Vitamin E is the second of the fat
soluble vitamins I’ll talk about here.
Vitamin E, like vitamin K
contains many compounds
and they’re categorized into two groups
known as the tocopherols
and the tocotrienols.
Within each group, there are various
stereoisomers that can occur.
This includes both cis trans isomers
as well as isomers relating
to the stereochemistry.
These molecules act like antioxidants
and they do this by
preventing the proliferation
of reactive oxygen
species as I will show.
Vitamin E inhibits the production of reactive
oxygen species by a chemical process,
not by an enzymatic process.
And this is a very important
way that it functions.
Vitamin E is the fat-soluble
vitamin equivalent of vitamin C,
which helps prevent the proliferation
of reactive oxygen species
in water soluble material.
An example of tocopherol and an example
of tocotrienol is shown on the right.
Now, vitamin E is found most abundantly in
wheat germ, sunflowers and safflower oils.
It acts counter to vitamin K and that it
actually reduces the amount of clotting.
So a person who was on Coumadin
or warfarin type medication
will have to monitor how much vitamin E
they’re actually getting in their diet
because they can actually be in danger
of reducing clotting too significantly
if they get too much vitamin E.
Now, vitamin E is really the vitamin
about which we know the least
and the reason for that it is
very rarely ever deficient.
There are few cases where it’s known
for deficiency but not very much.
Vitamin E therefore is little benefit
to people to take supplements,
although a lot of people do
take vitamin E supplements.
So there are some problems with overdose,
but it’s not as severe
as an overdose problem
as one might have with vitamin
A or vitamin D for example.
So this figure shows the different
forms of vitamin E that can exist
among both the tocopherols
and among the tocotrienols.
We see in the case of the tocopherols
that, in fact, of all these molecules
they differ primarily in the
structure of the components attached
on the ring at positions
R1, R2 and R3.
So these varying structures give vitamin
E a variety of different forms.
Remember also that the isoprenes
on the right side in the brackets
are varying place with numbers
of units that are out there.
So we can imagine vitamin E molecules are
quite varied and diverse
in their structures.
There is the R1, the
R2, and the R3.
Now, that dotted line that you
see within the isoprene unit
is actually a varying point among the
different tocopherols versus the trienols.
That bond is a single
bond in the tocopherols
which means that you wouldn’t
have a second line that's there.
Or it’s a double bond on the
tocotrienols which means
you would have double bond
or a second line there.
So we’ve compromised and put a dotted
line to indicate that it could be either
depending upon whether
it’s one form or the other.
The alpha tocopherol is preferentially
absorbed and stored in humans.
It prevents damage from reactive
oxygen species as I've noted.
And it protects the membrane
lipids in particular.
We remember that the membrane has
that very non-polar portion of it
and within that non-polar portion
is where alpha tocopherol
and the vitamin E compounds
will abundantly be found.
Alpha tocopherol inhibits the lipid
peroxidation chain reaction.
I’m going to show you that in a second,
but this is repetitive
reaction that can generate
a tremendous amount
of lipid peroxide.
And lipid peroxides are very
problematic within our body.
Alpha tocopherol inhibits protein kinase C,
which we've seen in another
of the presentations
and protein kinase C is
involved in a signaling process
and it also inhibits smooth
muscle growth as a result.
Another thing that alpha tocopherol
do is inhibit platelet stickiness.
And it’s through this mechanism
that the clotting tendency
of the blood clotting
process is reduced.
Because the platelets
sticking to each other
is the very first step in the
process of forming a clot.
It’s known as the cellular response and
stickiness is very critical for that process.
If vitamin K inhibits it,
it reduces the amount of clotting
that can occur in the body.
So for this reason, we don’t want
to take too much vitamin E.
And by the way, I’m using the term alpha
tocopherol interchangeably with vitamin E
because alpha tocopherol turns out to
be the most abundant form of vitamin E
and also the most effective.
It’s the one that is most easily
absorbed within our intestines.
Now, vitamin E may have a role
also in neurological function
and the reason we think this is case
is that deficiency of vitamin E,
though it’s not very common.
When it does occur, it seems to lead
to disorders among the nervous system.
On this slide, I want
to describe the lipid
peroxidation chain reaction
that I described earlier.
Now, this reaction occurs along
the fatty acids side chains,
fatty acids in fats and the
lipids of our membranes
or in other places
found in the cell.
In this reaction,
there are free radical molecules
that are reacting with the lipids.
Now, we see on the top reaction, first of
all, that there’s a hydroxyl free radical
that is interacting with the
unsaturated lipid on the left.
That unsaturated lipid gets changed
or altered in the process.
It loses water and moves the free radical
from being on the hydroxyl group
to being on the lipid itself.
So the fatty acid now is actually
a free radical on its own.
Free radicals can be very problematic
for the cell because they
proliferate very readily.
They are not stopped easily by enzymes.
And in fact, enzymes would
have a hard time keeping
up with what these
radicals actually can do.
The free radical of the lipid can combine
with molecular oxygen as you see here
to form the lipid peroxyl radical
that is shown on the right.
We’ve now proliferated
that into a new form
which can then interact
with yet another fatty acid
and create yet another
So we this sort of process
occurring over and over cyclically
and cyclic processes like that can
generate a tremendous amount of problem.
So what’s important with vitamin E
is vitamin E will actually prevent
each of these free radicals
the molecules that I
have described to you.
Vitamin E chemically reacts with each one
and stops it from being a free radical.
Now that’s a real value
of an antioxidant.
Vitamin C does a similar thing, as I
said, for other components of the cell.
This prevention of the
proliferation of the free radical
stops this oxidative
process from occurring.
Now, hat oxidative process that’s
occurring in the membranes of our cells
is really, really critical because it’s
involved in processes like atherosclerosis.
One of the steps in atherosclerosis
of lipids being carried in our blood
stream by molecules called LDLs.
And when they react in the
way that we’ve seen here,
the immune system attacks them and starts
the formation of an atherosclerotic plaque.
So preventing this formation in the
first place is a very critical feature.
So the free radicals with vitamin
E are destroyed, as I said.
The lipid peroxidation
is completely halted.
Vitamin E gets oxidized
and now we think about,
well, vitamin K had to be
regenerated once it got oxidized.
Vitamin E, itself, also has to be
regenerated after it’s been oxidized.
And it turns out that vitamin E is
regenerated by reduction using vitamin C,
the other antioxidant vitamin,
vitamin A or a compound
Any of those can help to
regenerate vitamin E.
Well, we’ve seen vitamin C gets
regenerated by DNA/DPA system
so with all of these things together,
the regenerated systems
can make essentially
enough of the various vitamins that we
need to have active at a given time.