Simon Geisler

Tryptophan breakdown is increased in euthymic overweight individuals with bipolar disorder: a preliminary report.

Individuals with bipolar disorder (BD) are disproportionately affected by symptoms of being overweight and metabolic syndrome when compared to the general population. The pertinence of this observation is underscored by observations that excess weight is associated with a more complex illness presentation, course, and outcome in BD. We present the first preliminary report of our BIPFAT study, which explored shared hypothesized pathophysiological pathways between being overweight and having BD.

Activated immune system and inflammation in healthy ageing: relevance for tryptophan and neopterin metabolism.

Immune activation not only accompanies inflammation in various disorders including infections, autoimmune syndromes and cancer, but it also represents a characteristic feature of ageing. Immune deviations which are most widely expressed in the elderly include increased neopterin production and tryptophan breakdown. These biochemical events result from the activation of the immune system and are preferentially triggered by pro-inflammatory stimuli, such as the Th1-type cytokine interferon-γ. They seem to play a role in the development of several age-related disorders and might be involved in the pathogenesis of common symptoms, including neurobehavioral disorders (e.g., cognitive and mood disturbances), anemia, cachexia, weight-loss but also immunodeficiency. Concentrations of the biomarkers neopterin and Kyn/Trp were found to be predictive of overall disease specific mortality in coronary artery disease, infections and various types of cancer. Immune activation and inflammation are also accompanied by high output of reactive oxygen species and thereby may lead to the development of oxidative stress and contribute to the vitamin deficiency which is often observed in the elderly. Accordingly, increases in neopterin were found to correlate with a substantial decline in key vitamins, including folate and vitamin-B6, - B12, -C, -D and -E.

Simultaneous measurement of phenylalanine and tyrosine by high performance liquid chromatography (HPLC) with fluorescence detection

OBJECTIVES An HPLC method was developed to quantify serum concentrations of phenylalanine and tyrosine simultaneously using fluorescence detection without derivatization. METHODS Serum protein is precipitated with trichloroacetic acid, 0.015mM dihydrogen-phosphate solution is used for separation on reversed-phase C18 material, and acetonitrile is avoided. Both amino acids are monitored utilizing their natural fluorescence at 210nm excitation and 302nm emission wavelengths. RESULTS One analytical run is completed within 7min. Lower detection limit for Phe and Tyr is 0.3μM. Comparison of the new method with a classical HPLC method for total amino acids and using UV-absorption detection reveals a highly significant relationship for Phe and Tyr. CONCLUSION The new HPLC method allows rapid and very sensitive measurement of phenylalanine and tyrosine concentrations.

Immune activation in patients with Alzheimer's disease is associated with high serum phenylalanine concentrations.

BACKGROUND Immune activation and inflammation represent critical factors in the pathogenesis of Alzheimers disease (AD) and are associated with increased blood concentrations of markers like neopterin and the kynurenine to tryptophan ratio (Kyn/Trp). In chronic inflammatory conditions, also increased serum phenylalanine concentrations and phenylalanine to tyrosine ratios (Phe/Tyr) were reported and could relate to neuropsychiatric symptoms. OBJECTIVE To examine serum phenylalanine and tyrosine concentrations in patients with AD and to compare results to neopterin and Kyn/Trp levels. MATERIALS AND METHODS Serum was collected from 43 patients with AD and concentrations of phenylalanine and tyrosine as well as neopterin, tryptophan and kynurenine were measured and Phe/Tyr and Kyn/Trp were calculated. RESULTS A subgroup of AD patients presented with increased phenylalanine and Phe/Tyr concentrations, phenylalanine levels correlated with neopterin (rs=0.329), kynurenine (rs=0.352) and Kyn/Trp levels (rs=0.288; all p<0.05). There was no significant relationship between phenylalanine metabolism and cognitive ability test scores mini-mental state examination and clock drawing test. CONCLUSIONS Higher serum phenylalanine concentrations related to immune activation are detectable in a subgroup of AD patients. The impaired conversion of phenylalanine may affect not only the production of tyrosine but also the biosynthesis of the neurotransmitters dopamine, norepinephrine and epinephrine. Further studies are justified in patients with AD to investigate a possible role of phenylalanine biochemistry in the development of neurovegetative and behavioral abnormalities.

TiO2 nanoparticles and bulk material stimulate human peripheral blood mononuclear cells

Highlights • Effects on immunobiochemical pathways of TiO2 materials were investigated in vitro.• TiO2 bulk and nanomaterial stimulated neopterin production in human PBMC.• There was no stimulatory influence of particles on tryptophan breakdown.• At high particles concentrations, tryptophan breakdown was suppressed.• Results suggest that the total effect of particles is even stronger pro-inflammatory.

Serum tryptophan, kynurenine, phenylalanine, tyrosine and neopterin concentrations in 100 healthy blood donors

Abstract Formation of neopterin, a biomarker of the activated human immune system, is linked with tryptophan (TRP) and phenylalanine (PHE) metabolism. To obtain normal values, in this study, serum concentrations of neopterin as well as of TRP, PHE and their respective metabolites kynurenine (KYN) and tyrosine (TYR) were investigated in 100 successive blood donor serum specimens from the University Clinics of Innsbruck, Austria. In addition, nitrite concentrations were determined. Donors had passed anamnestic examination at entry and were therefore considered as healthy. The mean age of participants was 49±11.4 (mean±SD) years; 18% were older than 60 years. Both genders were included in the analysis. Neopterin concentrations measured by enzyme-linked immunosorbent assay were 5.9±1.6 nmol/L (mean±SD). Levels of amino acids and metabolites were determined by HPLC. Mean KYN and TRP concentrations were 1.78±0.42 μmol/L and 67.4±10.2 μmol/L, respectively. KYN to TRP ratio (KYN/TRP), an estimate for the activity of tryptophan-degrading enzyme indoleamine 2,3-dioxygenase, was 26.7±6.2 μmol/mmol. Mean PHE and TYR concentrations were 65.2±11.1 μmol/L and 90.6±22.9 μmol/L. PHE to TYR ratio (PHE/TYR), an estimate for the activity of PHE-converting enzyme phenylalanine hydroxylase, was 0.75±0.14 μmol/μmol. Nitrite concentrations, estimated by Griess-Ilosvay reagent, were 44.9±32.0 μmol/L. Males were taller and heavier than females (both p<0.01), but body mass index did not differ. Males presented with significantly higher TRP and TYR concentrations than females (both p<0.05). There existed significant correlations between neopterin and KYN (rs=0.368), KYN/TRP (rs=0.453), TYR (rs=–0.267; all p<0.01) and PHE/TYR (rs=0.236; p<0.05) concentrations. Data indicate that also in a population of healthy individuals an association exists between “low-grade” immune activation as is indicated by slightly higher neopterin concentrations and biochemical alterations in the amino acid metabolism. Although minor, such changes may interfere with psychoneuroimmunological regulatory networks and thus be of clinical relevance.

Immunomodulatory properties of cacao extracts – potential consequences for medical applications

Anti-inflammatory properties of cacao, fruits of Theobroma cacao L. (Sterculiaceae), are well documented, and therapeutic applications are described for gastrointestinal, nervous, and cardiovascular abnormalities. Most, if not all of these disease conditions involve inflammation or immune activation processes. The pro-inflammatory cytokine interferon-γ (IFN-γ) and related biochemical pathways like tryptophan breakdown by indoleamine 2,3-dioxygenase (IDO) and neopterin formation are deeply involved in their pathogenesis. Neopterin concentrations and the kynurenine to tryptophan ratio (Kyn/Trp, an estimate of IDO activity) are elevated in a significant proportion of patients with virus infections, cancer, autoimmune syndrome, neurodegeneration, and coronary artery disease. Moreover, higher neopterin and Kyn/Trp concentrations are indicative for poor prognosis. When investigating the effect of aqueous or ethanolic extracts of cacao on IFN-γ, neopterin and Kyn/Trp concentrations in mitogen-stimulated human peripheral blood mononuclear cells, breakdown of tryptophan by IDO, and formation of neopterin and IFN-γ were dose-dependently suppressed. The effects observed in the cell-based assays are associated with the antioxidant activity of the cacao extracts as determined by the cell-free oxygen radical absorption capacity assay. The influence of cacao extracts on IDO activity could be of particular relevance for some of the beneficial health effects ascribed to cacao: tryptophan breakdown by IDO is strongly involved in immunoregulation, and the diminished availability of tryptophan limits the biosynthesis of neurotransmitter serotonin. The inhibition of tryptophan breakdown by cacao constituents could thus be relevant not only for immune system restoration in patients, but also contribute to mood elevation and thereby improve quality of life. However, the available data thus far are merely in vitro only and future studies need to investigate the influence of cacao on tryptophan metabolism in vivo.

Tryptophan Metabolism in Post-Withdrawal Alcohol-Dependent Patients

AIMS The aim of the study was to investigate the parameters of tryptophan and phenylalanine metabolism and their associations to immune system activation and to behavioural symptoms during medium-term withdrawal (4-12 weeks of abstinence) in alcohol-dependent patients. METHODS Biochemical assays and clinical assessments at the beginning of treatment (fourth week of alcohol abstinence in average) and prior to the discharge after 8 weeks of treatment. RESULTS Kynurenine to tryptophan ratio (Kyn/Trp) slightly correlated with neopterin levels in early post-withdrawal period (Week 4 of abstinence) but this association disappeared after 12 weeks of abstinence. Phenylalanine and tyrosine concentrations as well as phenylalanine to tyrosine ratio (Phe/Tyr) decreased between Weeks 4 and 12 of abstinence. Kynurenine and Kyn/Trp increased significantly at 12th week of abstinence when compared with the beginning of the study (Week 4 of abstinence). At Week 12, Kyn/Trp significantly correlated with such behavioural symptoms as fatigue, irritability and sleep disturbances. CONCLUSIONS Tryptophan breakdown in early stages may be influenced by the increased activity of indoleamine 2,3-dioxygenase but the increase of Kyn/Trp between Weeks 4 and 12 of abstinence seems to be independent of immune changes and correlates with behavioural symptoms in later stages of the post-withdrawal course. A possible role of kynurenine metabolites in mediation of the increased stress sensibility in post-withdrawal alcohol-dependent patients is discussed.

Immune activation and inflammation in patients with cardiovascular disease are associated with elevated phenylalanine-to-tyrosine ratios

Abstract Higher serum neopterin concentrations and kynurenine-to-tryptophan (Kyn/Trp) ratios are associated with increased mortality in patients with coronary artery disease (CAD). Preferentially, Th1-type cytokine interferon-γ stimulates tryptophan breakdown and neopterin production by GTP cyclohydrolase I (GCH-I) in parallel in monocyte-derived macrophages and dendritic cells. In other cells, activation of GCH-I leads to the formation of 5,6,7,8-tetrahydrobiopterin (BH4), the necessary cofactor of amino acid hydroxylases such as phenylalanine 4-hydroxylase (PAH) and nitric oxide synthases. In 31 CAD patients (70.3±9.9 years; 21 males, 10 females), we determined serum concentrations of phenylalanine, tyrosine, and Kyn/Trp by HPLC, neopterin by ELISA, and nitrite by the colorimetric Griess assay. The phenylalanine-to-tyrosine ratio (Phe/Tyr) served as an estimate of PAH enzyme activity. Elevated Phe/Tyr concentrations were detected in a subgroup of CAD patients and correlated with Kyn/Trp (r=0.396, p<0.05) and neopterin (r=0.354, p<0.05) and inversely with nitrite (r=–0.371, p<0.05) concentrations. Higher Phe/Tyr in patients is associated with immune activation and indicates subnormal PAH activity that might be involved in the precipitation of neuropsychiatric symptoms in CAD patients.

Immunological alterations in individuals exposed to metal(loid)s in the Panasqueira mining area, Central Portugal

Environmental studies performed in Panasqueira mine area (central Portugal) identified high concentrations of several metal(loid)s in environmental media, and individuals environmentally and occupationally exposed showed higher levels of As, Cr, Mg, Mn, Mo, Pb and Zn in blood, urine, hair and nails when compared to unexposed controls. To evaluate the presence of immunological alterations attributable to environmental contamination, we quantified neopterin, kynurenine, tryptophan, and nitrite concentrations in plasma, and analysed the percentage of several lymphocytes subsets, namely CD3(+), CD4(+) and CD8(+) T-cells, CD19(+) B-cells, and CD16(+)56(+) natural killer (NK) cells in a group of individuals previously tested for metal(loid) levels in different biological matrices. The environmentally exposed group had significantly lower levels of %CD8(+) and higher CD4(+)/CD8(+) ratios, whereas the occupationally exposed individuals showed significant decreases in %CD3(+) and %CD4(+), and significant increases in %CD16(+)56(+), when compared to controls. Analysed biomarkers were found to be influenced by age, particularly neopterin, kynurenine and kynurenine to tryptophan ratio (Kyn/Trp) with significantly higher levels in older individuals, and %CD3(+), %CD8(+) and %CD19(+) with significantly lower values in older individuals. Males environmentally exposed showed significantly lower values of %CD19(+) when compared to control females. The concentration of Pb in toenails was associated to the level of neopterin, kynurenine and Kyn/Trp ratio (all direct), and the concentration of Mn in blood to the level of %CD8(+), %CD19(+) (both inverse) and CD4(+)/CD8(+) ratio (direct). Overall our results show that the metal(loid) contamination in Panasqueira mine area induced immunotoxic effects in exposed populations, possibly increasing susceptibility to diseases.