Cell culture models mechanisms

With few exceptions, information on the anticonvulsant pharmacology of specific ion channel subunits analyzed in expression systems is scarce. Hitherto, a first understanding of the mechanism of action of most antiepileptic dtugs has evolved from analyses of somatic ion channel pharmacology either in isolated neurons from human or rodent neurons, or cell culture models. 

Carotenoid absorption and metabolism have been comprehensively reviewed (Erdman et al., 1993 Parker, 1996 van Vliet, 1996 Furr and Clark, 1997 Yeum and Russell, 2002) and this chapter will focus only on recent advances in these areas. A particular emphasis will be placed on studies that used in vitro and cell culture models as tools to understand better the mechanisms of absorption on the molecular level. 

Cell culture models are routinely used to assess permeability of new potential drug candidates. The simplicity and higher throughput of these models makes them a useful alternative to in vivo studies. These models are used to predict absorption in vivo, rank order compounds and examine absorption mechanism. Transcellular, paracellular, active uptake and efflux mechanisms can be studied with these models. 

The quantitative extent of CYP induction depends on the dosage (concentration) of the inducer and on the duration of exposure. However, the induction process, in contrast to inhibition, is not as straightforward to study in vitro, since induction requires intact cellular protein synthesis mechanisms as available in cell culture models (57-62). 

The mechanisms of toxic action of abrin and ricin are similar. The B-chain attains cell recognition and binding function to facilitate toxin transport across the cell membrane, whereas the A-chain, once internalized by the cell, blocks protein synthesis by catalytically modifying the ribosomes. Both toxins ultimately kill target cells in animal or cell culture models by both necrosis and apoptosis. 

Contribution of established renal cell culture models to the understanding of nephrotoxic mechanisms... 

The advantage of cell culture models is that they are able to measure active transport processes across the cell membranes and not just the interaction of a drug with a lipid bilayer. They can also be used to study passive and active transport routes indeed, much of the knowledge as to the active transport mechanisms in the intestine has been derived from cell culture studies. Despite the predominant route being passive diffusion, the research into transport mechanisms indicates that there are a large number of drugs that are used as substrates for active transporter and efflux systems, and it must therefore be appreciated that multiple transport routes may be involved in the intestinal drug transport. 

Cell culture models are described as either primary cultures or cell lines. Primary cultures are generated by the growth of cells that migrate out from a fragment of tissue or by growth of cells isolated by either enzymatic or mechanical dispersal of tissue.3 A primary culture may be subcultured or passaged by harvesting the cells... 

The appropriateness of any cell culture model used to study drug delivery processes, whether a primary or a cell line, should be based on certain basic criteria. These include but are not limited to the presence of a restrictive paracellular pathway that allows effective characterization of transcellular permeability, the presence of physiologically realistic cell architecture reflective of the tissue barrier of interest, the expression of functional transporter mechanisms representative of the tissue barrier of interest, and the ease, convenience, and reproducibility of the culture methods.4 However, pharmaceutical scientists must realize that cell culture models in use today are not ideal with respect to these criteria, and there will be advantages and limitations with any choice. 

Current technologies provide for availability of cell culture models from a selection of the significant tissue barriers as either primary cell culture systems or continuous cell line cultures. A number of endothelial and epithelial cell systems can now be grown onto permeable supports as monolayer systems to facilitate transcellular transport. These cell culture models provide powerful tools for the pharmaceutical chemist to characterize fundamental cellular transport mechanisms at the biochemical and molecular levels and effective screening systems to facilitate appropriate drug design and development. Moreover, they all have applications in... 

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