Heterogeneity of carnitine-palmitoyltransferase deficiency

Episodes with muscle ache, rhabdomyolysis and myoglobinuria with or without associated renal insufficiency are characteristic of muscle carnitinepalmitoyltransferase (CPT) deficiency. However, patients differ from each other in many aspects, such as the kind of stimulus that triggers rhabdomyolysis, the ability to produce ketone bodies when fasting, whether the enzyme defect is localized in skeletal muscle or is general, and the nature of the enzyme defect, which may be in CPT I or CPT II or both. Studies of muscle, liver and fibroblasts from a patient with recurrent rhabdomyolysis spontaneously occurring or triggered by exercise or fever, revealed a CPT deficiency in the muscle and liver biopsy samples but normal CPT activity in cultured cells, differing from previously reported patients. The enzyme defect in muscle was evidenced by two different methods, but not when determined with a method that measures the formation of palmitoylcarnitine. The enzyme abnormality in the patient's liver was associated with a delayed ketone body production and with a dramatic increase in long-chain acylcarnitines in the serum when fasting. Moreover the patient was unable to build up ketones when fed long-chain triglycerides (LCT) but showed prompt ketogenic response when fed medium-chain triglycerides (MCT). The heterogeneity of clinical presentations and of the biochemical findings in patients with CPT deficiency are discussed.

Carnitine and the development of steroidogenesis in rat ovary

We have measured the concentrations of carnitine and the activities of the carnitine acyltransferases in immature rat ovaries which had been stimulated to develop with pregnant mare gonadotropin. The concentration of carnitine increased from 700 nmol/g wet wt. to 1 mumol/g wet wt. of ovary after hormonal administration and the activities of the acyltransferases also rose. These increases corresponded with cell division. After replication had ceased, when the new cells were emerging and actively making steroid hormones, the concentration of carnitine and activities of the transferases fell.

Carnitine-acylcarnitine translocase catalyzes an equilibrating unidirectional transport as well

Besides carnitine-acylcarnitine translocase-catalyzed exchange diffusions, a relatively much slower unidirectional transport of carnitines also proceeds in mitochondria. The latter proceeds in the direction of the concentration gradient of carnitines and leads to the equilibration of carnitine concentration across the inner membrane. The same translocase that catalyzes exchange diffusion appears to catalyze unidirectional transport inasmuch as the two processes showed similar substrate specificity, sensitivity to inhibitors, high temperature coefficients, apparent affinity for carnitine, and a lack of energy requirement. The unidirectionally imported carnitine readily exchanged against medium carnitine, indicating that the two transport processes share the same pool of mitochondrial carnitine. Unidirectional transport appears to be functional in vivo; its operation seems not only to allow mitochondria to acquire carnitine but to adjust the rates of their faster exchange-diffusion reactions with changes in total tissue carnitine concentrations. The carnitine-acylcarnitine translocase was found to be about 15 times as active in mitochondria of rat liver as in those of heart.

Carnitine, acetylcarnitine and the activity of carnitine acyltransferases in seminal plasma and spermatozoa of men, rams and rats

The concentration of total carnitine (i.e. carnitine plus acetylcarnitine) was measured in seminal plasma and spermatozoa of men and rams. In ram semen, there was a close correlation between the concentration of spermatozoa and that of total carnitine in the seminal plasma, indicating that the epididymal secretion was the sole source of seminal carnitine. The percentage of total carnitine present as acetylcarnitine was 40% in seminal plasma and 70-80% in spermatozoa. The acetylation state of carnitine in seminal plasma was apparently not influenced by the metabolic activity of spermatozoa in ejaculated ram semen as no change was found in the plasma concentration of carnitine or acetylcarnitine up to 45 min after ejaculation. In spermatozoa, the activity of carnitine acetyltransferase (EC 2.3.1.7) was approximately equivalent to that of carnitine palmitoyltransferase (EC 2.3.1.21); and the activity of these enzymes was similar in ram and human spermatozoa but greater in rat spermatozoa. It is concluded that there is no correlation between the content of either total carnitine or the carnitine acyltransferases and the respiratory capacity of spermatozoa.

beta-Oxidation of the coenzyme A esters of elaidic, oleic, and stearic acids and their full-cycle intermediates by rat heart mitochondria

beta-Oxidation rates for the CoA esters of elaidic, oleic and stearic acids and their full-cycle beta-oxidation intermediates and for the carnitine esters of oleic and elaidic acids were compared over a wide range of substrate and albumin concentrations in rat heart mitochondria. The esters of elaidic acid were oxidized at about half the rate of the oleic acid esters, while stearoyl-CoA was oxidized equally as rapid as oleoyl-CoA. The full-cycle beta-oxidation intermediates of elaidoyl-CoA (trans-16 : 1 delta 7, -14 : 1 delta 5, and -12 : 1 delta 3) were found to be oxidized at rates nearly equal to those for the corresponding intermediates of oleoyl-CoA. Therefore, after the first cycle of beta-oxidation, oleoyl-CoA and elaidoyl-CoA are oxidized at nearly equal rates. The activity of fatty acyl-CoA dehydrogenase was higher with elaidoyl-CoA and its full-cycle intermediates as substrates than with the corresponding cisisomers. It was concluded that the slower oxidation rate of elaidic acid is not due to slower oxidation of any of its full-cycle beta-oxidation intermediates, nor to slower activity of fatty acyl-CoA dehydrogenase, nor to outer mitochondrial carnitine acyltransferase. Possible explanations to account for the slower oxidation rate of elaidic acid are discussed.

The effect of long-term fasting on the branched chain acylcarnitines and branched chain carnitine acyltransferases

The effect of fasting for 8 days on the levels of carnitine acyltransferases in heart, liver, liver mitochondria, skeletal muscle, skeletal muscle mitochondria, kidney, and testes in young adult male rats was determined. The specific activities of acetyl-, octanyl-, isobutyryl-, and isovaleryl-carnitine acyltransferase in mitochondria isolated from the livers of fasted animals were significantly higher than the levels of the transferases isolated from livers of fed animals. Similar results were obtained with the 500 x g supernatant fluids from liver. In contrast, the specific activities of carnitine acyltransferases of 500 x g supernatant fractions isolated from heart, skeletal muscle, kidney, and testes were the same for fed as fasted animals. The total carnitine content of liver, muscle, heart, and kidney was less in animals fasted for 8 days than in fed animals, but the amount/g of organ was higher in the animals fasted for 8 days. The amount of specific short-chain acylcarnitines in liver, muscle, and heart was determined for both fed and fasted animals. The amount of isobutyrylcarnitine and isovalerylcarnitine increased significantly in muscle from fasted animals. These data are consistent with the previous suggestion that carnitine may have a role in the metabolism of the branched-chain amino acids.

Effect of clofibrate and gemfibrozil on the activities of mitochondrial carnitine acyltransferases in rat liver. Dose--response relations

The effects of different doses of clofibrate and gemfibrozil on liver size, serum triglyceride concentration and the activities of hepatic mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) and carnitine acyltransferases were studied in male rats. Both clofibrate and gemfibrozil treatment effectively decreased the fructose-induced hypertriglyceridaemia and increased the liver to body weight ratio. Clofibrate treatment also induced an increase of many times in the activities of mitochondrial alpha-GPD and carnitine acyltransferases, the effect increasing with the dose used. The effect of gemfibrozil on the activities of the enzymes was significantly smaller. There was no correlation between the decrease in serum triglyceride concentration and the changes in the activities of the enzymes. Only clofibrate increased the rate of fatty acylcarnitine oxidation in isolated mitochondria. It is concluded that both drugs increased the size of the rat liver, but that only clofibrate influenced the mitochondrial enzyme activities of mitochondrial carnitine acyltransferases and the accelerated mitochondrial oxidation of fatty acids are not the mechanisms by which these drugs lower serum lipid levels.

Effect of carnitine on branched-chain amino acid oxidation by liver and skeletal muscle

The effect of L-carnitine (0.5-2.0 mM) on the rates of alpha-decarboxylation of 1-14C-labeled branched-chain amino acids by gastrocnemius muscle and liver homogenates of fed rats was investigated. Carnitine increased the rate of alpha-decarboxylation of leucine (125%) and valine (28%) by muscle, but it was without effect on the oxidation of these amino acids by liver. Carnitine increased the rate of alpha-decarboxylation of alpha-ketoisocaproate by both tissues. This effect was more pronounced in muscle (130% increase) than in liver (41% increase). The activity of carnitine acyltransferase, with isovaleryl-CoA as a substrate, was 18 times higher in muscle mitochondria than in liver mitochondria. Both starvation and diabetes increased the rate of alpha-decarboxylation of leucine by muscle without having a remarkable effect on the concentration of carnitine or the activity of carnitine acyltransferase. We conclude that: a) carnitine stimulates decarboxylation of branched-chain amino acids by increasing the conversion of their ketoanalogues into carnitine esters, b) a greater carnitine acyltransferase activity in muscle than in liver may be responsible for the greater carnitine effect in muscle, c) carnitine does not appear responsible for the enhancement of leucine oxidation by muscle of starved and diabetic rats.

Carnitine metabolism in human subjects. III. Metabolism in disease

Carnitine metabolism is reviewed in lipid storage myopathies, diabetes, vomiting sickness of Jamaica, malnutrition, hyperthyrodism, Duchenne dystrophy, and a few other disease states.

Carnitine-acylcarnitine translocase. Inhibition by alpha-cyano-4-hydroxycinnamate and evidence for separate identity from the pyruvate transporting system of mitochondria

Some of the known inhibitors of pyruvate transport inhibited the activity of carnitine-acylcarnitine translocase. Their order of effectiveness with millimolar concentration required for 50% inhibition given in parentheses, was: Compound UK-5099 (alpha-cyano-beta-(1-phenylindol-3-yl)acrylate) (0.1); alpha-cyano-4-hydroxycinnamate (0.17); alpha-cyano-3-hydroxycinnamate (1); alpha-cyanocinnamate (1); alpha-fluorocinnamate (7); transcinnamate (10); p-hydroxycinnamate (10); phenylpyruvate (22); p-hydroxyphenylpyruvate (25). Kinetically, the alpha-cyano-4-hydroxycinnamate inhibition was mixed and the p-hydroxyphenylpyruvate inhibition was noncompetitive with respect to external (-)-carnitine. The alpha-cyano-4-hydroxycinnamate inhibition was reversible and resulted from its ability to act as a thiol reagent. In general, alpha-cyanocinnamate and its derivatives inhibit carnitine transport at concentrations 100 to 5000 times as high as those known to pyruvate transport. At millimolar concentrations, alpha-cyano-4-hydroxycinnamate inhibited the mitochondrial transport of molecules other than carnitine as well as the activity of carnitine acyltransferases. Pyruvate and carnitine did not complete for transport into and out of mitochondria. These results establish that transmitochondrial transport mechanisms for carnitine and pyruvate involve different carriers.

Isolation and identification of aliphatic short-chain acylcarnitines from beef heart: possible role for carnitine in branched-chain amino acid metabolism

Aliphatic acylearnitines isolated from a water-soluble fraction of beef heart have been characterized by gas chromatography and mass spectrometry. The following acyl residues derived from the acylcarnitine fraction were unequivocally identified: acetyl, propionyl, isobutyryl, butyryl, alpha-methylbutyryl, valeryl, isovaleryl, tiglyl, and caproyl. beta-methylcrotonyl and methacrylyl were tentatively identified. This occurrence of considerable quantities of branched-chain acylcarnitines indicates a role for carnitine in branched-chain amino acid metabolism.