Biomedical subjects

X Yao

Publications and source records attributed to X Yao.

At least 19 recordsLinked to original sources

PubMed2003

A mechanosensitive cation channel in endothelial cells and its role in vasoregulation.

Ca2+ is an important intracellular second messenger in signal transduction of endothelial cells. It has long been recognized that a mechanosensitive Ca2+-permeable channel is present in vascular endothelial cells. The activity of this channel may increase intracellular Ca2+ level in endothelial cells. A recent finding is that the activity of this channel may be regulated by cGMP through a protein kinase G-dependent pathway. Inhibition of the channel by cGMP abolishes the Ca2+ influx elicited by flow. Several inhibitors of the cation channel including Gd3+, Ni2+, and SK&F-96365 also inhibit the Ca2+ influx due to flow stimulation. These data suggest that a mechanosensitive cation channel is the primary pathway mediating the flow-induced Ca2+ entry in vascular endothelial cells. Another important finding is that the opening of this mechanosensitive channel by KT5823 leads to endothelium-dependent vascular dilation. Therefore, it appears that this channel may play a crucial role in the regulation of vascular tone.

Animals↗

PubMed2002

Effect of 17beta-estradiol exposure on vasorelaxation induced by K(+) channel openers and Ca(2+) channel blockers.

17beta-Estradiol has been shown to relax blood vessels partly through inhibition of Ca(2+) channels at supraphysiological concentrations; however, it is unknown whether acute exposure of the isolated artery rings to near physiological concentrations of sex steroid hormones could modulate the ionic channels that are involved in regulation of vascular tone. Brief incubation (20 min) with 17beta-estradiol (1-3 nmol/l) did not alter the relaxant response to three blocking agents of L-type voltage-sensitive Ca(2+) channels, nifedipine, diltiazem and verapamil in either endothelium-intact or endothelium-denuded rat mesenteric artery rings. In contrast, 17beta-estradiol at 3 nmol/l significantly attenuated the relaxation induced by K(+) channel openers, cromakalim and pinacidil in endothelium-denuded rings. Similarly, preincubation with progesterone (3 nmol/l) inhibited pinacidil-induced relaxation with much less effect on cromakalim-induced relaxation. It appears that 17beta-estradiol and progesterone attenuated the cromakalim- and pinacidil-induced relaxation in a different manner. These results suggest that acute exposure to female sex steroid hormones at near physiological levels may reduce the activity of ATP-sensitive K(+) channels in the rat arteries.

Animals↗

PubMed2001

Different role of endothelium/nitric oxide in 17beta-estradiol- and progesterone-induced relaxation in rat arteries.

The present study was aimed to examine the different role of endothelium/nitric oxide in relaxation induced by two female sex hormones, 17beta-estradiol and progesterone in rat isolated aortas and mesenteric arteries. The isometric force of each ring was measured with Grass force-displacement transducers in the organ bathes. 17beta-Estradiol induced both endothelium-dependent and -independent relaxation in the rat aortas but only the endothelium-independent relaxation in the rat mesenteric arteries. In contrast. progesterone induced both endothelium-dependent and -independent relaxation in the rat mesenteric arteries but only endothelium-independent relaxation in rat aortas. N(G)-Nitro-L-arginine methyl ester and methylene blue attenuated the relaxant response to 17beta-estradiol in the aortic rings or to progesterone in the mesenteric arteries. Pretreatment with L-arginine antagonized the effect of N(G)-nitro-L-arginine methyl ester on sex hormone-induced relaxation. The endothelium contribution to relaxation seems to only relate to lower concentrations of 17beta-estradiol and progesterone. In summary, the present results clearly demonstrate a different role of the functional endothelium in the relaxant response to 17beta-estradiol or progesterone in the conduit vessel (aorta) and the resistance vessels (mesenteric artery). Nitric oxide contributes largely to the endothelium-dependent relaxation induced by 17beta-estradiol in the isolated aortas or by progesterone in the mesenteric arteries.

Animals↗

PubMed2001

Inhibitory effect of tetrabutylammonium ions on endothelium/nitric oxide-mediated vasorelaxation.

Apart from the well-described K+ channel blocking effects in vascular smooth muscle cells, monovalent quaternary ammonium ions may also interact with endothelial cells in the endothelium-intact mammalian arteries. The present study was aimed to examine the effect of tetrabutylammonium ions on endothelium-dependent and -independent relaxation in the rat isolated aortic rings. Pretreatment with tetrabutylammonium concentration dependently reduced the endothelium-dependent relaxation induced by acetylcholine, cyclopiazonic acid and ionomycin. Tetrabutylammonium also inhibited endothelium-independent relaxation induced by hydroxylamine or nitroprusside. Pretreatment of endothelium-denuded rings with tetrabutylammonium did not affect relaxation induced by NS1619 or by diltiazem. In contrast, tetrabutylammonium significantly reduced the pinacidil- or cromakalim-induced relaxation. Tetrabutylammonium also inhibited the acetylcholine- but not nitroprusside-induced increase of tissue content of cyclic GMP in the aortic rings. The present study indicates that tetrabutylammonium ions could inhibit endothelial and exogenous nitric oxide-mediated aortic relaxation while it had no effect on relaxation induced by activation of Ca2+-activated K+ channels (by NS1619) or by inhibition of voltage-gated Ca2+ channels (by diltiazem). The inhibitory effect on pinacidil- and cromakalim-induced relaxation suggests that tetrabutylammonium ions also inhibit ATP-sensitive K+ channels in aortic smooth muscle cells.

Animals↗

PubMed2001

Therapeutic efficacy of hepatitis B surface antigen-antibodies-recombinant DNA composite in HBsAg transgenic mice.

Therapeutic efficacy of HBsAg-anti-HBs-recombinant DNA harboring hepatitis B virus (HBV) S gene complex was compared with three other therapeutic vaccine candidates (recombinant HBsAg, HBsAg complexed to anti-HBs antibodies and naked plasmid DNA encoding the HBV S gene). After four injections at 3-week intervals, the most pronounced decrease of serum HBsAg, the highest titer of anti-HBs response, the highest level of interferon-gamma produced by splenocytes and potent cytotoxicity T cell response were observed in the HBsAg-anti HBs-sDNA immunized group. Reduced expression of HBsAg in hepatocytes was also shown. The therapeutic mechanism of HBsAg-anti-HBs-DNA was speculated as modulation of HBsAg presentation via both endogenous and exogenous pathways.

Animals↗

PubMed2001

Proteolytic 18O labeling for comparative proteomics: model studies with two serotypes of adenovirus.

A new method for proteolytic stable isotope labeling is introduced to provide quantitative and concurrent comparisons between individual proteins from two entire proteome pools or their subfractions. Two 18O atoms are incorporated universally into the carboxyl termini of all tryptic peptides during the proteolytic cleavage of all proteins in the first pool. Proteins in the second pool are cleaved analogously with the carboxyl termini of the resulting peptides containing two 16O atoms (i.e., no labeling). The two peptide mixtures are pooled for fractionation and separation, and the masses and isotope ratios of each peptide pair (differing by 4 Da) are measured by high-resolution mass spectrometry. Short sequences and/or accurate mass measurements combined with proteomics software tools allow the peptides to be related to the precursor proteins from which they are derived. Relative signal intensities of paired peptides quantify the expression levels of their precursor proteins from proteome pools to be compared, using an equation described in the paper. Observation of individual (unpaired) peptides is mainly interpreted as differential modification or sequence variation for the protein from the respective proteome pool. The method is evaluated here in a comparison of virion proteins for two serotypes (Ad5 and Ad2) of adenovirus, taking advantage of information already available about protein sequences and concentrations. In general, proteolytic 18O labeling enables a shotgun approach for proteomic studies with quantitation capability and is proposed as a useful tool for comparative proteomic studies of very complex protein mixtures.

Adenoviridae↗

PubMed2001

Increases in circulating and lymphoid tissue interleukin-10 in autoimmune lymphoproliferative syndrome are associated with disease expression.

Autoimmune lymphoproliferative syndrome (ALPS) is an inherited disorder in which genetic defects in proteins that mediate lymphocyte apoptosis, most often Fas, are associated with enlargement of lymph nodes and the spleen and a variety of autoimmune manifestations. Some patients with ALPS have relatives with these same apoptotic defects, however, who are clinically well. This study showed that the circulating levels of interleukin 10 (IL-10) were significantly higher (P <.001) in 21 patients with ALPS than in healthy controls. Moreover, the peripheral blood mononuclear cells (PBMCs) and lymphoid tissues of these patients with ALPS contained significantly higher levels of IL-10 messenger RNA (mRNA; P <.001 and P <.01, respectively). By fractionating PBMC populations, disproportionately high concentrations of IL-10 mRNA were found in the CD4(-)CD8(-) T-cell population, expansion of which is virtually pathognomonic for ALPS. Immunohistochemical staining showed intense IL-10 protein signals in lymph node regions known to contain CD4(-)CD8(-) T cells. Nonetheless, in vitro studies showed no influence of IL-10 on the survival of CD4(-)CD8(-) T cells. Overexpression of IL-10 in patients with inherited apoptotic defects is strongly associated with the overt manifestations of ALPS.

Apoptosis↗

PubMed2001

F-actin-like ATPase activity in a polymerization-defective mutant yeast actin (V266G/L267G).

Polymerization increases a low level G-actin ATPase activity yielding ADP-P(i) F-actin and then ADP F-actin following release of P(i). By monitoring P(i) release, we explored the relationship between the ATPase activity and polymerization characteristics of a mutant yeast actin, GG. In this mutant, two hydrophobic residues at the tip of a proposed hydrophobic plug between actin subdomains 3 and 4, Val(266) and Leu(267), were mutated to Gly. Although GG-actin does not polymerize by itself in vitro, GG cells are viable. We show that GG-actin ATPase activity increases under normal polymerization conditions, although stable filaments do not form. A plot of P(i) release rate versus actin concentration yields an apparent critical concentration, like that seen for actin polymerization, of approximately 8 microm for Mg(2+) GG-actin and 11 microm for Ca(2+) GG-actin. In contrast to WT-actin, P(i) release from GG-actin is cold-sensitive, reflecting the temperature sensitivity associated with mutations that decrease hydrophobicity in this region. Thus, under polymerization conditions, GG-actin exhibits a continuous F-actin-like ATPase activity resulting from the temperature-sensitive formation of unstable cycling F-actin oligomers. Tropomyosin limits the extent and rate of this activity and restores polymerization by capturing and stabilizing these oligomers rather than enhancing filament nucleation.

Actins↗

PubMed2001

Stretch-sensitive switching among different channel sublevels of an endothelial cation channel.

A mechanosensitive Ca(2+)-permeable cation channel was recorded by patch clamp in isolated rat aortic endothelial cells. A low level of channel activity could be observed after seal formation. The channel displayed some inward rectification and had a conductance for inward current of approx. 32 pS in Ca(2+)-free pipette and bath solutions. Negative suction of -10 to -20 mmHg increased the probability of the channel being open. When the negative pressure in the pipette was raised to -35 to -45 mmHg, the channel underwent an abrupt transition to a large conductance substate that was interrupted occasionally by two other low conductance levels. Under this condition, the overwhelming majority of openings and closings were between a main level of 83 pS and the closed level. Compared to the 32 pS substate, the 83 pS large conductance substate had shorter mean open and closed times. The two channel substates had similar ionic selectivity and both were sensitive to the inhibition of cGMP and protein kinase G. This is the first demonstration showing that mechanostress can change the single channel conductance level of an ion channel in eukaryotic cells.

Alkaloids↗

PubMed2001

Structural analysis of the N-terminal domain of the human T-cell leukemia virus capsid protein.

The N-terminal domain of the retroviral capsid (CA) protein is one of the least conserved regions encoded in the genome. Surprisingly, the three-dimensional structures of the CA from different genera exhibit alpha-helical structural features that are highly conserved. The N-terminal residues of the human immunodeficiency virus type 1 (HIV-1) and Rous sarcoma virus (RSV) capsid proteins form a beta-hairpin. To determine if this feature is conserved in the retroviral family, we cloned, expressed, purified, and solved the structure of a N-terminal 134 amino acid fragment (CA(134)) from the human T-cell leukemia virus type 1 (HTLV-I) using high resolution nuclear magnetic resonance (NMR) spectroscopy. The CA(134) fragment contains an N-terminal beta-hairpin and a central coiled-coil-like structure composed of six alpha-helices. The N-terminal Pro1 residue contacts Asp54 in the helical cluster through a salt bridge. Thus, the beta-hairpin is conserved and the helical cluster is structurally similar to other retroviral CA domains. However, although the same Asp residue defines the orientation of the hairpin in both the HTLV-1 and HIV-1 CA proteins, the HTLV-I hairpin is oriented away, rather than towards, the helical core. Significant differences were also detected in the spatial orientation and helical content of the long centrally located loop connecting the helices in the core. It has been proposed that the salt bridge allows the formation of a CA-CA interface that is important for the assembly of the conical cores that are characteristic of HIV-1. As HTLV-I forms spherical cores, the salt-bridge feature is apparently not conserved for this function although its role in determining the orientation of the beta-hairpin may be critical, along with the central loop. Comparison of three-dimensional structures is expected to elucidate the relationships between the retroviral capsid protein structure and its function.

Amino Acid Sequence↗

PubMed2001

Experimental study of the sampling artifact of chloride depletion from collected sea salt aerosols.

Sampling artifact of chloride depletion from collected sea salt particles was studied, based on simultaneous measurements of size distribution measurements by a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI) and of PM2.5 measurements by a Compact Porous Metal Denuder Sampler (PMDS) at a coastal site in Hong Kong on May 7, 8, 9, 11, and 29, 1998. The ambient concentrations of SO2, HNO3, HNO2, and NH3 were also measured by the PMDS. PM2.5 measurements by the PMDS, which is equipped with denuders and nylon back filters, are compared with the PM1.8 and PM3.1 measurements by the MOUDI. The percentages of chloride depletion from sea salt aerosols in PM1.8 and PM3.1 were 4-45% higher than that in PM2.5. This suggests that chloride evaporation in PM1.8 and PM3.1 collected on Teflon filters of the MOUDI during sampling was present. From the sum of the contributions of particles on the Teflon and nylon filters of the PMDS, nitrate formation almost completely accounts for chloride depletion in PM2.5 prior to collection since the equivalent ratio of [Na+] to ([NO3-] + [Cl-]) is close to the seawater ratio of 0.85. However, it was found that 22-74% of nitrate and 45-86% of chloride in the collected particles on the Teflon filter of the PMDS evaporated during sampling. Excess chloride depletion unexplained by NO3- and nss-SO4(2-) was found in the collected particles on the Teflon filter of the PMDS. Similarly, an amount of 3.7-27.2 nequiv m-3 of excess depleted chloride (equivalent to 8-55% of total chloride depletion) was found in supermicron particles collected by the MOUDI. In the 1.8-3.1 microns particles, the excess depleted chloride is positively correlated to the chloride evaporated from the deposited particles. Particle--particle interactions are proposed to explain the evaporation of nitrates and chlorides in the PMDS and MOUDI measurements. The observed chloride depletion from seasalt aerosols was partially attributed to sampling artifact due to particle--particle interactions.

Aerosols↗

PubMed2001

Prediction of enthalpy of alkanes by the use of radial basis function neural networks.

A new method for the prediction of enthalpy of alkanes between C6 and C10 from molecular structures has been proposed. Thirty five calculated descriptors were selected for the description of molecular structures. The first four scores of Principle Component Analysis on the calculated descriptors were used as inputs to predict the enthalpy of alkanes. Models relating relationships between molecular structure descriptors and enthalpy of alkanes were constructed by means of radial basis function neural networks. To get the best prediction results, some strategies were also employed to optimise the learning parameters of the radial basis function neural networks. For the test set, a predictive correlation coefficient of R = 0.9913 and root mean squared error of 0.5876 were obtained.

Journal Article↗

PubMed2001

Peripheral T-cell lymphoma with aberrant expression of CD79a and CD20: a diagnostic pitfall.

Immunohistochemical studies are increasingly used for the routine diagnosis of lymphomas as it is widely accepted that lymphomas of different cell lineages vary in their prognosis and response to therapy. A case of peripheral T-cell lymphoma with aberrant expression of B-cell-associated antigens L-26 (CD20) and mb-1 (CD 79a) is described. The disease pursued an aggressive clinical course, and the patient died of disease 6 weeks after presentation. Immunohistochemical studies demonstrated expression of both T- and B-cell-associated antigens, including CD3, CD8, CD43, TIA-1, CD20, and CD79a. Other markers expressed by the tumor cells included CD56 and S-100. Of interest, betaF-1 staining for the beta chain of T-cell receptor (TCR) complex was positive in the small admixed T lymphocytes but was negative in the tumor cells, raising the possibility of a gamma/delta T-cell lymphoma. Molecular studies by polymerase chain reaction (PCR) demonstrated clonal TCR-gamma chain gene rearrangement without evidence for a clonal rearrangement of the immunoglobulin heavy chain gene. PCR for HHV-8 related sequences was negative. Mb-1 is an IgM-associated protein that was thought to be restricted to normal and neoplastic B cells. Although its coexpression has been reported in up to 10% cases of precursor T-cell lymphoblastic lymphoma, the coexpression of both CD20 and CD79a has not been described in mature T-cell malignancies. Biphenotypic lymphomas associated with HHV-8 have been reported in immunodeficiency, but no evidence of immune deficiency was identified, and studies for EBV and HHV-8 were negative. This case illustrates that no marker has absolute lineage specificity and that immunophenotypic studies should always be performed with panels of monoclonal antibodies. Moreover, cases with ambiguous phenotypes may require genotypic studies for precise lineage assignment.

Aged↗

PubMed2001

Purification of phenylethanoids from Brandisia hancei and the antiproliferative effects on aortic smooth muscle.

The present study describes the isolation and purification of acteoside, 2'-acetylacteoside, poliumoside and brandioside, four phenylethanoid glycosides from Brandisia hancei. We examined their effects on the proliferation of cultured A7r5 rat aortic smooth muscle cells. The proliferative response was measured from the [(3)H]-thymidine incorporation into DNA. All four glycosides suppressed the proliferative response in the presence of 2 % or 5 % fetal bovine serum in a concentration-dependent manner. The rank order of effectiveness for inhibition of cell proliferation was: brandioside > or = poliumoside > 2'-acetylacteoside > or = acteoside. The acetyl group at position 2' of glucose does not seem necessary for the anti-proliferative effects of acteoside and 2'-acetylacteoside, while the hydroxy groups of the aromatic rings appear to play a role. Inhibition of smooth muscle cell proliferation by phenylethanoids indicates that these compounds may have preventative effects on arteriosclerosis.

Animals↗

PubMed2001

Methyl protogracillin (NSC-698792): the spectrum of cytotoxicity against 60 human cancer cell lines in the National Cancer Institute's anticancer drug screen panel.

Methyl protogracillin (NSC-698792) was a furostanol saponin isolated from the rhizome of Dioscorea collettii var. hypoglauca (Dioscoreaceae), a Chinese herbal remedy for the treatment of cervical carcinoma, carcinoma of urinary bladder and renal tumor for centuries, in our previous studies. In order to systematically evaluate its potential anticancer activity, methyl protogracillin was tested for its cytotoxicity in vitro against 60 human cancer cell lines in the National Cancer Institute (NCI)'s anticancer drug screen. As a result, it was found that methyl protogracillin was cytotoxic against all the tested cell lines from leukemia and solid tumors in the NCI's human cancer panel; it showed particular selectivity against one colon cancer line (KM12), one central nervous system (CNS) cancer line (U251), two melanoma lines (MALME-3M and M14), two renal cancer lines (786-0 and UO-31) and one breast cancer line (MDA-MB-231) with GI50< or =2.0 microM. The selectivity between these seven most sensitive lines and the least sensitive line (CCRF-CEM) ranged from 26- to 56-fold. In the same cancer subpanel, selectivity more than 15-fold was observed between MDA-MB-231 and MCF-7, NCI-ADR-RES, BT-549 in breast cancer. From a general view of the mean graph, CNS cancer is the most sensitive subpanel, while ovarian cancer and renal cancer are the least sensitive subpanels. Based on an analysis of the COMPARE computer program with methyl protogracillin as a seed compound, no compounds in the NCI's anticancer drug screen database have similar cytotoxicity patterns (mean graph) to that of methyl protogracillin, indicating a potential novel mechanism of the anticancer action involved.

Antineoplastic Agents↗

PubMed2001

Vasorelaxant effects of cardamonin and alpinetin from Alpinia henryi K. Schum.

The vascular effects of cardamonin and alpinetin from Alpinia henryi K. Schum. were examined in the rat isolated mesenteric arteries. 1H and 13C nuclear magnetic resonance spectra showed that cardamonin is present in trans-form, and single-crystal radiographic structure revealed that alpinetin is present in S configuration. Both cardamonin and alpinetin produced a rightward shift in the concentration-response curve for phenylephrine in a noncompetitive manner, and they induced relaxation of phenylephrine-preconstricted arteries with respective mean inhibitory concentrations (IC50) of 9.3+/-0.6 microM and 27.5+/-2.8 microM. Both compounds also relaxed arteries preconstricted by endothelin I or U46619. Their relaxant effects were decreased in endothelium-removed rings. Pretreatment with N(G)-nitro-L-arginine methyl ester or methylene blue inhibited relaxation induced by both agents, and pretreatment with L-arginine reversed the effect of N(G)-nitro-L-arginine methyl ester on cardamonin-induced endothelium-dependent relaxation. The relaxant effects of cardamonin and alpinetin were unaffected by indomethacin (3 microM). Cardamonin and alpinetin inhibited 60 mM K+-induced contraction with respective IC50 of 11.5+/-0.3 microM and 37.9+/-3.6 microM. In addition, both agents inhibited the transient contraction induced by 3 microM phenylephrine or by 10 mM caffeine in Ca2+-free Krebs solution. Finally, these two agents also concentration dependently relax the arteries preconstricted by 1 microM phorbol 12,13-diacetate in Ca2+-free Krebs solution. These results indicate that purified cardamonin and alpinetin from A. henryi K. Schum. relaxed rat mesenteric arteries through multiple mechanisms. They induced both endothelium-dependent and -independent relaxation; the former is likely mediated by nitric oxide whereas the latter is probably mediated through nonselective inhibition of Ca2+ influx and intracellular Ca2+ release and inhibition of the protein kinase C-dependent contractile mechanism.

Animals↗

PubMed2001

Deflection characteristics of a trapezoidal multilayer in-plane bending piezoelectric actuator.

A novel multilayer split-morph actuator has been designed and fabricated using the thick film screen-printing technology. Deflection characteristics of the split-morph actuator have been investigated by theoretical analysis and experimental measurement. The results indicate that the tip displacement is inversely proportional to the thickness of each piezoelectric layer, but is independent of the number of layers and the total thickness of the actuator. The displacement/voltage sensitivity of the trapezoidal actuator is larger than that of the rectangular design, assuming both have the same width of clamped end and the same thickness of the piezoelectric layers. The maximum displacement/voltage sensitivity of 0.157 micron/V was obtained with a split-morph actuator with 30-micron thick layers. The proposed actuator is a promising candidate for the secondary fine-tuning actuator of a dual stage head-positioning servo system in high density hard disk drives.

Journal Article↗

PubMed2001

Cloning and functional characterization of a high-affinity Na(+)/dicarboxylate cotransporter from mouse brain.

Neurons contain a high-affinity Na(+)/dicarboxylate cotransporter for absorption of neurotransmitter precursor substrates, such as alpha-ketoglutarate and malate, which are subsequently metabolized to replenish pools of neurotransmitters, including glutamate. We have isolated the cDNA coding for a high-affinity Na(+)/dicarboxylate cotransporter from mouse brain, called mNaDC-3. The mRNA coding for mNaDC-3 is found in brain and choroid plexus as well as in kidney and liver. The mNaDC-3 transporter has a broad substrate specificity for dicarboxylates, including succinate, alpha-ketoglutarate, fumarate, malate, and dimethylsuccinate. The transport of citrate is relatively insensitive to pH, but the transport of succinate is inhibited by acidic pH. The Michaelis-Menten constant for succinate in mNaDC-3 is 140 microM in transport assays and 16 microM at -50 mV in two-electrode voltage clamp assays. Transport is dependent on sodium, although lithium can partially substitute for sodium. In conclusion, mNaDC-3 likely codes for the high-affinity Na(+)/dicarboxylate cotransporter in brain, and it has some unusual electrical properties compared with the other members of the family.

Amino Acid Sequence↗