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L C Xu

Publications and source records attributed to L C Xu.

15 recordsLinked to original sources
PubMed2004

Study on the relation between occupational fenvalerate exposure and spermatozoa DNA damage of pesticide factory workers.

AIMS: To determine sperm nuclear DNA integrity and to investigate the relation between fenvalerate (FE) exposure and spermatozoa DNA damage. METHODS: Sperm DNA fragmentation was detected by a modified alkaline single cell gel electrophoresis (Comet) assay and a terminal deoxynucleotidyl transferase mediated dUTP nick end labelling (TUNEL) assay. The olive tail moment (OTM) and percentage tail DNA were measured by the Comet assay, and cell positive percentage was measured by the TUNEL assay for DNA damage evaluation. RESULTS: The DNA integrity of spermatozoa of external and internal control groups were both significantly greater than that of the FE exposed group. The median value of tail DNA percentage in the exposure group was 11.30, which was significantly higher than 5.60 in the internal control group and 5.10 in the external control group. The median value of OTM was 3.80 in the exposure group, significantly higher than 1.50 in the internal control group and 2.00 in the external control group. Mean cell positive was 31.2% in the exposure group, significantly higher than 17.4% in the internal control and 19.6% in the external control groups. Cell positive (%) was significantly correlated with tail DNA percentage and with OTM of whole subjects (n = 63). CONCLUSIONS: Results showed that occupational FE exposure is associated with an increase in sperm DNA damage. A combination of the Comet and TUNEL assays would offer more comprehensive information for a better understanding of sperm DNA damage, and the biological significance of sperm DNA damage in sperm function and male infertility.

Adult↗
PubMed2001

Effects of cadmium on rat sperm motility evaluated with computer assisted sperm analysis.

OBJECTIVE: To study effects of cadmium on rat sperm motility evaluated with computer assisted sperm analysis. METHODS: Different doses of cadmium chloride (0.2, 0.4, 0.8 mg Cd/kg BW) were administrated i.p. to adult male Sprague-Dawley rats. Control animals received the same volume of 0.9% NaCl solution. After 7 days, the rats were sacrificed with their testes removed. A part of one testis was used for testicular sperm head counts and daily sperm production observation. The motility of spermatozoa obtained from cauda epididymides using the "diffusion" method was measured by computer assisted sperm analysis (CASA). RESULTS: The sperm head counts and daily sperm production decreased significantly in the high dose group. The motility of spermatozoa in the middle dose group was reduced significantly. No motile sperm was found in the high dose group. The results suggest that germinal epithelium was impaired irreversibly in a short time to produce toxic effects on spermatogenesis at high cadmium doses. CONCLUSION: Cadmium may reduce sperm motility at a dose far below the dose affecting sperm production at this time point. The motility of sperm is an early and sensitive endpoint for the assessment of cadmium toxicity on male reproduction.

Animals↗
PubMed2000

Quantification of bacterial adhesion forces using atomic force microscopy (AFM).

This study demonstrated that atomic force microscopy (AFM) can be used to obtain high-resolution topographical images of bacteria, and to quantify the tip-cell interaction force and the surface elasticity. Results show that the adhesion force between the Si3N4 tip and the bacteria surface was in the range from -3.9 to -4.3 nN. On the other hand, the adhesion forces at the periphery of the cell-substratum contact surface ranged from -5.1 to -5.9 nN and those at the cell-cell interface ranged from -6.5 to -6.8 nN. The two latter forces were considerably greater than the former one, most likely due to the accumulation of extracellular polymer substance (EPS). Results also show that the elasticity varied on the cell surface.

Aluminum Silicates↗
PubMed2000

Changes in tissue metals after cadmium intoxication and intervention with chlorpromazine in male rats.

Cadmium (Cd), one of the most dangerous heavy metals, has a very similar ionic radius to calcium (Ca). The interference of cadmium in calcium homeostasis may play an important role in cadmium toxicity. Recent reports indicate that calmodulin (CaM) inhibitors such as trifluoperazine and chlorpromazine (CPZ) could protect rodents against cadmium toxicity. It was also reported that pretreatment of mice with zinc (Zn) could reduce the adverse effects induced by cadmium. The aim of this study is to determine whether Cd changes the balance of other essential metals such as Zn and copper (Cu) in rat tissues, and whether CPZ can reverse these changes which are induced by cadmium intoxication. Adult male Sprague-Dawley (SD) rats were injected intraperitoneally (i.p.) with cadmium chloride (CdCl2) (0.2, 0.4, 0.8 mg Cd/kg body weight) alone and 0.4 mg Cd/kg in association with CPZ (5 mg/kg) daily for a week. The control animals were injected with normal saline only. The results showed that the cadmium content in the liver, kidney and testis increased significantly with a dose-response relationship. Cadmium treatment markedly increased the Zn and Ca content in some of the tissues. Hepatic and renal metallothionein (MT) increased significantly after cadmium intoxication. CPZ treatment, however, reduced cadmium content in liver, but not blood and kidney. CPZ seemed to decrease the content of MT in liver and significantly increase the amounts of MT in kidney. These data suggest that the intervention of cadmium with tissue essential metals may play a role in cadmium toxicity in rats, and calmodulin inhibitors to some extent can reduce the adverse effect of cadmium by decreasing the cadmium load in tissues and reversing the unbalance of essential metals.

Animals↗
PubMed1998

Synthesis and evaluation of hydroxamamide-based tetradentate ligands as a new class of thiol-free chelating molecules for 99mTc radiopharmaceuticals.

Both N,N'-ethylene bis(benzohydroxamamide) [(C2(BHam)2)] and N,N'-propylene bis(benzohydroxamamide) [(C3(BHam)2)] were designed as new thiol-free chelating molecules for 99mTc radiopharmaceuticals. Synthetic procedures using oxadiazoline intermediates were developed for C2(BHam)2 and C3(BHam)2. Both C2(BHam)2 and C3(BHam)2 formed 99mTc complexes with high yields over a wide pH range (pH 3-12) at room temperature. Complexation yields of over 95% were achieved at ligand concentrations as low as 2.5 x 10(-6) M. Reversed-phase HPLC analyses indicated that both C2(BHam)2 and C3(BHam)2 formed 99mTc complexes as single species with stabilities much higher than those of 99mTc-BHam. Selective complex formation of 99mTc with the two ligands was observed in the presence of human IgG. No decomposition with low protein binding were demonstrated when the two 99mTc complexes were incubated in murine plasma. Although further structural studies are required, these findings implied that the Ham-based tetradentate ligands would serve as new chelating molecules for 99mTc radiopharmaceuticals.

Animals↗
PubMed1995

Growth factors and stromal support generate very efficient retroviral transduction of peripheral blood CD34+ cells from Gaucher patients.

We have achieved high-efficiency gene transfer into nonmobilized peripheral blood (PB) CD34+ cells from patients with Gaucher's disease using a clinically acceptable retroviral supernatant transduction protocol. In our studies, bone marrow (BM) and PB CD34+ cells were transduced using a high titer (10(8) particles/mL) retroviral supernatant once a day for 4 consecutive days in the presence of interleukin-3 (IL-3), IL-6, and stem cell factor (SCF), with or without an irradiated allogeneic BM stromal layer. The growth factors alone resulted in 29% +/- 10% gene transfer of PB CD34+ clonogenic cells in contrast with 71% +/- 17% gene transfer efficiency using stroma with the growth factors; a 2.5-fold increase. The increase in gene transfer efficiency was less prominent when BM CD34+ cells were used (40% +/- 16% without and 57% +/- 8% with stroma, a 1.5-fold increase). The overall transduction efficiency of both PB and BM CD34+ cells was lower when the cells were transduced over a stromal cell layer without added growth factors. The combination of IL-3, IL-6, and SCF with stroma transduced 75% of primitive long-term culture initiating cells (PB LTC-ICs) in comparison with 34% of LTC-ICs when IL-3, IL-6, and SCF were used without stromal support. Using this clinically acceptable supernatant/cytokines/stroma transduction protocol, correction of the glucocerebrosidase (GC) deficiency in the progeny cells of PBLTC-ICs from Gaucher's-disease patients has been accomplished. Efficient transduction of the PB CD34+ cells using this transduction protocol may allow repeated delivery of "GC-corrected" hematopoietic stem and progenitor cells to Gaucher's-disease patients.

Antigens, CD↗
PubMed1995

Long-term in vivo expression of the human glucocerebrosidase gene in nonhuman primates after CD34+ hematopoietic cell transduction with cell-free retroviral vector preparations.

Successful gene transfer into stem cells would provide a potentially useful therapeutic modality for treatment of inherited and acquired disorders affecting hematopoietic tissues. Coculture of primate bone marrow cells with retroviral producer cells, autologous stroma, or an engineered stromal cell line expressing human stem cell factor has resulted in a low efficiency of gene transfer as reflected by the presence of 0.1-5% of genetically modified cells in the blood of reconstituted animals. Our experiments in a nonhuman primate model were designed to explore various transduction protocols that did not involve coculture in an effort to define clinically useful conditions and to enhance transduction efficiency of repopulating cells. We report the presence of genetically modified cells at levels ranging from 0.1% (granulocytes) to 14% (B lymphocytes) more than 1 year following reconstitution of myeloablated animals with CD34+ immunoselected cells transduced in suspension culture with cytokines for 4 days with a retrovirus containing the glucocerebrosidase gene. A period of prestimulation for 7 days in the presence of autologous stroma separated from the CD34+ cells by a porous membrane did not appear to enhance transduction efficiency. Infusion of transduced CD34+ cells into animals without myeloablation resulted in only transient appearance of genetically modified cells in peripheral blood. Our results document that retroviral transduction of primate repopulating cells can be achieved without coculture with stroma or producer cells and that the proportion of genetically modified cells may be highest in the B-lymphoid lineage under the given transduction conditions.

Animals↗
PubMed1994

Poor transduction efficiency of human hematopoietic progenitor cells by a high-titer amphotropic retrovirus producer cell clone.

The transduction efficiency of human bone marrow CD34+ cells with supernatants from the retrovirus producer cell clone PA317/LGSN 16 was only one-fifth of that with supernatants from GP+ envAm12/LGSN 15, even though both producers had similar infection titers on 3T3 cells. PA317/LGSN 16-conditioned medium inhibited the proliferation of the bone marrow CD34+ cells, and this inhibitory effect was partially blocked by anti-transforming growth factor beta antibodies. These studies suggest that cytokine secretion plays a role in the suppression of retrovirus transduction of human CD34+ cells.

3T3 Cells↗
PubMed1993

Induction of cytochrome P450IA1 and its recombinant construct in H4IIE rat hepatoma cells.

1. Our previous studies have shown that benzo(a)pyrene (BP), 3-methylcholanthrene (3MC) and tetrachlorodibenzofuran (TCDBF) can induce the expression of the cytochrome P450IA1 mRNA in the rat hepatoma cell line, H4IIE, although the kinetics of induction differed. 2. In the present study, by using biochemical, immunochemical and recombinant DNA approaches, the effects of these inducers have been examined on the steady state level of endogenous cytochrome P450IA1 protein and on induction of chloramphenicol acetyltransferase activity (CAT) in the H4IIE cells transfected with pMC1CAT (a recombinant construct consisting of CAT linked to 5' upstream DNA sequence of the rat cytochrome P450IA1 gene). 3. From 7-ethoxyresorufin O-deethylase activity (EROD) and immunochemical analysis of cytochrome P450IA1, the optimal concentrations of BP, 3MC and TCDBF for induction in the H4IIE cells were determined as 1, 0.1-1 and 0.1 microM, respectively. 4. The elevated expression of the protein was more sustained in the TCDBF-exposed cells than in the BP or 3MC-treated cells. 5. After 1.5 hr of treatment, little if any detectable P450IA1 protein was observed in the H4IIE cells although a considerable amount of mRNA was present. 6. In addition, no cytochrome P450IA2 protein was detected in the control or induced H4IIE cells. 7. H4IIE cells were transfected by pMC1CAT, and the induction ratio of CAT expression in the transfected H4IIE cells after BP, 3MC or TCDBF treatment was 10-, 17- and 40-fold, respectively. 8. These results indicate that the rat H4IIE cell line offers a valid homologous system for studies of the regulation of the rat cytochrome P450IA1 gene.

Animals↗
PubMed1993

Rat CYP1A1 negative regulatory element: biological activity and interaction with a protein from liver and hepatoma cells.

Rat CYP1A1 promoter activity was suppressed by the presence of a cis negative regulatory element (NRE) at position -843 to -746 in transiently transfected rat H4IIE and human HepG2 hepatoma cells. Removal of the NRE from the promoter-fusion gene constructs caused an increase in the basal promoter activity of 2-6-fold. Co-transfection of the NRE-containing or non-NRE-containing CYP1A1 promoter-fusion gene constructs with a cloned rat NRE, i.e., pNRE, into HepG2 cells caused a 2-fold or greater reduction in constitutive and induced promoter activities. 2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced expression of the endogenous human CYPA1 was also inhibited by transfection of pNRE into HepG2 cells. Deletion of the sequence from base pairs (bp) -658 to -269 in the NRE-containing construct caused a dramatic decrease of constitutive expression in transiently transfected HepG2 cells, compared with an identical construct that lacked the NRE. Deletion of the sequences between bp -658 and -158 in the CYP1A1 promoter did not affect reporter gene activity, indicating a second site of interaction. At least three different rat liver nuclear proteins bound to the rat NRE, as determined by gel mobility shift and DNase I footprinting assays. A 32-bp sequence within the rat NRE, with significant sequence identity to the 26-bp c-myc, fos/jun-octamer-binding, NRE, was protected from DNAse I cleavage by rat liver nuclear extracts. These data suggested a role for this region in the negative regulation of rat CYP1A1.

Animals↗
PubMed1991

Upstream box/TATA box order is the major determinant of the direction of transcription.

Mammalian gene promoters for transcription by RNA polymerase II are typically organized in the following order: upstream sequence motif(s)/TATA box/initiation site. Here we report studies in which the order, orientation and DNA sequences of these three elements are varied to determine how these affect polarity of transcription. We have constructed promoters with an 'octamer' upstream sequence ATTTGCAT (or its complement ATGCAAAT) in combination with several different TATA boxes and initiation (cap) sites, and tested these promoters in transfection experiments with cultured cells. TATA boxes derived from the adenovirus major late promoter (TATAAAA), immunoglobulin kappa light chain (TTATATA) and heavy chain (TAAATATA) promoter functioned equally well or even better when inverted. Only the beta-globin TATA box (CATAAAA) was poorly active when inverted. In addition, a symmetrical TATA box (TATATATA) derived from a casein gene was very active. Our results suggest that the asymmetry of most TATA boxes (consensus TATAAAA) is not a primary determinant of the polarity of transcription. We also found that the initiation (cap) site, which usually consists of an adenine embedded in a pyrimidine-rich region (PyPyCAPyPyPyPyPy), was permissive towards sequence alterations; even a randomly composed sequence worked well. However, an inverted, hence purine-rich, cap site reduced transcript levels to 1/7th, as did an oligo G sequence. Irrespective of the presence of a cap site, the configuration: 'TATA box/octamer' yielded a strong leftward, rather than rightward transcription. From this, we conclude that the polarity of transcription is primarily determined by the linear order of an upstream sequence relative to a TATA box, rather than by the individual orientations of either of these two elements.

Adenoviridae↗
PubMed1991

Presence of the 4 S polycyclic hydrocarbon-binding protein in H4-II-E cells.

The 4 S polycyclic aromatic hydrocarbon (PAH)-binding protein had been implicated in regulating the expression of rat cytochrome P450IA1 which is most closely associated with aryl hydrocarbon hydroxylase (AHH). We have now investigated the presence of both the 4 S PAH-binding protein and the 8 S Ah receptor in rat hepatoma H4-II-E cells as well as the induction of P450IA1 upon their exposure to PAH's such as benzo[a]pyrene (BP) and 3-methylcholanthrene (3MC), and halogenated dioxins such as 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDBF). Sucrose density gradient analyses and hydroxylapatite assays indicate that, in addition to the 8 S protein, the 4 S PAH binding protein is present in these cells. This protein interacts in a saturable and high affinity manner with BP and 3MC, but not with TCDD or TCDBF. Using a P450IA1 probe, the induction of gene expression was observed by Northern blot analysis of total cellular RNA after exposure of the H4-II-E cells to BP, 3MC, or TCDBF. Since the 4 S protein was observed to interact only with BP and 3MC, these results suggest that this protein may also play a role in the PAH-induced expression of cytochrome P450IA1 gene expression in H4-II-E.

Animals↗
PubMed1990

Induction of cytochrome P450IA1 in rat hepatoma cell by polycyclic hydrocarbons and a dioxin.

In this study, the effects of benzo[a]pyrene (BP), 3-methylcholanthrene (3MC) and tetrachlorodibenzofuran (TCDBF) on the expression of the cytochrome P450IA1 gene in the rat hepatoma cell line H4IIE were examined. The initial rate of increase in the steady-state concentration of the mRNA for this gene was similar with each of these inducers; however, the elevated level of this mRNA was more sustained after TCDBF treatment. Nuclear run-off assays suggested that the elevated level of the mRNA was caused principally by an effect upon transcription.

Animals↗
PubMedDate not supplied

Bis(hydroxamamide)-based bifunctional chelating agent for 99mTc labeling of polypeptides.

To develop chelating molecules that provide 99mTc-labeled polypeptides of high in vivo stability and high specific activities under mild reaction conditions, an asymmetrical bis(benzohydroxamamide) compound with an amine group, 4'-aminomethyl-N,N'-trimethylenedibenzohydroxamamide [NH2-C3(BHam)2], was designed and synthesized. The amine residue of NH2-C3(BHam)2 was converted to a maleimide group by reaction with N-succinimidyl-6-maleimidohexanoate, and the conjugation product was coupled to thiol groups of a monoclonal antibody against osteogenic sarcoma (OST7, IgG1) pretreated with 2-iminothiolane to prepare C3(BHam)2-OST7. 99mTc radiolabeling of C3(BHam)2-OST7 was performed by the exchange reaction with [99mTc]glucoheptonate. [99mTc]C3(BHam)2-OST7 was further characterized using directly radioiodinated OST7 ([125I]OST7) and [111In]labeled OST7 with 1-[4-[(5-maleimidopentyl)amidobenzyl]ethylenediamine-N,N, N'N'-tetraacetic acid (EMCS-Bz-EDTA) as references. [99mTc]C3(BHam)2-OST7 was obtained with radiochemical yields of over 94% at protein concentrations as low as 0.2 mg/mL at room temperature for 1 h. [99mTc]C3(BHam)2-OST7 remained stable after incubation in freshly prepared murine plasma and in the presence of cysteine. Similar binding affinities to tumor cells were observed between [99mTc]C3(BHam)2-OST7 and [125I]OST7. When injected into normal mice, [99mTc]C3(BHam)2-OST7 exhibited radioactivity levels in the blood similar to [111In]-EMCS-Bz-EDTA-OST7 up to 24 h postinjection with significantly faster elimination rate of the radioactivity from the liver. In nude mice bearing osteogenic sarcoma, no significant differences were observed in the radioactivity levels in the blood and the tumor between [99mTc]C3(BHam)2-OST7 and [125I]OST7 at 24 h postinjection. These findings indicated that C3(BHam)2 provided 99mTc chelate of high stability at low concentrations even when conjugated to an intact antibody. Such characteristics render bis(hydroxamamide) compounds useful as chelating molecules for preparation of 99mTc-labeled polypeptides.

Amides↗