Low grade cirrhosis induces cognitive impairment and motor dysfunction in rats: Could be a model for minimal hepatic encephalopathy

Iron overload regulates cognitive function in rats with minimal hepatic encephalopathy by inducing an increase in frontal butyrylcholinesterase activity

Background and aims

This study aimed to investigate the effect of iron overload on acetylcholinesterase activity in the frontal lobe tissue of rats with minimal hepatic encephalopathy (MHE) and its relation to cognitive ability. By elucidating the potential mechanisms of cognitive impairment, this study may offer insights into novel therapeutic targets for MHE.

Materials and methods

Twelve Sprague-Dawley rats were purchased and randomly assigned to either the experimental or control group with six rats in each group. Following the induction of MHE, the Morris Water Maze (MWM) was utilized to assess spatial orientation and memory capacity. Subsequently, Magnetic Resonance Imaging (MRI) scans were performed to capture Quantitative Susceptibility Mapping (QSM) images of all rats' heads.

Results

Compared to the control group rats, the MHE model rats showed significantly reduced learning and memory capabilities as well as spatial orientation abilities (P < 0.05). Furthermore, the susceptibility values in the frontal lobe tissue of MHE model rats was significantly higher than that of the control group rats (P < 0.05), and the corresponding BuChE activity in the frontal lobe extract of model rats was significantly increased while BuChE activity in the peripheral blood serum was significantly decreased compared to the control group rats (P < 0.05). Meanwhile, our findings indicate a significant positive correlation between latency period and BuChE activity with susceptibility values in the MHE group.

Conclusion

The changes in BuChE activity in frontal lobe extract may be related to changes in spatial orientation and behavioral changes in MHE, and iron overload in the frontal lobe tissue may regulate changes in BuChE activity, BuChE levels appear to be iron-dependent.

Elucidating hippocampal proteome dynamics in moderate hepatic encephalopathy rats: insights from high-resolution mass spectrometry

Hepatic encephalopathy (HE) is a debilitating neurological disorder associated with liver failure and characterized by impaired brain function. Decade-long studies have led to significant advances in our understanding of HE; however, effective therapeutic management of HE is lacking, and HE continues to be a significant cause of morbidity and mortality in patients, underscoring the need for continued research into its pathophysiology and treatment. Accordingly, the present study provides a comprehensive overview aimed at elucidating the molecular underpinnings of HE and identifying potential therapeutic targets. A moderate-grade HE model was induced in rats using thioacetamide, which simulates the liver damage observed in patients, and its impact on cognitive function, neuronal arborization, and cellular morphology was also evaluated. We employed label-free LC-MS/MS proteomics to quantitatively profile hippocampal proteins to explore the molecular mechanism of HE pathogenesis; 2175 proteins were identified, 47 of which exhibited significant alterations in moderate-grade HE. The expression of several significantly upregulated proteins, such as FAK1, CD9 and Tspan2, was further validated at the transcript and protein levels, confirming the mass spectrometry results. These proteins have not been previously reported in HE. Utilizing Metascape, a tool for gene annotation and analysis, we further studied the biological pathways integral to brain function, including gliogenesis, the role of erythrocytes in maintaining blood-brain barrier integrity, the modulation of chemical synaptic transmission, astrocyte differentiation, the regulation of organ growth, the response to cAMP, myelination, and synaptic function, which were disrupted during HE. The STRING database further elucidated the protein‒protein interaction patterns among the differentially expressed proteins. This study provides novel insights into the molecular mechanisms driving HE and paves the way for identifying novel therapeutic targets for improved disease management.

Effect of Berberine against Cognitive Deficits in Rat Model of Thioacetamide-Induced Liver Cirrhosis and Hepatic Encephalopathy (Behavioral, Biochemical, Molecular and Histological Evaluations)

BACKGROUND

Liver cirrhosis (LC) is one of the chronic liver diseases with high disability and mortality accompanying hepatic encephalopathy (HE) followed by cognitive dysfunctions. In this work, the effect of berberine (Ber) on spatial cognition was studied in a rat model of LC induced by thioacetamide (TAA).

MATERIALS AND METHODS

Male Wistar rats (200-250 g) were divided into six groups: (1) control; (2) TAA, 200 mg/kg/day, i.p.; (3-5) TAA + Ber; received Ber (10, 30, and 60 mg/kg, i.p., daily after last TAA injection); (6) Dizocilpine (MK-801) + TAA, received MK-801 (2 mg/kg/day, i.p.) 30 m before TAA injection. The spatial memory, BBB permeability, brain edema, liver enzymes, urea, serum and brain total bilirubin, oxidative stress and cytokine markers in the hippocampus were measured. Furthermore, a histological examination of the hippocampus was carried out.

RESULTS

The BBB permeability, brain edema, liver enzymes, urea, total bilirubin levels in serum and hippocampal MDA and TNF-α increased significantly after TAA injection (p < 0.001); the spatial memory was impaired (p < 0.001), and hippocampal IL-10 decreased (p < 0.001). Ber reversed all the above parameters significantly (p < 0.05, p < 0.01 and p < 0.001). MK-801 prevented the development of LC via TAA (p < 0.001).

CONCLUSION

Results showed that Ber improves spatial learning and memory in TAA-induced LC by improving the BBB function, oxidative stress and neuroinflammation. Ber might be a promising therapeutic agent for cognitive improvement in LC.

Lactoferrin averts neurological and behavioral impairments of thioacetamide-induced hepatic encephalopathy in rats via modulating HGMB1/TLR-4/MyD88/Nrf2 pathway

Hepatic encephalopathy (HE) is a life-threatening disease caused by acute or chronic liver failure manifested by aberrant CNS changes. In the present study, we aimed to explore the neuroprotective effect of lactoferrin (LF) against thioacetamide (TAA)-induced HE in rats. Animals were divided into four groups, control, LF control, TAA-induced HE, and LF treatment, where LF was administered (300 mg/kg, p.o.) for 15 days in groups 2 and 4 meanwhile, TAA (200 mg/kg, i.p.) was given as two injections on days 13 and 15 for the 3rd and 4th groups. Pretreatment with LF significantly improved liver function observed as a marked decline in serum AST, ALT, and ammonia, together with lowering brain ammonia and enhancing motor coordination as well as cognitive performance. Restoration of brain oxidative status was also noted in the LF-treated group, where lipid peroxidation was hampered, and antioxidant parameters, Nrf2, HO-1, and GSH, were increased. Additionally, LF downregulated HMGB1, TLR-4, MyD88, and NF-κB signaling pathways, together with reducing inflammatory cytokine, TNF-α, and enhancing brain BDNF levels. Moreover, the histopathology of brain and liver tissues revealed that LF alleviated TAA-induced liver and brain deficits. In conclusion, the promising results of LF in attenuating HMGB1/TLR-4/MyD88 signaling highlight its neuroprotective role against HE associated with acute liver injury via ameliorating neuroinflammation, oxidative stress, and stimulating neurogenesis.

Hippocampus mitochondrial MnSOD activation by a SIRT3 activator, honokiol, correlates with its deacetylation and upregulation of FoxO3a and PGC1α in a rat model of ammonia neurotoxicity

We have recently reported that honokiol (HKL), by activating mitochondrial SIRT3, normalizes reactive oxygen species level and mitochondrial integrity in hippocampus of the moderate grade hepatic encephalopathy (MoHE) rat model of ammonia neurotoxicity. To delineate the mechanism by which HKL does so, the present study describes activity versus level of the deacetylated mitochondrial Mn-superoxide dismutase (MnSOD) and expression of MnSOD versus levels of its main transcription regulators, FoxO3a and PGC1α, in the hippocampus of the MoHE rats. MoHE in rat was developed by administration of 100 mg/kg bw thioacetamide i.p. for 10 days. The study parameters were compared between the control, the MoHE rats and the MoHE rats treated with HKL (10 mg/Kg b.w.) for 7 days. As compared to control, the hippocampus mitochondria from MoHE rats showed a significantly declined activity of MnSOD vs enhanced lipid peroxidation coinciding with the increased level of its acetylated form. The HKL treatment could, however, normalize all these parameters in those MoHE rats. Also, a significantly reduced expression of MnSOD in the hippocampus of the MoHE rats coincided with a similar decline in transcript level of Foxo3a and Pgc1α. This was consistent with the reduced level of immuno-stained Foxo3a and Pgc1α proteins in hippocampus DG, CA1 and CA3 regions of those MoHE rats. However, all these factors were observed to be restored back to their normal levels due to the treatment with HKL. As HKL is a specific activator of mitochondrial SIRT3, these findings suggest involvement of Sirt3 activation led deacetylation of MnSOD and upregulation of its transcription activators, FoxO3a and PGC1α, in restoring mitochondrial MnSOD level in the hippocampus of the MoHE rat model of ammonia neurotoxicity.

Amelioration of Hepatic Encephalopathy Using Dunaliella salina Microalgae in Rats: Modulation of Hyperammonemia/TLR4

Hepatic encephalopathy (HE) is a neuropsychiatric disease that is developed as a complication of both acute and chronic liver failure affecting psychomotor dysfunction, memory, and concentration. This study is aimed at evaluating the therapeutic effects of Dunaliella salina (D. salina) microalgae in thioacetamide- (TAA-) induced HE in rats. HE was induced by TAA (200 mg/kg; i.p.) for three successive days. Forty male Wister albino rats were divided into 4 groups; the first group was served as a normal, and the second group was injected with TAA and served as TAA control. The third and fourth groups were administered D. salina (100 and 200 mg/kg; p.o.), respectively, after TAA injection for 7 days. The behavioral and biochemical markers as well as histological aspects of HE were estimated. This study revealed that TAA caused behavioral changes, oxidative stress, neuroinflammation, nuclear pyknosis, and neurons degeneration. D. salina improved liver function and decreased oxidative stress and inflammatory mediator as TLR4 protein expression. Also, D. salina elevated HSP-25 and IGF-1 as well as improved brain histopathological alterations. In conclusion, D. salina exerted a therapeutic potential against HE via its antioxidant, antiinflammatory and cytoprotective effects.

Sirtuin-3 activation by honokiol restores mitochondrial dysfunction in the hippocampus of the hepatic encephalopathy rat model of ammonia neurotoxicity

The neurotoxic level of ammonia in the brain during liver cirrhosis causes a nervous system disorder, hepatic encephalopathy (HE), by affecting mitochondrial functions. Sirtuin-3 (SIRT3) is emerging as a master regulator of mitochondrial integrity, which is currently being focused as a pathogenic hotspot for HE. This article describes SIRT3 level versus mitochondrial dysfunction markers in the hippocampus of the control, the moderate-grade hepatic encephalopathy (MoHE), developed in thioacetamide-induced (100 mg/kg bw ip for 10 days) liver cirrhotic rats, and the MoHE rats treated with an SIRT3 activator, honokiol (HKL; 10 mg/kg bw ip), for 7 days from 8th day of the thioacetamide schedule. As compared with the control group rats, hippocampus mitochondria of MoHE rats showed a significant decline in SIRT3 expression and its activity with concordant enhancement of ROS and declined membrane permeability transition and organelle viability scores. This was consistent with the declined mitochondrial thiol level and thiol-regenerating enzyme, isocitrate dehydrogenase 2. Also, significantly declined activities of electron transport chain complexes I, III, IV, and Q₁₀ , decreased NAD⁺ /NADH and ATP/AMP ratios, and enhanced number of the shrunken mitochondria were recorded in the hippocampus of those MoHE rats. However, all these mitochondrial aberrations were observed to regain their normal profiles/levels, concordant to the enhanced SIRT3 expression and its activity due to treatment with HKL. The findings suggest a role of SIRT3 in mitochondrial structure-function derangements associated with MoHE pathogenesis and SIRT3 activation by HKL as a relevant strategy to protect mitochondrial integrity during ammonia neurotoxicity.

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

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

The effects of concurrent treatment of silymarin and lactulose on memory changes in cirrhotic male rats

Introduction: Chronic liver disease frequently accompanied by hepatic encephalopathy (HE). Changes in the permeability of the blood-brain barrier in HE, make an easier entrance of ammonia among other substances to the brain, which leads to neurotransmitter disturbances. Lactulose (LAC), causes better defecation and makes ammonia outreach of blood. Silymarin (SM) is a known standard drug for liver illnesses. The purpose of this research was to determine the results of LAC and SM combined treatment, on the changes in memory of cirrhotic male rats. Methods: The cirrhotic model established by treatment with thioacetamide (TAA) for 18 weeks. Cirrhotic rats randomized to four groups (n = 7): TAA group (received drinking water), LAC group (2 g/kg/d LAC in drinking water), SM group (50 mg/kg/d SM by food), SM+ LAC group (similar combined doses of both compounds) for 8 weeks. The control group received drinking water. The behavior examined by wire hanging (WH), passive avoidance (PA), and open field (OF) tests.

Results: Our findings showed that treatment with SM+LAC effectively increased PA latency, compared with the control group. The results showed that the administration of LAC and SM+LAC affected the number of lines crossed, the total distance moved and velocity in the OF tests.

Conclusion: SM and LAC have anti-inflammatory effects that are memory changing. It may be due to their useful effects. These results indicated that SM+LAC restored memory disturbance and irritated mood in the cirrhotic rats. Comparable neuroprotection was never previously informed. Such outcomes are extremely promising and indicate the further study of SM+LAC.

Targeted upregulation of uncoupling protein 2 within the basal ganglia output structure ameliorates dyskinesia after severe liver failure

Impaired motor function, due to the dysfunction of the basal ganglia, is the most common syndrome of hepatic encephalopathy (HE), and its etiology remains poorly understood. Neural oxidative stress is shown to be the major cellular defects contributing to HE pathogenesis. Mitochondrial uncoupling protein 2 (UCP2) has been implicated in neuroprotection in several neurological disorders. We explored the neuroprotective role of UCP2 within the substantia nigra pars reticulate (SNr), the output structure of the basal ganglia, in HE. The toxin thioacetamide (TAA) induced HE mice showed hypolocomotion, which was associated with decreased ATP levels and loss of antioxidant substances SOD and GSH within the SNr. Stable overexpression of UCP2 via AAV-UCP2 under the control of the UCP2 promoter in bilateral SNr preserved local ATP level, increased antioxidant substances, and ameliorated locomotion defects after severe liver failure. Contrary to UCP2 overexpression, targeted knockdown of UCP2 within bilateral SNr via AAV-UCP2 shRNA exacerbated the impaired mitochondrial dysfunction and hypokinesia in HE mice. The modulatory effects of UCP2 was due to mediation of K⁺-Cl^- cotransporter-2 (KCC2) expression on GABAergic neurons of SNr. Taken together, our results demonstrate that UCP2 exerts a neural protective role at the subcortical level by increasing the resistance of neurons to oxidative stress, which may offer a novel therapeutic target for the treatment of motor dysfunction diseases.

Mitochondrial SIRT3 and neurodegenerative brain disorders

Sirtuins are highly conserved NAD⁺ dependent class III histone deacetylases and catalyze deacetylation and ADP ribosylation of a number of non-histone proteins. Since, they require NAD⁺ for their activity, the cellular level of Sirtuins represents redox status of the cells and thereby serves as bona fide metabolic stress sensors. Out of seven homologues of Sirtuins identified in mammals, SIRT3, 4 & 5 have been found to be localized and active in mitochondria. During recent past, clusters of protein substrates for SIRT3 have been identified in mitochondria and thereby advocating SIRT3 as the main mitochondrial Sirtuin which could be involved in protecting stress induced mitochondrial integrity and energy metabolism. As mitochondrial dysfunction underlies the pathogenesis of almost all neurodegenerative diseases, a role of SIRT3 becomes an arguable speculation in such brain disorders. Some recent findings demonstrate that SIRT3 over expression could prevent neuronal derangements in certain in vivo and in vitro models of aging and neurodegenerative brain disorders like; Alzheimer's disease, Huntington's disease, stroke etc. Similarly, loss of SIRT3 has been found to accelerate neurodegeneration in the brain challenged with excitotoxicity. Therefore, it is argued that SIRT3 could be a relevant target to understand pathogenesis of neurodegenerative brain disorders. This review is an attempt to summarize recent findings on (1) the implication of SIRT3 in neurodegenerative brain disorders and (2) whether SIRT3 modulation could ameliorate neuropathologies in relevant models.

Candesartan, rather than losartan, improves motor dysfunction in thioacetamide-induced chronic liver failure in rats

Minimal hepatic encephalopathy is more common than the acute syndrome. Losartan, the first angiotensin-II receptor blocker (ARB), and candesartan, another widely-used ARB, have protected against developing fibrogenesis, but there is no clear data about their curative antifibrotic effects. The current study was designed to examine their effects in an already-established model of hepatic fibrosis and also their effects on the associated motor dysfunction. Low-grade chronic liver failure (CLF) was induced in 3-month old Sprague-Dawley male rats using thioacetamide (TAA, 50 mg·kg-1·day-1) intraperitoneally for 2 weeks. The TAA-CLF rats were randomly divided into five groups (n=8) treated orally for 14 days (mg·kg-1·day-1) as follows: TAA (distilled water), losartan (5 and 10 mg/kg), and candesartan (0.1 and 0.3 mg/kg). Rats were tested for rotarod and open-field tests. Serum and hepatic biochemical markers, and hepatic histopathological changes were evaluated by H&E and Masson's staining. The TAA-CLF rats showed significant increases of hepatic malondialdehyde, hepatic expression of tumor necrosis factor-α (TNF-α), and serum ammonia, alanine aminotransferase, γ-glutamyl transferase, TNF-α, and malondialdehyde levels as well as significant decreases of hepatic and serum glutathione levels. All treatments significantly reversed these changes. The histopathological changes were moderate in losartan-5 and candesartan-0.1 groups and mild in losartan-10 and candesartan-0.3 groups. Only candesartan significantly improved TAA-induced motor dysfunction. In conclusion, therapeutic antifibrotic effects of losartan and candesartan in thioacetamide-induced hepatic fibrosis in rats are possibly through angiotensin-II receptor blocking, antioxidant, and anti-inflammatory activities. Improved motor dysfunction by candesartan could be attributed to better brain penetration and slower "off-rate" from angiotensin-II receptors. Clinical trials are recommended.

Bacopa monnieri Extract (CDRI-08) Modulates the NMDA Receptor Subunits and nNOS-Apoptosis Axis in Cerebellum of Hepatic Encephalopathy Rats

Hepatic encephalopathy (HE), characterized by impaired cerebellar functions during chronic liver failure (CLF), involves N-methyl-D-aspartate receptor (NMDAR) overactivation in the brain cells. Bacopa monnieri (BM) extract is a known neuroprotectant. The present paper evaluates whether BM extract is able to modulate the two NMDAR subunits (NR2A and NR2B) and its downstream mediators in cerebellum of rats with chronic liver failure (CLF), induced by administration of 50 mg/kg bw thioacetamide (TAA) i.p. for 14 days, and in the TAA group rats orally treated with 200 mg/kg bw BM extract from days 8 to 14. NR2A is known to impart neuroprotection and that of NR2B induces neuronal death during NMDAR activation. Neuronal nitric oxide synthase- (nNOS-) apoptosis pathway is known to mediate NMDAR led excitotoxicity. The level of NR2A was found to be significantly reduced with a concomitant increase of NR2B in cerebellum of the CLF rats. This was consistent with significantly enhanced nNOS expression, nitric oxide level, and reduced Bcl2/Bax ratio. Moreover, treatment with BM extract reversed the NR2A/NR2B ratio and also normalized the levels of nNOS-apoptotic factors in cerebellum of those rats. The findings suggest modulation of NR2A and NR2B expression by BM extract to prevent neurochemical alterations associated with HE.

Pannexin1 as a novel cerebral target in pathogenesis of hepatic encephalopathy

Hepatic encephalopathy (HE) represents a nervous system disorder caused due to liver dysfunction. HE is broadly classified as acute/overt and moderate-minimal HE. Since HE syndrome severely affects quality of life of the patients and it may be life threatening, it is important to develop effective therapeutic strategy against HE. Mainly ammonia neurotoxicity is considered accountable for HE. Increased level of ammonia in the brain activates glutamate-NMDA (N-methyl-D-aspartate) receptor (NMDAR) pathway leading to Ca(2+) influx, energy deficit and oxidative stress in the post synaptic neurons. Moreover, NMDAR blockage has been found to be a poor therapeutic option, as this neurotransmitter receptor plays important role in maintaining normal neurophysiology of the brain. Thus, searching new molecular players in HE pathogenesis is of current concern. There is an evolving concept about roles of the trans-membrane channels in the pathogenesis of a number of neurological complications. Pannexin1 (Panx1) is one of them and has been described to be implicated in stroke, epilepsy and ischemia. Importantly, the pathogenesis of these complications relates to some extent with NMDAR over activation. Thus, it is speculated that HE pathogenesis might also involve Panx1. Indeed, some recent observations in the animal models of HE provide support to this argument. Since opening of Panx1 channel is mostly associated with the neuronal dysfunctions, down regulation of this channel could serve as a relevant therapeutic strategy without producing any serious side effects. In the review article an attempt has been made to summarize the current information on implication of Panx1 in the brain disorders and its prospects for being examined as pharmacological target in HE pathogenesis.