The effect of bile acids on the antioxidant capacity of loaches

Foreword

In recent years, high-density and intensive farming methods have increased the environmental pressure on loaches. On the other hand, the rise in fish meal prices and resource shortages have prompted the implementation of strategies to reduce or replace fish meal. However, all these conditions may lead to a decline in the growth performance of loaches, accompanied by a series of liver metabolic disorders and intestinal inflammation, which is not conducive to the sustainable development of aquaculture.

Bile acids, as additives in aquatic animal feed, can effectively address nutritional imbalances (such as high-fat, high starch, and high plant protein diets) and a series of adverse reactions caused by anti nutritional factors. The body's oxidation and antioxidant systems are in a dynamic equilibrium state. SOD is the main enzyme that clears superoxide anion radicals, GSH Px and CAT catalyze the decomposition of hydrogen peroxide (H202), and MDA indirectly reflects the degree of cell damage. The increase of ROS and lack of antioxidants in animals lead to oxidative stress, and exogenous supplementation of antioxidants (such as BA) can enhance antioxidant capacity.In this study, BA supplementation can improve the activity of liver and intestinal antioxidant enzymes (GSH Px, CAT, SOD, and GST) and the content of antioxidant substances (GSH), reduce MDA content, and enhance the antioxidant capacity of loaches.

Keap1-nrf2-are is an endogenous antioxidant signaling pathway in the body. NRF2 is a cell protective transcription factor that is crucial for maintaining the dynamic balance of cellular redox status. It then binds to antioxidant response elements to regulate the transcription levels of genes involved in cellular antioxidant and anti-inflammatory defense, thereby reducing oxidative stress.In this study, the expression levels of nrf2, SOD, CAT, and GSH-PX increased in the BA experimental group, and the highest activity of nrf2, CAT, and SOD was observed in the BA300 group. The expression of key antioxidant genes and the level of antioxidant enzyme activity increased, both of which indicate an overall improvement in the antioxidant capacity of loaches after supplementation with BA feed.

1.Analysis of antioxidant capacity

As shown in Figure 5A, the liver MDA content was significantly lower in all BA experimental groups than in the CON group (P<0.05), with the lowest MDA content observed in the BA300 group. The intestinal MDA content in the BA200, BA300, and BA400 groups was significantly lower than that in the CON and BA100 groups (P<0.05), with the BA300 group having the lowest intestinal MDA content. The GSH content in the liver and intestines of the BA200, BA300, and BA400 groups was significantly higher than that of the CON group (P<0.05); The peak GSH content was highest in the BA300 group, while the GSH content slightly decreased in the BA400 group (Figure 5B). The activity of glutathione peroxidase (GSH Px) in the liver showed an upward trend in all treatment groups, with the GSH Px activity in the BA300 and BA400 groups significantly higher than that in the CON group (P<0.05), with the highest peak in the BA300 group and a decrease in GSH Px activity in the BA400 group (Figure 5C). The activities of CAT and GST in the liver and GSH Px in the intestine were significantly higher in all treatment groups than in the CON group (P<0.05), with the highest peak in the BA300 group and a decrease in the BA400 group.

The CAT, GST, and SOD activities in the BA400 group (Figures 5C, D, and F) were significantly increased compared to the CON group in the BA200, BA300, and BA400 groups (P<0.05) (Figures 5D, E, and F). SOD and GST activity in the liver of all experimental groups were significantly increased compared to the CON group (P<0.05) (Figure 5E and F).

2. Expression of antioxidant related genes

As shown in Figures 6A, B, and D, the expression levels of intestinal SOD, CAT, and liver GSH-PX mRNA in the BA200, BA300, and BA400 groups were significantly higher than those in the CON group (P<0.05) (Figures 6A, B, and C). The expression levels of SOD, CAT, and NF2 mRNA in the liver of all treatment groups were significantly higher than those in the CON group (P<0.05), with the highest peak in the BA300 group and a slight decrease in the peak in the BA400 group. The expression levels of GSH-PX and NF2 mRNA in the gut of all treatment groups were significantly higher than CON (P<0.05), and the peak was highest in the BA200 group (Figure 6D).

3. Expression of inflammation related genes

As shown in the figure. The IL-10 mRNA expression and LysmRNA expression in the liver and intestine of the 7A and B, BA200, BA300, and BA400 groups were significantly higher than those in the CON group (P<0.05), with the BA300 group having the highest expression. The expression of lysozyme mRNA in the liver of BA300 and BA400 groups was significantly higher than that of CON group (P<0.05), with BA300 group showing the highest expression (Figure 7B). The expression of IL-1 β mRNA in liver and intestinal tissues of BA200 group, BA 300 group, and BA400 group was significantly decreased compared with CON group (P<0.05), with the lowest peak observed in BA300 group. In all treatment groups, the expression of TNF - α mRNA in the liver and intestine showed a decreasing trend. Compared with the control group, the expression of TNF - α mRNA in the liver of the BA experimental group was significantly reduced (P<0.05). Compared with the control group, the expression of TNF - α mRNA in the BA200, BA300, and BA400 groups was significantly reduced (P<0.05).

Conclusion

In this study, BA supplementation can improve the activity of liver and intestinal antioxidant enzymes (GSH Px, CAT, SOD, and GST) and the content of antioxidant substances (GSH), reduce MDA content, and enhance the antioxidant capacity of loaches. BA increased the expression levels of nrf2, SOD, CAT, and GSH-PX, and the BA300 group had the highest activity of nrf2, CAT, and SOD. The expression of key antioxidant genes and the level of antioxidant enzyme activity increased, both of which indicate an overall improvement in the antioxidant capacity of loaches after supplementation with BA. In the long run, improving the health of aquatic animals by supplementing functional feed additives is an effective strategy.

Author：Liu H, Zhang X, Li K, et al.

The original：Effects of dietary of bile acid on growth performance, antioxidant capacity, liver and intestinal health and immune function in loach (Misgurnus anguillicaudatus)

Link：https://doi.org/10.1016/j.aqrep.2024.102455

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