Lactobacillus lysates protect oral epithelial cells from pathogen-associated damage, increase secretion of pro-inflammatory cytokines and enhance barrier integrity

Periodontitis is a chronic gum disease characterised by inflammation and the loss of bone. We have explored the potential prophylactic effects of lysates from four Lactobacillus strains against the toxic effects of three periodontal pathogens (Porphyromonas gingivalis, Fusobacterium nucleatum, and Aggregatibacter actinomycetemcomitans). TR146 oral epithelial cells were pre-treated with Lactobacillus lysates (L. rhamnosus - GG, L. rhamnosus - SD11, L. reuteri and L. plantarum) and then challenged with pathogenic material (live cells, lysates, or supernatants). Cytokine analysis was performed on supernatants of cells treated with probiotic lysates from 1.5 h to 24 h. Effects of probiotic lysates on re-epithelialisation were determined using keratinocyte scratch assays, monitoring both migration and proliferation. Epithelial barrier function was observed after lysate addition by trans-epithelial electrical resistance (TEER) and by quantifying claudin-1 expression. Treatment of host cells with Lactobacillus lysates before pathogen exposure conferred significant protection against viability loss. Although extended pre-treatment did not generally increase protection, against live Aggregatibacter actinomycetemcomitans, significant increases in viability were seen after 24 h of pre-treatment for GG, SD11 and L. plantarum. Pro-inflammatory cytokines TNF-α, IP-10, IL-6, and IL-8 increased significantly with extended probiotic treatment, while IL-1β and IL-1α secretion significantly increased but remained constant over time. Secretion of the growth-promoting cytokine TGF-β increased after 3 h of treatment, however no increases in the regulatory cytokine IL-10 were recorded. Only exposure to SD11 significantly enhanced re-epithelialisation, TEER and claudin-1 expression while GG increased TEER but decreased claudin-1 expression. L. plantarum significantly inhibited re-epithelialisation but did not impact TEER or claudin-1 expression. All lysates significantly improved TEER in the presence of pathogenic material, demonstrating a protective effect on barrier function.