The detection of promutagen activation by extracts of cells expressing cytochrome P450Ia2 cDNa: preincubation dramatically increases revertant yield in the ames test

Introduction:
This text is a scientific article that describes a study on the detection of promutagen activation by extracts of cells expressing cytochrome P450Ia2 cDNa using the ames test, a widely used method for detecting potential carcinogens. The study found that preincubation dramatically increases revertant yield in the ames test when extracts of cytochrome P450Ia2-containing transfected cells or low concentrations of rat-liver extracts are used as the source of activating enzymes.

Key Points:

* The study compares two slightly different protocols in the ames Salmonella mutagen test: the plate incorporation method and the preincubation method.
* The preincubation method resulted in a higher number of revertant colonies in the ames test for 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (Melq), 1-aminoanthracene and several other promutagens when extracts of cytochrome P450Ia2-containing transfected cells or low concentrations of rat-liver extracts were used as the source of activating enzymes.
* The effect of preincubation was not due to the low protein concentrations in the assays, as increasing the total protein concentration did not abolish the requirement for preincubation for the detection of Melq activation at low concentrations of rat-liver extract.
* The plate incorporation protocol may underestimate the capacity of cell extracts to activate promutagens, making interlaboratory comparisons difficult and potentially leading to the unnecessary use of large quantities of cell extract protein.
* The study suggests that whenever ames test assays are carried out under conditions where P450 concentration limits revertant yield, it would be prudent to examine both the preincubation and plate incorporation protocol.
* The ames test is widely used to detect potential carcinogens based on their ability to act as mutagens for Salmonella typhimurium.
* The study highlights the importance of the choice of protocol in the ames test and the potential impact on the detection of promutagens.

Main Message:
The main message of this text is that the choice of protocol in the ames test can significantly impact the detection of promutagens, with the preincubation method resulting in a higher number of revertant colonies compared to the plate incorporation method when extracts of cytochrome P450Ia2-containing transfected cells or low concentrations of rat-liver extracts are used as the source of activating enzymes. The study suggests that both protocols should be examined when carrying out ames test assays under conditions where P450 concentration limits revertant yield. This is important for regulatory matters as the detection of potential carcinogens is crucial for ensuring public health and safety.

Trottier, Yvon, William I. Waithe, and alan anderson. “The Detection of Promutagen activation by Extracts of Cells Expressing Cytochrome P450Ia2 cDNa: Preincubation Dramatically Increases Revertant Yield in the ames Test.” Mutation Research Letters 281, no. 1 (January 1992): 39–45. https://doi.org/10.1016/0165-7992(92)90034-F.