Acute nitrite exposure-induced oxidative damage, endoplasmic reticulum stress, autophagy and apoptosis caused gill tissue damage of grass carp (Ctenopharyngodon idella): Relieved by dietary protein

Exploring the novel benefits of leucine: Protecting nitrite-induced liver damage in sub-adult grass carp (Ctenopharyngodon idella) through regulating mitochondria quality control

Leucine is an essential amino acid for fish. The ability of leucine to resist stress in fish has not been reported. Nitrite is a common pollutant in the aquatic environment. Therefore, we investigated the effects of dietary leucine on growth performance and nitrite-induced liver damage, mitochondrial dysfunction, autophagy, and apoptosis for sub-adult grass carp. A total of 450 grass carp (615.91 ± 1.15 g) were selected and randomly placed into 18 net cages. The leucine contents of the six diets were 2.91, 5.90, 8.92, 11.91, 14.93, and 17.92 g/kg, respectively. After a 9-week feeding trial, the nitrite exposure experiment was set up for 96 h. These results indicated that dietary leucine significantly promoted FW, WG, PWG, and SGR of sub-adult grass carp (P < 0.05). Appropriate levels of dietary leucine (11.91-17.92 g/kg) decreased the activities of serum parameters (glucose, cortisol, and methemoglobin contents, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and lactate dehydrogenase), the contents of reactive oxygen species (ROS), nitric oxide (NO) and peroxynitrite (ONOO-). In addition, appropriate levels of dietary leucine (11.91-17.92 g/kg) increased the mRNA levels of mitochondrial biogenesis genes (PGC-1α, Nrf1/2, TFAM), fusion-related genes (Opa1, Mfn1/2) (P < 0.05), and decreased the mRNA levels of caspase 3, caspase 8, caspase 9, fission-related gene (Drp1), mitophagy-related genes (Pink1, Parkin) and autophagy-related genes (Beclin1, Ulk1, Atg5, Atg7, Atg12) (P < 0.05). Appropriate levels of dietary leucine (8.92-17.92 g/kg) also increased the protein levels of AMP-activated protein kinase (AMPK), prostacyclin (p62) and decreased the protein levels of protein light chain 3 (LC3), E3 ubiquitin ligase (Parkin), and Cytochrome c (Cytc). Appropriate levels of leucine (8.92-17.92 g/kg) could promote growth performance and alleviate nitrite-induced mitochondrial dysfunction, autophagy, apoptosis for sub-adult grass carp. Based on quadratic regression analysis of PWG and serum GPT activity, dietary leucine requirements of sub-adult grass carp were recommended to be 12.47 g/kg diet and 12.55 g/kg diet, respectively.

Silybin prevented avermectin-induced cardiotoxicity in carp by modulating oxidative stress, inflammation, endoplasmic reticulum stress, mitochondrial apoptosis, and autophagy

Avermectin is one of the widely used anthelmintics in aquaculture and exhibits substantial toxicity to aquatic organisms. Silybin is extensively used for its anti-inflammatory, antioxidant and anti-apoptotic biological properties. Heart is essential for the survival of fish and plays a vital role in pumping blood oxygen and nutrients. Residual avermectin in water poses harm to carp. However, there is still insufficient research on whether silybin can mitigate the toxicity of avermectin to carp heart tissues. In this research, we established a model involving carp subjected to acute avermectin exposure and administered diets containing silybin to explore the potential protective effects of silybin against avermectin-induced cardiotoxicity. The results revealed that avermectin induced oxidative stress, inflammation, endoplasmic reticulum (ER) stress, mitochondrial pathway apoptosis and autophagy in the cardiac tissues of carp. Compared with the avermectin group, silybin significantly reduced ROS accumulation in cardiac tissues, restored antioxidant enzyme activity, inhibited mRNA transcript levels of pro-inflammatory-related factors, and attenuated ER stress, mitochondrial pathway apoptosis and autophagy. Protein-protein interaction (PPI) analysis demonstrated that silybin mitigated avermectin-induced cardiac oxidative stress, inflammation, ER stress, mitochondrial pathway apoptosis and autophagy. Silybin exerted anti-inflammatory effects through the Nuclear Factor kappa B (NF-κB) pathway, antioxidant effects through the Nuclear factor erythroid 2-related factor 2 (Nrf2) - Kelch-like ECH-associated protein 1 (Keap1) pathway, alleviated cardiac ER stress through the Glucose-regulated protein 78 (GRP78)/Activating Transcription Factor 6 (ATF6)/C/EBP homologous protein (CHOP) axis, suppressed apoptosis through the mitochondrial pathway, and inhibited excessive autophagy initiation through the PTEN-induced putative kinase 1 (PINK1)/Parkin RBR E3 ubiquitin protein ligase (PARKIN) signaling pathway. This study provided evidence supporting the protective effect of silybin against avermectin-induced cardiotoxicity in carp, highlighting its potential as a dietary additive to protect fish from adverse effects caused by avermectin exposure.

Nitrite induces hepatic glucose and lipid metabolism disorders in zebrafish through mitochondrial dysfunction and ERs response

Nitrite, a highly toxic environmental contaminant, induces various physiological toxicities in aquatic animals. Herein, we investigate the in vivo effects of nitrite exposure at concentrations of 0, 0.2, 2, and 20 mg/L on glucose and lipid metabolism in zebrafish. Our results showed that exposure to nitrite induced mitochondrial oxidative stress in zebrafish liver and ZFL cells, which were evidenced by increased levels of malondialdehyde (MDA) and reactive oxygen species (ROS) as well as decreased mitochondrial membrane potential (MMP) and adenosine triphosphate (ATP). Changes in these oxidative stress markers were accompanied by alterations in the expression levels of genes involved in HIF-1α pathway (hif1α and phd), which subsequently led to the upregulation of glycolysis and gluconeogenesis-related genes (gk, pklr, pdk1, pepck, g6pca, ppp1r3cb, pgm1, gys1 and gys2), resulting in disrupted glucose metabolism. Moreover, nitrite exposure activated ERs (Endoplasmic Reticulum stress) responses through upregulating of genes (atf6, ern1 and xbp1s), leading to increased expression of lipolysis genes (pparα, cpt1aa and atgl) and decreased expression of lipid synthesis genes (srebf1, srebf2, fasn, acaca, scd, hmgcra and hmgcs1). These results were also in consistent with the observed changes in glycogen, lactate and decreased total triglyceride (TG) and total cholesterol (TC) in the liver of zebrafish. Our in vitro results showed that co-treatment with Mito-TEMPO and nitrite attenuated nitrite-induced oxidative stress and improved mitochondrial function, which were indicated by the restorations of ROS, MMP, ATP production, and glucose-related gene expression recovered. Co-treatment of TUDCA and nitrite prevented nitrite-induced ERs response and which was proved by the levels of TG and TC ameliorated as well as the expression levels of lipid metabolism-related genes. In conclusion, our study suggested that nitrite exposure disrupted hepatic glucose and lipid metabolism through mitochondrial dysfunction and ERs responses. These findings contribute to the understanding of the potential hepatotoxicity for aquatic animals in the presence of ambient nitrite.

Hypoxia leads to gill endoplasmic reticulum stress and disruption of mitochondrial homeostasis in grass carp (Ctenopharyngodon idella): Mitigation effect of thiamine

Hypoxia in water environment is one of the important problems faced by intensive aquaculture. Under hypoxia stress, the effects of dietary thiamine were investigated on grass carp gill tissue damage and their mechanisms. Six thiamine diets with different thiamine levels (0.22, 0.43, 0.73, 1.03, 1.33 and 1.63 mg/kg) were fed grass carp (Ctenopharyngodon idella) for 63 days. Then, 96-hour hypoxia stress test was conducted. This study described that thiamine enhanced the growth performance of adult grass carp and ameliorated nutritional status of thiamine (pyruvic acid, glucose, lactic acid and transketolase). Additionally, thiamine alleviated the deterioration of blood parameters [glutamic oxalacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), glucose, cortisol, lactic dehydrogenase (LDH), erythrocyte fragility, and red blood cell count (RBC count)] caused by hypoxia stress, and reduced reactive oxygen species (ROS) content and oxidative damage to the gills. In addition, thiamine alleviated endoplasmic reticulum stress in the gills, which may be related to its inhibition of RNA-dependent protein kinase-like ER kinase (PERK)/eukaryotic translation initiation factor-2α (eIF2α)/activating transcription factor4 (ATF4), inositol-requiring enzyme 1 (IRE1)/X-Box binding protein 1 (XBP1) and activating transcription factor 6 (ATF6) pathways. Furthermore, thiamine maintaining mitochondrial dynamics balance was probably related to promoting mitochondrial fusion and inhibiting mitochondrial fission, and inhibiting mitophagy may involve PTEN induced putative kinase 1 (PINK1)/Parkin-dependent pathway and hypoxia-inducible factor (HIF)-Bcl-2 adenovirus E1B 19 kDa interacting protein 3 (BNIP3) pathway. In summary, thiamine alleviated hypoxia stress in fish gills, which may be related to reducing endoplasmic reticulum stress, regulating mitochondrial dynamics balance and reducing mitophagy. The thiamine requirement for optimum growth [percent weight gain (PWG)] of adult grass carp was estimated to be 0.81 mg/kg diet. Based on the index of anti-hypoxia stress (ROS content in gill), the thiamine requirement for adult grass carp was estimated to be 1.32 mg/kg diet.

Toxic effects of combined exposure to homoyessotoxin and nitrite on the survival, antioxidative responses, and apoptosis of the abalone Haliotis discus hannai

Homoyessotoxin (homo-YTX) and nitrite (NO2-N), released during harmful dinoflagellate cell lysis adversely affect abalones. However, their toxicity mechanisms in shellfish remain unclear. This study investigated the economic abalone species Haliotis discus hannai exposed to varying concentrations of homo-YTX (0, 2, 5, and 10 µg L-1) and NO2-N (0, 3, and 6 mg L-1) on the basis of their 12 h LC50 values (5.05 µg L-1 and 4.25 mg L-1, respectively) and the environmentally relevant dissolved concentrations during severe dinoflagellate blooms, including mixtures. The test abalones were exposed to homo-YTX and NO2-N for 12 h. The mortality rate (D), reactive oxygen species (ROS) levels, antioxidant defense capabilities, and expression levels of antioxidant-related, Hsp-related, and apoptosis-related genes in abalone gills were assessed. Results showed that the combined exposure to homo-YTX and NO2-N increased the D and ROS levels and upregulated B-cell lymphoma-2 (BCL2)-associated X (BAX) and caspase3 (CASP3) expression levels while reducing glutathione peroxidase (GPx) activity and GPx, CuZnSOD, and BCL2 expression levels. High concentrations of homo-YTX (10 µg L-1) and NO2-N (6 mg L-1) solutions and the combinations of these toxicants inhibited the activities of superoxide dismutase (SOD) and catalase (CAT) and downregulated the expression levels of MnSOD, CAT, Hsp70, and Hsp90. The ROS levels were negatively correlated with the activities of SOD, CAT, and GPx and the expression levels of MnSOD, CuZnSOD, CAT, GPx, Hsp70, Hsp90, and BCL2. These results suggest that homo-YTX, in conjunction with NO2-N, induces oxidative stress, disrupts antioxidant defense systems, and triggers caspase-dependent apoptosis in the gills of abalone. ROS-mediated antioxidative and heat-shock responses and apoptosis emerge as potential toxicity mechanisms affecting the survival of H. discus hannai due to homo-YTX and NO2-N exposure.