R- Is Superior to S-Form of α-Lipoic Acid in Anti-Inflammatory and Antioxidant Effects in Laying Hens

Abstract

The development of single enantiomers with high efficiency and low toxic activity has become a hot spot for the development and application of drugs and active additives. The aim of the present study was to investigate the effectiveness of the application of α-lipoic acid with a different optical rotation to alleviate the inflammation response and oxidative stress induced by oxidized fish oil in laying hens. Sixty-four 124-week-old Peking Red laying hens were randomly allocated to four groups with eight replicates of two birds each. The normal group was fed basal diets supplemented with 1% fresh fish oil (FO), and the oxidative stress model group was constructed with diets supplemented with 1% oxidized fish oil (OFO). The two treatment groups were the S-form of the α-lipoic acid model with 1% oxidized fish oil (OFO + S-LA) and the R-form of the α-lipoic acid model with 1% oxidized fish oil (OFO + R-LA) added at 100 mg/kg, respectively. Herein, these results were evaluated by the breeding performance, immunoglobulin, immune response, estrogen secretion, antioxidant factors of the serum and oviduct, and pathological observation of the uterus part of the oviduct. From the results, diets supplemented with oxidized fish oil can be relatively successful in constructing a model of inflammation and oxidative stress. The OFO group significantly increased the levels of the serum inflammatory factor (TNF-α, IL-1β, IL-6, and IFN-γ) and the oxidative factor MDA and decreased the activity of the antioxidant enzyme (T-AOC, T-SOD, GSH-Px, GSH, and CAT) in the oviduct. The addition of both S-LA and R-LA significantly reduced the levels of serum inflammatory factors (TNF-α, IL-1β, IL-6, and IFN-γ), increased the activity of antioxidant indexes (T-AOC, T-SOD, GSH-Px, GSH, and CAT), and decreased the MDA contents in the serum and oviduct. Meanwhile, the supplementation of S-LA and R-LA also mitigated the negative effects of the OFO on the immunoglobulins (IgA and IgM) and serum hormone levels (P and E2). In addition, it was worth noting that the R-LA was significantly more effective than the S-LA in some inflammatory (IL-1β) and antioxidant indices (T-SOD, GSH, and CAT). Above all, both S-LA and R-LA can alleviate the inflammation and oxidative damage caused by oxidative stress in aged laying hens, and R-LA is more effective than S-LA. Thus, these findings will provide basic data for the potential development of α-lipoic acid as a chiral dietary additive for laying hens.

Keywords: R-form of α-lipoic acid; S-form of α-lipoic acid; antioxidant; laying hen; oxidized fish oil.

Figure 1

Chemical structure of S-form of α-lipoic acid and R-form of α-lipoic acid.

Figure 2

Effect of different treatments on immunoglobulin of laying hens. (A) Immunoglobulin G (IgG); (B) immunoglobulin A (IgA); (C) immunoglobulin M (IgM). * Indicates minimum significant differences (p < 0.05), and ** indicates highly significant differences (p < 0.01).

Figure 3

Effect of different treatments on serum inflammatory factors of laying hens. (A) Tumor necrosis factor α (TNF-α); (B) interleukin 1β (IL-1β); (C) interleukin 6 (IL-6); (D) interferon γ (IFN-γ). * Indicates minimum significant differences (p < 0.05), and ** indicates highly significant differences (p < 0.01).

Figure 4

Effect of different treatments on serum estrogen of laying hens. (A) Progesterone (P); (B) estradiol (E2). * Indicates minimum significant differences (p < 0.05).

Figure 5

Effect of different treatments on serum antioxidant of laying hens. (A) Total superoxide dismutase (T-SOD); (B) total antioxidant capacity (T-AOC); (C) glutathione peroxidase (GSH-Px); (D) glutathione (GSH); (E) catalase (CAT); (F) malondialdehyde (MDA). ** indicates highly significant differences (p < 0.01).

Figure 6

Effect of different treatments on oviduct structure of laying hens. (A) CON group; (B) OFO group; (C) OFO + S-LA group; (D) OFO + R-LA group; (E) fold length in different treatments. * Indicates minimum significant differences (p < 0.05). Graphs were observed at 0.5×, the size unit of the photograph is 1000 µm.

Figure 7

Effect of different treatments on oviduct antioxidant of laying hens. (A) Total superoxide dismutase (T-SOD); (B) total antioxidant capacity (T-AOC); (C) glutathione peroxidase (GSH-Px); (D) glutathione (GSH); (E) catalase (CAT); (F) malondialdehyde (MDA). * Indicates minimum significant differences (p < 0.05), and ** indicates highly significant differences (p < 0.01).