The impact of ammonia and microcystin-LR on neurobehavior and glutamate/gamma-aminobutyric acid balance in female zebrafish (Danio rerio): ROS and inflammation as key pathways

Microcystis aeruginosa decreased fish appetite via inducing intestinal inflammation

Microcystis aeruginosa is a dominant and widely distributed cyanobacterium that plays a major role in the formation and recurrence of harmful algal blooms in lakes. While it is known to cause intestinal inflammation and appetite dysregulation in fish, the relationship between these effects and their underlying molecular mechanisms remains poorly understood. This study explored the impact of M. aeruginosa-induced intestinal inflammation on fish appetite, with a focus on the underlying molecular pathways, using Pseudorasbora parva exposed to M. aeruginosa for 96 h. We found a significant increase in inflammatory cells in the intestinal tract, accompanied by notable changes in glycerophospholipid and tryptophan metabolism, pathways associated with inflammation and appetite regulation. Key inflammatory markers interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-1 beta (IL-1β), Nuclear factor-kappaB (NF-κB), and tumor necrosis factor-alpha (TNF-α) were significantly elevated, while orexigenic factors orexins, ghrelin, acetylcholine (Ach), and dopamine (DA) were markedly reduced. In contrast, anorexigenic factors 5-Hydroxytryptamine (5-HT), gamma-aminobutyric acid (GABA), proopiomelanocortin (POMC), and glucagon-like peptide-1 (GLP-1) showed significant increases. Correlation analysis revealed that inflammatory markers were negatively correlated with orexigenic factors and positively correlated with anorexigenic factors. These findings indicate that M. aeruginosa-induced intestinal inflammation is a potential mechanism underlying reduced appetite in fish. This study provides novel insights into the toxic effects of M. aeruginosa on fish and offers a new perspective on the mechanisms by which it suppresses fish appetite, contributing to the broader understanding of the ecological and physiological impacts of cyanobacterial blooms.

Competitive Bio-Accumulation Between Ammonia and Nitrite Results in Their Antagonistic Toxicity to Hypophthalmichthys molitrix: Antioxidant and Immune Responses and Metabolic Detoxification Evidence

Ammonia and nitrite, as major aquatic pollutants, exhibit significant toxicity toward aquatic organisms. However, their interactive effects on fish are unclear. Aiming to determine their interactive effects, silver carp (Hypophthalmichthys molitrix) were exposed to ammonia, nitrite or ammonia + nitrite for 72 h. Silver carp exhibited pathological damage in the liver and spleen and significant increases in MDA, SOD and CAT in the liver and plasma after ammonia or nitrite exposure. Thus, ammonia and nitrite caused significant histology damage through inducing oxidative stress, and the antioxidative response of SOD-CAT was initiated by silver carp to defend them. A transcriptomic analysis suggested that disruptions in immune responses and metabolism were the main toxic effects caused by ammonia and nitrite. Specifically, nitrite decreased splenic TNF-α and IL-1β but increased splenic C4. Ammonia decreased splenic TNF-α and C4 but increased splenic IL-1β. We noted significant interactions between ammonia and nitrite, and the pathological changes and IBR in the co-exposure groups were less severe than those in the single-factor exposure groups, indicating that ammonia and nitrite have an antagonistic effect. Significant decreases in plasmatic ammonia and NO2-+NO3- were induced by nitrite and ammonia, respectively. Moreover, the plasmatic glutamine, urea-N, and glutamine synthetase and glutamate dehydrogenase activities increased significantly under ammonia and nitrite exposure, while T-NOS decreased significantly. These results suggest an antagonistic interaction between ammonia and nitrite in silver carp, possibly resulting from competitive bioaccumulation. Consequently, the simultaneous monitoring and control of both ammonia and nitrite concentrations are essential to mitigate their compounded toxic effects, which might be exacerbated under isolated exposure conditions.

Bisphenol-S exposure of zebrafish unveils the hidden risks of bisphenol paradigm with growth, developmental, and behavioral impacts similar to bisphenol-A

The introduction of bisphenol-S (BPS) in substitution of bisphenol-A (BPA) has become argumentative owing to their endocrine destructive properties and insufficient comparative ecotoxicity assessments. Thus, comparative effects of long-term, low-dose BPA and BPS exposure on the development of juvenile zebrafish (Danio rerio) were investigated. Juvenile zebrafish (age: 21 days; weight: ~ 61.5 mg; length: ~ 7.56 mm) were exposed to environmentally-relevant 50 µg/L of BPA, BPS, and control for ~ 60 days in triplicate. Both BPA and BPS significantly increased length (p = 0.00), weight (p = 0.00), specific growth rate (p = 0.00), female preponderance (p = 0.003), mortality (p = 0.017), ammonia excretion (p = 0.00), and aggression (p = 0.00) in zebrafish compared to control. Both bisphenols significantly reduced fish swimming speed in a comparable manner (p = 0.001). A notably higher female-biased-sex ratio was observed in BPS than in BPA (p = 0.003). The length gain (p = 0.014) and aggression (p = 0.032) were higher in BPA-treated fish than in BPS. However, a significant difference was not shown in body mass index (p = 0.295) and condition factor (p = 0.256) between bisphenols and control (p < 0.05). BPA and BPS exposure led to hyperplasia, mucous secretion, aneurism in fish gills, vacuolization and necrosis in liver. Therefore, BPS (~ 50 µg/L) also imposes noteworthy threats to aquatic wildlife, emphasizing the necessity of toxicity assessments and regular monitoring aiming at bespoken environmental standards for freshwater.

A time-dependent interactive effect of nitrite and ammonia on inflammatory and immune response in the head kidney of silver carp (Hypophthalmichthys molitrix)

Nitrite and ammonia stress frequently have harmful effects on aquatic animals. However, the effect of ammonia combined with nitrite on immunity is unclear. Aimed to determine their interactive effect on head kidney, silver carp were exposed to ammonia (15 mg/L), nitrite (10 mg/L), or ammonia+nitrite (15 mg/L + 10 mg/L), and control conditions for 48 h. The results showed that exposure to nitrite and ammonia caused loss of cytoplasm and vacuolar degeneration of cells in head kidney. Following exposure to nitrite and ammonia, tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β) levels decreased significantly, while immunoglobulin M (IgM) and complement 3 (C3) levels increased significantly (P < 0.05). Additionally, TNF-α and C3 were significantly affected synergistically by 24 h of exposure to ammonia+nitrite, while significantly antagonistic effect on IL-1β and C3 was observed after 48 h of exposure. After 48 h of exposure, differently expressed genes (DEGs) induced by ammonia, nitrite, and their combination were mainly assigned to molecular function and biological process, and complement and coagulation cascade pathway was enriched with the highest number of immunity-associated DEGs. Integrated biomarker response (IBR) in nitrite group was higher than that in ammonia group, and the combination of ammonia and nitrite increased and decreased the IBR induced by ammonia and nitrite after 24 and 48 h of exposure, respectively. In conclusion, the toxicities of ammonia and nitrite toward head kidney displayed inflammatory suppression and immune activation, and their had synergistic and antagonistic effects on head kidney at 24 h and 48 h, respectively.

Bloom-forming planktonic Microcystis and benthic Oscillatoria-induced oxidative stress and inflammatory responses in juvenile silver carp and bighead carp

As global warming and water eutrophication, the multiple proliferation of harmful cyanobacteria can form algal blooms and cause serious ecological problems. In recent years, the large-scale and persistent cyanobacterial blooms occur frequently worldwide and have attracted widespread attention due to the harmful impacts. Among these harmful bloom-forming cyanobacteria, the ecological and toxicological impacts of planktonic cyanobacteria have been extensively studied. However, research on the ecological risks and adverse effects of harmful benthic cyanobacteria is lagging. Filter-feeding fish could suffer from more toxic stimuli than other fish due to their special feeding habits. To investigate and compare the complex toxic effects of different kinds of harmful cyanobacteria on fish, three different-sized (i.e. small, medium, and large) juvenile silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) were exposed to cyanobacterial blooms-related density (1 × 106 cells/mL) of Microcystis aeruginosa (i.e. generating microcystins) and Oscillatoria sp. (i.e. generating cylindrospermopsin) for 3 d, after which biomarkers of oxidative stress and inflammation in the liver of fish were detected. The silver carp and bighead carp can effectively ingest Microcystis cells but cannot effectively ingest Oscillatoria cells through the measurement of the levels of cyanotoxins. Both Microcystis and Oscillatoria cells can induce different levels of oxidative stress and inflammatory responses in the liver of these juvenile filter-feeding fish via altering the biochemical parameters of the antioxidant system (e.g. superoxide dismutase activity) and immune system (e.g. interleukin-1β level). Therefore, our research identified potential data gaps that how the different types of cyanobacteria induce toxic effects in the liver of juvenile filter-feeding fish in a short time. This study contributes to a better understanding of the short-term adverse effects of different cyanobacterial species on juvenile fish, suggesting that the benthic toxic cyanobacteria-induced ecological and health risks require further attention.

Rice Straw-Derived Biochar Mitigates Microcystin-LR-Induced Hepatic Histopathological Injury and Oxidative Damage in Male Zebrafish via the Nrf2 Signaling Pathway

Microcystin-leucine arginine (MC-LR) poses a serious threat to aquatic animals during cyanobacterial blooms. Recently, biochar (BC), derived from rice straw, has emerged as a potent adsorbent for eliminating hazardous contaminants from water. To assess the joint hepatotoxic effects of environmentally relevant concentrations of MC-LR and BC on fish, male adult zebrafish (Danio rerio) were sub-chronically co-exposed to varying concentrations of MC-LR (0, 1, 5, and 25 μg/L) and BC (0 and 100 μg/L) in a fully factorial experiment. After 30 days exposure, our findings suggested that the existence of BC significantly decreased MC-LR bioavailability in liver. Furthermore, histopathological analysis revealed that BC mitigated MC-LR-induced hepatic lesions, which were characterized by mild damage, such as vacuolization, pyknotic nuclei, and swollen mitochondria. Compared to the groups exposed solely to MC-LR, decreased malondialdehyde (MDA) and increased catalase (CAT) and superoxide dismutase (SOD) were noticed in the mixture groups. Concurrently, significant changes in the mRNA expression levels of Nrf2 pathway genes (cat, sod1, gstr, keap1a, nrf2a, and gclc) further proved that BC reduces the oxidative damage induced by MC-LR. These findings demonstrate that BC decreases MC-LR bioavailability in the liver, thereby alleviating MC-LR-induced hepatotoxicity through the Nrf2 signaling pathway in zebrafish. Our results also imply that BC could serve as a potentially environmentally friendly material for mitigating the detrimental effects of MC-LR on fish.

Immunoregulation and male reproductive function: Impacts and mechanistic insights into inflammation

This paper investigates the complex relationship between the immune system and male reproductive processes, emphasizing how chronic inflammation can adversely affect male reproductive health. The immune system plays a dual role; it protects and regulates reproductive organs and spermatogenesis while maintaining reproductive health through immune privilege in the testes and the activities of various immune cells and cytokines. However, when chronic inflammation persists or intensifies, it can disrupt this balance, leading to immune attacks on reproductive tissues and resulting in infertility.This study provides a detailed analysis of how chronic inflammation can impair sperm production, sperm quality, and the secretion of gonadal hormones both directly and indirectly. It also delves into the critical roles of testicular immune privilege, various immune cells, and cytokines in sustaining reproductive health and examines the impacts of infections, autoimmune diseases, and environmental factors on male fertility.