Effect of Periplaneta americana Extract on Corneal Fibrosis and Epithelial Healing After Rabbit Lamellar Keratectomy

Abstract

Purpose

To evaluate Periplaneta americana extract (PAE) effects on corneal epithelial healing and fibrosis after superficial lamellar keratectomy (SLK) in rabbits.

Methods

SLK was performed on the right eyes of 48 New Zealand White rabbits, randomized into three treatment groups (n = 16/group): normal saline (NS), Tobradex eye drops (TE), and PAE group. Corneal opacity and epithelial defect area were quantified using slit-lamp imaging at postoperative days 3, 7, 14, and 28 (D3, D7, D14, and D28) and scored via the grading system. We performed histopathological analysis to visualize tissue structure and immunohistochemistry (IHC) localize and quantify TGF-β1 protein in corneal tissues.

Results

Significant intergroup differences in corneal epithelial defect area and opacity were observed on D3 and D7 (all P < 0.05). The TE group exhibited the largest epithelial defects but mildest corneal opacity, whereas the PAE group demonstrated the smallest epithelial defects and significantly reduced opacity compared to the NS group (P < 0.05). Time-dependent variations in epithelial defect area were noted across all groups (P < 0.05). The NS and TE groups displayed progressive corneal opacity increases, whereas the opacity of the PAE group peaked at D7 before declining. Histological analysis revealed epithelial detachment, stromal edema, and inflammatory infiltration in all groups, with the TE group showing milder inflammation. TGF-β1 expression levels initially increased followed by a decline in the NS and PAE groups, in contrast to the inverse trend of the TE group. No statistically significant differences in late-phase corneal opacity or TGF-β1 levels were observed between groups (all P > 0.05).

Conclusions

During the early phase after SLK, PAE accelerated corneal tissue regeneration, inhibited corneal scarring, and partially restored corneal clarity. This biphasic regulatory effect may be attributed to promoting TGF-β1 expression in the early stage, followed by its inhibition in the later stages.

Translational Relevance

PAE modulates TGF-β1 to balance corneal healing and fibrosis as a novel topical corticosteroid alternative, warranting human trials for its dual-phase healing/scarring action.

Introduction

The cornea plays a critical role in maintaining visual function and protecting the ocular surface; however, scarring and structural damage may result from autoimmune disorders, neuropathic conditions, or surgical trauma.¹ Corneal scarring contributes to 35% to 50% of blindness cases globally, affecting millions of individuals and accounting for 3.46% of total blindness worldwide, thereby representing a significant ophthalmic public health challenge.^2,3 Current therapeutic strategies to restore corneal transparency include pharmacological interventions and surgical procedures. Clinically used antifibrotic medications demonstrate suboptimal efficacy and notable side effects, and the most effective corneal transplantation procedures such as phototherapeutic keratectomy and penetrating keratoplasty face challenges including postoperative complications, donor tissue shortages, and infrastructural limitations.⁴ Emerging therapies such as gene therapy,^5,6 protein therapy,^7,8 and biomaterial therapy show promise but remain experimental due to prolonged timelines and cost barriers.⁹ Consequently, there is an urgent need to develop medications that can safely and effectively promote corneal repair while minimizing scar formation and avoiding severe side effects.

Periplaneta americana extract (PAE) is derived from a traditional medicinal insect classified in the order Blattidae (family Blattidae), commonly referred to as the American cockroach. Extensive preclinical studies confirm that PAE exhibits broad-spectrum antifibrotic, anti-inflammatory, antioxidant, and tissue-regenerative properties, with demonstrated efficacy in attenuating fibrosis across multiple organs, including the lungs, liver, and kidneys.¹⁰ Yang et al.¹¹ demonstrated the dual capacity of PAE to accelerate wound healing and prevent scar formation in a rat scald model, highlighting its translational potential for fibrotic disorders. This study pioneered the application of PAE in corneal repair using a rabbit superficial lamellar keratectomy (SLK) model. By directly comparing PAE with Tobradex eye drops (TE; Novartis, Basel, Switzerland), we developed novel mechanistic insights into the efficacy of PAE in corneal wound healing and fibrosis suppression, establishing a preclinical foundation for its therapeutic translation in ocular surface disorders.

Materials and Methods

Rabbit SLK Model

Forty-eight male New Zealand White (NZW) rabbits (6 months old; weight, 2.0–2.4 kg) were selected for the study. The rabbits were acclimatized to a stable environment for a week prior to the experiment. All procedures were approved by the Chengdu University of Traditional Chinese Medicine Animal Ethics Committee (approval no. 2022-34). General anesthesia was induced via intravenous injection of 1% sodium pentobarbital (3 mL/kg; Rongbai Biotechnology Co., Ltd., Yuyao, China) through the marginal ear vein. Local surface anesthesia was induced by instilling oxybuprocaine hydrochloride eye drops (Cravit; Santen Pharmaceutical, Osaka, Japan) into the conjunctival sac of the right eye. An eyelid opener (Eye Source Ophthalmic Medical Devices Co., Ltd., Shanghai, China) was used to fully expose the cornea, followed by central placement of a 7.0-mm sterile corneal trephine (Eye Source Ophthalmic Medical Devices Co., Ltd.) to delineate the surgical area (Fig. 1A). A surgical scalpel (Shanghai Medical Devices Co., Ltd., Shanhai, China) was then used to excise the corneal epithelium and anterior stroma along the markings (Fig. 1B). The left eye served as an untreated control. All rabbits successfully developed the SLK model (Fig. 1C).

Figure 1.

Surgical procedure for the rabbit SLK model. (A) Corneal trephine was used to determine the surgical extent. (B) Scalpel excision of superficial corneal tissue. (C) Successful establishment of the SLK model.

Experimental Grouping and Treatment

After completing the modeling procedure, the experimental animals were randomly allocated to one of three groups: normal saline (NS; Sichuan Kelun Pharmaceutical Co., Ltd., Sichuan, China); TE (S.A. Alcon-Couvreur N.V., Bornem, Belgium); and PAE (Sichuan Good Doctor Panxi Pharmaceutical Co., Ltd., Liangshan, China). Each group had 16 animals. PAE was the manufacturer's original solution, with its pH value and osmotic pressure adjusted. Each group was administered the corresponding eye drops four times daily for 28 consecutive days. To prevent infection, tobramycin ophthalmic ointment (S.A. Alcon-Couvreur N.V.) was applied at night for 14 days, and levofloxacin 0.5% eye drops (Cravit; Santen Pharmaceutical) were administered four times daily for 28 days.

Analysis of Corneal Opacity and Determination of Epithelial Damage Area

On day 3 (D3), D7, D14, and D28 after SLK, the right eye was dilated for 30 minutes using compound tropicamide eye drops (Mydrin; Santen Pharmaceutical). Photographs of the anterior segment of the eye were captured under standardized illumination at 10× magnification using the SL-D7 slit-lamp photographic system (Topcon, Tokyo, Japan), both with and without sodium fluorescein (Mydrin). Corneal opacity was independently scored by three researchers according to the standardized scale shown in Table 1. Three researchers independently used the ImageJ (National Institutes of Health, Bethesda, MD) program to measure and quantify the area of the corneal epithelial defect (cm²) following corneal staining under cobalt blue light using a slit-lamp. The absence of staining in the damaged area was used as the criterion to determine corneal healing.

Table 1.

Table for Standard Quantification of Corneal Opacity Scores

Score	Standardized Scale
0	Cornea completely clear with no clouding
1	Cornea mildly clouded with visible iris texture
2	Cornea moderately clouded with unclear iris texture
3	Cornea severely clouded with vaguely visible iris
4	Cornea very severely clouded with invisible iris
5	Cornea completely clouded

Corneal Histopathology

On D3, D7, D14, and D28 following surgery, four rabbits from each group were randomly selected for euthanasia via air embolization. The corneas from the right eyes were excised and sent to the laboratory for histopathological analysis. The corneal tissues were fixed in formaldehyde, dehydrated, and embedded according to standard protocols, then sectioned into 6-µm slices. Hematoxylin and eosin (H&E) staining was performed to examine the structural integrity of the corneal tissues in each group.

Immunohistochemistry for TGF-β1

After processing the corneal tissue sections using standard IHC protocols,¹² TGF-β1 index sections were selected for each group at each time point. For each section, three random fields at 200× magnification were observed and recorded. Image-Pro Plus 6.0 software (Media Cybernetics, Inc., Rockville, MD) was used to select uniform standard sections and to analyze the positive cumulative integrated optical density (IOD) and the pixel area (AREA) of the corresponding tissues. The immunohistochemical average optical density (AO) value was then calculated using the formula AO = IOD/AREA. A higher AO value indicates a greater level of positive TGF-β1 expression.¹³

Statistical Analyses

Statistical analyses were performed using SPSS Statistics 26.0 (IBM, Chicago, IL). The Shapiro–Wilk test was used to assess the normality of the data. Continuous variables are expressed as the mean ± standard deviation (SD). Between-group and overall within-group differences were assessed using either the Kruskal–Wallis test or a one-way analysis of variance (ANOVA), depending on the data distribution. For multiple comparisons, least significant difference (LSD) t-tests and Nemenyi tests were applied. Statistical significance was set at P < 0.05.

Results

Clinical Assessment

During the observation phase of the experiment, only the TE group experienced unnatural rabbit deaths, and the rabbits in the TE group were more emaciated than those in the other two groups. On D28, corneal neovascularization was observed exclusively in the PAE group, and no severe corneal infections developed in the remaining rabbits.

The specific values of corneal epithelial defect area in each group at different time points are shown in Table 2. On D3 and D7, there were significant variations in the area of corneal epithelium defects between the groups (P < 0.001 and P = 0.017, respectively) (Figs. 2B, 2D). The TE group exhibited the largest mean value of epithelial defects, and the PAE group exhibited the smallest mean value. The area of epithelial defects was larger in the TE and NS groups on D14 and D28, but the differences were not statistically significant (all P > 0.05) (Figs. 2B, 2D). The three groups experienced decreasing corneal epithelial damage over time, with significant differences in re-epithelialization (P = 0.023, P < 0.001, and P = 0.009, respectively) (Figs. 2B, 2F).

Table 2.

Comparison of Corneal Epithelial Defect Area in Each Group on D3, D7, D14, and D28

Day	NS (cm2)	TE (cm2)	PAE (cm2)	F/H	P
D3	0.108 ± 0.074a,b	0.245 ± 0.063b,c,d,e,f	0.111 ± 0.065a,b	21.619	<0.001
D7	0.066 ± 0.066	0.127 ± 0.071d,g	0.048 ± 0.054a	8.147	0.017
D14	0.060 ± 0.048	0.111 ± 0.064g	0.090 ± 0.079	1.065	0.363
D28	0.013 ± 0.019d	0.001 ± 0.001g	0.001 ± 0.002g	2.253	0.324
F/H	9.522	19.440	11.525	—	—
P	0.023	<0.001	0.009	—	—

F, F-statistic from one-way ANOVA; H, H-statistic from the Kruskal–Wallis test.

^aVersus TE group, P < 0.05.

^bVersus D28, P < 0.05.

^cVersus NS group, P < 0.05.

^dVersus PAE group, P < 0.05.

^eVersus D7, P < 0.05.

^fVersus D14, P < 0.05.

^gVersus D3, P < 0.05.

Figure 2.

Comparison of corneal opacity scores and epithelial defect area (10×). (A) Representative slit-lamp images after SLK. (B) Images stained with sodium fluorescein after SLK. (C) Corneal opacity scores among the groups at different time points after surgery. (D) Comparison of the epithelial defect areas of the groups as determined by ImageJ at various postoperative time periods. *P < 0.05, ***P < 0.001. (E) Corneal opacity scores at different time points within the group. (F) Comparison of epithelial defect areas measured using Image J at different time points within the group. *P < 0.05, ***P < 0.001.

The corneal opacity scores of each group at different time points are shown in Table 3. Statistically significant differences in corneal opacity were observed among the three groups on D3 and D7 (P = 0.002 and P = 0.044, respectively) (Figs. 2A, 2C), with the TE group exhibiting the least corneal opacity. On D14 and D28, the TE group continued to show the mildest opacity, but no significant differences were found compared to the other two groups (all P > 0.05) (Figs. 2A, 2C). Whereas corneal opacity in the NS and TE groups gradually increased over time, corneal opacity in the PAE group initially decreased to a minimum on D7 before increasing again (Figs. 2A, 2E). Within-group comparisons of corneal opacity for all three experimental groups showed no statistically significant differences (all P > 0.05).

Table 3.

Comparison of Scores for Corneal Opacity in Each Group on D3, D7, D14, and D28

Day	NS	TE	PAE	F/H	P
D3	2.031 ± 0.499a	1.333 ± 0.617b,c	2.079 ± 0.479a	12.548	0.002
D7	2.231 ± 0.388	1.773 ± 0.467	1.893 ± 0.561	6.226	0.044
D14	2.278 ± 0.363	1.900 ± 0.418	2.000 ± 0.333	3.625	0.163
D28	2.333 ± 0.606	2.000 ± 0.500	2.300 ± 0.447	0.967	0.617
F/H	2.343	6.374	3.831	—	—
P	0.504	0.095	0.280	—	—

^aVersus TE group, P < 0.05.

^bVersus NS group, P < 0.05.

^cVersus PAE group, P < 0.05.

Corneal Histopathological Findings

The HE results revealed that the normal rabbit corneal epithelium was intact, uniform in thickness, and characterized by strong intercellular connections, with no visible gaps. The fibroblasts appeared flattened, and the collagen fibers in the corneal stroma were evenly distributed and well organized (Fig. 3A). In cases of corneal damage, the epithelial layer was absent, allowing the stromal layer to become visible between the collagen fibers. This layer exhibited a loose structure with increased gaps, disorganized arrangement, and partial separation from the endothelial cell layer (Fig. 3B).

Figure 3.

Detailed images of HE staining and immunohistochemical staining between groups (200×). (A) H&E staining image of a healthy cornea. (B) H&E staining image of a damaged cornea. (C) Representative H&E staining images after SLK. (D) Representative IHC TGF-β1 staining images after SLK. (E) TGF-β1 expression among the groups at different time points after surgery. (F) TGF-β1 expression at different time points within the groups.

On D3, histological examination revealed that the corneas of all three experimental groups were thickened, exhibiting severe edema and a wavy structure. The corneal epithelium was completely detached, and epithelial cells proliferated and migrated to cover the defect. Additionally, the morphology and distribution of fibroblasts in the stroma were abnormal, with disordered collagen fiber arrangement and infiltration of inflammatory cells into the stroma. By D28, the corneal epithelium in all groups had gradually repaired and completely covered the defect. Corneal stromal edema and inflammation were reduced; however, intercellular junctions remained sparse, collagen fibers had been replaced by dense connective tissue, and epithelial repair in the TE group was slower compared to the other two groups (Fig. 3C).

Changes in the TGF-β1 Staining Intensity

The AO values for TGF-β1 in cornea tissues of the different groups at various time points are presented in Table 4. TGF-β1 immunoreactivity was predominantly expressed in the epithelial and anterior stromal regions across the experimental groups (Fig. 3D). The PAE group exhibited the highest AO value for corneal TGF-β1 expression on both D3 and D14. On D7, both the PAE and NS groups demonstrated significantly increased TGF-β1 expression compared to the TE group, with the NS group showing the highest AO value. On D28, the TE group exhibited the highest TGF-β1 expression (Fig. 3E). When comparing trends within each group, both the NS and PAE groups followed a pattern of increasing and then decreasing AO values over the observation period, peaking at D7. In contrast to the NS group, the AO values of the PAE group decreased more gradually, whereas the AO values of the TE group initially decreased and then increased (Fig. 3F). Statistically, no significant differences were observed among the three experimental groups (all P > 0.05).

Table 4.

Comparison of AO Values for TGF-β1 in the Cornea in Each Group on D3, D7, D14, and D28

Day	NS	TE	PAE	F/H	P
D3	0.297 ± 0.087	0.381 ± 0.521	0.329 ± 0.142	0.700	0.705
D7	2.333 ± 2.501	0.196 ± 0.120	1.696 ± 2.545	2.756	0.252
D14	0.617 ± 0.670	0.636 ± 0.624	1.129 ± 1.266	1.067	0.587
D28	0.207 ± 0.081	0.870 ± 0.769	0.887 ± 0.577	4.308	0.116
F/H	4.659	3.434	1.839	—	—
P	0.199	0.329	0.607	—	—

Discussion

Maintaining the integrity of the corneal epithelium is crucial for preserving corneal physiological function, as epithelial damage triggers a complex repair cascade mediated by cytokines, growth factors, and signaling pathways.¹⁴ Prompt epithelial regeneration downregulates stromal collagenase activity, subsequently mitigating inflammation and pathological neovascularization.¹⁵ PAE, referred to as “the product of flesh and blood with sentiments” in traditional Chinese medicine (TCM), demonstrates clinically validated anti-inflammatory, antifibrotic, and tissue-repairing properties, with established efficacy in gastrointestinal disease and wound management.^16,17 In this study, PAE was applied for the first time after corneal SLK to evaluate its impact on corneal wound healing. Our findings revealed that the PAE group exhibited significantly enhanced early epithelial healing compared to the TE group and a marginal improvement over the NS group, as evidenced by histological analysis of the harvested tissue samples. These findings indicate that epithelial regeneration proceeded more rapidly in the PAE group, especially within the first postoperative week. Conversely, TE treatment impeded epithelial regeneration. Although TE possesses anti-inflammatory and antibacterial properties, it may hinder corneal epithelial wound healing, and prolonged application could lead to a reduction in epithelial cell layers.^18,19 Notably, whereas dexamethasone eye drops at 1 g/L completely inhibited corneal epithelial growth, a lower concentration (0.1 g/L) enhanced corneal epithelial proliferation in experimental animals and concurrently attenuated the inflammatory response.^20,21

Repeated corneal epithelial stripping occurred in all three experimental groups, suggesting that epithelial repair in the laminectomy model is more complex than in the conventional epithelial scraping model. This increased complexity is likely attributed to the irregular stromal surface and prolonged healing duration post-modeling.²² Essepian et al.²³ reported that the laminectomy model exhibits higher sensitivity than the epithelial scraping model for assessing therapeutic efficacy in wound healing. Epithelial cell migration across irregular stromal surfaces is markedly compromised due to impaired adhesion and motility. Relative to the epithelial scraping model, lamellar keratotomy injuries extend the healing period by approximately 180%, with primary closure typically achieved 5 to 7 days postoperatively.

Corneal stromal injury is intrinsically linked to epithelial injury, as epithelial damage frequently triggers stromal cell death, followed by stromal repair and intricate cytokine crosstalk between epithelium and stromal cells.¹⁵ Excessive fibrosis during stromal healing may lead to corneal scarring,²⁴ with TGF-β1 playing a key role in fibrotic progression.²⁵ PAE modulates fibroblast activation, cytokine release, and extracellular matrix deposition, thereby potentially preventing scar formation.¹⁰ PAE has shown potential in treating organ fibrosis in the kidneys, liver, and lungs, indicating that it may be a promising antifibrotic treatment. Both clinical and histological analyses in this study revealed significantly reduced corneal opacity in the PAE group compared to the NS group, with particularly marked improvement evident by postoperative D7. These findings suggest that PAE may inhibit the early fibrotic response following SLK in rabbit corneas, consequently ameliorating corneal opacity. The TE group demonstrated optimal efficacy in reducing corneal clouding, likely through effective limitation inflammatory responses and fibroblast proliferation, thereby preventing scar formation. Nevertheless, it should be noted that glucocorticoid-based medications have significant adverse effects. TE (a widely used glucocorticoid medication in clinical practice) exhibit potent anti-inflammatory effects, inhibit capillary dilation, and prevent scar formation.²⁶ Glucocorticoids are commonly used to prevent regression and epithelial implantation after refractive surgery, and dexamethasone can be effective in treating subepithelial haze after laser corneal refractive surgery. However, long-term use of glucocorticoids may delay corneal wound healing, increase infection risk, and induce complications such as steroid-induced glaucoma.^27,28 In our study, only the TE group showed signs of unnatural death and wasting in NZW rabbits, suggesting that the TE treatment may interfere with the animal's metabolic processes, leading to electrolyte imbalances and other systemic issues that ultimately impair growth and immune function.

Sustained TGF-β1 production by corneal epithelial and stromal cells after injury facilitates early wound healing but may result in pathological scar formation if excessive.²⁹ Inhibiting TGF-β1 can reduce corneal fibrosis and stromal turbidity.^30,31 The results of our study indicate that PAE promotes early tissue repair and inhibits subsequent fibrosis. In the PAE group, the TGF-β1 concentration in the corneal tissue increased gradually after surgery, peaking at 7 days and then declining. IHC has been shown to be a reliable method for detecting TGF-β1 in corneal tissue,³² showing high agreement with western blot (WB).³³ The present investigation provides fresh evidence of biphasic regulation of TGF-β1 by PAE in corneal restoration. Yang et al.¹¹ similarly reported reduced corneal fibrosis via PAE-mediated TGF-β1 suppression in murine models using WB. They observed an increase in TGF-β1 levels on D5, followed by a decrease in TGF-β1 and IL-6 on D10, indicating that the extract aids early wound healing and reduces scarring through TGF-β1 regulation and inhibition of inflammatory factors.

Notably, transient neovascularization observed in individual PAE-treated corneas—a phenomenon also reported in natural extracts such as aloe vera gel (epithelial repair acceleration with mild neovascularization)³⁴ and honey (pro-healing but pro-angiogenic properties)^35,36—emphasizes the dualistic nature of botanical therapies. These precedents indicate that balancing therapeutic efficacy with side effects such as angiogenesis is a common challenge in the development of natural products. As a potent angiogenic factor, TGF-β plays a critical role in promoting ocular neovascularization following injury.³⁷ In this study, corneal neovascularization was observed only in the PAE group at 28 days postoperatively, but the expression of TGF-β1 in the PAE group was significantly higher during later experimental phases compared to controls, potentially explaining this PAE-specific neovascular response. Nevertheless, by stimulating fibroblast migration, enhancing collagen deposition, promoting controlled neovascularization, and modulating inflammatory responses, PAE accelerates wound healing and tissue regeneration.³⁸ However, persistent stromal inflammatory, characterized by inflammatory cell infiltration and sustained pro-inflammatory signaling, may disrupt the normal healing cascades of the tissue, ultimately leading to neovascularization and fibrosis.¹⁴

P . americana is an established medicinal insect in traditional medicine, and PAE possesses a wide range of therapeutic properties,¹⁷ including strengthening the spleen, eliminating malnutrition, promoting blood circulation, reducing swelling, and detoxifying.³⁹ In modern medicine, PAE is recognized for its diverse pharmacological benefits, such as antitumor properties, tissue regenerative capacity, and immunomodulatory effects.^40,41 Recent studies have explored its therapeutic potential in treating various conditions, with particular emphasis on tissue injury and fibrotic disorders.⁴² Our study revealed that PAE exerts biphasic regulation on TGF-β1 secretion, a key factor of tissue repair and fibrogenesis. During early healing phases, PAE upregulates TGF-β1 expression to facilitate corneal epithelial and stromal regeneration post-injury. Conversely, during later stages, PAE downregulates TGF-β1 secretion, thereby preventing excessive repair and reducing corneal fibrosis. This biphasic mechanism that promotes healing in the early stages while inhibiting over-repair in the later stages highlights the potential for PAE in promoting corneal wound healing and exerting antifibrotic effects. TCM has a long history of using such natural substances for therapeutic purposes, focusing on holistic regulation of the body. In recent years, the effectiveness of TCM has been further validated through evidence-based research. The unique diagnostic and therapeutic methods of TCM focus on restoring physiological equilibrium and modulating interconnected systems.^43–45 It is estimated that 20% to 30% of commonly used TCM formulations exhibit biphasic regulatory effects, helping the body re-establish its dynamic equilibrium.⁴⁶ This multi-target mechanism arises from TCM system-wide regulatory properties, where bioactive constituents interact with diverse molecular pathways to achieve therapeutic synergy, a hallmark of the foundational philosophy of TCM.⁴⁷ Our findings position PAE as a promising therapeutic candidate for pathological corneal fibrosis, offering novel avenues for mitigating corneal scarring.

Current postoperative corneal treatments, including corticosteroids (such as TE), frequently prioritize anti-inflammatory effects over maintaining the epithelium between epithelial regeneration and fibrotic suppression. Through biphasic modulation, our results showed that PAE specifically promotes early epithelial repair and subsequently suppresses fibrosis. A significant clinical gap is filled by this dual functioning, which maximizes tissue regeneration while avoiding eyesight loss brought on by scarring. Because of its natural source, PAE may be a safer option than steroids, which increase the risk of cataract development and glaucoma. To speed up translation, future clinical research should investigate PAE-based formulations for corneal procedures, concentrating on dosage optimization and pharmacokinetics unique to humans.

IHC reliably reflected the dynamics of TGF-β1, and future research will further explore the mechanism by which PAE promotes corneal damage repair. However, this study did not fully elucidate the mechanism of PAE-induced neoangiogenesis. Future work will be focused on refining the composition of PAE to reduce side effects while keeping the therapeutic advantages in order to improve clinical translation. Prior to clinical translation, further investigation into the composition and pharmacological effects of PAE is warranted, particularly its therapeutic potential in systemic fibrotic diseases. Furthermore, systematic studies are necessary to fully elucidate the molecular mechanisms of PAE and optimize its therapeutic applications for fibrosis and associated pathologies.

Conclusions

PAE promoted corneal tissue repair after SLK in rabbits, inhibiting fibrosis and reducing stromal opacity some extent. This biphasic regulatory effect was mechanistically linked to TGF-β1 modulation: Early-phase upregulation facilitated epithelial regeneration, and late-phase downregulation suppressed fibrotic remodeling.