Environmental mutagenesis in retrospect

50 years existence and active participation of EEMS (now EEMGS) in the scientific community: A driver of European and international scientific collaborations for the protection of the environment and human health from genome stressors

EEMS and its successor Society EEMGS have provided a dynamic and successful platform to stimulate research and exchanges among the different actors involved in the protection of the environment and of human health from exposure to genome stressors. It includes basic, translational and applied research projects. This was possible due to the enthusiasm, creativity and support of scientists convinced of the importance of these issues. In the future young scientists will take over with new questions, new challenges, new technologies, new discoveries and new applications. A major challenge is the ethical questions emerging from the impressive potential of present genetic technologies capable of impacting the evolution of nature and humankind. The EEMGS, where academics, regulators and industries meet, should play a central role in these aspects, in particular in support of primary prevention and the establishment of internationally recognized guidelines. Collaboration with colleagues and other teams are of great importance to establish a stimulating open dialogue on scientific questions. However the key issues remain to do careful and rigorous research; to use logic and background knowledge; to define adequate experimental designs; to provide transparency in the protocols; to check repeatability of the results and to combine several statistical approaches in the quest to get to the truth. Among the many challenges ahead, re-evaluation of some key fundamental questions is necessary, such as the interplay between genetics and epigenetics, the existence of specific germ cell mutagens or the identification of the mechanisms leading to mutagen induced diseases. Translational and applied research will further include the development of systemic biomonitoring protocols, if possible in a single biological sample, the redaction of internationally harmonized guidelines but also the organization of platforms between geneticists and physicians open to all actors in the field. The creation of an independent European center to assess risk from exposure to mutagens, in particular in the light of the problematic of global warming might be very helpful.

The use of transgenic mice for short-term, in vivo mutagenicity testing

In order to develop a short-term, in vivo assay to study the mutagenic effects of chemical exposure, transgenic mice were generated using a lambda shuttle vector containing a lacZ target gene. Following exposure to mutagens, this target can be rescued efficiently from genomic DNA prepared from tissues of the treated mice using restriction minus, in vitro lambda phage packaging extract and restriction minus Escherichia coli plating cultures. Mutations in the target gene appear as colorless plaques on a background of blue plaques when plated on indicator agar. Spontaneous background levels were approximately 1 x 10(-5) in each of three mouse lineages analyzed. Exposure of lambda transgenic mice to N-ethyl-N-nitrosourea resulted in as much as a 14-fold induction in detected mutations over background levels. The assay is currently being modified to incorporate lacI as the target for ease of mutation detection as well as in vivo excision properties of the Lambda ZAP vector, facilitating sequence analysis of mutant plaques.

International symposium on strategies for the control of mutagenic and carcinogenic risk: current status and perspectives, Friday, May 5, 1989, Bologna

The 18 posters, grouped under mutagenicity testing, metabolic activation, mechanisms of mutation and chromosome damage, human monitoring and safety are critically discussed. It is pointed out that rather than applying a single test, a battery of well-validated in vitro and in vivo tests is required. As a testing strategy, the one developed by Ashby is briefly mentioned. The value of the Salmonella assay and of in vitro cytogenetics as short term tests for detecting carcinogens, and of the bone marrow micronucleus test as one for assessing germ cell mutagenesis is pointed out. Various assays now available for measuring gene mutations in human lymphocytes and erythrocytes are briefly described. Since we have a considerable data-base for germ cell mutations in the mouse and data are now being collected for mutations in human somatic cells, the importance of studies on mutation induction in somatic cells of the mouse is emphasized. Such data on mouse somatic cells will help to define with greater precision mutation induction to be expected in human germ cells; that is genetic risks in humans on the basis of a "parallelogram-like" extrapolation using somatic mutations in man and germ cell mutations in the mouse can now be calculated.

Utility of short-term tests for genetic toxicity

By definition, short-term tests (STTs) for genetic toxicity detect genotoxic agents, not carcinogens specifically. However, there is sufficient evidence, based on mechanistic considerations alone, to say that genotoxic agents are potential carcinogens. STTs have high statistical power, are almost always replicated, can be performed rather easily under various sets of experimental conditions, are relatively inexpensive, and detect a variety of endpoints relevant to carcinogenesis. In addition, several STTs have shown considerable utility in evaluating the genotoxic effects of real-world, environmental complex mixtures as well as the antimutagenic effects of various pure compounds and complex mixtures. STTs are likely to continue to be refined, resulting in STTs that are increasingly more relevant to human mutation and disease. Their utility should not be judged solely against the questionable standard of a rodent carcinogenicity assay.

Models and assumptions underlying genetic risk assessment

Various methods employed for estimating the genetic risks of radiation are reviewed. With the doubling-dose method, genetic damage is expressed as an increase in cases of known genetic disease. The actual doubling dose is based on figures obtained with the mouse. There have been no recent data on induced mutation frequencies. Recent results suggest that the prevalence figure for multifactorial disease may be at least one order of magnitude higher than before. Various assumptions underlying the doubling-dose concept are discussed in the light of recent findings on: (1) spontaneous mutations resulting from insertion elements, and (2) the comparability between spontaneous and induced mutations. The so-called direct method makes use of figures for induction of dominant mutations affecting the skeleton and the lens of the eye in the mouse, and of translocation induction in monkeys. Induction rates are converted to overall rates of induced dominant effects in man by applying certain assumptions. The proportionality between dose and effect is the basis for all genetic risk assessments. The possible significance of data on human lymphocytes indicating a threshold below 4 rad and the induction of repair enzymes by low radiation doses is discussed. The parallelogram approach is based on the principle that estimates can be obtained on the amount of genetic damage that cannot always be assessed directly. Thus mutations in mouse germ cells can be predicted by using mutation frequencies in cultured mammalian cells and O6-ethylguanine adducts. Measurement of haemoglobin mutations in human and mouse erythrocytes, and of HPRT-deficient mutations in lymphocytes of man and mouse should make more precise estimates of mutation frequencies in human germ cells possible. The development of a database on mutations in somatic cells of the mouse, their induction frequencies and molecular nature are considered an important priority. Used in combination with mouse germ-cell mutation frequencies, they should enable more precise risk estimates on the basis of mutations in somatic cells of man.