Effect of cholesterol and ethanol on dermal delivery from DPPC liposomes

Abstract

The main objective of the present work was to compare the dermal delivery of minoxidil (Mx), a lipophilic drug from ethosomes versus classic liposomes, containing different cholesterol (CHOL) concentrations. All the systems were characterized for shape, lamellarity, particle size and entrapment efficiency percentage (EE), by transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), laser diffraction and ultracentrifugation or dialysis methods, respectively. Multilamellar vesicles (MLVs) were obtained and one to six lamellae were visualized by CLSM. The presence of ethanol in the formulations affects the particle size in terms of reducing this parameter. In addition, it was possible to appreciate the influence of CHOL on the vesicle size, because it was increased, as CHOL concentration was higher. When the EE was determined by two different methods (ultracentrifugation and dialysis methods), a clear losing of entrapped drug by the ultracentrifugation method was observed, because the strong energy transmitted to the samples disrupted vesicles.

Vesicles were non-occlusively applied on rat skin and the permeation pattern of the different systems, depth into the skin and the main permeation pathway were studied by using β-carotene as a fluorescent probe. CLSM studies showed that ethosomal systems were much more efficient at delivering the fluorescent substance into the skin in terms of quantity and depth, than either liposomes or hydroalcoholic solutions.

Introduction

For the last 2 decades, topical delivery of drugs from liposomal formulations has evoked a considerable interest. Many reports on enhancing percutaneous delivery focus on the use of liposomes, because they can aid the transport of hydrophilic and lipophilic compounds (Coderch et al., 1996). However, it is generally agreed that classic liposomes are of little or no value as carriers for transdermal drug delivery, because they do not deeply penetrate the skin, but rather remain confined to the upper layer of the stratum corneum. Only specially designed vesicles were shown to be able to allow transdermal delivery, such as transfersomes (Cevc et al., 1998, Cevc et al., 2002).

Ethanol is known as an efficient permeation enhancer. This solvent is commonly believed to act by affecting the intercellular region of the stratum corneum (Magnusson et al., 1997), although other mechanisms have been reported, such as coadjuvant to diminish the melting point of drugs, such as lidocaine, achieving a higher concentration in the oil phase of an emulsion and prolonging the anaesthetic latency time (Kang et al., 2001). Its inclusion in liposomes to form ethosomes has already been investigated by other authors (Kirjavainen et al., 1999, Dayan and Touitou, 2000, Godin and Touitou, 2004).

In this study, Mx was selected as a model lipophilic drug. It has potential applications in the case of androgenetic alopecia (Olsen et al., 2002). However, the appearance of some complaints in the patients with this treatment (pruritus and scaling of the scalp) as a consequence of irritant contact dermatitis, allergic contact dermatitis or an exacerbation of seborrheic dermatitis, has been reported (Friedman et al., 2002).

In this paper, vesicle systems (liposomes and ethosomes) were prepared. Ethosomal formulations included ethanol in relatively high concentrations, incorporating it in the aqueous phase. Mx was dissolved in the hydroethanolic solution and was included in the aqueous compartment of vesicles.

This paper focuses on the preparation and characterization of ethosomal formulations, for Mx transdermal delivery. So, the effect of ethanol and CHOL on the permeation of two lipophilic substances (Mx and carotene) through rat skin was evaluated.