We previously showed that Lactiplantibacillus plantarum K8 and its cell wall components have immunoregulatory effects. In this study, we demonstrate that pre-treatment of L. plantarum K8 lysates reduced LPS-induced TNF-α production in THP-1 cells by down-regulating the early signals of mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB). The down-regulation of signals may be caused by the induction of negative regulators involved in toll-like receptor (TLR)-mediated signaling. However, co-treatment with high concentrations of L. plantarum K8 lysates and lipopolysaccharide (LPS) activated the late signaling of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and NF-κB pathways and resulted in the induction of absent in melanoma 2 (AIM2) inflammasome-mediated interleukin (IL)-1β secretion. Intraperitoneal injection of L. plantarum K8 lysates in LPS-induced endotoxin shock mice alleviated mortality and reduced serum tumor-necrosis factor (TNF)-α, IL-1β, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels. In addition, the mRNA levels of TNF-α, IL-1β, and IL-6 decreased in livers from mice injected with L. plantarum K8 followed by LPS. Hematoxylin and eosin (H&E) staining of the liver showed that the cell size was enlarged by LPS injection and slightly reduced by L. plantarum K8 lysate pre-injection followed by LPS injection. Macrophage infiltration of the liver also decreased in response to the combination injection compared with mice injected with only LPS. Taken together, our results show that although L. plantarum K8 lysates differentially regulated the production of LPS-induced inflammatory cytokines in THP-1 cells, the lysates inhibited overall inflammation in mice. Thus, this study suggests that L. plantarum K8 lysates could be developed as a substance that modulates immune homeostasis by regulating inflammation.
Keywords: IL-1β; Lactiplantibacillus plantarum K8; THP-1; TNF-α; inflammatory cytokines; lipopolysaccharide (LPS); probiotic lysates; septic shock.