Does hyperphenylalaninemia induce brain glucose hypometabolism? Cerebral spinal fluid findings in treated adult phenylketonuric patients.

Despite numerous studies in human patients and animal models for phenylketonuria (PKU; OMIM#261600), the pathophysiology of PKU and the underlying causes of brain dysfunction and cognitive problems in PKU patients are not well understood. In this study, lumbar cerebral spinal fluid (CSF) was obtained immediately after blood sampling from early-treated adult PKU patients who had fasted overnight. Metabolite and amino acid concentrations in the CSF of PKU patients were compared with those of non-PKU controls. The CSF concentrations and CSF/plasma ratios for glucose and lactate were found to be below normal, similar to what has been reported for glucose transporter1 (GLUT1) deficiency patients who exhibit many of the same clinical symptoms as untreated PKU patients. CSF glucose and lactate levels were negatively correlated with CSF phenylalanine (Phe), while CSF glutamine and glutamate levels were positively correlated with CSF Phe levels. Plasma glucose levels were negatively correlated with plasma Phe concentrations in PKU subjects, which partly explains the reduced CSF glucose concentrations. Although brain glucose concentrations are unlikely to be low enough to impair brain glucose utilization, it is possible that the metabolism of Phe in the brain to produce phenyllactate, which can be transported across the blood-brain barrier to the blood, may consume glucose and/or lactate to generate the carbon backbone for glutamate. This glutamate is then converted to glutamine and carries the Phe-derived ammonia from the brain to the blood. While this mechanism remains to be tested, it may explain the correlations of CSF glutamine, glucose, and lactate concentrations with CSF Phe.

Glutamine and citrulline concentrations reflect nitric oxide synthesis in the human nervous system. / Las concentraciones de glutamina y citrulina reflejan la síntesis del óxido nítrico en el sistema nervioso humano.

INTRODUCTION: Although citrulline is produced by nitric oxide (NO) synthase upon activation of the NMDA glutamate receptor, nitrite and nitrate (NOx) concentration is considered the best marker of NO synthesis, as citrulline is also metabolised by other enzymes. This study analyses the correlation between human cerebrospinal fluid NOx and citrulline concentrations in order to determine the extent to which citrulline reflects NO synthesis and glutamatergic neurotransmission. METHODS: Participants were patients with acute neurological diseases undergoing lumbar puncture (n=240). NOx and amino acid concentrations were determined by HPLC. RESULTS: NOx concentrations did not vary significantly where infection (p=0,110) or inflammation (p=0,349) were present. Multiple regression analysis showed that NOx concentration was correlated with glutamine (r=-0,319, p<0,001) and citrulline concentrations (r=0,293, p=0,005) but not with the citrulline/arginine ratio (r=-0,160, p=0,173). ANCOVA confirmed that NOx concentration was correlated with citrulline concentration (F=7,6, p=0,007) but not with the citrulline/arginine ratio (F=2,2, p=0,136), or presence of infection (F=1,8, p=0,173) or inflammation (F=1,4, p=0,227). No association was found between NOx and arginine or glutamate concentrations. CONCLUSION: The results suggest that CSF citrulline concentration reflects NOx synthesis to some extent, despite the contribution of other metabolic pathways. In addition, this study shows that glutamine is an important modulator of NO synthase activity, and that arginine and glutamate are not correlated with NOx.

Cerebrospinal Fluid Spermidine, Glutamine and Putrescine Predict Postoperative Delirium Following Elective Orthopaedic Surgery.

Delirium is a marker of brain vulnerability, associated with increasing age, pre-existing cognitive impairment and, recently, cerebrospinal fluid (CSF) biomarkers of Alzheimer's disease. This nested case-control study used a targeted quantitative metabolomic methodology to profile the preoperative CSF of patients (n = 54) who developed delirium following arthroplasty (n = 28) and those who did not (n = 26). The aim was to identify novel preoperative markers of delirium, and to assess potential correlations with clinical data. Participants without a diagnosis of dementia (≥65 years) undergoing elective primary hip or knee arthroplasty were postoperatively assessed for delirium once-daily for three days. Groups were compared using multivariate, univariate and receiving operator characteristic (ROC) methods. Multivariate modelling using Orthogonal Partial Least Squares-Discriminant Analysis (OPLS-DA) of metabolomic data readily distinguished between delirium and control groups (R2 ≤ 0.56; Q2 ≤ 0.10). Three metabolites (spermidine, putrescine and glutamine) significantly differed between groups (P < 0.05; FDR < 0.07), and performed well as CSF biomarkers (ROC > 0.75). The biomarker performance of the two polyamines (spermidine/putrescine) was enhanced by ratio with CSF Aß42 (ROC > 0.8), and spermidine significantly correlated with Aß42 (pearson r = -0.32; P = 0.018). These findings suggest that spermidine and putrescine levels could be useful markers of postoperative delirium risk, particularly when combined with Aß42, and this requires further investigation.

Poor evidence for putative abnormalities in cerebrospinal fluid neurotransmitters in patients with depression versus healthy non-psychiatric individuals: A systematic review and meta-analyses of 23 studies.

BACKGROUND: Although investigated for decades, surprisingly no systematic review has ever been published on monoamines concentrations in cerebrospinal fluid (CSF) in major depressive disorder (MDD) versus healthy individuals (HC). METHODS: We did a systematic review and meta-analyses according to the PRISMA Statement based on comprehensive database searches for studies on CSF biomarkers of monoamines and their precursor and/or metabolites, and glutamine, glutamate and GABA in MDD versus HC. Risk of bias was systematically assessed. RESULTS: A total of 23 studies were included. Statistically significantly decreased levels between MDD and HC were found regarding CSF 5-HIAA (n = 2/13 (15%)), HVA (n = 2/11 (18%)), MHPG (n = 1/8 (13%)), and GABA (n = 2/4 (50%)), while increased levels were reported regarding NE (n = 1/2 (50%)), MHPG (n = 1/8 (13%)) and DOPEG (n = 1/1 (100%)). A majority of the studies found no statistically significant differences between MDD and HC regarding CSF 5-HIAA, HVA, NE, MHPG, glutamine, glutamate and GABA. Meta-analyses showed: 5-HIAA (-3.85, -8.89, 1.19, 0.14), HVA (-18.02, -30.99, -5.04, 0.01), MHPG (0.11, -2.96, 3.17, 0.95) and GABA (-33.20, -51.79, -14.62, 0.00) (mean difference, lower 95% CL, upper 95% CL, p-value). Most studies were influenced by risk of bias mainly due to small sample sizes, and not considering potential confounders as age, gender, severity of depression, body height and position during lumbar puncture, analytics of biomarkers and medication. CONCLUSION: The evidence for CSF 5-HIAA, HVA, NE, MHPG, DOPEG and GABA being related to the pathophysiology of MDD is poor. Future controlled studies of monoamines or metabolites should validate the null i.e., that the concentrations of these compounds are not abnormal in MDD.

Striatal neurometabolite levels in patients with schizophrenia undergoing long-term antipsychotic treatment: A proton magnetic resonance spectroscopy and reliability study.

Previous proton magnetic resonance spectroscopy (1H-MRS) studies have reported disrupted levels of various neurometabolites in patients with schizophrenia. An area of particular interest within this patient population is the striatum, which is highly implicated in the pathophysiology of schizophrenia. The present study examined neurometabolite levels in the striatum of 12 patients with schizophrenia receiving antipsychotic treatment for at least 1 year and 11 healthy controls using 3-Tesla 1H-MRS (PRESS, TE = 35 ms). Glutamate, glutamate+glutamine (Glx), myo-inositol, choline, N-acetylaspartate, and creatine levels were estimated using LCModel, and corrected for fraction of cerebrospinal fluid in the 1H-MRS voxel. Striatal neurometabolite levels were compared between groups. Multiple study visits permitted a reliability assessment for neurometabolite levels (days between paired 1H-MRS acquisitions: average = 90.33; range = 7-306). Striatal neurometabolite levels did not differ between groups. Within the whole sample, intraclass correlation coefficients for glutamate, Glx, myo-inositol, choline, and N-acetylaspartate were fair to excellent (0.576-0.847). The similarity in striatal neurometabolite levels between groups implies a marked difference from the antipsychotic-naïve first-episode state, especially in terms of glutamatergic neurometabolites, and might provide insight regarding illness progression and the influence of antipsychotic medication.

Abnormality in glutamine-glutamate cycle in the cerebrospinal fluid of cognitively intact elderly individuals with major depressive disorder: a 3-year follow-up study.

Major depressive disorder (MDD), common in the elderly, is a risk factor for dementia. Abnormalities in glutamatergic neurotransmission via the N-methyl-D-aspartate receptor (NMDA-R) have a key role in the pathophysiology of depression. This study examined whether depression was associated with cerebrospinal fluid (CSF) levels of NMDA-R neurotransmission-associated amino acids in cognitively intact elderly individuals with MDD and age- and gender-matched healthy controls. CSF was obtained from 47 volunteers (MDD group, N=28; age- and gender-matched comparison group, N=19) at baseline and 3-year follow-up (MDD group, N=19; comparison group, N=17). CSF levels of glutamine, glutamate, glycine, L-serine and D-serine were measured by high-performance liquid chromatography. CSF levels of amino acids did not differ across MDD and comparison groups. However, the ratio of glutamine to glutamate was significantly higher at baseline in subjects with MDD than in controls. The ratio decreased in individuals with MDD over the 3-year follow-up, and this decrease correlated with a decrease in the severity of depression. No correlations between absolute amino-acid levels and clinical variables were observed, nor were correlations between amino acids and other biomarkers (for example, amyloid-ß42, amyloid-ß40, and total and phosphorylated tau protein) detected. These results suggest that abnormalities in the glutamine-glutamate cycle in the communication between glia and neurons may have a role in the pathophysiology of depression in the elderly. Furthermore, the glutamine/glutamate ratio in CSF may be a state biomarker for depression.

1H-NMR-based metabolomic analysis of cerebrospinal fluid from adult bilateral moyamoya disease: comparison with unilateral moyamoya disease and atherosclerotic stenosis.

Although metabolomics has been increasingly used to observe metabolic pattern and disease-specific metabolic markers, metabolite profiling for moyamoya disease (MMD) has not yet been done in adults. This study investigated cerebrospinal fluid (CSF) metabolites specific to bilateral MMD (B-MMD) and compared them to those of unilateral MMD (U-MMD) or atherosclerotic stenosis with hydrogen-1 nuclear magnetic resonance spectroscopy to identify metabolic biomarkers associated with MMD in adults.CSF samples of B-MMD (n = 29), U-MMD (n = 11), and atherosclerotic cerebrovascular disease (ACVD) (n = 8) were recruited. Principal component analysis, partial least square discriminant analysis, and orthogonal projections to latent structure discriminant analysis (OPLS-DA) were done for the comparisons. Diagnostic performance was acquired by prediction of 1 left-out sample from the distinction model constructed with the rest of the samples.B-MMD showed an increase in glutamine (P < 0.001) and taurine (P = 0.004), and a decrease in glucose (P < 0.001), citrate (P = 0.002), and myo-inositol (P = 0.006) than those in ACVD. U-MMD showed a higher level of glutamine (P = 0.005) and taurine (P = 0.034), and a lower level of glutamate (P < 0.004) than those in ACVD. No difference at the metabolite level was observed between B-MMD and U-MMD. Cross-validation with the OPLS-DA model showed a high accuracy for the prediction of MMD.The results of the study suggest that a metabolomics approach may be helpful in confirming MMD and providing a better understanding of MMD pathogenesis. Elevated glutamine in the CSF may be associated with MMD pathogenesis, which was different from ACVD.

Glutamatergic neurometabolites in clozapine-responsive and -resistant schizophrenia.

BACKGROUND: According to the current schizophrenia treatment guidelines, 3 levels of responsiveness to antipsychotic medication exist: those who respond to first-line antipsychotics, those with treatment-resistant schizophrenia who respond to clozapine, and those with clozapine-resistant or ultra-treatment resistant schizophrenia. Proton magnetic resonance spectroscopy studies indicate that antipsychotic medication decreases glutamate or total glutamate + glutamine in the brains of patients with schizophrenia and may represent a biomarker of treatment response; however, the 3 levels of treatment responsiveness have not been evaluated. METHODS: Proton magnetic resonance spectroscopy spectra were acquired at 3 Tesla from patients taking a second generation non-clozapine antipsychotic (first-line responders), patients with treatment-resistant schizophrenia taking clozapine, patients with ultra-treatment resistant schizophrenia taking a combination of antipsychotics, and healthy comparison subjects. RESULTS: Group differences in cerebrospinal fluid-corrected total glutamate + glutamine levels scaled to creatine were detected in the dorsolateral prefrontal cortex [df(3,48); F = 3.07, P = .04, partial η(2) = 0.16] and the putamen [df(3,32); F = 2.93, P = .05, partial η(2) = 0.22]. The first-line responder group had higher dorsolateral prefrontal cortex total glutamate + glutamine levels scaled to creatine than those with ultra-treatment resistant schizophrenia [mean difference = 0.25, standard error = 0.09, P = .04, family-wise error-corrected]. Those with treatment-resistant schizophrenia had higher total glutamate + glutamine levels scaled to creatine in the putamen than the first-line responders (mean difference = 0.31, standard error = 0.12, P = .05, family-wise error-corrected) and those with ultra-treatment-resistant schizophrenia (mean difference = 0.39, standard error = 0.12, P = .02, family-wise error-corrected). CONCLUSIONS: Total glutamate + glutamine levels scaled to creatine in the putamen may represent a marker of response to clozapine. Future studies should investigate glutamatergic anomalies prior to clozapine initiation and following successful treatment.

Markers of glutamate signaling in cerebrospinal fluid and serum from patients with bipolar disorder and healthy controls.

Glutamate is the major excitatory neurotransmitter in the brain. Aberrations in glutamate signaling have been linked to the pathophysiology of mood disorders. Increased plasma levels of glutamate as well as higher glutamine+glutamate levels in the brain have been demonstrated in patients with bipolar disorder as compared to healthy controls. In this study, we explored the glutamate hypothesis of bipolar disorder by examining peripheral and central levels of amino acids related to glutamate signaling. A total of 215 patients with bipolar disorder and 112 healthy controls from the Swedish St. Göran bipolar project were included in this study. Glutamate, glutamine, glycine, L-serine and D-serine levels were determined in serum and in cerebrospinal fluid using high performance liquid chromatography with fluorescence detection. Serum levels of glutamine, glycine and D-serine were significantly higher whereas L-serine levels were lower in patients with bipolar disorder as compared to controls. No differences between the patient and control group in amino acid levels were observed in cerebrospinal fluid. The observed differences in serum amino acid levels may be interpreted as a systemic aberration in amino acid metabolism that affects several amino acids related to glutamate signaling.

Cerebrospinal fluid asparagine depletion during pegylated asparaginase therapy in children with acute lymphoblastic leukaemia.

L-asparaginase is an important drug in the treatment of childhood acute lymphoblastic leukaemia (ALL). Cerebrospinal fluid (CSF) asparagine depletion is considered a marker of asparaginase effect in the central nervous system (CNS) and may play a role in CNS-directed anti-leukaemia therapy. The objective of this study was to describe CSF asparagine depletion during 30 weeks of pegylated asparaginase therapy, 1000 iu/m(2) i.m. every second week, and to correlate CSF asparagine concentration with serum L-asparaginase enzyme activity. Danish children (1-17 years) with ALL, treated according to the Nordic Society of Paediatric Haematology and Oncology ALL2008 protocol, standard and intermediate risk, were included. CSF samples were obtained throughout L-asparaginase treatment at every scheduled lumbar puncture. A total of 128 samples from 31 patients were available for analysis. Median CSF asparagine concentration decreased from a pre-treatment level of 5·3 µmol/l to median levels ≤1·5 µmol/l. However, only 4/31 patients (five samples) had CSF asparagine concentrations below the limit of detection (0·1 µmol/l). In 11 patients, 24 paired same day serum and CSF samples were obtained. A decrease in CSF asparagine corresponded to serum enzyme activities above 50 iu/l. Higher serum enzyme activities were not followed by more extensive depletion. In conclusion, pegylated asparaginase 1000 iu/m(2) i.m. every second week effectively reduced CSF asparagine levels.

Metabolomic analysis of cerebrospinal fluid indicates iron deficiency compromises cerebral energy metabolism in the infant monkey.

Iron deficiency anemia affects many pregnant women and young infants worldwide. The health impact is significant, given iron's known role in many body functions, including oxidative and lipid metabolism, protein synthesis and brain neurochemistry. The following research determined if (1)H NMR spectroscopy-based metabolomic analysis of cerebrospinal fluid (CSF) could detect the adverse influence of early life iron deficiency on the central nervous system. Using a controlled dietary model in 43 infant primates, distinct differences were found in spectra acquired at 600 MHz from the CSF of anemic monkeys. Three metabolite ratios, citrate/pyruvate, citrate/lactate and pyruvate/glutamine ratios, differed significantly in the iron deficient infant and then normalized following the consumption of dietary iron and improvement of clinical indices of anemia in the heme compartment. This distinctive metabolomic profile associated with anemia in the young infant indicates that CSF can be employed to track the neurological effects of iron deficiency and benefits of iron supplementation.

Cerebrospinal fluid levels of glutamate and corticotropin releasing hormone in major depression before and after treatment.

BACKGROUND: Glutamate and corticotropin releasing hormone (CRH) are pro-stress neurotransmitters and may be altered in the plasma and cerebrospinal fluid (CSF) of persons with major depressive disorder (MDD). The goal of this study was to compare the CSF levels of glutamate, glutamine and CRH between patients with depression and healthy controls. METHODS: Eighteen patients with MDD and 25 healthy controls underwent a lumbar puncture (LP); CSF samples were withdrawn and assays were done for glutamine, glutamate, and CRH. Patients with MDD underwent 8 weeks of treatment with the antidepressant venlafaxine and then had a repeat LP post treatment. RESULTS: Patients had higher baseline scores on depression and suicide rating scales and those scales improved significantly post-treatment. Higher suicidal ratings at baseline were correlated with higher glutamate levels (p=0.016). There were no significant differences between the control and patient group in any baseline CSF measures of glutamate (p=0.761), glutamine (p=0.226) or CRH (p=0.675). Despite no significant change in glutamate (p=0.358) and CRH (p=0.331) in the treatment group, there was a post-treatment decrease in glutamine (p=0.045) in patients. LIMITATIONS: There was a small sample size, age discordance between patients and controls, lack of a follow-up LP in controls, absence of dexamethasone suppression testing, and fluctuating sample sizes among various measures. CONCLUSION: Although no significant differences were noted between patients and controls at baseline there was an association of high CSF glutamate and suicidal ideation and lower glutamine post-treatment which may be correlated with attenuation of dysfunction in the glutamatergic system after antidepressant treatment.

Amino acids in CSF and plasma in hyperammonaemic coma due to arginase1 deficiency.

UNLABELLED: We report the CSF and plasma amino acid concentrations and their ratios in a male patient with arginase1 deficiency with an unusual early presentation at 34 days of age. He developed hyperammonaemic coma (ammonia >400 µmol/L; normal <90 µmol/L) on postnatal day 35. CSF and plasma concentrations were assayed by ion-exchange chromatography on day 36. Arginine was increased both in plasma (971 µmol/L; controls (mean ± 2SD) 50 ± 42) and in CSF (157 µmol/L; controls 19 ± 8.6), resulting in a normal CSF/plasma ratio of 0.16 (controls 0.41 ± 0.26). Interestingly, glutamine was disproportionately high in CSF (3114 µmol/L; controls 470 ± 236) but normal in plasma (420 µmol/L; controls 627 ± 246); the ratio exceeded unity (7.4; controls 0.76 ± 0.31). The CSF/plasma ratios of most neutral amino acids were elevated but not those of the imino- and of the dibasic amino acids lysine and ornithine. The mechanism leading to the increase of most neutral amino acids in brain is not known. CONCLUSION: A normal glutamine in plasma does not exclude an increased concentration in CSF; it could be useful to ascertain by MRS that a high CSF glutamine concentration truly reflects a high concentration in brain tissue for better understanding its pathogenesis.

Neurometabolic effects of ACTH on free amino compounds in opsoclonus-myoclonus syndrome.

To evaluate the possible role of central free amino compounds in pediatric opsoclonus-myoclonus syndrome (OMS), 21 cerebrospinal fluid (CSF) amino compounds were measured by an amino acid analyzer or mass spectroscopy in 74 anesthetized children, 54 with OMS and 20 age-matched neurological controls. In OMS, only phosphoethanolamine was increased compared to controls; OMS severity and duration had significant converse effects on alanine and phosphoethanolamine. In contrast, corticotropin (ACTH) treatment was associated with increased alanine and phenylalanine, and decreased taurine compared to controls and untreated OMS, and increased glutamine, lysine, ornithine, and tyrosine compared to untreated OMS. Other than low taurine, these effects were not found with corticosteroid treatment, and non-steroidogenic immunotherapy had no effect. The ACTH dose-association was most apparent for alanine and phosphoethanolamine, but lysine and ornithine were also higher in the high-dose ACTH group. There were no significant disease- or treatment-associated perturbations in GABA, glycine, or other amino acids. These data suggest a unique pattern of ACTH effects on non-neurotransmitter CSF amino compounds, for the most part not shared by steroids.

Analysis of glutamine, glutamate, pyroglutamate, and GABA in cerebrospinal fluid using ion pairing HPLC with positive electrospray LC/MS/MS.

A simple and sensitive method for the separation and quantitation of glutamine, glutamate, pyroglutamate, and gamma-aminobutyric acid (GABA) in cerebrospinal fluid (CSF) is presented. The method utilizes ion pairing with heptafluorobutyric acid (HFBA) to achieve HPLC separation with detection by positive ESI LC/MS/MS. The method does not require extraction or derivatization, utilizes a heavy labeled internal standard for each analyte, and allows for rapid throughput with a 5 min run time. The method was developed with particular attention taken to prevent conversion between analytes known to occur under certain conditions. The lower limit of quantitation is 7.8 ng/ml for all analytes, and the intra-day and inter-day accuracy (%RE) and precision (%R.S.D.) are defined for all analytes. The method was developed as a sensitive, selective, and robust method to investigate the excitatory and inhibitory neurotransmitters (glutamate and GABA) as biomarkers in drug development.

Effects of coinfection with HIV and hepatitis C virus on the nervous system.

We evaluated a cohort of persons with late-stage HIV infection currently enrolled in a longitudinal tracking study to determine whether coinfection with hepatitis C virus (HCV) is associated with a greater prevalence and/or severity of HIV-associated cognitive-motor complex and distal predominantly sensory peripheral polyneuropathy compared with persons with HIV infection alone. Of 159 subjects, 31 tested positive for HCV, and this group was compared with 31 randomly selected subjects with HIV infection alone. All subjects underwent a structured neurological examination and a formal neuropsychological testing battery. Blood and cerebrospinal fluid samples were analyzed for cryoglobulins and glutamine levels, respectively. HIV/HCV-coinfected subjects showed a greater, statistically significant cognitive-motor impairment compared with those not coinfected. Despite the well-recognized neurological manifestations of both HIV infections and more recently hepatitis C, it is still uncertain whether the effects of HIV and HCV augment one another or are partially additive in their deleterious effects on the nervous system.

Metabolic alterations in medication-free patients with bipolar disorder: a 3T CSF-corrected magnetic resonance spectroscopic imaging study.

The objective of this study was to determine whether cerebrospinal fluid(CSF)-corrected concentrations of N-acetylaspartate are lower in several brain regions of drug- and medication-free subjects with bipolar disorder as compared with matched healthy controls. Bipolar subjects (n=21) and age- and sex-matched healthy control (n=21) were studied using proton magnetic resonance spectroscopic imaging on a 3T magnetic resonance (MR) scanner. Spectra were quantified using the LCModel, and metabolite values were CSF-corrected to yield metabolite concentrations. Fourteen regions of interest and five metabolite concentrations in each subject were selected for statistical analysis. We found that bipolar subjects had significantly decreased N-acetylaspartate concentrations in both caudate heads and the left lentiform nucleus. Choline and creatine in the head of the right caudate were also significantly decreased in bipolar subjects. Significantly increased myo-inositol was found in the left caudate head in bipolar subjects. Bipolar subjects showed significantly decreased glutamate/glutamine concentrations in the frontal white matter bilaterally and in the right lentiform nucleus. No differences were found for other metabolites examined. These preliminary findings suggest decreased neuronal density or viability in the basal ganglia and neurometabolic abnormalities in the frontal lobes of subjects with bipolar disorder.

Measurement of brain metabolites in patients with type 2 diabetes and major depression using proton magnetic resonance spectroscopy.

Type 2 diabetes and major depression are disorders that are mutual risk factors and may share similar pathophysiological mechanisms. To further understand these shared mechanisms, the purpose of our study was to examine the biochemical basis of depression in patients with type 2 diabetes using proton MRS. Patients with type 2 diabetes and major depression (n=20) were scanned along with patients with diabetes alone (n=24) and healthy controls (n=21) on a 1.5 T MRI/MRS scanner. Voxels were placed bilaterally in dorsolateral white matter and the subcortical nuclei region, both areas important in the circuitry of late-life depression. Absolute values of myo-inositol, creatine, N-acetyl aspartate, glutamate, glutamine, and choline corrected for CSF were measured using the LC-Model algorithm. Glutamine and glutamate concentrations in depressed diabetic patients were significantly lower (p<0.001) in the subcortical regions as compared to healthy and diabetic control subjects. Myo-inositol concentrations were significantly increased (p<0.05) in diabetic control subjects and depressed diabetic patients in frontal white matter as compared to healthy controls. These findings have broad implications and suggest that alterations in glutamate and glutamine levels in subcortical regions along with white matter changes in myo-inositol provide important neurobiological substrates of mood disorders.

A CSF and postmortem brain study of D-serine metabolic parameters in schizophrenia.

Clinical trials demonstrated that D-serine administration improves schizophrenia symptoms, raising the possibility that altered levels of endogenous D-serine may contribute to the N-methyl D-aspartate receptor hypofunction thought to play a role in the disease. We hypothesized that cerebro-spinal fluid (CSF) D-serine levels are decreased in the patients due to reduced synthesis and/or increased degradation in brain. We now monitored amino acid levels in CSF from 12 schizophrenia patients vs. 12 controls and in postmortem parietal-cortex from 15 control subjects and 15 each of schizophrenia, major-depression and bipolar patients. In addition, we monitored postmortem brain serine racemase and D-amino acid oxidase protein levels by Western-blot analysis. We found a 25% decrease in D-serine levels and D/L-serine ratio in CSF of schizophrenia patients, while parietal-cortex D-serine was unaltered. Levels of L-serine, L-glutamine and L-glutamate were unaffected. Frontal-cortex (39%) and hippocampal (21%) serine racemase protein levels and hippocampal serine racemase/D-amino acid oxidase ratio (34%) were reduced. Hippocampal D-amino-acid-oxidase protein levels significantly correlated with duration of illness (r=0.6, p=0.019) but not age. D-amino acid oxidase levels in patients with DOI>20 years were 77% significantly higher than in the other patients and controls. Our results suggest that reduced brain serine racemase and elevated D-amino acid oxidase protein levels may contribute to the lower CSF D-serine levels in schizophrenia.