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Biomedical subjects

Wei Li

Publications and source records attributed to Wei Li.

At least 73 records · Page 4Linked to original sources
PubMed2006

Determination of free L-carnitine in human seminal plasma by high performance liquid chromatography with pre-column ultraviolet derivatization and its clinical application in male infertility.

BACKGROUND: To develop and validate a simple and reliable high performance liquid chromatographic (HPLC) method for the analysis of free L-carnitine in human seminal plasma and to investigate its clinical significance as a potentially additional means of evaluating the infertile male. METHODS: After proteins in seminal plasma are precipitated with a mixture of acetonitrile and methanol (9:1; v/v), free L-carnitine in seminal plasma was derivatized to form its UV-absorbing ester. HPLC separation of the sample solution was performed on a Lichrospher SiO2 column and detected by ultraviolet absorbance at 260 nm. A mobile phase composed of acetonitrile-citric acid buffer (containing 12 mmol/L triethanolamine, pH 5.0) was found to be the most suitable for this separation at a flow rate of 1.2 mL/min and enabled the baseline separation of the free L-carnitine from interferences with isocratic elution. The free L-carnitine levels in seminal plasma were studied in both 30 control subjects and 87 patients with infertility. Ejaculates were classified into studied subgroups and defined as: asthenozoospermia (n=29), oligozoospermia (n=19) and oligoasthenoteratozoospermia (n=39). RESULTS: Under the chromatographic conditions described, the free L-carnitine derivative had a retention time of approximately 13 min. Good separation and detectability of free L-carnitine in human seminal plasma sample were obtained. The method proved to be linear in the range of L-carnitine from 0 micromol/L to 1000 micromol/L. The relative standard deviations of within- and between-assay for free L-carnitine analysis were 1.23 and 1.36 %, respectively. The recoveries were 91.6-96.5% for the human seminal plasma samples. Free L-carnitine concentrations in the populations were 392.66+/-107.18 micromol/L in the fertile group (n=30), 270.00+/-83.92 micromol/L in asthenozoospermia group, 187.97+/-43.90 micromol/L in oligozoospermia group and 175.65+/-67.07 micromol/L in oligoasthenozoospermia group. The large difference (P<0.01) between the fertile and infertile populations is evident and the difference between the subdivided groups in the infertile group is not significant (P>0.05). CONCLUSION: The determination of free L-carnitine level in seminal plasma may prove useful as a potentially biochemical marker of fertility and this is a useful guidance for the clinic therapy and the mechanismic study on the male reproduction.

Adult↗
PubMed2006

Genes affecting cell competition in Drosophila.

Cell competition is a homeostatic mechanism that regulates the size attained by growing tissues. We performed an unbiased genetic screen for mutations that permit the survival of cells being competed due to haplo-insufficiency for RpL36. Mutations that protect RpL36 heterozygous clones include the tumor suppressors expanded, hippo, salvador, mats, and warts, which are members of the Warts pathway, the tumor suppressor fat, and a novel tumor-suppressor mutation. Other hyperplastic or neoplastic mutations did not rescue RpL36 heterozygous clones. Most mutations that rescue cell competition elevated Dpp-signaling activity, and the Dsmurf mutation that elevates Dpp signaling was also hyperplastic and rescued. Two nonlethal, nonhyperplastic mutations prevent the apoptosis of Minute heterozygous cells and suggest an apoptosis pathway for cell competition . In addition to rescuing RpL36 heterozygous cells, mutations in Warts pathway genes were supercompetitors that could eliminate wild-type cells nearby. The findings show that differences in Warts pathway activity can lead to competition and implicate the Warts pathway, certain other tumor suppressors, and novel cell death components in cell competition, in addition to the Dpp pathway implicated by previous studies. We suggest that cell competition might occur during tumor development in mammals.

Animals↗
PubMed2006

APC gene methylation is inversely correlated with features of the CpG island methylator phenotype in colorectal cancer.

The notion of a CpG island methylator phenotype (CIMP) was proposed to describe a subset of colorectal cancers (CRC) displaying frequent and concordant methylation of CpG islands located within gene promoter regions. Some workers have failed to observe associations between CIMP and specific clinicopathological features of CRC, possibly because of the choice of genes used to define this phenotype. The aim of the current study was to determine whether the aberrant methylation of 6 genes implicated in CRC development was associated with the same phenotypic features of this tumour type. The MethyLight assay was used to provide quantitative estimates of MLH1, P16, TIMP3, P14, DAPK and APC methylation levels in 199 unselected colorectal tumours. The methylation of MLH1, P16, TIMP3 and P14 was highly concordant (p < 0.0001 for each pair) but that of DAPK and APC was not. An inverse association was observed between the methylation of APC and TIMP3 (p = 0.004). Methylation of the MLH1, P16, TIMP3 and P14 genes was associated with tumour infiltrating lymphocytes (p < 0.05), microsatellite instability (p < 0.001), BRAF mutation (p < 0.0001) and elevated concentrations of the methyl group carriers tetrahydrofolate (THF) and 5,10-methylene THF (p < 0.05). In contrast, APC methylation was associated with wildtype BRAF (p = 0.003) and with lower concentrations of methyl group carriers (p < 0.05). These findings highlight the importance of gene selection in studies that aim to characterize the biological features and clinical behaviour of CIMP+ tumours.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Human multidrug resistance protein 2 transports the therapeutic bile salt tauroursodeoxycholate.

The multidrug resistance protein 2 (MRP2/ABCC2) mediates the biliary excretion of glucuronide and glutathione conjugates of endogenous and exogenous compounds. We examined the activation of human MRP2-mediated ATP-dependent transport by the choleretic bile salt ursodeoxycholic acid (UDC) and its taurine and glycine amidates in Sf9 cell membranes expressing MRP2 using beta-estradiol 17-(beta-D-glucuronide) (E(2)17G) and beta-estradiol 3-(beta-D-glucuronide) (E(2)3G) as substrates. MRP2 transported E(2)3G via classic Michaelis-Menten kinetics (K(m) = 122 microM; V(max) = 3.0 nmol/mg/min), whereas E(2)17G transport showed positive cooperativity (Hill slope, 2.15; K(m) = 75 microM; V(max) = 3.8 nmol/mg/min). UDC, tauroursodeoxycholate, and glycoursodeoxycholate (80-100 microM) maximally stimulated E(2)3G transport 9-, 7.9-, and 3.6-fold, respectively, whereas higher concentrations (1-2 mM) inhibited transport. At low (0.3 microM) concentrations, tauroursodeoxycholate was transported only in the presence of E(2)17G or E(2)3G, but not other MRP2 substrates such as methotrexate, leukotriene C(4), or S-methylglutathione. Kinetic analysis of higher concentrations of tauroursodeoxycholate transport by MRP2 showed positive cooperativity (Hill slope, 1.84; K(m) = 127 microM; V(max) = 779 pmol/mg/min). Taurocholate (2-100 microM) was not detectably transported by MRP2 either alone or in the presence of E(2)17G but was transported in the presence of E(2)3G. Thus, UDC, tauroursodeoxycholate, and glycoursodeoxycholate activated MRP2 transport. Tauroursodeoxycholate was transported by MRP2 and demonstrated positive cooperativity, identifying it as the second MRP2 substrate able to stimulate its own transport. The data suggest MRP2 binding sites that can require specific complementarities between substrates and modulators of MRP2-mediated transport.

Biological Transport↗
PubMed2006

Induction of tobacco genes in response to oligochitosan.

Oligochitosan has a variety of biological activities. To understand its mechanism, DDRT-PCR, reverse Northern blot and quantitative relative RT-PCR were used to identify and isolate genes whose transcription were altered in cultured Nicotiana tabacum (var. Samsun NN) plants that were treated with oligochitosan. Three genes whose mRNA levels significantly changed in response to oligochitosan were isolated and identified. One gene is up-regulated, and two genes are down-regulated. These genes encode a DNAJ heat shock N-terminal domain-containing protein, a histone H1 gene and a hypothetical protein, whose function is unknown. The results suggest that the usefulness of mRNA differential display technique for the detection of plant metabolic pathways affected by oligochitosan.

Blotting, Northern↗
PubMed2006

Coupling between A-type horizontal cells is mediated by connexin 50 gap junctions in the rabbit retina.

There are many examples of neuronal coupling via gap junctions in the retina. Of these, perhaps the best known is the extensive coupling between horizontal cells. In the rabbit retina, there are two types of horizontal cells, A-type and B-type, both of which are independently coupled. Connexin 50 (Cx50) cDNA, encoding a 440 aa protein, was successfully isolated from rabbit retina RNA. Cx50 was also obtained from isolated A-type horizontal cells (A-type HCs) by single-cell RT-PCR. A-type HCs were visualized by intracellular dye injection or with an antibody against calbindin. Confocal analysis revealed all Cx50 labeling occurred on the A-type HC matrix, typically at dendritic intersections. The Cx50 plaques varied in size, from punctate signals in which fine dendrites cofasciculated, to giant plaques, >50 microm(2), in which large dendrites crossed. The numerous Cx50 plaques between A-type HCs may adequately account for the remarkable coupling observed in this network. We could not detect Cx50 staining on the tips of horizontal cell dendrites within the cone pedicle invagination. This distribution does not support a role for Cx50 in hemichannel-mediated feedback. In addition, the absence of Cx50 in B-type HCs suggests the presence of a different connexin for this cell type. In summary, these results suggest that gap junctions in the A-type horizontal cell matrix are composed from Cx50. Multiple neuronal connexins are expressed in the mammalian retina and different cell types express specific connexins.

Animals↗
PubMed2006

A C. elegans model of nicotine-dependent behavior: regulation by TRP-family channels.

Nicotine, the primary addictive substance in tobacco, induces profound behavioral responses in mammals, but the underlying genetic mechanisms are not well understood. Here we develop a C. elegans model of nicotine-dependent behavior. We show that worms exhibit behavioral responses to nicotine that parallel those observed in mammals, including acute response, tolerance, withdrawal, and sensitization. These nicotine responses require nicotinic acetylcholine receptor (nAChR) family genes that are known to mediate nicotine dependence in mammals, suggesting functional conservation of nAChRs in nicotine responses. Importantly, we find that mutant worms lacking TRPC (transient receptor potential canonical) channels are defective in their response to nicotine and that such a defect can be rescued by a human TRPC channel, revealing an unexpected role for TRPC channels in regulating nicotine-dependent behavior. Thus, C. elegans can be used to characterize known genes as well as to identify new genes regulating nicotine responses.

Amino Acid Sequence↗
PubMed2006

Spectroscopic and computational studies on the coordination-driven self-assembly complexes (ZnL)2 and (NiL)2 [L= bis(2,4-dimethyldipyrrin-3-yl)methane].

FT-IR, FT-Raman and electronic absorption spectroscopies were utilized in conjunction with density functional theory (DFT) calculations to investigate the ground and excited states of self-assembled dinuclear dimeric helicates (ZnL)2 and (NiL)2 [L = bis(2,4-dimethyldipyrrin-3-yl)methane]. These studies afford a detailed description of the ground-state geometric and electronic structures of (ZnL)2 and (NiL)2 and provide a comparison with similar geometrical metal-porphyrins. The results demonstrate that enlarging the basis set used in the DFT calculations results in an obvious alteration of the calculated bond lengths but negligible alteration of the calculated bond angles. The predicted spectra are in good agreement with the experimental ones with the deviations generally less than 30 cm(-1). In comparison with vibrational spectra of metal-porphyrins, the breathing vibration of the pyrrole ring is shifted by over 100 cm(-1) toward higher wavenumber due to local conjugation of molecular geometry. Time-dependent density functional theory (TD-DFT) provides a good description of the excitation energy. Because of the break in symmetry, the absorption band (corresponding to the Q-band of porphyrin) of (ZnL)2 and (NiL)2 is no longer weak. Local conjugation makes the absorption wavelength of (NiL)2 and (ZnL)2 shift to the blue compared with those of NiP and ZnP.

Journal Article↗
PubMed2006

Translational regulation of rat multidrug resistance-associated protein 2 expression is mediated by upstream open reading frames in the 5' untranslated region.

Multidrug resistance-associated protein 2 (Mrp2/Abcc2), an organic anion transporter present in the apical membrane of hepatocytes, renal epithelial cells, and enterocytes, is postulated to undergo translational regulation. Transcription of rat hepatic Mrp2 mRNA is initiated at multiple sites (-213, -163, -132, and -98 nucleotides relative to the Mrp2 ATG) and contains potential upstream open reading frames (uORFs) in the 5' untranslated region (UTR) starting at -213, -149 and -109 nucleotides. Ribonuclease protection assays demonstrated that transcription of the Mrp2 gene at the various initiation sites was tissue-specific, with the major initiation site in the liver and kidney being -98 and -132 nucleotides, respectively. In the jejunum, the primary and secondary initiation sites were -98 and -132 nucleotides, respectively, with the converse true in the ileum. The relative abundance of these Mrp2 transcripts expressed in tissues varied with age from birth to the adult. HepG2 transient expression assays and in vitro translation assays in which the 5'UTRs were fused with a luciferase reporter showed that the 5'UTR without any uORF (-98 nucleotide) expressed maximal luciferase activity compared with those with one (-132 nucleotides), two (-163 nucleotides), or three (-213 nucleotides) uORFs. Disruption of the uORF by site-directed mutagenesis at nucleotide -109 enhanced luciferase activity 2- to 3-fold, whereas disruption of the uORF at nucleotide -149 had little effect. We conclude that among the uORFs in the Mrp2 5'UTR, the uORF starting at nucleotide -109 probably plays an important role in the regulation of Mrp2 protein expression.

5' Untranslated Regions↗
PubMed2006

Preparation of graded zirconia hydroxyapatite composite bioceramic and its immunocompatibility in vitro.

To obtain immunocompatibility, graded zirconia-hydroxyapatite (ZrO(2)-HA) composite bioceramic and simplex ZrO(2)-HA composite bioceramic are prepared. Peripheral blood mononuclear cells (PBMCs) harvested from healthy individuals are cultured with the two ceramic extracts to assess their effect on the transformation of lymphocytes, apoptotic ratio, CD69 expression, and expression of cytokine of TNFalpha and IL-6, with or without phytohemoagglutinin (PHA)-stimulated cells. Ceramic extracts did not activate the resting lymphocytes, whereas the response of the PHA-stimulated cells was significantly modified. The PBMCs activated by graded ZrO(2)-HA composite bioceramic is noticeably smaller than that by simplex ZrO(2)-HA composite bioceramic; these results, however can only be seen under the amplified effect of PHA-stimulation.

Animals↗
PubMed2006

The Slc35d3 gene, encoding an orphan nucleotide sugar transporter, regulates platelet-dense granules.

Platelet dense granules are lysosome-related organelles which contain high concentrations of several biologically important low-molecular-weight molecules. These include calcium, serotonin, adenine nucleotides, pyrophosphate, and polyphosphate, which are necessary for normal blood hemostasis. The synthesis of dense granules and other lysosome-related organelles is defective in inherited diseases such as Hermansky-Pudlak syndrome (HPS) and Chediak-Higashi syndrome (CHS). HPS and CHS mutations in 8 human and at least 16 murine genes have been identified. Previous studies produced contradictory findings for the function of the murine ashen (Rab27a) gene in platelet-dense granules. We have used a positional cloning approach with one line of ashen mutants to establish that a new mutation in a second gene, Slc35d3, on mouse chromosome 10 is the basis of this discrepancy. The platelet-dense granule defect is rescued in BAC transgenic mice containing the normal Slc35d3 gene. Thus, Slc35d3, an orphan member of a nucleotide sugar transporter family, specifically regulates the contents of platelet-dense granules. Unlike HPS or CHS genes, it has no apparent effect on other lysosome-related organelles such as melanosomes or lysosomes. The ash-Roswell mouse mutant is an appropriate model for human congenital-isolated delta-storage pool deficiency.

Animals↗
PubMed2006

Activation of platelet alphaIIbbeta3 by an exogenous peptide corresponding to the transmembrane domain of alphaIIb.

A transmembrane domain heterodimer, acting in concert with a membrane-proximal cytoplasmic domain clasp, is thought to maintain integrins in a low affinity state. To test whether helix-helix interactions between the alphaIIb and beta3 transmembrane domains regulate the activity of integrin alphaIIbbeta3, we synthesized a soluble peptide corresponding to the alphaIIb transmembrane domain, designated alphaIIb-TM, and we studied its ability to affect alphaIIbbeta3 activity in human platelets. alphaIIb-TM was alpha-helical in detergent micelles and phospholipid vesicles, readily inserted into membrane bilayers, bound to intact purified alphaIIbbeta3, and specifically associated with the transmembrane domain of alphaIIb, rather than the transmembrane domains of beta3, alpha2, and beta1, other integrin subunits present in platelets. When added to suspensions of gel-filtered platelets, alphaIIb-TM rapidly induced platelet aggregation that was not inhibited by preincubating platelets with the prostaglandin E(1) or the ADP scavenger apyrase but was prevented by the divalent cation chelator EDTA. Furthermore, alphaIIb-TM induced fibrinogen binding to platelets but not the binding of osteopontin, a specific ligand for platelet alphavbeta3. The peptide also induced fibrinogen binding to recombinant alphaIIbbeta3 expressed by Chinese hamster ovary cells, confirming that its effect was independent of platelet signal transduction. Finally, transmission electron microscopy of purified alphaIIbbeta3 revealed that alphaIIb-TM shifted the integrin from a closed configuration with its stalks touching to an open configuration with separated stalks. These observations demonstrate that transmembrane domain interactions regulate integrin function in situ and that it is possible to target intra-membranous protein-protein interactions in a way that can have functional consequences.

Animals↗
PubMed2006

2,6-Disubstituted N-arylsulfonyl piperidines as gamma-secretase inhibitors.

A novel piperidine series of gamma-secretase inhibitors, potentially useful for the treatment of Alzheimer's disease, is disclosed. SAR investigation revealed the requirement for cis-stereochemistry of the substituents attached to the core, which resulted in the chair-like diaxial conformation of the piperidine ring. The series was optimized to provide inhibitors with IC(50)'s in the single-digit nanomolar range. Absolute stereochemistry of the active enantiomer was assigned.

Alzheimer Disease↗
PubMed2006

Circulating Chlamydia pneumoniae DNA and advanced coronary artery disease.

BACKGROUND: Chlamydia pneumoniae (C. pneumoniae) has been linked to atherosclerosis. Detection of this pathogen in peripheral blood cells may be valuable in the diagnosis of disease state. This study aimed to evaluate the prevalence of circulating C. pneumoniae DNA and its relationship with severity and extent of coronary artery disease (CAD). METHODS: Blood samples from 269 patients undergoing coronary angiography were collected. The presence of circulating C. pneumoniae DNA was determined by real-time PCR assay. Data regarding coronary risk factors and severity and extent of CAD were collected. Severity and extent of CAD was defined by the number of major epicardial coronary arteries with >50% stenosis and by the Duke jeopardy score. RESULTS: Sixteen of 269 specimens (5.9%) from the study cohort were positive for C. pneumoniae DNA. Thirteen specimens among 149 samples from patients with multi-vessel disease (8.7%) were positive for C. pneumoniae DNA compared with 3 of 120 (2.5%) among patients without multi-vessel CAD. The prevalence of circulating C. pneumoniae DNA was significantly associated with multi-vessel disease. The odds ratio was 5.1 (P=0.02) after adjustment for conventional risk factors. CONCLUSIONS: Presence of circulating C. pneumoniae DNA is associated with advanced CAD, suggesting C. pneumoniae infection as a contributing factor to progression of coronary atherosclerosis.

Bacteremia↗
PubMed2006

Computational exploration of the activated pathways associated with DNA damage response in breast cancer.

Molecular signaling events regulate cellular activity. Cancer stimulating signals trigger cellular responses that evade the regulatory control of cell development. To understand the mechanism of signaling regulation in cancer, it is necessary to identify the activated pathways in cancer. We have developed RepairPATH, a computational algorithm that explores the activated signaling pathways in cancer. The RepairPATH integrates RepairNET, an assembled protein interaction network associated with DNA damage response, with the gene expression profiles derived from the microarray data. Based on the observation that cofunctional proteins often exhibit correlated gene expression profiles, it identifies the activated signaling pathways in cancer by systematically searching the RepairNET for proteins with significantly correlated gene expression profiles. Analyzing the gene expression profiles of breast cancer, we found distinct similarities and differences in the activated signaling pathways between the samples from the patients who developed metastases and the samples from the patients who were disease free within 5 years. The cellular pathways associated with the various DNA repair mechanisms and the cell-cycle checkpoint controls are found to be activated in both sample groups. One of the most intriguing findings is that the pathways associated with different cellular processes are functionally coordinated through BRCA1 in the disease-free sample group, whereas such functional coordination is absent in the samples from patients who developed metastases. Our analysis revealed the potential cellular pathways that regulate the signaling events in breast cancer.

Algorithms↗
PubMed2006

Genome-wide analysis of estrogen receptor binding sites.

The estrogen receptor is the master transcriptional regulator of breast cancer phenotype and the archetype of a molecular therapeutic target. We mapped all estrogen receptor and RNA polymerase II binding sites on a genome-wide scale, identifying the authentic cis binding sites and target genes, in breast cancer cells. Combining this unique resource with gene expression data demonstrates distinct temporal mechanisms of estrogen-mediated gene regulation, particularly in the case of estrogen-suppressed genes. Furthermore, this resource has allowed the identification of cis-regulatory sites in previously unexplored regions of the genome and the cooperating transcription factors underlying estrogen signaling in breast cancer.

Adaptor Proteins, Signal Transducing↗