Introduction
Corneal ulceration is a breakdown of collagenous stromal tissue, a process that was once believed to be simple physical dissolution, described as corneal melting (Fini et al., 1996). We hypothesized that the stable gastric pentadecapeptide BPC 157 heals corneal ulcerations in rats, allowing them to regain corneal transparency. BPC 157 has effects on the NO system (Sikiric et al., 2014), nonsteroidal anti-inflammatory drug (NSAID) toxicity (Sikiric et al., 2013), gastrointestinal tract (Sikiric et al., 2010, Sikiric et al., 2011), wound-healing, blood vessels, and bleeding (Seiwerth et al., 2014). Notably, as an original anti-ulcer peptide, maintaining mucosal integrity, native and stable in human gastric juice, BPC 157 has a particular stability, and always applied alone, without carrier, for systemic, peroral, or local application (Sikiric et al., 2010, Sikiric et al., 2011, Sikiric et al., 2013, Sikiric et al., 2014, Seiwerth et al., 2014).
Total debridement of corneal epithelium was rescued with BPC 157 eye drops (μg- or ng-regimen), and recovery was markedly accelerated in eyes on topical BPC 157 (Lazic et al., 2005); further, corneal transparency was maintained, and there was no formation of corneal neovascularization. In a series of acute and chronic injury models, BPC 157 consistently promoted healing after severe injuries in various tissues that were unable to heal spontaneously (Cerovecki et al., 2010, Cesarec et al., 2013, Chang et al., 2011, Gjurasin et al., 2010, Hrelec et al., 2009, Keremi et al., 2009, Klicek et al., 2008, Krivic et al., 2006, Krivic et al., 2008, Mikus et al., 2001, Novinscak et al., 2008, Pevec et al., 2010, Sebecic et al., 1999, Seiwerth et al., 1997, Sever et al., 2009, Sikiric et al., 2003, Staresinic et al., 2003, Staresinic et al., 2006, Tudor et al., 2010, Vuksic et al., 2007). BPC 157 also heals hypovascular, hypocellular, and hyponeural tissues (Cerovecki et al., 2010, Chang et al., 2011, Gjurasin et al., 2010, Krivic et al., 2006, Krivic et al., 2008, Staresinic et al., 2003).
These findings have been attributed to the stimulation of early growth response-1 (egr-1) and its co-repressor, nerve growth factor 1-A-binding protein-2 (naB2) and its effects on cytokine and growth factor production and, thereby, early extracellular matrix (collagen) and blood vessel formation (Tkalcevic et al., 2007). The others correlated the BPC 157 beneficial effects with the activating a cellular focal adhesion kinase (FAK)-paxillin signal pathway, and subsequently demonstrated that BPC 157 dose- and time-dependently increased the expression of growth hormone receptor, Janus kinase 2 (JAK-2), the downstream signal pathway of growth hormone receptor (Chang et al., 2011, Chang et al., 2014).
These models might be particularly important, considering that the mechanism of corneal wound healing has not been determined. Further, the effects of BPC 157 alone in wound healing, without any carrier, suggest that they are attributed to its peptidergic activity (Cerovecki et al., 2010, Cesarec et al., 2013, Chang et al., 2011, Gjurasin et al., 2010, Hrelec et al., 2009, Keremi et al., 2009, Klicek et al., 2008, Krivic et al., 2006, Krivic et al., 2008, Mikus et al., 2001, Novinscak et al., 2008, Pevec et al., 2010, Sebecic et al., 1999, Seiwerth et al., 1997, Sever et al., 2009, Sikiric et al., 2003, Staresinic et al., 2003, Staresinic et al., 2006, Stupnisek et al., 2015, Tudor et al., 2010, Vuksic et al., 2007). BPC 157 also heals hypovascular, hypocellular, and hyponeural tissues (Cerovecki et al., 2010, Chang et al., 2011, Gjurasin et al., 2010, Krivic et al., 2006, Krivic et al., 2008, Staresinic et al., 2003).Various types of growth factors mediate corneal wound healing (Imanishi et al., 2000). However, epidermal growth factor (EGF), fibroblast growth factor (FGF), transforming growth factor (TGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), platelet-derived growth factor (PDGF), and insulin-like growth factor (IGF), promote wound healing only with carrier systems. Presumably, the healing attribution of these peptides which are given with carriers could be also uncertain (which of the two (peptide or carrier) or both (peptide + carrier-complex) should be crucial for the beneficial effect) (Sikiric et al., 2010, Sikiric et al., 2011, Sikiric et al., 2013). Thus, BPC 157 given alone, quite distinctive for standard growth factors, was applied dissolved in water as before (Lazic et al., 2005).
Thus, a penetrant linear incision was made in rat eyes, which were then treated with BPC 157 eye drops at μg, ng, and pg levels.
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Experimental procedure
Male Wistar Albino rats, 280–320 g in body weight, were randomly assigned, with at least 10 rats per experimental group; all experiments were approved by the local ethic committee.
The left eye was operated on under aseptic conditions by the same surgeon according to a modified model of Matsuda et al. (Matsuda et al., 1997). In deeply anaesthetized rats, a penetrant linear 2-mm incision was made and 2 drops of 0.4% oxybuprocaine topical anesthetic were given (Novesine, OmniVision, Puchheim,
Results
Generally, the spontaneous healing of corneal ulcerations in control rats was poor (Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7). The fluorescein test was positive after 120 h, and the Seidel test was positive (Fig. 1), showing corneal opacity (Fig. 1, Fig. 2, Fig. 3, Fig. 4). Aqueous cells remained present, as did edema, fibrin, and granulation tissue; the increase in granulocytes and mononuclear cells was confirmed by histology (Fig. 5). These were illustrated macroscopically (
Discussion
BPC 157 eye drops closed perforating corneal incisions in live rats. In an established protocol that accelerates healing after total debridement of corneal epithelium (Lazic et al., 2005), after perforation of corneal incisions, BPC 157 had rapid beneficial effects on the epithelium, lowering granulocyte and mononuclear cell levels and thereby decreasing aqueous cells, granulation tissue, edema, and fibrin formation. These findings are significant, because stromal ulceration is associated with
Acknowledgments
This research was supported by grant 108-1083570-3635 from Ministry of Science, Education and Sports, Republic of Croatia.