R-Tech Ueno, Ltd.

To evaluate the long-term protective effects of transscleral unoprostone (UNO) against retinal degeneration in transgenic (Tg) rabbits (Pro347Leu rhodopsin mutation).

The UNO release devices (URDs) were implanted into the sclerae of Tg rabbits and ERG, optical coherence tomography (OCT), and ophthalmic examinations were conducted for 40 weeks. Unoprostone metabolites in retina, choroid/RPE, aqueous humor, and plasma from wild-type (Wt) rabbits were measured using liquid chromatography-tandem mass spectrometry. In situ hybridization and immunohistochemistry evaluated the retinal distribution of big potassium (BK) channels, and RT-PCR evaluated the expressions of BK channels and m-opsin at 1 week after URD treatment.

The URD released UNO at a rate of 10.2 ±1.0 μg/d, and the release rate and amount of UNO decreased during 32 weeks. Higher ERG amplitudes were observed in the URD-treated Tg rabbits compared with the placebo-URD, or nontreated controls. At 24 weeks after implantation into the URD-treated Tg rabbits, OCT images showed preservation of retinal thickness, and histologic examinations (44 weeks) showed greater thickness of outer nuclear layers. Unoprostone was detected in the retina, choroid, and plasma of Wt rabbits. Retina/plasma ratio of UNO levels were 38.0 vs. 0.68 ng UNO*hour/mL in the URD-treated group versus control (topical UNO), respectively. Big potassium channels were observed in cone, cone ON-bipolar, and rod bipolar cells. Reverse-transcriptase PCR demonstrated BK channels and m-opsins increased in URD-treated eyes.

In Tg rabbits, URD use slowed the decline of retinal function for more than 32 weeks, and therefore provides a promising tool for long-term treatment of RP.

Editor, Vascular adhesion protein (VAP)-1 is a leucocyte adhesion molecule, which is expressed on the cellular membrane of vascular endothelial cells and mediates the transmigration steps of leucocyte recruitment (Salmi & Jalkanen 1992). So far, increased levels of VAP-1 have been reported in a number of inflammatory diseases such as rheumatoid arthritis, inflammatory bowel disease and diabetes, indicating that VAP-1 plays a role in the pathogenesis of inflammatory diseases. We previously reported that VAP-1 blockade suppressed pathological angiogenesis in animal models of choroidal and corneal neovascularization (Noda et al. 2008; Nakao et al. 2011). However, in the animal models, angiogenesis is predominantly induced by inflammatory response, but not ischaemia, which causes fibrovascular tissue formation in ischaemic retinal diseases such as retinopathy of prematurity (ROP). Therefore, we performed an experimental study using oxygen-induced retinopathy (OIR) model to determine whether VAP-1 blockade also attenuates ischaemic retinal neovascularization. To induce OIR, neonatal mice and their nursing dams were exposed to 75% oxygen between postnatal day 7 (P7) and P12 and then returned to room air on P12. Subsequently, the animals were randomly assigned to two groups, VAP-1 inhibitor-treated group receiving single i.p. injection of U-V002 analogue (1.0 mg/kg/day; R-Tech Ueno, Tokyo, Japan) or vehicle-treated group for 7 days (P19). U-V002 is a derivative of 1, 3-thiazole with an IC50 of 53.1 nm against mouse VAP-1, and U-V002 analogue used in this study showed an equivalent efficacy (IC50 of 50.6 nm against mouse VAP-1) with the U-V002. At P19, retinal flat mounts were obtained by cardiac perfusion with fluorescein-labelled dextran (Sigma-Aldrich, St. Louis, MO, USA). Digitized images of total retinal flat mounts were taken, and area ratios of pathological and physiological neovascularization to the flat-mounted retina were measured in masked fashion. Student’s t-test was used for statistical comparison between the groups in this study. The data showed that VAP-1 inhibitor treatment decreased pathological neovascularization in the ischaemic retina (6.79 ± 0.66%, n = 18, p < 0.01) compared with vehicle treatment (14.13 ± 1.73%, n = 14, Fig. 1A, B). By contrast, the ratio of normal vascularized area is higher in the animals treated with VAP-1 inhibitor (94.69 ± 0.82%, n = 18, p < 0.01) than those treated with vehicle (83.56 ± 1.56%, n = 14, Fig. 1C), indicating that VAP-1 blockade did not affect physiological vascular development in OIR model. Suppression of pathological, but not physiological, neovascularization by vascular adhesion protein (VAP)-1 blockade in oxygen-induced retinopathy (OIR) model. (A) Representative micrographs of retinal flat mounts from mice treated with vehicle (left) or VAP-1 inhibitor (right). Arrow indicates pathological neovascularization. (B, C) Effects of VAP-1 inhibitor U-V002 analogue on pathological neovascularization (B) or physiological neovascularization (C), n = 14–18, *p < 0.01. The present data demonstrated that VAP-1 blockade selectively prevents pathological retinal neovascularization without inhibiting physiological neovascularization. Previous data demonstrated that VAP-1 blockade attenuated the angiogenic response via suppression of recruitment of monocyte lineage cells (Noda et al. 2008; Nakao et al. 2011). As it has been elucidated that monocyte lineage cells are involved in the pathological neovascularization in OIR model (Ishida et al. 2003), it is likely that VAP-1 blockade attenuates the pathological neovascularization through suppression of macrophage recruitment. Interestingly, the current data also demonstrated that physiological neovascularization was not inhibited and rather increased in VAP-1 inhibitor-treated group compared with vehicle-treated group. It was reported that VAP-1 is expressed from embryonic day 14 in mouse retina, which may indicate that VAP-1 plays a role for vascularization during eye development (Valente et al. 2008). However, the current data showed that VAP-1 blockade did not suppress physiological neovascularization in OIR model and therefore suggested that the role of VAP-1 might not be identical in physiological and pathological angiogenesis. In the treatment of ROP, the therapeutic agents that suppress pathological, but not physiological, neovascularization are ideal. Further studies to evaluate the effect of VAP-1 blockade in OIR model are warranted.

The purpose of this study was to determine whether topical 0.15% isopropyl unoprostone (IU), a BK-channel activator, could improve or maintain the central retinal sensitivity in patients with middle- to late-stage retinitis pigmentosa (RP). IU was approved for glaucoma and ocular hypertension in 1994. The drug re-profiling strategy is one of the effective ways to develop safe drugs for patients with RP.

A randomized, double-blind, and placebo-controlled phase II safety/efficacy trial was conducted. One hundred and nine patients with middle- to late-stage RP having a visual acuity of ≥0.5 were studied at six ophthalmological centers in Japan. The treatments of IU/day were divided into three groups: placebo group; two-drop group; and four-drop group for 24 weeks. The primary outcome measure was changes in the retinal sensitivity from baseline in the central 2° determined by MP-1 microperimetry (MP-1, Nidek, Japan). The secondary outcomes were changes in best-correct visual acuity, contrast sensitivity, retinal sensitivity of the central 10° by MP-1, mean deviation (MD) by a Humphrey field analyzer (HFA; Carl Zeiss Meditec, Dublin, CA, USA) 10-2, and the Visual Functioning Questionnaire 25 (VFQ-25) questionnaire scores.

There was a tendency for a dose-dependent responsiveness in retinal sensitivity in the central 2°, MD, and total VFQ-25 score after 24 weeks of IU instillation by a simple linear regression analysis. A stratified analysis showed a significant dose-dependent responsiveness of the 2° central retinal sensitivity in more advanced patients (P = 0.028). The number of patients having a ≥4 dB decrease in the primary outcome measure was significantly fewer in the four-drop group than in the placebo group (P = 0.02). No adverse reactions were observed.

A higher dose of IU can delay progression of the central retinal sensitivity decrease through an improvement of retinal sensitivity.