Bacteria-free solution derived from Lactobacillus plantarum inhibits multiple NF-kappaB pathways and inhibits proteasome function.

BACKGROUND: Bacteria play a role in inflammatory bowel disease and other forms of intestinal inflammation. Although much attention has focused on the search for a pathogen or inciting inflammatory bacteria, another possibility is a lack of beneficial bacteria that normally confer anti-inflammatory properties in the gut. The purpose of this study was to determine whether normal commensal bacteria could inhibit inflammatory pathways important in intestinal inflammation.
METHODS: Conditioned media from Lactobacillus plantarum (Lp-CM) and other gut bacteria was used to treat intestinal epithelial cell (YAMC) and macrophage (RAW 264.7) or primary culture murine dendritic cells. NF-kappaB was activated through TNF-Receptor, MyD88-dependent and -independent pathways and effects of Lp-CM on the NF-kappaB pathway were assessed. NF-kappaB binding activity was measured using ELISA and EMSA. 1kappaB expression was assessed by Western blot analysis, and proteasome activity determined using fluorescence-based proteasome assays. MCP-1 release was determined by ELISA.
RESULTS: Lp-CM inhibited NF-kappaB binding activity, degradation of IkappaBalpha and the chymotrypsin-like activity of the proteasome. Moreover, Lp-CM directly inhibited the activity of purified mouse proteasomes. This effect was specific, since conditioned media from other bacteria had no inhibitory effect. Unlike other proteasome inhibitors, Lp-CM was not toxic in cell death assays. Lp-CM inhibited MCP-1 release in all cell types tested.
CONCLUSIONS: These studies confirm, and provide a mechanism for, the anti-inflammatory effects of the probiotic and commensal bacterium Lactobacillus plantarum. The use of bacteria-free Lp-CM provides a novel strategy for treatment of intestinal inflammation which would eliminate the risk of bacteremia reported with conventional probiotics.