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Biomedical subjects

B Xu

Publications and source records attributed to B Xu.

At least 91 records · Page 5Linked to original sources
PubMed2001

Functional comparison of the single-layer agarose microbeads and the developed three-layer agarose microbeads as the bioartificial pancreas: an in vitro study.

In this study, the insulin secretory characteristics of the microencapsulated hamster islets were studied during long-term culture. The hamster islets were encapsulated as single-layer agarose microbeads or three-layer agarose microbeads with agarose and agarose containing poly(styrene sulfonic acid) (PSSa), respectively. The influence of PSSa on the function of the rat islets microencapsulted in three-layer microbeads was primarily monitored. The aim of this study was to examine the influence of the PSSa on the in vitro function of the islets encapsulated in the agarose/PSSa microbeads compared with single-layer agarose microbeads during long-term culture. The microbeads were cultured for 30 days in medium of Eagle's MEM at 37 degrees C in 5% CO2 and 95% air. The basal insulin secretion into the culture medium was measured daily during the first 12 days and two times per week until 30 days. The microbeads were subjected to static incubation test on the 10th, 20th, and 30th day during culture. The basal insulin secretion level of the agarose/PSSa microbeads was significantly higher than that of single-layer agarose microbeads. The static incubation tests revealed a similar pattern of insulin secretion from both microbeads when they were exposed to high glucose challenge. In the static incubation test, both could significantly increase insulin release to more than 6.61 times (stimulation index) in response to high glucose stimulation and could significantly decrease when glucose concentration returned from high glucose to low glucose on the 10th, 20th, and 30th day of culture. This study demonstrated that the hamster islets enclosed in agarose/PSSa hydrogel not only continuously secreted basal amounts of insulin, but also maintained their response to high glucose stimulation similar to the agarose microbeads. The above results together with those of our previous in vivo study suggest that the three-layer microbeads (agarose/PSSa) are well suitable for xenotransplantation of islets for the clinical application.

Animals↗
PubMed2001

The influence of the anticomplement synthetic sulfonic polymers on the function of pancreatic islets: an in vitro study.

In a previous experiment, we demonstrated the anticomplementary efficacy of poly(stryrene sulfonic acid) (PSSa) and poly(2-acrylamido-2-methyl propane sulfonic acid) (PAMPS). The aim of this study was to examine their influence on the function of pancreatic islets in vitro. In this study, after culturing the rat islets with RPMI-1640 culture medium containing different concentrations of soluble PSSa or PAMPS for 24 h at 37 degrees C, we performed morphological and functional examination of the rat islets. We found that the islets maintained their normal morphology regardless of whether they were in the PSSa or PAMPS groups when the concentrations of soluble PSSa or PAMPS in the media were below 1 g/dl. In the static incubation study, the islets cultured in the PAMPS groups showed significantly high insulin secretory response to glucose challenge but those in the PSSa groups lost the response when the concentrations of soluble PSSa or PAMPS in the media were below 1 g/dl. The PAMPS not only had strong anticomplementry effect, but also maintained the good insulin secretory capacity of the islets. These results indicated that PAMPS is a promising bioartificial material for future clinical application of biohybrid artificial pancreas preparation. It is well suitable for xenotransplantation experiments.

Animals↗
PubMed2001

A retrospective study of continuous renal replacement therapy versus intermittent hemodialysis in severe acute renal failure.

OBJECTIVE: To investigate the efficacy of continuous renal replacement therapy (CRRT) versus intermittent hemodialysis (IHD) in patients with severe acute renal failure (ARF). METHODS: One hundred and ninety-three severe ARF patients who received renal support between December 1978 and December 1998 were involved in this study. Of them, 101 (52.3%) were treated with CRRT (CRRT group), and 92 (47.7%) with IHD (IHD group). RESULTS: Sixty (59.4%) patients in the CRRT group got through the acute phase of disease and 41 (40.6%) patients did not survive while in the IHD group 59 (64.1%) patients survived and 33 (35.9%) patients did not. No significant difference in survival rate was found between the two groups. 24 of 64 patients (37.5%) in the CRRT group with multiple organ dysfunction syndrome (MODS) survived, while in the IHD group, 8 out of 44 (27.3%) survived, their survival rate was much lower than that in the CRRT group. Patients in CRRT group were more severely ill, as manifested by lower mean arterial pressure, higher APACHE II score, more dysfunctioned organs and requiring mechanical ventilation and vasopressor support as compared with patients in the IHD group, CRRT was found to improve hemodynamic stability with a better fluid balance and control of biochemical status, increased nutritional intake and a shorter duration of acute renal failure (P < 0.05). CONCLUSION: CRRT perhaps may be the best choice in the treatment of severe ARF patients, for it can offer several distinct advantages compared to IHD. These may contribute to improving the survival rate of ARF patients, particularly those that are critically ill patients.

Acute Kidney Injury↗
PubMed2001

Relationship between lactone ring forms of HCPT and their antitumor activities.

AIM: To study the relationship between the lactone forms of 10-hydroxycamptothecin (HCPT) and their antitumor activities. METHODS: Antitumor activity of the two forms of HCPT was studied in vitro using seven cultured human and mouse tumor cell lines. Mice bearing sarcoma 180 and solid hepatoma were treated with HCPT (0.5, 1, and 2 mg/kg, ip) and tumor growth inhibition was assayed. HPLC method was employed to investigate the conversion of two forms of HCPT in different pH conditions and cultured tumor cells. RESULTS: It was found that both forms of HCPT (O-HCPT and C-HCPT) showed similar activities in vitro against a number of tumor cell lines at the same concentration; but C-HCPT was more effective (about two times) than O-HCPT in vivo. The difference between in vitro and in vivo results could be explained by the conversion of O-HCPT into C-HCPT in a certain condition, which was shown by the HPLC analysis of HCPT at different pH values and in cultured tumor cells. CONCLUSION: Both forms of HCPT were effective against tumor growth, but C-HCPT was more effective than O-HCPT, the latter could be converted into the former under certain conditions.

Animals↗
PubMed2001

High concentration of glucose inhibits endothelium-dependent vasorelaxation of rabbit aortic artery.

AIM: To determine whether high concentration of glucose inhibits endothelium-dependent vasorelaxation of rabbit aortic artery and possible mechanisms. METHODS: The organ-bath of rings of rabbit aorta was used to determine changes of tension of vessel in response to different concentrations of acetylcholine (ACh) and sodium nitroprusside (SNP) after removal of endothelium, coincubated with nitric oxide synthase (NOS) inhibitor L-NMMA, different concentrations of glucose, vitamin C, and cell-permeable superoxide dismutase-mimetic and oxygen-derived free radical scavenger manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin (MnTMPyP). RESULTS: ACh induced concentration- and endothelium-dependent aortic vasorelaxation. High concentration of glucose markedly inhibited this vasorelaxation, and vitamin C and MnTMPyP could not antaganize this inhibitory effect by high concentrations of glucose. SNP induced concentration-dependent and endothelium-independent vasorelaxation, and high concentration of glucose had no effect on the vasorelaxation by SNP. CONCLUSION: High concentration of glucose inhibited endothelium-dependent vasorelaxation and this effect was unlikely mediated through activating oxygen-derived free radical production.

Animals↗
PubMed2001

[The effects of dialysate and ultrafiltration flow rate on solute clearance during continuous renal replacement therapy].

OBJECTIVE: To study the solute clearance during various forms of continuous renal replacement therapy(CRRT) and test the formulas that allow the prediction of the influence of dialysate and ultrafiltration flow rate on small solute removal during CRRT. METHOD: Five patients with acute renal failure were included in the study and were treated by venovenous CRRT using the PRISMA predilution system. Solute clearance of urea nitrogen(UN), creatinine(Cr), uric acid(Ua), phosphate(P) and beta(2)-microglobulin(beta(2)-M) were evaluated during CRRT with different dialysates and ultrafiltration flow rates. RESULTS: The determined clearance of small molecular solutes during continuous venovenous hemofiltration (CVVH) and continuous venovenous hemodialysis(CVVHD) was similar with the following formulas: K(UF) = (Q(UF)/60) x Q(B)/(Q(B) + Q(UF)/60) (in CVVH), Kd = Q(D)/60 (in CVVHD), where K is the clearance, Q(B), Q(D) and Q(UF) are blood, dialysate and ultrafiltration flow rates, respectively. There was very significant correlation between calculated values of K(UF) and observed clearances of small solutes such as UN, Cr, Ua and P during CVVH, between calculated values of Kd and observed clearances of UN, Cr, Ua but not P during CVVHD (P < 0.001). Clearances of UN, Cr, Ua and P during CVVHD were greater than those during CVVH, but clearance of beta(2)-M during CVVHD was less than that during CVVH. Interaction between convection and diffusion was found during continuous venovenous hemodiafiltration (CVVHDF). CONCLUSIONS: The previous formulas can provide with the prediction of the clearance of small molecular solutes during CVVH and CVVHD. The present results demonstrate that diffusion is more efficient in removing small solutes than convection but less efficient in removing large solutes than convection. There is interaction between convection and diffusion during CVVHDF.

Acute Kidney Injury↗
PubMed2001

[Principle demonstration of nutrient delivery system in a space vegetable planting prototype facility].

Objective. To develop a nutrient delivery system for space vegetable planting prototype facility to be used in future space station, and to preliminarily testify its feasibility through ground-based demonstration experiments. Method. A nutrient delivery system in a space vegetable planting prototype facility was designed and fabricated, and ground based demonstration experiments of plant cultivation were conducted. Result. Nutrient could be steadily delivered to plant cultivation matrixes through capillary action, water content of planting matrixes could be controlled automatically and maintained constant, and the planted material lettuce showed basically normal morphology and color. Conclusion. The nutrient delivery system in a space vegetable planting prototype facility could basically meet the requirements for plant nutrient delivery under space microgravity environmental condition.

Capillary Action↗
PubMed2001

[The orthopedic treatment of skeletal class III malocclusion with maxillary protraction therapy].

OBJECTIVE: The aim of this study was to investigate the changes of skeletal anterior crossbite in early-stage after maxillary expansion and protraction therapy. METHODS: 40 chinese children with skeletal anterior crossbite were divided into two groups: the control group received no orthodontic treatment and the experimental group received maxillary expansion and protraction. The cephalometric analysis was used to evaluate the changes in both groups. RESULTS: In the experimental group, A point moved forward 3.5 mm (-1.75 mm in the control group). SNB, SNPg decreased and ANB, NP-PA increased. Protraction therapy to treat skeletal anterior crossbite in the middle and late stage of mixed dentition could influence craniofacial growth and development, such as accelerating forward growth of the maxilla, making mandible downward growth. CONCLUSIONS: Protraction therapy can achieve successful result in treatment of skeletal anterior crossbite in middle and late mixed dentition.

Child↗
PubMed2001

[A computer-aid study on the craniofacial features of Archang race in Yunnan province of China].

OBJECTIVE: Archang race is one of special minoritis in Yunnan province of China. However, there is not former report about overall craniofacial features in Archang race, therefore a computerized measurement on craniofacial features of Archang race was established in this study. METHODS: On the basis of the principles of random sampling, the craniofacial features of 196 normal adults of Archang race coming from Longchuan County, Dehong Dai Jingpo nationality autonomous prefecture in Yunnan province of China were investigated using the craniofacial video-computerized measurement system which was developed by us. RESULTS: Totally 41 measured items and 17 indexes of craniofacial features were obtained from male and female adults of Archang race. On the basis of 5 indexes, the people were classified according to the head, facial, and nose forms. CONCLUSION: The results of this study are of great importance in terms of that the reference is not only significant for anthropology, ethnology, but also for medicine and industry.

Aged↗
PubMed2001

[Spectra of Ce3+, Tb3+ and Gd3+ Ions in Ln(BO3,PO4) [Ln = La, Y]].

Emission and excitation spectra of Ce3+, Tb3+ and Gd3+ in lanthanum borophosphate and yttrium borophosphate are studied. The results show that Ce3+ emission weakens and Tb3+ emission enhances in La(BO3, PO4):Ce, Tb in the presence of Gd, and in Y(BO3, PO4):Ce, Tb, the Ce3+ and Tb3+ emissions are all enhanced, and the former increases more than the latter. In a whole, Gd3+ acts as intermediate of energy transfer from Ce3+ to Tb3+ and sensitizer in La(BO3, PO4):Ce, Tb, Gd; while in Y(BO3, PO4):Ce, Tb, Gd, Gd3+ acts only as sensitizer, and prevents energy transfer from Ce3+ to Tb3+. Compared with Y(BO3, PO4):Ce, Tb, Gd, La(BO3, PO4):Ce, Tb, Gd, phosphor absorbs ultraviolet radiation easily, and emits green light with higher purity and intensity under 254 nm excitation, so it is more suitable for green-emitting phosphor in fluorescent lamp.

Cerium↗
PubMed2000

Studies on the oxidative addition reaction of 1,1-dibromo-1-alkenes, alpha-dehalopalladation, and the intramolecular bis(carbopalladation) reaction of alkenes. An efficient entry to fused bicycles.

Twenty-three examples of 1,1-dihalo-1-alkenes were synthesized by the conventional alkylation methods. The oxidative addition reactions of 1,1-dibromo-2,2-diphenylethene or 1, 1-dibromo-2-phenylpropene with a stoichiometric amount of Pd(PPh(3))(4) afforded 1,2-diphenylacetylene and 1-phenylpropyne, respectively, indicating that alpha-dehalopalladation reaction occurred to afford vinylic carbene intermediates. However, alpha-dehalopalladation reaction was not observed in all 1, 1-dihalo-1-alkenes containing an extra C=C bond suitable for cyclic carbopalladation under the current reaction conditions probably due to the fast cyclic carbopalladation reaction of 40A-type of palladium intermediates; A series of bicycles, i.e., fused 5,6-, 6, 6-, 6,7-, and 7,7-bicyclic compounds, were prepared efficiently via this bicyclic carbopalladation protocol. Under condition A, within 0. 5 h, 10 afforded the monocyclic product 37 in 79%. With prolonged reaction time, 37 was converted to bicycle 36. Even with isolated 37, the corresponding reaction under condition A afforded 36 in 92% NMR yield, indicating a stepwise oxidative addition-cyclic carbopalladation-beta-elimination mechanism for this bicyclization reaction.

Journal Article↗
PubMed2000

Thyroid hormone response element sequence and the recruitment of retinoid X receptors for thyroid hormone responsiveness.

Thyroid hormone receptors (TRs) are transcription factors that bind to thyroid hormone response elements (TREs) in the regulatory regions of target genes. TRs are thought to activate transcription primarily as heterodimers with retinoid X receptors (RXRs), with RXR binding upstream to the two directly repeated half-sites in a typical TRE. However, given that TRs and RXRs prefer to bind to different DNA sequences (T(A/G)AGGTCA and GGGGTCA), we postulate that only certain TREs require RXR-TR heterodimerization, depending on the TRE sequence. We have tested this hypothesis by comparing in Saccharomyces cerevisiae the functional activity of TR +/- RXR on 10 naturally occurring mammalian TREs. S. cerevisiae was used as a model system because yeast lack endogenous nuclear receptors and thus can be manipulated to express TRs and/or RXRs. We first studied ligand-independent reporter gene activation, which reflects the activity of the activator function 1 (AF-1) domain. The 10 TREs formed a continuous spectrum from being fully dependent on RXR for TR AF-1 activity to being essentially independent of RXR. Relative independence of RXR generally was seen when the TRE upstream half-site has a TA or TG 5' to the core hexamer. Gel mobility shift assays revealed that functional independence of RXR correlates with the strong binding of TR alone, whereas more RXR dependence correlates with higher binding of RXR-TR heterodimers. Restoration of ligand-dependent (AF-2 domain) reporter gene activation was achieved by expression of the coactivator TIF2. This ligand-induced stimulation was stronger in the presence of TR alone than with RXR plus TR, suggesting a preference for TIF2 activation of TR homodimers. Overall the data support the notion that the TRE sequence plays an important role in determining the nuclear hormone receptor and coactivator requirements for TR action.

Base Sequence↗
PubMed2000

The role of brain-derived neurotrophic factor receptors in the mature hippocampus: modulation of long-term potentiation through a presynaptic mechanism involving TrkB.

The neurotrophin BDNF has been shown to modulate long-term potentiation (LTP) at Schaffer collateral-CA1 hippocampal synapses. Mutants in the BDNF receptor gene trkB and antibodies to its second receptor p75NTR have been used to determine the receptors and cells involved in this response. Inhibition of p75NTR does not detectably reduce LTP or affect presynaptic function, but analyses of newly generated trkB mutants implicate TrkB. One mutant has reduced expression in a normal pattern of TrkB throughout the brain. The second mutant was created by cre-loxP-mediated removal of TrkB in CA1 pyramidal neurons of this mouse. Neither mutant detectably impacts survival or morphology of hippocampal neurons. TrkB reduction, however, affects presynaptic function and reduces the ability of tetanic stimulation to induce LTP. Postsynaptic glutamate receptors are not affected by TrkB reduction, indicating that BDNF does not modulate plasticity through postsynaptic TrkB. Consistent with this, elimination of TrkB in postsynaptic neurons does not affect LTP. Moreover, normal LTP is generated in the mutant with reduced TrkB by a depolarization-low-frequency stimulation pairing protocol that puts minimal demands on presynaptic terminal function. Thus, BDNF appears to act through TrkB presynaptically, but not postsynaptically, to modulate LTP.

Animals↗
PubMed2000

Amperometric quantification of polar organic solvents based on a tyrosinase biosensor.

A novel amperometric biosensor for quantification of the electrochemically inert polar organic solvents based on tyrosinase electrode was preliminarily reported. The biosensor was fabricated by simply syringing an aqueous solution of tyrosinase/PVAVP (PVAVP: copolymer of poly(vinyl alcohol) grafting with 4-vinylpyridine) onto glassy carbon electrode surface followed by drying the modified electrode at +4 degrees C in a refrigerator. The current generated from electrochemical reduction of quinone is a probe signal. The biosensor can be used for quantification of polar organic solvents, and its mechanism was characterized with in situ steady-state amperometry-quartz crystal microbalance experiments. The detection limit, sensitivity, and dynamic range for certain organic solvents are dependent on the kind and concentration of the substrate probe and the hydrophobicity of the immobilization matrix. The response time for all the tested organic solvents is less than 2 min.

Acetonitriles↗
PubMed2000

beta(2)-adrenoceptors activate nitric oxide synthase in human platelets.

Nitric oxide (NO), generated by platelets through stimulation of nitric oxide synthase (NOS), limits platelet adhesion and aggregation after a prothrombotic stimulus. Platelet beta-adrenoceptors (betaARs) mediate inhibition of aggregation, but no direct link has been shown between these receptors and platelet adhesion or NO production. We examined NOS activity in human platelets from the conversion of L-[(3)H]-arginine to L-[(3)H]-citrulline, after betaAR stimulation or cAMP elevation. Basal NOS activity was 0.11+/-0.03 pmol L-citrulline/10(8) platelets. The betaAR agonist isoproterenol 1 micromol/L and the adenylyl cyclase activator forskolin 1 micromol/L each increased NOS activity, to 0.26+/-0.04 and 0.23+/-0.03 pmol L-citrulline/10(8) platelets, respectively (P<0.01 for each). Both responses were abolished by the adenylyl cyclase inhibitor SQ22536 50 micromol/L. NOS activation by isoproterenol or forskolin was not associated with a change in intracellular Ca(2+). In functional studies, isoproterenol inhibited U46619-induced platelet aggregation in a concentration-dependent manner, but this effect was not significantly diminished by NOS inhibition. In contrast, thrombin-stimulated platelet adhesion to cultured human umbilical vein endothelial cell monolayers was inhibited by isoproterenol, and this effect was abolished by NOS inhibition (1.3+/-0.2% versus 2.6+/-0.2% respectively; P<0.001). Effects of isoproterenol on NOS activity, platelet aggregation, and adhesion were mediated exclusively through beta(2)ARs, as determined by coincubation with betaAR subtype-selective antagonists. We conclude that beta(2)ARs activate platelet NOS by increasing cAMP, and that this activation is Ca(2+)-independent. beta(2)ARs may contribute to modulation of platelet aggregation and adhesion to endothelium, and our findings suggest that activation of the L-arginine/NO system mediates the effects of beta(2)ARs on adhesion but not aggregation.

Blood Platelets↗
PubMed2000

WNK1, a novel mammalian serine/threonine protein kinase lacking the catalytic lysine in subdomain II.

We have cloned and characterized a novel mammalian serine/threonine protein kinase WNK1 (with no lysine (K)) from a rat brain cDNA library. WNK1 has 2126 amino acids and can be detected as a protein of approximately 230 kDa in various cell lines and rat tissues. WNK1 contains a small N-terminal domain followed by the kinase domain and a long C-terminal tail. The WNK1 kinase domain has the greatest similarity to the MEKK protein kinase family. However, overexpression of WNK1 in HEK293 cells exerts no detectable effect on the activity of known, co-transfected mitogen-activated protein kinases, suggesting that it belongs to a distinct pathway. WNK1 phosphorylates the exogenous substrate myelin basic protein as well as itself mostly on serine residues, confirming that it is a serine/threonine protein kinase. The demonstration of activity was striking because WNK1, and its homologs in other organisms lack the invariant catalytic lysine in subdomain II of protein kinases that is crucial for binding to ATP. A model of WNK1 using the structure of cAMP-dependent protein kinase suggests that lysine 233 in kinase subdomain I may provide this function. Mutation of this lysine residue to methionine eliminates WNK1 activity, consistent with the conclusion that it is required for catalysis. This distinct organization of catalytic residues indicates that WNK1 belongs to a novel family of serine/threonine protein kinases.

Amino Acid Sequence↗
PubMed2000

ATM phosphorylates p95/nbs1 in an S-phase checkpoint pathway.

The rare diseases ataxia-telangiectasia (AT), caused by mutations in the ATM gene, and Nijmegen breakage syndrome (NBS), with mutations in the p95/nbs1 gene, share a variety of phenotypic abnormalities such as chromosomal instability, radiation sensitivity and defects in cell-cycle checkpoints in response to ionizing radiation. The ATM gene encodes a protein kinase that is activated by ionizing radiation or radiomimetic drugs, whereas p95/nbs1 is part of a protein complex that is involved in responses to DNA double-strand breaks. Here, because of the similarities between AT and NBS, we evaluated the functional interactions between ATM and p95/nbs1. Activation of the ATM kinase by ionizing radiation and induction of ATM-dependent responses in NBS cells indicated that p95/nbs1 may not be required for signalling to ATM after ionizing radiation. However, p95/nbs1 was phosphorylated on serine 343 in an ATM-dependent manner in vitro and in vivo after ionizing radiation. A p95/nbs1 construct mutated at the ATM phosphorylation site abrogated an S-phase checkpoint induced by ionizing radiation in normal cells and failed to compensate for this functional deficiency in NBS cells. These observations link ATM and p95/nbs1 in a common signalling pathway and provide an explanation for phenotypic similarities in these two diseases.

Ataxia Telangiectasia↗