Brain concentrations of benzodiazepines are elevated in an animal model of hepatic encephalopathy.

Abstract

Brain extracts from rats with hepatic encephalopathy due to thioacetamide-induced fulminant hepatic failure contained 4-to 6-fold higher concentrations of substances that inhibit radioligand binding to benzodiazepine receptors than corresponding control rat extracts. Both isocratic and gradient-elution HPLC indicated that this inhibitory activity was localized in 3-8 peaks with retention times corresponding to deschlorodiazepam, deschlorolorazepam, lorazepam, oxazepam, diazepam, and N-desmethyldiazepam. The presence of diazepam and N-desmethyldiazepam was confirmed by mass spectroscopy. Both mass spectroscopic and radiometric techniques indicated that the concentrations of N-desmethyldiazepam and diazepam in brain extracts from encephalopathic rats were 2-9 and 5-7 times higher, respectively, than in control brain extracts. While benzodiazepines have been identified previously in mammalian and plant tissues, this report demonstrates that concentrations of these substances are increased in a pathophysiological condition. These findings provide a rational basis for the use of benzodiazepine receptor antagonists in the management of hepatic encephalopathy in humans.Hepatic encephalopathy (HE) is a complex neuropsychiatric disorder arising from the metabolic abnormalities associated with acute or chronic liver failure (1). It has been proposed that an increase in the activity of y-aminobutyric acid (GABA)-containing pathways contributes to the manifestations of this disorder (2). Studies of visual evoked responses in the galactosamine-treated rabbit model of HE due to fulminant hepatic failure (FHF) (3) and in rats with HE due to thioacetamide (TAA)-induced FHF (4) indicate that central nervous system (CNS) GABAergic tone is increased in these models of HE. Electrophysiologic studies of single cerebellar Purkinje neurons in the rabbit model of HE further support this hypothesis. These neurons are hypersensitive to depression by the GABA receptor agonist muscimol and the benzodiazepine (BZ) receptor agonist flunitrazepam, but not to the a-adrenergic receptor agonist phenylephrine (5). In contrast, BZ receptor antagonists increase the spontaneous firing rate of these neurons and reverse their hypersensitivity to muscimol at concentrations that do not affect the firing rates of control neurons (5). Furthermore, BZ receptor antagonists correct the abnormalities in visual evoked responses associated with HE while transiently reversing the behavioral manifestations of this syndrome in both the rabbit and rat models of this disorder (3, 4).These observations indicate that the increase in "GABAergic tone" found in HE may be mediated by the BZ receptor, possibly as a consequence of an increase in the concentration or availability of a BZ receptor ligand with agonist (BZ-like) properties (6, 7). Elevated concentrations of substances that competitively and reversibly inhibit radioligand binding to BZ receptors have recently been found in extracts of brain and peripheral tissues from the TAA-treated rat model of HE (8)....

Benzodiazepine-insensitive mice generated by targeted disruption of the gamma 2 subunit gene of gamma-aminobutyric acid type A receptors.

“…By modulating GABAA receptor function, ligands of the BZ site can enhance or inhibit a wide variety of CNS states, including vigilance, anxiety, epileptic activity, and memory. Endogenous BZ-like ligands (6, 7) were found to be operative in pathological states such as hepatic encephalopathy and idiopathic stupor (8)(9)(10). However, the physiological relevance of the BZ site is unresolved.…”

Electrophysiological studies on oxindole, a neurodepressant tryptophan metabolite

“…In pathological situations, however, it is possible that blood and brain oxindole concentrations reach levels which are su cient to depress the function of excitable cells. In hepatic encephalopathy oxindole could participate in the symptomatology in association with other neurodepressant compounds Basile et al, 1990;Olasmaa et al, 1989). Phenylketonuria (Kochen et al, 1972) is another example of a pathological condition in which the concentrations of oxindole in biological¯uids reaches levels we found su cient to reduce cellular excitability.…”

Neuropsychological Aspects of Liver Disease and its Treatment

“…Elevated levels of BZs have been found in rats and rabbits in fulminant hepatic failure [23,24]. In an early human study, Mullen et al reported greater binding of ligands to BZ receptors in CSF taken from patients with severe HE, and plasma BZ activity was also significantly higher, and correlated with HE severity [25].…”