Particle-enhanced membrane uptake of a polynuclear aromatic hydrocarbon: a possible role in cocarcinogenesis.

One possible mechanism by which cocarcinogenesis occurs was investigated. The effect of a particulate, silica, upon the rate of membrane uptake of a polynuclear aromatic hydrocarbon, benz[a]anthracene (BA), was studied. The fluorescence emission spectrum and quantum yield of BA, when adsorbed to silica, underwent spectral shifts upon addition of phospholipid vesicles. These spectral changes appeared to result from the transfer of BA from the silica surface into the lipid bilayer. We used these spectral changes to measure the rates of membrane uptake of BA from the silica-adsorbed state and from the crystalline and microcrystalline states of BA. Our studies demonstrated that adsorption of BA to silica resulted in an increased rate of uptake of BA into dipalmitoyl-L-alpha-phosphatidylcholine vesicles compared to the uptake rate into these vesicles from crystalling states. Such particle-enhanced membrane uptake of chemical carcinogens may be of importance in explaining the enhanced carcinogenicity of the polynuclear aromatic hydrocarbons in the presence of particulate matter.