Lipid biodynamics: new perspectives

Abstract Active biological systems can be divided into five phases: the aqueous polar phase, the monolayer and/or bilayer interfacial phase, the apolar or hydrophobic phase, the solid or insoluble phase and the gaseous phase. The micellar phase is a special dispersed state of an interfacial phase. Molecules are distributed among these five phases according to their physicochemical properties. Herein is proposed a standardization in strict compliance with the CGS (cm, g, s) unit system and uses the mass/volumen, mole per cm 3 (mol·cm −3 chemical unit. This standardization requires a new set of symbols to clearly distinguish the concentrations in the different phases. The numerous implications of this standardization are discussed with respect to the quantitative classification of lipids based upon interphase partition coefficients, a new definition of micelles, simple models for the study of lipid biodynamic behavior and sites of action of lipid metabolism enzymes as well as determination of the physicochemical parameters of circulating lipoproteins. By compartmentalization in an aqueous polar phase, an interfacial phase comprising phospholipids and free cholesterol and an apolar phase comprising triglycerides and esterified cholesterol, this standardization will greatly simplify quantitative research on the factors regulating and disturbing cholesterol homeostasis. The notion of total cholesterol must be foresaken, since the biodynamic behavior of free cholesterol and esterified cholesterol are fundamentally different. Free cholesterol shares the fate of the interfacial phase of which it is a part, this fate being hinged on enzymatic biotransformations and/or ligand-receptor interactions. The proposed standardization gives rise to a new rationale using simple calculations and its advantage will be 2-fold:first, in the design of experimental protocols; and second, in allowing immediate and unambiguous comparison of experimental data based upon strictly defined parameters.