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Present and New Treatment Strategies in the Management of Glaucoma

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The Open Ophthalmology Journal
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Glaucoma is a neurodegenerative disease characterized by retinal ganglion cell (RGC) death and axonal loss. It remains a major cause of blindness worldwide. All current modalities of treatment are focused on lowering intraocular pressure (IOP), and it is evident that increased IOP is an important risk factor for progression of the disease. However, it is clear that a significant number of glaucoma patients show disease progression despite of pressure lowering treatments. Much attention has been given to the development of neuroprotective treatment strategies, but the identification of such has been hampered by lack of understanding of the etiology of glaucoma. Hence, in spite of many attempts no neuroprotective drug has yet been clinically approved. Even though neuroprotection is without doubt an important treatment strategy, many glaucoma subjects are diagnosed after substantial loss of RGCs. In this matter, recent approaches aim to rescue RGCs and regenerate axons in order to restore visual function in glaucoma. The present review seeks to provide an overview of the present and new treatment strategies in the management of glaucoma. The treatment strategies are divided into current available glaucoma medications, new pressure lowering targets, prospective neuroprotective interventions, and finally possible neuroregenrative strategies.
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The Open Ophthalmology Journal, 2015, 9, (Suppl 1: M5) 89-100 89
1874-3641/15 2015 Bentham Open
Open Access
Present and New Treatment Strategies in the Management of Glaucoma
M. Kolko*,1,2,3
1Department of Neuroscience and Pharmacology, the Panum Institute, University of Copenhagen, Denmark
2Department of Ophthalmology, Roskilde University Hospital, Copenhagen, Denmark
3Center of Healthy Aging, Department of Cellular and Molecular Medicine, the Panum Institute, University of
Copenhagen, Denmark
Abstract: Glaucoma is a neurodegenerative disease characterized by retinal ganglion cell (RGC) death and axonal loss. It
remains a major cause of blindness worldwide. All current modalities of treatment are focused on lowering intraocular
pressure (IOP), and it is evident that increased IOP is an important risk factor for progression of the disease. However, it
is clear that a significant number of glaucoma patients show disease progression despite of pressure lowering treatments.
Much attention has been given to the development of neuroprotective treatment strategies, but the identification of such
has been hampered by lack of understanding of the etiology of glaucoma. Hence, in spite of many attempts no
neuroprotective drug has yet been clinically approved. Even though neuroprotection is without doubt an important
treatment strategy, many glaucoma subjects are diagnosed after substantial loss of RGCs. In this matter, recent approaches
aim to rescue RGCs and regenerate axons in order to restore visual function in glaucoma. The present review seeks to
provide an overview of the present and new treatment strategies in the management of glaucoma. The treatment strategies
are divided into current available glaucoma medications, new pressure lowering targets, prospective neuroprotective
interventions, and finally possible neuroregenrative strategies.
Keywords: Glaucoma, intraocular pressure lowering drugs, neuroprotection, neuroregeneration, treatment strategies.
INTRODUCTION
Glaucoma refers to a group of eye conditions, which
cause progressive damage to the optic nerve, retinal ganglion
cell (RGC) death, and characteristic damage to the visual
field. According to The World Health Organization,
glaucoma accounted for 2 percent of visual impairment and
8 percent of global blindness in 2010, and the number of
glaucoma patients is estimated to increase due to a growing
population [1]. The classification of glaucoma relies on the
appearance and obstruction of the drainage pathway. In open
angle glaucoma (OAG) the drainage pathway appears normal
and in angle-closure glaucoma (ACG) the drainage pathway
is obstructed. Glaucoma is also classified according to
whether it is primary or associated with detectable
comorbidity, secondary glaucoma. The most common
subtype of glaucoma is primary OAG (POAG). Despite the
normal clinical appearance of the drainage pathway the
aqueous outflow is restricted in most POAG and referred to
as high-tension glaucoma (HTG). Hence, glaucoma is
associated with an increase in intraocular pressure (IOP), and
to date IOP lowering drugs remain the only clinically
validated treatment of glaucoma [2]. Despite the significant
importance of IOP in the risk of glaucoma progression, it is
recognized that elevated IOP appears in the absence of the
characteristic optic nerve changes (ocular hypertension
*Address correspondence to this author at the Department of Neuroscience
and Pharmacology, University of Copenhagen, Blegdamsvej 3b, 2200
Copenhagen, Denmark; Tel: 0045 29807667;
E-mail: mkolko@dadlnet.dk
(OHT)) and conversely glaucomatous optic nerve damage
appears in the absence of an elevated IOP (low-tension
glaucoma (LTG)).
Therefore, despite the fact that IOP lowering
interventions reduce the risk of progression and delay the
disease onset of glaucoma, the pathogenesis is controversial
and not completely understood. In this matter non-IOP-
dependent risk factors appear to be responsible for
approximately 30-70 percent of glaucoma cases [3-6].
The present review seeks to 1) briefly summarize the
current treatment strategies for glaucoma, 2) discuss future
treatment strategies for glaucoma i.e. new targets for IOP-
lowering, targets for neuroprotection, and targets for
neuroregeneration.
CURRENT TREATMENT STRATEGIES FOR
GLAUCOMA
Although glaucoma is a complex and poorly understood
disorder, the primary goal of therapy is lowering IOP [2].
Hence, lowering IOP by 20 - 40 percent has been shown to
reduce the rate of progressive visual field loss by half [7,8].
The first anti-glaucomatous drop was introduced in 1875
and there are currently several types of IOP-lowering eye
drops used to treat glaucoma (Table 1). In addition, two
systemic IOP-lowering drugs are available (Table 2). The
eye drops include β-blockers, carbonic anhydrase inhibitors,
prostaglandin analogs, α2-adrenergic agonists, and
parasympathomimetic drugs. In addition to the pure form,
90 The Open Ophthalmology Journal, 2015, Volume 9 M. Kolko
the eye-drops often come as combined drops. To date fixed-
combination eye-drops include prostaglandin analogs/β-
blockers, carbonic anhydrase inhibitors/β-blockers, and α2-
adrenergic agonists/β-blockers. Finally, a combination of
carbonic anhydrase inhibitors /α2-adrenergic agonists was
approved by the United States Food and Drug
Administration in April 2013, and as an exception a triple
fixed combination of prostaglandin analogs/α2-adrenergic
agonists/β-blockers is available in Mexico.
Table 1. Time line for the introduction of glaucoma
medication.
IOP Lowering medication and year of introduction. Modified from European
Glaucoma Society Therminology and Guidelines for Glaucoma, 4th edition.
Over all, the current available glaucoma eye-drops all
seek to decrease the IOP. They can be grouped into
therapeutic agents that decrease the production of aqueous
humor production and/or increase the drainage through the
trabecular meshwork (TM) and/or increase uveoscleral
outflow.
ß-Blockers
ß-blockers reduce the production of aqueous humor. In
addition, some ß-blockers contain α1 blocking effects
(levobunolol and nipradilol) [9-11], which reduce IOP by an
acceleration of the uveoscleral outflow. Ocular adverse reactions
include conjunctival allergies, conjunctival injection and corneal
epithelium disorder. Additionally, corneal sensitivity may be
reduced in case of the selective ß1-blocker, betaxolol, due to its
membrane-stabilizing effect. In contrast, another ß-blocker,
carteolol, has intrinsic sympathomimetic activity and therefore no
reduced corneal sensitivity [12]. One major challenge for the use
of ß-blockers is their frequent systemic adverse effect due to their
activation of both ß1- and ß2-receptors. In this matter adverse
effects of the respiratory system by ß2-blockers include
worsening of asthma attacks and chronic obstructive pulmonary
disease. To prevent the ß2-related side effects betaxolol can be
used in cases with respiratory issues [13]. The most critical
adverse effects of ß1-blockage are reduced heart rate and reduced
cardiac contractility. Hence, ß-blockers should be used with
caution in patients with slow or irregular heartbeat or congestive
heart failure. Finally, adverse effects from the use of ß-blockers
include depression, impotence, and drowsiness.
Carbonic Anhydrase Inhibitors
Carbonic anhydrase inhibitor (CAI)s reduce IOP by
inhibiting the ciliary epithelium and controlling aqueous
formation. Systemic CAIs have been used since 1956, but
are associated with a high incidence of adverse reactions,
including dysesthesia of the fingers and around the lips,
frequent urination, lassitude, anorexia, weight reduction,
kidney stones, metabolic acidosis, and hematopoietic cell
restraint anemia [14]. Since 1994 a topical CAI has been
available (Table 1). Even though the adverse effects are
much less compared to systemic administered CAIs, topical
CAIs have some ocular adverse reactions such as
conjunctival allergy and hyperemia [14]. Due to the fairly
acidic pH, CAIs generally cause ocular irritation. Moreover,
carbon anhydrase naturally exists in the endothelial cells,
and CAIs should be used with caution in patients with
corneal endothelial disorders [15]. No significant systemic
adverse reactions have been associated with the use of CAIs.
Prostaglandin Analogs
Prostaglandins lower IOP by accelerating the uveoscleral
outflow. The most common adverse effects are eye redness
or irritation, a change in eye color (mostly in hazel or green
eyes) [16,17], and an increase in thickness and number of
eyelashes [18]. In addition, prostaglandin administration has
been reported to recur corneal epithelium herpes, and should
therefore be used with caution in these patients [19]. No
significant systemic adverse reactions have been associated
with the use of prostaglandins.
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Time line for the Introduction of Glaucoma
Medication. Table 1
IOP Lowering medication and year of introduction.
Modified from European Glaucoma Society
Therminology and Guidelines for Glaucoma, 4th edition.
1875 Pilocarpine
1925 Epinephrine
1956 Diamox
1978 Timolol
1992 Pilocarpine/Timolol
1994 Dorzolamide
1996
Latanoprost
Brimonidine
1998
Brinzolamide
Dorzolamide/Timolol
2000 Bimatoprost
2001
Travoprost
Lantanoprost/Timolol
2005 Brimonidine/Timolol
2006
Bimatoprost/Timolol
Travoprost/Timolol
2008 Tafluprost
2009 Brinzolamide/Timolol
2013 Monoprost
2014
Brimonidine/Brinzolamide
Tafluprost/Timolol
Present and New Treatment Strategies in the Management of Glaucoma The Open Ophthalmology Journal, 2015, Volume 9 91
Sympathomimetic Drugs
Sympathomimetic drugs act on α2-receptors and activate
G protein-coupled receptors, thereby reducing cAMP. In this
way the production of aqueous humor production is reduced
and the uveoscleral outflow increased. Allergic reactions
frequently occur with this class of medication. Side effects
may further include irregular heart rate, elevated blood
pressure, headaches, blurred vision, fatigue, dry mouth, and
redness in or around the eye [20]. A randomized trial of the
α2-receptor agonist, brimonidine, versus the ß-blocker,
timolol, found evidence of a less likely visual field
progression in patients treated with brimonidine compared to
timolol, thereby indicating a neuroprotective role of α2
agonists [21].
Parasympathomimetic Drugs (Miotics)
Parasympathomimetic drugs are cholinergic agents that
cause the pupil to become much smaller in diameter and help
increase the rate of fluid drainage from the eye. The most
common ocular side effects include headache, red eyes,
miosis-caused visual field constriction, and night vision loss.
Systemic miotics may cause excessive salivation and tearing,
sweating, diarrhea, vomiting, and slowed heartbeat [22].
In addition to the main therapeutic agents all eye drops
contain additives, which stabilize the solution/suspension,
and/or extend the life of the drugs. The draw back of
additives is the ocular adverse reactions that follow these.
Hence, more anti-glaucomatous drops now come in
preservative free versions.
Another issue concerning adherence and adverse
reactions is the increasing introduction of generic glaucoma
medication. Within defined tolerances, generic drugs are
“equivalent” to original, patented medications. There is,
however, room for variability and error in manufacture,
packaging, and the adjuvants can vary considerably. Because
generic formulations do not necessarily undergo clinical
testing, physicians and patients need to make sure that the
medications are equally effective in real-life use. Even
though the challenge of adverse reactions from preservatives,
and the challenge of an increasing number of generic
products are important issues, these topics are beyond the
scope of this review.
FUTURE TREATMENT STRATEGIES FOR GLAUCOMA
Many mechanisms have been proposed to address the
pathogenesis of glaucoma. However, none seems to
characterize the disease sufficiently, and the multifactorial
etiologies of glaucoma become a fundamental challenge in
the development of new treatment strategies. Nevertheless
elevated IOP together with yet-to-be elucidated cellular and
molecular changes result in glaucomatous neurodegeneration.
In this aspect treatment strategies can be grouped into 1) IOP
Table 2 Current treatment strategies for glaucoma.
ß-blockers
Timolol (Optimol, Timacar Depot, Timoptol-LA, Timolol, Nyogel L.P., Timogel, Timosan, Aquanil)
Levobunolol*
Carteolol (Ocupress)*
Metipranolol (OptiPranolol)*
Betatoxol (Betoptic)
Nipradilol*
Carbon anhydrase inhibitors
Dorzolamide (Trusopt, Arzolamid, Dorzolamid)
Brinzolamide (Azopt)
Acetazolamide (Diamox) - oral medication
Methazolamide (Neptazane) - oral medication*
Prostaglandin analogs
Tafluprost (Taflutan, Saflutan, Zioptan*)
Latanoprost (Xalatan, Monoprost, Latanoprost)
Bimatoprost (Lumigan,)
Travoprost (Travatan)
Unoprostone isopropyl (Rescula)*
Sympathomimetic drugs
Brimonidine (Alphagan, Αlphagan-P*, Bimonidintartrat, Brimoratio, Glaudin)
Apraclonidine (Iopidine)
Dipivefrin (Propine)*
Epinephrine (Gluacon, Epifrin)*
Parasympathomimetic drugs
Pilocarpine (Pilokarpin, Isopto Carpine*, Pilocar*, Pilopine HS*)
Echothiophate (Phospholine Iodide)*
The list of glaucomatous medication is based on the current available products in Denmark.
* Requires special permission or is not available in Denmark.
92 The Open Ophthalmology Journal, 2015, Volume 9 M. Kolko
lowering strategies, 2) neuroprotective strategies, and 3)
neuroregenerative strategies (Table 3).
NEW TREATMENT STRATEGIES FOR IOP
LOWERING
It is clear that multiple factors give rise to glaucomatous
damage, and it is recognized that the most evident risk factor
is IOP. The cause of elevated IOP in POAG is thought to be
due to an increased accumulation of extracellular matrix
material (ECM) in the TM. From the current approved
glaucoma medications only prostaglandin analogues may
have a role on modulation of the molecular changes that
occur in the TM of glaucoma patients. Hence, prostaglandins
may induce stimulation of matrix metalloproteinases, and in
this way lead to increased spacing between the ciliary muscle
bundles [23,24].
Since the importance of IOP in the progression of
glaucoma is evident, current new strategies target IOP
lowering pathways. Among these exist two main approaches
that try to increase the outflow facilities in the TM. The first
strategy seeks to modulate the contractility of TM. It has
been shown that TM possesses smooth muscle cell-like
properties, and that TMs contractile properties can be
regulated by several enzymes [25-29]. The second
therapeutic concept includes alteration in the behavior of
TM, and strategies to affect the shape and loosen the cell-to-
cell junction and/or cell-to-ECM adhesion within the TM
have become experimental targets for lowering IOP [30]. In
addition, new therapeutic targets aim to decrease aqueous
humor production or to improve the uveoscleral outflow by
different subcellular pathways from those already existing
[31-33].
TREATMENT STRATEGIES TO INCREASE
TRABECULAR MESHWORK OUTFLOW
Rho-Associated Kinase
The Rho signaling pathway, mediated through Rho-
associated kinase (ROCK), plays a major role in regulation
of smooth muscle contraction. Therefore, ROCK inhibitors
may enhance aqueous drainage by acting on the actin
cytoskeleton and cellular motility in the TM, Schlemms
canal and ciliary muscle [34,35]. Multiple animal studies
have shown an IOP reduction by topical use of ROCK
inhibitors, and more ROCK inhibitors have been and are
currently tested in clinical trials for glaucoma and ocular
hypertension. The current (or completed without posted
results) clinical trials include K 115 (phase III, #JapicCTI-
111565), AMA0076 (phase II, #NCT01693315), AR-13324
(PG324) (phase III, #NCT02057575), AR12286 (Phase II,
#NCT02174991/ #NCT02173223) [36].
Although much attention is given to ROCK inhibition no
drugs are yet on the market, and during the clinical trials
concerns have been raised. Hence, ROCK inhibition in
humans seems to elicit different IOP responses compared to
animals and have resulted in side effects including moderate
to severe hyperemia, vascular disorders and other system
Table 3. Targets for new treatment strategies in the management of glaucoma.
IOP Lowering Strategies
Neuroprotective Strategies
Increasing Trabecular Meshwork Outflow
ROCK
Endothelin-1
Nitric Oxide
TGF
CTGF
Adenosine
Angiopoietin-like7 molecules
Cannabinoids
Cochlin
Latrunculins
Melatonin
Ghrelin
Increasing the Uveoscleral Outflow
Angiotensin II
Serotonin
Ghrelin
Cannabinoids
Decreasing Aqueous Humor Production
Forskolin
Serotonin
Cannabinoids
Angiotensin II
Exitotoxicity
NMDA antagonists (Memantine)
Modulation of Müller cells
Oxidative stress
Antioxidants (α-tocopherol)
Ginkgo Biloba
Mitochondrial Dysfunction
Mitochondrial targeted antioxidants (Q10)
Inflammation- Abnormal Immune Response
TNF-α
Biological response modifiers (Ethanrecept)
Agmatine
Modulation of T-cell reaction (Cop-1)
Modulation of PLA2-induced inflammation
Protein Misfolding
Agents targeting Aß
Heat shock proteins
Glial Cell Modulation
TGF-ß, CNTF, PDGF
Other Pathways
Estradiol
Statins
Erythropoietin
Current treatment strategies. Abbreviations are: Rho-associated Kinase (ROCK), Tumor Growth Factor-ß (TGF-ß), Connective Tissue Growth Factor (CTGF), Tumor Necrosis
Factor-α (TNF-α), Phospholipase A2 (PLA2), Amyloid-ß (Aß), Ciliary Neurotrophic Factor (CNTF), Platelet-derived Growth Factor (PDGF), Retinal Pigment Epithelial Cells (RPE),
Mesenchymal Stem Cells (MSC).
Present and New Treatment Strategies in the Management of Glaucoma The Open Ophthalmology Journal, 2015, Volume 9 93
problems [37-39]. Overall, ROCK inhibitors, however, offer
a potentially exciting alternative to the prostaglandin
analogues, and if one tested target overcomes the side effects
other beneficial effects of ROCK inhibition have been
shown. Hence, in addition to ROCK inhibitors modulative
effect on the TM, ROCK inhibition furthermore offers
neuroprotective effects as well as enhances blood flow to the
optic nerve [40].
Endothelin-1
Another modulator of TM is endothelin-1 (ET-1), and a
significant correlation has been found between IOP and ET-
1[41-43]. Hence, increased ET-1 levels may stimulate
contraction of both TM cells and the ECM, and thereby
reduce TM outflow [42,44]. In addition to reduced TM
outflow increased levels of ET-1 have been implicated in
vascular dysregulation. In this matter raised concentrations
of ET-1 in glaucoma patients may lead to vasoconstriction
by stimulation of ET-1 receptors on the vascular smooth
muscle cells [45,46]. In addition to a decreased IOP, ET-1
receptor inhibition has been shown to have neuroprotective
effects [47]. Overall, an ET-1 receptor antagonist constitutes
a potential treatment target to manage IOP reduction, which
may also favor the vascular regulation and RGC survival.
Nitric Oxide
Nitric oxide (NO) has been implicated in more
mechanisms related to glaucoma such as auto regulation
[48], RGC survival and death [49], and low-grade
inflammation [50]. Hence, dependent on the mechanism, it
may be beneficial or damaging to glaucomatous progression.
In relation to the IOP, NO agonists induce relaxation of TM
cells and thereby increase the outflow [51,52].
Transforming Growth Factor
Elevated levels of transforming growth factor-ß (TGF-β)
have been identified in the anterior chamber of glaucomatous
eyes [53], and increased levels of TGF-β have been
postulated to increase the risk of glaucoma [54]. TGF-β has
also been shown to directly cause increased IOP [55]. It is
believed that this occurs through complex interactions with
the TM, leading to decreased aqueous humor outflow
[55,56].
Beside a consistent beneficial effect by TGF-β inhibition
on IOP, the role of TGF-β in RGC maintenance has
contrasting beneficial effects. Hence, TGF-β has multiple
functions and among others, significant evidence shows a
neuroprotective effect of TGF-β [57-59]. Therefore, future
potential clinical relevance of TGF-β inhibition to reduce
IOP requires attention to potential side effects.
Connective Tissue Growth Factor
Recent studies have described a complex relationship
between increased connective tissue growth factor (CTGF)
expression, TGF-β activity, and fibrotic pathogenesis [60-
62], thereby highlighting the complex signaling interplay
between CTGF and TGF-β that results in increased fibrosis
in the TM. Hence, interfering with CTGF expression may
therefore prove beneficial in the treatment of glaucoma.
Adenosine
Adenosine and several adenosine derivatives increase
and/or decrease IOP via modulation of G protein coupled
receptors [63]. There are four adenosine receptor subtypes
known as A1, A2a, A2b, and A3. Activation of A1, A2a and
A3 agonists and A3 antagonists has been shown to lower
IOP by remodeling the ECM, through activation of
metalloproteinases, and thereby increase TM outflow [32].
A3 receptor antagonists have been shown to prevent
adenosine-induced activation of chloride channels of the
ciliary non-pigmented epithelial cells followed by an IOP
reduction [37,64]. Clinical trials are ongoing, but so far no
significant results have been reported (Phase II,
#NCT01917383) [37].
Other New Targets to Increase Trabecular Meshwork
Outflow
In the search for targets to increase TM outflow, multiple
molecules are in consideration. Among these are
angiopoietin-like7 (ANGPTL7), a member of the ANGPTL
family, which has been shown to increase TM outflow [65].
Other potential molecules that could be targeted in the
regulation of TM outflow are cannabinoids, cochlin,
latrunculins, melatonin, and ghrelin [66].
TREATMENT STRATEGIES TO INCREASE THE
UVEOSCLERAL OUTFLOW
Angiotensin II
Compounds that increase angiotensin-converting enzyme
2- (ACE2) activity and further the formation of angiotensin
(1-7) are new options as anti-glaucomatous drugs in addition
to classical ACE inhibitors and AT1 receptor blockers.
Furthermore, drugs that activate the angiotensin receptor
types, Mas receptors, directly have also been suggested as
possible targets for IOP lowering [67].
Other New Targets to Increase Uveoscleral Outflow
In addition to angiotensin II treatment, targets such as
serotonin [68], ghrelin [69], and cannabinoids [70] have also
been suggested as potential drugs to increase the uveoscleral
outflow [66].
TREATMENT STRATEGIES TO DECREASE
AQUEOUS HUMOR PRODUCTION
Forskolin
Foskolin is a lipid-soluble compound that activates
cAMP in the ciliary epithelium thereby reducing the aqueous
humor production. It has been shown to be able to decrease
IOP after topical application by a mechanism that is not used
by the other drugs [71].
94 The Open Ophthalmology Journal, 2015, Volume 9 M. Kolko
Other New Targets to Decrease Aqueous Humor
Production
In addition to foskolin, targets such as serotonin,
cannabinoids and angiotensin II have also been suggested as
potential drugs that decrease the aqueous humor production
[66].
NON-IOP DEPENDENT TREATMENT STRATEGIES
Beyond IOP, it is recognized that many other factors are
associated with an increased risk of developing glaucoma.
Hence, a significant number of glaucoma patients continue
to lose vision despite successful IOP control, and it has been
estimated that IOP-independent risk factors appear to be
responsible for approximately 30-70 percent of glaucoma
cases [4,6,72,73].
A variety of non-IOP dependent risk factors are being
proposed and in order to categorize and summarize the
current knowledge, this review seeks to group these into two
major groups i.e. neuroprotective- and neuroregenerative-
treatment strategies.
NEUROPROTECTIVE TREATMENT STRATEGIES
In order to simplify the complexity of the proposed new
neuroprotective treatment strategies, these can be grouped
into targets that interfere with excitotoxicity, oxidative
stress, mitochondrial dysfunction, inflammation - abnormal
immune response, protein misfolding, and glial cell
modulation. Obviously, such a division of treatment
strategies is not definite and most targets will interfere with
more pathways.
Excitotoxicity
Exitotoxicity refers to the pathological process by which
neurons are damaged by the overactivation of glutamate
receptors. In glaucoma, the initial insult to RGCs has been
suggested to lead to elevated levels of extracellular
glutamate [74-76]. In line with this, a chronic elevation of
glutamate concentrations in the inner eye has been shown in
glaucoma patients [77-79]. As a consequence of increased
levels of glutamate, ionotropic N-methyl-D-aspartate
(NMDA) receptors are overstimulated, resulting in a massive
influx of calcium into the neurons, thereby causing
glutamate-mediated RGC death. Strategies to modify
glutamate-induced neurotoxicity have been widely studied,
and in particular the NMDA antagonist, memantine, has
been shown to be a highly effective neuroprotective agent in
both acute and chronic animal models of RGC death [80-82].
In the well known memantine clinical trial no significant
benefit was found in the memantine-treated group compared
to the patients receiving placebo [83]. However, in line with
the substantive evidence that glutamate promotes RGC death
via NMDA over activation, the design and the clinical end
points of the memantine study have been questioned and it
still remains uncertain whether glutamate excitotoxicity is an
efficient target for therapeutical intervention in glaucoma
[83].
In addition to increased secretion of glutamate, reduced
clearance by the Müller cells may account for excitotoxicity
[84,85]. Hence, instead of, or together with, targeting the
ionotropic glutamate receptors, the homeostasis of Müller
cells could be a valuable target in the understanding of the
homeostasis in the inner retina. Furthermore, the
neurovascular junction (the interaction between pericytes,
Müller cells and inner retinal neurons) may account for
attention, since a dysfunctional nutrient and oxygen supply
may affect the Müller cells ability to remove excess
glutamate from the intercellular space and thereby their
ability to protect the RGCs [86,87].
Oxidative Stress
Oxidative stress reflects an imbalance between the
production of reactive oxygen species (ROS) and the cells
ability to readily detoxify the reactive intermediates or to
repair the resulting damage. Significant evidence has shown
that oxidative stress plays a role in RGC death in glaucoma,
and the concept of antioxidants as a neuroprotective
treatment strategy is widely accepted [88-92]. Among the
most studied antioxidants, vitamin E (α-tocopherol) and
gingko biloba have been shown to ameliorate NMDA-
induced RGC death. Vitamin E acts as a scavenger of
peroxyl radicals. Although some studies have suggested a
decreased rate of glaucomatous progression in patients
receiving vitamin E the long-term results are still lacking
[93,94]. To further elucidate a role of vitamin E in the
treatment of glaucoma, current studies are suggesting that
vitamin E, release from contact lenses may be used in
preventing ROS-induced glaucomatous damage [95,96].
Gingko biloba is an extract from Ginkgo biloba leaves. It
increases blood flow and has been shown to have a free
radical scavenger property [97]. In addition, gingko biloba
has been shown to interfere with glutamate signaling and to
preserve mitochondrial metabolism [98-100]. The precise
mechanism by which gingko biloba interferes with RGC
homeostasis is still not fully understood, however, the
studied literature on gingko biloba is in favor of a possible
beneficial effect on RGC survival [101].
Mitochondrial Dysfunction
In line with the role of oxidative stress in the
pathogenesis of glaucoma, increasing evidence points to a
mitochondrial dysfunction in glaucoma [102-105]. Even
though many antioxidants have shown promising effects on
RGC survival, many of them lack specificity to
mitochondria, the key regulator of ROS production. Hence,
compounds that specifically target the mitochondria have
been suggested to be more beneficial. Among mitochondrial-
targeted antioxidants, coenzyme Q10 (Q10) is one of the
most studied targets, and in animal models, Q10 protects
RGCs after ischemia [106,107] and oxidative stress [108].
To date, no human clinical trials have been published on the
use of Q10 in glaucoma.
Inflammation - Abnormal Immune Response
It is widely accepted that glaucomatous
neurodegeneration comes with an activation of glial cells and
Present and New Treatment Strategies in the Management of Glaucoma The Open Ophthalmology Journal, 2015, Volume 9 95
accompanying production of pro-inflammatory cytokines,
such as tumor necrosis factor alpha (TNF-α). TNF-α is
secreted by damaged glial cells and through the binding of
TNF-receptor-1 (TNF-R1) it causes apoptotic RGC death
[109]. However, the binding of TNF-R1 also triggers the
activation of transcription factor NF-KB, a cell survival
pathway [110,111]. Overall, growing evidence exists on the
role of TNF-α in RGC death [112-115], but opposing
consequences of TNF-α -signaling challenge any strategy for
neuroprotection [50,116].
More biologic response modifiers, such as ethanrecept,
have been shown to possess promising results as
neuroprotective agents by inhibiting TNF-α-induced RGC
damage [117].
Another anti-inflammatory agent, agmatine, has been
shown to protect RGCs from TNF-α-induced cell death
[118,119]. In addition, it is known that agmatine protects
neurons from apoptosis after exposure to NMDA and
glutamate [120]. Finally, agmatine has a role as an α2-
adrenergic agonist, and thus, can suppress RGC death by
neuroprotective mechanisms, and also protect RGCs by
lowering the IOP [121].
The inflammatory process in glaucoma has been found to
be associated with pro-inflammatory activities mediated in
part by T cell activity. In this aspect, Cop-1, a synthetic
peptide polymer, has been shown to modulate this T-cell
reaction by attenuating the normal inflammatory response.
Furthermore, it has been shown experimentally that
glutamate injections into the eye result in T cell reaction
[122,123], and in this aspect, Cop-1 immunization has
shown some protection against RGC death [122-124].
A recognized inflammatory pathway is initiated by
phospholipase A2 (PLA2) activity. Hence, PLA2 activation
leads to the cyclooxygenase-2 (COX-2)-mediated
prostaglandin synthesis. Studies have shown an induction of
COX-2 in RGCs in response to elevated IOP [125,126]. In
line with this, COX-2 inhibition has been found to rescue
RGCs [127].
The precursor of COX-2 medicated prostaglandin
synthesis is arachidonic acid (AA), which is released by
PLA2-cleavage of phospholipids. Both AA and PLA2 have
been shown to be involved in RGC maintenance. In this
matter AA was found to ameliorate RGC death [128].
Opposing results have revealed a negative role of PLA2 on
neuronal survival. Hence, PLA2 has been shown to act
synergistically with glutamate-induced exitotoxicity [129].
Moreover, levels of the PLA2 subgroup sPLA2-IIA was
found to be increased in the aqueous humor of glaucoma
patients [130,131], and studies from the brain have revealed
that increased levels of PLA2 instigate neuronal cell death
[132-134].
Protein Misfolding
Protein aggregation is a prominent factor in
neurodegenative disorders such as Alzheimer disease (AD).
In AD, the peptide amyloid-ß (Aß) has been implicated in
the neuropathology, and growing evidence suggests that
aggregation is also involved in the development of RGC
apoptosis. In line with this experimental studies for
glaucoma support the involvement of Aß, and different
agents targeting Aß formation have been shown to reduce
RGC apoptosis in models of glaucoma [135-138].
In addition to another mechanism of protein
aggregation involves heat shock proteins (HSP). HSPs are
thought to prevent the aggregation of denatured proteins and
immunohistochemical analysis has demonstrated that HSP-
60 and -27 are greater in glaucomatous eyes compared to
non glaucomatous eyes of humans [139], thereby suggesting
that HSPs may be part of a defense mechanism that is
activated in glaucomatous optic neuropathy. Furthermore,
HSP72 upregulation has been shown to correlate with
increased survival of RGCs in a rat model of acute glaucoma
[140]. In glaucoma the HSP-inducer, geranylgeraylacetone,
has furthermore been shown to induce HSP72 and thereby
ameliorate RGC death. Even though no current HSP-
inducing drugs have been administered to glaucoma patients,
it may be a future target for preventing glaucomatous
damage [141,142].
Glial Cell Modulation
Much attention has been given to RGC maintenance in
the search for new treatment targets in glaucoma. However,
it is clear, that the surrounding cells tightly regulate RGC
homeostasis. Hence, in the non-myelinated region of the
RGCs, Müller cells and astrocytes (macroglial cells) are the
major glial cells to provide support, as well as to create the
interface between RGCs and blood vessels. They remove
excess glutamate from the synapse thereby preventing
exitotoxicity [87,143], and help to maintain ion homeostasis
and extracellular pH. In addition, macroglial cells liberate
cytokines such as TGF [144], ciliary neurotrophic factor
(CNTF) [145], and platelet-derived growth factor [146].
Hence, modulation of macroglial cell activity may therefore
be a key target in the understanding of RGC protection
[147,148].
Other Pathways
Considerable evidence exists on estrogen as a
neuroprotective drug, and a recent study has provided strong
evidence that topical estrogen drops are neuroprotective in a
rodent model of glaucoma [149]. Another suggested drug to
prevent glaucomatous damage is statins. Hence, long-term
use of statins has been shown to be associated with a reduced
risk of glaucoma [150,151]. Finally, the glycoprotein,
erythropoietin (EPO), has been suggested to be a potential
therapeutic neuroprotectant in glaucoma [152,153].
NEUROREGENERATIVE TREATMENT STRATEGIES
Growing evidence suggests cell repair or cell-
replacement therapy as a new treatment approach. Within the
potential group of cell repair treatment strategies, axonal
growth has become a target for investigation. Furthermore,
surgical approaches to enhance regenerative capacity of
RGCs have been suggested. Finally, stem cells hold great
promise for neurodegenerative disorders such as glaucoma.
96 The Open Ophthalmology Journal, 2015, Volume 9 M. Kolko
Cell Repair
Although the critical first step in the treatment of
glaucoma is enhancing RGC survival, a significant number
of patients will be diagnosed at a later stage by which their
axons have already been injured. In these cases, preventing
apoptosis will not be sufficient and the ideal therapies should
encourage axon regeneration to rebuild connections from the
RGCs to the brain.
In this aspect, more molecules have been shown to
possess regenerative properties due to their inflammatory
stimulation [154-156]. Among these, CNTF has been shown
to induce axonal growth and thereby suggested to provide a
new neuroregenative approach [147,157,158].
Because of the promising experimental results, a phase-I
trial in glaucoma has recently been performed (Phase I, #
NCT01408472). Through search, no final outcome is yet
available, however, although the study is a phase 1 trial and
designed to evaluate safety in the patient population being
studied, any hint of efficacy would be expected to drive
investigation in later-phase trials.
In addition to CNTF, studies have shown a potential role
of Nogo-66 receptor (NgR)1 therapy for glaucoma to prevent
RGC death and promote optic nerve axonal regeneration.
Hence, inhibition of NgR1 by RNA interference or by
transfection of the dominant-negative form of NgR1, has
been shown to stimulate optic nerve axon regrowth.
Furthermore, knockout of NgR1 has been shown effective
for enhancing axonal regeneration after optic nerve crush
[159,160].
Surgical Approaches for Neuroregeneration
Penetrating injury as well as lens injury has been
suggested to result in the release of low-grade inflammatory
molecules, which secondly leads to axonal regeneration
[161,162]. In order to consider this strategy in humans, a
number of issues would have to be considered including a
rapid formation of cataract, infection, etc. Hence, pursuing
the molecular basis of the effect may prove more realistic for
translation to human glaucoma treatment.
Stem Cell Therapy
Stem cell therapy holds great promise for
neurodegenerative diseases and emerging studies try to
identify the use of stem cells in experimental glaucoma.
Substantial evidence has correlated neurotrophic factor
deprivation with RGC death and new therapies aim to
supplement these [163]. To avoid repeated injections of
growth factors, cell-based delivery of neurotrophic factors
have been proposed. In this matter, an ongoing phase-I
clinical trial for glaucoma is using genetically modified
CNTF-secreting retinal pigment epithelium cells (Phase I,
#NCT01408472). In addition, transplantation with
mesenchymal stem cells (MSC) has been suggested, since
these produce neurotrophic factors [164-167]. Furthermore,
intracranial human umbilical cord blood MSC
transplantation has been shown to protect RGC and to induce
axonal regeneration [168]. Overall, the neuroprotective and
neuroregenerative effect of MSCs on RGC survival is
evident, and currently, a clinical trial using bone marrow-
derived MSCs on glaucoma is processed. The outcome of
this study is expected in 2017 (Phase I, #NCT01920867).
CONCLUSION
The present review highlights current treatment strategies
and possible future ways to rescue and regenerate RGCs.
Glaucoma remains a major cause of blindness worldwide.
Various new targets to treat glaucoma have been suggested,
but to date the only available glaucoma medication is IOP
lowering compounds, which are only decreasing the rate of
progression. Hence, no cure for glaucoma exists. The
identification of new therapeutic targets has been hampered
by lack of understanding of the etiology of glaucoma, and
the limited number of animal models available that likely
represent only a small subset of human glaucoma cases.
Since glaucoma may be a spectrum of different pathologies
leading to the same endpoint, the outcome from clinical trials
may be lost in the diversification of etiologies. In order to
identify future RGC rescuing drugs, attention must be given
to the study design. Hence, a more stringent patient selection
and more efficient outcome measurements will be necessary
to document the effectiveness of these.
CONFLICT OF INTEREST
The authors confirm that this article content has no
conflict of interest.
ACKNOWLEDGEMENTS
The time spent for writing the present review was granted
by The Danish Council for Independent Research|Medical
Sciences and the Velux Foundation for whom I am grateful.
I thank Kurt Bang for providing information of currents
treatment strategies, and for his enthusiasm of the present
manuscript. My apologies to all colleagues whose work I
have not included.
REFERENCES
[1] Tham Y-C, Li X, Wong TY, Quigley HA, Aung T, Cheng C-Y.
Global prevalence of glaucoma and projections of glaucoma burden
through 2040: a systematic review and meta-analysis.
Ophthalmology 2014; 121(11): 2081-90.
[2] Chang EE, Goldberg JL. Glaucoma 2.0: neuroprotection,
neuroregeneration, neuroenhancement. Ophthalmology 2012;
119(5): 979-86.
[3] Gordon MO, Beiser JA, Brandt JD, et al. The ocular hypertension
treatment study: baseline factors that predict the onset of primary
open-angle glaucoma. Arch Ophthalmol 2002; 120(6): 714-20
discussion 829-30.
[4] Pinazo-Durán MD, Zanón-Moreno V, García-Medina JJ, Gallego-
Pinazo R. Evaluation of presumptive biomarkers of oxidative
stress, immune response and apoptosis in primary open-angle
glaucoma. Curr Opin Pharmacol 2013; 13(1): 98-107.
[5] Weinreb RN. Glaucoma neuroprotection: What is it? why is it
needed? Can J Ophthalmol 2007; 42(3): 396-8.
[6] Wierzbowska J, Robaszkiewicz J, Figurska M, Stankiewicz A.
Future possibilities in glaucoma therapy. Med Sci Monit 2010;
16(11): RA252-9.
[7] Heijl A, Bengtsson B, Hyman L, Leske MC, Early Manifest
Glaucoma Trial Group. Natural history of open-angle glaucoma.
Ophthalmology 2009; 116(12): 2271-6.
[8] Quigley HA. Glaucoma. Lancet 2011; 377(9774): 1367-77.
Present and New Treatment Strategies in the Management of Glaucoma The Open Ophthalmology Journal, 2015, Volume 9 97
[9] Metoki T, Ohguro H, Ohguro I, Mamiya K, Ito T, Nakazawa M.
Study of effects of antiglaucoma eye drops on N-methyl-D-
aspartate-induced retinal damage. Jpn J Ophthalmol 2005; 49(6):
453-61.
[10] Mizuno K, Koide T, Yoshimura M, Araie M. Neuroprotective
effect and intraocular penetration of nipradilol, a beta-blocker with
nitric oxide donative action. Invest Ophthalmol Vis Sci 2001;
42(3): 688-94.
[11] Mizuno K, Koide T, Saito N, et al. Topical nipradilol: effects on
optic nerve head circulation in humans and periocular distribution
in monkeys. Invest Ophthalmol Vis Sci 2002; 43(10): 3243-50.
[12] Inoue K, Okugawa K, Kato S, et al. Ocular factors relevant to anti-
glaucomatous eyedrop-related keratoepitheliopathy. J Glaucoma
2003; 12(6): 480-5.
[13] Schoene RB, Abuan T, Ward RL, Beasley CH. Effects of topical
betaxolol, timolol, and placebo on pulmonary function in asthmatic
bronchitis. Am J Ophthalmol 1984; 97(1): 86-92.
[14] Lichter PR, Newman LP, Wheeler NC, Beall OV. Patient tolerance
to carbonic anhydrase inhibitors. Am J Ophthalmol 1978; 85(4):
495-502.
[15] Konowal A, Morrison JC, Brown SV, et al. Irreversible corneal
decompensation in patients treated with topical dorzolamide. Am J
Ophthalmol 1999; 127(4): 403-6.
[16] Inoue K, Wakakura M, Inoue J, Matsuo H, Hara T, Tomita G.
Adverse reaction after use of latanoprost in Japanese glaucoma
patients. Nippon Ganka Gakkai Zasshi 2006; 110(8): 581-7.
[17] Camras CB, Alm A, Watson P, Stjernschantz J. Latanoprost, a
prostaglandin analog, for glaucoma therapy. Efficacy and safety
after 1 year of treatment in 198 patients. Latanoprost Study Groups.
Ophthalmology 1996; 103(11): 1916-24.
[18] Inoue K, Shiokawa M, Higa R, et al. Adverse periocular reactions
to five types of prostaglandin analogs. Eye (Lond) 2012; 26(11):
1465-72.
[19] Wand M, Gilbert CM, Liesegang TJ. Latanoprost and herpes
simplex keratitis. Am J Ophthalmol 1999; 127(5): 602-4.
[20] Butler P, Mannschreck M, Lin S, Hwang I, Alvarado J. Clinical
experience with the long-term use of 1% apraclonidine. Incidence
of allergic reactions. Arch Ophthalmol 1995; 113(3): 293-6.
[21] Krupin T, Liebmann JM, Greenfield DS, Ritch R, Gardiner S,
Low-Pressure Glaucoma Study Group. A randomized trial of
brimonidine versus timolol in preserving visual function: results
from the low-pressure glaucoma treatment study. Am J Ophthalmol
2011; 151(4): 671-81.
[22] Zimmerman TJ, Wheeler TM. Miotics: side effects and ways to
avoid them. Ophthalmology 1982; 89(1): 76-80.
[23] Weinreb RN, Lindsey JD. Metalloproteinase gene transcription in
human ciliary muscle cells with latanoprost. Invest Ophthalmol Vis
Sci 2002; 43(3): 716-22.
[24] Weinreb RN, Toris CB, Gabelt BT, Lindsey JD, Kaufman PL.
Effects of prostaglandins on the aqueous humor outflow pathways.
Surv Ophthalmol 2002; 47(Suppl 1): S53-64.
[25] Fukata Y, Amano M, Kaibuchi K. Rho-rho-kinase pathway in
smooth muscle contraction and cytoskeletal reorganization of non-
muscle cells. Trends Pharmacol Sci 2001; 22(1): 32-9.
[26] Honjo M, Tanihara H, Inatani M, et al. Effects of rho-associated
protein kinase inhibitor Y-27632 on intraocular pressure and
outflow facility. Invest Ophthalmol Vis Sci 2001; 42(1): 137-44.
[27] Rao PV, Deng P, Sasaki Y, Epstein DL. Regulation of myosin light
chain phosphorylation in the trabecular meshwork: role in aqueous
humour outflow facility. Exp Eye Res 2005; 80(2): 197-206.
[28] Tian B, Geiger B, Epstein DL, Kaufman PL. Cytoskeletal
involvement in the regulation of aqueous humor outflow. Invest
Ophthalmol Vis Sci 2000; 41(3): 619-23.
[29] Tian B, Brumback LC, Kaufman PL. ML-7, chelerythrine and
phorbol ester increase outflow facility in the monkey eye. Exp Eye
Res 2000; 71(6): 551-66.
[30] Kaufman PL. Pharmacologic trabeculocanalotomy. Facilitating
aqueous outflow by assaulting the meshwork cytoskeleton,
junctional complexes, and extracellular matrix. Arch Ophthalmol
1992; 110(1): 34-6.
[31] Beidoe G, Mousa SA. Current primary open-angle glaucoma
treatments and future directions. Clin Ophthalmol 2012; 6: 1699-
707.
[32] Lee AJ, Goldberg I. Emerging drugs for ocular hypertension.
Expert Opin Emerg Drugs 2011; 16(1): 137-61.
[33] Muñoz-Negrete FJ, Pérez-López M, Kim HRW, Rebolleda G. New
developments in glaucoma medical treatment. Arch Soc Esp
Oftalmol 2009; 84(10): 491-500.
[34] Fukiage C, Mizutani K, Kawamoto Y, Azuma M, Shearer TR.
Involvement of phosphorylation of myosin phosphatase by ROCK
in trabecular meshwork and ciliary muscle contraction. Biochem
Biophys Res Commun 2001; 288(2): 296-300.
[35] Nakajima E, Nakajima T, Minagawa Y, Shearer TR, Azuma M.
Contribution of ROCK in contraction of trabecular meshwork:
proposed mechanism for regulating aqueous outflow in monkey
and human eyes. J Pharm Sci 2005; 94(4): 701-8.
[36] Vohra V, Chawla H, Malvika G. Rock inhibitors: future of anti-
glaucoma medication. Ophthalmol Res 2014; 2(6): 361-7.
[37] Chen J, Runyan SA, Robinson MR. Novel ocular antihypertensive
compounds in clinical trials. Clin Ophthalmol 2011; 5: 667-77.
[38] Tanihara H, Inatani M, Honjo M, Tokushige H, Azuma J, Araie M.
Intraocular pressure-lowering effects and safety of topical
administration of a selective ROCK inhibitor, SNJ-1656, in healthy
volunteers. Arch Ophthalmol 2008; 126(3): 309-15.
[39] Tokushige H, Inatani M, Nemoto S, et al. Effects of topical
administration of y-39983, a selective rho-associated protein kinase
inhibitor, on ocular tissues in rabbits and monkeys. Invest
Ophthalmol Vis Sci 2007; 48(7): 3216-22.
[40] Rao VP, Epstein DL. Rho GTPase/Rho kinase inhibition as a novel
target for the treatment of glaucoma. BioDrugs 2007; 21(3): 167-
77.
[41] Sugiyama T, Moriya S, Oku H, Azuma I. Association of
endothelin-1 with normal tension glaucoma: clinical and
fundamental studies. Surv Ophthalmol 1995; 39(Suppl 1): S49-56.
[42] Choritz L, Machert M, Thieme H. Correlation of endothelin-1
concentration in aqueous humor with intraocular pressure in
primary open angle and pseudoexfoliation glaucoma. Invest
Ophthalmol Vis Sci 2012; 53(11): 7336-42.
[43] Källberg ME, Brooks DE, Gelatt KN, Garcia-Sanchez GA, Szabo
NJ, Lambrou GN. Endothelin-1, nitric oxide, and glutamate in the
normal and glaucomatous dog eye. Vet Ophthalmol 2007; 10(Suppl
1): 46-52.
[44] Renieri G, Choritz L, Rosenthal R, Meissner S, Pfeiffer N, Thieme
H. Effects of endothelin-1 on calcium-independent contraction of
bovine trabecular meshwork. Graefes Arch Clin Exp Ophthalmol
2008; 246(8): 1107-15.
[45] Cellini M, Strobbe E, Gizzi C, Balducci N, Toschi PG, Campos
EC. Endothelin-1 plasma levels and vascular endothelial
dysfunction in primary open angle glaucoma. Life Sci 2012; 91(13-
14): 699-702.
[46] Buckley C, Hadoke PWF, Henry E, O'Brien C. Systemic vascular
endothelial cell dysfunction in normal pressure glaucoma. Br J
Ophthal 2002; 86(2): 227-32.
[47] Minton AZ, Phatak NR, Stankowska DL, et al. Endothelin B
receptors contribute to retinal ganglion cell loss in a rat model of
glaucoma. PLoS ONE 2012; 7(8): e43199.
[48] Cherecheanu AP, Garhofer G, Schmidl D, Werkmeister R,
Schmetterer L. Ocular perfusion pressure and ocular blood flow in
glaucoma. Curr Opin Pharmacol 2013; 13(1): 36-42.
[49] Neufeld AH. Pharmacologic neuroprotection with an inhibitor of
nitric oxide synthase for the treatment of glaucoma. Brain Res Bull
2004; 62(6): 455-9.
[50] Vohra R, Tsai JC, Kolko M. The role of inflammation in the
pathogenesis of glaucoma. Surv Ophthalmol 2013; 58(4): 311-20.
[51] Nathanson JA, McKee M. Identification of an extensive system of
nitric oxide-producing cells in the ciliary muscle and outflow
pathway of the human eye. Invest Ophthalmol Vis Sci 1995; 36(9):
1765-73.
[52] Wiederholt M, Thieme H, Stumpff F. The regulation of trabecular
meshwork and ciliary muscle contractility. Prog Retin Eye Res
2000; 19(3): 271-95.
[53] Min SH, Lee T-I, Chung YS, Kim HK. Transforming growth
factor-beta levels in human aqueous humor of glaucomatous,
diabetic and uveitic eyes. Korean J Ophthalmol 2006; 20(3): 162-5.
[54] Trivedi RH, Nutaitis M, Vroman D, Crosson CE. Influence of race
and age on aqueous humor levels of transforming growth factor-
beta 2 in glaucomatous and nonglaucomatous eyes. J Ocul
Pharmacol Ther 2011; 27(5): 477-80.
[55] Prendes MA, Harris A, Wirostko BM, Gerber AL, Siesky B. The
role of transforming growth factor β in glaucoma and the
therapeutic implications. Br J Ophthalmol 2013; 97(6): 680-6.
98 The Open Ophthalmology Journal, 2015, Volume 9 M. Kolko
[56] Gottanka J, Chan D, Eichhorn M, Lütjen-Drecoll E, Ethier CR.
Effects of TGF-beta2 in perfused human eyes. Invest Ophthalmol
Vis Sci 2004; 45(1): 153-8.
[57] Walshe TE, Leach LL, D'Amore PA. TGF-β signaling is required
for maintenance of retinal ganglion cell differentiation and
survival. Neuroscience 2011; 189: 123-31.
[58] Ueda K, Nakahara T, Mori A, Sakamoto K, Ishii K. Protective
effects of TGF-β inhibitors in a rat model of NMDA-induced
retinal degeneration. Eur J Pharmacol 2013; 699(1-3): 188-93.
[59] Tao Y-J, Gao D-W, Yu M. TGF-β(1) in retinal ganglion cells in
rats with chronic ocular hypertension: its expression and anti-
apoptotic effect. Int J Ophthalmol 2011; 4(4): 396-401.
[60] Wang Q, Usinger W, Nichols B, et al. Cooperative interaction of
CTGF and TGF-β in animal models of fibrotic disease.
Fibrogenesis Tissue Repair 2011; 4(1): 4.
[61] O'Donovan HC, Hickey F, Brazil DP, et al. Connective tissue
growth factor antagonizes transforming growth factor-β1/Smad
signalling in renal mesangial cells. Biochem J 2012; 441(1): 499-
510.
[62] Faherty N, Curran SP, O'Donovan H, et al. CCN2/CTGF increases
expression of miR-302 microRNAs, which target the TGFβ type II
receptor with implications for nephropathic cell phenotypes. J Cell
Sci 2012; 125(Pt 23): 5621-9.
[63] Fredholm BB. Adenosine receptors as drug targets. Exp Cell Res
2010; 316(8): 1284-8.
[64] Civan MM, Macknight ADC. The ins and outs of aqueous humour
secretion. Exp Eye Res 2004; 78(3): 625-31.
[65] Comes N, Buie LK, Borrás T. Evidence for a role of angiopoietin-
like 7 (ANGPTL7) in extracellular matrix formation of the human
trabecular meshwork: implications for glaucoma. Genes Cells
2011; 16(2): 243-59.
[66] Rocha-Sousa A, Rodrigues-Araújo J, Gouveia P, et al. New
therapeutic targets for intraocular pressure lowering. ISRN
Ophthalmol 2013; 2013: 261386.
[67] Vaajanen A, Vapaatalo H. Local ocular renin-angiotensin system -
a target for glaucoma therapy? Basic Clin Pharmacol Toxicol 2011;
109(4): 217-24.
[68] Costagliola C, Parmeggiani F, Semeraro F, Sebastiani A. Selective
serotonin reuptake inhibitors: a review of its effects on intraocular
pressure. Curr Neuropharmacol 2008; 6(4): 293-310.
[69] Rocha-Sousa A, Pereira-Silva P, Tavares-Silva M, et al.
Identification of the ghrelin-GHSR 1 system and its influence in the
modulation of induced ocular hypertension in rabbit and rat eyes.
Peptides 2014; 57: 59-66.
[70] Pinar-Sueiro S, Rodríguez-Puertas R, Vecino E. Cannabinoid
applications in glaucoma. Arch Soc Esp Oftalmol 2011; 86(1): 16-
23.
[71] Metzger H, Lindner E. The positive inotropic-acting forskolin, a
potent adenylate cyclase activator. Arzneimittelforschung 1981;
31(8): 1248-50.
[72] Armaly MF, Krueger DE, Maunder L, et al. Biostatistical analysis
of the collaborative glaucoma study. I. Summary report of the risk
factors for glaucomatous visual-field defects. Arch Ophthalmol
1980; 98(12): 2163-71.
[73] Shiose Y, Kitazawa Y, Tsukahara S, et al. Epidemiology of
glaucoma in Japan--a nationwide glaucoma survey. Jpn J
Ophthalmol 1991; 35(2): 133-55.
[74] Furuya T, Pan Z, Kashiwagi K. Role of retinal glial cell glutamate
transporters in retinal ganglion cell survival following stimulation
of NMDA receptor. Curr Eye Res 2012; 37(3): 170-8.
[75] Lipton SA, Rosenberg PA. Excitatory amino acids as a final
common pathway for neurologic disorders. N Engl J Med 1994;
330(9): 613-22.
[76] Salt TE, Cordeiro MF. Glutamate excitotoxicity in glaucoma:
throwing the baby out with the bathwater? Eye (Lond) 2006; 20(6):
730-32.
[77] Brooks DE, Garcia GA, Dreyer EB, Zurakowski D, Franco-
Bourland RE. Vitreous body glutamate concentration in dogs with
glaucoma. Am J Vet Res 1997; 58(8): 864-7.
[78] Dreyer EB, Zurakowski D, Schumer RA, Podos SM, Lipton SA.
Elevated glutamate levels in the vitreous body of humans and
monkeys with glaucoma. Arch Ophthalmol 1996; 114(3): 299-305.
[79] Johnson EC, Deppmeier LM, Wentzien SK, Hsu I, Morrison JC.
Chronology of optic nerve head and retinal responses to elevated
intraocular pressure. Invest Ophthalmol Vis Sci 2000; 41(2): 431-
42.
[80] Greenfield DS, Girkin C, Kwon YH. Memantine and progressive
glaucoma. J Glaucoma 2005; 14(1): 84-6.
[81] Hare WA, WoldeMussie E, Lai RK, et al. Efficacy and safety of
memantine treatment for reduction of changes associated with
experimental glaucoma in monkey, I: Functional measures. Invest
Ophthalmol Vis Sci 2004; 45(8): 2625-39.
[82] Miguel-Hidalgo JJ, Alvarez XA, Cacabelos R, Quack G.
Neuroprotection by memantine against neurodegeneration induced
by beta-amyloid(1-40). Brain Res 2002; 958(1): 210-21.
[83] Osborne NN. Recent clinical findings with memantine should not
mean that the idea of neuroprotection in glaucoma is abandoned.
Acta Ophthalmol 2009; 87(4): 450-4.
[84] Martin KRG, Levkovitch-Verbin H, Valenta D, Baumrind L, Pease
ME, Quigley HA. Retinal glutamate transporter changes in
experimental glaucoma and after optic nerve transection in the rat.
Invest Ophthalmol Vis Sci 2002; 43(7): 2236-43.
[85] Sullivan RKP, WoldeMussie E, Macnab L, Ruiz G, Pow DV.
Evoked expression of the glutamate transporter GLT-1c in retinal
ganglion cells in human glaucoma and in a rat model. Invest
Ophthalmol Vis Sci 2006; 47(9): 3853-9.
[86] Attwell D, Buchan AM, Charpak S, Lauritzen M, Macvicar BA,
Newman EA. Glial and neuronal control of brain blood flow.
Nature 2010; 468(7321): 232-43.
[87] Toft-Kehler AK, Skytt DM, Poulsen KA, et al. Limited energy
supply in Müller cells alters glutamate uptake. Neurochem Res
2014; 39(5): 941-9.
[88] Feilchenfeld Z, Yücel YH, Gupta N. Oxidative injury to blood
vessels and glia of the pre-laminar optic nerve head in human
glaucoma. Exp Eye Res 2008; 87(5): 409-14.
[89] Javadiyan S, Burdon KP, Whiting MJ, et al. Elevation of serum
asymmetrical and symmetrical dimethylarginine in patients with
advanced glaucoma. Invest Ophthalmol Vis Sci 2012; 53(4): 1923-
7.
[90] Ko M-L, Peng P-H, Ma M-C, Ritch R, Chen C-F. Dynamic
changes in reactive oxygen species and antioxidant levels in retinas
in experimental glaucoma. Free Radic Biol Med 2005; 39(3): 365-
73.
[91] Moreno MC, Campanelli J, Sande P, Sánez DA, Keller Sarmiento
MI, Rosenstein RE. Retinal oxidative stress induced by high
intraocular pressure. Free Radic Biol Med 2004; 37(6): 80312.
[92] Tezel G, Yang X, Cai J. Proteomic identification of oxidatively
modified retinal proteins in a chronic pressure-induced rat model of
glaucoma. Invest Ophthalmol Vis Sci 2005; 46(9): 3177-87.
[93] Birich TV, Birich TA, Marchenko LN, Remizonova DN, Fedylov
AS. Vitamin E in the complex treatment of patients with primary
glaucoma. Vestn Oftalmol 1986; 102(2): 10-3.
[94] Cellini M, Caramazza N, Mangiafico P, Possati GL, Caramazza R.
Fatty acid use in glaucomatous optic neuropathy treatment. Acta
Ophthalmol Scand 1998; 227: 41-2.
[95] Hsu K-H, Lazon de la Jara P, Ariyavidana A, et al. Release of
betaine and dexpanthenol from vitamin E modified silicone-
hydrogel contact lenses. Curr Eye Res 2014; 15: 1-7.
[96] Peng C-C, Ben-Shlomo A, Mackay EO, Plummer CE, Chauhan A.
Drug delivery by contact lens in spontaneously glaucomatous dogs.
Curr Eye Res 2012; 37(3): 204-11.
[97] Janssens D, Michiels C, Delaive E, Eliaers F, Drieu K, Remacle J.
Protection of hypoxia-induced ATP decrease in endothelial cells by
ginkgo biloba extract and bilobalide. Biochem Pharmacol 1995;
50(7): 991-9.
[98] Abdel-Kader R, Hauptmann S, Keil U, et al. Stabilization of
mitochondrial function by Ginkgo biloba extract (EGb 761).
Pharmacol Res 2007; 56(6): 493-502.
[99] Chandrasekaran K, Mehrabian Z, Spinnewyn B, Chinopoulos C,
Drieu K, Fiskum G. Bilobalide, a component of the Ginkgo biloba
extract (EGb 761), protects against neuronal death in global brain
ischemia and in glutamate-induced excitotoxicity. Cell Mol Biol
(Noisy-le-grand) 2002; 48(6): 663-9.
[100] Eckert A, Keil U, Scherping I, Hauptmann S, Müller WE.
Stabilization of mitochondrial membrane potential and
improvement of neuronal energy metabolism by Ginkgo biloba
extract EGb 761. Ann N Y Acad Sci 2005; 1056: 474-85.
[101] Cybulska-Heinrich AK, Mozaffarieh M, Flammer J. Ginkgo biloba:
an adjuvant therapy for progressive normal and high tension
glaucoma. Mol Vis 2012; 18: 390-402.
Present and New Treatment Strategies in the Management of Glaucoma The Open Ophthalmology Journal, 2015, Volume 9 99
[102] Abu-Amero KK, Morales J, Bosley TM. Mitochondrial
abnormalities in patients with primary open-angle glaucoma. Invest
Ophthalmol Vis Sci 2006; 47(6): 2533-41.
[103] Chrysostomou V, Rezania F, Trounce IA, Crowston JG. Oxidative
stress and mitochondrial dysfunction in glaucoma. Curr Opin
Pharmacol 2013; 13(1): 12-5.
[104] Lee S, Sheck L, Crowston JG, et al. Impaired complex-I-linked
respiration and ATP synthesis in primary open-angle glaucoma
patient lymphoblasts. Invest Ophthalmol Vis Sci 2012; 53(4):
2431-7.
[105] Yu-Wai-Man P, Griffiths PG, Chinnery PF. Mitochondrial optic
neuropathies - disease mechanisms and therapeutic strategies. Prog
Retinal Eye Res 2011; 30(2): 81-114.
[106] Nucci C, Tartaglione R, Cerulli A, et al. Retinal damage caused by
high intraocular pressure-induced transient ischemia is prevented
by coenzyme Q10 in rat. Int Rev Neurobiol 2007; 82: 397-406.
[107] Russo R, Cavaliere F, Rombolà L, et al. Rational basis for the
development of coenzyme Q10 as a neurotherapeutic agent for
retinal protection. Prog Brain Res 2008; 173: 575-82.
[108] Nakajima Y, Inokuchi Y, Nishi M, Shimazawa M, Otsubo K, Hara
H. Coenzyme Q10 protects retinal cells against oxidative stress in
vitro and in vivo. Brain Res 2008; 1226: 226-33.
[109] McKinnon SJ. The cell and molecular biology of glaucoma:
common neurodegenerative pathways and relevance to glaucoma.
Invest Ophthalmol Vis Sci 2012; 53(5): 2485-7.
[110] Agarwal R, Agarwal P. Glaucomatous neurodegeneration: an eye
on tumor necrosis factor-alpha. Indian J Ophthalmol 2012; 60(4):
255-61.
[111] Tezel G. TNF-alpha signaling in glaucomatous neurodegeneration.
Prog Brain Res 2008; 173: 409-21.
[112] Fontaine V, Mohand-Said S, Hanoteau N, Fuchs C, Pfizenmaier K,
Eisel U. Neurodegenerative and neuroprotective effects of tumor
Necrosis factor (TNF) in retinal ischemia: opposite roles of TNF
receptor 1 and TNF receptor 2. J Neurosci 2002; 22(7): RC216.
[113] Lebrun-Julien F, Bertrand MJ, De Backer O, et al. ProNGF induces
TNFalpha-dependent death of retinal ganglion cells through a
p75NTR non-cell-autonomous signaling pathway. Proc Natl Acad
Sci USA 2010; 107(8): 3817-22.
[114] Nakazawa T, Nakazawa C, Matsubara A, et al. Tumor necrosis
factor-alpha mediates oligodendrocyte death and delayed retinal
ganglion cell loss in a mouse model of glaucoma. J Neurosci 2006;
26(49): 12633-41.
[115] Tezel G, Yang X, Yang J, Wax MB. Role of tumor necrosis factor
receptor-1 in the death of retinal ganglion cells following optic
nerve crush injury in mice. Brain Res 2004; 996(2): 202-12.
[116] Ahmed Z, Aslam M, Lorber B, Suggate EL, Berry M, Logan A.
Optic nerve and vitreal inflammation are both RGC neuroprotective
but only the latter is RGC axogenic. Neurobiol Dis 2010; 37(2):
441-54.
[117] Roh M, Zhang Y, Murakami Y, et al. Etanercept, a widely used
inhibitor of tumor necrosis factor-α (TNF-α), prevents retinal
ganglion cell loss in a rat model of glaucoma. PLoS ONE 2012;
7(7): e40065.
[118] Dong C-J, Guo Y, Agey P, Wheeler L, Hare WA. Alpha2
adrenergic modulation of NMDA receptor function as a major
mechanism of RGC protection in experimental glaucoma and
retinal excitotoxicity. Invest Ophthalmol Vis Sci 2008; 49(10):
4515-22.
[119] Pan Y-Z, Li D-P, Pan H-L. Inhibition of glutamatergic synaptic
input to spinal lamina II(o) neurons by presynaptic alpha(2)-
adrenergic receptors. J Neurophysiol 2002; 87(4): 1938-47.
[120] Hong S, Park K, Kim CY, Seong GJ. Agmatine inhibits hypoxia-
induced TNF-alpha release from cultured retinal ganglion cells.
Biocell 2008; 32(2): 201-5.
[121] Hong S, Kim CY, Lee WS, Shim J, Yeom HY, Seong GJ. Ocular
hypotensive effects of topically administered agmatine in a chronic
ocular hypertensive rat model. Exp Eye Res 2010; 90(1): 97-103.
[122] García E, Silva-García R, Mestre H, et al. Immunization with A91
peptide or copolymer-1 reduces the production of nitric oxide and
inducible nitric oxide synthase gene expression after spinal cord
injury. J Neurosci Res 2012; 90(3): 656-63.
[123] Schori H, Kipnis J, Yoles E, et al. Vaccination for protection of
retinal ganglion cells against death from glutamate cytotoxicity and
ocular hypertension: implications for glaucoma. Proc Natl Acad Sci
USA 2001; 98(6): 3398-403.
[124] Nilforushan N. Neuroprotection in glaucoma. J Ophthalmic Vis
Res 2012; 7(1): 91-3.
[125] Brust A-K, Ulbrich HK, Seigel GM, Pfeiffer N, Grus FH. Effects
of cyclooxygenase inhibitors on apoptotic neuroretinal cells.
Biomark Insights 2008; 3: 387-402.
[126] Collaço-Moraes Y, Aspey B, Harrison M, de Belleroche J. Cyclo-
oxygenase-2 messenger RNA induction in focal cerebral ischemia.
J Cereb Blood Flow Metab 1996; 16(6): 1366-72.
[127] Sakai Y, Tanaka T, Seki M, et al. Cyclooxygenase-2 plays a
critical role in retinal ganglion cell death after transient ischemia:
real-time monitoring of RGC survival using Thy-1-EGFP
transgenic mice. Neurosci Res 2009; 65(4): 319-25.
[128] Kawasaki A, Han M-H, Wei J-Y, Hirata K, Otori Y, Barnstable CJ.
Protective effect of arachidonic acid on glutamate neurotoxicity in
rat retinal ganglion cells. Invest Ophthalmol Vis Sci 2002; 43(6):
1835-42.
[129] Kolko M, DeCoster MA, de Turco EB, Bazan NG. Synergy by
secretory phospholipase A2 and glutamate on inducing cell death
and sustained arachidonic acid metabolic changes in primary
cortical neuronal cultures. J Biol Chem 1996; 271(51): 32722-8.
[130] Helin M, Rönkkö S, Puustjärvi T, Teräsvirta M, Uusitalo H.
Phospholipases A2 in normal human conjunctiva and from patients
with primary open-angle glaucoma and exfoliation glaucoma.
Graefes Arch Clin Exp Ophthalmol 2008; 246(5): 739-46.
[131] Rönkkö S, Rekonen P, Kaarniranta K, Puustjärvi T, Teräsvirta M,
Uusitalo H. Phospholipase A2 in chamber angle of normal eyes and
patients with primary open angle glaucoma and exfoliation
glaucoma. Mol Vis 2007; 13: 408-17.
[132] Yagami T, Ueda K, Sakaeda T, et al. Effects of an endothelin B
receptor agonist on secretory phospholipase A2-IIA-induced
apoptosis in cortical neurons. Neuropharmacology 2005; 48(2):
291-300.
[133] Yagami T, Ueda K, Asakura K, et al. Human group IIA secretory
phospholipase A2 induces neuronal cell death via apoptosis. Mol
Pharmacol 2002; 61(1): 114-26.
[134] Yagami T, Ueda K, Asakura K, et al. Human group IIA secretory
phospholipase A2 potentiates Ca2+ influx through L-type voltage-
sensitive Ca2+ channels in cultured rat cortical neurons. J
Neurochem 2003; 85(3): 749-58.
[135] Doh SH, Kim JH, Lee KM, Park HY, Park CK. Retinal ganglion
cell death induced by endoplasmic reticulum stress in a chronic
glaucoma model. Brain Res 2010; 1308: 158-66.
[136] Guo L, Salt TE, Luong V, et al. Targeting amyloid-beta in
glaucoma treatment. Proc Natl Acad Sci USA 2007; 104(33):
13444-9.
[137] McKinnon SJ, Lehman DM, Kerrigan-Baumrind LA, et al. Caspase
activation and amyloid precursor protein cleavage in rat ocular
hypertension. Invest Ophthalmol Vis Sci 2002; 43(4): 1077-87.
[138] Yoneda S, Hara H, Hirata A, Fukushima M, Inomata Y, Tanihara
H. Vitreous fluid levels of beta-amyloid((1-42)) and tau in patients
with retinal diseases. Jpn J Ophthalmol 2005; 49(2): 106-8.
[139] Tezel G, Hernandez R, Wax MB. Immunostaining of heat shock
proteins in the retina and optic nerve head of normal and
glaucomatous eyes. Arch Ophthalmol 2000; 118(4): 511-8.
[140] Qing G, Duan X, Jiang Y. Heat shock protein 72 protects retinal
ganglion cells in rat model of acute glaucoma. Yan Ke Xue Bao
2005; 21(3): 163-8.
[141] Ishii Y, Kwong JMK, Caprioli J. Retinal ganglion cell protection
with geranylgeranylacetone, a heat shock protein inducer, in a rat
glaucoma model. Invest Ophthalmol Vis Sci 2003; 44(5): 1982-92.
[142] Uchida S, Fujiki M, Nagai Y, Abe T, Kobayashi H.
Geranylgeranylacetone, a noninvasive heat shock protein inducer,
induces protein kinase C and leads to neuroprotection against
cerebral infarction in rats. Neurosci Lett 2006; 396(3): 220-4.
[143] Bringmann A, Grosche A, Pannicke T, Reichenbach A. GABA and
glutamate uptake and metabolism in retinal glial (Müller) cells.
Front Endocrinol (Lausanne) 2013; 2013; 4: 48.
[144] Junier MP. What role(s) for TGFalpha in the central nervous
system? Prog Neurobiol 2000; 62(5): 443-73.
[145] Liu X, Clark AF, Wordinger RJ. Expression of ciliary neurotrophic
factor (CNTF) and its tripartite receptor complex by cells of the
human optic nerve head. Mol Vis 2007; 13: 758-63.
[146] Gris P, Tighe A, Levin D, Sharma R, Brown A. Transcriptional
regulation of scar gene expression in primary astrocytes. Glia 2007;
55(11): 1145-55.
100 The Open Ophthalmology Journal, 2015, Volume 9 M. Kolko
[147] Leibinger M, Müller A, Andreadaki A, Hauk TG, Kirsch M,
Fischer D. Neuroprotective and axon growth-promoting effects
following inflammatory stimulation on mature retinal ganglion
cells in mice depend on ciliary neurotrophic factor and leukemia
inhibitory factor. J Neurosci 2009; 29(45): 14334-41.
[148] Rose K, Litterscheid S, Klumpp S, Krieglstein J. Fibroblast growth
factor 2 requires complex formation with ATP for neuroprotective
activity. Neuroscience 2009; 164(4): 1695-700.
[149] Prokai-Tatrai K, Xin H, Nguyen V, et al. 17β-estradiol eye drops
protect the retinal ganglion cell layer and preserve visual function
in an in vivo model of glaucoma. Mol Pharm 2013; 10(8): 3253-61.
[150] Marcus MW, Müskens RPHM, Ramdas WD, et al. Cholesterol-
lowering drugs and incident open-angle glaucoma: a population-
based cohort study. PLoS ONE 2012; 7(1): e29724.
[151] Stein JD, Newman-Casey PA, Talwar N, Nan B, Richards JE,
Musch DC. The relationship between statin use and open-angle
glaucoma. Ophthalmology 2012; 119(10): 2074-81.
[152] Zhong L, Bradley J, Schubert W, et al. Erythropoietin promotes
survival of retinal ganglion cells in DBA/2J glaucoma mice. Invest
Ophthalmol Vis Sci 2007; 48(3): 1212-8.
[153] Tsai JC, Wu L, Worgul B, Forbes M, Cao J. Intravitreal
administration of erythropoietin and preservation of retinal
ganglion cells in an experimental rat model of glaucoma. Curr Eye
Res 2005; 30(11): 1025-31.
[154] Bertrand J, Winton MJ, Rodriguez-Hernandez N, Campenot RB,
McKerracher L. Application of Rho antagonist to neuronal cell
bodies promotes neurite growth in compartmented cultures and
regeneration of retinal ganglion cell axons in the optic nerve of
adult rats. J Neurosci 2005; 25(5): 1113-21.
[155] Lehmann M, Fournier A, Selles-Navarro I, et al. Inactivation of
Rho signaling pathway promotes CNS axon regeneration. J
Neurosci 1999; 19(17): 7537-47.
[156] Sengottuvel V, Leibinger M, Pfreimer M, Andreadaki A, Fischer
D. Taxol facilitates axon regeneration in the mature CNS. J
Neurosci 2011; 31(7): 2688-99.
[157] Leibinger M, Andreadaki A, Fischer D. Role of mTOR in
neuroprotection and axon regeneration after inflammatory
stimulation. Neurobiol Dis 2012; 46(2): 314-24.
[158] Jo SA, Wang E, Benowitz LI. Ciliary neurotrophic factor is an
axogenesis factor for retinal ganglion cells. Neuroscience 1999;
89(2): 579-91.
[159] Fischer D, He Z, Benowitz LI. Counteracting the Nogo receptor
enhances optic nerve regeneration if retinal ganglion cells are in an
active growth state. J Neurosci 2004; 24(7): 1646-51.
[160] Su Y, Wang F, Teng Y, Zhao S-G, Cui H, Pan S-H. Axonal
regeneration of optic nerve after crush in Nogo66 receptor
knockout mice. Neurosci Lett 2009; 460(3): 223-6.
[161] Fischer D, Pavlidis M, Thanos S. Cataractogenic lens injury
prevents traumatic ganglion cell death and promotes axonal
regeneration both in vivo and in culture. Invest Ophthalmol Vis Sci
2000; 41(12): 3943-54.
[162] Mansour-Robaey S, Clarke DB, Wang YC, Bray GM, Aguayo AJ.
Effects of ocular injury and administration of brain-derived
neurotrophic factor on survival and regrowth of axotomized retinal
ganglion cells. Proc Natl Acad Sci USA 1994; 91(5): 1632-6.
[163] Johnson TV, Bull ND, Martin KR. Neurotrophic factor delivery as
a protective treatment for glaucoma. Exp Eye Res 2011; 93(2):
196-203.
[164] Johnson TV, Bull ND, Hunt DP, Marina N, Tomarev SI, Martin
KR. Neuroprotective effects of intravitreal mesenchymal stem cell
transplantation in experimental glaucoma. Invest Ophthalmol Vis
Sci 2010; 51(4): 2051-9.
[165] Li N, Li X-R, Yuan J-Q. Effects of bone-marrow mesenchymal
stem cells transplanted into vitreous cavity of rat injured by
ischemia/reperfusion. Graefes Arch Clin Exp Ophthalmol 2009;
247(4): 503-14.
[166] Ng TK, Fortino VR, Pelaez D, Cheung HS. Progress of
mesenchymal stem cell therapy for neural and retinal diseases.
World J Stem Cells 2014; 6(2): 111-9.
[167] Yu S, Tanabe T, Dezawa M, Ishikawa H, Yoshimura N. Effects of
bone marrow stromal cell injection in an experimental glaucoma
model. Biochem Biophys Res Commun 2006; 344(4): 1071-9.
[168] Zwart I, Hill AJ, Al-Allaf F, et al. Umbilical cord blood
mesenchymal stromal cells are neuroprotective and promote
regeneration in a rat optic tract model. Exp Neurol 2009; 216(2):
439-48.
Received: March 28, 2015 Revised: March 30, 2015 Accepted: March 30, 2015
© M. Kolko; Licensee Bentham Open.
This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/)
which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.
... These treatment options only function to slow progression and cannot reverse existing damage. Rho kinase inhibitors have shown promise as an emerging therapeutic, with a mechanism of enhancing aqueous drainage via the regulation of smooth muscle contraction through actin [121]. ...
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Background: Glaucoma is a group of optic neuropathies characterized by progressive degeneration of the retinal ganglion cells, axonal loss and irreversible visual field defects. Glaucoma is classified as primary or secondary, and worldwide, primary glaucoma is a leading cause of irreversible blindness. Several subtypes of glaucoma exist, and primary open-angle glaucoma (POAG) is the most common. The etiology of POAG is unknown, but current treatments aim to reduce intraocular pressure (IOP), thus preventing the onset and progression of the disease. Compared with traditional antiglaucomatous treatments, rho kinase inhibitors (ROKi) have a different pharmacodynamic. ROKi is the only current treatment that effectively lowers IOP by modulating the drainage of aqueous humor through the trabecular meshwork and Schlemm's canal. As ROKi are introduced into the market more widely, it is important to assess the efficacy and potential AEs of the treatment. Objectives: To compare the efficacy and safety of ROKi with placebo or other glaucoma medication in people diagnosed with open-angle glaucoma (OAG), primary open-angle glaucoma (POAG) or ocular hypertension (OHT). Search methods: We used standard Cochrane methods and searched databases on 11 December 2020. Selection criteria: We included randomized clinical trials examining commercially available ROKi-based monotherapy or combination therapy compared with placebo or other IOP-lowering medical treatments in people diagnosed with (P)OAG or OHT. We included trials where ROKi were administered according to official glaucoma guidelines. There were no restrictions regarding type, year or status of the publication. Data collection and analysis: We used standard methodological procedures expected by Cochrane. Two review authors independently screened studies, extracted data, and evaluated risk of bias by using Cochrane's RoB 2 tool. MAIN RESULTS: We included 17 trials with 4953 participants diagnosed with (P)OAG or OHT. Fifteen were multicenter trials and 15 were masked trials. All participants were aged above 18 years. Trial duration varied from 24 hours to 12 months. Trials were conducted in the USA, Canada and Japan. Sixteen trials were funded by pharmaceutical companies, and one trial provided no information about funding sources. The trials compared ROKi monotherapy (netarsudil or ripasudil) or combination therapy with latanoprost (prostaglandin analog) or timolol (beta-blocker) with placebo, timolol, latanoprost or netarsudil. Reported outcomes were IOP and safety. Meta-analyses were applied to 13 trials (IOP reduction from baseline) and 15 trials (ocular AEs). Of the trials evaluating IOP, seven were at low risk, three had some concerns, and three were at high risk of bias. Three trials found that netarsudil monotherapy may be superior to placebo (mean difference [MD] 3.11 mmHg, 95% confidence interval [CI] 2.59 to 3.62; I2 = 0%; 155 participants; low-certainty evidence). Evidence from three trials found that timolol may be superior to netarsudil with an MD of 0.66 mmHg (95% CI 0.41 to 0.91; I2 = 0%; 1415 participants; low-certainty evidence). Evidence from four trials found that latanoprost may be superior to netarsudil with an MD of 0.97 mmHg (95% CI 0.67 to 1.27; I2 = 4%; 1283 participants; moderate-certainty evidence). Evidence from three trials showed that, compared with monotherapy with latanoprost, combination therapy with netarsudil and latanoprost probably led to an additional pooled mean IOP reduction from baseline of 1.64 mmHg (95% CI -2.16 to -1.11; 1114 participants). Evidence from three trials showed that, compared with monotherapy with netarsudil, combination therapy with netarsudil and latanoprost probably led to an additional pooled mean IOP reduction from baseline of 2.66 mmHg (95% CI -2.98 to -2.35; 1132 participants). The certainty of evidence was moderate. One trial showed that, compared with timolol monotherapy, combination therapy with ripasudil and timolol may lead to an IOP reduction from baseline of 0.75 mmHg (95% -1.29 to -CI 0.21; 208 participants). The certainty of evidence was moderate. Of the trials assessing total ocular AEs, three were at low risk, four had some concerns, and eight were at high risk of bias. We found very low-certainty evidence that netarsudil may lead to more ocular AEs compared with placebo, with 66 more ocular AEs per 100 person-months (95% CI 28 to 103; I2 = 86%; 4 trials, 188 participants). We found low-certainty evidence that netarsudil may lead to more ocular AEs compared with latanoprost, with 29 more ocular AEs per 100 person-months (95% CI 17 to 42; I2 = 95%; 4 trials, 1286 participants). We found moderate-certainty evidence that, compared with timolol, netarsudil probably led to 21 additional ocular AEs (95% CI 14 to 27; I2 = 93%; 4 trials, 1678 participants). Data from three trials (1132 participants) showed no evidence of differences in the incidence rate of AEs between combination therapy with netarsudil and latanoprost and netarsudil monotherapy (1 more event per 100 person-months, 95% CI 0 to 3); however, the certainty of evidence was low. Similarly, we found low-certainty evidence that, compared with latanoprost, combination therapy with netarsudil and latanoprost may cause 29 more ocular events per 100 person-months (95% CI 11 to 47; 3 trials, 1116 participants). We found moderate-certainty evidence that, compared with timolol monotherapy, combination therapy with ripasudil and timolol probably causes 35 more ocular events per 100 person-months (95% CI 25 to 45; 1 trial, 208 participants). In all included trials, ROKi was reportedly not associated with any particular serious AEs. Authors' conclusions: The current evidence suggests that in people diagnosed with OHT or (P)OAG, the hypotensive effect of netarsudil may be inferior to latanoprost and slightly inferior to timolol. Combining netarsudil and latanoprost probably further reduces IOP compared with monotherapy. Netarsudil as mono- or combination therapy may result in more ocular AEs. However, the certainty of evidence was very low or low for all comparisons except timolol. In general, AEs were described as mild, transient, and reversible upon treatment discontinuation. ROKi was not associated with any particular serious AEs. Future trials of sufficient size and follow-up should be conducted to provide reliable information about glaucoma progression, relevant IOP measurements and a detailed description of AEs using similar terminology. This would ensure the robustness and confidence of the results and assess the intermediate- and long-term efficacy and safety of ROKi.
Article
Objective: To explore the possibility that the excitatory amino acid glutamate might be associated with the disease process of glaucoma, which is characterized by the death of retinal ganglion cell neurons and subsequent visual dysfunction.Methods: Amino acid analyses were performed on vitreous specimens that were obtained from patients who were undergoing cataract extraction. Samples were collected prospectively from those patients who sustained inadvertent rupture of the posterior capsule between 1988 and 1993. An additional set of specimens, obtained from both eyes of monkeys, was analyzed; in these monkeys, glaucoma had been experimentally induced in one eye only.Results: A twofold elevation in the level of glutamate was detected in the vitreous body of the group of patients with glaucoma when compared with that in a control population of patients with cataracts only. An even greater elevation of the glutamate level was found in the vitreous body of glaucomatous eyes of monkeys when compared with that in control eyes. No statistical differences were detected among other amino acid levels from the vitreous body of glaucomatous and nonglaucomatous eyes in humans or monkeys.Conclusions: The excitatory amino acid glutamate is found in the vitreous body of glaucomatous eyes at concentrations that are potentially toxic to retinal ganglion cells. The increased level of this known neurotoxin is consistent with an "excitotoxic" mechanism for the retinal ganglion cell and optic nerve damage in glaucoma. Therapies to protect neurons against glutamate toxic effects may prove to be useful in the management of this blinding disease.
Article
Background The Ocular Hypertension Treatment Study (OHTS) has shown that topical ocular hypotensive medication is effective in delaying or preventing the onset of primary open-angle glaucoma (POAG) in individuals with elevated intraocular pressure (ocular hypertension) and no evidence of glaucomatous damage.Objective To describe baseline demographic and clinical factors that predict which participants in the OHTS developed POAG.Methods Baseline demographic and clinical data were collected prior to randomization except for corneal thickness measurements, which were performed during follow-up. Proportional hazards models were used to identify factors that predicted which participants in the OHTS developed POAG.Results In univariate analyses, baseline factors that predicted the development of POAG included older age, race (African American), sex (male), larger vertical cup-disc ratio, larger horizontal cup-disc ratio, higher intraocular pressure, greater Humphrey visual field pattern standard deviation, heart disease, and thinner central corneal measurement. In multivariate analyses, baseline factors that predicted the development of POAG included older age, larger vertical or horizontal cup-disc ratio, higher intraocular pressure, greater pattern standard deviation, and thinner central corneal measurement.Conclusions Baseline age, vertical and horizontal cup-disc ratio, pattern standard deviation, and intraocular pressure were good predictors for the onset of POAG in the OHTS. Central corneal thickness was found to be a powerful predictor for the development of POAG.
Article
Objective: To identify the incidence and characteristics of allergic reactions associated with the long-term use of 1% apraclonidine hydrochloride. Methods: We undertook a retrospective analysis of 64 patients receiving long-term 1% apraclonidine therapy at the University of California—San Francisco Glaucoma Service. Patients were excluded if the duration of treatment was less than 2 weeks. Demographic data, initial intraocular pressure response, and incidence and characteristics of allergic reactions were obtained through chart review. Student's t test and χ 2 analysis were used to analyze the demographic data, and Kaplan-Meier survival analysis was used to estimate the long-term incidence of local reactions. Results: Sixty-four patients met the criteria for the study. Of these, 31 (48%) developed an allergic reaction (responders) that led to discontinuation of treatment with the medication, with a mean latency of 4.7 months. Mean follow-up was 13.3 months. Patients free of local reactions (nonresponders) for at least 10 months were able to successfully continue apraclonidine use. Responders tended to be older and female. Conclusions: Our data are specific for the 1% preparation; however, physicians prescribing apraclonidine on a long-term basis should be aware of possible allergic reactions. A substantial percentage of patients developed this side effect, but most tolerated the medication for up to 4 months, and those without a local reaction after 10 months appeared to be able to continue apraclonidine use indefinitely. This allergic reaction is likely related to the adrenergic agent itself, and not to preservatives.
Article
The report by Liang et al1 in this issue is significant for two reasons. It illustrates the power of the isolated preparation of organ-cultured human anterior ocular segment in identifying and studying the mechanism of action of potential new antiglaucoma pharmacologic agents. Such studies are usually performed initially in subprimate mammals, then in subhuman primates, and finally in the living human eye. While animal studies are useful, the physiologic and anatomic characteristics of subprimate mammals are often sufficiently different from those of humans to make extrapolation difficult. Primate studies are more relevant, but far more costly and difficult. With increasing concern over the use of animals, especially primates, in biomedical research, these studies have become even more difficult and expensive, threatening the efficient and costeffective development of new antiglaucoma medications. The advent of cell culture technology has brought some relief by allowing study of the effects of pharmacologic agents
Article
• A prospective collaborative study was conducted in five centers during a 13-year period to identify factors that influence the development of visual-field defects (GVFDs) of open angle glaucoma. In 5,000 subjects, GVFDs developed in only 1.7% of eyes. Statistical analysis of 26 factors at first examination identified five that were significantly related to the development of GVFDs—outflow facility, age, applanation pressure, cup-disc ratio, and pressure change after water drinking. Their absolute initial value, and not its change with time, was the important predictor. Multivariate analysis showed their collective predictive power to be undesirably poor, indicating that other factors must play an important role in the development of GVFDs. Mortality-table analysis indicated that during a period of five years, 98.54% of eyes with initial pressure less than 20 mm Hg continued to be free from GVFDs as compared with 93.34% of those with pressure 20 mm Hg or greater.
Article
Results: The intensity of the immunostaining and the number of labeled cells for heat shock proteins (HSPs) were greater in retina sections from glaucomatous eyes than in sections from normal eyes from age-matched donors. Retinal immunostaining of HSP 60 was prominent in the retinal ganglion cells and photoreceptors, whereas immunostaining of HSP 27 was prominent in the nerve fiber layer and ganglion cells as well as in the retinal vessels. In addition, retinal immunostaining of these HSPs exhibited regional and cellular differences. Optic nerve heads of glaucomatous eyes exhibited increased immunostaining of HSP 27, but not HSP 60, which was mostly associated with astroglial cells in the lamina cribrosa. Conclusion: The increased immunostaining of HSP 60 and HSP 27 in the glaucomatous eyes may reflect a role of these proteins as a cellular defense mechanism in response to stress or injury in glaucoma.
Article
Neuroprotection in glaucoma as a curative strategy complementary to current therapies to lower intraocular pressure (IOP) is highly desirable. This study was designed to investigate neuroprotection by 17β-estradiol (E2) to prevent retinal ganglion cell (RGC) death in a glaucoma model of surgically elevated IOP in rats. We found that daily treatment with E2-containing eye drops resulted in significant E2 concentration in the retina with concomitant profound neuroprotective therapeutic benefits, even in the presence of continually elevated IOP. The number of apoptotic cells in the RGC layer was significantly decreased in the E2-treated group, when compared to the vehicle-treated controls. Deterioration in visual acuity in these animals was also markedly prevented. Using mass spectrometry-based proteomics, beneficial changes in the expression of several proteins implicated in the maintenance of retinal health were also found in the retina of E2-treated animals. On the other hand, systemic side effects could not be avoided with the eye drops, as confirmed by the measured high circulating estrogen levels and through the assessment of the uterus representing a typical hormone-sensitive peripheral organ. Collectively, the demonstrated significant neuroprotective effect of topical E2 in the selected animal model of glaucoma provides a clear rationale for further studies aiming at targeting E2 into the eye while avoiding systemic E2 exposure to diminish undesirable off-target side effects.