Ascorbic acid encapsulated into negatively charged liposomes exhibits increased skin permeation, retention and enhances collagen synthesis by fibroblasts
ABSTRACT
Ascorbic acid (AA) is widely used in cosmetic formulations due to its antioxidant property and ability to increase collagen synthesis. Here, we encapsulated AA in vesicles with different lipid compositions. Negative liposome charge favored AA skin retention, with accumulation of 37 ± 12 and 74 ± 23 μg/cm2 in the epidermis and dermis, respectively, after 6 hours. Drug flux was influenced by the formulation composition, and both the presence of cholesterol and the liposomes surface charge were able to increase the amount of AA crossing the skin. The formulation was stable for at least 30 days and promoted a 7-fold increase in flux compared to free AA. Additionally, liposomes were able to interact better with keratinocytes and fibroblasts membranes. In vitro efficacy studies demonstrated that associating AA to these liposomes resulted in increased effectiveness of type I collagen synthesis by fibroblasts and regeneration of UVA-induced damage in keratinocytes. Our results demonstrate the applicability of AA-negatively charged liposomes in promoting AA cutaneous permeation and increasing the retention and flux of this molecule in the skin. This formulation also increased AA stability and effectiveness, opening new perspectives for its application in view of reducing certain skin ageing outcomes.
INTRODUCTION
Ascorbic acid (AA) is a water-soluble molecule with a fundamental role in the maintenance of various biological activities. Among its various functions, the beneficial effects on the skin stand out. AA acts as a cofactor for essential enzymes in the biosynthesis of collagen, especially types I and type III. These molecules are abundantly present in the dermis extracellular matrix and help support the skin. AA is able to increase mRNA levels by directly stimulating the synthesis of collagen in the skin. In addition, it increases the production of metalloproteinases inhibitors, avoiding the degradation of existing collagen 1,2,3,4. AA is also a potent antioxidant, being able to donate electrons and neutralize the free radicals present in the intra and extracellular matrix, avoiding lipid membrane, DNA and proteins damage that would be caused by oxidative stress 5,6,7. Furthermore, topical application of AA can provide anti-inflammatory 8,9 and depigmenting effects 10,11.
Skin aging occurs when degeneration overlap with regeneration events, reducing skin structural integrity and causing the loss of biological functions 12. AA effects on the skin layers motivate its use in cosmetic preparations, especially in formulations that inhibit or minimize the effect of skin aging 13,14. However, cutaneous application of AA is limited by its hydrophilic property and stratum corneum characteristics 15. This skin layer is the main responsible for the barrier function and consists of corneocytes immersed in a highly organized lipid matrix. Since water corresponds to only 15–30% of the stratum corneum, a hydrophilic substance can hardly penetrate this hydrophobic layer, and consequently permeate to the other layers of the skin 16,17. Besides, AA is unstable in aqueous media and upon certain conditions such as light exposure, high pH and temperature increase. It is also easily degraded in the presence of certain enzymes and metal ions, generating products with no biological activity 18,19,20.
Nanocarriers offer advantages for the topical and transdermal application of molecules. Nanostructured drug delivery systems can, for instance, increase the solubility and diffusion coefficient of molecules in the stratum corneum and also increase molecule stability 21,22,23,24,25,26. Liposomes, which are vesicles composed of phospholipid bilayers delimiting an aqueous compartment that can encapsulate hydrophilic substances, are among the most used types of nanocarriers 27,28. The challenge for encapsulating hydrophilic molecules in liposomes is their tendency to remain outside the vesicles in the aqueous medium in which the liposomes are dispersed, causing low encapsulation efficiency 29. Liposome production through the dehydration-rehydration vesicle method (DRV) enables the preparation of liposomes with greater encapsulation efficiency 30,31. In addition to the active compound characteristics, liposome formulation can also directly influence skin permeation. Lamellarity, surface charge, presence of cholesterol, lipid molecular weight and concentration have been related to changes in the retention and flux of molecules through the skin 24,32,33,34,35,36. In this work, we describe the technological development of a liposomal formulation containing AA. We demonstrate its suitability in increasing AA stability, promoting high interaction with biological membranes, and increasing skin retention and the effectiveness of AA in the treatment of events related to UV-damage related skin aging.
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Edited by Engadin, 04 June 2019 - 03:27 PM.
