Celecoxib, a selective cyclooxygenase-2 inhibitor, inhibits retinal vascular endothelial growth factor expression and vascular leakage in a streptozotocin-induced diabetic rat model

Diabetic Retinopathy: Vascular and Inflammatory Disease

Diabetic retinopathy (DR) is the leading cause of visual impairment in the working-age population of the Western world. The pathogenesis of DR is complex and several vascular, inflammatory, and neuronal mechanisms are involved. Inflammation mediates structural and molecular alterations associated with DR. However, the molecular mechanisms underlying the inflammatory pathways associated with DR are not completely characterized. Previous studies indicate that tissue hypoxia and dysregulation of immune responses associated with diabetes mellitus can induce increased expression of numerous vitreous mediators responsible for DR development. Thus, analysis of vitreous humor obtained from diabetic patients has made it possible to identify some of the mediators (cytokines, chemokines, and other factors) responsible for DR pathogenesis. Further studies are needed to better understand the relationship between inflammation and DR. Herein the main vitreous-related factors triggering the occurrence of retinal complication in diabetes are highlighted.

The safety, pharmacokinetics, and efficacy of intraocular celecoxib

PURPOSE

To determine safety, pharmacokinetics, and anti-inflammatory effects of intraocular celecoxib.

METHODS

The right eye of animals was injected with 1.5, 3, or 6 mg celecoxib prepared in dimethyl sulfoxide (DMSO). Left eyes served as controls and received 0.1 mL DMSO. Electroretinograms (ERG) were obtained at baseline and at 1, 4, and 12 weeks, and eyes were enucleated afterward for histopathologic analysis. For pharmacokinetics, 3 mg celecoxib was injected, and vitreous and retina/choroid drug levels were then analyzed at specific time points. For efficacy, 1 μg lipopolysaccharide was injected to induce inflammation; the right eye was then injected with 3 mg celecoxib (six eyes) or 2 mg triamcinolone acetonide (six eyes) and the left eye with saline. Twenty-four hours later, aqueous fluid was removed, and total leukocyte concentration and prostaglandin E2 (PGE2) concentration were determined.

RESULTS

Histologic and ERG studies demonstrated no signs of retinal or optic nerve toxicity. After a single 3-mg injection, vitreous (0.06 μg/mL) and retina/choroid (132.31 μg/g) celecoxib concentrations at 8 weeks exceeded median inhibitory concentration. Treatment with celecoxib and triamcinolone significantly reduced total leukocyte count by 40% (P = 0.02) and 31% (P = 0.01), respectively. Reduction in PGE2 levels paralleled reduction in leukocyte counts (P < 0.05). There was no increase in intraocular pressure, but cataract formation was observed at higher concentrations.

CONCLUSIONS

Intraocular injection of celecoxib appeared to be nontoxic and demonstrated excellent penetration into the retina/choroid and sustained drug levels out to 8 weeks. Celecoxib demonstrated potent anti-inflammatory effects, but there was an association with cataract formation at higher doses.

Effects of topical indomethacin, bromfenac and nepafenac on lipopolysaccharide-induced ocular inflammation†

Objectives

To evaluate the effects of topical non-steroidal anti-inflammatory drugs (NSAIDs) on retinal vascular leakage, and inflammatory markers in endotoxin-induced uveitis (EIU) in rats.

Methods

EIU was induced in rats by lipopolysaccharide (LPS). Topical 0.5% indomethacin, 0.09% bromfenac and 0.1% nepafenac were given before and after LPS. Twenty-four hours after LPS, the animals were euthanized and plasma along with retina were collected to assess prostaglandin-E2 (PGE2) and C-reactive protein (CRP) levels using enzyme-linked immunosorbent assay. Retinal vascular leakage was assessed by Evans blue. Molecular modelling was used to evaluate interaction of compounds with cyclooxygenase-2 (COX-2).

Key findings

All NSAIDs tested significantly prevented PGE2 production with higher effect of indomethacin and bromfenac in comparison with nepafenac. The three drugs did not affect plasma CRP levels. The analysis of retinal vascular leakage revealed a significant (P &lt; 0.01) decrease after treatment with indomethacin, but no significant changes were observed after treatment with bromfenac and nepafenac. Indomethacin had a different interaction with COX-2 in comparison with bromfenac and amfenac (active metabolite of nepafenac).

Conclusions

Topical treatment with indomethacin, bromfenac and nepafenac has significant anti-inflammatory effects. However, only indomethacin was able to prevent retinal vascular leakage in LPS-injected rats, likely due to the distinctive molecular mechanism.

Drug delivery to the posterior segment of the eye for pharmacologic therapy

Treatment of diseases of the posterior segment of the eye, such as age-related macular degeneration, cytomegalovirus retinitis, diabetic retinopathy, posterior uveitis and retinitis pigmentosa, requires novel drug delivery systems that can overcome the many barriers for efficacious delivery of therapeutic drug concentrations. This challenge has prompted the development of biodegradable and nonbiodegradable sustained-release systems for injection or transplantation into the vitreous as well as drug-loaded nanoparticles, microspheres and liposomes. These drug delivery systems utilize topical, systemic, subconjunctival, intravitreal, transscleral and iontophoretic routes of administration. The focus of research has been the development of methods that will increase the efficacy of spatiotemporal drug application, resulting in more successful therapy for patients with posterior segment diseases. This article summarizes recent advances in the research and development of drug delivery methods of the posterior chamber of the eye, with an emphasis on the use of implantable devices as well as micro- and nanoparticles.

The kallikrein-kinin system in diabetic retinopathy

Diabetic retinopathy (DR) is a major microvascular complication associated with type 1 and type 2 diabetes mellitus, which can lead to visual impairment and blindness. Current treatment strategies for DR are mostly limited to laser therapies, steroids, and anti-VEGF agents, which are often associated with unwanted side effects leading to further complications. Recent evidence suggests that kinins play a primary role in the development of DR through enhanced vascular permeability, leukocytes infiltration, and other inflammatory mechanisms. These deleterious effects are mediated by kinin B1 and B2 receptors, which are expressed in diabetic human and rodent retina. Importantly, kinin B1 receptor is virtually absent in sane tissue, yet it is induced and upregulated in diabetic retina. These peptides belong to the kallikrein-kinin system (KKS), which contains two separate and independent pathways of regulated serine proteases, namely plasma kallikrein (PK) and tissue kallikrein (TK) that are involved in the biosynthesis of bradykinin (BK) and kallidin (Lys-BK), respectively. Hence, ocular inhibition of kallikreins or antagonism of kinin receptors offers new therapeutic avenues in the treatment and management of DR. Herein, we present an overview of the principal features and known inflammatory mechanisms associated with DR along with the current therapeutic approaches and put special emphasis on the KKS as a new and promising therapeutic target due to its link with key pathways directly associated with the development of DR.

Topical nonsteroidal anti-inflammatory drugs for macular edema

Nonsteroidal anti-inflammatory drugs (NSAIDs) are nowadays widely used in ophthalmology to reduce eye inflammation, pain, and cystoid macular edema associated with cataract surgery. Recently, new topical NSAIDs have been approved for topical ophthalmic use, allowing for greater drug penetration into the vitreous. Hence, new therapeutic effects can be achieved, such as reduction of exudation secondary to age-related macular degeneration or diabetic maculopathy. We provide an updated review on the clinical use of NSAIDs for retinal diseases, with a focus on the potential future applications.

Role of phospholipases A2 in diabetic retinopathy: in vitro and in vivo studies

Diabetic retinopathy is one of the leading causes of blindness and the most common complication of diabetes with no cure available. We investigated the role of phospholipases A2 (PLA2) in diabetic retinopathy using an in vitro blood-retinal barrier model (BRB) and an in vivo streptozotocin (STZ)-induced diabetic model. Mono- and co-cultures of endothelial cells (EC) and pericytes (PC), treated with high or fluctuating concentrations of glucose, to mimic the diabetic condition, were used. PLA2 activity, VEGF and PGE2 levels and cell proliferation were measured, with or without PLA2 inhibition. Diabetes was induced in rats by STZ injection and PLA2 activity along with VEGF, TNFα and ICAM-1 levels were measured in retina. High or fluctuating glucose induced BRB breakdown, and increased PLA2 activity, PGE2 and VEGF in EC/PC co-cultures; inhibition of PLA2 in mono- or co-cultures treated with high or fluctuating glucose dampened PGE2 and VEGF production down to the levels of controls. High or fluctuating glucose increased EC number and reduced PC number in co-cultures; these effects were reversed after transfecting EC with small interfering RNA targeted to PLA2. PLA2 and COX-2 protein expressions were significantly increased in microvessels from retina of diabetic rats. Diabetic rats had also high retinal levels of VEGF, ICAM-1 and TNFα that were reduced by treatment with a cPLA2 inhibitor. In conclusion, the present findings indicate that PLA2 upregulation represents an early step in glucose-induced alteration of BRB, possibly upstream of VEGF; thus, PLA2 may be an interesting target in managing diabetic retinopathy.

Nanomedicines for back of the eye drug delivery, gene delivery, and imaging

Treatment and management of diseases of the posterior segment of the eye such as diabetic retinopathy, retinoblastoma, retinitis pigmentosa, and choroidal neovascularization is a challenging task due to the anatomy and physiology of ocular barriers. For instance, traditional routes of drug delivery for therapeutic treatment are hindered by poor intraocular penetration and/or rapid ocular elimination. One possible approach to improve ocular therapy is to employ nanotechnology. Nanomedicines, products of nanotechnology, having at least one dimension in the nanoscale include nanoparticles, micelles, nanotubes, and dendrimers, with and without targeting ligands. Nanomedicines are making a significant impact in the fields of ocular drug delivery, gene delivery, and imaging, the focus of this review. Key applications of nanotechnology discussed in this review include a) bioadhesive nanomedicines; b) functionalized nanomedicines that enhance target recognition and/or cell entry; c) nanomedicines capable of controlled release of the payload; d) nanomedicines capable of enhancing gene transfection and duration of transfection; f) nanomedicines responsive to stimuli including light, heat, ultrasound, electrical signals, pH, and oxidative stress; g) diversely sized and colored nanoparticles for imaging, and h) nanowires for retinal prostheses. Additionally, nanofabricated delivery systems including implants, films, microparticles, and nanoparticles are described. Although the above nanomedicines may be administered by various routes including topical, intravitreal, intravenous, transscleral, suprachoroidal, and subretinal routes, each nanomedicine should be tailored for the disease, drug, and site of administration. In addition to the nature of materials used in nanomedicine design, depending on the site of nanomedicine administration, clearance and toxicity are expected to differ.

Phytochemicals in ocular health: Therapeutic potential and delivery challenges

Diabetic retinopathy (DR) and age-related macular degeneration (AMD) are the leading causes of blindness in adults. The impact of these conditions on the quality of life is increasing in significance with a rise in life expectancy. The role of hyperglycemia, oxidative stress and inflammatory responses in the development and/or progression of DR and AMD, and several other sight threatening ocular diseases, is well established. In proliferative retinopathy, signals sent by the retina for nourishment, triggers the growth of fragile and abnormal blood vessels. Changes in ocular pressure may lead to rupture of these blood vessels causing severe vision problems. Recent in vitro and preclinical studies demonstrate that certain phytochemicals possessing potent antioxidant and anti-inflammatory activity and ocular blood flow enhancing properties may be very useful in the treatment of, or as a prophylactic measure for, DR and AMD. Apart from these properties they have also been investigated for their anti-bacterial, hormonal, enzyme stimulation, and anti-angiogenic activities. The attractive aspect of these potential therapeutic candidates is that they can act on multiple pathways identified in the etiology of DR, AMD, cataract and other ocular diseases. However, results from clinical trials have been somewhat ambiguous, raising questions about the concentrations of these bioflavonoids achieved in the neural retina following oral administration. Unfortunately, as of date, an efficient noninvasive means to deliver therapeutic agents/candidates to the back-of-the eye is still not available. This review examines some of these promising natural agents and discusses the challenges encountered in delivering them to the posterior segment ocular tissues through the oral route.

Nonsteroidal anti-inflammatory drugs for retinal disease

Nonsteroidal anti-inflammatory drugs (NSAIDs) are used extensively in ophthalmology for pain and photophobia after photorefractive surgery and to reduce miosis, inflammation, and cystoid macular edema following cataract surgery. In recent years, the US Food and Drug Administration has approved new topical NSAIDs and previously approved NSAIDs have been reformulated. These changes may allow for greater drug penetration into the retina and thereby offer additional therapeutic advantages. For example, therapeutic effects on diabetic retinopathy and age-related macular degeneration may now be achievable. We provide an updated review on the scientific rationale and clinical use of NSAIDs for retinal disease.

Per2 mutation recapitulates the vascular phenotype of diabetes in the retina and bone marrow

In this study, we assessed whether Per2 clock gene-mutant mice exhibit a vascular phenotype similar to diabetes. Per2 (B6.129-Per2(tm1Drw)/J) or wild-type control mice 4 and 12 months of age were used. To evaluate diabetes-like phenotype in Per2 mutant mice, retina was quantified for mRNA expression, and degree of diabetic retinopathy was evaluated. Bone marrow neuropathy was studied by staining femurs for tyrosine hydroxylase (TH) and neurofilament 200 (NF-200). The rate of proliferation and quantification of bone marrow progenitor cells (BMPCs) was performed, and a threefold decrease in proliferation and 50% reduction in nitric oxide levels were observed in Per2 mutant mice. TH-positive nerve processes and NF-200 staining were reduced in Per2 mutant mice. Both retinal protein and mRNA expression of endothelial nitric oxide synthase were decreased by twofold. Other endothelial function genes (VEGFR2, VEGFR1) were downregulated (1.5-2-fold) in Per2 mutant retinas, whereas there was an upregulation of profibrotic pathway mediated by transforming growth factor-β1. Our studies suggest that Per2 mutant mice recapitulate key aspects of diabetes without the metabolic abnormalities, including retinal vascular damage, neuronal loss in the bone marrow, and diminished BMPC function.

Retinal blood flow abnormalities following six months of hyperglycemia in the Ins2(Akita) mouse

The aim of this study was to characterize the microvascular flow abnormalities and oxygenation changes that are present following six months of hyperglycemia in the diabetic Ins2(Akita) mouse. Previous studies have shown decreased retinal blood flow in the first several weeks of hyperglycemia in rodents, similar to the decreases seen in the early stages of human diabetes. However, whether this alteration in the mouse retina continues beyond the initial weeks of diabetes has yet to be determined, as are the potential consequences of the decreased flow on retinal oxygenation. In this study, male Ins2(Akita) and age-matched C57BL/6 (non-diabetic) mice were maintained for a period of six months, at which time intravital microscopy was used to measure retinal blood vessel diameters, blood cell velocity, vascular wall shear rates, blood flow rates, and transient capillary occlusions. In addition, the presence of hypoxia was assessed using the oxygen-sensitive probe pimonidazole. The diabetic retinal microvasculature displayed decreases in red blood cell velocity (30%, p<0.001), shear rate (25%, p<0.01), and flow rate (40%, p<0.001). Moreover, transient capillary stoppages in flow were observed in the diabetic mice, but rarely in the non-diabetic mice. However, no alterations were observed in retinal hypoxia as determined by a pimonidazole assay, suggesting the possibility that the decreases seen in retinal blood flow may be dictated by a decrease in retinal oxygen utilization.

Update on twice-daily bromfenac sodium sesquihydrate to treat postoperative ocular inflammation following cataract extraction

Ophthalmic bromfenac sodium sesquihydrate is a topically applied selective cyclooxygenase (COX)-2 inhibitor. It is similar to amfenac, except for a bromine atom at the C(4) of the benzoyl ring position, which markedly affects its in vitro and in vivo potency, extends the duration of anti-inflammatory activity, and enhances its inhibitory effect on COX-2 absorption across the cornea and penetration into ocular tissues. The United States Food and Drug Administration approved bromfenac in 2005 for the treatment of postoperative inflammation and the reduction of ocular pain in patients who have undergone cataract surgery. Nonsteroidal anti-inflammatory drugs (NSAIDs), and among them bromfenac, could be even more effective than steroids at reestablishing the blood-aqueous barrier, as revealed by flare on slit-lamp examination and as quantitatively measured using ocular fluorophotometry. Similar to other NSAIDs, it has a role in inhibiting intraoperative miosis during cataract surgery. However, bromfenac also seems to be useful in other situations, such as refractive surgery, allergic conjunctivitis (not useful in dry eye), choroidal neovascularization, and even ocular oncology. No reports of systemic toxicity have been published and bromfenac has good topical tolerance with a low incidence of adverse effects.

Ocular application of the kinin B1 receptor antagonist LF22-0542 inhibits retinal inflammation and oxidative stress in streptozotocin-diabetic rats

PURPOSE

Kinin B(1) receptor (B(1)R) is upregulated in retina of Streptozotocin (STZ)-diabetic rats and contributes to vasodilation of retinal microvessels and breakdown of the blood-retinal barrier. Systemic treatment with B(1)R antagonists reversed the increased retinal plasma extravasation in STZ rats. The present study aims at determining whether ocular application of a water soluble B(1)R antagonist could reverse diabetes-induced retinal inflammation and oxidative stress.

METHODS

Wistar rats were made diabetic with STZ (65 mg/kg, i.p.) and 7 days later, they received one eye drop application of LF22-0542 (1% in saline) twice a day for a 7 day-period. The impact was determined on retinal vascular permeability (Evans blue exudation), leukostasis (leukocyte infiltration using Fluorescein-isothiocyanate (FITC)-coupled Concanavalin A lectin), retinal mRNA levels (by qRT-PCR) of inflammatory (B(1)R, iNOS, COX-2, ICAM-1, VEGF-A, VEGF receptor type 2, IL-1β and HIF-1α) and anti-inflammatory (B(2)R, eNOS) markers and retinal level of superoxide anion (dihydroethidium staining).

RESULTS

Retinal plasma extravasation, leukostasis and mRNA levels of B(1)R, iNOS, COX-2, VEGF receptor type 2, IL-1β and HIF-1α were significantly increased in diabetic retinae compared to control rats. All these abnormalities were reversed to control values in diabetic rats treated with LF22-0542. B(1)R antagonist also significantly inhibited the increased production of superoxide anion in diabetic retinae.

CONCLUSION

B(1)R displays a pathological role in the early stage of diabetes by increasing oxidative stress and pro-inflammatory mediators involved in retinal vascular alterations. Hence, topical application of kinin B(1)R antagonist appears a highly promising novel approach for the treatment of diabetic retinopathy.

Hydrophilic prodrug approach for reduced pigment binding and enhanced transscleral retinal delivery of celecoxib

Transscleral retinal delivery of celecoxib, an anti-inflammatory and anti-VEGF agent, is restricted by its poor solubility and binding to the melanin pigment in choroid-RPE. The purpose of this study was to develop soluble prodrugs of celecoxib with reduced pigment binding and enhanced retinal delivery. Three hydrophilic amide prodrugs of celecoxib, celecoxib succinamidic acid (CSA), celecoxib maleamidic acid (CMA), and celecoxib acetamide (CAA) were synthesized and characterized for solubility and lipophilicity. In vitro melanin binding to natural melanin (Sepia officinalis) was estimated for all three prodrugs. In vitro transport studies across isolated bovine sclera and sclera-choroid-RPE (SCRPE) were performed. Prodrug with the highest permeability across SCRPE was characterized for metabolism and cytotoxicity and its in vivo transscleral delivery in pigmented rats. Aqueous solubilities of CSA, CMA, and CAA were 300-, 182-, and 76-fold higher, respectively, than celecoxib. Melanin binding affinity and capacity were significantly lower than for celecoxib for all three prodrugs. Rank order for the % in vitro transport across bovine sclera and SCRPE was CSA > CMA ~ CAA ~ celecoxib, with the transport being 8-fold higher for CSA than celecoxib. CSA was further assessed for its metabolic stability and in vivo delivery. CSA showed optimum metabolic stability in all eye tissues with only 10-20% conversion to parent celecoxib in 30 min. Metabolic enzymes responsible for bioconversion included amidases, esterase, and cytochrome P-450. In vivo delivery in pigmented BN rats showed that CSA had 4.7-, 1.4-, 3.3-, 6.0-, and 4.5-fold higher delivery to sclera, choroid-RPE, retina, vitreous, and lens than celecoxib. CSA has no cytotoxicity in ARPE-19 cells in the concentration range of 0.1 to 1000 μM. Celecoxib succinamidic acid, a soluble prodrug of celecoxib with reduced melanin binding, enhances transscleral retinal delivery of celecoxib.

Anti-inflammatory therapy for diabetic retinopathy

Diabetic retinopathy (DR) is one of the most common complications of diabetes. This devastating disease is a leading cause of blindness in people of working age in industrialized countries and affects the daily lives of millions of people. Despite tight glycemic control, blood pressure control and lipid-lowering therapy, the number of DR patients keeps growing and therapeutic approaches are limited. Moreover, there are significant limitations and side effects associated with the current therapies. Thus, there is a great need for development of new strategies for prevention and treatment of DR. Studies have shown that DR has prominent features of chronic, subclinical inflammation. This article focuses on the role of inflammation in DR and summarizes the progress of studies of anti-inflammatory strategies for DR.

Inflammation in diabetic retinopathy

Diabetes causes a number of metabolic and physiologic abnormalities in the retina, but which of these abnormalities contribute to recognized features of diabetic retinopathy (DR) is less clear. Many of the molecular and physiologic abnormalities that have been found to develop in the retina in diabetes are consistent with inflammation. Moreover, a number of anti-inflammatory therapies have been found to significantly inhibit development of different aspects of DR in animal models. Herein, we review the inflammatory mediators and their relationship to early and late DR, and discuss the potential of anti-inflammatory approaches to inhibit development of different stages of the retinopathy. We focus primarily on information derived from in vivo studies, supplementing with information from in vitro studies were important.

Reduced choroidal neovascular membrane formation in cyclooxygenase-2 null mice

PURPOSE

To assess the degree of laser-induced choroidal neovascular membrane formation in wild-type (WT) and COX-2 null mice and to measure vascular endothelial growth factor (VEGF), interleukin (IL)-1β, and tumor necrosis factor (TNF)-α levels in the retina and choroid.

METHODS

Four laser burns were placed in each eye of WT and COX-2 null mice to induce choroidal neovascularization. Fluorescein angiography (FA) was performed at 14 days, and retinal pigment epithelium-choroid-sclera (choroidal) flat mounts were prepared. The retina and choroid were isolated from WT and COX-2 null mice at 24, 72, and 168 hours after laser photocoagulation and from unlasered eyes and were tested for VEGF, IL-1β, and TNF-α.

RESULTS

COX-2 null mice demonstrated 58% (P = 0.001) and 48% (P = 0.001) reductions in CNV formation on FA and choroidal flat mounts, respectively, compared with WT mice. For unlasered mice, mean VEGF concentrations in the retina and choroid were 1.2 ± 0.42 pg/mg protein for WT but only 0.42 ± 0.2 pg/mg protein for COX-2 null mice (P < 0.05). After laser photocoagulation, WT mice showed significantly greater VEGF and IL-β expression in the retina and choroid by 168 hours (P < 0.05) and 72 hours (P < 0.05), respectively, compared with COX-2 null mice.

CONCLUSIONS

COX-2 null mice exhibited significantly less choroidal neovascular membrane formation associated with reduced expression of VEGF. The results of this study suggest that COX-2 modulates VEGF expression in CNV and implicates a potential therapeutic role for nonsteroidal anti-inflammatory drugs.

Delivery of celecoxib for treating diseases of the eye: influence of pigment and diabetes

IMPORTANCE OF THE FIELD

Age-related macular degeneration (AMD) and diabetic retinopathy (DR) are two major causes of blindness. In these disorders, growth factors such as vascular endothelial growth factor (VEGF) are upregulated, leading to either enhanced vascular permeability or proliferation of endothelium. While corticosteroid therapies available at present suffer from side effects including cataracts and elevated intraocular pressure, anti-VEGF antibody therapies require frequent intravitreal injections, a procedure that can potentially lead to retinal detachment or endophthalmitis. Thus, there is a need to develop safe, sustained release therapeutic approaches for treating AMD and DR.

AREAS COVERED IN THIS REVIEW

This review discusses the pharmacological basis for using celecoxib, an anti-inflammatory drug capable of selectively inhibiting cycloxygenase 2, in treating AMD and DR. In addition, this article discusses the safety, delivery advantage and efficacy of celecoxib by transscleral retinal delivery, a periocular delivery approach that is less invasive to the globe compared with intravitreal injections.

WHAT THE READER WILL GAIN

The reader will gain insights into the development of a pharmacological agent and a sustained release delivery system for treating DR and AMD. Further, the reader will gain insights into the influence of eye physiology including pigmentation and disease states such as DR on retinal drug delivery.

TAKE HOME MESSAGE

Transscleral sustained delivery of anti-inflammatory agents is a viable option for treating retinal disorders.

Genetic deletion of COX-2 diminishes VEGF production in mouse retinal Müller cells

Non-steroidal anti-inflammatory drugs (NSAIDs), which inhibit COX activity, reduce the production of retinal VEGF and neovascularization in relevant models of ocular disease. We hypothesized that COX-2 mediates VEGF production in retinal Müller cells, one of its primary sources in retinal neovascular disease. The purpose of this study was to determine the role of COX-2 and its products in VEGF expression and secretion. These studies have more clearly defined the role of COX-2 and COX-2-derived prostanoids in retinal angiogenesis. Müller cells derived from wild-type and COX-2 null mice were exposed to hypoxia for 0-24 h. COX-2 protein and activity were assessed by western blot analysis and GC-MS, respectively. VEGF production was assessed by ELISA. Wild-type mouse Müller cells were treated with vehicle (0.1% DMSO), 10 microM PGE(2), or PGE(2) + 5 microM H-89 (a PKA inhibitor), for 12 h. VEGF production was assessed by ELISA. Hypoxia significantly increased COX-2 protein (p < 0.05) and activity (p < 0.05), and VEGF production (p < 0.0003). COX-2 null Müller cells produced significantly less VEGF in response to hypoxia (p < 0.05). Of the prostanoids, PGE(2) was significantly increased by hypoxia (p < 0.02). Exogenous PGE(2) significantly increased VEGF production by Müller cells (p < 0.0039), and this effect was inhibited by H-89 (p < 0.055). These data demonstrate that hypoxia induces COX-2, prostanoid production, and VEGF synthesis in Müller cells, and that VEGF production is at least partially COX-2-dependent. Our study suggests that PGE(2), signaling through the EP(2) and/or EP(4) receptor and PKA, mediates the VEGF response of Müller cells.

Nonsteroidal anti-inflammatory drugs in ophthalmology

Nonsteroidal anti-inflammatory drugs (NSAIDs) are increasingly employed in ophthalmology to reduce miosis and inflammation, manage scleritis, and prevent and treat cystoid macular edema associated with cataract surgery. In addition, they may decrease postoperative pain and photophobia associated with refractive surgery and may reduce the itching associated with allergic conjunctivitis. In recent years, the U.S. Food and Drug Administration has approved new topical NSAIDs, and previously approved NSAIDs have been reformulated. These additions and changes result in different pharmacokinetics and dosing intervals, which may offer therapeutic advantages. For example, therapeutic effects on diabetic retinopathy and age-related macular degeneration may now be achievable. We provide an updated review on NSAIDs and a summary of their current uses in ophthalmology with attention to potential future applications.

Intratracheal budesonide-poly (lactide-co-glycolide) microparticles reduce oxidative stress, VEGF expression, and vascular leakage in a benzo(a)pyrene-fed mouse model

The purpose of this study was to determine whether intratracheally instilled polymeric budesonide microparticles could sustain lung budesonide levels for one week and inhibit early biochemical changes associated with benzo(a)pyrene (B[a]P) feeding in a mouse model for lung tumours. Polymeric microparticles of budesonide-poly (dl-lactide-co-glycolide) (PLGA 50:50) were prepared using a solvent evaporation technique and characterized for their size, morphology, encapsulation efficiency, and in-vitro release. The microparticles were administered intratracheally (i.t.) to B[a]P-fed A/J mice. At the end of one week drug levels in the lung tissue and bronchoalveolar lavage (BAL) were estimated using HPLC and compared with systemic (intramuscular) administration. In addition, in-vivo end points including malondialdehyde (MDA), glutathione (GSH), total protein levels and vascular endothelial growth factor (VEGF) in BAL, and VEGF and c-myc mRNA levels in the lung tissue were assessed at the end of one week following intratracheal administration of budesonide microparticles. Budesonide-PLGA microparticles (1–2 μm), with a budesonide loading efficiency of 69–94%, sustained in-vitro budesonide release for over 21 days. Compared with the intramuscular route, intratracheally administered budesonide-PLGA microparticles resulted in higher budesonide levels in the BAL and lung tissue. In-vivo, B[a]P-feeding increased BAL MDA, lung VEGF mRNA, lung c-myc mRNA, BAL total protein, and BAL VEGF levels by 60, 112, 71, 154, and 78%, respectively, and decreased BAL GSH by 62%. Interestingly, intratracheally administered budesonide-PLGA particles inhibited these biochemical changes. Thus, biodegradable budesonide microparticles sustained budesonide release and reduced MDA accumulation, GSH depletion, vascular leakage, and VEGF and c-myc expression in B[a]P-fed mice, indicating the potential of locally delivered sustained-release particles for inhibiting angiogenic factors in lung cancer.

High glucose increases expression of cyclooxygenase-2, increases oxidative stress and decreases the generation of nitric oxide in mouse microvessel endothelial cells

Hyperglycaemia is a key factor that contributes to the development of diabetes-related microvascular disease. Both cyclooxygenase I and cyclooxygenase II are expressed in endothelial cells and play key roles in the regulation of cardiovascular function. In the current study we tested the hypothesis that hyperglycaemia-induced increased expression of cyclooxygenase II is a contributing factor both to the increased oxidative stress and to the reduction in the generation of nitric oxide in microvessel endothelial cells following their exposure to high glucose. We demonstrated that the exposure of mouse microvascular endothelial cells to high glucose for 3 days decreased the generation of nitric oxide and enhanced production of superoxide. Western blots illustrated that exposure to high glucose also increased endothelial nitric oxide synthase and cyclooxygenase II protein expression levels and decreased the dimer/monomer ratio of endothelial nitric oxide synthase protein. All the changes induced by the high glucose culture media could be reversed by either the cyclooxygenase II inhibitor CAY10404, the non-selective cyclooxygenase inhibitor indomethacin or the protein kinase C inhibitor chelerythrine, but not solely by preincubation with the antioxidant and putative NADPH oxidase inhibitor, apocynin. Our data indicate that high glucose induced oxidative stress is linked to an increase in the expression of cyclooxygenase II and a reduced generation of nitric oxide that is associated with an uncoupled endothelial nitric oxide synthase, possibly due to decreased dimer/monomer ratio.

Resistance of retinal inflammatory mediators to suppress after reinstitution of good glycemic control: novel mechanism for metabolic memory

Diabetic retinopathy resists arrest of its progression after reestablishment of good glycemic control that follows a profound period of poor glycemic control. The objective of this study was to elucidate the role of inflammation in the resistance of retinopathy to arrest after termination of hyperglycemia. Streptozotocin-diabetic rats were (a) maintained either in poor glycemic control [PC group; glycated hemoglobin (GHb)>11%] or in good glycemic control (GC group; GHb<7%) for 12 months or (b) allowed to be in poor glycemic control for 6 months followed by good glycemic control for 6 additional months. At 12 months, retina was analyzed for pro-inflammatory mediators. Twelve months of PC increased retinal interleukin 1beta (IL-1beta) mRNA by 2-fold and its protein expression by 25% compared with the values obtained from normal rat retina. Tumor necrosis factor alpha (TNF-alpha) was elevated approximately 3-fold (both mRNA and protein), and the receptors for IL-1beta and TNF-alpha were increased by 40% each. The concentrations of intercellular cell adhesion molecule 1 and vascular cell adhesion molecule 1 were elevated by 40% and 150%, respectively, and inducible nitric oxide synthase transcripts were elevated by 6-fold. Six months of good glycemic control that followed 6 months of poor glycemic control failed to reverse the elevations in IL-1beta, TNF receptor type I, and intercellular cell adhesion molecule 1 but had some beneficial effects on TNF-alpha, inducible nitric oxide synthase, and vascular cell adhesion molecule 1, however these mediators remained significantly elevated. However, the GC group showed no significant change in the retinal pro-inflammatory mediators compared with the normal rats. Failure to reverse retinal inflammatory mediators supports their important role in the resistance of retinopathy to arrest after cessation of hyperglycemia.

Gene delivery nanoparticles fabricated by supercritical fluid extraction of emulsions

Non-viral polymeric gene delivery systems offer increased protection from nuclease degradation, enhanced plasmid DNA (pDNA) uptake, and controlled dosing to sustain the duration of pDNA action. Such gene delivery systems can be formulated from biocompatible and biodegradable polymers such as poly(D,L-lactic-co-glycolic) acid (PLGA). Experimental loading of hydrophilic macromolecules such as pDNA is low in polymeric particles. The study purpose was to develop a supercritical fluid extraction of emulsions (SFEE) process based on CO(2) for preparing pEGFP-PLGA nanoparticles with high plasmid loading and loading efficiency. Another objective was to determine the efficacy of pFlt23k, an anti-angiogenic pDNA capable of inhibiting vascular endothelial growth factor (VEGF) secretion, following nanoparticle formation using the SFEE process. Results indicated that the SFEE process allows high actual loading of pDNA (19.7%, w/w), high loading efficiency (>98%), and low residual solvents (<50 ppm), due to rapid particle formation from efficient solvent removal provided by the SFEE process. pFlt23K-PLGA nanoparticles were capable of in vitro transfection, significantly reducing secreted VEGF from human lung alveolar epithelial cells (A549) under normoxic and hypoxic conditions. pFlt23K-PLGA nanoparticles did not exhibit cytotoxicity and are of potential value in treating neovascular disorders wherein VEGF levels are elevated.

Hypoxia and the expression of HIF-1alpha and HIF-2alpha in the retina of streptozotocin-injected mice and rats

Decreases in retinal blood flow in diabetics could render the retina hypoxic. In mouse and rat models of diabetes, a decrease in retinal blood flow occurs early, within 3-4 weeks of the induction of hyperglycemia, although information is scarce on whether this early decrease in flow induces hypoxia. The purpose of the current study was to determine whether hypoxia-inducible factor (HIF) levels increase following 4 and/or 12 weeks of hyperglycemia in streptozotocin (STZ)-injected mouse (C57BL/6) and rat (Wistar) retinas. Additionally, retinal tissue hypoxia was measured with pimonidazole following 12 weeks of hyperglycemia. These aims were accomplished via immunostaining of cross-sections from enucleated eyes. In mice, staining for HIF-1alpha and HIF-2alpha showed a contrasting pattern, with HIF-1alpha higher in the inner retina than outer, but HIF-2alpha higher in the outer retina than inner. However, in rats, staining for both HIF-1alpha and HIF-2alpha was more intense in the inner retina. The HIF-1alpha staining intensities and patterns were similar between diabetic animals and their non-diabetic counterparts following 4 and 12 weeks of hyperglycemia. The same was true for HIF-2alpha except for a trend toward an increase following 12 weeks of hyperglycemia in mice. Pimonidazole staining showed significant decreases throughout all layers of the central retina and most layers of the peripheral retina of rats (but not mice), following 12 weeks of hyperglycemia. In summary, despite early decreases in flow in rats and mice, retinal HIF-1alpha and HIF-2alpha were not found to be increased, and the extent of hypoxia may even decrease after 12 weeks of hyperglycemia in rats.

Pathophysiology of cyclooxygenase inhibition in animal models

Cyclooxygenase (COX) catalyzes the conversion of arachidonic acid into prostaglandins (PGs), which play a significant role in health and disease in the gastrointestinal tract (GI) and in the renal, skeletal, and ocular systems. COX-1 is constitutively expressed and found in most normal tissues, whereas COX-2 can be expressed at low levels in normal tissues and is highly induced by pro-inflammatory mediators. Inhibitors of COX activity include: (1) conventional nonselective, nonsteroidal anti-inflammatory drugs (ns-NSAIDs) and (2) COX-2 selective nonsteroidal anti-inflammatory drugs (COX-2 s-NSAIDs). Inhibition of COX-1 often elicits GI toxicity in animals and humans. Therefore, COX-2 s-NSAIDs were developed to provide a selective COX-2 agent, while minimizing the attendant COX-1-mediated GI toxicities. Rats and dogs overpredict COX inhibition for renal effects such as renal handling of electrolytes in humans. COX inhibitors are shown to have both beneficial and detrimental effects, such as on healing of ligament or tendon tears, on the skeletal system in animal models. Certain ophthalmic conditions such as glaucoma and keratitis are associated with increased COX-2 expression, suggesting a potential role in their pathophysiology.

4-HNE inhibits tube formation and up-regulates chondromodulin-I in human endothelial cells

The aim of the present study was to investigate the effects of 4-hydroxy-2-nonenal (4-HNE) on tube formation by human bone marrow endothelial cells (HBMEC). We found that 4-HNE at physiologically achievable concentrations (5 and 10 microM) inhibited the formation of tubes. Western blot analysis revealed that inhibition of tube formation by 4-HNE was associated with increased expression of chondromodulin-I (CHM-I), a protein with well-known anti-angiogenic properties. Cell viability assays showed that 4-HNE at concentrations of 10 microM or less did not cause HBMEC cell death. Luciferase reporter assays did not show any inducing effect of 4-HNE on the promoter activity of human CHM-I gene indicating that post-transcriptional or post-translational modifications may account for the up-regulation of CHM-I. Collectively, the results of the present study show for the first time that 4-HNE inhibits tube formation by HBMECs indicating a potential anti-angiogenic activity of 4-HNE. This inhibition occurs at least in part via 4-HNE-induced CHM-I protein expression.

Effect of diabetes on transscleral delivery of celecoxib

PURPOSE

To investigate the effects of diabetes on transscleral retinal delivery of celecoxib in albino and pigmented rats.

METHODS

Albino (Sprague Dawley-SD) and pigmented (Brown Norway-BN) rats were made diabetic by a single intraperitoneal injection of streptozotocin (60 mg/kg) following 24 h of fasting and diabetes was confirmed (blood glucose>250 mg/dL). Two months after diabetes induction, the integrity of blood-retinal-barrier in control versus diabetic rats from both strains was compared by using FITC-dextran leakage assay. Fifty microliter suspension of celecoxib (3 mg/rat) was injected periocularly in both the strains in one eye, 2 months following diabetes induction. The animals were euthanized at the end of 0.25, 0.5, 1, 2, 3, 4, 8, and 12 h post-dosing and celecoxib levels in ocular tissues and plasma were estimated using a HPLC assay.

RESULTS

Diabetes (2-month duration) resulted in 2.4 and 3.5 fold higher blood-retinal barrier leakage in diabetic SD and BN rats, respectively, compared to controls. The area under tissue celecoxib concentration versus time curves (AUC) for sclera, cornea, and lens were not significantly different between control and diabetic animals. However, retinal and vitreal AUCs of celecoxib in treated eyes were approximately 1.5-fold and 2-fold higher in diabetic SD and BN rats, respectively, as compared to the controls.

CONCLUSIONS

Transscleral retinal and vitreal delivery of celecoxib is significantly higher in diabetic animals of both strains. The increase in retinal delivery of celecoxib due to diabetes is higher in pigmented rats compared to albino rats. Higher delivery of celecoxib in diabetic animals compared to control animals can be attributed to the disruption of blood-retinal barrier due to diabetes.

Attenuation of diabetes-induced retinal vasoconstriction by a thromboxane receptor antagonist

Retinal blood flow has been reported to decrease early in human diabetes as well as in diabetic animal models. The purpose of the present study is to investigate the role of thromboxane receptor binding in the decrease of flow. C57BL/6 mice were injected with streptozotocin (STZ) at 11-12 weeks of age and remained hyperglycemic for 4 weeks. The mice were treated with a selective thromboxane receptor antagonist, GR32191B (vapiprost), in drinking water for the final three weeks at a dose of 1mg/kg/day. In separate experiments, vapiprost was administered only once, as an acute injection 25min prior to the experimental measurements. The measurements included retinal arteriolar and venular diameters and red blood cell (RBC) velocities, from which retinal blood flow was calculated. STZ induced decreases in vascular diameters and RBC velocities, resulting in an approximate 30% decrease in overall retinal blood flow. However, these decreases were not seen in mice given the three-week administration of vapiprost. Acute administration to diabetic mice of 1mg/kg vapiprost, but not 0.1mg/kg, induced arteriolar vasodilation, with the dilation more substantial in smaller feed arterioles. In summary, STZ-induced decreases in retinal blood flow can be attenuated by the thromboxane receptor antagonist vapiprost.

Inhibition of NADPH oxidase-related oxidative stress-triggered signaling by honokiol suppresses high glucose-induced human endothelial cell apoptosis

Angiopathy is a major complication of diabetes. Abnormally high blood glucose is a crucial risk factor for endothelial cell damage. Nuclear factor-kappaB (NF-kappaB) has been demonstrated as a mediated signaling in hyperglycemia or oxidative stress-triggered apoptosis of endothelial cells. Here we explored the efficacy of honokiol, a small molecular weight natural product, on NADPH oxidase-related oxidative stress-mediated NF-kappaB-regulated signaling and apoptosis in human umbilical vein endothelial cells (HUVECs) under hyperglycemic conditions. The methods of morphological Hoechst staining and annexin V/propidium iodide staining were used to detect apoptosis. Submicromolar concentrations of honokiol suppressed the increases of NADPH oxidase activity, Rac-1 phosphorylation, p22(phox) protein expression, and reactive oxygen species production in high glucose (HG)-stimulated HUVECs. The degradation of IkappaBalpha and increase of NF-kappaB activity were inhibited by honokiol in HG-treated HUVECs. Moreover, honokiol (0.125-1 microM) also suppressed HG-induced cyclooxygenase (COX)-2 upregulation and prostaglandin E(2) production in HUVECs. Honokiol could reduce increased caspase-3 activity and the subsequent apoptosis and cell death triggered by HG. These results imply that inhibition of NADPH oxidase-related oxidative stress by honokiol suppresses the HG-induced NF-kappaB-regulated COX-2 upregulation, apoptosis, and cell death in HUVECs, which has the potential to be developed as a therapeutic agent to prevent hyperglycemia-induced endothelial damage.

Contributions of inflammatory processes to the development of the early stages of diabetic retinopathy

Diabetes causes metabolic and physiologic abnormalities in the retina, and these changes suggest a role for inflammation in the development of diabetic retinopathy. These changes include upregulation of iNOS, COX-2, ICAM-1, caspase 1, VEGF, and NF-κB, increased production of nitric oxide, prostaglandin E2, IL-1β, and cytokines, as well as increased permeability and leukostasis. Using selective pharmacologic inhibitors or genetically modified animals, an increasing number of therapeutic approaches have been identified that significantly inhibit development of at least the early stages of diabetic retinopathy, especially occlusion and degeneration of retinal capillaries. A common feature of a number of these therapies is that they inhibit production of inflammatory mediators. The concept that localized inflammatory processes play a role in the development of diabetic retinopathy is relatively new, but evidence that supports the hypothesis is accumulating rapidly. This new hypothesis offers new insight into the pathogenesis of diabetic retinopathy, and offers novel targets to inhibit the ocular disease.

Celecoxib inhibits proliferation of retinal pigment epithelial and choroid-retinal endothelial cells by a cyclooxygenase-2-independent mechanism

Age-related macular degeneration (ARMD) is a leading cause of blindness. The major reason for severe vision loss in ARMD is choroidal neovascularization due to an elevation in the expression of angiogenic factors such as vascular endothelial growth factor (VEGF). Drugs with anti-VEGF and antiproliferative activities can be beneficial for the treatment of this disorder. We have previously demonstrated that celecoxib [a selective cyclooxygenase (Cox)-2 inhibitor] inhibits VEGF expression in retinal pigment epithelial cells. In this study, we investigated the antiproliferative effects of celecoxib in adult retinal pigment epithelial (ARPE-19) and choroidal endothelial (RF/6A) cells. The results indicate that celecoxib 1) causes a dose-dependent antiproliferative effect in ARPE-19 and RF/6A cells (IC(50) of 23 and 13 microM, respectively); 2) leads to a G(2)-M phase cell cycle arrest in these cell types; and 3) inhibits VEGF-induced proliferation of RF/6A cells (IC(50) of 20 microM). In addition, 4) the concentrations of celecoxib required for antiproliferative effects are lower than those required for the cytotoxicity. These effects of celecoxib are by mechanisms independent of its Cox-2 inhibitory activity because rofecoxib (another Cox-2 inhibitor) had no effects on the proliferation or cell cycle distribution of the two cell types, and flurbiprofen (an inhibitor of Cox-1 and Cox-2) had weak antiproliferative effects on ARPE-19 cells, with IC(50) of 90 microM. In summary, celecoxib has potent antiproliferative effects in RF/6A and ARPE-19 cells; thus, it can be a potential new treatment in proliferative disorders of the choroid-retina such as choroidal neovascularization in age-related macular degeneration.

Transforming growth factor-beta1 enhanced vascular endothelial growth factor synthesis in mesenchymal stem cells

Angiogenesis is essential for transplantation of mesenchymal stem cells (MSCs). Vascular endothelial growth factor (VEGF) is one of the most potent angiogenic factors identified to date. Elevated VEGF levels in MSCs correlate with the potential of MSCs transplantation. As an indirect angiogenic agent, transforming growth factor-beta1 (TGF-beta1) plays a pivotal role in the regulation of vasculogenesis and angiogenesis. However, the effect of TGF-beta1 on VEGF synthesis in MSCs is still unknown. Besides, the intracellular signaling mechanism by which TGF-beta1 stimulates this process remains poorly understood. In this article, we demonstrated that exposure of MSCs to TGF-beta1 stimulated the synthesis of VEGF. Meanwhile, TGF-beta1 stimulated the phosphorylation of Akt and extracellular signal-regulated kinase 1/2 (ERK1/2). Moreover, Ly 294002, a specific inhibitor of phosphatidylinositol-3-kinase (PI3K)/Akt significantly attenuated the VEGF synthesis stimulated by TGF-beta1. Additionally, U0126, a specific inhibitor of ERK1/2, also significantly attenuated the TGF-beta1-stimulated VEGF synthesis. These results indicated that TGF-beta1 enhanced VEGF synthesis in MSCs, and the Akt and ERK1/2 activation were involved in this process.

Action of Celecoxib on Hepatic Metabolic Changes Induced by the Walker-256 Tumour in Rats

The purpose of the present work was to investigate the influence of celecoxib on some hepatic metabolic parameters affected by the Walker-256 tumour in rats. Celecoxib was administered daily (5-50 mg/kg body weight) beginning at the day in which the tumour cells were inocculated. At day 14, the liver was isolated and perfused in order to measure alanine transformation, glycolysis and arginine transformation. Maximal reduction of tumour growth (75%), accompanied by an almost normal weight gain, was attained with a celecoxib dose of 12.5 mg/kg. Diminution of glucose utilization (glycolysis) and inhibition of gluconeogenesis and ureogenesis from alanine caused by the tumor were totally reversed by celecoxib. Oxygen uptake by the liver was also normalized by the drug. Hepatic arginine transformation, which is normally enhanced in rats bearing the Walker-256 tumour, remained elevated in celecoxib-treated animals. It was concluded that preservation of gluconeogenesis and normalization of hepatic glucose utilization can explain, partly at least, the clinical improvement of cancer patients treated with the drug. The lack of action of celecoxib on arginine hydrolysis might indicate that reduction in polyamine synthesis is not a factor contributing to the diminished tumour growth.

Sustained-release ophthalmic drug delivery systems for treatment of macular disorders: present and future applications

Macular disease currently poses the greatest threat to vision in aging populations. Historically, most of this pathology could only be dealt with surgically, and then only after much damage to the macula had already occurred. Current pathophysiological insights into macular diseases have allowed the development of effective new pharmacotherapies. The field of drug delivery systems has advanced over the last several years with emphasis placed on controlled release of drug to specific areas of the eye. Its unique location and tendency toward chronic disease make the macula an important and attractive target for drug delivery systems, especially sustained-release systems. This review evaluates the current literature on the research and development of sustained-release posterior segment drug delivery systems that are primarily intended for macular disease with an emphasis on age-related macular degeneration.Current effective therapies include corticosteroids and anti-vascular endothelial growth factor compounds. Recent successes have been reported using anti-angiogenic drugs for therapy of age-related macular degeneration. This review also includes information on implantable devices (biodegradable and non-biodegradable), the use of injected particles (microspheres and liposomes) and future enhanced drug delivery systems, such as ultrasound drug delivery. The devices reviewed show significant drug release over a period of days or weeks. However, macular disorders are chronic diseases requiring years of treatment. Currently, there is no 'gold standard' for therapy and/or drug delivery. Future studies will focus on improving the efficiency and effectiveness of drug delivery to the posterior chamber. If successful, therapeutic modalities will significantly delay loss of vision and improve the quality of life for patients with chronic macular disorders.

The effect of long-term treatment with sulindac on the progression of diabetic retinopathy

OBJECTIVE

To evaluate the effects of long-term treatment with sulindac on the progression of diabetic retinopathy (DR).

RESEARCH DESIGN AND METHODS

40 Japanese patients with type 2 diabetes were enrolled in a randomized, single-blind controlled trial in which the effects of sulindac (200 mg/day, 100 mg twice a day; n = 16 patients) on the progression of DR were compared to controls (24 patients) for 3 years. All patients were comparable in their age, gender, duration of disease, body mass index, dipstick proteinuria, insulin therapy, glycemic control, and clinical stages of DR. Outcome was determined by comparing parameters of retinopathy in fundus photographs that were taken at time 0 to those taken 1, 2, and 3 years after the initiation of treatment.

RESULTS

Patients in the sulindac group did not develop DR during the course of treatment nor was there progression of pathology in those who began the study with mild non-proliferative DR (NPDR). On the other hand, six patients progressed to mild NPDR in the control group--three at year 1 and three at year 3--and an additional patient progressed to severe NPDR from mild NPDR by year 1 and to proliferative DR by year 2. The findings at year 3 in the sulindac group were significantly (p < 0.05) different from the control group. None of the patients experienced any adverse effects of treatment.

CONCLUSIONS

Long-term treatment with sulindac was clinically effective in decreasing the progression of mild DR in type 2 diabetic patients in this pilot study.

AQ4, an antitumor anthracenedione, inhibits endothelial cell proliferation and vascular endothelial growth factor secretion: implications for the therapy of ocular neovascular disorders

Current clinical options for the treatment of neovascular disorders of the posterior segment of the eye have several drawbacks. Photocoagulation lasers can impair peripheral and night vision. Photodynamic therapies as well as intravitreal macromolecule injections (Macugen and Lucentis) require frequent, invasive administrations. Above all, only modest improvement in vision is achieved with any of the existing treatments. In order to overcome these limitations in the long run, this study investigated the antiangiogenic potential of AQ4, a low molecular weight anthracenedione. The results indicate that AQ4 enters the cell nucleus and inhibits proliferation of choroid-retina endothelial (RF/6A) cells and human retinal pigment epithelial (ARPE-19) cells under hypoxic (1% O(2)) as well as normoxic (21% O(2)) conditions. The IC(50) for these effects ranges from 5.5 to 6.9 muM. AQ4 does not affect the viability of non-dividing RF/6A or ARPE-19 cells up to 0.1 mM. Further, AQ4 (20 muM) reduces vascular endothelial growth factor (VEGF) protein secretion by about 50% in ARPE-19 cells under normoxia as well as hypoxia, possibly by reducing VEGF transcription. AQ4 arrests the growth of endothelial cells in S phase, consistent with interference of AQ4 with DNA replication. These results for the first time suggest that AQ4 can potentially alleviate the neovascularization of choroid/retina by a dual mechanism of inhibiting the proliferation of endothelial cells and by reducing mitogenic VEGF stimulus from retinal pigment epithelial cells.

Topical administration of nepafenac inhibits diabetes-induced retinal microvascular disease and underlying abnormalities of retinal metabolism and physiology

Pharmacologic treatment of diabetic retinopathy via eyedrops could have advantages but has not been successful to date. We explored the effect of topical Nepafenac, an anti-inflammatory drug known to reach the retina when administered via eyedrops, on the development of early stages of diabetic retinopathy and on metabolic and physiologic abnormalities that contribute to the retinal disease. Streptozotocin-induced diabetic rats were assigned to three groups (0.3% Nepafenac eyedrops, vehicle eyedrops, and untreated control) for comparison to age-matched nondiabetic control animals. Eyedrops were administered in both eyes four times per day for 2 and 9 months. At 2 months of diabetes, insulin-deficient diabetic control rats exhibited significant increases in retinal prostaglandin E(2), superoxide, vascular endothelial growth factor (VEGF), nitric oxide (NO), cyclooxygenase-2, and leukostasis within retinal microvessels. All of these abnormalities except NO and VEGF were significantly inhibited by Nepafenac. At 9 months of diabetes, a significant increase in the number of transferase-mediated dUTP nick-end labeling-positive capillary cells, acellular capillaries, and pericyte ghosts were measured in control diabetic rats versus nondiabetic controls, and topical Nepafenac significantly inhibited all of these abnormalities (all P < 0.05). Diabetes-induced activation of caspase-3 and -6 in retina was partially inhibited by Nepafenac (all P < 0.05). Oscillatory potential latency was the only abnormality of retinal function reproducibly detected in these diabetic animals, and Nepafenac significantly inhibited this defect (P < 0.05). Nepafenac did not have a significant effect on diabetes-induced loss of cells in the ganglion cell layer or in corneal protease activity. Topical ocular administration of Nepafenac achieved sufficient drug delivery to the retina and diabetes-induced alterations in retinal vascular metabolism, function, and morphology were inhibited. In contrast, little or no effect was observed on diabetes-induced alterations in retinal ganglion cell survival. Local inhibition of inflammatory pathways in the eye offers a novel therapeutic approach toward inhibiting the development of lesions of diabetic retinopathy.

Bovine and porcine transscleral solute transport: influence of lipophilicity and the Choroid-Bruch's layer

PURPOSE

To determine the influence of the choroid-Bruch's layer and solute lipophilicity on in vitro transscleral drug permeability in bovine and porcine eyes.

METHODS

The in vitro permeability of two VEGF inhibitory drugs, budesonide and celecoxib, which are lipophilic and neutral at physiologic pH, and of three marker solutes, 3H-mannitol (hydrophilic, neutral), sodium fluorescein (hydrophilic, anionic), and rhodamine 6G (lipophilic, cationic), were determined across freshly excised scleras, with or without the underlying choroid-Bruch's layer. Select studies were performed using porcine sclera with and without choroid-Bruch's layer. Neural retina was removed by exposure of the eyecup to isotonic buffer and wherever required, the retinal pigment epithelial (RPE) layer of the preparation was disrupted and removed by exposure to hypertonic buffer. Because of the poor solubility of celecoxib and budesonide, permeability studies were conducted with 5% wt/vol of hydroxypropyl-beta-cyclodextrin (HPbetaCD). For other solutes, permeability studies were conducted, with and without HPbetaCD. Partitioning of the solutes into bovine sclera and choroid-Bruch's layer was also determined.

RESULTS

The calculated log (distribution coefficient) values were -2.89, -0.68, 2.18, 3.12, and 4.02 for mannitol, sodium fluorescein, budesonide, celecoxib, and rhodamine 6G, respectively. Removal of RPE was confirmed by transmission electron microscopy and differences in the transport of mannitol. The order of the permeability coefficients (Papp) across sclera and sclera-choroid-Bruch's layers in bovine and porcine models was 3H-mannitol > fluorescein > budesonide > celecoxib > rhodamine 6G, with HPbetaCD, and 3H-mannitol > fluorescein > rhodamine 6G, without HPbetaCD. The presence of choroid-Bruch's layer reduced the bovine scleral permeability by 2-, 8-, 16-, 36-, and 50-fold and porcine tissue permeability by 2-, 7-, 15-, 33-, and 40-fold, respectively, for mannitol, sodium fluorescein, budesonide, celecoxib, and rhodamine 6G. The partition coefficients measured in bovine tissues correlated positively with the log (distribution coefficient) and exhibited a trend opposite that of transport. The partition coefficient ratio of bovine choroid-Bruch's layer to sclera was approximately 1, 1.5, 1.7, 2, and 3.5, respectively, for the solutes, as listed earlier.

CONCLUSIONS

The choroid-Bruch's layer is a more significant barrier to drug transport than is sclera. It hinders the transport of lipophilic solutes, especially a cationic solute, more than hydrophilic solutes and in a more dramatic way than does sclera. The reduction in transport across this layer directly correlates with solute binding to the tissue. Understanding the permeability properties of sclera and underlying layers would be beneficial in designing better drugs for transscleral delivery.

Nanoparticle formulation enhances the delivery and activity of a vascular endothelial growth factor antisense oligonucleotide in human retinal pigment epithelial cells

The objective of this study was to investigate the delivery and activity of a vascular endothelial growth factor (VEGF) antisense oligonucleotide in a human retinal pigment epithelial cell line (ARPE-19) using a biodegradable nanoparticulate delivery system. A 19-mer antisense phosphorothioate oligonucleotide (PS-ODN) complementary to bases 6-24 relative to the translational start site of the VEGF mRNA, a sense PS-ODN and a mismatch PS-ODN were examined for the inhibition of secretion and mRNA expression of VEGF using an enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction, respectively. Nanoparticles of the antisense oligonucleotides were formulated using a poly(lactide-co-glycolide) (50:50) copolymer using a double emulsion solvent evaporation method. After preparing nanoparticles, drug loading, encapsulation efficiency and particle size were determined. The cells were exposed to either plain solution of oligonucleotide or nanoparticles of oligonucleotide from Day 3 through Day 6. Alternatively, the cells were incubated with PS-ODNs and lipofectin for 4 h on Day 4. In all studies, VEGF secretion and mRNA expression were determined on Day 6. The particle size, drug loading and encapsulation efficiency were 252 nm, 5.5% and 16.5%, respectively. The antisense PS-ODN inhibited VEGF mRNA and protein secretion when delivered using nanoparticles or lipofectin but not in its free form. This was consistent with the ability of nanoparticles and lipofectin to elevate the cellular uptake of the oligonucleotide by 4-fold and 13-fold, respectively. Neither mismatch nor sense oligonucleotides inhibited VEGF secretion. In conclusion, biodegradable nanoparticles enhance cellular delivery of a VEGF antisense oligonucleotide and inhibit VEGF secretion and mRNA expression in a human retinal pigment epithelial cell line.