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Biomedical subjects

H Yang

Publications and source records attributed to H Yang.

At least 307 records · Page 17Linked to original sources
PubMed2000

Reduced mRNA abundance of the main enzymes involved in methionine metabolism in human liver cirrhosis and hepatocellular carcinoma.

BACKGROUND/AIMS: It has been known for at least 50 years that alterations in methionine metabolism occur in human liver cirrhosis. However, the molecular basis of this alteration is not completely understood. In order to gain more insight into the mechanisms behind this condition, mRNA levels of methionine adenosyltransferase (MAT1A), glycine methyltransferase (GNMT), methionine synthase (MS), betaine homocysteine methyltransferase (BHMT) and cystathionine beta-synthase (CBS) were examined in 26 cirrhotic livers, five hepatocellular carcinoma (HCC) tissues and ten control livers. METHODS: The expression of the above-mentioned genes was determined by quantitative RT-PCR analysis. Methylation of MAT1A promoter was assessed by methylation-sensitive restriction enzyme digestion of genomic DNA. RESULTS: When compared to normal livers MAT1A, GNMT, BHMT, CBS and MS mRNA contents were significantly reduced in liver cirrhosis. Interestingly, MAT1A promoter was hypermethylated in the cirrhotic liver. HCC tissues also showed decreased mRNA levels of these enzymes. CONCLUSIONS: These findings establish that the abundance of the mRNA of the main genes involved in methionine metabolism is markedly reduced in human cirrhosis and HCC. Hypermethylation of MAT1A promoter could participate in its reduced expression in cirrhosis. These observations help to explain the hypermethioninemia, hyperhomocysteinemia and reduced hepatic glutathione content observed in cirrhosis.

Carcinoma, Hepatocellular↗
PubMed2000

HLA class II haplotype associations with inflammatory bowel disease in Jewish (Ashkenazi) and non-Jewish caucasian populations.

Ulcerative colitis (UC) and Crohn's disease (CD) are the clinical entities comprising idiopathic inflammatory bowel disease (IBD). Previous studies on the association of IBD and human leukocyte antigen (HLA) class II genes suggested a role for HLA in this disease. Here we present HLA class II (DRB1, DQB1, DQA1, DPB1) allele and haplotype distributions determined using the polymerase chain reaction and sequence-specific oligonucleotide probe methods. A total of 578 UC and CD Caucasian patients and controls from Jewish (Ashkenazi) and non-Jewish populations was examined. Our previously reported association of DR1-DQ5 with CD was attributable to DRB1*0103. A dramatic association with IBD and the highly unusual DRB1*0103-DQA1*0501-DQB1*0301 haplotype (OR = 6.6, p = 0.036) was found. The more common DR1 haplotype, DRB1*0103-DQA1*0101-DQB1*0501, was also associated with IBD (OR = 3.1, p = 0.014), a result suggesting that interaction between DR and DQ may determine the extent of disease risk. Our previously reported association of DR2 with UC was attributable to DRB1*1502 (OR = 2.6, p = 0.006). At the DPB1 locus, a significant association of DPB1*0401 with CD was observed for the combined populations (OR = 1.85, p = 0.007). These observations indicate that some class II alleles and haplotypes confer susceptibility to both UC and CD, implying common immunogenetic mechanisms of pathogenesis, while others confer risk to only one of these diseases, and illustrate the value of DNA HLA typing in disease susceptibility analyses.

California↗
PubMed2000

Activation of the parapyramidal region in the ventral medulla stimulates gastric acid secretion through vagal pathways in rats.

Neurons synthesizing thyrotropin-releasing hormone, substance P and serotonin in the medullary caudal raphe nuclei project to the dorsal vagal complex and play a role in the central vagal regulation of gastric function. Neurons in the parapyramidal region in the ventral medulla share similar biochemical coding and projections as those in the caudal raphe nuclei. The role of the parapyramidal region in the autonomic regulation of gastric acid secretion was investigated in urethane-anesthetized rats. Unilateral microinjection of kainate into the parapyramidal region at 10, 15 and 20 ng induced a dose-related stimulation of gastric acid secretion (net increases: 22.2+/-11.2, 40.5+/-8.5 and 89.8+/-19.4 micromol/60 min, respectively), while injection of vehicle had no effect (net change: -0.1+/-1.4 micromol/60 min). Time-course studies showed a nine-fold peak increase over basal at 30 min after parapyramidal injection of kainate (20 ng) and acid secretion returned to basal level at 70 min. Microinjections of kainate (15-20 ng) outside the parapyramidal region or into the parapyramidal region in vagotomized rats had no effect. Exposure to cold (4 degrees C) for 2 h, which is known to induce vagally mediated gastric secretory and motor responses through medullary thyrotropin-releasing hormone pathways, increased the number of Fos-positive cells in the caudal, middle and rostral parts of the parapyramidal region to 4.3+/-0.4, 9.4+/-0.9 and 18.4+/-1.6/section, respectively, compared with 0.1+/-0. 1, 0.1+/-0.0 and 0.7+/-0.6/section, respectively, in rats maintained at room temperature. Most of the Fos-labeled cells co-expressed pro-thyrotropin-releasing hormone messenger RNA signal and/or were serotonin immunoreactive. These data show that chemical activation of neurons in the parapyramidal region results in a vagal-dependent stimulation of gastric acid secretion and that acute cold exposure activates parapyramidal neurons containing pro-thyrotropin-releasing hormone and/or serotonin, suggesting a potential role of the parapyramidal region, in addition to the caudal raphe nuclei, as medullary sites involved in the vagal regulation of gastric function.

Animals↗
PubMed2000

A new ent-kaurane diterpenoid from Isodon phyllostachys.

A new ent-kaurane diterpenoid, phyllostachysin C (1), together with five known compounds, sculponeatins B and C, nodosin, ursolic acid and 2 alpha-hydroxyursolic acid, were isolated from the leaves of Isodon phyllostachys. The structure of 1 was elucidated on the basis of its spectral properties.

Diterpenes↗
PubMed2000

Constituents of Craspedolobium schochii.

Nine phenolic compounds, including a new one, were isolated from 70% acetone extract of Craspedolobium schochii. The new compound was identified as 3-(3,4-dimethoxy-2-hydroxyphenyl)-7-hydroxy-coumarin (1) on the basis of spectroscopic evidence.

Coumarins↗
PubMed2000

New steroids from Clerodendrum colebrookianum.

Five new steroids, colebrin A-E (1-5) were isolated from the aerial parts of Clerodendrum colebrookianum. The structures of the new compounds were elucidated on the basis of spectral evidence.

Drugs, Chinese Herbal↗
PubMed2000

Absence or reduction of carbonic anhydrase II in the red cells of the beluga whale and llama: implications for adaptation to hypoxia.

Carbonic anhydrase (CA) expression was examined in the red cells of two mammals that have adapted to low oxygen stress: the llama, which has adapted to high altitudes, and the beluga (or white) whale, which routinely dives for extended periods. Immunodiffusion analyses of their Hb-free hemolysates and partial amino acid sequencing of their HPLC-separated nonheme proteins indicate that the low-activity CA I isozyme is the major nonheme protein in erythrocytes of both the beluga whale and the llama. The high-activity CA II isozyme was not detected in the whale red cells but was present at low levels in erythrocytes of the llama. These results suggest that the absence or decrease in the expression of the high-activity CA II isozyme may be advantageous under hypoxic conditions.

Amino Acid Sequence↗
PubMed2000

Molecular characterization of a parasitic tapeworm (Ligula) based on DNA sequences from formalin-fixed specimens.

Museum specimens of Ligula (Pseudophyllidea, Ligulidae), a fish parasite tapeworm, that have been preserved in ethanol or fixed permanently in formalin up to 24 years were used for DNA extraction and molecular characterization. DNA was amplified via PCR from samples collected from different fish hosts that lived in both salt and fresh water bodies in the Chinese Qinghai-Tibet Plateau, Russia, and England. Phylogenetic analyses based on partial nucleotide sequences of the 5'-end of nuclear 28S rRNA gene and the mitochondrial cytochrome c oxidase subunit I (COI) gene support the morphologically based taxonomy that groups the Chinese Ligula within the same species as their Europe counterpart: Lingula intestinalis. No nucleotide variation was detected in either the 28S rRNA gene or the COI gene among the seven plerocercoid samples, suggesting a considerable genetic homogeneity among Ligula from different regions. Our results show that geographic isolation, affinity of hosts, and host habitats are not reliable taxonomic criteria for Ligula classification. Our data also indicate a low genetic diversity in the Ligula prevalent in China and in Europe. Our experiments demonstrate that endogenous DNA from specimens that were subjected to permanent formalin fixation can be routinely amplified from parasitic tapeworms, suggesting that fixation time in formalin may not be a critical factor affecting DNA degradation in such museum specimens.

Animals↗
PubMed2000

Probing the roles of the only universally conserved leucine residue (Leu122) in the oligomerization and chaperone-like activity of Mycobacterium tuberculosis small heat shock protein Hsp16.3.

To understand the role of the only universally conserved hydrophobic residue among all the members of the sHsp family, this extremely well conserved Leu122 residue in Hsp16.3 was replaced by valine, alanine, asparigine, or aspartate residues. Only very small amounts of the L122D and L122N mutant Hsp16.3 proteins were expressed in the transformed E. coli; however, both the L122V and L122A were readily expressed. The L122V and L122A mutant proteins had similar oligomeric structures to the wild-type protein at room temperature. Examination of the L122A mutant protein by native pore gradient PAGE and CD spectroscopy, however, revealed a smaller oligomeric size and different secondary structure at 37 degrees C. Both L122V and L122A mutant proteins exhibited significantly lowered chaperone activities. Observations reported here suggest a very important role of this only universally conserved Leu residue in both the formation of specific oligomeric structures and the molecular chaperone activities of Hsp16.3.

Bacterial Proteins↗
PubMed2000

Ribozyme-mediated resistance to rice dwarf virus and the transgene silencing in the progeny of transgenic rice plants.

A hammerhead ribozyme (Rz) with long hybridizing arms targeting the mRNA of rice dwarf virus (RDV) segment 5 and a mutated nonfunctional ribozyme (mRz) were constructed. As predicted, Rz transcribed in vitro cleaved the target mRNA of RDV segment 5 into two fragments of 138 and 238 nucleotides in length. The Rz and mRz genes were each placed under the control of the CaMV 35S promoter and used to transform Japonica rice variety 'Tongling No. 1' via Agrobacterium tumefaciens. A total of 32 independent lines containing Rz or mRz was obtained as demonstrated by Southern blot analysis. Challenge inoculation with RDV viruliferous leafhoppers (Nephotettix cincticeps) showed that T1 plants containing the Rz transgene displayed high resistance or delayed and attenuated viral symptoms. In contrast, transgenic lines expressing mRz showed severe symptoms similar to the control plants transformed with the vector alone. These results suggest that Rz confers RDV resistance in transgenic rice. Genomic DNA PCR analysis confirmed that all of the examined T6 progeny plants contained the Rz transgene. However, accumulation of the Rz transcripts was detectable by RT-PCR only in the plants that were resistant to RDV. This suggested that loss of RDV resistance in progeny plants containing the Rz transgene may result from silencing of the Rz transgene.

Base Sequence↗
PubMed2000

Molecular cloning and characterization of OsPSK, a gene encoding a precursor for phytosulfokine-alpha, required for rice cell proliferation.

We previously characterized an OsPSK cDNA encoding a precursor of phytosulfokine-alpha (PSK-alpha), a peptide plant growth factor. Southern blot analysis suggested that OsPSK is a single-copy gene in rice, which we have isolated and characterized. The OsPSK gene consists of one large intron and two exons. The 5-amino acid PSK-alpha sequence located close to the COOH-terminus of the precursor is encoded in the second exon. A putative TATA box was found at position -68 with respect to the transcription initiation site. Upstream of this sequence, several potential regulatory elements, including one CAAT-box, three CCAAT-boxes, one enhancer core-like sequence, and three E-boxes could be identified. By constructing plasmids with various lengths of the 5'-upstream regions of the OsPSK gene fused to the coding sequence for bacterial beta-glucuronidase (GUS), we demonstrated a region 1.9 kb upstream of the transcription initiation point, which contains most of the putative 5'-regulatory elements, to be sufficient for maximal-level GUS expression in transformed rice Oc cells. The promoter of the OsPSK gene gave significantly higher levels of GUS expression than the CaMV 35S promoter. These results suggest that the OsPSK promoter could be useful for the constitutive expression of a foreign gene at high levels in transformed rice culture cells. Northern blot analyses suggest that the expression of OsPSK is reinforced by auxin and cytokinin.

Amino Acid Sequence↗
PubMed2000

Correction for range restriction: an expanded typology.

A common research problem is the estimation of the population correlation between x and y from an observed correlation rxy obtained from a sample that has been restricted because of some sample selection process. Methods of correcting sample correlations for range restriction in a limited set of conditions are well-known. An expanded classification scheme for range-restriction scenarios is developed that conceptualizes range-restriction scenarios from various combinations of the following facets: (a) the variable(s) on which selection occurs (x, y and/or a 3rd variable z), (b) whether unrestricted variances for the relevant variables are known, and (c) whether a 3rd variable, if involved, is measured or unmeasured. On the basis of these facets, the authors describe potential solutions for 11 different range-restriction scenarios and summarize research to date on these techniques.

Humans↗
PubMed2000

MJ0109 is an enzyme that is both an inositol monophosphatase and the 'missing' archaeal fructose-1,6-bisphosphatase.

In sequenced genomes, protein coding regions with unassigned function constitute between 10 and 50% of all open reading frames. Often key enzymes cannot be identified using sequence homology searches. For example, despite the fact that methanogens have an apparently functional gluconeogenesis pathway, standard tools have been unable to identify a fructose-1,6-bisphosphatase (FBPase) gene in the sequenced Methanoccocus jannaschii genome. Using a combination of functional and structural tools, we have shown that the protein product of the M. jannaschii gene MJ0109, which had been tentatively annotated as an inositol monophosphatase (IMPase), has both IMPase and FBPase activities. Moreover, several gene products annotated as IMPases from different thermophilic organisms also possess FBPase activity. Thus, we have found the FBPase that was 'missing' in thermophiles and shown that it also functions as an IMPase.

Amino Acid Sequence↗
PubMed2000

Characterization of the porcine gammadelta T-cell receptor structure and cellular distribution by monoclonal antibody PPT27.

The T-cell receptor (TCR) is the critical structure involved in antigen recognition of T lymphocytes. Although the pig has a large proportion of circulating T lymphocytes bearing the gammadelta TCR, their study has been impeded due to the lack of specific antibodies. Here a monoclonal antibody (mAb) PPT27 directed to gammadelta TCR is described. Flow cytometry analyses showed that the mAb recognized a subset of T lymphocytes of which the majority expressed no CD2, CD4 and CD8 whilst the minority bore CD2 and CD8. The mAb precipitated a protein of 86 000 MW under non-reducing conditions and a doublet of 43 000 MW under reducing conditions from peripheral blood T lymphocytes lysed in nonidet P-40 buffer, whilst it precipitated the CD3-TCR complex from the cells lysed in digitonin. Further analysis revealed that the antibody recognized the majority, but not all, of the gammadelta T cells, suggesting that there may be more isotypes of gammadelta TCR than currently believed. The antibody was unable to stimulate gammadelta T cells to proliferate in vitro, suggesting that these cells are activated by a different activation mechanism from that of alphabeta T cells.

Animals↗
PubMed2000

Child rotavirus infection in association with acute gastroenteritis in two Chinese sentinel hospitals.

Rotavirus gastroenteritis is an important pediatric disease in China. In a survey of rotavirus infection at two sentinel hospitals in China (Beijing Friendship Hospital and Changchun Children's Hospital), 296 cases were detected. A total of 283 (95.6%) cases of rotavirus infection occurred in children under 5 years of age. Serotype G1 (62%) was most prevalent followed by G2 (28.5%), G3 (5%) and G4 (2%). Mixed infections (n = 8, 3%) were rate, and 16 isolates (5.5%) remained non-typeable. A consistent epidemic occurred during the winter. Rotavirus was responsible for about 61.8% of diarrhea-related hospitalizations in children under 5 years of age, with a mean hospital stay of 5.6 days (1.0-21 days). The estimated rate of rotavirus-attributed hospitalizations was 16/1000 children under 5 years of age per year. Rotavirus-related death is rare in Changchun and Beijing. The present findings suggest that a rotavirus vaccine for the prevention of severe disease and a reduction of treatment costs would be of significant benefit to China.

Child, Preschool↗
PubMed2000

Hydrolyzable tannins and related polyphenols from Eucalyptus globulus.

Eucaglobulin (1), a new complex of gallotannin and monoterpene, was isolated from the leaves of Eucaloptus globulus. Its structure was elucidated on the basis of spectral data. Four known hydrolyzable tannins [tellimagrandin I (2), eucalbanin C (3), 2-O-digalloyl-1,3,4-tri-O-galloyl-beta-D-glucose (4), 6-O-digalloyl-1,2,3-tri-O-galloyl-beta-D-glucose (5)], as well as gallic acid (6) and (+)-catechin (7), were also isolated. The antibacterial effects of some of these compounds were examined.

Anti-Bacterial Agents↗
PubMed2000

ROC surface: a generalization of ROC curve analysis.

Receiver operating characteristic (ROC) curve analysis is widely used in biomedical research to assess the performance of diagnostic tests. Much of the work has been directed at developing accurate indices to describe ROC curves and appropriate statistics to test differences between them. The analysis, however, is largely built on the assumption that the test results are dichotomous. We generalize the ROC curve analysis to allow for tests to have more than two outcomes. The generalized ROC curve constitutes a surface. We propose to use the volume under the surface to measure the accuracy of a diagnostic test.

Algorithms↗