Short-chain acylcarnitines of human blood and urine

Effects of L-Carnitine Intake on Exercise-Induced Muscle Damage and Oxidative Stress: A Narrative Scoping Review

Exercise-induced muscle damage results in decreased physical performance that is accompanied by an inflammatory response in muscle tissue. The inflammation process occurs with the infiltration of phagocytes (neutrophils and macrophages) that play a key role in the repair and regeneration of muscle tissue. In this context, high intensity or long-lasting exercise results in the breakdown of cell structures. The removal of cellular debris is performed by infiltrated phagocytes, but with the release of free radicals as collateral products. L-carnitine is a key metabolite in cellular energy metabolism, but at the same time, it exerts antioxidant actions in the neuromuscular system. L-carnitine eliminates reactive oxygen and nitrogen species that, in excess, alter DNA, lipids and proteins, disturbing cell function. Supplementation using L-carnitine results in an increase in serum L-carnitine levels that correlates positively with the decrease in cell alterations induced by oxidative stress situations, such as hypoxia. The present narrative scoping review focuses on the critical evaluation of the efficacy of L-carnitine supplementation on exercise-induced muscle damage, particularly in postexercise inflammatory and oxidative damage. Although both concepts appear associated, only in two studies were evaluated together. In addition, other studies explored the effect of L-carnitine in perception of fatigue and delayed onset of muscle soreness. In view of the studies analyzed and considering the role of L-carnitine in muscle bioenergetics and its antioxidant potential, this supplement could help in postexercise recovery. However, further studies are needed to conclusively clarify the mechanisms underlying these protective effects.

Insights into the Effects of Crack Abuse on the Human Metabolome Using a NMR Approach

Approximately 255 million people consume illicit drugs every year, among which 18 million use cocaine. A portion of this drug is represented by crack, but it is difficult to estimate the number of users since most are marginalized. However, there are no recognized efficacious pharmacotherapies for crack-cocaine dependence. Inflammation and infection in cocaine users may be due to behavior adopted in conjunction with drug-related changes in the brain. To understand the metabolic changes associated with the drug abuse disorder and identify biomarkers, we performed a ¹H NMR-based metabonomic analysis of 44 crack users' and 44 healthy volunteers' blood serum. The LDA model achieved 98% of accuracy. From the water suppressed ¹H NMR spectra analyses, it was observed that the relative concentration of lactate was higher in the crack group, while long chain fatty acid acylated carnitines were decreased, which was associated with their nutritional behavior. Analyses of the aromatic region of CPMG ¹H NMR spectra demonstrated histidine and tyrosine levels increased in the blood serum of crack users. The reduction of carnitine and acylcarnitines and the accumulation of histidine in the serum of the crack users suggest that histamine biosynthesis is compromised. The tyrosine level points to altered dopamine concentration.

Rapid spectrophotometric determination of plasma carnitine concentrations

A spectrophotometric enzymatic assay for plasma carnitine concentrations has been automated on the Monarch 2000. Prior to the assay, each plasma sample was divided into three fractions, ie, free carnitine, acid-soluble carnitine and total carnitine, in order to determine the concentration of both free and esterified carnitine. Using the method developed by Tachikawa et al (Seikagaku 56:998, 1984), each of the samples was then chromatographed on an anion exchange resin to eliminate those compounds which could adversely impact the accuracy of the enzymatic assay for carnitine. After the completion of these preparatory steps, 32 specimens were assayed in less than 16 min on the Monarch 2000 with a high degree of both accuracy and precision. The assay was linear over a wide concentration range (5.0-80 mumol/liter), with the lower limit of sensitivity being 5.0 mumol/liter. The coefficient of variation (CV%) of the within run precision was 2.1%, 2.8%, and 6.7% for the determinations of free carnitine, acid-soluble carnitine, and total carnitine, and 17.4% and 27.8% for the calculated values of short-chain and long-chain acylcarnitines, respectively. The CV% of the between run precision for the same fractions was 6.5%, 2.7%, 3.8%, 14.2%, and 14.3%, respectively. When authentic L-carnitine was added to the plasma, the mean recovery rate was 94.7 +/- 11.0%. Reference values were determined using plasma obtained from 40 healthy adult volunteers.

Metabolic changes induced by maximal exercise in human subjects following L-carnitine administration

In double-blind cross-over experiments, ten moderately trained male subjects were submitted to two bouts of maximal cycle ergometer exercise separated by a 3 day interval. Each subject was randomly given either L-carnitine (2 g) or placebo orally 1 h before the beginning of each exercise session. At rest L-carnitine supplementation resulted in an increase of plasma-free carnitine without a change in acid-soluble carnitine esters. Treatment with L-carnitine induced a significant post-exercise decrease of plasma lactate and pyruvate and a concurrent increase of acetylcarnitine. The determination of the individual carnitine esters in urine collected for 24 h after the placebo exercise trial revealed a decrease of acetyl carnitine and a parallel increase of a C4 carnitine ester, probably isobutyrylcarnitine. Conversely, acetylcarnitine was strongly increased and C4 compounds were almost suppressed in the L-carnitine loading trial. These results suggest that L-carnitine administration prior to high-intensity exercise stimulates pyruvate dehydrogenase activity, thus diverting pyruvate from lactate to acetylcarnitine formation.

Alterations of serum and urinary carnitine profiles in cancer patients: hypothesis of possible significance

The present study examined the serum and urinary carnitine concentrations of 21 cancer patients with metastatic disease and 13 healthy age-matched controls by taking three consecutive samples during an 8-week period. The serum concentrations of all fractions of carnitine were significantly lower in the female cancer patients than in the female controls. The concentrations of urinary carnitine fractions were relatively higher in the total cancer population; however, only acid-insoluble acylcarnitine (AIAC) was statistically significant. The renal clearance of acid-soluble acylcarnitine (ASAC) and AIAC was significantly greater in cancer subjects than in controls. Significant inverse relationships were established between the ASAC and AIAC clearances and their respective serum concentrations. The renal tubular reabsorption of AIAC was significantly less in cancer patients than in control subjects as indicated by the fractional excretion of carnitine. The increased clearance of acylcarnitine and excretion of large amounts of AIAC are proposed to be a response to chemotherapy and represent a loss of energy to the cancer patient.

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.

The effects of post-exercise glucose and alanine ingestion on plasma carnitine and ketosis in humans

1. Several studies have hypothesized that alanine decreases plasma ketone body levels by increasing availability of oxaloacetate, thus allowing acetyl groups to enter the tricarboxylic acid cycle and releasing co-enzyme A (CoA). 2. Four, fasted adult males exercised at 50% of their maximal oxygen consumption for 1.5 h, then ingested 100 g of either glucose or alanine 2 h into recovery. 3. Post-exercise ketosis had developed at 2 h into recovery, as shown by a significantly elevated concentration of beta-hydroxybutyrate in the plasma. At this time plasma free fatty acids were elevated above resting levels while plasma free carnitine concentrations had fallen below resting values. 4. After either alanine or glucose ingestion beta-hydroxybutyrate concentrations fell to the same extent. After the alanine load free carnitine increased above that seen in the glucose trial. Following either alanine or glucose ingestion free fatty acid levels fell; they remained at resting levels in the alanine trial but decreased below rest in the glucose trial. 5. We assume that plasma carnitine concentrations largely reflect the hepatic carnitine pools; therefore, elevations in the plasma free carnitine are probably the result of an increased utilization of acetyl CoA. The significant elevation in plasma free carnitine concentration found after alanine ingestion is consistent with the hypothesis that alanine increases the oxidation of acetyl CoA by providing oxaloacetate for the tricarboxylic acid cycle.

The serum carnitine status of cancer patients

Carnitine is necessary for the translocation of fatty acids into the mitochondria, and the relative concentration of carnitine and acylcarnitine in the serum are known to reflect metabolic states. A survey of serum carnitine concentrations was made in 54 cancer and 81 noncancer patients for the purpose of determining the carnitine profile. The total carnitine, nonesterified carnitine, and acid-insoluble acylcarnitine concentrations of cancer patients were similar to noncancer patients and within the normal range; however, the acid-soluble acylcarnitine concentration was significantly lower in cancer patients than in controls (6.7 vs 11.5 nmol/ml). When percentages and ratios were calculated for the relative proportions of acylcarnitines, large variations were found to occur among cancer types. The acylcarnitine ratio (the sum of acid-soluble and acid-insoluble acylcarnitine divided by nonesterified carnitine) ranged from 0.17 in leukemia to 0.30 in breast cancer cases. Since the acylcarnitine concentration and ratio are reflective of the metabolic state, the depressed acylcarnitine ratio in cancer patients may be due to decreased production, increased utilization, or increased excretion of acid-soluble acylcarnitine. Elevated concentrations of nonesterified carnitine and total carnitine were observed in two patients, and some of the lowest acylcarnitine concentrations and ratios were observed in advanced cancer cases. The therapeutic regimen and/or the neoplastic process itself may be responsible for the observed differences in the serum carnitine profile.

Carnitine status, plasma lipid profiles, and exercise capacity of dialysis patients: effects of a submaximal exercise program

Carnitine status, blood lipid profiles, and exercise capacity were evaluated in a combined group of hemodialysis (N = 4) and continuous ambulatory peritoneal dialysis (N = 6) patients before and after an 8-week submaximal exercise program. Maximal aerobic capacity (VO2max) was only 18.5 +/- 5.9 (mean +/- SD) mL O2/kg/min, well below the expected 30 to 35 mL O2/kg/min for age-matched sedentary controls. Plasma short-chain acylated carnitine levels, which were two to three times normal values, were reduced after the exercise program, but the long-chain acylcarnitines were significantly reduced during acute exercise. Muscle biopsies of the vastus lateralis were performed at rest in five patients prior to and after the 8-week exercise program. Total carnitine in skeletal muscle was 3.09 (.076 SD) mumol/g ww, with only 11.3% acylated prior to the exercise program, which was much lower than the 4.25 +/- 1.27 mumol/g ww, with 28.5% acylated in a group of healthy athletic subjects (N = 28). Muscle free carnitine concentrations decreased significantly following the 8-week training period, with only a slight reduction in total carnitine. The percent of acylated carnitine was therefore significantly increased (P less than 0.05) from 11.3% to 25.2% after the experimental period. Pretraining carnitine palmitoyl transferase activity at rest was 0.57 +/- 0.28 nmol palmitoyl carnitine formed/5 min/mg mitochondrial protein, which was not changed by exercise training v 1.80 +/- 0.51 nmol/5 min/mg protein in 28 healthy normals (P less than 0.001). Free fatty acid concentrations were reduced significantly during acute exercise as a result of the exercise training program whereas other plasma lipids were not altered. (ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of oxidative metabolism by propionic acid and its reversal by carnitine in isolated rat hepatocytes

The present study was designed to study the interaction of propionic acid and carnitine on oxidative metabolism by isolated rat hepatocytes. Propionic acid (10 mM) inhibited hepatocyte oxidation of [1-14C]-pyruvate (10 mM) by 60%. This inhibition was not the result of substrate competition, as butyric acid had minimal effects on pyruvate oxidation. Carnitine had a small inhibitory effect on pyruvate oxidation in the hepatocyte system (210 +/- 19 and 184 +/- 18 nmol of pyruvate/60 min per mg of protein in the absence and presence of 10 mM-carnitine respectively; means +/- S.E.M., n = 10). However, in the presence of propionic acid (10 mM), carnitine (10 mM) increased the rate of pyruvate oxidation by 19%. Under conditions where carnitine partially reversed the inhibitory effect of propionic acid on pyruvate oxidation, formation of propionylcarnitine was documented by using fast-atom-bombardment mass spectroscopy. Propionic acid also inhibited oxidation of [1-14C]palmitic acid (0.8 mM) by hepatocytes isolated from fed rats. The degree of inhibition caused by propionic acid was decreased in the presence of 10 mM-carnitine (41% inhibition in the absence of carnitine, 22% inhibition in the presence of carnitine). Propionic acid did not inhibit [1-14C]palmitic acid oxidation by hepatocytes isolated from 48 h-starved rats. These results demonstrate that propionic acid interferes with oxidative metabolism in intact hepatocytes. Carnitine partially reverses the inhibition of pyruvate and palmitic acid oxidation by propionic acid, and this reversal is associated with increased propionylcarnitine formation. The present study provides a metabolic basis for the efficacy of carnitine in patients with abnormal organic acid accumulation, and the observation that such patients appear to have increased carnitine requirements ('carnitine insufficiency').

Metabolism and excretion of carnitine and acylcarnitines in the perfused rat kidney

Rat kidneys were perfused for 30 min with a Krebs-Henseleit bicarbonate buffer with 5 mM glucose. Albumin proved superior to pluronic polyols as oncotic agent with regard to carnitine reabsorption in the perfused kidney. The reabsorption of 30 microM (-)-[methyl-3 H]carnitine was approx. 96% during the first 10 min. At 750 microM the reabsorption decreased to 40%. The tubular reabsorptive maximum (Tmax) was approx. 170 nmol/min per kidney. The fractional reabsorption and clearance of (+)-carnitine, gamma-butyrobetaine, and carnitine esters did not deviate significantly from that of (-)-carnitine. (+)-Carnitine was not metabolized by the perfused kidney. In perfusions with (-)-carnitine or (-)-carnitine plus 10 mM alpha-ketoisocaproate or alpha-ketoisovalerate increased amounts of acetylcarnitine, isovalerylcarnitine and isobutyrylcarnitine were found. Propionate (5 mM) inhibited acetylcarnitine formation. Isovalerylcarnitine, isobutyrylcarnitine and propionylcarnitine were actively degraded to free (-)-carnitine. In urine, we found a disproportionally high excretion of carnitine or carnitine esters formed in the kidney, compared to the same derivatives when ultrafiltrated. Leakage of metabolites formed in the kidney into preurine may explain this phenomenon.

Isolation and identification of alpha-methyloctanylcarnitines from human urine

Medium-chain acylcarnitines were isolated from human urine using a combination of chloroform-methanol extraction, silicic acid column and molecular sieving chromatography and preparative HPLC. Three purified acylcarnitines were analyzed by fast atom bombardment mass spectrometry and were also saponified and the free fatty acids analyzed by gas chromatography and mass spectrometry. Combined electron impact mass spectrometry and fast atom bombardment mass spectrometry and periodate oxidation for location of double bonds, demonstrated the occurrence of delta 6-octenylcarnitine, 2-methyloctanylcarnitine and 2-methyl-delta 6-octenylcarnitine. These acylcarnitines were present in the thirteen urines obtained from normal humans, but were not detected in urines from three individuals who had been on total parenteral nutrition for more than a year. The occurrence of alpha-methyl medium-chain acylcarnitines in human urine indicates a role for carnitine in excretion (detoxification) of these acyl derivatives.

L-carnitine therapy in isovaleric acidemia

Isovaleric acidemia, resulting from isovaleryl-coenzyme A dehydrogenase deficiency, is associated with marked reduction of free carnitine in both plasma and urine. Fast atom bombardment-mass spectrometry, hydrolysis, and gas chromatography/mass spectrometry have unequivocally identified the existence of isovalerylcarnitine, a new metabolite specific for this disorder. Administration of equimolar amounts of glycine or L-carnitine separately with leucine demonstrated that isovaleryl-coenzyme A is removed by supplemental L-carnitine in the form of isovalerylcarnitine as effectively as it is by glycine, in the form of isovalerylglycine. When L-carnitine is given alone, excretion of isovalerylglycine decreases in preference to enhanced excretion of isovalerylcarnitine and hippurate. Treatment with L-carnitine alone has proven effective in preventing further hospitalizations in a patient with this genetic disorder.

Valproylcarnitine: a novel drug metabolite identified by fast atom bombardment and thermospray liquid chromatography-mass spectrometry

Urine samples from three children at different stages of chronic valproate therapy were partially purified using a cation exchange column. A signal consistent with either valproylcarnitine or octanoylcarnitine was observed in one of these extracts by direct fast atom bombardment-mass spectrometry analysis. These isomeric acylcarnitines were synthesized, separated and characterized by thermospray high performance liquid chromatography-mass spectrometry. This new technique was then employed to positively identify intact valproyl-carnitine in the patients' urine samples. The implications of this finding with regard to a mechanism to account for carnitine deficiency in patients receiving valproate are discussed.

Effect of hypoxia on pig heart short-chain acylcarnitines

The right ventricles of pig heart were perfused with hypoxic blood and the left ventricles were perfused with normally ventilated arterial blood. Free carnitine and short-chain acylcarnitines in hypoxic ventricles were lower than in perfused controls, and much lower than in non-perfused heart. Acetylcarnitine levels decreased and the branched-chain acylcarnitines and propionylcarnitine were elevated in the hypoxic perfused ventricles. These data indicate that both hypoxia and anaesthesia caused loss of carnitine and short-chain acylcarnitines from the heart and hypoxia also changed the distribution of short-chain acylcarnitines in the heart.

Carnitine metabolism and inborn errors

Current knowledge of the metabolic role, biosynthesis, cellular uptake, excretion and turnover of carnitine is reviewed. The clinical spectrum and possible aetiology of the primary muscle and primary systemic carnitine deficiency syndromes are considered and the various genetic defects of intermediary metabolism which can give rise to secondary carnitine deficiency are indicated.