|
Evaluation of the photostability of
different UV filter |
|
Abstract
¡@ |
|
| 1. Introduction Sunscreens have been recommended by dermatologists for a long time as a protective measure against excessive amounts of sunlight to prevent UV induced erythema and also because many studies show that regular use of sunscreens contribute to the prevention of skin photodamage (Tarras-Wahlberg et al., 1999). Although recently recommended sunscreens have a better UVA protective capacity, the absorption spectra of some sunscreens do change upon irradiation with UV radiation. If the absorption decreases while the shape of the absorption curve remains the same, there will be an increase in the amount of the same spectrum UV radiation reaching the basal epidermal cell layers. However, if the shape of the absorption spectrum also changes, leading to high UVA exposure, the situation ¡@ |
becomes more critical. The risk of melanoma development is enhanced, since the action spectrum for the induction of malignant melanoma is shifted towards UVA (Tarras-Wahlberg et al., 1999). Hence, in order to guarantee constant efficacy of the product throughout the exposure period, the UV filters used should not be altered by UV sunlight (Chatelain and Gabard, 2001; Vanquerp et al., 1999). Another reason for the development of photostable sunscreens as part of the product efficacy evaluation (Cambon et al., 2001) is that the reactive intermediates of photounstable filter substances come into direct contact with the skin, where they may behave as photo-oxidants or may also promote phototoxic or photoallergic contact dermatitis. The interaction of photodegradation products with sunscreen excipients or skin components like sebum may lead to the formation of new molecules with unknown toxicological properties (Cambon et al., 2001; Deleo et al., 1992; Rieger, 1997; Schrader et al., 1994; Gerhard et al., 2001). In the early 1980s, a few sunscreen photostability studies began examining the benzilidene camphor sunscreens (Beck et |
| al., 1981; Deflandre and Lang, 1988), and
then p-amino benzoic acid and its derivatives (Allen et al., 1996). During the 1990s, the photostability of the dibenzoylmethaneUVAsunscreenswas studied (Tarras-Wahlberg et al., 1999; Chatelain and Gabard, 2001). Several groups have reported work using UV filters in solution, in polymer films, in liquid films, on glass or stratum corneum and even on humans in vivo (Berset et al., 1996), but in most of them the photochemistry of sunscreen agents was examined in dilute solutions, which may not be particularly relevant. In thin films and in the skin, the photochemistry of photounstable sunscreens is more complex than in dilute solutions, consequently photochemistry studies based on thin films are more similar and relevant to practical applications than the ones that are done in dilute solutions. In 1995, the European Cosmetic Toiletry and Perfumery Association (COLIPA) task group published a collaborative initial test for photostability of four sunscreen agents used in products tested in liquid films on glass surfaces (Berset et al., 1996). The behavior of sunscreens is not predictable from the photostability of its individual filter. Thus, it is also important to evaluate the combinations of filters used in the formulation (Deflandre and Lang, 1988; Schwack and Rudolph, 1995; Vanquerp et al., 1999). Notwithstanding, the confounding effects of filter combinations on sunscreen product formula development, the toxicological implications of sunscreen photoinstability alone provide sufficient importance to further attention in this topic. Thus, the objective of this study was to evaluate and compare the photostability of four different UV filter combinations in a sunscreen by using HPLC analysis and spectrophotometry. 2. Materials and methods 2.1. Formulations studied Four UV filter combinations often used in SPF 15 sunscreen products were chosen for this study. The combined UV filters were added to a formulation containing 4% of a blend of ammonium acryloyldimethyl-taurate/VP copolymer and trilaureth-4 phosphate, 0.1% of dissodium EDTA, 0.05% of BHT, 5% of propyleneglycol, 2% of volatile silicone, 0.8% of phenoxyethanol and parabens and distilled water. The combinations |
were: 7% of octyl methoxycinnamate (OMC), 2%
of benzophenone-3 (BP-3) and 1.5% of octyl salicylate (OS) (formulation 1) (Gaspar and Maia Campos, 2003); 10% of OMC, 2% of avobenzone (AVB) and 2% of 4-methylbenzilidene camphor (MBC) (formulation 2); 7% of OMC, 4% of BP-3 and 5% of octocrylene (OC) (formulation 3); 5% of OMC, 2% of AVB and 7% of OC (formulation 4). 2.2. Photostability studies In these studies, formulation samples were irradiated and evaluated by two in vitro methodologies, HPLC analysis and spectrophotometry. For this, 40 mg of each formulation were spread onto a 10 cm2 (approximately 4 mg/cm2) area of a glass plate and left to dry for 30 min before exposure to different UVA/UVB irradiations (280¡V400 nm) from a 96,000 Oriel 150W Xenon arc solar simulator (Oriel Corporation, Stratford, CT). The radiation was filtered through a dichroic mirror (280¡V400 nm) and a WG 305 long pass filter, which allows no passage of light less than 280 nm. Irradiance, whichwas approximately 20 mW/cm2,was measured at 290 nm with a 70260 Oriel Radiant Power Meter equipped with a silicon probe (coupled with a 1 in. fused silica metallic neutral density filter-optical density 3.0) (Berset et al., 1996; Marginean Lazar et al., 1997). Glass plates containing dried formulations were exposed to three different UV doses (30, 60 and 120 min of a 20 mW/cm2 UV radiation). For each exposed plate, a duplicate plate serving as a negative (non-irradiated) control was kept in a dark place at 30oC. Three replicate pairs of samples were prepared. Exposed samples (formulations 1¡V4 and the vehicle without UV filters) were then immersed in 50mL of isopropanol and the dried films dissolved ultrasonically. The UV filters in this solution were quantified by HPLC analysis (Shimatzu) on a C18 column (5 m ODS, 250mm¡Ñ4 mm), with methanol:water (88:12, v/v) as mobile phase and detected at 325 nm, and by a Hitachi U-2001 spectrophotometer (280¡V400 nm). For spectrophotometric evaluation, samples were diluted (1:4, v/v) and the ratio of the mean UVA (320¡V400 nm) to the mean UVB (280¡V320 nm) absorbances was calculated as (Diffey, 1994):  |
¡@
Fig. 1. HPLC chromatographic analysis of (A) an
isopropanol solution of the six sunscreen agents studied. Peaks:
benzophenone-3, 4-methylbenzilidene camphor, ¡@ |
|
|
|
|
|
|
|
