# Dietary Tannic Acid Improves Hepatic Health and Capacity to Deal with Temperature Fluctuation in the Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

## TL;DR

Adding tannic acid to the diet of Chinese soft-shelled turtles improves liver health and helps them cope with temperature changes.

## Contribution

The study shows that 2 g/kg dietary tannic acid protects liver health during temperature fluctuations by boosting antioxidants and regulating lipid pathways.

## Key findings

- 2 g/kg tannic acid increased antioxidant enzyme activities and reduced liver injuries in turtles.
- Tannic acid regulated metabolic profiles and energy-related signaling pathways like adipocytokine and steroid biosynthesis.
- 4 g/kg tannic acid was toxic, but 2 g/kg was effective in protecting the liver during cold stress.

## Abstract

Great temperature variations increase the risk of illness or death in the Chinese soft-shelled turtle, potentially leading to significant economic losses in the farming industry. Therefore, it is crucial to find effective strategies to overcome temperature stress-induced damage in the farming industry. Herein, we evaluated the roles of dietary tannic acid in regulating liver health under temperature fluctuations. The results found that 2 g/kg dietary tannic acid improved the activities of antioxidant enzymes and alleviated histological injuries in the liver. Furthermore, it affected the metabolic profiles and regulated energy-related signaling pathways in the liver to deal with cold stress, such as adipocytokine signaling pathway, steroid biosynthesis, and α-linolenic acid metabolism. Generally, this research indicated that 2 g/kg TA could protect hepatic health from temperature fluctuations by enhancing the antioxidant capacity, reducing histological injuries, and regulating lipid-related signaling pathways.

To assess the impact of tannic acid (TA) on the hepatic health of the Chinese soft-shelled turtle, the individuals were fed diets containing 0 (CG), 0.5, 1, 2, and 4 g/kg TA diets for 60 days (0 hps). Afterwards, the turtles were challenged with 15 °C cold stress for 24 h (24 hps) and then recovered to 28 °C for 24 h (48 hps). The results indicated that 4 g/kg TA has a significant toxic effect on the turtles after 60-day administration. The hepatic T-SOD, CAT, GSH-Px, and T-AOC activities in the TA2 were increased at 0 hps and 24 hps (p < 0.05) compared with CG. Similarly, Sod1, Sod2, Cat, Gsh-px3, and Gsh-px4 mRNA levels in the TA2 were higher than in the other four groups at 0 hps and 24 hps (p < 0.05). The histology data showed that 4 g/kg TA induced injuries in liver at 0 hps and after temperature fluctuation, whereas the 2 g/kg TA effectively attenuated the hepatic injuries. A total of 202 differentially expressed metabolites (DEMs) in the CG vs. TA2 and 115 DEMs in the LTCG vs. LTTA2 were separately detected by the metabolome. The cephalosporin C, protoporphyrin, bis(2-ethylhexyl) phthalate, 2-acetamidoethylphosphonat, verbasosid, and norcocain, were obvious DEMs in the CG vs. TA2. Furthermore, valienone 7-phosphate, 5-HETE, pregnanetriolone, 4-keto-anhydrotetracyclin, dephospho-CoA, and lysoPC(18:4(6Z,9Z,12Z,15Z)/0:0) were top DEMs in the LTCG vs. LTTA2. The “adipocytokine signaling pathway” and “AMPK signaling pathway” were the key pathways enriched in the CG vs. TA2, while “fatty acid biosynthesis”, “steroid biosynthesis”, and “linoleic acid metabolism” were most abundant in the LTCG vs. LTTA2. Generally, this research indicated that 2 g/kg TA could protect hepatic health from temperature fluctuations by improving antioxidant capacity, reducing histological injuries, and regulating lipid-related signaling pathways.