This course familiarizes students with the novel concepts being used to revamp regulatory toxicology in response to a breakthrough National Research Council Report “Toxicity Testing in the 21st Century: A Vision and a Strategy.” We present the latest developments in the field of toxicology—the shift from animal testing toward human relevant, high content, high-throughput integrative testing strategies. Active programs from EPA, NIH, and the global scientific community illustrate the dynamics of safety sciences.
Introduction - What Is a Pathway of Toxicity, and Why Do We Need Them?
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来自 Johns Hopkins University 的课程
Toxicology 21: Scientific Applications
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Module 3
This module will familiarize you with the Human Toxome Project run by Johns Hopkins University in collaboration with several university, industry, and research agencies. Omics technologies, their advantages and disadvantages, as well as concepts of Adverse Outcome Pathways (AOP) and Pathways of Toxicity (PoT) will be discussed.
与讲师见面
Lena SmirnovaResearch Associate
Center for Alternatives to Animal Testing
Thomas HartungProfessor
Environmental Health and Engineering
Hi my name is Dr. Alexandra Martens and I'll be talking to you today
about Pathways of Toxicity from Omics Data.
So in the first section,
we're going to talk about basically what is a Pathway of Toxicity and why do we need one?
For our learning objectives we're going to focus on
how to describe a Pathway of Toxicity,
explain how this is different from previous ways of describing mechanisms of toxicity and
explain why this is important for hazard and risk assessment.
A Pathway of Toxicity represents a fundamental shift.
Previously, toxicology had focused on
black box animal models or very simple molecular models.
But now we're really trying to sort of push toxicity,
to understand its full complexity.
So if you think about a black box animal model,
if you do an LD-50 you're not going to get a lot of
data or understanding about what the mechanism of toxicity is,
you know it's toxic but you don't know why.
The other alternatives with very simple molecular models are focused on
one or two receptors but very few chemicals are that simple in their effects.
Most chemicals have multiple effect.
So a pathway of toxicity is really trying to bring toxicology into
the systems biology era by looking at the chemicals effects on a cell and its entirety.
So not just a part by part level and it's worth your
stopping and thinking a little bit about what systems biology means.
When you think about systems biology,
it's really an attempt to understand the cell at
a whole level rather than thinking about each individual part.
And a good analogy is if you had a transistor radio and you
just started taking a part one at a time you wouldn't really be able to understand it.
You might get an idea of what components were important or
not but you wouldn't understand how it functions as a whole.
Cells are at least as complex if not more so
but we've basically been taking a part by part approach to them.
Systems biology instead seeks to think about the whole cell and
its function as more organically.
What is a PoT? Well the formal definition of a Pathway of Toxicity is
a molecular definition of the cellular process is
shown to mediate adverse outcomes of toxicants.
You can kind of think about that a bit as being able to say
OK we understand every aspect of a toxicants effect,
if you go all the way from the transcription factor or
the receptor that it's affecting to the transcriptional response,
to the coordinated functional response and the physical consequences of that.
So it really is in a certain sense,
you can think of it as a molecular wiring diagram for the cell.
So why is this important?
Well I want you to imagine that you're
a research and development chemist and you want to
design something that's going to be less toxic than BPA.
So you think to yourself OK,
I'll look in Toxcast and I'll figure out what is
the most potent biological target of BPA.
Well it's simple.
That's the Estrogen Receptor Alpha.
And if I just add a sulphonyl group,
it's not going to bind to the Estrogen Receptor Alpha.
So all of a sudden I've got a much less toxic alternative to BPA.
So have I solved the problem of BPA? Maybe not yet.
As it turns out BPA binds to both Estrogen Receptor Alpha and Estrogen Receptor Gamma.
BPS is no better because it actually also binds to
estrogen receptor gamma with a much much higher affinity than BPA.
And would this have been detected by animal testing?
Well probably not.
Animal testing did not really find the effects of
BPA that we've learned about since it's been introduced commercially.
But right now we have 1 to 10 tons of BPS produced per year.
And this has happened over and over and
toxicology has happened with a lot of flame retardants where people have
tried to swap out a less toxic alternative to a chemical only to
find out that the alternative had toxic effects that they didn't really understand.
The take home messages that we cannot design
Safer Chemicals if we don't thoroughly understand toxic mechanisms.
And it's kind of important to sort of think about what that's going to mean.
How complex that's going to be.
If you think about on the left if you start to look at
this diagram that I pulled from a paper on MPTP toxicity,
you can see that this is just positing a very simple mechanism MPTP effects you know
iron it causes some oxidative stress and there's not
really a full understanding of the consequences.
If you look on the right, that's an example of
a comprehensive map of all the proteins genes and
metabolimic processes that are involved in
Parkinson's Disease and you can see it's hundreds,
if not thousands of genes,
enzymes metabolites and so that is the level of complexity that we will
have to understand in order to fully describe toxic mechanisms.
So it's a very tall task.
One of the reasons that this is all possible,
one of the reasons why we can start to think about these things at
a systems level is because we've entered the age of what's called the Omics data.
So what do we mean by Omics data or
another way to think of it as high content and high throughput data.
When you talk about Omics data,
that means it's high content and you can typically major
20,000 genes at a time or several thousand proteins.
And Omics data is essential for
systems toxicology because it captures the full range of effects of the cell.
And this only became possible about 10 years ago 10 or
15 years ago when we really started to develop these technologies that could,
all of a sudden, give us a much higher level view of what's going on in the cell.
High throughput data also known as high throughput screening data
such as Toxicast uses traditional in vitro assays
for example receptor binding assays or enzyme inhibition assays but it's facilitated
using robotics to do hundreds of tests at a time and
it typically uses a larger 96 well plates.
So HTS data is essential for
understanding mechanism this gives us a sense of which enzymes or
receptors are activated by a chemical that also has the advantage of being
done on human cells and with
a lot more reproduceability because it's not done one way in one lab,
and one way in another lab.
So in our next lecture,
we're going to talk a bit about the different types of
Omics Data and the ways that you can analyze it.
