Cell death kinetics

Among the techniques discussed, moist heat is the most economical and efficient for the general sterilization requirements of fermentation. Therefore, the following four sections describe cell death kinetics and sterilization operations utilizing moist heat. 

Engasser JM, Geaugey V Pinton H (1991) Potential and pitfalls of using LDH release for the evaluation of animal cell death kinetics. In Spier R, Griffiths JB Meigner B (eds) Production of Biologicals from Animal Cells in Culture, pp. 569-575. Butterworth-Heinemann, Oxford. 

The cell preparation prior to analysis is time-consuming, requiring additional time for cell culture, cell staining, and washing steps, and thus, real-time monitoring of cell death kinetics is problematic. 

We address applications here in which closure problems are not encountered. Thus, the average behavior of the population can be obtained from solving the first-order product density equation, and average fluctuations (of any order) about the mean can be calculated progressively by solving higher-order product density equations. In order to elucidate the nature of what can be obtained from such a theory, we shall consider a simple enough example for which analytical answers can be found. It is followed by a second example which has potential application to the study of cell death kinetics and hence to sterilization processes. 

In this section, we discuss the kinetics of thermal cell death and sterilization. The rates of thermal death of most microorganisms and spores can be given by Equation 10.1, which is similar in form to the rate equation for the first-order chemical reaction, such as Equation 3.10. 

The advances attained in the last decades in the knowledge of the biological fundamentals underlying animal cell culture have enabled significant improvements in cell culture processes in vitro. In this chapter, the mechanisms that determine cell proliferation and cell death are discussed. Aspects concerning the kinetics and the mathematical description of cell growth and cell death are dealt with in Chapter 8. 

Table 8.3 Kinetic expressions for specific cell death rate in ani mal cell systems ...

Understanding the biology and kinetics of the cell death process and realizing that cell culture is an artificial model system can help guide characterization experiments to develop the best assay possible. Probably the most common problem facing design of viability and apoptosis... 

Understanding the kinetics of cell death in your model system is critical. Some proteins, such as caspases, are expressed only transiently. Cultured cells undergoing apoptosis in vitro will eventually undergo secondary necrosis. 

Most drugs produce a reversible pharmacological response. However, some antibiotics, irreversible enzyme inhibitors, and anticancer agents incorporate irreversibly or covalently into a cell s metabolic pathway. This results in an irreversible effect—cell death. Complex kinetic models are used to explain the relationship of dose-chemotherapeutic effects for some drugs, such as methotrexate, cyclophosphamide, and arabinosylcytosine.f ... 

The release of LDH activity can be related to the total number of dead and lysed cells, as determined by conventional dye exclusion methods. This relationship allows the growth and death kinetics within the culture system to be evaluated. However, there are various phenomena that could complicate this evaluation (Marc et ah, 1991 Legrand et al, 1992 Wagner et al., 1992). 

In conclusion, as the kinetics of LDH release are affected by both cell type and cultural conditions, the relationship between cell death and LDH release should be determined for each new cell line or set of culture conditions. 

As a first approximation has often been considered as a constant. Yet more detailed kinetic analyses have shown that the specific rate of cell death is also affected by the chemical composition of the medium and several physicochemical parameters, such as pH, temperature and osmotic pressure. It is often lowest at the start of the culture, and then gradually increases due either to depletion of essential nutrients or accumulation of inhibitory metabolites. 

A rate expression for cell death is given in Equation 4.3.2. With its four terms it expresses the possible increase in the cell death rate due to limitations in glucose and glutamine or accumulations in lactate and ammonia. In this case, the different contributions are additive in order to take into account the effect of each component if the expression relative to one substrate becomes equal to zero, the effects of the other components remain visible in the calculation of the specific death rate. By proper adjustment of the values of the four parameters Q, C2, and K2 it is possible to account for differences in death kinetics from one cell line to another. 

The model proposed for mammalian cell cultures provides a description of the possible influence of four of the main medium components - glucose, glutamine, lactate and ammonia - on the rates of cellular growth, death and metabolism. It contains kinetic terms that quantify the influence of each of the components either in reducing the rate of cellular growth or in increasing the rate of cell death. 

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