Ammonia-induced production of free radicals in primary cultures of rat astrocytes

Excessive intragastric alcohol administration exacerbates hepatic encephalopathy and provokes neuronal cell death in male rats with chronic liver disease

Hepatic encephalopathy (HE) is defined as decline in neurological function during chronic liver disease (CLD). Alcohol is a major etiological factor in the pathogenesis of fibrosis/cirrhosis and has also been documented to directly impact the brain. However, the role of alcohol in the development of HE in CLD remains unclear. Here, we investigated the impact of excessive alcohol administration on neurological deterioration in rats with CLD. Starting day 7 post-BDL surgery, rats were administered alcohol twice daily (51% v/v ethanol, 3 g/kg, via gavage) for 4 weeks. Motor coordination was assessed weekly using rotarod and anxiety-like behavior was evaluated with open field and elevated plus maze at 5 weeks. Upon sacrifice, brains were collected for western blot and immunohistochemical analyses to investigate neuronal integrity and oxidative stress status. Alcohol worsened motor coordination performance and increased anxiety-like behavior in BDL rats. Impairments were associated with decreased neuronal markers of NeuN and SMI311, increased apoptotic markers of cleaved/pro-caspase-3 and Bax/Bcl2, increased necroptosis markers of pRIP3 and pMLKL, decreased total antioxidant capacity (TAC), and increased 4-hydroxynonenal (4-HNE)modified proteins in the cerebellum of BDL-alcohol rats when compared to respective controls. Immunofluorescence confirmed the colocalization of cleaved caspase-3 and pMLKL in the granular neurons of the cerebellum of BDL-alcohol rats. Excessive alcohol consumption exacerbates HE which leads to associated apoptotic and necroptotic neuronal loss in the cerebellum of BDL-alcohol rats. Additionally, higher levels of 4-HNE and decreased TAC in the cerebellum of BDL-alcohol rats suggest oxidative stress is the triggering factor of apoptotic and necroptotic neuronal loss/injury.

Mitigation of cold stress in Nile tilapia (Oreochromis niloticus) through dietary lipids supplementation: a preliminary network meta-analysis

There is a growing body of evidence suggesting that water temperature can significantly impact the dietary fatty acid requirements of Nile tilapia (Oreochromis niloticus). Therefore, this study assessed the effectiveness of different dietary lipid sources on the growth performance of Nile tilapia reared at suboptimal temperatures. A network meta-analysis was performed, including searches of PubMed and Scopus from inception to January 2022, for trials that evaluated the effects of lipid sources on cold-stressed Nile tilapia. The Bayesian hierarchical framework was used to pool and compare the effect sizes of growth parameters such as weight gain, feed intake, and feed conversion ratio (FCR). Furthermore, the surface under the cumulative ranking curve (SUCRA) was obtained to calculate the probability that each lipid source was the most effective against cold stress. All subsequent numbers refer to comparisons with diets containing only fish oil. Dietary Aurantiochytrium significantly increased weight gain (SMD = 2.00, CrI: 0.70 to 3.40). In contrast, diets containing coconut oil led to significantly lower weight gain (SMD = - 3.30, CrI: - 6.00 to - 0.63) and higher FCR (SMD = 17.0, CrI: 6.70 to 27.0). Additionally, dietary corn oil was associated with a decrease in feed intake (SMD = - 2.32, CrI: - 3.91 to - 0.80), while a combination of fish and corn oil reduced FCR (SMD = - 5.70, CrI: - 11.0 to - 0.81). In general, the analysis of SUCRA values revealed that in cold-stressed Nile tilapia, Aurantiochytrium, sunflower oil, and the combination of fish and corn oil were the most effective lipid sources for improving growth at suboptimal temperatures. The results of the current study can serve as a basis for future studies that focus on the use of dietary lipid sources to mitigate cold stress in Nile tilapia.

Ammonia Toxicity and Associated Protein Oxidation: A Single-Cell Surface Enhanced Raman Spectroscopy Study

Ammonia (NH3) is a commonly used industrial chemical to which exposure at high concentrations can result in severe skin damage. Moreover, high levels of ammonia in the human body can lead to hyperammonemia conditions and enhanced cancer metabolism. In this work, the toxicity mechanism of NH3 has been studied against human dermal fibroblast (HDF) cells using surface-enhanced Raman spectroscopy (SERS). For this purpose, gold nanoparticles of size 50 nm have been prepared and used as probes for Raman signal enhancement, after being internalized inside HDF cells. Following the exposure to ammonia, HDF cells showed a significant variation in the protein ternary structure's signals, demonstrating their denaturation and oxidation process, together with early signs of apoptosis. Meaningful changes were observed especially in the Raman vibrations of sulfur-containing amino acids (cysteine and methionine) together with aromatic residues. Fluorescence microscopy revealed the formation of reactive oxygen and nitrogen species in cells, which confirmed their stressed condition and to whom the causes of protein degradation can be attributed. These findings can provide new insights into the mechanism of ammonia toxicity and protein oxidation at a single-cell level, demonstrating the high potential of the SERS technique in investigating the cellular response to toxic compounds.

Inhibition of the urea cycle by the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin increases serum ammonia levels in mice

The aryl hydrocarbon receptor is a ligand-activated transcription factor known for mediating the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds. TCDD induces nonalcoholic fatty liver disease (NAFLD)-like pathologies including simple steatosis that can progress to steatohepatitis with fibrosis and bile duct proliferation in male mice. Dose-dependent progression of steatosis to steatohepatitis with fibrosis by TCDD has been associated with metabolic reprogramming, including the disruption of amino acid metabolism. Here, we used targeted metabolomic analysis to reveal dose-dependent changes in the level of ten serum and eleven hepatic amino acids in mice upon treatment with TCDD. Bulk RNA-seq and protein analysis showed TCDD repressed CPS1, OTS, ASS1, ASL, and GLUL, all of which are associated with the urea cycle and glutamine biosynthesis. Urea and glutamine are end products of the detoxification and excretion of ammonia, a toxic byproduct of amino acid catabolism. Furthermore, we found that the catalytic activity of OTC, a rate-limiting step in the urea cycle was also dose dependently repressed. These results are consistent with an increase in circulating ammonia. Collectively, the repression of the urea and glutamate-glutamine cycles increased circulating ammonia levels and the toxicity of TCDD.

Experimental hepatic encephalopathy causes early but sustained glial transcriptional changes

Hepatic encephalopathy (HE) is a common complication of liver cirrhosis, associated with high morbidity and mortality, for which no brain-targeted therapies exist at present. The interplay between hyperammonemia and inflammation is thought to drive HE development. As such, astrocytes, the most important ammonia-metabolizing cells in the brain, and microglia, the main immunomodulatory cells in the brain, have been heavily implicated in HE development. As insight into cellular perturbations driving brain pathology remains largely elusive, we aimed to investigate cell-type specific transcriptomic changes in the HE brain. In the recently established mouse bile duct ligation (BDL) model of HE, we performed RNA-Seq of sorted astrocytes and microglia at 14 and 28 days after induction. This revealed a marked transcriptional response in both cell types which was most pronounced in microglia. In both cell types, pathways related to inflammation and hypoxia, mechanisms commonly implicated in HE, were enriched. Additionally, astrocytes exhibited increased corticoid receptor and oxidative stress signaling, whereas microglial transcriptome changes were linked to immune cell attraction. Accordingly, both monocytes and neutrophils accumulated in the BDL mouse brain. Time-dependent changes were limited in both cell types, suggesting early establishment of a pathological phenotype. While HE is often considered a unique form of encephalopathy, astrocytic and microglial transcriptomes showed significant overlap with previously established gene expression signatures in other neuroinflammatory diseases like septic encephalopathy and stroke, suggesting common pathophysiological mechanisms. Our dataset identifies key molecular mechanisms involved in preclinical HE and provides a valuable resource for development of novel glial-directed therapeutic strategies.

Glial Glutamine Homeostasis in Health and Disease

Glutamine is an essential cerebral metabolite. Several critical brain processes are directly linked to glutamine, including ammonia homeostasis, energy metabolism and neurotransmitter recycling. Astrocytes synthesize and release large quantities of glutamine, which is taken up by neurons to replenish the glutamate and GABA neurotransmitter pools. Astrocyte glutamine hereby sustains the glutamate/GABA-glutamine cycle, synaptic transmission and general brain function. Cerebral glutamine homeostasis is linked to the metabolic coupling of neurons and astrocytes, and relies on multiple cellular processes, including TCA cycle function, synaptic transmission and neurotransmitter uptake. Dysregulations of processes related to glutamine homeostasis are associated with several neurological diseases and may mediate excitotoxicity and neurodegeneration. In particular, diminished astrocyte glutamine synthesis is a common neuropathological component, depriving neurons of an essential metabolic substrate and precursor for neurotransmitter synthesis, hereby leading to synaptic dysfunction. While astrocyte glutamine synthesis is quantitatively dominant in the brain, oligodendrocyte-derived glutamine may serve important functions in white matter structures. In this review, the crucial roles of glial glutamine homeostasis in the healthy and diseased brain are discussed. First, we provide an overview of cellular recycling, transport, synthesis and metabolism of glutamine in the brain. These cellular aspects are subsequently discussed in relation to pathological glutamine homeostasis of hepatic encephalopathy, epilepsy, Alzheimer's disease, Huntington's disease and amyotrophic lateral sclerosis. Further studies on the multifaceted roles of cerebral glutamine will not only increase our understanding of the metabolic collaboration between brain cells, but may also aid to reveal much needed therapeutic targets of several neurological pathologies.

Nano‑zinc enhances gene regulation of non‑specific immunity and antioxidative status to mitigate multiple stresses in fish

The toxicity of ammonia surged with arsenic pollution and high temperature (34 °C). As climate change enhances the pollution in water bodies, however, the aquatic animals are drastically affected and extinct from nature. The present investigation aims to mitigate arsenic and ammonia toxicity and high-temperature stress (As + NH₃ + T) using zinc nanoparticles (Zn-NPs) in Pangasianodon hypophthalmus. Zn-NPs were synthesized using fisheries waste to developing Zn-NPs diets. The four isonitrogenous and isocaloric diets were formulated and prepared. The diets containing Zn-NPs at 0 (control), 2, 4 and 6 mg kg^-1 diets were included. Superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione-s-transferase (GST) were noticeably improved using Zn-NPs diets in fish reared under with or without stressors. Interestingly, lipid peroxidation was significantly reduced, whereas vitamin C and acetylcholine esterase were enhanced with supplementation of Zn-NPs diets. Immune-related attributes such as total protein, globulin, albumin, myeloperoxidase (MPO), A:G ratio, and NBT were also improved with Zn-NPs at 4 mg kg^-1 diet. The immune-related genes such as immunoglobulin (Ig), tumor necrosis factor (TNFα), and interleukin (IL1b) were strengthening in the fish using Zn-NPs diets. Indeed, the gene regulations of growth hormone (GH), growth hormone regulator (GHR1), myostatin (MYST) and somatostatin (SMT) were significantly improved with Zn-NPs diets. Blood glucose, cortisol and HSP 70 gene expressions were significantly upregulated by stressors, whereas the dietary Zn-NPs downregulated the gene expression. Blood profiling (RBC, WBC and Hb) was reduced considerably with stressors (As + NH₃ + T), whereas Zn-NPs enhanced the RBC, WBC, and Hb count in fish reread in control or stress conditions. DNA damage-inducible protein gene and DNA damage were significantly reduced using Zn-NPs at 4 mg kg^-1 diet. Moreover, the Zn-NPs also enhanced the arsenic detoxification in different fish tissues. The present investigation revealed that Zn-NPs diets mitigate ammonia and arsenic toxicity, and high-temperature stress in P. hypophthalmus.

Ammonia Toxicity in the Bighead Carp (Aristichthys nobilis): Hematology, Antioxidation, Immunity, Inflammation and Stress

Ammonia is one of the main environmental pollutants that affect the survival and growth of fish. The toxic effects on blood biochemistry, oxidative stress, immunity, and stress response of bighead carp (Aristichthys nobilis) under ammonia exposure were studied. Bighead carp were exposed to total ammonia nitrogen (TAN) concentrations of 0 mg/L, 3.955 mg/L, 7.91 mg/L, 11.865 mg/L, and 15.82 mg/L for 96 h. The results showed that ammonia exposure significantly reduced hemoglobin, hematocrit, red blood cell, white blood cell count, and platelet count and significantly increased the plasma calcium level of carp. Serum total protein, albumin, glucose, aspartate aminotransferase, and alanine aminotransferase changed significantly after ammonia exposure. Ammonia exposure can induce intracellular reactive oxygen species (ROS), and the gene expression of antioxidant enzymes (Mn-SOD, CAT, and GPx) increases at the initial stage of ammonia exposure, while MDA accumulates and antioxidant enzyme activity decreases after ammonia stress. Ammonia poisoning changes the gene expression of inflammatory cytokines; promotes the gene expression of inflammatory cytokines TNF-α, IL-6, IL-12, and IL-1β; and inhibits IL-10. Furthermore, ammonia exposure led to increases in stress indexes such as cortisol, blood glucose, adrenaline, and T3, and increases in heat shock protein 70 and heat shock protein 90 content and gene expression. Ammonia exposure caused oxidative stress, immunosuppression, inflammation, and a stress reaction in bighead carp.

Effects of ammonia exposure on anxiety behavior, oxidative stress and inflammation in guppy (Poecilia reticulate)

Ammonia is one of the most important aquatic environmental factors, which is of great concern. In order to evaluate the effect of ammonia on guppy (Poecilia reticulate), fish were exposed to increased concentrations (0, 12.50, 25.00, 41.67, 62.50 mg/L) of ammonia for 48 h. After exposure, we measured the anxiety behavior, antioxidant enzymes and pro-inflammation genes (TNF-α, IL-1β and IL-6) of guppy. The results showed that ammonia stress induced fish anxiety, which was manifested by the increased latency to enter the upper half and decreased time spent in upper half compared with control fish. The guppy showed oxidative stress after 48 h of ammonia stress as evidenced by decreases in the activities of antioxidant enzymes and an increase in lipid hydroperoxide content. With prolonged ammonia stress, the expressions of HSP70, HSP90, TNF-α, IL-1β and IL-6 mRNA at first had an increasing trend, and then decreased, all of which were significantly higher than the control levels at 12 h and 24 h after ammonia stress (P < 0.05). Ammonia significantly upregulated these genes mRNA levels after 48 h exposure, suggesting that heat shock proteins and innate immune system may try to protect cells from oxidative stress induced by ammonia stress. Our study showed that higher ammonia exposure induced oxidative stress in exposed fish, since inhibition of antioxidant enzymes activity and increases in lipid peroxidation, and inflammation occurred. Furthermore, the results will be helpful to understand the mechanism of ammonia toxicity in guppys.

Evaluation of oxidative damage to biomolecules and inflammation in patients with urea cycle disorders

Urea cycle disorders (UCD) are inborn errors of metabolism that occur due to a loss of function in enzymes and transporters involved in the urea cycle, causing an intoxication by hyperammonemia and accumulation of metabolites. Patients can develop hepatic encephalopathy (HE), severe neurological and motor disabilities, and often death. The mechanisms involved in the pathophysiology of UCD are many and complex, but there are strong indications that oxidative stress and inflammation are present, being responsible for at least part of the cellular damage that occurs in these diseases. The aim of this study was to evaluate oxidative and nitrosative damage and inflammation in UCD, to better understand the pathophysiology mechanisms of these diseases. We evaluated the nitrite and nitrate content, thiobarbituric acid-reactive substances (TBARS), carbonyl protein content and a panel of cytokines in plasma sample of 14 patients. The UCD patients group consisted of individuals affected with ornithine transcarbamylase deficiency (n = 8), carbamoyl phosphate synthetase deficiency (n = 2), argininosuccinate synthetase deficiency (n = 2); arginase 1 deficiency (n = 1) and argininosuccinate lyase deficiency (n = 1). Patients mean age at diagnosis was 5.25 ± 9.86 years-old and mean concentrations were compared with healthy individuals of matched age and gender. We found a significant reduction in nitrogen reactive species in patients when compared to controls. TBARS was increased in patients, indicating lipid peroxidation. To evaluate protein oxidative damage in UCD, the carbonyl content was measured, and the results also demonstrated an increase in this biomarker. Finally, we found that UCD patients have enhanced concentrations of cytokines, with pro-inflammatory interleukins IL-6, IL-8, interferon-γ and TNF-α, and anti-inflammatory IL-10 being increased when compared to the control group. In conclusion, our results demonstrate that oxidative stress and inflammation occurs in UCD and probably contribute to the severe brain damage present in patients.

Cellular Pathogenesis of Hepatic Encephalopathy: An Update

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome derived from metabolic disorders due to various liver failures. Clinically, HE is characterized by hyperammonemia, EEG abnormalities, and different degrees of disturbance in sensory, motor, and cognitive functions. The molecular mechanism of HE has not been fully elucidated, although it is generally accepted that HE occurs under the influence of miscellaneous factors, especially the synergistic effect of toxin accumulation and severe metabolism disturbance. This review summarizes the recently discovered cellular mechanisms involved in the pathogenesis of HE. Among the existing hypotheses, ammonia poisoning and the subsequent oxidative/nitrosative stress remain the mainstream theories, and reducing blood ammonia is thus the main strategy for the treatment of HE. Other pathological mechanisms mainly include manganese toxicity, autophagy inhibition, mitochondrial damage, inflammation, and senescence, proposing new avenues for future therapeutic interventions.

Long-term exposure of PM2.5 components on the adults' depressive symptoms in China - Evidence from a representative longitudinal nationwide cohort

In recent years, there is growing evidence that long-term exposure to fine particulate matter (PM_2.5) is associated with depressive symptoms. However, little is known about the individual effects of PM_2.5 components, particularly in low-income and middle-income countries. We investigated the association between long-term exposure to major components of PM_2.5 and worsening depressive symptoms in Chinese adults based on a large, long-term, nationally representative, population-based prospective cohort. Our data were derived from China Family Panel Study (CFPS) wave 2012, 2016 and 2018 and a long-term (2010-2019) high-resolution PM_2.5 components dataset covering the whole China. We assessed respondents' depressive symptoms using standardized scales and applied advanced Fixed-effect ordered logit model (FE-ologit) to capture the ordinal nature of respondents' depressive symptoms and control for individual-specific and time-invariant effects to investigate their associations with PM_2.5 components. We included 9503 respondents and the FE-ologit model results indicated that the odds ratio of increase per standard unit was 1.118 (95 % CI: 1.020, 1.225) for black carbon, 1.134 (95 % CI: 1.028, 1.252) for organic matter, 1.127 for ammonium (95 % CI: 1.011, 1.255), 1.107 for nitrate (95 % CI: 0.981, 1.248), and 1.117 for sulfate (95 % CI: 1.020, 1.224). Our study suggests that long-term exposure to PM_2.5 components is significantly associated with worsening of depressive symptoms, and that different components may have different toxicity. Reducing PM_2.5 emissions, especially the major sources of organic matter and ammonium, may reduce the burden of depressive symptoms in Chinese adults.

Ammonia-induced excess ROS causes impairment and apoptosis in porcine IPEC-J2 intestinal epithelial cells

Ammonia is one of the most important toxic metabolites in the intestine of animals. It can cause intestinal damage and associated intestinal diseases through different endogenous or exogenous stimuli. However, the definition of harmful ammonia concentration and the molecular mechanism of ammonia - induced intestinal epithelial injury remain unclear. In this study, we found that the viability of porcine IPEC-J2 intestinal epithelial cells significantly decreased with the increase of NH₄Cl dose (20-80 mM). Ammonia (40 mM NH₄Cl) increased the expression level of ammonia transporter RHCG and disrupted the intestinal barrier function of IPEC-J2 cells by reducing the expression levels of the tight junction molecules ZO-1 and Claudin-1. Ammonia caused elevated levels of ROS and apoptosis in IPEC-J2 cells. This was manifested by decreased activity of antioxidant enzymes SOD and GPx, decreased mitochondrial membrane potential, and increased cytoplasmic Ca²⁺ concentration. In addition, the expression levels of apoptosis-related molecules Caspase-9, Caspase-3, Fas, Caspase-8, p53 and Bax were increased, the expression level of anti-apoptotic molecule Bcl-2 was decreased. Moreover, the antioxidant NAC (N-acetyl-L-cysteamine) effectively alleviated ammonia-induced cytotoxicity, reduced ROS level, Ca²⁺ concentration, and the apoptosis of IPEC-J2 cells. The results suggest that ammonia-induced excess ROS triggered apoptosis through mitochondrial pathway, death receptor pathway and DNA damage. This study can provide reference and theoretical basis for the definition of harmful ammonia concentration in pig intestine and the effect and mechanism of ammonia on pig intestinal health.

Overview of oxidative stress findings in hepatic encephalopathy: From cellular and ammonium-based animal models to human data

Oxidative stress is a natural phenomenon in the body. Under physiological conditions intracellular reactive oxygen species (ROS) are normal components of signal transduction cascades, and their levels are maintained by a complex antioxidants systems participating in the in-vivo redox homeostasis. Increased oxidative stress is present in several chronic diseases and interferes with phagocytic and nervous cell functions, causing an up-regulation of cytokines and inflammation. Hepatic encephalopathy (HE) occurs in both acute liver failure (ALF) and chronic liver disease. Increased blood and brain ammonium has been considered as an important factor in pathogenesis of HE and has been associated with inflammation, neurotoxicity, and oxidative stress. The relationship between ROS and the pathophysiology of HE is still poorly understood. Therefore, sensing ROS production for a better understanding of the relationship between oxidative stress and functional outcome in HE pathophysiology is critical for determining the disease mechanisms, as well as to improve the management of patients. This review is emphasizing the important role of oxidative stress in HE development and documents the changes occurring as a consequence of oxidative stress augmentation based on cellular and ammonium-based animal models to human data.

Dysregulation of Astrocytic Glutamine Transport in Acute Hyperammonemic Brain Edema

Acute liver failure (ALF) impairs ammonia clearance from blood, which gives rise to acute hyperammonemia and increased ammonia accumulation in the brain. Since in brain glutamine synthesis is the only route of ammonia detoxification, hyperammonemia is as a rule associated with increased brain glutamine content (glutaminosis) which correlates with and contributes along with ammonia itself to hyperammonemic brain edema-associated with ALF. This review focuses on the effects of hyperammonemia on the two glutamine carriers located in the astrocytic membrane: Slc38a3 (SN1, SNAT3) and Slc7a6 (y + LAT2). We emphasize the contribution of the dysfunction of either of the two carriers to glutaminosis- related aspects of brain edema: retention of osmotically obligated water (Slc38a3) and induction of oxidative/nitrosative stress (Slc7a6). The changes in glutamine transport link glutaminosis- evoked mitochondrial dysfunction to oxidative-nitrosative stress as formulated in the “Trojan Horse” hypothesis.

Hyperammonemia induces mitochondrial dysfunction and neuronal cell death

Background & Aims

In cirrhosis, astrocytic swelling is believed to be the principal mechanism of ammonia neurotoxicity leading to hepatic encephalopathy (HE). The role of neuronal dysfunction in HE is not clear. We aimed to explore the impact of hyperammonaemia on mitochondrial function in primary co-cultures of neurons and astrocytes and in acute brain slices of cirrhotic rats using live cell imaging.

Methods

To primary cocultures of astrocytes and neurons, low concentrations (1 and 5 μM) of NH₄Cl were applied. In rats with bile duct ligation (BDL)-induced cirrhosis, a model known to induce hyperammonaemia and minimal HE, acute brain slices were studied. One group of BDL rats was treated twice daily with the ammonia scavenger ornithine phenylacetate (OP; 0.3 g/kg). Fluorescence measurements of changes in mitochondrial membrane potential (Δψm), cytosolic and mitochondrial reactive oxygen species (ROS) production, lipid peroxidation (LP) rates, and cell viability were performed using confocal microscopy.

Results

Neuronal cultures treated with NH₄Cl exhibited mitochondrial dysfunction, ROS overproduction, and reduced cell viability (27.8 ± 2.3% and 41.5 ± 3.7%, respectively) compared with untreated cultures (15.7 ± 1.0%, both p <0.0001). BDL led to increased cerebral LP (p = 0.0003) and cytosolic ROS generation (p <0.0001), which was restored by OP (both p <0.0001). Mitochondrial function was severely compromised in BDL, resulting in hyperpolarisation of Δψm with consequent overconsumption of adenosine triphosphate and augmentation of mitochondrial ROS production. Administration of OP restored Δψm. In BDL animals, neuronal loss was observed in hippocampal areas, which was partially prevented by OP.

Conclusions

Our results elucidate that low-grade hyperammonaemia in cirrhosis can severely impact on brain mitochondrial function. Profound neuronal injury was observed in hyperammonaemic conditions, which was partially reversible by OP. This points towards a novel mechanism of HE development.

Lay summary

The impact of hyperammonaemia, a common finding in patients with liver cirrhosis, on brain mitochondrial function was investigated in this study. The results show that ammonia in concentrations commonly seen in patients induces severe mitochondrial dysfunction, overproduction of damaging oxygen molecules, and profound injury and death of neurons in rat brain cells. These findings point towards a novel mechanism of ammonia-induced brain injury in liver failure and potential novel therapeutic targets.

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Low concentrations of ammonia induce mitochondrial dysfunction, overproduction of ROS, and cell death in primary neurons.

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Hyperammonaemia in cirrhotic rats leads to ROS and LP overproduction, which was prevented by the ammonia scavenger OP.

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In neurons from cirrhotic rats, hyperpolarisation of Δψm was observed, which was restored by OP treatment.

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In a rat model of cirrhosis, profound neuronal loss was observed in the hippocampus.

Is the Brain Undernourished in Alzheimer's Disease?

Cerebrospinal fluid (CSF) amino acid (AA) levels and CSF/plasma AA ratios in Alzheimer Disease (AD) in relation to nutritional state are not known. Methods: In 30 fasting patients with AD (46% males, 74.4 ± 8.2 years; 3.4 ± 3.2 years from diagnosis) and nine control (CTRL) matched subjects, CSF and venous blood samples were drawn for AA measurements. Patients were stratified according to nutritional state (Mini Nutritional Assessment, MNA, scores). Results: Total CSF/plasma AA ratios were lower in the AD subpopulations than in NON-AD (p < 0.003 to 0.017. In combined malnourished (16.7%; MNA < 17) and at risk for malnutrition (36.6%, MNA 17−24) groups (CG), compared to CTRL, all essential amino acids (EAAs) and 30% of non-EAAs were lower (p < 0.018 to 0.0001), whereas in normo-nourished ADs (46.7%, MNA > 24) the CSF levels of 10% of EAAs and 25% of NON-EAAs were decreased (p < 0.05 to 0.00021). CG compared to normo-nourished ADs, had lower CSF aspartic acid, glutamic acid and Branched-Chain AA levels (all, p < 0.05 to 0.003). CSF/plasma AA ratios were <1 in NON-AD but even lower in the AD population. Conclusions: Compared to CTRL, ADs had decreased CSF AA Levels and CSF/plasma AA ratios, the degree of which depended on nutritional state.

Alleviative effect of melatonin on the decrease of uterine receptivity caused by blood ammonia through ROS/NF-κB pathway in dairy cow

High concentration of blood ammonia can affect the uterus receptivity and decrease fecundity in dairy cow. Melatonin can reduce reactive oxygen species (ROS) level and has antioxidant and anti-inflammatory effects. However, it is not clear whether melatonin can alleviate ammonia-induced apoptosis of endometrial epithelial cell (EEC) and reduced uterus receptivity. The bovine EEC were treated with ammonium chloride and/or melatonin. Cell viability, apoptosis, oxidative stress and mitochondrial membrane potential were measured and the expression of apoptosis-related genes (p53, Cyt-c, Bax, Bcl-2, caspase-8, caspase-9 and caspase-3), uterus receptivity related genes (VEGF, LIF and EGF) and inflammatory factors (TLR-4, IL-6 and NF-κB) were detected. In addition, the expression of VEGF was detected after adding NF-κB inhibitor (40 μM) and IL-6 (1 ng/mL and 50 ng/mL). The results showed that ammonia significantly increased intracellular ROS level, mRNA and protein expression of Bax, p53, Cyt-c, caspase-9, caspase-8, caspase-3, TLR-4, NF-κB and IL-6, promoted cell apoptosis, while decreased mitochondrial membrane potential, the mRNA and protein expression of VEGF and EGF. Interestingly, melatonin significantly mitigated ammonia-induced changes. However, melatonin could not alleviate ammonia-induced changes of IL-6 and VEGF when NF-κB signal pathway was inhibited. The addition of IL-6 significantly reduced mRNA and protein expression of VEGF. In conclusion, ammonia induced EEC apoptosis through ROS production and activation of mitochondrial apoptosis pathway, and induced inflammatory response through TLR4/NF-κB/IL-6 pathway. Melatonin alleviated EEC apoptosis by inhibiting ROS pathway, and reduced IL-6 expression by inhibiting TLR-4/NF-κB signal pathway, which eventually improved VEGF expression and uterus receptivity in dairy cows.

Impact of bacterial volatiles on phytopathogenic fungi: an in vitro study on microbial competition and interaction

Microorganisms in the rhizosphere are abundant and exist in very high taxonomic diversity. The major players are bacteria and fungi, and bacteria have evolved many strategies to prevail over fungi, among them harmful enzyme activities and noxious secondary metabolites. Interactions between plant growth promoting rhizobacteria and phytopathogenic fungi are potentially valuable since the plant would benefit from fungal growth repression. In this respect, the role of volatile bacterial metabolites in fungistasis has been demonstrated, but the mechanisms of action are less understood. We used three phytopathogenic fungal species (Sclerotinia sclerotiorum, Rhizoctonia solani, and Juxtiphoma eupyrena) as well as one non-phytopathogenic species (Neurospora crassa) and the plant growth promoting rhizobacterium Serratia plymuthica 4Rx13 in co-cultivation assays to investigate the influence of bacterial volatile metabolites on fungi on a cellular level. As a response to the treatment, we found elevated lipid peroxidation, which indirectly reflected the loss of fungal cell membrane integrity. An increase in superoxide dismutase, catalase, and laccase activities indicated oxidative stress. Acclimation to these adverse growth conditions completely restored fungal growth. One of the bioactive bacterial volatile compounds seemed to be ammonia, which was a component of the bacterial volatile mixture. Applied as a single compound in biogenic concentrations ammonia also caused an increase in lipid peroxidation and enzyme activities, but the extent and pattern did not fully match the effect of the entire bacterial volatile mixture.

Toxic Effects on Bioaccumulation, Hematological Parameters, Oxidative Stress, Immune Responses and Tissue Structure in Fish Exposed to Ammonia Nitrogen: A Review

Simple Summary

Ammonia nitrogen is a common environmental limiting factor in aquaculture, which can accumulate rapidly in water and reach toxic concentrations. In most aquatic environments, fish are vulnerable to the toxic effects of high levels of ammonia nitrogen exposure. It has been found that the toxic effects of ammonia nitrogen on fish are multi-mechanistic. Therefore, the purpose of this review is to explore the various toxic effects of ammonia nitrogen on fish, including oxidative stress, neurotoxicity, tissue damage and immune response.

Abstract

Ammonia nitrogen is the major oxygen-consuming pollutant in aquatic environments. Exposure to ammonia nitrogen in the aquatic environment can lead to bioaccumulation in fish, and the ammonia nitrogen concentration is the main determinant of accumulation. In most aquatic environments, fish are at the top of the food chain and are most vulnerable to the toxic effects of high levels of ammonia nitrogen exposure. In fish exposed to toxicants, ammonia-induced toxicity is mainly caused by bioaccumulation in certain tissues. Ammonia nitrogen absorbed in the fish enters the circulatory system and affects hematological properties. Ammonia nitrogen also breaks balance in antioxidant capacity and causes oxidative damage. In addition, ammonia nitrogen affects the immune response and causes neurotoxicity because of the physical and chemical toxicity. Thence, the purpose of this review was to investigate various toxic effects of ammonia nitrogen, including oxidative stress, neurotoxicity and immune response.

Hyperammonemia in Inherited Metabolic Diseases

Ammonia is a neurotoxic compound which is detoxified through liver enzymes from urea cycle. Several inherited or acquired conditions can elevate ammonia concentrations in blood, causing severe damage to the central nervous system due to the toxic effects exerted by ammonia on the astrocytes. Therefore, hyperammonemic patients present potentially life-threatening neuropsychiatric symptoms, whose severity is related with the hyperammonemia magnitude and duration, as well as the brain maturation stage. Inherited metabolic diseases caused by enzymatic defects that compromise directly or indirectly the urea cycle activity are the main cause of hyperammonemia in the neonatal period. These diseases are mainly represented by the congenital defects of urea cycle, classical organic acidurias, and the defects of mitochondrial fatty acids oxidation, with hyperammonemia being more severe and frequent in the first two groups mentioned. An effective and rapid treatment of hyperammonemia is crucial to prevent irreversible neurological damage and it depends on the understanding of the pathophysiology of the diseases, as well as of the available therapeutic approaches. In this review, the mechanisms underlying the hyperammonemia and neurological dysfunction in urea cycle disorders, organic acidurias, and fatty acids oxidation defects, as well as the therapeutic strategies for the ammonia control will be discussed.

Toxic effects of ammonia on the intestine of the Asian clam (Corbicula fluminea)

Intestines contain a large number of microorganisms that collectively play a vital role in regulating physiological and biochemical processes, including digestion, water balance, and immune function. In this study, we explored the effects of ammonia stress on intestinal inflammation, the antioxidant system, and the microbiome of the Asian clam (Corbicula fluminea). Exposure to varying ammonia concentrations (10 and 25 mg N/L) and exposure times (7 and 14 days) resulted in damage to C. fluminea intestinal tissue, according to histological analysis. Furthermore, intestinal inflammatory responses and damage to the antioxidant system were revealed through qPCR, ELISA, and biochemical analysis experiments. Inflammatory responses were more severe in the treatment group exposed to a lower concentration of ammonia. High-throughput 16S rDNA sequencing showed that ammonia stress under different conditions altered intestinal bacterial diversity and microbial community composition, particularly impacting the dominant phylum Proteobacteria and genus Aeromonas. These results indicate that ammonia stress can activate intestinal inflammatory reactions, damage the intestinal antioxidant system, and alter intestinal microbial composition, thereby impeding intestinal physiological function and seriously threatening the health of C. fluminea.

The neurogliovascular unit in hepatic encephalopathy

Hepatic encephalopathy (HE) is a neurological complication of hepatic dysfunction and portosystemic shunting. It is highly prevalent in patients with cirrhosis and is associated with poor outcomes. New insights into the role of peripheral origins in HE have led to the development of innovative treatment strategies like faecal microbiota transplantation. However, this broadening of view has not been applied fully to perturbations in the central nervous system. The old paradigm that HE is the clinical manifestation of ammonia-induced astrocyte dysfunction and its secondary neuronal consequences requires updating. In this review, we will use the holistic concept of the neurogliovascular unit to describe central nervous system disturbances in HE, an approach that has proven instrumental in other neurological disorders. We will describe HE as a global dysfunction of the neurogliovascular unit, where blood flow and nutrient supply to the brain, as well as the function of the blood-brain barrier, are impaired. This leads to an accumulation of neurotoxic substances, chief among them ammonia and inflammatory mediators, causing dysfunction of astrocytes and microglia. Finally, glymphatic dysfunction impairs the clearance of these neurotoxins, further aggravating their effect on the brain. Taking a broader view of central nervous system alterations in liver disease could serve as the basis for further research into the specific brain pathophysiology of HE, as well as the development of therapeutic strategies specifically aimed at counteracting the often irreversible central nervous system damage seen in these patients.

Rapid metabolic and bioenergetic adaptations of astrocytes under hyperammonemia - a novel perspective on hepatic encephalopathy

Hepatic encephalopathy (HE) is a well-studied, neurological syndrome caused by liver dysfunctions. Ammonia, the major toxin during HE pathogenesis, impairs many cellular processes within astrocytes. Yet, the molecular mechanisms causing HE are not fully understood. Here we will recapitulate possible underlying mechanisms with a clear focus on studies revealing a link between altered energy metabolism and HE in cellular models and in vivo. The role of the mitochondrial glutamate dehydrogenase and its role in metabolic rewiring of the TCA cycle will be discussed. We propose an updated model of ammonia-induced toxicity that may also be exploited for therapeutic strategies in the future.

Exploring the Multimodal Role of Yucca schidigera Extract in Protection against Chronic Ammonia Exposure Targeting: Growth, Metabolic, Stress and Inflammatory Responses in Nile Tilapia (Oreochromis niloticus L.)

Simple Summary

Ammonia is a problematic environmental toxicant for aquatic species. The current study aimed to declare the modulatory effect(s) of YSE against chronic ammonia intoxication in Nile tilapia through its effects on growth performance, haemato-biochemical and antioxidant-related parameters, and histopathological changes, as well as the molecular gene expression of some genes related to appetite and growth, glucose and lipid metabolism and some inflammatory cytokines. Our results indicated that Yucca schidigera extract alleviated the adverse impacts induced by ammonia intoxication. YSE could be used as a functional water supplement in aquaculture.

Abstract

Ammonia is a critical hazardous nitrogen metabolic product in aquaculture. Despite trials for its control, ammonia intoxication remains one of the most critical issues to overcome. In this study, we explored the modulatory effect and potential mechanism by which Yucca schidigera extract (YSE) can ameliorate ammonia intoxication-induced adverse effects on tilapia health and metabolism. A total number of 120 Nile tilapia were evenly assigned into four groups with three replicates each. The first group served as normal control group; the second group was exposed to ammonia alone from the beginning of the experiment and for four weeks. The third group was supplied with YSE in water at a dose of 8 mg/L and exposed to ammonia. The fourth group was supplied with YSE only in water at a dose of 8 mg/L. YSE supplementation succeeded in improving water quality by reducing pH and ammonia levels. Moreover, YSE supplementation markedly alleviated chronic ammonia-induced adverse impacts on fish growth by increasing the final body weight (FBW), specific growth rate (SGR), feed intake and protein efficiency ratio (PER) while reducing the feed conversion ratio (FCR) via improvements in food intake, elevation of hepatic insulin-like growth factor (ILGF-1) and suppression of myostatin (MSTN) expression levels with the restoration of lipid reserves and the activation of lipogenic potential in adipose tissue as demonstrated by changes in the circulating metabolite levels. In addition, the levels of hepato-renal injury biomarkers were restored, hepatic lipid peroxidation was inhibited and the levels of hepatic antioxidant biomarkers were enhanced. Therefore, the current study suggests that YSE supplementation exerted an ameliorative role against chronic ammonia-induced oxidative stress and toxic effects due to its free radical-scavenging potential, potent antioxidant activities and anti-inflammatory effects.

The Cerebral Effect of Ammonia in Brain Aging: Blood-Brain Barrier Breakdown, Mitochondrial Dysfunction, and Neuroinflammation

Aging occurs along with multiple pathological problems in various organs. The aged brain, especially, shows a reduction in brain mass, neuronal cell death, energy dysregulation, and memory loss. Brain aging is influenced by altered metabolites both in the systemic blood circulation and the central nervous system (CNS). High levels of ammonia, a natural by-product produced in the body, have been reported as contributing to inflammatory responses, energy metabolism, and synaptic function, leading to memory function in CNS. Ammonia levels in the brain also increase as a consequence of the aging process, ultimately leading to neuropathological problems in the CNS. Although many researchers have demonstrated that the level of ammonia in the body alters with age and results in diverse pathological alterations, the definitive relationship between ammonia and the aged brain is not yet clear. Thus, we review the current body of evidence related to the roles of ammonia in the aged brain. On the basis of this, we hypothesize that the modulation of ammonia level in the CNS may be a critical clinical point to attenuate neuropathological alterations associated with aging.

Hepatic Encephalopathy: From Metabolic to Neurodegenerative

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome of both acute and chronic liver disease. As a metabolic disorder, HE is considered to be reversible and therefore is expected to resolve following the replacement of the diseased liver with a healthy liver. However, persisting neurological complications are observed in up to 47% of transplanted patients. Several retrospective studies have shown that patients with a history of HE, particularly overt-HE, had persistent neurological complications even after liver transplantation (LT). These enduring neurological conditions significantly affect patient's quality of life and continue to add to the economic burden of chronic liver disease on health care systems. This review discusses the journey of the brain through the progression of liver disease, entering the invasive surgical procedure of LT and the conditions associated with the post-transplant period. In particular, it will discuss the vulnerability of the HE brain to peri-operative factors and post-LT conditions which may explain non-resolved neurological impairment following LT. In addition, the review will provide evidence; (i) supporting overt-HE impacts on neurological complications post-LT; (ii) that overt-HE leads to permanent neuronal injury and (iii) the pathophysiological role of ammonia toxicity on astrocyte and neuronal injury/damage. Together, these findings will provide new insights on the underlying mechanisms leading to neurological complications post-LT.

Pathomechanisms in hepatic encephalopathy

Hepatic encephalopathy (HE) is a frequent neuropsychiatric complication in patients with acute or chronic liver failure. Symptoms of HE in particular include disturbances of sensory and motor functions and cognition. HE is triggered by heterogeneous factors such as ammonia being a main toxin, benzodiazepines, proinflammatory cytokines and hyponatremia. HE in patients with liver cirrhosis is triggered by a low-grade cerebral edema and cerebral oxidative/nitrosative stress which bring about a number of functionally relevant alterations including posttranslational protein modifications, oxidation of RNA, gene expression changes and senescence. These alterations are suggested to impair astrocyte/neuronal functions and communication. On the system level, a global slowing of oscillatory brain activity and networks can be observed paralleling behavioral perceptual and motor impairments. Moreover, these changes are related to increased cerebral ammonia, alterations in neurometabolite and neurotransmitter concentrations and cortical excitability in HE patients.

Alterations in hematological and biochemical parameters, oxidative stress, and immune response in Takifugu rubripes under acute ammonia exposure

Ammonia is a major pollutant in aquatic environments and poses a considerable threat to the survival of fish. In this study, we investigated the toxic effects of ammonia on the hematological and biochemical parameters, oxidative stress, and immune responses in Takifugu rubripes. Juvenile T. rubripes (average weight 246.17 ± 3.54 g) were exposed to different concentrations of ammonia (0, 5, 50, 100, and 150 mg/L) for 96 h. The results showed that the hematological parameters (hemoglobin, hematocrit, red blood cell, and white blood cell count) were significantly reduced in response to ammonia exposure. Of the plasma components, such as serum total protein, albumin, glucose, glutamic-oxalacetic transaminase, and glutamic-pyruvic transaminase, were significantly altered in response to ammonia exposure. Additionally, the levels of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and glutathione peroxidase (GPx) were increased after exposure to low concentration ammonia exposure. However, when fish were exposed to a high concentration of ammonia, these parameters showed the opposite trend, suggesting that an increase in antioxidant enzymes during the early stages of ammonia exposure may contribute to the removal of the induced reactive oxygen species (ROS) and protect the cells from oxidative damage. However, as the ammonia concentration and exposure time increased, the overproduction of ROS accelerated the depletion of antioxidant enzymes. Ammonia exposure significantly increased the expression of heat shock proteins (HSP70 and HSP90). Ammonia poisoning elevated gene expressions of TLR-3, TNF-α, IL-6, IL-12, and IL-1β in the gills, causing an inflammatory response. Our findings provide new insights into the mechanisms involved in ammonia-induced aquatic toxicology in marine fish, which may aid in their captive management.

Exogenous inositol ameliorates the effects of acute ammonia toxicity on intestinal oxidative status, immune response, apoptosis, and tight junction barriers of great blue-spotted mudskippers (Boleophthalmus pectinirostris)

Ammonia toxicity can disrupt the intestinal health of aquatic animals. It is important to find substances that alleviate these adverse effects. The present study explored the possible protective role of myo-inositol (MI) in ammonia-induced toxicity in the fish intestine. Great blue-spotted mudskippers (Boleophthalmus pectinirostris) accumulated in artificial seawater (15‰ salinity, n = 600) were randomly selected and intraperitoneally injected with NaCl (0.68%) or MI (2.5 mg/g fish in 0.68% NaCl) then exposed to artificial seawater alone (NaCl and MI group) or seawater containing 57.025 mmol/L ammonium chloride (NH₃ and NH₃ + MI group). After a 24-h experiment, it showed that ammonia exposure down-regulated the mRNA expression levels of intestinal barrier function proteins (Zo-1, Ocln, Cldn-5, Cldn-12, and Cldn-15) and anti-inflammatory cytokines (Tgf-β and Il-10) while the acute ammonia stress up-regulated the apoptosis genes (p53, Bax, Caspase-3, and Caspase-9) and pro-inflammatory cytokines (Tnf-α and Il-1β). Furthermore, ammonia challenge also induced oxidative stress, as the malondialdehyde and the protein carbonyl contents were increased. In addition, ammonia stress down-regulated the antioxidant enzymes (Cu/Zn-Sod, Cat, Gpx, and Gst) activities as well as their gene transcription levels. The administration of the exogenous myo-inositol greatly ameliorated the ammonia-induced changes in redox capacity, immune response, apoptosis, inflammation, and tight junction barrier function to levels similar to those of the NaCl group. Furthermore, fish injected with MI alone showed no significant changes compared with the NaCl group. Taken together, pretreatment with myo-inositol had no obvious side-effects and effectively protected the mudskippers' intestine from the toxicity caused by acute ammonia stress.

Inhibition of PI3K/Akt/mTOR pathway by ammonium chloride induced apoptosis and autophagy in MAC-T cell

Ammonia is a harmful gas with a pungent odor, participates in the regulation of a variety of apoptosis and autophagy, which in turn affects the growth and differentiation of cells. To test the regulation of NH₃ on the apoptosis and autophagy of mammary epithelial cells, we selected NH₄Cl as NH₃ donor in vitro model. MTT and CCK-8 assay kits were employed to detect cell activity. Real-time quantitative PCR and western blot methods were used to detect the abundance of inflammatory molecules, apoptosis markers, and autophagy genes. We selected TUNEL kit and the Annexin-FITC/PI method to detect apoptosis. TEM analysis was used to detect autophagic vesicles, and MDC stain evaluated the formation of autophagosome. The results indicated that NH₄Cl reduced cell viability in a concentration-dependent manner and promoted cell inflammatory response, apoptosis, and autophagy. NH₄Cl stimulation notable increased the autophagosomes number. Interestingly, we also detected that the addition of LY294002 and Rapamycin inhibited the PI3K/Akt pathway and the mTOR pathway, respectively, resulting in changes in both apoptosis and autophagy. Therefore, we draw a conclusion that NH₃ may regulate the apoptosis and autophagic response of bovine mammary epithelial cells through the PI3K/Akt/mTOR signaling pathway. Further investigations on ammonia's function in other physiological respects, will be critical to provide theoretical help for the improvement of production performance. It will be also helpful for controlling the harmful gas ammonia concentration in the livestock house to protect the health of dairy cows.

The nuclear factor kappa B (NF-κB) signaling pathway is involved in ammonia-induced mitochondrial dysfunction

Hyperammonemia is very toxic to the brain, leading to inflammation, disruption of brain cellular energy metabolism and cognitive function. However, the underlying mechanism(s) for these impairments is still not fully understood. This study investigated the effects of ammonia in hippocampal astroglia derived from C57BL/6 mice. Parameters measured included oxygen consumption rates (OCR), ATP, cytochrome c oxidase (COX) activity, alterations in oxidative phosphorylation (OXPHOS), nuclear factor kappa B (NF-κB) subunits, key regulators of mitochondrial biogenesis (peroxisome proliferator-activated receptor gamma coactivator1-alpha (PGC-1α), calcium/calmodulin-dependent protein kinase II (CaMKII), cAMP-response element binding protein (CREB), nuclear factor (erythroid-derived 2)-like 2 (Nrf2), early growth response (Egr) factor family of proteins, and mitochondrial transcription factor A (TFAM). Ammonia was found to decrease mitochondrial numbers, potentially through a CaMKII-CREB-PGC1α-Nrf2 pathway in astroglia. Ammonia did not alter the levels of Egrs and TFAM in astroglia. Ammonia decreased OCR, ATP, COX, and OXPHOS levels in astroglia. To assess whether energy metabolism is reduced by ammonia through NF-κB associated pathways, astroglia were treated with ammonia alone or with NF-κB inhibitors such as Bay11-7082 or SN50. Mitochondrial OCR levels were reduced in the presence of NF-κB inhibitors; however co-treatment of NF-κB inhibitors and ammonia reversed mitochondrial deficits. Further, ammonia increased translocation of the NF-κB p65 into the nucleus of astroglia that correlates with an increased activity of NF-κB. These findings suggest that the NF-κB signaling pathway is putatively involved in ammonia-induced changes in bioenergetics in astroglia. Such research has critical implications for the treatment of disorders in which brain bioenergetics is compromised.

The protective effects of selenium on chronic ammonia toxicity in yellow catfish (Pelteobagrus fulvidraco)

Ammonia is toxic to most fish, and its negative effects can be eliminated by nutritional manipulation. In this study, triplicate groups of yellow catfish (0.58 ± 0.03 g) were fed diets supplemented with 0, 0.30 and 0.60 mg selenium (Se) kg^-1 diet for 56 days under three ammonia contents (0.00, 5.70 and 11.40 mg L^-1 total ammonia nitrogen). The results showed that ammonia toxicity could affects growth (weight gain, feed efficiency ratio, Se contents in muscle and whole body declined) and survival, leads to oxidative stress (total antioxidant capacity, superoxide dismutase, catalase and glutathione peroxidase activities declined and malondialdehyde accumulation), immunosuppression (lysozyme activity, 50% hemolytic complement, immunoglobulin M, respiratory burst and phagocytic index declined) and cytokines release (TNF, IL 1 and IL 8 elevated), induces up-regulation of antioxidant enzymes (Cu/Zn-SOD, Mn-SOD, CAT and GPx), cytokines (TNFα, IL 1 and IL 8) and pro-apoptotic genes (p53, Bax, Cytochrome c, Caspase 3 and Caspase 9) transcription, and down-regulation of anti-apoptotic gene Bcl2 transcription. The dietary Se supplementation could mitigate the adverse effect of ammonia poisoning on fish growth, oxidative damage, immunosuppression and apoptotic.

Comparison of the Effects of Nonprotein and Protein Nitrogen on Apoptosis and Autophagy of Rumen Epithelial Cells in Goats

Simple Summary

Proteins provide important raw materials for the self-renewal of cells in the gastrointestinal tract. Cell self-renewal is inseparable from the coordination between apoptosis and autophagy. Previous researchers have explored whether different nitrogen sources are linked to activation or inhibition of apoptosis/autophagy. However, information on the regulatory mechanism of apoptosis and autophagy induced by different nitrogen sources among cells in the gastrointestinal tract is limited. This study attempted to compare the effects of different nitrogen sources on apoptosis and autophagy of rumen epithelial cells in goats through molecular biology techniques such as flow cytometry, transmission electron microscopy, and fluorescence microscopy. On the basis of the obtained results, we found that autophagy had a less obvious ameliorative effect on ruminal epithelial cell apoptosis after treatment with protein nitrogen than after treatment with nonprotein nitrogen.

Abstract

Protein nutrition is particularly important for the self-renewal processes of gastrointestinal epithelial cells. The self-renewal of cells is inseparable from the interaction between apoptosis and autophagy. However, there are few reports on the relationship between different nitrogen sources and apoptosis/autophagy. In this study, the relative protein expression of Bcl-2-associated X protein(Bax), caspase-3, and p62 was significantly higher (p < 0.05), while that of Bcl-xl, Bcl-2, Beclin1, and Microtuble-associated protein light chain 3 (LC3-II) was significantly lower (p < 0.05), in the NH₄Cl group in comparison with the NH₄Cl + 4-phenylbutyric acid (4PBA) group. In addition, the relative protein expression of Bax and caspase-3 was significantly higher (p < 0.05), while that of Bcl-2 and Bcl-xl was decreased significantly (p < 0.05), in the NH₄Cl + 3-Methyladenine (3-MA) group and the methionine (Met) + 3-MA group in comparison with the NH₄Cl group. Furthermore, the relative protein expression of Beclin1 and LC3B-II was significantly lower (p < 0.05), while that of p62 was significantly higher (p < 0.05), in the NH₄Cl + Z-VAD-FMK group and the Met + Z-VAD-FMK group in comparison with the NH₄Cl group. In conclusion, our results suggested that endoplasmic reticulum (ER) stress played a critical role in the crosstalk between apoptosis and autophagy induced by NH₄Cl and Met. Autophagy had a more obvious ameliorative effect on ruminal epithelial cell apoptosis after treatment with nonprotein nitrogen than after treatment with protein nitrogen. These findings may reveal the molecular mechanism of apoptosis and autophagy induced by nonprotein nitrogen and protein nitrogen.

A SNP of the hemocyanin gene (LvHc) is a marker for high growth and ammonia-tolerance in Pacific white shrimp Litopenaeus vannamei

Expression levels of hemocyanin (LvHc), activating transcription factor 4 (LvAtf4), glutathione S-transferase (LvGst), caspase 2 (LvCasp2) and anti-lipopolysaccharide factor (LvAlf) were examined in the hepatopancreas of Pacific white shrimp Litopenaeus vannamei juveniles exposed to a lethal concentration of ammonia-N (32.15 mg/l). The expression levels of all transcripts except LvAlf were significantly greater (P < 0.05) in tolerant shrimp (Lv-AT; N = 30) that survived up to 72 h post treatment (hpt) than in susceptible shrimp (Lv-AS24 and Lv-AS72; N = 45 and 15), that died within 24 h or between 24 and 72 hpt, respectively. Subsequently, effects of non-lethal concentrations of ammonia-N (control, 10 and 20 mg/l) on the expression of LvHc in juvenile shrimp were examined. Compared to the control, expression levels of LvHc transcripts in hemocytes and the hepatopancreas of tested shrimp changed after exposure to ammonia-N. One SNP (C > T₅₄₅) was found in the LvHc₃₂₂ gene segment. Real-time PCR amplification of specific alleles (real-time PASA) was developed for detection of C > T₅₄₅ genotypes. Juveniles in the lethal exposure test that carried a C/T₅₄₅ genotype showed a greater average body weight and total length (8.46 ± 0.36 g and 10.05 ± 0.16 cm) than those with a C/C₅₄₅ genotype (7.48 ± 0.31 g and 9.60 ± 0.13 cm) (P < 0.05). Similar results were found in the second generation (G2) of a growth-improved stock (3 and 4 families of BIOTEC-G2-L1 and BIOTEC-G2-L2) and in commercially farmed shrimp (2 groups). Accordingly, expression levels and SNP of LvHc can serve as markers for selection high growth performance in ammonia-tolerant L. vannamei.

Acute ammonia poisoning in dolly varden char (Salvelinus malma) and effect of methionine sulfoximine

Ammonia is toxic to most bony fishes. However, little information is available on the toxicology mechanisms induced by ammonia and the means to mitigate the effects by various fishes. In this study, four groups of experiments were designed and carried out to test the response of dolly varden char to ammonia toxicity and their mitigation through methionine sulfoximine (MSO). NaCl group was injected with NaCl, NH₃ group was injected with ammonium acetate, NH₃+MSO group was injected with ammonium acetate and MSO, MSO group was injected with MSO. Results showed that ammonia toxicity could lead to blood deterioration (elevation in white blood cell and blood ammonia), free amino acid imbalance (elevation in glutamine, glutamate, arginine and ornithine, coupled with reduction of citrulline and aspartate), ammonia metabolism enzyme activity inhibition (reduction in carbamyl phosphate synthetase, ornithine transcarbamylase and arginase), oxidative stress (reduction in superoxide dismutase, catalase and glutathione peroxidase) and immunosuppression (reduction in lysozyme, 50% hemolytic complement, total immunoglobulin and phagocytic index), but the MSO can eliminate fatal effect of oxidative damage. In addition, ammonia poisoning could induce down-regulation of antioxidant enzymes coding genes (SOD, CAT and GPx) and up-regulation of inflammatory cytokine genes (TNFα, IL-1β and IL-8) transcription, suggesting that immunosuppression and inflammation may relate to oxidative stress in fish.

Induction of nitric oxide synthesis: a strategy to defend against high environmental ammonia-induced oxidative stress in primary hepatocytes of air-breathing catfish, Clarias magur

Air-breathing magur catfish (Clarias magur) regularly face the problem of exposure to high environmental ammonia (HEA) as one of the major pollutants in their natural habitats that causes considerable toxic effects at the cellular level, including that of oxidative stress. The major objective of the present study was to demonstrate the antioxidant activity of endogenously produced nitric oxide (NO) to defend against ammonia-induced oxidative stress in primary hepatocytes of magur catfish during exposure to HEA. Exposure to NH4Cl (5 mmol l-1) led to a significant increase in intracellular ammonia concentration with a sharp rise of hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations within 3 h in primary hepatocytes, which decreased gradually at later stages of treatment. This phenomenon was accompanied by a significant increase in superoxide dismutase (SOD) and catalase (CAT) activity as a consequence of induction of corresponding genes. HEA exposure also led to the stimulation of NO production due to induction of inducible nitric oxide synthase (iNOS) activity, as a consequence of up-regulation of the nos2 gene. Most interestingly, when NO production by hepatocytes under ammonia stress was blocked by adding certain inhibitors [aminoguanidine and 3-(4-methylphenylsulfonyl)-2-propenenitrile] to the culture medium, there was a further rise of H2O2 and MDA concentrations in hepatocytes. These were accompanied by the lowering of SOD and CAT activity with less expression of corresponding genes. Thus, it can be contemplated that magur catfish use the strategy of stimulation of NO production, which ultimately induces the SOD-CAT enzyme system to defend against ammonia-induced oxidative stress.

Effects of acute ammonia toxicity on oxidative stress, DNA damage and apoptosis in digestive gland and gill of Asian clam (Corbicula fluminea)

Ammonia is one of the major pollutants associated with the main river basins due to ammonification of uneaten food and animal excretion, which usually brings detrimental health effects to aquatic invertebrate. However, the mechanisms of ammonia toxicity in aquatic invertebrate have rarely been reported. In this study, C. fluminea was exposed to different levels of ammonia (control group, 10 mg/L, and 25 mg/L) for 24 h and 48 h, and digestive gland and gill were collected to explore toxic effects on oxidative stress, DNA damage and apoptosis under ammonia stress. The results showed that ammonia poisoning could increase the activity of oxidative stress enzyme (SOD and CAT), inducing differentially expressed genes (DRAM2, GADD45, P53, BAX, BCL2, CASP8, CASP9, CASP3, HSP70 and HSP90) and different cytokines (IL-1 beta, IL-8, IL-17 and TNF-alpha) of DNA damage and apoptosis. The difference of toxic effects induced by ammonia among digestive gland and gill were also observed by real-time PCR and TUNEL staining. Our results will be helpful to understand the mechanism of aquatic toxicology induced by ammonia in C. fluminea.

Astrocyte swelling in hepatic encephalopathy: molecular perspective of cytotoxic edema

Hepatic encephalopathy (HE) may occur in patients with liver failure. The most critical pathophysiologic mechanism of HE is cerebral edema following systemic hyperammonemia. The dysfunctional liver cannot eliminate circulatory ammonia, so its plasma and brain levels rise sharply. Astrocytes, the only cells that are responsible for ammonia detoxification in the brain, are dynamic cells with unique phenotypic properties that enable them to respond to small changes in their environment. Any pathological changes in astrocytes may cause neurological disturbances such as HE. Astrocyte swelling is the leading cause of cerebral edema, which may cause brain herniation and death by increasing intracranial pressure. Various factors may have a role in astrocyte swelling. However, the exact molecular mechanism of astrocyte swelling is not fully understood. This article discusses the possible mechanisms of astrocyte swelling which related to hyperammonia, including the possible roles of molecules like glutamine, lactate, aquaporin-4 water channel, 18 KDa translocator protein, glial fibrillary acidic protein, alanine, glutathione, toll-like receptor 4, epidermal growth factor receptor, glutamate, and manganese, as well as inflammation, oxidative stress, mitochondrial permeability transition, ATP depletion, and astrocyte senescence. All these agents and factors may be targeted in therapeutic approaches to HE.

Cerebral edema and liver disease: Classic perspectives and contemporary hypotheses on mechanism

Liver disease is a growing public health concern. Hepatic encephalopathy, the syndrome of brain dysfunction secondary to liver disease, is a frequent complication of both acute and chronic liver disease and cerebral edema (CE) is a key feature. While altered ammonia metabolism is a key contributor to hepatic encephalopathy and CE in liver disease, there is a growing appreciation that additional mechanisms contribute to CE. In this review we will begin by presenting three classic perspectives that form a foundation for a discussion of CE in liver disease: 1) CE is unique to acute liver failure, 2) CE in liver disease is only cytotoxic, and 3) CE in liver disease is primarily an osmotically mediated consequence of ammonia and glutamine metabolism. We will present each classic perspective along with more recent observations that call in to question that classic perspective. After highlighting these areas of debate, we will explore the leading contemporary mechanisms hypothesized to contribute to CE during liver disease.

Acute Liver Failure Induces Glial Reactivity, Oxidative Stress and Impairs Brain Energy Metabolism in Rats

Acute liver failure (ALF) implies a severe and rapid liver dysfunction that leads to impaired liver metabolism and hepatic encephalopathy (HE). Recent studies have suggested that several brain alterations such as astrocytic dysfunction and energy metabolism impairment may synergistically interact, playing a role in the development of HE. The purpose of the present study is to investigate early alterations in redox status, energy metabolism and astrocytic reactivity of rats submitted to ALF. Adult male Wistar rats were submitted either to subtotal hepatectomy (92% of liver mass) or sham operation to induce ALF. Twenty-four hours after the surgery, animals with ALF presented higher plasmatic levels of ammonia, lactate, ALT and AST and lower levels of glucose than the animals in the sham group. Animals with ALF presented several astrocytic morphological alterations indicating astrocytic reactivity. The ALF group also presented higher mitochondrial oxygen consumption, higher enzymatic activity and higher ATP levels in the brain (frontoparietal cortex). Moreover, ALF induced an increase in glutamate oxidation concomitant with a decrease in glucose and lactate oxidation. The increase in brain energy metabolism caused by astrocytic reactivity resulted in augmented levels of reactive oxygen species (ROS) and Poly [ADP-ribose] polymerase 1 (PARP1) and a decreased activity of the enzymes superoxide dismutase and glutathione peroxidase (GSH-Px). These findings suggest that in the early stages of ALF the brain presents a hypermetabolic state, oxidative stress and astrocytic reactivity, which could be in part sustained by an increase in mitochondrial oxidation of glutamate.

The role of Mu-type glutathione S-transferase in the mud crab (Scylla paramamosain) during ammonia stress

Glutathione S-transferase (GST) plays important roles in cellular detoxification and antioxidant defense. A Mu-type glutathione S-transferase (designated as SpMu-GST) was obtained from the mud crab Scylla paramamosain. The open reading frame of SpMu-GST was comprised a 690 bp, which encoded a putative protein of 229 amino acids. Quantitative real-time PCR (qRT-PCR) revealed that the SpMu-GST mRNA was expressed in all examined tissues, with highest expression in hepatopancreas. During ammonia exposure, the SpMu-GST transcriptions in hepatopancreas and gill were significantly up-regulated at early exposure time. Moreover, RNA interference (RNAi) experiment was designed to understand the roles of SpMu-GST under ammonia exposure. Ammonia exposure reduced the levels of glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT) and total antioxidative capacity (T-AOC), and increased the formation of malondialdehyde (MDA). After knockdown of the SpMu-GST level, GST activity and T-AOC were significantly decreased at some exposure time after ammonia exposure. However, the mortality of mud crabs and malondialdehyde (MDA) contents significantly increased under ammonia exposure. These results further suggested that SpMu-GST played a critical role in mud crab antioxidant defenses in response to environmental stress.

Molecular Mechanisms of Fuchs and Congenital Hereditary Endothelial Corneal Dystrophies

The cornea, the eye's outermost layer, protects the eye from the environment. The cornea's innermost layer is an endothelium separating the stromal layer from the aqueous humor. A central role of the endothelium is to maintain stromal hydration state. Defects in maintaining this hydration can impair corneal clarity and thus visual acuity. Two endothelial corneal dystrophies, Fuchs Endothelial Corneal Dystrophy (FECD) and Congenital Hereditary Endothelial Dystrophy (CHED), are blinding corneal diseases with varied clinical presentation in patients across different age demographics. Recessive CHED with an early onset (typically age: 0-3 years) and dominantly inherited FECD with a late onset (age: 40-50 years) have similar phenotypes, although caused by defects in several different genes. A range of molecular mechanisms have been proposed to explain FECD and CHED pathology given the involvement of multiple causative genes. This critical review provides insight into the proposed molecular mechanisms underlying FECD and CHED pathology along with common pathways that may explain the link between the defective gene products and provide a new perspective to view these genetic blinding diseases.

Ammonia toxicity in the mud crab (Scylla paramamosain): The mechanistic insight from physiology to transcriptome analysis

Ammonia is a major aquatic environmental pollutants. However, the underlying molecular mechanism of ammonia-induced toxicity is not fully understood. In this study, we investigated the physiological response and molecular mechanism in mud crab (Scylla paramamosain) exposed to the acute total ammonia (30 mg L^-1) for 48 h. The results shown that ammonia exposure induced oxidative stress, and subsequently led to cytological damage and DNA damage. Transcriptome analysis was applied to investigate the key genes and pathways involved in the responses to ammonia exposure. A total of 722 differentially expressed genes (DEGs) (526 up-regulated and 196 down-regulated) were identified. DEGs mainly involved in pathways including metabolism, cellular processes, signal transduction and immune functions. Additionally, transcriptome analysis revealed that ATM/p53-Caspase3 pathway involved in apoptosis induced by ammonia stress. These results provided a new insight into the mechanism of the potential toxic effects of ammonia on crustaceans.

Effect of acute ammonia exposure on the glutathione redox system in FFRC strain common carp (Cyprinus carpio L.)

Ammonia is one of the most common aquatic pollutants. To analyze the effect of ammonia exposure on the glutathione redox system, we investigated the levels of hydrogen peroxide (H₂O₂) and glutathione, and transcription and activities of glutathione-related enzymes in liver and gills of FFRC strain common carp (Cyprinus carpio L.) exposed to 0, 10, 20, and 30 mg/L of ammonia. The results showed that H₂O₂ content reached a maximum level at 48 h of exposure in the liver of fish. In gills, H₂O₂ increased rapidly at 6 h and reached to maximum levels at 24 h of exposure, indicating that gills experienced oxidative stress earlier than the liver of fish exposed to ammonia. Reduced glutathione (GSH) content and reduced glutathione/oxidized glutathione (GSH/GSSG) ratio increased significantly within 24 h of exposure. Meanwhile, the transcription and activities of glutathione S-transferase (GST) and glutathione reductase (GR) increased significantly in the liver, and glutathione peroxidase (GSH-Px) and GST increased in the gills of fish exposed to ammonia. Malondialdehyde (MDA) content kept at a low level after exposure to low concentration of ammonia, but increased significantly after exposure to 30 mg/L ammonia for 48 h along with a decrease in GSH content and GSH/GSSG ratio. These data showed that the glutathione redox system played an important role in protection against ammonia-induced oxidative stress in the liver and gills of FFRC strain common carp, though the defense capacity was not able to completely prevent oxidative damage occurring after exposure to higher concentration of ammonia. This research systematically studied the response of the glutathione redox system to ammonia stress and would provide novel information for a better understanding of the adaptive mechanisms of fish to environmental stress.

Transcriptome analysis reveals novel insights in air-breathing magur catfish (Clarias magur) in response to high environmental ammonia

The facultative air-breathing magur catfish (Clarias magur) frequently face different environmental challenges, such as hyper-ammonia, and desiccation stresses in their natural habitats. All these stresses lead to higher accumulation of body ammonia, thereby causing various harmful effects to the fish due to its toxicity. Nonetheless, the mechanisms underlying ammonia-induced toxicity is yet not clear. In the present study, we used RNA sequencing and utilized a modified method for de novo assembly of the transcriptome to provide an exhaustive study on the transcriptomic alterations of magur catfish in response to high environmental ammonia (HEA; 25 mM NH₄Cl). The final contig assembly produced a total of 311,076 unique transcripts (termed as unigenes) with a GC content of 48.3% and the average length of 599 bp. A considerable number of SSR marker associated with these unigenes were also detected. A total of 279,156 transcripts were successfully annotated by using various databases. Comparative transcriptomic analysis revealed a total of 3453 and 19,455 genes were differentially expressed in the liver and brain tissues, respectively, in ammonia-treated fish compared to the control. Enrichment analysis of the differentially expressed genes (DEGs) showed that several GO and KEGG pathway terms were significantly over-represented. Functional analysis of significantly elevated DEGs demonstrated that ammonia stress tolerance of the magur catfish was associated with quite a few pathways related to immune response, oxidative stress, and apoptosis, as well as few transporter proteins involved with ammonia and urea transport. Both liver and brain tissues showed HEA-mediated oxidative damage with consequent activation of antioxidant machinery. However, elevated ROS levels led to an activation of inflammatory cytokines and thus innate immune response in the liver. Conversely, in the brain ROS-mediated irreversible cell damages activated apoptosis via both p53-Bax-Bcl2 and caspase-mediated pathways. The present study provides a novel understanding of the molecular responses of this air-breathing catfish against the ammonia-induced stressors, which could elucidate the underlying mechanisms of adaptation of this facultative air-breather living under various environmental constraints.

Exposure to acute ammonia stress influences survival, immune response and antioxidant status of pacific white shrimp (Litopenaeus vannamei) pretreated with diverse levels of inositol

The effect of acute ammonia challenge on survival, immune response and antioxidant status of Litopenaeus vannamei pretreated with diets containing different inositol levels was investigated. Shrimp (initial mean weight 0.40 ± 0.00 g) were randomly allocated in 18 tanks (30 shrimp per tank) and triplicate tanks were fed with a control diet without myo-inositol (MI) supplementation (242.6 mg inositol kg^-1 diet) or diets containing diverse levels of inositol (368.8, 459.7, 673.1, 993.8 and 1674.4  mg kg^-1 diet) as treatment groups for 8-week. Randomly selected 10 shrimp per tank (final mean weight approximately 11.1-13.8g) were exposed to ammonia stress (total ammonia-nitrogen, 60.21  mg L^-1) for 24 h after feeding trial. The results showed that after exposed to ammonia stress, survival rates of MI-supplemented groups were enhanced by 31-77% when compared with the control group. MI supplementation increased activities of alkaline phosphatase (AKP) and acid phosphatase (ACP) in plasma, and reduced its activities in hepatopancreas. It also enhanced activities of total antioxidant capacity (T-AOC), glutathione S-transferase (GST) and glutathione peroxidase (GPX) and content of reduced glutathione (GSH), and lowered malondialdehyde (MDA) and protein carbonyl (PC) content in plasma or hepatopancreas. In addition, mRNA expression levels of ferritin (FT), arginine kinase (AK), thioredoxin (Trx), heat shock protein 70 (Hsp70), catalase (CAT) and peroxiredoxin (Prx) were significantly differentially regulated in hepatopancreas owing to MI supplementation. Therefore, it suggested that L. vannamei pretreated with higher dietary inositol content may have better ammonia stress tolerance and antioxidant status after ammonia stress, and the optimum levels ranged from 459.7 to 993.8 mg inositol kg^-1 when total ammonia-nitrogen concentration was 60.21  mg L^-1.