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Biomedical subjects

J Sun

Publications and source records attributed to J Sun.

At least 235 records · Page 13Linked to original sources
PubMed2000

Negatively charged residues in the H loop of PsaB subunit in Photosystem I from Synechocystis sp. PCC 6803 appear to be responsible for electrostatic repulsions with plastocyanin*.

Wild-type plastocyanin from the cyanobacterium Synechocystis sp. PCC 6803 does not form any kinetically detectable transient complex with Photosystem I (PS I) during electron transfer, but the D44R/D47R double mutant of copper protein does [De la Cerda et al. (1997) Biochemistry 36: 10125-10130]. To identify the PS I component that is involved in the complex formation with the D44R/D47R plastocyanin, the kinetic efficiency of several PS I mutants, including a PsaF-PsaJ-less PS I and deletion mutants in the lumenal H and J loops of PsaB, were analyzed by laser flash absorption spectroscopy. The experimental data herein suggest that some of the negative charges at the H loop of PsaB are involved in electrostatic repulsions with mutant plastocyanin. Mutations in the J loop demonstrate that this region of PsaB is also critical. The interaction site of PS I is thus not as defined as first expected but much broader, thereby revealing how complex the evolution of intermolecular electron transfer mechanisms in photosynthesis has been.

Journal Article↗
PubMed2000

Nonparametric tests for stratum effects in the Cox model.

This paper considers the stratified proportional hazards model with a focus on the assessment of stratum effects. The assessment of such effects is often of interest, for example, in clinical trials. In this case, two relevant tests are the test of stratum interaction with covariates and the test of stratum interaction with baseline hazard functions. For the test of stratum interaction with covariates, one can use the partial likelihood method (Kalbfleisch and Prentice, 1980; Lin, 1994). For the test of stratum interaction with baseline hazard functions, however, there seems to be no formal test available. We consider this problem and propose a class of nonparametric tests. The asymptotic distributions of the tests are derived using the martingale theory. The proposed tests can also be used for survival comparisons which need to be adjusted for covariate effects. The method is illustrated with data from a lung cancer clinical trial.

Humans↗
PubMed2000

Two-phase liquid culture system models normal human adult erythropoiesis at the molecular level.

We have studied the patterns of expression of various genes during maturation of normal human adult erythroid precursors cultured in a two-phase liquid culture method. In the first phase, peripheral blood mononuclear cells are cultured for one week in the presence of a combination of growth factors, but not erythropoietin (Epo). In Phase II, Epo is included in the medium. Cell samples were taken throughout phase II, and expression of globins, transcription factors, and cytokine receptors was assayed by RT-PCR and quantified by phosphor imaging. We have divided phase II into stages: early (days 0-5), intermediate (days 6-10) and late (days 11-15) and measured maximum expression of each gene. During early phase II, gamma-globin, Spl, and GATA-2 mRNAs were expressed at their highest levels. As the cells matured during the intermediate period, GATA-2 levels remained high, and then declined, while the transcription factors GATA-1, EKLF, NF-E2, and the Epo receptor (EpoR) reached maximum expression. In late phase II, beta-globin increased and reached its maximum level of expression. This erythroid culture system appears to recapitulate normal adult erythropoiesis at the molecular level, and thus may be a suitable model to examine the molecular basis of severe congenital or acquired disorders of erythropoiesis.

Adult↗
PubMed2000

Design of GFB-111, a platelet-derived growth factor binding molecule with antiangiogenic and anticancer activity against human tumors in mice.

We have designed a molecule, GFB-111, that binds to platelet-derived growth factor (PDGF), prevents it from binding to its receptor tyrosine kinase, and blocks PDGF-induced receptor autophosphorylation, activation of Erk1 and Erk2 kinases, and DNA synthesis. GFB-111 is highly potent (IC50 = 250 nM) and selective for PDGF over EGF, IGF-1, aFGF, bFGF, and HRGbeta (IC50 values > 100 microM), but inhibits VEGF-induced Flk-1 tyrosine phosphorylation and Erk1/Erk2 activation with an IC50 of 10 microM. GFB-111 treatment of nude mice bearing human tumors resulted in significant inhibition of tumor growth and angiogenesis. The results demonstrate the feasibility of designing novel growth factor-binding molecules with potent anticancer and antiangiogenic activity.

Angiogenesis Inhibitors↗
PubMed2000

Antibody repertoire development in fetal and newborn piglets, III. Colonization of the gastrointestinal tract selectively diversifies the preimmune repertoire in mucosal lymphoid tissues.

Changes in the VH-region repertoire of isolator piglets reared for 6 weeks under germ-free (GF) conditions and those colonized (COL) with a defined exclusion flora on the 1st day of life were compared. Although serum immunoglobulin levels were 20-100-fold higher in COL piglets than GF piglets, an analysis of peripheral blood B cells (PBBs) indicated that: GF and COL piglets used the same four VH genes and two DH segments during the 6-week period; proportional usage of VH genes and DH segments was the same as in fetal animals; and VH and DH usage did not differ between COL and GF animals. This pattern differed from the PBBs from 6-week-old conventional (CONV) piglets. When the sequences of 73 splenic CDR3 segments were analysed, DH usage and mutation frequency were the same in sequences from both 6-week-old GF and COL piglets; mutations were infrequent and occurred with the same frequency as in 110-day fetal spleen. However, the median CDR3 length in COL piglets was shifted upward due to 3' DH N-nucleotide additions. Neither COL nor GF animals made specific serum antibodies to phosphoryl choline given parenterally on a T-cell dependent carrier. In contrast to the near absence of a colonization effect in PBBs and splenic DNA, rearranged variable heavy-chain gene segments (VDJs) recovered from the DNA of mucosal lymphoid tissues of COL piglets showed pronounced differences from those recovered from GF animals in usage of DHA-, DHB-and VHB- and in the frequency of point mutation. The mucosal VDJ transcripts and those from the spleen were similarly affected by colonization. This effect on mucosal lymphoid tissue was consistent with the five-fold selective increase in serum immunoglobulin A (IgA) levels relative to IgM and IgG. Comparison of IgM and IgA transcripts from mucosal tissues suggested that IgA and IgM clones diversify in parallel. Our findings are the first to show that colonization of the gastrointestinal tract of offspring separated from their mothers, differs from 'conventionalized' GF animals in that colonization preferentially influences diversification and expansion of the preimmune IgM and IgA repertoire in mucosal lymphoid tissues but not in PBBs and seldom/modestly in VDJs from splenic DNA.

ATP-Binding Cassette Transporters↗
PubMed2000

A biodialysis system for liver support tested in a porcine hepatic failure model.

BACKGROUND: A practical liver support system for patients in fulminant hepatic failure (FHF) remains a needed therapeutic modality. A new method of bioartificial liver support, the liver biodialysis system (LBDS), is described. METHODS: Porcine hepatocytes, removed from direct contact with the treated subject's circulation, are in culture in a bioreactor which is combined in a dialysis circuit for patient treatment. The LBDS was tested in a porcine ischaemic hepatic failure model. RESULTS: The viable hepatocyte content of the bioreactor was 2.49 +/- 0.72 x 10(10). Cells remained viable in culture throughout the experiments (30 +/- 3 h) without evidence of immunological damage. A decrease in the degree of accumulation in the blood of ammonia (P < 0.02) and of 14 amino acids (P < 0.001) was achieved by the LBDS. Cerebral perfusion pressure was maintained at significantly higher levels in LBDS-treated animals (P < 0.05). CONCLUSIONS: In the LBDS, hepatocytes in large numbers and satisfactory culture conditions in a bioreactor have sustained viability and function. When combined in a dialysis circuit for the treatment of FHF pigs, immune reactions between the blood and hepatocytes were prevented and beneficial metabolic effects were observed.

Amino Acids↗
PubMed2000

Effects of retrograde cardioplegia on myocardial perfusion and energy metabolism in immature porcine myocardium.

OBJECTIVES: Retrograde cardioplegia has been widely used for the protection of adult hearts during cardiac operations. Its efficacy to protect immature myocardium is still unclear. This study was designed to assess the effects of retrograde cardioplegia on myocardial perfusion and energy metabolism in immature hearts. METHODS: Piglet hearts were divided into 3 groups. Hearts in group 1 were used to assess myocardial perfusion of retrograde cardioplegia by means of magnetic resonance imaging. Hearts in groups 2 and 3 were used to assess the effects of retrograde cardioplegia on myocardial energy metabolism by use of phosphorus 31 magnetic resonance spectroscopy. RESULTS: Magnetic resonance images showed that perfusion with retrograde cardioplegic solution was heterogeneous. A perfusion defect was noted during retrograde cardioplegia in the right ventricular wall and in a portion of the posterior wall of the left ventricle in 4 of 6 hearts. Phosphorus 31 spectra showed that at the end of 45-minute retrograde cardioplegia, myocardial intracellular pH was 6.83 +/- 0.17 and phosphocreatine was 53.5% +/- 27% of its prearrest value. The adenosine triphosphate level, however, remained normal throughout the retrograde cardioplegia period. Last, the hearts subjected to retrograde cardioplegia or antegrade cardioplegia showed similar and complete metabolic and functional recovery during reperfusion. CONCLUSIONS: Retrograde cardioplegia provides heterogeneous perfusion. Its ability to protect the right ventricular myocardium is poor and varies between individuals. Myocardial perfusion provided by retrograde cardioplegia is slightly less than that needed to sustain normal myocardial energy metabolism under normothermic conditions.

Animals↗
PubMed2000

The effects of retrograde cardioplegia technique on myocardial perfusion and energy metabolism: a magnetic resonance imaging and localized phosphorus 31 spectroscopy study in isolated pig hearts.

OBJECTIVE: The present work was designed to study the myocardial perfusion and energy metabolism during retrograde cardioplegia performed with different methods, including deep coronary sinus cardioplegia, coronary sinus orifice cardioplegia, and right atrial cardioplegia. METHODS: Isolated pig hearts were subjected to antegrade cardioplegia, right atrial cardioplegia, deep coronary sinus cardioplegia, and coronary sinus orifice cardioplegia in a random order. Cardioplegic distribution was assessed by T1-weighted magnetic resonance imaging in 1 group of hearts (n = 8). The flow dynamics of cardioplegia were assessed by T2*-weighted imaging in a second group of hearts (n = 8). RESULTS: T1-weighted images revealed an apparent perfusion defect in the posterior wall of the left ventricle, the posterior portion of the interventricular septum, and the right ventricular free wall during deep coronary sinus cardioplegia. The perfusion defect observed in the first 2 regions with deep coronary sinus cardioplegia resolved with coronary sinus orifice cardioplegia. Right atrial cardioplegia provided the most homogeneous perfusion to all regions of the myocardium relative to the other 2 retrograde cardioplegia modalities. T2*-weighted images showed that the 3 retrograde cardioplegia modalities provided similar cardioplegic flow velocities. Localized phosphorus 31 spectroscopy showed that the levels of adenosine triphosphate and phosphocreatine were significantly lower in the posterior wall (adenosine triphosphate, 42.86% +/- 5.91% of its initial value; phosphocreatine, 11.43% +/- 11.3%) than the anterior wall (adenosine triphosphate, 89.19% +/- 8.83%; phosphocreatine, 59.54% +/- 12.58%) of the left ventricle during 70 minutes of normothermic deep coronary sinus cardioplegia. CONCLUSIONS: Deep coronary sinus cardioplegia results in myocardial ischemia in the posterior wall of the left ventricle and the posterior portion of the interventricular septum, as well as in the right ventricular free wall. Coronary sinus orifice cardioplegia improves cardioplegic distribution in these regions. Relative to deep coronary sinus cardioplegia and coronary sinus orifice cardioplegia, right atrial cardioplegia provides the most homogeneous perfusion.

Adenosine Triphosphate↗
PubMed2000

A hemisphere array for non-invasive ultrasound brain therapy and surgery.

Ultrasound phased arrays may offer a method for non-invasive deep brain surgery through the skull. In this study a hemispherical phased array system is developed to test the feasibility of trans-skull surgery. The hemispherical shape is incorporated to maximize the penetration area on the skull surface, thus minimizing unwanted heating. Simulations of a 15 cm radius hemisphere divided into 11, 64, 228 and 512 elements are presented. It is determined that 64 elements are sufficient for correcting scattering and reflection caused by trans-skull propagation. An optimal operating frequency near 0.7 MHz is chosen for the array from numerical and experimental thermal gain measurements comparing the power between the transducer focus and the skull surface. A 0.665 MHz air-backed PZT array is constructed and evaluated. The array is used to focus ultrasound through an ex vivo human skull and the resulting fields are measured before and after phase correction of the transducer elements. Finally, to demonstrate the feasibility of trans-skull therapy, thermally induced lesions are produced through a human skull in fresh tissue placed at the ultrasound focus inside the skull.

Algorithms↗
PubMed2000

The ntrB and ntrC genes are involved in the regulation of poly-3-hydroxybutyrate biosynthesis by ammonia in Azospirillum brasilense Sp7.

Azospirillum brasilense Sp7 and its ntrA (rpoN), ntrBC, and ntrC mutants have been evaluated for their capabilities of poly-3-hydroxybutyrate (PHB) accumulation in media with high and low ammonia concentrations. It was observed that the ntrBC and ntrC mutants can produce PHB in both low- and high-C/N-ratio media, while no significant PHB production was observed for the wild type or the ntrA mutant in low-C/N-ratio media. Further investigation by fermentation analysis indicated that the ntrBC and ntrC mutants were able to grow and accumulate PHB simultaneously in the presence of a high concentration of ammonia in the medium, while little PHB was produced in the wild type and ntrA (rpoN) mutant during active growth phase. These results provide the first genetic evidence that the ntrB and ntrC genes are involved in the regulation of PHB synthesis by ammonia in A. brasilense Sp7.

Ammonia↗
PubMed2000

Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone.

A synthetic analogue (AOD9604) of the lipolytic domain of human growth hormone (hGH) has been studied for its metabolic actions in obese Zucker rats. Daily treatment with an oral dose of AOD9604 of 500 microg/kg body weight for 19 days reduced over 50% (15.8 +/- 0.6 vs. 35.6 +/- 0.8 g) body weight gain of the animals in comparison with the control. The adipose tissues of the AOD9604--treated animals were found to have an increase in lipolytic activity. In contrast to chronic treatment with intact hGH, chronic treatment with AOD9604 showed no adverse effect on insulin sensitivity of the animals, as demonstrated with euglycemic clamp techniques. The results in the present study suggest that the analogue of the hGH lipolytic domain may have the potential to be developed into an orally usable and safe therapeutic agent for obesity.

Adipose Tissue↗
PubMed2000

Severe bronchiectasis in patients with "cystlike" structures within the ciliary shafts.

Cilia are minute hairlike structures which sweep the respiratory tract clean by continuous beating. Ciliary dysfunction can occur which leads to development of bronchiectasis. We describe the clinical and investigation profiles of four patients who had early-onset severe and otherwise idiopathic bronchiectasis associated with a previously undescribed ciliary defect in which numerous cystlike structures are present within the ciliary shafts. The patients had otherwise normal ciliary microtubular ultrastructure and central microtubular orientation. Our newly described ciliary abnormality appears to be a primary defect and more systematic studies should be performed to evaluate this further.

Adult↗
PubMed2000

Conformational changes and coactivator recruitment by novel ligands for estrogen receptor-alpha and estrogen receptor-beta: correlations with biological character and distinct differences among SRC coactivator family members.

Ligands for the estrogen receptor (ER) that have the capacity to selectively bind to or activate the ER subtypes ERalpha or ERbeta would be useful in elucidating the biology of these two receptors and might assist in the development of estrogen pharmaceuticals with improved tissue selectivity. In this study, we examine three compounds of novel structure that act as ER subtype-selective ligands. These are a propyl pyrazole triol (PPT), which is a potent agonist on ERalpha but is inactive on ERbeta, and a pair of substituted tetrahydrochrysenes (THC), one enantiomer of which (S,S-THC) is an agonist on both ERalpha and ERbeta, the other (R,R-THC) being an agonist on ERalpha but an antagonist on ERbeta. To investigate the molecular mechanisms underlying the ER subtype-selective actions of these compounds, we have determined the conformational changes induced in ERalpha and ERbeta by these ligands using protease digestion sensitivity, and we have tested the ability of these ligands to promote the recruitment of representatives of the three SRC/p160 coactivator protein family members (SRC-1, GRIP-1, ACTR, respectively) to ERalpha and ERbeta using yeast two-hybrid and glutathione-S-transferase (GST) pull-down assays. We find that the ligand-ER protease digestion pattern is distinctly different for stimulatory and inhibitory ligands, and that this assay, as well as coactivator recruitment, are excellent indicators of their agonist/antagonist character. Interestingly however, compared with estradiol, the novel agonist ligands show some quantitative differences in their ability to recruit SRC-1, -2, and -3. This implies that while generally similar to estradiol, these ligands induce ER conformations that differ somewhat from that induced by estradiol, differences that are illustrative of the nature of their biological character. The application of methods to characterize the conformations induced in ER subtypes by novel ligands, as done in this study, enables a greater understanding of how ligand-receptor conformations relate to estrogen agonist or antagonist behavior.

Acetyltransferases↗
PubMed2000

Angiotensin II induces nuclear factor (NF)-kappaB1 isoforms to bind the angiotensinogen gene acute-phase response element: a stimulus-specific pathway for NF-kappaB activation.

The vasopressor angiotensin II (AII) activates transcriptional expression of its precursor, angiotensinogen. This biological "positive feedback loop" occurs through an angiotensin receptor-coupled pathway that activates a multihormone-responsive enhancer of the angiotensinogen promoter, termed the acute-phase response element (APRE). Previously, we showed that the APRE is a cytokine [tumor necrosis factor-alpha (TNFalpha)]- inducible enhancer by binding the heterodimeric nuclear factor-kappaB (NF-kappaB) complex Rel A x NF-kappaB1. Here, we compare the mechanism for NF-kappaB activation by the AII agonist, Sar1 AII, with TNFalpha in HepG2 hepatocytes. Although Sar1 AII and TNFalpha both rapidly activate APRE-driven transcription within 3 h of treatment, the pattern of inducible NF-kappaB binding activity in electrophoretic mobility shift assay is distinct. In contrast to the TNFalpha mechanism, which strongly induces Rel A x NF-kappaB1 binding, Sar1 AII selectively activates a heterogenous pattern of NF-kappaB1 binding. Using a two-step microaffinity DNA binding assay, we observe that Sar1 AII recruits 50-, 56-, and 96-kDa NF-kappaB1 isoforms to bind the APRE. Binding of all three NF-kappaB1 isoforms occurs independently of changes in their nuclear abundance or proteolysis of cytoplasmic IkappaB inhibitors. Phorbol ester-sensitive protein kinase C (PKC) isoforms are required because PKC down-regulation completely blocks AII-inducible transcription and inducible NF-kappaB1 binding. We conclude that AII stimulates the NF-kappaB transcription factor pathway by activating latent DNA-binding activity of NF-kappaB subunits through a phorbol ester-sensitive (PKC-dependent) mechanism.

Angiotensin II↗
PubMed2000

Contributions of the extracellular and cytoplasmic domains of platelet-endothelial cell adhesion molecule-1 (PECAM-1/CD31) in regulating cell-cell localization.

PECAM-1/CD31, a vascular cell adhesion/signaling molecule that has been implicated in a number of vascular functions (including angiogenesis and the transmigration of leukocytes through endothelium) is highly enriched at the cell-cell borders of adjacent endothelial cells. To identify the mechanisms responsible for this localization, a series of PECAM-1 mutants and chimeric PECAM-1 molecules were transfected into non-PECAM-expressing cells and the ability of the constructs to move to cell-cell borders of adjacent cells was determined using immunohistochemistry and confocal microscopy. Although neither the extracellular domain, by itself, nor the cytoplasmic domain, by itself, was sufficient to direct cell-cell localization, the combination of the extracellular and transmembrane domains with a small group of highly charged amino acids in a membrane proximal region of the cytoplasmic domain was sufficient to direct efficient localization of the molecule to cell-cell borders. Importantly, only constructs that supported PECAM-1 mediated adhesion localized to cell-cell borders. Our data are consistent with a 'diffusion trapping' model in which movement of PECAM-1 in the cell membrane occurs relatively freely until the 'stablized' extracellular domain of the molecule encounters its ligand on an adjacent cell. When this occurs, the complex is 'captured' at the cell-cell interface leading to localization at cell-cell borders.

Cell Membrane↗
PubMed2000

Dose-dependent changes in the spectrum of mutations induced by ionizing radiation.

We examined the influence of dose on the spectrum of mutations induced at the hypoxanthine guanine phosphoribosyltransferase (Hprt) locus in Chinese hamster ovary (CHO) cells. Independent CHO-K1 cell mutants at the Hprt locus were isolated from cells exposed to 0, 0.5, 1.5, 3.0 and 6.0 Gy (137)Cs gamma rays, and the genetic changes responsible for the mutations were determined by multiplex polymerase chain reaction (PCR)-based exon deletion analysis. We observed dose-dependent changes in mutation spectra. At low doses, the principal radiation-induced mutations were point mutations. With increasing dose, multibase deletion mutations became the predominant mutation type such that by 6.0 Gy, there were almost three times more deletion mutations than point mutations. The dose response for induction of point mutations was linear while that for multibase deletions fit a linear-quadratic response. There was a biphasic distribution of deletion sizes, and different dose responses for small compared to large deletions. The frequency of large (>36 kb) total gene deletions increased exponentially, implying that they develop from the interaction between two independent events. In contrast, the dose response for deletion mutations of less than 10 kb was nearly linear, suggesting that these types of mutations develop mostly from single events and not the interactions between two independently produced lesions. The observation of dose-dependent changes in radiation-induced mutation spectra suggests that the types of alterations and therefore the risks from low-dose radiation exposure cannot be easily extrapolated from high-dose effects.

Animals↗