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Biomedical subjects

B Li

Publications and source records attributed to B Li.

At least 19 recordsLinked to original sources
PubMed2002

Copper speciation and accumulation in the gill microenvironment of carp ( Cyprinus carpio) in the presence of kaolin particles.

Carp were exposed to copper adsorbed on kaolin particles at various concentrations (0-2.4 mg/L), and net accumulation due to elevated adsorbed copper in the surrounding water was observed. Copper speciation in the water and fish gill microenvironment was modeled in the presence and absence of kaolin using a chemical speciation program (MINTEQA2). The adsorption affinity constants of kaolin for copper at various pH values used in the speciation calculations were experimentally determined, and the quantitative relationship between the affinity constant and pH was modeled. Copper accumulations in fish gills exposed to kaolin-adsorbed copper was then observed. The results indicate that desorption occurred in the fish gill microenvironment due to both mucus competition of copper and slight increase in water pH. Furthermore, the available copper species increased as a result of desorption, causing a net accumulation of Cu by the gills.

Adsorption↗
PubMed2002

T cell infiltration and chemokine expression: relevance to the disease localization in murine graft-versus-host disease.

Acute graft-versus-host disease (GVHD) involves mainly skin, liver and intestines. Other organs such as heart, muscle and central nervous system are seldom affected, although their parenchymal cells also express alloantigens, such as MHC class I antigens. The mechanism of this selective involvement of distinct organs in acute GVHD is not well understood. We postulated that it might be related to the selective migration of activated alloreactive T cells. Indeed, T cell infiltration, revealed by examination of serial samples using flow cytometry and immunohistology, occurred early and continuously in the target organs such as the liver, but not in a non-target organ, the heart, in a murine acute GVHD model. Since T cell migration is largely controlled by the expression of chemokine and chemokine receptors, we investigated the chemokine spectrum in target/non-target organs of mice with acute GVHD. We found that in the spleen and liver MIP-1alpha, MIP-2 and Mig were the predominant chemokines expressed. In another target organ, the skin, MIP-1alpha, MIP-2, MCP-1 and MCP-3 were all highly expressed. In a non-target organ of acute GVHD, the heart, the predominant chemokines expressed were MCP-1 and MCP-3. This distinct pattern of chemokine expression in these organs may contribute to the preferential recruitment of inflammatory cells into the liver and skin, but not into the heart, in acute GVHD.

Acute Disease↗
PubMed2002

A novel conditional Akt 'survival switch' reversibly protects cells from apoptosis.

The anti-apoptotic Akt kinase is commonly activated by survival factors following plasma membrane relocalization attributable to the interaction of its pleckstrin homology (PH) domain with phosphatidylinositol 3-kinase (PI3K)-generated PI3,4-P(2) and PI3,4,5-P(3). Once activated, Akt can prevent or delay apoptosis by phosphorylation-dependent inhibition or activation of multiple signaling molecules involved in apoptosis, such as BAD, caspase-9, GSK3, and NF-kappaB and forkhead family transcription factors. Here, we describe and characterize a novel, conditional Akt controlled by chemically induced dimerization (CID). In this approach, the Akt PH domain has been replaced with the rapamycin (and FK506)-binding domain, FKBP12, to make F3-DeltaPH.Akt. To effect membrane recruitment, a myristoylated rapamycin-binding domain from FRAP/mTOR, called M-FRB, binds to lipid permeable rapamycin (and non-bioactive synthetic 'rapalogs'), leading to reversible heterodimerization of M-FRB with FKBP-DeltaPH.Akt. Like endogenous c-Akt, we show that the kinase activity of membrane-localized F3-DeltaPH.Akt correlates strongly with phosphorylation at T308 and S473; however, unlike c-Akt, phosphorylation and activation of inducible Akt (iAkt) is largely PI3K independent. CID-mediated activation of iAkt results in phosphorylation of GSK3, and contributes to NF-kappaB activation in vivo in a dose-sensitive manner. Finally, in Jurkat T cells stably expressing iAkt, CID-induced Akt activation rescued cells from apoptosis triggered by multiple apoptotic stimuli, including staurosporine, anti-Fas antibodies, PI3K inhibitors and the DNA damaging agent, etoposide. This novel inducible Akt should be useful for identifying new Akt substrates and for reversibly protecting tissue from apoptosis due to ischemic injury or immunological attack.

Apoptosis↗
PubMed2002

Seed and pollen flow and cline discordance among genes with different modes of inheritance.

The relationships between seed and pollen flow and cline discordance/concordance between cytoplasmic and nuclear genes, with the incorporation of the effects of natural selection, are formulated for one locus with two alleles, under assumptions of random mating, no drift and no mutation. Results show that under certain conditions, the relative roles of seed and pollen flow in shaping cline discordance/ concordance are very similar to their roles in influencing population differentiation for selectively neutral markers with different modes of inheritance. Where the disequilibria between cytoplasmic and nuclear genes are of the order similar to selection coefficient, cline discordance/concordance can be predicted from the relative values of the ratio of pollen to seed flow and the ratio of selection coefficients. Where the disequilibria attained by seed and pollen flow are significant, the integrated cytonuclear data are recommended for cline analysis. In both cases, the relative rates of selection coefficients between cytoplasmic and nuclear genes can be roughly estimated according to their characteristic length.

Alleles↗
PubMed2002

The prevalence of asthma and asthma-like symptoms among adults in rural Beijing, China.

No data have been reported on the prevalence of asthma in rural areas of China. The objective of the present study was to determine the prevalence of asthma-like symptoms, reported asthma and reported asthma attacks in rural Beijing, China, and to compare the prevalence in 20-44-yr-old participants with those reported for Canada and the European Community Respiratory Health Survey (ECRHS). For a cross-sectional survey, 30 villages were randomly selected in the counties of Shunyi and Tongxian, 50 km north and east respectively of the city of Beijing and within the municipality of Beijing. The International Union Against Tuberculosis and Lung Disease questionnaire on bronchial symptoms translated into Chinese was completed by village doctors for each individual of >15 yrs. The survey was completed by 22,561 individuals, representing 98% of the eligible population. The prevalence of asthma-like symptoms and reported asthma attacks was higher in females than in males and increased with age. Smoking significantly increased the prevalence of symptoms; the effect in females was greater than in males. Among the 20-44-yr-olds, the prevalence of reported asthma attacks in the previous 12 months was 0.67% in rural Beijing, very much lower than that reported in ECRHS centres (3.1%), urban Canada (6.9%) and semirural Canada (5.1%), after adjusting for age and sex. The prevalence of asthma-like symptoms was also very low in rural Beijing compared with ECRHS centres and Canada. It is concluded that the prevalence of asthma-like symptoms and reported asthma was low in rural China compared with other countries, consistent with reports of the relative scarcity of asthma in farms and the "hygiene hypothesis".

Adolescent↗
PubMed2002

Oxidation-reduction potential (ORP) regulation of nutrient removal in activated sludge wastewater treatment plants.

Redox potential (ORP) regulation of nutrient removal in aeration tanks was tested for one year in three activated sludge wastewater treatment plants in Cincinnati, OH. The experiment results show a good relationship between ORP values and nutrient removal. Macro-biodegradation and sorption of substrate by activated sludge can significantly increase wastewater ORP, indicating the improvement of redox status of the bulk liquor. DO higher than 1.0 mg/L is necessary for good biodegradation and the improvement of liquid redox status. ORP values at higher temperatures (Twater = 20-26 degrees C) were lower than ORP values at lower temperatures (Twater = 14-19 degrees C), caused by the lower oxygen saturation capacity in wastewater and the more rapid oxygen consumption by microorganism under warmer conditions. Nitrification occurred at higher ORP values (380 mV) than did organic substrate oxidation (250 mV). This verifies that different metabolic processes dominate in different ORP ranges. The pilot-scale experiment results demonstrate that the wastewater ORP values continued to increase throughout the whole 6-hour cycle when the influent COD was higher than 1,000 mg/L. For influent with low COD (40-120 mg/L), the wastewater ORP values did not increase in the second 3 hours of the cycle, during which time the microbial-biodegradation within the activated sludge floc dominated. High DO concentrations (6-8 mg/L) did not help improve the redox status. In fully-aerated wastewater, oxygen deeply penetrated into the activated sludge flocs, and microorganisms biodegraded the substrates within the flocs. Endogenous metabolism predominated.

Biodegradation, Environmental↗
PubMed2001

Modulation of L-type Ca2+ channels in UMR 106 cells by parathyroid hormone-related protein.

The effects of rat parathyroid hormone-related protein (rPTHrP) and bovine and rat parathyroid hormone (bPTH and rPTH) on L-type Ca2+ channels in UMR 106 cells were investigated using the patch clamp technique. rPTHrP increased the whole cell L-type Ca2+ channel currents and the increase was concentration dependent. rPTHrP, at a concentration of 62.5 nM, increased the L-type Ca2+ channel current by 122+/-25%. bPTH was less potent. A concentration of 7.5 microM bPTH increased the current by 99+/-24%. Results obtained with rPTH were similar to those obtained using bPTH. Single channel measurements, using the cell-attached version of the patch clamp technique, showed an increase in both the number of channel openings and the mean open time when the cells were exposed to rPTHrP. This suggested that rPTHrP affected the gating of L-type Ca2+ channels in UMR 106 cells. This study demonstrates that the actions of bPTH and rPTHrP in UMR cells are mediated in part by extracellular Ca2+ entry. PTHrP, a paracrine agent important in development, is more potent in regulating Ca2+ entry than PTH.

Animals↗
PubMed2001

Adaptation of PMLS neurons to prolonged optic flow stimuli.

Changes in neuronal responses during and after adaptation to prolonged optic flow stimulation were investigated by extracellular single-unit recording in the posteromedial lateral suprasylvian area (PMLS) of the cat. In comparison with translation stimuli, the complex optic flow patterns (radiation and rotation) produced more pronounced adaptation and after-effects by inducing larger response reduction, and altered the direction selectivity of many neurons obviously as well. Generally, the adaptation effects were direction-specific for radiation/rotation, but independent of the direction of test stimulus for translation. These results suggest that PMLS may play an important role in the perception of motion after-effects to complex optic flow fields, while the adaptation to simple translation might be generated at a relatively earlier level of the visual system.

Adaptation, Physiological↗
PubMed2001

Human sex reversal due to impaired nuclear localization of SRY. A clinical correlation.

SRY, an architectural transcription factor encoded by the sex-determining region of the Y chromosome, initiates testicular differentiation in mammalian embryogenesis. The protein contains a high-mobility group (HMG) box, a DNA-bending motif conserved among a broad class of nuclear proteins. Mutations causing human sex reversal (46, XY pure gonadal dysgenesis) are clustered in this domain. Basic N- and C-terminal regions of the HMG box are each proposed to provide nuclear localization signals. The significance of the C-terminal basic cluster (SRY residues 130-134) is uncertain, however, as its activity in cell culture varies with assay conditions. To test its importance, we have investigated a C-terminal sex-reversal mutation (R133W, position 78 of the HMG box). This de novo mutation impairs nuclear localization but not specific DNA binding or sharp DNA bending. Correlation between these properties and the phenotype of the patient suggests that nuclear localization of SRY is required for testicular differentiation and directed in part by the C-terminal basic cluster. To our knowledge, these results provide the first example of impaired organogenesis due to a nuclear localization signal mutation.

Amino Acid Sequence↗
PubMed2001

Discovery of small-molecule inhibitors of Bcl-2 through structure-based computer screening.

Bcl-2 belongs to a growing family of proteins which regulates programmed cell death (apoptosis). Overexpression of Bcl-2 has been observed in 70% of breast cancer, 30-60% of prostate cancer, 80% of B-cell lymphomas, 90% of colorectal adenocarcinomas, and many other forms of cancer. Thereby, Bcl-2 is an attractive new anti-cancer target. Herein, we describe the discovery of novel classes of small-molecule inhibitors targeted at the BH3 binding pocket in Bcl-2. The three-dimensional (3D) structure of Bcl-2 has been modeled on the basis of a high-resolution NMR solution structure of Bcl-X(L), which shares a high sequence homology with Bcl-2. A structure-based computer screening approach has been employed to search the National Cancer Institute 3D database of 206 876 organic compounds to identify potential Bcl-2 small-molecule inhibitors that bind to the BH3 binding site of Bcl-2. These potential Bcl-2 small-molecule inhibitors were first tested in an in vitro binding assay for their potency in inhibition of the binding of a Bak BH3 peptide to Bcl-2. Thirty-five potential inhibitors were tested in this binding assay, and seven of them were found to have a binding affinity (IC(50) value) from 1.6 to 14.0 microM. The anti-proliferative activity of these seven active compounds has been tested using a human myeloid leukemia cell line, HL-60, which expresses the highest level of Bcl-2 protein among all the cancer cell lines examined. Compound 6 was the most potent compound and had an IC(50) value of 4 microM in inhibition of cell growth using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Five other compounds had moderate activity in inhibition of cell growth. Compound 6 was further evaluated for its ability to induce apoptosis in cancer cells. It was found that 6 induces apoptosis in cancer cells with high Bcl-2 expression and its potency correlates with the Bcl-2 expression level in cancer cells. Furthermore, using NMR methods, we conclusively demonstrated that 6 binds to the BH3 binding site in Bcl-X(L). Our results showed that small-molecule inhibitors of Bcl-2 such as 6 modulate the biological function of Bcl-2, and induce apoptosis in cancer cells with high Bcl-2 expression, while they have little effect on cancer cells with low or undetectable levels of Bcl-2 expression. Therefore, compound 6 can be used as a valuable pharmacological tool to elucidate the function of Bcl-2 and also serves as a novel lead compound for further design and optimization. Our results suggest that the structure-based computer screening strategy employed in the study is effective for identifying novel, structurally diverse, nonpeptide small-molecule inhibitors that target the BH3 binding site of Bcl-2.

Amino Acid Sequence↗
PubMed2001

Hydrophobic hydration is an important source of elasticity in elastin-based biopolymers.

Molecular dynamics simulations with explicit waters have been employed to investigate the dominant source of elastin's elasticity. An elastin-like peptide, (VPGVG)(18), was pulled and released in molecular dynamics simulations, at 10 and 42 degrees C, lasting several nanoseconds, which is consistent with the experimentally determined dielectric and NMR relaxation time scales. At elastin's physiological temperature and degree of extension, the simulations indicate that the orientational entropy of waters hydrating hydrophobic groups decreases during pulling of the molecule, but it increases upon release. In contrast, the main-chain fluctuations and other measures of mobility suggest that elastin's backbone is more dynamic in the extended than released state. These results and the agreement between the simulations with various experimental observations suggest that hydrophobic hydration is an important source of the entropy-based elasticity of elastin. Moreover, elastin tends to reorder itself to form a hydrophobic globule when it was held in its extended state, indicating that the hydrophobic effect also contributes in the holding process. On the whole, our simulations support the hydrophobic mechanism of elasticity and provide a framework for description of the molecular basis of this phenomenon.

Biopolymers↗
PubMed2001

Synthesis and characterization of chiral N-O turns induced by alpha-aminoxy acids.

Chiral alpha-aminoxy acids of various side chains were synthesized with high optical purity starting from chiral alpha-amino acids. The conformations of diamides 13a-e, 15, and 16 were probed by using NMR, FT-IR, and CD spectroscopic methods as well as X-ray crystallography. The right-handed turns with eight-membered-ring intramolecular hydrogen bonds between adjacent residues (called the N-O turns) were found to be preferred for D-aminoxy acid residues, and they were independent of the side chains. The rigid chiral N-O turns should have great potential in molecular design.

Amino Acids↗
PubMed2001

CpG methylation as a basis for breast tumor-specific loss of NES1/kallikrein 10 expression.

The normal epithelial cell-specific-1 (NES1)/kallikrein 10 gene is expressed in normal mammary epithelial cells, but its expression is dramatically decreased in breast cancer cell lines. Now, we have cloned and characterized the active promoter region of NES1. Using a luciferase reporter system, we demonstrate that most tumor cell lines are able to support full or partial transcription from the NES1 promoter, suggesting a role for promoter-independent cis-acting mechanisms of loss of NES1 expression. We show that hypermethylation of the NES1 gene represents one such mechanism. Using methylation-specific PCR and sequence analysis of sodium bisulfite-treated genomic DNA, we demonstrate a strong correlation between exon 3 hypermethylation and loss of NES1 mRNA expression in a panel of breast cancer cell lines and in primary tumors. Treatment of NES1-nonexpressing cells with a demethylating agent led to reexpression of NES1, suggesting an important role of hypermethylation in the loss of NES1 expression. We suggest that hypermethylation is responsible for tumor-specific loss of NES1 gene expression. Our results also suggest that hypermethylation of the NES1 gene may serve as a potential marker for breast cancer.

Antimetabolites, Antineoplastic↗
PubMed2001

The discovery of sulfonylated dipeptides as potent VLA-4 antagonists.

Directed screening of a carboxylic acid-containing combinatorial library led to the discovery of potent inhibitors of the integrin VLA-4. Subsequent optimization by solid-phase synthesis afforded a series of sulfonylated dipeptide inhibitors with structural components that when combined in a single hybrid molecule gave a sub-nanomolar inhibitor as a lead for medicinal chemistry. Preliminary metabolic studies led to the discovery of substituted biphenyl derivatives with low picomolar activities. SAR and pharmacokinetic characterization of this series are presented.

Animals↗
PubMed2001

Deficiency of small GTPase Rac2 affects T cell activation.

Rac2 is a hematopoietic-specific GTPase acting as a molecular switch to mediate both transcriptional activation and cell morphological changes. We have examined the effect of Rac2 deficiency during T cell activation. In Rac2(-/-) T cells, proliferation was reduced upon stimulation with either plate-bound anti-CD3 or T cell receptor-specific antigen. This defect is accompanied with decreased activation of mitogen activated protein kinase extracellular signal-regulated kinase (ERK)1/2 and p38, and reduced Ca(2)+ mobilization. TCR stimulation-induced actin polymerization is also reduced. In addition, anti-CD3 cross-linking-induced T cell capping is reduced compared with wild-type T cells. These results indicate that Rac2 is important in mediating both transcriptional and cytoskeletal changes during T cell activation. The phenotypic similarity of Rac2(-/-) to Vav(-/-) cells implicates Rac2 as a downstream mediator of Vav signaling.

Animals↗
PubMed2001

Substituted imidazoles as glucagon receptor antagonists.

A modestly active, nonselective triarylimidazole lead was optimized for binding affinity with the human glucagon receptor. This led to the identification of a 2- and/or 4-alkyl or alkyloxy substituent on the imidazole C4-aryl group as a structural determinant for significant enhancement in binding with the glucagon receptor (e.g., 41, IC(50)=0.053 microM) and selectivity (>1000x) over p38MAP kinase in this class of compounds.

Animals↗