Factors influencing nominal effective concentrations of chemical compounds in vitro: cell concentration

A roadmap for the development of alternative (non-animal) methods for systemic toxicity testing

“…To determine the in vivo plasma concentration expected to elicit a target-tissue response similar to the cellular response in the in vitro assay, the free fraction must be determined in both the in vitro and in vivo exposures (Gulden et al, 2006;Gulden and Seibert, 2003;Teeguarden and Barton, 2004). To the extent that the cells in the in vitro assay are representative of the cells in the in vivo target tissue, equal free concentration in the medium and plasma will be associated with the same intracellular exposures (Gulden et al, 2001).…”

Peer Reviewed: Internal Exposure: Linking Bioavailability to Effects

“…EC50 nominal for cytotoxicity in various cellular test systems rises with increasing medium protein concentrations and increasing cell density. This means that in the presence of protein, more toxicant must be added to reach the same effect level, presumably because of sorption to the medium protein rather than exposure to the cells (13). Adsorption and absorption to cell material lead to a similar linearly increasing EC50 nominal with increasing cell density (14).…”

Development of a polydimethylsiloxane film‐based passive dosing method in the in vitro DR‐CALUX® assay

“…The concentration on the film in equilibrium was calculated by subtracting the determined concentration in the water or medium from the applied concentration on the film. The medium contains salts that influence the solubility, as well as serum components such as proteins and lipids that can bind compounds in a nonspecific way [3,21]. These experiments also showed that shaking before exposure is important to reach a rapid equilibrium between the concentration on the film and that in medium.…”

“…The exposure concentration is often expressed as the nominal concentration (total mass added/total volume). However, the freely dissolved unbound concentration of the target compound, which is generally responsible for the toxic effect in the bioassay, can be much lower as a result of processes such as binding to medium components, volatilization, or binding to the test system [3][4][5]. Nominal concentrations at which an effect is observed in toxicity tests of up to several orders of magnitude above the aqueous solubility of the test compounds have been reported [6][7][8].…”