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Biomedical subjects

X D Li

Publications and source records attributed to X D Li.

At least 19 recordsLinked to original sources
PubMed2003

Multivariate statistical study of heavy metal enrichment in sediments of the Pearl River Estuary.

The concentrations and chemical partitioning of heavy metals in the sediment cores of the Pearl River Estuary were studied. Based on Pearson correlation coefficients and principal component analysis results, Al was selected as the concentration normalizer for Pb, while Fe was used as the normalizing element for Co, Cu, Ni and Zn. In each profile, sections with metal concentrations exceeding the upper 95% prediction interval of the linear regression model were regarded as metal enrichment layers. The heavy metal accumulation mainly occurred at sites in the western shallow water areas and east channel, which reflected the hydraulic conditions and influence from riparian anthropogenic activities. Heavy metals in the enrichment sections were evaluated by a sequential extraction method for possible chemical forms in sediments. Since the residual, Fe/Mn oxides and organic/sulfide fractions were dominant geochemical phases in the enriched sections, the bioavailability of heavy metals in sediments was generally low. The 206Pb/207Pb ratios in the metal-enriched sediment sections also revealed the influence of anthropogenic sources. The spatial distribution of cumulative heavy metals in the sediments suggested that the Zn and Cu mainly originated from point sources, while the Pb probably came from non-point sources in the estuary.

China↗
PubMed2003

Effects of tea catechin inhalation on methicillin-resistant Staphylococcus aureus in elderly patients in a hospital ward.

We investigated the effects of inhalation of tea catechin on MRSA in the 24 elderly in patients, who were known to carry MRSA in sputum. The patients in the catechin group (N=12) were administered an inhalation of tea catechin extracts (in saline/bromhexine) (3.7 g/L catechins, 43% of them are composed of epigallocatechin gallate), three times daily with hand nebulizer for four weeks. The clinical effects were compared with the control group (N=12) who were given an inhalation of saline/bromhexine alone. After a week of the course, the numbers of the patients with decreased or disappearance of MRSA in their sputum was significantly higher in the catechin group, compared with that in the control group (seven vs. no patients; P<0.05). The number of patients discharged during the study was significantly increased, and the days of hospital stay were significantly decreased in the catechin group compared with those in the control group (six vs. one patient; P<0.05, 51+/-22 vs. 85+/-50 days, mean+/-S.D.;P <0.05, respectively). No adverse effects were observed in any patients during the study. Catechin inhalation seemed to be safe, and at least temporarily effective in the reduction of MRSA and shortening of hospitalization.

Activities of Daily Living↗
PubMed2002

Heavy metals in agricultural soils of the Pearl River Delta, South China.

There is a growing public concern over the potential accumulation of heavy metals in agricultural soils in China owing to rapid urban and industrial development and increasing reliance on agrochemicals in the last several decades. Excessive accumulation of heavy metals in agricultural soils may not only result in environmental contamination, but elevated heavy metal uptake by crops may also affect food quality and safety. The present study is aimed at studying heavy metal concentrations of crop, paddy and natural soils in the Pearl River Delta, one of the most developed regions in China. In addition, some selected soil samples were analyzed for chemical partitioning of Co, Cu, Pb and Zn. The Pb isotopic composition of the extracted solutions was also determined. The analytical results indicated that the crop, paddy and natural soils in many sampling sites were enriched with Cd and Pb. Furthermore, heavy metal enrichment was most significant in the crop soils, which might be attributed to the use of agrochemicals. Flooding of the paddy soils and subsequent dissolution of Mn oxides may cause the loss of Cd and Co through leaching and percolation, resulting in low Cd and Co concentrations of the paddy soils. The chemical partitioning patterns of Pb, Zn and Cu indicated that Pb was largely associated with the Fe-Mn oxide and residual fractions, while Zn was predominantly found in the residual phase. A significant percent fraction of Cu was bound in the organic/sulphide and residual phases. Based on the 206Pb/207Pb ratios of the five fractions, it was evident that some of the soils were enriched with anthropogenic Pb, such as industrial and automobile Pb. The strong associations between anthropogenic Pb and the Fe-Mn oxide and organic/sulphide phases suggested that anthropogenic Pb was relatively stable after deposition in soils.

Agriculture↗
PubMed2001

Identification of a novel cytokine, ML-1, and its expression in subjects with asthma.

A novel gene, designated ML-1, was identified from a human genomic DNA clone and human T cell cDNA sequences. The second exon of ML-1 gene shares significant sequence identity with the gene encoding IL-17 (IL-17). ML-1 gene expression was up-regulated in activated PBMCs, CD4(+) T cells, allergen-specific Th0, Th1, and Th2 clones, activated basophils, and mast cells. Increased expression of the ML-1 gene, but not IL-17, was seen following allergen challenge in four asthmatic subjects, suggesting its role in allergic inflammatory responses. ML-1 from transiently transfected COS-7 cells was able to induce gene expression and protein production for IL-6 and IL-8 (at 10 ng/ml of ML-1: for IL-6, 599.6 +/- 19.1 pg/ml; for IL-8, 1724.2 +/- 132.9 pg/ml; and at 100 ng/ml of ML-1: for IL-6, 1005.3 +/- 55.6 pg/ml; for IL-8, 4371.4 +/- 280.5 pg/ml; p < 0.05 for both doses vs baseline) in primary bronchial epithelial (PBE) cells. Furthermore, increased expression of ICAM-1 was found in ML-1-stimulated PBE cells (mean fluorescence intensity (MFI) = 31.42 +/- 4.39 vs baseline, MFI = 12.26 +/- 1.77, p < 0.05), a functional feature distinct from IL-17 (MFI = 11.07 +/- 1.22). This effect was not inhibited by a saturating amount of IL-17. These findings demonstrate that ML-1 is a novel cytokine with a distinct function, and suggest a different receptor for ML-1 on PBE cells.

Amino Acid Sequence↗
PubMed2001

High-yield expression and functional analysis of Escherichia coli glycerol-3-phosphate transporter.

The glycerol-3-phosphate (G3P) transporter, GlpT, from Escherichia coli mediates G3P and inorganic phosphate exchange across the bacterial inner membrane. It possesses 12 transmembrane alpha-helices and is a member of the Major Facilitator Superfamily. Here we report overexpression, purification, and characterization of GlpT. Extensive optimization applied to the DNA construct and cell culture has led to a protocol yielding approximately 1.8 mg of the transporter protein per liter of E. coli culture. After purification, this protein binds substrates in detergent solution, as measured by tryptophan fluorescence quenching, and its dissociation constants for G3P, glycerol-2-phosphate, and inorganic phosphate at neutral pH are 3.64, 0.34, and 9.18 microM, respectively. It also shows transport activity upon reconstitution into proteoliposomes. The phosphate efflux rate of the transporter in the presence of G3P is measured to be 29 micromol min(-1) mg(-1) at pH 7.0 and 37 degrees C, corresponding to 24 mol of phosphate s(-1) (mol of protein)(-1). In addition, the glycerol-3-phosphate transporter is monomeric and stable over a wide pH range and in the presence of a variety of detergents. This preparation of GlpT provides ideal material for biochemical, biophysical, and structural studies of the glycerol-3-phosphate transporter.

Biological Transport↗
PubMed2001

Heavy metal speciation and leaching behaviors in cement based solidified/stabilized waste materials.

A circuit board printing factory sludge containing high concentrations of copper, zinc and lead was stabilized and solidified (S/S) with different portions of ordinary Portland cement (OPC) and pulverized fly ash (PFA). The chemical speciation and leaching behavior of heavy metals in these cement-based waste materials were studied by different sequential extraction procedures, standard toxicity characteristic leaching procedure (TCLP) and progressive TCLP tests. The sequential extraction results showed that more than 80% of Cu, Pb and Zn were associated with Fraction 2 (weak acid soluble, extracted with 1M NaOAc at pH 5.0 with a solid to liquid ratio of 1:60). This indicated that the heavy metals could exist in the S/S matrix as metal hydrated phases or metal hydroxides precipitating on the surface of calcium silicate hydrates (C-S-H), PFA and sludge particles. The progressive TCLP test results and MINTEQA2 calculation also showed the importance of Cu and Zn oxides during the leaching process. The leaching behaviors of these metals in the S/S waste materials were mainly controlled by the alkaline nature and acid buffering capacity of the S/S matrix. During the progressive TCLP tests, the alkaline conditions and acid buffering capacity of the matrix decreased with the dissolution of calcium hydroxide and C-S-H, therefore, the leaching of heavy metals in the S/S waste materials increased. The leaching of heavy metals in the S/S materials can be considered as a pH dependent and corresponding metal hydroxide solubility controlled process.

Hydrogen-Ion Concentration↗
PubMed2001

Monomeric state and ligand binding of recombinant GABA transporter from Escherichia coli.

The gamma-aminobutyric acid (GABA) transporter from Escherichia coli was homologously overexpressed and purified to homogeneity with a yield of 1.0 mg per liter culture. The purification procedure consists of a cobalt affinity column, proteolytic cleavage of His- and myc-tags, and size-exclusion chromatography. The purified transporter exists as a monomer in FOS-Choline 12 detergent, with a Stokes radius of 45 A for the protein-detergent complex. In detergent solution the protein binds substrates, as indicated by tryptophan fluorescence quenching. Its dissociation constants (K(d)) for GABA, muscimol and nipecotic acid are 13.8, 13.3 and 27.9 microM, respectively. This protein preparation provides ideal starting materials for future biochemical, biophysical and structural studies of the GABA transporter.

Bacterial Proteins↗
PubMed2001

Homeostasis of naive and memory T cell subpopulations in peripheral blood and lymphoid tissues in the context of human immunodeficiency virus infection.

To understand the nature of naive and memory T cell depletion in human immunodeficiency virus (HIV) immunopathogenesis, their homeostasis in peripheral blood (PB) and lymph node (LN) compartments of HIV-infected patients was examined. Although the percentage of naive CD4+ cells was higher in LN than in PB mononuclear cells (LNMC and PBMC, respectively), the memory cells were higher in PBMC than in LNMC. The ratio of naive:memory CD4+ cells from PB positively correlated with that in LNs and with the absolute CD4+ cell counts and recall antigen responses, and the ratio inversely correlated with the cellular virus load from the corresponding compartment. These findings indicate that although the pattern of naive and memory cells in the LN and PB compartments appear divergent, their relationship is nonrandom and is significant. The naive&rcolon;memory ratio in PB appears to reflect the lymphoid microenvironment and may potentially be useful as a surrogate marker for treatment efficacy and immune reconstitution.

Adult↗
PubMed2001

Chemokine/CD4 receptor density ratios correlate with HIV replication in lymph node and peripheral blood of HIV-infected individuals.

OBJECTIVES: Lymphoid tissue is a major reservoir for virus replication in HIV-infected subjects. The relationship of CCR5 and CXCR4 coreceptor density and HIV replication in peripheral blood mononuclear cells (PBMC) and lymph node (LN) mononuclear cells (LNMC) of HIV-infected subjects was examined. METHODS: PBMC and cervical LNMC from 12 HIV-infected patients were examined for virological and immunological parameters including chemokine receptor density, HIV plasma and cellular viral load, coreceptor usage and CD38/HLA-DR expression. RESULTS: The number of CCR5 and CXCR4 molecules on CD4 lymphocytes in the LN were significantly higher than in PBMC. In contrast the number of CD4 molecules/CD4 T cell was higher in PBMC than in LNMC. The CXCR4/CD4 and CCR5/CD4 ratios in the LN were significantly higher than in the PBMC. This was associated with a cellular viral load in the LN that was approximately 110-fold higher than in PBMC. The absolute number of coreceptor molecules per cell did not correlate with the viral load. However, the CCR5/CD4 and CXCR4/CD4 ratios in the LN positively correlated with HIV cellular and plasma RNA. Characterization of the viral isolates suggested an association between clinical isolates using a distinct coreceptor and the upregulation of the corresponding chemokine receptor. CONCLUSIONS: The ratios of chemokine receptors to CD4 molecules in CD4 T cells from LN is higher than in PBMC and may account for the relative difference in cellular viral load in these compartments. Additionally, the coreceptor/CD4 ratios, particularly in the lymphoid tissue, were highly related to HIV replication.

Adult↗
PubMed2001

Profiling of differential gene expression in activated, allergen-specific human Th2 cells.

Th2 cells play a pivotal role in the pathogenesis of allergic diseases, including asthma, but the molecular basis of the Th1/Th2 dichotomy and the precise molecular pathways leading to Th2-dominant immune responses are still unclear. To this end, we have combined suppression subtractive hybridization (SSH) and high throughput analysis of cDNA arrays spotted with IMAGE clones to determine the profile of differential gene expression in human allergen-specific Th2 cells. Allergen-stimulated Th2 cells were used as the tester, and either resting Th2 cells or stimulated Th1 cells were used as the driver. SSH was used to equalize different mRNA levels and remove common sequences between the tester and the driver. Comparison of cDNA arrays probed with subtracted tester and non-subtracted driver provided a profile of Th2-selective gene expression. Analysis of 77 sequence-confirmed and differentially expressed genes in Th2 cells showed predominant EST sequences, representing 80% of sequences analyzed. The pattern of gene expression in 19 selected sequences was further analyzed in additional Th1 and Th2 clones. A total of 15 sequences showed predominant expression in Th2 cells, while the remaining four EST sequences showed no detectable amplification signal. The database containing Th2-selective genes will further our understanding of Th2 cell function and the genetic basis of allergic diseases.

Allergens↗
PubMed2001

The treatment of osteomyelitis with gentamicin-reconstituted bone xenograft-composite.

We have developed a new drug-delivery system using reconstituted bone xenograft to treat chronic osteomyelitis. This material, which has the capabilities of osteoinduction and osteoconduction, was supplemented with up to 2000 times the minimum inhibitory concentration of gentamicin against Staphylococcus aureus to prepare a gentamicin-reconstituted bone xenograft-composite (G-RBX-C). In a rabbit model, we evaluated the release of gentamicin from this composite in vivo, its capability for induction of ectopic bone and the repair of segmental defects of the radius. There was a high level of concentration of antibiotics, which was sustained for at least ten days. In the study of induction of ectopic bone, there was abundant woven bone in the G-RBX-C group two weeks after operation. At 16 weeks after implantation of G-RBX-C the radial defects had been repaired, with the formation of lamellar bone and recanalisation of the marrow cavity. Our findings suggest that G-RBX-C may be useful in the treatment of chronic osteomyelitis.

Animals↗
PubMed2001

[Construction of human bone morphogenetic protein-2 expressing eukaryotic vector].

OBJECTIVE: To construct human bone morphogenetic protein-2(hBMP-2) expressing eukaryotic vector and observe whether it can be expressed in eukaryotic cells. METHODS: pUC19 was digested with Sal I and Xba I. The resulting Sal I-Xba I fragment (1.24 kb) which contains the full length of human BMP-2 cDNA was separated on agarose gel and ligated into eukaryotic expression vector pcDNA3 digested with XhoI and XbaI. The recombinant pcDNA3-hBMP-2 plasmid was transferred into fibroblasts cell line NIH3T3. The stable expression of hBMP-2 in the positive cells G418 selected was determined by in situ hybridization and immunohistochemical analysis. RESULTS: The two fragments digested from recombinant pcDNA3-hBMP-2 plasmid by EcoR I and Xba I represented 1.3 kb and 5.38 kb respectively by agarose electrophoresis, meanwhile the Xho I site was disappeared in pcDNA3-hBMP-2 indicating the successful construction of recombinant pcDNA3-hBMP-2 plasmid. Stable expression of hBMP-2 in pcDNA3-hBMP-2 transfected cells was confirmed by in situ hybridization and immunohistochemical analysis. CONCLUSION: hBMP-2 expressing eukaryotic vector is successfully constructed and can be expressed in eukaryonic cells.

3T3 Cells↗
PubMed2001

Inhibitory role of GDP on saikosaponin (I) stimulated enzymes secretion and rising of [Ca2+]i in rat pancreatic acini.

AIM: To study the role of guanosine diphosphate (GDP) on enzyme secretion and rising of [Ca2+]i in saikosaponin (I) [SA(I)] stimulated rat pancreatic acini. METHODS: Cell membrane of isolated rat pancreatic acini were permeabilized using streptolysin O (SLO). Enzymes secretions were indicated by detecting total protein secretions. Intracellular Ca2+ ([Ca2+]i) was measured using Fluo-3 in SPEX spectrofluorimeter. RESULTS: The inhibition of GDP on SA(I) stimulated enzymes secretion increased with increasing GDP concentration. There were two peaks in the time course of increase in [Ca2+]i evoked by SA(I) 10 micromol/L. After adding GDP 5 mmol/L, [Ca2+]i rose gradually without the two peaks. In permeabilized acini, the accumulation of enzymes stimulated by SA(I) in 30 min reduced by 57 % compared with intact acini. GDP 5 mmol/L decreased the initial rate of secretion. CONCLUSION: Inhibition of GDP on increase in [Ca2+]i reduces SA(I) stimulated enzymes secretion in pancreatic acini.

Animals↗
PubMed2000

The interaction between the regulatory light chain domains on two heads is critical for regulation of smooth muscle myosin.

Recent findings have suggested that the interaction between the two heads is critical for phosphorylation-dependent regulation of smooth muscle myosin. We hypothesized that the interaction between the two regulatory light chains on two heads of myosin dictates the regulation of myosin motor function. To evaluate this notion, we engineered and characterized smooth muscle heavy meromyosin (HMM), which is composed of one entire HMM heavy chain and one motor domain truncated heavy chain containing the S2 rod and regulatory light chain (RLC) binding site, as well as the bound RLC (SMDHMM). SMDHMM was inactive for both actin-translocating activity and actin-activated ATPase activity in the dephosphorylated state, demonstrating that the interaction between the two RLC domains on the two heads and/or a motor domain and a RLC domain in a distinct head is sufficient for the inhibition of smooth muscle myosin motor activity. When phosphorylated, SMDHMM was activated for both actin-translocating activity and actin-activated ATPase activity; however, these activities were lower than those of double-headed HMM, implying partial release of inhibition by phosphorylation in SMDHMM and/or cooperativity between the two heads of smooth muscle myosin. The present results indicate that the RLC domain is critical for phosphorylation-dependent regulation of smooth muscle myosin motor activity. On the other hand, similar to double-headed HMM, SMDHMM showed both "folded" and "extended" conformations, and the ratio of those conformations is dependent on ionic strength, suggesting that the RLC domain is sufficient to regulate the conformational transition in myosin.

Actins↗
PubMed2000

Toxicity of cinnamomin--a new type II ribosome-inactivating protein to bollworm and mosquito.

The toxicity of cinnamomin, a new type II ribosome-inactivating protein purified from the seeds of camphor tree (Cinnamomum camphora), to bollworm (Helicoverpa armigera) and mosquito (Culex pipines pallens) during larval stage was tested. The LC50 of cinnamomin to bollworm larvae fed on diet containing cinnamomin was 1839 ppm and the LC50 to larvae of mosquito was 168 ppm. The gut extract of bollworm larvae could apparently hydrolyze cinnamomin. The inhibition of protein synthesis by cinnamomin was tested in in vitro translation system of bollworm larvae, and its LC50 was determined to be approx. 14 nM. Bollworm larvae ribosome treated with cinnamomin produced a specific RNA fragment (R-fragment) characterized on urea-denatured polyacrylamide gel. Evidence was provided that hidden breaks exist in the largest ribosomal RNA of bollworm larvae.

Algal Proteins↗