Kojic acid (5-hydroxy-2-hydroxymethyl-4H-pyran-4-one) is an organic acid derived from the fermentation of fungi of diverse genus such as Aspergillus and Penicillium, 1 and it was first isolated in 1907. 2,3 Its most common use is as a skin depigmenting agent, attributed mainly to the inhibition of tyrosinase, which is the key enzyme in melanin synthesis. Leucocyte modulation, copper-chelating action and free radical scavenging are also involved in kojic acid depigmenting mechanism. Besides that, antioxidant, antibacterial and anti-inflammatory activities were also reported. 4 There have been reports of antimicrobial and toxicity studies since the forties, 2 but mechanisms of action have not yet been fully elucidated.Among the disadvantages of this molecule, one can mention the possibility of causing contact dermatitis, sensitization, redness and erythema. 5 Kojic acid also has low stability, being sensitive to light
Melasma is a hard-to-treat hyperpigmentation disorder. Combined incorporation of kojic dipalmitate (KDP), the esterified form of kojic acid, and rosehip oil, an oil with antioxidant and skin-regenerating properties, into nanocarrier systems appears to be a suitable strategy to develop high-performance formulations. A high-energy method (Ultra-Turrax®) was used to develop nanoemulsions containing up to 2 mg/mL KDP, 5% rosehip oil, and 7.5% surfactant. Formulations were characterized regarding droplet size, size distribution, pH, density, morphology, KDP content, incorporation efficiency, and stability under different temperature conditions. A scale-up study was conducted. Skin permeation, antioxidant potential, and tyrosinase inhibitory activity were assessed in vitro. Cell viability studies were also performed. Results showed that nanoemulsions containing 1 and 2 mg/mL KDP had incorporation efficiencies greater than 95%, droplet size smaller than 130 nm, suitable size distribution, zeta potential of approximately −10 mV, and good stability over 30 days of refrigerated storage. The nanoemulsion containing 1 mg/mL KDP was chosen for further evaluation because it had lower nanocrystal formation, greater scale-up feasibility and allowed KDP permeation up to the epidermis similarly than observed for 2 mg/mL KDP. This formulation (1 mg/mL KDP) showed antioxidant and depigmenting efficacy, close to that of 1 mM ascorbic acid. No cytotoxicity was observed in formulations concentrations ranging from 0.06% to 1%.
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