Cerebrospinal fluid carnitine levels in patients with Alzheimer's disease

APOE ε4 and Alzheimer's disease diagnosis associated differences in L-carnitine, GBB, TMAO, and acylcarnitines in blood and brain

BACKGROUND

The apolipoprotein E (APOE) ε4 allele, involved in fatty acid (FA) metabolism, is a major genetic risk factor for Alzheimer's disease (AD). This study examined the influence of APOE genotypes on blood and brain markers of the L-carnitine system, necessary for fatty acid oxidation (FAO), and their collective influence on the clinical and pathological outcomes of AD.

METHODS

L-carnitine, its metabolites γ-butyrobetaine (GBB) and trimethylamine-n-oxide (TMAO), and its esters (acylcarnitines) were analyzed in blood from predominantly White community/clinic-based individuals (n = 372) and in plasma and brain from the Religious Order Study (ROS) (n = 79) using liquid chromatography tandem mass spectrometry (LC-MS/MS).

FINDINGS

Relative to total blood acylcarnitines, levels of short chain acylcarnitines (SCAs) were higher whereas long chain acylcarnitines (LCAs) were lower in AD, which was observed pre-clinically in APOE ε4s. Plasma medium chain acylcarnitines (MCAs) were higher amongst cognitively healthy APOE ε2 carriers relative to other genotypes. Compared to their respective controls, elevated TMAO and lower L-carnitine and GBB were associated with AD clinical diagnosis and these differences were detected preclinically among APOE ε4 carriers. Plasma and brain GBB, TMAO, and acylcarnitines were also associated with post-mortem brain amyloid, tau, and cerebrovascular pathologies.

INTERPRETATION

Alterations in blood L-carnitine, GBB, TMAO, and acylcarnitines occur early in clinical AD progression and are influenced by APOE genotype. These changes correlate with post-mortem brain AD and cerebrovascular pathologies. Additional studies are required to better understand the role of the FAO disturbances in AD.

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.

A variant at 9q34.11 is associated with HLA-DQB1*06:02 negative essential hypersomnia

Essential hypersomnia (EHS) is a lifelong disorder characterized by excessive daytime sleepiness without cataplexy. EHS is associated with human leukocyte antigen (HLA)-DQB1*06:02, similar to narcolepsy with cataplexy (narcolepsy). Previous studies suggest that DQB1*06:02-positive and -negative EHS are different in terms of their clinical features and follow different pathological pathways. DQB1*06:02-positive EHS and narcolepsy share the same susceptibility genes. In the present study, we report a genome-wide association study with replication for DQB1*06:02-negative EHS (408 patients and 2247 healthy controls, all Japanese). One single-nucleotide polymorphism, rs10988217, which is located 15-kb upstream of carnitine O-acetyltransferase (CRAT), was significantly associated with DQB1*06:02-negative EHS (P = 7.5 × 10^-9, odds ratio = 2.63). The risk allele of the disease-associated SNP was correlated with higher expression levels of CRAT in various tissues and cell types, including brain tissue. In addition, the risk allele was associated with levels of succinylcarnitine (P = 1.4 × 10^-18) in human blood. The leading SNP in this region was the same in associations with both DQB1*06:02-negative EHS and succinylcarnitine levels. The results suggest that DQB1*06:02-negative EHS may be associated with an underlying dysfunction in energy metabolic pathways.

Serum Levels of Acyl-Carnitines along the Continuum from Normal to Alzheimer's Dementia

This study aimed to determine the serum levels of free L-carnitine, acetyl-L-carnitine and 34 acyl-L-carnitine in healthy subjects and in patients with or at risk of Alzheimer’s disease. Twenty-nine patients with probable Alzheimer’s disease, 18 with mild cognitive impairment of the amnestic type, 24 with subjective memory complaint and 46 healthy subjects were enrolled in the study, and the levels of carnitine and acyl-carnitines were measured by tandem mass spectrometry. The concentrations of acetyl-L-carnitine progressively decreased passing from healthy subjects group (mean±SD, 5.6±1.3 μmol/L) to subjective memory complaint (4.3±0.9 μmol/L), mild cognitive impairment (4.0±0.53 μmol/L), up to Alzheimer’s disease (3.5±0.6 μmol/L) group (p<0.001). The differences were significant for the comparisons: healthy subjects vs. subjective memory complaint, mild cognitive impairment or Alzheimer’s disease group; and subjective memory complaint vs. Alzheimer’s disease group. Other acyl-carnitines, such as malonyl-, 3-hydroxyisovaleryl-, hexenoyl-, decanoyl-, dodecanoyl-, dodecenoyl-, myristoyl-, tetradecenoyl-, hexadecenoyl-, stearoyl-, oleyl- and linoleyl-L-carnitine, showed a similar decreasing trend, passing from healthy subjects to patients at risk of or with Alzheimer’s disease. These results suggest that serum acetyl-L-carnitine and other acyl-L-carnitine levels decrease along the continuum from healthy subjects to subjective memory complaint and mild cognitive impairment subjects, up to patients with Alzheimer’s disease, and that the metabolism of some acyl-carnitines is finely connected among them. These findings also suggest that the serum levels of acetyl-L-carnitine and other acyl-L-carnitines could help to identify the patients before the phenotype conversion to Alzheimer’s disease and the patients who would benefit from the treatment with acetyl-L-carnitine. However, further validation on a larger number of samples in a longitudinal study is needed before application to clinical practice.

Acetyl L-carnitine protects motor neurons and Rohon-Beard sensory neurons against ketamine-induced neurotoxicity in zebrafish embryos

Ketamine, a non-competitive antagonist of N-methyl-D-aspartate (NMDA) type glutamate receptors is commonly used as a pediatric anesthetic. Multiple studies have shown ketamine to be neurotoxic, particularly when administered during the brain growth spurt. Previously, we have shown that ketamine is detrimental to motor neuron development in the zebrafish embryos. Here, using both wild type (WT) and transgenic (hb9:GFP) zebrafish embryos, we demonstrate that ketamine is neurotoxic to both motor and sensory neurons. Drug absorption studies showed that in the WT embryos, ketamine accumulation was approximately 0.4% of the original dose added to the exposure medium. The transgenic embryos express green fluorescent protein (GFP) localized in the motor neurons making them ideal for evaluating motor neuron development and toxicities in vivo. The hb9:GFP zebrafish embryos (28 h post fertilization) treated with 2 mM ketamine for 20 h demonstrated significant reductions in spinal motor neuron numbers, while co-treatment with acetyl L-carnitine proved to be neuroprotective. In whole mount immunohistochemical studies using WT embryos, a similar effect was observed for the primary sensory neurons. In the ketamine-treated WT embryos, the number of primary sensory Rohon-Beard (RB) neurons was significantly reduced compared to that in controls. However, acetyl L-carnitine co-treatment prevented ketamine-induced adverse effects on the RB neurons. These results suggest that acetyl L-carnitine protects both motor and sensory neurons from ketamine-induced neurotoxicity.

A common X-linked inborn error of carnitine biosynthesis may be a risk factor for nondysmorphic autism

We recently reported a deletion of exon 2 of the trimethyllysine hydroxylase epsilon (TMLHE) gene in a proband with autism. TMLHE maps to the X chromosome and encodes the first enzyme in carnitine biosynthesis, 6-N-trimethyllysine dioxygenase. Deletion of exon 2 of TMLHE causes enzyme deficiency, resulting in increased substrate concentration (6-N-trimethyllysine) and decreased product levels (3-hydroxy-6-N-trimethyllysine and γ-butyrobetaine) in plasma and urine. TMLHE deficiency is common in control males (24 in 8,787 or 1 in 366) and was not significantly increased in frequency in probands from simplex autism families (9 in 2,904 or 1 in 323). However, it was 2.82-fold more frequent in probands from male-male multiplex autism families compared with controls (7 in 909 or 1 in 130; P = 0.023). Additionally, six of seven autistic male siblings of probands in male-male multiplex families had the deletion, suggesting that TMLHE deficiency is a risk factor for autism (metaanalysis Z-score = 2.90 and P = 0.0037), although with low penetrance (2-4%). These data suggest that dysregulation of carnitine metabolism may be important in nondysmorphic autism; that abnormalities of carnitine intake, loss, transport, or synthesis may be important in a larger fraction of nondysmorphic autism cases; and that the carnitine pathway may provide a novel target for therapy or prevention of autism.

Serum carnitine levels in childhood leukemia

In patients with malignancies, the system of carnitine seems abnormally expressed. The serum total, free, and acyl carnitine levels in 40 children and adolescents with acute leukemia were determined using electrospray tandem mass spectrometry in 4 different phases of the disease: at the diagnosis, 1 year after the initiation of chemotherapy, at the end of treatment, and 2.4+/-1.668 years after the completion of chemotherapy. The age, sex, hemoglobin values, serum biochemistry, somatometric features of the patients, and the risk group of the disease were examined. Although the carnitine levels were found higher in patients compared with the control group from diagnosis to treatment completion, statistically significant decrease in carnitine levels was observed in patients within different phases of the disease especially during induction and consolidation treatment (phase A to B) for both free and total (P=0.023) carnitine. In addition, a statistically significant recovery in carnitine levels was observed between phase B (end of intensive chemotherapy) and D (some years after the completion of treatment) for free and total carnitine (P=0.054 and 0.035, respectively). No statistical correlation was documented between the carnitine levels and somatometric parameters or other variables studied. In conclusion, a significant transient decrease in the levels of carnitine during the treatment was observed in children with acute leukemia. Further studies are required to clarify the role of carnitine status in patients with malignancies and possibly the necessity of carnitine supplementation during chemotherapy administration.

Metabolomic analysis of the cerebrospinal fluid reveals changes in phospholipase expression in the CNS of SIV-infected macaques

HIV infiltrates the CNS soon after an individual has become infected with the virus, and can cause dementia and encephalitis in late-stage disease. Here, a global metabolomics approach was used to find and identify metabolites differentially regulated in the cerebrospinal fluid (CSF) of rhesus macaques with SIV-induced CNS disease, as we hypothesized that this might provide biomarkers of virus-induced CNS damage. The screening platform used a non-targeted, mass-based metabolomics approach beginning with capillary reverse phase chromatography and electrospray ionization with accurate mass determination, followed by novel, nonlinear data alignment and online database screening to identify metabolites. CSF was compared before and after viral infection. Significant changes in the metabolome specific to SIV-induced encephalitis were observed. Metabolites that were increased during infection-induced encephalitis included carnitine, acyl-carnitines, fatty acids, and phospholipid molecules. The elevation in free fatty acids and lysophospholipids correlated with increased expression of specific phospholipases in the brains of animals with encephalitis. One of these, a phospholipase A2 isoenzyme, is capable of releasing a number of the fatty acids identified. It was expressed in different areas of the brain in conjunction with glial activation, rather than linked to regions of SIV infection and inflammation, indicating widespread alterations in infected brains. The identification of specific metabolites as well as mechanisms of their increase illustrates the potential of mass-based metabolomics to address problems in CNS biochemistry and neurovirology, as well as neurodegenerative diseases.

L-carnitine protects neurons from 1-methyl-4-phenylpyridinium-induced neuronal apoptosis in rat forebrain culture

1-Methyl-4-phenylpyridinium ion (MPP+), an inhibitor of mitochondrial complex I, has been widely used as a neurotoxin because it elicits a severe Parkinson's disease-like syndrome with an elevation of intracellular reactive oxygen species (ROS) and apoptosis. L-carnitine plays an integral role in attenuating the brain injury associated with mitochondrial neurodegenerative disorders. The present study investigates the effects of L-carnitine against the toxicity of MPP+ in rat forebrain primary cultures. Cells in culture were treated for 24 h with 100, 250, 500 and 1000 microM MPP+ alone or co-incubated with L-carnitine. MPP+ produced a dose-related increase in DNA fragmentation as measured by cell death ELISA (enzyme-linked immunosorbent assay), an increase in the number of TUNEL (terminal dUTP nick-end labeling)-positive cells and a reduction in the mitochondrial metabolism of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). No significant effect was observed with the release of lactate dehydrogenase (LDH), indicating that cell death presumably occurred via apoptotic mechanisms. Co-incubation of MPP+ with L-carnitine significantly reduced MPP+-induced apoptosis. Western blot analyses showed that neurotoxic concentrations of MPP+ decreased the ratio of BCL-X(L) to Bax and decreased the protein levels of polysialic acid neural cell adhesion molecules (PSA-NCAM), a neuron specific marker. L-carnitine blocked these effects of MPP+ suggesting its potential therapeutic utility in degenerative disorders such as Parkinson's disease, Alzheimer's disease, ornithine transcarbamylase deficiency and other mitochondrial diseases.

Early events of the exogenously provided L-Carnitine in murine macrophages, T- and B-lymphocytes: modulation of prostaglandin E1 and E2 production in response to arachidonic acid

L-carnitine is an essential energy-providing compound to the cell since it transports long chain fatty acids through the mitochondrial membrane and delivers them to the beta-oxidation pathway for catabolism and/or entrance to biosynthetic pathways. Some of the early events taking place in immune cells after L-carnitine inoculation in vitro are defined in this report. Using arachidonic acid as a fatty acid source, we determined the utilization rate of L-carnitine by murine T-, B-lymphocytes and macrophages within two hours of cell culture, its effect on prostaglandin E1 and E2 production and the levels of beta-hydroxy-butyrate. The results show that although all immune cells consume a small portion of L-carnitine, beta-hydroxy-butyrate decreases upon addition of arachidonic acid and/or L-carnitine indicating that active biosynthetic pathways are induced. L-carnitine is shown to increase the arachidonic acid-induced production of prostaglandins E1 and E2 in macrophages, while their secretion from T- and B-lymphocytes is decreased. These findings indicate the L-carnitine may very rapidly alter the activation state of immune cells and lead to the development of various reactions, beneficial or not to the organism.

Carnitine and hemodialysis

Carnitine, gamma-trimethyl-beta-hydroxybutyrobetaine, is a small molecule widely present in all cells from prokaryotic to eukaryotic. It is an important element in the beta-oxidation of fatty acids. A lack of carnitine in hemodialysis patients is caused by insufficient carnitine synthesis and particularly by the loss through dialytic membranes, leading in some patients to carnitine depletion with a relative increase of esterified forms. The authors found a decrease in plasma-triglyceride and increase of high-density lipoprotein cholesterol (HDL-Chol) in dialysis patients during carnitine treatment. Many studies have shown that L-carnitine supplementation leads to improvements in several complications seen in uremic patients, including cardiac complications, impaired exercise and functional capacities, muscle symptoms, increased symptomatic intradialytic hypotension, and erythropoietin-resistant anemia, normalizing the reduced carnitine palmitoyl transferase activity in red cells. In addition, carnitine supplementation may improve protein metabolism and insulin resistance. Recently, carnitine supplementation has been approved by the US Food and Drug Administration not only for the treatment, but also for the prevention of carnitine depletion in dialysis patients. Regular carnitine supplementation in hemodialysis patients can improve their lipid metabolism, protein nutrition, antioxidant status, and anemia requiring large doses of erythropoietin, It also may reduce the incidence of intradialytic muscle cramps, hypotension, asthenia, muscle weakness, and cardiomyopathy.

L-carnitine accelerates the in vitro regeneration of neural network from adult murine brain cells

The development, growth and regeneration of nerve cells remain an unresolved issue. The up-to-date reported brain repair mechanisms are numerous and evidence suggests that, apart from the required trophism, tropism, microenvironment and specificity of the brain, a plethora of chemical, physiological and immunological compounds can contribute to such events. Among these compounds, we concentrated our interest on L-carnitine (L-Cn), which regulates the beta-oxidation of long chain fatty acids necessary for brain development, myelinization and growth. In contrast to fetal brain cells that grow easily in culture, adult brain cells show limited neurogenesis. Here, using adult brain cells from experimental mice, we show that although L-Cn does not improve their proliferative activity in short-term cultures, it accelerates the growth and differentiation of neurons, astrocytes, oligodendrocytes and ependymal cells from neurospheres in long-term cultures. Thus, the formation of a confluent neural network requires a 2-month period in culture. These observations provide new insights for in vivo use of L-Cn to support brain cell development in cases of injury or brain degenerative diseases.

The action of acetyl-L-carnitine on the neurotoxicity evoked by amyloid fragments and peroxide on primary rat cortical neurones

The amyloid beta-peptides have been implicated in the excitotoxic mechanism of neuronal injury in the pathogenesis of Alzheimer's disease. In this paper we examine the effect of different amyloid fragments (beta A1-40, A1-28, and A25-35), as well as potential neuroprotective compounds on rat cortical neuron viability. Exposure of neurones to beta A25-35 or A1-40 at concentrations as low as 1 microgram/ml inhibited, significantly, the MTT response and this level of inhibition was similar after 24-h or three-day exposure. Furthermore, the level of inhibition was not affected by the presence or absence of 5% horse serum in the medium. Preexposure (10 min) of neurones to ALC at concentrations of 0.1, 1, 5, and 10 mM attenuated the inhibition of the MTT response caused by beta A25-35 (50 micrograms/ml) in serum free medium for 24 h. The treatment of cells with vitamin E (100 microM), catalase (4 mg/ml), NGF (0.1 and 10 ng/ml), or cycloheximide (0.1 microgram/ml) significantly restored the MTT response that was inhibited by beta A25-35. The mechanism for the protective actions of these compounds against beta A25-35 toxicity is not clear but may involve free radical scavenger action and preservation of energy production, although other mechanisms, especially for ALC, such as a direct effect on A-beta interaction with charged anionic phospholipids and/or stabilizing action on membranes, are also possible.