Effect of SPP 635, a renin inhibitor, on intraocular pressure in glaucomatous monkey eyes

The effect of topical application of SPP 635, a renin inhibitor, on intraocular pressure (IOP) was evaluated in the eyes of monkeys with laser induced unilateral glaucoma. A multiple-dose study was performed in 8 glaucomatous monkey eyes with 3 concentrations of SPP 635, 0.2%, 0.3% and 0.4%. IOP was measured hourly for 6 h on each day of the study beginning at 9:30 a.m. Following one baseline day (untreated) and one vehicle-treated day (50 μl drop of vehicle to the glaucomatous eye at 9:30 a.m.), a 50 μl drop (25 μl × 2) of SPP 635, 0.2%, 0.3% or 0.4%, was topically applied to the glaucomatous eye at 9:30 a.m. and 3:30 p.m. for 5 consecutive days. Twice daily administration of each of the 3 concentrations of SPP 635 for 5 days significantly (p < 0.05) reduced IOP. The maximum reduction in IOP occurred 3 or 4 h after morning dosing and was 4.3 ± 0.8 (mean ± SEM) mmHg (14%) for 0.2% SPP 635, 5.3 ± 1.0 mmHg, (19%) for 0.3% SPP 635, and 8.0 ± 1.3 mmHg (25%) for 0.4% SPP 635. The longest duration of IOP reduction was for 6 h with 0.2% or 0.3% SPP 635, and was for at least 18 h with 0.4% concentration. Compared to 0.2% or 0.3% concentrations, 0.4% SPP 635 produced a greater (p < 0.05) and longer duration of IOP reduction (18 vs. 6 h). Mild conjunctival discharge appeared in 2 of 8 eyes, and hyperemia appeared in 2 eyes with the 0.3% and 0.4% concentrations on treatment days 3 and 5. Topically applied SPP 635, a new renin inhibitor, reduces IOP in glaucomatous monkeys in a dose-dependent manner. Renin inhibitors, are a novel class of compounds which may have potential for the treatment of glaucoma.

Gene expression changes in steroid-induced IOP elevation in bovine trabecular meshwork

PURPOSE

To determine whether gene expression changes occur in the trabecular meshwork (TM) of cow eyes with steroid-induced intraocular pressure (IOP) elevation.

METHODS

Adult female Braford cows (n = 4) were subjected to uniocular prednisolone acetate treatment for 6 weeks. IOP was monitored with an applanation tonometer. At the conclusion of the experiment, animals were euthanized, eyes were enucleated, and the TM was dissected and stored in an aqueous nontoxic tissue storage reagent. RNA was extracted and subjected to microarray analysis using commercial oligonucleotide bovine arrays. Some of the genes differentially expressed between control and experimental eyes were confirmed by quantitative RT-PCR and some of the respective proteins were studied by immunoblotting.

RESULTS

IOP began to increase after 3 weeks of treatment, reaching a peak 2 weeks later. IOP differences between corticosteroid-treated and fellow control eyes were 6 ± 1 mm Hg (mean ± SD) at the conclusion of the study. Microarray analysis revealed that expression of 258 genes was upregulated, whereas expression of 187 genes was downregulated in the TM of eyes with steroid-induced IOP elevation. Genes identified to be differentially expressed include genes coding for cytoskeletal proteins, enzymes, growth and transcription factors, as well as extracellular matrix proteins and immune response proteins. A number of relevant gene networks were detected by bioinformatic analysis.

CONCLUSIONS

Steroid-induced IOP elevation alters gene expression in the bovine TM. Identification of genes with changing expression in this model of open-angle glaucoma may help elucidate the primary changes occurring at the molecular level in this condition.

Effect of SPP 301, an endothelin antagonist, on intraocular pressure in glaucomatous monkey eyes

PURPOSE

To evaluate the effect of topical application of avosentan (SPP 301), endothelin receptor type A antagonist, on intraocular pressure (IOP) in monkey eyes with laser-induced unilateral glaucoma.

MATERIALS AND METHODS

A multiple-dose study was performed in eight glaucomatous monkey eyes that were topically treated with SPP 301 by applying a 50 µl drop (25 µl × 2) at 9:30 a.m. and 3:30 p.m. for 5 consecutive days at three concentrations (0.003%, 0.03%, or 0.3%). IOP was measured hourly for 6 hrs on each day of the study beginning at 9:30 a.m. for one baseline day, one vehicle-treated day, and treatment days 1, 3, and 5.

RESULTS

Twice daily administration of each of the three concentrations of SPP 301 for 5 days significantly (p < 0.05) reduced IOP. The maximum reduction in IOP occurred 2 or 3 hrs after morning dosing and was 1.8 ± 0.8 (mean ± SEM) mmHg (6%) for 0.003% SPP 301, 4.1 ± 0.7 mmHg (13%) for 0.03% SPP 301, and 7.1 ± 1.3 mmHg (21%) for 0.3% SPP 301. The longest duration of IOP reduction was for 2 hrs with 0.003% SPP 301, and was for at least 6 hrs with 0.03% and 0.3% concentrations. Compared to 0.03% or 0.003% concentrations, 0.3% SPP 301 produced a greater (p < 0.05) IOP reduction. IOP was reduced in fellow untreated normal eyes 2 hr after morning dosing with 0.3% SPP 301, maximum reduction in IOP (11%) occurred on day 1. Of the eyes treated with 0.3% SPP 301, one eye demonstrated mild conjunctival discharge and one eye was closed for 5 min after dosing.

CONCLUSION

Topically applied SPP 301, an endothelin antagonist, reduced IOP in glaucomatous monkey eyes in a dose-dependent manner. Endothelin antagonists, a novel class of compound, may have potential for the treatment of glaucoma.

Suppression of corticosteroid-induced ocular hypertension in sheep by anecortave

OBJECTIVE

To confirm the ocular hypotensive effects of anecortave acetate on an ovine model for steroid-induced ocular hypertension. Eyes of normal sheep exhibit a robust steroid-induced ocular hypertensive response. Recent observations in an uncontrolled, interventional case series indicated that anecortave elicited hypotensive effects when administered as a sub-Tenon depot in the eyes of a small sample of patients with glaucoma.

METHODS

Intraocular pressure (IOP) was monitored by Perkins applanation tonometry in 16 normal sheep receiving topically administered prednisolone acetate, 0.5%, in both eyes, 3 times daily, a protocol that doubled IOP within 12 days. Half of the sheep had received a unilateral sub-Tenon injection of anecortave in 1 eye prior to the initiation of the bilateral prednisolone instillations, while the 8 remaining sheep received the unilateral anecortave sub-Tenon depot after the IOP was maximally elevated by the prednisolone instillations.

RESULTS

In these 2 sets of experiments, the presence of the anecortave depot suppressed the steroid-induced IOP elevation and reverted the elevated IOP to baseline levels. Measurements of aqueous outflow facility indicated that eyes treated with prednisolone plus anecortave exhibited a 5.8-fold higher outflow facility than the fellow eyes solely exposed to prednisolone, indicating that anecortave prevented the increase in outflow resistance produced by the corticosteroid.

CONCLUSION

Elucidation of the mechanisms of action of anecortave in animal models may prove relevant to the design of novel interventions for the management of primary open-angle glaucoma.

Morphologic changes in the outflow pathways of bovine eyes treated with corticosteroids

PURPOSE

To analyze morphologic changes in the trabecular meshwork (TM) of bovine eyes treated with topical prednisolone and exhibiting elevated intraocular pressure for 4 weeks.

METHODS

The TM of four adult Braford cow eyes treated with 0.5% prednisolone eye drops three times daily for 7 weeks and their contralateral eyes treated with artificial tear preparation and that of two adult untreated Braford cows and untreated young calves eyes were analyzed with light and electron microscopy. Increased extracellular matrix (ECM) under the outflow loops was evaluated quantitatively. Additionally, deparaffinized tissue of treated eyes was labeled with an antibody against type VI collagen for immunocytochemistry.

RESULTS

In steroid-treated eyes ECM (plaques) accumulated under the endothelium of the inner wall of the outflow loops. On electron microscopy, this material contained fine fibrils that labeled for type VI collagen. Plaques were also seen in the contralateral controls of the treated animals but here they were significantly less in amount. In the untreated Braford controls and in untreated calf eyes, plaques were nearly absent. In the TM cells of the treated eyes there was a loss of glycogen from the cytoplasm and an increase in basement membrane-like material. These changes were not seen in contralateral eyes or eyes of untreated animals.

CONCLUSIONS

Accumulations of ECM in the treated eyes resembled morphologic changes in human eyes with primary open-angle glaucoma and steroid-induced glaucoma. This animal model, therefore, provides a good tool in which to further study the pathogenesis of TM changes in glaucoma.

Penetrability of interleukin-1beta and its effect on the concentration of tumor necrosis factor-alpha and interleukin-6 in the aqueous humor of rabbits treated with interleukin-1beta

BACKGROUND

Interleukin (IL)-1beta may effectively decrease introcular pressure (IOP) when administered by subconjunctival injection in normal rabbit. However, IL-1beta is a large molecular agent and an inflammation factor. The aim of this study was to evaluate the penetrability of IL-1beta, and the concentrations of both tumor necrosis factor (TNF)-alpha and IL-6 in the aqueous humor of normal rabbits treated with IL-1beta.

METHODS

A total of 170 rabbits were used in the study and were assigned to several different treatment groups as follows: 125 of the rabbits were assigned to two groups. In one group, 33 rabbits were injected subconjunctivally with IL-1beta and 39 were injected with saline alone. In the other group, 27 rabbits were given eye drops containing IL-1beta (400 ng/ml) and 26 were given saline alone. Aqueous humor (AH) was drawn and the concentration of IL-1beta within the fluid measured. The IOP was measured in another six rabbits after administration of eye drops containing IL-1beta (400 ng/ml). A further 20 rabbits were assigned to 3 groups as follows: eight untreated normal controls; six injected subconjunctivally with IL-1beta; and six injected subconjunctivally with saline alone. AH was drawn and the concentration of TNF-alpha in the fluid was measured. Another 19 rabbits were assigned to 3 groups as follows: seven untreated normal controls; and six injected subconjunctivally with IL-1beta; and six injected subconjunctivally with saline alone. AH was drawn and the concentration of IL-6 in the fluid measured. Measurement of cytokine concentration was by radio-immunoassay in all cases.

RESULTS

The IL-1beta concentration in the AH was higher in those animals in which it had been administered subconjunctivally (P < 0.01). The IL-1beta concentration in the AH of the animals given eye drops was almost the same as that in the controls (P > 0.05). The administration of IL-1beta in the form of eye drops had little effect upon IOP reduction. Lower TNF-alpha concentrations were seen in the AH after the subconjunctival administration of IL-1beta, but the concentration of IL-6 was the same as in the normal controls.

CONCLUSIONS

IL-1beta shows good corneal penetrability after subconjunctival injection into normal rabbit eyes. The IOP reduction induced by IL-1beta is unlikely be associated with an inflammatory response.

Steroid-induced ocular hypertension in normal sheep

PURPOSE

To determine whether the ovine eye develops elevation of intraocular pressure (IOP) in response to corticosteroid applied topically.

METHODS

IOP was monitored by Perkins applanation tonometry in a group of 18 sheep receiving topically administered 0.5% prednisolone acetate in one eye (experimental), three times daily, for a period of 3 or four 4 weeks after the establishment of baseline IOP values. Perkins readings were converted to actual mm Hg using a calibration curve derived from in vivo manometric measurements. IOP was monitored for an additional 1 to 3 weeks after discontinuation of corticosteroid treatment.

RESULTS

Baseline IOP in normal sheep was 10.6+/-1.4 mm Hg (mean +/- SD; n=36 eyes). The IOP of the experimental eyes began to increase after 1 week of prednisolone treatment in all sheep and reached a peak 1 week later (27.5 mm Hg experimental vs. 11.7 mm Hg fellow, control eye; P<0.001). After the discontinuation of corticosteroid instillation, the IOP of the treated eyes declined to the baseline values over the course of 1 to 3 weeks.

CONCLUSIONS

Ovine eyes exhibit a robust steroid-induced ocular hypertensive response, with 100% occurrence in this trial. The mechanisms of steroid-induced glaucoma may be related to those involved in primary open-angle glaucoma and could provide insight into primary open-angle and clues to its treatment.

Effects of MISA A on actin cytoskeleton of cultured HTM cells and intraocular pressure of rats and glaucomatous monkeys

PURPOSE

To determine the effects of misakinolide (MISA) A, which leads to the disassembly of actin filaments, on the actin cytoskeleton of cultured human trabecular meshwork (HTM) cells and on intraocular pressure (IOP) in living rats and monkeys.

METHODS

Cultured HTM cells were treated with MISA A, and the changes in the actin cytoskeleton were determined by immunofluorescence microscopy. Elevated IOP was induced in cynomolgus monkeys by unilateral laser photocoagulation of the trabecular meshwork (TM). The IOP response after topical administration of MISA A was determined in normotensive rats (Tonopen) and glaucomatous monkeys (pneumotonometer and Tonopen) at 0.5, 1, 2, 3, 4, 5, and 6 hr.

RESULTS

MISA A caused dose- and time-dependent disruption of actin stress fibers in cultured HTM cells. Actin microfilaments and vinculin containing focal contacts deteriorated after 2 hr, 30 and 10 min of incubation with 5 nM, 10 nM, and 25 nM MISA A, respectively. Recovery was also dose- and time-dependent. The actin-disrupting effects were not reversible when the cells were incubated with MISA A at a low dose (10 nM) for 24 hr or a high dose (25 nM) for 30 min. Topical administration of MISA A significantly decreased IOP in rats by 5.8 +/- 0.5 (mean +/- SEM) (p < 0.05) Tonopen rat units. In monkeys, IOP was decreased by 3.8 +/- 0.5 mmHg (p < 0.001) in the normotensive eye and by 9.2 +/- 1.2 mmHg (p < 0.001) in the glaucomatous eye.

CONCLUSIONS

MISA A greatly altered the actin cytoskeleton and cellular adhesions and reduced IOP, suggesting that MISA A may be a useful antiglaucoma strategy.

Effect of 15-keto latanoprost on intraocular pressure and aqueous humor dynamics in monkey eyes

PURPOSE

To compare the ocular hypotensive effects of 15-keto latanoprost (KL) with the commercial preparation of latanoprost (Xalatan; Pfizer, New York, NY) in monkey eyes with laser-induced unilateral glaucoma and to evaluate the effects of topical 0.005% KL on aqueous humor dynamics in normal monkey eyes.

METHODS

Intraocular pressure (IOP) was measured hourly for 6 hours beginning at 9:30 AM on day 1 (untreated baseline); day 2 (vehicle only); and treatment days 1, 3, and 5 (topical, 30 microL of study drug) in the glaucomatous eyes of four to eight monkeys with unilateral laser-induced glaucoma. KL concentrations of 0.0001%, 0.001%, and 0.01% and latanoprost at 0.005% were studied separately, with a minimum washout period of 2 weeks between studies. Tonographic outflow facility (C) and fluorophotometric aqueous humor flow rates (F) were measured in nine normal monkeys before and after a single topical dose of 0.005% KL in one eye, with a vehicle-only control in the fellow eye.

RESULTS

When applied once daily to glaucomatous monkey eyes, all three concentrations of KL and a 0.005% concentration of latanoprost produced significant (P < 0.05) reductions in IOP, with the maximum reduction on treatment day 5, regardless of the drug or concentration studied. The maximum reduction (P < 0.001) from vehicle-only baseline IOP was (mean +/- SEM) 3.0 +/- 0.3 mm Hg (9%) for 0.0001% KL, 7.6 +/- 0.6 mm Hg (23%) for 0.001% KL, 6.3 +/- 0.4 mm Hg (18%) for 0.01% KL, and 6.6 +/- 0.6 mm Hg (20%) for 0.005% latanoprost. After application of a single dose of 0.005% KL in nine normal monkey eyes, neither C nor F was altered (P > 0.80) when compared with untreated baseline values or vehicle-treated control eyes.

CONCLUSIONS

The reduction in IOP produced by 0.001% KL was equivalent to, and at some measured time points, greater than the effect produced by 0.005% latanoprost. The IOP reduction by KL in normal monkeys appeared to have no effect on aqueous humor production or tonographic outflow facility and may thus indicate a drug-induced increase in uveoscleral outflow.

Topographic and Morphologic Analyses of Retinal Ganglion Cell Loss in Old DBA/2NNia Mice

PURPOSE

To evaluate the relationship between retinal ganglion cell (RGC) size, density distribution, and survival in senescent DBA2/NNia mice that develop pigmentary glaucoma. To evaluate the validity of nearest neighbor distance (NND), a measure of focal density for surviving RGCs in the retina, as a method to quantify RGC loss in mice.

METHODS

Fifteen-month-old DBA2/NNia mice were labeled retrogradely with fluorogold. Retinas were flat mounted and imaged in their entirety using an epifluorescence microscope with a motorized stage. Digital maps of the retinal wholemounts were constructed to automatically count and establish spatial coordinates for RGCs over the entire retina. RGC size and NND were determined from these maps.

RESULTS

RGC counts in the group of 15-month-old DBA/2NNia animals ranged from 22,330 to 92,157 cells per retina. Mean RGC cell size per retina ranged from 22.35 to 35.64 microm2 and correlated linearly with total RGC counts. NND distribution histograms were compared for retinas with variable degrees of RGC loss. The distribution of NNDs in each retina was skewed toward larger distance values in more affected retinas. In partially damaged retinas, areas with severe pathology coincided with areas of maximal loss of large RGCs, and areas of preserved RGCs correlated with larger cell sizes.

CONCLUSIONS

Damaged retinas have a smaller mean cell size, indicating preferential loss of larger RGCs or size reduction of surviving cells. NND analysis of the RGC population in a retina is a useful measure of glaucomatous RGC loss. The skewed NND distribution of surviving RGCs and the finding that RGC loss correlates with a shift/amplitude change in the mode of the histogram and its tail suggests two different patterns of RGC loss possibly attributable to different pathologic processes in glaucomatous DBA/2 mice.

Complement Component 1Q (C1Q) Upregulation in Retina of Murine, Primate, and Human Glaucomatous Eyes

PURPOSE

Complement has been implicated in the pathogenesis of neurodegenerative diseases. The purpose of this study was to investigate whether complement activation is part of the pathogenesis of retinal ganglion cell (RGC) loss in glaucoma.

METHODS

mRNA and protein was extracted from the retina and brain of DBA/2 and C57/BL6 mice and subjected to RT-PCR and immunoblot analysis, respectively. In addition, eyes from the same mouse strains were subjected to immunohistochemistry with antibodies specific to complement component 1q (C1q). Eyes from monkeys with unilateral experimental glaucoma were also subjected to immunohistochemical analysis, as were eyes from human subjects with or without glaucoma.

RESULTS

C1q mRNA and C1q protein were found to be upregulated in the retina of glaucomatous DBA/2 mice. Upregulation of C1q preceded the time of extensive RGC death and increased with increasing age to 15 months in the retina, but not in the brain. No age-related C1q upregulation was detected in the reference mouse strain (C57BL/6), which develops significant nonglaucomatous RGC loss toward the end of the same time frame. C1q upregulation was also detected in laser-induced glaucomatous monkey eyes and in some (but not all) eyes of patients with glaucoma. C1q upregulation was localized to the Müller cells within the retina and in the area of the inner limiting membrane.

CONCLUSIONS

Complement expression is upregulated in the retina of two commonly used glaucoma models (in the DBA/2 mouse and the monkey) and in some human glaucomatous eyes. The timing of this upregulation suggests that complement activation plays a significant role in the pathogenesis of glaucoma.

Characterization of retinal damage in the episcleral vein cauterization rat glaucoma model

Episcleral vein cauterization (EVC) is used in rats to generate a glaucoma model with high intraocular pressure (IOP). The long-term retinal damage in this glaucoma model, however, has not been accurately quantified. We report the location and amount of retinal ganglion cell (RGC) damage caused by (EVC) induced IOP elevation in two rat strains. IOP was raised in one eye of Wistar (N = 5) and Brown-Norway(B-N)(N = 7) rats by EVC and monitored monthly until IOP in contralateral eyes equalized at 5 months post-surgery. Animals were maintained for 3.5-4.5 additional months. B-N rats (N = 7) that had no EVC served as controls for this strain. Scotopic flash ERGs were recorded at baseline and just prior to euthanasia. Automated counts of all retrogradely labeled RGCs in retinal flat-mounts were determined and compared between contralateral eyes. RGC density maps were constructed and RGC size distribution was determined. Oscillatory potentials in the group of eyes which had elevated IOP were decreased at the time of euthanasia, when IOP had returned to normal. The group of normal B-N rats had similar RGC counts between contralateral eyes. In the experimental group the mean number of RGCs was not significantly different between control and experimental eyes, but 1 of 5 Wistar and 2 of 7 B-N experimental eyes had at least 30% fewer RGCs than contralateral control eyes. Total retinal area in B-N experimental eyes was higher compared to contralateral eyes. Cumulative IOP exposure of the experimental eyes was modestly correlated with RGC loss while oscillatory potentials appeared to be inversely related to RGC loss. In retinas with extensive (> 30% RGC loss) but not complete damage, smaller cells were preserved better than larger ones. The above results indicate that RGC loss in both Wistar and B-N strains is variable after a prolonged elevation of IOP via EVC. Such variability despite equivalent IOP levels and ERG abnormalities, suggests unknown factors that can protect IOP-stressed RGCs. Identification and enhancement of such factors could prove useful for glaucoma therapy.

Effect of CS-088, an angiotensin AT1 receptor antagonist, on intraocular pressure in glaucomatous monkey eyes

To evaluate the effect of CS-088, an angiotensin AT1 receptor antagonist, on intraocular pressure (IOP) in monkey eyes with unilateral laser-induced glaucoma. A multiple-dose study was performed in 8 glaucomatous monkey eyes. One 50 microl drop of CS-088, 2% or 4%, was topically applied to the glaucomatous eye at 9:30 a.m. and 3:30 p.m. for 5 consecutive days. IOP was measured hourly for 6 hours beginning at 9:30 a.m. for one baseline day, one vehicle-treated day, and daily for 5 days of treatment with CS-088. The washout period between the two drug concentrations was at least 2 weeks. Twice daily administration of 2 % CS-088 for 5 days did not reduce the IOP until the third dose on day 2 of the treatment regimen. A significant (p<0.02) reduction in IOP began 1 hour after the third dose, and lasted for 3 hours. The maximum reduction in IOP was 5.3+/- 0.8 (mean+/-SEM) mmHg (15%) (p<0.001), with the longest duration of IOP reduction of at least 6 hours after dosing on day 5. The 4% dose of CS-088 reduced (p<0.05) IOP from 1 to 5 hours after the first dose. The maximum reduction in IOP was 6.9+/-1.0 mmHg (20%), with the longest duration of IOP reduction of at least 18 hours after administration on day 5. Both 2% and 4% CS-088 showed enhancement of the ocular hypotensive effect with repeated dosing. 4% CS-088 produced greater (p<0.05) IOP reduction with longer duration of action than 2%. Topically applied CS-088, a new antagonist drug at the angiotensin AT1 receptor, reduced IOP in glaucomatous monkey eyes in a dose-dependent manner.

Steroid-induced ocular hypertension in normal cattle

OBJECTIVES

To determine whether the bovine eye develops elevation of intraocular pressure (IOP) in response to topical corticosteroid use and to develop a reliable model of steroid-induced elevation of IOP in an animal.

METHODS

Intraocular pressure was monitored by Perkins applanation tonometry in a group of 12 cows receiving topically administered prednisolone acetate in 1 eye 3 times a day for a period of 49 days after the establishment of baseline IOP values. Perkins readings were converted to IOP in mm Hg using calibration curves derived from in vitro cannulation manometric experiments and validated with in vivo manometric measurements. Intraocular pressure was also monitored for 50 days after the discontinuation of corticosteroid therapy.

RESULTS

Intraocular pressure began to increase after 3 weeks of treatment in 100% of the cow eyes receiving corticosteroid and reached a peak 1 week later. Peak interocular IOP differences between the corticosteroid-treated eye and the fellow control eye reached up to 15 mm Hg and began to decline after the discontinuation of treatment but remained significantly elevated for a period of 3 more weeks.

CONCLUSIONS

Bovine eyes exhibit a robust steroid-induced ocular hypertensive response, with 100% occurrence in this trial. The IOP elevation caused by corticosteroid slowly subsides after discontinuation of treatment. Clinical Relevance The mechanisms of steroid-induced glaucoma may be related to those involved in primary open-angle glaucoma and could provide the clues to elucidate the pathogenesis of the latter. The high prevalence of corticosteroid-induced elevation of IOP in the cow and the large amount of tissue available will permit studies on the mechanism of this phenomenon not previously possible.

Additivity of Bimatoprost or Travoprost to Latanoprost in GlaucomatousMonkey Eyes

OBJECTIVE

To compare the ocular hypotensive effect of the commercially available preparations of bimatoprost or travoprost added to latanoprost in monkey eyes with laser-induced unilateral glaucoma.

METHODS

Four monkeys with unilateral laser-induced glaucoma were used in each treatment group and received drops in the glaucomatous eye only. Intraocular pressure (IOP) was measured hourly for 6 hours, beginning at 9:30 am on day 1 (untreated baseline), days 6 and 7 (single-agent therapy), and days 13 and 14 (2-drug combination therapy). On days 2 through 7, 1 drop of the scheduled single agent was given immediately after the 9:30 am IOP measurement, and on days 8 through 14, the second scheduled drug was given 5 minutes after the first. The following 5 different dosing protocols were studied: latanoprost with bimatoprost added, bimatoprost with latanoprost added, latanoprost with travoprost added, travoprost with latanoprost added, and latanoprost with a second dose of latanoprost added.

RESULTS

There were no statistically significant (P =.95) differences among the mean baseline IOPs in any of the 5 treatment groups. When applied as single agents, latanoprost, bimatoprost, and travoprost all produced significant (P<.05) and equivalent (P =.98) reductions in IOP. The mean +/-SEM maximum reduction (P<.05) from baseline IOP was 7.0 +/- 0.4 mm Hg (20% reduction) with travoprost alone, 6.5 +/- 1.6 mm Hg (18%) with bimatoprost alone, and 7.5 +/- 1.0 mm Hg (22%) with latanoprost alone. The mean +/-SEM maximum additive reductions in IOP were 3.0 +/- 0.6 mm Hg (P<.05) for travoprost added to latanoprost; 2.0 +/- 0.4 mm Hg (P<.05) for latanoprost added to travoprost; 4.8 +/- 1.3 mm Hg (P<.05) for bimatoprost added to latanoprost; 4.3 +/- 0.6 mm Hg (P<.05) for latanoprost added to bimatoprost; and 0.3 +/- 0.5 mm Hg (P>.60) for latanoprost added to itself. The combination of bimatoprost and latanoprost produced a greater (P<.05) lowering of IOP at trough and peak than the combination of travoprost and latanoprost.

CONCLUSIONS

Latanoprost, bimatoprost, and travoprost used as monotherapy produced significant and equivalent reductions in IOP in glaucomatous monkey eyes. The IOP effects of the commercial concentrations of bimatoprost or travoprost were additive to that of latanoprost, with bimatoprost showing a greater additive response than travoprost. Clinical Relevance Because treatment with multiple medications is common among patients with glaucoma, determining which glaucoma medications produce an additive ocular hypotensive response when used in combination has practical implications for clinicians.

Glutamate-Induced Glutamine Synthetase Expression in Retinal Müller Cells after Short-term Ocular Hypertension in the Rat

PURPOSE

To determine the effect of intraocular pressure (IOP) elevation on glutamate-induced expression of glutamine synthetase (GS) in retinal Müller cells of rat eyes.

METHODS

Six groups of three rats each were studied. Group I was a normal control group. In Group II, one eye received an intravitreal glutamate injection (75 nmoles) while the contralateral eye served as control. In Groups III and IV, IOP was raised in one eye by episcleral vein cauterization. Moderately elevated IOP was maintained for 1 day in Group III or 1 week in Group IV (35 +/- 1.9-45 +/- 5.2 mm Hg). An additional two groups of rats received bilateral intravitreal glutamate injections (75 nmoles) immediately (Group V), or 6 days (Group VI), after induction of IOP elevation in one eye. One day after glutamate injection the rats in all groups were killed, and the eyes enucleated and fixed. Retinas from left and right eyes of each animal were embedded together in LR White resin (Ted Pella, Redding, CA). Sections were processed for GS immunolabeling with antibodies to GS by two-stage immunogold labeling with silver enhancement. Images of labeled retinas from the two eyes were captured under identical light microscopic conditions and the GS immunoreactivity in Müller cells was compared between the left and right retinas in the same section by image analysis. An additional five rats were included in Group II and the retinas were analyzed by Western blot analysis to confirm immunohistochemical findings.

RESULTS

Similar to the finding in the control group (Group I), the GS immunoreactivity of the left and right eyes of Group III and IV remained unchanged even though the right eyes in the two groups had elevation of IOP lasting for 24 hours and 1 week, respectively. However, GS levels were significantly increased by 40 +/- 5.7% in normotensive eyes 24 hours after intravitreal injection of glutamate (Group II). The rise in GS immunoreactivity was abolished in eyes with acute IOP elevation (Group V). In contrast, when the eyes were exposed to high IOP for 1 week (Group VI), the glutamate-induced increase in GS immunoreactivity was restored.

CONCLUSIONS

Elevated levels of vitreal glutamate can increase the expression of GS in retinal Müller cells. This increase was blocked if IOP was acutely elevated for 24 hours but was restored if IOP remained elevated for 1 week. This finding suggests that moderate elevation of IOP causes only short-term functional changes of glutamate metabolism (amidation) by retinal Müller cells. However, it is not known to what extent endogenous extracellular glutamate can regulate GS expression in normal eyes or in eyes with glaucoma.

Effects of topical H-7 on outflow facility, intraocular pressure, and corneal thickness in monkeys

OBJECTIVES

To determine if low concentrations of H-7 (1-[5-isoquinoline sulfonyl]-2-methyl piperazine) topically applied to the eye increases outflow facility and decreases intraocular pressure (IOP) without affecting the cornea in monkeys, and to evaluate if the effect of H-7 on IOP is pressure dependent.

METHODS

Single or multiple doses of 5% H-7 or vehicle (20 micro L) were administered topically to opposite eyes of normal monkeys. A single dose of 2% H-7 or vehicle (50 micro L) was administered to the glaucomatous eye of monkeys with laser-induced unilateral glaucoma, with vehicle on day 1 and H-7 on day 2.

RESULTS

In normotensive eyes, 1 dose of 5% H-7 maximally decreased IOP by a mean +/- SEM of 2.5 +/- 1.0 mm Hg (-16.7% +/- 5.5%) at 3 hours. Higher baseline IOP and repeated dosing were associated with greater IOP reduction. Outflow facility was increased, but central corneal thickness was not affected. In glaucomatous eyes, 1 dose of 2% H-7 maximally decreased IOP by a mean +/- SEM of 5.8 +/- 0.6 mm Hg (-16.9% +/- 1.6%) at 2 hours.

CONCLUSIONS

Five percent H-7 increases outflow facility and decreases IOP, but does not affect corneal thickness. Multiple doses of H-7 induce greater reduction of IOP than a single dose. The effect of H-7 on IOP may be pressure dependent. Clinical Relevance Multiple topical treatments with low doses of H-7 or analogues may substantially reduce outflow resistance in the hypertensive eye without meaningfully affecting the cornea.

Aqueous Humor Dynamics in Monkeys after Topical 8-Iso PGE2

PURPOSE

To determine in normotensive cynomolgus monkeys, the effects of topical 8-iso prostaglandin (PG)E(2) on intraocular pressure (IOP), aqueous humor formation (AHF), uveoscleral outflow (Fu), and total and trabecular outflow facility.

METHODS

IOP was measured by Goldmann applanation tonometry under ketamine anesthesia after single or twice-daily topical treatments with 8-iso PGE(2). With animals under pentobarbital anesthesia, AHF and flow to blood (equated to trabecular outflow) were determined by anterior chamber perfusion with radioactively labeled albumin solution. Fu and trabecular outflow facility were calculated from these measurements. Total outflow facility was measured by two-level, constant-pressure perfusion.

RESULTS

IOP was not significantly changed after single or multiple 10- micro g doses of 8-iso PGE(2). The 25- micro g dose significantly decreased IOP by 2 to 3 mm Hg compared to the contralateral vehicle-treated control 4 to 6 hours after a single dose and by 3 to 5 mm Hg within 1.5 hours after twice-daily treatments for 4 to 5 days. Total outflow facility corrected for control eye washout was increased by an apparent 37% (P < 0.02, n = 7) from 2 to 3.5 hours after the ninth dose, largely due to outlier values obtained in one monkey. Isotope studies performed after twice-daily treatments totaling 9 to 29 doses showed no change in AHF, trabecular outflow facility, or total outflow facility. Relative to AHF, trabecular outflow was significantly decreased, and the calculated Fu was significantly increased when all data were analyzed.

CONCLUSIONS

The present findings are consistent with lowering of IOP by 8-iso PGE(2), primarily by increasing Fu. A direct effect on the trabecular meshwork was not indicated by these in vivo studies.

Quantitative Analysis of Retinal Ganglion Cell (RGC) Loss in Aging DBA/2NNia Glaucomatous Mice: Comparison with RGC Loss in Aging C57/BL6 Mice

PURPOSE

To quantify the extent and pattern of retinal ganglion cell (RGC) loss in the DBA2/NNia glaucomatous mouse strain as a function of age and compare it with ganglion cell loss in a nonglaucomatous strain.

METHODS

All the ganglion cells in retinas of DBA/2NNia and C57/BL6 mice of various ages (five eyes per age group in 3-month intervals from 3 to 18 months of age) were counted. A novel counting method that does not rely on sampling and that uses retrograde labeling of RGCs with Fluorogold (Fluorochrome; Englewood, CO) was used. RGC loss in the glaucomatous DBA/2NNia mouse strain was contrasted to RGC loss in C57 mice at the same ages. The total number of Fluorogold-labeled cells per retina was compared within and among the two strains as a function of age. In addition, RGC density maps were constructed for each retina, and the range of densities for each age group was compared within and among the two strains. IOP in awake, nonsedated DBA/2NNia mice was measured with a rebound tonometer.

RESULTS

RGC loss started between 12 and 15 months of age in C57 mice and led to an approximate 46% reduction by 18 months of age. The rate of loss was best approximated by a second-order polynomial curve. In comparison, DBA/2NNia mice also began showing RGC loss at approximately 12 months of age, but it proceeded at a much faster rate, with approximately 64% of their RGCs dying by the 15th month of age but little additional loss thereafter. RGC loss in the DBA animals had a focal pattern that appeared more patchy and showed greater variability than the age-related loss in C57 mice, which was more diffuse. IOP and total retinal area in DBA/2NNia mice began to increase at approximately 6 months of age. IOP normalized after the 12th month of age.

CONCLUSIONS

Age-related RGC loss of up to 50% can occur in the C57 mouse by 18 months of age. The loss does not proceed linearly with age, as is often assumed, and differs both in extent and locational pattern from pathologic RGC loss secondary to glaucoma in DBA/2NNia mouse retinas.

Effect of WIN 55212-2, a cannabinoid receptor agonist, on aqueous humor dynamics in monkeys

OBJECTIVE

To evaluate the effects of WIN 55212-2, a cannabinoid receptor agonist, on intraocular pressure and aqueous humor dynamics in normal monkeys and monkeys with glaucoma.

METHODS

Intraocular pressure was measured prior to and up to 6 hours after the topical administration of WIN 55212-2 to 1 eye of 5 normal monkeys and to the glaucomatous eye of 8 monkeys with unilateral laser-induced glaucoma. Tonographic outflow facility and fluorophotometric flow rates of aqueous humor were measured in 6 normal monkeys before and after treatment.

RESULTS

In normal monkeys, a single dose of WIN 55212-2 reduced intraocular pressure for 4, 5, or 6 hours, with a maximum reduction of 1.4 +/- 0.4 (mean +/- SEM) mm Hg, 2.9 +/- 0.4 mm Hg, and 3.4 +/- 0.6 mm Hg following the 0.07%, 0.2%, and 0.5% concentrations, respectively (P =.08). In 8 glaucomatous monkey eyes, the ocular hypotensive effect was maintained for 5 days with twice-daily administration of 0.5% WIN 55212-2. Outflow facility was unchanged (P =.34) and aqueous humor flow was decreased by 18% (P =.04) in the treated eyes compared with vehicle-treated contralateral control eyes in normal monkeys.

CONCLUSIONS

WIN 55212-2, a cannabinoid agonist at the CB(1) receptor, reduces intraocular pressure in both normal and glaucomatous monkey eyes. A decrease of aqueous flow appears to account for the intraocular pressure reduction in normal monkey eyes.

CLINICAL RELEVANCE

Cannabinoid agonists at the CB(1) receptor, a new class of antiglaucoma agents that is different from currently used clinical drugs, may have clinical potential.

Cytoarchitecture of the retinal ganglion cells in the rat

PURPOSE

To determine the number and cytoarchitecture of retinal ganglion cells (RGCs) in the female Wistar rat, by using a newly devised procedure for rapid RGC counting in the entire retina that avoids assumptions about RGC spatial arrangement.

METHODS

RGCs of normal female Wistar rats were retrogradely labeled with a fluorescent tracer. Automated counting was accomplished by applying standard imaging software to analysis of all labeled cells in retinal flatmounts. The method was validated by comparison of automated and manual counts of 70,000 RGCs in frames covering the density range in the normal rat retina of 600 to 3600 RGC/mm(2). RGC numbers were determined for each retina and compared with the contralateral retina of the same animal. RGC density maps were constructed for each retina. RGC size distribution was determined.

RESULTS

Automated RGC counting showed a good linear correlation with manual counting (R(2) = 0.9416). Mean total RGC count in 10 rat eyes was 97,609 +/- 3,930 (SEM) per eye. Contralateral eyes differed by an average of 4.1% (3983 plus minus 5098 RGCs). Size analysis calculated from cell areas confirmed that the majority of rat RGCs are between 7 and 21.5 microm in equivalent diameter. The RGC counts for all frames at the same eccentricity in all 10 of the retinas showed that variability increased with eccentricity and increased further as the fractional area of the retina sampled at each eccentricity was reduced. There was also significant variability in the spatial density of the RGCs at the same eccentricity location between different eyes. Comparison of total RGC counts between left and right eyes estimated from RGC counts in sectors of the retina (hemiretinas or quadrants) showed increased variability compared with counting all the RGCs in a retina.

CONCLUSIONS

RGCs in the Wistar rat display significant variability in their cytoarchitecture. Such variability can make quantification by sampling problematic for diffuse, and particularly, for focal RGC losses resulting from experimental interventions, unless virtually the entire RGC population is counted.

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.