Metabolic profiles of difluprednate in rabbit ocular tissues after instillation of difluprednate ophthalmic emulsion

Abstract

1. Difluprednate (DFBA; 6α,9-difluoro-11β,17,21-trihydroxy-1,4-pregnadiene-3,20-dione 21-acetate 17-butyrate) is an effective anti-inflammatory agent derived from prednisolone. The present study aimed to evaluate the metabolite profile of DFBA in rabbit ocular tissues after instillation of DFBA ophthalmic emulsion.

2. The high-performance liquid chromatography with radiochemical detection was employed to analyze radioactivity in rabbit ocular tissues that had been instilled with a ³H-DFBA 0.05% ophthalmic emulsion. At 0.5 and 2 h after instillation, DFBA was not detected in the cornea, aqueous humor, or iris/ciliary body. Instead, 21-deacetylated DFBA (DFB), 17-debutylated DFB (DF), and an unknown metabolite were found.

3. The unknown metabolite was identified as de-17-side chain-glucocorticoid metabolite (DF21C), which is a novel glucocorticoid metabolite formed by the scission of the 17-side chain via an unknown metabolic reaction pathway. The K_i value of DF21C was 5.6 × 10⁻⁷ mol/L, indicating very weak glucocorticoid receptor binding of DF21C (approximately 1000-fold less than that of DFBA and DFB).

Keywords::

• Ocular tissue metabolite
• glucocorticoid activity
• de-17-side chain-glucocorticoid metabolite

Acknowledgements

The authors thank Dr. Yoshiaki Sato and Kouichi Shibusawa (Sekisui Medical Co., Ltd.) for conducting this study; Dr. Yoshihisa Shirasaki for assisting with the study; and Amy R. Loerch and Erin Parsons (Sirion Therapeutics) for their valuable comments, careful review, and editing of this manuscript.

Declaration of interest

Tetsuya Tajika, Hiroaki Takahashi, Yusuke Sakai, Hiroyuki Fujii, and Hideyuki Sakaki are employees for Senju Pharmaceutical Co., Ltd. Akiharu Isowaki is an employee for Senju USA, Inc. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.