Carnitine deficiency syndromes

Identifying the intervention mechanisms of polydatin in hyperuricemia model rats by using UHPLC-Q-Exactive Orbitrap mass spectroscopy metabonomic approach

Introduction

Polydatin is a biologically active compound found in mulberries, grapes, and Polygonum cuspidatum, and it has uric acid-lowering effects. However, its urate-lowering effects and the molecular mechanisms underlying its function require further study.

Methods

In this study, a hyperuricemic rat model was established to assess the effects of polydatin on uric acid levels. The body weight, serum biochemical indicators, and histopathological parameters of the rats were evaluated. A UHPLC-Q-Exactive Orbitrap mass spectrometry-based metabolomics approach was applied to explore the potential mechanisms of action after polydatin treatment.

Results

The results showed a trend of recovery in biochemical indicators after polydatin administration. In addition, polydatin could alleviate damage to the liver and kidneys. Untargeted metabolomics analysis revealed clear differences between hyperuricemic rats and the control group. Fourteen potential biomarkers were identified in the model group using principal component analysis and orthogonal partial least squares discriminant analysis. These differential metabolites are involved in amino acid, lipid, and energy metabolism. Of all the metabolites, the levels of L-phenylalanine, L-leucine, O-butanoylcarnitine, and dihydroxyacetone phosphate decreased, and the levels of L-tyrosine, sphinganine, and phytosphingosine significantly increased in hyperuricemic rats. After the administration of polydatin, the 14 differential metabolites could be inverted to varying degrees by regulating the perturbed metabolic pathway.

Conclusion

This study has the potential to enhance our understanding of the mechanisms of hyperuricemia and demonstrate that polydatin is a promising potential adjuvant for lowering uric acid levels and alleviating hyperuricemia-related diseases.

Embryonic exposure to acetyl-L-carnitine protects against valproic acid-induced cardiac malformation in zebrafish model

Worldwide, estimated counts of about 7.9 million children are born with serious birth defects. In addition to genetic factors, prenatal exposure to drugs and environmental toxicants represents a major contributing factor to congenital malformations. In earlier investigation, we explored cardiac malformation caused by valproic acid (VPA) during early developing stages of zebrafish. Since heart depends on mitochondrial fatty acid oxidative metabolism for energy demands in which carnitine shuttle has a major role, the present study aimed to investigate the effect of acetyl-L-carnitine (AC) against VPA-induced cardiac malformation in developing zebrafish. Initially, AC was subjected to toxicological evaluation, and two micromolar concentrations (25 µM and 50 µM) were selected for evaluation. A sub-lethal concentration of VPA (50 µM) was selected to induce cardiac malformation. The embryos were grouped and the drug exposures were made at 2.5 h post-fertilization (hpf). The cardiac development and functioning was monitored. A progressive decline in cardiac functioning was noted in group exposed to VPA 50 µM. At 96 hpf and 120 hpf, the morphology of heart was severely affected with the chambers which became elongated and string-like accompanied by histological changes. Acridine orange staining showed accumulation of apoptotic cells. Group exposed to VPA 50 µM with AC 50 µM showed a significant reduction in pericardial sac edema with morphological, functional and histological recovery in developing heart. Moreover, reduced number of apoptotic cells was noted. The improvement with AC might be due to restoration of carnitine homeostasis for cardiac energy metabolism in developing heart.

Development of a highly sensitive Prussian-blue-based enzymatic biosensor for L-carnitine employing the thiol/disulfide exchange reaction

This is the first report of conducting proof-of-concept study for amperometric acetyltransferase-based L-carnitine sensor by employing the thiol/disulfide exchange reaction. The carnitine acetyltransferase (CrAT) catalyzes the reaction between acetyl-CoA and L-carnitine to produce CoA which is difficult to detect directly by electrochemical methods owing to steric hindrance and electrostatic effect of CoA. The thiol/disulfide exchange reaction between CoA and cystamine was mediated in the enzymatic reaction to produce electrochemically detectable low molecular weight of cationic cysteamine. The sensor exhibited high sensitivity and selectivity for L-carnitine in the concentration range 0.28-50 µM with a limit of detection of 0.28 µM. This is a promising strategy for L-carnitine sensing in point-of-care testing applications.

Carnitines as Mitochondrial Modulators of Oocyte and Embryo Bioenergetics

Recently, the importance of bioenergetics in the reproductive process has emerged. For its energetic demand, the oocyte relies on numerous mitochondria, whose activity increases during embryo development under a fine regulation to limit ROS production. Healthy oocyte mitochondria require a balance of pyruvate and fatty acid oxidation. Transport of activated fatty acids into mitochondria requires carnitine. In this regard, the interest in the role of carnitines as mitochondrial modulators in oocyte and embryos is increasing. Carnitine pool includes the un-esterified l-carnitine (LC) and carnitine esters, such as acetyl-l-carnitine (ALC) and propionyl-l-carnitine (PLC). In this review, carnitine medium supplementation for counteracting energetic and redox unbalance during in vitro culture and cryopreservation is reported. Although most studies have focused on LC, there is new evidence that the addition of ALC and/or PLC may boost LC effects. Pathways activated by carnitines include antiapoptotic, antiglycative, antioxidant, and antiinflammatory signaling. Nevertheless, the potential of carnitine to improve energetic metabolism and oocyte and embryo competence remains poorly investigated. The importance of carnitine as a mitochondrial modulator may suggest that this molecule may exert a beneficial role in ovarian disfunctions associated with metabolic and mitochondrial alterations, including PCOS and reproductive aging.

Nodding Syndrome: A Scoping Review

Nodding syndrome (NS) is a debilitating yet often neglected neurological disease affecting thousands of children in several sub-Saharan African countries. The cause of NS remains unknown, and effective treatment options are lacking. Moreover, knowledge regarding NS is scarce and is based on a limited number of publications, with no comprehensive overview published to date. Therefore, the aim of this scoping review was to summarise the current evidence and identify existing knowledge gaps in order to help clinicians, scientists, and policymakers develop guidelines for prioritising this severe condition. We searched the Medline (Ovid), Embase (Ovid), Scopus, and Global Health Library databases in accordance with the PRISMA extension for scoping review guidance and in accordance with the Joanna Briggs Institute guidelines and methodology for a scoping review, using keywords describing NS. We then extracted and presented the original data regarding the epidemiology, aetiology, pathophysiology, clinical features, diagnosis, management, and outcomes of NS, as well as community perceptions and the psychosocial and economic impact of NS. Out of 1470 identified articles, a total of 69 were included in this scoping review. Major gaps exist in understanding the aetiology and pathogenesis of NS. Future research is urgently needed not only to address these gaps, but also to study the treatment options, epidemiology, and psychosocial and economic impacts of NS. Innovative interventions and rehabilitation programmes designed to address the psychosocial and economic burdens associated with NS are also urgently needed.

Carnitine Serum Levels in Frail Older Subjects

Frailty is an expression that reconciles and condenses loss of autonomy, both physical and cognitive decline and a wide spectrum of adverse outcomes due to aging. The decrease in physical and cognitive activity is associated with altered mitochondrial function, and energy loss and consequently morbidity and mortality. In this cross-sectional study, we evaluated the carnitine levels in frailty status. The mean serum concentrations of total carnitine (TC) were lower in frail elderly subjects than in prefrail ones (p = 0.0006), higher in frail vs. robust subjects (p < 0.0001), and higher in prefrail vs. robust subjects (p < 0.0001). The mean serum concentrations of free carnitine (FC) were lower in frail elderly subjects than in prefrail ones (p < 0.0001), lower in frail vs. robust subjects (p < 0.0001) and lower in prefrail vs. robust subjects (p = 0.0009). The mean serum concentrations of acylcarnitine (AC) were higher in frail elderly subjects than in prefrail ones (p = 0.054) and were higher in pre-frail vs. robust subjects (p = 0.0022). The mean urine concentrations of TC were lower in frail elderly subjects than in prefrail ones (p < 0.05) and lower in frail vs. robust subjects (p < 0.0001). The mean urine concentrations of free carnitine were lower in frail elderly vs. robust subjects (p < 0.05). The mean urine concentrations of acyl carnitines were lower in frail elderly subjects than those in both prefrail (p < 0.0001) and robust subjects (p < 0.0001). Conclusion: high levels of carnitine may have a favorable effect on the functional status and may treat the frailty status in older subjects.

The longitudinal effects of seated isometric yoga on blood biomarkers, autonomic functions, and psychological parameters of patients with chronic fatigue syndrome: a pilot study

Background

In a previous randomized controlled trial, we found that practicing seated isometric yoga regularly for 2 months improved the fatigue of patients with chronic fatigue syndrome (CFS) who are resistant to conventional therapy. The aim of this pilot study was to investigate the possible mechanisms behind this finding by comparing blood biomarkers, autonomic nervous function, and psychological indices before versus after an intervention period of seated isometric yoga practice.

Methods

Fifteen patients with CFS who did not show satisfactory improvements after at least 6 months of conventional therapy practiced seated isometric yoga (biweekly 20-min sessions with a yoga instructor and daily practice at home) for 2 months. The longitudinal effects of seated isometric yoga on fatigue, blood biomarkers, autonomic function, and psychological state were investigated by comparing the following parameters before and after the intervention period: Fatigue severity was assessed by the Chalder fatigue scale (FS) score. Levels of the blood biomarkers cortisol, DHEA-S, TNF-α, IL-6, prolactin, carnitine, TGF-β1, BDNF, MHPG, HVA, and α-MSH were measured. The autonomic nervous functions assessed were heart rate (HR) and HR variability. Psychological indices included the 20-item Toronto Alexithymia Scale (TAS-20) and the Hospital Anxiety and Depression Scale (HADS).

Results

Practicing seated isometric yoga for 2 months resulted in significant reductions in the Chalder FS (P = 0.002) and HADS-depression (P = 0.02) scores. No significant changes were observed in any other parameter evaluated. The change in Chalder FS score was not correlated with the change in HADS-depression score. However, this change was positively correlated with changes in the serum TNF-α levels (P = 0.048), the high frequency component of HR variability (P = 0.042), and TAS-20 scores (P = 0.001).

Conclusions

Regular practice of seated isometric yoga for 2 months reduced the fatigue and depressive symptom scores of patients with CFS without affecting any other parameters we investigated. This study failed to identify the markers responsible for the longitudinal fatigue-relieving effect of seated isometric yoga. However, considering that the reduced fatigue was associated with decreased serum TNF-α level and TAS-20 scores, fatigue improvement might be related to reduced inflammation and improved alexithymia in these patients.

Trial registration

University Hospital Medical Information Network (UMIN CTR) UMIN000009646. Registered Dec 27, 2012.

CMOS-compatible biosensor for L-carnitine detection

A CMOS-compatible ISFET with a Ta₂O₅ sensitive surface was developed. The structure was optimized for achieving high sensitivity using a subthreshold operation mode and by reducing the influence of the capacitances on the value of subthreshold swing. The developed ISFET was used as a basis for a biosensor for L-carnitine detection. To this end, carnitine acetyltransferase was immobilized on the ISFET sensitive surface. The immobilized enzyme was active (0.082 U/g _{model plate}). The complete microsystem, consisting of a packaged chip, an immobilized enzyme and a microfluidic channel, detected L-carnitine at a range of 0.2-100 μM with a LOD of 0.2 μM. The biosensor response was linear in the range of 0.2-50 μM of L-carnitine with sensitivity 18.0 ± 1.7 mV/μM. An experiment with artificial urine containing 1.3 μM L-carnitine showed that the proposed biosensor could be used on a real sample. Therefore, a new sensor specially optimized for biosensing CMOS-compatible ISFET structures and direct determination of L-carnitine with immobilized carnitine acetyltransferase was developed.

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.

Comparison of serum carnitine levels and clinical correlates between outpatients and acutely hospitalised individuals with bipolar disorder and schizophrenia: A cross-sectional study

OBJECTIVES

We sought to compare serum carnitine levels and clinical correlates between stable outpatients and acutely hospitalised individuals with diagnoses of bipolar disorder and schizophrenia.

METHODS

We obtained clinical information as well as serum levels for total and free carnitine, high-density lipoprotein (HDL) and triglycerides in 60 consenting individuals.

RESULTS

We found higher total serum carnitine levels in our outpatient group in comparison to acutely hospitalised psychiatric patients, with a statistically significant P value of 0.045. Metabolic syndrome was more prevalent in the outpatient (37.9%) versus inpatient group (16.1%). We identified significantly higher carnitine levels in patients who met the criteria for metabolic syndrome in comparison to the patients without metabolic syndrome, with respective P values for total and free carnitine of 0.0048 and 0.0029.

CONCLUSIONS

This study revealed a complex relationship among carnitine metabolism, metabolic syndrome and behavioural outcomes. Future studies of carnitine metabolism in the context of mental illness as well as metabolic syndrome are warranted.

Serum carnitine as an independent biomarker of malnutrition in patients with impaired oral intake

Carnitine is a vitamin-like compound that plays important roles in fatty acid β-oxidation and the control of the mitochondrial coenzyme A/acetyl-CoA ratio. However, carnitine is not added to ordinary enteral nutrition or total parenteral nutrition. In this study, we determined the serum carnitine concentrations in subjects receiving ordinary enteral nutrition (EN) or total parenteral nutrition (TPN) and in patients with inflammatory bowel diseases to compare its levels with those of other nutritional markers. Serum samples obtained from 11 EN and 11 TPN patients and 82 healthy controls were examined. In addition, 10 Crohn’s disease and 10 ulcerative colitis patients with malnutrition who were barely able to ingest an ordinary diet were also evaluated. Carnitine and its derivatives were quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The carnitine concentrations in EN and TPN subjects were significantly lower compared with those of the control subjects. Neither the serum albumin nor the total cholesterol level was correlated with the carnitine concentration, although a significant positive correlation was found between the serum albumin and total cholesterol levels. Indeed, patients with CD and UC showed significantly reduced serum albumin and/or total cholesterol levels, but their carnitine concentrations remained normal. In conclusion, only a complete blockade of an ordinary diet, such as EN or TPN, caused a reduction in the serum carnitine concentration. Serum carnitine may be an independent biomarker of malnutrition, and its supplementation is needed in EN and TPN subjects even if their serum albumin and total cholesterol levels are normal.

Carnitine Profile and Effect of Suppletion in Children with Renal Fanconi Syndrome due to Cystinosis

BACKGROUND

Cystinosis is an autosomal recessive disorder marked by intralysosomal cystine accumulation. Patients present with generalized proximal tubular dysfunction called renal Fanconi syndrome. Urinary carnitine loss results in plasma and muscle carnitine deficiency, but no clinical signs of carnitine deficiency have been described. Also, the optimal dose of carnitine supplementation is undefined. This study aimed to determine whether currently recommended carnitine doses result in adequate correction of plasma carnitine.

METHODS

Five cystinosis patients with renal Fanconi syndrome, aged 2-18 years, were included. L-carnitine was prescribed 50 mg/kg/day since diagnosis: median 36 (range 18-207) months. Total and free plasma and urine carnitine and carnitine profiles were measured at study onset, after stopping L-carnitine for 3 months and 3 months after reintroducing L-carnitine 50 mg/kg/day.

RESULTS

At study onset, plasma free carnitine was normal in all patients, total carnitine (1/5), acetylcarnitine (3/5), and several short- and medium-chain acylcarnitines ≤10 carbons (5/5) were increased indicating carnitine over-supplementation. Three months after cessation, carnitine profiles normalized and 3/5 patients showed plasma carnitine deficiency. Three months after reintroduction, plasma free carnitine normalized in all patients, however, carnitine profiles were disturbed in 4/5 patients. Urine free carnitine, acetylcarnitine, and acylcarnitines ≤10 carbons were increased in all patients independent of carnitine supplementation.

CONCLUSION

Administration of recommended doses L-carnitine (50 mg/kg/day) resulted in over-supplementation. Although the drug is considered to be rather safe, long-term effects of over-supplementation remain unknown warranting cautious use of high doses. Plasma carnitine profile might be used as a monitor, to prevent overdosing.

L-carnitine supplementation as a potential antioxidant therapy for inherited neurometabolic disorders

In recent years increasing evidence has emerged suggesting that oxidative stress is involved in the pathophysiology of a number of inherited metabolic disorders. However the clinical use of classical antioxidants in these diseases has been poorly evaluated and so far no benefit has been demonstrated. l-Carnitine is an endogenous substance that acts as a carrier for fatty acids across the inner mitochondrial membrane necessary for subsequent beta-oxidation and ATP production. Besides its important role in the metabolism of lipids, l-carnitine is also a potent antioxidant (free radical scavenger) and thus may protect tissues from oxidative damage. This review addresses recent findings obtained from patients with some inherited neurometabolic diseases showing that l-carnitine may be involved in the reduction of oxidative damage observed in these disorders. For some of these diseases, reduced concentrations of l-carnitine may occur due to the combination of this compound to the accumulating toxic metabolites, especially organic acids, or as a result of protein restricted diets. Thus, l-carnitine supplementation may be useful not only to prevent tissue deficiency of this element, but also to avoid oxidative damage secondary to increased production of reactive species in these diseases. Considering the ability of l-carnitine to easily cross the blood-brain barrier, l-carnitine supplementation may also be beneficial in preventing neurological damage derived from oxidative injury. However further studies are required to better explore this potential.

Serum carnitine levels and levocarnitine supplementation in institutionalized Huntington's disease patients

Along with antioxidant properties, carnitine is an important regulator of lipid metabolism in humans. While beneficial effects of carnitine have been demonstrated in animal models of Huntington's disease (HD), metabolism of carnitine has not been studied in humans with this illness. In this retrospective database review from 23 patients admitted to a HD-specialized nursing home unit, we found a relatively high prevalence of hypocarnitinemia (6 cases, 26%). Our review suggests that catabolism and chronic valproate use predisposed our patients to develop hypocarnitinemia. The patients with low serum carnitine levels who received levocarnitine supplementation, during a mean period of 7.3 months, showed improvement in motor, cognitive and behavioral measures. We hypothesize that observed improvement related to the resolution of reversible metabolic encephalopathy and myopathy associated with secondary carnitine deficiency. In conclusion, notwithstanding its limitations, this is the first study to report measurements of carnitine levels in HD patients, revealing relatively high prevalence of hypocarnitinemia in our population. Our findings suggest that HD patients with hypocarnitinemia may benefit from low-dose levocarnitine supplementation. Further studies of carnitine metabolism and supplementation in HD patients are warranted.

Clinical correlates of low serum carnitine levels in hospitalized psychiatric patients

OBJECTIVE

We sought to evaluate clinical correlates of low serum carnitine levels in hospitalized psychiatric patients.

METHODS

We retrospectively reviewed the charts of 40 psychiatric inpatients identified to have low serum carnitine levels.

RESULTS

Cognitive impairment was present in 38 (95%) cases, frequently accompanied by imbalance, agitation and extrapyramidal symptoms. Valproate therapy was encountered in 28 (70%) patients. The dosage of valproate negatively correlated with total and free carnitine levels (P = 0.003 and 0.0136). Polypharmacy also affected carnitine levels, indicating additional modulatory effects on carnitine metabolism. We encountered a disproportionately high prevalence of mental retardation and dementia in association with hypocarnitinemia.

CONCLUSION

We hypothesize that in the context of mental illness hypocarnitinemia may be associated with metabolic encephalopathy and cognitive impairment. As carnitine deficiency is a potentially treatable condition further studies are warranted.

Role of carnitine in disease

Carnitine is a conditionally essential nutrient that plays a vital role in energy production and fatty acid metabolism. Vegetarians possess a greater bioavailability than meat eaters. Distinct deficiencies arise either from genetic mutation of carnitine transporters or in association with other disorders such as liver or kidney disease. Carnitine deficiency occurs in aberrations of carnitine regulation in disorders such as diabetes, sepsis, cardiomyopathy, malnutrition, cirrhosis, endocrine disorders and with aging. Nutritional supplementation of L-carnitine, the biologically active form of carnitine, is ameliorative for uremic patients, and can improve nerve conduction, neuropathic pain and immune function in diabetes patients while it is life-saving for patients suffering primary carnitine deficiency. Clinical application of carnitine holds much promise in a range of neural disorders such as Alzheimer's disease, hepatic encephalopathy and other painful neuropathies. Topical application in dry eye offers osmoprotection and modulates immune and inflammatory responses. Carnitine has been recognized as a nutritional supplement in cardiovascular disease and there is increasing evidence that carnitine supplementation may be beneficial in treating obesity, improving glucose intolerance and total energy expenditure.

Clinical outcomes and low-dose levocarnitine supplementation in psychiatric inpatients with documented hypocarnitinemia: a retrospective chart review

BACKGROUND

Metabolic encephalopathy is one of the crucial manifestations of carnitine deficiency. In psychiatric patients, low serum carnitine levels may result from chronic valproate therapy. Despite the widespread use of valproate in psychiatry, neither carnitine deficiency nor supplementation has been studied in a psychiatric population.

OBJECTIVE

To describe clinical outcomes in hospitalized psychiatric patients with documented hypocarnitinemia who were receiving oral levocarnitine supplementation.

METHOD

Retrospective chart review.

RESULTS

In 38 patients with hypocarnitinemia, a low-dose oral levocarnitine supplementation, in association with comprehensive psychiatric therapy, did not result in any adverse psychiatric or medical outcomes, and was associated with overall improved behavioral, cognitive, and motor functioning. Initially all patients had some degree of cognitive impairment, but after correction of carnitine serum levels, scores on the Mini-Mental State Examination (MMSE) improved in most of the patients (mean improvement 5.5 points, P <0.0001), and normalized in 11 cases. This allowed a correction of the diagnosis in 8 of 14 patients who had initially been diagnosed with dementia. African-American patients achieved significantly lower serum carnitine levels and MMSE scores than Caucasian patients with comparable therapy.

CONCLUSION

We hypothesize that correction of carnitine depletion, either by levocarnitine supplementation or by valproate dose reduction, may enhance recovery from hypocarnitinemia-associated encephalopathy in psychiatric patients. Our findings also suggest that ethnic traits may affect carnitine bioavailability as well as cognitive outcomes in this clinical context. Further studies of carnitine metabolism and supplementation in psychiatric patients are warranted.

Carnitine/organic cation transporter OCTN2 (Slc22a5) is responsible for renal secretion of cephaloridine in mice

Carnitine/organic cation transporter (OCTN) 2 (SLC22A5) plays a pivotal role in renal tubular reabsorption of carnitine, a vitamin-like compound, on apical membranes of proximal tubules, but its role in relation to therapeutic drugs remains to be clarified. The purpose of the present study was to elucidate the involvement of OCTN2 in renal disposition of a beta-lactam antibiotic, cephaloridine (CER), based on experiments with juvenile visceral steatosis (jvs) mice, which have a functional deficiency of the octn2 gene. Renal clearance of CER during constant intravenous infusion in wild-type mice was much higher than could be accounted for by glomerular filtration, but was decreased by increasing the infusion rate with minimal change in kidney-to-plasma concentration ratio, suggesting the existence of saturable transport mechanism(s) across the apical membranes. The plasma concentration profile and kidney-to-plasma concentration ratio after intravenous injection in jvs mice were higher than those in wild-type mice, whereas renal clearance in jvs mice was much lower than that in wild-type mice and could be accounted for by glomerular filtration. Uptake of CER by mouse OCTN2 was shown in Xenopus laevis oocytes expressing mouse OCTN2. The CER transport by OCTN2 exhibited saturation with K(m) of approximately 3 mM, which is similar to the renal CER concentration exhibiting saturation in renal clearance in vivo. The OCTN2-mediated CER transport was inhibited by carnitine and independent of Na(+) replacement in the medium. These results show OCTN2 on apical membranes of proximal tubules plays a major role in renal secretion of CER in mice.

A case of early diagnosed carnitine deficiency presenting with respiratory symptoms

INTRODUCTION

Carnitine deficiency is an autosomal recessively inherited disease characterized by a low carnitine concentration in plasma and tissues. Primary carnitine deficiency (PCD) is caused by a deficiency in the plasma membrane carnitine transporter, with urinary carnitine wasting causing systemic carnitine depletion. The most common presentation of PCD is hypoketotic hypoglycemic encephalopathy. Cardiomyopathy can also be seen.

CASE REPORT

A 9-month-old girl was admitted to our clinic with wheezing, respiratory distress and nighttime cough. She was pale, expirium was prolonged, breath sounds were coarse bilaterally and were increased in the right hemithorax.

RESULTS

She had hypochromic microcytic anemia and the serum CPK level was elevated. Cardiothoracic index was increased (0.62). In the chest X-ray there was hyperaeration especially in the upper regions of the left lung, and paracardiac infiltration in the right lung. The echocardiogram showed dilated cardiomyopathy. In pulmonary perfusion scintigraphy, perfusion of the right lung was 26% and of the left lung 74%. Cardiomegaly and dilatation in main the pulmonary artery was detected in the MR angiogram. Plasma carnitine and acylcarnitine levels were found to be significantly low. Fat accumulation in myocytes and rare atrophic fibers were detected in a muscle biopsy. Oral carnitine supplementation was started at a dose of 100 mg/kg. All the symptoms and findings regressed within a short period of time.

DISCUSSION

This case was presented to emphasize that carnitine deficiency can present with respiratory tract symptoms like wheezing and recurrent respiratory tract infections. Although PCD usually presents with hypoketotic hypoglycemia in infants, it also has to be suspected in the etiology of dilated cardiomyopathy. Treatment is very easy and lifesaving once the correct diagnosis is made, and the prognosis is excellent with lifelong carnitine supplementation.

Serum carnitine levels in children with iron-deficiency anemia with or without pica

Carnitine is ingested through animal-derived foods as well as synthesized in vivo. It plays an important role in the energy metabolism of many tissues. Iron acts as a co-factor for the synthesis of carnitine. However, the importance of iron deficiency as a cause of secondary carnitine deficiency is not well established. The aim of this study was to investigate the serum levels of carnitine in children with iron-deficiency anemia compared to those of healthy children and to determine if serum carnitine levels in with or without pica differ. The mean serum carnitine concentration in the iron-deficiency group was significantly lower than that in healthy children (12.44+/- 5.09 and 32.48 +/- 7.92 micromol/L, respectively, p < .001). In the iron-deficient group, serum carnitine levels, ferritin levels, and other hematological parameters were lowest in patients with pica (p < .001). Pearson correlation test indicated a positive correlation between serum carnitine and ferritin levels in iron-deficient patients. Based on the evidence about the effect of low iron on carnitine stores in animal studies, the authors propose that low serum carnitine levels in these children may be secondary to iron-deficiency anemia. However, further large-scale studies are needed to establish the frequency of carnitine deficiency in children with iron-deficiency anemia.

Is sudden death with vitamin C deficiency caused by lack of carnitine?

We investigated the effect of carnitine supplementation during vitamin C (ASC) deficiency by measuring the levels of ASC and carnitine in plasma and cardiac muscle cells (CMC), and histological analysis with electron microscopy. The levels of carnitine were significantly decreased in ASC-deficient rats in plasma and the heart than those in the control. In carnitine supplemented ASC-deficient rats, a significant increase of carnitine levels were observed in both plasma and heart. The number of lipid droplets significantly increased in the ASC-deficient rats compared to the control rats, but did not increase in carnitine supplemented rats. These results indicate that ASC deficiency causes a generalized mitochondrial abnormality and accumulation of lipid droplets in CMC as observed in carnitine deficiency, and supplementation of carnitine prevented these changes even in the presence of ASC deficiency.

Hypocarnitinaemia Induced by Sodium Pivalate in the Rat is Associated with Left Ventricular Dysfunction and Impaired Energy Metabolism

Carnitine is a naturally occurring compound that is essential in energy metabolism of the mammalian heart. In addition to its essential role in facilitating beta-oxidation, carnitine eliminates excess toxic acyl residues and regulates the mitochondrial acetyl coenzyme A (CoA)/CoA ratio. Thus, it is not surprising that patients with carnitine deficiency syndromes exhibit defects in energy metabolism and in some cases demonstrate left ventricular dysfunction. Pivalic acid is commonly used to create prodrugs, such as pivampicillin and pivmecillinam, to facilitate enteral absorption and increase oral bioavailability. Pivalic acid released from the drug following absorption readily forms an ester with carnitine, which is then excreted as pivaloylcarnitine. Sustained loss of carnitine in the form of this ester induces a state of carnitine deficiency, exemplified by low plasma and tissue carnitine content. This review examines the effects in the rat of short- and long-term sodium pivalate treatment on: (1) cardiac carnitine content; (2) in vitro mechanical function; (3) markers of glycolytic and fatty acid metabolism; and (4) energy substrate metabolism. Treatment with sodium pivalate induces a gradual loss of cardiac carnitine content for up to 12 weeks. Doubling the duration of treatment is not associated with any further decrease in cardiac carnitine content. While heart function following short-term treatment (2 weeks) is normal under aerobic conditions, impaired recovery of function following ischaemia is seen. In contrast, long-term treatment (11-28 weeks) is associated with impaired heart function, which is dependent on workload and substrate availability. Impaired heart function is also associated with reductions in activity of 3-hydroxyacyl CoA dehydrogenase and rates of fatty acid oxidation. However, to maintain adenosine triphosphate production, glucose metabolism, expressed as hexokinase activity and glucose oxidation, is increased in carnitine-deficient hearts. Hearts from sodium pivalate-treated animals demonstrate a cardiomyopathy that is dependent on duration of treatment, workload and substrate supply. This model of hypocarnitinaemia may thus be useful to study the metabolic and cardiac consequences of carnitine-deficiency syndromes.

Relative carnitine deficiency in autism

A random retrospective chart review was conducted to document serum carnitine levels on 100 children with autism. Concurrently drawn serum pyruvate, lactate, ammonia, and alanine levels were also available in many of these children. Values of free and total carnitine (p < 0.001), and pyruvate (p = 0.006) were significantly reduced while ammonia and alanine levels were considerably elevated (p < 0.001) in our autistic subjects. The relative carnitine deficiency in these patients, accompanied by slight elevations in lactate and significant elevations in alanine and ammonia levels, is suggestive of mild mitochondrial dysfunction. It is hypothesized that a mitochondrial defect may be the origin of the carnitine deficiency in these autistic children.

Structural and mutational characterization of L-carnitine binding to human carnitine acetyltransferase

We report the crystal structure of a binary complex of human peroxisomal carnitine acetyltransferase and the substrate l-carnitine, refined to a resolution of 1.8 Angstrom with an R(factor) value of 18.9% (R(free)=22.3%). L-carnitine binds to a preformed pocket in the active site tunnel of carnitine acetyltransferase aligned with His(322). The quaternary nitrogen of carnitine forms a pi-cation interaction with Phe(545), while Arg(497) forms an electrostatic interaction with the negatively charged carboxylate group. An extensive hydrogen bond network also occurs between the carboxylate group and Tyr(431), Thr(444), and a bound water molecule. Site-directed mutagenesis and kinetic characterization reveals that Tyr(431), Thr(444), Arg(497), and Phe(545) are essential for high affinity binding of L-carnitine.

Prevention of ammonia and glutamate neurotoxicity by carnitine: molecular mechanisms

Carnitine has beneficial effects in different pathologies and prevents acute ammonia toxicity (ammonia-induced death of animals). Acute ammonia toxicity is mediated by excessive activation of the NMDA-type of glutamate receptors, which mediates glutamate neurotoxicity. We showed that carnitine prevents glutamate neurotoxicity in primary cultures of cerebellar neurons. This supports the idea that the protective effect of carnitine against ammonia toxicity is due to the protective effect against glutamate neurotoxicity. We are studying the mechanism by which carnitine protects against glutamate neurotoxicity. Carnitine increases the binding affinity of glutamate for metabotropic glutamate receptors. The protective effect of carnitine is lost if metabotropic glutamate receptors are blocked with specific antagonists. Moreover, activation of metabotropic glutamate receptors by specific agonists also prevents glutamate neurotoxicity. This indicates that the protective effect of carnitine against glutamate neurotoxicity is mediated by activation of metabotropic glutamate receptors. The molecule of carnitine has a trimethylamine group. Different compounds containing a trimethylamine group (carbachol, betaine, etc.) also prevent ammonia-induced animal death and glutamate-induced neuronal death. Moreover, metabotropic glutamate receptor antagonists also prevent the protective effect of most of these compounds. We summarize here some studies aimed to identify the mechanism and the molecular target that are responsible for the protective effect of carnitine against ammonia and glutamate neurotoxicity. Finally it is also shown that carnitine inhibits the hydrolysis of inositol phospholipids induced by activation of different types of metabotropic receptors, but this effect seems not responsible for its protective effects.

Medium-term open label trial of L-carnitine in Rett syndrome

Treatment strategies in Rett syndrome so far have been essentially symptomatic and supportive. In order to establish the medium-term effects of L-carnitine, an open label trial was performed in a cohort of 21 Rett syndrome females, with a control group of 62 Rett syndrome females of a similar age, for a 6-month period. Compared with the Rett syndrome controls, treatment with L-carnitine led to significant improvements in sleep efficiency (P=0.027), especially in the subjects with a baseline sleep efficiency less than 90%, energy level (P<0.005) and communication skills (P=0.004). There was no significant difference in the subject's level of physical activity, hand function or in the quality of life of the subject's parents. In addition, before and after comparisons of the treatment group showed improvements in expressive speech (P=0.011). Treatment with L-carnitine seems to be of significant benefit in a subgroup of girls with Rett syndrome. In these girls, small but discernible improvements may be of considerable importance to their parents and carers.

Carnitine-deficient myopathy as a presentation of tyrosinemia type I

Carnitine deficiency secondary to renal Fanconi's tubulopathy has been described in only a few inborn errors of metabolism: cystinosis, galactosemia, and Fanconi-Bieckel syndrome. We report a 27-month-old infant who presented with a sudden change in gait owing to proximal muscle weakness. The laboratory evaluation showed carnitine deficiency associated with Fanconi's tubulopathy. Eventually, tyrosinemia type I was diagnosed. Carnitine deficiency can contribute to the clinical picture of hepatorenal tyrosinemia and should therefore be evaluated and treated.

Plasma and liver carnitine status of children with chronic liver disease and cirrhosis

BACKGROUND

Carnitine is an essential cofactor in the transfer of long-chain fatty acids across the inner mitochondrial membrane for oxidation. As its synthesis is performed in the liver, alterations in carnitine metabolism is expected in liver diseases, especially in cirrhosis.

METHODS

In this study, we investigated plasma and liver carnitine concentrations of 68 children with chronic liver disease, 36 of whom had cirrhosis as well. Carnitine level was determined by enzymatic method.

RESULTS

Plasma and liver carnitine concentrations were not correlated. Mean plasma carnitine level of cirrhotic children was significantly lower than that of the control group (P<0. 0001). While there was no difference between liver carnitine concentrations of children with chronic liver disease and cirrhosis (P>0.05), mean plasma level of cirrhotics were lower (P<0.05). Plasma carnitine was correlated with albumin, triglyceride and gamma glutamyl transpeptidase (GGT) in patients with chronic liver disease (P<0.05). Liver carnitine was correlated with GGT in cirrhotic patients (P<0.005). Children with malnutrition had higher plasma and liver carnitine levels (P<0.05). The highest plasma and liver carnitine levels were detected in children with biliary atresia and criptogenic cirrhosis, respectively. Both the lowest plasma and liver carnitine levels were detected in Wilson's disease.

CONCLUSION

Children with cirrhosis have low plasma carnitine concentrations. This finding is prominent in children with Wilson's disease. As carnitine is an essential factor in lipid metabolism, the carnitine supplementation for patients with cirrhosis in childhood, especially with Wilson's disease, seems to be mandatory.

Effect of gamma-butyrobetaine on fatty liver in juvenile visceral steatosis mice

We pharmacokinetically examined the effect of gamma-butyrobetaine, a precursor of L-carnitine, on the change of fatty acid metabolism in juvenile visceral steatosis (JVS) mice, which have systemic L-carnitine deficiency due to lack of L-carnitine transporter activity. The concentrations of total free fatty acid (FFA), palmitic acid and stearic acid in the liver of JVS mice were significantly higher than those in wild-type mice. After intravenous administration of gamma-butyrobetaine (50 mg kg(-1)), the concentration of L-carnitine in the plasma of JVS mice reached about twice that of the control level and levels in the brain, liver and kidney were also significantly increased, whereas those in wild-type mice hardly changed. Although the plasma concentrations of FFA in both types of mice were unchanged after administration of gamma-butyrobetaine, the concentrations of palmitic acid and stearic acid were significantly decreased. In particular, the liver concentration of FFA in JVS mice was decreased to the wild-type control level, accompanied by significant decreases in long-chain fatty acids, palmitic acid and stearic acid, whereas those in wild-type mice were not changed. These results suggest that gamma-butyrobetaine can be taken up into organs, including the liver, of JVS mice, and transformed to L-carnitine. Consequently, administration of gamma-butyrobetaine may be more useful than that of L-carnitine itself for treatment of primary deficiency of carnitine due to a functional defect of the carnitine transporter.

Carbamyl phosphate synthetase 1 deficiency: a destructive encephalopathy

Carbamyl phosphate synthetase I is a urea cycle enzyme. Severe deficiency of carbamyl phosphate synthetase I presents in the neonatal period as hyperammonemic encephalopathy with altered consciousness and occasional seizures after feeding begins. Episodes of altered consciousness with or without seizures and focal neurologic deficits are seen later with patients of partial carbamyl phosphate synthetase I deficiency. Fatal cerebral edema with brain herniation may develop on occasion. Three patients presenting with carbamyl phosphate synthetase I deficiency are reported with neuroimaging and pathologic findings illustrating the destructive encephalopathy with acute cerebral edema, followed by diffuse cerebral atrophy and occasional cystic encephalomalacia. The deterioration in carbamyl phosphate synthetase I deficiency occurs during the hyperammonemic crises. This deficiency may be difficult to treat despite the current advances in treatment strategies, especially in neonatal-onset patients with low carbamyl phosphate synthetase I activity.

Molecular and functional characterization of organic cation/carnitine transporter family in mice

Carnitine is essential for beta-oxidation of fatty acids, and a defect of cell membrane transport of carnitine leads to fatal systemic carnitine deficiency. We have already shown that a defect of the organic cation/carnitine transporter OCTN2 is a primary cause of systemic carnitine deficiency. In the present study, we further isolated and characterized new members of the OCTN family, OCTN1 and -3, in mice. All three members were expressed commonly in kidney, and OCTN1 and -2 were also expressed in various tissues, whereas OCTN3 was characterized by predominant expression in testis. When their cDNAs were transfected into HEK293 cells, the cells exhibited transport activity for carnitine and/or the organic cation tetraethylammonium (TEA). Carnitine transport by OCTN1 and OCTN2 was Na(+)-dependent, whereas that by OCTN3 was Na(+)-independent. TEA was transported by OCTN1 and OCTN2 but not by OCTN3. The relative uptake activity ratios of carnitine to TEA were 1.78, 11.3, and 746 for OCTN1, -2, and -3, respectively, suggesting high specificity of OCTN3 for carnitine and significantly lower carnitine transport activity of OCTN1. Thus, OCTN3 is unique in its limited tissue distribution and Na(+)-independent carnitine transport, whereas OCTN1 efficiently transported TEA with minimal expression of carnitine transport activity and may have a different role from other members of the OCTN family.

Can serum carnitine levels distinguish hypertrophic cardiomyopathy from hypertensive hearts?

Although echocardiography is a useful diagnostic tool in hypertrophic cardiomyopathy (HCM), it is sometimes difficult to differentiate it from hypertensive heart disease (HHD): some patients with HCM show symmetrical hypertrophy, whereas patients with HHD sometimes show asymmetrical septal hypertrophy. We used a radioiodinated long-chain fatty acid tracer to visualize the altered myocardial fatty acid metabolism of HCM and HHD. Carnitine is the essential substance for the beta-oxidation of long-chain fatty acids. We recently reported that serum free carnitine levels in HCM were elevated and that they were significantly correlated with the severity of myocardial fatty acid metabolic disorder. Therefore, we investigated serum carnitine levels in patients with HCM and HHD, which can contribute to the differentiation of each other. We studied 56 patients with HCM and 20 patients with essential hypertension. Serum free carnitine levels were significantly higher in patients with HCM than those with HHD (HCM 52.5+/-9.5 nmol/mL, HHD 46.6+/-6.4 nmol/mL, P<0.01), but they showed no statistical difference between patients with HHD and normal subjects. Serum acylcarnitine levels were significantly lower in patients with HCM than those with HHD (HCM 10.1+/-4.0 nmol/mL, HHD 14.5+/-4.9 nmol/mL, P<0.0005), although they did not differ between patients with HHD and normal subjects. Scintigraphic analyses with a long-chain fatty acid analog revealed that myocardial tracer uptake was much reduced in patients with HCM compared with that in patients with HHD (quantitative analysis: HCM 2.11+/-0.12, HHD 2.22+/-0.17, P<0.05; semiquantitative analysis: HCM 13.6+/-6.3, HHD 2.0+/-1.5, P<0.0001). In conclusion, the differences in serum carnitine levels between HCM and HHD reflect altered myocardial fatty acid metabolic impairment, and the levels can help to distinguish these 2 diseases.

Familial carnitine transporter defect: A treatable cause of cardiomyopathy in children

Carnitine transporter defect is characterized by severely reduced transport of carnitine into skeletal muscle, fibroblasts, and renal tubules. All children with dilated cardiomyopathy or hypoglycemia and coma should be evaluated for this transporter defect because it is readily amenable to therapy that results in prolonged prevention of cardiac failure. This article details the cases of 3 children who have carnitine transporter defect, 2 of whom had severe dilated cardiomyopathy. Plasma and skeletal muscle carnitine levels were extremely low and both children were treated with oral L-carnitine, resulting in resolution of severe cardiomyopathy and prevention of recurrence or cardiac enlargement for more than 5 years. The third child had hypoglycemia and coma as presenting findings of the transporter defect and had mild left ventricular hypertrophy but no cardiac failure. The prognosis for long-term survival in pediatric dilated cardiomyopathy is poor. Children with carnitine transporter defect can have a different outcome if their underlying condition is detected early and treated medically.

Disorders of lipid metabolism in skeletal muscle

Lipid storage myopathies are typically present with recurrent episodes of myoglobinuria and hypoglycemia, triggered by fasting or infection. Dilated cardiomyopathy can occur. This article will discuss an approach to lipid storage myopathies and describes various forms of disorders by fatty acid oxidation.

Loss of wild-type carrier-mediated L-carnitine transport activity in hepatocytes of juvenile visceral steatosis mice

Juvenile visceral steatosis (JVS) mice, which show systemic L-carnitine deficiency, may be an animal model of Reye's syndrome because of its phenotype of fat deposition and mitochondrial abnormalities in the liver. In this study, we compared the characteristics of the L-carnitine transport in isolated hepatocytes from wild-type and JVS mice. The uptake of L-carnitine by wild-type hepatocytes was saturable and the Eadie-Hofstee plot showed 2 distinct components. The apparent Michaelis constant (K(m)) and the maximum transport rate (V(max)) were 4.6 micromol/L and 59.5 pmol/15 min/10(6) cells, respectively, for the high-affinity component, and 404 micromol/L and 713 pmol/15 min/10(6) cells, respectively, for the low-affinity component. The high-affinity L-carnitine uptake occurred via an active carrier-mediated transport mechanism, which is characterized by Na(+)-, energy-, and pH-dependency. On the other hand, the high-affinity uptake was absent in JVS hepatocytes, and the values of K(m) and V(max) for the low-affinity uptake were 475 micromol/L and 557 pmol/15 min/10(6) cells, respectively. The hepatic carnitine transport properties in wild-type hepatocytes were similar to those of high-affinity mouse Octn2-transfected HEK293 cells. This study suggests that Octn2-type carnitine transporter is dysfunctional in hepatocytes of JVS mice.

Direct chromatographic resolution of carnitine and O-acylcarnitine enantiomers on a teicoplanin-bonded chiral stationary phase

R-(-)-Carnitine (vitamin B(T)) plays an important role in human energy metabolism, by facilitating the transport of long-chained fatty acids across the mitochondrial membranes. Its (S)-enantiomer acts as a competitive inhibitor of carnitine acetyltransferase, causing depletion of the body R-(-)-carnitine stock. Consequently, the separation of carnitine enantiomers is very important both to study their biological activities and to control the enantiomeric purity of pharmaceutical formulations. In the present paper we describe an easy, fast and convenient procedure for the separation of the enantiomers of carnitine and O-acylcarnitines by enantioselective HPLC on a laboratory-made chiral column containing covalently bonded teicoplanin as selector. High enantioselectivity factors (alpha values ranging from 1.31 to 3.02) and short-time analyses characterize the analytical procedure; in addition, analytes are easily detected by evaporative light scattering with no need for preliminary derivatization. The effects of pH and ionic strength of the mobile phase and of the nature of the organic modifier on the enantioselective separations were also investigated.

Characteristics of L-carnitine transport in cultured human hepatoma HLF cells

The recently cloned organic cation transporter, OCTN2, isolated as a homologue of OCTN1, has been shown to be of physiological importance in the renal tubular reabsorption of filtered L-carnitine as a high-affinity Na+ carnitine transporter in man. Although the mutation of the OCTN2 gene has been proved to be directly related to primary carnitine deficiency, there is little information about the L-carnitine transport system in the liver. In this study, the characteristics of L-carnitine transport into hepatocytes were studied by use of cultured human hepatoma HLF cells, which expressed OCTN2 mRNA to a greater extent than OCTN1 mRNA. The uptake of L-carnitine into HLF cells was saturable and the Eadie-Hofstee plot showed two distinct components. The apparent Michaelis constant and the maximum transport rate were 6.59+/-1.85 microM (mean+/-s.d.) and 78.5+/-21.4 pmol/5 min/10(6) cells, respectively, for high-affinity uptake, and 590+/-134 microM and 1507+/-142 pmol/5 min/10(6) cells, respectively, for low-affinity uptake. The high affinity L-carnitine transporter was significantly inhibited by metabolic inhibitors (sodium azide, dinitrophenol, iodoacetic acid) and at low temperature (4 degrees C). Uptake of [3H]L-carnitine also required the presence of Na+ ions in the external medium. The uptake activity was highest at pH 7.4, and was significantly lower at acidic or basic pH. L-Carnitine analogues (D-carnitine, L-acetylcarnitine and gamma-butyrobetaine) strongly inhibited uptake of [3H] L-carnitine, whereas beta-alanine, glycine, choline, acetylcholine and an organic anion and cation had little or no inhibitory effect. In conclusion, L-carnitine is absorbed by hepatocytes from man by an active carrier-mediated transport system which is Na+-, energy- and pH-dependent and has properties very similar to those of the carnitine transporter OCTN2.

Rett syndrome: randomized controlled trial of L-carnitine

Rett syndrome is a severe neurodevelopmental disorder of unknown etiology, occurring almost exclusively in female patients. The etiology and functional significance of plasma carnitine deficiency seen in some patients with Rett syndrome is unknown. To investigate whether L-carnitine might be of benefit in Rett syndrome, a randomized, placebo-controlled, double-blind crossover trial of L-carnitine has been completed in 35 subjects. Eight-week treatment phases were completed for both a placebo and L-carnitine. Outcome was measured by parents/caregivers and at medical follow-up using three established tools: the Rett Syndrome Motor Behavioral Assessment, the Hand Apraxia Scale, and the Patient Well-Being Index. Analysis comparing change between baseline and week 8 of treatment for L-carnitine and the placebo showed that both parents/caregivers and medical follow-up detected improvements in the subjects' well-being. In addition, medical review showed an improvement on the Hand Apraxia Scale for a higher proportion of girls on L-carnitine. Identification of predictors of clinical improvement has been limited by the power of the study. These findings suggest that L-carnitine is of benefit in some patients with Rett syndrome. While L-carnitine did not lead to major functional changes in ability, the type of changes reported could still have a substantial impact on the girls and their families. Information is still needed, however, to determine if only subgroups of girls with the disorder are responsive to L-carnitine and the appropriate duration of therapy.

Pyruvate dehydrogenase kinase 4 mRNA is increased in the hypertrophied ventricles of carnitine-deficient juvenile visceral steatosis (JVS) mice

We isolated a mouse homologue cDNA of pyruvate dehydrogenase (PDH) kinase 4 (PDK4) with differential mRNA display as an up-regulated gene in the hypertrophied ventricles of juvenile visceral steatosis (JVS) mice with systemic carnitine deficiency. The PDK4 mRNA level was 5 times higher in JVS mice than in control mice under fed conditions. After 24 h starvation, this level increased to 20 times in JVS and 7 times in control, compared with the control fed level. On the other hand, carnitine administration reduced the high level of PDK4 mRNA in JVS mice to the control fed level. In control mice, the change in PDK4 mRNA was inversely correlated with the change in PDH activity. In JVS mice, however, the PDK4 mRNA level was not always correlated with the active-form PDH level.

Biotransformation of D(+)-carnitine into L(-)-carnitine by resting cells of Escherichia coli O44 K74

L(-)-carnitine was produced from D(+)-carnitine by resting cells of Escherichia coli O44 K74. Oxygen did not inhibit either the carnitine transport system or the enzymes involved in the biotransformation process. Aerobic conditions led to higher product yield than anaerobic conditions. The biotransformation yield depended both on biomass and initial substrate concentrations used; the selected values for these variables were 4.30 g l-1 cells and 100 mmol l-1 D(+)-carnitine. Under these conditions the L(-)-carnitine production rate was 0.55 g l-1 h-1, the process yield was 44%, and the productivity was 0.22 g l-1 h-1 after a 30 h incubation period. Crotonobetaine production, besides L(-)-carnitine, showed that the action of more than one enzyme occurred during the biotransformation process. On the other hand, the addition of fumarate at high substrate concentrations (250 and 500 mmol l-1) led to a higher metabolic activity, which meant an increment of L(-)-carnitine production.

Genetic disorders of carnitine metabolism and their nutritional management

Carnitine functions as a substrate for a family of enzymes, carnitine acyltransferases, involved in acyl-coenzyme A metabolism and as a carrier for long-chain fatty acids into mitochondria. Carnitine biosynthesis and/or dietary carnitine fulfill the body's requirement for carnitine. To date, a genetic disorder of carnitine biosynthesis has not been described. A genetic defect in the high-affinity plasma membrane carnitine-carrier(in) leads to renal carnitine wasting and primary carnitine deficiency. Myopathic carnitine deficiency could be due to an increase in efflux moderated by the carnitine-carrier(out). Defects in the carnitine transport system for fatty acids in mitochondria have been described and are being examined at the molecular and pathophysiological levels. the nutritional management of these disorders includes a high-carbohydrate, low-fat diet and avoidance of those events that promote fatty acid oxidation, such as fasting, prolonged exercise, and cold. Large-dose carnitine treatment is effective in systemic carnitine deficiency.

Diet- and valproate-induced transient hyperammonemia: effect of L-carnitine

Hyperammonemia is an adverse effect of valproate (VPA) treatment. In particular, transient hyperammonemia has been reported to occur in VPA-treated patients after protein-rich meals. This phenomenon may occur secondary to a VPA-mediated carnitine insufficiency. We sought to confirm that protein ingestion would result in transient hyperammonemia and to determine whether supplementation with L-carnitine would prevent this effect. We studied the effect of consumption of a standardized protein-rich meal (45 g protein) before (phase I) and after (phase II) administration of L-carnitine 50 mg/kg/day for 7 days in 11 epileptic children (13.3 +/- 2.3 years of age) receiving VPA. Venous blood was obtained during fasting (baseline) and at 2 and 4 hours after the protein-rich meal for analysis of ammonia (NH3), and VPA concentrations. Mean VPA trough concentrations did not differ significantly at any time. After protein ingestion, 2-hour NH3 concentration increased by 86% (P < .05) from baseline in phase I as compared with a 38% increase in phase II. In both phases I and II, 4-hour NH3 concentrations decreased toward baseline values. We conclude that (1) modest protein ingestion can result in significant transient increases in NH3 in VPA-treated children, (2) significant increases may occur in patients with normal fasting NH3 concentrations, (3) these increases can be significantly attenuated by L-carnitine supplementation, and (4) these changes do not appear to be related to changes in VPA concentration.

High uptake of [2-11C]acetyl-L-carnitine into the brain: a PET study

The brain uptake of acetylcarnitine was investigated in rhesus monkeys using different position labeled acetyl-L-carnitine and related molecules with 11C by positron emission tomography. The uptake values of radio-labeled acetylcarnitine into the brain were quite different depending on the labeling positions of 11C. That is, the uptake values of L-[methyl-11C]carnitine and acetyl-L-[methyl-11C]carnitine were almost the same and extremely low, while the uptake of [1-11C]-acetyl-L-carnitine was slightly higher. The uptake value of [2-11C]acetyl-L-carnitine was by far the highest among the 11C-labeled acetyl-L-carnitine and L-carnitine. The uptake of [2-11C]acetyl-L-carnitine into the brain was suppressed by the intravenous administration of glucose. These results suggest that endogenous serum acetyl-L-carnitine has some roles on conveying an acetyl moiety into the brain especially under an energy crisis, and that an unknown metabolic pathway of [2-11C]acetyl moiety might be rather active in the brain.