Effect of 8-Iso Prostaglandin E2 on Aqueous Humor Dynamics in Monkeys

LABORATORY SCIENCES

Effect of 8-iso Prostaglandin E2 on Aqueous Humor Dynamics in Monkeys

Rong-Fang Wang, MD; Ping-Yu Lee, MD; Thomas W. Mittag, PhD; Steven M. Podos, MD; Janet B. Serle, MD; Bernard Becker, MD

Objective: To evaluate the effects of 8-iso prostaglandin reduced the IOP (PϽ.01) for as long as 2 and 5 hours, re- E2 (8-isoPGE2;prosta-5,13-dien-1-oicacid,11,15-dihydroxy- spectively. The maximum reduction in the IOP was 4.6 ± 9-oxo-,[5Z,8␤-11X,13E,15S]-) on the intraocular pressure 0.8 mm Hg (0.05%) and 6.0 ± 0.8 mm Hg (0.1%) com- (IOP), outflow facility, and aqueous humor flow rates in pared with baseline measurements. The magnitude and normal monkeys and monkeys with glaucoma. duration of the ocular hypotensive effect were enhanced with twice-a-day administration for 5 consecutive days. Methods: The IOP was measured before and as long as Outflow facility in normal monkey eyes was increased 6 hours after the topical application of 8-iso PGE2 to 1 (PϽ.05) by 48% in the treated eyes, and aqueous humor eye of 6 normal monkeys and to the glaucomatous eye flow was unchanged (PϾ.10), compared with vehicle- of 8 monkeys with unilateral laser-induced glaucoma. The treated contralateral control eyes. Mild eyelid edema, con- pupil diameter was measured at the same times as the junctival edema, hyperemia, and discharge appeared in IOP measurements in the normal monkeys. Tono- some eyes treated with the 0.1% drug concentration. graphic outflow facility and fluorophotometric flow rates of aqueous humor were measured in 6 normal monkeys Conclusions: The use of 8-iso PGE2 reduces the IOP in before and after drug treatment. both normal and glaucomatous monkey eyes. An increase in outflow facility appears to account for most of Results: In normal monkeys, a single dose of 0.1% 8-iso the IOP reduction in normal monkeys. PGE2 reduced (PϽ.01) the IOP for 4 hours in the treated eyes with a maximum (mean ± SEM) reduction of 3.2 ± Clinical Relevance: The application of 8-iso PGE2 may 0.2 mm Hg, compared with the contralateral control eyes. have potential for the treatment of glaucoma as an out- The pupil size was smaller (PϽ.01) in the treated eyes by flow facility–increasing drug. as much as 1.0 ± 0.2 mm for 4 hours. In 8 glaucomatous monkey eyes, the application of 0.05% and 0.1% 8-iso PGE2 Arch Ophthalmol. 1998;116:1213-1216

EVERAL prostaglandin(PG)F2␣ key eyes and the mechanism by which 8-iso analogues and their prodrugs PGE2 alters IOP in normal monkeys. are potent ocular hypotensive agents in monkey eyes with RESULTS laser-induced glaucoma1-3 and are effective and well tolerated in patients The unilateral topical application of 0.1% S 4,5 withocularhypertensionorglaucoma. The 8-iso PGE2 to the eyes of 6 normal monkeys mechanism by which these drugs lower the reduced (PϽ.01) the IOP for 4 hours in the intraocular pressure (IOP) differentiates treatedeyes.ThemaximumdifferenceinIOP them from other agents used to treat glau- between treated eyes and contralateral con- coma. Prostaglandin F2␣ derivatives reduce trol eyes was 3.2 ± 0.2 mm Hg (Figure 1). the IOP primarily by increasing uveoscleral The pupil size was smaller (PϽ.01) in the From the Department of outflow, with minimal or no increase in tra- treated eyes than in the contralateral con- Ophthalmology, Mount Sinai becular outflow facility and without alter- trol eyes by as much as 1.0 ± 0.2 mm for 4 School of Medicine, New York, ing the aqueous humor flow rate.6 hours following treatment (Figure 2). Mild NY (Drs Wang, Lee, Mittag, Prostaglandins E1 and E2 and some of eyelid edema, conjunctival edema, and dis- Podos, and Serle), and the their derivatives reduce the IOP in rabbits charge occurred in 1 of 6 treated eyes, but Department of Ophthalmology and in normotensive human volunteers fol- aqueous flare and cells were not observed. and Visual Science, Washington lowing topical application.7,8 However, the In8monkeyswithunilateralglaucoma, University Medical School, isoprostanes are unique prostanoids formed administration to the glaucomatous eye of St Louis, Mo (Dr Becker). by peroxidation of arachidonic acid.9 This a single dose of 0.05%, 0.1%, and 0.2% 8-iso Dr Podos is a consultant to Alcon Laboratories Inc, Fort formation is not inhibited by cyclooxygen- PGE2 reduced (PϽ.01) the IOP for as long Worth, Tex. Drs Podos, Mittag, ase inhibitors. This study evaluates the ef- as 2, 5, and 3 hours, respectively. The maxi- and Becker have a proprietary fects of the isoprostane 8-iso PGE2 on IOP mum reduction in IOP occurred 2 hours af- interest in the drug evaluated in following single- and multiple-dose appli- ter dosing with each of the 3 concentrations this article. cations in normal and glaucomatous mon- and was 4.6 ± 0.9 mm Hg (0.05%), 6.0 ± 0.8

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©1998 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/29/2021 MATERIALS AND METHODS day, 25 µL of 8-iso PGE2 was applied to the glaucomatous eye at 9:30 AM. Following 1 baseline day (neither vehicle nor drug was administered) and 1 vehicle-treated day (vehicle Fourteen female cynomolgus monkeys, each weighing 3 to 5 to the glaucomatous eye at 9:30 AM and 3:30 PM), a multiple- kg, were used in this study. Six of the animals had IOPs in the dose study was carried out in 8 monkeys with unilateral glau- normal range. In 8 of the animals, glaucoma had been induced coma, with 0.1% 8-iso PGE2 applied to the glaucomatous eye unilaterally by repeated argon laser (65-120 spots; power, 1.1- twice a day (at 9:30 AM and 3:30 PM) for 5 consecutive days. 1.5W;size,50µm;duration,0.5second)ordiode(60-120spots; Outflow facility was measured with an electronic inden- power, 1.1-1.2 W; size, 75 µm; duration, 0.5 second) photo- tationtonograph(EDT-103,AlconLaboratories,Inc,FtWorth, coagulation of the midtrabecular meshwork for 360°. Tex) 4 hours before dosing and was remeasured 2 hours af- On each day of the study, the IOP was measured with a ter unilateral dosing with one 25-µL drop of 0.1% 8-iso PGE2 calibrated pneumatonometer (Model 30 classic, Mentor Inc, in 6 normal monkeys. Aqueous humor flow was measured Norwell, Mass) before drug administration (baseline), at 0.5 with a scanning computerized fluorophotometer (Coherent hour, and then hourly until 6 hours after drug administration. Fluorotron, Coherent Corp, Palo Alto, Calif) in 6 normal mon- Five minutes before tonometry, 0.5% proparacaine hydro- keys. (Breakdown of the blood-aqueous barrier in glaucoma- chloride, 1 drop, was applied topically, and ketamine hydro- tous monkey eyes makes them poor models to use for aque- chloride, 1 to 5 mg/kg of body weight, was administered ous flow measurements.) Iontophoresis was performed in the intramuscularly for adequate sedation. The pupil diameter was central corneas of both eyes of each monkey for 7 minutes us- measured in normal monkeys with a millimeter ruler under ing 10% fluorescein in 2% agar gel at 4 PM on the day before standard illumination immediately before and after each IOP aqueous flow measurements. Baseline aqueous humor flow measurement. Slitlamp examination for the detection of aque- rates were measured hourly for 4 hours beginning at 9:30 AM. ous humor flare and cells was performed in a dark room The following day, one 25-µL drop of 0.1% 8-iso PGE2 was before drug treatment and at 1, 3, and 5 hours after treatment. applied to 1 eye of each monkey, and the same volume of ve- 8-Iso-PGE2 (prosta-5,13-dien-1-oic acid, 11,15- hicle was instilled in the contralateral eye at 8:30 AM. Flow dihydroxy-9-oxo-,[5Z,8␤-11X,13E,15S]-, Cayman Chemi- rates were measured at the same times as on the baseline day cal Co Inc, Ann Arbor, Mich) was freshly prepared by beginning 1 hour after drug administration. The washout pe- dissolving in dimethyl sulfoxide (100 g/L). This stock solu- riod between each test on the same animal was at least 1 week. tion was further diluted with 0.9% sodium chloride to 0.05%, The 2-tailed paired t test was used for statistical analy- 0.1%, and 0.2% concentrations. Single-dose testing was per- sis before and after single-dose treatment, and the Bonfer- formed in 6 normal monkeys with the 0.1% concentration roni t test was used for the analysis of the multiple-dose and in 8 glaucomatous monkey eyes with 0.05%, 0.1%, and study. The Pearson product moment correlation coeffi- 0.2% concentrations. In normal monkeys, one 25-µL drop cient was used to analyze the relationship between IOP and of 8-iso PGE2 was randomly applied to 1 eye, and an equal outflow facility. All experimental studies complied with the volume of isotonic sodium chloride solution (the vehicle) Association for Research in Vision and Ophthalmology Reso- was applied to the contralateral control eye. In the mon- lution on the Use of Animals in Research and were ap- keys with glaucoma, the first day was the baseline day, and proved by the Mount Sinai School of Medicine, New York, one 25-µL drop of isotonic sodium chloride was adminis- NY, Institutional Animal Care and Utilization Committee. tered to the glaucomatous eye at 9:30 AM. On the second Data are given as mean ± SEM.

mm Hg (0.1%), and 4.6 ± 0.8 mm Hg (0.2%) compared with sured tonographically (Table). A significant correlation was the baseline measurements after treatment with the vehicle found between the IOP reduction and the increase of out- (Figure 3). flow facility (r = 0.81, PϽ.05). The coefficient of determi- The magnitude and duration of the ocular hypoten- nation (r2 = 0.66) indicated that the increase in outflow fa- sive effect were enhanced with twice-a-day administration cility accounted for most of the IOP reduction in these for 5 days to 8 glaucomatous monkey eyes. The IOP was normal monkey eyes. significantly (PϽ.05) reduced for 4 hours after the first dose For 4 hours following the administration of a single and for 18 hours after the sixth dose compared with val- dose of 0.1% 8-iso PGE2 to the treated eyes of 6 normal ues obtained on the day of vehicle treatment. The IOP was monkeys, aqueous humor flow rates were unchanged maximally reduced 2 hours after dosing and was 5.0 ± 0.3 (PϾ.10) compared with baseline values or values ob- mm Hg on day 1 and 9.6 ± 0.6 mm Hg on day 5, compar- tained in the contralateral vehicle-treated eyes (Table). ing the eyes with glaucoma on the drug- and vehicle-treated days (Figure 4). Intraocular pressures on the baseline and COMMENT vehicle-treated days were similar (PϾ.40). Mild superficial punctatekeratopathyappearedin1oftheeyesafterthefourth Single-dose administration of PGE1 and PGE2 to rabbits and dose and persisted thereafter. Mild conjunctival hyperemia PGE2 to normotensive volunteers ultimately reduced the 7,8 and mucous discharge appeared in 2 of the eyes. IOP after an initial rise. In contrast to PGE1 and PGE2, Two hours after the unilateral application of 25 µL of several PGE derivatives—RS-61565 and RS-20216— 0.1% 8-iso PGE2 to 6 normal monkeys, outflow facility was specific for the EP3 prostanoid receptor, produced greater increased (PϽ.05) by 48% in the drug-treated eyes com- reductions of the IOP without an initial ocular hyperten- pared with the vehicle-treated control eyes and by 43% com- sive response and less ocular irritation. In the present study, pared with baseline measurements. The IOP was reduced initial ocular hypertension was not observed following single (PϽ.05) at 2 hours in the drug-treated eyes when mea- doses of 8-iso PGE2 in normal and in glaucomatous mon-

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∗ ∗

IOP, mm Hg IOP, ∗ 17 30

∗ ∗ ∗ 0.1% 8-iso PGE2 Control 26

15 42 0123456 0.1% Hours

Figure 1. Effect of a single dose of 0.1% 8-iso prostaglandin E2 (8-iso PGE2)on intraocular pressure (IOP) in 6 normal monkeys. Points represent means and 38 the limits ± SEM. Asterisk indicates a significant reduction in the IOP of treated eyes compared with contralateral control eyes (2-tailed paired t test, PϽ.01). ∗ 34 5.0 ∗ ∗ IOP, mm Hg IOP, ∗ ∗

4.5

∗ 26 42 4.0 0.2% ∗ ∗ ∗ ∗ Pupil Diameter, mm Pupil Diameter, 38

3.5

0.1% 8-iso PGE2 Control 34 ∗ 3.0 ∗ ∗ 0123456 Hours 30

Figure 2. Effect of a single dose of 0.1% 8-iso prostaglandin E2 (8-iso PGE2)on pupillary diameter in 6 normal monkeys. Points represent means and the limits ± SEM. Asterisk indicates a significant reduction in the pupil diameter of treated 26 eyes compared with contralateral control eyes (2-tailed paired t test, PϽ.01). 0123456 Hours

key eyes. A dose-dependent ocular hypotensive effect was Figure 3. Effects of a single dose of 0.05%, 0.1%, and 0.2% 8-iso prostaglandin E2 (8-iso PGE2) on intraocular pressure (IOP) in 8 monkeys observed in the glaucomatous monkey eyes, with 0.1% with unilateral glaucoma. Points represent means and the limits ± SEM. 8-iso PGE2 producing a greater magnitude and a longer Asterisk indicates a significant reduction in the IOP of treated eyes with duration of IOP reduction than the 0.05% concentration. glaucoma compared with values obtained in vehicle-treated eyes on the Increasing the concentration to 0.2% did not increase the control baseline day (2-tailed paired t test, PϽ.01). magnitude of the IOP reduction. The 0.1% 8-iso PGE2 dos- age produced measurements that appeared to be near the in monkeys (Table), with little effect on aqueous humor top of the dose-response curve and, with twice-a-day ad- flow. Analysis of linear regression in the present study shows ministration, produced a sustained reduction of IOP for 5 an apparent close relationship (r = 0.81, PϽ.05) between days in glaucomatous monkey eyes. The prostanoid- IOP reduction and increased pressure-dependent outflow receptor profile of 8-iso PGE2 has not been reported. facility. If several assumptions are made, eg, episcleral ve- The effect of PGF2␣ on outflow facility measured in nous pressure is unchanged, the coefficient determina- cynomolgus monkeys has varied from increases of 25% to tion (r2 = 0.66) indicates that more than two thirds of the 10,11 no increases at all. Clinical trials, however, demon- reduction of IOP induced by 8-iso PGE2 may be explained strated only small increases in tonographically measured by the increase in outflow facility measured tonographi- 14-16 outflow facility in patients with ocular hypertension or pri- cally. Previous studies have demonstrated that PGF2␣ mary open angle glaucoma following the topical adminis- congeners can enlarge the spaces between the ciliary muscle 12 13 tration of PGF2␣-isopropyl ester or PhXA34. Com- bundles, reduce their connective tissue content, and in- pared with PGF2␣, the administration of 8-iso PGE2 gave a crease uveoscleral outflow, which under normal circum- consistent increase in tonographic outflow facility of 50% stances is predominantly pressure independent. This is the

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©1998 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/29/2021 40 Vehicle-Treated Day Day 1 Aqueous Humor Dynamics Measurements With the Day 5 Administration of 0.1% 8-iso ProstaglandineE2 (8-iso PGE2) in 6 Normal Monkeys*

35 Intraocular Aqueous Pressure, Outflow Facility, Humor Flow, ∗∗ Treatment mm Hg µL−1⅐min−1⅐mm Hg−1 µL/min ∗∗

30 8-iso PGE2 ∗ Treated 13.0 ± 0.7† 0.83 ± 0.10† 1.88 ± 0.21 IOP, mm Hg IOP, ∗ ∗ ∗ ∗ Baseline 16.3 ± 1.1 0.58 ± 0.03 1.69 ± 0.29 ∗ ∗ ∗ Vehicle‡ 25 Treated 15.7 ± 0.5 0.56 ± 0.06 1.78 ± 0.22 Baseline 15.7 ± 0.6 0.51 ± 0.04 2.01 ± 0.21

*Data are given as means ± SEMs. 20 †Significantly different from either baseline values or those obtained in 0123456 contralateral vehicle-treated control eyes (2 tailed paired t test, PϽ.05). Hours ‡Vehicle consists of 0.1% isotonic sodium chloride. Figure 4. Effects on intraocular pressure (IOP) of twice-a-day administration of 0.1% 8-iso prostaglandin E2 for 5 days to 8 monkeys with unilateral Accepted for publication May 7, 1998. glaucoma. Points represent means and the limits ± SEM of the IOP on the vehicle-treated day and day 1 and day 5 of treatment. Asterisk indicates a Supported in part by grant EY01867 from the Na- significant reduction in the IOP of treated eyes with glaucoma compared with tional Eye Institute, National Institutes of Health, Bethesda, values obtained in vehicle-treated eyes on the control baseline day (2-tailed Md, and an unrestricted grant from Research to Prevent Bonferroni t test, PϽ.05). Blindness Inc, New York, NY. Reprints: Steven M. Podos, MD, Box 1183, Mount Si- nai School of Medicine, One Gustave L. Levy Place, New major mechanism of action of PGF2␣ congeners, with little effect on trabecular facility. Furthermore, in isolated hu- York, NY 10029 (e-mil: [email protected]). man anterior-segment preparations that measure only out- 10 17 flow facility, PGE2, but not PGF2␣, increases facility. Based REFERENCES on the comparison with PGF2␣, we interpret the tono-

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