The influence of the calcium channel blocker verapamil on experimental glaucoma

The Effect of Levamlodipine in Glucose-Induced Acute Model of Glaucoma in Rabbits

BACKGROUND: Loss of vision and irreversible blindness are the main consequences of glaucoma. There are two main types of glaucoma: Chronic and acute. AIM: This work aimed to evaluate the intraocular effect of levamlodipine on the acute model of glaucoma in rabbits. METHODS: Eighteen white albino rabbits of both sexes weighing about 2 kg. We divided them into three groups (six animals in each group) used in the experiment. We use the right eye to evaluate the effect of the test drug and used the left eye as a control (vehicle only). We used the first group to evaluate levamlodipine (0.25%), the second group to estimate levamlodipine (0.5%), and the third group to assess pilocarpine 2% (positive control). Drugs were administered 30 min before induction. RESULTS: Glucose (5%) fluid produces a significant intraocular pressure (IOP) elevation after 30 min of administration in the left eye (p ˂ 0.001). Pre-treatment topical administration of levamlodipine (0.25%) prevents the rise in the IOP significantly (p ˂ 0.001) in the right eye when compared to the control group (left eye). Moreover, compared with the eyes of the control group at all stages of the experiment, the topical administration of levamlodipine (0.5%) has a significant preventable effect (p ˂ 0.001), compared with the control group. The IOP of the local pilocarpine (2%) in the third group was significantly decreased (p ˂ 0.001). Finally, compared with levamlodipine (0.5%), pilocarpine has a more significant effect in preventing a rapid increase in intraocular pressure (p ˂ 0.001). CONCLUSION: Levamlodipine is a promising therapeutic agent for patients vulnerable to acute glaucoma.

Effect of Topical Calcium Channel Blockers on Intraocular Pressure in Steroid-induced Glaucoma

Purpose: To evaluate the effect of 0.125% verapamil and 0.5% diltiazem eye drops on intraocular pressure (IOP) in steroid-induced glaucoma in rabbit eyes.

Methods: A total of 18 rabbits with steroid-induced glaucoma were divided into three groups (A, B and C; n = 6 each). Right eyes in groups A, B and C received 0.5% diltiazem, 0.125% verapamil and 0.5% timolol eye drops twice daily for 12 days, respectively; whereas, left eyes received distilled water. IOP was measured with Tono-pen XL at baseline, day 4, day 8, and day 12 of treatment.

Results: Both 0.5% diltiazem and 0.125% verapamil eye drops significantly reduced IOP compared to control eyes (p < 0.05). Reduction of IOP by 0.5% diltiazem, 0.125% verapamil eye drops were comparable to 0.5% timolol. No surface toxicity or systemic side effects were noted during the study period.

Conclusion: Calcium channel blockers, verapamil, and diltia-zem significantly reduced IOP in rabbiteyes. This group of drugs may have a potential role in treatment of glaucoma

How to cite this article: Ganekal S, Dorairaj S, Jhanji V, Kudlu K. Effect of Topical Calcium Channel Blockers on Intraocular Pressure in Steroid-induced Glaucoma. J Current Glau Prac 2014;8(1):15-19.

Thioredoxin interacting protein is a novel mediator of retinal inflammation and neurotoxicity

BACKGROUND AND PURPOSE

Up-regulation of thioredoxin interacting protein (TXNIP), an endogenous inhibitor of thioredoxin (Trx), compromises cellular antioxidant and anti-apoptotic defences and stimulates pro-inflammatory cytokines expression, implying a role for TXNIP in apoptosis. Here we have examined the causal role of TXNIP expression in mediating retinal neurotoxicity and assessed the neuroprotective actions of verapamil, a calcium channel blocker and an inhibitor of TXNIP expression.

EXPERIMENTAL APPROACH

Retinal neurotoxicity was induced by intravitreal injection of NMDA in Sprague-Dawley rats, which received verapamil (10 mg·kg(-1), p.o.) or vehicle. Neurotoxicity was examined by terminal dUTP nick-end labelling assay and ganglion cell count. Expression of TXNIP, apoptosis signal-regulating kinase 1 (ASK-1), NF-κB, p38 MAPK, JNK, cleaved poly-ADP-ribose polymerase (PARP), caspase-3, nitrotyrosine and 4-hydroxy-nonenal were examined by Western and slot-blot analysis. Release of TNF-α and IL-1β was examined by elisa.

KEY RESULTS

NMDA injection enhanced TXNIP expression, decreased Trx activity, causing increased oxidative stress, glial activation and release of TNF-α and IL-1β. Enhanced TXNIP expression disrupted Trx/ASK-1 inhibitory complex leading to release of ASK-1 and activation of the pro-apoptotic p38 MAPK/JNK pathway, as indicated by cleaved PARP and caspase-3 expression. Treatment with verapamil blocked these effects.

CONCLUSION AND IMPLICATIONS

Elevated TXNIP expression contributed to retinal neurotoxicity by three different mechanisms, inducing release of inflammatory mediators such as TNF-α and IL-1β, altering antioxidant status and disrupting the Trx-ASK-1 inhibitory complex leading to activation of the p38 MAPK/JNK apoptotic pathway. Targeting TXNIP expression is a potential therapeutic target for retinal neurodegenerative disease.

Comparative study of topical application of timolol and verapamil in patients with glaucoma within 6 months

INTRODUCTION

As glaucoma is one of the most significant causes of blindness, and administration of calcium channel blockers is effective in reducing intraocular pressure (IOP) in rabbits and patients with normotensive glaucoma, we administered topical verapamil 0.25% in the human eye to compare its effect with timolol 0.5% in reducing IOP.

PURPOSE

To compare the effect of timolol 0.5% and topical verapamil 0.25% in patients with open-angle glaucoma.

METHODS

It was a double-blinded study in which 118 eyes (59 individuals) were chosen and divided into 2 groups (30 individuals related to timolol and 29 individuals related to verapamil). Patients who used drugs (systemic or topical) that could alter IOP and those with IOP <22 mmHg were excluded from the study (19 eyes). We chose patients who did not use any drugs 24 h prior to the study. Then applanation tonometry was done exactly before the administration of drugs and 90 min later and the results were compared.

RESULTS

In timolol group, mean intraocular pressure in 52 eyes (27 right eyes and 25 left eyes) decreased from 32.545 to 30.230 and mean pressure in verapamil group decreased from 33.195 to 30.835.

CONCLUSION

It seems that topical verapamil has a similar effect to timolol in patients with open-angle glaucoma, so it can be considered as a lowering intraocular pressure agent in glaucoma patients.

Glutamate-induced internalization of Ca(v)1.3 L-type Ca(2+) channels protects retinal neurons against excitotoxicity

Glutamate-induced rise in the intracellular Ca(2+) level is thought to be a major cause of excitotoxic cell death, but the mechanisms that control the Ca(2+) overload are poorly understood. Using immunocytochemistry, electrophysiology and Ca(2+) imaging, we show that activation of ionotropic glutamate receptors induces a selective internalization of Ca(v)1.3 L-type Ca(2+) channels in salamander retinal neurons. The effect of glutamate on Ca(v)1.3 internalization was blocked in Ca(2+)-free external solution, or by strong buffering of internal Ca(2+) with BAPTA. Downregulation of L-type Ca(2+) channel activity in retinal ganglion cells by glutamate was suppressed by inhibitors of dynamin-dependent endocytosis. Stabilization of F-actin by jasplakinolide significantly reduced the ability of glutamate to induce internalization suggesting it is mediated by Ca(2+)-dependent reorganization of actin cytoskeleton. We showed that the Ca(v)1.3 is the primary L-type Ca(2+) channel contributing to kainate-induced excitotoxic death of amacrine and ganglion cells. Block of Ca(v)1.3 internalization by either dynamin inhibition or F-actin stabilization increased vulnerability of retinal amacrine and ganglion cells to kainate-induced excitotoxicity. Our data show for the first time that Ca(v)1.3 L-type Ca(2+) channels are subject to rapid glutamate-induced internalization, which may serve as a negative feedback mechanism protecting retinal neurons against glutamate-induced excitotoxicity.