Bamboo leaf flavonoids ameliorate cyclic heat stress-induced oxidative damage in broiler liver through activation of Keap1-Nrf2 signaling pathway

Heat stress (HS) induces oxidative stress in the liver and affects health and production attributes in poultry birds. Bamboo leaf flavonoid (BLF) is a natural plant flavonoid that is effective in controlling oxidative stress. Therefore, the aim of current study was to investigate the impact of BLF on growth performance, liver index, serum biochemical parameters of liver function, liver antioxidant enzyme activities, and expression of genes and proteins related to the liver Keap1-Nrf2 system in cyclic heat stress (CHS) broilers. Twenty-eight-day old Arbor Acres broilers (n = 200) were randomly assigned to 5 groups. TN group fed basal diet was reared in a thermoneutral environment (24 +/- 1 degrees C); CHS, 400 mg/kg BLF + CHS, 800 mg/kg BLF + CHS, and 1600 mg/kg BLF + CHS groups were reared in high temperature conditions (33 +/- 1 degrees C, 8 h/day), with the basal diet supplemented with 0, 400, 800, and 1600 mg/kg BLF. The results indicated that ADG and ADFI of broilers in 28 to 35d and 36 to 42d CHS groups were significantly lower compared to the TN group. BLF improves growth performance of CHS broilers by increasing ADG, ADFI and decreasing F:G. BLF improved live weight, liver weight, liver index and reduced serum AST, ALP, ALT, T-BIL levels and increased TP levels in CHS broilers. Meanwhile, BLF supplementation enhanced the activity of hepatic antioxidant enzymes, resulting in higher T-AOC, CAT, GSH-PX and T-SOD levels than those of CHS broilers, and significantly reduced MDA levels. In addition, BLF down- regulated the protein levels of Keap1 and P62, increased the expression levels of Nrf2 genes and proteins, and activated the expression of its downstream NQO1, HO-1, and SOD-1 antioxidant genes compared to CHS broilers. In summary, BLF regulates the expression of key genes and proteins in the Keap1-Nrf2 signaling pathway to alleviate liver injury in broilers by inhibiting oxidative stress, thereby promoting the growth performance of broilers with CHS.