Free Carnitine Research Articles

Targeted Metabolomic Analysis of a Mucopolysaccharidosis IIIB Mouse Model Reveals an Imbalance of Branched-Chain Amino Acid and Fatty Acid Metabolism.

Mucopolysaccharidoses (MPSs) are inherited disorders of the glycosaminoglycan (GAG) metabolism. The defective digestion of GAGs within the intralysosomal compartment of affected patients leads to a broad spectrum of clinical manifestations ranging from cardiovascular disease to neurological impairment. The molecular mechanisms underlying the progression of the disease downstream of the genetic mutation of genes encoding for lysosomal enzymes still remain unclear. Here, we applied a targeted metabolomic approach to a mouse model of PS IIIB, using a platform dedicated to the diagnosis of inherited metabolic disorders, in order to identify amino acid and fatty acid metabolic pathway alterations or the manifestations of other metabolic phenotypes. Our analysis highlighted an increase in the levels of branched-chain amino acids (BCAAs: Val, Ile, and Leu), aromatic amino acids (Tyr and Phe), free carnitine, and acylcarnitines in the liver and heart tissues of MPS IIIB mice as compared to the wild type (WT). Moreover, Ala, Met, Glu, Gly, Arg, Orn, and Cit amino acids were also found upregulated in the liver of MPS IIIB mice. These findings show a specific impairment of the BCAA and fatty acid catabolism in the heart of MPS IIIB mice. In the liver of affected mice, the glucose-alanine cycle and urea cycle resulted in being altered alongside a deregulation of the BCAA metabolism. Thus, our data demonstrate that an accumulation of BCAAs occurs secondary to lysosomal GAG storage, in both the liver and the heart of MPS IIIB mice. Since BCAAs regulate the biogenesis of lysosomes and autophagy mechanisms through mTOR signaling, impacting on lipid metabolism, this condition might contribute to the progression of the MPS IIIB disease.

Determination of Free and Total Choline and Free and Total Carnitine in Infant Formula and Adult/Pediatric Nutritional Formula by Liquid Chromatography/Tandem Mass Spectrometry (HPLC-MS/MS): A Multi-laboratory Testing Study, Final Action 2015.10.

A multi-laboratory study was conducted on AOAC First Action Method 2015.10 "Determination of Free and Total Choline and Free and Total Carnitine in Infant Formula and Adult/Pediatric Nutritional Formula by Liquid Chromatography/Tandem Mass Spectrometry (HPLC-MS/MS)." In this study, nine laboratories participated in the performance testing of the method using ten nutritional products tested as blind duplicates. Both free and total carnitine and free and total choline content of the samples were determined using separate extractions for the free and total results. For free choline and carnitine analysis, samples are diluted in water. For total choline and carnitine analysis, samples are extracted using acid-assisted microwave hydrolysis with nitric acid. For both the free and total methods, samples are then diluted with acetonitrile and analyzed using strong cation exchange (SCX) liquid chromatography coupled to a triple quadrupole tandem mass spectrometer (LCMS). Stable isotope labeled internal standards were utilized in all analyses to compensate for extraction inefficiencies and ionization suppression.

Newborn screening for primary carnitine deficiency and variant spectrum of SLC22A5 gene in Guangzhou

Objective: To evaluate and improve the performance of the newborn screening program for primary carnitine deficiency (PCD) based on tandem mass spectrometry and to investigate the incidence of PCD and molecular characteristics of SLC22A5 gene in Guangzhou. Methods: A total of 200 180 neonates born in Guangzhou from 2015 to 2019 were enrolled into the newborn screening program for PCD by tandem mass spectrometry at Guangzhou Newborn Screening Center. The positive results of screening for PCD was defined as free carnitine (C0) less than 10 μmol/L with decreased acylcarnitine species in dried blood spots of three to seven days after birth. Screen-positive newborns and their mothers were recalled for another blood spot sample. The diagnosis was confirmed based on decreased levels of C0 and acylcarnitine species in recalled blood spots and genetic analysis in SLC22A5 gene sequencing. The utility of using the sum of propionylcarnitine and palmitoylcarnitine (C3+C16) as a biomarker for acylcarnitine species in newborn screening was retrospectively evaluated. The levels of C0 and (C3+C16) at first screening were compared between newborns with PCD and newborns born to mothers with PCD by independent t test. The variant spectrum and known pathogenic variants carrier rate of SLC22A5 in 2 395 healthy children in Guangzhou Women and Children's Medical Center through whole exon sequencing were analyzed. Results: Among 200 180 neonates, 239 (0.12%) cases were screen-positive for PCD. A total of 37 patients including 15 newborns and 22 mothers had confirmed PCD. The incidence of PCD was 1/13 345 in newborns and 1/9 099 in mothers, respectively. The positive predictive value of this program was 15.5%. Taking cutoff values of C0<8.5 μmol/L or C0 8.5~9.9 μmol/L with (C3+C16)<2 μmol/L, the number of screen-positive cases would be reduced from 810 to 224 without additional false negative case, when compared with cutoff value C0<10 μmol/L only. Both levels of C0 and (C3+C16) at first screening were not significant difference between newborns with PCD and newborns born to mothers with PCD ((6.2±2.4) vs. (5.0±1.8) μmol/L, (1.4±0.4) vs. (1.2±0.5) μmol/L, t=3.826, 0.326; P=0.058, 0.572). Seven PCD mothers experienced moderate fatigue and dizziness in the morning. One of them presented with cardiomyopathy in pregnancy. Genetic analysis of the SLC22A5 gene showed that p.S467C, p.F17L, p.R254X were the three most common variants in newborns with PCD. In PCD mothers and healthy children, the p.S467C, p.F17L and R399W were the three most common whereas the severe variant p.R254X was rare. The population carrier rate for pathogenic variants was 1 in 65 and the estimated incidence of PCD was about 1/16 500. Conclusions: Newborn screening can detect PCD both in newborns and mothers. Adding a quantitative biomarker (C3+C16) <2 μmol/L into the newborn screening program can improve the PCD screen performance. The severe variant p.R253X was common in PCD newborns but rare in PCD mothers and healthy children, indicating that the current screening program maybe failed to detect all PCD newborns and under-estimated the incidence rate of PCD in Guangzhou.

Association Between the Serum Carnitine Level and Ammonia and Valproic Acid Levels in Patients with Bipolar Disorder.

Valproic acid (VPA) is not only an antiepileptic drug but also a mood stabilizer for patients with bipolar disorder. Long-term VPA therapy can cause carnitine deficiency, which may result in an increase in the blood ammonia level, in patients with epilepsy. However, information about this effect in patients with bipolar disorder is limited. The aim of this study was to investigate the associations between the serum VPA level and the carnitine and ammonia levels in psychiatric adult patients with epilepsy. The subjects were 182 consecutive Japanese adult patients (mean age 54.3 ± 19.5 years) diagnosed with bipolar disorder and treated with VPA. The serum VPA level, carnitine fraction, and plasma ammonia level were measured. Furthermore, the free carnitine and acylcarnitine fractions were measured using an enzyme cycling method. Sixty-nine patients (38%) had a low free carnitine level. There were significant differences in sex, height, VPA dose, serum VPA level, total carnitine level, acylcarnitine level, and acylcarnitine/free carnitine ratio between patients with a low free carnitine level and those with a normal range of free carnitine. The simple and multiple regression analyses revealed that the VPA dose and the serum VPA level were inversely and significantly correlated with the free carnitine level. The plasma ammonia level was correlated with the VPA dose, serum VPA level, and acylcarnitine level but not with the free carnitine level. These findings suggest that carnitine deficiency is associated with the VPA dose and the serum VPA level in patients with bipolar disorder. However, it is unlikely that carnitine deficiency is associated with hyperammonemia in patients with bipolar disorder.

Metabolic profile in Mexican young women breast cancer (YWBC) to predict pathologic complete response (pCR) to neoadjuvant chemotherapy (NAC).

e12652 Background: YWBC is associated with aggressive biology with a higher mortality rate and recurrence risk. Similar to older patients, pCR after NAC is a surrogate marker of disease-free survival and overall survival in YWBC. However, YWBC who did not achieve pCR did significantly worse. Metabolic profile (MP) has been used for biomarker discovery to monitor chemotherapy response. Few studies focus on using metabolomics to predict pCR in BC. The study aimed to identify MP in YWBC, before NAC to predict response to chemotherapy. Methods: A targeted metabolomics approach was employed to determine the concentration of 11 AAs, free carnitine, and 30 ACCs using electrospray tandem mass spectrometry in plasma of 30 YWBC patients, before NAC to select plasma biomarkers with the most predictive power to identify pCR in YWBC. Patients were classified in responders (R) and non-responders (NR), based on pCR or not-pCR reported by the pathologist department. The differences between R and NR groups were evaluated using an analysis of Random Forest decision trees according to the distribution of the variables. To evaluate the diagnostic power of each biomarker alone, we performed univariate receiver operating characteristics (ROC) analysis on each biomarker to obtain its ROC curve, ROC area under the curve (AUC), and standard error (SE) of the AUC. Results: We observed differences in MP between R and NR YWBC. Ten metabolites contributed most to differentiating between both groups. We developed a model that included two short-chain acyl-carnitines (AC4 and AC5:1) that allowed an AUC of 0.851 (0.767-0.921) and AUC of 0.737 (0.806-0.844) respectively, and ornithine with AUC of 0.723 (0.6-0.626). Conclusions: There are different MP among Mexican YWBC patients classified as R and NR to NAC. To our understanding, this is one of the first studies that evaluate MP in YWBC in Mexico. Further studies are needed to validate a metabolic signature to predict pCR in this patient group.

Determination of carnitine ester profile in the children with type 1 diabetes: a valuable step towards a better management

Objective: This study is designed to investigate the levels of carnitine and acylcarnitines (ACs) in the children with diabetes type 1 compared to the healthy subjects. Methods: Forty-two type 1 diabetic children and healthy subjects were recruited in the study, respectively. In addition to FBS and Hb A1C, free carnitine and ACs in butyl-ester form in the fasting blood samples were assessed by isotope dilution mass spectrometry for all diabetics and controls using the tandem mass spectrometry system. Results: Diabetic patients had a higher level of C, C4, C6, C14, C18:2, and C18:2OH. Females had elevated C14:2 compared to the males. The C18:2 and C18:2OH levels were elevated as the Hb A1C level increased. The C18:2, C14OH were mostly increased in the prediabetic and diabetic patients, respectively. Conclusion: Increased ACs level indicates the increased acyl-CoA intermediates for the fatty acids and amino acids oxidation.

Sexual Dimorphism in Energy Metabolism of Wistar Rats Using Data Analysis.

The prevalence of some chronic diseases, such as cancer or neurodegenerative disorders, differs between sexes. Animal models provide an important tool to adopt potential therapies from preclinical studies to humans. Laboratory rats are the most popular animals in toxicology, neurobehavioral, or cancer research. Our study aimed to reveal the basic differences in blood metabolome (amino acids, biogenic amines, and acylcarnitines) of the adult male (n = 10) and female (n = 10) Wistar rats. Partial least square-discrimination analysis (PLS-DA) and a variance im portance in projection (VIP) score was used to identify the key sex-specific metabolites. All groups of metabolites, as the main markers of energy metabolism, showed a significant sex-dependent pattern. The most important features calculated in PLS-DA according to VIP score were free carnitine (C0), tyrosine (Tyr), and acylcarnitine C5-OH. While aromatic amino acids, such as Tyr and phenylalanine (Phe), were significantly elevated in the blood plasma of males, tryptophan (Trp) was found in higher levels in the blood plasma of females. Besides, significant sex-related changes in urea cycle were found. Our study provides an important insight into sex-specific differences in energy metabolism in rats and indicates that further studies should consider sex as the main aspect in design and data interpretation.

National Program for External Quality Assessment of Chinese Newborn Screening Laboratories.

Objectives: To analyze the coefficient of variation (CV) of external quality assessment (EQA) in Chinese newborn screening (NBS) laboratories. Method: EQA’s robust CV was analyzed by the Clinet-EQA evaluation system. Results: Participating laboratories of the EQA program increased annually. There was more than a 11-fold increase in phenylalanine (Phe) and thyroid stimulating hormone (TSH). It has shown a declining robust CV, which has tended to level off in recent years. The interquartile range (IQR) of Phe and TSH’s robust CV has decreased from 15.5% to 1.5% and from 22.8% to 1.8%, respectively. Compared to bacterial inhibition assay (BIA), the robust CV of Phe has been shown to be relatively reduced in the fluorescence assay and quantitative enzymatic assay (QEA). The robust CV by ELISA was relatively unstable compared to DELFIA and FEIA. In addition, the robust CVs of glucose-6-phosphate dehydrogenase (G6PD) and 17-alpha-hydroxy progesterone (17-OHP) by Genetic Screening Processor (GSP) were lower than other systems. The median of robust CV by non-derivatized MS/MS (Fenghua) in Phe and free carnitine were around 2.2–4.7% and 2.6–5.2%. Conclusion: Neonatal screening has developed rapidly in China and the majority of participant laboratories had satisfactory performance for the quantitative results.

MON-065 Prevention of 6-Mercaptopurine-Induced Hypoglycemia by Levocarnitine Replacement

Background: Symptomatic hypoglycemia has been reported in children less than 6 years of age receiving 6-Mercaptopurine for acute lymphoblastic anemia (ALL); however, the mechanism of 6-Mercaptopurine-induced hypoglycemia has been unclear. Objective: The objective was to investigate the metabolism in a 3-year-old patient with hypoglycemia induced by 6-Mercaptopurine during maintenance therapy for ALL. Methods: We reviewed test results including serum total and free carnitine levels at time of hypoglycemia in a 3-year-old child with ALL who had repeatedly low plasma glucose as a side effect of 6-Mercaptopurine. Hypoglycemia defined as plasma glucose <50 mg/dL was detected using a glucose meter and each time verified in the clinical laboratory. After Levocarnitine was added to 6-Mercaptopurine therapy, the glycemic control was assessed using a glucose meter, the clinical laboratory, and a continuous glucose monitor; serum total and free carnitine levels were repeated when hypoglycemia resolved. Results: Our patient presented with fatigue, tremors and plasma glucose 39 mg/dL to 47 mg/dL, corrected with a sugary beverage. He had plasma ACTH 38 pg/mL, serum cortisol 10 mcg/dL, total carnitine 24 nmol/mL (expected 35 - 84), free carnitine 18 nmol/mL (expected 24 - 63), plasma free fatty acids 1.62 mmol/L (expected >1.5), beta-hydroxybutyrate of 0.2 mmol/L to 0.7 mmol/L (expected >2.0), and urine ketone bodies negative when plasma glucose was between 33 mg/dL and 39 mg/dL. Plasma insulin was undetectable at time of hypoglycemia, and serum glucose increased by less than 30 points in response to Glucagon IV. Serum IGF-1 as measure of growth hormone effect and thyroid function were normal. Hypoglycemia continued to daily recur especially during the night despite bedtime snacks high in complex carbohydrates and was prevented only by Levocarnitine 25 mg/kg/dose every 12 hours PO that raised serum total and free carnitine levels. The patient remained hypoglycemia-free one month after Levocarnitine was added to 6-Mercaptopurine therapy, in particular, he had average glucose 114 mg/dL with standard deviation 30 mg/dL, glucose 70 mg/dL to 140 mg/dL 93% of the time, and glucose <55 mg/dL 0% of the time. Conclusions: Our patient had symptomatic hypoketotic hypoglycemia related to moderately reduced serum total and free carnitine, corrected with Levocarnitine replacement. Increase in plasma free fatty acids without expected increase in plasma and urine ketone bodies may be sign of impaired synthesis of carnitine, which is required for transport of fatty acids into the mitochondria to produce ketone bodies. Measuring serum total and free carnitine in hypoglycemia induced by 6-Mercaptopurine is helpful in identifying children, who may benefit from Levocarnitine replacement.

Screening 3.4 million newborns for primary carnitine deficiency in Zhejiang Province, China

Testing for primary carnitine deficiency (PCD) has been implemented in many newborn screening (NBS) programs, but few large-scale studies on NBS for PCD have been reported in China. This study aimed to assess the incidence and biochemical, clinical, and genetic characteristics of PCD discovered by NBS. Dried blood spots from newborns were analyzed by tandem mass spectrometry (MS/MS) and suspected positive patients were further tested using molecular genetic analysis. Infants who carried two variants in SLC22A5 or those with extremely low free carnitine levels during recall were referred for follow-up and treatment. Over 3.4 million newborns were screened and 113 newborns were diagnosed with PCD, yielding a positive predictive value of 1.93%. In addition, 63 mothers with PCD were identified. The incidence of PCD in newborns and mothers in Zhejiang was 1:30,182 and 1:54,137, respectively. Thirty-seven distinct variants were identified in SLC22A5 of which 10 were novel. c.1400C > G (p.S467C) was the most prevalent variant in both newborns and mothers with PCD, while c.760C > T (p.R254*), which is reportedly common in other Chinese regions, was rarely detected in maternal PCD patients. This study reports the largest series of patients with PCD detected by NBS and identifies 10 novel variants, expanding the variant spectrum of SLC22A5.

Progressive Metabolic Dysfunction and Nutritional Variability Precedes Necrotizing Enterocolitis.

Necrotizing Enterocolitis (NEC) is associated with prematurity, enteral feedings, and enteral dysbiosis. Accordingly, we hypothesized that along with nutritional variability, metabolic dysfunction would be associated with NEC onset. Methods: We queried a multicenter longitudinal database that included 995 preterm infants (<32 weeks gestation) and included 73 cases of NEC. Dried blood spot samples were obtained on day of life 1, 7, 28, and 42. Metabolite data from each time point included 72 amino acid (AA) and acylcarnitine (AC) measures. Nutrition data were averaged at each of the same time points. Odds ratios and 95% confidence intervals were calculated using samples obtained prior to NEC diagnosis and adjusted for potential confounding variables. Nutritional and metabolic data were plotted longitudinally to determine relationship to NEC onset. Results: Day 1 analyte levels of alanine, phenylalanine, free carnitine, C16, arginine, C14:1/C16, and citrulline/phenylalanine were associated with the subsequent development of NEC. Over time, differences in individual analyte levels associated with NEC onset shifted from predominantly AAs at birth to predominantly ACs by day 42. Subjects who developed NEC received significantly lower weight-adjusted total calories (p < 0.001) overall, a trend that emerged by day of life 7 (p = 0.020), and persisted until day of life 28 (p < 0.001) and 42 (p < 0.001). Conclusion: Premature infants demonstrate metabolic differences at birth. Metabolite abnormalities progress in parallel to significant differences in nutritional delivery signifying metabolic dysfunction in premature newborns prior to NEC onset. These observations provide new insights to potential contributing pathophysiology of NEC and opportunity for clinical care-based prevention.

Liver-Oriented Acute Metabolic Effects of A Low Dose of L-Carnitine under Fat-Mobilizing Conditions: Pilot Human Clinical Trial.

The acute metabolic effect of low dosages of L-carnitine under fat-mobilizing conditions was investigated. Healthy subjects (Study 1: n=5; Study 2: n=6) were asked to fast overnight. Then, 30 min of aerobic exercise on a cycle ergometer was performed after supplementation, followed by a 3.5-h sedentary recovery phase. The following ingestion patterns were used: Study 1 (i) noningestion, (ii) 750 mg of L-carnitine (LC), and (iii) 750 mg of LC+50 g of carbohydrate (CHO); Study 2 (iv) noningestion, (v) 500 mg of LC, (vi) 30 mg of CoQ10, and (vii) 500 mg of LC+30 mg of CoQ10. The energy expenditure (EE) and nonprotein respiratory quotient (npRQ) were measured during the pre-exercise, postexercise, and recovery periods. Serum free carnitine, acetylcarnitine, total carnitine (Study 1 and 2), and ketone bodies (Study 2) were measured. The 750 mg LC treatment significantly facilitated fat oxidation during the recovery phases (p<0.05) without elevating EE. The higher fat oxidation associated with LC was completely suppressed by CHO. CoQ10 affected neither npRQ nor EE. npRQ was significantly correlated with the serum total ketone bodies (R=-0.68, p<0.001) and acetylcarnitine (R=-0.61--0.70, p<0.001). The highest correlation was found between acetylcarnitine and total ketone bodies immediately after exercise (R=0.85, p<0.001). In conclusion, LC enhanced liver fat utilization and ketogenesis in an acute manner without stimulating EE under fat-mobilizing conditions.

Effects of Exercise Training on Renal Carnitine Biosynthesis and Uptake in the High-Fat and High-Sugar-Fed Mouse.

(1) Background: Diet-induced obesity inhibits hepatic carnitine biosynthesis. Herein, the effects of high-fat (HF) and high-sugar (HFHS) feeding and exercise training (ET) on renal carnitine biosynthesis and uptake were determined. (2) Methods: Male C57BL/6J mice were assigned to the following groups: lean control (standard chow), HFHS diet, and HFHS diet with ET. ET consisted of 150 min of treadmill running per week for 12 weeks. Protein levels of γ-butyrobetaine hydroxylase (γ-BBH) and organic cation transporter-2 (OCTN2) were measured as markers of biosynthesis and uptake, respectively. (3) Results: HFHS feeding induced an obese diabetic state with accompanying hypocarnitinemia, reflected by decreased free carnitine levels in plasma and kidney. This hypocarnitinemia was associated with decreased γ-BBH (~30%) and increased OCTN2 levels (~50%). ET failed to improve the obesity and hyperglycemia, but improved insulin levels and prevented the hypocarnitinemia. ET increased protein levels of γ-BBH, whereas levels of OCTN2 were decreased. Peroxisome proliferator-activated receptor-alpha content was not changed by the HFHS diet or ET. (4) Conclusions: Our results indicate that ET prevents the hypocarnitinemia induced by HFHS feeding by increasing carnitine biosynthesis in kidney. Increased expression of OCTN2 with HFHS feeding suggests that renal uptake was stimulated to prevent carnitine loss.

Mass Spectrometric Analysis of L-carnitine and its Esters: Potential Biomarkers of Disturbances in Carnitine Homeostasis.

Purpose: After a golden age of classic carnitine research three decades ago, the spread of mass spectrometry opened new perspectives and a much better understanding of the carnitine system is available nowadays. In the classic period, several human and animal studies were focused on various distinct physiological functions of this molecule and these revealed different aspects of carnitine homeostasis in normal and pathological conditions. Initially, the laboratory analyses were based on the classic or radioenzymatic assays, enabling only the determination of free and total carnitine levels and calculation of total carnitine esters’ amount without any information on the composition of the acyl groups. The introduction of mass spectrometry allowed the measurement of free carnitine along with the specific and sensitive determination of different carnitine esters. Beyond basic research, mass spectrometry study of carnitine esters was introduced into the newborn screening program because of being capable to detect more than 30 metabolic disorders simultaneously. Furthermore, mass spectrometry measurements were performed to investigate different disease states affecting carnitine homeostasis, such as diabetes, chronic renal failure, celiac disease, cardiovascular diseases, autism spectrum disorder or inflammatory bowel diseases.Results: This article will review the recent advances in the field of carnitine research with respect to mass spectrometric analyses of acyl-carnitines in normal and various pathological states.Conclusion: The growing number of publications using mass spectrometry as a tool to investigate normal physiological conditions or reveal potential biomarkers of primary and secondary carnitine deficiencies shows that this tool brought a new perspective to carnitine research.

Comparison of LC-MS/MS and Enzymatic Methods for the Determination of Total Choline and Total Carnitine in Infant Formula and Milk Products.

Choline and l-carnitine are classified as pseudo-vitamins because of their conditionally essential status. As they are involved in multiple physiological metabolic pathways in the human body, they are routinely fortified in infant and adult nutritional formulas. The performance of an LC-MS/MS method for the analysis of choline and carnitine, compared with enzymatic methods in routine use for the analysis of total carnitine and total choline, is described. Powder samples were reconstituted, with release of carnitine and choline facilitated by both acid and alkaline hydrolysis and the extract analyzed by LC-MS/MS. Quantitation was by internal standard technique using deuterium-labeled carnitine and deuterium-labeled choline. Method range, specificity, sensitivity, precision, recovery, accuracy, and ruggedness were assessed for milk powders, infant formulas, and soy- and milk-based nutritional products. Spike recoveries of 94.0-108.4% were obtained for both total carnitine and choline, and no statistical bias (α = 0.05) between measured results and certified values (choline: P = 0.36; free carnitine: P = 0.67) was found for NIST 1849a certified reference material (NIST1849a). Precision, as repeatability relative standard deviation (RSD), was 2.0% RSDr for total carnitine and 1.7% RSDr for total choline. Equivalent results for total choline and total carnitine were obtained by LC-MS/MS and enzymatic methods (n = 30). The described LC-MS/MS method is fit for purpose for routine product compliance release testing environments. This validation study has confirmed that alternative enzymatic assays can be used with confidence in laboratories in which LC-MS/MS platforms are unavailable. An LC-MS/MS method was evaluated and found to be fit-for-purpose for routine product compliance release testing of infant formula. The LC-MS/MS method was compared with enzymatic methods for the analysis of total carnitine and total choline. Alternative enzymatic assays can be used with confidence in laboratories in which LC-MS/MS platforms are unavailable.

Relation of Whole Blood Amino Acid and Acylcarnitine Metabolome to Age, Sex, BMI, Puberty, and Metabolic Markers in Children and Adolescents.

Background: Changes in the metabolic fingerprint of blood during child growth and development are a largely under-investigated area of research. The examination of such aspects requires a cohort of healthy children and adolescents who have been subjected to deep phenotyping, including collection of biospecimens for metabolomic analysis. The present study considered whether amino acid (AA) and acylcarnitine (AC) concentrations are associated with age, sex, body mass index (BMI), and puberty during childhood and adolescence. It also investigated whether there are associations between amino acids (AAs) and acylcarnitines (ACs) and laboratory parameters of glucose and lipid metabolism, as well as liver, kidney, and thyroid parameters. Methods: A total of 3989 dried whole blood samples collected from 2191 healthy participants, aged 3 months to 18 years, from the LIFE Child cohort (Leipzig, Germany) were analyzed using liquid chromatography tandem mass spectrometry to detect levels of 23 AAs, 6 ACs, and free carnitine (C0). Age- and sex-related percentiles were estimated for each metabolite. In addition, correlations between laboratory parameters and levels of the selected AAs and ACs were calculated using hierarchical models. Results: Four different age-dependent profile types were identified for AAs and ACs. Investigating the association with puberty, we mainly identified peak metabolite levels at Tanner stages 2 to 3 in girls and stages 3 to 5 in boys. Significant correlations were observed between BMI standard deviation score (BMI-SDS) and certain metabolites, among them, branched-chain (leucine/isoleucine, valine) and aromatic (phenylalanine, tyrosine) amino acids. Most of the metabolites correlated significantly with absolute concentrations of glucose, glycated hemoglobin (HbA1c), triglycerides, cystatin C (CysC), and creatinine. After age adjustment, significant correlations were observed between most metabolites and CysC, as well as HbA1c. Conclusions: During childhood, several AA and AC levels are related to age, sex, BMI, and puberty. Moreover, our data verified known associations but also revealed new correlations between AAs/ACs and specific key markers of metabolic function.

Functional changes of the liver in the absence of growth hormone (GH) action – Proteomic and metabolomic insights from a GH receptor deficient pig model

ObjectiveThe liver is a central target organ of growth hormone (GH), which stimulates the synthesis of insulin-like growth factor 1 (IGF1) and affects multiple biochemical pathways. A systematic multi-omics analysis of GH effects in the liver has not been performed. GH receptor (GHR) deficiency is a unique model for studying the consequences of lacking GH action. In this study, we used molecular profiling techniques to capture a broad spectrum of these effects in the liver of a clinically relevant large animal model for Laron syndrome. MethodsWe performed holistic proteome and targeted metabolome analyses of liver samples from 6-month-old GHR-deficient (GHR-KO) pigs and GHR-expressing controls (four males, four females per group). ResultsGHR deficiency resulted in an increased abundance of enzymes involved in amino acid degradation, in the urea cycle, and in the tricarboxylic acid cycle. A decreased ratio of long-chain acylcarnitines to free carnitine suggested reduced activity of carnitine palmitoyltransferase 1A and thus reduced mitochondrial import of fatty acids for beta-oxidation. Increased levels of short-chain acylcarnitines in the liver and in the circulation of GHR-KO pigs may result from impaired beta-oxidation of short-chain fatty acids or from increased degradation of specific amino acids. The concentration of mono-unsaturated glycerophosphocholines was significantly increased in the liver of GHR-KO pigs without morphological signs of steatosis, although the abundances of several proteins functionally linked to non-alcoholic fatty liver disease (fetuin B, retinol binding protein 4, several mitochondrial proteins) were increased. Moreover, GHR-deficient liver samples revealed distinct changes in the methionine and glutathione metabolic pathways, in particular, a significantly increased level of glycine N-methyltransferase and increased levels of total and free glutathione. Several proteins revealed a sex-related abundance difference in the control group but not in the GHR-KO group. ConclusionsOur integrated proteomics/targeted metabolomics study of GHR-deficient and control liver samples from a clinically relevant large animal model identified a spectrum of biological pathways that are significantly altered in the absence of GH action. Moreover, new insights into the role of GH in the sex-related specification of liver functions were provided.

Efficient Oral Delivery of Poorly Water-Soluble Drugs Using Carnitine/Organic Cation Transporter 2-Mediated Polymeric Micelles

The intestine epithelium is considered to be the most critical obstacle for nanoparticles for oral delivery of water-insoluble and poorly absorbed drugs. Based on the specific transporters located on the apical membrane of the intestinal epithelium, the carnitine-conjugated polymeric micelles targeting to the carnitine/organic cation transporter 2 (OCTN2) were developed by combining carnitine-conjugated poly(2-ethyl-2-oxazoline)-poly(d,l-lactide) with monomethoxy poly(ethylene-glycol)-poly(d,l-lactide). The carnitine-conjugated micelles with favorable stability in gastrointestinal fluid were validated to remarkably increase the cellular internalization and transcellular transport, while these were not the cases in the presence of free carnitine. These were further confirmed by more distribution of the micelles within epithelial cells, on the apical and basolateral side of the epithelium in mice. Additionally, identification of the carnitine-conjugated micelles by OCTN2 was detected to facilitate cellular uptake of the micelles via fluorescence immunoassay. Both clathrin and caveolae/lipid rafts pathways mediated endocytosis and transcellular transport of the carnitine-conjugated micelles, implying the enrichment of endocytic and transcellular transport pathway compared with that of carnitine-unconjugated micelles. Further, the intracellular trafficking process of the carnitine-conjugated micelles was tracked under confocal laser scanning microscopy, which involved in intracellular compartments such as late endosomes, lysosomes, endoplasmic reticulum, and Golgi apparatus as well. In conclusion, the current study provided an efficient strategy to facilitate the oral absorption of water-insoluble and poorly absorbed agents using intestinal transporter-mediated polymeric micelles.

Metabolite Shifts Induced by Marathon Race Competition Differ between Athletes Based on Level of Fitness and Performance: A Substudy of the Enzy-MagIC Study.

This study compared metabolite shifts induced by training for, participation in, and recovery from a marathon race competition among athletes divided into three groups based on fitness (relative maximum oxygen uptake (VO2max)) and performance levels (net running time). Plasma samples from 76 male runners participating in the Munich Marathon were analyzed for metabolite shifts using a targeted metabolomics panel. For the entire cohort of runners, pronounced increases were measured immediately after the race for plasma concentrations of acylcarnitines (AC), the ratio (palmitoylcarnitine + stearoylcarnitine)/free carnitine that is used as a proxy for the activity of the mitochondrial enzyme carnitine palmitoyltransferase, and arginine-related metabolites, with decreases in most amino acids (AA) and phospholipids. Plasma levels of AA and phospholipids were strongly increased 24 and 72 h post-race. Post-race plasma concentrations of AC and arginine-related metabolites were higher in the low compared to top performers, indicating an accumulation of fatty acids and a reliance on protein catabolism to provide energy after the marathon event. This study showed that marathon race competition is associated with an extensive and prolonged perturbation in plasma metabolite concentrations with a strong AC signature that is greater in the slower, less aerobically fit runners. Furthermore, changes in the arginine-related metabolites were observed.

Dietary L-carnitine improves glycogen and protein accumulation in Nile tilapia via increasing lipid-sourced energy supply: An isotope-based metabolic tracking

L-carnitine is a functional aquafeed additive for enhancing lipid catabolism by elevating mitochondrial fatty acid β-oxidation and modulating energy metabolism to provide a “protein sparing effect”. However, results on the effects of dietary l-carnitine on nutrient metabolism in fish are still conflicting. We explored comprehensively the effects of dietary l-carnitine on energy metabolism in Nile tilapia. We fed Nile tilapia for eight weeks with diets supplemented with l-carnitine or not. We conducted metabolic tracking tests by intraperitoneally injecting individual fish with 14C-labeled palmitic acid (PA), glucose (Glu) and an amino acid mixture (AAs). After the feeding trial, insignificant growth-promoting effect of l-carnitine was obtained in treated fish. However, l-carnitine significantly reduced the lipid content in whole body and muscle accompanied by increasing the free carnitine concentration and fatty acid β-oxidation efficiency. Moreover, l-carnitine elevated concentrations of serum glucose, pyruvate and lactate, and increased glycogen and protein deposition in muscle. These results suggest that ingested glucose and protein prefer to be reserved in carnitine-fed fish with sufficient fatty acids oxidation for energy. Nevertheless, after a 14C-labeled single nutrient injection, carnitine-fed fish showed a higher oxidation rate of [1-14C]-PA, d-[1-14C]-Glu and l-[14C (U)]-AAs. Our study indicates that, the effects of l-carnitine on nutrient metabolism are correlated with the abundance of individual macronutrients such that an inadequate lipid supply would cause dietary l-carnitine supplementation to elevate higher breakdown of glucose and protein for energy generation. The present study provides new insights on the regulation mechanism of l-carnitine on nutrient metabolism in fish.