L-Carnitine

The effects of L-carnitine supplementation on cardiovascular risk factors in participants with impaired glucose tolerance and diabetes: a systematic review and dose-response meta-analysis

AIMS

L-carnitine plays a role related to cardiometabolic factors, but its effectiveness and safety in CVD are still unknown. We aim to assess the effect of L-carnitine supplementation on CVD risk factors.

METHODS

A systematic literature search was conducted in PubMed, Web of Science, and Scopus until October 2022. The main outcomes were lipid profiles, anthropometric parameters, insulin resistance, serum glucose levels, leptin, blood pressure, and inflammatory markers. The pooled weighted mean difference (WMD) was calculated using a random-effects model.

RESULTS

We included the 21 RCTs (n = 2900) with 21 effect sizes in this study. L-carnitine supplementation had a significant effect on TG (WMD = - 13.50 mg/dl, p = 0.039), LDL (WMD = - 12.66 mg/dl, p < 0.001), FBG (WMD = - 6.24 mg/dl, p = 0.001), HbA1c (WMD = -0.37%, p = 0.013) HOMA-IR (WMD = -0.72, p = 0.038 (, CRP (WMD = - 0.07 mg/dl, P = 0.037), TNF-α (WMD = - 1.39 pg/ml, p = 0.033), weight (WMD = - 1.58 kg, p = 0.001 (, BMI (WMD = - 0.28 kg/m2, p = 0.017(, BFP (WMD = - 1.83, p < 0.001) and leptin (WMD = - 2.21 ng/ml, p = 0.003 (in intervention, compared to the placebo group, in the pooled analysis.

CONCLUSIONS

This meta-analysis demonstrated that administration of L-carnitine in diabetic and glucose intolerance patients can significantly reduce TG, LDL-C, FBG, HbA1c, HOMA-IR, CRP, TNF-α, weight, BMI, BFP, and leptin levels. PROSPERO registration code: CRD42022366992.

A randomized clinical trial to evaluate the efficacy of L-carnitine L-tartrate to modulate the effects of SARS-CoV-2 infection

Introduction

L-carnitine (LC) has been associated with inflammatory mediator reduction and with downregulating the angiotensin-converting enzyme-2 (ACE2) receptor, which is the target of SARS-CoV-2 attachment.

Methods

This pilot phase 2 randomized, double-blind placebo-controlled trial contained two cohorts. Cohort 1 comprised 101 individuals with negative RT-PCR SARS-CoV-2 test results who cohabitated with an individual diagnosed with SARS-CoV-2 infection. Cohort 2 comprised 122 individuals with positive SARS-CoV-2 RT-PCR test results who were asymptomatic or had mild COVID-19 pneumonia symptoms. Participants in each cohort were randomized 1:1 to receive either 2 g elemental oral LC supplementation or placebo daily for 21 days. Primary endpoints included adverse events, SARS-CoV-2 infection incidence in Cohort 1, and disease progressions in Cohort 2. Secondary endpoints included between-group laboratory profile comparisons and Cohort 2 ACE1/ACE2 plasma levels. Disease progression was compared between the Cohort 2 groups using chest computed tomography.

Results

In Cohort 1, two SARS-CoV-2 infections occurred in each group. The common adverse events included headache, dyspnea, and tiredness. In Cohort 2, platelet counts were elevated, and fibrinogen levels reduced in the LC group compared with those of the placebo group.

Conclusion

Our study showed that LC was well-tolerated and suggests it modulates coagulation pathways. Furthermore, chest computed tomography images of the Cohort 2 LC group showed significant lung lesion improvement, suggesting that LC may slow COVID-19 progression.

Serum L-Carnitine Levels Are Associated With First Stroke in Chinese Adults With Hypertension

BACKGROUND

This study aimed to evaluate the association of serum L-carnitine with first stroke and explore potential effect modifiers.

METHODS

This is a nested, case-control study drawn from the China Stroke Primary Prevention Trial among rural Chinese adults with hypertension, including 557 first stroke cases and 557 age-matched, sex-matched, treatment group-matched, and residence-matched controls. Serum L-carnitine was measured by liquid chromatography with tandem quadrupole mass spectrometry. Multiple conditional logistic regression models were used to evaluate the association between L-carnitine and first stroke.

RESULTS

The mean level of serum L-carnitine in the stroke population was 4.7 μg/mL, which was significantly lower than that of the control group (5.7 μg/mL). When L-carnitine was assessed as quintiles, compared with the reference group (quintile 1, <3.3 μg/mL), the odds of stroke were 0.62 (95% CI, 0.39-1.00) in quintile 2, 0.66 (95% CI, 0.40-1.10) in quintile 3, 0.47 (95% CI, 0.28-0.81) in quintile 4, and 0.50 (95% CI, 0.30-0.84) in quintile 5. The trend test was significant (P=0.01). When quintiles 2 to 5 were combined, the adjusted odds ratio of first stroke was 0.58 (95% CI, 0.38-0.87) compared with quintile 1. Similar associations were found for ischemic stroke and hemorrhagic stroke. In subgroup analysis, a significant L-carnitine-stroke association was only observed in the normal folate group (P interaction, 0.039) and in the MTHFR CC genotype group (P interaction, 0.047).

CONCLUSIONS

In this study of rural Chinese adults with hypertension, serum L-carnitine had an inverse but nonlinear association with first stroke. Folate status and the MTHFR C677T variant were significant effect modifiers of the association.

Modulation of Perturbed Cardiac Metabolism in Rats Under High-Altitude Hypoxia by Combination Treatment With L-carnitine and Trimetazidine

High-altitude hypoxia has long been recognized as a vital etiology for high-altitude illnesses. High-altitude myocardial injury (HAMI) usually occurs in people who suffered from high-altitude exposure. To date, the molecular mechanism of HAMI remains elusive, which seriously hinders the prevention and treatment of HAMI. L-carnitine and trimetazidine are classic cardiovascular protective medicines. In this study, we used the metabolomic method, based on GC/MS, to explore the changes in metabolites in rats exposed to high-altitude hypoxia and then illustrate the metabolic pathways associated with the modulatory effect of L-carnitine combined with trimetazidine on rats with high-altitude exposure. The results showed that metabolites in the myocardium in rats under high-altitude hypoxia were markedly changed, such as branched-chain amino acids (BCAA, leucine, isoleucine, and valine), taurine, succinic acid, fumaric acid, lactic acid, pyruvic acid, 3-hydroxybutyrate, and docosahexaenoic acid (DHA), while L-carnitine combined with trimetazidine modulated and improved the abnormal changes in energy substances caused by high-altitude hypoxia. L-carnitine mainly promoted the metabolism of fatty acids, while trimetazidine enhanced the glycolysis process. The combined administration of the two components not only increased the metabolism of fatty acids but also promoted aerobic glycolysis. Meanwhile, it contributed to the decrease in the elevation in some of the intermediates of the tricarboxylic acid (TCA) cycle, decrease in the production of 3-hydroxybutyric acid, and relief of the abnormal energy metabolism process in organisms and the cardiac tissue. Our analysis delineates the landscape of the metabolites in the myocardial tissue of rats that were exposed to high altitude. Moreover, L-carnitine combined with trimetazidine can relieve the HAMI through modulated and improved abnormal changes in energy substances caused by high-altitude hypoxia.

The Effects of L-Carnitine on Echocardiographic Changes in Patients With β-Thalassemia Major and Intermedia

INTRODUCTION

Heart failure, fatal arrhythmias, and cardiac dilatation because of anemia are common causes of β-thalassemia major-related deaths. The aim of this study was to determine the effect of L-carnitine on echocardiographic changes in β-thalassemia major and intermedia patients in Besat Hospital in Sanandaj, Iran.

METHODS

In a randomized clinical trial, 60 β-thalassemia patients who were eligible for L-carnitine administration were randomly divided into 2 placebo and study drug groups. The duration of the study was 6 months. Using echocardiography and blood tests, cardiac parameters including left ventricular dilatation, left ventricular hypertrophy, and a number of cardiac blood indices were examined before and after the intervention. The data were analyzed using SPSS V.23 software, χ, and covariance statistical tests.

RESULTS

There was no significant difference between the 2 groups in terms of age and sex. Patients treated with L-carnitine have a reduced rate of left ventricular dilatation, left ventricular hypertrophy, and systolic blood pressure compared with controls (P<0.05). Cardiac output increased from 43.5 to 56.5 (P=0.002).

CONCLUSIONS

The results of this study showed that the drug has a positive effect on the improvement of cardiac indices in β-thalassemia patients. Therefore, we suggest that further studies with more samples and other diagnostic modalities of the drug's effect be investigated.

Metabolic characterization of tuberculous meningitis in a South African paediatric population using 1H NMR metabolomics

OBJECTIVE

To better characterize the cerebrospinal fluid (CSF) metabolic profile of tuberculous meningitis (TBM) cases using a South African paediatric cohort.

METHODS

¹H NMR metabolomics was used to analyse the CSF of a South African paediatric cohort. Univariate and multivariate statistical analyses were performed to compare a homogeneous control group with a well-defined TBM group.

RESULTS

Twenty metabolites were identified to discriminate TBM cases from controls. As expected, reduced glucose and elevated lactate were the dominating discriminators. A closer investigation of the CSF metabolic profile yielded 18 metabolites of statistical significance. Ten metabolites (acetate, alanine, choline, citrate, creatinine, isoleucine, lysine, myo-inositol, pyruvate and valine) overlapped with two other prior investigations. Eight metabolites (2-hydroxybutyrate, carnitine, creatine, creatine phosphate, glutamate, glutamine, guanidinoacetate and proline) were unique to our paediatric TBM cohort.

CONCLUSIONS

Through strict exclusion criteria, quality control checks and data filtering, eight unique CSF metabolites associated with TBM were identified for the first time and linked to: uncontrolled glucose metabolism, upregulated proline and creatine metabolism, detoxification and disrupted glutamate-glutamine cycle in the TBM samples. Associated with oxidative stress and chronic neuroinflammation, our findings collectively imply destabilization, and hence increased permeability, of the blood-brain barrier in the TBM cases.

The effects of carnitine supplementation on clinical characteristics of patients with non-alcoholic fatty liver disease: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

The beneficial effects of carnitine supplementation on nonalcoholic fatty liver disease are unclear. We conducted a systematic review and meta-analysis to evaluate the effects of carnitine supplementation on liver function, lipid profile, body mass index, body weight, and homeostasis model assessment of insulin resistance in patients with nonalcoholic fatty liver disease.

METHODS

A comprehensive search of PubMed, Web of Science, Scopus, Cochrane Library, and Google Scholar databases were performed. Only randomized placebo-controlled human studies that examined the effects of carnitine supplementation on liver function, lipid profile, body mass index, body weight, and homeostasis model assessment of insulin resistance up to September 2019 were included. Fixed effects or random-effects models were applied to compute the pooled effect size. Heterogeneity assessments were performed using Cochran's Q test and I-squared statistics. The quality of the studies was assessed using the Jaded scale.

RESULTS

A total of 5 articles were selected, including 334 individuals (167 in control and 167 in intervention groups). The results demonstrated that carnitine supplementation significantly reduced homeostasis model assessment of insulin resistance (HOMA-IR) (WMD: -0.91; 95 % CI: -1.11, -0.72; p < 0.001, I² = 0.0 %) and the levels of aspartate aminotransferase (AST) (WMD: -16.62; 95 % CI: -28.11, -5.14; IU/l; p = 0.005, I² = 93.5 %), alanine aminotransferase (ALT) (WMD: -33.39; 95 % CI: -45.13, -21.66; IU/l; p < 0.001, I² = 93.4 %), and triglycerides (TG) (WMD: -22.13; 95 % CI: -38.91, -5.34; mg/dl; p = 0.01; I² = 0.0 %). However, the results of the pooled effect size did not show any significant effect of carnitine supplementation on body mass index (BMI) (WMD: 0.07; 95 % CI: -0.15, 0.29; p = 0.55; I² = 0.0 %), body weight (WMD: -0.28; 95 % CI: -2.23, 1.68; p = 0.78; I² = 45.7 %), the levels of gamma-glutamyl transferase (γGT) (WMD: -11.31; 95 % CI: -24.35, 1.73; IU/l; p = 0.09, I² = 61.1 %), cholesterol (WMD: -13.58; 95 % CI: -46.77, 19.60; mg/dl; p = 0.42; I² = 94.9 %), high-density lipoprotein-cholesterol (HDL-C) (WMD: 1.36; 95 % CI: -0.96, 3.68; mg/dl; p = 0.25; I² = 64.7 %), and low density lipoprotein-cholesterol (LDL-C) (WMD: -14.85; 95 % CI: -45.43, 15.73; mg/dl; p = 0.34; I² = 96.4 %).

CONCLUSIONS

This analysis shows that carnitine supplementation for patients with nonalcoholic fatty liver disease demonstrates a reduction in AST, ALT, TG levels and HOMA-IR. However, no significant effect of carnitine supplementation was observed on BMI, body weight, the levels of γGT, TC, HDL-cholesterol and LDL-cholesterol.

Impaired acylcarnitine profile in transfusion-dependent beta-thalassemia major patients in Bangladesh

Patients with beta-thalassemia major (BTM) suffer from fatigue, poor physical fitness, muscle weakness, lethargy, and cardiac complications which are related to an energy crisis. Carnitine and acylcarnitine derivatives play important roles in fatty acid oxidation, and deregulation of carnitine and acylcarnitine metabolism may lead to an energy crisis. The present study aimed to investigate carnitine and acylcarnitine metabolites to gain an insight into the pathophysiology of BTM. Dried blood spots of 45 patients with BTM and 96 age-matched healthy controls were analyzed for free carnitine and 24 acylcarnitines by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Although medium chain acylcarnitine levels were similar in the patients with BTM and healthy controls, free carnitine, short chain acylcarnitines, long chain acylcarnitines, and total acylcarnitine levels were significantly lower in patients with BTM than in the healthy controls (P < 0.05). Moreover, an impaired fatty acid oxidation rate was observed in the patients with BTM, as manifested by decreased fatty acid oxidation indicator ratios, namely C2/C0 and (C2 + C3)/C0. Furthermore, an increase in the C0/(C16 + C18) ratio indicated reduced carnitine palmitoyltransferase-1 (CPT-1) activity in the patients with BTM compared with that in the healthy controls. Thus, a low level of free carnitine and acylcarnitines together with impaired CPT-1 activity contribute to energy crisis-related complications in the patients with BTM.

L-carnitine prevents memory impairment induced by chronic REM-sleep deprivation

Sleep deprivation (SD) negatively impacts memory, which was related to oxidative stress induced damage. L-carnitine is a naturally occurring compound, synthesized endogenously in mammalian species and known to possess antioxidant properties. In this study, the effect of L-carnitine on learning and memory impairment induced by rapid eye movement sleep (REM-sleep) deprivation was investigated. REM-sleep deprivation was induced using modified multiple platform model (8h/day, for 6 weeks). Simultaneously, L-carnitine was administered (300mg/kg/day) intraperitoneally for 6 weeks. Thereafter, the radial arm water maze (RAWM) was used to assess spatial learning and memory. Additionally, the hippocampus levels of antioxidant biomarkers/enzymes: reduced glutathione (GSH), oxidized glutathione (GSSG), GSH/GSSG ratio, glutathione peroxidase (GPx), catalase, and superoxide dismutase (SOD) and thiobarbituric acid reactive substance (TBARS) were assessed. The results showed that chronic REM-sleep deprivation impaired both short- and long-term memory (P<0.05), whereas L-carnitine treatment protected against this effect. Furthermore, L-carnitine normalized chronic REM-sleep deprivation induced reduction in the hippocampus ratio of GSH/GSSG, activity of catalase, GPx, and SOD. No change was observed in TBARS among tested groups (P>0.05). In conclusion, chronic REM-sleep deprivation induced memory impairment, and treatment with L-carnitine prevented this impairment through normalizing antioxidant mechanisms in the hippocampus.

Screening of Free Carnitine and Acylcarnitine Status in Children With Familial Mediterranean Fever

OBJECTIVES

This study aims to demonstrate the patterns of free carnitine (FC) and acylcarnitine (AC) esters in familial Mediterranean fever (FMF) patients.

PATIENTS AND METHODS

A total of 205 patients (106 males, 99 females; mean age 131.3±52.1 months; range 24 to 254 months) with FMF and 50 healthy controls (27 males, 23 females; mean age 125.7±49.6 months; range 32 to 217 months) were enrolled. Fasting dried blood samples were taken for showing FC and AC ester levels with tandem mass spectrometry from both patients and controls.

RESULTS

Screening of AC profile revealed increased FC, 3-hydroxypalmitoylcarnitine (C16-OH), and 3-Hydroxy octadecanoylcarnitine (C18:2-OH) carnitine levels, while decreased acetyl-carnitine (C2), propionyl-carnitine (C3), butyryl-carnitine (C4), tiglyl-carnitine (C5:1), hexanoyl-carnitine (C6), octanoyl-carnitine (C8), decenoylcarnitine (C10:1), decadienoylcarnitine (C10:2), malonylcarnitine (C3DC), methylmalonylcarnitine (C4DC), glutarylcarnitine (C5DC), hexadecenoylcarnitine (C16:1), 3-Hydroxy butyrylcarnitine (C4-OH), and 3-Hydroxy oleylcarnitine (C18:1-OH) carnitine levels in FMF patients compared to controls. Total AC levels (p<0.001) and AC to FC ratio (p<0.001) were also lower in FMF patients than the controls.

CONCLUSION

In this study, we were able to detect some of the AC profile variations in FMF patients; however, usage of carnitine in all patients with FMF is not recommended since we were not able to demonstrate secondary carnitine deficiency in FMF patients of this study.

Carnitine Deficiency and Pregnancy

We present two cases of carnitine deficiency in pregnancy. In our first case, systematic screening revealed L-carnitine deficiency in the first born of an asymptomatic mother. In the course of her second pregnancy, maternal carnitine levels showed a deficiency as well. In a second case, a mother known with carnitine deficiency under supplementation was followed throughout her pregnancy. Both pregnancies had an uneventful outcome. Because carnitine deficiency can have serious complications, supplementation with carnitine is advised. This supplementation should be continued throughout pregnancy according to plasma concentrations.

Distribution, molecular structure and functional analysis of carnitine transporter (SLC22A5) in canine lens epithelial cells

While carnitine has been reported to have an anti-oxidative role on the ocular surface, there has been no report on the existence of a carnitine transporter (SLC22A5) in the lens. Therefore, we investigated the carnitine transport activity of canine lens epithelial cells (LEC) and determined the molecular structure of canine SLC22A5. The carnitine transport activity was 7.16 ± 0.48 pmol/mg protein/30 min. Butyrobetaine, the analogue of carnitine, reduced 30% of the activity at 50 µM. A coding sequence of canine carnitine transporter was 1694 bp long and was predicted to encode 557 amino acid polypeptides. The deduced amino acid sequence of canine carnitine transporter showed >80% similarity to that of mouse and human. Western blot analysis detected the band at 60 kDa in the membrane of lens epithelial cells. The high content of carnitine in the lens is possibly transported from aqueous humor by SLC22A5.

Pharmacological agents for nonalcoholic steatohepatitis

The rationale for specific pharmacologic therapy in nonalcoholic steatohepatitis (NASH) is determined by the potential for disease progression and the difficulties, in many patients, to successfully implement diet and lifestyle changes in the long term. Because they correct insulin resistance, insulin-sensitizing agents are attractive candidates for the treatment of NASH. However, two randomized studies have shown that vitamin E, despite having no effect on insulin sensitivity, achieves interesting histological and biochemical efficacy. This review provides an insight into the therapeutic efficacy and safety issues of different pharmacological agents tested in human NASH.

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.

Potential nephroprotective effects of l-carnitine against drug-induced nephropathy: a review of literature

INTRODUCTION

Drug-induced nephrotoxicity (DIN) has been reported with a great number of medications and contributes to ∼ 20% of hospital admissions. l-carnitine owing to its antioxidant, anti-inflammatory and antiapoptotic properties has been proposed as a candidate for nephroprotection against DIN. Increasing need to use nephrotoxic therapeutic agents necessitated this review.

AREAS COVERED

The present review covers all published clinical and animal researches on nephroprotective effects of l-carnitine against DIN. l-carnitine significantly ameliorates DIN in animal studies especially against cisplatin-induced renal damage. Inhibition of reactive oxygen species generation, lipid peroxidation, matrix remodeling and apoptosis, anti-inflammatory properties and improvement in carnitine deficiency has been suggested as probable nephroprotective mechanisms of l-carnitine.

EXPERT OPINION

In spite of the evidences that support the nephroprotective effect of l-carnitine, the main problems in this area are inadequacy of reliable studies in humans and difficulty of translating the experimental results into clinical practice. In most of the described studies, l-carnitine treatment is prophylactically given. Use of l-carnitine as a prophylactic agent in clinical situations with an indication for nephrotoxic therapies is rarely possible except for contrast-induced nephrotoxicity. Development of validated early biomarkers to detect DIN may provide the opportunity to use prophylactic nephroprotective agents at golden time.

OCTN2 is associated with carnitine transport capacity of rat skeletal muscles

AIM

Carnitine plays an essential role in fat oxidation in skeletal muscles; therefore carnitine influx could be crucial for muscle metabolism. OCTN2, a sodium-dependent solute carrier, is assumed to transport carnitine into various organs. However, OCTN2 protein expression and the functional importance of carnitine transport for muscle metabolism have not been studied. We tested the hypothesis that OCTN2 is expressed at higher levels in oxidative muscles than in other muscles, and that the carnitine uptake capacity of skeletal muscles depends on the amount of OCTN2.

METHODS

Rat hindlimb muscles (soleus, plantaris, and the surface and deep portions of gastrocnemius) were used for Western blotting to detect OCTN2. Tissue carnitine uptake was examined by an integration plot analysis using l-[(3)H]carnitine as a tracer. Tissue carnitine content was determined by enzymatic cycling methods. The percentage of type I fibres was determined by histochemical analysis.

RESULTS

OCTN2 was detected in all skeletal muscles although the amount was lower than that in the kidney. OCTN2 expression was significantly higher in soleus than in the other skeletal muscles. The amount of OCTN2 was positively correlated with the percentage of type I fibres in hindlimb muscles. The integration plot analysis revealed a positive correlation between the uptake clearance of l-[(3)H]carnitine and the amount of OCTN2 in skeletal muscles. However, the carnitine content in soleus was lower than that in other skeletal muscles.

CONCLUSION

OCTN2 is functionally expressed in skeletal muscles and is involved in the import of carnitine for fatty acid oxidation, especially in highly oxidative muscles.

L-carnitine supplementation to diet: a new tool in treatment of nonalcoholic steatohepatitis--a randomized and controlled clinical trial

OBJECTIVES

Nonalcoholic steatohepatitis (NASH) is a known metabolic disorder of the liver. No treatment has been conclusively shown to improve NASH or prevent disease progression. The function of L-carnitine to modulate lipid profile, glucose metabolism, oxidative stress, and inflammatory responses has been shown. The aim of this study was to evaluate the effects of L-carnitine's supplementation on regression of NASH.

METHODS

In patients with NASH and control subjects, we randomly dispensed one 1-g L-carnitine tablet after breakfast plus diet and one 1 g tablet after dinner plus diet for 24 weeks or diet alone at the same dosage and regimen. We evaluated liver enzymes, lipid profile, fasting plasma glucose, C-reactive protein (CRP), tumor necrosis factor (TNF)-alpha, homeostasis model assessment (HOMA)-IR, body mass index, and histological scores.

RESULTS

At the end of the study, L-carnitine-treated patients showed significant improvements in the following parameters: aspartate aminotransferase (P=0.000), alanine aminotransferase (ALT) (P=0.000), gamma-glutamyl-transpeptidase (gamma-GT) (P=0.000), total cholesterol (P=0.000), low-density lipoprotein (LDL) (P=0.000), high-density lipoprotein (HDL) (P=0.000), triglycerides (P=0.000), glucose (P=0.000), HOMA-IR (P=0.000), CRP (P=0.000), TNF-alpha (P=0.000), and histological scores (P=0.000).

CONCLUSIONS

L-carnitine supplementation to diet is useful for reducing TNF-alpha and CRP, and for improving liver function, glucose plasma level, lipid profile, HOMA-IR, and histological manifestations of NASH.

L-carnitine in beta thalassemia

This study was conducted to determine L-carnitine levels in regularly transfused and chelated beta thalassemia patients (n=40; mean age, 17.5+/-5.0 years). Ten age matched controls were also studied. The mean L-carnitine level in thalassemic patients was 23.71+/- 7.3 microM as compared to control 29.26+/-2.37 microM (P<0.0001). Mean carnitine was significantly lower (P=0.037) in those with ferritin greater than 2000 ng/dL (22.80+/-6.97 microM) in comparison to those with ferritin less than 2000 ng/dL (30.1+/-7.77 microM). Although carnitine levels in non vegetarians was higher (26.91+/-8.4 microM) than in vegetarians (22.34+/-6.55 microM), this difference was not statistically significant (P=0.072). We conclude that L-carnitine levels were found to be lower in thalassemics as compared to age matched controls.

Pulmonary hypertension in beta-thalassemia major and the role of L-carnitine therapy

Cardiac complications, such as pulmonary hypertension (PHT), are the leading cause of death in beta-thalassemia patients. L-Carnitine, due to its role in fatty acid oxidation, might help control the elevation in pulmonary artery systolic pressure (PASP). The objectives of this study were to assess the prevalence of PHT in beta-thalassemia major patients, identify clinical predictors for its development, and determine the potential effects of L-carnitine. In total, 32 patients with beta-thalassemia major were recruited; 16 age- and sex-matched children constituted the control group. Cardiac evaluation was performed by using echocardiography. The patients with PHT received 50 mg/kg/day L-carnitine orally for 3 months and were then reevaluated. Based on PASP, the patients were divided into group A without PHT and group B with PHT. The prevalence of PHT was 37.5%. The other echocardiographic measurements were not significantly different between groups A and B. PASP did not have any significant correlation with the following variables: age, total number of blood units received, splenic status, serum ferritin level, and ejection fraction. Following the administration of L-carnitine, there was a significant decrease in the mean PASP from 33.96 +/- 7.85 to 24.11 +/- 7.61. All cardiac dimensions decreased following L-carnitine, but the changes were not statistically significant. Even though beta-thalassemia major resulted in an elevation in the PASP in only a fraction of the patients, it seems to have an impact on the heart dimensions and function of all patients. No clinical predictors were identified. Oral administration of L-carnitine appears to significantly improve PASP.

Supplementation with l-carnitine does not reduce the efficacy of epirubicin treatment in breast cancer cells

One of the cornerstones of therapy for invasive breast cancer includes the use of anthracyclines. Epirubicin, a stereoisomer of doxorubicin, is one of the commonly used anthracyclines. Anthracyclines while effective therapy for breast cancer, have their own unique toxicities, such as cardiomyopathy. l-Carnitine, a quarternary ammonium compound synthesized from methionine and lysine, is required for oxidative metabolism in mitochondria. Cardiac function is closely linked with oxidative metabolism whereby l-carnitine is an essential cofactor. A hypothesis is being investigated to determine if supplementation with carnitine in breast cancer patients treated with epirubicin will reduce the development of cardiac toxicity. We determined whether addition of l-carnitine altered the tumor cytotoxic effects of epirubicin using a number of in vitro cell viability assays in different breast cancer cell lines including BT549, MDA-MB-435, NCI-ADR-RES, MCF7 and T47D. Additionally we investigated the ability of cells to respond to l-carnitine following analysis of the expression of carnitine metabolic enzymes by RT-PCR. We determined that supplementation with l-carnitine had no effect on the ability of epirubicin to kill a variety of breast cancer cell lines. Additionally, no differences in the induction of apoptosis by epirubicin were observed. Furthermore, all cell lines examined expressed proteins required for carnitine uptake and use. Our data suggest that supplementation with l-carnitine does not impair the ability of epirubicin to kill breast cancer cells. These results suggest that supplementation with l-carnitine in patients undergoing epirubicin treatment could be safely used to reduce associated cardiotoxicities without fear that the efficacy of chemotherapy is jeopardized.

Effect of L-carnitine on the physical fitness of thalassemic patients

Poor physical fitness is a common problem among thalassemic patients. L-Carnitine plays an essential role in fatty acid beta-oxidation, a process especially important in the organs that preferentially use fatty acid as a source of energy such as the myocardium and the skeletal muscles. The main objective of this study is to assess the effect of the administration of oral L-carnitine on exercise tolerance and physical fitness in patients with thalassemia major. Thirty patients followed up at the New Cairo University Children Hospital were included in this study. Clinical, laboratory, and cardiopulmonary exercise testing were performed before and after 6 months of oral L-carnitine therapy (50 mg/kg/day). The oxygen consumption, cardiac output, and oxygen pulse at maximal exercise significantly increased after L-carnitine therapy (p<0.001, p=0.002 and p<0.001, respectively). However, there was no significant change in minute ventilation and ventilatory equivalent of carbon dioxide (p=0.07 and p=0.06, respectively). A weak but positive correlation between the age of the patients and the degree of improvement in exercise parameters was noted. There was also significant increase in the blood transfusion intervals after L-carnitine administration (p=0.008). However, there was no significant change in hemoglobin concentration (p=0.4). L-Carnitine seems to be a safe and effective adjunctive therapeutic approach in thalassemic patients. It improves their cardiac performance and physical fitness. The younger the patients are, the higher is the degree of improvement in their exercise parameters.

Mitochondrial dysfunction in NASH: causes, consequences and possible means to prevent it

Calorie-enriched diet and lack of exercise are causing a worldwide surge of obesity, insulin resistance and lipid accretion in liver (i.e. hepatic steatosis), which can lead to steatohepatitis. Steatosis and nonalcoholic steatohepatitis (NASH) can also be induced by drugs such as amiodarone, tamoxifen and some antiretroviral drugs, including stavudine and zidovudine. There is accumulating evidence that mitochondrial dysfunction (more particularly respiratory chain deficiency) plays a key role in the physiopathology of NASH whatever its initial cause. In contrast, the mitochondrial beta-oxidation of fatty acids can be either increased (as in insulin resistance-associated NASH) or decreased (as in drug-induced NASH). However, in both circumstances, generation of reactive oxygen species (ROS) by the damaged respiratory chain can be augmented. ROS generation in an environment enriched in lipids in turn induces lipid peroxidation which releases highly reactive aldehydic derivatives (e.g. malondialdehyde) that have diverse detrimental effects on hepatocytes and other hepatic cells. In hepatocytes, ROS, reactive nitrogen species and lipid peroxidation products further impair the respiratory chain, either directly or indirectly through oxidative damage to the mitochondrial genome. This consequently leads to the generation of more ROS and a vicious cycle occurs. Mitochondrial dysfunction can also lead to apoptosis or necrosis depending on the energy status of the cell. ROS and lipid peroxidation products also increase the generation of several cytokines (TNF-alpha, TGF-beta, Fas ligand) playing a key role in cell death, inflammation and fibrosis. Recent investigations have shown that some genetic polymorphisms can significantly increase the risk of steatohepatitis and that several drugs can prevent or even reverse NASH. Interestingly, most of these drugs could exert their beneficial effects by improving directly or indirectly mitochondrial function in liver. Finding a drug, which could fully prevent oxidative stress and mitochondrial dysfunction in NASH is a major challenge for the next decade.

Apoptosis in thalassemia major reduced by a butyrate derivative

BACKGROUND AND OBJECTIVES

In cases of beta-thalassemia major, apoptosis appears to be greatly enhanced in the early-stage erythroid precursors in the bone marrow leading to ineffective erythropoiesis. L-Carnitine is found to strongly reduce apoptosis in different diseases. We investigated the effect of oral L-carnitine therapy on apoptosis in thalassemia major patients.

METHODS

Eighteen thalassemia major patients with a mean age of 12.2 +/- 6.6 years were included. Detection of apoptosis was done by photometric enzyme immunoassay (ELISA) and agarose gel electrophoresis before and after 6 months of oral therapy with L-carnitine (50 mg/kg/day).

RESULTS

A significant decrease of apoptosis frequency in the erythroid precursors in the bone marrow of studied cases was noted after therapy. The quantity of nucleosomes measured by ELISA dropped from 3.65 +/- 1.338 to 1.60 +/- 0.65 after therapy (p = 0.005). A positive ladder pattern reflecting apoptosis on agarose gel electrophoresis was detected in 88.9% of cases prior to treatment versus 16.7% after therapy (p = 0.006). Patients also had a significant decrease in the frequency of transfusions and increase in the pre-transfusion hemoglobin levels after therapy.

CONCLUSION

L-Carnitine seems to be a good modulator of apoptotic processes in thalassemic patients leading to a decreased frequency of programmed erythroblast death and general improvement of the disease condition.

Expression of novel organic cation/carnitine transporter (OCTN2) in the mouse pancreas

Among the organic cation transporters, OCTN2 is identified as the most important carnitine transporter owing to the ability to transport carnitine. Although the OCTN2 is previously found in various tissues, there have been no reports showing the OCTN2 in the pancreas. In this study, we examined the expression and localization of OCTN2 in the mouse pancreas by the aid of an in situ hybridization technique and immunohistochemistry with anti-OCTN2 antibody. As a result, the OCTN2 expression was found in the A-cells for the first time. OCTN2 was not expressed in B-cells, notwithstanding that the metabolism of long-chain fatty acids, which are transported into the mitochondria with the help of carnitine, was expected for fatty acid-stimulated insulin secretion. Thus, this study suggests the possibility of carnitine uptake in the pancreatic A-cells through OCTN2 and implies the presence of carnitine transporter(s) other than OCTN2 in the B-cell.

Serum carnitine levels in patients with homozygous beta thalassemia: a possible new role for carnitine?

Carnitine (beta-hydroxy-gamma-trimethylaminobutyric acid) facilitates the transfer of activated long-chain fatty acids from the cytoplasm to the mitochondria, the site of their beta-oxidation. Carnitine deficiency results in a reduced usage of fatty acids in energy production and therefore the appearance of clinical symptoms such as myalgia and muscle weakness. In the present study, serum carnitine levels were measured in 45 children and 20 adults with homozygous beta thalassemia. A decrease in serum carnitine levels (total, free and acyl) was found, without any evidence of disorder in the process of mitochondrial beta-oxidation. The possible cause of this finding could be related to a reduced hepatic carnitine biosynthesis.

CONCLUSION

In patients with homozygous beta thalassemia, the reduction of serum carnitine levels might play an important role in the appearance of muscular dysfunction. It is possible that L : -carnitine administration in these patients might improve or even resolve the aforementioned symptom.

Carnitine and Sports Medicine: Use or Abuse?

Carnitine has important roles in skeletal muscle bioenergetics. Skeletal muscle carnitine deficiency is associated with profound impairment of muscle function. It has thus been natural to ask if carnitine supplementation can improve skeletal muscle function and athletic performance in healthy individuals. Oral carnitine doses of several grams cause no significant clinical toxicity, further encouraging the use of carnitine as a supplement. Despite this strong foundation and 20 years of research, no compelling evidence exists that carnitine supplementation can improve physical performance in healthy subjects. The available data have been reviewed in recent publications. Several key issues are relevant to a potential therapeutic benefit of carnitine supplementation, and addressing these may provide insight into trials of carnitine therapy in healthy subjects: (1) Can carnitine supplementation increase skeletal muscle carnitine content in healthy subjects? Muscle carnitine content is not easily increased with carnitine supplementation. This reflects both the systemic pharmacokinetics of carnitine and the systems controlling transmembrane transport of carnitine in skeletal muscle. (2) How much carnitine is required to support optimal metabolism in skeletal muscle? Data are not available to definitively define the relationship between muscle carnitine content and muscle metabolic function. Extrapolation of data from several models suggests that very low amounts of carnitine are required to support muscle function. (3) Does carnitine supplementation alter energy homeostasis in healthy subjects? Several, but not all, studies suggest that subjects on carnitine supplementation have altered regulation of fuel homeostasis. However, the mechanisms of these changes, the tissues affected, and the relevance of these phenomena to exercise performance are all ill defined. (4) How can changes in performance be assessed in healthy subjects? Most studies have failed to demonstrate an objective performance improvement in healthy subjects taking carnitine. However, these negative studies must be interpreted with caution. Performance studies in athletes are conducted against a background of aggressive training regimens and nutritional interventions. Small changes, which may be very important to the athlete, may be very hard to objectify in the laboratory. Assessments must differentiate between changes in maximal aerobic capacity, ability to sustain effort at varied workloads, and the subject's perception of exertion. The interaction of carnitine supplementation with exercise training may be particularly important on theoretical and experimental bases. Systematic research in each of these areas is required to better understand the physiology, biochemistry, and pharmacology of carnitine supplementation. While data do not allow a conclusion to be drawn that carnitine is beneficial, the negative has not been proven either.

The ins and outs of mitochondrial dysfunction in NASH

Rich diet and lack of exercise are causing a surge in obesity, insulin resistance and steatosis, which can evolve into steatohepatitis. Steatosis and nonalcoholic steatohepatitis (NASH) can also be induced by drugs such as amiodarone, tamoxifen and some antiretroviral drugs. There is growing evidence that mitochondrial dysfunction, and more specifically respiratory chain deficiency, plays a role in the pathophysiology of NASH whatever its initial cause. In contrast, the B-oxidation of fatty acids can be either increased (as in insulin resistance-associated NASH) or decreased (as in drug-induced NASH). However, in both circumstances, the generation of reactive oxygen species (ROS) by the damaged respiratory chain is augmented, as components of this chain are over-reduced by electrons, which then abnormally react with oxygen to form increased amounts of ROS. Concomitantly, ROS oxidize fat deposits to release lipid peroxidation products that have detrimental effects on hepatocytes and other hepatic cells. In hepatocytes, ROS and lipid peroxidation products further impair the respiratory chain, either directly or indirectly through oxidative damage to the mitochondrial genome. This, in turn, leads to the generation of more ROS and a vicious cycle ensues. Mitochondrial dysfunction can also lead to apoptosis or necrosis depending on the energy status of the cell. ROS and lipid peroxidation products also activate stellate cells, thus resulting in fibrosis. Finally, ROS and lipid peroxidation increase the generation of several cytokines (TNF-alpha, TGF-B, Fas ligand) that play sundry roles in the pathogenesis of NASH. Recent investigations have shown that some genetic polymorphisms can significantly increase the risk of steatohepatitis and that several drugs can prevent or even reverse NASH. For the next decade, reducing the incidence of NASH will be a major challenge for hepatologists.

Dyslipidemia, oxidative stress and cardiac dysfunction in children with chronic renal failure: effects of L-carnitine supplementation

BACKGROUND

Secondary carnitine deficiency may develop in chronic renal failure (CRF) patients undergoing long-term hemodialysis (HD), with a resulting higher incidence of cardiovascular diseases, dyslipidemia and oxidative stress. We studied the efficacy of 12 months of L-carnitine supplementation on the amelioration of dyslipidemia, oxidative stress and cardiac dysfunction in 24 CRF children undergoing long-term HD compared with 24 age- and sex-matched controls.

METHODS

Plasma samples were analyzed spectrophotometerically before and after dialysis sessions and after 2-month supplementation with oral L-carnitine (50 mg/kg/day) for free carnitine (FC), the lipid profile, and oxidative stress markers. Echocardiography the day following dialysis measured cardiac diameters, wall thicknesses, left ventricular mass index (MI), end diastole and systole volume indices and functions.

RESULTS

The pre-dialysis FC concentration was substantially lower than controls and decreased significantly at the end of the dialysis session. Pre- and post-dialysis plasma levels of free fatty acids (FFAs), trigyleride (TG), total cholesterol (TC) and oxidative stress markers significantly increased while high-density lipoprotein cholesterol (HDL-C) and phospholipids significantly decreased compared to controls. Echocardiography detected a significant increase in cardiac diameters and thickness, and systolic and diastolic cardiac dysfunction. After L-carnitine supplementation, plasma levels of FC increased to normal levels. FFAs, TC and HDL-C returned to control levels while TG, phospholipids, and the oxidative stress markers decreased but remained significantly higher than controls. There was a significant decrease in cardiac diameters and an increase in left ventricular diastolic function (E/A ratio), but no correlation between FC levels and echocardiographic parameters. Pre-dialysis, post-dialysis and after treatment, plasma FC level showed a significant positive correlation with HDL-C and phospholipids and a significant negative correlation with each of oxidative stress markers, FFAs, TG and TC. On the other hand, FFAs showed a significant positive correlation with TG, TC, DC, NO and a significant negative correlation with HDL-C and phospholipids.

CONCLUSION

This study demonstrates that CRF children under regular HD suffer from a decrease in the level of plasma FC, dyslipidemia, oxidative stress, and an increase in cardiac diameters and thickness with impairment of cardiac functions. Oral L-carnitine supplementation at a dose of 50 mg/kg for 2 months can increase plasma FC level, improve dyslipidemia, decrease oxidative stress with reduction of cardiac diameters and increase in diastolic function.

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.

Carnitine levels and the ketogenic diet

PURPOSE

To determine the long-term effect of the ketogenic diet (KD) on carnitine levels and whether carnitine depletion is a significant cause of clinical complications during KD initiation or treatment.

METHODS

Carnitine levels at 0, 1, 6, 12, and 24 months of diet treatment, carnitine antiepileptic drug (AED) history, lowest blood glucose and time to achieve ketosis during diet initiation, and diet complications were analyzed for 38 consecutive patients who initiated the KD from May 1997 to March 2000. Carnitine levels at follow-up were analyzed for eight patients started on the diet before to May 1997.

RESULTS

Total carnitine (TC) at diet initiation correlated negatively with the number of AEDs at diet initiation but not with number of past AEDs, lowest blood glucose, or time to ketosis. TC decreased in the first months of diet treatment and then stabilized or increased slightly with long term treatment. Only 19% of patients were supplemented with carnitine for low TC. No patient showed clinical signs of carnitine deficiency.

CONCLUSIONS

Multiple AED exposure lowers TC, but actual TC deficiency in patients initiating the KD is not common, and TC levels do not appear to predict hypoglycemia or problems achieving ketosis. Mild carnitine depletion may occur early in KD treatment and occasionally TC decreases out of the normal range, without clinical symptoms. TC stabilizes or increases back toward baseline with long-term treatment, and most patients do not require carnitine supplementation.

Zellweger syndrome knockout mouse models challenge putative peroxisomal beta-oxidation involvement in docosahexaenoic acid (22:6n-3) biosynthesis

The putative involvement of peroxisomal beta-oxidation in the biosynthetic pathway of docosahexaenoic acid (22:6n-3, DHA) synthesis is critically reviewed in light of experiments with two recently developed knockout mouse models for Zellweger syndrome, a peroxisomal disorder affecting brain development. These mice were generated by targeted disruption of the PEX2 and PEX5 peroxisomal assembly genes encoding targeting signal receptor peroxins for the recognition and transport of a set of peroxisomal enzymes, including those of peroxisomal beta-oxidation, to the peroxisomal matrix. Analysis of esterified 22:6n-3 concentrations in PEX2-/- and PEX5-/- mice do not support the hypothesized requirement of peroxisomal beta-oxidation in 22:6n-3 synthesis, as only brain, but not liver or plasma, 22:6n-3 levels were decreased. Supplementation of PEX5+/- dams with 22:6n-3, although restoring the levels of brain 22:6n-3 in total lipids to that of controls, did not normalize the phenotype. These decreased brain 22:6n-3 concentrations appear to be secondary to impaired plasmalogen (sn-1-alkyl-, alkenyl-2-acyl glycerophospholipids) synthesis, probably at the level of the dihydroxyacetonephosphate acyltransferase (DHAP-AT), a peroxisomal enzyme catalyzing the first step in the synthesis of 22:6n-3-rich plasmalogens. To diminish the confounding effects of impaired plasmalogen synthesis in the brains of these Zellweger syndrome mouse models, kinetic experiments with labeled precursors, such as 18:3n-3 or 20:5n-3, in liver or isolated hepatocytes, which have negligible amounts of plasmalogens, are suggested to establish the rates of 22:6n-3 biosynthesis and precursor-product relationships. Similar experiments using brain of the acyl-CoA oxidase knockout mouse model are proposed to confirm the lack of peroxisomal beta-oxidation involvement in 22:6n-3 synthesis, since this mutation would not impair plasmalogen synthesis.

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.

Primary systemic carnitine deficiency is caused by mutations in a gene encoding sodium ion-dependent carnitine transporter

Primary systemic carnitine deficiency (SCD; OMIM 212140) is an autosomal recessive disorder characterized by progressive cardiomyopathy, skeletal myopathy, hypoglycaemia and hyperammonaemia. SCD has also been linked to sudden infant death syndrome. Membrane-physiological studies have suggested a defect of the carnitine transport system in the plasma membrane in SCD patients and in the mouse model, juvenile visceral steatosis. Although the responsible loci have been mapped in both human and mouse, the underlying gene has not yet been identified. Recently, we cloned and analysed the function of a novel transporter protein termed OCTN2. Our observation that OCTN2 has the ability to transport carnitine in a sodium-dependent manner prompted us to search for mutations in the gene encoding OCTN2, SLC22A5. Initially, we analysed the mouse gene and found a missense mutation in Slc22a5 in jvs mice. Biochemical analysis revealed that this mutation abrogates carnitine transport. Subsequent analysis of the human gene identified four mutations in three SCD pedigrees. Affected individuals in one family were homozygous for the deletion of a 113-bp region containing the start codon. In the second pedigree, the affected individual was shown to be a compound heterozygote for two mutations that cause a frameshift and a premature stop codon, respectively. In an affected individual belonging to a third family, we found a homozygous splice-site mutation also resulting in a premature stop codon. These mutations provide the first evidence that loss of OCTN2 function causes SCD.

Fatty acid oxidation defects in muscle

Fatty acid oxidation defects can cause recurrent rhabdomyolysis or chronic progressive muscle weakness. Diagnosis is often possible on blood using tandem mass spectrometry or molecular genetic techniques. Riboflavin and carnitine are effective in some cases of multiple acyl-CoA dehydrogenase deficiency and primary carnitine deficiency, respectively. Controlled trials are needed to evaluate other proposed forms of treatment.

Molecular and functional identification of sodium ion-dependent, high affinity human carnitine transporter OCTN2

Primary carnitine deficiency, because of a defect of the tissue plasma membrane carnitine transporters, causes critical symptoms. However, the transporter has not been molecularly identified. In this study, we screened a human kidney cDNA library and assembled a cDNA-encoding OCTN2 as a homologue of the organic cation transporter OCTN1, and then we examined the function of OCTN2 as a carnitine transporter. OCTN2-cDNA encodes a polypeptide of 557 amino acids with 75.8% similarity to OCTN1. Northern blot analysis showed that OCTN2 is strongly expressed in kidney, skeletal muscle, heart, and placenta in adult humans. When OCTN2 was expressed in HEK293 cells, uptake of L-[3H]carnitine was strongly enhanced in a sodium-dependent manner with Km value of 4.34 microM, whereas typical substrates for previously known organic cation transporters, tetraethylammonium and guanidine, were not good substitutes. OCTN2-mediated L-[3H]carnitine transport was inhibited by the D-isomer, acetyl-D,L-carnitine, and gamma-butyrobetaine with high affinity and by glycinebetaine with lower affinity, whereas choline, beta-hydroxybutyric acid, gamma-aminobutyric acid, lysine, and taurine were not inhibitory. Because the observed tissue distribution of OCTN2 is consistent with the reported distribution of carnitine transport activity and the functional characteristics of OCTN2 coincide with those reported for plasma membrane carnitine transport, we conclude that OCTN2 is a physiologically important, high affinity sodium-carnitine cotransporter in humans.

Analysis of the putative role of 24-carbon polyunsaturated fatty acids in the biosynthesis of docosapentaenoic (22:5n-6) and docosahexaenoic (22:6n-3) acids

The recent literature on the putative involvement of a single cycle of peroxisomal beta-oxidation of 24:5n-6 and 24:6n-3 polyunsaturated fatty acids in the biosynthesis of the respective docosapentaenoic (22:5n-6) and docosahexaenoic (22:6n-3) fatty acids is critically reviewed. Present evidence suggests that in vitro data in support of the above proposition is an artifact of a low 2,4-dienoyl-CoA reductase activity due to depletion of NADPH resulting from incubation conditions. Kinetic studies with radiolabeled precursors in cell cultures have shown lower initial rates of labeling of 24:6n-3 than that of 22:6n-3, indicating that 24:6n-3 is an elongation product of 22:6n-3 rather than its precursor. Analysis of other literature data supports the proposal that 22:5n-6 and 22:6n-3 are synthesized in mitochondria via channeled carnitine-dependent pathways involving separate n-6- and n-3-specific desaturases. It is proposed that impaired peroxisomal function in some peroxisomal disorders is a secondary consequence of defective mitochondrial synthesis of 22:6n-3; moreover, some disorders of peroxisomal beta-oxidation show normal or increased 22:5n-6 concentrations, indicating that 22:5n-6 is synthesized by independent desaturases without peroxisomal involvement.

Improvement in exercise tolerance in isovaleric acidaemia with L-carnitine therapy

The effect of 4 weeks' treatment with oral-L-carnitine (100 mg/kg per day) on carnitine status and metabolic parameters during an incremental ramp exercise test in a 12-year-old girl with isovaleric acidaemia was examined to determine its possible therapeutic role. The maximum work rate achieved increased from 110 to 120 watts; oxygen consumption at anaerobic threshold from 600 to 800 L/min; peak oxygen consumption from 1270 to 1450 L/min; and oxygen pulse, a measure of cardiac output, from 7.0 to 8.1 L/beat. These changes were associated with increases in plasma and urinary free and acyl carnitine concentrations but no change in physical activity. This observed effect of L-carnitine on exercise performance may be on cardiac or skeletal muscle function or both. We conclude that, in this single patient with isovaleric acid-aemia, L-carnitine supplementation had objective benefits and further studies on more patients are warranted.