A comparison of two sources of methionine supplemented at different levels on heat shock protein 70 expression and oxidative stress product of Peking ducks subjected to heat stress

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Birds were vulnerable to high temperatures during summer because of the insufficient heat dissipation after a meal, especially possible for waterfowl (e.g., duck). Heat stress (HS) badly effects on both immune function and production (Humphrey, 2006). Further, HS results in negative effects on growth performance and the relevant mechanisms were explored to mitigate the negative effects (Quinteirofilho et al., 2010; Quinteiro‐Filho et al., 2012; Sandhu, Mirza, Afzal, & Mukhtar, 2012; Song et al., 2013). On the cellular level, high temperature promotes proteolysis and induces the production of excessive free radicals which caused oxidative stress damaging different organs of the body (Del Vesco et al., 2015), such as the liver and intestine.
Methionine (Met) had been recognized as the first limiting amino acid and a functional amino acid for poultry. For example, it affects the synthesis of glutathione (GSH) and taurine in poultry (Bunchasak, 2009). The GSH participates in various biological actions, including preventing host from toxic compounds and defending against free radicals (Morand et al., 1997). Taurine is also derived from biosynthesis in Met and cysteine metabolism and exerts protective effects against oxidative injury by inhibiting of free radicals biosynthesis. The positive effects of supplementing Met were observed under HS. However, the results were not consistent in some cases. The discrepancy might partly attribute to the sources and concentrations of Met supplementation in the diets. Further, in an in vitro study, DL‐2‐hydroxy‐4‐methylthiobutyrate (HMTBA) was preferentially diverted to the trans‐sulphuration pathway, which gave more antioxidant metabolites such as taurine and GSH (Martín‐Venegas et al., 2013). In vivo experiment showed that HMTBA supplementation was more efficient in alleviating high temperature‐induced oxidative damage compared with DL‐Met (DLM) supplementation (a chemically synthesized Met substitute) in plasma (Willemsen et al., 2011). These results suggest that under HS condition, dietary supplementation of Met on an adequate level could act as an antioxidant to mitigate oxidative stress induced by HS. And HMTBA may be a more efficient antioxidant compared with DLM. Also in our previous study with HS, body weight of bird was significantly increased by HMTBA supplementation compared with DLM on day 16, and there is a tendency to improve average daily gain (ADG) and average daily feed intake (ADFI) with the supplementation of HMTBA in day 4–35, and to enhance feed conversion ratio (FCR) along with the supplemental levels of Met (0.05%, 0.20% and 0.35%) during day 4–35 (under review in PLOS ONE journal).
Heat shock proteins (HSPs) were conservative expressed in all living, which was up‐regulated by a variety of physiological, emergency and environmental insults. Among all HSPs,HSP70 was the most widely studied. It played an important role in protecting against stress and had numerous important functions as a molecular chaperone. In vivo, up‐regulation of HSP70 expression significantly improves balance of oxidation–reduction system by effectively scavenging reactive oxygen species (ROS), reducing the damage of mucosal tissue cells (Gu, Hao, & Wang, 2012). In vitro, the positive impact of HSP70 to mitigate oxidative stress in gut epithelial cell lines has been consistently demonstrated in various settings (Arvans et al., 2005; Nobuhiro Ueno et al., 2011; Paszti‐Gere et al., 2012; Segawa et al., 2011). Thus, the augmentation of HSP70 expression may become a potential element in maintaining health, especially under stress conditions. In human however, researchers were attempting to improve therapies of modern cancer treatment by targeting agonist of HSP70 or to develop novel drugs to improve inflammation recently (Kumar et al., 2016; Shevtsov & Multhoff, 2016). Furthermore, researches have been carried out attempting to find the co‐inducers of HSP70 in diet to promote the expression of HSP70 with or without an external a stressor (Eden, 2015).
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