Toxicity testing using lipid monolayers at the air-water interface

Epifluorescence microscopy can be used to visualize the coexistence of two immiscible fluid phases in lipid monolayers composed of binary mixtures of L-alpha-dimyristoylphosphatidylcholine (DMPC) and cholesterol at the air-water interface. Fluorescent probes are used to distinguish between the liquid domains rich in DMPC and those domains rich in cholesterol. Dissipation of the cholesterol-rich domains is observed when cholesterol oxidase is dissolved into a subphase. It is shown that, even in the presence of cholesterol oxidase, the monolayer remains an entirely interacting, well-ordered system. Furthermore, the presence of toxic substances in solution can be visualized by means of quantifiable changes in this domain-dissipating phenomenon. In this paper, it is shown that the lipid monolayer system can be used as a sensitive system for detecting the presence of toxic substances in solution. By observing the effects that certain toxic substances have on the enzymatic activity of cholesterol oxidase, and hence the rate of domain dissipation, the presence and relative levels of specific toxins can be quantified. (C) 1997 Published by Elsevier Science Limited.