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Biomedical subjects

J Liu

Publications and source records attributed to J Liu.

At least 199 records · Page 11Linked to original sources
PubMed2003

Reversal of cancer multidrug resistance by tea polyphenol in KB cells.

Tea polyphenols, (-)-epigallocatechin gallate in particular, were examined for their modulating effects on the drug resistance KB-A-1 cells and drug sensitive KB-3-1 cells. Both KB-3-1 and KB-A-1 cells were equally sensitive to tea polyphenol and (-)-epigallocatechin gallate. When 10 microgram/ml (-)-epigallocatechin gallate or 40 microgram/ml tea polyphenol were present simultaneously with doxorubicin, the IC50 of doxorubicin on KB-A-1 cells decreased from 10.3 +/- 0.9 microgram/ml to 4.2 +/- 0.2 or 2.0 +/- 0.1 microgram/ml. Tea polyphenol and (-)-epigallocatechin gallate enhanced the cytotoxicity of doxorubicin on KB-A-1 cells by 5.2 and 2.5 times, respectively, but did not show a modulating effect on KB-3-1 cells. Both tea polyphenol and (-)-epigallocatechin gallate showed reversal effects on the multidrug resistance phenotype.

Camellia sinensis↗
PubMed2003

cDNA cloning and high-level expression of a thrombin-like enzyme from Agkistrodon acutus venom.

Agkistrodon acutus (Guenther), a poisonous snake species of the family of Crotalidae, is mainly found south of the Yellow River in China. The main symptom of this poison is massive hemorrhage, in which thrombin-like enzymes (TLEs) in the venom play an important role. TLEs are abundant, especially in the venom of A. acutus. We isolated the total RNA from the venom gland tissue of A. acutus and amplified the cDNAs of the TLEs using reverse transcription-polymerase chain reaction (RT-PCR). The cDNAs were cloned into vector pThioHis B and were expressed as fusion proteins in the form of inclusion bodies, which accounted for nearly 50% of the total cell proteins. The inclusion bodies were washed, dissolved, refolded and purified by affinity chromatography. The purity was higher than 97%, as indicated by capillary zone electrophoresis. The renatured recombinant enzyme exhibited arginine esterase activity, as tested by the BAEE method, and also showed a fibrinogen cleavage effect, as detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). This method provides a fast and convenient system for studying the structure-function relationships in TLE isoenzymes, and also a practical way for mass production of TLEs in the pharmaceutical industry.

Agkistrodon↗
PubMed2003

Survival of avian influenza virus H7N2 in SPF chickens and their environments.

The survival or clearance of the avian influenza virus (AIV) of subtype H7N2 in its chicken host was evaluated using experimentally infected specific pathogen free (SPF) chickens of different age groups. Birds of different ages were successfully infected with infectious doses ranging between 10(4.7) and 10(5.7) ELD50 per bird. In infected birds, the infective virus was undetectable usually by the third week following exposure. The infectivity or inactivation time of the H7N2 AIV in various environmental conditions was studied using chicken manure, heat, ethanol, pH, and disinfectants. The H7N2 AIV was effectively inactivated by field chicken manure in less than a week at an ambient temperature of 15-20 degrees C. At a pH 2, heating at 56 degrees C, and exposure to 70% ethanol or a specific disinfectant, the AIV infectivity was destroyed in less than 30 min.

Animals↗
PubMed2003

Expression of activin/inhibin signaling components in the human adrenal gland and the effects of activins and inhibins on adrenocortical steroidogenesis and apoptosis.

Activins and inhibins are structurally related glycoprotein hormones modulating pituitary FSH secretion and gonadal steroidogenesis. Activins and inhibins are also produced in the adrenal cortex where their physiological role is poorly known. Hormonally active human adrenocortical tumors express and secrete inhibins, while in mice adrenal inhibins may function as tumor suppressors. To clarify the significance of adrenal activins and inhibins we investigated the localization of activin/inhibin signaling components in the adrenal gland, and the effects of activins and inhibins on adrenocortical steroidogenesis and apoptosis. Activin receptor type II/IIB and IB, activin signal transduction proteins Smad2/3, and inhibin receptor betaglycan were expressed throughout the adrenal cortex, whereas Smad4 expression was seen mainly in the zona reticularis and the innermost zona fasciculata as evaluated by immunohistochemistry. Treatment of cultured adrenocortical carcinoma NCI-H295R cells with activin A inhibited steroidogenic acute regulatory protein and 17alpha-hydroxylase/17,20-lyase mRNA accumulation as evaluated by the Northern blot technique, and decreased cortisol, androstenedione, dehydroepiandrosterone and dehydroepiandrosterone sulfate secretion as determined by specific enzyme immunoassays. Activin A increased apoptosis as measured by a terminal deoxynucleotidyl transferase in situ apoptosis detection method. Inhibins had no effect on steroidogenesis or apoptosis. In summary, activin/inhibin signaling components are coexpressed in the zona reticularis and the innermost zona fasciculata indicating full signaling potential for adrenal activins and inhibins in these layers. Activin inhibits steroidogenic enzyme gene expression and steroid secretion, and increases apoptosis in human adrenocortical cells. Thus, the activin-inhibin system may have a significant role in the regulation of glucocorticoid and androgen production and apoptotic cell death in the human adrenal cortex.

Activin Receptors, Type I↗
PubMed2003

Use of insulin-like growth factor-I during embryo culture and treatment of recipients with gonadotropin-releasing hormone to increase pregnancy rates following the transfer of in vitro-produced embryos to heat-stressed, lactating cows.

An experiment was conducted to determine whether pregnancy rates following the transfer of in vitro-produced embryos to heat-stressed cows could be improved by 1) culturing embryos in the presence of IGF-I and 2) treating recipients with GnRH. Lactating Holstein cows (n = 260) were synchronized using a timed ovulation protocol. Embryos were produced in vitro and cultured with or without 100 ng/mL of IGF-I. On d 7 after anticipated ovulation (d 0), a single embryo was transferred to all recipients with a palpable corpus luteum (n = 210). A subset of recipients (n = 164) was injected with either GnRH or placebo on d 11. Plasma progesterone concentrations on d 0 and 7 were used to determine the synchrony of recipients. Pregnancy was diagnosed at d 53 and 81 by rectal palpation. Among all recipients, transfer of IGF-I-treated embryos increased pregnancy rate at d 53 (P < 0.05) and tended to increase pregnancy rate at d 81 (P < 0.06). Calving rate also tended to be higher for recipients that received IGF-I-treated embryos (P < 0.07). Among the subset of synchronized recipients (n = 190), pregnancy rate at d 53 and d 81 and calving rate were higher (P < 0.05) for IGF-I-treated embryos. The GnRH tended to increase pregnancy rate at d 53 for all recipients (P < 0.08) and the subset of synchronized recipients (P < 0.10). There were no effects of GnRH (P > 0.10) for pregnancy rate at d 81 and calving rate. The overall proportion of male calves was 64.3%. There was no effect (P > 0.10) of embryo treatment or GnRH on the birth weight or sex ratio of calves. Results of this experiment indicate that treatment of embryos with IGF-I can improve pregnancy and calving rates following transfer of in vitro-produced embryos. Further research is necessary to determine whether the treatment of recipients with GnRH is a practical approach to increase pregnancy rates following in vitro embryo transfer.

Animals↗
PubMed2003

Reoperation in a Jehovah's Witness 22 years after aortic allograft reconstruction of the right ventricular outflow tract.

We report the case of a 29-year-old male Jehovah's Witness who presented with hemolysis and right heart failure as a consequence of extreme calcification of an aortic valve-containing allograft and Dacron prosthesis that had been placed 22 years earlier to repair tetralogy of Fallot. Reoperation had been denied by several other centers, because of the patient's refusal to undergo blood transfusion. For 2 weeks preoperatively, we raised the patient's hemoglobin level by treating him with recombinant erythropoietin, oral iron, and folic acid. At surgery, under normothermic cardiopulmonary bypass, we replaced the aortic allograft in the right ventricular outflow tract with a cryopreserved pulmonary allograft, also containing a valve. The postoperative course was uneventful, and the patient was released from the hospital on the 13th postoperative day in excellent condition.

Adult↗
PubMed2002

Bitumen-clay interactions in aqueous media studied by zeta potential distribution measurement.

A novel technique to investigate the interactions between bitumen and clays in an aqueous solution from the measurement of zeta potential distributions is described. For a single component suspension (i.e., clay or bitumen), a single modal zeta potential distribution was obtained under a given solution condition. In the case of a two-component (i.e., bitumen and clay) mixture system, the measured zeta potential distribution showed either one or two distribution peaks, depending on the chemical condition of the suspension and the type/amount of clays present. In the absence of added calcium ions, a mixture of bitumen emulsion and clay suspension exhibited two distinct zeta potential distribution peaks, corresponding to the peaks measured individually for the bitumen and clays, respectively. With the addition of 1 mM calcium ions, however, only one zeta potential distribution peak was obtained for the mixture of bitumen emulsion and montmorillonite clay suspension. Depending on the montmorillonite clay to bitumen ratio, the peak position in this case shifted toward the value for montmorillonite clay suspension alone. For kaolinite, the addition of 1 mM calcium ions did not cause a substantial change in the bimodal zeta potential distribution. The results suggest qualitatively a stronger interaction of bitumen with montmorillonite clay than with kaolinite clay, when calcium ions were present. The slime coating of montmorillonite clay on bitumen droplets in the presence of 1 mM calcium was validated. The conclusions obtained from this study further justified our mechanistic hypothesis for the observed depression of bitumen flotation by montmorillonite but not by kaolinite clay addition when calcium ions were added. This study demonstrated that zeta potential distribution measurement could be a powerful tool to study slime coating phenomena in a complex colloidal system.

Journal Article↗
PubMed2002

Authentication of Panax ginseng and Panax quinquefolius using amplified fragment length polymorphism (AFLP) and directed amplification of minisatellite region DNA (DAMD).

AFLP profiles characteristic to Panax ginseng and Panax quinquefolius were generated using primers E-AGG/M-CAA. P. ginseng samples from different farms in China and Korea are homogeneous genetically [similarity index (SI) = 0.88-0.99], whereas samples of P. quinquefolius from different sources are much more heterogeneous (SI = 0.64-0.96). Detailed analysis of one of the polymorphic bands in P. ginseng led to the identification of a minisatellite Pg2, which contains eight repeats of 5'-AGGACTCATCACATTGTTACTC. The minisatellite DNA was consequently used in directed amplification minisatellite region DNA analysis to authenticate the two ginsengs.

Base Sequence↗
PubMed2002

Neuronal activity in primate striatum and pallidum related to bimanual motor actions.

To assess whether striatal and pallidal neurones may contribute to bimanual co-ordination, two macaque monkeys were trained to perform a delayed conditional sequence of co-ordinated pull and grasp movements, executed either bimanually or unimanually. Most of the 58 task-related neurones, recorded from the caudate nucleus, putamen, external and internal divisions of the globus pallidus, exhibited an activity related to the execution of the movements. Only a quarter of neurones displayed preparatory activity. The majority of units exhibited a significant modulation of activity in unimanual trials irrespective of the hand used to perform the task. In bimanual trials, one-third of units exhibited discharge patterns reflecting a bimanual synergy, suggesting a possible role for basal ganglia in inter-limb co-operation.

Animals↗
PubMed2002

13C-NMR analysis of glucose metabolism during citric acid production by Aspergillus niger.

The effect of glucose concentration on glycolytic metabolism under conditions of citric acid accumulation by Aspergillus niger was studied with 13C-labelled glucose. The results show that during cultivation at high glucose (14%, w/v), most of the label in citric acid is in C-2/C-4, and is thus due to the pyruvate carboxylase reaction. However, a significant portion is also present in C-1/C-5, whose origin is less clear but most likely due to reconsumption of glycerol and erythritol. Formation of trehalose and mannitol is high during the early phase of fermentation and declines thereafter. The early fermentation phase is further characterized by a high rate of anaplerosis from oxaloacetate to pyruvate, which also decreases with time. At low glucose concentrations (2%, w/v), which lead to a significantly reduced citric acid yield and formation rate, labelling of citrate in C-2/C-4 is decreased and C-l/C-5 labelling increased. Growth on 2% glucose is also characterized by an appreciable scrambling of mannitol and considerable backflux from mannitol to trehalose (indicating tight glycolytic control at the fructose-6-phosphate step) and an increased anaplerotic formation of pyruvate from oxaloacetate. These data indicate that cultivation on high sugar concentrations shifts control of glycolysis from fructose-6-phosphate to the glyceraldehyde-3-phosphate dehydrogenase step.

Aspergillus niger↗
PubMed2002

Canine RBC osmotic tolerance and membrane permeability.

The objective of this study was to determine the cryobiological characteristics of canine red blood cells (RBC). These included the hydraulic conductivity (L(p)), the permeability coefficients (P(s)) of common cryoprotectant agents (CPAs), the associated reflection coefficient (sigma), the activation energies (E(a)) of L(p) and P(s) and the osmotic tolerance limits. By using a stopped-flow apparatus, the changes of fluorescence intensity emitted by intracellularly entrapped 5-carboxyfluorescein diacetate (CFDA) were recorded when cells were experiencing osmotic volume changes. After the determination of the relationship between fluorescence intensity and cell volume, cell volume changes were calculated. These volume changes were used in three-parameter fitting calculations to determine the values of L(p), P(s), and sigma for common CPAs. These volume measurements and data analyses were repeated at three different temperatures (22, 14, 7 degrees C). Using the Arrhenius equation, the activation energies of L(p) and P(s) in the presence of CPAs were determined. The osmotic tolerance limits for canine RBC were determined by measuring the percentage of free hemoglobin in NaCl solutions with various osmolalities compared to that released by RBC incubated in double distilled water. The upper and lower osmotic tolerance limits were found to be 150mOsm (1.67V(iso)) and 1200mOsm (0.45V(iso)), respectively. These parameters were then used to calculate the amount of non-permeating solute needed to keep cell volume excursions within the osmotic tolerance limits during CPA addition and removal.

Animals↗
PubMed2002

Joint strength of laser-welded titanium.

OBJECTIVE: The objective of this study was to examine the joint strength of titanium laser-welding using several levels of laser output energy [current (A)]. METHODS: Cast titanium plates (0.5 x 3.0 x 40 and 1.0 x 3.0 x 40 mm(3)) were prepared and perpendicularly cut at the center of the plate. After the cut halves were fixed in a jig, they were laser-welded using a Nd: YAG laser at several levels of output energy in increments of 30A from 180 to 300A. The penetration depths of laser to titanium were measured under various conditions for output energy, pulse duration, and spot diameter to determine the appropriate conditions for these parameters. Based on the correlation between the results obtained for penetration depth and the size of the specimens (thickness: 0.5 and 1.0 mm, width: 3.0 mm), the pulse duration and spot diameter employed in this study were 10 ms and 1.0 mm, respectively. Three laser pulses (spot diameter: 1.0 mm) were applied from one side to weld the entire joint width (3.0 mm) of the specimens. Uncut specimens served as the non-welded control specimens. Tensile testing was conducted at a crosshead speed of 2 mm/min and a gage length of 10 mm. The breaking force (N) was recorded, and the data (n=5) were statistically analyzed. RESULTS: For the 0.5 mm thick specimens, the breaking force of the specimens laser-welded at currents of 240, 270, and 300A were not statistically (P>0.05) different from the non-welded control specimens. There were no significant differences in breaking force among the 1.0mm thick specimens laser-welded at currents of 270 and 300A, and the non-welded control specimens. SIGNIFICANCE: Under appropriate conditions, joint strengths similar to the strength of the non-welded parent metal were achieved.

Aluminum Silicates↗
PubMed2002

Pre-treatment with R-lipoic acid alleviates the effects of GSH depletion in PC12 cells: implications for Parkinson's disease therapy.

Oxidative stress is believed to play a key role in the degeneration of dopaminergic neurons in the substantia nigra (SN) of Parkinson's disease (PD) patients. An important biochemical feature of PD is a significant early depletion in levels of the thiol antioxidant compound glutathione (GSH) which may lead to the generation of reactive oxygen species (ROS), mitochondrial dysfunction, and ultimately to subsequent neuronal cell death. In earlier work from our laboratory, we demonstrated that depletion of GSH in dopaminergic PC12 cells affects mitochondrial integrity and specifically impairs the activity of mitochondrial complex I. Here we report that pre-treatment of PC12 cells with R-lipoic acid acts to prevent depletion of GSH content and preserves the mitochondrial complex I activity which normally is impaired as a consequence of GSH loss.

Animals↗
PubMed2002

Interleukin-2 gene therapy of chronic neuropathic pain.

Previous research has revealed an antinociceptive (analgesic) effect of interleukin-2 (IL-2) in central and peripheral nervous systems. Unfortunately IL-2 is very short-lived in vivo, so it is impractical to apply IL-2 for analgesia in clinic. This study was performed to evaluate the effect of intrathecal delivery of human IL-2 gene on rat chronic neuropathic pain induced by chronic constriction injury of the sciatic nerve. Human IL-2 cDNA was cloned into pcDNA3 containing a cytomegalovirus promoter. The paw-withdrawal latency induced by radiant heat was used to measure the pain threshold. The results showed that recombinant human IL-2 had a dose-dependent antinociceptive effect, but that this only lasted for 10-25 min. The pcDNA3-IL-2 or pcDNA3-IL-2/lipofectamine complex in contrast also showed dose-dependent antinociceptive effects, but these reached a peak at day 2-3 and were maintained for up to 6 days. Liposome-mediated pcDNA3-IL-2 produced a more powerful antinociceptive effect than pcDNA3-IL-2 alone. The paw-withdrawal latencies were not affected by control treatments such as vehicle, lipofectamine, pcDNA3, or pcDNA3-lipofectamine. In the experimental groups, human IL-2 mRNA was detected by reverse transcription-polymerase chain reaction in the lumbar spinal pia mater, dorsal root ganglion, sciatic nerve, and spinal dorsal horn, but not in gastrocnemius muscle. The expressed IL-2 profile detected by western blot coincided with its mRNA profile except it was present in the spinal dorsal horn at a higher level. Furthermore, human IL-2 assayed by enzyme-linked immunosorbent assay in cerebrospinal fluid could still be detected at day 6, but lower than day 3. The antinociceptive effect of pcDNA3-IL-2 could be blocked by naloxone, showing some relationship of the antinociceptive effect produced by IL-2 gene to the opioid receptors. It is hoped that the new delivery approach of a single intrathecal injection of the IL-2 gene described here may be of some practical use as a part of a gene therapy for treating neuropathic pain.

Animals↗
PubMed2002

Adaptation to chronic PCP results in hyperfunctional NMDA and hypofunctional GABA(A) synaptic receptors.

Schizophrenia is currently thought to be associated with a hypoglutamatergic state that is mimicked by acute phencyclidine (PCP), an antagonist of the N-methyl-D-aspartate (NMDA) receptor subtype. In this study we tested the hypothesis that chronic treatment of rats with this antagonist may be a more appropriate animal model than acute exposure since it could result in adaptive synaptic responses that would model certain aspects of the schizophrenic state in humans. In vitro intracellular electrophysiological recordings employing brain slices from rats treated chronically in vivo with PCP demonstrated that chronic PCP caused a substantial increase in synaptic responses mediated by NMDA receptors without any significant changes in alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate-mediated synaptic responses. At the same time, GABA(A) receptor-mediated inhibitory responses were depressed significantly. Pharmacological and paired-pulse facilitation experiments demonstrated that these adaptive responses following chronic PCP administration were not the result of altered glutamate or GABA release. Immunoblot analyses suggest that the hyperfunctional NMDA response is at least partially mediated by an increased synthesis of NR1 and NR2A subunits as well as a change in the subunit stoichiometry of the NMDA receptor. This change in receptor composition was also supported by pharmacological experiments with a subunit selective NMDA antagonist. Our data support a reconsideration of NMDA and GABA(A) receptor responsiveness following a chronic, not acute, exposure to PCP and the adaptations that persist after such a regimen.

Animals↗
PubMed2002

Two-photon excitation studies of hypocrellins for photodynamic therapy.

The photophysical and photochemical properties of hypocrellins (HA and HB) are examined with two-photon excitations at 800 nm using femtosecond pulses from a Ti:sapphire laser. The two-photon excited fluorescence spectra of HA and HB are very similar to those obtained by one-photon excitation, which may indicate that the two-photon induced photodynamic processes of hypocrellins are similar to one-photon induced photodynamic processes. The two-photon excitation cross sections of HA and HB are measured at 800 nm as about 34.8 x 10(-50) cm(4) s/photon and 21.3 x 10(-50) cm(4) s/photon, respectively. The large two-photon cross sections of both HA and HB, suggest that the hypocrellins can be potential two-photon phototherapeutic agents. As an example for two-photon photodynamic therapy of hypocrellins, we also further examine the cell-damaging effects of HA upon two-photon illumination. Our preliminary results of cell viability test indicate hypocrellins can effectively damage the Hela cells under two-photon illumination.

Models, Molecular↗