Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0595921 (intraocular pressure)
 11,750 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Carbonic anhydrase was extracted from the excised processes of the ciliary bodies of 10 pairs of enucleated human eyes, and the isoenzyme composition was assayed by measuring the degree of inhibition produced by acetazolamide at two standard concentrations. Also, the effect of incubating with iodoacetate was determined in two pairs of these eyes. Only isoenzyme C was detected. Accordingly, it seems that differences in reduction of intraocular pressure that are common among patients treated for glaucoma with systemic carbonic anhydrase inhibitors, despite uniform serum concentrations, are not attributable to interindividual variation of carbonic anhydrase isoenzymes in the ciliary processes.
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PMID:Identification of isoenzyme C as the principal carbonic anhydrase in human ciliary processes. 11 Jul 25

This article reviews standard treatment modalities for patients with glaucoma and describes 3 classes of drugs which are undergoing development: apraclonidine (aplonidine, ALO 2145), an alpha 2-adrenergic agonist which has been released for clinical use; topical carbonic anhydrase inhibitors, a modification of the systemic carbonic anhydrase inhibitors currently in use; and prostaglandins (PGs), a new class of drugs with topical ocular hypotensive activity. Standard treatment modalities include parasympathomimetic agents such as pilocarpine, carbachol, and phospholine iodide, which lower intraocular pressure (IOP) by increasing aqueous outflow through the trabecular meshwork. A newer form of pilocarpine as a gel produces a longer action. Adrenergic agonist medications, such as epinephrine (adrenaline) and its prodrug dipivefrine (dipivalyl epinephrine), function by increasing uveoscleral outflow and trabecular outflow facility. A decrease in aqueous formation by the ciliary processes is thought to be the mechanism of action of beta-adrenoceptor antagonists, but the physiological basis for this action has not been clearly demonstrated. A newer beta-blocker, betaxolol, has relatively selective beta 1-blocking activity. Carbonic anhydrase inhibitors are nonbacteriostatic sulphonamide derivatives which decrease aqueous formation by the ciliary body. Almost 50% of patients taking these medications are unable to tolerate them because of their adverse effects, and there is thus much interest in the development of a topical carbonic anhydrase inhibitor with the potential for fewer adverse effects. MK 507 is the most recent and most potent compound in the series of topically active carbonic anhydrase inhibitors. Apraclonidine hydrochloride is a derivative of clonidine hydrochloride, an alpha 2-adrenergic agonist. Clonidine has previously been shown to lower IOP significantly, but has the potential to produce marked lowering of both systolic and diastolic blood pressures. Its major ocular effect appears to be a decrease in aqueous production. The structural modification to apraclonidine decreases corneal absorption and the drug's ability to cross the blood-brain barrier, minimising the risk of centrally mediated cardiovascular side effects. Apraclonidine may also influence secondary avenues of aqueous outflow, such as uveoscleral outflow, and may also affect conjunctival and episcleral vascular flow. It produces a mean decrease in IOP of 25% for as long as 12 hours. Adverse effects include blanching of the conjunctiva, minimal mydriasis and eyelid retraction. This drug has been approved in the US for use in prevention of elevated IOP after argon laser trabeculoplasty and iridotomy, and has potential uses in preventing an IOP rise after YAG laser posterior capsulotomy and cataract surgery in patients already on other antiglaucomatous medications.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:New developments in the drug treatment of glaucoma. 171 57

Carbonic anhydrase (CA) activity plays an important role in controlling aqueous humor production in the eye and in regulating intraocular pressure. Prior studies identified the soluble isozymes CA II and CA I in the human eye and also suggested a distinct membrane-associated CA. We used an antibody to CA IV, the membrane-anchored isozyme from human lung, to study CA IV in eye tissues and to compare its distribution with that of CA II. We found intense immunostaining for CA IV associated with endothelial cells of one specific uveal capillary bed, the choriocapillaris. CA IV was not detected in endothelial cells of the contiguous capillaries of the iris or in endothelial cells of other vessels. Immunoreactivity for CA IV was also intense in epithelial and fiber cells of the lens but was not detectable in the neuroretina, the ciliary process (except for capillaries), and the cornea, all sites where immunostaining with anti-CA II antibody was intense. These studies indicate that the membrane-associated CA in human eye, which was suspected from histochemical studies, is CA IV. Defining the physiological role of this ocular isozyme remains a challenge.
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PMID:Localization of carbonic anhydrase IV in a specific capillary bed of the human eye. 190 14

Carbonic anhydrase inhibitor (CAI) side effects are common, but not well understood. Many ideas have surfaced on how to reduce these side effects, even though there is little scientific evidence to support some of the advice. One recommendation involves switching drugs when patients are intolerant of a particular CAI agent. This study included 44 glaucoma patients who needed a CAI drug. All patients were placed on acetazolamide tablets 250 mg qid. Of those who could not tolerate this drug (26 patients), 22 were switched to methazolamide. Half of these 22 (50%) were considered to have "severe" side effects to methazolamide, while 88% of them had "severe" side effects to acetazolamide. Reduction of intraocular pressure was similar on the two drugs. Other than switching drugs to reduce CAI side effects, one can try reduced dosages, a gradual dosage increase, and patience. Administering sodium bicarbonate or potassium, or taking the CAI drug with meals are unproven remedies.
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PMID:Reducing side effects of carbonic anhydrase inhibitors. 723 16

Carbonic anhydrase inhibitors (CAIs) lower intraocular pressure by reducing aqueous flow. It has been thought that this pharmacologic reduction of aqueous flow is mediated by the ciliary epithelium, but it is not known whether this cellular action is effected by inhibition of the membranal (CA IV) and/or cytosolic (CA II) carbonic anhydrases of the ciliary epithelium. The isolated ciliary epithelial bilayer maintains its anatomic and functional polarity and generates a transepithelial potential difference (TEP) in an Ussing type chamber. Depletion of HCO3-, accomplished either with an HCO3(-)-free solution bathing the epithelial bilayer, or, with addition of freely permeant CAIs to HCO3(-)-containing media, (from either the PE or NPE side of the bilayer) depolarizes the preparation. Addition of CAIs to an HCO3(-)-depleted preparation has no further effect, indicating the specific action of the CAIs. The CAI, 2-p-NH2 benzenesulfonamido-1,3,4,-thiadiazole-5-SO2NH2, linked to polybutadiene maleic acid yields an impermeant polymer of 20000 Da with no loss of activity. At 45 microM this impermeant polymer caused a 60% increase in the SCC, seen only when the compound was applied to the NPE side of the bilayer. This latter result indicates an effect from inhibition of CA IV in the basolateral membranes of the NPE. Thus there are probably two different cellular actions of CAIs upon the ciliary epithelium to reduce aqueous inflow, cytoplasmic and membranal. The action of NPE basolateral membranal CA IV is probably linked to the chloride/bicarbonate exchanger.
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PMID:Membrane carbonic anhydrase (IV) and ciliary epithelium. Carbonic anhydrase activity is present in the basolateral membranes of the non-pigmented ciliary epithelium of rabbit eyes. 879 59

The importance of the conjunctival/scleral pathway as a route of entry into the ciliary body, and in particular uptake and deposition by vessels, was investigated. A constant concentration of methazolamide analogs as well as 6-carboxyfluorescein (6-CB) and rhodamine B (RB) was maintained on either the cornea or the conjunctiva/sclera tissue, the latter excluding the cornea. The solutions were applied with the use of a cylindrical well affixed to the cornea of an anesthetized white rabbit. After two hours, concentrations of drug or dye were measured in cornea, aqueous humor or iris/ciliary body for both routes of entry. Confocal microscopy methods were used to determine reflected fluorescence images for 6-CB and RB. Carbonic anhydrase inhibition, partitioning, solubility and intraocular pressure (IOP) measurements were also determined. Permeability calculations were estimated for drug diffusing against aqueous flow within the posterior chamber. The conjunctival/scleral route of entry produced higher iris/ciliary body concentrations for all compounds except for the lipophilic RB. Confocal microscopy results suggested that drug is gaining entry into the ciliary body through vessel uptake in the sclera. Following entry of drug into the conjunctival/scleral tissue, a significant portion enters scleral vessels and deposits within the ciliary body. Calculations are given that indicate that once drug penetrates the cornea it is highly unlikely drug diffuses through the pupil against aqueous flow to enter the posterior chamber and reach the ciliary body.
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PMID:Penetration into the anterior chamber via the conjunctival/scleral pathway. 902 39

Carbonic anhydrase inhibitors (CAI) have been investigated for topical administration in glaucoma therapy during the past few years. Dorzolamide is the first topical CAI to become available for clinical use. CAI's lower intraocular pressure (IOP) by the inhibition of bicarbonate secretion into the posterior chamber by the ciliary epithelium, thereby suppressing aqueous humor production and lowering the IOP. A topical CAI with ocular hypotensive efficacy is comparable with that of oral agents, but without their systemic effects would represent a major advance in medical treatment of glaucoma and ocular hypertension. Data from clinical trials with dorzolamid (Trusopt) have shown this topical carbonic anhydrase inhibitor to be comparable in efficacy to beta-blockers when used as monotherapy, and as effective as pilocarpine when used as an adjunct to beta-blocker therapy. The aim of this paper was to present the results of long-term clinical and experimental studies with dorzolamid (Trusopt).
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PMID:[Trusopt--a new form of drug for treating glaucoma]. 945 71

Carbonic anhydrase (CA) plays an important role in the secretion of aqueous humor. The orally administered CA inhibitor acetazolamide lowers the intraocular pressure (IOP) of patients with glaucoma. However, approximately 50% of patients stop treatment with acetazolamide as a consequence of intolerable side effects due to the extraocular inhibition of the enzyme. This prompted attempts to develop a topically active CA inhibitor. Merck Research Laboratories focused on developing a water- and solvent-soluble compound to penetrate the cornea. Dorzolamide hydrochloride is a potent inhibitor of human CA isoenzyme II, with an IC50 value of 0.18 nM in vitro. In contrast, its inhibitory activity against human CA isozyme I is much weaker (IC50 value of 600 nM). Topically administered dorzolamide penetrated the ciliary body, inhibited its CA activity and had a hypotensive effect in rabbits; in contrast, topical administration of acetazolamide or methazolamide did not decrease IOP. In clinical trials, dorzolamide administered 3 times daily was effective in lowering IOP in patients with open-angle glaucoma or ocular hypertension. The hypotensive effect of dorzolamide 0.5% was similar to that of oral CA inhibitors or timolol (0.25%) twice daily. Dorzolamide did not induce the severe systemic adverse events associated with oral CA inhibitors. Dorzolamide was as effective as pilocarpine or dipivefrine as an adjunctive therapy in patients receiving beta-adrenergic antagonists. Dorzolamide also reduced IOP and accelerated retinal arteriovenous passage time in addition to improving visual function in patients with normal-tension glaucoma.
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PMID:[Pharmacological profiles of the potent carbonic anhydrase inhibitor dorzolamide hydrochloride, a topical antiglaucoma agent]. 1094 64

Carbonic anhydrase inhibitors are effective in lowering intraocular pressure, the primary indication of glaucoma. Human carbonic anhydrase II, and possibly carbonic anhydrase IV (CAII and CAIV, respectively), help regulate fluid secretion into the anterior chamber of the eye. Because inhibitors currently formulated as drugs to treat glaucoma were designed to target CAII, an understanding of the structural basis of CAII-CAIV discrimination by inhibitors would be useful for probing the role of each isozyme in the etiology of the disease. Here, we report the X-ray crystal structures of three novel thieno[3,2-e]-1,2-thiazine-6-sulfonamides complexed with CAII and the computationally predicted structures of the same compounds complexed with CAIV. All three compounds bind with similar affinity to CAII, but they bind with up to 100-fold lower affinities to CAIV. Comparisons of experimentally determined structures of CAII-inhibitor complexes and computationally predicted structures of CAIV-inhibitor complexes allow us to rationalize these affinity trends and outline molecular features that may contribute to high-affinity inhibitor binding to CAIV. This study demonstrates how experimental structure determination methods and computational structure prediction methods can be used together to answer questions that cannot be answered by either method alone.
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PMID:Structural aspects of isozyme selectivity in the binding of inhibitors to carbonic anhydrases II and IV. 1183

The oxygen tension of the optic nerve is regulated by the intraocular pressure and systemic blood pressure, the resistance in the blood vessels and oxygen consumption of the tissue. The oxygen tension is autoregulated and moderate changes in intraocular pressure or blood pressure do not affect the optic nerve oxygen tension. If the intraocular pressure is increased above 40 mmHg or the ocular perfusion pressure decreased below 50 mmHg the autoregulation is overwhelmed and the optic nerve becomes hypoxic. A disturbance in oxidative metabolism in the cytochromes of the optic nerve can be seen at similar levels of perfusion pressure. The levels of perfusion pressure that lead to optic nerve hypoxia in the laboratory correspond remarkably well to the levels that increase the risk of glaucomatous optic nerve atrophy in human glaucoma patients. The risk for progressive optic nerve atrophy in human glaucoma patients is six times higher at a perfusion pressure of 30 mmHg, which corresponds to a level where the optic nerve is hypoxic in experimental animals, as compared to perfusion pressure levels above 50 mmHg where the optic nerve is normoxic. Medical intervention can affect optic nerve oxygen tension. Lowering the intraocular pressure tends to increase the optic nerve oxygen tension, even though this effect may be masked by the autoregulation when the optic nerve oxygen tension and perfusion pressure is in the normal range. Carbonic anhydrase inhibitors increase the optic nerve oxygen tension through a mechanism of vasodilatation and lowering of the intraocular pressure. Carbonic anhydrase inhibition reduces the removal of CO2 from the tissue and the CO2 accumulation induces vasodilatation resulting in increased blood flow and improved oxygen supply. This effect is inhibited by the cyclo-oxygenase inhibitor, indomethacin, which indicates that prostaglandin metabolism plays a role. Laboratory studies suggest that carbonic anhydrase inhibitors might be useful for medical treatment of optic nerve and retinal ischemia, potentially in diseases such as glaucoma and diabetic retinopathy. However, clinical trials and needed to test this hypotheses.
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PMID:Optic nerve oxygenation. 1570 31


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