00:02
We've come a long way.
00:03
We've talked about, normal hemostasis.
00:06
We've talked about, pro and anticoagulant factors.
00:09
We've talked about, how to bring
platelets into the equation
and the important role of endothelial cells.
00:15
We've talked about, how to measure
the various coagulation factors
and we've talked about, bleeding
and thrombotic disorders.
00:25
Finally, we're going to talk about, therapies.
00:27
So, ultimately, it's
important to know all of this,
that's come before, because,
it very much informs, how we
treat patients who either,
too coagulant or not coagulant enough.
00:41
In other words, they're clotting
inappropriately or they're
bleeding inappropriately
and knowing, how to, modulate
the coagulation cascade,
how to affect platelet function,
is going to be a major
weapon in your armamentarium,
when you're treating patients,
so really important to know.
01:00
Therapies, so, this is where we've come
all the way through down our road map
and we're getting now into the
final step, so, hang in there,
we're almost done.
01:12
Oh my goodness,
we're back to the intrinsic and extrinsic pathway,
having to do with coagulation.
01:18
That's because, we're going to be
talking about the various ways,
that we can impact, this
multi-step protein cascade.
01:27
Heparin, is one of the mainstays.
01:30
Heparin, as you will recall, endothelial
cells make a heparin-like molecule,
that interacts with antithrombin
III and that affects,
that regulates turns off the activity
of factors XII, XI, IX, X and IIa.
01:49
We can give exogenous heparin and
activate more of the antithrombin III
and so inhibit the coagulation of those factors
and so we do this to prevent
people from thrombosing,
if they're lying around in a hospital bed,
you will regularly dose patients,
who are relatively immobile,
not getting out of bed,
with, subcutaneous heparin,
to drive exactly this inhibitory
pathway. That's great.
02:18
There are some downsides, so about 5%
of the population can develop antibodies,
that form against heparin and a platelet factor.
02:29
So, this is so called the heparin
induced thrombocytopenia disease.
02:35
When that happens, we go to
a different form of heparin,
we use, “Low molecular
weight heparin,” "L-M-A-W-H."
And that acts, not so much, on XII, XI, IX,
X, but acts on just factor IIa thrombin.
02:54
It tends not to induce as
much of that heparin-induced,
thrombocytopenia or hit syndrome.
03:00
So, in many cases where
there may be a risk of that,
we will give that low molecular weight heparin,
but it blocks very effectively the IIa.
03:11
A variety of drugs, that you will
encounter, have an “x,” in the name.
03:14
So, "x" marks the spot.
03:16
Fondaparinux, rivaroxaban, apixaban,
All those, act on factor X
and prevent its activation.
03:26
So, this easy to remember if you
see x with some rare exception.
03:30
So, that's another way that we can block
the common pathway involving factor X.
03:37
We can give, argatroban, dabigatran, bivalirudin,
these will specifically inhibit
the activity of thrombin.
03:47
These are incredibly potent.
03:50
So, the nice thing about heparin
and low molecular weight heparin,
they are relatively easy to turn on and turn off.
03:57
Fondaparinux is the next level up,
so, the things that activate and
inactivate factor 10 next level up,
somewhat more difficult to regulate and fine-tune
and then when we get into
the argatroban and company,
acting at thrombin, those can be
very, very potent anticoagulants
and will can cause a lot of bleeding.
04:23
Finally, coumadin, going
to be one of the mainstays,
that you will use in the treatment of patients,
who have a procoagulant tendency.
04:34
That's because it acts on both sides
of the intrinsic and extrinsic pathway.
04:39
It will, act to prevent the development
as we'll see in the next slide,
of activated factors II, VII, IX, and X.
04:51
How is this happening?
So factors II, VII, IX, and X,
require a second carboxy group,
to be added to glutamates.
05:02
So that step, converts glutamate
to a carboxy glutamate,
in the final protein.
05:08
By having those two carboxyl groups, side-by-side,
that gives us a localized negative charge of -2,
that will chelate or will interact with calcium.
05:20
So, that allows factors II, VII, IX, and X,
to specifically localize to
calcium in phospholipid areas,
so that, we can get the appropriate activation
and if we don't put the second carboxyl
group on, those factors are not active.
05:34
So, how do we put the second carboxyl group on?
It requires the activity of a vitamin K.
05:40
And by going from glutamate to
carboxy glutamate, from left to right,
that vitamin K gets inactivated.
05:47
Now, GI tract microbiome and our
own intrinsic synthetic capacity,
does make vitamin K, but
if at an inadequate level,
if we're not constantly regenerating
activated vitamin K, from the inactive form
and that, there is an enzyme
pathway that does that.
06:05
That back activation pathway, that we
need to keep vitamin K levels up to snuff,
can be turned off by coumadin.
06:14
So, that's the activity of coumadin.
06:16
And the reason that it was used so
effectively originally as a rat poison,
is that basically, you were causing the
inactivation of factors II, VII, IX, and X,
because you didn't add the carboxy group
and rats that ate the poison
that had coumadin in it,
were bleeding to death, they
were not clotting appropriately.
06:38
We don't give the same levels of
coumadin as we do in rat poison,
to people, but we do give
very low levels that allow us
to coregulate the activities II, VII, IX, and X.
06:50
Okay, so that's the coagulation pathway.
06:53
The proteins and how we can impact those.
06:56
How can we affect platelets?
So, recall that, ADP and there
are other molecules as well,
but ADP, primarily through a
receptor, the ADP receptor,
on the surface of platelets,
will drive a variety of
pathways within that platelet.
07:11
Along the top line, we will
get IIb/IIIa activation,
so that we can get platelet to platelet
interaction through fibrinogen.
07:18
We will drive the metabolic
breakdown of arachidonic acid,
via cyclooxygenase to produce thromboxane a2,
which drives greater platelet aggregation,
but will also drive granule release.
07:33
So, there are a lot of things
that happen once we bind ADP,
“Adenosine Diphosphate.”
Wow, there are lots of targets
here let's start hitting them.
07:42
So, there are drugs that will block
that ADP-ADP receptor interaction,
clopidogrel and ticlopidine
and these are very commonly used
to inhibit platelet activity.
07:54
We can give aspirin or any of the other
non-steroidal anti-inflammatory agents,
which will, block the cyclooxygenase,
which means, we don't make thromboxane A2,
which means, we don't get granular
release and further platelet activation.
08:07
We can also block, IIb/IIIa, this
is with a variety of molecules,
including a monoclonal antibody
called abciximab or tirofiban
and both of those, will block,
that interaction linking platelet to
platelet through the glycoprotein IIb/IIIa,
surface molecule.