Klaus-Dieter Schuster

Tamoxifen induces suppression of cell viability and apoptosis in the human hepatoblastoma cell line HepG2 via down‐regulation of telomerase activity

Background/Aims: Antiproliferative action of tamoxifen in the estrogen receptor‐α‐negative human hepatoblastoma cell line HepG2 was investigated.

An algebraic solution to dead space determination according to Fowler's graphical method

According to Fowlers method, anatomical dead space (VD) can be determined graphically or computer-aided by iteration procedures by which phase III of a fraction-volume expirogram F(V) is back-extrapolated by a straight line R(V). Whereas Fowler visually partitioned phase II into two equal areas bordered by F(V), R(V), and VD, in the present paper the area between F(V) and R(V) is set equal to the area of a trapezoid, one side of which is the unknown VD to be determined. We obtained two algebraic equations for both possible conditions, nonsloping and sloping alveolar plateau, and, as the main result, an even more general third equation that includes both Bohrs and Fowlers solution. The formulas exactly represent Fowlers graphical method and can be applied to all gases which are applicable in dead space determination. The derived equations were tested in experimental situations, showing equality between values of dead space determined by using the algebraic solution and the graphical method. Their major advantage is facilitating and speeding up computer-aided on-line determinations of VD.

The overall fractionation effect of isotopic oxygen molecules during oxygen transport and utilization in humans.

The aim of the study was to clarify (1) whether fractionation effects of isotopic oxygen molecules due to respiratory processes can be neglected in tracer studies, (2) whether additional information about respiratory processes can be obtained from measuring isotope fractionations. Experiments were performed on 7 healthy humans at rest. Samples were taken from inspiratory and expiratory gas. After having removed the carbon dioxide from the samples, the oxygen was completely burnt with graphite to CO2, and the 16O18O/16O2 ratio of the CO2 generated was analysed by mass spectrometry. The 16O18O/16O2 ratio of the expiratory gas was 0.21 +/- 0.07% greater than that of the inspiratory air. The overall rate constant for uptake, subsequent transport and utilization was higher for 16O2 by 0.91 +/- 0.24% than for 16O18O. These results together with model calculations including data from literature suggest: (1) the fractionation effects between 16O18O and 16O2 as well as between 18O2 and 16O2 are small enough for both isotopic species to be considered appropriate labels in the investigation of respiratory processes, (2) the effect measured could be due to limitations of oxygen transport by utilization, (3) additional processes such as the reaction of oxygen with hemoglobin could be involved in forming the overall fractionation effect.

Single-breath diffusing capacity of NO independent of inspiratory NO concentration in rabbits

Pulmonary diffusing capacity of NO (Dl NO) was determined by performing single-breath experiments on six anesthetized paralyzed supine rabbits, applying inspiratory concentrations of NO (Fi NO) within a range of 10 parts per million (ppm) ≤ Fi NO ≤ 800 ppm. Starting from residual volume, the rabbit lungs were inflated by 50 ml of a NO-nitrogen-containing indicator gas mixture. Breath-holding time was set at 0.1, 1, 3, 5, and 7 s. Alveolar partial pressure of NO was determined by analyzing the end-tidal portion from expirates, with the use of respiratory mass spectrometry. In the six animals, pulmonary diffusing capacity of NO averaged Dl NO = 1.92 ± 0.21 ml ⋅ mmHg-1 ⋅ min-1(mean ± SD value). Despite extreme variations in Fi NO, we found very similar Dl NOvalues, and in three rabbits we found identical values even at such different Fi NO levels of 80 ppm or 500, 20, or 200 ppm as well as 10 or 800 ppm. There was also no dependence of Dl NO on the respective duration of the single-breath maneuvers. In addition, the time course of NO removal from alveolar space was independent of applied Fi NOlevels. These results suggest that Dl NOdeterminations are neither affected by chemical reactions of NO in alveolar gas phase as well as in lung tissue nor biased by endogenous release of NO from pulmonary tissue. It is our conclusion that the single-breath diffusing capacity of NO is able to provide a measure of alveolar-capillary gas conductance that is not influenced by the biochemical reactions of NO.

Fractionation of Oxygen Isotopes Due to Equilibration of Oxygen with Hemoglobin

The aim of the study was to answer the question as to whether the chemical reaction of oxygen with hemoglobin exhibits a source of isotopic fractionation, which could be of significance in forming the overall fractionation effect of respiration recently determined in man. Investigations were performed on bovine hemoglobin solutions adjusted to normal values of Hb concentration and pH. After degassing in vacuo, the hemoglobin solution was equilibrated in a closed system with pure oxygen of suitable pressure so that oxygen saturation levels of 30, 50 and 100% were achieved. After complete equilibration, isotope analysis of oxygen by mass spectrometry resulted in 16O18O/16O2 ratios which were 0.35 +/- 0.02% lower in the oxygen bound to hemoglobin than that of the gas phase during all levels of oxygenation. Model calculations suggest the following: (1) the fractionation during oxygen uptake in the lung at rest is primarily determined by the reaction with hemoglobin, (2) the overall fractionation effect of respiration can be explained as due to single effects of the constituent processes when assuming the oxygen transport to be limited by utilization.

Pulmonary 15NO uptake in man.

Nitric oxide (NO) is commonly thought to reveal more precise values of pulmonary gas uptake through alveolar-capillary membranes (DL) than the normally used carbon monoxide (CO). Since such measurements are influenced by a significant endogenous NO delivery within human airways, we propose the use of the naturally occurring 15N-labelled stable nitric oxide isotope 15NO. It occurs with a relative abundance of 0.37% of the dominating isotope 14NO. Therefore, the endogenous 15NO production can be neglected. In the present pilot study we demonstrate the workability of 15NO in determining DL in healthy individuals. In seven female and 15 male volunteers, averaged values of DL increase with increasing mean alveolar volume as well as individual body height (P=0.000001). Due to the very high significance level obtained from the multiple regression analysis, we conclude that the application of 15NO establishes a novel approach to calculate standard values of DL. Such calculations can be employed to predict a reference for patients who suffer from pulmonary diffusion limitation.

Dependency of overall fractionation effect of respiration on hemoglobin concentration within blood at rest.

In this study it was investigated in which way varying hemoglobin concentrations within blood influence overall fractionation effect of respiration, meaning a change in composition of isotopic oxygen molecules 16O2 and 16O18O within oxygen transported during entire respiration. Since overall fractionation effect of respiration is known to consist of different fractionating and non-fractionating processes, measuring it under condition of anemia could be useful in relating changes in isotopic compositions of oxygen to limitations of entire oxygen transport caused by one or more of these processes. Experiments were performed on 6 patients suffering from various degrees of anemia of a variety of etiologies and on 6 healthy humans. All test subjects breathed air at rest. Samples from inspiratory and expiratory gas were taken in order to analyse 16O18O/16O2 ratios with the aid of respiratory mass spectrometry. Values of overall fractionation effect decreased with respect to a drop in hemoglobin concentration from 17.6 to 6.6 g/100 ml in terms of a linear relationship (r = 0.79) provided that values of overall fractionation effect were normalized so as to exclude the influence of varying ventilatory conditions. It could be shown that at a value of hemoglobin content of 6.6 g/100 ml, 16O2 was transported in preference to 16O18O with a 0.57% higher rate compared to a value of 0.78% obtained at a hemoglobin concentration of 17.6 g/100 ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigation of The Human Oxygen Transport System During Conditions of Rest and Increased Oxygen Consumption By Means of Fractionation Effects of Oxygen Isotopes

The aim of the study was to assess various pathways of the oxygen transport system at rest and ergometer work by the utility of information derivable from different behaviour of the isotopic oxygen molecules 16O2 and 16O18O during transport. 6 healthy humans were studied at rest and at different levels of ergometer work, ranging from 50 to 250 W. Isotope analysis was performed by applying a reference technique. Samples of inspiratory and expiratory gas, taken during steady state conditions, were analysed by a respiratory mass spectrometer on their 16O18O/16O2 ratios by comparing them with a reference gas of appropriate composition. Ventilatory minute volume, oxygen consumption and end-expiratory oxygen partial pressure were also measured. At rest, the delta IU-value quantifying the isotope effect of the overall oxygen transport amounted to 0.74 +/- 0.08%. During ergometer work, the fractionation factor steadily decreased with increasing oxygen consumption, yielding the regression line delta IU [%] = 0.74 -1.3.10(-4).VO2, where VO2 is oxygen consumption given in ml/min. With respect to oxygen transport from inspiratory gas to tissue, this result suggests: convective processes of oxygen transport become more limiting with increasing oxygen consumption, whereas diffusion does not become a major limiting step up to oxygen consumption rates of 3600 ml/min, otherwise a reverse relationship between fractionation factor and oxygen consumption should have been found.

Single-breath diffusing capacities for NO, CO and C18O2 in rabbits

Abstract Nitric oxide (NO) has been introduced recently for studying alveolar-capillary gas transfer. Due to extremely fast reaction kinetics for the association of NO with haemoglobin, pulmonary NO uptake is expected to depend only on diffusion, whereas in the case of carbon monoxide (CO) or oxygen-labelled carbon dioxide (C18O2) the alveolar-capillary transfer is, in addition, known to depend on a blood uptake component. To provide further data for NO, CO and C18O2, we determined the pulmonary diffusing capacities (DL) for the indicator gases mentioned, performing single-breath manoeuvres on ten rabbits. The inspired gas mixtures contained 0.05% NO and/or 0.2% CO or 1% C18O2 in nitrogen. Applying respiratory mass spectrometry to the expirates we obtained the following mean ± SD values: DL,NO/DL,CO = 3.55 ± 0.4, DL,C18O2/DL,NO = 6.0 ± 0.6, DL,C18O2/DL,CO = 21.4 ± 2.5. Graham’s law predicts DL ratios of 1.9 for NO/CO, 12 for C18O2/NO, and 23 for C18O2/CO. Thus we equally underestimated the predicted DL ratios for C18O2/NO and CO/NO by a factor of approximately 0.5. From this, and by excluding significant interactions between the indicator gases and lung tissues, we conclude that the closest approximation of the diffusive component of DL is indeed obtained by using NO.

Dependence of overall fractionation effect of respiration on ventilation at rest

The influence of ventilation on overall fractionation effect of respiration (δIU) between the stable isotopic oxygen molecules 16O2 and 16O18O is investigated by experiments performed on 6 healthy humans breathing air at rest. The δIU-values increase with rising ventilatory rate in terms of a linear relationship of ΔIU-values to alveolar partial pressure of oxygen PAQ2. The slope of that increase is calculated to be 0.078%. per 1 mmHg of increase in PAQ2. With the aid of a model of respiration, it is concluded that overall fractionation effect of respiration can be split into the contributing fractionating and non-fractionating processes.