Mathematical modeling of synergistic interaction of sequential thermoradiation action on mammalian cells

Data obtained by other authors for mammalian cells treated by sequential action of ionizing radiation and hyperthermia were used to estimate the dependence of synergistic enhancement ratio on the ratio of damages induced by these agents. Experimental results were described and interpreted by means of the mathematical model of synergism in accordance with which the synergism is expected to result from the additional lethal damage arising from the interaction of sublesions induced by both agents.     

Analysis of synergistic effects during thermoradiation exposure of bacteriophage T4 and Bacillus subtilis spores

Experimental data are interpreted in terms of a half-empiric model of synergism obtained for bacteriophage T4 and Bacillus subtilis spores exposed to ionizing radiation of different dose rates at elevated temperatures. The model permits to optimize the ratio of both factors for effective sterilization.     

Mathematical modeling of mortality dynamics of mammalian populations exposed to radiation

A mathematical model is developed which describes the dynamics of radiation-induced mortality of a non-homogeneous (in radiosensitivity) mammalian population. It relates statistical biometric functions with statistical and dynamic characteristics of a critical system in organism of specimens composing this population. The model involves two types of distributions, the normal and the log-normal, of population specimens with respect to the radiosensitivity of the critical system cells. This approach suggests a new pathway in developing the methods of radiation risk assessment.     

Mathematical modeling and analysis of glucose and glutamine utilization and regulation in cultures of continuous mammalian cells

A number of factors have been shown to affect the metabolism of glucose and glutamine in mammalian cells and their mechanisms have been partially elucidated. Despite these efforts, a quantitative knowledge of the significance of these factors, the regulation of glucose and glutamine utilization, and particularly the interactions of these two nutrients is still lacking. Controversies exist in the literature. To clarify some of these controversies, mathematical models are proposed in this work which enable to separate and identify the effects of individual factors. Experimental data from five cell lines obtained in batch, fed-batch, and continuous cultures, both under steady-state and transient conditions, were used to verify the model formulations. The resulting kinetic models successfully describe all these cultures. According to the models, the specific consumption rate of glucose (Q(Glc)) of continuous animal cells under normal culture conditions can be expressed as a sum of three parts: a part owing to cell growth; a part owing to glucose excess; and a part owing to glutamine regulation. The specific consumption rate of glutamine (q(Glc)7) can be expressed as a sum of only two parts: a part owing to cell growth; and a part owing to glutamine excess. Using the kinetic models the interaction and regulation of glucose and glutamine utilizations are quantitatively analyzed. The results indicate that, whereas q(Glc) is affected by glutamine, q(Gln) appears to be not or less significantly affected by glucose. It is also shown that the relative utilizations of glucose and glutamine by anabolism and catabolism are mainly affected by the residual concentrations of the respective compounds and are less sensitive to growth rate and the nature of growth limitation.(c) 1995 John Wiley & Sons, Inc.     

Mathematical modeling of nucleotide excision repair reveals efficiency of sequential assembly strategies

Nucleotide excision repair (NER) requires the concerted action of many different proteins that assemble at sites of damaged DNA in a sequential fashion. We have constructed a mathematical model delineating hallmarks and general characteristics for NER. We measured the assembly kinetics of the putative damage-recognition factor XPC-HR23B at sites of DNA damage in the nuclei of living cells. These and other in vivo kinetic data allowed us to scrutinize the dynamic behavior of the nucleotide excision repair process in detail. A sequential assembly mechanism appears remarkably advantageous in terms of repair efficiency. Alternative mechanisms for repairosome formation, including random assembly and preassembly, can readily become kinetically unfavorable. Based on the model, new experiments can be defined to gain further insight into this complex process and to critically test model predictions. Our work provides a kinetic framework for NER and rationalizes why many multiprotein processes within the cell nucleus show sequential assembly strategy.     

Mechanism of the cytotoxic action of formaldehyde on cultured mammalian cells

Induction and repair of DNA lesions cell inactivation and repair of potentially lethal damages (PLD) were studied after the treatment of cultured cells with formaldehyde. Formaldehyde induced the appearance of a rapidly sedimentating DNA--membrane complex. This complex may contain up to 50% of choline and no more than 3-5% of leucine or lysine incorporated in the acid insoluble cell fraction, Inhibition of DNA synthesis, induction of single strand DNA breaks and/or alkali-labile sites increased with the raise of formaldehyde concentration. A good correlation is observed between with the raise of formaldehyde concentration. A good correlation is observed between with the raise of formaldehyde concentration. A good correlation is observed between the increasing DNA quantities in the rapid sedimentation complex and the cell lethality.     

Cytostatic action of methylmercuric chloride on mammalian duodenal cells

Adult male mice of the ICR/Swiss Webster strain received a single intragastric administration of methylmercuric chloride 1,000 ppm, at dose levels of 5,10,15,20,25 and 30 mg/kg of body weight. The animals were killed six hours later. Tissue samples from the duodenum were fixed in 10% neutral buffered formalin for light microscopy. Chromosome clumping was observed in dividing cells at all dose levels, resembling a C-mitotic effect. It would lead to reduced mitotic cell formation on account of the subsequent lysis of the arrested metaphases. The cytostatic effect was brought about by the inactivation of the microtubule spindle fiber polymerization mechanism induced by methylmercuric chloride. There was a direct positive correlation between the varying dose levels of methylmercury and the proportion of cells arrested in metaphase in the crypts of the duodenum.     

Cryoprotective effects of D-allose on mammalian cells

D-allose, an aldo-hexose, is a rare sugar whose biological functions remain largely unclear. Recently, we demonstrated a novel inhibitory effect of D-allose on production of reactive oxygen species (ROS). Here, we focused on investigating cryoprotective effects of D-allose on cell viability. Mammalian cell lines including OVCAR-3 (human ovarian cancer), HeLa (human cervical cancer), HaCaT (human skin keratinocytes), HDF (human dermal fibroblasts) and NIH3T3 (murine fibroblasts) cells were frozen at -80 degrees C in culture media with various D-allose concentrations. Cells were allowed to recover for 24 h, 1 week or 1 month prior to survival assessment using the trypan blue dye exclusion test, when cell proliferation was evaluated by MTT assay. A beneficial protective role of D-allose on cell survival was found, similar to that of trehalose (disaccharide of glucose), a recognized cryoprotectant. The results suggest that D-allose as a sole additive may provide effective protection for mammalian cells during freezing. Practical studies now need to be performed with D-allose, for example to determine optimal freezing protocols and explore potential for preservation of tissues or organs at non-freezing temperatures.     

Mathematical modeling of calcium homeostasis in yeast cells

In this study, based on currently available experimental observations on protein level, we constructed a mathematical model to describe calcium homeostasis in normally growing yeast cells (Saccharomyces cerevisiae). Simulation results show that tightly controlled low cytosolic calcium ion level can be a natural result under the general mechanism of gene expression feedback control. The calmodulin (a sensor protein) behavior in our model cell agrees well with relevant observations in real cells. Moreover, our model can qualitatively reproduce the experimentally observed response curve of real yeast cell responding to step-like disturbance in extracellular calcium ion concentration. Further investigations show that the feedback control mechanism in our model is as robust as it is in real cells.     

Mathematical modeling of movement of cilia in olfactory cells

A mathematical model of the movement of olfactory cilia in different conditions was constructed. The realization of the model includes the development of a mechanical mathematical rheological model of the behavior of a continuous deformable medium, the development of the method of solution adapted to this problem, and obtaining a numerical solution, which takes into account different starting data. The mathematical modeling of the dynamic behavior of a deformable medium was performed using a system of equations for the dynamics of the deformable medium and the solution of the corresponding nonstationary system of equations in partial derivatives.     

Effects of thermoradiation on bacteria.

A 60Co source was used to determine the effects of thermoradiation on Achromobacter aquamarinus, Staphylococcus aureus, and vegetative and spore cells of Bacillus subtilis var. globigii. The rate of inactivation of these cultures, except vegetative-cell populations of B. subtilis, was exponential and in direct proportion to temperature. The D10 (dose that inactivates 90% of the microbial population) value for A. aquamarinus was 8.0 Krad at 25 degrees C and 4.9 Krad at 35 degrees C. For S. aureus, D10 was 9.8 and 5.3 Krad at 35 and 45 degrees C, respectively. Vegetative cells of B. subtilis demonstrated a rapid initial inactivation followed by a steady but decreased exponential rate. The D10 at 25 degrees C was 10.3 Krad, but at 35 and 45 degrees C this value was 6.2 and 3.8 Krad, respectively. Between 0 and 95 Krad, survival curves for B. subtilis spores at 75 degrees C showed slight inactivation, increasing in rat at and above 85 degrees C. The D10 values for spores at 85 and 90 degrees C were 129 and 92 Krad, respectively. Significant synergism between heat and irradiation was noted at 35 degrees C for A. aquamarinus and 45 degrees C for S. aureus. The presence of 0.1 mM cysteine in suspending media afforded protection to both cultures at these critical temperatures. On the other hand, cysteine sensitized B. subtilis spores at radiation doses greater than 100 Krad. The combined effect of heat and irradiation was more destructive to bacteria than either method alone.     

Mathematical modeling of marker influx and efflux in cells

The tumor promoter, phorbol 12-myristate 13-acetate (PMA), affects the processing of fluid that enters a cell from the ambient medium. Previous work showed that marker accumulates to a higher level in PMA-treated than in untreated cells. Since PMA also affects the physical activity of the membrane and stimulates the normal process of taking up extracellular fluid, called endocytosis, it is important to learn whether the perturbations in fluid processing can be attributed entirely to a change in the cell’s limiting membrane. To this end, a model for fluid uptake and processing was developed and applied to experiments in which a marker for extracellular fluid was added to cells. From previous work on marker accumulation, it was deduced that there were at least two functional compartments involved in fluid movement. Compartment I is a rapidly filling and rapidly recycling compartment. Compartment II is a slowly filling and emptying compartment. Three routes of vesicle traffic must be considered, one mediating influx from the ambient medium into compartment I, a second, efflux from compartment I to the medium, and a third efflux from compartment I into compartment II. Using earlier models for processing, workers found it difficult to estimate rates of movement through either of the latter routes, as well as the volume of compartment I. The difficulty arises from the fact that only one kinetic constant can be estimated directly from data, namely the instantaneous uptake rate. The remaining data depend on measuring the total mass of marker in the cells. Since the concentration of marker in the cell changes continuously, it is advantageous to employ differential equations to simulate the tracer movement. By applying the model to experimental values, we found estimates for all three rates of fluid movement and the volume of compartment I. It is thought that the model will enable us to determine whether apparent alterations in the time course of uptake arise solely from altered properties of the limiting membrane. This revised version submitted December, 2000. Research supported in part by a grant from the National Institutes of Health, R15 CA78322-01.     

Biological effects of Trichoderma harzianum peptaibols on mammalian cells

Trichoderma species isolated from water-damaged buildings were screened for toxicity by using boar sperm cells as indicator cells. The crude methanolic cell extract from Trichoderma harzianum strain ES39 inhibited the boar sperm cell motility at a low exposure concentration (50% effective concentration, 1 to 5 microg [dry weight] ml of extended boar semen(-1)). The same exposure concentration depleted the boar sperm cells of NADH(2). Inspection of the exposed boar sperm cells by transmission electron microscopy revealed damage to the plasma membrane. By using the black lipid membrane technique, it was shown that the semipurified metabolites (eluted from a SepPak C(18) cartridge) of T. harzianum strain ES39 induced voltage-dependent conductivity. The high-performance liquid chromatography-purified metabolites of T. harzianum strain ES39 dissipated the mitochondrial membrane potential (Deltapsi(m)) of human lung epithelial carcinoma cells (cell line A549). The semipurified metabolites (eluted from a SepPak C(18) cartridge) of T. harzianum strain ES39 were analyzed by mass spectrometry (MS). Matrix-assisted laser desorption ionization and nanoflow electrospray ionization MS revealed five major peptaibols, each of which contained 18 residues and had a mass ranging from 1,719 to 1,775 Da. Their partial amino acid sequences were determined by collision-induced dissociation tandem MS.     

Flow effects on the viability and lysis of suspended mammalian cells

A mouse myeloma cell line growing in suspension was subjected intermittently to flow through a sudden contraction and turbulent flow in a capillary tube. The probability of lysis per pass through the capillary tube increased with average wall shear stress level and with residence time per pass in the tube. Lysis was first observed at a threshold average wall shear stress level of 1800 dyn/cm². Although the flow caused lysis, it had no effect on cell viability.