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Biomedical subjects

H X Xu

Publications and source records attributed to H X Xu.

At least 19 recordsLinked to original sources
PubMed1998

A new antiplatelet diarylheptanoid from Alpinia blepharocalyx.

A new diarylheptanoid, 1,7-bis(4-hydroxyphenyl)-3-hydroxy-1,3-heptadien-5-one (1), along with seven other known compounds, were isolated from the seeds of Alpinia blepharocalyx. Of these, compounds 1 and 3 showed strong inhibition of collagen-induced, arachidonic acid-induced, and adenosine diphosphate-induced platelet aggregation of human whole blood. Compound 3 also strongly inhibited ristocetin-induced platelet aggregation. Structures of these compounds were elucidated by spectroscopic and chemical means.

China↗
PubMed1998

Effects of tannins from Geum japonicum on the catalytic activity of thrombin and factor Xa of blood coagulation cascade.

Bioassay-guided fractionation of the MeOH extract of the whole plant of Geum japonicum led to the isolation of seven known tannins. They were identified by spectroscopic methods as penta-O-galloyl-beta-glucoside (1), pedunculagin (2), 2, 3-(S)-hexahydroxydiphenoyl-D-glucose (3), tellimagrandin II (4), 2, 6-di-O-galloyl-D-glucose (5), casuariin (6), and 5-desgalloylstachyurin (7). Compounds 1, 2, 4, 6, and 7 showed potent anticoagulant activity by significantly prolonging the clotting of rabbit plasma. The inhibitory effect of 2 was competitively directed against thrombin. Its IC50 values for inhibition of the enzymatic activity of thrombin on synthetic substrate and fibrinogen were 0.18 and 0.15 microM, respectively. On the other hand, compounds 1, 4, 6, and 7 are mixed noncompetitive inhibitors of thrombin. Their IC50 values for inhibition of fibrinogen hydrolysis were twofold to sevenfold lower than those for the inhibition of synthetic substrate hydrolysis. Factor Xa was competitively inhibited by compounds 1, 2, 4, 6, and 7. The phenolic hydroxyl groups of the active tannins appear to play an important role in their inhibitory effect on the enzymes.

Animals↗
PubMed1996

A transcription map of the major histocompatibility complex (MHC) class I region.

We have applied cDNA hybridization selection to nine YACs spanning 3 Mb of genomic DNA from a region centromeric to HLA-A to the histone cluster that lies telomeric to the human major histocompatibility complex (MHC). In addition to Class I genes and pseudogenes, we describe over 63 genes and 23 additional expressed sequence tags distributed throughout the region. Many of the full-length genes belong to gene families. Prominent among these are a group of genes encoding proteins showing homology to the carboxyl-terminal sequences of butyrophilin and an additional group of zinc finger genes. We also detected several previously undefined genes that are specifically expressed in cells of the immune system, indicating a more complex role of the MHC in the immune response than has been appreciated.

Amino Acid Sequence↗
PubMed1996

In vitro response of Blastocystis hominis against traditional Chinese medicine.

This is the first inn vitro study on the activity of 20 kinds of crude extracts of traditional Chinese medicine (TCM) on the intestinal parasite, Blastocystis hominis using the criteria of living cell count (LCC) and living cell rate (LCR). LCC and LCR were applied as observation indicators, the former as a fixed-quantity and the latter as a fixed-quality method. LCR calculated percentage rate of living cells using eosin-brilliant cresyl blue staining which could differentiate between living cells and dying or dead cells. There were five extracts with no inhibitory activity, thirteen with moderate inhibition and two with high inhibition. The crude extracts of Coptis chinensis (CC) and Brucea javanica (BJ) were found to be most active against B. hominis. The active concentration of CC was 100 micrograms/ml. The active concentration of BJ was 500 micrograms/ml. The active concentration of metronidazole (MD) was 10 micrograms/ml and this was taken as an active standard drug for B. hominis.

Animals↗
PubMed1996

Anti-HIV triterpene acids from Geum japonicum.

The methanol extract from the whole plant of Geum japonicum was found to inhibit the human immunodeficiency virus (HIV-1) protease. Through bioassay-directed fractionation of the extract, a new triterpene acid along with five known triterpene acids, ursolic acid, epipomolic acid, maslinic acid, euscaphic acid, and tormentic acid, were isolated. The structure of the new compound was determined by spectral means including 1H-1H COSY, HMQC, HMBC, and NOE experiments to be 2 alpha, 19 alpha-dihydroxy-3-oxo-12-ursen-28-oic acid (1). Of these compounds, 1, ursolic acid, and maslinic acid showed potent inhibitory activity against HIV-1 protease.

Amino Acid Sequence↗
PubMed1993

Inhibitory effect of the water extract of spikes of Miscanthus sinensis on IgE formation in mice.

The effects of four different plant extracts of the spikes of Miscanthus sinensis, Phragmites communis, and Imperata cylindrica var. major, and of the spikelets of Coix lachryma-jobi on IgE antibody formation were investigated in mice. The IgE antibody titer was tested by the passive cutaneous anaphylaxis (PCA) method in rats. Of these, the water extract of M. sinensis showed an appreciable inhibitory effect on IgE formation. Furthermore, an undialyzable fraction of the water extract with a relative molecular mass of more than 50,000 d, designated as MSIS, showed the most potent inhibitory activity on IgE formation. MSIS was also a potent inhibitor of IgE formation when given intraperitoneally or intranasally to mice the day before injection of dinitrophenyl (DNP)-ovalbumin (OVA) antigen in both the primary and secondary immune responses. Moreover, MSIS clearly suppressed on-going IgE antibody formation in both primary and secondary immune responses.

Animals↗
PubMed1993

2'-Hydroxymatteucinol, a new C-methyl flavanone derivative from Matteccia orientalis; potent hypoglycemic activity in streptozotocin (STZ)-induced diabetic rat.

The CHCl3 extract of Matteccia orientalis showed very strong hypoglycemic activity in streptozotocin (STZ)-induced diabetic rats. A new C-methyl flavanone derivative, 2'-hydroxymatteucinol (3) was isolated from the hypoglycemic activity bearing fraction, along with two known compounds, demethoxymatteucinol (1) and matteucinol (2). The structures of these isolated compounds were elucidated by spectroscopic methods. One of the compounds isolated from CHCl3 extract, 2'-hydroxymatteucinol (3), showed dose-dependent hypoglycemic activity, and a blood sugar lowering effect was observed even at the dose of 10 mg/kg (p.o.) in STZ-induced diabetic rats.

Animals↗
PubMed1993

Isolation and structure of woodorien, a new glucoside having antiviral activity, from Woodwardia orientalis.

Hot aqueous and methanol extracts of the rhizomes of Woodwardia orientalis were tested for their in vitro antiviral activity against herpes simplex virus type 1 (HSV-1), poliovirus type 1, and measles virus by plaque reduction assay. The aqueous extract of W. orientalis reduced the plaque forming ability of HSV-1 and poliovirus more strongly than did the methanol extract. By bioassay-directed fractionation of the aqueous extract, a new glucoside, woodorien (1), along with five known compounds were isolated from an EtOAc-soluble fraction that had antiviral activity. The structures of these compounds were determined by the use of two dimensional (2D) NMR techniques (1H-1H correlation spectroscopy (COSY), 1H-13C COSY and heteronuclear multiple-bond multiple-quantum coherence (HMBC)). Woodorien (1) was the most potent inhibitor against HSV-1 among the isolated compounds.

Animals↗
PubMed1991

Urinary excretion of nitrate, N-nitrosoproline, 3-methyladenine, and 7-methylguanine in a Colombian population at high risk for stomach cancer.

Urinary excretion levels of nitrate and N-nitrosoproline were determined in 160 individuals in a Colombian population at high risk for gastric cancer. In 156 of these subjects urinary levels of 3-methyladenine and 7-methylguanine were determined. Gastric biopsy specimens were obtained from 118 individuals and were histologically characterized according to pathological criteria into the following groups: normal, superficial gastritis, chronic atrophic gastritis, chronic atrophic gastritis with intestinal metaplasia, and dysplastic. The histological changes were correlated with the four variables listed above. There were no significant differences in the excretion of nitrate, N-nitrosoproline, 3-methyladenine, or 7-methylguanine in subjects with different pathological changes. A statistically significant correlation was present between nitrate and N-nitrosoproline excretion in the total population group (r = 0.297, P = 0.0001). A highly significant correlation (r = 0.56, P = 0.0002) was noted for urinary nitrate and N-nitrosoproline excretion in individuals with intestinal metaplasia and dysplasia. An increase in the urinary excretion of 3-methyladenine and 7-methylguanine was associated with tobacco smoking in the total population group.

Adenine↗
PubMed1991

Analysis of volatile N-nitrosamines in beer and food in China.

Capillary gas chromatography-thermal energy analysis was used for the study of volatile N-nitrosamines in comestibles. The finding of a comparatively high content of N-nitrosodimethylamine in some Chinese beers confirms the results of other authors. We describe studies of Chinese foods and environmental samples carried out in this laboratory in collaboration with epidemiological groups. The concentrations of N-nitrosamines could be correlated with mortality from digestive cancer.

Beer↗
PubMed1991

Comparison of urinary nitrate, N-nitrosoproline, 7-methylguanine and 3-methyladenine levels in a human population at risk for gastric cancer.

We have measured the urinary excretion of nitrate, N-nitrosoproline, 3-methyladenine and 7-methylguanine in a human population at high risk for gastric cancer. A strong correlation was observed between nitrate and N-nitrosoproline excretion (p less than 0.00000); statistically significant correlations (p less than 0.05) were also observed for N-nitrosoproline with 3-methyladenine (p = 0.003) and with 7-methylguanine (p = 0.03) and for 7-methyl-guanine with nitrate (p = 0.02), although these correlations were sensitive to outliers. Smokers appeared to excrete slightly higher levels of 3-methyladenine than nonsmokers; no other difference was observed between smokers and nonsmokers or between drinkers and nondrinkers. The correlation between N-nitrosoproline excretion and nitrate excretion supports the hypothesis that elevated endogenous nitrate levels may contribute to elevated endogenous formation of N-nitroso compounds.

Adenine↗
PubMed1990

Coding and noncoding sequences at the 3' end of yeast histone H2B mRNA confer cell cycle regulation.

Yeast (Saccharomyces cerevisiae) histone mRNA synthesis is tightly regulated to the S phase of the cell division cycle as a result of both transcriptional and posttranscriptional regulation. We focused on the role of posttranscriptional control in histone H2B1 gene (HTB1) regulation and studied a portion of the HTB1 message required for cell-cycle-specific accumulation. The 3' end of the HTB1 gene containing a 17-amino-acid coding sequence and entire noncoding sequence was fused to the bacterial neomycin phosphotransferase II gene (neo) under control of the GAL1 promoter. The expression of the endogenous and chimeric HTB1 genes was analyzed during the yeast cell cycle. As yeast cells entered a synchronous cell cycle following release from alpha-factor arrest, the level of GAL1-promoter-controlled neo-HTB1 message increased approximately 12-fold during S phase and dropped to basal level when the cells left S phase. This indicates that the 3' end of the HTB1 mRNA is capable of conferring cycle-specific regulation on a heterologous message. Deletion analysis of the 3' end showed that the signal for cell cycle control of HTB1 mRNA includes contiguous coding and noncoding sequences surrounding the stop codon. This differs from the situation in mammalian cells, whose posttranscriptional regulation of histone genes is mediated through a short sequence containing a stem-loop structure near the very terminus of the untranslated 3' end.

Base Sequence↗
PubMed1990

[The structure of astrachrysosid A and the study of 2D-NMR on astrasieversianin XV and 7,2'-dihydroxy-3',4'-dimethoxy-isoflavane-7-O-beta-D-glycoside].

Six compounds were isolated from the root of Astragalus chrysopterus Bunge. One of them was identified as a new triterpenoid glycoside, named astrachrysoside A. Its structure was elucidated as 3-O-[alpha-L-rhamnopyranosyl (1----2) beta-D-xylopyranosyl]-cycloastragenol on the basis of physicochemical evidence and chemical reactions. The others were shown to be known compounds, astrasieversianin XV (II), 7,2'-dihydroxy-3',4'-dimethoxy-isoflavane-7-O-beta-D-glucoside (III), soyasaponin I, daucosterol and beta-sitosterol. Full assignment of the chemical shift signals of II and III were established by various 2D-NMR techniques.

Chemical Phenomena↗
PubMed1985

Establishment and characterization of human malignant pleural mesothelioma cell line SMC-1.

A cell line (SMC-1) has been established from the resected tissue of a patient with malignant pleural mesothelioma which has been pathologically confirmed to be the mixed type. The cell line is characterized by the pleomorphy and multilayered growth of the cells with the population-doubling time of approximately 32 h, the highest mitotic index of 46--50% and the modal chromosome number of 69-70. Transplantation of the cells into the animals can produce tumors bearing histological resemblance to the original material. The cultured cells, xenografted tumor cells and the cells from the host specimen show similar histochemical expressions. These data meet the requirements of a human malignant pleural mesothelioma cell line. The establishment of this cell line will serve as a useful tool in clinical research of diagnosis and treatment of this devastating disease.

Adult↗