Maria Eugenia Carlotti

On the stability of ascorbic acid in emulsified systems for topical and cosmetic use

Several O/W microemulsions, O/W and W/O emulsions and a W/O/W multiple emulsion were prepared using non-ionic, non-ethoxylated, skin compatible emulsifiers. Ascorbic acid (vitamin C) was added to the emulsified systems and its stability against oxidation was studied at 45.0 degrees C in aerobic conditions and compared with that in aqueous solutions at different pH values. All emulsified systems provided protection to ascorbic acid, as its degradation rate, which increased with increasing pH, was slower in emulsified systems than in aqueous solutions. The highest protection of ascorbic acid was when it was dissolved in the inner aqueous phase of the W/O/W multiple emulsion, both at 45 and at 20 degrees C for long storage. A pseudo first-order mechanism was hypothesised for ascorbic acid degradation in the experimental conditions for as long as abundant dissolved oxygen was present.

Sterilization and freeze-drying of drug-free and drug-loaded solid lipid nanoparticles

Solid lipid nanoparticles (SLN) have been prepared from three oil-in-water microemulsions, whose internal phase was constituted of different lipid matrices. The dispersion media were two aqueous solution of trehalose and Pluronic F68 at 2% besides distilled water. SLN were sterilized by autoclaving, were stable during sterilization and maintained a spherical shape and narrow size distribution as confirmed by TEM analysis. SLN dispersions in water did not present nanoparticles larger than 1 μm after storage at 4°C for 1 year; they were freeze-dried after sterilization to obtain dry products. Diazepam was used as model drug to incorporate into SLN, where it was shown by calorimetric analysis to be in amorphous form.

PREPARATION OF GRISEOFULVIN NANOPARTICLES FROM WATER-DILUTABLE MICROEMULSIONS

Nanoparticles of griseofulvin, a model drug with poor solubility and low bioavailability, were prepared from water dilutable microemulsions by the solvent diffusion technique. Solvent-in-water microemulsion formulations containing water, butyl lactate, lecithin, taurodeoxycholate sodium salt (TDC) or dipotassium glycyrrhizinate (KG), 1,2-propanediol or ethanol were used. The formation of macroscopically homogeneous, stable, fluid, optically transparent, isotropic solutions (microemulsions) was investigated by constructing pseudo-ternary phase diagrams. In the presence of TDC or KG, microemulsion systems that remained transparent on water dilution could be obtained. The displacement of butyl lactate, with an excess of water, from the internal phase of the microemulsions containing the drug into the external phase, lead to successful fabrication of drug nanosuspensions. Nanoparticle size was dependent on microemulsion composition: using KG, griseofulvin nanoparticles below 100 nm with low polydispersity and an increased dissolution rate were obtained.

Role of particle coating in controlling skin damage photoinduced by titania nanoparticles

TiO2 nanoparticles hazard is associated to their photocatalytic activity causing release of DNA damaging ROS (Reactive Oxygen Species), lipid peroxidation and skin damage. Various coatings have been proposed to minimize photocatalysis, while keeping the potential to block UV radiations. Uncoated and variously coated commercial nano-titania have been classified on the basis of UVB-induced lipoperoxidation of linoleic acid. A selection of the most and the least protective specimens was then examined by ESR (Electron Spin Resonance) to evidence the presence of surface paramagnetic centres and the release of ROS in aqueous suspensions (spin trapping). Paramagnetic centres and ROS were correlated with the extent of lipid peroxidation. When tested on porcine skin (mimicking the human one), titania acted as on linoleic acid. The combined use of lipid peroxidation of simple fatty acids with ESR analysis is here proposed as a possible screening tool for the evaluation of the potential toxicity of nano-titania in sunscreen preparations.

Photochemincal processes involving nitrite in surface water samples

Abstract.A study into nitrite photochemistry was carried out on surface (both lake and river) water samples. In the tested samples, nitrite photolysis accounted for 0–60 % of .OH photoproduction, nitrate for 0–40 %, and dissolved organic matter (DOM) photochemistry played on average the main role. In real surface waters, an effect of radiation extinction by the water column would also be observed, and is expected to inhibit nitrate photochemistry at a higher extent compared to nitrite or DOM. Nitrite showed a definite time evolution with irradiation. Photodegradation prevailed in samples with the highest initial concentrations, while photogeneration with DOM transformation was evident in the presence of undetectable initial nitrite levels. Nitrite also accounted for up to 9 % of .OH scavenging, which would produce up to 66 % of photoformed nitrogen dioxide. The remaining percentage of nitrogen dioxide generation is accounted for by nitrate photolysis. Photogenerated nitrogen dioxide could then be involved in significant processes of aromatic nitration, in particular in the transformation of phenol into nitrophenols.

Investigation of the phase behaviour of systems containing lecithin and 2-acyl lysolecithin derivatives

A series of modified phospholipids (m-PC) possessing different acyl chains in position 2, from butanoyl to hexadecanoyl, were prepared by partial synthesis from soybean lysolecithin. They were used with soybean lecithin to construct phase diagrams containing ethanol as cosolvent, water and medium chain triglycerides (MCT) or isopropyl myristate (IPM) as oils. The weight ratios lecithin:m-PC and surfactants:ethanol were kept constant at 1:1. The results indicate that the m-PCs have a strong effect on the microemulsion (L) and liquid crystalline (LC) domains in the water-rich/oil-poor part of the phase diagrams, although all diagrams correspond to a single lecithin:m-PC ratio. On decreasing the acyl chain length, and thus increasing the hydrophilicity of the surfactant, there was a corresponding increase in the L area, which moved towards the aqueous corner of the phase diagrams. The LC phase was detected only in the presence of the hexadecanoyl derivative for the systems containing MCT, and it was not detected only in the presence of the butanoyl derivative for the systems containing IPM. The use of a second hydrophilic surfactant to adjust the packing properties of the lecithin-alcohol systems, and/or to increase the fluidity of the surfactant film, increased the region of existence of the isotropic systems. This may be of importance in the formulation of drug delivery systems, especially those which are diluted by biological fluids upon administration.

Photostability and photolability of dissolved organic matter upon irradiation of natural water samples under simulated sunlight

Abstract.In this study the photostability/photolability of Dissolved Organic Matter (DOM) was assessed in both lake and groundwater. DOM in groundwater can undergo significant irradiation when drawn to the surface for agricultural purposes. DOM was generally photostable in lake and photolabile in groundwater, with a more elevated rate constant of DOM disappearance in groundwater samples with higher Non-Purgeable Organic Carbon (NPOC). DOM in lake water became photolabile upon acidification. The parallel decrease of both Total Organic Carbon (TOC) and NPOC suggests that actual photomineralisation took place in the samples. The •OH radicals play a secondary role into DOM photomineralisation in lake water, despite the fact that their generation rate considerably increases at acidic pH. The role of •OH is also minor in the photomineralisation of DOM contained in nitrate-rich groundwater.

Photostability and Stability over Time of Retinyl Palmitate in an O/W Emulsion and in SLN Introduced in the Emulsion

Solid lipid nanoparticles (SLNs) have been introduced as a novel carrier system for drugs and cosmetics. It has been found that SLNs themselves show physical UV‐blocking action. Cetyl palmitate, glyceryl behenate, and palmitic acid SLNs, all loaded with retinyl (vitamin A) palmitate, were prepared and introduced in an O/W emulsion. SLNs in O/W emulsion protect retinyl palmitate from the photo degradation induced by UVA and UVB radiation. This effect is probably due to the light‐scattering properties of SLN. Nanoparticles also protect vitamin A palmitate from thermal degradation. DSC thermal analytical examination, Z potential determination, and particle size measurement confirmed the solid character of the nanoparticles and the encapsulation of retinyl palmitate, their easy dispersion due to their negative charge on the surface, and their mean diameters in the nanometer range.

Photostability of Trolox in Water/Ethanol, Water, and Oramix CG 110 in the Absence and in the Presence of TiO2

Abstract Trolox (synthetic, hydrosoluble phenolic derivative of vitamin E, used as an active in cosmetic products) can undergo photooxidation upon UVB and UVA irradiation, the main degradation intermediate being Trolox C quinone. Trolox photodegradation rate decreases with decreasing polarity of the solvent, most likely because a more apolar environment inhibits oxidative processes. Ethanol is thus able to protect Trolox from degradation. Micellar solutions of Oramix CG 110® can incorporate Trolox in their core and protect it from photodegradation, either by providing an apolar environment or by competing for light absorption. Trolox can be degraded in the presence of titanium dioxide (an additive in many cosmetic products) under photocatalytic conditions, and both ethanol and Oramix show a certain protection effect towards Trolox photocatalytic degradation. However, concerning both direct photolysis and photocatalytic degradation, the protection given by ethanol and Oramix to Trolox results in at most 50% reduction of the transformation rate. Ethanol and Oramix (representative of the actual composition of cosmetic products) thus reduce but do not eliminate Trolox photodegradation. The solution to this problem might consist in the use of non‐transparent bottles for Trolox‐containing compounds and in the choice of titanium dioxide samples showing limited photocatalytic activity.

Specific effects of single antioxidants in the lipid peroxidation caused by nano-titania used in sunscreen lotions

The effect of some additives, phenylalanine, ascorbyl palmitate and sodium ascorbyl phosphate on the oxidation of linoleic acid and porcine ear skin induced by UV irradiation was investigated, in the absence and in the presence of variously uncoated and coated titania powders. Such additives have, on the one hand, a scavenging activity toward the oxidizing species photogenerated by TiO(2), and on the other one an inhibitory effect toward UVB-induced peroxidation. Sodium ascorbyl phosphate and ascorbyl palmitate displayed a stronger antioxidant effect than phenylalanine toward linoleic acid peroxidation. On porcine skin all the three molecules exhibited both antiradical and antioxidant activity. Their protective effect against peroxidation was higher with porcine skin lipids than with linoleic acid, referable to the chemical differences in the two lipid substrates.