Neuroprotective Effect of Nipradilol [3,4-dihydro-8-(2-hydroxy-3-isopropylamino)-propoxy-3-nitroxy-2H-1-benzopyran] in a Rat Model of Optic Nerve Degeneration:

Effect of Latanoprostene Bunod on Optic Nerve Head Blood Flow

SIGNIFICANCE

Topical latanoprostene bunod increases capillary oxygen saturation and blood volume at the optic nerve head in healthy individuals.

PURPOSE

This study aimed to evaluate the effect of topical latanoprostene bunod on optic nerve blood volume and oxygen saturation in a population of healthy participants.

METHODS

In this prospective double-blind crossover study, 23 healthy participants aged from 21 to 62 years were recruited. Optic nerve head capillary blood volume (ONHvol) and oxygen saturation (ONHSaO2) baselines were measured over a period of 2 hours using multichannel spectroscopic reflectometry and were remeasured after a 7-day once-daily instillation regimen of either latanoprost 0.005% or latanoprostene bunod 0.024%. After a 30-day washout period, participants were crossed over to the alternate product, and measurements were repeated. Participants were used as their own baselines to calculate variation in ONHvol and ONHSaO2 across time and pharmacological agents. The Friedman test was used to establish significant differences in optic nerve head parameters from baseline values, and Conover post hoc analysis was carried for multiple between-group comparisons.

RESULTS

Latanoprostene bunod 0.024% induced a significant increase of 4% in ONHSaO2 compared with latanoprost 0.005% (P < .001). Furthermore, latanoprostene bunod increased ONHvol levels by more than twofold at all time points (P < .001 at T60, T90, and T120). The increase in ONHvol was 66.2% higher than levels achieved with latanoprost at T60 (P = .001), 47% higher at T90 (P < .001), and 45% higher at T120 (P < .01).

CONCLUSIONS

Latanoprostene bunod 0.024% induces a significant increase in optic nerve head blood volume and oxygen saturation in healthy subjects, when compared with latanoprost 0.005%. Future studies are needed to evaluate whether similar responses are elicited in patients suffering from glaucomatous optic neuropathy.

The nitric oxide-guanylate cyclase pathway and glaucoma

Glaucoma is a prevalent optic neuropathy characterized by the progressive dysfunction and loss of retinal ganglion cells (RGCs) and their optic nerve axons, which leads to irreversible visual field loss. Multiple risk factors for the disease have been identified, but elevated intraocular pressure (IOP) remains the primary risk factor amenable to treatment. Reducing IOP however does not always prevent glaucomatous neurodegeneration, and many patients progress with the disease despite having IOP in the normal range. There is increasing evidence that nitric oxide (NO) is a direct regulator of IOP and that dysfunction of the NO-Guanylate Cyclase (GC) pathway is associated with glaucoma incidence. NO has shown promise as a novel therapeutic with targeted effects that: 1) lower IOP; 2) increase ocular blood flow; and 3) confer neuroprotection. The various effects of NO in the eye appear to be mediated through the activation of the GC- guanosine 3:5'-cyclic monophosphate (cGMP) pathway and its effect on downstream targets, such as protein kinases and Ca²⁺ channels. Although NO-donor compounds are promising as therapeutics for IOP regulation, they may not be ideal to harness the neuroprotective potential of NO signaling. Here we review evidence that supports direct targeting of GC as a novel pleiotrophic treatment for the disease, without the need for direct NO application. The identification and targeting of other factors that contribute to glaucoma would be beneficial to patients, particularly those that do not respond well to IOP-dependent interventions.

Novel Therapeutics in Glaucoma Management

BACKGROUND

Glaucoma is a progressive optic neuropathy characterized by retinal ganglion cell death and alterations of visual field. Elevated intraocular pressure (IOP) is considered the main risk factor of glaucoma, even though other factors cannot be ruled out, such as epigenetic mechanisms.

OBJECTIVE

An overview of the ultimate promising experimental drugs to manage glaucoma has been provided.

RESULTS

In particular, we have focused on purinergic ligands, KATP channel activators, gases (nitric oxide, carbon monoxide and hydrogen sulfide), non-glucocorticoid steroidal compounds, neurotrophic factors, PI3K/Akt activators, citicoline, histone deacetylase inhibitors, cannabinoids, dopamine and serotonin receptors ligands, small interference RNA, and Rho kinase inhibitors.

CONCLUSIONS

The review has been also endowed of a brief chapter on last reports about potential neuroprotective benefits of anti-glaucoma drugs already present in the market.

Targets of Neuroprotection in Glaucoma

Progressive neurodegeneration of the optic nerve and the loss of retinal ganglion cells is a hallmark of glaucoma, the leading cause of irreversible blindness worldwide, with primary open-angle glaucoma (POAG) being the most frequent form of glaucoma in the Western world. While some genetic mutations have been identified for some glaucomas, those associated with POAG are limited and for most POAG patients, the etiology is still unclear. Unfortunately, treatment of this neurodegenerative disease and other retinal degenerative diseases is lacking. For POAG, most of the treatments focus on reducing aqueous humor formation, enhancing uveoscleral or conventional outflow, or lowering intraocular pressure through surgical means. These efforts, in some cases, do not always lead to a prevention of vision loss and therefore other strategies are needed to reduce or reverse the progressive neurodegeneration. In this review, we will highlight some of the ocular pharmacological approaches that are being tested to reduce neurodegeneration and provide some form of neuroprotection.

Periocular injection of in situ hydrogels containing Leu-Ile, an inducer for neurotrophic factors, promotes retinal ganglion cell survival after optic nerve injury

Intraocular administration of neurotrophic factors has been shown to delay irreversible degeneration of retinal ganglion cells (RGCs). It would be beneficial for the treatment of optic nerve (ON) injury if such neurotrophic factors could be delivered in a less-invasive manner. The dipeptide leucine-isoleucine (Leu-Ile) appears to induce the production of neurotrophic factors, including brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF), in the brain. We therefore administered Leu-Ile via periocular depot injection in rats and investigated the dipeptide's ability to induce BDNF and GDNF in the retina and to delay RGC loss in an ON injury model. Poloxamer-alginate hydrogels containing Leu-Ile were injected into the subconjunctival space of intact or ON-injured rats. BDNF and GDNF levels in the retina were determined by an enzyme immunoassay. Survival of RGCs was assessed in retinal flatmounts. Activation of extracellular signal-regulated kinases (ERK) and cAMP response element binding protein (CREB) in the retina was examined by Western blotting. At 2 h after injection of fluorescein isothiocyanate-conjugated Leu-Ile, the fluorescence intensities in the retina were 4.3-fold higher than those in the saline control. Treatment with Leu-Ile significantly increased the retinal levels of BDNF at 6 h and GDNF at 6-72 h after injection. Treatment with Leu-Ile significantly increased RGC survival to 14 days after ON injury and enhanced the activation of ERK at 72 h and CREB at 48 h after injection in the ON-injured retina. These results suggest that periocular delivery of Leu-Ile induces BDNF and GDNF production in the retina, which may eventually enhance RGC survival after ON injury.

Neuroprotection in glaucoma: recent and future directions

PURPOSE OF REVIEW

The concept of neuroprotective therapy for glaucoma is that damage to retinal ganglion cells (RGCs) may be prevented by intervening in neuronal death pathways. This review focuses on strategies for neuroprotection and summarizes preclinical studies that have investigated potential agents over the last 2 years.

RECENT FINDINGS

Part of the challenge of studies in neuroprotection has been the utilization of an animal model that resembles human glaucoma. Several models have been utilized including acute and chronic intraocular pressure elevation, the DBA/2J mouse, optic nerve axotomy and crush. NMDA inhibitors continued to be explored however with limited success in human trials. Memantine failed to demonstrate neuroprotection in phase III clinical trials. Although its mechanism of neuroprotection has not been fully elaborated, topical brimonidine has shown some neuroprotective benefits. Exogeneous neurotrophins delay, but do not prevent, RGC death. Bioenergetic neuroprotection that is enhancing the energy supply to RGC has been explored with benefits in animal models. Other strategies include TNF-α, modulation of the immune system and inflammation, and blocking apoptotic signals and stem cells.

SUMMARY

Animal models of glaucoma and neuroprotective strategies continue to be refined. Establishing consensus guidelines for the execution and design of translational research in neuroprotection may optimize the facilitation of neuroprotection research.

Blood pressure treatment in acute ischemic stroke: a review of studies and recommendations

PURPOSE OF REVIEW

Elevated blood pressure (BP) is frequent in patients with acute ischemic stroke. Pathophysiological data support its usefulness to maintain adequate perfusion of the ischemic penumba. This review article aims to summarize the available evidence from clinical studies that examined the prognostic role of BP during the acute phase of ischemic stroke and intervention studies that assessed the efficacy of active BP alteration.

RECENT FINDINGS

We found 34 observational studies (33,470 patients), with results being inconsistent among the studies; most studies reported a negative association between increased levels of BP and clinical outcome, whereas a few studies showed clinical improvement with higher BP levels, clinical deterioration with decreased BP, or no association at all. Similarly, the conclusions drawn by the 18 intervention studies included in this review (1637 patients) were also heterogeneous. Very recent clinical data suggest a possible beneficial effect of early treatment with some antihypertensives on late clinical outcome.

SUMMARY

Observational and interventional studies of management of acute poststroke hypertension yield conflicting results. We discuss different explanations that may account for this and discuss the current guidelines and pathophysiological considerations for the management of acute poststroke hypertension.