Objective:To explore the glucuronic acid metabolism of acacetin in human liver and intestinal microsomes to better characterize human uridine 5'-diphospho (UDP)-glucuronosyltransferase (UGT) isoforms.In addition,i...Objective:To explore the glucuronic acid metabolism of acacetin in human liver and intestinal microsomes to better characterize human uridine 5'-diphospho (UDP)-glucuronosyltransferase (UGT) isoforms.In addition,interspecies comparisons were performed to identify the most appropriate experimental animal model for an in vivo study.Methods:Liquid chromatography tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR) were used to confirm the successful biosynthesis of acacetin-7-O-glucuronide.Human isoforms of UGT and isozyme-specific chemical inhibitors were used for recombinant assays.Acacetin glucuronidation kinetics were assessed by combining acacetin with recombinant human UGT isoforms or with microsomes from humans or experimental animals.Kinetic differences between species were assessed in vitro using the same approach.Results:We identified multiple UGT isoforms that facilitated acacetin glucuronidation,and found that UGT1A1 was the major isoform that catalyzed this process.Acacetin-7-O-glucuronide formation exhibited clear substrate inhibition kinetics when combined with recombinant UGTs or with liver/intestinal microsomes derived from humans,monkeys,rats,mice,dogs,or pigs.Intrinsic metabolic clearance values of human intestinal microsomes were two-fold greater than those of human liver microsomes.Among the evaluated species,the Km value of dog microsomes (0.86 μM) was greatest in acacetin glucuronidation,while mice exhibited the highest CLint value,5.05 mL/min/mg.The CLint values of microsomes derived from monkeys and minipigs were 1.99 mL/min/mg and 2.12 mL/min/mg,respectively,exhibiting similar intrinsic metabolic clearance activity to that observed in humans.Conclusion:Monkey may represent a suitable model for experimental studies of acacetin pharmacokinetics owing to a high sequence homology of UGT1A1 and similar UGT1A1 glucuronidation activity to humans.展开更多
In the present study, we developed and validated an analytical method using ultra performance liquid chromatography-mass spectrometry (UPLC/MS) for the quantitative determination of 2,2',4,4'-tetrabromodipheny...In the present study, we developed and validated an analytical method using ultra performance liquid chromatography-mass spectrometry (UPLC/MS) for the quantitative determination of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) metabolism by rat hepatic microsomes. BDE-47 is a brominated flame retardant that was widely used in a variety of consumer products and has subsequently been identified as a ubiquitous environmental contaminant. Hydroxy-bromodiphenyl ethers (OH-BDEs) were isolated from rat hepatic microsomes by liquid-liquid extraction. Chromatographic separation was achieved by UPLC on a C18 column with gradient elution using a mobile phase consisting of methanol and water, each containing 0.1% formic acid, at a flow rate of 0.2 mL/min. Detection and quantification were performed using a mass spectrometer in single ion recording mode with negative electrospray ionization. The UPLC/MS method was validated for linearity, limit of quantification (LOQ), accuracy, precision and recovery. The weighted calibration curves (1/X2) were linear over a concentration range of 5 - 250 nM with LOQ values between 5 nM and 50 nM for the individual OH-BDEs. Intra- and inter- day accuracy (%DEV) and precision (%RSD) values ranged from –11.7% to 9.5% and 5.9% to 16.5%, respectively. Recovery values of 70% to 90% were obtained for all OH-BDEs. The validated method allowed us to successfully analyze metabolite formation following incubation of BDE-47 with hepatic microsomes prepared from phenobarbital-treated rats. Results demonstrate that the UPLC/MS method has sufficient sensitivity and reproducibility to fully characterize the in vitro metabolism of BDE-47 and possibly other PBDEs.展开更多
Genistein, the main isoflavone from soy, and bisphenol A (BPA), a food contaminant, are considered ubiquitous xenoestrogens. Here we investigated the influence of genistein and BPA on estrone (El) metabolism in ra...Genistein, the main isoflavone from soy, and bisphenol A (BPA), a food contaminant, are considered ubiquitous xenoestrogens. Here we investigated the influence of genistein and BPA on estrone (El) metabolism in rat liver microsomes. Both substances inhibited the 2-hydroxylation and 16a-hydroxylation of E1, but in different degrees, thereby reducing the 2-OH-E1/16a-OH-E1 ratio,展开更多
Objective: To study the stereoselective glucuronidation of carvedilol (CARV) by three Chinese liver microsomes. Methods: The metabolites of CARV were identified by a hydrolysis reaction with β-glucuronidase and HPLC-...Objective: To study the stereoselective glucuronidation of carvedilol (CARV) by three Chinese liver microsomes. Methods: The metabolites of CARV were identified by a hydrolysis reaction with β-glucuronidase and HPLC-MS/MS. The enzyme kinetics for CARV enantiomers glucuronidation was determined by a reversed phase-high pressure liquid chromatogra-phy (RP-HPLC) assay using (S)-propafenone as internal standard after precolumn derivatization with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosylisothiocyanate. Results: Two CARV glucuronides were found in three Chinese liver microsomes incubated with CARV. The non-linear regression analysis showed that the values of Km and Vmax for (S)-CARV and (R)-CARV enantiomers were (118±44) μmol/L, (2 500±833) pmol/(min·mg protein) and (24±7) μmol/L, (953±399) pmol/(min·mg protein), respectively. Conclusion: These results suggested that there was a significant (P<0.05) stereoselective glucuronidation of CARV enantiomers in three Chinese liver microsomes, which might partly explain the enantioselective pharmacokinetics of CARV.展开更多
Objective To determine whether the cytochrome P4502B6(CYP2B6)is involved in the oxidation of propofol by human liver microsomes.Methods The change of propofol concentration in an incubation mixture with human liver mi...Objective To determine whether the cytochrome P4502B6(CYP2B6)is involved in the oxidation of propofol by human liver microsomes.Methods The change of propofol concentration in an incubation mixture with human liver microsomes was monitored by the high performance liquid chromatography(HPLC),in order to calculate the rate constants of metabolism of propofol.The correlation between the rate constants and the rate of metabolism of CYP2B6 selective substrate bupropion,and the effect of two different CYP2B6 specific inhibitors on the propofol metabolism were examined.Results The mean rate constant of propofol metabolism by liver microsomes obtained from twelve individuals was 3.9(95% confidence intervals 3.3,4.5)nmol·min-1·mg-1 protein.The rate constants of propofol metabolism by liver microsomes were significantly correlated with bupropion hydroxylation(r=0.888,P<0.001).Both selective chemical inhibitors of CYP2B6,orphenadrine and N,N',N″-triethylenethiophosphoramide(thioTEPA),reduced the rate constants of propofol metabolism by 37.5%(P<0.001)and 42.7%(P<0.001)in liver microsomes,respectively.Conclusions CYP2B6 is predominantly involved in the oxidation of propofol by human liver microsomes.展开更多
In this study, the effects of several fluoroquinolones (FQs), such as Ciprofloxacin (CPFX);Orbifloxacin (OBFX);Norfloxacin (NFX);Ofloxacin (OFX);and Enerofloxacin (EFX) on activities of both Cytochrome P450 1A (CYP1A)...In this study, the effects of several fluoroquinolones (FQs), such as Ciprofloxacin (CPFX);Orbifloxacin (OBFX);Norfloxacin (NFX);Ofloxacin (OFX);and Enerofloxacin (EFX) on activities of both Cytochrome P450 1A (CYP1A) and Cytochrome P450 3A (CYP3A) of feline microsomes by <i>in vitro</i> tests were studied. Ethoxyresorufin O-deethylation (EROD) and Midazolam 1' hydroxylation and 4-hydroxylation (MDZ1'H and MDZ4H) were analyzed by High Performance Liquid Chromatography (HPLC). All the FQs inhibited the reactions by a competitive or noncompetitive and irreversible manner. The inhibitory constants (K<sub>i</sub>) were as followings: CYP1A;ranged from 0.12 to 1.23 mM for NFX, OBFX, EFX, CPFX, OFX and CYP3A, for MDZ1'H;ranged from 5.8 to 35 and MDZ4H;9 to 29 mM, respectively. As these values are higher by 24 to 200-times of given single clinical dose of serum levels after application of FQs. It indicates that if co-administrated with these FQs by reversible inhibitory manner, the inhibition of CYP1A and CYP3A effect on CYP1A and 3A actions is not very significant to cause drug interaction with above mentioned enzyme substrates. Out of the FQs tested, CPFX and NFX for CYP1A, and CPFX for CYP3A showed irreversible inhibitory effects (time-dependent), so it has been concluded that these drugs may cause drug-drug interaction by accumulation, when they are repeatedly administrated. Since EFX is biotransformed to CPFX by the liver, it could have the identical risk too.展开更多
<span style="font-family:Verdana;">The effects of each of the flavonoids;genistein (G), quercetin (Q) and</span><span style="font-family:""><span style="font-family:V...<span style="font-family:Verdana;">The effects of each of the flavonoids;genistein (G), quercetin (Q) and</span><span style="font-family:""><span style="font-family:Verdana;"> kaempferol (K) at several doses on lipid peroxides (LP) and reduced glutathione (GSH) in pooled human liver microsomes (HLMs) were investigated following the oxidative damage for 4, 6, 18 and 24 hr. HLMs (1 mg/ml) were exposed to each of the above flavonoids at 0, 5, 10, 15, 20 or 25 μM and incubated for the respective times as previously stated. Our hypothesis was that HLMs exposed to the flavonoids for the respective exposure times can decrease LP and increase GSH in HLMs to better cope with the oxidative stress. </span><span style="font-family:Verdana;">The results of our studies indicate that each of the flavonoids significantly (p < 0.01) decreased LP compared to their respective controls. The highest decrease in LP was observed for K followed by Q and G. Significant increases (p < 0.01) in GSH were observed for the flavonoid doses tested with the highest</span><span style="font-family:Verdana;"> levels observed for Q for the 24-hr. incubation. The findings suggest that the flavonoids modulate oxidative stress in HLMs by decreasing LP and such decreases in LPs may be due to the increasing and or the replenished levels of GSH in the said cells to better cope with the oxidative stress.</span></span>展开更多
AIM To study the influence of inducers BNFand PB on the stereoselective metabolism ofpropranolol in rat hepatic microsomes.METHODS Phase Ⅰ metabolism of propranololwas studied by using the microsomes induced byBNF an...AIM To study the influence of inducers BNFand PB on the stereoselective metabolism ofpropranolol in rat hepatic microsomes.METHODS Phase Ⅰ metabolism of propranololwas studied by using the microsomes induced byBNF and PB and the non-induced microsome asthe control.The enzymatic kinetic parameters ofpropranolol enantiomers were calculated byregression analysis of Lineweaver-Burk plots.Propranolol concentrations were assayed byHPLC.RESULTS A RP-HPLC method was developed todetermine propranolol concentration in rathepatic microsomes.The linearity equations forR(+)-propranolol and S(-)-propranolol wereA=705.7C+311.2C(R = 0.9987)and A= 697.2C+311.4C(R = 0.9970)respectively.Recoveriesof each enantiomer were 98.9%,99.5%,101.0%at 60 μmol/L,120 μmol/L,240 μmol/Lrespectively.At the concentration level of120 μmol/L,propranolol enantiomers weremetabolized at different rates in differentmicrosomes.The concentration ratio R(+)/S(-)of control and PB induced microsomesincreased with time,whereas that of microsomeinduced by BNF decreased.The assayed enzymeparameters were:1.Km.Control group:R(+)30+<sub>8</sub>,S(-)18+<sub>5</sub>;BNFgroup:R(+)34+3,S(-)39±7;PB group:R(+)38±17,S(-)36±10.2.Vmax.Control group:R(+)1.5+0.2,S(-)2.9±0.3;BNF group:R(+)3.8±0.3,S(-)3.3±0.5;PB group:R(+)0.07±0.03,S(-)1.94±0.07.3.Clint.Control group:R(+)60±3,S(-)170±30;BNF group:R(+)111.0±1,S(-)84± 5;PBgroup:R(+)2.0±2,S(-)56.0±1.Theenzyme.parameters compared with unpaired ttests showed that no stereoselectivity wasobserved in enzymatic affinity of threemicrosomes to enantiomers and their catalyticabilities were quite different and hadstereoselectivities.Compared with the control,microsome induced by BNF enhanced enzymeactivity to propranolol R(+)-enantiomer,andmicrosome induced by PB showed less enzymeactivity to propranolol S(-)-enantiomer whichremains the same stereoselectivities as that ofthe control.CONCLUSION Enzyme activity centers of themicrosome were changed in composition andregioselectivity after the induction of BNF andPB,and the stereoselectivities of propranololcytochrome P450 metabolism in rat hepaticmicrosomes were likely due to thestereoselectivities of the catalyzing function inenzyme.CYP1A subfamily induced by BNFexhibited pronounced contribution to propranololmetabolism with stereoselectivity to R(+)-enantiomer.CYP2B subfamily induced by PBexhibited moderate contribution to propranololmetabolism,but still had the stereoselectivity ofS(-)-enantiomer.展开更多
Nitroaromatic compounds were reductively metabolized to the corresponding amine compounds via the intermediate hydroxylamines by liver microsomes from pig,rat,chook,cattle,sheep,paralichthys olivaceus and cyprinoid in...Nitroaromatic compounds were reductively metabolized to the corresponding amine compounds via the intermediate hydroxylamines by liver microsomes from pig,rat,chook,cattle,sheep,paralichthys olivaceus and cyprinoid in varied reactivity.Similar with baker's yeast,the pig,rat and sheep liver microsomes exhibited high reactivity toward 4-nitro-1,2-dicyanbenzen(1a),while the cyprinoid liver microsomes were inefficient.Contrasted to compound 1a,monocyannitrobenzene(2a) was difficult to reduce by pig liver microsomes.In opposition to grape cells,pig liver microsomes exhibited activities toward some aromatic hydroxylamine compounds.展开更多
Objective Re Du Ning Injection (RDN), a Chinese materia medica injection, is made from the extracts of LoniceraeJaponicae Flos, Gardeniae Fructus, and Artemisiae Annuae Herba. Since last decade, RDN has been widely ...Objective Re Du Ning Injection (RDN), a Chinese materia medica injection, is made from the extracts of LoniceraeJaponicae Flos, Gardeniae Fructus, and Artemisiae Annuae Herba. Since last decade, RDN has been widely used in China for the treatment of viral infection, fever, and inflammation. To assess the potential interacting of RDN with co-administered drugs, the inhibitory effects of RDN on the enzyme activities (CYP1A1, CYP1A2, CYP2C11, CYP2D1, and CYP3A1/2) of rat liver microsomes were investigated by a cocktail method. Methods A sensitive and specific LC-MS method capable of simultaneous quantification of five metabolites in rat liver microsomes was developed and validated. Then RDN (0.625%-1.0%) was incubated with rat liver microsomes and specific substrates. The enzyme activities were expressed as the formation rate of the specific metabolites of the substrates (pmol- mg. protein-1 . min-1). Results RDN competitively inhibited the activities of CYP1A2 and CYP2C11, with inhibition constant (/~) values determined to be 0.18% and 0.63%, respectively. RDN exhibited the mixed inhibition on the activity of CYP2D1, with a K1 value of 0.15%. The activities of CYP1A1 and CYP3A1/2 were not markedly inhibited even by 1.0% RDN. Conclusion RDN could inhibit the rat enzyme activities of CYP1A2, 2Cll, and 2D1 in vitro with different inhibition modes, which is worthy of promoting safety and efficacy of RDN.展开更多
Objective Nomilin and obacunone are two important limonoids that are well known for their anticancer effect. Previous studies showed that limonoids had inhibitory effect on cytochrome P450 3A4(CYP3A4). However these...Objective Nomilin and obacunone are two important limonoids that are well known for their anticancer effect. Previous studies showed that limonoids had inhibitory effect on cytochrome P450 3A4(CYP3A4). However these effects are inconclusive with regards to prediction of potential drug interactions. Methods Nomilin or obacunone was pre-incubated with HLMs for 30 min. Following 10-fold dilution from the pre-incubation concentration, a second incubation was performed in the presence of NADPH and cytochrome P450 substrates for 15 min. The reaction was quenched and the supernatants were analyzed by chromatography/mass spectrometry. Results In this study, nomilin and obacunone showed potent inhibitory effect on CYP3A4 with the IC_(50) values of 3.50 and 6.08 μmol/L, respectively. The inhibition of CYP3A4 was in a time-, concentration-and NADPH-dependent manner with Ki values of 2.92 and 1.25 μmol/L and Kinact values of 0.033 and 0.078 min^(-1) for nomilin and obacunone respectively. These results elucidated that they were time-dependent inhibitors for CYP3A4. Conclusion Concomitant use of limonoids and other drugs may call for extra caution for purposes of clinical safety.展开更多
Objective The purpose of this work is to evaluate the in vitro inhibitory effect of magnolol(MN) and honokiol(HN) on rat / human cytochrome P450(CYP) enzymes(1A2/1A2, 2D/2D6, 3A/3A4, 2E1/2E1, and 2C/2C9). Meth...Objective The purpose of this work is to evaluate the in vitro inhibitory effect of magnolol(MN) and honokiol(HN) on rat / human cytochrome P450(CYP) enzymes(1A2/1A2, 2D/2D6, 3A/3A4, 2E1/2E1, and 2C/2C9). Methods Rat liver microsomes(RLM) and human liver microsomes(HLM) were used as the enzyme sources. After the probe substrate of each CYP isoforms was co-incubated individually with MN or HN in RLM or HLM, the metabolite production of each probe substrate in RLM and HLM incubation medium was determined and used to evaluate the activity of corresponding CYP isoforms. Results MN inhibited rat CYP1A2 and human CYP3A4 with the IC50 values of 10.0 and 56.2 μmol/L, respectively. HN inhibited rat CYP1A2 and CYP2E1, human CYP1A2 and CYP3A4 with the IC50 values of 12.1, 12.6, 17.8, and 43.9 μmol/L, respectively. Conclusion HN is a moderate or weak inhibitor of human CYP1A2. Both MN and HN are weak or non inhibitors of the other tested human CYP isoforms. The results suggest that no significant metabolic interaction seems likely to occur when the substrate drugs of CYP isoforms tested in the present work are co-administered with MN and HN.展开更多
Objective: Anthraquinone(AQ), a major bioactive component of the traditional Chinese medicine He ShouW u, has widespread applications in industry and medicine. The objective of the current study is to explore the diff...Objective: Anthraquinone(AQ), a major bioactive component of the traditional Chinese medicine He ShouW u, has widespread applications in industry and medicine. The objective of the current study is to explore the differences in the bioavailability of anthraquinones in vivo and the metabolism in liver microsomes. Materials and Methods: In vivo, we used a reliable UPLC?ESI?Qq Q?MS/MS method to measure seven AQ compounds in the jugular vein plasma of rats following oral administration of He Shou Wu. Furthermore, in order to quantify the bioavailability of AQs in vivo and to further understand the metabolism of these compounds, we compared the in vitro metabolism of AQ in different species with respect to metabolic profiles, the enzymes involved, and catalytic efficiency using liver microsomes from human(HLM), mouse(MLM), rat(RLM), and beagle dog(DLM). Results: We identified two metabolic pathways, including the hydroxylation and glucuronidation of AQ, in the liver microsomes of humans and other species using UPLC?ESI?Q?TOF. We found that substitutions on the AQ ring were crucial to the activity and regioselectivity of its hydroxylation. In general, hydroxylation activity decreased greatly with β?COOH(rhein) and enhanced dramatically with β?OH(emodin). We also found that glucuronidation of the compound emodin?8?O?β?D?glucoside acts as the main isoform in AQ hydroxylation in HLM and DLM. Total microsomal intrinsic clearance values for AQ were greatest in mouse microsomes, followed by those in dog, human, and rat microsomes. Conclusion: The absorption of different anthrquinone compounds varied based on the compound structure, the metabolism types and products of anthraquinones in liver microsomes were different in different species. These findings provide vital information for a deeper unuunderstanding of the metabolism of AQs.展开更多
Ⅰ. INTRODUCTION Since many severe diseases are caused by lipid peroxidation, a large number of investigations on the mechanisms underlying this oxidative deterioration have been carried out, and the lipid peroxidatio...Ⅰ. INTRODUCTION Since many severe diseases are caused by lipid peroxidation, a large number of investigations on the mechanisms underlying this oxidative deterioration have been carried out, and the lipid peroxidation becomes an usual indicatrix in a variety of pathological studies. The main processes of lipid peroxidation occurring in chemical system have been proposed.展开更多
Using guinea pig andrenal microsomes, we studied the inhibitory effects of 20α-hydroxyprogesterone on steroid hydroxylation reactions catalyzed by cytochromes P-450. When 17α-hydroxyprogesterone was used as a substr...Using guinea pig andrenal microsomes, we studied the inhibitory effects of 20α-hydroxyprogesterone on steroid hydroxylation reactions catalyzed by cytochromes P-450. When 17α-hydroxyprogesterone was used as a substrate, 20α-hydroxyprogesterone functioned as a competitive inhibitor on the C<sub>17</sub>—C<sub>20</sub> bond cleavage reaction of P-450<sub>17α lyase</sub>. The inhibition constant, K<sub>i</sub> was 1.37 μmol/L. 20α-hydroxyprogesterone also competitively inhibited the convertion of 17α-bydroxyprogesterone to 11-deoxycortisol by the action of P-450<sub>c21</sub>. The value of K<sub>i</sub> was 1.73μmol/L. When progesterone was used as a substrate, 20α-hydroxyprogesterone inhibited neither the 21-hydroxylation of P-450<sub>c21</sub>. the C<sub>17</sub>—C<sub>20</sub> bond cleavage, nor 17α-hydroxylation of P-450<sub>17α lyase</sub>. Based on the seresults, we can deduce that the production of androstenedione from progesterone by the action of P-450<sub>17α lyase</sub> proceeds through a successive monooxygenase reaction.展开更多
Background: T-2 toxin poses a great threat to human health because it has the highest toxicity of the currently known trichothecene mycotoxins. To understand the in vivo toxicity and transformation mechanism of T-2 to...Background: T-2 toxin poses a great threat to human health because it has the highest toxicity of the currently known trichothecene mycotoxins. To understand the in vivo toxicity and transformation mechanism of T-2 toxin, we investigated the role of two principal phase Ⅰ drug-metabolizing enzymes(cytochrome P450 [CYP450] enzymes) on the metabolism of T-2 toxin, which are crucial to the metabolism of endogenous substances and xenobiotics. We also investigated carboxylesterase, which also plays an important role in the metabolism of toxic substances.Methods: A chemical inhibition method and a recombinant method were employed to investigate the metabolism of the T-2 toxin by the CYP450 enzymes, and a chemical inhibition method was used to study carboxylesterase metabolism. Samples incubated with human liver microsomes were analyzed by high performance liquid chromatography-triple quadrupole mass spectrometry(HPLC- Qq Q MS) after a simple pretreatment.Results: In the presence of a carboxylesterase inhibitor, only 20% T-2 toxin was metabolized. When CYP enzyme inhibitors and a carboxylesterase inhibitor were both present, only 3% of the T-2 toxin was metabolized. The contributions of the CYP450 enzyme family to T-2 toxin metabolism followed the descending order CYP3A4, CYP2E1, CYP1A2, CYP2B6 or CYP2D6 or CYP2C19.Conclusions: Carboxylesterase and CYP450 enzymes are of great importance in T-2 toxin metabolism, in which carboxylesterase is predominant and CYP450 has a subordinate role. CYP3A4 is the principal member of the CYP450 enzyme family responsible for T-2 toxin metabolism. The metabolite produced by carboxylesterase is HT-2, and the metabolite produced by CYP 3A4 is 3'-OH T-2. The different metabolites show different toxicities. Our results will provide useful data concerning the toxic mechanism, the safety evaluation, and the health risk assessment of T-2 toxin.展开更多
Objective:To investigate the propensity of plumbagin to inhibit the three isoforms of human cytochrome P450(CYP),ie.,CYP1A2,CYP2C19,and CYP3A4 using human liver microsomes in ritro.Methods:Inhibitory effects of plumba...Objective:To investigate the propensity of plumbagin to inhibit the three isoforms of human cytochrome P450(CYP),ie.,CYP1A2,CYP2C19,and CYP3A4 using human liver microsomes in ritro.Methods:Inhibitory effects of plumbagin on the three human CYP isoformswere investigated using pooled human liver microsomes.Phenacetin O-deethylation,omeprazole hydroxylation and nifedipine oxidation were used as selective substrates for CYP1A2,CYP2C19 and CYP3A4 activities,respectively.Concentrations of paracetamol,5-hydroxyomeprazole,and oxidized nifedipine were determined in microsomal incubation mixture using high performance liquid chromatography.Results:Plumbagin showed significantinhibitory effects on all CYP isoforms.but with the most potent activity on CYP2C19-mediated omeprazole hydroxylation.The IC50(concentration that inhibits enzyme activity by 50%) values of plumbagin and nootkatone(selective inhibitor) for CYP2C19 were(0.78±0.01) and(27.31±0.66) μM,respectively.The inhibitory activities on CYP1 A2-mediated phenacetin O-deethylation and CYP3A4-mediated nifedipine oxidation were moderate.The IC_(50) values of plumbagin and-naphthoflavone(selective inhibitor) for CYP1A2 were(1.39±0.01) and(0.02±.0.36) μM,respectively.The corresponding IC_(50) values of plumbagin and ketoconazole(selective inhibitor) for CYP3A4 were(2.37+0.10) and(0.18±0.06) μM,respectively.Conclusions:Clinical relevance of the interference of human drug metabolizing enzymes should be aware of for further development scheme of plumbagin as antimalarial drug when used in combination with other antimalarial drugs which are metabolized by these CYP isoforms.展开更多
Objective To investgate the metabolism of terephthalic acid (TPA) in rats and its mechanism. Methods Metabolism was evaluated by incubating sodium terephthalate (NaTPA) with rat normal liver microsomes, or with mi...Objective To investgate the metabolism of terephthalic acid (TPA) in rats and its mechanism. Methods Metabolism was evaluated by incubating sodium terephthalate (NaTPA) with rat normal liver microsomes, or with microsomes pretreated by phenobarbital sodium, or with 3-methycholanthrene, or with diet control following a NADPH-generating system. The determination was performed by high performance liquid chromatography (HPLC), and the mutagenic activation was analyzed by umu tester strain Salmonella typhimurium NM2009. Expression of CYP4B 1 mRNA was detected by RT-PCR. Results The amount of NaTPA (12.5-200 μmol-L^1) detected by HPLC did not decrease in microsomes induced by NADPH-generating system. Incubation of TPA (0.025-0.1 mmol-L^-1) with induced or noninduced liver microsomes in an NM2009 umu response system did not show any mutagenic activation. TPA exposure increased the expression of CYP4B1 mRNA in rat liver, kidney, and bladder. Contusion Lack of metabolism of TPA in liver and negative genotoxic data from NM2009 study are consistent with other previous short-term tests, suggesting that the carcinogenesis in TPA feeding animals is not directly interfered with TPA itself and/or its metabolites.展开更多
Phenytoin(5,5-diphenylhydantoin;DPH) induces expression of cytochromes P450(CYPs). Interactions between DPH and tacrolimus suggested that the persistence of CYP induction after discontinuation of DPH is dependent on t...Phenytoin(5,5-diphenylhydantoin;DPH) induces expression of cytochromes P450(CYPs). Interactions between DPH and tacrolimus suggested that the persistence of CYP induction after discontinuation of DPH is dependent on the history of administration and dosing period of DPH. However, the relationship between the duration of DPH administration and expression of CYPs in the liver and small intestine of rats is not known. Alterations in levels of P-glycoprotein(P-gp;MDR1;ABCB1) as well as CYPs cause drug interactions in the small intestine. We examined the effects of the duration of DPH administration on expression of CYPs and P-gp in the liver and small intestine of rats. Rats were treated with DPH(100 mg/kg,peroral(p.o.) twice a day(b.d.)) for 2, 4, 8, and 16 d. mRNA levels of CYPs and P-gp were examined using the total RNA extracted from the liver and duodenum 2 h and 24 h after the final administration of DPH. CYP3 A activities were determined using microsomes. DPH administration for 2 d and 4 d markedly increased m RNA levels of CYPs such as CYP3 A1, CYP3 A2,CYP2 B1, and CYP2 B2 in the liver. A relatively long duration of DPH administration(8 d and16 d) resulted in abolition of the induction of hepatic CYP but increased CYP3 A activities were maintained. These results suggest that the duration of DPH administration could be an important determinant of hepatic CYP induction.展开更多
基金the National Natural Science Foundation of China(81473800).
文摘Objective:To explore the glucuronic acid metabolism of acacetin in human liver and intestinal microsomes to better characterize human uridine 5'-diphospho (UDP)-glucuronosyltransferase (UGT) isoforms.In addition,interspecies comparisons were performed to identify the most appropriate experimental animal model for an in vivo study.Methods:Liquid chromatography tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR) were used to confirm the successful biosynthesis of acacetin-7-O-glucuronide.Human isoforms of UGT and isozyme-specific chemical inhibitors were used for recombinant assays.Acacetin glucuronidation kinetics were assessed by combining acacetin with recombinant human UGT isoforms or with microsomes from humans or experimental animals.Kinetic differences between species were assessed in vitro using the same approach.Results:We identified multiple UGT isoforms that facilitated acacetin glucuronidation,and found that UGT1A1 was the major isoform that catalyzed this process.Acacetin-7-O-glucuronide formation exhibited clear substrate inhibition kinetics when combined with recombinant UGTs or with liver/intestinal microsomes derived from humans,monkeys,rats,mice,dogs,or pigs.Intrinsic metabolic clearance values of human intestinal microsomes were two-fold greater than those of human liver microsomes.Among the evaluated species,the Km value of dog microsomes (0.86 μM) was greatest in acacetin glucuronidation,while mice exhibited the highest CLint value,5.05 mL/min/mg.The CLint values of microsomes derived from monkeys and minipigs were 1.99 mL/min/mg and 2.12 mL/min/mg,respectively,exhibiting similar intrinsic metabolic clearance activity to that observed in humans.Conclusion:Monkey may represent a suitable model for experimental studies of acacetin pharmacokinetics owing to a high sequence homology of UGT1A1 and similar UGT1A1 glucuronidation activity to humans.
文摘In the present study, we developed and validated an analytical method using ultra performance liquid chromatography-mass spectrometry (UPLC/MS) for the quantitative determination of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) metabolism by rat hepatic microsomes. BDE-47 is a brominated flame retardant that was widely used in a variety of consumer products and has subsequently been identified as a ubiquitous environmental contaminant. Hydroxy-bromodiphenyl ethers (OH-BDEs) were isolated from rat hepatic microsomes by liquid-liquid extraction. Chromatographic separation was achieved by UPLC on a C18 column with gradient elution using a mobile phase consisting of methanol and water, each containing 0.1% formic acid, at a flow rate of 0.2 mL/min. Detection and quantification were performed using a mass spectrometer in single ion recording mode with negative electrospray ionization. The UPLC/MS method was validated for linearity, limit of quantification (LOQ), accuracy, precision and recovery. The weighted calibration curves (1/X2) were linear over a concentration range of 5 - 250 nM with LOQ values between 5 nM and 50 nM for the individual OH-BDEs. Intra- and inter- day accuracy (%DEV) and precision (%RSD) values ranged from –11.7% to 9.5% and 5.9% to 16.5%, respectively. Recovery values of 70% to 90% were obtained for all OH-BDEs. The validated method allowed us to successfully analyze metabolite formation following incubation of BDE-47 with hepatic microsomes prepared from phenobarbital-treated rats. Results demonstrate that the UPLC/MS method has sufficient sensitivity and reproducibility to fully characterize the in vitro metabolism of BDE-47 and possibly other PBDEs.
基金supported by a POSDRU grantNo.159/1.5/S/136893 grant with title:‘Parteneriat strategic pentru crecterea calitarii cercetarii stiintifice din universitatile medicale prin acordarea de burse doctorale?i postdoctorale-Doc Med.Net_2.0’
文摘Genistein, the main isoflavone from soy, and bisphenol A (BPA), a food contaminant, are considered ubiquitous xenoestrogens. Here we investigated the influence of genistein and BPA on estrone (El) metabolism in rat liver microsomes. Both substances inhibited the 2-hydroxylation and 16a-hydroxylation of E1, but in different degrees, thereby reducing the 2-OH-E1/16a-OH-E1 ratio,
基金the National Natural Science Foundation of China (No. 30225047)the Science and Technology Foundation of Zhejiang Province, China (No. 2005C13026)
文摘Objective: To study the stereoselective glucuronidation of carvedilol (CARV) by three Chinese liver microsomes. Methods: The metabolites of CARV were identified by a hydrolysis reaction with β-glucuronidase and HPLC-MS/MS. The enzyme kinetics for CARV enantiomers glucuronidation was determined by a reversed phase-high pressure liquid chromatogra-phy (RP-HPLC) assay using (S)-propafenone as internal standard after precolumn derivatization with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosylisothiocyanate. Results: Two CARV glucuronides were found in three Chinese liver microsomes incubated with CARV. The non-linear regression analysis showed that the values of Km and Vmax for (S)-CARV and (R)-CARV enantiomers were (118±44) μmol/L, (2 500±833) pmol/(min·mg protein) and (24±7) μmol/L, (953±399) pmol/(min·mg protein), respectively. Conclusion: These results suggested that there was a significant (P<0.05) stereoselective glucuronidation of CARV enantiomers in three Chinese liver microsomes, which might partly explain the enantioselective pharmacokinetics of CARV.
文摘Objective To determine whether the cytochrome P4502B6(CYP2B6)is involved in the oxidation of propofol by human liver microsomes.Methods The change of propofol concentration in an incubation mixture with human liver microsomes was monitored by the high performance liquid chromatography(HPLC),in order to calculate the rate constants of metabolism of propofol.The correlation between the rate constants and the rate of metabolism of CYP2B6 selective substrate bupropion,and the effect of two different CYP2B6 specific inhibitors on the propofol metabolism were examined.Results The mean rate constant of propofol metabolism by liver microsomes obtained from twelve individuals was 3.9(95% confidence intervals 3.3,4.5)nmol·min-1·mg-1 protein.The rate constants of propofol metabolism by liver microsomes were significantly correlated with bupropion hydroxylation(r=0.888,P<0.001).Both selective chemical inhibitors of CYP2B6,orphenadrine and N,N',N″-triethylenethiophosphoramide(thioTEPA),reduced the rate constants of propofol metabolism by 37.5%(P<0.001)and 42.7%(P<0.001)in liver microsomes,respectively.Conclusions CYP2B6 is predominantly involved in the oxidation of propofol by human liver microsomes.
文摘In this study, the effects of several fluoroquinolones (FQs), such as Ciprofloxacin (CPFX);Orbifloxacin (OBFX);Norfloxacin (NFX);Ofloxacin (OFX);and Enerofloxacin (EFX) on activities of both Cytochrome P450 1A (CYP1A) and Cytochrome P450 3A (CYP3A) of feline microsomes by <i>in vitro</i> tests were studied. Ethoxyresorufin O-deethylation (EROD) and Midazolam 1' hydroxylation and 4-hydroxylation (MDZ1'H and MDZ4H) were analyzed by High Performance Liquid Chromatography (HPLC). All the FQs inhibited the reactions by a competitive or noncompetitive and irreversible manner. The inhibitory constants (K<sub>i</sub>) were as followings: CYP1A;ranged from 0.12 to 1.23 mM for NFX, OBFX, EFX, CPFX, OFX and CYP3A, for MDZ1'H;ranged from 5.8 to 35 and MDZ4H;9 to 29 mM, respectively. As these values are higher by 24 to 200-times of given single clinical dose of serum levels after application of FQs. It indicates that if co-administrated with these FQs by reversible inhibitory manner, the inhibition of CYP1A and CYP3A effect on CYP1A and 3A actions is not very significant to cause drug interaction with above mentioned enzyme substrates. Out of the FQs tested, CPFX and NFX for CYP1A, and CPFX for CYP3A showed irreversible inhibitory effects (time-dependent), so it has been concluded that these drugs may cause drug-drug interaction by accumulation, when they are repeatedly administrated. Since EFX is biotransformed to CPFX by the liver, it could have the identical risk too.
文摘<span style="font-family:Verdana;">The effects of each of the flavonoids;genistein (G), quercetin (Q) and</span><span style="font-family:""><span style="font-family:Verdana;"> kaempferol (K) at several doses on lipid peroxides (LP) and reduced glutathione (GSH) in pooled human liver microsomes (HLMs) were investigated following the oxidative damage for 4, 6, 18 and 24 hr. HLMs (1 mg/ml) were exposed to each of the above flavonoids at 0, 5, 10, 15, 20 or 25 μM and incubated for the respective times as previously stated. Our hypothesis was that HLMs exposed to the flavonoids for the respective exposure times can decrease LP and increase GSH in HLMs to better cope with the oxidative stress. </span><span style="font-family:Verdana;">The results of our studies indicate that each of the flavonoids significantly (p < 0.01) decreased LP compared to their respective controls. The highest decrease in LP was observed for K followed by Q and G. Significant increases (p < 0.01) in GSH were observed for the flavonoid doses tested with the highest</span><span style="font-family:Verdana;"> levels observed for Q for the 24-hr. incubation. The findings suggest that the flavonoids modulate oxidative stress in HLMs by decreasing LP and such decreases in LPs may be due to the increasing and or the replenished levels of GSH in the said cells to better cope with the oxidative stress.</span></span>
基金the National Natural Science Foundation of China,No.39370805.
文摘AIM To study the influence of inducers BNFand PB on the stereoselective metabolism ofpropranolol in rat hepatic microsomes.METHODS Phase Ⅰ metabolism of propranololwas studied by using the microsomes induced byBNF and PB and the non-induced microsome asthe control.The enzymatic kinetic parameters ofpropranolol enantiomers were calculated byregression analysis of Lineweaver-Burk plots.Propranolol concentrations were assayed byHPLC.RESULTS A RP-HPLC method was developed todetermine propranolol concentration in rathepatic microsomes.The linearity equations forR(+)-propranolol and S(-)-propranolol wereA=705.7C+311.2C(R = 0.9987)and A= 697.2C+311.4C(R = 0.9970)respectively.Recoveriesof each enantiomer were 98.9%,99.5%,101.0%at 60 μmol/L,120 μmol/L,240 μmol/Lrespectively.At the concentration level of120 μmol/L,propranolol enantiomers weremetabolized at different rates in differentmicrosomes.The concentration ratio R(+)/S(-)of control and PB induced microsomesincreased with time,whereas that of microsomeinduced by BNF decreased.The assayed enzymeparameters were:1.Km.Control group:R(+)30+<sub>8</sub>,S(-)18+<sub>5</sub>;BNFgroup:R(+)34+3,S(-)39±7;PB group:R(+)38±17,S(-)36±10.2.Vmax.Control group:R(+)1.5+0.2,S(-)2.9±0.3;BNF group:R(+)3.8±0.3,S(-)3.3±0.5;PB group:R(+)0.07±0.03,S(-)1.94±0.07.3.Clint.Control group:R(+)60±3,S(-)170±30;BNF group:R(+)111.0±1,S(-)84± 5;PBgroup:R(+)2.0±2,S(-)56.0±1.Theenzyme.parameters compared with unpaired ttests showed that no stereoselectivity wasobserved in enzymatic affinity of threemicrosomes to enantiomers and their catalyticabilities were quite different and hadstereoselectivities.Compared with the control,microsome induced by BNF enhanced enzymeactivity to propranolol R(+)-enantiomer,andmicrosome induced by PB showed less enzymeactivity to propranolol S(-)-enantiomer whichremains the same stereoselectivities as that ofthe control.CONCLUSION Enzyme activity centers of themicrosome were changed in composition andregioselectivity after the induction of BNF andPB,and the stereoselectivities of propranololcytochrome P450 metabolism in rat hepaticmicrosomes were likely due to thestereoselectivities of the catalyzing function inenzyme.CYP1A subfamily induced by BNFexhibited pronounced contribution to propranololmetabolism with stereoselectivity to R(+)-enantiomer.CYP2B subfamily induced by PBexhibited moderate contribution to propranololmetabolism,but still had the stereoselectivity ofS(-)-enantiomer.
基金Supported by the National Basic Research Program of China(No.2009CB724706)the National Natural Science Foundation of China(No.20876025)
文摘Nitroaromatic compounds were reductively metabolized to the corresponding amine compounds via the intermediate hydroxylamines by liver microsomes from pig,rat,chook,cattle,sheep,paralichthys olivaceus and cyprinoid in varied reactivity.Similar with baker's yeast,the pig,rat and sheep liver microsomes exhibited high reactivity toward 4-nitro-1,2-dicyanbenzen(1a),while the cyprinoid liver microsomes were inefficient.Contrasted to compound 1a,monocyannitrobenzene(2a) was difficult to reduce by pig liver microsomes.In opposition to grape cells,pig liver microsomes exhibited activities toward some aromatic hydroxylamine compounds.
基金National Science and Technology Major Project“Creation of Major New Drugs”from China(No.2013ZX09402203)Natural Science Foundation of Jiangsu Province(No.BK2013403)
文摘Objective Re Du Ning Injection (RDN), a Chinese materia medica injection, is made from the extracts of LoniceraeJaponicae Flos, Gardeniae Fructus, and Artemisiae Annuae Herba. Since last decade, RDN has been widely used in China for the treatment of viral infection, fever, and inflammation. To assess the potential interacting of RDN with co-administered drugs, the inhibitory effects of RDN on the enzyme activities (CYP1A1, CYP1A2, CYP2C11, CYP2D1, and CYP3A1/2) of rat liver microsomes were investigated by a cocktail method. Methods A sensitive and specific LC-MS method capable of simultaneous quantification of five metabolites in rat liver microsomes was developed and validated. Then RDN (0.625%-1.0%) was incubated with rat liver microsomes and specific substrates. The enzyme activities were expressed as the formation rate of the specific metabolites of the substrates (pmol- mg. protein-1 . min-1). Results RDN competitively inhibited the activities of CYP1A2 and CYP2C11, with inhibition constant (/~) values determined to be 0.18% and 0.63%, respectively. RDN exhibited the mixed inhibition on the activity of CYP2D1, with a K1 value of 0.15%. The activities of CYP1A1 and CYP3A1/2 were not markedly inhibited even by 1.0% RDN. Conclusion RDN could inhibit the rat enzyme activities of CYP1A2, 2Cll, and 2D1 in vitro with different inhibition modes, which is worthy of promoting safety and efficacy of RDN.
基金National Natural Science Foundation of China(No.81373890 and 81430096)National Key Research and Development Program(No.2016YFE0121400)Program for Changjiang Scholars and Innovative Research Team in University(No.IRT_14R41)
文摘Objective Nomilin and obacunone are two important limonoids that are well known for their anticancer effect. Previous studies showed that limonoids had inhibitory effect on cytochrome P450 3A4(CYP3A4). However these effects are inconclusive with regards to prediction of potential drug interactions. Methods Nomilin or obacunone was pre-incubated with HLMs for 30 min. Following 10-fold dilution from the pre-incubation concentration, a second incubation was performed in the presence of NADPH and cytochrome P450 substrates for 15 min. The reaction was quenched and the supernatants were analyzed by chromatography/mass spectrometry. Results In this study, nomilin and obacunone showed potent inhibitory effect on CYP3A4 with the IC_(50) values of 3.50 and 6.08 μmol/L, respectively. The inhibition of CYP3A4 was in a time-, concentration-and NADPH-dependent manner with Ki values of 2.92 and 1.25 μmol/L and Kinact values of 0.033 and 0.078 min^(-1) for nomilin and obacunone respectively. These results elucidated that they were time-dependent inhibitors for CYP3A4. Conclusion Concomitant use of limonoids and other drugs may call for extra caution for purposes of clinical safety.
基金supported financially by the Hubei Province Natural Science Funds (No.2013ZR009)
文摘Objective The purpose of this work is to evaluate the in vitro inhibitory effect of magnolol(MN) and honokiol(HN) on rat / human cytochrome P450(CYP) enzymes(1A2/1A2, 2D/2D6, 3A/3A4, 2E1/2E1, and 2C/2C9). Methods Rat liver microsomes(RLM) and human liver microsomes(HLM) were used as the enzyme sources. After the probe substrate of each CYP isoforms was co-incubated individually with MN or HN in RLM or HLM, the metabolite production of each probe substrate in RLM and HLM incubation medium was determined and used to evaluate the activity of corresponding CYP isoforms. Results MN inhibited rat CYP1A2 and human CYP3A4 with the IC50 values of 10.0 and 56.2 μmol/L, respectively. HN inhibited rat CYP1A2 and CYP2E1, human CYP1A2 and CYP3A4 with the IC50 values of 12.1, 12.6, 17.8, and 43.9 μmol/L, respectively. Conclusion HN is a moderate or weak inhibitor of human CYP1A2. Both MN and HN are weak or non inhibitors of the other tested human CYP isoforms. The results suggest that no significant metabolic interaction seems likely to occur when the substrate drugs of CYP isoforms tested in the present work are co-administered with MN and HN.
基金financial support from the Major Scientific and Technological Special Project for"Significant New Drugs Creation"(No.2014ZX09304307)
文摘Objective: Anthraquinone(AQ), a major bioactive component of the traditional Chinese medicine He ShouW u, has widespread applications in industry and medicine. The objective of the current study is to explore the differences in the bioavailability of anthraquinones in vivo and the metabolism in liver microsomes. Materials and Methods: In vivo, we used a reliable UPLC?ESI?Qq Q?MS/MS method to measure seven AQ compounds in the jugular vein plasma of rats following oral administration of He Shou Wu. Furthermore, in order to quantify the bioavailability of AQs in vivo and to further understand the metabolism of these compounds, we compared the in vitro metabolism of AQ in different species with respect to metabolic profiles, the enzymes involved, and catalytic efficiency using liver microsomes from human(HLM), mouse(MLM), rat(RLM), and beagle dog(DLM). Results: We identified two metabolic pathways, including the hydroxylation and glucuronidation of AQ, in the liver microsomes of humans and other species using UPLC?ESI?Q?TOF. We found that substitutions on the AQ ring were crucial to the activity and regioselectivity of its hydroxylation. In general, hydroxylation activity decreased greatly with β?COOH(rhein) and enhanced dramatically with β?OH(emodin). We also found that glucuronidation of the compound emodin?8?O?β?D?glucoside acts as the main isoform in AQ hydroxylation in HLM and DLM. Total microsomal intrinsic clearance values for AQ were greatest in mouse microsomes, followed by those in dog, human, and rat microsomes. Conclusion: The absorption of different anthrquinone compounds varied based on the compound structure, the metabolism types and products of anthraquinones in liver microsomes were different in different species. These findings provide vital information for a deeper unuunderstanding of the metabolism of AQs.
文摘Ⅰ. INTRODUCTION Since many severe diseases are caused by lipid peroxidation, a large number of investigations on the mechanisms underlying this oxidative deterioration have been carried out, and the lipid peroxidation becomes an usual indicatrix in a variety of pathological studies. The main processes of lipid peroxidation occurring in chemical system have been proposed.
文摘Using guinea pig andrenal microsomes, we studied the inhibitory effects of 20α-hydroxyprogesterone on steroid hydroxylation reactions catalyzed by cytochromes P-450. When 17α-hydroxyprogesterone was used as a substrate, 20α-hydroxyprogesterone functioned as a competitive inhibitor on the C<sub>17</sub>—C<sub>20</sub> bond cleavage reaction of P-450<sub>17α lyase</sub>. The inhibition constant, K<sub>i</sub> was 1.37 μmol/L. 20α-hydroxyprogesterone also competitively inhibited the convertion of 17α-bydroxyprogesterone to 11-deoxycortisol by the action of P-450<sub>c21</sub>. The value of K<sub>i</sub> was 1.73μmol/L. When progesterone was used as a substrate, 20α-hydroxyprogesterone inhibited neither the 21-hydroxylation of P-450<sub>c21</sub>. the C<sub>17</sub>—C<sub>20</sub> bond cleavage, nor 17α-hydroxylation of P-450<sub>17α lyase</sub>. Based on the seresults, we can deduce that the production of androstenedione from progesterone by the action of P-450<sub>17α lyase</sub> proceeds through a successive monooxygenase reaction.
基金supported by the Key Projects in the National Science & Technology Pillar Program of China (2011BAK10B07)the National Major Special Projects in the Ministry of Science and Technology of China (2012 2X09301003-001-010)
文摘Background: T-2 toxin poses a great threat to human health because it has the highest toxicity of the currently known trichothecene mycotoxins. To understand the in vivo toxicity and transformation mechanism of T-2 toxin, we investigated the role of two principal phase Ⅰ drug-metabolizing enzymes(cytochrome P450 [CYP450] enzymes) on the metabolism of T-2 toxin, which are crucial to the metabolism of endogenous substances and xenobiotics. We also investigated carboxylesterase, which also plays an important role in the metabolism of toxic substances.Methods: A chemical inhibition method and a recombinant method were employed to investigate the metabolism of the T-2 toxin by the CYP450 enzymes, and a chemical inhibition method was used to study carboxylesterase metabolism. Samples incubated with human liver microsomes were analyzed by high performance liquid chromatography-triple quadrupole mass spectrometry(HPLC- Qq Q MS) after a simple pretreatment.Results: In the presence of a carboxylesterase inhibitor, only 20% T-2 toxin was metabolized. When CYP enzyme inhibitors and a carboxylesterase inhibitor were both present, only 3% of the T-2 toxin was metabolized. The contributions of the CYP450 enzyme family to T-2 toxin metabolism followed the descending order CYP3A4, CYP2E1, CYP1A2, CYP2B6 or CYP2D6 or CYP2C19.Conclusions: Carboxylesterase and CYP450 enzymes are of great importance in T-2 toxin metabolism, in which carboxylesterase is predominant and CYP450 has a subordinate role. CYP3A4 is the principal member of the CYP450 enzyme family responsible for T-2 toxin metabolism. The metabolite produced by carboxylesterase is HT-2, and the metabolite produced by CYP 3A4 is 3'-OH T-2. The different metabolites show different toxicities. Our results will provide useful data concerning the toxic mechanism, the safety evaluation, and the health risk assessment of T-2 toxin.
基金the financial support provided by Thammasat University Research Fund under the TU Research Scholar,Contract No 78/2557Commission on Higher Education,Ministry of Education of Thailand,Office of Higher Education Commission,Thammasat University(Excellence Center in Pharmacology and Molecular Biology of Malaria and Cholangiocarcinoma),Thammasat University and the Thailand Research Fund through a Royal Golden Jubilee Ph.D.scholarship to Wiriyaporn Sumsakul(Grant no.PHD/0326/2551)
文摘Objective:To investigate the propensity of plumbagin to inhibit the three isoforms of human cytochrome P450(CYP),ie.,CYP1A2,CYP2C19,and CYP3A4 using human liver microsomes in ritro.Methods:Inhibitory effects of plumbagin on the three human CYP isoformswere investigated using pooled human liver microsomes.Phenacetin O-deethylation,omeprazole hydroxylation and nifedipine oxidation were used as selective substrates for CYP1A2,CYP2C19 and CYP3A4 activities,respectively.Concentrations of paracetamol,5-hydroxyomeprazole,and oxidized nifedipine were determined in microsomal incubation mixture using high performance liquid chromatography.Results:Plumbagin showed significantinhibitory effects on all CYP isoforms.but with the most potent activity on CYP2C19-mediated omeprazole hydroxylation.The IC50(concentration that inhibits enzyme activity by 50%) values of plumbagin and nootkatone(selective inhibitor) for CYP2C19 were(0.78±0.01) and(27.31±0.66) μM,respectively.The inhibitory activities on CYP1 A2-mediated phenacetin O-deethylation and CYP3A4-mediated nifedipine oxidation were moderate.The IC_(50) values of plumbagin and-naphthoflavone(selective inhibitor) for CYP1A2 were(1.39±0.01) and(0.02±.0.36) μM,respectively.The corresponding IC_(50) values of plumbagin and ketoconazole(selective inhibitor) for CYP3A4 were(2.37+0.10) and(0.18±0.06) μM,respectively.Conclusions:Clinical relevance of the interference of human drug metabolizing enzymes should be aware of for further development scheme of plumbagin as antimalarial drug when used in combination with other antimalarial drugs which are metabolized by these CYP isoforms.
基金This work was supported by the National Natural Science Foundation of China (No. 30170798), the Preliminary Study of an ImportantProject in the National Basic Research, MOST (No. 2001CCA04900) and the Greatest Project in the National Basic Research (No.2002CB512908).
文摘Objective To investgate the metabolism of terephthalic acid (TPA) in rats and its mechanism. Methods Metabolism was evaluated by incubating sodium terephthalate (NaTPA) with rat normal liver microsomes, or with microsomes pretreated by phenobarbital sodium, or with 3-methycholanthrene, or with diet control following a NADPH-generating system. The determination was performed by high performance liquid chromatography (HPLC), and the mutagenic activation was analyzed by umu tester strain Salmonella typhimurium NM2009. Expression of CYP4B 1 mRNA was detected by RT-PCR. Results The amount of NaTPA (12.5-200 μmol-L^1) detected by HPLC did not decrease in microsomes induced by NADPH-generating system. Incubation of TPA (0.025-0.1 mmol-L^-1) with induced or noninduced liver microsomes in an NM2009 umu response system did not show any mutagenic activation. TPA exposure increased the expression of CYP4B1 mRNA in rat liver, kidney, and bladder. Contusion Lack of metabolism of TPA in liver and negative genotoxic data from NM2009 study are consistent with other previous short-term tests, suggesting that the carcinogenesis in TPA feeding animals is not directly interfered with TPA itself and/or its metabolites.
文摘Phenytoin(5,5-diphenylhydantoin;DPH) induces expression of cytochromes P450(CYPs). Interactions between DPH and tacrolimus suggested that the persistence of CYP induction after discontinuation of DPH is dependent on the history of administration and dosing period of DPH. However, the relationship between the duration of DPH administration and expression of CYPs in the liver and small intestine of rats is not known. Alterations in levels of P-glycoprotein(P-gp;MDR1;ABCB1) as well as CYPs cause drug interactions in the small intestine. We examined the effects of the duration of DPH administration on expression of CYPs and P-gp in the liver and small intestine of rats. Rats were treated with DPH(100 mg/kg,peroral(p.o.) twice a day(b.d.)) for 2, 4, 8, and 16 d. mRNA levels of CYPs and P-gp were examined using the total RNA extracted from the liver and duodenum 2 h and 24 h after the final administration of DPH. CYP3 A activities were determined using microsomes. DPH administration for 2 d and 4 d markedly increased m RNA levels of CYPs such as CYP3 A1, CYP3 A2,CYP2 B1, and CYP2 B2 in the liver. A relatively long duration of DPH administration(8 d and16 d) resulted in abolition of the induction of hepatic CYP but increased CYP3 A activities were maintained. These results suggest that the duration of DPH administration could be an important determinant of hepatic CYP induction.