Ammonia exposure induces endoplasmic reticulum stress and apoptosis in Chinese striped-necked turtle (Mauremys sinensis)

Fasting influences the muscle quality of fish during transportation by regulating the balance between energy metabolism and ammonia nitrogen stress

INTRODUCTION

Fasting has been widely applied in aquaculture to improve the welfare of fish. However, fasting regulate the interplay of energy metabolism and ammonia nitrogen stress on the muscle quality unclear.

OBJECTIVES

To clarify the impact of fasting on the energy metabolism, ammonia nitrogen stress, and muscle quality.

METHODS

Blunt snout bream (Megalobrama amblycephala) were fasted for different days before transportation. Then changes in energy metabolism, stress response, cell apoptosis, and muscle quality were assessed using UPLC-QTOF-MS untargeted metabolomics along with classical molecular biology techniques.

RESULTS

Our findings revealed that short-term fasting (2-3 d) effectively alleviated ammonia nitrogen stress. The cortisol and superoxide dismutase decreased gradually as the fasting time was extended from 0 to 3 d, with decreased of 28.60 % and 55.39 %. Regarding the energy reserves, a reduction in muscle glycogen, protein, and lipid content was observed after fasting. These changes were attributed to the intensified tricarboxylic acid cycle, amino acid metabolism, and lipid metabolism. Furthermore, fasting enhanced the glycolysis of glycogen, and the gluconeogenesis of glutamic acid and aspartic acid to generate adenosine triphosphate. Notably, short-term fasting alleviated muscle cell apoptosis via down-regulating expression of Caspase 9 and Bax. Moreover, the water holding capacity, shear force, and springiness were better improved after fasting 2 d, reaching 79.88 %, 407.11 g, and 0.78 g, respectively. However, when fasting was extended to 4 d, there was a decrease in energy substances in the fish muscle and an increase in oxidative stress and apoptosis, thereby inducing a decrease in the muscle quality.

CONCLUSION

Our data concluded that fasting affects cell apoptosis by regulating the balance between energy metabolism and stress, ultimately impacting muscle quality. For long-distance transportation, a fasting period of 2-3 d is optimal.

Thiacloprid Exposure Induces Oxidative Stress, Endoplasmic Reticulum Stress, and Apoptosis in the Liver of Mauremys reevesii

Among neonicotinoid insecticides, thiacloprid (THI) is extensively utilized in agricultural practices, which poses a potential toxicity risk to aquatic fauna. Turtles, integral to aquatic ecosystems, have not yet been comprehensively assessed for their vulnerability to THI exposure. In this study, we aimed to evaluate the effects of THI on oxidative stress, endoplasmic reticulum stress (ERS), and apoptosis in aquatic turtles. We categorized Mauremys reevesii into three groups: a control group and two experimental groups exposed to environmentally relevant (4.5 μg/mL) and high (15 mg/mL) concentrations of THI, respectively. Transcriptome analysis revealed that genes significantly associated with the elimination of superoxide radicals, organelle inner membrane functions, peroxiredoxin activity, and apoptotic pathways were abundantly expressed in the high-concentration THI group. Notably, exposure to high concentrations of THI led to a marked increase in glutathione peroxidase (GPX) and superoxide dismutase (SOD) activities, whereas catalase (CAT) activity declined and malondialdehyde (MDA) levels rose, indicating the presence of oxidative stress. Moreover, THI upregulated the expression of the ER stress marker GRP78. Simultaneously, the mRNA levels of pivotal unfolded protein response genes, including AFT6, AFT4, IRE1α, CHOP, XBP1, and eIF2α, were significantly elevated in response to THI exposure. Furthermore, high concentrations of THI significantly activated the activities of caspase-3, caspase-8, and caspase-9 enzymes in the liver tissue. The expression of anti-apoptotic gene Bcl-2 was downregulated, whereas the pro-apoptotic genes Bax and caspase-3 were upregulated, leading to an increase in hepatic apoptotic cells following THI exposure. Collectively, our study indicates that THI can induce hepatic damage in turtles through the promotion of oxidative stress, ERS, and apoptosis. These findings gain a deeper understanding of the toxic effects of THI on keystone species in aquatic ecosystems, thereby improving our overall understanding of their environmental impacts.

Thiacloprid exposure disrupts the gut-liver axis and induces liver dysfunction in the Reeves' turtles (Mauremys reevesii)

As one of the neonicotinoid insecticides, thiacloprid (THI) is extensively used in agriculture and frequently detected in various aquatic environments, posing a potential threat to aquatic organisms. However, the effects of THI exposure on aquatic turtles remain unknown. In this study, we focused on investigating whether THI has a toxic effect on the gut-liver axis in aquatic turtles. The Reeves' turtles (Mauremys reevesii) were exposed to 0.0178 μM, 6 μM, and 60 μM THI for 5 consecutive weeks. The results revealed that THI altered the composition of intestinal flora, with a decrease in the relative abundance of Romboutsia, and an increase in Clostridium_sensu_stricto_1, Cetobacterium, Enterococcus. This disruption of the intestinal barrier led to an increase in lipopolysaccharide (LPS), THI, and other harmful substances entering the liver. Metabolomic and transcriptomic analyses indicated that metabolic dysregulation and differences in gene expression were concentrated in amino acid metabolism and lipid metabolism, ultimately resulting in severe liver damage and steatosis. Furthermore, elevated levels of liver function indicators, including aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), total bile acid (TBA), and triglyceride (TG), were positively correlated with increased THI concentrations. Our findings demonstrate that THI impairs the intestinal barrier and causes liver dysfunction and damage in turtles, providing new insights into evaluating the toxic effects of thiacloprid on aquatic organisms.

Effects of Dietary Fish Oil Supplementation on the Growth, Proximate Composition, and Liver Health of Chinese Stripe-Necked Turtle (Mauremys sinensis)

Dietary lipids provide energy for animals and can also be converted into other nutrients (such as non-essential amino acids), which play a role in saving protein. The Chinese stripe-necked turtle is a protected and endangered species that has been bred in captivity; however, basic data on lipid requirements remain unavailable. In this study, 360 Mauremys sinensis (body weight of 65.32 ± 0.15 g) were randomly divided into six groups with three replicates per group; the turtles were fed experimental diets supplemented with various levels of fish oil (i.e., 1% (control group, CG), 3.5% (HF-1), 6% (HF-2), 8.5% (HF-3), 11% (HF-4), and 13.5% (HF-5)) for 10 weeks. The results showed that compared with CG, increasing the fish oil level promoted the growth performance of turtles, and the HF-3 group achieved the best effect. The HF-4 group showed the highest increases in the hepatosomatic index and viscerosomatic index. In addition, increased lipid levels also increased the crude lipid content and reduced the crude protein content in muscle tissue. Oil red O staining showed that the liver lipid content increased with the level of supplemented fish oil, which is consistent with the results of the hepatosomatic index. Compared with CG, triglyceride, total cholesterol, and low-density lipoprotein cholesterol increased significantly in both the liver and serum when fish oil levels exceeded 8.5% (p < 0.05), while high-density lipoprotein cholesterol decreased significantly. Aspartate transaminase and cerealthirdtransaminase levels in serum increased significantly when fish oil levels exceeded 8.5% (p < 0.05). Moreover, the activities of antioxidant enzymes (GSH-Px, SOD, T-AOC, and CAT) and MDA showed similar results, indicating that high fish oil levels (8.5-13.5%) caused liver tissue damage in M. sinensis. Increased fish oil levels significantly upregulated the expression levels of cytokines (IFN-γ, TNF-α, TGF-β1, IL-10, and IL-12) (p < 0.05), downregulated the expression levels of antioxidant enzyme-related genes (cat, mn-sod, and gsh-px), and increased apoptosis of liver cells. Supplementation of the diet with 3.5-6% fish oil improved the growth performance of M. sinensis, and the turtles maintained a beneficial immune status. The results provide a scientific basis for optimizing the commercial feed formula of M. sinensis.

Comparative toxic effect of ammonia exposure on Mauremys sinensis and invasive species Trachemys scripta elegans

As one of main pollutants, ammonia could cause adverse effects to aquatic animals. To explore the toxic effects of ammonia on Chinese striped-necked turtles (Mauremys sinensis) and invasive species red-eared slider (Trachemys scripta elegans), we compared the activities of antioxidant enzymes, the mRNA levels of genes involved in immune status, endoplasmic reticulum stress and apoptosis between T. s. elegans and M. sinensis under ammonia exposure for 30 days. The results showed that ammonia obviously increased the activities of SOD, CAT, GPX and T-AOC in both T. s. elegans and M. sinensis, especially CAT and GPX in T. s. elegans were higher than that in M. sinensis. The expression levels of JAK, RELA and Mcl-1 in T. s. elegans obviously increased, while IL-6 mRNA levels significantly increased in M. sinensis. In addition, Bip and IRE1 levels in M. sinensis showed a marked increase, and were significantly higher than that in T. s. elegans. Bcl-2 and Bcl-xL transcriptional levels in T. s. elegans showed an increase, especially Bcl-xL were significantly higher than that in M. sinensis. These results indicated that T. s. elegans exhibited more stronger antioxidant defense and immune function than M. sinensis under ammonia exposure. M. sinensis was more likely to occur endoplasmic reticulum stress and inflammation in ammonia environment. This research reveals the physiological response of turtles to ammonia, helps to understand adverse effects of environmental pressure on aquatic turtles, and further explains the tolerance of invasive species T. s. elegans to environmental pollution.

Transcriptome analysis of Chinese mitten crabs (Eriocheir sinensis) gills in response to ammonia stress

The Chinese mitten crab (Eriocheir sinensis) is an important commercial species in China. E. sinensis is typically farmed in rice-crab symbiosis, as an important ecological farming model. However, E. sinensis is often exposed to a high ammonia environment due to the application of nitrogen fertilizers essential for rice growth. We investigated the molecular mechanisms in the gills of E. sinensis exposed to high ammonia at transcriptional and histological levels. We randomly assigned E. sinensis to two groups (control group, CG; ammonia stress group, AG), and gill samples were excised from the CG and AG groups for histopathological and transcriptome analyses. The histopathological evaluation revealed that ammonia stress damaged the gills of E. sinensis. The transcriptome analysis showed that some essential genes, including Xanthine dehydrogenase (XDH), Ubiquitin C-terminal hydrolase-L3 (UCHL3), O-linked N-acetylglucosamine transferase (OGT), Cathepsin B (CTSB), and Ubiquitin-conjugating enzyme E2 W (UBE2W) changed significantly during ammonia exposure. These genes are related to ammonia detoxification, the immune response, and apoptosis. This study demonstrated the molecular response mechanism of E. sinensis gills to ammonia stress at the transcriptional and histological levels. This study provides insight for further study on the molecular mechanism of ammonia stress in crustaceans and supplies technical support for rice crab symbiosis.

Effect of Butyl Paraben on Oxidative Stress in the Liver of Mauremys sinensis

Butyl paraben (BuP) has been widely used as a preservative in the cosmetics, food, and medicine industries. Recently, it has become a new pollutant and has attracted much attention. In order to evaluate the toxic effect of BuP on aquatic animals, Chinese striped-neck turtles (Mauremys sinensis) were exposed to BuP solutions with different concentrations of 0, 5, 50, 500, and 5000 µg/L for 20 weeks. The results showed that with an increase in BuP concentration, the activity of antioxidant enzymes (SOD, CAT and GSH-PX) in liver decreased. The expression of key genes in the Nrf2-Keap1 signal pathways first increased and then decreased, while the expression of the HSP70 and HSP90 genes increased. In addition, the liver had an inflammatory reaction. The expression of the BAFF and IL-6 genes increased and then decreased with an increase in BuP concentration, while the expression of P50 and P65 increased significantly. Oxidative stress induced apoptosis, and the expression of pro-apoptosis genes (BAX, cytc, Caspase3 and Caspase9) increased, while the expression of the anti-apoptosis gene Bcl2 decreased. The results provide an important reference for the comprehensive ecological and health risk assessment of environmental BuP.

Divergent responses in the gut microbiome and liver metabolome to ammonia stress in three freshwater turtles

Ammonia is a common pollutant in aquaculture system, and toxic to all aquatic animals. However, different aquatic animals exhibit diverse physiological responses to high-level ammonia exposure, potentially indicating their divergent resistance to ammonia stress. In this study, juveniles of three freshwater turtles (Mauremys reevesii, Pseudemys nelsoni and Trachemys scripta elegans) were exposed to different concentrations of ammonia (0, 0.3 and 3.0 mg/L) for 30 days, and their swimming, growth performance, gut microbiota, and hepatic metabolites were measured to evaluate the interspecific difference in physiological responses to ammonia stress. Despite no differences in swimming ability, growth rate, and gut microbial diversity, observable changes in microbial community composition and hepatic metabolite profiles were shown in ammonia-exposed turtles. A relatively higher abundance of potentially pathogenic bacteria was found in M. reevesii than in the other two species. Moreover, microbial compositions and metabolic responses differed significantly among the three species. M. reevesii was, out of the three tested species, the one in which exposure to ammonia had the greatest effect on changes in bacterial genera and hepatic metabolites. Conversely, only a few metabolites were significantly changed in T. scripta elegans. Integrating these findings, we speculated that native M. reevesii should be more vulnerable to ammonia stress compared to the invasive turtle species. Our results plausibly reflected divergent potential resistance to ammonia among these turtles, in view of differential physiological responses to ammonia exposure at environmentally relevant concentrations.

Effect of ammonia stress on AMPK regulating-carbohydrate and lipid metabolism in Chinese striped-neck turtle (Mauremys sinensis)

In aquatic organisms, ammonia is one of the major factors that affect energy levels when it exceeds its optimal concentration. Numerous studies have examined the effects of ammonia on aquatic animals, but its effect on metabolism is still unknown. The effect of ammonia on carbohydrates and lipid metabolism in the Chinese striped neck turtle (Mauremys sinensis) was investigated in this study by exposing the turtle to two different ammonia concentrations (A100: 1.53 mg L^-1) and (A200: 2.98 mg L^-1) for 24 and 48 h, respectively. Our results showed that the mRNA expression of adenosine monophosphate-activated protein kinase α1 (AMPKα1) significantly increased only in A100 at 24 h, whereas its activity increased in both ammonia-exposed groups. The two AMPK-regulated transcription factors responsible for carbohydrate metabolism also exhibited changes in ammonia-treated groups, as hepatocyte nuclear factor-4-alpha (HNF4α) increased and forkhead box protein O1 (FoxO1) decreased. The expression of phosphofructokinase (PFK) and glucose-6-phosphatase (G-6-PAS) was subsequently downregulated. In addition, transcription factors, carbohydrate-responsive element-binding protein (ChREBP), and sterol regulatory element-binding protein 1c (SREBP-1c), which are known to be involved in lipogenesis, were suppressed. These downstream genes include fatty acid synthase, stearoyl CoA desaturase, and acetyl-CoA carboxylase (FAS, SCD-1 and ACC). Moreover, the glucose content decreased, whereas the triglyceride content increased significantly in A200 at 24 h. We concluded that AMPK signaling inhibits gluconeogenesis and lipogenesis, and promotes glycolysis to meet energy demand under stressful conditions in M. sinensis.

Gut Microbial Composition and Liver Metabolite Changes Induced by Ammonia Stress in Juveniles of an Invasive Freshwater Turtle

As the most common pollutant in aquaculture systems, the toxic effects of ammonia have been extensively explored in cultured fish, molluscs, and crustaceans, but have rarely been considered in turtle species. In this study, juveniles of the invasive turtle, Trachemys scripta elegans, were exposed to different ammonia levels (0, 0.3, 3.0, and 20.0 mg/L) for 30 days to evaluate the physiological, gut microbiomic, and liver metabolomic responses to ammonia in this turtle species. Except for a relatively low growth rate of turtles exposed to the highest concentration, ammonia exposure had no significant impact on the locomotor ability and gut microbial diversity of turtles. However, the composition of the microbial community could be altered, with some pathogenic bacteria being increased in ammonia-exposed turtles, which might indicate the change in their health status. Furthermore, hepatic metabolite profiles via liquid chromatography-mass spectrometry revealed extensive metabolic perturbations, despite being primarily involved in amino acid biosynthesis and metabolism. Overall, our results show that ammonia exposure causes gut dysbacteriosis and disturbs various metabolic pathways in aquatic turtle species. Considering discrepant defense mechanisms, the toxic impacts of ammonia at environmentally relevant concentrations on physiological performance might be less pronounced in turtles compared with fish and other invertebrates.

The use of selenomethionine to reduce ammonia toxicity in porcine spleen by inhibiting endoplasmic reticulum stress and autophagy mediated by oxidative stress

Ammonia (NH3) is a typical pollutant in the atmosphere and is well known for its harmful effects on plants, animals as well as human health. Previous studies have shown that NH3 exposure can cause damage to immune organs and impaired immune function in animals. Selenomethionine is a kind of organic selenium, which can not only promote the growth and development of the body, but also inhibit the generation of intracellular reactive oxygen species (ROS), and effectively improve the immune function of the body. Therefore, this study evaluated the toxic effect of NH3 exposure on spleen from a new perspective and investigated the protective effect of selenomethionine on ammonia-induced immunotoxicity. Twenty-four Large White*Duroc*Min pigs were randomly assigned to 4 groups: control group, NH3 group, selenium group, and NH3 + selenium group. Our results showed that NH3 inhalation caused autophagy in the pig spleen, a decrease in lymphocytes, and an increase in autophagic vesicles. Also, NH3 exposure led to a decrease in the activity of some antioxidant enzymes (decreased by about 50%) and a significant increase in the expression of genes related to oxidative stress and endoplasmic reticulum stress (ERS). Our results indicated that selenomethionine mitigated ammonia toxicity in pigs (alleviated about 20-55%). In summary, our findings should be of value in providing a theoretical basis for revealing the toxicity of the high-risk gas NH3, and providing a new perspective on the mechanism of Se against toxic substances.

Oxidative Stress Can Be Attenuated by 4-PBA Caused by High-Fat or Ammonia Nitrogen in Cultured Spotted Seabass: The Mechanism Is Related to Endoplasmic Reticulum Stress

Oxidative stress is a common phenomenon in aquaculture, which can be induced by nutritional or environmental factors. Generally, oxidative stress causes poor growth performance, metabolic dysregulation, and even the death of aquatic animals. To identify a nutritional intervention strategy, high-fat diet (HFD) feeding (Experiment I) and acute ammonia nitrogen challenge (Experiment II) tests were carried out. In Experiment I, HFD feeding significantly decreased the growth performance concomitantly with excessive fat deposition in the liver and abdomen. The addition of 4-PBA in the diet improved the excessive fat accumulation. The activities of antioxidative enzymes were suppressed, and the levels of lipid and protein peroxidation were increased, indicating that HFD feeding induced oxidative stress. The endoplasmic reticulum stress (ERs) related genes were downregulated in the HFD group. Under a transmission electron microscope (TEM), more swollen and dilated ER lumen could be observed. These results indicated that the HFD induced ERs activation. Although 4-PBA acted as a potent ERs inhibitor, as evidenced by the alleviated alterations of ERs molecules and the ER ultrastructure, the oxidative stress was also attenuated by 4-PBA. In Experiment II, dietary 4-PBA improved the tolerance to the acute ammonia nitrogen challenge, as lower mortality and serum aminotransferase activity was found. Further results showed that 4-PBA decreased the peroxidation content and attenuated ERs, thus confirming the correlation between oxidative stress and ERs. Our findings showed that dietary 4-PBA supplementation can attenuate oxidative stress induced by a HFD or acute ammonia challenge; the mechanism is related to its potent inhibition effect for ERs.