Lipoprotein metabolism with a focus on COVID 19 kidney patients

Abstract

Definition and functionLipids: are biomolecules, chemically heterogeneous, which are characterized by being insoluble in water. 1 The main lipids for humans are: fatty acids (FA), triglycerides (TG), phospholipids (PL) and cholesterol. 2,3 Fatty acids: the most important for man's nutrition are long-chain (C 12 -C 20 ), containing evenly numbered carbon atoms. They were defined as: saturated (not present double bond inside the molecule, e.g. steariaric C 18:0 ), monounsaturated (have a double bond, e.g. oleic C 18:1 ) and polyunsaturated (have more than a double bond, e.g. linoleic C 18:3 ). In general, saturated FA of animal origin and unsaturated ones of plant origin predominate in the diet. Longchain FA is oxidized for energy production by the process known as β oxidation, which results in sequential reduction of the chain every two carbon atoms, and the production of Acetyl-Coenzyme-A (Acetyl-Co-A) that enters the tricarboxylic acid cycle (Krebs cycle) to generate energy. The FA has an energetic function, participate in the synthesis of prostaglandins and provide Acetyl-Co-A for the synthesis of other lipids.Triglycerides: are obtained by diet or produced by the body, from the esterification of glycerol with three molecules of FA, in liver or adipose tissue. It has an essentially energetic role, for immediate or subsequent storage use. Phospholipids: have a glycerol molecule as the backbone, in which two FA are esterified. The third hydroxyl group is attached to alcohol through phosphodiester binding. Therefore, PL have both domains: one hydrophilic (phosphate group) and another hydrophobic (FA), which give it structural function in the double layer that make up cell membranes and on the surface of lipoprotein particles.Cholesterol: Is the main steroid of man, unsaturated monohydric alcohol, derived from the pentanoperhydrophenantrene cycle and is present in all cells of the body and in most fluids. It may be in free form (structural component of cell membranes and on the surface of lipoprotein), or esterified (stored inside cells or inside lipoproteins). Cholesterol esterification occurs in the blood plasma by the action of the enzyme LCAT (lecithin cholesterol acyl transferase), activated by apo A-I, which transfers an FA of lecithin to the 3-beta-hydroxide cholesterol position. Intracellular esterification occurs by the action of ACAT (acyl-CoA-cholesterol acyl transferase). Cholesterol is present in foods, with the exception of vegetables, but most of it found in the body comes from the synthesis of new from acetate (Acetyl-Co-A). The step that regulates the speed in the synthesis pathway is the conversion of 3-hydroxy-3-methylglutaryl-coenzyme A to mevalonate, catalyzed by the enzyme hydroxy-methyl-glutariICoA reductase (HMGCoA reductase). The liver is the organ responsible for most of the synthesis of new cholesterol. Cholesterol also serves as a precursor for synthesis of steroid hormones, vitamin D and bile acids.