Comparative tolerability of topical carbonic anhydrase inhibitor MK-927 and its S-enantiomer MK-417

A single-dose, randomised, double-masked, placebo-controlled, five-period cross-over comparative ocular tolerance study was undertaken with the topical carbonic anhydrase inhibitor (CAI) MK-927 (1% and 2% concentrations) and its S-enantiomer MK-417 (1 and 1.8% concentrations) in 20 healthy, normal volunteers. Subjects received one drop of placebo (common vehicle) or CAI in each eye on five different days that were separated by washout intervals of 1 week. The incidence of burning increased significantly after treatment with 2% MK-927 (P<0.01) and 1.8% MK-417 (P < 0.05) as compared with placebo. The mean duration of burning following placebo was 16.8 s, somewhat less than that following CAI application (23–37.1 s). The duration of tearing following CAI treatment was also significantly prolonged (P < 0.05). Pupil size was not changed by CAIs. No other side effects were observed. At 3 h after instillation, intraocular pressure (IOP) was found to be decreased following all four CAI treatments, significantly so with 1% and 1.8% MK-417. The reasonable single-dose tolerability of MK-927 and MK-417 in this sensitive normal-volunteer model supports their potential as topical glaucoma medications. This study suggests that MK-417 may possess greater IOP-lowering activity than MK-927 in man.E.A. Lippa (Director, Clinical Research), F.L. Brunner-Ferber (Assistant Director, Clinical Pharmacology) and D. Panebianco (statistician) are employes of Merck & Co., Inc.; N. Pfeiffer, J. Gerling and F. Grehn have no commercial or proprietary interest in the drugs investigated Offprint requests to: N. Pfeiffer     

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

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

A single dose of the topical carbonic anhydrase inhibitor MK-927 decreases IOP in patients.

MK-927 is a novel topical carbonic anhydrase inhibitor (CAI). We present the first single-dose clinical trial of MK-927 in 24 patients with bilateral primary open-angle glaucoma or ocular hypertension. This investigation was conducted as a two-centre, double-masked, randomised, placebo controlled study. Patients received one drop of 2% MK-927 in one eye and placebo in the other eye. Modified diurnal intraocular pressure (IOP) curves were performed before the study and on one treatment day. A single dose of 2% MK-927 induced a peak mean IOP decrease of 10.5 mmHg at 4.5 hours postdose. With compensation for diurnal variation, as determined by the prestudy diurnal pressure curve, the net peak mean reduction of IOP caused by MK-927 was 7.5 mmHg versus a corresponding net change of 1.4 mmHg in the contralateral placebo treated eye. Thus a single dose of MK-927 gave a clinically significant IOP reduction in patients.     

Comparison of intraocular pressure lowering by topical and systemic carbonic anhydrase inhibitors in the rabbit.

We compared the effect on intraocular pressure (IOP) of maximal doses of a topical carbonic anhydrase inhibitor (CAI) at acidic and alkaline pH where it is maximally effective with full systemic CA inhibition in ocular normotensive New Zealand Albino rabbits. Tonometric IOP levels were measured hourly during 3 hour control period. Topical MK-417 (pKa 5.8, 8.3), a close congener of MK-507 (Dorzolamide) was given as a 1.4% solution at pH 4.5 (n=6) and pH 9.2 (n=6). MK-417 was instilled to the left eye with the right eye used as an untreated control. One hour later methazolamide was given intravenously at 10 mg/kg, a dose known to give full inhibition of the enzyme. Control IOP (mm Hg) was 19.12+/-0.50. One hour following MK-417, the left eye IOP was 13.40 +/-0.70 (pH 4.5) and 13.25+/-0.70 (pH 9.2). The right eye pressure was unchanged. Methazolamide injection at this time gave no further drop in the left eye IOP at either pH. IOP in the right eye fell to 14.00+/-0.70 so that 2 hours after methazolamide injection, the 2 eyes had the same pressure. In conclusion, topical CAI in sufficient dose and correct pH yields IOP lowering equivalent to a maximally effective dose of systemic CAI in rabbits.     

Effect of a topical carbonic anhydrase inhibitor, 6-hydroxybenzo[b]thiophene-2-sulfonamide, on intraocular pressure in normotensive subjects

A prospective randomized clinical trial was carried out to determine the efficacy of 6-hydroxybenzo[b]thiophene-2-sulfonamide, a potent new carbonic anhydrase inhibitor, in lowering intraocular pressure (IOP) in normotensive volunteers. The drug was administered as a 2% suspension twice daily for 1 week to one eye in 10 subjects. Ten other subjects, serving as controls, received a placebo drop to one eye on the same schedule. Subjects and examiners were unaware of whether the drug or placebo was being used. IOP was measured before the study began and twice daily on days 1, 2, 4 and 8 of the study. The drug had no significant effect on IOP. The most likely explanation is failure of an adequate concentration of the drug to reach the ciliary body.     

最新型局部碳酸酐酶抑制剂派立明的临床前及临床研究

派立明是一种最新型的局部碳酸酐酶抑制剂。此药可选择性、高亲和力及明显地抑制碳酸酐酶同功酶Ⅱ的活性,有效地降低眼压。本品滴眼后可快速进入眼组织,在虹膜、睫状体、脉络膜、视网膜、晶状体和血液中有较长的半衰期(数天)。虽然用派立明滴眼后,可在全血中测出药物浓度,提示陔药可全身吸收,但主药和其代谢产物的血浆浓度非常低,在稳定状态下药物与红细胞内碳酸酐酶的结合达不到完全饱和。因此,不会出现全身酸中毒或其他与口服碳酸酐酶抑制剂有关的副作用。对兔眼滴用派立明还町增加视乳头血流量,而对全身酸碱平衡的影响极小。如这一作用在人眼被证实,将对有视神经病变的青光眼患者十分有益。1％派立明每日滴眼2次的降眼压效果最好,且患者的耐受性较多佐胺好,这可提高患者长期用药的依从性。滴眼后最常见的剐作用是视物模糊(6％)及口苦、口酸等味觉异常(6％),总之,派立明的降眼压作用强,副作用小,滴眼舒适,患者耐受性好,是一种非常有价值的抗青光眼新药。     

A comparison of L-671,152 and MK-927, two topically effective ocular hypotensive carbonic anhydrase inhibitors, in experimental animals

L-671,152 is a water-soluble, carbonic anhydrase inhibitor structurally similar to MK-927, a carbonic anhydrase inhibitor that, on topical administration, lowers the intraocular pressure (IOP) of experimental animals and humans. L-671,152 was more potent than MK-927 at inhibiting purified, human erythrocyte carbonic anhydrase II in vitro, as reflected in their respective IC50 values of 0.16 nM and 1.19 nM. Both compounds were compared for topical, ocular hypotensive activity in pigmented rabbits and cynomolgus monkeys. Ocular hypertension was induced in the latter by argon laser photocoagulation of the trabecular meshwork. A 2% solution of L-671,152 was more potent than 2% MK-927 in lowering the IOP of ocular hypertensive monkeys, the maximum reductions being 13.8 mm Hg (37%) and 9.6 mm Hg (27%) at 5 hr and 4 hr, respectively. Moreover, the duration of action of L-671,152 was superior to that of MK-927. The ocular hypotensive effect of L-671,152 was greater than that of MK-927 over a range of concentrations (0.5%-2%) in pigmented rabbits whose IOP was inherently elevated. The peak declines in the IOP of these rabbits after the instillation of 2% solutions of L-671,152 and MK-927 were 6.1 mm Hg and 4.8 mm Hg, respectively. L-671,152 was very effective in lowering the elevated IOP of alpha-chymotrypsinized rabbits and the unilateral instillation of 0.5% L-671,152 into the contralateral eye failed to decrease the elevated IOP of the alpha-chymotrypsinized eye. This finding indicates that the site of action of topically applied L-671,152 is local. The enhancement in the potency of L-671,152 over MK-927 is attributed to a greater inhibition of carbonic anhydrase activity.     

Pharmacological and ocular hypotensive properties of topical carbonic anhydrase inhibitors

There was a time gap of over 40 years between the demonstrated oral effectiveness of acetazolamide in lowering the intraocular pressure (IOP) of glaucoma patients and the introduction of a topical carbonic anhydrase (CA) inhibitor. This is due to the fact that CA-II, the isoenzyme which most likely plays an important role in the production of aqueous humor in humans, must be essentially inhibited by 100% to elicit a pharmacological response. The lack of success with earlier attempts to obtain a topical agent stems from an inability to attain and maintain a sufficiently high intraocular concentration of drug to achieve the required inhibition of CA. Dorzolamide and brinzolamide are two topical CA inhibitors which are currently available to treat ocular hypertension and/or glaucoma. Dorzolamide is a very potent inhibitor of CA-II and its site of action is local within the eye. Like oral CA inhibitors, topically applied dorzolamide lowers IOP by decreasing the production of aqueous humor. The drug is used in monotherapy as a 2% solution administered three times daily. Its ocular hypotensive effect is comparable to that of timolol at peak but is somewhat less at trough. The IOP lowering effect of timolol is enhanced by the twice daily administration of 2% dorzolamide either concomitantly or in combination. Topically applied dorzolamide is generally well tolerated and had a low drop-out rate in clinical studies. The most frequent ocular adverse experience is burning and/or stinging. Corneal and lenticular problems have generally not been encountered with long-term therapy with dorzolamide. Topically applied dorzolamide penetrates directly to the posterior segment of the eye and its presence is consistent with the initial report that dorzolamide increases retinal blood flow velocity in patients with normal tension glaucoma. The most frequent systemic adverse experience is a transient bitter taste. Biochemical changes indicative of the systemic inhibition of CA have not been observed in monotherapy studies lasting up to 2 years. This is in harmony with the inability of dorzolamide at steady-state to saturate CA in the red blood cell and the failure to detect its presence in plasma. A 1% suspension of brinzolamide is comparable to 2% dorzolamide in lowering IOP, both drugs being administered three times daily. Although brinzolamide has a lower incidence of burning/ stinging, it elicits more blurred vision.     

Topical rivastigmine, a selective acetylcholinesterase inhibitor, lowers intraocular pressure in rabbits.

Non-selective acetylcholinesterase (AChE) inhibitors are known hypotensive agents. The purpose of the present investigation was carried out to ascertain whether rivastigmine, a selective carbamate-type inhibitor of AChE, which inhibits selectively an isoform of this enzyme found almost exclusively in the central nervous system, is able to depress the intraocular pressure (IOP) in normotensive rabbits. IOP was monitored with a TonoPen XL in conscious adult rabbits before and hourly up to 8 hr after administration of the drug. Baseline measurements without treatment and after one single topical application of rivastigmine [1% (n=8); 2% (n=4); and 5% (n=6)] to the right eye and of the vehicle alone to the left one were performed. Rivastigmine reduced the IOP of treated eyes significantly (p<0.05) in a dose-independent manner. Maximal effects of 23.2% (5% rivastigmine), 19.6% (2% rivastigmine) and 15.2% (1% rivastigmine) were achieved 1, 3 and 5 hr after application of the drug. A non-significant reduction of IOP in the contralateral eye was also observed. Rabbits evidenced no signs of discomfort after administration of rivastigmine. No conjunctival discharge or other signs of drug related local toxicity were found. Rivastigmine, a selective antagonist of AChE, lowers IOP significantly and may thus be of potential use in glaucoma therapy.     

Electroretinal changes in the presence of a carbonic anhydrase inhibitor

A specific carbonic anhydrase activity inhibitor (methazolamide) was injected into one vitreous body each of 4 New Zealand White rabbits. Electroretinograms (ERG) were recorded before and several times after the methazolamide injection. The stimulus levels maximized the rod and cone response characteristics of the rabbit ERG. The effects of methazolamide were followed over 5 h. During this time, the electroretinograms showed a decline in amplitude of both a and b waves at both stimulus levels. The data support the involvement of carbonic anhydrase in the excitatory physiological events in the retina. Preliminary evidence indicates a slow recovery of the carbonic-anhydrase-inhibited ERG.     

A myosin light chain kinase inhibitor,ML-9, lowers the intraocular pressure in rabbit eyes

The role of myosin light chain kinase (MLCK) in regulating the intraocular pressure (IOP) and outflow facility in rabbit eyes were studied. The IOP and pupil diameter were determined before and after intracameral and intravitreal administration of ML-9, a specific MLCK inhibitor. Total outflow facility and uveoscleral outflow facility was determined 3hr after intracameral administration of ML-9. Immunoblotting was performed to identify MLCK and the 20-kDa light chain of myosin (MLC) isoforms in human trabecular meshwork (TM) cells. The phosphorylation status of MLC was examined following ML-9 treatment. The effects of ML-9 on the morphology and actin and vinculin distribution in cultured TM cells were also studied. In rabbit eyes, administration of ML-9 resulted in a dose-dependent decrease in IOP. An increase of the outflow facility was also observed. Immunoblot analysis revealed the presence of MLCK in human TM cells. Exposure to ML-9 dose-dependently inhibited MLC phosphorylation/activation. The inhibitor caused retraction and dissociation of cells, disruption of actin bundles and impairment of focal adhesion formation in TM cells. ML-9 induces a reduction in IOP and an increase in the outflow facility in rabbit eyes. The IOP-lowering effects may be related to alterations in TM cell shapes. Inhibitors of MLCK may potentially be developed into novel medications for glaucoma.     

Reduction of intraocular pressure by topical administration of an inhibitor of the Rho-associated protein kinase

PURPOSE: Rho-associated coiled coil-forming protein kinase (ROCK) is a downstream target of a small GTPase, Rho. The kinase has been reported to regulate actomyosin-based contractility of smooth muscles by modulation of myosin phosphatase activity. Contractility of ciliary muscle could be implicated in regulation of intraocular pressure while that of ocular vessels could affect blood flow to retina. The present study has been performed to investigate the effect of a ROCK inhibitor on intraocular pressure in rabbits. METHODS: An inhibitor of ROCK, Y-27632, was dissolved in an ophthalmic solution and topically administered to the eye of a Japanese white rabbit. Intraocular pressure was measured by pneumatonography (n = 12, 24 eyes). Constriction of ciliary muscle was measured by the Magnus method using 12 eyes. RESULTS: Topical application of 0.1 and 0.03% Y-27632 significantly decreased the intraocular pressure, with maximum decreases of 5.3 and 4.3 mm Hg after 90 minutes compared with the control eye. Y-27632 inhibited the carbachol-induced constriction of rabbit ciliary muscle. CONCLUSIONS: The ROCK inhibitor reduced intraocular pressure in rabbits by topical instillation. The inhibitor relaxed the excised ciliary muscle which was previously constricted by carbachol suggesting that the inhibitor acts to increase the uveoscleral outflow. Our results suggest that the ROCK inhibitor is a promising treatment for glaucoma therapy in the next generation.     

碳酸酐酶抑制剂的局部应用对大鼠角膜新生血管形成过程中水通道蛋白1表达的影响

背景研究表明,水通道蛋白1（AQP1）与大鼠碱烧伤后角膜新生血管（CNV）的形成密切相关,碳酸酐酶抑制剂具有抑制AQP1的作用,从而可间接抑制CNV,但其全身应用不良反应较重,因此局部碳酸酐酶抑制剂布林佐胺滴眼液对CNV的作用受到关注。目的研究局部应用布林佐胺滴眼液对大鼠碱烧伤后CNV形成过程中AQP1表达的影响。方法健康SD大鼠35只按随机数字表法随机分为正常对照组5只10只眼、模型组15只30只眼和布林佐胺组15只30只眼。模型组和布林佐胺组大鼠用浸有1mol／LNaOH溶液的滤纸贴附于角膜40s建立角膜碱烧伤大鼠模型,布林佐胺组大鼠在造模后用布林佐胺滴眼液点眼,正常对照组和模型组大鼠用生理盐水点眼。造模后3d裂隙灯下对角膜烧伤程度进行分级;造模后3、5、7、10d对大鼠角膜混浊度进行评分,同时测量CNV的生长面积。造模后第10天获取大鼠角膜组织并行苏木精-伊红染色观察大鼠角膜的组织病理学改变,透射电子显微镜下观察各组角膜超微结构的改变。应用免疫组织化学法检测AQP1及血管内皮生长因子（VEGF）在各组大鼠角膜中的表达。结果裂隙灯下模型组与布林佐胺组大鼠角膜碱烧伤的评分差异无统计学意义（t=0．97,P〉0．05）。正常对照组大鼠角膜无水肿、无混浊,无CNV生成;造模后5d布林佐胺组大鼠角膜水肿、混浊评分低于模型组（t=2．18,P〈0．05）,CNV面积小于模型组（t=6．58,P〈0．01）。角膜组织病理学检查显示,布林佐胺组大鼠较模型组大鼠CNV及炎性细胞少。透射电子显微镜检查显示,模型组大鼠CNV旺盛,布林佐胺组大鼠角膜较模型组大鼠角膜血管腔少见。免疫组织化学检测表明,正常对照组大鼠角膜组织中可见AQP1和VEGF呈弱表达;模型组及布林佐胺组大鼠角膜碱烧伤后角膜组织中VEGF灰度值分别为84．92±9．49和78．18±11．41,差异有统计学意义（t=2．48,P=0．02）,2个组AQP1灰度值分别为88．01±11．03和58．10±12．14,差异有统计学意义（t=9．99,P=0．00）。结论布林佐胺滴眼液能抑制大鼠角膜碱烧伤后CNV形成过程中AQP1的高表达,从而间接影响VEGF的表达,抑制或延缓CNV的形成。     

Ocular pulse amplitude, intraocular pressure and beta blocker/carbonic anhydrase inhibition in combined therapy of primary open-angle glaucoma

BACKGROUND: Beyond intraocular pressure (IOP, German abbreviation: IOD) ocular perfusion is increasingly discussed in the pathogenesis of the glaucomas. The present study was designed to investigate for ocular pulse amplitude (OPA) in primary open angle glaucoma patients with elevated intraocular pressure (POAG, German abbreviation: POWG) following application of timolol, a beta-blocker and dorzolamide a topical carbonic anhydrase inhibitor. METHODS: OPA (Ocular Blood Flow System, OBF Labs U.K.) IOP, heart rate, systolic and diastolic brachial artery pressures were measured before and 4 weeks following application of timolol and additional 4 weeks following application of a timolol/dorzolamide combination in 14 POAG patients. RESULTS: Following administration of timolol, IOP was highly significantly reduced in drug treated POAG eyes; this effect was additively enhanced by dorzolamide. Timolol did not affect OPA, whereas dorzolamide significantly increased OPA in drug treated POAG eyes. Systemic perfusion parameters were unchanged. CONCLUSION: Timolol and dorzolamide drastically reduced IOP, in addition dorzolamide increased OPA in POAG, an ocular microcirculatory effect which may further help to improve prognosis of POAG.     

6-amino-2-benzothiazole-sulfonamide. The effect of a topical carbonic anhydrase inhibitor on aqueous humor formation in the normal human eye

The carbonic anhydrase inhibitor, 6-amino-2-benzothiazolesulfonamide, formulated as a 3% suspension in a gel vehicle was instilled in one eye of 21 human subjects in a single dose study to determine its effect on aqueous dynamics. A small but statistically significant effect on aqueous humor flow was observed 2 to 7 hours after application. By 8 hours, the effect had disappeared, and intraocular pressure (IOP) measured 8 hours after application of a single dose was unchanged in these normal volunteers. The drug and its vehicle caused local side effects including irritation, hyperemia, and blurred vision. The authors wondered if multiple doses would produce a greater effect. Four subjects received up to four doses of the drug over 2 days and were restudied. Marked bulbar injection and follicular conjunctivitis, attributable to either the drug or the vehicle, developed in two of the subjects, both contact lens wearers. A milder form of bulbar injection and follicular conjunctivitis developed in a third subject, who received three doses of the drug and was not a contact lens wearer. These side effects precluded additional multiple-dose testing of this formulation of the drug, and no conclusions about the effect of the drug on aqueous flow can be drawn from this portion of the study.     

Relations among IOP reduction, ocular disposition and pharmacology of the carbonic anhydrase inhibitor ethoxzolamide.

We have measured sequentially the concentrations of ethoxzolamide (6-ethoxybenzothiazole-2-sulfonamide) in ocular tissues following its intravenous or topical administration to normal albino rabbits. This was done in parallel with determinations of intraocular pressure (IOP) measured by tonometer or direct manometry. Ethoxzolamide was used because of its very high activity against carbonic anhydrase and experience showing that there is little or no other receptor in tissues. During the course of these experiments it was discovered that the lipid-soluble ethoxzolamide is converted in vivo to a water-soluble metabolite, while retaining high activity against the enzyme. Presumably this is the 6-O-glucuronide adduct. At the minimal dose for maximal effect (4 mg kg-1 i.v. at 45 min) the IOP lowering was 4.2 mmHg, the concentration in anterior uvea was 2.5 mumol kg-1, and the fractional inhibition of the enzyme (i) was 0.9995. The effect of free drug in the anterior uvea and other tissues. Following topical administration i was measured as a function of drug and enzyme in ciliary process. IOP lowering at 1 hr was -1.9 mmHg and i = 0.9993. By 4 hr i = 0.9980 and the pharmacological effect disappeared. At 8 hr the concentration of ethoxzolamide in the ciliary process is 0.4 mumol kg-1, essentially that of enzyme, with no free drug present: drug is now a marker for enzyme. Ethoxzolamide also labels the red cell carbonic anhydrases in the rabbit as well as other species including man. There appears to be no ethoxzolamide receptor other than carbonic anhydrase.(ABSTRACT TRUNCATED AT 250 WORDS)     

A cyclic AMP phosphodiesterase inhibitor, 8'-pivaloyloxymethyl ester (POM-ester) of griseolic acid, lowers rabbit intraocular pressure.

The effects of griseolic acid (GA), a cyclic-AMP phosphodiesterase (PDE) inhibitor, and its 8'-pivaloyloxymethyl (POM) ester on intraocular pressure (IOP) in rabbits were investigated. When 50 microliters of 1 and 2% GA POM ester solutions were topically applied to one eye in normal rabbits, significant IOP decreases were detected at 2 hrs and at 1 to 5 hrs, respectively. Other than ocular hypotension, no other ocular effects were detected locally even after administration of 2% GA POM ester. A more marked reduction in IOP occurred after the intravitreal injection of the GA POM ester. IOP was also reduced when GA was used in an intravitreal injection but not when it was topically applied. The difference in permeability between GA and GA POM ester across the corneal epithelium may explain why GA failed to reduced IOP following topical administration. GA and the GA POM ester inhibited cAMP PDE in rabbit ciliary body at low concentrations, the I50 being 0.075 microM and 2.4 microM, respectively, with 0.25 microM cAMP as substrate. GA and the GA POM ester markedly increased cAMP levels in vitro in iris-ciliary body specimens. Possibly, GA POM ester or its analogues may represent a new mechanistic class of ocular hypotensive agents.