Lipoproteins are considered complex molecules that have a central core that contains cholesterol esters and triglycerides, which in turn are surrounded by free cholesterol, phospholipids, and apoliproteins. Their functions include: absorption and transport of dietary lipids and transport of toxic foreign compounds. A lipoprotein is an assembly of both lipids and proteins, hence the name and are classified based on their DENSITY. Because lipids are LIGHTER than proteins, particles that contain more lipids are LARGER in size but have LOWER density and those containing more proteins are SMALLER in size but have HIGHER density.
Although it has gained a BAD reputation as a high-risk factor for cardiovascular diseases, cholesterol is an ESSENTIAL component of all animal cells. And amongst other numerous cellular processes it provides cell membrane FLUIDITY, serves as a PRECURSOR for the production of bile, steroid hormones, and vitamin D. Its synthesis can be both endogenous (regulated via a negative feedback mechanism) or obtain cholesterol from food.
Lipids are classified by the main features and properties of the different lipid particles, going from the smallest in size, HDL to the largest one, Chylomicrons. Thus, HDL is the smallest of the group ( 5-12nm), it works to take cholesterol from tissues to the liver and has important positive functions in our body as it is an anti-atherogenic, anti-oxidant/inflammatory/thrombotic/apoptotic. LDL Is mainly made of cholesterol and Apo B-100, and it works to carry most of the cholesterol in circulation and small dense LDL. IDL is comprised of triglycerides and cholesterol. And like LDL and VLDL its major Apolipoproteins are: Apo B-100 (and also Apo-E and Apo-C). It is mainly pro-atherogenic which means that it works in the formation of atherosclerosis plaques in the vessels. VLDL is a transporter for triglycerides and is also pro-atherogenic. Finally, Chylomicrons. It is the biggest lipoprotein, it transports dietary TGs and cholesterol to peripheral tissues and liver for the cycle to begin again (Figure).
To conclude, there is a variety of lipid particles in our system with different functions. Some are seen as “bad” like VLDL as they contain more lipids and thus are pro-atherogenic; while others like HDL are considered “good” and have anti-inflammatory purposes amongst other functions.
By Valentina Frias, Osmaida Zumbi, Fatim-Zahra Tanji & Luis D’Marco
