Metabolomic changes in adults with status epilepticus: A human case-control study

OBJECTIVE

Status epilepticus (SE) is a life-threatening prolonged epileptic seizure that affects ~40 per 100 000 people yearly worldwide. The persistence of seizures may lead to excitotoxic processes, neuronal loss, and neuroinflammation, resulting in long-term neurocognitive and functional disabilities. A better understanding of the pathophysiological mechanisms underlying SE consequences is crucial for improving SE management and preventing secondary neuronal injury.

METHODS

We conducted a comprehensive untargeted metabolomic analysis, using liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS), on plasma and cerebrospinal fluid (CSF) samples from 78 adult patients with SE and 107 control patients without SE, including 29 with CSF for both groups. The metabolomic fingerprints were compared between patients with SE and controls. Metabolites with differences in relative abundances that could not be attributed to treatment or nutrition provided in the intensive care unit were isolated. Enrichment analysis was performed on these metabolites to identify the most affected pathways.

RESULTS

We identified 76 metabolites in the plasma and 37 in the CSF that exhibited differential expression in patients with SE compared to controls. The enrichment analysis revealed that metabolic dysregulations in patients with SE affected primarily amino acid metabolism (including glutamate, alanine, tryptophan, glycine, and serine metabolism), pyrimidine metabolism, and lipid homeostasis. Specifically, patients with SE had elevated levels of pyruvate, quinolinic acid, and keto butyric acid levels, along with lower levels of arginine, N-acetylaspartylglutamate (NAAG), tryptophan, uracil, and uridine. The tryptophan kynurenine pathway was identified as the most significantly altered in SE, resulting in the overproduction of quinolinic acid, an N-methyl-d-aspartate (NMDA) receptor agonist with pro-inflammatory properties.

SIGNIFICANCE

This study has identified several pathways that may play pivotal roles in SE consequences, such as the tryptophan kynurenine pathway. These findings offer novel perspectives for the development of neuroprotective therapeutics.

Higher concentrations of kynurenic acid in CSF are associated with the slower clinical progression of Alzheimer's disease

INTRODUCTION

The kynurenine pathway's (KP) malfunction is closely related to Alzheimer's disease (AD), for antagonistic kynurenic acid (KA) and agonistic quinolinic acid act on the N-methyl-D-aspartate receptor, a possible therapeutic target in treating AD.

METHODS

In our longitudinal case-control study, KP metabolites in the cerebrospinal fluid were analyzed in 311 patients with AD and 105 cognitively unimpaired controls.

RESULTS

Patients with AD exhibited higher concentrations of KA (β = 0.18, P < 0.01) and picolinic acid (β = 0.20, P < 0.01) than the controls. KA was positively associated with tau pathology (β = 0.29, P < 0.01), and a higher concentration of KA was associated with the slower progression of dementia.

DISCUSSION

The higher concentrations of neuroprotective metabolites KA and picolinic acid suggest that the activation of the KP's neuroprotective branch is an adaptive response in AD and may be a promising target for intervention and treatment. Highlights Patients with Alzheimer's disease (AD) exhibited higher concentrations of kynurenic acid and picolinic acid than controls. Higher concentrations of kynurenic acid were associated with slower progression of AD. Potential neurotoxic kynurenines were not increased among patients with AD. Activation of the kynurenine pathway's neuroprotective branch may be an adaptive response in AD.

The kynurenine pathway in Alzheimer's disease: a meta-analysis of central and peripheral levels

OBJECTIVE

Changes in the kynurenine pathway are recognized in psychiatric disorders, but their role in Alzheimer's disease (AD) is less clear. We aimed to conduct a systematic review and meta-analysis to determine whether tryptophan and kynurenine pathway metabolites are altered in AD.

METHODS

We performed a systematic review and random-effects meta-analyses. Inclusion criteria were studies that compared AD and cognitively normal (CN) groups and assessed tryptophan or kynurenine pathway metabolites in cerebrospinal fluid or peripheral blood.

RESULTS

Twenty-two studies with a total of 1,356 participants (664 with AD and 692 CN individuals) were included. Tryptophan was decreased only in peripheral blood. The kynurenine-to-tryptophan ratio was only increased in peripheral blood of the AD group. 3-Hydroxykynurenine was decreased only in cerebrospinal fluid and showed higher variability in the CN group than the AD group. Kynurenic acid was increased in cerebrospinal fluid and decreased in peripheral blood. Finally, there were no changes in kynurenine and quinolinic acid between the groups.

CONCLUSIONS

Our results suggested a shift toward the kynurenine pathway in both the brain and in the periphery, as well as a shift towards increased kynurenic acid production in the brain but decreased production in peripheral blood. In addition, our analysis indicated dissociation between the central and peripheral levels, as well as between plasma and serum for some of these metabolites. Finally, changes in the kynurenine pathway are suggested to be a core component of AD. More studies are warranted to verify and consolidate our results.

Decreased cerebrospinal fluid kynurenic acid in epileptic spasms: A biomarker of response to corticosteroids

Background

Epileptic (previously infantile) spasms is the most common epileptic encephalopathy occurring during infancy and is frequently associated with abnormal neurodevelopmental outcomes. Epileptic spasms have a diverse range of known (genetic, structural) and unknown aetiologies. High dose corticosteroid treatment for 4 weeks often induces remission of spasms, although the mechanism of action of corticosteroid is unclear. Animal models of epileptic spasms have shown decreased brain kynurenic acid, which is increased after treatment with the ketogenic diet. We quantified kynurenine pathway metabolites in the cerebrospinal fluid (CSF) of infants with epileptic spasms and explored clinical correlations.

Methods

A panel of nine metabolites in the kynurenine pathway (tryptophan, kynurenine, kynurenic acid, 3-hydroxykynurenine, xanthurenic acid, anthranilic acid, 3-hydroxyanthranilic acid, quinolinic acid, and picolinic acid) were measured using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). CSF collected from paediatric patients less than 3 years of age with epileptic spasms (n=34, 19 males, mean age 0.85, median 0.6, range 0.3–3 yrs) were compared with other epilepsy syndromes (n=26, 9 males, mean age 1.44, median 1.45, range 0.3–3 yrs), other non-inflammatory neurological diseases (OND) (n=29, 18 males, mean age 1.47, median 1.6, range 0.1–2.9 yrs) and inflammatory neurological controls (n=12, 4 males, mean age 1.80, median 1.80, range 0.8–2.5 yrs).

Findings

There was a statistically significant decrease of CSF kynurenic acid in patients with epileptic spasms compared to OND (p<0.0001). In addition, the kynurenic acid/kynurenine (KYNA/KYN) ratio was lower in the epileptic spasms subgroup compared to OND (p<0.0001). Epileptic spasms patients who were steroid responders or partial steroid responders had lower KYNA/KYN ratio compared to patients who were refractory to steroids (p<0.005, p<0.05 respectively).

Interpretation

This study demonstrates decreased CSF kynurenic acid and KYNA/KYN in epileptic spasms, which may also represent a biomarker for steroid responsiveness. Given the anti-inflammatory and neuroprotective properties of kynurenic acid, further therapeutics able to increase kynurenic acid should be explored.

Funding

Financial support for the study was granted by Dale NHMRC Investigator grant APP1193648, Petre Foundation, Cerebral Palsy Alliance and Department of Biochemistry at the Children's Hospital at Westmead. Prof Guillemin is funded by NHMRC Investigator grant APP1176660 and Macquarie University.

Kynurenine pathway metabolites in cerebrospinal fluid and blood as potential biomarkers in Huntington's disease

Converging lines of evidence from several models, and post-mortem human brain tissue studies, support the involvement of the kynurenine pathway (KP) in Huntington's disease (HD) pathogenesis. Quantifying KP metabolites in HD biofluids is desirable, both to study pathobiology and as a potential source of biomarkers to quantify pathway dysfunction and evaluate the biochemical impact of therapeutic interventions targeting its components. In a prospective single-site controlled cohort study with standardised collection of cerebrospinal fluid (CSF), blood, phenotypic and imaging data, we used high-performance liquid-chromatography to measure the levels of KP metabolites-tryptophan, kynurenine, kynurenic acid, 3-hydroxykynurenine, anthranilic acid and quinolinic acid-in CSF and plasma of 80 participants (20 healthy controls, 20 premanifest HD and 40 manifest HD). We investigated short-term stability, intergroup differences, associations with clinical and imaging measures and derived sample-size calculation for future studies. Overall, KP metabolites in CSF and plasma were stable over 6 weeks, displayed no significant group differences and were not associated with clinical or imaging measures. We conclude that the studied metabolites are readily and reliably quantifiable in both biofluids in controls and HD gene expansion carriers. However, we found little evidence to support a substantial derangement of the KP in HD, at least to the extent that it is reflected by the levels of the metabolites in patient-derived biofluids.

Sex and race differences of cerebrospinal fluid metabolites in healthy individuals

INTRODUCTION

Analyses of cerebrospinal fluid (CSF) metabolites in large, healthy samples have been limited and potential demographic moderators of brain metabolism are largely unknown.

OBJECTIVE

Our objective in this study was to examine sex and race differences in 33 CSF metabolites within a sample of 129 healthy individuals (37 African American women, 29 white women, 38 African American men, and 25 white men).

METHODS

CSF metabolites were measured with a targeted electrochemistry-based metabolomics platform. Sex and race differences were quantified with both univariate and multivariate analyses. Type I error was controlled for by using a Bonferroni adjustment (0.05/33 = .0015).

RESULTS

Multivariate Canonical Variate Analysis (CVA) of the 33 metabolites showed correct classification of sex at an average rate of 80.6% and correct classification of race at an average rate of 88.4%. Univariate analyses revealed that men had significantly higher concentrations of cysteine (p < 0.0001), uric acid (p < 0.0001), and N-acetylserotonin (p = 0.049), while women had significantly higher concentrations of 5-hydroxyindoleacetic acid (5-HIAA) (p = 0.001). African American participants had significantly higher concentrations of 3-hydroxykynurenine (p = 0.018), while white participants had significantly higher concentrations of kynurenine (p < 0.0001), indoleacetic acid (p < 0.0001), xanthine (p = 0.001), alpha-tocopherol (p = 0.007), cysteine (p = 0.029), melatonin (p = 0.036), and 7-methylxanthine (p = 0.037). After the Bonferroni adjustment, the effects for cysteine, uric acid, and 5-HIAA were still significant from the analysis of sex differences and kynurenine and indoleacetic acid were still significant from the analysis of race differences.

CONCLUSION

Several of the metabolites assayed in this study have been associated with mental health disorders and neurological diseases. Our data provide some novel information regarding normal variations by sex and race in CSF metabolite levels within the tryptophan, tyrosine and purine pathways, which may help to enhance our understanding of mechanisms underlying sex and race differences and potentially prove useful in the future treatment of disease.

Kynurenine Pathway Activation in Human African Trypanosomiasis

Background

The kynurenine pathway of tryptophan oxidation is associated with central nervous system (CNS) inflammatory pathways. Inhibition of this pathway ameliorates CNS inflammation in rodent models of the late (meningoencephalitic) stage of human African trypanosomiasis (HAT). In this study, we evaluate whether the kynurenine pathway is activated in clinical HAT and associated with CNS inflammatory responses.

Methods

We measured cerebrospinal fluid (CSF) tryptophan and kynurenine metabolite concentrations in patients infected with Trypanosoma brucei rhodesiense, using liquid chromatography-mass spectrometry.

Results

Kynurenine concentration in CSF was increased in both the early and late stages of disease, with a progressive increase in tryptophan oxidation associated with stage progression. Kynurenine pathway activation was associated with increases in neuroinflammatory markers, but there was no clear relationship to neurological symptoms.

Conclusions

CNS kynurenine pathway activation occurs during HAT, including cases prior to the current diagnostic cutoff for late-stage infection, providing evidence for early CNS involvement in HAT. Metabolite data demonstrate that the kynurenine-3-monooxygenase and kynurenine aminotransferase branches of the kynurenine pathway are active. The association between tryptophan oxidation and CNS inflammatory responses as measured by CSF interleukin 6 (IL-6) concentration supports a role of kynurenine metabolites in the inflammatory pathogenesis of late-stage HAT.

Increased levels of kynurenine and kynurenic acid in the CSF of patients with schizophrenia

BACKGROUND

The kynurenic acid (KYNA) hypothesis for schizophrenia is partly based on studies showing increased brain levels of KYNA in patients. KYNA is an endogenous metabolite of tryptophan (TRP) produced in astrocytes and antagonizes N-methyl-D-aspartate and α7* nicotinic receptors.

METHODS

The formation of KYNA is determined by the availability of substrate, and hence, we analyzed KYNA and its precursors, kynurenine (KYN) and TRP, in the cerebrospinal fluid (CSF) of patients with schizophrenia. CSF from male patients with schizophrenia on olanzapine treatment (n = 16) was compared with healthy male volunteers (n = 29).

RESULTS

KYN and KYNA concentrations were higher in patients with schizophrenia (60.7 ± 4.37 nM and 2.03 ± 0.23 nM, respectively) compared with healthy volunteers (28.6 ± 1.44 nM and 1.36 ± 0.08 nM, respectively), whereas TRP did not differ between the groups. In all subjects, KYN positively correlated to KYNA.

CONCLUSION

Our results demonstrate increased levels of CSF KYN and KYNA in patients with schizophrenia and further support the hypothesis that KYNA is involved in the pathophysiology of schizophrenia.

High throughput analysis of tryptophan metabolites in a complex matrix using capillary electrophoresis coupled to time-of-flight mass spectrometry

A capillary electrophoresis method for separation and detection with time-of-flight mass spectrometry is described for tryptophan metabolites in the kynurenic pathway. Tryptophan metabolites are usually difficult to detect with electrospray mass spectrometry since they have low surface activity and occur in low nanomolar to micromolar range in body fluids. Modification of the silica-wall with 1-(4-iodobutyl)4-aza-1-azoniabicyclo[2,2,2]octane iodide, also named M7C4I, has successfully been used to deactivate the fused silica wall and generate a stable reversed electroosmotic flow. Utilizing this advantage together with electrospray ionization time-of-flight mass spectrometry, which generates high resolution and fast acquisition monitoring of species, proved to be successful even for such a complex matrix like human cerebrospinal fluid.

Metabolites of the kynurenine pathway of tryptophan metabolism in the cerebrospinal fluid of Malawian children with malaria

A retrospective study of 100 Malawian children (87 with malaria and 13 with a diagnosis other than malaria) was conducted to determine the relationship between levels of metabolites of the kynurenine pathway in cerebrospinal fluid (CSF) and disease outcome. Three metabolites were measured: quinolinic acid (QA), an excitotoxin; kynurenic acid (KA), a neuroprotective receptor antagonist; and picolinic acid (PA), a proinflammatory mediator. Elevated levels of QA and PA in CSF were associated with a fatal outcome in Malawian children with cerebral malaria (CM). QA was associated with a history of convulsions. An increase in the QArcolon;KA ratio, which favors neurotoxicity, was observed only in the 3 patients with tuberculosis meningitis. Compared with Vietnamese adults with malaria, Malawian children with malaria had higher concentrations of KA. Elevated levels of KA in children with CM may serve to contain injury in the developing brain, which is more susceptible to excitotoxic damage than is the adult brain.

The clinical significance of cerebrospinal fluid levels of kynurenine pathway metabolites and lactate in severe malaria

A retrospective study of 261 Vietnamese adults with severe malaria was conducted to determine the relationship between cerebrospinal fluid (CSF) levels of metabolites of the kynurenine pathway, the incidence of neurologic complications, and the disease outcome. Three metabolites were measured: the excitotoxin quinolinic acid (QA); the protective receptor antagonist kynurenic acid (KA); and the proinflammatory mediator picolinic acid (PA). These measurements were related prospectively to CSF lactate levels. QA and PA levels were elevated, compared with those of controls. There was no difference in the levels of KA between these groups. Although >40% of malaria patients had QA CSF concentrations in the micromolar range, there was no association with convulsions or depth of coma. Levels of QA and PA were associated significantly with death, but a multivariate analysis suggested that these elevations were a consequence of impaired renal function. CSF lactate remained an independent and significant predictor of poor outcome.

Increased neopterin production and tryptophan degradation in advanced Parkinson's disease

Large amounts of neopterin are produced by interferon-(IFN)-gamma-stimulated human monocytes/macrophages, and increased neopterin concentrations indicate cellular immune activation. In parallel, IFN-gamma induces indoleamine 2,3-dioxygenase which degrades 1-tryptophan to kynurenine. Increased tryptophan degradation rates are indicated by an increased kynurenine/tryptophan ratio (kyn/trp-ratio), reflecting immune system activation, too. In 22 patients with Parkinson's disease (PD) and in 11 age-matched controls, serum and cerebrospinal fluid (CSF) neopterin concentrations were measured by ELISA. Tryptophan and kynurenine concentrations were determined by HPLC. Neopterin concentrations and kyn/trp-ratios were increased both in serum and CSF of patients as compared to controls. Serum tryptophan was lower in patients. Patients with the highest disease activity presented with highest degree of immune activation. Significant correlations existed between neopterin concentrations and kyn/trp-ratios in serum and CSF. Increased formation of neopterin and enhanced degradation of tryptophan suggest activated cell-mediated immune response in a subgroup of patients with advanced Parkinson's disease.

Mechanism of increases in L-kynurenine and quinolinic acid in renal insufficiency

Marked increases in metabolites of the L-tryptophan-kynurenine pathway, L-kynurenine and quinolinic acid (Quin), were observed in serum and cerebrospinal fluid (CSF) of both the rat and human with renal insufficiency. The mechanisms responsible for their accumulation after renal insufficiency were investigated. In patients with chronic renal insufficiency, elevated levels of serum L-kynurenine and Quin were reduced by hemodialysis. In renal-insufficient rats, Quin and L-kynurenine levels in serum, brain, and CSF were also increased parallel to the severity of renal insufficiency. Urinary excretion of Quin (3.5-fold) and L-kynurenine (2.8-fold) was also increased. Liver L-tryptophan 2,3-dioxygenase activity (TDO), a rate-limiting enzyme of the kynurenine pathway, was increased in proportion to blood urea nitrogen and creatinine levels. Kynurenine 3-hydroxylase and quinolinic acid phosphoribosyltransferase were unchanged, but the activities of kynureninase, 3-hydroxyanthranilate dioxygenase, and aminocarboxymuconate-semialdehyde decarboxylase (ACMSDase) were significantly decreased. Systemic administrations of pyrazinamide (ACMSDase inhibitor) increased serum Quin concentrations in control rats, demonstrating that changes in body ACMSDase activities in response to renal insufficiency are important factors for the determination of serum Quin concentrations. We hypothesize the following ideas: that increased serum L-kynurenine concentrations are mainly due to the increased TDO and decreased kynureninase activities in the liver and increased serum Quin concentrations are due to the decreased ACMSDase activities in the body after renal insufficiency. The accumulation of CSF L-kynurenine is caused by the entry of increased serum L-kynurenine, and the accumulation of CSF Quin is secondary to Quin from plasma and/or Quin precursor into the brain.

Central nervous system activation of the indoleamine-2,3-dioxygenase pathway in human T cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis

Human T cell lymphotropic virus type I (HTLV-I) is associated with a chronic neurologic disease called HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The potential mechanisms of HAM/TSP pathogenesis were assessed by examination of 2 pathways initiated by interferon-gamma, a predominant cytokine in HAM/TSP. Jamaican HAM/TSP patients (n=17) were compared with patients with other neurologic diseases (ONDs; n=13) with respect to cerebrospinal fluid levels of the following: neopterin; nitrite plus nitrate, a stable indicator of nitric oxide; and tryptophan and kynurenine, metabolites of the indoleamine-2,3-dioxygenase (IDO) pathway. HAM/TSP patients had significantly elevated levels of neopterin (P=.003) and kynurenine (P=.05) and a significantly decreased level of tryptophan (P=.003), compared with patients with ONDs. These results support immune activation within the central nervous system and activation of the IDO pathway. Thus, activation of the IDO pathway may play a role in HAM/TSP.

Quantification of anthranilic acid and its related enzyme activity in several different species

Anthranilic acid (AA) has been attracted considerable attention as one of the L-tryptophan-kynurenine pathway metabolites in the central nervous system. In this study, the concentration of L-kynurenine (L-KYN) and AA in serum and CSF, and its related enzyme activities were determined in several species. In rabbits, CSF AA concentrations were lower and serum AA concentrations were slightly higher than those in other species. However, the concentrations of L-KYN were substantially higher in rabbits in both serum and CSF compared with other species. Tissue enzyme activities varied among species. In rabbits, lung IDO activities were higher, but liver kynurenine 3-hydroxylase activities were lower than those of the other species tested. Furthermore, brain kynurenine 3-hydroxylase activities were higher in gerbils than those in other species. These results clearly demonstrated that kynurenine pathway enzyme activities and metabolite concentrations vary with species.

Developmental changes in cerebrospinal fluid concentrations of monoamine-related substances revealed with a Coulochem electrode array system

The relationship between age and cerebrospinal fluid concentrations of monoamine-related substances, including kynurenine, were investigated using a Coulochem electrode array system, to clarify developmental changes in monoamine-related substances in the human central nervous system. In neurologically normal children, significant inverse correlations with age were observed for the cerebrospinal fluid concentrations of 5-hydroxytryptophan, 5-hydroxyindole-acetic acid, kynurenine, homovanillic acid, 3-methoxy-4-hydroxyphenyl glycol, and 3-O-methyl-dopamine. The concentrations of their precursors, tryptophan and tyrosine, were not related to age. This is the first comprehensive study revealing developmental changes in monoamine-related substances including their precursors and metabolites.

TRH increases cerebrospinal fluid concentration of kynurenine

We have analyzed changes in cerebrospinal fluid (CSF) concentrations of monoamine-related substances to clarify the mechanism of the antiepileptic action of thyrotropin-releasing hormone (TRH). TRH-tartrate was administered to 14 patients with intractable epilepsy. Before and 2 weeks after TRH administration, CSF was collected and analyzed for tryptophan and tyrosine metabolites. Among monoamine-related substances, only CSF concentrations of kynurenine were increased after TRH therapy. Considering the fact that kynurenic acid acts as antagonist on the NMDA receptor complex, the results of this study may explain at least one of the mechanisms of the effectiveness of TRH therapy for intractable epilepsy.

Sources of the neurotoxin quinolinic acid in the brain of HIV-1-infected patients and retrovirus-infected macaques

This study investigated the sources of quinolinic acid, a neurotoxic tryptophan-kynurenine pathway metabolite, in the brain and blood of HIV-infected patients and retrovirus-infected macaques. In brain, quinolinic acid concentrations in HIV-infected patients were elevated by > 300-fold to concentrations that exceeded cerebrospinal fluid (CSF) by 8.9-fold. There were no significant correlations between elevated serum quinolinic acid levels with those in CSF and brain parenchyma. Because nonretrovirus-induced encephalitis confounds the interpretation of human postmortem data, rhesus macaques infected with retrovirus were used to examine the mechanisms of increased quinolinic acid accumulations and determine the relationships of quinolinic acid to encephalitits and systemic responses. The largest kynurenine pathway responses in brain were associated with encephalitis and were independent of systemic responses. CSF quinolinic acid levels were also elevated in all infected macaques, but particularly those with retrovirus-induced encephalitis. In contrast to the brain changes, there was no difference in any systemic measure between macaques with encephalitis vs. those without. Direct measures of the amount of quinolinic acid in brain derived from blood in a macaque with encephalitis showed that almost all quinolinic acid (>98%) was synthesized locally within the brain. These results demonstrate a role for induction of indoleamine-2,3dioxygenase in accelerating the local formation of quinolinic acid within the brain tissue, particularly in areas of encephalitis, rather than entry of quinolinic acid into the brain from the meninges or blood. Strategies to reduce QUIN production, targeted at intracerebral sites, are potential approaches to therapy.

Increase of tryptophan in serum and in cerebrospinal fluid of patients with HIV infection during zidovudine therapy

A high percentage of patients with human immunodeficiency virus infection presents with decreased tryptophan concentrations in serum and cerebrospinal fluid. In parallel degradation products of tryptophan like kynurenine and quinolinic acid are increased. We investigated the behavior of tryptophan concentrations in 14 patients with HIV infection before and during treatment with zidovudine, and we found a significant increase of tryptophan in serum and cerebrospinal fluid after 4-14 months of therapy. In parallel, neopterin concentrations decreased significantly. Moreover, an association existed in cerebrospinal fluid between the degree of tryptophan increase and neopterin decrease. Thus, treatment with zidovudine contributes to a gradual normalization of tryptophan metabolism in patients with HIV-1 infection. The data imply that zidovudine therapy is associated not only with a reduction of virus replication but also immune activation is reduced.

Indoleamine concentrations in cerebrospinal fluid from patients with Alzheimer type and Binswanger type dementias before and after administration of citalopram, a synthetic serotonin uptake inhibitor

We studied changes in the concentrations of serotonin (5-HT), kynurenine, and other indoleamines in the cerebrospinal fluid of patients with Alzheimer type dementia (ATD) and those with Binswanger type vascular dementia (VDBT), and changes in these indoleamine concentrations 2 weeks after administration of citalopram, a 5-HT uptake inhibitor. The concentrations of total 5-HT (p < 0.005) and kynurenine (p < 0.005) were significantly decreased in ATD patients in comparison to those of the controls. After citalopram administration, there was a remarkable increase in 5-HT concentration (249%, p < 0.0001) and a significant decrease in 5-HIAA concentration (22%, p < 0.02). In the VDBT patients, only 5-HT showed a significant decrease (p < 0.005) in comparison to the control values. It also increased significantly (214%) after citalopram administration. The 5-HT/tryptophan and kynurenine/tryptophan ratios were not correlated for the controls, but did significantly for the ATD and VDBT patients; after citalopram treatment, the increase in 5-HT/tryptophan was correlated significantly with that of kynurenine/tryptophan for ATD, but not for VDBT. These results suggest that both the serotonin and kynurenine pathways are impaired in ATD; whereas, the serotonin pathway alone is in VDBT, and that these impairments are ameliorated by the administration of citalopram.

Cerebrospinal fluid levels of kynurenine pathway metabolites in patients with eating disorders: relation to clinical and biochemical variable

In brain, most L-tryptophan is metabolized to indoleamines, whereas in systemic tissues L-tryptophan is catabolized to kynurenine pathway metabolites. Among these latter compounds are: quinolinic acid, an N-methyl-D-aspartate receptor agonist; kynurenic acid, an antagonist of excitatory amino acid receptors that also reduces quinolinic acid-mediated neurotoxicity; and L-kynurenine, a possible convulsant. Because the metabolism of L-tryptophan through the kynurenine pathway is dependent upon adequate nutrition, we sought to determine whether the impaired nutrition characteristic of eating-disordered patients might be associated with specific disturbances in this metabolic pathway. Cerebrospinal fluid levels of L-tryptophan, quinolinic acid, kynurenic acid, L-kynurenine, and 5-hydroxyindoleacetic acid were measured in medication-free female patients meeting DSM-III-R criteria for either anorexia nervosa (n = 10) or normal-weight bulimia nervosa (n = 22), studied at varying stages of nutritional recovery. Eight healthy, normal-weight females served as a comparison group. Cerebrospinal fluid levels of kynurenic acid were significantly reduced in underweight anorectics, compared to normal females, but returned to normal values with restoration of normal body weight. Although cerebrospinal fluid quinolinic acid levels were not different from controls, the ratio of quinolinic acid to kynurenic acid was significantly increased during the underweight phase of anorexia nervosa. Furthermore, in the eating-disordered patients, kynurenic acid levels in cerebrospinal fluid correlated positively with percent-of-population average body weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyrotropin-releasing hormone in treatment of intractable epilepsy: neurochemical analysis of CSF monoamine metabolites

The efficacy of thyrotropin-releasing hormone in children with intractable epilepsy was investigated and changes in cerebrospinal fluid monoamine metabolites were analyzed. The 18 patients had either West syndrome (12 patients) or Lennox-Gastaut syndrome (6 patients), which was intractable to antiepileptic drug therapy and to adrenocorticotrophic hormone. Thyrotropin-releasing hormone-tartrate was administered for 4 weeks. Before and after the thyrotropin-releasing hormone administration, cerebrospinal fluid was collected and analyzed for 5-hydroxyindoleacetic acid, kynurenine, homovanillic acid, and 3-methoxy-4-hydroxyphenyl glycol. The patients were classified into 3 groups, based on seizure frequency and electroencephalographic effects: cessation of seizures and seizure discharges (very effective; group A), reduction of seizures and/or seizure discharges (effective; group B), and no changes in frequency of seizures or discharges (not effective; group C). There were 6 patients in group A, 3 in group B, and 9 in group C. There were no significant differences in monoamine metabolites before and after the thyrotropin-releasing hormone therapy. A trial of thyrotropin-releasing hormone for the treatment of intractable epilepsy is warranted and further study is required on the mechanism of the antiepileptic action of thyrotropin-releasing hormone.

Neopterin production and tryptophan degradation in acute Lyme neuroborreliosis versus late Lyme encephalopathy

Fourteen patients with Borrelia burgdorferi infection were investigated for possible abnormalities of tryptophan and neopterin metabolism. Four patients (2 were investigated before therapy, 2 when therapy had been already started) had acute Lyme neuroborreliosis, and 10 patients were investigated months to years after an acute infection. Increased concentrations of neopterin and of the tryptophan-degradation product, L-kynurenine, were detected in the cerebrospinal fluid of patients with acute Lyme neuroborreliosis; one patient presented with subnormal tryptophan. Similar but less marked changes were seen in the treated patients and in some of the patients with Lyme encephalopathy. No such abnormalities were seen in the serum of the patients. The data indicate a role of the immune system and particularly of endogenously formed cytokines, like interferon-gamma and tumour necrosis factor-alpha, effecting tryptophan and neopterin metabolism in patients with acute Lyme neuroborreliosis.

A multidimensional approach to analysis of cerebrospinal fluid biogenic amines in schizophrenia: I. Comparisons with healthy control subjects and neuroleptic-treated/unmedicated pairs analyses

Recent hypotheses and findings indicate that measurements of interactions between cerebrospinal fluid (CSF) biogenic amine systems, rather than measurement of CSF biogenic amine metabolites, better correlate with clinically important findings in schizophrenia. To test hypotheses, we used a recent technological advance in high performance liquid chromatography with electrochemical detection and combined it with multivariate statistical analyses to study biogenic amine concentrations in CSF in schizophrenia. This approach enabled the study of the interactions of several metabolites of each of the three major neurotransmitter pathways (dopaminergic, noradrenergic, and serotonergic) to test existing hypotheses regarding the neurobiochemical basis of schizophrenia. Twenty biogenic amines, their metabolites, and other compounds from 24 medication-free schizophrenic patients and 12 normal control subjects were simultaneously measured using a recently developed technique of gradient high performance liquid chromatography coupled with a 16-channel electrochemical array detector. After covariation for storage time, results of a stepwise discriminant function analysis comparing the control and patient groups identified tryptophan, tryptophol, and epinephrine as discriminating variables. Hotelling's paired T2 test from a subgroup of schizophrenic patients studied while they were and were not receiving neuroleptic treatment did not yield any significant differences between subgroups. A discussion of the findings and a comparison with previous studies of CSF biogenic amines in schizophrenia are presented.

A multidimensional approach to analysis of cerebrospinal fluid biogenic amines in schizophrenia: II. Correlations with psychopathology

As part of a multidimensional study of cerebrospinal fluid biogenic amine metabolites in schizophrenia, the relationship between neurochemical measures and psychopathology assessed using the Psychiatric Symptom Assessment Scale (PSAS) was analyzed. In a group of 20 unmedicated patients, 3,4-dihydroxyphenylacetic acid (DOPAC) was a predictor of symptom severity in a stepwise multiple regression model. Values of 3-hydroxykynurenine and metanephrine in the unmedicated state predicted clinical response in a stepwise multiple regression model, as measured by improvement in PSAS mean item score following 6 weeks on a standard dose of neuroleptic. In a subgroup of 14 patients in whom both off- and on-medication concentrations of cerebrospinal fluid biogenic amines and metabolites were measured, change in 3-hydroxykynurenine predicted clinical outcome in a multiple regression model. These findings point toward the need to examine the role of the kynurenine pathway of tryptophan metabolism in the pathophysiology of schizophrenia.

Kynurenine pathway metabolites in cerebrospinal fluid and serum in complex partial seizures

The kynurenine pathway metabolites, quinolinic acid (QUIN) and L-kynurenine are convulsants, whereas kynurenic acid (KYNA) is an antagonist of excitatory amino acid receptors. Imbalances in the concentrations of these metabolites have been implicated in the etiology of human seizure disorders. In the present study, L-kynurenine and QUIN concentrations in both cerebrospinal fluid (CSF) and serum were reduced in patients with intractable complex partial seizures (CPS) in both the postictal period (15-75 min after a seizure) and the interictal period (absence of seizure for > 24 h) as compared with neurologically normal control subjects. Linear regression analyses and analysis of covariance showed that the reductions in serum QUIN and L-kynurenine were correlated to blood antiepileptic medication. L-Tryptophan (L-TRP) levels also tended to be lower in both CSF and serum of the seizure patients. CSF KYNA and serum 3-hydroxykynurenine concentrations were not affected in seizure patients, whereas serum levels of KYNA were reduced. 3-Hydroxykynurenine was not detected in the CSF of either control or seizure patients. The results do not support a role for a generalized reduction in KYNA concentrations or an increased ratio of QUIN:KYNA, or increases in CSF L-kynurenine in initiation and maintenance of intractable CPS humans.

Kynurenic acid is decreased in cerebrospinal fluid of patients with infantile spasms

Cerebrospinal fluid (CSF) from 8 patients with symptomatic infantile spasms was collected before specific treatment for infantile spasms. The concentration of CSF kynurenic acid (KYA) and 3-hydroxykynurenine (3-OHKY) in infantile spasms was analyzed by high-performance liquid chromatography and compared with CSF KYA from 10 age-matched controls. The levels of CSF KYA were significantly lower in infantile spasm patients compared to controls (P < .05). In contrast, the levels of CSF 3-OHKY were significantly higher in infantile spasm patients than in controls (P < .05). These findings suggest that the presence of seizures in infantile spasms is associated with altered metabolism of 3-OHKY. The possibility that seizures may be related to increased or decreased production of certain kynurenine metabolites is discussed.

Alterations in the concentration of serotonergic and dopaminergic substances in the cerebrospinal fluid of patients with Parkinson's disease, and their changes after L-dopa administration

In untreated patients with Parkinson's disease (PD), the total (free and conjugated) serotonin (5-HT) and dopamine (DA) concentrations in the cerebrospinal fluid decreased significantly. While the 5-HT concentration displayed a non-significant trend of negative correlation with the DA concentration in controls, it had a significant positive correlation with the DA concentration in untreated PD patients. In L-dopa-treated patients, the DA concentration increased remarkably, whereas the 5-HT concentration decreased further compared with untreated patients. The tryptophan, 5-hydroxyindolacetic acid (5-HIAA), and 3-OH kynurenine concentrations had significant positive correlations with L-dopa doses. The 5-HT concentration had a significant positive correlation with scores of psychomatric testing in L-dopa-treated patients.

Concentrations of serotonin and its related substances in the cerebrospinal fluid of parkinsonian patients and their relations to the severity of symptoms

We evaluated the concentrations of free and total serotonin (5-hydroxytryptamine, 5-HT) and its related substances in the cerebrospinal fluid from patients with Parkinson's disease (PD). The concentrations of total 5-HT, 5-hydroxytryptophan, kynurenine and 3-hydroxykynurenine decreased significantly in PD patients compared with controls. The concentration of total 5-HT had significant negative correlations with Hoehn and Yahr's stages, the severity of rigidity, akinesia and gait freezing; the correlation with gait freezing was most conspicuous.

[Changes in CSF tryptophan metabolite levels in infantile spasms]

Cerebrospinal fluid (CSF) from 6 cases of asymptomatic infantile spasms (IS) (mean age, 6.1 months) was collected before and after treatment with adrenocorticotropic hormone (ACTH). The concentration of CSF tryptophan (TRP) metabolites was analyzed using HPLC and compared to the metabolite concentration in CSF from 10 age-matched controls (mean age, 6.7 months). Levels of CSF serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and kynurenine (KYN) at pretreatment were significantly lower in IS patients compared to controls (p < 0.05). In contrast, the levels of CSF 3-hydroxykynurenine (3-OHKY) before ACTH treatment were significantly higher in IS patients than in controls (p < 0.05). After the treatment, significant increases in 5-HIAA and decreases in KYN and 3-OHKY levels (p < 0.05) were observed in CSF of infants whose seizures were eliminated by ACTH. These findings suggested that the presence of seizures in IS was associated with a significant decrease in serotonergic activity, or that the turnover in the direction of 3-OHKY was altered. The possibility that elimination of seizures by ACTH might be related to decreased production of kynurenine metabolites was discussed.

Quinolinic acid and kynurenine pathway metabolism in inflammatory and non-inflammatory neurological disease

Neurological dysfunction, seizures and brain atrophy occur in a broad spectrum of acute and chronic neurological diseases. In certain instances, over-stimulation of N-methyl-D-aspartate receptors has been implicated. Quinolinic acid (QUIN) is an endogenous N-methyl-D-aspartate receptor agonist synthesized from L-tryptophan via the kynurenine pathway and thereby has the potential of mediating N-methyl-D-aspartate neuronal damage and dysfunction. Conversely, the related metabolite, kynurenic acid, is an antagonist of N-methyl-D-aspartate receptors and could modulate the neurotoxic effects of QUIN as well as disrupt excitatory amino acid neurotransmission. In the present study, markedly increased concentrations of QUIN were found in both lumbar cerebrospinal fluid (CSF) and post-mortem brain tissue of patients with inflammatory diseases (bacterial, viral, fungal and parasitic infections, meningitis, autoimmune diseases and septicaemia) independent of breakdown of the blood-brain barrier. The concentrations of kynurenic acid were also increased, but generally to a lesser degree than the increases in QUIN. In contrast, no increases in CSF QUIN were found in chronic neurodegenerative disorders, depression or myoclonic seizure disorders, while CSF kynurenic acid concentrations were significantly lower in Huntington's disease and Alzheimer's disease. In inflammatory disease patients, proportional increases in CSF L-kynurenine and reduced L-tryptophan accompanied the increases in CSF QUIN and kynurenic acid. These responses are consistent with induction of indoleamine-2,3-dioxygenase, the first enzyme of the kynurenine pathway which converts L-tryptophan to kynurenic acid and QUIN. Indeed, increases in both indoleamine-2,3-dioxygenase activity and QUIN concentrations were observed in the cerebral cortex of macaques infected with retrovirus, particularly those with local inflammatory lesions. Correlations between CSF QUIN, kynurenic acid and L-kynurenine with markers of immune stimulation (neopterin, white blood cell counts and IgG levels) indicate a relationship between accelerated kynurenine pathway metabolism and the degree of intracerebral immune stimulation. We conclude that inflammatory diseases are associated with accumulation of QUIN, kynurenic acid and L-kynurenine within the central nervous system, but that the available data do not support a role for QUIN in the aetiology of Huntington's disease or Alzheimer's disease. In conjunction with our previous reports that CSF QUIN concentrations are correlated to objective measures of neuropsychological deficits in HIV-1-infected patients, we hypothesize that QUIN and kynurenic acid are mediators of neuronal dysfunction and nerve cell death in inflammatory diseases. Therefore, strategies to attenuate the neurological effects of kynurenine pathway metabolites or attenuate the rate of their synthesis offer new approaches to therapy.

Inter-relationships between quinolinic acid, neuroactive kynurenines, neopterin and beta 2-microglobulin in cerebrospinal fluid and serum of HIV-1-infected patients

Quinolinic acid (QUIN) is an neurotoxic N-methyl-D-aspartate receptor agonist and an L-tryptophan metabolite of the kynurenine pathway. Increased concentrations of QUIN occur in both cerebrospinal fluid (CSF) and blood of patients infected with human immunodeficiency virus (HIV)-1, particularly those with neurologic disturbances. In the present study of HIV-1 infected patients in Walter Reed stages 4, 5 and 6, reductions in L-tryptophan accompanied proportional increases in L-kynurenine and QUIN in both serum and CSF. Further, close inter-correlations exist between QUIN kynurenic acid and L-kynurenine with both beta 2-microglobulin and neopterin in CSF and serum. These correlations support the hypotheses that the kynurenine pathway is activated in association with inflammation and induction of indoleamine-2,3-dioxygenase. There were no relationships between CSF QUIN, L-kynurenine or kynurenic acid with the ratio of serum:CSF albumin concentrations, which indicates that the increases in CSF QUIN, L-kynurenine or kynurenic acid were not dependent on a breakdown of the blood-brain barrier. Kynurenic acid is also a kynurenine pathway metabolite that can attenuate the excitotoxic effects of QUIN when present in higher molar concentrations. While CSF kynurenic acid levels were increased in HIV-1-infected patients, the magnitude of the increases were smaller than those of QUIN and the molar concentrations of kynurenic acid were consistently lower than QUIN by at least one order of magnitude. We conclude that immune activation increases the levels of neuroactive kynurenines within the central nervous system of HIV-1-infected patients secondary to activation of indoleamine-2,3-dioxygenase.

Tryptophan metabolism via the kynurenine pathway in patients with the eosinophilia-myalgia syndrome

OBJECTIVE

To investigate the metabolism of L-tryptophan (LT) via the kynurenine pathway in patients with the eosinophilia-myalgia syndrome (EMS).

METHODS

Measurement of LT, L-kynurenine, and quinolinic acid in plasma and cerebrospinal fluid (CSF) from subjects with EMS, from asymptomatic users of LT, and from normal subjects.

RESULTS

Plasma LT concentrations were lower in untreated EMS patients (n = 5) than in corticosteroid-treated EMS patients (n = 5; P less than 0.05) and in asymptomatic users of LT (n = 5; P less than 0.05). Untreated EMS patients, who had discontinued LT weeks to months prior to study, had significantly higher plasma levels of L-kynurenine and quinolinic acid than did corticosteroid-treated EMS patients (P less than 0.05), normal subjects (P less than 0.02), and asymptomatic users of LT (P less than 0.05). EMS patients also had significantly elevated levels of L-kynurenine (P less than 0.05) and quinolinic acid (P less than 0.001) in CSF compared with normal subjects. After a 1-gm oral dose of LT, untreated EMS patients (n = 4) showed lower peak levels of LT and accentuated synthesis of L-kynurenine and quinolinic acid, compared with these values in corticosteroid-treated EMS patients (n = 2), who responded like normal subjects (n = 5).

CONCLUSION

These data demonstrate that during the active phase of EMS, LT metabolism via the kynurenine pathway was accentuated, probably secondary to induction of the enzyme indoleamine-2,3-dioxygenase. Ingestion of large amounts of LT (median daily dose 1.5 gm) resulted in high concentrations of kynurenine-pathway metabolites in blood and extrahepatic tissues, which was accentuated in EMS patients and which may have played a significant role in the pathogenesis of the disease.

Neuroactive kynurenines in Lyme borreliosis

Although neurologic dysfunction occurs frequently in patients with Lyme borreliosis, it is rarely possible to demonstrate the causative organism within the neuraxis. This discordance could arise if neurologic symptoms were actually due to soluble neuromodulators produced in response to infection. Since immune stimulation is associated with the production of quinolinic acid (QUIN), an excitotoxin and N-methyl-D-aspartate (NMDA) agonist, we measured levels of CSF and serum QUIN, and lymphokines. Samples were obtained from 16 patients with CNS Borrelia burgdorferi infection, eight patients with Lyme encephalopathy (confusion without intra-CNS inflammation), and 45 controls. CSF QUIN was substantially elevated in patients with CNS Lyme and correlated strongly with CSF leukocytosis. In patients with encephalopathy, serum QUIN was elevated with corresponding increments in CSF QUIN. Lymphokine concentrations were not consistently elevated. We conclude that CSF QUIN is significantly elevated in B burgdorferi infection--dramatically in patients with CNS inflammation, less in encephalopathy. The presence of this known agonist of NMDA synaptic function--a receptor involved in learning, memory, and synaptic plasticity--may contribute to the neurologic and cognitive deficits seen in many Lyme disease patients.

Studies on CSF tryptophan metabolism in infantile spasms

Cerebrospinal fluid from 8 patients with infantile spasms (mean age: 6.1 months) was collected before treatment. The concentration of cerebrospinal fluid tryptophan metabolites was analyzed using high-performance liquid chromatography and compared to metabolite concentrations in cerebrospinal fluid from 20 age-matched controls (mean age: 5.8 months). The levels of cerebrospinal fluid serotonin, 5-hydroxyindoleacetic acid, and kynurenine were significantly lower in infantile spasm patients compared to controls (P less than .05). In contrast, the levels of cerebrospinal fluid 3-hydroxykynurenine were significantly higher in infantile spasm patients than in controls (P less than .05). There were no significant differences in the levels of cerebrospinal fluid tryptophan and 5-hydroxytryptophan. Although the study population was small, these findings suggest that the presence of seizures in infantile spasms is associated with a decrease in serotonergic metabolites which, in turn, may indicate a decrease in serotonergic activity, altered clearance of these metabolites, or altered turnover in the direction of 3-hydroxykynurenine. The perturbance caused by increased 3-hydroxykynurenine and decreased kynurenine in the homeostatic balance between these 2 tryptophan metabolites could further contribute to the pathogenesis of infantile spasms.

Changes in CSF neurotransmitters in infantile spasms

Cerebrospinal fluid (CSF) from 7 patients with infantile spasms (mean age: 6.7 months) was collected before and after treatment with adrenocorticotropic hormone (ACTH). The concentration of neurotransmitter metabolites was analyzed using high-performance liquid chromatography and compared to the metabolite concentration in the CSF from 7 age-matched controls (mean age: 6.1 months). Pretreatment levels of CSF 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid, 3-methoxy-4-hydroxyphenyl glycol (MHPG), and kynurenine were significantly lower in infantile spasm patients compared to controls. Following treatment, marked increases in 5-HIAA and decreases in kynurenine levels were observed in the CSF of the 5 infants whose seizures were eliminated or reduced by ACTH. In the 2 nonresponders 5-HIAA levels decreased. The level of MHPG was reduced slightly in 5 infants, including the 2 nonresponders, and was increased in 2 responders. CSF homovanillic acid levels increased in 4 infantile spasm infants and decreased in 3 following ACTH. These data demonstrate that the presence of seizures in infantile spasms is associated with a significant decrease in serotonergic activity and that elimination of seizures by ACTH is accompanied by increased serotonin turnover. The simultaneous increase of 5-HIAA and decrease of kynurenine, an alternate metabolite of tryptophan, suggests an underlying disturbance of tryptophan metabolism in infantile spasms. The possibility that elimination of seizures by ACTH may be related to decreased production of certain kynurenine metabolites, particularly quinolinic acid, is discussed.

Cerebrospinal fluid and serum neopterin and biopterin in D-retrovirus-infected rhesus macaques (Macaca mulatta): relationship to clinical and viral status

Increases in serum and cerebrospinal fluid (CSF) neopterin concentrations accompany many inflammatory diseases, including infection with HIV-1 and may reflect activation of guanosine triphosphate (GTP) cyclohydrolase 1 by gamma-interferon and other cytokines. In the present study, macaques with clinical simian AIDS (SAIDS) infected with the immunosuppressive type-D retrovirus D/1/California had increased concentrations of CSF neopterin but not of biopterin beginning soon after seroconversion. Normal neopterin concentrations in the CSF were found in macaques with SAIDS-related complex as well as asymptomatic, viremic macaques. CSF biopterin, serum neopterin and serum biopterin concentrations of D/1/California-infected macaques were not different from the levels in control animals. The increase in CSF neopterin may reflect local inflammatory responses and paralleled previously documented changes in L-tryptophan metabolism in these macaques. However, the absence of macrophage infiltrates in the brain of the infected macaques suggests a non-macrophage source of both increased CSF neopterin and tryptophan metabolites in the SAIDS macaques.

Increased cerebrospinal fluid quinolinic acid, kynurenic acid, and L-kynurenine in acute septicemia

Increases in brain quinolinic acid have been implicated in neurodegeneration and convulsions that may accompany infectious diseases. In three rhesus macaques (Macaca mulatta) with septicemia, both CSF and serum quinolinic acid concentrations were markedly elevated and were accompanied by increases in CSF kynurenic acid levels that were of a smaller magnitude. Elevated serum and CSF L-kynurenine concentrations also occurred and are consistent with activation of indoleamine-2,3-dioxygenase and increased substrate flux through the kynurenine pathway. Although it is probable that the marked increases in CSF quinolinic acid and kynurenic acid concentrations are reflected in the extracellular fluid space of brain, it remains to be determined whether the magnitude of such increases influences the activity of excitatory amino acid receptors in brain to produce excitotoxic pathology or noncytolytic disruption of functions mediated by excitatory amino acid receptors.

Studies on kynurenine in human cerebrospinal fluid: lowered levels in epilepsy

Kynurenine, tryptophan and 5-hydroxyindoleacetic acid were measured in human lumbar and cisternal cerebrospinal fluid (CSF) taken during pneumoencephalography. The results do not support the hypothesis that any substantial part of the CSF kynurenine is of central origin. However, the results suggest that CSF kynurenine is reduced in some epileptic subjects and this seems to be due to the disease rather than anticonvulsants. This finding is of interest in view of the reported convulsant effect of kynurenine in experimental animals.

Determination of kynurenine by a simple gas-liquid chromatographic method applicable to urine, plasma, brain and cerebrospinal fluid

A simple, sensitive and specific method for the determination of kynurenine is described. This is based on alkaline cleavage of kynurenine, followed by solvent extraction, trifluoroacetylation and gas--liquid chromatography with electron capture detection. Using this method kynurenine has been determined in urine and plasma, and for the first time in brain and cerebrospinal fluid. Increases in kynurenine in brain, plasma and urine are demonstrated following tryptophan administration to man and rat.