Pathogenesis of acute hepatic encephalopathy

Increased neuronal survival in the brainstem during liver injury: role of γ-aminobutyric acid and serotonin chitosan nanoparticles

γ-Aminobutyric acid (GABA)- and serotonin (5-HT)-mediated cell signaling, neuronal survival enhancement, and reduced neuronal death in brainstem during liver injury followed by active liver regeneration have a critical role in maintaining routine bodily functions. In the present study, GABAB and 5-HT2A receptor functional regulation, interrelated actions of neuronal survival factors, and expression of apoptotic factors in the brainstem during GABA and 5-HT chitosan nanoparticles-induced active liver regeneration in partially hepatectomized rats were evaluated. Partially hepatectomized rats were treated with the nanoparticles, and receptor assays and confocal microscopic studies of GABAB and 5-HT2A receptors, gene expression studies of GABAB and 5-HT2A receptors, nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNF-α), Akt-1, phospholipase C, Bax, and caspase-8 were performed with the brainstems of experimental animals. A significant decrease in GABAB and 5-HT2A receptor numbers and gene expressions denoted a homeostatic adjustment by the brain to trigger the sympathetic innervations during elevated DNA synthesis in the liver. The neuronal apoptosis resulting from the loss of liver function after partial hepatectomy was minimized by nanoparticle treatment in rats compared with rats with no treatment during regeneration. This was confirmed from the gene expression patterns of NF-κB, TNF-α, Akt-1, phospholipase C, Bax, and caspase-8. The present study revealed the potential of GABA and 5-HT chitosan nanoparticles for increasing neuronal survival in the brainstem during liver injury following regeneration, which avoids many neuropsychiatric problems.

Behavioral effects of subchronic inorganic manganese exposure in rats

BACKGROUND

Manganese, an essential micronutrient, is a potential neurotoxicant in prolonged overexposure. Parkinson-like syndrome, motor deficit, disturbed psychomotor development are typical signs of neuropathological alterations due to Mn in humans.

METHODS

Young adult rats, in three groups of 16 each, received 15 and 59 mg/kg b.w. MnCl(2), (control: distilled water) via gavage for 10 weeks, and were kept for further 12 weeks. Correlation of MnCl(2) exposure to body and organ weights, neurobehavioral effects (spatial memory, exploratory activity, psychomotor performance, pre-pulse inhibition), and histopathological changes (gliosis) was sought.

RESULTS

By the end of treatment, Mn accumulated in blood, cortex, hippocampus, and parenchymal tissues. Body and organ weights were reduced in high dose rats. All treated rats showed hypoactivity, decreased memory performance, and diminished sensorimotor reaction. In the dentate gyrus of these, GFAP immunoreactivity increased. During the post-treatment period, body weight of the high dose group remained decreased, locomotor activity returned to control, but the lasting effect of MnCl(2) could be revealed by amphetamine.

CONCLUSION

Using complex methodology, new data were obtained regarding the relationship between the long-term effects of MnCl(2) at neuronal and behavioral level.

Glutamate uptake

Brain tissue has a remarkable ability to accumulate glutamate. This ability is due to glutamate transporter proteins present in the plasma membranes of both glial cells and neurons. The transporter proteins represent the only (significant) mechanism for removal of glutamate from the extracellular fluid and their importance for the long-term maintenance of low and non-toxic concentrations of glutamate is now well documented. In addition to this simple, but essential glutamate removal role, the glutamate transporters appear to have more sophisticated functions in the modulation of neurotransmission. They may modify the time course of synaptic events, the extent and pattern of activation and desensitization of receptors outside the synaptic cleft and at neighboring synapses (intersynaptic cross-talk). Further, the glutamate transporters provide glutamate for synthesis of e.g. GABA, glutathione and protein, and for energy production. They also play roles in peripheral organs and tissues (e.g. bone, heart, intestine, kidneys, pancreas and placenta). Glutamate uptake appears to be modulated on virtually all possible levels, i.e. DNA transcription, mRNA splicing and degradation, protein synthesis and targeting, and actual amino acid transport activity and associated ion channel activities. A variety of soluble compounds (e.g. glutamate, cytokines and growth factors) influence glutamate transporter expression and activities. Neither the normal functioning of glutamatergic synapses nor the pathogenesis of major neurological diseases (e.g. cerebral ischemia, hypoglycemia, amyotrophic lateral sclerosis, Alzheimer's disease, traumatic brain injury, epilepsy and schizophrenia) as well as non-neurological diseases (e.g. osteoporosis) can be properly understood unless more is learned about these transporter proteins. Like glutamate itself, glutamate transporters are somehow involved in almost all aspects of normal and abnormal brain activity.

Renal elimination of protein S-100beta in pigs with acute encephalopathy

BACKGROUND

Protein S-100beta is an established biochemical marker for cerebral injury in serum. For the further interpretation and possible use of S-100beta serum measurements in acute hepatic encephalopathy, renal elimination of S-100beta was measured in pigs with elevated S-100beta levels due to hepatic encephalopathy.

METHODS

Eighteen female Norwegian Landrace pigs were randomly allocated to either hepatic devascularization (n=13) or sham operation (n=5). Repeated samples from the common carotid artery, right renal vein, and urine were simultaneously drawn for S-100beta analysis, using the Sangtec100 Liamat immunoassay.

RESULTS

In hepatic devascularized pigs, arterial serum levels of S-100beta increased from 0.96+/-0.04 microg/L (mean +/- SEM) at t = 0h to 1.74+/-0.11 microg/L (mean +/- SEM) at t = 5 h. Urinary excretion increased simultaneously from 8.48+/-3.66 ng/h (mean +/- SEM) to 20.4+/-9.54 ng/h (mean +/- SEM), while renal arterial-venous fluxes for both kidneys increased from 1022+/-404 ng/h (mean +/- SEM) to 2444+/-590 ng/h (mean +/- SEM).

CONCLUSIONS

Increased arterial S-100beta levels in pigs with acute hepatic encephalopathy are not a result of decreased renal elimination. The large difference between the renal arterial venous S-100beta concentrations and the urinary excretion of S-100beta indicate that renal metabolism is the major route of elimination.

Protein S-100beta: a biochemical marker for increased intracranial pressure in pigs with acute hepatic failure

BACKGROUND

Acute hepatic failure (AHF) may cause encephalopathy. Intracranial pressure (ICP) is frequently monitored to guide therapy, but such monitoring may cause intracerebral haemorrhagic complications. We hypothesize that determination of serum levels of S-100beta, a protein synthesized in astroglial cells, will provide useful clinical information on the presence and extent of intracranial hypertension in AHF.

METHODS

Continuous intraparenchymatous ICP monitoring and serial S-100beta measurements in serum were performed in 11 Norwegian Landrace pigs with surgically induced AHF and in 4 sham-operated controls.

RESULTS

ICP increased hour by hour in the devascularized pigs in parallel with increased serum levels of protein S-100beta. In the sham-operated controls S-100beta was not detectable at any time point.

CONCLUSIONS

Serum levels of S-100beta are increased early in experimental AHF. Determination of protein S-100beta may provide useful information on the presence and extent of intracranial hypertension in AHF.

Effect of ammonia on GABA uptake and release in cultured astrocytes

While the pathogenesis of hepatic encephalopathy (HE) is unclear, there is evidence of enhanced GABAergic neurotransmission in this condition. Ammonia is believed to play a major pathogenetic role in HE. To determine whether ammonia might contribute to abnormalities in GABAergic neurotransmission, its effects on GABA uptake and release were studied in cultured astrocytes, cells that appear to be targets of ammonia neurotoxicity. Acutely, ammonium chloride (5 mM) inhibited GABA uptake by 30%, and by 50-60% after 4-day treatment. GABA uptake inhibition was associated with a predominant decrease in Vmax; the Km was also decreased. Ammonia also enhanced GABA release after 4-day treatment, although such release was initially inhibited. These effects of ammonia (inhibition of GABA uptake and enhanced GABA release) may elevate extracellular levels of GABA and contribute to a dysfunction of GABAergic neurotransmission in HE and other hyperammonemic states.