Wound Healing After Alkali Burn Injury of the Cornea Involves Nox4-Type NADPH Oxidase

Abstract

Purpose Corneal injury that occurs after burning with alkali initiates wound-healing processes, including inflammation, neovascularization, and fibrosis. Excessive reactions to injury can reduce corneal transparency and thereby compromise vision. The NADPH oxidase (Nox) enzyme complex is known to be involved in cell signaling for wound-healing angiogenesis, but its role in corneal neovascularization has been little studied. Methods The center corneas of wild-type and Nox4 knockout (KO) mice were injured with 3 µL 1 M NaOH, while the contralateral corneas remained untouched. On day 7, mRNA expression levels of NADPH oxidase isoforms, the proangiogenic factors VEGF-A and TGFβ1, and proinflammatory genes ICAM-1 and VCAM-1 were determined. Corneal neovascularization and fibrosis were visualized using PECAM-1 antibody and picrosirius red staining, respectively, on the same day. Results Expressions of both Nox2 and Nox4 gene isoforms as well as the above genes were markedly increased in the injured corneas at 7 days. Injured corneas showed neovascularization and fibrosis as well as an increase in clinical opacity score. All responses stimulated by alkali burn were abrogated in Nox4 KO mice. Conclusions Nox4 could be a new target to treat pathologic corneal wound-healing responses and such targeting might prevent blindness caused by burn injuries.

Longitudinal assessment of the effect of alkali burns on corneal biomechanical properties using optical coherence elastography

“…Normally, alkali solutions tend to penetrate the cornea rapidly causing destruction of the stromal proteoglycan ground substance and thus, increasing the collagen fibril density, which leads to tissue stiffening [2,58,59]. The relative increase of Young's modulus 14 days postburn could be due to the development of chronic inflammation, neovascularization, and, most importantly, the increased fibrotic response associated with the wound healing process [16,56]. During the early repair phase (i.e., 8-20 days postburn) of the wound healing process, the normal structural elements of the stroma are replaced by excessive accumulation of the ECM matrix and distorted distribution of collagen fibers, resulting in fibrosis which is characterized by scarring and stiffening of tissue [2,16,56,60].…”

“…The relative increase of Young's modulus 14 days postburn could be due to the development of chronic inflammation, neovascularization, and, most importantly, the increased fibrotic response associated with the wound healing process [16,56]. During the early repair phase (i.e., 8-20 days postburn) of the wound healing process, the normal structural elements of the stroma are replaced by excessive accumulation of the ECM matrix and distorted distribution of collagen fibers, resulting in fibrosis which is characterized by scarring and stiffening of tissue [2,16,56,60]. Different from the results of the current study, uniaxial tensile testing on porcine corneas demonstrated weakening of alkali-lesioned and cultured tissues compared with their healthy and fresh counterparts on day 7 post-AB [18].…”

“…As discussed above, both the initial phase of the alkali insult and the wound healing process may lead to the modulation of the collagen fibril organization and destruction of the ground substance. This damage to the ground substance increases the fibril density, which in turn results in the significant stiffening of the ECM matrix [15,16]. Attributed to the continuous remodeling of the ECM matrix, an injured cornea is likely to exhibit variable viscoelastic properties during the wound healing process.…”

Extracellular Matrix Deposition and Remodeling after Corneal Alkali Burn in Mice

“…In this study, we used the well-established AB mouse model to assess the change in GAG composition during corneal wound healing 5 and 14 days after a chemical injury. This model leads to inflammatory cell infiltration and corneal scarring, and the loss of transparency is evident at both 5 and 14 days after AB [ 56 , 57 , 58 , 59 , 60 ]. Disaccharide analysis revealed there was a significant increase in CS expression after AB, and, thus, CSPGs are important constituents of the provisional matrix in the cornea.…”

Hyperstable EGF-like bleogen derived from cactus accelerates corneal healing in rats

“…The acute corneal alkali-induced wounding of rats was performed as previously described ( Choi et al, 2017 ; Hakami et al, 2020 ). At the beginning of the study, randomization was performed based on body weight prior to the induction of the injury.…”