Self-assembly of diclofenac prodrug into nanomicelles for enhancing the anti-inflammatory activity

Abstract

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely prescribed for the treatment of various types of inflammatory conditions. Diclofenac is a very common NSAID that is utilized to relieve pain and reduce fever and, most importantly, inflammation. However, it suffers from low water solubility and a low dissolution profile. Therefore, we aim to develop a new drug delivery system based on the synthesis of amphiphilic structures that are capable of self assembling into nano-micelles which will be a water-soluble delivery system for the diclofenac. The amphiphilic structure consists of a hydrophilic moiety of triethylene glycol (TEG), polyethylene glycol PEG 400, or PEG 600 linked with the hydrophobic drug diclofenac through an ester linkage. The diclofenac derivatives were successfully synthesized as confirmed by nuclear magnetic resonance. Moreover, the formation of the micellar structure of the synthesized amphiphilic derivatives was confirmed by atomic force microscopy obtaining a spherical shape of the micelles with average diameters of 200 nm for Dic-PEG400-Dic, and 110 nm for Dic-PEG600-Dic. The critical micelle concentration has been determined as 2.7 × 10^-3 mg mL^-1 for Dic-PEG400-Dic, and 1 × 10^-4 mg mL^-1 for Dic-PEG600-Dic. The in vitro diclofenac release profile by esterase enzyme was conducted and showed almost complete conversion to free diclofenac within 35 h in the case of Dic-PEG400-Dic micelles and more than 85% of Dic-PEG600-Dic micelles. Then the anti-inflammatory activity was determined by testing the TNF-α production in LPS-stimulated Balb/c mice. Diclofenac micelles significantly suppressed TNF-α production after a 5 mg kg^-1 dose was given. The developed micelles showed TNF-α inhibition up to 87.4% and 84% after 48 hours of treatment in the case of Dic-PEG400-Dic and Dic-PEG600-Dic micelles respectively in comparison to 42.3% in the case of diclofenac alone. Dic-PEG400-Dic micelles showed the most potent anti-inflammatory activity with improved TNF-α suppression through time progress. Therefore, the developed nano-micelles provide a facile synthetic approach to enhance diclofenac water solubility, improve the anti-inflammatory effect and achieve a sustained release profile to get better patient compliance.

Scheme 1. Graphical demonstration of the self-assembled diclofenac nanomicelles.

Scheme 2. Synthetic scheme of the different amphiphiles of diclofenac with TEG, PEG 400, or PEG 600.

Fig. 1. Representative ¹H NMR spectra of (A) Dic-TEG-Dic; (B) Dic-PEG400-Dic; (C) Dic-PEG600-Dic.

Fig. 2. Atomic force microscopy for (A) Dic-PEG400-Dic; (B) Dic-PEG600-Dic.

Fig. 3. Critical micelle concentrations of (A) Dic-PEG400-Dic; (B) Dic-PEG600-Dic.

Fig. 4. In vitro release of diclofenac from (A) Dic-PEG400-Dic; (B) Dic-PEG600-Dic.

Fig. 5. Percentage of TNF-α inhibition after treatment of diclofenac, Dic-PEG400-Dic, and Dic-PEG600-Dic at four different time intervals (3 h, 6 h, 24 h, 48 h).