Good cholesterol

Cholesterol is biosynthesized in the liver trans ported throughout the body to be used in a va riety of ways and returned to the liver where it serves as the biosynthetic precursor to other steroids But cholesterol is a lipid and isn t soluble in water How can it move through the blood if it doesn t dis solve in if The answer is that it doesn t dissolve but IS instead carried through the blood and tissues as part of a lipoprotein (lipid + protein = lipoprotein) The proteins that carry cholesterol from the liver are called low density lipoproteins or LDLs those that return it to the liver are the high-density lipoproteins or HDLs If too much cholesterol is being transported by LDL or too little by HDL the extra cholesterol builds up on the walls of the arteries caus mg atherosclerosis A thorough physical examination nowadays measures not only total cholesterol con centration but also the distribution between LDL and HDL cholesterol An elevated level of LDL cholesterol IS a risk factor for heart disease LDL cholesterol is bad cholesterol HDLs on the other hand remove excess cholesterol and are protective HDL cholesterol IS good cholesterol... 

Heterogeneous reaction (Section 6 1) A reaction involving two or more substances present in different phases Hydro genation of alkenes is a heterogeneous reaction that takes place on the surface of an insoluble metal catalyst Heterolytic cleavage (Section 4 16) Dissociation of a two electron covalent bond in such a way that both electrons are retained by one of the initially bonded atoms Hexose (Section 25 4) A carbohydrate with six carbon atoms High density lipoprotein (HDL) (Section 26 11) A protein that carries cholesterol from the tissues to the liver where it is metabolized HDL is often called good cholesterol Histones (Section 28 9) Proteins that are associated with DNA in nucleosomes... 

High-density lipoprotein (HDL) (Section 26.11) Aprotein that carries cholesterol from the tissues to the liver where it is metabolized. HDL is often called good cholesterol. ... 

LDL, or "bad," cholesterol builds up as a plaque-like deposit on the interior walls of arteries. This process used to be called hardening of the arteries today it is referred to as atherosclerosis. It can lead to cardiovascular diseases, including strokes and heart attacks. In contrast, HDL or "good" cholesterol retards or even reduces arterial deposits. 

Krieger, M, 1999. Charting the fate of the good cholesterol Identification and characterization of the high-density lipoprotein receptor SR-BI. Annu Rev Biochem 68, 523-558. 

High cholesterol (overweight individuals often have higher levels of bad cholesterol and lower levels of good cholesterol) ... 

Further research on serum cholesterol revealed that is exists in two forms, high and low density lipoprotein. The high density lipoprotein appears to consist of cholesterol that is being moved to the liver for metabolism while low density lipoprotein appears to be cholesterol that is likely to block arteries. This has led to the labelling of high density lipoprotein as good cholesterol and of low density lipoprotein as bad cholesterol. 

The recent years have seen the success of statins like Lipitor (atorvastatin) as hypolipidemic agents that help treating cardiovascular disease primarily by lowering low-density lipoproteins ( bad cholesterol ) levels. Another novel strategy is to tackle the same problem by elevating high-density lipoproteins (H D L or good cholesterol ) levels via inhibition of cholesteryl ester transfer protein (CETP). 

Cholesterol is carried in the bloodstream by hpoproteins such as low density lipoprotein (LDL, or bad cholesterol ) and high density lipoprotein (HDL, good cholesterol ). LDL carries cholesterol from the liver to other parts of the body. LDL attaches to receptors (see Chapter 2) on the cell surface and is taken into the cell interior. It is then degraded and the cholesterol is used as a component for the cell membrane. When there is excessive cholesterol inside the cell, it leads to a reduction in the synthesis of LDL receptors. 

HDL (high-density lipoprotein) a protein-lipid complex that carries cholesterol away from the tissues good cholesterol. ... 

Many studies have now linked consumption of trans fats to elevated LDL or bad" cholesterol levels, decreased HDL or "good" cholesterol levels, and a presumed higher risk of atherosclerosis, just as with saturated fats. 

Trans fats come from hydrogenated oils like Crisco. Researchers have linked trans fats to heart disease, blocked blood vessels, higher levels of "bad" cholesterol, and lower levels of "good" cholesterol in the body. Trans fats seem to be so unhealthy that the Food and Drug Administration decided in 2003 that all food labels should show the amount of trans fats so that people could make better decisions about eating them. 

Relatively few INDs die in a phase III trial, but it certainly does happen. A recent example is torcetrapib (2.27), a drug designed to elevate HDL cholesterol levels (Figure 2.11). HDL cholesterol is the good cholesterol. A phase III trial of torcetrapib was halted when a quarterly study of clinical data revealed elevated mortality rates in patients receiving torcetrapib in comparison to a placebo.22... 

Moderate amounts of alcohol, such as one drink for a woman and two for a man, may have some good effects. Alcohol causes a small reduction in fat levels, a small increase in good cholesterol, and it dilates the blood vessels. This can help prevent heart disease. However, the amount of alcohol consumed must be low enough so it does not cause liver damage or trigger heavier drinking. -... 

High-density lipoproteins (HDLs) contain a different apolipoprotein form, Apolipoprotein A. These proteins are about half lipid and half protein by weight. Phospholipids and cholesterol esters are the most important lipid components. HDL is sometimes referred to as good cholesterol because a higher ratio of HDL to LDL corresponds to a lower rate of coronary artery disease. 

The relationship between elevated triglycerides (TGRs) as a risk factor for CAD is less clear. However, serum TGRs are often inversely related to high-density lipoprotein (HDL—the good cholesterol). Therefore, reduction in TGR levels are associated with a rise in HDL, which has a negative correlation (protective effect) with CAD. 

Although some amount of saturated fat in the diet is beneficial, general dietary advice is to avoid saturated fats. Trans-fats have been implicated in raising total cholesterol, lowering HDL ( good cholesterol ) and raising LDL ( bad cholesterol ). 

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