Most important in causing CAD:- (AIIMS May 2009)
a. Each native LDL particle contains a single apolipoprotein B-100 molecule (Apo B-100) which circulates the fatty acids, keeping them soluble in the aqueous environment.
b. LDL particles equates to a higher risk factor for coronary artery disease (CAD)
c. Because LDLs transport cholesterol to the arteries and can be retained there by arterial proteoglycans starting the formation of plaques, increased levels are associated with atherosclerosis, and thus heart attack, stroke, and peripheral vascular disease. For this reason, cholesterol inside LDL lipoproteins is often called "bad" cholesterol.
d. LDL is formed as VLDL lipoproteins lose triglyceride through the action of lipoprotein lipase (LPL) and become smaller and denser, containing a higher proportion of cholesterol.
e. A hereditary form of high LDL is familial hypercholesterolemia (FH). Increased LDL is termed hyperlipoproteinemia type II (after the Fredrickson classification).
f. LDL poses a risk for cardiovascular disease when it invades the endothelium and becomes oxidized, since the oxidized form is more easily retained by the proteoglycans. A complex set of biochemical reactions regulates the oxidation of LDL, chiefly stimulated by presence of free radicals in the endothelium. Nitric oxide down-regulates this oxidation process catalyzed by L-arginine.
g. The lipid profile does not measure LDL level directly but instead estimates it using the Friedewald equation using levels of other cholesterol such as HDL:
In mg/dl: LDL cholesterol = total cholesterol – HDL cholesterol – (0.20 × triglycerides)
In mmol/l: LDL cholesterol = total cholesterol – HDL cholesterol – (0.45 × triglycerides)
h. In the USA, the American Heart Association, NIH, and NCEP provide a set of guidelines for fasting LDL-Cholesterol levels, estimated or measured, and risk for heart disease. As of 2003, these guidelines were:
|Level mg/dL||Level mmol/L||Interpretation|
|<100||<2.6||Optimal LDL cholesterol, corresponding to reduced, but not zero, risk for heart disease|
|100 to 129||2.6 to 3.3||Near optimal LDL level|
|130 to 159||3.3 to 4.9||Borderline high LDL level|
|160 to 189||4.1 to 4.9||High LDL level|
|>190||>4.9||Very high LDL level, corresponding to highest increased risk of heart disease|