An exploratory single-center, cross-sectional study for the characterisation of human variability in toxicodynamics: towards the development of quantitative adverse outcome pathways.

Currently, risk assessment is based on animal experimentation. These studies do
not reflect human biology or involve mechanistic toxicodynamic information.
However, accurate risk assessment using human cells is hampered by limitations
in the understanding of the population variability of toxicodynamics. An
uncertainty factor of 100 was introduced to provide guidance in extrapolating
experimental animal data to humans (WHO/FAO, 2009, Lehman and Fitzhugh, 1954).
These uncertainty factors were assumed to cover interspecies (animal-to-human)
variability, and inter-individual (human-to-human) variability, which allowed
human populations to be compared with healthy experimental animals. However,
this uncertainty factor was arbitrarily set without much scientific basis.
Therefore, it is needed to improve the understanding of the population
variability of critical toxicity-related pathways to derive uncertainty factors
for toxicodynamics that will also ensure protection of the most vulnerable
citizens.

Our current understanding of variability at the level of toxicodynamic
properties is very limited. With regard to human adverse events, there is clear
evidence on high susceptibility of some individuals to specific groups, such as
responses to warfarin or various drugs that cause drug-induced liver injury,
and relate to idiosyncratic drug toxicities (Osanlou et al., 2018). Genome-wide
association studies have identified specific genetic polymorphisms that are
associated with these adversities (Osanlou et al., 2018), but toxicodynamics
safety factors for the general population have not yet been derived. On the
other hand, a large panel of iPSC-derived cardiomyocytes from up to 43 donors
was used to establish the variability in cardiotoxic responses (Blanchette et
al., 2020; Burnett et al., 2021). Moreover, a panel of lymphoblastic cell lines
established from >1,086 donors have been applied to determine the cytotoxicity
of more than 179 chemicals (Nour et al., 2015). So far these studies only
looked at endpoints of toxicity and did not determine the variability in
mechanistic markers of toxicity that represent adverse outcome pathway key
events. These studies also used cell line panels, which may reflect
experimental variability rather than bona fide human population variability.

Previously, the use of high-throughput transcriptomics on a large panel of
isolated primary human hepatocytes was performed to establish human variability
(Niemeijer et al., 2021). However, these cultured primary human hepatocytes may
still have experimental confounding factors that prohibit reliable assessment
of toxicodynamics-related safety factors. Therefore, we will apply our current
knowledge and expertise to study population variability in toxicity pathway
activation using freshly isolated peripheral blood mononuclear cells (PBMCs)
from healthy volunteers from various sex, age groups and genetic background.
The use of a systematic transcriptomics-based analysis of toxicodynamics
properties of diverse chemical entities, in combination with statistical
modelling approaches, will provide a scientific basis for setting
toxicodynamics uncertainty factors for implementation in risk assessment. In
order to expand and explain the variation of individual toxicodynamic profiles,
an exploratory approach is taken to define the exposome through comprehensive
methodology covering lipidomics and metabolomics. The exposome represents the
environmental exposures that an individual encounters throughout life and might
represent an important contributor to their toxicodynamic profile.

Primary:
Part A:
. Evaluate the toxicodynamic variability in an evenly distributed cohort of
male and female healthy volunteers

Part B:
. Evaluate the toxicodynamic variability among age, sex and ethnic backgrounds

Exploratory:
. Correlation of flow cytometry read-outs to transcriptomics read-outs in a
subset of 50 arbitrarily chosen subjects.
. Determination of the exposome-related variation.

The study will comprise a single ambulant visit per donor, no in-clinic stays
are required.

. Telephonic questionnaire:
A telephonic questionnaire will be performed for subjects that have made
contact with the CHDR based on their interest in partaking in the study. In
this questionnaire, preliminary eligibility with the study protocol will be
determined based on sex, age, brief medical history and demographics.
Afterwards, an informed consent form will be provided to these prospective
subjects by mail in order to familiarize themselves with the study prior to the
study visit. A visit to the CHDR for signing of the informed consent, official
determination of subject characteristics and blood collection will be
scheduled. No data will be entered in the eCRF in this stage.

. Screening:
No formal screening is needed for this study. However, all study assessments
will only be performed after full written, verbal and signed informed consent
has been obtained, according to CHDR standard operating procedures. Afterwards,
the subject*s sex, age, brief medical history and demographics will be repeated
for entry in the eCRF.

. Blood collection:
Blood collection will be performed using a venepuncture. Completion of blood
collection marks the End of Study (EOS) for the subject.

. Follow-up:
No follow-up is planned.

No investigational drug will be administered to the volunteers. The invasive
procedures under this protocol will be restricted to blood sample collection
(venipuncture). The burden for the volunteer related to the study procedures is
limited. Only well-established methods of sample collection will be applied,
with a known and limited risk and no or mild discomfort for the volunteer. In
addition, all collections will be performed by qualified medical staff.