Depression of glutamate and GABA release by presynaptic GABAB receptors in the entorhinal cortex in normal and chronically epileptic rats

Presynaptic GABAB receptors (GABABR) control glutamate and GABA release at many synapses in the nervous system. In the present study we used whole-cell patch-clamp recordings of spontaneous excitatory and inhibitory synaptic currents in the presence of TTX to monitor glutamate and GABA release from synapses in layer II and V of the rat entorhinal cortex (EC)in vitro. In both layers the release of both transmitters was reduced by application of GABABR agonists. Quantitatively, the depression of GABA release in layer II and layer V, and of glutamate release in layer V was similar, but glutamate release in layer II was depressed to a greater extent. The data suggest that the same GABABR may be present on both GABA and glutamate terminals in the EC, but that the heteroreceptor may show a greater level of expression in layer II. Studies with GABABR antagonists suggested that neither the auto- nor the heteroreceptor was consistently tonically activated by ambient GABA in the presence of TTX. Studies in EC slices from rats made chronically epileptic using a pilocarpine model of temporal lobe epilepsy revealed a reduced effectiveness of both auto- and heteroreceptor function in both layers. This could suggest that enhanced glutamate and GABA release in the EC may be associated with the development of the epileptic condition. Copyright © 2006 S. Karger AG

In vivo evaluation of CUP1A2 and CYP2A6 activities in a Greek population during menopause

Human CYP enzyme system is involved in the metabolism of various endogenous compounds. Previous studies have shown that CYP activity is influenced by age and gender. In the present study caffeine metabolites were used for the evaluation of CYP1A2 and CYP2A6 in vivo activities during menopause in a Greek population. Both enzymes were significantly smaller in post menopausal women suggesting that menopause affects CYP1A2 as well as CYP2A6 activities. ©PHARMAKON-Press

Determination of N-acetylation phenotyping in a Greek population using caffeine as a metabolic probe

Studies of isoniazid, the well known antituberculosis drug, have revealed that N-acetylation polymorphism, is of great clinical importance. In humans, N-acetylation is one of the most important pathways in the inactivation of isoniazid. Caffeine, which is also biotransformed by N-acetylation, has been widely used as an in vivo probe for the assessment of N-acetyltransferase polymorphism. The activity of N-acctyltransferase can be estimated from the urinary metabolic ratio of two caffeine metabolites, namely, 5-acetylamino-6-formy-lamino-3-methyluracil (AFMU), and 1-methylxanthine (1X) after the ingestion of caffeine. In the present study caffeine was used as a metabolic probe to determine N-acetyltransferase polymorpism in 83 healthy Creek volunteers by means of the molar ratio of AFMU and 1X determined in urine following ingestion of 200 mg caffeine. Frequency distribution analysis of the metabolic ratios AFMU/1X revealed two distinct groups with 66.3% (n = 55) slow acetylators and 33.7 % (n = 28) rapid acetylators. No statistically significant difference was detected between slow and fast acetylators in terms of gender, smoking habits and caffeine-intake habits. These results are in agreement with previous studies on N-acetyltransferase activity in Caucasians using caffeine as a metabolic probe. They also agree with reports on N-acetyltransferase activity in Greek tuberculosis patients using isoniazid as a metabolic probe. Thus, the use of caffeine as a metabolic probe is a reliable method for the assessment of N-acetyltransferase activity in the Greek population

Acute in vivo exposure to fentanyl reduces GABA immunoreactivity in the CA1 area of the rat hippocampus

The effect of in vivo fentanyl treatment on GABAergic immunoreactivity was studied in the CA1 area of the rat hippocampus. Animals were treated either with saline or fentanyl (4x80 μg/kg, s.c./15min). GABA immunohistochemistry revealed lower GABA content in processes and neuronal somata suggesting reduced GABA release onto pyramidal neurons. Thus, acute in vivo exposure to fentanyl may result in a long-lasting alteration in the excitability within the CA1 area of the hippocampus. These findings are in line with previously reported reduced GABA mediated transmission and may provide evidence regarding mechanisms involved in the early stages of tolerance development towards the analgesic effects of opioids. ©PHARMAKON-Press

Caffeine metabolism in liver cirrhosis

Caffeine is metabolized primarily by CYP1A2. Several methods have been developed for the in vivo assessment of CYP1A2 activity using caffeine as a probe drug (2). These methods include the determination of caffeine clearance as well as the estimation of caffeine metabolic ratios in urine, saliva and plasma samples and they have been proposed to assess the in vivo activity of hepatic enzymes in healthy subjects and in patients with liver disease (3-6). Caffeine metabolites in urine are 1-methyluric acid (1U), 5-acetylamino-6-formylamino-3- methyluracil (AFMU), 1-methylxanthine (1X), 1,7-dimethyluric acid (17U) and 1,7-dimethylxanthine (17X). The activity of CYP1A2, xanthine oxidase (XO) and CYP2A6 can be estimated from the urinary metabolic ratios (AFMU+1U+1X)/17U, 1U/1X and 17U/17X, respectively. The purpose of the present study was to use caffeine in vivo as a probe drug in patients with liver disease in order to assess the effects of the severity of the disease on the enzymatic activity of CYP1A2, CYP2A6 and XO. The present study included 38 healthy volunteers and patients with compensated (n=33) and decompensated (n=19) liver cirrhosis. The subjects were requested to avoid consumption of any food and beverages containing caffeine, methylxanthines, alcohol and medication for at least 24 hours before they were administered a capsule containing 200 mg caffeine. A spot urine sample was collected 6 hours later. Samples were analyzed by reversed-phase HPLC. The five metabolites and the internal standard (4-acetamidophenol) were extracted with liquid/liquid extraction using chloroformisopropanol (85:15, v/v). The accuracy of the method ranged between 90.2% and 110.4%. The intraday (n=5) and interday (n=5) precision (CV%) were 0.05) and decompensated (median 1.19, p>0.05) cirrhosis as compared to healthy subjects (median 1.67). Similarly, there was no statistically significant difference in XO index between patients with compensated (median 1.30, p>0.05) and decompensated (median 1.28, p>0.05) cirrhosis as compared to healthy subjects (median 1.16). In conclusion, CYP1A2 activity is reduced in patients with liver cirrhosis. (AFMU+1U+1X)/17U calculated from a spot urine sample may be used as a simple, non-invasive method for the in vivo assessment of CYP1A2 activity in patients with liver cirrhosis