Search PubMed⌕ Search

Biomedical subjects

R Liu

Publications and source records attributed to R Liu.

At least 55 records · Page 3Linked to original sources
PubMed2001

Kainate excitotoxicity in organotypic hippocampal slice cultures: evidence for multiple apoptotic pathways.

The mechanisms underlying kainate (KA) neurotoxicity are still not well understood. We previously reported that KA-mediated neuronal damage in organotypic cultures of hippocampal slices was associated with p53 induction. Recently, both bax and caspase-3 have been demonstrated to be key components of the p53-dependent neuronal death pathway. Caspase activation has also been causally related to the release of mitochondrial cytochrome c (Cyto C) in the cytoplasm as a result of the collapse of the mitochondrial membrane potential (Deltapsi(M)) and the opening of mitochondrial permeability transition pores (mPTP). In the present study, we observed a rapid induction of bax in hippocampal slice cultures after KA treatment. In addition, the levels of Cyto C and caspase-3 were increased in the cytosol while the level of the caspase-9 precursor was decreased. There was also a complete reduction of Rhodamine 123 fluorescence after KA treatment, an indication of Deltapsi(M) dissipation. Furthermore, inhibition of mPTP opening by cyclosporin A partially prevented Cyto C release, caspase activation and neuronal death. These data suggest the involvement of bax, several caspases, as well as Cyto C release in KA-elicited neuronal death. Finally, inhibition of caspase-3 activity by z-VAD-fmk only partially protected neurons from KA toxicity, implying that multiple mechanisms may be involved in KA excitotoxicity.

Amino Acid Chloromethyl Ketones↗
PubMed2001

Microfabricated polycarbonate CE devices for DNA analysis.

The microchip capillary electrophoresis (CE) devices were fabricated in polycarbonate (PC) plastic material by compression molding. The molded devices were enclosed utilizing thermal bonding to another PC wafer. These thermal bonds do not yield up to an applied force equivalent to 150 psi. Aqueous fluid transport inside the plastic CE devices was enhanced by UV irradiation treatment of the hydrophobic polycarbonate plastic surfaces prior to thermal bonding. In comparison to glass microchannels, electroosmotic flow (EOF) in native PC channels is low and is independent of buffer pH at pH 7 and 9. UV irradiation of PC surfaces increases surface hydrophilicity and increases EOF. CE DNA separation was demonstrated in these PC CE devices with good resolution and run-to-run reproducibility. The on-chip PCR/CE analysis of a 500-bp region of bacteriophage lambda DNA was also demonstrated.

DNA↗
PubMed2001

Regulation of CSF1 promoter by the SWI/SNF-like BAF complex.

The mammalian BAF complex regulates gene expression by modifying chromatin structure. In this report, we identify 80 genes activated and 2 genes repressed by the BAF complex in SW-13 cells. We find that prior binding of NFI/CTF to the NFI/CTF binding site in CSF1 promoter is required for the recruitment of the BAF complex and the BAF-dependent activation of the promoter. Furthermore, the activation of the CSF1 promoter requires Z-DNA-forming sequences that are converted to Z-DNA structure upon activation by the BAF complex. The BAF complex facilitates Z-DNA formation in a nucleosomal template in vitro. We propose a model in which the BAF complex promotes Z-DNA formation which, in turn, stabilizes the open chromatin structure at the CSF1 promoter.

Base Sequence↗
PubMed2001

Automatic Edman microsequencing of peptides containing multiple unnatural amino acids.

It is now routine using automatic Edman microsequencing to determine the primary structure of peptides or proteins containing natural amino acids; however, a deficiency in the ability to readily sequence peptides containing unnatural amino acids remains. With the advent of synthetic peptide chemistry, combinatorial chemistry, and the large number of commercially available unnatural amino acids, there is a need for efficient and accurate structure determination of short peptides containing many unnatural amino acids. In this study, 35 commercially available alpha-unnatural amino acids were selected to determine their elution profile on an ABI protein sequencer. Using a slightly modified gradient program, 19 of these 35 PTH amino acids can be readily resolved and distinguished from common PTH amino acids at low picomole levels. These unnatural amino acids in conjunction with the 20 natural amino acids can be used as building blocks to construct peptide libraries, and peptide beads isolated from these libraries can be readily microsequenced. To demonstrate this, we synthesized a simple tripeptide "one-bead one-compound" combinatorial library containing 14 unnatural and 19 natural amino acids and screened this library for streptavidin-binding ligands. Microsequencing of the isolated peptide-beads revealed the novel motif Bpa-Phe(4-X)-Aib, wherein X = H, OH, and CH3.

Amino Acids↗
PubMed2001

[The role of PMN apoptosis delay in acute lung injury induced by administrating LPS].

OBJECTIVE: To investigate the law of apoptosis and necrosis of the peripheral PMN and the PMN extravasated into pulmonary tissue, and its relationship with lung injury and the mechanisms involved. METHODS: Fifty rats were subjected to acute lung injury by administrating intraperitoneally LPS (O(55)B(5), 3 mg/kg). Blood was harvested and bronchoalveoli was lavaged pre-LPS and 2, 4, 8, 12 h after LPS administration. PMNs were isolated by density gradient centrifugation and apoptosis, necrosis and respiratory burst were detected by flow cytometry. LDH activity, TNF, IL-1beta, IL-6, and lung permeability index were also measured. RESULTS: Viable PMN in bronchoalveolar lavage fluid (BLF) increased and apoptosis was delayed compared with that in peripheral blood. Meanwhile, TNF, IL-1beta and IL-6 in BLF were obviously higher and endured longer compared with those in peripheral blood. Moreover, the LDH activity in BLF and the lung permeability index were also remarkably increased. CONCLUSION: Retention of PMN in tissues and the abnormality in apoptotic pathway inevitably caused by higher level cytokines and temporal increased of intracellular free Ca(2+) generate persistent activation of PMN and excessive release of toxic substances, resulting in tissue injury.

Animals↗
PubMed2001

MDR1 causes resistance to the antitumour drug miltefosine.

Miltefosine (hexadecylphosphocholine) is used for topical treatment of breast cancers. It has been shown previously that a high percentage of breast carcinomas express MDR1 or MRP. We investigated the sensitivity of MDR1 -expressing cells to treatment with miltefosine. We show that cells overexpressing MDR1 (NCI/ADR-RES, KB-8-5, KB-C1, CCRF/VCR1000, CCRF/ADR5000) were less sensitive to miltefosine treatment when compared to the sensitive parental cell lines. HeLa cells transfected with MDR1 exhibited resistance to the compound, indicating that expression of this gene is sufficient to reduce the sensitivity to miltefosine. The resistance of MDR1-expressing cells to miltefosine was less pronounced than that to adriamycin or vinblastine. Expression of MDR2 did not correlate with the resistance to miltefosine. As shown by a fluorescence quenching assay using MIANS-labelled P-glycoprotein (PGP), miltefosine bound to PGP with a K(d)of approximately 7 microM and inhibited PGP-ATPase activity with an IC(50)of approximately 35 microM. Verapamil was not able to reverse the resistance to miltefosine. Concentrations of miltefosine up to approximately 60 microM stimulated, whereas higher concentrations inhibited the transport of [3H]-colchicine with an IC(50)of approximately 297 microM. Binding studies indicated that miltefosine seems to interact with the transmembrane domain and not the cytosolic nucleotide-binding domain of PGP. These data indicate that expression of MDR1 may reduce the response to miltefosine in patients and that this compound interacts with PGP in a manner different from a number of other substrates.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2001

Enhancement of radiosensitivity by proteasome inhibition: implications for a role of NF-kappaB.

PURPOSE: NF-kappaB is activated by tumor necrosis factor, certain chemotherapeutic agents, and ionizing radiation, leading to inhibition of apoptosis. NF-kappaB activation is regulated by phosphorylation of IkappaB inhibitor molecules that are subsequently targeted for degradation by the ubiquitin-proteasome pathway. PS-341 is a specific and selective inhibitor of the proteasome that inhibits NF-kappaB activation and enhances cytotoxic effects of chemotherapy in vitro and in vivo. The objective of this study was to determine if proteasome inhibition leads to enhanced radiation sensitivity. METHODS AND MATERIALS: Inhibition of NF-kappaB activation in colorectal cancer cells was performed by treatment of LOVO cells with PS-341 or infection with an adenovirus encoding IkappaB super-repressor, a selective NF-kappaB inhibitor. Cells were irradiated at 0, 2, 4, 6, 8, and 10 Gy with or without inhibition of NF-kappaB. NF-kappaB activation was determined by electrophoretic mobility gel shift assay, and apoptosis was evaluated using the TUNEL assay. Growth and clonogenic survival data were obtained to assess effects of treatment on radiosensitization. In vitro results were tested in vivo using a LOVO xenograft model. RESULTS: NF-kappaB activation was induced by radiation and inhibited by pretreatment with either PS-341 or IkappaBalpha super-repressor in all cell lines. Inhibition of radiation-induced NF-kappaB activation resulted in increased apoptosis and decreased cell growth and clonogenic survival. A 7-41% increase in radiosensitivity was observed for cells treated with PS-341 or IkappaBalpha. An 84% reduction in initial tumor volume was obtained in LOVO xenografts receiving radiation and PS-341. CONCLUSIONS: Inhibition of NF-kappaB activation increases radiation-induced apoptosis and enhances radiosensitivity in colorectal cancer cells in vitro and in vivo. Results are encouraging for the use of PS-341 as a radiosensitizing agent in the treatment of colorectal cancer.

Adenoviridae↗
PubMed2001

Enhanced chemosensitivity to CPT-11 with proteasome inhibitor PS-341: implications for systemic nuclear factor-kappaB inhibition.

Inducible activation of nuclear factor-kappaB (NF-kappaB) inhibits the apoptotic response to chemotherapy and irradiation. Activation of NF-kappaB via phosphorylation of an inhibitor protein IkappaB leads to degradation of IkappaB through the ubiquitin-proteasome pathway. We hypothesized that inactivation of proteasome function will inhibit inducible NF-kappaB activation, thereby increasing levels of apoptosis in response to chemotherapy and enhancing antitumor effects. To assess the effects of proteasome inhibition on chemotherapy response, human colorectal cancer cells were pretreated with the dipeptide boronic acid analogue PS-341 (1 microM) prior to exposure to SN-38, the active metabolite of the topoisomerase I inhibitor, CPT-11. Inducible activation of NF-kappaB and growth response were evaluated in vitro and in vivo. Effects on p53, p21, p27 and apoptosis were determined. Pretreatment with PS-341 inhibited activation of NF-kappaB induced by SN-38 and resulted in a significantly higher level of growth inhibition (64-75%) compared with treatment with PS-341 alone (20-30%) or SN-38 alone (24-47%; P < 0.002). Combination therapy resulted in a 94% decrease in tumor size compared with the control group and significantly improved tumoricidal response to treatment compared with all treatment groups (P = 0.02). The level of apoptosis was 80-90% in the treatment group that received combination treatment compared with treatment with single agent alone (10%). Proteasome inhibition blocks chemotherapy-induced NF-kappaB activation, leading to a dramatic augmentation of chemosensitivity and enhanced apoptosis. Combining proteasome inhibition with chemotherapy has significant potential to overcome the high incidence of chemotherapy resistance. Clinical studies are currently in development to evaluate the role of proteasome inhibition as an important adjuvant to systemic chemotherapy.

Animals↗
PubMed2001

Elevated superoxide production by active H-ras enhances human lung WI-38VA-13 cell proliferation, migration and resistance to TNF-alpha.

Accumulating evidence has suggested that cellular production of superoxide acts as an intracellular messenger to regulate gene expression and modulate cellular activities. In this report, we set out to investigate the role of active H-ras-mediated superoxide production on tumor cell malignancy in a SV-40 transformed human lung WI-38 VA-13 cell line. Stable transfection and expression of constitutively active mutant V12-H-ras (V12-H-ras) dramatically increased intracellular production of superoxide. The expression of V12-H-ras significantly enhanced cell proliferation, migration and resistance to TNF-alpha treatment compared to that of parental and vector control cells, while expression of wild type H-ras (WT-H-ras) only had modest effects. Upon scavenging by superoxide dismutase and other molecules that decrease the intracellular level of active H-ras mediated superoxide production, cell proliferation, migration and resistance to TNF-alpha were significantly reduced. Furthermore, we demonstrated that the activation of membrane NADPH oxidase activity by expression of active H-ras contributed to the intracellular superoxide production. The causal relationship between membrane superoxide production and increased cell proliferation, migration, and resistance to TNF-alpha by the expression of active H-ras, has provided direct evidence to demonstrate that superoxide acts as an intracellular messenger to cascade ras oncogenic signal relay and to modulate tumor malignant activity.

Acetophenones↗
PubMed2001

Metabolic characterization of spinocerebellar ataxia type 6.

BACKGROUND: Spinocerebellar ataxia type 6 (SCA6) is a neurodegenerative disorder characterized by slowly progressive ataxia and dysarthria. The mutational basis is an expanded CAG repeat sequence within the coding regions of the CACNL1A4 gene. Basic clinical, neuroimaging, and pathological, and epidemiological features have been described in the literature. However, the metabolic features of SCA6 have not been elucidated. OBJECTIVE: To investigate the metabolic features of SCA6. PATIENTS AND METHODS: Seven patients with SCA6 and 7 healthy individuals underwent positron emission tomography using fluorodeoxyglucose F 18. RESULTS: Cerebral glucose utilization in the 7 patients with SCA6 was characterized by significant hypometabolism in widespread structures, including cortical regions and basal ganglia, as well as the cerebellar hemispheres and brainstem. CONCLUSIONS: The results of the multiple-regional brain hypometabolism suggest that brain dysfunction associated with SCA6 may not be limited to the cerebellum and inferior olive, as previously suggested by the results of other pathologic studies.

Adult↗
PubMed2001

Exploring the structure and function of the P-glycoprotein multidrug transporter using fluorescence spectroscopic tools.

P-glycoprotein is an ABC protein that functions as an efflux pump for multiple drugs, natural products and peptides. It is proposed to operate as a hydrophobic vacuum cleaner, expelling non-polar compounds from the membrane bilayer to the exterior, driven by the energy of ATP hydrolysis. The nucleotide-binding domains of P-glycoprotein appear to operate by an alternating sites mechanism to power drug transport. In recent years, purification and functional reconstitution of the protein has allowed the application of fluorescence spectroscopic techniques. This approach has led to insights into the structural architecture of the P-glycoprotein molecule, and a more detailed understanding of the way in which it interacts with nucleotides and drugs.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

The study of spectrosgraphic properties and molecular recognition of cali.

The absorption spectrum and fluorescence spectrum of calix[n]arenes are studied systematically. The self-association of calix[n]arenes is proposed and the self-association constant is also obtained. The recognition properties of calix[n]arenes are studied and the inclusion constant is calculated.

Calixarenes↗
PubMed2001

Interaction of morin with CTMAB: aggregation and location in micellar.

The aggregation and location of morin in CTMAB micellar solution was studied by light scattering spectra, electronic absorption spectra and pulsed FT NMR techniques. The difference in the light scattering property of morin with and without CTMAB proved that a large particle of the morin-CTMAB associate formed. Morin has a self-assembly tendency, but the assembly number is not high. With the increase of morin concentration, morin changed from a monomer to dimer. The hyperchromic and bathochromic effect of morin, with the increase in pH value or

Cetrimonium↗
PubMed2001

Interaction of morin-cetyltrimethylammonium bromide with nucleic acids and determination of nucleic acids at nanograms per milliliter levels based on the enhancement of preresonance light scattering.

A new preresonance light scattering (PRLS) assay of nucleic acids is presented. At pH 7.30, the weak PRLS of morin-cetyltrimethylammonium bromide (CTMAB) can be greatly enhanced by the addition of nucleic acids, owing to the interaction between the nucleic acid and morin-CTMAB. After the addition of morin and CTMAB to DNA, the zeta potential of DNA decreases and changes from negative to positive, which is due to the formation of an associate, the aggregation of morin on nucleic acids and the electric neutralization between DNA and the cationic surfactant CTMAB. Mechanism studies showed that the enhanced PRLS comes from the aggregation of morin in the presence of nucleic acids and CTMAB. The enhanced intensity of PRLS is in proportion to the concentration of nucleic acids in the range 7.5 x 10(-9)-1.0 x 10(-5) g ml(-1) for calf thymus DNA, 7.5 x 10(-9)-1.0 x 10(-6) g ml(-1) for salmon sperm DNA and 1.0 x 10(-8)-1.0 x 10(-6) g ml(-1) for yeast RNA. The detection limits are 3.4, 6.2 and 4.1 ng ml(-1) for calf thymus DNA, salmon sperm DNA and yeast RNA, respectively. Synthetic samples were analyzed satisfactorily.

Animals↗
PubMed2001

Towards case-based performance measures: uncovering deficiencies in applied medical care.

Measures are designed to evaluate the processes and outcomes of care associated with the delivery of clinical (and non-clinical) services. They allow for intra- and interorganizational comparison to be used continuously to improve patient health outcomes. The use of performance measures always means to abstract the complex reality (medical scenarios and procedures) in order to provide an understandable and comparable output. Measures can focus on global performance. The more detailed data are available the more specific judgements with respect to the appropriateness of clinical decision-making and implementation of evidence are feasible. Externally reported measures are intended both to inform and lead to action. By providing this information, deficiencies in patient care and unnecessary variations in the care process can be uncovered. Such variations have contributed to disparities in morbidity and mortality. The developments in information technology, especially world-wide interconnectivity, standards for electronic data exchange and facilities to store and manage large amounts of data, offer the opportunity to analyse health-relevant information in order to make the delivery of healthcare services more transparent for consumers and providers. Global performance measures, such as the overall life expectancy (mortality) in a country, can give a rough orientation of how well health systems perform but they do not offer general solutions nor specific insights into care processes that have to be improved. In contrast to population-based measures, case-based performance measures use a defined group of patients depending on specific patient characteristics and features of disease. By means of these measures we are able to compare the number of patients that receive a necessary medical procedure against those patients who do not. The use of case-based measures is a bottom-up approach to improve the overall performance in the long run. They are not only a tool for global orientation but can offer a straightforward link to the areas of deficient care and the underlying procedures. Performance measures are relevant to providers as well as consumers, from their own individual perspective. Cased-based measures focus on the management of individual patient. This approach to performance measurement can inform physicians in a meaningful and constructive way by monitoring their individual performance and by pointing out possible areas of improvement.

Case-Control Studies↗
PubMed2001

beta-Amyloid efflux mediated by p-glycoprotein.

A large body of evidence suggests that an increase in the brain beta-amyloid (Abeta) burden contributes to the etiology of Alzheimer's disease (AD). Much is now known about the intracellular processes regulating the production of Abeta, however, less is known regarding its secretion from cells. We now report that p-glycoprotein (p-gp), an ATP-binding cassette (ABC) transporter, is an Abeta efflux pump. Pharmacological blockade of p-gp rapidly decrease extracellular levels of Abeta secretion. In vitro binding studies showed that addition of synthetic human Abeta1-40 and Abeta1-42 peptides to hamster mdr1-enriched vesicles labeled with the fluorophore MIANS resulted in saturable quenching, suggesting that both peptides interact directly with the transporter. Finally, we were able to directly measure transport of Abeta peptides across the plasma membranes of p-gp enriched vesicles, and showed that this phenomenon was both ATP- and p-gp-dependent. Taken together, our study suggests a novel mechanism of Abeta detachment from cellular membranes, and represents an obvious route towards identification of such a mechanism in the brain.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Role of polyamine metabolism in kainic acid excitotoxicity in organotypic hippocampal slice cultures.

Polyamines are ubiquitous cations that are essential for cell growth, regeneration and differentiation. Increases in polyamine metabolism have been implicated in several neuropathological conditions, including excitotoxicity. However, the precise role of polyamines in neuronal degeneration is still unclear. To investigate mechanisms by which polyamines could contribute to excitotoxic neuronal death, the present study examined the role of the polyamine interconversion pathway in kainic acid (KA) neurotoxicity using organotypic hippocampal slice cultures. Treatment of cultures with N1,N(2)-bis(2,3-butadienyl)-1,4-butanediamine (MDL 72527), an irreversible inhibitor of polyamine oxidase, resulted in a partial but significant neuronal protection, especially in CA1 region. In addition, this pre-treatment also attenuated KA-induced increase in levels of lipid peroxidation, cytosolic cytochrome C release and glial cell activation. Furthermore, pre-treatment with a combination of cyclosporin A (an inhibitor of the mitochondrial permeability transition pore) and MDL 72527 resulted in an additive and almost total neuronal protection against KA toxicity, while the combination of MDL 72527 and EUK-134 (a synthetic catalase/superoxide dismutase mimetic) did not provide additive protection. These data strongly suggest that the polyamine interconversion pathway partially contributes to KA-induced neurodegeneration via the production of reactive oxygen species.

Animals↗