Dr Mike MacDonald

Low density lipoprotein

Low-density lipoprotein (LDL) is one of the five major groups of lipoproteins. These groups, from largest to smallest (least dense versus more dense compared with the surrounding water), are: chylomicrons (ULDL), very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), LDL, and high-density lipoprotein (HDL), all of them, particles far smaller than human cells. Lipoproteins transfer fats through the bloodstream, then the intracellular (water) to all cells around the body. Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells. They are typically composed of 80-100 proteins/particle (organized by a single ApoB for LDL and the larger particles) and transporting about 3,000 to 6,000 fat molecules/particle. The fats carried include cholesterol, phospholipids, and triglycerides; amounts of each quite variable. LDL particles pose a risk for cardiovascular disease when they invade the endothelium and become oxidized, since the oxidized forms are more easily retained by the proteoglycans. A complex set of biochemical reactions regulates the oxidation of LDL particles, chiefly stimulated by presence of necrotic cell debries and free radicals in the endothelium. Increasing concentrations, low to high, of LDL particles are strongly associated with increasing amounts, low to high, of atherosclerosis within the walls of arteries over time, eventually resulting in sudden plaque ruptures and triggering clots within the artery opening, or a narrowing or closing of the opening, i.e. cardiovascular disease, stroke, and other vascular disease complications. LDL particles (though far different from cholesterol per se) are sometimes referred to as bad cholesterol because they can transport their content of fat molecules into artery walls, attract macrophages, and thus drive atherosclerosis. In contrast, HDL particles (though far different from cholesterol per se) are often called good cholesterol or healthy cholesterol because they can remove fat molecules from macrophages in the wall of arteries. A hereditary form of high LDL is familial hypercholesterolemia (FH). Increased LDL is termed hyperlipoproteinemia type II (after the dated Fredrickson classification).

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