Oh
it’s been one of those days. Everything that could go did go wrong. So to try
to salvage something of the day and not start November with a complete and
utter fail, I thought I’d use the next hour I have to wait before I can do
anything to the (probably failed) peptides I have (not) managed to make today
writing something interesting. On the plus side, I get a witty title out of it-
let’s view this as an offering to the Gods of Science to get them back on my
side so that they will make my experiments work again! It’s worth a try.
As I
am in the lab, I thought that I would take something lab-related as my
inspiration, so today I will be focussing on the all-out baddy and the compound
we all love to hate, acrylamide. You may be familiar with the name due to the
abundance of articles in the press about how bad burnt/roasted/cooked food is
for you and how it will give you cancer. I know about it because my lab uses
acrylamide on a day-to-day basis to make things called SDS PAGE gels. SDS PAGE
stands for Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis and is an
incredibly clever and useful technique used to separate proteins. So it’s not
really a complete baddy. It’s just all about context.
Let’s
start with the good side of acrylamide: PAGE. PAGE is a fantastic technique and
has lots of applications. Basically, a gel made from polymerised acrylamide
(lots of molecules of acrylamide joined together to make a large structure) is
made between two glass plates. Samples of protein which have been denatured using
various chemicals and heating are loaded into wells in the top of the plate and
a charge is applied across the plate so that the top is negatively charged and
the bottom is positively charged. The denatured protein is negatively charged,
so moves towards the bottom of the plate. The size of the protein determines
how far it moves through the gel, so it will be deposited as a band at a
particular point on the gel, which will show up in a rather fetching shade of
blue when stained with a special protein stain. If you also load a reference
mixture with pre-stained proteins of known molecular weight, you can compare
the protein you are investigating to the reference and see what molecular
weight your protein is, whether your samples contain a mixture of protein and if
you have what you want. Which is great. Plus the gels can look really pretty.
Usually prettier than this:
So far so useful. But what about the bad side?
And how is this related to food? I promise that there is a point, which I will
be getting to rather shortly. As in now. Acrylamide is really blooming toxic.
It’s a neurotoxin, which means it affects the nervous system and disrupts major
signalling pathways in the body which really aren't meant to be disrupted. We
aren't allowed to use it as a powder in the lab in case we inhale it and die.
It’s less toxic as a liquid and when it’s part of a gel (unless you decide that
to eat it) and we all have to treat it with care and follow all of the
excellent safety procedures we have in place for using it to avoid nasty
accidents.
Unfortunately,
as I alluded to in the introduction to this post, acrylamide is practically everywhere
in the world of food. It is made due to the oxidation of the amino acid
asparagine, which occurs at high temperatures1 and is found in foods
which are high in starch and, according to the Food Standards Agency, baked,
fried, grilled or roasted2. So basically all cooked foods. Yay.
The
risk was first identified by scientists in Sweden in the late 1990s and
prompted an enormous number of studies, reviews and comment in both the
scientific literature and standard press. If you type “acrylamide food” into
PubMed you get 1009 hits and it’s not surprising. Acrylamide was already known
to cause cancer in mice and so had been classified as a possible human
carcinogen3. The way in which it is proposed to cause damage is by
being metabolised to form an epoxide called glycidamide, which is a very reactive
species containing oxygen in a three-membered ring. Epoxides are generally bad
news in the body, as they react with DNA. This can cause problems with the
regulation of cell replication and lead to uncontrolled cell proliferation, which
is one of the key features of cancer. A very clever study by the Swedish
scientists4 made use of the fact that acrylamide also binds to the
N-terminal amino acid valine (ie. nitrogen-containing end) in haemoglobin to
form an adduct called CEV (N-(2-carbamoylethyl)-valine, which allows background
levels of acrylamide in the body to be assessed. The team fed some rats a diet
which was high in fried foods and had a control group of rats fed on a diet of
unfried food. They found much higher levels (almost 10-fold) of CEV in the rats
fed on a fried diet than those in the control group, meaning that fried foods
did seem to be causing increased levels of acrylamide in the body. A later
study in 2002 by Rosen et al found high levels of acrylamide in foods such as
crisps, bread and cereals5. Since then, the major culprits have
commonly been found to be bread, fried potato products, baked goods and coffee.
How upsetting.
However,
there is no need to panic yet! Lots of agencies, including the WHO, European
Commission and European Food Safety Authority have been working on this for
some time and have been developing codes of practice and better knowledge about
acrylamide levels in food. Right now, all they recommend is that acrylamide
levels in processed foods be as low as possible, and that when you are making
chips or toast you make them as pale as acceptably possible to reduce
acrylamide levels2-the burnt stuff is particularly bad (see title!).
Which is no fun, but probably
worthwhile. A lot of work is being done to make more sense of the link between
acrylamide and cancer, as the data so far is unclear6. It’s fair to
say that enjoying a balanced diet and minimising your intake of starchy fried
goods can be no bad thing, but right now the jury is out on just how much
acrylamide is safe to consume without increasing the risk of cancer. I'm not trying
to preach here, not least because I am the first one to be found eating a chip
butty with a cup of coffee on the side, but it is something to bear in mind.
I’m
always fascinated by the dual personalities found in science. The everyday
objects of the lab can be extremely harmful if treated without respect or if
they turn up in significant amounts in the wrong place. The story of
acrylamide, in particular, also shows that there are lots and lots of really
clever scientists out there studying what we eat in minute detail and having a
huge impact on public health. ‘Cooking a fry-up for rats’ may have sounded a
little bit bonkers to a lot of people at the time, but the outcomes of the
study have led to some really serious work and a much better understanding of
how what we put in our mouths affects our bodies in a very real and sometimes
quite scary way. There’s still work to be done on this and so much more. So get
out there, all of you sciency people, and keep finding it out. Then let the
rest of us know what you find.
Addendum:
Monday 4th November. I checked my peptides-they didn't work. Even my really pretty interesting blog post (!) couldn't please the
Science Gods. Apparently science doesn't work like that. Oh well, maybe next
time…
References:
1)
Tareke, E. et al, J Agric Food Chem. 2009,57(20):9730-3.
3)
Orellana, C. Lancet
Oncol. 2002, 3(6):325.
4)
Tareke, E. et al. Chem Res Toxicol. 2000, 13
(6):517-22.
6)
Pedreschi, F. et al J Sci
Food Agric. 2013 Aug 12. doi: 10.1002/jsfa.6349. [Epub ahead of print]
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