In Vitro Application of Langmuir Monolayer Model to Study In Vivo Biological Systems

Abstract

ABSTRACTLangmuir monolayer model is applied to study molecular interactions between phospholipids and surface active compounds and to determine the lateral elasticity and compressibility of the surface films at air-liquid interface. The interaction of the synthetic Methionine-enkephalin (Met-enk) and its amidated derivative (Met-enk-NH2) with monolayers of the zwitterionic dimyristoylphosphatidylcholine and the negatively charged dimyristoylphosphatidylglycerol were evaluated by measurements of surface tension (γ, mN/m) - time dependencies after injection of enkephalins under the Langmuir monolayer. The decrease of γ values during time showed that there was a strong penetration effect of both types of Met-enk molecules into the monolayers, being significantly stronger for the amidated derivate, Met-enk-NH2.The behavior of tear film lipid layer (TFLL) is studied in dynamic conditions by compression/expansion cycling of Langmuir films. It allows determining reciprocal compressibility, CS−1, and reversibility, Rv, of the tear films at air-liquid interface. Our results showed very high lateral elasticity (i.e. low reciprocal compressibility) and high structural reversibility of the meibomian surface films which was confirmed by Brewster Angle Microscopy images. It is shown that even at low surface pressures (between 0.5 and 10 mN/m) human meibum forms rough continuous multilayer films at the air/water interface that get more uniform when surface pressure increases.Our results demonstrate the potential of lipid monolayers formed in Langmuir's through to be successfully used as an elegant and simple model to study molecular interactions and properties of surface films at the air/water interface.