Biomedical subjects

X Quan

Publications and source records attributed to X Quan.

30 records · Page 2Linked to original sources

PubMed2000

Long-term results of ammonia removal and transformation by biofiltration.

In this paper, long-term (>8 month) results of ammonia removal in biofilters was studied. Compost was used as the biofilter medium and activated carbon as an added material. The ammonia removal was normally >95% at influent ammonia concentrations of 20-500ppmv. According to the test results, the influent ammonia concentration should be <200ppmv (0.1570g ammonia/kg media per day) so that the effluent concentration of ammonia is <1.0mg/m(3) (the emission standard of China), and the biofiltration system can achieve good long-term performance. In the biofiltration system utilized in this study, the shortest retention time that the system could attain was 0.532min. However, the retention time can be decreased further without decreasing the ammonia removal efficiency. Countercurrent flow is favorable, as it enhances the moisture retention ability of the media. In the bioreactors, ammonia can be converted into the nitrate. The bioreactors have a stratification phenomenon for ammonia removal over the biofiltration depth, which implies that different parts of the bioreactor play different roles in the ammonia removing process.

Air Pollution↗

PubMed2000

Quantitative structure-property relationships for direct photolysis quantum yields of selected polycyclic aromatic hydrocarbons

By the use of partial least squares (PLS) method and 11 quantum chemical descriptors computed by PM3 Hamiltonian, Quantitative Structure-Property Relationships (QSPRs) for direct photolysis quantum yields of selected polycyclic aromatic hydrocarbons (PAHs) were obtained. Direct photolysis quantum yields were predicted for PAHs for which experimental quantum yield values were lacking. Based on the QSPR models, significant PAH molecular characters governing their direct photolysis quantum yields were identified. It can generally be concluded that PAHs with large average molecular polarizability, molecular weight, and heat of formation values tend to have small photolysis quantum yields. PAHs with large values of the energy of the lowest unoccupied molecular orbital (Elumo), small values of the energy of the highest occupied molecular orbital (Ehomo), and large Elumo-Ehomo values, tend to have great photolysis quantum yields.

Journal Article↗

PubMed2000

The use of PLS algorithms and quantum chemical parameters derived from PM3 hamiltonian in QSPR studies on direct photolysis quantum yields of substituted aromatic halides.

The Partial Least-Squares (PLS) method was used to further study Quantitative Structure-Property Relationship (QSPR) for photohydrolysis quantum yields of selected aromatic halides. The cluster of substituted bromobenzenes and iodobenzenes was further grouped into two clusters, substituted bromobenzenes and substituted iodobenzenes, for which QSPRs were obtained, respectively. The QSPRs obtained by PLS are more significant than those obtained in previous studies. The studies showed that only when the compounds belonging to different groups are studies separately, inherent relationships between molecular properties and their structure characteristics can be revealed. It can be generally concluded that the photohydrolysis quantum yields of the substituted aromatic halides are dependent on the overall characters of the molecules, the characters of the carbon-halogen bonds to be broken in the photolysis, and the character of the halogen atoms to be replaced in the photolysis. Electronegativity has great relevance to the photohydrolysis processes of the compounds. Substituted aromatic halides with large average molecular polarizability and molecular weight values tend to have low photolysis quantum yields.

Algorithms↗

PubMed2000

Pregnancy-associated bovine and ovine glycoproteins exhibit spatially and temporally distinct expression patterns during pregnancy.

The pregnancy-associated glycoproteins (PAG) constitute a large family of recently duplicated genes. They show structural resemblance to pepsin and related aspartic proteinases. A total of 21 bovine (bo) PAG and 9 ovine (ov) PAG cDNA have been identified. Phylogenetic analysis indicated that the PAG are divided into two main groupings that accurately reflect their tissue expression, as determined by in situ hybridization. In the first pattern, represented by ovPAG-2 and boPAG-2, -8, -10, and -11 (where the numbering is arbitrary and reflects order of discovery within species), expression occurred throughout the outer epithelial layer of the placenta (trophectoderm). The second pattern was predominant localization to binucleate cells. Ribonuclease protection assays, which allow discrimination between closely related transcripts, have shown that the expression of PAG varies in a temporal manner over pregnancy. Of those bovine PAG expressed predominantly in binucleate cells, boPAG-1, -6, and -7 are expressed weakly, if at all, by Day 25 placenta, but are present at the middle and end of pregnancy. Others, such as boPAG-4, -5, and -9, are expressed at Day 25 and at earlier stages. Although not among the earliest PAG produced by the trophoblast, boPAG-1 has been used for pregnancy diagnosis, particularly in dairy cows, where there is a major need for a sensitive method capable of detecting pregnancy within 1 mo of conception. It seems likely that some of the newly discovered PAG will be better candidates than PAG-1 for pregnancy diagnosis.

Animals↗

PubMed2000

Localization of new, microdissection- generated, anonymous markers and of the genes Pcsk1, Dhfr, Ndub13, and Ccnb1 to rat chromosome region 2q1.

The centromeric region of rat chromosome 2 (2q1) harbors unidentified quantitative trait loci of genes that control tumor growth or development. To improve the mapping of this chromosome region, we microdissected it and generated 10 new microsatellite markers, which we included in the linkage map and/or radiation hybrid map of 2q1, together with other known markers, including four genes: Pcsk1 (protein convertase 1), Dhfr (dihydrofolate reductase), Ndub13 (NADH ubiquinone oxidoreductase subunit b13), and Ccnb1 (cyclin B1). To generate anchor points between the different maps, the gene Ndub13 and the microsatellite markers D2Ulb25 and D2Mit1 were also localized cytogenetically. The radiation map generated in region 2q1 extends its centromeric end of about 150 cR.

Animals↗

PubMed1999

Pathophysiology of antigen 85 in patients with active tuberculosis: antigen 85 circulates as complexes with fibronectin and immunoglobulin G.

Antigen 85 (Ag85) complex proteins are major secretory products of Mycobacterium tuberculosis and induce strong cellular and humoral immune responses in infected experimental animals and human beings. We have previously shown that nanogram doses of these 30- to 32-kDa fibronectin-binding proteins inhibit local expression of delayed hypersensitivity by a T-cell fibronectin-dependent mechanism. Circulating levels of Ag85 might be expected to be elevated in patients with active tuberculosis and possibly to play a role in systemic anergy in these patients. To test this hypothesis, Ag85 was measured in serum and urine by a monoclonal antibody-based dot immunobinding assay in 56 patients and controls with known skin test reactivity. Median serum Ag85 levels were 50- to 150-fold higher in patients with active tuberculosis than in patients with active M. avium-intracellulare disease or other nontuberculous pulmonary disease or in healthy controls (P < 0.001). The median and range of serum Ag85 in patients with active tuberculosis was not significantly different between skin test-positive and -negative subjects. Patients with active M. avium disease could be distinguished from those with disease due to M. tuberculosis by monoclonal anti-Ag85 antibodies of appropriate specificities. No increases in urinary Ag85 were detected in any patient, regardless of the Ag85 level in serum. Chromatographic analysis and immunoprecipitation studies of serum revealed that Ag85 existed in the serum of these patients complexed to either fibronectin or immunoglobulin G (IgG). Uncomplexed circulating Ag85 was demonstrable in serum from fewer than 20% of patients with active tuberculosis. In patients with active tuberculosis, Ag85 is therefore likely to circulate primarily as complexes with plasma fibronectin and IgG rather than in unbound form. The existence of Ag85 complexes with plasma proteins would account for its lack of urinary clearance.

Acyltransferases↗

PubMed1998

Biophysical properties of descending brain neurons in larval lamprey.

In the brains of larval lamprey, biophysical properties of reticulospinal (RS) neurons were determined by applying depolarizing and hyperpolarizing current pulses under current clamp conditions. In response to above threshold depolarizing current pulses, almost all RS neurons produced an initial relatively high spiking frequency (Fi) followed by a variable decay to a steady-state firing frequency (Fss). Spike-frequency adaptation (SFA), defined as [(Fi - Fss)/Fi] x 100%, was minimal at the lowest currents and more pronounced with larger applied current pulses. Some RS neurons, particularly those in the posterior rhombencephalic reticular nucleus (PRRN), either adapted very quickly, and stopped firing, or fired in short bursts during a constant depolarizing current pulse. Several types of RS neurons, including some Muller cells and unidentified neurons in the middle rhombencephalic reticular nucleus (MRRN), displayed delayed excitation (DE) in which spiking in response to a depolarizing current pulse was delayed if preceded by a hyperpolarizing prepulse. Very few neurons fired action potentials following a hyperpolarizing pulse, such as in the case of post-inhibitory rebound (PIR), and no neurons were found that displayed plateau potentials. The possible contributions of these properties to the descending activation of spinal locomotor networks is discussed.

Animals↗

PubMed1997

[Studies on serum regulatory protein for cell growth in patients with lung cancer exposed to indoor coal-burning].

Seven kinds of serum regulatory gene coding protein for cell growth were determined with enzyme linked immunodotting in 19 indoor coal-burning exposed patients with lung cancer (Group A), 22 exposed cases without lung cancer (Group B), and 19 nonexposed cases without lung cancer (Group C) to study pathogenesis of lung cancer patients exposed to indoor coal-burning. Results showed that serum concentrations of ras, p53 and neu protein in Group A were significantly higher than those in Groups B and C, with a statistically significant difference (P < 0.05) or a very significant difference (P < 0.01). Six cases in Group A were positive for ras protein (with two strong positive), three for p53, neu and jun each, and one for p16. Two in Group B were positive for ras protein and one for p16. It suggests that serum regulatory protein for cell growth can be regarded as biological markers for environment-related lung cancer.

Air Pollution, Indoor↗

PubMed1995

Enhancement of delayed hypersensitivity inflammatory reactions in guinea pig skin by 12(R)-hydroxy-5,8,14-eicosatrienoic acid.

Delayed-type hypersensitivity (DTH) reactions are initiated by sensitized T cells. Their progression is dependent upon the local release of various autacoids, including cytokines and eicosanoids, by T cells, infiltrating inflammatory cells, and resident tissue cells. 12(R)-hydroxy-5,8,14-eicosatrienoic acid [12(R)-HETrE], an eicosanoid produced by skin and cornea, possesses potent proinflammatory properties at picomolar concentrations including vasodilation, increase in membrane permeability, neutrophil chemotaxis, and angiogenesis. Because DTH reactions are associated with many of these same phenomena, we examined the effect of 12(R)-HETrE and related 12-hydroxyeicosanoids on the expression of DTH to purified protein derivative of tuberculin in sensitized guinea pigs. In the absence of purified protein derivative of tuberculin, none of the eicosanoids evoked erythema or edema after intradermal injection at doses up to 100 pmol. When injected together with purified protein derivative of tuberculin, 12(R)-hydroxy-5,8,10,14-eicosatetraenoic acid [12(R)-HETE], but not its enantiomer 12(S)-HETE, significantly inhibited macroscopic expression of delayed reactivity (erythema) only at the highest dose tested, 10 pmol. In contrast, 12(R)-HETrE significantly enhanced expression of DTH at doses between 1 fmol and 1 pmol (50% and 30% increases above control, respectively). Its stereoisomer, 12(S)-HETrE, did not enhance DTH at any tested dose, but was able to block the activity of 12(R)-HETrE when injected simultaneously. Enhancement or inhibition of visible skin responses was not associated with qualitative or quantitative changes in cellular infiltrates at the reaction site. 12(R)-HETrE had no effect on the nonimmunologic inflammatory skin reaction induced by phorbol myristate acetate, suggesting selectivity toward DTH. We conclude that 12(R)-HETrE enhances DTH via a yet to be determined mechanism and that its stereoisomer, 12(S)-HETrE, may be a useful antagonist for studying the inflammatory actions of this eicosanoid.

8,11,14-Eicosatrienoic Acid↗

PubMed1994

The role of coenzyme A in the biotransformation of 2-arylpropionic acids.

A number of 2-arylpropionic acid non-steroidal anti-inflammatory drugs ('profens') undergo highly enantioselective inversion from the (R)- to (S)-enantiomer. The mechanism of this inversion reaction involves the initial enantioselective formation of a coenzyme A thioester followed by epimerization and finally hydrolysis to regenerate free acids. Long-chain fatty acyl-CoA synthetase appears to mediate the initial thioester formation and an epimerase of an unknown physiologic function effects the second step. The hydrolases mediating the final step are poorly defined. Available evidence suggests that the liver is quantitatively the most important tissue site of inversion but local tissue inversion may influence the pharmacological and toxicological response of a given organ. Data from isolated rat hepatocytes indicate that other xenobiotics can modulate the formation and hydrolysis of ibuprofenyl-CoA by influencing inversion pathways, non-inversion pathways or both. Interactions between xenobiotics may therefore accentuate inter-individual variability in response to 2-aryl-propionic acids. The formation of 2-arylpropionyl-CoA thioesters in vivo has the potential to disrupt numerous biochemical pathways in addition to enhancing individual exposure to the potent anti-inflammatory (S)-enantiomers.

Acyl Coenzyme A↗

PubMed1994

Inhibition of expression of delayed hypersensitivity by neutralizing monoclonal anti-T-cell fibronectin antibody.

T-cell fibronectin (FN) is a unique cellular FN that is rapidly synthesized by memory T cells in response to antigen. Monoclonal anti-T-cell FN antibodies have been used to clarify the role of T-cell FN in the in vivo expression of delayed hypersensitivity. IgGl(kappa) mouse anti-human T-cell FN monoclonal antibodies 231 and 248 recognized epitopes on the FN cell-binding domain, were cross-reactive with plasma FN, and neutralized human and guinea-pig T-cell FN monocyte agglutinating activity. When injected intradermally together with tuberculin or 30 min before topical application of reactive sensitizer, antibody 231 significantly decreased macroscopic expression of guinea-pig delayed hypersensitivity at 24 hr in a dose-dependent manner. Similar doses of antibody 248 caused a slight statistically non-significant enhancement of delayed-type hypersensitivity (DTH) expression. Inhibition of visible skin responses was not associated with qualitative or quantitative changes in cellular infiltrates at the reaction site. Antibody 231 modulated expression of delayed hypersensitivity in a qualitatively and quantitatively similar manner to the FN-binding mycobacterial antigen 85 proteins. This is consistent with anti-T-cell FN and antigen 85 acting on the same molecule in vivo.

Agglutination↗

PubMedDate not supplied

Sternocleidomastoid pseudotumor of infants and congenital muscular torticollis: fine-structure research.

Fifty cases, 16 with sternocleidomastoid pseudotumor of infants (SCMPOI) and 34 with congenital muscular torticollis (CMT), were investigated by light and electron microscopy. The ultrastructure of the pseudotumor revealed that there were myoblasts, fibroblasts, myofibroblasts, and mesenchyme-like cells, which consisted of fibrous tissue and were regarded as fibroblasts only in the literature. The myoblasts showed the various stages of differentiation and degeneration. For those cases without mass, the collagen fibrils and fibrocytes were often arranged in tight parallel bundles in which some muscles showed normal structure and some with decreased myofibrillae. The mesenchyme-like cells and myoblasts found in the pseudotumor may be the key point to its pathologic characteristics.

Child↗