Determination of the thermodegradation of deoxyArbutin in aqueous solution by high performance liquid chromatography

Using a Cellular System to Directly Assess the Effects of Cosmetic Microemulsion Encapsulated DeoxyArbutin

DeoxyArbutin (dA) is a tyrosinase inhibitor that has effective skin-lightening activity and has no obvious cytotoxicity toward melanocytes. With the aim of directly evaluating the effects of microemulsions containing dA on cells, we developed oil-in-water (O/W) microemulsions with relatively lower cytotoxicities by using polysorbate-series surfactants. Measurement of the transparent properties and particle size analysis at different storage time periods revealed that the developed microemulsions were stable. Moreover, the developed microemulsions had direct effects on B16-F10 mouse melanoma cells. The anti-melanogenesis activities of dA-containing microemulsions were evidently better than that of the free dA group. The results demonstrated that the developed microemulsion encapsulating dA may allow the use of deoxyArbutin instead of hydroquinone to treat dermal hyperpigmentation disorders in the future.

Structural and kinetic considerations on the catalysis of deoxyarbutin by tyrosinase

Deoxyarbutin, a potent inhibitor of tyrosinase, could act as substrate of the enzyme. Oxytyrosinase is able to hydroxylate deoxyarbutin and finishes the catalytic cycle by oxidizing the formed o-diphenol to quinone, while the enzyme becomes deoxytyrosinase, which evolves to oxytyrosinase in the presence of oxygen. This compound is the only one described that does not release o-diphenol after the hydroxylation step. Oxytyrosinase hydroxylates the deoxyarbutin in ortho position of the phenolic hydroxyl group by means of an aromatic electrophilic substitution. As the oxygen orbitals and the copper atoms are not coplanar, but in axial/equatorial position, the concerted oxidation/reduction cannot occur and the release of a copper atom to bind again in coplanar position, enabling the oxidation/reduction or release of the o-diphenol from the active site to the medium. In the case of deoxyarbutin, the o-diphenol formed is repulsed by the water due to its hydrophobicity, and so can bind correctly and be oxidized to a quinone before being released. Deoxyarbutin has been characterized with: [Formula: see text] = 1.95 ± 0.06 s-1 and [Formula: see text] = 33 ± 4 μM. Computational simulations of the interaction of β-arbutin, deoxyarbutin and their o-diphenol products with tyrosinase show how these ligands bind at the copper centre of tyrosinase. The presence of an energy barrier in the release of the o-diphenol product of deoxyarbutin, which is not present in the case of β-arbutin, together with the differences in polarity and, consequently differences in their interaction with water help understand the differences in the kinetic behaviour of both compounds. Therefore, it is proposed that the release of the o-diphenol product of deoxyarbutin from the active site might be slower than in the case of β-arbutin, contributing to its oxidation to a quinone before being released from the protein into the water phase.

Study of Hydroquinone Mediated Cytotoxicity and Hypopigmentation Effects from UVB-Irradiated Arbutin and DeoxyArbutin

Arbutin (Arb) and deoxyArbutin (dA) are both effective hypopigmentation agents. However, they are glucoside derivatives of hydroquinone (HQ), which may be decayed into HQ under higher energy environments. Therefore, safety and toxicity are very important issues when considering the usage of these compounds. However, no study has verified the properties of Ultra-Violet B (UVB)-irradiated Arb and dA. In this work, we investigated the cytotoxicity and hypopigmentation effects of UVB-irradiated Arb and dA in Detroit 551 human fibroblast cells and B16-F10 mouse melanoma cells. The results showed that UVB-irradiated Arb and dA have strong cytotoxicity for the fibroblast cells, especially for dA, the caspase-3 is also activated by the treatment of UVB-irradiated dA in Detroit 551 cells. The results correlated with the produced HQ. In addition, UVB-irradiated Arb and dA suppressed the production of melanin in melanoma cells; this is due to the release of HQ that compensates for the UVB triggered Arb and dA decomposition.

The unravelling of the complex pattern of tyrosinase inhibition

Tyrosinases are responsible for melanin formation in all life domains. Tyrosinase inhibitors are used for the prevention of severe skin diseases, in skin-whitening creams and to avoid fruit browning, however continued use of many such inhibitors is considered unsafe. In this study we provide conclusive evidence of the inhibition mechanism of two well studied tyrosinase inhibitors, KA (kojic acid) and HQ (hydroquinone), which are extensively used in hyperpigmentation treatment. KA is reported in the literature with contradicting inhibition mechanisms, while HQ is described as both a tyrosinase inhibitor and a substrate. By visualization of KA and HQ in the active site of TyrBm crystals, together with molecular modeling, binding constant analysis and kinetic experiments, we have elucidated their mechanisms of inhibition, which was ambiguous for both inhibitors. We confirm that while KA acts as a mixed inhibitor, HQ can act both as a TyrBm substrate and as an inhibitor.

Formulation, Characterisation, and in Vitro Skin Diffusion of Nanostructured Lipid Carriers for Deoxyarbutin Compared to a Nanoemulsion and Conventional Cream

The long-term use of topical hydroquinone as an anti-hyperpigmentation treatment has well-known, unwanted effects. Deoxyarbutin (4-[(tetrahydro-2H-pyran-2-yl)oxy]phenol) is a relatively new tyrosinase inhibitor, with stronger inhibitory potency than hydroquinone, that exhibited decreased cytotoxicity against melanocytes and other cells. This study developed novel nanostructured lipid carriers (NLCs) for improved topical delivery of deoxyarbutin (dArb), leading to improved depigmenting efficacy. dArb is a hydrophobic substance, but it easily degrades in aqueous medium and is thermolabile. Screening and optimisation of the solid lipid, liquid lipid, surfactant, co-surfactant and production methods were performed to choose the optimum particle size and stability for NLCs. One percent dArb NLCs were obtained from a combination of cetyl palmitate (CP) and caprylic/capric tryglicerides (Myr) in 12% total lipids using poloxamer 188 (P-188) and polyethylene glycol (PEG) 400 as a surfactant and co-surfactant, respectively, with a particle diameter of approximately 500 nm and a polydispersity index (PI) <0.4. These NLCs were produced using the simple method of high-shear homogenisation (10,000 rpm, 5 minutes) and ultrasonication (3.5 min). The compatibility between the substances in the formula was evaluated using Fourier Transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The morphology of the NLCs was observed using transmission electron microscopy (TEM). In vitro penetration of dArb NLCs was evaluated and compared to the nanoemulsion (NE) and conventional emulsion (CR) delivery methods across Spangler’s membrane (SS). Delivery improvement was clearly observed, and after 8 h of application, dArb gel-NLCs showed the highest dArb penetration, followed by liquid NLCs, NE, and CR.

Comparative study on the photostability of arbutin and deoxy arbutin: sensitivity to ultraviolet radiation and enhanced photostability by the water-soluble sunscreen, benzophenone-4

Arbutin and deoxy arbutin may release hydroquinone under some conditions. We therefore investigated the photostability of arbutin and deoxy arbutin in an aqueous solution. The results revealed arbutin and deoxy arbutin to be photolabile in an aqueous solution. Deoxy arbutin was less stable than arbutin when exposed to UV radiation. The hydroquinone concentration was also increased during the radiation period in both solutions. Benzophenone-4 could clearly improve the photostability of arbutin during the period of UV radiation, but only slightly enhance the photostability of deoxy arbutin.

Chitosonic® Acid as a Novel Cosmetic Ingredient: Evaluation of its Antimicrobial, Antioxidant and Hydration Activities

Chitosonic^® Acid, carboxymethyl hexanoyl chitosan, is a novel chitosan material that has recently been accepted by the Personal Care Products Council as a new cosmetic ingredient with the INCI (International Nomenclature of Cosmetic Ingredients) name Carboxymethyl Caprooyl Chitosan. In this study, we analyze several important cosmetic characteristics of Chitosonic^® Acid. Our results demonstrate that Chitosonic^® Acid is a water-soluble chitosan derivative with a high HLB value. Chitosonic^® Acid can form a nano-network structure when its concentration is higher than 0.5% and can self-assemble into a nanosphere structure when its concentration is lower than 0.2%. Chitosonic^® Acid has potent antimicrobial activities against gram-positive bacteria, gram-negative bacteria and fungus. Chitosonic^® Acid also has moderate DPPH radical scavenging activity. Additionally, Chitosonic^® Acid exhibits good hydration activity for absorbing and retaining water molecules with its hydrophilic groups. From a safety point of view, Chitosonic^® Acid has no cytotoxicity to L-929 cells if its concentration is less than 0.5%. Moreover, Chitosonic^® Acid has good compatibilities with various normal cosmetic ingredients. Therefore, we propose that Chitosonic^® Acid has the potential to be a widely used ingredient in various types of cosmetic products.

Kinetic study on the tyrosinase and melanin formation inhibitory activities of carthamus yellow isolated from Carthamus tinctorius L

Carthamus yellow (CY) is the major component of the yellow pigments of Carthamus tinctorius L. CY has been extensively used as a natural color additive for food and cosmetics. Here, our results demonstrate that carthamus yellow reduced the activity of mushroom tyrosinase in a dose-dependent manner with a half maximal inhibitory concentration (IC(50)) value of approximately 1.01 ± 0.03 mg/mL. A kinetic study of carthamus yellow on tyrosinase exhibited a mode of competitive inhibition with a Ki of 0.607 mg/mL. Moreover, cell viability analysis indicated that carthamus yellow used at concentrations of 1.0-4.0 mg/mL had no cytotoxicity in B16F10 melanoma cells. Melanin content analysis showed that melanin production in B16F10 melanoma cells treated with 4 mg/mL carthamus yellow can decrease to 82.3 ± 0.4% of the levels of melanin production of untreated cells. Thus, carthamus yellow has the potential to become a useful skin-whitening agent in the future.

Study on the stability of deoxyArbutin in an anhydrous emulsion system

The skin-whitening agent, deoxyArbutin, is a potent tyrosinase inhibitor that is safer than hydroquinone and arbutin. However, it is thermolabile in aqueous solutions, where it decomposes to hydroquinone. Pharmaceutical and cosmetic emulsions are normally oil-in-water (o/w) or water-in-oil (w/o) systems; however, emulsions can be formulated with no aqueous phase to produce an anhydrous emulsion system. An anhydrous emulsion system could offer a stable vehicle for compounds that are sensitive to hydrolysis or oxidation. Therefore, to enhance the stability of deoxyArbutin in formulations, we chose the polyol-in-silicone, anhydrous emulsion system as the basic formulation for investigation. The quantity of deoxyArbutin and the accumulation of hydroquinone in both hydrous and anhydrous emulsions at various temperatures were analyzed through an established high performance liquid chromatographic (HPLC) method. The results indicated that water increased the decomposition of deoxyArbutin in the formulations and that the polyol-in-silicone, oil-based, anhydrous emulsion system provided a relatively stable surrounding for the deoxyArbutin that delayed its degradation at 25 °C and 45 °C. Moreover, the composition of the inner hydrophilic phase, containing different amounts of glycerin and propylene glycol, affected the stability of deoxyArbutin. Thus, these results will be beneficial when using deoxyArbutin in cosmetics and medicines in the future.