Dietmar Fuchs

Kynurenine pathway metabolism and immune activation: Peripheral measurements in psychiatric and co-morbid conditions.

Immune activation is inextricably linked with dysregulation of the tryptophan metabolism, shifting catabolic routes towards oxidative breakdown along the kynurenine axis. Several enzymes are able to metabolize tryptophan, but activity of inducible indoleamine 2,3-dioxygenase (IDO-1) plays a major role under pro-inflammatory, interferon-γ (IFN-γ) dominated settings. Accelerated breakdown of tryptophan into kynurenine, dysregulation of further downstream metabolism and impaired enzymatic activities due to the absence of oxidation sensitive cofactors are associated with a broad variety of primary disorders and co-morbidities. Deprivation of the essential amino acid tryptophan suppresses growth of pathogens or tumor cells but also restricts T cell proliferation, which favors immunosuppression. In addition, diminished levels of tryptophan lead to lower synthesis of neurotransmitter serotonin, this being probably the most important biochemical cause of psychiatric co-morbidities associated with a broad variety of chronic inflammatory disorders. Also other frequent co-occurring symptoms and conditions such as anemia or cachexia may be at least partially caused by the lowered levels of the essential growth factor tryptophan. Tissue and cell specific expression of kynurenine downstream processing enzymes and their defective regulation may contribute to symptom diversification. Several kynurenine downstream metabolites show potent bioactivities, thus leading to the defects in a variety of affected target pathways. Measuring peripheral tryptophan breakdown, which is usually done by estimating the kynurenine to tryptophan ratio, in parallel to determination of other immune activation markers to confirm the involvement of IDO-1 activity in deregulated breakdown, is a reliable tool to monitor status and progression of a variety of disorders and has great potential to be applied to monitor treatments and to predict e.g. the necessity of psychiatric interventions before aggravation of symptoms, thus in helping to personalize therapeutic strategies. This article is part of the Special Issue entitled The Kynurenine Pathway in Health and Disease.

Intratumoral Th2 predisposition combines with an increased Th1 functional phenotype in clinical response to intravesical BCG in bladder cancer

Th1-type immunity is considered to be required for efficient response to BCG in bladder cancer, although Th2 predisposition of BCG responders has recently been reported. The aim was to evaluate the relationship of Th1 and Th2 components in 23 patients undergoing BCG treatment. Peripheral blood, serum and urine samples were prospectively collected at baseline, during and after BCG. Th1 (neopterin, tryptophan, kynurenine, kynurenine-to-tryptophan ratio (KTR), IL-12, IFN-γ, soluble TNF-R75 and IL-2Rα) and Th2 (IL-4, IL-10) biomarkers as well as CD4 expression in T helper (Th), effector and regulatory T cells were determined. Local immune cell subsets were measured on formalin-fixed, paraffin-embedded cancer tissue by immunohistochemistry to examine expression of transcription factors that control Th1 (T-bet) and Th2-type (GATA3) immunity. We confirmed a Th2 predisposition with a mean GATA3/T-bet ratio of 5.51. BCG responders showed significantly higher levels of urinary (pxa0=xa00.003) and serum neopterin (pxa0=xa00.012), kynurenine (pxa0=xa00.015), KTR (pxa0=xa00.005), IFN-γ (pxa0=xa00.005) and IL-12 (pxa0=xa00.003) during therapy, whereas levels of IL-10 decreased significantly (pxa0<xa00.001) compared to non-responders. GATA3/T-bet ratio correlated positively with serum neopterin (pxa0=xa00.008), IFN-γ (pxa0=xa00.013) and KTR (pxa0=xa00.018) after the first BCG instillation. We observed a significant increase in CD4 expression in the Th cell population (pxa0<xa00.05), with only a modest tendency toward higher frequency in responders compared to non-responders (pxa0=xa00.303). The combined assessment of GATA3/T-bet ratio, neopterin and KTR may be a useful biomarker in predicting BCG response. Th2-promoting factors such as GATA3 may trigger Th1-type immune responses and thus contribute to the BCG success.

Blood–brain barrier integrity, intrathecal immunoactivation, and neuronal injury in HIV

Objective: Although blood–brain barrier (BBB) impairment has been reported in HIV-infected individuals, characterization of this impairment has not been clearly defined. Methods: BBB integrity was measured by CSF/plasma albumin ratio in this cross-sectional study of 631 HIV-infected individuals and 71 controls. We also analyzed CSF and blood HIV RNA and neopterin, CSF leukocyte count, and neurofilament light chain protein (NFL) concentrations. The HIV-infected participants included untreated neuroasymptomatic patients, patients with untreated HIV-associated dementia (HAD), and participants on suppressive antiretroviral treatment (ART). Results: The albumin ratio was significantly increased in patients with HAD compared to all other groups. There were no significant differences between untreated neuroasymptomatic participants, treated participants, and controls. BBB integrity, however, correlated significantly with CSF leukocyte count, CSF HIV RNA, serum and CSF neopterin, and age in untreated neuroasymptomatic participants. In a multiple linear regression analysis, age, CSF neopterin, and CSF leukocyte count stood out as independent predictors of albumin ratio. A significant correlation was found between albumin ratio and CSF NFL in untreated neuroasymptomatic patients and in participants on ART. Albumin ratio, age, and CD4 cell count were confirmed as independent predictors of CSF NFL in multivariable analysis. Conclusions: BBB disruption was mainly found in patients with HAD, where BBB damage correlated with CNS immunoactivation. Albumin ratios also correlated with CSF inflammatory markers and NFL in untreated neuroasymptomatic participants. These findings give support to the association among BBB deterioration, intrathecal immunoactivation, and neuronal injury in untreated neuroasymptomatic HIV-infected individuals.

Blood-Brain Barrier Disruption Is Initiated During Primary HIV Infection and Not Rapidly Altered by Antiretroviral Therapy.

BackgroundnWe explored the establishment of abnormal blood-brain barrier (BBB) permeability and its relationship to neuropathogenesis during primary human immunodeficiency virus (HIV) infection by evaluating the cerebrospinal fluid (CSF) to serum albumin quotient (QAlb) in patients with primary HIV infection. We also analyzed effects of initiating combination antiretroviral therapy (cART).nnnMethodsnThe QAlb was measured in longitudinal observational studies of primary HIV infection. We analyzed trajectories of the QAlb before and after cART initiation, using mixed-effects models, and associations between the QAlb and the CSF level of neurofilament light chain (NFL), the ratio of N-acetylaspartate to creatinine levels (a magnetic resonance spectroscopy neuronal integrity biomarker), and neuropsychological performance.nnnResultsnThe baseline age-adjusted QAlb was elevated in 106 patients with primary HIV infection (median time of measurement, 91 days after infection), compared with that in 64 controls (P = .02). Before cART initiation, the QAlb increased over time in 84 participants with a normal baseline QAlb (P = .006) and decreased in 22 with a high baseline QAlb (P = .011). The QAlb did not change after a median cART duration of 398 days, initiated at a median interval of 225 days after infection (P = .174). The QAlb correlated with the NFL level at baseline (r = 0.497 and P < .001) and longitudinally (r = 0.555 and P < .001) and with the ratio of N-acetylaspartate to creatinine levels in parietal gray matter (r = -0.352 and P < .001 at baseline and r = -0.387 and P = .008 longitudinally) but not with neuropsychological performance.nnnConclusionnThe QAlb rises during primary HIV infection, associates with neuronal injury, and does not significantly improve over a year of treatment. BBB-associated neuropathogenesis in HIV-infected patients may initiate during primary infection.

No support for premature central nervous system aging in HIV-1 when measured by cerebrospinal fluid phosphorylated tau (p-tau)

ABSTRACT Background: The prevalence of neurocognitive deficits are reported to be high in HIV-1 positive patients, even with suppressive antiretroviral treatment, and it has been suggested that HIV can cause accelerated aging of the brain. In this study we measured phosphorylated tau (p-tau) in cerebrospinal fluid (CSF) as a potential marker for premature central nervous system (CNS) aging. P-tau increases with normal aging but is not affected by HIV-associated neurocognitive disorders. Methods: With a cross-sectional retrospective design, p-tau, total tau (t-tau), neopterin and HIV-RNA were measured in CSF together with plasma HIV-RNA and blood CD4+ T-cells of 225 HIV-infected patients <50 y of age, subdivided into 3 groups: untreated neuroasymptomatic (NA) (n = 145), on suppressive antiretroviral treatment (cART) (n = 49), and HIV-associated dementia (HAD) (n = 31). HIV-negative healthy subjects served as controls (n = 79). Results: P-tau was not significantly higher in any HIV-infected group compared to HIV-negative controls. Significant increases in t-tau were found as expected in patients with HAD compared to NA, cART, and control groups (p < 0.001 ). Conclusions: P-tau was not higher in HIV-infected patients compared to uninfected controls, thus failing to support a role for premature or accelerated brain aging in HIV infection.

Increased breakdown of kynurenine towards its neurotoxic branch in bipolar disorder

Introduction Bipolar disorder (BD) is a chronic psychiatric disease which can take most different and unpredictable courses. It is accompanied by unspecific brainstructural changes and cognitive decline. The neurobiological underpinnings of these processes are still unclear. Emerging evidence suggests that tryptophan catabolites (TRYCATs), which involve all metabolites of tryptophan towards the kynurenine (KYN) branch, are involved in the etiology as well as in the course of BD. They are proposed to be mediators of immune-inflammation and neurodegeneration. In this study we measured the levels of KYN and its main catabolites consisting of the neurotoxic hydroxykynurenine (3-HK), the more neuroprotective kynurenic acid (KYNA) and anthranilic acid (AA) and evaluated the ratios between end-products and substrates as proxies for the specific enzymatic activity (3-HK/KYN, KYNA/KYN, AA/KYN) as well as 3-HK/KYNA as a proxy for neurotoxic vs. neuroprotective end-product relation in individuals with BD compared to healthy controls (HC). Methods We took peripheral TRYCAT blood levels of 143 euthymic to mild depressive BD patients and 101 HC. For statistical analyses MANCOVA’s controlled for age, sex, body mass index, cardiovascular disease and smoking were performed. Results The levels of KYNA (F = 5,579; p <.05) were reduced in BD compared to HC. The enzymatic activity of the kynurenine-3-monooxygenase (KMO) reflected by the 3-HK/KYN ratio was increased in BD individuals compared to HC (F = 5,394; p <.05). Additionally the ratio of 3-HK/KYNA was increased in individuals with BD compared to healthy controls (F = 11,357; p <.01). Discussion In conclusion our findings subserve the concept of KYN -pathway alterations in the pathophysiology of BD. We present evidence of increased breakdown towards the neurotoxic branch in KYN metabolism even in a euthymic to mild depressive state in BD. From literature we know that depression and mania are accompanied by inflammatory states which should be capable to produce an even greater imbalance due to activation of key enzymes in the neurotoxic direction of KYN -conversion. These processes could finally be involved in the development of unspecific brain structural changes and cognitive deficits which are prevalent in BD. Further research should focus on state dependent changes in TRYCATs and its relation to cognition, brain structure and staging parameters.

Mechanisms of Inflammation-Associated Depression: Immune Influences on Tryptophan and Phenylalanine Metabolisms

Metabolic parameters have a direct role in the regulation of immune cell function. Thereby the inflammation-induced metabolism of aromatic amino acids, most importantly of tryptophan and phenylalanine, plays a central role. In addition, neuropsychiatric conditions that go along with disorders that are characterized by acute or chronic inflammation, such as the development of depression, decreased quality of life or cognitive impairments, are connected to disturbed amino acid and subsequent neurotransmitter metabolism.The bioanalytical procedures for the determination of concentrations of tryptophan and phenylalanine and their respective first stable intermediates kynurenine and tyrosine as well as some analytical finesses and potential sources of errors are discussed in this chapter. Monitoring of these immunometabolic parameters throughout therapies in addition to biomarkers of immune response and inflammation such as neopterin can be useful to determine disease progression but also to plan psychiatric interventions timely, thus to establish personalized treatments.

Changes in T Cell and Dendritic Cell Phenotype from Mid to Late Pregnancy Are Indicative of a Shift from Immune Tolerance to Immune Activation

During pregnancy, the mother allows the immunologically distinct fetoplacental unit to develop and grow. Opinions are divided as to whether this represents a state of fetal-specific tolerance or of a generalized suppression of the maternal immune system. We hypothesized that antigen-specific T cell responses are modulated by an inhibitory T cell phenotype and modified dendritic cell (DC) phenotype in a gestation-dependent manner. We analyzed changes in surface markers of peripheral blood T cells, ex vivo antigen-specific T cell responses, indoleamine 2,3-dioxygenase (IDO) activity (kynurenine/tryptophan ratio, KTR), plasma neopterin concentration, and the in vitro expression of progesterone-induced blocking factor (PIBF) in response to peripheral blood mononuclear cell culture with progesterone. We found that mid gestation is characterized by reduced antigen-specific T cell responses associated with (1) predominance of effector memory over other T cell subsets; (2) upregulation of inhibitory markers (programmed death ligand 1); (3) heightened response to progesterone (PIBF); and (4) reduced proportions of myeloid DC and concurrent IDO activity (KTR). Conversely, antigen-specific T cell responses normalized in late pregnancy and were associated with increased markers of T cell activation (CD38, neopterin). However, these changes occur with a simultaneous upregulation of immune suppressive mechanisms including apoptosis (CD95), coinhibition (TIM-3), and immune regulation (IL-10) through the course of pregnancy. Together, our data suggest that immune tolerance dominates in the second trimester and that it is gradually reversed in the third trimester in association with immune activation as the end of pregnancy approaches.

Frailty status in older adults is related to alterations in indoleamine 2,3-dioxygenase 1 and guanosine triphosphate cyclohydrolase I enzymatic pathways

BACKGROUNDnFrailty is a multidimensional syndrome correlated to the loss of homeostasis and increased vulnerability to stressors, which is associated with increase in the risk of disability, comorbidity, hospitalization, and death in the elderly. It is based on the interplay of physiological, psychological, social, and environmental factors.nnnOBJECTIVESnBecause aging involves a detrimental immune response, this work aimed to assess the possible role of chronic low-grade immune stimulation on frailty status in the elderly.nnnMETHODSnBiomarkers involved in indoleamine 2,3-dioxygenase 1 and guanosine triphosphate cyclohydrolase I enzymatic pathways (namely neopterin, tryptophan, kynurenine, phenylalanine, tyrosine, and nitrite) were analyzed in a population of Spanish older adults aged 65xa0years and above, and their relationships with frailty status were evaluated.nnnRESULTSnSignificant increases in neopterin levels, kynurenine/tryptophan ratio, and phenylalanine/tyrosine ratio, and significant decreases in tryptophan, nitrite and tyrosine concentrations in frail individuals compared with nonfrail persons were obtained. Significant correlations were also observed between immune biomarkers, indicating they change in parallel, thus, pointing to interrelated causes. Besides, reference ranges for a number of immune biomarkers in the population of robust older adults were established for the first time.nnnCONCLUSIONSnResults obtained in the present study are consistent with the idea that frailty status in the elderly is associated with an additional degree of immune stimulation, manifested in a more intense disturbance of indoleamine 2,3-dioxygenase 1 and guanosine triphosphate cyclohydrolase I pathways than in nonfrail or prefrail older adults.

Tryptophan breakdown and cognition in bipolar disorder

INTRODUCTIONnIt has been demonstrated that bipolar disorder (BD) is often accompanied by cognitive deficits across all subdomains including verbal memory, attention and executive functioning. Cognitive deficits are observed both during episodes of mania or depression, as well as during the euthymic phase. It has been proposed that chronic immune-mediated inflammation in the central nervous system results in alterations in neural structures that subserve cognitive function. Kynurenine is an intermediate in the inflammatory cascade and can be peripherally measured to proxy inflammatory activity. Herein, we sought to determine whether serum levels of kynurenine and/or its metabolites were associated with cognitive function in BD.nnnMETHODSnIn this investigation 68 euthymic individuals with BD according to DSM-IV completed a cognitive test battery to asses premorbid intelligence (Multiple Choice Word Test; MWT-B), verbal memory (California Verbal Learning Test; CVLT), attention (d2 Test of Attention; d2 test, Trail Making Test-A; TMT-A, Stroop word reading/Stroop color naming) and executive functioning (TMT-B, Stroop interference). In addition, fasting blood samples were taken and serum levels of kynurenine and its metabolites 3-hydroxykynurenine and kynurenic acid were analyzed. Subsequently ratios were formed from individual parameters. Patient data were compared with those of a mentally healthy control group (n=93).nnnRESULTSnIn male participants with BD only we found a significant negative correlation between the 3-hydroxykynurenine to kynurenic acid ratio and performance on the CVLT. Additionally, the kynurenine to 3-hydroxykynurenine ratio was associated with performance on a sub-score of the CVLT. Those associations were neither present in female individuals with BD nor in the control group.nnnDISCUSSIONnOur findings suggest that a shift towards the hydroxykynurenine arm of the kynurenine pathway may be associated with poorer memory performance due to its effects on neuronal functioning and neurogenesis in the hippocampus. Our results implicate a mechanistic role of central inflammatory processes in cognitive functions in adults with bipolar disorder.