3.3.3 Effect of GP on LPS in colon contents.
It should be noted that lipopolysaccharide (LPS), one of the components of the cell walls of Gram-negative bacteria in intestinal flora, can cause chronic intestinal inflammation. We determined the levels of endotoxin in colon content (LPS), and it increased by a ratio of 1.45-folds after DSS stimulation. GP treatment reversed the LPS nearly to the normal level.
Corroborating the above data and the previous reports (Goris, de Boer, & van der Waaij, 1988; Zhang et al., 2019), we demonstrated that the increase level of LPS was associated with the rising abundance of Gram-negative bacteria in the intestines of the model rats induced by DSS, and that GP could regulate the structure of gut microbiota and reduce the abundance of Gram-negative bacteria producing LPS.
3.4 GP quenched intestinal injury and restored DSS-decreased levels of autophagy in DSS-induced rats.
When the abundance of Gram-negative bacteria increases, the content of LPS increased consequently and is then recognized by Toll-like receptor 4 (TLR4) on the intestinal cell membrane. This directs a subsequent intracellular reaction and finally leads to an inflammatory response and autophagy inhibition (Chassaing, Koren, Carvalho, Ley, & Gewirtz, 2014). The expression levels of TLR4, IκBα, and NF-κB p65 protein from the rat colon are associated with the inflammatory response and were analyzed by immunofluorescence and Western blot, as shown in Fig. 4. Compared with the blank group, the fluorescence of TLR4 in the model group was significantly enhanced, which indicated the protein expression level was increased. Notably, GP significantly reversed the DSS-increased expression of TLR4. As expected, GP treatment markedly suppressed the DSS-activated NF-κB pathway, indicated by the decrease in phosphorylated IκBα and p65.