NEW RESISTANT LIPOSOME COATED WITH POLYSACCHARIDE FILM FOR COSMETIC APPLICATION 235 Our observations were confi rmed by the viscosity values presented in Figure 3. Com- pared to the control acrylate gel, the incorporation of free and entrapped MgCl2 de- creased the acrylate gel viscosity. There was an important difference between the effects of MgCl2 whether in its entrapped or free form. 0.24% of free MgCl2 de- creased the viscosity of acrylate gel by about 41 times. However, when the same amount of MgCl2 was entrapped in coated liposomes (2%), the viscosity of acrylate gel decreased about 14 times compared to the control. These results were consider- ably different and showed that MgCl2 was partly entrapped into coated liposomes and some MgCl2 remained outside the coated liposome. Consequently, only nonen- trapped MgCl2 decreases the viscosity of acrylates gel. Figure 3 shows that viscosities of the control and acrylate gel containing free MgCl2 were stable for 30 days of storage at 25°C. Because of the strong encapsulation effi ciency of our technology, the viscosity of coated MgCl2 gel at Day 0 and Day 30 is not considerably different (Figure 3). This result re- vealed that coated liposome membrane is very resistant and does not allow the release of MgCl2 during the period of storage. Aqueous suspensions of MCCL were diluted with distilled water (1/2, 1/10) and then intro- duced into an acrylates gel to potentially induce a diffusion of MgCl2 through the coated lipo- some membrane. An equivalent amount of free MgCl2 was incorporated into acrylate gel. Figure 4 presents the viscosity of acrylate gels containing 2% of MCCL (i.e., 0.24% MgCl2), 4% of MCCL suspension diluted by half to maintain an equivalent amount of MgCl2 (i.e., 0.24% MgCl2), and 20% of MCCL suspension diluted to 1/10 (i.e., 0.24% MgCl2). Our results showed that there was no effect on the MgCl2 release after the external medium dilution of coated lipo- somes. If the membrane permeability of coated liposomes depended on the osmotic gradient, distilled water dilution would have induced the release of MgCl2 from coated liposomes. Our MgCl2 equilibrium hypothesis was then refuted because all acrylate gels containing different concentrations of entrapped MgCl2 had the same viscosity profi le. This study confi rmed that coated liposome membrane is very resistant to MgCl2 release. Liposome membranes are semi- permeable to molecules depending on different characteristics. The permeability of liposome Figure 4. Effect of dilution on magnesium chloride release from coated liposomes (Acrylates gels viscosity was measured at 25°C).

JOURNAL OF COSMETIC SCIENCE 236 membrane to ions varies considerably (25). Protons and hydroxyl ions pass rapidly across liposo- mal membrane. However, the permeability of liposome membranes to divalent and multivalent ions is slower than monovalent ions. This could be due to the charge increasing and the hydra- tion shell of ions. IMPROVEMENT OF MAGNESIUM CHLORIDE DETOXIFICATION ACTIVITY Ex vivo study of the MCCL effi cacy to improve the skin availability of active mole- cules was performed. Because of its destabilization in contact with 12% of MgCl2, noncoated liposomes were not tested in this ex vivo test. Indeed, MgCl2 was entrapped in coated liposomes, and its effect on P-gp skin explants activity was evaluated versus non-entrapped MgCl2. Acrylates/xanthan (1:0.5 w/w) gel containing 3% of MCCL or an equivalent amount of free MgCl2 (0.36%) was used to evaluate the P-gp activity in a model of normal human skin explants. Figure 5 presents the quantity of ATP consumed by P-gp per μg of proteins. Compared to the nontreated explants (control), placebo and free MgCl2 did not have signifi cant effect on the consumption of ATP by P-gp transporter. However, MCCL increased the consumption of ATP (p = 0.06) sig- nifi cantly, followed by the activity of P-gp transporter. P-gp is a transmembrane bio- logical target involved in cell detoxifi cation system and waste elimination (26–28). Hamada and Tsuruo (7) found that magnesium is essential for P-gp ATPase activity. However, high concentrations of Mg2+ inhibited the ATPase activity of P-gp (7). Ac- cording to this fi nding, we can conclude that 0.36% of MgCl2 inhibited the ATPases activity of P-gp transporter. Figure 5 shows that coated liposomes improved the pen- etration of MgCl2 through skin explants signifi cantly compared to nonentrapped MgCl2. We can suppose that the entrapment of MgCl2 decreased its concentration in external aqueous medium of coated liposome suspension and then increased the ac- tivity of ATPase. During the incubation time, the long-lasting release of MgCl2 re- duced potential metabolism inhibition of P-gp ATPase in the presence of high salt contents. Figure 5. P-gp activity in human normal skin explants model (MCCL: Magnesium chloride coated liposomes).