Sulfisoxazole, an endothelin receptor antagonist, protects retinal neurones from insults of ischemia/reperfusion or lipopolysaccharide

Ex Vivo Model of Spontaneous Neuroretinal Degeneration for Evaluating Stem Cells' Paracrine Properties

Ex vivo neuroretina cultures closely resemble in vivo conditions, retaining the complex neuroretina cells dynamics, connections, and functionality, under controlled conditions. Therefore, these models have allowed advancing in the knowledge of retinal physiology and pathobiology over the years. Furthermore, the ex vivo neuroretina models represent an adequate tool for evaluating stem cell therapies over neuroretinal degeneration processes.Here, we describe a physically separated co-culture of neuroretina explants with stem cells to evaluate the effect of stem cells paracrine properties on spontaneous neuroretinal degeneration.

Magnesium acetyltaurate protects against endothelin-1 induced RGC loss by reducing neuroinflammation in Sprague dawley rats

Endothelin-1 (ET-1), a potent vasoconstrictor, plays a significant role in the pathophysiology of ocular conditions like glaucoma. Glaucoma is characterized by apoptotic loss of retinal ganglion cells (RGCs) and loss of visual fields and is a leading cause of irreversible blindness. In glaucomatous eyes, retinal ischemia causes release of pro-inflammatory mediators such as interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α and promotes activation of transcription factors such as nuclear factor kappa B (NFKB) and c-Jun. Magnesium acetyltaurate (MgAT) has previously been shown to protect against ET-1 induced retinal and optic nerve damage. Current study investigated the mechanisms underlying these effects of MgAT, which so far remain unknown. Sprague dawley rats were intravitreally injected with ET-1 with or without pretreatment with MgAT. Seven days post-injection, retinal expression of IL-1β, IL-6, TNF-α, NFKB and c-Jun protein and genes was determined using multiplex assay, Western blot and PCR. Animals were subjected to retrograde labeling of RGCs to determine the extent of RGC survival. RGC survival was also examined using Brn3A staining. Furthermore, visual functions of rats were determined using Morris water maze. It was observed that pre-treatment with MgAT protects against ET-1 induced increase in the retinal expression of IL-1β, IL-6 and TNF-α proteins and genes. It also protected against ET-1 induced activation of NFKB and c-Jun. These effects of MgAT were associated with greater RGC survival and preservation of visual functions in rats. In conclusion, MgAT prevents ET-1 induced RGC loss and loss of visual functions by suppressing neuroinflammatory reaction in rat retinas.

Posttreatment Intervention With Lycium Barbarum Polysaccharides is Neuroprotective in a Rat Model of Chronic Ocular Hypertension

Purpose

To investigate the neuroprotective effects of Lycium barbarum polysaccharides (LBP) against chronic ocular hypertension (OHT) in rats and to consider if effects differed when treatment was applied before (pretreatment) or during (posttreatment) chronic IOP elevation.

Methods

Sprague-Dawley rats (10-weeks old) underwent suture implantation around the limbus for 15 weeks (OHT) or 1 day (sham). Four experimental groups were studied, three OHT groups (n = 8 each) treated either with vehicle (PBS), LBP pretreatment or posttreatment, and a sham control (n = 5) received no treatment. LBP (1 mg/kg) pre- and posttreatment were commenced at 1 week before and 4 weeks after OHT induction, respectively. Treatments continued up through week 15. IOP was monitored twice weekly for 15 weeks. Optical coherence tomography and ERG were measured at baseline, week 4, 8, 12, and 15. Eyes were collected for ganglion cell layer (GCL) histologic analysis at week 15.

Results

Suture implantation successfully induced approximately 50% IOP elevation and the cumulative IOP was similar between the three OHT groups. When compared with vehicle control (week 4: -23 ± 5%, P = 0.03), LBP pretreatment delayed the onset of retinal nerve fiber layer (RNFL) thinning (week 4, 8: -2 ± 7%, -11 ± 3%, P > 0.05) and arrested further reduction up through week 15 (-10 ± 4%, P > 0.05). LBP posttreatment intervention showed no significant change in rate of loss (week 4, 15: -25 ± 4.1%, -28 ± 3%). However, both LBP treatments preserved the retinal ganglion cells (RGC) and retinal functions up to week 15, which were significantly reduced in vehicle control.

Conclusions

LBP posttreatment arrested the subsequent neuronal degeneration after treatment commencement and preserved RGC density and retinal functions in a chronic OHT model, which was comparable with pretreatment outcomes.

Folic Acid Antagonists: Antimicrobial and Immunomodulating Mechanisms and Applications

: Bacterial, protozoan and other microbial infections share an accelerated metabolic rate. In order to ensure a proper functioning of cell replication and proteins and nucleic acids synthesis processes, folate metabolism rate is also increased in these cases. For this reason, folic acid antagonists have been used since their discovery to treat different kinds of microbial infections, taking advantage of this metabolic difference when compared with human cells. However, resistances to these compounds have emerged since then and only combined therapies are currently used in clinic. In addition, some of these compounds have been found to have an immunomodulatory behavior that allows clinicians using them as anti-inflammatory or immunosuppressive drugs. Therefore, the aim of this review is to provide an updated state-of-the-art on the use of antifolates as antibacterial and immunomodulating agents in the clinical setting, as well as to present their action mechanisms and currently investigated biomedical applications.

Mesenchymal stem cells provide paracrine neuroprotective resources that delay degeneration of co-cultured organotypic neuroretinal cultures

Through the paracrine effects of stem cells, including the secretion of neurotrophic, immunomodulatory, and anti-apoptotic factors, cell-based therapies offer a new all-encompassing approach to treatment of neurodegenerative diseases. In this study, we used physically separated co-cultures of porcine neuroretina (NR) and human mesenchymal stem cells (MSC) to evaluate the MSC paracrine neuroprotective effects on NR degeneration. NR explants were obtained from porcine eyes and cultured alone or co-cultured with commercially available MSCs from Valladolid (MSCV; Citospin S.L.; Valladolid, Spain), currently used for several approved treatments. Cultures were maintained for 72 h. MSC surface markers were evaluated before and after co-culture with NRs. Culture supernatants were collected and the concentration of brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), and glial-derived neurotrophic factor (GDNF) were determined by enzyme-linked immunosorbent assays. NR sections were stained by haematoxylin/eosin or immunostained for terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL), glial fibrillary acidic protein, β-tubulin III, and neuronal nuclei marker. NR morphology, morphometry, nuclei count, apoptosis rate, retinal ganglion cells, and glial cell activation were evaluated. Treatment effects were statistically analysed by parametric or non-parametric tests. The MSCs retained stem cell surface markers after co-culture with NR. BDNF and CNTF concentrations in NR-MSCV co-cultures were higher than other experimental conditions at 72 h (p < 0.05), but no GDNF was detected. NR general morphology, total thickness, and cell counts were broadly preserved in co-cultures, and the apoptosis rate determined by TUNEL assay was lower than for NR monocultures (all p < 0.05). Co-cultures with MSCV also protected retinal ganglion cells from degenerative changes and reduced reactive gliosis (both p < 0.05). In this in vitro model of spontaneous NR degeneration, the presence of co-cultured MSCs retarded neuroglial degeneration. This effect was associated with elevated concentrations of the neurotrophic factors BDNF and CNTF. Our data suggest that the paracrine secretion of these, and possibly other molecules, are a potential resource for the treatment of several neuroretinal diseases.

Endothelin receptor-A antagonist attenuates retinal vascular and neuroretinal pathology in diabetic mice

PURPOSE

We sought to determine the effects of atrasentan, a selective endothelin-A receptor antagonist, on the retinal vascular and structural integrity in a db/db mouse, an animal model of type 2 diabetes and diabetic retinopathy.

METHODS

Diabetic mice, 23 weeks old, were given either atrasentan or vehicle treatment in drinking water for 8 weeks. At the end of the treatment period, eyes underwent trypsin digest to assess the retinal vascular pathology focusing on capillary degeneration, endothelial cell, and pericyte loss. Paraffin-embedded retinal cross sections were used to evaluate retinal sublayer thickness both near the optic nerve and in the retinal periphery. Immunohistochemistry and TUNEL assay were done to evaluate retinal cellular and vascular apoptosis.

RESULTS

Compared with untreated db/db mice, atrasentan treatment was able to ameliorate the retinal vascular pathology by reducing pericyte loss (29.2% ± 0.4% vs. 44.4% ± 2.0%, respectively, P < 0.05) and capillary degeneration as determined by the percentage of acellular capillaries (8.6% ± 0.3% vs. 3.3% ± 0.41%, respectively, P < 0.05). A reduction in inner retinal thinning both at the optic nerve and at the periphery in treated diabetic mice was also observed in db/db mice treated with atrasentan as compared with untreated db/db mice (P < 0.05). TUNEL assay suggested that atrasentan may decrease enhanced apoptosis in neuroretinal layers and vascular pericytes in the db/db mice.

CONCLUSIONS

Endothelin-A receptor blockade using atrasentan significantly reduces the vascular and neuroretinal complications in diabetic mice. Endothelin-A receptor blockade is a promising therapeutic target in diabetic retinopathy.

Dietary ω-3 deficiency and IOP insult are additive risk factors for ganglion cell dysfunction

AIM

Dietary deficiencies in ω-3 polyunsaturated fatty acids are known to effect retinal function including retinal ganglion cell (RGC) activity, which may have implications for glaucoma. In this study we consider retinal function after dietary manipulation and intraocular pressure (IOP) stress designed to compromise RGCs.

METHODS

Sprague-Dawley dams were fed either ω-3 sufficient (ω-3, n=15) or deficient (ω-3, n=16) diets 5 weeks before conception with pups subsequently weaned onto their mothers diets. At 20 weeks of age, acute IOP elevation was induced repeatedly through anterior chamber cannulation to 70 mm Hg for 1 hour on 3 separate occasions separated by 1 week. Electroretinograms were recorded 1 week after each IOP elevation to assay the photoreceptors (PIII), ON-bipolar cells (PII), and ganglion/amacrine cells (STR).

RESULTS

Repeat IOP insult results in a specific RGC dysfunction (pSTR -14.5%, P<0.035) as does ω-3 deficiency (-26.4%, P<0.01). However, the combination of both causes an even larger RGC functional loss (-40.1%, P<0.001) than does either diet or IOP insult in isolation (P<0.001).

CONCLUSIONS

Both ω-3 deficiency and repeat acute IOP insult cause RGC dysfunction and the combination of these factors results in a cumulative effect. Our data indicate that sufficient dietary ω-3 improves RGC function making it less susceptible to IOP insult.

The primary vascular dysregulation syndrome: implications for eye diseases

Vascular dysregulation refers to the regulation of blood flow that is not adapted to the needs of the respective tissue. We distinguish primary vascular dysregulation (PVD, formerly called vasospastic syndrome) and secondary vascular dysregulation (SVD). Subjects with PVD tend to have cold extremities, low blood pressure, reduced feeling of thirst, altered drug sensitivity, increased pain sensitivity, prolonged sleep onset time, altered gene expression in the lymphocytes, signs of oxidative stress, slightly increased endothelin-1 plasma level, low body mass index and often diffuse and fluctuating visual field defects. Coldness, emotional or mechanical stress and starving can provoke symptoms. Virtually all organs, particularly the eye, can be involved. In subjects with PVD, retinal vessels are stiffer and more irregular, and both neurovascular coupling and autoregulation capacity are reduced while retinal venous pressure is often increased. Subjects with PVD have increased risk for normal-tension glaucoma, optic nerve compartment syndrome, central serous choroidopathy, Susac syndrome, retinal artery and vein occlusions and anterior ischaemic neuropathy without atherosclerosis. Further characteristics are their weaker blood–brain and blood-retinal barriers and the higher prevalence of optic disc haemorrhages and activated astrocytes. Subjects with PVD tend to suffer more often from tinnitus, muscle cramps, migraine with aura and silent myocardial ischaemic and are at greater risk for altitude sickness. While the main cause of vascular dysregulation is vascular endotheliopathy, dysfunction of the autonomic nervous system is also involved. In contrast, SVD occurs in the context of other diseases such as multiple sclerosis, retrobulbar neuritis, rheumatoid arthritis, fibromyalgia and giant cell arteritis. Taking into consideration the high prevalence of PVD in the population and potentially linked pathologies, in the current article, the authors provide recommendations on how to effectively promote the field in order to create innovative diagnostic tools to predict the pathology and develop more efficient treatment approaches tailored to the person.

Endothelin-1 role in human eye: a review

Endothelin is a potent vasoactive peptide occurring in three isotypes, ET-1, ET-2, and ET-3. Through its two main receptors, endothelin A and endothelin B, it is responsible for a variety of physiological functions, primarily blood flow control. Recent evidence from both human and animal models shows involvement of endothelin in diabetes, retinal circulation, and optic neuropathies. Increased circulating levels of endothelin-1 (ET-1) have been found in patients with diabetes, and a positive correlation between plasma ET-1 levels and microangiopathy in patients with type-2 diabetes has been demonstrated. In addition to its direct vasoconstrictor effects, enhanced levels of ET-1 may contribute to endothelial dysfunction through inhibitory effects on nitric oxide (NO) production. Experimental studies have shown that chronic ET-1 administration to the optic nerve immediately behind the globe causes neuronal damage, activation of astrocytes, the major glial cell in the anterior optic nerve, and upregulation of endothelin B receptors. This paper outlines the ubiquitous role of endothelin and its potential involvement in ophthalmology.

The role of endothelin in the pathophysiology of glaucoma

IMPORTANCE OF THE FIELD

Glaucoma is the second leading cause of blindness worldwide. To date, treatment of glaucoma has focused on lowering intraocular pressure (IOP) though there are other mechanisms that might damage the optic nerve, leading to characteristic visual field loss. Endothelin, a potent vasoconstrictor, is believed to play a role in the pathogenesis of glaucomatous optic neuropathy.

AREAS COVERED IN THIS REVIEW

We review the evidence from the last 20 years exploring the action of endothelin in the eye, its association with the pathophysiology of glaucoma, as well as the potential therapeutic role of targeting the endothelin pathway to affect disease progression in glaucomatous eyes.

WHAT THE READER WILL GAIN

The goal of this paper is to inform readers about endothelin structure, actions, and role in ocular pathology, pharmacology, and potential areas of future research.

TAKE HOME MESSAGE

Overall, we believe that the body of evidence supports the following conclusions; i) endothelin is a potent vasoconstrictor that plays a role in ocular physiology, ii) endothelin may play a role in the pathophysiology of glaucoma and iii) modulation of the endothelin system with newly discovered potent antagonists holds promise in treating glaucoma through both pressure-dependent and pressure-independent pathways.

Role of the ETB receptor in retinal ganglion cell death in glaucoma

Recent observations suggest that the vasoactive peptide endothelin-1 (ET-1) may be an important contributor to the etiology of glaucoma. ET-1 administration has been shown to produce optic nerve axonal loss and apoptosis of retinal ganglion cells. Ocular ET-1 levels are elevated in aqueous humor in response to elevated intraocular pressure both in glaucoma patients and in animal models of glaucoma; however, the precise mechanisms by which ET-1 mediates glaucomatous optic neuropathy are not clear. Presently we report that ET-1-mediated apoptosis was markedly attenuated in ETB receptor-deficient rats, suggesting a key role for ETB receptors in apoptosis of retinal ganglion cells by ET-1 treatment. Using virally transformed rat retinal ganglion cells (RGC-5 cells), we found that ET-1 (100 nmol/L) treatment produced apoptotic changes in these cells that was determined by flow cytometric analyses, release of mitochondrial cytochrome c to the cytosol, and increased phosphorylation of c-Jun N-terminal kinase. Pretreatment with the ETB-receptor antagonist BQ788 (1 micromol/L) was able to significantly attenuate ET-1-mediated apoptosis in RGC-5 cells. ET-1-mediated apoptotic changes in RGC-5 cells were associated with ETB-receptor activation and were accompanied by a significant upregulation of ETB-receptor expression. These studies suggest that ocular ET-1 acts through ETB receptors to mediate apoptosis of retinal ganglion cells, a key event in glaucoma and related optic neuropathies.

The flavonoid baicalin counteracts ischemic and oxidative insults to retinal cells and lipid peroxidation to brain membranes

The purpose of the present study was to determine whether the flavonoid, baicalin is effective at blunting the negative influence of ischemia/reperfusion to the rat retina in situ and of various insults to a transformed retinal ganglion cells (RGC-5 cells) in culture. Baicalin was administered intraperitoneally just before and after an ischemic insult to retina of one eye of a rat. Ischemia was delivered by raising the intraocular pressure above the systolic blood pressure for 50min. Seven days after ischemia, retinas were analysed for the localisation of various antigens. Retinal extracts were also analysed for various mRNAs. Moreover, the content of specific proteins was deduced in retinal and optic nerve extracts. Also, RGC-5 cells in culture were given one of three different insults, light (1000lx for 2 days), hydrogen peroxide (200microM H(2)O(2) for 24h) or serum deprivation (48h) where cell survival and reactive oxygen species (ROS) formation was assayed. Moreover, a lipid peroxidation assay was used to compare the antioxidant capacity of baicalin with the flavonoid, epigallocatechin gallate (EGCG). Ischemia/reperfusion to the retina affected the localisation of Thy-1 and choline acetyltransferase (ChAT) and the content of various proteins (optic nerve and retina) and mRNAs (retina). Importantly, baicalin statistically blunted most of the effects induced by ischemia/reperfusion. Only the increase in caspase-8 and caspase-3 mRNAs caused by ischemia/reperfusion were unaffected by baicalin treatment. Baicalin also attenuated significantly the negative insult of light, hydrogen peroxide and serum withdrawal to RGC-5 cells. In the lipid peroxidation studies, baicalin was also found to be equally effective as EGCG to act as an antioxidant. Significantly, the negative insult of serum withdrawal on RGC-5 cell survival was blunted by baicalin but not by EGCG revealing the different properties of the two flavonoids.

Endothelin-1 (ET-1) causes death of retinal neurons through activation of nitric oxide synthase (NOS) and production of superoxide anion

Endothelin-1 (ET-1) is the most potent and long-acting vasoconstricting peptide presently known. In addition to its vascular effects, endothelin signaling pathway exists in the central nervous system (CNS), which is deeply related to neuronal degeneration. In the present study, we evaluated the effect of ET-1 on death of retinal neurons consisting mainly of amacrine cells, and its interaction with nitric oxide synthase (NOS) and superoxide production. Cultured retinal neurons from fetal rats were exposed to various doses of ET-1 (0.1, 1.0, 10 and 100nM). Neuronal toxicity of ET-1 was assessed by trypan blue exclusion, Hoechst 33,258 staining and TUNEL assay at different times. Intracellular levels of nitric oxide (NO), superoxide and peroxynitrite were determined semiquantitatively by DAF2-DA, hydroethidine and dihydrorhodamine-123, respectively. The effects of adding SOD (100U/ml) and L-NAME with ET-1 on these changes were evaluated. In addition, the receptor mechanisms involved in these reactions were determined by BQ-123 and BQ-788, receptor antagonists for ET A and ET B receptors, respectively. Exposure of cultured retinal neurons to ET-1 reduced the percentage of living cells in a dose- and time-dependent way, and the percentage of living cells was significantly increased by addition of SOD and L-NAME. Fluorometric analyses revealed that ET-1 increased the intracellular NO level in a dose- and time-dependent manner. The intracellular superoxide and peroxynitrite levels were also significantly increased 24h after incubation with 100nM of ET-1, and this elevation was suppressed by SOD and L-NAME. These ET-1-induced alterations were significantly suppressed when both BQ-123 and BQ-788 were added simultaneously with ET-1 to the medium. These results indicate that the neuronal death caused by ET-1 is most likely mediated by the activation of NOS in association with the formation of superoxides and peroxynitrite.

Nicotinamide attenuates retinal ischemia and light insults to neurones

The aim of the present studies was to determine whether nicotinamide is effective in blunting the negative influence of ischemia/reperfusion to the rat retina in situ and of light to transformed retinal ganglion cells (RGC-5 cells) in culture. Ischemia was delivered to the retina of one eye of rats by raising the intraocular pressure. Nicotinamide was administered intraperitoneally just before ischemia and into the vitreous immediately after the insult. Electroretinograms (ERGs) of both eyes were recorded before and 5 days after ischemia. Seven days after ischemia, retinas were analysed for the localization of various antigens. Retinal and optic nerve extracts were also prepared for analysis of specific proteins and mRNAs. Also, RGC-5 cells in culture were given a light insult (1000 lux, 48 and 96 h) and evidence for reduced viability and apoptosis determined by a variety of procedures. Nicotinamide was added to some cultures to see whether it reversed the negative effect of light. Ischemia/reperfusion to the retina affected the localization of Thy-1, neuronal nitric oxide synthase (NOS) and choline acetyltransferase (ChAT), the a- and b-wave amplitudes of the ERG, the content of various retinal and optic nerve proteins and mRNAs. Significantly, nicotinamide statistically blunted many of the effects induced by ischemia/reperfusion which included the activation of poly-ADP-ribose polymerase (PARP). Light-induced apoptosis of RGC-5 cells in culture was attenuated by nicotinamide and the PARP inhibitor NU1025. The presented data show that nicotinamide attenuates injury to the retina and RGC-5 cells in culture caused by ischemia/reperfusion and by light, respectively. Evidence is provided to suggest that nicotinamide acts as a PARP inhibitor and possibly an antioxidant.

Pentosan polysulfate protects brain endothelial cells against bacterial lipopolysaccharide-induced damages

Peripheral inflammation can aggravate local brain inflammation and neuronal death. The blood-brain barrier (BBB) is a key player in the event. On a relevant in vitro model of primary rat brain endothelial cells co-cultured with primary rat astroglia cells lipopolysaccharide (LPS)-induced changes in several BBB functions have been investigated. LPS-treatment resulted in a dose- and time-dependent decrease in the integrity of endothelial monolayers: transendothelial electrical resistance dropped, while flux of permeability markers fluorescein and albumin significantly increased. Immunostaining for junctional proteins ZO-1, claudin-5 and beta-catenin was significantly weaker in LPS-treated endothelial cells than in control monolayers. LPS also reduced the intensity and changed the pattern of ZO-1 immunostaining in freshly isolated rat brain microvessels. The activity of P-glycoprotein, an important efflux pump at the BBB, was also inhibited by LPS. At the same time production of reactive oxygen species and nitric oxide was increased in brain endothelial cells treated with LPS. Pentosan polysulfate, a polyanionic polysaccharide could reduce the deleterious effects of LPS on BBB permeability, and P-glycoprotein activity. LPS-stimulated increase in the production of reactive oxygen species and nitric oxide was also decreased by pentosan treatment. The protective effect of pentosan for brain endothelium can be of therapeutical significance in bacterial infections affecting the BBB.