Improvement of antioxidant capability by dietary N-acetyl cysteine supplementation alleviates bone loss induced by chronic heat stress in finisher broilers

Abstract

Heat stress (HS) incidence is associated with the accumulation of reactive substances, which might be associated with bone loss. N-Acetylcysteine (NAC) exhibits strong antioxidants due to its sulfhydryl group and being as the precursor for endogenous glutathione synthesis. Therefore, interplay between oxidative stress and bone turnover of broilers and the effects of dietary NAC inclusion on antioxidant capability and “gut-bone” axis were evaluated during chronic HS. Implementing cyclic chronic HS (34 °C for 7 h/d) evoked reactive oxygen species excessive production and oxidant stress, which was accompanied by compromised tibia mass. The RNA-seq of proximal tibia also revealed the enrichment of oxidation–reduction process and inflammatory outbursts during HS. Although no notable alterations in the growth performance and cecal microbiota were found, the diet contained 2 g/kg NAC enhanced the antioxidant capability of heat-stressed broiler chickens by upregulating the expression of Nrf2 in the ileum, tibia, and bone marrow. Simultaneously, NAC tended to hinder NF-κB pathway activation and decreased the mRNA levels of the proinflammatory cytokines in both the ileum and bone marrow. As a result, NAC suppressed osteoclastogenesis and osteoclast activity, thereby increasing osteocyte-related gene expression. Furthermore, the inclusion of NAC tended to increase the ash content and density of the whole tibia, as well as improve cortical thickness and bone volume of the diaphysis. These findings HS-mediated outburst of oxidant stress accelerates bone resorption and negatively regulates the bone quality of tibia, which is inhibited by NAC in broilers.