Emerging Issues in Food
Endocrinal Effects of Chemical Mixtures in Vivo and in Vitro
RIKILT, The Netherlands
Toine studied Molecular Science, at Wageningen University, and worked
several years in the pharmaceutical industry. Since 1992 he has worked at
RIKILT – Wageningen UR, in the departments of Microbiology, Toxicology,
and Molecular Biology.
His 2006 PhD thesis, entitled: “Development, validation and routine
application of the in vitro REA and DR-CALUX reporter gene bioassays for
the screening of estrogenic compounds and dioxins in food and feed”,
was awarded with the Joep van den Bercken award for the best thesis in Toxicology in the Netherlands.
Since 2011 Toine is an OECD expert member of the VGM-NA for Screening and Testing of Endocrine
Disrupters for Mammalian Effects and for the OECD VGM-NA for The Use of Metabolising Systems for In
Vitro Testing of Endocrine Disruptors.
He has been a co-promoter of several PhD students, opposed at the defence of several PhDs, and
(co)authored over 50 peer reviewed research papers, and is a member of the editorial board of ALTEX.
Public concern about endocrine disrupting chemicals (EDCs) has risen since the publication of “Our
Stolen Future” in 1996 by Theo Colborn and co-authors. Another impulse was given by the publication in
1996 in Science by Arnold et al., “Synergistic activation of estrogen receptor with combinations of
environmental chemicals”, but that study was retracted in 1997. Ever since researchers have been
struggling with mixture effects and how to mimic possible in vivo effects of complex mixtures with in
vitro test systems.
For several compounds, such as antibiotics, this is relative simple, and synergistic effects can be observed
with inhibition assays, which can be used to detect several classes of antibiotics at their MRLs. Complex
mixtures of dioxins and PCBs act additively, as their main mode of action is activation of the AhR (key
event). The more potent dioxins and PCBs have stronger binding affinities with the AhR and activate the
receptor at lower doses, resulting in the application of the so-called TEQ-principle. The situation for
estrogens seems a little more complex. Proliferative responses of breast cells by exposure to estrogens is
enhanced by certain growth factors (IGF and EGF), but still involves the activation of the estrogen
receptor (ER) (key event), as the ER is indirectly activated by these growth factors. But “estrogenic”
effects in vivo, e.g. feminisation of fish, might also result from anti-androgenic activities or by a
compounds ability to affect the steroid biosynthesis. This will be further demonstrated with BPA as an
example. Concluding from this, it is clear that complex mixture testing demands complex systems (e.g.
whole target organism: in vivo animal or in vitro bacteria) and can, in case of animals, most likely only be
mimicked in vitro by integrating various testing strategies.