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Biomedical subjects

X Cheng

Publications and source records attributed to X Cheng.

At least 127 records · Page 7Linked to original sources
PubMed1998

Regulation of expression of neuropeptide Y Y1 and Y2 receptors in the arcuate nucleus of fasted rats.

Neuropeptide Y is expressed in neurons of the hypothalamic arcuate nucleus and has been ascribed a role as a stimulant of food intake. Neuropeptide Y Y1 and Y2 receptors are also localised in the arcuate nucleus, and it has been suggested that the Y1 receptor mediates part of the effect of neuropeptide Y on feeding behaviour. In the present study, immunohistochemistry and in situ hybridization were used to investigate the effect of food deprivation on the expression of Y1 and Y2 receptors in the arcuate nucleus of the rat. Fasting for 48 h induced a decrease in the number and area of Y1 receptor immunoreactive neurons in the arcuate nucleus. Furthermore, arcuate Y1 receptor mRNA levels also decreased after food deprivation. The decrease in the number of the Y1 receptor immunoreactive neurons was partially attenuated by supplementing the drinking water with 10% glucose. In contrast, fasting did not significantly change Y2 receptor mRNA levels in the arcuate nucleus. These results support the view that Y1 receptors in the arcuate nucleus play a role in the feeding pattern induced by neuropeptide Y.

Animals↗
PubMed1998

Agrobacterium-transformed rice plants expressing synthetic cryIA(b) and cryIA(c) genes are highly toxic to striped stem borer and yellow stem borer.

Over 2,600 transgenic rice plants in nine strains were regenerated from >500 independently selected hygromycin-resistant calli after Agrobacterium-mediated transformation. The plants were transformed with fully modified (plant codon optimized) versions of two synthetic cryIA(b) and cryIA(c) coding sequences from Bacillus thuringiensis as well as the hph and gus genes, coding for hygromycin phosphotransferase and beta-glucuronidase, respectively. These sequences were placed under control of the maize ubiquitin promoter, the CaMV35S promoter, and the Brassica Bp10 gene promoter to achieve high and tissue-specific expression of the lepidopteran-specific delta-endotoxins. The integration, expression, and inheritance of these genes were demonstrated in R0 and R1 generations by Southern, Northern, and Western analyses and by other techniques. Accumulation of high levels (up to 3% of soluble proteins) of CryIA(b) and CryIA(c) proteins was detected in R0 plants. Bioassays with R1 transgenic plants indicated that the transgenic plants were highly toxic to two major rice insect pests, striped stem borer (Chilo suppressalis) and yellow stem borer (Scirpophaga incertulas), with mortalities of 97-100% within 5 days after infestation, thus offering a potential for effective insect resistance in transgenic rice plants.

Bacillus thuringiensis↗
PubMed1998

CD4+, but not CD8+, T cells from mammary tumor-bearing mice have a down-regulated production of IFN-gamma: role of phosphatidyl serine.

IFN-gamma production is dramatically reduced in T cells from mice bearing large mammary tumors. This inhibition of IFN-gamma gene expression occurs mostly in CD4+ T cells, as determined by ELISA and reverse transcriptase-PCR. The effects of known mammary tumor factors in normal T cells and its subsets were evaluated. Pretreatment with granulocyte-macrophage CSF resulted in increased IFN-gamma levels by T cells, while PGE2 pretreatment equally decreased the levels of this cytokine in CD4+ and CD8+ T cells from normal mice. Interestingly, phosphatidyl serine (PS) down-regulated the IFN-gamma production of CD4+, but not that of CD8+, T cells. Methylation analysis indicated that the CpG dinucleotide in SnaBI site of the IFN-gamma 5' promoter flank region was hypermethylated in CD4+, but not in CD8+, T cells of large tumor bearers and of normal mice pretreated with PS. Electrophoresis mobility shift assay using an oligonucleotide probe corresponding to the IFN-gamma promoter core region sequence showed a greatly reduced binding of a 90-kDa nuclear protein in CD4+ T cells from tumor bearers and in those from PS-pretreated normal mice. Since IL-2 production is not affected in either CD4+ or CD8+ T cells from tumor bearers, these studies indicate that IFN-gamma production can be regulated independently from that of other type 1 cytokines in vivo. Our data further suggest that PS is involved in IFN-gamma gene down-regulation during mammary tumorigenesis and contributes to the generalized immunosuppression associated with tumor growth.

Animals↗
PubMed1998

Glutathione concentration may be a useful predictor of response to second-line chemotherapy in patients with ovarian cancer.

BACKGROUND: No useful predictor of resistance or sensitivity to second-line chemotherapy is known for ovarian cancer. The objective of this prospective study was to determine the utility of tumor glutathione S-transferase-pi (GST-pi) expression or glutathione (GSH) concentration in predicting ovarian cancer patients' responses to second-line chemotherapy. METHODS: Tumor samples were obtained from 26 patients with relapsed epithelial ovarian cancer 3-4 weeks before the initiation of second-line chemotherapy with etoposide (daily on Days 1-5) and cisplatin (on Day 5). The expression of GST-pi in tumor samples was determined by immunohistochemical staining and Western blot analysis. GSH concentration was measured by an enzymatic assay. RESULTS: The response rate was 38.4%. The estimated 3-year survival rate for the responders (66.7%) significantly exceeded that for the nonresponders (9.1%). Expression of GST-pi by immunohistochemical staining was more frequently observed in nonresponders (2 of 10 responders vs. 11 of 16 nonresponders). Western blot analysis detected GST-pi in all cases. There was no significant difference in the relative density values of the GST-pi Western blot analysis between the two groups. The mean value of GSH concentration in nonresponders was significantly higher than in responders (18.4 +/- 9.7 vs. 7.5 +/- 8.2 microg/mg protein). GSH concentration was below the cutoff point (10.3 microg/mg protein) in all responders except one. CONCLUSIONS: Second-line chemotherapy consisting of etoposide and cisplatin is effective in the treatment of relapsed epithelial ovarian cancer. In addition, tumor concentration of GSH may be a useful predictor of the response to this therapy.

Adult↗
PubMed1998

Interactive and dominant effects of residues 128 and 141 on cyclic nucleotide and DNA bindings in Escherichia coli cAMP receptor protein.

The molecular events in the cAMP-induced allosteric activation of cAMP receptor protein (CRP) involve interfacial communications between subunits and domains. However, the roles of intersubunit and interdomain interactions in defining the selectivity of cAMP against other cyclic nucleotides and cooperativity in ligand binding are still not known. Natural occurring CRP mutants with different phenotypes were employed to address these issues. Thermodynamic analyses of subunit association, protein stability, and cAMP and DNA binding as well as conformational studies of the mutants and wild-type CRPs lead to an identification of the apparently dominant roles of residues 128 and 141 in the cAMP-modulated DNA binding activity of CRP. Serine 128 and the C-helix were implicated as playing a critical role in modulating negative cooperativity of cyclic nucleotide binding. A correlation was established between a weak affinity for subunit assembly and the relaxation of cyclic nucleotide selectivity in the G141Q and S128A/G141Q mutants. These results imply that intersubunit interaction is important for cyclic nucleotide discrimination in CRP. The double mutant S128A/G141Q, constructed from two single mutations of S128A and G141Q, which exhibit opposite phenotypic characteristics of CRP- and CRP*, respectively, assumes a CRP* phenotype and has biochemical properties similar to those of the G141Q mutant. These observations suggest that mutation G141Q exerts a dominant effect over mutation S128A and that the subunit realignment induced by the G141Q mutation can override the local structural disruption created by mutation S128A.

Cyclic AMP↗
PubMed1998

Differential perturbation of intersubunit and interdomain communications by glycine 141 mutation in Escherichia coli CRP.

Upon binding of cAMP, concomitant changes in CRP structure across the subunit and domain interfaces are observed. In order to identify the structural elements involved in the coupling of interfacial interactions, structural perturbation was introduced at residue 141 by site-directed mutagenesis. Thermodynamic parameters defining protein stability, cAMP binding, and subunit assembly of the mutant were determined. Conformational changes probed by proteolytic digestion and fluorescence signal reported by the fluorescein-labeled C178 lead to a dissection of the contribution of the intersubunit and interdomain interactions, respectively, in the cAMP-modulated DNA binding of CRP. In the absence of cAMP, mutant G141Q is sensitive to protease attack at the subunit interface, an established property of wild type CRP observed only in the presence of cAMP. Although the G141Q mutant assumes a subunit alignment similar to that of the activated CRP, this mutant absolutely requires cyclic nucleotide for specific DNA interaction. Monitoring the fluorescence probe attached to the C-terminal DNA binding domain of the G141Q mutant showed that the DNA binding domain responds quantitatively to the binding of cyclic nucleotide to the N-terminal domain. This result suggests that domain reorientation is a required structural change in addition to subunit alignment. In summary, mutation at G141 has differentially perturbed the communication network which involves the interfacial interactions between subunits and domains. The G141Q CRP mutant assumes a conformation that partially resembles the active form represented by the observed subunit realignment, but complete activation of the mutant requires binding of cyclic nucleotide which induces the reorientation of domains. Furthermore, the G --> Q mutation leads to a loss in the discriminatory power of CRP for only cAMP. Other cyclic nucleotides are capable of activating this mutant.

Bacterial Proteins↗
PubMed1998

Pressor and vasoconstrictor effects of methylene blue in endotoxaemic rats.

Nitric oxide (NO) is a primary mediator of hypotension in sepsis. We examined the effects of methylene blue (MB), an inhibitor of the NO/cGMP pathway, on mean arterial pressure (MAP), cardiac output (CO), total peripheral resistance (TPR), mesenteric blood flow (MBF) and renal blood flow (RBF) in pentobarbitone-anaesthetised rats injected with lipopolysaccharide (LPS, 7.5 mg/kg). MB (1, 3 or 10 mg/kg x h) or vehicle was i.v. infused into four groups at 2.5 h after i.v. injection of LPS. Two other groups received MB or vehicle at 2.5 h after receiving saline. LPS reduced MAP, CO, RBF as well as MBF at 2.5 and 4 h, and increased TPR at 2.5 but not 4 h. Whereas MB alone had no effects on measured variables in control rats at 4 h, in LPS-treated rats, it elevated TPR at all doses and attenuated the fall in MAP at the two low doses. CO was unaltered by low doses of MB but reduced by the high dose. MBF was unaltered, but RBF was increased by the lowest dose but decreased by the highest dose of MB. Therefore, in endotoxaemia, a low dose of MB increases MAP and TPR but does not alter CO; a high dose of MB does not raise MAP but increases TPR and reduces CO.

Animals↗
PubMed1998

Genetic and serological analysis of the immunogenic 67-kDa lipoprotein of Mycoplasma sp. bovine group 7.

The gene encoding a lipoprotein of 67 kDa, named P67, was cloned from Mycoplasma sp. bovine group 7 strain PG50 and expressed in Escherichia coli K12. Analysis of the amino acid sequence derived from the DNA sequence of the P67 gene revealed a typical prokaryotic signal peptidase II membrane lipoprotein lipid attachment site and a transmembrane structure domain in the leader sequence at the amino-terminal end of the protein. Protein P67 showed 91% identical amino acid residues to the lipoprotein P72 of Mycoplasma mycoides subsp. mycoides small colony type (SC) and 53% identical amino acid residues to a peptide of an unassigned gene on the genome of Mycoplasma capricolum subsp. capricolum. Antibodies made against recombinant P67 reacted with a 67-kDa protein in all Mycoplasma sp. bovine group 7 strains tested and also, to some extent, with P72 of Mycoplasma mycoides subsp. mycoides SC. The gene encoding P67 was present in all strains of Mycoplasma sp. bovine group 7 analysed, but not in other Mycoplasma sp. of the "mycoides cluster" and not in the phylogenetically related Mycoplasma putrefaciens. PCR and restriction fragment analysis revealed that the gene of P67 is conserved in all strains of Mycoplasma sp. bovine group 7. A specific PCR reaction based on the P67 gene sequence enabled rapid identification of strains belonging to Mycoplasma sp. bovine group 7.

Amino Acid Sequence↗
PubMed1998

Structures of HhaI methyltransferase complexed with substrates containing mismatches at the target base.

Three structures have been determined for complexes between HhaI methyltransferase (M.HhaI) and oligonucleotides containing a G:A, G:U or G:AP (AP = abasic or apurinic/apyrimidinic) mismatch at the target base pair. The mismatched adenine, uracil and abasic site are all flipped out of the DNA helix and located in the enzyme's active-site pocket, adopting the same conformation as in the flipped-out normal substrate. These results, particularly the flipped-out abasic deoxyribose sugar, provide insight into the mechanism of base flipping. If the process involves the protein pushing the base out of the helix, then the push must take place not on the base, but rather on the sugar-phosphate backbone. Thus rotation of the DNA backbone is probably the key to base flipping.

Base Pair Mismatch↗
PubMed1998

Development of a monoclonal antibody to a Ureaplasma urealyticum serotype 9 antigen.

We produced a monoclonal antibody (MAb) to Ureaplasma urealyticum Vancouver, the serotype 9 standard strain. By immunoblotting, this MAb showed a single, 85-kDa band with the homologous serotype and a minor, 100-kDa band with serotype 2 but did not react with any other serotype standard strain. Clinical isolates of U. urealyticum were tested with this MAb and with two sets of polyclonal antisera against the 14 serotype standard strains. The use of MAb 9-2H9 correctly identified certain serotype 9 strains but did not react with wild-type strains lacking the serotype 9 determinant.

Animals↗
PubMed1998

Base flipping.

Base flipping is the phenomenon whereby a base in normal B-DNA is swung completely out of the helix into an extrahelical position. It was discovered in 1994 when the first co-crystal structure was reported for a cytosine-5 DNA methyltransferase binding to DNA. Since then it has been shown to occur in many systems where enzymes need access to a DNA base to perform chemistry on it. Many DNA glycosylases that remove abnormal bases from DNA use this mechanism. This review describes systems known to use base flipping as well as many systems where it is likely to occur but has not yet been rigorously demonstrated. The mechanism and evolution of base flipping are also discussed.

Base Pair Mismatch↗
PubMed1998

Antibiotic activities and affinities for bacterial cell wall analogue of N-demethylvancomycin and its derivatives.

N-Demethylvancomycin, which has been clinically used in China, is one member of vancomycin group (glycopeptide) antibiotics. It differs from vancomycin only in that methyl group on the amino group of the N-terminal residue of vancomycin has been replaced by H. By reductive alkylation of N-demethylvancomycin, we synthesized N-alkyl and N,N'-dialkyl N-demethylvancomycins, which closely correlated with vancomycin in structure. The association constants of the complexes of N-demethylvancomycin and its analogues with di-N-Ac-L-Lys-D-Ala-D-Ala and the antibiotic activity against Staphylococcus aureus of the glycopeptides were determined. Results showed that N-demethylvancomycin has higher affinity for bacterial cell wall analogue di-N-Ac-L-Lys-D-Ala-D-Ala and more potent antibiotic activity against Staphylococcus aureus than vancomycin. Both N-alkylation and N,N'-dialkylation of N-demethylvancomycin reduced the affinity and antibiotic activity. The longer the alkyl groups, the less potent antibiotic activities and lower affinities have the glycopeptides. The antibiotic activities against Staphylococcus aureus of N-demethylvancomycin and its analogues roughly parallel their affinities for di-N-Ac-L-Lys-D-Ala-D-Ala.

Alkylation↗
PubMed1998

[Effect of crushing of sciatic nerve on neuron of lumbar spinal cord].

In order to investigate the effect of nerve compression on neurons, the commonly used model of chronic nerve compression was produced in 48 SD rats. The rats were sacrificed in 1, 2, 3, 4, 5 and 6 months after compression, respectively. The number of neuron and ultrashruchure of alpha-motor neurons and ganglion cells of the corresponding spinal segment were examined. The results showed as following: After the sciatic nerve were crushed, the number of neuron and ultrastructure of alpha-motor neurons and ganglion cells might undergo ultrastructural changes, and even the death might occur. These changes might be aggravated as the time of crushing was prolonged and the compression force was increased. It was concluded that for nerve compression, decompression should be done as early as possible in order to avoid or minimize the ultructural changes of the neuron.

Animals↗
PubMed1998

[The comprehensive treatment of varicosis of lower extremity with chronic ulcer of leg].

From Oct. 1993 to Dec. 1995, nineteen refractory cases with varicosis and chronic ulcer of lower limb were treated. The average age of these patients was sixty-eight, the disease history was more than 20 years. The size of the ulcer of the leg ranged from the minimum of 10 cm x 8 cm to the maximum of 30 cm x 15 cm. All of them had once received saphenectomy and split skin graft without ulcer healing before they were admitted in our department. Both venography and ultrasonography showed superficial venous valve incompetence. The following comprehensive treatment was adopted. Firstly, myoplasty around popliteal vein was done. Secondly, phlebexairesis and phleborrhaphy were done for the variciform veins through minor incision. Then through debridement of the ulcer was performed. Delayed split skin graft was exerted one week later. The result showed that all the cases were successful: the ulcer was healed and there was no recurrence of varicosis.

Aged↗
PubMed1998

[Prediction of cephalopelvic disproportion by ultrasonographic cephalopelic].

OBJECTIVE: To develop a prospective antepartum method of identifying cephalopelvic disproportion by comparing the diameters of fetal head with those of the maternal midpelvis. METHODS: Transvaginal ultrasound pelvimetry was performed on 190 healthy primigravidas with cephalic presentation at 28-35 weeks of gestation, and the diameters of their fetal heads were meassured within one week prior to delivery. These indices the cephalopelvic indices of diameter, cirumference and area, were calculated and compared. RESULTS: The cephalopelvic index of diameter (CID), defined as the difference between the mean diameter of the midpelvis and the fetal biparetal diaameter (BPD), showed the highest degree of accuracy (77.9%). Eighty three percent of women with CID less than 15.8 needed operative delivery; 76.2% of those with CId more than 15.8 mm underwent vaginal delivery. CONCLUSIONS: Transvaginal ultrasound pelvimetry and the CID by and large seems to be able to identify cephalopelvic disproportion before labor and may help obsetricians choose the most appropriate form of delivery in an uncomplicated vertex presentation.

Adult↗
PubMed1998

[Effect of prolonged inhalation of nitric oxide on chronically hypoxic rats].

OBJECTIVE: To explore the effect of prolonged nitric oxide (NO) inhalation on chronically hypoxic rats. METHODS: Male Wistar rats were randomly divided into 3 groups: 1) room-air control (C); 2) hypoxia (H); 3) hypoxia with the inhalation of 20 ppm NO(2NH). RV/LV + S, mPAP and the histopathology of the lung were examined. Plasma levels of ET-1 and cGMP were detected by radioimmunoassay. RESULTS: 1. Hypoxia caused marked elevation in mPAP and RV/LV + s (both P < 0.001 vs Group C). NO significantly reduced mPAP and RV/LV + S; 2. Hypoxia raised the percentage of intra-acinar muscular artery (MA) and lowered that of nonmuscular artery (NAM). MA decreased from 35.2% to 16.8% in Group 2NH; NMA increased from 43.6% to 64.8% in Group 2NH, 3. The plasma level of ET-1 increased and that of cGMP droped significantly in Group H(both P < 0.001 vs Group C). NO resulted in a marked reduction in the plasma ET-1 and an increase in plasma cGMP; 4. Inhalation of NO had no effect on methemoglobin and lung index in hypoxic rats. CONCLUSIONS: Prolonged inhalation of 20 ppm NO can attenuate hypoxic pulmonary hypertension and inhibit the hypertrophy of the pulmonary vascular smooth muscle and the right ventricle NO, when inhalated at a concentration of 20 ppm for a long duration, will cause no toxicity in chronically hypoxic rats.

Administration, Inhalation↗
PubMed1998

[The effect of nitric oxide administration on pateints with pulmonary hypertension: a dose-response study].

OBJECTIVE: To explore the dose-response relationship in patients with pulmonary hypertension after inhalation of nitric oxide (NO). METHODS: The effect of various concentrations (20, 40, 60 and 80 ppm) of NO on hemodynamics and cardiac function in 16 patients with pulmonary hypertension was studied with right heart catheterization. RESULTS: Pulmonary artery pressure and pulmonary vascular resistance reduced significantly after inhalation of various concentrations (20, 40, 60 and 80 ppm) of NO. The vascular response to NO was not concentration-dependant with a maximal effect obtained at 20 ppm. At inhalation of low dose of NO (20 ppm), the mean pulmonary artery pressure and pulmonary vascular resistance dropped by 26.5% and 40.3% (P < 0.0001), respectively. With the increase of inhaled NO concentration, pulmonary artery pressure and pulmonary vascular resistance did not decline. CONCLUSION: The best concentration of inhaled NO was not more than 20 ppm in the patients of this study.

Administration, Inhalation↗