Diffusion Tensor Imaging Supports the Cytotoxic Origin of Brain Edema in a Rat Model of Acute Liver Failure

doi:10.1053/j.gastro.2009.10.003

Gastroenterology

Volume 138, Issue 4, April 2010, Pages 1566-1573

https://doi.org/10.1053/j.gastro.2009.10.003 Get rights and content

Background & Aims

Brain edema is a severe complication of acute liver failure (ALF) that has been related to ammonia concentrations. Two mechanisms have been proposed in the pathogenesis: vasogenic edema that is secondary to the breakdown of the blood–brain barrier and cytotoxic edema caused by ammonia metabolites in astrocytes.

Methods

We applied magnetic resonance techniques to assess the intracellular or extracellular distribution of brain water and metabolites in a rat model of devascularized ALF. The brain water content was assessed by gravimetry and blood–brain barrier permeability was determined from the transfer constant of ¹⁴C-labeled sucrose.

Results

Rats with ALF had a progressive decrease in the apparent diffusion coefficient (ADC) in all brain regions. The average decrease in ADC was significant in precoma (−14%) and coma stages (−20%). These changes, which indicate an increase of the intracellular water compartment, were followed by a significant increase in total brain water (coma 82.4% ± 0.3% vs sham 81.6% ± 0.3%; P = .0001). Brain concentrations of glutamine (6 hours, 540%; precoma, 851%; coma, 1086%) and lactate (6 hours, 166%; precoma, 998%; coma, 3293%) showed a marked increase in ALF that paralleled the decrease in ADC and neurologic outcome. In contrast, the transfer constant of ¹⁴C-sucrose was unaltered.

Conclusions

The pathogenesis of brain edema in an experimental model of ALF involves a cytotoxic mechanism: the metabolism of ammonia in astrocytes induces an increase of glutamine and lactate that appears to mediate cellular swelling. Therapeutic measures should focus on removing ammonia and improving brain energy metabolism.

Section snippets

Animal Models

This study was performed in Sprague–Dawley male rats (250–300 g; Harlan, Udine, Italy). Animals were housed in polycarbonate cages under standard laboratory conditions: a 12/12 hours light/dark cycle, a constant temperature of 22°C ± 2°C, and a relative humidity of approximately 50%. Standard food (A04; Panlab, Barcelona, Spain) and water were available ad libitum. All procedures were performed in accordance with Spanish legislation and approved by the Catalan Animal Research Committee in the

Experiment A: PCA rats

PCA rats did not show any change either in T2 or ADC values in all the studied regions (data not shown). However, the metabolic profile obtained by MR-spectroscopy was significantly altered (Figure 2): myoinositol and choline derivates decreased (ratio of myoinositol to creatine: PCA, 0.750 ± 0.121, versus sham, 0.908 ± 0.111, P = .040; ratio of choline derivates to creatine [GPC + PCh/Cr]: PCA, 0.134 ± 0.0013, versus sham, 0.219 ± 0.009, P < .001), whereas glutamine and lactate increased

Discussion

The study shows a decrease in the ADC in an experimental model of ALF in which the development of brain edema can be shown. This observation is in accordance with a cytotoxic origin of brain edema that is supported by the lack of increase in the BBB permeability to ¹⁴C-sucrose.

No MR techniques are easily available to quantify brain water in vivo. In their absence, diffusion-weighted imaging has been used to investigate different experimental situations that are accompanied with brain edema. The

References (35)

A.T. Blei et al.
Pathophysiology of cerebral edema in fulminant hepatic failure
J Hepatol
(1999)
J. Cordoba et al.
Glutamine, myo-inositol, and organic brain osmolytes after portocaval anastomosis in the rat: implications for ammonia-induced brain edema
Hepatology
(1996)
J. Cordoba et al.
The development of low-grade cerebral edema in cirrhosis is supported by the evolution of (1)H-magnetic resonance abnormalities after liver transplantation
J Hepatol
(2001)
J.H. Nguyen et al.
Matrix metalloproteinase-9 contributes to brain extravasation and edema in fulminant hepatic failure mice
J Hepatol
(2006)
J.P. Donovan et al.
Cerebral oedema and increased intracranial pressure in chronic liver disease
Lancet
(1998)
N. Chatauret et al.
Effects of hypothermia on brain glucose metabolism in acute liver failure: a H/C-nuclear magnetic resonance study
Gastroenterology
(2003)
F. Tofteng et al.
Cerebral microdialysis in patients with fulminant hepatic failure
Hepatology
(2002)
R. Friolet et al.
In vivo 31P NMR spectroscopy of energy rich phosphates in the brain of the hyperammonemic rat
Biochem Biophys Res Commun
(1989)
F. Staub et al.
Swelling of glial cells in lactacidosis and by glutamate: significance of Cl(-)-transport
Brain Res
(1993)
J.R. McConnell et al.
Proton spectroscopy of brain glutamine in acute liver failure
Hepatology
(1995)

J. Cordoba et al.

Brain edema and hepatic encephalopathy

Semin Liver Dis

(1996)

I. Loubinoux et al.

Spreading of vasogenic edema and cytotoxic edema assessed by quantitative diffusion and T2 magnetic resonance imaging

Stroke

(1997)

D. Haussinger et al.

Pathogenetic mechanisms of hepatic encephalopathy

Gut

(2008)

R. Lodi et al.

Diffusion MRI shows increased water apparent diffusion coefficient in the brains of cirrhotics

Neurology

(2004)

M. Kato et al.

Electron microscopic study of brain capillaries in cerebral edema from fulminant hepatic failure

Hepatology

(1992)

C. Pierpaoli et al.

Histopathologic correlates of abnormal water diffusion in cerebral ischemia: diffusion-weighted MR imaging and light and electron microscopic study

Radiology

(1993)

S.H. Lee et al.

Portacaval shunt in the rat

Surgery

(1961)

Cited by (47)

Interstitial ion homeostasis and acid-base balance are maintained in oedematous brain of mice with acute toxic liver failure
2018, Neurochemistry International
Citation Excerpt :
There is a consensus that human ALF of varying causes is associated with decreased ADC, which is interpreted to reflect domination of cytotoxic oedema over vasogenic oedema (Chavarria and Cordoba, 2015, and references therein). Decreased ADC was also recorded in the liver devascularization ALF model in rat (Chavarria et al., 2010). The here observed significant decrease of ADC in the AOM model (Fig. 1A) provides, to our knowledge for the first time, distinctive evidence for cytotoxic oedema in ATLF.
Acute toxic liver failure (ATLF) rapidly leads to brain oedema and neurological decline. We evaluated the ability of ATLF-affected brain to control the ionic composition and acid-base balance of the interstitial fluid. ATLF was induced in 10–12 weeks old male C57Bl mice by single intraperitoneal (i.p.) injection of 100 μg/g azoxymethane (AOM). Analyses were carried out in cerebral cortex of precomatous mice 20–24 h after AOM administration. Brain fluid status was evaluated by measuring apparent diffusion coefficient [ADC] using NMR spectroscopy, Evans Blue extravasation, and accumulation of an intracisternally-injected fluorescent tracer. Extracellular pH ([pH]_e) and ([K⁺]_e) were measured in situ with ion-sensitive microelectrodes. Cerebral cortical microdialysates were subjected to photometric analysis of extracellular potassium ([K⁺]_e), sodium ([Na⁺]_e) and luminometric assay of extracellular lactate ([Lac]_e). Potassium transport in cerebral cortical slices was measured ex vivo as ⁸⁶Rb uptake. Cerebral cortex of AOM-treated mice presented decreased ADC supporting the view that ATLF-induced brain oedema is primarily cytotoxic in nature. In addition, increased Evans blue extravasation indicated blood brain barrier leakage, and increased fluorescent tracer accumulation suggested impaired interstitial fluid passage. However, [K⁺]_e, [Na⁺]_e, [Lac]_e, [pH]_e and potassium transport in brain of AOM-treated mice was not different from control mice. We conclude that in spite of cytotoxic oedema and deregulated interstitial fluid passage, brain of mice with ATLF retains the ability to maintain interstitial ion homeostasis and acid-base balance. Tentatively, uncompromised brain ion homeostasis and acid-base balance may contribute to the relatively frequent brain function recovery and spontaneous survival rate in human patients with ATLF.
MRS studies of neuroenergetics and glutamate/glutamine exchange in rats: Extensions to hyperammonemic models
2017, Analytical Biochemistry
Citation Excerpt :
Portocaval anastomosis (PCA) in rats is a popular model to study type B HE and is associated with limited liver dysfunction (liver atrophy and loss of perivenous hepatocytes) and hyperammonemia [93]. The main findings of these studies were increased cerebral glutamine and ammonia levels with sometimes reductions in brain osmolytes reflecting an osmoregulatory response [3,89,94–97]. In a PCA rat model, an additional increase in Lac/Cr was measured while no modifications were found for Glu/Cr and Tau/Cr [89].
In vivo Magnetic Resonance Spectroscopy is a useful tool to characterize brain biochemistry as well as its alteration in a large number of major central nervous system diseases. The present review will focus on the study of the glutamate-glutamine cycle, an important biochemical pathway in excitatory neurotransmission, analyzed using in vivo MRS of different accessible nuclei: ¹H, ¹³C, ¹⁵N and ³¹P. The different methodological aspects of data acquisition, processing and absolute quantification of the MRS data for each nucleus will be presented, as well as the description of the mathematical modeling approach to interpret the MRS measurements in terms of biochemical kinetics. The unique advantages of MRS, especially its non-invasive nature enabling longitudinal monitoring of brain disease progression and/or effect of treatment is illustrated in the particular context of hyperammonemic disorders with a specific focus on animal models. We review the current possibilities given by in vivo MRS to investigate some of the molecular mechanisms involved in hyperammonemic disorders and to give a better understanding of the process of development of hepatic encephalopathy, a severe neuropsychiatric disorder that frequently accompanies liver disease.
Evaluation of [<sup>14</sup>C] and [<sup>13</sup>C]Sucrose as Blood–Brain Barrier Permeability Markers
2017, Journal of Pharmaceutical Sciences
Nonspecific quantitation of [¹⁴C]sucrose in blood and brain has been routinely used as a quantitative measure of the in vivo blood–brain barrier (BBB) integrity. However, the reported apparent brain uptake clearance (K_in) of the marker varies widely (∼100-fold). We investigated the accuracy of the use of the marker in comparison with a stable isotope of sucrose ([¹³C]sucrose) measured by a specific liquid chromatography–tandem mass spectrometry method. Rats received single doses of each marker, and the K_in values were determined. Surprisingly, the K_in value of [¹³C]sucrose was 6- to 7-fold lower than that of [¹⁴C]sucrose. Chromatographic fractionation after in vivo administration of [¹⁴C]sucrose indicated that the majority of the brain content of radioactivity belonged to compounds other than the intact [¹⁴C]sucrose. However, mechanistic studies failed to reveal any substantial metabolism of the marker. The octanol:water partition coefficient of [¹⁴C]sucrose was >2-fold higher than that of [¹³C]sucrose, indicating the presence of lipid-soluble impurities in the [¹⁴C]sucrose solution. Our data indicate that [¹⁴C]sucrose overestimates the true BBB permeability to sucrose. We suggest that specific quantitation of the stable isotope (¹³C) of sucrose is a more accurate alternative to the current widespread use of the radioactive sucrose as a BBB marker.
Brain magnetic resonance in hepatic encephalopathy
2014, Seminars in Ultrasound, CT and MRI
The term hepatic encephalopathy (HE) covers a wide spectrum of neuropsychiatric abnormalities caused by portal-systemic shunting. The diagnosis requires demonstration of liver dysfunction or portal-systemic shunts and exclusion of other neurologic disorders. Most patients with this condition have liver dysfunction caused by cirrhosis, but it also occurs in patients with acute liver failure and less commonly, in patients with portal-systemic shunts that are not associated with hepatocellular disease. Various magnetic resonance (MR) techniques have improved our knowledge about the pathophysiology of HE. Proton MR spectroscopy and T1-weighted imaging can detect and quantify accumulations of brain products that are normally metabolized or eliminated such as glutamine and manganese. Other MR techniques such as T2-weighted and diffusion-weighted imaging can identify white matter abnormalities resulting from disturbances in cell volume homeostasis secondary to brain hyperammonemia. Partial or complete recovery of these abnormalities has been observed with normalization of liver function or after successful liver transplantation. MR studies have undoubtedly improved our understanding of the mechanisms involved in the pathogenesis of HE, and some findings can be considered biomarkers for monitoring the effects of therapeutic measures focused on correcting this condition.
Increased brain lactate is central to the development of brain edema in rats with chronic liver disease
2014, Journal of Hepatology
The pathogenesis of brain edema in patients with chronic liver disease (CLD) and minimal hepatic encephalopathy (HE) remains undefined. This study evaluated the role of brain lactate, glutamine and organic osmolytes, including myo-inositol and taurine, in the development of brain edema in a rat model of cirrhosis.
Six-week bile-duct ligated (BDL) rats were injected with ¹³C-glucose and de novo synthesis of lactate, and glutamine in the brain was quantified using ¹³C nuclear magnetic resonance spectroscopy (NMR). Total brain lactate, glutamine, and osmolytes were measured using ¹H NMR or high performance liquid chromatography. To further define the interplay between lactate, glutamine and brain edema, BDL rats were treated with AST-120 (engineered activated carbon microspheres) and dichloroacetate (DCA: lactate synthesis inhibitor).
Significant increases in de novo synthesis of lactate (1.6-fold, p <0.001) and glutamine (2.2-fold, p <0.01) were demonstrated in the brains of BDL rats vs. SHAM-operated controls. Moreover, a decrease in cerebral myo-inositol (p <0.001), with no change in taurine, was found in the presence of brain edema in BDL rats vs. controls. BDL rats treated with either AST-120 or DCA showed attenuation in brain edema and brain lactate. These two treatments did not lead to similar reductions in brain glutamine.
Increased brain lactate, and not glutamine, is a primary player in the pathogenesis of brain edema in CLD. In addition, alterations in the osmoregulatory response may also be contributing factors. Our results suggest that inhibiting lactate synthesis is a new potential target for the treatment of HE.
Brain edema in acute liver failure and chronic liver disease: Similarities and differences
2013, Neurochemistry International
Citation Excerpt :
Therefore, in the development of HE, increased brain lactate levels reflect energy impairment (dysregulations in lactate shuttle), as opposed to energy failure (a decrease in ATP). The role of lactate in astrocyte swelling has been well described in vitro (Staub et al., 1990) as well as in animal models of ALF (Chatauret et al., 2003; Chavarria et al., 2010; Sen et al., 2006; Zwingmann et al., 2003). In ALF rats, induced by liver-devascularization, an increase in brain lactate was found at coma stages with brain edema, along with an increase in de novo lactate synthesis from glucose (Zwingmann et al., 2003).
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.

View all citing articles on Scopus

: Conflicts of interest The authors disclose no conflicts

: Funding This project was supported by grant PI080698. CIBEREHD is supported by Instituto de Salud Carlos III.

View full text

Basic—Liver, Pancreas, and Biliary TractDiffusion Tensor Imaging Supports the Cytotoxic Origin of Brain Edema in a Rat Model of Acute Liver Failure

Background & Aims

Methods

Results

Conclusions

Section snippets

Animal Models

Experiment A: PCA rats

Discussion

J Hepatol

Hepatology

J Hepatol

J Hepatol

Lancet

Gastroenterology

Hepatology

Biochem Biophys Res Commun

Brain Res

Hepatology

Brain edema and hepatic encephalopathy

Semin Liver Dis

Spreading of vasogenic edema and cytotoxic edema assessed by quantitative diffusion and T2 magnetic resonance imaging

Stroke

Pathogenetic mechanisms of hepatic encephalopathy

Gut

Diffusion MRI shows increased water apparent diffusion coefficient in the brains of cirrhotics

Neurology

Electron microscopic study of brain capillaries in cerebral edema from fulminant hepatic failure

Hepatology

Histopathologic correlates of abnormal water diffusion in cerebral ischemia: diffusion-weighted MR imaging and light and electron microscopic study

Radiology

Portacaval shunt in the rat

Surgery

Basic—Liver, Pancreas, and Biliary Tract
Diffusion Tensor Imaging Supports the Cytotoxic Origin of Brain Edema in a Rat Model of Acute Liver Failure