The mitochondrial carnitine system plays an obligatory role in beta-oxidation of long-chain fatty acids by catalyzing their transport into the mitochondrial matrix. This transport system consists of the malonyl-CoA sensitive carnitine palmitoyltransferase I (CPT-I) localized in the mitochondrial outer membrane, the carnitine:acylcarnitine translocase, an integral inner membrane protein, and carnitine palmitoyltransferase II localized on the matrix side of the inner membrane. Carnitine palmitoyltransferase I is subject to regulation at the transcriptional level and to acute control by malonyl-CoA. The N-terminal domain of CPT-I is essential for malonyl-CoA inhibition. In liver CPT-I activity is also regulated by changes in the enzyme's sensitivity to malonyl-CoA. As fluctuations in tissue malonyl-CoA content are parallel with changes in acetyl-CoA carboxylase activity, which in turn is under the control of 5'-AMP-activated protein kinase, the CPT-I/malonyl-CoA system is part of a fuel sensing gauge, turning off and on fatty acid oxidation depending on the tissue's energy demand. Additional mechanism(s) of short-term control of CPT-I activity are emerging. One proposed mechanism involves phosphorylation/dephosphorylation dependent direct interaction of cytoskeletal components with the mitochondrial outer membrane or CPT-I. We have proposed that contact sites between the outer and inner mitochondrial membranes form a microenvironment which facilitates the carnitine transport system. In addition, this system includes the long-chain acyl-CoA synthetase and porin as components.

Partially glucose-capped oligosaccharides are found on the hemoglobins of the deep-sea tube worm Riftia pachyptila

We report here the structural determination of N-linked oligosaccharides found on extracellular hemoglobins of the hydrothermal vent tube worm Riftia pachyptila. Structures were elucidated by a combination of electrospray ionization tandem mass spectrometry, matrix-assisted laser desorption/ionization mass spectrometry, normal-phase high performance liquid chromatography, and exoglycosidase digestion. The sugar chains were found to consist mainly of high-mannose-type glycans with some structures partially capped by one or two terminal glucose residues. The present study represents the first report of the occurrence of glucose capping of N-linked carbohydrates in a secreted glycoprotein of a metazoan. Previously, glucose capping has only been described for a membrane-bound surface glycoprotein from the unicellular parasite Leishmania mexicana amazonensis.

Dietary fatty acids influence the activity and metabolic control of mitochondrial carnitine palmitoyltransferase I in rat heart and skeletal muscle

The fatty acid composition of the diet has been found to influence the activity and sensitivity of mitochondrial carnitine palmitoyltransferase I (CPT I; EC 2.3.1.21) to inhibition by malonyl CoA in rat heart and skeletal muscle. The nutritional state of rats has been shown to have less influence on the activity and metabolic control of mitochondrial CPT I in heart and skeletal muscle tissue than in the liver, a tissue in which CPT I activity and sensitivity to inhibition by malonyl CoA can be shown to be regulated acutely under different nutritional conditions. However, because manipulation of the nutritional state in these previous studies was restricted mainly to examining the effect of starvation, this study was undertaken to determine whether, as in liver, the fatty acid content and composition of the diet can regulate the activity and metabolic control of CPT I in heart and skeletal muscle. Rats were fed for up to 10 wk either a nonpurified low fat diet (30 g fat/kg) or a high fat diet (200 g fat/kg) containing one of the following five oil types: hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO) or menhaden (fish) oil (MO). Feeding a diet enriched in MO had the most pronounced effect. Rats fed MO had a significantly greater skeletal muscle CPT I specific activity and tissue capacity, and a lower sensitivity of CPT I to malonyl CoA inhibition compared with rats fed a low fat diet, but the duration of feeding required to modulate this sensitivity was longer than that observed previously for the liver enzyme. Progressively greater sensitivity of heart CPT I to malonyl CoA occurred with feeding duration in all groups. These studies indicate that the fatty acid composition of the diet is involved in the regulation of mitochondrial CPT I activity in heart and skeletal muscle.

Ethylmalonic adipic aciduria--a treatable hepatomuscular disorder in two adult brothers

An adult male presented at 28 years of age with muscle weakness and liver dysfunction. His brother had died suddenly 2 years earlier after presenting with Reye's syndrome. Urine organic acid analysis and muscle and cultured fibroblast fatty acid oxidation studies confirmed a diagnosis of ethylmalonic/adipic aciduria-an inherited defect of fatty acid oxidation. The patient responded favourably to treatment with a low fat/high carbohydrate diet supplemented with riboflavin. This case highlights the importance of considering inborn errors of metabolism, in particular fatty acid oxidation defects, in adults with liver disease, muscle disease or Reye's syndrome.

Acetate represents a major product of heptanoate and octanoate beta-oxidation in hepatocytes isolated from neonatal piglets

An experiment was conducted to explore the nature of the radiolabel distribution in acid-soluble products (ASPs) resulting from the oxidation of [1-14C]C7:0 or C8:0 by isolated piglet hepatocytes. The differences between odd and even chain-length and the impacts of valproate and malonate upon the rate of beta-oxidation and ASP characteristics were tested. A minor amount of fatty acid carboxyl carbon (< or = 10% of organic acids identified by radio-HPLC) accumulated in ketone bodies regardless of chain-length or inhibitor used. In all cases, acetate represented the major reservoir of carboxyl carbon, accounting for 60-70% of radiolabel in identified organic acids. Cells given [1-14C]C7:0 accumulated 85% more carboxyl carbon in Krebs cycle intermediates when compared with C8:0, while accumulation in acetate was unaffected. The results are consistent with the hypothesis that anaplerosis from odd-carbon fatty acids affects the oxidative fate of fatty acid carbon. The piglet appears unique in that non-ketogenic routes of fatty acid carbon flow (i.e. acetogenesis) predominate in the liver of this species.

The effects of 3-hydroxy-3-methylglutaryl-CoA reductase inhibition on tissue levels of carnitine and carnitine acyltransferase activity in the rabbit

Recently, a new class of lipid lowering agents [3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors] was introduced into clinical practice. The use of these agents could lead to a secondary deficiency in carnitine, which may manifest clinically as a myalgia/myositis-a side effect that is occasionally seen with this class of drugs. In the present study, we examined the effect of an HMG-CoA reductase inhibitor (lovastatin) on serum and tissue levels of carnitine and carnitine acyltransferase activities in the rabbit. Rabbits (n = 6) were fed chow containing lovastatin (30 mg/d) for 16 wk. Blood was collected and tissues (liver, heart, and skeletal muscle) harvested at sacrifice. Free and total carnitine were measured in serum and tissues by a radioenzymatic method. Carnitine acetyltransferase and carnitine palmitoyltransferase (CPT) activities were determined and expressed relative to DNA. Serum free (24.0 +/- 2.6 vs. 29.4 +/- 3.1 microM) and total (35.1 +/- 4.7 vs. 52.8 +/- 8.8 microM) carnitine levels increased significantly with 16 wk of treatment. This increase in total carnitine was mainly due to an increase in the levels of serum acylcarnitine (12.7 +/- 3.1 vs 26.5 +/- 5.7 microM). Tissue levels of total carnitine were significantly decreased by the treatment. Carnitine acetyltransferase was unaffected by the treatment, whereas there was a significant increase in the activity of CPT in the liver and heart.

Deficiency of complex II of the mitochondrial respiratory chain in late-onset optic atrophy and ataxia

Defects of the mitochondrial respiratory chain are increasingly being recognized as an important cause of neurological disease in humans. In many of these patients, the biochemical defect results from an abnormality of the mitochondrial genome. Respiratory chain defects involving complex II, which is entirely encoded by the nuclear genome, are comparatively rare. We report the clinical and biochemical findings in 2 elderly sisters who presented with late-onset neurodegenerative disease. In both patients, a partial deficiency of complex II (approximately 50% of control values) was shown to be present in mitochondria from muscle and platelets. The enzyme defect was not expressed in cultured skin fibroblasts or immortalized lymphocytes. There was an overexpression of the 70-kd flavoprotein subunit in muscle mitochondria from both patients, although we showed that this subunit is present in normal amounts in mitochondrial membranes. Our studies highlight the diversity of the clinical presentation of respiratory chain disease and that complex II deficiency should enter the differential diagnosis of certain patients with late-onset neurodegenerative disease.

Neonatal Fanconi syndrome due to deficiency of complex III of the respiratory chain

Fanconi syndrome is an important presentation of respiratory chain disease. We report three patients who presented in the neonatal period with Fanconi syndrome, lactic acidosis and intrauterine growth retardation. In all three patients the major biochemical defect was in complex III of the mitochondrial respiratory chain, a relatively uncommon defect. The diagnosis could only be made by muscle biopsy as the defect was not expressed in cultured skin fibroblasts. Treatment with vitamins C and K3 and ubiquinone did not alter the course of the disease and all patients died before the age of 4 months.

Redox control of beta-oxidation in rat liver mitochondria

Coupled rat liver mitochondria were incubated with [U-14C]hexadecanoate and carnitine which resulted in the formation of acyl-, 2-enoyl- and 3-hydroxyacyl-CoA and carnitine esters. The production of 2-enoyl-CoA and 3-hydroxyacyl-CoA esters was associated with a significant lowering of the NAD+/NADH ratio, in contrast to rat muscle mitochondria [Eaton, S., Bhuiyan, A. K. M. J., Kler, R. S., Turnbull, D. M. & Bartlett, K. (1993) Biochem. J. 289, 161-172], suggesting that control by the respiratory chain is important under normal conditions. When NAD+/NADH ratios were held low by succinate-induced reverse electron flow, 3-enoyl-CoA esters were also detected, probably formed by the action of 3,2-enoyl-CoA isomerase. Measurement of the flux of beta-oxidation at different osmolalities showed that flux was strongly dependent on osmolality changes in the physiological range. Measurement of the CoA and carnitine esters resulting from incubations made at different osmolalities showed that there was an increase in the amounts of the saturated acyl-CoA esters with respect to 2-enoyl-CoA and 3-hydroxyacyl-CoA esters, consistent with control by the electron-transfer flavoprotein-ubiquinone segment [Halestrap, A. P. & Dunlop, J. L. (1986) Biochem. J. 239, 559-565]. This however could not be the only factor operating as indicated by the continued presence of 2-enoyl-CoA and 3-hydroxyacyl-CoA esters at high osmolalities.

Succinate-cytochrome c reductase: assessment of its value in the investigation of defects of the respiratory chain

Defects of the respiratory chain are important causes of human disease and one of the most commonly used assays in the investigation of these patients is the measurement of succinate-cytochrome c reductase. However, this assay measures several components of the respiratory chain and the ability to detect a partial defect in one enzyme complex will depend on the amount of control exerted by that enzyme step on overall electron flux. We show that measurement of succinate-cytochrome c reductase activity may fail to detect partial defects of complex III and therefore is of limited diagnostic value in the identification of complex III defects. However, complex II is a major point of control of flux through succinate-cytochrome reductase and it is likely that measurement of the latter will detect defects of complex II.

Intramitochondrial control of the oxidation of hexadecanoate in skeletal muscle. A study of the acyl-CoA esters which accumulate during rat skeletal-muscle mitochondrial beta-oxidation of [U-14C]hexadecanoate and [U-14C]hexadecanoyl-carnitine

1. We describe the acyl-CoA and acyl-carnitine esters which arise from the incubation of well-coupled State 3 rat skeletal-muscle mitochondrial fractions with [U-14C]hexadecanoate and [U-14C]hexadecanoyl-carnitine. 2. Acyl-CoA ester intermediates of chain length 16, 14, 12, 10 and 8 carbons were detected. 3. Although incubations were in steady state in respect of oxygen consumption, 14CO2 production and generation of acid-soluble radioactivity, quantitative analysis of acyl-CoA esters showed that steady state was not achieved in respect of all intermediates. 4. 3-Hydroxyacyl- and 2-enoyl-CoA and -carnitine esters were found under normoxic conditions. 5. Direct measurement of NAD+ and NADH shows that under identical incubation conditions our observations cannot be explained by gross perturbation of the [NAD+]/[NADH] ratio. 6. We hypothesize that there is a small pool of rapidly recycling NAD+ channelled between complex I of the respiratory chain and the newly described mitochondrial-inner-membrane-associated beta-oxidation trifunctional enzyme [Uchida, Izai, Orii and Hashimoto (1992) J. Biol. Chem. 267, 1034-1041].

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.

Uneven distribution of mitochondrial DNA mutation in MERRF dizygotic twins

A new family of myoclonic epilepsy with ragged-red fibers (MERRF) was studied at clinical, histological, biochemical and molecular genetic levels. There was a remarkable variation in the age of onset, the clinical presentation and the severity of symptoms. Multiple defects affecting respiratory chain complexes I, III and IV were detected in 2 patients. The point mutation at 8344 of the mitochondrial genome was found in all the maternal lineage with a relatively narrow range of variation in the percentage of mutant mitochondrial genomes. The one exception was represented by a set of dizygotic twins, one clinically affected and showing high proportions of mutant mitochondrial DNAs (mtDNAs) in blood cells, while the other was asymptomatic and showed very small amounts of mutant mt-DNAs in blood and skin. This could suggest an early segregation of the mitochondrial genome during ovogenesis.

The measurement of carnitine and acyl-carnitines: application to the investigation of patients with suspected inherited disorders of mitochondrial fatty acid oxidation

We describe an improved radio-enzymatic method for the measurement of carnitine, short-chain acyl-carnitine and long-chain acyl-carnitine in plasma and tissue. An internal standard, hexadecanoyl-[CH3-3H]-carnitine was synthesised and used to improve the determination of long-chain acyl-carnitine. The between and within batch precisions were 10.4 and 7%, respectively. Control data for neonates, infants, children and adults in the fed and fasted state are documented. In addition we confirm the hypocarnitinaemia associated with pregnancy. Patients with medium-chain acyl-CoA dehydrogenase deficiency were studied during episodes of hypoglycaemia. In both fasted controls and patients there were high concentrations of short-chain acyl-carnitine, however in the latter group there were also low concentrations of free carnitine. We suggest that the monitoring of plasma carnitine and its derivatives is a useful adjunct to the investigation of children suspected to suffer from inherited disorders of mitochondrial beta-oxidation. We also describe a sample preparation procedure suitable for high performance liquid chromatographic analysis of specific acyl-carnitines from urine, plasma and tissue homogenates. The recoveries of acetyl-carnitine, octanoyl-carnitine and hexadecanoyl carnitine from urine were 101.5, 95 and 91% and from plasma 99.5, 91.5 and 85.5%, respectively. Acyl-carnitines (C2-C16) were analysed as their p-bromophenacyl derivatives by reverse-phase high performance liquid chromatography using a ternary gradient of acetonitrile/water/triethylamine phosphate. We report ten patients who excreted octanoyl-carnitine, hexanoyl-carnitine and in some cases a small amount of decanoyl-carnitine. In most of these cases suberylglycine and dicarboxylic acids were also detected by GC/MS. We had access to cultured fibroblasts from five of these patients and were able to demonstrate medium-chain acyl-CoA dehydrogenase deficiency by direct enzyme assay.

The measurement of mitochondrial beta-oxidation by release of 3H2O from [9,10-3H]hexadecanoate: application to skeletal muscle and the use of inhibitors as models of metabolic disease

We describe the use of a simple assay for beta-oxidation which depends on the release of 3H2O from [9,10-3H]hexadecanoate. This was compared with the use of [1-14C]hexadecanoate which gave comparable results when all the products of beta-oxidation were measured. The prediction that 75% of the tritium is released as 3H2O and 25% as [2-3H]acetyl units was confirmed. The assay was used successfully to demonstrate impaired beta-oxidation in tissue preparations from rats treated with etomoxir and methylenecyclopropylpyruvate which are known inhibitors of beta-oxidation. Abnormalities of beta-oxidation were also detected in skeletal muscle from patients with defects of mitochondrial oxidation.

Defects of the mitochondrial respiratory chain complexes in three pediatric cases with hypotonia and cardiac involvement

Three children displaying hypotonia, cardiac involvement and defects of the mitochondrial respiratory chain complexes are reported. The first case showed severe neonatal hypotonia, failure to thrive, hepatomegaly, dilation of the right cardiac cavities, profound lactic acidosis and amino aciduria. The boy died at the age of 7 weeks. In the second case hypotonia, severe cardiomyopathy, cyclic neutropenia, lactic acidosis and 3-methylglutaconic aciduria occurred. The boy died at the age of 27 months. The third case presented at the age of 16 months as an acute hypokinetic hypertrophic cardiomyopathy with transient hypotonia and mild lactic acidosis. Spontaneous clinical remission occurred. In all cases muscle biopsy was performed. Morphological studies failed to show ragged-red fibers but there was lipid storage myopathy and decreased cytochrome c oxidase activity. Biochemical studies confirmed the cytochrome c oxidase deficiency in muscle in all cases. It was associated with complex I III deficiency in case 1 and with severe deficits of all respiratory chain complexes in case 2. Post-mortem studies in case 1 indicated that complex IV was reduced in the liver but not in the heart and quantitative analysis of mtDNA revealed a depletion in muscle. Cases 1 and 2 shared some clinical features with fatal infantile myopathy associated with cytochrome c oxidase deficiency, while case 3 displayed a very unusual clinical presentation. The histochemical enzyme reaction of cytochrome c oxidase is useful for the diagnosis of mitochondrial myopathy because ragged-red fibers may be lacking. Finally, biochemical measurement of the different mitochondrial respiratory chain complexes is required because multiple defects are frequent and occasionally related to mtDNA depletion.

Synthesis, characterisation and high-performance liquid chromatography of C6-C16 dicarboxylyl-mono-coenzyme A and -mono-carnitine esters

The synthesis and purification of the mono-coenzyme A and mono-carnitine esters of the homologous series of straight-chain even-numbered dicarboxylic acids (C6-C16) is described. The corresponding 3-hydroxyacyl- and 2-enoyl-CoA esters were prepared enzymatically. A reversed-phase high-performance liquid chromatographic (HPLC) system for the analysis of the intact CoA esters is described and their chromatographic behaviour documented. Reversed-phase HPLC systems for the analysis of the 4-bromophenacyl derivatives of the dicarboxylyl-mono-carnitines and the 4-nitrobenzyl derivatives of the free acids are also described. Some preliminary studies of the metabolism of [U-14C]hexadecanedionoyl-mono-CoA by rat liver peroxisomes and rat skeletal muscle mitochondria are described illustrating the application of these methods.

Respiratory chain abnormalities in skeletal muscle from patients with Parkinson's disease

Parkinson's disease is one of the commonest neurodegenerative disorders in Western society. Although the neuropathological changes have been well documented, the underlying biochemical defect is unknown. Toxins may play a part in the aetiology of this disorder. It has been shown that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces a Parkinson-like syndrome in both man and primates and 1-methyl-4-phenylpyridine (MPP+), a metabolite of MPTP, inhibits NADH-ubiquinone oxidoreductase (complex I) of the mitochondrial respiratory chain. We studied mitochondrial respiratory chain function in skeletal muscle from patients with Parkinson's disease because, like brain, it has a high dependence on oxidative metabolism. Our results show low activity in all complexes studied (I, II and IV). The implications of these findings are discussed in relation to the aetiology of Parkinson's disease.

Multiple defects of the mitochondrial respiratory chain in a mitochondrial encephalopathy (MERRF): a clinical, biochemical and molecular study

We describe a young man with a progressive neurological disorder including myoclonus, mental retardation, muscle weakness and a mitochondrial myopathy (myoclonus epilepsy and ragged red fibres--MERRF). Multiple abnormalities of the mitochondrial respiratory chain in skeletal muscle are shown by direct measurement of the flux through the individual complexes, low-temperature redox spectroscopy and decreased immunodetectable subunits of complexes I and IV by immunoblotting. No abnormality of mitochondrial DNA was found. This is the first report of combined defects of complexes I, III and IV as a cause of this clinical syndrome. However, we propose that the occurrence of multiple respiratory chain defects may be more common than previously recognised and that this particular combination of defects, involving complexes I, III and IV, may be the predominant biochemical abnormality in MERRF.

Products and intermediates of the beta-oxidation of [U-14C]hexadecanedionoyl-mono-CoA by rat liver peroxisomes and mitochondria

1. The synthesis of [U-14C]hexadecanedionoyl-mono-CoA is described. 2. The beta-oxidation of [U-14C]hexadecanedionoyl-mono-CoA by purified rat liver peroxisomes and mitochondria is demonstrated. 3. The products of mitochondrial beta-oxidation of [U-14C]hexadecanedionoyl-mono-CoA include ketone bodies, citrate and acetylcarnitine. 4. Tetradecadionoyl-mono-CoA, hexadec-2-enedionyl-mono-CoA and hexadionoyl-mono-CoA were the only detectable intermediates formed by mitochondrial beta-oxidation, whereas acetyl-CoA and all saturated even-numbered intermediates of chain length C6-C16 were generated by peroxisomal beta-oxidation. 5. Hexadecanedionoyl-mono-CoA and hexadecanoyl-CoA were equally effective substrates for peroxisomal beta-oxidation, but hexadecanedionoyl-mono-CoA was a relatively poorer substrate for the mitochondrial pathway.

Intermediates of peroxisomal beta-oxidation. A study of the fatty acyl-CoA esters which accumulate during peroxisomal beta-oxidation of [U-14C]hexadecanoate

1. 14C-labelled fatty acyl-CoA esters resulting from beta-oxidation of [U-14C]hexadecanoate by peroxisomal fractions isolated from rats treated with clofibrate showed the presence of the full range of saturated intermediates down to acetyl-CoA. 2. The pattern of intermediates generated was fairly constant. At low concentrations of [U-14C]hexadecanoate (50 microM), decanoyl-CoA was present in lowest amounts. At higher concentrations of [U-14C]hexadecanoate (greater than 100 microM), all intermediates of chain length shorter than 12 carbon atoms (except acetyl-CoA) were present at similar low concentrations; the process of beta-oxidation now resembling chain-shortening of hexadecanoate by two cycles of beta-oxidation. 3. In the absence of an NAD(+)-regenerating system [pyruvate and lactate dehydrogenase (EC 1.1.1.28)] 2-enoyl- and 3-hydroxyacyl-CoA esters were generated, suggesting that re-oxidation of NADH is essential for optimal rates of peroxisomal beta-oxidation in vitro. 4. At high concentrations of [U-14C]hexadecanoate (greater than 100 microM), 3-oxohexadecanoyl-CoA was produced, suggesting that thiolase (acetyl-CoA acetyltransferase; EC 2.3.1.9) can become rate-limiting for peroxisomal beta-oxidation.

Impaired mitochondrial beta-oxidation in a patient with an abnormality of the respiratory chain. Studies in skeletal muscle mitochondria

Defects of complex I of the mitochondrial respiratory chain are important causes of neurological disease. We report studies that demonstrate a severe deficiency of complex I activity with less severe abnormalities of complexes III and IV (less than 5, 63, and 30% of control values, respectively) in a skeletal muscle mitochondrial fraction from a 22-yr-old female with weakness, lactic acidemia, and the deposition of intramuscular neutral lipid. The observation that lipid accumulates in this and other patients with complex I deficiency suggests impaired mitochondrial fatty acid oxidation. To investigate this mechanism we have shown impaired flux through beta-oxidation [( U-14C]hexadecanoate oxidation was 66% of control rate) and accumulation of specific acyl-CoA ester intermediates. The changes in fatty acid metabolism in complex I deficiency are secondary to the reduced state within the mitochondrial matrix with low NAD+/NADH ratios.

Familial intermittent ataxia due to a defect of the E1 component of pyruvate dehydrogenase complex

Disturbances of pyruvate metabolism have been implicated in the aetiology of several neurological disorders including Leigh's disease and familial ataxia. We have re-investigated a patient whose initial description documented intermittent ataxia, a presumed disorder of pyruvate metabolism and an X-linked pattern of inheritance. Recent studies showed he had slow oxidation of pyruvate, low pyruvate dehydrogenase complex (PDC) activity and immunochemical evidence of E1 deficiency in skeletal muscle mitochondria. This is consistent with the recent finding that the gene for E1 alpha is on the X chromosome.

Multiple defects of the respiratory chain including complex II in a family with myopathy and encephalopathy

We report severe deficiency of complex II of the mitochondrial respiratory chain and low activities of complex I and II in skeletal muscle mitochondria from a young woman with progressive muscle weakness and encephalopathy. Defects of complex II have only very rarely been described and this is the first report of decreased immunoreactive subunits associated with severe deficiency of this enzyme.

Measurement of the acyl-CoA intermediates of beta-oxidation by h.p.l.c. with on-line radiochemical and photodiode-array detection. Application to the study of [U-14C]hexadecanoate oxidation by intact rat liver mitochondria

The quantitative isolation of acyl-CoA esters of chain length C2-C17 from mitochondrial incubations and their analysis by reverse-phase radio-h.p.l.c. is described. Photodiode-array detection was used to characterize 2-enoyl-CoA esters. The chromatographic behaviour of all 27 intermediates of the beta-oxidation of hexadecanoyl-CoA is documented. Only C16, C14 and C12 intermediates were detected in uncoupled mitochondria oxidizing [U-14C]hexadecanoyl-CoA in the presence of fluorocitrate and carnitine, providing evidence for some organization of the enzymes of beta-oxidation [Garland, Shepherd & Yates (1965) Biochem. J. 97, 587-594; Sumegi & Srere (1984) J. Biol. Chem. 259, 8748-8752]. Rotenone increased concentrations of 3-hydroxyacyl-CoA and 2-enoyl-CoA esters and inhibited flux. These experiments provide the first direct unambiguous measurements of acyl-CoA esters in intact respiring rat liver mitochondrial fractions.

Tissue specific defect of complex I of the mitochondrial respiratory chain

Deficiency of complex I is one of the most commonly reported defects of the mitochondrial respiratory chain in man. Clinical evidence of tissue specific expression of complex I deficiency has not previously been confirmed biochemically. We report here slow oxidation of NAD+-linked substrates, low activity of complex I and low amounts of immunoreactive complex I peptides in skeletal muscle mitochondria from a patient with muscle weakness and lactic acidosis. In liver mitochondria complex I activity was normal and all the immunoreactive subunits of complex I were present in normal amounts.

A case of carnitine palmitoyltransferase II deficiency in human skeletal muscle

A 20-year-old man was shown to have a deficiency of carnitine palmitoyltransferase (CPT) II in skeletal muscle. The evidence was: (i) there was no significant oxidation of [9,10-3H]-palmitate or of [1-14C]palmitate in mitochondrial fractions from fresh skeletal muscle from the patient; (ii) all the CPT activity in a homogenate of fresh muscle from the patient was overt (CPT I) with no increase in activity after the inner membrane was disrupted; (iii) all the CPT activity in the patient's muscle was inhibited by malonyl-CoA; and (iv) an immunoreactive peptide of 67 kDa corresponding to CPT II, present in mitochondria from controls, was absent in those from the patient.

Cytochrome oxidase deficiency: immunological studies of skeletal muscle mitochondrial fractions

We report a 2-year-old girl who presented with delayed development, weakness and persistent vomiting. She had a demyelinating peripheral neuropathy. The activity of cytochrome oxidase in skeletal muscle from the patient was 10% of controls. Immunochemical studies using antibodies to holo-cytochrome oxidase and the individual subunits showed a low concentration of all detectable subunits.