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This
is Lizzie Velasquez, a 24 year old with a genetic
form
of lipodystrophy. She must consume 5000-
8000
calories and eat 80 times each day just to survive.
Her
condition is called neonatal progeroid syndrome,
which
includes premature aging and an oversized head
along
with the lipodystrophy. She has dealt with more
than
any person should have to, and now is a
motivational
speaker – "it’s going to get better" is her
theme.
Her second book, Be Beautiful, Be You
is a
must read. The picture is from one of her public talks.
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There is a group of disorders known as the lipodystrophies (lipo = fat, dys = bad, and trophy =
nourishment) in which afflicted people can't store any fat. Their stories tell us that being skinny is no blessing.
Lipodystrophies can be congenital
(con = with, genitus = to beget), so they are present from conception, or they can be acquired. In congenital cases, the genetic
mutation sometimes has little to do with fat, sometimes it does. There are four
known mutations in four different proteins that can all lead to a
lipodystrophy.
People with a congenital lipodystrophy tend to develop type
II diabetes. They also get arthritis and other disorders. Some mutations also
carry higher risks of mental retardation and most increase the risk of cardiac
disease and cirrhosis of the liver.
These can kill you.
Acquired forms often result from drug treatment. In HIV
retroviral treatment, there can by lipodystrophy and lipoatrophy – which is loss of fat from one particular anatomic
location, usually the face. On the other hand, visceral fat (fat around the
internal organs) is increased during anti-HIV treatment. It matters, since
visceral fat is associated with more heart and liver disease.
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Lipoatrophy
refers to the loss of fat in a particular area of the
body.
On the left is the facial atrophy seen in patients on anti-
viral
therapy in HIV infection. On the right is a specific
lipoatrophy surrounding an insulin injection sight for diabetes.
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Fat may be considered evil, but it serves a purpose. The
problems that lipodystrophy patients encounter underline that fat is a
necessary tissue for animals. Problems arise when you accumulate too much of
it, either under your skin, around your organs, or in your blood. If you don’t
use the calories you take in for energy, your body will store them for later.
Chemically, a fat is made up of three fatty acids (see below) attached
to a 3-carbon glycerol molecule. In adipose tissue (from latin aipem = fat) and subcutaneous fat, these
triglycerides, also called triacylglycerols (tri = 3, glycer =
glycerol, and acyl = acid) are stored
until they are released to the blood stream as fatty acids alone. The fatty
acids can then be broken down and used to generate ATP in the cells.
Fats are a much more efficient storage form of energy as
compared to glucose or glycogen. There is 4.5 x more energy in fat as compared
to the same mass of glycogen or glucose. In addition, since fats are
hydrophobic (hydro = water, and phobic = fearing), they can be stored
without water. These two factors mean that a lot of energy can be stored in a
little space.
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A
fat molecule is really a triglyceride. The right structure is a
typical
triglyceride with three fatty acids in black connected
to
the bluish glycerol. By ester bonds in dark red. A trans
double
bond is shown in green. On the right is the partial
hydrogenation
process that converts a polyunsaturated fat
into
a trans fat. Usually there is a mix of products, with some
cis bonds being converted to trans bonds.
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A fatty acid is a chain of carbons with a carboxyl group
(HO-C=O) on one end. If the chain of carbons contains only single bonds, then
the fatty acid is called saturated.
If there is one double bond between carbons, then it is an unsaturated fatty acid, and if there are two or more double bonds
(unsaturations), then it is a polyunsaturated
fatty acid.
The same terminology is used for triglycerides (fats) made
from the fatty acids. A fat with only saturated fatty acids is a saturated fat.
The double bond type also makes a difference for the fatty acid and fat. If the
bond is in one configuration, it is called cis,
and it creates a bend in the chain. If the double bond is in the other configuration,
then it is called trans, and it is
much straighter, like a saturated fatty acid.
You have heard of the benefits of polyunsaturated fats as
opposed to saturated fats, and of the evils of trans-fats. Saturated fats tend
to produce bad results in the blood stream. Their breakdown results in more
acetates which stimulate cholesterol production. Also, saturated fats tend to
clump together and form blockages in vessels. This leads to atherosclerosis and
can kill you.
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The
left cartoon shows the buildup of plaque over time in
atherosclerosis.
It takes along time, but we all seem to be
working
hard to make it happen. The right image is a
photomicrograph
showing the blockage in a large coronary
artery.
Think the amount of blood getting through is enough
to nourish your heart? Think it’s going to have a happy ending?
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The vast majority of trans fats we eat are
industrially made. The trans double bonds are created in the hydrogenation process
(adding hydrogens to reduce the number of double bonds). Some cis- double bonds
become trans- double bonds during the process.
Industry likes the saturated and trans-fats because they
tend to be more solid at room temperature (higher melting temperatures).
Saturated and trans-fats have more hydrogens (see picture above). The kink in
trans-fats also increases the melting temperature.
The hydrogens and kinks lead to more interactions between
the different molecules – they hold on to one another more tightly. Melting is
basically making the different molecules separate by adding energy, so the
added hydrogens have the end result of raising the melting temperature. This is
good for making things like margarine.
Unfortunately, trans-fats tend to increase low-density
lipoprotein (LDL) production; these contribute greatly to artery clogging and
heart disease. The blocking of arteries is bad enough, but if they occur in the
brain, or if part of a plaque breaks off, travels to the brain and blocks a
vessel – that’s a stroke. There’s not much that’s worse than a stroke.
Saturated fats also raise the levels of LDL’s - so why are
trans-fats worse for you than saturated fats? The levels of LDLs are only one
aspect in disease promotion, the level of the good-for-you HDLs (high density
lipoproteins) is just as important. It's the ratio of LDL:HDL that matters.
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In
the space of the vessel are some large cells with very
light
cytoplasm that looks like Swiss cheese. There are
many
small clear droplets and some larger ones. These
are
fat droplets and give the cells their name – foam cells.
You
can see that some have more than one nucleus. Two
diseased
macrophages will often merge into
multinucleate giant cells.
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The next question then is how do HDLs help prevent disease
caused by LDLs? LDLs supply cholesterol to the cells that need it – and that’s
all your cells (more on this next week). But if there is too much LDL, then
they start to accumulate in the vessels and can form things like foam cells.
Foam cells are tissue macrophages located in/on the vessel
walls. The job of macrophages is to eat things, so these macrophages eat up the extra LDLs
in the area - but they don’t break them down. They build up and start to look
like foam inside the cell. Unfortunately, the macrophages then become part of the problem; as
they accumulate they form fat streaks in the vessel wall. This is the beginning
of plaque formation and atherosclerosis.
A 2005 review looked at how HDLs are health promoting. It
turns out that they steal cholesterol from LDLs, but they don’t promote the
formation of foam cells and plaques because of their different structure.
Therefore, having more HDLs will rescue more cholesterol from LDLs and transport
it to the liver for eventual destruction.
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The
top cartoon shows how HDL help get rid cholesterol
after
it has been phagocytosed by a macrophage foam cell.
A
pre-HDL interacts with receptors on the macrophage
which
then transfer cholesterol to the HDL. This is taken to
the
liver where it is broken down and reused for bile
production.
This is called reverse cholesterol transport. The
bottom
image shows the functions of HDL, even beyond its
ability to negate the unhealthy effects of LDLs.
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Oxidation of LDLs leads to oxygen radicals can damage vessel
cells and promote plaque formation. But HDL complexes include an enzyme called
paraoxonase, which prevents the oxidation of closely associated LDL molecules.
Preventing oxidation also reduced the production of pro-inflammatory molecules
in the vessel wall and decreased the recruitment of some inflammatory cell to
the area. Hurrah for HDL!
But wait – of course there’s an exception. HDLs from
patients with existing diseases, like coronary artery disease (CAD) or chronic
kidney dysfunction (CKD) actually contribute
to plaque formation rather than prevent it! A 2013 review talked about how HDLs
from CAD patients limit the anti-inflammatory and repair processes in the
vessels cells, and in CKD patients promote inflammation and raise blood
pressure. I guess the best way to prevent atherosclerosis is to not develop
atherosclerosis.
Overall, you want to reduce fat intake, but especially trans-fats and saturated fats. Food labels are now required to show how much trans
fat is in the product, but the manufacturers are getting around the regulation. They combine different fatty acids in a fat and they call them interestrified fats. Partial hydrogenation is still a major factor,
but they aren’t called trans-fats. This
allows them to keep it below the FDA radar. Interesterified fats don’t exist in
nature – that should tell us all we need to know.
What we need is a way to partially hydrogenate the
polyunsaturated fats that does not create trans-fats – you work on that while I
butter my bagel. Next week we can look at more aspects of fats, and how they
are different from the other lipids.
For
more information or classroom activities, see:
Trans
fats –
interesterification
–
LDL:HDL
–
http://www.medindia.net/news/reverse-cholesterol-transport-a-cholesterol-removal-system-116495-1.htm
Really the blogging is spreading its wings quickly.
ReplyDeletePretty! This was an extremely wonderful post.
ReplyDeleteŚwietny blog! Czy Twój motyw jest wykonany na zamówienie, czy pobrałeś go skądś?
ReplyDeleteMotyw taki jak twój z kilkoma prostymi dostosowaniami naprawdę sprawiłby, że mój blog by się wyróżniał.
Daj mi znać, skąd masz swój projekt. Dzięki dużo