COSMETIC LIPOSOMES 127 Table II Effect of the Type of Phospholipid and of the Loading Technique on the Percentage of DPH in the Vesicles % DPH in liposomes Phospholipid Method A Method B EPC 74.9 + 3.6 54.1 - 3.0 P90 71.2 + 3.2 52.6 + 3.1 evaluated. The turbidity initially increased, indicating that surfactant molecules were incorporated by the vesicles then it decreased almost linearly because of the formation of mixed micelies (9). The trend of these curves can be directly related to the stability of the aggregated structure in the form of vesicles (7). Results reported in Figure 1, which refer to several different preparations and phospholipid concentrations, indicate that no difference was observed between the two types of liposomes. CONCLUSIONS From an overall comparison between EPC and P90 liposomes, reported results indicate that the differences, although detectable in some cases, are never such that they support the use of the 99% pure and much more expensive product for large scale or commercial preparations. 1,5 1,0 0,5 0,0 0 5 10. 15 20 Triton X-100 (M x 104 ) Figure 1. Effect of increasing surfactant concentration on the turbidity of liposome dispersions. Turbidity changes are expressed as the ratio between the value observed in the presence of Triton X-100 and that of the reference without surfactant. Reported experiments refer to EPC and P90 liposomes. Phospholipid concentrations were 0.30 mg/ml and 0.90 mg/ml. For the higher phospholipid concentration, abscissa values must be multiplied by 3.0.

128 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Experimental results indicate also that the amount of lipophilic probe in the liposome structure is affected by the loading method consequently, the possibility of incorpo- rating hydrophobic substances in empty liposomes (that can be found directly on the market) can lead to a product that is different from that obtained when liposomes are prepared from a co-precipitated film. REFERENCES (1) H. Lautenschliiger, J. RiSding, and M. Ghyczy, The use of liposomes from soya phospholipids in cosmetics, SOFW, 114, 531-534 (1988). (2) J. Pikul and F. A. Kummerow, Thiobarbituric acid reactive substance formation as affected by distribution of polyenoic fatty acids in individual phospholipids, J. Agric. Food. Chem., 39, 451-457 (1991). (3) B. J. Litman and Y. Barenholz, Fluorescent probe: Diphenyhexatriene, Methods Enzymol., 81, 678- 685 (1982). (4) T. Parasassi, G. De Stasio, R. M. Rush, and E. Gratton, A photophysical model for diphenyl- hexatriene fluorescence decay in solvents and in phospholipid vesicles, Biophys. J., 59, 466-475 (1991). (5) H. Ringsdorf, B. Schlarb, and J. Venzmer, Molecular architecture and function of polymeric oriented systems: Models for the study of organization, surface recognition and dynamics of biomembranes, Angew. Chem. Int. Ed. Engl., 27, 113-158 (1988). (6) K. Anzai, H. Utsumi, K. Inoue, S. Nojima, and T. Kwan, Electron spin resonance studies on the interaction between liposomal membrane and Triton X-100, Chem. Pharm. Bull., 28, 1762-1767 (1980). (7) G. Strauss, F. Alhaique, A. Memoli, E. Santucci, and F. M. Riccieri, The stability ofdrugocarrying liposomes in the presence of detergents, Polymer Preprints, 27, 48 (1986). (8) N.J. Turro, M. Griitzel, and A.M. Braun, Photophysical and photochemical processes in micellar systems, Angew. Chem. Int. Ed. Engl., 19, 675-696 (1980). (9) A. K. Mathur, C. Agarwal, B. S. Pangtey, A. Sing, and B. N. Gupta, Surfactant-induced fluores- cence changes in fluorescein dye, Int. J. Cosmet. Sci., 10, 213-218 (1988). (10) Y. H. Paik and S.C. Shim, Photophysical properties of psoralens in micellar solutions, J. Photochem. Photobiol. A, 56, 349-358 (1991).