Biomedical subjects

Hongyan Yuan

Publications and source records attributed to Hongyan Yuan.

8 recordsLinked to original sources

PubMed2007

CE detector based on light-emitting diodes.

CE detectors based on light-emitting diodes (LEDs) as light sources are receiving considerable attention due to their exceptionally high stability, high intensity, low cost, and a variety of wavelengths in the UV and visible spectrum. This article is a comprehensive review on CE methods using LED-based detectors with absorbance and fluorescence detection, and several applications on the determination of riboflavin, bacteria, drug, and amino acids in biological samples are described.

Electrophoresis, Capillary↗

PubMed2006

Determination of agmatine in biological samples by capillary electrophoresis with optical fiber light-emitting-diode-induced fluorescence detection.

A capillary electrophoresis (CE)/optical fiber light-emitting diode (LED)-induced fluorescence detection method is developed for the determination of agmatine in biological samples. The agmatine was precolumn-derivatized with fluorescence tagging reagent, fluorescein isothiocyanate (FITC). Optimal separation and determination for agmatine were obtained with an electrophoretic buffer of 20 mM sodium borate (pH 9.2). Under the optimal conditions, the determination of agmatine was achieved in less than 4 min, and the detection limit was 4.1x10(-9) M (S/N = 3). The relative standard deviation (RSD) for 11 parallel determination of agmatine was less than 3.0%. The present CE-LED induced fluorescence detection method has been applied to detect agmatine in rat brain tissue, rat stomach tissue, human serum, and human urine. The level of agmatine in human urine was quantified by CE for the first time and found to be in the range 2.5-4.1x10(-7) M.

Agmatine↗

PubMed2006

3-phosphoinositide-dependent protein kinase-1 (PDK1) promotes invasion and activation of matrix metalloproteinases.

BACKGROUND: Metastasis is a major cause of morbidity and mortality in breast cancer with tumor cell invasion playing a crucial role in the metastatic process. PDK1 is a key molecule that couples PI3K to cell proliferation and survival signals in response to growth factor receptor activation, and is oncogenic when expressed in mouse mammary epithelial cells. We now present evidence showing that PDK1-expressing cells exhibit enhanced anchorage-dependent and -independent cell growth and are highly invasive when grown on Matrigel. These properties correlate with induction of MMP-2 activity, increased MT1-MMP expression and a unique gene expression profile. METHODS: Invasion assays in Matrigel, MMP-2 zymogram analysis, gene microarray analysis and mammary isografts were used to characterize the invasive and proliferative function of cells expressing PDK1. Tissue microarray analysis of human breast cancers was used to measure PDK1 expression in invasive tumors by IHC. RESULTS: Enhanced invasion on Matrigel in PDK1-expressing cells was accompanied by increased MMP-2 activity resulting from stabilization against proteasomal degradation. Increased MMP-2 activity was accompanied by elevated levels of MT1-MMP, which is involved in generating active MMP-2. Gene microarray analysis identified increased expression of the ECM-associated genes decorin and type I procollagen, whose gene products are substrates of MT1-MMP. Mammary fat pad isografts of PDK1-expressing cells produced invasive adenocarcinomas. Tissue microarray analysis of human invasive breast cancer indicated that PDK1pSer241 was strongly expressed in 90% of samples. CONCLUSION: These results indicate that PDK1 serves as an important effector of mammary epithelial cell growth and invasion in the transformed phenotype. PDK1 mediates its effect in part by MT1-MMP induction, which in turn activates MMP-2 and modulates the ECM proteins decorin and collagen. The presence of increased PDK1 expression in the majority of invasive breast cancers suggests its importance in the metastatic process.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2006

Determination of excitatory amino acids in biological fluids by capillary electrophoresis with optical fiber light-emitting diode induced fluorescence detection.

The capillary electrophoresis (CE) system with optical fiber light-emitting diode (optical fiber LED) induced fluorescence detector was developed for the analysis of the excitatory amino acids (EAAs) tagged with naphthalene-2,3-dicarboxaldehyde (NDA). The separation of EAAs was carried out in an uncoated fused-silica capillary (50 cm x 75 microm i.d.) with a buffer of 10 mM borate at pH 9.3 and an applied voltage of 20 kV. High sensitivity was obtained by the use of optical fiber LED induced fluorescence detector with a violet LED as the excitation light source. The limits of detection (S/N = 3) for glutamic acid (Glu) and aspartic acid (Asp) were 2.1 x 10(-8) and 2.3 x 10(-8) M, respectively. The detection approach was successfully applied to the analysis of Glu and Asp in biological fluids including human serum, rabbit serum and human cerebrospinal fluid (CSF) with satisfactory results.

Animals↗

PubMed2006

Determination of folic acid by capillary electrophoresis with chemiluminescence detection.

A rapid and simple method is presented for the determination of folic acid (FA) by capillary electrophoresis (CE) with chemiluminescence (CL) detection. This method was based on enhance effect of FA on the CL reaction between luminol and BrO(-) in alkaline aqueous solution. Optimal separation and determination was obtained with an electrophoretic buffer of 35 mM sodium borate (pH 9.4) containing 0.8 mM luminol, and an oxidizer solution of 1.6 mM NaBrO in 100 mM NaCO(3) buffer solution (pH 12.0). Under the optimal conditions, the determination of FA was achieved in less than 20 min, and the detection limit was 2.0 x 10(-8) M (S/N=3). The relative standard deviations (RSDs) on peak area and migration time were in the 1.5 and 1.1%, respectively. The present CE-CL method was applied to the determination of FA in commercial pharmaceutical tablets, apple juices and human urine.

Electrophoresis, Capillary↗

PubMed2006

Optical fiber light-emitting diode-induced fluorescence detection for capillary electrophoresis.

A highly sensitive optical fiber light-emitting diode (LED)-induced fluorescence detector for CE has been constructed and evaluated. In this detector, a violet or blue LED was used as the excitation source and an optical fiber with 40 microm OD was used to transmit the excitation light. The upper end of the fiber was inserted into the separation capillary and was situated right at the detection window. Fluorescence emission was collected by a 40 x microscope objective, focused on a spatial filter, and passed through a cutoff filter before reaching the photomultiplier tube. Output signals were recorded and processed with a computer using in-house written software. The present CE/fluorescence detector deploys a simple and inexpensive optical system that requires only an LED as the light source. Its utility was successfully demonstrated by the separation and determination of amino acids (AAs) labeled with naphthalene-2,3-dicarboxaldehyde (NDA) and FITC. Low detection limits were obtained ranging from 17 to 23 nM for NDA-tagged AAs and 8 to 12 nM for FITC-labeled AAs (S/N=3). By virtue of such valuable features as low cost, convenience, and miniaturization, the presented detection scheme was proven to be attractive for sensitive fluorescence detection in CE.

Amino Acids↗

PubMed2005

3-phosphoinositide-dependent protein kinase-1 activates the peroxisome proliferator-activated receptor-gamma and promotes adipocyte differentiation.

Adipocyte differentiation is regulated largely through the actions of the peroxisome proliferator-activated receptor (PPAR) gamma nuclear receptor and the insulin signaling pathway. 3-phosphoinositide-dependent protein kinase-1 (PDK1) serves as a critical regulatory point in insulin signaling through its ability to phosphorylate the activation loop of several protein kinase families. The present study was undertaken to determine the interrelationships between the PDK1 and PPARgamma signaling pathways, and their association with adipocyte differentiation. Coexpression of PDK1 and PPARgamma1 in 293T cells stimulated PPARgamma response element-dependent reporter gene activity in either the presence or absence of ligand. PDK1-mediated stimulation of PPARgamma1 activity was comparable in magnitude to the coactivator activated in breast cancer-1, and was blocked by either the corepressor silencing mediator of retinoid and thyroid hormone receptor or dominant-negative PAX8-PPARgamma1. Heterologous Gal4-PPARgamma1 assays indicated that PDK1 interacted with the ligand binding domain, and physically associated with PPARgamma1; however, PDK1-mediated stimulation was not dependent on phosphorylation of PPARgamma1 by PDK1. PDK1 stimulatory activity was eliminated by mutation of the alpha-helical hydrophobic motifs in PDK1, L(268)XII, and V(313)XXLL, and expression of the alpha-helical region encompassing these motifs stimulated PPARgamma response element-dependent transcription. PDK1-PPARgamma interaction was confirmed by chromatin immunoprecipitation analysis of the lipoprotein lipase and adipocyte fatty acid-binding protein promoters. In cells expressing PDK1 and PPARgamma, binding to PPARgamma response elements occurred, which was enhanced by treatment with a PPARgamma agonist. Expression of PDK1 in 3T3-L1 or COMMA-1D mammary epithelial cells promoted adipocyte differentiation in the presence of a PPARgamma agonist that was comparable to the response of PPARgamma1-transfected cells in the presence of agonist; expression of PDK1 and PPARgamma resulted in a synergistic effect. Adipocyte differentiation in the presence of a PPARgamma agonist was markedly attenuated in PDK1 null cells. These results suggest that PDK1 can function as a PPARgamma1 coactivator independently of its catalytic activity and establishes an important mechanistic link between adipocyte differentiation and the insulin signaling pathway.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2005

Detection of d-Serine in rat brain by capillary electrophoresis with laser induced fluorescence detection.

A capillary zone electrophoresis method with laser induced fluorescence detection for the chiral separation of highly fluorescent enantiomeric derivatives of d/l-Serine from 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-d/l-Serine) was developed and optimized. Enantiomeric separation of NBD-d/l-Serine was accomplished by using 40 mM hydroxypropyl-beta-cyclodextrin (HP-beta-CD) contained in 100 mM borate buffer, pH 10.0. A 70 cm (effective length of 50 cm) uncoated fused-silica capillary at a voltage of 15 kV was used for the separation. The optimized electrophoretic conditions were subsequently applied to the analysis of d-Serine in rat brain, and satisfactory analytical results with respect to accuracy were obtained. This assay showed acceptable precision, with linearity in the d-Serine concentration range of 0.2-20.0 microM. The limit of detection for d-Serine was 3.0 x 10(-7)M.

4-Chloro-7-nitrobenzofurazan↗