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Good morning. Good morning,
yes, thank you. Well, we were

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coming to the end of the
term rather soon. That's sad.

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And, what I'd like to do today is,
picking up on some of the stuff that

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Bob has been doing, begin
to show how the things we've

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learned about understanding
molecular biology,

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biochemistry, genetics, all
come together to help us treat

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disease. That is after
all the point of all this.

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Bob spoke about this with respect
to cancer. Today my goal is to talk

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about this with respect to heart
disease. We've got about 50 minutes

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or so, and I'd like to see if we
could solve heart disease by the end

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of the period. That seems
like a reasonable goal.

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And so, I would like you,
by the end of today's class,

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to design a therapy to cure most
people or at least to prevent a

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couple million heart attacks,
all right? So, that's our goal.

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So, we'd better get to work if
we're going to accomplish that in

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the allotted time. So,
first off, you need to know a

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little something
about heart disease.

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The heart: that's obviously an
important component of understanding

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heart disease.
What's the heart do?

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The heart pumps blood, and
to and from tissues providing

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nutrients, hormones,
removing waste products,

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cells, for example, it pumps
around red blood cells and

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white blood cells and things like
that, and of course oxygen in the

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blood. These are incredibly
important things that your heart

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does. If your heart should stop
doing it for even relatively brief

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periods of time,
it's very bad news.

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This is extremely serious not
to have your heart pumping,

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as you all know. One of
the ways in which you run

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into trouble with your heart pumping
is if the vessels that carry blood

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away from the heart to the
periphery arteries become clogged.

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Just simple plumbing problem here:
if they become clogged and the

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arterial wall gets build ups
here, we have what is called

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arteriosclerosis. And,
it can lead eventually to

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nearly complete blockade of
a vessel. And if that vessel,

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for example, were to be supplying
something important like,

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for example, the blood supply
to the heart muscles itself,

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that would be extremely bad, all
right, because then your heart

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muscles wouldn't have oxygen,
and they would quickly die.

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Other problems can happen here too,
where you could have insufficient

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blood supply to the brain.
What happens when your brain

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doesn't get enough oxygen: stroke.
So, we have many, many of these

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issues. So, if it's the brain:
stroke. If the tissue that doesn't

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get enough oxygen is the heart,
you've got enough heart attack.

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And so, we want to prevent this
process of the buildup of plaques in

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the arteries. And these plaques
are made up of complex mixtures of

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proteins, lipids, and
cholesterol, and surely by now

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you all know that cholesterol
was this evil molecule,

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and it will indeed be the
villain of today's story.

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So, that's the basic plan there.
I'll draw your basic plumbing

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diagram here just so you have it.
We've got a heart here. This is

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your heart, somewhat simplified
picture here. The heart pumps blood

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that goes out to the body, to
the heart itself, to the brain,

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and of course this before it's
doing it is receiving oxygenated

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blood from the lungs. So,
it's really all of these places

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that we're trying to keep flowing.
The number of heart attacks, deaths

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from heart attacks, and other
cardiovascular disease is

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extraordinarily high.
It's on the order of 1.

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million deaths per year. By
contrast, number of deaths from

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cancer is about 600, 00
or so, something like that.

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And, this has been coming down
a little bit for cardiovascular

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disease partly because of some of
the things we'll talk about today.

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But it still is a leading
killer of adults in this country,

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and indeed the leading killer
of adults in this country,

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although there are projections that
cancer may take over in that role.

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Heart disease is
incredibly important. So,

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if we're going to try to understand
how we're going to prevent these

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plaques, and I've told you already,
and you know from the media that

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these plaques have lots
of cholesterol in them,

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and that you all know that
high cholesterol is bad,

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how do we know that
high cholesterol is bad?

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Correlation. Epidemiological
correlation is one,

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and as we will see today, there
are some other, more direct

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results coming out of genetics
that point to this as well.

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What is cholesterol? Let's
talk about cholesterol.

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So, this is
the structure

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of cholesterol.

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There we go. That's cholesterol.
It's a very complex, interesting

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molecule here with lots of rings.
It is a waxy substance. If you

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were to look at a test tube
with a lot of cholesterol in it,

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it would look like wax. And,
it is extremely hydrophobic. It

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will not dissolve in water. So,
if cholesterol is such an evil

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molecule as you all know from
the news media, why do we have

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this evil molecule?
Sorry? Well, because it's

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absolutely essential for life. I
mean, despite it's rep as an evil

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molecule, it's extraordinarily
important. The uses of cholesterol

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are many. One you've already said.
It plays a structural role in cell

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membranes, the plasma membrane.
This is not a big player role in the

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cell membrane. But about
half of all the lipids in

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the cell membrane are cholesterol.
It's a huge component. Cholesterol

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molecules, because of their funny
shape, helps stiffen membranes and

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strengthen membranes. So they
strengthen and stiffen the

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membrane. Also, not
only are half of the

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lipids in your cell membranes
cholesterol, half of the cholesterol

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in your body is in
the cell membranes. So,

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that's the major location.
They're also used, these complex

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molecules, as precursors for the
synthesis of steroid hormones.

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Steroid hormones, of course,
also are evil these days.

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Those of you who checked the New
York Times today saw that Jason

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Giambi admitted using steroids to
a grand jury. But steroids are also,

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notwithstanding those kinds
of things, good for you.

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What are some important steroids
in your bodies: testosterone,

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estrogen, glucocorticoids,
all of these things are made

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from cholesterol.
It was a precursor.

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And if you look at the
structure of steroid hormones,

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you recognize that this coupled ring
structure here is very similar to

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what's in them. And
indeed, they're derivatized

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from them. It's also a precursor
for the synthesis of vitamin D.

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And, it is a precursor for
the synthesis of bile acids.

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When your body takes in
triglycerides in your food supply

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and you need to transport fats like
triglycerides across your intestine,

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they need to be emulsified. The way
that triglycerides are emulsified

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are with bile acids. So, you
secrete bile acids into your

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digestive tract. It helps
emulsify fats and helps

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you take them up. So,
cholesterol plays a crucial

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structural role, a
biochemical role with regard to

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hormones, with regard to vitamin D
synthesis, and with regard to bile

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acid synthesis. So,
cholesterol was a good thing,

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all right. Now, if
cholesterol is so

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extraordinarily hydrophobic,
how is it that cholesterol gets

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around the body? It's
almost entirely non-polar.

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It doesn't dissolve in water.
It has one little hydroxyl there.

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It's not going to help a lot. Yep?
Well, the first thing actually is

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it's chemically modified to make
it a little hydrophilic and then it

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does bind to hydrophilic
proteins and particles that help

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get it around. So, the
first thing that happens,

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to be able to, even just to store
cholesterol in any useful form,

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it's not stored as cholesterol
because it's so waxy.

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It would just collapse as a waxy
deposit. What happens is it is

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stored and transported
as cholesterol ester.

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A cholesterol ester,

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or CE, and its esterified by adding
to it, here's my cholesterol again.

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I'll be even
less, there we go.

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This hydroxyl here is used
now for a fatty acid linkage.

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And with this fatty acid
attached to the cholesterol,

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you have a cholesterol ester.
And this is somewhat more soluble.

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All right, where do you
get your cholesterol from?

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Diet. Do we eat cholesterol?
Butter's got cholesterol. What

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else has got cholesterol?
Eggs, a lot of cholesterol.

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So, we eat cholesterol.
So, let's get our sources of

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cholesterol: number one,
diet. And, sources, eggs,

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butter, etc. What
else beyond diet?

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Yeah? Your body actually makes it.
Your own endogenous synthesis. And

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you would imagine that this is
pretty important because cholesterol,

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being half of all plasma membranes,
you can't just count on cholesterol

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being sufficiently
there in your diet.

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So, your body also synthesizes
cholesterol. The synthesis of

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cholesterol is a thing of beauty.
It starts with an incredibly simple

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molecule, acetic acid, right?
And it goes through many

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steps and becomes cholesterol,
which I will summarize here as many

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steps, OK? We'll come
back and talk a moment

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about a few of those steps. But
it's one of these real triumphs

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of biochemistry; the people have
worked out the whole pathway for

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cholesterol biosynthesis. But
it's not, I think, necessary to

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remember all of the steps there.
But it is quite remarkable to go

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from such an extremely simple
molecule like acetic acid all the

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way to cholesterol. And the
fact that people worked all

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this out was a great achievement.
All right, so those are some of the

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things you need.
Then, carrying on here,

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we've got cholesterol coming
in by diet. We're synthesizing

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cholesterol. We're
making cholesterol esters.

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We've got to get them
around the body. So now,

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we're going to take these
cholesterol esters and we're going

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to package them up and send them
off. So, you were saying that proteins

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would be used. Hydrophilic
proteins might be used.

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And indeed, that is the case.
Lipoproteins and lipoprotein

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particles, lipo being fat, of
course, are used to transport

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cholesterol and actually
triglycerins too.

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They are transported in particles
that look roughly like this.

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They have a monolayer of
phospholipids with some protein

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stuck in this monolayer
of phospholipid.

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And, inside is where these
cholesterol esters go.

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So, actually this is where
cholesterols go unesterified.

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So, cholesterol goes in here. In
the cell, we want it esterified.

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When it's in the package,
it's unesterified. So we have a

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monolayer of phospholipids.
We've got some protein stuck in

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that monolayer, and it's
a very little particle.

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Now, these particles
come in different flavors.

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These are very creative
names: low-density lipoprotein

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particles, or LDL. There
are high density lipoprotein

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particles, HDL, and very
low density lipoprotein

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particles, VLDL, and
some other things called

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kilomicrons. Now, you can
imagine that these names

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were assigned based on not so much
information, just based on density,

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right? Somebody was purifying
lipoprotein particles and said,

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well, there are some that
are high density, low density,

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oh, and you just discovered
some very low density ones.

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And this is not a highly
informative description of these

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particles, right? So,
people later worked out that

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these particles were really quite
different, and particularly the

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proteins that are in them, and
those proteins turn out to have

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important addressing roles in
sending these particles to different

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places. The ones that I'll be
interested in today are the LDL

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particles. The LDL particles have
a particular protein in them that is

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called apoprotein
B-100. It doesn't matter,

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but that's the particular targeting
protein there that's in that.

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And these particles are very
large. They are about two and a half

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million Daltons, about
220 angstroms in size,

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and each of them contains
about 1, 00 cholesterols.

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That's a description of
these LDL particles, OK?

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So, cholesterol, if it's
going to be transported in

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the blood, gets packaged up
into LDL particles, and it gets

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sent off to cells. How does
cholesterol get taken up by

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cells from these LDL particles?
How is that cell going to take up

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an LDL particle: a receptor,
right? It stands to reason that

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there's going to be a receptor
that's going to recognize probably

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the protein on the surface of this
thing that'll recognize that and

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internalize this particle. Now,
this stands to reason to us to

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you guys because you guys are
highly sophisticated about all this.

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But how was it that people came to
know this, to find these receptors?

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Well here is a little bit of
an interesting story about how,

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not so long ago, when people didn't
have all the tools in molecular

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biology and all this? And
very few of these cellular

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receptors were known. Two
young medical students began

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studying a fascinating condition.
The young medical students were

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named Joe Goldstein and Mike Brown.
And in fact, at least early in

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their careers they were
working here in Boston. So,

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they studied a fascinating condition
called familial hypercholesterolemia.

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What does hypercholesterolemia
mean? Cholesterol, hyper, a lot of

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cholesterol, emia,
in the blood, right?

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So, a lot of cholesterol in
the blood was this condition.

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And it was characterized, as
you might guess, by the fact that

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patients had a lot of cholesterol in
the blood and that it was familial,

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meaning what? It
transmitted in families.

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In fact, it transmitted in
families like a Mendelian trait,

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and it transmitted as an
autosomal co-dominant trait.

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In particular,

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if we looked at most
individuals in the population,

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which we'll assume have
genotype plus over plus,

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and we look at their cholesterol
levels, what we find is maybe they

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have 150 mg per desalude.
Now, some people have higher

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cholesterols than that, but
I'm going to take that as an

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average. Individuals who,
by virtue of their genetics,

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appear to be FH over plus
heterozygotes would have

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cholesterols more like
300 mg per desalude,

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or about double the normal
level. And, individuals who are FH

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homozygotes, FH over FH based on
the pedigree analysis here would have

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greater than 600
milligrams per desalude.

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In terms of heart attacks, normal
individuals would have heart

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attacks at the normal age.
That doesn't say anything,

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does it, because the normal
individuals, the age at which they

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have heart attacks is defined
as the normal age. But,

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what you will know that's striking
is that individuals who are

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heterozygotes would tend to have
heart attacks 10-20 years earlier

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than normal age. And,
individuals who are homozygotes

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00:25:13 --> 00:25:19
would tend to have heart
attacks below the age of 20.

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So this might be heart attacks
when you're 60. This might be heart

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attacks in your 40s and 50s, and
this might be heart attacks in

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your 20s or teens. In
addition, some of these

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individuals have very big
cholesterol deposits and things like

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00:25:46 --> 00:25:53
that. So, this was a very striking
phenotype: simple Mendelian trait,

252
00:25:53 --> 00:26:00
autosomal co-dominant, and
to see teenagers or younger,

253
00:26:00 --> 00:26:05
kids under the age of ten with
massively occluded vessels,

254
00:26:05 --> 00:26:10
and serious heart disease, and dying
of heart attacks was very striking.

255
00:26:10 --> 00:26:15
So, Brown and Goldstein decided
that if we wanted to understand

256
00:26:15 --> 00:26:20
heart disease in the general
population, we should understand

257
00:26:20 --> 00:26:26
heart disease in patients with
familial hypercholesterolemia,

258
00:26:26 --> 00:26:31
particularly the homozygotes. Now,
I note that this is about one per

259
00:26:31 --> 00:26:35
one million individuals. And
you could make a pretty strong

260
00:26:35 --> 00:26:39
case that Brown and Goldstein are
out of their minds trying to study

261
00:26:39 --> 00:26:43
familial hypercholesterolemia at
a frequency of one in a million and

262
00:26:43 --> 00:26:47
try to imagine that that's going to
tell them about heart disease in the

263
00:26:47 --> 00:26:50
general population. All
right, and people made that

264
00:26:50 --> 00:26:54
case to them and said, what
are you doing? Let's see,

265
00:26:54 --> 00:26:58
if this is P2, that means
the frequency of the,

266
00:26:58 --> 00:27:02
Q2, the allele is one in a
thousand in the population, right?

267
00:27:02 --> 00:27:05
If one in a million people are
homozygotes, the allele is one in 1,

268
00:27:05 --> 00:27:09
00. And so, the heterozygote
should be about one in 500.

269
00:27:09 --> 00:27:13
Well, OK, so one in 500's not a
terrible, it's not a small number.

270
00:27:13 --> 00:27:17
One in 500 people are heterozygotes
for FH. That's maybe a little

271
00:27:17 --> 00:27:21
better, but still not even a percent.
It's a fifth of a percent of the

272
00:27:21 --> 00:27:25
population are heterozygotes for FH.
It's still something of a gamble to

273
00:27:25 --> 00:27:29
imagine that by studying this
relatively rare disease we're going

274
00:27:29 --> 00:27:33
to learn about stuff in
the general population.

275
00:27:33 --> 00:27:36
But, Brown and Goldstein
felt strongly that they would.

276
00:27:36 --> 00:27:39
And they did. They wanted to know,
what was the problem with these

277
00:27:39 --> 00:27:43
individuals? Did they have
problems synthesizing their LDL?

278
00:27:43 --> 00:27:46
Did they have problems degrading
LDL? Why was there so much LDL

279
00:27:46 --> 00:27:50
cholesterol in the blood stream?
Maybe they didn't take up the LDL

280
00:27:50 --> 00:27:53
from the blood stream.
What was wrong? And so,

281
00:27:53 --> 00:27:57
they studied just
these individuals.

282
00:27:57 --> 00:28:02
And what they found, to
make an interesting and long

283
00:28:02 --> 00:28:07
story short was that when they
studied the binding of radioactive

284
00:28:07 --> 00:28:13
LDL particles to cells from these
patients, they found that the

285
00:28:13 --> 00:28:18
homozygotes were virtually
unable to take up LDL particles.

286
00:28:18 --> 00:28:24
There was very low uptake of LDL
particles. They also found that the

287
00:28:24 --> 00:28:29
heterozygotes had only about half
the normal uptake of LDL particles.

288
00:28:29 --> 00:28:35
What's your hypothesis about
what the problem is? Sorry?

289
00:28:35 --> 00:28:39
Well, it's with the uptake, and
what do you think the genetic

290
00:28:39 --> 00:28:43
basis of this is?
Yep? Well, let's see,

291
00:28:43 --> 00:28:47
if there's zero in the homozygote,
half the level in the heterozygote,

292
00:28:47 --> 00:28:51
could be the receptor. And what
could be the problem with receptor?

293
00:28:51 --> 00:28:55
Mutation of the receptor gene.
What if homozygotes or FH had a

294
00:28:55 --> 00:29:00
mutation that
abolished the receptor?

295
00:29:00 --> 00:29:07
OK, that turned out to be the case.
Was the FH was due to mutations in

296
00:29:07 --> 00:29:15
the LDL receptor on cells?
And indeed, until this point,

297
00:29:15 --> 00:29:22
the LDL receptor hadn't
been characterized on cells,

298
00:29:22 --> 00:29:30
but by virtue of Brown and Goldstein
demonstrating that when they did

299
00:29:30 --> 00:29:38
radioactive labeled
LDL uptake assays,

300
00:29:38 --> 00:29:43
and they found that FH
homozygotes had no uptake,

301
00:29:43 --> 00:29:48
virtually no uptake, and that
the heterozygotes had half

302
00:29:48 --> 00:29:54
the normal level, and that
the wild type individuals,

303
00:29:54 --> 00:29:59
plus over plus, had the normal level,
they inferred that the gene product

304
00:29:59 --> 00:30:05
that was mutant in these
individuals encoded the LDL receptor.

305
00:30:05 --> 00:30:10
And they proceeded to clone this
gene product, and determined that

306
00:30:10 --> 00:30:16
the gene product encoded a protein
that sat on the cell surface.

307
00:30:16 --> 00:30:21
It had a cytoplasmic tale.
It had an extracellular tale,

308
00:30:21 --> 00:30:27
and what it did was it bound
to the apo B-100 protein on

309
00:30:27 --> 00:30:34
the LDL particle. When it
bound the cell made a little

310
00:30:34 --> 00:30:42
pit, and in this coded pit, it
came and internalized the LDL

311
00:30:42 --> 00:30:50
receptor, carrying with it
the LDL particle. And then,

312
00:30:50 --> 00:30:58
this then went into the cell. The
LDL particle was then degraded,

313
00:30:58 --> 00:31:06
releasing cholesterol that
could be used by the cell.

314
00:31:06 --> 00:31:10
And the receptor itself got recycled
back to the surface to work another

315
00:31:10 --> 00:31:15
day. And this is quite a general
mechanism that is used there by a

316
00:31:15 --> 00:31:19
lot of trafficking receptors like
this that grab things from the cell

317
00:31:19 --> 00:31:24
surface, bring them into the cell,
release something into a vesicle,

318
00:31:24 --> 00:31:29
and then go back onto the surface
there, and that the problem was that

319
00:31:29 --> 00:31:34
patients FH did not have
functional LDL receptors.

320
00:31:34 --> 00:31:39
Now, this pointed out, LDL
receptors were very important

321
00:31:39 --> 00:31:44
here because cells needed to take
up cholesterol from the blood stream,

322
00:31:44 --> 00:31:49
although they could make
some of their own cholesterol.

323
00:31:49 --> 00:31:54
But one of the most important
places where cholesterol was

324
00:31:54 --> 00:32:00
sequestered and taken up from
the blood stream was the liver.

325
00:32:00 --> 00:32:09
It turns out that the biggest
problem for these patients with

326
00:32:09 --> 00:32:18
familial hypercholesterolemia was
that the liver is supposed to be

327
00:32:18 --> 00:32:27
taking up large amounts of LDL to
clear the blood stream and keep the

328
00:32:27 --> 00:32:36
levels of LDL at the desirable
amount. So, the liver normally is

329
00:32:36 --> 00:32:45
responsible for taking up clearing
about 75% of LDL from the blood.

330
00:32:45 --> 00:32:49
If someone has, and other
cells are responsible for

331
00:32:49 --> 00:32:53
the rest, non-liver cells
take up about 25% of the LDL.

332
00:32:53 --> 00:32:57
Suppose somebody has half
the level of LDL receptors,

333
00:32:57 --> 00:33:01
they will take up half as
much of these LDL particles,

334
00:33:01 --> 00:33:05
and the average level in the
blood would be much higher, about

335
00:33:05 --> 00:33:09
twofold higher. Suppose
somebody has no LDL

336
00:33:09 --> 00:33:12
receptors. Well, then the
LDL receptor pathway is not

337
00:33:12 --> 00:33:16
going to take up these particles,
and they're going to have

338
00:33:16 --> 00:33:19
outrageously high levels of LDL.
Other mechanisms will kick in and

339
00:33:19 --> 00:33:22
slightly prevent it from
going to infinity, of course,

340
00:33:22 --> 00:33:26
because there are other
ways things get cleared out.

341
00:33:26 --> 00:33:29
But they get huge levels
of LDL because they have no

342
00:33:29 --> 00:33:33
such receptors. So, this
is the major reason that

343
00:33:33 --> 00:33:37
there's so much LDL cholesterol
particles in the blood in these

344
00:33:37 --> 00:33:42
patients who are FH homozygotes.
And then, FH heterozygotes have a

345
00:33:42 --> 00:33:47
lot. And, well, what are
we going to do about it?

346
00:33:47 --> 00:33:51
How do you solve a problem like
this? The liver is not doing its

347
00:33:51 --> 00:33:56
job. Now, I should note, the
liver does one other thing.

348
00:33:56 --> 00:34:01
the liver not only is the major
source of taking cholesterol,

349
00:34:01 --> 00:34:06
but it's the major source of
producing LDL cholesterol as well.

350
00:34:06 --> 00:34:10
The liver produces, I
remember every cell is able to

351
00:34:10 --> 00:34:14
synthesize cholesterol, but
most of the cholesterol in the

352
00:34:14 --> 00:34:18
body is synthesized from the
liver and put out. And so,

353
00:34:18 --> 00:34:22
here we have the liver is
a source of cholesterol,

354
00:34:22 --> 00:34:26
and it's in this disease not
acting as an appropriate sake for a

355
00:34:26 --> 00:34:30
cholesterol. It ought to be sucking
up cholesterol and maintaining a

356
00:34:30 --> 00:34:34
balance of producing cholesterol
and soaking it back up there.

357
00:34:34 --> 00:34:39
We've got a real problem. Well,
we need to know one more fact,

358
00:34:39 --> 00:34:45
and then we can solve the disease.
Well, we're not going to solve the

359
00:34:45 --> 00:34:50
disease, but we'll do
the best we can here. So,

360
00:34:50 --> 00:34:56
cholesterol synthesis, I
just want to tell you one more

361
00:34:56 --> 00:35:02
fact about it and then toss you
the problem. Cholesterol synthesis,

362
00:35:02 --> 00:35:08
I said, was acetate,
acetic acid, goes to stuff,

363
00:35:08 --> 00:35:15
and let me tell you just
a little bit more about it.

364
00:35:15 --> 00:35:21
It goes to acetyl CO-A, which
goes to HMG CO-A, which goes

365
00:35:21 --> 00:35:28
to mevalonate, which goes
on to make cholesterol,

366
00:35:28 --> 00:35:35
and that the key committed step of
cholesterol synthesis is carried out

367
00:35:35 --> 00:35:42
by an enzyme called
HMG CO-A reductase, OK?

368
00:35:42 --> 00:35:48
Now you have all the facts. We
know we've got these particles

369
00:35:48 --> 00:35:55
that contain cholesterol. We
understand that the liver makes

370
00:35:55 --> 00:36:02
cholesterol, that you get
cholesterol from your diet.

371
00:36:02 --> 00:36:08
The liver makes cholesterol.
It takes up cholesterol. We have

372
00:36:08 --> 00:36:14
some problems with its uptake of
cholesterol. Let's get to work and

373
00:36:14 --> 00:36:20
design a therapy. How
are we going to do this?

374
00:36:20 --> 00:36:27
So, we've got patients
designing a rational therapy.

375
00:36:27 --> 00:36:45
OK, here's your
digestive tract.

376
00:36:45 --> 00:36:56
You've got some liver here
it's going to take up by

377
00:36:56 --> 00:37:06
means of diet. It's going
to synthesize cholesterol.

378
00:37:06 --> 00:37:15
It's going to use cholesterol
to make bile acids.

379
00:37:15 --> 00:37:24
Those bile acids are going to help
bring back fats because it's going

380
00:37:24 --> 00:37:31
to emulsify the fats. And so,
the bile acids get recycled.

381
00:37:31 --> 00:37:35
It's going to put out cholesterol
to the body, and LDL particles are

382
00:37:35 --> 00:37:39
going to get internalized into
the liver. So, we have our LDLs.

383
00:37:39 --> 00:37:43
OK, so has everybody got the
action? You take up a cholesterol,

384
00:37:43 --> 00:37:48
and fats, and things like
that through our diet.

385
00:37:48 --> 00:37:52
You've got some cholesterol in
our body. We synthesize cholesterol

386
00:37:52 --> 00:37:56
from acetic acid. We
have this pathway here.

387
00:37:56 --> 00:38:01
We use cholesterol
to make bile acids.

388
00:38:01 --> 00:38:06
We take up cholesterol from the
blood stream, and all of these

389
00:38:06 --> 00:38:11
things together working as a system
control how much cholesterol is in

390
00:38:11 --> 00:38:16
your body, and most importantly,
how much cholesterol's in your blood

391
00:38:16 --> 00:38:21
stream in the form of LDL particles.
OK, we have a patient. Maybe it's

392
00:38:21 --> 00:38:26
a patient with FH homozygosity.
But let's start easier. Let's

393
00:38:26 --> 00:38:32
start with a patient who's
a heterozygote for FH.

394
00:38:32 --> 00:38:45
What's our first advice? Eat
well, get plenty of exercise:

395
00:38:45 --> 00:38:58
this is always good advice.
So, plan one, so strategy number

396
00:38:58 --> 00:39:11
one: diet, dietary reduction
of cholesterol intake.

397
00:39:11 --> 00:39:16
Eat less cholesterol.
It's a good bit of advice.

398
00:39:16 --> 00:39:21
Stop eating eggs, whatever,
you have a serious condition,

399
00:39:21 --> 00:39:26
don't eat so much better. Does
it do much to reduce LDL levels?

400
00:39:26 --> 00:39:31
It turns out, not much.
Why doesn't it do much?

401
00:39:31 --> 00:39:36
What if I reduce dramatically
my intake of cholesterol?

402
00:39:36 --> 00:39:40
Well, it only makes about a
10% reduction in LDL levels,

403
00:39:40 --> 00:39:45
which is not enough to get
close to normal. Why? Well,

404
00:39:45 --> 00:39:50
it turns out your body, number
one, gets more efficient at

405
00:39:50 --> 00:39:54
taking up cholesterol from your diet.
So, you have some cholesterol there,

406
00:39:54 --> 00:39:59
and if you're eating less, it
takes up with higher efficiency

407
00:39:59 --> 00:40:03
the cholesterol that's there.
Your body's good at doing things

408
00:40:03 --> 00:40:06
like that. It also starts
synthesizing cholesterol.

409
00:40:06 --> 00:40:10
Don't have enough cholesterol?
We'll make more cholesterol. So,

410
00:40:10 --> 00:40:13
the liver will make more cholesterol,
put cholesterol out into the blood

411
00:40:13 --> 00:40:16
stream, and these guys can't take
up the cholesterol with the LDL

412
00:40:16 --> 00:40:19
receptor as well, and
it clogs it up again.

413
00:40:19 --> 00:40:22
So in the end, between more
efficient uptake of what is in the

414
00:40:22 --> 00:40:26
diet and greater synthesis,
we've got to complex the human

415
00:40:26 --> 00:40:29
system with feedback, and all
you've tried to do is affect

416
00:40:29 --> 00:40:34
one variable, dietary intake. And
the system regulates so that you

417
00:40:34 --> 00:40:41
haven't made a very big dent
in the problem. All right,

418
00:40:41 --> 00:40:49
next strategy, let's try to deplete
some cholesterol from the body.

419
00:40:49 --> 00:40:56
If we could get some cholesterol
out of the body by some pathway,

420
00:40:56 --> 00:41:04
we might be able to decrease the
overall levels of cholesterol.

421
00:41:04 --> 00:41:08
So, where do we have access
to a cholesterol product here?

422
00:41:08 --> 00:41:13
In the digestive system, we have
bile acids. Got any ideas of what

423
00:41:13 --> 00:41:18
we could do about the bile acids?
Suppose we could somehow deplete

424
00:41:18 --> 00:41:23
your bile acids while they're
in your digestive tract.

425
00:41:23 --> 00:41:28
Then your body would not be
able to recycle those bile acids,

426
00:41:28 --> 00:41:33
but would have to make more bile
acids. And it would be a sink for

427
00:41:33 --> 00:41:38
cholesterol, right? It would
start having to use up more

428
00:41:38 --> 00:41:42
cholesterol to produce enough bile
acids because it would have to use

429
00:41:42 --> 00:41:46
up more cholesterol. The
liver might have to work harder

430
00:41:46 --> 00:41:51
to get cholesterol, you know,
synthesizing cholesterol,

431
00:41:51 --> 00:41:55
but it would also probably up
regulate its LDL receptors to try to

432
00:41:55 --> 00:42:00
draw in more cholesterol
from the blood stream.

433
00:42:00 --> 00:42:04
So, this was the clever idea.
Let's try to get ride of bile acids,

434
00:42:04 --> 00:42:08
or not completely rid of them, but
let's try to complete bile acids.

435
00:42:08 --> 00:42:12
Therefore, the liver is going
to not be able to reuse them.

436
00:42:12 --> 00:42:17
It's going to have to make more
bile acids. It's going to need

437
00:42:17 --> 00:42:21
cholesterol. And so it's going
to up regulate the gene for LDL

438
00:42:21 --> 00:42:25
receptors and draw in more from the
blood stream. It turns out that you

439
00:42:25 --> 00:42:29
can feed people bile acid binding
resins. It's perfectly fine.

440
00:42:29 --> 00:42:34
Just eat them, and you can give
people bile acid binding resins.

441
00:42:34 --> 00:42:41
So, strategy number two, and
what they will do is then they

442
00:42:41 --> 00:42:49
will, in their feces, eliminate
some fraction of the bile

443
00:42:49 --> 00:42:56
acids and as a result they will
be able to get rid of some of their

444
00:42:56 --> 00:43:04
cholesterol, and they will be
able to decrease their overall

445
00:43:04 --> 00:43:14
cholesterol levels.
Does this work?

446
00:43:14 --> 00:43:28
It does, and you can get
maybe a 20-25% reduction. But

447
00:43:28 --> 00:43:37
what's the problem? You can't
completely get rid of them,

448
00:43:37 --> 00:43:41
right, because they're necessary.
So, we'll be able to get rid of

449
00:43:41 --> 00:43:46
some bile acids. That's
really the problem is,

450
00:43:46 --> 00:43:50
see, we're sitting here saying so
cleverly we're going to feed the

451
00:43:50 --> 00:43:55
body less cholesterol. We're
going to draw cholesterol out

452
00:43:55 --> 00:43:59
of the body by removing bile acids,
and force the liver to take up more

453
00:43:59 --> 00:44:04
cholesterol from the
blood stream, right?

454
00:44:04 --> 00:44:07
And hopefully it'll help regulate
the gene. And it does help regulate

455
00:44:07 --> 00:44:10
the gene. When starved for
cholesterol, cells up regulate their

456
00:44:10 --> 00:44:13
LDL receptor gene and make
more LDL receptors. That works.

457
00:44:13 --> 00:44:16
But we've forgotten one aspect of
the system, and that was the liver

458
00:44:16 --> 00:44:19
has another option, which
was synthesize its own

459
00:44:19 --> 00:44:22
cholesterol. So, we've
got a complex system with

460
00:44:22 --> 00:44:25
multiple feedbacks. We've
affected it at the level of

461
00:44:25 --> 00:44:28
diet. We've affected at the
level here of drawing stuff out.

462
00:44:28 --> 00:44:32
We've managed to get some up
regulation the LDL receptor gene.

463
00:44:32 --> 00:44:38
But it's not enough because the
liver's choosing to make more

464
00:44:38 --> 00:44:45
cholesterol through its
endogenous synthesis pathway.

465
00:44:45 --> 00:44:51
So, let's keep going.
What do you recommend?

466
00:44:51 --> 00:44:58
Yes? Ooh, ooh, I like that. What
do you think will happen then?

467
00:44:58 --> 00:45:02
So, I won't make as much cholesterol.
What's the liver going to have to

468
00:45:02 --> 00:45:06
do then? And it will up regulate
its LDL receptors to do that,

469
00:45:06 --> 00:45:10
take up more cholesterol
from the blood stream. So now,

470
00:45:10 --> 00:45:14
we back the liver into a corner,
right? It needs more cholesterol.

471
00:45:14 --> 00:45:18
We're going to inhibit the
synthesis of cholesterol,

472
00:45:18 --> 00:45:22
and therefore it's going
to go to its second source,

473
00:45:22 --> 00:45:26
which is uptake from the blood,
and it's going to induce more LDL

474
00:45:26 --> 00:45:30
reception. Everybody got
your plan? So, let's see.

475
00:45:30 --> 00:45:36
Strategy would be inhibit
cholesterol synthesis.

476
00:45:36 --> 00:45:42
This is in addition also
inhibit cholesterol synthesis.

477
00:45:42 --> 00:45:48
And, you wanted to inhibit one
of those steps. Any preference of

478
00:45:48 --> 00:45:54
where you'd like to inhibit the step?
How about the first committed step

479
00:45:54 --> 00:46:00
of cholesterol synthesis?
So, how about H, M, G, CO-A

480
00:46:00 --> 00:46:15
reductase inhibitors?

481
00:46:15 --> 00:46:19
Well, it turns out that people
found HMG CO-A reductase inhibitors.

482
00:46:19 --> 00:46:23
Lovastatin, a fungal product
inhibits HMG CO-A reductase.

483
00:46:23 --> 00:46:27
And then, companies, Merck
and then many other companies,

484
00:46:27 --> 00:46:31
developed all sorts of what
are called statin drugs that

485
00:46:31 --> 00:46:35
inhibit that enzyme. I would
venture to say that a large

486
00:46:35 --> 00:46:39
fraction of your parents take
statin drugs to lower cholesterol.

487
00:46:39 --> 00:46:44
And this is how it works. It
inhibits the endogenous synthesis

488
00:46:44 --> 00:46:48
pathway at the step
HMG CO-A reductase. And,

489
00:46:48 --> 00:46:53
in addition, if they do things
like take bile acid binding resins,

490
00:46:53 --> 00:46:58
and there's some combinations of
those things, and also controlled

491
00:46:58 --> 00:47:02
your dietary intake of cholesterol,
and FH heterozygote can get a 60%

492
00:47:02 --> 00:47:07
reduction in LDL particle
loss. That is mighty good.

493
00:47:07 --> 00:47:12
That brings them down to normal.
Yeah? Yeah? Yep. So we're not

494
00:47:12 --> 00:47:17
talking about totally removing it.
We're talking about decreasing it.

495
00:47:17 --> 00:47:22
We're bringing it back down
to a normal level. Well,

496
00:47:22 --> 00:47:27
it turns out that the cells out
there will up regulate their LDL

497
00:47:27 --> 00:47:33
receptors as well, and I
haven't focused on that.

498
00:47:33 --> 00:47:36
But they're taking care of
themselves. It turns out,

499
00:47:36 --> 00:47:39
you have to worry about all these
strategies. This is too clever by

500
00:47:39 --> 00:47:42
half because you're going to
mess up things in the periphery.

501
00:47:42 --> 00:47:45
But it turns out the peripheral
cells take care of themselves.

502
00:47:45 --> 00:47:49
They'll up regulate their LDL
receptors enough to get things in.

503
00:47:49 --> 00:47:52
And the big problem is that
the liver's not doing its job.

504
00:47:52 --> 00:47:55
But you have to do the clinical
tests to see that that's the case.

505
00:47:55 --> 00:47:58
This turns out to be a
strategy for FH heterozygotes.

506
00:47:58 --> 00:48:02
But I just said that many of
your parents take these drugs.

507
00:48:02 --> 00:48:05
Most of your parents
aren't FH heterozygotes.

508
00:48:05 --> 00:48:09
Perhaps none of your
parents are FH heterozygotes.

509
00:48:09 --> 00:48:12
That turned out to be one of the
most remarkable outcomes of studying

510
00:48:12 --> 00:48:16
this rare genetic disease.
Well, as it turned out, this

511
00:48:16 --> 00:48:19
strategy, which had been the
understanding that had been

512
00:48:19 --> 00:48:23
developed from this exceedingly
rare genetic disease,

513
00:48:23 --> 00:48:26
and the strategy that had been
developed with an eye towards these

514
00:48:26 --> 00:48:30
FH heterozygotes turns out to also
work in normal individuals with high

515
00:48:30 --> 00:48:33
cholesterol not because of a
complete mutation in the LDL

516
00:48:33 --> 00:48:37
receptor, but because of,
perhaps, other differences,

517
00:48:37 --> 00:48:40
genetic differences that are weaker.
And in fact, tens of millions of

518
00:48:40 --> 00:48:44
people take these therapies that
were developed for this very rare

519
00:48:44 --> 00:48:47
situation. This is a perfect
example of where understanding a

520
00:48:47 --> 00:48:51
rare genetic disease points us
to the basis for a physiological

521
00:48:51 --> 00:48:54
pathway, in particular, all
these feedback loops that allow

522
00:48:54 --> 00:48:58
us to do something that
helps everybody. So,

523
00:48:58 --> 00:49:02
this has become a
major, major therapy.

524
00:49:02 --> 00:49:06
Who were the only people who don't
benefit from this particular therapy

525
00:49:06 --> 00:49:10
of tricking the body into up
regulating the LDL receptors?

526
00:49:10 --> 00:49:15
Homozygotes, because they don't
have a gene to be up regulated.

527
00:49:15 --> 00:49:19
They don't have a functional
gene to be up regulated.

528
00:49:19 --> 00:49:24
And so, homozygotes need
something else. What do they need?

529
00:49:24 --> 00:49:28
Gene therapy. The best idea that
people have here since the liver

530
00:49:28 --> 00:49:33
regenerates tremendously would be
able to take out some liver cells,

531
00:49:33 --> 00:49:37
add back genes for LDL receptors,
and repopulate a liver with LDL

532
00:49:37 --> 00:49:42
receptor transgenic cells.
And that would help them.

533
00:49:42 --> 00:49:46
Anyway, this is meant to illustrate
the power of rational therapy,

534
00:49:46 --> 00:49:51
that understanding things, can you
imagine trying to do this by hit or

535
00:49:51 --> 00:49:55
miss? It was your design knowing
the pieces that God is here,

536
00:49:55 --> 00:50:00
and this is basically what we're
trying to do with all of medicine is

537
00:50:00 --> 00:50:04
get to the point where we can
design things that really do work.

538
00:50:04 --> 50:09
See you
next time.