An array of eight porous monolithic columns, prepared in a Zeonor polymeric chip by UV-initiated polymerization of butyl methacrylate and ethylene dimethacrylate, was tested for solid-phase extraction (SPE) cleanup of biological samples prior to directly coupled electrospray mass spectrometry (ESI-MS). The chip, fabricated by hot embossing and thermal bonding, consists of eight parallel channels (10 mm long, 360 microm i.d.) connected via external fused-silica capillaries. The monomer mixture was aspirated simultaneously into the eight channels using a homemade vacuum manifold device and polymerized in parallel for 20 min under UV irradiation. The porous monolithic columns were then characterized by scanning electron microscopy and evaluated by ESI-MS applications with respect to sample capacity, recovery, reproducibility of peak area or peak height ratios, and linearity between peak height ratio and concentration using imipramine as a pharmaceutical test compound. The average sample capacity was estimated to be 0.30 microg with a relative standard deviation (RSD) of 26.5% for the eight monolithic columns on the same polymeric chip. For two chips prepared using the same monomer mixture, the difference in average sample capacity was 7.0%. The average recovery for the eight monolithic SPE columns on the same chip was 79.1% with an RSD of 7.9%. Using imipramine-d3 as an internal standard, the RSD of peak height ratios for the eight different columns was 2.0% for a standard solution containing 1 microg/mL imipramine. A linear calibration curve (R2 = 0.9995) was obtained for standard aqueous solutions of imipramine in the range from 0.025 to 10 microg/mL. To demonstrate the analytical potential of the chip-based SPE system, two different types of real-world samples including human urine sample and P450 drug metabolism incubation mixture were tested. Similar to standard aqueous solution, a linear correlation (R2 = 0.9995) was also found for human urine sample spiked with imipramine in the range of 0.025-10 microg/ mL. When aliquots of a human urine sample spiked with 1 microg/mL imipramine were loaded onto eight different monolithic columns, the RSD of peak height ratios was 3.8%. For a P450-imipramine incubation mixture, the formation of the N-demethylated metabolite (m/z 267.2) and the monohydroxylated metabolite (m/z 297.2) of imipramine was observed following chip-based monolithic SPE sample cleanup and preconcentration.

A chip-based P450 in vitro metabolism assay coupled with ESI-MS and ESI-MS/MS detection is described in this paper. The chips were made of a cyclic olefin polymer using a hot embossing process. The introduction of reagent solutions into the chip was carried out using fused-silica capillaries coupled to two syringes with the flow rate controlled by a syringe pump. Initial experiments described here employed a small commercial guard column in an off-chip format to desalt and concentrate the products of the enzymatic reaction prior to ESI-MS analysis. The system was used both to yield the Michaelis constant (K m ) of the P450 biotransformation of imipramine into desipramine and to determine the IC50 value of a chemical inhibitor (tranylcypromine) for this CYP2C19-mediated reaction. The results demonstrated that the kinetics of the reaction inside the 4-µL volume within the channels of the cyclic olefin polymer chip provided results in agreement with those reported in the literature using conventional assays. The above reactions were carried out using human liver microsomes, and the metabolites were detected by ESI-MS showing the potential of the chip-based P450 reaction for metabolite screening studies as well as for P450 inhibition assays. A porous monolithic column was subsequently integrated into the chip to perform the reaction mixture cleanup process in an integrated fashion on the chip that is necessary for ESI-MS detection. The miniature monolithic SPE column was prepared in situ inside the chip via UV-initiated polymerization. The results obtained using the integrated system demonstrated the possibility of performing P450 enzymatic reactions in a microvolume reaction chamber coupled directly to ESI-MS detection and required less than 4 µg of HLM protein.

ABSTRACT:Ginseng extract has been reported to decrease the incidence of 7,12-dimethylbenz[a]anthracene (DMBA)-initiated tumorigenesis in mice. A potential mechanism for this effect by ginseng is inhibition of DMBA-bioactivating cytochrome P450 (P450) enzymes. In the present in vitro study, we examined the effect of a standardized Panax ginseng (or Asian ginseng) extract (G115), a standardized Panax quinquefolius (or North American ginseng) extract (NAGE), and individual ginsenosides (Rb1, Rb2, Rc, Rd, Re, Rf, and Rg1) on CYP1 catalytic activities, as assessed by 7-ethoxyresorufin O-dealkylation. G115 and NAGE decreased human recombinant CYP1A1, CYP1A2, and CYP1B1 activities in a concentration-dependent manner. Except for the competitive inhibition of CYP1A1 by G115, the mode of inhibition was the mixed-type in the other cases. A striking finding was that NAGE was 45-fold more potent than G115 in inhibiting CYP1A2. Compared with G115, NAGE also preferentially inhibited 7-ethoxyresorufin O-dealkylation activity in human liver microsomes. Rb1, Rb2, Rc, Rd, Re, Rf, and Rg1, either individually or as a mixture and at the levels reflecting those found in an inhibitory concentration (100 g/ml) of NAGE or G115, did not influence CYP1 activities. However, at a higher ginsenoside concentration (50 g/ml), Rb1, Rb2, Rc, Rd, and Rf inhibited these activities. Overall, our in vitro findings indicate that standardized NAGE and G115 extracts, which were not treated with calf serum or subjected to acid hydrolysis, inhibited CYP1 catalytic activity in an enzyme-selective and extract-specific manner, but the effects were not due to Rb1, Rb2, Rc, Rd, Re, Rf, or Rg1.Ginseng is one of the most commonly used herbal products by American consumers (Eliason et al., 1997;Harnack et al., 2001), and the annual sales of ginseng in the United States are more than $300 million (Gillis, 1997). Ginseng refers to the roots of species of the genus Panax. There are several species of ginseng (Soldati, 2000), including Panax ginseng C. A. Meyer (or Asian ginseng), which is mainly from Korea and Eastern China, and Panax quinquefolius L. (or North American ginseng), which is primarily from Wisconsin and British Columbia, Canada. To date, approximately 200 substances have been isolated and characterized from P. ginseng (Soldati, 2000). The characteristic markers of both species are the ginsenosides (Attele et al., 1999), which are steroidal saponins (Attele et al., 1999). Ginseng is used as a general body tonic, and it is touted to counteract fatigue, boost the immune system, improve physical stamina, and stimulate the appetite (Elias and Masline, 1995). The mechanism of action of ginseng is not known, but it is thought to have effects on learning, memory and behavior, cardiovascular function perhaps through mediation by nitric oxide, neuroendocrine function, carbohydrate and lipid metabolism, and immune function (Liu and Xiao, 1992).The oral administration of red ginseng extracts, which were produced by steam treatment of the roots of P. ginseng, was ...

No abstract

Although there is evidence in the literature of the participation of CYP2B6 in the metabolism of selegiline, it is not clear which other CYP isoforms contribute to its metabolism. The aim of this study was to investigate the P450 isozymes (CYPs) involved in the metabolism of selegiline to desmethylselegiline (DMS) and methamphetamine (MA) using four assays: incubation of selegiline with cDNA expressed CYPs, inhibition of DMS and MA formations in human liver microsomes by CYP-selective chemical inhibitors or CYP-specific antibodies, and correlation analysis. Correlation analysis, performed in a bank of 15 individual human liver microsomes, yielded correlation coefficients for DMS and MA formation of 0.769 and 0.792, respectively, for CYP2B6 (p<0.0001) and 0.333 and 0.349, respectively, for CYP3A4 (p<0.05). These results were supported by chemical/specific antibody inhibition assays. The results of correlation analysis and chemical inhibition also indicated that CYP2A6 seems to play a small role in the metabolism of selegiline. These findings confirm that CYP2B6 plays a major role in the metabolism of selegiline and also suggest the involvement of CYP3A4 and CYP2A6.

1. The aim was to identify the individual human cytochrome P450 (CYP) enzymes responsible for the in vitro N-demethylation of hydromorphone and to determine the potential effect of the inhibition of this metabolic pathway on the formation of other hydromorphone metabolites. 2. Hydromorphone was metabolized to norhydromorphone (apparent Km = 206 - 822 microM, Vmax = 104 - 834 pmol min(-1) mg(-1) protein) and dihydroisomorphine (apparent Km = 62 - 557 microM, Vmax = 17 - 122 pmol min(-1) mg(-1) protein) by human liver microsomes. 5. In pooled human liver microsomes, troleandomycin, ketoconazole and sulfaphenazole reduced norhydromorphone formation by an average of 45, 50 and 25%, respectively, whereas furafylline, quinidine and omeprazole had no effect. In an individual liver microsome sample with a high CYP3A protein content, troleandomycin and ketoconazole inhibited norhydromorphone formation by 80%. 5. The reduction in norhydromorphone formation by troleandomycin and ketoconazole was accompanied by a stimulation in dihydroisomorphine production. Recombinant CYP3A4, CYP3A5, CYP2C9 and CYP2D6, but not CYP1A2, catalysed norhydromorphone formation, whereas none of these enzymes was active in dihydroisomorphine formation. 6. In summary, CYP3A and, to a lesser extent, CYP2C9 catalysed hydromorphone N-demethylation in human liver microsomes. The inhibition of norhydromorphone formation by troleandomycin and ketoconazole resulted in a stimulation of microsomal dihydroisomorphine formation.

No abstract

Metabolic activation of pradefovir to 9-(2-phosphonylmethoxyethyl)adenine (PMEA) was evaluated by using cDNA-expressed CYP isozymes in portal vein-cannulated rats following oral administration and in human liver microsomes. The enzyme induction potential of pradefovir was evaluated in rats following multiple oral dosing and in primary cultures of human hepatocytes. The results indicated that CYP3A4 is the only cDNA-expressed CYP isozyme catalyzing the conversion of pradefovir to PMEA. Pradefovir was converted to PMEA in human liver microsomes with a K m of 60 M, a maximum rate of metabolism of 228 pmol/min/mg protein, and an intrinsic clearance of about 359 ml/min. Addition of ketoconazole and monoclonal antibody 3A4 significantly inhibits the conversion of pradefovir to PMEA in human liver microsomes, suggesting the predominant role of CYP3A4 in the metabolic activation of pradefovir. Pradefovir at 0.2, 2, and 20 M was neither a direct inhibitor nor a mechanism-based inhibitor of CYP3A4, CYP2D6, CYP2C9, CYP2C19, CYP2E1, and CYP1A2 in human liver microsomes. In rats, the liver was the site of metabolic activation of pradefovir, whereas the small intestine did not play a significant role in the metabolic conversion of pradefovir to PMEA. Daily oral dosing (300 mg/kg of body weight) to rats for 8 days showed that pradefovir was not an inducer of P450 enzymes in rats. Furthermore, pradefovir at 10 g/ml was not an inducer of either CYP1A2 or CYP3A4/5 in primary cultures of human hepatocytes.9-(2-Phosphonylmethoxyethyl)adenine (PMEA) (Fig. 1) is an acyclic phosphonate analogue of adenine which has been shown to be effective against the hepatitis B virus (HBV) in stably transfected human hepatocellular carcinoma cell lines, primary duck hepatocytes infected with duck hepatitis B virus, and a duck model of hepatitis B (8, 9). PMEA is phosphorylated to PMEA diphosphate (PMEApp) by cellular kinases or 5-phosphoribosyl-1-pyrophosphate synthetase, which inhibits HBV DNA polymerase (reverse transcriptase) by competing with the natural substrate dATP (15) and by causing DNA chain termination after its incorporation into viral DNA (1). However, PMEA is poorly absorbed in a number of species, including rats (20), monkeys (4), and humans (3). The low oral bioavailability of PMEA appears to be a consequence, in part, of the limited intestinal permeation of phosphonate, which is ionized at physiological pH (18).Adefovir dipivoxil is an oral prodrug of PMEA. Marcellin et al. (14) reported that in patients with HBeAg-positive chronic hepatitis B, 48 weeks of treatment with 10 or 30 mg of adefovir dipivoxil per day resulted in histological liver improvement, reduced serum HBV DNA and alanine aminotransferase levels, and increased the rates of HBeAg seroconversion. The 10-mg dose has a favorable risk-benefit profile for long-term treatment. No adefovir-associated resistance mutations were identified in the HBV DNA polymerase gene. Hadziyannis et al. (7) reported that in patients with HBeAg-negative chronic hepatitis B, 48 weeks of ...