ATP sensitive potassium channel openers: A new class of ocular hypotensive agents

Influence of Trace Elements on Neurodegenerative Diseases of The Eye-The Glaucoma Model

Glaucoma is a heterogeneous group of chronic neurodegenerative disorders characterized by a relatively selective, progressive damage to the retinal ganglion cells (RGCs) and their axons, which leads to axon loss and visual field alterations. To date, many studies have shown the role of various elements, mainly metals, in maintaining the balance of prooxidative and antioxidative processes, regulation of fluid and ion flow through cell membranes of the ocular tissues. Based on the earlier and current research results, their relationship with the development and progression of glaucoma seems obvious and is increasingly appreciated. In this review, we aimed to summarize the current evidence on the role of trace elements in the pathogenesis and prevention of glaucomatous diseases. Special attention is also paid to the genetic background associated with glaucoma-related abnormalities of physiological processes that regulate or involve the ions of elements considered as trace elements necessary for the functioning of the cells.

Differential Intraocular Pressure Measurements by Tonometry and Direct Cannulation After Treatment with Soluble Adenylyl Cyclase Inhibitors

PURPOSE

To validate the increase in intraocular pressure (IOP) caused by soluble adenylyl cyclase (sAC) inhibitors and determine reasons behind variation in IOP measurements performed by tonometry.

METHODS

C57BL/6J mice were administered DMSO solubilized sAC inhibitors (KH7 or LRE-1) by intraperitoneal injection. Two hours post-treatment, mice were anesthetized with avertin or ketamine/xylazine/acepromazine (KXA). IOP was measured by a rebound tonometer or direct cannulation of the anterior chamber. Spectral-domain optical coherence tomography was used to measure anterior chamber depth and corneal thickness in live mice. Outflow facility was measured in perfused, enucleated mouse eyes.

RESULTS

Compared with DMSO controls, KH7 treatment caused an increased IOP in avertin- and KXA-anesthetized mice when measured by direct cannulation [avertin: 14.4 ± 2.1 mmHg vs. 11.1 ± 1.0 mmHg (P = 0.003); KXA: 14.4 ± 1.0 mmHg vs. 11.3 ± 0.8 mmHg (P < 0.001)] and tonometry [avertin: 10.8 ± 1.4 mmHg vs. 7.4 ± 0.6 mmHg (P < 0.001); KXA: 11.9 ± 0.9 mmHg vs. 10.3 ± 1.7 mmHg (P = 0.283)]. However, treatment with KH7 in nonanesthetized mice showed a significant decrease in IOP measured by tonometry and compared with DMSO-treated animals [13.1 ± 2.6 mmHg vs. 15.6 ± 0.5 mmHg (P = 0.003)]. Both KH7- and DMSO-treated groups anesthetized with avertin showed increased corneal thickness, whereas KH7-treated mice anesthetized with KXA exhibited a shallower anterior chamber compared with untreated mice. KH7 decreased outflow facility by 85.1% in nonanesthetized, enucleated eyes (P < 0.003).

CONCLUSIONS

Systemically administered DMSO and anesthesia have significant effects on anterior chamber characteristics, resulting in altered IOP readings measured by tonometry. In the presence of DMSO and anesthesia, tonometry IOP readings should be confirmed with direct cannulation.

ATP-sensitive potassium (KATP) channel openers diazoxide and nicorandil lower intraocular pressure by activating the Erk1/2 signaling pathway

Elevated intraocular pressure is the most prevalent and only treatable risk factor for glaucoma, a degenerative disease of the optic nerve. While treatment options to slow disease progression are available, all current therapeutic and surgical treatments have unwanted side effects or limited efficacy, resulting in the need to identify new options. Previous reports from our laboratory have established a novel ocular hypotensive effect of ATP-sensitive potassium channel (KATP) openers including diazoxide (DZ) and nicorandil (NCD). In the current study, we evaluated the role of Erk1/2 signaling pathway in KATP channel opener mediated reduction of intraocular pressure (IOP). Western blot analysis of DZ and NCD treated primary normal trabecular meshwork (NTM) cells, human TM (isolated from perfusion cultures of human anterior segments) and mouse eyes showed increased phosphorylation of Erk1/2 when compared to vehicle treated controls. DZ and NCD mediated pressure reduction (p<0.02) in human anterior segments (n = 7 for DZ, n = 4 for NCD) was abrogated by U0126 (DZ + U0126: -9.7 ± 11.5%, p = 0.11; NCD + U0126: -0.1 ± 11.5%, p = 1.0). In contrast, U0126 had no effect on latanoprostfree acid-induced pressure reduction (-52.5 ± 6.8%, n = 4, p = 0.001). In mice, DZ and NCD reduced IOP (DZ, 14.9 ± 3.8%, NCD, 16.9 ± 2.5%, n = 10, p<0.001), but the pressure reduction was inhibited by U0126 (DZ + U0126, 0.7 ± 3.0%; NCD + U0126, 0.9 ± 2.2%, n = 10, p>0.1). Histologic evaluation of transmission electron micrographs from DZ + U0126 and NCD + U0126 treated eyes revealed no observable morphological changes in the ultrastructure of the conventional outflow pathway. Taken together, the results indicate that the Erk1/2 pathway is necessary for IOP reduction by KATP channel openers DZ and NCD.