Effect of pilocarpine 4% in combination with latanoprost 0.005% or 8-iso prostaglandin E2 0.1% on intraocular pressure in laser-induced glaucomatous monkey eyes

PURPOSE

To compare the effect of pilocarpine, an agent that reduces uveoscleral outflow, on the ocular hypotensive efficacy of latanoprost and 8-iso prostaglandin E2 (PGE2).

METHODS

Each of the two treatment groups was composed of the same eight monkeys with unilateral laser-induced glaucoma. Intraocular pressure (IOP) was measured hourly for 6 hours beginning at 9:00 AM on the baseline day (Thursday before treatment week) and on treatment days 1, 3, and 5 (Monday, Wednesday, and Friday). On all five treatment days, one drop of pilocarpine 4% was administered at 9:00 AM and 3:00 PM and one drop of latanoprost 0.005% or 25 microL of 8-iso PGE2 0.1% was administered at 10:00 AM and 4:00 PM.

RESULTS

One hour after pilocarpine instillation on day 1, the reduction of IOP was similar (P > 0.90) in both treatment groups, 7.6 +/- 1.1 mm Hg (mean +/- standard error of the mean ) in the latanoprost group and 7.4 +/- 0.8 mm Hg in the 8-iso PGE2 group. However, the IOP effects of the two treatment groups became significantly different (P < 0.05) beginning 2 hours after dosing with latanoprost or 8-iso PGE, on day 1. A difference (P < 0.05) between the two groups persisted at all subsequent measurements. The reduction of IOP lessened with repeated dosing in the latanoprost and 8-iso PGE2 groups. Three hours after dosing with pilocarpine and two hours after dosing with the prostanoids, the IOP reduction was 8.3 +/- 0.9 mm Hg in the latanoprost group and 9.9 +/- 0.6 mm Hg in the 8-iso PGE2 group on day 1, and 2.1 +/- 1.0 mm Hg in the latanoprost group and 7.3 +/- 0.9 mm Hg in the 8-iso PGE1 group on day 5.

CONCLUSIONS

The smaller reductions in IOP with pilocarpine and latanoprost than with pilocarpine and 8-iso PGE2 show that pilocarpine blocks much more of the ocular hypotensive effect of latanoprost than of 8-iso PGE2. The results also indicate that pilocarpine and latanoprost are mutually antagonistic. Enhancement of uveoscleral outflow appears to account for most of the ocular hypotensive effect of latanoprost and for much less of the ocular hypotensive effect of 8-iso prostaglandin E2.

Electroretinographic abnormalities in a rat glaucoma model with chronic elevated intraocular pressure

The purpose of this study was to determine the ability of electroretinographic (ERG) measurements to document progression of the retinopathy in a rat glaucoma model. Thirty four rats with a chronic intraocular pressure (IOP) elevation induced in one eye by cautery of three episcleral/extra-orbital veins were studied in four separate groups. ERGs were recorded sequentially in Group A rats (n = 12) at baseline, and after approximately 20, 40 and 60 days of high IOP, and in three additional groups of rats (n = 6 or 10 per group) after approximately 58, 30 and 175 days of high IOP, respectively. Scotopic ERG parameters recorded simultaneously from both eyes in Group A rats were: a- and b-wave amplitudes, implicit times, oscillatory potential amplitudes (OPs) determined at three different light-flash intensities, and the light-adapted (photopic) ERG b-wave amplitude. In the other groups of rats, only scotopic ERG a-wave, b-wave and OP amplitudes were measured.In Group A rats that were followed sequentially, all the ERG parameters recorded with attenuated stimuli showed significant time-dependent changes in glaucomatous eyes relative to their contralateral normal eyes, with OPs showing the earliest significant difference after only 3 weeks of high IOP. When different groups of unilateral glaucomatous rats were compared beyond 8 weeks of elevated IOP only the OPs showed a continued decrease with time and good discrimination between glaucoma and normal eyes. Over a 25 week period of high IOP the scotopic OPs measured with attenuated light stimuli declined at the rate of approximately 1.5% per week and provided the best ERG measure to monitor progression of retinal pathophysiology in the vein-occlusion rat glaucoma model.

Maintaining Mitochondrial Membrane Impermeability

Apoptosis may contribute to retinal ganglion cell loss in glaucoma and glaucoma models. Recent research has suggested that mitochondrially dependent apoptosis signaling may contribute to apoptosis in a rat model of glaucoma involving chronic increases in intraocular pressure. In some forms of apoptosis, mitochondrially dependent signaling involves increases in mitochondrial membrane permeability and the mitochondrial release of factors that signal for cell degradation. Opening of a multi-protein, mitochondrial megapore is one factor that contributes to the increased permeability and some anti-apoptotic proteins, particularly BCL-2 and BCL-X(L), bind at the megapore and facilitate megapore closure and reduce increases in mitochondrial membrane permeability. Phosphorylated protein kinase B (Akt) serves as an integrator for cellular survival signals and facilitates the megapore actions of BCL-2 and BCL-X(L), which could protect retinal ganglion cells against insults that induce apoptosis. Several anti-apoptotic agents are being evaluated for use in glaucoma, including brimonidine and propargylamines, which oppose mitochondrially dependent apoptosis through pathways involving phosphorylated Akt.

Retinal morphology and ERG response in the DBA/2NNia mouse model of angle-closure glaucoma

PURPOSE

To document the time course of retinal dysfunction by scotopic electroretinography (ERG) and by quantitative morphology in eyes of the DBA/2NNia substrain of mouse (DBA) with inherited angle-closure glaucoma.

METHODS

DBA and control C57BL/6J (C57) mice were studied by ERG recordings from 5 to 15 months of age, and by morphology from 1 to 14 months of age. Scotopic ERGs were simultaneously recorded from both eyes of dark-adapted anesthetized mice. Changes in the central neuronal retina were evaluated by quantitative morphometry performed on serial semithin sections of Epon-embedded eyes.

RESULTS

When compared with normal C57 mice, DBA mice showed significant reductions of the a-wave and b-wave amplitudes by 7 to 8 months, and the decline continued as the animals aged. The b-wave implicit time in DBA mice showed a gradual prolongation beginning at 8 months of age, when compared with C57 mice. Logistic regression analyses revealed significant correlations in a- and b-wave amplitude reductions between ipsilateral and contralateral eyes of DBA mice at ages when ERG parameters were greatly altered. Morphologically, thinning of the whole retina was already evident in DBA mice at 4 months of age, but loss of ganglion cells and thinning of the outer plexiform layer were first seen in 7- to 8-month-old animals. These changes progressed to the end of the 13-month period studied.

CONCLUSIONS

Progressive thinning of the outer retinal layers in DBA mice was found to correlate with decreases in ERG a- and b-wave amplitudes, both occurring from the age of 7 to 8 months onward. Similarities with the findings in human late-stage glaucomatous retinopathy indicate the relevance of this animal model in further glaucoma research.

Comparison of the ocular hypotensive effect of brimonidine, dorzolamide, latanoprost, or artificial tears added to timolol in glaucomatous monkey eyes

PURPOSE

To investigate the additive ocular hypotensive effect of brimonidine, dorzolamide, latanoprost, or artificial tears to timolol in monkey eyes with laser-induced unilateral glaucoma.

METHODS

Eight monkeys were used and each animal received all four combinations of drugs in a randomized fashion during the study. The washout period between each combination was at least 2 weeks. Intraocular pressure (IOP) was measured at 8:30 AM, 11:00 AM, 1:00 PM, and 3:30 PM on day 1 (untreated baseline), day 2 (timolol treatment alone), and days 3 through 5 (combination therapy with two drugs). One drop of 0.5% timolol was topically applied at 3:45 PM on day 1 and at 8:45 AM and 3:45 PM on days 2 through 5. One drop of 0.2% brimonidine or 2% dorzolamide or artificial tears was added on day 2 at 4:00 PM and at 9:00 AM and 4:00 PM on days 3 through 5, or latanoprost was added at 9:00 AM on days 3 through 5.

RESULTS

Compared with timolol alone, the maximal additive reduction in IOP which occurred on day 5 was 4.8 +/- 0.8 mm Hg (mean +/- standard error of the mean) with timolol plus brimonidine, 5.6 +/- 1.0 mm Hg with timolol plus dorzolamide, 4.3 +/- 1.0 mm Hg with timolol plus latanoprost, and 2.0 +/- 0.5 mm Hg with timolol plus artificial tears (P < 0.01). At all measurements, timolol plus brimonidine, timolol plus dorzolamide, and timolol plus latanoprost caused greater (P < 0.05) IOP reductions than did timolol plus artificial tears. The additive IOP-lowering effect was similar (P > 0.60) when comparing timolol plus brimonidine and timolol plus dorzolamide, timolol plus brimonidine and timolol plus latanoprost, timolol plus dorzolamide and timolol plus latanoprost at all measurements, but timolol plus dorzolamide caused a greater (P < 0.05) reduction of IOP than did timolol plus latanoprost at 0 hours on day 5.

CONCLUSIONS

The addition of brimonidine, dorzolamide, or latanoprost to timolol caused similar additional reductions of IOP in glaucomatous monkey eyes.

Retinal damage after 3 to 4 months of elevated intraocular pressure in a rat glaucoma model

PURPOSE

To characterize a long-term elevated intraocular pressure (IOP) glaucoma model in the rat with respect to electroretinographic (ERG) changes and the pattern and mechanism of retinal ganglion cell (RGC) death. METHODS; An approximate doubling of IOP was induced in one eye (G) of female Wistar rats (150-180 g) by cautery of 3 episcleral/limbal veins. At intervals over 3 to 4 months, measurements of IOP and ERG changes (contact-lens electrode) were made in both the G and contralateral normal (N) eyes. At the end of 3 to 4 months of elevated IOP, RGCs were fluorescently labeled with Fluorogold (retrogradely from the superior colliculus), or retinas were labeled by intravitreal injection of a mitochondrial potential indicator dye and stained for apoptotic nuclei with a DNA dye. Flatmounts of fixed, dye-labeled retinas were examined by epifluorescence, confocal, or interference contrast microscopy.

RESULTS

Elevated IOP was consistently maintained for up to 4 months in G eyes, but ERG a- and b-waves showed a statistically significant decline, of 30% to 40% in amplitude, after 3 months. Loss of RGCs in G retinas was primarily focal with no statistically significant loss demonstrable outside of the focal areas when assessed by an area sampling method for counting RGCs, which totaled 2% to 3% of the entire retinal area. Mitochondrial membrane potential of cells in the RGC layer was reduced by 17.5% (P: < 0.05) in regions surrounding areas of focal loss compared with comparable locations in control N eyes. After 3.5 months' elevated IOP the G retinas showed cell nuclei at various stages of apoptosis, from initial DNA condensation to fragmentation.

CONCLUSIONS

The three-vein episcleral/limbal vein occlusion model for inducing glaucomatous pathology in the rat eye gives a consistent long-term elevation of IOP. After 3 to 4 months of approximately 100% increased IOP, the ERG responses begin to decline, there is a variable focal loss of RGCs, and some of the remaining RGCs show characteristics of stress and apoptosis. These changes seem consistent with retinal damage in human glaucoma (focal field defects), and this rat model appears to mimic some features of primary open-angle glaucoma.

Comparisons of the amplitude size and the reproducibility of three different electrodes to record the corneal flash electroretinogram in rodents

To compare corneal electrodes commonly used in rodent eyes for repeat and left versus right eye accuracy and variability to record the flash electroretinogram (ERG). Animals studied were eight C57BL/6 mice and eight rats of the Wistar strain. Scotopic ERGs were recorded from eyes of dark-adapted anesthetized rodents to compare a custom-made gold-wire contact lens electrode (CLE), a cotton-wick silver-silver chloride electrode (SCLE), and a coiled stainless steel wire electrode (SSE). Compared to SCLE and SSE. the potentials recorded by CLE are characterized by significantly larger ERG amplitudes and oscillatory potentials in both rats and mice (p <0.0001). In analyzing test-retest data comparing the three different electrodes the coefficient of variation was smaller (range, 10.3-15.5%) and the interclass correlation coefficient (0.77-0.93) showed a better agreement for the CLE. Recording scotopic ERGs with custom-made gold-wire contact lens electrodes records large amplitudes and shows a good reproducibility and reliability to monitor retinal function in rodent eyes.

Diffuse retinal hemorrhages (ocular decompression syndrome) after trabeculectomy with mitomycin C for neovascular glaucoma

PURPOSE

To describe a case of ocular decompression syndrome in a patient after trabeculectomy with mitomycin C for neovascular glaucoma.

RESULTS

Diffuse retinal hemorrhages developed in the posterior pole of a patient with neovascular glaucoma after he underwent trabeculectomy with mitomycin C. The hemorrhages persisted for less than 9 months.

CONCLUSIONS

Acute decompression of the eye in patients with high intraocular pressure can lead to the development of posterior pole hemorrhages. The course of this rare syndrome is relatively benign.

Effect of latanoprost or 8-iso prostaglandin E2 alone and in combination on intraocular pressure in glaucomatous monkey eyes

OBJECTIVE

To evaluate the possible additivity of the effects of latanoprost and 8-iso prostaglandin E2 (8-iso PGE2) on intraocular pressure (IOP) in monkey eyes with laser-induced glaucoma.

METHODS

The IOP was measured hourly for 6 hours beginning at 9:30 AM on day 1 (baseline day), days 6 and 7 (single-agent therapy), and days 13 and 14 (combination therapy with both agents). Following 1 day of baseline measurement, 4 monkeys with unilateral glaucoma received monotherapy) twice daily with either 1 drop of 0.005% latanoprost, or 0.1% 8-iso PGE2, 25 microL, at 9:30 AM and 3:30 PM from days 2 through 7. From days 8 through 14, both agents were applied twice daily 5 minutes apart.

RESULTS

The maximum reduction of IOP (mean +/- SEM) was 8.8 +/- 1.9 mmHg (26%) (P<.05) with latanoprost alone and 6.5 +/- 1.0 mmHg (21%) (P<.0l) with 8-iso PGE2 alone, 2 hours after the morning dosing on day 7. A further reduction of IOP of 4.0 +/- 0.6 mm Hg was produced when 8-iso PGE2 was added to latanoprost and of 3.0 +/- 0.7 mm Hg was produced when latanoprost was added to 8-iso PGE2 on day 13 before the morning dosing. Combination therapy with both agents caused maximum IOP reductions from baseline of 11.3 +/- 3.0 mm Hg (33%) (P<.05) (latanoprost with 8-iso PGE2 added) and of 9.8 +/- 1.3 mm Hg (31%) (P<.01) (8-iso PGE2 with latanoprost added) on day 14.

CONCLUSION

Latanoprost and 8-iso PGE2 have an additive effect on IOP in glaucomatous monkey eyes.

CLINICAL RELEVANCE

At least 50% of patients are treated with more than 1 ocular hypotensive medication. Thus, the determination of the additive effects on IOP of glaucoma medications will help to define optimum treatment regimens.

The effect of divalent cations on bovine retinal NOS activity

The divalent cation requirements of NOS activity in bovine retina homogenate supernatant were investigated. Supernatants were assayed under standard conditions (in mM: EDTA 0.45, Ca2+ 0.25, Mg2+ 4.0). In order to investigate the enzyme's dependence on divalent cations, the tissue homogenate was depleted of di- and trivalent cations by passing it over a cation-exchange column (Chelex 100). Surprisingly, NOS activity was 50-100% higher in this preparation. However, addition of either EDTA (33 microM) or EGTA (1 mM) almost fully inhibited NOS activity, suggesting a requirement for residual divalent metal cation(s). Phenanthroline or iminodiacetic acid at low concentrations had little effect on activity, suggesting no requirement for Fe2+, Zn2+ or Cu2+. Ca2+ had a moderate stimulatory effect, with an optimum activity around 0.01 mM. Mg2+ or Mn2+ had little effect at concentrations < 0.25 mM. However, in the presence of EDTA, Mn2+ or Ca2+ markedly stimulated NOS activity with the optimum at 0.1 mM. At high concentrations (> 0.1-0.2 mM), all divalent cations tested (Ba2+, Zn2+, Co2+, Mn2+, Mg2+, Ca2+), as well as La3+, dose-dependently inhibited NOS activity. We propose that retinal NOS requires low concentrations of naturally occurring divalent metal ions, most probably Ca2+, for optimal activity and is inhibited by high di- and trivalent metal concentrations, probably by competition with Ca2+.

Effect of ticrynafen on aqueous humor dynamics in monkeys

OBJECTIVE

To determine the effect of ticrynafen, a nonsulfhydryl-reactive compound similar to ethacrynic acid, on outflow facility in normotensive monkey eyes and on intraocular pressure (IOP) in monkey eyes with laser-induced glaucoma.

METHODS

In normotensive eyes, facility (perfusion) was measured shortly before and after bolus or exchange intracameral infusion of ticrynafen or vehicle in opposite eyes, and 3.5 to 4.5 hours after 5 days of twice-daily 2% ticrynafen or vehicle ointment. In glaucomatous eyes, baseline and vehicle diurnal IOP curves were established, 2% ticrynafen ointment was given twice daily for 5 days, and IOP was measured immediately before and 0.5 to 6 hours after each morning treatment.

RESULTS

In normotensive eyes, exchange 2-mL influsion of 0.2-, 1-, or 4-mmol/L ticrynafen increased facility by 33% +/- 6% (mean +/- SEM), 73% +/- 18%, and 60% +/- 11%, respectively. Day 5 posttreatment facility was higher in the ticrynafen group than in controls by 28% +/- 9%. In glaucomatous eyes, maximum IOP decline, from approximately 35 mm Hg, was 7.5 +/- 2.0 mm Hg on day 4 and 9.8 +/- 2.4 mm Hg on day 5 of twice-daily ticrynafen treatment.

CONCLUSION

The facility-increasing, IOP-lowering action of ticrynafen, ethacrynic acid, and derivatives may not depend entirely on sulfhydryl reactivity.

CLINICAL RELEVANCE

Whether such drugs as ethacrynic acid and ticrynafen prove valuable for glaucoma therapy, at the least they are useful probes to study aqueous outflow mechanisms.

Glutamate receptor subunit GluR2 and NMDAR1 immunoreactivity in the retina of macaque monkeys with experimental glaucoma does not identify vulnerable neurons

Excitatory amino acid neurotoxicity has been proposed as a mechanism underlying selective neuronal death in glaucoma. The relationships between the cellular distribution of glutamate receptor subunit proteins GluR2 and NMDAR1 and the vulnerability of restricted retinal neuron subpopulations was explored in experimental glaucoma in macaque monkeys, produced by treating the trabecular meshwork in one eye with argon or diode laser burns. Immunostaining of retinal segments was performed using specific monoclonal antibodies to the GluR2 and NMDAR1 subunit proteins as well as neurofilament protein. The distribution of immunoreactivity was qualitatively assessed in the retina, and ganglion cells were counted in the paracentral and peripheral regions of each retinal segment. Immunoreactivity for both of these glutamate receptor subunit proteins was widely distributed in most retinal neuron types in control eyes and was colocalized with neurofilament protein in ganglion cells. In the glaucomatous eyes, densities of GluR2- and NMDAR1-immunoreactive ganglion cells were dramatically reduced compared to unaffected fellow eyes, but GluR2- and NMDAR1-immunoreactive populations of horizontal, bipolar, and amacrine cells were not affected. These data parallel previous observations on the selective vulnerability of ganglion cells in this experimental model of glaucoma. However, GluR2 and NMDAR1 subunits do not constitute cell type-specific markers of vulnerability in glaucoma as they are present in neurons prone to degeneration as well as in resistant ones. While retinal pathology in glaucoma involves excitotoxic mechanisms that may be related to glutamate receptor subunits regulating calcium fluxes, the specific pattern of neuronal vulnerability clearly depends on other cellular characteristics such as morphology, connectivity, and other aspects of the neurochemical phenotype.

Effect of 8-iso prostaglandin E2 on aqueous humor dynamics in monkeys

OBJECTIVE

To evaluate the effects of 8-iso prostaglandin E2 (8-iso PGE2; prosta-5,13-dien-1-oic acid,11,15-dihydroxy-9-oxo-,[5Z,8beta-11X,13E,15 S]-) on the intraocular pressure (IOP), outflow facility, and aqueous humor flow rates in normal monkeys and monkeys with glaucoma.

METHODS

The IOP was measured before and as long as 6 hours after the topical application of 8-iso PGE2 to 1 eye of 6 normal monkeys and to the glaucomatous eye of 8 monkeys with unilateral laser-induced glaucoma. The pupil diameter was measured at the same times as the IOP measurements in the normal monkeys. Tonographic outflow facility and fluorophotometric flow rates of aqueous humor were measured in 6 normal monkeys before and after drug treatment.

RESULTS

In normal monkeys, a single dose of 0.1% 8-iso PGE2 reduced (P<.01) the IOP for 4 hours in the treated eyes with a maximum (mean +/- SEM) reduction of 3.2 +/- 0.2 mm Hg, compared with the contralateral control eyes. The pupil size was smaller (P<.01) in the treated eyes by 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 reduced the IOP (P<.01) for as long as 2 and 5 hours, respectively. The maximum reduction in the IOP was 4.6 +/- 0.8 mm Hg (0.05%) and 6.0 +/- 0.8 mm Hg (0.1%) compared with baseline measurements. The magnitude and duration of the ocular hypotensive effect were enhanced with twice-a-day administration for 5 consecutive days. Outflow facility in normal monkey eyes was increased (P<.05) by 48% in the treated eyes, and aqueous humor flow was unchanged (P>.10), compared with vehicle-treated contralateral control eyes. Mild eyelid edema, conjunctival edema, hyperemia, and discharge appeared in some eyes treated with the 0.1% drug concentration.

CONCLUSIONS

The use of 8-iso PGE2 reduces the IOP in both normal and glaucomatous monkey eyes. An increase in outflow facility appears to account for most of the IOP reduction in normal monkeys.

CLINICAL RELEVANCE

The application of 8-iso PGE2 may have potential for the treatment of glaucoma as an outflow facility-increasing drug.

A comparative study of latanoprost (Xalatan) and isopropyl unoprostone (Rescula) in normal and glaucomatous monkey eyes

Latanoprost (PhXA41, Xalatan) and isopropyl unoprostone (UF-021, unoprostone, Rescula) two new prostanoid derivatives, have been shown to reduce intraocular pressure (IOP) significantly in patients with glaucoma or ocular hypertension. This study was designed to compare the ocular hypotensive effects of latanoprost and unoprostone in cynomologus monkeys with glaucoma and characterizes the prostanoid's mechanisms of action in normal cynomolgus monkey eyes. Intraocular pressure was measured daily at 0, 0.5, and 1 hour and hourly for 5 additional hours during 1 baseline day, 1 vehicle-treated day, and 5 days of therapy with either 0.005% latanoprost or 0.12% unoprostone applied twice daily, at 9:30 AM and 3:30 PM, to the glaucomatous eye of eight monkeys with unilateral laser-induced glaucoma. Outflow facility was measured in six normal monkeys 3 hours prior to dosing and 1 hour after unilateral dosing with either drug. Aqueous humor flow rates were measured in six normal monkeys hourly for 4 hours on 1 baseline day and on 1 treatment day beginning 1 hour after administration of either drug to one eye. Intraocular pressure was significantly (P < 0.005) reduced after the first application for 4 hours with latanoprost and for 2 hours with unoprostone, up to 5.4 +/- 0.8 mm Hg (mean +/- SEM) (latanoprost) and 3.8 +/- 0.5 mm Hg (unoprostone). Intraocular pressure was significantly (P < 0.005) reduced for at least 18 hours following each PM dose of latanoprost. Intraocular pressure was not reduced (P > .05) 18 hours after each PM dose of unoprostone. An enhancement of the ocular hypotensive effect was observed from day 1 to day 5 with repeated dosing of either drug. Latanoprost produced a greater magnitude of IOP reduction for a longer duration of time than unoprostone after each application. Neither drug altered outflow facility or aqueous humor flow rates. Latanoprost and unoprostone appear to reduce IOP in monkeys by enhancing uveoscleral outflow. Latanoprost appears to be more efficacious and potent than unoprostone in reducing IOP in glaucomatous monkey eyes.

A comparison of argon laser and diode laser photocoagulation of the trabecular meshwork to produce the glaucoma monkey model

PURPOSE

To create an experimental glaucoma monkey model using high-power diode laser photocoagulation of the trabecular meshwork, and to compare this with the experimental glaucoma monkey model induced by argon laser photocoagulation of the trabecular meshwork.

METHODS

One eye each of eight adult cynomolgus monkeys underwent repeated application of diode laser photocoagulation of the trabecular meshwork until sustained intraocular pressure (IOP) elevation was achieved. 50 to 120 spots were applied to midtrabecular meshwork for 360 degrees; spot size, 75 microns; power, 1.2 W; duration, 0.5 seconds. Intraocular pressure, tonographic outflow facility, and ophthalmoscopically and photographically documented optic nerve head evaluations were carried out before and after treatment. Data were compared retrospectively with similar data from an experimental glaucoma monkey model after argon laser photocoagulation of the trabecular meshwork (n = 10).

RESULTS

The average number of laser treatments to achieve stable IOP elevation was 3.0 with both diode and argon laser trabecular treatments (p > 0.99). On week 4 after initial pressure elevation, peak IOP was greater--(p < 0.05) 43.0 mmHg +/- 2.4 mmHg (mean +/- SEM) and 37.4 mmHg +/- 1.3 mmHg--in the diode laser-induced than in the argon laser-induced glaucomatous eyes, respectively. Outflow facility (microliter/min/mmHg) was reduced (p < 0.001) in both diode (0.09 +/- 0.01 microliter/min/mmHg) and argon (0.10 +/- 0.01 microliter/min/mmHg) laser-induced glaucomatous eyes compared with untreated fellow eyes. Both the diode and argon laser techniques produced the earliest signs of optic nerve head excavation within about one month of IOP elevation.

CONCLUSIONS

Repeat diode laser photocoagulation of the trabecular meshwork produced higher (p < 0.05) IOP elevation than argon laser photocoagulation of the trabecular meshwork in this study. No significant differences in outflow facility and optic nerve head change were observed between these two laser techniques. The experimental glaucoma monkey model can be created with either the diode or argon laser photocoagulation of the trabecular meshwork.

Nitric oxide synthase activity in tissues of the bovine eye

BACKGROUND

Nitric oxide synthase (NOS) is present in many ocular tissues where it may have different physiological functions. This warrants a thorough characterization of NOS activity in the eye.

METHODS

NOS distribution and its biochemical properties were determined in the retina, choroid, ciliary processes (CP), and trabecular meshwork (TM).

RESULTS

Retinal NOS required NADPH (diphenylene-iodonium, a flavoprotein inhibitor, which inhibited enzyme activity with an IC50 of 0.36 microM, FAD (40 microM), FMN (40 microM), and BH4 (4 microM) as cofactors for optimal activity. Ocular NOS appeared to be regulated by free divalent cations, since its activity was inhibited by EDTA (slopes > 3.0 and IC50 values of 12.8, 19.7, and 53 microM, respectively). Ocular NOS required calmodulin, since NOS activity was inhibited by trifluoperazine (calmodulin inhibitor, IC50 = 41 microM). NOS activity is widely distributed in the eye, (choroid > retina > CP > TM) and is mainly cytosolic (70-95%). L-Arginine analogs inhibited NOS in the retina, choroid, and TM. In all three tissues, NG-methyl-L-arginine displayed the highest affinity for inhibition (IC50 = 0.2-0.7 microM) followed by canavanine (IC50 = 13-33 microM), while aminoguanidine only weakly inhibited NOS (IC50 = 93-179 microM).

CONCLUSION

In all tissues, the order of potency of inhibition points to the presence of constitutive rather than inducible NOS. Moreover, it is possible that TM contains more than a single form of NOS.

Effect of 5-methylurapidil, an alpha 1a-adrenergic antagonist and 5-hydroxytryptamine1a agonist, on aqueous humor dynamics in monkeys and rabbits

PURPOSE

To evaluate the effects of 5-methylurapidil (5-MU) on intraocular pressure (IOP) and aqueous humor dynamics in female cynomolgus monkeys and albino rabbits.

METHODS

IOP was measured by pneumatonometer prior to and up to 6 hours after AM administration of 5-MU to one eye of each of 8 normal monkeys and to the laser-induced glaucomatous eye of 8 monkeys. During single-dose and 5-day multiple-dose testing, pupillary diameter (PD) was measured at the same time and same intervals as IOP measurements in the normal monkeys. Outflow facility and aqueous humor flow rates were measured in 8 normal monkeys before and after treatment. Uveoscleral outflow was measured in 8 rabbits before and after treatment.

RESULTS

In normal monkeys, unilateral topical application of 2 x 25 microliters of 1% or 2% 5-MU significantly (p < 0.05) reduced pupil size and IOP bilaterally as compared to baseline measurements. The reduction in IOP (mean +/- SEM, mmHg) was up to 2.8 +/- 0.7 (1% 5-MU) and 4.4 +/- 0.5 (2% 5-MU) in the treated eyes, and 2.3 +/- 0.8 (1%) and 3.0 +/- 0.7 (2%) in the contralateral eyes. In glaucomatous monkeys, the maximum reduction in IOP was 6.5 +/- 1.0 mmHg (1%) and 7.5 +/- 0.8 mmHg (2%). The ocular hypotensive effect increased over time with twice-daily administration for 5 days. Compared with baseline values, outflow facility and aqueous flow rates in the treated eyes of normal monkeys were increased (p < 0.01) by 51% and by 11%, respectively. Uveoscleral outflow was unaltered (p > 0.3) in rabbits compared with baseline values. Mild corneal edema, corneal punctate erosions, and conjunctival discharge occurred in some eyes treated with either 1% or 2% 5-MU.

CONCLUSIONS

5-Methylurapidil, an antagonist at the alpha 1A-adrenergic receptor subtype and an agonist at the 5-HT1A receptor subtype, lowers IOP predominantly by increasing outflow facility and may have potential for the therapy of glaucoma.

Magnocellular and parvocellular visual pathways are both affected in a macaque monkey model of glaucoma

PURPOSE

Neurochemical changes in nerve cells were investigated in the lateral geniculate nucleus (LGN) and primary visual cortex of macaque monkeys with experimentally induced glaucoma.

METHODS

Glaucomatous damage was induced in one eye of experimental animals by elevation of intraocular pressure following laser burns to the trabecular meshwork. Staining for the metabolic marker cytochrome oxidase, as well as immunolabelling for the neuronal markers synaptophysin and neurofilament proteins, was conducted on sections of the LGN and primary visual cortex.

RESULTS

In the LGN, staining for cytochrome oxidase and immunolabelling for synaptophysin were reduced in the parvocellular and magnocellular layers that received input from the glaucomatous eye and neurofilament protein labelling was reduced in the parvocellular layers. Cytochrome oxidase staining demonstrated the presence of denervated ocular dominance columns in layer IVC of the primary visual cortex of experimental animals.

CONCLUSIONS

Pre- and post-synaptic neurochemical alterations in the magnocellular and parvocellular visual pathways of the brain are associated with experimentally induced glaucoma in macaque monkeys.

Elevated glutamate levels in the vitreous body of humans and monkeys with glaucoma

OBJECTIVE

To explore the possibility that the excitatory amino acid glutamate might be associated with the disease process of glaucoma, which is characterized by the death of retinal ganglion cell neurons and subsequent visual dysfunction.

METHODS

Amino acid analyses were performed on vitreous specimens that were obtained from patients who were undergoing cataract extraction. Samples were collected prospectively from those patients who sustained inadvertent rupture of the posterior capsule between 1988 and 1993. An additional set of specimens, obtained from both eyes of monkeys, was analyzed; in these monkeys, glaucoma had been experimentally induced in one eye only.

RESULTS

A twofold elevation in the level of glutamate was detected in the vitreous body of the group of patients with glaucoma when compared with that in a control population of patients with cataracts only. An even greater elevation of the glutamate level was found in the vitreous body of glaucomatous eyes of monkeys when compared with that in control eyes. No statistical differences were detected among other amino acid levels from the vitreous body of glaucomatous and nonglaucomatous eyes in humans or monkeys.

CONCLUSIONS

The excitatory amino acid glutamate is found in the vitreous body of glaucomatous eyes at concentrations that are potentially toxic to retinal ganglion cells. The increased level of this known neurotoxin is consistent with an "excitotoxic" mechanism for the retinal ganglion cell and optic nerve damage in glaucoma. Therapies to protect neurons against glutamate toxic effects may prove to be useful in the management of this blinding disease.

Differential vulnerability of neurochemically identified subpopulations of retinal neurons in a monkey model of glaucoma

The vulnerability of subpopulations of retinal neurons delineated by their content of cytoskeletal or calcium-binding proteins was evaluated in the retinas of cynomolgus monkeys in which glaucoma was produced with an argon laser. We quantitatively compared the number of neurons containing either neurofilament (NF) protein, parvalbumin, calbindin or calretinin immunoreactivity in central and peripheral portions of the nasal and temporal quadrants of the retina from glaucomatous and fellow non-glaucomatous eyes. There was no significant difference between the proportion of amacrine, horizontal and bipolar cells labeled with antibodies to the calcium-binding proteins comparing the two eyes. NF triplet immunoreactivity was present in a subpopulation of retinal ganglion cells, many of which, but not all, likely correspond to large ganglion cells that subserve the magnocellular visual pathway. Loss of NF protein-containing retinal ganglion cells was widespread throughout the central (59-77% loss) and peripheral (96-97%) nasal and temporal quadrants and was associated with the loss of NF-immunoreactive optic nerve fibers in the glaucomatous eyes. Comparison of counts of NF-immunoreactive neurons with total cell loss evaluated by Nissl staining indicated that NF protein-immunoreactive cells represent a large proportion of the cells that degenerate in the glaucomatous eyes, particularly in the peripheral regions of the retina. Such data may be useful in determining the cellular basis for sensitivity to this pathologic process and may also be helpful in the design of diagnostic tests that may be sensitive to the loss of the subset of NF-immunoreactive ganglion cells.

Microbial contamination of medications used to treat glaucoma

AIMS

A study was conducted to estimate the frequency of contamination of topical antiglaucoma medications used by asymptomatic patients.

METHODS

The drops and the bottle tips of 194 in use topical medications and the conjunctiva from 109 treated glaucoma patients were cultured.

RESULTS

Bacteria were recovered from 55 (28%) medications. The bottle tip was more frequently contaminated than the drops (p = 0.008). Gram positive organisms were cultured from 50 (91%) of 55 contaminated medications. Thirteen patients (12%) had the same microorganism recovered from the conjunctiva and from the contaminated medication. The frequency of contamination of medications increased with increasing duration of use. Bacterial contamination occurred in 19% of eyedrops less than 8 weeks old in contrast with 40% of bottles used for more than 8 weeks.

CONCLUSION

Our data suggest that ocular medications to treat glaucoma frequently become contaminated with bacteria and that contamination is related to duration of use. We therefore recommend that opened topical antiglaucoma eyedrops should be replaced on a regular basis.

Role of G-proteins in ciliary process adenylyl cyclase responses of the albino rabbit eye

After intravitreal injections of cholera or pertussis toxin (CTX or PTX, 0.5 -1 microgram/eye) into the albino rabbit eye, the in vitro responses of ciliary process adenylyl cyclase (AC) to isoproterenol, vasoactive intestinal peptide (VIP), and forskolin (FSK) were increased 21-40% for PTX, but for CTX-injected eyes AC responses to fluoroaluminate, VIP and FSK decreased 70-50%. The increased responses after PTX suggests that this toxin blocked an inhibitory Gi control of AC that is present in the control tissue. However, prolonged (> 24 hr) in vivo exposure to CTX appears to down-regulate the AC enzyme. In contrast to the in vivo findings, AC responsiveness was unaffected by PTX pre-treatment of membranes in vitro, while CTX pre-treatment increased basal activity (+600%), and the FSK response (+30%), but decreased responsiveness to fluoroaluminate, VIP and isoproterenol by 88-56%. Treatment of ciliary process membranes with 32P-NAD and CTX or PTX followed by SDS-PAGE autoradiography of labelled proteins gave two bands for the G-protein alpha-subunits of Gs (45, 56 kDa) and one broad band centered at 40 kDa for Gi-type subunits respectively. Western blots using specific antibodies showed the presence of Gi type I or III, but no detectable Gi type II or Go in rabbit ciliary processes. We conclude that the changes in adenylyl cyclase enzyme responses after intraocular CTX or PTX may not correlate with cAMP levels and intraocular pressure effects. However, the in vitro biochemical data on AC responses and on G-proteins provide evidence for dual regulation of ciliary process AC by activating and inhibitory G-proteins.

Effects of topical ethacrynic acid ointment vs timolol on intraocular pressure in glaucomatous monkey eyes

OBJECTIVE

To evaluate the long-term effects of ethacrynic acid (ECA) ointment, compared with timolol maleate on intraocular pressure (IOP) in cynomolgus monkey eyes with argon laser-induced glaucoma.

METHODS

In a 5-day study, IOP was measured for 7 hours after once-daily topical applications of ECA ointment to four glaucomatous monkey eyes. For this study, ECA ointment was given in 0.5%, 1.0%, 1.5%, or 2.5% concentrations. In a separate 30-day study, IOP was measured after once-daily topical applications of ECA ointment in concentrations of 0.75% or 1.5%. The results were compared with IOP after the application of 0.5% timolol maleate administered twice daily on weekdays and once daily on weekends.

RESULTS

In the 5-day study, 2.5% ECA ointment had the greatest effect on lowering IOP, with a maximum reduction of 8.5 +/- 2.9 mm Hg (mean +/- SEM). A more pronounced reduction in IOP was observed on the fifth day of treatment for each of the four concentrations. In the 30-day study, 1.5% ECA ointment or 0.5% timolol maleate reduced IOP as much as 11.5 +/- 3.7 mmHg and 14.0 +/- 4.5 mmHg, respectively. With repetitive dosing, the effect on IOP after using 1.5% ECA ointment increased with time. Mild eyelid edema, conjunctival hyperemia, and discharge were observed in some eyes treated with the highest concentrations. One eye of four treated with 1.5% ECA ointment for 30 days developed a superficial corneal erosion in the 30-day study.

CONCLUSIONS

The ECA ointment reduced IOP in glaucomatous monkey eyes. This reduction was evident by the fifth day of treatment with all the concentrations tested. The reduction in IOP produced by once-daily treatment with 1.5% ECA ointment was comparable with that of 0.5% timolol maleate administered twice daily. Therefore, drugs in this class of compound may prove to be useful in glaucoma therapy.

The nerve of glaucoma!

Contemporary concepts of open angle glaucoma suggest that the current emphasis on reduction of elevated intraocular pressure could be augmented by other therapeutic approaches. In this article, we describe significant recent developments in the molecular and cellular biology and neuropharmacology of nerve damage that are likely, in coming years, to suggest new therapeutic approaches to the management of glaucoma. These developments may lead to the achievement of pharmacologic protection of the optic nerve from damage or possibly promotion of reversal of damage. We review selected studies of excitotoxins and N-methyl-D-aspartate receptor antagonists, Ca(2+)-induced damage and calcium channel blockers, the intracellular messenger nitric oxide and its perturbation, free-radical damage and scavengers, nerve regeneration, and growth factors. Several basic research questions are posed, answers to which may transform our concepts of glaucoma therapy.

Segmental analysis of computerized optic nerve head imaging

We evaluated a new method of segmental analysis of the array of numbers representing the depths at points on the optic nerve as generated by a computerized retinal topographic imaging system (the Humphrey Retinal Analyzer). We divided the observed optic nerve head into five rectangular areas, determined the mean depth of each of these areas, and compared them statistically. Intraobserver, interimage, and interobserver variability were calculated. The range of intraobserver variability (+/-SEM) was +/-1.2 to +/-12.0 mum, median 4.6 mum. Interimage variability ranged from +/-3.0 to +/-30.8 mum, median 14.7 mum. Interobserver variability, assessed by intraclass correlation coefficient and two-way analysis of variance, showed observer-to-observer variability was not significant as compared to subject variance and subject-observer interaction variance. Clinical studies further evaluating this segmental analysis of computerized data from the Heidelberg Retinal Tomograph are in progress.

Effect of oxymetazoline on aqueous humor dynamics and ocular blood flow in monkeys and rabbits

OBJECTIVE

To evaluate the ocular effects of oxymetazoline hydrochloride, an alpha 2 agonist, in cynomolgus monkeys and albino rabbits.

METHODS

Intraocular pressure was measured before and for 6 hours after application to glaucomatous monkey eyes. Outflow facility and aqueous flow rates were measured in normal monkey eyes. Uveoscleral outflow was measured in rabbit eyes. Ocular peak pulse volume was determined with the ocular blood flow system in normal and glaucomatous monkey eyes.

RESULTS

Single applications of ozymetazoline reduced (P < .001) intraocular pressure up to 6.0 +/- 1.0 mm Hg (mean +/- SEM). Enhancement of the ocular hypotensive effect was observed with 5-day twice-daily administration. Outflow facility was unaltered; aqueous flow rate was decreased (P < .001) by 39% in the treated eyes compared with baseline values; and uveoscleral outflow was increased (P < .005) by 56% in the treated eye. Peak pulse volume was unchanged.

CONCLUSION

Oxymetazoline reduces intraocular pressure by decreasing aqueous humor flow rates and increasing uveoscleral outflow. Oxymetazoline may have clinical potential as an ocular hypotensive drug.

Effects of Al3+ and Be2+ ions combined with NaF on ciliary process adenylyl cyclase activity and aqueous humor dynamics in the rabbit eye

PURPOSE

The activity of Al3+, Ga3+, and Be2+ ions in the presence of NaF to directly activate G-proteins was investigated by their potentiative effect on forskolin (FSK)-activated adenylyl cyclase in rabbit ciliary process membranes and their effects on aqueous humor dynamics in vivo.

METHODS

Adenylyl cyclase (AC) was determined by radiometric conversion of ATP to cAMP by the particulate fraction of rabbit ciliary processes. Intravitreal injections of sterile solutions of analytical grade salts were made into the center of the vitreous in a volume of 20 microliters. Intraocular pressure, aqueous humor flow, and uveoscleral outflow measurements were made by pneumatonometry, fluorophotometry, and fluorescein-dextran method, respectively. Outflow facility was determined by tonography in the intact eyes and by two-level constant pressure perfusion in cannulated eyes.

RESULTS

Both Al3+ (EC50, 40 mumol/l) and Be2+ (EC50, 11 mumol/l) in the presence of 0.5-2 mM NaF activated the stimulatory G-protein Gs. Ga3+ was ineffective and did not antagonize the activation by Al3+. Intravitreal injections of Al3+ (1 mumol/eye) or Be2+ (0.5 or 1 mumol/eye) had no significant intraocular pressure (IOP) effect, nor did 1.5 or 3 mumol/eye of NaF, but when either cation was injected together with NaF, IOP decreased by up to 40% for up to 140 hr. At the time of maximum IOP effect (72 hr) aqueous humor flow determined by fluorophotometry was decreased in BeCl2+ NaF-treated eyes by 40% relative to BeCl2-treated eyes; however, tonographic facility of outflow was unaffected. Uveoscleral flow was also decreased by 38% in BeCl2+ NaF treated eyes.

CONCLUSIONS

These findings support the hypothesis that Gs activation of ciliary process adenylyl cyclase decreases aqueous humor formation rate in rabbit eyes, and that activation of G-proteins mediates contraction of ciliary muscles causing a decrease of aqueous humor outflow via the uveoscleral route. The results suggest that G-proteins putatively involved in trabecular facility changes are less sensitive to activation by BeF3- than are other parameters of aqueous humor dynamics.

Polylysine stimulated protein phosphorylation in rabbit ciliary processes: casein kinase activities

Protein phosphorylation in response to polylysine was investigated in vitro in rabbit ciliary process homogenates by SDS-PAGE autoradiography. The degree of phosphorylation was greater in the soluble/cytoplasmic fraction than in the particulate fraction and was antagonized by heparin. Time and dose-dependent studies indicated several different kinetic patterns of phosphorylation/dephosphorylation among the approximately 15 significantly 32P-labeled bands found in each fraction. These results are consistent with phosphorylation of endogenous substrates by casein kinase II, and dephosphorylations by type I and type II phosphoprotein phosphatase enzymes. The presence of EGF receptors in ciliary processes was indicated by high affinity (kD < 0.5 nM) binding sites and by intraocular pressure and blood-aqueous barrier responses to injection of low doses of EGF (100 ng per eye). EGF did not stimulate protein phosphorylation in ciliary process homogenates in vitro. The results show that casein kinase II is a significant kinase activity in ciliary processes and may have a modulatory role on signal transduction proteins involved in cellular response to hormones.

Influence of treatment protocol on the long-term efficacy of argon laser trabeculoplasty

Forty-five phakic eyes of 36 patients with open-angle glaucoma and uncontrolled intraocular pressure despite maximally tolerated medication underwent initial argon laser trabeculoplasty (ALT) in 1981 and 1982 as part of a prospective, randomized study to evaluate the effectiveness of different treatment standards. Each eye had been randomly assigned to receive either 100 laser applications over 360 degrees of trabecular meshwork, 50 applications over 180 degrees , or 50 applications over 360 degrees in a single session. Further treatment in each group was based on clinical standards prevailing at the time. The long-term results were analyzed using Kaplan-Meier survival analyses. By 4 years after initial ALT, six of the 15 remaining eyes in group 1 (40%), one of 14 eyes in group 2 (7%), and two of 13 eyes in group 3 (15%) had undergone filtration surgery, and one eye in group 1 (7%), three eyes in group 2 (21%), and three eyes in group 3 (23%) had received further ALT. By 7 years after initial ALT, seven of the nine remaining eyes in group 1 (78%), one of 12 eyes in group 2 (8%), and four of 12 eyes in group 3 (33%) received filtration surgery, and two eyes in group 1 (22%), three eyes in group 2 (25%), and four eyes in group 3 (33%) had received further ALT. Kaplan-Meier survival curves predict the following probabilities of avoiding either repeat ALT or filtration surgery at 4 years after an initial ALT: group 1, 54 +/- 12%; group 2, 76 +/- 12%; and group 3, 62 +/- 11%. Our results suggest that performing 50 rather than 100 burns at initial ALT may significantly delay the need for additional surgical or repeat laser intervention.

Intraocular pressure reduction with PhXA34, a new prostaglandin analogue, in patients with ocular hypertension

In a randomized, double-masked, parallel study, one drop of 0.003% (1 microgram; n = 9) or 0.01% (3 micrograms; n = 10) PhXA34, a new phenyl-substituted prostaglandin F2 alpha analogue (13,14-dihydro-15[R,S]-17-phenyl-18,19,20-trinor-prostaglandin F2 alpha-1-isopropyl ester), or its vehicle (n = 10) was applied topically twice daily for 6 days to one eye in each of 29 patients with ocular hypertension. Compared with either baseline, contralateral, or vehicle control values, PhXA34 caused a significant (P < .001) dose-dependent reduction of intraocular pressure. The reduction lasted at least 12 hours after each drop and 24 to 48 hours after the last drop, with a significant (P < .0001) mean +/- SEM reduction of as much as 10 +/- 1 mm Hg (40%). Conjunctival hyperemia was not produced by 0.003% PhXA34, but was noted in some eyes treated with 0.01% PhXA34, and after repeated tonometry with either concentration. The prostaglandin analogue did not produce clinically obvious miosis, anterior chamber flare or cellular response, or any subjective adverse effects. PhXA34 is a potent, effective, and well-tolerated ocular hypotensive agent based on our results in this small, short-term study. Its potential as a new drug for glaucoma therapy warrants further investigation in long-term, larger studies.

Six week safety study of 2% MK-927 administered twice daily to ocular hypertensive volunteers

Ocular hypertensive patients were enrolled in a 6-week double-masked safety study of 2% MK-927 (27 patients), a topically active carbonic anhydrase inhibitor, administered bilaterally b.i.d.; 9 additional patients received 0.5% timolol as the control agent. Intraocular pressure (IOP) was measured weekly prior to a.m. drug administration; twelve hour diurnal curves were performed prestudy and at 3 and 6 weeks. The mean reduction of IOP prior to a.m. drug administration ranged from 1.2 +/- 4.4 mm Hg (SD) to 3.0 +/- 4.2 mm Hg with MK-927 and from 4.7 +/- 3.9 mm Hg to 8.8 +/- 0.6 mm Hg with timolol. Mean outflow facility measured tonographically prestudy and on days 33 to 42 four hours after a.m. drug administration was unchanged in both groups. Corneal sensitivity (Cochet-Bonnet), corneal thickness (ultrasound pachymetry), Schirmer tear testing, and extensive ophthalmologic and medical examinations, and hematologic studies were not substantially altered throughout the study. In this longest chronic administration study to date, MK-927 did not cause adverse ocular or systemic side effects.

Antioxidant and anticataractogenic effects of topical captopril in diquat-induced cataract in rabbits

1-[(2s)-3-Mercapto-2-methylpropionyl]-L-proline (captopril), an antihypertensive and free radical scavenger, protected the rabbit lens from peroxidative and oxidative damage induced by 1 mM diquat in vitro. To evaluate the anticataract efficacy of captopril, an experimental group of five rabbits was treated with topical captopril (1% in 0.15 M NaCl, w/v), and 50 microliters was instilled onto both eyes four times a day for a total of 8 weeks. Following the same procedure, the eyes of five rabbits were treated with topical 0.15 M NaCl as a control for captopril treatment. At the end of the first week of treatment, a single intravitreal dose of 120 nmole diquat in 30 microliters of 0.15 M NaCl was injected into the right eye of each rabbit of both the groups. As a control for intravitreal diquat injection, the left eye of all the rabbits were injected with the diluent, 30 microliters per eye. The intravitreal diquat or its diluent injection was only for one time. From slit-lamp biomicroscopic observation of the diquat-injected right eyes, the anticataract effect of captopril in the treatment group was indicated by the finding that in four of five rabbits the cataract did not advance; whereas in four of five rabbits treated with the diluent the cataract progressed to grade 3. The lenses in the diluent-injected control left eyes of the rabbits treated with the captopril or diluent were normal. However, since the number of animals used for the in vivo studies was few, further confirmation of the anticataract effect of captopril is necessary. In diquat-injected right eyes of animals treated with captopril, the integrated rate of O2- production was about 50% less (p less than .001) in the aqueous humor, vitreous humor, and lens, compared with O2-, 33.49 +/- 2.26 microM (mean +/- SEM) in the aqueous humor, 17.12 +/- 0.75 microM in the vitreous humor, and 31.44 +/- 1.29 nmole/g wet weight in the lens of the diquat-injected right eyes treated with the diluent. Similar significant (p less than .01) differences in the production of .OH and H2O2 in eye tissues were also observed.(ABSTRACT TRUNCATED AT 400 WORDS)

A clinical trial of metipranolol, a noncardioselective beta-adrenergic antagonist, in ocular hypertension

In randomized, double-masked fashion, 24 volunteers with ocular hypertension received 0.3% or 0.6% metipranolol, a noncardioselective beta blocker; or placebo twice daily to both eyes for six weeks. Intraocular pressure (mean +/- SEM) was reduced (P = .01) in the metipranolol-treated patients (baseline measurement, 25.9 +/- 0.5 mm Hg to 18.1 +/- 1.2 mm Hg at six weeks, 0.6% concentration; baseline measurement, 27.1 +/- 0.4 mm Hg to 21.6 +/- 1.5 mm Hg at six weeks, 0.3% concentration). Intraocular pressure was not markedly changed in placebo-treated patients. Outflow facility was unaltered two hours after instillation of metipranolol at study week 2 compared to baseline measurement. Aqueous humor flow rates were reduced (P = .02) 20% after 0.6% or 0.3% metipranolol instillation and were unchanged after placebo administration compared to baseline measurement. Mean systolic blood pressure, diastolic blood pressure, and pulse rate were not markedly altered. Metipranolol reduces intraocular pressure by suppressing aqueous humor flow rates.

MK-507 (L-671,152), a topically active carbonic anhydrase inhibitor, reduces aqueous humor production in monkeys

An investigation was carried out to determine the mechanism by which MK-507 (L-671,152), a water-soluble inhibitor of human carbonic anhydrase II in vitro, reduces intraocular pressure when applied topically to monkey eyes. Intraocular pressure, tonographically measured outflow facility, and fluorophotometrically determined aqueous humor flow were measured before and after therapy in eight normal cynomolgus monkeys. Fifty microliters of 2% MK-507 was instilled in one eye and diluent in the contralateral eye. Baseline values for intraocular pressure, outflow facility, and aqueous humor flow were similar in the drug-treated and diluent-treated control eyes. After therapy, intraocular pressure was significantly (P less than .05) reduced from 1 to 7 hours (eg, 14.0 +/- 1.0 and 15.9 +/- 0.9 mm Hg [mean +/- SEM], treated and control eyes, respectively, at 3 hours). Outflow facility was not significantly (P greater than .40) changed at 3 hours, and aqueous humor flow measured over 5 hours was significantly (P less than .05) reduced (38%) in treated (0.9 +/- 0.1 microL/min) as compared with control eyes (1.5 +/- 0.1 microL/min). The results suggest that MK-507 reduces intraocular pressure by decreasing aqueous humor production.

Selective alpha 2-adrenergic agonists B-HT 920 and UK14304-18. Effects on aqueous humor dynamics in monkeys

Selective alpha 2-adrenergic agonists UK14304-18 and B-HT 920 were evaluated in the eyes of cynomolgus monkeys. In normal monkeys, unilateral topical application of 0.3%, 0.5%, or 1% UK14304-18 or B-HT 920 reduced (P less than .05) intraocular pressure bilaterally up to 9.9 +/- 1.2 mm Hg (mean +/- SEM) and 8.4 +/- 1.4 mm Hg in treated and contralateral eyes, respectively. Five-day twice-daily 0.5% UK14304-18 administration reduced (P less than .05) intraocular pressure up to 49% in eight glaucomatous monkeys. In eight normal monkeys, 0.5% B-HT 920 and 0.5% UK14304-18 produced no alterations in outflow facility. Following unilateral application of 0.5% B-HT 920 or 0.5% UK14304-18, fluorophotometrically measured aqueous humor production was reduced (P less than .05) bilaterally up to 67% compared with baseline values. Also, 0.5% UK14304-18 reduced (P less than .025) systolic and diastolic blood pressure. UK14304-18 and B-HT 920 seem to reduce intraocular pressure by decreasing aqueous production. They are potential new agents for the treatment of glaucoma.

Additivity of prostaglandin F2 alpha-1-isopropyl ester to timolol in glaucoma patients

The effect on intraocular pressure (IOP) of adding prostaglandin F2 alpha-1-isopropyl ester (PGF2 alpha-IE) to timolol was studied in 21 eyes of 13 patients with newly diagnosed primary open-angle glaucoma that was inadequately controlled with timolol alone. After at least 2 weeks of twice daily timolol 0.5% therapy, PGF2 alpha-IE, 0.5 microgram in 30 microliters, was topically applied twice daily at 8 AM and 8 PM, 5 minutes before each timolol dose, for 7 days. Intraocular pressures were measured before timolol treatment, and at 8 AM, 8:30 AM, 12 PM, 2 PM, and 4 PM on the day before the addition of PGF2 alpha-IE, and on day 1 and on day 7 of combined therapy. Mean IOP was 39 +/- 2 mmHg (+/- standard error) before timolol therapy and 31 +/- 2 mmHg after at least 2 weeks of treatment with timolol alone. A significant (P = 0.004) further reduction of IOP was first observed 4 hours after the first dose of PGF2 alpha-IE, which was maintained throughout the duration of combined therapy. During the last day of combined treatment and at 12 hours after the final dose, IOP was reduced a mean of 6 to 9 mmHg (mean, 9.0 +/- 1.5 mmHg at 12 hours) below baseline values obtained with timolol alone. These results indicate that adding PGF2 alpha-IE in patients treated with timolol causes a further reduction of IOP that may prove to be clinically useful in glaucoma therapy.

Free radical enhancer xenobiotic is an inducer of cataract in rabbit

Free radical enhancers, diquat, paraquat, plumbagin and juglone were used to study the oxy radical-induced damage to the rabbit lens in vitro and in vivo. Each compound caused a 6-8 fold increase in malondialdehyde (MDA) and a 30-55% decrease in reduced glutathione of the lens in vitro. These peroxidative and oxidative changes were potentiated in the presence of 100% O2, abolished by N2 and prevented by desferal-Mn (III) (DF-Mn) or liposomal superoxide dismutase (LSOD) indicating the involvement of O2-. Diquat injected intravitreally as a single dose (300 nmole in 30 microliters of isotonic saline) in the right eye of a 5-wk-old Dutch belted rabbit, induced early cataract after 24-72 h. The lens of the contralateral control eye injected with isotonic saline had no change. In the right eye, O2-. and OH. productions were significantly (P less than 0.01) higher; O2-. was about 16 fold higher in the aqueous humor and vitreous humor, and 5 fold in the lens and retina, and OH. was 35 fold higher in the aqueous humor, 2 fold in vitreous humor and 5 fold in the lens and retina as compared to the respective tissues of the control eye. Enhanced lipid peroxidation in the lens was apparent from the higher levels of MDA and formation of aminophospholipid.MDA Schiff-base conjugates. We propose that cyclic oxidation-reduction of xenobiotics coupled to the endogenous redox systems in the eye, could generate oxy radicals in excessive amounts, triggering cataractogenesis.

Effects of prostaglandins F2 alpha, A2, and their esters in glaucomatous monkey eyes

The effect of prostaglandin (PG) F2 alpha-isopropyl ester (IE), PGA2, or PGA2-IE on intraocular pressure (IOP) was tested in eight cynomolgus monkey eyes with argon laser-induced glaucoma. Dose-response testing and baseline IOP measurements were done. For multiple dose testing, 5 micrograms in 25 microliters (0.02%) of each PG was topically applied twice daily for 5 days. The IOP was measured at 30- or 60-minute intervals for 6 hours after the morning dose each day. A significant (P less than 0.05) reduction of IOP peaked at 5-9 mm Hg below baseline values on the 5th day of treatment for each PG. The ocular hypotensive effect of these PGs progressively became more pronounced during the course of twice-daily dosing, with a significant reduction maintained at least 17 hours after some doses. No more than trace aqueous flare and no cells were observed in any eye during the course of treatment. These findings demonstrate that PGs other than F2 alpha are potent ocular hypotensive agents in primates.

MK-927, a topical carbonic anhydrase inhibitor. Dose response and reproducibility

We investigated the dose-response and reproducibility of the intraocular pressure-lowering effect of MK-927 in ocular hypertensive patients. Patients were enrolled until at least 8 "marked responders" (peak reduction in intraocular pressure comparing the MK-927-treated eye with the placebo-treated eye greater than or equal to 6 mm Hg) and 7 "mild responders" (peak reduction in intraocular pressure comparing the MK-927-treated eye with the placebo-treated eye less than or equal to 3 mm Hg) were identified. In part A, 27 patients received one drop of 2% MK-927 in one eye (baseline mean +/- SEM intraocular pressure, 28.0 +/- 1.0 mm Hg) and placebo in the contralateral eye. Intraocular pressure was measured at baseline and 1, 2, 3, 4, and 6 hours. Maximum reduction in intraocular pressure was 4.0 +/- 0.8 mm Hg at 3 hours, with a duration of 4 hours. Ten patients were identified as marked responders and 7 as mild responders. In part B, 8 of the marked responders entered a four-period crossover study and received 2%, 0.5%, and 0.125% MK-927 and placebo in the same treated eye as in part A, and placebo in the contralateral eye. The 7 mild responders in part C received 2% MK-927 in a similar fashion as in part A. MK-927 in concentrations of 0.125% and 0.5% had little or no effect on intraocular pressure in patients with a marked response to 2% MK-927. Within-patient variability in peak response to single doses of 2% MK-927 was substantial (coefficient of variation of 0.3 and 0.5 for marked responder and mild responder groups, respectively.

The ocular hypotensive effect of the topical carbonic anhydrase inhibitor L-671,152 in glaucomatous monkeys

L-671,152, a new potent water-soluble inhibitor of human carbonic anhydrase II in vitro, was applied topically to cynomolgus monkey eyes in which glaucoma had been produced by argon laser photocoagulation of the trabecular mesh-work. Intraocular pressure was measured at 0 hours, 0.5 hours, and hourly for 8 hours in eight eyes for 2 baseline days, 1 day receiving the vehicle and 5 days receiving therapy with 2% L-671,152 twice a day, after initial single-dose trials of various concentrations. Intraocular pressure was not significantly different comparing baseline and vehicle-treated days. Significant intraocular pressure reductions occurred from 1 to 8 hours after the first dose, and lasted for at least 16 hours after the second dose. The reduction in intraocular pressure became more pronounced from day 1 to day 5 at each time interval. The mean (+/- SEM) maximum reduction in intraocular pressure was 7.8 +/- 2.1 mm Hg on day 1 and 10.1 +/- 2.4 mm Hg on day 5 at 3 hours after administration, comparing the intraocular pressure in drug-treated and vehicle-treated eyes. L-671,152 has a longer duration of action than does previously studied MK-927 in glaucomatous monkeys. It appears to have great clinical potential.

The effect of MK-927, a topical carbonic anhydrase inhibitor, on IOP in glaucomatous monkeys

MK-927 is a water soluble, potent inhibitor of human carbonic anhydrase (CA) II in vitro. Topical administration of MK-927 reduces intraocular pressure (IOP) in rabbits. Elevated IOP was produced in cynomolgus monkey eyes by argon laser photocoagulation of the trabecular meshwork. IOP was measured at 0 hr, 0.5 hr and hourly for 8 hrs in 8 eyes for two baseline days, one day on vehicle and five days of therapy with 2% MK-927 b.i.d., after initial single-dose trials of various concentrations. IOP was not significantly different comparing baseline and vehicle treated days. Significant (p less than 0.05) reductions of IOP occurred for five days lasting at least 8 hrs after each dosing. At 3 hrs after treatment with vehicle the IOP was 31.6 +/- 3.4 (SE) mm Hg. Maximum reduction of IOP occurred at 3 hrs after application of MK-927, the IOP decreasing from day 1 (19.9 +/- 1.0 mm Hg) to day 5 (16.5 +/- 1.6 mm Hg). MK-927 appears to have great clinical potential.

Maintained reduction of intraocular pressure by prostaglandin F2 alpha-1-isopropyl ester applied in multiple doses in ocular hypertensive and glaucoma patients

In a randomized, double-masked, placebo-controlled study, 0.25 microgram (n = 11) or 0.5 microgram (n = 13) of prostaglandin F2 alpha-1-isopropyl ester (PGF2 alpha-IE) was applied topically twice daily for 8 days to one eye of ocular hypertensive or chronic open-angle glaucoma patients. Compared with contralateral, vehicle-treated eyes, PGF2 alpha-IE significantly (P less than 0.05) reduced intraocular pressure (IOP), beginning 4 hours after the first 0.5-microgram dose and lasting at least 12 hours after the fourteenth dose, with a significant (P less than 0.005) mean reduction of 4 to 6 mmHg maintained throughout the last day of therapy with either dose. A contralateral effect was not observed. Mean tonographic outflow facility was significantly (P less than 0.05) higher in PG-treated compared with vehicle-treated eyes (0.17 +/- 0.02 versus 0.12 +/- 0.01 microliter/minute/mmHg, respectively; +/- standard error of the mean) for the 0.5 microgram dose. Conjunctival hyperemia reached a maximum at 30 to 60 minutes after PGF2 alpha-IE application. Some patients reported mild irritation lasting several minutes after some doses. Visual acuity, accommodative amplitude, pupillary diameter, aqueous humor flare, anterior chamber cellular response, Schirmer's test, pulse rate, and blood pressure were not significantly altered. Our findings show that PGF2 alpha-IE is a potent ocular hypotensive agent and a promising drug for glaucoma therapy.