Inorganic and organic UV filters: Their role and efficacy in sunscreens and suncare products

Minerals such as titanium dioxide, TiO₂, and zinc oxide, ZnO, are well known active semiconductor photocatalysts used extensively in heterogeneous photocatalysis to destroy environmental pollutants that are organic in nature. They are also extensively used in sunscreen lotions as active broadband sunscreens that screen both UVB (290-320 nm) and UVA (320-400 nm) sunlight radiation and as high SPF makers. When so photoactivated by UV light, however, these two particular metal oxides are known to generate highly oxidizing radicals (OH and ) and other reactive oxygen species (ROS) such as H₂O₂ and singlet oxygen, ¹O₂, which are known to be cytotoxic and/or genotoxic. Hydroxyl (OH) radicals photogenerated from photoactive TiO₂ specimens extracted from commercial sunscreen lotions [R. Dunford, A. Salinaro, L. Cai, N. Serpone, S. Horikoshi, H. Hidaka, J. Knowland, FEBS Lett. 418 (1997) 87] induce damage to DNA plasmids in vitro and to whole human skin cells in cultures. Accordingly, the titanium dioxide particle surface was modified to produce TiO₂ specimens of considerably reduced photoactivity. Deactivation of TiO₂ diminishes considerably, in some cases completely suppresses damage caused to DNA plasmids, to human cells, and to yeast cells compared to non-modified specimens exposed to UVB/UVA simulated solar radiation. The photostabilities of sunscreen organic active agents in neat polar and apolar solvents and in actual commercial formulations have been examined [N. Serpone, A. Salinaro, A.V. Emeline, S. Horikoshi, H. Hidaka, J. Zhao, Photochem. Photobiol. Sci. 1 (2002) 970]. With rare exceptions, the active ingredients undergo photochemical changes (in some cases form free radicals) and the sunscreen lotions lose considerable Sun protection efficacy only after a relatively short time when exposed to simulated sunlight UVB/UVA radiation, confirming the recent findings by Sayre et al. [R.M. Sayre, J.C. Dowdy, A.J. Gerwig, W.J. Shields, R.V. Lloyd, Photochem. Photobiol. 81 (2005) 452].     

Evaluation of detection distance‐dependent reflectance spectroscopy for the determination of the sun protection factor using pig ear skin

Determination of sun protection factors (SPFs) is currently an invasive method, which is based on erythema formation (phototest). Here we describe an optical setup and measurement methodology for the determination of SPFs based on diffuse reflectance spectroscopy, which measures UV‐reflectance spectra at 4 distances from the point of illumination. Due to a high spatial variation of the reflectance data, most likely due to inhomogeneities of the sunscreen distribution, data of 50 measurement positions are averaged. A dependence of the measured SPF on detection distance is significant for 3 sunscreens, while being inconclusive for 2 sunscreens due to high inter‐sample variations. Using pig ear skin samples (n=6), the obtained SPF of 5 different commercial sunscreens corresponds to the SPF values of certified test institutes in 3 cases and is lower for 2 sunscreens of the same manufacturer, suggesting a formulation specific reason for the discrepancy. The results demonstrate that the measurement can be performed with a UV dose below the minimal erythema dose. We conclude the method may be considered as a potential noninvasive in vivo alternative to the invasive in vivo phototest, but further tests on different sunscreen formulations are still necessary.

     

Survey of cytotoxic and UV protection effects of biosynthesized cerium oxide nanoparticles

Cerium oxide nanoparticles (CeO₂ NPs) are among the important nanoparticles that are extensively utilized in cosmetics, automotive industries, ultraviolet (UV) filtration, gas sensors, and pharmaceutical products. In this study, CeO₂ NPs were synthesized using an aqueous extract of Ziziphus jujube fruit. The synthesized nanoparticles were characterized using UV‐visible spectroscopy, powder X‐ray diffraction, Fourier transform infrared spectroscopy, energy‐dispersive spectroscopy, field energy scanning electron microscopy, and Raman methods. The results indicated that the size of synthesized nanoparticles is between 18 and 25 nm, and they have a spherical shape. UV absorbance of the synthesized nanoparticles was measured through spectrophotometric method in the range of 290 to 320 nm. The cytotoxic activity of synthesized CeO₂ NPs against colon (HT‐29) cancer cell line was surveyed through 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay. The results showed that synthesized nanoparticles are nontoxic on HT‐29 cells under 400 μg/mL concentrations after 24 hours of treatment time periods. The increase in treatment time cases increases cytotoxic activity of synthesized nanoparticles. Sun protection factor of CeO₂ NPs, as a criterion for amount of sunlight radiation protection, was determined by applying Mansur equation. The results demonstrated that synthesized CeO₂ NPs have excellent UV protection and sunscreen physical absorption properties.     

Metabolic effects of TiO2 nanoparticles,a common component of sunscreens and cosmetics,on human keratinocytes

The long-term health risks of nanoparticles remain poorly understood, which is a serious concern given their prevalence in the environment from increased industrial and domestic use. The extent to which such compounds contribute to cellular toxicity is unclear, and although it is known that induction of oxidative stress pathways is associated with this process, the proteins and the metabolic pathways involved with nanoparticle-mediated oxidative stress and toxicity are largely unknown. To investigate this problem further, the effect of TiO₂ on the HaCaT human keratinocyte cell line was examined. The data show that although TiO₂ does not affect cell cycle phase distribution, nor cell death, these nanoparticles have a considerable and rapid effect on mitochondrial function. Metabolic analysis was performed to identify 268 metabolites of the specific pathways involved and 85 biochemical metabolites were found to be significantly altered, many of which are known to be associated with the cellular stress response. Importantly, the uptake of nanoparticles into the cultured cells was restricted to phagosomes, TiO₂ nanoparticles did not enter into the nucleus or any other cytoplasmic organelle. No other morphological changes were detected after 24-h exposure consistent with a specific role of mitochondria in this response.     

Effect of sunscreens,irradiance and resting periods on the germination ofMetarhizium flavoviride conidia

Chemical sunscreens were incorporated into oil formulations of conidia of two isolates of the entomopathogenic fungusMetarhizium spp. and the formulations exposed to simulated solar radiation. After 2 h exposure several sunscreens gave protection as demonstrated by conidial germination after 24 h incubation on gelatin plates at 26°C but only the formulations with Eusolex 8021 showed higher germination than the unprotected control after 48 h incubation. During 5h of exposure, Eusolex 8021 failed to offer significant protection as demonstrated by conidial germination after 48 h incubation. Conidial damage was proportional to the duration of radiation received. Allowing periods of darkness between exposures did not result in decreased loss of viability. Storing conidia, after exposure to simulated radiation, for 24 h prior to germination reduced their viability.     

Sources of mycosporine-like amino acids in planktonic Chlorella-bearing ciliates (Ciliophora)

1. Mycosporine‐like amino acids (MAAs) are a family of secondary metabolites known to protect organisms exposed to solar UV radiation. We tested their distribution among several planktonic ciliates bearing Chlorella isolated from an oligo‐mesotrophic lake in Tyrol, Austria. In order to test the origin of these compounds, the MAAs were assessed by high performance liquid chromatography in both the ciliates and their symbiotic algae. 2. Considering all Chlorella‐bearing ciliates, we found: (i) seven different MAAs (mycosporine‐glycine, palythine, asterina‐330, shinorine, porphyra‐334, usujirene, palythene); (ii) one to several MAAs per species and (iii) qualitative and quantitative seasonal changes in the MAAs (e.g. in Pelagodileptus trachelioides). In all species tested, concentrations of MAAs were always <1% of ciliate dry weight. 3. Several MAAs were also identified in the Chlorella isolated from the ciliates, thus providing initial evidence for their symbiotic origin. In Uroleptus sp., however, we found evidence for a dietary source of MAAs. 4. Our results suggest that accumulation of MAAs in Chlorella‐bearing ciliates represents an additional benefit of this symbiosis and an adaptation for survival in sunlit, UV‐exposed waters.     

Design,synthesis and biological evaluation of novel hydroxy-phenyl-1H-benzimidazoles as radical scavengers and UV-protective agents

An ever-increasing incidence of skin neoplastic diseases is registered. Therefore, it is important to protect the skin from the UV radiation that reaches the epidermis and dermis but also to block ROS generated by them. Our attention was attracted in developing new compounds provided with both UV filtering and antioxidant capacities. To this end, 2-phenyl-1H-benzimidazole-5-sulfonic acid (PBSA), a known UV filter, was selected as lead compound for its lack of antioxidant activity, high water solubility and good safety profile. PBSA was sequentially modified introducing hydroxyls on the phenyl ring and also substituting the functional group in position 5 of the benzimidazole ring. At the end of the synthetic study, a new, very potent class of antioxidants has been obtained. Surprisingly some of the developed molecules, while devoid of significant UV-filtering activity was endowed with potent UV-filtering booster capability if associated with known commercial UVB and UVA filters.