pharmaceuticals Article Apremilast Microemulsion as Topical Therapy for Local Inflammation: Design, Characterization and Efficacy Evaluation Paulo Sarango-Granda 1,2 , Marcelle Silva-Abreu 1,2 , Ana Cristina Calpena 1,2,* , Lyda Halbaut 1,2, María-José Fábrega 3 , María J. Rodríguez-Lagunas 4,5 , Natalia Díaz-Garrido 4,6, Josefa Badia 4 and Lupe Carolina Espinoza 1,2,7 1 Department of Pharmacy, Pharmaceutical Technology and Physical Chemistry, Faculty of Pharmacy and Food Sciences, University of Barcelona, 08028 Barcelona, Spain; [email protected] (P.S.-G.); [email protected] (M.S.-A.); [email protected] (L.H.); [email protected] (L.C.E.) 2 Institute of Nanoscience and Nanotechnology (IN2UB), University of Barcelona, 08028 Barcelona, Spain 3 Department of Experimental and Health Sciences, Parc de Recerca Biomèdica de Barcelona, University Pompeu Fabra (UPF), 08005 Barcelona, Spain; [email protected] 4 Department of Biochemistry and Physiology, Faculty of Pharmacy and Food Sciences, University of Barcelona, 08028 Barcelona, Spain; [email protected] (M.J.R.-L.); [email protected] (N.D.-G.); [email protected] (J.B.) 5 Nutrition and Food Safety Research Institute (INSA-UB), 08921 Santa Coloma de Gramenet, Spain 6 Institute of Biomedicine of the University of Barcelona (IBUB), Sant Joan de Déu Research Institute, 08028 Barcelona, Spain 7 Departamento de Química y Ciencias Exactas, Universidad Técnica Particular de Loja, Loja 1101608, Ecuador * Correspondence: [email protected] Received: 24 November 2020; Accepted: 16 December 2020; Published: 21 December 2020 Abstract: Apremilast (APR) is a selective phosphodiesterase 4 inhibitor administered orally in the treatment of moderate-to-severe plaque psoriasis and active psoriatic arthritis. The low solubility and permeability of this drug hinder its dermal administration. The purpose of this study was to design and characterize an apremilast-loaded microemulsion (APR-ME) as topical therapy for local skin inflammation. Its composition was determined using pseudo-ternary diagrams. Physical, chemical and biopharmaceutical characterization were performed. Stability of this formulation was studied for 90 days. Tolerability of APR-ME was evaluated in healthy volunteers while its anti-inflammatory potential was studied using in vitro and in vivo models. A homogeneous formulation with Newtonian behavior and droplets of nanometric size and spherical shape was obtained. APR-ME released the incorporated drug following a first-order kinetic and facilitated drug retention into the skin, ensuring a local effect. Anti-inflammatory potential was observed for its ability to decrease the production of IL-6 and IL-8 in the in vitro model. This effect was confirmed in the in vivo model histologically by reduction in infiltration of inflammatory cells and immunologically by decrease of inflammatory cytokines IL-8, IL-17A and TNFα. Consequently, these results suggest that this formulation could be used as an attractive topical treatment for skin inflammation. Keywords: apremilast; phosphodiesterase 4; microemulsion; skin diseases; inflammation 1. Introduction Inflammation constitutes a defense mechanism of the body. It is the response of the immune system against numerous harmful stimuli, among which include pathogens, toxic compounds and damaged cells [1]. However, inappropriate or excessive inflammatory responses can trigger chronic Pharmaceuticals 2020, 13, 484; doi:10.3390/ph13120484 www.mdpi.com/journal/pharmaceuticals Pharmaceuticals 2020, 13, x 2 of 25 damaged cells [1]. However, inappropriate or excessive inflammatory responses can trigger chronic inflammation implicated in the pathogenesis of a wide variety of skin disorders [2]. The skin inflammatoryPharmaceuticals response2020, 13, 484 is mediated by cytokine secretions in response to injury, including2 of 25tumor necrosis factor-alpha (TNF-α) and interleukin (IL) -6, IL-8 and IL-17. Therapeutic treatment involves treating symptoms by interrupting the inflammatory process [3]. The mechanism based on phosphodiesteraseinflammation implicated 4 (PDE4) inenzyme the pathogenesis inhibition has of a been wide used variety for ofthe skin treatment disorders of inflammatory [2]. The skin and inflammatory response is mediated by cytokine secretions in response to injury, including tumor autoimmune diseases. PDE4 is one of the many classes of phosphodiesterase enzymes (PDE) that necrosis factor-alpha (TNF-α) and interleukin (IL) -6, IL-8 and IL-17. Therapeutic treatment participateinvolves in treating the hydrolysis symptoms of bycAMP interrupting [4]. PDE4 the inhibition inflammatory causes process a decrease [3]. The in mechanismthe expression based of pro- inflammatoryon phosphodiesterase cytokines, 4such (PDE4) as interleukin enzyme inhibition (IL)-17 has and been tum usedor necrosis for the treatment factor alpha of inflammatory (TNF-α), and an increaseand autoimmunein anti-inflammatory diseases. PDE4 mediators, is one ofsuch the manyas IL- classes10 [5]. ofA phosphodiesterasepremilast (APR) is enzymes a selective (PDE) PDE4 inhibitorthat participate chemically in the identified hydrolysis ofas cAMP N-{2 [-4[(1]. PDE4S)-1-(3 inhibition-ethoxy-4 causes-methoxyphenyl) a decrease in-2 the-(methylsulfonyl) expression ethyl]of- pro-inflammatory2,3-dihydro-1,3-dioxo cytokines,-1H-isoindole such as interleukin-4-yl} acetamide. (IL)-17 and It is tumor a small necrosis and versatile factor alpha molecule (TNF-α whose), formulaand anand increase molecular in anti-inflammatory weight are C22H mediators,24N2O7S and such 460.5 as IL-10 g/mol, [5]. Apremilastrespectively (APR) [6,7] is. Figure a selective 1 shows the chemicalPDE4 inhibitor structure chemically of APR identified [8]. APR as Nwas-{2-[(1S)-1-(3-ethoxy-4-methoxyphenyl)-2-(methylsulfonyl) approved in 2014 by the United States Food and Drug Administrationethyl]-2,3-dihydro-1,3-dioxo-1 (FDA) as oral therapyH-isoindole-4-yl} for the treatment acetamide. of It moderate is a small and-to-severe versatile plaque molecule psoriasis whose and activeformula psoriatic and moleculararthritis [9,10] weight. This are C drug22H24 Ncauses2O7S and an 460.5intracellular g/mol, respectively accumulation [6,7]. of Figure cyclic1 shows adenosine the chemical structure of APR [8]. APR was approved in 2014 by the United States Food and Drug monophosphate (cAMP), resulting in a modification in the signaling pathways of cells belonging to Administration (FDA) as oral therapy for the treatment of moderate-to-severe plaque psoriasis and the innate (monocytes) and adaptive (T cells) immune system as well as non-immune cells active psoriatic arthritis [9,10]. This drug causes an intracellular accumulation of cyclic adenosine (keratinocytes)monophosphate [11,12] (cAMP),. In the resulting last decade, in a modificationnovel drug delivery in the signaling systems pathways for APR of has cells been belonging reported in orderto to the improve innate (monocytes) its solubility and and adaptive bioavailability (T cells) immuneincluding system PLGA as nanoparticles well as non-immune [13], amorphous cells solid(keratinocytes) dispersion [14], [11,12 nanostructured]. In the last decade, lipid novel carriers drug delivery[15] and systems nanocrystal for APR-based has been formulations reported in [16]. Currently,order to APR improve is available its solubility in tablet and bioavailability form of 10, 20 including and 30 PLGA mg for nanoparticles oral administration [13], amorphous [17]. However, solid this dispersionroute of administration [14], nanostructured presents lipid carriersnotable [15 disadvantages] and nanocrystal-based related with formulations adverse [16 effect]. Currently,s, first-pass metabolismAPR is available and, moreover, in tablet form is not of 10,suitable 20 and for 30 mgpatients for oral with administration swallowing [17 difficulties]. However,. thisIn particular, route topicalof administration therapy targeting presents notablea specific disadvantages inflammatory related mediator with adverse on e ffects,the first-passskin promises metabolism a local pharmacologicaland, moreover, effect is not with suitable fewer for patientsside effects with [18] swallowing. This route difficulties. represents In particular, a convenient topical and therapy painless targeting a specific inflammatory mediator on the skin promises a local pharmacological effect with alternative in the treatment of dermatological diseases because it allows drugs to be directed to the fewer side effects [18]. This route represents a convenient and painless alternative in the treatment affected sites within the skin [19]. However, the main obstacle of topical formulations is to overcome of dermatological diseases because it allows drugs to be directed to the affected sites within the the skinstratum [19]. However,corneum the(SC), main which obstacle limits of topical the formulationsspeed of transdermal is to overcome diffusion the stratum of corneumvarious (SC),drugs to achievewhich the limits intended the speed therapeutic of transdermal effect di [20ffusion–22]. of Drug various permeation drugs to achieve through the the intended skin depends therapeutic on the physicochemicaleffect [20–22]. Drugcharacteristics permeation of through the drug the skin as dependswell as onthe the chemical physicochemical composition characteristics and physical of propertiesthe drug of as the well carrier. as the chemical APR is compositioncategorized andas a physical class IV properties drug, according of the carrier. to the APR Biopharmaceutical is categorized