De mens in de milieutoxicologie – The Human in Environmental Toxicology
Inaugural Speech Prof.dr.ir. Juliette Legler
Wednesday, May 8, 2013, VU University Amsterdam
“Water” by Giuseppe Arcimboldo, 1566, Kunsthistorisches Museum, Vienna
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Dear Rector Magnificus, Dean Oudega, members of the Executive Board, Professors and other
members of the university community, ladies and gentleman,
As a child growing up in Canada I would spend hours in the backyard, that magical place we
called the “dream world”, digging with my hands through the dirt, coming home to show my
mom and dad the treasures I had found: worms, flowers, jars full of tadpoles…I realized already
then what I am standing here telling you now, we are part of nature while at the same time we
stand above it. We influence it and we have the power to destroy it. By polluting the
environment we live in, we ultimately pollute ourselves. Mens en het milieu, humans and the
environment, we are intricately interwoven, and to know something about one, we have to
know something about the other. Giuseppe Arcimboldo painted this painting called Water in
1566 and I think it’s beautifully symbolic for the unity of humans and the environment.
In the next 45 minutes I will take you on a journey of how an environmental toxicologist
focused on fish became fascinated with the aspects of toxicology that investigate human health
and even tested the new waters of epidemiology …. Along the way you will see a number of
slides that many of you will recognize as well as people who have been pivotal in my research.
Understanding mechanisms of toxicity has always been a central theme of my research because
it is what couples the researcher in me who wants to understand biological processes at their
most profound level with the environmentalist who wants to do something to protect this earth.
Toxicology is the perfect combination for the biologist and the environmentalist in me and I feel
challenged and privileged to be a position to take this science a step further, and to be in the
position to teach and hopefully inspire the next generation of environmental scientists.
Slide 1: Headlines from Dutch newspapers, 1996
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Endocrine disrupting chemicals
This is a slide I made at the beginning of my PhD period in 1996. I still remember standing in the
hall of the Department of Toxicology in Wageningen at the copy machine, arranging these
headlines from various Dutch newspapers. The age of endocrine disruption had just started.
We were just becoming aware of the possible effects of chemicals on the endocrine system,
that overarching system that regulates glands such as the pancreas, adrenals, sex organs and
parts of the brain. Chemicals such as pesticides, chemicals used in industrial processes such as
the polychlorinated biphenyls and brominated flame retardants, chemicals produced by
incomplete combustion like dioxins and polycyclic aromatic hydrocarbons, but even the
chemicals we take as medicine or add to our food or our personal care products which get
released back into the environment through our waste water treatment plants, these chemicals
have the potential to interfere with the endocrine system of humans and animals in nature.
At the time I started my PhD research there was much attention on the effects of chemicals
that mimic female hormones, the estrogens, and the pioneering work done by Professor John
Sumpter, shown here on the left at my PhD defense. Professor Sumpter showed the world that
chemicals excreted by humans are not entirely removed in waste water treatments and may
ultimately be discharged into rivers, where they may feminize male fish.
Slide 2: Members of my PhD defense committee, Wageningen 2001
My earlier work focused on developing tests or assays to identify chemicals that activate
estrogen receptors, and involved the development of a genetically altered human breast cancer
cell line, the ER-CALUX, that can distinguish chemicals that bind to estrogen receptors (Legler et
al, 1999). The ER-CALUX is still being used, albeit in different forms, to screen chemicals and
environmental samples for estrogenic activity.
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Now, about 15 years later, endocrine disrupting chemicals are still an important topic of
research in toxicology and these chemicals are still a headache for industry and regulators. In
February of this year, the United Nations Environment Programme and the World Health
Organization released The State of the Science of Endocrine Disrupting Chemicals (WHO, 2013).
This report, edited by our close collaborator Ake Bergman from the University of Stockholm,
synthesizes recent data from wildlife, laboratory animal and epidemiological studies and
suggests an even greater role for endocrine disrupting chemicals in disease than was predicted
10 years ago. The report shows that endocrine related diseases and disorders are on the rise
over the past 40 years. These include low semen quality, genital malformations, adverse
pregnancy outcomes, early onset of breast development in girls, neurobehavioral disorders,
and endocrine-related cancers such as breast, testicular and thyroid cancer. The prevalence of
obesity and type 2 diabetes, both diseases in which endocrine function is impaired, has
skyrocketed with 1.5 billion adults worldwide who are overweight or obese. In fact there are
now more overweight people in the world than undernourished. It is estimated that 1 out of
every 3 babies born will develop diabetes in their lifetime. The incidence of these endocrine
diseases has risen so quickly in recent decades that genetic factors cannot by the only
explanation. Environmental factors such as exposure to endocrine disrupting chemicals must be
involved. The environmental contribution to diseases is estimated to be about 30% of the
global disease burden (Smith et al, 1999) So it is clear that that the issue of endocrine
disruption, often referred to in the earlier days as a “hype,” is far from over, and the scope of
effects of EDCs has clearly broadened from feminized fish to a playing a role in the major
human health challenges of our time.
Developmental Origins of Health and Disease
Importantly, the State of the Science report also signals another trend in endocrine disruptor
research: the shift in focus from investigating adult exposure and disease outcomes to
examining developmental exposure and disease outcome later in life. It is now generally
accepted that early development (in utero and during the first years of life) is an extremely
sensitive life stage for chemical induced health effects (Kortenkamp et al, 2011). This focus on
early development in toxicology has been sparked by an increasing awareness in the field of
biology and preventative medicine that susceptibility to disease can be programmed early in life.
The so called “developmental origins of health and disease paradigm” proposes that an adverse
environment during fetal and postnatal development leads to a functional change in developing
tissues that increases susceptibility to disease later in life (Gluckman & Hanson, 2004). An
adverse fetal environment can be caused by factors such as maternal undernutrition or
overnutrition, stress and smoking during pregnancy. Exposure to chemicals has been added to
this list of early life stressors that may have profound effects on disease susceptibility.
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Slide 3:: The early stages of development may be the most sensitive to endocrine disrupting
chemicals
Perhaps some of the most convincing evidence of the developmental origins of health and
disease paradigm comes from studies carried out with people who were born during the Dutch
Hunger Winter at the end of World War II (Roseboom et al, 2011).. The Dutch Hunger W
Winter
lasted 6 months, when food supplies wer
were cut off mainly in the west of the Netherlands, and
many people suffered from famine and malnutrition. Children born in this period had a
significantly lower birth weight compared to children from other parts of the Netherlands.
Studies have shown that these
hese children
children, now in their 60s, have as adults significantly higher
incidences of disease such as cardiovascular disease, obesity and cognitive dysfunction. The
Hunger Winter studies
tudies show very
ve convincingly how an adverse environment during
development,, in this case prenatal famine, plays a role in an increased onset of disease later in
life.
As many of you know I have taken a particular interest in obesity.. When I think about it seems
almost logical that something I’ve spent my whole life struggling with has become a focus of my
research. Obesity is manifested as an excess number of adipocytes or fat cells. And while the
calories in and calories out paradigm has dictated how we perceive and fight obesity, it is clear
that we really know very little aabout this multifactorial
tifactorial and complex disease. The
T conventional
therapies to treat obesity, eat less and exercise more, are remarkably ineffective over the long
term (Taubes, 2013). There is more to this dis
disorder than meets the eye.
Obesity as I mentioned already is an endocrine disease, and the adipocyte is not just an inert
storage depot of lipids.. The adipocyte is an active cell which produces a number of adipokines,
which are hormones and molecules with different endocrine functions,
functions, all of which play an
important role in appetite regulation and energy metabolism . Examples are leptin, which is
released by the fat cell and regulates appetite in the brain, and adiponectin which increases
sensitivity to insulin. The adipocyte
dipocyte also secretes estrogen. Pertubations in the homeostasis of
these hormones is associated with a number of diseases such as type 2 diabetes and disturbed
lipid metabolism.
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Slide 4: The adipocyte is an active cell that produces adipokines and is a target for endocrine
disrupting chemicals
Research in the past 5 years or so has shown that prenatal exposure of laboratory animals such
as mice to selected endocrine disrupting chemicals causes animals to become overweight, as
shown in the hallmark studies of Retha Newbold who exposed her mice during pregnancy to
the synthetic estrogen DES. Low dosages of DES during prenatal life caused the animals to grow
fatter in adulthood, many months after the exposure had stopped (Newbold et al, 2007). These
studies, and others, have indicated the sensitivity of early development to chemicals that
disrupt fat cell differentiation or the programming of energy metabolism.
OBELIX
I have had to the privilege to coordinate a European project called OBELIX which is in its fourth
and final year. I have been working with this talented group of scientists of various backgrounds,
many of whom are in the room today, and we have been tackling the question if early life
exposure to endocrine disrupting chemicals plays a role in the development of obesity later in
life. This multidisciplinary project combines epidemiological studies in mother-child cohorts
with laboratory studies with rodents and mechanistic in vitro studies (Legler et al, 2011).
The classes of endocrine disrupting chemicals we are studying are the chemicals that are found
in our food and in our everyday life. These include the persistent organic pollutants that tend
to accumulate in fatty foods such as fish, including dioxins, polychlorinated biphenyls or PCBs,
brominated flame retardants PBDEs and HBCD, organochlorine pesticides like DDT and HCB,
and perfluorinated compounds such as PFOS.
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In addition we are investing exposure to phthalates, additives that make plastics soft and
present in food packaging, and in our lab, talented chemical technicians like Jacco Koekkoek
have developed sensitive new methods to measure these compounds in human milk and blood
taken from the umbilical cord at birth. These samples represent the earliest exposure of the
baby to endocrine disrupting chemicals.
Slide 5: IVM chemist Jacco Koekkoek develops new methods to analyze EDCs in cord blood
and breast milk (photo John Collins, 2012)
Our first published study led by our colleagues at VITO Belgium has shown an inverse
relationship between PCB and birth weight in a meta-analysis of 12 European birth cohorts
covering over 7000 children, the largest study of its kind up to now (Govarts et al., 2012).
Decreases in birth weight of 150 g with each 1 μg/L increase of PCB 153 in cord serum were
found. This means that PCB exposure is related to lower birth weight. This overall decrease in
birth weight is similar to the changes found in birth weight in Dutch Hunger Winter babies, and
similar to the effect of smoking during pregnancy, a known risk factor for low birth weight as
well as childhood obesity. The question is, do these low birth weights indeed translate to
heavier children later in life? The Hunger Winter studies would suggest they would. In one of
our cohorts from Slovakia with historically high levels of PCBs, preliminary studies indicate an
association with prenatal exposure and elevated markers of adiposity such as leptin at age 7
(Palkovicova et al, in preparation). OBELIX scientists are currently examining the growth rates of
the children of our cohorts, and differentiating between pre- and postnatal exposure to EDCs. It
is clear that postnatal exposure, breastfeeding, is a major source of chemical exposure in the
developing infant that has largely been overlooked in epidemiological studies, certainly those
studying chemical-obesity links. Preliminary analyses indicate divergent effects of pre- and
postnatal exposure to EDCs on the growth of children.
Animal studies in OBELIX have been carried out mainly by this bright young lady, Joantine van
Esterik, in the lab of Dr. Leo van der Ven at RIVM. Joantine’s studies have revealed clearly
divergent sex-specific effects of developmental exposure to the endocrine disrupting chemical
bisphenol A, a major component of plastics, the perfluorinated alkyl acid PFOA, and the dioxin
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TCDD (van Esterik et al, in preparation). In her bisphenol A study, male offspring of mice
exposed during pregnancy and lactation to low concentrations of BPA showed a modest gain in
body weight and effects on the size of the fat cells making up the white and brown adipose
tissue. Interestingly, Joantine found an opposite effect in the females exposed during
development to BPA. Depending on the sex, the levels of endocrine hormones like glucagon,
insulin and adiponectin were different in the exposed animals than the non-exposed animals.
And remember, these hormones were measured in adulthood, months after the exposure was
stopped.
Slide 6: PhD candidate Joantine van Esterik is studying the effects of perinatal exposure to
EDCs in mice
The question that we have been investigating is, how is that exposure to a chemical during
development stably changes the function of a tissue or organ so that the release of hormones is
changed long after the exposure has stopped? In other words, how do chemicals program an
organism during development to be more susceptible to diseases such as obesity? If we are to
understand this we must dig down into the very basics of life, to understand how genes and
molecules called DNA work. It has been 60 years since Frances Crick and James Watson
discovered that hereditary information is encoded in the double helix of DNA. Their discovery
led to the central dogma of how genes work, that they flow in a linear fashion from DNA
sequence to messenger RNA to protein, to manifest finally as a phenotype, basically the way I
portrayed it on the cover of Toxicological Sciences 14 years ago (Legler et al, 1999). It is clear
that this is a too simplistic view as to how our genes work. At the end of the human genome
project, it was estimated that only 1% of our DNA encodes the 20000 genes that code for
proteins, the rest being so called “junk DNA”. In the meantime, the Encyclopedia of DNA
elements or ENCODE project, has recently shown that at least 80% of the genome is transcribed
to RNA. Thousands of RNA molecules have been discovered that do not encode proteins but are
now known to have key regulatory functions. It is clear that there are more unknowns than
knowns in this field (Ball, 2013). Newfound insights will help us understand how chemicals can
alter these basic processes.
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Epigenetics
It is clearly an exciting time in molecular and evolutionary biology, and I’m happy to be tagging
along as a toxicologist, learning as we go. One area of molecular biology where new discoveries
are made on what appears to me to be a daily basis is the field of epigenetics. Epigenetics
describes the array of chemical markers and switches that lie along the length of the DNA and
provide instructions to genes for what to do, and where and when to do it. Epigenetics involves
3 main processes, as far as we know: histone modifications, DNA methylation and micro RNAs.
Chromosomes containing our genetic information are made up of strands of DNA. These
strands of DNA are wrapped around proteins called histones forming a unit called a nucleosome.
The way in which these histones are modified by enzymes changes the accessibility of the
underlying genes for expression, leading to either activation or repression of genes. DNA
methylation is a process by which enzymes called methyltransferases attach methyl groups to
specific nucleotides on DNA. DNA methylation alters the expression of genes and generally,
increased methylation is associated with repression of gene expression.
Our research up to now has focused on DNA methylation, an important epigenetic process of
regulating gene expression during development. The methylation of genes during development
is dynamic and occurs in sex-specific waves of demethylation and remethylation depending on
the stage of development. DNA methylation stably alters the expression of genes in cells as
they divide and differentiate from embryonic stem cells into specific tissues. The resulting
change is normally permanent and unidirectional, preventing one tissue from reverting to a
stem cell or converting into another type of tissue. Such a dynamic process is sensitive to
environmental stress, including exposure to chemicals, which may result in a changed
differentiation or function of a tissue (Legler, 2010).
In the OBELIX project we are studying how epigenetics plays a role in the long term effects of
prenatal exposure to chemicals. Two hypotheses we are investigating is if early life exposure to
endocrine disrupting chemicals leads to an adult obese phenotype by inducing the
differentiation of adipocytes, and if this enhanced adipogenesis early in development is
accompanied by epigenetic changes such as DNA methylation.
EDCs
Early exposure
Epigenetics?
(DNA methylation)
Adult phenotype?
Adipocyte differentiation?
Slide 7: In the OBELIX project we examine how early exposure to EDCs leads to an obese adult
phenotype
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PhD candidate Liana Bastos Sales has been working on an in vitro cell culture method by which
she cultures mouse 3T3 L1 preadipocyte or early fat cells in petri dishes. The cells can be
induced to mature fat cells by adding a cocktail of hormones such as insulin.
Slide 8: PhD candidate Liana Bastos Sales investigates the effects of EDCs on fat cell
differentiation using cell culture models (photo John Collins, 2012)
Liana has just recently published a paper in which she shows that a number of endocrine
disrupting chemicals, including the pesticide tributyl tin, the plastics component bisphenol A
and the brominated flame retardant BDE 47, induce elevated differentiation of fat cells in
culture (Bastos Sales et al, 2013). For tributyltin, the effect on inducing fat cell differentiation
was accompanied by a decrease in global methylation of DNA. This means that a number of
genes in the mouse fat cell genome were demethylated by exposure to an endocrine disrupting
chemical in vitro, indicating a permanent epigenetic change.
Jorke Kamstra has continued this work, and expertly shown that the brominated flame
retardant BDE 47 induces fat cell differentiation at concentrations as low as 3 nM (Kamstra et al,
in preparation). His work has shown that BDE 47 causes elevated expression of genes involved
in adipogenesis, including leptin, the hormone which regulates appetite, and PPARγ, the main
regulatory gene in fat cell differentiation. Importantly Jorke has developed new methods in our
laboratory to investigate DNA methylation of specific genes, and he has showed that the
methylation of the PPARγ gene is reduced upon BDE 47 exposure.
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Slide 9: Research technician and MSc candidate Jorke Kamstra is studying how EDCs affect
specific gene methylation
There is so much work to be done in this exciting new science of epigenetics and how it plays a
role in understanding the contribution of chemical exposure to the developmental origins of
human disease, not only for obesity, but other diseases such as diabetes, cardiovascular disease,
neurodevelopmental disorders and cancer (Legler, 2010). Aspects that I will continue to
investigate include alternate mechanisms of DNA methylation including hydroxymethylation
and the effects of chemical exposure on histone modifications and micro RNAs. We need to
keep in mind that we cannot blindly translate the effects and mechanisms we find in rodent
models to humans. Recent studies for example show considerable differences between the
3T3-L1 mouse and human adipocyte transcriptome and epigenome (Hartig et al, 2012). These
differences highlight the importance of using of human in vitro models for predicting effects in
humans.
For this reason we are also investigating human cell lines and differentiation models and
comparing effects between rodents and humans. I am particularly interested in the application
of induced pluripotent stem cells or ICPS in toxicology, cells that are taken from mature
differentiated cells such as adult human fibroblasts and undergo forced expression of
pluripotency genes. The resulting cells share many of the same properties of embryonic stem
cells, in particular the potential to differentiate in multiple lineages, such as neuronal, liver and
pancreas (Scott et al, 2011). These cells could be a particularly useful model in toxicology, and
this coupled with in silico information from for example the 1000 genomes project, will help us
understand the applicability of our models to humans.
However my main emphasis will be on another alternative model to the rodent and I will
continue on what has been a 15 year quest to make the zebrafish indispensable in mechanistic
toxicology. I’m showing this picture especially for my mom, who the first time she saw it, said
to me “I’ve never seen you look at a man the way you look at your fish” (sorry Guus but I know
you feel this way about fish too). Yes it is a model I have grown to love and I have surrounded
myself by people who love it too.
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Slide 10: Zebrafish are an important model in toxicology and human health (photo John
Collins, 2012)
Zebrafish in Toxicology
For those not familiar with the zebrafish, it is a small freshwater fish about 4 cm in length. It is
naturally found in streams in Asian countries such as India, Pakistan and Bangladesh. Zebrafish
are popular aquarium fish because they breed easily, lay many eggs and are easy to look after
in a small aquarium tank. By far most of the research done in zebrafish is performed in embryos,
early developmental stages of the fish. This image shows some of the major morphological
features of a five day old zebrafish. You can see it has some of the same major organs and body
parts as a human, e.g. brain, eyes, ears, heart, muscle.
The main advantage of the zebrafish is its rapid and transparent development. You can study its
well characterized development in a period of days and due to many advances in molecular
biology, it has become a major model in studying gene function during vertebrate development,
and it has become a major model for studying human diseases such as cancer, cardiovascular
disease and tuberculosis, research performed by colleagues at the VUMC. You can localize
gene expression, inactivate or knock down genes, or visualize genes with marker proteins using
advanced transgenesis technology, all in a living organism.
The days of my own transgenic zebrafish line, developed to visualize exposure to estrogenic
chemicals (Legler et al, 2000), seem long past when you see these images of what is now being
accomplished with the zebrafish embryo. The so-called brainbow fish in which neurons are
labelled with red, blue and green fluorescent proteins, which are taken up by the various
neurons allow researchers to follow the development of the brain and nervous system in a
living organism (Pan et al, 2011). An award winning image of a transgenic fish with a
fluorescent blood brain barrier even made the Metro newspaper last year
(http://www.nikonsmallworld.com). And a recent news-making item is the work of a group of
Spanish researchers who induced the development of limbs instead of fins in zebrafish embryos
by overexpression of mouse Hoxd13, an important gene in distinguishing body parts during
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embryological development (Freitas et al., 2013).
2013) This work sheds light on how it was possible
that limbs evolved from fins thousands of years ago.
My lab has made significant headway using the zebrafish embryo both to test chemicals for
their effects on development,, and to unravel mechanisms of development toxicity.
toxicity The PhD
work of this
his young man, Thijs van Boxtel, was a dream come true for me, the merging of
toxicology and developmental biology. Thijs’ work with the dithiocarbamate pesticides,
pesticides one of
the most widely used groups of fungicides on fruits and vegetables, not only revealed
reveale novel
effects and mechanisms of toxicity of these pesticides, but in doing so, identified a new role for
a relatively understudied family of genes in development. Thijs discovered that pesticides
pesticide like
metam, thiram and disulfiram cause abnormal development
nt of cartilage and bone elements
that make up the zebrafish craniofacial skeleton,
skeleton, here stained blue and pink in the top panel.
panel
Thijs showed that dithiocarbamates inhibit lysyl oxidase activity
activity, proteins which cross-link
elastin and collagen monomers into the fibers that make up connective tissue (van Boxtel et al,
2010a; 2010b). He also showed the importance of lysyl oxidases in zebrafish development,
development such
as loxl3b, whose expression is shown as the blue stained developing cartilage in the bottom
right panel (van Boxtel et al, 2011).
2011)
Slide 11: Researcher Dr. Thijs van Boxtel discovered novel roles for lysyl oxidase genes in
zebrafish development and teratogenicity during his PhD research at IVM
My work on developmental toxicity in the zebrafish embryo has continued,
continued and we have
discovered novel mechanisms of developmental toxicity of metabolites of brominated flame
retardants (van Boxtel et al, 2008),
200 and are currently working on how and which chemicals
cause neurological effects, DNA damage and effects on energy metabolism (Legradi et al, in
preparation) and thyroid hormone function. I have had the privilege of receiving funding the
Netherlands Science Foundation to develop the zebrafish as a model
model for the obesity-chemical
obesity
link. You may be thinking, how can fish be a model for obesity in humans? Well humans and
zebrafish share a number of similarities. Their digestive organs, adipose tissues, and skeletal
muscle are physically arranged in a manner
manner similar to their human counterparts, and the
machinery of lipid synthesis and transport used by humans is present
present in the zebrafish (Schlegel
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& Stainier, 2007). Zebrafish can become overweight on a high caloric diet (Oka et al, 2010).
Importantly, methods are available to stain lipids and easily visualize fat cells in the living fish
(Hölttä-Vuori et al 2010).
That being said, relatively little is known about the differentiation of fat cells during zebrafish
development, and the role of genes like PPARγ and leptin that are so important in human and
mouse fat cell development. So you can imagine my excitement when I got a phone call in my
office from these 3 ladies proclaiming “we’ve got fat cells!”.
We’ve got fat cells!!!
Renate Kopp
Marjo den Broeder
Frances Agu
Slide 12: Renate Kopp, Marjo den Broeder and Frances Agu study adipocyte differentiation in
the zebrafish
We have been able to visualize clearly by using a fluorescent lipid stain that fat cells develop
around 15 days post fertilization. Renate Kopp, Marjo den Broeder and Frances Agu are all
working on the development of the zebrafish as a model for obesity, and their work will
characterize the role of important genes in fat cell development, both by inactivating them
using TALEN technology, and making transgenic lines. These new models will allow us test
chemicals early in life for their effects on fat cell differentiation, and importantly, will allow us
to perform multigenerational studies with the zebrafish to see if susceptibility for obesity is
transferred from generation to generation, and if epigenetics plays a role in this process.
Importantly, the zebrafish model for obesity will allow us to examine some of the novel risk
factors in obesity. As I wrote in a recent invited commentary for the journal Obesity, there are
many unanswered questions (Legler, 2013). Do chemicals influence underlying circadian
rhythms that may perturb energy metabolism? This is work that researcher Dr. Renate Kopp is
tackling in my group. Do chemicals play a role in inflammation in adipose tissue, which in turn is
a risk factor for cardiovascular disease? What about chemicals and gut microbiota? Chemical
exposure can affect the populations of microorganisms in the digestive tract, and studies show
that gut microorganisms are different between the obese and non-obese. And there is of
course the challenging task of examining combinations of stressors such as chemicals and
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quality of diet. And what about chemical mixtures? We are exposed to a cocktail of
o chemicals at
the same time, a mixture of hundreds if not thousands of chemicals in our everyday life.
Effect directed analysis
My work with mixtures has taken off thanks to my privileged position of working at the Institute
for Environmental Studies together wit
with world class chemists like the lady to the right of me in
this picture, Marja Lamoree, not to mention Jacob de Boer on the left of me, and of course this
young lady getting her PhD a few years ago,
ago Corine Houtman.. Thanks to them,
them I have been
introduced to the world of effect directed analysis (Houtman et al, 2006)..
Slide 13:: PhD defense of Corine Houtman, who developed EDA methodology at IVM (photo
Hans Stol, 2007)
Effect directed analysis (EDA) is an approach in which we combine chemistry and toxicology, to
break down complex environmental samples containingg thousands of chemicals into
manageable parts, whose toxicity can be tested in a living cell or organism, and whose
who identity
can be revealed by state of the art chemical analysis. In a recent study, we used an effect
directed analysis approach and identified new chemicals in polluted soil that cause
developmental toxicityy in zebrafish (Legler et al, 2011).
It is our goal to further develop effect directed analysis using the zebrafish given all its
advantages and the possibility to test samples in a 96 well or smaller setup. In fact it’s these
advantages that have already brought the zebrafish into the realm of high throughput drug
discovery testing where there have already been successful cases of human drugs first
discovered in the zebrafish.. I call this work our toxicant discovery testing, and Jessica Legradi is
leading this work by combining the methods she’s developed in our lab into a SMART zebrafish
embryotoxicity (ZFET) test, so that we can identify chemicals in complex environmental samples
that not only cause effects on morphology but also affect sensitive biological systems relevant
to human prenatal exposure, such as neurotoxicity and energy metabolism.
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Slide 14: Researcher Dr. Jessica Legradi is developing “smart” EDA methods to identify
chemicals in environmental samples with specific effects on zebrafish development
Teaching in Environmental Toxicology
So up to this point in my speech I’ve been talking about the human side of environmental
toxicology in terms of my research on understanding the effects of chemical exposure on
humans. There are more human sides to environmental toxicology, and equally important are
the students who make up the next generation of environmental toxicologists. We’ve really
made our mark on undergraduate teaching, with the zebrafish developmental toxicology
practicals expertly lead by researchers like Peter Cenijn being integrated in various Bachelor
courses in various programmes like Biomedical Sciences, Health and Life Sciences and Medicine.
Slide 15: Peter Cenijn leads the zebrafish developmental toxicology practical in 1st year
"Human Development and Evolution" course
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I’m proud to have started a new Master track in Environmental Chemistry and Toxicology
within the Master of Ecology, thanks to a wonderful collaboration with animal ecologists here
at the VU and environmental chemists and toxicologists at the University of Amsterdam. The
programme is still young, but has attracted a small group of dedicated Master students who like
me are fascinated with the opportunity to combine basic research with environmental
protection. It is my hope that this program will continue to grow and continue to attract bright
young minds, and that in the near future we can develop a second Master programme more
oriented towards the biomedical aspects of toxicology.
The VU: Looking Further
On a final note, these are turbulent times at the VU University: a management crisis, financial
losses, reorganisation plan, low rankings and the resignation of our former Rector Magnificus
(Ad Valvas, 2013). The new Rector Frank van der Duyn Schouten’s main priority is to
increase the quality of our teaching. The new Rector has been described as an adversary of the
“zesjes cultuur” , the attitude that just passing a course without too much additional effort is
good enough. I wholeheartedly support all efforts to improve the quality of our teaching as I
believe that education is the cornerstone of every university. Our students deserve a good
education, and I’m all for challenging students and having high expectations of them. I hope
that the improvement in teaching at the VU boils down to investment and not new bureaucracy
or a further increase of “efficiency”, a word we hear a lot at the VU these days. I think it also
means taking a critical look at the number of students we are teaching. I just can’t provide the
same type of interaction and feedback with a first year course of 250 students compared to one
of 60 students. One positive thing that will hopefully come out of the VU crisis is the recognition
that somewhere along the way, we lost sight of the core tasks of a university, namely high
quality research and teaching, in the quest for up scaling and efficiency. We need to get back to
the basics. And to do this, we need internal funding that realistically covers the amount of time
it takes to teach, and a good support system with our administrative and financial support staff
left intact. Our researchers and lecturers who already work so hard should be left to focus on
their main task: research and teaching.
Acknowledgements
As I come to the end of this speech, I would like to express my gratitude that even in these
turbulent times, the VU University is investing in new professors and supporting my chair in
Toxicology and Environmental Health. I would also like give thanks to the many people who
have supported me in the journey leading up to this podium, too many to mention here but I
will take a moment to thank a few in particular. You’ve already seen a number of key people in
my research pass by, all of whom I sincerely thank for their contribution to my research.
First of all, my mentors during my PhD period inspired me and played an important role in the
scientist I am today: Professor Jan Koeman, who unfortunately could not be here today, one of
the founding fathers of toxicology in the Netherlands; Dr. Bart van der Burg, who introduced
me to the world of molecular biology and the zebrafish model at the Hubrecht Lab; and
Professor Tinka Murk, who welcomed me in Wageningen and into the world of environmental
toxicology and inspired me with her personal way of mentoring.
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The entire department of IVM’s Chemistry and Biology is a group of the most hardworking but
generous and fun people you can imagine, and it is a real pleasure to work with you all. At the
head of this group is Professor Jacob de Boer, whom I deeply thank for his support and for
giving me the freedom to pursue my research goals. Jacob, with you at the head of our IVM
ship, I have no doubt that we will soon be sailing in smoother waters.
There is one colleague in particular I’d like to thank for years of support and friendship: Dr.
Timo Hamers. Timo and I invented the phrase “wij kunnen alles”, we can do everything, and I
when I’m brainstorming with Timo, I really believe we can.
Now on to my family. This is my Saturday morning family and thanks to the inspirational
leadership of our meester Mark Bresser shown here on the right I get to pound and kick out my
frustrations and stress on a weekly basis and clear my mind. And according to Mark, it keeps
me young, so it’s worth it!
My dearest family, thank you all for coming from all around the world to share this moment
with me. Words can’t express how much it means to me that you are here. I’m so sorry my
father could not be here in person today to share this moment with us, but I’m so happy my
mom is here. Dear mom and dad, thank you for being such wonderful parents and for
encouraging us to realize our dreams, even if it meant that an ocean would come between us.
Nu nog een paar laatste woorden in het Nederlands. Mijn lieve schoonfamilie, mijn genereuze
schoonmoeder Riet die ook een geweldige oma is, en mijn schoonzusje Dian en haar familie,
dank jullie wel voor alle steun de afgelopen 20 jaar. En nu kan de wereld zien wat er eigenlijk
onder deze toga zit.
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En dan, last but not least, deze lieve mensen, lieve Guus, Vincent, Diana, jullie zijn het zonnetje
in mijn leven, en jullie zorgen ervoor dat ik straal. Dank jullie wel voor jullie onvoorwaardelijke
liefde. Guus, dank je voor alle steun.
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So the image I will leave you with today is this one,, the view of the lake at the summer home of
my parents in Canada, a breathtaking
reathtaking picture taken by my brother in law Javier Garcia. For me it
is representative of the beauty of nature, and of the responsibility that we have, as humans in
the environment, to
o protect it. Thank you all very much for your attention.
Ik heb gezegd.
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