Genotoxicity is an important aspect of preclinical safety testing of new drugs. There are various tests for the genotoxicity of drugs. Ames test: the most common way to detect genotoxicity. Developed by Ames et al, it's a quick and specific way to check for compounds that can cause DNA mutations. This test has been used to ascertain the mutagenicity of many substances.

Ace Therapeutics offers a range of screening options to help our clients assess the mutagenic potential of stroke drugs in the Ames test.

Related Services

• High-Throughput ADME Screening Services for Stroke Drug Discovery and Development
• Safety Assessment Services for Stroke Drug Discovery & Development

What is the Ames Test?

Ames test-a bacterial test that detects molecules that could be mutated in DNA. With its use of specific strains of bacteria (Salmonella typhimurium, E. coli), this test is fast and inexpensive to test for mutagenicity of chemicals. It is particularly useful in toxicology to help identify potential carcinogens and measure the genotoxicity of compounds.

Fig.1. Genetic approach for assessing the mutagenicity in Salmonella strains. (Vijay, et al., 2018)

The Principle of the Ames Test

The Ames test utilizes specific bacterial strains with mutations preventing histidine or tryptophan synthesis. These strains require these amino acids for growth. When these bacteria are exposed to a potential mutagen, they may experience reverse mutations that enable them to synthesize histidine or tryptophan again. The degree of this reversion, indicating their newfound independence from these amino acids, is measured to evaluate the mutagenic potential of the substance tested.

Fig.2. Principe of Ames test. (Himri, et al., 2018)

Tester Strains Required for Mutagenicity Testing in the Ames Assay?

Five tester strains are necessary for mutagenicity testing in the Ames assay because each strain is designed to identify specific types of genetic damage. By including multiple strains, the assay can effectively detect a broader spectrum of mutational events.

What Controls Are Included in the Ames Test?

Positive controls are known mutagens 2-nitrofluorene and 4-nitroquinoline-N-oxide for the assay without S9 and 2-aminoanthracene in the assay with S9. The negative control is the appropriate vehicle control.

What Can Ames Testing Offer?

The Ames test involves plating His− Salmonella typhimurium on media with trace histidine and adding potential mutagens. Colonies only form if a compound can reverse the mutation, converting His− to His+.

To simulate mammalian metabolism, liver extracts are added to mimic liver enzyme activity. A variety of concentrations of each chemical are usually tested to generate a dose–response curve. The analysis of these curves highlights various aspects, including the activity spectrum in tester strains, classification of the chemical as either frame-shift or base-substitution mutagens, the mutagenic potency (minimum concentration required for exhibiting mutagenicity), and the minimal concentration at which auxotroph growth is inhibited.

The Ames test is designed to assess a chemical's potential genotoxicity by measuring its ability to induce reverse mutations at specific loci in various bacterial strains.

Limitations of the Ames Test

The Ames assay, which uses Salmonella typhimurium strains, is not a perfect model for humans. To address this, a mouse liver S9 hepatic fraction is added to assess the mutagenicity of metabolites resulting from mammalian metabolic activation. However, differences in metabolism between humans and mice can impact test results.

1. Vijay, U., et al. (2018). Microbial mutagenicity assay: Ames test. Bio-protocol, 8(6), e2763-e2763.
2. Himri, I., et al. (2018). Place of the genotoxicity in the ecotoxicology domain. SMETox Journal, 1(1), 10-17.