Effects of lipopolysaccharide exposure on the inflammatory response, butyrate flux, and metabolic function of the ruminal epithelium using an ex vivo model.

ABSTRACT

Acidotic conditions in the rumen have been associated with compromised barrier function of the ruminal epithelium and translocation of microbe-associated molecular patterns (MAMP) such as lipopolysaccharide (LPS). Interaction of MAMP with the ruminal epithelium may also induce a local proinflammatory response. The aim of this study was to evaluate the potential proinflammatory response of the ruminal epithelium following LPS exposure in Ussing chambers, to investigate whether LPS exposure affects the flux and metabolism of butyrate. Ruminal epithelial tissue from 9 Holstein bull calves were mounted into Ussing chambers and exposed to 0, 10,000, 50,000, or 200,000 endotoxin units (EU)/mL LPS for a duration of 5 h. Radiolabeled 14C-butyrate (15 mM) was added to the mucosal buffer to assess the mucosal-to-serosal flux of 14C-butyrate. Additional Ussing chambers, without radioisotope, were exposed to either 0 or 200,000 EU/mL LPS and were used to measure the release of ß-hydroxybutyrate (BHB) and IL1B into the buffer, and to collect epithelial tissue for analysis of gene expression. Genes associated with inflammation (TNF, IL1B, CXCL8, PTGS2, TGFB1, TLR2, TLR4), nutrient transport (MCT1, MCT4, SLC5A8, GLUT1), and metabolic function (ACAT1, BDH1, MCU, IGFBP3, IGFBP5) were selected and analyzed using quantitative real-time PCR. Butyrate flux was not significantly affected by LPS exposure; however, we detected a tendency for the mucosal-to-serosal butyrate flux to increase linearly with LPS dose. Bidirectional releases of BHB and IL1B were not affected by LPS exposure. Expression of PTGS2, TGFB1, TLR4, and MCU were downregulated following exposure to LPS ex vivo. We detected no effects on the expression of genes associated with nutrient transport. The results of the present study are interpreted to indicate that, although the inflammatory response of the ruminal epithelium was slightly suppressed, exposure to LPS may have altered metabolic function.