Each cell contains several thousand unique lipid molecules. There are several lipid classes based on lipids having various head groups (e.g. choline, ethanolamine, serine or inositol), whereas differences in hydrophobic fatty acyl chains give rise to a diversity of species within each class. By using mass spectrometry analysis it is now possible to quantify approx. 1000 lipid species in one sample.
Until recently most researchers studying lipids or membranes focused on the role of the various lipid classes. In this perspective article Skotland and Sandvig provide examples of how the chain length and the number of double bonds in the acyl chains result in different properties. They discuss in detail how the phosphatidylserine species PS 18:0/18:1 seems to play an important role for membrane structure and probably also for intracellular signaling. They stress that it is important that when people use model systems such as liposomes or perform theoretical molecular calculations based on model membranes, these models should be more similar to biological membranes than those often used. In particular, they show examples of how liposomes with an asymmetric distribution of lipids, i.e. with different lipids in the two leaflets of the membrane, give different results than liposomes with a symmetric distribution of lipids. They also discuss that it is important that the lipid species used in such models are more similar to those of biological membranes than the species often used in such membrane models. This perspective article also includes several points of recommendations for future studies that the authors find essential to improve our understanding of cellular membranes and the interactions between the two membrane leaflets.
Nanoparticles in Biomedicine: In vivo studies