Role of dopaminergic and serotonergic neurotransmitters in behavioral alterations observed in rodent model of hepatic encephalopathy

Short Working Memory Impairment Associated with Hippocampal Microglia Activation in Chronic Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a major neuropsychological condition that occursas a result of impaired liver function. It is frequently observed in patients with advanced liver disease or cirrhosis. Memory impairment is among the symptoms of HE; the pathophysiologic mechanism for this enervating condition remains unclear. However, it is possible that neuroinflammation may be involved, as recent studies have emphasized such phenomena. Therefore, the aim of the present study is to assess short working memory (SWM) and examine the involvement of microglia in a chronic model of HE. The study was carried out with male Wistar rats that were induced by repeated thioacetamide (TAA) administration (100 mg/kg i.p injection for 10 days). SWM function was assessed through Y-maze, T-Maze, and novel object recognition (NOR) tests, together with an immunofluorescence study of microglia activation within the hippocampal areas. Our data showed impaired SWM in TAA-treated rats that was associated with microglial activation in the three hippocampal regions, and which contributed to cognitive impairment.

Co-exposure to lead, mercury, and cadmium induces neurobehavioral impairments in mice by interfering with dopaminergic and serotonergic neurotransmission in the striatum

Humans are exposed to lead (Pb), mercury (Hg), and cadmium (Cd) through various routes, including drinking water, and such exposure can lead to a range of toxicological effects. However, few studies have investigated the toxic effects of exposure to mixtures of metals, particularly in relation to neurotoxicity. In this study, 7-week-old male mice were exposed to Pb, Hg, and Cd individually or in combination through their drinking water for 28 days. The mice exposed to the metal mixture exhibited significantly reduced motor coordination and impaired learning and memory abilities compared to the control group and each of the single metal exposure groups, indicating a higher level of neurotoxicity of the metal mixture. The dopamine content in the striatum was significantly lower in the metal mixture exposure group than in the single metal exposure groups and the control group. Furthermore, compared to the control group, the metal mixture exposure group showed a significantly lower expression level of tyrosine hydroxylase (TH) and significantly higher expression levels of dopamine transporter (DAT), tryptophan hydroxylase 1 (TPH1), and serotonin reuptake transporter (SERT). Notably, there were no significant differences in SERT expression between the single metal exposure groups and the control group, but SERT expression was significantly higher in the metal mixture exposure group than in the single metal and control groups. These findings suggest that the key proteins involved in the synthesis and reuptake of dopamine (TH and DAT, respectively), as well as in the synthesis and reuptake of serotonin (TPH1 and SERT, respectively), play crucial roles in the neurotoxic effects associated with exposure to metal mixtures. In conclusion, this study demonstrates that simultaneous exposure to different metals can impact key enzymes involved in dopaminergic and serotonergic neurotransmission processes, leading to disruptions in dopamine and serotonin homeostasis and consequently a range of detrimental neurobehavioral effects.

Bile duct ligation increased dopamine levels in the cerebral cortex of rats partly due to induction of tyrosine hydroxylase

BACKGROUND AND PURPOSE

Liver failure is associated with psychiatric alterations, partly resulting from the increased brain dopamine levels. We investigated the relationship between increased dopamine levels and mental abnormalities using bile duct ligation (BDL) rats and the mechanism by which liver failure increased dopamine levels in SH-SY5Y cells. Behavioural tests were carried out on day 13 and 27 following BDL, along with measurements of dopamine and metabolites, expressions of enzymes and transporters related to dopamine metabolism, and its transport into the cortex and the hippocampus. SH-SY5Y cells were used to investigate whether NH₄ Cl, bile acids and bilirubin affected expression of tyrosine hydroxylase or not. Tyrosine hydroxylase (TH) expression in SH-SY5Y cells co-incubated with bilirubin and signal pathway inhibitors was measured.

KEY RESULTS

Open-field test results demonstrated BDL rats showed anxiety-like behaviour, accompanied by increased dopamine levels and expression of TH protein in the cortex. Membrane bound long form (MB)-COMT, slightly but significantly decreased. SH-SY5Y cells indicated that increased bilirubin levels was a factor in inducing TH expression. Both inhibitor of NF-κB pathway BAY 11-7082 and silencing NF-κB p65 reversed bilirubin-induced upregulation of TH protein. NF-κB activator TNF-α increased expression of TH protein. Roles of bilirubin in increases of TH protein expressions and dopamine levels were measured using hyperbilirubinemia rats. Anxiety-like behaviour, was associated with increased dopamine levels and TH protein expressions in hyperbilirubinemia rats.

CONCLUSION AND IMPLICATIONS

BDL significantly increased dopamine levels in rat cortex partly due to bilirubin-mediated TH induction. Increased bilirubin induced TH expression via activating NF-κB signalling pathway.

Peroxisome proliferator-activated receptor-γ doesn't modify altered electrophysiological properties of the CA1 pyramidal neurons in a rat model of hepatic cirrhosis

Regarding the low quality of life due to the cognitive complications in the patients with hepatic cirrhosis (HC), the goal of this study was to examine the possible neuroprotective effect of pioglitazone (PIO) on the electrophysiological alterations of hippocampus, a major area of cognition, in the experimental model of bile duct ligation (BDL). We used adult male Wistar rats in the present study to perform BDL or sham surgery. Pioglitazone was administered in BDL rats two weeks after the surgery for the next continuous four weeks. The effects of pioglitazone on BDL-induced electrophysiological alterations of the CA1 pyramidal neurons in the hippocampus were evaluated by whole-cell patch clamp recordings. Our findings demonstrated that chronic administration of PIO could not reverse the electrophysiological changes in the CA1 pyramidal neurons of the hippocampus in BDL rats but could improve the hepatic dysfunction.Together, the results of this study suggest that PIO administration cannot counteract altered intrinsic properties of the hippocampal neurons which has been shown recently as an involved mechanism of the cognitive impairments in hepatic encephalopathy (HE).

Ameliorative effect of oregano (Origanum vulgare) versus silymarin in experimentally induced hepatic encephalopathy

Hepatic encephalopathy (HE) is a deterioration of brain function in patients suffering from chronic liver disease, cirrhosis as a result of elevated blood ammonia and the production of pseudo-neurotransmitters. Herein, we investigated the chemical composition of hexane extract from Origanum vulgare (O. vulgare) leaves as well as its possible protective effects against thioacetamide (TAA)-induced HE in rats. GC-MS analysis of the extract revealed tentative identification of twenty-five compounds (82.93%), predominated by cholesten-3-one (27.30%), followed by γ-tocopherol (13.52%), α-tocopherol (5.01%), β-amyrin (5.24%) and α-amyrin (4.89%). Albino rats were distributed into seven groups (n = 7). G₁ served as negative control; G₂ and G₃ served as controls treated with O. vulgare (100 and 200 mg/kg/p.o b.w, respectively); G₄ served as TAA-positive control group (100 mg/kg/day/i.p., three alternative days per week for six weeks); G5, G6, and G7 served as TAA -induced HE rat model that received O. vulgare 100, O. vulgare 200, and silymarin (100 mg/kg of SILY, as standard drug), respectively. TAA showed depressive and anxiety-like behaviors in forced swimming test (FST) and reduction of cognitive score in elevated plus-maze test (EPMT) as well as impairment of locomotor and exploratory activities in open-field test (OFT). TAA caused a significant decline in body weight gain; however, the relative liver weight and brain water content were statistically increased. TAA-intoxicated rats showed significant increase of serum biomarker enzymes, proinflammatory cytokines, blood ammonia levels, brain serotonin, acetyl cholinesterase and cellular lipid peroxidation with significant decrease of brain dopamine, norepinephrine, antioxidant status. The hepatoprotective/neuro-protective activities of O. vulgare was found to be comparable with that of SILY in HE rats model. Where, treatment of TAA-intoxicated rats with O. vulgare attenuated anxiety, depressive-related behaviors, and reduced the biochemical changes in HE-induced by TAA. Therefore, O. vulgare could be an excellent hepato-/neuroprotective against hepatic injury and HE via improving the oxidative/inflammatory status through its antioxidant and neuro-modulatory properties and its effect is equal to that of SILY.

Metabolic changes of the reduction of manganese intake in the hepatic encephalopathy rat: NMR- and MS-based metabolomics study

To investigate the metabolic changes in type C hepatic encephalopathy (CHE) rats after reducing manganese (Mn) intake. A total of 80 Sprague-Dawley rats were divided into control group and CHE groups (induced by intraperitoneal injection of thioacetamide at a dose of 250 mg/kg of body weight twice a week for 6 weeks). CHE rats were subdivided into 1Mn group (fed a standard diet, with 10 mg Mn/kg feed), 0.5Mn group (half-Mn diet), 0.25Mn group (quarter-Mn diet) and 0Mn group (no-Mn diet) for 4 to 8 weeks. Morris water maze (MWM), Y maze and narrow beam test (NBT) were used to evaluate cognitive and motor functions. Blood ammonia, brain Mn content, the number of GS-positive cells, and glutamine synthetase (GS) activity were measured. The metabolic changes of CHE rats were investigated using hydrogen-nuclear magnetic resonance and mass spectrometry. Multivariate statistical analysis was used to analyze the results. Significantly decreased numbers of entries in target area of MWM and Y maze, longer NBT latency and total time, higher blood ammonia, brain Mn content and GS activity were found in CHE rats. After reducing Mn intake, CHE rats had better behavioral performance, significantly lower blood ammonia, brain Mn content and GS activity. The main up-regulated metabolites were Ala, GABA, Glu, Gln, Lac, Tyr, Phe in 1Mn rats. After reducing Mn intake, metabolites returned to normal level at different degrees. Reducing Mn intake could reduce brain Mn content and blood ammonia, regulate GS activity and amino acid metabolism, ultimately improve behavioral performance in CHE rats.

Cholestasis alters brain lipid and bile acid composition and compromises motor function in neonatal piglets

Infants with neonatal cholestasis are prone to neurodevelopmental deficits, however, the underlying pathogenesis is unclear. Lipid malabsorption and accumulation of potentially neurotoxic molecules in the blood such as bile acids are important yet relatively unexplored pathways. Here, we developed a translational piglet model to understand how the molecular bile acid and lipid composition of the brain is affected by this disease and relates to motor function. Piglets (8-days old) had bile duct ligation or sham surgery and were fed a formula diet for 3 weeks. Alongside sensory-motor deficits observed in bile duct-ligated animals, we found a shift toward a more hydrophilic and conjugated bile acid profile in the brain. Additionally, comprehensive lipidomics of the cerebellum revealed a decrease in total lipids including phosphatidylinositols and phosphatidylserines and increases in lysophospholipid species. This was paralleled by elevated cerebellar expression of genes related to inflammation and tissue damage albeit without significant impact on the brain transcriptome. This study offers new insights into the developing brain's molecular response to neonatal cholestasis indicating that bile acids and lipids may contribute in mediating motor deficits.

Hepatic Encephalopathy and Melatonin

Hepatic encephalopathy (HE) is a severe metabolic syndrome linked with acute/chronic hepatic disorders. HE is also a pernicious neuropsychiatric complication associated with cognitive decline, coma, and death. Limited therapies are available to treat HE, which is formidable to oversee in the clinic. Thus, determining a novel therapeutic approach is essential. The pathogenesis of HE has not been well established. According to various scientific reports, neuropathological symptoms arise due to excessive accumulation of ammonia, which is transported to the brain via the blood–brain barrier (BBB), triggering oxidative stress and inflammation, and disturbing neuronal-glial functions. The treatment of HE involves eliminating hyperammonemia by enhancing the ammonia scavenging mechanism in systemic blood circulation. Melatonin is the sole endogenous hormone linked with HE. Melatonin as a neurohormone is a potent antioxidant that is primarily synthesized and released by the brain’s pineal gland. Several HE and liver cirrhosis clinical studies have demonstrated impaired synthesis, secretion of melatonin, and circadian patterns. Melatonin can cross the BBB and is involved in various neuroprotective actions on the HE brain. Hence, we aim to elucidate how HE impairs brain functions, and elucidate the precise molecular mechanism of melatonin that reverses the HE effects on the central nervous system.

Effect of a specific Escherichia coli Nissle 1917 strain on minimal/mild hepatic encephalopathy treatment

BACKGROUND

Hepatic encephalopathy (HE) can be considered a result of dysregulated gut-liver-brain axis function, where cognitive impairment can be reversed or prevented by the beneficial effects induced by "gut-centric" therapies, such as the administration of nonabsorbable disaccharides, nonabsorbable antibiotics, probiotics and prebiotics.

AIM

To assess the short-term efficacy and safety of the probiotic Escherichia coli Nissle (EcN) 1917 strain compared to lactulose and rifaximin in patients with minimal/mild HE.

METHODS

From January 2017 to March 2020, a total of 45 patients with HE were enrolled in this prospective, single-centre, open-label, randomized study. Participants were randomly assigned at a ratio of 1:1:1 to one of the treatment groups: The EcN group (n = 15), lactulose group (n = 15) or rifaximin group (n = 15) for a 1 mo intervention period. The main primary outcomes of the study were changes in serum ammonia and Stroop test score. The secondary outcomes were markers of a chronic systemic inflammatory response (ІL-6, ІL-8, and IFN-γ) and bacteriology of the stool flora evaluated by specialized nonculture techniques after a 1 mo intervention period.

RESULTS

Patients who were given rifaximin or EcN showed a more significant reduction in serum ammonia and normalization of Bifidobacteria and Lactobacilli abundance compared to the lactulose group. However, the most pronounced restoration of the symbiotic microflora was associated with EcN administration and characterized by the absence of E. coli with altered properties and pathogenic enterobacteria in patient faeces. In the primary outcome analysis, improvements in the Stroop test parameters in all intervention groups were observed. Moreover, EcN-treated patients performed 15% faster on the Stroop test than the lactulose group patients (P = 0.017). Both EcN and rifaximin produced similar significant reductions in the proinflammatory cytokines INF-γ, IL-6 and IL-8. EcN was more efficient than lactulose in reducing proinflammatory cytokine levels.

CONCLUSION

The use of the probiotic EcN strain was safe and quite efficient for HE treatment. The probiotic reduced the ammonia content and the level of serum proinflammatory cytokines, normalized the gut microbiota composition and improved the cognitive function of patients with HE. The application of the EcN strain was more effective than lactulose treatment.

Evaluation of the protective effect of curcumin on encephalopathy caused by intrahepatic and extrahepatic damage in male rats

Objective(s):

Along with increased intracranial pressure (ICP) and brain damage, brain edema is the most common cause of death in patients with hepatic encephalopathy. Curcumin can pass the blood-brain barrier and possesses anti-inflammatory and anti-oxidant properties. This study focuses on the curcumin protective effect on intrahepatic and extrahepatic damage in the brain.

Materials and Methods:

One hundred and forty-four male Albino N-Mary rats were randomly divided into 2 main groups: intrahepatic injury group and extrahepatic cholestasis group. In intra-hepatic injury group intrahepatic damage was induced by intraperitoneal (IP) injection of acetaminophen (500 mg/kg) [19] and included four subgroups: 1. Sham, 2. Acetaminophen (APAP), 3. Normal saline (Veh) which was used as curcumin solvent, and 4. Curcumin (CMN). In extrahepatic cholestasis group intrahepatic damage was caused by common bile duct litigation (BDL) and included four subgroups: 1. Sham, 2. BDL, 3. Vehicle (Veh), and 4. Curcumin (CMN). In both groups, 72 hr after induction of cholestasis, brain water content, blood-brain barrier permeability, serum ammonia, and histopathological indicators were examined and ICP was measured every 24 hr for three days.

Results:

The results showed that curcumin reduced brain edema, ICP, serum ammonia, and blood-brain barrier permeability after extrahepatic and intrahepatic damage. The maximum effect of curcumin on ICP was observed 72 hr after the injection.

Conclusion:

According to our findings, it seems that curcumin is an effective therapeutic intervention for treating encephalopathy caused by extrahepatic and intrahepatic damage.

Is the Exposome Involved in Brain Disorders through the Serotoninergic System?

Serotonin (5-hydroxytryptamine, 5-HT) is a biogenic monoamine acting as a neurotransmitter in the central nervous system (CNS), local mediator in the gut, and vasoactive agent in the blood. It has been linked to a variety of CNS functions and is implicated in many CNS and psychiatric disorders. The high comorbidity between some neuropathies can be partially understood by the fact that these diseases share a common etiology involving the serotoninergic system. In addition to its well-known functions, serotonin has been shown to be a mitogenic factor for a wide range of normal and tumor cells, including glioma cells, in vitro. The developing CNS of fetus and newborn is particularly susceptible to the deleterious effects of neurotoxic substances in our environment, and perinatal exposure could result in the later development of diseases, a hypothesis known as the developmental origin of health and disease. Some of these substances affect the serotoninergic system and could therefore be the source of a silent pandemic of neurodevelopmental toxicity. This review presents the available data that are contributing to the appreciation of the effects of the exposome on the serotoninergic system and their potential link with brain pathologies (neurodevelopmental, neurodegenerative, neurobehavioral disorders, and glioblastoma).

AMPA induced cognitive impairment in rats: Establishing the role of endoplasmic reticulum stress inhibitor, 4-PBA

Glutamate excitotoxicity and endoplasmic reticulum (ER) recently have been found to be instrumental in the pathogenesis of various neurodegenerative diseases. However, the paucity of literature deciphering the inter-linkage among glutamate receptors, behavioral alterations, and ER demands thorough exploration. Reckoning the aforesaid concerns, a prospective study was outlined to delineate the influence of ER stress inhibition via 4-phenylbutyric acid (PBA) on α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) excitotoxicity-induced behavioral aspects and possible ER stress-glutamate linkage. Male SD rats were randomly divided into four groups namely sham (surgical control+vehicle, group 1), AMPA-induced excitotoxic group 2 receive a single intra-hippocampal injection of 10 mM AMPA, group 3 received AMPA along with PBA (i.p, 100 mg/kg body weight) for 15 days, and group 4 received PBA alone. Behavioral analyses were performed prior to the sacrifice of animals and hippocampus was extracted thereafter for further analysis. AMPA-induced excitotoxicity exhibited significant impairment of locomotion as well as cognitive functions. The levels of neurotransmitters such as dopamine, homo vanillic acid (HVA), norepinephrine, and serotonin were reduced accompanied by reduced expression of GLUR1 and GLUR4 (glutamate receptor) as well as loss of neurons in different layers of hippocampus. ER stress markers were upregulated upon AMPA excitotoxicity. However, chemical chaperone PBA supplementation remarkably mitigated the behavioral alterations along with expression of glutamate and ER stress intermediates/markers in AMPA excitotoxic animals. Therefore, the present exploration convincingly emphasizes the significance of ER stress and its inhibition via PBA in combating cognitive impairment as well as improving locomotion in excitotoxic animals.

Study of the Neurotransmitter Changes Adjusted by Circadian Rhythm in Depression Based on Liver Transcriptomics and Correlation Analysis

Depression has drawn increasing attention from the public around the world in recent years. Studies have shown that liver injury caused by chronic stress is relevant to depression and neurotransmitter changes. It is essential to clarify the relationship between neurotransmitter changes and hepatic gene expression in depression. In this study, we used the chronic unpredictable mild stress (CUMS) model combined with UHPLC-MS to explore the changes of neurotransmitters in serum and hippocampus and to decipher the differential gene expression in the liver by using the RNA-Seq combined with multivariate statistical analysis. Compared with the control group, the levels of neurotransmitters including 5-hydroxytryptamine (5-HT), acetylcholine, glutamate (Glu), and dopamine (DA) in the hippocampus and 5-HT, norepinephrine, γ-aminobutyric acid (GABA), and 5-hydroxyindoleacetic acid in serum were significantly changed in the CUMS rats. The results of liver transcriptomic analysis and correlation analysis showed that the Glu, DA, 5-HT, and GABA were impacted by 68 liver genes which were mainly enriched in three pathways including circadian rhythm, serotonergic synapse, and p53 signaling pathway. The expressive levels of clock genes and serotonergic synapse genes were validated by using q-PCR, and the diurnal rhythms of neurotransmitters were validated by in vivo hippocampus microdialysis. The CUMS stressors might cause phase advance of Glu and GABA by adjusting clock genes. The transcriptomic technique combined with correlation analysis and in vivo microdialysis could be used to discover comprehensive pathways of depression. It provides a new strategy for the rational assessment of the mechanism of disease.

A multi-omic study for uncovering molecular mechanisms associated with hyperammonemia-induced cerebellar function impairment in rats

Patients with liver cirrhosis may develop covert or minimal hepatic encephalopathy (MHE). Hyperammonemia (HA) and peripheral inflammation play synergistic roles in inducing the cognitive and motor alterations in MHE. The cerebellum is one of the main cerebral regions affected in MHE. Rats with chronic HA show some motor and cognitive alterations reproducing neurological impairment in cirrhotic patients with MHE. Neuroinflammation and altered neurotransmission and signal transduction in the cerebellum from hyperammonemic (HA) rats are associated with motor and cognitive dysfunction, but underlying mechanisms are not completely known. The aim of this work was to use a multi-omic approach to study molecular alterations in the cerebellum from hyperammonemic rats to uncover new molecular mechanisms associated with hyperammonemia-induced cerebellar function impairment. We analyzed metabolomic, transcriptomic, and proteomic data from the same cerebellums from control and HA rats and performed a multi-omic integrative analysis of signaling pathway enrichment with the PaintOmics tool. The histaminergic system, corticotropin-releasing hormone, cyclic GMP-protein kinase G pathway, and intercellular communication in the cerebellar immune system were some of the most relevant enriched pathways in HA rats. In summary, this is a good approach to find altered pathways, which helps to describe the molecular mechanisms involved in the alteration of brain function in rats with chronic HA and to propose possible therapeutic targets to improve MHE symptoms.

The Role of Intestinal Bacteria and Gut-Brain Axis in Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a neurological disorder that occurs in patients with liver insufficiency. However, its pathogenesis has not been fully elucidated. Pharmacotherapy is the main therapeutic option for HE. It targets the pathogenesis of HE by reducing ammonia levels, improving neurotransmitter signal transduction, and modulating intestinal microbiota. Compared to healthy individuals, the intestinal microbiota of patients with liver disease is significantly different and is associated with the occurrence of HE. Moreover, intestinal microbiota is closely associated with multiple links in the pathogenesis of HE, including the theory of ammonia intoxication, bile acid circulation, GABA-ergic tone hypothesis, and neuroinflammation, which contribute to cognitive and motor disorders in patients. Restoring the homeostasis of intestinal bacteria or providing specific probiotics has significant effects on neurological disorders in HE. Therefore, this review aims at elucidating the potential microbial mechanisms and metabolic effects in the progression of HE through the gut–brain axis and its potential role as a therapeutic target in HE.

Thymoquinone improves behavioral and biochemical deficits in hepatic encephalopathy induced by thioacetamide in rats

Hepatic encephalopathy (HE) is a cerebral function alteration in patients with liver dysfunction. The present study aimed to evaluate the therapeutic effects of thymoquinone (TQ) on behavioral deficits and its possible mechanism(s) in a thioacetamide (TAA)-induced HE model. HE was induced in male Wistar rats by intraperitoneal (i.p.) injection of TAA (200 mg/kg) for once every 48 h for 14 consecutive days. Thymoquinone (5, 10, and 20 mg/kg) was administered for seven consecutive days (i.p.) after HE induction. Anxiety and depression-like behaviors assessed by standard paradigms respectively. Finally, their brain hippocampus sections prepared to evaluate the oxidative stress changes in rats. Data showed treatment HE rats with TQ ameliorated anxiety and depression-like behaviors. TQ administration also reduced oxidative stress due to its potential to enhance the levels of glutathione-peroxidase (GPx), catalase (CAT), and total thiol content in the hippocampus. These findings suggest that TQ has notable effects against acute hepatic failure and HE complications through modulation of oxidative stress.

The Association between Hepatic Encephalopathy and Diabetic Encephalopathy: The Brain-Liver Axis

Hepatic encephalopathy (HE) is one of the main consequences of liver disease and is observed in severe liver failure and cirrhosis. Recent studies have provided significant evidence that HE shows several neurological symptoms including depressive mood, cognitive dysfunction, impaired circadian rhythm, and attention deficits as well as motor disturbance. Liver disease is also a risk factor for the development of diabetes mellitus. Diabetic encephalopathy (DE) is characterized by cognitive dysfunction and motor impairment. Recent research investigated the relationship between metabolic changes and the pathogenesis of neurological disease, indicating the importance between metabolic organs and the brain. Given that a diverse number of metabolites and changes in the brain contribute to neurologic dysfunction, HE and DE are emerging types of neurologic disease. Here, we review significant evidence of the association between HE and DE, and summarise the common risk factors. This review may provide promising therapeutic information and help to design a future metabolic organ-related study in relation to HE and DE.

Interaction of Manganese and Ammonia in the Brain of Hepatic Encephalopathy Rats

Background: Both ammonia and manganese (Mn) play a key role in the pathogenesis of hepatic encephalopathy (HE) and cause similar morphological and functional changes in astrocytes. Objectives: To investigate the interaction between brain Mn and ammonia in HE rats. Methods: Three rat models of minimal HE (MHE), chronic manganism (CHM), and chronic hyperammonemia (CHA) were constructed. A total of 48 Sprague-Dawley rats were divided into one control group (n = 6), MHE groups (n = 18, among which six rats were used to evaluate the MHE model), CHM groups (n = 12), and CHA groups (n = 12). The CHM, CHA, and the rest of MHE rats were randomly divided further into two subgroups, according to the MgSO4 treatment (oral administration of 496 mg/kg/day for seven weeks): MHE-7W and MHE + Mg-7W; CHM-7W and CHM + Mg-7W; and CHA-7W and CHA + Mg-7W, respectively. Rats’ blood ammonia, brain Mn, glutamine synthetase (GS), and glutamine (GLN) levels were measured and compared among groups. Results: Significantly higher brain Mn content in MHE-7W and CHM-7W rats, higher blood ammonia levels, brain GS activity, and GLN content were observed in MHE-7W, CHM-7W, and CHA-7W rats than in control rats. After MgSO4 treatment for seven weeks, significantly lower brain Mn content, blood ammonia levels, and GLN content were observed in MHE, CHM, and CHA rats. Conclusions: Our study showed that brain Mn accumulation could increase brain ammonia levels, while the accumulation of brain ammonia had no effect on the content of brain Mn.

Pro-inflammatory cytokines serve as communicating molecules between the liver and brain for hepatic encephalopathy pathogenesis and Lycium barbarum polysaccharides protection

ETHNOPHARMACOLOGICAL RELEVANCE

Gogi berry is a traditional food supplement and medical herbal which has been widely used in Eastern Asian countries. Lycium barbarum polysaccharides (LBP) are the major active components of Gogi berry and have been proved to possess a lot of biological activities.

AIM OF THE STUDY

We aimed to delineate the protective effect and mechanism of LBP on hepatic encephalopathy (HE).

MATERIALS AND METHODS

We investigated the protective mechanism of LBP in a thioacetamide (TAA, intraperitoneally injected, 400 mg/kg) induced acute HE mice model. Key phenotypes of clinical HE were phenocopied in the mice model, including high mortality, severe hepatic histology injury, increased hepatic oxidative stress, apoptosis, enhanced circulating levels of pro-inflammatory cytokines and ammonia, suppressed tryptophan hydroxylase activity, and deficits in locomotor activity.

RESULTS

The pathological alterations were effectively ameliorated by the oral administration with LBP (5 mg/kg, oral gavage, everyday), which were mediated by regulating MAPK pathways in both the liver and brain. Knockout of pro-inflammatory cytokines TNF-α or IL-6 effectively ameliorated impaired mice locomotor activity and MAPK activation in the brain. In an in vitro TNF-α-, IL-6-, or ammonia-induced microglia damaged cell model, cell injuries were evidently protected by the co-administration with LBP (50 μg/ml).

CONCLUSION

LBP ameliorated the hepatic/brain injuries and impaired locomotor activities in a HE mice model. Pro-inflammatory cytokines may serve as communicating molecules linking the liver and brain for the HE pathogenesis, partly through MAPK regulation.

Effects of altered maternal folate and vitamin B12 on neurobehavioral outcomes in F1 male mice

Maternal folate and vitamin B₁₂ status during pregnancy may influence development of central nervous system (CNS) in the offspring. Very little attention has been paid to understand the combined effects of both the vitamins during pregnancy. The present study was designed to evaluate the biochemical and behavioral outcomes following alterations in folate and vitamin B₁₂ levels in C57BL/6 mice. The female mice were fed with different combinations of folate and vitamin B₁₂ whereas; males were fed with normal diet for 4 weeks. The mice were mated and the pregnant mice received the same diets as before pregnancy. The F1 male mice were further continued on maternal diet for 6 weeks following neurobehavioral and biochemical assessment. The body weight of the F1 male mice was significantly decreased in the mice that received folate and vitamin B₁₂ deficient diet. Altered cognitive functions were observed in the folate and B₁₂ deficient F1 male mice as assessed by Morris water maze and novel object recognition tests. Spontaneous locomotor activity was decreased in F1 male mice fed with folate and B₁₂ deficient diets. Elevated homocysteine levels and decreased hydrogen sulfide levels were also observed in the brain of F1 male mice on folate and B₁₂ deficient diets. However, GSH and GSSG levels were increased in the brain of the animals supplemented with folate deficient diet with different combinations of B₁₂. The study suggests that exposure of female mice to folate and vitamin B₁₂ deficiency during pregnancy effects in-utero development of fetus, which further leads to behavioral anomalies in adult life and is sufficient to cause impaired cognitive behavior in the subsequent generation. Thus, elucidating the role and importance of maternal dietary folate and B₁₂ ratio during pregnancy.

Peripheral inflammation induces neuroinflammation that alters neurotransmission and cognitive and motor function in hepatic encephalopathy: Underlying mechanisms and therapeutic implications

Several million patients with liver cirrhosis suffer minimal hepatic encephalopathy (MHE), with mild cognitive and coordination impairments that reduce their quality of life and life span. Hyperammonaemia and peripheral inflammation act synergistically to induce these neurological alterations. We propose that MHE appearance is because of the changes in peripheral immune system, which are transmitted to brain, leading to neuroinflammation that alters neurotransmission leading to cognitive and motor alterations. We summarize studies showing that MHE in cirrhotic patients is associated with alterations in the immune system and that patients died with HE show neuroinflammation in cerebellum, with microglial and astrocytic activation and Purkinje cell loss. We also summarize studies in animal models of MHE on the role of peripheral inflammation in neuroinflammation induction, how neuroinflammation alters neurotransmission and how this leads to cognitive and motor alterations. These studies identify therapeutic targets and treatments that improve cognitive and motor function. Rats with MHE show neuroinflammation in hippocampus and altered NMDA and AMPA receptor membrane expression, which impairs spatial learning and memory. Neuroinflammation in cerebellum is associated with altered GABA transporters and extracellular GABA, which impair motor coordination and learning in a Y maze. These alterations are reversed by treatments that reduce peripheral inflammation (anti-TNFα, ibuprofen), neuroinflammation (sulphoraphane, p38 inhibitors), GABAergic tone (bicuculline, pregnenolone sulphate) or increase extracellular cGMP (sildenafil or cGMP). The mechanisms identified would also occur in other chronic diseases associated with inflammation, aging and some mental and neurodegenerative diseases. Treatments that improve MHE may also be beneficial to treat these pathologies.

Effects of erythropoietin on bile duct ligation-induced neuro-inflammation in male rats

Hepatic encephalopathy (HE) is a brain disorder as a result of liver failure. Previous studies have indicated that erythropoietin (EPO) has neuroprotective effects in different neurological diseases. This study addressed the therapeutic effect of a four-week treatment with EPO on neuronal damages in bile duct-ligated rats. Forty male Wistar rats (250–280 g) were used in the present study. The animals were randomly divided into four groups consisting of 10 animals each, including sham, sham + EPO, bile duct ligation (BDL), and BDL + EPO. EPO was intraperitoneally administered every other day (5,000 U/Kg) in the last four weeks after BDL. Biochemical and histological studies were performed to evaluate neurodegeneration. The results revealed that BDL increases the level of hepatic enzymes and total bilirubin. Furthermore, neurodegeneration was significantly increased in the BDL group compared to sham groups. EPO preserved hepatic enzymes and total bilirubin in the treated group. In addition, EPO significantly decreased the neurodegeneration in BDL + EPO compared to the BDL group. Results of this study showed that EPO has neuroprotective effects in the rat model of HE, possibly due to its anti-inflammatory and anti-oxidant properties. Complementary studies are required to clarify the exact mechanisms.

Propamocarb exposure decreases the secretion of neurotransmitters and causes behavioral impairments in mice

Propamocarb (PM) is a type of fungicide, which is widely used in the greenhouse-based production of vegetables and fruits globally. It has been considered to have generally low toxicity. However, the teratogenicity or neurotoxicity for mammals remains unclear. In this study, we aimed to explore its effect on the secretion of neurotransmitters and behavioral impairments. Male adult mice were exposed to 10 and 40 mg/L PM for 2 weeks (acute exposure) or 3 and 10 mg/L PM for 10 weeks (chronic exposure). It was observed that acute or chronic exposure to PM changed the levels of serotonin (5-HT) and dopamine in the serum and colon and the transcription of TPH2 and DRD2 in the colons of mice. In addition, the locomotor test, the open field test, and the Morris water maze analysis also showed that acute exposure to PM caused behavioral impairments to some extent. The results obtained in the present study indicated that PM has the potential to induce neurotoxicity in animals.

Neuroinflammation in acute hepatic encephalopathy rats: imaging and therapeutic effectiveness evaluation using 11C-PK11195 and 18F-DPA-714 micro-positron emission tomography

Neuroinflammation has an important influence in pathogenesis of acute hepatic encephalopathy (AHE). ¹¹C-PK11195 and ¹⁸F-DPA-714 targeted to translocator protein (TSPO) have potential application in positron emission tomography (PET) as a molecular probe of neuroinflammation. The aim of this study was to compare these two radiotracers and their effectiveness in detecting neuroinflammation for the imaging of AHE rat models. Furthermore, using the new radiotracer ¹⁸F-DPA-714, we analyzed the effectiveness of therapeutic treatment for neuroinflammation in AHE. First, we performed a comparative study of ¹¹C-PK1195 and ¹⁸F-DPA-714 PET to image neuroinflammation in AHE rats induced by thioacetamide. Twenty-four rats were divided into either control group (n = 12) or AHE group (n = 12). Next, each group was subdivided depending on the radiotracer used during PET imaging (n = 6). Radiotracer uptake values encompassing the whole brain were compared. Lastly, we used the optimized tracer to monitor anti-neuroinflammation effects in AHE-induced rats. Forty-six rats were divided into four groups: [normal saline (NS) group (n = 13), minocycline (MINO) group (n = 11), dexamethasone (DEXA) group (n = 11), MINO+DEXA group (n = 11)]. ¹⁸F-DPA-714 PET was performed and the uptake values were calculated. The rotarod test, biochemical indices, and histopathological examinations were quantitatively measured and compared. AHE rats showed reduced motor ability, elevated ammonia levels, and higher liver function indices (all P < 0.05) with unchanged inflammatory factors (all P > 0.05), compared to control group. Both ¹¹C-PK11195 and ¹⁸F-DPA-714 PET can detect neuroinflammation of AHE rats. Behavioral studies showed that MINO and/or DEXA improved the motor ability in AHE rats (P < 0.05); however, no differences were found for liver function or inflammatory markers among the four groups (all P > 0.05). The average uptake values of whole brain and multiple brain areas in the MINO+DEXA group were lower compared to all other groups (all P < 0.05), which was demonstrated by CD11b stains of microglia. Our results show that both ¹¹C-PK11195 and ¹⁸F-DPA-714 PET can detect neuroinflammation in AHE-induced rat models. Additionally, the combined use of minocycline and dexamethasone can effectively inhibit neuroinflammation in AHE-induced rats, which can be sensitively monitored by ¹⁸F-DPA-714 PET.

Hyperammonemia in Hepatic Encephalopathy

The precise mechanism underlying the neurotoxicity of Hepatic Encephalopathy (HE) is remains unclear. The dominant view has been that gut-derived nitrogenous toxins are not extracted by the diseased liver and thereby enter the brain. Among the various toxins proposed, the case for ammonia is most compelling. Events that lead to increased levels of blood or brain ammonia have been shown to worsen HE, whereas reducing blood ammonia levels alleviates HE. Clinical, pathological, and biochemical changes observed in HE can be reproduced by increasing blood or brain ammonia levels in experimental animals, while exposure of cultured astrocytes to ammonium salts reproduces the morphological and biochemical findings observed in HE. However, factors other than ammonia have recently been proposed to be involved in the development of HE, including cytokines and other blood and brain immune factors. Moreover, recent studies have questioned the critical role of ammonia in the pathogenesis of HE since blood ammonia levels do not always correlate with the level/severity of encephalopathy. This review summarizes the vital role of ammonia in the pathogenesis of HE in humans, as well as in experimental models of acute and chronic liver failure. It further emphasizes recent advances in the molecular mechanisms involved in the progression of neurological complications that occur in acute and chronic liver failure.

Neuroprotective Effect of Hydrogen Sulfide in Hyperhomocysteinemia Is Mediated Through Antioxidant Action Involving Nrf2

Homocysteine (Hcy) is a sulfur-containing amino acid derived from methionine metabolism. Elevated plasma Hcy levels (> 15 µM) result in a condition called hyperhomocysteinemia (HHcy), which is an independent risk factor in the development of various neurodegenerative disorders. Reactive oxygen species (ROS) produced by auto-oxidation of Hcy have been implicated in HHcy-associated neurological conditions. Hydrogen sulfide (H₂S) is emerging as a potent neuroprotective and neuromodulator molecule. The present study was aimed to evaluate the ability of NaHS (a source of H₂S) to attenuate Hcy-induced oxidative stress and altered antioxidant status in animals subjected to HHcy. Impaired cognitive functions assessed by Y-maze and elevated plus maze in Hcy-treated animals were reversed on NaHS administration. Increased levels of ROS, lipid peroxidation, protein carbonyls, and 4-hydroxynonenal (4-HNE)-modified proteins were observed in the cortex and hippocampus of Hcy-treated animals suggesting accentuated oxidative stress. This increase in Hcy-induced oxidative stress was reversed following NaHS supplementation. GSH/GSSG ratio, activity of antioxidant enzymes viz; superoxide dismutase, glutathione peroxidase, glutathione reductase, and glutathione-S-transferase were decreased in Hcy-treated animals. NaHS supplementation, on the otherhand, restored redox ratio and activity of antioxidant enzymes in the brains of animals with HHcy. Further, NaHS administration normalized nuclear factor erythroid 2-related factor 2 expression and acetylcholinesterase (AChE) activity in the brain of Hcy-treated animals. Histopathological studies using cresyl violet indicated higher number of pyknotic neurons in the cortex and hippocampus of HHcy animals, which were reversed by NaHS administration. The results clearly demonstrate that NaHS treatment significantly ameliorates Hcy-induced cognitive impairment by attenuating oxidative stress, improving antioxidant status, and modulating AChE activity thereby suggesting potential of H₂S as a therapeutic molecule.

Chronic infection with Mycobacterium lepraemurium induces alterations in the hippocampus associated with memory loss

Murine leprosy, caused by Mycobacterium lepraemurium (MLM), is a chronic disease that closely resembles human leprosy. Even though this disease does not directly involve the nervous system, we investigated a possible effect on working memory during this chronic infection in Balb/c mice. We evaluated alterations in the dorsal region of the hippocampus and measured peripheral levels of cytokines at 40, 80, and 120 days post-infection. To evaluate working memory, we used the T-maze while a morphometric analysis was conducted in the hippocampus regions CA1, CA2, CA3, and dentate gyrus (DG) to measure morphological changes. In addition, a neurochemical analysis was performed by HPLC. Our results show that, at 40 days post-infection, there was an increase in the bacillary load in the liver and spleen associated to increased levels of IL-4, working memory deterioration, and changes in hippocampal morphology, including degeneration in the four subregions analyzed. Also, we found a decrease in neurotransmitter levels at the same time of infection. Although MLM does not directly infect the nervous system, these findings suggest a possible functional link between the immune system and the central nervous system.

Systemic inflammation without gliosis mediates cognitive deficits through impaired BDNF expression in bile duct ligation model of hepatic encephalopathy

Chronic liver disease per se induces neuroinflammation that contributes to cognitive deficits in hepatic encephalopathy (HE). However, the processes by which pro-inflammatory molecules result in cognitive impairment still remains unclear. In the present study, a significant increase in the activity of liver function enzymes viz. alanine transaminase (ALT), aspartate transaminase (AST) and alkaline phosphatase (ALP) was observed along with increase in plasma ammonia levels after four weeks of bile duct ligation (BDL) in rats suggesting hepatocellular damage. A significant increase was observed in mRNA expression of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α) and monocyte chemoattractant protein-1 (MCP-1) in brain regions and liver of BDL rats. Concomitantly, IL-6, TNF-α and MCP-1 protein levels were also increased in brain regions, liver and serum of BDL rats suggesting the involvement of blood-brain-axis in inflammatory response. However, a significant decrease was observed in glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule-1 (Iba-1) expression at transcriptional and translation level in brain of BDL rats. Immunohistochemical and flowcytometric analysis revealed reduced number of GFAP-immunopositive astrocytes and Iba1-immunopositive microglia in the brain regions of BDL rats. Further, a significant decline was observed in cognitive functions in BDL rats assessed using Morris water maze and novel object recognition tests. Expression of pro and mature form of brain derived neurotrophic factor (BDNF) and its upstream transcription element showed significant reduction in brain of BDL rats. Taken together, the results of the present study suggest that systemic inflammation and reduced expression of BDNF and its upstream transcription factor plays a key role in cognitive decline in HE.

Mitochondrial dysfunctions contribute to energy deficits in rodent model of hepatic encephalopathy

Perturbations in the cerebral energy metabolism are anticipated to be an important factor by which ammonia may exert its toxic effects on the central nervous system. The present study was designed to investigate the role of impaired mitochondrial functions and cerebral energy metabolism in the development hepatic encephalopathy (HE) induced by of bile duct ligation (BDL). After four weeks of BDL, a significant increase in hepatic hydroxyproline and collagen content was observed which confirmed biliary fibrosis. Brain regions viz. cortex, hippocampus, striatum and cerebellum of BDL rats had impaired activity of mitochondrial respiratory chain enzymes. This was accompanied by increase in mitochondrial reactive oxygen species (ROS), malondialdehyde (MDA) and protein carbonyl levels in the brain. Mitochondrial redox ratio was significantly reduced in the brain of BDL rats. In addition, mitochondria from brain of BDL rats were depolarized and swollen compared to the sham controls. Ultrastructure analysis of mitochondria from cortex and hippocampus of BDL animals revealed aberrant cristae, ruptured membranes and non-dense matrix. Further, a significant decrease was observed in creatine kinase activity, glucose uptake and CO₂ production in the brain regions of BDL rats. ATP/ADP ratio, a critical parameter of cellular energy status, was also significantly reduced in brain regions of rats with HE. Overall, the findings clearly demonstrate that BDL induced HE involves mitochondrial respiratory chain dysfunctions, mitochondrial depolarization and swelling that accentuates oxidative stress which in turn leads to compromise in cerebral energy metabolism thereby contributing to the pathophysiology of chronic HE.

Neuroprotective Effect of Nortriptyline in Overt Hepatic Encephalopathy Through Attenuation of Mitochondrial Dysfunction

Hyperammonemia associated with overt hepatic encephalopathy (OHE) causes excitotoxic neuronal death through activation of the cytochrome C (CytC)-mediated mitochondria-dependent apoptotic pathway. We tested the therapeutic effect of nortriptyline (NT), a mitochondrial permeability transition pore (mPTP) blocker that can possibly inhibit mitochondrial CytC efflux to the cytosol on in vivo and in vitro OHE models. After ensuring the generation of OHE rats, established by bile duct ligation (BDL), they were intraperitoneally administered either 20 mg/kg NT (i.e., BDL+NT) or another vehicle (i.e., BDL+VEH) for 14 days. Compared with the control, BDL+VEH showed an increment of motor deficits, cell death, synaptic loss, apoptosis, and mitochondria with aberrant morphology in substantia nigra compacta dopaminergic (DA-ergic) neurons. However, the extent was significantly reversed in BDL+NT. Subsequently, we studied the neuroprotective mechanism of NT using PC-12 cells, a DA-ergic cell line, which exposed glutamate used as an excitotoxin. Compared with the control, the cells exposed to 15 mM glutamate (i.e., GLU) showed incremental cell death, apoptosis, and demise in mitochondrial respiration. Importantly, efflux of CytC from mitochondria to cytosol and the dissipation of mitochondrial membrane potential (△Ψm), an indicator of mPTP opening, were prominent in GLU. However, compared with the GLU, the cells cotreated with 10 μM NT (i.e., GLU+NT) showed a significant reduction in the aforementioned phenomenon. Together, we concluded that NT can be used for OHE therapeutics, mitigating the excitotoxic death of substantia nigra compacta DA-ergic neurons via mPTP-associated mitochondrial dysfunction inhibition.

Recent advances in hepatic encephalopathy

Hepatic encephalopathy describes the array of neurological alterations that occur during acute liver failure or chronic liver injury. While key players in the pathogenesis of hepatic encephalopathy, such as increases in brain ammonia, alterations in neurosteroid levels, and neuroinflammation, have been identified, there is still a paucity in our knowledge of the precise pathogenic mechanism. This review gives a brief overview of our understanding of the pathogenesis of hepatic encephalopathy and then summarizes the significant recent advances made in clinical and basic research contributing to our understanding, diagnosis, and possible treatment of hepatic encephalopathy. A literature search using the PubMed database was conducted in May 2017 using "hepatic encephalopathy" as a keyword, and selected manuscripts were limited to those research articles published since May 2014. While the authors acknowledge that many significant advances have been made in the understanding of hepatic encephalopathy prior to May 2014, we have limited the scope of this review to the previous three years only.

Characterization of the CA1 pyramidal neurons in rat model of hepatic cirrhosis: insights into their electrophysiological properties

Although the key contributors of altering neurological function in hepatic encephalopathy are relatively well known, the electrophysiological mechanism of CA1 damage, a key vulnerable area during hyperammonemia, have not yet been defined. Therefore, here we focus on the electrophysiological mechanisms of cognitive impairments following bile duct ligation (BDL). We performed patch-clamp recordings from the CA1 pyramidal neurons in hippocampus of male Wistar rats, which underwent sham or BDL surgery. A striking electrophysiological change of hippocampal neurons in experimental model of BDL was observed in the present study. Spontaneous firing frequency and rate of action potential (AP) rebound was decreased and afterhyperpolarization amplitude (AHP) was increased significantly in hippocampal cells of BDL animals compared to sham group. Together, the results suggest that altered intrinsic properties of the hippocampal neurons may contribute to the cognitive abnormalities during hepatic encephalopathy (HE), highlighting the electrophysiological mechanisms for providing new treatments against HE.

Blood-Brain Barrier Permeability Is Exacerbated in Experimental Model of Hepatic Encephalopathy via MMP-9 Activation and Downregulation of Tight Junction Proteins

The present study was designed to investigate the mechanisms involved in blood-brain barrier (BBB) permeability in bile duct ligation (BDL) model of chronic hepatic encephalopathy (HE). Four weeks after BDL surgery, a significant increase was observed in serum bilirubin levels. Masson trichrome staining revealed severe hepatic fibrosis in the BDL rats. ^99mTc-mebrofenin retention was increased in the liver of BDL rats suggesting impaired hepatobiliary transport. An increase in permeability to sodium fluorescein, Evans blue, and fluorescein isothiocyanate (FITC)-dextran along with increase in water and electrolyte content was observed in brain regions of BDL rats suggesting disrupted BBB. Increased brain water content can be attributed to increase in aquaporin-4 mRNA and protein expression in BDL rats. Matrix metalloproteinase-9 (MMP-9) mRNA and protein expression was increased in brain regions of BDL rats. Additionally, mRNA and protein expression of tissue inhibitor of matrix metalloproteinases (TIMPs) was also increased in different regions of brain. A significant decrease in mRNA expression and protein levels of tight junction proteins, viz., occludin, claudin-5, and zona occluden-1 (ZO-1) was observed in different brain regions of BDL rats. VCAM-1 mRNA and protein expression was also found to be significantly upregulated in different brain regions of BDL animals. The findings from the study suggest that increased BBB permeability in HE involves activation of MMP-9 and loss of tight junction proteins.

Oral administration of trace element magnesium significantly improving the cognition and locomotion in hepatic encephalopathy rats

The therapeutic effects of iron, zinc and magnesium trace elements, as well as rifaximin were investigated and compared in HE rats. In this study, HE rats were treated with either ferrous sulfate (HE-Fe, 30 mg/kg/day), zinc sulfate (HE-Zn, 30 mg/kg/day), magnesium sulfate (HE-Mg, 50 mg/kg/day) or rifaximin (HE-Rf, 50 mg/kg/day), which was mixed with water and administered orally for 61 days. The Morris water maze (MWM) and open-field tests were used to evaluate cognitive and locomotor function. The blood ammonia levels before and after administration of the glutamine challenge test, manganese concentration and glutamine synthetase (GS) activity were measured. Significantly longer MWM escape latencies, less locomotor activity, higher blood ammonia levels, higher brain manganese concentrations and higher GS activity were observed in HE rats. However, HE-Mg and HE-Rf rats had significantly shorter MWM escape latencies, increased locomotor activity, lower blood ammonia, lower brain manganese concentrations and lower GS activity. Partial improvements were observed in HE-Fe and HE-Zn rats. The results indicated that oral administration of magnesium can significantly improve the cognitive and locomotor functions in HE rats by reducing the brain manganese concentration and regulating GS activity.

Hydrogen sulfide attenuates homocysteine-induced cognitive deficits and neurochemical alterations by improving endogenous hydrogen sulfide levels

Hyperomocysteinemia (HHcy) has been associated with mild cognitive impairment and dementia. Hydrogen sulfide (H₂ S) has been suggested to be an endogenous modulator of neuronal functions. However, the effect and mechanisms involved in beneficial effect of H₂ S has not been investigated in homocysteine (Hcy)-induced cognitive deficits. This study has been designed to evaluate the effect of exogenous H₂ S on behavioral deficits and neurochemical alterations in HHcy animals. Hcy levels were significantly elevated in plasma, cortex, and hippocampus of Hcy administered animals. A progressive decline in memory functions and increased anxiolytic behavior was observed in HHcy animals. This was accompanied by decrease in endogenous H₂ S levels along with decreased activity of cystathionase (CSE) and cystathionine β-synthase (CBS). However, a significant increase in CSE and CBS mRNAs was observed. In addition, the catecholamine and serotonin levels were reduced and the activity of monoamine oxidase A and B were increased in brain regions of HHcy animals. Haematoxylin and eosin staining revealed higher number of pyknotic cells in brain regions of HHcy animals. H₂ S administration was found to lower elevated plasma and brain Hcy levels. The activities of CBS, CSE, and levels of H₂ S were restored in HHcy animals administered H₂ S. Exogenous H₂ S also ameliorated behavioral deficits accompanied by significant increase in catecholamines. Histological analysis revealed normal cell morphology in Hcy-treated animals supplemented with H₂ S. These results clearly demonstrate that the protective effect of H₂ S on Hcy-induced cognitive deficits is mediated through increased catecholamine and H₂ S levels thereby suggesting its beneficial role in preventing HHcy-induced neurodegeneration. © 2016 BioFactors, 43(3):434-450, 2017.

Assessing the brain through the eye: New ways to explore hepatic encephalopathy

BACKGROUND & AIMS

Minimal hepatic encephalopathy (mHE) has been shown to affect daily functioning, quality of life, driving and overall mortality. However, little is known about treating or diagnosing early impairments in mHE. We studied one of its precipitating factors, portal hypertension which is driving the inflammatory process behind mHE. The purpose was to describe an indirect diagnostic method able to detect the pathology at early stages based on the study of the vascularization and mast cells conjunctival hyperplasia as secondary inflammatory response associated to portal hypertension. Finally, we correlated the presence of histological changes in the eye in mHE with deficits in behavioral task acquisition.

METHODS

Rats were trained on a stimulus-response task and a spatial working memory task using the Morris water maze. Two groups of animals were used: a SHAM (sham-operated) group (n=10) and a portal hypertension (HT) group (n=10). The triple portal vein ligation method was used to create an animal model of mHE. Latencies to reach the platform, number of glial fibrillary acidic protein-immunoreactive astrocytes (GFAP-IR), mast cell expression and presence/absence of blood and lymphatic vessels were examined.

RESULTS

There were differences in stimulus-response behavioral performance, with a deficit in the acquisition in the HT group. However, no differences between groups were found on the spatial working memory task. At the same time, differences between groups were found in the GFAP-IR density, which was lower in the HT group, and in the number of mast cells and the presence of vessels, which were higher in the HT group.

CONCLUSIONS

In this study, we provide the first preliminary insight into the validity of exploring the eye as a possible tool to assess the diagnosis of mHE conditions.

Estimation of ellagic acid and/or repaglinide effects on insulin signaling, oxidative stress, and inflammatory mediators of liver, pancreas, adipose tissue, and brain in insulin resistant/type 2 diabetic rats

Even though ellagic acid has previously been valued in many models of cancer, so far its full mechanistic effect as a natural antiapoptotic agent in the prevention of type 2 diabetes complications has not been completely elucidated, which was the goal of this study. We fed albino rats a high-fat fructose diet (HFFD) for 2 months to induce insulin resistance/type 2 diabetes and then treated the rats with ellagic acid (10 mg/kg body weight, orally) and/or repaglinide (0.5 mg/kg body weight, orally) for 2 weeks. At the serum level, ellagic acid challenged the consequences of HFFD, significantly improving the glucose/insulin balance, liver enzymes, lipid profile, inflammatory cytokines, redox level, adipokines, ammonia, and manganese. At the tissue level (liver, pancreas, adipose tissue, and brain), ellagic acid significantly enhanced insulin signaling, autophosphorylation, adiponectin receptors, glucose transporters, inflammatory mediators, and apoptotic markers. Remarkably, combined treatment with both ellagic acid and repaglinide had a more pronounced effect than treatment with either alone. These outcomes give new insight into the promising molecular mechanisms by which ellagic acid modulates numerous factors induced in the progression of diabetes.

Evaluation of prepulse inhibition and memory impairments at early stage of cirrhosis may be considered as a diagnostic index for minimal hepatic encephalopathy

Minimal hepatic encephalopathy (MHE), which represents the early stage of this condition, is not clinically apparent and is prevalent in up to 80% of patients. The poor outcomes of MHE encouraged us to identify more simple methods for early diagnosis of MHE. To this purpose, we evaluated the contemporary manifestations of motor, cognitive and sensorimotor gaiting deficits following bile duct-ligation (BDL). Male Wistar rats were undergone BDL to induce cirrhosis and locomotor, spatial learning and memory and sensorimotor gating were assessed 2, 3, and 4weeks after the operation by rotarod, Morris water-maze and prepulse inhibition (PPI) tests. PPI was examined 6weeks after BDL until appearance of hepatic encephalopathy. Results showed that although PPI was significantly enhanced in the 6-week BDL animals, locomotor activity reduced in 4-week BDL rats compared to the BDL rats after a 2-week period. The total distance travelled and swimming time to reach the platform increased in the 4-week BDL rats and, in contrast, the percentage of time spent and space travelled in correct quadrant decreased. Moreover, memory index decreased in the 3-week BDL group compared to sham-operated group. It was observed an increase in global PPI in 3- and 4-week BDL animals in comparison with either 2-week BDL or sham-operated rats. Consequently, it is indicated that BDL animals manifest spatial learning and memory deficits and PPI disruption in early stage of HE and evaluation of these factors can be considered as indices for simple and early diagnosis of MHE.

Structural Features and Potent Antidepressant Effects of Total Sterols and β-sitosterol Extracted from Sargassum horneri

The purified total sterols and β-sitosterol extracted from Sargassum horneri were evaluated for their antidepressant-like activity using the forced swim test (FST) and tail suspension test (TST) in mice. Total sterols and β-sitosterol significantly reduced the immobility time in the FST and TST. Total sterols were administered orally for 7 days at doses of 50, 100, and 200 mg/kg, and β-sitosterol was administered intraperitoneally at doses of 10, 20, and 30 mg/kg. β-sitosterol had no effect on locomotor activity in the open field test. In addition, total sterols and β-sitosterol significantly increased NE, 5-HT, and the metabolite 5-HIAA in the mouse brain, suggesting that the antidepressant-like activity may be mediated through these neurotransmitters.

Combined Intraperitoneal and Intrathecal Etanercept Reduce Increased Brain Tumor Necrosis Factor-Alpha and Asymmetric Dimethylarginine Levels and Rescues Spatial Deficits in Young Rats after Bile Duct Ligation

BACKGROUND

Rats subjected to bile duct ligation (BDL) exhibit increased systemic oxidative stress and brain dysfunction characteristic of hepatic encephalopathy (HE), including fatigue, neurotransmitter alterations, cognitive and motor impairment, and brain inflammation. The levels of tumor necrosis factor-alpha (TNF-α) and asymmetric dimethylarginine (ADMA) are both increased in plasma and brain in encephalopathy induced by chronic liver failure. This study first determined the temporal profiles of TNF-α and ADMA in the plasma, brain cortex, and hippocampus in young BDL rats. Next, we examined whether etanercept was beneficial in preventing brain damage.

METHODS

Young rats underwent sham ligation or BDL at day 17 ± 1 for 4 weeks. Treatment group rats were administered etanercept (10 mg/kg) intraperitoneally (IP) three times per week with or without etanercept (100 μg) intrathecally (IT) three times in total.

RESULTS

We found increased plasma TNF-α, soluble tumor necrosis factor receptor 1 (sTNFR1), soluble tumor necrosis factor receptor 2 (sTNFR2), and ADMA levels, increased cortical TNF-α mRNA and protein and ADMA, and hippocampal TNF-α mRNA and protein, and spatial defects in young BDL rats. The increase in cortex TNF-α mRNA and ADMA were reduced by IP etanercept or combined IP and IT etanercept. Dually IP/IT etanercept administration reduced the increased cortical and hippocampal TNF-α mRNA and protein level as well as spatial deficits.

CONCLUSIONS

We conclude that combined intraperitoneal and intrathecal etanercept reduce increased brain TNF-α and ADMA levels and rescues spatial deficits in young rats after BDL.

(18)F-DPA-714 PET Imaging for Detecting Neuroinflammation in Rats with Chronic Hepatic Encephalopathy

Neuroinflammation is considered to be the pathogenesis of hepatic encephalopathy (HE), and imaging neuroinflammation is implicated in HE management. ¹¹C-PK11195, a typical translocator protein (TSPO) radiotracer, is used for imaging neuroinflammation. However, it has inherent limitations, such as short half-life and limited availability. The purpose of this study was to demonstrate the efficiency of new generation TSPO radiotracer, ¹⁸F-DPA-714, in detecting and monitoring neuroinflammation of chronic HE. This study was divided into two parts. The first part compared ¹⁸F-DPA-714 and ¹¹C-PK11195 radiotracers in ten HE induced rats [bile duct ligation (BDL) and fed hyperammonemic diet (HD)] and 6 control rats. The animal subjects underwent dynamic positron emission tomography (PET) during 2-day intervals. The ¹¹C-PK11195 PET study showed no differences in whole brain average percent injected dose per gram (%ID/g) values at all time points (all P>0.05), while the ¹⁸F-DPA-714 PET study showed higher whole brain average %ID/g values in HE rats compared to control group rats at 900 s to 3300 s after injecting radiotracer (all P<0.05). The second part of the study evaluated the effectiveness of ibuprofen (IBU) treatment to chronic HE. Forty rats were classified into six groups, including Sham+normal saline (NS), Sham+IBU, BDL+NS, BDL+HD+NS, BDL+IBU, and BDL+HD+IBU groups. ¹⁸F-DPA-714 PET was used to image neuroinflammation. Whole and regional brain average %ID/g values, neurological features, inflammatory factors and activated microglia showed better in the IBU groups than in the NS groups (all P<0.05) and no difference was seen in the Sham groups compared to IBU groups (all P>0.05). In conclusion, this study demonstrated that ¹⁸F-DPA-714 is an ideal TPSO radiotracer for imaging neuroinflammation and monitoring anti-neuroinflammation treatment efficacy of chronic HE.