Psoralen loaded liposomal nanocarriers for improved skin penetration and efficacy of topical PUVA in psoriasis

Abstract

Psoralen in combination with ultraviolet A radiation (PUVA) is an FDA recommended therapy for clinical application in the management of severe recalcitrant psoriasis. Psoralen acts by intercalation of DNA and upon exposure to UV-A, it forms monoadducts which in turn induce apoptosis. Poor skin deposition, weak percutaneous permeability of psoralen and adverse effects of severe burning, blisters, pigmentation associated with conventional topical psoralen vehicles hinders the therapeutic efficacy and safety of topical PUVA. The aim of the present study is to formulate psoralen loaded liposomal nanocarriers for enhanced skin penetration, safety and efficacy of topical PUVA in psoriasis. Two different liposomal compositions i.e., cationic liposomes composed of DC-Chol, cholesterol and anionic liposomes composed of egg lecithin, cholesterol, tetramyristoyl cardiolipin were prepared for the topical delivery of psoralen. Liposomal carriers were characterized with respect to size, zeta potential, entrapment efficiency, stability, in vitro drug release and in vivo studies. Both liposomes were prepared with particle size of nearly 100 nm. Zeta potential and entrapment efficiency of cationic liposomes were + 25.8 mV, 75.12% and anionic liposomes were − 28.5 mV, 60.08% respectively. Liposomal dermal distribution demonstrated higher penetration of both liposomal carriers over solution. Similarly, skin permeation study indicated 5 fold increase in permeation of psoralen with liposomal carriers. Topical application of psoralen liposomal gels on imiquimod induced psoriatic plaque model reduced the symptoms of psoriasis and levels of key psoriatic cytokines such as tumor necrosis factor-α, IL-17 and IL-22. In conclusion, the developed liposomal carriers of psoralen were found to be promising and can find application for optimal safety and efficacy of topical PUVA in psoriasis.

Introduction

Psoriasis is considered as a chronic autoimmune inflammatory disorder characterized by thickened inflamed skin lesions covered with scales (Traub and Marshall, 2007). It is an undermining illness with significant physical, psychological and social implications (Su and Fang, 2008). Several treatment options are available to alleviate the symptoms of psoriasis by targeting against keratinocytes, inflammation and angiogenesis that lead to expansion of therapeutic strategies in treating psoriasis (Bayliffe et al., 2004). Modes of treatment in psoriasis include topical therapy, phototherapy and systemic therapy with their respective pros and cons (Mendonca and Burden, 2003). Phototherapy i.e., psoralen (PSR) + ultraviolet light A (UVA) radiation (PUVA) slows down skin cell proliferation and has been approved by US food and drug administration (FDA) for clinical application (dos Santos and Eriksson, 2006). When activated by UVA light, PSR undergo cycloaddition with pyrimidine bases of nucleic acids forming stable cycloadducts and this mechanism was found to be very effective in treating psoriasis (Sinico et al., 2006).

Topical PUVA is preferable to systemic PUVA as it offers many advantages over the later. Topical preparations containing psoralen are convenient to use and offer better compliance due to negligible systemic side effects and lower cumulative UVA dose (Kc and Karn, 2015). PSR and its trimethyl derivative (4, 5′, 8 trimethyl psoralen) are considered suitable for topical PUVA owing to their physicochemical properties (Pathak et al., 1977, Said et al., 1997). Conventional topical vehicles of PSR i.e., ointment, lotion and tincture necessitates frequent drug administration due to their poor skin deposition and weak skin permeability of PSR which in turn leads to adverse reactions (Zhang et al., 2014b). In addition to these factors, these vehicles lead to severe sun burn, blisters and abnormal dark pigmentation due to uncontrolled reaction of PSR with UVA. This is a consequence of presence and direct contact of free drug with skin from these available dosage forms (Garg et al., 2010). These issues associated with conventional vehicles hinder the safety and efficacy of topical PUVA which further necessitates the development of nanocarriers for topical delivery of psoralen.

Drugs like PSR which cause adverse reactions when delivered through conventional vehicles are considered interesting for vesicle encapsulation (Sinico et al., 2006). Liposomes offer prolonged retention time of drug in skin layers (Dragicevic Curic et al., 2010), enhance the penetration of encapsulated drugs (Pavelic et al., 2004) and serve as controlled drug delivery systems (Dragicevic Curic et al., 2009). Composition of the liposomes influences their physicochemical characteristics such as size, charge, thermodynamic phase, lamellarity and permeability (Puglia et al., 2005). Incorporation of cholesterol (Chol) into vesicle composition influence stability, permeability and drug entrapment (Singla et al., 2012). The electrostatic properties of liposomes affect the stability of liposomes (Hernandez Caselles et al., 1993) as well as cutaneous permeation of drugs (Gillet et al., 2011).

Zhang et al., compared the effect of conventional liposomes and ethosomes on permeation of PSR and showed that permeability of ethosomes was superior to that of liposomes (Zhang et al., 2014a). However, no reports were available on application of charged liposomes for the topical delivery of PSR. Charged liposomes are considered as promising carriers for drugs that are administered by the percutaneous route (Gonzalez Rodriguez and Rabasco, 2011) due to their enhanced penetration properties through the skin (Bozzuto and Molinari, 2015). In this study, for the first time, two different charged liposome compositions were formulated for topical delivery of PSR. Further, topical PUVA with PSR liposomal nanocarriers was evaluated using in vivo psoriasis model. Fig. 1 gives the outline of work in the present study designed to overcome the concerns associated with conventional PSR vehicles.