Calcium channels and their blockers in intraocular pressure and glaucoma

Long Term Systemic Use of Calcium Channel Blockers and Incidence of Primary Open Angle Glaucoma

PURPOSE

To evaluate the association between the systemic use of calcium channel blockers (CCBs) and primary open-angle glaucoma (POAG) using a diverse nationwide dataset.

DESIGN

Retrospective cohort study SUBJECTS: 213,424 individuals aged 40 years and older in the National Institutes of Health (NIH) All of Us dataset, notable for its demographic, geographic and medical diversity and inclusion of historically underrepresented populations. Patients with a diagnosis of POAG prior to use of any kind of anti-hypertensive medication were excluded.

METHODS

Bivariate and multivariable regression analyses were performed to evaluate associations between CCB use and POAG. CCB use was further divided into exposure to dihydropyridine CCBs and non-dihydropyridine CCBs, and subgroup analyses were performed using Chi-square and Fisher's tests.

MAIN OUTCOME MEASURES

Diagnosis of POAG RESULTS: Within our cohort, 2,772 participants (1.3%) acquired a diagnosis of POAG, while 210,652 (98.7%) did not. Among patients who developed POAG, the mean age was 73.3 years, 52.5% were female, and 48.2% identified as White. Among POAG patients, 32.6% used one or more CCB, 28.2% used a dihydropyridine CCB, and 2.2% used a non-dihydropyridine CCB. In bivariate analysis, use of any CCBs was associated with an increased risk of POAG (OR: 1.29, 95% CI: 1.27-1.31, p<0.001). In multivariable analysis adjusting for age, gender, race, ethnicity, and comorbidities such as diabetes, hyperlipidemia, and hypertension, use of any CCBs remained associated with an increased risk of developing POAG (OR: 1.52, 95% CI: 1.33-1.74, p<0.001). When stratified by type of CCB, the use of dihydropyridine CCBs (OR: 1.31, 95% CI: 1.14-1.50, p<0.001) was associated with increased POAG risk.

CONCLUSIONS

Use of dihydropyridine calcium channel blockers was associated with a significantly higher risk of developing POAG, both before and while adjusting for demographic factors and comorbid medical conditions.

Association between dietary calcium, potassium, and magnesium consumption and glaucoma

BACKGROUND

Calcium (Ca), potassium (K) and magnesium (Mg) may be involved in the occurrence and development of glaucoma by influencing the retinal oxidative stress and regulate blood pressure. However, epidemiological opinions on dietary intake of macroelement related to glaucoma are inconsistent. Herein, this study aims to explore the association between dietary Ca, K, and Mg consumption and glaucoma.

METHODS

Data of 7,042 adults aged ≥40 years old who received the glaucoma examinations were extracted from the National Health and Nutrition Examination Survey (NHANES) database from 2005 to 2008 in this cross-sectional study. Univariate and multivariate logistic regression were used to explore the association between dietary Ca, K, and Mg intake and glaucoma with the odd ratios (ORs) and 95% confidence intervals (CIs). We also investigated this relationship in individuals of different age, with/without hypertension and visual field defect (VFD).

RESULTS

There were 502 (8.11%) participants had glaucoma. After adjusted for covariables, we found that enough dietary Ca consumption was related to a decreased risk of glaucoma [OR = 0.59, 95%CI: (0.42-0.81)], whether in persons with/without hypertension (all P<0.05). In particular, dietary K intake may be a potential protect factor for glaucoma in non-hypertension populations [OR = 0.47, 95%CI: (0.22-0.99), P = 0.049]. Additionally, hypertension/non-hypertension persons who aged <65 years old or with/without VFD should all pay attention to the enough dietary supplement of Ca, K, and Mg according to their own circumstances.

CONCLUSION

Enough dietary Ca, K, and Mg consumption may be potential protect factors of glaucoma that could provide some dietary reference for developing targeted glaucoma prevention and control measures.

L- and T-type Ca2+ channels dichotomously contribute to retinal ganglion cell injury in experimental glaucoma

Retinal ganglion cell apoptotic death is the main pathological characteristic of glaucoma, which is the leading cause of irreversible blindness. Disruption of Ca²⁺ homeostasis plays an important role in glaucoma. Voltage-gated Ca²⁺ channel blockers have been shown to improve vision in patients with glaucoma. However, whether and how voltage-gated Ca²⁺ channels are involved in retinal ganglion cell apoptotic death are largely unknown. In this study, we found that total Ca²⁺ current densities in retinal ganglion cells were reduced in a rat model of chronic ocular hypertension experimental glaucoma, as determined by whole-cell patch-clamp electrophysiological recordings. Further analysis showed that L-type Ca²⁺ currents were downregulated while T-type Ca²⁺ currents were upregulated at the later stage of glaucoma. Western blot assay and immunofluorescence experiments confirmed that expression of the Ca_V1.2 subunit of L-type Ca²⁺ channels was reduced and expression of the Ca_V3.3 subunit of T-type Ca²⁺ channels was increased in retinas of the chronic ocular hypertension model. Soluble tumor necrosis factor-α, an important inflammatory factor, inhibited the L-type Ca²⁺ current of isolated retinal ganglion cells from control rats and enhanced the T-type Ca²⁺ current. These changes were blocked by the tumor necrosis factor-α inhibitor XPro1595, indicating that both types of Ca²⁺ currents may be mediated by soluble tumor necrosis factor-α. The intracellular mitogen-activated protein kinase/extracellular signal-regulated kinase pathway and nuclear factor kappa-B signaling pathway mediate the effects of tumor necrosis factor-α. TUNEL assays revealed that mibefradil, a T-type calcium channel blocker, reduced the number of apoptotic retinal ganglion cells in the rat model of chronic ocular hypertension. These results suggest that T-type Ca²⁺ channels are involved in disrupted Ca²⁺ homeostasis and apoptosis of retinal ganglion cells in glaucoma, and application of T-type Ca²⁺ channel blockers, especially a specific Ca_V3.3 blocker, may be a potential strategy for the treatment of glaucoma.

The influence of trace elements on the therapeutic success of suprachoroidal draining devices

PURPOSE

The therapeutic success of minimal invasive glaucoma surgery (MIGS) is challenging due to many factors including fibrotic or occlusive events. Recent clinical data show sudden peaks of intraocular pressure (IOP) in the postoperative care of glaucoma patients after suprachoroidal draining stents. Yet, the reasons for the IOP peaks are speculative. As a link between trace elements and fibrosis had been previously observed in systemic disorders, the present study aimed to investigate the impact of trace elements on the therapeutic success of the suprachoroidal draining stents in patients with open-angle glaucoma (OAG).

MATERIAL AND METHODS

An analysis of a prospective single-center study was done: fifty-five eyes of patients with OAG (29 female, 26 male) underwent Cypass Micro-Stent implantation either as a stand-alone procedure or combined with cataract surgery. All patients underwent pre-operatively an ophthalmological examination which included slit lamp biomicroscopy and fundoscopy. IOP was measured by Goldmann applanation tonometry. Functional and morphometric data were assessed by Octopus G1-perimetry, which included measurement of retinal nerve fiber layer thickness (Spectralis OCT). Data of the patients' follow-ups were recorded during 18 months post-operatively. The therapeutic success of CyPass Micro-Stent was classified as 'success' (IOP reduction ≥20% compared to a pre-operative baseline without any medication), 'qualified success' (IOP reduction ≥20 % with same or lower additional eye medication), and 'failure' (IOP reduction ≤20 % or additional surgical treatment necessary). Aqueous humour was extracted once during surgery for analysis of the level of 14 trace elements: Copper (Cu), Cadmium (Cd), Cobalt (Co), Chromium (Cr), Iron (Fe), Lithium (Li), Magnesium (Mg), Manganese (Mn), Phosphorus (P), Lead (Pb), Titanium (Ti), Uranium (U), Vanadium (V), and Zinc (Zn). Analysis of the trace elements was done using an ELEMENT 2, ICP-sf-MS instrument (Thermo-Fisher Scientific, Bremen, Germany). Analysis of levels of trace elements was done across the patients' groups of the three subclasses of therapeutic success. Statistical investigations for substantial differences were conducted using the method of least squares to fit general linear models and mixed models. The last one for the repeated measurements of IOP.

RESULTS

Levels of Mg were significantly lower one month postoperatively in the success group (LS-Mean 1.30 mg/L) compared to the qualified success group (LS-Mean 1.22 mg/L; p-value = 0.04). Fe was significantly increased in the failure group (LS-Mean 2.07 µg/L) compared to the qualified success group (LS-Mean 1.64 µg/L; p-value = 0.019) after 3 months of follow-up. Additionally, Fe levels were significantly lower in the success group (LS-Mean 1.47 µg/L) compared to the failure cohort (LS-Mean 2.07 µg/L; p-value = 0.009). After a period of 18 months, significantly higher levels of Mn were observed in the success group (LS-Mean 1.24 µg/L) than in the failure group (LS Mean 0.30 µg/L, p-value = 0.019).

CONCLUSION

The present data might suggest that trace elements can influence therapeutic success of suprachoroidal draining devices postoperatively and thus offer first hints for potential novel therapeutic options.

A general pattern of non-spiking neuron dynamics under the effect of potassium and calcium channel modifications

Electrical activity of excitable cells results from ion exchanges through cell membranes, so that genetic or epigenetic changes in genes encoding ion channels are likely to affect neuronal electrical signaling throughout the brain. There is a large literature on the effect of variations in ion channels on the dynamics of spiking neurons that represent the main type of neurons found in the vertebrate nervous systems. Nevertheless, non-spiking neurons are also ubiquitous in many nervous tissues and play a critical role in the processing of some sensory systems. To our knowledge, however, how conductance variations affect the dynamics of non-spiking neurons has never been assessed. Based on experimental observations reported in the biological literature and on mathematical considerations, we first propose a phenotypic classification of non-spiking neurons. Then, we determine a general pattern of the phenotypic evolution of non-spiking neurons as a function of changes in calcium and potassium conductances. Furthermore, we study the homeostatic compensatory mechanisms of ion channels in a well-posed non-spiking retinal cone model. We show that there is a restricted range of ion conductance values for which the behavior and phenotype of the neuron are maintained. Finally, we discuss the implications of the phenotypic changes of individual cells at the level of neuronal network functioning of the C. elegans worm and the retina, which are two non-spiking nervous tissues composed of neurons with various phenotypes.

Quantitative OCT Angiography Assessment of the Effect of Peribulbar Anesthesia on Retinal Microvasculature in Primary Open-Angle Glaucoma Patients Undergoing Cataract Surgery

Objective

To assess the effect of peribulbar anesthesia on retinal microvasculature in primary open-angle glaucoma (POAG) patients undergoing cataract surgery using OCT Angiography.

Participants

Forty-nine patients undergoing cataract surgery were divided into two groups. Group I included patients with no history of glaucoma, while group II included patients previously diagnosed as POAG with controlled IOP. Each participant received 6 mL of peribulbar anesthetic injection of 4 mL lidocaine 2% containing 150 IU hyaluronidase and 2 mL bupivacaine 0.5%. They were scanned with the OCT-A 10 minutes before and 10 minutes after injection for foveal deep (DCP), superficial (SCP) capillary plexuses density and total vessel density, foveal avascular zone (FAZ) diameter, optic disc total vessel density, and radial peripapillary capillary (RPC) network density. In addition, IOP was checked before and 10 minutes after injection.

Results

Median percent change in DCP post-injection was significantly greater in group II (−43%) than in group I (−2.5%) (P < 0.001). Also, DCP total density median percent change post-injection was significantly higher in group II (−21%) than in group I (−0.9%) (P < 0.001). Foveal SCP vessel density and total vessel density median percent change post-injection were −62.6% and −16.2%, respectively, in group II and were −2.6% and −1.1%, respectively, in group I, which are statistically significant (P < 0.001). The FAZ diameter median percentage change post-injection was higher in group II (40.6%) than in group I (2.5%) (P < 0.001). Optic disc total vessel density and radial peripapillary capillary (RPC) network density post-injection median percent change were significantly higher in group II (−13.6%) and (−13.1%) respectively than in group I (−1.1%) and (−1.25%) respectively (P < 0.001).

Conclusion

Peribulbar anesthesia harbors a deleterious ischemic effect on the retinal vascular tree of glaucoma patients, which could harmfully affect the vision and the visual field in those vulnerable patients.

Mitoquinone intravitreal injection ameliorates retinal ischemia-reperfusion injury in rats involving SIRT1/Notch1/NADPH axis

Retinal ischemia-reperfusion injury (RIRI) is an important pathological process of many ocular diseases. Mitoquinone (MitoQ), a mitochondrial targeted antioxidant, is a potential compound for therapeutic development of RIRI. This study observed the effect of MitoQ on RIRI, and further explored its possible molecular mechanism. Temporary increase in intraocular pressure was used to establish rat model of RIRI to observe the effect of MitoQ treatment on retinal function, pathological injury, oxidative stress, inflammation and apoptosis. Immunohistochemistry and Western blot were used to detect expressions of cleaved caspase 3, B cell leukemia/lymphoma 2 associated X (Bax), nicotinamide adenine dinucleotide phosphate oxidase (NOX1), NOX4, cleaved-Notch 1, hairy and enhancer of split 1 (Hes1), and sirtuin 1 (SIRT 1) in retina were detected by immunohistochemistry and Western blot. MitoQ treatment significantly improved retinal function and pathological injury, inhibited the over-production of reactive oxygen species, increased the expression of superoxide dismutase 1 (SOD 1), suppressed the releases of inflammatory cytokines, and inhibited retinal cells apoptosis. MitoQ also down-regulated the expressions of cleaved caspase 3, Bax, NOX 1, NOX 4, cleaved-Notch 1, and Hes 1, increased the expression of SIRT 1 protein and its activity. These effects were significantly reversed by SIRT1 inhibitor EX527. Our data suggests that MitoQ, as a potentially effective drug for improving RIRI, may act through the SIRT1/Notch1/NADPH signal axis.

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.

Prophylactic anti-glaucoma therapy in dogs with primary glaucoma: A practitioner survey of current medical protocols

AIM

To examine the use of prophylactic anti-glaucoma medications in the normotensive fellow eye in dogs with unilateral overt primary glaucoma by veterinary ophthalmology clinicians.

METHODS

A survey of veterinary ophthalmology clinicians was distributed over two international list serves servicing veterinary ophthalmologists, trainees, and individuals whose practice consisted primarily of ophthalmic patients. The survey was developed following analysis of historical and currently available medical options for control of intraocular pressure and for neuroprotection.

RESULTS

Responses from 199 veterinary ophthalmology clinicians were evaluated. While a large variety of topical anti-hypertensive drugs and protocols were used, the most commonly used medications were aqueous humor production suppressors such as dorzolamide 2.0% ophthalmic solution, timolol 0.5% ophthalmic solution, and a combination product containing both drugs. Latanoprost 0.005% ophthalmic solution was used infrequently for prophylaxis by comparison. The majority of respondents do not use concurrent anti-inflammatory medications (61.22%), although a sizeable minority used prednisolone acetate, dexamethasone, or ketorolac as prophylactic treatment. Systemically administered ocular anti-hypertensive agents were rarely used. Only 40% of respondents used neuroprotectant agents; the most commonly prescribed were the calcium channel blocker amlodipine and the nutraceutical Ocu-Glo™. Recommended intervals between re-examination by the clinician ranged from one month to one year, with most re-evaluations occurring every 3 to 6 months. The majority of respondents recommended more frequent assessments of IOP at intervals between once monthly and once every 3 months.

CONCLUSIONS

Data analysis of medical therapy for the normotensive fellow eye of dogs previously diagnosed with primary glaucoma suggests that there is a great need for well-designed, prospective, controlled, multi-center studies to determine which protocols have the greatest efficacy in delaying an overt attack in the previously normotensive eye in dogs with a genetic predisposition to glaucoma. Prospective studies utilizing a carbonic anhydrase inhibitor such as dorzolamide and a prostaglandin analogue such as latanoprost would be reasonable as these two drugs are widely used in the treatment of overt glaucoma and would allow for an exploration of the impact of different mechanisms of action of lowering IOP on the pathophysiology of primary glaucoma.

Neuroprotective Strategies for Retinal Ganglion Cell Degeneration: Current Status and Challenges Ahead

The retinal ganglion cells (RGCs) are the output cells of the retina into the brain. In mammals, these cells are not able to regenerate their axons after optic nerve injury, leaving the patients with optic neuropathies with permanent visual loss. An effective RGCs-directed therapy could provide a beneficial effect to prevent the progression of the disease. Axonal injury leads to the functional loss of RGCs and subsequently induces neuronal death, and axonal regeneration would be essential to restore the neuronal connectivity, and to reestablish the function of the visual system. The manipulation of several intrinsic and extrinsic factors has been proposed in order to stimulate axonal regeneration and functional repairing of axonal connections in the visual pathway. However, there is a missing point in the process since, until now, there is no therapeutic strategy directed to promote axonal regeneration of RGCs as a therapeutic approach for optic neuropathies.

A pyruvate dehydrogenase kinase inhibitor prevents retinal cell death and improves energy metabolism in rat retinas after ischemia/reperfusion injury

We aimed to assess the neuroprotective effect of a pyruvate dehydrogenase kinase (PDK) inhibitor, Nov3r after ischemia/reperfusion (IR) injury in rats. IR injury was induced by applying 150 mmHg of intraocular pressure for 50 min. Nov3r was orally administered (100 mg/kg) 3 h before and 24 h after IR injury. TUNEL-positive cells increased and immunoreactive RBPMS-positive cells decreased in the rat retinas after IR injury. Administration of Nov3r significantly ameliorated the increase in TUNEL-positive cells and prevented the RBPMS-positive cell decrease. Similarly, the number of IR-induced Iba1-positive microglial cells was significantly reduced with Nov3r treatment. Among metabolic parameters, IR damage induced the elevation of lactate and pyruvate, and the reduction of ATP. Oral administration of Nov3r ameliorated these changes. Our data suggest that the Nov3r had a retinal neuroprotective effect in IR injury in rats. This finding suggests that the regulation of pyruvate dehydrogenase (PDH) activity has potential therapeutic value by enabling metabolic reprograming in diseases associated with ischemic retinal damage, such as diabetic retinopathy, retinopathy of prematurity, retinal vein occlusion, ischemic optic neuropathy and glaucoma.

Human umbilical cord mesenchymal stem cells derived-exosomes in diseases treatment

Exosomes are extracellular vesicles with the size of 40-100 nm in diameter and a density of 1.13-1.19 g/mL, containing proteins, mRNAs, miRNAs, and DNAs. Exosomes change the recipient cells biochemical features through biomolecules delivery and play a role in cellular communication. These vesicles are produced from body fluids and different cell types like mesenchymal stem cells (MSCs). Evidence suggests that mesenchymal stem cells-derived exosome (MSC-EXO) exhibit functions similar to MSCs with low immunogenicity and no tumorization. MSCs can also be isolated from a variety of sources including human umbilical cord (HUC). Because of the non-invasive collection method, higher proliferation and lower immunogenicity, HUCMSC-EXO has been frequently used in regenerative medicine and various diseases treatment compared to the other MSC-EXO resources. This review aimed to investigate the applications of HUCMSC-EXO in different diseases.

Systemic Medication Associations with Presumed Advanced or Uncontrolled Primary Open-Angle Glaucoma

PURPOSE

To identify associations between systemic medications and primary open-angle glaucoma (POAG) requiring a procedure using United States insurance claims data in a hypothesis-generating study.

DESIGN

Database study.

PARTICIPANTS

In total, 6130 POAG cases (defined as patients with POAG undergoing a glaucoma procedure) were matched to 30 650 controls (defined as patients undergoing cataract surgery but without a coded glaucoma diagnosis, procedure, or medication) by age, gender, and region of residence.

METHODS

Participant prescription drug use was calculated for the 5-year period before the glaucoma procedure or cataract surgery. Separately for individual generic drugs and drug classes, logistic regression was used to assess the association with POAG status. This was done across all generic drugs and drug classes that were prescribed in at least 1% of cases and controls. Analyses were adjusted for age, sex, region of residence, employment status, insurance plan type, and the total number of drugs prescribed.

MAIN OUTCOME MEASURES

Odds ratio (OR) and 95% confidence intervals (CIs) for the association between each drug or drug class and POAG.

RESULTS

The median age of participants was 72 years, and 52% were women. We tested for associations of POAG with 423 drug classes and 1763 generic drugs, resulting in a total of 2186 statistical tests and a Bonferroni-adjusted significance threshold of P < 2.3 × 10^-5. Selective serotonin reuptake inhibitors (SSRIs) were strongly associated with a reduced risk of POAG (OR, 0.70; 95% CI, 0.64-0.76; P = 1.0 × 10^-15); the most significant drug in this class was citalopram (OR, 0.66; 95% CI, 0.57-0.77; P = 1.2 × 10^-7). Calcium channel blockers were strongly associated with an increased risk of POAG (OR, 1.26; 95% CI, 1.18-1.35; P = 1.8 × 10^-11); the most significant drug in this class was amlodipine (OR, 1.27; 95% CI, 1.18-1.37; P = 5.9 × 10^-10).

CONCLUSIONS

We present data documenting potential associations of SSRIs and calcium channel blockers with POAG requiring a procedure. Further research may be indicated to better evaluate any associates of serotonin metabolism or calcium channels in glaucoma, or establish whether the associations are due to variations in the patterns for prescribing these drugs.

Hydrogen sulfide supplement attenuates the apoptosis of retinal ganglion cells in experimental glaucoma

Glaucoma is a group of neurodegenerative eye diseases characterized by progressive impairment of visual function due to loss of retinal ganglion cells (RGC). As hydrogen sulfide (H₂S) was reported to play a role in the process of glaucomatous neuropathy and improve RGC survival in experimental glaucoma, the authors aimed to investigate the anti-apoptosis effect of H₂S supplement in a rat glaucoma model, and further tried to explore the involved factors in the neuroprotection. A chronic ocular hypertension (COH) rat model induced by intracameral injection of cross-linking hydrogel was employed to simulate glaucoma and 288 rats were subjected to experimental procedures in the present study. After 4 weeks of sodium hydrosulfide (NaHS) administration following COH induction, the apoptosis of RGC isolated from experimented rats as well as apoptosis of neurons in ganglion cell layer (GCL), intrinsic apoptotic pathway activity, mitochondrial function, glial activation, NF-κB pathway activity, NADPH oxidase activity, autophagy activity and TNF-α level in retina were evaluated. The results showed that H₂S supplement effectively attenuated the apoptosis of RGC in experimental glaucoma, and the neuroprotection by H₂S might correlate with preservation of mitochondrial function, attenuation of oxidative stress, suppression of glial activation, inhibition of inflammatory pathways and downregulation of autophagy. Our study indicated that H₂S supplement resulted in significant neuroprotection through attenuation of RGC apoptosis which might be linked with multiple factors in experimental glaucoma. The new therapeutic strategy might potentially contribute to benefit glaucoma treatment, which is worth further concerns.

Calcium channels are involved in EphB/ephrinB reverse signaling‑induced apoptosis in a rat chronic ocular hypertension model

Erythropoietin-producing hepatocyte receptor B (EphB)/ephrinB reverse signaling has been revealed to be activated in chronic ocular hypertension (COH) by increasing the apoptosis of retinal ganglion cells (RGCs). However, the exact mechanism is not well understood. The present study investigated the involvement of Ca²⁺ channels in the apoptosis of RGCs induced by EphB/ephrinB reverse signaling in a rat CHO model, which was established by cauterizing 3 out of the 4 episcleral veins. The expression levels of four voltage-gated Ca²⁺ channel subunits (Ca_v3.1–3.3 and Ca_v1.2) were detected using immunofluorescence and western blot analysis. TUNEL staining was performed to assess RGC apoptosis following an injection with the T type Ca²⁺ channel blocker. Ca²⁺ channels, mainly the T type, were upregulated in COH rat retinas when compared with the sham group (P<0.01). Additionally, the Ca_v3.2 subunit of T type calcium channels was predominantly expressed in Müller cells and RGCs, such as ephrinB2. Furthermore, an intravitreal injection of the Ca²⁺ channel blocker Mibefradil (3 µM) reduced EphB2-fragment crystallizable region-induced RGC apoptosis in normal rats. Thus, the results suggest that Ca²⁺ channels in a COH model may be a pathway involved in ephrinB/EphB signaling-induced RGC apoptosis.

Systems genetics identifies a role for Cacna2d1 regulation in elevated intraocular pressure and glaucoma susceptibility

Glaucoma is a multi-factorial blinding disease in which genetic factors play an important role. Elevated intraocular pressure is a highly heritable risk factor for primary open angle glaucoma and currently the only target for glaucoma therapy. Our study helps to better understand underlying genetic and molecular mechanisms that regulate intraocular pressure, and identifies a new candidate gene, Cacna2d1, that modulates intraocular pressure and a promising therapeutic, pregabalin, which binds to CACNA2D1 protein and lowers intraocular pressure significantly. Because our study utilizes a genetically diverse population of mice with known sequence variants, we are able to determine that the intraocular pressure-lowering effect of pregabalin is dependent on the Cacna2d1 haplotype. Using human genome-wide association study (GWAS) data, evidence for association of a CACNA2D1 single-nucleotide polymorphism and primary open angle glaucoma is found. Importantly, these results demonstrate that our systems genetics approach represents an efficient method to identify genetic variation that can guide the selection of therapeutic targets.

Elevated intraocular pressure (IOP) is a heritable risk factor for primary open angle glaucoma. Using forward mouse genetics, cell biology, pharmacology and human genetic data, the authors identify CACNA2D1 as an IOP risk gene that can be therapeutically targeted by the drug pregabalin in animal models.

Cannabinoid CB1 and CB2 receptors differentially modulate L- and T-type Ca2+ channels in rat retinal ganglion cells

Endocannabinoid signaling system is involved in regulating multiple neuronal functions in the central nervous system by activating G-protein coupled cannabinoid CB1 and CB2 receptors (CB1Rs and CB2Rs). Growing evidence has shown that CB1Rs and CB2Rs are extensively expressed in retinal ganglion cells (RGCs). Here, modulation of L- and T-types Ca²⁺ channels by activating CB1Rs and CB2Rs in RGCs was investigated. Triple immunofluorescent staining showed that L-type subunit Ca_V1.2 was co-localized with T-type subunits (Ca_V3.1, Ca_V3.2 and Ca_V3.3) in rat RGCs. In acutely isolated rat RGCs, the CB1R agonist WIN55212-2 suppressed both peak and steady-state Ca²⁺ currents in a dose-dependent manner, with IC₅₀ being 9.6 μM and 8.4 μM, respectively. It was further shown that activation of CB1Rs by WIN55212-2 or ACEA, another CB1R agonist, significantly suppressed both L- and T-type Ca²⁺ currents, and shifted inactivation curve of T-type one toward hyperpolarization direction. While the effect on L-type Ca²⁺ channels was mediated by intracellular cAMP/protein kinase A (PKA), mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and calcium/calmodulin-dependent protein kinase II (CaMKII) signaling pathways, only CaMKII signaling pathway was involved in the effect on T-type Ca²⁺ channels. Furthermore, CB65 and HU308, two specific CB2R agonists, significantly suppressed T-type Ca²⁺ channels, which was mediated by intracellular cAMP/PKA and CaMKII signaling pathways, but had no effect on L-type channels. These results imply that endogenous cannabinoids may modulate the excitability and the output of RGCs by differentially suppressing the activity of L- and T-type Ca²⁺ channels through activation of CB1Rs and CB2Rs. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Nimodipine Ophthalmic Formulations for Management of Glaucoma

PURPOSE

Preparation and evaluation of topical ophthalmic formulations containing nimodipine-CD complexes prepared using HP-β-CD, SBE-β-CD and M-β-CD for the management of glaucoma.

METHODS

Nimodipine-CD complexes were prepared using a freeze-drying method. Two different molar ratios (NMD:CD) were used for each cyclodextrin. The inclusion complexes were characterized using DSC, FTIR, yield (%), drug content and in vitro release characteristics. NMD-CD complexes incorporated into chitosan eye drops and a temperature-triggered in situ gelling system were evaluated for their pH, viscosity and in vitro release characteristics. We determined the intraocular pressure (IOP) lowering effect of NMD-hydroxypropylmethylcellulose (HPMC) eye drops through a single dose response design using C57BL/6J mice. The minimum effective concentration (MEC) of nimodipine was further applied to mice that vary in the parental allele of Cacna1s, the drug target of nimodipine. Cytotoxicity was also evaluated.

RESULTS

Our ophthalmic formulations possessed pH and viscosity values that are compatible with the eye. In vitro release of nimodipine was significantly increased from chitosan eye drops containing NMD-CD complexes compared to uncomplexed drug. Administration of nimodipine can lower IOP significantly after a single drop of drug HPMC suspension. The IOP-lowering response of the MEC (0.6%) was significantly influenced by the parental allele of Cacna1s.

CONCLUSIONS

Nimodipine can be used as a promising topical drug for management of glaucoma through ocular delivery.

Exosomes derived from MSCs ameliorate retinal laser injury partially by inhibition of MCP-1

Although accumulated evidence supports the notion that mesenchymal stem cells (MSCs) act in a paracrine manner, the mechanisms are still not fully understood. Recently, MSC-derived exosomes (MSC-Exos), a type of microvesicle released from MSCs, were thought to carry functional proteins and RNAs to recipient cells and play therapeutic roles. In the present study, we intravitreally injected MSCs derived from either mouse adipose tissue or human umbilical cord, and their exosomes to observe and compare their functions in a mouse model of laser-induced retinal injury. We found that both MSCs and their exosomes reduced damage, inhibited apoptosis, and suppressed inflammatory responses to obtain better visual function to nearly the same extent in vivo. Obvious down-regulation of monocyte chemotactic protein (MCP)-1 in the retina was found after MSC-Exos injection. In vitro, MSC-Exos also down-regulated MCP-1 mRNA expression in primarily cultured retinal cells after thermal injury. It was further demonstrated that intravitreal injection of an MCP-1-neutralizing antibody promoted the recovery of retinal laser injury, whereas the therapeutic effect of exosomes was abolished when MSC-Exos and MCP-1 were administrated simultaneously. Collectively, these results suggest that MSC-Exos ameliorate laser-induced retinal injury partially through down-regulation of MCP-1.

Neuroprotection in Glaucoma

Glaucoma is a degenerative optic neuropathy characterized by retinal ganglion cell (RGC) loss and visual field defects. It is known that in some glaucoma patients, death of RGCs continues despite intraocular pressure (IOP) reduction. Neuroprotection in the field of glaucoma is defined as any treatment, independent of IOP reduction, which prevents RGC death. Glutamate antagonists, ginkgo biloba extract, neurotrophic factors, antioxidants, calcium channel blockers, brimonidine, glaucoma medications with blood regulatory effect and nitric oxide synthase inhibitors are among compounds with possible neuroprotective activity in preclinical studies. A few agents (such as brimonidine or memantine) with neuroprotective effects in experimental studies have advanced to clinical trials; however the results of clinical trials for these agents have not been conclusive. Nevertheless, lack of compelling clinical evidence has not prevented the off-label use of some of these compounds in glaucoma practice. Stem cell transplantation has been reported to halt experimental neurodegenerative disease processes in the absence of cell replacement. It has been hypothesized that transplantation of some types of stem cells activates multiple neuroprotective pathways via secretion of various factors. The advantage of this approach is a prolonged and targeted effect. Important concerns in this field include the secretion of unwanted harmful mediators, graft survival issues and tumorigenesis. Neuroprotection in glaucoma, pharmacologically or by stem cell transplantation, is an interesting subject waiting for broad and multidisciplinary collaborative studies to better clarify its role in clinical practice.

Indirect traumatic optic neuropathy

Indirect traumatic optic neuropathy (ITON) refers to optic nerve injury resulting from impact remote to the optic nerve. The mechanism of injury is not understood, and there are no confirmed protocols for prevention, mitigation or treatment. Most data concerning this condition comes from case series of civilian patients suffering blunt injury, such as from sports- or motor vehicle-related concussion, rather than military-related ballistic or blast damage. Research in this field will likely require the development of robust databases to identify patients with ITON and follow related outcomes, in addition to both in-vivo animal and virtual human models to study the mechanisms of damage and potential therapies.

Current perspective of neuroprotection and glaucoma

Glaucoma is the second leading cause of blindness worldwide and is most notably characterized by progressive optic nerve atrophy and advancing loss of retinal ganglion cells (RGCs). The main concomitant factor is the elevated intraocular pressure (IOP). Existing treatments are focused generally on lowering IOP. However, both RGC loss and optic nerve atrophy can independently occur with IOP at normal levels. In recent years, there has been substantial progress in the development of neuroprotective therapies for glaucoma in order to restore vital visual function. The present review intends to offer a brief insight into conventional glaucoma treatments and discuss exciting current developments of mostly preclinical data in novel neuroprotective strategies for glaucoma that include recent advances in noninvasive diagnostics going beyond IOP maintenance for an enhanced global view. Such strategies now target RGC loss and optic nerve damage, opening a critical therapeutic window for preventative monitoring and treatment.

Neuroprotection in the treatment of glaucoma--A focus on connexin43 gap junction channel blockers

Glaucoma is a form of optic neuropathy and a common cause of blindness, affecting over 60 million people worldwide with an expected rise to 80 million by 2020. Successful treatment is challenging due to the various causes of glaucoma, undetectable symptoms at an early stage and inefficient delivery of drugs to the back of the eye. Conventional glaucoma treatments focus on the reduction of elevated intraocular pressure (IOP) using topical eye drops. However, their efficacy is limited to patients who suffer from high IOP glaucoma and do not address the underlying susceptibility of retinal ganglion cells (RGC) to degeneration. Glaucoma is known as a neurodegenerative disease which starts with RGC death and eventually results in damage of the optic nerve. Neuroprotective strategies therefore offer a novel treatment option for glaucoma by not only preventing neuronal loss but also disease progression. This review firstly gives an overview of the pathophysiology of glaucoma as well as current treatment options including conventional and novel delivery strategies. It then summarizes the rational for neuroprotection as a novel therapy for glaucomatous neuropathies and reviews current potential neuroprotective strategies to preserve RGC, with a focus on connexin43 (Cx43) gap junction channel blockers.

The Role of Magnesium in the Pathogenesis and Treatment of Glaucoma

Glaucoma is characterized by chronic optic neuropathy resulting in progressive vision loss. Not only is glaucoma considered as a condition of elevated intraocular pressure (IOP), but also other risk factors may play a role in the pathogenesis of glaucomatous optic nerve damage. Vascular dysregulation in ocular blood flow and oxidative stress are currently suggested as important risk factors for glaucomatous retinal ganglion cell loss. New treatment modalities that improve ocular blood flow and reduce oxidative stress have been investigated in many studies. Magnesium (Mg) is thought to be one of the molecules that has a treatment potential in glaucoma. Mg has been shown to improve blood flow by modifying endothelial function via endothelin-1 (ET-1) and endothelial nitric oxide (NO) pathways. Mg also exhibits neuroprotective role by blocking N-methyl-D-aspartate (NMDA) receptor-related calcium influx and by inhibiting the release of glutamate, and hence protects the cell against oxidative stress and apoptosis. Both improvement in ocular blood flow and prevention of ganglion cell loss would make magnesium a good candidate for glaucoma management. Further studies on the effect of Mg may open a new therapeutic era in glaucoma.

Prolonged mydriasis after inadvertent topical administration of the calcium channel antagonist amlodipine: implications for glaucoma drug development

CONTEXT

Calcium channel inhibitors are being investigated as potential therapeutic adjuncts to reduce painful ciliary muscle spasm and control intraocular pressure in glaucoma. Relatively little is known about the effect of topical administration of calcium channel blockers in humans.

OBJECTIVE

(1) To describe prolonged fixed pupil dilation resulting from exposure to topical amlodipine (2) to review the evidence that links calcium channel blockers with mydriasis and (3) to discuss the implications for glaucoma pharmacotherapy.

DESIGN

Single interventional case report, literature review (including human and animal studies) and analysis of reported adverse drug reactions (ADRs) records in the USA and UK.

CASE

A 35-year-old female doctor presented to eye casualty with blurred vision and bilateral, fixed, dilated pupils. A history of exposure to liquid amlodipine while preparing a paediatric chemotherapy regimen for a neuroblastoma patient was elicited. The patient was reassured and observed.

RESULTS

Pupil function returned to normal within 48 h. A multi-national review of adverse drug reactions reports was conducted, as well as an extensive literature search for case reports and experimental studies. To the authors' knowledge this is the first report of amlodipine causing mydriasis and we discuss the potential molecular mechanism.

CONCLUSIONS

This case is the first to suggest that calcium channel blockers can cause prolonged mydriasis. These agents have been investigated as potential adjuncts in glaucoma therapy. As accidental topical exposure to amlodipine can cause prolonged pupil dilation, it could precipitate angle closure in predisposed patients.