Biomedical subjects

Z Zhao

Publications and source records attributed to Z Zhao.

At least 145 records · Page 8Linked to original sources

PubMed1999

Stereoselective hydroxylation of nonpeptidic HIV protease inhibitors by CYP2D6.

PNU-106893, N-{3-[1-(4-hydroxy-2-oxo-6-phenyl-6-propyl-5, 6-dihydro-2H-pyran-3-yl)-2, 2-dimethylpropyl]phenyl}-1-methyl-1H-imidazole-4-sulfonamide, is a selective HIV aspartyl protease inhibitor under evaluation as a potential oral treatment of acquired immunodeficiency disease. PNU-106893 is a mixture of four stereoisomers, designated PNU-109165 (3alphaR, 6S), PNU-109166 (3alphaR, 6R), PNU-109167 (3alphaS, 6S), and PNU-109168 (3alphaS, 6R). The major P450 isoforms involved in the metabolism of PNU-106893 and its pure stereoisomers are identified as CYP2D6 and CYP3A4. The major oxidative biotransformation pathway of PNU-106893 which occurs in microsomal incubations appears to be hydroxylation of the phenylethyl side chain attached to the C-6 carbon of the dihydropyrone ring. This hydroxylation is mediated by CYP2D6 only and the process is stereoselective for the 6R absolute stereochemistry. The configuration at position 3 appears to play a minor role in the CYP2D6 mediated hydroxylation. These insights have impacted drug candidate selection for this class of compounds.

Animals↗

PubMed1999

2'-Deoxyadenosine causes cell death in embryonic chicken sympathetic ganglia and brain.

Previous work has shown that nucleosides produce apoptosis in sympathetic ganglion (SG) cells in vitro. The present study examined the effects of nucleosides on the development of the chick embryo in vivo with special attention to the SG and the optic tectum of the central nervous system. In the presence of an adenosine deaminase inhibitor, adenosine and 2'-deoxyadenosine (2'-dAdo) produced different toxicity patterns: both adenosine and 2'-dAdo were toxic to E3 embryos, but only 2'-dAdo was toxic at later stages (E6 1/2, E11). Dosage experiments on E6 1/2 embryos showed that adenosine was less toxic than 2'-dAdo and that 2'-dAdo in sublethal doses was teratogenic. We also examined the effects of 2'-dAdo on embryonic chicken SG and optic tectum in vivo to determine whether sublethal doses of 2'-dAdo produced cell death in these centers on E6 1/2 and 10. In the E6 1/2 SG, 2'-dAdo produced significant neuron loss (83%) and a decrease in SG volume (65%); however, at E10, there was only minor cell loss (7%) and no significant change in SG volume. In the optic tectum at E6 1/2, cell loss was confined mainly to the tectal ventricular zone, but there was little sign of cell loss in this organ at E10. Since cell production is vigorous in the SG and optic tectum at E6 1/2 but relatively low at E10, 2'-dAdo appears to work by stopping cell proliferation. The ineffectiveness of 2'-dAdo at E10 may result from the lethality of 2'-dAdo to the embryo at low concentrations (30 microM) in vivo, well below the apoptosis-inducing concentrations employed in vitro (100-300 microM). These data extend previous findings showing that purine and pyrimidine metabolism plays an important role in development.

Animals↗

PubMed1999

Equilibrium distribution of HIV antiviral drugs into human peripheral blood mononuclear cells (PBMC) is controlled by free drug concentration in the extracellular medium.

Effect of protein binding on the equilibrium distribution of selected HIV antiviral drugs into isolated human peripheral blood mononuclear cells (PBMC, mainly lymphocytes) was investigated. Human PBMC from a single healthy human donor were isolated, purified, and cryopreserved. Uptake of non-peptide HIV-1 protease inhibitors PNU-96988 and PNU-103017 by these cells in vitro was evaluated as a function of increasing concentration of human serum in the cell incubation media. Both PNU-96988 and PNU-103017 were extensively bound to serum proteins. Uptake/efflux kinetics were very rapid such that accumulation by the cells was thermodynamically, not kinetically, controlled. Accumulation by human PBMCs in vitro was directly proportional to the free and not the total drug concentration in the media. For comparative purposes, the serum protein binding effect on the distribution of two HIV reverse transcriptase (RT) inhibitors, delavirdine (RESCRIPTOR) and zidovudine (AZT), was also evaluated. Like the HIV-1 protease inhibitors, delavirdine was found to be extensively associated with serum proteins and its accumulation by human PBMCs in vitro to be proportional to the free and not total drug concentration. In contrast, AZT was not bound to serum proteins to any significant extent. The uptake of this drug by human PBMCs in vitro was independent of serum concentration. However, the intrinsic cellular accumulation of PNU-96988, PNU-103017 and delavirdine were all greater than AZT. Thus, the extent to which drugs uptake by cells is affected by serum appears proportional to the binding affinity of the serum proteins for the drug.

Adult↗

PubMed1999

Identification of losartan degradates in stressed tablets by LC-MS and LC-MS/MS.

Three unknown peaks were observed in the severely stressed losartan tablets (at 40 degrees C and 75% relative humidity for 3 years) analyzed by a stability indicating HPLC method. The sample solutions were subjected to liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis to obtain the chemical identities of these potential degradates. High accuracy and sensitivity of losartan and its degradates were obtained by using atmospheric pressure chemical ionization (APCI) technique in the LC-MS/MS analysis. Three trace level degradates (< or = 0.1%) were found to be the aldehyde and dimeric derivatives of losartan. The structural assignment was further confirmed by comparing the tandem mass spectra of the unknowns with those of the authentic materials of each corresponding degradate. Finally, the mechanistic pathways for the formation of the dimers are discussed.

Aldehydes↗

PubMed1999

Stopped-flow studies of the binding of 2-n-heptyl-4-hydroxyquinoline-N-oxide to fumarate reductase of Escherichia coli.

We have studied the kinetics of binding of the menaquinol analog 2-n-heptyl-4-hydroxyquinoline-N-oxide (HOQNO) by fumarate reductase (FrdABCD) using the stopped-flow method. The results show that the fluorescence of HOQNO is quenched when HOQNO binds to FrdABCD. The observed quenching of HOQNO fluorescence has two phases and it can be best fitted to a double exponential equation. A two-step equilibrium model is applied to describe the binding process in which HOQNO associates with FrdABCD by a fast bimolecular step to form a loosely bound complex; this is subsequently converted into a tightly bound complex by a slow unimolecular step. The rates of the forward and the reverse reactions for the first equilibrium (k1 and k2) are determined to be k1 = (1.1 +/- 0.1) x 10(7) M-1.s-1, and k2 = 6.0 +/- 0.6 s-1, respectively. The dissociation constants of the first equilibrium (Kd1 = k2/k1) is calculated to be about 550 nM. The overall dissociation constant for the two-step equilibrium, Kd overall = Kd1/[1+ (1/Kd2)], is estimated to be < or = 7 nM. Comparison of the kinetic parameters of HOQNO binding by FrdABCD and by dimethyl sulfoxide reductase provides important information on menaquinol binding by these two enzymes.

Escherichia coli↗

PubMed1999

Endomorphin-1 reduces carrageenan-induced fos expression in the rat spinal dorsal horn.

Intraplantar injection of carrageenan induced significant Fos expression in the superficial and deep spinal dorsal horn at the L(4)-L(5)segments and extensive peripheral edema of the ipsilateral foot in rats. Intraplantar injection of endomorphin-1, endogenous ligand for mu opioid receptor, in the same region produced dose-dependent reduction of carrageenan-induced Fos expression and peripheral edema, which were completely blocked by co-administration of intraplantar injection of naloxone (20 microgram). The systemic injection of the highest dose of endomorphin-1 (50 microgram) had no significant reductory effect on Fos expression and peripheral edema. These results further provided a strong evidence for involvement of mu opioid receptor in peripheral analgesia, particularly in inflammation pain.

Analgesics, Opioid↗

PubMed1999

Sialyl Lewis X, Lewis X, and N-acetyllactosamine expression on normal and glaucomatous eyes.

PURPOSE: Sialyl Lewis X (sLex), Lewis X (Lex), and N-acetyllactosamine are carbohydrate chains of neolactoglycoconjugates which are expressed by specific cell types and are important in the functioning of cells within an organism. This study attempts to determine the expression of these glycoconjugates on the conjunctiva, cornea, and trabecular meshwork (TM) of both normal and glaucomatous eyes. METHODS: Frozen anterior segment sections of both normal and glaucomatous human cadaver eyes, as well as rabbit eyes, were stained with a panel of monoclonal antibodies (mAbs) to neolactoglycoconjugates using an Avidin Biotin Peroxidase Complex/Alkaline Phosphatase staining method. RESULTS: SLex characteristically stained both human conjunctival and corneal epithelia in normal (n=5) and glaucomatous (n=5) sections. SLex stained corneal and conjunctival epithelia of glaucomatous eyes much more intensely than normal eyes. Rabbit cornea sections stained for sLex, Lex, and N-acetyllactosamine. However, human cornea only consistently stained with sLex. Normal and glaucomatous human TM sections did not stain for sLex, Lex, or N-acetyllactosamine. CONCLUSIONS: The expression of glycoconjugates with sLex side chains appears to be upregulated in the conjunctival and corneal epithelia of glaucomatous eyes. Distinct species specific differences were noted in Lex and N-acetyllactosamine staining patterns in rabbit and human corneal epithelia.

Aged↗

PubMed1999

The septal chondromucosal island pedicle flap: anatomic study and clinical application.

A study was made of the facial regions of 10 fresh cadavers. The vascular anatomy of the perinasal region and the septum consistently confirmed the existence of a nasal alar basal artery and a nasal alar basal nerve to the septum. A new septal chondromucosal flap, supplied by the nasal alar basal artery and nerve, is proposed in this article. The composite flap can be used safely to restore partial or entire tarsoconjunctival defects of the upper or lower eyelid or combined defects of the upper and lower eyelid.

Adult↗

PubMed1999

Crystallographic analysis of potent and selective factor Xa inhibitors complexed to bovine trypsin.

Factor Xa is a serine protease which activates thrombin (factor IIa) and plays a key regulatory role in the blood-coagulation cascade. Factor Xa is, therefore, an important target for the design of anti-thrombotics. Both factor Xa and thrombin share sequence and structural homology with trypsin. As part of a factor Xa inhibitor-design program, a number of factor Xa inhibitors were crystallographically studied complexed to bovine trypsin. The structures of one diaryl benzimidazole, one diaryl carbazole and three diaryloxypyridines are described. All five compounds bind to trypsin in an extended conformation, with an amidinoaryl group in the S1 pocket and a second basic/hydrophobic moiety bound in the S4 pocket. These binding modes all bear a resemblance to the reported binding mode of DX-9065a in bovine trypsin and human factor Xa.

Animals↗

PubMed1999

S-allylcysteine, a garlic constituent, fails to inhibit N-methylnitrosourea-induced rat mammary tumorigenesis.

Epidemiological and experimental studies suggest that consumption of garlic may protect against several types of cancer. Moreover, a plausible hypothesis has been proposed that the biological effects of garlic can be attributed to the enhancing action of a variety of organosulfur compounds, present in garlic, on hepatic phase II carcinogen detoxification enzymes. We have used the N-methylnitrosourea (NMU)-induced rat mammary tumor model to test the chemopreventive effects of a water-soluble organosulfur constituent derived from aged garlic, S-allylcysteine (SAC). Rats were fed diets supplemented with 666 and 2,000 ppm SAC beginning seven days before initiation with NMU (55 days of age) to termination (18 wk post-NMU), at which time mammary tumors were enumerated. At neither dose did SAC exert an inhibitory effect on any index of tumor development, including incidence, latency, multiplicity, or volume, compared with untreated controls. Weight gains in all groups were similar. Assay of serum SAC levels in supplemented groups indicated that SAC concentrations were beneath the limits of detection of the high-performance liquid chromatography system used. These results contradict previous animal model studies indicating that SAC acts as an inhibitory agent in experimental mammary tumorigenesis; reasons for this discrepancy include the possibility that SAC may exhibit nonlinear dose effects.

Adenocarcinoma↗

PubMed1999

Effect of dietary lycopene on N-methylnitrosourea-induced mammary tumorigenesis.

Epidemiological studies suggest protective effects of lycopene-rich foods on several types of cancer, including prostate and gastrointestinal tract. Moreover, an inverse association between serum lycopene concentrations and several types of cancer has been reported. However, few studies have focused on breast cancer, and they have shown little association between lycopene consumption and cancer risk. In this report, we used the N-methylnitrosourea (NMU)-induced rat mammary tumor model to compare the effects of pure lycopene with a lycopene-rich tomato carotenoid oleoresin (TCO) on NMU-induced mammary tumorigenesis. Rats were fed diets supplemented with 250 and 500 ppm crystalline lycopene or TCO beginning seven days before initiation with NMU (55 days of age) to termination (18 wk after NMU). Neither pure lycopene nor lycopene in the form of a mixed carotenoid oleoresin exerted an inhibitory effect on tumor incidence, latency, multiplicity, volume, or total tumors per group compared with unsupplemented controls. Weight gains in all groups were similar. Assay of serum lycopene concentrations in lycopene-supplemented groups indicated that median levels of 7,12,60, and 87 ng/ml were attained in blood of groups supplemented with 250 and 500 ppm lycopene and 250 and 500 ppm TCO, respectively. The results of this animal study are consistent with epidemiological reports indicating that lycopene does not protect against breast cancer.

Animals↗

PubMed1999

Activated sulfonamides are cleaved by glutathione-S-transferases.

In preclinical pharmacokinetic studies and in in vitro rat, dog, and human primary hepatocyte incubations, the sulfonamide (-NH-SO(2)-) bond of a potent inhibitor of the HIV-1 protease containing the p-cyanopyridinyl moiety (PNU-109112), undergoes metabolic cleavage to form the corresponding amine metabolite (PNU-143070). Strikingly, a compound, PNU-140690, obtained by substituting the cyanopyridinyl group of PNU-109112 with a trifluoropyridinyl moiety, was stable under the same in vivo and in vitro conditions used for PNU-109112. The apparent "sulfonamidase activity" present in liver was localized to the cytosolic fraction and shown to be an enzyme-mediated reaction requiring reduced glutathione (GSH). The enzyme responsible was purified in a single step on a GSH immobilized gel and was identified as glutathione-S-transferase (GST) by sequence analysis of peptides obtained by tryptic digestion of the purified protein. Moreover, a mixture of GST isoenzymes purified from rat liver, and three recombinant human GST isoforms, A1-1, M1-1, and P1-1, were active toward PNU-109112 sulfonamide cleavage; the three isoforms exhibited differential rates of PNU-109112 cleavage, demonstrating isoenzyme selectivity.

Amino Acid Sequence↗

PubMed1999

Mechanism, structure-activity studies, and potential applications of glutathione S-transferase-catalyzed cleavage of sulfonamides.

The mechanism of sulfonamide cleavage of PNU-109112, a potent HIV-1 protease inhibitor, by glutathione-S-transferase (GST) was investigated in the presence of reduced GSH. GST-catalyzed sulfonamide cleavage takes place via the nucleophilic attack of GSH on the pyridine moiety of the substrate with formation of the GS-para-CN-pyridinyl conjugate, the corresponding amine, and sulfur dioxide. Structure activity studies with a variety of sulfonamides indicate that an electrophilic center alpha to the sulfonyl group is required for cleavage. Substituents that withdraw electron density from the carbon atom alpha- to the sulfonyl group facilitate nucleophilic attack by the GS(-) thiolate bound to GST. The rate of sulfonamide cleavage is markedly affected by the nature of the electrophilic group; replacement of para-CN by para-CF(3) on the pyridine ring of PNU-109112 confers stability against sulfonamide cleavage. On the other hand, stability of sulfonamides is less dependent on the nature of the amine moiety. These principles can be applied to the synthesis of sulfonamides, labile toward cellular GST, that may serve as prodrugs for release of bioactive amines. Tumors are particularly attractive targets for these sulfonamide prodrugs as GST expression is significantly up-regulated in many cancer cells. Another potential application could be in organic synthesis, where protection of amines as the corresponding activated sulfonamides can be reversed by GST/GSH under mild conditions.

Caco-2 Cells↗

PubMed1999

[Abnormal expression of several oncogenes during hepatocarcinogenesis in WHV/myc transgenic mice].

OBJECTIVE: To explore at cellular level the abnormal expression of related oncogenes during hepatocarcinogenesis in the WHV/myc transgenic mice. METHODS: With specific molecular probes, in situ hybridization was used to detect the expression of c-myc transgene,IGF-II gene as well as c-jun, c-fos, and c-H-ras oncogenes in the liver sections from WHV/myc transgenic mice in different stages of the carcinogenic process. RESULTS: The overexpression of c-myc transgene and IGF-II gene transcripts were detected in liver sections from the earlier neonatal transgenic mice. Then, the expression levels of these two genes were rapidly decreased and undetectable. At the time of the liver tumor development, the expression of c-myc transgene and IGF-II gene resumed. The c-jun, c-fos and c-H-ras genes expressed more intensely in the livers from preneoplastic WHV/myc mice than from normal mice. CONCLUSION: The overexpressions of c-myc transgene and IGF-II gene in the earlier neonatal stage and tumoral stage may be of importance for the development and maintenance of a transformed phenotype. During the prenoplastic "silent" period of c-myc transgene expression in WHV/myc transgenic mice, several oncogenes are overexpressed in the livers.

Animals↗

PubMed1999

[A study on expression of autotaxin mRNA in hepatocellular carcinoma].

OBJECTIVE: To know if ATX is expressed in hepatocellular carcinoma. METHODS: 7721 hepatoma cell lines in culture, 5 normal liver tissues, and 32 histologically verified HCC specimens were obtained. Semiquantitative reverse transcription polymerase chain reaction was used to detect mRNA expression of ATX. RESULTS: The cDNA sequence of RT-PCR product of 7721 hepatoma cell lines was measured, it showed that nucleotides measured were 332 bp. ATX cDNA nucleotide sequence in HCC was found to share 99.7% homology with that in Melanoma. ATX was expressed in all of the 32 HCC and 5 normal liver tissues. The mean expression level of ATX gene in HCC samples was higher than that in normal liver tissues (0.68 +/- 0.1 vs 0.3 +/- 0.08, P < 0.01). CONCLUSION: ATX gene was found to be in existence in HCC and normal liver tissues. The homology of ATX cDNA sequence between HCC and human Melanoma was 99.7%, and ATX may play an important role in HCC metastatic mechanism.

Carcinoma, Hepatocellular↗

PubMed1999

New buccinator myomucosal island flap: anatomic study and clinical application.

The authors studied the vascular anatomy of the buccinator muscle by dissecting fresh cadavers. The anatomy of the buccal branches of the facial artery consistently confirmed the existence of a posterior buccal branch, a few inferior buccal branches, and anterior buccal branches to the posterior, inferior, and anterior portions of the buccinator. The buccal artery and posterior buccal branch anastomose to each other and ramify over the muscle. Several veins originate from the lateral aspect of the muscle, converge into the buccal venous plexus, and drain into the facial vein (from two to four tributaries) or into the pterygoid plexus and the internal maxillary vein (from the buccal vein). These vessels and nerves enter the posterior half of the buccinator posterolaterally. The facial artery and vein are located at variable distances from each other around the oral commissure and the nasal base. Two patterns of buccinator musculomucosal island flaps supplied by these buccal arterial branches are proposed in this article. The buccal musculomucosal neurovascular island flap (posteriorly based), supplied by the buccal artery, its posterior buccal branch, and the long buccal nerve, can be passed through a tunnel under the pterygomandibular ligament for closure of mucosal defects in the palate, pharyngeal sites, the alveolus, and the floor of the mouth. The buccal musculomucosal reversed-flow arterial island flap (superiorly based), supplied by the distal portion of the facial artery through the anterior buccal branches, can be used to close mucosal defects in the anterior hard palate, alveolus, maxillary antrum, nasal floor and septum, lip, and orbit. The authors have used the flaps in 12 patients. There has been no flap necrosis, and results have been satisfactory, both aesthetically and functionally.

Adult↗

PubMed1999

Expression of autotaxin mRNA in human hepatocellular carcinoma.

OBJECTIVE: To investigate the expression of autotaxin (ATX) mRNA existed in the human hepatocellular carcinoma (HCC), and whether there is relation between the level of ATX expression and clinicopathological features of HCC. METHODS: Five normal liver tissues and 32 histologically verified HCC specimens were obtained. Semi-quantitative reverse transcription polymerase chain reaction was used to detect mRNA expression of ATX. RESULTS: ATX was expressed in all 32 HCC and 5 normal liver tissues. The mean expression level of ATX gene in HCC samples was higher than that in normal liver tissues (68.23% +/- 15.31% vs. 31.97% +/- 8.05%, P < 0.001). Patients were divided into two groups: low ATX HCC (15 cases) and high ATX HCC (17 cases) by the cutoff point of median value. Intrahepatic metastasis, vascular invasion and poor differentiation were more frequently noted in HCC patients with high ATX expression than in patients with low ATX expression. CONCLUSION: ATX gene was found to be overexpressed in some HCC and correlated with HCC development and metastases.

Carcinoma, Hepatocellular↗

PubMed1999

[Analysis of clinical characteristics and drug sensitivity tests of lower respiratory tract infection by Xanthomonas maltophilia].

OBJECTIVE: To analyse the clinical characteristics of lower respiratory tract infection caused by Xanthomonas maltophilia and to investigate the antibiotic sensitivity of Xanthomonas maltophilia strains. METHODS: Retrospective study of the clinical data of 54 cases with lower respiratory tract infection by Xanthomonas maltophilia, including risk factors of morbidity, clinical symptoms and signs, X-ray findings, blood routine test, treatment and prognosis. Drug sensitivity against strains of Xanthomonas maltophilia by K-B method was studied. RESULTS: There were 39 males and 15 females, the mean age being 51 +/- 17 years. 87% of the cases had underlying diseases, most of which were COPD complicated by respiratory failure. 57% of the cases were immunocompromised. 39% of the cases were in ICU or CCU. 54% of the cases accepted invasive treatments, and 93% of the cases were given broad-spectrum antibiotics. Clinical manifestations include chill (72%), fever (80%), cough (94%) and expectoration (91%). The chest X-ray revealed infiltration in lower lobes of both lungs. 16 cases had consolidations, and 11 cases were complicated with pleural effusions. The drug sensitivity test in vitro showed that these strains were multiresistant to commonly used antibiotics, and drugs whose sensitive rate were over 50% included SMZco, ceftazidine, and timentin. CONCLUSIONS: The lower respiratory tract infections caused by Xanthomonas maltophilia develop at patients with various underlying diseases, especially in the immunocompromised patients. Risk factors of morbidity were: patients in ICU or CCU, acceptance of invasive treatment and inappropriate use of broad-spectrum antibiotics. Clinical manifestations include severely toxic symptoms and some cases had pulmonary consolidations and pleural effusions.

Adolescent↗