N-acetylaspartic acid (NAA) and N-acetylaspartylglutamic acid (NAAG) in human ventricular, subarachnoid, and lumbar cerebrospinal fluid

Plasma N-acetylaspartate: Development and validation of a quantitative assay based on HPLC-MS-MS and sample derivatization

N-acetylaspartate is a human endogenous compound synthesized by neurons, which is involved in neuronal metabolism. It is used as a marker in brain magnetic resonance spectroscopy to investigate several neurological and metabolic disorders, that can be related to a variation of its concentration with respect to reference values. N-acetylaspartate is present also in biological fluids, such as plasma, urine, and cerebrospinal fluid, where it can be quantified. Here we describe the development and validation, in compliance with the EMA guidelines, of a novel assay method for the quantification of N-acetylaspartate in plasma based on tandem mass spectrometry coupled to liquid chromatography. Its peculiarity lies in the fact that sample preparation includes an esterification step, which significantly improves the chromatographic performances and, consequently, also the method sensitivity, reproducibility and accuracy. Instrumental LLOQ is 0.06 ng/mL, i.e. at least 300 times lower than the medium N-acetylaspartate concentration in samples, accuracy is in the range 98-103%, while precision lies between 1 and 3%. The method robustness was tested in about 1000 injections of plasma samples, 96 of which were used also to assess the reference ranges in control subjects (16.46-63.40 ng/mL). Controls were then compared to plasma samples from type 2 diabetic patients. Contrary to brain magnetic resonance spectroscopy, which demonstrated a decrease in the N-acetylaspartate levels in right frontal and parieto-temporal region of type 2 diabetic patients, plasma analysis showed no statistical difference with respect to controls. However, the method here described can be profitably used in studies concerning different disorders with CNS involvement, as confirmed by reports available in the literature.

Elevated cerebrospinal fluid concentrations of N-acetylaspartate correlate with poor outcome in a pilot study of severe brain trauma

Primary objective: Examine the correlation between acute cerebrospinal fluid (CSF) levels of N-acetylaspartate (NAA) and injury severity upon admission in addition to long-term functional outcomes of severe traumatic brain injury (TBI). Design and rationale: This exploratory study assessed CSF NAA levels in the first four days after severe TBI, and correlated these findings with Glasgow Coma Scale (GCS) score and long-term outcomes at 3, 6, 12, and 24 months post-injury. Methods: CSF was collected after passive drainage via an indwelling ventriculostomy placed as standard of care in a total of 28 people with severe TBI. NAA levels were assayed using triple quadrupole mass spectrometry. Functional outcomes were assessed using the Glasgow Outcomes Scale (GOS) and Disability Rating Scale (DRS). Results: In this pilot study, better functional outcomes, assessed using the GOS and DRS, were found in individuals with lower acute CSF NAA levels after TBI. Key findings were that average NAA level was associated with GCS (p = .02), and GOS at 3 (p = .01), 6 (p = .04), 12 (p = .007), and 24 months (p = .002). Implications: The results of this study add to a growing body of neuroimaging evidence that raw NAA values are reduced and variable after TBI, potentially impacting patient outcomes, warranting additional exploration into this finding. This line of inquiry could lead to improved diagnosis and prognosis in patients with TBI.

Omega-3 supplementation improves cognition and modifies brain activation in young adults

OBJECTIVE

The current study aimed to investigate the effects of eicosapentaenoic acid (EPA)-rich and docosahexaenoic acid (DHA)-rich supplementations on cognitive performance and functional brain activation.

DESIGN

A double-blind, counterbalanced, crossover design, with a 30-day washout period between two supplementation periods (EPA-rich and DHA-rich) was employed. Functional magnetic resonance imaging scans were obtained during performance of Stroop and Spatial Working Memory tasks prior to supplementation and after each 30-day supplementation period.

RESULTS

Both supplementations resulted in reduced ratio of arachidonic acid to EPA levels. Following the EPA-rich supplementation, there was a reduction in functional activation in the left anterior cingulate cortex and an increase in activation in the right precentral gyrus coupled with a reduction in reaction times on the colour-word Stroop task. By contrast, the DHA-rich supplementation led to a significant increase in functional activation in the right precentral gyrus during the Stroop and Spatial Working Memory tasks, but there was no change in behavioural performance.

CONCLUSIONS

By extending the theory of neural efficiency to the within-subject neurocognitive effects of supplementation, we concluded that following the EPA-rich supplementation, participants' brains worked 'less hard' and achieved a better cognitive performance than prior to supplementation. Conversely, the increase in functional activation and lack of improvement in time or accuracy of cognitive performance following DHA-rich supplementation may indicate that DHA-rich supplementation is less effective than EPA-rich supplementation in enhancing neurocognitive functioning after a 30-day supplementation period in the same group of individuals.

More than cell dust: microparticles isolated from cerebrospinal fluid of brain injured patients are messengers carrying mRNAs, miRNAs, and proteins

Microparticles are cell-derived, membrane-sheathed structures that are believed to shuttle proteins, mRNA, and miRNA to specific local or remote target cells. To date best described in blood, we now show that cerebrospinal fluid (CSF) contains similar structures that can deliver RNAs and proteins to target cells. These are, in particular, molecules associated with neuronal RNA granules and miRNAs known to regulate neuronal processes. Small RNA molecules constituted 50% of the shuttled ribonucleic acid. Using microarray analysis, we identified 81 mature miRNA molecules in CSF microparticles. Microparticles from brain injured patients were more abundant than in non-injured subjects and contained distinct genetic information suggesting that they play a role in the adaptive response to injury. Notably, miR-9 and miR-451 were differentially packed into CSF microparticles derived from patients versus non-injured subjects. We confirmed the transfer of genetic material from CSF microparticles to adult neuronal stem cells in vitro and a subsequent microRNA-specific repression of distinct genes. This first indication of a regulated transport of functional genetic material in human CSF may facilitate the diagnosis and analysis of cerebral modulation in an otherwise inaccessible organ.

Extensive aspartoacylase expression in the rat central nervous system

Aspartoacylase (ASPA) catalyzes deacetylation of N-acetylaspartate (NAA) to generate acetate and aspartate. Mutations in the gene for ASPA lead to reduced acetate availability in the CNS during development resulting in the fatal leukodystrophy Canavan disease. Highly specific polyclonal antibodies to ASPA were used to examine CNS expression in adult rats. In white matter, ASPA expression was associated with oligodendrocyte cell bodies, nuclei, and some processes, but showed a dissimilar distribution pattern to myelin basic protein and oligodendrocyte specific protein. Microglia expressed ASPA in all CNS regions examined, as did epiplexus cells of the choroid plexus. Pial and ependymal cells and some endothelial cells were ASPA positive, as were unidentified cellular nuclei throughout the CNS. Astrocytes did not express ASPA in their cytoplasm. In some fiber pathways and nerves, particularly in the brainstem and spinal cord, the axoplasm of many neuronal fibers expressed ASPA, as did some neurons. Acetyl coenzyme A synthase immunoreactivity was also observed in the axoplasm of many of the same fiber pathways and nerves. All ASPA-immunoreactive elements were unstained in brain sections from tremor rats, an ASPA-null mutant. The strong expression of ASPA in oligodendrocyte cell bodies is consistent with a lipogenic role in myelination. Strong ASPA expression in cell nuclei is consistent with a role for NAA-derived acetate in nuclear acetylation reactions, including histone acetylation. Expression of ASPA in microglia may indicate a role in lipid synthesis in these cells, whereas expression in axons suggests that some neurons can both synthesize and catabolize NAA.

Bioanalysis of N-acetyl-aspartyl-glutamate as a marker of glutamate carboxypeptidase II inhibition

We report the characterization of two methods for the analysis of N-acetyl-aspartyl-glutamate (NAAG) in biological fluids. In the first method, NAAG concentrations were calculated based on differences between glutamate concentrations before and after NAAG hydrolysis with exogenous glutamate carboxypeptidase II (GCP II) using high-performance liquid chromatography (HPLC) followed by fluorescence detection. In the second method, NAAG levels were quantified directly using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Analyses of NAAG levels in human cerebrospinal fluid samples using either method gave similar results within experimental error, confirming the validity of the two independent measurements. These methods will be useful in future clinical trials to assess drug-induced GCP II inhibition in biological matrices.

N-acetylglutamate and N-acetylaspartate in soybeans (Glycine max L.), maize (Zea mays L.), [corrected] and other foodstuffs

N-Acetylglutamate (NAG) and N-acetylaspartate (NAA) are amino acid derivatives with reported activities in a number of biological processes. However, there is no published information on the presence of either substance in foodstuffs. We developed a method for extracting and quantifying NAG and NAA from soybean seeds and maize grain using ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS). The lower limit of quantification for both NAG and NAA was 1 ng/mL. The method was then utilized to quantify NAG and NAA in other foodstuffs (fruits, vegetables, meats, grains, milk, coffee, tea, cocoa, and others). Both NAG and NAA were present in all of the materials analyzed. The highest concentration of NAG was found in cocoa powder. The highest concentration of NAA was found in roasted coffee beans. Both NAG and NAA were found at quantifiable concentrations in all foods tested indicating that these two acetylated amino acids are common components of the human diet.

Antipsychotic drugs increase N-acetylaspartate and N-acetylaspartylglutamate in SH-SY5Y human neuroblastoma cells

N-Acetylaspartate (NAA) and N-acetylaspartylglutamate (NAAG) are related neuronal metabolites associated with the diagnosis and treatment of schizophrenia. NAA is a valuable marker of neuronal viability in magnetic resonance spectroscopy, a technique which has consistently shown NAA levels to be modestly decreased in the brains of schizophrenia patients. However, there are conflicting reports on the changes in brain NAA levels after treatment with antipsychotic drugs, which exert their therapeutic effects in part by blocking dopamine D(2) receptors. NAAG is reported to be an agonist of the metabotropic glutamate 2/3 receptor, which is linked to neurotransmitter release modulation, including glutamate release. Alterations in NAAG metabolism have been implicated in the development of schizophrenia possibly via dysregulation of glutamate neurotransmission. In the present study we have used high performance liquid chromatography to determine the effects of the antipsychotic drugs haloperidol and clozapine on NAA and NAAG levels in SH-SY5Y human neuroblastoma cells, a model system used to test the responses of dopaminergic neurons in vitro. The results indicate that the antipsychotic drugs haloperidol and clozapine increase both NAA and NAAG levels in SH-SY5Y cells in a dose and time dependant manner, providing evidence that NAA and NAAG metabolism in neurons is responsive to antipsychotic drug treatment.

N-Acetylaspartate in the CNS: from neurodiagnostics to neurobiology

The brain is unique among organs in many respects, including its mechanisms of lipid synthesis and energy production. The nervous system-specific metabolite N-acetylaspartate (NAA), which is synthesized from aspartate and acetyl-coenzyme A in neurons, appears to be a key link in these distinct biochemical features of CNS metabolism. During early postnatal central nervous system (CNS) development, the expression of lipogenic enzymes in oligodendrocytes, including the NAA-degrading enzyme aspartoacylase (ASPA), is increased along with increased NAA production in neurons. NAA is transported from neurons to the cytoplasm of oligodendrocytes, where ASPA cleaves the acetate moiety for use in fatty acid and steroid synthesis. The fatty acids and steroids produced then go on to be used as building blocks for myelin lipid synthesis. Mutations in the gene for ASPA result in the fatal leukodystrophy Canavan disease, for which there is currently no effective treatment. Once postnatal myelination is completed, NAA may continue to be involved in myelin lipid turnover in adults, but it also appears to adopt other roles, including a bioenergetic role in neuronal mitochondria. NAA and ATP metabolism appear to be linked indirectly, whereby acetylation of aspartate may facilitate its removal from neuronal mitochondria, thus favoring conversion of glutamate to alpha ketoglutarate which can enter the tricarboxylic acid cycle for energy production. In its role as a mechanism for enhancing mitochondrial energy production from glutamate, NAA is in a key position to act as a magnetic resonance spectroscopy marker for neuronal health, viability and number. Evidence suggests that NAA is a direct precursor for the enzymatic synthesis of the neuron specific dipeptide N-acetylaspartylglutamate, the most concentrated neuropeptide in the human brain. Other proposed roles for NAA include neuronal osmoregulation and axon-glial signaling. We propose that NAA may also be involved in brain nitrogen balance. Further research will be required to more fully understand the biochemical functions served by NAA in CNS development and activity, and additional functions are likely to be discovered.

Effects of NAAG peptidase inhibitor 2-PMPA in model chronic pain - relation to brain concentration

N-acetylated-alpha-linked-acidic peptidase (NAAG peptidase) converts N-acetyl-aspartyl-glutamate (NAAG, mGluR3 agonist) into N-acetyl-aspartate and glutamate. The NAAG peptidase inhibitor 2-PMPA (2-(phosphonomethyl)pentanedioic acid) had neuroprotective activity in an animal model of stroke and anti-allodynic activity in CCI model despite its uncertain ability to penetrate the blood-brain barrier. The NAAG concentration in brain ECF under basal conditions and its alteration in relation to the brain ECF concentration of 2-PMPA is unclear. We therefore assessed those brain concentrations after i.p. administration of 2-PMPA, using in vivo microdialysis combined with LC/MS/MS analysis. Administration of 2-PMPA (50mg/kg) produced a mean peak concentration of 2-PMPA of 29.66+/-8.1microM. This concentration is about 100,000 fold more than is needed for inhibition of NAAG peptidase, and indicates very good penetration to the brain. Application of 2-PMPA was followed by a linear increase of NAAG-concentration reaching a maximum of 2.89+/-0.42microM at the end of microdialysis. However, during the time the anti-allodynic effects of 2-PMPA were observed, the NAAG concentration in the ECF did not reach levels which are likely to have an impact on any known target. It appears therefore that the observed behavioural effects of 2-PMPA may not be mediated by NAAG nor, in turn, by mGluR3 receptors.

Severe hypomyelination associated with increased levels of N-acetylaspartylglutamate in CSF

BACKGROUND

Two unrelated girls had early onset of nystagmus and epilepsy, absent psychomotor development, and almost complete absence of myelin on cerebral MRI. The clinical features and MR images of both patients resembled the connatal form of Pelizaeus-Merzbacher disease (PMD), which is an X-linked recessive disorder caused by duplications or mutations of the proteolipid protein gene (PLP).

OBJECTIVE

To define a unique neurometabolic disorder with failure of myelination.

METHOD

S AND RESULTS: 1H-NMR of CSF in both girls was performed repeatedly, and both showed highly elevated concentrations of N-acetylaspartylglutamate (NAAG). The coding sequence of the gene coding for glutamate carboxypeptidase II, which converts NAAG to N-acetylaspartate (NAA) and glutamate, was entirely sequenced but revealed no mutations. Even though both patients are girls, the authors sequenced the PLP gene and found no abnormality.

CONCLUSIONS

NAAG is an abundant peptide neurotransmitter whose exact role is unclear. NAAG is implicated in two cases of unresolved severe CNS disorder. Its elevated concentration in CSF may be the biochemical hallmark for a novel neurometabolic disorder. The cause of its accumulation is still unclear.

Decreased levels of N-acetylaspartate in dorsolateral prefrontal cortex in a case of intractable severe sympathetically mediated chronic pain (complex regional pain syndrome, type I)

In our previous in vivo proton magnetic resonance spectroscopy ((1)H MRS) study we found reduced levels of N-acetylaspartate in dorsolateral prefrontal cortex of chronic back pain patients. This study tests whether these chemical abnormalities can be detected in other pain states. Using (1)H MRS, we measured levels for N-acetylaspartate and other identifiable chemicals relative to creatine in four bilateral brain regions, including dorsolateral prefrontal cortex, orbitofrontal cortex, cingulate, and thalamus, in a case of intractable severe sympathetically mediated chronic pain [complex regional pain syndrome (CRPS) type I]. The subject's chemical variations in the brain were compared to the same regional chemicals in 10 normal subjects (age- and sex-matched). Univariate statistics showed reduced levels of N-acetylaspartate in bilateral dorsolateral prefrontal cortex and increased levels of myo-inositol in left orbitofrontal cortex of the patient with intractable severe CRPS type I. These data support our original hypothesis that depletion of N-acetylaspartate in dorsolateral prefrontal cortex is a chemical marker of chronic pain, indicating for neuronal degeneration. Unpredicted changes of orbitofrontal myo-inositol may be related to the specific mood/affective state in an extreme pain perception. This is the first report, which identifies chemical markers in the prefrontal cortex for objective measurement and monitoring of CRPS type I. This information might lead to valuable insights into diagnosis and future effective interventions of CRPS type I (e.g., prefrontal brain stimulation).

Effect of posterior temporal-parietal hematoma on orbital frontal chemistry in relation to a cognitive and anxiety state: a combined 1H-MRS and neuropsychological study of an unusual case as compared with 16 healthy subjects

The authors report the unusual case of a 58-year-old woman (MJP) suffering from left temporal throbbing headache, associated with confusion. Magnetic resonance imaging showed a 5 x 3 x 2 cm hematoma at the left posterior temporal--parietal junction (PTPJ). Repeated MRI of MJP's brain performed during a 4-month follow-up period showed decrease in hematoma size (2.3 x 1.5 x 1) with evidence for development of encephalomalacia and resorption of blood products involving the area of hemorrhage. MJP had mild transcortical sensory aphasia characterized by difficulty with reading and processing, with semantic paraphasic errors while speaking and some difficulty with repetition. MJP had remained normotensive and seizure free, on Vasotec therapy and Dilantin prophylaxis. An in vivo proton magnetic resonance spectroscopy (1H-MRS) performed during an 8-month follow-up period showed reduced concentration for N-acetyl aspartate (NAA) by 19.3% (F=4.09, P<0.04), and myo-inositol by 32.0% (F=5.16, P<0.02) in the left orbital frontal cortex (OFC) as compared with 16 healthy subjects (age- and sex-matched). Cognitive tests (the Wechsler abbreviated scale of intelligence (WASI) and the Stroop color--word interference) showed a significant impairment suggesting involvement of higher-order cognitive functioning (memory, learning, and general intelligence) and attentional system. The Spielberger state-trait anxiety inventory (STAI) showed increased anxiety at the moment of the current examination and decreased tendency to be anxious over a long period of time. The Beck Anxiety and Depression Inventory revealed minimal anxiety and mild to moderate levels of depression. It is hypothesized that the PTPJ hematoma triggered long-distance pathways linking PTPJ area and frontal lobe, including OFC, which resulted in abnormal chemical changes in the left OFC and in cognitive tests impairment, and in long-term anxiety state changes.

Aging alters regional multichemical profile of the human brain: an in vivo 1H-MRS study of young versus middle-aged subjects

Age-related differences in the multichemical proton magnetic resonance spectroscopy (1H-MRS) profile of the human brain have been reported for several age groups, and most consistently for ages from neonates to 16-year-olds. Our recent 1H-MRS study demonstrated a significant age-related increase of total chemical concentration (relative to creatine) in the prefrontal and sensorimotor cortices within young adulthood (19-31-year-olds). In the present study we test the hypothesis that the level of brain chemicals in the same cortices, which show increased chemical levels during normal development, are reduced with normal aging after young adulthood. The multichemical 1H-MRS profile of the brain was compared between 19 young and 16 middle-aged normal subjects across multiple brain regions for all chemicals of 1H-MRS spectra. Chemical concentrations were measured relative to creatine. Over all age groups the total relative chemical concentration was highest in the prefrontal cortex. Middle-aged subjects demonstrated a significant decrease of total relative chemical concentration in the dorsolateral prefrontal (F = 54.8, p < 10(-7), ANOVA), orbital frontal (F = 3.7, p < 0.05) and sensorimotor (F = 15.1, p < 0.0001) cortices, as compared with younger age. Other brain regions showed no age-dependent differences. The results indicate that normal aging alters multichemical 1H-MRS profile of the human brain and that these changes are region-specific, with the largest changes occuring in the dorsolateral prefrontal cortex. These findings provide evidence that the processes of neuronal maturation of the human brain, and neurotransmitters and other chemical changes as the marker of these neuronal changes are almost finished by young adulthood and then reduced during normal aging toward middle age period of life. The present data also support the notion of heterochronic regressive changes of the aging human brain, where the multichemical brain regional profile seems to inversely recapitulate cortical chemical maturation within normal development.

Chemical mapping of anxiety in the brain of healthy humans: an in vivo 1H-MRS study on the effects of sex, age, and brain region

We recently presented results in an in vivo study of human brain chemistry in 'physiologic' anxiety, i.e., the anxiety of normal everyday life. Normal subjects with high anxiety demonstrated increased concentration of chemicals in orbital frontal cortex (OFC) as compared to lower anxiety. In a separate study of aging we demonstrated a decrease of total chemical concentration in OFC of middle-aged subjects, as compared with younger age. This brain region also showed gender dependence; men demonstrating decreased chemical concentration compared to women. We hypothesized that these sex- and age-dependent differences in OFC chemistry changes are a result of anxiety effects on this brain region. In the present study we examined these sex- and age-differential regional brain chemistry changes (as identified by localized in vivo proton magnetic resonance spectroscopy [1H-MRS]) in relation to the state-trait-anxiety (as measured by the State-Trait Anxiety Inventory) in 35 healthy subjects. The concentrations for all nine chemicals of 1H-MRS spectra were measured relative to creatine across multiple brain regions, including OFC in the left hemisphere. Analysis of variance showed anxiety-specific effects on chemical concentration changes in OFC, which were different for both sexes and age groups. Male subjects showed larger effect of anxiety on OFC chemistry as compared to females when the same sex high-anxiety subjects were compared to lower anxiety. Similarly, middle-aged subjects showed larger effect of anxiety on OFC chemistry as compared to younger age when the same age subjects with high anxiety were compared to lower anxiety. Largest effect of anxiety on OFC chemistry was due to changes of N-Acetyl aspartate. The results indicate that the state-trait anxiety has sex- and age-differential patterns on OFC chemistry in healthy humans, providing new information about the neurobiological roots of anxiety.

Canavan's spongiform leukodystrophy: a clinical anatomy of a genetic metabolic CNS disease

Canavan disease (CD) is a globally distributed early-onset leukodystrophy. It is genetic in nature, and results from an autosomally inherited recessive trait that is characterized by loss of the axon's myelin sheath while leaving the axons intact, and spongiform degeneration especially in white matter. There is also a buildup of N-acetyl-L-aspartate (NAA) in brain, as well as NAA acidemia and NAA aciduria. The cause of the altered NAA metabolism has been traced to several mutations in the gene for the production of aspartoacylase, located on chromosome 17, which is the primary enzyme involved in the catabolic metabolism of NAA. In this review, an attempt is made to correlate the change in NAA metabolism that results from the genetic defects in CD with the processes involved in the development of the CD syndrome. In addition, present efforts to counter the results of the genetic defects in this disease are also considered.

Modeling brain compartmental lactate response to metabolic challenge: a feasibility study

Magnetic resonance spectroscopy has been used to characterize abnormal brain lactate response in panic disorder (PD) subjects following lactate infusion. The present study integrated water quantification and tissue segmentation to evaluate compartmental lactate response within brain and cerebrospinal fluid (CSF). As there is evidence of brain parenchymal pH changes during lactate infusion, water scans were collected at baseline and post-infusion to address brain water stability. Water levels remained essentially stable across the protocol suggesting internal water provides an improved reference signal for measuring dynamic changes in response to metabolic challenge paradigms such as lactate infusion. To model brain lactate changes by compartments, we took the null hypothesis that lactate rises occur only in tissue. The approach referenced lactate amplitude (potentially from both compartments) to 'voxel' water (water scan corrected for differential T(2) between CSF brain at long-echo times - synonymous to a short-echo water scan). If the magnitude of lactate rise in CSF was equal to or greater than brain, voxels with substantial CSF fractions should demonstrate an equivalent or elevated response to voxels comprised only of tissue. The magnitude of lactate increases paralleled voxel tissue fraction suggesting the abnormal lactate rise observed in PD is tissue-based. The feasibility of lactate quantification and compartmental modeling are discussed.