Effects of 4-hydroxyphenylacetic acid, a phenolic acid compound from Yucca schidigera extract, on immune function and intestinal health in meat pigeons

This study aimed to evaluate the effects of 4-hydroxyphenylacetic acid ( 4-HPAA ), a phenolic acid compound from Yucca schidigera extract, in Caco-2 cells and artificial rearing of pigeons. In vitro experiments showed that 4-HPAA at different levels exhibited higher cell viability than shikimic acid and 3,4-dihydroxybenzoic acid, and with the highest viability observed at 600 μM. Additionally, 600 μM 4-HPAA alleviated LPS-induced upregulation of IL-1β and CASPASE1 expressions ( P < 0.05) . In vivo results demonstrated that supplemental 4-HPAA at 500, 1000, and 2000 mg/kg levels did not affect the body weight of 25-day-old pigeons ( P > 0.05), but all levels increased immunoglobulin G ( IgG ) and IgM levels ( P < 0.05). Compared with control, 2000 mg/kg 4-HPAA significantly reduced serum L-lactic acid, D-lactic acid and lactate dehydrogenase ( LDH ) activity ( P < 0.05); increased spleen and bursa of Fabricius indices and intestinal total antioxidant capacity activity of 25-day-old pigeons ( P < 0.05); and elevated ileal barrier-related genes ( OCCLUDIN, CLAUDIN1 and MUC2) in 7-day-old pigeons, as well as jejunal MUC2 and ileal OCCLUDIN in 25-day-old meat pigeons ( P < 0.05). It also inhibited glycolytic gene hexokinase 2 expression, while upregulating the signaling pathway genes CAMK2G and MKNK1 ( P < 0.05). Supplemental 500 and 1000 mg/kg 4-HPAA significantly increased serum total cholesterol levels ( P < 0.05). Notably, 500 mg/kg 4-HPAA had an adverse effect on intestinal integrity, as indicated by the highest serum diamine oxidase content, and increased glycolytic gene LDH-B expression; However, it enhanced microbial richness and diversity in the intestines of 7-day-old pigeon ( P < 0.05). Besides, 1000 mg/kg 4-HPAA impaired intestinal morphology, as evidenced by a lower ileal villus height-to-crypt depth ratio ( P < 0.05), but resulted in the highest abundance of Lactococcus in 25-day-old pigeons. In conclusion, 600 μM 4-HPAA exhibits anti-inflammatory activity in Caco-2 cells, and 2000 mg/kg 4-HPAA promotes immune function and intestinal barrier integrity while inhibiting glycolytic gene expression and the production of related serum metabolites in meat pigeons.