Changes in free amino acids of cerebrospinal fluid and plasma in various neurological diseases

Upgraded Methodology for the Development of Early Diagnosis of Parkinson's Disease Based on Searching Blood Markers in Patients and Experimental Models

Numerous attempts to develop an early diagnosis of Parkinson's disease (PD) by searching biomarkers in biological fluids were unsuccessful. The drawback of this methodology is searching markers in patients at the clinical stage without guarantee that they are also characteristic of either preclinical stage or prodromal stage (preclinical-prodromal stage). We attempted to upgrade this methodology by selecting only markers that are found both in patients and in PD animal models. HPLC and RT-PCR were used to estimate the concentration of amino acids, catecholamines/metabolites in plasma and gene expression in lymphocytes in 36 untreated early-stage PD patients and 52 controls, and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice at modeling the clinical ("symptomatic") stage and preclinical-prodromal ("presymptomatic") stage of PD. It was shown that among 13 blood markers found in patients, 7 markers are characteristic of parkinsonian symptomatic mice and 3 markers of both symptomatic and presymptomatic mice. According to our suggestion, the detection of the same marker in patients and symptomatic animals indicates adequate reproduction of pathogenesis along the corresponding metabolic pathway, whereas the detection of the same marker in presymptomatic animals indicates its specificity for preclinical-prodromal stage. This means that the minority of markers found in patients-decreased concentration of L-3,4-dihydroxyphenylalanine (L-DOPA) and dihydroxyphenylacetic acid (DOPAC) and increased dopamine D3 receptor gene expression-are specific for preclinical-prodromal stage and are suitable for early diagnosis of PD. Thus, we upgraded a current methodology for development of early diagnosis of PD by searching blood markers not only in patients but also in parkinsonian animals.

Structure, function, and pharmacology of NMDA receptor channels

NMDA receptors have received much attention over the last few decades, due to their role in many types of neural plasticity on the one hand, and their involvement in excitotoxicity on the other hand. There is great interest in developing clinically relevant NMDA receptor antagonists that would block excitotoxic NMDA receptor activation, without interfering with NMDA receptor function needed for normal synaptic transmission and plasticity. This review summarizes current understanding of the structure of NMDA receptors and the mechanisms of NMDA receptor activation and modulation, with special attention given to data describing the properties of various types of NMDA receptor inhibition. Our recent analyses point to certain neurosteroids as NMDA receptor inhibitors with desirable properties. Specifically, these compounds show use-dependent but voltage-independent block, that is predicted to preferentially target excessive tonic NMDA receptor activation. Importantly, neurosteroids are also characterized by use-independent unblock, compatible with minimal disruption of normal synaptic transmission. Thus, neurosteroids are a promising class of NMDA receptor modulators that may lead to the development of neuroprotective drugs with optimal therapeutic profiles.

Lipidome analysis in multiple sclerosis reveals protein lipoxidative damage as a potential pathogenic mechanism

Metabolomic and lipidomic analyses have been used for the profiling of neurodegenerative processes, both in targeted and untargeted approaches. In this work we have applied these techniques to the study of CSF samples of multiple sclerosis (MS) patients (n = 9), compared with samples of non-MS individuals (n = 9) using mass-spectrometry. We have used western-blot and analyzed cell culture to confirm pathogenic pathways suggested by mass-spectrometric measurements. The results of the untargeted approach of metabolomics and lipidomics suggest the existence of several metabolites and lipids discriminating both populations. Applying targeted lipidomic analyses focused to a pathogenic pathway in MS, oxidative stress, reveal that the lipid peroxidation marker 8-iso-prostaglandin F2α is increased in CSF from MS patients. Furthermore, as lipid peroxidation exerts its pathogenical effects through protein modification, we studied the incidence of protein lipoxidation, revealing specific increases in carboxymethylated, neuroketal and malondialdehyde-mediated protein modifications in proteins of CSF from MS patients, despite the absence of their precursors glyoxal and methylglyoxal. Finally, we report that the level of neuroketal-modified proteins correlated with a hitherto unknown increased amount of autoantibodies against lipid peroxidation-modified proteins in CSF, without compensation by signaling induced by lipid peroxidation via peroxisome proliferator-activated receptor γ (PPARγ). The results, despite the limitation of being obtained in a small population, strongly suggest that autoimmunity against in situ produced epitopes derived from lipid peroxidation can be a relevant pathogenic factor in MS.

The glycine deportation system and its pharmacological consequences

The glycine deportation system is an essential component of glycine catabolism in man whereby 400 to 800mg glycine per day are deported into urine as hippuric acid. The molecular escort for this deportation is benzoic acid, which derives from the diet and from gut microbiota metabolism of dietary precursors. Three components of this system, involving hepatic and renal metabolism, and renal active tubular secretion help regulate systemic and central nervous system levels of glycine. When glycine levels are pathologically high, as in congenital nonketotic hyperglycinemia, the glycine deportation system can be upregulated with pharmacological doses of benzoic acid to assist in normalization of glycine homeostasis. In congenital urea cycle enzymopathies, similar activation of the glycine deportation system with benzoic acid is useful for the excretion of excess nitrogen in the form of glycine. Drugs which can substitute for benzoic acid as substrates for the glycine deportation system have adverse reactions that may involve perturbations of glycine homeostasis. The cancer chemotherapeutic agent ifosfamide has an unacceptably high incidence of encephalopathy. This would appear to arise as a result of the production of toxic aldehyde metabolites which deplete ATP production and sequester NADH in the mitochondrial matrix, thereby inhibiting the glycine deportation system and causing de novo glycine synthesis by the glycine cleavage system. We hypothesize that this would result in hyperglycinemia and encephalopathy. This understanding may lead to novel prophylactic strategies for ifosfamide encephalopathy. Thus, the glycine deportation system plays multiple key roles in physiological and neurotoxicological processes involving glycine.

Glutamatergic dysfunction in OCD

The role of glutamatergic dysfunction in the pathophysiology of OCD has hardly been explored despite recent reports implicating glutamatergic dysfunction in OCD. We decided to investigate CSF glutamate levels in adult OCD probands compared to psychiatrically normal controls. In total, 21 consenting psychotropic drug-naïve adult OCD patients, diagnosed using SCID-IV-CV, and 18 consenting psychiatrically normal controls with age within 10 years of age of the patients, who did not have any history of head injury or neurological illness, were included into the study. Aseptically collected and stored CSF samples obtained from the patients and control subjects were used for glutamate estimation, which was carried out by a modification of the procedure described by Lund (1986). CSF glutamate (micromol/l) level was found to be significantly higher [F(1,31)=6.846, p=0.014] in OCD patients (47.12+/-4.25) compared to control subjects (41.36+/-3.63) on analysis of covariance. There was no effect of gender, age, duration of illness, Y-BOCS score, or CGI-S score on CSF glutamate levels. Our study provides preliminary evidence implicating glutamatergic excess in the pathophysiology of OCD, which needs to be further explored by studies from other centers involving larger sample sets from different age groups.

Assessment of reliability and biological significance of glutamate levels in cerebrospinal fluid

The published information on glutamate levels in cerebrospinal fluid (CSF) and modifications in neurological disorders is controversial. In the present study, we demonstrated a metabolic instability of glutamate in untreated CSF and a spurious elevation of its levels by the current methods of CSF acidification. These findings may explain the discrepancies observed with different methods of CSF processing and analysis. We suggest a method of inactivating CSF enzymes that yields stable glutamate levels under different storage conditions. Use of such a method may be necessary for clinical studies.

High-resolution 1H NMR spectroscopy of cerebrospinal fluid in spinal diseases

Twenty-nine patients with disk herniations, 7 patients with intraspinal tumors, 4 patients with multiple sclerosis and one patient with infection by borrelia have been studied by CT, myelography and/or MR. To gain information on the metabolism of central nervous system disease (CNS), and thus, to improve diagnosis the cerebrospinal fluid (CSF) was studied in all cases using high-resolution 1H NMR spectroscopy at 360 MHz. Seventeen metabolites could be identified in CSF in addition to the usual clinical chemical parameters. As compared to a control group discrimination of tumors from inflammation was possible by means of different metabolites and/or metabolite concentration. The CSF in disk herniations differed in the concentration of acetate from the control group. In CSF of tumors, multiple sclerosis and of infection by borrelia distinct differences in the concentrations of putrescine, citrate, valine, alpha-alanine, acetate, creatinine, glucose, beta-hydroxy-butyric acid, glutamine and creatine have been observed both as compared directly and in comparison to the control group. Thus, high-resolution 1H NMR spectroscopy of CSF gives speedy information on metabolism, since a variety of metabolites, usually examined only in different tests, can be studied in one single step. Thus, high-resolution 1H NMR spectroscopy supports imaging, especially MR, as morphological changes in diseases may be differentiated by means of different metabolite profiles. This assumption needs further confirmation on a prospective study with a larger patient population.

Increased plasma concentrations of aspartate, glutamate and glycine in Parkinson's disease

We measured fasting plasma amino acids in 20 patients with Parkinson's disease (PD) and 20 controls matched for age and sex. PD patients had significant elevations in plasma levels of aspartate, glutamate and glycine. The levels of other amino acids were not significantly different from those found in controls. No correlation was noted between PD severity and the degree of abnormality of plasma amino acids. We conclude that excitatory amino acids may be altered in patients with PD, and raise the possibility that neuroexcitotoxic mechanisms may be involved in the neurodegeneration of PD.

Abnormal excitatory amino acid metabolism in amyotrophic lateral sclerosis

Recently, the excitatory amino acid neurotransmitter glutamate was implicated in the pathogenesis of a variety of chronic degenerative neurological diseases in humans and animals. This report describes abnormalities in excitatory amino acids in the central nervous system of 18 patients with amyotrophic lateral sclerosis (ALS). The concentration of the excitatory amino acids glutamate and aspartate in the cerebrospinal fluid were increased significantly (p less than 0.01) by 100 to 200% in patients with ALS. Similarly, the concentrations of the excitatory neuropeptide N-acetyl-aspartyl glutamate and its metabolite, N-acetyl-aspartate, were elevated twofold to threefold in the cerebrospinal fluid from the patients. There was no relationship between amino acid concentrations and duration of disease, clinical impairment, or patient age. In the ventral horns of the cervical region of the spinal cord, the level of N-acetyl-aspartyl glutamate and N-acetyl-aspartate was decreased by 60% (p less than 0.05) and 40% (p less than 0.05), respectively, in 8 patients with ALS. Choline acetyltransferase activity was also diminished by 35% in the ventral horn consistent with motor neuron loss. We conclude that excitatory amino acid metabolism is altered in patients with ALS. Based on neurodegenerative disease models, these changes may play a role in motor neuron loss in ALS.

Reference values for amino acids in cerebrospinal fluid of children determined using ion-exchange chromatography with fluorimetric detection

One thousand specimens of CSF were collected from subjects ranging in age from newborn to 18 yr, who were undergoing a diagnostic lumbar puncture. Sixty-two samples were judged retrospectively as being suitable for calculating reference age-related values. The analyses were performed by an amino acid analyser using ion-exchange chromatography with fluorimetric detection giving a tenfold increase in sensitivity, thereby enhancing the diagnostic capabilities. As many as 36 known compounds could be detected, additionally 10 we could not identify. In children older than 3 yr nine of the identified compounds showed age-dependency. We found 22 amino acids to be significantly higher in infants younger than 1 yr, with only gamma-aminobutyric acid being significantly lower in infants. Alpha-aminoadipic acid showed a sex difference, being slightly higher in girls.

Release of glutamate and of free fatty acids in vasogenic brain edema

The pathophysiological potential of mediator substances in manifestations of secondary brain damage is attracting increased attention. This is particularly true of the excitatory transmitters glutamate and arachidonic acid. Noxious properties of these compounds in central nervous tissue have been demonstrated. The current study was performed to determine whether glutamate and arachidonate are released in brain tissue secondary to focal trauma. For this purpose, a cold injury of exposed cerebral cortex was induced in cats. Marked accumulation of glutamate was observed in interstitially drained edema fluid, reaching 10 to 15 times the level that was assessed in normal cerebrospinal fluid (CSF) prior to trauma. The extracellular release of glutamate was further dramatically enhanced by a critical decrease of the cerebral perfusion pressure due to a malignant increase of intracranial pressure. Under these conditions, glutamate concentrations 1000 to 1500 times normal levels accumulated in vasogenic edema fluid, demonstrating a relationship between the extent of the release of glutamate in damaged brain and the severity of the insult. Although under normal conditions glutamate concentrations in plasma were considerably higher than in the interstitial fluid, the pronounced increase of glutamate in this compartment due to trauma cannot be explained by transport of the compound together with the plasma-like edema from the intravascular space. Corresponding findings were obtained for free fatty acid concentrations in edema fluid. Almost all fatty acids that were studied had a significantly higher concentration in edema fluid than in normal CSF obtained as a control prior to trauma. However, contrary to the findings for glutamate, fatty acid concentrations in edema fluid were lower than in plasma. Accumulation of fatty acids in vasogenic edema fluid might, therefore, have resulted from uptake of the material together with edema fluid through the breached blood-brain barrier. Arachidonic acid was an exception. Its concentrations were significantly higher in edema fluid than in plasma, suggesting that it was released from cerebral parenchyma as the underlying mechanism of its extracellular accumulation. The current observations provide further support for a mediator function of glutamate and arachidonic acid in acute traumatic lesions of the brain. Quantitative assessment of the release of highly active mediator substances in brain tissue may facilitate analysis of the therapeutic efficiency of specific treatment aimed at interfering with the release or pathological function of mediators of secondary brain damage.

Quantitation of free amino acids in biological samples by high-performance liquid chromatography. Application of the method in evaluating amino acid levels in cerebrospinal fluid and plasma of patients with multiple sclerosis

An automatic on-line high-performance liquid chromatographic method based on a precolumn derivatization with o-phthalaldehyde has been developed to quantitate levels of free amino acids in cerebrospinal fluid (CSF) and plasma samples from 12 patients with multiple sclerosis (MS) and 12 controls. The analytical method gave reproducible results with relative standard deviations of 0.5-3% for all amino acids. The separation of 24 amino acids was performed on a reversed-phase C18 column, using two solvents and a multiple-step gradient. Each chromatographic experiment was completed within 40 min. The results showed higher levels of Glu, Gln, Gly and Ala and lower levels of Met, Val, Phe and Lys in plasma of MS patients. In CSF, increased levels of Gln, Arg, Ser and Tyr and decreased levels of Asp, Glu, Met, gamma-aminobutyric acid and Phe were found in MS patients, whereas the levels of other amino acids remained more or the less same in both groups.

Elevated cerebrospinal fluid histidine in alcohol withdrawal

Cerebrospinal fluid (CSF) histidine concentration was significantly elevated in seven patients early in the alcohol withdrawal syndrome (206.3 +/- 74.4 (SEM) nanomols/ml CSF). When these same patients were restudied an average of six days later when alcohol withdrawal was clinically resolved, their mean CSF histidine concentration continued to be significantly elevated (164.7 +/- 24.7) when compared to normal (12.0 +/- 0.5 nanomols/ml CSF). Other amino acids (aspartic acid, serine, alanine, methionine, leucine, tyrosine, phenylalanine, lysine and arginine) showed no definite changes from normal, and no change during the course of alcohol withdrawal. Possible reasons for these high concentrations and the extreme variability (especially early in alcohol withdrawal) are discussed.

Cerebrospinal fluid free amino acids in patients with spinal space-occupying lesions. A preliminary report

18 different free amino acids were determined in the cerebrospinal fluid of 28 patients with various spinal space--occupying lesions. The study group included 15 patients with lumbar disc lesions (control group), 8 patients with cervical radiculopathy, 4 patients with cervical myelopathy, and 1 patient with a thoracic spinal angioma. The values from the control group were in general accord with those previously observed in normal adults of 5 studies of the literature. Comparison of the values in the different subgroups showed normal values of all amino acids in patients with cervical myelopathy, and significantly higher levels of glutamic acid in patients with cervical radiculopathy. In the case of a thoracic spinal angioma however most free amino acids were extremely high. The authors conclude that this may be due to alterations of the spinal metabolism and that determination of free amino acids in CSF of patients with intradural spinal lesions may help to improve preoperative diagnosis in addition to neuroradiological methods.

Abnormalities of serum and plasma components in patients with multiple sclerosis

Qualitative and quantitative abnormalities in protein and non-protein components of serum and plasma in patients with multiple sclerosis have been the subjects of numerous reports. In this review many of the more recent observations are documented and evaluated. It is concluded that at present the welter of information that has been gathered does not contribute in any major, coherent way to our understanding of the etiology or pathogenesis of the disorder. Several of the abnormalities that have been observed may be future candidates for biochemical markers for multiple sclerosis; at present none is sufficiently reliable, distinctive or easily performed to warrant the status of a useful diagnostic or prognostic test.

Increased cerebrospinal fluid free amino acid concentrations in children with bacterial meningitis

19 free amino acids were measured by Durrum high pressure chromatography in the cerebrospinal fluid of 19 children, 9 with and 10 without bacterial meningitis. Each of the amino acids, except for gamma-amino butyric acid, was significantly increased in meningitis. Values were elevated upon admission of these patients to the hospital, but the highest concentration for most of the amino acids was noted in specimens collected 24-48 h after initiation of antibiotic treatment. Upon the completion of successful antibiotic therapy, the amino acid concentrations returned to normal or near normal levels.