Carnitine deficiency in premature infants receiving total parenteral nutrition

Transporters and drug secretion into human breast milk

INTRODUCTION

Medication use is highly prevalent in breastfeeding persons, posing potential risks for drug exposure to nursing infants. Transporters in the lactating mammary gland carry pharmacological and toxicological significance, as they can mediate the active transfer of drugs and nutrients into breastmilk.

AREAS COVERED

In this narrative review, we searched and compiled current knowledge on the transport of drugs in the human mammary gland from literature indexed in PubMed (current as of 25 October 2024), and clinical evidence demonstrating active transport of drugs into milk is provided. In vitro and in vivo models of the mammary gland are outlined in brief and known drug transporters at the blood-milk barrier and their potential relevance to drug concentrations in milk are described in detail.

EXPERT OPINION

Although clinical data show that membrane transporters mediate the transfer of multiple drugs into breast milk, our ability to predict milk concentrations for these drugs is limited. Improving our understanding of the transporter biology and pharmacology in the mammary gland is crucial for developing models to predict drug concentrations in human milk, which will support clinicians and lactating individuals in making rational decisions to balance the benefits of breastfeeding and the risks of drug exposure to infants.

Case report: Tackling the complexities of an extremely premature newborn with intrauterine growth restriction and congenital metabolic disorders through a multidisciplinary approach

Background and objectives

The premature birth of a newborn can present a complex challenge for healthcare providers, particularly in cases of extreme prematurity combined with intrauterine growth restriction and multiple metabolic deficiencies. In this report, we aim to shed light on the difficulties and considerations involved in the management of such a case. In addition, our study is aimed to raise awareness of the importance of a multidisciplinary team in managing an extreme premature case with multiple comorbidities.

Case presentation and main findings

We present the case of a 28-week premature female newborn with very low birth weight (660 g, percentile <10%) and intrauterine growth restriction. She was born through emergency cesarean delivery due to maternal Hemolysis, Elevated Liver enzymes, and Low Platelet count (HELLP) syndrome and had a high-risk pregnancy (spontaneous twin pregnancy, with one fetus stopping development at 16 weeks and maternal hypertension). In the first hours of life, she presented with persistent hypoglycemia requiring progressive glucose supplementation up to 16 g/kg/day to maintain normal blood glucose levels. The baby then showed favorable progress. However, from days 24 to 25, hypoglycemia recurred and did not respond to glucose boluses or supplementation in both intravenous and oral feeds, leading to the suspicion of a congenital metabolic disorder. Endocrine and metabolic screenings led to suspicion of primary carnitine deficiency and a deficiency in hepatic form of carnitine-palmitoyltransferase type I (CPT1) on the second screening.

Conclusion and clinical implications

The study highlights rare metabolic anomalies that can be due to both organ and system immaturity and delayed enteral feeding and excessive use of antibiotics. The clinical implications of this study emphasize the need for careful monitoring and comprehensive care of premature infants to prevent and manage potential metabolic abnormalities by neonatal metabolic screening.

The Use of Carnitine in Pediatric Nutrition

Carnitine is synthesized endogenously from methionine and lysine in the liver and kidney and is available exogenously from a meat and dairy diet and from human milk and most enteral formulas. Parenteral nutrition (PN) does not contain carnitine unless it is extemporaneously added. The primary role of carnitine is to transport long-chain fatty acids across the mitochondrial membrane, where they undergo beta-oxidation to produce energy. Although the majority of patients are capable of endogenous synthesis of carnitine, certain pediatric populations, specifically neonates and infants, have decreased biosynthetic capacity and are at risk of developing carnitine deficiency, particularly when receiving PN. Studies have evaluated for several decades the effects of carnitine supplementation in pediatric patients receiving nutrition support. Early studies focused primarily on the effects of supplementation on markers of fatty acid metabolism and nutrition markers, including weight gain and nitrogen balance, whereas more recent studies have evaluated neonatal morbidity. This review describes the role of carnitine in metabolic processes, its biosynthesis, and carnitine deficiency syndromes, as well as reviews the literature on carnitine supplementation in pediatric nutrition.

The Carnitine Palmitoyl Transferase (CPT) System and Possible Relevance for Neuropsychiatric and Neurological Conditions

The carnitine palmitoyl transferase (CPT) system is a multiprotein complex with catalytic activity localized within a core represented by CPT1 and CPT2 in the outer and inner membrane of the mitochondria, respectively. Two proteins, the acyl-CoA synthase and a translocase also form part of this system. This system is crucial for the mitochondrial beta-oxidation of long-chain fatty acids. CPT1 has two well-known isoforms, CPT1a and CPT1b. CPT1a is the hepatic isoform and CPT1b is typically muscular; both are normally utilized by the organism for metabolic processes throughout the body. There is a strong evidence for their involvement in various disease states, e.g., metabolic syndrome, cardiovascular diseases, and in diabetes mellitus type 2. Recently, a new, third isoform of CPT was described, CPT1c. This is a neuronal isoform and is prevalently localized in brain regions such as hypothalamus, amygdala, and hippocampus. These brain regions play an important role in control of food intake and neuropsychiatric and neurological diseases. CPT activity has been implicated in several neurological and social diseases mainly related to the alteration of insulin equilibrium in the brain. These pathologies include Parkinson's disease, Alzheimer's disease, and schizophrenia. Evolution of both Parkinson's disease and Alzheimer's disease is in some way linked to brain insulin and related metabolic dysfunctions with putative links also with the diabetes type 2. Studies show that in the CNS, CPT1c affects ceramide levels, endocannabionoids, and oxidative processes and may play an important role in various brain functions such as learning.

Carnitine supplementation in premature neonates: Effect on plasma and red blood cell total carnitine concentrations, nutrition parameters and morbidity

BACKGROUND & AIMS

Carnitine may be considered conditionally essential in the neonatal population. The purpose of this study was to evaluate the effects of long-term carnitine supplementation on total carnitine status and morbidity in premature neonates.

METHODS

In this prospective, randomized, placebo-controlled, double-blinded study, premature neonates received carnitine supplementation (20mg/kg/day) or placebo. Plasma (nmol/ml) and red blood cell (RBC) (nmol/mg hemoglobin) total carnitine concentrations, 24-h nitrogen excretion, intake and weight, and respiratory, gastroesophageal, and infectious morbidity were assessed.

RESULTS

Twenty-nine neonates (13 placebo, 16 carnitine; 27+/-2 weeks gestation; 976+/-259g birthweight) were studied for up to 8 weeks. Plasma total carnitine concentrations exceeded the reference range in the carnitine group (weeks 1-8); however, concentrations did not reach reference range until week 4 in the placebo group. RBC total carnitine concentrations increased, but remained below reference range in both the carnitine (weeks 1-6) and placebo (weeks 1-8) groups. Carnitine group neonates regained their birthweight more rapidly than placebo group neonates (day of life 11.8+/-6 vs. 16.9+/-6.3, P=0.034). In addition, percent periodic breathing calculated from cardiopulmonary trend monitor data (weeks 1-8) was lower in the carnitine group (0.4+/-0.9 vs. 1.4+/-1.9, P=0.014). There was no difference with respect to other markers of respiratory, gastroesophageal and infectious morbidity or nitrogen balance.

CONCLUSIONS

Carnitine supplementation at 20mg/kg/day results in increased plasma and RBC total carnitine concentrations, has a positive effect on catch-up growth, and may improve periodic breathing in premature neonates.

l-Carnitine transport in human placental brush-border membranes is mediated by the sodium-dependent organic cation transporter OCTN2

Maternofetal transport of l-carnitine, a molecule that shuttles long-chain fatty acids to the mitochondria for oxidation, is thought to be important in preparing the fetus for its lipid-rich postnatal milk diet. Using brush-border membrane (BBM) vesicles from human term placentas, we showed that l-carnitine uptake was sodium and temperature dependent, showed high affinity for carnitine (apparent Km= 11.09 ± 1.32 μM; Vmax= 41.75 ± 0.94 pmol·mg protein−1·min−1), and was unchanged over the pH range from 5.5 to 8.5. l-Carnitine uptake was inhibited in BBM vesicles by valproate, verapamil, tetraethylammonium, and pyrilamine and by structural analogs of l-carnitine, including d-carnitine, acetyl-d,l-carnitine, and propionyl-, butyryl-, octanoyl-, isovaleryl-, and palmitoyl-l-carnitine. Western blot analysis revealed that OCTN2, a high-affinity, Na+-dependent carnitine transporter, was present in placental BBM but not in isolated basal plasma membrane vesicles. The reported properties of OCTN2 resemble those observed for l-carnitine uptake in placental BBM vesicles, suggesting that OCTN2 may mediate most maternofetal carnitine transport in humans.

Dobutamine alters carnitine metabolism in the neonatal piglet heart

The use of inotropic agents to support the neonatal heart after sepsis or hypoxia increases cardiac energy demand. Carnitine plays a vital role in energy, fuel metabolism. To test the hypothesis that inotropic agents affect carnitine metabolism, hearts from sow-fed piglets were isolated and perfused with an oxygenated buffer containing glucose and palmitate. Increasing dosages of dobutamine (DOB 2.5–15 µg/Kg body wt per min, 0.007–0.044 µmol/kg per min) or saline vehicle (SAL) were administered. Heart rate (HR), left ventricular systolic (LVSP) and end diastolic pressures (LVEDP) were measured. Left ventricular developed pressure (LVDP = LVSP - LVEDP) and pressure-rate product (LVDP × HR) were calculated. Coronary effluent was collected to measure flow and metabolites. Heart tissue samples were collected for metabolite analysis. Results: DOB increased HR, LVEDP and the pressure-rate product [LVDP × HR]. Mean lactate production increased in DOB, but not in SAL control hearts, and was correlated with heart acylcarnitine, but not with coronary flow. Tissue acylcarnitine levels were higher in the DOB than in the SAL group. Plasma total carnitine was correlated with [LVDP × HR] and LVDP, but not with HR. The findings demonstrate that DOB alters myocardial carnitine metabolism and suggest that carnitine status may affect cardiac response to inotropic agents.Key words: carnitine, dobutamine, neonate, swine, isolated perfused heart.

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

Measurement of free carnitine and acylcarnitines allows the detection of several inborn errors of metabolism in neonatal screening. Because available data for premature infants is limited, we studied longitudinal changes in acylcarnitine profiles of full-term and preterm neonates over the first 4 weeks of life. One hundred twenty infants were divided into four groups of 30: A, gestational age 22 to 27 wk; B, 28 to 31 wk; C, 32 to 36 wk; and D, 37 to 41 wk. Blood samples spotted on a Guthrie card were taken on days 5 and 28. Additional specimens (groups A and B only) were collected on days 1, 3, 7, and 14. Carnitine and its acyl esters were detected by looking for the precursor ions of m/z = 85 using a PE Sciex API 365 electrospray ionization tandem mass spectrometer. Concentrations of free carnitine and most acylcarnitines were significantly higher in group A compared with group D postnatally. Groups B and C displayed intermediate values. Carnitine levels in infants from group A and B decreased steadily from day 1 to day 7, and recovered up to day 14 in group B only. On day 28 carnitine concentrations had further decreased in group A, while reaching postnatal levels again in group B. Postnatal carnitine levels are higher in very immature preterm infants compared with full-term infants, but become lower on day 28. However, the commonly used metabolite ratios should still allow the detection of inborn errors of metabolism.

Transporter gene expression in lactating and nonlactating human mammary epithelial cells using real-time reverse transcription-polymerase chain reaction

Transporter-mediated processes in the lactating mammary gland may explain the significant accumulation of certain drugs in breast milk. The purpose of this study was to identify potential candidate drug transport proteins involved in drug accumulation in milk. Quantitative reverse transcription-polymerase chain reaction methods were developed to determine the relative RNA levels of 30 different drug transporter genes. Transporter gene RNA levels in lactating mammary epithelial cells (MEC) purified from pooled fresh breast milk samples were compared with levels in nonlactating MEC, liver, and kidney tissue. Transcripts were detected in lactating MEC for OCT1, OCT3, OCTN1, OCTN2, OATP-A, OATP-B, OATP-D, OATP-E, MRP1, MRP2, MRP5, MDR1, CNT1, CNT3, ENT1, ENT3, NCBT1, PEPT1, and PEPT2. No transcripts were detected for OCT2, OAT1, OAT2, OAT3, OAT4, OATP-C, MRP3, MRP4, CNT2, ENT2, and NCBT2. Lactating MEC demonstrated more than 4-fold higher RNA levels of OCT1, OCTN1, PEPT2, CNT1, CNT3, and ENT3, and more than 4-fold lower RNA levels of MDR1 and OCTN2 relative to nonlactating MEC. Lactating MEC showed significantly higher RNA levels of CNT3 relative to liver and kidney, increased PEPT2 RNA levels relative to liver, and increased OATP-A RNA levels relative to kidney. These data imply CNT3 may play a specialized role in nucleoside accumulation in milk and may identify an important role for PEPT2 and OATP-A transporters at the lactating mammary epithelium. Furthermore, transporters expressed in lactating MEC identify a potential role for these transporters in drug disposition at the mammary gland.

Parenteral nutrition-associated liver complications in children

Parenteral nutrition is a life-saving therapy for patients with intestinal failure. It may be associated with transient elevations of liver enzyme concentrations, which return to normal after parenteral nutrition is discontinued. Prolonged parenteral nutrition is associated with complications affecting the hepatobiliary system, such as cholelithiasis, cholestasis, and steatosis. The most common of these is parenteral nutrition-associated cholestasis (PNAC), which may occur in children and may progress to liver failure. The pathophysiology of PNAC is poorly understood, and the etiology is multifactorial. Risk factors include prematurity, long duration of parenteral nutrition, sepsis, lack of bowel motility, and short bowel syndrome. Possible etiologies include excessive caloric administration, parenteral nutrition components, and nutritional deficiencies. Several measures can be undertaken to prevent PNAC, such as avoiding overfeeding, providing a balanced source of energy, weaning parenteral nutrition, starting enteral feeding, and avoiding sepsis.

Lipid metabolism of the micropremie

Intravenous lipid emulsions often provide substance for the very low-birth weight or extremely low-birth weight infant that need total parenteral nutrition. The process used in this type of treatment as well as the effects of such treatment are discussed at length in this article. Some of the main compounds of representative lipid emulsions are listed and evaluated and the benefits and consequences of their use are presented.

Neonatal nutritional carnitine deficiency: a piglet model

The clinical significance of nutritional carnitine deficiency remains controversial. To investigate this condition under controlled conditions, an animal model was developed using the parenterally alimented, carnitine-deprived newborn piglet. Forty-five piglets received total parenteral nutrition for 2-3 wk that was either carnitine-free or supplemented with 100-400 mg/L L-carnitine. Blood and a muscle biopsy were taken at the initial surgery. Carnitine balance studies were performed at 11-14 d of age. Blood, liver, heart, and skeletal muscle were taken at sacrifice for analysis of carnitine, electron microscopy, and oxidation studies. Carnitine-deprived piglets were in negative carnitine balance and had lower blood, urine, and tissue levels of carnitine than carnitine-supplemented animals. There was a positive correlation between excretion and plasma concentrations of free carnitine with an apparent renal threshold between 15 and 35 micromol/L. Plasma levels were correlated with liver and heart, but not muscle, concentrations of total acid-soluble carnitine. Carnitine-deprived piglets had evidence of lipid deposition in liver and skeletal muscle and tended to have a higher incidence of muscle weakness and cardiac failure. Basal rates of oxidation of [14C]palmitate to 14CO2 and 14C-acid-soluble products were lower in liver homogenates from carnitine-deprived piglets than in those from carnitine-supplemented animals and increased in a dose-dependent fashion with the addition of L-carnitine (0, 50, and 500 micromol/L) in vitro. In summary, carnitine deprivation in the neonatal piglet resulted in low carnitine status and morphologic/functional disturbances compatible with carnitine deficiency. The described animal model appears to be suitable for the investigation of neonatal nutritional carnitine deficiency.

Sodium-dependent carnitine transport in human placental choriocarcinoma cells

The JAR human placental choriocarcinoma cells were found to transport carnitine into the intracellular space by a Na(+)-dependent process. The transport showed no requirement for anions. The Na+-dependent process was saturable and the apparent Michaelis-Menten constant for carnitine was 12.3 +/- 0.5 microM. Na+ activated the transport by increasing the affinity of the transport system for carnitine. The transport system specifically interacted with L-carnitine, D-carnitine, acetyl-DL-carnitine and betaine. 6-N-Trimethyllysine and choline had little or no effect on carnitine transport. Of the total transport measured, transport into the intracellular space represented 90%. Plasma membrane vesicles prepared from JAR cells were found to bind carnitine in a Na(+)-dependent manner. The binding was saturable with an apparent dissociation constant of 0.66 +/- 0.08 microM. The binding process was specific for L-carnitine, D-carnitine, acetyl-DL-carnitine, and betaine. 6-N-Trimethyllysine and choline showed little or no affinity. It is concluded that the JAR cells express a Na(+)-dependent high-affinity system for carnitine transport and that the Na(+)-dependent high-affinity carnitine binding detected in purified JAR cell plasma membrane vesicles is possibly related to the transmembrane transport process.

Carnitine metabolism in chronic liver disease

The liver is a central organ for carnitine metabolism and for the distribution of carnitine to the body. It is therefore not surprising that carnitine metabolism is impaired in patients and experimental animals with certain types of chronic liver disease. In this review, the changes in carnitine metabolism associated with chronic liver disease and the role of carnitine as a therapeutic agent in some of these conditions are discussed.

Sodium-dependent high-affinity binding of carnitine to human placental brush border membranes

The interaction of carnitine with human placental brush-border membrane vesicles was investigated. Carnitine was found to associate with the membrane vesicles in a Na(+)-dependent manner. The time course of this association did not exhibit an overshoot, which is typical of a Na+ gradient-driven transport process. The absolute requirement for Na+ was noticeable whether the association of carnitine with the vesicles was measured with a short time incubation or under equilibrium conditions, indicating Na(+)-dependent binding of carnitine to the human placental brush-border membranes. The binding was saturable and was of a high-affinity type with a dissociation constant of 1.37 +/- 0.03 microM. Anions had little or no influence on the binding process. The binding process was specific for carnitine and its acyl derivatives. Betaine also competed for the binding process, but other structurally related compounds did not. Kinetic analyses revealed that Na+ increased the affinity of the binding process for carnitine and the Na+/carnitine coupling ratio for the binding process was 1. The dissociation constant for the interaction of Na+ with the binding of carnitine was 24 +/- 4 mM. This constitutes the first report on the identification of Na(+)-dependent high-affinity carnitine binding in the plasma membrane of a mammalian cell. Studies with purified rat renal brush-border membrane vesicles demonstrated the presence of Na+ gradient-driven carnitine transport but no Na(+)-dependent carnitine binding in these membrane vesicles. In contrast, purified intestinal brush-border membrane vesicles posses neither Na+ gradient-driven carnitine transport nor Na(+)-dependent carnitine binding.

Renal handling of carnitine in ill preterm and term neonates

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Amino acid and energy needs of pediatric patients receiving parenteral nutrition

The technique of parenteral nutrition has become such an established part of modern pediatric care that it is difficult to imagine how pediatricians, as recently as 25 years ago, managed a large group of very difficult patients; however, despite its obvious nutritional advantages, the technique is not without problems. Many of these can be circumvented or controlled by careful attention to all aspects of the technique. Certainly the incidence of these problems can be maintained at a level sufficiently low that the benefits of the technique far outweigh its risks; however, the technique clearly can be further improved. One requirement for doing so is to recognize that the technique is deceptively simple and that it should not be used indiscriminantly without careful consideration of indications and alternative strategies for nutritional management. Additional research also is required. As discussed earlier, the available parenteral amino acid mixtures and lipid emulsions, although considerably improved over earlier versions, remain far from optimal. Some of the actual and theoretic problems that should be addressed in the near future are discussed in the preceding sections; there also are many others.

Weanling and adult rats differ in fatty acid and carnitine metabolism during sepsis

Increased oxidation of fat is an important host response to sepsis, and carnitine is essential for long-chain fatty acid oxidation. Because neonates have low levels of carnitine, their ability to respond to a septic insult may be impaired. The purpose of this study was to compare fatty acid and carnitine metabolism in septic weanling (60 to 85 g) and septic adult (285 to 310 g) rats. Sepsis was induced in weanling and adult male Sprague-Dawley rats by cecal ligation and puncture (CLP). The rats were killed 16 hours after CLP or sham operation, and serum glucose, lactate, beta-hydroxybutyrate, fatty acid, carnitine, liver fatty acid, and tissue carnitine levels were measured. The data suggest that during sepsis weanling rats may be more dependent on fatty acid oxidation than adult rats are, as evidenced by their elevated serum fatty acid and acylcarnitine levels, and relative hypoglycemia and hyperketonemia. In addition, although total serum carnitine levels were increased in both adult and weanling septic rats, tissue carnitine levels of weanling rats became significantly depleted during sepsis, unlike in adult rats. This study supports further investigation regarding the role of exogenous carnitine in newborn sepsis.

Organic acidurias and related abnormalities

Organic acid analysis is a powerful technique in the diagnosis of inborn errors of metabolism. Since the development of the technique over twenty-five years ago, it has evolved into a sophisticated and powerful method and is an essential tool in the diagnosis of the organic acidurias. The chemistry and biochemistry of organic acids, as well as sample preparation, instrumentation, and many aspects of the more commonly used methods for the analysis of these compounds, are reviewed. The biochemical and clinical characteristics of each of the primary organic acidurias are described. In addition, the various noninherited causes of secondary organic acidurias that lead to the excretion of abnormal organic acids are also described, and ways of differentiating primary from secondary causes are discussed.

Hepatobiliary complications of total parenteral nutrition

The relationships between various hepatobiliary disorders and the administration of total parenteral nutrition (TPN) were reviewed and, in particular, the role of TPN in their pathogenesis was critically evaluated. Several clinical and pathological entities including steatosis, steatohepatitis, cholestasis, and cholelithiasis have been commonly linked to TPN, and instances of chronic decompensated liver disease have been reported. However, it is concluded that it is often difficult to extricate the effects of TPN on hepatobiliary function from many other hepatotoxic factors that may be operative in these patients. Thus, whereas considerable evidence exists to support a role fro carbohydrate or calorie excess in TPN solutions in the pathogenesis of steatosis, a loss of enteric stimulation and not TPN per se may be the primary factor in the development of cholestasis, biliary sludge, and gallstones. The apparent predilection of infants to TPN-related cholestasis may be based on the relative immaturity of the neonatal biliary excretory system.

Carnitine deficiency associated with ornithine transcarbamylase deficiency

An infant with X-linked recessive ornithine transcarbamylase deficiency is described who also had severe deficiency of plasma and liver carnitine during normoammonemic periods. Treatment with L-carnitine (100 mg/kg/day) for 12 months decreased the frequency of hospitalizations for hyperammonemia, although it did not alter his neurologic status. This report demonstrates that persistent carnitine deficiency may be present in patients with ornithine transcarbamylase deficiency even when plasma ammonia is normal. Carnitine evaluation and supplementation may be important in the treatment of patients with this metabolic disorder.

Carnitine deficiency in surgical neonates receiving total parenteral nutrition

Carnitine plays a key role in the oxidation of fatty acids. Most solutions for parenteral nutrition do not contain carnitine. Because endogenous carnitine synthesis is insufficient in newborns, they are prone to developing a carnitine deficiency when they are dependent on total parenteral nutrition (TPN). Stimulated by the clinical observation of manifest clinical symptoms of carnitine deficiency in one patient, a study of 13 consecutive neonates who received TPN for over 2 weeks was begun. Their plasma carnitine levels before and during carnitine supplementation were determined. All patients had a carnitine intake far below the recommended minimal need of 11 mumol/kg per day. Although only three of them clearly showed clinical symptoms described as carnitine deficiency, carnitine supplementation for all neonates receiving TPN for over 2 weeks is recommended.

Lipid tolerance in the very low birth weight infant on intravenous and enteral feedings

Nutrition is of critical importance to very low birth weight (VLBW) survival. Intravenous (iv) lipid tolerance has been studied using a soybean or safflower-based lipid emulsion. We studied lipid levels in a group of VLBW infants on both intravenous lipids (soybean-safflower emulsion) and on enteral feedings (24 cal/oz premature formula). Levels were obtained on 1, 2, and 3 g/kg/day of iv lipid and after 3 and 10 days of feeding. Triglyceride (TG) and free fatty acid (FFA) proved the most sensitive indicator of both iv and enteral tolerance. The higher the lipid dose, the more likely there would be elevated lipid levels, especially FFA. Mean lipid levels for the group of enteral-fed infants were normal. Comparison of lipid levels on iv to those on enteral feedings showed significant differences in trough iv levels of TG compared to preprandial TG. FFAs tended to be significantly higher on iv feedings. Monitoring lipid levels on iv and enteral feedings is appropriate to document tolerance.

Carnitine plasma concentrations in 353 metabolically healthy children

Carnitine plasma concentrations were determined by an enzymatic radioisotopic method in 353 metabolically healthy children and in 41 adults. There was a positive correlation between total and free carnitine plasma concentrations and the age of the children. Both free and acylcarnitine concentrations were elevated on the 1st day of life, reflecting an increased rate of fatty acid oxidation. Carnitine plasma concentrations decreased after the 1st day and subsequently increased during the 1st year. From the 2nd year of life until adulthood, no further change was noted. Up to 17 years of age no differences were seen between male and female individuals. However, adult males had higher carnitine concentrations in plasma than adult females. Total carnitine concentrations were higher in 10- to 17-year-old females and lower in 10- to 17-year-old males compared with adults of the same sex, indicating a possible role for sex hormones in the regulation of carnitine plasma concentrations.

Lipoprotein lipase, hepatic lipase, and carnitine in premature infants

Twenty six preterm infants were studied at the age of 2, 7, and 26 days. The activities of lipoprotein and hepatic lipase in plasma taken 15 minutes after a heparin bolus of 100 IU/kg had been given and the concentrations of carnitine in serum and urine were measured. The mean gestational age was 31 weeks (range 26-35 weeks) and birth weight 1580 g (range 840-2280 g). Thirteen infants weighed under 1500 g at birth (very low birth weight), 20 were of appropriate weight for gestational age and six were small for gestational age. Lipoprotein lipase activity was higher in the preterm infants of appropriate weight than in the infants of very low birth weight and those who were small for gestational age. At the age of 2 or 7 days the activity of lipoprotein lipase in the preterm infants (mean (SEM) 46.2 (4.3) mumol free fatty acid/ml/hour) was, however, higher than in term infants and adults. Multivariate regression analyses showed that weight and relative birth weight together explained 58% of the variance of lipoprotein lipase activity but only 3% of the variance of hepatic lipase activity. Serum carnitine concentration was lower in the preterm infants than in term infants. Urinary excretion of carnitine increased progressively with age but was independent of serum concentration and carnitine intake. Urinary excretion of total carnitine was significantly greater in the infants who were small for gestational age (mean (SEM) 754 (203) nmol/mg of creatinine, n = 6) than in the infants of appropriate weight (161 (22.0) nmol/mg of creatinine, n = 12) but acyl/free carnitine ratio was smaller in the infants who were small for gestational age than in infants of appropriate weight (0.56 v 5.5). The results indicate that the slow elimination of fat from the circulation in preterm infants less mature than 32 weeks of gestation can hardly be explained by low lipoprotein lipase activity.

L-carnitine therapy in home parenteral nutrition patients with abnormal liver tests and low plasma carnitine concentrations

Persistent abnormalities of liver function tests occur in approximately 15% of home parenteral nutrition (HPN) patients and are associated with steatosis, steatohepatitis, and, rarely, fibrosis or cirrhosis. Approximately one-third of patients with gut failure on long-term HPN have low total and free plasma carnitine concentrations, and it has been suggested that a deficiency of L-carnitine may be responsible for the steatosis and steatohepatitis in HPN patients. To determine whether administration of L-carnitine is capable of reversing steatosis in HPN patients, 4 adult women on HPN for a mean of 53 mo (range 21-80 mo) were studied before and after 1 mo of intravenous L-carnitine supplementation (1 g/day). All patients had abnormalities in standard liver function tests and low total and free plasma carnitine values. The mean total and free plasma carnitine concentrations and the mean total hepatic carnitine concentration were reduced before supplementation and rose to normal values after treatment (27.4 +/- 2.3 to 35.5 +/- 3.1 nmol/ml, 19.4 +/- 2.8 to 25.7 +/- 2.5 nmol/ml, and 3.5 +/- 0.65 to 6.5 +/- 1.2 nmol/mg of noncollagen protein, respectively). However, there were no significant changes in mean serum aspartate aminotransferase and alkaline phosphatase levels (65 +/- 21 vs. 54 +/- 12 IU and 429 +/- 220 vs. 472 +/- 224 IU, respectively), plasma free fatty acids, plasma triglycerides, hepatic free fatty acid and triglyceride concentrations, or the grade of hepatic steatosis on light microscopy. These results suggest that carnitine deficiency is not a major cause of steatosis and steatohepatitis in patients receiving HPN.

The metabolic effects of oral L-carnitine administration in infants receiving total parenteral nutrition with fat

beta-Oxidation, an important pathway in the metabolism of free fatty acids, occurs within the mitochondria in mammals. L-Carnitine is an essential cofactor in the transfer of long-chain fatty acids across the inner mitochondrial membrane. Maintenance of normal carnitine concentrations in whole blood and tissues, either through diet or biosynthesis, would appear necessary for adequate utilization of fat as an energy source. Infants, especially premature ones, without an exogenous dietary source of carnitine, have decreased plasma carnitine levels compared with infants receiving carnitine-supplemented feedings. To determine the importance of carnitine supplementation in a total parenteral nutrition program in infants in which a fat emulsion serves as a major calorie source, the following study was undertaken. Twelve infants receiving total parenteral nutrition (TPN) with fat for seven days were divided into two treatment groups. Group 1 was orally supplemented for seven days with carnitine (70 mumol/l/kg/24 h in 24 mL of 5% dextrose), while the second group received seven days of placebo supplementation (dextrose 5%, 24 cc/24 h). Plasma carnitine levels in the carnitine-supplemented group were significantly higher (29 +/- 8 nmol/mL) than in the control group (12.4 +/- 3.5 nmol/mL) after seven days of treatment. However, clearance of serum triglycerides and free fatty acids was not significantly different between the two groups. Baseline triglyceride levels in the carnitine-supplemented group were 96 +/- 42 mg/dL, increased to 242 +/- 101 mg/dL after the lipid challenge and decreased to 121 +/- 47 mg/dL two hours after the lipid infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Carnitine deficiency

Carnitine is an essential cofactor in the transfer of long-chain fatty acids across the inner mitochondrial membrane. Carnitine is metabolized from lysine, trimethyllysine and butyrobetaine. Butyrobetaine undergoes hydroxylation in the liver, brain and kidney to form carnitine which in turn is transported via the plasma to the heart and skeletal muscle where it is important for allowing beta oxidation of fatty acids. Three clinical forms of carnitine deficiency have been described: myopathic, systemic and mixed forms. Carnitine deficiency results in accumulation of neutral lipid within skeletal muscle, myocardium and liver. Ultrastructurally, myofibrils are disrupted and there is an accumulation of large aggregates of mitochondria and lipid deposits within the skeletal muscle and myocardium. Carnitine therapy has been effective in the treatment of the myopathic and some cases of systemic and mixed forms. Several syndromes of secondary carnitine deficiency have been described; these may be secondary to genetic defects of intermediary metabolism and to other conditions, particularly following hemodialysis.

Total parenteral nutrition in children

This article first focuses on the indications for total parenteral nutrition and the effect of its use on the outcome of various nutrient-depleting diseases in infants and children. This is followed by a discussion of some of the newer nutrient additions to total parenteral nutrition regimens, such as biotin, carnitine, zinc, copper, iron, and others.

Does long-term home parenteral nutrition in adult patients cause chronic liver disease?

Sixty patients with gut failure were treated with home parenteral nutrition for 2000 patient months. Fifty-one of these 60 patients had either no abnormalities or mild and transient elevations of their liver chemistries and did not have liver biopsies. Nine (15%) of 60 patients had abnormalities of liver tests that persisted from 8 to 95 months (median, 18 months) which prompted one or more liver biopsies per patient. Three patients had prolonged jaundice, one died of hepatic encephalopathy, and another with protracted intrahepatic cholestasis died following a biliary tract exploration. A third patient remains ill with signs and symptoms of chronic liver disease. Steatohepatitis was found in eight of the nine patients and was characterized by centrilobular and midzonal microvesicular and macrovesicular fatty changes with fat cysts, focal necrosis, and mixed inflammatory infiltrates. Centrilobular fibrosis was present in three patients and evidence of nodular regeneration in one. In the three patients demonstrating cholestasis, bile pigment was identified both in hepatocytes and canaliculi. Ceroid pigment in Kupffer cells was a consistent finding and much more severe than expected from the mildness of the hepatitis. Persistent abnormalities of liver chemistries in nine patients and progressive liver disease while receiving home parenteral nutrition in three patients are quite worrisome and suggest that home parenteral nutrition-associated steatohepatitis with or without cholestasis may progress to chronic liver disease.

Tolerance of intravenously administered lipid in newborns

The tolerance for intravenously administered Intralipid in 262 premature and sick newborns was studied. The serum concentrations of triglycerides and of free fatty acids were determined during total parenteral nutrition including Intralipid in a maximum daily dose of 2 g/kg. A serum concentration of 1.5 mmol/l or higher was found in 270 out of 985 triglyceride determinations (27.4%). In the 262 infants serum triglyceride concentrations were found elevated once or more in 117 cases (44.7%). Serum free fatty acids concentrations were normal. A highly significant inverse correlation (p less than 0.001) between birth weight and triglyceride level was found. Elevated serum triglyceride concentrations were observed especially in preterm small-for-gestational-age infants.

Effect of carnitine on lipid metabolism in the neonate. II. Carnitine addition to lipid infusion during prolonged total parenteral nutrition

The effect of carnitine administration on lipid metabolism and carnitine and acylcarnitine plasma values of newborn infants, given total parenteral nutrition for the first 7 days of life, was studied during a 4-hour infusion of Intralipid. An increase in plasma concentrations of total carnitine, free carnitine, and short-chain and long-chain acylcarnitine was found, but no significant change in triglycerides, free fatty acids, glycerol, or beta-hydroxybutyrate plasma values was noted, as compared with values obtained without carnitine administration. Moreover, the low free carnitine and short-chain and long-chain acylcarnitine plasma levels found in newborn infants after 7 days of total parenteral nutrition did not seem to impair the utilization of infused lipids. The results support the concept that the relation between the carnitine pool and lipid metabolism can be influenced by intravenous glucose infusion. Low carnitine plasma concentrations do not necessarily signify a depletion of body carnitine, and sufficient tissue carnitine concentrations can probably maintain good lipid utilization for an extended period.

Carnitine metabolism and inborn errors

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

Improved N-retention during L-carnitine-supplemented total parenteral nutrition

The influence of intravenously administered L-carnitine on lipid- and nitrogen-metabolism was studied during total parenteral nutrition of piglets (mean weight 4077 g; n = 9). The infusion protocol was divided into three isocaloric and isonitrogenous 48-hr periods. Amino acids (3 g/kg day) were administered throughout all three periods: 140 cal/kg/day were given as nonprotein calories, consisting only of glucose during period 1; during periods 2 and 3, an amount of glucose calorically equivalent to 4 g fat/kg/day was substituted with a lipid emulsion, and L-carnitine (1.5 mg/kg/day) was added in period 3. Key parameters of fat- and nitrogen-metabolism were determined during the entire regime. Indirect calorimetry was performed and the respiratory quotient calculated during all three periods. The results demonstrate a more effective lipolysis and oxidation of fatty acids during L-carnitine supplementation. These changes produce an increased energy gain from exogenously administered fat and a distinct improvement in nitrogen balance.

Carnitine deficiency in premature infants receiving total parenteral nutrition: effect of L-carnitine supplementation

To investigate whether L-carnitine supplementation may correct nutritional carnitine deficiency and associated metabolic disturbances in premature infants receiving total parenteral nutrition, an intravenous fat tolerance test (1 gm/kg Intralipid over four hours) was performed in 29 premature infants 6 to 10 days of age (15 receiving carnitine supplement 10 mg/kg . day L-carnitine IV, and 14 receiving no supplement). Total carnitine plasma values were normal or slightly elevated in supplemented but decreased in nonsupplemented infants. In both groups, fat infusion resulted in an increase in plasma concentrations of triglycerides, free fatty acids, D-beta-hydroxybutyrate, and short-chain and long-chain acylcarnitine, but total carnitine values did not change. After fat infusion, the free fatty acids/D-beta-hydroxybutyrate ratios were lower and the increase of acylcarnitine greater in supplemented infants of 29 to 33 weeks' gestation than in nonsupplemented infants of the same gestational age. This study provides evidence that premature infants of less than 34 weeks' gestation requiring total parenteral nutrition develop nutritional carnitine deficiency with impaired fatty acid oxidation and ketogenesis. Carnitine supplementation improves this metabolic disturbance.

Postnastal changes in the concentration of carnitine and acylcarnitines in the rat brain

The concentration of total and free carnitine (TC and FC) together with short-chain and long-chain acylcarnitines (SCAC and LCAC) has been determined in whole brain of female rats from birth to maturity. The concentration of TC and SCAC increases postnatally to reach a peak 10 days after birth. The concentration of LCAC is high relative to adult brain between 1 and 10 days of age before falling to a low level. The change in LCAC concentration correlates with previously described developmental changes of palmitoyl-CoA: carnitine acyl transferase activity and fatty acid oxidation. The ratio of LCAC/FC declines postnatally while the SCAC/FC ratio is high at birth and increases further in adult brain. The results are consistent with the concepts of carnitine participating in exchange of short-chain acyl groups and in the transfer of fatty acids into mitochondria as an alternative energy supply in neonatal rat brain.

Tissue carnitine concentrations after total parenteral nutrition with and without L-carnitine supplementation

The concentrations (mumoles/g dry weight) of total carnitine (TC), free carnitine (FC) and acylcarnitine (AC) were determined in skeletal muscle, heart, liver, kidney and brain cortex of male mini pigs (4000-5000 g) after seven days of total parenteral nutrition (TPN) with amino acids 5% (3.0g/kg/d), glucose (25g/kg/d) and lipids 20% (4g/kg/d). This regime was administered with L-carnitine supplementation (1.5 mg/kg/d; n = 7) (group 1) and without it (n = 5) (group 2). Orally alimented animals (n = 5) served as controls (group 3). (Average carnitine intake: 3 mg/d) Carnitine free TPN affected only the concentrations in muscle. TC was markedly reduced (3.6 +/- 0.8) when compared with oral controls (5.8 +/- 0.7) (p<0.01). This decrease was exclusively due to AC, whereas FC concentrations remained almost unchanged. In group 1 the concentrations of TC in skeletal muscle, heart and brain cortex were higher than in both the other groups. The increase was mainly due to AC and FC remained unchanged in heart and brain. The concentrations in liver and kidney were not affected by either carnitine free or carnitine supplemented TPN. AC, determined as described, consists almost entirely of acid soluble acetyl-carnitine, the major product of fatty acid oxidation. Since the AC concentrations were almost exclusively altered by the two TPN-regimes we conclude that the observed changes reflect regulatory changes of fatty acid oxidation. Thus the decrease of muscle TC in group 2 is considered a consequence of an insulin induced down regulation (plasma insulin: mean 20 muU/ml; maximum: 60 muU/ml) of fatty acid oxidation in consequence of high glucose intake (25 g/kg/d). The increased TC concentrations after carnitine supplemented TPN are discussed to reflect an enhancement of oxidative degradation of fatty acids as a pharmacological effect of L-carnitine.

Carnitine in human nutrition

The oxidation of long-chain fatty acids is carnitine-dependent. Indeed, only when they are bound to carnitine, in the form of acyl-carnitines, do fatty acids penetrate into the mitochondria to be oxidized. To meet the need for carnitine, animals depend on both endogenous synthesis and an exogenous supply. A diet rich in meat supplies a lot of carnitine, while vegetables, fruits, and grains furnish relatively little. Although it has a low molecular weight and acts at low doses in a vital metabolic pathway, carnitine should not be considered a vitamin, but rather a nutritive substance. Indeed, it seems that the diet of the adult human need not necessarily furnish carnitine: the healthy organism, given a balanced nutrition (sufficiently rich in lysine and methionine), may well be able to meet all its needs. Furthermore, it seems that a reduction of the exogenous supply of carnitine results in a lowering of its elimination in the urine. However, dietary carnitine is more important during the neonatal period. The transition from fetal to extrauterine life is accompanied by an increased role of lipids in meeting energy needs. This change is accompanied by a rise in the body of the levels of carnitine, which is mainly supplied in the maternal milk. Finally, this review briefly surveys the illnesses in which a dietary carnitine supplement proves useful.

Carnitine blood concentrations and fat utilization in parenterally alimented premature newborn infants

To investigate the relationships among carnitine intake, carnitine blood concentrations, and the ability to utilize exogenous fat, total carnitine, free carnitine, acylcarnitine, beta-hydroxybutyrate, free fatty acid and triglyceride plasma concentrations were measured in 26 parenterally alimented appropriate-for-gestational-age premature infants before and at the end of a four-hour infusion of Intralipid, 1 gm/kg body weight. There was an increase in plasma levels of AC, BOB, FFA, and TG, but a decrease of FC, TC was unaffected by the infusion, but strongly correlated with calculated carnitine intake. At the end of the fat infusion, AC and BOB were positively correlated, and FFA negatively correlated with TC. The results demonstrate the proportion of AC to FC to be an additional indicator of fatty acid utilization and suggest that decreased carnitine intake in premature infants may impair fatty acid oxidation and ketogenesis.

Fatal lipid storage myopathy with deficiency of cytochrome-c-oxidase and carnitine. A contribution to the combined cytochemical-finestructural identification of cytochrome-c-oxidase in longterm frozen muscle

Two newborn female siblings fell ill with apathy, failure of suckling and a generalized progressive muscular hypotonia. Death occured at the age of 7 weeks, obviously caused by impairment of respiratory musculature. Biochemical studies in one child revealed carnitine deficiency especially in skeletal muscle; hepatic encephalopathy was absent. Both children had a generalized hyperaminoaciduria, an unusual finding in primary carnitine deficiency. Besides fatty metamorphosis of the liver, bilateral hydroureters and tubular calcifications of both kidneys, morphological studies showed a generalized lipid storage myopathy which predominated in Type-I-fibres and was accentuated in the muscles of the neck. Enzymehistochemical electron microscopy in longterm frozen muscle demonstrated that cytochrome-c-oxidase activity was absent not only in myopathic but also in most of the morphological unchanged muscle fibres. Only some fibres and endothelial cells displayed normal activity of mitochondria. Biochemically no cytochrome aa3 (cytochrome-c-oxidase) could be found in skeletal muscle; cytochrome b was almost undetectable. --In newborns with fatal lipid storage myopathy and carnitine deficiency it seems necessary to look for additional defects in the respiratory chain. Enzyme histochemical electron microscopy is a sensitive method in identifying cytochrome-c-oxidase even after a 12 months period of storage.