Biomedical subjects

D Zhong

Publications and source records attributed to D Zhong.

At least 19 recordsLinked to original sources

PubMed2006

Metabolism and excretion of imrecoxib in rat.

The metabolism and excretion of imrecoxib, a novel and moderately selective cyclooxygenase-II inhibitor, were investigated in rat. The structures of metabolites were identified by mass spectrometry (MSn) and nuclear magnetic resonance. Metabolic profiles of imrecoxib in urine, bile and faeces were obtained by HPLC and LC/MSn, and cumulative excretion was determined by LC/MSn. Imrecoxib was extensively metabolized in rat after intravenous administration, with less than 2% of the dose excreted as parent drug in either urine or faeces. The major metabolic pathway was that the 4'-methyl group of imrecoxib was first oxidized to the 4'-hydroxymethyl metabolite (M4), followed by additional oxidation to 4'-carboxylic acid metabolite (M2). The dihydroxylated metabolite, 4'-hydroxymethyl-5-hydroxyl imrecoxib (M3), was further oxidized to 4'-hydroxymethyl-5-carbonyl metabolite (M5), and glucuronide conjugates of M2-4 were formed. After intravenous (5 mg kg-1) administration, the majority of the dose was recovered in the faeces. The dose was primarily excreted as the carboxylic acid metabolite in addition to the 4'-hydroxymethyl metabolite. The carboxylic acid metabolite was mainly excreted in faeces, while the 4'-hydroxymethyl metabolite was mainly excreted in urine.

Animals↗

PubMed2005

Catalytic activities of human cytochrome P450 2C91, 2C93 and 2C9*13.

Cytochrome P450 2C9 (CYP2C9) is a geneticly polymorphic enzyme responsible for the metabolism of some clinically important drugs. CYP2C9*13 is an allele identified in a Chinese poor metabolizer of lornoxicam which has a Leu90Pro amino acid substitution. This paper reports on a study aimed at comparing the catalytic properties of CYP2C9*13 with those of the wild-type CYP2C9*1 and mutant CYP2C9*3 (Ile359Leu) in the COS-7 expression system using various substrates. CYP2C9*3 and *13 produced far lower luminescence than CYP2C9*1 in luciferin H metabolism. CYP2C9*13 exhibited an 11-fold increase in Km but no change in Vmax with tolbutamide as the substrate, a five-fold increase in Km and an 88.8% reduction in Vmax with diclofenac. These data indicate that CYP2C9*13 exhibits reduced metabolic activity toward all studied CYP2C9 substrates. The magnitude of the CYP2C9*13-associated decrease in intrinsic clearance (Vmax/Km) is greater than that associated with CYP2C9*3.

Amino Acid Substitution↗

PubMed2005

Expression of interleukin-17 in ischemic brain tissue.

Ischemic brain injury is acute local inflammation, leading to accumulation of pro-inflammatory cytokines. Cytokines influence the recruitment of leucocytes and play a key role in the inflammatory injury processes. Recently, a number of studies have demonstrated a close relationship between brain ischemia and cytokines. Interleukin-17 (IL-17) is a newly identified T-cell-specific cytokine. In this study, we evaluated the source and the action of IL-17 over the course of cerebral ischemia in rats (Sprague-Dawley) and humans. The levels of IL-17 in the ischemic hemisphere of the human brain, which was removed at necropsy, were assayed immunohistochemically. In rats, permanent middle cerebral artery occlusion (pMCAO) was obtained by inserting nylon monofilament into the right external carotid artery, occluding the right middle cerebral artery. The expression of IL-17 mRNA in rat was assayed using oligoprobe in situ hybridization. IL-17 production by neuroglial cells was assayed by double-staining using antibody glial fibrillary acidic protein (GFAP) and antibody IL-17. Levels of IL-17 were elevated in the ischemic hemispheres of human brain compared with the opposite normal hemispheres and peaked at days 3-5 after brain ischemia. The IL-17-positive cells were found in the ischemic lesion region. IL-17 mRNA was also elevated in ischemic hemispheres of pMCAO-operated rats, which were slightly elevated after 1 h and peaked at 6 days. IL-17 and GFAP double-stained were extensive in rat ischemic hemisphere. The ischemia-induced IL-17 expression in human brain reported here for the first time was very similar to that in rat model except that the peak was slightly earlier. We found for the first time that IL-17 was involved in an intense inflammatory reaction of brain ischemic injury in human. In pMCAO-operated rats, our findings suggest that IL-17 is produced by the neuroglial cells in the brain region undergoing ischemic insult. We suggest that in additional to T cells the neuroglial cell may be another cellular origin of IL-17 in later progression of brain ischemia.

Animals↗

PubMed2003

Pharmacokinetics of a new sustained-release formulation of theophylline sodium glycerinate in healthy subjects with a new asymmetric dosage regimen.

Pharmacokinetics of a new sustained-release formulation of theophylline sodium glycerinate in healthy subjects was studied. In this study, a new asymmetric dosage regimen was presented to achieve a better accordance with the chronotherapy of asthma. Each of 10 subjects was administered one tablet (equivalent to 0.1 g anhydrous theophylline) in the morning and four tablets in the evening for a consecutive 6 days and blood samples were collected at the predetermined time and analyzed by a validated HPLC method. This new regimen produced a steady and effective level of theophylline in plasma for the whole day, especially in the evening. A lower dose in the morning could reach the effective level (C(min)4.97 +/- 1.60 microg/mL and C(max)10.68 +/- 1.80 micro g/mL over the a.m. dosing interval) and a higher dose in the evening did not result in toxic levels but led to a reasonable concentration range (C(max)9.72 +/- 1.56 microg/mL over p.m. dosing interval), which could maintain a higher plasma theophylline concentration without the risk of serious adverse events and control asthmatic symptoms probably occurring during the night or early in the morning. The results suggested that the proposed asymmetric regimen was necessary, practicable and safe for twice daily sustained-release tablets of theophylline sodium glycerinate and also provides the basis for the clinical dosage regimen of other theophylline formulated products.

Adult↗

PubMed2002

In vitro and in vivo characterization of [125I]iodomethyllycaconitine in the rat.

The in vitro and in vivo binding characteristics of [125I]iodomethyllycaconitine ([125I]iodoMLA) were determined in the rat. [125I]iodoMLA binding to rat cerebral cortex membranes was saturable and reversible and its specific binding represented approximately 70-80% of the total binding. [125I]iodoMLA labeled a single site with Kd = 1.8 +/- 0.4 nM and Bmax = 68 +/- 3 fmol/mg protein. Kinetic analysis revealed a t1/2 for association and dissociation of 10.5 +/- 3.1 and 10.3 +/- 1.6 min, respectively. Pharmacological characterization of [125I]iodoMLA binding indicated that it was specific for the alpha7 nAChR. In vitro brain region binding studies revealed greater binding in regions known to contain high numbers of alpha7 nAChRs. The analysis of the biodistribution of intravenously administered [125I]iodoMLA indicated that it was rapidly cleared and exhibited poor brain penetration; nevertheless, the levels of [125I]iodoMLA in alpha7 nAChR-rich target regions were significantly increased compared to the nontarget region (cerebellum) 60-120 min after administration. No metabolism of MLA by human liver S9 fraction was detected. Our results suggest that [125I]iodoMLA will be a useful radioligand to study the alpha7 nAChR in vitro and in vivo.

Animals↗

PubMed2001

The anticancer drug-DNA complex: femtosecond primary dynamics for anthracycline antibiotics function.

The anthracycline-DNA complex, which is a potent agent for cancer chemotherapy, has a unique intercalating molecular structure with preference to the GC bases of DNA, as shown by Rich's group in studies of single-crystal x-ray diffraction. Understanding cytotoxicity and its photoenhancement requires the unraveling of the dynamics under the solution-phase, physiological condition. Here we report our first study of the primary processes of drug function. In a series of experiments involving the drug (daunomycin and adriamycin) in water, the drug-DNA complexes, the complexes with the four nucleotides (dGTP, dATP, dCTP, and dTTP), and the drug-apo riboflavin-binding protein, we show the direct involvement of molecular oxygen and DNA base-drug charge-separation-the rates for the reduction of the drug and dioxygen indicate the crucial role of drug/base/O(2) in the efficient and catalytic redox cycling. These dynamical steps, and the subsequent reactions of the superoxide product(s), can account for the photoenhanced function of the drug in cells, and potentially for the cell death.

Animals↗

PubMed2001

Femtosecond dynamics of a drug-protein complex: daunomycin with Apo riboflavin-binding protein.

In this contribution, we report studies of the primary dynamics of the drug-protein complexes of daunomycin with apo riboflavin-binding protein. With femtosecond resolution, we observed the ultrafast charge separation between daunomycin and aromatic amino acid residues of the protein, tryptophan(s). Electron transfer occurs from tryptophan(s) to daunomycin with two reaction times, 1 ps and 6 ps, depending on the local complex structure. The formation of anionic daunomycin radical is crucial for triggering a series of chemical reactions in redox cycling. One of the subsequent reactions is the reduction of dioxygen to form active superoxide by the reduced daunomycin. This catalytic process was found to occur within 10 ps. In the absence of dioxygen, charge recombination takes a much longer time, more than 100 ps. These results, along with similar findings in DNA and nucleotides, elucidate that the ultrafast generation of reduced daunomycin radicals by photoactivation is a primary step for the observed photoenhancement of drug cytotoxicity by several orders of magnitude. We also studied the dependence of the dynamics on protein conformations at different ionic strengths and denaturant concentrations. We observe a sharp transition from the tertiary structure to the unfolding state at 2 M of denaturant concentration.

Carrier Proteins↗

PubMed2001

Femtosecond dynamics of flavoproteins: charge separation and recombination in riboflavine (vitamin B2)-binding protein and in glucose oxidase enzyme.

Flavoproteins can function as hydrophobic sites for vitamin B(2) (riboflavin) or, in other structures, with cofactors for catalytic reactions such as glucose oxidation. In this contribution, we report direct observation of charge separation and recombination in two flavoproteins: riboflavin-binding protein and glucose oxidase. With femtosecond resolution, we observed the ultrafast electron transfer from tryptophan(s) to riboflavin in the riboflavin-binding protein, with two reaction times: approximately 100 fs (86% component) and 700 fs (14%). The charge recombination was observed to take place in 8 ps, as probed by the decay of the charge-separated state and the recovery of the ground state. The time scale for charge separation and recombination indicates the local structural tightness for the dynamics to occur that fast and with efficiency of more than 99%. In contrast, in glucose oxidase, electron transfer between flavin-adenine-dinucleotide and tryptophan(s)/tyrosine(s) takes much longer times, 1.8 ps (75%) and 10 ps (25%); the corresponding charge recombination occurs on two time scales, 30 ps and nanoseconds, and the efficiency is still more than 97%. The contrast in time scales for the two structurally different proteins (of the same family) correlates with the distinction in function: hydrophobic recognition of the vitamin in the former requires a tightly bound structure (ultrafast dynamics), and oxidation-reduction reactions in the latter prefer the formation of a charge-separated state that lives long enough for chemistry to occur efficiently. Finally, we also studied the influence on the dynamics of protein conformations at different ionic strengths and denaturant concentrations and observed the sharp collapse of the hydrophobic cleft and, in contrast, the gradual change of glucose oxidase.

Carrier Proteins↗

PubMed2001

Two butylated aminooligosaccharides isolated from the culture filtrate of Streptomyces luteogriseus.

Two novel aminooligosaccharides, butytatins M03 and M13 were isolated and purified from the culture filtrate of Streptomyces luteogriseus. Analysis by liquid chromatography coupled to electrospray ionization mass spectrometry indicated their resemblance to isovalertatin, with a four-carbon acyl group. Their structures were established by NMR as aminooligosaccharide derivatives possessing a butylated side chain.

Carbon Isotopes↗

PubMed2001

[(125)I]3beta-(4-ethyl-3-iodophenyl)nortropane-2beta-carboxylic acid methyl ester ([(125)I]EINT): a potent and selective radioligand for the brain serotonin transporter.

The binding characteristics of [(125)I]3beta-(4-ethyl-3-iodophenyl)nortropane-2beta-carboxylic acid methyl ester ([(125)I]EINT), a high-affinity selective ligand for the serotonin transporter (5-HTT), and its binding characteristics to rat brain membranes were determined. [(125)I]EINT binding to rat cerebral cortex membranes was saturable and reversible, and its specific binding represented approximately 90% of the total binding. [(125)I]EINT labeled a single site with K(d) = 0.22 +/- 0.03 nM and B(max) = 583 +/- 38 fmol/mg protein. Kinetic analysis revealed a t(1/2) for association and dissociation of 20 and 24 min, respectively. Pharmacological characterization of [(125)I]EINT confirmed its high specificity for the 5-HTT. The pattern of brain region distribution in vivo of intravenously administered [(125)I]EINT indicated greater accumulation of the radioligand in 5-HTT-rich brain regions. However, the signal-to-background ratio was low. Thus, [(125)I]EINT appears to be a useful radioligand for studying the 5-HTT in vitro, but it may not be a good in vivo ligand.

Animals↗

PubMed2001

Profiling of isovalertatin family aminooligosaccharides extracted from the culture of Streptomyces luteogriseus by using liquid chromatography/electrospray ionization mass spectrometry.

A rapid and novel procedure using the liquid chromatography coupled to an electrospray ionization ion trap mass spectrometry technique was applied for the profiling of isovalertatin-family aminooligosaccharides in the extract from the culture filtrate of Streptomyces luteogriseus. The aminooligosaccharides were separated on a C-8 reversed-phase column with an acetonitrile-alkaline water gradient. The desired homologues were detected using the multiple reaction monitoring mode, and the chemical structures were confirmed by analyzing the characteristic fragment ions in their collision-induced dissociation spectra. This facile procedure led to the identification of all the five known aminooligosaccharides, isovalertatins M03, M13, M23, D03, and D23, in addition to the characterization of at least 41 novel isovalertatins, the molecular weights of which ranged from 729 to 2,793. This kind of assay should be intended as a simple and convenient way for the high-throughput analysis of screening aminooligosaccharides and potentially other structural families of natural products.

Amines↗

PubMed2001

Processing of beta-dystroglycan by matrix metalloproteinase disrupts the link between the extracellular matrix and cell membrane via the dystroglycan complex.

The dystroglycan complex is a membrane-spanning complex composed of two subunits, alpha- and beta-dystroglycan. alpha-dystroglycan is a cell surface peripheral membrane protein which binds to the extracellular matrix (ECM), whereas beta-dystroglycan is an integral membrane protein which anchors alpha-dystroglycan to the cell membrane. The dystroglycan complex provides a tight link between the ECM and cell membrane. Dysfunction of the dystroglycan complex has commonly been implicated in the molecular pathogenesis of severe forms of hereditary neuromuscular diseases, including Duchenne muscular dystrophy, Fukuyama-type congenital muscular dystrophy and sarcoglycanopathy (LGMD2C, -D, -E and -F). To begin to clarify the pathway by which the dysfunction of the dystroglycan complex could lead to muscle cell degeneration, we investigated the proteolytic processing of the dystroglycan complex in this study. We demonstrate that (i) a 30 kDa fragment of beta-dystroglycan is expressed in peripheral nerve, kidney, lung and smooth muscle, but not skeletal muscle, cardiac muscle or brain, and (ii) this fragment is the product of proteolytic processing of the extracellular domain of beta-dystroglycan by the membrane-associated matrix metalloproteinase (MMP) activity. Importantly, furthermore, we demonstrate that this processing disintegrates the dystroglycan complex. Our results indicate that the processing of beta-dystroglycan by MMP causes the disruption of the link between the ECM and cell membrane via the dystroglycan complex, which could have profound effects on cell viability. Based on these and previously reported findings, we propose a hypothesis that this processing may play a crucial role in the molecular pathogenesis of sarcoglycanopathy.

Animals↗

PubMed2001

Simultaneous determination of flupirtine and its major active metabolite in human plasma by liquid chromatography-tandem mass spectrometry.

A rapid, selective and sensitive HPLC-tandem mass spectrometry method was developed and validated for simultaneous determination of flupirtine and its active metabolite D-13223 in human plasma. The analytes and internal standard diphenhydramine were extracted from plasma samples by liquid-liquid extraction, and chromatographed on a C18 column. The mobile phase consisted of acetonitrile-water-formic acid (60:40:1, v/v/v), at a flow rate of 0.5 ml/min. Detection was performed on a triple quadrupole tandem mass spectrometer by selected reaction monitoring (SRM) mode via atmospheric pressure chemical ionization (APCI). The method has a limit of quantitation of 10 ng/ml for flupirtine and 2 ng/ml for D-13223, using 0.5-ml plasma sample. The linear calibration curves were obtained in the concentration range of 10.0-1500.0 ng/ml for flupirtine and 2.0-300.0 ng/ml for D-13223. The intra- and inter-run precision (RSD), calculated from quality control (QC) samples was less than 7.2% for flupirtine and D-13223. The accuracy as determined from QC samples was less than 5% for the analytes. The overall extraction recoveries of flupirtine and D-13223 were determined to be about 66% and 78% on average, respectively. The method was applied for the evaluation of the pharmacokinetics of flupirtine and active metabolite D-13223 in volunteers following peroral administration.

Aminopyridines↗

PubMed2001

Structural revision of isovalertatins M03, M13, and M23 isolated from the culture of Streptomyces luteogriseus.

Three aminooligosaccharides, isovalertatins M03 (1), M13 (2), and M23 (3) were isolated and purified from the culture filtrate of Streptomyces luteogriseus. Their physicochemical properties, liquid chromatographic behavior, and spectroscopic data were in full accordance with the reported compounds [Xu, Q.; Wang, Q.; Lu, D. CN Patent 1100756, 1995; Chem. Abstr. 1995, 123, 110278n], but their structures were reinvestigated and revised by spectroscopic methods, including ESI multistage mass spectrometry and 2-dimensional NMR techniques.

Amines↗

PubMed2001

Factor IXa:factor VIIIa interaction. helix 330-338 of factor ixa interacts with residues 558-565 and spatially adjacent regions of the a2 subunit of factor VIIIa.

The physiologic activator of factor X consists of a complex of factor IXa, factor VIIIa, Ca(2+) and a suitable phospholipid surface. In one study, helix 330 (162 in chymotrypsin) of the protease domain of factor IXa was implicated in binding to factor VIIIa. In another study, residues 558-565 of the A2 subunit of factor VIIIa were implicated in binding to factor IXa. We now provide data, which indicate that the helix 330 of factor IXa interacts with the 558-565 region of the A2 subunit. Thus, the ability of the isolated A2 subunit was severely impaired in potentiating factor X activation by IXa(R333Q) and by a helix replacement mutant (IXa(helixVII) in which helix 330-338 is replaced by that of factor VII) but it was normal for an epidermal growth factor 1 replacement mutant (IXa(PCEGF1) in which epidermal growth factor 1 domain is replaced by that of protein C). Further, affinity of each 5-dimethylaminonaphthalene-1-sulfonyl (dansyl)-Glu-Gly-Arg-IXa (dEGR-IXa) with the A2 subunit was determined from its ability to inhibit wild-type IXa in the tenase assay and from the changes in dansyl fluorescence emission signal upon its binding to the A2 subunit. Apparent K(d(A2)) values are: dEGR-IXa(WT) or dEGR-IXa(PCEGF1) approximately 100 nm, dEGR-IXa(R333Q) approximately 1.8 micrometer, and dEGR-IXa(helixVII) >10 micrometer. In additional experiments, we measured the affinities of these factor IXa molecules for a peptide comprising residues 558-565 of the A2 subunit. Apparent K(d(peptide)) values are: dEGR-IXa(WT) or dEGR-IXa(PCEGF1) approximately 4 micrometer, and dEGR-IXa(R333Q) approximately 62 micrometer. Thus as compared with the wild-type or PCEGF1 mutant, the affinity of the R333Q mutant for the A2 subunit or the A2 558-565 peptide is similarly reduced. These data support a conclusion that the helix 330 of factor IXa interacts with the A2 558-565 sequence. This information was used to model the interface between the IXa protease domain and the A2 subunit, which is also provided herein.

Amino Acid Substitution↗

PubMed2001

Quantitative determination of nitrendipine and its metabolite dehydronitrendipine in human plasma using liquid chromatography-tandem mass spectrometry.

A sensitive and high-throughput LC-MS-MS method was developed for simultaneous determination of nitrendipine (NIT) and its major metabolite, dehydronitrendipine (DNIT) in human plasma using nifedipine as the internal standard. Plasma samples were prepared based on a simple liquid-liquid extraction. The extracted samples were analyzed on a Zorbax SB C(18) column interfaced with a triple quadrupole tandem mass spectrometer. Positive atmospheric pressure chemical ionization was employed as the ionization source. The analytes were detected by use of selected reaction monitoring mode. Standard curves were linear (r > or = 0.995) over the concentration range of 0.4-40 ng/mL for NIT and 0.2-20 ng/mL for DNIT. The intra- and inter-run precision was measured to be below 8.5% for NIT and DNIT. The inter-run accuracy was less than 4% for the analytes. The overall extraction recoveries of NIT and DNIT were determined to be about 75% and 78% on average, respectively. The chromatographic run time was approximately 3 min. More than 120 samples could be assayed daily with this method, including sample preparation, data acquisition and processing. The method developed was successfully used to investigate plasma concentrations of NIT and DNIT in a pharmacokinetic study of volunteers who received NIT orally.

Antihypertensive Agents↗

PubMed2001

Applications of liquid chromatography-tandem mass spectrometry in drug and biomedical analyses.

BACKGROUND: Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is one of the major tools for bioanalytical works. These instruments can be used for quantitative determination of plasma samples in pharmacokinetic studies. LC-MS/MS techniques frequently provide specific, selective and sensitive quantitative results often with reduced sample preparation and analysis time relative to other commonly employed techniques. METHODS: The applications of these instruments include analysis of nine corticosteroids illegally adulterated in traditional Chinese medicines, identification of drug metabolites of roxithromycin, propafenone and some glucuronide conjugates and the quantitative determination of plasma samples containing amlodipine, nitrendipine, flupirtine and their major metabolites. CONCLUSIONS: LCQ is ideally suited for the rapid identification of metabolites because it provides on-line LC/MS(n) capability, enabling multiple MS stages to obtain the maximum amount of structural information, while TSQ provides excellent precise and accurate results for quantitative assays at very low detection limits.

Amlodipine↗

PubMed2001

Biflavonoids from the aerial part of Stephania tetrandra.

Investigation of the aerial part of Stephania tetrandra led to the isolation of two biflavonoids, stephaflavone A and stephaflavone B, with a 3-6" linkage pattern, together with beta-sitosterol. Their structures were established on the basis of their spectroscopic data and their physicochemical properties.

Flavonoids↗