Biomedical subjects

T Li

Publications and source records attributed to T Li.

At least 181 records · Page 10Linked to original sources

PubMed2000

A conditional rescue system reveals essential functions for the ecdysone receptor (EcR) gene during molting and metamorphosis in Drosophila.

In Drosophila, pulses of the steroid hormone ecdysone trigger larval molting and metamorphosis and coordinate aspects of embryonic development and adult reproduction. At each of these developmental stages, the ecdysone signal is thought to act through a heteromeric receptor composed of the EcR and USP nuclear receptor proteins. Mutations that inactivate all EcR protein isoforms (EcR-A, EcR-B1, and EcR-B2) are embryonic lethal, hindering analysis of EcR function during later development. Using transgenes in which a heat shock promoter drives expression of an EcR cDNA, we have employed temperature-dependent rescue of EcR null mutants to determine EcR requirements at later stages of development. Our results show that EcR is required for hatching, at each larval molt, and for the initiation of metamorphosis. In EcR mutants arrested prior to metamorphosis, expression of ecdysone-responsive genes is blocked and normal ecdysone responses of both imaginal and larval tissues are blocked at an early stage. These results show that EcR mediates ecdysone signaling at multiple developmental stages and implicate EcR in the reorganization of imaginal and larval tissues at the onset of metamorphosis.

Animals↗

PubMed2000

Inhibitory effect of PGE2 on EGF-induced MAP kinase activity and rabbit corneal epithelial proliferation.

PURPOSE: To determine in rabbit corneal epithelial cells in culture whether epidermal growth factor (EGF)-induced increases in prostaglandin (PG) E2 production inhibit both the extracellular signal-regulated kinase 2 (Erk-2), a mitogen-activated protein kinase (MAPK), cascade activation, and the mitogenic response to this growth factor. METHODS: Serum starvation for 24 to 36 hours was used to synchronize cultures of SV40-transformed rabbit corneal epithelial (RCE) cells. The effects of exogenous PGE2, inhibition of PGE2 synthesis, and modulation of protein kinase A (PKA) activity on EGF-induced Erk-2 activation were assessed by immunoprecipitation, kinase assays, and Western blot analysis. PGE2 synthesis was measured by using enzyme-linked immunosorbent assay. [3H]-Thymidine incorporation was used to measure RCE cell proliferation rates. RESULTS: EGF (5 ng/ml) significantly increased PGE2 production in a time-dependent manner up to 94%+/-8% after 3 hours. EGF-induced PGE2 production was suppressed by AACOCF3, a phospholipase A2 (cPLA2) inhibitor. EGF-induced Erk-2 activation reached a maximal level at 15 minutes, followed by a decline toward the control level after 3 hours. In the presence of either PGE2 (50 microg/ml) or 8-CPT-cAMP (100 microM), the EGF-induced Erk-2 activation was lessened. PKA was activated by applications of EGF or PGE2 and suppressed by AACOCF3. On the other hand, either inhibition of PGE2 production with AACOCF3 or H-89, a PKA inhibitor, enhanced EGF-induced Erk-2 activity. Raf-1 activity was stimulated by EGF to maximal activity at 5 minutes and returned toward its control level after 60 minutes. As with the dependence of Erk-2 activity on PKA activity, in the presence of H-89, the EGF-induced Raf-1 activation was significantly enhanced. DNA synthesis was increased 59%+/-5% (n = 4) after EGF stimulation, indicating a mitogenic effect of EGF in RCE cells. Inhibition of cPLA2 activity with AACOCF3 increased DNA synthesis in RCE cells by another 64% relative to the effect of EGF alone. In contrast, with either PGE2 or 8-CPT-cAMP present the mitogenic response to EGF was totally suppressed. CONCLUSIONS: EGF-induced increases in PGE2 production dampened the mitogenic response to this growth factor. This suppression appears to be a consequence of PGE2-elicited increases in PKA activity, which leads to inhibition of EGF-induced activation of MAPK cascades at the level of Raf-1 and further affects downstream events including Erk-2. These results indicate that the mitogenic response to EGF in vivo in the proliferating basal cell layer may be dependent on the level of its PKA activity.

Animals↗

PubMed2000

Genetic characterization of gram-positive homologs of the XerCD site-specific recombinases.

Homologs of the XerCD enzymes, which in Escherichia coli have been shown to be responsible for resolving chromosomal multimers prior to chromosome segregation, were identified in the genomes of Staphylococcus aureus and Streptococcus pneumoniae. Phylogenetic and conservation pattern analysis suggests that the S. aureus gene products are orthologs of XerC and D. A S. aureus xerC null mutant displayed in vitro characteristics consistent with the segregation defect reported for E. coli xer mutants, and was found to be attenuated in a murine infection model. Strikingly, the S. aureus xerD gene appears to be absolutely required for viability, and may therefore be the first example of an essential gene of the lambda integrase family. In contrast, phylogenetic and conservation pattern analysis show that the S. pneumoniae gene products are more closely related to phage integrases than to XerCD. S. pneumoniae xer1, 2 and 3 null mutants were each found to be attenuated in a murine infection model, suggesting that they may control processes which affect virulence.

Alleles↗

PubMed2000

Purification and characterization of a 4-hydroxybenzoate decarboxylase from an anaerobic coculture.

The oxygen-sensitive 4-hydroxybenzoate decarboxylase (4OHB-DC) activity from a phenol-carboxylating coculture, consisting of Clostridium-like strain 6 and an unidentified strain 7, was studied. Assays done with cell extracts showed that the optimal pH was 5.0-6.5 and the Km was 5.4 mM. The activity decreased by 50% in the presence of 5 mM EDTA, and it was restored and even enhanced by the addition of Mg++, Mn++, Zn++, or Ca++. After purification, the molecular mass of the enzyme was estimated as 420 kDa by gel chromatography, and as 119 kDa by SDS-PAGE, suggesting a homotetrameric structure. Its pI was 5.6. The N-terminal amino acid sequence showed 95% and 76% homology with the pyruvate-flavodoxin oxidoreductase (nifJ gene product) from Enterobacter agglomerans and Klebsiella pneumoniae, respectively. The purified enzyme also slowly catalyzed the reverse reaction, that is the phenol carboxylation. These characteristics suggest that this enzyme is different from other known decarboxylases. This includes the 4OHB-DC from Clostridium hydroxybenzoicum, which is the only one that had been purified before.

Amino Acid Sequence↗

PubMed2000

The large scale synthesis of "unnatural" amino acids.

The introduction of a stereogenic centre to produce an "unnatural" amino acid can be accomplished in a variety of ways ranging from asymmetric hydrogenation to biotransformations based on transaminase enzymes. Our transaminase approach can be used to access a wide variety of L- and D-amino acids from an alpha-keto acid substrate. It is run as a whole cell biotransformation and uses coupled enzyme systems. In addition, formation of amino acids with small side chains, such as 2-aminobutyrate, can cause significant isolation problems due to the presence of small amounts of other amino acids, such as alanine. The improvements we have made to the approach are illustrated with 2-aminobutyrate as the example. Aspartic acid is used as the amino donor and gives rise to the formation of pyruvate, a substrate for the transaminase enzymes. We have now developed an alternative approach where lysine is used as the amino donor to allow formation of a cyclic by-product that is removed from the equilibrium.

Amino Acids↗

PubMed2000

[Inhibiting effect of antisense oligodeoxynucleotide of alpha 1(I) Precollagen gene on hypertrophic scar in an animal model].

OBJECTIVE: To study the effect of antisense oligodeoxynucleotide (ODN) of alpha 1(I) precollagen gene on hypertrophic scar in an animal model. METHOD: Hypertrophic scar was explanted in athymic mice. The effect of antisense oligodeoxynucleotide 1 and 2 on the animal model and the inhibition of ODN1 and ODN2 were observed. RESULT: It was showed that antisense oligo (ODN1, 21 bp) located 5'end from the translation start region and antisense oligo (ODN2, 22 bp) between the first exon and the first intron could effectively inhibit scar hypertrophy. However the control groups showed no inhibition. CONCLUSION: Antisense oligodeoxynucleotide could effectively inhibit scar hypertrophy by inhibiting the synthesis of type I collagen protein.

Animals↗

PubMed2000

[Effect of different source iron on piglet's growth, metabolism and environment].

In order to approach the effect of different source Fe on piglet's growth, metabolism and environment, an experiment was conducted with 158 suckling pigs from 15 litters, which were randomly allocated to group I, II and III, and fed with diet I (basal diet + FeSO4.H2O), II (basal diet + Fe-citric acid) and III (basal diet + Fe-methionine complex), respectively. Each of the diets contained 146 mg.kg-1 Fe. The results show that after the experiment ended, the body weight, daily increment, grades for appearance and behavior, hemoglobin concentration in blood, Fe-transferring albumen concentration in plasma, and Fe contents in plasma and liver of 35 days old piglets in group II and III were higher (P < 0.05 or P < 0.01) than those in group I, while the feed conversion, diarrhea incidence, fecal amount and its Fe content of the piglets in group II and III were lower (P < 0.05 or P < 0.01) than those in group I. The body weight and daily gain of the piglets in group III were also higher (P < 0.05) than those in group II, but no significant differences (P > 0.05) in other traits between group II and III. It is suggested that Fe-methionine complex and Fe-citric acid could improve piglet's health, growth and development, feed conversion, and physiological and biochemical parameters, increase the absorption and utilization of Fe by piglet's body, and decrease the fecal amount and its Fe content. Both of them should be effective and safe Fe sources for suckling pigs.

Animals↗

PubMed2000

Transcatheter closure of secundum atrial septal defects using Amplatzer device.

OBJECTIVE: To evaluate the feasibility and short term results of transcatheter closure of secundum atrial septal defects (TCSASDs) using Amplatzer occluder device. A new self-centering device, the Amplatzer atrial septal occluder, has recently been evaluated in an animal model with excellent results. This paper reports our clinical research with this device. METHODS: 30 patients underwent an attempt at TCSASDs at an average age of 35.6 +/- 15.9 y (range, 5-62 y) and average weight of 63.6 +/- 14.5 kg (range, 17-78 kg) using the Amplatzer atrial septal occluder. The average ASD diameter measured by transesophageal echocardiography (TEE) was 23.6 +/- 4.0 mm (range, 16-31 mm), and the average atrial septal defects (ASD) balloon stretched diameter was 25.2 +/- 5.8 mm (range, 9-34 mm). All patients had right atrial and ventricular volume overload with a Qp/Qs of 3.4 +/- 1.2 (1.4-5.2). A F8-12 catheter was used for delivery of the device in all patients. RESULTS: The device was placed correctly in all patients. There was immediate and complete closure in 30 patients. The average device waist size used to close the defect was 25.6 +/- 5.9 mm (range, 9-34 mm). There was no episode of device embolization or any other complication. Follow-up was performed using transthoracic echocardiography (TTE) 1 day, 1 month, 3 months, 6 months and 1 year after the procedure. The first day after operation; there was complete closure of the ASD in all patients; there have been no episodes of endocarditis, thromboembolism, or wire fracture. CONCLUSION: TCSASDs using the Amplatzer occluder device was an efficient nonsurgical method which had a very high technical success rate and satisfactory short term and follow-up results.

Adult↗

PubMed2000

[Total wrist arthroplasty].

OBJECTIVE: To review the history and current status of total wrist arthroplasty. METHODS: The original articles about wrist arthroplasty in recent years were reviewed. RESULTS: The properties of wrist prosthesis of different generations were reviewed, with the emphasis on the prosthesis design and biomechanical behaviours. The surgical techniques, complications and salvage procedures were also discussed. CONCLUSION: Although wrist arthrodesis is highly successful in treating the end-stage wrist arthritis, total wrist arthroplasty using well-designed prosthesis remains an alternative for the patients with special demands of hand functions.

Animals↗

PubMed2000

[Expression of p53 protein during 4NQO-induced lingual carcinogenesis in two strains of rats].

OBJECTIVE: To investigate p53 protein expression during lingual carcinogenesis in two strains of rats. METHODS: Dark-Agouti (DA) and Wistar/Furth (WF) rats were administrated with 4-nitroquinoline 1-oxide (4NQO) in drinking water and expression of p53 was studied using experimental materials obtained at 2, 4, 8, 12, 16, and 26 weeks of 4NQO treatment. RESULTS: Epithelial clusters of p53 positive cells appeared earlier and more in numbers in DA rats than in WF. A marked increase of p53+ clusters in DA rats was noted at later stages of the experiment, whereas those in WF rats appeared to be unchanged. CONCLUSIONS: These results suggest that there may be genetically determined variations in the p53 response to 4NQO between DA and WF rats, and these differences may contribute to their contrasting susceptibility during lingual carcinogenesis.

4-Nitroquinoline-1-oxide↗

PubMed2000

[Endovascular embolization treatment of intracranial aneurysms].

OBJECTIVE: To evaluate the effect of endovascular embolization of intracranial aneurysms with detachable coil and detachable balloon and emphasize the mainpoint of embolic technique. METHODS: 194 patients underwent complete cerebral angiography using microcatheter under DSA imaging. 80 cases with 90 aneurysms were emboliced by MDS, 69 cases with 71 aneurysms were emboliced by GDC. 37 of 40 giant aneurysms were emboliced by detachable balloon, 2 aneurysms by GDC, 1 by MDS. RESULTS: 194 patients with 201 aneurysms were cured successfully; 191 cases recovered clinically, 3 patients died. 187 aneurysms achieved 100% embolization, 8 with 95% embolization, 4 with 90% embolization, and 1 with 80% embolization. Four aneurysms reputured during the embolization, 4 patients had cerebral infarction, one patient died by hard-treated cerebral vasospasm which was affected by microcoil escape. Two recurrent cases were cured by second GDC embolization. CONCLUSIONS: The method of endovascular embolization to treat intracranial aneurysm is safe, reliable and effective. Those cases with giant aneurysms will have high recurrence in the future. Patients who suffer from SAH repeatedly may have great possibility of aneurysm rupture during embolization.

Adult↗

PubMed2000

[Effects of Asiaticoside on hypertrophic scars in a nude mice model].

OBJECTIVE: To study the effect of Asiaticoside on the fibroblast collagen biosynthesis in vitro culture and on the hypertrophic scar in a nude mice model, and its mechanism. METHODS: Light microscope (LM) and electron microscope (EM) were employed to study the morphological changes in fibroblast before and after the application of Asiaticoside. The fibroblast collagen synthesis was assayed by (3)H-proline incorporation. A nude mice model with hypertrophic scar was established for observing the effect of Asiaticoside given by local injection. RESULTS: It was found that Asiaticoside could significantly affect the ultrastructure of fibroblast and inhibit its collagen synthesis in vitro culture (P < 0.01) in a manner of dose-effect relationship. Local injection of Asiaticoside into the nude mouse body could inhibit the proliferation of scar without any toxic effect. CONCLUSION: The possible mechanism of the effect of Asiaticoside on hypertrophic scars is related to its inhibitory action on the fibroblast proliferation and collagen synthesis.

Animals↗

PubMed2000

[Pharmacokinetic analysis of lactosaminated human growth hormone and human growth hormone].

This study was undertaken to explore and compare the pharmacokinetic features of lactosaminated human growth hormone(hGH-L) and human growth hormone (hGH). Radioimmunoassay (RIA) technique was used. After mice were intravenously injected with hGH-L, their blood and liver samples were collected and handled. The blood drug concentration and liver drug concentration were determined using RIA technique. Then the pharmacokinetic parameters were obtained by analysing the curves of blood drug concentration-time and liver drug concentration-time. hGH was determinated with the same methods. The results showed that the area under curve (AUC) of blood drug concentration-time curve of hGH-L was 32,686.90, the mean remain time (MRT) of hGH-L in blood was 21.37 minutes, but the AUC of blood drug concentration-time curve of hGH was 36,913.08 and the MRT of hGH in blood was 24.98 minutes. Therefore, in blood, the uptake of hGH-L was less than that of hGH, the removal of hGH-L was faster than the removal of hGH. In liver, for hGH-L, the half-time of distribution (t1/2 alpha) was 1.84 minutes, the half-time of removal(t1/2 beta) was 11.09 minutes, the AUC of liver drug concentration-time curve was 17,621.9; for hGH, the t1/2 alpha was 2.11 minutes, the t1/2 beta was 75.65 minutes, the AUC of liver drug concentration-time curve was 12,148.2. Therefore, in liver, the uptake of hGH-L was more than that of hGH, the distribution and removal of hGH-L were faster than those of hGH. Therefore, the pharmacokinetic features of hGH-L was better than the feature of hGH.

Amino Sugars↗

PubMed2000

[Study on the xenoantigens of pancreatic tissues of Chinese Neijiang pig].

The expression and distribution of xenoantigens in pancreatic tissue of Neijiang pig were investigated with immunohistochemistry technique. BSIB4, normal human serum and anti-human A, B, H monoclonal antibodies were used as the primary antibody to examine the expression of xenoantigens in the pancreatic tissues from 10 Neijiang pigs. The results demonstrate that compared with the negative results of human blood B and H type antigens, the alpha-Gal antigen was highly expressed on the pancreatic vascular endothelial cells and the duct epithelium. The human blood A type antigen was highly expressed on some islet cells, some exocrine secretory cells and all the duct epithelium. Since there are pre-exited xenoantibodies against pig pancreas cells in human serum, cross-matching test and graft pre-treatment are needed before clinical transplantation of pancreas. The expression of xenoantigens in Neijiang pig is different from other pig strains reported by others, which suggests that looking for a pig strain that contains less xenoantigens is possible.

ABO Blood-Group System↗

PubMed2000

[The regulation effects of growth factors on the procollagen gene expressions of human mandibular condylar cartilage cells].

OBJECTIVE: At the early stage of osteoarthrosis (OA) and joint damage, the cartilage cells proliferation increases dramatically, but this repair process is finally replaced by the progressive destruction of the cartilage. The reason, in accordance to the latest research, is the abnormal phenotype of the involved cartilage cell. This result suggests that the regulation of cartilage cell phenotype may be an effective way in the treatment of OA and other cartilage destructive diseases. In this study, the effects of transforming growth factor-beta(TGF-beta), insulin-like growth factor-I (IGF-I) and basic fibroblast growth factor (bFGF) on collagen expression of human mandibular condylar cartilage cells was investigated. METHODS: Chondrocytes were isolated from human fetus by enzymatic method. The second passage of the cells was used in this study. They were cultured in DMEM medium supplemented with 20% newborn calf serum (NCS). After the cells reached confluence, the medium was replaced by DMEM containing 0.4% NCS. Then the cells were exposed to different growth factors including IGF-I (10 ng/ml), TGF-beta (5 ng/ml) and bFGF (50 ng/ml). The steady state mRNA levels of different samples were examined by slot-blot hybridization. The results were analysed by Student t test. RESULTS: IGF-I had the least effects on the mRNA levels of three kinds of procollagen (type I, type II and type III). On the other hand, bFGF and TGF-beta could inhibit the expression of type II collagen by 0.352 and 0.685 times comparing with the control groups separately. TGF-beta increased type I collagen expression. Besides, bFGF and TGF-beta also increased the value of type I collagen/type II collagen. None of the three kinds of growth factors had obvious effects on the expression of type III collagen. CONCLUSION: IGF-I can maintain the chondrocyte differentiated phenotype, while TGF-beta and bFGF have inhibitory effects.

Cells, Cultured↗

PubMed2000

[Neuroprotective effect of alpha-dihydroergocryptine depends on activation of nuclear factor kappa B].

AIM: To investigate the relationship between the neuroprotective effect of alpha-dihydroergocryptine (alpha-DHEC) and the activation of nuclear factor Kappa B (NF-Kappa B). METHODS: Adult male rats were subjected to cerebral ischemia induced by middle cerebral artery occlusion (MCAO). DNA binding activity of NF-Kappa B was determined with electrophoretic mobility shift assay (EMSA) in animals subjected to varying durations of cerebral ischemia. Neuroapoptosis induced by ischemic damage was measured by deoxynucleotidy transferase-mediated dUTP nick end labeling (TUNEL) assay and flow cytometry (FCM) analysis. RESULTS: No change was observed in nuclear NF-Kappa B DNA binding in normal animal. A low level of constitutive NF-Kappa B DNA binding was detected in animals subjected to cerebral ischemia of 1 h, and significant increase in the amount of active NF-Kappa B in nuclear extracts was observed after cerebral ischemia of 3 h, 6 h, and 12 h. Peak of NF-Kappa B DNA binding was observed at the time point of 3 h. Animals subjected to cerebral ischemia of 3 h potentially initiates neuroapoptosis and activates NF-Kappa B in nuclear extract. Alpha-DHEC (100 micrograms.kg-1 and 150 micrograms.kg-1) showed significant protective effect on neuroapoptosis-induced by cerebral ischemia of 3 h, and inhibiting NF-Kappa B activation using 100 mg.kg-1 pyrrolidinedithiocarbamate (PDTC) in the continuous presence of alpha-DHEC, the neuroprotective effect of alpha-DHEC was blocked. CONCLUSION: The findings suggest that the neuroprotetive effect of alpha-DHEC may depend on the activation of NF-Kappa B.

Animals↗

PubMed2000

[Use of Hopkins rod-lens coupled with grasping forceps sheaths for extraction of tracheobronchial foreign bodies].

OBJECTIVE: To study the clinical application of Hopkins rod-lens coupled with gasping forceps sheaths in the extraction of tracheobronchial foreign bodies. METHODS: Sixty-two patients with tracheobronchial foreign bodies were operated on with Hopkins rod-lens coupled with grasping forceps sheaths under direct telescopic view or TV watching. High frequency jet ventilation was used and BPs ECGs SaO2 were monitored in all cases. RESULTS: Sixty-two patients were all successfully operated on. The extraction was primarily successful in 90% of the cases; and secondarily successful in 7% of the cases. No death and serious complication occurred. CONCLUSION: Compared with conventional bronchoscopic foreign body extraction, this new instrument and technique make it possible for the operator to clamp and extract foreign body under direct telescopic view or TV watching. It has increased the accuracy and safety of bronchoscopic extraction of tracheobronchial foreign bodies.

Adolescent↗

PubMed2000

[Investigation of the nasal T/NK cell lymphomas in 14 cases].

OBJECTIVE: To study the biologic behavior, pathologic features as well as clinic manifestations of the nasal T/NK cell lymphomas, and to provide experiences for the diagnosis and treatment of the tumor. METHODS: Specimens of 23 cases lethal midline granulomas (LMG) were examined: (1) HE stain for immunohistochemical staining for TIA-1, CD43, CD20, CD3 epsilon, CD56 and in situ hybridization for EBV encoded small nuclear RNA(EBER1/2, Y017, DAK0). (2) The cases histories were reviewed. RESULTS: (1) 14 cases were confirmed by histological features. In the 14 cases, tumor cells expressed TIA-1, CD56, CD3 epsilon, CD43, EBER1/2 positive. (2) Among them 8 cases (57%) showed special clinic features of LMG, Nasopharynx, pharynx and laryngeal involvement were found in other 6 cases. One case revealed lymphoid leukemia. In other 2 cases, gastrointestinal tract were involved. Hemophagocytic syndrome (HPS) complication happened in 1 case. CONCLUSION: The tumor cells of nasal T/NK cell lymphomas expressed TIA-1, CD56, CD43, CD3 epsilon may suggest it originates from NK cell. The high association with EBV may suggest in situ hybridization. 57% patients showed that the special clinic features of the LMG, and gastrointestinal tract, bone marrow, peripheral blood were involved in some cases. One case complicated with hemophagocytic syndrome (HPS).

Herpesvirus 4, Human↗