Aromatic Amino Acids Alleviate Intestinal Inflammation in Piglets through Calcium-Sensing Receptor Activation

B. Tan^{†, #}, B. Huang^{†, ‡}, J. Wang^{†, ‡}, G. P. Guang^†, C. B. Yang^{†, #}, and Yulong Yin^{†, *}

^† National Engineering Laboratory for Pollution Control and Waste Utilization in Livestock and Poultry Production, Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, Hunan, China

^‡ University of Chinese Academy of Sciences, Beijing 100008, China

^# Department of Animal Science, Faculty of Agricultural and Food Sciences, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada.

ABSTRACT: Ca²⁺-sensing receptor (CaSR) plays a key role in the maintenance of intestinal barrier function and represents a potential therapeutic target for inflammatory bowel diseases. CaSR strongly prefers aromatic amino acid ligands, such as tryptophan, phenylalanine and tyrosine. Therefore, this study was conducted to investigate the regulatory effects of dietary supplement with aromatic amino acid——tryptophan, phenylalanine and tyrosine (TPT) on CaSR signaling pathway and intestinal inflammatory response in piglets. A total of 40 weaned piglets (landrace ×large white ) with similar weight were used in a 2 × 2 factorial design according to diet ( basal diet or supplement with 0.24% Phe + 0.16% Trp + 0.24% Tyr) and inflammatory challenge (intraperitoneally injected with saline or LPS). On the morning of days 21 after the initiation of treatment, the piglets of each dietary treatment were intraperitoneally injected with LPS at 100 μg/kg body weight or the same amount of sterilized saline, respectively. Blood and intestine samples were collected 4 h after inflammation challenged. The results showed that piglets challenged with LPS have a significant increase in rectal temperature, histopathological injury as well as colon myeloperoxidase (MPO) activity, whereas dietary supplementation with TPT significantly alleviated piglets histopathological injury induced by LPS and significantly decreased MPO activity induced by LPS. Dietary supplement with TPT significantly decrease piglets serum pro-inflammatory cytokines concentrations of interleukin (IL)1β, IL6, IL8, IL12, GM-CSF and tumor necrosis factor alpha (TNF-α) as well as intestinal abundances of pro-inflammatory cytokines mRNA but significantly enhance anti-inflammatory cytokine IL4 and TGFβ level (p < 0.05). Dietary supplement with TPT significantly increased CaSR and PLCβ2 protein expressions level, but decreased p-NF-κB, IKKα/β, and IκB protein expressions level in LPS-challenged piglets (p < 0.05). Based on these results, supplement with TPT can alleviate intestinal inflammation in piglets induced by LPS, this may be concomitant with the activation of CaSR and the inhibition of NF-κB signaling pathways.