Biomedical subjects

N Wu

Publications and source records attributed to N Wu.

At least 19 recordsLinked to original sources

PubMed2007

Anomalous intracranial venous drainage associated with basal ganglia calcification.

We describe the neuroradiologic findings in a 7-year-old boy with anomalous intracranial venous drainage and cerebral calcification. CT scans demonstrated that his scalp mass was a plexus of scalp veins filled through the emissary foramen, and there were cerebral calcifications. Angiography revealed bilateral sigmoid sinus atresia with most of the intracranial venous drainage via the prominent mastoid emissary veins into dilated scalp vein. The possible relationship between cerebral calcification and anomalous intracranial venous drainage is discussed.

Basal Ganglia Diseases↗

PubMed2006

Optical absorption and valence band photoemission from uncapped CdTe nanocrystals.

CdTe nanocrystals have been successfully fabricated by a mechanical alloying process. X-ray diffraction (XRD) patterns demonstrate that a single-phase CdTe compound with a zinc blende structure has been formed after ball milling elemental Cd and Te mixture powders for 27 h. The large broadening effect for the width of the {111} diffraction peak of uncapped CdTe nanocrystals on smaller size was observed in slowly scanned XRD patterns. The X-ray photoelectron spectrum was used to study the surface of the uncapped CdTe nanocrystals within both core level and valence band regions. The presence of tellurium oxide film on the surface of the uncapped CdTe nanocrystals has been detected in the X-ray photoelectron spectrum of the Te 3d core level, which was comparable to the observed amorphous oxide thin layer on the surface of uncapped CdTe nanocrystals in a high resolution transmission electron microscopy (HRTEM) image. The energy of the valence band maximum for uncapped CdTe powders blue shifts to the higher energy side with smaller particle sizes. In UV-visible optical absorption spectra of the suspension solution containing uncapped CdTe nanocrystals, the absorption peaks were locating within the ultraviolet region, which shifted toward the higher energy side with prolonged ball milling time. Both blue shifts of valence band maximum energy and absorption peaks with decreasing particle size provide a unique pathway to reveal the quantum confinement effect of uncapped CdTe nanocrystals.

Journal Article↗

PubMed2006

Photodynamic therapy increases brain edema and intracranial pressure in a rabbit brain tumor model.

The objective of this study was to evaluate the effect of a single photodynamic therapy (PDT) on brain edema and intracranial pressure (ICP) in a rabbit model of brain tumor. A total of 57 adult New Zealand rabbits were assigned to 3 groups: the PDT group, the tumor group, and the tumor plus PDT group. Rabbits in the PDT group (n = 9) received PDT but no tumor implantation; rabbits in the tumor group (n = 18) received VX2 carcinoma implantation but no PDT; rabbits in the tumor plus PDT group (n = 30) received tumor implantation with subsequent PDT 16 days later. Brain edema and ICP levels were then evaluated. We found that ICP in the PDT group was 7.43 +/- 0.50 mmHg. After tumor implantation, ICP increased rapidly (18.43 +/- 1.10 mmHg, 21 days later). PDT alone did not increase ICP, but compared with that in the tumor group, ICP increased significantly in the tumor plus PDT group (9.55 +/- 1.32 vs. 13.31 +/- 1.13 mmHg, p < 0.01) 24 hours after treatment. Brain water content in the tumor group increased rapidly after tumor implantation. PDT again increased perineoplastic brain edema 24 hours after treatment (81.09 +/- 0.97% vs. 78.32 +/- 0.49%, p < 0.01). It should be noted that PDT alone did not induce brain edema. In conclusion, PDT causes transient brain edema and increases ICP in a rabbit brain tumor model.

Animals↗

PubMed2005

FK506 enhances triptolide-induced down-regulation of cyclooxygenase-2, inducible nitric oxide synthase as well as their products PGE2 and NO in TNF-alpha-stimulated synovial fibroblasts from rheumatoid arthritic patients.

OBJECTIVE: To explore the effects of FK506 on the inhibition of cell proliferation and the expression of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS) and their products PGE subset2 and NO in TNF-alpha-stimulated human rheumatoid arthritis synovial fibroblasts (RASF) treated with triptolide (TP), and to study the mechanisms involved when combining FK506 and TP in RA therapy. MATERIALS AND METHODS: RASF used in the experiments were obtained from the synovial tissue of patients with RA before being cultured. RASF were pretreated with FK506 (10 approximately 1000 nM) for 2 hours before being stimulated with TNF-alpha (20 ng/ml) in the presence or absence of TP (10 ng/ml) . RASF proliferation was determined by [3 supersetH]-TdR incorporation. Production of PGE subset2 and NO in culture supernatants of RASF was detected by competitive ELISA and enzymatic reduction of nitrate, respectively. Expressions of COX-2 and iNOS mRNA in RASF were analyzed by semi-quantitative RT-PCR. Expressions of COX-2 and iNOS protein were estimated by Western-blot and a cellular enzyme immunoassay. NFkappaB activity in whole-cell extract of treated RASF was also measured using an ELISA-based method. RESULTS: Neither FK506 nor TP at a lower concentration (10 ng/ml) affected TNF-alpha-induced COX-2 and iNOS expressions or PGE subset2 and NO productions in synovial cells. Combined treatment of FK506 and a lower concentration of TP (10 ng/ml) reduced both COX-2 and iNOS mRNA and protein expression, and correspondingly reduced PGE subset2 and NO produced by synovial fibroblasts. This effect was highly correlated with FK506 concentration (10 approximately 1000 nM). NFkappaB activity in TNF-alpha-stimulated synovial cells was suppressed more profoundly by FK506 plus TP (10 ng/ml) than by TP (10 ng/ml) alone. However, no change was observed regarding the inhibition of synovial cell proliferation after combined treatment of FK506 and TP. CONCLUSION: FK506 enhanced TP-mediated down-regulation of COX-2 and iNOS as well as their products PGE subset2 and NO in human TNF-alpha-stimulated RASF by more profoundly suppressing the activity of NFkappaB.

Arthritis, Rheumatoid↗

PubMed2005

Association of RANTES with the replication of severe acute respiratory syndrome coronavirus in THP-1 cells.

BACKGROUND: Severe acute respiratory syndrome (SARS) is a novel infectious disease which is characterized by an overaggressive immune response. Chemokines are important inflammatory mediators and regulate disease due to viral infection. In previous study, we found that SARS-CoV has the ability to replicate in mononuclear cells. In present work, we sought to characterize the replication of SARS-CoV at the presence of RANTES in THP-1 cells. METHODS: To determine whether RANTES play an role in the process of SARS, THP-1 cells were incubated with heat-inactivated SARS-CoV and ELISA was used to test RANTES levels in the supernatants; Then the effect of dexamethasone on the induced secretion was evaluated. Real-time PCR was used to investigate the effort of RANTES on the replication of SARS-CoV in vitro. Macrophages, induced by THP-1 cells, were used as cell model. FINDINGS: Inactive SARS-CoV could induce THP-1 cells secret RANTES and this increase effect could not be suppressed by DXM. RANTES itself could inhibit the replication of SARS-CoV in THP-1 cells when it was added into the culture before or at the same time with the virus; No inhibition effect was shown when RANTES were added into the culture after SARS-CoV infected the cells.

Animals↗

PubMed2005

Sensitive assay for laboratory evolution of hydroxylases toward aromatic and heterocyclic compounds.

Powerful directed evolution methods have been developed for tailoring proteins to our needs in industrial applications. Here, the authors report a medium-throughput assay system designed for screening mutant libraries of oxygenases capable of inserting a hydroxyl group into a C-H bond of aromatic or O-heterocyclic compounds and for exploring the substrate profile of oxygenases. The assay system is based on 4-aminoantipyrine (4-AAP), a colorimetric phenol detection reagent. By using 2 detection wavelengths (509 nm and 600 nm), the authors achieved a linear response from 50 to 800 microM phenol and standard deviations below 11% in 96-well plate assays. The monooxygenase P450 BM-3 and its F87A mutant were used as a model system for medium-throughput assay development, identification of novel substrates (e.g., phenoxytoluene, phenylallyether, and coumarone), and discovery of P450 BM-3 F87A mutants with 8-fold improvement in 3-phenoxytoluene hydroxylation activity. This activity increase was achieved by screening a saturation mutagenesis library of amino acid position Y51 using the 4-AAP protocol in the 96-well format.

Bacterial Proteins↗

PubMed2004

Leukotriene A4 hydrolase as a target for cancer prevention and therapy.

Leukotriene A4 hydrolase (LTA4H) is a bifunctional zinc enzyme with the activities of epoxide hydrolase and aminopeptidase. As an epoxide hydrolase, LTA4H catalyzes the hydrolysis of the epoxide LTA4 to the diol, leukotriene B4 (LTB4), which mainly functions as a chemoattractant and an activator of inflammatory cells. As an aminopeptidase, LTA4H may process peptides related to inflammation and host defense. In a chronic inflammation-associated animal model of esophageal adenocarcinoma, we have shown that LTA4H was overexpressed in tumor as compared to normal tissues. Bestatin, an LTA4H inhibitor, suppresses tumorigenesis in this animal model. Since LTA4H has long been regarded as an anti-inflammatory target, we propose LTA4H as a target for prevention and therapy of cancers, especially those associated with chronic inflammation. Here we review the gene structure, expression, regulation and functions of LTA4H, as well as its involvement in carcinogenesis. We believe LTA4H/LTB4 may play an important role in chronic inflammation associated carcinogenesis by at least two mechanisms: a) the inflammation-augmenting effect on inflammatory cells through positive feedback mediated by its receptors and downstream signaling molecules; and b) the autocrine growth-stimulatory effect of LTB4 produced by epithelial cells, and the paracrine growth-stimulatory effect of LTB4 produced by inflammatory cells, on precancerous and cancer cells. Based on our present knowledge, inhibitors of LTA4H or antagonists of LTB4 receptors may be used alone or in combination with other agents (e.g., cyclooxygenase 2 inhibitors) in cancer prevention and treatment trials to test their effectiveness.

Animals↗

PubMed2001

Applications of new liquid chromatography-tandem mass spectrometry technologies for drug development support.

We have evaluated (i) a multiplexed electrospray interface, (ii) serial sample introduction, and (iii) a quadrupole time-of-flight mass spectrometer for quantitative bioanalysis in compliance with good laboratory practice. These evaluations were done using a 96-well plate liquid chromatography-tandem mass spectrometry method for the quantitation of loratadine and its metabolite, descarboethoxyloratadine. The assay has a dynamic range of 1-1000 ng/ml with 5.56 pg of each analyte being injected on-column at the limit of quantitation. For the four-channel multiplexed electrospray experiments, one-run validations were performed simultaneously in rat, rabbit, mouse and dog plasma. In the four-stream serial experiments, the total run time of the assay was reduced from 3.5 to 0.35 min, resulting in a net acquisition time of 11 s. Four simulated validation runs with standard and quality control solutions were analyzed. Precision and accuracy for standards and quality control samples met US Food and Drug Administration recommended criteria for both the drug and the metabolite using those two approaches. In addition, a quadrupole time-of-flight mass spectrometer was used as a detector in the tandem mass spectrometry mode for the loratadine assay. Our results demonstrated that a dynamic range of three orders of magnitude could be achieved using the quadrupole time-of-flight mass spectrometer, making it useful for quantitation in preclinical toxicology studies.

Animals↗

PubMed2001

Overexpression of Smad2 reveals its concerted action with Smad4 in regulating TGF-beta-mediated epidermal homeostasis.

Members of the transforming growth factor-beta (TGF-beta) superfamily are critical regulators for epithelial growth and can alter the differentiation of keratinocytes. Transduction of TGF-beta signaling depends on the phosphorylation and activation of Smad proteins by heteromeric complexes of ligand-specific type I and II receptors. To understand the function of TGF-beta and activin-specific Smad, we generated transgenic mice that overexpress Smad2 in epidermis under the control of keratin 14 promoter. Overexpression of Smad2 increases endogenous Smad4 and TGF-beta 1 expression while heterozygous loss of Smad2 reduces their expression levels, suggesting a concerted action of Smad2 and -4 in regulating TGF-beta signaling during skin development. These transgenic mice have delayed hair growth, underdeveloped ears, and shorter tails. In their skin, there is severe thickening of the epidermis with disorganized epidermal architecture, indistinguishable basement membrane, and dermal fibrosis. These abnormal phenotypes are due to increased proliferation of the basal epidermal cells and abnormalities in the program of keratinocyte differentiation. The ectodermally derived enamel structure is also abnormal. Collectively, our study presents the first in vivo evidence that, by providing an auto-feedback in TGF-beta signaling, Smad2 plays a pivotal role in regulating TGF-beta-mediated epidermal homeostasis.

Animals↗

PubMed2001

Assessing the balance between protein-protein interactions and enzyme-substrate interactions in the channeling of intermediates between polyketide synthase modules.

6-Deoxyerythronolide B synthase (DEBS) is the modular polyketide synthase (PKS) that catalyzes the biosynthesis of 6-deoxyerythronolide B (6-dEB), the aglycon precursor of the antibiotic erythromycin. The biosynthesis of 6-dEB exemplifies the extraordinary substrate- and stereo-selectivity of this family of multifunctional enzymes. Paradoxically, DEBS has been shown to be an attractive scaffold for combinatorial biosynthesis, indicating that its constituent modules are also very tolerant of unnatural substrates. By interrogating individual modules of DEBS with a panel of diketides activated as N-acetylcysteamine (NAC) thioesters, it was recently shown that individual modules have a marked ability to discriminate among certain diastereomeric diketides. However, since free NAC thioesters were used as substrates in these studies, the modules were primed by a diffusive process, which precluded involvement of the covalent, substrate-channeling mechanism by which enzyme-bound intermediates are directly transferred from one module to the next in a multimodular PKS. Recent evidence pointing to a pivotal role for protein-protein interactions in the substrate-channeling mechanism has prompted us to develop novel assays to reassess the steady-state kinetic parameters of individual DEBS modules when primed in a more "natural" channeling mode by the same panel of diketide substrates used earlier. Here we describe these assays and use them to quantify the kinetic benefit of linker-mediated substrate channeling in a modular PKS. This benefit can be substantial, especially for intrinsically poor substrates. Examples are presented where the k(cat) of a module for a given diketide substrate increases >100-fold when the substrate is presented to the module in a channeling mode as opposed to a diffusive mode. However, the substrate specificity profiles for individual modules are conserved regardless of the mode of presentation. By highlighting how substrate channeling can allow PKS modules to effectively accept and process intrinsically poor substrates, these studies provide a rational basis for examining the enormous untapped potential for combinatorial biosynthesis via module rearrangement.

Acyl Carrier Protein↗

PubMed2001

Membrane resonance and subthreshold membrane oscillations in mesencephalic V neurons: participants in burst generation.

Trigeminal mesencephalic (Mes V) neurons are critical components of the circuits controlling oral-motor activity. The possibility that they can function as interneurons necessitates a detailed understanding of the factors controlling their soma excitability. Using whole-cell patch-clamp recording, in vitro, we investigated the development of the ionic mechanisms responsible for the previously described subthreshold membrane oscillations and rhythmical burst discharge in Mes V neurons from rats ages postnatal day (P) 2-12. We found that the oscillation amplitude and frequency increased during development, whereas bursting emerged after P6. Furthermore, when bursting was initiated, the spike frequency was largely determined by the oscillation frequency. Frequency domain analysis indicated that these oscillations emerged from the voltage-dependent resonant properties of Mes V neurons. Low doses of 4-aminopyridine (<100 microm) reduced the oscillations and abolished resonance in most neurons, suggesting that the resonant current is a steady-state K(+) current (I(4-AP)). Sodium ion replacement or TTX reduced substantially the oscillations and peak amplitude of the resonance, suggesting the presence of a persistent Na(+) current (I(NaP)) that functions to amplify the resonance and facilitate the emergence of subthreshold oscillations and bursting.

4-Aminopyridine↗

PubMed2001

Evaluation of a four-channel multiplexed electrospray triple quadrupole mass spectrometer for the simultaneous validation of LC/MS/MS methods in four different preclinical matrixes.

A four-channel multiplexed electrospray interface on a triple quadrupole mass spectrometer was evaluated for the simultaneous validation of LC/MS/MS methods for the quantitation of loratadine and its metabolite, descarboethoxyloratadine, in four different biological matrixes. The assays were performed in rat, rabbit, mouse, and dog plasma from 1 to 1000 ng/mL using 96-well solid-phase extraction for sample preparation. The limit of quantitation of 1 ng/mL corresponded to 5.56 pg of each analyte injected on-column. For the drug, quality control samples (n = 6 at four concentrations) had precision ranging from 0.967 to 16.0% and accuracy ranging from -8.44 to 10.5% across all four species. For the metabolite, the precision ranged from 0.684 to 11.0% and the accuracy was between 6.36 and -9.06%. Intersprayer cross talk for the multiplexed electrospray ion source was evaluated as a function of analyte concentration and was less than 0.08% at concentrations as high as 1000 ng/mL. These results demonstrate the feasibility of using parallel analysis to reduce the time required for method validation and to increase sample throughput in drug development studies.

Animals↗

PubMed2001

Comparison of empirical peak capacities for high-efficiency capillary chromatographic techniques.

Experimental peak capacities for capillary gas chromatography (GC), capillary liquid chromatography (CLC), and capillary electrochromatography (CEC) were compared. To obtain a meaningful comparison, the following constraints were applied. First, the same sample (mixture of alkylbenzenes) was used as a test mixture for all three techniques; second, the same packing material and column diameter were used in CLC and CEC; and third, isothermal conditions were used in GC, while isocratic conditions were used both in CLC and in CEC. Comparison of peak capacities for the same total column efficiency (approximately 36000 plates) showed that the peak capacity of GC is greater than those of the liquid-phase separation techniques. Comparison of CEC and CLC for constant retention factor was also carried out. For this condition, the results depend on the particle size used; for 3-microm porous particles, CEC had a peak capacity larger than CLC due to higher efficiency from the flow profile generated by electroosmotic flow. However, when 1.5-microm nonporous particles were used, the peak capacities were approximately the same for both techniques. The effect of linear velocity on peak capacity was also studied for all three techniques. Practical conditions aimed at increasing peak capacities of liquid-phase separation techniques are discussed.

Journal Article↗

PubMed2001

Practical aspects of ultrahigh pressure capillary liquid chromatography.

A novel pressure-balanced injection valve was evaluated for use with ultrahigh pressure liquid chromatography (UHPLC) at pressures up to 120 MPa (1,200 bar). Fused-silica capillaries (30-33 cm x 100 microm I.D.) packed with nonporous 1.5 microm isohexylsilane-modified (C6) silica particles were employed to study maximum pressure, injection reproducibility, injection time, and sample amount consumed for an injection. The new valve was more reproducible, convenient, and required much less sample than previously used injection systems. The effect of column diameter on efficiency and sensitivity was studied. The 100 microm I.D. columns demonstrated approximately 40% lower efficiency but 10-fold higher sensitivity than the 29 microm I.D. columns. Columns packed with nonporous C6 particles produced higher efficiencies than columns packed with a 1.5 microm porous octadecylsilane-modified (C18) material.

Chromatography, High Pressure Liquid↗

PubMed2001

Intermodular communication in polyketide synthases: comparing the role of protein-protein interactions to those in other multidomain proteins.

Although the role of protein-protein interactions in transducing signals within biological systems has been extensively explored, their relevance to the channeling of intermediates in metabolism is not widely appreciated. Polyketide synthases (PKSs) and nonribosomal peptide synthetases (NRPSs) are two related families of modular megasynthases that channel covalently bound intermediates from one active site to the next. Recent biochemical studies have highlighted the importance of protein-protein interactions in these chain transfer processes. The information available on this subject is reviewed, and its possible mechanistic implications are placed in context by comparisons with selected well-studied multicomponent protein systems.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗

PubMed2001

Red wine, dealcoholized red wine, and especially grape juice, inhibit atherosclerosis in a hamster model.

The French have low coronary heart disease mortality with high fat consumption; this epidemiological anomaly is known as the "French Paradox" and is commonly attributed to the consumption of red wine. However, epidemiology studies have not convincingly shown a superiority of red wine vs. alcohol or other alcoholic beverages. We have used the hamster model of atherosclerosis to determine the active ingredient(s) of red wine responsible for the beneficial effect. Hamsters (nine in each group) were given a cholesterol/saturated fat for 10 weeks to induce foam cell formation. Water or 6.75% ethanol was given to the control groups. Beverages tested included red wine, dealcoholized red wine, and red grape juice, all diluted in half. Ethanol and all beverages caused a significant reduction in atherosclerosis. The combination of ethanol in red wine had the largest effect in decreasing atherosclerosis by both hypolipemic and antioxidant mechanisms. When compared with dealcoholized wine and normalized to polyphenol dose, red wine's beneficial effects can be attributed entirely to the polyphenols. Grape juice had a significant benefit at a much lower dose of polyphenols than the wines. Grape juice was calculated to be much more effective than red wine or dealcoholized red wine at the same polyphenol dose in inhibiting atherosclerosis and improving lipids and antioxidant parameters. This data suggests that polyphenolic beverages from grapes are beneficial in inhibiting atherosclerosis by several mechanisms. Grape juice or non-alcoholic red wine are an excellent alternative to red wine in this model of atherosclerosis.

Animals↗

PubMed2001

Crystal structure of colicin E3: implications for cell entry and ribosome inactivation.

Colicins kill E. coli by a process that involves binding to a surface receptor, entering the cell, and, finally, intoxicating it. The lethal action of colicin E3 is a specific cleavage in the ribosomal decoding A site. The crystal structure of colicin E3, reported here in a binary complex with its immunity protein (IP), reveals a Y-shaped molecule with the receptor binding domain forming a 100 A long stalk and the two globular heads of the translocation domain (T) and the catalytic domain (C) comprising the two arms. Active site residues are D510, H513, E517, and R545. IP is buried between T and C. Rather than blocking the active site, IP prevents access of the active site to the ribosome.

Bacterial Proteins↗

PubMed2001

6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase: suiting structure to need, in a family of tissue-specific enzymes.

The present review addresses recent advances in research into a family of bifunctional enzymes that are responsible for the twofold task of synthesizing and hydrolyzing fructose-2,6-bisphosphate (Fru-2,6-P2), which in turn regulates the rate of glycolysis in most cells. The structure of the synthetic kinase, conjoined at its carboxyl-terminus to the phosphatase, is very highly conserved throughout evolution and differentiation, with isotypic expression arising from highly variable amino-terminal and carboxyl-terminal regulatory domains. These domains, which frequently contain protein-kinase-catalyzed phosphorylation motifs, are responsible for the widely divergent kinetics observed in various tissues and species, and for the hormonal modulation that alters intracellular levels of Fru-2,6-P2. The present review discusses recent advances in relating structure to function, and the identification of new pathways of transcriptional regulation of this important family of regulatory enzymes.

Adrenal Cortex Hormones↗