Diphenylhexatriene (DPH)-labeled lipids as a potential tool for studies on lipid peroxidation in monolayer films

Using the fluorescence of diphenylhexatriene (DPH), lipid peroxidation in monomolecular films of phospholipids has been monitored dynamically to elucidate the efficacy of such a probe and to elucidate the effects of molecular organization on such peroxidation processes. Behavior in well-controlled model systems may be used to obtain insight into oxidative processes in complex biological systems. Mixed monolayers of hexadecanoyl-DPH-phosphatidylcholine (HDPH-PC) and diarachidonoyl-PC (DAA-PC) 1/10 (mol/mol) were prepared on a Langmuir trough. With pure water as subphase, and under an atmosphere of N2/O2 (3/1, v/v), DPH fluorescence remained stable over several hours, even under continuous illumination. However, over copper sulfate solution, rapid decay in the fluorescence intensity was observed and correlated with both the copper ion concentration and film pressure. No change in fluorescence was observed in absence of subphase copper ions or under an N2 atmosphere. Substitution of dioleoyl phosphatidylcholine for DAA-PC in systems above gave no decrease in fluorescence intensity. This lipid alone is not susceptible to free radical chain reaction. Absorption spectra from HDPH-PC/DAA-PC monolayers confirm that DPH is actually destroyed during film oxidation. We thus propose this system as a new experimental model for studies on lipid peroxidation in organized systems.