BALACI Teodora Dalila 1, OZON Emma Adriana1*, FIȚA Cătălina Ancuța1, MITITELU Magdalena 1, GÎRD Cerasela1, NIȚULESCU Georgiana1
1”Carol Davila” University of Medicine and Pharmacy, 6, Traian Vuia Street, 020956, Bucharest (ROMANIA)
*corresponding author, emmacretu@yahoo.com
Abstract
The exposure to UV radiation is responsible for damaging the skin’s natural defense, leading to various adverse effects, from sunburns to skin cancer; due to this it is necessary to apply on the skin photoprotective products which are safe and efficient. The studies we have carried out in this paper consist in the following: selection of the active ingredients and the use of a proper technological process for obtaining a dermocosmetic product having a good physical and chemical stability, as well as suitable organoleptic and rheological properties in order to ensure the innocuity and pleasant administrating features. We have used one new organic filtering photoprotective substance: 1-(4-carboxy)-phenyl-2-(4-methoxyphenyl)-H-1,3-benzimidazole. In order to reduce the toxicity and the amount of UV filters used in cosmetic formulations, UV filter was incorporated into nanostructured lipid carriers (NLCs). The preparation of NLCs was the melt emulsification method coupled with high shear homogenization. NLCs characterization was based on particle size analysis (by dynamic light scattering), PdI and Zeta potential analysis, after this, they were included in a dermocosmetic product which was studied under the following aspects: the organoleptic properties, pH, spreadibility, viscosity and in vitro determination of SPF. The obtained pharmaceutical form has proved qualities for skin application possessing suitable physicochemical characteristics.
Keywords: benzimidazole compound, nanostructured lipid carriers, photoprotective compound, dermocosmetic product, UV filter
Introduction
The new trends in research and development of photoprotective products are pursuing the goal of decreasing, down to the elimination if it’s possible, of the negative influences on the skin (high allergenic potential, risk of tissue accumulation, hyper pigmentation) throughout the accomplishment of complex formulations [1, 2].
The studies we have carried out in this paper consist in the following: selection of the excipients and active ingredients (organic and inorganic filter and/or screen substances, natural products, antioxidants) and the use of a proper technological process for obtaining a dermocosmetic product having a good physical and chemical stability, as well as suitable organoleptic and rheological properties in order to ensure the innocuity and pleasant administrating features [3, 4, 5].
For the present study we chose one new organic filtering photoprotective substance: 1-(4-carboxy)-phenyl-2-(4-methoxyphenyl)-H-1,3-benzimidazole and we encapsulated it into nanostructured lipid carriers (NLCs). These lipid nanostructures are new colloidal delivery systems developed from oil/ water emulsions type, where the oil phase was replaced by a mixture of solid and liquid lipids. NLCs are submicron particles with spherical shape and average diameters raging of 40-500 nm that are generally used for the delivery of lipophilic compounds. The lipid matrix is formed by physiological lipids that are not toxic. Despite the presence of liquid lipid, NLC matrix is solid at room/body temperature. NLCs adopt mixtures of a solid lipid and liquid lipid and remain in the solid state by controlling the content of liquid lipid [6, 7, 22].
Several studies used NLCs in order to develop photoprotective nano-formulations by encapsulating organic UV filters such as benzophenone-3, oxybenzone, avobenzone, octocrylene, and diethylamino hydroxybenzoyl hexyl benzoate [8, 9, 10].
1-(4carboxy)-phenyl-2-(4-methoxyphenyl)-H-1,3-benzimidazole absorbs UVB or UVA radiations, having extended conjugation throughout the molecule and does not present toxicity [11].
Materials and methods
Ingredients:
– one new organic filtering photoprotective substance: 1-(4carboxy)-phenyl-2-(4-methoxyphenyl)-H-1,3-benzimidazole. In order to reduce the toxicity and the amount of UV filter used in cosmetic formulation, benzimidazole derivative was incorporated into nanostructured lipid carriers (NLCs).
– two inorganic screen photoprotective substances: titanium dioxide coated with alumina and silicon (titanium dioxide M170) and zinc oxide who acts on the entire UVA and UVB spectrum [12];
– vegetal extracts: Sophore extract (flavonoids with antioxidant action and protective capillary), Meliloti extract (coumarins with screen effect) [13, 14];
– one protein substance: collagen used for the skin elasticity, skin hydration, firmness and revitalizing effect [15, 16];
– natural antioxidants: vitamins A, E and C;
– natural products having a slight photoprotective, a hydrating and emollient actions like argan oil, jojoba oil, sesame oil, grape oil seed; cacao butter and olive oil, viscosity modifying agents; preservatives, natural perfumed composition [17, 18].
Methods:
Synthesis of benzimidazole compound: Two-stage process was applied: the synthesis of 2-substituted benzimidazole, followed by the application of
Mannich base to the nitrogen atom at position 1. The progress of the synthesis reaction was controlled by HPLC.
The preparation method of NLCs was the melt emulsification method coupled with high shear homogenization method. The two phases (lipid and aqueous) were separately heated at 85°C while stirring. Then, the lipid phase was gradually added over the aqueous phase. The emulsion was heated under stirring at 85°C for 1 h, and then homogenized by applying 25000 rpm for 10 min (High-shear homogenizer PRO250). To remove the water, the dispersions were frozen for 24 h and then lyophilized using a Christ Alpha 1-2 LD Freeze Dryer for 72 h at -55ºC.
NLCs characterization:
Particle size analysis. The particles size was measured by dynamic light scattering (DLS) using a Zetasizer Nano ZS system. The average particle size of nanoparticles in dispersion and the polydispersity index (PdI) were measured at 90° scattering angle and at a temperature of 25°C.
Zeta potential analysis. The Zeta potential (ZP) of nanostructured lipid carriers was determined by measuring the electrophoretic mobility of the nanoparticles in an electric field using a Zetasizer Nano ZS system. The electrophoretic mobility was converted into zeta potential using Helmholtz Smoluchowski equation. [19] Formulation and obtaining the cosmetic preparation: For an appropriate formulation of the sunscreen product a number of issues that might affect its efficiency were considered: the amount of NLCs containing the UV filter, depending on the absorption potential of the UV radiation, and the selection of the other ingredients. The formulation is shown in Table I.
Table I – The formulation of the photoprotective product
| Ingredients | Quantity (g) |
| NLCs containing 1-(4carboxy)-phenyl-2-(4-methoxyphenyl)-H-1,3-benzimidazole | 10 |
| Titanium dioxide M170 | 1 |
| Zinc oxide | 1 |
| Sophore extract | 1 |
| Meliloti extract | 1 |
| Collagen | 0.5 |
| Vitamin A | 150000 UI |
| Vitamin C | 0.5 |
| Vitamin E | 0.2 |
| Argan oil | 1 |
| Jojoba oil | 2 |
| Sesame oil | 1 |
| Grape oil seed | 2 |
| Olive oil | 35 |
| Cocoa butter | 4 |
| Cholesterol | 1 |
| Lanolin | 6 |
| Sodium hydrogen carbonate | 0.2 |
| Butyl hydroxy anisole | 0.05 |
| Perfume | q.s. |
| Distilled water | 70 |
The lipid components and zinc oxide were melted together on a water bath heated at a temperature of about 60-70ºC. The aqueous phase in which titanium dioxide was dispersed, was heated separately at a temperature slightly higher than that of the lipid phase, and then they were gradually brought together while stirring. The obtained emulsion was cooled to a temperature of 30ºC, temperature that allowed the incorporation of NLCs, collagen, Sophore and Meliloti extracts, vitamin A, C, E and perfume.
Quality control of the photoprotective product
The organoleptic control (appearance, color, smell, finesse, adhesion) was performed according to F.R.X guidelines.
The pH determination was carried out in an aqueous phase, which was obtained by shaking 1 g of product into 10 ml heated water.
Spreadability on the skin. The determination was performed using the extensiometric method. This analysis determines the deformation ability of the product when several forces are acting on it, by using Ojeda Arbussa method.
The viscosity. In order to evaluate the structural characteristics of the product we used Thermo Haake VT550 (ViscoTesterVT550), Thermo Electron (Karlsruhe) GmbH, Germany, a rheometer with the cylinder assembly SV – DIN (0 – 100 range of shear speeds, 10 ml volume). The primary registration and processing of the dates was done by using Haake RheoWin DataManager, Versiune 4.30.0011, Thermo Electron (Karlsruhe) GmbH, Germany, a compatible specialized software. For analysis of product’s flowability, the recorded data has been evaluated by applying the Ostwald de Waele model.
The determination of SPF. In this study, the SPF was determined in vitro according to the methodology of Diffey-Robson, using an UV- VIS Spectrometer V670 apparatus (Jasco) equipped with integrating sphere and adequate software. The method is based on measuring the transmittance of radiation transmitted by the sample deposited on the substrate (2 mg/cm2), by recording the photocurrent from 5 to 5 nm on 290-400 nm (UVB, UVA). The cosmetic preparation was applied to a synthetic skin (Transpore tape) and subjected to spectrophotometric analysis in six different points. The average recorded values were used to calculate the SPF, according to the equation:
SPF =Σ ΕλΒλ / Σ (ΕλΒλ)/ΜPFλ
where Eλ is the spectral irradiance of terrestrial sun light under defined conditions; Bλ is the erythema effectiveness; MPFλ is the monochromatic protection factor for each wavelength increment. [19]
Results and Discussion
NLCs characterization:
Nanostructured lipid carriers loaded with 4carboxy)-phenyl-2-(4-methoxyphenyl)-H-1,3-benzimidazole having average sizes of 207 nm and polydispersity index (PdI) of 0.25 were obtained. NLC show ZP values more electro-negative than -50 mV, thus, this electric charge can assure a good physical stability over time (Table II).
Table II – NLCs properties
| Property | Value |
| Mean particle size (nm) | 207 |
| PdI | 0.25 |
| Zeta potential (mV) | -52 |
Photoprotective product characteristics
The cosmetic formulation showed a homogeneous appearance, with white to yellowish color and a pleasant smell. These characteristics remained unchanged during 3 months storage. The formulation presented a pH of 5.8, immediately after preparation, and 5.9 after 90 days. These values are compatible with the skin pH and do not causes skin irritation when applied. The plasticity control results are shown in the figure 1.
Figure 1 – Extensiometric curve of the cosmetic product
We can notice that the surface of display increases with increasing the added weights, showing a good plasticity which is maintained during the storage time of 90 days. The formulation has a very good spreadability.
The experimental results obtained for the photoprotective product are presented by variation in shear tension as a function of shear speed and viscosity.
The flowability is an essential element both for the purpose of ensuring compliance, but also to ensure a controlled deformation after administration, favorable for drug release.
The coefficients of correlation between experimental and estimated data, according to the model, present values higher than 0.999. We can remark the sub-unit values of the flow indices, which are confirming the pseudoplastic character of the product [20, 21].
Figure 2 – Variation of viscosity
The determination of SPF
UV protection factor of the final product was 13, value considered to be satisfactory, the product being able to offer a good protection. This value is due to the NLC form of the benzimidazole compound, and also to the other ingredients used in the formulation (titanium dioxide, zinc oxide, Sophore and Meliloti extract, argan oil, jojoba oil, sesame oil, grape oil seed and olive oil), leading to the conclusion that the selected ingredients had a synergic mechanism of action.
Conclusions
Starting from the lyophilized benzimidazole-lipid nanostructures, efficient cosmetic formulation with broad photoprotective properties was obtained by using the new benzimidazole compound (1-(4carboxy)-phenyl-2-(4-methoxyphenyl)-H-1,3-benzimidazole) as organic UV filter, metal oxides as inorganic filters, and vegetable extracts, oils and other ingredients with emollient, protective and moisturizing effect. The obtained cosmetic product has proved qualities for skin application possessing suitable physicochemical characteristics (pH, viscosity) and spreadability. The studied product has a pseudoplastic flow behavior, this being confirmed by applying the Ostwald de Waele method, and also it can be easily spread on the skin.
The SPF value of the product is 13, the final pharmaceutical form showing an adequate protection of the skin from sunburn.
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