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High-density lipoprotein (HDL) is one of the five major groups of lipoproteins. 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 one, two or three ApoA; more as the particles enlarge picking up and carrying more fat molecules) and transporting none up to hundreds of fat molecules/particle. Unlike the larger lipoprotein particles which deliver fat molecules to cells, HDL particles remove fat molecules from cells which want to export fat molecules. The fats carried include cholesterol, phospholipids, and triglycerides; amounts of each quite variable. Lipoproteins, in order of molecular size, largest to smallest, are chylomicrons, very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL), and HDL. Lipoprotein molecules (all particles far smaller than human cells), enable the transportation of all lipids, such as cholesterol, phospholipids, and triglycerides, within the water around cells (extracellular fluid), including the bloodstream. For perspective on particle size; see: Cell Size and Scale,.. HDL particles, unlike the larger particles, transfer fats away from cells, artery walls and tissues (around the body, body wide) through the bloodstream, back to both (a) LDL particles and (b) back to the liver for other disposition. Increasing concentrations of HDL particles are strongly associated with decreasing accumulation of atherosclerosis within the walls of arteries() over weeks, years, decades. This is important because atherosclerosis, eventually, results in sudden plaque ruptures triggering clots within the artery opening, narrowing/closing the opening(s), i.e. cardiovascular disease, stroke(s) and other vascular disease complications body wide. HDL particles (though vastly different from just cholesterol and other fat molecules ''per-se'') are sometimes referred to as good cholesterol because they can transport fat molecules (including cholesterol, triglycerides, etc.) out of artery walls, reduce macrophage accumulation, and thus help prevent, even regress atherosclerosis over weeks, years, decades, thereby helping prevent cardiovascular disease, stroke(s) and other vascular disease complications body wide. In contrast, LDL particles (also far different from cholesterol ''per-se'') are often called bad cholesterol or unhealthy cholesterol, because they deliver fat molecules to macrophages in the wall of arteries.() However, studies have shown that HDL lacking mice still have the ability to transport cholesterol to bile, suggesting that there are alternative mechanisms for cholesterol removal.〔Betteridge, et. al (2 September 2008). "Structural requirements for PCSK9-mediated degradation of the low-density lipoprotein receptor". PNAS. 105 �(35): 13045–13050〕 In addition to this another research group showed that transgenic mice retain the ability to metabolize bile and form gallstones in the absence of HDL.〔Amigo, L et al (7 December 2010). Apolipoprotein A-I deficiency does not affect biliary lipid secretion and gallstone formation in mice. 31(2):263-71. doi: 10.1111/j.1478-3231.2010.02421.x. Epub 2010 Dec 7〕 This may also suggest that HDL is not as 'good' as popular belief claims. ==Testing== Because of the high cost of directly measuring HDL and LDL protein particles, blood tests are commonly performed for the surrogate value, HDL-C, i.e. the cholesterol associated with ApoA-1/HDL particles. In healthy individuals, about 30% of blood cholesterol, along with other fats, is carried by HDL. This is often contrasted with the amount of cholesterol estimated to be carried within low-density lipoprotein particles, LDL, and called LDL-C. HDL particles remove fats and cholesterol from cells, including within artery wall atheroma, and transport it back to the liver for excretion or re-utilization; thus the cholesterol carried within HDL particles (HDL-C) is sometimes called "good cholesterol" (despite being the same as cholesterol in LDL particles). Those with higher levels of HDL-C tend to have fewer problems with cardiovascular diseases, while those with low HDL-C cholesterol levels (especially less than 40 mg/dL or about 1 mmol/L) have increased rates for heart disease. Higher native HDL levels are correlated with better cardiovascular health; however, it does not appear that further increasing one's HDL improves cardiovascular outcomes. The remainder of the serum cholesterol after subtracting the HDL is the non-HDL cholesterol. The concentration of these other components, which may cause atheroma, is known as the non-HDL-C. This is now preferred to LDL-C as a secondary marker as it has been shown to be a better predictor and it is more easily calculated. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「High-density lipoprotein」の詳細全文を読む スポンサード リンク
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