The tryptophan catabolite or kynurenine pathway in schizophrenia: meta-analysis reveals dissociations between central, serum, and plasma compartments.

The tryptophan catabolite (TRYCAT) pathway is implicated in the pathophysiology of schizophrenia (SCZ) since the rate-limiting enzyme indoleamine-dioxygenase (IDO) may be induced by inflammatory and oxidative stress mediators. This systematic review searched PubMed, Web of Science, and Google Scholar for papers published from inception until August 2021 and meta-analyzed the association between SCZ and TRYCATs in the central nervous system (CNS) and peripheral blood. We included 61 studies comprising 2813 patients and 2948 healthy controls. In the CNS we found a significant (p < 0.001) increase in the kynurenine/tryptophan (KYN/TRP) (standardized mean difference, SMD = 0.769, 95% confidence interval, CI: 0.456; 1.082) and kynurenic acid (KA)/KYN + TRP (SMD = 0.697, CI: 0.478-0.917) ratios, KA (SMD = 0.646, CI: 0.422; 0.909) and KYN (SMD = 1.238; CI: 0.590; 1.886), while the 3OH-kynurenine (3HK) + KYN-3-monooxygenase (KMO)/KYN ratio was significantly reduced (SMD = -1.089, CI: -1.682; -0.496). There were significant differences between KYN/TRP, (KYN + KA)/TRP, (3HK + KMO)/KYN, KA, and KYN levels among the CNS and peripheral blood, and among serum and plasma KYN. The only useful peripheral marker of CNS TRYCATs findings was the increased KYN/TRP ratio in serum (SMD = 0.211, CI: 0.056; 0.366, p = 0.007), but not in plasma. There was no significant increase in a neurotoxic composite score based on KYN, 3HK, and picolinic, xanthurenic, and quinolinic acid. SCZ is accompanied by increased IDO activity in the CNS and serum, and reduced KMO activity and a shift towards KA production in the CNS. This CNS TRYCATs profile indicates neuroprotective, negative immunoregulatory and anti-inflammatory effects. Peripheral blood levels of TRYCATs are dissociated from CNS findings except for a modest increase in serum IDO activity.

Brain Versus Blood: A Systematic Review on the Concordance Between Peripheral and Central Kynurenine Pathway Measures in Psychiatric Disorders.

Objective: Disturbances in the kynurenine pathway have been implicated in the pathophysiology of psychotic and mood disorders, as well as several other psychiatric illnesses. It remains uncertain however to what extent metabolite levels detectable in plasma or serum reflect brain kynurenine metabolism and other disease-specific pathophysiological changes. The primary objective of this systematic review was to investigate the concordance between peripheral and central (CSF or brain tissue) kynurenine metabolites. As secondary aims we describe their correlation with illness course, treatment response, and neuroanatomical abnormalities in psychiatric diseases. Methods: We performed a systematic literature search until February 2021 in PubMed. We included 27 original research articles describing a correlation between peripheral and central kynurenine metabolite measures in preclinical studies and human samples from patients suffering from neuropsychiatric disorders and other conditions. We also included 32 articles reporting associations between peripheral KP markers and symptom severity, CNS pathology or treatment response in schizophrenia, bipolar disorder or major depressive disorder. Results: For kynurenine and 3-hydroxykynurenine, moderate to strong concordance was found between peripheral and central concentrations not only in psychiatric disorders, but also in other (patho)physiological conditions. Despite discordant findings for other metabolites (mainly tryptophan and kynurenic acid), blood metabolite levels were associated with clinical symptoms and treatment response in psychiatric patients, as well as with observed neuroanatomical abnormalities and glial activity. Conclusion: Only kynurenine and 3-hydroxykynurenine demonstrated a consistent and reliable concordance between peripheral and central measures. Evidence from psychiatric studies on kynurenine pathway concordance is scarce, and more research is needed to determine the validity of peripheral kynurenine metabolite assessment as proxy markers for CNS processes. Peripheral kynurenine and 3-hydroxykynurenine may nonetheless represent valuable predictive and prognostic biomarker candidates for psychiatric disorders.

Dysregulated activities of proline-specific enzymes in septic shock patients (sepsis-2).

The proline-specific enzymes dipeptidyl peptidase 4 (DPP4), prolylcarboxypeptidase (PRCP), fibroblast activation protein α (FAP) and prolyl oligopeptidase (PREP) are known for their involvement in the immune system and blood pressure regulation. Only very limited information is currently available on their enzymatic activity and possible involvement in patients with sepsis and septic-shock. The activity of the enzymes was measured in EDTA-plasma of patients admitted to the intensive care unit (ICU): 40 septic shock patients (sepsis-2) and 22 ICU control patients after major intracranial surgery. These data were used to generate receiver operating characteristic (ROC) curves. A survival analysis (at 90 days) and an association study with other parameters was performed. PRCP (day 1) and PREP (all days) enzymatic activities were higher in septic shock patients compared to controls. In contrast, FAP and DPP4 were lower in these patients on all studied time points. Since large differences were found, ROC curves were generated and these yielded area under the curve (AUC) values for PREP, FAP and DPP4 of 0.88 (CI: 0.80-0.96), 0.94 (CI: 0.89-0.99) and 0.86 (CI: 0.77-0.95), respectively. PRCP had a lower predicting value with an AUC of 0.71 (CI: 0.58-0.83). A nominally significant association was observed between survival and the DPP4 enzymatic activity at day 1 (p<0.05), with a higher DPP4 activity being associated with an increase in survival. All four enzymes were dysregulated in septic shock patients. DPP4, FAP and PREP are good in discriminating between septic shock patients and ICU controls and should be further explored to see whether they are already dysregulated in earlier stages, opening perspectives for their further investigation as biomarkers in sepsis. DPP4 also shows potential as a prognostic biomarker. Additionally, the associations found warrant further research.

A mood state-specific interaction between kynurenine metabolism and inflammation is present in bipolar disorder.

OBJECTIVES: Cytokines are thought to contribute to the pathogenesis of psychiatric symptoms by kynurenine pathway activation. Kynurenine metabolites affect neurotransmission and can cause neurotoxicity. We measured inflammatory markers in patients with bipolar disorder (BD) and studied their relation to kynurenine metabolites and mood. METHODS: Patients with BD suffering from an acute mood episode were assigned to the depressive (n = 35) or (hypo)manic (n = 32) subgroup. Plasma levels of inflammatory markers [cytokines, C-reactive protein] and kynurenine metabolites [tryptophan (TRP), kynurenine (KYN), 3-hydroxykynurenine (3-HK), quinolinic acid (QA), kynurenic acid (KYNA)] were measured on 6 time points during 8 months follow-up. Biological marker levels in patients were compared to controls (n = 35) and correlated to scores on mood scales. Spearman correlations and linear mixed models were used for statistical analysis. RESULTS: Twenty patients of the manic subgroup, 29 of the depressive subgroup, and 30 controls completed the study. The manic subgroup had a rapid remission of mood symptoms, but in the depressive subgroup subsyndromal symptoms persisted. No differences in inflammation were found between groups. A strong correlation between tumor necrosis factor-α and KYN, KYN/TRP, 3-HK and QA (ρ > 0.60) was specific for the manic group, but only at baseline (during mania). The depressive subgroup had a lower neuroprotective ratio (KYNA/3-HK, P = .0004) and a strong association between interferon-y and kynurenine pathway activation (P < .0001). KYNA was low in both patient groups versus controls throughout the whole follow-up (P = .0008). CONCLUSIONS: Mania and chronic depressive symptoms in BD are accompanied by a strong interaction between inflammation and a potentially neurotoxic kynurenine metabolism.

Immune and Neuroendocrine Trait and State Markers in Psychotic Illness: Decreased Kynurenines Marking Psychotic Exacerbations.

Objective: Different patterns of immune system upregulation are present in the acute vs. post-treatment states of psychotic illness. We explored the existence of state and trait markers in the peripheral immune system and two immune-associated neuroendocrine pathways (IDO and GTP-CH1 pathway) in a longitudinal sample of psychosis patients. We also evaluated the association of these markers with neuropsychiatric symptomatology. Method: Plasma concentrations of peripheral blood markers were measured in a transdiagnostic group of 49 inpatients with acute psychosis and 52 matched healthy control subjects. Samples were obtained in patients within 48 h after hospital admission for an acute psychotic episode (before initiation of antipsychotics), after 1-2 weeks and again after 8 weeks of treatment. Kynurenine, kynurenic acid (KA), 3-hydroxykynurenine (3-HK), quinolinic acid (QA), phenylalanine, tyrosine, nitrite, and neopterin were measured using HPLC and LC-MS/MS analysis. Concentrations of CRP, CCL2 (MCP1) and cytokines were determined with multiplex immunoassay. PANSS interviews and cognitive tests were performed at baseline and follow-up. Mixed model analyses were used to identify trait and state markers. Results: Patients had significantly higher plasma concentrations of CRP, CCL2, IL1RA, and lower concentrations of KA and KA/Kyn at all time points (F7.5-17.5, all p < 0.001). Increased concentrations of IL6, IL8, IL1RA, TNFα, and CCL2 and decreased QA and 3-HK (F8.7-21.0, all p < 0.005) were found in the acute psychotic state and normalized after treatment. Low nitrite concentrations at admission rose sharply after initiation of antipsychotic medication (F42.4, p < 0.001). PANSS positive scale scores during the acute episode correlated with pro-inflammatory immune markers (r ≥ |0.5|), while negative scale scores correlated inversely with IDO pathway markers (r ≥ |0.4|). Normalization of KA and 3-HK levels between admission and follow-up corresponded to a larger improvement of negative symptoms (r = 0.5, p < 0.030) A reverse association was found between relative improvement of SDST scores and decreasing KA levels (r = 0.5, p < 0.010). Conclusion: The acute psychotic state is marked by state-specific increases of immune markers and decreases in peripheral IDO pathway markers. Increased CRP, CCL2, and IL1RA, and decreased KA and KA/Kyn are trait markers of psychotic illness.

Serum Tryptophan, Tryptophan Catabolites and Brain-derived Neurotrophic Factor in Subgroups of Youngsters with Autism Spectrum Disorders.

BACKGROUND: There is evidence that changes in neuro-immune responses coupled with dysfunctions in serotonin metabolism underpin the pathophysiology of autism spectrum disorders (ASD). OBJECTIVE: This study aimed to delineate whether ASD subgroups or characteristics show aberrations in tryptophan and brain-derived neurotrophic factor (BDNF) metabolism. METHODS: 65 individuals with ASD (diagnosed according to ICD criteria) and 30 healthy control patients were included. Measured were serum levels of tryptophan, kynurenine (KYN), kynurenic acid (KA), quinolinic acid (QA), BDNF and PRO-BDNF and total blood 5-HT and 5-OH-tryptophan (5-HTP). RESULTS: Elevated BDNF levels and lower tryptophan and KA levels were characteristics of both childhood autism and intellectual disability disorder, whilst elevated tryptophan and lower 5-HT synthesis were hallmarks of Asperger syndrome. A pathological MRI was associated with elevated tryptophan and lowered KA. Abnormal EEG results and dysmorphology were both associated with an elevated BDNF/ PRO-BDNF ratio. Any brain pathology and gastro-intestinal symptoms were accompanied by lowered KA. CONCLUSIONS: Increased BDNF production and changes in the metabolism of tryptophan are associated with many ASD characteristics, showing particularly strong associations with childhood autism and Intellectual and Developmental Disabilities. Peripheral BDNF and tryptophan metabolism appear to take part in the pathophysiology of autism spectrum disorders and their phenotypes.

Acute Ischemic Stroke Severity, Progression, and Outcome Relate to Changes in Dipeptidyl Peptidase IV and Fibroblast Activation Protein Activity.

Dipeptidyl peptidase IV (DPPIV) inhibition may be a promising therapeutic strategy for acute stroke treatment, given its potential to prolong the biological half-life of neuroprotective substrates. A related protease, fibroblast activation protein (FAP), was recently shown to inactivate the same substrates. Therefore, it should also be investigated as a potential target in stroke. The study aimed to investigate whether stroke severity and outcome correlate with DPPIV and FAP activities and their kinetics shortly after acute ischemic stroke. DPPIV and FAP activities were analyzed in the serum of 50 hyperacute stroke patients at admission, 1 day, 3 days, and 7 days after stroke onset and in 50 age-matched healthy controls. This was done as part of the Middelheim's Interdisciplinary Stroke Study. DPPIV activity tended to increase shortly after stroke compared to the control population. DPPIV and FAP activities steadily decreased in the first week after stroke onset. Higher infarct volumes (≥5 ml) and a more severe stroke (NIHSS >7) at admission were correlated with a stronger decrease in the activities of both enzymes. Moreover, these patients more often developed a progressive stroke, were more often institutionalized. Patients with a stronger increase in DPPIV activity at admission and decrease in the activity of both DPPIV and FAP during the first week after stroke onset had a more severe stroke and worse short-term outcomes.

Kynurenine Pathway in Autism Spectrum Disorders in Children.

BACKGROUND: There is increasing evidence that altered immune responses play a role in the pathogenesis of autism spectrum disorders (ASD), together with dysfunction of the serotonergic and glutamatergic systems. Since the kynurenine (KYN) pathway that degrades tryptophan (TRP) is activated in various neuroinflammatory states, we aimed to determine whether this pathway is activated in ASD. METHODS: Sixty-five pediatric ASD patients (including 52 boys) were enrolled from an epidemiological survey covering 2 counties in Norway; 30 (46.5%) of these patients were diagnosed with childhood autism, 16 (24.6%) with Asperger syndrome, 12 (18.5%) with atypical autism, 1 (1.5%) with Rett syndrome, and 6 (9.2%) with other ASD. The serum levels of the following markers were measured in the children with ASD and compared to those in 30 healthy children: TRP, KYN, kynurenic acid (KA), 3-hydroxykynurenine, and quinolinic acid. RESULTS: The mean serum level of KA was significantly lower in the ASD group than in the healthy controls (28.97 vs. 34.44 nM, p = 0.040), while the KYN/KA ratio was significantly higher in the ASD group (61.12 vs. 50.39, p = 0.006). The same relative values were found when comparing the childhood autism subgroup with the controls. Also, the mean serum level of TRP was significantly lower in children with a subdiagnosis of childhood autism than in those with Asperger syndrome (67.26 vs. 77.79 µM, p = 0.020). CONCLUSION: Our study indicates that there is an increased neurotoxic potential and also a possible lower KYN aminotransferase activity in ASD.

Increased plasma levels of competing amino acids, rather than lowered plasma tryptophan levels, are associated with a non-response to treatment in major depression.

Lowered plasma tryptophan (TRP) and TRP/competing amino acid (CAA) ratio may be involved in the pathophysiology of major depression (MDD). Increased cortisol and immune-inflammatory mediators in MDD may affect the availability of TRP to the brain. We investigated whether baseline or post-treatment TRP, CAAs and TRP/CAA ratio are associated with a treatment response in MDD and whether these effects may be mediated by cortisol or immune biomarkers. We included 50 medication-free MDD patients with a depressive episode (DSM diagnosis) and assessed symptom severity with the Inventory of Depressive Symptomatology (IDS) before and after treatment as usual for 12 weeks (endpoint). Plasma levels of TRP, CAAs, the ratio, cortisol, CRP and 6 selected cytokines were assayed. The primary outcome was a 50% reduction in the IDS, while the secondary was a remission of the depressive episode. In IDS non-responders, CAAs increased and the TRP/CAA ratio decreased, while in IDS responders CAAs decreased and the TRP/CAA ratio increased from baseline to endpoint. In patients who were still depressed at endpoint TRP and CAAs levels had increased from baseline, while in remitted patients no such effects were found. Increases in CAAs were inversely correlated with changes in interleukin-1 receptor antagonist levels. The results show that increased CAA levels from baseline to endpoint are associated with a non-response to treatment in MDD patients. This suggests that the mechanism underpinning the CAA-related treatment resistance may be related to changes in immune pathways. CAA levels and amino acid metabolism may be new drug targets in depression.

Multiprobe molecular imaging of an NMDA receptor hypofunction rat model for glutamatergic dysfunction.

There are many indications of a connection between abnormal glutamate transmission through N-methyl-d-aspartate (NMDA) receptor hypofunction and the occurrence of schizophrenia. The importance of metabotropic glutamate receptor subtype 5 (mGluR5) became generally recognized due to its physical link through anchor proteins with NMDAR. Neuroinflammation as well as the kynurenine (tryptophan catabolite; TRYCAT) pathway are equally considered as major contributors to the pathology. We aimed to investigate this interplay between glutamate release, neuronal activation and inflammatory markers, by using small-animal positron emission tomography (PET) in a rat model known to induce schizophrenia-like symptoms. Daily intraperitoneal injection of MK801 or saline were administered to induce the model together with N-Acetyl-cysteine (NAc) or saline as the treatment in 24 male Sprague Dawley rats for one month. Biweekly in vivo [(11)C]-ABP688 microPET was performed together with mGluR5 immunohistochemistry. Simultaneously, weekly in vivo [(18)F]-FDG microPET imaging data for glucose metabolism was acquired and microglial activation was investigated with biweekly in vivo [(18)F]-PBR111 scans versus OX42 immunohistochemistry. Finally, plasma samples were analyzed for TRYCAT metabolites. We show that chronic MK801 administration (and thus elevated endogenous glutamate) causes significant tissue loss in rat brain, enhances neuroinflammatory pathways and may upregulate mGluR5 expression.

Serum Phenylalanine, Tyrosine, and their Ratio in Acute Ischemic Stroke: on the Trail of a Biomarker?

Fast diagnosis and appropriate treatment are of utmost importance to improving the outcome in patients with acute ischemic stroke (AIS). A rapid and sensitive blood test for ischemic stroke is required. The aim of this study was to examine the usefulness of phenylalanine (PHE) and tyrosine (TYR) as diagnostic biomarkers in AIS. Serum levels of PHE and TYR, measured using HPLC, and their ratio (PHE/TYR) were compared between 45 patients with AIS and 40 healthy control subjects. The relationship between PHE/TYR and the serum levels of several cytokines were also examined. PHE/TYR was significantly higher in AIS patients than in healthy controls (1.75 vs 1.24, p < 0.001). A receiver operating characteristic (ROC) curve analysis of PHE/TYR in AIS patients relative to healthy controls revealed promising sensitivity and specificity, which at an optimal cutoff of 1.45 were 76 and 85 %, respectively. PHE/TYR was positively correlated with interleukin (IL)-1ß (r = 0.37, p = 0.011) and IL-6 (r = 0.33, p = 0.025). This study shows that PHE/TYR is highly elevated in the acute phase of AIS, and that this elevation is coupled to the inflammatory response. The ROC analysis documents the possible value of PHE/TYR as a biomarker for AIS and demonstrates its clinical potential as a blood-based test for AIS.

Ongoing episode of major depressive disorder is not associated with elevated plasma levels of kynurenine pathway markers.

BACKGROUND: It has been suggested that the development of depressive symptoms as a result of cytokine therapy is attributable to cytokine-induced elevated activity of the kynurenine pathway. The few studies of this mechanism in patients with common major depressive disorder (MDD) have yielded inconsistent results. The aim of the present study was to identify markers of the kynurenine pathway in a clinical MDD sample with increased cytokine levels. METHODS: Fifty medication-free MDD patients with a depressive episode and 34 healthy controls were included at baseline; the patients were followed for 12 weeks. Before initiating treatment, the patients were diagnosed and assessed for depressive symptoms and their blood was analyzed for tryptophan and its metabolites in the kynurenine pathway. The clinical assessments and metabolite measurements were repeated after 12 weeks of "treatment as usual". RESULTS: We did not find significant elevation of kynurenine plasma markers in patients with a depressive episode compared to healthy controls, despite elevated cytokine levels in the patients. Clinical depression scores were significantly reduced after 12 weeks, but no significant change in the plasma kynurenine pathway plasma markers was observed. CONCLUSION: The obtained results do not support the hypothesis that MDD depressive episodes are associated with elevated activity in the kynurenine pathway. This suggests that the pathophysiology underlying depressive episodes in common MDD differs from that of interferon induced depression. Our results warrant further study of the interplay between the kynurenine pathway and the cytokine activation patterns in these conditions.

Prolyl carboxypeptidase activity decline correlates with severity and short-term outcome in acute ischemic stroke.

Prolyl carboxypeptidase (PRCP) is an enzyme associated with cerebrovascular risk factors such as hypertension, diabetes mellitus, obesity and hyperlipidemia. We aim to evaluate the relation between serum PRCP activity and severity, evolution and outcome of acute ischemic stroke. We used a specific RP-HPLC activity assay to measure PRCP activity in serum of 50 stroke patients at admission, and at 24 h, 72 h and 7 days after stroke onset to assess correlations with stroke severity based on the National Institutes of Health Stroke scale score (NIHSS), infarct volume on brain MRI scan, stroke outcome based on the modified Rankin scale (mRS) and mortality at 3 months after stroke. The average PRCP activity in serum decreased significantly the first 24 h after stroke onset and returned to baseline values at day 7. High NIHSS scores and infarct volumes at admission were related with a more pronounced decrease of PRCP in the first 24 h after stroke (ΔPRCP24, r = 0.31, P < 0.05; r = 0.30, P < 0.05). In addition, patients who displayed a more pronounced decrease in PRCP levels during the first 24 h after stroke were more likely to be institutionalized upon discharge (n = 21) (ΔPRCP24 ± SD, 0.05 ± 0.10 U/L vs. 0.17 ± 0.14 U/L, P = 0.001). The decrease in PRCP levels in the first 24 h after stroke onset is associated with stroke severity and an unfavourable short-term stroke outcome.

Extended structure-activity relationship and pharmacokinetic investigation of (4-quinolinoyl)glycyl-2-cyanopyrrolidine inhibitors of fibroblast activation protein (FAP).

Fibroblast activation protein (FAP) is a serine protease related to dipeptidyl peptidase IV (DPPIV). It has been convincingly linked to multiple disease states involving remodeling of the extracellular matrix. FAP inhibition is investigated as a therapeutic option for several of these diseases, with most attention so far devoted to oncology applications. We previously discovered the N-4-quinolinoyl-Gly-(2S)-cyanoPro scaffold as a possible entry to highly potent and selective FAP inhibitors. In the present study, we explore in detail the structure-activity relationship around this core scaffold. We report extensively optimized compounds that display low nanomolar inhibitory potency and high selectivity against the related dipeptidyl peptidases (DPPs) DPPIV, DPP9, DPPII, and prolyl oligopeptidase (PREP). The log D values, plasma stabilities, and microsomal stabilities of selected compounds were found to be highly satisfactory. Pharmacokinetic evaluation in mice of selected inhibitors demonstrated high oral bioavailability, plasma half-life, and the potential to selectively and completely inhibit FAP in vivo.

Activation of the kynurenine pathway in the acute phase of stroke and its role in fatigue and depression following stroke.

Many stroke survivors suffer from poststroke fatigue (PSF) and poststroke depression (PSD), indicating the importance of increasing the base of knowledge about the mechanisms underlying these sequelae. The primary aim of this study was to determine whether activation of the kynurenine (KYN) pathway predicts subsequent fatigue or depression in acute ischemic stroke (AIS) patients. Acute serum levels of 5-hydroxytryptamine (5-HT), tryptophan (TRP) catabolites (TRYCATs), and competing amino acids, as well as subsequent fatigue and depression, were measured in 45 stroke patients. TRP index [=100 × TRP / (tyrosine + valine + phenylalanine + leucine + isoleucine)] was significantly lower in patients with a Fatigue Severity Scale (FSS) score of ≥4 at 12 months than in those with an FSS score of <4 (p = 0.039). Furthermore, the serum level of kynurenic acid in the acute stroke phase was significantly higher in patients with an FSS of score ≥4 at 18 months than in those with an FSS score of <4 (p = 0.026). These findings indicate that stroke patients with PSF have a lower bioavailability of TRP for 5-HT synthesis in the brain in the acute stroke phase. However, they also appear to have greater neuroprotective potential in that phase. In contrast to PSF, no predictors of PSD were found. These findings together with those of previous studies suggest that the immune response and indoleamine 2,3-dioxygenase activation that follows AIS can predict PSF but not PSD.

Validation of a specific prolylcarboxypeptidase activity assay and its suitability for plasma and serum measurements.

Prolylcarboxypeptidase (PRCP, EC 3.4.16.2), a lysosomal carboxypeptidase, was discovered 45 years ago. However, research has been hampered by a lack of well-validated assays that are needed to measure low activities in biological samples. Two reversed-phase high-performance liquid chromatography (RP-HPLC) methods for quantifying PRCP activity in crude homogenates and plasma samples were optimized and validated. PRCP activity was determined by measuring the hydrolysis of N-benzyloxycarbonyl-l-proline (Z-Pro)-Phe. The enzymatically formed Z-Pro and Phe were measured independently under different HPLC conditions. The in-house methods showed good precision, linearity, accuracy, and specificity. Based on Michaelis-Menten constants, Z-Pro-Phe was chosen over Z-Pro-Ala as the substrate of preference. Cross-reactivity studies with dipeptidyl peptidases (DPPs) 2, 4, and 9 and prolyl oligopeptidase (PREP) confirmed the specificity of the PRCP activity assay. The average PRCP activity in plasma and serum of 32 healthy individuals was found to be 0.65 ± 0.02 and 0.72 ± 0.03 U/L, respectively. Both methods can be used to measure PRCP activity specifically in different biological samples and are well suited to evaluate PRCP inhibitors. These well-validated methods are valuable tools for studying PRCP's role in cardiovascular diseases, stroke, inflammation, and metabolic syndrome.

Inflammation-induced catabolism of tryptophan and tyrosine in acute ischemic stroke.

Whether the inflammatory response that accompanies acute ischemic stroke induces the kynurenine pathway is currently a matter of conjecture. Activation of this pathway may disturb active metabolites. The aim of this study was thus to characterize the catabolism of tryptophan and tyrosine in acute ischemic stroke (AIS) patients, and its association with cytokines, C-reactive protein, and glucose. Serum levels of 5-hydroxytryptamine, tryptophan catabolites, and competing amino acids and significant ratios of these were measured in 45 AIS patients and compared to those of 40 control subjects. Furthermore, associations between the serum levels of these biomarkers and serum levels of cytokines, C-reactive protein, and glucose were determined. Significantly lower levels of tryptophan and tyrosine in the stroke group indicate increased tryptophan and tyrosine oxidation in acute ischemic stroke, while significantly lowered tryptophan index and tyrosine index indicate a reduced capacity for the synthesis of 5-hydroxytryptamine and catecholamines in the brain, respectively. Furthermore, our findings indicate that the proinflammatory response in acute ischemic stroke may be responsible for a reduced capacity for the biosynthesis of brain catecholamines and mediate neurotoxic effects. Meanwhile, the anti-inflammatory IL-10 may exert a neuroprotective effect and prevent the putative reduced capacity for 5-hydroxytryptamine synthesis in the brain. These mechanisms may be involved in several sequelae following stroke, such as cognitive impairment, depression, and fatigue.

Depressive symptoms in Crohn's disease: relationship with immune activation and tryptophan availability.

Crohn's disease (CD) is associated with immune activation and depressive symptoms. This study determines the impact of anti-tumor necrosis factor (TNF)-α treatment in CD patients on depressive symptoms and the degree to which tryptophan (TRP) availability and immune markers mediate this effect. Fifteen patients with CD, eligible for anti-TNF-α treatment were recruited. Disease activity (Harvey-Bradshaw Index (HBI), Crohn's Disease Activity Index (CDAI)), fatigue (Multidimensional Fatigue Inventory (MFI)), quality of life (Inflammatory Bowel Disease Questionnaire (IBDQ)), symptoms of depression and anxiety (Symptom Checklist (SCL-90), Beck Depression Inventory (BDI), Hamilton Depression Rating Scale (HDRS)), immune activation (acute phase proteins (APP)), zinc and TRP availability were assessed before treatment and after 2, 4 and 8 weeks. Anti-TNF-α increased IBDQ scores and reduced all depression scores; however only SCL-90 depression scores remained decreased after correction for HBI. Positive APPs decreased, while negative APPs increased after treatment. After correction for HBI, both level and percentage of γ fraction were associated with SCL-90 depression scores over time. After correction for HBI, patients with current/past depressive disorder displayed higher levels of positive APPs and lower levels of negative APPs and zinc. TRP availability remained invariant over time and there was no association between SCL-90 depression scores and TRP availability. Inflammatory reactions in CD are more evident in patients with comorbid depression, regardless of disease activity. Anti-TNF-α treatment in CD reduces depressive symptoms, in part independently of disease activity; there was no evidence that this effect was mediated by immune-induced changes in TRP availability.