Biomedical subjects

Xiang Fang

Publications and source records attributed to Xiang Fang.

27 records · Page 2Linked to original sources

PubMed2004

Epoxyeicosatrienoic acids (EETs): metabolism and biochemical function.

Epoxyeicosatrienoic acids (EETs), which are synthesized from arachidonic acid by cytochrome P450 epoxygenases, function primarily as autocrine and paracrine effectors in the cardiovascular system and kidney. They modulate ion transport and gene expression, producing vasorelaxation as well as anti-inflammatory and pro-fibrinolytic effects. EETs are incorporated into the sn-2 position of phospholipids and are rapidly mobilized when a cell is treated with a Ca(2+) ionophore, suggesting that they may play a role in phospholipid-mediated signal transduction processes. Soluble epoxide hydrolase (sEH) converts EETs to dihydroxyeicosatrienoic acids (DHETs), and inhibition of sEH is a potential approach for enhancing the biological activity of EETs. EETs also undergo chain-elongation and beta-oxidation, and the accumulation of partial beta-oxidation products increases when sEH is inhibited. Some functional effects of EETs occur through activation of either the guanine nucleotide binding protein Galphas or the Src signal transduction pathways, suggesting that EETs act by binding to membrane receptors. However, other evidence indicates that the modulation of gene expression occurs through an intracellular action of EETs. Because of the diversity of biochemical and functional responses produced by EETs, it is doubtful that a single mechanism or signal transduction pathway can account for all of their actions.

8,11,14-Eicosatrienoic Acid↗

PubMed2003

20-hydroxyeicosatetraenoic acid (20-HETE) metabolism in coronary endothelial cells.

We have investigated the role of endothelial cells in the metabolism of 20-hydroxyeicosatetraenoic acid (20-HETE), a vasoactive mediator synthesized from arachidonic acid by cytochrome P450 omega-oxidases. Porcine coronary artery endothelial cells (PCEC) incorporated 20-[(3)H]HETE primarily into the sn-2 position of phospholipids through a coenzyme A-dependent process. The incorporation was reduced by equimolar amounts of arachidonic, eicosapentaenoic or 8,9-epoxyeicosatrienoic acids, but some uptake persisted even when a 10-fold excess of arachidonic acid was available. The retention of 20-[(3)H]HETE increased substantially when methyl arachidonoyl fluorophosphonate, but not bromoenol lactone, was added, suggesting that a Ca(2+)-dependent cytosolic phospholipase A(2) released the 20-HETE contained in PCEC phospholipids. Addition of calcium ionophore A23187 produced a rapid release of 20-[(3)H]HETE from the PCEC, a finding that also is consistent with a Ca(2+)-dependent mobilization process. PCEC also converted 20-[(3)H]HETE to 20-carboxy-arachidonic acid (20-COOH-AA) and 18-, 16-, and 14-carbon beta-oxidation products. 20-COOH-AA produced vasodilation in porcine coronary arterioles, but 20-HETE was inactive. These results suggest that the incorporation of 20-HETE and its subsequent conversion to 20-COOH-AA in the endothelium may be important in modulating coronary vascular function.

Animals↗

PubMed2003

Differences in positional esterification of 14,15-epoxyeicosatrienoic acid in phosphatidylcholine of porcine coronary artery endothelial and smooth muscle cells.

Epoxyeicosatrienoic acids (EETs) are readily incorporated into phospholipids of smooth muscle cells (SMC) and endothelial cells (EC). Incorporation of EETs into intact porcine coronary arteries potentiates EC-dependent relaxation, but not vasorelaxation induced by agents that act solely on SMC. To explore the potential mechanisms responsible for this difference, porcine coronary artery SMC and EC preloaded with [3H]14,15-EET were treated with calcium ionophore A23187. Although the amount of EET incorporated into EC and SMC was similar, A23187 stimulated a five-fold increase in release of radioactivity from EC, but only a 21% increase in release from SMC. Thin layer chromatography (TLC) examination of cell lipids demonstrated that > 70% of the incorporated radioactivity was present in phosphatidylcholine (PC) in both SMC and BC. After treatment of EC PC with PLA2, TLC analysis indicated that approximately equal to 75% of radioactivity was present as free EET, and 25% of radioactivity was present as lyso-PC. Therefore, most of the 14,15-EET was esterified into the sn-2 position of PC in EC. However, in SMC, approximately equal to 70% of radioactivity was present as lyso-PC after PLA2 treatment, indicating that the EET was predominately esterified into the sn-1 position. In contrast, all of the 14,15-EET was esterified into the sn-2 position of PI in both EC and SMC. These results suggest that the preferential incorporation of 14,15-EET into the sn-1 position of PC in SMC may help to explain the greater retention of the compound in SMC, while incorporation into the sn-2 position of PC in EC may facilitate agonist-induced 14,15-EET release and potentiation of EC-dependent porcine coronary artery relaxation.

8,11,14-Eicosatrienoic Acid↗

PubMed2003

Spectroscopic and electrochemical studies of DNA breakage induced by dopamine and copper ion.

Dopamine may show some biological activities in antitumor and cell apoptosis. Herein, we attempted to employ UV-Vis, CD, and electrochemical methods to investigate the interaction between DNA and dopamine. Both the spectroscopic and electrochemical evidence indicated that dopamine, which was a cation, could interact with polyanion DNA. However, this kind of interaction, mainly by a static electronic force, did not result in any damage of the DNA structure. This situation was quite different when Cu ion was added to the dopamine-DNA system; an obvious change in the color of the solution and in the spectra of UV-Vis and CD showed that some chemical changes occurred in this system, and that the DNA native structure was destroyed. The results of gel electrophores further revealed that DNA might be broken into small segments by dopamine in the presence of Cu ion. The possible reaction mechanisms are discussed.

Circular Dichroism↗

PubMed2002

Human coronary endothelial cells convert 14,15-EET to a biologically active chain-shortened epoxide.

Cytochrome P-450 epoxygenase-derived epoxyeicosatrienoic acids (EETs) play an important role in the regulation of vascular reactivity and function. Conversion to the corresponding dihydroxyeicosatrienoic acids (DHETs) by soluble epoxide hydrolases is thought to be the major pathway of EET metabolism in mammalian vascular cells. However, when human coronary artery endothelial cells (HCEC) were incubated with (3)H-labeled 14,15-EET, chain-shortened epoxy fatty acids, rather than DHET, were the most abundant metabolites. After 4 h of incubation, 23% of the total radioactivity remaining in the medium was converted to 10,11-epoxy-hexadecadienoic acid (16:2), a product formed from 14,15-EET by two cycles of beta-oxidation, whereas only 15% was present as 14,15-DHET. Although abundantly present in the medium, 10,11-epoxy-16:2 was not detected in the cell lipids. Exogenously applied (3)H-labeled 10,11-epoxy-16:2 was neither metabolized nor retained in the cells, suggesting that 10,11-epoxy-16:2 is a major product of 14,15-EET metabolism in HCEC. 10,11-Epoxy-16:2 produced potent dilation in coronary microvessels. 10,11-Epoxy-16:2 also potently inhibited tumor necrosis factor-alpha-induced production of IL-8, a proinflammatory cytokine, by HCEC. These findings implicate beta-oxidation as a major pathway of 14,15-EET metabolism in HCEC and provide the first evidence that EET-derived chain-shortened epoxy fatty acids are biologically active.

8,11,14-Eicosatrienoic Acid↗

PubMed2002

Oxidative stress in human abdominal aortic aneurysms: a potential mediator of aneurysmal remodeling.

Abdominal aortic aneurysm (AAA) is an inflammatory disorder characterized by localized connective tissue degradation and smooth muscle cell (SMC) apoptosis, leading to aortic dilatation and rupture. Reactive oxygen species are abundantly produced during inflammatory processes and can stimulate connective tissue-degrading proteases and apoptosis of SMCs. We hypothesized that reactive oxygen species are locally increased in AAA and lead to enhanced oxidative stress. In aortas from patients undergoing surgical repair, superoxide levels (measured by lucigenin-enhanced chemiluminescence) were 2.5-fold higher in the AAA segments compared with the adjacent nonaneurysmal aortic (NA) segments (6638+/-2164 versus 2675+/-1027 relative light units for 5 minutes per millimeter squared, respectively; n=7). Formation of thiobarbituric acid-reactive substances and conjugated dienes, 2 indices of lipid peroxidation, were increased 3-fold in AAA compared with NA segments. Immunostaining for nitrotyrosine was significantly greater in AAA tissue. Dihydroethidium staining indicated that increased superoxide in AAA segments was localized to infiltrating inflammatory cells and to SMCs. Expression of the NADPH oxidase subunits p47(phox) and p22(phox) and NAD(P)H oxidase activity were increased in AAA segments compared with NA segments. Thus, oxidative stress is markedly increased in AAA, in part through the activation of NAD(P)H oxidase, and may contribute to the disease pathogenesis.

Aged↗

PubMed2002

The oxygen radical scavenger pyrrolidine dithiocarbamate enhances interleukin-1beta-induced cyclooxygenase-2 expression in cerebral microvascular smooth muscle cells.

Oxidative stress and inducible cyclooxygenase-2 (COX-2)-mediated prostaglandin (PG) formation have been proposed to play an important role in cytokine-induced vascular pathology. To explore the relationship between oxidative stress and COX-2 induction, cultured murine cerebral microvascular smooth muscle cells (SMCs) were stimulated with interleukin-1beta (IL-1beta) in the presence or absence of an oxygen radical scavenger, pyrrolidine dithiocarbamate (PDTC). IL-1beta increased COX-2 protein expression in a dose- and time-dependent manner, an increase that was further enhanced by PDTC in a dose-dependent manner. PDTC did not, however, affect the expression of COX-1 protein. In the presence of 100 microM PDTC, PGE(2) production induced by IL-1beta (5 ng/ml) was increased by threefold as compared with IL-1beta alone. Although PDTC enhanced COX-2 protein expression, it did not increase IL-1beta-induced expression of COX-2 mRNA, indicating that the regulatory effect occurred at the posttranscriptional level. The time course of COX-2 protein degradation indicated that PDTC also did not alter the stability of the COX-2 protein induced by IL-1beta. These results suggest that endogenous oxygen radicals may blunt COX-2 induced by IL-1beta through an effect on translation.

Animals↗

PubMed2001

Isolation and characterization of XKaiso, a transcriptional repressor that associates with the catenin Xp120(ctn) in Xenopus laevis.

The Armadillo family of catenin proteins function in multiple capacities including cadherin-mediated cell-cell adhesion and nuclear signaling. The newest catenin, p120(ctn), differs from the classical catenins and binds to the membrane-proximal domain of cadherins. Recently, a novel transcription factor Kaiso was found to interact with p120(ctn), suggesting that p120(ctn) also possesses a nuclear function. We isolated the Xenopus homolog of Kaiso, XKaiso, from a Xenopus stage 17 cDNA library. XKaiso contains an amino-terminal BTB/POZ domain and three carboxyl-terminal zinc fingers. The XKaiso transcript was present maternally and expressed throughout early embryonic development. XKaiso's spatial expression was defined via in situ hybridization and was found localized to the brain, eye, ear, branchial arches, and spinal cord. Co-immunoprecipitation of Xenopus p120(ctn) and XKaiso demonstrated their mutual association, whereas related experiments employing differentially epitope-tagged XKaiso constructs suggest that XKaiso additionally self-associates. Finally, reporter assays employing a chimera of XKaiso fused to the GAL4 DNA binding domain indicate that XKaiso is a transcriptional repressor. These data suggest that XKaiso functions throughout development and that its repressor functions may be most apparent in the context of neural tissues. The significance of the XKaiso-p120(ctn) interaction has yet to be determined, but it may include transducing information from cadherin-mediated cell-cell contacts to transcriptional processes within the nucleus.

Amino Acid Sequence↗

PubMedDate not supplied

GFFD: Generalized free-form deformation with scalar fields.

The novel free-form deformation(FFD) technique presented in the paper uses scalar fields defined by skeletons with arbitrary topology. The technique embeds objects into the scalar field by assigning a field value to each point of the objects. When the space of the skeleton is changed, the distribution of the scalar field changes accordingly, which implicitly defines a deformation of the space. The generality of skeletons assures that the technique can freely define deformable regions to produce a broader range of shape deformations.

Computer Graphics↗