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Biomedical subjects

B Wirleitner

Publications and source records attributed to B Wirleitner.

36 records · Page 2Linked to original sources
PubMed2001

Is hyperhomocysteinemia due to the oxidative depletion of folate rather than to insufficient dietary intake?

Hyperhomocysteinemia is considered as a risk factor for cardiovascular diseases. Usually, an inverse relationship exists between homocysteine and folate levels, and supplementation with folate lowers homocysteine concentrations in patients. Therefore, hyperhomocysteinemia is mainly ascribed to the insufficient dietary intake of folate. Hyperhomocysteinemia has also been observed in infections and inflammatory diseases. Oxidative stress appears to be involved in the pathogenesis of these disorders, and associations have been found between homocysteine and e.g., neopterin concentration. Increased neopterin concentration indicates immune system activation and also allows an estimate of thus elicited oxidative stress. It may be relevant that the active cofactor, tetrahydrofolate, is very susceptible to oxidation. Immunologically induced oxidative stress could lead to folate depletion resulting in hyperhomocysteinemia. Thus, hyperhomocysteinemia in patients can be considered as an indirect consequence of hyperconsumption of antioxidant vitamins during prolonged states of immune activation.

Dementia, Vascular↗
PubMed2000

Oxidation of 7,8-dihydroneopterin by hypochlorous acid yields neopterin.

In vitro, interferon-gamma stimulates primate monocytes/macrophages to produce the pteridines neopterin and 7,8-dihydroneopterin. These pteridines are capable of modulating the oxidative potential of reactive species. Neopterin is pro-oxidative whereas 7, 8-dihydroneopterin is an effective antioxidant. In the presence of oxygen, 7,8-dihydroneopterin is rapidly oxidized and after loosing the side chain 7,8-dihydroxanthopterin is formed. It is considered that under physiological conditions, 7,8-dihydroneopterin cannot be a source for neopterin production. In this study it is demonstrated that hypochlorous acid is capable to oxidize 7,8-dihydroneopterin yielding neopterin. Neopterin is less affected by hypochlorous acid, and in a mixture of both pteridines similar to the in vivo situation, only 7,8-dihydroneopterin is oxidized, thereby increasing the ratio towards neopterin. The findings may beat relevance for the in vivo situation since hypochlorous acid shifts the neopterin/7, 8-dihydroneopterin ratio towards the side of neopterin, hence probably increasing the oxidative potential in a micro-environment.

Chromatography, High Pressure Liquid↗
PubMed2000

Histamine suppresses neopterin production in the human myelomonocytoma cell line THP-1.

Histamine, an important inflammatory mediator in allergic diseases and asthma, was reported to have modulatory effects on T cells by down-regulating Th1-type cell cytokines like interleukin 2 (IL-2) and interferon-gamma (IFN-gamma). In this study we examined the effect of histamine and the histamine-receptor antagonists cimetidine and diphenhydramine on the production of neopterin after stimulation with IFN-gamma in the myelomonocytoma cell line THP-1. Increasing concentrations of histamine markedly suppressed IFN-gamma induced neopterin formation. Simultaneous preincubation of THP-1 cells with histamine, IFN-gamma and different concentrations of the H(2)-receptor antagonist cimetidine showed a clear antagonizing effect on neopterin formation. In contrast, the H(1)-receptor antagonist diphenhydramine was not able to abrogate the suppressive effect of histamine on neopterin production. Our results suggest, that histamine may be a potent inhibitor of effects or mechanisms induced by IFN-gamma in monocytes/macrophages. Cimetidine, and possibly other H(2)-receptor antagonists, may reverse down-regulatory actions of endogenously formed histamine on activated monocytic cells.

Adjuvants, Immunologic↗
PubMed2000

Enhanced tryptophan degradation in systemic lupus erythematosus.

In vitro and in vivo, tryptophan degradation was found to be associated with T cell functional loss and tolerance induction. In systemic lupus erythematosus (SLE) besides the Th2-type cytokine interleukin-10, Th1-type cytokines including interferon-gamma (IFN-gamma) are expressed especially during exacerbation of the disease. IFN-gamma stimulates the enzyme indoleamine (2,3)-dioxygenase (IDO) converting tryptophan to the metabolite kynurenine which in macrophages is subsequently degraded to other, partly neurotoxic compounds like quinolinic acid, and finally to nicrotinamides. We measured kynurenine and tryptophan concentrations in the sera of 55 SLE patients. In these patients, the concentrations of tryptophan (median, interquartile range: 53.9, 45.7-64.1 microM) were lower (p < 0.0001), and the kynurenine concentrations (2.45, 1.75-3.40 microM) were increased (p < 0.0005) compared to healthy blood donors (70.0, 63.8-80.6; 1.80, 1.45-2.27 microM, respectively). Also the kynurenine per tryptophan quotients (K/T), which allow to estimate IDO activity, were significantly higher in patients than in normals (0.043, 0.033-0.062 vs. 0.027, 0.021-0.030; p < 0.0001), indicating enhanced IDO-induced tryptophan degradation in SLE. There was no significant relationship between tryptophan, kynurenine and the SLEDAI, and also the correlation of K/T with SLEDAI was rather weak (rs = 0.243, p < 0.05). Higher K/T was found in patients presenting with serositis (p = 0.01), decrease of complement (c3, c4; p < 0.01) and blood count change (anemia, leucopenia, lymphopenia; p = 0.032) than in patients without such disease manifestations. The significant correlation found between K/T and neopterin (rs = 0.808, p < 0.001), a marker of immune activation, points to a role of immune activation to be responsible for tryptophan degradation in SLE patients.

Adult↗
PubMed2000

Reduced pteridine derivatives induce apoptosis in human neuronal NT2/HNT cells.

Elevated concentrations of the pteridine compound neopterin, usually accompanied by 7,8-dihydroneopterin were found in cerebrospinal fluids of patients with neurodegenerative diseases and central nervous system infections. Here, the potential of pteridines to induce apoptosis of the human neuronal cell line (NT2) was investigated. Reduced neopterin, biopterin- and folate derivatives led to a time-dependent increase of apoptosis of cells. In contrast, non-reduced pteridines did not significantly alter cell survival. After differentiation of neuronal precursor cells to neurons and astrocyte-like cells, similar effects were detected. Antioxidants partly protected NT2 from pteridines-induced apoptosis, suggesting the involvement of reactive oxygen intermediates. In vitro experiments using dichlorofluorescin-diacetate further indicated a direct formation of reactive oxygen species in cells. Results implicate that high concentrations of reduced pteridines, might contribute to the loss of neuronal cells in neurodegenerative diseases.

Acetylcysteine↗
PubMed2000

Inflammation marker 7,8-dihydroneopterin induces apoptosis of neurons and glial cells: a potential contribution to neurodegenerative processes.

Since neopterin is elevated in the cerebrospinal fluid of patients with inflammatory neurological disorders we investigated the source of neopterin in the brain and a possible contribution of biological active pteridines to the development of brain lesions. Astrocytic, neuronal and microglial cell lines were shown to be negative for neopterin production even after stimulation with interferon-gamma (IFN-gamma) indicating that infiltrating monocytes/macrophages might be responsible for neopterin level in CNS. Whereas neopterin did not affect viability of brain cells, its derivative 7,8-dihydroneopterin (7,8-DHN) induced dose-dependently cellular apoptosis in astrocytes and neurons probably via enhancement of nitric oxide synthase (iNOS) expression. This mechanism might represent a possible link between inflammation in the brain and neurodegeneration.

Acid Phosphatase↗
PubMed2000

Cellular immune activation, neopterin production, tryptophan degradation and the development of immunodeficiency.

Cellular (Th1-type) immune response is centrally involved in the pathogenesis of various diseases. Within the immunological cascades of Th1-type immunity, interferon gamma (IFN-gamma), among other cytokines, is critically involved. It triggers a series of immune-relevant reactions mostly directed towards forward regulation of the antigen specific immune response. However, in chronic states of immune activation, systemically increased IFN-gamma is no longer antigen specific and is associated with the development of immunodeficiency. IFN-gamma also stimulates the production of neopterin, a low-mass compound, in human monocytes/macrophages. Accordingly, neopterin concentrations in humans reflect the degree of Th1-type immune activation. Since IFN-gamma also stimulates the release of reactive oxygen species (ROS) from immunocompetents cells, the amount of neopterin produced also serves as an indirect estimate of oxidative stress. In parallel, IFN-gamma activates the degradation of tryptophan, which appears to limit the growth of intracellular pathogens and the proliferation of cells, including T lymphocytes. Thus, during persisting states of immune activation, the production of IFN-gamma is not only associated with forward regulation of the immune response, but also with immunosuppressive mechanisms. The increased formation of neopterin and degradation of tryptophan may result in a decreased T cell responsiveness and development of immunodeficiency.

Humans↗
PubMed1999

Formation of oxygen radicals in solutions of 7,8-dihydroneopterin.

Neopterin and 7,8-dihydroneopterin, two compounds which are secreted by activated macrophages, have been shown to interfere with radicals generated by cellular and certain chemical systems. Reduced pterins were reported to scavenge whereas aromatic pterins promoted or reduced radical mediated reactions or had no effect. However, recently it was found that high concentrations of 7, 8-dihydroneopterin enhanced luminol dependent chemiluminescence and T-cell apoptosis, suggesting an enhancement of free radical formation. In this study hydroxylation of salicylic acid was used for detection of hydroxyl radicals. It is shown that in solutions of 7,8-dihydroneopterin hydroxyl radicals were formed in the absence of any radical source. The presence of EDTA chelated iron enhanced hydroxyl radical formation. Whereas the addition of iron accelerated the hydroxylation reaction, 7,8-dihydroneopterin was responsible for the amount of hydroxylation products. In the presence of superoxide dismutase or catalase, as well as by helium purging, hydroxylation was inhibited. Our data suggest that in solutions of 7, 8-dihydroneopterin superoxide radicals are generated which are converted to hydroxyl radicals by Fenton or Haber-Weiss type reactions. While superoxide might be generated during autoxidation of ferrous iron, dihydroneopterin seems to be involved in regeneration of ferrous iron from the ferric form.

Catalase↗
PubMed1999

Neopterin-induced expression of intercellular adhesion molecule-1 (ICAM-1) in type II-like alveolar epithelial cells.

Production and release of proinflammatory mediators such as tumour necrosis factor-alpha and neopterin are common events following the activation of the cellular immune system. Concerning inflammatory disorders of the lung, e.g. sepsis or sarcoidosis, high serum neopterin levels have been reported to correlate well with the severity of the disease. These situations are often associated with an increased expression of ICAM-1 reported to be induced in type II alveolar epithelial cells. In our study we investigated the potential effects of neopterin on ICAM-1 synthesis in the type II-like pneumocyte cell line L2. Detection of ICAM-1 gene expression by reverse transcriptase-polymerase chain reaction revealed a dose-dependent effect of neopterin, with maximum impact following 12-h incubations. Comparable results were obtained when ICAM-1 protein synthesis was measured via a cell-based ELISA. In a second set of experiments we were able to show that coincubation of L2 cells with pyrrolidine dithiocarbamate (PDTC) significantly suppressed neopterin-induced ICAM-1 synthesis. Since PDTC is known to be a potent inhibitor of NF-kappaB, the stimulating effects of neopterin on ICAM-1 gene expression and protein generation may be mediated by activation of this transcription factor. From these data we conclude that neopterin stimulates ICAM-1 production in L2 cells. In vivo, these effects may contribute to the prolongation of the inflammatory response, including cytotoxic cell host defence mechanisms that impair the functions of the airway epithelium.

Animals↗
PubMed1999

Consequences of acute normovolaemic haemodilution on haemostasis during major orthopaedic surgery.

Acute preoperative normovolaemic haemodilution (NHD) is an accepted tool for reducing allogeneic blood transfusion requirements during surgery. At present, little is known of its impact on haemostasis. We have investigated the consequences of NHD on haemostasis by comparing conventional global tests (prothrombin time (PT), activated partial thromboplastin time (aPTT) with more specific measures of coagulation (prothrombin fragment 1 + 2 (F 1 + 2), thrombin-antithrombin III complex (TAT) and fibrinolysis (D-dimer (DD), plasmin-alpha 2-antiplasmin complex (PAP)). Blood samples were collected from two groups (NHD and controls) undergoing elective spinal surgery or pelvic osteotomy until day 3 after operation. The conventional global tests remained within normal limits: there were no significant differences between groups. Although surgery induced significant increases in the more specific measures of coagulation and fibrinolysis, there were no differences between NHD and control patients. Major orthopaedic surgery strongly activates coagulation and fibrinolysis. As the degree of these alterations was similar in haemodiluted and control patients, we suggest that acute preoperative normovolaemic haemodilution itself does not appear to be associated with greater perioperative disturbances in haemostasis.

Adult↗
PubMed1998

7,8-Dihydroneopterin-induced apoptosis in Jurkat T lymphocytes: a comparison with anti-Fas- and hydrogen peroxide-mediated cell death.

Activated cell-mediated immunity, associated for example with HIV infection, is accompanied by elevated concentrations of neopterin and 7,8-dihydroneopterin. Recent data have indicated a role of neopterin derivatives in virus activation and apoptotic cell death, processes likely to involve the action of oxygen free radicals. Because T cell death in AIDS is likely to involve the Fas/Fas ligand system and the action of oxygen free radicals and 7,8-dihydroneopterin, we compared the kinetics and sensitivity of apoptotic cell death of human leukemic Jurkat T cells to that of treatments with 7,8-dihydroneopterin, anti-Fas, and H2O2. Upon incubation with 5 mM 7,8-dihydroneopterin and 50 microM hydrogen peroxide over a period of 24 hr, bimodal kinetics were observed with peaks at 5.5 hr (7,8-dihydroneopterin, 13.1%; H2O2, 11.4%) and at 24 hr (7,8-dihydroneopterin, 11.2%; H2O2, 13.2%). In contrast, anti-Fas (20 ng/mL)-induced apoptosis increased steadily over time, peaking at 11 hr (43.2%). Interestingly, anti-Fas-induced apoptosis was suppressed upon co-incubation with 7,8-dihydroneopterin and H2O2 by 62% and 68%, respectively. We also compared the sensitivity to drug treatments of apoptosis induced by 7,8-dihydroneopterin, anti-Fas antibodies, and H2O2. 7,8-Dihydroneopterin-mediated, and similarly anti-Fas- and H2O2-mediated, apoptosis was not inhibited by a broad range of pharmacological inhibitors, such as actinomycin D, cycloheximide, cyclosporin A, and various protein kinase inhibitors. On the contrary, inhibitors with antioxidant abilities, such as pyrrolidinedithiocarbamate, significantly blocked 7,8-dihydroneopterin-, H2O2- as well as anti-Fas-mediated apoptosis. These results imply that 7,8-dihydroneopterin-, H2O2-, and anti-Fas-mediated cell death might involve related redox sensitive signal transduction pathways.

Antibodies↗
PubMed1998

Neopterin derivatives modulate the nitration of tyrosine by peroxynitrite.

The impact of neopterin and 7,8-dihydroneopterin on peroxynitrite-induced nitration of l-tyrosine was studied. Neopterin derivatives and peroxynitrite are formed during immune response. Tyrosine nitration represents one major effect of nitric oxide-mediated cytotoxicity. Peroxynitrite formed in situ was co-incubated with tyrosine and neopterin or 7,8-dihydroneopterin or other pteridine derivatives, respectively. The nitration product, 3-nitro-l-tyrosine, was measured by HPLC via UV absorption at 360 nm. Neopterin (200 microM) increased the nitration rate between pH 4.0 and 5.5 up to +60%. 7,8-Dihydroneopterin inhibited tyrosine nitration over the whole pH range examined. In a series of various pteridine derivatives, neopterin and 7,8-dihydroneopterin achieved the strongest modulating effects on tyrosine nitration. Interactions of peroxynitrite with hydroxypropyl side chains of fully aromatic pterin derivatives may increase nitration, while partially hydrated pyrazino ring structures abate the reactivity of peroxynitrite. The results of this study suggest a potential impact of neopterin derivatives on peroxynitrite-mediated cytotoxicity.

Hydrogen-Ion Concentration↗
PubMed1998

Neopterin induces nitric oxide-dependent apoptosis in rat vascular smooth muscle cells.

Numerous studies indicate that proinflammatory substances like tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) as well as macrophage-derived neopterin are increased in atherosclerotic tissue and thus are potentially involved in the process of atherogenesis. Since apoptotic death of vascular smooth muscle cells (VSMC) is reported to occur in atherosclerotic lesions, we investigated the effects of neopterin, TNF-alpha, and IFN-gamma on apoptosis in cultured VSMC. Morphological changes characteristic of apoptosis as well as DNA fragmentation were detected in cells treated with neopterin, TNF-alpha/IFN-gamma, and neopterin + TNF-alpha/IFN-gamma. Simultaneously, neopterin, TNF-alpha/IFN-gamma, and neopterin + TNF-alpha/IFN-gamma led to inducible nitric oxide synthase (iNOS) gene expression and nitric oxide (NO) synthesis. NO generation was significantly reduced when cells were cotreated with the competitive iNOS inhibitor aminoguanidine. This was accompanied by decreased percentual apoptosis as detected by FACS analysis using all kinds of stimuli. We conclude that neopterin as well as TNF-alpha/IFN-gamma are potent mediators of apoptotic death in VSMC which is at least in part triggered by NO synthesis induced by these proinflammatory mediators.

Animals↗
PubMed1996

Neopterin and 7,8-dihydroneopterin induce apoptosis in the rat alveolar epithelial cell line L2.

The neopterin derivatives, neopterin and 7,8-dihydroneopterin, modulate the cellular oxidant-antioxidant balance as well as the expression of the inducible nitric oxide synthase (iNOS) gene. Since apoptosis can be induced by reactive oxygen intermediates and nitric oxide (NO) we investigated whether these neopterin derivatives induce apoptotic cell death. As model we selected the rat alveolar epithelial cell line L2. 24 h incubation of neopterin (1-1000 microM) as well as 7,8-dihydroneopterin (1-1000 microM) resulted in a significant increase of percent apoptotic cells (measured by FACS analysis). Coincubation of both pteridines with the cytomix (interferon-gamma plus tumor necrosis factor-alpha) led to a significantly higher apoptosis than the cytomix alone. In contrast to the cytomix, no iNOS gene expression and no NO release could be detected after incubation with neopterin or 7,8-dihydroneopterin. We conclude that neopterin and 7,8-dihydroneopterin are per se inducers of apoptosis which is not mediated by nitric oxide. This may be of importance in inflammatory pulmonary diseases associated with an activation of the cellular immune system.

Animals↗
PubMed1996

Two different store-operated Ca2+ entry pathways in MDCK cells.

Whole cell patch clamp experiments in conjunction with Fura-2 fluorescence microscopy were performed to study the mechanisms of 'store-operated' (capacitative) Ca2+ entry. In MDCK cells, depletion of inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ stores activates a store-operated cation current (SOCC) predominantly selective for Ca2+ than for Na+ or Mn2+ [Delles C., Haller T., Dietl P. A highly calcium-selective cation current activated by intracellular calcium release in MDCK cells. J Physiol 1995, 486: 557-569]. In the presence of extracellular Ca2+, thapsigargin (TG) stimulated both SOCC and a Ca(2+)-dependent K+ current (IK(Ca)), reflecting stimulation of store-operated Ca2+ entry. The Ca2+ entry blocker 1-[3-(4-methoxyphenyl) propoxyl]-1-(4-methoxyphenyl)-ethyl-1H-imidazole HCI (SK&F96365; 30 microM) did not inhibit SOCC. At the same concentration, it exerted a transient partial inhibition on IK(Ca) activated by TG-induced Ca2+ entry. It did, however, not directly inhibit IK(Ca). This was demonstrated by an unchanged relationship between the cytosolic Ca2+ concentration ([Ca2+]i) and IK(Ca) in experiments where [Ca2+]i was measured under whole cell patch clamp conditions and by a lacking effect of SK&F96365 on IK(Ca) prestimulated by a high 'clamped' [Ca2+]i. La3+ partially, but not directly, inhibited the TG-induced IK(Ca) at a concentration (10 microM) sufficient to entirely block SOCC. La3+ and SK&F96365 in combination exerted an additive reduction on the TG-induced whole cell conductance (G) and completely blocked IK(Ca) stimulated by TG. We conclude that two Ca2+ entry pathways with different pharmacological and biophysical properties are involved in 'store-operated' Ca2+ entry in MDCK cells.

Animals↗
PubMed1995

Activation of L-type Ca2+ channels after purinoceptor stimulation by ATP in an alveolar epithelial cell (L2).

In the alveolar epithelium, ATP increases the intracellular Ca2+ concentration ([Ca2+]i) and stimulates the secretion of surfactant. We investigated the effects of extracellular ATP on the membrane potential (Vm), the whole cell current, and [Ca2+]i in a cloned rat alveolar epithelial cell line (L2). In microelectrode experiments, ATP caused a sustained depolarization of Vm, resulting from the activation of cation and Cl- conductances, as revealed by ion replacements. The depolarizing phase of the Vm shift was superimposed by Ca(2+)-dependent depolarizing spikes. Spikes were also induced by depolarizing Vm with charybdotoxin or maitotoxin. Replacement of bath Ca2+ with Ba2+ or Sr2+ also evoked repetitive spikes. Ca2+ (Ba2+, Sr2+)-induced spikes were unaffected by pretreatment with ionomycin or thapsigargin. They were, however, completely abolished by (+)-isradipine (100 nM) and stimulated by BAY K 8644 (100 nM). Whole cell L-type Ca2+ (Ba2+, Sr2+) currents were similarly abolished by (+)-isradipine and enhanced by BAY K 8644. L-type Ca2+ channels were further confirmed by demonstrating high-affinity dihydropyridine receptors stereoselectively labeled by (+)-[3H]-isradipine, apparent dissociation constant < 1 nM. In fura 2 experiments, ATP evoked a transient elevation of [Ca2+]i in the absence of Ca2+ and a biphasic sustained elevation in the presence of Ca2+, indicating intracellular Ca2+ release and Ca2+ entry. The ATP-induced fura 2 signals were unaffected by (+)-isradipine. We conclude that in L2 cells, L-type Ca2+ channels are activated after purinoceptor stimulation by ATP. The overall [Ca2+]i response is, however, mediated by Ca2+ entry through and (+)-isradipine-insensitive mechanism and by intracellular Ca2+ release.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMedDate not supplied

Increased neopterin concentrations in patients with cancer: indicator of oxidative stress?

In vitro, large amounts of neopterin are produced by human monocytes/macrophages upon stimulation with interferon-gamma. In vivo increased neopterin concentrations in human serum and urine indicate activation of cell-mediated (Th1-type) immune response, e.g., during virus infections, autoimmune diseases, allograft rejection and in certain types of malignancy. In various groups of patients with malignant diseases neopterin concentrations correlate to the stage of disease, and higher neopterin concentrations in serum, urine or ascitic fluid were shown to significantly predict worse prognosis regarding relapse and survival. The amounts of neopterin produced by activated monocytes/macrophages correlate with their capacity to release reactive oxygen species (ROS). With this background, neopterin concentrations in body fluids can be regarded as an indirect estimate of the degree of oxidative stress emerging during cell-mediated immune response. Moreover, recently neopterin was found itself to be capable of enhancing toxic effects induced by ROS. In vitro, neopterin derivatives were able to interfere with intracellular signal transduction pathways involved in, e.g., programmed cell death and the induction of proto-oncogene c-fos or nuclear factor-chi B. The data support the view that increased production of ROS--indicated by increased neopterin concentrations--could modulate the development, the proliferation and the survival of malignant cells.

Anemia↗