Biomedical subjects

R Xu

Publications and source records attributed to R Xu.

At least 91 records · Page 5Linked to original sources

PubMed2000

Anatomic considerations of costotransverse screw placement in the thoracic spine.

BACKGROUND: Numerous techniques have been reported to restore spinal stability and to correct spinal deformities, including rods with wires/hooks, and rods or plates with pedicular screws. It was thought that posterior fixation of the thoracic spine through the costotransverse joint may be another alternative. METHODS: Nine cadavers were obtained for study of screw fixation of the costotransverse joint for posterior thoracic instrumentation. The entrance point for screw insertion was designed to be at the posterior center of the clubbed extremity of the transverse process. From this point, a 3-mm drill bit was used to create the screw path penetrating the costotransverse joint and the ventral cortex of the rib. Under direct visualization of the costotransverse joint, the drill bit was directed parallel to the sagittal plane and toward the upper portion of the rib. Measurements included the screw path length and sagittal angulation. Also, the distance between the superior borders of the transverse process and the tubercle of the rib and the anatomic relationship of the drill bit exit to the intercostal vessels and nerves were evaluated. RESULTS: The maximum length of the screw path was found at T1 (19.7 mm), whereas the minimum length was noted at T4-T5 (13.9 mm). This value decreased gradually from T1 to T4-T5, and slightly increased to T10. The larger sagittal angles of the screw path were found at the levels of T1-T4 (78-86 degrees ), whereas the smaller were noted at the levels below T5 (53-61 degrees ). The mean distance between the superior borders of the transverse process and the tubercle of the rib was smaller at T1-T5 (0.2-0.4 mm), and significantly increased to T8 (5. 1 mm), and then slightly decreased to T10. The variation of this parameter was remarkable. All of the exit points for the drill bit were located in the upper half of the rib, and away from the intercostal vessels. CONCLUSIONS: The ideal screw orientation is parallel to the sagittal plane, and angled 80-90 degrees relative to the frontal plane for T1-T4 and 50-70 degrees for T5-T10 superiorly, starting at the posterior center of the transverse process. Costotransverse screw fixation in the thoracic spine may be an alternative to pre-existing methods.

Aged↗

PubMed2000

Long-term tracking of murine hematopoietic cells transduced with a bicistronic retrovirus containing CD24 and EGFP genes.

Hematopoietic stem cells (HSCs) are attractive targets for gene therapy, but current gene transfer methodologies are inadequate for efficient HSC transduction and perpetual transgene expression. To improve gene transfer vectors and transduction protocols, it is vital to establish a system to evaluate transgene expression and the long-term behavior of transduced cells in vivo. For this purpose, we constructed a bicistronic retrovirus encoding the human CD24 (as the first cistron) and the enhanced green fluorescent protein (EGFP; as the second cistron). Murine bone marrow cells were transduced with this vector and the transgene expression was monitored along with hematopoietic reconstitution. Stable expression of CD24 and EGFP was demonstrated in the long-term repopulating cells for at least 6 months, and multi-parameter flow cytometry illustrated expression of both markers in all the lymphohematopoietic lineages examined (B and T lymphoid, erythroid and myeloid). Sustained expression was also shown in the secondary transplants for 6 months, suggesting that self-renewing HSCs were transduced by this vector. Overall, EGFP-tagged bicistronic retroviruses would provide powerful tools for detailed in vivo analysis of transduced hematopoietic cells, such as transgene expression in conjunction with lineage differentiation. Gene Therapy (2000) 7, 1193-1199.

Animals↗

PubMed2000

Growth hormone-releasing hormone decreases voltage-gated potassium currents in GH4C1 cells.

The electrophysiological properties of anterior pituitary somatotropes integrally involve the function of voltage-gated K+ currents. In this study, we have used GH4C1 cell lines to investigate the effect of human GHRH on voltage-gated K+ currents. Because of a clear 'rundown' of the K+ current with classic whole cell recording (WCR) without ATP in pipette solution, nystatin-perforated WCR was the major recording configuration used. Using a low Ca2+ (0.5 mM) bath solution containing Co2+ (1 mM) and TTX (1 microM), GH4 cells predominantly exhibited an outward delayed rectifier K+ current (IK). Local application of growth hormone releasing hormone (GHRH) (100 nM) reversibly reduced the amplitude of the K+ currents (to 83% of control). There was no effect of GHRH on the activation curve of the K+ current and no difference observed using 2.5 mM Ca2+ or low Ca2+ (0.5 mM Ca2++1 mM Co2+) bath solutions. Under the condition of low Ca2+ bath solution, the application of apamin (1 microM) or charybdotoxin (1 microM), two specific blockers of the Ca2+-activated K+ current, did not alter the K+ current or the response to GHRH. This reduction in the K+ current by GHRH was also observed with classic WCR with a pipette solution containing ATP (2 mM). The GHRH-induced reduction in the K+ current was completely abolished by the presence of GDP-beta-s (500 microM) in the pipette solution or by addition of PKC inhibitors, calphostin C (100 nM) and chelerythrine (1 microM), in bath solution. Inhibitor for cAMP-PKA system (Rp-cAMP and H89) did not affect the K+ current response to GHRH. These results suggest that GHRH reduces the voltage-gated K+ current in GH4C1 cells, a response that is mediated by G-proteins and PKC system but not by cAMP-PKA system. The reduction in the K+ current may partially contribute to the GHRH-stimulated growth hormone (GH) secretion.

Apamin↗

PubMed2000

Diverse intracellular signalling systems used by growth hormone-releasing hormone in regulating voltage-gated Ca2+ or K channels in pituitary somatotropes.

Influx of Ca2+ via Ca2+ channels is the major step triggering exocytosis of pituitary somatotropes to release growth hormone (GH). Voltage-gated Ca2+ and K+ channels, the primary determinants of the influx of Ca2+, are regulated by GH-releasing hormone (GHRH) through G-protein-coupled intracellular signalling systems. Using whole-cell patch-clamp techniques, the changes of the Ca2+ and K+ currents in primary cultured ovine and human somatotropes were recorded. Growth hormone-releasing hormone (10 nmol/L) increased both L- and T-type voltage-gated Ca2+ currents. Inhibition of the cAMP/protein kinase A (PKA) pathway by either Rp-cAMP or H89 blocked this increase in both L- and T-type Ca2+ currents. Growth hormone-releasing hormone also decreased voltage-gated transient (IA) and delayed rectified (IK) K+ currents. Protein kinase C (PKC) inhibitors, such as calphostin C, chelerythrine or downregulation of PKC, blocked the effect of GHRH on K+ currents, whereas an acute activation of PKC by phorbol 12, 13-dibutyrate (1 micromol/L) mimicked the effect of GHRH. Intracellular dialysis of a specific PKC inhibitor (PKC19-36) also prevented the reduction in K+ currents by GHRH. It is therefore concluded that GHRH increases voltage-gated Ca2+ currents via cAMP/PKA, but decreases voltage-gated K+ currents via the PKC signalling system. The GHRH-induced alteration of Ca2+ and K+ currents augments the influx of Ca2+, leading to an increase in [Ca2+]i and the GH secretion.

Alkaloids↗

PubMed2000

Serum supplement, inoculum cell density, and accessory cell effects are dependent on the cytokine combination selected to expand human HPCs ex vivo.

BACKGROUND: The prolonged periods of pancytopenia associated with cord blood transplants suggest that in some cases cell numbers may be limiting. The possibility that limiting cell numbers may be overcome and prolonged periods of pancytopenia abrogated by the transplantation of human umbilical cord blood cells expanded ex vivo has led to efforts to define optimal culture conditions for these cells. STUDY DESIGN AND METHODS: Cord blood CD34+ cells were cultured with three cytokine combinations: SCF+G-CSF+GM-CSF+MGDF (SGGM); IL-6+ SCF+MGDF+Flt3-ligand (6SMF); and IL-1+IL-3+IL-6+G-CSF+GM-CSF+SCF+Epo (GFmix). Serum effects, inoculum concentration (cells/mL) seeding density (cell/cm(2)) and accessory cell effects on the expansion of CD34+ cells were determined. RESULTS: Cellular outputs were significantly higher with fetal calf serum (FCS) than with cord blood serum (CBS) or adult group AB serum (ABS) in the presence of 6SMF, however, CBS was as effective as FCS. The best seeding concentrations varied for each of the cytokine combinations, and inoculum densities exceeding 1000 cells per cm(2) proved detrimental for cultures containing GFmix and SGGM. Accessory cell studies indicated that populations expressing the CD33 antigen inhibited the expansion of purified CD34+ cells in the presence of GFmix or SGGM, but not in the presence of 6SMF. CONCLUSION: Serum supplement, inoculum cell concentration, seeding densities, and accessory cell effects are dependent upon the cytokine combination selected to expand cord blood HPCs ex vivo. Thus, each of these measures should be assessed to establish reproducible and reliable conditions for the selection of different cytokine combinations to culture cord blood HPCs.

Adult↗

PubMed2000

Estimating average regression effect under non-proportional hazards.

We present an estimator of average regression effect under a non-proportional hazards model, where the regression effect of the covariates on the log hazard ratio changes with time. In the absence of censoring, the new estimate coincides with the usual partial likelihood estimate, both estimates being consistent for a parameter having an interpretation as an average population regression effect. In the presence of an independent censorship, the new estimate is still consistent for this same population parameter, whereas the partial likelihood estimate will converge to a different quantity that depends on censoring. We give an approximation of the population average effect as integral beta(t)dF(t). The new estimate is easy to compute, requiring only minor modifications to existing softwares. We illustrate the use of the average effect estimate on a breast cancer dataset from Institut Curie. The behavior of the estimator, its comparison with the partial likelihood estimate, as well as the approximation by integral beta(t)dF(t)are studied via simulation.

Journal Article↗

PubMed2000

Molecular analysis of thermoregulation of phaseolotoxin-resistant ornithine carbamoyltransferase (argK) from Pseudomonas syringae pv. phaseolicola.

The phaseolotoxin-resistant ornithine carbamoyltransferase (ROCT) and phaseolotoxin are produced by Pseudomonas syringae pv. phaseolicola at 18 degrees C but not at 28 degrees C. At 28 degrees C, the pathogen produces a protein(s) that binds (in vitro) to a 485-bp fragment (thermoregulatory region, TRR) from a heterologous clone from the pathogen genomic library, which in multiple copies overrides thermoregulation of phaseolotoxin production in wild-type cells (K. B. Rowley, D. E. Clements, M. Mandel, T. Humphreys, and S. S. Patil, Mol. Microbiol. 8:625-635, 1993). We report here that DNase I protection analysis of the 485-bp fragment shows that a single site is protected from cleavage by the protein in the 28 degrees C extract and that this site contains two repeats of a core motif G/C AAAG separated by a 5-bp spacer. Partially purified binding protein forms specific complexes with a synthetic oligonucleotide containing four tandem repeats of this motif. A 492-bp upstream fragment from argK encoding ROCT also forms specific complexes with the protein in the 28 degrees C crude extract, and a 260-bp subfragment from the TRR containing the binding site cross competes with the argk fragment, indicating that the same protein binds to nucleotides in both fragments. DNase I protection analysis of the fragment from argK revealed four separate protected sequence elements, with element III containing half of the core motif sequence (CTTTG), and the other elements containing similar sequences. Gel shift assays were done with DNA fragments from which one or all of the sites were removed as competitor DNAs against the argK probe. The results of these experiments confirmed that the binding sites (in argK) are necessary for the protein to bind to the argK fragment in a specific manner. Taken together, the results of studies presented here suggest that in cells of P. syringae pv. phaseolicola grown at high temperature argK may be negatively regulated by the protein produced at this temperature.

Bacterial Proteins↗

PubMed2000

Evolutionary relationships of endemic/epidemic and sylvatic dengue viruses.

Endemic/epidemic dengue viruses (DEN) that are transmitted among humans by the mosquito vectors Aedes aegypti and Aedes albopictus are hypothesized to have evolved from sylvatic DEN strains that are transmitted among nonhuman primates in West Africa and Malaysia by other Aedes mosquitoes. We tested this hypothesis with phylogenetic studies using envelope protein gene sequences of both endemic/epidemic and sylvatic strains. The basal position of sylvatic lineages of DEN-1, -2, and -4 suggested that the endemic/epidemic lineages of these three DEN serotypes evolved independently from sylvatic progenitors. Time estimates for evolution of the endemic/epidemic forms ranged from 100 to 1,500 years ago, and the evolution of endemic/epidemic forms represents relatively recent events in the history of DEN evolution. Analysis of envelope protein amino acid changes predicted to have accompanied endemic/epidemic emergence suggested a role for domain III in adaptation to new mosquito and/or human hosts.

Base Sequence↗

PubMed2000

Inhibition of Rho protein stimulates iNOS expression in rat vascular smooth muscle cells.

Inducible nitric oxide synthase (iNOS) in vascular smooth muscle cells (VSMCs) is upregulated in arterial injury and plays a role in regulating VSMC proliferation and restenosis. Inflammatory cytokines [e.g., interleukin-1beta (IL-1beta)] released during vascular injury induce iNOS. Small GTP-binding proteins of the Ras superfamily play a major role in IL-1beta-dependent signaling pathways. In this study, we examined the role of Rho GTPases in regulating iNOS expression in VSMCs. Treatment of VSMCs with mevastatin, which inhibits isoprenylation of Rho and other small GTP-binding proteins, produced significantly higher amounts of IL-1beta-evoked NO and iNOS protein compared with control. Similarly, bacterial toxins [Toxin B from Clostridium difficile and C3 ADP-ribosyl transferase (C3) toxin from Clostridium botulinium] that specifically inactivate Rho proteins increased NOS products (NO and citrulline) and iNOS expression. Toxin B increased the activity of iNOS promoter-reporter construct in VSMCs. Both toxins enhanced IL-1beta-stimulated iNOS expression and NO production. These data demonstrate for the first time that inhibition of Rho induces iNOS and suggest a role for Rho protein in IL-1beta-stimulated NO production in VSMCs.

ADP Ribose Transferases↗

PubMed2000

The lumbosacral nerves in relation to dorsal S1 screw placement and their locations on plain radiographs.

Seven adult cadaver lumbopelvises were harvested to study the anatomic relationship of the L4 and L5 nerves to S1 dorsal screw placement and the location of the L4, L5, and S1 nerves on plain radiographs. The mean lateral angle of S1 screw trajectory toward the L4 nerve was 31+/-8 degrees, and the mean screw trajectory length was 53+/-8 mm. The mean lateral angle of the screw trajectory toward the L5 nerve was 21+/-8 degrees, and the mean screw trajectory length was 38+/-4 mm. On both inlet and outlet radiographs, the lateral angle of the nerves increased from L4 to S1. The L4 nerve coursed over the middle third of the superior ala in the inlet view and the middle third of the lateral mass in the outlet view. The L5 nerve coursed over the inner third of the superior ala and inner third of the lateral mass. On the lateral view, the mean distances from the sacral promontory to the L4, L5, and S1 nerves along the anterior border of the sacrum were 4+/-7 mm, 12+/-5 mm, and 28+/-8 mm, respectively. This study suggests that S1 sacral screws be directed between 30 degrees and 40 degrees lateral to avoid compromising the lumbosacral trunk and sacroiliac joint.

Adult↗

PubMed2000

Computed tomography in the determination of transarticular C1-C2 screw length.

This study evaluated the significance of computed tomographic (CT) measurements of the upper cervical vertebrae and their clinical implications in transarticular C1-C2 screw placement. In the first part of the study, analysis of axial CT scans of the atlas of 46 patients who had a normal C1-C2 region was performed. Measurements included the vertical distance between the middle of the ventral cortex of the lateral mass and the anterior-most point of the anterior tubercle, and the angle of the anterior ring of C1 relative to the frontal plane. In the second part, axial CT scans of the upper cervical spine were performed in seven cadaveric cervical spines and analyzed using the same criteria. Using the Magerl technique of transarticular C1-C2 screw placement, one screw was placed in each cervical spine. Following each placement, a strict lateral radiograph was taken and the distance between the tip of the screw and the anterior-most point of the anterior tubercle of C1 was measured. Analysis of the cervical cadaveric specimens showed the vertical distance between the middle of the ventral cortex and the anterior-most part of the anterior tubercle when measured on CT scan corresponded to the distance measured on lateral radiographs after placement of the C1-C2 transarticular screw. The study of the 46 patients with normal C1-C2 region had shown the mean values of linear and angular measurements to be greater in males than in females, although no significant difference was found between the two groups (P>.05). The mean distance between the anterior-most point of the anterior tubercle and the middle of the ventral cortex of the lateral mass was 6.5+/-1 mm, and the mean transverse angle of the anterior ring relative to the frontal plane was 22 degrees+/-3.1 degrees. Axial CT evaluation of the individual anatomic relationships of the atlas is simple and may be a useful guide in the determination of the length of the transarticular screw when performed during surgery under lateral fluoroscopic control.

Adolescent↗

PubMed2000

Anatomic considerations of a modified anterior approach to the cervicothoracic junction.

The results of a study on 30 adult human cadavers showed that the anterior aspect of T-3 can be easily exposed through a modified anterior approach to the cervicothoracic spinal junction. Anterior exposure of T-4 caused significant tension on the brachiocephalic vein in 57%; in 7% the vein actually tore. The location of the vital structures is as follows: the left brachiocephalic vein is at T-1 and T-2 in 80%; the aortic arch is at T-2 and T-3 in 90%; the right recurrent laryngeal nerve reaches the tracheoesophageal groove at the level of C-6 in 50%; the thoracic duct empties into the systemic venous system from C-7 to T-2. Adequate exposure of the low cervical to the upper thoracic spine can be obtained with this approach. Preoperative computed tomographic evaluation of the location of the left brachiocephalic vein with respect to the vertebral levels is recommended.

Adult↗

PubMed2000

Quantitative anatomy of the scapula.

Thirty adult bony scapulae were used to report detailed bony dimensions of the scapula. The measurements of bony dimensions of the scapula included the glenoid, coracoid, spine, and body. The results of the measurements showed that the thickest bony stock (posteroanterior diameter), with a mean value of 13 mm to 23 mm in the glenoid process, was found in the middle third of the area within 1 cm medial to the glenoid rim. In the scapular spine region, the greatest superoinferior diameter of the bone was noted in the lateral portion of the spine, followed by the medial portion. It was also found that smallest superoinferior diameter (2 mm to 7 mm) of the spine was located at the middle portion between the base and ridge along the whole spine. On the lateral border of the scapula, the posteroanterior diameter of bone was relatively greater for the upper portion (8 mm) than for the lower portion, including the inferior angle (6 mm). This information may be helpful in open reduction and internal fixation of significantly displaced scapular fractures.

Adult↗

PubMed2000

Location of the vertebral artery in the cervicothoracic junction.

Eight sectioned specimens and 8 cadavers were used to evaluate the location of the vertebral artery in the cervicothoracic junction. The results of the measurements showed that there was no significant difference between either sides at the C7-T1 junction in terms of all distances taken. The mean width of the vertebral artery was 2.9 mm at the levels of the C-7 and T-1. The sagittal distance between the vertebral artery and the posterior cortex was 16.8+/-3.0 mm at the C7 and 21.7+/-2.8 mm at T-1. The coronal distance between the vertebral artery and the midline of the vertebra was 17.5+/-1.8 mm at the C7 and 22.3+/-2.9 mm at the T-1. The mean angle between the line connecting the lateral border of the vertebral artery with the posterior midway of the lateral mass and the parasagittal line at C-7 was 14.1+/-6.1 degrees. The mean angle of the vertebral artery with respect to the midline was 22.8+/-6.4 degrees. This study suggests that the vertebral artery has closer anatomic relationship to the C-7 lateral mass. Care should be taken to avoid injury to the vertebral artery if lateral mass screw fixation at the C-7 is intended.

Bone Screws↗

PubMed2000

Computed tomographic evaluation of length of screw paths for anterior cervical plating.

Thirty patients' computed tomographic (CT) scans of the cervical spine were used to measure screw path lengths with respect to anterior plating. The results indicated that all screw paths were longer in men than in women, and the majority of lengths differed significantly by sex (P < or = .05). The mean length of the sagittal, parasagittal, and convergent screw paths for both men and women was 16 mm. The mean length of the safe divergent screw path was 15 mm. Therefore, the safe screw length may be 16 mm for convergent placement and 15 mm for divergent placement. Convergent screw placement is recommended. Preoperative CT or magnetic resonance imaging evaluation and measurement of the intended screw trajectories are recommended.

Adult↗

PubMed2000

Anatomic study of the cervicothoracic spinal nerves and their relation to the pedicles.

Twelve cadavers were dissected for the study of the cervicothoracic junction. The results showed that the mean heights and widths of the ganglia tend to decrease from the C-6 to T-4 nerve. The mean distances between the dura and the ganglion and the mean spinal nerve angles increased consistently from C-5 to T-4. The mean distances from the spinal nerves to the superior and inferior pedicles ranged 0.8-2.3 mm. It was noted that the mean value was significantly greater for the distance from the spinal nerve to the superior pedicle than that to the inferior pedicle for the spinal nerves C5-7 (P< or =.05). This information, in conjunction with imaging studies, may minimize spinal nerve injury during posterior pedicle screw fixation in the cervicothoracic spine.

Aged↗

PubMed2000

[Preparation and identification of hammerhead ribozyme in vitro against rat caspase-3 mRNA fragment].

OBJECTIVE: To study the transcript effect and cleavage activity in vitro of rat Caspase-3 specific ribozyme (Rz107 and Rz544). METHODS: Rat caspase-3 gene fragment was cloned into T-vector under the control of T7 promoter. (32)P-labeled caspase-3 transcript was target-RNA. Rz107 and Rz544 genes against caspase-3 mRNA were cloned and transcribed in vitro. Cleavage reaction was detected. RESULTS: It was found that Rz107 was active at 37 degrees C and more so at higher temperature within allowing temperature range. The optimal temperature was 50 degrees C. For Rz107, Km and kcat was 14.13 nmol/L and 2.31 min(-1), respectively. However, the Rz544 had no cleavage activity at all. CONCLUSION: Rz107 prepared in vitro possesses the perfect specific catalytic cleavage activity. It is hopeful that Rz107 would be developed to be a new nucleic acid drug that could effectively inhibit the inflammation of hepatitis through cleaving the key gene, caspase-3, in apoptosis in vivo.

Animals↗

PubMed2000

Clinical observation on the long-term therapeutic effects of traditional Chinese medicine for treatment of liver fibrosis.

48 patients with liver fibrosis due to hepatitis B were treated for 2 years with the drugs for tonifying the kidney, supplementing qi, cooling and invigorating the blood and detoxification. The symptoms were markedly improved, and serum ALT and bilirubin were recovered and kept normal in most of the cases. The mean levels of serum hyaluronic acid, procollagen peptide III and circulating immune complex were decreased and returned to normal after the treatment. B-ultrasonography showed that the portal vein kept in normal size in 82% of the patients, the enlarged portal vein diminished in diameter, and the enlarged spleen reduced.

Adult↗