Oculohypotensive effect of angiotensin-converting enzyme inhibitors in acute and chronic models of glaucoma

Effect of selected antihypertensives, antidiabetics, statins and diuretics on adjunctive medical treatment of glaucoma: a population based study

BACKGROUND

The prevalence of open angle glaucoma increases with age, with many patients also receiving medications for non-ocular systemic diseases. Little is known about how systemic medications impact on the need for adjunctive therapy with prostaglandin analogues (PGA).

OBJECTIVES

To evaluate whether systemic medications for hypertension, cholesterol, or glucose influence the need for adjunctive intraocular pressure (IOP) lowering medications in patients using PGAs.

METHODS

Pharmaceutical records from the Québec prescription database provided a sample of patients receiving prescriptions for bimatoprost, latanoprost, or travoprost, from which subjects receiving > or =1 prescription for antihypertensives, antidiabetics. diuretics, and statins were identified. Chi-square tests compared proportions using PGAs to those using PGAs + adjunctive therapy, based on the use or non-use of systemic medications; a logistic regression was performed post hoc to adjust for gender and age.

RESULTS

Of the 8548 evaluated patients (all using PGAs); 2934 (34.3%) took none of the studied systemic drugs. For the 5614 patients taking systemic medications, significantly fewer (p < 0.001) required an additional IOP lowering medication if taking a systemic antihypertensive medication. The use of a statin or a diabetic medication, alone or in combination, in addition to a PGA, made no significant difference in the need for adjunct glaucoma therapy. Individual drugs associated with significantly less utilization of adjunctive glaucoma medications were calcium-channel blockers, angiotensin-converting enzyme (ACE), and combination antihypertensive therapies.

DISCUSSION

A profound association between systemic antihypertensive use and a reduced need for adjunct topical IOP lowering medications in patients using the same prostaglandin analogue for at least one year was found.

LIMITATIONS

The use of a prescription claims database without patient compliance or patient outcomes may not reflect actual patient medication use. In addition, these findings may not be applicable to all patients initiating prostaglandin analogues.

CONCLUSIONS

In this real-world population-based evaluation, a significant association exists between using systemic antihypertensive medications and reduced use of adjunctive IOP lowering therapies. These results confirm findings from previous studies suggesting an IOP lowering effect with systemic agents or some synergy with topical therapies.

Activities of angiotensin-converting enzymes ACE1 and ACE2 and inhibition by bioactive peptides in porcine ocular tissues

PURPOSE

An active local renin-angiotensin system (RAS) has recently been found in the human eye. The aim of the present study was to compare the activities of central RAS enzymes (ACE1 and 2) in porcine ocular tissues, morphologically and physiologically close to the human eye. In addition, the effects of three ACE-inhibitory tripeptides on these enzymes were evaluated.

METHODS

Enucleated fresh porcine eyes were used. Activities of ACE1 and ACE2 and their inhibition by bioactive tripeptides (Ile-Pro-Pro, Val-Pro-Pro, Leu-Pro-Pro) as well as by a standard ACE-inhibitor captopril were assayed in the vitreous body, the retina and the ciliary body using fluorometric detection methods.

RESULTS

Activity of ACE1 as well as ACE2 was found in all tissues evaluated. ACE1 activity was markedly higher in the ciliary body (3.7 +/- 0.7 mU/mg protein) than in retina (0.2 +/- 0.02 mU/mg), whereas ACE2 activities in the ciliary body (0.2 +/- 0.02 mU/mg) and retina (0.2 +/- 0.01 mU/mg) were at the same level. In the vitreous body ACE1 activity (8.2 +/- 0.31 nmol/min/mL) was manifold compared to that of ACE2 (0.1 +/- 0.02 nmol/min/mL). The tripeptides inhibited ACE1 at one-thousandth of the concentration needed to inhibit ACE2. All peptides studied evinced about equal inhibitory activities.

CONCLUSION

To our knowledge the present findings constitute the first evidence of ACE2 activity in the ciliary and vitreous bodies, in addition to previously described activity in the retina. The known favorable effects of ACE2 products vs. those of ACE1 suggest a counterbalancing interaction of these two enzyme homologues in physiological regulation of ocular circulation and pressure and possible protective role in certain ophthalmic disorders such as glaucoma and diabetic retinopathy.

Does the renin-angiotensin system also regulate intra-ocular pressure?

The renin-angiotensin-aldosterone system is known to play an essential role in controlling sodium balance and body fluid volumes, and thus blood pressure. In addition to the circulating system which regulates urgent cardiovascular responses, a tissue-localized renin-angiotensin system (RAS) regulates long-term changes in various organs. Many recognized RAS components have also been identified in the human eye. The highly vasoconstrictive angiotensin II (Ang II) is considered the key peptide in the circulatory RAS. However, the ultimate effect of RAS activation at tissue level is more complex, being based not only on the biological activity of Ang II but also on the activities of other products of angiotensinogen metabolism, often exerting opposite effects to Ang II action. In recent studies, orally administered angiotensin II type 1 receptor blockers and angiotensin-converting enzyme inhibitors lower intra-ocular pressure (IOP), likewise topical application of these compounds, the effect being more prominent in ocular hypertensive eyes. Based on previous findings and our own experimental data, it can strongly be suggested that the RAS not only regulates blood pressure but is also involved in the regulation of IOP.

No relation between angiotensin-converting enzyme gene polymorphism and pseudoexfoliation

AIMS

To determine the association between the angiotensin-converting enzyme insertion/deletion (I/D) polymorphism and pseudoexfoliation (PEX) in Turkish patients.

METHODS

This prospective study consisted of 89 patients with PEX, and 120 controls. The I/D polymorphism of the angiotensin-converting enzyme gene was measured with the use of the polymerase chain reaction method.

RESULTS

The distribution of the polymorphism was not significantly different in cases with PEX and controls. The frequencies of the I and D alleles were not significantly different between the groups.

CONCLUSION

According to our findings, I/D polymorphism in the angiotensin-converting enzyme gene does not play any role in the pathogenesis of PEX.

Regulation of myosin light chain phosphorylation in the trabecular meshwork: role in aqueous humour outflow facility

Cellular contraction and relaxation and integrity of the actin cytoskeleton in trabecular meshwork (TM) tissue have been thought to influence aqueous humour outflow. However, the cellular pathways that regulate these events in TM cells are not well understood. In this study, we investigated physiological agonist-mediated regulation of myosin light chain (MLC) phosphorylation in the TM, and correlated such effects with alterations in aqueous outflow facility, since MLC phosphorylation is a critical biochemical determinant of cellular contraction in TM cells. Treatment of serum starved human TM cells with endothelin-1 (0.1 microM), thromboxane A2 mimetic U-46619 (1.0 microM), or angiotensin II (1 microM), all of which are agonists of G-protein coupled receptors, triggered activation of MLC phosphorylation, as determined by urea/glycerol-based Western blot analysis. Agonist-stimulated increase in MLC phosphorylation was associated with activation of Rho GTPase in TM cells, as determined in pull-down assays. In contrast, treatment of human TM cells with a novel Rho-kinase inhibitor H-1152 (0.1-2 microM), in the presence of serum reduced basal MLC phosphorylation. H-1152 also increased aqueous outflow facility significantly in a dose-dependent fashion, in perfusion studies with cadaver porcine eyes. This effect of H-1152 on outflow facility was associated with decreased MLC phosphorylation in TM tissue of drug-perfused eyes. Collectively, this study identifies potential physiological regulators of MLC phosphorylation in human TM cells and demonstrates the significance of Rho/Rho-kinase pathway-mediated MLC phosphorylation in modulation of aqueous outflow facility through TM.

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

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

The effects of antiglaucoma and systemic medications on ocular blood flow

Based on the body of evidence implicating ocular blood flow disturbances in the pathogenesis of glaucoma, there is great interest in the investigation of the effects of antiglaucoma drugs and systemic medications on the various ocular vascular beds. The primary aim of this article was to review the current data available on the effects of antiglaucoma drugs and systemic medications on ocular blood flow. We performed a literature search in November 2002, which consisted of a textword search in MEDLINE for the years 1968-2002. The results of this review suggest that there is a severe lack of well-designed long-term studies investigating the effects of antiglaucoma and systemic medications on ocular blood flow in glaucomatous patients. However, among the 136 articles dealing with the effect of antiglaucoma drugs on ocular blood flow, only 36 (26.5%) investigated the effects of medications on glaucoma patients. Among these 36 articles, only 3 (8.3%) were long-term studies, and only 16 (44.4%) were double-masked, randomized, prospective trials. Among the 33 articles describing the effects of systemic medications on ocular blood flow, only 11 (33.3%) investigated glaucoma patients, of which only one (9.1%) was a double-masked, randomized, prospective trial. Based on this preliminary data, we would intimate that few antiglaucoma medications have the potential to directly improve ocular blood flow. Unoprostone appears to have a reproducible antiendothelin-1 effect, betaxolol may exert a calcium-channel blocker action, apraclonidine consistently leads to anterior segment vasoconstriction, and carbonic anhydrase inhibitors seem to accelerate the retinal circulation. Longitudinal, prospective, randomized trials are needed to investigate the effects of vasoactive substances with no hypotensive effect on the progression of glaucoma.

Pathophysiologic implications of angiotensin I-converting enzyme as a mechanosensor: diabetes

If somatic angiotensin I-converting enzyme (ACE) were a mechanosensor, as recently claimed, it would provide insight into the molecular origin of most adult diseases, such as diabetes, cancer, autoimmune diseases, and psychiatric disease, as well as aging itself. The "ACE as mechanosensor" hypothesis holds that tissue ACE is activated by turbulent flow with each heart beat, so that age-dependent diseases begin with a signal from the vasculature. Activation of ACE would thus represent the first of many amplification steps ("cascades"), placing it at the origin of most age-dependent diseases. As a corollary, effective inhibition of tissue ACE might significantly delay the progression of most diseases of aging. In this paper we will explore how useful this hypothesis is in explaining the molecular pathogenesis of diabetes and its complications, in which aging is accelerated.

Influence of ANG II on cytoplasmic sodium in cultured rabbit nonpigmented ciliary epithelium

Angiotensin (ANG) II receptors have been reported in the nonpigmented ciliary epithelium (NPE) of the eye. In cultured NPE, we found ANG II caused a dose-dependent rise of cytoplasmic sodium. The sodium increase was inhibited by the AT(1)-AT(2) receptor antagonist saralasin (IC(50) = 3.7 nM) and the AT(1) antagonist losartan (IC(50) = 0.6 nM) but not by the AT(2) antagonist PD-123319. ANG II also caused a dose-dependent increase in the rate of ouabain-sensitive (86)Rb uptake. The ANG II-induced cell sodium increase and (86)Rb uptake increase were reduced by dimethylamiloride (DMA; 10 microM). On the basis of this finding, we propose that Na(+)/H(+) exchange is stimulated by ANG II. Simultaneously, ANG II appears to inhibit H(+)-ATPase-mediated proton export. Thus Ang II (10 nM) did not alter the baseline cytoplasmic pH (pH(i)) but reduced pH(i) in cells that were also exposed to 10 microM DMA. Consistent with the notion of H(+)-ATPase inhibition in ANG II-treated NPE, bafilomycin A(1) (100 nM) (BAF) and ANG II were both observed to suppress the pH(i) increase that occurs upon exposure to a mixture of epinephrine (1 microM) and acetylcholine (10 microM) and the pH(i) increase elicited by depolarization. In ATP hydrolysis measurements, H(+)-ATPase activity (bafilomycin A(1)-sensitive ATP hydrolysis) was reduced significantly in cells that had been pretreated 10 min with 10 nM ANG II. In summary, these studies suggest that ANG II causes H(+)-ATPase inhibition and an increase of cell sodium due to activation of Na(+)/H(+) exchange.

Metabolism of angiotensin I by guinea pig aqueous humor

We investigated the degradation of angiotensin I (Ang I) by guinea pig aqueous humor at physiological pH (pH 7.4) and assessed the activity of responsible enzymes using various enzyme inhibitors. The aqueous humor was incubated with Ang I in the presence or absence of an enzyme inhibitor at 37°C for the appropriate time period. The resulting peptides were analyzed by a Beckman HPLC system with a Waters µBondapak C18 analytical column using a 30-min increasing linear gradient of 10 to 40% acetonitrile containing 0.05% trifluoroacetic acid (TFA) and H2O containing 0.05% TFA at a flow rate of 1 mL/min. Detection was done by absorbance at 214 nm. Angiotensin II (Ang II) was a major product (39.3 ± 4.10 nmol·h–1·mL–1, n = 5) of Ang I hydrolysis. Traces of angiotensin 1–9, angiotensin IV, and angiotensin 1–7 were also produced. Chymostatin (0.05 mmol/L), EDTA (1 mmol/L), enalaprilat (0.1 mmol/L), and ebelacton B (0.01 mmol/L) inhibited generation of Ang II from Ang I by guinea pig aqueous humor by 89 ± 4.6, 56 ± 7.6, 33 ± 5.1, 20 ± 6.5 %, respectively. Our findings indicate that guinea pig aqueous humor contains several enzymes that can form Ang II. The chymostatin-sensitive type of enzyme was the most active one found in guinea pig aqueous humor. Angiotensin I converting enzyme, carboxypeptidase A, and deamidase may also contribute to angiotensin II formation in guinea pig ocular fluid.Key words: aqueous humor, angiotensin I, angiotensin II, chymase-like activity, ACE, guinea pig.

The impact of glaucoma medication on parameters of ocular perfusion

Whereas intraocular pressure is considered a major risk factor in glaucoma, growing evidence now indicates that ocular ischemia plays a major role too. By virtue of this and because many existing medications are able to interact with vasculature, altering ocular blood flow, it is essential that current and future medications for glaucoma be evaluated for their effect on ocular circulation. The authors review published papers examining the effect of topical and some systemic medications on ocular blood flow, focusing mostly on data from the human eye. The authors provide a comprehensive review on the effect of subclasses of medications (eg, carbonic anhydrase inhibitors, beta-blockers, alpha-adrenergic agonists, and prostaglandin analogues on optic nerve head, and on retinal, choroidal, and retrobulbar circulation. The various claims for enhancements or reduction of ocular circulation within each class of medication are reviewed and evaluated.