Resveratrol prevents ammonia toxicity in astroglial cells

Glioprotective Effects of Sulforaphane in Hypothalamus: Focus on Aging Brain

Sulforaphane is a natural compound with neuroprotective activity, but its effects on hypothalamus remain unknown. In line with this, astrocytes are critical cells to maintain brain homeostasis, and hypothalamic astrocytes are fundamental for sensing and responding to environmental changes involved in a variety of homeostatic functions. Changes in brain functionality, particularly associated with hypothalamic astrocytes, can contribute to age-related neurochemical alterations and, consequently, neurodegenerative diseases. Thus, here, we investigated the glioprotective effects of sulforaphane on hypothalamic astrocyte cultures and hypothalamic cell suspension obtained from aged Wistar rats (24 months old). Sulforaphane showed anti-inflammatory and antioxidant properties, as well as modulated the mRNA expression of astroglial markers, such as aldehyde dehydrogenase 1 family member L1, aquaporin 4, and vascular endothelial growth factor. In addition, it increased the expression and extracellular levels of trophic factors, such as glia-derived neurotrophic factor and nerve growth factor, as well as the release of brain-derived neurotrophic factor and the mRNA of TrkA, which is a receptor associated with trophic factors. Sulforaphane also modulated the expression of classical pathways associated with glioprotection, including nuclear factor erythroid-derived 2-like 2, heme oxygenase-1, nuclear factor kappa B p65 subunit, and AMP-activated protein kinase. Finally, a cell suspension with neurons and glial cells was used to confirm the predominant effect of sulforaphane in glial cells. In summary, this study indicated the anti-aging and glioprotective activities of sulforaphane in aged astrocytes.

Lessons on brain edema in HE: from cellular to animal models and clinical studies

Brain edema is considered as a common feature associated with hepatic encephalopathy (HE). However, its central role as cause or consequence of HE and its implication in the development of the neurological alterations linked to HE are still under debate. It is now well accepted that type A and type C HE are biologically and clinically different, leading to different manifestations of brain edema. As a result, the findings on brain edema/swelling in type C HE are variable and sometimes controversial. In the light of the changing natural history of liver disease, better description of the clinical trajectory of cirrhosis and understanding of molecular mechanisms of HE, and the role of brain edema as a central component in the pathogenesis of HE is revisited in the current review. Furthermore, this review highlights the main techniques to measure brain edema and their advantages/disadvantages together with an in-depth description of the main ex-vivo/in-vivo findings using cell cultures, animal models and humans with HE. These findings are instrumental in elucidating the role of brain edema in HE and also in designing new multimodal studies by performing in-vivo combined with ex-vivo experiments for a better characterization of brain edema longitudinally and of its role in HE, especially in type C HE where water content changes are small.

S100B Secretion in Astrocytes, Unlike C6 Glioma Cells, Is Downregulated by Lactate

S100B is a calcium-binding protein produced and secreted by astrocytes in response to various extracellular stimuli. C6 glioma cells are a lineage commonly employed for astroglial studies due to the expression of astrocyte specific markers and behavior. However, in high-glucose medium, C6 S100B secretion increases, in contrast to the trend in primary astrocyte cultures. Additionally, S100B secretion decreases due to fluorocitrate (FC), a Krebs cycle inhibitor, highlighting a connection between S100B and metabolism. Herein, we investigate the impact of FC on S100B secretion in primary astrocyte cultures, acute hippocampal slices and C6 glioma cells, as well as lactate mediation. Our results demonstrated that C6 responded similarly to astrocytes in various parameters, despite the decrease in S100B secretion, which was inversely observed in astrocytes and slices. Furthermore, FC inversely altered extracellular lactate in both models, suggesting a role for lactate in S100B secretion. This was reinforced by a decrease in S100B secretion in hippocampal slices treated with lactate and its agonist, but not in C6 cells, despite HCAR1 expression. Our findings indicate that extracellular lactate mediates the decrease in S100B secretion in astrocytes exposed to FC. They also emphasize the differences in C6 glioma cells regarding energetic metabolism. The proposed mechanism via HCAR1 provides further compelling evidence of the relationship between S100B and glucose metabolism.

Glioprotective effects of resveratrol in hypothalamic astrocyte cultures obtained from interferon receptor knockout (IFNα/βR-/-) mice

Astrocytes play essential roles in the central nervous system (CNS), such as the regulation of glutamate metabolism, antioxidant defenses, and inflammatory/immune responses. Moreover, hypothalamic astrocytes seem to be crucial in the modulation of inflammatory processes, including those related to type I interferon signaling. In this regard, the polyphenol resveratrol has emerged as an important glioprotective molecule to regulate astrocyte functions. Therefore, this study aimed to investigate the immunomodulatory and protective effects of resveratrol in hypothalamic astrocyte cultures obtained from mouse depleted of type I interferon receptors (INF-α/β^-/-), a condition that can impair immune and inflammatory functions. Resveratrol upregulated glutamate transporter and glutamine synthetase gene expression, as well as modulated the release of wide range of cytokines and genes involved in the control of inflammatory response, besides the expression of adenosine receptors, which display immunomodulatory functions. Resveratrol also increased genes associated with redox balance, mitochondrial processes, and trophic factors signaling. The putative genes associated with glioprotective effects of resveratrol, including nuclear factor erythroid derived 2 like 2 (Nrf2), heme oxygenase 1 (HO-1), sirtuin 1 (SIRT1), and phosphoinositide 3-kinase (PI3K)/Akt, were further upregulated by resveratrol. Thus, our data show that resveratrol was able to modulate key genes associated with glial functionality and inflammatory response in astrocyte cultures derived from IFNα/βR^-/- mice. These data are in agreement with previous results, reinforcing its glioprotective effects even in hypothalamic astrocytes with altered inflammatory and immune signaling. Finally, this polyphenol can prepare astrocytes to better respond to injuries, including those associated with neuroimmunology defects.

Inhibition of Autotaxin Ameliorates LPA-Mediated Neuroinflammation and Alleviates Neurological Dysfunction in Acute Hepatic Encephalopathy

Growing evidence suggests an essential role of neuroinflammation in behavioral abnormalities associated with hepatic encephalopathy (HE). Here, we report the involvement of autotaxin-lysophosphatidic acid (LPA) signaling in HE's pathogenesis. We demonstrate that the autotaxin (ATX) inhibitor PF-8380 attenuates neuroinflammation and improves neurological dysfunction in the mouse model of HE. In the thioacetamide (TAA)-induced model of HE, we found a twofold increase in the levels of ammonia in the brain and in plasma along with a significant change in HE-related behavioral parameters. Mice with HE show an increased brain weight, increased levels of tumor necrosis factor-α (TNF-α), IL-1β (interleukin-1β), interleukin-6 (IL-6), and LPA 18:0 in the cerebral cortex and hippocampus, and increased levels of LPA 18:0 in plasma. Treatment with the autotaxin inhibitor (ATXi) did not affect liver injury, as we observed no change in liver function markers including aspartate aminotransferase (AST), alanine aminotransferase (ALT), and total bilirubin (TBIL) and no change in ammonia levels in the brain and plasma. However, ATXi treatment significantly ameliorated the neuroinflammation, reduced the levels of LPA 18:0 in the cerebral cortex and hippocampus in the brain and plasma, and reduced brain edema and the levels of IL1β, IL-6, and TNF-α. The neurobehavioral symptoms for HE such as the cognitive and motor function deficit and overall clinical grading score were significantly improved in ATXi-treated mice. Mouse astrocytes and microglia stimulated with NH₄CL with or without ATXi showed significant attenuation of oxidative stress and the neuroinflammatory effect of NH4CL in ATXi-treated cells.

Methylmalonic acid induces inflammatory response and redox homeostasis disruption in C6 astroglial cells: potential glioprotective roles of melatonin and resveratrol

Methylmalonic acidemia is a neurometabolic disorder biochemically characterized by the accumulation of methylmalonic acid (MMA) in different tissues, including the central nervous system (CNS). In this sense, it has been shown that high levels of this organic acid have a key role in the progressive neurological deterioration in patients. Astroglial cells actively participate in a wide range of CNS functions, such as antioxidant defenses and inflammatory response. Considering the role of these cells to maintain brain homeostasis, in the present study, we investigated the effects of MMA on glial parameters, focusing on redox homeostasis and inflammatory process, as well as putative mediators of these events in C6 astroglial cells. MMA decreased cell viability, glutathione levels, and antioxidant enzyme activities, increased inflammatory response, and changed the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), nuclear factor kappa B (NFκB), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), and adenosine receptors, suggesting that these transcriptional factors and proteins may underlie the glial responses induced by MMA. Moreover, we also demonstrated the protective roles of melatonin and resveratrol against MMA-induced inflammation and decrease in glutathione levels. In summary, our findings support the hypothesis that astroglial changes are associated with pathogenesis of methylmalonic acidemia. In addition, we showed that these cells might be potential targets for preventive/therapeutic strategies by using molecules, such as melatonin and resveratrol, which mediated glioprotection in this inborn error of metabolism.

Glioprotective Effects of Resveratrol Against BMAA-Induced Astroglial Dysfunctions

Astroglial cells play important roles in maintaining central nervous system (CNS) homeostasis. The neurotoxin β-N-methylamino-L-alanine (BMAA) has usually been associated with neurodegeneration due to its toxic effects on neurons. However, little is known about the effects of BMAA on astroglial cells. Resveratrol, a natural polyphenol, represents a potential protective strategy against brain injuries. In the present study, we sought to investigate BMAA-induced astroglial dysfunctions and the glioprotective roles of resveratrol. BMAA did not impair astroglial cellular viability, but increased glutamate uptake, glutamate metabolism into glutamine, and reactive oxygen species production, while decreased glutathione (GSH) and superoxide dismutase (SOD)-based antioxidant defenses and triggers an inflammatory response. In contrast, resveratrol was able to prevent most of these BMAA-induced functional changes in astroglial cells. Moreover, both BMAA and resveratrol modulated the gene expression of molecular pathways associated with glutamate metabolism, redox homeostasis, and inflammatory response, which characterize their roles on astroglial functions. In this regard, BMAA downregulated adenosine receptors, peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1α), phosphoinositide-3-kinase (PI3K), and Akt, while resveratrol prevented these effects and upregulated nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1). Our study, for the first time, demonstrates that BMAA directly impacts key astroglial functions, contributing to elucidating the cellular and molecular mechanisms of this toxin in the CNS. In addition, we reinforce the glioprotective effects of resveratrol against BMAA-induced astroglial dysfunctions.

Lipopolysaccharide Induces Gliotoxicity in Hippocampal Astrocytes from Aged Rats: Insights About the Glioprotective Roles of Resveratrol

Astrocytes may undergo a functional remodeling with aging, acquiring a pro-inflammatory state. In line with this, resveratrol represents an interesting strategy for a healthier brain aging since it can improve glial functions. In the present study, we investigated the glioprotective role of resveratrol against lipopolysaccharide (LPS)-induced gliotoxicity in hippocampal aged astrocytes. Astrocyte cultures were obtained from aged rats (365 days old) and challenged in vitro with LPS in the presence of resveratrol. Cultured astrocytes from newborn rats were used as an age comparative for evaluating LPS gliotoxicity. In addition, aged rats were submitted to an acute systemic inflammation with LPS. Hippocampal astrocyte cultures were also obtained from these LPS-stimulated aged animals to further investigate the glioprotective effects of resveratrol in vitro. Overall, our results show that LPS induced a higher inflammatory response in aged astrocytes, compared to newborn astrocytes. Several inflammatory and gene expression alterations promoted by LPS in aged astrocyte cultures were similar in hippocampal tissue from aged animals submitted to in vivo LPS injection, corroborating our in vitro findings. Resveratrol, in turn, presented anti-inflammatory effects in aged astrocyte cultures, which were associated with downregulation of p21 and pro-inflammatory cytokines, Toll-like receptors (TLRs), and nuclear factor κB (NFκB). Resveratrol also improved astroglial functions. Upregulation of sirtuin 1 (SIRT1), nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase 1 (HO-1) represent potential molecular mechanisms associated with resveratrol-mediated glioprotection. In summary, our data show that resveratrol can prime aged astrocytes against gliotoxic stimuli, contributing to a healthier brain aging.

Gliotoxicity and Glioprotection: the Dual Role of Glial Cells

Glial cells (astrocytes, oligodendrocytes and microglia) are critical for the central nervous system (CNS) in both physiological and pathological conditions. With this in mind, several studies have indicated that glial cells play key roles in the development and progression of CNS diseases. In this sense, gliotoxicity can be referred as the cellular, molecular, and neurochemical changes that can mediate toxic effects or ultimately lead to impairment of the ability of glial cells to protect neurons and/or other glial cells. On the other hand, glioprotection is associated with specific responses of glial cells, by which they can protect themselves as well as neurons, resulting in an overall improvement of the CNS functioning. In addition, gliotoxic events, including metabolic stresses, inflammation, excitotoxicity, and oxidative stress, as well as their related mechanisms, are strongly associated with the pathogenesis of neurological, psychiatric and infectious diseases. However, glioprotective molecules can prevent or improve these glial dysfunctions, representing glial cells-targeting therapies. Therefore, this review will provide a brief summary of types and functions of glial cells and point out cellular and molecular mechanisms associated with gliotoxicity and glioprotection, potential glioprotective molecules and their mechanisms, as well as gliotherapy. In summary, we expect to address the relevance of gliotoxicity and glioprotection in the CNS homeostasis and diseases.

Therapeutic Applications of Resveratrol in Hepatic Encephalopathy through Its Regulation of the Microbiota, Brain Edema, and Inflammation

Hepatic encephalopathy is a common complication in patients with liver cirrhosis and portosystemic shunting. Patients with hepatic encephalopathy present a variety of clinical features, including neuropsychiatric manifestations, cognitive dysfunction, impaired gut barrier function, hyperammonemia, and chronic neuroinflammation. These pathogeneses have been linked to various factors, including ammonia-induced oxidative stress, neuronal cell death, alterations in the gut microbiome, astrocyte swelling, and blood-brain barrier disruptions. Many researchers have focused on identifying novel therapeutics and prebiotics in the hope of improving the treatment of these conditions. Resveratrol is a natural polyphenic compound and is known to exert several pharmacological effects, including antioxidant, anti-inflammatory, and neuroprotective activities. Recent studies suggest that resveratrol contributes to improving the neuropathogenic effects of liver failure. Here, we review the current evidence describing resveratrol's effects in neuropathogenesis and its impact on the gut-liver axis relating to hepatic encephalopathy. We highlight the hypothesis that resveratrol exerts diverse effects in hepatic encephalopathy and suggest that these effects are likely mediated by changes to the gut microbiota, brain edema, and neuroinflammation.

Resveratrol prevents brain edema, blood-brain barrier permeability, and altered aquaporin profile in autism animal model

Autism spectrum disorder can present a plethora of clinical conditions associated with the disorder, such as greater brain volume in the first years of life in a significant percentage of patients. We aimed to evaluate the brain water content, the blood-brain barrier permeability, and the expression of aquaporin 1 and 4, and GFAP in a valproic acid-animal model, assessing the effect of resveratrol. On postnatal day 30, Wistar rats of the valproic acid group showed greater permeability of the blood-brain barrier to the Evans blue dye and a higher proportion of brain water volume, prevented both by resveratrol. Prenatal exposition to valproic acid diminished aquaporin 1 in the choroid plexus, in the primary somatosensory area, in the amygdala region, and in the medial prefrontal cortex, reduced aquaporin 4 in medial prefrontal cortex and increased aquaporin 4 levels in primary somatosensory area (with resveratrol prevention). Valproic acid exposition also increased the number of astrocytes and GFAP fluorescence in both primary somatosensory area and medial prefrontal cortex. In medial prefrontal cortex, resveratrol prevented the increased fluorescence. Finally, there was an effect of resveratrol per se on the number of astrocytes and GFAP fluorescence in the amygdala region and in the hippocampus. Thus, this work demonstrates significant changes in blood-brain barrier permeability, edema formation, distribution of aquaporin 1 and 4, in addition to astrocytes profile in the animal model of autism, as well as the use of resveratrol as a tool to investigate the mechanisms involved in the pathophysiology of autism spectrum disorder.

Resveratrol: Change of SIRT 1 and AMPK signaling pattern during the aging process

One of the causes for aging is free radical damage. Resveratrol (RSV), a polyphenolic compound has been shown to act as an antioxidant and anti-inflammatory. The objective this study was to verify in an oxidative stress environment in Human Mononuclear cells from Middle aged and Elderly donors, the existence of a change in the SIRT1 and AMPK signaling pattern by RSV. In both age groups there was a reduction in reactive oxygen species (ROS) in cells stimulated with RSV. It was observed that in the Elderly group there was a higher production of ROS and that the reduction from RSV was smaller compared to the other group. There was an increased activity of Superoxide Dismutase in cells exposed to RSV in the elderly group. It was observed that for the Middle Aged group, SIRT 1 and AMPK are antioxidant pathways and RSV acts via SIRT1. In the elderly, the SIRT1 remains antioxidant and RSV ceases its operation via SIRT1. RSV has an antioxidant action in both age groups, and that in aging there was a change in the cellular context characterized by the silencing of the AMPK pathway antioxidant character.

Effects of ammonia exposure on antioxidant function, immune response and NF-κB pathway in Chinese Strip-necked Turtle (Mauremys sinensis)

As one of the main toxic substances in aquaculture water, ammonia causes seriously physiological harm to aquatic animals. In order to investigate the effects of ammonia exposure on the antioxidant defense, immune response, and NF-κB signaling pathway in Chinese Strip-necked Turtle (Mauremys sinensis), we designed two experimental groups (control and 6.45 mM ammonia), and sampled at 6 h, 24 h, 48 h, re 24 h (recover 24 h), and re 48 h. The results showed that the blood ammonia (BA) content was significantly increased when the turtles were subjected to ammonia, and the activities of cholinesterase (CHE) and aspartate aminotransferase (AST) in the serum also showed a significant upward trend. The malondialdehyde (MDA) content continuously increased during ammonia exposure, and more than doubled at 48 h compared with the control group. The activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), catalase (CAT) and their corresponding relative mRNA expression levels in the liver during ammonia exposure were obviously increased when compared to the control group, but most decreased to the normal levels at re 48 h. In addition, the relative mRNA and protein expression levels of NF-E2 related factor 2 (Nrf2) showed similar up-regulation patterns to antioxidase during ammonia exposed periods; whereas kelch-like ECH-binding protein 1 (Keap1), as Nrf2 negative regulator, showed opposite patterns. Moreover, the relative mRNA expression levels of heat shock proteins (HSP70, HSP90) significantly elevated upon the exposure of ammonia. Furthermore, ammonia increased the relative mRNA and protein expression levels of p50 and p65 at different exposed times. The reative mRNA expression levels of immune cytokines (BAFF and IL-6) were upregulated during ammonia exposured time, while there was a decline but did not return to normal levels, in the recovery periods. Taken together, these results indicated that antioxidation, immunity, and NF-κB signaling played a certain protective role for Mauremys sinensis under ammonia exposure. Our results will be helpful to understand the mechanism of aquatic toxicology induced by ammonia in turtles.

Effects of resveratrol on alterations in cerebrum energy metabolism caused by metabolites accumulated in type I citrullinemia in rats

We investigated the in vitro effects of citrulline (0.1, 2.5 and 5.0 mM) and ammonia (0.01, 0.1 and 1.0 mM), and the influence of resveratrol (0.01 mM, 0.1 mM and 0.5 mM) on pyruvate kinase, citrate synthase, succinate dehydrogenase (SDH), complex II, and cytochrome c oxidase activities in cerebral cortex, cerebellum and hippocampus homogenates of 60-day-old male Wistar rats. Results showed that 2.5 and 5.0 mM citrulline decreased pyruvate kinase activity in cerebral cortex and, at a concentration of 5.0 mM, increased its activity in hippocampus. Additionally, 5.0 mM citrulline increased citrate synthase activity in the cerebellum of rats. Citrulline (5.0 mM) reduced complex II and cytochrome c oxidase activities in cerebral cortex and hippocampus. With regard to ammonia, at 0.1 and 1.0 mM, decreased complex II activity in cerebral cortex and at 1.0 mM decreased its activity in cerebellum and hippocampus. Ammonia (1.0 mM) also decreased cytochrome c oxidase activity in cerebral cortex and cerebellum of rats. Resveratrol was able to prevent most of the alterations caused by these metabolites in the biomarkers of energy metabolism measured in the cerebrum of rats. Data suggest that these alterations in energy metabolism, caused by citrulline and ammonia, are probably mediated by the generation of free radicals, which can in turn be scavenged by resveratrol.

Sulforaphane Induces Glioprotection After LPS Challenge

Sulforaphane is a natural compound that presents anti-inflammatory and antioxidant properties, including in the central nervous system (CNS). Astroglial cells are involved in several functions to maintain brain homeostasis, actively participating in the inflammatory response and antioxidant defense systems. We, herein, investigated the potential mechanisms involved in the glioprotective effects of sulforaphane in the C6 astrocyte cell line, when challenged with the inflammogen, lipopolysaccharide (LPS). Sulforaphane prevented the LPS-induced increase in the expression and/or release of pro-inflammatory mediators, possibly due to nuclear factor κB and hypoxia-inducible factor-1α activation. Sulforaphane also modulated the expressions of the Toll-like and adenosine receptors, which often mediate inflammatory processes induced by LPS. Additionally, sulforaphane increased the mRNA levels of nuclear factor erythroid-derived 2-like 2 (Nrf2) and heme oxygenase-1 (HO1), both of which mediate several cytoprotective responses. Sulforaphane also prevented the increase in NADPH oxidase activity and the elevations of superoxide and 3-nitrotyrosine that were stimulated by LPS. In addition, sulforaphane and LPS modulated superoxide dismutase activity and glutathione metabolism. Interestingly, the anti-inflammatory and antioxidant effects of sulforaphane were blocked by HO1 pharmacological inhibition, suggesting its dependence on HO1 activity. Finally, in support of a glioprotective role, sulforaphane prevented the LPS-induced decrease in glutamate uptake, glutamine synthetase activity, and glial-derived neurotrophic factor (GDNF) levels, as well as the augmentations in S100B release and Na⁺, K⁺ ATPase activity. To our knowledge, this is the first study that has comprehensively explored the glioprotective effects of sulforaphane on astroglial cells, reinforcing the beneficial effects of sulforaphane on astroglial functionality.

Resveratrol Protects Optic Nerve Head Astrocytes from Oxidative Stress-Induced Cell Death by Preventing Caspase-3 Activation, Tau Dephosphorylation at Ser422 and Formation of Misfolded Protein Aggregates

Optic nerve head astrocytes (ONHAs) are the major cell type within the optic nerve head, providing both structural and nutrient support to the optic nerve. Astrocytes are necessary for the survival of neurons with controlled activation of astrocytes being beneficial to neurons. However, overactive astrocytes can be harmful and the loss of normal astrocyte function can be a primary contributor to neurodegeneration. The neuroprotective properties of reactive astrocytes can be lost or they might gain neurotoxic properties in neurodegenerative diseases. The activated astrocytes are crucial in the development of glaucoma, where they serve as a source for cytotoxic substances that participate in ganglion apoptosis. There is increasing evidence indicating that neuroinflammation is an important process in glaucoma. Under pathological conditions, astrocytes can induce an inflammatory response. Extensive evidence shows that inflammatory responses mediated by astrocytes can also influence pathology development, synapse health, and neurodegeneration. The elimination of activated astrocytes by apoptosis is also expected in unfavorable conditions. In neurodegenerative diseases, a common feature is the presence of aggregates found in astrocytes, which can disrupt astrocyte function in such a way as to be detrimental to the viability of neurons. The biological processes involved in vision loss in glaucoma are not well understood. Despite the rapid advances in our understanding of optic nerve head (ONH) structure and function, numerous potential contributions of the ONHAs to optic nerve damage remain unanswered. The present study investigated the role of ONHAs during oxidative stress in order to determine novel cell biological processes underlying glaucoma pathogenesis. ONHAs were exposed to chemically induced oxidative stress using tert-butyl hydroperoxide (tBHP) in order to model extracellular oxidative stress as it occurs in the glaucomatous retina and ONH. In order to determine the impact of an intervention approach employing potential glioprotective treatments for central nervous system tissue we pretreated cells with the polyphenolic phytostilbene and antioxidant trans-resveratrol (3,5,4'-trihydroxy-trans-stilbene). ONHAs exposed to tBHP-mediated oxidative stress displayed decreased viability and underwent apoptosis. In addition, increased levels of activated caspases, dephosphorylation of Tau protein at Ser422, an important site adjacent to the caspase cleavage site controlling Tau cleavage, caspase-mediated Tau cleavage, and cytoskeletal changes, specifically formation of neurofibrillary tangles (NFTs) were detected in ONHAs undergoing oxidative stress. When cells were pretreated with resveratrol cell viability increased along with a significant decrease in activated caspases, cleaved Tau, and NFT formation. Taken together, ONHAs appear to act similar to neurons when undergoing oxidative stress, where proteolytic cleavage of Tau by caspases leads to NFT formation. In addition, resveratrol appears to have promise as a potential protective treatment preventing ONHA dysfunction and degeneration. There is currently no cure for glaucoma or a neuro- and glioprotective treatment that directly targets the pathogenic mechanisms in the glaucomatous retina and optic nerve. The present study identified a potential mechanism underlying degeneration of astrocytes that is susceptible to pharmaco-therapeutic intervention in the eye and potentially elsewhere in the central nervous system. Identification of such mechanisms involved in glaucoma and other disorders of the eye and brain is critical to determine novel targets for effective therapies.

SIRT1 activation by resveratrol reverses atrophy of apical dendrites of hippocampal CA1 pyramidal neurons and neurobehavioral impairments in moderate grade hepatic encephalopathy rats

A preliminary observation about resveratrol (RSV) dependent normalization of inflammatory and apoptotic factors in the cortex of hyperammonemic rat model of moderate grade hepatic encephalopathy (MoHE) led us to evaluate whether RSV is ultimately able to confer neuroprotection against MoHE pathogenesis and that it does so by activating its bonafide molecular target SIRT1. The present study compared the profile of relevant neurobehavioral pattern vs neuromorphometry of hippocampal CA1 neurons and SIRT1 activity in the hippocampus of the chronic liver failure (CLF) model of moderate grade HE (MoHE) rats induced by administration of 100 mg/kg body weight of thioacetamide i.p. for 10 days and in the CLF/MoHE rats treated with 10 mg/kg body weight RSV i.p. for 7 days. As compared to the control group rats, the MoHE rats showed significantly deranged pattern of memory and motor functions on MWM and rota rod tests, respectively. These behavioural deficits were associated with a significant reduction in apical dendrite length and number of branching points in the CA1 pyramidal neurons. Interestingly, all these parameters were found to be recovered back to their normal levels in the MoHE rats treated with RSV. Concordantly, MoHE associated declined SIRT1 activity in the hippocampus could be normalized back due to RSV treatment to those MoHE rats. Our findings suggest that RSV is able to normalize MoHE associated memory impairments and motor deficits vis a vis reversal of CA1 dendritic atrophy via SIRT1 activation.

Additive Effect of Resveratrol on Astrocyte Swelling Post-exposure to Ammonia, Ischemia and Trauma In Vitro

Swelling of astrocytes represents a major component of the brain edema associated with many neurological conditions, including acute hepatic encephalopathy (AHE), traumatic brain injury (TBI) and ischemia. It has previously been reported that exposure of cultured astrocytes to ammonia (a factor strongly implicated in the pathogenesis of AHE), oxygen/glucose deprivation, or to direct mechanical trauma results in an increase in cell swelling. Since dietary polyphenols have been shown to exert a protective effect against cell injury, we examined whether resveratrol (RSV, 3,5,4'-trihydroxy-trans-stilbene, a stilbenoid phenol), has a protective effect on astrocyte swelling following its exposure to ammonia, oxygen-glucose deprivation (OGD), or trauma in vitro. Ammonia increased astrocyte swelling, and pre- or post-treatment of astrocytes with 10 and 25 µM RSV displayed an additive effect, while 5 µM did not prevent the effect of ammonia. However, pre-treatment of astrocytes with 25 µM RSV slightly, but significantly, reduced the trauma-induced astrocyte swelling at earlier time points (3 h), while post-treatment had no significant effect on the trauma-induced cell swelling at the 3 h time point. Instead, pre- or post-treatment of astrocytes with 25 µM RSV had an additive effect on trauma-induced astrocyte swelling. Further, pre- or post-treatment of astrocytes with 5 or 10 µM RSV had no significant effect on trauma-induced astrocyte swelling. When 5 or 10 µM RSV were added prior to, or during the process of OGD, as well as post-OGD, it caused a slight, but not statistically significant decline in cell swelling. However, when 25 µM RSV was added during the process of OGD, as well as after the cells were returned to normal condition (90 min period), such treatment showed an additive effect on the OGD-induced astrocyte swelling. Noteworthy, a higher concentration of RSV (25 µM) exhibited an additive effect on levels of phosphorylated forms of ERK1/2, and p38^MAPK, as well as an increased activity of the Na⁺-K⁺-Cl^- co-transporter-1 (NKCC1), factors known to induce astrocytes swelling, when the cells were treated with ammonia or after trauma or ischemia. Further, inhibition of ERK1/2, and p38^MAPK diminished the RSV-induced exacerbation of cell swelling post-ammonia, trauma and OGD treatment. These findings strongly suggest that treatment of cultured astrocytes with RSV enhanced the ammonia, ischemia and trauma-induced cell swelling, likely through the exacerbation of intercellular signaling kinases and ion transporters. Accordingly, caution should be exercised when using RSV for the treatment of these neurological conditions, especially when brain edema is also suspected.

Tadalafil restores long-term memory and synaptic plasticity in mice with hepatic encephalopathy

BACKGROUND AND AIM

Tadalafil displays important neuroprotective effects in experimental models of neurodegenerative diseases, however its mechanisms of action remain poorly understood. The aim of the present study was to investigate the action of Tadalafil on learning and memory, neuroinflammation, glial cell activation and neuroprotection in the experimental model of hepatic encephalopathy (HE) induced by Thioacetamide (TAA) in mice.

METHODS

Mice received intraperitoneal injections of TAA, for 3 consecutive days, reaching the final dose of 600 mg/kg. Tadalafil 15 mg/kg body weight was administered by gavage during 15 days after TAA induction. Mice underwent a Barnes maze for learning and memory evaluation.

RESULTS

Animals with hepatic encephalopathy showed reduced learning and spatial memory in the Barnes Maze, presented astrocyte and microglia activation and increased neuroinflammatory markers such as TNF-α, IL-1β, IL-6, p-p38, p-ERK and p-NF-kB. In addition, the signaling pathway PKA/PKG/CREB/BDNF/NeuN/synaptophysin and glutamate receptors were deregulated by TAA. Tadalafil treatment regulated the inflammation signaling pathways restoring learning and spatial memory.

CONCLUSION

Tadalafil significantly reduced neuroinflammation, promoted neuroprotection and plasticity, regulated the expression of hippocampal glutamate receptor and restored spatial learning ability and memory.

Ammonia exposure induced abnormal expression of cytokines and heat shock proteins via glucose metabolism disorders in chicken neutrophils

Ammonia (NH₃) is a highly irritant, alkaline gas. Atmospheric emission of NH₃ was recognized as an environmental challenge. As a global issue, the NH₃ emission survey with spatially detailed information demonstrated that the sources of atmospheric NH₃ include agriculture (livestock wastes, fertilizers) and some industrial activities. As an environmental pollution, excessive NH₃ exposure can induce many bird dysfunction. Neutrophils respond to multiple invading pathogens through different mechanisms. In order to investigate the effect of NH₃ exposure on broilers' neutrophil, 1-day-old broilers were treated with/without NH₃ for 28 days. We extracted neutrophils from peripheral blood of chicken with/without NH₃ exposure and subsequently stimulated with PMA. Changes of cytokines and inflammatory bodies, heat shock proteins (HSPs), and glucose metabolism of neutrophil were examined in both cases. We not only explored that the index associated with inflammation changed due to NH₃ exposure but also observed the status of neutrophils which was treated with PMA stimulation. After NH₃ exposure, IL-1β and IL-6 were significantly increased on broilers neutrophil. Inflammatory-related factors (NLRP3, ASC, and caspase-1) were significantly elevated. The mRNA expression of HSP70 and HSP90 was increased significantly. All glucose metabolism indicators were reduced. In summary, we concluded that NH₃ enhanced inflammation and disrupted glucose metabolism, and increased the expression of HSPs and inflammatory factors. In addition, the sensitivity of neutrophils to exogenous stimuli was diminished. This information can not only be used to evaluate the damage of NH₃-spiked neutrophils to chickens, but also provide clues for human health pathophysiology caused by excess NH₃, providing valuable information for NH₃ risk management.

Adenosine receptors as a new target for resveratrol-mediated glioprotection

Resveratrol, a natural polyphenolic compound, has been studied as a neuroprotective molecule. Our group has demonstrated that such effect is closely associated with modulation of glial functionality, but the underlying mechanisms are not fully understood. Because astrocytes actively participate in the brain inflammatory response, and activation of adenosine receptors can attenuate inflammatory processes, the aim of this study was to investigate the role of adenosine receptors as a mechanism for resveratrol glioprotection, particularly regarding to neuroinflammation. Therefore, primary astrocyte cultures were co-incubated with resveratrol and selective antagonists of A₁, A_2A, and A₃ adenosine receptors, as well as with caffeine (a non-selective adenosine receptor antagonist), and then challenged with bacterial inflammogen lipopolysaccharide (LPS). Caffeine and selective adenosine receptor antagonists abolished the anti-inflammatory effect of resveratrol. In accordance with these effects, resveratrol prevented LPS-induced decrease in mRNA levels of adenosine receptors. Resveratrol could also prevent the activation of pro-inflammatory signaling pathways, such as nuclear factor κB (NFκB) and p38 mitogen-activated protein kinase (p38 MAPK) in a mechanism dependent on adenosine receptors. Conversely, trophic factors and protective signaling pathways, including sirtuin 1 (SIRT1), nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and phosphoinositide 3-kinase (PI3K)/Akt were positively modulated by resveratrol in both LPS-stimulated and unstimulated astrocytes, but adenosine receptor antagonism did not abrogate all effects of resveratrol. To our knowledge, our data provide the first evidence that adenosine receptors are involved in the anti-inflammatory activity of resveratrol in astrocytes, thus exerting an important role for resveratrol-mediated glioprotection.

Effects of ammonia on apoptosis and oxidative stress in bovine mammary epithelial cells

Ammonia, produced mainly from the deamination of amino acids and glutamine, is one of the major toxic components in blood and tissues that may affect bovine health. However, the physiological and pathological roles of ammonia in the mammary glands are not understood clearly. In the present study, the bovine mammary epithelial cell line (MAC-T) was utilised as an in vitro model to determine the effects of ammonia on bovine mammary gland. We demonstrated that ammonia stimulated the production of intracellular reactive oxygen species, decreased mitochondrial membrane potential, interrupted intracellular calcium ion (Ca2+) homeostasis and induced cell apoptosis. Ammonia also significantly reduced cell viability and increased the proportion of apoptotic cells through enhancing the level of p53 phosphorylation and increasing the expressions of BAX, caspase 8, caspase 9, caspase 3. Interestingly, bumetanide, a specific Na+ K+ 2Cl--cotransporter inhibitor, dramatically abolished the damaging effects of ammonia on the cells. These data suggest that ammonia exposure induces apoptosis in bovine mammary epithelial cells via activation of the p53 pathway and the mitochondrial apoptotic pathway, and that these effects involved the Na+ K+ 2Cl--cotransporter.

Resveratrol and pinostilbene confer neuroprotection against aging-related deficits through an ERK1/2-dependent mechanism

Age-related declines in motor function may be due, in part, to an increase in oxidative stress in the aging brain leading to dopamine (DA) neuronal cell death. In this study, we examined the neuroprotective effects of natural antioxidants resveratrol and pinostilbene against age-related DAergic cell death and motor dysfunction using SH-SY5Y neuroblastoma cells and young, middle-aged, and old male C57BL/6 mice. Resveratrol and pinostilbene protected SH-SY5Y cells from a DA-induced decrease in cell viability. Dietary supplementation with resveratrol and pinostilbene inhibited the decline of motor function observed with age. While DA and its metabolites (DOPAC and HVA), dopamine transporter, and tyrosine hydroxylase levels remain unchanged during aging or treatment, resveratrol and pinostilbene increased ERK1/2 activation in vitro and in vivo in an age-dependent manner. Inhibition of ERK1/2 in SH-SY5Y cells decreased the protective effects of both compounds. These data suggest that resveratrol and pinostilbene alleviate age-related motor decline via the promotion of DA neuronal survival and activation of the ERK1/2 pathways.

Resveratrol prevents ammonia-induced mitochondrial dysfunction and cellular redox imbalance in C6 astroglial cells

BACKGROUND

Resveratrol is a polyphenolic compound that presents several protective effects in the central nervous system, including gliotoxicity associated to hyperammonemia, a key element for the development of hepatic encephalopathy. In this condition, mitochondrial dysfunction leads to a reactive oxygen species (ROS) overproduction, which, in turn, exacerbates mitochondrial failure and causes cellular damage.

OBJECTIVE

This study sought to determine whether prevention of mitochondrial dysfunction and the maintenance of cellular redox status by resveratrol contribute to its protective action toward ammonia toxicity.

METHODS

C6 astrocyte cell line was pre-incubated in the presence or absence of resveratrol (100 μM) for 1 hour. After pre-incubation, resveratrol was maintained and 5 mM ammonia was added for 24 hours, followed by the evaluation of ROS production, mitochondrial functionality, antioxidant enzymatic and non-enzymatic defenses, energy metabolic parameters, and genotoxicity.

RESULTS

We showed that resveratrol prevented the increase in ROS production, the decrease of mitochondrial membrane potential (ΔΨ_m), and bioenergetics deficit caused by ammonia in C6 astroglial cells. In addition, resveratrol avoided the ammonia-induced upregulation of NOX activity and impairment in enzymatic and non-enzymatic antioxidant defenses. Ammonia also induced DNA damage that was prevented by resveratrol, indicating its genoprotective effect.

CONCLUSIONS

In summary, our study demonstrates that resveratrol prevents ammonia-induced cytotoxicity, as well as supports the role of resveratrol on mitochondrial/cellular redox functionality.

Differential expression analysis of the broiler tracheal proteins responsible for the immune response and muscle contraction induced by high concentration of ammonia using iTRAQ-coupled 2D LC-MS/MS

Ammonia has been considered the contaminant primarily responsible for respiratory disease in poultry. Even though it can cause tracheal lesions, its adverse effects on the trachea have not been sufficiently studied. The present study investigated tracheal changes in Arbor Acres broilers (Gallus gallus) induced by high concentration of ammonia using isobaric tag for relative and absolute quantification (iTRAQ)-based proteome analysis. In total, 3,706 proteins within false discovery rate of 1% were identified, including 119 significantly differentially expressed proteins. Functional analysis revealed that proteins related to immune response and muscle contraction were significantly enriched. With respect to the immune response, up-regulated proteins (like FGA) were pro-inflammatory, while down-regulated proteins participated in antigen processing and antigen presenting (like MYO1G), immunoglobulin and cathelicidin production (like fowlicidin-2), and immunodeficiency (like PTPRC). Regarding muscle contraction, all differentially expressed proteins (like TPM1) were up-regulated. An over-expression of mucin, which is a common feature of airway disease, was also observed. Additionally, the transcriptional alterations of 6 selected proteins were analyzed by quantitative RT-PCR. Overall, proteomic changes suggested the onset of airway obstruction and diminished host defense in trachea after ammonia exposure. These results may serve as a valuable reference for future interventions against ammonia toxicity.

Artesunate restores spatial learning of rats with hepatic encephalopathy by inhibiting ammonia-induced oxidative damage in neurons and dysfunction of glutamate signaling in astroglial cells

BACKGROUND

Artesunate (ART) is an antimalarial drug with potential anti-inflammatory effect. This study aimed to explore the potential protective role of ART in hepatic encephalopathy (HE), involving its function against ammonia toxicity.

METHODS

HE rats were induced by the administration of thioacetamide (TAA, 300mg/kg/day). Spatial learning ability was tested in both Morris water and eight-arm radial maze. Rat cerebellar granule neurons (CGNs) were prepared for ammonia treatment in vitro, in line with SH-SY5Y and C6 cells. ART was administrated at 50 or 100mg/kg/day in vivo or added at 50 or 100μM in vitro. Oxidative damages were evaluated by the changes of cell viability, reactive oxygen species (ROS) levels and glutathione (GSH) content, while glutamate uptake and release, and the activities of glutamine synthetase (GS) and Na⁺K⁺-ATPase were measured to indicate the dysfunction of glutamate signaling.

RESULTS

Decreased escape latency and increased numbers of working errors were observed in TAA-induced HE rats, which could be significantly restored by ART at a dosage-dependent manner. Decreased cell viability and GSH content and increased ROS accumulation were detected in ammonia-treated SH-SY5Y and CGNs, while ammonia-treated C6 cells showed reduced glutamate uptake, increased glutamate release, and decrease of GSH content, GS and Na⁺K⁺-ATPase activity. In contrast, ART, especially at 100μM, strongly reversed all changes induced by ammonia, showing a similar dosage-dependent manner in vitro.

CONCLUSION

This study revealed a new neuroprotective role of ART in the pathogenesis of HE, by protecting neurons and astroglial cells from ammonia-induced damages and dysfunctions.

Fluctuations in glucose levels induce glial toxicity with glutamatergic, oxidative and inflammatory implications

Astrocytes are dynamic cells that maintain brain homeostasis by regulating neurotransmitter systems, antioxidant defenses, inflammatory responses and energy metabolism. Astroglial cells are also primarily responsible for the uptake and metabolism of glucose in the brain. Diabetes mellitus (DM) is a pathological condition characterized by hyperglycemia and is associated with several changes in the central nervous system (CNS), including alterations in glial function. Classically, excessive glucose concentrations are used to induce experimental models of astrocyte dysfunction; however, hypoglycemic episodes may also cause several brain injuries. The main focus of the present study was to evaluate how fluctuations in glucose levels induce cytotoxicity. The culture medium of astroglial cells was replaced twice as follows: (1) from 6mM (control) to 12mM (high glucose), and (2) from 12mM to 0mM (glucose deprivation). Cell viability, mitochondrial function, oxidative/nitrosative stress, glutamate metabolism, inflammatory responses, nuclear factor κB (NFκB) transcriptional activity and p38 mitogen-activated protein kinase (p38 MAPK) levels were assessed. Our in vitro experimental model showed that up and down fluctuations in glucose levels decreased cell proliferation, induced mitochondrial dysfunction, increased oxidative/nitrosative stress with consequent cellular biomolecular damage, impaired glutamate metabolism and increased pro-inflammatory cytokine release. Additionally, activation of the NFκB and p38 signaling pathways were putative mechanisms of the effects of glucose fluctuations on astroglial cells. In summary, for the first time, we show that changes in glucose concentrations, from high-glucose levels to glucose deprivation, exacerbate glial injury.

Higher Vulnerability of Menadione-Exposed Cortical Astrocytes of Glutaryl-CoA Dehydrogenase Deficient Mice to Oxidative Stress, Mitochondrial Dysfunction, and Cell Death: Implications for the Neurodegeneration in Glutaric Aciduria Type I

Patients affected by glutaric aciduria type I (GA-I) show progressive cortical leukoencephalopathy whose pathogenesis is poorly known. In the present work, we exposed cortical astrocytes of wild-type (Gcdh ^+/+ ) and glutaryl-CoA dehydrogenase knockout (Gcdh ^-/- ) mice to the oxidative stress inducer menadione and measured mitochondrial bioenergetics, redox homeostasis, and cell viability. Mitochondrial function (MTT and JC1-mitochondrial membrane potential assays), redox homeostasis (DCFH oxidation, nitrate and nitrite production, GSH concentrations and activities of the antioxidant enzymes SOD and GPx), and cell death (propidium iodide incorporation) were evaluated in primary cortical astrocyte cultures of Gcdh ^+/+ and Gcdh ^-/- mice unstimulated and stimulated by menadione. We also measured the pro-inflammatory response (TNFα levels, IL1-β and NF-ƙB) in unstimulated astrocytes obtained from these mice. Gcdh ^-/- mice astrocytes were more vulnerable to menadione-induced oxidative stress (decreased GSH concentrations and altered activities of the antioxidant enzymes), mitochondrial dysfunction (decrease of MTT reduction and JC1 values), and cell death as compared with Gcdh ^+/+ astrocytes. A higher inflammatory response (TNFα, IL1-β and NF-ƙB) was also observed in Gcdh ^-/- mice astrocytes. These data indicate a higher susceptibility of Gcdh ^-/- cortical astrocytes to oxidative stress and mitochondrial dysfunction, probably leading to cell death. It is presumed that these pathomechanisms may contribute to the cortical leukodystrophy observed in GA-I patients.

Neurotoxicity of Ammonia

Abnormal liver function has dramatic effects on brain functions. Hyperammonemia interferes profoundly with brain metabolism, astrocyte volume regulation, and in particular mitochondrial functions. Gene expression in the brain and excitatory and inhibitory neurotransmission circuits are also affected. Experiments with a number of pertinent animal models have revealed several potential mechanisms which could underlie the pathological phenomena occurring in hepatic encephalopathy.

Ornithine and Homocitrulline Impair Mitochondrial Function, Decrease Antioxidant Defenses and Induce Cell Death in Menadione-Stressed Rat Cortical Astrocytes: Potential Mechanisms of Neurological Dysfunction in HHH Syndrome

Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome is caused by deficiency of ornithine translocase leading to predominant tissue accumulation and high urinary excretion of ornithine (Orn), homocitrulline (Hcit) and ammonia. Although affected patients commonly present neurological dysfunction manifested by cognitive deficit, spastic paraplegia, pyramidal and extrapyramidal signs, stroke-like episodes, hypotonia and ataxia, its pathogenesis is still poorly known. Although astrocytes are necessary for neuronal protection. Therefore, in the present study we investigated the effects of Orn and Hcit on cell viability (propidium iodide incorporation), mitochondrial function (thiazolyl blue tetrazolium bromide-MTT-reduction and mitochondrial membrane potential-ΔΨm), antioxidant defenses (GSH) and pro-inflammatory response (NFkB, IL-1β, IL-6 and TNF-α) in unstimulated and menadione-stressed cortical astrocytes that were previously shown to be susceptible to damage by neurotoxins. We first observed that Orn decreased MTT reduction, whereas both amino acids decreased GSH levels, without altering cell viability and the pro-inflammatory factors in unstimulated astrocytes. Furthermore, Orn and Hcit decreased cell viability and ΔΨm in menadione-treated astrocytes. The present data indicate that the major compounds accumulating in HHH syndrome impair mitochondrial function and reduce cell viability and the antioxidant defenses in cultured astrocytes especially when stressed by menadione. It is presumed that these mechanisms may be involved in the neuropathology of this disease.

Insulin Stimulates S100B Secretion and These Proteins Antagonistically Modulate Brain Glucose Metabolism

Brain metabolism is highly dependent on glucose, which is derived from the blood circulation and metabolized by the astrocytes and other neural cells via several pathways. Glucose uptake in the brain does not involve insulin-dependent glucose transporters; however, this hormone affects the glucose influx to the brain. Changes in cerebrospinal fluid levels of S100B (an astrocyte-derived protein) have been associated with alterations in glucose metabolism; however, there is no evidence whether insulin modulates glucose metabolism and S100B secretion. Herein, we investigated the effect of S100B on glucose metabolism, measuring D-(3)H-glucose incorporation in two preparations, C6 glioma cells and acute hippocampal slices, and we also investigated the effect of insulin on S100B secretion. Our results showed that: (a) S100B at physiological levels decreases glucose uptake, through the multiligand receptor RAGE and mitogen-activated protein kinase/ERK signaling, and (b) insulin stimulated S100B secretion via PI3K signaling. Our findings indicate the existence of insulin-S100B modulation of glucose utilization in the brain tissue, and may improve our understanding of glucose metabolism in several conditions such as ketosis, streptozotocin-induced dementia and pharmacological exposure to antipsychotics, situations that lead to changes in insulin signaling and extracellular levels of S100B.

Hepatic injury is associated with cell cycle arrest and apoptosis with alteration of cyclin A and D1 in ammonium chloride-induced hyperammonemic rats

Hyperammonemia is considered to be central to the pathophysiology of hepatic encephalopathy in patients exhibiting hepatic failure (HF). It has previously been determined that hyperammonemia is a serious metabolic disorder commonly observed in patients with HF. However, it is unclear whether hyperammonemia has a direct adverse effect on hepatic cells or serves as a cause and effect of HF. The present study investigated whether hepatic injury is caused by hyperammonemia, and aimed to provide an insight into the causes and mechanisms of HF. Hyperammonemic rats were established via intragastric administration of ammonium chloride solution. Hepatic tissues were assessed using biochemistry, histology, immunohistochemistry, flow cytometry (FCM), semi-quantitative reverse transcription-polymerase chain reaction and western blot analysis. Hyperammonemic rats exhibited significantly increased levels of liver function markers, including alanine transaminase (P<0.01), aspartate aminotransferase (P<0.01), blood ammonia (P<0.01) and direct bilirubin (P<0.05), which indicated hepatic injury. A pathological assessment revealed mild hydropic degeneration, but no necrosis or inflammatory cell infiltration. However, terminal deoxynucleotidyl transferase dUTP nick end-labeling assays confirmed a significant increase in the rate of cellular apoptosis in hyperammonemic rat livers (P<0.01). FCM analysis revealed that there were significantly more cells in the S phase and fewer in the G₂/M phase (P<0.01), and the expression levels of cyclin A and D1 mRNA and proteins were significantly increased (P<0.01). In summary, cell cycle arrest, apoptosis and an alteration of cyclin A and D1 levels were all markers of hyperammonemia-induced hepatic injury. These findings provide an insight into the potential mechanisms underlying hyperammonemia-induced hepatic injury, and may be used as potential targets for treating or preventing hepatic damage caused by hyperammonemia, including hepatic encephalopathy.

Gap Junction Intercellular Communication Mediates Ammonia-Induced Neurotoxicity

Astrocytes are important brain targets of ammonia, a neurotoxin implicated in the development of hepatic encephalopathy. During hyperammonemia, the pivotal role of astrocytes in brain function and homeostasis is impaired. These cells are abundantly interconnected by gap junctions (GJ), which are intercellular channels that allow the exchange of signaling molecules and metabolites. This communication may also increase cellular vulnerability during injuries, while GJ uncoupling could limit the extension of a lesion. Therefore, the current study was performed to investigate whether astrocyte coupling through GJ contributes to ammonia-induced cytotoxicity. We found that carbenoxolone (CBX), an effective GJ blocker, prevented the following effects induced by ammonia in astrocyte primary cultures: (1) decrease in cell viability and membrane integrity; (2) increase in reactive oxygen species production; (3) decrease in GSH intracellular levels; (4) GS activity; (5) pro-inflammatory cytokine release. On the other hand, CBX had no effect on C6 astroglial cells, which are poorly coupled via GJ. To our knowledge, this study provides the first evidence that GJ play a role in ammonia-induced cytotoxicity. Although more studies in vivo are required to confirm our hypothesis, our data suggest that GJ communication between astrocytes may transmit damage signals and excitotoxic components from unhealthy to normal cells, thereby contributing to the propagation of the neurotoxicity of ammonia.

Octadecaneuropeptide ODN prevents hydrogen peroxide-induced oxidative damage of biomolecules in cultured rat astrocytes

Oxidative stress, associated with a variety of disorders including neurodegenerative diseases, is a major cause of cellular dysfunction and biomolecule damages which play a crucial role in neuronal apoptosis. Astrocytes specifically synthesize and release endozepines, a family of regulatory peptides, including the octadecaneuropeptide ODN. We have recently shown that ODN is a potent glioprotective agent that prevents hydrogen peroxide (H2O2)-induced oxidative stress and apoptosis. The purpose of the present study was to investigate the potential protective effect of ODN on oxidative-generated damage of biomolecules in cultured rat astrocytes. Incubation of cells with subnanomolar concentrations of ODN (0.1fM-0.1nM) inhibited H2O2-evoked reactive oxygen species accumulation and cell death in a concentration-dependent manner. Exposure of H2O2-treated cells to 0.1nM ODN inhibited superoxide anion generation and blocked oxidative damage of cell molecules caused by H2O2i.e. formation and accumulation of lipid oxidation products, malondialdehydes and conjugated dienes, and protein carbonyl compounds. Taken together, these data demonstrate for the first time that ODN prevents oxidative stress-induced alteration of cellular constituents. ODN is thus a potential candidate to reduce neuronal damage in various pathological conditions involving oxidative neurodegeneration.

Ammonia impairs glutamatergic communication in astroglial cells: protective role of resveratrol

Ammonia is a key toxin in the precipitation of hepatic encephalopathy (HE), a neuropsychiatric disorder associated with liver failure. In response to ammonia, various toxic events are triggered in astroglial cells, and alterations in brain glutamate communication are common. Resveratrol is a polyphenolic compound that has been extensively studied in pathological events because it presents several beneficial effects, including some in the central nervous system (CNS). We previously described that resveratrol is able to significantly modulate glial functioning and has a protective effect during ammonia challenge in vitro. In this study, we addressed the mechanisms by which resveratrol can protect C6 astroglial cells from glutamatergic alterations induced by ammonia. Resveratrol was able to prevent all the effects triggered by ammonia: (i) decrease in glutamate uptake activity and expression of the EAAC1 glutamate transporter, the main glutamate transporter present in C6 cells; (ii) increase of glutamate release, which was also dependent on the activation of the Na(+)-K(+)-Cl(-) co-transporter NKCC1; (iii) reduction in GS activity and intracellular GSH content; and (iv) impairment of Na(+)K(+)-ATPase activity. Interestingly, resveratrol, per se, also positively modulated the astroglial functions evaluated. Moreover, we demonstrated that heme oxygenase 1 (HO1), an enzyme that is part of the cellular defense system, mediated some of the effects of resveratrol. In conclusion, the mechanisms of the putative protective role of resveratrol against ammonia toxicity involve the modulation of pathways and molecules related to glutamate communication in astroglial cells.

Carbon Tetrachloride Increases the Pro-inflammatory Cytokines Levels in Different Brain Areas of Wistar Rats: The Protective Effect of Acai Frozen Pulp

Acai offers health benefits associated with its high antioxidante capacity, phytochemical composition, nutritional and sensory value. Therefore, the objective of this study was to evaluate the protective effect of acai frozen pulp on carbon tetrachloride (CCl4)-induced damage via modulation of anti- and pro-inflammatory cytokines in rat brain tissue. The rats were treated via oral (gavage) daily with water or acai frozen pulp for 14 days at a dose of 7 μL/g. On the 15th day, the animals in each group received a single intraperitoneal injection of CCl4 in a dose of 3.0 mL/kg or the same volume of mineral oil. After 4 h, the animals were euthanized by decapitation and the cerebral cortex, hippocampus and cerebellum were dissected and homogenated to evaluate the levels of tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), interleukin 18 (IL-18), interleukin 6 (IL-6) and interleukin 10 (IL-10). Data were statistically analyzed by analysis of variance followed by the Tukey post hoc test. It was observed that CCl4 increased TNF-α, IL-1β and IL-18 levels in all brain tissues, and that acai frozen pulp was able to prevent this increase. IL-6 and IL-10 brain tissue levels remained unchanged during all treatments. CCl4 experimental model was suitable to investigate brain tissue anti and pro-inflammatory cytokines. Acai frozen pulp prevented an increase in IL-1β, IL-18 and TNF-α, while IL-6 and IL-10 levels remained unchanged. The precise pathway by which inflammation contribute to hepatic encephalopathy, as well as to how this pathway can be modulated, is still under investigation.

Signal transduction in inherited metabolic disorders: a model for a possible pathogenetic mechanism

Signal transduction is the process by which external or internal signals exert their intracellular biological effects and by which intracellular communication is regulated. An important component of the signalling pathway is the second messenger, which is produced upon stimulation of the cell and mediates its effects downstream through phosphorylation and dephosphorylation of target proteins. Intracellular accumulation or deficiency of metabolites that serve as second messengers, due to inborn errors of their metabolism, may lead to perturbation of signalling pathways and disruption of the balance between them, serving as a missing link between the genotype, biochemical phenotype and clinical phenotype. The main second messengers that are putatively associated with the pathogenesis of IEM are 'bioactive lipids' (complex lipids and long-chain fatty acids), 'calcium', 'stress' (osmotic, reactive oxygen/nitorgen species, misfolded proteins and others) and 'metabolic' (AMP/ATP ratio, leucine, glutamine). They act through protein kinase C, calcium dependent kinases (CamK) and phosphatase (CN), 'stress-mediated' kinases (MAPK) and AMP/ATP-dependent kinase (AMPK). These signalling pathways lead to cell proliferation, inflammatory response, autophagy (and mitophagy) and apoptosis, suggesting that there are only few final common pathways involved in this pathogenetic mechanism. Questions remain regarding the complexity of the effects of the accumulating metabolites on different signalling pathways, and regarding the relative role and origin of 'proxy' second messengers such as reactive oxygen species. A better understanding of the signalling pathways in IEM may enhance the development of novel therapies in situations where normalising intracellular concentrations of the second messenger is impossible or impractical.

Induction of a Proinflammatory Response in Cortical Astrocytes by the Major Metabolites Accumulating in HMG-CoA Lyase Deficiency: the Role of ERK Signaling Pathway in Cytokine Release

3-Hydroxy-3-methylglutaric aciduria (HMGA) is an inherited metabolic disorder caused by 3-hydroxy-3-methylglutaryl-CoA lyase deficiency. It is biochemically characterized by predominant tissue accumulation and high urinary excretion of 3-hydroxy-3-methylglutarate (HMG) and 3-methylglutarate (MGA). Affected patients commonly present acute symptoms during metabolic decompensation, including vomiting, seizures, and lethargy/coma accompanied by metabolic acidosis and hypoketotic hypoglycemia. Although neurological manifestations are common, the pathogenesis of brain injury in this disease is poorly known. Astrocytes are important for neuronal protection and are susceptible to damage by neurotoxins. In the present study, we investigated the effects of HMG and MGA on important parameters of redox homeostasis and cytokine production in cortical cultured astrocytes. The role of the metabolites on astrocyte mitochondrial function (thiazolyl blue tetrazolium bromide (MTT) reduction) and viability (propidium iodide incorporation) was also studied. Both organic acids decreased astrocytic mitochondrial function and the concentrations of reduced glutathione without altering cell viability. In contrast, they increased reactive species formation (2'-7'-dichlorofluorescein diacetate (DCFHDA) oxidation), as well as IL-1β, IL-6, and TNF α release through the ERK signaling pathway. Taken together, the data indicate that the principal compounds accumulating in HMGA induce a proinflammatory response in cultured astrocytes that may possibly be involved in the neuropathology of this disease.

Lipoic acid and N-acetylcysteine prevent ammonia-induced inflammatory response in C6 astroglial cells: The putative role of ERK and HO1 signaling pathways

Hyperammonemia induces significant changes in the central nervous system (CNS) in direct association with astroglial functions, such as oxidative damage, glutamatergic excitotoxicity, and impaired glutamine synthetase (GS) activity and pro-inflammatory cytokine release. Classically, lipoic acid (LA) and N-acetylcysteine (NAC) exhibit antioxidant and anti-inflammatory activities by increasing glutathione (GSH) biosynthesis and decreasing pro-inflammatory mediator levels in glial cells. Thus, we evaluated the protective effects of LA and NAC against ammonia cytotoxicity in C6 astroglial cells. Ammonia decreased GSH levels and increased cytokine release and NFκB transcriptional activation. LA and NAC prevented these effects by the modulation of ERK and HO1 pathways. Taken together, these observations show that LA and NAC prevent the ammonia-induced inflammatory response.

Ammonia-induced oxidative damage in neurons is prevented by resveratrol and lipoic acid with participation of heme oxygenase 1

Ammonia is a metabolite that, at high concentrations, is implicated in neurological disorders, such as hepatic encephalopathy (HE), which is associated with acute or chronic liver failure. Astrocytes are considered the primary target of ammonia toxicity in the central nervous system (CNS) because glutamine synthetase (GS), responsible for ammonia metabolism in CNS, is an astrocytic enzyme. Thus, neuronal dysfunction has been associated as secondary to astrocytic impairment. However, we demonstrated that ammonia can induce direct effects on neuronal cells. The cell viability was decreased by ammonia in SH-SY5Y cells and cerebellar granule neurons. In addition, ammonia induced increased reactive oxygen species (ROS) production and decreased GSH intracellular content, the main antioxidant in CNS. As ammonia neurotoxicity is strongly associated with oxidative stress, we also investigated the potential neuroprotective roles of the antioxidants, resveratrol (RSV) and lipoic acid (LA), against ammonia toxicity in cerebellar granule neurons. RSV and LA were able to prevent the oxidative damage induced by ammonia, maintaining the levels of ROS production and GSH close to basal values. Both antioxidants also decreased ROS production and increased GSH content under basal conditions (in the absence of ammonia). Moreover, we showed that heme oxygenase 1 (HO1), a protein associated with protection against stress conditions, is involved in the beneficial effects of RSV and LA in cerebellar granule neurons. Thus, this study reinforces the neuroprotective effects of RSV and LA. Although more studies in vivo are required, RSV and LA could represent interesting therapeutic strategies for the management of HE.

A(a)LS: Ammonia-induced amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a dreadful, devastating and incurable motor neuron disease. Aetiologically, it is a multigenic, multifactorial and multiorgan disease. Despite intense research, ALS pathology remains unexplained. Following extensive literature review, this paper posits a new integrative explanation. This framework proposes that ammonia neurotoxicity is a main player in ALS pathogenesis. According to this explanation, a combination of impaired ammonia removal- mainly because of impaired hepatic urea cycle dysfunction-and increased ammoniagenesis- mainly because of impaired glycolytic metabolism in fast twitch skeletal muscle-causes chronic hyperammonia in ALS. In the absence of neuroprotective calcium binding proteins (calbindin, calreticulin and parvalbumin), elevated ammonia-a neurotoxin-damages motor neurons. Ammonia-induced motor neuron damage occurs through multiple mechanisms such as macroautophagy-endolysosomal impairment, endoplasmic reticulum (ER) stress, CDK5 activation, oxidative/nitrosative stress, neuronal hyperexcitability and neuroinflammation. Furthermore, the regional pattern of calcium binding proteins' loss, owing to either ER stress and/or impaired oxidative metabolism, determines clinical variability of ALS. Most importantly, this new framework can be generalised to explain other neurodegenerative disorders such as Huntington's disease and Parkinsonism.

High Concentrations of Atmospheric Ammonia Induce Alterations in the Hepatic Proteome of Broilers (Gallus gallus): An iTRAQ-Based Quantitative Proteomic Analysis

With the development of the poultry industry, ammonia, as a main contaminant in the air, is causing increasing problems with broiler health. To date, most studies of ammonia toxicity have focused on the nervous system and the gastrointestinal tract in mammals. However, few detailed studies have been conducted on the hepatic response to ammonia toxicity in poultry. The molecular mechanisms that underlie these effects remain unclear. In the present study, our group applied isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic analysis to investigate changes in the protein profile change in hepatic tissue of broilers exposed to high concentrations of atmospheric ammonia, with the goal of characterizing the molecular mechanisms of chronic liver injury from exposure to high ambient levels of ammonia. Overall, 30 differentially expressed proteins that are involved in nutrient metabolism (energy, lipid, and amino acid), immune response, transcriptional and translational regulation, stress response, and detoxification were identified. In particular, two of these proteins, beta-1 galactosidase (GLB1) and a kinase (PRKA) anchor protein 8-like (AKAP8 L), were previously suggested to be potential biomarkers of chronic liver injury. In addition to the changes in the protein profile, serum parameters and histochemical analyses of hepatic tissue also showed extensive hepatic damage in ammonia-exposed broilers. Altogether, these findings suggest that longtime exposure to high concentrations of atmospheric ammonia can trigger chronic hepatic injury in broilers via different mechanisms, providing new information that can be used for intervention using nutritional strategies in the future.