Effect of fasting on free and esterified carnitine levels in human serum and urine: correlation with serum levels of free fatty acids and beta-hydroxybutyrate

Abnormal carnitine metabolism in hemodialysis patients on different anticoagulants

INTRODUCTION

We aimed to determine whether unfractionated heparin (UH) and low molecular weight heparin (LH) contribute to aberrant carnitine metabolism in patients receiving hemodialysis.

METHODS

The rate of increase in serum free fatty acids (FFAs) and the ratio of acylcarnitine to free carnitine (AC/FC) from before to after hemodialysis were determined in patients receiving UH and LH. Additionally, the effect of switching patients to UH from LH was examined.

RESULTS

AC/FC was significantly higher in the UH group. In addition, serum FFAs in that group increased to 0.825 ± 0.270 after dialysis from 0.172 ± 0.160 before dialysis, showing a positive correlation with AC/FC. Furthermore, AC/FC was observed to be significantly higher in patients who were switched to UH from LH at 3 months after the change.

CONCLUSION

Compared with UH, LH has a lesser effect on lipid metabolism, suggesting that it also has a lesser effect on carnitine metabolism.

Exacerbation-prone pediatric asthma is associated with arginine, lysine, and methionine pathway alterations

BACKGROUND

The asthma of some children remains poorly controlled, with recurrent exacerbations despite treatment with inhaled corticosteroids. Aside from prior exacerbations, there are currently no reliable predictors of exacerbation-prone asthma in these children and only a limited understanding of the potential underlying mechanisms.

OBJECTIVE

We sought to quantify small molecules in the plasma of children with exacerbation-prone asthma through mass spectrometry-based metabolomics. We hypothesized that the plasma metabolome of these children would differ from that of children with non-exacerbation-prone asthma.

METHODS

Plasma metabolites were extracted from 4 pediatric asthma cohorts (215 total subjects, with 41 having exacerbation-prone asthma) and detected with a mass spectrometer. High-confidence annotations were retained for univariate analysis and were confirmed by a sensitivity analysis in subjects receiving high-dose inhaled corticosteroids. Metabolites that varied by cohort were excluded. MetaboAnalyst software was used to identify pathways of interest. Concentrations were calculated by reference standardization.

RESULTS

We identified 32 unique, cohort-independent metabolites that differed in children with exacerbation-prone asthma compared to children with non-exacerbation-prone asthma. Comparison of metabolite concentrations to literature-reported values for healthy children revealed that most metabolites were decreased in both asthma groups, but more so in exacerbation-prone asthma. Pathway analysis identified arginine, lysine, and methionine pathways as most impacted.

CONCLUSIONS

Several plasma metabolites are perturbed in children with exacerbation-prone asthma and are largely related to arginine, lysine, and methionine pathways. While validation is needed, plasma metabolites may be potential biomarkers for exacerbation-prone asthma in children.

Metabolic Impairment in Coronary Artery Disease: Elevated Serum Acylcarnitines Under the Spotlights

Coronary artery disease (CAD) remains the leading cause of death worldwide. Expanding patients' metabolic phenotyping beyond clinical chemistry investigations could lead to earlier recognition of disease onset and better prevention strategies. Additionally, metabolic phenotyping, at the molecular species level, contributes to unravel the roles of metabolites in disease development. In this cross-sectional study, we investigated clinically healthy individuals (n = 116, 65% male, 70.8 ± 8.7 years) and patients with CAD (n = 54, 91% male, 67.0 ± 11.5 years) of the COmPLETE study. We applied a high-coverage quantitative liquid chromatography-mass spectrometry approach to acquire a comprehensive profile of serum acylcarnitines, free carnitine and branched-chain amino acids (BCAAs), as markers of mitochondrial health and energy homeostasis. Multivariable linear regression analyses, adjusted for confounders, were conducted to assess associations between metabolites and CAD phenotype. In total, 20 short-, medium- and long-chain acylcarnitine species, along with L-carnitine, valine and isoleucine were found to be significantly (adjusted p ≤ 0.05) and positively associated with CAD. For 17 acylcarnitine species, associations became stronger as the number of affected coronary arteries increased. This implies that circulating acylcarnitine levels reflect CAD severity and might play a role in future patients' stratification strategies. Altogether, CAD is characterized by elevated serum acylcarnitine and BCAA levels, which indicates mitochondrial imbalance between fatty acid and glucose oxidation.

The Effects of Streptozotocin-Induced Diabetes and Insulin Treatment on Carnitine Biosynthesis and Renal Excretion

Carnitine insufficiency is reported in type 1 diabetes mellitus. To determine whether this is accompanied by defects in biosynthesis and/or renal uptake, liver and kidney were obtained from male Sprague-Dawley rats with streptozotocin-induced diabetes. Diabetic rats exhibited the metabolic consequences of type 1 diabetes, including hypoinsulinemia, hyperglycemia, and increased urine output. Systemic hypocarnitinemia, expressed as free carnitine levels, was evident in the plasma, liver, and kidney of diabetic rats. Compared to control rats, the low free carnitine in the plasma of diabetic rats was accompanied by decreased expression of γ-butyrobetaine hydroxylase in liver and kidney, suggesting impaired carnitine biosynthesis. Expression of organic cation transporter-2 in kidney was also reduced, indicating impaired renal reabsorption, and confirmed by the presence of elevated levels of free carnitine in the urine of diabetic rats. Insulin treatment of diabetic rats reversed the plasma hypocarnitinemia, increased the free carnitine content in both kidney and liver, and prevented urinary losses of free carnitine. This was associated with increased expression of γ-butyrobetaine hydroxylase and organic cation transporter-2. The results of our study indicate that type 1 diabetes induced with streptozotocin disrupts carnitine biosynthesis and renal uptake mechanisms, leading to carnitine insufficiency. These aberrations in carnitine homeostasis are prevented with daily insulin treatment.

Acylcarnitine profile in Alaskan sled dogs during submaximal multiday exercise points out metabolic flexibility and liver role in energy metabolism

Alaskan sled dogs develop a particular metabolic strategy during multiday submaximal exercise, allowing them to switch from intra-muscular to extra-muscular energy substrates thus postponing fatigue. Specifically, a progressively increasing stimulus for hepatic glycogenolysis and gluconeogenesis provides glucose for both fueling exercise and replenishing the depleted muscle glycogen. Moreover, recent studies have shown that with continuation of exercise sled dogs increase their insulin-sensitivity and their capacity to transport and oxidize glucose and carbohydrates rather than oxidizing fatty acids. Carnitine and acylcarnitines (AC) play an essential role as metabolic regulators in both fat and glucose metabolism; they serve as biomarkers in different species in both physiologic and pathologic conditions. We assessed the effect of multiday exercise in conditioned sled dogs on plasma short (SC), medium (MC) and long (LC) chain AC by tandem mass spectrometry (MS/MS). Our results show chain-specific modification of AC profiles during the exercise challenge: LCACs maintained a steady increase throughout exercise, some SCACs increased during the last phase of exercise and acetylcarnitine (C2) initially increased before decreasing during the later phase of exercise. We speculated that SCACs kinetics could reflect an increased protein catabolism and C2 pattern could reflect its hepatic uptake for energy-generating purposes to sustain gluconeogenesis. LCACs may be exported by muscle to avoid their accumulation to preserve glucose oxidation and insulin-sensitivity or they could be distributed by liver as energy substrates. These findings, although representing a “snapshot” of blood as a crossing point between different organs, shed further light on sled dogs metabolism that is liver-centric and more carbohydrate-dependent than fat-dependent and during prolonged submaximal exercise.

Isobutyrylcarnitine as a Biomarker of OCT1 Activity and Interspecies Differences in its Membrane Transport

Genome-wide association studies have identified an association between isobutyrylcarnitine (IBC) and organic cation transporter 1 (OCT1) genotypes. Higher IBC blood concentrations in humans with active OCT1 genotypes and experimental studies with mouse OCT1 suggested an OCT1-mediated efflux of IBC. In this study, we wanted to confirm the suggested use of IBC as an endogenous biomarker of OCT1 activity and contribute to a better understanding of the mechanisms behind the association between blood concentrations of carnitine derivatives and OCT1 genotype. Blood and urine IBC concentrations were quantified in healthy volunteers regarding intra- and interindividual variation and correlation with OCT1 genotype and with pharmacokinetics of known OCT1 substrates. Furthermore, IBC formation and transport were studied in cell lines overexpressing OCT1 and its naturally occurring variants. Carriers of high-activity OCT1 genotypes had about 3-fold higher IBC blood concentrations and 2-fold higher amounts of IBC excreted in urine compared to deficient OCT1. This was likely due to OCT1 function, as indicated by the fact that IBC correlated with the pharmacokinetics of known OCT1 substrates, like fenoterol, and blood IBC concentrations declined with a 1 h time delay following peak concentrations of the OCT1 substrate sumatriptan. Thus, IBC is a suitable endogenous biomarker reflecting both, human OCT1 (hOCT1) genotype and activity. While murine OCT1 (mOCT1) was an efflux transporter of IBC, hOCT1 exhibited no IBC efflux activity. Inhibition experiments confirmed this data showing that IBC and other acylcarnitines, like butyrylcarnitine, 2-methylbutyrylcarnitine, and hexanoylcarnitine, showed reduced efflux upon inhibition of mOCT1 but not of hOCT1. IBC and other carnitine derivatives are endogenous biomarkers of hOCT1 genotype and phenotype. However, in contrast to mice, the mechanisms underlying the IBC-OCT1 correlation in humans is apparently not directly the OCT1-mediated efflux of IBC. A plausible explanation could be that hOCT1 mediates cellular concentrations of specific regulators or co-substrates in lipid and energy metabolism, which is supported by our in vitro finding that at baseline intracellular IBC concentration is about 6-fold lower alone by OCT1 overexpression.

A Multi-Platform Metabolomics Approach Identifies Urinary Metabolite Signatures That Differentiate Ketotic From Healthy Dairy Cows

Ketosis and subclinical ketosis are widespread among dairy cows especially after calving. Etiopathology of ketosis has been related to negative energy balance. The objective of this study was to investigate metabolite fingerprints in the urine of pre-ketotic, ketotic, and post-ketotic cows to identify potential metabolite alterations that can be used in the future to identify susceptible cows for ketosis and metabolic pathways involved in the development of disease. In this study, NMR, DI/LC-MS/MS, and GC-MS-based metabolomics were used to analyze urine samples from 6 cows diagnosed with ketosis and 20 healthy control (CON) cows at -8 and -4 weeks prepartum, the week (+1 to +3) of ketosis diagnosis, and at +4 and +8 weeks after parturition. Univariate and multivariate analyses were used to screen metabolite panels that can identify cows at their pre-ketotic stage. A total of 54, 42, 48, 16, and 31 differential metabolites between the ketotic and CON cows were identified at -8 and -4 weeks prepartum, ketosis week, and at +4, and +8 weeks postpartum, respectively. Variable importance in projection (VIP) plots ranked the most significant differential metabolites, which differentiated ketotic cows from the CON ones. Additionally, several metabolic pathways that are related to ketosis were identified. Moreover, two promising metabolite panels were identified which clearly separated ketotic from CON cows with excellent level of sensitivity and specificity. Overall, multiple urinary metabolite alterations were identified in pre-ketotic, ketotic, and post-ketotic cows. The metabolite panels identified need to be validated in the future in a larger cohort of animals.

Human gut microbiome composition and tryptophan metabolites were changed differently by fast food and Mediterranean diet in 4 days: a pilot study

Diets rich in animal source foods vs plant-based diets have different macronutrient composition, and they have been shown to have differential effects on the gut microbiome. In this study, we hypothesized that diets with very different nutrient composition are able to change gut microbiome composition and metabolites in a very short period. We compared a fast food (FF) diet (ie, burgers and fries) with a Mediterranean (Med) diet, which is rich in vegetables, whole grains, olive oil, nuts, and fish. Ten healthy subjects participated in a controlled crossover study in which they consumed a Med diet and FF diet in randomized order for 4 days each, with a 4-day washout between treatments. Fecal DNA was extracted and the 16S V4 region amplified using polymerase chain reaction followed by sequencing on an Illumina MiSeq. Plasma metabolites and bile acids were analyzed using liquid chromatography-mass spectrometry. Certain bile-tolerant microbial genera and species including Collinsella, Parabacteroides, and Bilophila wadsworthia significantly increased after the FF diet. Some fiber-fermenting bacteria, including Lachnospiraceae and Butyricicoccus, increased significantly after the Med diet and decreased after the FF diet. Bacterially produced metabolites indole-3-lactic acid and indole-3-propionic acid, which have been shown to confer beneficial effects on neuronal cells, increased after the Med diet and decreased after the FF diet. Interindividual variability in response to the treatments may be related to differences in background diet, for example as shown by differences in Bilophila response in relationship to the saturated fat content of the baseline diet. In conclusion, an animal fat-rich, low-fiber FF diet v. a high-fiber Med diet altered human gut microbiome composition and its metabolites after just 4 days.

Acylcarnitine metabolomic profiles inform clinically-defined major depressive phenotypes

BACKGROUND

Acylcarnitines have important functions in mitochondrial energetics and β-oxidation, and have been implicated to play a significant role in metabolic functions of the brain. This retrospective study examined whether plasma acylcarnitine profiles can help biochemically distinguish the three phenotypic subtypes of major depressive disorder (MDD): core depression (CD+), anxious depression (ANX+), and neurovegetative symptoms of melancholia (NVSM+).

METHODS

Depressed outpatients (n = 240) from the Mayo Clinic Pharmacogenomics Research Network were treated with citalopram or escitalopram for eight weeks. Plasma samples collected at baseline and after eight weeks of treatment with citalopram or escitalopram were profiled for short-, medium- and long-chain acylcarnitine levels using AbsoluteIDQ®p180-Kit and LC-MS. Linear mixed effects models were used to examine whether acylcarnitine levels discriminated the clinical phenotypes at baseline or eight weeks post-treatment, and whether temporal changes in acylcarnitine profiles differed between groups.

RESULTS

Compared to ANX+, CD+ and NVSM+ had significantly lower concentrations of short- and long-chain acylcarnitines at both baseline and week 8. In NVSM+, the medium- and long-chain acylcarnitines were also significantly lower in NVSM+ compared to ANX+. Short-chain acylcarnitine levels increased significantly from baseline to week 8 in CD+ and ANX+, whereas medium- and long-chain acylcarnitines significantly decreased in CD+ and NVSM+.

CONCLUSIONS

In depressed patients treated with SSRIs, β-oxidation and mitochondrial energetics as evaluated by levels and changes in acylcarnitines may provide the biochemical basis of the clinical heterogeneity of MDD, especially when combined with clinical characteristics.

Changes in pediatric plasma acylcarnitines upon fasting for refined interpretation of metabolic stress

BACKGROUND

Childhood fasting intolerance is a life-threatening problem associated with various inborn errors of metabolism. Plasma acylcarnitines reflect fatty acid oxidation and help determine fasting intolerance etiology. Pediatric reference values of plasma acylcarnitines upon fasting are not available, complicating interpretation of stress samples.

METHODS

Retrospective analysis of supervised clinical fasting studies between 01/2005-09/2012. Exclusion criteria involved patients with (suspected) disorders, repeated tests or incomplete results. Remaining children were grouped according to age: group A (≤24 months), B (25-84 months) and C (≥85 months). Median and 2.5^th to 97.5^th percentiles of basic metabolic parameters and acylcarnitines were determined at start and end of testing on the ward and analyzed for significant differences (p<0.05).

RESULTS

Out of 127 fasting studies, 48 were included: group A (n=13), B (n=23) and C (n=12). Hypoglycemia occurred in 21%. Children from group C demonstrated significantly higher end glucose concentrations while end ketone body concentrations were significantly lower compared to younger children. In all groups, free carnitine and C3-carnitine significantly decreased upon fasting, while C2-, C6-, C12:1-, C12-, C14:1-, C14-, C16:1- and C16-carnitine significantly increased. End concentrations of C6-, C12:1-, C12-, C14:1-, C14-, C16:1-, C16- and C18:1-carnitine were significantly lower in children ≥85 months compared to younger children.

CONCLUSIONS

Fasting-induced counter-regulatory mechanisms to maintain energy homeostasis are age-dependent. This influences the changes in basic metabolic parameters and acylcarnitine profiles. Our data enable improved interpretation of the individual fasting response and may support assessment of minimal safe fasting times or treatment responses in patients.

Are low birth weight children predisposed to renal loss of carnitine?

Aim: The plasma homeostasis of both free and esterified carnitines is mostly regulated by renal tubular reabsorption, which may be disturbed in low birth weight children. The aim of study was to check whether disturbances in excretion of l-carnitine (LC) and its main ester, acetyl-carnitine (ALC), may be the result of renal dysfunction in low birth weight children (LBW).Methods: This study included 59 LBW children (2165 g [1490-2440]) and 22 children with normal birth weight as a reference group (3500 g [3275-3650]). Subjects were divided into three groups: 0-3 months, 4-12 months and over 1 year at the time of testing. Urinary levels of carnitine were measured spectrophotometrically.Results: The urine excretion of Free LC, Free LC/cr, Total LC and Total LC/cr. Were significantly higher in 0-3 and 4-12-month old LBW infants study groups when compared to the reference groups. We found statistically significant higher urine excretion of ALC and ALC/cr. in all age groups of LBW infants compared to the reference group. There was a negative correlation between birth weight and free LC/cr. (r= -0.3, p < .05), Total LC/cr. (r= -0.34, p < .05), and ALC/cr. (r= -39, p < .05), and in the children >12-month-old strong negative correlation between eGFR and free LC/cr. (r= -0.6, p < .05), Total LC/cr. (r= -0.61, p < .05), ALC/cr. (r= -0.61, p < .05.)Conclusion: Higher urine excretion of both LC and ALC and its negative correlation with birth weight and eGFR may reflect some degree of renal dysfunction in LBW infants.

Urinary Metabolomics Profiles Associated to Bovine Meat Ingestion in Humans

SCOPE

The impact of meat consumption on human health is widely examined in nutritional epidemiological studies, especially due to the connection between the consumption of red and processed meat and the risk of colon cancer. Food questionnaires do not assess the exposure to different methods of meat cooking. This study aimed to identify biomarkers of the acute ingestion of bovine meat cooked with two different processes.

METHODS AND RESULTS

Non-targeted UPLC-MS metabolite profiling was done on urine samples obtained from 24 healthy volunteers before and 8 h after the ingestion of a single meal composed of intrinsically ¹⁵ N labelled bovine meat, either cooked at 55 °C for 5 min or at 90 °C for 30 min. A discriminant analysis extension of independent components analysis was applied to the mass spectral data. After meat ingestion, the urinary excretion of 1-methylhistidine, phenylacetylglutamine, and short- and medium-chained acylcarnitines was observed. ¹⁵ N labelling was detected in these metabolites, thus confirming their origin from ingested meat. However, no difference was observed in urinary metabolomic profiles according to the meat cooking process used.

CONCLUSION

Meat ingestion led to the excretion of several nitrogen-containing compounds, but although a metabolic signature was detected for meat ingestion, the impact of the cooking process was not detectable at the level of urinary metabolic signature in our experimental conditions.

Significance of l-carnitine for human health

Carnitine acyltransferases catalyze the reversible transfer of acyl groups from acyl-coenzyme A esters to l-carnitine, forming acyl-carnitine esters that may be transported across cell membranes. l-Carnitine is a wáter-soluble compound that humans may obtain both by food ingestion and endogenous synthesis from trimethyl-lysine. Most l-carnitine is intracellular, being present predominantly in liver, skeletal muscle, heart and kidney. The organic cation transporter-2 facilitates l-carnitine uptake inside cells. Congenital dysfunction of this transporter causes primary l-carnitine deficiency. Carnitine acetyltransferase is involved in the export of excess acetyl groups from the mitochondria and in acetylation reactions that regulate gene transcription and enzyme activity. Carnitine octanoyltransferase is a peroxysomal enzyme required for the complete oxidation of very long-chain fatty acids and phytanic acid, a branched-chain fatty acid. Carnitine palmitoyltransferase-1 is a transmembrane protein located on the outer mitochondrial membrane where it catalyzes the conversion of acyl-coenzyme A esters to acyl-carnitine esters. Carnitine acyl-carnitine translocase transports acyl-carnitine esters across the inner mitochondrial membrane in exchange for free l-carnitine that exits the mitochondrial matrix. Carnitine palmitoyltransferase-2 is anchored on the matrix side of the inner mitochondrial membrane, where it converts acyl-carnitine esters back to acyl-coenzyme A esters, which may be used in metabolic pathways, such as mitochondrial β-oxidation. l-Carnitine enhances nonoxidative glucose disposal under euglycemic hyperinsulinemic conditions in both healthy individuals and patients with type 2 diabetes, suggesting that l-carnitine strengthens insulin effect on glycogen storage. The plasma level of acyl-carnitine esters, primarily acetyl-carnitine, increases during diabetic ketoacidosis, fasting, and physical activity, particularly high-intensity exercise. Plasma concentration of free l-carnitine decreases simultaneously under these conditions. © 2017 IUBMB Life, 69(8):578-594, 2017.

Stabilization of the thermolabile variant S113L of carnitine palmitoyltransferase II

OBJECTIVE

Muscle carnitine palmitoyltransferase (CPT) II deficiency, the most common defect of lipid metabolism in muscle, is characterized by attacks of myoglobinuria without persistent muscle weakness.

METHODS

His6-N-hCPT2 (wild-type) and His6-N-hCPT2/S113L (variant) were produced recombinantly in prokaryotic host and characterized according to their functional and regulatory properties.

RESULTS

The wild-type and the variant S113L showed the same enzymatic activity and thermostability at 30°C. The mutated enzyme, however, revealed an abnormal thermal destabilization at 40°C and 45°C. This was consistent with an increased flexibility (B-factor) of the variant at 40°C compared with that of the wild-type shown by molecular dynamics analysis. Preincubation of the enzymes with l-carnitine and acyl-l-carnitines containing more than 10 carbons in the acyl side-chain stabilized the mutated enzyme against thermal inactivation. In contrast, palmitoyl-CoA destabilized both enzymes.

CONCLUSIONS

The problems in CPT II deficiency originating from the S113L mutation are not caused by the loss of catalytically active enzyme. They might be at least partially related to an impaired thermal stability of the protein. The lower thermodynamic stability of the variant might explain why fever and prolonged exertion provoke attacks of myoglobinuria in CPT II deficiency. The stabilization by acyl-l-carnitines might provide the basis for possible preventive therapy of CPT II deficiency.

Isolation of soluble scFv antibody fragments specific for small biomarker molecule, L-Carnitine, using phage display

Isolation of single chain antibody fragment (scFv) clones from naïve Tomlinson I+J phage display libraries that specifically bind a small biomarker molecule, L-Carnitine, was performed using iterative affinity selection procedures. L-Carnitine has been described as a conditionally essential nutrient for humans. Abnormally high concentrations of L-Carnitine in urine are related to many health disorders including diabetes mellitus type 2 and lung cancer. ELISA-based affinity characterization results indicate that selectants preferentially bind to L-Carnitine in the presence of key bioselecting component materials and closely related L-Carnitine derivatives. In addition, the affinity results were confirmed using biophysical fluorescence quenching for tyrosine residues in the V segment. Small-scale production of the soluble fragment yielded 1.3mg/L using immunopure-immobilized protein A affinity column. Circular Dichroism data revealed that the antibody fragment (Ab) represents a folded protein that mainly consists of β-sheets. These novel antibody fragments may find utility as molecular affinity interface receptors in various electrochemical biosensor platforms to provide specific L-Carnitine binding capability with potential applications in metabolomic devices for companion diagnostics and personalized medicine applications. It may also be used in any other biomedical application where detection of the L-Carnitine level is important.

¹H-NMR and MS based metabolomics study of the intervention effect of curcumin on hyperlipidemia mice induced by high-fat diet

Curcumin, a principle bioactive component of Curcuma longa L, is well known for its anti-hyperlipidemia effect. However, no holistic metabolic information of curcumin on hyperlipidemia models has been revealed, which may provide us an insight into the underlying mechanism. In the present work, NMR and MS based metabolomics was conducted to investigate the intervention effect of curcumin on hyperlipidemia mice induced by high-fat diet (HFD) feeding for 12 weeks. The HFD induced animals were orally administered with curcumin (40, 80 mg/kg) or lovastatin (30 mg/kg, positive control) once a day during the inducing period. Serum biochemistry assay of TC, TG, LDL-c, and HDL-c was conducted and proved that treatment of curcumin or lovastatin can significantly improve the lipid profiles. Subsequently, metabolomics analysis was carried out for urine samples. Orthogonal Partial Least Squares-Discriminant analysis (OPLS-DA) was employed to investigate the anti-hyperlipidemia effect of curcumin and to detect related potential biomarkers. Totally, 35 biomarkers were identified, including 31 by NMR and nine by MS (five by both). It turned out that curcumin treatment can partially recover the metabolism disorders induced by HFD, with the following metabolic pathways involved: TCA cycle, glycolysis and gluconeogenesis, synthesis of ketone bodies and cholesterol, ketogenesis of branched chain amino acid, choline metabolism, and fatty acid metabolism. Besides, NMR and MS based metabolomics proved to be powerful tools in investigating pharmacodynamics effect of natural products and underlying mechanisms.

Metabolomic analysis of arginine metabolism in acute hepatic injury in rats

To clarify the relationship between arginine metabolism and hepatic injury, metabolomic analysis was performed in rats treated with 3 representative hepatotoxicants, monocrotaline (MCT), concanavalin A (ConA), and α-naphthyl isothiocyanate (ANIT); or a myotoxicant, tetramethyl-p-phenylenediamine (TMPD). A single dose of MCT, ConA, or ANIT dose-dependently induced hepatocellular necrosis accompanied by decreased blood arginine and increased blood alanine aminotransferase (ALT) and arginase. A close correlation was detected between arginine and ALT (r = -0.746, -0.795, -0.787 for MCT, ConA, ANIT, respectively) or between arginine and arginase (r = -0.605, -0.808, -0.672 for MCT, ConA, ANIT, respectively) in all three hepatic injury models. In contrast, neither hepatocellular necrosis nor alterations in arginine were found in the skeletal muscle injury model, although ALT was slightly increased. An in vitro assay revealed that blood samples obtained from ConA-treated rats transformed external arginine to ornithine, and the reaction was totally inhibited by an arginase inhibitor. These results suggest that blood arginase plays a crucial role in arginine metabolism associated with hepatic injury. In metabolomic analysis, nearly 450 endogenous metabolites were identified in blood obtained from all the models. Among the 13 metabolites involved in arginine metabolism, decreased arginine and increased ornithine occurred in common in the hepatic injury models, whereas citrulline and other metabolites were not altered. These results indicate that arginine metabolism, especially the arginine-to-ornithine pathway, is altered in association with acute hepatic injury. Furthermore, blood arginine and ornithine are possibly specific biomarkers for hepatic injury.

Refractory hypoglycemia and subsequent cardiogenic shock in starvation and refeeding: report of three cases

OBJECTIVE

Although starvation is associated with high in-hospital mortality, its related cardiac complications are not sufficiently understood. The aim of this study was to determine the clinical course and pathogenesis of cardiac complications in malnourished patients.

METHODS

We reviewed three cases of hypoglycemia and hypotriglyceridemia with cardiac complications in starvation.

RESULTS

This report concerns three patients, respectively suffering from anorexia nervosa, esophageal carcinoma, and Parkinson's disease. Their ages ranged from 18 to 70 y, body mass index was 11.5 ± 1.5 kg/m2 (mean ± SD), and the main symptom was coma. The average blood glucose level was 15.7 ± 7.8 mg/dL without any history of insulin use or diabetes mellitus. In all cases, hypoglycemia was refractory and repetitive so that continuous glucose administration was required to maintain euglycemia. Serum triglyceride and non-esterified fatty acid levels were also very low (7 ± 4 mg/dL and 10 ± 9.1 μEq/L, respectively). Levels of serum potassium, phosphate, and magnesium were almost normal at admission. The main cardiac complications included Takotsubo cardiomyopathy and cardiac arrest. All patients survived as a result of intensive treatment.

CONCLUSIONS

Repetitive severe hypoglycemia without known background causes should be viewed as an important sign. Once this occurs, the administration of a much higher caloric input than usual accompanied by intensive monitoring will be required to maintain appropriate glucose levels. The early identification of such patients seems to be essential to reduce the high risk for cardiac complications during starvation and refeeding.

Impaired fasting tolerance among Alaska native children with a common carnitine palmitoyltransferase 1A sequence variant

A high prevalence of the sequence variant c.1436C→T in the CPT1A gene has been identified among Alaska Native newborns but the clinical implications of this variant are unknown. We conducted medically supervised fasts in 5 children homozygous for the c.1436C→T variant. Plasma free fatty acids increased normally in these children but their long-chain acylcarnitine and ketone production was significantly blunted. The fast was terminated early in two subjects due to symptoms of hypoglycemia. Homozygosity for the c.1436C→T sequence variant of CPT1A impairs fasting ketogenesis, and can cause hypoketotic hypoglycemia in young children. Trial registration www.clinical trials.gov NCT00653666 "Metabolic Consequences of CPT1A Deficiency"

Changes in lipid and carnitine concentrations following repeated fasting-refeeding in mice

The purpose of this study was to evaluate the effects of repeated fasting and refeeding on lipid metabolism. Thirty male ICR mice, aged 6 weeks, were fed an AIN-93 control diet during the experimental period. The mice were divided into 5 groups: Non fasting group (ad libitum-fed, NF), fasting for 3 days (F), fasting for 3 days and then refeeding for 4 days repeated once (FRF1), fasting for 3 days and then refeeding for 4 days repeated twice (FRF2), and fasting for 3 days and then refeeding for 4 days repeated three times (FRF3). Rates of body weight gain, epididymal fat weight, and serum TG were significantly decreased in the F, FRF1, FRF2, and FRF3 groups, compared to the NF group. LDL-cholesterol was significantly higher in the FRF3 group than the NF and F groups, but HDL-cholesterol and HDL/TC were significantly lower in the FRF3 group than in the NF and F groups. Serum total carnitine was significantly lower in the FRF1, FRF2, FRF3 groups than the NF and F groups. However, rates of serum and hepatic acyl-carnitine concentration were significantly lower in FRF1, FRF2, and FRF3 than in NF and F. Repeated fasting-refeeding resulted in visible reductions of body weight and fat mass, but it caused ill-effects with lipid and carnitine metabolism in the body.

Fasting and fat-loading tests provide pathophysiological insight into short-chain acyl-coenzyme a dehydrogenase deficiency

OBJECTIVE

To gain insight into the pathophysiological and clinical consequences of short-chain acyl-coenzyme A dehydrogenase deficiency (SCADD).

STUDY DESIGN

A retrospective study of 15 fasting and 6 fat-loading tests in 15 Dutch patients with SCADD, divided into 3 genotype groups. Metabolic and endocrinologic measurements and the biochemical characteristics of SCADD, ethylmalonic acid (EMA), and C4-carnitine were studied.

RESULTS

Three patients had development of hypoglycemia during fasting; all of these had originally presented with hypoglycemia. Metabolic and endocrinologic measurements remained normal during all tests. The EMA excretion increased in response to fasting and fat loading, and plasma C4-carnitine remained stable. Test results did not differ between the 3 genotype groups.

CONCLUSIONS

The metabolic profiles of the 3 patients with development of hypoglycemia resemble idiopathic ketotic hypoglycemia. Because hypoglycemia generally requires a metabolic work-up and because SCADD is relatively prevalent, SCADD may well be diagnosed coincidently, thus being causally unrelated to the hypoglycemia. If SCADD has any other pathologic consequences, the accumulation of potentially toxic metabolites such as EMA is most likely involved. However, the results of our study indicate that there is no clear pathophysiological significance, irrespective of genotype, supporting the claim that SCADD is not suited for inclusion in newborn screening programs.

Muscle acylcarnitines during short-term fasting in lean healthy men

The transition from the fed to the fasted resting state is characterized by, among other things, changes in lipid metabolism and peripheral insulin resistance. Acylcarnitines have been suggested to play a role in insulin resistance, as well as other long-chain fatty acid metabolites. Plasma levels of long-chain acylcarnitines increase during fasting, but this is unknown for muscle long-chain acylcarnitines. In the present study we investigated whether muscle long-chain acylcarnitines increase during fasting and we investigated their relationship with glucose/fat oxidation and insulin sensitivity in lean healthy humans. After 14 h and 62 h of fasting, glucose fluxes, substrate oxidation, and plasma and muscle acylcarnitines were measured before and during a hyperinsulinaemic–euglycaemic clamp. Hyperinsulinaemia decreased long-chain muscle acylcarnitines after 14 h of fasting, but not after 62 h of fasting. In both the basal state and during the clamp, glucose oxidation was lower and fatty acid oxidation was higher after 62 h compared with 14 h of fasting. Absolute changes in glucose and fatty acid oxidation in the basal compared with hyperinsulinaemic state were not different. Muscle long-chain acylcarnitines did not correlate with glucose oxidation, fatty acid oxidation or insulin-mediated peripheral glucose uptake. After 62 h of fasting, the suppression of muscle long-chain acylcarnitines by insulin was attenuated compared with 14 h of fasting. Muscle long-chain acylcarnitines do not unconditionally reflect fatty acid oxidation. The higher fatty acid oxidation during hyperinsulinaemia after 62 h compared with 14 h of fasting, although the absolute decrease in fatty acid oxidation was not different, suggests a different set point.

Changes of the plasma metabolome during an oral glucose tolerance test: is there more than glucose to look at?

The oral glucose tolerance test (oGTT) is a common tool to provoke a metabolic challenge for scientific purposes, as well as for diagnostic reasons, to monitor the kinetics of glucose and insulin. Here, we aimed to follow the variety of physiological changes of the whole metabolic pattern in plasma during an oGTT in healthy subjects in a nontargeted reversed-phase ultra performance liquid chromatography coupled to electrospray ionization quadrupole time of flight mass spectrometric metabolomics approach. We detected 11,500 metabolite ion masses/individual. Applying multivariate data analysis, four major groups of metabolites have been detected as the most discriminating oGTT biomarkers: free fatty acids (FFA), acylcarnitines, bile acids, and lysophosphatidylcholines. We found in detail 1) a strong decrease of all saturated and monounsaturated FFA studied during the oGTT; 2) a significant faster decline of palmitoleate (C16:1) and oleate (C18:1) FFA levels than their saturated counterparts; 3) a strong relative increase of polyunsaturated fatty acids in the fatty acid pattern at 120 min; and 4) a clear decrease in plasma C10:0, C12:0, and C14:1 acylcarnitine levels. These data reflect the switch from beta-oxidation to glycolysis and fat storage during the oGTT. Moreover, the bile acids glycocholic acid, glycochenodeoxycholic acid, and glycodeoxycholic acid were highly discriminative, showing a biphasic kinetic with a maximum of a 4.5- to 6-fold increase at 30 min after glucose ingestion, a significant decrease over the next 60 min followed by an increase until the end of the oGTT. Lysophosphatidylcholines were also increased significantly. The findings of our metabolomics study reveal detailed insights in the complex physiological regulation of the metabolism during an oGTT offering novel perspectives of this widely used procedure.

PPARα Mediates Transcriptional Upregulation of Novel Organic Cation Transporters-2 and -3 and Enzymes Involved in Hepatic Carnitine Synthesis

We tested the hypothesis that transcription of novel organic cation transporters (OCTNs) is directly regulated by peroxisome proliferator–activated receptor (PPAR)-α. Therefore, wild-type mice and mice deficient in PPARα (PPARα−/−) were treated with the PPARα agonist WY 14,643. Wild-type mice treated with WY 14,643 had a greater abundance of OCTN2 mRNA in their liver, muscle, kidney, and small intestine and a greater abundance of OCTN3 mRNA in kidney and small intestine than did untreated wild-type mice ( P < 0.05). Moreover, wild-type mice treated with WY 14,643 had greater mRNA abundances of enzymes involved in hepatic carnitine synthesis (4-N-trimethylaminobutyraldehyde dehydrogenase, γ-butyrobetaine dioxygenase) and increased carnitine concentrations in liver and muscle than did untreated wild-type mice ( P < 0.05). Untreated PPARα−/− mice had a lower abundance of OCTN2 mRNA in liver, kidney, and small intestine and lower carnitine concentrations in plasma, liver, and kidney than did untreated wild-type mice ( P < 0.05). In PPARα−/− mice, treatment with WY 14,643 did not influence mRNA abundance of OCTN2 and OCTN3 and carnitine concentrations in all tissues analyzed. The abundance of OCTN1 mRNA in all the tissues analyzed was not changed by treatment with WY 14,643 in wild-type or PPARα−/− mice. In conclusion, this study shows that transcriptional upregulation of OCTN2 and OCTN3 in tissues and of enzymes involved in hepatic carnitine biosynthesis are mediated by PPARα. It also shows that PPARα mediates changes of whole-body carnitine homeostasis in mice by upregulation of carnitine transporters and enzymes involved in carnitine synthesis.

Urinary excretion of L-carnitine and its short-chain acetyl-L-carnitine in patients undergoing carboplatin treatment

PURPOSE

To evaluate the effect of the anti-cancer drug carboplatin on plasma concentrations and urinary excretion of L-carnitine (LC) and its main ester, acetyl-L-carnitine (ALC), in cancer patients.

METHODS

Plasma and urine concentrations of LC and ALC from 11 patients on carboplatin therapy (1 h intravenous infusion; AUC dose 4.8 +/- 1.1 mg/ml min) in combination with docetaxel, paclitaxel or vinorelbine, were determined by high-performance liquid chromatography with fluorimetric detection.

RESULTS

Before carboplatin therapy, the mean +/- SD plasma concentrations of LC and ALC were 47.8 +/- 10.9 and 7.04 +/- 1.04 nmoles/ml, respectively, and remained constant throughout the entire study period. In contrast, urinary excretion of LC and ALC, increased significantly during the chemotherapy from 115 +/- 105 to 480 +/- 348 micromoles/day (P < 0.01) and from 41 +/- 41 to 89 +/- 52 micromoles/day (P < 0.05) for LC and ALC, respectively, subsequently reverting to normal 6 days after the end of chemotherapy. Similarly, the renal clearance of LC and ALC increased substantially during chemotherapy from 1.67 +/- 1.43 to 9.05 +/- 9.52 ml/min (P < 0.05) and from 4.02 +/- 4.51 to 7.97 +/- 5.05 ml/min (P = not significant) for LC and ALC, respectively, reverting to normal 6 days after the end of chemotherapy. Plasma concentrations and urinary excretion of glucose, phosphate and urea nitrogen and creatinine clearance, however, were not affected by carboplatin therapy, indicating no impaired kidney function.

CONCLUSION

Treatment with carboplatin was associated with a marked urinary loss of LC and ALC, most likely due to inhibition of carnitine reabsorption in the kidney.

Monitoring of ketogenic diet for carnitine metabolites by subcutaneous microdialysis

The ketogenic diet (KD) provides ketones from the degradation of free fatty acids for energy metabolism. It is a therapeutic option for pharmacoresistant epilepsies. Carnitine is the carrier molecule that transports fatty acids across the mitochondrial membrane for degradation into ketones. The integrity of this transport system is a prerequisite for an adequate ketogenic response. For monitoring of tissue metabolism with KD, we used the sampling method of s.c. microdialysis (MD), which permits minimally invasive, frequent, and extensive metabolic monitoring independent of blood tests. By using this new method, we monitored changes in carnitine metabolism induced by KD, particularly in free carnitine (C0), acetylcarnitine (C2), and hydroxybutyrylcarnitine (C4OH). Correlation of microdialysate and tissue concentrations for carnitines in vitro was about 85%. Carnitine metabolism was monitored in seven children started on a KD for pharmacoresistant epilepsy after a conventional initial fasting period. Detected metabolic changes consisted of a slight decrease in s.c. C0 and a marked increase in C2/CO and C4OH/CO levels. The levels of s.c. C4OH strongly correlate with beta-hydroxybutyrate (beta-OHB) levels in plasma providing an additional parameter for the carnitine reserve of the body and reflect an optimal ketogenic energy supply. Subcutaneous MD allows close and extensive monitoring of metabolism with a KD.

Pregnancy increases urinary loss of carnitine and reduces plasma carnitine in Korean women

This study compared plasma and urinary carnitine concentrations in pregnant and non-pregnant Korean women. The subjects were fifty pregnant women and thirty non-pregnant women aged 24-28 years. During the first trimester, dietary carnitine intakes in the pregnant women were much lower than in non-pregnant women (70.00 (SD 29.22) micromol/d), but over the course of pregnancy carnitine intake increased from 44.64 (SD 24.84) micromol/d during the first trimester to 96.11 (SD 36.56) micromol/d during the third trimester. Pregnant women had a significantly lower plasma carnitine concentration than non-pregnant women. Plasma concentrations of non-esterified carnitine, acid-soluble acylcarnitine and total carnitine were significantly lower during the second and third trimesters than the first. Plasma acid-insoluble acylcarnitine levels, which tended to be higher in the non-pregnant women compared with the pregnant women, increased significantly as gestation proceeded. The urinary excretion of non-esterified carnitine, acid-soluble acylcarnitine and total carnitine was significantly higher in the pregnant women during the first and second trimesters than in non-pregnant women and decreased significantly as gestation proceeded. We found that there was a significant decrease in plasma carnitine level even though dietary carnitine intake increased as gestation proceeded. The low urinary excretion of carnitine in late pregnancy may be caused by an increased demand during pregnancy.

Metabolic, antioxidant, nutraceutical, probiotic, and herbal therapies relating to the management of hepatobiliary disorders

Many nutraceuticals, conditionally essential nutrients, and botanical extracts have been proposed as useful in the management of liver disease. The most studied of these are addressed in terms of proposed mechanisms of action, benefits, hazards, and safe dosing recommendations allowed by current information. While this is an area of soft science, it is important to keep an open and tolerant mind, considering that many major treatment discoveries were in fact serendipitous accidents.

Pharmacokinetics of L-carnitine

L-Carnitine is a naturally occurring compound that facilitates the transport of fatty acids into mitochondria for beta-oxidation. Exogenous L-carnitine is used clinically for the treatment of carnitine deficiency disorders and a range of other conditions. In humans, the endogenous carnitine pool, which comprises free L-carnitine and a range of short-, medium- and long-chain esters, is maintained by absorption of L-carnitine from dietary sources, biosynthesis within the body and extensive renal tubular reabsorption from glomerular filtrate. In addition, carrier-mediated transport ensures high tissue-to-plasma concentration ratios in tissues that depend critically on fatty acid oxidation. The absorption of L-carnitine after oral administration occurs partly via carrier-mediated transport and partly by passive diffusion. After oral doses of 1-6g, the absolute bioavailability is 5-18%. In contrast, the bioavailability of dietary L-carnitine may be as high as 75%. Therefore, pharmacological or supplemental doses of L-carnitine are absorbed less efficiently than the relatively smaller amounts present within a normal diet.L-Carnitine and its short-chain esters do not bind to plasma proteins and, although blood cells contain L-carnitine, the rate of distribution between erythrocytes and plasma is extremely slow in whole blood. After intravenous administration, the initial distribution volume of L-carnitine is typically about 0.2-0.3 L/kg, which corresponds to extracellular fluid volume. There are at least three distinct pharmacokinetic compartments for L-carnitine, with the slowest equilibrating pool comprising skeletal and cardiac muscle.L-Carnitine is eliminated from the body mainly via urinary excretion. Under baseline conditions, the renal clearance of L-carnitine (1-3 mL/min) is substantially less than glomerular filtration rate (GFR), indicating extensive (98-99%) tubular reabsorption. The threshold concentration for tubular reabsorption (above which the fractional reabsorption begins to decline) is about 40-60 micromol/L, which is similar to the endogenous plasma L-carnitine level. Therefore, the renal clearance of L-carnitine increases after exogenous administration, approaching GFR after high intravenous doses. Patients with primary carnitine deficiency display alterations in the renal handling of L-carnitine and/or the transport of the compound into muscle tissue. Similarly, many forms of secondary carnitine deficiency, including some drug-induced disorders, arise from impaired renal tubular reabsorption. Patients with end-stage renal disease undergoing dialysis can develop a secondary carnitine deficiency due to the unrestricted loss of L-carnitine through the dialyser, and L-carnitine has been used for treatment of some patients during long-term haemodialysis. Recent studies have started to shed light on the pharmacokinetics of L-carnitine when used in haemodialysis patients.

Investigation of the mechanisms of therapy-related hypoglycaemia in children with acute lymphoblastic leukaemia

AIM

To determine the mechanisms of fasting hypoglycaemia occurring during maintenance therapy (MT) for childhood acute lymphoblastic leukaemia (ALL).

METHODS

Thirty-five children and adolescents with ALL, aged 2.4-17.4 y, were fasted for up to 16 h during MT. Nineteen of the children developed hypoglycaemia after 11 to 16 h of fasting. Blood samples for determination of metabolic changes were taken on completion of fasting. Nineteen patients underwent a glucagon stimulation test after 4 to 16 h of fasting during MT. Erythrocyte concentrations of the metabolites of methotrexate (E-MTX) and 6-mercaptopurine (E-TGN) were measured at the time of fasting. Fifteen out of 19 patients who became hypoglycaemic were re-studied 3 to 4 mo after cessation of therapy.

RESULTS

In the hypoglycaemia group, plasma levels of gluconeogenic amino acids alanine and glutamine were lower (medians 117 vs 190 micromol L(-1), p = 0.009, and medians 396 vs 448 micromol L(-1), p = 0.031, respectively) than in the normoglycaemia group. Serum levels of free carnitine were lower (medians 20.3 vs 29.8 micromol L(-1), p = 0.027), free fatty acids higher (medians 3.09 vs 1.23 mmol L(-1), p < 0.001) and marked dicarboxylic aciduria was more common in the patients with hypoglycaemia (in 14/16 vs in 2/14, p < 0.001). Impaired responses to glucagon stimulation occurred in 36% (4/11) in the hypoglycaemia group and in 12.5% (1/8) in the normoglycaemia group (p = 0.243). No significant differences were detected in E-MTX and E-TGN between the groups. Most of the metabolic abnormalities returned to normal after cessation of chemotherapy.

CONCLUSIONS

Low levels of gluconeogenic amino acids, especially of alanine, are associated with hypoglycaemia. Reduced hepatic glycogen stores may also be involved in the aetiology.

Free carnitine levels in children with steroid-sensitive nephrotic syndrome

BACKGROUND

Carnitine transports long-chain fatty acids across the inner mitochondrial membrane. Carnitine metabolism is disturbed in some renal diseases, such as chronic renal failure. Previous studies have shown that children had normal serum free carnitine (FC) and total carnitine levels in idiopathic nephrotic syndrome, IgA nephropathy, non-IgA nephropathy and focal segmental glomerulosclerosis. The aim of the present study was to determine FC concentrations in plasma and urine during acute and remission periods of steroid-sensitive nephrotic syndrome (SSNS) and its association with hyperlipidemia.

METHODS

Plasma and urinary FC concentrations were assayed in 15 children with SSNS in acute and in 16 children in remission period. Six of them were followed-up longitudinally in both periods.

RESULTS

Plasma FC concentrations were significantly higher in the acute period of the disease than in the remission period and of the controls. The patients had lower FC levels in the remission period as compared to the controls. Urinary FC concentration was decreased in acute disease period when compared to the remission period and the controls. The FC concentrations in plasma and urine did not correlate with each other. Plasma FC exhibited significant positive correlation with low-density lipoprotein cholesterol, total cholesterol and trygliceride, but negative correlation with high-density lipoprotein cholesterol.

CONCLUSIONS

The present study showed disturbed FC concentration in SSNS. Increased plasma and decreased urinary FC levels in acute disease might be associated with its altered renal handling or some extrarenal factors such as hyperlipidemia.

Plasma carnitine levels of pregnant adolescents in labor

STUDY OBJECTIVE

To determine the concentration of plasma carnitine (total, free, and acylcarnitine) during the delivery of uncomplicated pregnancies of adolescent women. To investigate the relationship between maternal and neonatal levels of carnitine and to compare these carnitine levels between pregnant and nonpregnant adolescents.

DESIGN

Samples of maternal and umbilical blood were taken at the time of delivery and examined for the determination of the carnitine-total, free, and acylcarnitine-concentration by the use of an enzymatic-radioisotope method. Twenty-two cases of uncomplicated adolescent pregnancies with a normal labor and without perinatal complications were examined. The plasma level of carnitine was also examined in 17 healthy nonpregnant adolescent women, which constituted the control group.

RESULTS

The concentrations of plasma carnitine in adolescent pregnancies at the time of delivery were calculated at 19.6 +/- 2.15 microMol/L (total), 12.62 +/- 1.31 microMol/L (free), and 6.98 +/- 1.55 microMol/L (acylcarnitine). The corresponding mean values in umbilical plasma were 30.31 +/- 2.06 microMol/L, 22.39 +/- 1.64 microMol/L, and 7.92 +/-.96 mucroMol/L. There is a statistically significant difference between the mean values in maternal and umbilical plasma (P <.0001 for total and free carnitine and P <.012 for acylcarnitine). The correlations between adolescent pregnant women and their infants as regards total, free, and acylcarnitine were 0.137, 0.018, and 0.33, respectively. Neither of these parameters was statistically significant. The corresponding mean values of carnitine in nonpregnant adolescent women were statistically significantly higher than in adolescent pregnant women (total carnitine: 41.61 +/- 3.09 microMol/L, free: 31.39 +/- 2.81 microMol/L, acylcarnitine: 10.22 +/- 1.88 microMol/L, P <.0001).

CONCLUSIONS

The concentration of plasma carnitine at the end of adolescent pregnancy is low compared to the levels of umbilical carnitine at birth and that found in nonpregnant adolescent women. It may not have an obvious impact on the utilization of fatty acids in an uncomplicated full-term pregnancy; however, it suggests the potential risk for neonatal fatty-acid oxidation in a preterm or complicated pregnancy.

Continuous ambulatory peritoneal dialysis (CAPD) adequacy influences serum free carnitine level

OBJECTIVE

An evaluation of serum free carnitine level in CAPD patients in relation to dietary intake, nutritional status and CAPD adequacy and duration.

STUDY DESIGN

Food diaries, nutritional (total body mass, lean body mass, serum level of proteins, carnitine, cholesterol) and adequacy (Kt/V, PCR, tCcr, EN) parameters were obtained in 23 CAPD patients.

RESULTS

Normal carnitine level (41.8+/-6.7 micromol/l) was found in 17 patients being on CAPD through 11.1+/-9.6 months, whereas in 6 persons treated with CAPD through 9.7+/-4.1 months carnitine level was 25.4+/-5.7 micromol/l. Significant differences between low and normal carnitine groups were in tCcr (82.7+/-16.7 v. 65.9+/-13.2 l/wk/1.73 m2 BSA), effluent volume (10.9+/-0.8 v. 9.9+/-1.5 l/day), effluent glucose concentration (729+/-167 v. 530+/-220 mg/dl) and serum globulin level (22.6+/-6.4 v. 29.3+/-4.4 g/l). Significant correlation coefficients (for n = 23) were found between serum carnitine level and effluent volume (r=-0.509) or plasma globulin level (r=+0.522).

CONCLUSION

Patients with higher CAPD adequacy show lower serum free carnitine levels and this is related to higher effluent volumes.

Dynamic changes of plasma acylcarnitine levels induced by fasting and sunflower oil challenge test in children

The dynamic changes of plasma acylcarnitine levels in 1- to 7-y-old children during fasting and after the ingestion of sunflower oil were studied. Glucose, 3-hydroxybutyrate, acetoacetate, FFA, and individual plasma acylcarnitine levels were monitored in both conditions. Fasting experiments lasted for 20 h, and acylcarnitine concentrations were analyzed at 0, 15, and 20 h of fasting. During the fat load, acylcarnitine levels were analyzed at 0, 60, 120, and 180 min. In both tests, a generalized increase of all plasma straight-chain acylcarnitines was observed. Acetylcarnitine contributed the most to the increase of total esterified carnitine. In addition, we demonstrated that the relative increase of each individual acylcarnitine during enhanced fatty acid oxidation is tightly related to its molecular structure and chain length. Fasting as well as the fat load primarily resulted in an increase of unsaturated acylcarnitines. During fasting, C(12:1) and C(14:1) showed a relatively high increase, whereas after the fat load C(16:2) and C(14:2), metabolites of linoleic acid (66% of the fat load), were the main acylcarnitines that increased.

Effects of Palmitoyl Carnitine on Perfused Heart and Papillary Muscle

BACKGROUND: Palmitoyl carnitine accumulation during ischemia causes profound electrophysiological changes, resulting in arrhythmias. We studied the electrophysiological and contractile effects of palmitoyl carnitine. METHODS AND RESULTS: Extracellular recordings made by using the endocardial unipolar paced evoked response (PER) in isolated perfused rabbit hearts were compared with action potentials (AP) recorded from septal artery perfused rabbit papillary muscle. Left ventricular pressure was monitored in isolated hearts. In perfused hearts palmitoyl carnitine (30 µmol/L, 30 minutes) significantly (P <.001) increased the latency of activation (St-R interval) by 58% +/- 8% and reduced repolarization time (R-E interval) by 39% +/- 4%. PER duration (St-E interval), was reduced by 30% +/- 3%. Palmitoyl carnitine (30 µmol/L) significantly (P <.001) decreased resting membrane potential (19 +/- 2 mV) of AP, reduced peak amplitude (33.5 +/- 8 mV) and rate of rise of phase 0 (41 +/- 8 V/s). Significant reductions (P <.001) in the action potential duration 50% (129.4 +/- 28 ms) and 90% (139.8 +/- 32 ms) were also observed. An initial positive inotropic effect, which declined as irreversible contracture developed, was also observed. Verapamil (1 µmol/L), nifedipine (1 µmol/L), and caffeine (10 mmol/L) failed to abolish the positive inotropy. CONCLUSIONS: We suggest that palmitoyl carnitine disrupts intracellular calcium homeostasis leading to disturbances in electrical and contractile activity. Its accumulation during myocardial ischemia could contribute to calcium overloading and initiate lethal arrhythmias.

Age-and sex-related differences of serum carnitine in a Japanese population

OBJECTIVE

The objective of this study was to assess age- and sex-related differences of serum carnitine in a Japanese population.

METHODS

Fasting blood samples were obtained from 296 Japanese males and 258 females 0 to 65 years of age. Serum free carnitine and acylcarnitine levels were determined by a fluorometric method using carnitine dehydrogenase. Of these, serum samples from 20 males 10 to 20 years of age and 23 females 40 to 60 years of age were assayed for testosterone and estradiol, respectively. Fasting blood samples and 24-hour urine samples were also obtained from 20 males and 23 females 0 to 50 years of age for the assessment of renal carnitine reabsorption.

RESULTS

Serum free carnitine increased with age in children of both sexes, reaching adult value between 15 to 20 years of age in males and between 2 to 10 years of age in females. The mean free carnitine in males (50.3 +/- 7.5 mumol/L) was significantly higher than that in female (41.2 +/- 7.5 mumol/L) between 15-50 years of age (p < 0.05). Serum acylcarnitine remained constant (14.7 +/- 3.3 mumol/L) in each subject of various ages in both sexes. A significant negative correlation was observed between serum free carnitine and estradiol in females (r = -0.55, p < 0.01), but was not observed between serum free carnitine and testosterone in males (r = 0.015). The percent renal reabsorption of free carnitine showed no age-related and sex-related differences.

CONCLUSIONS

Serum free carnitine level is related to age and sex, while serum acylcarnitine level remains constant. Our findings suggest that estrogen decreases serum free carnitine and causes sex-related differences.

Acetyl-L-carnitine deficiency as a cause of altered nerve myo-inositol content, Na,K-ATPase activity, and motor conduction velocity in the streptozotocin-diabetic rat

Defective metabolism of long-chain fatty acids and/or their accumulation in nerve may impair nerve function in diabetes by altering plasma or mitochondrial membrane integrity and perturbing intracellular metabolism and energy production. Carnitine and its acetylated derivatives such as acetyl-L-carnitine (ALC) promote fatty acid beta-oxidation in liver and prevent motor nerve conduction velocity (MNCV) slowing in diabetic rats. Neither the presence nor the possible implications of putative ALC deficiency have been definitively established in diabetic nerve. This study explored sciatic nerve ALC levels and the dose-dependent effects of ALC replacement on sciatic nerve metabolites, Na,K-ATPase, and MNCV after 2 and 4 weeks of streptozotocin-induced diabetes (STZ-D) in the rat. ALC treatment that increased nerve ALC levels delayed (to 4 weeks) but did not prevent nerve myo-inositol (MI) depletion, but prevented MNCV slowing and decreased ouabain-sensitive (but not -insensitive) ATPase activity in a dose-dependent fashion. However, ouabain-sensitive ATPase activity was also corrected by subtherapeutic doses of ALC that did not increase nerve ALC or affect MNCV. These data implicate nerve ALC depletion in diabetes as a factor contributing to alterations in nerve intermediary and energy metabolism and impulse conduction in diabetes, but suggest that these alterations may be differentially affected by various degrees of ALC depletion.

Renal handling of carnitine in ill preterm and term neonates

OBJECTIVE

To investigate the renal handling of carnitine in preterm and term ill neonates.

METHODS

We studied the fractional tubular reabsorption of carnitine and the proximal renal tubular function of infants in the first week of life who were receiving very little or no carnitine in their diets.

RESULTS

Mean plasma levels were low: total carnitine was 16.4 +/- 7.0 mumol/L, free carnitine was 9.2 +/- 5.0 mumol/L, and acylcarnitine was 7.2 +/- 4.1 mumol/L. The most premature group of neonates (gestation age, 26 to 31 weeks) had a fractional tubular reabsorption rate of free carnitine of 94.3% +/- 3.3%, which was lower than in the other two groups (98.1% +/- 2.4% for gestational age 32 to 36 weeks, p = 0.001; and 99.2% +/- 0.6% for gestational age 37 to 42 weeks, p = 0.002). In all patients the fractional tubular reabsorption of acylcarnitine was lower than that of free carnitine, indicating possible tubular secretion of acylcarnitine. It correlated with the total plasma carnitine levels (r = 0.53; p = 0.002). The fractional tubular reabsorption of free carnitine also correlated with gestational age (r = 0.60; p < 0.001).

CONCLUSIONS

Ill neonates have a fractional tubular reabsorption rate of free carnitine within the normal range. It increases with gestational age, and has the same maturation rate as the other known indexes of proximal tubular function.

Changes in carnitine metabolism with ketone body production in obese glucose-intolerant patients

To elucidate the relationship between carnitine metabolism and plasma ketone body concentrations in moderately obese patients with mild glucose intolerance, the ketone body and carnitine levels in the basal state were determined in 72 obese patients: 20 with normal glucose tolerance (NGT), 29 with impaired glucose tolerance (IGT), and 23 with non-insulin-dependent diabetes mellitus (NIDDM) having a fasting plasma glucose (FPG) level of less than 200 mg/dl. Total ketone body (TKB) levels significantly (P < 0.05) increased in the order of NGT, IGT, NIDDM, while the FPG and free fatty acid (FFA) concentrations were significantly (P < 0.05) higher in the NIDDM group than in the other two groups. In contrast, the insulin, glucagon and glycerol levels were comparable in the three groups. The plasma short-chain acylcarnitine (SCAC) concentration and the acylcarnitine/free carnitine (AC/FC) ratio were similar in the IGT and NIDDM groups, and significantly (P < 0.05) greater than those in the NGT group. The AC/FC ratio correlated significantly with the FPG and FFA, but not with the TKB. These results suggest that the combination of IGT with simple obesity may trigger the acceleration of hepatic ketogenesis in conjunction with an elevated SCAC and an increased AC/FC ratio. In addition, the data also imply that, in patients with mild NIDDM, factors other than the carnitines may play a greater role in enhancing ketonemia.

The aetiology of diabetic neuropathy: the combined roles of metabolic and vascular defects

A combination of metabolic and vascular defects have been implicated in the pathogenesis of diabetic neuropathy. Animal studies have demonstrated that a reduction in nerve blood flow may be an important early defect and that vasodilators can prevent or ameliorate nerve dysfunction. The potential factors contributing to nerve ischaemia include structural defects in the endoneurial microvasculature together with rheological abnormalities, abnormalities in vasoactive agents which regulate nerve blood flow including nitric oxide and the eicosanoids, and alterations in tone of the autonomic innervation of the nerve vasculature. The principle metabolic defects which have been implicated include disruption of the polyol pathway, altered lipid metabolism, advanced glycosylated end-product formation, increased oxidative stress, and diabetes-induced defects in growth factors. The demonstration that activation of the polyol pathway in experimental diabetes may affect nerve blood flow, and conversely that vasoactive agents appear to be important in regulating some aspects of nerve metabolism, has highlighted the interdependence of the metabolic and vascular defects in the pathogenesis of this condition. Thus, selective intervention aimed at a key defect early in this cascade may subsequently correct a number of later abnormalities offering therapeutic hope in this chronic debilitating complication.

Plasma carnitine in fasting neonatal and adult northern elephant seals

Maintenance of adequate body carnitine stores is a requisite for fasting mammals, whose energy is derived mainly from free fatty acid oxidation. The impact of longterm fasting on carnitine status is unclear, and there have been no reports of carnitine during naturally occurring fasts. Total (TC), free (FC), and acylated (AC) plasma carnitine levels were determined in 10 weaned and 11 adult northern elephant seals (Mirounga angustirostris) during natural fasts lasting from 1 to 3 mo. In pups, TC declined little and AC increased only slightly [P greater than 0.05, analysis of variance (ANOVA)] through 11 wk of fasting. Plasma FC dropped by 53 and 26% from week 1 values at 10 and 11 wk fasting, respectively (P = 0.014, ANOVA). The AC/FC ratio did not approach 1.0 until 7 wk of fasting. TC was 38.6 +/- 1.4 microM and 47.6 +/- 4.1 microM in adult females and males, respectively. Adult AC/FC ratios were 0.71 +/- 0.10 (females) and 0.08 +/- 0.04 (males). Plasma TC status is not negatively affected by extended fasting in adult and weaned northern elephant seals. These data support the hypothesis that fasting northern elephant seals defend plasma TC and maintain an attenuated AC/FC ratio well into their prolonged natural fast.

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.

Prevalence of carnitine depletion in critically ill patients with undernutrition

The aim of this study was to evaluate to what extent secondary carnitine deficiency may exist based on the prevalence of subnormal carnitine status in patients with critical illness and abnormal nutritional state. Healthy control patients (n = 12) were investigated and compared with patients with possible secondary carnitine deficiency, ie, patients with overt severe protein-energy malnutrition (PEM, n = 28), postoperative long-term (greater than 14 days) parenteral glucose feeding (250 g glucose/d, n = 7), severe liver disease (n = 10), renal insufficiency (n = 7), and sustained septicemia with increased metabolic rate (n = 8). Nutritional status, energy expenditure, creatinine excretion, and blood biochemical tests were measured in relationship to free and total carnitine concentrations in plasma and skeletal muscle tissue, as well as urinary excretion of free and total carnitine. The overall mortality rate was 48% within 30 days of the investigation in study patients with the highest mortality in liver disease (90%). The hospitalization range was 14 to 129 days in study patients. Most study patients had lost weight (4% to 19%) and had abnormal body composition. Patients with liver disease, septicemia, renal insufficiency, and those on long-term glucose feeding had significantly higher than predicted metabolic rate (+25% +/- 3%), while patients with severe malnutrition had decreased metabolic rate compared with controls. Patients with liver disease had increased plasma concentrations of free (96 +/- 16 mumol/L) and total (144 +/- 27 mumol/L) carnitine compared with controls (45 +/- 3, 58 +/- 7 mumol/L, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

The fasting test in paediatrics: application to the diagnosis of pathological hypo- and hyperketotic states

A 24-h fasting test was performed in 48 control children, in 9 hypoketotic patients with inherited defects of fatty acid oxidation and in 2 hyperketotic patients with inherited defects of ketolysis. The control group was then divided into three age groups on the basis of different adaptation to fasting. Concentrations of blood glucose, lactate, free fatty acids (FFA), 3-hydroxybutyrate, acetoacetate and carnitine were measured after 15 h, 20 h and 24 h of fasting. Significant negative correlations were found in the control group between plasma total ketone bodies (KB) and plasma glucose (P less than 0.001), plasma carnitine (P less than 0.005) and the amplitude of glycaemic response to glucagon at the end of the fast (P less than 0.01). FFA/KB ratio and the product of final fasting values of glucose and ketones were useful to differentiate between hypoketotic or hyperketotic patients and normal subjects. In children with a suspected or definite hyperketotic or hypoketotic disorder, a fasting test must only be performed in healthy patients, in good nutritional condition with non-diagnostic basal biochemical investigations. Carefully supervised fasting should be continued sufficiently to allow ketogenesis and ketolysis to become activated.

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.

Muscle carnitine pools in cancer patients

Muscle and plasma concentrations of free and acylated carnitine (short-chain acylcarnitine and long-chain acylcarnitine) were determined by employing an optimized radiochemical-enzymatic assay in 14 healthy volunteers and in 10 patients with oesophageal carcinoma prior to elective operation. No significant correlations between total carnitine and its subfractions in muscle and plasma were observed and no sex differences were apparent. The estimated total carnitine pool in the patients (75.0 +/- 27 mmol) was significantly reduced compared to controls (130 +/- 24.3 mmol). The reduction was still present when expressed per kg muscle tissue (3.5 +/- 1.0 mmol versus 4.5 +/- 0.7 mmol) in order to consider age related decreased muscle mass in the patients. The muscular ratio of acylcarnitines to free carnitine was higher in the patients (0.23 +/- 0.10) than in healthy subjects (0.15 +/- 0.07), whereas the corresponding plasma quotient in the patients (0.22 +/- 0.09) was lowered compared to controls (0.30 +/- 0.10), indicating that instead of glucose, oxidation of fatty acids can be maintained, resulting in a preservation of the glycogen stores and thus an energy-conserving metabolic adaptation as a response to prolonged energy deficit.

Palmitoyl-L-carnitine increases the release of prostacyclin from vascular endothelial cells

Prostacyclin biosynthesis is dramatically increased in patients with acute myocardial infarction. As palmitoylcarnitine accumulates during myocardial ischemia, the action of this metabolite on the endothelial production of prostacyclin was studied. Palmitoyl-L-carnitine (10-100 microM) enhanced the release of prostacyclin and free arachidonic acid from bovine aortic endothelial cells. This action was mimicked by lysophosphatidylcholine, but by none of the following compounds: acetylcarnitine, carnitine, palmitic acid, sphingosine, dihydrosphingosine and N-stearoyl-dihydrosphingosine. In addition to mobilizing free arachidonate, palmitoylcarnitine induced the release of free choline and phosphorylcholine presumably via the activation of phospholipases C and D. Palmitoyl-L-carnitine had also a cytotoxic effect on the endothelial cells. These data suggest that the increased biosynthesis of prostacyclin in myocardial infarction might be partially explained by the accumulation and release of palmitoyl-L-carnitine.