The terms chole, which means bile, stereos, which means solid, and -ol, which indicates alcohol, are the roots of the word cholesterol. It is a lipid and an organic substance because it is a sterol. It can be biosynthesized by all animal cells, making it a crucial component of the membrane's structural makeup. Other names for it include cholesterin and cholesteryl alcohol. The number of rotatable bonds is 5, and the donor and acceptor for hydrogen bonds have property values of 1 and 1, respectively. The most well-known lipid in the steroid family is cholesterol. It is a waxy, fatty-like substance that is largely found in animal and human cells, where it also serves as the main sterol. Cholesterol can be found in both its free and stored forms in all cells and bodily fluids. In milligrams (mg) of cholesterol per deciliter (DL) of blood, cholesterol levels are measured. The recommended range for average cholesterol is 200–300 mg/DL. Because blood is a water-based fluid and cholesterol is an oil-based fluid, they are insoluble in each other. Plaques are formed as the cholesterol forms into lumps and enter the bloodstream.
A waxy molecule that resembles fat, cholesterol is primarily derived from the liver and our diet. Both plant-based and animal-based foods, such as milk, milk products, eggs, whole grains, fruits, nuts, veggies, etc., contain cholesterol. Foods that contain cholesterol aren't always good for you. Therefore, good sources of soluble fibre include whole grains, dairy products that are low in fat or fat-free, egg whites, fresh fruits, and vegetables.
A lipid is known as amphipathic, cholesterol. It can be discovered in human bodily cells, blood, and lipids. It is employed to create the human skin barrier and cell membranes. Additionally, it produces hormones, which are crucial for digestion. Cholesterol is important for the production of vitamin D and is used in the construction of cells and cell membranes, hormone synthesis, and digestion. Additionally, cholesterol aids in the creation of bile acids, which are essential to the functioning of the human digestive system.
Why Does High Cholesterol Occur?
Unhealthy lifestyle choices are the most frequent cause of elevated cholesterol. This may consist of:
- Unhealthy eating patterns, such as consuming a lot of trans fats. Certain meats, dairy items, chocolate, baked goods, deep-fried foods, and processed foods all contain saturated fat. Some fried and processed meals include another form of fat called trans-fat. You can increase your LDL (bad) cholesterol by consuming these lipids.
- Lack of exercise and excessive sitting down are also contributing factors to this. Your HDL (good) cholesterol declines as a result.
- Smoking, reduces HDL cholesterol, particularly in females. Additionally, it increases LDL cholesterol.
- Another consideration is the likelihood that high cholesterol runs in families. Familial hypercholesterolemia is one type of genetic high cholesterol (FH). Numerous medications and other medical issues can also cause high cholesterol.
What Makes Me More Likely To Have High Cholesterol?
Numerous factors can increase your risk of having high cholesterol, including:
- Age: As you get older, your cholesterol levels tend to go up. High cholesterol can also affect younger people, including children and teenagers, though it is less prevalent.
- Heredity: A family history of high blood cholesterol may exist.
- Weight: You have higher cholesterol if you are obese or overweight.
- Race: Some races may have a higher risk of elevated cholesterol. For instance, compared to white people, African Americans often have higher levels of HDL and LDL cholesterol.
Components of Risk
Your probability of having abnormal cholesterol levels may be influenced by the following variables:
- Unhealthy cholesterol levels may be caused by consuming too much saturated or trans-fat. Saturated fats are present in both fatty animal cuts and full-fat dairy products. Trans fats are frequently found in packaged desserts and snacks.
- An individual with a body mass index (BMI) of 30 or greater is at risk of having high cholesterol.
- Your body's HDL, or "good" cholesterol, levels rise as a result of exercise.
- Smoking. Smoking cigarettes may cause your HDL, or "good," cholesterol, to decline.
The blood's lipoproteins carry cholesterol around the body. These lipoproteins include:
- Low-density lipoprotein is one of the two main lipoproteins (LDL). LDL is frequently referred to as "the nasty cholesterol."
- High-density lipoprotein is the other main lipoprotein (HDL). HDL is the "good cholesterol."
- Very low-density lipoproteins (VLDL), which contain triglycerides, are found in the blood.
Difference Between HDL and LDL Cholesterol in Tabular Form
|Parameters of Comparison||HDL||LDL|
|Other Name||Wholesome cholesterol||Lower cholesterol|
|Definition||Healthy or high-density cholesterol the liver uses lipoprotein, one of the several forms of lipoproteins that are found in blood, to transport triglycerides and cholesterol for excretion or re-use.||Small Density Another type of lipid found in the blood is a lipoprotein, also referred to as "bad cholesterol." If present in high amounts, it tends to accumulate in arteries and result in obstruction.|
|Moving cholesterol from tissues and arteries to the liver and other organs like the ovary, testis, and adrenal glands is the function of good cholesterol.||The main function of LDL is to transport cholesterol to tissues and arteries.|
|Recommended Range||1.55 mmol/L or more of healthy cholesterol is advised.||LDL (bad cholesterol) levels should be 2.6 mmol/L or lower.|
|Source||Onions and Omega-3 fatty acids like flax oil, salmon, and foods high in fibre like cereals, oats, and bran are sources of HDL.||Foods high in trans fatty acids, refined carbohydrates like white sugar and flour, foods high in cholesterol like egg yolk, liver, kidney, dairy products like cream cheese, etc., and alcohol are sources of poor cholesterol.|
What is HDL (High-density Lipoprotein)?
One of the five main categories of lipoproteins is high-density lipoprotein (HDL). Lipoproteins are multiprotein complex particles that move all lipids (fat molecules) through the body's extracellular fluid (water). 80–100 proteins on average make up each particle, which is structured by one, two, or three Apol. While moving through the circulation, HDL particles grow, accumulating additional fat molecules and carrying up to hundreds of fat molecules per particle. According to density/size (an inverse relationship), which also correlates with function and the frequency of cardiovascular events, lipoproteins are categorized into 5 subgroups. HDL particles remove fat molecules from cells, in contrast to bigger lipoprotein particles that supply fat molecules to cells. Triglycerides, phospholipids, and cholesterol are among the lipids transported; the amounts of each vary.
Atherosclerosis buildup within artery walls is connected with rising HDL particle concentrations, which lowers the risk of rapid plaque ruptures, cardiovascular disease, stroke, and other vascular illnesses. Because they transfer fat molecules out of arterial walls, decrease macrophage buildup, and so aid in the prevention or even regression of atherosclerosis, HDL particles are often referred to as "good cholesterol. “The smallest lipoprotein particle, HDL ranges in size from 5 to 17 nm. Because the ratio of protein to lipids is the largest, it is the densest. Apolipoproteins A-I and A-II are the two that are most prevalent in it. It has been shown that the rare genetic variant ApoA-1 Milano is significantly more effective in preventing and treating arterial disease atherosclerosis.
These lipoproteins are produced by the liver as complexes of apolipoproteins and phospholipids that resemble cholesterol-free flattened spherical lipoprotein particles and whose NMR structure has just recently been published. The complexes can pick up cholesterol from cells through interaction with the ATP-binding cassette transporter A1 (ABCA1). The free cholesterol is changed by the plasma enzyme lecithin-cholesterol acyltransferase (LCAT) into cholesteryl ester, which is then secluded into the core of the lipoprotein particle, eventually leading the newly formed HDL to take on a spherical shape. By interacting with the ABCG1 transporter and the phospholipid transport protein, for example, HDL particles can take in more cholesterol and phospholipid molecules from cells and other lipoproteins as they move through the bloodstream (PLTP). HDL mostly transports cholesterol to the liver or steroidogenic organs such as the testicles, ovary, and adrenals through direct and indirect pathways. One of the HDL receptors that eliminates HDL is the scavenger receptor BI (SR-BI), which mediates the selective uptake of cholesterol from HDL. The most significant method in humans is probably the indirect one, which is mediated by cholesteryl ester transfer protein (CETP). This protein exchanges the triglycerides of VLDL for the cholesteryl esters of HDL. As a result, VLDLs are changed into LDL, which the LDL receptor pathway then excretes from the bloodstream. Hepatic lipase breaks down the HDL triglycerides because they are unstable, leaving only minute HDL particles that can once again take up cholesterol from cells.
HDL carries a wide variety of lipid and protein species, some of which are physiologically extremely active while having very low concentrations. For instance, HDL and the lipid and protein that make up the molecule help to stop the oxidation, inflammation, activation of endothelial cells, coagulation, and platelet aggregation. Although it is still unclear which of these traits is most important, all of them could aid HDL in preventing atherosclerosis. Some HDL also protects the protozoan parasite Trypanosoma brucei. The HDL subfraction known as trypanosome lytic factor (TLF) is composed of specialized proteins that are particularly active and unique to the TLF molecule. It has been suggested that, as opposed to the concentration of all HDL particles, the concentration of big HDL particles more precisely reflects the protective function. This ratio of large HDL to total HDL particles varies greatly and can only be determined by more complex lipoprotein assays using either the original method, electrophoresis, which was developed in the 1970s, or more recent NMR spectroscopy methods, which were developed in the 1990s.
What is Low-Density Lipoprotein?
One of the five main lipoprotein subgroups, low-density lipoprotein transports all fat molecules in extracellular water throughout the body (LDL). Chylomicrons (also known as ULDL by the overall density name system), very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL), and high-density lipoprotein make up these groupings in decreasing density order (HDL). Cells receive fat molecules from LDL. Atherosclerosis is brought on by the oxidation of LDL within the walls of the arteries.
Emulsification, or surrounding the fatty acids being carried, is made possible by each native LDL particle, allowing the fats to circulate in the body in the water outside of cells. One apolipoprotein B-100 molecule (Apo B-100, a protein with 4536 amino acid residues and a mass of 514 kDa) and 80 to 100 auxiliary proteins are found in each particle. Each LDL comprises a very hydrophobic core made up of polyunsaturated fatty acid linoleate and hundreds to thousands of esterified and unesterified cholesterol molecules (around 1500 is typically given as the average). The single copy of Apo B-100, phospholipids and unesterified cholesterol surround this core, which also contains different amounts of triglycerides and other fats. LDL particles range in size from 22 nm (0.00000087 in.) to 27.5 nm and weigh around 3 million Daltons. There is a variation in LDL particle mass and size because they contain a variable and varying quantity of fatty acid molecules. Due to its heterogeneous structure, figuring out the structure of LDL has been challenging. With a resolution of about 16 Angstroms and employing cryogenic electron microscopy, the structure of LDL at human body temperature in its natural state has recently been revealed.
LDL particles having oxidatively changed structural elements are referred to as oxidized LDL. As a result, the lipid and protein components of LDL can both be oxidized in the arterial wall by the free radical attack. In addition to the oxidative processes occurring in the arterial wall, oxidized dietary lipids can also be the source of LDL oxidized lipids. Since oxidized LDL has been linked to the onset of atherosclerosis, it has received extensive research as a potential risk factor for cardiovascular illnesses. The lack of recognition of oxidation-modified LDL structures by the LDL receptors, which prevents the normal metabolism of LDL particles and ultimately results in the development of atherosclerotic plaques, has been used to explain the atherogenicity of oxidized LDL. LDL receptors linked to LDL are transported to the endosome in vesicles. LDL receptors go through a conformation change and release LDL in the presence of low pHs, such as that present in the endosome. After that, LDL is transported to the lysosome, where its cholesterol esters are hydrolyzed. Normally, LDL receptors return to the plasma membrane, where they complete this cycle once more. However, LDL receptor trafficking is diverted to the lysosome, where it is destroyed, if LDL receptors bind to PCSK9.
Difference Between HDL and LDL Cholesterol In Points
- Atherosclerosis is brought on by higher levels of LDL cholesterol leaving the arterial walls. Higher HDL levels are crucial because they reduce the risk of cardiovascular disease.
- Cholesterol makes up about 50% of an LDL particle's weight, while protein makes up only 25%. High-density lipoprotein particles, on the other hand, are made up of 50% protein and 20% cholesterol by weight.
- LDL particles are thought to promote atherosclerosis more. HDL is thought to be anti-atherogenic.
- LDL particles are more likely to become oxidized. HDL particles, on the other hand, possess anti-oxidant, anti-inflammatory, anti-thrombotic, and anti-apoptotic capabilities.
- LDL provides the tissue with cholesterol. HDL, on the other hand, transports and deposits cholesterol in the liver.
Since cholesterol is a lipid, it cannot freely circulate through your blood and does not combine with water. As a result, your body must mix cholesterol with proteins to form a complex known as a lipoprotein to transport cholesterol through your bloodstream to the cells that need it for various purposes. Low-density lipoproteins (LDL) and high-density lipoproteins are two separate types of lipoproteins that carry cholesterol and are referred to as LDL cholesterol and HDL cholesterol, respectively (HDL). Although LDL and HDL both contribute to the movement of cholesterol throughout the body, there are significant differences in the two lipids' structures, functions, and consequences on health.
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