Acylcarnitine profiles of preterm infants over the first four weeks of life

Carnitine Intake and Serum Levels Associate Positively with Postnatal Growth and Brain Size at Term in Very Preterm Infants

Carnitine has an essential role in energy metabolism with possible neuroprotective effects. Very preterm (VPT, <32 gestation weeks) infants may be predisposed to carnitine deficiency during hospitalization. We studied the associations of carnitine intake and serum carnitine levels with growth and brain size at term equivalent age (TEA) in VPT infants. This prospective cohort study included 35 VTP infants admitted to Kuopio University Hospital, Finland. Daily nutrient intakes were registered at postnatal weeks (W) 1 and 5, and serum carnitine levels were determined at W1, W5, and TEA. The primary outcomes were weight, length, and head circumference Z-score change from birth to TEA, as well as brain size at TEA in magnetic resonance imaging. Carnitine intake at W1 and W5, obtained from enteral milk, correlated positively with serum carnitine levels. Both carnitine intake and serum levels at W1, W5, and TEA showed a positive correlation with weight, length, and head circumference Z-score change and with brain size at TEA. In linear models, independent positive associations of carnitine intake and serum carnitine levels with length and head circumference Z-score change and brain size at TEA were seen. In VPT infants, sufficient carnitine intake during hospitalization is necessary since it is associated with better postnatal growth and larger brain size at term age.

Progressive Metabolic Abnormalities Associated with the Development of Neonatal Bronchopulmonary Dysplasia

Objective: To assess the longitudinal metabolic patterns during the evolution of bronchopulmonary dysplasia (BPD) development. Methods: A case-control dataset of preterm infants (<32-week gestation) was obtained from a multicenter database, including 355 BPD cases and 395 controls. A total of 72 amino acid (AA) and acylcarnitine (AC) variables, along with infants’ calorie intake and growth outcomes, were measured on day of life 1, 7, 28, and 42. Logistic regression, clustering methods, and random forest statistical modeling were utilized to identify metabolic variables significantly associated with BPD development and to investigate their longitudinal patterns that are associated with BPD development. Results: A panel of 27 metabolic variables were observed to be longitudinally associated with BPD development. The involved metabolites increased from 1 predominant different AC by day 7 to 19 associated AA and AC compounds by day 28 and 16 metabolic features by day 42. Citrulline, alanine, glutamate, tyrosine, propionylcarnitine, free carnitine, acetylcarnitine, hydroxybutyrylcarnitine, and most median-chain ACs (C5:C10) were the most associated metabolites down-regulated in BPD babies over the early days of life, whereas phenylalanine, methionine, and hydroxypalmitoylcarnitine were observed to be up-regulated in BPD babies. Most calorie intake and growth outcomes revealed similar longitudinal patterns between BPD cases and controls over the first 6 weeks of life, after gestational adjustment. When combining with birth weight, the derived metabolic-based discriminative model observed some differences between those with and without BPD development, with c-statistics of 0.869 and 0.841 at day 7 and 28 of life on the test data. Conclusions: The metabolic panel we describe identified some metabolic differences in the blood associated with BPD pathogenesis. Further work is needed to determine whether these compounds could facilitate the monitoring and/or investigation of early-life metabolic status in the lung and other tissues for the prevention and management of BPD.

Optimizing the Phenylalanine Cut-Off Value in a Newborn Screening Program

Phenylketonuria (PKU) was the first disorder for which newborn screening (NBS) was introduced in the early 1960s. Slovenia started the NBS program for PKU in 1979, and the fluorimetric method was implemented in 1992, with a phenylalanine (Phe) cut-off set at 120 mol/L. This value has been in use for almost thirty years and has never been revised. We aimed to analyze the DBS samples and review the data from a large nationwide cohort of newborns to optimize the cut-off values for HFA screening to minimize the number of false positives while maintaining the highest level of sensitivity by detecting all those who needed to be treated. In the first prospective part of the study, we analyzed samples of all newborns in Slovenia in 2019 and 2020, and in the second retrospective part, we reviewed data from all known patients with hyperphenylalaninemia (HFA) in Slovenia born from 2000 to 2018. We defined true screening-positive cases as those that required a low-Phe diet. The sensitivity, specificity and positive predictive values of the modeling elevation of the Phe cut-off value from 120 µmol/L to 200 µmol/L were assessed. The number of recalls at the cut-off of 120 µmol/L was 108 out of 37,784 samples at NBS (2019–2020). Six newborns were defined as true positives and 102 samples as false positives. If the cut-off value was adjusted to 160 µmol/L, only 12 samples exceeded it and all six true positive newborns would be detected. Among the 360,000 samples collected at the NBS between 2000 and 2018, 72 HFA patients in need of a low-Phe diet were found. All the diagnosed cases would have been detected if the cut-off was set to 160 µmol/L. We demonstrated in a large group of newborns (400,000 in 20 years) that using the fluorimetric approach, a cut-off value of 160 µmol/L, rather than 120 mol/L, is safe and that there were no missing true positive patients who required treatment. By increasing the cut-off, this method becomes more precise, resulting in a significantly reduced rate of false positives and thus being less burdensome on both families and the healthcare system.

Perinatal Reduced Blood Concentrations of Free Carnitine and Acylcarnitines in Infants with Cystic Fibrosis

OBJECTIVE

Cystic fibrosis (CF) is a multisystemic inherited disease. The aim of this study was to determine free carnitine (FC) and acylcarnitine concentrations in CF newborns with various mutations of the CFTR gene perinatally.

STUDY DESIGN

FC/acylcarnitines were determined in dried blood spots via liquid chromatography-tandem mass spectrometry (LC-MS/MS) on the third day of life of full-term normal (n = 50) and CF (n = 28) newborns. For infants with elevated immunoreactive trypsinogen values, FC/acylcarnitines were quantified again 48 hours later, followed by mutational analysis of CFTR gene via Sanger sequencing.

RESULTS

Initial FC and sums of acylcarnitine concentrations were statistically significantly lower in CF patients than in controls and even lower 48 hours later. The mutations F508del and 621 + 1G > T were predominantly identified among CF patients.

CONCLUSION

Low FC and acylcarnitine concentrations were measured perinatally in CF patients, for all CFTR mutations detected. Carnitine supplementation of breastfeeding mothers could be beneficial.

Neonatal hyperoxia inhibits proliferation and survival of atrial cardiomyocytes by suppressing fatty acid synthesis

Preterm birth increases the risk for pulmonary hypertension and heart failure in adulthood. Oxygen therapy can damage the immature cardiopulmonary system and may be partially responsible for the cardiovascular disease in adults born preterm. We previously showed that exposing newborn mice to hyperoxia causes pulmonary hypertension by 1 year of age that is preceded by a poorly understood loss of pulmonary vein cardiomyocyte proliferation. We now show that hyperoxia also reduces cardiomyocyte proliferation and survival in the left atrium and causes diastolic heart failure by disrupting its filling of the left ventricle. Transcriptomic profiling showed that neonatal hyperoxia permanently suppressed fatty acid synthase (Fasn), stearoyl-CoA desaturase 1 (Scd1), and other fatty acid synthesis genes in the atria of mice, the HL-1 line of mouse atrial cardiomyocytes, and left atrial tissue explanted from human infants. Suppressing Fasn or Scd1 reduced HL-1 cell proliferation and increased cell death, while overexpressing these genes maintained their expansion in hyperoxia, suggesting that oxygen directly inhibits atrial cardiomyocyte proliferation and survival by repressing Fasn and Scd1. Pharmacologic interventions that restore Fasn, Scd1, and other fatty acid synthesis genes in atrial cardiomyocytes may, thus, provide a way of ameliorating the adverse effects of supplemental oxygen on preterm infants.

Neonatal carnitine concentrations in relation to gestational age and weight

BACKGROUND

Free carnitine has been measured in the Dutch newborn screening (NBS) program since 2007 with a referral threshold of ≤5 μmol/L, regardless of gestational age or birthweight. However, several studies suggest that carnitine concentrations may depend on gestational age and birthweight. We evaluated differences in postnatal day-to-day carnitine concentrations in newborns based on gestational age (GA) and/or weight for GA (WfGA).

METHODS

A retrospective study was performed using data from the Dutch NBS. Dried blood spot (DBS) carnitine concentrations, collected between the 3rd and 10th day of life, of nearly 2 million newborns were included. Individuals were grouped based on GA and WfGA. Median carnitine concentrations were calculated for each group. Mann-Whitney U tests, and chi-square tests were applied to test for significant differences between groups.

RESULTS

Preterm, postterm, and small for GA (SGA) newborns have higher carnitine concentrations at the third day of life compared to term newborns. The median carnitine concentration of preterm newborns declines from day 3 onwards, and approximates that of term newborns at the sixth day of life, while median concentrations of postterm and SGA newborns remain elevated at least throughout the first 10 days of life. Carnitine concentrations ≤5 μmol/L were found less frequently in SGA newborns and newborns born between 32 and 37 weeks of gestation, compared to term newborns.

CONCLUSIONS

Median carnitine concentrations in NBS DBS vary with day of sampling, GA, and WfGA. It is important to take these variables into account when interpreting NBS results..

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.

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.

The significant role of carnitine and fatty acids during pregnancy, lactation and perinatal period. Nutritional support in specific groups of pregnant women

BACKGROUND & AIMS

Pregnancy is characterized by a complexity of metabolic processes that may impact fetal health and development. Women's nutrition during pregnancy and lactation is considered important for both mother and infant. This review aims to investigate the significant role of fatty acids and carnitine during pregnancy and lactation in specific groups of pregnant and lactating women.

METHODS

The literature was reviewed using relevant data bases (e.g. Pubmed, Scopus, Science Direct) and relevant articles were selected to provide information and data for the text and associated Tables.

RESULTS

Dynamic features especially of plasma carnitine profile during pregnancy and lactation, indicate an extraordinarily active participation of carnitine in the intermediary metabolism both in pregnant woman and in neonate and may also have implications for health and disease later in life. Maternal diets rich in trans and saturated fatty acids can lead to impairments in the metabolism and development of the offspring, whereas the consumption of long chain-polyunsaturated fatty acids during pregnancy plays a beneficial physiologic and metabolic role in the health of offspring.

CONCLUSIONS

Pregnant women who are underweight, overweight or obese, with gestational diabetes mellitus or diabetes mellitus and those who choose vegan/vegetarian diets or are coming from socially disadvantaged areas, should be nutritionally supported to achieve a higher quality diet during pregnancy and/or lactation.

Carnitine longitudinal pattern in preterm infants <1800 g body weight: a case-control study

BACKGROUND

The aim of this study is to investigate free carnitine (C0) and total acylcarnitine levels (AC) in preterm infants with BW < 1800 g and the relationship with neonatal and perinatal factors.

METHODS

Ninety-three thousand two hundred and ninety-three newborns were screened between 2011 and 2013. Dried blood samples (DBS) were collected at 48-72 h, 14, and 30 days of age. We studied 92 consecutive preterm (BW < 1800 g) infants with low carnitine levels at 30 days of life (Group 1). As controls, we included the first 92 cases (BW < 1800 g) with normal carnitine levels (Group 2) and another 92 at or near-term newborns with BW > 1800 g (Group 3).

RESULTS

Compared to 48-72 h levels, C0 and AC decreased at 14 and 30 days of life in Groups 1 and 2 (p < 0.001). In Group 2, the percentage of children with carnitine-free parenteral nutrition (PN) and BW < 1000 g was lower than in Group 1 (p < 0.001). Only in Group 2 did C0 increase at 30 days (p < 0.001). The multivariate regression analysis confirmed the influence of body weight and type of nutrition on C0 and AC.

CONCLUSION

Body weight and type of nutrition influenced the carnitine longitudinal pattern.

Diagnosis of Carnitine Deficiency in Extremely Preterm Neonates Related to Parenteral Nutrition: Two Step Newborn Screening Approach

Currently, there is no evidence in the literature to support the routine supplementation of all parenterally fed premature infants with l-carnitine. In our study, we found that about 8.56% of extremely preterm neonates are diagnosed with carnitine deficiency secondary to malnutrition, either due to reduced stores at birth or related to total parenteral nutrition (TPN). Our two step approach of performing newborn screening (NBS) again at 32 weeks gestational age (GA) equivalent helps to diagnose 81.4% more preterm babies with carnitine deficiency-who would otherwise be missed-and supplement them with l-carnitine for optimal growth. We performed a retrospective cohort study to diagnose carnitine deficiency related to malnutrition in two groups: those presenting at birth and those presenting later in life. We found that there was a statistically significant difference in the median GA and birth weight (BW) between the two groups, but there was no difference in the free carnitine levels.

[Levels of blood free carnitine in preterm infants with different gestational ages and birth weights]

OBJECTIVE

To examine blood concentrations of free carnitine (FC) in preterm infants with different gestational ages (GA) and birth weights (BW).

METHODS

A total of 3 368 preterm infants were enrolled as subjects. According to GA, they were divided into extremely preterm birth (EPTB) group (GA <28 weeks; n=39), very preterm birth (VPTB) group (28 ≤GA <32 weeks; n=405), moderately preterm birth (MPTB) group (32 ≤GA <34 weeks; n=507), and late preterm birth (LPTB) group (34 ≤GA <37 weeks; n=2 417); according to BW, they were divided into extremely low birth weight (ELBW) group (BW <1 000 g; n=36), very low birth weight (VLBW) group (1 000 g ≤BW <1 500 g; n=387), low birth weight (LBW) group (1 500 g ≤BW <2 500 g; n=1 873), and normal birth weight (NBW) group (2 500 g ≤ BW <4 000 g; n=1 072). Blood concentrations of FC were measured between 72 hours and 7 days after birth.

RESULTS

The EPTB and VPTB groups had significantly higher FC concentrations than the MPTB and LPTB groups (P<0.05), and the MPTB group had significantly higher FC concentrations than the LPTB group (P<0.05). The lower limit of the 95% medical reference range of FC increased with the reduction in GA. The ELBW and VLBW groups had significantly higher FC concentrations than the LBW and NBW groups (P<0.05). The LBW group had significantly higher FC concentrations than the NBW group (P<0.05). The lower limit of the 95% medical reference range of FC increased with the reduction in BW.

CONCLUSIONS

There is a significant increase in blood FC concentrations in very/extremely preterm infants and very/extremely low birth weight infants, and tend to decrease with the increases in GA and BW.

Acylcarnitine profiles in serum and muscle of dairy cows receiving conjugated linoleic acids or a control fat supplement during early lactation

Acylcarnitines (ACC) are formed when fatty acid (FA)-coenzyme A enters the mitochondria for β-oxidation and the tricarboxylic acid cycle through the carnitine shuttle. Concentrations of ACC may vary depending on the metabolic conditions, but can accumulate when rates of β-oxidation exceed those of tricarboxylic acid. This study aimed to characterize muscle and blood serum acylcarnitine profiles, to determine the mRNA abundance of muscle carnitine acyltransferases, and to test whether dietary supplementation (from d 1 in milk) with conjugated linoleic acids (CLA; 100 g/d; each 12% of trans-10,cis-12 and cis-9,trans-11 CLA; n = 11) altered these compared with control fat-supplemented cows (CTR; n = 10). Blood samples and biopsies from the semitendinosus musclewere collected on d -21, 1, 21, and 70 relative to parturition. Serum and muscle ACC profiles were quantified using a targeted metabolomics approach. The CLA supplement did not affect the variables examined. The serum concentration of free carnitine decreased with the onset of lactation. The concentrations of acetylcarnitine, hydroxybutyrylcarnitine, and the sum of short-chain ACC in serum were greater from d -21 to 21 than thereafter. The serum concentrations of long-chain ACC tetradecenoylcarnitine (C14:1) and octadecenoylcarnitine (C18:1) concentrations were greater on d 1 and 21 compared with d -21. Muscle carnitine remained unchanged, whereas short- and medium-chain ACC, including propenoylcarnitine (C3:1), hydroxybutyrylcarnitine, hydroxyhexanoylcarnitine, hexenoylcarnitine (C6:1), and pimelylcarnitine were increased on d 21 compared with d -21 and decreased thereafter. In muscle, the concentrations of long-chain ACC (from C14 to C18) were elevated on d 1. The mRNA abundance of carnitine palmitoyltransferase 1, muscle isoform (CPT1B) increased 2.8-fold from d -21 to 1, followed by a decline to nearly prepartum values by d 70, whereas that of CPT2 did not change over time. The majority of serum and muscle short- and long-chain ACC were positively correlated with the FA concentrations in serum, whereas serum carnitine and C5 were negatively correlated with FA. Time-related changes in the serum and muscle ACC profiles were demonstrated that were not affected by the CLA supplement at the dosage used in the present study. The elevated concentrations of long-chain ACC species in muscle and of serum acetylcarnitine around parturition point to incomplete FA oxidation were likely due to insufficient metabolic adaptation in response to the load of FA around parturition.

Carnitine deficiency in preterm infants: A national survey of knowledge and practices

OBJECTIVE

Lipid supplementation improves developmental outcomes in preterm infants. Carnitine is essential for lipid metabolism; however, despite high risk for carnitine deficiency, there are no standards for carnitine supplementation in preterm infants receiving total parenteral nutrition (TPN). Our objective was to assess knowledge, beliefs and practices regarding preterm carnitine deficiency and supplementation among neonatal practitioners.

METHODS

Cross-sectional electronic survey administered via a nationally representative listserv of neonatal practitioners.

RESULTS

492 respondents participated in the survey. Only 21% of respondents were aware that carnitine is secreted by the placenta. 72% believed that carnitine deficiency was common, and 60% believed deficiency could have serious consequences. Five percent routinely screened for deficiency, and 40% routinely provided carnitine supplementation. Respondents with >5 years' experience were more likely to report using carnitine supplementation (50% vs. 38%).

CONCLUSIONS

Although most respondents believed that carnitine deficiency is common and could have serious consequences, few screened for deficiency and fewer than half routinely supplemented. Thus, many preterm infants remain at risk for carnitine deficiency. Further research is needed to elucidate the risks of carnitine deficiency in these vulnerable infants.

Effects of birth weight on profiles of dried blood amino-acids and acylcarnitines

Background

Birth weight influences profiles of dried blood amino-acids and acylcarnitines in newborn screening. This study aimed to define a more appropriate cut-off value to reduce the false positive rate and the number of recalled patients in newborn screening.

Methods

All babies who underwent newborn screening in our center were included; they were divided into groups by birth weight: 2500–3999 g (comparator group), <1000 g (group 1), 1000–1499 g (group 2), 1500–2499 g (group 3), and >4000 g (group 4). The 0.5th and 99.5th percentiles were used as the cut-off values. Comparisons were done on amino acid and acylcarnitines concentrations between the groups. False positive rate, positive predictive value, corrected false positive rate by birth weights were determined.

Results

Data on a total of 578,287 newborn infants were included in the analysis. The total false positive rate was 0.75%, and positive predictive value 2.89%. The false positive rate was 0.69%, 0.54% and 5.31% in infants with normal birth weight, birth weight of >4000 (group 4) and low birth weight of < 2500 g (groups 1, 2 and 3), respectively. Low-birth weight infants had much higher phenylalanine, tyrosine, methionine, arginine, propionylcarnitine, isovalerylcarnitine and octadecanoylcarnitine concentrations. Free carnitines and palmitoylcarnitine concentrations were lower. After adjusting for birth weight, false positive rate of all indices decreased to 0.53%, and positive predictive value increased to 4.31%.

Conclusions

Amino acid and carnitine concentrations in low-birth weight newborn infants may differ from the normal term newborn infants. The cut-off values of individual metabolites should be adjusted based on birth weight, to reduce false positive rate and increase positive predictive value.

Gestational dating by metabolic profile at birth: a California cohort study

BACKGROUND

Accurate gestational dating is a critical component of obstetric and newborn care. In the absence of early ultrasound, many clinicians rely on less accurate measures, such as last menstrual period or symphysis-fundal height during pregnancy, or Dubowitz scoring or the Ballard (or New Ballard) method at birth. These measures often underestimate or overestimate gestational age and can lead to misclassification of babies as born preterm, which has both short- and long-term clinical care and public health implications.

OBJECTIVE

We sought to evaluate whether metabolic markers in newborns measured as part of routine screening for treatable inborn errors of metabolism can be used to develop a population-level metabolic gestational dating algorithm that is robust despite intrauterine growth restriction and can be used when fetal ultrasound dating is not available. We focused specifically on the ability of these markers to differentiate preterm births (PTBs) (<37 weeks) from term births and to assign a specific gestational age in the PTB group.

STUDY DESIGN

We evaluated a cohort of 729,503 singleton newborns with a California birth in 2005 through 2011 who had routine newborn metabolic screening and fetal ultrasound dating at 11-20 weeks' gestation. Using training and testing subsets (divided in a ratio of 3:1) we evaluated the association among PTB, target newborn characteristics, acylcarnitines, amino acids, thyroid-stimulating hormone, 17-hydroxyprogesterone, and galactose-1-phosphate-uridyl-transferase. We used multivariate backward stepwise regression to test for associations and linear discriminate analyses to create a linear function for PTB and to assign a specific week of gestation. We used sensitivity, specificity, and positive predictive value to evaluate the performance of linear functions.

RESULTS

Along with birthweight and infant age at test, we included 35 of the 51 metabolic markers measured in the final multivariate model comparing PTBs and term births. Using a linear discriminate analyses-derived linear function, we were able to sort PTBs and term births accurately with sensitivities and specificities of ≥95% in both the training and testing subsets. Assignment of a specific week of gestation in those identified as PTBs resulted in the correct assignment of week ±2 weeks in 89.8% of all newborns in the training and 91.7% of those in the testing subset. When PTB rates were modeled using the metabolic dating algorithm compared to fetal ultrasound, PTB rates were 7.15% vs 6.11% in the training subset and 7.31% vs 6.25% in the testing subset.

CONCLUSION

When considered in combination with birthweight and hours of age at test, metabolic profile evaluated within 8 days of birth appears to be a useful measure of PTB and, among those born preterm, of specific week of gestation ±2 weeks. Dating by metabolic profile may be useful in instances where there is no fetal ultrasound due to lack of availability or late entry into care.

Effects of L-carnitine supplementation on respiratory distress syndrome development and prognosis in premature infants: A single blind randomized controlled trial

The aim of the present study was to investigate the efficacy of L-carnitine therapy on the occurrence and prognosis of respiratory distress syndrome (RDS). A single blind, randomized controlled trial study was conducted on 130 infants with gestational ages of 28-36 weeks. Infants were assigned to experimental groups (groups 1 and 2) and control groups (groups 3 and 4). Groups 1 and 3 consisted of infants with RDS, and groups 2 and 4 groups were composed of infants without RDS. The experimental groups were treated with carnitine. No statistically significant differences in serum carnitine levels were detected between the study and the control groups on day 1 of treatment (P=0.06). However, on day 7 of treatment, serum carnitine levels in the experimental groups were significantly increased (P=0.02), as compared with the control groups. The surfactant requirement value, which is how many rounds of surfactant therapy were required, was 1.56±0.97 in group 1, and 2.12±0.99 in group 3 (P<0.001). The mean duration of mechanical ventilation required was 3.04±3.60 days in group 1, and 4.73±5.63 days in group 3 (P<0.001). The present results indicate that carnitine supplementation in premature infants with RDS may help to increase carnitine levels, thus decreasing the duration of mechanical ventilation and surfactant requirement.

Acylcarnitines are anticoagulants that inhibit factor Xa and are reduced in venous thrombosis, based on metabolomics data

In many patients with deep vein thrombosis and pulmonary embolism (venous thromboembolism, VTE), biomarkers or genetic risk factors have not been identified. To discover novel plasma metabolites associated with VTE risk, we employed liquid chromatography-mass spectrometry-based untargeted metabolomics, which do not target any specific metabolites. Using the Scripps Venous Thrombosis Registry population for a case-control study, we discovered that 10:1 and 16:1 acylcarnitines were low in plasmas of the VTE patient group compared with matched controls, respectively. Data from targeted metabolomics studies showed that several long-chain acylcarnitines (10:1, 12:0, 12:2, 18:1, and 18:2) were lower in the VTE group. Clotting assays were used to evaluate a causal relationship for low acylcarnitines in patients with VTE. Various acylcarnitines inhibited factor Xa-initiated clotting. Inhibition of factor Xa by acylcarnitines was greater for longer acyl chains. Mechanistic studies showed that 16:0 acylcarnitine had anticoagulant activity in the absence of factor Va or phospholipids. Surface plasmon resonance investigations revealed that 16:0 acylcarnitine was bound to factor Xa and that binding did not require the γ-carboxy glutamic acid domain. In summary, our study identified low plasma levels of acylcarnitines in patients with VTE and showed that acylcarnitines have anticoagulant activity related to an ability to bind and inhibit factor Xa.

Evaluation of carnitine deficit in very low birth weight preterm newborns small for their gestational age

OBJECTIVE

To verify whether small-for-gestational-age (SGA) preterm newborns represent a special risk group for carnitine deficiency. Secondary outcome includes assessment of longitudinal differences of total carnitine (TC), free carnitine (FC) and acylcarnitines between SGA and appropriate-for-gestational-age (AGA).

METHODS

A retrospective study to evaluate carnitine and acylcarnitines profile on 144 very-low-birth weight newborns (VLBW), classified as AGA (n = 73) and SGA (n = 71), was performed by tandem mass spectrometry, during their first 5 weeks of life. Carnitine deficiency was defined as FC <40 µmol/L and FC/TC <0.7.

RESULTS

Carnitine deficiency was observed in the two study groups throughout the monitoring period (maximum FC: 36.05 µmol/L in AGA and 32.24 µmol/L in SGA). FC/TC remains under 0.7 in both with progressive improvement. Unlike expected, a comparatively higher value of TC, FC and total acylcarnitines (tAC) was found in SGA during the first 2 weeks, with significant relevance on day 3-5, especially for tAC (p < 0.001). The only acylcarnitine with persistently lower value in SGA is C5 (p < 0.05 in first 2 weeks).

CONCLUSIONS

A carnitine deficiency was demonstrated in all VLBW. Although birth weight restriction has been suggested as a risk factor for impaired carnitine status, in our study, SGA was not related with higher carnitine deficiency.

Analysis and interpretation of acylcarnitine profiles in dried blood spot and plasma of preterm and full-term newborns

BACKGROUND

Acylcarnitines are biomarkers of fatty acid metabolism, and examining their patterns in preterm newborn may reveal metabolic changes associated with particular conditions related to prematurity. Isomeric acylcarnitines in dried blood spots (DBS) and plasma have never been assessed in preterm infants.

METHODS

We studied 157 newborn divided into four groups by weeks of gestational age (GA), as follows: 22-27 wk in group 1; 28-31 wk in group 2; 32-36 wk in group 3; and 37-42 wk in group 4. Samples were collected on the third day of life. Acylcarnitines were separated and quantified using ultra-performance liquid chromatography tandem mass spectrometry.

RESULTS

Acylcarnitine concentrations correlated significantly with GA and birth weight in both DBS and plasma samples. Concentrations were lower in preterm newborn, except for acylcarnitines derived from branched-chain amino acids, which were higher and correlated with enteral feeding. On day 3 of life, no correlations emerged with gender, respiratory distress syndrome, bronchopulmonary dysplasia, surfactant administration, or mechanical ventilation.

CONCLUSION

We established GA-based reference ranges for isomeric acylcarnitine concentrations in preterm newborn, which could be used to assess nutritional status and the putative neuroprotective role of acylcarnitines.

Inborn errors of metabolism and expanded newborn screening: review and update

Inborn errors of metabolism (IEM) are a phenotypically and genetically heterogeneous group of disorders caused by a defect in a metabolic pathway, leading to malfunctioning metabolism and/or the accumulation of toxic intermediate metabolites. To date, more than 1000 different IEM have been identified. While individually rare, the cumulative incidence has been shown to be upwards of 1 in 800. Clinical presentations are protean, complicating diagnostic pathways. IEM are present in all ethnic groups and across every age. Some IEM are amenable to treatment, with promising outcomes. However, high clinical suspicion alone is not sufficient to reduce morbidities and mortalities. In the last decade, due to the advent of tandem mass spectrometry, expanded newborn screening (NBS) has become a mandatory public health strategy in most developed and developing countries. The technology allows inexpensive simultaneous detection of more than 30 different metabolic disorders in one single blood spot specimen at a cost of about USD 10 per baby, with commendable analytical accuracy and precision. The sensitivity and specificity of this method can be up to 99% and 99.995%, respectively, for most amino acid disorders, organic acidemias, and fatty acid oxidation defects. Cost-effectiveness studies have confirmed that the savings achieved through the use of expanded NBS programs are significantly greater than the costs of implementation. The adverse effects of false positive results are negligible in view of the economic health benefits generated by expanded NBS and these could be minimized through increased education, better communication, and improved technologies. Local screening agencies should be given the autonomy to develop their screening programs in order to keep pace with international advancements. The development of biochemical genetics is closely linked with expanded NBS. With ongoing advancements in nanotechnology and molecular genomics, the field of biochemical genetics is still expanding rapidly. The potential of tandem mass spectrometry is extending to cover more disorders. Indeed, the use of genetic markers in T-cell receptor excision circles for severe combined immunodeficiency is one promising example. NBS represents the highest volume of genetic testing. It is more than a test and it warrants systematic healthcare service delivery across the pre-analytical, analytical, and post-analytical phases. There should be a comprehensive reporting system entailing genetic counselling as well as short-term and long-term follow-up. It is essential to integrate existing clinical IEM services with the expanded NBS program to enable close communication between the laboratory, clinicians, and allied health parties. In this review, we will discuss the history of IEM, its clinical presentations in children and adult patients, and its incidence among different ethnicities; the history and recent expansion of NBS, its cost-effectiveness, associated pros and cons, and the ethical issues that can arise; the analytical aspects of tandem mass spectrometry and post-analytical perspectives regarding result interpretation.

Differences in circulating carnitine status of preterm infants fed fortified human milk or preterm infant formula

OBJECTIVE

The aim of the study was to compare plasma carnitine profiles in fortified human milk (HM)-fed preterm infants or formula-fed preterm infants.

METHODS

Plasma acylcarnitine concentrations were determined in 20 formula-fed and 18 HM-fed preterm infants (birth weights between 1000 and 2200 g) by isotope dilution ESI MS/MS technique on study days 0, 14, and 28.

RESULTS

Concentrations of free carnitine (FC) and different acylcarnitines did not change during the 4 weeks of the study in infants fed HM. In contrast, in infants fed formula FC increased markedly (day 0: 29.989 [16.646] μmol/L, median [interquartile range], day 14: 43.972 [8.455], P < 0.05) along with increases of short-chain esters (C2 day 0: 5.300 [3.272], day 14: 6.773 [2.127], P < 0.05; C3 day 0: 0.070 [0.059], day 14: 0.110 [0.069], P < 0.05). In contrast, some medium-chain (C8:1, C12) and long-chain esters (C14, C16) decreased significantly in infant formula by day 14, whereas FC and C2 and C3 esters increased further by day 28 (FC: 47.672 [14.753], C2: 7.430 [4.688], C3: 0.107 [0.047]).

CONCLUSIONS

The altered carnitine ester profile likely reflects active involvement of the carnitine molecule in the buffering, metabolism, and elimination of nonphysiological acyl moieties.

Amino acid and acylcarnitine profiles in premature neonates: a pilot study

OBJECTIVE

To investigate the longitudinal changes in amino acid (AA) and acylcarnitine (AC) profiles of preterm neonates over the first 2 wk of life, and to detect any significant deviation from full term values that requires change of cut-off values used for detection of metabolic disorders in preterm neonates.

METHODS

This observational analytical longitudinal study was conducted on 131 premature neonates (gestational age ranged from 27 to 36 wk) and 143 healthy full-term neonates. Dried blood spots were taken on the 5th and 14th postnatal day from the premature neonates and on day 5 from full term neonates for neonatal screening. Samples were analyzed for AA and AC using tandem mass spectrometer.

RESULTS

Most AA significantly decreased on day 14 compared to day 5 among preterm neonates (p < 0.05). The combined values of total carnitine (TC), total acylcarnitine (tAC) and short-chain acylcarnitines on day 5 among preterm neonates were statistically significantly higher compared to the day 14 sample (p 0.0001), whereas no statistically significant difference was found regarding the values of medium-, long-chain acylcarnitines, tAC/FC, and FC/TC (p > 0.05). The levels of AA of preterm neonates were statistically significantly higher than that of the controls (p < 0.05). The values of TC, tAC, short-, medium- and long-chain acylcarnitines, were significantly higher than those of the controls (p < 0.05). The reference ranges for preterm neonates were determined using the 1st and 99.9th percentiles.

CONCLUSIONS

AA and AC showed an age-related distribution of their concentrations. This underlines the importance of using appropriate reference values when working with a prematurely born population.

Carnitine deficiency in OCTN2-/- newborn mice leads to a severe gut and immune phenotype with widespread atrophy, apoptosis and a pro-inflammatory response

We have investigated the gross, microscopic and molecular effects of carnitine deficiency in the neonatal gut using a mouse model with a loss-of-function mutation in the OCTN2 (SLC22A5) carnitine transporter. The tissue carnitine content of neonatal homozygous (OCTN2^−/−) mouse small intestine was markedly reduced; the intestine displayed signs of stunted villous growth, early signs of inflammation, lymphocytic and macrophage infiltration and villous structure breakdown. Mitochondrial β-oxidation was active throughout the GI tract in wild type newborn mice as seen by expression of 6 key enzymes involved in β-oxidation of fatty acids and genes for these 6 enzymes were up-regulated in OCTN2^−/− mice. There was increased apoptosis in gut samples from OCTN2^−/− mice. OCTN2^−/− mice developed a severe immune phenotype, where the thymus, spleen and lymph nodes became atrophied secondary to increased apoptosis. Carnitine deficiency led to increased expression of CD45-B220⁺ lymphocytes with increased production of basal and anti-CD3-stimulated pro-inflammatory cytokines in immune cells. Real-time PCR array analysis in OCTN2^−/− mouse gut epithelium demonstrated down-regulation of TGF-β/BMP pathway genes. We conclude that carnitine plays a major role in neonatal OCTN2^−/− mouse gut development and differentiation, and that severe carnitine deficiency leads to increased apoptosis of enterocytes, villous atrophy, inflammation and gut injury.

Use of diagnostic neutral losses for structural information on unknown aromatic metabolites: an experimental and theoretical study

This work presents the use of neutral losses (NL) for the identification of compounds related to the metabolism of tyrosine. The mass spectra of all the studied compounds, recorded at several collision energies, are compared. The fragmentation mechanism of protonated molecules, MH(+), is explained by combining collision-induced dissociation (CID) mass spectra and density functional theory (DFT) calculations. The results show that the first fragmentation is the elimination from MH(+) of a neutral molecule including a functional group of the linear chain. Three primary neutral losses are observed: 17 u (NH(3)), 18 u (H(2)O) and 46 u (H(2)O+CO) characterizing amino, hydroxyl and carboxylic functions on the linear chain. The presence and abundance of ions corresponding to these losses are dependent on (i) the position of the functional group on the linear chain, (ii) the initial localisation of the protonating hydrogen, and (iii) the substitution of the aromatic ring. For compounds including a functional group on the benzylic carbon atom, the investigation of the other functions requires the knowledge of secondary fragmentations. Among these secondary fragmentations we have retained the loss of NH(3) from [MH-18u](+) and the loss of ketene from [MH-17u](+). Experimentally these fragmentations are detected using losses of 35 u and 59/73 u. In other words, NL35 identifies hydroxy and amino compounds and NL 46 and/or NL59/73 identify carboxylic acids. The search for characteristic neutral losses is used for the analysis of compounds in a mixture and the analysis of biological fluid. We show that selective search of several neutral losses allows also the unambiguous differentiation of isomers and gives the opportunity to identify compounds in biological fluids.

Newborn screening for methylmalonic acidurias--optimization by statistical parameter combination

With the introduction of tandem mass spectrometry, newborn screening for disorders of propionate metabolism became widely available. However, there is controversy whether population screening for these disorders should be performed. The most widely used primary metabolite C(3) itself has a poor specificity or lacks 100% sensitivity for milder forms and/or defects of cobalamin metabolism. Strategies to improve specificity have included the calculation of metabolite ratios (e.g. C(3)/C(2)) or second-tier strategies with analysis of methylmalonic acid or 2-methylcitric acid from the primary screening specimen. We report the results of a new statistical approach to identify parameter combinations that allow for 100% sensitivity as well as increased specificity. The promising results of this alternative approach will have to be substantiated on larger data sets.

Serum carnitine, triglyceride and cholesterol profiles in Korean neonates

This study evaluated carnitine and lipid status of fifty Korean newborns. Each subject was assigned to two groups: one according to body weight at birth and the other according to gestational age. Serum total, HDL- and LDL-cholesterol were significantly lower and triacylglycerols were significantly higher, by 14 %, in the low birth weight infant (LBWI, 1310–2490 g) group compared with the normal birth weight infant (NBWI, 2570–4420 g) group. Neither birth weight nor gestational age affected serum total carnitine concentrations. However, serum ASAC (acid-soluble acylcarnitine) concentrations were 43 % higher (P < 0·001) in the LBWI group compared with the NBWI group, and approximately twice as high (P < 0·05) in the 28–32 gestational age group compared with the other gestational age groups. NEC (non-esterified acyl carnitine) fractions were significantly higher in the NBWI and 28–32 week groups (P < 0·001 andP < 0·05); consequently serum acyl/NEC carnitine ratios were four times higher in the LBWI group compared with the NBWI group and 2–3 times higher in the 25–32 week age group compared with the more advanced gestational age groups. Urinary carnitine excretion, including the NEC fraction and total carnitine, was significantly higher (P < 0·001) for LBWI than for NBWI. By gestational age, NEC excretion of the 28–32 week group was significantly (P < 0·05) higher than that of the other two groups, but total carnitine excretion was not different among the groups. This study demonstrated that Korean immature and preterm newborns have higher serum triacylglycerol concentrations but lower carnitine status than NBWI. Therefore, the lower carnitine status and moderately higher triacylglycerols may suggest that LBWI in Korea might be at risk for poor carnitine status and decreased capacity to utilise fatty acids for energy.

Long-Term Stability of Amino Acids and Acylcarnitines in Dried Blood Spots

Background: Dried blood filter cards, collected for newborn screening, are often stored for long periods of time. They may be suitable for the retrospective diagnosis of inborn errors of metabolism, but no data are currently available on the long-term stability of amino acids and acylcarnitine species.

Methods: We analyzed amino acids and acylcarnitines by tandem mass spectrometry in 660 anonymous, randomly selected filter cards from 1989 through 2004. We assessed long-term stability of metabolites by linear regression and estimated annual decrease of concentration for each metabolite.

Results: Concentrations of free carnitine increased by 7.6% per year during the first 5 years of storage and decreased by 1.4% per year thereafter. Alanine, arginine, leucine, methionine, and phenylalanine decreased by 6.5%, 3.3%, 3.1%, 7.3%, and 5.7% per year, respectively. Acetylcarnitine, propionylcarnitine, citrulline, glycine, and ornithine decreased by 18.5%, 27.4%, 8.1%, 14.7%, and 16.3% per year during the first 5 years, respectively; thereafter the decline was more gradual. Tyrosine decreased by 1.7% per year during the first 5 years and 7.9% per year thereafter. We could not analyze medium- and long-chain acylcarnitine species because of low physiological concentrations.

Conclusions: Estimation of the annual decrease of metabolites may allow for the retrospective diagnosis of inborn errors of metabolism in filter cards that have been stored for long periods of time.

Use of tandem mass spectrometry for multianalyte screening of dried blood specimens from newborns

BACKGROUND

Over the past decade laboratories that test for metabolic disorders have introduced tandem mass spectrometry (MS/MS), which is more sensitive, specific, reliable, and comprehensive than traditional assays, into their newborn-screening programs. MS/MS is rapidly replacing these one-analysis, one-metabolite, one-disease classic screening techniques with a one-analysis, many-metabolites, many-diseases approach that also facilitates the ability to add new disorders to existing newborn-screening panels.

METHODS

During the past few years experts have authored many valuable articles describing various approaches to newborn metabolic screening by MS/MS. We attempted to document key developments in the introduction and validation of MS/MS screening for metabolic disorders. Our approach used the perspective of the metabolite and which diseases may be present from its detection rather than a more traditional approach of describing a disease and noting which metabolites are increased when it is present.

CONTENT

This review cites important historical developments in the introduction and validation of MS/MS screening for metabolic disorders. It also offers a basic technical understanding of MS/MS as it is applied to multianalyte metabolic screening and explains why MS/MS is well suited for analysis of amino acids and acylcarnitines in dried filter-paper blood specimens. It also describes amino acids and acylcarnitines as they are detected and measured by MS/MS and their significance to the identification of specific amino acid, fatty acid, and organic acid disorders.

CONCLUSIONS

Multianalyte technologies such as MS/MS are suitable for newborn screening and other mass screening programs because they improve the detection of many diseases in the current screening panel while enabling expansion to disorders that are now recognized as important and need to be identified in pediatric medicine.

Expanded newborn screening for inborn errors of metabolism by electrospray ionization-tandem mass spectrometry: results, outcome, and implications

OBJECTIVE

The aims of this study were to determine the impact of expanded newborn screening using tandem mass spectrometry (MS/MS) on the overall detection rate of inborn errors of metabolism in Germany and to assess the outcome for the patients that were diagnosed.

METHODS

During the period of study, 250,000 neonates in a German population were investigated for 23 inborn errors of metabolism by electrospray ionization-MS/MS. The overall value of the screening program was estimated by 1) complete ascertainment of all positive tests; 2) definite assignment of all diagnoses including reconfirmation at 12 months; and 3) clinical follow-up of all detected patients in an overall interval of 42 months. The mean observation period was 13.5 months per child.

RESULTS

In 106 newborns, confirmed inborn errors of metabolism were found. The disorders were classified as 50 classic forms and 56 variants. A total of 825 tests (0.33%) were false-positives. Seventy of the 106 newborns with confirmed disorders were judged to require treatment. Six children developed symptoms despite treatment. Three children had died. Among 9 children who became symptomatic before report of the results of screening, in 6 the diagnosis had been made in advance of the screening report. In evaluation of the screening program, 61 of the 106 identified children (58% of true-positives, or 1 of 4100 healthy newborns) were judged to have benefited from screening and treatment, because the diagnosis had not been made before screening. None of these infants had died and none developed psychomotor retardation or metabolic crisis during the follow-up period.

CONCLUSIONS

The screening by MS/MS for up to 23 additional disorders has approximately doubled the detection rate compared with that achieved by the conventional methods used in Germany. This strategy represents valuable preventive medicine by enabling diagnosis and treatment before the onset of symptoms.