Effect of topical bovine colostrum in wound healing of corneal surface after acute ocular alkali burn in mice

Highlights

• Bovine colostrum promotes corneal re-epithelialization and wound healing.

• Burned bovine colostrum-treated corneas showed higher levels of IL-10 and TGF-β.

• Burned saline solution-treated corneas exhibited strong neovascularization.

Abstract

The purpose of this study was to evaluate the effect of bovine colostrum (BC) in the regeneration of corneal epithelial cells on an ocular alkali burn model. Twenty-four C57BL/6 mice were categorized into two gender/age-matched groups for treatment. Two days after inducing a corneal alkali burn in all left eyes with 4 μl of sodium hydroxide 0.15 mol/l, both eyes of group 1 were treated with BC 4 times per day, and both eyes of group 2 were treated with isotonic saline solution (SS). The epithelial defect was photographed and measured by fluorescein staining on days two, four, seven, and ten. Ocular burn damage was assessed with a pre-established classification in clock hours from the limbus. After 10 days both eyes were processed, half of the group's corneas were assessed histopathologically, and the other half was used for pro/anti-inflammatory cytokine quantification using ELISA. BC treated (Group 1) corneas revealed significantly improved fluorescein staining score for limbal involvement when compared to SS treated (Group 2) corneas at days 4 (p = 0.013), 7 (p < 0.001), and 10 (p < 0.001), respectively. No differences were noted in limbal involvement at day 2 between the two groups (p > 0.99). The overall change (difference in slope) in fluorescein staining for limbal involvement between days 2 and 10 was −0.1669 (p = 0.006). Histologic examinations and cytokine measurements of group 2 demonstrated a strong inflammatory component compared to group 1. Our data indicates that topical application of BC facilitates corneal re-epithelialization and wound healing by suppressing the inflammatory process in an ocular alkali burn model.

Introduction

Biological fluids have been used for decades to treat corneal surface diseases and studies done in vivo have proven their beneficial effect in corneal surface cell regeneration without scarring (Herretes et al., 2006; Quinto et al., 2012, 2016; Sharma et al., 2018). Chemical burns are among the most common worldwide ophthalmic emergencies threatening eyesight even if promptly managed (Logothetis et al., 2014). Alkali compounds can penetrate through all corneal layers causing tissue saponification with denaturation of corneal epithelial cells and melting of stromal collagenous matrix (Barouch and Colby, 2008; Bradford, 2004; Luisi et al., 2021). This corneal insult could precipitate the destruction of the epithelial stem cell niche leading to corneal re-epithelialization failure with extension of the conjunctival epithelium across the limbus (Dua et al., 2001). Basement membrane loss leads to activation of quiescent keratocytes to myofibroblasts secreting irregular stromal matrix, thus resulting in corneal haze, neovascularization, chronic inflammation, and persistent epithelial defects (Dua et al., 2001; Wagoner, 1997). The retina and optic nerve may also be at risk in chemically burned eyes as the proinflammatory cytokines released can diffuse from the anterior to the posterior segment (Paschalis et al., 2017). Although transplantation techniques of corneal limbal cells and corneal tissues are available, they require controlling the ocular surface inflammation and depend on the availability of a good quality transplantation donor (Atallah et al., 2016).

Treatment of ocular chemical burns with topical drops are still an area of investigation. Few studies have investigated the wound healing properties of colostrum. It is known that colostrum is loaded with immune and tissue repairing factors essential for cell support and viability (Ballard and Morrow, 2013; Uruakpa et al., 2002). Studies involving colostrum show the presence of typical immune-modulatory molecules such as immunoglobulin A (IgA), lactoferrin, and peroxidase to novel protective bioactive factors in it (Ballard and Morrow, 2013; Buescher and Malinowska, 1996; Goldman, 1993; Sharp et al., 2016). Analyses done in a variety of biospecimens have determined its important role in suppressing inflammatory processes in vivo (Agarwal et al., 2011; He et al., 2016). In some countries, instillation of colostrum eye drops to the newborn has become a common practice in preventing and decreasing the rate of conjunctival infections (Bucolo et al., 2015; Ghaemi et al., 2014; Singh et al., 1982).

Bovine colostrum (BC) from pasture-fed cows contains specific immunoglobulins that protect against many human pathogens, and has been used to treat dystrophic eye lesions involving epithelial cell breakdown due to severe dry eye (Chaumeil et al., 1994; Liotet and Perrin, 1982). BC-borne anti-inflammatory cytokines, pluripotent polypeptides, and developmental factors have been thought to be implicated in cell movement and immune cell trafficking, promoting wound repair (Bucolo et al., 2015; Buescher and Malinowska, 1996; He et al., 2016). This study is undertaken to investigate the wound healing effects of colostrum after an acute ocular burn injury in mice via topical drop treatments.