Neuroprotective role of lipoic acid against acute toxicity of N-acetylaspartic acid

N-Acetylaspartic acid (NAA) accumulates in Canavan disease, a severe inherited neurometabolic disorder clinically characterized by mental retardation, hypotonia, macrocephaly, and seizures. The mechanisms of brain damage in this disease remain poorly understood. Recent studies developed by our research group showed that NAA induces oxidative stress in vitro and in vivo in cerebral cortex of rats. Lipoic acid is considered as an efficient antioxidant which can easily cross the blood–brain barrier. Considering the absence of specific treatment to Canavan disease, this study evaluates the possible prevention of the oxidative stress promoted by NAA in vivo by the antioxidant lipoic acid to preliminarily evaluate lipoic acid efficacy against pro-oxidative effects of NAA. Fourteen-day-old Wistar rats received an acute administration of 0.6 mmol NAA/g body weight with or without lipoic acid (40 mg/kg body weight). Catalase (CAT), glutathione peroxidase (GPx), and glucose 6-phosphate dehydrogenase activities, hydrogen peroxide content, thiobarbituric acid-reactive substances (TBA-RS), spontaneous chemiluminescence, protein carbonyl content, total antioxidant potential, and DNA–protein cross-links were assayed in the cerebral cortex of rats. CAT, GPx activities, and total antioxidant potential were significantly reduced, while hydrogen peroxide content, TBA-RS, spontaneous chemiluminescence, and protein carbonyl content were significantly enhanced by acute administration of NAA. Those effects were all prevented by lipoic acid pretreatment. Our results clearly show that lipoic acid may protect against the oxidative stress promoted by NAA. This could represent a new therapeutic approach to the patients affected by Canavan disease.     

METABOLISM OF THE ASPARTYL MOIETY OF N-ACETYL-l-ASPARTIC ACID IN THE RAT BRAIN

The metabolism of N-acetyl-l -aspartic acid (NAA) was studied in rat brain. [Aspartyl-U-¹⁴C]NAA was metabolized predominantly by deacylation. Studies of NAA biosynthesis from l -[U-¹⁴C]aspartic acid have confirmed previous reports that NAA turns over slowly in rat brain. However, intracerebrally-injected N-acetyl-l -[U-¹⁴C]asparticacid was rapidly metabolized. Exogenous NAA appears to be taken up rapidly into a small, metabolically-active pool. This pool serves as substrate for a tricarboxylic acid cycle associated with the production of glutamate for the biosynthesis of glutamine. The bulk of the NAA content in brain appears to be relatively inactive metabolically.     

N-acetylaspartate in the vertebrate brain: metabolism and function

N-Acetyl-l-aspartate (NAA) is an amino acid that is present in the vertebrate brain. Its concentration is one of the highest of all free amino acids and, although NAA is synthesized and stored primarily in neurons, it cannot be hydrolyzed in these cells. Furthermore, neuronal NAA is dynamic and turns over more than once each day by virtue of its continuous efflux, in a regulated intercompartmental cycling via extracellular fluids, between neurons and a second compartment in oligodendrocytes. The metabolism of NAA, between its anabolic compartment in neurons and its catabolic compartment in oligodendrocytes, and its possible physiological role in the brain has been the subject of much speculation. There are two human inborn errors in metabolism of NAA. One is Canavan disease (CD), in which there is a buildup of NAA (hyperacetylaspartia) and associated spongiform leukodystrophy, caused by a lack of aspartoacylase activity. The other is a singular human case of lack of NAA (hypoacetylaspartia), where the enzyme that synthesizes NAA is apparently absent. There are two animal models currently available for studies of CD. One is a rat with a natural deletion of the catabolic enzyme, and the other a gene knockout mouse. In addition to the presence of NAA in neurons, its prominence in ¹H nuclear magnetic resonance spectroscopic studies has led to its wide use in diagnostic human medicine as both an indicator of brain pathology and of disease progression in a variety of CNS diseases. In this review, various hypotheses regarding the metabolism of NAA and its possible role in the CNS are evaluated. Based on this analysis, it is concluded that although NAA may have several functions in the CNS, an important role of the NAA intercompartmental system is osmoregulatory, and in this role it may be the primary mechanism for the removal of intracellular water, against a water gradient, from myelinated neurons.     

Ovarian Cyst Fluid of Serous Ovarian Tumors Contains Large Quantities of the Brain Amino Acid N-acetylaspartate

Background

In humans, N-acetyl L-aspartate (NAA) has not been detected in other tissues than the brain. The physiological function of NAA is yet undefined. Recently, it has been suggested that NAA may function as a molecular water pump, responsible for the removal of large amounts of water from the human brain. Ovarian tumors typically present as large cystic masses with considerable fluid accumulation.

Methodology and Principal Findings

Using Gas Chromatography-Mass Spectrometry, we demonstrated that NAA was present in a high micromolar concentration in oCF of epithelial ovarian tumors (EOTs) of serous histology, sometimes in the same range as found in the extracellular space of the human brain. In contrast, oCF of EOTs with a mucinous, endometrioid and clear cell histological subtype contained a low micromolar concentration of NAA. Serous EOTs have a cellular differentiation pattern which resembles the lining of the fallopian tube and differs from the other histological subtypes. The NAA concentration in two samples of fluid accumulation in the fallopian tube (hydrosalpinx) was in the same ranges as NAA found in oCF of serous EOTs. The NAA concentration in oCF of patients with serous EOTs was mostly 10 to 50 fold higher than their normal serum NAA concentration, whereas in patients with other EOT subtypes, serum and cyst fluid NAA concentration was comparable.

Conclusions and Significance

The high concentration of NAA in cyst fluid of serous EOTs and low serum concentrations of NAA in these patients, suggest a local production of NAA in serous EOTs. Our findings provide the first identification of NAA concentrations high enough to suggest local production outside the human brain. Our findings contribute to the ongoing research understanding the physiological function of NAA in the human body.     

Evidence that the tri-cellular metabolism of N-acetylaspartate functions as the brain’s “operating system”: how NAA metabolism supports meaningful intercellular frequency-encoded communications

N-acetylaspartate (NAA), an acetylated derivative of l-aspartate (Asp), and N-acetylaspartylglutamate (NAAG), a derivative of NAA and l-glutamate (Glu), are synthesized by neurons in brain. However, neurons cannot catabolize either of these substances, and so their metabolism requires the participation of two other cell types. Neurons release both NAA and NAAG to extra-cellular fluid (ECF) upon stimulation, where astrocytes, the target cells for NAAG, hydrolyze it releasing NAA back into ECF, and oligodendrocytes, the target cells for NAA, hydrolyze it releasing Asp to ECF for recycling to neurons. This sequence is unique as it is the only known amino acid metabolic cycle in brain that requires three cell types for its completion. The results of this cycling are two-fold. First, neuronal metabolic water is transported to ECF for its removal from brain. Second, the rate of neuronal activity is coupled with focal hyperemia, providing stimulated neurons with the energy required for transmission of meaningful frequency-encoded messages. In this paper, it is proposed that the tri-cellular metabolism of NAA functions as the “operating system” of the brain, and is essential for normal cognitive and motor activities. Evidence in support of this hypothesis is provided by the outcomes of two human inborn errors in NAA metabolism.     

N-Acetylaspartate (NAA) and N-Acetylaspartylglutamate (NAAG) Promote Growth and Inhibit Differentiation of Glioma Stem-like Cells

Metabolic reprogramming is a pathological feature of cancer and a driver of tumor cell transformation. N-Acetylaspartate (NAA) is one of the most abundant amino acid derivatives in the brain and serves as a source of metabolic acetate for oligodendrocyte myelination and protein/histone acetylation or a precursor for the synthesis of the neurotransmitter N-acetylaspartylglutamate (NAAG). NAA and NAAG as well as aspartoacylase (ASPA), the enzyme responsible for NAA degradation, are significantly reduced in glioma tumors, suggesting a possible role for decreased acetate metabolism in tumorigenesis. This study sought to examine the effects of NAA and NAAG on primary tumor-derived glioma stem-like cells (GSCs) from oligodendroglioma as well as proneural and mesenchymal glioblastoma, relative to oligodendrocyte progenitor cells (Oli-Neu). Although the NAA dicarboxylate transporter NaDC3 is primarily thought to be expressed by astrocytes, all cell lines expressed NaDC3 and, thus, are capable of NAA up-take. Treatment with NAA or NAAG significantly increased GSC growth and suppressed differentiation of Oli-Neu cells and proneural GSCs. Interestingly, ASPA was expressed in both the cytosol and nuclei of GSCs and exhibited greatest nuclear immunoreactivity in differentiation-resistant GSCs. Both NAA and NAAG elicited the expression of a novel immunoreactive ASPA species in select GSC nuclei, suggesting differential ASPA regulation in response to these metabolites. Therefore, this study highlights a potential role for nuclear ASPA expression in GSC malignancy and suggests that the use of NAA or NAAG is not an appropriate therapeutic approach to increase acetate bioavailability in glioma. Thus, an alternative acetate source is required.     

Transient alterations of creatine, creatine phosphate, N-acetylaspartate and high-energy phosphates after mild traumatic brain injury in the rat

In this study, the concentrations of creatine (Cr), creatine phosphate (CrP), N-acetylaspartate (NAA), ATP, ADP and phosphatidylcholine (PC) were measured at different time intervals after mild traumatic brain injury (mTBI) in whole brain homogenates of rats. Anaesthetized animals underwent to the closed-head impact acceleration “weight-drop” model (450 g delivered from 1 m height = mild traumatic brain injury) and were killed at 2, 6, 24, 48 and 120 h after the insult (n = 6 for each time point). Sham-operated rats (n = 6) were used as controls. Compounds of interest were synchronously measured by HPLC in organic solvent deproteinized whole brain homogenates. A reversible decrease of all metabolites but PC was observed, with minimal values recorded at 24 h post-injury (minimum of CrP = 48 h after impact). In particular, Cr and NAA showed a decrease of 44.5 and 29.5%, respectively, at this time point. When measuring NAA in relation to other metabolites, as it is commonly carried out in “in vivo” ¹H-magnetic resonance spectroscopy (¹H-MRS), an increase in the NAA/Cr ratio and a decrease in the NAA/PC ratio was observed. Besides confirming a transient alteration of NAA homeostasis and ATP imbalance, our results clearly show significant changes in the cerebral concentration of Cr and CrP after mTBI. This suggests a careful use of the NAA/Cr ratio to measure NAA by ¹H-MRS in conditions of altered cerebral energy metabolism. Viceversa, the NAA/PC ratio appears to be a better indicator of actual NAA levels during energy metabolism impairment. Furthermore, our data suggest that, under pathological conditions affecting the brain energetic, the Cr–CrP system is not a suitable tool to buffer possible ATP depletion in the brain, thus supporting the growing indications for alternative roles of cerebral Cr.     

The Molecular Mechanisms Affecting N-Acetylaspartate Homeostasis Following Experimental Graded Traumatic Brain Injury

To characterize the molecular mechanisms of N-acetylaspartate (NAA) metabolism following traumatic brain injury (TBI), we measured the NAA, adenosine triphosphate (ATP) and adenosine diphosphate (ADP) concentrations and calculated the ATP/ADP ratio at different times from impact, concomitantly evaluating the gene and protein expressions controlling NAA homeostasis (the NAA synthesizing and degrading enzymes N-acetyltransferase 8-like and aspartoacylase, respectively) in rats receiving either mild or severe TBI. The reversible changes in NAA induced by mild TBI were due to a combination of transient mitochondrial malfunctioning with energy crisis (decrease in ATP and in the ATP/ADP ratio) and modulation in the gene and protein levels of N-acetyltransferase 8-like and increase of aspartoacylase levels. The irreversible decrease in NAA following severe TBI, was instead characterized by profound mitochondrial malfunctioning (constant 65% decrease of the ATP/ADP indicating permanent impairment of the mitochondrial phosphorylating capacity), dramatic repression of the N-acetyltransferase 8-like gene and concomitant remarkable increase in the aspartoacylase gene and protein levels. The mechanisms underlying changes in NAA homeostasis following graded TBI might be of note for possible new therapeutic approaches and will help in understanding the effects of repeat concussions occurring during particular periods of the complex NAA recovery process, coincident with the so called window of brain vulnerability.     

In vitro study of astrocytic tumour metabolism by proton magnetic resonance spectroscopy

In vivo magnetic resonance spectroscopy (MRS) studies of glial brain tumours reported that higher grade of astrocytoma is associated with increased level of choline-containing compounds (Cho) and decreased levels of N-acetylaspartate (NAA) and creatine and phosphocreatine (Cr). In this work, we studied the metabolism of glioma tumours by in vitro proton magnetic resonance spectroscopy (1H-MRS). 1H-MR spectra were recorded in vitro from perchloric acid extracts of astrocytoma (WHO II) and glioblastoma multiforme (WHO IV) samples. We observed differences between astrocytoma and glioblastoma multiforme in the levels of Cho, alanine, lactate, NAA, and glutamate/glutamine. In astrocytoma samples, we found higher MR signal of NAA and lower signal of Cho and alanine. MR spectra of glioblastoma samples reported significantly higher levels of lactate and glutamate/glutamine. In contrast, levels of Cr were the same in both tumour types. We also determined NAA/Cr and Cho/Cr ratios in the tumour samples. The NAA/Cr ratio was higher in astrocytomas than in glioblastomas multiforme. Conversely, the Cho/Cr ratio was higher in glioblastoma multiforme. The results indicate that MRS is a promising method for distinguishing pathologies in human brain and for pre-surgical grading of brain tumours.     

An anti-inflammatory role for N-acetyl aspartate in stimulated human astroglial cells

Although N-acetyl-L-aspartate (NAA) has been shown to be important to myelin synthesis and osmotic regulation, the biological rationale for the high levels of NAA found in the brain remains unknown. Here, a human astroglial cell line (STTG) was treated with NAA and stimulated with ionomycin, ionomycin/PMA, or IL-1beta. PGE(2) levels in ionomycin-stimulated STTG cells decreased by 76% and > 95% at NAA concentrations of 10 and 20mM, respectively. NAA also decreased the levels of COX-2 protein and activated NF-kappaB in IL-1beta-stimulated STTG cells but had little effect on unstimulated cells. Also, NAA significantly decreased intracellular calcium levels in ionomycin/PMA-stimulated cells. NAA had no effect on total COX-2 activity or COX-2 mRNA. Acetylation of IkappaBalpha kinase, an acetylation target of aspirin, was not observed when NAA was present. These results demonstrate that NAA appears to be important in the modulation of inflammation in the human STTG astroglial cell line. The results of these findings are discussed in relation to neuronal pathologies that exhibit abnormal NAA levels within the brain.     

Fatty acids in callus cultures: Influence of growth factors on fatty acid composition of total lipids in callus cells

Callus tissues were derived from cotyledon segments of Cucumis melo and Cucumis sativus. Four combinations of growth factors, i.e., naphthalene acetic acid (NAA) plus coconut water (CW); NAA plus kinetin; NAA plus 6-benzylaminopurine (BAP) and indole 3-butyric acid plus BAP, were incorporated in the medium for callus initiation as well as for growth of excised callus in culture for six passages. The proportion of total saturated to unsaturated acids and the ratio of linoleic to linolenic acid was influenced by the change in the type of auxin and cytokinin in the combinations used. A many fold increase of myristic acid was recorded for the indole 3-butyric acid plus BAP combination.     

Bound auxin metabolism in cultured crown-gall tissues of tobacco

Bound auxin metabolism in cultured crown-gall tumor cells and pith callus of tobacco was examined by feeding radiolabeled auxins and auxin conjugates. In all tissues fed [¹⁴C]indoleacetic acid (IAA), at least one-third of the IAA was decarboxylated, and most of the remaining radiolabel occurred in a compound(s) which did not release IAA with alkaline hydrolysis. In cells transformed by the A6 strain of Agrobacterium tumefaciens, the only detectable IAA conjugate was indole-3-acetylaspartic acid (IAAsp), whereas cells transformed by the gene 2 mutant strain A66 produced an unidentified amide conjugate but no IAAsp. By contrast, cells fed [¹⁴C]naphthaleneacetic acid (NAA) accumulated several amide and ester conjugates. The major NAA metabolite in A6-transformed cells was naphthaleneacetylaspartic acid (NAAsp), whereas the major metabolites in A66-transformed cells were NAA esters. In addition, A66-transformed cells produced an amide conjugate of NAA which was not found in A6-transformed cells and which showed chromatographic properties similar to the unknown IAA conjugate. Pith callus fed [¹⁴C] NAA differed from both tumor lines in that it preferentially accumulated amide conjugates other than NAAsp. Differences in the accumulation of IAA and NAA conjugates were attributed in part to the high capacity of tobacco cells to oxidize IAA and in part to the specificity of bound auxin hydrolases. All tissues readily metabolized IAAsp and indole-3-acetyl-myo-inositol, but hydrolyzed NAAsp very slowly. Indirect evidence is provided which suggests that ester conjugates of NAA are poorly hydrolyzed as well. Analysis of tissues fed [¹⁴C]NAA together with high concentrations of unlabeled IAA or NAA indicates that tissue-specific differences in NAA metabolism were not the result of variation in endogenous auxin levels. Our results support the view that bound auxin hydrolysis is highly specific and an important factor controlling bound auxin accumulation.     

In vitro auxin binding to cellular membranes of cucumber fruits

Specific binding of 1-naphthaleneacetic acid (NAA) to crude membrane preparations from cucumber (Cucumis sativus L.) was demonstrated. This in vitro binding had a pH optimum of 3.75 and an equilibrium dissociation constant of 10 to 20 micromolar with 1250 picomoles binding sites per gram fresh weight. The NAA-binding sites were pronase sensitive. The supernatant from the fruit partially inhibited the in vitro NAA binding to fruit membranes. NAA, 2-naphthoxyacetic acid, 3-indoleacetic acid, 2-4-dichlorophenoxyacetic acid, and 2,3,5-triiodobenzoic acid, which are reported to be very good inducers of parthenocarpy in cucumber, showed a high degree of specific binding to cucumber fruit membranes. In comparison, 2-naphthaleneacetic acid and indolepropionic acid, which are reported to be very weak auxins in corn coleoptile, pea stem, and strawberry fruit growth bioassays, did not bind efficiently to cucumber fruit membranes. In vitro binding studies with fruit membranes suggest that auxin stimulated fruit growth may be mediated by membrane-associated, auxin-binding protein(s).     

Direct determination of the N-acetyl-L-aspartate synthesis rate in the human brain by (13)C MRS and [1-(13)C]glucose infusion

A non-invasive (13)C magnetic resonance spectroscopy (MRS) technique is described for the determination of the N-acetyl-L-aspartate (NAA) synthesis rate, V(NAA), in the human brain in vivo. In controls, the mean V(NAA) was 9.2 +/- 3.9 nmol/min/g. In Canavan disease, where [NAA] is increased (p < 0.001) and [aspartate] is deceased (p < 0.001), V(NAA) was significantly reduced to 3.6 +/- 0.1 nmol/min/g (p < 0.001). These rates are in close agreement with the activity of the biosynthetic enzyme measured in vitro in animals, and with the rate of urinary excretion of NAA in human subjects with Canavan disease. The present result is consistent with the regulation of NAA synthesis by the activity of a single enzyme, L-aspartate-N-acetyltransferase, in vivo, and with its control in Canavan disease by limited substrate supply and/or product inhibition. The (13)C MRS technique provides the means for further determination of abnormal rates of neuronal NAA synthesis among neurological disorders in which low cerebral [NAA] has been identified.     

Simultaneous determination of N-acetylaspartic acid, N-acetylglutamic acid, and N-acetylaspartylglutamic acid in whole brain of 3-mercaptopropionic acid-treated rats using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

The measurement of N-acetylaspartic acid (NAA), N-acetylglutamic acid (NAG), and N-acetylaspartylglutamic acid (NAAG) in the whole brain of 3-mercaptopropionic acid (3-MPA)-treated rats has been developed using liquid chromatography-mass spectrometry with an atmospheric pressure ionization interface system. The recoveries of these compounds were 90.85 +/- 3.43% for NAA, 91.62 +/- 5.47% for NAG, and 92.29 +/- 4.44% for NAAG. The detection limits for NAA, NAG, and NAAG were 12, 15, and 20 microg/ml, respectively. After administration of 3-MPA, the concentrations of NAA, NAG, and NAAG in the whole brain over 10 min increased 177.25, 134.23, and 127.70%, respectively. These concentrations then decreased over the next 60 min. The simultaneous determination of NAA, NAG, and NAAG using this method was found to be very useful for studies of metabolism of NAA, NAG, and NAAG in biological samples.     

Effect of Acid treatment of plant cuticles on sorption of selected auxins

Sorption characteristics of 2-(1-naphthyl)acetic acid (NAA), 2-(1-naphthyl)acetamide (NAAm), and 2,4-dichlorophenoxyacetic acid (2,4-D) were determined for cuticles enzymically isolated from mature tomato (Lycopersicon esculentum Mill. cv Sprinter) and pepper (Capsicum annuum L.) fruit. Sorption equilibrium for NAA and 2,4-D by tomato cuticular membranes (CM) and dewaxed cuticular membranes (DCM) was achieved within 24 hours at 25°C. The average K (partition coefficient) values for NAA in tomato CM and DCM were 166 and 204, respectively, whereas the corresponding K values for 2,4-D were 292 and 383, respectively. Sorption equilibrium for 2,4-D and NAA in pepper cuticles was not achieved after 18 and 63 days, respectively. Sorption equilibrium for NAAm in tomato and pepper CM and DCM was attained within 48 hours. Acid pretreatment (2.0 n HCl, 10 minutes) had no effect on NAA, 2,4-D, or NAAm sorption by tomato CM and DCM, or on NAAm sorption by pepper CM and DCM. Acid pretreatment of pepper CM and DCM led to slightly lower K^pH (apparent partition coefficient) values for both NAA and 2,4-D. More significantly, sorption equilibrium for NAA and 2,4-D in pepper CM and DCM was achieved within 24 hours after acid treatment.     

Oxidation of Endogenous N-Arachidonoylserotonin by Human Cytochrome P450 2U1

Cytochrome P450 (P450) 2U1 has been shown to be expressed, at the mRNA level, in human thymus, brain, and several other tissues. Recombinant P450 2U1 was purified and used as a reagent in a metabolomic search for substrates in bovine brain. In addition to fatty acid oxidation reactions, an oxidation of endogenous N-arachidonoylserotonin was characterized. Subsequent NMR and mass spectrometry and chemical synthesis showed that the main product was the result of C-2 oxidation of the indole ring, in contrast to other human P450s that generated different products. N-Arachidonoylserotonin, first synthesized chemically and described as an inhibitor of fatty acid amide hydrolase, had previously been found in porcine and mouse intestine; we demonstrated its presence in bovine and human brain samples. The product (2-oxo) was 4-fold less active than N-arachidonoylserotonin in inhibiting fatty acid amide hydrolase. The rate of oxidation of N-arachidonoylserotonin was similar to that of arachidonic acid, one of the previously identified fatty acid substrates of P450 2U1. The demonstration of the oxidation of N-arachidonoylserotonin by P450 2U1 suggests a possible role in human brain and possibly other sites.     

Cerebral energetic effects of creatine supplementation in humans

There has been considerable interest in the use of creatine (Cr) supplementation to treat neurological disorders. However, in contrast to muscle physiology, there are relatively few studies of creatine supplementation in the brain. In this report, we use high-field MR (31)P and (1)H spectroscopic imaging of human brain with a 7-day protocol of oral Cr supplementation to examine its effects on cerebral energetics (phosphocreatine, PCr; ATP) and mitochondrial metabolism (N-acetyl aspartate, NAA; and Cr). We find an increased ratio of PCr/ATP (day 0, 0.80 +/- 0.10; day 7, 0.85 +/- 09), with this change largely due to decreased ATP, from 2.7 +/- 0.3 mM to 2.5 +/- 0.3 mM. The ratio of NAA/Cr also decreased (day 0, 1.32 +/- 0.17; day 7 1.18 +/- 0.13), primarily from increased Cr (9.6 +/- 1.9 to 10.1 +/- 2.0 mM). The Cr-induced changes significantly correlated with the basal state, with the fractional increase in PCr/ATP negatively correlating with the basal PCr/ATP value (R = -0.74, P < 0.001). As NAA is a measure of mitochondrial function, there was also a significant negative correlation between basal NAA concentrations with the fractional change in PCr and ATP. Thus healthy human brain energetics is malleable and shifts with 7 days of Cr supplementation, with the regions of initially low PCr showing the largest increments in PCr. Overall, Cr supplementation appears to improve high-energy phosphate turnover in healthy brain and can result in either a decrease or an increase in high-energy phosphate concentrations.     

Decreased NAA in Gray Matter is Correlated with Decreased Availability of Acetate in White Matter in Postmortem Multiple Sclerosis Cortex

Multiple sclerosis (MS) is an inflammatory neurodegenerative disease of the central nervous system (CNS) which leads to progressive neurological disability. Our previous studies have demonstrated mitochondrial involvement in MS cortical pathology and others have documented decreased levels of the neuronal mitochondrial metabolite N-acetyl aspartate (NAA) in the MS brain. While NAA is synthesized in neurons, it is broken down in oligodendrocytes into aspartate and acetate. The resulting acetate is incorporated into myelin lipids, linking neuronal mitochondrial function to oligodendrocyte-mediated elaboration of myelin lipids in the CNS. In the present study we show that treating human SH-SY5Y neuroblastoma cells with the electron transport chain inhibitor antimycin A decreased levels of NAA as measured by HPLC. To better understand the significance of the relationship between mitochondrial function and levels of NAA and its breakdown product acetate on MS pathology we then quantitated the levels of NAA and acetate in MS and control postmortem tissue blocks. Regardless of lesion status, we observed that levels of NAA were decreased 25 and 32 % in gray matter from parietal and motor cortex in MS, respectively, compared to controls. Acetate levels in adjacent white matter mirrored these decreases as evidenced by the 36 and 45 % reduction in acetate obtained from parietal and motor cortices. These data suggest a novel mechanism whereby mitochondrial dysfunction and reduced NAA levels in neurons may result in compromised myelination by oligodendrocytes due to decreased availability of acetate necessary for the synthesis of myelin lipids.