Effects of H-7 on the iris and ciliary muscle in monkeys

Contractile effect of aqueous Pleurotus tuberregium extract on the isolated bovine iris

BACKGROUND

Aqueous extract of Pleurotus tuberregium (PT) has been shown to reduce intraocular pressure (IOP) but the underlying mechanism has not been explained.

PURPOSE

To investigate the effect of PT on the bovine iris in vitro in comparison with acetylcholine (ACh).

METHOD

Strips of the iris were mounted in 10 ml organ baths and exposed to increasing concentrations of PT, ACh and a combination of both agents. The effect of atropine on the responses to the agents was also investigated.

RESULTS

PT and ACh separately caused contractile responses on the iris, but their effect reduced with higher concentrations. Combination of PT and ACh did not significantly alter the reduced responses seen with high concentrations of either agent. Atropine completely abolished the contractile responses of the agents.

CONCLUSION

The contractile effect of PT on muscarinic receptor-containing iris muscle may explain its IOP reducing property.

Effect of H-7 on secondary cataract after phacoemulsification in the live rabbit eye

PURPOSE

This study is aimed to determine if the serine-threonine kinase inhibitor H-7 inhibits secondary cataract after phacoemulsification in the live rabbit eye.

METHODS

Eighteen rabbits underwent extracapsular lens extraction by phacoemulsification in 1 eye. The eye was treated with intravitreal H-7 (300 or 1,200 μM; n = 6 or 5) or balanced salt solution (BSS) (n = 7) immediately after the surgery and twice weekly for 10 weeks. Each eye received slit lamp biomicroscopy once a week, during which posterior capsule opacification (PCO) was evaluated. The eye was then enucleated and the lens capsule was prepared, fixed, and imaged. PCO was evaluated again on the isolated lens capsule under a phase microscope. Soemmering's ring area (SRA) and the entire lens capsule area were measured from capsule images on a computer and the percentage of SRA (PSRA) in the entire capsule area was calculated. Wet weight of the capsule (WW) was determined on a balance.

RESULTS

No significant difference in PCO was observed in any comparison. No significant differences in SRA, PSRA, and WW were observed between the 300 μM H-7-treated eye and the BSS-treated eye. However, SRA, PSRA, and WW in the 1,200 μM H-7-treated eye were significantly smaller than those in the BSS-treated eye [28.3 ± 16.2 vs. 61.4 ± 8.86 mm(2) (P = 0.001), 33% ± 20% vs. 65% ± 15% (P = 0.01), and 65.6 ± 27.9 vs. 127.0 ±37.3 mg (P = 0.01)].

CONCLUSIONS

Intravitreal H-7 (1,200 μM) significantly inhibits Soemmering's ring formation in the live rabbit eye, suggesting that agents that inhibit the actomyosin system in cells may prevent secondary cataract after phacoemulsification.

Combined Effects of H7 and Pilocarpine on Anterior Segment Physiology in Monkey Eyes

PURPOSE

To determine, in monkey eyes in vivo if low doses of the cholinergic agonist pilocarpine (PILO) can enhance the outflow facility responses to a maximal dose of the serine-threonine kinase inhibitor H7 without producing apparent miosis and/or excessive accommodation.

METHODS

Outflow facility was determined by two-level constant pressure perfusion in living monkeys after 24.5 microM phenylephrine (PE) bilaterally (stimulates the iris dilator without influencing the iris sphincter, ciliary muscle, or outflow facility, and facilitates the measurement of miosis and accommodation), 24.5 microM PE + 300 microM H7 (maximal outflow facility-effective dose) bilaterally, or 24.5 microM PE + 300 microM H7 +/- 2 or 10 microM PILO (2 microM PILO alone does not significantly increase outflow facility or accommodation but moderately constricts the pupil; 10 microM PILO is a threshold outflow facility-effective dose) in opposite eyes. Pupil diameter (Vernier calipers) and accommodation (coincidence refractometer) were measured essentially concurrently.

RESULTS

Outflow facility in the PE + H7 + 10 microM PILO eyes was 73% higher than that in the PE + H7 eyes (n = 6; p < 0.05). Accommodation was greater (n = 4; 2.6 vs. 0.6 D; p < 0.05) and pupil diameter was smaller (n = 6; 3.4 vs. 7.6 mm; p < 0.02) in the former than in the latter. No significant difference in outflow facility, accommodation or pupil diameter was observed between the PE + H7 + 2 microM PILO eyes and the PE + H7 eyes.

CONCLUSIONS

In living monkeys, 10 microM PILO, but not 2 microM PILO, enhances the 300 microM H7-induced increase in outflow facility with only approximately 3 diopters of accommodation, whereas 300 microM H7 partially inhibits the 2 microM PILO-induced, but not the 10 microM PILO-induced miosis. This suggests that, although the miosis following the threshold facility-effective dose of PILO cannot be reduced by combination with the maximal facility-effective dose of H7, the combination may at least benefit young glaucoma or ocular hypertension patients who are bothered by PILO-induced myopia more than by miosis.

Nonmuscle myosin II is responsible for maintaining endothelial cell basal tone and stress fiber integrity

Cultured confluent endothelial cells exhibit stable basal isometric tone associated with constitutive myosin II regulatory light chain (RLC) phosphorylation. Thrombin treatment causes a rapid increase in isometric tension concomitant with myosin II RLC phosphorylation, actin polymerization, and stress fiber reorganization while inhibitors of myosin light chain kinase (MLCK) and Rho-kinase prevent these responses. These findings suggest a central role for myosin II in the regulation of endothelial cell tension. The present studies examine the effects of blebbistatin, a specific inhibitor of myosin II activity, on basal tone and thrombin-induced tension development. Although blebbistatin treatment abolished basal tension, this was accompanied by an increase in myosin II RLC phosphorylation. The increase in RLC phosphorylation was Ca(2+) dependent and mediated by MLCK. Similarly, blebbistatin inhibited thrombin-induced tension without interfering with the increase in RLC phosphorylation or in F-actin polymerization. Blebbistatin did prevent myosin II filament incorporation and association with polymerizing or reorganized actin filaments leading to the disappearance of stress fibers. Thus the inhibitory effects of blebbistatin on basal tone and induced tension are consistent with a requirement for myosin II activity to maintain stress fiber integrity.

Effect of H-7 and Lat-B on retinal physiology

PURPOSE

To investigate the effects of H-7 and Latrunculin B (Lat-B) on retinal vascular permeability and electrophysiology at concentrations that increase outflow facility in monkeys.

METHODS

One eye of 1 rhesus and 22 cynomolgus monkeys received an intravitreal bolus injection of H-7 or Lat-B; the opposite eye received vehicle. Multifocal electroretinograms (mfERGs), and photopic and scotopic full-field electroretinograms (ffERGs, sERGs) were recorded in subsets of monkeys at baseline and at multiple time-points post-H-7 or Lat-B. Vitreous fluorophotometry (VF) and fluorescein angiography (FA) were also performed.

RESULTS

No differences between the H-7 or Lat-B treated and control eyes were found in ffERGs, mfERGs, sERGs, or in FAs in any monkey. No significant difference was found in vitreous fluorescein levels between H-7 treated or Lat-B treated vs. control eyes.

CONCLUSIONS

No effect on retinal vascular permeability or retinal electrophysiology was apparent after intravitreal administration of H-7 or Lat-B at doses that increase outflow facility and lower IOP when given intracamerally.

Effects of novel ethacrynic acid derivatives on human trabecular meshwork cell shape, actin cytoskeletal organization, and transcellular fluid flow

To determine efficacy and therapeutic index in the context of ocular hypotensive activity of the new ethacrynic acid (ECA) derivatives of the series (SA8,248 and SA8,389), 9,000 series (SA9,000, SA9,622 and SA9,995) and ticrynafen, we undertook a comparative evaluation of the dose-dependent effects of these compounds on human trabecular meshwork (HTM) cell shape, actin cytoskeletal organization, focal adhesions and transcellular fluid flow. Responses were either scored using an arbitrary scale of 1-5 or quantified. Compounds of the 9000 series (SA9,995>SA9,000>SA9,622) were found to be 14- to 20-fold more potent than ECA, ticrynafen or analogs from the 8,000 series (SA8,389>SA8,248) in terms of ability to induce cell shape alterations in HTM cells. Similarly, compounds of the 9,000 series (SA9,995>SA9,622>SA9,000) were found to be much stronger (2 to 20 fold) than ECA, ticrynafen or analogs of the 8000 series in terms of affecting decreases in actin stress fiber content in HTM cells. Analogs of the 9000 series (SA9,622>SA9,995>SA9,000) were also observed to be 8 to 10 fold more potent than ECA (SA8,389>ECA>SA8,248>ticrynafen) at eliciting decreases in cellular focal adhesions. Interestingly, analogs of the 9000 series (SA9,000>SA9,622>SA9,995) and SA8,248 demonstrated a huge increase (by many folds) in transcellular fluid flow of HTM cell monolayers as compared to ECA and ticrynafen. Collectively, these analyses revealed that the structural modification of ECA improves its ocular hypotensive efficacy, indicating that the SA9,000 series compounds might be promising novel ocular hypotensive drugs.

Contribution of ROCK in contraction of trabecular meshwork: proposed mechanism for regulating aqueous outflow in monkey and human eyes

Aqueous outflow in the conventional outflow pathway is regulated by the contraction and relaxation of the ciliary muscle (CM) and the trabecular meshwork (TM). Rho-associated coiled coil-forming protein kinase (ROCK) is thought to regulate actomyosin-based contractility in many types of cells by phosphorylation of ROCK substrates. In animal models, ROCK inhibitor Y-39983 relaxed CM and TM and decreased intraocular pressure (IOP). Thus, ROCK is implicated in the regulation of aqueous outflow and IOP. However, the site of action of ROCK in monkey and man is unknown. In the present communication, RT-PCR analysis of monkey tissues showed higher levels of mRNAs for ROCK and ROCK substrates in TM compared to CM. Human TM also showed higher levels of mRNAs for ROCK and ROCK substrates compared to CM. Differences between TM and CM in human were not as high as in monkey. ROCK inhibitor Y-39983 led to a dose-dependent relaxation of carbachol-induced, contracted TM from monkey. In contrast, Y-39983 was only slightly effective in relaxing CM. Our results suggested that TM was one of the major sites for regulating IOP by ROCK. ROCK inhibitor Y-39983 might be a candidate drug for lowering IOP by increasing conventional outflow and producing fewer side effects on accommodation and miosis.

Effects of the Rho kinase inhibitor Y-27632 and the phosphatase inhibitor calyculin A on outflow facility in monkeys

Previous studies have shown that the inhibition of Rho kinase is involved in the regulation of outflow facility in the live rabbit eye and the enucleated porcine eye. However, it is unknown whether the Rho kinase inhibition will do the same in non-human primates. To determine if the Rho kinase inhibitor Y-27632 will reduce outflow resistance in the live monkey eye, if Y-27632 and the phosphatase inhibitor calyculin A (Caly-A which antagonises Y-27632-induced MLC dephosphorylation) will affect outflow facility differently, and if the latter will inhibit effect of the former on facility, we studied effects of Y-27632 and Caly-A on outflow facility in living monkeys separately and concurrently. Total outflow facility was measured by 2-level constant pressure perfusion of the anterior chamber (AC) before and after exchange with different doses of Y-27632 (1, 10 and 100 microM) or Caly-A (10, 50 and 100 nM), or vehicles, followed by continuous AC infusion of corresponding drug/vehicle solution, in opposite eyes of cynomolgus or rhesus monkeys. The effect of 100 microM Y-27632 or 100 nM Caly-A vs vehicle and the effect of 100 microM Y-27632+100 nM Caly-A vs 100 microM Y-27632 alone on outflow facility were also determined in monkeys pre-treated topically with 10 microl of 1% atropine in both eyes 1 hr before perfusion. Both Y-27632 and Caly-A dose-dependently increased outflow facility by up to 2-3 fold in monkeys, adjusted for baseline and contralateral control eye washout. Pre-treatment with 1% topical atropine partially inhibited the effect of 100 nM Caly-A, but not 100 microM Y-27632, on outflow facility. 100 nM Caly-A gradually and partially inhibited the Y-27632-induced facility increase. In conclusion, Y-27632 increases outflow facility in monkeys presumably by inhibiting cellular contractility in the TM. Caly-A increases outflow facility by complicated mechanisms perhaps including drug-induced ciliary muscle contraction and cytoskeletal reorganisation in TM cells. The partial inhibitory effect of Caly-A on the Y-27632-induced increase in outflow facility may reflect the former partially inhibiting the latter's relaxation of cells in the TM.

New ethacrynic acid derivatives as potent cytoskeletal modulators in trabecular meshwork cells

A series of ethacrynic acid (ECA) derivatives were synthesized and examined for ocular hypotensive activity. Efficacy was evaluated in a cell-shape assay, using human trabecular meshwork cells, and cytotoxicity in a (3-(4,5-dimethylthiazole-2-yl)-5-(3-carboxymethoxy phenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay, using cultured bovine trabecular meshwork cells. Many of the derivatives demonstrated efficacy equal to or greater than that of ECA. SA9000 was selected as the most promising candidate for a novel ocular hypotensive drug with few side effects.

Early molecular events in the assembly of the focal adhesion-stress fiber complex during fibroblast spreading

Cell adhesion to the extracellular matrix triggers the formation of integrin-mediated contact and reorganization of the actin cytoskeleton. Examination of nascent adhesions, formed during early stages of fibroblast spreading, reveals a variety of forms of actin-associated matrix adhesions. These include: (1). small ( approximately 1 microm), dot-like, integrin-, vinculin-, paxillin-, and phosphotyrosine-rich structures, with an F-actin core, broadly distributed over the ventral surfaces of the cells; (2). integrin-, vinculin-, and paxillin-containing "doublets" interconnected by short actin bundles; (3). arrays of actin-vinculin complexes. Such structures were formed by freshly plated cells, as well as by cells recovering from latrunculin treatment. Time-lapse video microscopy of such cells, expressing GFP-actin, indicated that long actin cables are formed by an end-to-end lining-up and apparent fusion of short actin bundles. All these structures were prominent during cell spreading, and persisted for up to 30-60 min after plating. Upon longer incubation, they were gradually replaced by stress fibers, associated with focal adhesions at the cell periphery. Direct examination of paxillin and actin reorganization in live cells revealed alignment of paxillin doublets, forming long and highly dynamic actin bundles, undergoing translocation, shortening, splitting, and convergence. The mechanisms underlying the assembly and reorganization of actin-associated focal adhesions and the involvement of mechanical forces in regulating their dynamic properties are discussed.

A new dimension in retrograde flow: centripetal movement of engulfed particles

Centripetal motion of surface-adherent particles is a classic experimental system for studying surface dynamics on a eukaryotic cell. To investigate bead migration over the entire cell surface, we have developed an experimental assay using multinuclear giant fibroblasts, which provide expanded length scales and an unambiguous frame of reference. Beads coated by adhesion ligands concanavalin A or fibronectin are placed in specific locations on the cell using optical tweezers, and their subsequent motion is tracked over time. The adhesion, as well as velocity and directionality of their movement, expose distinct regions of the cytoplasm and membrane. Beads placed on the peripheral lamella initiate centripetal motion, whereas beads placed on the central part of the cell attach to a stationary cortex and do not move. Careful examination by complementary three-dimensional methods shows that the motion of a bead placed on the cell periphery takes place after engulfment into the cytoplasm, whereas stationary beads, placed near the cell center, are not engulfed. These results demonstrate that centripetal motion of adhering particles may occur inside as well as outside the cell. Inhibition of actomyosin activity is used to explore requirements for engulfment and aspects of the bead movement. Centripetal movement of adherent particles seems to depend on mechanisms distinct from those driving overall cell contractility.

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.

The regulation of trabecular meshwork and ciliary muscle contractility

Current models of aqueous humor outflow no longer treat trabecular meshwork (TM) as an inert tissue passively distended by the ciliary muscle (CM). Instead, ample evidence supports the theory that trabecular meshwork possess smooth muscle-like properties and is actively involved in the regulation of aqueous humor outflow and intraocular pressure. In this model, trabecular meshwork and ciliary muscle appear as functional antagonists, with ciliary muscle contraction leading to a distension of trabecular meshwork with subsequent reduction in outflow. and with trabecular meshwork contraction leading to the opposite effect. Smooth-muscle relaxing substances would therefore appear to be ideal candidates for glaucoma therapy with the dual goal of reducing intraocular pressure via the trabecular meshwork and of improving vascular perfusion of the optic nerve head. However, for such substances to effectively lower intraocular pressure, the effect on the ciliary muscle would have to he minimal. For this reason, more information is needed on the signalling processes involved in regulating trabecular meshwork and ciliary muscle contractility. This review attempts to outline current knowledge of signal transduction pathways leading to relaxation and contraction of ciliary muscle and trabecular meshwork. Pathways can be classified as involving or not involving changes of membrane voltage and of requiring or not requiring external calcium: possibly, other pathways exist. These different pathways involve different ion channels and isoforms of PKC and are expressed to a differing degree in ciliary muscle and trabecular meshwork, leading to differential responses when exposed to relaxing or contracting pharmacological agents. Some of these agents. like tyrosine kinase inhibitors and inhibitors of PKC. have been shown to relax trabecular meshwork while leaving ciliary muscle comparatively unaffected. This profile makes these substances appear as ideal drugs for simultaneously improving ocular outflow and retinal circulation, parameters that determine the time course of visual deterioration in glaucoma.

Advances in glaucoma diagnosis and therapy for the next millennium: new drugs for trabecular and uveoscleral outflow

Advances in our understanding of the physiology and molecular biology of the trabecular and uveoscleral outflow pathways of the eye will lead to the development of new approaches for glaucoma therapy. Therapies of the future will target the structures and enzymes involved in maintaining cell shape and cell-cell and cell-extracellular matrix interactions. Altering the extracellular matrix in the ciliary muscle has been important in the intraocular pressure lowering effects of prostaglandins and will be developed further as an approach to enhancing outflow through the trabecular meshwork. Gene therapy may be used to enhance or suppress the endogenous targets that are ultimately responsible for the outflow enhancement triggered by these agents.

Molecular diversity of cell-matrix adhesions

In this study we have examined for molecular heterogeneity of cell-matrix adhesions and the involvement of actomyosin contractility in the selective recruitment of different plaque proteins. For this purpose, we have developed a novel microscopic approach for molecular morphometry, based on automatic identification of matrix adhesions, followed by quantitative immunofluorescence and morphometric analysis. Particularly informative was fluorescence ratio imaging, comparing the local labeling intensities of different plaque molecules, including vinculin, paxillin, tensin and phosphotyrosine-containing proteins. Ratio imaging revealed considerable molecular heterogeneity between and within adhesion sites. Most striking were the differences between focal contacts, which are vinculin- and paxillin-rich and contain high levels of phosphotyrosine, and fibrillar adhesions, which are tensin-rich and contain little or no phosphotyrosine. Ratio imaging also revealed considerable variability in the molecular substructure of individual focal contacts, pointing to a non-uniform distribution of phosphotyrosine and the different plaque constituents. Studying the quantitative relationships between the various components of the submembrane plaque indicated that the levels of vinculin, paxillin and phosphotyrosine in adhesion sites are positively correlated with each other and negatively correlated with the levels of tensin. Tyrosine phosphorylation of focal contacts was highly sensitive to cellular contractility, and was diminished within 5 minutes after treatment with the kinase inhibitor H-7, an inhibitor of actomyosin contractility. This was followed by the loss of paxillin and vinculin from the focal adhesions. Tensin-rich fibrillar adhesions were relatively insensitive to H-7 treatment. These findings suggest a role for contractility in the generation of matrix adhesion diversity.