Cholesterol is the principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils.
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 per particle. HDL particles enlarge while circulating in the blood, aggregating more fat molecules and transporting up to hundreds of fat molecules per particle.
Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons, very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL) and high-density lipoprotein (HDL). LDL delivers fat molecules to cells. LDL is involved in atherosclerosis, a process in which it is oxidized within the walls of arteries.
A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, surrounded by a phospholipid outer shell, with the hydrophilic portions oriented outward toward the surrounding water and lipophilic portions oriented inward toward the lipid center. A special kind of protein, called apolipoprotein, is embedded in the outer shell, both stabilising the complex and giving it a functional identity that determines its role.
Very-low-density lipoprotein (VLDL), density relative to extracellular water, is a type of lipoprotein made by the liver. VLDL is one of the five major groups of lipoproteins that enable fats and cholesterol to move within the water-based solution of the bloodstream. VLDL is assembled in the liver from triglycerides, cholesterol, and apolipoproteins. VLDL is converted in the bloodstream to low-density lipoprotein (LDL) and intermediate-density lipoprotein (IDL). VLDL particles have a diameter of 30–80 nanometers (nm). VLDL transports endogenous products, whereas chylomicrons transport exogenous (dietary) products. In the early 2010s both the lipid composition and protein composition of this lipoprotein were characterised in great detail.
Hypercholesterolemia, also called high cholesterol, is the presence of high levels of cholesterol in the blood. It is a form of hyperlipidemia, hyperlipoproteinemia, and dyslipidemia.
Dyslipidemia is a metabolic disorder characterized by abnormally high or low amounts of any or all lipids or lipoproteins in the blood. Dyslipidemia is a risk factor for the development of atherosclerotic cardiovascular diseases (ASCVD), which include coronary artery disease, cerebrovascular disease, and peripheral artery disease. Although dyslipidemia is a risk factor for ASCVD, abnormal levels don't mean that lipid lowering agents need to be started. Other factors, such as comorbid conditions and lifestyle in addition to dyslipidemia, is considered in a cardiovascular risk assessment. In developed countries, most dyslipidemias are hyperlipidemias; that is, an elevation of lipids in the blood. This is often due to diet and lifestyle. Prolonged elevation of insulin resistance can also lead to dyslipidemia. Likewise, increased levels of O-GlcNAc transferase (OGT) may cause dyslipidemia.
Apolipoproteins are proteins that bind lipids to form lipoproteins. They transport lipids in blood, cerebrospinal fluid and lymph.
Hyperlipidemia is abnormally high levels of any or all lipids or lipoproteins in the blood. The term hyperlipidemia refers to the laboratory finding itself and is also used as an umbrella term covering any of various acquired or genetic disorders that result in that finding. Hyperlipidemia represents a subset of dyslipidemia and a superset of hypercholesterolemia. Hyperlipidemia is usually chronic and requires ongoing medication to control blood lipid levels.
Torcetrapib was a drug being developed to treat hypercholesterolemia and prevent cardiovascular disease. Its development was halted in 2006 when phase III studies showed excessive all-cause mortality in the treatment group receiving a combination of atorvastatin (Lipitor) and torcetrapib.
Cholesteryl ester transfer protein (CETP), also called plasma lipid transfer protein, is a plasma protein that facilitates the transport of cholesteryl esters and triglycerides between the lipoproteins. It collects triglycerides from very-low-density (VLDL) or Chylomicrons and exchanges them for cholesteryl esters from high-density lipoproteins (HDL), and vice versa. Most of the time, however, CETP does a heteroexchange, trading a triglyceride for a cholesteryl ester or a cholesteryl ester for a triglyceride.
Foam cells, also called lipid-laden macrophages, are a type of cell that contain cholesterol. These can form a plaque that can lead to atherosclerosis and trigger myocardial infarction and stroke.
Lecithin cholesterol acyltransferase deficiency is a disorder of lipoprotein metabolism. The disease has two forms: Familial LCAT deficiency, in which there is complete LCAT deficiency, and Fish-eye disease, in which there is a partial deficiency.
Hepatic lipase (HL), also called hepatic triglyceride lipase (HTGL) or LIPC (for "lipase, hepatic"), is a form of lipase, catalyzing the hydrolysis of triacylglyceride. Hepatic lipase is coded by chromosome 15 and its gene is also often referred to as HTGL or LIPC. Hepatic lipase is expressed mainly in liver cells, known as hepatocytes, and endothelial cells of the liver. The hepatic lipase can either remain attached to the liver or can unbind from the liver endothelial cells and is free to enter the body's circulation system. When bound on the endothelial cells of the liver, it is often found bound to heparan sulfate proteoglycans (HSPG), keeping HL inactive and unable to bind to HDL (high-density lipoprotein) or IDL (intermediate-density lipoprotein). When it is free in the bloodstream, however, it is found associated with HDL to maintain it inactive. This is because the triacylglycerides in HDL serve as a substrate, but the lipoprotein contains proteins around the triacylglycerides that can prevent the triacylglycerides from being broken down by HL.
Endothelial lipase (LIPG) is a form of lipase secreted by vascular endothelial cells in tissues with high metabolic rates and vascularization, such as the liver, lung, kidney, and thyroid gland. The LIPG enzyme is a vital component to many biological processes. These processes include lipoprotein metabolism, cytokine expression, and lipid composition in cells. Unlike the lipases that hydrolyze Triglycerides, endothelial lipase primarily hydrolyzes phospholipids. Due to the hydrolysis specificity, endothelial lipase contributes to multiple vital systems within the body. On the contrary to the beneficial roles that LIPG plays within the body, endothelial lipase is thought to play a potential role in cancer and inflammation. Knowledge obtained in vitro and in vivo suggest the relations to these conditions, but human interaction knowledge lacks due to the recent discovery of endothelial lipase. Endothelial lipase was first characterized in 1999. The two independent research groups which are notable for this discovery cloned the endothelial lipase gene and identified the novel lipase secreted from endothelial cells. The anti-Atherosclerosis opportunity through alleviating plaque blockage and prospective ability to raise High-density lipoprotein (HDL) have gained endothelial lipase recognition.
Blood lipids are lipids in the blood, either free or bound to other molecules. They are mostly transported in a phospholipid capsule, and the type of protein embedded in this outer shell determines the fate of the particle and its influence on metabolism. Examples of these lipids include cholesterol and triglycerides. The concentration of blood lipids depends on intake and excretion from the intestine, and uptake and secretion from cells. Hyperlipidemia is the presence of elevated or abnormal levels of lipids and/or lipoproteins in the blood, and is a major risk factor for cardiovascular disease.
Sterol O-acyltransferase is an intracellular protein located in the endoplasmic reticulum that forms cholesteryl esters from cholesterol.
The chronic endothelial injury hypothesis is one of two major mechanisms postulated to explain the underlying cause of atherosclerosis and coronary heart disease (CHD), the other being the lipid hypothesis. Although an ongoing debate involving connection between dietary lipids and CHD sometimes portrays the two hypotheses as being opposed, they are in no way mutually exclusive. Moreover, since the discovery of the role of LDL cholesterol (LDL-C) in the pathogenesis of atherosclerosis, the two hypotheses have become tightly linked by a number of molecular and cellular processes.
A lipid profile or lipid panel is a panel of blood tests used to find abnormalities in blood lipid concentrations. The results of this test can identify certain genetic diseases and can determine approximate risks for cardiovascular disease, certain forms of pancreatitis, and other diseases.
Evacetrapib was a drug under development by Eli Lilly & Company that inhibits cholesterylester transfer protein. CETP collects triglycerides from very low-density lipoproteins (VLDL) or low-density lipoproteins (LDL) and exchanges them for cholesteryl esters from high-density lipoproteins (HDL), and vice versa, but primarily increasing high-density lipoprotein and lowering low-density lipoprotein. It is thought that modifying lipoprotein levels modifies the risk of cardiovascular disease. The first CETP inhibitor, torcetrapib, was unsuccessful because it increased levels of the hormone aldosterone and increased blood pressure, which led to excess cardiac events when it was studied. Evacetrapib does not have the same effect. When studied in a small clinical trial in people with elevated LDL and low HDL, significant improvements were noted in their lipid profile.
