Electrostatically optimized adapalene-loaded emulsion for the treatment of acne vulgaris

Abstract

Adapalene (AD) is an FDA-approved drug that shows good therapeutic efficacy for the treatment of acne vulgaris. However, due to its negative charge, AD cannot efficiently penetrate across the also negatively-charged skin membrane. This study is the first to assess the treatment of acne vulgaris using electrostatically optimized AD emulsions prepared using anionic AD with methoxy polyethylene glycol-b-poly(ε-caprolactone) (MC) as an anionic emulsifier coupled with a newly synthesized MC with different contents of an amine pendant-group (MC-[NH₂]_x) as a cationic emulsifier. The AD emulsion prepared using MC-[NH₂]_x with high cationic charge potential was significantly stable in the short-term studies compared with anionic MC or no emulsifier. Furthermore, the AD emulsion prepared with the cationic MC-[NH₂]_x emulsifier provided a two or three times stronger therapeutic effect against acne vulgaris than the AD emulsion prepared with the anionic MC emulsifier or no emulsifier in an animal study. Additionally, the AD emulsion with high cationic charge potential exerted a remarkable inhibition of macrophage expression, as confirmed by histological analysis. Therefore, the electrostatic interaction between the negatively-charged skin membrane and the AD emulsion prepared with the cationic MC-[NH₂]_x emulsifier provides a promising therapeutic strategy for acne vulgaris.

Keywords: Acne vulgaris; Adapalene; Electrostatic emulsifier; Electrostatic interaction; Emulsion.

Graphical abstract

Fig. 1

Schematic representation of (a) adapalene (AD), the anionic MC copolymer and cationic MC-[NH₂]_x copolymer; (b) preparation of AD emulsion (AD only emulsion, AD-MC emulsion using MC, and AD-MC-[NH₂]_x emulsion using MC-[NH₂]_x); and (c) skin permeation of each AD emulsion.

Fig. 2

Preparation of the anionic MC and cationic MC-[NH₂]_x copolymer.

Fig. 3

Zeta potential of (a) the anionic MC and cationic MC-[NH₂]_x copolymer solutions and (b) AD alone and solution mixtures of AD with anionic MC and cationic MC-[NH₂]_x.

Fig. 4

(a) Images and (b) zeta potential of the emulsion containing AD only (F1), AD emulsion with MC (F2), and AD emulsion with MC-[NH₂]_x (F3, F4, and F5) (∗p ​< ​0.05).

Fig. 5

Changes in particle size of the AD only emulsion (F1), AD emulsion with MC (F2), and AD emulsions with MC-[NH₂]_x (F3, F4, and F5) at 4, 37, and 65 ​°C for 4 weeks.

Fig. 6

(a) Viability of Raw 264.7 ​cells measured by the MTT assay at 1, 4, and 7 days and (b) relative ratios by proportional calculation of each formulation at the corresponding days after treatment with AD emulsions (F1–F5) compared with the PBS-treated group (as measured by the (a) results of the MTT assay) (∗p ​< ​0.05, ∗∗p ​< ​0.005).

Fig. 7

(a) Images of skins of nude mice and acne-induced skin areas after non-treatment and AD emulsion treatment (F1–F5) of nude mice with acne vulgaris, and (b) acne volume for each treatment as a function of time.

Fig. 8

(a) H&E staining, (b) quantitative analysis of skin thickness (determined by H&E staining images) (∗p ​< ​0.001), and (c) decreasing rate constant of skin thickness after non-treatment and treatment with AD emulsions (F1–F5) as a function of time.

Fig. 9

(a) ED1 staining, (b) quantitative analysis of ED1 positive cells (determined by ED1 staining images) (∗p ​< ​0.05, ∗∗p ​< ​0.01), and (c) decreasing rate constant of ED1-positive cells after non-treatment and treatment with AD emulsions (F1–F5) as a function of time.