Selective alterations of brain osmolytes in acute liver failure: protective effect of mild hypothermia.

The principal cause of mortality in patients with acute liver failure (ALF) is brain herniation resulting from intracranial hypertension caused by a progressive increase of brain water. In the present study, ex vivo high-resolution 1H-NMR spectroscopy was used to investigate the effects of ALF, with or without superimposed hypothermia, on brain organic osmolyte concentrations in relation to the severity of encephalopathy and brain edema in rats with ALF due to hepatic devascularization. In normothermic ALF rats, glutamine concentrations in frontal cortex increased more than fourfold at precoma stages, i.e. prior to the onset of severe encephalopathy, but showed no further increase at coma stages. In parallel with glutamine accumulation, the brain organic osmolytes myo-inositol and taurine were significantly decreased in frontal cortex to 63\% and 67\% of control values, respectively, at precoma stages (p<0.01), and to 58\% and 67\%, respectively, at coma stages of encephalopathy (p<0.01). Hypothermia, which prevented brain edema and encephalopathy in ALF rats, significantly attenuated the depletion of myo-inositol and taurine. Brain glutamine concentrations, on the other hand, did not respond to hypothermia. These findings demonstrate that experimental ALF results in selective changes in brain organic osmolytes as a function of the degree of encephalopathy which are associated with brain edema, and provides a further rationale for the continued use of hypothermia in the management of this condition.

Systemic and regional hemodynamics in pigs with acute liver failure and the effect of albumin dialysis.

OBJECTIVE: Acute liver failure (ALF) is haemodynamically characterized by a hyperdynamic circulation. The aims of this study were to investigate the systemic and regional haemodynamics in ALF, to measure changes in nitric oxide metabolites (NOx) and to evaluate whether these haemodynamic disturbances could be attenuated with albumin dialysis. MATERIAL AND METHODS: Norwegian Landrace pigs (23-30 kg) were randomly allocated to groups as controls (sham-operation, n = 8), ALF (hepatic devascularization, n = 8) and ALF + albumin dialysis (n = 8). Albumin dialysis was started 2 h after ALF induction and continued for 4 h. Systemic and regional haemodynamics were monitored. Creatinine clearance, nitrite/nitrate and catecholamines were measured. A repeated measures ANOVA was used to analyse the data. RESULTS: In the ALF group, the cardiac index increased (PGT < 0.0001), while mean arterial pressure (PG = 0.02) and systemic vascular resistance decreased (PGT < 0.0001). Renal resistance (PG = 0.04) and hind-leg resistance (PGT = 0.003) decreased in ALF. There was no difference in jejunal blood flow between the groups. ALF pigs developed renal dysfunction with increased serum creatinine (PGT = 0.002) and decreased creatinine clearance (P = 0.02). Catecholamines were significantly higher in ALF, but NOx levels were not different. Albumin dialysis did not attenuate these haemodynamic or renal disturbances. CONCLUSIONS: The haemodynamic disturbances during the early phase of ALF are characterized by progressive systemic vasodilatation with no associated changes in metabolites of NO. Renal vascular resistance decreased and renal dysfunction developed independently of changes in renal blood flow. After 4 h of albumin dialysis there was no attenuation of the haemodynamic or renal disturbances.

Contractile response of femoral arteries in pigs with acute liver failure.

BACKGROUND: Acute liver failure (ALF) is characterized haemodynamically by a progressive hyperdynamic circulation. The pathophysiological mechanism is unknown, but impaired contractility of vascular smooth muscle may play an important role. The aim of this study was to evaluate the vascular response to stimulation with norepinephrine and angiotensin II in endothelium-denuded femoral artery rings. METHODS: Norwegian Landrace pigs weighing 27.1 +/- 0.5 kg (mean +/- sx (standard error of the mean)) were used. ALF was induced by performing a portacaval shunt followed by ligation of the hepatic arteries (n = 6). Sham-operated animals served as controls (n = 5). Cumulative isometric concentration contraction curves were obtained after in vitro stimulation of the femoral artery rings with either angiotensin II (10(-13) - 10(-5) mol/L) or norepinephrine (10(-13) - 10(-3) mol/L). RESULTS: Pigs suffering from ALF developed a hyperdynamic circulation with an increased ca^rdiac index (P = 0.017) and decreased systemic vascular resistance index (P = 0.015). Studies of the hind leg revealed a decreased vascular resistance index and increased blood flow compared to sham-operated controls (P = 0.003 and P = 0.01, respectively). Angiotensin II caused a concentration-dependent contraction of the arterial segments, with no significant differences in vascular responses between the two groups. Maximum force generated did not differ (55 +/- 7 versus 56 +/- 7 mN, P = 0.95). Furthermore, there were no differences for norepinephrine in the cumulative concentration-response curves and the maximum contractile force was not significantly different (87 +/- 8 versus 93 +/- 16 mN, P = 0.55). CONCLUSIONS: This study documents for the first time that there are no signs of endothelium-independent peripheral vascular hyporesponsiveness to angiotensin II and norepinephrine in pigs with ALF.

Keeping cool in acute liver failure: rationale for the use of mild hypothermia.

Encephalopathy, brain edema and intracranial hypertension are neurological complications responsible for substantial morbidity/mortality in patients with acute liver failure (ALF), where, aside from liver transplantation, there is currently a paucity of effective therapies. Mirroring its cerebro-protective effects in other clinical conditions, the induction of mild hypothermia may provide a potential therapeutic approach to the management of ALF. A solid mechanistic rationale for the use of mild hypothermia is provided by clinical and experimental studies showing its beneficial effects in relation to many of the key factors that determine the development of brain edema and intracranial hypertension in ALF, namely the delivery of ammonia to the brain, the disturbances of brain organic osmolytes and brain extracellular amino acids, cerebro-vascular haemodynamics, brain glucose metabolism, inflammation, subclinical seizure activity and alterations of gene expression. Initial uncontrolled clinical studies of mild hypothermia in patients with ALF suggest that it is an effective, feasible and safe approach. Randomized controlled clinical trials are now needed to adequately assess its efficacy, safety, clinical impact on global outcomes and to provide the guidelines for its use in ALF.

Effect of albumin dialysis on intracranial pressure increase in pigs with acute liver failure: a randomized study.

BACKGROUND: Increased intracranial pressure (ICP) worsens the outcome of acute liver failure (ALF). This study investigates the underlying pathophysiological mechanisms and evaluates the therapeutic effect of albumin dialysis in ALF with use of the Molecular Adsorbents Recirculating System without hemofiltration/dialysis (modified, M-MARS). METHODS: Pigs were randomized into three groups: sham, ALF, and ALF + M-MARS. ALF was induced by hepatic devascularization (time = 0). M-MARS began at time = 2 and ended with the experiment at time = 6. ICP, arterial ammonia, brain water, cerebral blood flow (CBF), and plasma inflammatory markers were measured. RESULTS: ICP and arterial ammonia increased significantly over 6 hrs in the ALF group, in comparison with the sham group. M-MARS attenuated (did not normalize) the increased ICP in the ALF group, whereas arterial ammonia was unaltered by M-MARS. Brain water in the frontal cortex (grey matter) and in the subcortical white matter at 6 hrs was significantly higher in the ALF group than in the sham group. M-MARS prevented a rise in water content, but only in white matter. CBF and inflammatory mediators remained unchanged in all groups. CONCLUSION: The initial development of cerebral edema and increased ICP occurs independently of CBF changes in this noninflammatory model of ALF. Factor(s) other than or in addition to hyperammonemia are important, however, and may be more amenable to alteration by albumin dialysis.

Limited capacity for ammonia removal by brain in chronic liver failure: potential role of nitric oxide.

Chronic liver failure leads to hyperammonemia and consequently increased brain ammonia concentrations, resulting in hepatic encephalopathy. When the liver fails to regulate ammonia concentrations, the brain, devoid of a urea cycle, relies solely on the amidation of glutamate to glutamine through glutamine synthetase, to efficiently clear ammonia. Surprisingly, under hyperammonemic conditions, the brain is not capable of increasing its capacity to remove ammonia, which even decreases in some regions of the brain. This non-induction of glutamine synthetase in astrocytes could result from possible limiting substrates or cofactors for the enzyme, or an indirect effect of ammonia on glutamine synthetase expression. In addition, there is evidence that nitration of the enzyme resulting from exposure to nitric oxide could also be implicated. The present review summarizes these possible factors involved in limiting the increase in capacity of glutamine synthetase in brain, in chronic liver failure.

Manganese deposition in basal ganglia structures results from both portal-systemic shunting and liver dysfunction.

BACKGROUND & AIMS: Manganese (Mn) deposition could be responsible for the T(1)-weighted magnetic resonance signal hyperintensities observed in cirrhotic patients. These experiments were designed to assess the regional specificity of the Mn increases as well as their relationship to portal-systemic shunting or hepatobiliary dysfunction. METHODS: Mn concentrations were measured in (1) brain samples from basal ganglia structures (pallidum, putamen, caudate nucleus) and cerebral cortical structures (frontal, occipital cortex) obtained at autopsy from 12 cirrhotic patients who died in hepatic coma and from 12 matched controls; and from (2) brain samples (caudate/putamen, globus pallidus, frontal cortex) from groups (n = 8) of rats either with end-to-side portacaval anastomosis, with biliary cirrhosis, or with fulminant hepatic failure as well as from sham-operated and normal rats. RESULTS: Mn content was significantly increased in frontal cortex (by 38\%), occipital cortex (by 55\%), pallidum (by 186\%), putamen (by 66\%), and caudate (by 54\%) of cirrhotic patients compared with controls. Brain Mn content did not correlate with patient age, etiology of cirrhosis, or history of chronic hepatic encephalopathy. In cirrhotic and portacaval-shunted rats, Mn content was increased in pallidum (by 27\% and 57\%, respectively) and in caudate/putamen (by 57\% and 67\%, respectively) compared with control groups. Mn concentration in pallidum was significantly higher in portacaval-shunted rats than in cirrhotic rats. No significant changes in brain Mn concentrations were observed in rats with acute liver failure. CONCLUSIONS: These findings suggest that brain Mn deposition results both from portal-systemic shunting and from liver dysfunction.

Increased extracellular brain glutamate in acute liver failure: decreased uptake or increased release?

Glutamatergic dysfunction has been suggested to play an important role in the pathogenesis of hepatic encephalopathy (HE) in acute liver failure (ALF). Increased extracellular brain glutamate concentrations have consistently been described in different experimental animal models of ALF and in patients with increased intracranial pressure due to ALF. High brain ammonia levels remain the leading candidate in the pathogenesis of HE in ALF and studies have demonstrated a correlation between ammonia and increased concentrations of extracellular brain glutamate both clinically and in experimental animal models of ALE Inhibition of glutamate uptake or increased glutamate release from neurons and/or astrocytes could cause an increase in extracellular glutamate. This review analyses the effect of ammonia on glutamate release from (and uptake into) both neurons and astrocytes and how these pathophysiological mechanisms may be involved in the pathogenesis of HE in ALF.

Loss of noradrenaline transporter sites in frontal cortex of rats with acute (ischemic) liver failure.

There is increasing evidence that central noradrenaline (NA) transport mechanisms are implicated in the central nervous system complications of acute liver failure. In order to assess this possibility, binding sites for the high affinity NA transporter ligand [3H]-nisoxetine were measured by quantitative receptor autoradiography in the brains of rats with acute liver failure resulting from hepatic devascularization and in appropriate controls. In vivo microdialysis was used to measure extracellular brain concentrations of NA. Severe encephalopathy resulted in a significant loss of [3H]-nisoxetine sites in frontal cortex and a concomitant increase in extracellular brain concentrations of NA in rats with acute liver failure. A loss of transporter sites was also observed in thalamus of rats with acute liver failure. This loss of NA transporter sites could result from depletion of central NA stores due to a reserpine-like effect of ammonia which is known to accumulate to millimolar concentrations in brain in ischemic liver failure. Impaired NA transport and the consequent increase in synaptic concentrations and increased stimulation of neuronal and astrocytic noradrenergic receptors could be implicated in the pathogenesis of the encephalopathy and brain edema characteristic of acute liver failure.

Decreased glutamate transporter (GLT-1) expression in frontal cortex of rats with acute liver failure.

It has been suggested that reduced astrocytic uptake of neuronally released glutamate contributes to the pathogenesis of hepatic encephalopathy in acute liver failure. In order to further address this issue, the recently cloned and sequenced astrocytic glutamate transporter GLT-1 was studied in brain preparations from rats with ischemic liver failure induced by portacaval anastomosis followed 24 h later by hepatic artery ligation and from appropriate sham-operated controls. GLT-1 expression was studied using reverse transcriptase-polymerase chain reaction (RT-PCR). Expression of GLT-1 transcript was significantly decreased in frontal cortex at coma stages of acute liver failure. Western blotting using a polyclonal antibody to GLT-1 revealed a concomitant decrease in expression of transporter protein in the brains of rats with acute liver failure. Reduced capacity of astrocytes to reuptake neuronally released glutamate, resulting from a GLT-1 transporter deficit and the consequently compromised neuron-astrocytic trafficking of glutamate could contribute to the pathogenesis of hepatic encephalopathy and brain edema, two major complications of acute liver failure.