Mangiferin and naringenin affect the photostability and phototoxicity of sunscreens containing avobenzone

Highlights

• The influence of two antioxidants on the photostability and phototoxicity of three UV-filters was assessed.

• Naringenin and avobenzone degraded after UV exposure.

• 3T3 NRU phototoxicity test showed avobenzone presented a pronounced phototoxicity.

• Combination CN (OMC, OCT, AVO, naringenin) presented phototoxic potential.

• Mangiferin increased the photostability and reduced the phototoxic potential of naringenin and avobenzone combination.

Abstract

Efficient UV-absorbing molecules are designed to protect against UV-light exposure. However, the development of photostable sunscreens is important to preserve the photoprotective efficacy and to prevent the formation of reactive oxygen species (ROS) and photodegradation products, which can promote phototoxic or photoallergic contact dermatitis. The aim of this study was to evaluate the effects of mangiferin and naringenin on the photostability and phototoxicity of sunscreens containing avobenzone. Cosmetic sunscreen formulations containing octocrylene (OCT), octyl methoxycinnamate (OMC) and avobenzone (AVO) were prepared and supplemented or not with mangiferin, naringenin, or with both compounds in combination. For photostability studies, samples of the formulations were spread onto glass plates, exposed to UVA radiation and then analyzed by high performance liquid chromatography (HPLC) to determine UV filters and the antioxidants recovery. The phototoxicity of the UV filters and antioxidants was evaluated using 3T3 fibroblast cultures that were subjected (or not) to irradiation according to OECD TG 432. The photostability studies demonstrated that AVO and naringenin showed the highest photodegradation when present in formulation FN (containing octocrylene, avobenzone, octyl methoxycinnamate and naringenin). The addition of mangiferin to this combination (FMN) resulted in an improved photostability of both substances compared to FN. The in vitro phototoxicity test showed that only avobenzone was considered phototoxic. The combination containing AVO/naringenin exhibited phototoxic potential; however, this was reduced by the addition of mangiferin (combination CMN). The results of this study are promising because it was demonstrated that mangiferin could increase the photostability and reduce the phototoxic potential of the combination of naringenin and AVO.

Introduction

It is well known that exposure to the ultraviolet radiation (UV) present in sunlight can be potentially dangerous, and as such, can result in adverse health outcomes [1]. UVB radiation, although mainly restricted to penetration of the upper layers of the skin, can cause DNA damage and sunburn, which can lead to skin cancer [2], [3]. In contrast to UVB radiation, UVA radiation directly affects the dermis and is therefore thought to be the major factor responsible for photoaging and DNA damage, mainly caused by the generation of reactive oxygen species (ROS) [3], [4], [5].

Therefore, many efforts have been made to develop sunscreens with a broad absorption spectrum, which allows then to absorb both UVA and UVB light, without the need for high amounts of chemicals, because some have been associated with allergic reactions [6], [7], [8]. The presence of different UV filters can lead to synergistic effects in terms of both the final performance and photostabilization of the sunscreens, but in some cases may accelerate their decomposition if a photoreaction occurs between the components [9].

The photodecomposition of the UV filters not only reduces their UV absorptive capacity, but can also promote phototoxic or photoallergic contact dermatitis. In addition, the interaction of photodegradation products with sunscreens excipients or skin components such as sebum may lead to the formation of new molecules with unknown toxicological properties [7], [10], [11]. Consequently, there have been increasing concerns about the phototoxicity and photoallergic properties of UV filters [12], [13], [14].

Avobenzone (butyl methoxydibenzoylmethane) is one of the most common UVA filters present in cosmetic formulations; however, it is significantly degraded under UV exposure, reducing its UVA protecting effects, which results in a loss of efficacy and the generation of photoproducts [10], [15], [16]. Photoallergic reactions have often been associated with avobenzone due to the generation of photodegradation products such as arylglyoxals and benzils [17].

Following this photoreaction, avobenzone can react with octyl methoxycinnamate to form cycloaddition products, thus destabilizing the otherwise photostable cinnamate molecule [11]. Many efforts have been made by cosmetic companies and scientists to improve the photostability of avobenzone and its combinations. A good example is the development of octocrylene, a UVB absorber, which improves the photostability of avobenzone via a triplet quenching mechanism [18], [19]. However, octocrylene is frequently associated to photoallergic contact dermatitis [20], [21]. Furthermore, there are some cases that the available substances do not efficiently neutralize the free radicals generated by avobenzone photofragmentation [22], [13]. These data indicate that it is very important to develop new strategies for avobenzone photostabilization.

There has recently been a tendency to use natural compounds, such as polyphenols, in an effort to improve the potential of sunscreens to prevent UV-induced harmful effects. This is mainly due to some limitations of the conventional organic UV filters, which are characterized by their narrow spectrum of protection and low photostability [23]. Polyphenols have several biological properties, including anti-inflammatory, anticarcinogenic and immunomodulatory effects, and they can act as potent antioxidants [24], [25]. In addition, they also absorb UV radiation between 300 and 350 nm, which suggests that they may have a biologically relevant filter activity as well [12].

Mangiferin is a xanthone glucoside which is abundant in the fruit, leaves and stem bark of Mangifera indica L (Mango) [26]. It exhibits several beneficial pharmacological properties, such as antioxidant, antiviral, anti-photoaging, anti-inflammatory and hepatoprotective effects [27], [28], [29], [30], [31]. It was demonstrated that topical application of mangiferin inhibited UVB-induced increases in skin thickness, wrinkle formation, and collagen fiber loss in male hairless mice [29]. The application of mangiferin on SKH-1 mouse skin inhibited UVB-induced edema and showed a significant protection against DNA damage [32].

Naringenin is a flavanone found especially in citrus fruits, such grapefruit [33], and it exhibits antioxidant, anti-inflammatory, antiproliferative and anticancer properties [33], [34], [35]. According to a recent study, naringenin can prevent the deleterious effects of UVB irradiation by enhancing the removal of cyclobutane pyrimidine dimers (CPD) and inhibiting apoptosis. Furthermore, it increased the long-term survival of HaCaT cells upon UVB-induced DNA damage [36]. However, other studies have demonstrated that naringenin, under certain conditions, can also display prooxidant activity [37], [38], [39], [40].

The testing of finished cosmetic products in animals in the European Union has been prohibited since 2004, and a full ban on the animal testing of cosmetic ingredients came into force in March 2013 [41]. Consequently, many alternative methods to animal experimentation have been developed due to changes in legislation, and there has been a global trend toward the assessment of ingredients and products using these alternative methods.

The validated 3T3 Neutral Red Uptake Phototoxicity Test (3T3 NRU PT) was accepted in 2000 by the European Community (EC) for regulatory purposes and was later accepted by the Organisation for Economic Co-operation and Development (OECD) in 2004 as Test Guideline (TG) 432. It compares the cytotoxicity of a chemical tested in the presence and absence of exposure to a non-cytotoxic dose of UVA/visible light [42], [43]. The 3T3 NRU identifies phototoxicological hazards with 100% sensitivity and is thus accepted as the tier-one test that correctly identifies the absence of phototoxic potential. However, because it does not take into consideration the skin bioavailability, positive results in the 3T3 NRU PT often do not translate to a clinical risk of phototoxicity [44], [45].

Therefore, the aim of this study was to evaluate the effects of mangiferin and naringenin on the photostability and phototoxicity of sunscreens containing avobenzone.