Rate Of Cell Damage Research Articles

A Two-State Cell Damage Model Under Hyperthermic Conditions: Theory and In Vitro Experiments

The ultimate goal of cancer treatment utilizing thermotherapy is to eradicate tumors and minimize damage to surrounding host tissues. To achieve this goal, it is important to develop an accurate cell damage model to characterize the population of cell death under various thermal conditions. The traditional Arrhenius model is often used to characterize the damaged cell population under the assumption that the rate of cell damage is proportional to exp(-EaRT), where Ea is the activation energy, R is the universal gas constant, and T is the absolute temperature. However, this model is unable to capture transition phenomena over the entire hyperthermia and ablation temperature range, particularly during the initial stage of heating. Inspired by classical statistical thermodynamic principles, we propose a general two-state model to characterize the entire cell population with two distinct and measurable subpopulations of cells, in which each cell is in one of the two microstates, viable (live) and damaged (dead), respectively. The resulting cell viability can be expressed as C(tau,T)=exp(-Phi(tau,T)kT)(1+exp(-Phi(tau,T)kT)), where k is a constant. The in vitro cell viability experiments revealed that the function Phi(tau,T) can be defined as a function that is linear in exposure time tau when the temperature T is fixed, and linear as well in terms of the reciprocal of temperature T when the variable tau is held as constant. To determine parameters in the function Phi(tau,T), we use in vitro cell viability data from the experiments conducted with human prostate cancerous (PC3) and normal (RWPE-1) cells exposed to thermotherapeutic protocols to correlate with the proposed cell damage model. Very good agreement between experimental data and the derived damage model is obtained. In addition, the new two-state model has the advantage that is less sensitive and more robust due to its well behaved model parameters.

Study of the Synergistic Effect on Hepatoma 22 Tumor Cells by Focused Ultrasound Activation of Hematoporphyrin

The synergistic effect of ultrasound and drugs on tumor cells is known as sonodynamic therapy (SDT). The purpose of this study was to evaluate the effects of SDT on lipid peroxidation and the activity of antioxidative enzymes in isolated hepatoma 22 (H-22) cells to better understand the bioeffects of SDT. The viability of cells was evaluated by the Trypan blue dye exclusion test. The morphologic changes of H-22 cells were observed by a scanning electron microscope immediately after treatment. The intracellular reactive oxygen species levels were detected by 2',7'-dichlorofluorescein diacetate. Colorimetry and enzymatic chemical methods were used to measure the lipid peroxidation levels and activities of key antioxidant enzymes (ie, superoxide dismutase, selenium-dependent glutathione peroxidase, and catalase) in H-22 tumor cells. Our experiments indicated that the ultrasonically induced cell damage rate was increased with 100-microg/mL hematoporphyrin, whereas no cell damage was observed with hematoporphyrin alone. Generation of reactive oxygen species in cell suspensions after SDT treatment was remarkably higher than in controls. The malondialdehyde content was remarkably enhanced, and antioxidative enzyme activities were obviously decreased compared with controls. This study suggests that oxygen free radicals may play an important role in improving membrane lipid peroxidation and decreasing the activities of key antioxidant enzymes in cells. It was speculated that this biological mechanism might be involved in mediating the killing effect of H-22 cells in SDT.

Study of cell killing effect on S180 by ultrasound activating protoporphyrin IX

The present study was initiated to investigate the potential biological mechanism of cell killing effect on isolate sarcoma 180 (S180) cells induced by ultrasound activating protoporphyrin IX (PPIX). S180 cells were exposed to ultrasound for 30s duration, at a frequency of 2.2MHz and an acoustic power of 3W/cm2 in the presence of 120μM PPIX. The viability of cells was evaluated using trypan blue staining. The generation of oxygen free radicals in cell suspensions was detected immediately after treatment using a reactive oxygen detection kit. A copper reagent colorimetry method was used to measure the level of FFAs released into cell suspensions by the process of cell damage induced by ultrasound and PPIX treatment. Oxidative stress was assessed by measuring the activities of key antioxidant enzymes (i.e., SOD, CAT, GSH-PX) in S180 tumor cells. Treatment with ultrasound and PPIX together increased the cell damage rate to 50.91%, while treatment with ultrasound alone gave a cell damage rate to 24.24%, and PPIX alone kept this rate unchanged. Colorimetry and enzymatic chemical methods showed that the level of FFAs in cell suspension increased significantly after the treatment, while the activity of all the above enzymes decreased in tumor cells at different levels, and were associated with the generation of oxygen free radicals in cell suspension after treatment. The results indicate that oxygen free radicals may play an important role in improving the membrane lipid peroxidation, degrading membrane phospholipids to release FFAs, and decreasing the activities of the key antioxidant enzymes in cells. This biological mechanism might be involved in mediating the effects on S180 cells and resulting in the cell damage seen with SDT.

The Cumulative and Sublethal Effects of Turbulence on Erythrocytes in a Stirred-Tank Model

Mechanical forces generated by prosthetic heart devices (artificial valves, artificial hearts, ventricular assist devices) have been known to cause damage and destruction of erythrocytes. Turbulent flow within such devices generates shear stresses and can induce cell damage. Current models of cell damage rate utilize only the power input per unit mass as a modeling parameter. A stirred-tank reactor provides for a more extensive characterization of turbulence through eddy scale calculations. Through a simplified model, turbulence can be characterized by evaluating the Kolmogorov microscale. Our analysis of erythrocyte rupture in a stirred tank reactor suggests that parameters such as eddy wavelength and eddy velocity may better characterize and model the turbulent damage. Further, hemolysis of red blood cells by turbulent effects has been shown to have a fixed rate for constant levels of power input. Damage inflicted on the remaining, intact erythrocytes (sublethal damage) was evaluated by exposure to turbulence followed by osmotic fragility (OF) testing. Logistic models were fit to the OF data indicating a significant osmotic sensitivity in the sublethal damaged population between control and turbulence-exposed cells (chi(2) test; p < 0.001). This susceptibility indicates a significant cell population more susceptible to destruction as a result of turbulent exposure. This work has therefore helped identify optimization parameters for evaluating cell damage potential when engineering cardiovascular prosthetic devices.

Determination of Effective Shear Rate in a Pilot-plant External Loop Airlift Reactor

Shear rate is an important design parameter in bio-reactors for its role in estimating cell-damage rate in shear-sensitive environment as well as in correlating hydrodynamics and mass transfer coefficients in non-Newtonian systems. One of the serious shortcomings in the analysis of non-Newtonian behaviour in airlift loop reactors is the lack of a reliable method for determining effective shear rate and viscosity appropriate to the airlift geometry.This work has been carried out in a pilot-plant external loop airlift reactor of 6.5 m in height and 0.225 m diameter of both riser and downcomer. Biological media were simulated using non-Newtonian solutions of xanthan gum and carboxymethyl cellulose. The resulting shear rates are compared to the available literature, and show an increase in shear rate with increasing superficial gas velocity. Also, it has been found that non-Newtonian solutions with similar rheological properties and different chemical structure have different shear rate trends at a given superficial gas velocity.

On the estimation of effective shear rate in external loop airlift reactors: non-Newtonian fluids

Abstract The determination of shear rate in column bioreactors is an important step to estimate the cell damage rate in shear-sensitive biosystems as well as for correlating hydrodynamic and mass transfer parameters. Due to the complexity of local shear rate measurement, it has been widely assumed that an average shear rate exists and is proportional to superficial gas velocity. The most serious shortcoming in the analysis of non-Newtonian behaviour in airlift reactors is the lack of a reliable method for determining a shear rate and an effective viscosity appropriate to the airlift geometry. Recently Shi et al. (Chem. Eng. Commun. 1990; 89: 22–35) presented an empirical correlation of effective shear rate as a function of superficial gas velocity and based on downcomer liquid circulation velocity. The external loop airlift reactor used by Shi et al. was 1.4 m in height, 0.194 m in riser diameter and 0.06 m in downcomer diameter. To validate Shi's et al. promising approach, this work has been carried out in a larger reactor of 6.5 m in height and 0.225 m in both riser and downcomer diameter. However, the rheological properties of the studied liquids and the superficial gas velocities were similar to those used by Shi et al.

Cell Damage and Oxygen Mass Transfer during Cultivation of Nicotiana tabacum in a Stirred‐Tank Bioreactor

AbstractCell damage and oxygen mass transfer were investigated during the batch culture of Nicotiana tabacum (tobacco) cells in a 3‐L Applikon stirred‐tank bioreactor equipped with a marine‐blade impeller. Total cell density, % culture viability, viable cell density, and kLa in the culture were measured over a 24‐day cultivation period at impeller speeds of 100–325 rpm under a fixed air flow of 0.43 wm and a temperature of 27 °C. The maximum total biomass density decreased from 11.8 g of dry cell weight (DCW)/L at 100 rpm to 8.6 g of DCW/L at 325 rpm. The net specific biomass production rate of viable cells (μv) during the exponential phase and the viable cell death rate (kd) during the stationary phase were estimated from semilog plots of viable cell density vs cultivation time. Values for μv decreased from 0.175 to 0.077 day−1 whereas values for kd increased from 0.042 to 0.109 day−1 with increasing impeller tip speed (from 24 to 77 cm/s), clearly showing that increasing agitation intensity increased the rate of cell damage. The effect was most pronounced at tip speeds of 24–60 cm/s. With respect to oxygen mass transfer, culture kLa values were about 10–20% higher than their corresponding initial kLa° values, but as the cell density increased, the values for kLa ultimately decreased. Despite the reduction in oxygen mass transfer rates, at impeller speeds of 100–325 rpm and an aeration rate of 0.43 wm, oxygen starvation was not observed. Therefore, the reduction in biomass productivity can be attributed to cell damage by hydrodynamic forces and not by inadequate oxygen mass transfer.

Cold lymphocytotoxic antibodies in systemic lupus erythematosus.

Optimum conditions were established for the assay of cold lymphocytotoxic antibodies (cLCTA) in serum from patients with systemic lupus erythematosus (SLE). The optimum temperature of the incubation step with complement was 15 degrees C. For target cells incubated with dextran a significantly higher percentage of damaged cells (p less than 0.005), a faster rate of cell damage (p less than 0.001) and a requirement for less complement was observed than for target cells not incubated with dextran. Under optimum conditions in the cytotoxicity assay, 62% of SLE sera damaged more than 60% of the target cells, whereas 73% of the sera from control donors damaged less than 20% of the target cells. In multiple serum samples obtained during follow-up of 30 patients with SLE, the serum cytotoxic activity or titer of cLCTA fluctuated and did not relate to clinical symptoms of disease activity. In sera obtained during active disease the cytotoxic activity was related to the anti-dsDNA antibody level and with levels of circulating immune complexes measured by the Raji cell assay and the indirect granulocyte phagocytosis test. We found no restricted reactivity of cLCTA against phenotypically distinct T-lymphocyte subpopulations with different immunoregulatory functions. The reactivity pattern of cLCTA towards the various T-lymphocyte subpopulations was not related to disease activity. We conclude that cLCTA in patients with SLE represent an epiphenomenon, being the result of a hyperreactive B-cell system rather than the cause of the disease.