Impact of β-1,3-glucan Isolated from Euglena Gracilis on Corneal Epithelial Cell Migration and on Wound Healing in a Rat Alkali Burn Model

Purpose: To determine the impact of β-1,3-glucan isolated from Euglena gracilis on corneal epithelial cell migration and on wound healing in a rat alkali burn model.

Methods: Immortalized human corneal epithelial cells (HCECs) were cultured in media with 50, 100 and 200 μg/mL laminarin (β-1,3- and β-1,6-glucans), β-1,3-glucan and hyaluronic acid (HA)-conjugated β-1,3-glucan; Dulbecco's modified Eagle's medium (DMEM)/nutrient mixture F-12 (negative control) and serum containing DMEM/nutrient mixture F-12 (positive control). Migration assays were conducted via the manual scraping of HCECs. Next, alkali injuries were induced using 1 N NaOH in 40 eyes of 40 Sprague-Dawley male rats. The injury-only group (n = 10) received topical phosphate-buffered saline four times a day for 2 d. The study groups received 200 μg/mL topical laminarin (n = 10), β-1,3-glucan (n = 10) and β-1,3-glucan HA (n = 10). Using slit-lamp biomicroscopy, injured corneas were evaluated in terms of re-epithelialization and opacity, and tissue sections were histologically analyzed.

Results: Migration assay rates were enhanced as laminarin and β-1,3-glucan increased, compared to negative control cells (all p < 0.05). In the comparison between β-1,3-glucan and its HA conjugate form, β-1,3-glucan-HA showed more enhanced migration rate than β-1,3-glucan (p < 0.05). In rat alkali burn model, wound-healing ratio was greatest in β-1,3-glucan-HA groups (96.0 ± 4.1%), followed by β-1,3-glucan (86.0 ± 6.5%), laminarin (67.0 ± 7.5%) and injury-only group (54.0 ± 6.5%) (p < 0.0001; ANOVA). The opacity score was also lowest in β-1,3-glucan-HA groups (3.0 ± 0.75), followed by β-1,3-glucan (3.4 ± 0.5), laminarin (3.7 ± 0.8) and injury-only group (4.7 ± 0.46) (p < 0.0001; ANOVA) Histologically, relatively fewer polymorphonuclear leukocytes infiltrated the corneal stroma in the β-1,3-glucan and β-1,3-glucan-HA groups, compared to the injury-only group.

Conclusions: β-1,3-Glucan, particularly when conjugated with HA, promoted epithelial wound healing in vitro and suppressed the acute inflammatory reaction in corneal alkali burns.