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.
When a hydroxyl free radicals interacts with unsaturated lipid,
the lipid losses an H atom to the hydroxyl free radical
and in the process forms the lipid free radical and water.
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 lipid radical.
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 from proliferating
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 involves oxidation
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 called ubiquinol.
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.