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Sunday, October 13, 2013

Large LDL and small HDL particles: The best combination

Large-density lipoprotein (HDL) is one particular of the five major varieties of lipoproteins identified in circulation, with each other with very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), reduced-density lipoprotein (LDL), and chylomicrons.

Right after a fatty food, the blood is loaded with chylomicrons, which carry triglycerides (TGAs). The TGAs are transferred to cells from chylomicrons by way of the activity of enzymes, in the form of cost-free fatty acids (FFAs), which are utilised by individuals cells as resources of vitality.

Right after offering FFAs to the cells, the chylomicrons progressively lose their TGA content and “shrink”, eventually being absorbed and recycled by the liver. The liver exports component of the TGAs that it receives from chylomicrons back to cells for use as vitality as properly, now in the kind of VLDL. As VLDL particles provide TGAs to the cells they shrink in dimension, similarly to chylomicrons. As they shrink, VLDL particles first turn into IDL and then LDL particles.

The determine under (click on on it to enlarge), from Elliott & Elliott (2009 reference at the stop of this submit), exhibits, on the very same scale: (a) VLDL particles, (b) chylomicrons, (c) LDL particles, and (d) HDL particles. The darkish bar at the base of each and every shot is 1000 A in length, or 100 nm (A = angstrom nm = nanometer 1 nm = 10 A).


As you can see from the determine, most of the LDL particles revealed are about 1/four of the size of the dim bar in diameter, typically marginally more, or about 25-27 nm in dimension. They arrive in distinct dimensions, with sizes in this range  being the most frequent. The smaller and denser they are, the more most likely they are to contribute to the development of atherosclerotic plaque in the presence of other variables, such as continual irritation. The more substantial they grow to be, which usually happens in diet plans high in saturated body fat, the considerably less likely they are to kind plaque.

Observe that the HDL particles are relatively tiny compared to the LDL particles. Shouldn’t they result in plaque then? Not truly. Apparently they have to be tiny, compared to LDL particles, to do their occupation properly.

HDL is a entirely different animal from VLDL, IDL and LDL. HDL particles are produced by the liver as dense disk-like particles, acknowledged as nascent HDL particles. These nascent HDL particles progressively pick up cholesterol from cells, as properly as performing a variety of other functions, and “fatten up” with cholesterol in the procedure.

This method also involves HDL particles selecting up cholesterol from plaque in the artery walls, which is one of the factors why HDL cholesterol is informally referred to as “good” cholesterol. In reality, neither HDL nor LDL are genuinely cholesterol HDL and LDL are particles that have cholesterol, protein and excess fat.

As far as particle dimension is anxious, LDL and HDL are opposites. Big LDL particles are the minimum most likely to lead to plaque formation, since LDL particles have to be around twenty five nm in diameter or smaller to penetrate the artery partitions. With HDL the reverse looks to be true, as HDL particles need to be little (when compared with LDL particles) to easily penetrate the artery walls in buy to choose up cholesterol, leave the artery partitions with their cargo, and have it returned back to the liver.

Interestingly, some study indicates HDL particles that are bigger in measurement, when in comparison with other HDL particles (not with LDL particles), seem to do a far better job than very tiny HDL particles in terms of reducing chance of cardiovascular ailment. It is also achievable that a high variety of more substantial HDL particles in the blood is indicative of elevated amounts of "effective" HDL particles i.e., particles that are efficient at finding up cholesterol from the artery partitions in the initial area.

One more interesting element of this cycle is that the return to the liver of cholesterol picked up by HDL appears to be accomplished mostly through IDL and LDL particles (Elliott & Elliott, 2009), which get the cholesterol directly from HDL particles! Daily life is not that simple.

Reference:

William H. Elliott & Daphne C. Elliott (2009). Biochemistry and Molecular Biology. 4th Version. New York: NY: Oxford University Push.
Title: Large LDL and small HDL particles: The best combination
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