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Biomedical subjects

X H Xu

Publications and source records attributed to X H Xu.

At least 19 recordsLinked to original sources
PubMed2006

Development changes of cuticular hydrocarbons in Chrysomya rufifacies larvae: potential for determining larval age.

Age determination is the basis of determining the postmortem interval using necrophagous fly larvae. To explore the potential of using cuticular hydrocarbons for determining the ages of fly larvae, changes of cuticular hydrocarbons in developing larvae of Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae) were investigated using gas chromatography with flame-ionization detection and gas chromatography-mass spectrometry. This study showed that the larvae produced cuticular hydrocarbons typical of insects. Most of the hydrocarbons identified were alkanes with the carbon chain length of 21-31, plus six kinds of alkenes. The hydrocarbon composition of the larvae correlated with age. The statistical results showed that simple peak ratios of n-C29 divided by another eight selected peaks increased significantly with age; their relationships with age could be modelled using exponential or power functions with R(2) close to or > 0.80. These results suggest that cuticular hydrocarbon composition is a useful indicator for determining the age of larval C. rufifacies, especially for post-feeding larvae, which are difficult to differentiate by morphology.

Aging↗
PubMed2006

Characterization of HLA-B*5516, -B*1313, -B*9512, and -DRB1*1457 alleles identified in a southwest Chinese population.

The human leukocyte antigen (HLA)-B*5516 allele differs from the B*5502 by a single 97 T --> C substitution (His to Tyr at position 33) in exon 2. The B*1313 allele results from 419 T --> A and 420 A --> C substitutions, encoding a Leu to Tyr substitution at 140 in exon 2 of the B*1301 allele. The B*9512 allele differs from B*1502 by a single 360 G --> C substitution (Gln to His at 120) in exon 3. The DRB1*1457 allele appears to be a hybrid molecule generated by recombination between the DRB1*13 and DRB1*14 alleles. The serological equivalents of these new alleles are HLA-B22, -B13, -B15, and DR13, respectively. Family studies detected two rare haplotypes: A*11, B*9512, DRB1*14 and A*24, B*52, Cw*07, DRB1*1457, DRB3*020201, DQB1*050301. The gene frequencies of these alleles in the Chinese population are less than 0.0001.

Alleles↗
PubMed2006

Relationship between common functional polymorphisms of the p22phox gene (-930A > G and +242C > T) and nephropathy as a result of Type 2 diabetes in a Chinese population.

OBJECTIVE: Genetic determinants are important in diabetic nephropathy (DN). Oxidative stress has also emerged as an important pathogenic factor in DN and vascular NADH oxidase is a major source of reactive oxygen species (ROS). Previous small studies reported a strong but contradictory association between functional genetic variation of p22(phox), an important subcomponent of NADH oxidase, and DN. We investigated the association between two common functional single nucleotide polymorphisms (SNPs) (-930 A > G and +242 C > T) and DN in a much larger group of Chinese patients with Type 2 diabetes mellitus (T2DM). RESEARCH DESIGN AND METHODS: Case-control study of Chinese subjects with long-standing T2DM (> 10 years). Cases (n = 306) were subjects with a spot urinary albumin : creatinine ratio (ACR) of > 113 mg/mmol or elevated serum creatinine. Control subjects (n = 306) had ACR < 3.3 mg/mmol and normal serum creatinine. Genotyping was carried out by standard PCR and restriction fragment length polymorphism analysis. RESULTS: Gender distribution, age, duration of diabetes and HbA(1c) were similar in cases and control subjects. Distribution of genotypes in the control subjects for both SNPs was consistent with the Hardy-Weinberg equilibrium. Distribution of genotypes did not differ significantly between cases and control subjects for both polymorphisms-+2424C > T: cases CC 84.6%, CT 15.0%, TT 0.4% and control subjects CC 87.6%, CT 11.8%, TT 0.6% (P = 0.45); -930 A > G: cases AA 40.5%, AG 41.8%, GG 17.7% and control subjects AA 38.2%, AG 49.0%, GG 12.8% (P = 0.12). Distribution of alleles was also similar-+2424 C > T: cases C 92.2%, T 7.8% and control subjects C 93.5%, T 6.5% (P = 0.66); -930 A > G cases A 61.4%, G 38.6% and control subjects A 62.7%, G 37.3% (P = 0.38). We estimated that our study has approximately 80% power to detect a relative risk of 1.65 (for +242 C > T) and 1.35 (for -930 A > G) conferred by the minor allele, respectively. CONCLUSIONS: In contrast with previous small studies, our data suggest that these SNPs do not confer significantly increased susceptibility to DN secondary to T2DM in Chinese subjects.

Aged↗
PubMed2005

SVM classification of human intergenic and gene sequences.

Despite constant improvement in prediction accuracy, gene-finding programs are still unable to provide automatic gene discovery with the desired correctness. This paper presents an analysis of gene and intergenic sequences from the point of view of language analysis, where gene and intergenic regions are regarded as two different subjects written in the four-letter alphabet {A,C,G,T}, and high frequency simple sequences are taken as keywords. A measurement alpha(l(tau)) was introduced to describe the relative repeat ratio of simple sequences. Threshold values were found for keyword selections. After eliminating 'noise', 178 short sequences were selected as keywords. DNA sequences are mapped to 178-dimensional Euclidean space, and SVM was used for prediction of gene regions. We showed by cross-validation that the program we developed could predict 93% of gene sequences with 7% false positives. When tested on a long genomic multi-gene sequence, our method improved nucleotide level specificity by 21%, and over 60% of predicted genes corresponded to actual genes.

Algorithms↗
PubMed2004

The kinetic model and simulation of blood coagulation--the kinetic influence of activated protein C.

The paper described a limited part of the coagulation pathway, and in particular the inhibitory effects of activated protein C in the context of thrombin production. This is a computational modeling study with various assumption made of kinetic rates laws and their summation. The level of complexity and assumed parameters makes conclusions uncertain. However, an interesting outcome is that kinetic reaction rates may show oscillation behavior under particular, high levels of protein C feedback inhibition. The model would defy quantitative practical use, but could have predictive value as a qualitative descriptor of coagulation.

Biological Clocks↗
PubMed2004

Numerical study of nonlinear pulsatile flow in S-shaped curved arteries.

The nonlinear pulsatile blood flow in S-shaped curved arteries was studied with finite element method. Numerical simulations for flows in two models of S-shaped curved arteries with different diameters and under the same boundary conditions were performed. The temporal and spatial distributions of hemodynamic variables during the cardiac cycle such as velocity field, secondary flow, pressure, and wall shear stresses in the arteries were analyzed. Results of numerical simulations showed that the secondary flow in the larger S-shaped curved artery is more complex than that in the smaller one; stronger eddy flow occurred in the inner bends of curved arteries; pressure and wall shear stresses changed violently in the curved arteries, especially in the larger model. These hemodynamic variables in curved arteries will cause important effects on the function of arterial endothelium in the region. For instance, they may lead to the proliferation of smooth muscle cells and the thickening of the intima, and cardiovascular diseases such as atherosclerosis may develop in such regions. Due to having the special blood flow characteristics in the S-shaped arteries, it is worthwhile to study flow in this kind of curved artery. The comprehensive theoretical foundation showed in the present study can be extended to approach problems of nonlinear pulsatile flow in curved arteries with more complex geometrical shape.

Animals↗
PubMed2003

The use of rice hulls for sustainable control of NOx emissions in deep space missions.

The use of the activated carbon produced from rice hulls to control NOx emissions for future deep space missions has been demonstrated. The optimal carbonization temperature range was found to be between 600 and 750 degrees C. A burnoff of 61.8% was found at 700 degrees C in pyrolysis and 750 degrees C in activation. The BET surface area of the activated carbon from rice hulls was determined to be 172 m2/g when prepared at 700 degrees C. The presence of oxygen in flue gas is essential for effective adsorption of NO by activated carbon. On the contrary, water vapor inhibits the adsorption efficiency of NO. Consequently, water vapor in flue gas should be removed by drying agents before adsorption to ensure high NO adsorption efficiency. All of the NO in the flue gas was removed for more than 1.5 h when 10% oxygen was present and the ratio of the carbon weight to the flue gas flow rate (W/F) was 15.4 g min/L. Reduction of the adsorbed NO to form N2 could be effectively accomplished under anaerobic conditions at 550 degrees C. The adsorption capacity of NO on the activated carbon was found to be 5.02 mg of NO/g of carbon. The loss of carbon mass was determined to be about 0.16% of the activated carbon per cycle of regeneration if the regeneration occurred when the NO in the flue gas after the carbon bed reached 4.8 ppm, the space maximum allowable concentration. The reduction of the adsorbed NO also regenerated the activated carbon, and the regenerated activated carbon exhibited an improved NO adsorption efficiency.

Adsorption↗
PubMed2001

Toll-like receptor-4 is expressed by macrophages in murine and human lipid-rich atherosclerotic plaques and upregulated by oxidized LDL.

BACKGROUND: Inflammation is implicated in atherogenesis and plaque disruption. Toll-like receptor 2 (TLR-2) and TLR-4, a human homologue of drosophila Toll, play an important role in the innate and inflammatory signaling responses to microbial agents. To investigate a potential role of these receptors in atherosclerosis, we assessed the expression of TLR-2 and TLR-4 in murine and human atherosclerotic plaques. METHODS AND RESULTS: Aortic root lesions of high-fat diet-fed apoE-deficient mice (n=5) and human coronary atherosclerotic plaques (n=9) obtained at autopsy were examined for TLR-4 and TLR-2 expression by immunohistochemistry. Aortic atherosclerotic lesions in all apoE-deficient mice expressed TLR-4, whereas aortic tissue obtained from control C57BL/6J mice showed no TLR-4 expression. All 5 lipid-rich human plaques expressed TRL-4, whereas the 4 fibrous plaques and 4 normal human arteries showed no or minimal expression. Serial sections and double immunostaining showed TLR-4 colocalizing with macrophages both in murine atherosclerotic lesions and at the shoulder region of human coronary artery plaques. In contrast to TLR-4, none of the plaques expressed TLR-2. Furthermore, basal TLR-4 mRNA expression by human monocyte-derived macrophages was upregulated by ox-LDL in vitro. CONCLUSIONS: Our study demonstrates that TLR-4 is preferentially expressed by macrophages in murine and human lipid-rich atherosclerotic lesions, where it may play a role to enhance and sustain the innate immune and inflammatory responses. Moreover, upregulation of TLR-4 in macrophages by oxidized LDL suggests that TLR-4 may provide a potential pathophysiological link between lipids and infection/inflammation and atherosclerosis.

Animals↗
PubMed2001

Primary study of vascular endothelial growth factor immunohistochemical staining in the diagnosis of early acute myocardial ischemia.

The expression of vascular endothelial growth factor (VEGF) in the model of rat early acute myocardial ischemia was studied by Strept-Avidin-Biotin-Peroxidase Complex (SABC) immunohistochemical staining. After ligating the anterior descending branch of the left coronary artery, an initial rapid (30min) positive expression of VEGF in myocardial ischemic areas was observed, the intensity of positive expression of VEGF increased with the continuation of myocardial ischemia. After 5h infarction, the strongly positive myocytes of SABC-VEGF staining were predominantly limited to perimyocardial infarction areas. No positive expression of VEGF was found in the control group. These findings suggested that SABC-VEGF method could give a sensitive, specific, simple and objective morphologic evidence to the diagnosis of sudden cardiac death caused by acute early myocardial ischemia.

Animals↗
PubMed2001

Novel solution-phase immunoassays for molecular analysis of tumor markers.

at 3 x 10(9) M(-1) and a step-wise binding process with PSA-free MAB. Thus, this solution-phase quantitative ECL immunoassay allowed measurement of the affinity of serum PSAs with their MABs and screening of PSAs based upon their affinity to MABs. Unlike other immunoassays, this immunoassay demonstrated one-step rapid analysis while simultaneously eliminating immobilization, separation and washing steps and detected PSA at a level of 1.7 pg mL(-1), which is 1000-fold more sensitive than current PSA immunoassays. Furthermore, single-molecule (SM) phosphorescence microscopy was developed to detect single serum PSA-free and PSA-complex molecules in solution with no use of antibody showing that PSA-free molecules diffused faster than PSA-complex molecules in solution. This finding is consistent with ECL measurements and implies the possibility of screening individual analytes in a complex mixture using their distinct SM diffusion distance. This is the first report describing the detection of single protein molecules labeled with a metal-complex using phosphorescence microscopy and also the screening of serum tumor markers using ECL and SM phosphorescence solution-phase assays.

Antigen-Antibody Reactions↗
PubMed2001

[Optimization analysis of ventilation and dehumidification in manned spacecraft].

OBJECTIVE: To achieve the optimized design of system operational parameters and system components in air ventilation and dehumidification of manned spacecraft. METHOD: Mathematical-physical model of air ventilation and dehumidification system was established. Through the design of optimal operational parameters for system performance, heat and moisture in the cabin of manned spacecraft could be removed effectively, dewing could be prevented, and the comfort demand of the astronauts could be met. Equivalent mass of the system in different operational parameters and system components was analyzed by calculation. RESULT: The dew point temperature and the comfortability depended on the temperature and humidity of the influx, ventilation rate, and evaporation of moisture in the cabin. There were two ways to control the operational parameters of air ventilation and dehumidification system. The method based on controlling temperature didn't use recuperative heat exchangers in the loop, and the system structure for the design was simple, but it didn't meet the requirement of dissipating moisture in some conditions. The other method was based on controlling the moisture, and it could steadily keep the dew point temperature in the cabin and control the occurrence of dew. But the system structure of this design was relatively complex. CONCLUSION: Mass and power consumption of the system could be reduced by selecting appropriate parameters and adopting the measures of optimization.

Air Conditioning↗
PubMed2001

[Mass optimization of thermal network model of coupled dual-loop thermal control system in spacecraft].

OBJECTIVE: To deal with the mass optimization of thermal control system as well as environmental control and life support system (ECLSS) of manned spacecraft. METHOD: The thermo-hydraulic network composed of coupled liquid dual-loop and gas loops was studied. Physical and mathematical models were established and used for flow, heat transfer and mass calculation in the network. The influences of various operational and structural parameters on the mass were analyzed. RESULT: There were optimal pipe diameters for internal loop and external loop; there existed an upper limit of flow rate in the internal loop and lower limit in the external loop; there were also optimal flow rates in the loops and optimal exit temperature of the radiator. CONCLUSION: Reasonable design of these parameters were very important for reducing the system mass.

Air Conditioning↗
PubMed2001

Hypercholesterolemia alters vascular functions and gene expression of potassium channels in rat aortic smooth muscle cells.

AIM: To investigate the effects of hypercholesterolemia on functions of rat aorta and on gene expression of inward rectifier and ATP-sensitive potassium channels in aortic smooth muscle. METHODS: Rats were treated with high-cholesterol emulsion ig for 2 weeks; the aortic rings with and without endothelium were prepared to examine the aortic contractile and relaxation responses; RT-PCR was used to observe the gene expression of inward rectifier and ATP-sensitive potassium channels. RESULTS: Hypercholesterolemia damaged the endothelium-dependent vascular functions severely, but did not affect the endothelium-independent vascular functions; Kir6.2 mRNA expression was upregulated (P < 0.05) and Kir3.1 mRNA expression was downregulated markedly (P < 0.05) in hypercholesterolemic smooth muscle. CONCLUSION: Hypercholesterolemia altered the vascular functions and regulated gene expression levels of specific inward rectifier and ATP-sensitive potassium channel subtypes.

Animals↗
PubMed2001

[Determination of angiotensin-converting enzyme activity by micellar electrokinetic capillary chromatography].

A sensitive and rapid method was developed for angiotensin-converting enzyme (ACE) activity determination by micellar electrokinetic capillary chromatography (MECC). MECC was carried out to separate and quantify the products of the enzymatic reacting using Hip-Leu-His as the substrate in 20 mmol/L boric acid-borate buffer (pH 9.0) including 50 mmol/L SDS as the run buffer at an applied voltage of 8.1 kV. The electrophoresis was monitored at 228 nm, and completed in 6 minutes. The detection limits of ACE activity was 5 pmol/min(signal to noise ratio was 2).

Buffers↗
PubMed2001

[Effect of KB-R7943 on Na(+)-Ca2+ exchange current in guinea pig ventricular myocytes].

AIM: To study whether KB-R7943 has selective inhibitory effect on the inward and outward Na(+)-Ca2+ exchange current (INa-Ca) in guinea pig ventricular myocytes. METHODS: Through setting up the model of intracellular Na(+)-overload during myocardial ischemia and reperfusion, the current-voltage relationship of INa-Ca was recorded using whole-cell patch clamp technique under bi-directional ionic conditions. RESULTS: Currents were elicited by a declining ramp pulse depolarized immediately from holding potential of -40 mV to +60 mV, then repolarized to -100 mV at a speed of 80 mV.s-1 and returned to the holding potential under bi-directional ionic conditions, while the [Na+] was 25 mmol.L-1 in the pipette solution. The currents increased time-dependently and voltage-dependently which reached from (2.51 +/- 0.15) pA.pF-1 to (5.94 +/- 0.13) pA.pF-1 at mV and from (-1.92 +/- 0.13) pA.pF-1 to (-3.17 +/- 0.16) pA.pF-1 at -80 mV (n = 12) after 3 min and there is no significant run-down of the current. KB-R7943 10(-6) mol.L-1 was found to decrease the current to (4.62 +/- 0.05) pA.pF-1 by 29.4% at mV and to (-2.30 +/- 0.18) pA.pF-1 by 22.1% at -80 mV (n = 5) after 5 min. While 10(-5) mol.L-1 KB-R7943 was shown to decrease the current to (3.13 +/- 0.03) pA.pF-1 by 61.7% at mV and to (-1.62 +/- 0.03) pA.pF-1 by 56.9% at -80 mV (n = 7). CONCLUSION: KB-R7943 can block INa-Ca in guinea pig ventricular myocytes. But, it did not show selective inhibition effect on inward and outward currents.

Animals↗
PubMed2000

[Clinical study on nosocomial infection in patients with burns].

OBJECTIVE: To study clinical characters and related factors of nosocomial infection in patients with burns. METHODS: To study 782 cases of burns as a group hospitalized in our department for more than 48 h, from January, 1993 to December, 1996. Prospective and retrospective investigation of infection locations, infection rates, pathogen and drug sensibility was carried out. RESULTS: The infection most often found in blood and wound, less often in respiratory system. Nosocomial infection rates in patients with burns were closely related to the severe degree, diagnosis and therapy of these patients and hospital surroundings. Infection bacteria species: Gram-positive bacterium accounted for 43.82%, and mainly were staphylococcus aureus and anaerobic peptococcus. Gram-negative bacterium accounted for 52.81%, of which pseudomonas aeruginosa and nitrate-negative bacillus constituted the majority. CONCLUSION: According to these characters and related factors of nosocomial infection in patients with burns, effective measures of preventing and controlling infection should be taken, so that the incidence of nosocomial infection in these patients will drop.

Adolescent↗