CAPSAICIN AFFECTS THE STRUCTURE AND PHASE ORGANIZATION OF PHOSPHOLIPID-MEMBRANES

Capsaicin is a natural compound with pharmacological and toxicological effects, which given its hydrophobicity, can influence the structure of membranes. The interaction of capsaicin with model membranes of dip almitoylphosphatidylcholine and dielaidoylphosphatidylethanolamine has been studied by using differential scanning calorimetry, fluorescent probe spectroscopy and P-31-nuclear magnetic resonance. Capsaicin rema rkably affects the phase transition of dipalmitoylphosphatidylcholine, shifting the transition temperature to lower values, and giving rise, at relatively high capsaicin concentrations, to the appearance of two peaks in the thermogram. These peaks may correspond to separated phas es as indicated by the partial phase diagram. Whereas capsaicin did no t affect the fluorescence polarization of the probes diphenylhexatrien e and trimethylammonium-diphenylhexatriene, it clearly affected that o f the probe 2-anthroyloxystearic acid, indicating that the perturbatio n produced by capsaicin on the membrane would be mainly at the positio n where this fluorophore is located. On the other hand, capsaicin, at relatively low concentrations, gives rise to immiscible phases in the presence of dielaidoylphoshatidylethanolamine and decrease the tempera ture of the lamellar to hexagonal H-II phase transition. At concentrat ions of capsaicin higher than 0.3 mol fraction, isotropic phases were detected. The possible implications of the effects of capsaicin on bio logical membranes are discussed.