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Biomedical subjects

H Wachter

Publications and source records attributed to H Wachter.

At least 145 records · Page 8Linked to original sources
PubMed1993

Neopterin modulates toxicity mediated by reactive oxygen and chloride species.

Neopterin, a pyrazino-pyrimidine derivative, is synthesized in excess by human monocytes/macrophages upon stimulation with interferon-gamma, a cytokine derived from activated I cells. Neopterin is furthermore produced constitutively. A relatively constant ratio between neopterin and its reduced form. 7,8-dihydroneopterin, has been described in human serum. In the study presented here we tested the ability of neopterin and its reduced form to modulate the effects of cytotoxic substances like hydrogen peroxide or hypochlorous acid and N-chloramine derivatives. We show that 7,8-dihydroneopterin potently reduces biological and chemical effects of these substances independently from the pH value. In contrast, at slightly alkaline pH (pH 7.5) neopterin enhances hydrogen peroxide and chloramine-T activity. This is demonstrated by increase of signal intensity in a luminol assay and also by enhancement of toxicity towards bacteria. Thus, the macrophage derived substance neopterin is able both to enhance and to reduce cytotoxicity in dependence of pH value and its oxidation state, and it may have a pivotal role in modulation of macrophage mediated effector mechanism.

Animals↗
PubMed1993

Effect of pteridine derivatives on intracellular calcium concentration in human monocytic cells.

Pteridines are heterocyclic compounds which are synthesized and released by human monocytes/macrophages following stimulation by interferon-gamma. Their concentration in various body fluids proved to be indicative for the stimulation of the cellular immune system, and determination of pteridines has become an important diagnostic tool. We show that pteridine derivatives, namely neopterin (N), 7,8-dihydroneopterin (NH2), and 5,6,7,8-tetrahydrobiopterin (BH4) increase intracellular calcium (Cai) in human monocytic cells. Significant increases of Cai are observed at 10 nmol/l NH2, at 100 nmol/l BH4 and at 1 mol/l N, i.e. at concentrations encountered in vivo. At a concentration of 1 mumol/l, Cai is increased (from a control value of 145 +/- 7 nmol/l) to 464 +/- 62 nmol/l (NH2), 340 +/- 41 nmol/l (BH4) and 344 +/- 46 nmol/l (N), respectively. The increase of Cai depends on the presence of extracellular calcium and is likely to be due to activation of a calcium channel. We show that the absence of extracellular calcium or the addition of lanthanum ions to the extracellular fluid fully reverses the pteridine-induced increase of Cai. According to these observations, pteridines may mimic the effects of other inflammatory mediators on monocytic cells and seem to be involved in the crosstalk of immunocompetent cells.

Biopterins↗
PubMed1993

Pteridine biosynthesis in human endothelial cells. Impact on nitric oxide-mediated formation of cyclic GMP.

Stimulation of nitric oxide (NO) synthase in endothelial cells by Ca2+ influx leads to increased intracellular levels of cGMP. NO synthase from various sources is known to use tetrahydrobiopterin, flavins, and NADPH as cofactors. We studied the effect of interferon-gamma, tumor necrosis factor-alpha, and lipopolysaccharide on tetrahydrobiopterin biosynthetic activities in human umbilical vein endothelial cells (HUVEC). These stimuli led to an up to 40-fold increase of GTP cyclohydrolase I (EC 3.5.4.16) activity and to increased accumulation of neopterin and tetrahydrobiopterin in HUVEC. Further enzyme activities of tetrahydrobiopterin biosynthesis, i.e. 6-pyruvoyl tetrahydropterin synthase and sepiapterin reductase (EC 1.1.1.153), remained unchanged. NO synthase activity in protein fractions from homogenates of cells treated with interferon-gamma plus tumor necrosis factor-alpha was not influenced as compared with untreated controls. However, interferon-gamma alone or in combination with tumor necrosis factor-alpha significantly increased intracellular cGMP formation in intact HUVEC by 50 and 80%, respectively. These stimuli increased intracellular tetrahydrobiopterin concentrations up to 14-fold. NO-triggered cGMP formation was similarly increased by incubation of otherwise untreated cells with sepiapterin, leading to elevated intracellular tetrahydrobiopterin levels. Thus, cytokines indirectly stimulate the activity of constitutive NO synthase in HUVEC by upregulating production of the cofactor tetrahydrobiopterin.

Amino Acid Oxidoreductases↗
PubMed1993

Ca2+/calmodulin-dependent nitric oxide synthase activity in the human cervix carcinoma cell line ME-180.

We show here that the human cervix carcinoma cell line ME-180 expresses a constitutive nitric oxide (NO) synthase, as demonstrated by formation of [3H]citrulline and nitrite. The enzyme is dependent on tetrahydrobiopterin, NADPH, flavins and Ca2+/calmodulin. Enzyme activity is located in the cytosol rather than in the membrane fraction and can be inhibited by NG-monomethyl-L-arginine (NMMA). An antiserum to NO synthase purified from porcine cerebellum inhibited the enzyme activity. ME-180 cells released NO, as was shown by stimulation of guanylate cyclase (EC 4.6.1.2) in RFL-6 detector cells; this release was stimulated 8-fold by the Ca2+ ionophore A23187 and 2-fold by increasing the intracellular tetrahydrobiopterin levels with cytokines. This is the first characterization of a Ca2+/calmodulin-dependent NO synthase activity in human epithelial-type tumour cells.

Amino Acid Oxidoreductases↗
PubMed1993

Neopterin and prognosis in patients with adenocarcinoma of the colon.

Concentrations of neopterin, a sensitive indicator for the activation of cellular immunity, were measured in urine samples of 44 patients with adenocarcinoma of the colon at diagnosis. To judge the relative predictive value of neopterin concentrations, other routine clinical and laboratory variables were concomitantly determined. The patients were then followed up to 10 yr, and the abilities of all variables to predict death from cancer were assessed. Neopterin concentrations were not correlated with either tumor stage or Dukes' stage. In univariate analyses using the product-limit approach, four variables were significant indicators of poor prognosis: presence of distant metastases (P = 0.0001); high Dukes' stage (P = 0.0009); high urinary neopterin concentration (P = 0.0034); and advanced stage (P = 0.030). Presence versus absence of lymph node metastases was not associated with prognosis. Multivariate survival analyses by the proportional hazards technique demonstrated that neopterin provided statistically independent predictive information in addition to either presence versus absence of distant metastases or Dukes' stage. When neopterin and tumor stage were investigated for joint prediction, stage failed to be included in the model. Thus, neopterin concentrations provide valuable and statistically independent prognostic information in patients with adenocarcinoma of the colon.

Adenocarcinoma↗
PubMed1993

Translational regulation via iron-responsive elements by the nitric oxide/NO-synthase pathway.

Nitric oxide (NO) produced from L-arginine by NO synthases (NOS) is a transmitter known to be involved in diverse biological processes, including immunomodulation, neurotransmission and blood vessel dilatation. We describe a novel role of NO as a signaling molecule in post-transcriptional gene regulation. We demonstrate that induction of NOS in macrophage and non-macrophage cell lines activates RNA binding by iron regulatory factor (IRFs), the central trans regulator of mRNAs involved in cellular iron metabolism. NO-induced binding of IRF to iron-responsive elements (IRE) specifically represses the translation of transfected IRE-containing indicator mRNAs as well as the biosynthesis of the cellular iron storage protein ferritin. These findings define a new biological function of NO and identify a regulatory connection between the NO/NOS pathway and cellular iron metabolism.

Amino Acid Oxidoreductases↗
PubMed1993

Weight loss in patients with hematological neoplasias is associated with immune system stimulation.

Weight loss is the main symptom of so-called tumor cachexia. The pathogenetic mechanisms underlying cachexia are poorly understood; however, it appears that enhanced formation of cytokines such as interferon-gamma and tumor necrosis factor-alpha are involved. In 94 patients suffering from hematological neoplasias we compared body weight changes with serum neopterin, tryptophan, and kynurenine. Biochemical changes, the formation of neopterin, the degradation of tryptophan are closely related to interferon-gamma activity. The majority of our patients had increased neopterin and decreased tryptophan concentrations. Weight loss was seen particularly in patients with higher neopterin and lower tryptophan values. An association between higher neopterin levels and greater weight loss was apparent at study entry and during the follow-up of patients. Our data support the concept that weight loss is closely linked to endogenous interferon-gamma activity.

Biomarkers↗
PubMed1993

A note on the low-dimensional display of multivariate data using neural networks.

A novel neural network technique has been proposed (Livingstone et al. J. Mol. Graphics 1991, 9, 115-118) which is useful for a low-dimensional display of multivariate data sets. The method makes use of the activity values of the hidden neurons in a trained three-layer feed-forward network to produce the low-dimensional display. It was claimed that in contrast to conventional techniques, such as principal components analysis or nonlinear mapping, this technique could be used also to reconstruct, from a given point in the low-dimensional display, the corresponding multivariate input vector via the completely known weight matrices of a suitably trained network. We show here that this claim is unjustified in this general form. When previously unknown, grossly different input vectors are presented to the trained network, they can occupy, for example, exactly the same point in the low-dimensional display which is occupied also by a given training vector, if certain linear relationships between the vector components are fulfilled. Thus, an infinite set of different linearly dependent input vectors is projected onto one single point in the low-dimensional display. Reconstruction of a multivariate vector, starting from this point in the low-dimensional display, is able to lead back to only one multivariate vector (in the example given, to the original training vector).

Guanine↗
PubMed1993

Serum soluble tumour necrosis factor receptor 55 is increased in patients with haematological neoplasias and is associated with immune activation and weight loss.

Enhanced concentrations of soluble forms of the receptor for tumour necrosis factor (TNF)-alpha have been detected in the serum of cancer patients. We determined serum concentrations of soluble TNF receptor p55 (sTNF-R55) in patients with haematological neoplasias, 50 patients suffering from non-Hodgkin's lymphoma (n = 35), Hodgkin's disease (n = 10) and multiple myeloma (n = 5). Compared with healthy controls and with patients with potential thyroid disease, significantly elevated concentrations of sTNF-R55 were found (mean +/- standard error: 2.68 +/- 0.22 vs. 1.23 +/- 0.21 ng/ml, P < 0.0001 and 2.18 +/- 0.32 ng/ml, P = 0.03). Likewise, neopterin concentrations were raised (19.6 +/- 3.66 vs. 5.3 +/- 0.25 nmol/l in controls, P < 0.0001). We found a significant correlation between sTNF-R55 and neopterin concentrations (Rs = 0.544, P < 0.001). Patients with weight loss showed higher sTNF-R55 concentrations than patients with stable weight. Our results confirm the relevance of sTNF-R55 concentrations in serum of patients with cancer.

Biopterins↗
PubMed1993

The prognostic value of nuclear roundness and neopterin in ovarian cancer.

The prognostic value of clinical factors, morphometric features and neopterin, a marker for macrophage activation, was investigated retrospectively in 68 ovarian carcinoma patients. Nuclear roundness was a good predictor of patient survival. About 50% of our patients showed neopterin concentrations above the cut-off level of 275 mumol/mol creatinine. Interestingly, those patients with elevated urinary neopterin concentration, and thus displaying a sign of activation of cell-mediated immunity, had a shorter survival than those with normal concentration. Applying a multivariate Cox regression analysis, the only independent parameters predicting patient survival were FIGO stage, residual disease, nuclear roundness and neopterin.

Adult↗