Food Protection Trends - November/December 2017 - 431

particular in the field of environmental toxicity, effect-based
approaches on entire organisms, such as the zebrafish (8)
or certain algae (20), are pursued. An example of a cell
culture-based biological test system, outlined in detail in
previous overview articles on the status of effect-based
analytics (5, 6), is the CALUX (Chemical-Activated
Luciferase Gene Expression) assay. This test is based on the
specific binding of dibenzodioxins and similar substances to
the aryl hydrocarbon receptor which, as a ligand-activated
transcription factor, subsequently initiates the transcription
of a firefly-derived luciferase reporter gene that is controlled
by an aryl hydrocarbon receptor-responsive promoter
region. Comparable reporter gene-based test systems
already exist for various hormonal effects mediated via
androgen or estrogen receptors (20). The reporter genes
used here can be integrated in a stable manner into the
genome of a permanent mammalian cell line (Fig. 1A).
There is currently a legal requirement in food control
to conduct an analytical identification of the substance
responsible for a positive finding in an effect-driven test
system. Accordingly, effect-based approaches are currently
used primarily as screening methods to identify in a large
number of samples those that are to be subsequently
examined by means of classic analytics for the presence of
specific substances known to be toxicologically relevant.
A "positive" finding in an effect-based sytem therefore
involves the identification of substances by use of classic
analytical methods, which can be complex and timeconsuming. A tiered procedure of this kind involving effectbased screening followed by chemical analytics proved its
value in the last dioxin crisis, where it was necessary to test
a large number of samples within a short time (see also
(6)). Repeated cycles of sample fractioning and the use
of effect-based test systems prior to chemical-analytical
substance identification can help to limit the chemical
complexity of a sample (3).
For this reason, a decisive boost for the further
distribution and application of effect-based methods in
the field of food and feed control could in the future lie in
departing, at least partially, from the principle used now.
For example, assuming the availability of appropriately
validated effect-based methods, which enable not only
the qualitative detection but also the quantifiability of a
certain biological effect with sufficient precision, the mere
detection of a biological effect above a certain potency, to
be defined individually for each biological test system and
which would assume the function of a limit value in classic
chemical analytics, could be recognized as sufficient for
any decisions to be made or consequences to be drawn.
This would be desirable, especially in view of the fact that
some toxicologically relevant xenobiotic-binding nuclear
receptors bind substances that are hardly related from a
chemical point of view (an aspect to be dealt with in more
detail later in the text). This lack of chemical similarity

could lead to difficulties in the subsequent search for a
specific individual substance causing the effect at such a
promiscuous receptor.
The current state of using luciferase reporter systems
for effect-centered analysis in food control is limited to
individual endpoints such as that addressed by the CALUX
assay. This present state of effect-based analytics has been
the focus of a previous paper in this journal (5). The
aim of this paper, however, is to sketch potential future
development of existing techniques applied in effect-based
analytics and to present novel approaches focused on the
detection of transcriptional alterations of endogenous
cellular gene transcription that appear promising for
future application in effect-based analytics. This will be
done in the following paragraphs, starting with possible
further developments of luciferase-based methodologies
and their possible limitations, and then continuing with
the use of single transcript markers and transcriptomic
signatures. This manuscript thereby reaches far beyond
previously published work in the field, including our own
previous paper (5), thus making this work interesting for
experimental researchers and method developers, as well as
for readers who are concerned with food surveillance and
regulatory issues.
Further development through establishment of a
reporter gene test battery
In principle, a large number of different cellular effects
or mechanisms of action can be recorded through effectbased test systems based on reporter assays of this kind.
Reporter gene systems allow the precise quantification
of the examined biological effect and enable the easy
establishment of dose-response relationships, which does
not automatically apply to the same extent to every other
effect-based system. Established and well-characterized
reporter systems are available in the meantime, in
particular for a panel of nuclear receptors, which function
as ligand-activated transcription factors and are known to
constitute important molecular switchpoints with many
toxicologically-relevant processes, as well as for numerous
transcription factors acting downstream of important
cellular signaling pathways. These assays could be prepared
for use in routine analysis in validation studies. At the end
of a development of this kind, a battery of reporter gene
test systems that would be suitable for recording a large
number of different, toxicologically relevant signals could
be available (Fig. 1B). Various reporter gene systems are
available (firefly luciferase, Gaussia luciferase, Renilla
luciferase, fluorescent proteins such as GFP), which differ
in their substrates, reaction conditions and detection and
which can, therefore, be used simultaneously for detection
of several endpoints in a single biological system, for
example in the classic "dual luciferase test" in which two
luciferases with different substrate specificities and reaction

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