Clinically correlated dose of the amniotic membrane extract is superior to its transplantation in corneal wound healing.

Abstract

Purpose: This study investigates the superiority of sterile lyophilized amniotic membrane extract (AME) prepared at a clinically correlated dose over amniotic membrane transplantation (AMT) in an experimental corneal wound model.

Methods: AME was prepared from a pool of five amniotic membranes. After homogenizing the membranes, they were lyophilized and sterilized by gamma radiation to obtain sterile, lyophilized AME powder. The total protein amount and growth factor levels were measured in the AME samples. AME eye drops were prepared considering the protein concentration of the standard-size amniotic membrane weight used for transplantation, and this total amount was used as the daily dose. For the experimental animal corneal wound model, a full-thickness mechanical corneal epithelial defect was created in 15 eyes of 15 New Zealand rabbits. The rabbits were divided into four groups: Group 1: AME eye drop (n = 4 eyes), Group 2: AMT (n = 4 eyes), Group 3: preservation-free artificial tear (n = 4 eyes), and Group 4: control (n = 3 eyes). Daily anterior segment evaluation and photography were performed to determine the clinical efficacy of the AME. The rabbits were euthanized on day 7, and wound healing was examined histopathologically.

Results: The total protein amount in the AME was 0.149 ± 0.01 mg/ml. The growth factor levels were as follows: EGF = 41.19, FGF = 43.11, HGF = 203.67, KGF = 328.03, NGF = 207.92, and TGF-β = 506.93 pg/ml AME. On clinical examination, the mean wound closure times in Groups 1, 3, and 4 were 2.75 ± 0.50 (2-3), 3.5 ± 1.0 (3-5), and 3.33 ± 1.52 (2-5) days, respectively (p > 0.05). Histopathological examination revealed Group 1 corneal epithelium with full thickness, regular healing pattern, and normal anterior stromal keratocytes. In the remaining three groups, there were interruptions in epithelial healing, and loss of anterior stromal keratocytes was evident. Inflammation was more prominent in Group 2.

Conclusions: AME is a liquid product that contains the essence of the amniotic membrane after homogenization and centrifugation. AME has the potential to overcome the disadvantages of AMT, such as surgery requirement and the limitation of postoperative objective clinical observation due to the semi-opaque nature of the amniotic membrane. Although, there are studies showing the advantages of AME over AMT in the literature, the preparation, preservation and sterilization of AME are still controversial. This study is specifically addressing the shortcomings of acquiring AME in the literature, such as minimizing inter-donor variability in AME by pooling amniotic membranes from different donors, lyophilizing AME to preserve its biochemical composition, and preventing infection transmission by using gamma sterilization. Herein, we observed that the AME prepared with this method contains high concentrations of growth factors. In the present study, the dose of AME was correlated with clinical use for the first time, and for the first time, the superiority of sterile lyophilized AME over AMT was clinically demonstrated in a corneal wound model. Furthermore, histopathological findings confirmed that AME seems to not only promote epithelial proliferation during wound healing but also prevent stromal keratocyte loss, inhibit inflammation and accelerate collagen remodeling.