Ion-pairing high-performance liquid chromatographic method for the detection of N-acetylaspartate and N-acetylglutamate in cerebral tissue extracts

Metabolic Diaschisis in Mild Traumatic Brain Injury

Neurophysiological diaschisis presents in traumatic brain injury (TBI) as functional impairment distant to the lesion site caused by axonal neuroexcitation and deafferentation. Diaschisis studies in TBI models have evaluated acute phase functional and microstructural changes. Here, in vivo biochemical changes and cerebral blood flow (CBF) dynamics following TBI are studied with magnetic resonance. Behavioral assessments, magnetic resonance spectroscopy (MRS), and CBF measurements on rats followed cortical impact TBI. Data were acquired pre-TBI and 1-3 h, 2-days, 7-days, and 14-days post-TBI. MRS was performed on the ipsilateral and contralateral sides in the cortex, striatum, and thalamus. Metabolites measured by MRS included N-acetyl aspartate (NAA), aspartate (Asp), lactate (Lac), glutathione (GSH), and glutamate (Glu). Lesion volume expanded for 2 days post-TBI and then decreased. Ipsilateral CBF dropped acutely versus baseline on both sides (-62% ipsilateral, -48% contralateral, p < 0.05) but then recovered in cortex, with similar changes in ipsilateral striatum. Metabolic changes versus baseline included increased Asp (+640% by Day 7 post-TBI, p < 0.05) and Lac (+140% on Day 2 post-TBI, p < 0.05) in ipsilateral cortex, while GSH (-67% acutely, p < 0.05) and NAA decreased (-50% on Day 2, p < 0.05). In contralateral cortex Lac decreased (-73% acutely, p < 0.05). Analysis of variance showed significance for Side (p < 0.05), Time after TBI (p < 0.05), and interactions (p < 0.005) for Asp, GSH, Lac, and NAA. Transient decreases of GSH (-30%, p < 0.05, acutely) and NAA (-23% on Day 2, p < 0.05) occurred in ipsilateral striatum with reduced GSH (-42%, p < 0.005, acutely) in the contralateral striatum. GSH was decreased in ipsilateral thalamus (-59% ipsilateral on Day 2, p < 0.05). Delayed increases of total choline were seen in the contralateral thalamus were noted as well (+21% on Day 7 post-TBI, p < 0.05). Both CBF and neurometabolite concentration changes occurred remotely from the TBI site, both ipsilaterally and contralaterally. Decreased Lac levels on the contralateral cortex following TBI may be indicative of reduced anaerobic metabolism during the acute phase. The timing and locations of the changes suggest excitatory and inhibitory signaling processes are affecting post-TBI metabolic fluctuations.

An enzymatic fluorimetric assay for determination of N-acetylaspartate

N-acetylaspartate (NAA) is an abundant metabolite in the mammalian brain and a precursor of the neuropeptide N-acetylaspartylglutamate (NAAG). The physiological role of NAA is not fully understood and requires further studies. We here describe the development of a coupled enzymatic fluorimetric assay for the determination of NAA in biological samples. Deproteinized tissue extracts are first passed through a strong cation exchange column to remove aspartate. NAA in the sample is hydrolysed by aspartoacylase and released aspartate oxidized using l-aspartate oxidase. Generated H₂O₂ is measured with peroxidase in a fluorimetric assay using Ampliflu Red. The limit of detection and the lower limit of quantification are 1.0 μM (10 pmol/well) and 3.3 μM (33 pmol/well), respectively, with a linear range to 100 μM. Specificity of the assay was confirmed using samples from mice deficient in NAA synthase Nat8l that were spiked with NAA. Analysis of samples from aspartoacylase-deficient mice showed a 2 to 3-fold increase in brain NAA concentration, in line with previous reports. Mice lacking NAAG synthetases had a slightly reduced (-10%) brain NAA level. Thus, the new fluorimetric enzymatic assay is useful to perform sensitive and large scale quantification of NAA in biological samples without the need for expensive equipment.

Mass spectrometry-based quantitation combined with time-dependent metabolomics to discover metabolic features in human neurogenesis using neural constructs generated from neural progenitor cells

Direct studies focusing on the human brain are difficult to plan and conduct due to ethical and practical reasons. The advent of human pluripotent stem cell (hPSC)-derived neurons has revolutionized the research of the human brain and central nervous system, but relevant analytical techniques have been much less explored. Herein, we have designed a novel bioanalytical strategy to discover the characteristics of human neurogenesis using liquid chromatography-mass spectrometry-based quantitation and time-dependent metabolomics in combination with hPSC-derived neural constructs. To examine the growth of neurons in vitro, a quantitative method for the simultaneous measurement of N-acetylaspartic acid (NAA) and N-acetylglutamic acid (NAG) in a culture medium was established. The analysis of endogenous NAA and NAG concentrations over 28 days of neural cell culture not only illustrated the growth and maturation process of neural progenitors, but also confirmed the successful achievement of human neural constructs. Depending on the quantitative results, day 0, 10, 18, and 28 samples representing different growth phases were selected for further investigation of the global metabolic changes in developing human neurons. A versatile non-targeted, time-dependent metabolomics study identified 17 significantly changed metabolites and revealed the altered metabolic pathways including amino acid metabolism (tryptophan, phenylalanine, aspartate and beta-alanine metabolisms), pantothenate and coenzyme A biosynthesis, fatty acid metabolism, and purine and pyrimidine metabolism. The new metabolite profiles and overall metabolic pathways advance our understanding of human neurodevelopment. Additionally, the bioanalytical approach proposed in this study opens an interesting window for the capture and evaluation of the complex metabolic states of human neural cells, which would potentially be utilized in other in vitro models relevant to pathophysiology and treatment of neurological disorders, benefiting biomarker discovery and metabolic mechanism interpretation.

Oxidative Stress in Traumatic Brain Injury

Traumatic Brain Injury (TBI) remains a major cause of disability worldwide. It involves a complex neurometabolic cascade, including oxidative stress. The products of this manuscript is examining the underlying pathophysiological mechanism, including reactive oxygen species (ROS) and reactive nitrogen species (RNS). This process in turn leads to secondary injury cascade, which includes lipid peroxidation products. These reactions ultimately play a key role in chronic inflammation and synaptic dysfunction in a synergistic fashion. Although there are no FDA approved antioxidant therapy for TBI, there is a number of antioxidant therapies that have been tested and include free radical scavengers, activators of antioxidant systems, inhibitors of free radical generating enzymes, and antioxidant enzymes. Antioxidant therapies have led to cognitive and functional recovery post TBI, and they offer a promising treatment option for patients recovering from TBI. Current major challenges in treatment of TBI symptoms include heterogenous nature of injury, as well as access to timely treatment post injury. The inherent benefits of antioxidant therapies include minimally reported side effects, and relative ease of use in the clinical setting. The current review also provides a highlight of the more studied anti-oxidant regimen with applicability for TBI treatment with potential use in the real clinical setting.

A mild form of adenylosuccinate lyase deficiency in absence of typical brain MRI features diagnosed by whole exome sequencing

Background

Adenylosuccinate lyase (ADSL) deficiency is a defect of purine metabolism affecting purinosome assembly and reducing metabolite fluxes through purine de novo synthesis and purine nucleotide recycling pathways. The disorder shows a wide spectrum of symptoms from slowly to rapidly progressing forms. The most severe form is characterized by neonatal encephalopathy, absence of spontaneous movement, respiratory failure, intractable seizures, and early death within the first weeks of life. More commonly, ADSL presents purely neurologic clinical picture characterized by severe psychomotor retardation, microcephaly, early onset of seizures, and autistic features (type I) or a more slowly progressing form with later onset, and major features including slight to moderate psychomotor retardation, and transient contact disturbances (type II). Diagnostic markers are the presence of succinylaminoimidazole carboxamide riboside (SAICAr) and succinyladenosine (SAdo) in extracellular fluids. ADSL is a rare disorder, although its prevalence remains unknown. Of note, the wide range of essentially nonspecific manifestations and lack of awareness of the condition often prevent diagnosis.

Case presentation

We present here the case of particularly mild, late onset ADSL that has been unsuccessfully investigated until whole exome sequencing (WES) was performed.

Conclusions

Besides emphasizing the valuable diagnostic value of WES, this report provides new data further documenting the relatively wide clinical manifestation of ADSL.

Electronic supplementary material

The online version of this article (doi:10.1186/s13052-017-0383-7) contains supplementary material, which is available to authorized users.

Extracellular N-Acetylaspartate in Human Traumatic Brain Injury

N-acetylaspartate (NAA) is an amino acid derivative primarily located in the neurons of the adult brain. The function of NAA is incompletely understood. Decrease in brain tissue NAA is presently considered symptomatic and a potential biomarker of acute and chronic neuropathological conditions. The aim of this study was to use microdialysis to investigate the behavior of extracellular NAA (eNAA) levels after traumatic brain injury (TBI). Sampling for this study was performed using cerebral microdialysis catheters (M Dialysis 71) perfused at 0.3 μL/min. Extracellular NAA was measured in microdialysates by high-performance liquid chromatography in 30 patients with severe TBI and for comparison, in radiographically “normal” areas of brain in six non-TBI neurosurgical patients. We established a detailed temporal eNAA profile in eight of the severe TBI patients. Microdialysate concentrations of glucose, lactate, pyruvate, glutamate, and glycerol were measured on an ISCUS clinical microdialysis analyzer. Here, we show that the temporal profile of microdialysate eNAA was characterized by highest levels in the earliest time-points post-injury, followed by a steady decline; beyond 70 h post-injury, average levels were 40% lower than those measured in non-TBI patients. There was a significant inverse correlation between concentrations of eNAA and pyruvate; eNAA showed significant positive correlations with glycerol and the lactate/pyruvate (L/P) ratio measured in microdialysates. The results of this on-going study suggest that changes in eNAA after TBI relate to the release of intracellular components, possibly due to neuronal death or injury, as well as to adverse brain energy metabolism.

Traumatic brain injury: oxidative stress and neuroprotection

SIGNIFICANCE

A vast amount of circumstantial evidence implicates high energy oxidants and oxidative stress as mediators of secondary damage associated with traumatic brain injury. The excessive production of reactive oxygen species due to excitotoxicity and exhaustion of the endogenous antioxidant system induces peroxidation of cellular and vascular structures, protein oxidation, cleavage of DNA, and inhibition of the mitochondrial electron transport chain.

RECENT ADVANCES

Different integrated responses exist in the brain to detect oxidative stress, which is controlled by several genes termed vitagens. Vitagens encode for cytoprotective heat shock proteins, and thioredoxin and sirtuins.

CRITICAL ISSUES AND FUTURE DIRECTIONS

This article discusses selected aspects of secondary brain injury after trauma and outlines key mechanisms associated with toxicity, oxidative stress, inflammation, and necrosis. Finally, this review discusses the role of different oxidants and presents potential clinically relevant molecular targets that could be harnessed to treat secondary injury associated with brain trauma.

The pathophysiology of concussion

Concussion is defined as a biomechanically induced brain injury characterized by the absence of gross anatomic lesions. Early and late clinical symptoms, including impairments of memory and attention, headache, and alteration of mental status, are the result of neuronal dysfunction mostly caused by functional rather than structural abnormalities. The mechanical insult initiates a complex cascade of metabolic events leading to perturbation of delicate neuronal homeostatic balances. Starting from neurotoxicity, energetic metabolism disturbance caused by the initial mitochondrial dysfunction seems to be the main biochemical explanation for most postconcussive signs and symptoms. Furthermore, concussed cells enter a peculiar state of vulnerability, and if a second concussion is sustained while they are in this state, they may be irreversibly damaged by the occurrence of swelling. This condition of concussion-induced brain vulnerability is the basic pathophysiology of the second impact syndrome. N-acetylaspartate, a brain-specific compound representative of neuronal metabolic wellness, is proving a valid surrogate marker of the post-traumatic biochemical damage, and its utility in monitoring the recovery of the aforementioned "functional" disturbance as a concussion marker is emerging, because it is easily detectable through proton magnetic resonance spectroscopy.

Biochemical and neurochemical sequelae following mild traumatic brain injury: summary of experimental data and clinical implications

Although numerous studies have been carried out to investigate the pathophysiology of mild traumatic brain injury (mTBI), there are still no standard criteria for the diagnosis and treatment of this peculiar condition. The dominant theory that diffuse axonal injury is the main neuropathological process behind mTBI is being revealed as weak at best or inconclusive, given the current literature and the fact that neuronal injury inherent to mTBI improves, with few lasting clinical sequelae in the vast majority of patients. Clinical and experimental evidence suggests that such a course, rather than being due to cell death, is based on temporal neuronal dysfunction, the inevitable consequence of complex biochemical and neurochemical cascade mechanisms directly and immediately triggered by the traumatic insult. This report is an attempt to summarize data from a long series of experiments conducted in the authors' laboratories and published during the past 12 years, together with an extensive analysis of the available literature, focused on understanding the biochemical damage produced by an mTBI. The overall clinical implications, as well as the metabolic nature of the post-mTBI brain vulnerability, are discussed. Finally, the application of proton MR spectroscopy as a possible tool to monitor the full recovery of brain metabolic functions is emphasized.

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.

Assessment of mitochondrial impairment in traumatic brain injury using high-resolution proton magnetic resonance spectroscopy

Object

The goal of this study was to demonstrate the posttraumatic neurochemical damage in normal-appearing brain and to assess mitochondrial dysfunction by measuring N-acetylaspartate (NAA) levels in patients with severe head injuries, using proton (1H) magnetic resonance (MR) spectroscopy.

Methods

Semiquantitative analysis of NAA relative to creatine-containing compounds (Cr) and choline (Cho) was carried out from proton spectra obtained by means of chemical shift (CS) imaging and single-voxel (SV) methods in 25 patients with severe traumatic brain injuries (TBIs) (Glasgow Coma Scale scores ≤ 8) using a 1.5-tesla MR unit. Proton MR spectroscopy was also performed in 5 healthy volunteers (controls).

Results

The SV studies in patients with diffuse TBI showed partial reduction of NAA/Cho and NAA/Cr ratios within the first 10 days after injury (means ± standard deviations 1.59 ± 0.46 and 1.44 ± 0.21, respectively, in the patients compared with 2.08 ± 0.26 and 2.04 ± 0.31, respectively, in the controls; nonsignificant difference). The ratios gradually declined in all patients as time from injury increased (mean minimum values NAA/Cho 1.05 ± 0.44 and NAA/Cr 1.05 ± 0.30, p < 0.03 and p < 0.02, respectively). This reduction was greater in patients with less favorable outcomes. In patients with focal injuries, the periphery of the lesions revealed identical trends of NAA/Cho and NAA/Cr decrease. These reductions correlated with outcome at 6 months (p < 0.01). Assessment with multivoxel methods (CS imaging) demonstrated that, in diffuse injury, NAA levels declined uniformly throughout the brain. At 40 days postinjury, initially low NAA/Cho levels had recovered to near baseline in patients who had good outcomes, whereas no recovery was evident in patients with poor outcomes (p < 0.01).

Conclusions

Using 1H-MR spectroscopy, it is possible to detect the posttraumatic neurochemical damage of the injured brain when conventional neuroimaging techniques reveal no abnormality. Reduction of NAA levels is a dynamic process, evolving over time, decreasing and remaining low throughout the involved tissue in patients with poor outcomes. Recovery of NAA levels in patients with favorable outcomes suggests marginal mitochondrial impairment and possible resynthesis from vital neurons.

Hypothesis of the postconcussive vulnerable brain: experimental evidence of its metabolic occurrence

OBJECTIVE

We evaluated the effects of two consecutive concussive injuries on brain energy metabolism and N-acetylaspartate (NAA) to investigate how the temporal interval between traumatic events influences overall injury severity.

METHODS

Rats were injured to induce diffuse traumatic brain injury (TBI) (mild, 450 g/1 m; severe, 450 g/2 m). In two groups, two mild TBIs were delivered in 3- or 5-day intervals. Three additional animal groups were used: single mild TBI, single severe TBI, and sham. All animals were killed 48 hours postinjury. Adenosine 5'-triphosphate (ATP), adenosine diphosphate, and NAA concentrations were analyzed with high-performance liquid chromatography on deproteinized whole brain extracts.

RESULTS

In control animals, the NAA concentration was 9.17 +/- 0.38 micromol/g wet weight, the ATP concentration was 2.25 +/- 0.21 micromol/g wet weight, and the ATP-to-adenosine diphosphate ratio was 9.38 +/- 1.23. These concentrations decreased to 6.68 +/- 1.12 micromol/g wet weight, 1.68 +/- 0.24 micromol/g wet weight, and 6.10 +/- 1.21 micromol/g wet weight, respectively, in rats that received two mild TBIs at a 5-day interval (P < 0.01; not different from results in rats with single mild TBI). When a second TBI was delivered after 3 days, the NAA concentration was 3.86 +/- 0.53 micromol/g wet weight, the ATP concentration was 1.11 +/- 0.18 micromol/g wet weight, and the ATP-to-adenosine diphosphate ratio was 2.64 +/- 0.43 (P < 0.001 versus both controls and 3-day interval; not different from rats receiving a single severe TBI).

CONCLUSION

The biochemical modification severity in double TBI is dependent on the interval between traumatic events, which demonstrates the metabolic state of the vulnerable brain after mild TBI. These data support the hypothesis of the application of proton magnetic resonance spectroscopy to measure NAA as a possible tool to monitor the full recovery of brain metabolic functions in the clinical setting, particularly in sports medicine.

Extracellular N-acetylaspartate depletion in traumatic brain injury

N-Acetylaspartate (NAA) is almost exclusively localized in neurons in the adult brain and is present in high concentration in the CNS. It can be measured by proton magnetic resonance spectroscopy and is seen as a marker of neuronal damage and death. NMR spectroscopy and animal models have shown NAA depletion to occur in various types of chronic and acute brain injury. We investigated 19 patients with traumatic brain injury (TBI). Microdialysis was utilized to recover NAA, lactate, pyruvate, glycerol and glutamate, at 12-h intervals. These markers were correlated with survival and a 6-month Glasgow Outcome Score. Eleven patients died and eight survived. A linear mixed model analysis showed a significant effect of outcome and of the interaction between time of injury and outcome on NAA levels (p = 0.009 and p = 0.004, respectively). Overall, extracellular NAA was 34% lower in non-survivors. A significant non-recoverable fall was observed in this group from day 4 onwards, with a concomitant rise in lactate-pyruvate ratio and glycerol. These results suggest that mitochondrial dysfunction is a significant contributor to poor outcome following TBI and propose extracellular NAA as a potential marker for monitoring interventions aimed at preserving mitochondrial function.

Simultaneous high performance liquid chromatographic separation of purines, pyrimidines, N-acetylated amino acids, and dicarboxylic acids for the chemical diagnosis of inborn errors of metabolism

OBJECTIVES

To set up a novel simple, sensitive, and reliable ion-pairing HPLC method for the synchronous separation of several purines, pyrimidines, N-acetylated amino acids, and dicarboxylic acids for the chemical diagnosis and screening of inborn errors of metabolism (IEM).

DESIGN AND METHODS

The separation was set up using a Hypersil C-18, 5-microm particle size, 250 x 4.6 mm column, and a step gradient using two buffers and tetrabutylammonium hydroxide as the pairing reagent. A highly sensitive diode array UV detector was set up at a wavelength between 200 and 300 nm that revealed purines and pyrimidines at 260 nm and other compounds at 206 nm.

RESULTS

Compounds were determined in the plasma of 15 healthy adults, in the urine of 50 healthy subjects (1-3 years, 4-6 years, 8-10 years, 12-18 years, 25-35 years), and in 10 non-pathological amniotic fluid samples. To assess the validity of the chemical diagnosis of IEM, plasma and urine samples were analyzed in patients affected by Canavan disease (n = 10; mean age 4.6 +/- 2.3). Low plasma levels of N-acetylaspartate (16.96 +/- 19.57 micromol/L plasma; not detectable in healthy adults) and dramatically high urinary N-acetylaspartate concentrations (1872.03 +/- 631.86 micromol/mmol creatinine; 450 times higher than that which was observed in age-matched controls) were recorded. Neither N-acetylglutamate nor N-acetylaspartylglutamate could be detected in the plasma or urine of controls or patients with Canavan disease.

CONCLUSIONS

The results demonstrate the suitability of the present ion-pairing HPLC separation with UV detection of cytosine, cytidine, creatinine, uracil, uridine, beta-pseudouridine, adenine, 3-methyladenine, hypoxanthine, xanthine, xanthosine, inosine, guanosine, ascorbic acid, thymine, thymidine, uric acid, 1-methyluric acid, orotic acid, N-acetylaspartate, N-acetylglutamate, N-acetylaspartylglutamate, malonic acid, methylmalonic acid, GSH, and GSSG as a reliable method for the prenatal and neonatal chemical diagnosis and screening of IEM using biological fluids.

Cerebral oxidative stress and depression of energy metabolism correlate with severity of diffuse brain injury in rats

OBJECTIVE

The combined effect of traumatic brain injury (TBI) and secondary insult on biochemical changes of cerebral tissue is not well known. For this purpose, we studied the time-course changes of parameters reflecting ROS-mediated oxidative stress and modifications of cell energy metabolism determined in rats subjected to cerebral insult of increasing severity.

METHODS

Rats were divided into four groups: 1) sham-operated, 2) subjected to 10 minutes of hypoxia and hypotension (HH), 3) subjected to severe diffuse TBI, and 4) subjected to severe diffuse TBI + HH. Rats were killed at different times after injury, and analyses of malondialdehyde, ascorbate, high-energy phosphates, nicotinic coenzymes, oxypurines, nucleosides, and N-acetylaspartate (NAA) were made by high-performance liquid chromatography on whole-brain tissue extracts.

RESULTS

Data indicated a close relationship between degree of oxidative stress and severity of brain insult, as evidenced by the highest malondialdehyde values and lowest ascorbate levels in rats subjected to TBI + HH. Similarly, modifications of parameters related to cell energy metabolism were modulated by increasing severity of brain injury, as demonstrated by the lowest values of energy charge potential, nicotinic coenzymes, and NAA and the highest levels of oxypurines and nucleosides recorded in TBI + HH rats. Both the intensity of oxidative stress-mediated cerebral damage and perturbation of energy metabolism were minimally affected in rats subjected to HH only.

CONCLUSION

These results showed that the severity of brain insult can be graded by measuring biochemical modifications, specifically, reactive oxygen species-mediated damage, energy metabolism depression, and NAA, thereby validating the rodent model of closed-head diffuse TBI coupled with HH and proposing NAA as a marker with diagnostic relevance to monitor the metabolic state of postinjured brain.

Effects of AAV-2-mediated aspartoacylase gene transfer in the tremor rat model of Canavan disease

The tremor rat is a spontaneous epilepsy model with a seizure phenotype caused by a deletion in the aspartoacylase (ASPA) gene. The absence of ASPA expression in these animals results in undetectable levels of enzyme activity and the accumulation of the substrate N-acetyl-aspartate (NAA) in brain, leading to generalized myelin vacuolation and severe motor and cognitive impairment. In support of human gene therapy for CD, recombinant adeno-associated viral vector (AAV-2) expressing ASPA was stereotactically delivered to the tremor rat brain and effects on the mutant phenotype were measured. AAV-ASPA gene transfer resulted in elevated aspartoacylase bioactivity compared to untreated mutant animals and elicited a significant decrease in the pathologically elevated whole-brain NAA levels. Assessment of motor function via quantitative rotorod testing demonstrated that rats injected with AAV-ASPA significantly improved on tests of balance and coordinated locomotion compared to animals receiving control vectors. This study provides evidence that AAV-2-mediated aspartoacylase gene transfer to the brain improves biochemical and behavioral deficits in tremor rat mutants (tm/tm) and supports the rationale of human gene transfer for Canavan disease.

The Protective Effect of Cyclosporin A upon N-Acetylaspartate and Mitochondrial Dysfunction following Experimental Diffuse Traumatic Brain Injury

Pre- and post-injury Cyclosporin A (CsA) administration has shown neuroprotective properties by ameliorating mitochondrial damage. The aim of this study was to assess the effect of CsA upon N-acetylaspartate (NAA) reduction and ATP loss, two sensitive markers of mitochondrial dysfunction and bioenergetic impairment. Adult male Sprague-Dawley rats were exposed to impact acceleration traumatic brain injury (2 m/450 g) and randomized into the following experimental groups: intrathecal CsA/vehicle treated (n = 12), intravenous CsA/vehicle treated (n = 18) and sham (n = 12). Intrathecal treatment consisted of post-injury (30 min) cisternal bolus of CsA or Vehicle (0.15 mL, 10 mg/kg). Intravenous administration consisted of 30 min post-injury continuous 1 hour infusion of either 20 or 35 mg/kg CsA or Vehicle. Quantitative HPLC analysis of whole brain samples was performed 6 h post-injury for levels of NAA and ATP. Following intrathecal delivery CsA demonstrated significant neuroprotection blunting a 30% NAA reduction (p < 0.001) and restoring 26% of the ATP loss (p < 0.005). The 20 mg/kg intravenous dose failed to ameliorate the biochemical damages while the 35 mg/kg dosage showed 36% NAA recovery and 39% ATP restoration (p < 0.001). In conclusion, CsA is capable of restoring ATP and blunting NAA reduction. Intravenous infusion of 35 mg/kg appears to be the optimal therapeutic strategy in this model. These findings contribute to the notion that CsA achieves neuroprotection, preserving mitochondrial function, and provides a rationale for the assessment of CsA in the clinical setting where MR spectroscopy can monitor NAA and ATP in brain-injured patients.

Single-sample preparation for simultaneous cellular redox and energy state determination

A simple and reliable method for the preparation of biological samples for the evaluation of biochemical parameters representative of the redox and energy states, such as glutathione (GSH), oxidized glutathione (GSSG), oxidized nicotinamide adenine dinucleotide (NAD+), reduced nicotinamide adenine dinucleotide (NADH), oxidized nicotinamide adenine dinucleotide phosphate (NADP+), reduced nicotinamide adenine dinucleotide phosphate (NADPH), coenzyme A (CoASH), oxidized CoASH, ascorbate, malondialdehyde, oxypurines, nucleosides, and energy metabolites, is presented. Fast deproteinization under nonoxidizing conditions is obtained by tissue homogenization in ice-cold, nitrogen-saturated CH3CN + 10 mM KH2PO4 (3:1; v:v), pH 7.40. After sample centrifugation to pellet precipitated proteins, organic solvent removal is performed on clear supernatants by three washings with large volumes of high-performance liquid chromatography (HPLC)-grade chloroform. The remaining aqueous phase, free of solvent and any lipid-soluble substances that may interfere with the further metabolite analysis, is used for the simultaneous ion-pairing HPLC determination of 39 compounds by means of a Kromasil C-18, 250 x 4.6-mm, 5-microm-particle-size column with tetrabutylammonium hydroxide as the pairing reagent. Results obtained by using the present method to prepare different rat tissue extracts demonstrate that it is possible to perform a single tissue preparation only for monitoring, in the same sample, compounds representative of the redox state (through the direct determination of GSH, GSSG, NAD+, NADH, NADP+, NADPH, CoASH, and oxidized CoASH) and of the cell energy state (by the analysis of oxypurines, nucleosides, and energy metabolites). Applicability of this sample processing procedure to quantify variations of the aforementioned compounds under pathological conditions was effected in rats subjected to moderate closed-head trauma.

Development of generic liquid chromatography-mass spectrometry methods using experimental design

Standard approaches to development of liquid chromatography-mass spectrometry (LC-MS) methods, either ion-pairing or reversed-phase liquid chromatography, have been through trial and error or intentional variation of experimental factors. These approaches to method optimization fail to take into account interactions between experimental factors and therefore the results may not be optimal for the combination of experimental factors. Another approach to optimization is through the use of chemometrics. Chemometric approaches can be more efficient than trial and error or intentional variation because chemometrics make use of multivariate designs; experimental factors are varied simultaneously at the various levels. Therefore chemometrics can take into account interactions between factors. The goal of this study was to develop a generic ion-pair LC-MS method for the analysis of acidic compounds using a chemometric approach called design of experiments (DOE). Four acidic compounds which cover three classes of acidic functional groups: 1-naphthyl phosphate (1), 1-naphthalenesulfonic acid (2), 2-naphthalenesulfonic acid (3), and (1-naphthoxy)acetic acid (4) were used as model compounds to develop the generic method. This study illustrates that LC-MS conditions can be optimized efficiently with minimal amount of experimentation using a chemometric approach to experimental design.

N-Acetylaspartate reduction as a measure of injury severity and mitochondrial dysfunction following diffuse traumatic brain injury

N-Acetylaspartate (NAA) is considered a neuron-specific metabolite and its reduction a marker of neuronal loss. The objective of this study was to evaluate the time course of NAA changes in varying grades of traumatic brain injury (TBI), in concert with the disturbance of energy metabolites (ATP). Since NAA is synthesized by the mitochondria, it was hypothesized that changes in NAA would follow ATP. The impact acceleration model was used to produce three grades of TBI. Sprague-Dawley rats were divided into the following four groups: sham control (n = 12); moderate TBI (n = 36); severe TBI (n = 36); and severe TBI coupled with hypoxia-hypotension (n = 16). Animals were sacrificed at different time points ranging from 1 min to 120 h postinjury, and the brain was processed for high-performance liquid chromatography (HPLC) analysis of NAA and ATP. After moderate TBI, NAA reduced gradually by 35% at 6 h and 46% at 15 h, accompanied by a 57% and 45% reduction in ATP. A spontaneous recovery of NAA to 86% of baseline at 120 h was paralleled by a restoration in ATP. In severe TBI, NAA fell suddenly and did not recover, showing critical reduction (60%) at 48 h. ATP was reduced by 70% and also did not recover. Maximum NAA and ATP decrease occurred with secondary insult (80% and 90%, respectively, at 48 h). These data show that, at 48 h post diffuse TBI, reduction of NAA is graded according to the severity of insult. NAA recovers if the degree of injury is moderate and not accompanied by secondary insult. The highly similar time course and correlation between NAA and ATP supports the notion that NAA reduction is related to energetic impairment.

Intraneuronal N-acetylaspartate supplies acetyl groups for myelin lipid synthesis: evidence for myelin-associated aspartoacylase

Despite its growing use as a radiological indicator of neuronal viability, the biological function of N-acetylaspartate (NAA) has remained elusive. This is due in part to its unusual metabolic compartmentalization wherein the synthetic enzyme occurs in neuronal mitochondria whereas the principal metabolizing enzyme, N-acetyl-L-aspartate amidohydrolase (aspartoacylase), is located primarily in white matter elements. This study demonstrates that within white matter, aspartoacylase is an integral component of the myelin sheath where it is ideally situated to produce acetyl groups for synthesis of myelin lipids. That it functions in this manner is suggested by the fact that myelin lipids of the rat optic system are well labeled following intraocular injection of [14C-acetyl]NAA. This is attributed to uptake of radiolabeled NAA by retinal ganglion cells followed by axonal transport and transaxonal transfer of NAA into myelin, a membrane previously shown to contain many lipid synthesizing enzymes. This study identifies a group of myelin lipids that are so labeled by neuronal [14C]NAA, and demonstrates a different labeling pattern from that produced by neuronal [14C]acetate. High performance liquid chromatographic analysis of the deproteinated soluble materials from the optic system following intraocular injection of [14C]NAA revealed only the latter substance and no radiolabeled acetate, suggesting little or no hydrolysis of NAA within mature neurons of the optic system. These results suggest a rationale for the unusual compartmentalization of NAA metabolism and point to NAA as a neuronal constituent that is essential for the formation and/or maintenance of myelin. The relevance of these findings to Canavan disease is discussed.