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Neuroprotective effect of systemic and/or intravitreal
rosuvastatin administration in rat glaucoma model
Metin Unlu1, Zeynep Aktas2, Pinar Uyar Gocun3, Sevil Ozger Ilhan4, Murat Hasanreisoglu2, Berati Hasanreisoglu2
1Department of Ophthalmology,
Erciyes University, School
of Medicine, Kayseri 38039, Turkey
2Department of Ophthalmology, Gazi University, School of
Medicine, Besevler, Ankara 06560, Turkey
3Department of Pathology,
Gazi University, School of
Medicine, Besevler, Ankara 06560, Turkey
4Department of Pharmacology, Gazi University, School of Medicine,
Besevler, Ankara 06560, Turkey
Correspondence
to:
Metin Unlu.
Kilicaslan Mah Kizilirmak
Cad Kilicaslan apt B blok no:4, Kayseri
38030, Turkey. drunlumetin@hotmail.com
Received: 2015-06-12 Accepted:
2015-09-14
Abstract
AIM:
To evaluate the neuroprotective effect of rosuvastatin, in a rat experimental
glaucoma model.
METHODS: Ocular hypertension was induced in right eyes of Long-Evans rats (n=30)
by cauterization of three episcleral veins. Left eyes were defined as controls.
Rats were divided into five groups: oral rosuvastatin, intravitreal rosuvastatin,
oral+intravitreal rosuvastatin, intravitreal sham and glaucoma without intervention. Rats were
sacrificed at day 14. Retinal ganglion cell (RGC) number was assessed by
histopathological analysis. Terminal deoxynucleotidyl transferase-mediated
dUTP-nick end-labeling (TUNEL) staining and the expression of glial fibrillary
acidic protein (GFAP) in RGC layer was also examined.
RESULTS: A significant intraocular pressure (IOP) elevation was seen (P=0.002). Elevated IOP resulted in a significant
decrease in number of RGCs in group 5 (70.33±8.2 cells/mm²) when compared with
controls (92.50±13.72 cells/mm²; P=0.03).
The RGC number in group 1 (92.4±7.3 cells/mm²) was significantly higher than
group 5 (P=0.03). The numbers of RGC
in groups 2, 3 (57.3±8.2 cells/mm², 60.5±12.9 cells/mm²) were comparable with that of
group 5 (P=0.18 and P=0.31). The apoptosis rates with TUNEL
staining were also parallel to RGC number. Animals with experimentally induced
glaucoma showed an increase in retinal GFAP immunoreactivity.
CONCLUSION: Decrease in RGC loss and apoptosis suggest the
neuroprotective potential of oral rosuvastatin treatment in a rat model of
ocular hypertension. However intravitreal rosuvastatin showed a contrary effect
and further studies are required.
KEYWORDS: rat glaucoma model; retinal ganglion cell number; rosuvastatin; neuroprotection
DOI:10.18240/ijo.2016.03.03
Citation: Unlu M, Aktas Z, Gocun PU,
Ilhan SO, Hasanreisoglu M, Hasanreisoglu B.
Neuroprotective effect of systemic and/or intravitreal rosuvastatin
administration in rat glaucoma model. Int J Ophthalmol
2016;9(3):340-347
INTRODUCTION
Statins, also known as 3-hydroxy-3-methylglutaryl
co-enzyme A (HMG-CoA) reductase inhibitors, are commonly used as
cholesterol-lowering drugs in patients with hyperlipidemia. Current literature
shows the efficacy of statins in reduction of the incidence of cerebrovascular
and cardiovascular events, uncommitted of their effect on cholesterol levels[1-4]. During the past decade, evidence has emerged that
statins also have neuroprotective effects in patients with several diseases of
the central nervous system, including Alzheimer’s disease (AD), Parkinson
disease (PD), multiple sclerosis (MS), and ischemic stroke[5]. Statins
upregulate endothelial nitric oxide synthase and inhibit inducible nitric oxide
synthase, which may have neuroprotective effects[6-7]. Statins
may also attenuate the inflammatory cytokine responses that accompany cerebral
ischemia and possess antioxidant properties that may ameliorate ischemic
oxidative stresses in the brain[7-9]. The
preservation of endothelial nitric oxide synthase activity in cerebral
vasculature may be important in maintaining blood flow and limiting neuronal
loss.
In glaucoma, retinal ganglion cell (RGC) death and
atrophy of optic nerve lead to progressive vision loss and visual dysfunction.
Elevated intraocular pressure (IOP) is a major risk factor for glaucoma. Many
patients, however, continue to lose vision despite adequate IOP control. This
evidence suggests that other mechanisms than IOP also contribute to disease
progression.
The results of the studies investigating the
beneficial effect of statins in glaucoma patients are inconsistent[10-11]. While some studies suggest that statins
may have protective effect[12-13], some do not support this effect[10-11]. Stein
et al[14]
evaluated the relationship
between open angle glaucoma (OAG) and statin use and found a significant reduction in
the risk of OAG after statin usage among persons with hyperlipidemia. However a
prospective study which is interventional might provide additional extents into
the role of statins in the prevention of early OAG.
In our study, we evaluated the neuroprotective effect
of systemic and/or intravitreal rosuvastatin administration in a rat
experimental glaucoma model.
MATERIALS AND METHODS
Animals Sixty eyes of 30 adult male Long-Evans rats (290-330
g) were included in this study. There were 5 groups consisted of 6 animals per
group; group 1 (oral 1 mg/kg/d rosuvastatin), group 2 (intravitreal 2 µL/30 µmol/L rosuvastatin), group 3 (combined oral 1 mg/kg/d +
intravitreal 2 µL/30 µmol/L rosuvastatin), group 4 (intravitreal 2 µL sham with
glaucoma model) and group 5 (glaucoma without intervention) (Figure 1).
Glaucoma was induced in the right eye of each animal by cauterizating three
episcleral veins, as described by Shareef et
al[15]. The left eye of each animal
had sham surgery (conjunctival incision without cauterization) and served as the control eyes. Animals were kept with a
12-hour light/dark cycle with standard food and water provided.
The
research followed the ARVO Statement for the Use of Animals in Ophthalmic and
Vision Research; and the research was approved by the institutional review
board. All efforts
were made to minimize the number of animals used and their suffering.
Figure
1 Flowchart diagram of the study Rsv: Rosuvastatin.
Methods
Drug administration and
intravitreal injection The 1 mg/kg/d rosuvastatin was administered in the form of
crushed tablets (Crestor; AstraZeneca) suspended in sterile water via oral gavage in groups 1 and 3. After
4wk of oral treatment experimental glaucoma was induced. Administration
of oral rosuvastatin was also continued after the induction of glaucoma for 2wk.
For intraocular injections, animals were anesthetized
by intramuscular (IM) injection of ketamine hydrochloride, 50 mg/kg and
xylazine hydrochloride, 0.5 mg/kg. Liquid volume in the vitreous was considered
to be approximately 80 µL in average. Two microliters of rosuvastatin (final
concentration in the eye: 30 µmol/L; dissolved in 15% dimethylsulfoxide; Sigma,
Taufkirchen, Germany) were injected into the vitreous body posterior to the ora
serrata by using 30-gauge syringe (Becton, Dickinson & Co. Ltd., Dogheda,
Ireland) and experimental glaucoma induced at the same session. Two microliters
of 15% dimethylsulfoxide were injected into the vitreous body posterior to the
ora serrata and experimental glaucoma was induced in the sham with glaucoma
group.
Experimental glaucoma
induced by occlusion of episcleral veins Glaucoma was induced by cauterization of the three
episcleral veins in the right eye of each animal. The rats were anesthetized by
IM injection of ketamine hydrochloride, 50 mg/kg and xylazine hydrochloride,
0.5 mg/kg. Before the procedure, IOP was checked with a tonometer (Tono-Pen;
Medtronic Solan, FL, USA). A small conjunctival incision was made in each
quadrant at the limbus, and the extraocular muscles were isolated. Four major
limbal draining veins were identified based on deep location under the rectus
muscles, relative immobility, larger caliber, and branching pattern. Two dorsal
episcleral veins under the superior rectus muscle and one temporal episcleral
vein under the lateral rectus muscle were cauterized using a surgical
microscope (Olympus, Tokyo, Japan) and a cautery (Bovie Co., FL, USA)[16].
After surgery, chloramphenicol eye drops and oxytetracycline ointment were
applied to the eyes. Only the eyes that did not suffer scleral burns with
subsequent necrosis or any complications from the surgery were used. The left
eye of each animal had sham surgery (conjunctival incision without
cauterization) and served as control.
Intraocular pressure
measurement IOP was measured using a tonometer (Tono-Pen;
Medtronic Solan, FL, USA) after IM injection of ketamine hydrochloride, 50
mg/kg and xylazine hydrochloride, 0.5 mg/kg in both eyes. IOP measured three
times holding the probe perpendicular to the central cornea and the
measurements were averaged. IOPs were checked at 1st day, 1st
week and 2nd week.
Evaluation of retinal
ganglion cell densities Enucleated globes were fixed in 10% buffered formalin.
The globes were cut into two halves with horizontal sections from optic nerve
to cornea. Each half was processed and embedded in paraffin blocks. Tissue
sections of 3 microns were cut from representative formalin-fixed and
paraffin-embedded tissue blocks. Sections were de-parafinized in xylene and
rehydrated. Each sample was stained with haematoxylin-eosin. The pathologist
(Gocun PU) counting the RGCs was blind to the experimental procedures. Four
visual fields were sampled from the posterior portion of each retina using a
40× objective (Olympus, BX51, Japan). Cell counts in the RGC layer were
performed at this magnification by using a graduated graticule measuring 0.25
mm². The RGC numbers were also quantified in each visual field, and the total
count for the four sampled fields was expressed in mm². If the cells appeared
in the RGC layer and had large, round cell bodies, they were categorized as
RGCs. Counts were made horizontally along the full length of the visual streak
from the center of the optic nerve head, extending out towards the far retinal
periphery. Care was taken to remain in the central area of the visual streak.
As counts got on along the axis, retinal areas above and below the central
regions were inspected to procure that the fields with highest cell densities
were always picked out for counting[17].
TUNEL staining Apoptotic cells were detected by TdT-dUTP terminal
nick end-labelling (TUNEL) in each half of retinas. TUNEL was performed as
previously defined using the ApopTag Peroxidase In Situ Apoptosis detection kit (S7110, Millipore, Inc., Temecula, CA, USA), following the
manufacturer’s instructions. Peroxidase substrate 3, 3-diaminobenzidine was
used to stain for apoptotic cells. Methyl green (0.5%) was used as a nuclear
stain. TUNEL positive cells were observed under a light microscope (Olympus, BX51,
Japan). The numbers of TUNEL-positive cells in the RGC layer per retina were
counted in three or more sections. The mean cell counts of these sections were
used to set the proportion of cells undergoing apoptosis for each layer of each
particular eye[17].
Glial fibrillary acidic
protein immunoreactivity Glial fibrillary acidic protein (GFAP) immunoreactivity in the retina was evaluated after
glaucoma induction in right eyes and control left eyes. GFAP
immunostaining was performed as previously described using the following the GFAP
antibody-Astrocyte Marker 100 µL (ab4648, ABCAM, Cambridge, UK) manufacturer’s
instructions. GFAP expression was viewed under the light microscope (Olympus,
BX51, Japan). GFAP expression was assessed by using extent and severity scale
(severity; absence of stain, mild, moderate, severe and
extent; focal, diffuse). Pathologist evaluating RGC
densities, TUNEL staining and GFAP immunoreactivity was blind to all study
groups.
Statistical Analysis Statistical significance of the differences in IOP
between before and after the episcleral vein cauterization procedure was
determined by the Wilcoxon test. The differences’ statistical significance in
RGC number and proportion of cells undergoing apoptosis in RGC layer between
treatment groups and fellow control eyes were determined by Kruskal Wallis
test. Chi-square test was used to compare GFAP expression between treatment
groups and fellow control eyes. The results of the left eyes were compared with
the rights eyes of the same groups, but not between the right eyes in other
groups. Statistical
analyses were performed with SPSS 18.0 for windows (SPSS Inc, Chicago,
Illinois, USA). The level of statistical significance was set at P<0.05.
RESULTS
Intraocular Pressure Animals used in the present study had elevated IOP
throughout the experiment (Figure 2). IOP values in eyes before the induction of
glaucoma [15.31±1.30 mm Hg (12.50-17.75)] were similar to those reported in the literature. One
day after induction of glaucoma, a significant increase in IOP was observed in
the ipsilateral eye [28.73±2.45 mm Hg (25.50-34.00), P=0.002]. Two weeks after the induction of glaucoma, IOP was
elevated 1.9 fold in the ipsilateral eye [28.08±0.92 mm Hg (27.50-30.00), P=0.002], compared to contralateral eye [14.70±1.45 mm Hg (14.20-15.75)].
Figure 2 Elevated IOP in rat eyes
that underwent unilateral cauterization of three episcleral veins (operated)
compared with the opposite left eyes (control) IOP was measured on the
indicated times in eyes treated with oral rosuvastatin (group 1), intravitreal
rosuvastatin (group 2), oral and intravitreal rosuvastatin (group 3), intravitreal sham (group 4)
and glaucoma without intervention (group 5). The difference in mean IOP between
cauterized eyes and control eyes was significant at all time points after
surgery (P<0.05). All values are
mean±SD (n=6). R: Right eye; L: Left eye.
Oral rosuvastatin treatment had no effect on IOP. In
glaucomatous animals, oral rosuvastatin had no effect on IOP in either
ipsilateral (28.20±1.40 mm Hg) or contralateral (14.70±1.60 mm Hg) eyes. Intravitreal sham injection had also no effect on IOP. Intravitreal rosuvastatin injection
had also no effect on IOP. IOP values of group 2 were comparable with that of
group 5 (26.95±0.81 mm Hg, 28.08±2.82 mm Hg respectively, P=0.40).
Evaluation of Retinal
Ganglion Cell Densities and TUNEL Staining Light microscopic examination of Group 5 revealed
decreased number of RGC, together with significant morphologic alterations and
apoptosis (Figures 3-6). In group 5, the number of RGC appeared to be significantly
reduced, and the rate of cells undergoing apoptosis was found to be
significantly greater when compared with the control eyes [70.33±8.2 cells/mm² (44-93), 92.50±13.72
cells/mm² (72-106); P=0.03 and 5.6% (4.5-7.9), 0; P=0.001, respectively]. In group 1, the number of RGC and the rate of cells
undergoing apoptosis in the RGC layer was detected to be similar compared with
the control eyes [92.4±7.3 cells/mm² (75-104), 94.83±9.7 (84-109); P=0.90 and 0.9% (0-1.3), 0; P=0.3, respectively].
When a comparison regarding the
number of RGC and the proportion of cells undergoing apoptosis in the RGC layer
was made between groups 1 and 5, increased rate of cells undergoing apoptosis
and statistically significant cell loss were detected in group 5 (P=0.03, P=0.001, respectively; Table 1). Oral rosuvastatin treatment
significantly reduced the RGC loss and TUNEL-positive cells in the ganglion
cell layer.
Figure 3 Effect of rosuvastatin
treatment on RGC number
Retinal photomicrographs
were obtained at 2wk in control left eye (A), after oral rosuvastatin treatment
(B), intravitreal rosuvastatin treatment (C) and glaucoma without intervention
(D). Disruption of retinal architecture, cell loss in retinal ganglion cell
(RGC) layer (arrow) were remarkable (HE×200) in glaucoma without intervention
and intravitreal rosuvastatin groups. Vacuolization of retinal ganglion cell (RGC)
was seen (arrow head). Retinal architecture in RGC layer was relatively to be
well-preserved (HE×200) in oral rosuvastatin group.
Figure 4 The mean number of RGC in
retina
The mean numbers of RGC at
2wk after IOP elevation were analyzed. Statistical significance was evaluated
by Kruskal Wallis test (n=6). aP<0.05 compared to fellow
control eyes. RGC: Retinal ganglion
cell; iv: Intravitreal.
Figure 5 The rate of TUNEL-positive
cells in the retina
Cross sections from the
retina at 2wk after IOP elevation were analyzed. The rate of TUNEL-positive
cell in the ganglion cell layer are shown. Statistical significance was
evaluated by Kruskal Wallis test. (n=6).
aP<0.05 compared to fellow control eyes. RGC: Retinal ganglion cell; iv: Intravitreal.
Figure 6 Effect of rosuvastatin
treatment on TUNEL-positive cells in the retina Retinal photomicrographs
were obtained at 2wk in control glaucoma without intervention (A), after intravitreal
rosuvastatin (B). No TUNEL-positive cells are detected in retinal tissue
sections obtained from control left
eyes. After episcleral vein cauterization and elevation of IOP, TUNEL-positive
cells were present only in the GCL (arrows). Oral rosuvastatin treatment
reduced retinal cell apoptosis induced by ocular hypertension in rats.
Table 1 Comparison of
total number of cells and the apoptosis rate of RGC layer in groups 1 and 5
|
Parameters |
Group 1 (oral rosuvastatin) |
Group 5 (glaucoma without
intervention) |
P |
|
RGC (cell/mm²) |
92.4±7.3 (75-104) |
70.33±8.2 (44-93) |
0.03a |
|
Apoptosis (%) |
0.9±0.2 (0-1.3) |
5.6±1.4 (4.5-7.9) |
0.001a |
aP<0.05, Kruskal Wallis test. RGC: Retinal ganglion cell.
However, in groups 2 and 3 ,
the number of RGC was found to be lower and the proportion of cells undergoing
apoptosis was found to be higher in the RGC layer compared with that of their
controls [57.3±8.2 cells/mm² (47-66),
60.5±12.9 cells/mm² (50-78) and 10.4% (8.5-12.4), 3.3% (2-3.8); respectively]. The distribution of the number of RGC and rate of
cells undergoing apoptosis in the RGC layer of all groups can be seen in Figures 3-6.
Furthermore, when a
comparison was made between groups 2 and 5, the proportion of cells undergoing
apoptosis was higher in group 2, and the difference was statistically
significant (P=0.001). But, there was
no significant difference regarding the number of RGC between the two groups (P=0.18; Table 2).
Table 2 Comparison of total number
of cells and the apoptosis rate of RGC layer in groups 2 and 5
|
Parameters |
Group 2 (iv rosuvastatin) |
Group 5 (glaucoma without intervention) |
P |
|
RGC (cell/mm²) |
57.33±8.23 (47-66) |
70.33±18.30 (44-93) |
0.18 |
|
Apoptosis (%) |
10.4±2.2 (8.5-12.4) |
5.6±1.4 (4.5-7.9) |
0.001a |
aP<0.05,
Kruskal Wallis test. RGC: Retinal ganglion
cell; iv: Intravitreal.
When a comparison was made
between groups 3 and 5, the number of RGC and proportion of cells undergoing
apoptosis in the RGC layer were also comparable (P=0.31, P=0.15;
respectively, Table 3).
Table 3 Comparison of total number of cells and the
apoptosis rate of RGC layer in groups 3 and 5
|
Parameters |
Group 3 (oral+iv rosuvastatin) |
Group 5 (glaucoma without
intervention) |
P
|
|
RGC (cell/mm²) |
60.50±12.90
(50-78) |
70.33±18.30
(44-93) |
0.31 |
|
Apoptosis (%) |
3.3±0.9
(2.0-3.8) |
5.6±1.4
(4.5-7.9) |
0.15 |
Kruskal Wallis test. RGC:
Retinal ganglion cell; iv: Intravitreal.
In cross
section, no TUNEL-positive cells were found in the fellow control eyes. After
induction of ocular hypertension, positive TUNEL reaction was markedly
increased. The TUNEL-positive cells were specifically located in the RGC layer.
Oral rosuvastatin treatment significantly reduced TUNEL-positive cells in the
RGC layer.
Expression of Glial
Fibrillary Acidic Protein After the induction of
experimental glaucoma by occlusion of episcleral veins, GFAP immunostaining was
performed to evaluate the glial cell activation in response to retinal stress
or injury caused by IOP elevation and the effects of rosuvastatin
administration. In the retina of control fellow eyes, GFAP immunoreactivity was
limited to astrocytes and to the end feet of Müller cells at the inner limiting
membrane. Animals with experimentally induced glaucoma showed an increase in
retinal GFAP immunoreactivity that extended to the outer nuclear layer (P=0.03) (Figure 7). Oral rosuvastatin treatment caused decrease in
GFAP expression compared with that of untreated cauterized eyes but it was not
statistically significant (P=0.2).
Figure 7 Effect of oral rosuvastatin
treatment on GFAP immunoreactivity in the retina A: In the normal retina, GFAP immunoreactivity was limited
to astrocytes and to the end feet of Müller cells at the inner limiting
membrane; B: Oral rosuvastatin treatment reduced GFAP expression compared with
untreated cauterized eyes (P=0.2); C: After episcleral vein cauterization and elevation of
IOP (group 5), GFAP immunoreactivity was increased (P=0.03) (GFAP immunreactivity can be seen
with intracytoplasmic staining as a ground glass appearance in diffuse
extension pattern between the white dots). Statistical significance was evaluated by Chi-square
test (n=6).
DISCUSSION [Top]
In the present study, we
examined the effects of the rosuvastatin on RGC loss, apoptosis and glial
activation in experimental glaucoma model. This is the first study examining
the role of rosuvastatin in an animal model of glaucoma. Two weeks after the
induction of glaucoma, we found that oral rosuvastatin exerted a significant
neuroprotective effect on RGC density, resulting in reduced loss of RGC and
proportion of cells undergoing apoptosis but intravitreal administrated
rosuvastatin showed a contrary effect.
Among the several members of
the statin family, rosuvastatin is one of the most potent statins and is able
to form multiple polar bonds with the HMG-CoA reductase enzyme[18]. It is also relatively
hydrophilic and displays a potential protective effect in cerebral ischemia in
mice[19], if administered for 10d before the
ischemic insult.
Cauterization of 2 or more extraocular veins of the
rat has been described to increase IOP[15].
The mean IOP increase correlates with the number of cauterized veins. Most
researchers typically occluded three veins in their studies. This procedure
induces apoptotic death of RGC, thinning of the nerve fiber layer, cupping of
the optic disc, and degeneration of the optic nerve[20-23].
In our experiment, rosuvastatin had no effect on IOP.
The absence of decreased IOP in oral rosuvastatin-treated animals supports the
idea that instead of reducing IOP, it has a direct neuroprotective action on
RGCs.
In our study, percentage of RGC loss is in general
agreement with those reported by others using similar models[20-23]. We
observed 2.5% loss in RGCs in glaucomatous eyes of orally treated animals;
compared to 23.9% loss in control eyes (untreated), 37.6% loss in intravitreally
treated eyes and 33.1% loss in orally+intravitreally treated eyes.
Furthermore, selective TUNEL-positive cells were found
in the RGC layer in the experimental glaucoma model. Control eyes had no
TUNEL-positive cells and 2wk after cauterization, TUNEL-positive cells were
significantly increased. However, we observed 0.9% TUNEL-positive cells in RGCs
in glaucomatous eyes of orally treated animals; compared to 10.4%
TUNEL-positive cells in control glaucoma (P=0.001).
TUNEL-positive cells decreased indicating that apoptosis of RGCs was decreased
by treatment.
To evaluate retinal damage due to ocular hypertension,
expression of GFAP may also been monitored. GFAP is a form of intermediate
filament, which is present in Müller cells and astrocytes in the normal retina.
When retinal damage occurs, GFAP expression is primarily elevated in Müller
cells and astrocytes. The classic hallmark of glial cell activation is
increased expression of GFAP[24-25]. Hypertrophic
morphology and increased GFAP immunostaining in retinal astrocytes and Müller
cells in glaucomatous eyes indicate that activation of retinal macroglial cells
has occurred in the glaucomatous retina[24-25]. In our study, after the induction
of IOP elevation, cauterized eyes showed a significant increase in GFAP
expression 2wk after the injury. Before IOP elevation, GFAP immunoreactivity
might be confined to astrocytes and the end feet of Müller cells at the inner
limiting membrane, but after IOP elevation, it might extend to the outer
nuclear layer. Increased GFAP expression might show glial cell activation after
the IOP elevation. However, in the current study, GFAP immunoreactivity was
found to be decreased in eyes of animals received oral rosuvastatin treatment
compared to those of untreated cauterized eyes (group 5).
Kretz et al[26]
demonstrated that intravitreal simvastatin injection
induced heat shock protein expression in axotomized RGCs, protected neurons
from apoptotic death and enhanced RGC survival early and even delayed after
optic nerve injury. However, we have not been able to demonstrate the benefical
effects of intravitreal rosuvastatin in our study. On the contrary, we have
found a significant association between the intravitreal rosuvastatin injection
and RGC loss. Rosuvastatin exhibited specificity for uptake into the liver in rats[27] as the liver is the target organ, this may
translate into an advantageous clinical characteristic. Rosuvastatin is administered
as the active form however, simvastatin is a prodrug which is administered as
inactive forms and activated in liver with enzimatic reaction. According
to the current literature, rosuvastatin has lower metabolization rate, higher
water solubility and longer half life (19h versus 3h) compared to simvastatin.
While lipophilicity results in efficient hepatic shunting, the same property
will result in ready passage through nonhepatic cell membranes[28].
These might explain why intravitreal rosuvastatin decreased RGC survival
in our study whereas some reports suggest that intravitreal simvastatin might be
neuroprotective.
Sicard
et al[29]
evaluated influence of rosuvastatin on
the NAD(P)H oxidase activity in the retina and electroretinographic response of
genetically hypertensive rats. They concluded that; rosuvastatin
therapy could decrease production of retinal superoxide anion through the
inhibition of NAD(P)H oxidase activity, independently of a reduction in plasma
and tissue cholesterol levels, but might not be sufficient to restore retinal
function.
There are conflicting findings in the literature
regarding whether statins may be beneficial in patients with glaucoma. A
case-control study by McGwin et al[12]
demonstrated that individuals prescribed statins for >24mo had 40% reduced
odds of developing OAG. A prospective study by Leung et al[13]
demonstrated that statin use was associated with visual field stabilization
over 3y among patients with normal tension glaucoma. De Castro et al[30]
showed that statin use slowed glaucomatous changes to the optic nerve and nerve
fiber layer on confocal scanning laser ophthalmoscopy. In a recent
retrospective longitudinal cohort analysis by Stein et al[14]
statin use was associated with a significant reduction in the risk of OAG among
persons with hyperlipidemia. A large case-control study by Owen et al[10]
using information from a primary care database in the United Kingdom, found no
relationship between statin use and OAG.
It is clear that statins exert neuroprotective effects
in experimental animals and in vitro
conditions, while clinical trials suggest that statins may also have beneficial
effects in neurodegenerative conditions in humans. Acute stroke, AD, PD, MS and
glaucoma are different conditions, and the evidence for statins to inhibit
disease specific pathogenic processes is inconclusive.
Statins exert both peripheral and central effects
which might be protective under diverse neuropathogenic conditions.
Particularly, their ability to improve blood flow, to modulate the immune
response and to reduce oxidative damage may lead to neuroprotection. Although
some statins can cross the blood-brain and blood-retina barrier, it is unclear to what
extent they affect metabolism and signalling in the brain and vitreous, and
particularly at what dosage they start influencing isoprenoid production. This
may account for why promising experimental in
vivo findings have so far translated into disappointing clinical results.
We suggest that the pharmacology of statins in the brain and vitreous should be
further investigated to eliminate this uncertainty.
Decrease
in RGC loss and apoptosis suggest the neuroprotective potential of oral
rosuvastatin treatment in a rat model of ocular hypertension. Since
intravitreal drug injection is one of the most popular treatment approaches in
ophthalmology currently, we wanted to compare this approach with systemical
administration of rosuvastatin. However we did not find any significant
neuroprotective effect in intravitreal injection group. In the current study,
intravitreal rosuvastatin showed a contrary effect and further studies will
shed light on intravitreal rosuvastatin pharmacokinetics, intravitreal dosage
of rosuvastatin.
In conclusion, we demonstrated that oral rosuvastatin
has a neuroprotective effect in a rat model of glaucoma. However intravitreal
administration of rosuvastatin had an inverse effect. Because statins are
safely and widely used to treat hyperlipidemia, clinical administration of oral
rosuvastatin for the purpose of pharmacologic neuroprotection may be a new and
beneficial therapy for patients with glaucoma in the future.
ACKNOWLEDGEMENTS [Top]
Foundation: Supported by Gazi University Research and Education
Fund.
Conflicts of Interest: Unlu M,
None; Aktas Z, None; Gocun PU, None; Ilhan SO, None; Hasanreisoglu M, None; Hasanreisoglu B, None.
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