Microdialysis sampling of the isothiazolone, PD-161374, and its thiol and disulfide metabolites

Distribution and metabolism of gastrodin in rat brain

Gastrodin is the major and bioactive component in Tianma (Gastrodia elata Bl.) and has sedative, anticonvulsive and neuroprotective effects. Since little is known about its neuropharmacokinetics and brain metabolism, this study was undertaken to investigate the kinetic inter-relationship of gastrodin in rat plasma, cerebrospinal fluid (CSF) and brain microdialysate (frontal cortex, hippocampus, thalamus and cerebellum). Gastrodin was administered via the femoral vein at a dose of 200mg/kg, and blood, CSF and brain microdialysate were collected at timed intervals for the measurement of gastrodin concentrations by high-performance liquid chromatography. The samples were analyzed on a Diamonsil C18 column (5 microm, 250 mm x 4.6mm i.d.) with a mobile phase consisting of acetonitrile-water (5% acetonitrile for brain microdialysate, 2.5% acetonitrile for plasma and CSF), and detected with a UV detector at 221 nm. The distribution of gastrodin in rat showed that levels of gastrodin declined rapidly after drug administration, and the entry of gastrodin into the brain was rapid. However, the ratios of AUC(brain)/AUC(plasma) were not high. The individual ratios of the AUC in the CSF, frontal cortex, hippocampus, thalamus and cerebellum to the AUC in the plasma were 4.8+/-2.4%, 3.3+/-1.2%, 3.0+/-0.7%, 3.3+/-1.3% and 6.1+/-1.9%, respectively. The AUC in the cerebellum was significantly higher than that in other brain regions (P<0.05). The concentrations of p-hydroxybenzyl alcohol, the main metabolite of gastrodin, were very low both in the CSF and plasma.

Evaluation of rat striatal L-dopa and DA concentration after intraperitoneal administration of L-dopa prodrugs in liposomal formulations

Parkinson's disease is a neurodegenerative disease and its symptoms are relieved by administration of L-dopa (LD), which is converted by neuronal aromatic L-aminoacid decarboxylase (AADC), restoring dopamine (DA) levels in surviving neurons. In order to minimize unfavourable side effects, we studied new dimeric LD derivatives, as potential prodrugs for Parkinson's therapeutic treatment. To improve the bioavailability of the synthesized prodrugs, they were encapsulated in unilamellar liposomes of dimiristoylphosphatidylcholine (DMPC) and cholesterol (CHOL). In vivo microdialysis was used to monitor the striatal LD and DA concentrations after i.p. administration of new delivery systems. Bioavailability evaluation was performed by means of the HPLC-EC method. The striatal levels of LD and DA were remarkably elevated after i.p. administration of liposomal formulation of prodrug (+)-1b ([(O,O-diacetyl)-L-dopa-methylester]-succinyldiamide). This formulation showed about 2.5-fold increase in the basal levels of DA in dialysate rat striatum, suggesting that liposomal formulation of (+)-1b significantly increases LD and DA concentrations with respect to equimolar administration of LD itself or free prodrug (+)-1b.

Detection of levodopa, dopamine and its metabolites in rat striatum dialysates following peripheral administration of l-DOPA prodrugs by mean of HPLC–EC

A high performance liquid chromatography (HPLC) method was developed to detected simultaneously L-dihydroxyphenylalanine (L-DOPA), dopamine (DA), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in rat striatum dilaysates following oral administration of L-DOPA or its prodrugs. The chromatographic system uses a reversed-phase C18 column with electrochemical detection at +0.30 V. Mobile phase consisted of 0.05 M citric acid, sodium EDTA 50 microM, sodium octylsulphonate 0.4 nM at pH of 2.9 and 8% methanol (v/v) at a flow rate of 1 ml/min. The calibration curves were linear over the concentration range of 10nm to 100 microM and the lower limits of detections were 125 fmol for L-DOPA, 50 fmol for DOPAC, 250 fmol for DA and 150 fmol for HVA at signal noise to ratio of 3. The repeatability (or intra-day precision), expressed by the relative standard deviation, were better than 4%. The construction of microdialysis probes has been described. The in vitro relative recoveries of each microdialysis probe were evaluated and the results show that they are similar and reproducible for all the analytes with CVs from 1 to 4%. The HPLC-EC method was applied to detect the extracellular levels of L-DOPA, DA, DOPAC and HVA in the striatum dialysates of freely moving rats after oral administration of six new potential L-DOPA prodrugs.

A review of membrane sampling from biological tissues with applications in pharmacokinetics, metabolism and pharmacodynamics

This review provides an overview of membrane sampling techniques, microdialysis and ultrafiltration, and cites illustrations of their applications in pharmacokinetics, metabolism and/or pharmacodynamics. The review organizes applications by target tissue and general type of information gleaned. It focuses on recently published microdialysis studies (1999 to this writing) and offers the first review of ultrafiltration sampling studies. The advantages and limitations of using microdialysis and ultrafiltration sampling as tools for obtaining pharmacokinetic and metabolism data are discussed. Numerous examples are described including studies in which several types of data are collected simultaneously. Reports that study local metabolism of drug delivered through the probe are also presented.