Genetic disorders of carnitine metabolism and their nutritional management

TMT-based proteomics analysis of the cerebral cortex of TauT knockout rats

Background

Taurine serves a variety of nutritional and physiological roles, and it is mostly transported in cells via taurine transporter (TauT). The effect of taurine transporter in cerebral cortex is still unknown. We employed TMT label-based proteomics to find differences in proteins in the cerebral cortex of TauT knockout rats in this investigation. The goal of this research was to see how TauT deletion affected protein alterations in brain tissue and to see if there was a new research area for TauT.

Methods

The cerebral cortex of TauT knockout rats and wild-type control rats were analyzed using TMT-based proteomics, and differentially expressed proteins were analyzed by bioinformatics analysis means such as GO and KEGG, the association between the proteins was found by PPI, and biologically significant and interesting proteins were selected for verification by WB and immunohistochemistry.

Results

There were total of 8275 proteins found, but only 35 differentially expressed proteins were identified (27 up-regulated and 8 down-regulated), and gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to predict the biological pathways and functional classification of the proteins. The results show that these differentially expressed proteins are mainly enriched in lysine degradation, cell cycle, chronic myeloid leukemia, and longevity regulating pathways-multiple species, renal cell carcinoma, pathways in cancer, etc. To verify the proteomic data, we analyzed the expression of Annexin6 and Pik3r2 by western blotting and immunofluorescence. The results are consistent with proteomics, which proves the reliability of our proteomics data.

Conclusion

Through TMT-based proteomics, we have a comprehensive understanding of the effect of TauT knockout on the changes of other proteins in the cerebral cortex, providing new evidence for further understanding the function of TauT.

Investigation of the Effects of L-carnitine and magnesium on Oxidative Stress and Cytokines in the Tissue of Experimental diabetic rats

The aim of this study was to determine the effects of L-carnitine and magnesium on the levels of tissue malondialdehyde, 8-hydroxy-2’-deoxyguanosine, and cytokines (tumor necrosis factor alpha, interleukin-6) in streptozotocin-induced experimental diabetes in rats. Eighty male Wistar albino rats (200-250 g) were divided into 8 groups with 10 rats in each group. The groups received the following treatments: Control group; 2 ml distilled water (by gavage); Group 2: 50 mg/kg (b.w.) i.p. streptozotocin; Group 3: 125 mg/kg (b.w.) magnesium; Group 4: 300 mg/kg (b.w.) L-carnitine; Group 5: 125 mg/kg (b.w.) magnesium +300 mg/kg (b.w.) L-carnitine; Group 6: 50 mg/kg (b.w.) streptozotocin +125 mg/kg (b.w.) magnesium; Group 7: 50 mg/kg (b.w.) streptozotocin +300 mg/kg (b.w.) L-carnitine and Group 8: 50 mg/kg (b.w.) streptozotocin +125 mg/ kg (b.w.) magnesium+300 mg/kg (b.w.) L-carnitine administered for 4 weeks. Liver and kidney malondialdehyde, 8-hydroxy-2’-deoxyguanosine, tumor necrosis factor alpha and interleukin-6 levels did not change in the magnesium, L-carnitine, and magnesium + L-carnitine groups compared to the control. The highest levels of malondialdehyde, 8-hydroxy-2’-deoxyguanosine, tumor necrosis factor alpha and interleukin-6 were determined only in the group with diabetes (Group 2). Lipid peroxidation, DNA damage, and cytokine levels were significantly reduced in diabetic animals with the administration of magnesium and L-carnitine separately or in combination. Based on the obtained results it can be concluded that magnesium and L-carnitine may have antidiabetic effects, especially in combination.

Comparison of 3- and 6-Month Outcomes of Combined Oral L-Carnitine Fumarate and Acetyl-L-Carnitine Therapy, Included in an Antioxidant Formulation, in Patients with Idiopathic Infertility

The male factor is responsible for infertility in about 35-40% of all cases. Idiopathic oligo- and/or astheno- and/or therato-zoospermia is one of the most common male fertility disorders and remains a significant therapeutic challenge. The primary cause of idiopathic male infertility remains unknown but seems to be associated with oxidative stress. Objective: The use of antioxidative formulation to improve qualitative and quantitative deficiencies in the male gametes.In total, 78 subjects were treated with a combination of 1,725 mg L-carnitine fumarate, 500 mg acetyl-L-carnitine, 90 mg vitamin C, 20 mg coenzyme Q10, 10 mg zinc, 200 µg folic acid, 50 µg selenium, and 1.5 µg vitamin B12 (Proxeed® Plus, Sigma-Tau, Italy) for 6 months; the preparation was taken twice daily from the time idiopathic infertility was diagnosed. Basic seminal parameters were evaluated by a European Society of Human Reproduction and Embryology (ESHRE) -certified embryologist following the fifth edition of the World Health Organisation (2010) guidelines at three time points: at baseline and 3 and 6 months of treatment.Improvements in semen parameters (differing in terms of dynamics) were evident at 3 months and gradually improved over the 6 months of treatment. Each parameter: sperm concentration, total sperm count, sperm total and progressive motility improved significantly after treatment except for the percentage of sperm of abnormal morphology and ejaculate volume.Proxeed Plus was effective for patients with idiopathic infertility; however, a long treatment period is needed to achieve optimal results.

Oxidative Stress and Male Fertility: Role of Antioxidants and Inositols

Infertility is defined as a couple’s inability to conceive after at least one year of regular unprotected intercourse. This condition has become a global health problem affecting approximately 187 million couples worldwide and about half of the cases are attributable to male factors. Oxidative stress is a common reason for several conditions associated with male infertility. High levels of reactive oxygen species (ROS) impair sperm quality by decreasing motility and increasing the oxidation of DNA, of protein and of lipids. Multi-antioxidant supplementation is considered effective for male fertility parameters due to the synergistic effects of antioxidants. Most of them act by decreasing ROS concentration, thus improving sperm quality. In addition, other natural molecules, myo-inositol (MI) and d-chiro–inositol (DCI), ameliorate sperm quality. In sperm cells, MI is involved in many transduction mechanisms that regulate cytoplasmic calcium levels, capacitation and mitochondrial function. On the other hand, DCI is involved in the downregulation of steroidogenic enzyme aromatase, which produces testosterone. In this review, we analyze the processes involving oxidative stress in male fertility and the mechanisms of action of different molecules.

Salivary metabolites associated with a 5-year tooth loss identified in a population-based setting

BACKGROUND

Periodontitis is among the most common chronic diseases worldwide, and it is one of the main reasons for tooth loss. Comprehensive profiling of the metabolite content of the saliva can enable the identification of novel pathways associated with periodontitis and highlight non-invasive markers to facilitate time and cost-effective screening efforts for the presence of periodontitis and the prediction of tooth loss.

METHODS

We first investigated cross-sectional associations of 13 oral health variables with saliva levels of 562 metabolites, measured by untargeted mass spectrometry among a sub-sample (n = 938) of the Study of Health in Pomerania (SHIP-2) using linear regression models adjusting for common confounders. We took forward any candidate metabolite associated with at least two oral variables, to test for an association with a 5-year tooth loss over and above baseline oral health status using negative binomial regression models.

RESULTS

We identified 84 saliva metabolites that were associated with at least one oral variable cross-sectionally, for a subset of which we observed robust replication in an independent study. Out of 34 metabolites associated with more than two oral variables, baseline saliva levels of nine metabolites were positively associated with a 5-year tooth loss. Across all analyses, the metabolites 2-pyrrolidineacetic acid and butyrylputrescine were the most consistent candidate metabolites, likely reflecting oral dysbiosis. Other candidate metabolites likely reflected tissue destruction and cell proliferation.

CONCLUSIONS

Untargeted metabolic profiling of saliva replicated metabolic signatures of periodontal status and revealed novel metabolites associated with periodontitis and future tooth loss.

Significance of Levocarnitine Treatment in Dialysis Patients

Carnitine is a naturally occurring amino acid derivative that is involved in the transport of long-chain fatty acids to the mitochondrial matrix. There, these substrates undergo β-oxidation, producing energy. The major sources of carnitine are dietary intake, although carnitine is also endogenously synthesized in the liver and kidney. However, in patients on dialysis, serum carnitine levels progressively fall due to restricted dietary intake and deprivation of endogenous synthesis in the kidney. Furthermore, serum-free carnitine is removed by hemodialysis treatment because the molecular weight of carnitine is small (161 Da) and its protein binding rates are very low. Therefore, the dialysis procedure is a major cause of carnitine deficiency in patients undergoing hemodialysis. This deficiency may contribute to several clinical disorders in such patients. Symptoms of dialysis-related carnitine deficiency include erythropoiesis-stimulating agent-resistant anemia, myopathy, muscle weakness, and intradialytic muscle cramps and hypotension. However, levocarnitine administration might replenish the free carnitine and help to increase carnitine levels in muscle. This article reviews the previous research into levocarnitine therapy in patients on maintenance dialysis for the treatment of renal anemia, cardiac dysfunction, dyslipidemia, and muscle and dialytic symptoms, and it examines the efficacy of the therapeutic approach and related issues.

l-carnitine and l-acetylcarnitine supplementation for idiopathic male infertility

Fifteen percent of couples are globally estimated to be infertile, with up to half of these cases attributed to male infertility. Reactive oxidative species (ROS) are known to damage sperm leading to impaired quantity and quality. Although not routinely assessed, oxidative stress is a common underlying pathology in infertile men. Antioxidants have been shown to improve semen analysis parameters by reducing ROS and facilitating repair of damage caused by oxidative stress, but it remains unclear whether they improve fertility. Carnitines are naturally occurring antioxidants in mammals and are normally abundant in the epididymal luminal fluid of men. We conducted a systematic review and meta-analysis to evaluate the safety and efficacy of carnitine supplementation for idiopathic male infertility. We searched ClinicalKey, ClinicalTrials.gov, Cochrane Central Register of Controlled Trials (CENTRAL), EMBASE, MEDLINE, PubMed and ScienceDirect for relevant studies published from 1 January 2000 to 30 April 2020. Of the articles retrieved, only eight randomised controlled trials were identified and included. Analysis showed that carnitines significantly improve total sperm motility, progressive sperm motility and sperm morphology, but without effect on sperm concentration. There was no demonstrable effect on clinical pregnancy rate in the five studies that included that outcome, although patient numbers were limited. Therefore, the use of carnitines in male infertility appears to improve some sperm parameters but without evidence of an increase in the chance of natural conception.

Dietary supplementation with a novel l-carnitine multi-micronutrient in idiopathic male subfertility involving oligo-, astheno-, teratozoospermia: A randomized clinical study

OBJECTIVE

To study the influence of a multi-component nutrient dietary supplement on sperm parameters and pregnancy rates in idiopathic male infertility (IMI) with oligo-, astheno-, and teratozoospermia.

DESIGN

A randomized, double-blind, placebo-controlled, prospective, parallel arms (1:1 allocation ratio), multi-center clinical trial.

SETTINGS

Eight urology/reproductive health clinical centers located in Ukraine.

PATIENTS

Eighty-three males aged 21-50 years with IMI and at least 1 of 3 abnormal values: total sperm concentration < 15 million/ml or/and spermatozoa progressive motility < 32% or/and forms with normal morphology < 4%.

INTERVENTION(S)

Patients were randomly allocated verum test dietary supplement (TDS) containing l-carnitine/acetyl-l-carnitine, l-arginine, glutathione, co-enzyme Q10, zinc, vitamin B₉ , vitamin B₁₂ , selenium, or placebo 1 time daily for 6 months.

MAIN OUTCOME(S)

The primary outcome measure was the percentage of normal spermiograms (concentration ≥ 15 million/ml and ≥ 32% of spermatozoa with progressive motility and ≥ 4% of normal forms) at month 0, 2, and 4. The percentage of pregnancies served the secondary outcome endpoint. Differences between the groups were assessed in z-test for proportions.

RESULTS

All males finished the study. At month 4, 29/42 (69.0%) males in the verum and 9/41 (22.0%) had normal spermiograms (P < .001). The percentage of spontaneous pregnancies in the verum group was greater than in the placebo group (10/42, 23.8% vs. 2/41, 4.9%, respectively, P = .017). There were no reportable supplement-associated adverse events.

CONCLUSION

Specific multi-nutrient combination l-carnitine/l-acetyl-carnitine, l-arginine, glutathione, co-enzyme-Q, zinc, folic acid, cyanocobalamin, and selenium can improve sperm quality in males with IMI and increase pregnancy rates.

The neural stem cell/carnitine malnutrition hypothesis: new prospects for effective reduction of autism risk?

Autism spectrum disorders (ASDs) are developmental neuropsychiatric disorders with heterogeneous etiologies. As the incidence of these disorders is rising, such disorders represent a major human health problem with escalating social cost. Although recent years witnessed advances in our understanding of the genetic basis of some dysmorphic ASDs, little progress has been made in translating the improved understanding into effective strategies for ASD management or minimization of general ASD risk. Here we explore the idea, described in terms of the neural stem cell (NSC)/carnitine malnutrition hypothesis, that an unappreciated risk factor for ASD is diminished capacity for carnitine-dependent long-chain fatty acid β-oxidation in neural stem cells of the developing mammalian brain. The basic premise is that fetal carnitine status is a significant metabolic component in determining NSC vulnerability to derangements in their self-renewal program and, therefore, to fetal ASD risk. As fetal carnitine status exhibits a genetic component that relates to de novo carnitine biosynthesis and is sensitive to environmental and behavioral factors that affect maternal circulating carnitine levels, to which the fetus is exposed, we propose that reduced carnitine availability during gestation is a common risk factor that lurks beneath the genetically complex ASD horizon. One major prediction of the NSC/carnitine malnutrition hypothesis is that a significant component of ASD risk might be effectively managed from a public policy perspective by implementing a carnitine surveillance and dietary supplementation strategy for women planning pregnancies and for women in their first trimester of pregnancy. We argue that this prediction deserves serious clinical interrogation.

Double-blind, randomised, placebo-controlled trial on the effect of L-carnitine and L-acetylcarnitine on sperm parameters in men with idiopathic oligoasthenozoospermia

Carnitine is essential for energy metabolism and spermatozoa maturation. Combining L-carnitine and L-acetylcarnitine with micronutrients has been investigated as a treatment for infertility in men. We evaluated the effects of a therapeutic formulation, Proxeed Plus, on sperm parameters in oligoasthenozoospermic men. This prospective, randomised, double-blind, placebo-controlled clinical trial involved 175 males (19-44 years) with idiopathic oligoasthenozoospermia who failed to impregnate their partners (12 months). Males received Proxeed Plus or placebo for 3 and 6 months. Sperm volume, progressive motility and vitality significantly (p < 0.001) improved after 6 months compared to baseline. Sperm DNA fragmentation index significantly decreased compared to baseline (p < 0.001) and the 3-month therapy (p = 0.014) in treated men. Increased seminal carnitine and α-glucosidase concentration also positively correlated with improved progressive motility. Decreased DNA fragmentation index was the good predictor of progressive sperm motility >10%, and simultaneous measurement of changes in sperm vitality and DNA fragmentation index gave the highest probability of sperm motility 10% (AUC = 0.924; 95% CI = 0.852-0.996; p < 0.001). Logistic regression analyses revealed DNA fragmentation index decrease as the only independent predictor of sperm motility 10% (OR = 1.106; p = 0.034). We have demonstrated the beneficial effects of carnitine derivatives on progressive motility, vitality and sperm DNA fragmentation. Combining metabolic and micronutritive factors is beneficial for male infertility.

Antioxidants and Male Fertility: from Molecular Studies to Clinical Evidence

Spermatozoa are physiologically exposed to reactive oxygen species (ROS) that play a pivotal role on several sperm functions through activation of different intracellular mechanisms involved in physiological functions such as sperm capacitation associated-events. However, ROS overproduction depletes sperm antioxidant system, which leads to a condition of oxidative stress (OS). Subfertile and infertile men are known to present higher amount of ROS in the reproductive tract which causes sperm DNA damage and results in lower fertility and pregnancy rates. Thus, there is a growing number of couples seeking fertility treatment and assisted reproductive technologies (ART) due to OS-related problems in the male partner. Interestingly, although ART can be successfully used, it is also related with an increase in ROS production. This has led to a debate if antioxidants should be proposed as part of a fertility treatment in an attempt to decrease non-physiological elevated levels of ROS. However, the rationale behind oral antioxidants intake and positive effects on male reproduction outcome is only supported by few studies. In addition, it is unclear whether negative effects may arise from oral antioxidants intake. Although there are some contrasting reports, oral consumption of compounds with antioxidant activity appears to improve sperm parameters, such as motility and concentration, and decrease DNA damage, but there is not sufficient evidence that fertility rates and live birth really improve after antioxidants intake. Moreover, it depends on the type of antioxidants, treatment duration, and even the diagnostics of the man’s fertility, among other factors. Literature also suggests that the main advantage of antioxidant therapy is to extend sperm preservation to be used during ART. Herein, we discuss ROS production and its relevance in male fertility and antioxidant therapy with focus on molecular mechanisms and clinical evidence.

Effects of l-Carnitine on the Follicle-Stimulating Hormone, Luteinizing Hormone, Testosterone, and Testicular Tissue Oxidative Stress Levels in Streptozotocin-Induced Diabetic Rats

The present study was designed to investigate the antioxidant property of l-carnitine (LC) on serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (TH) and testis oxidative stress in streptozotocin (STZ)-induced diabetic rats. The rats were divided into the following groups: group I, control; group II, LC 100 mg/kg/d; group III, diabetic; and groups IV to VI, diabetic rats treated with 50, 100, and 200 mg/kg/d of LC, respectively. Daily injections were given intraperitoneally for 7 weeks. At the end of experimental period, after sacrificing the rats, FSH, LH, TH, total antioxidant capacity (TAC), malondialdehyde (MDA), glutathione (GSH), catalase (CAT), mitochondrial function (MTT), protein carbonyl (PC), and reactive oxygen species (ROS) levels were measured. STZ caused an elevation of MDA, ROS, and PC (P < .001) with reduction of GSH, CAT, TAC, and MTT (P < .001) in the serum levels. Group VI had significantly increased FSH, LH, and TH levels versus the untreated diabetic group (P < .001). Although groups V and VI significantly decreased MDA (P < .001), PC (P < .01), and ROS (P < .01) compared with the untreated diabetic group; only in group VI, the activity of GSH (P < .001), CAT (P < .01), TAC (P < .001), and MTT (P < .001) significantly increased. The results of the present study suggest that LC decreased diabetes-induced oxidative stress complications and also improved serum level of FSH, LH, and TH by reducing levels of lipid peroxidation and increasing antioxidant enzymes.

Role of carnitine and its derivatives in the development and management of type 2 diabetes

Type 2 diabetes is a highly prevalent chronic metabolic disorder characterized by hyperglycemia and associated with several complications such as retinopathy, hyperlipidemia and polyneuropathy. The dysregulated fatty acid metabolism along with tissue lipid accumulation is generally assumed to be associated in the development of insulin resistance and T2D. Moreover, several studies suggest a central role for oxidative stress in the pathogenesis of the disease. Since L-carnitine (LC) has an indispensable role in lipid metabolism via its involvement in the β-oxidation of long-chain fatty acids and it has antioxidant properties as well, carnitine supplementation may prove to be an effective tool in the management of the clinical course of T2D. In this review we summarize the results from animal and clinical studies demonstrating the effects of supplementation with LC or LC derivatives (acetyl-LC, propionyl-LC) on various metabolic and clinical parameters associated with T2D.

L-carnitine Derived Zwitterionic Betaine Materials

An L-carnitine derived zwitterionic betaine material was developed. The synthesized L-carnitineMA was the first zwitterionic betaine monomer from natural feedstocks. In the models of Surface coating and hydrogel, the L-carnitineMA material was able to achieve superior anti-fouling performance as good as state-of-the-art zwitterionic betaine materials.

Infant with hepatomegaly and hypoglycemia: A setting for fatty acid oxidation defects

Fatty acid oxidation defects (FAOD) are one of the commonest metabolic liver diseases (MLDs) that can have varied presentations in different age groups. An infant presented with short history of jaundice and irritability, examination showed soft hepatomegaly. Investigations revealed non-ketotic hypoglycemia suggesting FAOD which was later confirmed as carnitine uptake defect with gas chromatography and mass spectrometry and mutation analysis. Patient improved with acute management of metabolic crisis, carnitine supplementation and corn starch therapy with reversal of encephalopathy, reduction in hepatomegaly, maintenance of euglycemia and improvement in liver function tests and creatine phosphokinase on follow up. Non-ketotic hypoglycemia is a characteristic finding in FAODs. Early diagnosis and appropriate management can result in excellent outcomes in patients with FAODs.

Nutrients Turned into Toxins: Microbiota Modulation of Nutrient Properties in Chronic Kidney Disease

In chronic kidney disease (CKD), accumulation of uremic toxins is associated with an increased risk of death. Some uremic toxins are ingested with the diet, such as phosphate and star fruit-derived caramboxin. Others result from nutrient processing by gut microbiota, yielding precursors of uremic toxins or uremic toxins themselves. These nutrients include l-carnitine, choline/phosphatidylcholine, tryptophan and tyrosine, which are also sold over-the-counter as nutritional supplements. Physicians and patients alike should be aware that, in CKD patients, the use of these supplements may lead to potentially toxic effects. Unfortunately, most patients with CKD are not aware of their condition. Some of the dietary components may modify the gut microbiota, increasing the number of bacteria that process them to yield uremic toxins, such as trimethylamine N-Oxide (TMAO), p-cresyl sulfate, indoxyl sulfate and indole-3 acetic acid. Circulating levels of nutrient-derived uremic toxins are associated to increased risk of death and cardiovascular disease and there is evidence that this association may be causal. Future developments may include maneuvers to modify gut processing or absorption of these nutrients or derivatives to improve CKD patient outcomes.

Expression of OCTN2 and OCTN3 in the apical membrane of rat renal cortex and medulla

Immunological assays and transport measurements in apical membrane vesicles revealed that the apical membrane of rat kidney cortex and medulla presents OCTN2 and OCTN3 proteins and transports L-[(3)H]-carnitine in a Na(+)-dependent and -independent manner. OCTN2 mediates the Na(+)/L-carnitine transport activity measured in medulla because (i) the transport showed the same characteristics as the cortical Na(+)/L-carnitine transporter and (ii) the medulla expressed OCTN2 mRNA and protein. The Na(+)-independent L-carnitine transport activity appears to be mediated by both OCTN2 and OCTN3 since: (i) Na(+)-independent L-carnitine uptake was inhibited by both, anti-OCTN2 and anti-OCTN3 antibodies, (ii) kinetics studies revealed the involvement of a high- and a low-affinity transport systems, and (iii) Western and immunohistochemistry studies revealed that OCTN3 protein is located at the apical membrane of the kidney epithelia. The Na(+)-independent L-carnitine uptake exhibited trans-stimulation by intravesicular L-carnitine or betaine. This trans-stimulation was inhibited by anti-OCTN3 antibody, but not by anti-OCTN2 antibody, indicating that OCTN3 can function as an L-carnitine/organic compound exchanger. This is the first report showing a functional apical OCTN2 in the renal medulla and a functional apical OCTN3 in both renal cortex and medulla.

Experimental colitis: decreased Octn2 and Atb0+ expression in rat colonocytes induces carnitine depletion that is reversible by carnitine-loaded liposomes

Carnitine transporters have recently been implicated in susceptibility to inflammatory bowel disease (IBD). Because carnitine is required for beta-oxidation, it was suggested that decreased carnitine transporters, and hence reduced carnitine uptake, could lead to impaired fatty acid oxidation in intestinal epithelial cells, and to cell injury. We investigated this issue by examining the expression of the carnitine transporters OCTN2 and ATB0+, and butyrate metabolism in colonocytes in a rat model of IBD induced by trinitrobenzene sulfonic acid (TNBS). We found that Octn2 and Atb0+ expression was decreased in inflammatory samples at translational and functional level. Butyrate oxidation, evaluated based on CO2 production and acetyl-coenzyme A synthesis, was deranged in colonocytes from TNBS-treated rats. Treatment with carnitine-loaded liposomes corrected the butyrate metabolic alterations in vitro and reduced the severity of colitis in vivo. These results suggest that carnitine depletion in colonocytes is associated with the inability of mitochondria to maintain normal butyrate beta-oxidation. Our data indicate that carnitine is a rate-limiting factor for the maintenance of physiological butyrate oxidation in colonic cells. This hypothesis could also explain the contradictory therapeutic efficacy of butyrate supplementation observed in clinical trials of IBD.

Haplotype analysis of carnitine transporters and left ventricular mass in human essential hypertension

OBJECTIVE

The carnitine-associated alteration of myocardial fatty acid metabolism may be one of the molecular mechanisms underlying left ventricular hypertrophy (LVH) in essential hypertension. We tested the hypothesis that polymorphisms of the genes involved in carnitine transport, OCTN2, CPT1A, CPT1B, and CPT2, might be associated with LVH.

DESIGN

Haplotype-based association analysis in an observational study.

SETTING

Outpatients from the Nephrology Division of the University Hospital.

PATIENTS

A total of 215 never-treated, middle-aged patients with mild essential hypertension.

METHODS

Relationships between left ventricular mass index (LVMI) (measured with m-mode echocardiography) and haplotype combinations for 13 common genetic variants selected from single nucleotide polymorphism database (dbSNPs).

RESULTS

The SNPs were selected to cover the genomic region of the four loci, and a total of 23 haplotypes were identified: 8 for OCTN2 (H1 to H8), 8 for CPT1A (H9 to H16), 3 for CPT1B (H17 to H19), and 4 for CPT2 (H20 to H23). In a multilocus haplotype analysis, after adjusting for sex, age, systolic blood pressure, diastolic blood pressure, body mass index, and duration of hypertension, a significant effect on LVMI was seen for H13 (+8.9, P = .05), H14 (-5.63, P = .05), H15 (-18.79, P = .0006), H18 (-1.66, P = .03), and H22 (-3.42, P = .004). These significant haplotypes were respectively 3.7%, 1.6%, 1.6%, 39.3%, and 29.7% of the total population.

CONCLUSIONS

These results identify the carnitine-transporter gene family as candidate modifiers of LVMI in human hypertension. The use of common SNPs to define informative haplotypes associated with the phenotype of interest is the starting point for progress toward identification of the trapped contributing SNP(s).

Impaired long-chain fatty acid metabolism in mitochondria causes brain vascular invasion by a non-neurotropic epidemic influenza A virus in the newborn/suckling period: implications for influenza-associated encephalopathy

The neuropathogenesis of influenza-associated encephalopathy in children and Reye's syndrome remains unclear. A surveillance effort conducted during 2000-2003 in South-West Japan reveals that almost all fatal and handicapped influenza-associated encephalopathy patients exhibit a disorder of mitochondrial beta-oxidation with elevated serum acylcarnitine ratios (C(16:0)+C(18:1))/C(2). Here we show invasion by a non-neurotropic epidemic influenza A H3N2 virus in cerebral capillaries with progressive brain edema after intranasal infection of mice having impaired mitochondrial beta-oxidation congenitally or posteriorly in the newborn/ suckling periods. Mice genetically lacking of carnitine transporter OCTN2, resulting in carnitine deficiency and impaired beta-oxidation, exhibited significant higher virus-genome numbers in the brain, accumulation of virus antigen exclusively in the cerebral capillaries and increased brain vascular permeability compared to in wild type mice. Mini-plasmin, which proteolytically potentiates influenza virus multiplication in vivo and destroys the blood-brain barrier, accumulated with virus antigen in the brain capillaries of OCTN2-deficient mice but only a little in wild-type mice. These results suggest that the impaired mitochondrial beta-oxidation changes the susceptibility to a non-neurotropic influenza A virus as to multiplication in the brain capillaries and to cause brain edema. These pathological findings in the brain of mice having impaired mitochondrial beta-oxidation after influenza virus infection may have implications for human influenza-associated encephalopathy.

Functional expression of the organic cation/carnitine transporter 2 in rat astrocytes

In this study, we sought to identify the transporters that mediate the uptake of L-carnitine and acetyl-L-carnitine in cultured rat cortical astrocytes. L-[(3)H]carnitine and acetyl-L-[(3)H]carnitine uptake were both saturable, and mediated by a single Na(+)-dependent transport system. Uptake of both was inhibited by L-carnitine, D-carnitine, acetyl-L-carnitine and various organic cations. Acylcarnitines (acetyl-, butyryl-, hexanoyl-, octanoyl- and palmitoyl-L-carnitine) also interacted with L-[(3)H]carnitine and acetyl-L-[(3)H]carnitine transport. 2-Amino-2-norbornane carboxylic acid, a known inhibitor of amino acid transporter B(0,+) (ATB(0,+)), did not cause any significant inhibition. A highly significant correlation was found between the potencies of acylcarnitines in the inhibition of L-[(3)H]carnitine and acetyl-L-[(3)H]carnitine uptake and the acyl chain length of acylcarnitines. The expression of mRNA for organic cation/carnitine transporters (OCTNs), carnitine transporter 2 (CT2) and ATB(0,+) in astrocytes was investigated by reverse transcription (RT)-PCR. OCTN2 mRNA was expressed in astrocytes, whereas the expression of OCTN1, OCTN3 and CT2 mRNA could not be detected. ATB(0,+) mRNA was expressed at very low levels in astrocytes. Western blotting analysis indicated that anti-OCTN2 polyclonal antibody recognized a band of 70 kDa in both kidney and astrocyte preparations. OCTN2 immunoreactivity was detected in rat astrocytes by immunocytochemical staining. Inhibition of OCTN2 expression by RNA interference significantly inhibited L-[(3)H]carnitine and acetyl-L-[(3)H]carnitine uptake into astrocytes. These results suggest that OCTN2 is functionally expressed in rat astrocytes, and is responsible for L-carnitine and acetyl-L-carnitine uptake in these cells.

Attenuation of Cardiac Hypertrophy in Carnitine-Deficient Juvenile Visceral Steatosis (JVS) Mice Achieved by Lowering Dietary Lipid

We examined the development of cardiac hypertrophy in juvenile visceral steatosis (JVS) mice, a model of systemic carnitine deficiency, by varying the amount of lipid in the diet. Cardiac hypertrophy was markedly attenuated by decreasing soy bean oil (SBO) from 5% (w/w) to 1%. Triglyceride contents of the ventricles of JVS mice fed 1% SBO were significantly lower than in JVS mice fed 5% SBO. The addition of medium-chain triglycerides metabolically utilized by JVS mice did not affect the development of cardiac hypertrophy. On the other hand, the mRNA levels of atrial natriuretic peptide and skeletal alpha-actin, which are related to cardiac hypertrophy, were also attenuated by decreasing lipid in the diet. Adenylate energy charge and creatine phosphate in the heart of JVS mice at the early stage of hypertrophy were not significantly different from control mice given the same laboratory chow (4.6% of lipid). Although urinary prostaglandin F(2alpha) levels were found to be increased in JVS mice at 15 days of age when they developed cardiac hypertrophy, administration of aspirin was not efficacious. We, therefore, propose that the proportion of lipid in the diet is important in the development of cardiac hypertrophy in carnitine-deficient JVS mice, and that this is not related to prostaglandin formation.

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.

Plasma carnitine ester profile in adult celiac disease patients maintained on long-term gluten free diet

AIM: To determine the fasting plasma carnitine ester in patients with celiac disease.

METHODS: We determined the fasting plasma carnitine ester profile using ESI triple quadrupol mass spectrometry in 33 adult patients with biopsy-confirmed maturity onset celiac disease maintained on long term gluten free diet.

RESULTS: The level of free carnitine did not differ as the celiac disease patients were compared with the healthy controls, whereas the acetylcarnitine level was markedly reduced (4.703 ± 0.205 vs 10.227 ± 0.368 nmol/mL, P<0.01). The level of propionylcarnitine was 61.5%, butyrylcarnitine 56.9%, hexanoylcarnitine 75%, octanoylcarnitine 71.1%, octenoylcarnitine 52.1%, decanoylcarnitine 73.1%, cecenoylcarnitine 58.3%, lauroylcarnitine 61.5%, miristoylcarnitine 66.7%, miristoleylcarnitine 62.5% and oleylcarnitine 81.1% in the celiac disease patients compared to the control values, respectively (P<0.01).

CONCLUSION: The marked decrease of circulating acetylcarnitine with 50-80 % decrease of 11 other carnitine esters shows that the carnitine ester metabolism can be influenced even in clinically asymptomatic and well being adult celiac disease patients, and gluten withdrawal alone does not necessarily normalize all elements of the disturbed carnitine homeostasis.

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.

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.

OCTN3: A Na+-independent L-carnitine transporter in enterocytes basolateral membrane

L-carnitine transport has been measured in enterocytes and basolateral membrane vesicles (BLMV) isolated from chicken intestinal epithelia. In the nominally Na+-free conditions chicken enterocytes take up L-carnitine until the cell to medium L-carnitine ratio is 1. This uptake was inhibited by L-carnitine, D-carnitine, gamma-butyrobetaine, acetylcarnitine, tetraethylammonium (TEA), and betaine. L-3H-carnitine uptake into BLMV showed no overshoot, and it was (i) Na+-independent, (ii) trans-stimulated by intravesicular L-carnitine, and (iii) cis-inhibited by TEA and cold L-carnitine. L-3H-carnitine efflux from L-3H-carnitine preloaded enterocytes was also Na+-independent, and trans-stimulated by L-carnitine, D-carnitine, gamma-butyrobetaine, acetylcarnitine, TEA, and betaine. Both, uptake and efflux of L-carnitine were inhibited by verapamil and unaffected by either extracellular pH or palmitoyl-L-carnitine. RT-PCR with specific primers for the mouse OCTN3 transporter revealed the existence of OCTN3 mRNA in mouse intestine, which was confirmed by in situ hybridization studies. Immunohystochemical analysis showed that OCTN3 protein was mainly associated with the basolateral membrane of rat and chicken enterocytes, whereas OCTN2 was detected at the apical membrane. In conclusion, the results demonstrate for the first time that (i) mammalian small intestine expresses OCTN3 mRNA along the villus and (ii) that OCTN3 protein is located in the basolateral membrane. They also suggest that OCTN3 could mediate the passive, Na+ and pH-independent L-carnitine transport activity measured in the three experimental conditions.

Carnitine in type 2 diabetes

Carnitine, the L-beta-hydroxy-gamma-N-trimethylaminobutyric acid, is synthesized primarily in the liver and kidneys from lysine and methionine. Carnitine covers an important role in lipid metabolism, acting as an obligatory cofactor for beta-oxidation of fatty acids by facilitating the transport of long-chain fatty acids across the mitochondrial membrane as acylcarnitine esters. Furthermore, since carnitine behaves as a shuttle for acetyl groups from inside to outside the mitochondrial membrane, it covers also a key role in glucose metabolism and assists in fuel-sensing. A reduction of the fatty acid transport inside the mitochondria results in the cytosolic accumulation of triglycerides, which is implicated in the pathogenesis of insulin resistance. Acute hypercarnitinemia stimulates nonoxidative glucose disposal during euglycemic hyperinsulinemic clamp in healthy volunteers. Similar results were obtained in type 2 diabetic patients. The above findings were confirmed in healthy volunteers using the minimal modeling of glucose kinetics. The total end-clamp glucose tissue uptake was significantly increased by the administration of doses of acetyl-L-carnitine (ALC) from 3.8 to 5.2 mg/kg/min, without a significant dose-response effect. In conclusion, both L-carnitine and ALC are effective in improving insulin-mediated glucose disposal either in healthy subjects or in type 2 diabetic patients. Two possible mechanisms might be invoked in the metabolic effect of carnitine and its derivative: the first is a regulation of acetyl and acyl cellular trafficking for correctly meeting the energy demand; the second is a control action in the synthesis of key glycolytic and gluconeogenic enzymes.

Carnitine replacement in end-stage renal disease and hemodialysis

In patients with chronic renal failure, not yet undergoing hemodialysis (HD), plasma acylcarnitines accumulate in part due to a decreased renal clearance of esterified carnitine moieties. In these patients, a high acylcarnitine/free-carnitine ratio is usually found in plasma. Patients undergoing maintenance HD, usually present with plasma carnitine insufficiency, due to accumulation of metabolic intermediates combined with impaired carnitine biosynthesis, reduced protein intake and increased removal via HD. Plasma carnitine concentrations rapidly decrease to 40% of baseline level during the dialysis session, with a slow restoration of the carnitine concentration during the interdialytic period, mainly from organs of storage (skeletal muscle). Dietary intake also plays an important role in carnitine homeostasis of HD patients since the prevalence of malnutrition ranges from 18% to 75% of these cases. This could differentially affect various body compartments, with clinical consequences such as impaired muscle function, decreased wound healing, altered ventilatory response, and abnormal immune function. Repeated hemodialytic treatments are associated with decreased carnitine stores in skeletal muscle. The administration of intravenous L-carnitine (LC) postdialysis replenishes the free carnitine removed from the blood and contributes to replenishment of muscle carnitine content. LC supplementation in selected uremic patients may yield clinical benefits by ameliorating several conditions, such as erythropoietin-resistant anemia, decreased cardiac performance, intradialytic hypotension, muscle symptoms, as well as impaired exercise and functional capacities. Furthermore, LC may positively influence the nutritional status of HD patients by promoting a positive protein balance, and by reducing insulin resistance and chronic inflammation, possibly through an effect on leptin resistance.

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.

Organic cation transporters

Over the last 15 years, a number of transporters that translocate organic cations were characterized functionally and also identified on the molecular level. Organic cations include endogenous compounds such as monoamine neurotransmitters, choline, and coenzymes, but also numerous drugs and xenobiotics. Some of the cloned organic cation transporters accept one main substrate or structurally similar compounds (oligospecific transporters), while others translocate a variety of structurally diverse organic cations (polyspecific transporters). This review provides a survey of cloned organic cation transporters and tentative models that illustrate how different types of organic cation transporters, expressed at specific subcellular sites in hepatocytes and renal proximal tubular cells, are assembled into an integrated functional framework. We briefly describe oligospecific Na(+)- and Cl(-)-dependent monoamine neurotransmitter transporters ( SLC6-family), high-affinity choline transporters ( SLC5-family), and high-affinity thiamine transporters ( SLC19-family), as well as polyspecific transporters that translocate some organic cations next to their preferred, noncationic substrates. The polyspecific cation transporters of the SLC22 family including the subtypes OCT1-3 and OCTN1-2 are presented in detail, covering the current knowledge about distribution, substrate specificity, and recent data on their electrical properties and regulation. Moreover, we discuss artificial and spontaneous mutations of transporters of the SLC22 family that provide novel insight as to the function of specific protein domains. Finally, we discuss the clinical potential of the increasing knowledge about polymorphisms and mutations in polyspecific organic cation transporters.

Pathways and control of ketone body metabolism: on the fringe of lipid biochemistry

Ketone bodies become major body fuels during fasting and consumption of a high-fat, low-carbohydrate (ketogenic) diet. Hyperketonemia is associated with potential health benefits. Ketone body synthesis (ketogenesis) is the last recognizable step of lipid energy metabolism, a pathway that links dietary lipids and adipose triglycerides to the Krebs cycle and respiratory chain and has three highly regulated control points: (1) adipocyte lipolysis, (2) mitochondrial fatty acids entry, controlled by the inhibition of carnitine palmityl transferase I by malonyl coenzyme A (CoA) and (3) mitochondrial 3-hydroxy-3-methylglutaryl CoA synthase, which catalyzes the irreversible first step of ketone body synthesis. Each step is suppressed by an elevated circulating insulin level or insulin/glucagon ratio. The utilization of ketone bodies (ketolysis) also determines circulating ketone body levels. Consideration of ketone body metabolism reveals the mechanisms underlying the extreme fragility of dietary ketosis to carbohydrate intake and highlights areas for further study.

Accumulation of mini-plasmin in the cerebral capillaries causes vascular invasion of the murine brain by a pneumotropic influenza A virus: implications for influenza-associated encephalopathy

The infectivity and pathogenicity of influenza virus are primarily determined by host cellular trypsin-type processing proteases which cleave the viral membrane fusion glycoprotein hemagglutinin (HA). Therefore the distribution of the processing protease is a major determinant of the infectious organ tropism. The common epidemic human influenza A virus is pneumotropic and the HA processing proteases tryptase Clara, mini-plasmin, tryptase TC30 and ectopic anionic trypsin have all been isolated from mammalian airways. However, the pneumotropic influenza virus occasionally causes severe brain edema, particularly in children presenting with Reye's syndrome treated with aspirin, or in children with influenza-associated encephalopathy without antipyretic treatment. We have observed that, after influenza virus infection, the accumulation of mini-plasmin in the cerebral capillaries in mice with a congenital or acquired abnormality of mitochondrial beta-oxidation mimicking the pathological findings of Reye's syndrome, causes an invasion and multiplication of the pneumotropic influenza virus at these same locations. From these findings, we hypothesize that the accumulated mini-plasmin modifies the brain capillaries from a non-permissive to a permissive state, thereby allowing multiplication of pneumotropic influenza virus. In addition, mini-plasmin proteolytically destroys the blood-brain barrier. These pathologic findings, consistent with encephalopathy in mice with a systemic impairment of beta-oxidation, may have implications for human influenza encephalopathy.

Carnitine palmitoyltransferase II deficiency: a clinical, biochemical, and molecular review

Congenital deficiency of carnitine palmitoyltransferase (CPT) II has been known for at least 30 years now, and its phenotypic variability remains fascinating. Three distinct clinical entities have been described, the adult, the infantile, and the perinatal, all with an autosomal recessive inheritance pattern. The adult CPT II clinical phenotype is somewhat benign and requires additional external triggers such as high-intensity exercise before the predominantly myopathic symptoms are elicited. The perinatal and infantile forms involve multiple organ systems. The perinatal disease is the most severe form and is invariably fatal. The introduction of mass spectrometry to analyze blood acylcarnitine profiles has revolutionized the diagnosis of fatty acid oxidation disorders including CPT II deficiency. Its use in expanded neonatal screening programs has made presymptomatic diagnosis a reality. An increasing number of mutations are being identified in the CPT II gene with a distinct genotype-phenotype correlation in most cases. However, clinical variability in some patients suggests additional genetic or environmental modifiers. Herein, we present a new case of lethal perinatal CPT II deficiency with a rare missense mutation, R296Q (907G>A) associated with a previously described 25-bp deletion on the second allele. We review the clinical features, the diagnostic protocol including expanded neonatal screening, the treatment, and the biochemical and molecular basis of CPT II deficiency.

The role of carnitine in normal and altered fatty acid metabolism

Carnitine is a low-molecular-weight compound obtained from the diet that also is biosynthesized from the essential amino acids lysine and methionine. Carnitine has been identified in a variety of mammalian tissues and has an obligate role in the mitochondrial oxidation of long-chain fatty acids through the action of specialized acyltransferases. Other roles for carnitine include buffering of the acyl coenzyme A (CoA)-CoA ratio, branched-chain amino acid metabolism, removal of excess acyl groups, and peroxisomal fatty acid oxidation. The growing body of evidence about carnitine function has led to increased understanding and identification of disorders associated with altered carnitine metabolism. Disorders of fatty acid oxidation and metabolism typically are associated with primary and secondary forms of carnitine deficiency. These disorders, which include increased lipolysis, increased lipid peroxidation, accumulation of acylcarnitines, and altered membrane permeability, have significant consequences for patients with myocardial diseases and kidney failure. Therapeutic administration of carnitine shows promise in treating selected groups of patients who have altered carnitine homeostasis, resulting in improved cardiac function, increased exercise capacity, reduced muscle cramps, and reduced intradialytic complications.

Management of fatty acid oxidation disorders: a survey of current treatment strategies

Standardization of the nutritional care for patients with fatty-acid oxidation disorders is lacking. A literature review and national survey of metabolic dietitians describes the range of therapeutic strategies currently employed in the U.S. to treat patients with fatty-acid oxidation disorders. Questionnaire responses provided by dietitians specializing in metabolic disorders evaluated practices used for treatment of fatty acid oxidation disorders, medium-chain acyl-CoA dehydrogenase deficiency (MCAD), very-long-chain acyl-CoA dehydrogenase deficiency (VLCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHAD), long-chain acyl-CoA dehydrogenase deficiency (LCAD), and Trifunctional Protein deficiency (TFP). This survey reveals a significant lack of evidence supporting the protocols in use. Recent advances in tandem mass spectrometry technology promises an increase in the number of identified patients with fatty-acid oxidation disorders, which reinforces the need for comprehensive, clinical research studies to determine optimal care for patients with these genetic disorders.

Diagnosis and management of defects of mitochondrial beta-oxidation

PURPOSE OF REVIEW

At least 22 different inborn errors of metabolism affecting beta-oxidation in skeletal muscle and other tissues have been identified in the past 30 years. Early diagnosis and therapeutic diets offer the best chance for normal growth and development in most patients.

RECENT FINDINGS

Clinical heterogeneity has become the hallmark of defects in beta-oxidation. In many cases a correct diagnosis will only be made if these disorders are specifically considered and appropriate studies are obtained, since screening tests which detect other inborn errors of metabolism are often normal in patients with beta-oxidation defects. Dietary management provides the only opportunity for therapy in many cases, including carbohydrate supplements intended to provide more extended delivery of glucose to the bloodstream. Use of a novel odd chain fat supplement as an alternative fuel source in long chain fat metabolism defects offers promise of alleviating muscular symptoms not well controlled by diet. The introduction of expanded newborn screening will lead to the recognition of an increasing number of individuals with these disorders, placing greater demand for services on practitioners knowledgeable in their therapy. Study of the clinical outcome in these patients will provide a better understanding of defects of beta-oxidation.

SUMMARY

Clinical symptoms, diagnostic testing, and issues of newborn screening for this important group of disorders are discussed.

Hypocarnitinemia in lysinuric protein intolerance

Carnitine deficiency in lysinuric protein intolerance (LPI) has been reported only in a single case. We describe hypocarnitinemia in a 11 year-old male patient with LPI and relate its development to intake, biosynthesis, and uptake of carnitine.

Metabolic approaches to the treatment of ischemic heart disease: the clinicians' perspective

This review article discusses pharmacological approaches to optimizing myocardial metabolism during ischemia. Fatty acids are the main fuel for the healthy heart, with a lesser contribution coming from the oxidation of glucose and lactate. Myocardial ischaemia dramatically alters fuel metabolism, causing an accelerated rate of glucose conversion to lactate and a switch from lactate uptake by the heart to lactate production. This causes a dramatic disruption in cell homeostasis (e.g. lactate accumulation and a decrease in pH and ATP). Paradoxically, moderately ischemic tissue (approximately 50% of normal flow) continues to derive most of its energy (50-70%) from the oxidation of fatty acids despite a high rate of lactate production. This ischaemia-induced disruption in cardiac metabolism can be minimized by metabolic agents that reduce fatty acid oxidation and increase the combustion of glucose and lactate, resulting in clinical benefit to the ischemic patient. Agents that inhibit fatty acid beta-oxidation, such as ranolazine and trimetazidine, have proven to be effective in the treatment of stable angina. Treatment of acute myocardial infarction patients with an infusion of the glucose-insulin-potassium, which results in suppression of myocardial fatty acid oxidation and greater glucose combustion, has proven effective in reducing mortality. These metabolic therapies are free of direct hemodynamic or chronotropic effects, and thus are well positioned for use alongside traditional agents such as beta-adrenergic receptor antagonists or calcium channel antagonists.

Na+- and Cl--coupled active transport of carnitine by the amino acid transporter ATB(0,+) from mouse colon expressed in HRPE cells and Xenopus oocytes

1. ATB(0,+) is an amino acid transporter energized by transmembrane gradients of Na+ and Cl(-) and membrane potential. We cloned this transporter from mouse colon and expressed the clone functionally in mammalian (human retinal pigment epithelial, HRPE) cells and Xenopus laevis oocytes to investigate the interaction of carnitine and its acyl esters with the transporter. 2. When expressed in mammalian cells, the cloned ATB(0,+) was able to transport carnitine, propionylcarnitine and acetylcarnitine. The transport process was Na(+) and Cl(-) dependent and inhibitable by the amino acid substrates of the transporter. The Michaelis constant for carnitine was 0.83 +/- 0.08 mM and the Hill coefficient for Na(+) activation was 1.6 +/- 0.1. 3. When expressed in Xenopus laevis oocytes, the cloned ATB(0,+) was able to induce inward currents in the presence of carnitine and propionylcarnitine under voltage-clamped conditions. There was no detectable current in the presence of acetylcarnitine. Carnitine-induced currents were obligatorily dependent on the presence of Na(+) and Cl(-). The currents were saturable with carnitine and the Michaelis constant was 1.8 +/- 0.4 mM. The analysis of Na(+)- and Cl(-)-activation kinetics revealed that 2 Na(+) and 1 Cl(-) were involved in the transport of carnitine via the transporter. 4. These studies describe the identification of a novel function for the amino acid transporter ATB(0,+). Since this transporter is expressed in the intestinal tract, lung and mammary gland, it is likely to play a significant role in the handling of carnitine in these tissues. 5. A Na(+)-dependent transport system for carnitine has already been described. This transporter, known as OCTN2 (novel organic cation transporter 2), is expressed in most tissues and transports carnitine with high affinity. It is energized, however, only by a Na(+) gradient and membrane potential. In contrast, ATB(0,+) is a low-affinity transporter for carnitine, but exhibits much higher concentrative capacity than OCTN2 because of its energization by transmembrane gradients of Na(+) and Cl(-) as well as by membrane potential.

Carnitine: an osmolyte that plays a metabolic role

Carnitine, gamma-trimethyl-beta-hydroxybutyrobetaine, is a small molecule widely present in all cells from prokaryotic to eukaryotic ones. It is the sole source of carbon and nitrogen in some bacteria; it serves as osmoprotectant in others. It is a carrier of acyl moieties, and exclusively of long-chain fatty acids for mitochondrial beta-oxidation in mammals. The conspicuously similar composition of the intracellular milieu among widely different species in relation to organic osmolyte systems involves the methylamine family to which carnitine belongs. This prompted us to examine the osmolytic properties of carnitine in an attempt to clarify the metabolic functions carnitine has acquired during evolution. An understanding of the metabolic functions of this organic compatible solute impinge on research involving this compound.

Defect in peroxisome proliferator-activated receptor alpha-inducible fatty acid oxidation determines the severity of hepatic steatosis in response to fasting

Fasting causes lipolysis in adipose tissue leading to the release of large quantities of free fatty acids into circulation that reach the liver where they are metabolized to generate ketone bodies to serve as fuels for other tissues. Since fatty acid-metabolizing enzymes in the liver are transcriptionally regulated by peroxisome proliferator-activated receptor alpha (PPARalpha), we investigated the role of PPARalpha in the induction of these enzymes in response to fasting and their relationship to the development of hepatic steatosis in mice deficient in PPARalpha (PPARalpha(-/-)), peroxisomal fatty acyl-CoA oxidase (AOX(-/-)), and in both PPARalpha and AOX (double knock-out (DKO)). Fasting for 48-72 h caused profound impairment of fatty acid oxidation in both PPARalpha(-/-) and DKO mice, and DKO mice revealed a greater degree of hepatic steatosis when compared with PPARalpha(-/-) mice. The absence of PPARalpha in both PPARalpha(-/-) and DKO mice impairs the induction of mitochondrial beta-oxidation in liver following fasting which contributes to hypoketonemia and hepatic steatosis. Pronounced steatosis in DKO mouse livers is due to the added deficiency of peroxisomal beta-oxidation system in these animals due to the absence of AOX. In mice deficient in AOX alone, the sustained hyperactivation of PPARalpha and up-regulation of mitochondrial beta-oxidation and microsomal omega-oxidation systems as well as the regenerative nature of a majority of hepatocytes containing numerous spontaneously proliferated peroxisomes, which appear refractory to store triglycerides, blunt the steatotic response to fasting. Starvation for 72 h caused a decrease in PPARalpha hepatic mRNA levels in wild type mice, with no perceptible compensatory increases in PPARgamma and PPARdelta mRNA levels. PPARgamma and PPARdelta hepatic mRNA levels were lower in fed PPARalpha(-/-) and DKO mice when compared with wild type mice, and fasting caused a slight increase only in PPARgamma levels and a decrease in PPARdelta levels. Fasting did not change the PPAR isoform levels in AOX(-/-) mouse liver. These observations point to the critical importance of PPARalpha in the transcriptional regulatory responses to fasting and in determining the severity of hepatic steatosis.

Fatty acid import into mitochondria

The mitochondrial carnitine system plays an obligatory role in beta-oxidation of long-chain fatty acids by catalyzing their transport into the mitochondrial matrix. This transport system consists of the malonyl-CoA sensitive carnitine palmitoyltransferase I (CPT-I) localized in the mitochondrial outer membrane, the carnitine:acylcarnitine translocase, an integral inner membrane protein, and carnitine palmitoyltransferase II localized on the matrix side of the inner membrane. Carnitine palmitoyltransferase I is subject to regulation at the transcriptional level and to acute control by malonyl-CoA. The N-terminal domain of CPT-I is essential for malonyl-CoA inhibition. In liver CPT-I activity is also regulated by changes in the enzyme's sensitivity to malonyl-CoA. As fluctuations in tissue malonyl-CoA content are parallel with changes in acetyl-CoA carboxylase activity, which in turn is under the control of 5'-AMP-activated protein kinase, the CPT-I/malonyl-CoA system is part of a fuel sensing gauge, turning off and on fatty acid oxidation depending on the tissue's energy demand. Additional mechanism(s) of short-term control of CPT-I activity are emerging. One proposed mechanism involves phosphorylation/dephosphorylation dependent direct interaction of cytoskeletal components with the mitochondrial outer membrane or CPT-I. We have proposed that contact sites between the outer and inner mitochondrial membranes form a microenvironment which facilitates the carnitine transport system. In addition, this system includes the long-chain acyl-CoA synthetase and porin as components.

beta-lactam antibiotics as substrates for OCTN2, an organic cation/carnitine transporter

Therapeutic use of cephaloridine, a beta-lactam antibiotic, in humans is associated with carnitine deficiency. A potential mechanism for the development of carnitine deficiency is competition between cephaloridine and carnitine for the renal reabsorptive process. OCTN2 is an organic cation/carnitine transporter that is responsible for Na(+)-coupled transport of carnitine in the kidney and other tissues. We investigated the interaction of several beta-lactam antibiotics with OCTN2 using human cell lines that express the transporter constitutively as well as using cloned human and rat OCTN2s expressed heterologously in human cell lines. The beta-lactam antibiotics cephaloridine, cefoselis, cefepime, and cefluprenam were found to inhibit OCTN2-mediated carnitine transport. These antibiotics possess a quaternary nitrogen as does carnitine. Several other beta-lactam antibiotics that do not possess this structural feature did not interact with OCTN2. The interaction of cephaloridine with OCTN2 is competitive with respect to carnitine. Interestingly, many of the beta-lactam antibiotics that were not recognized by OCTN2 were good substrates for the H(+)-coupled peptide transporters PEPT1 and PEPT2. In contrast, cephaloridine, cefoselis, cefepime, and cefluprenam, which were recognized by OCTN2, did not interact with PEPT1 and PEPT2. The interaction of cephaloridine with OCTN2 was Na(+)-dependent, whereas the interaction of cefoselis and cefepime with OCTN2 was largely Na(+)-independent. Furthermore, the Na(+)-dependent, OCTN2-mediated cellular uptake of cephaloridine could be demonstrated by direct uptake measurements. These studies show that OCTN2 plays a crucial role in the pharmacokinetics and therapeutic efficacy of certain beta-lactam antibiotics such as cephaloridine and that cephaloridine-induced carnitine deficiency is likely to be due to inhibition of carnitine reabsorption in the kidney.