Xenobiotic-metabolizing cultured cells

In vitro systems with varying levels of complexity have been used to study xenobiotic metabolism. These include purified proteins, subcellular fractions/cell lysates, intact whole cells, tissue slices and whole organ culture. Advantages and disadvantages of the approaches are summarized below. 

Cells in suspension may be maintained for a limited period of time in defined media or for longer periods in nutrient, but less well-defined, media. In either case these cultures are often used for studies of xenobiotic metabolism. 

Over the last decades, cell and tissue cultures of renal epithelial cells have become powerful tools to study basic renal physiological functions, including transport, metabolism, and the effects of external stimuli such as oxygen tension, nutrition, hormones, and xenobiotics. Indeed, cultured renal tubular epithelial cells were one of the first cells utilized for investigating drug-induced injury. In this chapter, we describe the methods used to isolate different types of renal cells, aspects of primary cell culture, and tools to immortalize primary cells. We summarize the desired characteristics of various renal cell types and review the most widely used. Finally, we address important aspects of renal cell culture. 

Gotz C, Pfeiffer R, Tigges J, Blatz V, Jackh C et al (2012) Xenobiotic metabolism capacities of human skin in comparison with a 3D epidermis model and keratinocyte-based cell culture as in vitro alternatives for chemical testing activating enzymes (Phase I). Exp Dermatol 21 358-363... 

Key words Xenobiotic metabolism, Cytochrome P450, CYP, Cell culture, Cell lines... 

Cell lines have been used extensively to study the cytotoxicity of substances to fish cells12,184. Most studies have employed tests of general or basal cytotoxicity rather than tests of injury to differentiated cells and their functions. Basal cytotoxicity refers to impairment to cellular activities shared by all or most cells. Evaluating basal cytotoxicity can be done in a variety of ways, which will be referred to as cell viability assays. Usually these tests are performed on cultures after exposure to putative toxicants for 72 h or less and can be described as short-term or acute assays. As a result of this short exposure, toxicants that act by inducing a particular cellular process, such as the xenobiotic metabolism, or by causing cumulative damage might be missed. 

Because the liver is the major organ of xenobiotic metabolism, hepatocytes are an appropriate cell in which to conduct genotoxicity tests. Because they do not divide readily in culture, they are not so useful in tests for chromosomal aberrations or mutations, but they can be used to detect DNA damage or repair where dividing cells are not needed. In studies with fresh hepatocytes, it is not necessary to include S9 mix. 

It also is possible to use intact ceils as a source of xenobiotic metabolizing enzymes. Activation for tissue culture systems can be provided by primary rat liver cells and irradiated hamster embryo cells which are plated as a feeder layer for the indicator cells. In the case of compounds which yield a spec-... 

Although the rate of metabolism of a chemical is dependent upon the plant system in which it is placed, a standardized screen with certain plant species would provide a basis for initial comparison, which could be modified as more specific results were obtained. Proponents of a standardized method for comparison of xenobiotic metabolism in plant cell cultures have developed a flow diagram for such a screening procedure using soybean and wheat cell suspensions (Figure 6) (59). Using this procedure, the authors compared metabolism of di-(2 ethylhexyl)-phthalate. (DEEP), pentachlorophenol (PCP). 

The metabolism in cell culture experiments is provided now by rat liver cell extracts. This methodology probably reflects poorly the dynamics of human metabolism of xenobiotics. We hope that techniques that we and others are developing will allow whole human cells to be used as metabolizing elements and thus reduce such uncertainties. 

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