Biomedical subjects

Y C Li

Publications and source records attributed to Y C Li.

At least 73 records · Page 4Linked to original sources

PubMed1999

The individual and combined effects of feeding moniliformin, supplied by Fusarium fujikuroi culture material, and deoxynivalenol in young turkey poults.

The effects of feeding diets containing either 20 mg deoxynivalenol (DON)/kg, 100 mg moniliformin (M)/kg, or a combination of DON and M (20 mg/kg DON and 100 mg M/kg) were evaluated in growing turkey poults, from 1 to 21 d of age. Feed intake and BW gains were decreased (P < 0.05) by dietary treatments containing M. Feed conversion was not affected by any of the dietary treatments, and no interactive effects on performance were evident between M and DON. Absolute weights of hearts and kidneys were increased (P < 0.05) in poults fed diets containing M. Mean cell volume was decreased by the M and DON-M treatments; however, the decrease was much smaller in poults fed the combination DON-M treatment resulting in a significant (P < 0.05) DON by M interaction. Mean cell hemoglobin and mean cell hemoglobin concentrations were not affected by any of the dietary treatments. No histological lesions were seen in control poults or poults fed DON alone. Lesions associated with dietary treatments were only observed in the heart and kidney. Poults fed diets containing M alone or the DON-M combination exhibited an increased incidence of variable sized cardiomyocyte nuclei, with numerous large giant nuclei, and a generalized loss of cardiomyocyte cross striations. Isolated renal tubules in sections of kidney were noted to have mild diffuse mineralization in poults fed M and the combination DON-M treatments. None of the response variables measured were affected by DON alone. No toxic synergy was observed when these toxins were fed simultaneously to turkey poults for 21 d.

Animal Feed↗

PubMed1999

Effects of fumonisin B1 on selected immune responses in broiler chicks.

Three experiments were conducted to evaluate immune responses in chicks fed fumonisin B1 (FB1). Day-old male chicks were randomly allotted to dietary treatments: 0, 50, 100, or 200 mg FB1/kg diet. In Experiment 1, chicks were fed diets for 3 wk and were injected intravenously with 4.6x10(6) Escherichia coli on Day 21. Blood samples were collected at 60, 120, and 180 min postinjection, and liver, spleen, and lung were collected after 180 min. Chicks fed 200 mg FB1/kg diet had significantly higher numbers of bacterial colonies in blood, spleen, and liver (P<0.05) than control chicks. In Experiment 2, chicks were placed on the diets for 4 wk and were injected with 0.5 mL inactivated Newcastle Disease virus vaccine on Weeks 2 and 3 of the experiment, and primary and secondary antibody titers were measured 7 d after each injection. The secondary antibody response in chicks fed 200 mg FB1/kg diet was significantly lower (P<0.05) than that of control chicks. In Experiment 3, lymphocyte proliferation in chicks exposed to FB1 in vivo or in vitro was determined. Results of the in vivo study showed that cell proliferation in response to mitogens was lower (P<0.05) in chicks fed 200 mg FB1/kg diet than in control chicks. For the in vitro study, cell proliferation was lower (P<0.05) when cells were exposed to > or = 2.5 microg FB1/mL. Data of the current study suggested that FB1 is immunosuppressive in chicks when present in the ration at 200 mg FB1/kg diet.

Animals↗

PubMed1999

The physiological response of thrombopoietin (c-Mpl ligand) to thrombocytopenia in the rat.

It has been suggested that circulating levels of thrombopoietin (TPO) are determined primarily by platelet and megakaryocyte clearance of TPO and not by changes in hepatic TPO production. The experimental evidence accumulated so far to support this hypothesis is incomplete. We have therefore developed a new model of non-immune thrombocytopenia in the rat and used it to assess the relationship of TPO (c-mpl ligand) to the platelet mass. 14 d following the administration of busulphan, the platelet count reached a nadir of <2% of its initial value and remained at this level for up to 6 d. Circulating TPO was measured by two different bioassays which were sensitive enough to measure normal levels of TPO and levels rose from 106 +/- 29 pg/ml in animals with a normal platelet count to 2015 +/- 544 pg/ml in those with thrombocytopenia. These elevated levels of TPO were solely a response to the low platelet count since transfusion of a normal mass of platelets into the thrombocytopenic animals returned the TPO levels exactly to normal. The increase in TPO levels in thrombocytopenic animals was not due to increased TPO production since the thrombocytopenic animals did not show any increase in TPO mRNA in total or polysome-associated hepatic RNA. Rather, rat platelets were able to bind and stoichiometrically remove TPO from thrombocytopenic plasma via high-affinity receptors (Kd = 38 +/- 10 pm; 233 +/- 32 receptors/platelet). These results serve as a proof that the circulating level of TPO is determined not by alterations in TPO transcription or translation but by the ability of the platelet mass to bind and remove TPO from the circulation.

Animals↗

PubMed1998

Mapping the subsite preferences of protein tyrosine phosphatase PTP-1B using combinatorial chemistry approaches.

Protein tyrosine phosphatases (PTPases) are important regulators of signal transduction systems, but the specificity of their action is largely unexplored. We have approached this problem by attempting to map the subsite preferences of these enzymes using combinatorial chemistry approaches. Protein-tyrosine peptidomimetics containing nonhydrolyzable phosphotyrosine analogues bind to PTPases with high affinity and act as competitive inhibitors of phosphatase activity. Human PTP-1B, a PTPase implicated to play an important role in the regulation of growth factor signal transduction pathways, was used to screen a synthetic combinatorial library containing malonyltyrosine as a phosphotyrosine mimic. Using two cross-validating combinatorial chemistry screening approaches, one using an iterative method and the other employing library affinity selection-mass spectrometric detection, peptides with high affinity for PTP-1B were identified and subsite preferences were detailed by quantitatively comparing residues of different character. Consistent with previous observations, acidic residues were preferred in subsites X-3 and X-2. In contrast, aromatic substitutions were clearly preferred at the X-1 subsite. This information supports the concept that this class of enzymes may have high substrate specificity as dictated by the sequence proximal to the phosphorylation site. The results are discussed with regards to the use of combinatorial techniques in order to elucidate the interplay between enzyme subsites.

Computer Simulation↗

PubMed1998

Solution structure of the catalytic domain of human stromelysin-1 complexed to a potent, nonpeptidic inhibitor.

The full three-dimensional structure of the catalytic domain of human stromelysin-1 (SCD) complexed to a novel and potent, nonpeptidic inhibitor has been determined by nuclear magnetic resonance spectroscopy (NMR). To accurately mimic assay conditions, the structure was obtained in Tris buffer at pH 6.8 and without the presence of organic solvent. The results showed that the major site of enzyme-inhibitor interaction occurs in the S1' pocket whereas portions of the inhibitor that occupy the shallow S2' and S1 pockets remained primarily solvent exposed. Because this relatively small inhibitor could not deeply penetrate stromelysin's long narrow hydrophobic S1' pocket, the enzyme was found to adopt a dramatic fold in the loop region spanning residues 221-231, allowing occupation of the solvent-accessible S1' channel by the enzyme itself. This remarkable conformational fold at the enzyme binding site resulted in constriction of the S1' loop region about the inhibitor. Examination of the tertiary structure of the stromelysin-inhibitor complex revealed few hydrogen-bonding or hydrophobic interactions between the inhibitor and enzyme that can contribute to overall binding energy; hence the resultant compact structure may in part account for the relatively high potency exhibited by this inhibitor.

Amino Acid Sequence↗

PubMed1998

Persistence of an alternate chromatin structure at silenced loci in the absence of silencers.

In Saccharomyces cerevisiae, genes placed near telomeres or the silent HML and HMR mating-type loci are transcriptionally repressed by a heterochromatin-like structure. We have generated nonreplicating DNA rings by recombination in vivo to examine the role of chromosomal context on transcriptional repression. Specifically, recombination at HMR was used to produce rings that lacked the E and I silencers. An altered level of DNA supercoiling was observed in these rings but not in comparable rings from derepressed loci. Our results indicate that a repressive chromatin structure persists in an extrachromosomal environment immediately following removal of the cis-acting control elements. Examination of both chromatin footprints and DNA sequence dependence revealed that changes in nucleosome number could account for the topology shifts. Upon continued cell growth, the differences in supercoiling were lost and transcriptional competence was restored. These results show that silencers are required for sustained persistence of repressive chromatin structure, even in the absence of DNA replication.

Chromatin↗

PubMed1998

Protein N-arginine methylation in adenosine dialdehyde-treated lymphoblastoid cells.

Protein arginine methyltransferase was recently identified to be associated with some proteins in signal transduction pathways. N-Arginine methylation in RNA binding proteins with arginine- and glycine-rich RGG motifs is known to be the major protein methylation in cells. Considering that arginine methylation might be involved in certain human disorders, we used human lymphoblastoid cells that can be easily prepared from lymphocytes as a model system to study the methylation. Lymphoblastoid cells grown in the presence of 20 microM indirect methyltransferase inhibitor adenosine dialdehyde (AdOx) for 72 h appeared to accumulate high levels of hypomethylated proteins for the endogenous protein methyltransferase or recombinant glutathion S-transferase-fused yeast arginine methyltransferase (RMT1). Analysis of methyl-accepting polypeptides in AdOx-treated lymphoblastoid cells by SDS-PAGE and fluorography showed that many polypeptides between 29,000 and 90,000 Da were methylated by the endogenous methyltransferase. A few polypeptides could be methylated to a higher extent upon the addition of yeast GST-RMT1 fusion protein. A peptide (GGRGRGGGF) could compete for the majority of the methyl-accepting protein substrates in the AdOx-treated lymphoblastoid cell extracts, whether or not exogenous yeast RMT1 was included in the reaction. When the arginine residues in the peptide were replaced by lysine, no competition was observed. The results indicated that the protein methyl acceptors in lymphoblastoid cells share similar RGG motifs and that arginine residues should be the site of methylation.

Adenosine↗

PubMed1998

Five new diterpenoids from the wood of Cunninghamia konishii.

Five new diterpenes, 3beta-acetoxyabieta-8,11,13-trien-12-ol (1), 8alpha-hydroxy-13(16),14-labdadien-19-al (2), 16-hydroxy-19-oxomanoyl oxide (3), 15-nor-14-oxo-8(17), 12-labdadiene-18-ol (4), and 15,16-bisnor-13-oxo-8(17), 11-labdadien-18-ol (5), were isolated from the wood of Cunninghamia konishii. Their structures were elucidated by 2D NMR spectroscopy and by chemical methods.

Carbohydrate Sequence↗

PubMed1998

Engineering subtilisin YaB: restriction of substrate specificity by the substitution of Gly124 and Gly151 with Ala.

The 3-D structure of subtilisin YaB was computer modelled using the structures of subtilisin BPN', subtilisin Carlsberg and thermitase as templates. Gly124 and Gly151 located on both sides of the waist of the S1 pocket were selected for site-directed mutagenesis based on the modelled structure. The mutated ale genes coding for the mutant subtilisin YaB were expressed in Bacillus subtilis DB104. All of the G124 and G151 series of mutants exhibited an increase of relative catalytic activity for elastin-orcein against casein and myofibrillar proteins. The S1 substrate specificity of G124A, G124V and G151A mutants were assessed using various carbobenzoxy-amino acid-nitrophenyl esters and succinyl-Ala-Ala-(Pro or Val)-(Ala, Phe or Leu)-p-nitroanilide [AA(P/V) (A/F/L)]. While G124A and G124V mutants hydrolyzed only Ala and Gly esters, G151A mutant hydrolyzed Ala, Leu and Gly esters. The G124A and G124V mutants did not hydrolyze AAPF and AAPL. However, these two mutants hydrolyzed AAPA and AAVA with kcat/Km values approximately 3-10-fold higher than those of the wild-type enzyme. The G151A mutant did not hydrolyze AAPF, but hydrolyzed AAPL, AAPA and AAVA with kcat/Km values approximately 1-4-fold higher than those of the wild-type enzyme. These results clearly indicate that the S1 substrate specificity of G124A and G124V mutants was restricted to Ala and Gly, and G151A mutant to Ala, Gly and Leu.

Alanine↗

PubMed1998

Normalization of mineral ion homeostasis by dietary means prevents hyperparathyroidism, rickets, and osteomalacia, but not alopecia in vitamin D receptor-ablated mice.

1,25-Dihydroxyvitamin D3 plays a major role in intestinal calcium transport. To determine what phenotypic abnormalities observed in vitamin D receptor (VDR)-ablated mice are secondary to impaired intestinal calcium absorption rather than receptor deficiency, mineral ion levels were normalized by dietary means. VDR-ablated mice and control littermates were fed a diet that has been shown to prevent secondary hyperparathyroidism in vitamin D-deficient rats. This diet normalized growth and random serum ionized calcium levels in the VDR-ablated mice. The correction of ionized calcium levels prevented the development of parathyroid hyperplasia and the increases in PTH messenger RNA synthesis and in serum PTH levels. VDR-ablated animals fed this diet did not develop rickets or osteomalacia. However, alopecia was still observed in the VDR-ablated mice with normal mineral ions, suggesting that the VDR is required for normal hair growth. This study demonstrates that normalization of mineral ion homeostasis can prevent the development of hyperparathyroidism, osteomalacia, and rickets in the absence of the genomic actions of 1,25-dihydroxyvitamin D3.

Alopecia↗

PubMed1998

Analysis of vitamin D-dependent calcium-binding protein messenger ribonucleic acid expression in mice lacking the vitamin D receptor.

To investigate the roles of the receptor-dependent actions of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] in the regulation of vitamin D-dependent calcium-binding proteins (calbindin-D), the messenger RNA (mRNA) levels of calbindin-D9k and -28k were examined in vitamin D receptor (VDR)-ablated mice and control littermates. In VDR-ablated mice, calbindin-D9k mRNA was dramatically reduced in the intestine, kidneys, lungs, and brain; however, calbindin-D28k mRNA was only moderately decreased in the kidney. After 1,25-(OH)2D3 injection, calbindin-D9k mRNA levels and renal and alveolar calbindin-D28k mRNA levels were induced in control animals, but not in the homozygous mice. When the mice were fed a diet high in lactose, calcium, and phosphorus, intestinal calbindin-D9k mRNA levels in the homozygous mice were restored to those in their control littermates. However, this diet failed to normalize extraintestinal calbindin mRNA levels. These findings demonstrate that the receptor-dependent actions of 1,25-(OH)2D3 regulate calbindin-D9k gene expression and that tissue-specific factors modulate the effects of 1,25-(OH)2D3 on calbindin-D28k gene expression. These data also demonstrate that in the absence of a functional VDR, a high local concentration of calcium, phosphorus, and/or lactose in the intestinal lumen can normalize intestinal calbindin-D9k mRNA levels.

Animals↗

PubMed1998

Trunk muscle use during pulling tasks: effects of a lifting belt and footing conditions.

Pulling tasks require the torso to act as a rigid link in order to facilitate the force transmission between the ground and the hands. In this study, we tested the hypothesis that a lifting belt increases the rigidity of the torso, thereby increasing pulling strength or reducing trunk muscle forces, or both, as pulling tasks are performed. Twelve volunteers performed maximal and submaximal isometric pulling exertions; the latter were performed on nonslippery and slippery surfaces. Electromyographic data from 8 trunk muscles, trunk kinematic data, and ground reaction forces were sampled during each exertion. Results indicated that the lifting belt had no effect during maximal exertions on the maximal pull forces generated or the muscle recruitment levels, irrespective of the pulling posture. The lifting belt did not affect the EMG data obtained during the submaximal (40% of maximum) exertions, even when participants pulled on a slippery surface. However, the slippery surface increased the coactivation within the trunk musculature, perhaps stiffening the torso in the event of a slip. The absence of a statistical interaction effect between the lifting belt and the footing condition (slipperiness) indicates that the belt did not alter the coactivation pattern and hence was not relied upon by the participants as a protective mechanism. The data presented here will assist those who must make decisions regarding lifting-belt use and those who train individuals in manual materials handling techniques.

Adult↗

PubMed1997

Targeted ablation of the vitamin D receptor: an animal model of vitamin D-dependent rickets type II with alopecia.

Vitamin D, the major steroid hormone that controls mineral ion homeostasis, exerts its actions through the vitamin D receptor (VDR). The VDR is expressed in many tissues, including several tissues not thought to play a role in mineral metabolism. Studies in kindreds with VDR mutations (vitamin D-dependent rickets type II, VDDR II) have demonstrated hypocalcemia, hyperparathyroidism, rickets, and osteomalacia. Alopecia, which is not a feature of vitamin D deficiency, is seen in some kindreds. We have generated a mouse model of VDDR II by targeted ablation of the second zinc finger of the VDR DNA-binding domain. Despite known expression of the VDR in fetal life, homozygous mice are phenotypically normal at birth and demonstrate normal survival at least until 6 months. They become hypocalcemic at 21 days of age, at which time their parathyroid hormone (PTH) levels begin to rise. Hyperparathyroidism is accompanied by an increase in the size of the parathyroid gland as well as an increase in PTH mRNA levels. Rickets and osteomalacia are seen by day 35; however, as early as day 15, there is an expansion in the zone of hypertrophic chondrocytes in the growth plate. In contrast to animals made vitamin D deficient by dietary means, and like some patients with VDDR II, these mice develop progressive alopecia from the age of 4 weeks.

Alopecia↗

PubMed1997

Novel point mutation within intron 10 of FMR-1 gene causing fragile X syndrome.

The majority of cases involving fragile X syndrome are due to expansion of a (CGG)n trinucleotide repeat at the 5' untranslated region of the FMR-1 gene. Deletion and intragenic loss of function mutations of the FMR-1 gene also have been reported. Here, we report a C to T point mutation at the 14th nucleotide in intron 10 of the FMR-1 gene in three unrelated fragile X patients. However, the (CGG)n repeat of FMR-1 in those patients does not expand. To determine the effect of this mutation on the patients' FMR-1 transcripts, total RNA from peripheral blood cells was reverse transcribed and amplified by polymerase chain reaction (RT-PCR). Direct and subcloned sequencing of the RT-PCR products revealed that the transcripts from the allele with C to T mutation skip exon 10 entirely, resulting in a joining of exons 9 and 11. Deletion of exon 10 results in frame-shift and premature termination of translation, which removes the highly conserved region that encoding the KH2 and RGG box domains of FMRP. Interestingly, a male of the three patients has another G to A substitution in exon 15. However, the intron 10 mutation is sufficient for development of fragile X syndrome.

Adolescent↗

PubMed1997

Steroid hormone receptors activate transcription in glial cells of intact retina but not in primary cultures of retinal glial cells.

We have compared the steroid responsiveness of Müller glial cells of intact embryonic chicken retina with that of primary cultures derived from Müller glia. Appropriately constructed fusion genes were found to be highly glucocorticoid inducible after their cotransfection with an expression vector encoding the human glucocorticoid receptor (GR) into intact embryonic d-10 (E10) or E5.5 retina. Dramatically attenuated inductions were obtained after contransfection of Müller cell primary cultures. The progesterone receptor (PR) was also demonstrated to function in intact retina, but not in Müller cell primary cultures. An immunochemical assay was utilized to confirm that a glucocorticoid-responsive, beta-galactosidase-encoding fusion gene was specifically induced in Müller cells after its transfection into intact retina. Thus, in contrast to Müller cells in intact retina, Müller cells in primary culture have lost the capacity to achieve transcriptional activation by steroid receptors. We postulate that coordinate expression of the GR, and other more general factors required for steroid inducibility, is lost by dispersion and primary culture of retinal Müller glial cells.

Animals↗

PubMed1997

Influence of alkaline buffers on cytoplasmic pH in myocardial cells exposed to hypoxia.

The fluorescent intracellular probe 2',7'-bis-(carboxyethyl)-5,6-carboxyfluorescein acetoxymethyl ester was used in this experimental study to investigate the effects of different alkaline buffers on cytoplasmic pH in suspended myocardial cells under normal as well as hypoxic conditions. A dose-dependent intracellular acidification was achieved after addition of sodium bicarbonate or Tris buffer mixture (Tribonat) to the myocardial cells under normal conditions. After this immediate decrease in cytoplasmic pH, a tendency for the pH to rise again was recorded during the observation period, but this elevation of pH occurred to variable degrees with the different agents and dosages. Addition of larger volumes of Tribonat caused the cytoplasmic pH to return to the initial value during the observation time. Addition of Ringer's acetate produced a significant and persistent cytoplasmic acidification. Larger volumes of Carbicarb as well as pure trometamol (Tris) caused a lasting intracellular alkalinization. Hypoxia per se caused a marked intracellular acidosis in the cardiomyocytes. During hypoxia, addition of sodium bicarbonate caused a further decrease of cytoplasmic pH, turning into an increase during the observation period. Also, Tribonat caused an immediate further acidification, but 15 min after the addition the intracellular pH-value had reached the normal level of normoxic cells. Addition of Ringer's acetate caused a further significant and lasting decrease of intracellular pH. The effect of Carbicarb was a persistent alkalinization of the cell interior. Trometamol produced the most pronounced rise of cytoplasmic pH. In conclusion, this in vitro study shows that Tris buffer mixture (Tribonat) possesses important qualities for correction of metabolic acidosis due to hypoxia and may perhaps be preferred over other alkaline buffers in some situations.

Animals↗

PubMed1997

Bioactive conformation of a potent stromelysin inhibitor determined by X-nucleus filtered and multidimensional NMR spectroscopy.

The biologically active conformation of a novel, very potent, nonpeptidic stromelysin inhibitor was determined by X-nucleus filtered and multidimensional NMR spectroscopy. This bound conformer was subsequently docked into the stromelysin catalytic domain (SCD) using intermolecular distance constraints derived from NOE data. The complex showed the S1' pocket of stromelysin to be the major site of enzyme-inhibitor interaction with other portions of the inhibitor spanning the S2' and S1 binding sites. Theoretical predictions of SCD-inhibitor binding from molecular modeling studies were consistent with the NMR data. Comparison of modeled enzyme-inhibitor complexes for stromelysin and collagenase revealed an alternate binding mode for the inhibitor in collagenase, suggesting a similar binding interaction might also be possible for stromelysin. The NMR results, however, revealed a single SCD-inhibitor binding mode and provided a structural template for the design of more potent stromelysin inhibitors.

Binding Sites↗

PubMed1997

Traumatic brain injury registry in Taiwan.

This project was designed to examine the epidemiology of traumatic brain injury (TBI) in Taiwan. A total of 58,563 cases of TBI was collected from 114 hospitals in Taiwan during the period July 1, 1988-June 30, 1994. Traffic accident was the major cause of TBI (69.4%), followed by falls and assaults. Motorcyclists accounted for the vast majority of TBI cases among traffic accident victims (64.5%). The Glasgow Coma Scale was used in assessing the severity. 41,646 cases (79.5%) were considered mild, 4,637 cases (8.9%) moderate, and 6,078 cases (11.6%) severe. Skull x-ray showed fracture in 7,663 cases (14.6%). Intracranial hemorrhage was identified in 28.6% of patients receiving CT scanning. Craniotomy was performed in 5,226 cases (9%). The outcome of TBI was determined by the Glasgow Outcome Scale. Death occurred in 2,621 cases (5.4%), vegetative state in 429 cases (0.9%), severe disability in 1,293 cases (2.6%), moderate disability in 1,890 cases (3.9%), and good recovery in 42,596 cases (87.2%). The severity and outcome were worse than those of Western reports. In order to alleviate this problem, a helmet use persuasion program was conducted by the Police Department in Taipei City from January to June, 1994. Results of this program showed a significant reduction of TBI-related hospitalization, severity and fatality during this period of intervention. This study points out the seriousness of TBI in Taiwan and suggests some approaches and priorities for prevention.

Accidents, Traffic↗