Article

IPCS framework for analyzing the relevance of a noncancer mode of action for humans.

Section of Experimental Medicine and Toxicology, Division of Medicine, Imperial College London, London, UK.
Critical Reviews in Toxicology (Impact Factor: 6.41). 02/2008; 38(2):87-96. DOI: 10.1080/10408440701749421
Source: PubMed

ABSTRACT Structured frameworks are extremely useful in promoting transparent, harmonized approaches to the risk assessment of chemicals. One area where this has been particularly successful is in the analysis of modes of action (MOAs) for chemical carcinogens in experimental animals and their relevance to humans. The International Programme on Chemical Safety (IPCS) recently published an updated version of its MOA framework in animals to address human relevance (cancer human relevance framework, or HRF). This work has now been extended to noncancer effects, with the eventual objective of harmonizing framework approaches to both cancer and noncancer endpoints. As in the cancer HRF, the first step is to determine whether the weight of evidence based on experimental observations is sufficient to establish a hypothesized MOA. This comprises a series of key events causally related to the toxic effect, identified using an approach based on the Bradford Hill criteria. These events are then compared qualitatively and, next, quantitatively between experimental animals and humans. The output of the analysis is a clear statement of conclusions, together with the confidence, analysis, and implications of the findings. This framework provides a means of ensuring a transparent evaluation of the data, identification of key data gaps and of information that would be of value in the further risk assessment of the compound, such as on dose-response relationships, and recognition of potentially susceptible subgroups, for example, based on life-stage considerations.

Full-text

Available from: Bette Meek, May 29, 2015
2 Followers
  • [Show abstract] [Hide abstract]
    ABSTRACT: Testing strategies are anticipated to increasingly rely on in vitro data as a basis to characterize early steps or key events in toxicity at relevant dose levels in human tissues. Such strategies require quantitative in vitro to in vivo extrapolation to characterize dose–response as a basis for comparison with exposure to estimate risk. Current experience in the incorporation of mechanistic and in vitro data in risk assessment is considered here in the context of identified principles to increase the potential for timely acceptance of more progressive and tailored testing strategies by the regulatory community. These principles are outlined as transitioning in a familiar context, tiering to acquire experience and increase confidence, contextual knowledge transfer to facilitate interpretation and communication, coordination and development of expertise and continuing challenge. A proposed pragmatic tiered data driven framework which includes increasing reliance on in vitro data and quantitative in vitro to in vivo extrapolation is considered in the context of these principles. Based on this analysis, possible additional steps that might facilitate timely evolution and potentially, uptake are identified.
    Toxicology 01/2015; DOI:10.1016/j.tox.2015.01.010 · 3.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Inorganic arsenic (iAs) at high doses is a known human carcinogen, inducing tumors of the skin, urinary bladder, and lung. It is also associated with non-cancer toxicities. An understanding of the mode of action (MOA) for arsenic-induced effects is needed to develop a scientifically-based risk assessment. To determine an MOA for iAs induced toxicities, it is necessary to understand the metabolism, kinetics, cell transport, and interaction with specific proteins of iAs. Based on in vitro investigations using animal and human cells, studies from animal models, and clinical and epidemiological studies, we have proposed an MOA involving formation of sufficient levels of reactive trivalent metabolites which interact with critical free sulfhydryl groups, leading to cytotoxicity and regenerative cell proliferation. There is a strong correlation between in vitro cytotoxicity (>0.1 μmol/L trivalent arsenicals) and the no effect levels in rodents [approximately 1 ppm (1 ppm = 1 mg/L) of water or diet]. In epithelial target tissues, the cytotoxic effects of iAs result in chronic precursor lesions which have the potential for an increased risk of developing cancer. In non-epithelial tissues, non-cancer toxicities such as hypertension and atherosclerosis develop. This MOA implies a non-linear, threshold dose–response relationship for both non-cancer and cancer end points of exposure to iAs.
    Chinese Science Bulletin 04/2014; 59(11):1078-1082. DOI:10.1007/s11434-014-0150-8 · 1.37 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This scientific report provides a review of modern methodologies and tools to depict toxicokinetic and toxicodynamic processes and their application for the human hazard assessment of chemicals. The application of these methods is illustrated with examples drawn from the literature and international efforts in the field. First, the concepts of mode of action/adverse outcome pathway are discussed together with their associated terminology and recent international developments dealing with human hazard assessment of chemicals. Then modern methodologies and tools are presented including in vitro systems, physiologically-based models, in silico tools and OMICs technologies at the level of DNA/RNA (transcriptomics), proteins (proteomics) and the whole metabolome (metabolomics). Future perspectives for the potential applications of these modern methodologies and tools in the context of prioritisation of chemicals, integrated test strategies and the future of risk assessment are discussed. The report concludes with recommendations for future work and research formulated from consultations of EFSA staff, expert Panels and other international organisations.