Biomedical subjects

R Xu

Publications and source records attributed to R Xu.

At least 55 records · Page 3Linked to original sources

PubMed2001

Selection and orientation of adjacent genes influences DAM-mediated male sterility in transformed maize.

Anther-targeted expression of E. coli DNA (Adenosine-N6-)-Methyltransferase (DAM) in maize was tested as a means to produce male-sterile plants. A high frequency of male-sterile plants with reduced anther size was observed when DAM was regulated by the maize anther-specific promoter 5126 (5126:DAM) and placed upstream of the herbicide resistance gene, pat, regulated by the cauliflower mosaic virus (CaMV) 35S promoter (35S:PAT). In contrast, placement of 5126:DAM upstream of a pat gene regulated by either the maize ubiquitin (UBI:PAT) or rice actin (rACTIN:PAT) promoters resulted in male-fertile plants. Based on these observed differences, DAM-mediated sterility was used as a phenotypic marker to assess the contribution of factors affecting gene expression such as orientation of the transcription units, choice of regulatory sequences mediating expression of adjacent genes, and effects of varying the anther-specific promoter regulating DAM. Constructs that place a portion of the CaMV 35S promoter, including the native AS-1 sequences, between 5126:DAM and UBI:PAT yielded a high frequency of male-sterile plants with reduced anther size. Significant differences in the frequency of male-sterile events and the associated anther size were also observed when the position of 35S:PAT was changed relative to 5126:DAM. These data provide evidence that gene expression in transformed maize plants can be impacted by simply altering the order, orientation or regulatory sequences of adjacent genes.

Acetyltransferases↗

PubMed2001

Quantitative comparison of expression with adeno-associated virus (AAV-2) brain-specific gene cassettes.

This study compared a range of mammalian CNS expression cassettes in recombinant adeno-associated virus (AAV-2) vectors using strong endogenous promoter sequences, with or without a strong post-regulatory element and polyadenylation signal. Changes in these elements led to transgene expression varying by over three orders of magnitude. In experiments conducted in primary cell culture and in >100 stereotactically injected rats, we observed highly efficient and stable (>15 months) gene expression in neurons and limited expression in glia; the highest expression occurred with endogenous, nonviral promoters such as neuron-specific enolase and beta-actin. The packaging size of AAV-2 was maximized at 5.7 kb without impairing gene expression, as judged by direct comparison with a number of smaller AAV-2 constructs. The genomic insert size and titer were confirmed by Southern blot and quantitative PCR, and infectivity was tested by particle titer using ELISA with a conformation-dependent epitope that requires the full intact capsid. A packaging and purification protocol we describe allows for high-titer, high-capacity AAV-2 vectors that can transduce over 2 x 10(5) neurons in vivo per microliter of vector, using the strongest expression cassette.

Animals↗

PubMed2001

Umbilical cord blood progeny cells that retain a CD34+ phenotype after ex vivo expansion have less engraftment potential than unexpanded CD34+ cells.

BACKGROUND: Because of the limitation of cell numbers associated with cord blood harvests, there is a need to determine the efficacy of using ex vivo-expanded cord blood cells in a transplantation setting. In this study, limiting-dilution analysis was used in nonobese diabetic mice with severe combined immunodeficiency (NOD/SCID) to compare the engraftment potential of progeny cells expressing the CD34+ phenotype after expansion with that of uncultured CD34+ cells. STUDY DESIGN AND METHODS: Cord blood CD34+ cells were cultured in Iscove's modified Dulbecco medium supplemented with 10-percent fetal calf serum (FCS) and IL-6, SCF, megakaryocyte growth and development factor, and Flt3 ligand. The resulting ex vivo-expanded products were assessed for total numbers of nucleated cells, CD34+ cells, and CFUs and long-term culture-initiating cell activity. The engraftment potentials of cultured progeny CD34+ cells and uncultured CD34+ cells were determined by using NOD/SCID mice. RESULTS: After 14 days of culture, total nucleated cell counts increased over input values by 180 +/- 59-fold, CD34+ cell numbers by 44 +/- 13-fold, CFU activity by 23 +/- 5-fold, and long-term culture-initiating cell activity by 20 +/- 6-fold (mean +/- SD; n = 6). The frequency of SCID-repopulating cells (SRC) in mice transplanted with uncultured products was 1 per 20,000 CD34+ cells (95% CI, 1:10,000-1:38,000) and that in mice receiving ex vivo-expanded products was 1 per 418,000 progeny CD34+ cells (95% CI, 1:158,000-1:1,100,000). Taken together, these data indicated that, after 2 weeks of culture, there was a modest twofold increase in the total number of SRCs. However, the levels of human CD45 cell engraftment in NOD/SCID recipients of progeny CD34+ cells were significantly lower than those in mice receiving equivalent numbers of uncultured CD34+ cells (p<0.05). CONCLUSION: Umbilical cord blood progeny cells retaining a CD34+ phenotype after ex vivo expansion have less engraftment potential than do unexpanded CD34+ cells.

Animals↗

PubMed2001

A semiparametric estimate of treatment effects with censored data.

A semiparametric estimate of an average regression effect with right-censored failure time data has recently been proposed under the Cox-type model where the regression effect beta(t) is allowed to vary with time. In this article, we derive a simple algebraic relationship between this average regression effect and a measurement of group differences in k-sample transformation models when the random error belongs to the G(rho) family of Harrington and Fleming (1982, Biometrika 69, 553-566), the latter being equivalent to the conditional regression effect in a gamma frailty model. The models considered here are suitable for the attenuating hazard ratios that often arise in practice. The results reveal an interesting connection among the above three classes of models as alternatives to the proportional hazards assumption and add to our understanding of the behavior of the partial likelihood estimate under nonproportional hazards. The algebraic relationship provides a simple estimator under the transformation model. We develop a variance estimator based on the empirical influence function that is much easier to compute than the previously suggested resampling methods. When there is truncation in the right tail of the failure times, we propose a method of bias correction to improve the coverage properties of the confidence intervals. The estimate, its estimated variance, and the bias correction term can all be calculated with minor modifications to standard software for proportional hazards regression.

Biometry↗

PubMed2001

In vitro phosphorylation of COOH termini of the epithelial Na(+) channel and its effects on channel activity in Xenopus oocytes.

Recent findings have suggested the involvement of protein phosphorylation in the regulation of the epithelial Na(+) channel (ENaC). This study reports the in vitro phosphorylation of the COOH termini of ENaC subunits expressed as glutathione S-transferase fusion proteins. Channel subunits were specifically phosphorylated by kinase-enriched cytosolic fractions derived from rat colon. The phosphorylation observed was not mediated by the serum- and glucocorticoid-regulated kinase sgk. For the gamma-subunit, phosphorylation occurred on a single, well-conserved threonine residue located in the immediate vicinity of the PY motif (T630). The analogous residue on beta(S620) was phosphorylated as well. The possible role of gammaT630 and betaS620 in channel function was studied in Xenopus laevis oocytes. Mutating these residues to alanine had no effect on the basal channel-mediated current. They do, however, inhibit the sgk-induced increase in channel activity but only in oocytes that were preincubated in low Na(+) and had a high basal Na(+) current. Thus mutating gammaT630 or betaS620 may limit the maximal channel activity achieved by a combination of sgk and low Na(+).

Animals↗

PubMed2001

Anatomic considerations of the posterolateral lumbar disk region.

Sixteen embalmed cadavers were dissected to determine the location of the lumbar nerve root and sympathetic trunk with reference to the superior border of transverse process. In the posterolateral lumbar disk region, a safe zone was found between the anterior limit of the lumbar nerve and the posterior limit of the sympathetic trunk. It has a transverse dimension of 22 mm at the T12-L1 disk region and 25 mm at the L4-L5 disk region. The only exception to this was the genitofemoral nerve running close to the lateral margin of the L2-L3 disk. The study provides an understanding of the posterolateral orientation of the lumbar nerves and sympathetic trunk.

Aged↗

PubMed2001

Bone density of the first sacral vertebra in relation to sacral screw placement: a computed tomography study.

A visual three-dimensional image of the first sacral vertebra was constructed using computer software to predict the sites of strong density for better screw purchase of upper sacrum. Forty dry sacrum specimens were scanned in the prone position. An axial section, 10 mm below the S1 end plate, was selected for determining density at the region of interest. All images were stored on an optic disc and studied using the NIH Image 1.61 program. Plot analysis assessed the bone density in different regions. Also, three-dimensional pictures of the different screw paths and the related bone density in the upper sacrum were analyzed. Bone density in the anterolateral part of S1 was 115.1 +/- 10.4 pixel. Bone density for males (-99.7 +/- 11.3) was greater than for females (-131.4 +/- 9.6). Bone density in the anterolateral alar region was -108 +/- 10.6. The bone density for males (-95.6 +/- 9.8) and females (121.4 +/- 11.7) was more than the body region. Bone density in the middle anterior cortex of the ala was 759.8 +/- 11.6. Bone density for males (878.2 +/- 10.7) was greater than for females (637.6 +/- 11.9). Using surface plot, the midanterior cortex of the ala had high cortical density compared with other areas. The midanterior cortex of the sacral ala had the highest bone density. Sacral screw purchase in the midanterior cortex provides better mechanical fixation.

Aged↗

PubMed2001

Axial computed tomography of the pedicle in the lower cervical spine.

Using axial computed tomography (CT), we measured pedicle width, pedicle axis length, pedicle transverse angle, and distance between screw entry point and vertebrae midline in the cervical spines (C3-C7) of 40 patients. All measurements were greater in men than in women, and we noted significant sex differences at most levels of pedicle inner and outer widths (P < or = .05 or P < or = .01). Mean pedicle inner and outer widths for all levels and all patients ranged from 2.3 to 3.0 mm and from 5.0 to 6.0 mm, respectively. Mean distances between screw entry point and vertebrae midline ranged from 22.2 to 23.7 mm. Results of this study-along with axial CT measurements of individual pedicle diameter, pedicle transverse angle, and screw entry point-would be useful when considering and performing transpedicular screw fixation in the cervical spine.

Adult↗

PubMed2001

Survival analysis with time-varying relative risks: a tree-based approach.

A tree-based method for estimating time-varying effects of baseline patient characteristics on survival is introduced. A Cox-type model for censored survival data is used in which the time-varying relative risks are modelled as piecewise constants. The tree method consists of three steps: 1. Growing the tree, in which a fast algorithm using maximized score statistics is utilized to determine the optimal change points; 2. A pruning algorithm is applied to obtain more parsimonious models; 3. Selection of a final tree, which may be either via bootstrap resampling or based on a measure of explained variation. The piecewise constant model is more suitable for clinical interpretation of the regression parameters than the more continuously time-varying models (spline, loess, etc.) that have been proposed previously.

Algorithms↗

PubMed2001

[Prevention and treatment of recurrent urinary system infection with estrogen cream in postmenopausal women].

OBJECTIVE: To evaluate the effect and feasibility of using estrogen cream for the prevention and treatment of recurrent urinary tract infection (UTI) in postmenopausal women. METHODS: Forty-five postmenopausal women with a history of recurrent UTI were divided into two groups (group premarin and group antibiotic). Participants were assigned to apply intravaginal premarin cream (group premarin, n = 30) or oral antibiotic (group antibiotic, n = 15) for 3 months respectively. Urine routine test, midstream urine and vaginal cultures, vaginal health score (VHS), vaginal cell maturation value (MV), endometrial thickness and blood estrogen level were obtained before and after the study. RESULTS: The incidence of UTI in the group premarin was significantly reduced as compared with that in the group antibiotic (2/27 vs. 12/15, P < 0.001). In the group premarin Lactobacilli reappeared (from 0 to 59.3%) and MV (from 9.2 +/- 6.8 to 74.6 +/- 14.1) and VHS (from 5.2 +/- 0.4 to 13.4 +/- 2.5) were improved after 3 months. There was no significant change in the group antibiotic. CONCLUSION: It seems that intravaginal use of estrogen cream would effectively prevent and reduce the UTI in postmenopausal women.

Aged↗

PubMed2001

Neuronal cdc-2 like kinase in developing kindling rat hippocampus.

OBJECTIVE: To test the hypothesis that neuronal cdc2-like kinase (Cdk5/p35nck5a) plays an important role in neuronal maturation and sprouting. METHODS: Changes kinase activity, expression levels and subcellular localizations of Cdk5 and p35nck5a in the rat hippocampus were studied during kindling progression by Western blot analysis, immunohistochemistry, immunoprecipitation and kinase assay. RESULTS: Kinase activity in kindling rats was significantly higher than that in normal adult rats. The kinase activity at stage 3 was most prominent among all stages of kindling progression. The changes in kinase activity coincided with those of p35nck5a expression in kindling rats. In contrast, the expression of Cdk5 was constant throughout the progression of kindling stages. However, subcellular localization of Cdk5 dramatically changed in the hippocampal neurons of kindling rats. Cdk5 was translocated from axon to soma when kinase activity was high. p35nck5a was always localized in the soma throughout kindling progression. CONCLUSIONS: Neuronal cdc2-like kinase plays an important role in synaptic reorganization, and the translocation of Cdk5 to the soma from the axon may be a novel regulatory mechanism to control kinase activity.

Animals↗

PubMed2001

Activity identification of anti-caspase-3 mRNA hammerhead ribozyme in both cell-free condition and BRL-3A cells.

OBJECTIVE: To study the transcription effects and cleavage activities of rat caspase-3 specific hammerhead ribozyme (Rz107) in both cell-free conditions and BRL-3A cells. METHODS: Rat caspase-3 gene fragment was cloned into the pGEM-T EASY vector under the T7 promoter control. The 32P-labeled caspase-3 transcript was the target-RNA. Rz107 genes designed against caspase-3 mRNA were cloned into vector p1.5 between 5'-cis-Rz and 3'-cis-Rz. 32P-labeled ribozyme transcripts were incubated with target-RNAs at different conditions and autoradiographed after denaturing gel-electrophoresis. Rz107 was electroporated into BRL-3A cells and the Rz107 expression was analyzed by RT-PCR. RESULTS: In cell-free conditions, Rz107 was active at 37 degrees C. The optimal temperature was 50 degrees C. The Km and Kcat were 14.13 nmol/L and 2.31.min-1 respectively. Intracellular cleavage efficiency of Rz107 was 37%, as analyzed by RT-PCR. This indicated that the design of Rz107 was correct, and Rz107 had the activity of common enzymes. CONCLUSIONS: Rz107 in cell-free conditions possessed perfect specific catalytic cleavage activity, and it can also cleave the target RNA successfully in cells. The results illustrate the feasibility of ribozyme therapy as a potential alternative approach for treating liver disease caused by apoptosis.

Animals↗

PubMed2001

[A prospective study of histological changes after AraAMP treatment in patients with chronic hepatitis B infection].

OBJECTIVE: To investigate the histological changes in liver biopsy tissue induced by AraAMP therapy for 50 days in patients with chronic hepatitis B infection. METHODS: Eleven patients were enrolled into this prospective study. All the patients had liver biopsy performed within 1 week before starting AraAMP therapy. A second liver biopsy was taken for comparison six months after the end of therapy. Blinded biopsies were scored according to Knodell's histology activity index (HAI), and examined for HBeAg and alpha-smooth muscle actin with immunohistochemistry as well as HBV DNA by using in situ hybridization. RESULTS: Histological improvement of >or=2 points decrease in the necroinflammatory HAI scores was seen in 8 of the 11 (72.7%) of patients after treatment. In these patients histological assessment revealed a significant improvement in intralobular inflammation and fibrosis as compared with pretreatment values(P < 0.05). There was significant difference of HAI changes in 6 cases graded as G3 based on the degree of periportal interface hepatitis and spotty parenchymal injury, but not in 5 cases graded as G2. HBeAg disappeared from liver tissue in 4 of the 9 cases and a significant reduction of activated liver stellate cells was demonstrated in the second biopsy(P = 0.018). Of the nine cases with HBV DNA positive at the first biopsy with in situ hybridization examination, 4 were negative at the second biopsy. CONCLUSION: Significant improvement in intralobular inflammation and fibrosis can be observed in liver tissue from patients with chronic hepatitis B infection treated with AraAMP.

Adolescent↗

PubMed2001

[A multicenter clinical study on clinical effects of meglumine cyclic adenylate in treating patients with chronic pulmonary heart disease].

OBJECTIVE: To observe the clinical effects of meglumine cyclic adenylate (MCA) in treating patients with chronic pulmonary heart disease. METHODS: 785 patients with chronic pulmonary heart disease were divided into two groups: MCA group and control group. Both groups of patients were treated with the same ordinary methods, but MCA was given in the MCA group. The period of treatment was 5-7 days. The degree of improvement in clinical symptoms, signs, ECG, pulmonary ventilation function and arterial blood gas analysis of the two groups before and after treatment were compared. RESULTS: The rates of improvement in clinical symptoms and signs were 92.2% and 73.6% in MCA group and control group respectively. VC increased (426 +/- 123) ml and (313 +/- 145) ml respectively as compared with the values before the treatment. FEV(1) increased (134 +/- 54) ml and (95 +/- 55) ml, PEF increased (0.78 +/- 0.32) L/s and (0.47 +/- 0.32) L/s and PaO(2) increased (23.4 +/- 9.5) mm Hg and (17.3 +/- 10.4) mm Hg respectively. The rates of ECG improvement were 63.7% and 41.2% respectively. There was significant difference between the two groups (P < 0.01 and 0.05). CONCLUSION: Significant therapeutic effects were obtained in treating patients of chronic pulmonary heart disease with respiratory and cardiac failure by using ordinary treatment measures combined with MCA injection.

Aged↗

PubMed2001

[Ecological characteristics of phytoplankton in waters of biological-controlling and ordinary rice fields].

Through investigations from March to June 1998 on the phytoplankton in waters of biological-controlled and ordinary rice fields, 112 species of phytoplankton were found, of which, Bacillariophyta, Euglenophyta and Chlorophyta were dominant. The comparison of the species in two rice fields showed that in biological-controlled rice field, there were more species of Euglenophyta, with 5 most dominant species, i.e., 2 of Euglenophyta, 2 of Bacillariophyta and 1 of Chlorophyta. In ordinary rice field, there were more Bacillariophyta species, in which, 5 most dominant species belonged to Bacillariophyta, except Scenedesmus bijuga to Chlorophyta. The biodiversities of phytoplankton and their evennesses were also analyzed with the period from the seedlings being planted to the rice fields being dried, showing that a little increase in their biodiversity mainly caused by the increase of species number and an evident decrease in their evennesses.

Ecosystem↗

PubMed2001

Signal transduction pathway of nitric oxide inducing PC12 cell death.

OBJECTIVE: To study signal transduction pathway of nitric oxide inducing death of PC12 cells. METHODS: Cell survival rate was measured with MTT assay, and caspase-3 activity with caspase-3 assay kits after PC12 cells were incubated with sodium nitroprusside (SNP), caspase-3 inhibitor II plus SNP or p38 inhibitor-SB203580 plus SNP. RESULTS: SNP induced death of PC12 cells in dose- and time-dependent manner and enhanced caspase-3 activity gradually. Both caspase-3 inhibitor II and SB203580 reduced cell death, but SB203580 reduced caspase-3 activity significantly. CONCLUSIONS: NO may induce death of PC12 cells through activation of p38 and caspase-3.

Animals↗

PubMed2001

Relationship between changes of N-methyl-D-aspartate receptor activity and brain edema after brain injury in rats.

OBJECTIVE: To investigate the relationship between the changes of N-methyl-D aspartate (NMDA) receptor activity and brain edema after injury in rats. METHODS: The brain injury models were made by using a free-falling body. The treatment model was induced by means of injecting AP5 into lateral ventricle before brain injury; water contents in brain cortex were measured with dry-wet method; and NMDA receptor activity was detected with a radio ligand binding assay. RESULTS: The water contents began to increase at 30 minutes and reached the peak at 6 hours after brain injury. The maximal binding (B(max)) of NMDA receptor increased significantly at 15 minutes and reached the peak at 30 minutes, then decreased gradually and had the lowest value 6 hours after brain injury. Followed the treatment with AP5, NMDA receptor activity in the injured brain showed a normal value; and the water contents were lower than that of AP5-free injury group 24 hours after brain injury. CONCLUSIONS: It suggests that excessive activation of NMDA receptor may be one of the most important factors to induce the secondary cerebral impairments, and AP5 may protect the brain from edema after brain injury.

Animals↗

PubMed2001

[Trend and characteristics of HIV/AIDS epidemic in Guangdong province, 1986 - 1999].

OBJECTIVE: To analyze the epidemic characteristics and risk factors of HIV/AIDS in Guangdong province and to search for measure of control. METHODS: Data from routine, sentinel, behavior and laboratory surveillance programs were collected and evaluated. RESULTS: Since the first HIV case in IDUs was found by the end of 1996, the number of HIV/AIDS has increased by 86.2% yearly and the proportion of cases infected through IDU increased rapidly from 1.4% before 1996 to 91.0% in 1999. HIV-1 C subtype in IDUs accounted for 61.3%. CONCLUSIONS: Number of HIV/AIDS cases has increased rapidly in recent years in Guangdong. The major transmission route was through IDU. It was important to prevent HIV/AIDS spreading from IDUs to sex workers then to the general population through behavioral surveillance and intervention.

Acquired Immunodeficiency Syndrome↗