Research of heat-killed Loigolactobacillus coryniformis NA-3 and Lactiplantibacillus plantarum NA as potential substitutes for live strains in immune regulation and anti-inflammatory effects.

Abstract

The safety of live probiotics remains debated due to concerns regarding their viability and functional efficacy under harsh in vivo and in vitro conditions. Inflammatory bowel disease (IBD) is a complex disease stemming from various factors. It has been reported that probiotics shows anti-inflammatory function. This study evaluated the immunomodulatory and anti-inflammatory properties of heat-killed Lactobacillus strains (a form of postbiotics). Because viable Loigolactobacillus coryniformis NA-3 exhibited lower in vitro viability than Lactiplantibacillus plantarum NA, we first evaluated the phagocytic activity and TLR2-mediated immunoregulatory effects of heat-killed L. coryniformis NA-3 in RAW 264.7 cells, and conducted a preliminary comparative assessment of both live and heat-killed L. coryniformis NA-3 in murine models. We further investigated two distinct heat-killed strains: L. coryniformis NA-3 and Lactiplantibacillus plantarum NA. Heat-killed L. coryniformis NA-3 induced TLR2-dependent immunomodulatory effects in vitro and showed effects comparable to those of its live counterpart in vivo under the conditions tested. Both heat-killed strains were associated with changes in inflammatory markers, including decreased levels of pro-inflammatory cytokines (IL-6, TNF-α) and increased levels of anti-inflammatory mediators (IL-4, IL-10, TGF-β) in mice. In addition, they were associated with alterations in antioxidant parameters, including changes in SOD, GSH-Px, GR, NQO1, HO-1, Nrf2, and MDA levels, as well as increased expression of the tight junction proteins claudin-1 and occluding. Observations from this study are consistent with the potential involvement of the TLR2/NF-κB p65 signaling pathway. These findings highlight the potential of heat-killed probiotics as safe and effective alternatives to live strains in immune regulation and anti-inflammation.