Endotoxemia produces coma and brain swelling in bile duct ligated rats

Loss of tyrosine hydroxylase expression within the nigro-striato-cortical pathways in the cirrhotic rat: the possible restorative effect of the neurosteroid dehydroepiandrosterone sulfate

Hepatic encephalopathy (HE) is a neuropsychiatric disorder occurring as a consequence of both acute and chronic liver failure. Advanced HE is generally accompanied with extrapyramidal symptoms including rigidity and tremor, which may reflect alterations of the dopaminergic system. Recently we reported a beneficial effect of the neuroactive steroid dehydroepiandrosterone sulfate (DHEAS) in cirrhotic rats, however the mechanisms of such an effect by DHEAS were not addressed. In the present study, we describe the changes of the dopaminergic system occurring in the cirrhotic rats and concomitantly we investigated the effect of DHEAS on this system in Sprague-Dawley rats using the expression of tyrosine hydroxylase (TH) as a neuronal marker. Rats were submitted to bile duct ligation (BDL) surgery and TH immunohistochemistry was assessed in the Substantia nigra pars compacta (SNc), striatum, ventral tegmental area (VTA) and the cortex. TH immunoreactivity showed a significant diminution in both SNc and VTA concomitantly with the cortical and the striatal outputs in the BDL rats vs. controls. Three daily injections of 5mg/kg of DHEAS to BDL rats significantly normalized TH expression decrease in both SNc and VTA as well as dopaminergic projections to the striatum and the cortex of BDL rats. The present data support an involvement of the dopaminergic system in mild HE and a possible beneficial effect of the neurosteroid DHEAS as a potential pharmacological treatment of mild HE.

Microglia contribute to ammonia-induced astrocyte swelling in culture

Brain edema, a lethal complication of acute liver failure (ALF), is believed to be largely cytotoxic due to the swelling of astrocytes. Ammonia, a principal neurotoxin in ALF, has been strongly implicated in the development of the brain edema. It was previously shown that treatment of cultured astrocytes with ammonia (5 mM NH₄Cl) results in cell swelling. While ammonia continues to exert a direct effect on astrocytes, it is possible that ammonia can affect other neural cells, particularly microglia. Microglia are capable of evoking an inflammatory response, a process known to contribute to the brain edema. We therefore examined the potential role of microglia in the mechanism of ammonia-induced astrocyte swelling. Conditioned media (CM) derived from ammonia-treated cultured microglia when added to cultured astrocytes resulted in significant cell swelling. Such swelling was synergistically increased when astrocytes were additionally treated with 5 mM ammonia. CM from ammonia-treated microglia also showed significant release of oxy-radicals and nitric oxide into the CM. CM from ammonia-treated microglia containing Tempol (a superoxide scavenger) or uric acid (a peroxynitrite scavenger) when added to astrocytes resulted in marked reduction in the cell swelling. Together, these studies indicate that microglia contribute to the ammonia-induced astrocyte swelling by a mechanism involving oxidative/nitrosative stress.

Gut microbiota and hepatic encephalopathy

There is a strong relationship between liver and gut; while the portal venous system receives blood from the gut, and its contents may affect liver functions, liver in turn, affects intestinal functions through bile secretion. There is robust evidence that the pathogenesis of hepatic encephalopathy (HE) is linked to alterations in gut microbiota and their by-products such as ammonia, indoles, oxindoles, endotoxins, etc. In the setting of intestinal barrier and immune dysfunction, these by-products are involved in the pathogenesis of complications of liver cirrhosis including HE and systemic inflammation plays an important role. Prebiotics, probiotics and synbiotics may exhibit efficacy in the treatment of HE by modulating the gut flora. They improve derangement in flora by decreasing the counts of pathogenic bacteria and thus improving the endotoxemia, HE and the liver disease. Current evidence suggest that the trials evaluating the role of probiotics in the treatment of HE are of not high quality and all trials had high risk of bias and high risk of random errors. Therefore, the use of probiotics for patients with HE cannot be currently recommended. Further RCTs are required. This review summarizes the main literature findings about the relationships between gut flora and HE, both in terms of the pathogenesis and the treatment of HE.

Inflammation and hepatic encephalopathy

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome associated with both acute and chronic liver dysfunction, spanning a spectrum that ranges from mild neuropsychological disturbances to coma. The central role of ammonia in the pathogenesis of HE remains incontrovertible however, there is a robust evidence base indicating the important role of inflammation in exacerbating the neurological effects of HE. Inflammation can arise directly within the brain itself as a result of deranged nitrogen and energy homeostasis, with resultant neuronal, astrocyte and microglial dysfunction. Inflammation may also originate in the peripheral circulation and exert effects on the brain indirectly, via the release of pro-inflammatory mediators which directly signal to the brain via the vagus nerve. This review summarises the data that demonstrate the synergistic relationship of inflammation and ammonia that culminates in the manifestation of HE. Sterile inflammation arising from the inflamed or necrotic liver, circulating endotoxin arising from the gut (bacterial translocation) inducing immune dysfunction, and superimposed sepsis will be comprehensively discussed. Finally, this review will provide an overview of the existing and novel treatments on the horizon which can target the inflammatory response, and how they might translate into clinical practise as therapies in the prophylaxis and treatment of HE.

Effect of endotoxin on heart rate dynamics in rats with cirrhosis

Reduced heart rate variability (HRV) is a hallmark of systemic inflammation which carries negative prognostic information in sepsis. Decreased HRV is associated with partial uncoupling of cardiac pacemaker from cholinergic neural control during systemic inflammation. Sepsis is a common complication in liver cirrhosis with high mortality. The present study was aimed to explore the hypothesis that endotoxin uncouples cardiac pacemaker from autonomic neural control and reduces HRV in an experimental model of cirrhosis. Cirrhosis was induced by surgical ligation of the bile duct in rats. Cirrhotic rats were given intraperitoneal injection of either saline or lipopolysaccharide (endotoxin, 1mg/kg). Changes in HRV indices were studied in conscious rats using implanted telemetric probes. The atria were isolated and chronotropic responsiveness to cholinergic stimulation was assessed in vitro. Endotoxin injection induced a significant tachycardia and decreased short-term and long-term HRV indices in control rats. However, endotoxin was unable to increase heart rate in cirrhotic animals. In contrast with control rats, endotoxin induced biphasic changes in short-term HRV in cirrhotic rats. Acute endotoxin challenge reduced long-term HRV with 60-min delay in comparison with control animals. Endotoxin injection was associated with a significant hypo-responsiveness to cholinergic stimulation in control rats in vitro. Endotoxin did not change atrial chronotropic responsiveness to cholinergic stimulation in cirrhotic rats. Our data shows that cirrhosis is associated with development of tolerance to cardiac chronotropic effect of endotoxin in rats.

Cirrhosis is associated with development of tolerance to cardiac chronotropic effect of endotoxin in rats

BACKGROUND/AIMS

Sepsis is a common complication of cirrhosis with a high mortality. Cirrhosis is associated with cardiac chronotropic and inotropic dysfunction, which is known as cirrhotic cardiomyopathy and might be linked to endotoxaemia. This study was aimed to explore the hypothesis that the inflammatory response induced by administration of low dose of lipopolysaccharide (LPS) exacerbates cardiac chronotropic dysfunction in cirrhotic rats; and if so, whether this is associated with altered cardiac toll-like receptor expression.

METHODS

Cirrhosis was induced by surgical ligation of the bile duct in male Wister rats. Four weeks after bile duct ligation or sham surgery, the subjects were given intraperitoneal injection of either saline or LPS (0.1 mg/kg). Five hours after LPS injection, the atria were isolated and spontaneously beating rate and chronotropic responsiveness to β-adrenergic stimulation was assessed using standard organ bath. The expression of toll-like receptor 4 (TLR4) was assessed the atria using immunohistochemistry as well as quantitative RT-PCR.

RESULTS

LPS injection could induce a significant hypo-responsiveness to adrenergic stimulation in sham-operated rats. However, in cirrhotic rats, the chronotropic responses did not change after acute injection of LPS. Immunohistochemical study showed that TLR4 is mainly expressed in the myocardium in control atria and its expression is markedly decreased in myocardial layer following chronic bile duct ligation.

CONCLUSION

Our data showed that cirrhosis is associated with development of tolerance to cardiac chronotropic effect of LPS in rats and this might be caused by altered localization of TLR4 in myocardium.

Systemic inflammation and ammonia in hepatic encephalopathy

Infection and inflammation have been associated with the development of delirium for many centuries and there is a rapidly growing evidence base supporting the role of inflammation in exacerbating the neurological manifestations of both acute and chronic liver failure. Inflammation in the context of hepatic encephalopathy (HE) can arise directly within the brain itself resulting in astrocytic, microglial and neuronal dysfunction, impacting on the development of 'brain failure'. Inflammation may also develop systemically and indirectly influence brain function. Systemic inflammation develops following liver injury, resulting in hyperammonemia and a 'cytotoxic soup' of pro-inflammatory mediators which are released into the circulation and modulate the impact of ammonia on the brain. The aim of this review is to summarise the current evidence base supporting the synergistic role of systemic inflammation and hyperammonemia in the pathogenesis of hepatic encephalopathy. Systemic inflammation and ammonia induce neutrophil degranulation and release reactive oxygen species into the peripheral circulation that may ultimately cross the blood brain barrier. Circulating endotoxin arising from the gut (bacterial translocation), superimposed sepsis, and hyperammonemia upregulate the expression of microbial pattern recognition receptors such as Toll-like receptors. The early recognition and management of systemic inflammation may not only facilitate improved outcomes in HE but supports the development of novel therapeutic strategies that reduce circulating endotoxemia and immune cell dysfunction.

Brain magnetic resonance in experimental acute-on-chronic liver failure

BACKGROUND & AIM

Acute-on-chronic liver failure is the term that refers to sustained liver injury with acute decompensation, usually induced by a precipitating factor. A common link between ensuing failures of various organs is impairment of the vascular supply, which may also induce vasogenic oedema in the brain. The aim of this study was to perform magnetic resonance (MR) study of the brain in a rat model combining bile duct ligation (BDL) and lipopolysaccharide (LPS) administration to investigate brain oedema in liver failure.

METHODS

Bile duct-ligated rats underwent in vivo brain MR imaging at 4, 5 and 6 weeks, and after superimposed administration of LPS. The MR techniques applied enabled assessment of brain metabolites, and intra- or extracellular water distribution. Brain water content was assessed by gravimetry.

RESULTS

MR spectroscopy showed an increase in brain glutamine and a decrease in myo-inositol and choline in relation to progression of liver disease. BDL rats showed a slight, progressive increase in the amount of cortical brain water that was significant after LPS injection. These changes did not modify the apparent diffusion coefficient, supporting a mixed origin of brain oedema (vasogenic and cytotoxic).

CONCLUSIONS

The mechanisms leading to the development of brain oedema in an experimental liver disease model were related to the time course of liver failure and to pro-inflammatory stimuli. MR findings support the presence of cytotoxic and vasogenic mechanisms in induced brain oedema in BDL rats exposed to LPS.

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.

Pathogenesis of hepatic encephalopathy

Hepatic encephalopathy can be a serious complication of acute liver failure and chronic liver diseases, predominantly liver cirrhosis. Hyperammonemia plays the most important role in the pathogenesis of hepatic encephalopathy. The brain-blood barrier disturbances, changes in neurotransmission, neuroinflammation, oxidative stress, GABA-ergic or benzodiazepine pathway abnormalities, manganese neurotoxicity, brain energetic disturbances, and brain blood flow abnormalities are considered to be involved in the development of hepatic encephalopathy. The influence of small intestine bacterial overgrowth (SIBO) on the induction of minimal hepatic encephalopathy is recently emphasized. The aim of this paper is to present the current views on the pathogenesis of hepatic encephalopathy.

Acute-on chronic liver failure

Acute-on-chronic liver failure (ACLF) is an increasingly recognised entity encompassing an acute deterioration of liver function in patients with cirrhosis, which is usually associated with a precipitating event and results in the failure of one or more organs and high short term mortality. Prospective data to define this is lacking but there is a large body of circumstantial evidence suggesting that this condition is a distinct clinical entity. From the pathophysiologic perspective, altered host response to injury and infection play important roles in its development. This review focuses upon the current understanding of this syndrome from the clinical, prognostic and pathophysiologic perspectives and indicates potential biomarkers and therapeutic targets for intervention.

Serum endotoxin and inflammatory mediators in patients with cirrhosis and hepatic encephalopathy

BACKGROUND

Recent observations suggest that inflammatory response may be important in the pathogenesis of hepatic encephalopathy. The aim of the study was to measure arterial ammonia, tumour necrosis factor-alpha, Interleukin-6, Interleukin-18, and serum endotoxin levels and their correlation with different grades of hepatic encephalopathy.

METHODS

120 patients with cirrhosis were enrolled: 20 patients each of cirrhosis with grades I, II, III and IV hepatic encephalopathy, cirrhosis with and without minimal hepatic encephalopathy and healthy controls were tested for arterial ammonia, tumour necrosis factor-alpha, Interleukin-6, Interleukin-18 and serum endotoxin levels.

RESULTS

Median arterial ammonia, tumour necrosis factor-alpha, Interleukin-6, Interleukin-18 and serum endotoxin levels were significantly higher in patient with hepatic encephalopathy and minimal hepatic encephalopathy as compared to patients without minimal hepatic encephalopathy and healthy controls. Arterial ammonia (r = 0.72, p = 0.03), tumour necrosis factor alpha (r = 0.87, p = 0.02), Interleukin-6 (r = 0.50, p = 0.05), Interleukin-18 (r = 0.76, p = 0.02) and serum endotoxin (r = 0.91, p = 0.01) correlated with higher grades of hepatic encephalopathy.

CONCLUSION

In hepatic encephalopathy arterial ammonia, inflammatory mediators, and serum endotoxin are elevated and correlate with encephalopathy grade.

Role of predisposition, injury, response and organ failure in the prognosis of patients with acute-on-chronic liver failure: a prospective cohort study

INTRODUCTION

Acute deterioration of cirrhosis is associated with high mortality rates particularly in the patients who develop organ failure (OF), a condition that is referred to as acute-on-chronic liver failure (ACLF), which is currently not completely defined. This study aimed to determine the role of predisposing factors, the nature of the precipitating illness and inflammatory response in the progression to OF according to the PIRO (predisposition, injury, response, organ failure) concept to define the risk of in-hospital mortality.

METHODS

A total of 477 patients admitted with acute deterioration of cirrhosis following a defined precipitant over a 5.5-year period were prospectively studied. Baseline clinical, demographic and biochemical data were recorded for all patients and extended serial data from the group that progressed to OF were analysed to define the role of PIRO in determining in-hospital mortality.

RESULTS

One hundred and fifty-nine (33%) patients developed OF, of whom 93 patients died (58%) compared with 25/318 (8%) deaths in the non-OF group (P < 0.0001). Progression to OF was associated with more severe underlying liver disease and inflammation. In the OF group, previous hospitalisation (P of PIRO); severity of inflammation and lack of its resolution (R of PIRO); and severity of organ failure (O of PIRO) were associated with significantly greater risk of death. In the patients who recovered from OF, mortality at three years was almost universal.

CONCLUSIONS

The results of this prospective study shows that the occurrence of OF alters the natural history of cirrhosis. A classification based on the PIRO concept may allow categorization of patients into distinct pathophysiologic and prognostic groups and allow a multidimensional definition of ACLF.

Role of cerebral endothelial cells in the astrocyte swelling and brain edema associated with acute hepatic encephalopathy

Brain edema is an important complication of acute hepatic encephalopathy (AHE), and astrocyte swelling is largely responsible for its development. Elevated blood and brain ammonia levels have been considered as major etiological factors in this edema. In addition to ammonia, recent studies have suggested that systemic infection, inflammation (and associated cytokines (CKs)), as well as endotoxin (lipopolysaccharide (LPS)) are also involved in AHE-associated brain edema. As endothelial cells (ECs) are the first resident brain cells exposed to blood-borne "noxious agents" (i.e., ammonia, CKs, LPS) that are present in AHE, these cells may be in a critical position to react to these agents and trigger a process resulting in astrocyte swelling/brain edema. We therefore examined the effect of conditioned media (CM) from ammonia, LPS and cytokine-treated cultured brain ECs on cell swelling in cultured astrocytes. CM from ammonia-treated ECs when added to astrocytes caused significant cell swelling, and such swelling was potentiated when astrocytes were exposed to CM from ECs treated with a combination of ammonia, LPS and CKs. We also found an additive effect when astrocytes were exposed to ammonia along with CM from ammonia-treated ECs. Additionally, ECs treated with ammonia showed a significant increase in the production of oxy-radicals, nitric oxide (NO), as well as evidence of oxidative/nitrative stress and activation of the transcription factor nuclear factor kappa B (NF-κB). CM derived from ECs treated with ammonia, along with antioxidants (AOs) or the NF-κB inhibitor BAY 11-7082, when added to astrocytes resulted in a significant reduction in cell swelling, as compared to the effect of CM from ECs-treated only with ammonia. We also identified increased nuclear NF-κB expression in rat brain cortical ECs in the thioacetamide (TAA) model of AHE. These studies suggest that ECs significantly contribute to the astrocyte swelling/brain edema in AHE, likely as a consequence of oxidative/nitrative stress and activation of NF-κB.

Prevention of acute kidney injury in a rodent model of cirrhosis following selective gut decontamination is associated with reduced renal TLR4 expression

BACKGROUND & AIMS

Superimposed infection and/or inflammation precipitate renal failure in cirrhosis. This study aimed at testing the hypothesis that increased gut bacterial translocation in cirrhosis primes the kidney to the effect of superimposed inflammation by upregulating expression of Toll-like receptor 4 (TLR4), NFκB, and cytokines. A well-characterized bile-duct ligated (BDL) model of cirrhosis, which develops renal failure following superimposed inflammatory insult with lipopolysaccharide (LPS), was used and selective gut decontamination was performed using norfloxacin.

METHODS

Sprague-Dawley rats were studied: Sham, Sham+LPS; BDL, BDL+LPS; an additional BDL and BDL+LPS groups were selectively decontaminated with norfloxacin. Plasma biochemistry, plasma renin activity (PRA) and cytokines and, protein expression of TLR4, NFκB, and cytokines were measured in the kidney homogenate. The kidneys were stained for TLR4, TLR2, and caspase-3. Endotoxemia was measured using neutrophil burst and Limulus amoebocyte lysate (LAL) assays.

RESULTS

The groups treated with norfloxacin showed significant attenuation of the increase in plasma creatinine, plasma and renal TNF-α and renal tubular injury on histology. The increased renal protein expression of TLR4, NFκB, and caspase-3 in the untreated animals was significantly attenuated in the norfloxacin treated animals. PRA was reduced in the treated animals and severity of endotoxemia was also reduced.

CONCLUSIONS

The results show for the first time that kidneys in cirrhosis show an increased expression of TLR4, NFκB, and the pro-inflammatory cytokine TNF-α, which makes them susceptible to a further inflammatory insult. This increased susceptibility to LPS can be prevented with selective decontamination, providing novel insights into the pathophysiology of renal failure in cirrhosis.

Systemic oxidative stress is implicated in the pathogenesis of brain edema in rats with chronic liver failure

Chronic liver failure leads to hyperammonemia, a central component in the pathogenesis of hepatic encephalopathy (HE); however, a correlation between blood ammonia levels and HE severity remains controversial. It is believed oxidative stress plays a role in modulating the effects of hyperammonemia. This study aimed to determine the relationship between chronic hyperammonemia, oxidative stress, and brain edema (BE) in two rat models of HE: portacaval anastomosis (PCA) and bile-duct ligation (BDL). Ammonia and reactive oxygen species (ROS) levels, BE, oxidant and antioxidant enzyme activities, as well as lipid peroxidation were assessed both systemically and centrally in these two different animal models. Then, the effects of allopurinol (xanthine oxidase inhibitor, 100mg/kg for 10days) on ROS and BE and the temporal resolution of ammonia, ROS, and BE were evaluated only in BDL rats. Similar arterial and cerebrospinal fluid ammonia levels were found in PCA and BDL rats, both significantly higher compared to their respective sham-operated controls (p<0.05). BE was detected in BDL rats (p < 0.05) but not in PCA rats. Evidence of oxidative stress was found systemically but not centrally in BDL rats: increased levels of ROS, increased activity of xanthine oxidase (oxidant enzyme), enhanced oxidative modifications on lipids, as well as decreased antioxidant defense. In PCA rats, a preserved oxidant/antioxidant balance was demonstrated. Treatment with allopurinol in BDL rats attenuated both ROS and BE, suggesting systemic oxidative stress is implicated in the pathogenesis of BE. Analysis of ROS and ammonia temporal resolution in the plasma of BDL rats suggests systemic oxidative stress might be an important "first hit", which, followed by increases in ammonia, leads to BE in chronic liver failure. In conclusion, chronic hyperammonemia and oxidative stress in combination lead to the onset of BE in rats with chronic liver failure.

Reduction in hyperammonaemia by ornithine phenylacetate prevents lipopolysaccharide-induced brain edema and coma in cirrhotic rats

OBJECTIVE

In liver failure, inflammation synergistically exacerbates the deleterious cerebral effects of ammonia. The aims were to test whether treatment with the ammonia-lowering agent ornithine phenylacetate (OP) and/or anti-TNF-α (infliximab) prevent the deleterious brain consequences of lipopolysaccharide (LPS) in cirrhotic rats.

DESIGN

Rats 4 weeks following bile duct-ligation (BDL), sham-operation (sham) and/or 7 days hyperammonemic feed (HD), were randomized to receive LPS (1 mg/kg) or saline, and treatment with either 3 days intraperitoneal injections of OP (0.6 g/kg) and/or infliximab, 10 mg/kg. Animals were sacrificed at coma stages or at 3 h.

RESULTS

In sham rats, both HD and LPS increased brain water, with an increase in ammonia in the former and brain cytokines in the latter but with no effect on consciousness. BDL + HD rats caused significantly higher plasma ammonia, TNF-α and IL-6 levels compared to sham. LPS significantly worsened coma stage, increased brain water and plasma and brain TNF-α. OP significantly delayed LPS-induced progression to coma stages (P < 0.009), reduced arterial ammonia and brain water (P < 0.001 and P < 0.01 respectively), which was associated with a significant reduction in cytokines. Infliximab significantly reduced plasma and brain cytokines, but not brain water. OP + infliximab attenuated increase in brain water and delayed occurrence of coma, which was not different to OP alone. In BDL rats, OP reduced the expression of brain iNOS and NFκB.

CONCLUSION

Reduction in ammonia with OP in cirrhotic rats prevents LPS-induced brain edema and delays coma, suggesting that ammonia may prime the brain to the deleterious effect of LPS, possibly through effects on iNOS and NFκB related mechanisms.

Ammonia reduction with ornithine phenylacetate restores brain eNOS activity via the DDAH-ADMA pathway in bile duct-ligated cirrhotic rats

Ammonia is central in the pathogenesis of hepatic encephalopathy, which is associated with dysfunction of the nitric oxide (NO) signaling pathway. Ornithine phenylacetate (OP) reduces hyperammonemia and brain water in cirrhotic animals. This study aimed to determine whether endothelial NO synthase activity is altered in the brain of cirrhotic animals, whether this is associated with changes in the endogenous inhibitor, asymmetric-dimethylarginine (ADMA) and its regulating enzyme, dimethylarginine-dimethylaminohydrolase (DDAH-1), and whether these abnormalities are restored by ammonia reduction using OP. Sprague-Dawley rats were studied 4-wk after bile duct ligation (BDL) (n = 16) or sham operation (n = 8) and treated with placebo or OP (0.6 g/kg). Arterial ammonia, brain water, TNF-α, plasma, and brain ADMA were measured using standard techniques. NOS activity was measured radiometrically, and protein expression for NOS enzymes, ADMA, DDAH-1, 4-hydroxynonenol ((4)HNE), and NADPH oxidase (NOX)-1 were measured by Western blotting. BDL significantly increased arterial ammonia (P < 0.0001), brain water (P < 0.05), and brain TNF-α (P < 0.01). These were reduced significantly by OP treatment. The estimated eNOS component of constitutive NOS activity was significantly lower (P < 0.05) in BDL rat, and this was significantly attenuated in OP-treated animals. Brain ADMA levels were significantly higher and brain DDAH-1 significantly lower in BDL compared with sham (P < 0.01) and restored toward normal following treatment with OP. Brain (4)HNE and NOX-1 protein expression were significantly increased in BDL rat brain, which were significantly decreased following OP administration. We show a marked abnormality of NO regulation in cirrhotic rat brains, which can be restored by reduction in ammonia concentration using OP.

Suppression of the HPA axis during extrahepatic biliary obstruction induces cholangiocyte proliferation in the rat

Cholestatic patients often present with clinical features suggestive of adrenal insufficiency. In the bile duct-ligated (BDL) model of cholestasis, the hypothalamic-pituitary-adrenal (HPA) axis is suppressed. The consequences of this suppression on cholangiocyte proliferation are unknown. We evaluated 1) HPA axis activity in various rat models of cholestasis and 2) effects of HPA axis modulation on cholangiocyte proliferation. Expression of regulatory molecules of the HPA axis was determined after BDL, partial BDL, and α-naphthylisothiocyanate (ANIT) intoxication. The HPA axis was suppressed by inhibition of hypothalamic corticotropin-releasing hormone (CRH) expression by central administration of CRH-specific Vivo-morpholinos or by adrenalectomy. After BDL, the HPA axis was reactivated by 1) central administration of CRH, 2) systemic ACTH treatment, or 3) treatment with cortisol or corticosterone for 7 days postsurgery. There was decreased expression of 1) hypothalamic CRH, 2) pituitary ACTH, and 3) key glucocorticoid synthesis enzymes in the adrenal glands. Serum corticosterone and cortisol remained low after BDL (but not partial BDL) compared with sham surgery and after 2 wk of ANIT feeding. Experimental suppression of the HPA axis increased cholangiocyte proliferation, shown by increased cytokeratin-19- and proliferating cell nuclear antigen-positive cholangiocytes. Conversely, restoration of HPA axis activity inhibited BDL-induced cholangiocyte proliferation. Suppression of the HPA axis is an early event following BDL and induces cholangiocyte proliferation. Knowledge of the role of the HPA axis during cholestasis may lead to development of innovative treatment paradigms for chronic liver disease.

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.

The neurological manifestations of acute liver failure

Acute liver failure is a disorder which impacts on multiple organ systems and results from hepatocellular necrosis in a patient with no previous history of chronic liver disease. It typically culminates in the development of liver dysfunction, coagulopathy and encephalopathy, and is associated with high mortality in poor prognostic groups. In acute liver failure, some patients may develop cerebral edema and increased intracranial pressure although recent data suggest that intracranial hypertension is less frequent than previously described, complicating 29% of acute cases who have proceeded to grade 3/4 coma. Neurological manifestations are primarily underpinned by the development of brain edema. The onset of encephalopathy can be rapid and dramatic with the development of asterixis, delirium, hyperreflexia, clonus, seizures, extensor posturing and coma. Ammonia plays a definitive role in the development of cytotoxic brain edema. Patients with acute liver failure have a marked propensity to develop renal insufficiency and hence impaired ammonia excretion. The incidence of both bacterial and fungal infection occurs in approximately one third of patients. The relationship between inflammation, as opposed to infection, and progression of encephalopathy is similar to that observed in chronic liver disease. Intracranial pressure monitoring is valuable in identifying surges in intracranial hypertension requiring intervention. Insertion of an intracranial bolt should be considered only in the subgroup of patients who have progressed to grade 4 coma. Risk factors for developing intracranial hypertension are those with hyperacute and acute etiologies, progression to grade 3/4 hepatic encephalopathy, those who develop pupillary abnormalities (dilated pupils, sluggishly responsive to light) or seizures, have systemic inflammation, an arterial ammonia >150 μmol/L, hyponatremia, and those in receipt of vasopressor support. Strategies employed in patients with established encephalopathy (grade 3/4) aim to maintain freedom from infection/inflammatory milieu, provide adequate sedation, and correct hypo-osmolality.

Interaction between cytokines and ammonia in the mitochondrial permeability transition in cultured astrocytes

Hepatic encephalopathy (HE) is the major neurological complication occurring in patients with acute and chronic liver failure. Elevated levels of blood and brain ammonia are characteristic of HE, and astrocytes are the primary target of ammonia toxicity. In addition to ammonia, recent studies suggest that inflammation and associated cytokines (CKs) also contribute to the pathogenesis of HE. It was previously established that ammonia induces the mitochondrial permeability transition (mPT) in cultured astrocytes. As CKs have been shown to cause mitochondrial dysfunction in other conditions, we examined whether CKs induce the mPT in cultured astrocytes. Cultures treated with tumor necrosis factor-α, interleukin-1β, interleukin-6, and interferon-γ, individually or in a mixture, resulted in the induction of the mPT in a time-dependent manner. Simultaneous treatment of cultures with a mixture of CKs and ammonia showed a marked additive effect on the mPT. As oxidative stress (OS) is known to induce the mPT, so we examined the effect of CKs and ammonia on hemeoxygenase-1 (HO-1) protein expression, a marker of OS. Such treatment displayed a synergistic effect in the upregulation of HO-1. Antioxidants significantly blocked the additive effects on the mPT by CKs and ammonia, suggesting that OS represents a major mechanism in the induction of the mPT. Treatment of cultures with minocycline, an antiinflammatory agent, which is known to inhibit OS, also diminished the additive effects on the mPT caused by CKs and ammonia. Induction of the mPT in astrocytes appears to represent a major pathogenetic factor in HE, in which CKs and ammonia are critically involved.

AST-120 (spherical carbon adsorbent) lowers ammonia levels and attenuates brain edema in bile duct-ligated rats

The pathogenesis of hepatic encephalopathy is multifactorial, involving gut-derived toxins such as ammonia, which has been demonstrated to induce oxidative stress. Therefore, a primary hepatic encephalopathy treatment target is reducing ammonia production in the gastrointestinal tract. AST-120, an oral adsorbent of engineered activated carbon microspheres with surface areas exceeding 1600 m2/g, acts as a sink for neurotoxins and hepatotoxins present in the gut. We evaluated the capacity of AST-120 to adsorb ammonia in vitro and to lower blood ammonia, oxidative stress and brain edema in cirrhotic rats. Cirrhosis was induced in rats by bile duct ligation for 6 weeks. AST-120 was administered by gavage preventively for 6 weeks (0.1, 1, and 4 g/kg/day). In addition, AST-120 was evaluated as a short-term treatment for 2 weeks and 3 days (1 g/kg/day) and as a sink to adsorb intravenously infused ammonium acetate. In vitro, AST-120 efficiently adsorbed ammonia. Ammonia levels significantly decreased in a dose-dependent manner for all AST-120-treated bile duct-ligated rats (nontreated: 177.3 ± 30.8 μM; AST-120, 0.1 g/kg/day: 121.9 ± 13.8 μM; AST-120, 1 g/kg/day: 80.9 ± 30.0 μM; AST-120, 4 g/kg/day: 48.8 ± 19.6 μM) and significantly correlated with doses of AST-120 (r = -0.6603). Brain water content and locomotor activity normalized after AST-120 treatments, whereas arterial reactive oxygen species levels remained unchanged. Furthermore, AST-120 significantly attenuated a rise in arterial ammonia after ammonium acetate administration (intravenously).

CONCLUSION

AST-120 treatment decreased arterial ammonia levels, normalized brain water content and locomotor activity but did not demonstrate an effect on systemic oxidative stress. Also, AST-120 acts as an ammonia sink, efficiently removing blood-derived ammonia. Additional studies are warranted to evaluate the effects of AST-120 on hepatic encephalopathy in patients with advanced liver disease.

Pro-inflammatory cytokines are raised in extrahepatic portal venous obstruction, with minimal hepatic encephalopathy

BACKGROUND AND AIMS

Minimal hepatic encephalopathy (MHE) and hyperammonemia are seen in patients with extrahepatic portal venous obstruction (EHPVO). Inflammation has been shown to play an important role in the pathogenesis of hepatic encephalopathy in cirrhotics. This study assessed serum pro-inflammatory cytokines and their correlation with hyperammonemia, (1)H-magnetic resonance (MR) spectroscopy-derived brain glutamine, and diffusion tensor imaging (DTI)-derived metrics in patients with EPHVO, with and without MHE.

METHODS

Neuropsychological tests, DTI, (1)H-MR spectroscopy, and estimation of blood ammonia and pro-inflammatory cytokines (tumor necrosis factor-α[TNF-α] and interleukin-6 [IL-6]) were done in 20 patients with EHPVO and eight healthy controls.

RESULTS

Pro-inflammatory cytokines (TNF-α and IL-6), blood ammonia, brain glutamine, and mean diffusivity were increased in both patient groups, as compared to controls. Patients with MHE (n-12) had significantly higher TNF-α, IL-6, blood ammonia, brain glutamine, and mean diffusivity, signifying brain edema, than controls. A significant, positive correlation was seen between TNF-α and IL-6 and between blood ammonia and TNF-α, IL-6, and brain glutamine. Significant, positive correlations of TNF-α, IL-6, and blood ammonia with mean diffusivity values were seen in various brain regions, including spectroscopy voxel-derived mean diffusivity.

CONCLUSION

Patients with extrahepatic portal vein obstruction have inflammation and hyperammonemia made evident by higher blood TNF-α, IL-6, ammonia, and brain glutamine levels. A significant correlation between hyperammonemia, pro-inflammatory cytokines, and cerebral edema on DTI in various brain regions suggests that both these factors play a role in the pathogenesis of MHE in these patients.

Infection and systemic inflammation, not ammonia, are associated with Grade 3/4 hepatic encephalopathy, but not mortality in cirrhosis

BACKGROUND & AIMS

Patients with cirrhosis are prone to infection which is a frequent precipitant of hepatic encephalopathy (HE). Clinical studies have examined the importance of inflammation and infection in modulating the manifestation of symptoms of HE in acute liver failure and patients with cirrhosis and minimal/low grade HE. It would be logical to presume that this relationship persists in patients who develop severe HE in cirrhosis although this has not been examined to date.

METHODS

We report the findings of a prospective audit of 100 consecutive patients with cirrhosis admitted between Jan 2000 and March 2008 to a liver Intensive Care Unit (ICU) where HE was the primary indication for admission (59% Grade 3; 41% Grade 4). Haematological and microbiological data were collected at ICU admission, and organ scores and outcomes were recorded.

RESULTS

46% of patients had positive cultures taken within ± 48h from admission to ICU [25% blood] and a further 22% were culture negative but had evidence of systemic inflammation (SIRS). SIRS score (p=0.03) and SOFA score (p=0.006) were significantly higher in those patients with Grade 4 HE, who were also less likely to survive (p<0.001). HE grade/coma score did not correlate with ammonia, biochemistry or MELD score. Fifty-two percent of patients survived their ICU stay while the remainder developed progressive multiorgan failure and died; 38% survived to discharge, and 16% were transplanted.

CONCLUSIONS

These data support an association between infection/SIRS and not ammonia, in patients with cirrhosis that develop severe HE. The presence or absence of infection/SIRS did not determine survival.

Hepatic encephalopathy: from pathophysiology to therapeutic management

Hepatic encephalopathy is a complex and potentially reversible neuropsychiatric syndrome complicating acute or chronic liver disease. Clinical manifestations are multiple and varied, ranging from minimal neurological changes to coma. Ammonia is the main toxic substance involved in the pathogenesis of hepatic encephalopathy, although other mechanisms, such as modifications of the blood-brain barrier, disruptions in neurotransmission and abnormalities in GABAergic and benzodiazepine pathways may also play a role. The identification and treatment of precipitating factors is crucial in the management of patients with hepatic encephalopathy. Current treatments are based on reducing intestinal ammonia load by agents such as antibiotics or disaccharides, although their efficacy is yet to be clearly established.

Marked potentiation of cell swelling by cytokines in ammonia-sensitized cultured astrocytes

Background

Brain edema leading to high intracranial pressure is a lethal complication of acute liver failure (ALF), which is believed to be cytotoxic due to swelling of astrocytes. In addition to the traditional view that elevated levels of blood and brain ammonia are involved in the mechanism of brain edema in ALF, emerging evidence suggests that inflammatory cytokines also contribute to this process. We earlier reported that treatment of astrocyte cultures with a pathophysiological concentration of ammonia (5 mM NH₄Cl) resulted in the activation of nuclear factor-kappaB (NF-κB) and that inhibition of such activation diminished astrocyte swelling, suggesting a key role of NF-κB in the mechanism of ammonia-induced astrocyte swelling. Since cytokines are also well-known to activate NF-κB, this study examined for additive/synergistic effects of ammonia and cytokines in the activation of NF-κB and their role in astrocyte swelling.

Methods

Primary cultures of astrocytes were treated with ammonia and cytokines (TNF-α, IL-1, IL-6, IFN-γ, each at 10 ng/ml), individually or in combination, and cell volume was determined by the [³H]-O-methylglucose equilibration method. The effect of ammonia and cytokines on the activation of NF-κB was determined by immunoblots.

Results

Cell swelling was increased by ammonia (43%) and by cytokines (37%) at 24 h. Simultaneous co-treatment with cytokines and ammonia showed no additional swelling. By contrast, cultures pretreated with ammonia for 24 h and then exposed to cytokines for an additional 24 h, showed a marked increase in astrocyte swelling (129%). Treatment of cultures with ammonia or cytokines alone also activated NF-κB (80-130%), while co-treatment had no additive effect. However, in cultures pre-treated with ammonia for 24 h, cytokines induced a marked activation of NF-κB (428%). BAY 11-7082, an inhibitor of NF-κB, completely blocked the astrocyte swelling in cultures pre-treated with ammonia and followed by the addition of a mixture of cytokines.

Conclusion

Our results indicate that ammonia and a mixture of cytokines each cause astrocyte swelling but when these agents are added simultaneously, no additive effects were found. On the other hand, when cells were initially treated with ammonia and 24 h later given a mixture of cytokines, a marked potentiation in cell swelling and NF-κB activation occurred. These data suggest that the potentiation in cell swelling is a consequence of the initial activation of NF-κB by ammonia. These findings provide a likely mechanism for the exacerbation of brain edema in patients with ALF in the setting of sepsis/inflammation.

Serum proinflammatory cytokines correlate with diffusion tensor imaging derived metrics and 1H-MR spectroscopy in patients with acute liver failure

Hyperammonemia and inflammation are major contributing factors in the development of cerebral edema (CE) in acute liver failure (ALF). Aim of this study was to look for the relationship between proinflammatory cytokines with diffusion tensor imaging (DTI) derived metrics and (1)H-MR spectroscopy ((1)H-MRS) derived Glutamate/Glutamine (Glx). Fourteen patients with ALF and 14 age/sex matched controls were included in this study. All subjects had undergone clinical, biochemical, MR imaging and (1)H-MRS studies. Serum proinflammatory cytokines (IL-6 and TNF-α), blood ammonia level and Glx were computed for independent t-test and Pearson correlation. Serum proinflammatory cytokines, blood ammonia level and brain Glx were significantly increased in ALF patients as compared to controls. Blood ammonia level and Glx showed significant positive correlation with proinflammatory cytokines. Spectroscopy voxel derived spherical anisotropy (CS) showed positive correlation with Glx while mean diffusivity (MD) showed negative correlation. Proinflammatory cytokines showed positive correlation with CS and negative correlation with MD in various brain regions including spectroscopy voxel. Significant correlation of Glx, CS and MD with proinflammatory cytokines suggests that both DTI derived metrics and (1)H-MRS measure the synergistic effect of hyperammonemia and proinflammatory cytokines and may be used as non-invasive tools for understanding the pathogenesis of CE in ALF.

Changing face of hepatic encephalopathy: Role of inflammation and oxidative stress

The face of hepatic encephalopathy (HE) is changing. This review explores how this neurocognitive disorder, which is associated with both acute and chronic liver injury, has grown to become a dynamic syndrome that spans a spectrum of neuropsychological impairment, from normal performance to coma. The central role of ammonia in the pathogenesis of HE remains incontrovertible. However, over the past 10 years, the HE community has begun to characterise the key roles of inflammation, infection, and oxidative/nitrosative stress in modulating the pathophysiological effects of ammonia on the astrocyte. This review explores the current thoughts and evidence base in this area and discusses the potential role of existing and novel therapies that might abrogate the oxidative and nitrosative stresses inflicted on the brain in patients with, or at risk of developing, HE.

Role of aquaporin-4 in the development of brain oedema in liver failure

BACKGROUND & AIMS

Liver failure is associated with progressive cytotoxic brain oedema (astrocyte swelling), which underlies hepatic encephalopathy (HE). Ammonia and superimposed inflammation are key synergistic factors in HE, but the mechanism(s) involved remain unknown. We aimed to determine whether aquaporin-4 (AQP4), an astrocyte endfeet bi-directional water channel, is associated with the brain oedema of HE.

METHOD

Rats (n=60) received sham-operation (sham), 5 days hyperammonaemia-inducing diet (HD), galactosamine (GALN) induced acute liver failure (ALF), 4 weeks bile duct-ligation (BDL) induced cirrhosis, or caecal ligation and puncture (CLP), a 24h model of bacterial peritonitis. Rats from every group (except CLP) were randomised to receive intraperitoneal injections of lipopolysaccharide (LPS; 1mg/kg) or saline, prior to termination 3h later. Brain water, AQP4 protein expression (western blot) and AQP4 localisation by immunogold electron microscopy were investigated.

RESULTS

Significant hyperammonaemia was observed in saline-injected BDL (p<0.05), GALN (p<0.01), and HD (p<0.01), compared to sham rats. LPS injection did not affect arterial ammonia or plasma biochemistry in any of the treatment groups. Increased brain water was observed in saline-injected GALN (p<0.05), HD (p<0.01), and CLP (p<0.001) compared to sham rats. Brain water was numerically increased in BDL rats, but this failed to reach significance (p=0.09). LPS treatment further increased oedema significantly in all treatment groups (p<0.05, respectively). AQP4 expression was significantly increased in saline-injected BDL (p<0.05), but not other treatment groups, compared to sham rats. Membrane polarisation was maintained in BDL rats.

CONCLUSION

The results suggest that AQP4 is not directly associated with the development of brain oedema in liver failure, hyperammonaemia, or sepsis. In cirrhosis, there is increased AQP4 protein expression, but membrane polarisation, is maintained, possibly in a compensatory attempt to limit severe brain oedema.

Ammonia and the neutrophil in the pathogenesis of hepatic encephalopathy in cirrhosis

Hepatic encephalopathy (HE) constitutes a neuropsychiatric syndrome which remains a major clinical problem in patients with cirrhosis. In the severest form of HE, cirrhotic patients may develop varying degrees of confusion and coma. Ammonia has been regarded as the key precipitating factor in HE, and astrocytes have been the most commonly affected cells neuropathologically. Although the evidence base supporting a pivotal role of ammonia is robust, in everyday clinical practice a consistent correlation between the concentration of ammonia in the blood and the manifest symptoms of HE is not observed. More recently the synergistic role of inflammation and infection in modulating the cerebral effects of ammonia has been shown to be important. Furthermore, it has been recognized that infection impairs brain function both in the presence and absence of liver disease. Thus it could be postulated that in the presence of ammonia, the brain is sensitized to a systemic inflammatory stimulus and is able to elicit an inflammatory response involving both proinflammatory and neurotransmitter pathways. Ammonia is not only directly toxic to astrocytes but induces neutrophil dysfunction with the release of reactive oxygen species, which contribute to oxidative stress and systemic inflammation. This may further exacerbate the cerebral effects of ammonia and potentially reduce the capacity of the neutrophil to fight microbial attack, thus inducing a vicious circle. This evidence supports the neutrophil in addition to ammonia as being culpable in the pathogenesis of HE, making the neutrophil a target for future anti-inflammatory therapeutic strategies in addition to ammonia lowering therapies.

Cerebral net exchange of large neutral amino acids after lipopolysaccharide infusion in healthy humans

INTRODUCTION

Alterations in circulating large neutral amino acids (LNAAs), leading to a decrease in the plasma ratio between branched-chain and aromatic amino acids (BCAA/AAA ratio), may be involved in sepsis-associated encephalopathy. We hypothesised that a decrease in the BCAA/AAA ratio occurs along with a net cerebral influx of the neurotoxic AAA phenylalanine in a human experimental model of systemic inflammation.

METHODS

The BCAA/AAA ratio, the cerebral delivery, and net exchange of LNAAs and ammonia were measured before and 1 hour after a 4-hour intravenous infusion of Escherichia coli lipopolysaccharide (LPS) in 12 healthy young men.

RESULTS

LPS induced systemic inflammation, reduced the BCAA/AAA ratio, increased the cerebral delivery and unidirectional influx of phenylalanine, and abolished the net cerebral influx of the BCAAs leucine and isoleucine. Furthermore, a net cerebral efflux of glutamine, which was independent of the cerebral net exchange of ammonia, was present after LPS infusion.

CONCLUSIONS

Systemic inflammation may affect brain function by reducing the BCAA/AAA ratio, thereby changing the cerebral net exchange of LNAAs.

Interaction of oxidative stress, astrocyte swelling and cerebral ammonia toxicity

PURPOSE OF REVIEW

Description of the role of oxidative stress in the pathogenesis of cerebral ammonia toxicity and hepatic encephalopathy.

RECENT FINDINGS

Ammonia plays a key role in the pathogenesis of hepatic encephalopathy, which manifests as a neuropsychiatric syndrome accompanying acute and chronic liver failure. One consequence of ammonia action on the brain is astrocyte swelling, which triggers the generation of oxidative/nitrosative stress at the level of NADPH oxidase, nitric oxide synthases and the mitochondria. A self-amplifying signaling loop between oxidative stress and astrocyte swelling has been proposed. Consequences of the ammonia-induced oxidative/nitrosative stress response are protein modifications through nitration of tyrosine residues and oxidation of astrocytic and neuronal RNA. Nitrosative stress also mobilizes zinc from intracellular stores with impact on gene expression. These alterations may at least in part mediate cerebral ammonia toxicity through disturbances of intracellular and intercellular signaling and of synaptic plasticity.

SUMMARY

Oxidative/nitrosative stress and a low-grade cerebral edema as key events in the pathogenesis of ammonia toxicity and hepatic encephalopathy may offer potential new strategies for treatment. Ammonia-induced oxidation of RNA and proteins may impair postsynaptic protein synthesis, which is critically involved in learning and memory consolidation. RNA oxidation offers a novel explanation for multiple disturbances of neurotransmitter systems and gene expression and the cognitive deficits observed in hepatic encephalopathy.

Severe sepsis in cirrhosis

Sepsis is physiologically viewed as a proinflammatory and procoagulant response to invading pathogens. There are three recognized stages in the inflammatory response with progressively increased risk of end-organ failure and death: sepsis, severe sepsis, and septic shock. Patients with cirrhosis are prone to develop sepsis, sepsis-induced organ failure, and death. There is evidence that in cirrhosis, sepsis is accompanied by a markedly imbalanced cytokine response ("cytokine storm"), which converts responses that are normally beneficial for fighting infections into excessive, damaging inflammation. Molecular mechanisms for this excessive proinflammatory response are poorly understood. In patients with cirrhosis and severe sepsis, high production of proinflammatory cytokines seems to play a role in the worsening of liver function and the development of organ/system failures such as shock, renal failure, acute lung injury or acute respiratory distress syndrome, coagulopathy, or hepatic encephalopathy. In addition, these patients may have sepsis-induced hyperglycemia, defective arginine-vasopressin secretion, adrenal insufficiency, or compartmental syndrome. In patients with cirrhosis and spontaneous bacterial peritonitis (SBP), early use of antibiotics and intravenous albumin administration decreases the risk for developing renal failure and improves survival. There are no randomized studies that have been specifically performed in patients with cirrhosis and severe sepsis to evaluate treatments that have been shown to improve outcome in patients without cirrhosis who have severe sepsis or septic shock. These treatments include recombinant human activated C protein and protective-ventilation strategy for respiratory failure. Other treatments should be evaluated in the cirrhotic population with severe sepsis including the early use of antibiotics in "non-SBP" infections, vasopressor therapy, hydrocortisone, renal-replacement therapy and liver support systems, and selective decontamination of the digestive tract or oropharynx.

The interaction between high ammonia diet and bile duct ligation in developing rats: assessment by spatial memory and asymmetric dimethylarginine

Bile duct ligation (BDL) in developing rats causes cholestasis, impaired liver function and cognition. Because both nitric oxide (NO) and ammonia are implicated in hepatic encephalopathy (HE), we hypothesized that asymmetric dimethylarginine (ADMA), an endogenous NO synthase inhibitor, and ammonia affect cognition in young rats with BDL. Four groups of young male Sprague-Dawley rats ages 17 days were used: rat underwent laparotomy (SC group), rat underwent laparotomy plus a 30% ammonium acetate diet (SC+HA group), rat underwent BDL (BDL group), rats underwent BDL plus high ammonia diet (BDL+HA group). Spatial memory was assessed by Morris water maze task. Plasma was collected for biochemical and ADMA analyses. Liver and brain cortex were collected for determination of protein arginine methyltransferase-1 (PRMT1, ADMA-synthesizing enzyme) and dimethylarginine dimethylaminohydrolase (DDAH, ADMA-metabolizing enzyme). We found BDL group had significantly higher plasma direct/total bilirubin, aspartate aminotransferase, alanine aminotransferase, ADMA, liver p22(phox), and worse spatial performance as compared with SC group. High ammonia diet increased plasma ammonia and ADMA concentration, and aggravated spatial deficit in the presence of BDL-induced cholestasis. We conclude plasma ADMA plays a role in BDL-induced spatial deficit. High ammonia aggravated the spatial deficits encountered in cholestatic young rats.

L-ornithine and phenylacetate synergistically produce sustained reduction in ammonia and brain water in cirrhotic rats

Treatment of hyperammonemia and hepatic encephalopathy in cirrhosis is an unmet clinical need. The aims of this study were to determine whether L-ornithine and phenylacetate/phenylbutyrate (administered as the pro-drug phenylbutyrate) (OP) combined are synergistic and produce sustained reduction in ammonia by L-ornithine acting as a substrate for glutamine synthesis, thereby detoxifying ammonia, and the phenylacetate excreting the ornithine-derived glutamine as phenylacetylglutamine in the urine. Sprague-Dawley rats were studied 4 weeks after bile duct ligation (BDL) or sham operation. Study 1: Three hours before termination, an internal carotid sampling catheter was inserted, and intraperitoneal saline (placebo), OP, phenylbutyrate, or L-ornithine were administered after randomization. BDL was associated with significantly higher arterial ammonia and brain water and lower brain myoinositol (P < 0.01, respectively), compared with sham-operated controls, which was significantly improved in the OP-treated animals; arterial ammonia (P < 0.001), brain water (P < 0.05), brain myoinositol (P < 0.001), and urinary phenylacetylglutamine (P < 0.01). Individually, L-ornithine or phenylbutyrate were similar to the BDL group. In study 2, BDL rats were randomized to saline or OP administered intraperitoneally for 6 hours or 3, 5, or 10 days and were sacrificed between 4.5 and 5 weeks. The results showed that the administration of OP was associated with sustained reduction in arterial ammonia (P < 0.01) and brain water (P < 0.01) and markedly increased arterial glutamine (P < 0.01) and urinary excretion of phenylacetylglutamine (P < 0.01) in each of the OP treated groups.

CONCLUSION

The results of this study provide proof of the concept that L-ornithine and phenylbutyrate/phenylacetate act synergistically to produce sustained improvement in arterial ammonia, its brain metabolism, and brain water in cirrhotic rats.

Cerebral microglia recruit monocytes into the brain in response to tumor necrosis factoralpha signaling during peripheral organ inflammation

In inflammatory diseases occurring outside the CNS, communication between the periphery and the brain via humoral and/or neural routes results in central neural changes and associated behavioral alterations. We have recently identified another immune-to-CNS communication pathway in the setting of organ-centered peripheral inflammation: namely, the entrance of immune cells into the brain. In our current study, using a mouse model of inflammatory liver injury, we have confirmed the significant infiltration of activated monocytes into the brain in mice with hepatic inflammation and have defined the mechanism that mediates this trafficking of monocytes. Specifically, we show that in the presence of hepatic inflammation, mice demonstrate elevated cerebral monocyte chemoattractant protein (MCP)-1 levels, as well as increased numbers of circulating CCR2-expressing monocytes. Cerebral recruitment of monocytes was abolished in inflamed mice that lacked MCP-1/CCL2 or CCR2. Furthermore, in mice with hepatic inflammation, microglia were activated and produced MCP-1/CCL2 before cerebral monocyte infiltration. Moreover, peripheral tumor necrosis factor (TNF)alpha signaling was required to stimulate microglia to produce MCP-1/CCL2. TNFalpha signaling via TNF receptor 1 (TNFR1) is required for these observed effects since in TNFR1 deficient mice with hepatic inflammation, microglial expression of MCP-1/CCL2 and cerebral monocyte recruitment were both markedly inhibited, whereas there was no inhibition in TNFR2 deficient mice. Our results identify the existence of a novel immune-to-CNS communication pathway occurring in the setting of peripheral organ-centered inflammation which may have specific implications for the development of alterations in cerebral neurotransmission commonly encountered in numerous inflammatory diseases occurring outside the CNS.

Signaling factors in the mechanism of ammonia neurotoxicity

Mechanisms involved in hepatic encephalopathy (HE) still remain poorly understood. It is generally accepted that ammonia plays a major role in this disorder, and that astrocytes represent the principal target of ammonia neurotoxicity. In recent years, studies from several laboratories have uncovered a number of factors and pathways that appear to be critically involved in the pathogenesis of this disorder. Foremost is oxidative and nitrosative stress (ONS), which is largely initiated by an ammonia-induced increase in intracellular Ca(2+). Such increase in Ca(2+) activates a number of enzymes that promote the synthesis of reactive oxygen-nitrogen species, including constitutive nitric oxide synthase, NADPH oxidase and phospholipase A2. ONS subsequently induces the mitochondrial permeability transition, and activates mitogen-activated protein kinases and the transcription factor, nuclear factor-kappaB (NF-kappaB). These factors act to generate additional reactive oxygen-nitrogen species, to phosphorylate various proteins and transcription factors, and to cause mitochondrial dysfunction. This article reviews the role of these factors in the mechanism of HE and ammonia toxicity with a focus on astrocyte swelling and glutamate uptake, which are important consequences of ammonia neurotoxicity. These pathways and factors provide attractive targets for identifying agents potentially useful in the therapy of HE and other hyperammonemic disorders.

Role of artificial liver support in hepatic encephalopathy

Hepatic encephalopathy (HE) refers to the reversible neuropsychiatric disorders observed in acute liver failure and as a complication of cirrhosis and/or portal hypertension. This review aims to describe the pathophysiology of HE, the rationale for the use of artificial liver support in the treatment of HE, the different concepts of artificial liver support and the results obtained. Ammonia has been considered central to its pathogenesis but recently an important role for its interaction with inflammatory responses and auto-regulation of cerebral hemodynamics has been suggested. Artificial liver support might be able to decrease ammonia and modulate inflammatory mediators and cerebral hemodynamics. Bioartificial liver support systems use hepatocytes in an extracorporeal device connected to the patient's circulation. Artificial liver support is intended to remove protein-bound toxins and water-soluble toxins without providing synthetic function. Both systems improve clinical and biochemical parameters and can be applied safely to patients. Clinical studies have shown that artificial liver support, especially albumin dialysis, is able to improve HE in acute and acute-on-chronic liver failure. Further studies are required to better understand the mechanism, however, artificial liver support can be added to the therapeutic bundle in treating HE.

S 35171 exerts protective effects in spontaneously hypertensive stroke-prone rats by preserving mitochondrial function

S 35171 is one of a family of compounds that have been designed to protect mitochondrial function. We tested the hypothesis that S 35171 exerts protective effects in spontaneously hypertensive stroke-prone rats (SHRSPs), an animal model developing spontaneous brain damage preceded by proteinuria and systemic inflammation revealed by the urinary accumulation of acute-phase proteins (APPs) originating in the liver. Male SHRSPs fed a permissive diet received vehicle or S 35171 (10 mg/kg/day) started simultaneously with a high-sodium diet (group A) or after the establishment of proteinuria (group B). The drug delayed urinary APPs accumulation and the appearance of magnetic resonance imaging (MRI)-monitored brain lesions (after 62+/-3 days in group A, and 51+/-2 days in controls, P<0.01). The delay was more pronounced in group B as 30% of the animals survived the entire 90-day experimental period without brain abnormality. Proteomic analysis showed no significant alteration in the expression pattern of brain mitochondrial proteins, but the liver mitochondrial levels of carbamoylphosphate synthase I (CPS-I), an enzyme involved in urea metabolism) and the antioxidant peroxiredoxin-3 spot were affected by hypertension and S 35171. Stress reduces CPS-I and induces the peroxiredoxin-3 spot, whereas S 35171 brought about normal CPS-I expression and a 12-fold higher level of the peroxiredoxin-3 spot. As both enzymes are involved in maintaining mitochondrial functions, their increased expression after S 35171 treatment may be responsible for delaying the pathological condition that leads to the development of brain damage in SHRSPs.

Ammonia impairs neutrophil phagocytic function in liver disease

Hyperammonemia is a feature of liver failure, which is associated with increased risk of infection. The aims of the present study were to determine in vitro, in rats fed an ammoniagenic diet and in patients with cirrhosis, whether induction of hyperammonemia results in neutrophil dysfunction. As hyperammonemia produces cell swelling, we explored the role of the osmoregulating, p38 mitogen-activated protein kinase (p38(MAPK)) pathway in mediating this neutrophil dysfunction. Neutrophils were isolated from blood of healthy volunteers and incubated with either 75 microM ammonia or phosphate-buffered saline. Both groups were studied under hyponatremic conditions and/or with the addition of p38(MAPK) modulators. Neutrophil phagocytosis was measured in naive rats and rats fed an ammoniagenic diet and in patients with stable cirrhosis given placebo (n = 8) or an amino acid solution inducing hyperammonemia (n = 8). Cell volume and phagocytosis was analyzed by fluorescent-activated cell sorting using fluorescein isothiocyanate-labeled E. coli. p38(MAPK) phosphorylation was measured by western blotting. In healthy neutrophils incubated with ammonia and in rats fed an ammoniagenic diet, neutrophils showed evidence of swelling, impaired phagocytosis, and increased spontaneous oxidative burst compared to controls. Phagocytosis was significantly impaired in patients with induced hyperammonemia compared to placebo. The effects of hyperammonemia and hyponatremia were synergistic. The p38(MAPK) intracellular signaling pathways were activated in healthy neutrophils exposed to ammonia in association with increased burst activity. Neutrophil phagocytic dysfunction was abrogated by the addition of a p38(MAPK) agonist.

CONCLUSION

Ammonia produces neutrophil swelling and impairs neutrophil phagocytosis. The p38(MAPK) intracellular signaling pathway has been shown to be important in mediating the ammonia-induced neutrophil dysfunction.