Mutagenicity and toxicity testing

Toxicity tests are conducted to evaluate chemicals—including medicines, food additives, and industrial, consumer, and agricultural chemicals—for their potential to cause cancer, birth defects, and other adverse health effects. Information from toxicity testing serves as an important part of the basis for public health and regulatory decisions concerning toxic chemicals.

Geneblitz® offers the following services:

1. Mini and Full-Ames Test
2. Algal growth inhibition assay
3. Daphnia acute immobilisation assay

1. Mini and Full Ames testing (OECD Guideline 471)

The Ames version of the bacterial reverse mutation test uses specialised test strains of Salmonella typhimurium and E. coli to detect point mutations which restore their functional capability to synthesise the essential amino acid, histidine. The revertant bacteria are thus detected by their ability to grow in the absence of the amino acid which is required by the parent test strain. The bacterial reverse mutation test is commonly employed as an initial screen for genotoxic activity and for point mutation-inducing activity. Many chemicals that are positive in this test also exhibit mutagenic activity in other tests.

Point mutations are the cause of many human genetic diseases and there is substantial evidence that point mutations in oncogenes and tumour suppressor genes of somatic cells are involved in tumour formation in humans and experimental animals. The Ames test can be used to determine mutagenic potential, which can then be used as an indicator of likely carcinogenicity. There are examples of mutagenic agents which are not detected by this test; reasons for these shortcomings can be ascribed to the specific nature of the endpoint detected, differences in metabolic activation or differences in bioavailability.

Please note: The bacterial reverse mutation test may not be appropriate for the evaluation of certain classes of chemicals, for example highly bactericidal compounds e.g. certain antibiotics and those which are thought (or known) to interfere specifically with the mammalian cell replication system e.g. some topoisomerase inhibitors and some nucleoside analogues. In such cases, mammalian mutation tests may be more appropriate. It is not considered that the solvent tested here will fall into this category.

Although many compounds that are positive in this test are mammalian carcinogens, the correlation is not absolute. It is dependent on chemical class and there are carcinogens that are not detected by this test because they act through other, non-genotoxic mechanisms or mechanisms absent in bacterial cells.

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2.0 Aglal growth inhibition assay (OECD code 201).

Algae are ubiquitous in aquatic ecosystems, where they incorporate solar energy into biomass, produce oxygen, function in nutrient cycling and serve as food for animals. Because of their ecological importance, sensitivity to many toxicants, ready availability, ease of culture, and fast growth rates (rendering it possible to conduct a multi-generation test in a short period of time), algae are often used in toxicity testing. The purpose of this test is to determine the effects of chemical compounds at a range of concentrations on the growth of freshwater algae over a defined period of time (usually 3-4 days). The test endpoint is inhibition of growth expressed as a logarithmic increase in biomass over the test period. From the average specific growth rates, the concentration bringing about a 50% inhibition of growth is determined and expressed as ErC50.

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3.Daphnia acute immobilisation (OECD code 202).

This test serves for testing the effect of chemicals on plankton organisms. Daphnia magna is a small arthropod of approximately 1 - 5mm in size and is part of the freshwater zooplankton. It is often found in large numbers and feeds on plankton and organic detritus. Studies on daphnia play a vital role in ecotoxicity studies because daphnia serve as food for fish and hence are an important component of water biocoenosis and food chain. Young daphnids (species) aged less than 24 hours at the start of the test, are exposed to the test substance at a range of concentrations (at least five) for a period of 48 hours. Immobilisation is recorded after 48 hours and compared with control values. The results are tabulated and analysed in order to calculate the approximate EC50 at 48hrs.

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