Atherogenic lipoproteins are molecules that carry cholesterol in the bloodstream. They are distinguished from other lipids because of a tendency to accumulate in blood vessels and block circulation, causing cardiovascular disease. Most commonly, these lipids derive from intake of foods high in cholesterol. They also form embolisms that lead to vessel blockage, heart attacks, and strokes. Some individuals may have a genetic predisposition for higher than average levels of atherogenic lipoproteins in their blood.
Lipoproteins are molecules that transport lipids in the bloodstream. Low-density lipoproteins (LDL) are atherogenic, and colloquially are called the "bad" kind of cholesterol. LDL carries the majority of the cholesterol in the blood serum, and is the main lipid that accumulates in arterial plaques. High-density lipoproteins (HDL), conversely, carry LDL cholesterol out of the bloodstream and into the liver, where it is metabolized and cannot block blood vessels.
Atherogenesis is the formation of hardened plaques, made from lipids, inside arteries. It is caused when atherogenic lipoproteins such as LDL are oxidized by free radical molecules. When these particles attach to the arterial wall, inflammation occurs as the immune system tries to repair the damage. Over time, this leads to atherosclerosis, as more arteries become narrow and blocked, causing cardiovascular disease, a leading cause of death in the industrialized world.
In some cases, smaller pieces of plaque can break out of a blocked vessel and circulate in the bloodstream. These fragments, called emboli, include atherogenic lipoproteins. Some cause strokes or heart attacks if lodged in a major blood vessel. In addition to LDL, an embolus may contain other lipids and cells formed from the inflammatory response inside the blood vessel. In some instances, plaques that do not fully block one artery may eventually drift into a critical position in another and cause severe impairment or death.
Some lipid-storing tissues are potentially atherogenic. For instance, much of the fat within the body is stored in adipose tissue as triglycerides. These molecules are generally kept out of the bloodstream and are not in a strict sense atherogenic. But some lipoproteins with triglycerides also contain LDL cholesterol, and thus contribute to arterial plaque formation. For this reason, high blood triglyceride levels can be interpreted as an increased risk of cardiovascular disease.
In the late 20th century, some scientific studies indicated that people with coronary artery disease may have a different type of atherogenic lipoprotein circulating in their blood. Further studies suggested that a heritable phenotype caused these patients to have small, dense LDL particles that increased their risk of disease. Called the small, dense LDL phenotype, this is usually found in individuals also presenting with endothelial disease in their blood vessel lining, and with reduced levels of HDL.