Increased brain concentrations of polyamines in rats with encephalopathy due to a galactosamine-induced fulminant hepatic failure

Exchange-mode glutamine transport across CNS cell membranes

CNS cell membranes possess four transporters capable of exchanging Lglutamine (Gln) for other amino acids: the large neutral amino acid (LNAA) transporters LAT1 and LAT2, the hybrid basic amino acid (L-arginine (Arg), L-leucine (Leu)/LNAA transporter y⁺LAT2, and the L-alanine/L-serine/L-cysteine transporter 2 (ASCT2). LAT1/LAT2 and y⁺LAT2 are present in astrocytes, neurons and the blood brain barrier (BBB) - forming cerebral vascular endothelial cells (CVEC), while the location of ASCT2 in the individual cell types is a matter of debate. In the healthy brain, contribution of the exchangers to Gln shuttling from astrocytes to neurons and thus their role in controlling the conversion of Gln to the amino acid neurotransmitters l-glutamate (Glu) and γ-aminobutyric acid (GABA) and Gln flux across the BBB appears negligible as compared to the system A and system N uniporters. Insofar, except for the contribution of LAT1 to the maintenance of Gln homeostasis in the interstitial fluid (ISF), no well-defined CNS-specific function has been established for either of the three transporters in the healthy brain. The Gln-accepting amino acid exchangers appear to gain significance under conditions of excessive brain Gln load (glutaminosis). Excess Gln efflux across the BBB enhances influx into the brain of L-tryptophan (Trp). Excess of Trp is responsible for overloading the brain with neuroactive compounds: serotonin, kynurenic acid, quinolinic acid and/or oxindole, which contribute to neurotransmission imbalance accompanying hyperammonemia. In turn, alterations of y⁺LAT2-mediated Gln/Arg exchange and Arg uptake in astrocyte, modulate astrocytic nitric oxide synthesis and oxidative/nitrosative stress in ammonia-overexposed brain. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

Hepatoprotective and behavioral effects of jigrine in galactosamine-induced hepatopathy in rats

The hepatoprotective activity of jigrine, a polypharmaceutical herbal formulation, at a dose of 1 mL/kg/day p.o. was evaluated against galactosamine (400 mg/kg b.wt.)-induced hepatopathy in rats. Biochemical parameters such as alanine trasaminase (ALT), alkaline phosphatase (ALP), and bilirubin were estimated to assess liver function. Jigrine was also evaluated for its effect on the possible behavioral alterations secondary to liver damage produced by galactosamine (d-Gal) administration in rats. The d-Gal-induced elevation in serum levels of ALT, ALP, and bilirubin was significantly reduced (p values <0.01, <0.01, and <0.05, respectively) in jigrine- and silymarin-pretreated rats. Jigrine pretreatment also exhibited beneficial effects on d-Gal-induced behavioral abnormalities in rats. Silymarin (25 mg/kg/day p.o.) was used as reference standard. The biochemical observations were supplemented with histopathological examination of rat liver sections. Histopathological evaluation showed marked improvement in the livers of jigrine- and silymarin-treated animals.

A surgical model of fulminant hepatic failure in rabbits

AIM

Animal models of fulminant hepatic failure (FHF) have been developed for characterization of disease progression and to evaluate the effectiveness of liver-assist devices, some by treatment with hepatotoxic drugs, viral hepatitis or surgical procedures. We have developed a model in the rabbit by combining resection of the three anterior lobes with ligation of the pedicle of the right lateral lobes, resulting in liver necrosis; the remnant quadrate lobes are left intact.

MATERIALS AND METHODS

Adult male New Zealand white rabbits (n=16) were used. Six animals were killed to measure the weight of the separate liver lobes. The others (n=10) underwent left neck central line placement to monitor continuous blood pressure and collect blood for laboratory analysis, and a burr hole on the right parietal bone to monitor the intracranial pressure (ICP). Blood laboratory analysis, clinical hepatic encephalopathy and ICP levels were measured in FHF animals (n=6). Animals (n=4) undergoing a sham operation served as controls.

RESULTS

All FHF animals died between 12 and 26 h after liver surgery from FHF characterized by a progressive increase in liver enzymes, ammonia, total bilirubin, coagulopathy, hepatic encephalopathy and intracranial hypertension. Histological features of the ischaemic lobes showed coagulative necrosis of hepatocytes with absence of nuclei and collapse of cell plates. Brain histology revealed hypoxic cell damage.

CONCLUSION

We have developed a simple, reproducible model of FHF in rabbits that has a number of features comparable with clinical FHF patients and is well suited for testing experimental bioartificial liver systems and investigating the pathogenesis of FHF.