Effects Of Histamine On The Inflammatory Pathways In Rumen Epithelial Cell Of Cattle With Subacute Rumen Acidosis

Ruminant with subacute ruminal acidosis（SARA） existed low pH environmentand fermentation dysfunction in rumen, which resulted in the accumulation ofhistamine, endotoxin, lactic acid. Thus, large amount of histamine transfer into bloodthrough rumen wall, and results in ruminitis. NF-κB pathway is the maininflammatory signaling pathway. It is unclear whether histamine can activate theNF-κB pathway and then induce inflammatory damage or not. Therefore, in this study,the blood biochemical indexs were detected in healthy and SARA cows to evaluatethe level of imflamatory. In vitro, ruminal epithelium cells were cultured and treatedwith different concentrations of histamine and PDTC (NF-κB inhibitor). The effect ofhistamine on the NF-κB signaling pathway and the inflammatory cytokines wasdetected, which provided valuable information to investigate the mechanism ofinflammatory injury in ruminal epithelium cells induced by histamine in cows withSARA.The concentration of blood biochemical indexes in healthy and SARA cows,such as, lipopolysaccharide (LPS), lipopolysaccharide binding protein (LBP),histamine, glucose (GLU), alanine aminotransferase (ALT), Aspartatetransaminase(AST), direct bilirubin (DBIL), total bilirubin (TBIL), indirect bilirubin(IBIL), total protein (TP), albumin (ALB), globulin (GLO), creatinine (CREA) andβ-hydroxybutyric acid (BHBA) were determined. The levels of these parameters(except Glu) were significantly higher in SARA cows than in healthy cows, whichindicated that there was different of inflammatory reaction in cows with SARA.In vitro, ruminal epithelium cells were cultured and treated with differentconcentrations of histamine and PDTC (NF-κB inhibitor). The expression of keymolecule involved in NF-κB signaling pathway and inflammatory cytokines weredetermined. For time course experiments, the phosphorylation levels of IκB α werehighest at6h of histamine treatment.For dose-response experiments, hepatocyteswere treated with different concentrations of histamine (0.5,2.5,12.5and62.5μM),10μM PDTC and10μM PDTC+12.5μM histamine, respectively. The results shownthat histamine treatment could significantly increase the mRNA expression andphosphorylation levels of IκB α and NF-κB p65and in an dose-dependent manner. Furthermore, the transcriptional activity and nuclear translocation of NF-κB p65werealso significantly increased. Consequently, the expression of inflammatory cytolinesTNF-α, IL-6and IL-1β were also significantly increased, thereby the inflammatoryinjury were induced in ruminal epithelium cells. In addition, the NF-κB inhibitorPDTC could decrease the phosphorylation levels of IκB α and NF-κB p65, NF-κBp65transcriptional activity, and inflammatory cytolines content.In conclusion, the present data indicate that higher concentrations of histaminecan overactivate the NF-κB signaling pathway, thereby increasing the expression andrelease of pro-inflammatory factors TNF-α, IL-6and IL-1β and then inducinginflammatory injury in cattle ruminal epithelium cell.