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Biomedical subjects

Y Xia

Publications and source records attributed to Y Xia.

At least 91 records · Page 5Linked to original sources
PubMed2000

Transforming growth factor beta3 promotes fascial wound healing in a new animal model.

HYPOTHESIS: Transforming growth factor beta(3) (TGF-beta(3)) promotes fascial wound healing in a new animal model, as measured by wound breaking strength, collagen deposition, and cellular proliferation. DESIGN/INTERVENTION: Bilateral, longitudinal incisions were made in the anterior rectus sheaths of 24 male New Zealand white rabbits. One incision was treated with 1 microg of TGF-beta(3); the contralateral incision served as a control. The wounds were harvested at 1, 2, 3, 4, 6, and 8 weeks after creation ("wounding"). MAIN OUTCOME MEASURES: Wound tissue was tested for breaking strength using a tensiometer and processed for histological examination of collagen deposition and cellular proliferation at all time points after wounding. Collagen deposition and cellular proliferation were measured in histological cross sections of wounds with Masson trichrome staining and proliferating cell nuclear antigen immunohistochemistry, respectively. RESULTS: At all time points after wounding, treatment with TGF-beta(3) significantly increased the wound breaking strength (up to 138%) and collagen deposition (up to 150%) over the control group. Cellular proliferation was increased during the first 3 weeks after wounding (up to 147%), but returned to baseline levels by the fourth week. CONCLUSIONS: Transforming growth factor beta(3) promotes fascial wound healing. In this new animal model of fascial wound healing, TGF-beta(3) increased fascia breaking strength, collagen deposition, and cellular proliferation. These results are similar to findings in cutaneous wound models and demonstrate, for the first time, a pharmacologic agent to accelerate fascial healing.

Animals↗
PubMed2000

Heterogeneity of cartilage laminae in MR imaging.

The purpose of this study was to investigate the discrepancy in the number of laminae observed in magnetic resonance (MR) images of articular cartilage (the magic angle effect in MRI of cartilage). Microscopic MR imaging (muMRI) experiments were carried out at 14-micrometer pixel resolution on full-depth cartilage-bone plugs from several locations (central, intermediate, and peripheral) on the humeral heads of two young healthy beagles. When the articular surface of the plug was perpendicular to the direction of the magnetic field, the cartilage appeared to have two layers in the plugs from the central locations of the humeral head, three layers in the plugs from the greater tubercle side of the humeral head, and three or five layers in the plugs from the lesser tubercle side. This heterogeneity of cartilage laminae was observed within a single humeral head and was symmetrical about the median plane of the animal. This result suggests that some structural variations related to cartilage structure in various regions of load bearing may cause some unique laminar patterns seen in MRI of cartilage. This novel and new observation may resolve the controversy about whether cartilage appears as two or three layers in MR images. A comprehensive model for the collagen structure over a curved two-dimensional surface of a joint is suggested as a replacement of the classic three-zone model of fiber orientation in collagen. This heterogeneity of cartilage laminae is speculated to be related to the load-bearing status of the tissue in the joint. The ability to visualize such structural heterogeneity is important because of the direct connection between collagen structure and the mechanical characteristics of cartilage.

Animals↗
PubMed2000

NF-kappaB-dependent fractalkine induction in rat aortic endothelial cells stimulated by IL-1beta, TNF-alpha, and LPS.

Fractalkine is an endothelial cell-derived CX3C chemokine that is chemotactic mainly to mononuclear cells. Fractalkine was induced in rat aortic endothelial cells (RAEC) by interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), and lipopolysaccharide (LPS) transcriptionally and translationally. This induction correlated with increased NF-kappaB DNA binding activity as determined by gel mobility shift assay. Supershift assays revealed that the NF-kappaB subunits p50 and p65 were responsible for kappaB binding. Accordingly, we examined the role of NF-kappaB in fractalkine induction in RAEC through the use of an adenovirus-mediated mutant IkappaB as a specific inhibitor. Delivery of a dominant-negative form of IkappaBalpha in RAEC dramatically reduced the induction of fractalkine by these stimuli, suggesting a role for NF-kappaB activation in fractalkine induction. The inhibition of fractalkine expression by two potent NF-kappaB inhibitors, sulfasalazine and sanguinarine, further supported the central role of NF-kappaB in fractalkine transcription regulation and suggested a novel therapeutic target aimed at modulating leukocyte endothelial cell interaction.

Animals↗
PubMed2000

Protein dynamics measurements by TROSY-based NMR experiments.

The described TROSY-based experiments for investigating backbone dynamics of proteins make it possible to elucidate internal motions in large proteins via measurements of T(1), T(2), and NOE of backbone (15)N nuclei. In our proposed sequences, the INEPT sequence is eliminated and the PEP sequence is replaced by the ST2-PT sequence from the HSQC-based experiments. This has the benefit of shortening the pulse sequences by 5.4 ms (=1/2J) and results in an increase in the intrinsic sensitivity of the proposed TROSY-based experiments. The TROSY-based experiments are on average of 13% more sensitive than the corresponding HSQC-based experiments on a uniformly (15)N-labeled Xenopus laevis calcium-bound calmodulin sample on a 750-MHz spectrometer at 5 degrees C. The amide proton linewidths of the TROSY-based experiments are 2-13 Hz narrower than those of the HSQC experiments. More sensitivity gain and higher resolution are expected if the protein sample is deuterated.

Amides↗
PubMed2000

Sensitivity enhancement of HCACO by using an HMQC magnetization transfer scheme.

Previous theoretical calculations have demonstrated that the multiquantum relaxation rate of (1)H(alpha)-(13)C(alpha)(R(MQ)) is, on average, 1.3 +/- 0.4 or 1.7 +/- 0.6 times slower than the single-quantum relaxation rate of (13)C(alpha)(R(C)) for a sample with or without, respectively, amide protons. By taking advantage of this fact and by using the PEP sensitivity enhancement scheme, an HMQC version of the HCACO experiment has been developed. We demonstrate that this new experiment is 23 and 55% more sensitive than the original HSQC version of the HCACO experiment, at constant times of 7 and 27 ms, respectively, for a sample of the BC domain of the ciliary neurotrophic factor receptor protein dissolved in D(2)O at 20 degrees C.

Algorithms↗
PubMed2000

A J-multiplied HMQC (MJ-HMQC) experiment for measuring (3)J(HNHalpha) coupling constants.

The J-multiplied HSQC experiment (MJ-HSQC: S. Heikkinen et al., J. Magn. Reson 137, 243 (1999)) amplifies J coupling constants m times and allows direct observation of the (3)J(HNHalpha) coupling constants of peptides and proteins (<10 kDa). The drawbacks to this method are line broadening in the f(1)-dimension and lower sensitivity. In the J-multiplied HMQC (MJ-HMQC) experiment described here, the PEP-HSQC pulse sequence is replaced by a sensitivity-enhanced HMQC section, and the total decay time for the J-coupling and the chemical shift evolution is shortened by a period of t(1). This experiment affords narrower linewidth and enhances the sensitivity by 34%, on an average of 105 well-isolated peaks, when compared with the MJ-HSQC experiment.

Algorithms↗
PubMed2000

Determination of internucleotide (h)J(HN) couplings by the modified 2D J(NN)-correlated [(15)N, (1)H] TROSY.

Recent developments in the direct observation of J couplings across hydrogen bonds in proteins and nucleic acids provide additional information for structure and function studies of these molecules by NMR spectroscopy. A J(NN)-correlated [(15)N, (1)H] TROSY experiment proposed by Pervushin et al. (Proc. Natl. Acad. Sci. USA 95, 14147-14151, 1998) can be applied to measure (h)J(HN) in smaller nucleic acids in an E.COSY manner. However, it cannot be effectively applied to large nucleic acids, such as tRNA(Trp), since one of the peaks corresponding to a fast relaxing component will be too weak to be observed in the spectra of large molecules. In this Communication, we proposed a modified J(NN)-correlated [(15)N, (1)H] TROSY experiment which enables direct measurement of (h)J(HN) in large nucleic acids.

Bacillus subtilis↗
PubMed2000

Collagen-embedded platelet-derived growth factor DNA plasmid promotes wound healing in a dermal ulcer model.

BACKGROUND: Gene therapy has shown limited efficacy for treating congenital diseases, partly due to temporary gene expression and host immune responses. Such results suggest that gene therapy is ideal for chronic wound treatment where limited duration of target gene expression is required. This study tested the wound healing effects of topically applied platelet-derived growth factor (PDGF)-A or -B chain DNA plasmids embedded within a collagen lattice. MATERIALS AND METHODS: Four 6-mm dermal ulcer wounds were created in the ears of young adult New Zealand White rabbits made ischemic by division of the central and rostral arteries. Wounds were treated with lyophilized collagen containing PDGF-B DNA (1.0-3.0 mg), PDGF-A DNA (1.0 mg), irrelevant DNA (1.0 mg), or collagen alone. Wounds were dressed and harvested after 10 days for measurement of granulation tissue formation, epithelialization, and wound closure. Results were evaluated with a paired two-tailed Student t test, with P values < 0.05 considered significant. RESULTS: PDGF-B DNA increased new granulation tissue (NGT) formation up to 52% and epithelialization 34% compared with controls. Wound closure was increased up to threefold. At 1.0 mg DNA, PDGF-A and PDGF-B stimulated similar responses. No difference in NGT or epithelialization was seen between control groups. CONCLUSIONS: PDGF DNA gene therapy is effective at accelerating wound healing in ischemic dermal ulcers and provides a viable alternative to peptide growth factor therapy.

Animals↗
PubMed2000

Inducible nitric oxide synthase knockout mouse macrophages disclose prooxidant effect of interferon-gamma on low-density lipoprotein oxidation.

To test our hypothesis that interferon-gamma (IFN-gamma) has a direct prooxidant effect on macrophage-mediated LDL oxidation behind its antioxidant effect via induction of inducible nitric oxide synthase (iNOS), we incubated LDL with wild-type (iNOS(+/+)) or iNOS knockout mouse (iNOS(-/-)) macrophages preincubated with IFN-gamma or IFN-gamma plus lipopolysaccharide (IFN-gamma/LPS) for 24 h. LDL oxidation was measured in terms of formation of thiobarbituric acid reactive substances (TBARS) and electrophoretic mobility. Thiol production, nitrite production, and superoxide production from macrophages were measured by using Ellman's assay, the Griess reagent, and the SOD-inhibitable cytochrome c reduction method, respectively. IFN-gamma alone or combined with LPS induced iNOS expression and increased nitrite production in iNOS(+/+) macrophages, but not in iNOS(-/-) macrophages. TBARS formation from LDL was suppressed in IFN-gamma- and IFN-gamma/LPS-treated iNOS(+/+) macrophages but was increased in IFN-gamma-treated iNOS(-/-) macrophages. In the presence of N(G)-monomethyl-l-arginine (l-NMMA), a NOS inhibitor, the suppressive effect of IFN-gamma and IFN-gamma/LPS was abolished and TBARS formation was even increased to a level above that of untreated iNOS(+/+) macrophage. NOC 18, an NO donor, dose dependently inhibited macrophage-mediated LDL oxidation. IFN-gamma increased superoxide and thiol productions in both types of macrophages. We conclude that IFN-gamma promotes macrophage-mediated LDL oxidation by stimulating superoxide and thiol production under conditions where iNOS-catalyzed NO release is restricted.

Animals↗
PubMed2000

Critical role of Kupffer cell CR3 (CD11b/CD18) in the clearance of IgM-opsonized erythrocytes or soluble beta-glucan.

Liver macrophages (Kupffer cells) play a major role in blood clearance of both C3-opsonized immune complexes and therapeutic beta-glucan polysaccharides. Human Kupffer cells express three types of C3-receptors: CR1 (C3b-receptor; CD35), CR3 (iC3b- and beta-glucan-receptor), and CR4 (iC3b-receptor; CD11c/CD18). Studies of isolated macrophages have suggested that CR3 is the major receptor mediating capture of either C3-opsonized erythrocytes (E) or beta-glucans. In this investigation, the organ distribution and function of CR3 in the clearance of IgM-opsonized E and soluble CR3-binding polysaccharides were explored in normal vs. CR3-knockout (CR3-KO) mice. Analysis of intravenously (i.v.) injected 125I-anti-CR3 showed that the major vascular reservoir of CR3 was the liver, followed by spleen and lungs. By contrast, clearance of 125I-anti-CR1 appeared to be mediated predominantly by splenic B lymphocytes, as only subsets of splenic macrophages or Kupffer cells were found to express CR1. Clearance of IgM-opsonized 51Cr-E occurred rapidly to the livers of normal mice but was nearly absent in CR3-KO mice. Soluble 125I-beta-glucan exhibited rapid clearance to the liver in normal mice, whereas clearance in CR3-KO mice was significantly reduced. In conclusion, Kupffer cell CR3 plays a crucial role in the clearance of both IgM-opsonized E and beta-glucans.

Animals↗
PubMed2000

Mechanisms underlying hypoxia-induced neuronal apoptosis.

In vivo models of cerebral hypoxia-ischemia have shown that neuronal death may occur via necrosis or apoptosis. Necrosis is, in general, a rapidly occurring form of cell death that has been attributed, in part, to alterations in ionic homeostasis. In contrast, apoptosis is a delayed form of cell death that occurs as the result of activation of a genetic program. In the past decade, we have learned considerably about the mechanisms underlying apoptotic neuronal death following cerebral hypoxia-ischemia. With this growth in knowledge, we are coming to the realization that apoptosis and necrosis, although morphologically distinct, are likely part of a continuum of cell death with similar operative mechanisms. For example, following hypoxia-ischemia, excitatory amino acid release and alterations in ionic homeostasis contribute to both necrotic and apoptotic neuronal death. However, apoptosis is distinguished from necrosis in that gene activation is the predominant mechanism regulating cell survival. Following hypoxic-ischemic episodes in the brain, genes that promote as well as inhibit apoptosis are activated. It is the balance in the expression of pro- and anti-apoptotic genes that likely determines the fate of neurons exposed to hypoxia. The balance in expression of pro- and anti-apoptotic genes may also account for the regional differences in vulnerability to hypoxic insults. In this review, we will examine the known mechanisms underlying apoptosis in neurons exposed to hypoxia and hypoxia-ischemia.

Animals↗
PubMed2000

A recurrent neural network for solving linear projection equations.

Linear projection equations arise in many optimization problems and have important applications in science and engineering. In this paper, we present a recurrent neural network for solving linear projection equations in real time. The proposed neural network has two layers and is amenable to parallel implementation with simple hardware. In the theoretical aspect, we prove that the proposed neural network can converge globally to the solution set of the problem when the matrix involved in the problem is positive semidefinite and can converge exponentially to a unique solution when the matrix is positive definite. In addition, we analyze the stability of the related dynamic system in detail. As an application, we show that the proposed neural network can be used directly to solve linear and convex quadratic programming problems and linear complementary problems with positive semidefinite matrices. The validity and transient behavior of the neural network are demonstrated by using three numerical examples.

Linear Models↗
PubMed2000

The ABA-1 allergen of Ascaris lumbricoides: sequence polymorphism, stage and tissue-specific expression, lipid binding function, and protein biophysical properties.

The ABA-1 protein of Ascaris lumbricoides (of humans) and Ascaris suum (of pigs) is abundant in the pseudocoelomic fluid of the parasites and also appears to be released by the tissue-parasitic larvae and the adult stages. The genes encoding the polyprotein precursor of ABA-1 (aba-1) were found to be arranged similarly in the two taxa, comprising tandemly repeating units encoding a large polyprotein which is cleaved to yield polypeptides of approximately 15 kDa which fall into 2 distinct classes, types A and B. The polyprotein possibly comprises only 10 units. The aba-1 gene of A. lumbricoides is polymorphic, and the majority of substitutions observed occur in or near predicted loop regions in the encoded proteins. mRNA for ABA-1 is present in infective larvae within the egg, and in all parasitic stages, but was not detectable in unembryonated eggs. ABA-1 mRNA was confined to the gut of adult parasites, and not in body wall or reproductive tissues. Recombinant protein representing a single A-type unit for the A. lumbricoides aba-1 gene was produced and found to bind retinol (Vitamin A) and a range of fatty acids, including the pharmacologically active lipids lysophosphatidic acid, lysoplatelet activating factor, and there was also evidence of binding to leukotrienes. It failed to bind to any of the anthelmintics screened. Differential Scanning Calorimetry showed that the recombinant protein was highly stable, and unfolded in a single transition at 90.4 degrees C. Analysis of the transition indicated that the protein occurs as a dimer and that the dimer dissociates simultaneously with the unfolding of the monomer units.

Allergens↗
PubMed2000

Transverse relaxation optimized 3D and 4D 15n/15N separated NOESY experiments of 15N labeled proteins.

NMR studies of protein structures require knowledge of spectral assignments through correlation spectroscopy and the measurement of dipolar interactions by NOESY-type experiments. In order to obtain NOEs for protons with degenerate chemical shifts, which is particularly common for large proteins with significant helical content, 3D and 4D 15N/15N separated NOESY experiments (HSQC-NOESY-HSQC) are essential for NMR studies of these proteins. TROSY sections could replace the latter or both HSQC parts of the 3D and 4D 15N/15N separated HSQC-NOESY-HSQC pulse sequences to enhance signal sensitivity and improve resolution. For a 1.0 mM, 100% 15N and 70% 2H-labeled Trichosanthin sample (approximately 27 kDa) at 5 degrees C it is found that sensitivity enhancements could only be obtained when TROSY sections replace the latter HSQC parts of 3D and 4D 15N/15N separated HSQC-NOESY-HSQC pulse sequences. The sensitivities of 3D and 4D HSQC-NOESY-TROSY experiments are enhanced by 62% and 8% at 5 degrees C, respectively, compared to their corresponding 3D and 4D HSQC-NOESY-HSQC experiments. Furthermore, the corresponding linewidths are, on average, decreased by 20% and 18% Hz in the HN and N2 dimensions, respectively. This enhancement of sensitivity depends on the molecular mass of the sample used and the lengths of the evolution times in the indirectly and directly detected dimensions.

Deuterium↗
PubMed2000

Glutamate receptors in the enteric nervous system: ionotropic or metabotropic?

Intracellular recording methods were used to investigate actions of glutamate on morphologically identified neurones in the myenteric and submucous plexuses of guinea-pig small intestine. Glutamate evoked a tetrodotoxin-resistant, slowly activating depolarizing response in most of the submucous neurones (86 of 125, 69%) and a smaller number of myenteric neurones (6 of 60, 10%). The depolarizing responses were restricted to S-type neurones with uniaxonal morphology. The group I metabotropic glutamate receptor (mGluRs) agonists quisqualate, 1S, 3R-ACPD and DHPG mimicked the depolarizing action of glutamate. A group I mGluRs antagonist, S-4-carboxyphenylglycine (S-4CPG), suppressed the glutamate responses with an IC50 of 357 microM at 30 microM glutamate. Group II or III mGluRs agonists did not produce depolarizing responses and group II or III mGluRs antagonists did not alter glutamate-evoked depolarization. The ionotropic glutamate receptor (iGluRs) agonists NMDA, AMPA, or kainate did not evoke depolarizing responses and glutamate-evoked depolarization was unaffected by the iGluRs antagonists D-APV, MK-801, or DNQX. No rapidly activating fast depolarizing responses reminiscent of fast excitatory postsynaptic potentials (EPSPs) were ever observed during application of glutamate or AMPA and stimulus-evoked fast EPSPs were unaffected by DNQX. The results suggest that the excitatory action of glutamate on enteric neurones is mediated by group I metabotropic glutamate receptors and that ionotropic glutamate receptors are not involved. The results also suggest that glutamate-mediated fast EPSPs may not be present in myenteric and submucous neurones in guinea-pig small bowel.

Animals↗
PubMed2000

Thrombopoietin and the TPO receptorduring platelet storage.

BACKGROUND: For most cells, the addition of a specific growth factor has improved cellular viability by preventing programmed cell death (apoptosis). To determine whether the platelet-specific hematopoietic growth factor thrombopoietin (TPO) might improve platelet viability, endogenous TPO and the platelet TPO receptor were analyzed during storage, and the effect of recombinant TPO on platelet viability was assessed. STUDY DESIGN AND METHODS: During platelet storage, TPO stability was assessed by SDS-PAGE, TPO receptor function was measured, and the platelet TPO receptor was characterized by a (125)I-rHuTPO competitive-binding assay. A recombinant TPO, pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), was added to platelet concentrates during storage, and its effect on pH, LDH, and metabolic activity was determined. RESULTS: During storage, the molecular weight and concentration of endogenous TPO (125 +/- 19 pg/mL) and exogenous TPO (5720 +/- 140 pg/mL) were constant for 12 days; the number (33 +/- 4), binding affinity (149 +/- 33 pM), and function of the platelet TPO receptors were constant for 7 days. Metabolic activity measured with the MTT and MTS assays closely correlated with changes in the pH and LDH. The addition of PEG-rHuMGDF did not alter the pH, LDH, or metabolic activity of platelets during storage, but it did increase by 65 percent the uptake of (35)S-methionine into platelets. Finally, platelet concentrates obtained from donors treated with PEG-rHuMGDF retained normal metabolic activity for 12 days, as compared with 5 to 6 days for normal platelet concentrates. CONCLUSIONS: TPO and its platelet receptor are present in normal amounts and have normal function during platelet storage. The addition of recombinant TPO increased platelet methionine transport but did not alter platelet viability during storage. Other means to prevent apoptosis during platelet storage should be considered, and the measurement of platelet metabolic activity by MTT and MTS assays may assist this effort.

Blood Platelets↗