0000000000056172
AUTHOR
Karlfried Groebe
Proliferative activity and tumorigenic conversion: impact on cellular metabolism in 3-D culture
Oxygen consumption, glucose, lactate, and ATP concentrations, as well as glucose and lactate turnover rates, have been studied in a three-dimensional carcinogenesis model of differently transformed rat embryo fibroblasts (spontaneously immortalized Rat1 and myc-transfected M1, and the ras-transfected, tumorigenic descendants Rat1-T1 and MR1) to determine metabolic alterations that accompany tumorigenic conversion. Various bioluminescence techniques, thymidine labeling, measurement of[Formula: see text] distributions with microelectrodes, and determination of cellular oxygen uptake rates (Q˙[Formula: see text]) have been applied. In the ras-transfected, tumorigenic spheroid types, the size d…
Time Courses of Erythrocytic Oxygenation in Capillaries of the Lung: Lower and Upper Bounds on Red Cell Transit Times
With the aid of a 2-dimensional computer simulation (Groebe and Thews, 1986), time courses of erythrocytic oxygen uptake in the lung were calculated.
Problems in Precise Measurement of Tidal Volumes
Respiratory gas flows and volumes can conveniently be measured by pneumo-tachography.3 However, the pneumotachographic signal depends on gas temperature, humidity, and composition, and therefore the achievable precision of measurement is limited to about 5–10%2,8 — which is not sufficient for determining the human ventilation distribution with satisfactory accuracy.6,7,5 As a — potentially more accurate — alternative, a plethysmographic method may be used in which the tested subject breathes out of and into bags that are suspended in a large tank of constant volume (Figure 1). Volume V and pressure P in the system (consisting of tank, tubings, valves, and the subject) are related via Boyle-…
Diameter Control in the Arteriolar Tree by Changes in Post-Capillary Resistance
Presently, the mechanisms underlying local adjustment of organ perfusion to the metabolic needs of the tissue are not well understood. Even though a large number of vasoactive substances is known to be released upon variations in tissue metabolism,24,28 the exact mechanisms of their action are unclear: Because diffusion is a slow and inefficient transport process for covering long distances, arterioles can only sense those changes in concentration and hence in release rate of these mediators with acceptable spatial and temporal resolution that originate from their immediate vicinity. On the other hand, perfusion needs to be regulated such that also the worst supplied tissue regions located …
Basic Mechanisms of Diffusive and Diffusion-Related Oxygen Transport in Biological Systems: A Review
In mammals, energy metabolism of active tissues requires permanent availability of oxygen. Because cessation of O 2 supply results in loss of organ function within seconds or minutes, continual feed of adequate amounts of O 2 to tissue is the most vital task for living organisms. For many years, it therefore has been one of the greatest challenges to physiologists to understand the mechanisms provided by nature to satisfy this need for oxygen.
Biological response of multicellular emt6 spheroids to exogenous lactate
The influence of elevated lactate concentrations, as found in tumor microregions, on cellular growth, viability, and metabolic state was studied employing the multicellular spheroid model. Spheroids of EMT6/Ro cells were cultured at 37 degrees C in 5% or 20% (v/v) oxygen, using stirred media with various concentrations of exogenous lactate ranging from 0.0 mM (standard conditions) to 20.0 mM. Elevated concentrations of exogenous lactate led to a considerable decrease of the maximum spheroid diameter at growth saturation, e.g., for 20% O2 from around 1700 microns to 700 microns in 0.0 and 20.0 mM lactate respectively. Histological investigations showed that the thickness of the viable cell r…
Glucose Diffusion Coefficients Determined from Concentration Profiles in Emt6 Tumor Spheroids Incubated in Radioactively Labeled L-Glucose
In order to theoretically assess tissue energetic status, conditions for substance exchange need to be known. One group of parameters important in this context are diffusion coefficients of nutrients and metabolic waste products which may be assessed by incubating spheroids in a medium containing tracer amounts of the radioactively labeled substance in question, for a defined period of time. In previous studies, the overall amount of 14C-labeled substance taken up by the spheroids was measured by scintillation counters (e.g.[1]), or the concentration of 3H-labeled substance in the spheroid center was determined by autoradiography and grain counting (e.g. [4]). From a number of such measurem…
Precapillary Servo Control of Blood Pressure and Postcapillary Adjustment of Flow to Tissue Metabolic Status
Background There are several shortcomings in current understanding of how the microvasculature maintains tissue homeostasis. Presently unresolved issues include (1) integration of the potentially conflicting needs for capillary perfusion and hydrostatic pressure regulation, (2) an understanding of signal transmission pathways for conveying information about tissue energetic status from undersupplied tissue sites to the arterioles, (3) accounting for the experimentally observed interrelations between precapillary and postcapillary resistances, and (4) an explanation of how precise local adjustment of perfusion to metabolic demands is achieved. Methods and Results A novel conceptualization o…
Oncogene-Associated Growth Behavior and Oxygenation of Multicellular Spheroids from Rat Embryo Fibroblasts
It is now well documented that naturally occurring and experimentally induced tumors develop by a multistep process involving different stages such as unlimited growth, metastasis, and invasiveness. There is much evidence that malignant transformation involves activation of oncogenes and/or loss of suppressor genes (= anti-oncogenes). The former fundamental class of genes, including the ras and myc families, are associated with cell proliferation and differentiation and may mediate tumor initiation, promotion and progression (for reviews see: Spandidos, 1985; Spandidos and Anderson, 1987, Weinberg, 1989).
Practical Applications of Models of Oxygen Supply, Diffusion, and Consumption
It is the objective of this paper to describe, what models of oxygen supply, diffusion, and consumption have been and can be used for and to discuss some common problems in employing mathematical models of O2 transport. In a first part, four typical fields for model applications are selected from the wide variety of former investigations and are illustrated with some recent examples.
Theoretical Analysis of Factors Influencing Recovery of Ventilation Distributions from Inert Gas Washout Data
For the quantitative analysis of intraregional ventilation inhomogeneities, one classically applies the inert gas washout method [7,24] in which an inert gas of negligible solubility in blood and tissue is washed into the lungs. After washin is complete, the inspiratory inert gas fraction is set to a smaller value and the time course of the mixed endexpiratory inert gas fraction during the subsequent inert gas washout is recorded. The determinants of this time course are: The endexpiratory alveolar volume at the instant of change in inspiratory inert gas fraction, the anatomical dead space, the gas exchange ratio, the respiratory frequency, the in- and expiratory tidal volumes, and the inho…
Regulation of Local Perfusion
The present paper is going to report some basic information on the regulation of local perfusion that is important for modeling the involved systems. Moreover, approaches to and problems in doing so are discussed.
O2Transport in Skeletal Muscle: Development of Concepts and Current State
When comparing oxygen consumption rates(V O2) of various organs — as shown in Fig. 1 —skeletal muscle is exceptional in two respects: Its consumption rate attains the second largest absolute value of all organs and may vary between rest (0.2 mlO 2.100g-1’• min -1 ) and maximum performance (16 m1O 2.100g-1 • min -1 for electrical stimulation) by a factor of 80, thus covering a range that is by far larger than in any other tissue. In order to understand muscle O 2 transport one has to identify transport mechanisms and evaluate their importance towards bringing about the observed high O 2 fluxes and allowing for their enormous variability.
Relating Measuring Signals From P O 2 Electrodes to Tissue P O 2: A Theoretical Study
Organ surface P O 2 measurement by oxygen sensitive electrodes has proved to be an efficient tool for monitoring changes in tissue oxygenation status in a number of experimental and clinical situations. A parameter giving more direct information is the P O 2 distribution within tissue cells which, however, can only be assessed by more invasive methods. To date, a quantitative relation between P O 2 electrode measurements and P O 2 in tissue cells has not been established. Part of this problem lies in the fact that any surface electrode P O 2 measurement is not confined to tissue cells but rather represents some average over P O 2 values in a certain volume containing not only tissue cells b…
Calibration of misonidazole labeling by simultaneous measurement of oxygen tension and labeling density in multicellular spheroids
To correlate misonidazole concentrations and oxygen pressures (Po2) at identical locations within EMT6/Ro multi-cell spheroids (mean diameters +/- SD: 867 +/- 20 microns), Po2 measurements were performed with oxygen-sensitive microelectrodes during incubation of these spheroids with tritiated misonidazole (10 mg/I; 445 microCi/mg). In each individual spheroid, Po2 profiles were correlated with the corresponding spatial distribution of misonidazole as quantified by conventional autoradiography and grain counting. To compare the oxygenation status of spheroids in the measuring chamber with that of spheroids in spinner culture, misonidazole labeling was performed in both environments following…
Three-dimensional cell culture induces novel proliferative and metabolic alterations associated with oncogenic transformation
To date, cell biological characteristics of oncogene-transfected cells have been investigated either in relatively homogeneous monolayer cultures or in heterogeneous tumors in vivo. To evaluate the emergence of cellular heterogeneity during tumor formation, we have established a multicellular spheroid system from an oncogene-dependent, genetically determined 2-stage carcinogenesis model for 3-dimensional growth under well-defined conditions. The effect of T24Ha-ras transfection on cellular growth, proliferation, cell viability and oxygenation was investigated using spontaneously immortalized (Rat1) and c-myc-transfected (M1) Fisher 344 rat embryo fibroblasts and a tumorigenic T24Ha-ras-tran…
Mathematical Modelling of Local Regulation of Blood Flow by Veno-Arterial Diffusion of Vasoactive Metabolites
It is widely accepted that vasoactive substances which are consumed or produced by tissue metabolism play a role in the adjustment of local perfusion rate to the metabolic needs of the tissue. In order to evoke a response of the vascular system, these substances — in the following for simplicity denoted by “vasodilators” even though oxygen, for example, is a vasoconstrictor — need to get into close contact with the small arterioles which represent the most powerful effectors in perfusion control. On the other hand, tissue sites in which supply with nutrients is most critical (“lethal corners”) and in which a vasodilator signal may be generated earliest, are located hundreds of µm away from …