NON-PENETRA TING SUNSCREENS (NPSUNS) A form of s unscreens, the skin NPSUNs, could be used in cosmetics and pharmaceuti- cal personal care products. The main reason that led to the design of the new photopro- tectors was the immobilization of UV-absorbing moieties contained in the chemical backbone of Jojoba oil. Thus, several forms of fi lters were created that included conju- gates of Jojoba oil with UV sunscreen molecules. Jojoba oil consists of esters of fatty acids (C18–C22) with fatty alcohols (C18–C22) and has a wax structure. Its use is rather common in cosmetics and pharmaceutical products. NPSUNs have physico- chemical characteristics, which allow these derivatives to stay on the upper SC, where sunscreen molecules are activated, and, thus, no further penetration to the inner dermal strata or into the systemic circulation is feasible. It was found that OMC-NPSUN pos- sesses a similar UV absorption spectrum as OMC and could be easily formulated in cosmetic and pharmaceutical topical products. No permeation of OMC-NPSUN across the skin was observed in 24-h in vitro permeation experiments after application of ei- ther neat substances or OMC-NPSUNs formulated in oil-in-water cream, in water-in- oil cream, or in Jojoba oil (74). LIPID CARRI ERS Lipid carri ers seem to be a good alternative to formulate chemical UV fi lters reducing their skin penetration while maintaining good photo-protective abilities. Gilbert et al. compared percutaneous absorption and cutaneous bioavailability of BP-3 (concentration 5% w/w) loaded into SLNs, nanostructured lipid carriers (NLCs), nanostructured poly- meric lipid carriers (NPLCs), and NCs. The NLCs ar e considered as the second generation of SLNs that allow a) more effective drug loading, b) an adjustment of the drug distribution profi le, and c) an extended drug entrapment during storage. NCs and NPLCs have a characteristic hydrophobic polymer around their lipid core (Figure 2). This polymeric lipid layer of NCs allows lipophilic compounds to be released and protects the encapsulated molecules from photodegradation. A penetrati on and permeation study was carried out, on porcine ear skin, according to OECD TG 428 guideline (2004). Static Franz diffusion cells were used to evaluate the percutaneous permeation of BP-3 from the developed suspensions. Porcine skin was mounted between donor and receptor compartments. Donor media were composed of 1 mL of the tested formulations containing 5% of BP-3 to ensure BP-3 infi nite dose conditions. Every hour for the six fi rst hours, and then, 22, 23, and 24 h after formulations were applied into Franz cell donor compartment, an aliquot of 500 μL of receptor medium was withdrawn and immediately replaced with an equal volume of freshly prepared one. BP-3 skin dis- tribution study was carried out 24 h after the permeation experiment. Skin samples were removed from Franz diffusion cells and cleaned with a swab that was previously moistened into distilled water. SC was entirely removed applying 20 successive tape stripping (TS) at the skin surface. Samples were analyzed using high-performance liquid chromatography. Results show ed that BP-3 partition coeffi cient between the SC and SLN suspension did not signifi cantly differ from that obtained with the BP-3 albumin aqueous solution (AAS). Compared to SLNs and AAS, BP-3 showed a better affi nity for NLC, NPLC, and NC suspensions, and once BP-3 crosses the SC barrier, it showed a higher tendency to penetrate the epidermis compartment. NLCs did not permit to maintain BP-3 into the SC because JOURNAL OF COSMETIC SCIENCE 314
of the high BP-3 partition coeffi cient between the epidermis and the SC when BP-3 was formulated into NLC suspension (76). The effectiv eness of EHT and the ability to limit any possible toxicological effects has been made possible by the restricted percutaneous penetration of lipid microparticles (LMs). EHT encapsulation in LMs on its diffusion through the SC with glyceryl behenate and phosphatidylcholine has been examined. Creams with EHT in free or encapsulated in LM form combined with OMC and BMDBM, which are the most common UV fi lters and were applied on the skin of human volunteers. What was also examined was the fraction of the cream dose that was applied and had permeated in different SC layers. The cream that contained the nonencapsulated sunscreen agent presented a percentage of 21.9 ± 4.9% of the EHT dose, which was diffused in the SC. This percentage did not differ a lot from the smaller molecular weight OMC, which was found at 22.2 ± 7.6%, and BMDBM, which was found at 20.5 ± 3.7%. The cream that contained microencapsulated EHT gave an important reduction in 45.7% in skin permeation (77). Nanostructured Pol ymer and Lipid Carriers. Polymeric (PLC) a nd SLNs were prepared and characterized to act as BP-3 carriers, aiming at optimizing the safety of sunscreen products. The nanoprecipitation method was used to encapsulate BP-3 (1.6% w/w) in poly nanoparticles (epsilon-caprolactone) (PCL) and hot high pressure homogenization, to encapsulate BP-3 in SLNs. In both cases, the particles remained stable for 40 d. The BP-3 encapsulated in PCL nanoparticles was released faster than BP-3 encapsulated in SLNs. A raise in the sun protection factor concurred with the encapsulation of BP-3 in both nanostructures. Also, BP-3, encapsulated in SLNs, did not seem to cause any cytotoxic Figure 2. Schematic representation of lipid nanoparticles [SLNs and nanostructured lipid carrier (NLC)] and lipid NCs NPLC and NCs in aqueous media [modifi ed from Kaul et al. (75)]. DISTRIBUTION OF UV FILTERS ON THE SKIN 315
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