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

Farnesoid X receptor activation alleviates hepatic encephalopathy by improving hepatic ammonia metabolism in murine models

BACKGROUND

Hepatic encephalopathy (HE) is a mental and neurological complication induced by acute or chronic hepatic failure. Emerging evidence indicates that the farnesoid X receptor (FXR), a multifunctional nuclear receptor and transcription factor, plays a pivotal role in regulating the expression of key genes associated with ammonia metabolism. However, the effect of FXR activation on HE has remained largely uncharted.

METHODS

We established mouse models of HE by intraperitoneal injection of thioacetamide (TAA) and partial hepatectomy (PHx). Subsequently, we administered obeticholic acid (OCA) to activate FXR and investigated its effects on HE through comprehensive biochemical, biological, histological and behavioral analysis. Additionally, in vitro experiments were conducted to examine the impact of FXR activation on ammonia stress.

FINDINGS

In the animal model of HE, activation of FXR upregulated the expression of key enzymes involved in ammonia metabolism pathway within the liver, thereby enhancing urea cycle functionality, reducing plasma ammonia levels, and mitigating liver injury. Furthermore, FXR activation significantly improved behavioral activities in mice and mitigated inflammation in the brain. Finally, our findings demonstrated that activating FXR could enhance ammonia metabolism and ammonia tolerance of C3A cells.

INTERPRETATION

Our data provide novel evidence demonstrating that the activation of FXR by OCA exerts regulatory control over the expression of enzymes involved in ammonia metabolism, thereby effectively alleviating HE. Consequently, FXR could emerge as a promising novel target for HE treatment.

FUNDING

This study was supported by the National Natural Science Foundation of China No: 81970726 (to W-D Chen), and Henan Provincial Key Project of Medical Science and Technology Research No: SBGJ202102215 (to WL Ye).

Upregulation of HDAC3 mediates behavioral impairment in the bile duct ligation model of hepatic encephalopathy

Hepatic encephalopathy (HE), an outcome of chronic liver disease is characterized by behavioral impairments. The present study investigated the role of HDAC-mediated transcriptional regulation causing behavioral impairments in the bile duct ligation (BDL) model of HE. Post-BDL surgery in rats, dynamic alterations in liver function tests, liver morphology were observed. In BDL rats, histological staining in brain demonstrated reduced neuronal viability and warped neuronal architecture. Additionally, BDL animals showed impaired spatial learning, memory, and increased anxiety in the open field, Barnes maze, and Y maze tests. Further, the Golgi cox staining revealed a significantly altered spine density and spine clustering patterns of granular neuron in dentate gyrus of BDL rats. Concordantly, a significant downregulation of memory encoding genes was also observed in BDL rats that may account for aberrant behavior. Molecular analysis of modifiers, such as HDAC, showed significant changes in the expression of HDAC3 and HDAC6 in both the cortex and hippocampus of BDL rats. Upregulation of HDAC3 promoted its localization on the promoter of genes like c-Fos, NPAS4, Arc, and others, likely causing their decreased expression. Our findings suggest that increased HDAC3 activity downregulates key synaptic plasticity and memory-related genes, potentially driving neurobehavioral changes in BDL rats.

Neuronal nitric oxide synthase activation by tadalafil protects neurological impairments in a zebrafish larva model of hyperammonemia

AIMS

Hyperammonaemia (HA) is a metabolic disorder characterized by increased ammonia levels in the blood and is associated with severe neurological impairments. Some previous findings have shown the involvement of the nitric oxide pathway in HA-induced neurological impairments. The current study explored the impact of tadalafil on neurological impairments induced by HA in a zebrafish larval model due to its reported indirect interactions with the nitric oxide pathway.

MATERIAL AND METHODS

HA was induced in zebrafish larvae by ammonium acetate exposure from 2 to 9 days post fertilization (dpf). Locomotor and cognitive functions were analysed following the treatment. The levels of gamma-aminobutyric acid (GABA), glutamate, and dopamine were measured in the larval head. The expression of genes associated with apoptosis (baxa and bcl2a), selected neurotransmitter receptors and bdnf was analysed. The protein levels of CREB and nNOS were also quantified.

KEY FINDINGS

Tadalafil incubation reversed the HA-associated locomotor and cognitive impairments in larvae. The treatment modulated GABA, dopamine, and glutamate levels. An upregulation in the expression of grin1a, gria2b, drd1b, drd2b, bdnf, and bcl2a, and downregulation of gabrz, gabrd, gabrg2 and baxa was observed following tadalafil treatment. The protein expression showed increased nNOS, p-CREB(Ser133), and decreased p-nNOS(Ser847) levels in the larvae incubated with tadalafil.

SIGNIFICANCE

The study concluded that tadalafil mitigates HA-induced neurological impairments by activating neuronal nitric oxide synthase. The study highlighted the possible application of tadalafil in the symptomatic management of neurological impairments in HA provided its efficacy and safety are further ensured in higher mammals.

Hepatic encephalopathy: experimental drugs in development and therapeutic potential

INTRODUCTION

Hepatic encephalopathy (HE) presents a complex pathophysiology, creating multiple potential treatment avenues. This review covers current and emerging treatments for HE.

AREAS COVERED

Standard therapies, including non-absorbable disaccharides and rifaximin, are widely used but show inconsistent efficacy. Alternatives such as polyethylene glycol and L-ornithine L-aspartate have been effective in certain cases. Advancements in understanding HE reveal a growing need for personalized treatments. Novel approaches targeting immune modulation and neuroinflammation are under investigation, though clinical translation is slow. Nutritional interventions and fecal microbiota transplantation show potential but lack robust evidence. Innovative therapies like gene and cell therapies, as well as extracellular vesicles from mesenchymal stem cells, present promising avenues for liver disease treatment, potentially benefiting HE.

EXPERT OPINION

A key challenge in HE research is the design of randomized clinical trials, which often suffer from small sample sizes, heterogeneity in patient population, and inconsistent blinding. Additionally, the multifactorial nature of HE, together with a high spontaneous response rate, complicates efforts to isolate treatment effects. Despite current limitations, ongoing research and technological advances hold promise for more effective and individualized HE treatments in the future.

Infection, inflammation and hepatic encephalopathy from a clinical perspective

Hepatic encephalopathy (HE) is a syndrome that is associated with both acute and chronic liver injury. It manifests as a wide spectrum of neuropsychological abnormalities, ranging from subtle impairments in executive higher functions observed in cirrhosis, through to coma in acute liver failure. In acute liver failure, the central role of ammonia in the development of brain oedema has remained undisputed for 130 years. It latterly became apparent that infection and inflammation were profound determinants for the development of severe hepatic encephalopathy, associated with the development of cerebral oedema and intracranial hypertension. The relationship of the development of hepatic encephalopathy with blood ammonia levels in cirrhosis is less clear cut and the synergistic interplay of inflammation and infection with ammonia has been identified as being fundamental in the development and progression of hepatic encephalopathy. A perturbed gut microbiome and the presence of an impaired gut epithelial barrier that facilitates translocation of bacteria and bacterial degradation products into the systemic circulation, inducing systemic inflammation and innate and adaptive immune dysfunction, has now become the focus of therapies that treat hepatic encephalopathy in cirrhosis, and may explain why the prebiotic lactulose and rifaximin are efficacious. This review summarises the current clinical perspective on the roles of inflammation and infection in hepatic encephalopathy and presents the evidence base for existing therapies and those in development in the setting of acute and chronic liver failure.

Multimodal action of phosphodiesterase 5 inhibitors against neurodegenerative disorders: An update review

Phosphodiesterase type 5 (PDE5) is an enzyme primarily found in the smooth muscle of the corpus cavernosum and also highly expressed in the substantia nigra, cerebellum, caudate, hippocampal regions and cerebellar purkinje cells, responsible for selectively breaking down cyclic guanosine monophosphate (cGMP) into 5'-GMP and regulate intracellular cGMP levels. As a second messenger, cyclic GMP enhances signals at postsynaptic receptors and triggers downstream effector molecules, leading to changes in gene expression and neuronal responses. Additionally, cGMP signaling transduction cascade, present in the brain, is also essential for learning and memory processes. Mechanistically, PDE5 inhibitors share structural similarities with cGMP, competitively binding to PDE5 and inhibiting cGMP hydrolysis. This action enhances the effects of nitric oxide, resulting in anti-inflammatory and neuroprotective effects. Neurodegenerative disorders entail the progressive loss of neuron structure, culminating in neuronal cell death, with currently available drugs providing only limited symptomatic relief, rendering neurodegeneration considered incurable. PDE5 inhibitors have recently emerged as a potential therapeutic approach for neurodegeneration, neuroinflammation, and diseases involving cognitive impairment. This review elucidates the principal roles of 3',5'-cyclic adenosine monophosphate (cAMP) and cGMP signaling pathways in neuronal functions, believed to play pivotal roles in the pathogenesis of various neurodegenerative disorders. It provides an updated assessment of PDE5 inhibitors as disease-modifying agents for conditions such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, cerebral ischemia, Huntington's disease, and neuroinflammation. The paper aims to review the current understanding of PDE5 inhibitors, which concurrently regulate both cAMP and cGMP signaling pathways, positing that they may exert complementary and synergistic effects in modifying neurodegeneration, thus presenting a novel direction in therapeutic discovery. Moreover, the review provides critical about biological functions, therapeutic potentials, limitations, challenges, and emerging applications of selective PDE5 inhibitors. This comprehensive overview aims to guide future academic and industrial endeavors in this field.

Unveiling the protective potential of mirabegron against thioacetamide-induced hepatic encephalopathy in rats: Insights into cAMP/PPAR-γ/p-ERK1/2/p S536 NF-κB p 65 and p-CREB/BDNF/TrkB in parallel with oxidative and apoptotic trajectories

Hepatic encephalopathy (HE) is one of the most prevalent and severe hepatic and brain disorders in which escalation of the oxidative, inflammatory and apoptotic trajectories pathologically connects acute liver injury with neurological impairment. Mirabegron (Mira) is a beta3 adrenergic receptor agonist with proven antioxidant and anti-inflammatory activities. The current research pointed to exploring Mira's hepato-and neuroprotective impacts against thioacetamide (TAA)-induced HE in rats. Rats were distributed into three experimental groups: the normal control group, the TAA group, received TAA (200 mg/kg/day for three consecutive days) and the Mira-treated group received Mira (10 mg/kg/day; oral gavage) for 15 consecutive days and intoxicated with TAA from the 13th to the 15th day of the experimental period. Mira counteracted hyperammonemia, enhanced rats' locomotor capability and motor coordination. It attenuated hepatic/neurological injuries by its antioxidant, anti-apoptotic as well as anti-inflammatory potentials. Mira predominantly targeted cyclic adenosine monophosphate (cAMP)/phosphorylated extracellular signal-regulated kinase (p-Erk1/2)/peroxisome proliferator-activated receptor gamma (PPARγ) dependent pathways via downregulation of p S536-nuclear factor kappa B p65 (p S536 NF-κB p 65)/tumor necrosis alpha (TNF-α) axis. Meanwhile, it attenuated nuclear factor erythroid 2-related factor (Nrf2) depletion in parallel with restoring of the neuroprotective defensive pathway by upregulation of cerebral cAMP/PPAR-γ/p-ERK1/2 and p-CREB/BDNF/TrkB besides reduction of GFAP immunoreactivity. Mira showed anti-apoptotic activity through inhibition of Bax immunoreactivity and elevation of Bcl2. To summarize, Mira exhibited a hepato-and neuroprotective effect against TAA-induced HE in rats via shielding antioxidant defense and mitigation of the pathological inflammatory and apoptotic axis besides upregulation of neuroprotective signaling pathways.

Neurological recovery in rats with portocaval anastomosis-induced hepatic encephalopathy treated with leuprolide acetate, a GnRH agonist

Hepatic encephalopathy (HE) is a neuropsychiatric complication of acute liver failure or chronic liver injury. Liver dysfunction impairs ammonia detoxification, allowing it to cross the blood-brain barrier (BBB) and disrupt brain function. The hippocampus becomes a crucial target during elevated ammonia levels, causing spatial memory impairment and decreased learning ability. Leuprolide acetate (LA), a GnRH agonist, has been implicated in neuroprotection and neuroregeneration in several regions of the central nervous system (CNS) including hippocampus. In this study, we aim to evaluate the effects of LA treatment on hippocampus of rats with HE induced by portocaval anastomosis (PCA) trough cognitive tests, histology analysis and expression of neuronal recovery marker proteins, such as neurofilament (NF200) and neurabin II, and astrocyte marker glial fibrillary acidic protein (GFAP). Rats were divided into three groups: SHAM, portocaval anastomosis with saline solution (PCA + SS) and portocaval anastomosis treated with LA (PCA + LA). To evaluate learning and spatial memory elevated T-maze (ETM) and Y-maze test (YMT) were respectively used. Results indicated that LA-treated rats performed significantly better in ETM and YMT than untreated rats. Histological analysis of hippocampus showed increased neuron density, nuclear area, and layer thickness in dentate gyrus of PCA + LA group compared to PCA + SS. Additionally, neurabin II and NF200 expression were higher in LA-treated rats, while GFAP expression was elevated in the PCA + SS group compared to control and PCA + LA groups. In conclusion, LA enhances hippocampal neuron recovery and reduces astrogliosis, suggesting its potential as a therapeutic intervention for attenuating hippocampal damage during HE.

Therapeutic Effect of Levetiracetam Against Thioacetamide-Induced Hepatic Encephalopathy Through Inhibition of Oxidative Stress and Downregulation of NF-κB, NLRP3, iNOS/NO, Pro-Inflammatory Cytokines and Apoptosis

Hepatic encephalopathy (HE) is a serious brain disorder which associated with neurological and psychiatric manifestations. Oxidative stress and neuroinflammation and apoptosis play main roles in the development of brain damage in HE. Levetiracetam is an antiseizure drug with established antioxidant and anti-inflammatory activities. In the present study we investigated the therapeutic effects of levetiracetam against brain injury in HE and its underlying mechanisms of action. Male C57BL/6 mice were subjected to the induction of HE by the injection of thioacetamide (200 mg/kg) for 2 days. Mice were treated with levetiracetam at two doses (50 or 100 mg/kg/day) for 3 days in the treatment groups. Animals were subjected to a behavioral test and the brain tissues were dissected for histopathological, biochemical, gene expression and immunofluorescence analysis. The results showed that levetiracetam alleviated body weight loss and improved locomotor activity of mice with HE. Levetiracetam treatment decreased the histopathological changes, lipid peroxidation and protein carbonylation while restored the antioxidants (GSH, SOD and CAT) in the brain. Levetiracetam decreased the expression and activity of NF-κB, NOD-like receptor pyrin domain-containing protein 3 (NLRP3) and pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IFN-γ) in the brain tissue. Administration of levetiracetam inhibited iNOS/NO pathway and myeloperoxidase (MPO) activity in the brain. Moreover, caspase-3 was decreased and the ratio of Bcl2/Bax was increased in the brain of mice treated with levetiracetam. These findings suggest that levetiracetam may be a promising therapeutic agent for brain injury in HE through inhibiting the oxidative, inflammatory and apoptotic pathways.

The potential therapeutic effect of phosphodiesterase 5 inhibitors in the acute ischemic stroke (AIS)

Acute ischemic stroke (AIS) is a focal neurological disorder that accounts for 85% of all stroke types, due to occlusion of cerebral arteries by thrombosis and emboli. AIS is also developed due to cerebral hemodynamic abnormality. AIS is associated with the development of neuroinflammation which increases the severity of AIS. Phosphodiesterase enzyme (PDEs) inhibitors have neuro-restorative and neuroprotective effects against the development of AIS through modulation of the cerebral cyclic adenosine monophosphate (cAMP)/cyclic guanosine monophosphate (cGMP)/nitric oxide (NO) pathway. PDE5 inhibitors through mitigation of neuroinflammation may decrease the risk of long-term AIS-induced complications. PDE5 inhibitors may affect the hemodynamic properties and coagulation pathway which are associated with thrombotic complications in AIS. PDE5 inhibitors reduce activation of the pro-coagulant pathway and improve the microcirculatory level in patients with hemodynamic disturbances in AIS. PDE5 inhibitors mainly tadalafil and sildenafil improve clinical outcomes in AIS patients through the regulation of cerebral perfusion and cerebral blood flow (CBF). PDE5 inhibitors reduced thrombomodulin, P-selectin, and tissue plasminogen activator. Herein, PDE5 inhibitors may reduce activation of the pro-coagulant pathway and improve the microcirculatory level in patients with hemodynamic disturbances in AIS. In conclusion, PDE5 inhibitors may have potential roles in the management of AIS through modulation of CBF, cAMP/cGMP/NO pathway, neuroinflammation, and inflammatory signaling pathways. Preclinical and clinical studies are recommended in this regard.

Protective effects of Tinospora cordifolia miers extract against hepatic and neurobehavioral deficits in thioacetamide-induced hepatic encephalopathy in rats via modulating hyperammonemia and glial cell activation

ETHNOPHARMACOLOGICAL RELEVANCE

Tinospora cordifolia (TC) a potential medicinal herb, has been ethnobotanically used as an eco-friendly supplement to manage various diseases, including cerebral fever. Earlier studies have shown that TC exhibits diverse beneficial effects, including hepatoprotective and neuroprotective effects. However, the effects of TC remain unexplored in animal models of encephalopathy including hepatic encephalopathy (HE).

AIM OF THE STUDY

To evaluate the effects of TC stem extract against thioacetamide (TAA)-induced behavioural and molecular alterations in HE rats.

METHODS AND MATERIALS

The extract was preliminarily screened through phytochemical and HR-LC/MS analysis. Animals were pre-treated with TC extract at doses 30 and 100 mg/kg, orally. Following 7 days of TC pre-treatment, HE was induced by administering TAA (300 mg/kg, i. p. thrice). Behavioural assessments were performed after 56 h of TAA first dose. The animals were then sacrificed to assess biochemical parameters in serum, liver and brain. Liver tissue was used for immunoblotting and histological studies to evaluate inflammatory and fibrotic signalling. Moreover, brain tissue was used to evaluate brain edema, activation of glial cells (GFAP, IBA-1) and NF-κB/NLRP3 downstream signalling via immunoblotting and immunohistochemical analysis in cortex and hippocampus.

RESULTS

The pre-treatment with TC extract effective mitigated TAA-induced behavioural alterations, lowered serum LFT (AST, ALT, ALP, bilirubin) and oxidative stress markers in liver and brain. TC treatment significantly modulated hyperammonemia, cerebral edema and preserved the integrity of BBB proteins in HE animals. TC treatment attenuated TAA-induced histological changes, tissue inflammation (pNF-κB (p65), TNF-α, NLRP3) and fibrosis (collagen, α-SMA) in liver. In addition, immunoblotting analysis revealed TC pre-treatment inhibited fibrotic proteins such as vimentin, TGF-β1 and pSmad2/3 in the liver. Our study further showed that TC treatment downregulated the expression of MAPK/NF-κB inflammatory signalling, as well as GFAP and IBA-1 (glial cell markers) in cortex and hippocampus of TAA-intoxicated rats. Additionally, TC-treated animals exhibited reduced expression of caspase3/9 and BAX induced by TAA.

CONCLUSION

This study revealed promising insights on the protective effects of TC against HE. The findings clearly demonstrated that the significant inhibition of MAPK/NF-κB signalling and glial cell activation could be responsible for the observed beneficial effects of TC in TAA-induced HE rats.

Avanafil mediated dual inhibition of IKKβ and TNFR1 in an experimental paradigm of Alzheimer's disease: in silico and in vivo approach

In Alzheimer's disease pathology, inhibitors of nuclear factor kappa-β kinase subunit β (IKKB) and Tumor necrosis factor receptor 1 (TNFR1) signaling are linked to neuroinflammation-mediated cognitive decline. We explored the role of a phosphodiesterase 5 inhibitor (PDE5I) with dual antagonistic action on IKKB and TNFR1 to inhibit nuclear factor kappa B (NF-kB) and curb neuroinflammation. In the in silico approach, the FDA-approved Zinc 15 library was docked with IKKB and TNFR1. The top compound with dual antagonistic action on IKKB and TNFR1 was selected based on bonding and non-bonding interactions. Further, induced fit docking (IFD), molecular mechanics-generalized Born and surface area (MMGBSA), and molecular dynamic studies were carried out and evaluated. Lipopolysaccharide (LPS) administration caused a neuroinflammation-mediated cognitive decline in mice. Two doses of avanafil were administered for 28 days while LPS was administered for 10 days. Morris water maze (MWM) along with the passive avoidance test (PAT) were carried out. Concurrently brain levels of inflammatory markers, oxidative parameters, amyloid beta (Aβ), IKKB and NF-kB levels were estimated. Avanafil produced good IKKB and TNFR1 binding ability. It interacted with crucial inhibitory amino acids of IKKB and TNFR1. MD analysis predicted good stability of avanafil with TNFR1 and IKKB. Avanafil 6 mg/kg could significantly improve performance in MWM, PAT and oxidative parameters and reduce Aβ levels and inflammatory markers. As compared to avanafil 3 mg/kg, 6 mg/kg dose was found to exert better efficacy against elevated Aβ , neuroinflammatory cytokines and oxidative markers while improving behavioural parameters.Communicated by Ramaswamy H. Sarma.

Fructooligosaccharide (FOS) and Galactooligosaccharide (GOS) Improve Neuroinflammation and Cognition By Up-regulating IRS/PI3K/AKT Signaling Pathway in Diet-induced Obese Mice

Increasing evidence has indicated that prebiotics as an alternative treatment for neuropsychiatric diseases. This study evaluated the prebiotics Fructooligosaccharides (FOS) and Galactooligosaccharides (GOS) on the modulation of neuroinflammation and cognition in an experimental model of mice high-fat diet fed. Initially, mice were distributed in the following groups: (A) control standard diet (n = 15) and (B) HFD for 18 weeks (n = 30). In the 13th week, the mice were later divided into the following experimental groups: (A) Control (n = 15); (B) HFD (n = 14); and (C) HFD + Prebiotics (n = 14). From the 13th week, the HFD + Prebiotics group received a high-fat diet and a combination of FOS and GOS. In the 18th week, all animals performed the T-maze and Barnes Maze, and were later euthanized. Biochemical and molecular analyzes were performed to assess neuroinflammation, neurogenesis, synaptic plasticity, and intestinal inflammation. Mice fed HFD had higher blood glucose, triglyceridemia, cholesterolemia, and higher serum IL-1β associated with impaired learning and memory. These obese mice also showed activation of microglia and astrocytes and significant immunoreactivity of neuroinflammatory and apoptosis markers, such as TNF-α, COX-2, and Caspase-3, in addition to lower expression of neurogenesis and synaptic plasticity markers, such as NeuN, KI-67, CREB-p, and BDNF. FOS and GOS treatment significantly improved the biochemistry profile and decreased serum IL-1β levels. Treatment with FOS and GOS also reduced TNF-α, COX-2, Caspase-3, Iba-1, and GFAP-positive cells in the dentate gyrus, decreasing neuroinflammation and neuronal death caused by chronic HFD consumption. In addition, FOS and GOS promoted synaptic plasticity by increasing NeuN, p-CREB, BDNF, and KI-67, restoring spatial learning ability and memory. Moreover, FOS and GOS on HFD modulated the insulin pathway, which was proved by up-regulating IRS/PI3K/AKT signaling pathway, followed by a decreasing Aβ plate and Tau phosphorylation. Furthermore, the prebiotic intervention reshaped the HFD-induced imbalanced gut microbiota by modulating the composition of the bacterial community, markedly increasing Bacteroidetes. In addition, prebiotics decreased intestinal inflammation and leaky gut. In conclusion, FOS and GOS significantly modulated the gut microbiota and IRS/PI3K/AKT signaling pathway, decreased neuroinflammation, and promoted neuroplasticity improving spatial learning and memory. Schematic summarizing of the pathways by FOS and GOS improves memory and learning through the gut-brain axis. FOS and GOS improve the microbial profile, reducing intestinal inflammation and leaky gut in the distal colon. Specifically, the administration of FOS and GOS decreases the expression of TLR4, TNF-α, IL-1β, and MMP9 and increases the expression of occludin and IL-10. Prebiotics inhibit neuroinflammation, neuronal apoptosis, and reactive gliosis in the hippocampus but restore synaptic plasticity, neuronal proliferation, and neurogenesis.

Anti-inflammatory strategies for hepatic encephalopathy: preclinical studies

Hepatic encephalopathy (HE) is a potentially reversible neuropsychiatric syndrome. Often, HE causes cognitive and motor dysfunctions due to an acute or chronic insufficiency of the liver or a shunting between the hepatic portal vein and systemic vasculature. Liver damage induces peripheral changes, such as in the metabolism and peripheral inflammatory responses that trigger exacerbated neuroinflammation. In experimental models, anti-inflammatory strategies have demonstrated neuroprotective effects, leading to a reduction in HE-related cognitive and motor impairments. In this scenario, a growing body of evidence has shown that peripheral and central nervous system inflammation are promising preclinical targets. In this review, we performed an overview of FDA-approved drugs and natural compounds which are used in the treatment of other neurological and nonneurological diseases that have played a neuroprotective role in experimental HE, at least in part, through anti-inflammatory mechanisms. Despite the exciting results from animal models, the available data should be critically interpreted, highlighting the importance of translating the findings for clinical essays.

Hepatic encephalopathy: investigational drugs in preclinical and early phase development

INTRODUCTION

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome, in patients with liver disease, which affects life quality and span. Current treatments are lactulose or rifaximin, acting on gut microbiota. Treatments aiming ammonia levels reduction have been tested with little success.

AREAS COVERED

Pre-clinical research shows that the process inducing HE involves sequentially: liver failure, altered microbiome, hyperammonemia, peripheral inflammation, changes in immunophenotype and extracellular vesicles and neuroinflammation, which alters neurotransmission impairing cognitive and motor function. HE may be reversed using drugs acting at any step: modulating microbiota with probiotics or fecal transplantation; reducing peripheral inflammation with anti-TNFα, autotaxin inhibitors or silymarin; reducing neuroinflammation with sulforaphane, p38 MAP kinase or phosphodiesteras 5 inhibitors, antagonists of sphingosine-1-phosphate receptor 2, enhancing meningeal lymphatic drainage or with extracellular vesicles from mesenchymal stem cells; reducing GABAergic neurotransmission with indomethacin or golexanolone.

EXPERT OPINION

A factor limiting the progress of HE treatment is the lack of translation of research advances into clinical trials. Only drugs acting on microbiota or ammonia reduction have been tested in patients. It is urgent to change the mentality on how to approach HE treatment to develop clinical trials to assess drugs acting on the immune system/peripheral inflammation, neuroinflammation or neurotransmission to improve HE.

Naringenin mitigates thioacetamide-induced hepatic encephalopathy in rats: targeting the JNK/Bax/caspase-8 apoptotic pathway

Hepatic encephalopathy (HE) is a serious neurological disorder which is related to liver dysfunction. HE was induced by thioacetamide (TAA) injection (350 mg kg^-1, i.p.) for 3 consecutive days. This study was performed to investigate the prophylactic impact of naringenin against TAA-induced HE. Naringenin (100 mg kg^-1) was orally administered for 7 days starting 4 days prior to TAA injection. Naringenin effectively mitigated TAA-induced behavioural, structural and functional alterations. Naringenin ameliorated TAA-induced cognitive impairment as evidenced by the increase in the fall-off time in the rotarod test, decrease in the escape latency in the Morris water maze test and increase in the time spent in the center and in the number of rearing in the open field test. Additionally, naringenin significantly decreased the serum levels of transaminases, alkaline phosphatase, gamma-glutamyl transferase, bile and ammonia. Moreover, naringenin succeeded in reducing the levels of hepatic and cerebral c-Jun N-terminal kinases (JNK) as well as hepatic SORT1 levels. In addition, naringenin successfully elevated the levels of hepatic and cerebral pro-brain-derived neurotrophic factor (pro-BDNF) and BDNF in addition to the cerebral SORT1 level. Finally, naringenin markedly decreased the expression of Bax and caspase-8 as presented by the immunohistochemical results. Collectively, the ameliorative effect of naringenin on the development of HE might be attributed to the modulation of the JNK/Bax/caspase-8 apoptotic pathway.

Chitooligosaccharides Attenuated Hepatic Encephalopathy in Mice through Stabilizing Gut-Liver-Brain Disturbance

SCOPE

Hepatic encephalopathy (HE) refers to neurological dysfunction associated with hepatic inadequacy and gut dysbiosis. Chitooligosaccharides (COS) possesses prominent biological activities including incalculable hepatoprotective, neuroprotective and prebiotic effects. This study evaluates the protective effects of COS on HE from the influence of gut-liver-brain axis in mice.

METHODS AND RESULTS

Hepatic injured mice show minimal symptoms of HE, reflecting in cognitive impairment, and learning and memory retardation, while they are reversed by COS following orally administrated. Furthermore, COS ameliorates brain function through inhibiting microglial and astrocyte activation in cerebral cortex and hippocampus, promoting neuronal regeneration characterized by the increase of neuron-specific marker (neuronal nuclear antigen, NeuN). Concurrently, neuroinflammation and hepatitis are restrained by COS through descending toll-like receptors 4/Nuclear factor kappa B (TLR4/NF-κB) pathway. Additionally, the dysbiosis of the composition and structure of gut microbiota is displayed in mice with HE, while it is modified by COS through decreasing the relative abundances of Muribaculaceae, Lactobacillus, and Enterorhabdus. The enhancement of blood ammonia is crucially slipped to basal levels by COS.

CONCLUSION

The present study shows that COS could prevent the pathological process of HE through regulating the gut-liver-brain cross-talk, which provids new insight into fundamental roles of COS.

The role of brain inflammation and abnormal brain oxygen homeostasis in the development of hepatic encephalopathy

Hepatic encephalopathy (HE) is a frequent complication of chronic liver disease (CLD) and has a complex pathogenesis. Several preclinical and clinical studies have reported the presence of both peripheral and brain inflammation in CLD and their potential impact in the development of HE. Altered brain vascular density and tone, as well as compromised cerebral and systemic blood flow contributing to the development of brain hypoxia, have also been reported in animal models of HE, while a decrease in cerebral metabolic rate of oxygen and cerebral blood flow has consistently been observed in patients with HE. Whilst significant strides in our understanding have been made over the years, evaluating all these mechanistic elements in vivo and showing causal association with development of HE, have been limited through the practical constraints of experimentation. Nonetheless, improvements in non-invasive assessments of different neurophysiological parameters, coupled with techniques to assess changes in inflammatory and metabolic pathways, will help provide more granular insights on these mechanisms. In this special issue we discuss some of the emerging evidence supporting the hypothesis that brain inflammation and abnormal oxygen homeostasis occur interdependently during CLD and comprise important contributors to the development of HE. This review aims at furnishing evidence for further research in brain inflammation and oxygen homeostasis as additional therapeutic targets and potentially diagnostic markers for HE.

Carvedilol attenuates brain damage in mice with hepatic encephalopathy

Brain injury is the most common and serious consequence of hepatic encephalopathy (HE), and its pathophysiology is poorly understood. Excessive inflammatory, oxidative and apoptotic responses are the major mechanisms involved in the progression of brain injury induced by HE. Carvedilol is an adrenergic receptor antagonist with pronouncedantioxidant and anti-inflammatory activity. The present study aimed to investigatethe effects and underlying mechanisms of carvedilol on HE-induced brain damage in mice. Experimental model of HE was induced by the injection of thioacetamide (200 mg/kg) for two consecutive days and then mice were treated with carvedilol (10 or 20 mg/kg/day, orally) for 3 days in treatment groups. After the behavioral test, animals were sacrificed and the brain tissues were collected for biochemical, real time PCR and immunohistochemical analysis. The results showed that carvedilol improved locomotor impairment and reduced mortality rate in mice with HE. Carvedilol treatment decreased the brain levels of oxidative stress markers and induced Nrf2/HO-1 pathway. Carvedilol inhibited the activity of nuclear factor kappa B (NF-κB) and the expression of pro-inflammatory cytokines TNF-α, IL1β and IL-6 in the brain tissues. Treatment of mice with carvedilol caused a significant reduction in the brain levels of iNOS/NO, myeloperoxidase (MPO), cyclooxygenase (COX)-2 and chemokine MCP-1 as proinflammatory mediators in HE. Moreover, the ratio of Bcl2/Bax was increased and apoptotic cell death was decreased in the brain of mice treated with carvedilol. In conclusion, carvedilol exerted protective effect against HE-induced brain injury through increasing antioxidant defense mechanisms and inhibitionof inflammatory and apoptotic pathways.

Comprehensive Analysis of lncRNAs, miRNAs and mRNAs in Mouse Hippocampus With Hepatic Encephalopathy

Hepatic encephalopathy (HE) often presents with varying degrees of cognitive impairment. However, the molecular mechanism of its cognitive impairment has not been fully elucidated. Whole transcriptome analysis of hippocampus between normal and HE mice was performed by using RNA sequencing. 229 lncRNAs, 49 miRNAs and 363 mRNAs were differentially expressed in HE mice. The lncRNA-miRNA-mRNA interaction networks were established, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed. Dysregulated RNAs in interaction networks were mainly involved in synaptic plasticity and the regulation of learning and memory. In NH4Cl-treated hippocampal neurons, the dendritic spine density and maturity decreased significantly, the amplitude and frequency of mIPSC increased, while the amplitude and frequency of mEPSC decreased. These manifestations can be reversed by silencing SIX3OS1. Further research on these no-coding RNAs may lead to new therapies for the treatment and management of brain dysfunction caused by HE.

Ferrostatin-1 Ameliorates Liver Dysfunction via Reducing Iron in Thioacetamide-induced Acute Liver Injury in Mice

Background and Aims: Hepatic iron overload always leads to oxidative stress, which has been found to be involved in the progression of liver disease. However, whether iron disorder is involved in acute liver disease and the further molecular mechanisms remain unclear.

Methods: A mice model of acute liver injury (ALI) was established via intraperitoneal injection of thioacetamide (TAA) (250 mg/kg/day) for 3 consecutive days. Ferrostatin-1 (Fer-1) was administered intraperitoneally (2.5 μM/kg/day) starting 3 days before TAA treatment. Deferoxamine (DFO) was intraperitoneally injected (200 mg/kg/day) with TAA treatment for 3 days. We further observed the effect of Fer-1 on TAA model with high-iron diet feeding. ALI was confirmed using histological examination and liver function activity. Moreover, expressions of iron metabolism and ferroptosis proteins were measured by Western blot analysis.

Results: The study revealed that the iron accumulation and ferroptosis contributed to TAA-induced ALI pathogenesis. TAA induced prominent inflammation and vacuolar degeneration in the liver as well as liver dysfunction. In addition, protein expression of the cystine/glutamate antiporter SLC7A11 (xCT) and glutathione peroxidase 4 (GPX4) was significantly decreased in the liver, while transferrin receptor 1 (TfR1), ferroportin (Fpn) and light chain of ferritin (Ft-L) expression levels were increased after TAA exposure. As the same efficiency as DFO, pre-administration of Fer-1 significantly decreased TAA-induced alterations in the plasma ALT, AST and LDH levels compared with the TAA group. Moreover, both Fer-1 and DFO suppressed TfR1, Fpn and Ft-L protein expression and decreased iron accumulation, but did not affect xCT or GPX4 expression in the liver. Both Fer-1and DFO prevented hepatic ferroptosis by reducing the iron content in the liver. Furthermore, Fer-1 also reduced iron and reversed liver dysfunction under iron overload conditions.

Conclusion: These findings indicate a role of TAA-induced iron accumulation and ferroptosis in the pathogenesis of ALI model. The effect of Fer-1 was consistent with that of DFO, which prevented hepatic ferroptosis by reducing the iron content in the liver. Thus, Fer-1 might be a useful reagent to reverse liver dysfunction and decreasing the iron content of the liver may be a potential therapeutic strategy for ALI.

Tadalafil Treatment of Mice with Fetal Growth Restriction and Preeclampsia Improves Placental mTOR Signaling

Fetal growth restriction (FGR) is a major cause of poor perinatal outcomes. Although several studies have been conducted to improve the prognosis of FGR in infants, no effective intrauterine treatment method has been established. This study aimed to use tadalafil, a phosphodiesterase 5 inhibitor (PDE5) inhibitor, as a novel intrauterine treatment and conducted several basic and clinical studies. The study investigated the effects of tadalafil on placental mTOR signaling. Tadalafil was administered to mice with L-NG-nitroarginine methyl ester (L-NAME)-induced FGR and associated preeclampsia (PE). Placental phosphorylated mTOR (p-mTOR) signaling was assessed by fluorescent immunohistochemical staining and Western blotting. The expression of p-mTOR was significantly decreased in mice with FGR on 13 days post coitum (d.p.c.) but recovered to the same level as that of the control on 17 d.p.c. following tadalafil treatment. The results were similar for 4E-binding protein 1 (4E-BP1) and S6 ribosomal (S6R) protein, which act downstream in the mTOR signaling pathway. We demonstrate that the tadalafil treatment of FGR in mice improved placental mTOR signaling to facilitate fetal growth. Our study provides the key mechanistic detail about the mode of action of tadalafil and thus would be helpful for future clinical studies on FGR.

Activation of PKG-CREB-KLF15 by melatonin attenuates Angiotensin II-induced vulnerability to atrial fibrillation via enhancing branched-chain amino acids catabolism

Mitochondrial reactive oxygen species (ROS) damage and atrial remodeling serve as the crucial substrates for the genesis of atrial fibrillation (AF). Branched-chain amino acids (BCAAs) catabolic defect plays critical roles in multiple cardiovascular diseases. However, the alteration of atrial BCAA catabolism and its role in AF remain largely unknown. This study aimed to explore the role of BCAA catabolism in the pathogenesis of AF and to further evaluate the therapeutic effect of melatonin with a focus on protein kinase G (PKG)-cAMP response element binding protein (CREB)-Krüppel-like factor 15 (KLF15) signaling. We found that angiotensin II-treated atria exhibited significantly elevated BCAA level, reduced BCAA catabolic enzyme activity, increased AF vulnerability, aggravated atrial electrical and structural remodeling, and enhanced mitochondrial ROS damage. These deleterious effects were attenuated by melatonin co-administration while exacerbated by BCAA oral supplementation. Melatonin treatment ameliorated BCAA-induced atrial damage and reversed BCAA-induced down-regulation of atrial PKGIα expression, CREB phosphorylation as well as KLF15 expression. However, inhibition of PKG partly abolished melatonin-induced beneficial actions. In summary, these data demonstrated that atrial BCAA catabolic defect contributed to the pathogenesis of AF by aggravating tissue fibrosis and mitochondrial ROS damage. Melatonin treatment ameliorated Ang II-induced atrial structural as well as electrical remodeling by activating PKG-CREB-KLF15. The present study reveals additional mechanisms contributing to AF genesis and highlights the opportunity of a novel therapy for AF by targeting BCAA catabolism. Melatonin may serve as a potential therapeutic agent for AF intervention.

Tadalafil and bergapten mitigate streptozotocin-induced sporadic Alzheimer's disease in mice via modulating neuroinflammation, PI3K/Akt, Wnt/β-catenin, AMPK/mTOR signaling pathways

Sporadic Alzheimer's disease (SAD) is a slowly progressive neurodegenerative disorder. This study aimed to investigate neuroprotective potential of tadalafil (TAD) and bergapten (BG) in SAD-induced cognitive impairment in mice. SAD was induced by single injection of streptozotocin (STZ; 3 mg/kg, ICV). STZ resulted in AD-like pathologies including Aβ deposition, tau aggregation, impaired insulin and Wnt/β-catenin signaling, as well as autophagic dysfunction and neuroinflammation. Administration of TAD or BG at doses of 20 and 25 mg/kg, respectively, for 21 consecutive days attenuated STZ-induced hippocampal insult, preserved neuronal integrity, and improved cognitive function in the Morris water maze and object recognition tests paralleled by reduction in Aβ expression by 79 and 89% and tau hyperphosphorylation by 60 and 61%, respectively. TAD and BG also enhanced protein expression of pAkt, pGSK-3β, beclin-1 and methylated protein phosphatase 2A (PP2A) and gene expression of cyclin D1, while raised BDNF immunoreactivity. Furthermore, TAD and BG boosted hippocampal levels of cGMP, PKG, Wnt3a, and AMPK and reduced expression of β-catenin and mTOR by 74% and 51%, respectively. TAD and BG also halted neuroinflammation by reducing IL-23 and IL-27 levels, as well as protein expression of NF-κB by 62% & 61%, respectively. In conclusion, this study offers novel insights on the neuroprotective effects of TAD or BG in the management of SAD as evidenced by improved cognitive function and histological architecture. This could be attributed to modulation of the crosstalk among PI3K/Akt/GSK-3β, PP2A, mTOR/autophagy, cGMP/PKG, and Wnt/β-catenin signaling cascades and mitigation of neuroinflammation.

Ashwagandha (Withania somnifera) root extract attenuates hepatic and cognitive deficits in thioacetamide-induced rat model of hepatic encephalopathy via induction of Nrf2/HO-1 and mitigation of NF-κB/MAPK signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Ashwagandha (ASH) is one of the medicinal plants used in traditional Indian, Ayurvedic, and Unani medicines for their broad range of pharmacological activities including, tonic, aphrodisiac, energy stimulant, and counteracting chronic fatigue. Besides, it is used in the treatment of nervous exhaustion, memory-related conditions, insomnia, as well as improving learning ability and memory capacity. ASH is preclinically proven to be efficient in hepatoprotection and improving cognitive impairment, however, its beneficial effects against hepatic encephalopathy (HE) is still unclear. Therefore, this study aimed at investigating the protective effects of ASH root extract against thioacetamide (TAA)-induced HE and delineate the underlying behavioral and pharmacological mechanisms.

MATERIALS AND METHODS

ASH metabolites were identified using UPLC-HRMS. Rats were pretreated with ASH (200 and 400 mg/kg) for 29 days and administrated TAA (i.p, 350 mg/kg) in a single dose. Then, behavioral (open field test, Y-maze, modified elevated plus maze and novel object recognition test), and biochemical (ammonia and hepatic toxicity indices) assessments, as well as oxidative stress markers (MDA and GSH) were evaluated. The hepatic and brain levels of glutamine synthetase (GS), nuclear factor erythroid 2-related factor 2 (Nrf2), heme-oxygenase (HO)-1, inducible nitric oxide synthase (iNOS) were detected by enzyme-linked immunosorbent assay (ELISA). The mRNA expressions of p38/ERK½ were determined using real-time polymerase chain reaction (PCR). Moreover, histopathological investigations and immunohistochemical (NF-κB and TNF-α immunohistochemical expressions) examinations were performed.

RESULTS

Metabolite profiling of ASH revealed more than 45 identified metabolites including phenolic acids, flavonoids and steroidal lactone triterpenoids. Compared to the TAA-intoxicated group, ASH improved the locomotor and cognitive deficits, serum hepatotoxicity indices and ammonia levels, as well as brain and hepatic histopathological alterations. ASH reduced hepatic and brain levels of MDA, GS, and iNOS, and increased their GSH, Nrf2, and HO-1 levels. Also, ASH downregulated p38 and ERK½ mRNA expressions, and NF-κB and TNF-α immunohistochemical expressions in brain and hepatic tissues.

CONCLUSIONS

Our results provided insights into the promising hepato- and neuroprotective effects of ASH, with superiority to 400 mg/kg ASH, to ameliorate HE with its sequential hyperammonemia and liver/brain injuries. This could be attributed to the recorded increase in the spontaneous alternation % and recognition index, antioxidant and anti-inflammatory activities, as well as upregulation of Nrf2 and downregualtion of MAPK signaling pathways.

2021 ISHEN guidelines on animal models of hepatic encephalopathy

This working group of the International Society of Hepatic Encephalopathy and Nitrogen Metabolism (ISHEN) was commissioned to summarize and update current efforts in the development and characterization of animal models of hepatic encephalopathy (HE). As defined in humans, HE in animal models is based on the underlying degree and severity of liver pathology. Although hyperammonemia remains the key focus in the pathogenesis of HE, other factors associated with HE have been identified, together with recommended animal models, to help explore the pathogenesis and pathophysiological mechanisms of HE. While numerous methods to induce liver failure and disease exist, less have been characterized with neurological and neurobehavioural impairments. Moreover, there still remains a paucity of adequate animal models of Type C HE induced by alcohol, viruses and non-alcoholic fatty liver disease; the most common etiologies of chronic liver disease.

Thymoquinone improves cognitive and hippocampal long-term potentiation deficits due to hepatic encephalopathy in rats

OBJECTIVES

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome that causes brain disturbances. Thymoquinone (TQ) has a wide spectrum of activities such as antioxidant, anti-inflammatory, and anticancer. This study aimed to evaluate the effects of TQ on spatial memory and hippocampal long-term potentiation (LTP) in rats with thioacetamide (TAA)-induced liver injury and hepatic encephalopathy.

MATERIALS AND METHODS

Adult male Wistar rats were divided into six groups randomly: 1) Control; 2) HE, received TAA (200 mg/kg); 3-5) Treated groups (HE+TQ5, HE+TQ10, and HE+TQ20). TQ (5, 10, and 20 mg/kg) was injected intraperitoneally (IP) for 12 consecutive days from day 18 to 29. Subsequently, spatial memory performance was evaluated by the Morris water maze paradigm and hippocampal LTP was recorded from the dentate gyrus (DG) region. Activity levels of Malondialdehyde (MDA) and superoxide dismutase (SOD) were measured in the hippocampal tissue.

RESULTS

Data showed that the hippocampal content of MDA was increased while SOD activities were decreased in TAA-induced HE. TQ treatment significantly improved spatial memory and LTP. Moreover, TQ restored the levels of MDA and SOD activities in the hippocampal tissue in HE rats.

CONCLUSION

Our data confirm that TQ could attenuate cognitive impairment and improve LTP deficit by modulating the oxidative stress parameters in this model of HE, which leads to impairment of spatial cognition and LTP deficit. Thus, these results suggest that TQ may be a promising agent with positive therapeutic effects against liver failure and HE defects.

Follicle-stimulating hormone worsens osteoarthritis by causing inflammation and chondrocyte dedifferentiation

Previous studies have found follicle‐stimulating hormone (FSH) receptors on chondrocytes (cartilage cells), but the mechanism of FSH action on chondrocytes is not clear. The purpose of this experiment is to study whether FSH affects chondrocytes and how it causes changes in these cells. Our results show that osteoarthritis became worse after FSH injection in the knee joint of mice. After the stimulation of chondrocytes by FSH, a total of 664 up‐regulated genes, such as Col12a1 and Col1a1, and 644 down‐regulated genes, such as MGP, were screened by transcriptomics. A subset of extracellular matrix (ECM)‐related genes and pathways underwent Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, and the downregulation of MGP, the upregulation of EGR1 and Col1a1, and the increase of IL‐6 were verified. It was also observed that FSH can inhibit the cAMP/PKA and MKK4/JNK signaling pathway. In conclusion, we demonstrated that FSH can increase cartilage inflammatory response and promote chondrocyte dedifferentiation by inhibiting the cAMP/PKA and MKK4/JNK signaling pathways.

Roflumilast and tadalafil improve learning and memory deficits in intracerebroventricular Aβ1-42 rat model of Alzheimer's disease through modulations of hippocampal cAMP/cGMP/BDNF signaling pathway

BACKGROUND

Alzheimer's disease (AD) is the most prevalent age-dependent neurodegenerative disease characterized by progressive impairment of memory and cognitive functions. Cyclic nucleotides like cAMP and cGMP are well-known to play an important role in learning and memory functions. Enhancement of cAMP and cGMP levels in the hippocampus by phosphodiesterase (PDE) inhibitors might be a novel therapeutic approach for AD. Thus, the present study was planned to explore the therapeutic potential of roflumilast (RFM) and tadalafil (TDF) phosphodiesterase inhibitors in intracerebroventricular (ICV) Aβ1-42 induced AD in rats.

METHODS

ICV Aβ1-42 was administered in rats followed by treatment with RFM (0.05 mg/kg) and TDF (0.51 mg/kg) for 15 days. Novel object recognition (NOR), and Morris water maze (MWM) test were performed during the drug treatment schedule. On the day, 22 rats were sacrificed, and hippocampus was separated for biochemical, neuroinflammation, and histopathological analysis.

RESULTS

Aβ1-42 infused rats were induce behavioral impairment and increased AChE, BACE-1, Aβ1-42, GSK-3β, phosphorylated tau (p-Tau), pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) levels, oxidative stress (increased MDA, Nitrite and decreased GSH), histopathological changes, and reduced cAMP, cGMP, and BDNF levels. RFM and TDF significantly attenuated Aβ1-42 induced memory deficits and neuropathological alterations in the hippocampus.

CONCLUSION

The outcomes of the current study indicate that RFM and TDF lead to memory enhancement through upregulation of cAMP/cGMP/BDNF pathway, thus they may have a therapeutic potential in cognitive deficits associated with AD.

Sildenafil beyond erectile dysfunction and pulmonary arterial hypertension: Thinking about new indications

Sildenafil, approved two decades ago, is the inhibitor of phosphodiesterase 5 (PDE5). First of all, it was designated for angina pectoris, but soon it showed a wonderful efficacy in erectile dysfunction (ED) and then pulmonary arterial hypertension (PAH). Due to the distribution of phosphodiesterase (PDE) in almost all organs, maybe it effects other diseases. Hence, a great number of investigations began to understand the role of PDEi in different organs. Preliminary research on sildenafil in cell culture and animal models has yielded promising results. Soon, a greater number of animal researches and clinical trials joined them. The results disclosed sildenafil can have beneficial effects in each organ such as heart, liver, kidney, brain, and intestines. Furthermore, it has significantly improved the prognosis of organ ischemia in various animal models. Clinical trials in several diseases, such as recurrent spontaneous miscarriage, fatty liver disease, bronchopulmonary dysplasia (BPD), heart failure, and premature ejaculation (PE) brought promising results. Although some clinical trials are available on the effects of sildenafil on various diseases, further studies on humans are needed to consolidate the ultimate effects of sildenafil. The aim of this review was to describe the effects of sildenafil on each organ and explain its mechanisms of action. Further, other PDE inhibitors such as tadalafil and vardenafil have been briefly discussed in parts of this review.

Tadalafil Reversed H-89 - and Scopolamine - Induced Spatial Learning Impairments in Male Rats

Accumulated evidence shows that the cAMP and cGMP signaling pathway plays an important role in memory function and neuronal plasticity. Phosphodiesterase 5 (PDE5) is a hopeful therapeutic target in AD (Alzheimer disease), and PDE5 inhibition may be a good therapeutic strategy for the treatment of AD. In the present study, the four-day bilateral intra-hippocampal infusion of H-89 as a protein kinase AII inhibitor (10 µM/side) and intra-peritoneal injections of tadalafil (20 mg/kg) and scopolamine (0.5 mg/kg) alone and also on combination on spatial learning in Morris water maze (MWM) were investigated. DMSO and saline were used as controls for H-89 and other mentioned drugs, respectively. Rats were trained for 4 days; each day included one block of four trials. Post- training probe trial tests were performed on day 5. Administration of H-89 and scopolamine led to a significant impairment in spatial learning compared to their related controls. But, combination of tadalafil/H-89 or tadalafil/scopolamine reversed H-89 or scopolamine- induced spatial learning deficits in MWM. Taken together, these results showed the probable regulatory effects of cGMP on cholinergic and cAMP/PKA signaling pathways in co-administrations of these mentioned drugs on spatial learning in MWM.

cGMP signaling pathway in hepatic encephalopathy neuroinflammation and cognition

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome that results from liver failure and is characterized by a wide range of symptoms such as alteration in the sleep-waking cycle, neuromuscular coordination, mood, and cognition. The deregulation of nitric oxide (NO)/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) signaling pathway is thought to play an important role in the etiology and progression of neurodegenerative diseases, and several studies pointed that the cGMP signaling is impaired in patients with HE and experimental models of chronic hyperammonemia. This review aimed to briefly present the current knowledge of the cGMP signaling pathways in neuroinflammation, neurogenesis, and memory in hepatic encephalopathy and its potential therapeutic role.

Tadalafil alleviates preeclampsia and fetal growth restriction in RUPP model of preeclampsia in mice

BACKGROUND

- Tadalafil, a long-acting phosphodiesterase 5 (PDE5) inhibitor, alleviates preeclampsia (PE), and decreases the fetal and infant deaths associated with fetal growth restriction (FGR) in phase II clinical trial. Recently, we demonstrated that tadalafil alleviates FGR and hypertension in the dams with PE induced by l-NAME.

OBJECTIVE

-The aim of present study was to clarify the effect of tadalafil in another mouse model of PE, murine reduced uterine perfusion pressure (RUPP) model we have recently developed.

METHODS

-At 14.5 dpc we performed RUPP operation in mice to induce PE, administered the animals with tadalafil or vehicle in the drinking water daily from 15.5 dpc, and sacrificed them at 18.5 dpc for analyses.

RESULTS

-Tadalafil improved maternal hypertension and glomerular endotheliosis in RUPP mice. Moreover, tadalafil prolonged pregnancy period, and improved survival and growth of the embryos. RUPP increased content of sFlt-1 protein in the placenta, and tadalafil corrected it back to control levels.

CONCLUSION

- Tadalafil alleviates PE-like phenotype and FGR in RUPP murine model. RUPP model could help understand the mechanism of how tadalafil works on PE and FGR.