Therapeutic potential of Pirfenidone for treating equine corneal scarring

Corneal fibrosis: From in vitro models to current and upcoming drug and gene medicines

Fibrotic diseases are characterised by myofibroblast differentiation, uncontrolled pathological extracellular matrix accumulation, tissue contraction, scar formation and, ultimately tissue / organ dysfunction. The cornea, the transparent tissue located on the anterior chamber of the eye, is extremely susceptible to fibrotic diseases, which cause loss of corneal transparency and are often associated with blindness. Although topical corticosteroids and antimetabolites are extensively used in the management of corneal fibrosis, they are associated with glaucoma, cataract formation, corneoscleral melting and infection, imposing the need of far more effective therapies. Herein, we summarise and discuss shortfalls and recent advances in in vitro models (e.g. transforming growth factor-β (TGF-β) / ascorbic acid / interleukin (IL) induced) and drug (e.g. TGF-β inhibitors, epigenetic modulators) and gene (e.g. gene editing, gene silencing) therapeutic strategies in the corneal fibrosis context. Emerging therapeutical agents (e.g. neutralising antibodies, ligand traps, receptor kinase inhibitors, antisense oligonucleotides) that have shown promise in clinical setting but have not yet assessed in corneal fibrosis context are also discussed.

Elucidating the mechanism of corneal epithelial cell repair: unraveling the impact of growth factors

The repair mechanism for corneal epithelial cell injuries encompasses migration, proliferation, and differentiation of corneal epithelial cells, and extracellular matrix remodeling of the stromal structural integrity. Furthermore, it involves the consequential impact of corneal limbal stem cells (LSCs). In recent years, as our comprehension of the mediating mechanisms underlying corneal epithelial injury repair has advanced, it has become increasingly apparent that growth factors play a pivotal role in this intricate process. These growth factors actively contribute to the restoration of corneal epithelial injuries by orchestrating responses and facilitating specific interactions at targeted sites. This article systematically summarizes the role of growth factors in corneal epithelial cell injury repair by searching relevant literature in recent years, and explores the limitations of current literature search, providing a certain scientific basis for subsequent basic research and clinical applications.

Pirfenidone: A Promising Drug in Ocular Therapeutics

Pirfenidone, initially indicated for lung fibrosis, has gone beyond its original purpose, and shown promise in eye care. This detailed review tracks its evolution from lung treatment to aiding eye healing as evidenced by published literature. Pirfenidone's multifaceted attributes extend to mitigating corneal fibrosis, inflammation, and trauma. Through rigorous investigations, its efficacy emerges in diabetic retinopathy, macular degeneration, and postoperative glaucoma interventions. As an unheralded protagonist, pirfenidone reshapes ocular care paradigms, inviting renewed research opportunities.

Antifibrotic Effects of Caffeine, Curcumin and Pirfenidone in Primary Human Keratocytes

We evaluated the small molecules (AFM) caffeine, curcumin and pirfenidone to find non-toxic concentrations reducing the transformation of activated human corneal stromal keratocytes (aCSK) to scar-inducing myofibroblasts (MYO-SF). CSK were isolated from 16 human corneas unsuitable for transplantation and expanded for three passages in control medium (0.5% FBS). Then, aCSK were exposed to concentrations of caffeine of 0−500 μM, curcumin of 0−200 μM, pirfenidone of 0−2.2 nM and the profibrotic cytokine TGF-β1 (10 ng/mL) for 48 h. Alterations in viability and gene expression were evaluated by cell viability staining (FDA/PI), real-time polymerase chain reaction (RT-PCR) and immunocytochemistry. We found that all AFMs reduced cell counts at high concentrations. The highest concentrations with no toxic effect were 100 µM of caffeine, 20 µM of curcumin and 1.1 nM of pirfenidone. The addition of TGF-β1 to the control medium effectively transformed aCSK into myofibroblasts (MYO-SF), indicated by a 10-fold increase in α-smooth muscle actin (SMA) expression, a 39% decrease in lumican (LUM) expression and a 98% decrease in ALDH3A1 expression (p < 0.001). The concentrations of 100 µM of caffeine, 20/50 µM of curcumin and 1.1 nM of pirfenidone each significantly reduced SMA expression under TGF-β1 stimulation (p ≤ 0.024). LUM and ALDH3A1 expression remained low under TGF-β1 stimulation, independently of AFM supplementation. Immunocytochemistry showed that 100 µM of caffeine, 20 µM of curcumin and 1.1 nM of pirfenidone reduce the conversion rate of aCSK to SMA+ MYO-SF. In conclusion, in aCSK, 100 µM of caffeine, 20 µM of curcumin and 1.1 nM of pirfenidone significantly reduced SMA expression and MYO-SF conversion under TGF-β1 stimulation, with no influence on cell counts. However, the AFMs were unable to protect aCSK from characteristic marker loss.

Evaluation of CRISPR/Cas9 mediated TGIF gene editing to inhibit corneal fibrosis in vitro

Corneal wound healing is influenced by many factors including transcriptional co-repressors and co-activators. Interactions of co-activators and co-repressors with Smads influence mechanistic loop facilitating transcription of alpha-smooth muscle actin (α-SMA), a key profibrotic gene, in corneal repair. The role of a transcriptional repressor, 5'TG3'-interacting factor (TGIF), in the regulation of α-SMA and myofibroblast formation in the cornea was shown previously by our group. This study tested a hypothesis if TGIF1 gene editing via CRISPR/Cas9 can ease myofibroblast formation in the cornea using an in vitro model. Primary human corneal stromal fibroblasts (hCSFs) generated from donor corneas received gene-editing plasmid facilitating loss (CRISPR/Cas9 knockout) or gain (CRISPR activation) of TGIF function by UltraCruz transfection reagent. Phase-contrast microscopy, immunoblotting, immunocytochemistry and quantitative polymerase chain reaction (qPCR) were used to measure levels of myofibroblast profibrotic genes (α-SMA, fibronectin, Collagen-I, and Collagen-IV) in hCSFs lacking or overexpressing TGIF1 after growing them in± transforming growth factor beta1 (TGF-β1) under serum-free conditions. The CRISPR-assisted TGIF1 activation (gain of function) in hCSFs demonstrated significantly decreased myofibroblast formation and messenger ribonucleic acid (mRNA) and protein levels of profibrotic genes. Conversely, CRISPR/Cas9-assisted TGIF knockdown (loss of function) in hCSFs demonstrated no significant change in the levels of myofibroblast formation or profibrotic genes under similar conditions. These results suggest that TGIF gene-editing approach can be employed to modulate the transcriptional activity of α-SMA in controlling pathological and promoting physiological wound healing in an injured cornea.

Evaluation of a novel combination of TRAM-34 and ascorbic acid for the treatment of corneal fibrosis in vivo

Corneal injury and aberrant wound healing commonly result in corneal fibrosis and subsequent vision loss. Intermediate-conductance calmodulin/calcium-activated K+ channels (KCa3.1) have been shown to promote fibrosis in non-ocular and ocular tissues via upregulation of transforming growth factor beta (TGFβ). TRAM-34 is a selective inhibitor of KCa3.1 and reduces fibrosis by downregulation of TGFβ-induced transdifferentiation of stromal fibroblasts to myofibroblasts. Ascorbic acid has been demonstrated to be effective in promoting corneal re-epithelialization and reduction of neovascularization via anti-VEGF and anti-MMP mechanisms. This study evaluates tolerability and efficacy of a novel combination of TRAM-34 (25μM) and ascorbic acid (10%) topical treatment for corneal fibrosis using an established in vivo rabbit model and conducting clinical eye examinations. Markers of corneal fibrosis were evaluated in all corneas at study endpoint via histopathology, immunofluorescence, and quantitative real-time PCR. The eyedrop treated eyes showed significantly improved clinical outcomes based on modified McDonald Shadduck scores, reduction of clinical haze on Fantes scores, and reduction of central corneal thickness (CCT). At cellular and molecular levels, eyedrop treatment also significantly reduced expression of alpha smooth muscle actin (α-SMA) mRNA and protein, collagen III mRNA, and fibronectin mRNA compared to non-treated eyes. Our study suggests that a tested new bimodal eyedrop is well tolerated and effectively reduces corneal fibrosis/haze in rabbits in vivo.

[Pirfenidone inhibits proliferation of rabbit tenon fibroblasts by down-regulating TGF-β3 in the TGF-β/Smad pathway]

OBJECTIVE

To investigate the molecular mechanism by which pirfenidone inhibits scar formation through the TGF-β/Smad pathway.

METHODS

Cultured rabbit tenon fibroblasts (RTFs) were treated with different concentrations of pirfenidone to determine its initial active concentration and optimum concentration of pirfenidone for inhibiting RTF proliferation using CCK-8 assay. In RTFs treated with pirfenidone at the initial and optimal concentrations, expressions of TGF-β3, collagen I and collagen III were examined with both immunofluorescence assay and Western blotting, and their mRNA expression levels were detected using RT-PCR.

RESULTS

The initial and optimal concentrations of pirfenidone for inhibiting RTF proliferation were 0.1 mg/mL and 0.27 mg/mL, respectively. In RTFs treated with pirfenidone at the two concentrations for 24 h, both immunofluorescence assay and Western blotting showed significantly lowered protein expressions of TGF-β3, collagen I and collagen III as compared with those in the control group (P < 0.05). The mRNA expressions of TGF-β3, collagen I and collagen III in the RTFs were also significantly lowered after treatment with pirfenidone at the initial and optimal concentrations (P < 0.05).

CONCLUSIONS

Pirfenidone concentration-dependently inhibits the proliferation of RTFs possibly by down-regulating the expression of TGF-β3 in the TGF-β/Smad pathway.

Comparative Analysis of KGF-2 and bFGF in Prevention of Excessive Wound Healing and Scar Formation in a Corneal Alkali Burn Model

PURPOSE

Basic fibroblast growth factor (bFGF) is an effective drug for corneal injury. However, the explicit role of bFGF in corneal scar formation still remains unclear. Keratinocyte growth factor-2 (KGF-2) is associated with the treatment of wound healing. We aimed to compare the efficacy of bFGF and KGF-2 in prevention of excessive wound healing and consequent scar formation in a rat alkali burn model, which provides important clues on the significance of KGF-2 to be developed as a new drug for such injuries.

METHODS

The epithelial defect area was evaluated using fluorescein sodium at a concentration of 0.5%. The therapeutic effect of KGF-2 and bFGF on proliferation of rabbit corneal fibroblasts (RCFs) was evaluated by methylthiazoletetrazolium. RCF migration assays were performed with a modified scratch method. Activation of mitogen-activated protein kinase (MAPK) was evaluated by Western blot with specific antibodies.

RESULTS

All corneal wounds treated with KGF-2 were found closed within 7 days; however, the wounds treated with bFGF or phosphate buffer saline (PBS) required 14 days to close. RCFs treated with KGF-2 or bFGF showed similar dose-dependent proliferation. The KGF-2 group significantly promoted cell migration compared with the bFGF group. The KGF-2 group showed less expression of α-smooth muscle actin (SMA) and numbers of myofibroblasts compared with the bFGF group. Our findings suggested identification of cascade reaction of extracellular regulated protein kinases (ERK)1/2 and p38 signals in KGF-2- and bFGF-induced proliferation and migration of RCFs. In addition, KGF-2 showed stronger effects during ERK1/2 and p38 phosphorylation in methylthiazoletetrazolium proliferation assay and scratch migration assay.

CONCLUSIONS

KGF-2 exhibited better effects than bFGF in reepithelialization, acceleration of migration, and reduction of scar formation, which has potential to become a new drug to cure corneal injury.

The role of pirfenidone in alkali burn rat cornea

To evaluate the effects of pirfenidone in the treatment of HUVEC using an in vitro model and on rat corneal wound healing, edema, cornea neovascularization (CNV) and inflammation after alkali burn in vivo model. In vitro, CCK-8 assay was used to detect the effect of pirfenidone on the viability of HUVECs. The effects of pirfenidone on migration and tube formation of HUVEC were evaluated by HUVEC cell wound closure and tube formation assay. In vivo, Eye drops containing pirfenidone or phosphate buffered saline (PBS) were administered to an alkali-burn-induced corneal inflammatory and neovascularization model four times daily. The clinical evaluations, including fluorescent staining and cornea edema, were performed on days 1, 4, 7 and 14 using slit lamp microscopy. Global specimens were collected on day 7 and processed for immunofluorescent staining Collagen IV, α-smooth muscle actin (α-SMA), vascular endothelial growth factor (VEGF), pigment epithelium derived factor (PEDF) and cluster of differentiation34 (CD34). The levels of α-SMA, VEGF, PEDF, CD34, CD31 and nuclear factor-kappa B (NF-κB) proteins in the corneas were determined by western blot. Pirfenidone affects HUVEC viability, migration and tube formation in a dose-dependent manner. High concentration of pirfenidone can inhibit HUVEC viability, migration and tube formation in vitro and reduce alkali burn rat cornea edema, promote corneal wound healing, inhibit CNV and inflammation after alkali burn in vivo. Pirfenidone promotes corneal wound healing, and inhibits cornea neovascularization and inflammation after alkali burn in vitro and in vivo. Pirfenidone may be the potential anti-inflammation agent for the clinical treatment of CNV.

Efficacy and Safety Comparison Between Suberoylanilide Hydroxamic Acid and Mitomycin C in Reducing the Risk of Corneal Haze After PRK Treatment In Vivo

PURPOSE

This study compared the efficacy and safety of suberoylanilide hydroxamic acid (SAHA) and mitomycin C (MMC) up to 4 months in the prevention of corneal haze induced by photorefractive keratectomy (PRK) in rabbits in vivo.

METHODS

Corneal haze in rabbits was produced with -9.00 diopter PRK. A single application of SAHA (25 μM) or MMC (0.02%) was applied topically immediately after PRK. Effects of the two drugs were analyzed by slit-lamp microscope, specular microscope, TUNEL assay, and immunofluorescence.

RESULTS

Single topical adjunct use of SAHA (25 μM) or MMC (0.02%) after PRK attenuated more than 95% corneal haze and myofibroblast formation (P < .001). SAHA did not reduce keratocyte density, cause keratocyte apoptosis, or increase immune cell infiltration compared to MMC (P < .01 or .001). Furthermore, SAHA dosing did not compromise corneal endothelial phenotype, density, or function in rabbit eyes, whereas MMC application did (P < .01 or .001).

CONCLUSIONS

SAHA and MMC significantly decreased corneal haze after PRK in rabbits in vivo. SAHA exhibited significantly reduced short- and long-term damage to the corneal endothelium compared to MMC in rabbits. SAHA is an effective and potentially safer alternative to MMC for the prevention of corneal haze after PRK. Clinical trials are warranted. [J Refract Surg. 2017;33(12):834-839.].

Pirfenidone reduces subchondral bone loss and fibrosis after murine knee cartilage injury

Pirfenidone is an anti-inflammatory and anti-fibrotic drug that has shown efficacy in lung and kidney fibrosis. Because inflammation and fibrosis have been linked to the progression of osteoarthritis, we investigated the effects of oral Pirfenidone in a mouse model of cartilage injury, which results in chronic inflammation and joint-wide fibrosis in mice that lack hyaluronan synthase 1 (Has1^-/- ) in comparison to wild-type. Femoral cartilage was surgically injured in wild-type and Has1^-/- mice, and Pirfenidone was administered in food starting after 3 days. At 4 weeks, Pirfenidone reduced the appearance, on micro-computed tomography, of pitting in subchondral bone at, and cortical bone surrounding, the site of cartilage injury. This corresponded with a reduction in fibrotic tissue deposits as observed with gross joint surface photography. Pirfenidone resulted in significant recovery of trabecular bone parameters affected by joint injury in Has1^-/- mice, although the effect in wild-type was less pronounced. Pirfenidone also increased Safranin-O staining of growth plate cartilage after cartilage injury and sham operation in both genotypes. Taken together with the expression of selected extracellular matrix, inflammation, and fibrosis genes, these results indicate that Pirfenidone may confer chondrogenic and bone-protective effects, although the well-known anti-fibrotic effects of Pirfenidone may occur earlier in the wound-healing response than the time point examined in this study. Further investigations to identify the specific cell populations in the joint and signaling pathways that are responsive to Pirfenidone are warranted, as Pirfenidone and other anti-fibrotic drugs may encourage tissue repair and prevent progression of post-traumatic osteoarthritis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:365-376, 2018.

Altering equine corneal fibroblast differentiation through Smad gene transfer

OBJECTIVE

To explore the impact of equine corneal fibroblast (ECF) to myofibroblast (ECM) differentiation by altering the expression of the Smad genes either individually or in combination. Specifically, we sought to examine the ECF differentiation after (a) silencing of Smad2, 3, and 4 profibrotic genes individually and (b) overexpression of antifibrotic Smad7 gene and in a combination with pro- and antifibrotic Smad genes.

METHODS

Equine corneal fibroblast primary cultures were generated as previously described. ECFs were transfected with individual plasmids which silenced gene expression of either Smad2, 3, or 4 or in combination with a plasmid overexpressing Smad7 using Lipofectamine 2000™ or Lipofectamine BLOCK-iT™. Smad-transfected clones were then exposed to TGF-β1 to induce differentiation to myofibroblasts. Immunofluorescence and qRT-PCR techniques quantified levels of ECF differentiation to ECM by measuring alpha smooth muscle actin, a known marker of ECM transdifferentiation.

RESULTS

Silencing of individual Smad2, 3, or 4 genes or overexpression of Smad7 showed significant inhibition of ECF transdifferentiation (73-83% reduction). Silencing of Smad2 showed the greatest inhibition of ECF transdifferentiation in (a) and was therefore utilized for the combination gene transfer testing. The combination gene transfer consisting of Smad7 overexpression and Smad2 silencing attenuated ECF differentiation significantly; however, the level was not significant compared to the overexpression of Smad7 individually.

CONCLUSIONS

Using gene transfer technology involving profibrotic Smad silencing, antifibrotic Smad overexpression or its combination is a novel strategy to control TGF-β1-mediated fibrosis in equine fibroblasts. Combination gene therapy was not better than single gene therapy in this study.

Development of a novel ex vivo equine corneal model

OBJECTIVE

To develop an ex vivo equine corneal organ culture model. Specifically, to assess the equine cornea's extracellular matrix and cellularity after 7 days using two different culture techniques: either (i) immersion system or (ii) air/liquid interface system, to determine the best ex vivo equine corneal model.

ANIMALS STUDIED

Fourteen healthy equine corneas of various breeds.

PROCEDURES

Equine corneas with 2 mm of perilimbal sclera were freshly harvested from 7 horses undergoing humane euthanasia. One corneal-scleral ring (CSR) from each horse was randomly placed in the (i) immersion condition organ culture system (IC), with the contralateral CSR being placed in the (ii) air/liquid interface organ culture system (ALC) for 7 days. All corneas were evaluated using serial daily gross photography, histology, qPCR, and TUNEL assay.

RESULTS

corneal-scleral rings placed in the IC (i) had complete loss of corneal transparency on gross photography by 7 days, showed a significant level of corneal stromal disorganization, significantly increased α-SMA levels on qPCR, and apoptosis on TUNEL assay compared to controls. The ALC (ii) had weak stromal disorganization on histopathologic examination and was not significantly different from normal equine corneal controls on all other evaluated parameters.

CONCLUSIONS

The air-liquid interface organ culture system maintains the equine cornea's extracellular matrix and preserves corneal transparency, while the immersion condition results in near complete degradation of normal equine corneal architecture after 7 days in culture. The air-liquid organ culture is a viable option to maintain a healthy equine cornea in an ex vivo setting for wound healing studies.