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G Reibnegger

Publications and source records attributed to G Reibnegger.

At least 73 records · Page 4Linked to original sources
PubMed1993

Determination of renal clearance of neopterin by a pharmacokinetic approach.

Pharmacokinetic modelling was used to determine the glomerular filtration rate and tubular secretion of neopterin, a marker for cellular immune activation. The method involves parameter identification employing the transient venous plasma concentration profiles of marker substances. By combined i.v. injection of neopterin and inulin which is excreted exclusively via glomerular filtration, neopterin was shown to be excreted in addition to glomerular filtration, by tubular secretion: clearance of inulin, 112 (S.D. 2.2) ml/liter; clearance of neopterin, 499 (S.D. 79.7) ml/min. A pilot experiment using in addition p-amino hippuric acid suggests that neopterin and p-amino hippuric acid may employ the same carrier system for tubular secretion.

Adult↗
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

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

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

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↗
PubMed1993

Weight loss in HIV-1 infection is associated with immune activation.

OBJECTIVE: To assess the risk of developing weight loss, a decline in CD4+ T-cell count and AIDS-defining infections using urinary neopterin levels and CD4+ T-cell count. DESIGN: Retrospective record review. SETTING: A primary care clinic for patients at any stage of HIV infection at the University Hospital in Innsbruck, Austria, to which all patients with HIV-related diseases from the Austrian Tyrol are referred. PATIENTS, PARTICIPANTS: Seventy-nine out of the 311 HIV-seropositive individuals attending our clinic between July 1985 and December 1991 participated in the study. The selection was made after complete examination (clinical and laboratory) and follow-up of at least 6 months, up to 48 months (median, 28 months). Patients with severe diarrhoea were excluded. MAIN OUTCOME MEASURES: Correlation between body mass index, urinary neopterin and CD4+ T-cell count; development of AIDS-defining infections, weight loss, and a decline in CD4+ T-cells. Weight loss was recognized if > 10% of body weight, and there had been no concomitant AIDS-defining infection for at least 2 months. RESULTS: Initial urinary neopterin (P = 0.04), but not initial CD4+ T-cell count (P = 0.94), correlated with the body mass index obtained at the end of follow-up. Using the product-limit method, urinary neopterin predicted weight loss (P < 0.0001), decline in CD4+ T-cell count to < 200 x 10(6)/l (P = 0.006) and AIDS-defining infections (P = 0.009). CD4+ T-cell count was a better predictor of AIDS-defining infections (P < 0.0001) than of weight loss (P = 0.002). Results were confirmed by multivariate analysis. CONCLUSIONS: Weight loss > 10% of body weight is associated with immune activation.

AIDS-Related Opportunistic Infections↗
PubMed1993

Stimulated cellular immune system in patients with congestive heart failure.

In this cross-sectional study, we analysed serum concentrations of soluble markers of cellular immune activation, namely, interferon-gamma, neopterin (a product of activated macrophages), soluble interleukin-2 receptor, and soluble CD8, in 25 patients with congestive heart failure. Ten (40%) patients showed increased concentrations (i.e. above the reference ranges of healthy controls) of neopterin, 14 (56%) showed increased soluble interleukin-2 receptor, and 6 (24%) showed increased soluble CD8. Endogenous interferon-gamma was detectable in 10 patients (40%). In addition, we found significant correlations between neopterin and interferon-gamma (rs = 0.417, p < 0.05), and between neopterin and soluble CD8 concentrations (rs = 0.430, p < 0.05). All patients with increased soluble CD8 also had increased soluble interleukin-2 receptor. However, no significant correlations of soluble interleukin-2 receptor with soluble CD8 or any of the other quantities were observed. Increased concentrations of soluble interleukin-2 receptors, soluble CD8 and neopterin indicate that cellular immunity is stimulated in patients with congestive heart failure. Activated CD8-positive T-lymphocytes may represent the source of increased soluble CD8. Endogenous interferon-gamma, which is derived from activated T-cells, may induce neopterin release by monocytes/macrophages.

Adult↗
PubMed1993

Self-organizing neural networks as a means of cluster analysis in clinical chemistry.

Connectionist systems (often termed "neural networks") are an alternative way to solve data processing tasks. They differ radically from conventional "von-Neumann" computing devices. Recent work on neural networks in clinical chemistry was done using supervised learning schemes, resulting in models which resemble classical discriminant analysis. The aim of the present study is to make clinical chemists familiar with basic concepts of self-organizing neural networks employing unsupervised learning schemes. Using a benchmark data set on the composition of milk from 22 different mammals, it is demonstrated that self-organizing neural networks are capable of performing tasks similar to classical cluster analysis and principal component analysis. Self-organizing neural networks could be envisaged to provide an alternative way for reducing the dimensionality of complex multivariate data sets, thus producing easily comprehensible low-dimensional "maps" of essential features.

Animals↗
PubMed1993

The role of neopterin in assessing disease activity in Crohn's disease: classification and regression trees.

Neopterin, a product of human monocytes/macrophages stimulated by gamma-interferon, was previously found to be correlated with clinical activity of Crohn's disease. The present investigation attempted to identify more precisely the role of neopterin for assessment of clinical activity in a multivariate setting. A broad panel of clinical and laboratory variables was obtained on 76 patients. Neopterin was determined in urine by high performance liquid chromatography. Using a 4-point clinical activity score as dependent variable, multivariate linear discriminant analyses were performed in order to identify subsets of statistically independent laboratory activity indices. Neopterin was shown to be an independent indicator for clinical activity. The significant variables were then tested together with the eight constituent variables of the Crohn's Disease Activity Index. The resulting model, which consisted of the three laboratory variables--erythrocyte sedimentation rate, serum protein and neopterin, together with pain score--was further subjected to two multivariate techniques for comparison: polychotomous logistic regression analysis and the technique of classification and regression trees. By all methods, neopterin was included into the multivariate models, confirming that its determination aids in the assessment of clinical activity in Crohn's disease.

Adult↗
PubMed1992

Critical study of consensus analysis.

Consensus analysis has been proposed as a statistical method by which the efficacy of clinical and laboratory tests of inflammatory activity can be assessed. This technique is claimed to overcome the need for an external "gold standard" as a reference method; instead, the consensus of all tests is used as the gold standard. We have evaluated the reliability of consensus analysis using data collected from patients with Crohn's disease. Our results demonstrate that the technique depends strongly on the correlation structure underlying the set of measures of disease used for analysis. This observation was supported by a series of conventional cluster analyses of the same set of variables. Furthermore, slight modifications of the algorithm had profound effects on the final result. We conclude that for the evaluation of tests of inflammatory activity, an external reference method, albeit an imperfect one, remains indispensable.

Clinical Laboratory Techniques↗