Experimental evaluation of Folic acid effect on Corneal burn ulcer healing in new Zealand white rabbit

Corneal ulcer is one of the most common eye diseases, which can be caused by trauma, chemical agents, and some bacteria, viruses, and chlamydia. Treatment of corneal ulcer has been always a concern in ophthalmology. This concern is due to the major role of cornea in providing and preserving normal vision. Alkali-induced corneal ulcer creates an intense inflammatory reaction to traumatic injuries and this intense inflammation can inhibit the natural epithelial growth and cause fibrosis or scar on cornea.Cornea is an organ in the eye that creates a smooth and clear surface and so, it provides the possibility of light regularly passing through the eye. Any injury of this layer eliminates its transparency and protective capacity. Cornea has few cells and no vessels. Various bacterial, viral, parasitic, and fungal agents can cause severe infections in cornea. After the occurrence of corneal injury, the cells surrounding the injured area including epithelial, stromal, and endothelial cells try to improve the injury by cell division and calling the immune system cells such as neutrophils, macrophages, and monocytes; as a result of this process, the injured area becomes inflamed and edematous. In most cases, due to basic membrane decay and leakage of proteinase, epithelial cells will not be able to provide the connections required for retrieving the layers. So, the distance between epithelial cells increase and the bond between them become weak. As a result of corneal ulcer, increased activity of destructive proteinases and decreased activity of proteases leads to rapid detachment of collagen and other extracellular components of corneal matrix. Significant increase of reactive oxygen species (ROS), increased oxidative condition, and decreased components of antioxidant system occur following corneal injury. In histological studies, various cells of immune system including neutrophils, lymphocytes, monocytes, and macrophages are found in cornea. Increased reactive oxygen species (ROS), increased oxidative stress, and decreased components of antioxidant system are observed in pathologic conditions and in the case of corneal injury. Various studies have reported the role of antioxidants in prevention and treatment of corneal ulcer. The recent studies have indicated that folic acid restores decreased enzymatic and non-enzymatic antioxidants. also, its improving effect is due to inhibition of reactive oxygen species (ROS).

This study was carried out to investigate the effects of folic acid on corneal burn ulcer healing in 20 adult New Zealand white rabbits in similar weight and age range. The pure folic acid powder needed for this study was purchased from Sigma-USA Co. After general anesthesia, corneal ulcer was induced in the left eye of all rabbits and immediately fluoresce in staining was done to ensure that all of the ulcers were identical in size (6 mm). The rabbits were then divided into four equal groups including three experimental groups and a control group. After the surgery, the experimental groups (first to third groups) were gavaged with 2, 5 and 10 mg/kg body weight folic acid every day for 21 days. Histopathology At the end of the third week, the animals were anesthetized and the eye balls were harvested. After the eyeballs were isolated, the specimens were placed in 10% formalin. After the specimens were fixed in the laboratory, the corneal ulcer was isolated from eyeball. After preparation, the paraffin block sections of 4 microns were prepared and stained using Masson's trichrome staining method. In histopathological grading, the indices affecting wound healing, including angiogenesis, the absence of epithelial layers, corneal edema (stromal edema), irregularities in collagen filaments, and presence or absence of inflammatory cells were investigated. Results and

The histopathological studies showed that vascularization, inflammation, and corneal matrix edema were significantly reduced, but the epithelium of cornea was increased in folic acid treated rabbits compared to control group (p