Dual influence of colloidal silica on skin deposition of vitamins C and E simultaneously incorporated in topical microemulsions.
BACKGROUND
Colloidal silica is the thickener of interest for topical formulations and can therefore be used to optimize the viscosity of both hydrophilic and lipophilic microemulsions (MEs). To the best of our knowledge, no information is available about the effect of topically applied colloidal silica on skin penetration of drugs. So, our aim was to determine its influence on the effectiveness of ME in the simultaneous delivery of vitamins C and E to the skin.


METHODS
Two different aspects of silica possible function were investigated. Its effects on formulation characteristics were studied by determination of partition coefficient of the vitamins, their solubility and release profile. The direct impact of silica on the skin was further evaluated by transepidermal water loss measurements, scanning electron microscopy (SEM), and cell toxicity determination (MTT assay).


RESULTS
The addition of colloidal silica to ME was shown to increase significantly the vitamins' solubility and their partition to the phase in which they were less soluble. Its presence also increased the amount of both vitamins in epidermis, which was confirmed by release studies. Furthermore, we demonstrated that colloidal silica interacts with excised skin. It decreased transepidermal water loss, probably by retaining water in the stratum corneum because of its massive accumulation in the upper layers, as revealed by SEM.


CONCLUSIONS
The results confirmed that addition of colloidal silica in ME simultaneously loaded with vitamins C and E enhanced vitamins' skin bioavailability by its dual influence on delivery characteristics of ME as well as on skin properties.
Department of Pharmaceutical Technology, Faculty of Pharmacy, University of Ljubljana, Ljubljana, Slovenia.
Branka
B
Rozman
Mirjam
M
Gosenca
Mirjana
M
Gasperlin
Karine
K
Padois
Franciose
F
Falson
D000279:Administration, Cutaneous; D000818:Animals; D001205:Ascorbic Acid / Q000008:administration & dosage* / Q000737:chemistry / Q000493:pharmacokinetics*; D003102:Colloids; D004337:Drug Carriers; D045703:Emulsifying Agents; D004655:Emulsions; D012822:Silicon Dioxide; D013552:Swine; D013678:Technology, Pharmaceutical; D014810:Vitamin E / Q000008:administration & dosage* / Q000737:chemistry / Q000493:pharmacokinetics*; D014815:Vitamins / Q000008:administration & dosage / Q000737:chemistry / Q000493:pharmacokinetics
D003102:Colloids; D004337:Drug Carriers; D045703:Emulsifying Agents; D004655:Emulsions; D014815:Vitamins; D014810:Vitamin E; D012822:Silicon Dioxide; D001205:Ascorbic Acid