Biomedical subjects

Dafang Zhong

Publications and source records attributed to Dafang Zhong.

At least 19 recordsLinked to original sources

PubMed2007

Synthesis and biological evaluation of 1,3,3,4-tetrasubstituted pyrrolidine CCR5 receptor antagonists. Discovery of a potent and orally bioavailable anti-HIV agent.

A series of 1,3,3,4-tetrasubstituted pyrrolidine containing CCR5 receptor antagonists were designed, which were elaborated either by condensation of a lithium salt of 3-(N,N-dibenzyl)aminopropionic acid methyl ester with ethyl benzoformate or by Baylis-Hillman reaction of ethyl acrylate with ethyl benzoformate and subsequent 1,4-addition of benzylamine, in the key steps. These compounds bearing 4-(N,N-disubstituted)amino piperidine units showed low nanomolar potency against the CCR5 receptor, whereas molecules with a 4-phenylpiperidine moiety displayed poor activity. Asymmetric synthesis of the most potent compound 23 a gave rise to the (3R,4S)-enantiomer 30 and the (3S,4R)-enantiomer 31, which showed IC(50) values of 2.9 and 385.9 nM, respectively. These results indicated that (3R,4S)-configuration in the series of compounds is favored for their interaction with the CCR5 receptor. The possible binding mode of these antagonists with the CCR5 receptor was discussed using a computer-modeling method. Compound 30 displayed excellent replication inhibition of seven genetically diverse R5 HIV-1 strains in the PBMC model, in a concentration-dependent manner with EC(50) values ranging from 0.3 nM to 30 nM. This molecule showed oral bioavailabilities of 41.2 % and 21.6 % in rats and dogs, respectively. Thus, compound 30 is a promising candidate for the treatment of HIV-1 infection.

Administration, Oral↗

PubMed2006

Pharmacokinetics and metabolism of the flavonoid scutellarin in humans after a single oral administration.

Scutellarin is widely used in treating various cardiovascular diseases. Few data are available regarding its metabolism and pharmacokinetics in humans. The objectives of this study were to develop methods to identify major metabolites of scutellarin in human urine and plasma and to determine simultaneously the parent drug and its major metabolites in human plasma for pharmacokinetic studies. Four metabolites were detected in urine samples by liquid chromatography coupled with electrospray multi-stage mass spectrometry (MS), but only one of them was found in plasma. Its structure was confirmed as scutellarein 6-O-beta-D-glucuronide by MS, NMR, and UV absorbance spectra. The plasma concentrations of scutellarin and the major metabolite were simultaneously determined using liquid chromatography-tandem MS. After a single p.o. administration of 60 mg of scutellarin to 20 healthy subjects, the plasma concentrations of scutellarin were very low, and its plasma concentration-time curve was also anomalous. Plasma concentration of the major metabolite was comparatively high, and the peak plasma concentration was 87.0 +/- 29.1 ng/ml. The Tmax was late (7.85 +/- 1.62 h), and part of individual pharmacokinetic profiles showed double peaks, which indicated scutellarin could be absorbed into the intestine after hydrolysis to its aglycone by bacterial enzymes. This was followed by reconjugation in the intestinal cell and/or liver with glucuronic acid catalyzed by the phase II enzyme, which showed regioselectivity and species difference. The regioselectivity of glucuronoconjugation for scutellarin may be of importance for pharmacological activity. Plasma concentration of isoscutellarin can be used as a biomarker of scutellarin intake.

Administration, Oral↗

PubMed2006

Biotransformation of tolbutamide to 4'-hydroxytolbutamide by the fungus Cunninghamella blakesleeana.

The hypoglycemic drug tolbutamide is commonly used as a probe drug to evaluate CYP2C9 enzyme activity in terms of production of 4'-hydroxytolbutamide. In the present study, an initial screening of seven filamentous fungi was carried out to identify which was most competent to transform tolbutamide into 4'-hydroxytolbutamide. From this screening, the fungus Cunninghamella blakesleeana AS 3.910 was selected as a suitable bioconverter. At a concentration of 1.2 mg ml(-1), the growing fungus transformed 95.0% of tolbutamide into 4'-hydroxytolbutamide in 96 h. With resting culture, the yield could reach 91.7% and exceeded 91.0% even when the tolbutamide concentration was increased to 4.0 mg ml(-1). On scale-up to 3 l buffer containing 12.0 g tolbutamide, 90% of tolbutamide was transformed into 4'-hydroxytolbutamide in 96 h. Work-up of the broth by column chromatography and recrystallization yielded 6.5 g (53.9% recovered) of 4'-hydroxytolbutamide with a purity of more than 99%. These results suggest C. blakesleeana AS 3.910 is a useful biosynthetic tool in the preparation of 4'-hydroxytolbutamide.

Biotransformation↗

PubMed2006

Stability of glufosfamide in phosphate buffers and in biological samples.

Glufosfamide is a new, potential chemotherapeutic agent currently under investigation. Stability of glufosfamide was investigated in sodium phosphate buffers with different pH and temperature and in biological samples. Glufosfamide and isophosphamide mustard were quantified simultaneously using a liquid chromatography-ion trap mass spectrometric method; precision and accuracy were within 15% for each analyte. Glufosfamide was stable in neutral buffers, but decomposed to form isophosphoramide mustard under acidic and basic conditions, which was pH- and temperature-dependent. The stability of glufosfamide varied in different biological samples. Results indicated that glufosfamide was unstable in some biological samples, such as the small intestine, smooth muscles, pancreas and urine, especially in the small intestine homogenate, with a half-life of 1.1 h. But the pH (<8) and beta-glucosidase of the tissue homogenate was found to have negligible contribution to the degradation of glufosfamide. The enzymatic inhibition experiment with the specific inhibitor, saccharo-1,4-lactone, demonstrated that it was glucuronidase that resulted in the degradation of glufosfamide in small intestine homogenate. Methanol was recommended to be used to homogenize the tissue in an ice water bath, and the container for urine collection should also be maintained in an ice water bath, and all the biological samples collected should be preserved in frozen condition until analysis.

Animals↗

PubMed2006

Determination of zolmitriptan in human plasma by liquid chromatography-tandem mass spectrometry method: application to a pharmacokinetic study.

A sensitive and selective liquid chromatography-tandem spectrometry method for the determination of zolmitriptan was developed and validated over the linearity range 0.05-30 ng/ml with 0.5 ml of plasma using diphenhydramine as the internal standard. Liquid-liquid extraction using a mixture of diethyl ether and dichloromethane was used to extract the drug and the internal standard from plasma. The mass spectrometer was operated under the selected reaction monitoring (SRM) mode using the atmospheric pressure chemical ionization (APCI) technique. The instrument parameters were optimized to obtain 3.0 min run time. The mobile phase consisted of acetonitrile-water-formic acid (70:30:0.5), at a flow rate of 0.5 ml/min. In positive mode, zolmitriptan produced a protonated precursor ion at m/z 288 and a corresponding product ion at m/z 58. And internal standard produced a protonated precursor ion at m/z 256 and a corresponding product ion at m/z 167. The inter- and intra-day precision (%R.S.D.) were less than 8.5% and accuracy (%error) was less than -2.5%. The method had a lower limit of quantification of 0.05 ng/ml for zolmitriptan, which offered increased sensitivity and selectivity of analysis, compared with existing methods. The method was successfully applied to a pharmacokinetic study of zolmitriptan after an oral administration of 5 mg zolmitriptan to 20 healthy volunteers.

Administration, Oral↗

PubMed2006

Assignments of 1H and 13C NMR spectral data for ondansetron and its two novel metabolites, 1-hydroxy-ondansetron diastereoisomers.

Assignments of 1H and 13C NMR chemical shifts were made by means of heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) experiments for ondansetron, and by means of 1H-1H correlation spectroscopy (1H-1H COSY) and two-dimensional nuclear Overhauser effect spectroscopy (NOESY) experiments for two novel metabolites (M1 and M2) of ondansetron. These two metabolites were isolated for the first time from Mucor circinelloides.

Carbon Isotopes↗

PubMed2006

Development and validation of a liquid chromatographic/tandem mass spectrometric method for the determination of sertraline in human plasma.

A sensitive and rapid liquid chromatographic/tandem mass spectrometric method was developed and validated for the determination of sertraline in human plasma. The analyte and internal standard (IS, diphenhydramine) were extracted with 3 mL of diethyl ether/dichloromethane (2:1, v/v) from 0.25 mL plasma, then separated on a Zorbax Eclipse XDB C18 column using methanol/water/formic acid (75:25:0.1, v/v/v) as the mobile phase. The triple quadrupole mass spectrometry was applied via an atmospheric pressure chemical ionization (APCI) source for detection. The fragmentation pattern of the protonated sertraline was elucidated with the aid of product mass spectra of isotopologous peaks. Quantification was performed using selected reaction monitoring of the transitions of m/z 306 --> 159 for sertraline and m/z 256 --> 167 for the IS. The method was linear over the concentration range of 0.10-100 ng/mL. The intra-day and inter-day precisions, expressed by relative standard deviation, were both less than 6.7%. Assay accuracies were within +/-6.9% as terms of relative error. The lower limit of quantification (LLOQ) was identifiable and reproducible at 0.10 ng/mL with a precision of 8.3% and an accuracy of 9.6%. The validated method has been successfully applied for the pharmacokinetic study and bioequivalence evaluation of sertraline in 18 healthy volunteers after a single oral administration of 50 mg sertraline hydrochloride tablets.

Chromatography, Liquid↗

PubMed2006

Screening for in vivo metabolites of isovalertatin family oligosaccharides in rats by liquid chromatography coupled to electrospray ionization tandem mass spectrometry.

Liquid chromatography/electrospray ionization tandem mass spectrometry (LC/MS(n)) was used to identify trace levels of in vivo metabolites after the administration of isovalertatin M23 or isovalertatin D23 to rats. The biosamples of urine, feces, and ileum incubation were pre-treated by solid-phase extraction (SPE), and then chromatographed with a reversed-phase C8 column with acetonitrile/1.5 mM aqueous ammonia (18:82, v/v) as the mobile solvent. The parent drug and the possible metabolites were identified by two independent qualitative parameters, retention time and collision-induced dissociation product ions. Nine and seven metabolites were successfully characterized from biosamples after administration of isovalertatins M23 and D23, respectively, to rats. The metabolism seemed to take place in the rat intestinal tract, and metabolic pathways were identified including isovaleryl de-esterification and hydrolysis of alpha-glucose units located either at the reducing or the non-reducing terminus.

Amines↗

PubMed2006

Pharmacokinetics of telmisartan in healthy Chinese subjects after oral administration of two dosage levels.

To study the pharmacolkinetics of telmisartan in healthy Chinese male subjects after oral administration of two dosage levels, 36 healthy subjects were divided into two groups and given a single oral dose of 40 or 80 mg telmisartan (CAS 144701-48-4, MicardisPlus). A sensitive liquid chromatography-tandem mass spectrometry method (LC-MS-MS) was used for the determination of telmisartan in plasma. Both, a non-compartmental and compartmental method were used for analysis of parameters of kinetics. The main pharmacokinetic parameters of the 40 mg and 80 mg regimen group were as follows: t(max) (1.76 +/- 1.75) h, (1.56 +/- 1.09) h, C(max) (163.2 +/- 128.4) ng/mL, (905.7 +/- 583.4) ng/mL, t1/2 (23.6 +/- 10.8) h, (23.0 +/- 6.4) h, AUC(o-t) (1456 +/- 1072) ng x h/mL, (6759 +/- 3754) ng x h/mL, AUC(o-infinity (1611 +/- 1180) ng x h/mL, (7588 +/- 4661) ng x h/mL, respectively. After dose normalization, there was significant difference for main pharmacokinetic parameters C(max) AUC(o-t) and AUC(o-infinity) between two dosage level groups. The plasma concentration-time profile of telmisartan was characterized by a high degree of inter-individual variability and the disposition of telmisartan in healthy Chinese subjects was dose-dependent. The pharmacokinetic parameters C(max) and AUC(o-inifinity) of the 80 mg regimen group increased to about 5-fold compared to that of the 40 mg regimen group, but there was no significant difference for t(max) and t1/2 between the two dose groups.

Adult↗

PubMed2005

Identification and quantitative determination of benproperine metabolites in human plasma and urine by liquid chromatography-tandem mass spectrometry.

Two novel metabolites of benproperine (BPP), 1-[1-methyl-2-[2-(phenylmethyl)phenoxy]ethyl]-3-piperidinol (3-OH-BPP) and 1-[1-methyl-2-[2-(phenylmethyl)phenoxy]ethyl]-4-piperidinol (4-OH-BPP), were confirmed by comparison of retention times and mass spectra with those of synthetic standards using liquid chromatography-tandem mass spectrometry. Selective and sensitive procedures were developed for the simultaneous determination of BPP, 3-OH-BPP and 4-OH-BPP in human plasma and urine. The analytes were extracted from plasma sample and enzymatically hydrolyzed urine samples by liquid-liquid extraction, separated through a Diamonsil C(18) column (150 mm x 4.6 mm i.d.) and determined by tandem mass spectrometry with an electrospray ionization interface in selected reaction monitoring mode. Dextromethorphan was used as internal standard. The mobile phase consisted of acetonitrile-water-formic acid (34:66:1, v/v/v), and flow-rate was 0.5 ml min(-1). This method has a lower limit of quantification (LLOQ) of 60, 4.0 and 4.0 nmol l(-1)for BPP, 3-OH-BPP and 4-OH-BPP in plasma, 4.9, 4.7 and 2.4 nmol l(-1) in urine, respectively. The intra- and inter-run precision were measured to be below 9.2%, and the accuracy was within +/-4.3% for the analytes. The method was successfully used to determine BPP, 3-OH-BPP and 4-OH-BPP in plasma and urine for pharmacokinetic investigation. The results indicated residue of 3-OH-BPP in the body at least 192 h after an oral dose of BPP.

Antitussive Agents↗

PubMed2005

Pharmacokinetic differences between pantoprazole enantiomers in rats.

PURPOSE: The purpose of this study was to quantitatively clarify the contribution of the absorption, protein binding, and metabolism of cytochrome P450 enzymes to the enantioselective pharmacokinetics of pantoprazole enantiomers in rats. METHODS: The enantioselective pharmacokinetics of pantoprazole enantiomers was estimated by an oral administration of racemic pantoprazole to rats. The pharmacokinetic differences between pantoprazole enantiomers were evaluated by the experiments of the in situ perfusion into rat small intestine, the protein binding, and the in vitro metabolism in rat liver microsomes of pantoprazole enantiomers. RESULTS: The mean area under the curve value of S-pantoprazole was 1.5 times greater than that of R-pantoprazole after administration of racemic pantoprazole to rats (20 mg/kg, p.o.). There were significant differences in k(e) (p < 0.05), t1/2 (p < 0.01), and mean residence time (p < 0.01) values between the two enantiomers. In the in situ absorption study, the absorption rate constants were of no significant differences between the two enantiomers. The mean unbound fraction of R-pantoprazole was slightly greater than that of S-pantoprazole. The intrinsic clearance (CLint) of the formation of the 5'-O-demethyl metabolite from S-pantoprazole was 4-fold lower than that from R-pantoprazole. However, the CLint value for the sulfone and 6-hydroxy metabolites from S-pantoprazole was higher than that from R-pantoprazole. The sum of the CLint of the formation of all three metabolites was 3.06 and 4.82 mL/min/mg protein for S- and R-pantoprazole, respectively. CONCLUSIONS: This study suggests that the enantioselective pharmacokinetics of pantoprazole enantiomers in rats is probably ascribable to their enantioselective metabolism, which is contributed by all the three metabolic pathways, including sulfoxide oxidation, 4'-O-demethylation, and 6-hydroxylation.

2-Pyridinylmethylsulfinylbenzimidazoles↗

PubMed2005

Stability of baicalin in biological fluids in vitro.

The stability of baicalin in buffered aqueous solutions at different pHs and in biological fluids, including plasma, urine and tissue homogenates, were investigated in vitro. Structures of the degradation products of baicalin were elucidated by liquid chromatography-electrospray ion trap mass spectrometry and the degradation mechanism was proposed with the aid of electron paramagnetic resonance spectrometry. The results showed that the degradation of baicalin was pH- and temperature-dependent. The oxidation-reduction reaction intermediated by phenoxyl radicals is the major degradation process for baicalin in plasma and urine in vitro, whereas baicalin mainly undergoes hydrolysis and phase II metabolic pathways when spiked in tissue homogenates. It is found that acidification can stabilize baicalin in urine and plasma (the final pH adjusted to 3.0-4.0), and baicalin is relatively stable in tissues homogenized with methanol.

Animals↗

PubMed2005

Absorption and enterohepatic circulation of baicalin in rats.

Pharmacokinetics of baicalin, in form of its parent drug (BG) and conjugated metabolites (BGM), were studied following intravenous and oral administration of baicalin to intact rats. The enterohepatic circulation of BG and BGM was also assessed in a linked-rat model. Multiple plasma and urine samples were collected, and concentrations of BG and BGM were determined using a liquid chromatography/tandem mass spectrometry method. The concentration of BGM was assayed in the form of baicalein after treatment with beta-glucuronidase/sulfatase. After i.v. administration, plasma concentration of BG rapidly declined with the elimination half-life (T1/2) of 0.1 till 4 h post dose, followed by slight increase from 4-8 h in plasma concentrations after drug administration. These plasma concentrations resulted in a significant prolongation of the terminal elimination half-life of BG (T1/2 TER, 9.7 h). BG also displayed slight increase in plasma concentrations (12-24 h) after oral administration, with T1/2 TER of 12.1 h. Based on the AUC of BG and BGM, the absolute bioavailability of baicalin was 2.2+/-0.2% and 27.8+/-5.6%, respectively. The exposure of baicalin to the systemic circulation was approximately 118-fold lower than that of BGM after oral administration (AUC0-t, 4.43 versus 523.97 nmol.h/mL). The high extent of glucuronidation suggested the possible presence of enterohepatic circulation, which was confirmed in the linked-rat model since plasma concentrations of BG and BGM were observed in bile-recipient rats at 4 to 36 h. The extent of enterohepatic circulation after intravenous administration of baicalin was 4.8% and 13.3% for BG and BGM, respectively. It was determined that 18.7% and 19.3% of the administered baicalin were subjected to enterohepatic circulation for BG and BGM, respectively, after oral administration. These results confirm that BG undergoes extensive first-pass glucuronidation and that enterohepatic circulation contributes significantly to the exposure of BG and BGM in rats.

Animals↗

PubMed2005

Sensitive liquid chromatography-tandem mass spectrometry method for the determination of cefixime in human plasma: application to a pharmacokinetic study.

A sensitive and selective liquid chromatographic-tandem mass spectrometric (LC-MS-MS) method was developed to determine cefixime ((6R,7R)-7-[(Z)-2-(2-amino-4-thiazolyl)-2-(carboxymethoxyimino)acetamido]-8-oxo-3-vinyl-5-thia-1-azabicyclo-[4,2,0]-oct-2-ene-2-carboxylic acid) in human plasma. After a simple protein precipitation using acetonitrile, the post-treatment samples were analyzed on a C(8) column interfaced with a triple quadrupole tandem mass spectrometer. Positive electrospray ionization was employed as the ionization source. The mobile phase consisted of acetonitrile-water-formic acid (40:60:0.5, v/v/v). The analyte and internal standard cefetamet were both detected by use of selected reaction monitoring mode. The method was linear in the concentration range of 0.05-8.0 microg/ml. The lower limit of quantification was 0.05 microg/ml. The intra- and inter-day relative standard deviation across three validation runs over the entire concentration range was less than 12.7%. The accuracy determined at three concentrations (0.05, 0.80 and 7.2 microg/ml for cefixime) was within +/-2.0% in terms of relative error. Each plasma sample was chromatographed within 3.5 min. The method herein described was successfully applied for the evaluation of pharmacokinetic profiles of cefixime capsule in 24 healthy volunteers.

Anti-Bacterial Agents↗

PubMed2005

Simultaneous determination of methylephedrine and noscapine in human plasma by liquid chromatography-tandem mass spectrometry.

A selective and sensitive method has been developed and validated for simultaneous quantification of methylephedrine and noscapine in human plasma. Analytes were extracted from human plasma samples by liquid-liquid extraction, separated on a Diamonsil C18 column and detected by tandem mass spectrometer with an atmospheric pressure chemical ionization (APCI) interface. Diphenhydramine was used as the internal standard (I.S.). The method was found to be precise and accurate within the linear range 0.1-100 ng/ml for each analyte. The intra- and inter-day relative standard deviations (R.S.D.s) were below 5.2% for methylephedrine and 6.7% for noscapine. The inter-day relative error (RE) as determined from quality control samples (QCs) was less than 3.0% for each analyte. The assay was successfully employed in a pharmacokinetic study after an oral administration of a multicomponent formulation containing 20 mg DL-methylephedrine hydrochloride, 16 mg noscapine, 300 mg paracetamol and 1mg of chlorpheniramine maleate.

Atmospheric Pressure↗

PubMed2005

Sensitive liquid chromatography-tandem mass spectrometry method for the simultaneous determination of paracetamol and guaifenesin in human plasma.

A rapid and sensitive method for the simultaneous determination of paracetamol and guaifenesin in human plasma was developed and validated, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. After extracted from plasma samples by diethyl ether-dichloromethane (3:2, v/v), the analytes and internal standard osalmide were chromatographed on a C18 column. Detection was performed on a triple quadrupole tandem mass spectrometer by selected reaction monitoring (SRM) mode via atmospheric pressure chemical ionization (APCI). The method was linear in the concentration range of 0.05-20.0 microg/ml for paracetamol and 5.0-2000.0 ng/ml for guaifenesin. The intra- and inter-day precision was within 14% for both paracetamol and guaifenesin. The assay accuracy was within +/-2.4% for the analytes. This is the first assay method described for the simultaneous determination of paracetamol and guaifenesin in plasma using one chromatographic run. The method was successfully employed in a pharmacokinetic study after an oral administration of a multicomponent formulation, containing 650 mg paracetamol, 200 mg guaifenesin, 60 mg pseudoephedrine and 20 mg dextrorphan.

Acetaminophen↗

PubMed2005

Determination of dioscin in rat plasma by liquid chromatography-tandem mass spectrometry.

A sensitive and specific high-performance liquid chromatography-tandem mass spectrometric (LC-MS/MS) assay for dioscin in rat plasma was developed. Ginsenoside Rh2 was employed as an internal standard. Dioscin is a naturally occurring saponin present in many traditional Chinese medicinal plants. Dioscin was determined after the acetonitrile-mediated plasma protein precipitation. The mobile phase consisted of acetonitrile:10 mmol/l aqueous ammonium acetate (95:5, v:v), which was pumped at 0.8 ml/min. The analytical column (100 mm x 4.6 mm i.d.) was packed with Hypersil ODS material (5 microm). The standard curve was linear from 1 to 100 ng/ml. The assay was specific, accurate (percentage deviations from nominal concentrations were <10%), precise and reproducible (within- and between-day coefficients of variation <10%). Dioscin in rat plasma was stable over three freeze-thaw cycles and at ambient temperatures for 24 h. The utility of the assay was demonstrated by determining dioscin plasma concentrations in five rats for 120 h following a single oral gavage dose of 90 mg/kg.

Animals↗

PubMed2005

Characterization of the pharmacokinetics of dioscin in rat.

Dioscin (diosgenyl 2,4-di-O-alpha-l-rhamnopyranosyl-beta-d-glucopyranoside) is an important constituent of some traditional Chinese medicines with several bioactivities. We have investigated the pharmacokinetics of dioscin in rat after intravenous and oral administrations. Compartmental methods were used to perform pharmacokinetic data analysis. The dose-dependent pharmacokinetics of dioscin was characterized after intravenous administrations (0.064, 0.16, 0.4 and 1.0mg/kg) to rats. There was significant decrease in clearance with increasing dose (4.67+/-0.09 ml/min/kg (0.064 mg/kg) versus 3.49+/-0.23 ml/min/kg (1.0 mg/kg), P<0.05), and the plot of reciprocal clearance values versus the doses was linear (r=0.909, P<0.05). After an I.V. dose of 1mg/kg, simultaneous oral gavage of activated charcoal did not change the pharmacokinetic parameters indicating enterohepatic recycling of dioscin is not important in rat. The absolute oral bioavailability was very low (0.2%). In tissue distribution and bile excretion studies after I.V. and oral administrations, dioscin was shown to undergo a prolonged absorption from the intestinal tract and slow elimination from organs, and only a small amount of drug was recovered in bile. The cumulative amounts of dioscin in feces and urine indicated that the parent drug is mainly excreted in the feces.

Administration, Oral↗