Comparison between Isopropyl Unoprostone and Latanoprost by Prostaglandin E 2 Induction, Af®nity to Prostaglandin Transporter, and Intraocular Metabolism KENJI KASHIWAGI a *,NAOAKIKANAI b ,TAKAYUKI TSUCHIDA c ,MICHIHIRO SUZUKI d , YOKO IIZUKA a ,YUKOTANAKA a AND SHIGEO TSUKAHARA a a Department of Ophthalmology, Yamanashi Medical University, Japan, b Department of Biomedical Engineering, Tokai University, Japan, c Department of Urology, Yamanashi Medical University, Japan and d Corporation for Production and Research of Laboratory Primates, Japan Received Erlangen 27 April 2001 and accepted in revised form 27 August 2001) The pharmacological differences between isopropyl unoprostone referred to as unoprostone) and latanoprost, concerning their induction of endogenous prostaglandin E 2 PGE 2 ) and af®nity to a human prostaglandin transporter PGT), were investigated. Freshly dissected bovine iris tissues were incubated with major intraocular metabolites of uno- prostone, M1 and M2, acid of latanoprost, or PGF 2a , and PGE 2 induction was measured. Af®nities of M1, M2, latanoprost, acid of latanoprost, and PGF 2a to PGT molecule were measured using PGT-cDNA transfected HeLa cells by an isotopic in¯ux assay. 3 H-unoprostone was incubated with freshly prepared serum, aqueous humor, or frozen stored fetal bovine serum FBS), and the radioactivity of supernatants was measured to investigate their metabolism of 3 H-unoprostone. M2, acid of latanoprost, and PGF 2a signi®cantly increased a release of PGE 2 compared with the control. 10 mM indomethacin completely inhibited PGE 2 induction by acid of latanoprost and PGF 2a , while 100 mM indomethacin was required to inhibit PGE 2 induction completely by M1 and M2. Unoprostone, M1, M2, and latanoprost showed little af®nity to PGT, while acid of latanoprost had an af®nity to PGT. Freshly prepared serum and aqueous humor metabolized unoprostone, but frozen stored FBS did not. The release of endogenous PGE 2 may play an important role of action by means of PG analogs, and differences in indomethacin-related inhibition of PGE 2 release and in af®nities to PGT may in part cause their different actions. # 2002 Elsevier Science Ltd Key words: isopropyl unoprostone; latanoprost; prostaglandin transporter; indomethacin; glaucoma. 1. Introduction PGF 2a -related compounds, isopropyl unoprostone referred to as unoprostone) and latanoprost, are now widely used as anti-glaucoma ophthalmic solutions because of their ef®cacy in reducing intra- ocular pressure IOP) and their few side effects Alm, 1993; Azuma, 1993; Haria and Spencer, 1996; Bito, 1997; Camras and Alm, 1997). Previous studies have revealed many pharmacological differences between unoprostone and latanoprost Azuma, 1993; Camras and Alm, 1997; Serle et al., 1998), but the reason for these differences is not clear. Latanoprost has a high af®nity to FP receptor and reduces IOP by increasing the uveoscleral out¯ow. Many studies have been performed to clarify the mechanism of IOP reduction Nilsson et al., 1989; Lindsey et al., 1997a, b; Weinreb et al., 1997). However, the mechanism of IOP reduction by uno- prostone is largely unknown Sakurai, et al., 1991, 1993; Ueno et al., 1992; Taniguchi et al., 1996). Unoprostone has low af®nities against all PG receptors Goh and Kihino, 1994). Although Yousufzai, Ye and Abdel-Latif 1996) have reported that latanoprost induces endogenous PGE 2 synthesis and have hypoth- esized that this induction may play an important role in IOP reduction, endogenous PG induction by unoprostone has not been suf®ciently veri®ed. Latanoprost is de-esteri®ed by passing through the cornea and is eliminated from the eye without further metabolization Sjoquist et al., 1998; Sjoquist Johansson and Stjernschantz, 1999a; Sjoquist, Tajallaei and Stjernschantz, 1999b). Unoprostone is de-esteri®ed by passing through the cornea Watanabe et al., 1992; Babiole and Schoch 1998), but it is consequently metabolized by b-oxidation and o-oxidation in the eye, as reported by the previous in vivo study Kashiwagi, Iizuka and Tsukahara 1999). The intraocular pharmacokinetics of these two compounds seem to be dissimilar and the precise cellular based intraocular pharmacodynamics of these two compounds remain unclear. PGs are usually transported inside the cell by means of PG transporter PGT) and metabolized by enzymes Chan, et al., 1998) such as 15-hydroxy-prosta- glandin dehydrogenase 15-PGDH), delta13-reductase Exp. Eye Res. 2002) 74, 41±49 doi:10.1006/exer.2001.1104, available online at http://www.idealibrary.com on 0014-4835/02/01004109 $35.00/0 # 2002 Elsevier Science Ltd * Address correspondence to: Kenji Kashiwagi, Department of Ophthalmology, Yamanashi Medical University, 1110 Shimokato, Tamaho, Yamanashi 409-3898, Japan. E-mail: kenjik@res.yama- nashi-med.ac.jp