Search PubMed⌕ Search

Biomedical subjects

L Liu

Publications and source records attributed to L Liu.

At least 235 records · Page 13Linked to original sources
PubMed2001

Deletion of rapQONML from the rapamycin gene cluster of Streptomyces hygroscopicus gives production of the 16-O-desmethyl-27-desmethoxy analog.

Five contiguous genes in the rapamycin gene cluster, rapQONML, of Streptomyces hygroscopicus ATCC29253 were replaced with a neomycin resistance marker by double homologous recombination. The resulting strain, if fed pipecolate, produced the analog 16-O-desmethyl-27-desmethoxyrapamycin instead of rapamycin. This indicates that the P450 hydroxylase encoded by rapN is specific for C-27, and that the O-methyltransferases encoded by rapQ and rapM methylate the hydroxyl groups on C-16 and C-27. By inference, the remaining P450 hydroxylase and methyltransferase genes (rapI and rapJ) are responsible for hydroxylation of C-9 and methylation of the C-39 hydroxyl, consistent with their homology to fkbD and fkbM, respectively, in the FK506 cluster. The relatively high level of 16-O-desmethyl-27-desmethoxyrapamycin produced indicates that the reactions at C-9 and C-39 do not require previous modification of the macrolactone precursor at either C-16 or C-27.

Anti-Bacterial Agents↗
PubMed2001

[Painting the chromosomes of fishes with human sex chromosome-specific DNA probes].

Chromosome painting is one of the effective methods in studying the evolution of genomes. The chromosomes of the species of fishes--M. aculeatus, M. albus and D. rerio were painted respectively with human X and Y chromosome-specific DNA probes. The results showed that some homologous segments of human X chromosome were found in the genomes of all the three kind of fishes, all the segments were scattered on several pairs of homologous chromosomes in each kind of fish. But no homologous segment of the human Y chromosome was found.

Animals↗
PubMed2001

Psychometric properties of the driVR: a virtual reality driving assessment.

This study provides data on the psychometric properties of the driVR, a virtual reality assessment used to assess driving in persons with brain injury. Several driVR measures were compared to other established indicators of driving performance. Many concurrent validity coefficients over r = 0.3 were identified between driVR measures of lane tracking with on-road, Trail Making Test, and the Driver Performance Test II scores. The results provide further evidence to support the concurrent validity of the driVR. Continued research addressing other aspects of validity and reliability is recommended.

Adult↗
PubMed2001

The suitability of hepatocyte culture models to study various aspects of drug metabolism.

Since the liver is the main organ involved in the metabolism and the toxicity of xenobiotics, isolated rat hepatocytes have been increasingly used in recent years as a model to identify pharmacological and toxicological responses of drugs. However, it is generally recognised that isolated hepatocytes retain most of their functions only for a short period. For this reason, numerous models and techniques have been developed to study and improve the metabolic capacity of hepatocytes in vitro over an extended time period and in application for drug metabolism studies. In the present study, we compared four different cell culture models to fulfill these requirements and have therefore harvested hepatocytes and cultured them in different culture systems over two weeks. In order to prove certain advantages or disadvantages of each model, we compared the metabolic capacity, albumin secretion, the release of cytosolic and mitochondrial enzymes, as well as the capacity to metabolise diclofenac (DF). We found that rat hepatocytes in all studied culture models (except the Unisyn Bioreactor) were able to metabolise DF to the same extent as found in vivo. However, the concentration of metabolites was found to decrease with culture time using the monolayer although the DF metabolite level in the collagen Sandwich culture was higher than that of the monolayer culture. The 3D-membrane bioreactor preserved the metabolic capacity for a prolonged period of time. The concentrations of DF metabolites in the Unisyn hollow fiber bioreactor were below the detection limit, which corresponded to other parameters such as albumin secretion and cytochrome P450 activity, disqualifying this culture system clearly for the use of in vitro primary hepatocyte cultures. The other three systems all have their place in drug metabolism with different advantages. However, our studies clearly showed that hepatocytes cultured within a collagen sandwich or in the 3D-membrane bioreactor qualify to study various aspects of drug metabolisms over a long time period. Further studies are needed to prove if the later two culture models may really help to reduce animal testing.

Alanine Transaminase↗
PubMed2001

[Reduction of FHIT gene expression in primary lung cancer: relationship with the proliferation and apoptosis of tumor cell].

OBJECTIVE: To investigate the role of FHIT(fragile histidine triad) gene in oncogenesis and progression of human lung cancer and explore the relationship of FHIT gene expression with the proliferation and apoptosis of tumor cells. METHODS: The expression of FHIT gene and that of Ki-67 were detected in 166 lung cancer samples and 37 lung benign lesion tissues as control by immunohistochemistry, and the apoptotic level of tumor cell was detected by terminal deoxynucl neotidyl transferase mediated dUTP nick end labelling(TUNEL). RESULTS: (1)The expression level of FHIT gene was found to be significantly lower in lung cancer tissues than in benign lesion tissues (P<0.01); (2)The expression level of FHIT gene was closely related to histological classification, cancer cell differentiation, P-TNM stages and lymph node involvement in lung cancer patients (P<0.05); (3)Lasting and heavy smoking might be one of the important reasons of reduction of FHIT gene expression in lung cancer patients; (4)The postoperative survival time of patients in high FHIT expression group was significantly longer than those in low expression group (P<0.05); (5)The reduction of FHIT gene expression might be related with the over-proliferation and suppression of apoptosis of lung cancer cell(P<0.01). CONCLUSION: FHIT gene may play a role in the regulation of proliferation and apoptosis of lung cancer cell. And reduction of FHIT gene expression may be related to the pathogenesis and development of lung cancer.

Acid Anhydride Hydrolases↗
PubMed2001

[Expression of delta 6-fatty acid desaturase gene from Mortierella alpina in Saccharomyces cerevisiae].

delta 6-fatty acid desaturase is the rate-limiting enzyme of the desaturation of linoleic acid in the production of an essential fatty acid, gamma-linolenic acid. The 1.4 kb fragment in plasmid pTMACL6 encoding delta 6-fatty acid desaturase from Mortieralla alpina ATCC16266 was subcloned into the yeast-E. coli shuttle vector pYES2.0, thus an expression recombinant plasmid pYMAD6 containing target gene was constructed and obtained in the SC-Ura media. The pYMAD6 was introduced into defective mutant INCSc1 of Saccharomyces cerevisiae by LiAc method. When linoleic acid was provided as an exogenous substrate to the yeast cultures expressing delta 6-fatty acid desaturase activity under appropriate media and temperature condition, the level of gamma-linolenic acid reached 31.6% of the total yeast fatty acids by GC-MS detecting, which is the highest report of delta 6-fatty-acid desaturase gene in S. cerevisiae.

Fatty Acid Desaturases↗
PubMed2001

[Effect of dissolved oxygen on the suspension culture of Taxus chinensis].

The effect of dissolved oxygen controlled level on the taxol production by suspended cell culture of Taxus chinensis was examined in shake flasks and in a 20L aerated and agitated bioreactor with a six-flat-bladed turbine. It was found in shake flasks that oxygen supply exhibited significant influence on the production of taxol. Further investigation in bioreactor showed that noly 1.5 mg/L taxol was produced when DO(dissolved oxygen) level was 20%. Taxol production increased when DO level was increased to 40%-60%. Moreover, taxol accumulation was remarkably improved by the cultivation of cells initially at the DO level of 60% during the growth phase for 14 days followed by changing the DO level to 20%-40% during the taxol production phase for another 10 days. An optimum taxol level of 7.2 mg/L was obtained by the dissolved oxygen controlled process.

Cell Culture Techniques↗
PubMed2001

[The cloning and verification of the Sox9 gene of the rice field eel].

The Sox 9 gene plays important roles in sex determination, which is conserved in a variety of species including mammals and chicken. The positive lambda clone of the Sox 9 gene of the rice field eel was analyzed by restriction enzymes and the restriction map was constructed. This clone was further verified to be the Sox9 gene by PCR amplification and sequencing of the HMG box region. The cloning of the Sox9 gene of the rice field eel further suggests the evolutionary conservation of this gene.

Animals↗
PubMed2001

[Modeling research about bioremediation of organic pollutants in soil-water-microbes system].

A new Theory, organic pollutant sequestration inside soil particles, was applied in the research in order to explain the persistence of residual chemicals in remediation sites. Based on this theory, a mathematical model which simulates organic pollutant bioremediation process in soil-water-microbes system was developed. In the model, diffusion is represented by Fick's second law, reversible sorption-desorption by a linear isotherm, irreversible sequestration by a pseudo-first order kinetics, and biodegradation by Monod kinetics. Model results match successfully with experimental data. Model simulations are performed in the study. It is noteworthy that the mathematical model will be useful in quantitatively predicting the time and degradation extend of organic pollutant in remediation sites.

Biodegradation, Environmental↗
PubMed2001

[Phenotyping and genotyping studies in a family with the compound heterozygosity for a deletional delta beta-thalassemia and a beta-thalassemia].

OBJECTIVE: To investigate the relationship between genotype and phenotype of a deletional delta beta-thalassemia and explore an approach to rapid prenatal diagnosis for compound heterozygotes of this defect and a beta-thalassemia. METHODS: A total of ten members in a Chinese family who had a 5-year-old propositus with thalassemia major and requested prenatal diagnosis for the second pregnancy were investigated. For genotyping analysis, the deletional delta beta-thalassemia was characterized by gap-PCR method and beta-thalassemia mutations were defined by reverse dot blot(RDB). For phenotyping analysis, hematological data including the RBC indices, quantification of HbF and HbA2 by Hb electrophoresis and the ratio of globin chain Ggamma/(Ggamma+Agamma) analyzed by capillary electrophoresis (CE) were obtained. RESULTS: The propositus inherited her mother's delta beta-thalassemia gene mutation and her father's CD41-42(-CTTT) frameshift mutation. Of nine members in this family screened for this type of deletion, four were positive and the phenotype could be explained satisfactorily by genotype. The results of prenatal diagnosis showed that the fetus was normal and had no beta-globin gene defects in both chromosomes. CONCLUSION: This is the first time to have performed prenatal diagnosis in Chinese family at-risk of compound heterozygotes for beta-thalassemia and delta beta-thalassemia in mailand China. The strategy to analyze the disease presented here may be a valuable reference to the similar problem.

Adolescent↗
PubMed2001

Temozolomide: the effect of once- and twice-a-day dosing on tumor tissue levels of the DNA repair protein O(6)-alkylguanine-DNA-alkyltransferase.

Temozolomide (TMZ) is a methylating agent of the imidotetrazine class, whose cytotoxic product is O(6)-methylguanine DNA adducts, which initiate a futile recycling of the mismatch repair pathway causing DNA strand breaks and apoptotic cell death in mismatch repair proficient cells. The DNA repair protein O(6)-alkylguanine DNA alkyltransferase (AGT) repairs these adducts in a suicide manner and reduces the cytotoxic action of TMZ. An antitumor threshold is reached when sufficient adducts are formed by TMZ to inactivate AGT. In this study, we evaluated the relation between TMZ dosing and AGT depletion in patients with deep visceral tumors and in peripheral blood mononuclear cells (PBMCs) to determine whether the dose of TMZ was sufficient to inactivate AGT and lead to therapeutic efficacy. To do so, we compared single dose therapy with a novel twice daily regimen in a laboratory correlate-driven Phase I dose escalation study. p.o. bolus dose TMZ 200 mg/m(2) daily times five was compared with the same bolus on day 1 followed by nine doses at 12-h intervals of 50, 75, 90, or 100 mg/m(2). Dose-limiting toxicity in the bid regimen (grade IV thrombocytopenia and neutropenia) was seen at 100 mg/m(2), cumulative dose 1100 mg/m(2), and the maximum tolerated dose was 1010 mg/m(2). The degree of tumor tissue AGT activity depletion measured in biopsies before and on day 5 of therapy varied widely, between 0 (in 3 patients) and 99% (in 1), with the majority of patients (10 of 15) having 52-84% tumor AGT depletion. In contrast, AGT activity in PBMCs fell rapidly during TMZ administration to undetectable levels in all dosage groups on day 5 but did not correlate with tumor AGT depletion. TMZ pharmacokinetics were dose proportional; no accumulation occurred >5-day period in the bid regimen. Two partial responses were seen, lasting 3 and 4 months. Five additional patients achieved prolonged stabilization of disease for 4-6 monthly cycles. This is the first study to document that at maximum tolerated doses, TMZ depletes PBMC AGT but only partially and variably depletes visceral tumor AGT in most patients, even during twice daily dosing. Drug combinations or schedules designed to maximally deplete tumor AGT might improve TMZ efficacy.

Adult↗
PubMed2001

Differential degradation rates of inactivated alkyltransferase in blood mononuclear cells and tumors of patients after treatment with O(6)-benzylguanine.

O(6)-Alkylguanine-DNA alkyltransferase (AGT) repairs O(6)-alkylating DNA adducts generated by alkylating therapeutic agents. Therefore, AGT activity may be an important marker of tumor and normal tissue sensitivity to chemotherapeutic agents and a predictor for the success of chemotherapeutic regimens. It is rapidly inactivated by O(6)-benzylguanine (BG) that mimics its substrates, O(6)-methylguanine and O(6)-chloroethylguanine DNA adducts. In a Phase I clinical trial, BG was given in increasing doses (from 10 to 120 mg/m(2)) by 1-h infusion. We previously reported depletion of AGT activity, and in this report, we demonstrate the relationship between degradation of BG-inactivated AGT protein and the depletion of AGT activity in peripheral blood mononuclear cells (PBMCs) and tumor samples obtained by computed tomography-guided cutting needle biopsy from patients prior to BG and either 2 or 18 h after BG. In PBMCs, BG inactivated AGT activity by over 95-100% at the end of a 1-h infusion, and depletion was maintained for 18 h. In contrast, AGT protein remained almost unchanged for up to 18 h after BG, suggesting that inactivated AGT proteins remain immunoreactive and are not rapidly degraded in PBMCs. In patient tumor biopsies, AGT activity was depleted approximately 90% 2 h after BG. Tumor AGT protein levels were reduced to approximately 40% of pretreatment values when detected by either Western blot or immunohistochemistry staining. In tumor samples obtained 18 h after BG, >95% inactivation of tumor AGT activity was observed at BG doses of 36-80 mg/m(2), and complete depletion of tumor AGT activity occurred at 120 mg/m(2) BG. However, residual AGT protein (5-10% of baseline) was detectable in all tumor samples. Therefore, the degradation of BG-inactivated AGT protein appeared to be much more rapid in tumors than that in PBMCs, which may impact on AGT regeneration rates as well. Because degradation of BG-inactivated AGT takes place slowly, antibody-based measurements of AGT protein correlate poorly with depletion of AGT activity immediately after BG. Thus, biochemical activity measurements remain the appropriate monitor of AGT during therapeutic modulation. These data provide the first and conclusive evidence of differential degradation rates of inactivated AGT in PBMCs and tumors of patients after treatment with BG and suggest that immunoreactive AGT measurements in PBMCs are a poor surrogate for AGT activity in tumor tissue.

Biopsy↗
PubMed2001

[Cytotoxic T lymphocyte activity induced by genetic immunization with NV-HC/NS].

OBJECTIVE: To investigate the immunoprophylactic and immunotherapeutic effects of DNA vaccine (NV-HC/NS(3)) after inoculation of mice by target tumor loading technique. METHODS: Before or after inoculation with NV-HC/NS(3) intramuscularly, BALB/c mice in the experimental group were planted with target tumor cells (SP2/0-NS(3)), which were derived from BALB/c mice and stably transfected with the recombinant plasmid NV-HC/NS(3). Tumor growth and survival rate of the mice immunized with NV-HC/NS(3) were compared with those in the control group. RESULTS: Tumor mass grew well in all mice in the control group in a few days, while no visible tumor mass growth in 40% mice immunized with NV-HC/NS(3) could be seen. The survival rate and life span of mice in the experimental group were significantly longer than those in the control group. CONCLUSIONS: Specific immune activity could be induced by immunization with NV-HC/NS(3). Such effects are immunoprophylactic and immunotherapeutic.

Animals↗
PubMed2001

The study of levels of norepinephrine and dopamine-beta-hydroxylase in patients with pregnancy-induced hypertension.

BACKGROUND: The present work aimed to study the changes of both norepinephrine (NE) and dopamine-beta-hydroxylase (DbetaH) in pregnancy-induced hypertension (PIH). METHODS: NE levels and DbetaH activity in blood were determined in 116 patients with pregnancy-induced hypertension and 40 normal control subjects using high performance liquid chromatography (HPLC) and ultraviolet (UV) spectrophotometry. Among patients with PIH, 28 were graded as mild, 34 moderate and 54 severe. The normal control subjects were selected from patients at a normal term pregnancy receiving elective cesarean section. RESULTS: NE levels and DbetaH activity in blood were significantly higher in patients with severe PIH than those in control subjects (p < 0.05 for both). Both patients and control subjects had higher NE levels and DbetaH activity in the umbilical artery blood than in the umbilical vein blood (p < 0.05). NE levels and DbetaH activity in both umbilical artery and vein blood were higher in the moderate and severe PIH groups than in the mild (p < 0.05) and control (p < 0.05) groups. NE levels in the umbilical artery blood were five times higher than those in the maternal blood, and DbetaH activity was three times higher. NE levels and DbetaH activity in the umbilical artery blood were significantly higher in the PIH group with complicated intrauterine growth retardation (IUGR) or fetal distress than in the PIH group without such complication. CONCLUSIONS: The pathogenesis of PIH may relate to increase of excitability of the sympathetic nervous system in fetus.

Adult↗
PubMed2001

Sequential tumor biopsies in early phase clinical trials of anticancer agents for pharmacodynamic evaluation.

PURPOSE: In the setting of target-based anticancer drug development, it is critical to establish that the observed preclinical activity can be attributed to modulation of the intended target in early phase trials in human subjects. This paradigm of target modulation allows us to determine a Phase II or III dose (optimal biochemical/biological modulatory dose) that may not necessarily be the maximum tolerated dose. A major obstacle to target-based (often cytostatic) drug development has been obtaining relevant tumor tissue during clinical trials of these novel agents for laboratory analysis of the putative marker of drug effect. EXPERIMENTAL DESIGN: From 1989 to present, we have completed seven clinical trials in which the end point was a biochemical or biological modulatory dose in human tumor tissues (not surrogate tissue). Eligibility enrollment required that patients have a biopsiable lesion either with computerized tomography (CT) guidance or direct visualization and consent to sequential (pre and posttreatment) biopsies. RESULTS: A total of 192 biopsies were performed in 107 patients. All but 8 patients had sequential pre and posttreatment biopsies. Seventy-eight (73%) of the 107 patients had liver lesion biopsies. In eight patients, either one or both biopsies contained insufficient viable tumor tissue or no tumor tissue at all for analysis. Of a total of 99 patients in whom we attempted to obtain paired biopsies, a total of 87 (88%) were successful. Reasons for failure included patient refusal for a second biopsy (n = 2), vasovagal reaction with first biopsy precluding a second biopsy (n = 1), subcapsular hepatic bleeding (n = 1), and most commonly obtaining necrotic tumor, fibrous, or normal tissue in one of the two sequential biopsies (n = 8). CONCLUSIONS: This is the first and largest reported series demonstrating that with adequate precautions and experience, sequential tumor biopsies are feasible and safe during early phase clinical trials.

Animals↗
PubMed2001

Cyclic GMP-dependent protein kinase activation and induction by exisulind and CP461 in colon tumor cells.

These studies report on the activation and induction of cGMP-dependent protein kinase (PKG) by exisulind and analogs and test the hypothesis that PKG is involved in the induction of apoptosis in colon tumor cells. Exisulind and analogs are proapoptotic drugs developed as inhibitors of cGMP phosphodiesterase gene families 5 and 2 that have been shown to sustain increased cGMP in SW480 and HT29 cells. At concentrations that induced apoptosis, both exisulind and CP461 increased PKG activity in SW480 cell supernatants. PKG activation was dose-dependent and sustained. Activation of PKG by exisulind and analogs was also seen in the colon tumor cell lines HT29, T84, and HCT116. The guanylyl cyclase activators YC-1 and guanylin increased PKG activity secondary to increased cellular cGMP and induced apoptosis in colon tumor cells. Exisulind and CP461 had no direct effect on purified PKG activity or on basal and stimulated PKG activity from cell supernatants. An additional effect of exisulind after 8 h of drug treatment was a dose-dependent increase of PKG Ibeta protein expression. beta-Catenin, a potential new substrate for PKG, whose regulation influences apoptosis, was phosphorylated by PKG in vitro. 32P-labeled cells treated with exisulind showed increased phosphorylation of beta-catenin. These data indicate that exisulind and analogs activate and induce PKG, resulting in increased phosphorylation of beta-catenin and enhanced apoptosis to promote colon tumor cell death.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2001

[GC-MS analysis of supercritical carbon dioxide extract from seeds of Zanthoxylum bungeanun Maxim].

The chemical components of supercritical carbon dioxide extracts from seeds of Zanthoxylum bungeanun Maxim. were studied by GC-MS-DS. Thirty-five compounds which account for 96.22% of the total area of the chromatographic peaks, were identified. The results showed that fatty acids and esters occupied 90.83% of total chromatographic efflux of the extracts. The main components of the extracts are oleic acid(38.91%), palmitic acid (29.45%), linoleic acid methyl ester(10.80%), linolenic acid methyl ester(8.64%), et al.

Carbon Dioxide↗