Head of the Department of Toxicology, Centre for Radiation, Environmental and Chemical Hazards (CRCE) Public Health England
Professor Gant summarised Day 1 discussions into a number of steps that should be taken together (in no specific order), and a number of questions that should be the basis of the brainstorm discussions of Day 2:
Step 1: Semantics and Definitions: Four definitions of ‘Epigenetics’ were heard today; all four were similar and concordant. Therefore, there is optimism that the scientific community can agree on a single reference definition of ‘Epigenetics’.
Step 2: Decide what to measure: miRNA; methylation; hydroxymethylation; histone modifications – or gene transcription. (Whilst gene transcription measurements are not epigenetic measurements, they are necessary to put the epigenetic change in the context of mechanism/MoA.) Which of these are going to be the least variant, most informative and related to an adverse outcome? Do we measure the whole genome or part of a genome? Should we make molecular measures or concentrate on the phenotype?
Step 3: Incorporate Epidemiology: How do we determine epigenetic change in tissues for epidemiological studies? For DNA sequence, change determination of the genome sequence in one tissue will be the same as that in the tissue of interest. This is not true for epigenetic change. Can PBMLs act as a sentinel? Are sperms useful in epidemiology? What about females? What about mosaicism? Ancestry can confound exposure associations. All cells are unlikely to be epigenetically altered in the same manner throughout all cells in the tissue.
Step 4: Understand which epigenetics changes are adverse and which are adaptive. Can we identify epigenetic markers which are predictive of adverse change?
Step 5: Decide on the appropriate Model Systems: Relationship to humans, cost, throughput, which organs/tissue, measurements – specific or global? Cells/Fish/Mammals?
Step 6: Reproducibility: To ensure regulators, the scientific community and industry can have confidence in the findings of epigenetic studies – and that they can be reproduced: Strains and species differ in their epigenetic profiles; do we need to decide on appropriate strains for epigenetic studies? In reproducing studies, it is likely to be essential to ensure that the same species and strain is used? This will be essential information of any TG amendments.
Step 7: Address Hazard vs Risk: Are the effects we are seeing in model systems at such high doses that they are irrelevant for public health and only of academic interest? How do we examine long-term, low-dose exposure? Are early life stages of more importance? How do we take these into account? What about gametes?
Step 8: Proof of Principal and Test Guideline Discussions: Where he suggested that more research to identify epigenetic endpoints and markers is needed before these can be incorporated into testing. This was further developed by Miriam Jacobs who had prepared an overview of all the current TGs and where they might be adapted to start incorporating epigenetic measurements/assessment, which would augment and improve endpoint interpretations (See Room Document, Appendix 4). This would start to address regulators’ need for understanding the link between molecular epigenetic changes and apical endpoints of concern in in vivo assays, but also address development of relevant in vitro assays that can help elucidate the mechanisms involved. One suggestion to support this will be to include the option of collection of relevant tissues in test guidelines for later retrospective analysis to develop an augmented TG.
Furthermore, for regulatory purposes, the discussion about transgenerational effects was considered not relevant. Miriam Jacobs emphasised that the bottom line is that the regulatory community and the wider public need test guidelines and integrated approaches to testing and assessment protective of early life chemical exposure and later life diseases such as cancers, obesity, diabetes etc, in the current generation, as well as subsequent generations. The intention is not to create new in vivo test methods solely for epigenetics. Rather it is to understand the normal range of epigenetic marks and which epigenetic markers are key events in disease progression. Then, this information would be used to further improve the current battery of regulatory tests and so further improve public health protection. This is the key challenge to be met.