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Biomedical subjects

Li Xu

Publications and source records attributed to Li Xu.

162 records · Page 9Linked to original sources
PubMed2002

Distribution and transportation of polycyclic aromatic hydrocarbons in suspended particulate matter and surface sediment from the Pearl River Estuary.

Based on the quantitative and qualitative analysis of sixteen Polycyclic Aromatic Hydrocarbons (PAHs) with GC and GC-MSD, the concentrate distribution and transportation characteristics of PAHs in suspended particulate matter (SPM) and surface sediments (SS) from the Pearl River Estuary were studied. Whether in SPM or in SS, the concentration distribution of PAHs were characterized by acenaphthene (mean 55.5 microg/g in SPM, 226 ng/g in SS) with subordinate amounts of the tri- and tetra-cycle PAHs such as fluorene, fluoranthene, phenaphene and pyrene. However, PAHs had different composition and concentration in SPM and SS. Pentacyclic PAHs appeared in SS and seldom in SPM because of their low solubility and high molecular weight. The concentrations of the tri-, tetracyclic PAHs in SPM were 100-300 times higher than those in SS. The total PAHs varied from 12-281 microg/g (mean 77 microg/g) in SPM and 208-1849 ng/g (mean 537 ng/g) in SS respectively. There were similar correlations between the concentrations of PAHs in SPM and salinity, and between the distance of the stations from the river outlet moving seawards and the concentrations of PAHs. These indicated that PAHs were degraded or transported along with the salinity gradient in SPM and the distance from the river outlet in SS. It was also suggested that the sources of these PAHs are from sewage and shipping discharge-pollutants. Pearl River Estuary had been lightly contaminated by PAHs.

Environmental Monitoring↗
PubMed2002

Transgenic study of the function of chymase in heart remodeling.

OBJECTIVES: To study the function of chymase on heart remodeling by overexpression of human chymase in the heart of transgenic mice. METHODS: Transgenic mice were produced by microinjection. The chymase mRNA levels in the heart and other tissues were assessed by competitive reverse transcriptase-polymerase chain reaction (RT-PCR). The expression of collagen I/III genes was analyzed by Northern blot hybridization. Chymase and angiotensin-converting enzyme (ACE) activities, and angiotensin II (Ang II) content in the heart were determined by radioimmunoassay (RIA). The matrix metalloprotease-9 (MMP-9) in protein and activity levels were measured by Western blot and zymogram, respectively. RESULTS: A model of transgenic mice with selective overexpression of a rat myosin light chain 2 promoter-human heart chymase (MLC(2-)-hChymase) fusion gene was produced. In MLC(2)-hChymase transgenic mice (the F(6) line), the human heart chymase gene was expressed at a high level in heart and at lower levels in skeletal muscle and kidney, while no expression was detected in the liver or lung. The heart chymase activity increased markedly in the F(6) transgenic mice versus non-transgenic mice (0.274 +/- 0.071 U/mg versus 0.152 +/- 0.021 U/mg) ( P < 0.05), with no difference in ACE activity. Heart Ang II level in the F(6) transgenic mice increased nearly threefold (1984 +/- 184 versus 568 +/- 88 pg/g protein) ( P < 0.05) but was unchanged in plasma. MMP-9 activity increased significantly in the cardiac tissue of F(6) transgenic mice ( P < 0.05), while both collagen I and the ratio of collagen I : III mRNA levels decreased significantly (both P < 0.05). The F(6) transgenic mice showed no significant changes in cardiac parameters. CONCLUSIONS: We have demonstrated selective overexpression of human chymase gene in the heart of transgenic mice, and the results support the hypothesis of a dual Ang II-forming pathway from chymase and ACE in the cardiac tissue in vivo. The results also suggest that chymase may play a role in heart remodeling by increasing Ang II formation and activating MMP-9, and the regulation of collagen I gene expression.

Angiotensin II↗
PubMed2002

Features of stimulation affecting tonal-speech perception: implications for cochlear prostheses.

Tone languages differ from English in that the pitch pattern of a single-syllable word conveys lexical meaning. In the present study, dependence of tonal-speech perception on features of the stimulation was examined using an acoustic simulation of a CIS-type speech-processing strategy for cochlear prostheses. Contributions of spectral features of the speech signals were assessed by varying the number of filter bands, while contributions of temporal envelope features were assessed by varying the low-pass cutoff frequency used for extracting the amplitude envelopes. Ten normal-hearing native Mandarin Chinese speakers were tested. When the low-pass cutoff frequency was fixed at 512 Hz, consonant, vowel, and sentence recognition improved as a function of the number of channels and reached plateau at 4 to 6 channels. Subjective judgments of sound quality continued to improve as the number of channels increased to 12, the highest number tested. Tone recognition, i.e., recognition of the four Mandarin tone patterns, depended on both the number of channels and the low-pass cutoff frequency. The trade-off between the temporal and spectral cues for tone recognition indicates that temporal cues can compensate for diminished spectral cues for tone recognition and vice versa. An additional tone recognition experiment using syllables of equal duration showed a marked decrease in performance, indicating that duration cues contribute to tone recognition. A third experiment showed that recognition of processed FM patterns that mimic Mandarin tone patterns was poor when temporal envelope and duration cues were removed.

Acoustic Stimulation↗
PubMed2002

Cortical neurons that localize sounds.

Efforts to locate a cortical map of auditory space generally have proven unsuccessful. At moderate sound levels, cortical neurons generally show large or unbounded spatial receptive fields. Within those large receptive fields, however, changes in sound location result in systematic changes in the temporal firing patterns such that single-neuron firing patterns can signal the locations of sound sources throughout as much as 360 degrees of auditory space. Neurons in the cat's auditory cortex show accurate localization of broad-band sounds, which human listeners localize accurately. Conversely, in response to filtered sounds that produce spatial illusions in human listeners, neurons signal systematically incorrect locations that can be predicted by a model that also predicts the listeners' illusory reports. These results from the cat's auditory cortex, as well as more limited results from nonhuman primates, suggest a model in which the location of any particular sound source is represented in a distributed fashion within individual auditory cortical areas and among multiple cortical areas.

Animals↗
PubMed2002

Expression patterns of cytochrome P4501B1 (Cyp1b1) in FVB/N mouse eyes.

Homozygous and compound heterozygous mutations in cytochrome P4501B1 (CYP1B1) cause primary congenital glaucoma (PCG) in humans. It is hypothesized that developmental anomalies of the trabecular meshwork prevent appropriate drainage of the aqueous humor and cause PCG in human patients. In this report, we studied the expression patterns of Cyp1b1 in the eye of albino FVB/N mouse at different developmental stages. We isolated a cDNA fragment corresponding to the 3'untranslated region (3'UTR) of the Cyp1b1 gene by PCR and used it to make an (35)S-labelled riboprobe for in situ hybridization. We found that Cyp1b1 is expressed in both anterior and posterior segments of the eye. Anteriorly, the expression is confined to the ciliary body, most likely in the outer/pigmented ciliary epithelial cells. Cyp1b1 mRNA can be detected in these cells at postnatal day 4 (P4) and the expression continues into adulthood. Surprisingly, no above-background levels of Cyp1b1 mRNA were found at or around the trabecular meshwork at all the stages we examined. In the posterior region of the embryonic day 15 (E15) eye, Cyp1b1 is expressed in the retinal neuroepithelium and in the tissues surrounding the optic nerve, but not in the optic nerve itself. In the P7 retina, Cyp1b1 mRNA is found in the inner nuclear layer. Based on our finding that Cyp1b1 is expressed in the developing and mature ciliary body of the mouse eye, we speculate that mutation in this gene can directly contribute to the abnormal elevation of the intraocular pressure (IOP) in the PCG patients or indirectly affect the aqueous outflow by disrupting the proper development of the trabecular meshwork in these patients.

3' Untranslated Regions↗
PubMed2002

Clinical evaluation of bioactive glass in the treatment of periodontal intrabony defects.

OBJECTIVE: To evaluate the effect of a new product of bioactive glass, Perioglas((R)) on human periodontal intrabony defects. METHODS: Twenty periodontal intrabony defects in 10 healthy adults were selected. Four weeks after an initial therapy, they were randomly assigned to either a BAG experimental (open flap debridement with BAG, totally 13 defects) or a control OFD (simple open flap debridement, totally 7 defects) group. For both groups, routine flap procedure was performed, but the Perioglas((R)) was implanted only in the BAG group. The followings were recorded before the operation and repeated at the 3rd and 6th month evaluations: plaque index (PLI), bleeding index (BI), gingival recession (REC), probing depth (PD) and clinical attachment loss (CAL). RESULTS: At the 3rd and 6th months after operation, both groups showed significant reduction in PD and CAL. PD and CAL in BAG group at baseline were 6.19 mm and 6.31 mm, which were 3.23 mm and 3.65 mm at 6th after surgery, respectively. PD and CAL in OFD group at baseline were 6.86 mm and 7.71 mm, which were 4.50 mm and 5.35 mm at 6 th after surgery, respectively. And the BAG group showed significant reduction in BI, which from 2.77 at baseline to 0.65 at 6th month post-operation. BI, PD and CAL in BAG group were significantly lower than those in OFD group. The reduction of BI in BAG group was significantly more than that in OFD group. CONCLUSIONS: The bioactive glass is effective as an adjunct to conventional surgery in the treatment of intrabony defects.

Adult↗
PubMed2002

[Clinical analysis of 55 ovarian metastatic tumors from digestive system].

BACKGROUND & OBJECTIVES: Ovarian metastasis of digestive system tumors is a special way of tumor metastasis, which the diagnosis and treatment are difficult. The objective of this paper is to seek the clinical characteristics of ovarian metastatic tumors from digestive system, to aid correct diagnosis and treatment, so that to improve their curative effect. METHODS: The authors collected the information of 55 patients with ovarian metastatic tumors from digestive system, and analyzed 12 items of the patients including their age, menorrhea and child-bearing, details of original tumors and metastatic tumors, pathologic types, ascites, clinical symptoms, tumor markers, time of metastasis, diagnosis, treatment, curative effect, etc. RESULTS: Misdiagnosis rate of the team was 30.9%. Survival rate of 1 year, 3 years, and 5 years were 22.4%, 4.1%, and 2.0% in 49 patients, followed up respectively. CONCLUSION: Ovarian metastatic tumors from digestive system are easy to be misdiagnosed, and have poor prognosis. Careful long-term follow-up and active operation and chemotherapy may be effective to improve their curative effect.

Adult↗
PubMed2002

[Affection of neoadjuvant chemotherapy on cell apoptosis and proliferation in breast cancer].

BACKGROUND & OBJECTIVE: Although the researches had verified various kinds of chemotherapic agents can cause the apoptosis of breast cancer cells, but the reports with in vivo data are still scarce. This paper is to investigate whether neoadjuvant chemotherapy could induce tumor cell apoptosis in breast cancer patients, and its effect on cell proliferation. METHODS: Apoptosis index (AI) of tumor cells is assayed by TdT-mediated dUTP nick end labeling(TUNEL) and proliferating cell nuclear antigen (PCNA) is examined by immunohistochemical labelled streptavidin biotin (ISAB) in 100 beast cancer samples. RESULTS: Tumor cell AI in neoadjuvant group (mean = 7.47%) was significantly higher than that in control group (mean = 4.83%) (P < 0.01). PCNA positive expression rate in neoadjuvant group (mean = 33.71%) was significantly lower than that in control group (mean = 51.52%) (P < 0.01). There was significant negative association between AI and PCNA in both neoadjuvant chemotherapy group and control group (P < 0.05). CONCLUSION: Neoadjuvant chemotherapy could induce tumor cell apoptosis and inhibit tumor cell proliferation in human breast cancer.

Apoptosis↗
PubMed2002

Teeth with periodontal bone loss, cigarette smoking and plasma cotinine levels.

The aim of the present study is to assess teeth with periodontal bone loss, cigarette smoking and plasma cotinine levels. We enrolled 120 untreated periodontal patients with chronic periodontitis into the study. The group comprised 48 men and 72 women, ranging in age from 21 to 75 years (mean age, 42.4 years). We divided the patients into five groups based on self-reported smoking status: (1) heavy smokers (n=35); (2) light smokers (n = 17); (3) recent former smokers (n = 8); (4) long-term former smokers (n = 17); (5) non-smokers (n = 43). We calculated packyear: (number of cigarette/day/20 x years) for all smokers. Smoking status was confirmed by measurement of plasma cotinine levels in 116 subjects. Periodontal disease was assessed on a full set of periapical radiographs. The number of teeth with bone loss was scored in four categories (no bone loss, light bone loss, moderate bone loss or serious bone loss) in all patients. The results demonstrated that plasma cotinine levels correlated significantly with the number of cigarettes smoked per day. Moreover, heavy smokers had fewer teeth with no bone loss (P < 0.001) and more teeth with moderate bone loss (P < 0.001) than non-smokers. In addition, we found a negative correlation between packyears and the number of teeth with no bone loss (P < 0.04) and a positive correlation between packyears and the number of teeth with light bone loss (P < 0.005). However, we found no correlation between plasma cotinine levels and the number of teeth with bone loss. These clinical findings suggest that cigarette smoking affects the number of teeth with or without periodontal bone loss, and this effect is related to the degree of smoking exposure.

Adult↗
PubMed1999

Down-regulation of Hsp90 could change cell cycle distribution and increase drug sensitivity of tumor cells.

AIM:To construct Hsp90 antisense RNA eukaryotic expression vector, transfect it into SGC7901 and SGC7901/VCR of MDR-type human gastric cancer cell lines, HCC7402 of human hepatic cancer and Ec109 of human esophageal cancer cell lines, and to study the cell cycle distribution of the gene transected cells and their response to chemotherapeutic drugs.METHODS:A 1.03kb cDNA sequence of Hsp90beta was obtained from the primary plasmid phHSP90 by EcoR I and BamH I nuclease digestion and was cloned to the EcoR I and BamH I site of the pcDNA by T4DNA ligase and an antisense orientation of Hsp90beta expression vector was constructed. The constructs were transfected with lipofectamine and positive clones were selected with G418. The expression of RNA was determined with dot blotting and RNase protection assay, and the expression of Hsp90 protein determined with western blot. Cell cycle distribution of the transfectants was analyzed with flow cytometry, and the drug sensitivity of the transfectants to Adriamycin (ADR), vincrinstine (VCR), mitomycin (MMC) and cyclophosphamide (CTX) with MTT and intracellular drug concentration of the transfectants was determined with flow cytometry.RESULTS:In EcoR I and BamH I restriction analysis, the size and the direction of the cloned sequence of Hsp90beta remained what had been designed and the gene constructs were named pcDNA-Hsp90.AH-SGC7901, AH-SGC7901/VCR, AH-HCC7402 and AH-Ec109 cell clones all expressed Hsp90 anti-sense RNA. The expression of Hsp90 was down-regulated in AH-SGC7901, AH-SGC7901/VCR, AH-HCC7402 and AH-Ec109 cell clones. Cell cycle distribution was changed differently. In AH-SGC7901/VCR and AH-Ec109 cells, G(1) phase cells were increased; S phase and G(2) phase cells were decreased as compared with their parental cell lines. In AH-SGC7901 cell, G(1)phase cells were decreased, G(2) phase cells increased and S phase cells were not changed, and in AH-HCC7402 cells G(1), S and G(2) phase cells remained unchanged as compared with their parental cell lines. The sensitivity of AH-SGC7901, AH-SGC7901/VCR, AH-HCC7402 and AH-Ec109 to chemotherapeutic drugs, the sensitivity of AH-SGC7901/VCR to ADR, VCR, MMC and CTX the sensitivity of AH-HCC7402 to ADR and VCR, and the sensitivity of Ec109 to ADR, VCR and CTX all increased as compared with their parental cell lines. The mean fluorescence intensity of ADR in AH-SGC7901, AH-SGC7901/VCR, AH-HCC7402 and AH-Ec109 was also significantly elevated (P < 0.05).CONCLUSION: Down-regulation of Hsp90 could change cell cycle distribution and increase the drug sensitivity of tumor cells.

Journal Article↗
PubMed1996

Functional Domains of the Regulatory Factor PHO81 of Saccharomyces cerevisiae.

It is found that minor changes around the basic motif (88-160) and the acidic motif (771-810) of the PHO81 protein can lead to the constitutive expression of the acid phosphatase gene (PHO5), and the two motifs work cooperatively. The PHO81 protein has six ankyrin repeats, which are the recognition sites of PHO81 protein with the PHO80-PHO85 protein complex. It is found that the ankyrin repeats 1,2,4,5 and 6 are important for the PHO81 protein, but the deletion of Pro(509) and Leu(510) in ankyrin repeat 3 does not affect the PHO81 protein. We have found a candidate nucleoplasmin-like nuclear location sequence at 701-719 of the PHO81 protein and the deletion of the corresponding DNA fragment inactivates the PHO81 protein. However, when the conservative amino acids Arg701 and Lys702 are constituted by Ser and Gln, or Lys717 replaced by Asn, or Arg719 is turned to Ser, the function PHO81 protein is not affected.

Journal Article↗
PubMedDate not supplied

Pharmacological analysis of the rat cone electroretinogram.

The electroretinogram (ERG) of the cone system provides a useful noninvasive measure of the activity of the cone pathway. Despite a wide application of the cone ERG in the study of rodent models of human hereditary retinal disease, the cellular origins of the rat cone ERG have not been well defined. Here, we address this issue using a pharmacological approach that has been used previously to derive ERG response components. Agents that impair synaptic transmission at well-defined retinal loci were dissolved in saline and injected into the vitreous of adult Sprague-Dawley rats anesthetized with ketamine/xylazine, and cone ERGs were recorded approximately 2 h later. Analysis of the resulting waveforms indicated that the rat cone ERG includes a relatively small-amplitude component of negative polarity that is derived from the activity of cone photoreceptors, and perhaps retinal glial (Müller) cells. The cone depolarizing bipolar cell pathway contributes a positive potential of large amplitude to the rat cone ERG. In comparison, the contribution of hyperpolarizing bipolar cells is of negative polarity and of much smaller amplitude. The inner retina contributes a negative wave upon which higher frequency oscillations are superimposed. These results provide a foundation for interpreting changes in the waveform of the rat cone ERG that may be observed following genetic alteration or other experimental treatment.

Adult↗
PubMedDate not supplied

Spatial composition of prostate cancer spheroids in mixed and static cultures.

Aggregation of neoplastic cells produces multicellular spheroids resembling micrometastases. The objective of this study was to investigate the effects of mixing culture medium on the spatial composition of spheroids prepared from well (LNCaP) and poorly (DU 145) differentiated human prostate cancer cells. Spheroids were cultured in a mixed suspension within a high-aspect rotating wall vessel and static liquid-overlay plate. Results from this study demonstrate that mixed cultures consistently manifested differences in morphology and composition between DU 145 and LNCaP spheroids. For example, 40 +/- 12% of DU 145 cells were Ki-67 positive 100 microm from the surface within mixed spheroids versus 0% for LNCaP cells; there was no significant difference in this spatial profile for static cultures. The results suggest that poorly differentiated spheroids may be more likely to experience a change in composition from mixing culture medium than well-differentiated spheroids, due to low tissue density. Immunostaining for P-glycoprotein is representative of this trend; average staining intensity increased 50% for DU 145 spheroids on mixing but was unchanged for LNCaP spheroids. The effects of mixing on spheroid composition were attributed to faster interstitial mass transport. Applications include drug development and delivery, as well as basic research on drug action and resistance.

Cell Line, Tumor↗
PubMedDate not supplied

Regulation of LDL receptor expression by the effect of curcumin on sterol regulatory element pathway.

To investigate the molecular mechanisms of the effect of curcumin on up-regulation of LDL receptor expression, a sterol regulatory report system was established in Xenopus laevis oocytes by microinjection of a plasmid pLXRN-4SRE-fPA, in which green fluorescence protein (GFP) gene was constructed downstream from the sterol regulatory element-1 (SRE-1), in the nucleus of the oocytes. The oocytes were treated with different kinds of natural medicines: curcumin, tea polyphenols, tanshinone, ligustrazine, ginkgolide, astragalosides. The expression of GFP was induced only by curcumin. In addition, it was also proved that the curcumin can increase the expression of functional LDL receptors in human liver hepatoma cell line HepG2. In conclusion, curcumin may up-regulate the expression of LDL receptor by its effect on SRE pathway.

Animals↗