Altered expression of zonula occludens-2 precedes increased blood-brain barrier permeability in a murine model of fulminant hepatic failure

Hepatotoxicity evaluations of different surface charged carbon quantum dots in vivo and in vitro

Recently, carbon quantum dots (CQDs) have become popular because of their simple synthesis and potential applications. Although CQDs have high biocompatibility, their biotoxicity must be verified to reduce the possible risks associated with large-scale application. In this study, the hepatotoxicity of three CQD types, namely diammonium citrate (AC)-based (CQDs-AC), spermidine trihydrochloride (Spd)-based (CQDs-Spd), and AC- and Spd-based CQDs (CQDs-AC/Spd), were evaluated in vivo and in vitro. It was observed in vivo that CQDs-Spd and CQDs-AC/Spd, but not CQDs-AC, caused histopathological damage, including liver steatosis and mild mixed inflammatory cell infiltration; however, reduced liver function was only observed in CQD-Spd-treated mice. The in vitro results revealed that only CQDs-Spd significantly decreased the number of viable HepG2 cells (NADH depletion) and induced oxidative stress (heme oxygenase-1 activation) after 24 h of exposure, which promoted inflammatory factor secretion (NF-κB activation). Additionally, decreasing zonula occludens-2 and α1-antitrypsin protein expression in HepG2 cells suggested that CQD-Spd exposure increases the risk of liver diseases. Our results revealed that CQDs-Spd had greater hepatotoxic potential than CQDs-AC and CQDs-AC/Spd, which might be attributable to their high positive surface charge. Overall, the risk of CQD-induced hepatotoxic risk must be considered when applying positively charged CQDs.

The neurogliovascular unit in hepatic encephalopathy

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

Implementation and characterization of a physiologically relevant flow waveform in a 3D microfluidic model of the blood-brain barrier

Previous in vitro studies interrogating the endothelial response to physiologically relevant flow regimes require specialized pumps to deliver time-dependent waveforms that imitate in vivo blood flow. The aim of this study is to create a low-cost and broadly adaptable approach to mimic physiological flow, and then use this system to characterize the effect of flow separation on velocity and shear stress profiles in a three-dimensional (3D) topology. The flow apparatus incorporates a programmable linear actuator that superposes oscillations on a constant mean flow driven by a peristaltic pump to emulate flow in the carotid artery. The flow is perfused through a 3D in vitro model of the blood-brain barrier designed to induce separated flow. Experimental flow patterns measured by microparticle image velocimetry and modeled by computational fluid dynamics reveal periodic changes in the instantaneous shear stress along the channel wall. Moreover, the time-dependent flow causes periodic flow separation zones, resulting in variable reattachment points during the cycle. The effects of these complex flow regimes are assessed by evaluating the integrity of the in vitro blood-brain barrier model. Permeability assays and immunostaining for proteins associated with tight junctions reveal barrier breakdown in the region of disturbed flow. In conclusion, the flow system described here creates complex, physiologically relevant flow profiles that provide deeper insight into the fluid dynamics of separated flow and pave the way for future studies interrogating the cellular response to complex flow regimes.

Nanotechnology as a therapeutic strategy to prevent neuropsychomotor alterations associated with hypercholesterolemia

Hypercholesterolemia has been linked to neurodegenerative disease development. Previously others and we demonstrated that high levels of plasma cholesterol-induced memory impairments and depressive-like behavior in mice. More recently, some evidence reported that a hypercholesterolemic diet led to motor alterations in rodents. Peripheral inflammation, blood-brain barrier (BBB) dysfunction, and neuroinflammation seem to be the connective factors between hypercholesterolemia and brain disorders. Herein, we aimed to investigate whether treatment with gold nanoparticles (GNPs) can prevent the inflammation, BBB disruption, and behavioral changes related to neurodegenerative diseases and depression, induced by hypercholesterolemic diet intake in mice. Adult Swiss mice were fed a standard or a high cholesterol diet for eight weeks and concomitantly treated with either vehicle or GNPs by the oral route. At the end of treatments, mice were subjected to behavioral tests. After that, the blood, liver, and brain structures were collected for biochemical analysis. The high cholesterol diet-induced an increase in the plasma cholesterol levels and body weight of mice, which were not modified by GNPs treatment. Hypercholesterolemia was associated with enhanced liver tumor necrosis factor- α (TNF-α), BBB dysfunction in the hippocampus and olfactory bulb, memory impairment, cataleptic posture, and depressive-like behavior. Notably, GNPs administration attenuated liver inflammation, BBB dysfunction, and improved behavioral and memory deficits in hypercholesterolemic mice. Also, GNPs increased mitochondrial complex I activity in the prefrontal cortex of mice. It is worth highlight that GNPs' administration did not cause toxic effects in the liver and kidney of mice. Overall, our results indicated that GNPs treatment potentially mitigated peripheral, brain, and memory impairments related to hypercholesterolemia.

The Status of Bile Acids and Farnesoid X Receptor in Brain and Liver of Rats with Thioacetamide-Induced Acute Liver Failure

Acute liver failure (ALF) leads to neurological symptoms defined as hepatic encephalopathy (HE). Although accumulation of ammonia and neuroinflammation are generally accepted as main contributors to HE pathomechanism, a buildup of bile acids (BA) in the blood is a frequent component of liver injury in HE patients. Recent studies have identified the nuclear farnesoid X receptor (FXR) acting via small heterodimer partner (SHP) as a mediator of BA-induced effects in the brain of ALF animals. The present study investigated the status of the BA–FXR axis in the brain and the liver, including selective changes in pertinent genes in thioacetamide (TAA)-induced ALF in Sprague–Dawley rats. FXR was found in rat neurons, confirming earlier reports for mouse and human brain. BA accumulated in blood but not in the brain tissue. Expression of mRNAs coding for Fxr and Shp was reduced in the hippocampus and of Fxr mRNA also in the cerebellum. Changes in Fxr mRNA levels were not followed by changes in FXR protein. The results leave open the possibility that mobilization of the BA–FXR axis in the brain may not be necessarily pathognomonic to HE but may depend upon ALF-related confounding factors.

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

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

Direct Comparison of the Thioacetamide and Azoxymethane Models of Type A Hepatic Encephalopathy in Mice

Acute liver failure is a devastating consequence of hepatotoxic liver injury that can lead to the development of hepatic encephalopathy. There is no consensus on the best model to represent these syndromes in mice, and therefore the aim of this study was to classify hepatic and neurological consequences of azoxymethane- and thioacetamide-induced liver injury. Azoxymethane-treated mice were euthanized at time points representing absence of minor and significant stages of neurological decline. Thioacetamide-treated mice had tissue collected at up to 3 days following daily injections. Liver histology, serum chemistry, bile acids, and cytokine levels were measured. Reflexes, grip strength measurement, and ataxia were calculated for all groups. Brain ammonia, bile acid levels, cerebral edema, and neuroinflammation were measured. Finally, in vitro and in vivo assessments of blood-brain barrier function were performed. Serum transaminases and liver histology demonstrate that both models generated hepatotoxic liver injury. Serum proinflammatory cytokine levels were significantly elevated in both models. Azoxymethane-treated mice had progressive neurological deficits, while thioacetamide-treated mice had inconsistent neurological deficits. Bile acids and cerebral edema were increased to a higher degree in azoxymethane-treated mice, while cerebral ammonia and neuroinflammation were greater in thioacetamide-treated mice. Blood-brain barrier permeability exists in both models but was likely not due to direct toxicity of azoxymethane or thioacetamide on brain endothelial cells. In conclusion, both models generate acute liver injury and hepatic encephalopathy, but the requirement of a single injection and the more consistent neurological decline make azoxymethane treatment a better model for acute liver failure with hepatic encephalopathy.

Lipopolysaccharide-Induced Striatal Nitrosative Stress and Impaired Social Recognition Memory Are Not Magnified by Paraquat Coexposure

Systemic inflammation triggered by lipopolysaccharide (LPS) administration disrupts blood-brain barrier (BBB) homeostasis in animal models. This event leads to increased susceptibility of several encephalic structures to potential neurotoxicants present in the bloodstream. In this study, we investigated the effects of alternate intraperitoneal injections of LPS on BBB permeability, social recognition memory and biochemical parameters in the striatum 24 h and 60 days after treatments. In addition, we investigated whether the exposure to a moderate neurotoxic dose of the herbicide paraquat could potentiate LPS-induced neurotoxicity. LPS administration caused a transient disruption of BBB integrity, evidenced by increased levels of exogenously administered sodium fluorescein in the striatum. Also, LPS exposure caused delayed impairment in social recognition memory (evaluated at day 38 after treatments) and increase in the striatal levels of 3-nitrotyrosine. These events were observed in the absence of significant changes in motor coordination and in the levels of tyrosine hydroxylase (TH) in the striatum and substantia nigra. PQ exposure, which caused a long-lasting decrease of striatal mitochondrial complex I activity, did not modify LPS-induced behavioral and striatal biochemical changes. The results indicate that systemic administration of LPS causes delayed social recognition memory deficit and striatal nitrosative stress in adult mice and that the coexposure to a moderately toxic dose of PQ did not magnify these events. In addition, PQ-induced inhibition of striatal mitochondrial complex I was also not magnified by LPS exposure, indicating the absence of synergic neurotoxic effects of LPS and PQ in this experimental model.

Gene Expression Changes in Long-Term In Vitro Human Blood-Brain Barrier Models and Their Dependence on a Transwell Scaffold Material

Disruption of the blood-brain barrier (BBB) is the hallmark of many neurovascular disorders, making it a critically important focus for therapeutic options. However, testing the effects of either drugs or pathological agents is difficult due to the potentially damaging consequences of altering the normal brain microenvironment. Recently, in vitro coculture tissue models have been developed as an alternative to animal testing. Despite low cost, these platforms use synthetic scaffolds which prevent normal barrier architecture, cellular crosstalk, and tissue remodeling. We created a biodegradable electrospun gelatin mat "biopaper" (BP) as a scaffold material for an endothelial/astrocyte coculture model allowing cell-cell contact and crosstalk. To compare the BP and traditional models, we investigated the expression of 27 genes involved in BBB permeability, cellular function, and endothelial junctions at different time points. Gene expression levels demonstrated higher expression of transcripts involved in endothelial junction formation, including TJP2 and CDH5, in the BP model. The traditional model had higher expression of genes associated with extracellular matrix-associated proteins, including SPARC and COL4A1. Overall, the results demonstrate that the BP coculture model is more representative of a healthy BBB state, though both models have advantages that may be useful in disease modeling.

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.

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.

Annexin A1 restores Aβ1-42 -induced blood-brain barrier disruption through the inhibition of RhoA-ROCK signaling pathway

The blood–brain barrier (BBB) is composed of brain capillary endothelial cells and has an important role in maintaining homeostasis of the brain separating the blood from the parenchyma of the central nervous system (CNS). It is widely known that disruption of the BBB occurs in various neurodegenerative diseases, including Alzheimer's disease (AD). Annexin A1 (ANXA1), an anti‐inflammatory messenger, is expressed in brain endothelial cells and regulates the BBB integrity. However, its role and mechanism for protecting BBB in AD have not been identified. We found that β‐Amyloid 1‐42 (Aβ42)‐induced BBB disruption was rescued by human recombinant ANXA1 (hrANXA1) in the murine brain endothelial cell line bEnd.3. Also, ANXA1 was decreased in the bEnd.3 cells, the capillaries of 5XFAD mice, and the human serum of patients with AD. To find out the mechanism by which ANXA1 recovers the BBB integrity in AD, the RhoA‐ROCK signaling pathway was examined in both Aβ42‐treated bEnd.3 cells and the capillaries of 5XFAD mice as RhoA was activated in both cases. RhoA inhibitors alleviated Aβ42‐induced BBB disruption and constitutively overexpressed RhoA‐GTP (active form of RhoA) attenuated the protective effect of ANXA1. When pericytes were cocultured with bEnd.3 cells, Aβ42‐induced RhoA activation of bEnd.3 cells was inhibited by the secretion of ANXA1 from pericytes. Taken together, our results suggest that ANXA1 restores Aβ42‐induced BBB disruption through inhibition of RhoA‐ROCK signaling pathway and we propose ANXA1 as a therapeutic reagent, protecting against the breakdown of the BBB in AD.

Elevated adiponectin prevents HIV protease inhibitor toxicity and preserves cerebrovascular homeostasis in mice

HIV protease inhibitors are key components of HIV antiretroviral therapies, which are fundamental in the treatment of HIV infection. However, the protease inhibitors are well-known to induce metabolic dysfunction which can in turn escalate the complications of HIV, including HIV associated neurocognitive disorders. As experimental and epidemiological data support a therapeutic role for adiponectin in both metabolic and neurologic homeostasis, this study was designed to determine if increased adiponectin could prevent the detrimental effects of protease inhibitors in mice. Adult male wild type (WT) and adiponectin-overexpressing (ADTg) mice were thus subjected to a 4-week regimen of lopinavir/ritonavir, followed by comprehensive metabolic, neurobehavioral, and neurochemical analyses. Data show that lopinavir/ritonavir-induced lipodystrophy, hypoadiponectinemia, hyperglycemia, hyperinsulinemia, and hypertriglyceridemia were attenuated in ADTg mice. Furthermore, cognitive function and blood-brain barrier integrity were preserved, while loss of cerebrovascular markers and white matter injury were prevented in ADTg mice. Finally, lopinavir/ritonavir caused significant increases in expression of markers of brain inflammation and decreases in synaptic markers in WT, but not in ADTg mice. Collectively, these data reinforce the pathophysiologic link from metabolic dysfunction to loss of cerebrovascular and cognitive homeostasis; and suggest that preservation and/or replacement of adiponectin could prevent these key aspects of HIV protease inhibitor-induced toxicity in clinical settings.

Bile Acid Signaling Is Involved in the Neurological Decline in a Murine Model of Acute Liver Failure

Hepatic encephalopathy is a serious neurological complication of liver failure. Serum bile acids are elevated after liver damage and may disrupt the blood-brain barrier and enter the brain. Our aim was to assess the role of serum bile acids in the neurological complications after acute liver failure. C57Bl/6 or cytochrome p450 7A1 knockout (Cyp7A1(-/-)) mice were fed a control, cholestyramine-containing, or bile acid-containing diet before azoxymethane (AOM)-induced acute liver failure. In parallel, mice were given an intracerebroventricular infusion of farnesoid X receptor (FXR) Vivo-morpholino before AOM injection. Liver damage, neurological decline, and molecular analyses of bile acid signaling were performed. Total bile acid levels were increased in the cortex of AOM-treated mice. Reducing serum bile acids via cholestyramine feeding or using Cyp7A1(-/-) mice reduced bile acid levels and delayed AOM-induced neurological decline, whereas cholic acid or deoxycholic acid feeding worsened AOM-induced neurological decline. The expression of bile acid signaling machinery apical sodium-dependent bile acid transporter, FXR, and small heterodimer partner increased in the frontal cortex, and blocking FXR signaling delayed AOM-induced neurological decline. In conclusion, circulating bile acids may play a pathological role during hepatic encephalopathy, although precisely how they dysregulate normal brain function is unknown. Strategies to minimize serum bile acid concentrations may reduce the severity of neurological complications associated with liver failure.

TGFβ1 exacerbates blood-brain barrier permeability in a mouse model of hepatic encephalopathy via upregulation of MMP9 and downregulation of claudin-5

Recent studies have found that vasogenic brain edema is present during hepatic encephalopathy following acute liver failure and is dependent on increased matrix metalloproteinase 9 (MMP9) activity and downregulation of tight junction proteins. Furthermore, circulating transforming growth factor β1 (TGFβ1) is increased following liver damage and may promote endothelial cell permeability. This study aimed to assess whether increased circulating TGFβ1 drives changes in tight junction protein expression and MMP9 activity following acute liver failure. Blood-brain barrier permeability was assessed in azoxymethane (AOM)-treated mice at 6, 12, and 18 h post-injection via Evan's blue extravasation. Monolayers of immortalized mouse brain endothelial cells (bEnd.3) were treated with recombinant TGFβ1 (rTGFβ1) and permeability to fluorescein isothiocyanate-dextran (FITC-dextran), MMP9 and claudin-5 expression was assessed. Antagonism of TGFβ1 signaling was performed in vivo to determine its role in blood-brain barrier permeability. Blood-brain barrier permeability was increased in mice at 18 h following AOM injection. Treatment of bEnd.3 cells with rTGFβ1 led to a dose-dependent increase of MMP9 expression as well as a suppression of claudin-5 expression. These effects of rTGFβ1 on MMP9 and claudin-5 expression could be reversed following treatment with a SMAD3 inhibitor. AOM-treated mice injected with neutralizing antibodies against TGFβ demonstrated significantly reduced blood-brain barrier permeability. Blood-brain barrier permeability is induced in AOM mice via a mechanism involving the TGFβ1-driven SMAD3-dependent upregulation of MMP9 expression and decrease of claudin-5 expression. Therefore, treatment modalities aimed at reducing TGFβ1 levels or SMAD3 activity may be beneficial in promoting blood-brain barrier integrity following liver failure.

Matrix metalloproteinase-9 as a therapeutic target for the progression of fulminant liver failure with hepatic encephalopathy: A pilot study in mice

AIM

If progressive liver injury and subsequent hepatic encephalopathy can be prohibited in fulminant liver failure (FLF), it would be ideal for intensive care of FLF and provide an expanded opportunity for liver transplantation (LT). We hypothesized that matrix metalloproteinase (MMP)-9 plays an important role in FLF progression, and investigated MMP-9 behaviors in a murine FLF model, especially at the coma stage.

METHODS

The murine FLF model with azoxymethane recapitulates FLF in humans. The detailed coma status was evaluated, on the assumption that LT is indicated at early, but not late, stage 3. To investigate whether MMP-9 deletion or reduction has beneficial effects, an MMP-9 inhibitor (GM6001) and transfection of tissue inhibitor of metalloproteinases (TIMP)-1 cDNA were used. Mice were divided into five groups: control; FLF; FLF with GM6001 pretreatment; FLF with TIMP-1 plasmid transfection 24 h before disease onset; and FLF with TIMP-1 plasmid transfection 48 h before disease onset. Neurological findings, including survival, were followed. Samples were obtained at early and late stage 3. Biochemical examinations and histopathological assessments were performed. The expression and function of MMP-9 and TIMP-1 were evaluated by western blotting and zymography. A brain permeability study was also performed.

RESULTS

MMP-9 was strongly increased in FLF. The MMP-9 inhibitions worked well, and prolonged the survival, interval to stage 3 and duration of early stage 3. MMP-9 inhibition improved the liver and subsequent brain injuries at early stage 3, with no remarkable improvements at late stage 3.

CONCLUSION

MMP-9 has therapeutic potential for FLF progression.

Lipopolysaccharide precipitates hepatic encephalopathy and increases blood-brain barrier permeability in mice with acute liver failure

BACKGROUND & AIMS

Acute liver failure (ALF) is frequently complicated by infection leading to precipitation of central nervous system complications such as hepatic encephalopathy (HE) and increased mortality. There is evidence to suggest that when infection occurs in ALF patients, the resulting pro-inflammatory mechanisms may be amplified that could, in turn, have a major impact on blood-brain barrier (BBB) function. The aim of this study was to investigate the role of endotoxemia on the progression of encephalopathy in relation to BBB permeability during ALF.

METHODS

Adult male C57-BL6 mice with ALF resulting from azoxymethane-induced toxic liver injury were administered trace amounts of the endotoxin component lipopolysaccharide (LPS). Effects on the magnitude of the systemic inflammatory response, liver pathology and BBB integrity were measured as a function of progression of HE, defined as time to loss of corneal reflex (coma).

RESULTS

Lipopolysaccharide caused additional two- to seven-fold (P < 0.001) increases in circulating pro-inflammatory cytokines (TNF-α, IL-1β, IL-6), worsening liver pathology and associated increases of circulating transaminases as well as increased hyperammonaemia consistent with a further loss of viable hepatocytes. LPS treatment of ALF mice led to a rapid precipitation of hepatic coma and the BBB became permeable to the 25-kDa protein immunoglobulin G (IgG). This extravasation of IgG was accompanied by ignificant up-regulation of matrix metalloproteinase-9 (MMP-9), an endopeptidase known to modulate opening of the BBB in a wide range of neurological disorders.

CONCLUSIONS

These findings represent the first direct evidence of inflammation-related BBB permeability changes in ALF.

The liver-brain axis in liver failure: neuroinflammation and encephalopathy

Systemic inflammation is common in liver failure and its acquisition is a predictor of hepatic encephalopathy severity. New studies provide convincing evidence for a role of neuroinflammation (inflammation of the brain per se) in liver failure; this evidence includes activation of microglia, together with increased synthesis in situ of the proinflammatory cytokines TNF, IL-1β and IL-6. Liver-brain signalling mechanisms in liver failure include: direct effects of systemic proinflammatory molecules, recruitment of monocytes after microglial activation, brain accumulation of ammonia, lactate and manganese, and altered permeability of the blood-brain barrier. Ammonia and cytokines might act synergistically. Existing strategies to reduce ammonia levels (including lactulose, rifaximin and probiotics) have the potential to dampen systemic inflammation, as does albumin dialysis, mild hypothermia and N-acetylcysteine, the latter two agents acting at both peripheral and central sites. Minocycline, an agent with potent central anti-inflammatory properties, reduces neuroinflammation, brain oedema and encephalopathy in liver failure, as does the anti-TNF agent etanercept.

Brain edema in acute liver failure: role of neurosteroids

Brain edema is a major neurological complication of acute liver failure (ALF) and swelling of astrocytes (cytotoxic brain edema) is the most prominent neuropathological abnormality in this condition. Elevated brain ammonia level has been strongly implicated as an important factor in the mechanism of astrocyte swelling/brain edema in ALF. Recent studies, however, have suggested the possibility of a vasogenic component in the mechanism in ALF. We therefore examined the effect of ammonia on blood-brain barrier (BBB) integrity in an in vitro co-culture model of the BBB (consisting of primary cultures of rat brain endothelial cells and astrocytes). We found a minor degree of endothelial permeability to dextran fluorescein (16.2%) when the co-culture BBB model was exposed to a pathophysiological concentration of ammonia (5mM). By contrast, lipopolysaccharide (LPS), a molecule well-known to disrupt the BBB, resulted in an 87% increase in permeability. Since increased neurosteroid biosynthesis has been reported to occur in brain in ALF, and since neurosteroids are known to protect against BBB breakdown, we examined whether neurosteroids exerted any protective effect on the slight permeability of the BBB after exposure to ammonia. We found that a nanomolar concentration (10nM) of the neurosteroids allopregnanolone (THP) and tetrahydrodeoxycorticosterone (THDOC) significantly reduced the ammonia-induced increase in BBB permeability (69.13 and 58.64%, respectively). On the other hand, we found a marked disruption of the BBB when the co-culture model was exposed to the hepatotoxin azoxymethane (218.4%), but not with other liver toxins commonly used as models of ALF (thioacetamide and galactosamine, showed a 29.3 and 30.67% increase in permeability, respectively). Additionally, THP and THDOC reduced the effect of TAA and galactosamine on BBB permeability, while no BBB protective effect was observed following treatment with azoxymethane. These findings suggest that ammonia does not cause a significant BBB disruption, and that the BBB is intact in the TAA or galactosamine-induced animal models of ALF, likely due to the protective effect of neurosteroids that are synthesized in brain in the setting of ALF. However, caution should be exercised when using azoxymethane as an experimental model of ALF as it caused a severe breakdown of the BBB, and neurosteriods failed to protect against this breakdown.

Effects of short-term portacaval anastomosis on the peripheral and brain disposition of the blood-brain barrier permeability marker sodium fluorescein in rats

Contradictory results have been reported with regard to the effects of various models of hepatic encephalopathy on the blood-brain barrier (BBB) permeability, which may be due partly to the use of brain concentrations of BBB markers without attention to their peripheral pharmacokinetics. The purpose of the current study was to investigate the effects of short-term portacaval anastomosis (PCA), a type B model of hepatic encephalopathy, on the peripheral pharmacokinetics and brain distribution of sodium fluorescein (FL), which is a small molecule marker of BBB passive permeability. A single 25mg/kg dose of FL was administered intravenously to 10-day PCA and sham-operated rats, and serial blood and bile (0-30min) and terminal (30min) brain samples were collected, and the concentrations of FL and its glucuronidated metabolite (FL-Glu) were measured by HPLC. Additionally, the free fractions of FL (fu) in all the plasma samples were determined, and the effects of bile salts on fu were investigated in vitro. Passive permeability of BBB to FL was estimated by brain uptake clearance (Kin) based on both the brain concentrations of FL and plasma concentrations of free (unbound) FL. PCA caused a 26% increase in the fu of FL in plasma, which was due to competition of bile acids with FL for binding to plasma proteins. Additionally, PCA reduced the biliary excretion of FL-Glu by 55%. However, free Kin values (µl/min/g brain) for the sham (0.265±0.034) and PCA (0.228±0.038) rats were not significantly different. It is concluded that whereas 10-day PCA alters the peripheral pharmacokinetics of FL, it does not significantly affect the BBB permeability to the marker.

TIMP-1 attenuates blood-brain barrier permeability in mice with acute liver failure

Blood-brain barrier (BBB) dysfunction in acute liver failure (ALF) results in increased BBB permeability that often precludes the patients from obtaining a life-saving liver transplantation. It remains controversial whether matrix metalloproteinase-9 (MMP-9) from the injured liver contributes to the deregulation of BBB function in ALF. We selectively upregulated a physiologic inhibitor of MMP-9 (TIMP-1) with a single intracerebroventricular injection of TIMP-1 cDNA plasmids at 48 and 72 hours, or with pegylated-TIMP-1 protein. Acute liver failure was induced with tumor necrosis factor-α and D-(+)-galactosamine in mice. Permeability of BBB was assessed with sodium fluorescein (NaF) extravasation. We found a significant increase in TIMP-1 within the central nervous system (CNS) after the administration of TIMP-1 cDNA plasmids and that increased TIMP-1 within the CNS resulted in an attenuation of BBB permeability, a reduction in activation of epidermal growth factor receptor and p38 mitogen-activated protein kinase signals, and a restoration of the tight junction protein occludin in mice with experimental ALF. Pegylated TIMP-1 provided similar protection against BBB permeability in mice with ALF. Our results provided a proof of principle that MMP-9 contributes to the BBB dysfunction in ALF and suggests a potential therapeutic role of TIMP-1 in ALF.

P-glycoprotein and multidrug resistance-associated protein 2 are oppositely altered in brain of rats with thioacetamide-induced acute liver failure

BACKGROUND

P-glycoprotein (P-GP) and multidrug resistance-associated protein 2 (MRP2) are involved in transport of many drugs across blood-brain barrier (BBB). The function and expression of P-GP and MRP2 may be modulated by different pathologies. Acute liver failure (ALF) was reported to impair BBB function, resulting in the increased BBB permeability.

AIMS

We investigated whether ALF altered function and expression of P-GP and MRP2 in brain of thioacetamide-induced ALF rats.

METHODS

ALF was induced by intraperitoneal injection of thioacetamide (300 mg/kg) for 2 days with a 24-h interval. The rats were used for experiments at 6, 12 and 24 h after the second administration. P-GP and MRP2 function in brain were determined using the brain-to-plasma ratios of corresponding substrates (rhodamine 123 and vincristine for P-GP; sulfobromophthalein and dinitrophenyl-S-glutathione for MRP2). Evans blue was used for examining the BBB integrity. Western blot was accomplished to determine P-GP and MRP2 protein expression.

RESULTS

The brain-to-plasma ratios of rhodamine 123 and vincristine were significantly increased in ALF-6 h rats and almost returned to normal levels in ALF-24 h rats, whereas those of sulfobromophthalein and dinitrophenyl-S-glutathione were decreased in all ALF rats. Western blot results showed that ALF decreased brain P-GP levels at 6 and 12 h, whereas increased MRP2 levels at 6, 12 and 24 h. No significant difference of Evans blue concentrations in brain was found among the four groups.

CONCLUSIONS

Function and expression of P-GP and MRP2 in brain of thioacetamide-induced ALF rats were oppositely altered.

Brain edema in acute liver failure and chronic liver disease: similarities and differences

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome that typically develops as a result of acute liver failure or chronic liver disease. Brain edema is a common feature associated with HE. In acute liver failure, brain edema contributes to an increase in intracranial pressure, which can fatally lead to brain stem herniation. In chronic liver disease, intracranial hypertension is rarely observed, even though brain edema may be present. This discrepancy in the development of intracranial hypertension in acute liver failure versus chronic liver disease suggests that brain edema plays a different role in relation to the onset of HE. Furthermore, the pathophysiological mechanisms involved in the development of brain edema in acute liver failure and chronic liver disease are dissimilar. This review explores the types of brain edema, the cells, and pathogenic factors involved in its development, while emphasizing the differences in acute liver failure versus chronic liver disease. The implications of brain edema developing as a neuropathological consequence of HE, or as a cause of HE, are also discussed.

Fulminant liver failure models with subsequent encephalopathy in the mouse

BACKGROUND

A reliable model of fulminant liver failure (FLF) is urgently required in this research field. This study aimed to develop a murine FLF model.

METHODS

We used three groups of male C57BL/6 mice: control, with azoxymethane treatment (AOM group), and with galactosamine and tumor necrosis factor-alpha treatment (Gal+TNF-alpha group). The effects of body temperature (BT) control on survival in all three groups were investigated. Using BT control, we compared the survival, histopathological findings and biochemical/coagulation profiles between the two experimental groups. The effects of hydration on international normalized ratios of prothrombin time (PT-INRs) were also checked. Dose-dependent survival curves were constructed for both experimental groups. Neurological behavior was assessed using a coma scale.

RESULTS

No unexpected BT effects were seen in the control group. The AOM group, but not the Gal+TNF-alpha group, showed a significant difference in survival curves between those with and without BT care. Histopathological assessment showed consistent FLF findings in both experimental groups with BT care. There were significant differences between the experimental groups in aspartate aminotransferase levels and PT-INRs, and significant differences in PT-INRs between the sufficiently and insufficiently hydrated groups. There were significant differences between FLF models in the duration of each coma stage, with significant differences in stages 1 and 3 as percentages of the disease state (stages 1-4). The two FLF models with BT care showed different survival curves in the dose-dependent survival study.

CONCLUSIONS

AOM provides a good FLF model, but requires a specialized environment and careful BT control. Other FLF models may also be useful, depending on the research purpose. Thoughtful attention to caregiving and close observation are indispensable for successful FLF models.

Blood-brain barrier in acute liver failure

Brain edema remains a challenging obstacle in the management of acute liver failure (ALF). Cytotoxic mechanisms associated with brain edema have been well recognized, but evidence for vasogenic mechanisms in the pathogenesis of brain edema in ALF has been lacking. Recent reports have not only shown a role of matrix metalloproteinase-9 in the pathogenesis of brain edema in experimental ALF but have also found significant alterations in the tight junction elements including occludin and claudin-5, suggesting a vasogenic injury in the blood-brain barrier (BBB) integrity. This article reviews and explores the role of the paracellular tight junction proteins in the increased selective BBB permeability that leads to brain edema in ALF.

Fulminant liver failure model with hepatic encephalopathy in the mouse

AIM

To develop a reliable murine model for fulminant liver failure (FLF).

MATERIAL AND METHODS

We treated three groups of male C57BL/6 mice:as controls, with azoxymethane (AOM), and with galactosamine (Gal) and tumor necrosis factor-alpha (TNFα). Effects of body temperature (BT) control on survival, in all three groups were investigated. Using BT control, survival, histopathological findings and biochemical/coagulation profiles were compared between the experimental groups. Effects of hydration on international normalized ratios of prothrombin time (PT-INR) were also checked. Dose-dependent survival curves were made for both experimental groups. Neurological behaviors were assessed using a coma scale.

RESULTS

No unexpected BT effects were seen in the control group. The AOM group, but not the Gal+TNFα group, showed significant differences in survival curves between those with and without BT care. Histopathological assessment showed consistent FLF findings in both experimental groups with BT care. Between the experimental groups, there were significant differences in aspartate aminotransferase levels and PT-INR; and significant differences in PT-INRs between sufficiently- and insufficiently-hydrated groups. There were significant differences between FLF models, in the duration of each coma stage, with significant differences in stages 1 and 3 as percentages of the diseased state (stages 1-4). The two FLF models with BT care showed different survival curves in the dose-dependent survival study.

CONCLUSION

Azoxymethane can provide a good FLF model, but requires a specialized environment and careful BT control. Other FLF models may also be useful, depending on research purpose. Thoughtful attention to caregiving and close observation are indispensable for successful FLF models.

TRPC-mediated actin-myosin contraction is critical for BBB disruption following hypoxic stress

Hypoxia-induced disruption of the blood-brain barrier (BBB) is the result of many different mechanisms, including alterations to the cytoskeleton. In this study, we identified actin-binding proteins involved in cytoskeletal dynamics with quantitative proteomics and assessed changes in subcellular localization of two proteins involved in actin polymerization [vasodilator-stimulated phosphoprotein (VASP)] and cytoskeleton-plasma membrane cross-linking (moesin). We found significant redistribution of both VASP and moesin to the cytoskeletal and membrane fractions of BBB endothelial cells after 1-h hypoxic stress. We also investigated activation of actin-myosin contraction through assessment of phosphorylated myosin light chain (pMLC) with confocal microscopy. Hypoxia caused a rapid and transient increase in pMLC. Blocking MLC phosphorylation through inhibition of myosin light chain kinase (MLCK) with ML-7 prevented hypoxia-induced BBB disruption and relocalization of the tight junction protein ZO-1. Finally, we implicate the transient receptor potential (TRP)C family of channels in mediating these events since blockade of TRPC channels and the associated calcium influx with SKF-96365 prevents hypoxia-induced permeability changes and the phosphorylation of MLC needed for actin-myosin contraction. These data suggest that hypoxic stress triggers alterations to cytoskeletal structure that contribute to BBB disruption and that calcium influx through TRPC channels contributes to these events.

An overview of animal models for investigating the pathogenesis and therapeutic strategies in acute hepatic failure

Acute hepatic failure (AHF) is a severe liver injury accompanied by hepatic encephalopathy which causes multiorgan failure with an extremely high mortality rate, even if intensive care is provided. Management of severe AHF continues to be one of the most challenging problems in clinical medicine. Liver transplantation has been shown to be the most effective therapy, but the procedure is limited by shortage of donor organs. Although a number of clinical trials testing different liver assist devices are under way, these systems alone have no significant effect on patient survival and are only regarded as a useful approach to bridge patients with AHF to liver transplantation. As a result, reproducible experimental animal models resembling the clinical conditions are still needed. The three main approaches used to create an animal model for AHF are: surgical procedures, toxic liver injury and infective procedures. Most common models are based on surgical techniques (total/partial hepatectomy, complete/transient devascularization) or the use of hepatotoxic drugs (acetaminophen, galactosamine, thioacetamide, and others), and very few satisfactory viral models are available. We have recently developed a viral model of AHF by means of the inoculation of rabbits with the virus of rabbit hemorrhagic disease. This model displays biochemical and histological characteristics, and clinical features that resemble those in human AHF. In the present article an overview is given of the most widely used animal models of AHF, and their main advantages and disadvantages are reviewed.