Antibacterial, Cytotoxicity and Mechanism of the Antimicrobial Peptide KR-32 in Weaning Piglets

Diarrhea is a serious issue among livestock, and pathogens and viral infections are the main causes of diarrhea, especially in weaned piglets. Additionally, overuse of antibiotics can lead to severe environment pollution. Therefore, our objective was to study a 32-residue engineered antimicrobial peptide, KR-32, that displays high antimicrobial activity with minimal hemolytic activity and cytotoxicity. Minimum inhibitory concentration and scanning electron microscopy results indicated that antimicrobial peptide KR-32 exerted its antimicrobial activity by destroying the cell membrane integrity. Piglets with clinical diarrhea were divided into three groups and treated with saline (control), KR-32 for 3 days. The antimicrobial peptide KR-32 alleviated the diarrhea of the weaned piglets by reducing the diarrheal rate and index, and it significantly decreased the IL-6 and TNF-α levels compared with the control group levels. To further study the inflammation of the piglets, we tested the effects of KR-32 on IPEC-J2 in vitro. We found that KR-32 attenuated lipopolysaccharides (LPS)-induced inflammation by activating the STAT-1 signaling pathway. In addition, KR-32 significantly reduced pro-inflammation factors IL-6, IL-8 and TNF-α compared with the LPS-treated group. LPS-induced inflammation also affected intestinal barrier functions, but KR-32 enhanced the intestinal barrier by increasing expression of TJ proteins (claudin-1 and occludin) in IPEC-J2. In conclusion, our research reveals AMP KR-32 may have potential application for the control of infectious disease in livestock, and furthermore, AMP KR-32 is a potent antibacterial agent.