Eyelid lymphatics I: histochemical comparisons between the monkey and human

PURPOSE

To study the lymphatic drainage of the cynomolgus monkey and human eyelid and periocular tissue by means of histochemistry.

METHODS

Eyelid and periocular tissue from three cynomolgus monkeys undergoing sacrifice for glaucoma and retina research purposes and discarded tissue from a wedge resection of one human eyelid were used for histochemical analysis. Lymphatic capillaries were distinguished histochemically in monkey and human eyelids by light microscopy with a 5'-nucleotidase (5'-Nase) staining method. Identification of lymphatic vessels was based on strict morphologic criteria combined with specific 5'-Nase staining.

RESULTS

Histochemical analysis with 5'-nucleotidase revealed a subcutaneous and pretarsal lymphatic plexus in both the human and monkey.

CONCLUSIONS

Histochemical results demonstrate similar lymphatic plexi in the monkey and human. Future studies will help to clarify the lymphatic drainage pathways of monkey and human eyelids.

Effects of the marine macrolides swinholide A and jasplakinolide on outflow facility in monkeys

PURPOSE

To determine effects of the marine macrolides swinholide A (Swin A) and jasplakinolide (Jas), alone or in conjunction with latrunculin B (Lat B) on outflow facility in monkeys.

METHODS

Total outflow facility was measured by two-level constant-pressure perfusion of the anterior chamber before and after exchange with Swin A, Jas, or vehicles followed by continuous anterior chamber infusion of drug or vehicle, in opposite eyes of cynomolgus monkeys. The effect of a facility-ineffective dose of Jas plus a threshold or submaximal facility-effective dose of the actin depolymerizer Lat B on outflow facility was also determined.

RESULTS

Ten or 100 nM Swin A or 20, 100, or 500 nM Jas had no significant effect on outflow facility. However, 500 nM Swin A and 2.5 microM Jas significantly increased facility by 80% +/- 21% and 157% +/- 57% (mean +/- SEM) respectively, adjusted for corresponding baselines and resistance washout in contralateral control eyes. The facility increase in the eye treated with 500 nM Jas with 60 or 200 nM Lat B was similar to that in the eye treated with 60 or 200 nM Lat B only.

CONCLUSIONS

Swin A (which severs actin filaments and sequesters actin dimers) and Lat B (which sequesters actin monomers) similarly increase outflow facility. The potent inducer of actin polymerization Jas (500 nM) neither inhibits nor potentiates the facility increase induced by Lat B (60 or 200 nM). A higher dose of Jas increases rather than decreases outflow facility.

Atrophy of relay neurons in magno- and parvocellular layers in the lateral geniculate nucleus in experimental glaucoma

PURPOSE

To determine whether in glaucoma there is atrophy of relay neurons in magnocellular and/or parvocellular lateral geniculate nucleus (LGN) layers projecting to the visual cortex and to compare the degree of neuronal atrophy in magnocellular layers with that in parvocellular layers.

METHODS

Seven cynomolgus monkeys with unilateral experimentally induced glaucoma and five control monkeys were studied. The left LGN neurons in magnocellular layer 1 and parvocellular layers 4 and 6, connected to the right glaucomatous eye were examined. Immunocytochemistry with antibody to parvalbumin was used to specifically label relay neurons connecting to the visual cortex. Neuronal cell body cross-sectional area was estimated using unbiased point-counting methodology. Experimental and control groups were compared using t-tests. Analysis of covariance (ANCOVA) tests were used to compare the percentage of decrease in mean neuronal area between layers 1, 4, and 6, as a function of percentage of optic nerve fiber loss or mean IOP. There was significant correlation between percentage of optic nerve fiber loss and mean IOP.

RESULTS

The mean cross-sectional area of relay neurons in magnocellular layer 1 and parvocellular layers 4 and 6 were significantly decreased in glaucoma compared with controls by 28%, 37%, and 45%, respectively. Neuronal area decreased in a linear fashion, with increasing optic nerve fiber loss or increasing mean IOP for layers 1, 4, and 6. The percentage of neuronal shrinkage in each of parvocellular layers 4 and 6, as a function of optic nerve fiber loss (P = 0.05; P = 0.001, respectively) or mean IOP (P = 0.046; P = 0.0008, respectively), was greater than that seen in magnocellular layer 1.

CONCLUSIONS

Relay neurons in the LGN, which project to the visual cortex, undergo significant shrinkage in glaucoma, and neurons in parvocellular layers undergo significantly more shrinkage than neurons in magnocellular layers.

Expression of myocilin/TIGR in normal and glaucomatous primate optic nerves

Myocilin/TIGR was the first molecule discovered to be linked with primary open angle glaucoma (POAG), a blinding disease characterized by progressive loss of retinal ganglion cells. Mutations in myocilin/TIGR have been associated with age of disease onset and severity. The function of myocilin/TIGR and its role in glaucoma is unknown. Myocilin/TIGR has been studied in the trabecular meshwork to determine a role in regulation of intraocular pressure. The site of damage to the axons of the retinal ganglion cells is the optic nerve head (ONH). The myocilin/TIGR expression was examined in fetal through adult human optic nerve as well as in POAG. Myocilin/TIGR was expressed in the myelinated optic nerve of children and normal adults but not in the fetal optic nerve before myelination. Also examined was the expression in monkeys with experimental glaucoma. The results demonstrate that optic nerve head astrocytes constitutively express myocilin/TIGR in vivo in primates. Nevertheless, myocilin/TIGR is apparently reduced in glaucomatous ONH. The colocalization of myocilin/TIGR to the myelin suggests a role of myocilin/TIGR in the myelinated optic nerve.

Increased elastin expression in astrocytes of the lamina cribrosa in response to elevated intraocular pressure

PURPOSE

To determine whether abnormal elastin synthesis in the glaucomatous optic nerve head and lamina cribrosa is due to elevated intraocular pressure (IOP) or secondary to axonal injury, monkeys with elevated IOP and with optic nerve transection were compared.

METHODS

Unilateral, chronic elevated IOP was induced in 11 rhesus monkeys by laser scarification of the trabecular meshwork. IOP was monitored weekly and maintained within 25 to 45 mm Hg for 7 to 36 weeks. In 6 monkeys, unilateral, optic nerve transection was performed, and monkeys were killed after 4 weeks. Optic nerve damage was assessed by stereoscopic slit-lamp biomicroscopy and fundus photography and by confocal scanning laser ophthalmoscopy. The eyes were enucleated and processed for immunohistochemistry and in situ hybridization and for electron microscopic immunogold detection of elastin. Axonal loss was evaluated in cross sections of the optic nerve stained with phenylenediamine.

RESULTS

Compared with normal contralateral controls, the lamina cribrosa of eyes with elevated IOP exhibited markedly increased elastin and the presence of elastotic aggregates in the extracellular matrix and upregulation of elastin mRNA in the astrocytes. In transected eyes, elastin appeared as fine fibers in the lamina cribrosa, without elastotic aggregates, and without new synthesis or abnormal deposition of elastin. At the transected site, new synthesis of elastin was present in the pia mater but not in astrocytes in the glial scar.

CONCLUSIONS

This study demonstrates that abnormal elastin synthesis in experimental glaucomatous optic neuropathy in the monkey is specific to elevated IOP and not secondary to axonal loss. The mechanisms by which elevated IOP induces enhanced elastin synthesis in laminar astrocytes are unknown but differ from those involved in acute axonal injury such as transection, where inflammation and breakdown of the blood-nerve barrier occur.

Non-invasive observation of repeated adenoviral GFP gene delivery to the anterior segment of the monkey eye in vivo

BACKGROUND

Glaucoma is a group of chronic eye diseases often associated with an elevated intraocular pressure (IOP). If not controlled, the condition leads to blindness. The eye tissue responsible for maintaining aqueous humor resistance and thus normal IOP is the trabecular meshwork (TM). Adenoviral vectors are capable of transducing the TM in several rodent species. Because of the relevance of the non-human primate model in the study of glaucoma, gene transfer to the eyes of cynomolgus monkeys was investigated.

METHODS

Four cynomolgus monkeys were injected with AdenoGFP into the anterior chamber: two monkeys received 10(9) pfu and the other two 10(7) pfu. One monkey received four consecutive injections into the same eye (10(7) pfu in each injection) over a 7-month period. In vivo gene transfer (fluorescence) and IOP were evaluated by standard clinical ophthalmic instruments (slit lamp biomicroscopy, gonioscopy and tonometry). Histopathology and cellular distribution were assessed postmortem.

RESULTS

The first injection of the lower viral dose resulted in marked TM-preferred gene transfer visible non-invasively by in vivo gonioscopy. The expression of the transgene lasted for 3-4 weeks with little or no signs of clinical inflammation. Gene transfer was achieved on three sequential occasions (3-4 weeks each) but failed and induced substantial, albeit reversible, corneal abnormalities on the fourth occasion.

CONCLUSIONS

Gene transfer to the TM and cornea can be monitored non-invasively in non-human primates, allowing correlation of gene transfer with physiological parameters. Because of ocular immune privilege, repeated anterior chamber administrations of adenoviral vectors expressing appropriate genes may have therapeutic potential for glaucoma.

Effects of serotonergic compounds on aqueous humor dynamics in monkeys

PURPOSE

The effects of several serotonergic agonists on aqueous humor formation (AHF), total outflow facility (OF) and intraocular pressure (IOP) were investigated in living cynomolgus monkeys.

METHODS

We determined the effect of a single topical unilateral 300 microg or 3 mg dose of the 5-HT agonists serotonin, 5-carboxamidotryptamine (5-CT), sumatripan, gepirone, and 8-hydroxy-2(di-n-propylaminotetralin) (8-OH-DPAT) and a 450 microg dose of flesinoxan on IOP (Goldmann applanation tonometry), AHF (scanning ocular fluorophotometry) and total OF (8-OH-DPAT only, topically and intracamerally).

RESULTS

Serotonin, 5-CT, sumatripan or gepirone had no significant effect on IOP or AHF. 8-OH-DPAT caused an AHF increase of approximately 70% over 6 hr in both ipsilateral drug- and contralateral vehicle-treated eyes, but no significant change in IOP compared with baseline measured on a separate occasion in the same animals. 8-OH-DPAT did not increase protein levels or rate of entry of systemically administered fluorescein in the anterior chamber aqueous humor compared to historic controls, and no difference was seen between ipsilateral and contralateral eyes. Flesinoxan had no effect on IOP and produced an insignificant 25% increase in flow in treated eyes compared to baseline.

CONCLUSION

The results for 8-OH-DPAT and possibly flexinoxan indicate the presence of a secretion-stimulating 5-HT1A receptor in monkey ciliary epithelium that has little effect on IOP. OF was unchanged following 8-OH-DPAT administered topically or following intracameral exchange.

Increased matrix metalloproteinases 1, 2, and 3 in the monkey uveoscleral outflow pathway after topical prostaglandin F(2 alpha)-isopropyl ester treatment

OBJECTIVE

To investigate the effects of topical prostaglandin F(2 alpha)--isopropyl ester (PGF(2 alpha)-IE) administration on immunoreactivity of matrix metalloproteinases (MMPs) 1, 2, and 3 within the anterior segment tissues of monkey eyes.

METHODS

Eight eyes from 4 cynomolgus monkeys were evaluated. One eye from each monkey was treated with 2 mg of PGF(2 alpha)-IE twice daily for 5 days, and intraocular pressure reduction was measured. After fixation and processing, deparaffinized sections of anterior segments were immunostained using antibodies to MMP-1 (interstitial collagenase), MMP-2 (gelatinase A), or MMP-3 (stromelysin-1). Optical density along 2 line segments overlying the iris root, ciliary muscle, and adjacent sclera and perpendicular to their long axes was measured using imaging densitometry.

RESULTS

Compared with the contralateral vehicle-treated eyes, statistically significant increases in optical density scores were observed in the iris root, ciliary muscle, and adjacent sclera for all 3 MMPs (P<.01). In these tissues, MMP-1 immunoreactivity was increased by a mean +/- SD of 89% +/- 16%, 61% +/- 8%, and 66% +/- 57%, respectively; MMP-2 immunoreactivity by 129% +/- 53%, 82% +/- 27%, and 267% +/- 210%, respectively; and MMP-3 immunoreactivity by 207% +/- 84%, 83% +/- 49%, and 726% +/- 500%, respectively.

CONCLUSIONS

Treatment of monkey eyes with PGF(2 alpha)-IE induces elevation of MMP-1, MMP-2, and MMP-3 in tissues of the uveoscleral outflow pathway. These increases suggest that MMPs might play an important role in the increased uveoscleral outflow observed with topical prostaglandin treatment.

CLINICAL RELEVANCE

Immunoreactivity of MMPs in tissues of the monkey uveoscleral outflow pathway is increased after topical treatment with PGF(2 alpha)-IE. This response also might be involved in the intraocular pressure--lowering effect of other prostanoids used to treat glaucoma.

Reduced TIGR/myocilin protein in the monkey ciliary muscle after topical prostaglandin F(2alpha) treatment

PURPOSE

Mutations in the trabecular meshwork inducible glucocorticoid response (TIGR) gene, also known as myocilin, have recently been linked to some forms of glaucoma. Recent studies have shown that TIGR protein also is expressed in the ciliary muscle. Because uveoscleral outflow, which traverses the ciliary muscle, is increased by prostaglandins (PGs), the present study assessed whether topical PGs alter the amount of TIGR protein within the ciliary muscle.

METHODS

Vehicle was topically applied to one eye, and 2 microg PGF(2alpha)-isopropyl ester (PGF(2alpha)-IE) was applied to the other eye of cynomolgus monkeys twice daily for 5 days. Pressure reductions of 5 mm Hg in the PGF(2alpha)-IE-treated eyes were confirmed. The eyes were then fixed and paraffin sections were cut from each eye. The distribution of TIGR protein in the ciliary muscle was determined by confocal scanning laser microscopy. Additional sections were immunostained with a polyclonal antibody to recombinant TIGR protein or with a polyclonal antibody to a synthetic peptide corresponding to the leucine zipper region within the TIGR protein. Staining intensity in the ciliary muscle was assessed by measuring optical density (OD) along two line segments overlying the ciliary muscle, by using a high-resolution imaging densitometer.

RESULTS

TIGR protein immunoreactivity was observed in ciliary muscle fibers throughout the ciliary muscle. Extracellular TIGR immunoreactivity colocalized with collagen type IV immunoreactivity. Intracellular staining also was present. Immunoreactivity was less intense in the sections from the PGF(2alpha)-IE-treated eyes compared with the vehicle-treated eyes. This was reflected in the reduction of mean OD scores in each monkey. Overall, the reduction of mean OD scores in the treated eyes was 42.1% +/- 9.9% (P < 0.005) with the anti-recombinant TIGR antibody and 27.3% +/- 10.4% with the anti-TIGR peptide antibody (P < 0.005).

CONCLUSIONS

TIGR protein immunoreactivity was present both intracellularly and extracellularly in the ciliary muscle of the cynomolgus monkey. This suggests that extracellular TIGR protein is in contact with aqueous humor in the uveoscleral outflow pathway. Moreover, IOP-lowering topical PGF(2alpha)-IE treatment decreases the amount of TIGR protein in the ciliary muscle.

Effect of H-7 on cultured human trabecular meshwork cells

PURPOSE

To determine the effect of the serine-threonine kinase inhibitor H-7, which blocks actomyosin contractility and increases outflow facility in live monkeys, on morphology, cytoskeleton, and cellular adhesions of human trabecular meshwork (HTM) cells in culture.

METHODS

Cultured HTM cells were videographically recorded and evaluated before and after exposure to H-7 at different concentrations. The subcellular distribution of the actin-based cytoskeleton and associated anchor proteins including vinculin, paxillin, and beta-catenin, as well as phosphotyrosine-containing proteins were evaluated by fluorescence immunocytochemistry and digital fluorescence microscopy.

RESULTS

H-7 induced pronounced but reversible HTM cell thickening toward the cell center and deterioration of the actin cytoskeletal network. Cell-extracellular matrix (ECM) and cell-cell adhesions were also affected, but the beta-catenin-rich, vinculin-containing adherens junctions were clearly more resistant than focal contacts. Phosphotyrosine labeling in focal contacts was highly sensitive to H-7.

CONCLUSIONS

H-7 induces alterations in cell shape, actin cytoskeleton, and associated focal adhesions in cultured HTM cells, which may be responsible for the effects of H-7 on outflow facility in live monkey eyes.

Intravitreal injection of plasminogen kringle 5, an endogenous angiogenic inhibitor, arrests retinal neovascularization in rats

AIMS/HYPOTHESIS

Plasminogen kringle 5 is an endogenous angiogenic inhibitor. The purpose of the present study was to explore the potential application of kringle 5 in the treatment of retinal neovascularization.

METHODS

Plasminogen kringle 5 was expressed in E. coli and affinity-purified. Its anti-angiogenic activity was determined in cultured primary human capillary endothelial cells. Retinal neovascularization was induced in newborn rats by exposure to hyperoxia and then normoxia. Kringle 5 was intravitreally injected into the rat model. Retinal neovascularization was visualized by fluorescein angiography on flat-mounted retina and quantified by counting preretinal vascular cells.

RESULTS

Plasminogen kringle 5 inhibited primary endothelial cells but not retinal neuronal cells, suggesting cell type-specific inhibition. The oxygen-induced retinopathy rat model showed an over-expression of vascular endothelial growth factor, preretinal neovascularization and haemorrhage. Intravitreal injection of kringle 5 before the development of neovascularization resulted in fewer neovascular tufts and pre-retinal vascular cells than in control rats with PBS injection (p < 0.01). Moreover, injection of kringle 5 after the development of neovascularization inhibited the increase in the preretinal vascular cells (p < 0.05). These results suggest that kringle 5 both prevents the development and arrests the progression of retinal neovascularization. The injection of kringle 5 did not result in any detectable inflammatory response in the retina or histological toxicity to retina neurons and pre-existing vessels.

CONCLUSION/INTERPRETATION

These observations suggest that intravitreal delivery of angiogenic inhibitors could have therapeutic benefits in neovascular diseases of the retina.

Ultrasound biomicroscopy of the aging rhesus monkey ciliary region

Ultrasound biomicroscopy of the living rhesus monkey ocular ciliary region was undertaken to identify age-dependent changes that might relate to the progression of presbyopia. Monkeys were anesthetized and pharmacologically cyclopleged, the eyelids were held open with a lid speculum, and sutures were placed beneath the medial and lateral rectus muscles. Ultrasound biomicroscopy imaging of the nasal and temporal quadrants of the eye were performed, and the live images were recorded to videotape. Subsequent image analysis was performed to obtain objective morphometric measurements of the ciliary body region. The ciliary body inner radius of curvature, outer radius of curvature, inner arc length, area, thickness, perimeter, zonular fiber length, and circumlental space were measured. Zonular space was calculated. The circumlental space decreased with increasing age in the temporal quadrant. The other morphologic measurements were not significantly correlated with age or body weight. Most morphologic measurements were significantly different comparing temporal vs. nasal quadrants. Bifurcation of the posterior zonular fibers was frequently observed. Although temporal circumlental space was the only measurement found to change with age, ultrasound biomicroscopy of the living rhesus ciliary region did identify distinct nasal vs. temporal asymmetries, which may reflect anatomical requirements for convergence-associated accommodation.

Acute effects of H-7 on ciliary epithelium and corneal endothelium in monkey eyes

PURPOSE

Topical or intracameral administration of H-7 doubles outflow facility and reduces intraocular pressure in cynomolgus monkeys, by relaxing and expanding the trabecular meshwork (TM) and Schlemm's canal (SC). Since H-7 may have anti-glaucoma potential, we determined its effects on the corneal endothelium and ciliary epithelium for safety considerations.

METHODS

Following topical H-7, aqueous humor flow (AHF), corneal endothelial transfer coefficient (k(a)) and anterior chamber (AC) entry of i.v. fluorescein were measured by fluorophotometry; AC aqueous protein concentration ([Protein](AC)) was determined by Lowry assay; and corneal thickness and endothelial cell density and morphology were measured by ultrasonic pachymetry and specular microscopy respectively. Following intracameral H-7, specular and/or light and electron microscopy of the corneal endothelium or ciliary epithelium were performed.

RESULTS

Following unilateral topical H-7: (1) AHF and k(a) were essentially unchanged at 0.5--3.0, 3.5--6.0, and 0.5--6.0 hr, with an insignificant increase from 0.5--1.5 hr; (2) [Protein]( AC) was insignificantly increased at 1-1.5 hr but had returned to baseline by 2.5 hr; (3) entry of i.v. fluorescein into aqueous or cornea was modestly and transiently increased; (4) the central cornea thickened significantly at 1--2.5 hr, gradually returning to baseline 2.5 hr after H-7, while peripheral corneal thickness was less affected; (5) corneal endothelial cell borders became indistinct by 1 hr, but cell morphology was recovering by 3--5 hr and had completely returned to normal by 24 hr; (6) corneal endothelial cell density was unchanged at 5--24 hr. Following intracameral H-7, no significant changes were observed in corneal endothelial cell density or morphology by specular microscopy, nor in corneal endothelial or ciliary epithelial morphology by light and electron microscopy.

CONCLUSIONS

A facility-effective intracameral dose of H-7 had no discernible structural effect on the corneal endothelium or ciliary epithelium. It is not yet clear whether carefully chosen topical doses of H-7 or analogues can enhance outflow facility without meaningfully affecting the cornea and ciliary processes.

Aging of the human lens: changes in lens shape at zero-diopter accommodation

Scheimpflug photographs of the zero-diopter-accommodated anterior segments of 100 human subjects, aged 18 to 70 yr and evenly spaced over this range, were digitized and analyzed to characterize lens and lens nucleus shape as a function of age by the Hough transform and other image analysis methods. Anterior and posterior lens surface curves exhibit a decrease in radius of curvature with increasing age, in qualitative but not quantitative agreement with the earlier observations of Brown [Exp. Eye Res. 19, 175 (1974)]. In contrast, the shape of the lens nuclear boundaries changes little with age. Overall lens volume at zero diopters increases with age, but the volume of the lens nucleus remains unchanged. The lens center of mass moves anteriorly with increasing age, as does the central clear region of the lens. Although these data sets were found to be more variable than those of Brown, the complementary variability of other factors, such as anterior chamber depth, for each subject leads to a very high statistical correlation between lens shape and lens location relative to the cornea. This supports the finding of previous work that image formation on the retina for a given individual results from the multifactorial balancing of related factors.

The effects of panretinal photocoagulation on the primary visual cortex of the adult monkey

PURPOSE

To determine the effects of panretinal photocoagulation (PRP) on the levels of cytochrome oxidase (CO), Zif268, synaptophysin, and growth-associated protein 43 (GAP-43) in the primary visual cortex of adult monkeys.

METHODS

Ten adult primates underwent unilateral argon laser PRP with instrument settings at 300 to 500 microns spot diameter, 200 to 500 mW power intensity, and 0.1 to 0.2 second duration, causing moderate to severe burns in the peripheral retina. At 20 hours, 12 days, 6 months, and 13 months after laser treatment, the visual cortex was assessed histologically for CO and immunohistochemically for Zif268, synaptophysin, and GAP-43.

RESULTS

PRP resulted in transneuronal changes in the relative distributions of CO, Zif268, synaptophysin, and GAP-43 in the primary visual cortex. CO activity was relatively decreased in the lasered eye's ocular dominance columns at 12 days post-PRP, with recovery by 13 months post-PRP. The level of Zif268 was dramatically decreased in the lasered eye's ocular dominance columns at 20 hours post-PRP, with gradual recovery by 13 months post-PRP. Levels of synaptophysin and GAP-43 immunoreactivity were increased in both the lasered and the nonlasered eyes' ocular dominance columns at 6 months post-PRP.

CONCLUSION

PRP treatment results in metabolic activity changes in the visual cortex of the adult monkey. These changes are followed chronologically by spatial redistribution of synaptophysin and GAP-43, neurochemicals known to play a role in cortical plasticity. This study demonstrates, for the first time, that PRP as used in the treatment of diabetic retinopathy results in a redistribution of neurochemicals in the adult monkey visual cortex. Such changes may help explain the anomalous visual functional loss often reported by patients after PRP.

ML-7, chelerythrine and phorbol ester increase outflow facility in the monkey Eye

Baseline or post-drug outflow facility was measured by two-level constant pressure perfusion of the anterior chamber (AC). The AC of one eye of cynomolgus monkeys was exchanged with the myosin light chain kinase (MLCK) inhibitor ML-7, the protein kinase (PK) C inhibitor chelerythrine (CHEL), or the PKC activator phorbol myristate acetate (PMA), followed by continuous AC infusion of the drug. The opposite eye similarly received the corresponding vehicle solution. The facility-effectiveness of subthreshold doses of ML-7 or CHEL + a subthreshold dose of the serine-threonine kinase inhibitor H-7, and of facility-effective doses of CHEL + a subthreshold or effective dose of PMA, were also determined. In 45 min post-exchange perfusions, 100 and 500 microM ML-7 increased outflow facility by 32 and 76%, while 100 and 500 microM CHEL increased facility by 68 and 101%, respectively, adjusted for baseline and contralateral control eye resistance washout. In 90 min post-exchange perfusions, 100 microM ML-7 or CHEL time-dependently increased outflow facility by 23, 49 and 69%, or by 44, 108 and 125% in the first, second and third 30 min periods, respectively. At 50 microM, ML-7 was ineffective, but CHEL increased outflow facility by 36% in the third 30 min period. Ten microM H-7 potentiated the outflow facility effect of 50 microM ML-7 or 20 microM CHEL by 36 and 28%, respectively, in the second 30 min period, and that of 50 microM CHEL by 44% in the overall 60 min post-exchange perfusion, compared to the H-7 only-treated contralateral eye. Ten, 50 or 100 n M PMA dose-dependently increased outflow facility by 23, 62 or 174%. Ten n M PMA + 50 microM CHEL did not induce any additional significant changes in outflow facility compared to 50 n M CHEL alone, while the effect of 50 n M PMA and 100 microM CHEL together was 63% more than that of 100 microM CHEL alone. In conclusion, ML-7/CHEL may increase outflow facility by a cytoskeletal mechanism. Separate or combined treatment with CHEL and PMA increases outflow facility, suggesting that PKC inhibition may not be involved in the facility-increase with either drug.

Effect of latrunculin-A on morphology and actin-associated adhesions of cultured human trabecular meshwork cells

PURPOSE

Determine the effects of the actin cytoskeleton disrupting compound latrunculin-A (LAT-A) on morphology, cytoskeleton, and cellular adhesions of cultured human trabecular meshwork (HTM) cells.

METHODS

HTM cells were cultured to high confluence with endothelial-like morphology and treated with LAT-A at different doses and duration. Topography of living cells was evaluated by videomicroscopy. Distribution and organization of the actin-based cytoskeleton, vinculin- and paxillin-containing focal contacts, and beta-catenin-rich intercellular adhesions were determined by immunofluorescence and digital microscopy.

RESULTS

LAT-A induced pronounced but highly reversible rounding of HTM cells, intercellular separation, and disruption of actin filaments. beta-catenin-rich intercellular adherens junctions were particularly sensitive to LAT-A. Vinculin- and paxillin-containing focal contacts were only partially affected and appeared to be more resistant to the drug than the intercellular interactions.

CONCLUSIONS

The increase in outflow facility in the living primate eye induced by LAT-A may be due to the disorganization and disruption of the actin cytoskeleton and its associated cellular adhesions in the trabecular meshwork.

H-7 effects on the structure and fluid conductance of monkey trabecular meshwork

OBJECTIVE

To determine the effects of H-7 (1-[5-isoquinoline sulfonyl]-2-methyl piperazine) on the structure and fluid conductance of the trabecular meshwork of live cynomolgus monkeys.

METHODS

Fluid outflow was measured by constant pressure perfusion of the anterior chamber with cationized and noncationized gold solution with or without H-7 in opposite eyes. The eyes were fixed by infusing Ito solution and enucleated. Anterior segments were cut into 4 sections, fixed in immersion solution, and embedded in epoxy resin-812. Trabecular meshwork morphologic features were studied by light and electron microscopy.

RESULTS

H-7 affected trabecular meshwork organization and increased fluid outflow. H-7 expanded the intercellular spaces in the juxtacanalicular meshwork, accompanied by removal of extracellular material. The inner wall cells of the Schlemm canal became highly extended, yet cell-cell junctions were maintained. Colloidal gold particles were detected only in limited areas along the subcanalicular region in control eyes; after H-7 treatment, gold was widely seen along the entire inner canal wall. Most inner wall cells in H-7-treated eyes, but only few cells in control eyes, contained gold-loaded vesicles.

CONCLUSION

H-7 inhibits cell contractility, leading to "relaxation" of the trabecular outflow pathway, expanding the draining surface, and permitting more extensive flow through the meshwork.

CLINICAL RELEVANCE

By inhibiting cellular contractility and relaxing the trabecular meshwork, the protein kinase inhibitor H-7 increases outflow facility and reduces intraocular pressure and thus has potential as an ocular hypotensive antiglaucoma medication. Arch Ophthalmol. 2000;118:955-962

Latrunculins' effects on intraocular pressure, aqueous humor flow, and corneal endothelium

PURPOSE

To determine the effects of latrunculin (LAT)-A or -B on intraocular pressure (IOP), aqueous humor flow (AHF), anterior chamber (AC) protein concentration ([protein]AC), corneal endothelial permeability and morphology, and corneal thickness in living cynomolgus monkeys.

METHODS

Topical LAT-A or LAT-B was administered to one eye, and vehicle to the other. IOP was measured by Goldmann tonometry, AHF and corneal endothelium transfer coefficient (ka) by fluorophotometry, [protein]Ac by Lowry assay, corneal endothelial cell morphology by specular microphotography, and corneal thickness by ultrasound pachymetry.

RESULTS

LAT-A began to lower IOP at 6 hours and maximally reduced IOP by 4.6 mm Hg at 9 hours. LAT-B lowered IOP within 1 hour and maximally reduced IOP by 3.1 mm Hg at 6 hours. LAT-A increased AHF by 87% for 3 hours and increased ka by 94% over 6 hours; LAT-B increased ka by 39% over 6 hours without affecting AHF. LAT-A increased IV fluorescein entry into the cornea approximately 10 fold, but did not affect IV fluorescein entry into the AC. LAT-A increased [protein]AC by 25% at 2 hours but not 5.5 hours. LAT-B variably and insignificantly increased [protein]AC: at 1 hour but not at 6.5 hours. LAT-A induced extensive corneal endothelial pseudoguttata within 1 hour, with normal cell counts by 7 days. LAT-B increased central corneal thickness maximally by 47 microm at 3.5 hours.

CONCLUSIONS

LAT-A and -B significantly reduced IOP and were consistent in their facility-increasing effect, indicating that pharmacologic disorganization of the actin cytoskeleton in the trabecular meshwork by latrunculins may be a useful antiglaucoma strategy. However, effects on corneal endothelium or ciliary epithelium are a potential safety issue.

Low doses of pilocarpine do not significantly increase outflow facility in the cynomolgus monkey

Low doses (10(-9)-10(-6) M) of pilocarpine reportedly increase outflow facility in the organ-cultured human eye, suggesting a direct action on the trabecular meshwork. M3 muscarinic receptors have been found in both cultured human trabecular meshwork cells and tissue. We determined whether low pilo doses would increase outflow facility in the living monkey. The anterior chambers of both eyes of 17 pentobarbital anesthetized cynomolgus monkeys were cannulated and outflow facility measured bilaterally by 2-level constant pressure perfusion after an initial 2 ml exchange with Bárány's perfusand containing 24.5 microM phenylephrine (PE). Two subsequent exchanges were performed with one eye receiving Bárány's + PE + 10(-10)-10(-4) M pilocarpine and the contralateral eye receiving only Bárány's + PE. Outflow facility was measured for 35-40 min following each exchange. Accommodation and pupil diameter were measured before each exchange and approximately every 10 min during facility measurements. Outflow facility was significantly increased by 154 and 313% in eyes treated with 10(-5) M and 10(-4) M pilocarpine, respectively, related to contralateral controls. Accommodation and miosis also were induced only at 10(-5) M (accommodation, 3.3 +/- 1.6 diopters, NS; miosis, -4.1 +/- 0.5 mm, P < or = 0.001) and 10(-4) M (accommodation, 10.6 +/- 0.0 diopters, P < or = 0.02; miosis, -3.4 +/- 1.0 mm, P < or = 0.025) pilocarpine. We conclude that low anterior chamber doses of pilocarpine do not increase outflow facility in the living monkey as reported in the organ-cultured human eye, nor do they induce miosis or accommodation. All three parameters respond to pilocarpine at similar doses, and there is no functional evidence of a meaningful outflow facility-relevant pilocarpine effect on the trabecular meshwork at doses lower than those which affect the ciliary muscle.

Experimental glaucoma and cell size, density, and number in the primate lateral geniculate nucleus

PURPOSE

To examine the effects that elevated intraocular pressure (IOP), a glaucoma risk factor, has on the size, density, and number of neurons in the primate lateral geniculate nucleus (LGN).

METHODS

The monkey model of experimental glaucoma was combined with standard histologic staining and analysis techniques. Fourteen animals were examined.

RESULTS

Mean IOPs higher than 40 mm Hg for 2.5, 4, 8, and 24 weeks resulted in reductions of 10% to 58% in the cross-sectional areas of LGN neurons receiving input from the glaucomatous eye. Reductions for animals with lower mean IOPs (37 and 28 mm Hg) for 16 and 27 weeks were 16% and 30%, respectively. Neurons receiving input from the normal eye also were reduced in size (4 -26%). No differential effect in cell size was seen for magnocellular versus parvocellular neurons. Elevation of IOP resulted in an increase in cell density in all layers of the LGN. The increase was approximately two times greater in parvocellular (59%) than magnocellular (31%) layers. When corrected for volumetric shrinkage of the LGN, the estimated loss of neurons was approximately four times greater in the magnocellular than parvocellular layers (38% versus 10%).

CONCLUSIONS

Elevation of IOP affects the size, density, and number of neurons in the LGN, and the volume of the nucleus itself. Although higher mean pressures (more than 40 mm Hg) reduce the period during which these changes occur, comparable damage can be achieved by even moderate (28 -37 mm Hg) levels of elevated IOP. On the basis of cell loss, elevation of IOP appears to have a more profound degenerative effect on the magnocellular than on the parvocellular regions of the LGN.