Glutamine improves heat stress-induced oxidative damage in the broiler thigh muscle by activating the nuclear factor erythroid 2-related 2/Kelch-like ECH-associated protein 1 signaling pathway

Abstract

The aim of the present study was to evaluate the effect of glutamine (Gln) on modulating heat stress-induced oxidative damage in the broiler thigh muscle through nuclear factor erythroid 2-related 2/Kelch-like ECH-associated protein 1 (Nrf2-Keap1) pathway. Three-hundred 22-day-old Arbor Acres broilers were reallocated into 5 groups: a control group (24 °C) fed with basal diet and 4 heat stress (HS) groups (34 °C for 8 h/D) fed with basal diet containing 0, 0.5, 1.0, and 1.5% Gln. This experiment lasted 21 D. Heat stress decreased (P < 0.05) pH, redness, and Gln levels, and increased (P < 0.05) luminance, water loss rate, and cooking loss (CL) values of the thigh meat. Compared with the HS group, supplementation with 1.5% Gln increased (P < 0.05) pH, redness, and Gln levels, but decreased (P < 0.05) luminance and CL values in the thigh meat. There were significant decreases (P < 0.05) in glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), and Nrf2 levels, but significant increases (P < 0.05) in the malondialdehyde (MDA) and Keap1 levels of the thigh muscle after HS treatment. Compared with the HS group, supplementation with 1.0, and 1.5% Gln decreased (P < 0.05) MDA and Keap1 levels; supplementation with 1.5% Gln increased (P < 0.05) GSH, GSH-Px, T-AOC, CAT, SOD, and Nrf2 levels in the thigh muscle of heat-stressed broilers. Furthermore, HS decreased (P < 0.05) Nrf2, SOD, CAT, and GSH-Px mRNA expression levels, but increased (P < 0.05) Keap1 mRNA level in the thigh muscle of broiler. Dietary supplementation with 1.5% Gln increased (P < 0.05) Nrf2, GSH-Px, CAT, and SOD mRNA expression levels, but decreased (P < 0.05) Keap1 mRNA level in the thigh muscle of heat-stressed broilers. In conclusion, dietary Gln improved the resistance of heat-stressed broiler muscles to oxidative damage possibly through reversing the muscle Gln level and inducing the expression of the Nrf2-Keap1 pathway.

Keywords: Nrf2-Keap1 signaling pathway; antioxidant capacity; glutamine; heat stress; meat quality.

Figure 1

Effect of heat stress and glutamine on glutamine concentration of thigh muscle in broilers. ^a,bGroups without common letters differ significantly (P < 0.05); Duncan's test was used to compare statistical differences among the CON, HS, HS-0.5% Gln, HS-1.0% Gln, and HS-1.5% Gln groups. CON = broilers were kept in the normal-temperature environment and fed a basal diet; HS = broilers were kept in the circular heat stress environment and fed a basal diet; HS-0.5% Gln, HS-1.0% Gln, and HS-1.5% Gln = broilers were kept in the circular heat stress environment and fed basal diets supplemented with 0.5, 1.0, and 1.5 Gln. CON, control; Gln, glutamine; HS, heat stress.

Figure 2

Effect of heat stress and glutamine on the mRNA expression of antioxidant enzymes of thigh muscle in broilers. ^a,b,c,dGroups without common letters differ significantly (P < 0.05); Duncan's test was used to compare statistical differences among the CON, HS, HS-0.5% Gln, HS-1.0% Gln, and HS-1.5% Gln groups. CON = broilers were kept in the normal-temperature environment and fed a basal diet; HS = broilers were kept in the circular heat stress environment and fed a basal diet; HS-0.5% Gln, HS-1.0% Gln, and HS-1.5% Gln = broilers were kept in the circular heat stress environment and fed basal diets supplemented with 0.5, 1.0, and 1.5 Gln. SOD, superoxide dismutase; GSH-Px, glutathione peroxidase; CAT, catalase. The mRNA expression of each gene of the CON was set to be 1. CON, control; Gln, glutamine; HS, heat stress.

Figure 3

Effect of heat stress and Gln on the protein expression of Nrf2 and Keap1 of the thigh muscle in broilers. ^a,b,c Groups without common letters differ significantly (P < 0.05); Duncan's test was used to compare statistical differences among the CON, HS, HS-0.5% Gln, HS-1.0% Gln, and HS-1.5% Gln groups. CON = broilers were kept in the normal-temperature environment and fed a basal diet; HS = broilers were kept in the circular heat stress environment and fed a basal diet; HS-0.5% Gln, HS-1.0% Gln, and HS-1.5% Gln = broilers were kept in the circular heat stress environment and fed basal diets supplemented with 0.5, 1.0, and 1.5 Gln. Nrf2, nuclear factor erythroid 2–related 2; Keap1, kelch-like ECH-associated protein 1. The protein expression of each protein of the CON was set to be 1. CON, control; Gln, glutamine; HS, heat stress.

Figure 4

Effect of heat stress and Gln on the mRNA expression of Nrf2 and Keap1 of the thigh muscle in broilers. ^a,b Groups without common letters differ significantly (P < 0.05); Duncan's test was used to compare statistical differences among the CON, HS, HS-0.5% Gln, HS-1.0% Gln, and HS-1.5% Gln groups. CON = broilers were kept in the normal-temperature environment and fed a basal diet; HS = broilers were kept in the circular heat stress environment and fed a basal diet; HS-0.5% Gln, HS-1.0% Gln, and HS-1.5% Gln = broilers were kept in the circular heat stress environment and fed basal diets supplemented with 0.5%, 1.0%, and 1.5% Gln. Nrf2, nuclear factor erythroid 2–related 2; Keap1, kelch-like ECH-associated protein 1. The mRNA expression of each gene of the CON was set to be 1. CON, control; Gln, glutamine; HS, heat stress.