Oral Administration of Heat-Killed <i>Fructobacillus Fructosus</i> FMO-85 Alleviates the Reduction in Tear Fluid in a Stress-Induced Dry Eye Mouse Model

Dry eye disease is an ocular disease in which the stability of tear fluid decreases, causing ocular discomfort and abnormal visual function as well as damage to the ocular surface. It has been reported that specific types of food ingredients can promote lachrymal secretion, which is expected to prevent and improve dry eye. Here, we evaluated the effects of a heat-killed form of Fructobacillus fructosus FMO-85, a species of fructophilic lactic acid bacteria (FLAB) that is derived from the digestive tract of honeybees, on lacrimal fluid secretion using a stress-induced dry eye mouse model. Male C57BL/6J mice were fed a 3% FLAB-mixed diet 3 weeks before stress loading. We observed that the tear fluid volume was decreased after stress loading, which was significantly improved by FLAB treatment after 7 and 11 days. Mechanistically, the mRNA levels of brain-derived neurotrophic factor (Bdnf), one of the important growth factors involved in lacrimal fluid secretion, isoform-2 and -6 were increased in the hippocampus of FLAB-treated mice. Furthermore, the plasma levels of an anti-inflammatory cytokine, interleukin-10 (IL-10), increased in the FLAB-treated mice. These results suggested that the ingredients contained in dried FLAB increase tear fluid volume by affecting the lacrimal secretion mechanism and the production of inhibitory cytokines. In conclusion, the decrease in tear fluid volume after stress loading was suppressed by FLAB intake. These results indicated that FLAB supplementation may be a useful strategy for the prevention and treatment of dry eye.