Carcinogenic and non-carcinogenic aromatic hydrocarbons in lipid membranes. A fluorescence study of pyrene and benzo[a]pyrene

Abstract

1. The fluorescence behavior of a non-carcinogenic (pyrene) and a carcinogenic (benzo[a]pyrene) aromatic hydrocarbon was examined in the presence of a phospholipid bilayer membrane in the gel phase. 2. The monomer emission spectrum of pyrene in the membrane is very similar to that in micelles indicating a site near the aqueous surface region. Benzo[a[pyrene monomer spectra exhibit a red shift in the membrane relative to aliphatic hydrocarbon solvents. On the basis of spectral shifts in other homogeneous solvents, it is inferred that the carcinogen is located in the upper portion of the membrane acyl region, a more polarizable environment than the hydrocarbon core of the bilayer. 3. Analysis of the excimer to monomer emission intensity ratio as a function of probe molar ratio indicates that pyrene is much less soluble in the membrane than benzo[a]pyrene. 4. These results complement published EPR data which show that carcinogenic aromatic hydrocarbons cause structural changes in the membrane, while non-carcinogenic ones do not. These differences in membrane solubility and ability to alter membrane structure are discussed in the context of the different carcinogenic potencies of the hydrocarbons.