Special thanks to William Biggs MD for making this available here and on misc.health.diabetes.

 

Here is Lipids 101, with attention to small denser low density lipoprotein, sd LDL.

First we define our terms:

PARTICLES - think of these as "trucks"

HDL - high density lipoprotein - a carrier for cholesterol

IDL - intermediate density lipoprotein carrier for triglycerides and cholesterol

LDL - low density lipoprotein - another carrier for cholesterol

VLDL - very low density lipoprotein - carrier for triglycerides and cholesterol

CHLYOMICRONS - Crude mixture of mostly triglycerides and a little cholesterol.

APOLIPOPROTEINS - these are the protein building blocks, the proteins that "trucks" are made out of.

Apolipoprotein E. You can have E2, E3, or E4. Choose any two.
You get one from each parent.

Apolipoprotein B, such as B100 and B48.

FREIGHT - What you load and transport in the "trucks"

Triglycerides - the major fat fuel source

Cholesterol - special type of fat needed for steroid synthesis.Gets into arteries and forms plaque.

How Fat gets into the body , deposited, or used up:

1) You eat a fatty meal.

2) The TRIGLYCERIDES and CHOLESTEROL are absorbed throught the small intestine into the blood stream as fat droplets called CHYLOMICRONS. The chylomicrons are made up mostly of triglycerides, with a little cholesterol, and Apo B48.

3) The enzyme lipoprotein lipase "dissolves" the Chylomicron in the blood stream. This frees up some free cholesterol and triglycerides, which are then picked up by available HDL particles. (Thus it is good to have lots of HDL..)

4) After the chylomicron has had most of the fat removed from it it, is termed a "Remnant" . Think of it as a burned out dwarf star of a lipid molecule. It's fate is to land in the liver where the remnant of the chylomicron is absorbed.

How you regulate your fat levels between meals ?
(the simplified version).

1) Your body senses you need to burn fat. This occurs while fasting at night.

2) Your liver responds by releasing VLDL, which is mostly triglycerides and Apo B100, but does contain a little cholesterol and Apo E.

3) The enzyme lipoprotein lipase "dissolves" the VLDL. The lipids released are again picked up by the HDL.

4) After some of the fat is removed from VLDL, it is called IDL.

5) After almost all of the fat is removed, leaving behind mostly apo B100, cholesterol, and some Apo E, the truck is now called LDL. This is the dwarf star version of VLDL.

6) There are receptors in the liver for B-100 and ApoE. The LDL are then reabsorbed in the liver. The apolipoproteins are saved and used later when fat needs to be released again in the form of VLDL.

Refresher:

HDL - particles that scavenge free cholesterol and triglycerides for processing in the liver. Think of it as the recycling truck.

VLDL - fresh, new fat containing protein secreted by the liver. Mostly triglycerides with a little cholesterol.

LDL - used up and burned out VLDL, after the triglycerides have been removed.

 

What do your lab tests report ?

HDL Cholesterol = Cholesterol content carried in HDL particles

LDL Cholesterol = Cholesterol content carried in LDL particles

Triglycerides = Triglyceride content in chylomicrons, VLDL, and to a minor extent, free fatty acids.

 

Why measure this fasting?

Because fasting you should have NO chylomicrons left. You only should see these after meals. This allows you to estimate

VLDL since chylomicrons and free fatty acids should be very low at this time.

 

Why do we care about oxidation ?

The atherosclerotic plaques contain cholesterol derived from LDL, and it is largely oxidized. Small dense (sd) LDL is more easily oxidized, thus the concern.

Furthermore, sd LDL has reduced binding to the liver's LDL receptors, increased time in serum, increased time for penetration into arterial walls, and preferential binding to artery walls.

The genesis of too much sd LDL doesn't appear to be conversion of large LDL to sd LDL. Rather, it is the failure of sd LDL to be absorbed by the liver.

Who gets excess sd LDL ?

It is associated with insulin resistance, increased visceral (abdominal) fat (also known as the apple shape), high triglycerides, and low HDL.

Hope you aren't overloaded at this point.

Cheers,

William C Biggs, MD

 

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