Carnitine: a nutritional, biosynthetic, and functional perspective

Changes of lymph metabolites in a rat model of sepsis induced by cecal ligation and puncture

BACKGROUND

Sepsis is a clinical syndrome defined by a systemic response to infection and remains a prevalent clinical challenge. The underlying pathophysiology of sepsis is poorly understood. Using a metabolomic method, the present study observed changes in lymph composition during sepsis in a septic model in an attempt to find out new biomarkers for the early diagnosis and treatment of sepsis.

METHODS

Adult male Sprague-Dawley rats underwent cecal ligation and puncture. Blood samples were obtained via the lateral caudal vein, and lymph was obtained from the thoracic duct. Cytokines were measured in plasma and lymph samples by enzyme-linked immunosorbent assay at different time points after cecal ligation and puncture. Rat lymph samples were analyzed by high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Multivariate analysis was used to profile potential biomarkers in rat septic lymph samples.

RESULTS

Plasma and lymph tumor necrosis factor α, interleukin 1β, and interleukin 6 levels were elevated in septic group as compared with the control. Of the 10 characteristic metabolites identified in the septic model, six (palmitoyl-L-carnitine, creatinine, phenylalanine, isonicotinic acid, choline, and 5-azacytidine) were high, and four (1-O-Hexadecyl-2-lyso-glycero-3-phosphorylcholine, alanine, 4-amino-5-hydroxymethyl-2-methylpyrimidine, and asymmetric dimethylarginine) were low.

CONCLUSION

These biomarkers were mainly involved in energy metabolism and vascular tone and may prove beneficial to distinguish sepsis from other inflammatory conditions or predict outcomes.

Drp1-mediated mitochondrial dynamics and survival of developing chick motoneurons during the period of normal programmed cell death

Mitochondrial morphology is dynamically remodeled by fusion and fission in neurons, and this process is implicated in nervous system development and pathology. However, the mechanism by which mitochondrial dynamics influence neuronal development is less clear. In this study, we found that the length of mitochondria is progressively reduced during normal development of chick embryo motoneurons (MNs), a process partly controlled by a fission-promoting protein, dynamin-related protein 1 (Drp1). Suppression of Drp1 activity by gene electroporation of dominant-negative mutant Drp1 in a subset of developing MNs increased mitochondrial length in vivo, and a greater proportion of Drp1-suppressed MNs underwent programmed cell death (PCD). By contrast, the survival of nontransfected MNs in proximity to the transfected MNs was significantly increased, suggesting that the suppression of Drp1 confers disadvantage during the competition for limited survival signals. Because we also monitored perturbation of neurite outgrowth and mitochondrial membrane depolarization following Drp1 suppression, we suggest that impairments of ATP production and axonal growth may be downstream factors that influence the competition of MNs for survival. Collectively, these results indicate that mitochondrial dynamics are required for normal axonal development and competition-dependent MN PCD.

Free carnitine and acylcarnitines in obese patients with polycystic ovary syndrome and effects of pioglitazone treatment

OBJECTIVE

To determine fasting and insulin-stimulated levels of carnitine precursors, total and free carnitine, and acylcarnitines, and evaluate the impact of pioglitazone treatment in obese patients with polycystic ovary syndrome (PCOS).

DESIGN

The present study is a secondary analysis of a previously published case-control study, followed by a double-blind randomized clinical trial.

SETTING

Academic tertiary care medical center.

PATIENT(S)

Thirty obese premenopausal patients with PCOS and 14 healthy women.

INTERVENTION(S)

Sixteen weeks of blinded treatment with pioglitazone (30 mg/d) or placebo.

MAIN OUTCOME MEASURE(S)

Total and free carnitine and acylcarnitines.

RESULT(S)

Contrary to controls, patients with PCOS were characterized with slightly lower levels of fasting total and free carnitine, its precursors, and derivatives. Total and free carnitine correlated inversely to sex hormone-binding globulin (SHBG) in patients with PCOS, whereas no associations were found between acylcarnitines and androgenes. Insulin stimulation-induced changes in the levels of total and free carnitine, carnitine precursors, and acylcarnitines in the PCOS group followed the same trends as in the control group. Pioglitazone treatment significantly increased fasting levels of serum-free carnitine, propionyl carnitine, and total carnitine. The analysis of between group differences revealed significant changes in the isovaleryl carnitine levels and lipid oxidation rates after pioglitazone treatment compared with placebo.

CONCLUSION(S)

Acute insulin stimulation was associated with increased serum levels of free carnitine in both patients and healthy controls. Treatment with pioglitazone is able to redistribute free fatty acids from insulin-sensitive tissues, diminish demand for carnitine, and influence the overall carnitine turnover.

CLINICAL TRIAL REGISTRATION NUMBER

NCT00145340.

Changing metabolic signatures of amino acids and lipids during the prediabetic period in a pig model with impaired incretin function and reduced β-cell mass

Diabetes is generally diagnosed too late. Therefore, biomarkers indicating early stages of β-cell dysfunction and mass reduction would facilitate timely counteraction. Transgenic pigs expressing a dominant-negative glucose-dependent insulinotropic polypeptide receptor (GIPR(dn)) reveal progressive deterioration of glucose control and reduction of β-cell mass, providing a unique opportunity to study metabolic changes during the prediabetic period. Plasma samples from intravenous glucose tolerance tests of 2.5- and 5-month-old GIPR(dn) transgenic and control animals were analyzed for 163 metabolites by targeted mass spectrometry. Analysis of variance revealed that 26 of 163 parameters were influenced by the interaction Genotype × Age (P ≤ 0.0001) and thus are potential markers for progression within the prediabetic state. Among them, the concentrations of seven amino acids (Phe, Orn, Val, xLeu, His, Arg, and Tyr) were increased in 2.5-month-old but decreased in 5-month-old GIPR(dn) transgenic pigs versus controls. Furthermore, specific sphingomyelins, diacylglycerols, and ether phospholipids were decreased in plasma of 5-month-old GIPR(dn) transgenic pigs. Alterations in plasma metabolite concentrations were associated with liver transcriptome changes in relevant pathways. The concentrations of a number of plasma amino acids and lipids correlated significantly with β-cell mass of 5-month-old pigs. These metabolites represent candidate biomarkers of early phases of β-cell dysfunction and mass reduction.

Investigating potential mechanisms of obesity by metabolomics

Obesity is a serious health problem with an increased risk of several common diseases including diabetes, cardiovascular disease, and cancer. Metabolomics is an emerging analytical technique for systemic determination of metabolite profiles, which is useful for understanding the biochemical changes in obesity or related diseases both in individual organs and at the organism level. Increasingly, this technology has been applied to the study of obesity, complementing transcriptomics and/or proteomics analyses. Indeed, the alterations of metabolites in biofluids/tissues are direct indicators of variations in physiology or pathology. In this paper, we will examine the obesity-related alterations in significant metabolites that have been identified by metabolomics as well as their metabolic pathway associations. Issues concerning the screening of biologically significant metabolites related to obesity will also be discussed.

Post-treatment with the combination of 5-aminoimidazole-4-carboxyamide ribonucleoside and carnitine improves renal function after ischemia/reperfusion injury

Renal ischemia/reperfusion (I/R) injury is a major clinical problem where main metabolic pathways are compromised and cellular homeostasis crashes after ATP depletion. Fatty acids are major energy source in the kidneys. Carnitine palmitoyltransferase I (CPT1), a mitochondrial membrane enzyme, utilizes carnitine to transport fatty acids to mitochondria for the process of β-oxidation and ATP generation. In addition, CPT1 activity is indirectly regulated by adenosine monophosphate-activated protein kinase, which can be activated by 5-aminoimidazole-4-carboxyamide ribonucleoside (AICAR). We hypothesized that administration of carnitine and AICAR could reestablish the energetic balance after reperfusion and ameliorate renal I/R injury. Male adult rats were subjected to renal I/R by bilateral renal pedicle clamping for 60 min, followed by administration of saline (vehicle), carnitine (250 mg/kg BW), AICAR (30 mg/kg BW), or combination of both drugs. Blood and renal tissues were collected 24 h after reperfusion for various measurements. Renal carnitine levels decreased 53% after I/R. The combined treatment significantly increased CPT1 activity and ATP levels and lowered renal malondialdehyde and serum TNF-α levels against the vehicle group. It led to improvement in renal morphology and histological damage score associated with diminution in serum creatinine, blood urea nitrogen, and aspartate aminotransferase levels. Moreover, the combined treatment significantly improved the survival rate in comparison to the vehicle group. In contrast, administration of either drug alone did not show a significant improvement in most of the measurements. In conclusion, enhancing energy metabolism by combination of carnitine and AICAR provides a novel modality to treat renal I/R injury.

Analysis of acylcarnitine profiles in umbilical cord blood and during the early neonatal period by electrospray ionization tandem mass spectrometry

Acylcarnitine profiling by electrospray ionization tandem mass spectrometry (ESI-MS/MS) is a potent tool for the diagnosis and screening of fatty acid oxidation and organic acid disorders. Few studies have analyzed free carnitine and acylcarnitines in dried blood spots (DBS) of umbilical cord blood (CB) and the postnatal changes in the concentrations of these analytes. We have investigated these metabolites in healthy exclusively breastfed neonates and examined possible effects of birth weight and gestational age. DBS of CB were collected from 162 adequate for gestational age neonates. Paired DBS of heel-prick blood were collected 4-8 days after birth from 106 of these neonates, the majority exclusively breastfed. Methanol extracts of DBS with deuterium-labeled internal standards were derivatized before analysis by ESI-MS/MS. Most of the analytes were measured using a full-scan method. The levels of the major long-chain acylcarnitines, palmitoylcarnitine, stearoylcarnitine, and oleoylcarnitine, increased by 27, 12, and 109%, respectively, in the first week of life. Free carnitine and acetylcarnitine had a modest increase: 8 and 11%, respectively. Propionylcarnitine presented a different behavior, decreasing 9% during the period. The correlations between birth weight or gestational age and the concentrations of the analytes in DBS were weak (r ≤ 0.20) or nonsignificant. Adaptation to breast milk as the sole source of nutrients can explain the increase of these metabolites along the early neonatal period. Acylcarnitine profiling in CB should have a role in the early detection of metabolic disorders in high-risk neonates.

Metabolomic analysis reveals that carnitines are key regulatory metabolites in phase transition of the locusts

Phenotypic plasticity occurs prevalently and plays a vital role in adaptive evolution. However, the underlying molecular mechanisms responsible for the expression of alternate phenotypes remain unknown. Here, a density-dependent phase polyphenism of Locusta migratoria was used as the study model to identify key signaling molecules regulating the expression of phenotypic plasticity. Metabolomic analysis, using high-performance liquid chromatography and gas chromatography-mass spectrometry, showed that solitarious and gregarious locusts have distinct metabolic profiles in hemolymph. A total of 319 metabolites, many of which are involved in lipid metabolism, differed significantly in concentration between the phases. In addition, the time course of changes in the metabolic profiles of locust hemolymph that accompany phase transition was analyzed. Carnitine and its acyl derivatives, which are involved in the lipid β-oxidation process, were identified as key differential metabolites that display robust correlation with the time courses of phase transition. RNAi silencing of two key enzymes from the carnitine system, carnitine acetyltransferase and palmitoyltransferase, resulted in a behavioral transition from the gregarious to solitarious phase and the corresponding changes of metabolic profiles. In contrast, the injection of exogenous acetylcarnitine promoted the acquisition of gregarious behavior in solitarious locusts. These results suggest that carnitines mediate locust phase transition possibly through modulating lipid metabolism and influencing the nervous system of the locusts.

Transfer of metabolites across the peroxisomal membrane

Peroxisomes perform a large variety of metabolic functions that require a constant flow of metabolites across the membranes of these organelles. Over the last few years it has become clear that the transport machinery of the peroxisomal membrane is a unique biological entity since it includes nonselective channels conducting small solutes side by side with transporters for 'bulky' solutes such as ATP. Electrophysiological experiments revealed several channel-forming activities in preparations of plant, mammalian, and yeast peroxisomes and in glycosomes of Trypanosoma brucei. The properties of the first discovered peroxisomal membrane channel - mammalian Pxmp2 protein - have also been characterized. The channels are apparently involved in the formation of peroxisomal shuttle systems and in the transmembrane transfer of various water-soluble metabolites including products of peroxisomal β-oxidation. These products are processed by a large set of peroxisomal enzymes including carnitine acyltransferases, enzymes involved in the synthesis of ketone bodies, thioesterases, and others. This review discusses recent data pertaining to solute permeability and metabolite transport systems in peroxisomal membranes and also addresses mechanisms responsible for the transfer of ATP and cofactors such as an ATP transporter and nudix hydrolases.

Role of carnitine in the regulation of glucose homeostasis and insulin sensitivity: evidence from in vivo and in vitro studies with carnitine supplementation and carnitine deficiency

BACKGROUND

Although carnitine is best known for its role in the import of long-chain fatty acids (acyl groups) into the mitochondrial matrix for subsequent β-oxidation, carnitine is also necessary for the efflux of acyl groups out of the mitochondria. Since intracellular accumulation of acyl-CoA derivatives has been implicated in the development of insulin resistance, carnitine supplementation has gained attention as a tool for the treatment of insulin resistance. More recent studies even point toward a causative role for carnitine insufficiency in developing insulin resistance during states of chronic metabolic stress, such as obesity, which can be reversed by carnitine supplementation.

METHODS

The present review provides an overview about data from both animal and human studies reporting effects of either carnitine supplementation or carnitine deficiency on parameters of glucose homeostasis and insulin sensitivity in order to establish the less well-recognized role of carnitine in regulating glucose homeostasis.

RESULTS

Carnitine supplementation studies in both humans and animals demonstrate an improvement of glucose tolerance, in particular during insulin-resistant states. In contrast, less consistent results are available from animal studies investigating the association between carnitine deficiency and glucose intolerance. The majority of studies dealing with this question could either find no association or even reported that carnitine deficiency lowers blood glucose and improves insulin sensitivity.

CONCLUSIONS

In view of the abovementioned beneficial effect of carnitine supplementation on glucose tolerance during insulin-resistant states, carnitine supplementation might be an effective tool for improvement of glucose utilization in obese type 2 diabetic patients. However, further studies are necessary to explain the conflicting observations from studies dealing with carnitine deficiency.

Cellular stress responses, hormetic phytochemicals and vitagenes in aging and longevity

Modulation of endogenous cellular defense mechanisms represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. This paper introduces the emerging role of exogenous molecules in hormetic-based neuroprotection and the mitochondrial redox signaling concept of hormesis and its applications to the field of neuroprotection and longevity. Maintenance of optimal long-term health conditions is accomplished by a complex network of longevity assurance processes that are controlled by vitagenes, a group of genes involved in preserving cellular homeostasis during stressful conditions. Vitagenes encode for heat shock proteins (Hsp) Hsp32, Hsp70, the thioredoxin and the sirtuin protein systems. Dietary antioxidants, such as polyphenols and L-carnitine/acetyl-L-carnitine, have recently been demonstrated to be neuroprotective through the activation of hormetic pathways, including vitagenes. Hormesis provides the central underpinning of neuroprotective responses, providing a framework for explaining the common quantitative features of their dose response relationships, their mechanistic foundations, their relationship to the concept of biological plasticity as well as providing a key insight for improving the accuracy of the therapeutic dose of pharmaceutical agents within the highly heterogeneous human population. This paper describes in mechanistic detail how hormetic dose responses are mediated for endogenous cellular defense pathways including sirtuin, Nrfs and related pathways that integrate adaptive stress responses in the prevention of neurodegenerative diseases. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Randomised clinical trial: the efficacy and safety of propionyl-L-carnitine therapy in patients with ulcerative colitis receiving stable oral treatment

BACKGROUND

Ulcerative colitis (UC) is characterised by impaired fatty-acid oxidation; l-carnitine has a key role in fatty-acid metabolism and short-chain fatty acids such as butyrate and propionate are important energy source for intestinal epithelial cells.

AIM

To evaluate efficacy and safety of colon-release propionyl-L-carnitine (PLC) in patients with mild-to-moderate UC receiving stable oral aminosalicylate or thiopurine therapy.

METHODS

In a multicentre, phase II, double-blind, parallel-group trial, patients were randomised to receive PLC 1 g/day, PLC 2 g/day or placebo. Main inclusion criteria were as follows: age 18-75; disease activity index (DAI) score 3-10 inclusive, be under oral stable treatment with aminosalicylate or thiopurine. The primary endpoint was clinical/endoscopic response, defined as a decrease in DAI score ≥ 3 points or remission, defined as a DAI score ≤ 2 with no individual sub-score > 1.

RESULTS

Of 121 patients who were randomised, 57 of 79 (72%) patients receiving PLC (combined 1 g and 2 g cohort) had a clinical/endoscopic response vs. 20 of 40 (50%) receiving placebo (P = 0.02). Specifically, in PLC 1 g/day group, 30 of 40 (75%) patients had clinical/endoscopic response (P = 0.02 vs. placebo) and 27 of 39 (69%) in the PLC 2 g/day group (P = 0.08 vs. placebo). Rates of remission were 22/40 (55%), 19/39 (49%), 14/40 (35%) in the PLC 1 g, PLC 2 g, and placebo groups, respectively. PLC had a similar safety profile to placebo; the most common adverse events were gastrointestinal.

CONCLUSION

Propionyl-L-carnitine 1 g/day should be investigated further as a co-treatment for mild-to-moderate ulcerative colitis (NCT-01026857).

Effect of L-carnitine on the hepatic transcript profile in piglets as animal model

Background

Carnitine has attracted scientific interest due to several health-related effects, like protection against neurodegeneration, mitochondrial decay, and oxidative stress as well as improvement of glucose tolerance and insulin sensitivity. The mechanisms underlying most of the health-related effects of carnitine are largely unknown.

Methods

To gain insight into mechanisms through which carnitine exerts its beneficial metabolic effects, we fed piglets either a control or a carnitine supplemented diet, and analysed the transcriptome in the liver.

Results

Transcript profiling revealed 563 genes to be differentially expressed in liver by carnitine supplementation. Clustering analysis of the identified genes revealed that most of the top-ranked annotation term clusters were dealing with metabolic processes. Representative genes of these clusters which were significantly up-regulated by carnitine were involved in cellular fatty acid uptake, fatty acid activation, fatty acid β-oxidation, glucose uptake, and glycolysis. In contrast, genes involved in gluconeogenesis were down-regulated by carnitine. Moreover, clustering analysis identified genes involved in the insulin signaling cascade to be significantly associated with carnitine supplementation. Furthermore, clustering analysis revealed that biological processes dealing with posttranscriptional RNA processing were significantly associated with carnitine supplementation.

Conclusion

The data suggest that carnitine supplementation has beneficial effects on lipid and glucose homeostasis by inducing genes involved in fatty acid catabolism and glycolysis and repressing genes involved in gluconeogenesis.

High-resolution analysis of metabolic cycles in the intertidal mussel Mytilus californianus

Inhabitants of the marine rocky intertidal live in an environment that alternates between aquatic and terrestrial due to the rise and fall of the tide. The tide creates a cyclical availability of oxygen with animals having access to oxygenated water during episodes of submergence, while access to oxygen is restricted during aerial emergence. Here we performed liquid chromatography and gas chromatography-mass spectrometry enabled metabolomic profiling of gill samples isolated from the California ribbed mussel, Mytilus californianus, to investigate how metabolism is orchestrated in this variable environment. We created a simulated intertidal environment in which mussels were acclimated to alternating high and low tides of 6 h duration, and samples were taken every 2 h for 72 h to capture reproducible changes in metabolite levels over six high and six low tides. We quantified 169 named metabolites of which 24 metabolites cycled significantly with a 12-h period that was linked to the tidal cycle. These data confirmed the presence of alternating phases of fermentation and aerobic metabolism and highlight a role for carnitine-conjugated metabolites during the anaerobic phase of this cycle. Mussels at low tide accumulated eight carnitine-conjugated metabolites, arising from the degradation of fatty acids, branched-chain amino acids, and mitochondrial β-oxidation end products. The data also implicate sphingosine as a potential signaling molecule during aerial emergence. These findings identify new levels of metabolic control whose role in intertidal adaptation remains to be elucidated.

Metabolic agents that enhance ATP can improve cognitive functioning: a review of the evidence for glucose, oxygen, pyruvate, creatine, and L-carnitine

Over the past four or five decades, there has been increasing interest in the neurochemical regulation of cognition. This field received considerable attention in the 1980s, with the identification of possible cognition enhancing agents or "smart drugs". Even though many of the optimistic claims for some agents have proven premature, evidence suggests that several metabolic agents may prove to be effective in improving and preserving cognitive performance and may lead to better cognitive aging through the lifespan. Aging is characterized by a progressive deterioration in physiological functions and metabolic processes. There are a number of agents with the potential to improve metabolic activity. Research is now beginning to identify these various agents and delineate their potential usefulness for improving cognition in health and disease. This review provides a brief overview of the metabolic agents glucose, oxygen, pyruvate, creatine, and L-carnitine and their beneficial effects on cognitive function. These agents are directly responsible for generating ATP (adenosine triphosphate) the main cellular currency of energy. The brain is the most metabolically active organ in the body and as such is particularly vulnerable to disruption of energy resources. Therefore interventions that sustain adenosine triphosphate (ATP) levels may have importance for improving neuronal dysfunction and loss. Moreover, recently, it has been observed that environmental conditions and diet can affect transgenerational gene expression via epigenetic mechanisms. Metabolic agents might play a role in regulation of nutritional epigenetic effects. In summary, the reviewed metabolic agents represent a promising strategy for improving cognitive function and possibly slowing or preventing cognitive decline.

L-carnitine enhances oocyte maturation and development of parthenogenetic embryos in pigs

The objective was to determine whether adding L-carnitine in IVM/IVC medium enhanced maturation and developmental competence of porcine oocytes in vitro. Oocyte maturation rates did not differ significantly among groups supplemented with 0, 0.25, 0.5, or 1 mg/mL of L-carnitine added during IVM (although 2 mg/mL of L-carnitine reduced maturation rate). Compared with control oocytes, those treated with 0.5 mg/mL of L-carnitine during IVM had greater (P < 0.05) rates of blastocyst formation after parthenogenetic activation, and these blastocysts had less (P < 0.05) apoptosis. Adding 0.5 mg/mL of L-carnitine during IVM also significantly reduced intracellular reactive oxygen species (ROS), and increased glutathione (GSH) concentrations. With or without glucose supplementation, 0.5 mg/mL of L-carnitine in the IVM medium significantly hastened nuclear maturation of oocytes. Moreover, supplementing the IVM medium with either glucose or L-carnitine increased (P < 0.05) percentages of oocytes that reached the metaphase II (MII) stage, relative to a control group. Final maturation rates in IVM medium containing either glucose or L-carnitine were not significantly different. Adding L-carnitine (0 to 2 mg/mL) to IVC medium for activated porcine oocytes did not significantly affect development. However, 0.5 mg/mL of L-carnitine in IVC medium significantly reduced reactive oxygen species levels and apoptosis in activated blastocysts, although glutathione concentrations were not significantly altered. In conclusion, adding L-carnitine during IVM/IVC improved developmental potential of porcine oocytes, and also the quality of parthenogenetic embryos, probably by accelerating nuclear maturation, and preventing oxidative damage and apoptosis.

Practical and Efficient Utilisation of (R)-3-chloro-1,2-Propanediol in Synthesis of L-Carnitine

As a by-product originating from Salen Co(III) catalysed hydrolytic kinetic resolution (HKR) of (±)-epichlorohydrin in the manufacturing procedure of L-Carnitine, ( R)-3-chloro-1,2-propanediol was utilised as a starting chiral material to prepare via key nitrile intermediates and by a final hydrolysis L-Carnitine. The new synthetic approach demonstrated an efficient utilisation of the by-product.

Changes in the metabolic profile of rat liver after α-tocopherol deficiency as revealed by metabolomics analysis

Metabolomics is an approach in which the profiles of metabolites in different tissues and/or biofluids are investigated to understand the changes induced following a modulation. We used this approach to investigate the biochemical effects of α-tocopherol in the liver using a rat model. Rats (21-day-old) were fed either an α-tocopherol-sufficient control (n = 10) or an α-tocopherol-deficient (n = 10) diet for 2 months before sacrifice. Livers were homogenized in methanol-chloroform-water (3 : 1 : 1, v/v/v), and the polar phase extracts of the liver samples were analyzed using (1) H NMR. Multivariate statistical analysis of the data was performed using principal component analysis and orthogonal partial least squares-discriminant analysis. Identification of (1) H NMR signals was performed primarily using the Human Metabolome Database, Biological Magnetic Resonance Data Bank and previous literature, and confirmed by spiking with metabolites and applying two-dimensional NMR. The statistical analysis revealed that α-tocopherol deficiency caused an increase in carnitine, choline, L-valine, L-lysine, tyrosine and inosine content and a reduction in glucose and uridine 5'-monophosphate content. Changes in carnitine and glucose suggest a possible shift in energy metabolism.

Carnitine regulates myocardial metabolism by Peroxisome Proliferator-Activated Receptor-alpha (PPARalpha) in alcoholic cardiomyopathy

BACKGROUND

Chronic alcohol intake exerts myocardial damage en route to the development of alcoholic cardiomyopathy (ACM), although the precise pathogenesis of ACM is unknown. Carnitine is known to participate in the regulation of metabolism in a number of heart diseases. This study was designed to examine the interplay between myocardial metabolism and carnitine in the development of ACM.

MATERIAL/METHODS

Experimental animals were divided into 3 groups: (i) group A: alcohol-fed. (ii) group B: alcohol/carnitine: (200mg/kg/d, p.o. by mixing carnitine in rat chow). (iii) group C: control. Blood levels of free fatty acid (FFA), total carnitine (TC) and free carnitine (FC) were monitored in rats receiving alcohol with or without carnitine. Mitochondrial adenine nucleotide translocator-1 (ANT1) activity, ATPase activity, high energy phosphate concentration, peroxisome proliferator-activated receptor-α (PPARα), carnitine-palmitoyl transferase I (CPT-I), medium-chain acyl-coenzyme A dehydrogenase (MCAD), ANT1 and ATPase mRNA and protein expression were also monitored in myocardial tissue.

RESULTS

Experimental animals received alcohol with or without carnitine for six 6 months. Our results indicated that FFA increased abruptly. TC and FC were significantly decreased in groups receiving alcohol at 4 months. The concentration of ATP, ADP and AMP in the myocardium decreased following 2 months of alcohol administration. mRNA and protein expression of PPARα, CPT-I, MCAD, ANT1 and ATPase expressions were gradually altered in groups following alcohol feeding.

CONCLUSIONS

These observations suggest that abnormal metabolism is present in the myocardium during the development of ACM. Carnitine may improve myocardial metabolism by elevating the content of PPARα, CPT-I and MCAD.

L-carnitine protects against nickel-induced neurotoxicity by maintaining mitochondrial function in Neuro-2a cells

Mitochondrial dysfunction is thought to be a part of the mechanism underlying nickel-induced neurotoxicity. L-carnitine (LC), a quaternary ammonium compound biosynthesized from the amino acids lysine and methionine in all mammalian species, manifests its neuroprotective effects by improving mitochondrial energetics and function. The purpose of this study was to investigate whether LC could efficiently protect against nickel-induced neurotoxicity. Here, we exposed a mouse neuroblastoma cell line (Neuro-2a) to different concentrations of nickel chloride (NiCl₂) (0.25, 0.5, 1, and 2 mM) for 24 h, or to 0.5 mM and 1 mM NiCl₂ for various periods (0, 3, 6, 12, or 24 h). We found that nickel significantly increased the cell viability loss and lactate dehydrogenase (LDH) release in Neuro-2a cells. In addition, nickel exposure significantly elevated reactive oxygen species (ROS) and malondialdehyde (MDA) levels, disrupted the mitochondrial membrane potential (ΔΨ(m)), reduced adenosine-5'-triphosphate (ATP) concentrations and decreased mitochondrial DNA (mtDNA) copy numbers and mtRNA transcript levels. However, all of the cytotoxicities and mitochondrial dysfunctions that were triggered by nickel were efficiently attenuated by pretreatment with LC. These protective effects of LC may be attributable to its role in maintaining mitochondrial function in nickel-treated cells. Our results suggest that LC may have great pharmacological potential in protecting against the adverse effects of nickel in the nervous system.

Integrated ionization approach for RRLC-MS/MS-based metabonomics: finding potential biomarkers for lung cancer

An integrated ionization approach of electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI) combining with rapid resolution liquid chromatography mass spectrometry (RRLC-MS) has been developed for performing global metabonomic analysis on complex biological samples. This approach was designed to overcome the low ionization efficiencies of endogenous metabolites due to diverse physicochemical properties as well as ion suppression, and obtain comprehensive metabolite profiles in LC-MS analysis. Ionization capability and applicability were manifested by improved ionization efficiency and enlarged metabolite coverage in analysis on typical urinary metabolite standards and urine samples from healthy volunteers. The method was validated by the limit of detection and precision. When applied to the global metabonomic studies of lung cancer, more comprehensive biomarker candidates were obtained to reflect metabolic traits between healthy volunteers and lung cancer patients, including 74 potential biomarkers in positive ion mode and 59 in negative ion mode. Taking identical potential biomarkers of any two or three ionization methods into account, analysis using ESI-MS in positive (+) and negative (-) ion mode contributed to 70 and 64% of the total potential biomarkers, respectively. The biomarker discovery capability of (+/-) APCI-MS accounted for 45 and 42% of the overall; meanwhile (+/-) APPI-MS amounted for 39 and 54%. These results indicated that potential biomarkers with vital biological information could be missed if only a single ionization method was used. Furthermore, 11 potential biomarkers were identified including amino acids, nucleosides, and a metabolite of indole. They revealed elevated amino acid and nucleoside metabolism as well as protein degradation in lung cancer patients. This proposed approach provided a more comprehensive picture of the metabolic changes and further verified identical biomarkers that were obtained simultaneously using different ionization methods.

Metabolomic analysis of livers and serum from high-fat diet induced obese mice

Liver and serum metabolites of obese and lean mice fed on high fat or normal diets were analyzed using ultraperformance liquid chromatography-quadrupole-time-of-flight mass spectrometry, gas chromatography-mass spectrometry, and partial least-squares-discriminant analysis (PLS-DA). Obese and lean groups were clearly discriminated from each other on PLS-DA score plot and major metabolites contributing to the discrimination were assigned as lipid metabolites (fatty acids, phosphatidylcholines (PCs), and lysophosphatidylcholines (lysoPCs)), lipid metabolism intermediates (betaine, carnitine, and acylcarnitines), amino acids, acidic compounds, monosaccharides, and serotonin. A high-fat diet increased lipid metabolites but decreased lipid metabolism intermediates and the NAD/NADH ratio, indicating that abnormal lipid and energy metabolism induced by a high-fat diet resulted in fat accumulation via decreased β-oxidation. In addition, this study revealed that the levels of many metabolites, including serotonin, betaine, pipecolic acid, and uric acid, were positively or negatively related to obesity-associated diseases. On the basis of these metabolites, we proposed a metabolic pathway related to high-fat diet-induced obesity. These metabolites can be used to better understand obesity and related diseases induced by a hyperlipidic diet. Furthermore, the level changes of these metabolites can be used to assess the risk of obesity and the therapeutic effect of obesity management.

Effects of acetyl-L-carnitine and oxfenicine on aorta stiffness in diabetic rats

BACKGROUND

We compared the haemodynamic and metabolic effects of acetyl-L-carnitine (one of the carnitine derivatives) and of oxfenicine (a carnitine palmitoyltransferase-1 inhibitor) in streptozotocin-induced diabetes in male Wistar rats.

MATERIALS AND METHODS

Diabetes was induced by a single tail vein injection of 55mgkg(-1) streptozotocin. The diabetic animals daily treated with either acetyl-L-carnitine (150mgkg(-1) in drinking water) or oxfenicine (150mgkg(-1) by oral gavage) for 8weeks,were compared with the untreated age-matched diabetic controls. Arterial wave reflection was derived using the impulse response function of the filtered aortic input impedance spectra. Thiobarbituric acid reactive substances (TBARS) measurement was used to estimate malondialdehyde (MDA) content.

RESULTS

Oxfenicine, but not acetyl-L-carnitine, increased total peripheral resistance in diabetes, which paralleled its elevation in plasma levels of free fatty acids. By contrast, acetyl-L-carnitine, but not oxfenicine, resulted in a significant increase in wave transit time and a decrease in wave reflection factor, suggesting that acetyl-L-carnitine may attenuate the diabetes-induced deterioration in systolic loading condition for the left ventricle. This was in parallel with its lowering of MDA/TBARS content in plasma and aortic walls in diabetes. Acetyl-L-carnitine therapy also prevented the diabetes-related cardiac hypertrophy, as evidenced by the reduction in ratio of the left ventricular weight to body weight.

CONCLUSION

 Acetyl-L-carnitine, but not oxfenicine, attenuates aortic stiffening and cardiac hypertrophy, possibly through its decrease of lipid oxidation-derived MDA/TBARS in the rats with insulin deficiency.

Role of carnitine in cancer chemotherapy-induced multiple organ toxicity

In the last few years, cancer chemotherapy has been successfully employed in the treatment of different types of human tumours. Unfortunately, the optimal clinical usefulness of this important treatment modality is usually limited secondary to the development of life-threatening multiple organ toxicity. Cancer chemotherapy may cause these toxic effects by mechanisms not involved in their anticancer activity that can severely affect the life of patients and represent a direct cause of death. Several experimental and clinical studies have demonstrated that some important anticancer drugs interfere with the absorption, synthesis, and excretion of carnitine in non-tumour tissues, resulting in a secondary carnitine deficiency which is reversed by carnitine treatment without affecting anticancer therapeutic efficacy. Prototypes of anticancer drugs that alter carnitine system are doxorubicin, cisplatin, carboplatin, oxaliplatin, cyclophosphamide and ifosfamide. Furthermore, cachectic cancer patients are especially at risk for carnitine deficiency due to decreased oral intake and/or increased renal losses. Altered serum and urine carnitine levels have been reported in cancer patients with various forms of malignant diseases. Recent studies in our laboratory have demonstrated that carnitine deficiency constitute a risk factor and should be viewed as a mechanism during development of oxazaphosphorines-induced cardiotoxicity in rats. Similarly, inhibition of gene expression of heart fatty acid-binding protein and organic cation/carnitine transporter in doxorubicin cardiomyopathic rat model has been reported. In view of these facts and in view of irreplaceability of these important anticancer drugs, this review aimed to highlight the role of carnitine depletion and supplementation during development of chemotherapy-induced multiple organ toxicity.

Colon OCTN2 gene expression is up-regulated by peroxisome proliferator-activated receptor gamma in humans and mice and contributes to local and systemic carnitine homeostasis

In the large intestine organic cation transporter type-2 (OCTN2) is recognized as a transporter of compounds such as carnitine and colony sporulation factor, promoting health of the colon intestinal epithelium. Recent reports suggest that OCTN2 expression in small intestine is under control of peroxisome proliferator-activated receptor-alpha (PPARalpha). However, PPARalpha contribution to colonic OCTN2 expression remains controversial. Here we examined the transcriptional regulation of colon OCTN2 gene by PPARgamma. To exclude any additional modulation of other PPAR to OCTN2 expression, we used both in vivo and in vitro PPAR-null models and specific PPAR inhibitors. The PPARgamma agonists thiazolidinediones increased both OCTN2 mRNA and protein expression in colonic epithelial cell lines independently by PPARalpha expression. The induction was blocked only by PPARgamma antagonists or by gammaORF4, a PPARgamma isoform with dominant negative activity, suggesting a PPARgamma-dependent mechanism. A conserved noncanonical PPAR-responsive element was found by computational analysis in the first intron of human OCTN2 gene and validated by EMSA assay. Promoter-reporter assays further confirmed transcriptional functionality of the putative PPAR response element, whereas selective mutation caused complete loss of responsiveness to PPARgamma activation. Finally, adenovirus-mediated overexpression of constitutively active PPARgamma mutant increased colon OCTN2 expression in PPARalpha(-/-) mice. Interestingly, animals overexpressing colon PPARgamma showed a significant increase in plasma carnitine, thus demonstrating the functional contribution of large intestine to systemic carnitine homeostasis. This study reveals a PPARgamma-dependent absorption machinery in colon that is likely involved in the health of colon epithelium, in the microbiota-host interactions and in the absorption of nutraceuticals and drugs.

Progression of cyclophosphamide-induced acute renal metabolic damage in carnitine-depleted rat model

BACKGROUND

Little information is available regarding the mechanism of cyclophosphamide (CP)-induced renal damage. Therefore, this study examined whether carnitine deficiency constitutes a risk factor in and should be viewed as a mechanism during development of CP-induced nephrotoxicity and explored whether carnitine supplementation, using propionyl-L-carnitine (PLC), could offer protection against this toxicity.

METHODS

Experimental rats were assigned to one of six groups; the first three groups were injected intraperitoneally with normal saline, PLC (250 mg/kg/day) or D-carnitine (250 mg/kg/day) + Mildronate (200 mg/kg/day), respectively, for 10 successive days. The 4th, 5th and 6th groups received the same doses of normal saline, PLC or D-carnitine + Mildronate, respectively, for 5 successive days before and after a single dose of CP (200 mg/kg).

RESULTS

CP significantly increased serum creatinine, blood urea nitrogen (BUN), intramitochondrial acetyl-coenzyme A (CoA) and thiobarbituric acid reactive substances, significantly decreased total carnitine, intramitochondrial CoA-SH, adenosine triphosphate (ATP) and ATP/adenosine diphosphate (ADP) and reduced glutathione in kidney tissues. In carnitine-depleted rats, CP resulted in dramatic increase in serum nephrotoxicity indices and acetyl-CoA and induced progressive reduction in total carnitine, CoA-SH and ATP as well as severe histopathological lesions in kidney tissues. Interestingly, PLC completely reversed the biochemical and histopathological changes induced by CP to normal values.

CONCLUSIONS

Oxidative stress is not involved in CP-induced renal injury in this model. Carnitine deficiency and energy starvation constitute risk factors in and should be viewed as a mechanism during CP-induced nephrotoxicity. PLC prevents development of CP-induced nephrotoxicity by increasing intracellular carnitine content, intramitochondrial CoA-SH/acetyl-CoA ratio and energy production.

Low availability of carnitine precursors as a possible reason for the diminished plasma carnitine concentrations in pregnant women

BACKGROUND

It has been shown that plasma carnitine concentrations decrease markedly during gestation. A recent study performed with a low number of subjects suggested that this effect could be due to a low iron status which leads to an impairment of carnitine synthesis. The present study aimed to confirm this finding in a greater number of subjects. It was moreover intended to find out whether low carnitine concentrations during pregnancy could be due to a reduced availability of precursors of carnitine synthesis, namely trimethyllysine (TML) and gamma-butyrobetaine (BB).

METHODS

Blood samples of 79 healthy pregnant women collected at delivery were used for this study.

RESULTS

There was only a weak, non-significant (P > 0.05), correlation between plasma concentration of ferritin and those of free and total carnitine. There was no correlation between other parameters of iron status (plasma iron concentration, hemoglobin, MCV, MCH) and plasma concentration of free and total carnitine. There were, however, significant (P < 0.05) positive correlations between concentrations of TML and BB and those of free and total carnitine in plasma.

CONCLUSIONS

The results of this study suggest that an insufficient iron status is not the reason for low plasma carnitine concentrations observed in pregnant women. It is rather indicated that low plasma carnitine concentrations are caused by a low availability of precursors for carnitine synthesis during gestation.

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.

A novel mutation in type II methemoglobinemia

Type II methemoglobinemia is a somatic deficiency of cytochrome b5 reductase with severe global neurologic impairment. We report a novel mutation in exon 3 of the CYB5R3 gene on chromosome 22 consisting of homozygous 1-base pair (bp) deletion noted as c.215delG; p.Gly72AlafsX100. The patient had improvement of gross motor skills, chewing, and swallowing that may be due to the initiation of daily ascorbic acid therapy. We hypothesize that a possible response to ascorbic acid may be related to the effect of making additional ferrous iron available for its role as a cofactor in carnitine synthesis.

Electron transport chain-dependent and -independent mechanisms of mitochondrial H2O2 emission during long-chain fatty acid oxidation

Oxidative stress in skeletal muscle is a hallmark of various pathophysiologic states that also feature increased reliance on long-chain fatty acid (LCFA) substrate, such as insulin resistance and exercise. However, little is known about the mechanistic basis of the LCFA-induced reactive oxygen species (ROS) burden in intact mitochondria, and elucidation of this mechanistic basis was the goal of this study. Specific aims were to determine the extent to which LCFA catabolism is associated with ROS production and to gain mechanistic insights into the associated ROS production. Because intermediates and by-products of LCFA catabolism may interfere with antioxidant mechanisms, we predicted that ROS formation during LCFA catabolism reflects a complex process involving multiple sites of ROS production as well as modified mitochondrial function. Thus, we utilized several complementary approaches to probe the underlying mechanism(s). Using skeletal muscle mitochondria, our findings indicate that even a low supply of LCFA is associated with ROS formation in excess of that generated by NADH-linked substrates. Moreover, ROS production was evident across the physiologic range of membrane potential and was relatively insensitive to membrane potential changes. Determinations of topology and membrane potential as well as use of inhibitors revealed complex III and the electron transfer flavoprotein (ETF) and ETF-oxidoreductase, as likely sites of ROS production. Finally, ROS production was sensitive to matrix levels of LCFA catabolic intermediates, indicating that mitochondrial export of LCFA catabolic intermediates can play a role in determining ROS levels.