L-Tyrosine enhances tight junction integrity and anti-inflammatory properties: a potential alternative to antibiotic...

The increasing threat of antibiotic-resistant bacteria has prompted the search for alternatives to antibiotic growth promoters (AGPs). Phenyl lactate (PLA) was recently reported to exert an effect on broiler growth promoters in high doses; however, it is not registered as a feed additive. L-tyrosine (L-Tyr), a metabolite of PLA, is often used in the livestock industry. In this study, we evaluated the effects of L-Tyr on gut microbiota, tight junction integrity, and immune response using epithelial cells (Caco-2) as well as various immune cells, including natural killer cells, macrophages, and dendritic cells. We found that L-Tyr improved tight junction integrity at low concentrations, similar to AGPs. In addition, L-Tyr reduced several pro-inflammatory cytokines (TNF-α, IL-6, and IL-12p70) from macrophages and dendritic cells, as well as IFN-γ from natural killer cells, at lower concentrations than AGPs. L-Tyr was metabolized by various microbial species; however, the dissolution tests indicated that enteric-coated L-Tyr was more effective than non-coated L-Tyr at low doses. These findings indicate that coated L-Tyr may serve as an alternative to AGPs, mitigating the risk of antimicrobial resistance.