The Effect of Dietary Protein Imbalance during Pregnancy on the Growth, Metabolism and Circulatory Metabolome of Neonatal and Weaned Juvenile Porcine Offspring

Protein imbalance during pregnancy affects women in underdeveloped and developing countries and is associated with compromised offspring growth and an increased risk of metabolic diseases in later life. We studied in a porcine model the glucose and urea metabolism, and circulatory hormone and metabolite profile of offspring exposed during gestation, to maternal isoenergetic low-high (LP-HC), high-low (HP-LC) or adequate (AP) protein-carbohydrate ratio diets. At birth, LP-HC were lighter and the plasma acetylcarnitine to free carnitine ratios at 1 day of life was lower compared to AP offspring. Plasma urea concentrations were lower in 1 day old LP-HC offspring than HP-LC. In the juvenile period, increased insulin concentrations were observed in LP-HC and HP-LC offspring compared to AP, as was body weight from HP-LC compared to LP-HC. Plasma triglyceride concentrations were lower in 80 than 1 day old HP-LC offspring, and glucagon concentrations lower in 80 than 1 day old AP and HP-LC offspring. Plasma urea and the ratio of glucagon to insulin were lower in all 80 than 1 day old offspring. Aminoacyl-tRNA, arginine and phenylalanine, tyrosine and tryptophan metabolism, histidine and beta-alanine metabolism differed between 1 and 80 day old AP and HP-LC offspring. Maternal protein imbalance throughout pregnancy did not result in significant consequences in offspring metabolism compared to AP, indicating enormous plasticity by the placenta and developing offspring.

Association of gut-related metabolites with outcome in acute heart failure

BACKGROUND

Trimethylamine N-oxide (TMAO), a gut-related metabolite, is associated with heart failure (HF) outcomes. However, TMAO is the final product of a complex metabolic pathway (ie, choline/carnitine) that has never been entirely investigated in HF. The present study investigates a panel of metabolites involved in the TMAO-choline/carnitine metabolic pathway for their associations with outcome in acute HF patients.

METHODS

In total, 806 plasma samples from acute HF patients were analyzed for TMAO, trimethyllysine, L-carnitine, acetyl-L-carnitine, γ-butyrobetaine, crotonobetaine, trimethylamine, betaine aldehyde, choline, and betaine using a developed liquid chromatography-tandem mass spectrometry method. Associations with outcome of all-cause mortality (death) and a composite of all-cause mortality and/or rehospitalization caused by HF (death/HF) at 30 days and 1 year were investigated.

RESULTS

TMAO, trimethyllysine, L-carnitine, acetyl-L-carnitine, and γ-butyrobetaine were associated with death and death/HF at 30 days (short term; hazard ratio 1.30-1.49, P≤ .021) and at 1 year (long term; hazard ratio 1.15-1.25, P≤ .026) when adjusted for cardiac risk factors. L-carnitine and acetyl-L-carnitine were superior for short-term outcomes whereas TMAO was the superior metabolite for association with long-term outcomes. Furthermore, acetyl-L-carnitine and L-carnitine were superior for in-hospital mortality and improved risk stratification when combined with current clinical risk scores (ie, Acute Decompensated HEart Failure National REgistry, Organized Program To Initiate Lifesaving Treatment In Hospitalized Patients With Heart Failure, and Get With The Guidelines-Heart Failure; odds ratio (OR) ≥ 1.52, P≤ .020).

CONCLUSIONS

Carnitine-related metabolites show associations with adverse outcomes in acute HF, in particular L-carnitine and acetyl-L-carnitine for short-term outcomes, and TMAO for long-term outcomes. Further studies are warranted to investigate the role and implications of carnitine metabolites including intervention in the pathogenesis of HF.

Acetylcarnitine Is Associated With Cardiovascular Disease Risk in Type 2 Diabetes Mellitus

OBJECTIVE

This study aimed to identify the association between specific short-chain acylcarnitines and cardiovascular disease (CVD) in type 2 diabetes mellitus (T2DM).

METHOD

We retrieved 1,032 consecutive patients with T2DM who meet the inclusion and exclusion criteria from the same tertiary care center and extracted clinical information from electronic medical records from May 2015 to August 2016. A total of 356 T2DM patients with CVD and 676 T2DM patients without CVD were recruited. Venous blood samples were collected by finger puncture after 8 h fasting and stored as dried blood spots. Restricted cubic spline (RCS) analysis nested in binary logistic regression was used to identify possible cutoff points and obtain the odds ratios (ORs) and 95% confidence intervals (CIs) of short-chain acylcarnitines for CVD risk in T2DM. The Ryan-Holm step-down Bonferroni procedure was performed to adjust p-values. Stepwise forward selection was performed to estimate the effects of acylcarnitines on CVD risk.

RESULT

The levels of C2, C4, and C6 were elevated and C5-OH was decreased in T2DM patients with CVD. Notably, only elevated C2 was still associated with increased CVD inT2DM after adjusting for potential confounders in the multivariable model (OR = 1.558, 95%CI = 1.124-2.159, p = 0.008). Furthermore, the association was independent of previous adjusted demographic and clinical factors after stepwise forward selection (OR = 1.562, 95%CI = 1.132-2.154, p = 0.007).

CONCLUSIONS

Elevated C2 was associated with increased CVD risk in T2DM.

A simple MALDI target plate with channel design to improve detection sensitivity and reproducibility for quantitative analysis of biomolecules

Overcoming the detrimental effects of sweet spots during crystallization is an important step to improve the quantitative abilities of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. In this study, we introduce MALDI targets, which exhibit a channel design to reduce sweet spot phenomena and improve reproducibility. The size of the channels was 3.0 mm in length, 0.35 mm in depth, and 0.40 mm in width, adjusted to the width of the implemented laser beam. For sample deposition, the matrix/sample mixture was homogenously deposited into the channels using capillary action. To demonstrate the proof-of-principle, the novel plates were used for the quantification of acetyl-L-carnitine in human blood plasma using a combined standard addition and isotope dilution method. The results showed that the reproducibility of acetyl-L-carnitine detection was highly improved over a conventional MALDI-MS assay, with RSD values of less than 5.9% in comparison with 15.6% using the regular MALDI method. The limits of quantification using the new plates were lowered approximately two-fold in comparison with a standard rastering approach on a smooth stainless-steel plate. Matrix effects were also assessed and shown to be negligible. The new assay was subsequently applied to the quantification of acetyl-L-carnitine in human plasma samples.

Carnitine supplementation improves metabolic flexibility and skeletal muscle acetylcarnitine formation in volunteers with impaired glucose tolerance: A randomised controlled trial

Background

Type 2 diabetes patients and individuals at risk of developing diabetes are characterized by metabolic inflexibility and disturbed glucose homeostasis. Low carnitine availability may contribute to metabolic inflexibility and impaired glucose tolerance. Here, we investigated whether carnitine supplementation improves metabolic flexibility and insulin sensitivity in impaired glucose tolerant (IGT) volunteers.

Methods

Eleven IGT- volunteers followed a 36-day placebo- and L-carnitine treatment (2 g/day) in a randomised, placebo-controlled, double blind crossover design. A hyperinsulinemic-euglycemic clamp (40 mU/m²/min), combined with indirect calorimetry (ventilated hood) was performed to determine insulin sensitivity and metabolic flexibility. Furthermore, metabolic flexibility was assessed in response to a high-energy meal. Skeletal muscle acetylcarnitine concentrations were measured in vivo using long echo time proton magnetic resonance spectroscopy (¹H-MRS, TE=500 ms) in the resting state (7:00AM and 5:00PM) and after a 30-min cycling exercise. Twelve normal glucose tolerant (NGT) volunteers were included without any intervention as control group.

Results

Metabolic flexibility of IGT-subjects completely restored towards NGT control values upon carnitine supplementation, measured during a hyperinsulinemic-euglycemic clamp and meal test. In muscle, carnitine supplementation enhanced the increase in resting acetylcarnitine concentrations over the day (delta 7:00 AM versus 5:00 PM) in IGT-subjects. Furthermore, carnitine supplementation increased post-exercise acetylcarnitine concentrations and reduced long-chain acylcarnitine species in IGT-subjects, suggesting the stimulation of a more complete fat oxidation in muscle. Whole-body insulin sensitivity was not affected.

Conclusion

Carnitine supplementation improves acetylcarnitine formation and rescues metabolic flexibility in IGT-subjects. Future research should investigate the potential of carnitine in prevention/treatment of type 2 diabetes.

The Type 2 Diabetes Susceptibility PROX1 Gene Variants Are Associated with Postprandial Plasma Metabolites Profile in Non-Diabetic Men

The prospero homeobox 1 (PROX1) gene may show pleiotropic effects on metabolism. We evaluated postprandial metabolic alterations dependently on the rs340874 genotypes, and 28 non-diabetic men were divided into two groups: high-risk (HR)-genotype (CC-genotype carriers, n = 12, 35.3 ± 9.5 years old) and low-risk (LR)-genotype (allele T carriers, n = 16, 36.3 ± 7.0 years old). Subjects participated in two meal-challenge-tests with high-carbohydrate (HC, carbohydrates 89%) and normo-carbohydrate (NC, carbohydrates 45%) meal intake. Fasting and 30, 60, 120, and 180 min after meal intake plasma samples were fingerprinted by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). In HR-genotype men, the area under the curve (AUC) of acetylcarnitine levels was higher after the HC-meal [+92%, variable importance in the projection (VIP) = 2.88] and the NC-meal (+55%, VIP = 2.00) intake. After the NC-meal, the HR-risk genotype carriers presented lower AUCs of oxidized fatty acids (−81–66%, VIP = 1.43–3.16) and higher linoleic acid (+80%, VIP = 2.29), while after the HC-meal, they presented lower AUCs of ornithine (−45%, VIP = 1.83), sphingosine (−48%, VIP = 2.78), linoleamide (−45%, VIP = 1.51), and several lysophospholipids (−40–56%, VIP = 1.72–2.16). Moreover, lower AUC (−59%, VIP = 2.43) of taurocholate after the HC-meal and higher (+70%, VIP = 1.42) glycodeoxycholate levels after the NC-meal were observed. Our results revealed differences in postprandial metabolites from inflammatory and oxidative stress pathways, bile acids signaling, and lipid metabolism in PROX1 HR-genotype men. Further investigations of diet–genes interactions by which PROX1 may promote T2DM development are needed.

Extended Duration Nocturnal Hemodialysis and Changes in Plasma Metabolite Profiles

BACKGROUND AND OBJECTIVES

In-center, extended duration nocturnal hemodialysis has been associated with variable clinical benefits, but the effect of extended duration hemodialysis on many established uremic solutes and other components of the metabolome is unknown. We determined the magnitude of change in metabolite profiles for patients on extended duration nocturnal hemodialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a 52-week prospective, observational study, we followed 33 patients receiving conventional thrice weekly hemodialysis who converted to nocturnal hemodialysis (7-8 hours per session, three times per week). A separate group of 20 patients who remained on conventional hemodialysis (3-4 hours per session, three times per week) served as a control group. For both groups, we applied liquid chromatography-mass spectrometry-based metabolite profiling on stored plasma samples collected from all participants at baseline and after 1 year. We examined longitudinal changes in 164 metabolites among those who remained on conventional hemodialysis and those who converted to nocturnal hemodialysis using Wilcoxon rank sum tests adjusted for multiple comparisons (false discovery rate <0.05).

RESULTS

On average, the nocturnal group had 9.6 hours more dialysis per week than the conventional group. Among 164 metabolites, none changed significantly from baseline to study end in the conventional group. Twenty-nine metabolites changed in the nocturnal group, 21 of which increased from baseline to study end (including all branched-chain amino acids). Eight metabolites decreased after conversion to nocturnal dialysis, including l-carnitine and acetylcarnitine. By contrast, several established uremic retention solutes, including p-cresol sulfate, indoxyl sulfate, and trimethylamine N-oxide, did not change with extended dialysis.

CONCLUSIONS

Across a wide array of metabolites examined, extended duration hemodialysis was associated with modest changes in the plasma metabolome, with most differences relating to metabolite increases, despite increased dialysis time. Few metabolites showed reduction with more dialysis, and no change in several established uremic toxins was observed.

The Effect of Chinese Herbal Medicine Formula mKG on Allergic Asthma by Regulating Lung and Plasma Metabolic Alternations

Asthma is a chronic inflammatory disorder of the airway and is characterized by airway remodeling, hyperresponsiveness, and shortness of breath. Modified Kushen Gancao Formula (mKG), derived from traditional Chinese herbal medicines (TCM), has been demonstrated to have good therapeutic effects on experimental allergic asthma. However, its anti-asthma mechanism remains currently unknown. In the present work, metabolomics studies of biochemical changes in the lung tissue and plasma of ovalbumin (OVA)-induced allergic asthma mice with mKG treatment were performed using ultra high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). Partial least squares–discriminate analysis (PLS−DA) indicated that the metabolic perturbation induced by OVA was reduced after mKG treatment. A total of twenty-four metabolites involved in seven metabolic pathways were identified as potential biomarkers in the development of allergic asthma. Among them, myristic acid (L3 or P2), sphinganine (L6 or P4), and lysoPC(15:0) (L12 or P16) were detected both in lung tissue and plasma. Additionally, l-acetylcarnitine (L1), thromboxane B2 (L2), 10-HDoHE (L10), and 5-HETE (L11) were first reported to be potential biomarkers associated with allergic asthma. The treatment of mKG mediated all of those potential biomarkers except lysoPC(15:0) (P16). The anti-asthma mechanism of mKG can be achieved through the comprehensive regulation of multiple perturbed biomarkers and metabolic pathways.

Newborn screening for homocystinurias and methylation disorders: systematic review and proposed guidelines

Newborn screening (NBS) is justified if early intervention is effective in a disorder generally not detected early in life on a clinical basis, and if sensitive and specific biochemical markers exist. Experience with NBS for homocystinurias and methylation disorders is limited. However, there is robust evidence for the success of early treatment with diet, betaine and/or pyridoxine for CBS deficiency and good evidence for the success of early betaine treatment in severe MTHFR deficiency. These conditions can be screened in dried blood spots by determining methionine (Met), methionine-to-phenylanine (Met/Phe) ratio, and total homocysteine (tHcy) as a second tier marker. Therefore, we recommend NBS for cystathionine beta-synthase and severe MTHFR deficiency. Weaker evidence is available for the disorders of intracellular cobalamin metabolism. Early treatment is clearly of advantage for patients with the late-onset cblC defect. In the early-onset type, survival and non-neurological symptoms improve but the effect on neurocognitive development is uncertain. The cblC defect can be screened by measuring propionylcarnitine, propionylcarnitine-to-acetylcarnitine ratio combined with the second tier markers methylmalonic acid and tHcy. For the cblE and cblG defects, evidence for the benefit of early treatment is weaker; and data on performance of Met, Met/Phe and tHcy even more limited. Individuals homozygous or compound heterozygous for MAT1A mutations may benefit from detection by NBS using Met, which on the other hand also detects asymptomatic heterozygotes. Clinical and laboratory data is insufficient to develop any recommendation on NBS for the cblD, cblF, cblJ defects, glycineN-methyltransferase-, S-adenosylhomocysteinehydrolase- and adenosine kinase deficiency.

Transorgan fluxes in a porcine model reveal a central role for liver in acylcarnitine metabolism

Acylcarnitines are derived from mitochondrial acyl-CoA metabolism and have been associated with diet-induced insulin resistance. However, plasma acylcarnitine profiles have been shown to poorly reflect whole body acylcarnitine metabolism. We aimed to clarify the individual role of different organ compartments in whole body acylcarnitine metabolism in a fasted and postprandial state in a porcine transorgan arteriovenous model. Twelve cross-bred pigs underwent surgery where intravascular catheters were positioned before and after the liver, gut, hindquarter muscle compartment, and kidney. Before and after a mixed meal, we measured acylcarnitine profiles at several time points and calculated net transorgan acylcarnitine fluxes. Fasting plasma acylcarnitine concentrations correlated with net hepatic transorgan fluxes of free and C2- and C16-carnitine. Transorgan acylcarnitine fluxes were small, except for a pronounced net hepatic C2-carnitine production. The peak of the postprandial acylcarnitine fluxes was between 60 and 90 min. Acylcarnitine production or release was seen in the gut and liver and consisted mostly of C2-carnitine. Acylcarnitines were extracted by the kidney. No significant net muscle acylcarnitine flux was observed. We conclude that liver has a key role in acylcarnitine metabolism, with high net fluxes of C2-carnitine both in the fasted and fed state, whereas the contribution of skeletal muscle is minor. These results further clarify the role of different organ compartments in the metabolism of different acylcarnitine species.

Quantification of plasma carnitine and acylcarnitines by high-performance liquid chromatography-tandem mass spectrometry using online solid-phase extraction

Carnitine is an amino acid derivative that plays a key role in energy metabolism. Endogenous carnitine is found in its free form or esterified with acyl groups of several chain lengths. Quantification of carnitine and acylcarnitines is of particular interest for screening for research and metabolic disorders. We developed a method with online solid-phase extraction coupled to high-performance liquid chromatography and tandem mass spectrometry to quantify carnitine and three acylcarnitines with different polarity (acetylcarnitine, octanoylcarnitine, and palmitoylcarnitine). Plasma samples were deproteinized with methanol, loaded on a cation exchange trapping column and separated on a reversed-phase C8 column using heptafluorobutyric acid as an ion-pairing reagent. Considering the endogenous nature of the analytes, we quantified with the standard addition method and with external deuterated standards. Solid-phase extraction and separation were achieved within 8 min. Recoveries of carnitine and acylcarnitines were between 98 and 105 %. Both quantification methods were equally accurate (all values within 84 to 116 % of target concentrations) and precise (day-to-day variation of less than 18 %) for all carnitine species and concentrations analyzed. The method was used successfully for determination of carnitine and acylcarnitines in different human samples. In conclusion, we present a method for simultaneous quantification of carnitine and acylcarnitines with a rapid sample work-up. This approach requires small sample volumes and a short analysis time, and it can be applied for the determination of other acylcarnitines than the acylcarnitines tested. The method is useful for applications in research and clinical routine.

[Analysis of propionylcarnitine in blood and methylmalonic acid in urine of 162 patients with methylmalonic acidemia]

OBJECTIVE

To analyze the levels of methylmalonic acid and methylcitrate in urine, propionylcarnitine (C3) in plasma and C3/acetylcarnitine (C2) of patients with methylmalonic acidemia (MMA) and explore their applications in the diagnosis of MMA.

METHODS

From December 2003 to March 2012, a total of 162 patients with MMA (MMA group) and 200 healthy children (control group) of Xinhua Hospital, Shanghai Jiaotong University School of Medicine were recruited. MMA patients with a definite classification were divided into 2 groups: isolate MMA group (n = 51) and MMA complicated with homocysteinemia group (n = 65). Gas chromatography-mass spectrometry was used to measure the urine levels of methylmalonic acid and methylcitrate and tandem mass spectrometry to measure the blood levels of free carnitine (C0), acylcarnitines and methionine (Met).

RESULTS

In the MMA group, the median levels of methylmalonic acid (259.10 (6.73 - 6429.28)), methylcitrate (4.39 (0 - 248.96)), C3 (8.52 (1.50 - 52.11) µmol/L) and C3/C2 (0.73(0.28 - 2.89)) were all higher than the upper limit values (0.2 - 3.6, 0 - 1.1, 0.50 - 4.00 µmol/L and 0.04 - 0.25 respectively). And they were all higher than those in the control group (0 (0 - 1.87), 0.10 (0 - 1.84), 1.40 (0.53 - 3.90) µmol/L, 0.10 (0.04 - 0.23), all P < 0.01). C3/C2 increased significantly in 15 patients while the C3 level remained normal. The median level of Met was normal in the isolate MMA group. But in patients with homocysteinemia, the level of 8.71 (0.68 - 31.95) µmol/L was below the reference value (10.00 - 35.00 µmol/L) and lower than that in the isolate MMA group (15.35 (4.18 - 59.50) µmol/L) and the control group (15.59 (10.20 - 34.68) µmol/L, all P < 0.05).

CONCLUSIONS

Significant increases in the urine level of methylmalonic acid and C3/C2 may be specific to MMA. Organic acid analyses of gas chromatography-mass spectrometry and acylcarnitines with tandem mass spectrometry are required for a definite diagnosis of this disorder. And repeated tests and genomic mutation analysis are necessary for patients with mildly abnormal biochemical indices.

Proton NMR-based metabolite analyses of archived serial paired serum and urine samples from myeloma patients at different stages of disease activity identifies acetylcarnitine as a novel marker of active disease

BACKGROUND

Biomarker identification is becoming increasingly important for the development of personalized or stratified therapies. Metabolomics yields biomarkers indicative of phenotype that can be used to characterize transitions between health and disease, disease progression and therapeutic responses. The desire to reproducibly detect ever greater numbers of metabolites at ever diminishing levels has naturally nurtured advances in best practice for sample procurement, storage and analysis. Reciprocally, since many of the available extensive clinical archives were established prior to the metabolomics era and were not processed in such an 'ideal' fashion, considerable scepticism has arisen as to their value for metabolomic analysis. Here we have challenged that paradigm.

METHODS

We performed proton nuclear magnetic resonance spectroscopy-based metabolomics on blood serum and urine samples from 32 patients representative of a total cohort of 1970 multiple myeloma patients entered into the United Kingdom Medical Research Council Myeloma IX trial.

FINDINGS

Using serial paired blood and urine samples we detected metabolite profiles that associated with diagnosis, post-treatment remission and disease progression. These studies identified carnitine and acetylcarnitine as novel potential biomarkers of active disease both at diagnosis and relapse and as a mediator of disease associated pathologies.

CONCLUSIONS

These findings show that samples conventionally processed and archived can provide useful metabolomic information that has important implications for understanding the biology of myeloma, discovering new therapies and identifying biomarkers potentially useful in deciding the choice and application of therapy.

Acetyl-L-carnitine improves behavior and dendritic morphology in a mouse model of Rett syndrome

Rett syndrome (RTT) is a devastating neurodevelopmental disorder affecting 1 in 10,000 girls. Approximately 90% of cases are caused by spontaneous mutations in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2). Girls with RTT suffer from severe motor, respiratory, cognitive and social abnormalities attributed to early deficits in synaptic connectivity which manifest in the adult as a myriad of physiological and anatomical abnormalities including, but not limited to, dimished dendritic complexity. Supplementation with acetyl-L-carnitine (ALC), an acetyl group donor, ameliorates motor and cognitive deficits in other disease models through a variety of mechanisms including altering patterns of histone acetylation resulting in changes in gene expression, and stimulating biosynthetic pathways such as acetylcholine. We hypothesized ALC treatment during critical periods in cortical development would promote normal synaptic maturation, and continuing treatment would improve behavioral deficits in the Mecp2(1lox) mouse model of RTT. In this study, wildtype and Mecp2(1lox) mutant mice received daily injections of ALC from birth until death (postnatal day 47). General health, motor, respiratory, and cognitive functions were assessed at several time points during symptom progression. ALC improved weight gain, grip strength, activity levels, prevented metabolic abnormalities and modestly improved cognitive function in Mecp2 null mice early in the course of treatment, but did not significantly improve motor or cognitive functions assessed later in life. ALC treatment from birth was associated with an almost complete rescue of hippocampal dendritic morphology abnormalities with no discernable side effects in the mutant mice. Therefore, ALC appears to be a promising therapeutic approach to treating early RTT symptoms and may be useful in combination with other therapies.

Newborn screening for methylmalonic aciduria by tandem mass spectrometry: 7 years' experience from two centers in Taiwan

BACKGROUND

The clinical course of methylmalonic aciduria (MMA) is fulminant in neonates and emergency management is necessary to save lives. It is therefore very important to differentiate affected from unaffected neonates immediately when there are abnormal results regarding MMA in newborn screening.

METHODS

Between January 2002 and December 2008, 598,522 newborns were screened for MMA by 2 neonatal screening centers: the Chinese Foundation of Health and the Taipei Institute of Pathology. A total of 22 newborns were referred to confirmatory medical centers, and 7 were confirmed as having MMA. The initial propionylcarnitine (C3) level, C3/acetylcarnitine (C2) ratio, plasma ammonia, liver function tests, blood pH and bicarbonate were compared between the true-positive and false-positive groups.

RESULTS

The C3/C2 ratio and plasma ammonia were markedly higher in the true-positive MMA group (p < 0.0001). Blood gas pH (p = 0.029), bicarbonate (p = 0.019), and aspartate aminotransferase (p = 0.005) also significantly differed between these 2 groups.

CONCLUSION

Referred newborns with elevated plasma C3/C2 ratios > 0.4 or ammonia levels > 200 mg/dL should be highly suspected of having MMA.

A case of holocarboxylase synthetase deficiency with insufficient response to prenatal biotin therapy

Holocarboxylase synthetase (HCS) deficiency is an inborn error of biotin metabolism, leading to a multiple carboxylases deficiency. As the affected fetus sometimes presents with enlargement of the cerebral ventricles and intrauterine growth retardation (IUGR), prenatal administration of biotin has been attempted in some pregnancies. We present herein the case of a Japanese neonate with HCS deficiency who received maternal administration of biotin (10mg/day) from 33 weeks' gestation. After biotin administration, the fetal body weight increased and gestation was continued to full term. However, lactic acidemia and metabolic acidosis were observed after birth. To evaluate the effects of prenatal therapy, we collected serum samples and measured the acylcarnitine profiles using high-performance liquid chromatography electrospray ionization tandem mass spectrometry. At birth, levels of propionylcarnitine and 3-hydroxyisovalerylcarnitine had already increased. At 2h after birth, these levels of acylcarnitines were further increased. At 3.5h after the start of biotin, these chemical findings were slightly improved. In conclusion, we considered that prenatal biotin therapy at 10mg/day may have been inadequate to avoid neonatal acidotic crisis in this case.

Debate Forum: Levocarnitine Therapy Is Rational and Justified in Selected Dialysis Patients

Carnitine is a metabolic cofactor which is essential for normal fatty acid metabolism. Patients with chronic kidney disease on dialysis have been shown both to suffer from disordered fatty acid metabolism and to have a significant deficiency in plasma and tissue carnitine. Aberrant fatty acid metabolism has been associated with a number of cellular abnormalities such as increased mitochondrial permeability (a promoter of apoptosis), insulin resistance, and enhanced generation of free radicals. These cellular abnormalities have, in turn, been correlated with pathological clinical conditions common in dialysis patients including cardiomyopathy with attendant hypotension and resistance to the therapeutic effect of recombinant human erythropoietin (EPO). In 1999, the Food and Drug Administration approved levocarnitine injection for the prevention and treatment of carnitine deficiency in patients on dialysis based on documentation of free plasma carnitine levels in dialysis patients similar to other serious carnitine deficiency states for which treatment was required. Data analysis performed by expert panels convened by both the American Association of Kidney Patients and, subsequently, the National Kidney Foundation recommended a trial of levocarnitine therapy for specific subsets of dialysis patients including those with EPO resistance, dialysis-related hypotension, cardiomyopathy and muscle weakness. In 2003, the Centers for Medicare and Medicaid services convened a Medical Advisory Committee which established reimbursement on a national level for carnitine-deficient dialysis patients who had either dialysis-related hypotension or EPO resistance. Recently, a correlation between reductions in hospitalization rates of dialysis patients receiving levocarnitine therapy has been demonstrated in a large retrospective study. Despite data-based recommendations and national reimbursement, only a small minority of dialysis patients have been prescribed a therapeutic trial of levocarnitine. Whereas the reasons for the reluctance of nephrologists to prescribe this therapeutic trial are unclear, possible explanations include a lack of appreciation of the pivotal role played by carnitine in cellular metabolism and the strength of evidence for a substantial deficiency of carnitine in dialysis patients, an underestimation of the prognostic import of EPO resistance and dialysis-related hypotension, inadequate dissemination of the clinical trial data supporting the use of levocarnitine in dialysis patients, and the heterogeneous clinical response of dialysis patients to levocarnitine therapy. Difficulties in documenting both initial eligibility and evidence of improvement as a result of therapy may also be a contributing factor. This paper discusses the biological role of carnitine and its particular relevance to dialysis patients. Clinical trial data concerning an effect of therapy on EPO resistance and dialysis-related hypotension are summarized along with a discussion of the logic behind the use of levocarnitine in dialysis. Finally, the difficulties posed by a reimbursement policy based on clinical as opposed to laboratory endpoints and a heterogeneous response to therapy are addressed.

Impact of hemodialysis on endogenous plasma and muscle carnitine levels in patients with end-stage renal disease

BACKGROUND

End-stage renal disease (ESRD) patients undergoing hemodialysis treatment have reduced plasma L-carnitine levels; however, the relationship between dialysis age and carnitine status is poorly understood. This study examined the relationship between duration of dialysis and plasma and skeletal muscle concentrations of L-carnitine and its esters in ESRD patients.

METHODS

Blood samples were collected from 21 patients at baseline and throughout the first 12 months of hemodialysis. In 5 patients, muscle samples were obtained after 0, 6, and 12 months of hemodialysis. Blood and muscle samples were collected from an additional 20 patients with a mean dialysis age of 5.10 years. L-carnitine, acetyl-L-carnitine, and total L-carnitine were measured by high-performance liquid chromatography (HPLC).

RESULTS

The mean +/- SD plasma L-carnitine concentration in ESRD patients who had not yet started hemodialysis was 50.6 +/- 20.0 micromol/L. Significantly lower concentrations were observed after 12 months (29.7 +/- 10.5 micromol/L) and >12 months (22.0 +/- 5.4 micromol/L) of hemodialysis treatment. Acetyl-L-carnitine also declined with dialysis age, while plasma nonacetylated acylcarnitines continued to increase with the progression of hemodialysis therapy. An inverse relationship between dialysis age and muscle L-carnitine concentrations was observed.

CONCLUSION

Long-term hemodialysis treatment is associated with a significant reduction in endogenous plasma and muscle L-carnitine levels and a significant increase in plasma acylcarnitines. The majority of the change in plasma L-carnitine concentrations occurs within the first few months of hemodialysis, while muscle levels continue to decline after 12 months of treatment.

Acetyl-L-carnitine permeability across the blood-brain barrier and involvement of carnitine transporter OCTN2

OCTN2 (SLC22A5), an organic cation/carnitine transporter, is widely distributed throughout the body, including the brain. In the present study, the involvement of OCTN2 in acetyl-L-carnitine (ALCAR) permeation across the blood-brain barrier (BBB) was examined using a microdialysis method in mouse. OCTN2 function was examined by comparison of wild-type mice with jvs mice, which express defective OCTN2 and are considered a model for primary systemic carnitine deficiency. Zero-net-flux method analysis indicated higher in vivo recovery of ALCAR and lower physiological ALCAR concentration in thalamus extracellular fluid (ECF) in jvs mice compared with wild-type mice. Externally added ALCAR showed significantly slower initial uptake across the BBB in jvs mouse. These results indicated that OCTN2 is functionally involved in ALCAR transfer across the BBB. Total radioactivity in ECF after i.v. administration of radiolabelled ALCAR remained constant for the rest of the experimental period. Accordingly, our results indicate that ALCAR is transported from blood to brain ECF by OCTN2 at least in part, and its concentration in brain ECF is regulated by other events such as protein binding and anabolic reactions in the brain, as well as by transport across the BBB.

Hplc determination and pharmacokinetics of endogenous acetyl-l-carnitine (alc) in human volunteers orally administered a single dose of alc

Acetyl-L-carnitine (ALC), a naturally occurring endogenous compound, has been shown to improve the cognitive performance of patients with senile dementia Alzheimer's type, and to be involved in cholinergic neurotransmission. Because ALC is an endogenous compound, validation of the analytical methods of ALC in the biological fluids is very important and difficult. This study was presented validation and correction for plasma ALC concentrations and pharmacokinetics after oral administration of ALC to human volunteers. ALC concentrations in human plasma were corrected by subtracting the concentration of blank plasma from each sample. Precision and accuracy (bias %) for uncorrected ALC concentrations were below 2.6 and 6.5% for intra-days, and 4.0 and 9.4% for inter-days, respectively. Precision and accuracy (bias %) for corrected ALC concentrations were below 10.9 and 6.0% for intra-days, and 10.5 and 16.9% for inter-days, respectively. Quantitation limit was 0.1 microg/mL. After oral administration of a 500 mg ALC tablet to 8 healthy volunteers, the principle pharmacokinetic parameters were 4.2 h of the half-life (t(1/2,beta)), the area under the curve (AUC(0-8)) of 9.88 microg.h/mL, and 3.1 h of the time (Tmax) to reach Cmax. This study first describes the pharmacokinetic study after oral administration of a single dose of ALC in human volunteers.

Response to therapy in carnitine/acylcarnitine translocase (CACT) deficiency due to a novel missense mutation

Deficiency of carnitine/acylcarnitine translocase (CACT) is an autosomal recessive disorder of the carnitine cycle resulting in the inability to transfer fatty acids across the inner mitochondrial membrane. Only a limited number of affected patients have been reported and the effect of therapy on this condition is still not well defined. Here, we report a new patient with this disorder and follow the response to therapy. Our patient was the product of a consanguineous marriage. He presented shortly after birth with cardiac myopathy and arrhythmia coupled with severe non-ketotic hypoglycemia. Initial metabolic studies indicated severe non-ketotic C6-C10 dicarboxylic aciduria, plasma carnitine deficiency, and a characteristic elevation of plasma C:16:0, C18:1, and C18:2 acylcarnitine species. Enzyme assay confirmed deficiency of CACT activity. Molecular studies indicated that this child was homozygous, and both parents heterozygous, for a single bp change converting glutamine 238 to arginine (Q238R). Therapy with a formula providing most of the fat via medium chain triglycerides (MCT) and carnitine supplementation reduced the concentration of long-chain acylcarnitines and reversed cardiac symptoms and the hypoglycemia. These results suggest that carnitine and MCT may be effective in treating this defect of long-chain fatty acid oxidation.

[Assay of carnitine in plasma and urine of healthy adults]

OBJECTIVE

To determine the levels of carnitine in plasma and daily excretion of carnitine in urine of healthy adults so as to provide the reference standard for studying the changes of carnitine in patients.

METHODS

Carnitine in plasma and urine was assayed with high performance liquid chromatography (HPLC). The levels of total carnitine (TC), free carnitine (FC) and acetyl-carnitine (AC) in fasting plasma and the daily excretion of TC, FC and AC in urine were assayed in 40 healthy adults (20 men and 20 women) with standard diet.

RESULTS

Good linearity (r 2 > or = 0.999) was observed in assaying TC, FC and AC. The relative standard deviation (RSD) was lower than 9.1% and bias lower than 5.6%. It was showed that the plasmatic levels of TC, FC and AC in healthy men [(53.1 +/- 8.5), (41.2 +/- 6.1), (6.2 +/- 0.6) mumol/L] were significantly higher than those in healthy women [(45.4 +/- 5.6), (35.2 +/- 4.9), (5.7 +/- 0.7) mumol/L] (P = 0.002, 0.002, 0.035). The daily urinary excretion of TC, FC and AC in healthy men [(386.1 +/- 22.9), (180.5 +/- 31.8), (33.8 +/- 3.3) mumol] were also significantly higher than those in healthy women [(240.1 +/- 35.6), (112.7 +/- 22.6), (29.3 +/- 4.3) mumol] (P < 0.0005, < 0.0005, < 0.0005) when the adults were given standard diet. Both the plasmatic levels and the daily urinary excretion of TC, FC and AC were of significantly positive correlation with lean body mass (LBM) (r = 0.501-0.856). The (TC-FC)/FC ratios in plasma were 0.29 +/- 0.05 for male and 0.29 +/- 0.04 for female.

CONCLUSION

Good precision and accuracy were observed in assaying carnitine with HPLC. After standard diet, both the level of carnitine in fasting plasma and the daily urinary carnitine excretion of healthy adults were positively correlated with LBM.

Lethal neonatal presentation of carnitine palmitoyltransferase I deficiency

A neonate subsequently diagnosed with carnitine palmitoyltransferase I deficiency died at 34 h of untreatable bradycardia. There was fatty infiltration of the liver and increased free carnitine and reduced acylcarnitines in the blood.

L-carnitine supplementation in breeding pigeons: impact on zootechnical performance and carnitine metabolism

In the first experiment (Exp1), three consecutive breeding rounds were performed by two groups of six pigeon couples in order to study the impact of L-carnitine supplementation (80 mg x d(-1)) of parent pigeons on zootechnical performance. Both in the second and third experiments (Exp2, Exp3), one breeding round was performed by two groups of six pigeon couples to reveal the biochemical background of the increase in squab growth, the limitation of body weight decrease in male parent birds and the tendency for an improved cumulative feed efficiency due to L-carnitine supplementation in Exp1. Growth improvement of the squabs with L-carnitine was only seen when the parent pigeons were supplemented, together with a marked rise in the body weight of the parent birds around hatching. Based on the results of the crop milk analysis, growth improvement was probably due to a quantitative impact on crop milk production. The crop milk from the supplemented groups in both Exp2 and Exp3 had increased levels of carnitine. Carnitine, gamma-butyrobetaine and acetylcarnitine were increased in plasma samples of the supplemented parent pigeons. No differences were present in the squabs' plasma for these parameters. In the squabs of Exp3, no changes were seen in the proportional growth or the protein content of the heart, breast muscle and liver, but the breast muscle of the squabs from the supplemented group in Exp3 showed a considerable rise in carnitine and a marked decrease in gamma-butyrobetaine.

Pharmacokinetics of propionyl-L-carnitine in humans: evidence for saturable tubular reabsorption

AIMS

Propionyl-L-carnitine (PLC) is an endogenous compound which, along with L-carnitine (LC) and acetyl-L-carnitine (ALC), forms a component of the endogenous carnitine pool in humans and most, if not all, animal species. PLC is currently under investigation for the treatment of peripheral artery disease, and the present study was conducted to assess the pharmacokinetics of intravenous propionyl-L-carnitine hydrochloride.

METHODS

This was a placebo-controlled, double-blind, parallel group, dose-escalating study in which 24 healthy males were divided into four groups of six. Four subjects from each group received propionyl-L-carnitine hydrochloride and two received placebo. The doses (1 g, 2 g, 4 g and 8 g) were administered as a constant rate infusion over 2 h and blood and urine were collected for 24 h from the start of the infusion. PLC, ALC and LC in plasma and urine were quantified by h.p. l.c.

RESULTS

All 24 subjects successfully completed the study and the infusions were well tolerated. In addition to the expected increase in PLC levels, the plasma concentrations and urinary excretion of LC and ALC also increased above baseline values following intravenous propionyl-L-carnitine hydrochloride administration. At a dose of 1 g, PLC was found to have a mean (+/- s.d.) half-life of 1.09 +/- 0.15 h, a clearance of 11.6 +/- 0.24 l h-1 and a volume of distribution of 18.3 +/- 2.4 l. None of these parameters changed with dose. In placebo-treated subjects, endogenous PLC, LC and ALC underwent extensive renal tubular reabsorption, as indicated by renal excretory clearance to GFR ratios of less than 0.1. The renal-excretory clearance of PLC, which was 0.33 +/- 0.38 l h-1 under baseline condition, increased (P < 0. 001) from 1.98 +/- 0.59 l h-1 at a dose of 1 g to 5.55 +/- 1.50 l h-1 at a dose of 8 g (95% confidence interval for the difference was 2.18,4.97). As a consequence, the percent of the dose excreted unchanged in urine increased (P < 0.001) from 18.1 +/- 5.5% (1 g) to 50.3 +/- 13.3% (8 g). The renal-excretory clearance of LC and ALC also increased substantially after PLC administration and there was evidence for renal metabolism of PLC to LC and ALC.

CONCLUSIONS

Intravenous administration of propionyl-L-carnitine hydrochloride caused significant increases in the renal excretory clearances of PLC, LC and ALC, due to saturation of the renal tubular reabsorption process - as a consequence there was a substantial increase with dose in the fraction excreted unchanged in urine. Despite the marked increase in the renal clearance of PLC, total clearance remained unchanged, suggesting a compensatory reduction in the clearance of the compound by non excretory routes.

Pharmacokinetics of L-carnitine in patients with end-stage renal disease undergoing long-term hemodialysis

OBJECTIVE

L-Carnitine is an endogenous molecule involved in fatty acid metabolism. Secondary carnitine deficiency may develop in patients with end-stage renal disease undergoing long-term hemodialysis because of dialytic loss. In these patients L-carnitine can be administered to restore plasma and tissue levels. The objective of this study was to evaluate the pharmacokinetics of intravenous L-carnitine in patients undergoing long-term hemodialysis.

METHODS

Twelve patients undergoing three dialysis sessions/week received L-carnitine intravenously (20 mg x kg(-1)) at the end of each dialysis session for 9 weeks. Plasma samples were analyzed for L-carnitine, acetyl-L-carnitine, and total carnitine by HPLC.

RESULTS

Under baseline conditions, the mean +/- SD predialysis plasma concentration of L-carnitine was 19.5 +/- 5.6 micromol/L, decreasing to 5.6 +/- 1.9 micromol/L at the end of the dialysis session. These concentrations were substantially lower than endogenous levels in healthy human beings. Under baseline conditions the extraction ratios of L-carnitine and acetyl-L-carnitine by the dialyser were 0.74 +/- 0.07 and 0.71 +/- 0.11, respectively. During repeated dosing, there was accumulation of L-carnitine in plasma, and after 9 weeks of dosing, the predialysis and postdialysis plasma levels were 191 +/- 54.1 and 41.8 +/- 13.0 micromol/L, respectively. The predialysis and postdialysis plasma levels of L-carnitine decreased once dosing was ceased but had not returned to pretreatment levels after 6 weeks.

CONCLUSION

The study demonstrated that removal of L-carnitine by hemodialysis is extremely efficient and that patients undergoing hemodialysis had plasma concentrations that were substantially lower than normal, particularly during dialysis. During repeated administration of L-carnitine, the predialysis and postdialysis concentrations of the compound increased steadily, reaching an apparent steady state after about 8 weeks. It is proposed that this accumulation arose from the distribution of L-carnitine into a deep tissue pool that includes skeletal muscle.

Acetyl-L-carnitine infusion increases glucose disposal in type 2 diabetic patients

Little information is available in the literature on the effect of L-carnitine to improve glucose disposal in healthy control subjects and type 2 diabetic patients. No data are reported on the pharmacological properties of acetyl-L-carnitine (ALC) in type 2 diabetes mellitus. The present study evaluates glucose uptake and oxidation rates with either ALC or placebo administration in 18 type 2 diabetic patients. On different days, each patient received both a primed-constant infusion of ALC (5 mg/kg body weight [BW] priming bolus and either 0.025, 0.1, or 1.0 mg/kg BW/min constant infusion) and a comparable placebo formulation. During the infusion period, continuous indirect calorimetric monitoring and a euglycemic-hyperinsulinemic clamp (EHC) study were performed. The total end-clamp glucose tissue uptake (M value) was significantly increased by the administration of ALC (from 3.8 to 5.2 mg/kg/min, P = .006), and the dose dependence of this effect reached borderline statistical significance (P = .037). The increase in the M/I ratio was also highly significant after ALC administration (from 3.9 to 5.8 x 10(-2) mg/kg/min/(microUI/mL, P < .001), while no statistically significant effect was attributable to the different dosages. The increase in the M value was related to increased glucose storage (highly significant effect of ALC) rather than increased glucose oxidation (no statistical significance). In conclusion, the effect of ALC on glucose disposal has no relationship to the amount administered. This could be due to an effect of ALC on the enzymes involved in both the glycolytic and gluconeogenetic pathways, and a possible reversibility of glycogen synthase inhibition in diabetic subjects.

Newborn screening in Wisconsin: program overview and test addition

The prevention of congenital anomalies and their sequelae is an important public health objective. One strategy for preventing morbidity and mortality due to congenital disorders is Wisconsin's Newborn Screening Program. Wisconsin has been a national leader in newborn screening since its inception with phenylketonuria screening in 1966. Wisconsin's program is a collaborative effort of the State Maternal and Child Health Program, housed within the Division of Public Health of the Department of Health and Family Services; the State Laboratory of Hygiene; physicians and other health professionals; and families. After in-depth consideration, the Department recently approved the addition of 14 fatty acid oxidation disorders and organic acidemias. This paper provides an overview of the Newborn Screening Program and introduces the disorders that Wisconsin added to the newborn screening panel in April 2000. Technologic advances have provided Wisconsin with yet another tool to improve the health of its citizens and prevent significant morbidity and mortality.

[Atypical course of a multiple acyl-CoA-dehydrogenase deficiency]

In a female newborn presenting with rapid metabolic deterioration (hypoketotic hypoglycaemia and acidosis) clinically accompanied by a "sweaty feet"-odour, the excretion pattern of organic acids in the urine suggested on the fourth day of live multiple acyl-CoA-dehydrogenase-deficiency, a potentially lethal autosomal-recessively inherited inborn error of fatty acid beta-oxidation and of the metabolism of certain amino acids. Diagnosis was confirmed by tandem-mass-spectrometry of acyl-carnitines in blood. Despite the poor prognosis of neonatal-onset multiple acyl-CoA-dehydrogenase-deficiency, treatment with carnitine, riboflavine, and a high-energy diet low in fat and high in carbonhydrates resulted in clinical stabilization. The infant survived various infection-associated decompensations and developed satisfyingly up to the age of 15 months, when another metabolic crisis resulted in multiorgan failure and death.

DISCUSSION

Patients with neonatal-presenting multiple acyl-CoA-dehydrogenase-deficiency but without severe malformations may survive the first months of life. Tandem mass-spectrometry is a suitable tool to differentiate between multiple acyl-CoA-dehydrogenase-deficiency and other defects of fatty acid beta-oxidation.

Entry of [(1,2-13C2)acetyl]-L-carnitine in liver tricarboxylic acid cycle and lipogenesis: a study by 13C NMR spectroscopy in conscious, freely moving rats

The biochemical pathways involved in acetyl-L-carnitine utilization were investigated in conscious, freely moving rats by 13C NMR spectroscopy. Following 4-h [(1,2-13C2)acetyl]-L-carnitine infusion in fasted animals, the free carnitine levels in serum were increased, and an efflux of unlabelled acetyl-L-carnitine from tissues was observed. [(1,2-13C2)Acetyl]-L-carnitine was found to enter biosynthetic pathways in liver, and the acetyl moiety was incorporated into both cholesterol and 3-hydroxybutyrate carbon skeleton. In accord with the entry of [(1,2-13C2)acetyl]-L-carnitine in the mitochondrial acetylCoA pool associated with tricarboxylic acid cycle, the 13C label was also found in liver glutamate, glutamine, and glutathione. The analysis of the 13C-labelling pattern in 3-hydroxybutyrate and cholesterol carbon skeleton provided evidence that the acetyl-L-carnitine-derived acetylCoA pool used for ketone bodies synthesis in mitochondria was homogeneous, whereas cholesterol was synthesized from two different acetylCoA pools located in the extra- and intramitochondrial compartment, respectively. Furthermore, cholesterol molecules were shown to be preferentially synthesized by the metabolic route involving the direct channelling of CoA-activated mitochondria-derived ketone bodies into 3-hydroxy-3-methylglutarylCoA pathway, prior to equilibration of their acyl groups with extramitochondrial acetylCoA pool via acetoacetylCoA thiolase.

Free carnitine and acetyl carnitine plasma levels and their relationship with body muscular mass in athletes

The purpose of the present study was to investigate the relationship between plasma carnitine concentration and body composition variation in relation to muscular and fat masses since there is no experimentally proved correlation between plasma carnitine and body masses. We used bioelectric impedance analysis (BIA), to determine body composition and to have a complete physical fitness evaluation. The post-absorptive plasma free carnitine and acetyl carnitine plasma levels, body composition as Fat-Free Mass (FFM) and Fat Mass (FM) in kg, as well as in percent of body mass, were analysed in 33 healthy subjects. A significant negative correlation was found between plasma acetyl carnitine and FFM in weight (kg) as well as in percent of body mass (respectively p < 0.0001; p < 0.01); a significant positive correlation was found only between FM in percent and plasma acetyl carnitine (p < 0.01). The observed negative correlation between plasma acetyl carnitine and muscular mass variation might reflect an oxidative metabolic muscle improvement in relation to muscular fat free mass increment and might be evidence that muscle metabolism change is in relation to plasma acetyl carnitine concentration.

Acetyl-L-carnitine modulates glucose metabolism and stimulates glycogen synthesis in rat brain

The effects of acetyl-L-carnitine on cerebral glucose metabolism were investigated in rats injected with differently 14C- and 13C-labelled glucose and sacrificed after 15, 30, 45, and 60 min. Acetyl-L-carnitine was found to reduce total 14CO2 release from [U-14C]glucose along with the decrease in [1-13C]glucose incorporation into cerebral amino acids and tricarboxylic acid cycle intermediates. However the 13C labelling pattern within different carbon positions of glutamate, glutamine, GABA, and aspartate was unaffected by acetyl-L-carnitine administration. Furthermore, the cerebral levels of newly-synthesized proglycogen were higher in rats treated with acetyl-L-carnitine than in untreated ones. These results suggest that acetyl-L-carnitine was able to modulate cerebral glucose utilization and provide new insights on the mechanisms of action of this molecule in the central nervous system.

Simultaneous determination of an active metabolite and open-ring metabolites by high performance liquid chromatography and pharmacokinetic studies of a penem antibiotic, FCE22891, in dogs

A sensitive high performance liquid chromatographic method for the simultaneous determination of an active metabolite (FCE22101) and open-ring metabolites (P1, P2) of a penem antibiotic, FCE22891, in dog plasma was developed. Plasma samples were pretreated only by ultrafiltration for the determination of the metabolites. The filtrates were directly analyzed by a reversed-phase high-performance liquid chromatographic system using a two-sided bracketing injection technique. The quantitation limits of FCE22101, P1 and P2 were 0.03, 0.1 and 0.15 microgram ml-1, respectively. Analysis of the spiked plasma samples demonstrated the good accuracy and precision of the method. The proposed method was applied to the pharmacokinetic studies of an active metabolite and open-ring metabolites after oral administration of a penem antibiotic, FCE22891, in dogs. In addition, the plasma levels of unchanged FCE22891 and the possible changes of formaldehyde and acyl-L-carnitine levels in plasma, which will be generated from the ester group of FCE22891, were also investigated.

Acetyl-carnitine deficiency in AIDS patients with neurotoxicity on treatment with antiretroviral nucleoside analogues

OBJECTIVE

A severe dose limiting axonal peripheral neuropathy may develop in subjects on treatment with the nucleoside analogues didanosine (ddl), zalcitabine (ddC), and stavudine (d4T). The impairment of mitrochondrial DNA synthesis is crucial to the pathogenesis of this disorder although other mechanisms have not been ruled out. The depletion of acetyl-carnitine, which regulates the metabolism and function of peripheral nerves could contribute to the neurotoxicity of these compounds.

DESIGN

Non-randomized, cross-sectional study of selected patients.

METHODS

We measured the serum levels of acetyl- and total carnitine in 12 subjects with axonal peripheral neuropathy developed on treatment with different regimens of neurotoxic nucleoside analogues (ddl, ddC, d4T). Subjects who did not develop peripheral neuropathy while staying on treatment with ddl (n = 10) or zidovudine (n = 11) served as the control groups. HIV-negative subjects with axonal on demyelinating autoimmune neuropathies (n = 10) and healthy individuals (n = 13) were additional control groups.

RESULTS

Subjects experiencing axonal peripheral neuropathy on treatment with ddl, ddC and d4T had significantly reduced levels of acetyl-carnitine in comparison to the control groups. No difference was observed in the levels of total carnitine between study subjects and the control groups.

CONCLUSIONS

Our results demonstrate that subjects who developed peripheral neuropathy while staying on treatment with ddl, ddC and d4T had acetyl-carnitine deficiency. The normal levels of total carnitine in the study group appear to indicate the specificity of the defect and rule out coexisting relevant nutritional problems. The critical role of acetyl-carnitine for the metabolism and function of the peripheral nerves supports the view that the acetyl-carnitine deficiency found in these subjects may contribute to the neurotoxicity of ddl, ddC and d4T, even though the interference with mitochondrial DNA synthesis is regarded as the main cause of their toxicity.

L-carnitine and acetyl-L-carnitine status during hemodialysis with acetate in humans: a kinetic analysis

The effects of the acetate content of hemodialysis fluids on the relation between L-carnitine (free carnitine, cr FC) and acetyl-L-carnitine (AC) have not previously been examined in detail. The net fluxes of FC, AC, and acetate between intra- and extracellular pools during hemodialysis were calculated using a kinetic model with dialysates containing three concentrations of FC (0, 40, and 80 mumol/L) and either 40 or 3 mmol acetate/L. Radioenzymatic assays of FC and AC were optimized for use with samples taken during hemodialysis. Acetate stimulated a tissue uptake of FC (P < 0.05) that could exceed the rate of FC delivery and was related to the dialysate FC composition (P < 0.02). There were associated changes in tissue AC output. With dialysate containing 40 mmol acetate/L, AC tissue output was directly related to the dialysate FC composition (P < 0.05). The AC tissue output was less with dialysate containing 3 mmol acetate/L (P < 0.05) but the significant increase with the provision of FC in the dialysate was retained (P < 0.05). Hemodialysis may therefore represent an acute period of relative carnitine deficiency when regeneration of free coenzyme A from acetyl coenzyme A consequent to metabolism of acetate is limited.

Determination of L-carnitine, acetyl-L-carnitine and propionyl-L-carnitine in human plasma by high-performance liquid chromatography after pre-column derivatization with 1-aminoanthracene

A new sensitive high-performance liquid chromatographic procedure for the determination of L-carnitine (LC), acetyl-L-carnitine (ALC) and propionyl-L-carnitine (PLC) in human plasma has been developed. Precolumn derivatization with 1-aminoanthracene (1AA), performed in phosphate buffer in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) as catalyst, is involved. The fluorescent derivatives were isocratically separated on a reversed-phase column (C18). The eluate was monitored with a fluorimetric detector set at 248 nm (excitation wavelength) and 418 nm (emission wavelength). Because of the presence of endogenous carnitines, the validation was performed using dialyzed plasma. The identity of the derivatized compounds was assessed by mass spectrometry and the purity of the chromatographic peaks was confirmed by HPLC-tandem mass spectrometry. The limits of quantitation were 5 nmol/ml for LC, 1 nmol/ml for ALC and 0.25 nmol/ml for PLC. The recovery of the extraction procedure was in the range 82.6%-95.4% for all 3 compounds. Good linearity (R approximately 0.99) was observed within the calibration ranges studied: 5-160 nmol/ml for LC, 1-32 nmol/ml for ALC and 0.25-8 nmol/ml for PLC. Precision was in the range 0.3-16.8% and accuracy was always lower than 10.6%.

Carnitine-related alterations in patients with intermittent claudication: indication for a focused carnitine therapy

BACKGROUND

Carnitine metabolism is altered in peripheral arterial disease. L-carnitine supplementation may correct these alterations and improve walking performance.

METHODS AND RESULTS

Plasma levels of carnitine and its esters were measured at rest and after maximally tolerated exercise in 22 claudicant patients and 8 normal subjects. One week later, this protocol was repeated in patients after random administration of placebo or L-carnitine (500 mg IV as a single bolus). Two groups of patients emerged. In 10 patients (group IC1), the plasma level of acetylcarnitine at rest was 3.7 +/- 0.2 micromol/L and increased significantly (P<.01) at maximally tolerated exercise. In 12 patients (group IC2), the resting level of plasma acetylcarnitine was elevated (7.9 +/- 0.7 micromol/L, P<.01) and decreased with exercise. Furthermore, group IC2 patients had a significantly lower walking capacity than group IC1 patients. In both groups, placebo did not affect the metabolic profile, nor did it improve exercise performance. Conversely, after L-carnitine administration, all but one patient in group IC2 (n=7) showed an increase in plasma acetylcarnitine concentration during exercise versus the decrease observed without L-carnitine. This metabolic effect was accompanied by a significant increase (P<.01) in walking capacity. Interestingly, in group IC1 patients (n=5), L-carnitine neither improved walking capacity nor modified the metabolic profile. Statistical analysis showed that changes in walking capacity with L-carnitine treatment were influenced exclusively by exercise-induced changes in plasma acetylcarnitine.

CONCLUSIONS

In patients with intermittent claudication, assessment of plasma acetylcarnitine at rest and after exercise may be a means to select a target population for L-carnitine therapy.

Interference of heparin in plasma levocarnitine determination with radioenzyme assay

This paper describes the interference of heparin (CAS 9005-49-6) in whole plasma used for free and total levocarnitine (L-carnitine, CAS 541-15-1) analysis. Alkaline hydrolysis required for total L-carnitine measurement does not overcome the problem. The same interference is also present in long-chain acyl-L-carnitine assay, because heparin precipitates together with proteins and long-chain esters of L-carnitine in the acid insoluble fraction of perchloric acid treated plasma sample. In this case an appropriate cleaning of the sample is recommended before the assay.

Diagnosis of inborn errors of metabolism from blood spots by acylcarnitines and amino acids profiling using automated electrospray tandem mass spectrometry

Acylcarnitine profiling from blood or plasma samples by electrospray tandem mass spectrometry (ESI-MS/MS) has been recognized recently as a useful tool in the biochemical diagnosis of propionic acidemia, methylmalonic acidemia together with short-chain and medium-chain acyl-CoA dehydrogenase deficiencies. In the current study, we have investigated the diagnostic capabilities of ESI-MS/MS in other types of organic acidemias and amino acid catabolism disorders. Using multiple scanning functions, we examined the potential for the simultaneous profiling of both acylcarnitines and amino acids, in each of the samples. Our method was found to be specific and accurate; allowing quantification of acylcarnitines and amino acids well below, and significantly above, published normal levels. Complete automation of sample introduction has been achieved, allowing the analysis of up to 200 samples in one injection sequence, at a rate of one sample every 3 min, with excellent separation between successive injections. In our hands, this method permits screening for 20 organic acid and amino acid disorders, using a single sample injection. In our laboratory, more than 2000 blood samples have been analyzed, and 52 new cases were diagnosed by this method. We also confirmed the diagnosis of another 75 previously known cases.

Determination of L-carnitine, acylcarnitine and total carnitine levels in plasma and tissues of camel (Camelus dromedarius)

The total, free and acyl carnitine levels were measured in plasma and tissues of the Arabian camel (Camelus dromedarius). Significant variation in carnitine concentrations were observed in plasma and tissues of the camel when compared with other animal species. A higher proportion of acyl carnitine was found in plasma and skeletal muscle of the camel than other animal species. Among the camel tissues, skeletal muscle possessed the highest amount of carnitine while the lowest amount was found in kidney. The higher carnitine content and a higher proportion of acyl carnitine in plasma and tissues of the Arabian camel suggest an adaptive mechanism that could be common to desert animal species.

Serum and urine levels of levocarnitine family components in genetically diabetic rats

Serum concentration and urinary excretion of levocarnitine (L-carnitine, CAS 541-15-1) family components were evaluated in a Wistar derived strain of genetically diabetic rats BB/BB, in comparison with normal Wistar rats, and their control rats BB/WB of both sexes. BB/BB diabetic animals have lower serum concentration of total-L-carnitine (TC), L-carnitine (LC), acetyl-L-carnitine (ALC), and short chain L-carnitine esters (SCLCE) than both the strains of non-diabetic rats, as previously observed in streptozotocin diabetic rats. No or marginal variations between control and diabetic rats were detected in cumulative urinary excretion of L-carnitine family components. A strain difference was observed between Wistar and BB/WB non-diabetic rats, BB/WB showing higher serum concentration and lower cumulative urinary excretion of LC and TC than Wistar animals. Renal clearance of L-carnitine components proved to be markedly higher in BB/BB diabetic rats, as previously shown in streptozotocin rats. The reduction of serum concentration of the carnitines endogenous pool may explain this finding. The lack of an increased urinary excretion of L-carnitine components in diabetic animals despite the high increase of diuresis suggests that the saturable tubular reabsorption of L-carnitine family components also in diabetes is the primary mechanism to preserve the homeostatic equilibria of the L-carnitine family, the variation in serum concentration being attributable to the complex systemic metabolic alterations typical of diabetes. In agreement with previous investigations, male animals of all the strains showed higher serum concentration and urinary excretion of L-carnitine components as compared to females.

Quantification of free carnitine, individual short- and medium-chain acylcarnitines, and total carnitine in plasma by high-performance liquid chromatography

This paper describes a method for the quantitative determination of free carnitine, acetylcarnitine, propionylcarnitine, hexanoylcarnitine, octanoylcarnitine, and total carnitine in plasma. Carnitine and acylcarnitines were extracted from 100 microliters of plasma with acetonitrile/methanol and isolated using 0.5-ml columns of silica gel. Samples were then derivatized with 4'-bromophenacyl trifluoromethanesulfonate and quantified by high-performance liquid chromatography with detection at 260 nm. Carnitine and acylcarnitines were quantified in normal human plasma and the plasma of patients diagnosed with methylmalonic aciduria, propionic acidemia, and medium-chain acyl-CoA dehydrogenase deficiency.

Automated analysis for free and short-chain acylcarnitine in plasma with a centrifugal analyzer

We describe a fully automated, spectrophotometric assay of free and total carnitine in plasma ultrafiltrates. The method, suitable for routine application in most hospital laboratories, incorporates the hydrolysis of acylcarnitines to free carnitine within the program of a Cobas Fara II centrifugal analyzer. The hydrolysis is monitored and calibrated with standard solutions containing octanoylcarnitine. Results correlated well with those from a reference isotope-dilution mass spectrometric assay. The ability to analyze a batch of samples for both free and total carnitine within 90 min enables analysis of > or = 100 samples per day. Used in conjunction with acylcarnitine species identification by mass spectrometry, the Cobas assay facilitates the diagnosis of carnitine-deficiency syndromes and specific metabolic disorders.

Plasma acetyl-carnitine concentrations during and after a muscular exercise test in patients with liver disease

In many human tissues, fuel is stored for immediate use, as well as for energy exchange between different parts of the body. Fat and glycogen represent, together with proteins, the principal energy storage materials. During energy requirement, e.g. muscular exercise, glycogen as a local reserve, is used first to supply energy needs. Acetyl-carnitine, as an active molecular group, represents an intermediate substrate, usable directly in the working tissue. The present study investigates whether plasma acetyl-carnitine could be a useful biochemical measure for information on fuel exchange in the body, and whether it is a rapidly available energy source exchangeable among tissues with different metabolic functions, such as muscle and liver. The present study investigated control and hepatopathic subjects after maximal and submaximal muscular exercise. Hepatopathic patients may be a useful model, as liver carnitine metabolism is likely to be impaired. Plasma acetyl-carnitine before, during and after maximal exercise in hepatopathic subjects did not differ, while in normal subjects it increased. After submaximal exercise, acetyl-carnitine increased in patients, as well in controls. In the patients (n = 9) with liver metabolism disorders we observed that during maximal exercise plasma acetyl-carnitine varied from 3.26 +/- 2.18 mumol/l (time 0 min) to 4.30 +/- 2.02 mumol/l (time 20 min) and from 1.99 +/- 1.36 mumol/l to 4.83 +/- 2.60 mumol/l (p less than 0.05) in the controls (n = 7).(ABSTRACT TRUNCATED AT 250 WORDS)

Improved methodology to assay carnitine and levels of free and total carnitine in human plasma

Carnitine, once known as vitamin Bt, is intrinsic to human tissue and is biochemically established as being acylated with fatty acids by Acyl-CoA to give Acyl-carnitines which then are transported to the inner mitochondrial membrane by a translocase. Carnitine is of increasing clinical interest and importance, and endomyocardial deficiencies of carnitine have been reported for patients in heart failure. Consequently, a reproducible and accurate analysis of human tissue specimens for levels of free carnitine and Acyl-carnitine to guide and to support continuing clinical studies of disease states is needed. We have devised an analytical method which utilizes 5,5'-dithiobis-2-nitro-benzoate and demonstrated recovery, reproducibility and precision. Hydrolysis of a specimen at 90 degrees C for 15 min, and control of pH below 6.0 are critical steps. The mean levels of free carnitine and total carnitine in 17 ordinary subjects were 50.6 +/- 9.7 nmol./ml and 62.6 +/- 11.7 nmol./ml. respectively.

Effect of propionyl-L-carnitine on mechanical function of isolated rabbit heart

We studied the acute and chronic effects of propionyl-L-carnitine (PLC) on mechanical function of isolated rabbit heart. Propionyl-L-carnitine was either directly delivered in the perfusate (10(-9) to 10(-3) M) or intraperitoneally injected (250 mg/kg) for 10 days to the animals. When added acutely, propionyl-L-carnitine had no effect on inotropism, heart rate, or coronary perfusion pressure. When added chronically, propionyl-L-carnitine induced a positive inotropic effect, with no changes in heart rate or in coronary perfusion pressure, and it ameliorated the pressure-volume relationship. This effect of propionyl-L-carnitine was independent of the calcium concentration of the perfusion medium, but it was correlated with an increase in the myocardial content of propionyl-L-carnitine. The effect was not apparent after 5 days of treatment, although the tissue content of propionyl-L-carnitine remained unchanged. These data suggest that propionyl-L-carnitine, when given chronically, exerts a positive inotropic effect.