Tissue incubation systems

The long incubation times of many human virus diseases indicate that they replicate slowly in host cells. In tissue culture systems it has been shown that most human viruses take from 4 to 24 hours to complete a single replication cycle, contrasting with the 30 or so minutes for many bacterial viruses. 

Bartsch, H., Camus, A.-M. and Malaveille, C. (1976). Comparative mutagenicity of N-nitrosamines in a semi-solid and in a liquid incubation system in the presence of rat or human tissue fractions. Mutation Res. 37 149-162. 

Since the introduction of the Krumdieck slicer (Krumdieck 1980) and a new incubation system for slices (Smith 1985) tissue slices are commonly used in drug metabolism and toxicity studies. 

Figure 9.15 The rate of adrenaline formation using a homogenate of rat hypothalamus as enzymes at 37°C. Standard incubation system containing 10 mg of tissue was used. (From Trocewicz et al., 1982.)...

Common for all the membrane-, cell- and tissue-based systems used to determine drug permeation, is the need for an incubation solution preserving the viability, functionality and/or integrity of the membranes, cells or tissue. It is also important that the incubation solution does not influence the permeability characteristics of the epithelial membrane or lipid bilayer and that the drug compound is chemically and physically stable and sufficiently soluble in the buffer. In all models, aqueous incubation solutions are used, often with slight modifications depending on the purpose of the study. 

The P-C isomer selectivity seems to be tissue-specific a preferential uptake of the all-trans isomer was shown in hepatic stellate HSC-T6 cells and in cell-free system from rat liver microsomes, but not in endothelial EAHY cells or U937 monocyte-macrophages (During et al., 2002). When Caco-2 cells were incubated with only 9-cis P-C, all -trans P-C did not increase in cells or in the basolateral medium, indicating that there is no cis-trans isomerization occurring in intestinal cells. Thus, the isomerization of 9-cis P-C observed in vivo (You et al., 1996) could take place in the... 

---