Topical microemulsions containing vitamins C and E: from formulation optimisation to evaluation using reconstructed human epidermisRozman, Branka (Avtor) Gašperlin, Mirjana (Mentor) The novel role of oxidants and antioxidants in skin ageing as well as in various skin disorders and diseases has opened new research areas in several disease states and their therapeutic strategies. Successful prophylaxis and therapy of reactive-oxygen mediated skin ageing and phatogenesis would necessitate control of oxidant/antioxidant balance in the affected site, which can be achieved by external supply of skin endogenous antioxidants. However, antioxidants’ skin biovailability is usually low, mainly due to their poor aqueous solubility, inefficient permeability or instability during the storage. Colloidal drug delivery systems, like microemulsions (ME), nanoparticles or liposomes, are applicable to overcome the stability and pharmacokinetic problems associated with antioxidant delivery. These systems offer better targeting to upper skin layers, with faster onset and lower concentrations of the antioxidants needed. Moreover, liposomes and ME have a unique ability to simultaneously deliver both lipid- and water-soluble antioxidants. The thesis focuses on topical ME simultaneously loaded with lipophilic vitamin E, skin’s major membrane antioxidant and hydrophilic vitamin C, the main component of skin water-soluble antioxidant defence. Initially, viscosity of liquid o/w and w/o ME both composed of the same ingredients has been optimized for topical application. Among thickening agents tested carbomer, colloidal silica and mixture of xanthan and alginate revealed as suitable thickeners for o/w ME and white wax and colloidal silica for w/o ME. Transparent microemulsion gel (gel-like ME) that has been formed upon the addition of specific amounts of water to liquid o/w ME has been investigated as an alternative solution to viscosity problem. Gel-like ME was found to offer the best protection for both vitamins, although other ME also significantly increased their stability compared to solution. In the presence of vitamin C no decrease in vitamin E content occurred. The addition of thickeners to ME changed the stability of at least one vitamin, but the systems still protected vitamins better than solutions, the exception being o/w ME thickened with mixture of xanthan and alginate. By varying the composition of ME, absorption of vitamins C and E in reconstructed human epidermis was significantly modulated. The absorption of vitamins C and E in epidermal and collagen layer was in general enhanced by ME when compared to solutions. The location of the antioxidants in the ME and affinity for the vehicle appeared to be crucial in the case of non-thickened ME. Addition of collidal silica to ME enhanced the deposition of vitamins E and C in the reconstructed human epidermis. The addition of colloidal silica to either o/w or w/o ME also increased skin bioavailability of both vitamins. Dual influence of colloidal silica on skin delivery of vitamins C and E from topical ME was confirmed: it affected formulation characteristics and had a direct impact on the skin. The temperature-driven changes in the microstructure of gel-like ME together with their influence on skin deposition of vitamins C and E were confirmed by rotational rheometry, viscosity measurements, droplet size determination and pig ear permeation studies. The release studies have shown that the vitamins’ release at skin temperature from gel-like ME were comparable to those from o/w ME and were much faster and more complete than from o/w ME conventionally thickened with polymer (o/w ME carbomer). Concerning effectiveness in skin delivery of both vitamins o/w ME was found the most appropriate, followed by gel-like ME and by o/w ME carbomer. Finally, the irritation potential of ME was assessed in comparison to commercially available ME. Two different models were used: reconstructed human epidermis as ECVAM validated model for skin irritation testing and NCTC 2544 human keratinocyte cell cultures. Both models confirmed our ME less irritant than commercial product. In summary, ME have been proved effective and non-irritant vehicles with functionally suitable consistency for simultaneous topical delivery of a hydrophilic vitamin C and a lipophilic vitamin E.[B. Rozman]20092021-05-14 12:52:59Doktorska disertacija127054sl