Positively charged microemulsions for topical application.

The study reports pig-skin permeation and skin accumulation of miconazole nitrate (MCZ) from positively charged microemulsions containing water, 1-decanol/1-dodecanol (2:1, w/w), lecithin and/or decyl polyglucoside at different weight ratios, propylene glycol, 1,2 hexanediol and a cationic charge-inducing agent (stearylamine (ST), l-alanine benzyl ester (ALAB) or cetyltrimethylammonium bromide (CTAB)). Zeta-potential values of the positively charged microemulsions ranged from 14.2 to 37.5 mV and mean droplet size from 6.0 to 16.8 nm. In vitro pig-skin permeation of MCZ after a single 24h application was negligible for all microemulsions; accumulation from positively charged microemulsions was nearly twice that from their negatively charged counterparts. The increased accumulation might be ascribed to the interaction between positive microemulsive systems and negatively charged skin sites; no significant difference was observed among the various cationic charge-inducing agents. Skin accumulation from the microemulsion containing most lecithin was lower than those of other microemulsions; this was ascribed to the phase transformation from microemulsion to a liquid crystal system after skin contact. These results suggest that positively charged microemulsions could be used to optimize drug targeting without a concomitant increase in systemic absorption; ALAB, an ester of a natural amino acid, is an appropriate cationic charge-inducing agent.

Photodegradation of retinol and anti-aging effectiveness of two commercial emulsions.

Two commercial anti-aging products, RETI C and RETI C concentrate emulsions, containing retinol and vitamin C, were studied. The concentration of vitamin A was determined over time, subjecting the creams to an accelerated stability test. Both emulsions, when stored at 25 degrees C, showed a moderate decrease over time in retinol concentration, while after storage at 40 degrees C the percentage of retinol degraded increased over time. Under UVA irradiation, the retinol degraded to a greater extent than under UVB irradiation, both in RETI C and RETI C concentrate emulsions. In order to verify the anti-aging effectiveness of the emulsions, an in vivo test on some female volunteers was carried out, evaluating the visible results of the application of the creams on the skin surface. The creams were rather unstable after storage at 40 degrees C, but they were effective in treating the signs of aging and in reducing facial wrinkles.

O/W microemulsion as a vehicle for sunscreens.

In recent years, transparent dispersions or diluted milks have been used as sunscreens. These products contain water-soluble sunscreen agents, and quite frequently are washed away from the skin. However, O/W microemulsions are now being prepared as transparent vehicles for sunscreens. They are waterproof, nonsticky, and easily spreadable. The microemulsions are prepared by using pseudoternary diagrams, by combining lipids with surfactant blends and a polar phase. Soya lecithin and decylpolyglucose produce transparent systems with the lowest percentage of surfactants. These microemulsions contain 4-methylbenzilidene camphor or octylmethoxycinnamate as sunscreen agents. Cyclomethicone, menthol, and allantoin give products a good skin feel, and stearyl methicone gives the waterproof effect. These systems show a Newtonian flux. Little permeation of the sunscreens' trough lipophilic and hydrophilic membrane is evidenced.

Photodegradation of phenol and salicylic acid by coated rutile-based pigments: a new approach for the assessment of sunscreen treatment efficiency.

The treatments used in many commercial sunscreen pigments (organic additives and inorganic surface coating) to lower the pigments' ability to degrade molecules under photocatalytic conditions are effective in inhibiting the degradation of phenol, but much less effective towards the degradation of salicylic acid. The reason is in the different degradation pathways that phenol and salicylic acid follow under photocatalytic conditions. The treatments are thus effective in inhibiting the degradation pathways initiated by Ti(IV)-*OH(surf) (also named *OH(ads)), as in the case of phenol, but much less effective towards electron-transfer processes involving surface complexes, as in the case of salicylic acid. These results indicate that the techniques currently adopted by the cosmetic industry to develop organic additives for use as pigment treatments are likely to be inadequate. The problem most likely is that treatments are optimized following the inhibition of the photocatalytic degradation of a single model molecule, which results in blocking just one photocatalytic degradation pathway (usually the one initiated by Ti(IV)-*OH(surf)) and not the other (electron transfer processes). The possible implications for sunscreen pigments are briefly discussed, and a new approach for the evaluation of the photocatalytic activity of inorganic sunscreens is proposed.

Solid lipid nanoparticles formed by solvent-in-water emulsion-diffusion technique: development and influence on insulin stability.

Insulin-loaded solid lipid nanoparticles (SLN), obtained by the solvent-in-water emulsion-diffusion technique, were produced using isovaleric acid (IVA) as organic phase, glyceryl mono-stearate (GMS) as lipid, soy lecithin and sodium taurodeoxycholate (TDC) as emulsifiers. IVA, a partially water-miscible solvent with low toxicity, was used to dissolve both insulin and lipids. SLN of spherical shape were obtained by simple water dilution of the O/W emulsion. Analysis of SLN content after processing showed interesting encapsulation efficiency with respect to therapeutic doses; moreover, insulin did not undergo any chemical modification within the nanoparticles and most of it remained stable after incubation of the SLN with trypsin solution. The biological activity of insulin, i.e. the ability to decrease glycemia in rats, was not negatively influenced by the SLN production process, as after subcutaneous administration of insulin extracted from SLN to animals, the blood glucose levels were quite similar to those obtained after administration of a conventional insulin suspension. Consequently, SLN seem to have interesting possibilities as delivery systems for oral administration of insulin.