PubMed Health⌕ Search

Biomedical subjects

Xin Jiang

Publications and source records attributed to Xin Jiang.

At least 73 records · Page 4Linked to original sources
PubMed2004

[Kinetic characteristics of Cd2+ desorption in minerals and soils under simulated acid rain].

The kinetic characteristics of Cd2+ desorption in minerals and soils under simulated acid rain were studied by using the flow-stirred method. It showed that Cd2+ desorption could be described by first-order kinetics. Percents of desorption amounts of Cd2+ calculated were 70%-100% in red soil and goethite, and 25%-50% in latosols and kaolinite. Parabolic diffusion could describe Cd2+ desorption kinetics in latosols and not suitable for red soil and goethite and kaolinite. Cd2+ desorption, regarded as a heterogeneous diffusion in minerals and soils, could be fitted by Elovich equation more than Parabolic diffusion and two-constant equation. Cd2+ desorption could be divided into fast reaction and slow reaction. Except for latosols, fast reaction would be over during 60 min and be close to quasi-equilibrium. Adsorption forms of Cd2+ in soil surface could be exchangeable and specific. Fast reaction was relative to easily desorbed Cd2+. The affinity of edge hydroxyl to Cd2+ would lead to the difference of Cd2+ desorption rate and amounts. Increase of pH value in effluent indicated H+ consumption in the processes of Cd2+ desorption.

Acid Rain↗
PubMed2004

The expression of matrix metalloproteinases-9, transforming growth factor-beta1 and transforming growth factor-beta receptor I in human atherosclerotic plaque and their relationship with plaque stability.

BACKGROUND: Transforming growth factor-beta (TGF-beta) and matrix metalloproteinases-9 (MMP-9) have been implicated in the pathogenesis of human atherosclerosis but their relationship during lesion progression are poorly understood. The objective of this study was to investigate the expression of MMP-9, TGF-beta1 and TGF-beta receptor I (TbetaR-I) in human atherosclerotic plaque and their relationship and plaque stability. METHODS: Specimens of human coronary artery atherosclerotic plaques were obtained from 41 patients undergoing coronary endarterectomy, and were paraffin embedded, sectioned at 4 microm intervals then stained with haematoxylin and eosin. They were divided into stable (with no or only little lipid core) and unstable plaque groups (with lipid core size > 40%): the immunohistochemical staining were performed for MMP-9, TGF-beta1 and TbetaR-I. RESULTS: The expression of MMP-9 in the unstable plaques was much higher than in the stable ones, but the expression of TGF-beta1 was higher in the stable plaques. There was no similar significant difference for TbetaR-I. Correlation analysis showed that there was a negative correlation between the expression of MMP-9 and TGF-beta1 (r = -0.332, P = 0.034 for average areal density; r = -0.373, P = 0.016 for average optical density). CONCLUSIONS: There were close relationships between MMP-9, TGF-beta1 and plaque stability. Enhanced production of MMP-9 may participate in the formation of unstable plaque, while TGF-beta1 maybe an important stabilizing factor in preventing transition into an unstable plaque phenotype.

Activin Receptors, Type I↗
PubMed2003

Neurosteroid analogues. 9. Conformationally constrained pregnanes: structure-activity studies of 13,24-cyclo-18,21-dinorcholane analogues of the GABA modulatory and anesthetic steroids (3alpha,5alpha)- and (3alpha,5beta)-3-hydroxypregnan-20-one.

The hydrogen-bond-acceptor properties of the carbonyl moiety in the 17beta-acetyl group on the D-ring of the anesthetic steroids (3alpha,5alpha)- and (3alpha,5beta)-3-hydroxypregan-20-one form an important part of the anesthetic steroid pharmacophore. 13,24-Cyclo-18,21-dinorcholanes containing a ketone or conjugated ketone group at C-20, C-22, C-23, or C-24 were prepared as conformationally constrained analogues of these anesthetic steroids and were used to probe for alternate locations for the D-ring hydrogen-bond-accepting carbonyl group. The analogues were evaluated (1). in [(35)S]-tert-butylbicyclophosphorothionate binding experiments, (2). in electrophysiological experiments using rat alpha(1)beta(2)gamma(2L) GABA(A) receptors expressed in Xenopus laevis oocytes, and (3). as tadpole anesthetics. In the binding assay, the relative order of potencies for the analogues in the 5alpha- and 5beta-series is identical. For the ketones, the order is 24-one >or= 23-one > 20-one > 22-one. Likewise, for the enones, the order is delta(22)-24-one > delta(20(22))-23-one > delta(22)-20-one > delta(23)-22-one. Similar relative orders of potencies are also found in the other two bioassays. The activities of the 24-one and delta(22)-24-one compounds were expected to be very low, because the carbonyl group in these compounds is located over the steroid C-ring and oriented toward C-8. Instead, these compounds have the highest activities in their respective series, with the delta(22)-24-one compounds having activities comparable to those of the reference anesthetic steroids. The electrophysiology results obtained with the 24-oxo-cyclosteroids suggest that rat alpha(1)beta(2)gamma(2L) GABA(A) receptors contain more than one donor for the hydrogen-bond-acceptor group of anesthetic steroids. The family of cyclosteroids should be useful for future structure-activity relationship studies of steroid modulation of other GABA(A) receptor subtypes.

Anesthetics↗
PubMed2003

Use of an array technology for profiling and comparing transcription factors activated by TNFalpha and PMA in HeLa cells.

Multiple signal transduction pathways are generally triggered simultaneously by a single extracellular stimulus. As a result, multiple transcription factors (TFs) can be activated downstream to mediate the inducible expression of target genes. Profiling the activation of all TFs will aid in the dissection of the numerous pathways of signal transduction. Tumor necrosis factor alpha (TNFalpha) and phorbol 12-myristate 13-acetate (PMA) mediate many biological functions, including cell proliferation and apoptosis, by stimulating signaling pathways. Two TFs, nuclear factor kappaB (NFkappaB) and activating factor 1 (AP1), have been identified as targets of both TNFalpha and PMA activation. Here, we describe the use of a protein/DNA array system to identify additional TFs activated by TNFalpha and PMA in HeLa cells. From a total of 150 targeted TFs, six-CREB, E2F, CETP/CRE, c-Rel, MSP1, and Pax6-were identified whose activities, like NFkappaB and AP1, were regulated by both TNFalpha- and PMA-induced pathways. Interestingly, the TF E47 was shown to be specifically activated by TNFalpha but was not affected by treatment with PMA. In addition, GATA, NF-E1, and ISRE were shown to be specifically activated by PMA but not TNFalpha. These findings suggest that TNFalpha and PMA both stimulate unique signaling pathways while mediating transcriptional activation through common pathways.

DNA Fingerprinting↗
PubMed2003

E. coli selection of human genes encoding secreted and membrane proteins based on cDNA fusions to a leaderless beta-lactamase reporter.

Although several signal peptide-trapping methods have been devised and used to detect signal sequences, none have relied on using E.coli to identify eukaryotic proteins with signal peptides. Here, we describe a system for selecting human secreted and membrane proteins in E. coli followed by the direct validation of secretion in human cells. The method is based on cDNA fusions to a leaderless beta-lactamase reporter gene to isolate clones encoding signal peptides of human genes. We found that beta-lactamase fusion proteins carrying a eukaryotic signal peptide at its N-terminus were able to direct their export into the periplasm in E. coli to confer survival upon challenge with carbenicillin. When libraries constructed from 5' end-enriched cDNAs fused to beta-lactamase were screened in E.coli, approximately 0.5%-1% of the cDNAs are selected, and over half of the surviving clones were found to encode for secreted fusion proteins when tested in human cells. These clones were sequenced and shown to represent human genes encoding signal peptides of secreted and membrane proteins. We conclude that this is an efficient and effective strategy to easily enrich cDNA libraries for the identification of novel genes likely to encode secreted enzymes, growth factors, and receptors.

Base Sequence↗
PubMed2003

Optimization of the abnormal Beckmann rearrangement: application to steroid 17-oximes.

A novel and practical procedure was developed for the abnormal Beckmann rearrangement of steroid 17-oximes. Treatment of the 17-oximes with TFA/CH(OMe)(3) in boiling THF for 2 h gives the corresponding 13,17-seco alkene nitrile products in unprecedented high yields (70-92%). Since the alkene nitriles can be subsequently converted into 18-norsteroids, this general method provides a highly efficient route to these biologically important compounds and, by extension, to other structurally related natural products.

Journal Article↗
PubMed2003

Nonmonotonic bias voltage dependence of the magnetocurrent in GaAs-based magnetic tunnel transistors.

Magnetic tunnel transistors are used to study spin-dependent hot electron transport in thin CoFe films and across CoFe/GaAs interfaces. The magnetocurrent observed when the orientation of a CoFe base layer moment is reversed relative to that of a CoFe emitter, is found to exhibit a pronounced nonmonotonic variation with electron energy. A model based on spin-dependent inelastic scattering in the CoFe base layer and strong electron scattering at the CoFe/GaAs interface, resulting in a broad electron angular distribution, can well account for the variation of the magnetocurrent in magnetic tunnel transistors with GaAs(001) and GaAs(111) collectors.

Journal Article↗
PubMed2003

Tubular graphite cones.

We report the synthesis of tubular graphite cones using a chemical vapor deposition method. The cones have nanometer-sized tips, micrometer-sized roots, and hollow interiors with a diameter ranging from about 2 to several tens of nanometers. The cones are composed of cylindrical graphite sheets; a continuous shortening of the graphite layers from the interior to the exterior makes them cone-shaped. All of the tubular graphite cones have a faceted morphology. The constituent graphite sheets have identical chiralities of a zigzag type across the entire diameter, imparting structural control to tubular-based carbon structures. The tubular graphite cones have potential for use as tips for scanning probe microscopy, but with greater rigidity and easier mounting than currently used carbon nanotubes.

Journal Article↗
PubMed2003

Tumor oxygen dynamics: comparison of 19F MR EPI and frequency domain NIR spectroscopy.

Oxygen plays a key role in tumor therapy and may be related to tumor development: e.g., angiogenesis and metastasis. Using noninvasive techniques to accurately measure tumor oxygenation could assist in developing novel therapies. Here, we have used the FREDOM (Fluorocarbon Relaxometry using Echo planar imaging for Dynamic Oxygen Mapping) approach based on hexafluorobenzene (HFB) to monitor tissue oxygen tension (pO2) of rat breast and prostate tumors and compared the results with changes in tumor vascular hemoglobin saturation (sO2) and concentration observed using a new dual wavelength homodyne near-infrared (NIR) system. The dynamic changes in pO2 and sO2 were assessed while rats were breathing various gases. NIR showed significant changes in vascular oxygenation accompanying respiratory interventions. 19F MR-EPI also showed significant changes in tissue pO2 and revealed considerable regional heterogeneity in both absolute values and rate of change accompanying interventions. Generally, changes in vascular sO2 preceded tissue pO2, particularly for smaller tumors.

Animals↗
PubMed2003

Relationship between levels of serum C-reactive protein, leucocyte count and carotid plaque in patients with ischemic stroke.

In order to study the relationship between serum C-reactive protein (CRP) levels, leukocyte count and carotid plaque in patients with ischemic stroke, carotid duplex examination was performed by high-definition imaging (HDI) 5000 triplex system. Serum CRP was measured by nephelometry within 72 h after index ischemic stroke. A lesion was considered a plaque in the presence of a maximum intimal-medial wall thickness (IMT) 1.2 mm. Results of carotid ultrasonography were divided into two groups: M1, normal (IMT < 1.2 mm) and M2, abnormal (IMT > or = 1.2 mm). The results showed that the mean age of M2 was significantly older than that of M1 (69.7 +/- 10.4 versus 62.5 +/- 9.6, P = 0.001). The patients with hypertension and diabetes mellitus (78%, 35% respectively) in M2 were significantly more than those (52%, 18% respectively) in M1 (P < 0.01, P < 0.05). There were 32 (65%) patients with elevated CRP levels in M2, but 33 (46%) patients with elevated CRP levels in M1, with the difference being significant between the two groups (P < 0.05). The levels of serum glucose and leukocyte count (8.1 +/- 5.5, 10.3 +/- 4.0, respectively) in abnormal CRP group were significantly higher than that of normal CRP group (6.4 +/- 2.8, 8.7 +/- 3.4) (P < 0.05, P < 0.05); elevated CRP levels was found in 42 (62%) patients with territory infarction and 23 (43%) patients with lacunar infarction respectively, with the difference being significant between these two groups (P < 0.05). It was concluded that the elevation of CRP levels was an significant clinical index for carotid plaque in patients with acute cerebral infarction.

Adult↗
PubMed2003

Effects of natural and enantiomeric cholesterol on the thermotropic phase behavior and structure of egg sphingomyelin bilayer membranes.

Phospholipids, sphingolipids, and sterols are the major lipid components of the plasma membranes of eukaryotic cells. Because these three lipid classes occur naturally as enantiomerically pure compounds, enantiospecific lipid-lipid and lipid-sterol interactions could in principle occur in the lipid bilayers of eukaryotic plasma membranes. Although previous biophysical studies of phospholipid and phospholipid-sterol model membrane systems have consistently failed to observe such enantiomerically selective interactions, a recent monolayer study of the interactions of natural and enantiomeric cholesterol with egg sphingomyelin has apparently revealed the existence of enantiospecific sterol-sphingolipid interactions. To determine whether enantiospecific sterol-sphingolipid interactions also occur in more biologically relevant lipid-bilayer systems, differential scanning calorimetric, x-ray diffraction, and neutral buoyant-density measurements were utilized to study the effects of natural and enantiomeric cholesterol on the thermotropic phase behavior and structure of egg sphingomyelin bilayers. The calorimetry experiments show that the natural and enantiomeric cholesterol have essentially identical effects on the temperature, enthalpy, and cooperativity of the gel/liquid-crystalline phase transition of egg sphingomyelin bilayers within the limits of experimental error. As well, the x-ray diffraction and neutral buoyancy experiments indicate that bilayers formed from mixtures of natural or enantiomeric cholesterol and egg sphingomyelin have, within experimental uncertainty, the same structure and mass density. We thus conclude that significant enantioselective cholesterol-sphingolipid interactions do not occur in this lipid-bilayer model membrane system.

Calorimetry, Differential Scanning↗
PubMed2003

[The influence of simulated acid rain on acidity and K+ leaching regulation of different soil layers].

The influence of simulated acid rain on acidity and K+ release of different soil layers of red soil from Jiangxi was investigated in the lab when surface soil was mixed with KCl. The results indicated that pH of leaching solution first decreased, then increased in the different soil layers, but pH at the beginning moment of leaching existed prominent differences and pH of leachate of pH 2.5 acid rain in A and AB layers again decreased during subsequent stage. There was a peak value of EC of leachate appearing at the beginning stage, it showed that nutrient ions in soil rapidly moved downwards into lower depth of profile. K+ concentration of effluent solution was related to acidity of acid rain and the pH2.5 value of acid rain accelerated K+ transportation downwards along profile. K+ release of A soil layer was divided into two moments which one was the rapid rate of K+ release process at the moment of beginning and then into the middle rate of release process. As to pH 4.5 value of acid rain, it also existed rapid and slow rate processes.

Acid Rain↗
PubMed2003

[C-reactive protein as an important prognostic marker for ischemic stroke].

OBJECTIVE: There is growing evidence indicating that reactions of inflammatory system play an important role in stroke and development of carotid plaques. It is purposed to understand the relationship between serum level of c-reactive protein (CPR) and size of cerebral infarction, carotid plaques and prognosis of ischemic stroke. METHODS: A total of 121 patients with ischemic stroke were included in the study. Serum level of CRP was measured within 72 hours after onset of index stroke. All patients were scored by CNDF based on deficit in their clinical neurological function, and examined with CT/MRI and carotid duplex ultrasound scanning. RESULTS: Leukocyte count and blood glucose level at admission were significantly higher in the group with abnormal serum level of CRP than those with normal one (P = 0.045 and P = 0.021, respectively). Incidence of territory infarction (42 cases, 61.76%) was also significantly higher than that of lacunar infarction (23 cases, 43.4%), with P = 0.044. Occurrence of carotid plaques was higher in the former (32 cases, 65.30%) than that in the latter (17 cases, 34.69%), with P = 0.035. CNFD scores were higher in the former (ranging 6 - 35, with a median of 18) than those in the latter (ranging 6 - 28, with a median of 11), with Mann-Whitney U test, P = 0.0001. And, more severe prognosis was also found in the former than in the latter, with P = 0.0001. CONCLUSION: Serum level of CRP was an important prognostic marker for carotid plaque and stroke.

Aged↗
PubMed2003

Aortic arch and intra-/extracranial cerebral arterial atherosclerosis in patients suffering acute ischemic strokes.

OBJECTIVE: To determine the distribution of aortic arch and intra/extracranial cerebral arterial atherosclerosis in Chinese patients who had suffered acute ischemic strokes. METHODS: Eighty-nine patients with acute ischemic strokes were included in this study. Transesophageal echocardiography (TEE) was used to evaluate potential sources of embolisms in the aortic arch and in the heart; duplex ultrasound was used for the carotid artery; and intracranial Doppler (TCD) imaging was used for the middle cerebral artery (MCA), anterior cerebral artery (ACA), posterior cerebral artery (PCA), and basilar artery (BA). An atherosclerotic lesion in the aortic arch was defined as normal (0); mild plaque (1); moderate plaque (2); and protruding plaque or mobile plaque (3). A lesion in the carotid artery was considered a plaque if the maximal carotid plaque thickness was 1.2 mm. TCD results were deemed abnormal if flow velocity was either greater or lower than normal, and, in the case of the MCA, if an asymmetry index above 21% was measured. RESULTS: Of the 89 patients, 52 (58.43%) patients showed evidence of aortic arch atherosclerosis (AAA), including 11 (12.36%) patients graded mild, 18 (20.22%) patients graded moderate, and 23 (25.84%) patients graded severe. Of the 23 patients with severe AAA, AAA was determined to be an important potential embolic source in 14 patients. Forty-nine (50.56%) patients had carotid arterial plaques (CAPs). The incidence of carotid plaques was higher among patients with AAA than among patients without AAA (71.15% vs 21.62%, OR = 3.291, 95% CI = 1.740 - 6.225, P < 0.001). TCD abnormalities affecting the MCA were found in 54 (60.67%) patients. Differences in incidence of TCD abnormalities between patients with AAA and without AAA (69.23% vs 48.65%) were not significant (OR = 1.423, 95% CI = 0.976 - 2.076, P = 0.05). There was a higher incidence of AAA in older, male patients with a history of diabetes and smoking. CONCLUSIONS: AAA is an important potential source of cerebral embolic strokes. The presence of carotid arterial plaques correlates with AAA incidence. Most of carotid artery lesion were plaques other than severe stenosis, it may be the character of carotid atherosclerosis of stroke patients. It appears that atherosclerosis does not mainly occur in the intracranial arteries in stroke patients as thought before. Aged, male, diabetes, and smoking are important risk factors to the AAA.

Acute Disease↗
PubMed2002

Sequence-dependent denaturation energetics: A major determinant in amyloid disease diversity.

Several misfolding diseases commence when a secreted folded protein encounters a partially denaturing microenvironment, enabling its self assembly into amyloid. Although amyloidosis is modulated by numerous environmental and genetic factors, single point mutations within the amyloidogenic protein can dramatically influence disease phenotype. Mutations that destabilize the native state predispose an individual to disease; however, thermodynamic stability alone does not reliably predict disease severity. Here we show that the rate of transthyretin (TTR) tetramer dissociation required for amyloid formation is strongly influenced by mutation (V30M, L55P, T119M, V122I), with rapid rates exacerbating and slow rates reducing amyloidogenicity. Although these rates are difficult to predict a priori, they notably influence disease penetrance and age of onset. L55P TTR exhibits severe pathology because the tetramer both dissociates quickly and is highly destabilized. Even though V30M and L55P TTR are similarly destabilized, the V30M disease phenotype is milder because V30M dissociates more slowly, even slower than wild type (WT). Although WT and V122I TTR have nearly equivalent tetramer stabilities, V122I cardiomyopathy, unlike WT cardiomyopathy, has nearly complete penetrance-presumably because of its 2-fold increase in dissociation rate. We show that the T119M homotetramer exhibits kinetic stabilization and therefore dissociates exceedingly slowly, likely explaining how it functions to protect V30MT119M compound heterozygotes from disease. An understanding of how mutations influence both the kinetics and thermodynamics of misfolding allows us to rationalize the phenotypic diversity of amyloid diseases, especially when considered in concert with other genetic and environmental data.

Amyloidosis↗
PubMed2002

Total synthesis of ent-cholesterol via a steroid C,D-ring side-chain synthon.

For the first time, one of the two enantiomers of cholesterol (ent-cholesterol) has been synthesized by a synthetic route that starts from a precursor containing the D-ring and entire side chain of cholesterol. As part of the reported synthetic route, a method of general utility for the large scale (>10 g) preparation of each enantiomer of [1 alpha(R*),7a alpha]-1-(1,5-dimethylhexyl)-1,2,3,6,7,7a-hexahydro-7a-methyl-5H-inden-5-one, C,D ring-side chain synthons that can be used for the synthesis of enantiomers of vitamin D(3), cholesterol, and their analogues was also developed. Using the enantiomer of the C,D-ring side-chain synthon that leads to ent-cholesterol, the A- and B-rings were elaborated from a linear fragment that is sequentially cyclized to form the steroid B- and A-rings. Using this route, ent-cholesterol was prepared in 23 steps from the methyl ester of (1 alpha,5 alpha,6 alpha)-(+/-)-6-methyl-2-oxo-bicyclo[3.1.0]hexane-1-carboxylic acid in a total yield of 2.6%.

Catalysis↗
PubMed2002

The E1beta and E2 subunits of the Bacillus subtilis pyruvate dehydrogenase complex are involved in regulation of sporulation.

The pdhABCD operon of Bacillus subtilis encodes the pyruvate decarboxylase (E1alpha and E1beta), dihydrolipoamide acetyltransferase (E2), and dihydrolipoamide dehydrogenase (E3) subunits of the pyruvate dehydrogenase multienzyme complex (PDH). There are two promoters: one for the entire operon and an internal one in front of the pdhC gene. The latter may serve to ensure adequate quantities of the E2 and E3 subunits, which are needed in greater amounts than E1alpha and E1beta. Disruptions of the pdhB, pdhC, and pdhD genes were isolated, but attempts to construct a pdhA mutant were unsuccessful, suggesting that E1alpha is essential. The three mutants lacked PDH activity, were unable to grow on glucose and grew poorly in an enriched medium. The pdhB and pdhC mutants sporulated to only 5% of the wild-type level, whereas the pdhD mutant strain sporulated to 55% of the wild-type level. This difference indicated that the sporulation defect of the pdhB and pdhC mutant strains was due to a function(s) of these subunits independent of enzymatic activity. Growth, but not low sporulation, was enhanced by the addition of acetate, glutamate, succinate, and divalent cations. Results from the expression of various spo-lacZ fusions revealed that the pdhB mutant was defective in the late stages of engulfment or membrane fusion (stage II), whereas the pdhC mutant was blocked after the completion of engulfment (stage III). This analysis was confirmed by fluorescent membrane staining. The E1beta and E2 subunits which are present in the soluble fraction of sporulating cells appear to function independently of enzymatic activity as checkpoints for stage II-III of sporulation.

Bacillus subtilis↗