Rabbit Conjunctival Fibroblasts Research Articles

Anti-fibrosis potential of pirarubicin via inducing apoptotic and autophagic cell death in rabbit conjunctiva

This study investigated the potential efficacy of pirarubicin (THP) in modulating rabbit conjunctival fibrosis both in vitro and in vivo and characterized the underlying mechanisms. Primary rabbit conjunctival fibroblasts (RCF) were cultured and treated with THP or mitomycin C (MMC) for 5 min, followed by assaying for cell viability, cell cycle distribution, apoptotic and autophagic pathways. The production of reactive oxygen species (ROS) and chemotaxis of macrophages by RCF were evaluated using 2′,7′-dichlorofluorescein diacetate (DCFH-DA) labeling and transwell migration assay, respectively. Limbal stem cell excision in combination with alkali burn was performed on the rabbits to establish a model of limbal deficiency and conjunctival fibro-vascular invasion. After three months, the modeled fibro-vascular tissue was excised combined with topical subconjunctival 5-min exposure to THP compared with MMC intraoperatively. The recurrence of postoperative fibrosis and the expression of apoptosis, autophagy, and inflammation markers were evaluated by immunohistochemistry. All modeled rabbits developed conjunctival fibro-vascular lesions, which were similar to human recurrent pterygium (HRP). Both THP and MMC inhibited RCF proliferation and arrested cell cycle at the G0/G1 phase. In particular, 7.5 μmol/L THP remarkably promoted RCF autophagy by upregulating the levels of Beclin 1, Atg 5/12 conjugate, and LC3B, whereas, 15 μmol/L THP significantly triggered a cascade of mitochondrial-associated RCF apoptosis. THP induced the production of ROS and enhanced the chemoattraction of macrophages by RCF. Similar to 600 μmol/L MMC, both 7.5 μmol/L and 15 μmol/L THP attenuated postoperative conjunctival fibrosis in the models; 7.5 μmol/L THP preferentially enhanced autophagy while causing fewer side effects. THP exerted its antifibrotic action by modulating autophagy in RCF, inducing cell cycle arrest, and mitochondrial-mediated apoptosis. THP at the dose of 7.5 μmol/L prevented postoperative conjunctival fibrosis in an animal model.

Transforming Growth Factor β1-Induced NADPH Oxidase-4 Expression and Fibrotic Response in Conjunctival Fibroblasts.

Fibrotic scarring after ocular surgeries and chemical burn injuries can impede clarity of the cornea and cause vision impairment. Transforming growth factor β (TGFβ) signaling pathway is known to mediate fibrotic scarring, and NADPH oxidase-derived reactive oxygen species has been shown to be an effector molecule that facilitates TGFβ1-mediated responses. The present study explores the expression profile and functional importance of NADPH oxidase (Nox) in conjunctival fibroblasts. In addition, the effect of curcumin on the TGFβ1-induced NADPH oxidase expression and collagen synthesis was also investigated. The mRNA expression of Nox isoforms in rabbit conjunctival fibroblasts was measured by real-time PCR. The production of hydrogen peroxide (H2O2) and total collagen by these cells was measured by Amplex Red assay and Picro-Sirius red assay, respectively. Nox4 was knocked down by adenovirus-mediated siRNA targeting Nox4 (Adv-Nox4i). We describe for the first time that conjunctival fibroblasts express mRNA encoding for Nox2, Nox3, Nox4, and Nox5. TGFβ1 was found to induce Nox4 mRNA expression and total collagen release by these cells (P < 0.05; n = 4), and both responses are blocked by Smad3 inhibitor SIS3. Suppressing Nox4 gene transcription with Adv-Nox4i completely attenuated TGFβ1-stimulated H2O2 release and collagen production by conjunctival fibroblasts (P < 0.05; n = 4-6). Similarly, curcumin also inhibited TGFβ1-induced Smad3 phosphorylation, Nox4-derived H2O2 production, and total collagen synthesis by conjunctival fibroblasts (P < 0.05; n = 4-6). The present study suggests that TGFβ1-mediated production of collagen by conjunctival fibroblasts involves Nox4-derived H2O2 pathway and this effect of Nox4 is abrogated by curcumin. This mechanism might be exploited to prevent fibrotic scarring after surgeries and chemical burn injuries in the eye.

Ranibizumab Is a Potential Prophylaxis for Proliferative Vitreoretinopathy, a Nonangiogenic Blinding Disease

Proliferative vitreoretinopathy (PVR) exemplifies a disease that is difficult to predict, lacks effective treatment options, and substantially reduces the quality of life of an individual. Surgery to correct a rhegmatogenous retinal detachment fails primarily because of PVR. Likely mediators of PVR are growth factors in vitreous, which stimulate cells within and behind the retina as an inevitable consequence of a breached retina. Three classes of growth factors [vascular endothelial growth factor A (VEGF-A), platelet-derived growth factors (PDGFs), and non-PDGFs (growth factors outside of the PDGF family)] are relevant to PVR pathogenesis because they act on PDGF receptor α, which is required for experimental PVR and is associated with this disease in humans. We discovered that ranibizumab (a clinically approved agent that neutralizes VEGF-A) reduced the bioactivity of vitreous from patients and experimental animals with PVR, and protected rabbits from developing disease. The apparent mechanism of ranibizumab action involved derepressing PDGFs, which, at the concentrations present in PVR vitreous, inhibited non-PDGF-mediated activation of PDGF receptor α. These preclinical findings suggest that available approaches to neutralize VEGF-A are prophylactic for PVR, and that anti-VEGF-based therapies may be effective for managing more than angiogenesis- and edema-driven pathological conditions.

A Potential Role for PDGF-C in Experimental and Clinical Proliferative Vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is a disorder characterized by the formation of cellular membranes on both surfaces of the retina and within the vitreous cavity. It occurs in 5% to 10% of patients who undergo retinal reattachment surgery. In the rabbit model of the disease, the platelet-derived growth factor alpha receptor (PDGFRalpha) is dramatically more capable of promoting PVR than is closely related PDGFRbeta. To test the ligand hypothesis (i.e., that this phenomenon can be explained by a predominance of PDGFRalpha-specific ligands) this study was conducted to determine the profile of PDGF ligands expressed by cells that induce PVR and in the vitreous of rabbits that have PVR. In addition, we examined which PDGF isoforms were present in the vitreous of patients with PVR, to assess the relevance of the rabbit model to the clinical setting. PDGF isoforms were detected and quantified by Western blot analysis and ELISA. An assay was performed of conditioned medium from mouse embryo fibroblasts expressing the PDGFRalpha (Falpha) and rabbit conjunctival fibroblasts (RCFs), both of which cause PVR in the experimental model, and from human retinal pigment epithelial cells (ARPE-19). Because PDGF-C is secreted in a latent form and must be proteolytically processed to become biologically active, a PDGF-C processing assay was established, and conditioned medium was tested from these cells lines, for processing activity. Vitreous specimens, from control and PVR rabbits and from patients undergoing vitrectomy surgery, either to repair retinal detachment or for other reasons, were also tested for PDGF isoforms and for PDGF-C processing activity. PDGF isoforms that activate PDGFRbeta (PDGF-B and -D) were either undetectable or were present at very low levels in all the samples tested. Relatively low levels of PDGF-A and -AB were detected, whereas PDGF-C was the predominant isoform. Falpha, RCFs, and ARPE-19 cells accumulated PDGF-C in the conditioned medium at an average rate of 2.0 +/- 0.2, 2.9 +/- 0.3, and 71.3 +/- 6.0 ng/mL per day, respectively. Although there was no detectable PDGF-C in the vitreous of control rabbits (n = 8), there was an average of 1784 +/- 1150 ng/mL latent PDGF-C in the vitreous from rabbits with PVR (n= 14). Of the patients with PVR, eight of nine contained PDGF-C (range, 50-1000 ng/mL). In contrast, PDGF-C was detected in only 1 of 16 of the patients without PVR. In both conditioned medium and vitreous samples, the latent (instead of the active) form of PDGF-C was detected, even though processing activity was present in all the samples tested. The predominance of PDGF isoforms that activate PDGFRalpha support the ligand hypothesis as an explanation of why PDGFRalpha is more capable of inducing PVR than is PDGFRbeta. Furthermore, the profile of PDGF isoforms observed in the rabbit model accurately reflected the clinical specimens from patients with PVR. Finally, these findings implicate one of the new PDGF family members as an important contributor to experimental and clinical PVR.

Enhancement of the Mechanical and Biological Properties of a Biomembrane for Tissue Engineering the Ocular Surface

In this study, we have developed and optimised a novel gelatin-chitosan (GC) substrate for use as a cellular carrier for tissue-engineered conjunctival epithelium. The substrate was fabricated by casting and the mechanical properties of the substrate, including tensile strength and elongation, were measured. Using the MTT, cell proliferation assay with rabbit conjunctival fibroblasts, we optimised the G:C ratio to enhance cytocompatibility. Rabbit conjunctival epithelial cells were immunostained using monoclonal antibodies for keratin 4 and pancytokeratin to investigate the biological effects of the GC substrate on the proliferation and differentiation of epithelial cells. We found that increasing the amount of gelatin resulted in an increase in elasticity (from 1:9 to 1:1 ratio), reaching a maximum (101.89% +/- 7.13%) at a ratio of 1:1. The MTT assay showed that the proliferation of conjunctival fibroblasts significantly increased from 0.068 +/- 0.017 to 0.177 +/- 0.011 (P = 0.014) as the gelatin was increased from 20% (1:4) to 50% (1:1). Additional studies using tissue-cultured conjunctiva explants showed that these explants grew well on the substrate, forming a multilayered epithelium. Cell morphology on this substrate was similar to that of cells grown on culture dishes alone. Positive staining of keratin 4 and pancytokeratin indicated that the substrate supported normal differentiation of conjunctival epithelial cells. By enhancing the proportion of gelatin, both the mechanical and biological properties of the chitosan substrate were improved. The results also suggest that this GC biomembrane may be a useful candidate for reconstructive tissue engineering of the conjunctiva.

Platelet-derived Growth Factor Receptor Kinase Inhibitor AG1295 and Inhibition of Experimental Proliferative Vitreoretinopathy

Purpose: Receptor tyrosine kinase (RTK) activation is critical for growth factor-mediated cell proliferation. The present study was designed to determine the effect of tyrphostin AG1295, a selective blocker of platelet-derived growth factor (PDGF) RTK, on proliferative vitreoretinopathy (PVR) development. Methods: Rabbit conjunctival fibroblasts cells (1 × 10 4) were seeded into 96-well plates and maintained in Dulbecco's modified essentialmedium (DMEM) with 0.5% fetal bovine serum. The cells were exposed to 50 ng/mL PDGF-AAor PDGF-BBor phosphate-buffered saline with or without AG1295 (1 μM, 10 μM, and 100 μM). After 3 days, the viable cells in each well were measured by 3,(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Homologous rabbit conjunctival fibroblasts were injected intravitreally, followed by injection of 100 μM of AG1295. The development of tractional retinal detachment (TRD) was assessed to evaluate the effect of AG1295 in vivo. Electroretinography and histologic studies were performed after intravitreal injection of AG1295 into untreated eyes to evaluate toxicity. Results: Two concentrations of AG1295 (10 and 100 μM) significantly inhibited rabbit conjunctival fibroblast cell growth stimulated by PDGF-AA or PDGF-BB in vitro. Development of TRD was significantly attenuated ( P < .01) with 100 μM of AG1295 until day 21. No significant histologic or retinal functional damage was found in the AG1295-treated group. Conclusions: PDGF receptor specific inhibitor AG1295 attenuated PVR without significant side effects in rabbits. This reagent could be a useful treatment to prevent PVR.

Gene transfer of soluble TGF-beta type II receptor inhibits experimental proliferative vitreoretinopathy.

This study was conducted to investigate a method of gene therapy for proliferative vitreoretinopathy (PVR) by inhibiting type beta transforming growth factor (TGF-beta). PVR was induced in pigmented rabbits by intravitreal injection of 50 000 rabbit conjunctival fibroblasts after vitrectomy. Subsequently, the eyes received an intravitreal application of adenovirus vector encoding a soluble type II TGF-beta receptor (AdTbeta-ExR, n = 10) or adenoviral vector expressing beta-galactosidase (AdLacZ) (n = 10) or balanced salt solution (BSS) (n = 6). The eyes were examined ophthalmoscopically for 28 days after surgery, and the clinical stage of PVR was evaluated on a scale of zero to five. Histological examinations were performed on the treated eyes on day 28. All control eyes injected with AdLacZ or BSS developed PVR, characterized by retinal detachment and the formation of intravitreal membranes within 7 days. The eyes injected with AdTbeta-ExR also developed features of PVR, but the average severity from day 5 to day 28 was significant lower than in the control eyes (P < 0.05). TGF-beta plays an important role in PVR progression in a PVR model, and prevention of TGF-beta signaling could be therapeutically useful.

The antidepressant hypericin inhibits progression of experimental proliferative vitreoretinopathy

PURPOSE. Hypericin, a polycyclic dione used as an antidepressant, has been shown to inhibit the protein kinase C (PKC) pathway. Many of the pathologic responses found in proliferative vitreoretinopathy (PVR) are dependent upon PKC. Therefore, we studied the effect of hypericin on the treatment of experimental PVR. METHODS. PVR was induced in pigmented rabbits by intravitreal injection of 50,000 rabbit conjunctival fibroblasts after vitrectomy. Subsequently, the eyes received an intravitreal injection of either balanced salt solution (BSS, 0.1 mL) (group A, control) or hypericin (0.1 mL) in doses of 1 µM (group B), 10 µM (group C), and 100 µM (group D). The eyes were examined ophthalmoscopically on days 1, 3, 7, 14, and 28 after surgery and the stage of PVR was evaluated (0 to V). The effect of hypericin on retinal morphology and function was also determined for the eyes injected with 100 µM hypericin with no fibroblasts by light microscopy and electroretinogram (ERG). RESULTS. In the control eyes, the retina was detached after 5 days, membranes had formed on and beneath it, and the PVR had progressed to higher stages over time. In the eyes injected with hypericin, the PVR also progressed; however, the severity of PVR on each day was lower than that in control eyes on that day. PVR was significantly inhibited in groups C and D as compared with the control eyes after day 5 (P < 0.05). Histological examination of the hypericin-treated control eyes disclosed no morphological change, and ERG analysis revealed no significant functional change. CONCLUSIONS. Intravitreal injection of hypericin is a safe and effective means of reducing experimental PVR.

N-linked glycoside and glucuronide conjugates of the retinoid, acitretin, are biologically active in cornea and conjunctiva.

The purpose of this study was to test two water-soluble, synthetic retinoids, glucoseamido acitretin and glucuronamido acitretin, for biological activity in cells of the cornea and conjunctiva. Vitamin A-deficient, xerophthalmic rats were treated topically with these retinoids, and corneas were examined histologically for effects on epithelial keratinization. The effect of these retinoids on the proliferation of rabbit conjunctival fibroblasts in culture was also investigated. Glucoseamido acitretin treatment restored a normal cornea after eight to nine days of treatment, while no improvement was observed in the vehicle-treated corneas. Likewise, glucuronamido acitretin application restored a normal corneal surface and reversed keratinization after eight to ten days of treatment. These retinoids caused no irritation of the eye or ocular adnexa. In culture, exposure of conjunctival fibroblasts to glucoseamide acitretin inhibited cell proliferation. Cultures exposed to glucoseamido acitretin at 10(-8) M or 10(-6) M had cell densities 77.3% and 51.9% of control, respectively, after seven days. Glucuronamido acitretin also inhibited cell proliferation. Cultures exposed to glucuronamido acitretin at 10(-8) M had a cell density of 69.2% of control at day seven, while at 10(-6) M this retinoid completely inhibited cell proliferation. These results show that glucoseamide acitretin and glucuronamido acitretin are biologically active in the cornea and conjunctiva, and may be considered for ophthalmic use in diseases involving abnormalities of ocular surface cell differentiation or hyperproliferation of fibroblasts.

The inhibition of vitamin K3 on rabbit fibroblast proliferation in vitro.

Vitamin K3 that is commonly used to treat hemorrhagic diseases can inhibit human lymphatic neoplasms in vitro. This study was undertaken to investigate the effects of vitamin K3 on rabbit conjunctival fibroblast proliferation in cell culture. Vitamin K3 was added to cultured rabbit conjunctival fibroblasts. Remarkable inhibition was observed at a concentration of 4 mg/l. Because of its lower toxicity, vitamin K3 may prove to be of significant value in the treatment of intraocular proliferative disorders.

Biological activity of N-(4-hydroxyphenyl) retinamide-O-glucuronide in corneal and conjunctival cells of rabbits and humans.

Previous studies of topical retinoic acid for treatment of ocular surface disease met with limited success due to instability and irritancy of the retinoid and lack of efficacy in keratoconjunctivitis sicca. There has, however, been continued interest in the treatment of mucin deficiency and cicatrizing conjunctival diseases, such as ocular cicatricial pemphigoid (OCP), topically with retinoids. In this study the biological activity of stable, water-soluble, synthetic retinoid, N-(4-hydroxyphenyl) retinamide-O-glucuronide (4-HPROG) was investigated in vivo and in vitro using conjunctival and corneal epithelium and fibroblasts. Vitamin A-deficient rabbits with stage 3-4 corneal xerosis and squamous metaplasia confirmed by conjunctival impression cytology were treated with topical 0.1% 4-HPROG in an artificial tear vehicle for 3 weeks. Impression cytology was repeated at 2 and 3 weeks and at 3 weeks conjunctival biopsies were fixed for histology. Growth curves were generated using conjunctival fibroblasts of rabbits and humans (normals and patients with cicatrizing conjunctival disease including OCP and Stevens-Johnson syndrome) cultured in the 10(-8)-10(-6) M 4-HPROG. In vivo, corneal xerosis cleared in three days. A normal conjunctival epithelium was restored by 2 weeks and goblet cells were present by 3 wk, with no change in vehicle-treated controls. No ocular irritation occurred. In vitro, 10(-6) M 4-HPROG inhibits growth of rabbit conjunctival fibroblasts. The retinoid had no effect on proliferation of conjunctival fibroblasts from normal humans but the doubling time of cells from patients with OCP increased significantly, from 50.9 +/- 10.01 h (control) to 61.5 +/- 8.95 h (retinoid). Proliferation of conjunctival fibroblasts from a patient with Stevens-Johnson syndrome was also inhibited. N-(4-hydroxyphenyl) retinamide-O-glucuronide is biologically active and merits further study to determine its efficacy in controlling conjunctival fibrosis and treating ocular surface squamous metaplasia.