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Biomedical subjects

X G Chen

Publications and source records attributed to X G Chen.

At least 19 recordsLinked to original sources
PubMed1999

Baculovirus expression of the major surface antigen of Toxoplasma gondii and the immune response of mice injected with the recombinant P30.

The major surface antigen (P30) of the Toxoplasma gondii was expressed by an insect cell culture system infected with recombinant baculovirus. About 750 microg of purified (95% purity) P30 was obtained from a culture of 10(8) insect Sf21 cells. The recombinant P30 was used to immunize mice to induce immune response. Mice injected with the recombinant protein produced specific humoral and cellular immune responses. Immunization with P30 also prolonged the period of survival of mice infected by Toxoplasma. The average survival time of control group is 13.25+/-1.16 days, but are 16.13+/-2.1 days, 19.50+/-3.21 days, 20.38+/-3.38 days in different immunized groups, respectively.

Animals↗
PubMed1998

PCR cloning and expression of the molt-inhibiting hormone gene for the crab (Charybdis feriatus).

A PCR-based genomic DNA walking technique was used to clone the gene for the molt-inhibiting hormone of the crab, Charybdis feriatus. Several overlapping genomic clones were isolated, and the MIH gene for the crab was reconstructed. DNA sequence determination of the overlapping clone reveals that the MIH gene spans 4.3kb and consists of three exons and two introns. Exons 1 and 2 carry a coding sequence for the signal peptide, and exons 2 and 3 consist of coding sequence for the mature peptide. The exon-intron boundary of the crab MIH gene also follows the 'GT-AG rule' for the splice donor and acceptor. The deduced amino acid sequence of MIH shows the highest overall similarity to those of the crabs, Callinectes sapidus and Carcinus maenas, and the gonad-inhibiting hormone (GIH) of the lobster. The putative polyadenylation signal is approximately 1.0kb 3' downstream of the termination codon (TGA). Genomic Southern blot analysis indicates that few genomic fragments were hybridized to the cDNA probe. The 5' flanking region contains a putative promoter with several putative cis elements similar to some vertebrate neuropeptide genes. The 530-bp flanking region was subcloned separately to two promoterless reporter plasmids carrying either the Green Fluorescent Protein gene (GFP) or the Choramphenicol Acetyltransferase gene (CAT). The DNA constructs were transfected into insect cells (Sf21) and mouse pituitary cells (GH4ZR7), respectively. Green fluorescent protein was detected in some of the transfected insect cells, and expression of the CAT was detected in cells transfected with DNA constructs containing the crab promoter. By RT-PCR, MIH transcripts can be detected in the eyestalk of shrimp in intermolt, early premolt, late premolt stages and females that brood their eggs. It can also be found in the brain, but not in the ovary, hepatopancreas, muscle and epidermis. During early larval development, MIH mRNA can be detected in the pre-hatched and the newly hatched larvae. Unlike the adult, the expression of the MIH in the larvae is exclusively in the brain.

Amino Acid Sequence↗
PubMed1998

UV resonance Raman-selective amide vibrational enhancement: quantitative methodology for determining protein secondary structure.

We have directly determined the amide band resonance Raman spectra of the "average" pure alpha-helix, beta-sheet, and unordered secondary structures by exciting within the amide pi-->pi* transitions at 206.5 nm. The Raman spectra are dominated by the amide bands of the peptide backbone. We have empirically determined the average pure alpha-helix, beta-sheet, and unordered resonance Raman spectra from the amide resonance Raman spectra of 13 proteins with well-known X-ray crystal structures. We demonstrate that we can simultaneously utilize the amide I, II, and III bands and the Calpha-H amide bending vibrations of these average secondary structure spectra to directly determine protein secondary structure. The UV Raman method appears to be complementary, and in some cases superior, to the existing methods, such as CD, VCD, and absorption spectroscopy. In addition, the spectra are immune to the light-scattering artifacts that plague CD, VCD, and IR absorption measurements. Thus, it will be possible to examine proteins in micelles and other scattering media.

Amides↗
PubMed1997

Simultaneous assessment of conformation and aggregation of beta-amyloid peptide using electrospray ionization mass spectrometry.

Electrospray ionization mass spectrometry was used to study conformation and aggregation of the synthetic beta-amyloid peptide, residues 1-40 (betaA4), as a function of concentration and sample aging. All mass spectra showed a major envelope of peaks corresponding to charge states of 7-3 of the monomeric form of betaA4. In addition, weaker envelopes of peaks corresponding to charge states of dimeric, trimeric, and tetrameric betaA4 species were seen under gentle ionization conditions. The average charge state of the envelope associated with the monomeric form decreased by ca. 0.5 z as samples were aged, indicating that the relatively open form (likely random coil) of the peptide was modified into the more compact form (likely beta-sheet) as a function of sample aging. The aggregate forms became weaker and ultimately were absent both in the more dilute solutions and in aged aliquots of the concentrated sample. These aggregates were interpreted as assemblies of the random coil form. We interpret our inability to see an ion envelope that can be associated with aggregates of the beta-sheet form to be a consequence of the presumed very compact nature of this form. A model for the formation of betaA4 fibrils is proposed and discussed.

Amyloid beta-Peptides↗
PubMed1997

The infection status of anisakid larvae in marine fish and cephalopods from the Bohai Sea, China and their taxonomical consideration.

The infection status of anisakid larvae was examined in 290 marine fish of 25 species and in 108 cephalopods of 3 species purchased in Bayuquan region, Yingko city nearby the coast of the Bohai Sea from may to August 1992. A total of 7,327 larvae were collected from 156 fish of 19 species and 8 squids of one species. The 3rd-stage larvae of Anisakis simplex were collected from 121 fish (63.4%) of 15 species (N = 191) and from 8 squids (14.8%) of one species (N = 54), and they were total, 5,992 (81.8%). Out of remaining 1,335 larvae, 154 (2.1%) were classified as Thynnascaris type B from 23 fish of 4 species, 1,013 (13.8%) as Thynnascaris type C from 79 fish of 13 species. 164 (2.2%) as Hysterothylacium China type V from 20 fish of 4 species, 3 (0.04%) as Raphidascaris from 3 fish of 2 species and one was Pseudoterranova decipiens larva.

Animals↗
PubMed1995

Calculation of the dose in the build-up region for high energy photon beam. Treatment planning when beam spoilers are employed.

Recoil electrons from a polystyrene sheet (beam spoiler) placed in a photon beam were used to modulate the dose in the build-up region. The effects of the beam spoiler on the dosimetry in simple phantoms were studied for both 6 MV and 15 MV photon beams at 100 cm source-to-surface distance (SSD) as a function of (1) the thickness of the spoiler, (2) the spoiler-to-surface distance (SD) and (3) the field size. A radiotherapy treatment planning (RTP) algorithm was used that employs pencil beam dose deposition kernels to evaluate the three-dimensional (3D) dose distribution due to photons and electrons in the build-up region. To determine the energy deposition kernels for the recoil electrons emanating from the spoiler, their energy spectrum needs to be known. Monte Carlo simulations were performed to derive the spectrum of electrons from the beam spoiler. The recoil electron spectrum was found to be nearly independent of field size, SD, and spoiler thickness. The pencil beam energy deposition kernel was calculated for the recoil electrons from the spoiler and inserted in the treatment planning algorithm. The dose calculation algorithm permits merging the photon and recoil electron dose components. In all cases the calculation agrees to within 3% of the measured results.

Algorithms↗
PubMed1994

Sialidase in rabbit blood. Characterization of sialidase purified from rabbit erythrocyte membrane.

Sialidase activities of rabbit blood cells and serum were measured. The leucocyte particulate fraction showed the highest specific activity of sialidase towards mixed gangliosides and sialyllactose, and the cytosolic fraction showed for fetuin. Predominant sialidase activity in the blood was detected in erythrocyte particulate fraction when mixed gangliosides were used as substrate. The sialidase for ganglioside was solubilized from the erythrocyte ghosts by using Triton X-100. The solubilized sialidase was purified 1886-fold by sequential chromatographies on DEAE-cellulose, EAH-Sepharose 4B, Octyl-Sepharose CL-4B, Sephadex G-100, concanavalin-A--Sepharose, N-(p-aminophenyl)oxamic acid-agarose and Heparin-Sepharose CL-6B. The optimum pH of purified sialidase was 4.5 for ganglioside mixture, and this enzyme exhibited M(r) = 48,000 by gel filtration. When the purified sialidase was subjected to SDS/PAGE, a major sialidase-active protein band at M(r) = 54,000 and another fainter inactive protein band with M(r) = 115,000 were observed. The purified enzyme was active towards oligosaccharides, gangliosides, fetuin glycopeptide and 4-methylumbelliferyl alpha-D-N-acetylneuraminic acid except for glycoproteins tested. Fe2+, Fe3+ and dithiothreitol significantly inhibited the enzyme activity, while Triton X-100 activated the enzyme. Inside-out vesicles and unsealed ghosts of rabbit erythrocyte showed the sialidase activity for mixed gangliosides but not for resealed ghosts or intact erythrocytes. These results indicate that the active site of this sialidase is oriented mainly on the inside of the erythrocyte membrane and not on the outside. Treatment of rabbit erythrocyte unsealed ghosts with phosphatidylinositol-specific phospholipase C liberated no sialidase activity toward mixed gangliosides from the ghosts.

Animals↗
PubMed1994

[Effect of glycyrrhetinic acid on DNA damage and unscheduled DNA synthesis induced by benzo (a) pyrene].

Glycyrrhetinic acid (GA) is an active component of Glycyrrhiza uralensis Fisch. In this study, the effects of glycyrrhetinic acid on DNA damage and unscheduled DNA synthesis induced by benzo (alpha) pyrene were studied. Mouse ear edema was visible obviously at the 6th h after topical application of single dose croton oil. A topical application of croton oil on the back of ICR mice for 5 h, induced elevation of ornithine decarboxylase (ODC) activity in epidermal. The administration of glycyrrhetinic acid (50-200 mg.kg-1.d-1) to animals for 3 days exhibited 20%-80% inhibition of epidermal ornithine decarboxylase activity in a dose-dependent manner. Benzo (alpha) pyrene obviously caused DNA damage and unscheduled DNA synthesis mediated by S9 fraction in Chinese hamster lung cell line. Glycyrrhetinic acid was found to protect the rapid DNA damage induced by benzo (alpha) pyrene. At concentration of 5 micrograms.ml-1, glycyrrhetinic acid exhibited 70% protection. At 20 micrograms.ml-1, this action was more potent and approached to 80%. The addition of hydroxyurea 10 mmol.L-1 suppressed DNA replicative synthesis to 84.04% and benzo (alpha) pyrene stimulated the DNA repair synthesis (6-fold). Glycyrrhetinic acid (20 micrograms.ml-1 and 50 micrograms.ml-1 significantly decreased the stimulation of DNA repair synthesis induced by benzo (alpha) pyrene. This suggests that glycyrrhetinic acid has effective anti-initiating and anti-promoting activities and could be used for cancer chemopreventive purpose.

Animals↗
PubMed1993

Combining multileaf fields to modulate fluence distributions.

PURPOSE: A method for modulating beam fluence from a linear accelerator is discussed. The beam modulation is accomplished remotely using a multileaf collimator and does not require entering the treatment room. METHODS AND MATERIALS: The multileaf collimator is used to define a series of field shapes that are superimposed at a fixed gantry angle to produce any desired fluence pattern. A heuristic technique for deriving the field shapes and corresponding monitor unit settings is described. The technique has been tested on randomly generated fluence distributions and on distributions with a limited number of peaks and valleys. The second type of distribution more closely simulates fluence patterns obtained with dose optimization software. Estimates of the time required to use this approach to treat a four-field plan are given and compared to the technique of placing a physical compensator in each beam. RESULTS: It has been demonstrated that complex fluence patterns within a 15 x 15 cm2 field can be achieved with less than 20 fields. Estimates show that this technique is faster than entering the treatment room to change physical compensators. Some limitations of the method are discussed. CONCLUSION: Optimized distributions that conform the dose to irregularly shaped target volumes that wrap around critical structures are possible using superimposed multileaf fields. A method for defining the field shapes is presented.

Humans↗
PubMed1990

Pattern and duration of the inhibitory effect of alcohol administered acutely on suckling-induced prolactin in lactating rats.

We have characterized the pattern and duration of the inhibitory effect of acute alcohol administration on suckling-induced prolactin (PRL) release in the lactating rat. On day 2 of lactation, litters were adjusted to eight pups. On day 6, dams were implanted with an atrial catheter and experiments were conducted on day 10 of lactation. Pups were removed from the dams at 0800 hr. An extension tube filled with heparinized saline was attached to the catheter at 1300 hr. At 1400 hr, a preinfusion (PRE 0) blood sample was removed and was followed by infusion of saline (control) or alcohol in saline (0.5, 1.0, 2.0, 2.5 g/kg body weight doses) solutions. Following the removal of a postinfusion (POST 0) blood sample, pups were returned to the mother. Subsequent blood samples were obtained 10, 30, 60, 120, and 180 min after initiation of suckling. In separate groups, the effects of alcohol on basal PRL were studied by collecting blood samples PRE 0, POST 0 and 20, 40, 60, 80, 100, and 120 min following infusion of saline or alcohol in saline to lactating rats also separated from their pups for 6 hr. Alcohol infusion did not alter basal PRL. However, suckling-induced PRL was inhibited at 10, 30, 60, and 120 min of suckling by alcohol administered at doses greater than or equal to 1.0 g/kg body weight. After 180 min of suckling, plasma PRL levels were comparable among groups. The suckling latency for the 2.5 g/kg body weight alcohol group was greater than for other groups, but the quantities of milk consumed during the 3-hr suckling period were comparable.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

[Influence of the active compounds isolated from pilose antler on syntheses of protein and RNA in mouse liver].

The polyamines of pilose antler (PASPA) consist of putrescine (PU, 70.9%), spermidine (SPD, 26.3%) and spermine (SP, 2.8%). The incorporations of [3H] leucine into protein and [3H] uridine into RNA in mouse liver tissue were increased when PASPA was given orally to mice at the dose of 30 mg/kg for 4 successive days. The incorporations of [3H] leucine into liver protein and [3H] uridine into the cytosolic and nuclear RNA were also increased by treatment with PU (21 mg/kg). In addition, the RNA polymerase activity in the solubilized liver nuclear fraction of PU (21 mg/kg)-treated mice was increased. SPD only promoted the synthesis of protein in mouse liver tissue at the dose of 8 mg/kg. However, SP showed no effect on the synthesis of protein and RNA polymerase activity under the used dose (1 mg/kg). The results suggest that PASPA is the main active substance responsible for the promotion of the synthesis of protein and RNA in mouse liver.

Animals↗
PubMed1990

[Effect of polyamines isolated from pilose antler (PASPA) on RNA polymerase activities in mouse liver].

The incorporations of [3H] leucine into protein and [3H] uridine into RNA in mouse liver were increased when PASPA was given to mice at a dose of 30 mg/kg for 4 successive days. The RNA polymerase activity, especially the RNA polymerase II activity in the solubilized liver nuclear fraction of PASPA-treated mice was also increased. In vitro experiment demonstrated that PASPA increased the RNA polymerase activity significantly in mouse liver nuclei at a concentration of 1 microgram/ml. These results suggest that the enhancement of RNA polymerase activities, particularly RNA polymerase II activity, induced by PASPA treatment is responsible for the increase in synthesis of protein and RNA in mouse liver tissue.

Animals↗
PubMed1989

[Inhibitory effect of hypoxanthine on monoamine oxidase activity].

Hypoxanthine was demonstrated to have a dose-dependent inhibitory effect on type B monoamine oxidase (MAO-B) activity in liver and brain tissues, and slight inhibitory effect on type A MAO(MAO-A) activity when given orally to mice at doses of 25-500 mg/kg. When mice were given orally hypoxanthine 500 mg/kg, MAO-A and -B activities were all inhibited significantly 16 hours after administration, but the inhibitory action on MAO-A was weaker. Subcutaneous injection of the agent also produced obvious inhibition of MAO activity in the liver but no significant influence on MAO activity in brain tissue was observed. In vitro experiment showed that the action of hypoxanthine on MAO-B was competitive inhibition and that on MAO-A was competitive mixed with noncompetitive inhibition.

Animals↗
PubMed1986

Ultrastructure of the gastric mucosa harboring Campylobacter-like organisms.

The association between Campylobacter-like organisms (CLOs) and lesions of the gastric mucosa was studied in 59 consecutive biopsies. Hematoxylin and eosin and Warthin-Starry silver stains, as well as high-resolution light microscopy (HRLM) and transmission electron microscopy (TEM), were used. The organisms were found in intimate contact with foveolar cells showing abundant phagolysosomes and alterations of the intercellular complexes. CLOs also were seen in close proximity of parietal cells in resting phase, some of which showed degenerative changes. The findings are discussed in light of recent reports linking CLOs to the cause of gastritis.

Campylobacter↗