Biotransformation of geniposide by human intestinal microflora on cytotoxicity against HepG2 cells

Intestinal microflora (IM) is able to produce toxic and carcinogenic metabolites and induce more potent cytotoxicity against cells than non-metabolites. This study was performed to investigate the cytotoxic responses of geniposide (GS) and its metabolite and to determine the role of metabolism by IM in GS-induced cytotoxicity. Genipin (GP), a GS metabolite, increased cytotoxic effects in cells, but GS did not. Following GS incubation with IM for metabolic activation, increased cytotoxicity was detected compared to GS. Western blot analysis revealed that the activated GS inhibited Bcl-2 expression with a subsequent increase in Bax expression. Likewise, GS activation by IM stimulated caspase-3 and the production of reactive oxygen species (ROS). In addition, activated GS-induced apoptosis was confirmed by apoptosis and ROS assays; N-acetyl-l-cysteine (NAC) suppressed ROS production and apoptotic cell death. Activated GS induced sustained JNK phosphorylation. Moreover, activated GS-induced cell death was reversed by SP600125. Taken together, these findings suggest that human IM is able to metabolize GS into GP, and the related biological activities induce apoptosis through ROS/JNK signaling.     

Simultaneous determination of L-arginine, asymmetric dimethylarginine, and symmetric dimethylarginine in the plasma of rodents with LC-MS/MS

Nitric oxide (NO) is synthesized from L-arginine (Arg) by NO synthase (NOS), and asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) are endogenous inhibitors of NO formation. Normal distribution values of Arg, ADMA, and SDMA are required to evaluate the effects of cardiovascular drugs on blood vessels, but insufficient normal reference values from rat and mouse plasma exist for new drug development and screening. To determine the means and variations in the basal endogenous materials concentration, Arg, ADMA, and SDMA in blank rat (n = 24) and mouse (n = 37) plasma samples were quantified using LC-MS/MS equipped with an electrospray ionization interface to generate positive mode ions. Accuracy and precision were within 90.42-110.91%, and 0.88-13.84%, respectively, for analyses of Arg, ADMA, and SDMA. The average plasma concentrations of Arg, ADMA, and SDMA were 175.38 +/- 13.87 microM, 0.79 +/- 0.20 microM, and 0.84 +/- 0.20 microM, respectively, in rats and 70.81 +/- 19.38 microM, 0.66 +/- 0.21 microM, and 0.42 +/- 0.10 microM, respectively, in mice. These results will provide a basis on which to evaluate cardiovascular drug effects on ARG, ADMA, and SDMA levels in new drug development.     

Determination of a novel low-voltage-activated calcium channel blocker (HYP-10) in rat plasma by liquid chromatography-mass spectrometry

A novel T-type calcium channel blocker, 4-amino-1-{4-[(4-chloro-phenyl)-phenyl-methyl]-piperazin-1-yl}-butan-1-one (HYP-10) has been synthesized, and the compound has shown promise as both a nociceptive and inflammatory pain reliever as well as an analgesic in a rat neuropathic pain model. A quantification method was developed for the determination of HYP-10 in rat plasma. After simple protein precipitation with methanol, HYP-10 and the internal standard, methaqualone were chromatographed on a reversed-phase column and detected by liquid chromatography/tandem mass spectrometry with electrospray ionization. The accuracy and precision of the assay were in accordance with FDA regulations for validation of bioanalytical methods. This method was applied to measure the plasma HYP-10 concentration after a single intravenous administration of the compound in rats.     

Reverse migration order of sibutramine enantiomers as a function of cyclodextrin concentration in capillary electrophoresis

The current study demonstrates the reversal of enantiomer migration order (EMO) in capillary electrophoresis (CE) based separations of sibutramines (SIB) as a function of the concentration of two types of cyclodextrin (CD), native β-CD and acetyl-β-CD. At normal working concentrations (<10mM) of either CD, (S)-SIB migrated first. However, at CD concentrations greater than 10mM, (R)-SIB was the first to migrate. This study describes factors involved in determining EMO for sibutramine enantiomers at low and high concentrations of CDs. The reversal of EMO could be explained in terms of the opposing effects of the stability and the limiting complex mobility of the SIB-CD complexes. The enantioseparation of SIB with methyl- and 2-hydroxypropyl-β-CD was possible based on differences in the binding constants of complexes. However, reverse EMO was not observed because of equal mobilities of SIB enantiomers complexed with methyl- and 2-hydroxypropyl-β-CD.     

Globular adiponectin inhibits ethanol-induced apoptosis in HepG2 cells through heme oxygenase-1 induction

Hepatocellular apoptosis is an essential pathological feature of alcoholic liver disease. Adiponectin, an adipokine predominantly secreted from adipose tissue, has been shown to play beneficial roles in alcoholic liver disease against various inflammatory and pro-apoptotic molecules. However, the effects of adiponectin on ethanol-induced apoptosis in liver cells are largely unknown. Herein, we investigated the role of globular adiponectin (gAcrp) in the prevention of ethanol-induced apoptosis and further tried to decipher the potential mechanisms involved. In the present study, we demonstrated that gAcrp significantly inhibits both ethanol-induced increase in Fas ligand expression and activation of caspase-3 in human hepatoma cell lines (HepG2 cells), suggesting that gAcrp plays a protective role against ethanol-induced apoptosis in liver cells. This protective effect of gAcrp was mediated through adiponectin receptor R1 (adipoR1). Further, globular adiponectin treatment caused induction of heme oxygenase-1 (HO-1) through, at least in part, nuclear factor (erythroid-derived 2)-like 2, (Nrf2) signaling. Treatment with SnPP, a pharmacological inhibitor of HO-1, and knockdown of HO-1 with small interfering RNA (siRNA) restored caspase-3 activity suppressed by gAcrp, indicating a critical role of HO-1 in mediating the protective role of gAcrp in ethanol-induced apoptosis in liver cells. In addition, carbon monoxide, a byproduct obtained from the catabolism of free heme was found to contribute to the anti-apoptotic effect of adiponectin. In conclusion, these data demonstrated that globular adiponectin prevents ethanol-induced apoptosis in HepG2 cells via HO-1 induction and revealed a novel biological response of globular adiponectin in the protection of liver injury from alcohol consumption.     

Contribution of pH to systemic exposure of niflumic acid following oral administration of talniflumate

Purpose  

Systemic exposure to niflumic acid was significantly increased when talniflumate was given orally together with a meal. To clarify the underlying mechanism, an in vitro dissolution study of talniflumateonducted at different pH values, and magnesium hydroxide was co-administered in healthy volunteers.     

Effects of smoking on the pharmacokinetics and pharmacodynamics of a nicotine patch

The effect of smoking on the pharmacokinetics and pharmacodynamics of a nicotine transdermal delivery system, administered as a single dose or multiple doses, was examined in smokers (n=12) and nonsmokers (n=12). The study was a two‐period, parallel trial. In the first period, a single dose of the Nicotinell TTS 20 patch was administered, followed by a 1‐week washout period. Then, in the second period, multiple doses of the Nicotinell TTS 20 patch were administered over 4 days. Regarding the pharmacokinetics of nicotine, the AUC_36h and AUC_τ of smokers were about 20% and 40% greater, respectively, than those of nonsmokers. Significant differences in heart rate were observed between smokers and nonsmokers at 10, 12, 16 and 24 h, and significant differences in systolic blood pressure were seen between smokers and nonsmokers at 12, 30 and 36 h in the single‐dose study. With multiple doses, significant differences in systolic and diastolic blood pressures were detected between smokers and nonsmokers only at 72.5 and 82 h. Here, it is demonstrated for the first time that the pharmacokinetic and hemodynamic effects of a nicotine patch are significantly different between smokers and nonsmokers. Copyright © 2008 John Wiley & Sons, Ltd.     

Protective Effects of Diallyl Sulfide against Thioacetamide-Induced Toxicity: A Possible Role of Cytochrome P450 2E1

Effects of diallyl sulfide (DAS) on thioacetamide-induced hepatotoxicity and immunotoxicity were investigated. When male Sprague-Dawley rats were treated orally with 100, 200 and 400 mg/kg of DAS in corn oil for three consecutive days, the activity of cytochrome P450 (CYP) 2E1-selective p-nitrophenol hydroxylase was dose-dependently suppressed. In addition, the activities of CYP 2B-selective benzyloxyresorufin O-debenzylase and pentoxyresorufin O-depentylase were significantly induced by the treatment with DAS. Western immunoblotting analyses also indicated the suppression of CYP 2E1 protein and/or the induction of CYP 2B protein by DAS. To investigate a possible role of metabolic activation by CYP enzymes in thioacetamide-induced hepatotoxicity, rats were pre-treated with 400 mg/kg of DAS for 3 days, followed by a single intraperitoneal treatment with 100 and 200 mg/kg of thioacetamide in saline for 24 hr. The activities of serum alanine aminotransferase and aspartate aminotransferase significantly elevated by thioacetamide were protected in DAS-pretreated animals. Likewise, the suppressed antibody response to sheep erythrocytes by thioacetamide was protected by DAS pretreatment in female BALB/c mice. Taken together, our present results indicated that thioacetamide might be activated to its toxic metabolite(s) by CYP 2E1, not by CYP 2B, in rats and mice.     

CYP2J2 and CYP2C19 Are the Major Enzymes Responsible for Metabolism of Albendazole and Fenbendazole in Human Liver Microsomes and Recombinant P450 Assay Systems

Albendazole and fenbendazole are broad-spectrum anthelmintics that undergo extensive metabolism to form hydroxyl and sulfoxide metabolites. Although CYP3A and flavin-containing monooxygenase have been implicated in sulfoxide metabolite formation, the enzymes responsible for hydroxyl metabolite formation have not been identified. In this study, we used human liver microsomes and recombinant cytochrome P450s (P450s) to characterize the enzymes involved in the formation of hydroxyalbendazole and hydroxyfenbendazole from albendazole and fenbendazole, respectively. Of the 10 recombinant P450s, CYP2J2 and/or CYP2C19 was the predominant enzyme catalyzing the hydroxylation of albendazole and fenbendazole. Albendazole hydroxylation to hydroxyalbendazole is primarily mediated by CYP2J2 (0.34 μl/min/pmol P450, which is a rate 3.9- and 8.1-fold higher than the rates for CYP2C19 and CYP2E1, respectively), whereas CYP2C19 and CYP2J2 contributed to the formation of hydroxyfenbendazole from fenbendazole (2.68 and 1.94 μl/min/pmol P450 for CYP2C19 and CYP2J2, respectively, which are rates 11.7- and 8.4-fold higher than the rate for CYP2D6). Correlation analysis between the known P450 enzyme activities and the rate of hydroxyalbendazole and hydroxyfenbendazole formation in samples from 14 human liver microsomes showed that albendazole hydroxylation correlates with CYP2J2 activity and fenbendazole hydroxylation correlates with CYP2C19 and CYP2J2 activities. These findings were supported by a P450 isoform-selective inhibition study in human liver microsomes. In conclusion, our data for the first time suggest that albendazole hydroxylation is primarily catalyzed by CYP2J2, whereas fenbendazole hydroxylation is preferentially catalyzed by CYP2C19 and CYP2J2. The present data will be useful in understanding the pharmacokinetics and drug interactions of albendazole and fenbendazole in vivo.     

Comparison of average,scaled average,and population bioequivalence methods for assessment of highly variable drugs: An experience with doxifluridine in beagle dogs

Several strategies for overcoming the challenge of establishing bioequivalence (BE) for highly variable drugs (HVDs; drugs having within-subject variability >0.3) have been considered in recent years. Within-subject variability of the area under the curve (AUC_4 h) and peak concentration (C_max) of doxifluridine in the minimal group (n = 24) were 0.444 and 0.491, respectively, meeting the criteria for an HVD. For the large group (n = 60), within-subject variability of the AUC_4 h and C_max were 0.431 and 0.493, respectively. The 90% confidence interval for the AUC_4 h and C_max of the ratio of the test drug to the reference drug exceeded the acceptable BE limits (0.80–1.25) of the ABE (average bioequivalence), in both the minimal and large groups. However, the 90% CI fell within the extended BE limits (0.61–1.64) of the SABE (scaled average bioequivalence), calculated using within-subject variability. The 95% CI of the AUC_4 h and C_max of the ratio of test to reference drug were within the extended BE limit (<1.73) of the PBE (population bioequivalence), calculated using total variance. Our results suggest that the SABE method may be useful for evaluating the BE of HVDs and for meeting the need for international guidelines for BE.