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Biomedical subjects

C Tian

Publications and source records attributed to C Tian.

At least 19 recordsLinked to original sources
PubMed2006

Persistence of antigen is required to maintain transplantation tolerance induced by genetic modification of bone marrow stem cells.

Genetic modification of hematopoietic stem cells (HSCs) resulting in a state of molecular chimerism can be used to induce donor-specific tolerance to allografts. However, the requirements for maintaining tolerance in molecular chimeras remain unknown. Here, we examined whether long-term expression of a retrovirally encoded alloantigen in hematopoietic cells is required to maintain donor-specific tolerance in molecular chimeras. To this end, mice were reconstituted with syngeneic bone marrow transduced with retroviruses carrying the gene encoding the allogeneic MHC class I molecule Kb. Following induction of molecular chimerism, mice were depleted of cells expressing Kb by administration of the anti-Kb monoclonal antibody Y-3. Mice that were effectively depleted of cells expressing the retrovirally encoded MHC class I antigen rejected Kb disparate skin allografts. In contrast, control molecular chimeras accepted Kb disparate skin allografts indefinitely. These data suggest maintenance of tolerance in molecular chimeras requires long-term expression of retrovirally transduced alloantigen on the progeny of retrovirally transduced HSCs.

Animals↗
PubMed2006

Inhibition of CD26 peptidase activity significantly improves engraftment of retrovirally transduced hematopoietic progenitors.

It has previously been shown that inhibition of CD26 (DPPIV/dipeptidylpeptidase IV) peptidase activity improves homing of hematopoietic stem cells (HSCs) to the bone marrow and increases engraftment efficiency. Here, we demonstrate that treatment of retrovirally transduced mouse bone marrow cells with the tri-peptide Diprotin A (Ile-Pro-Ile), a specific inhibitor of CD26, significantly enhances engraftment of retrovirally transduced HSCs. Treatment of transduced bone marrow cells with Diprotin A permitted long-term expression of a retrovirally encoded MHC class I gene on multiple hematopoietic cell lineages after transplantation of a suboptimal number of transduced cells. Secondary transfer experiments revealed that expression of the transduced MHC class I gene resulted from engraftment of transduced HSCs. Expression of the allogeneic MHC class I antigen on bone marrow-derived cells following transplantation of Diprotin A-treated cells was sufficient to induce transplantation tolerance. Therefore, inhibition of CD26 activity significantly enhances engraftment of limited numbers of genetically modified HSCs, resulting in physiologically relevant levels of gene transfer.

Animals↗
PubMed2005

Quantitative analysis of PPARdelta mRNA by real-time RT-PCR in 86 rectal cancer tissues.

AIM: The purpose of this study is to clarify the expression change of PPARdelta gene in human colorectal cancer tissues. METHODS: Applying real-time RT-PCR, we quantified PPARdelta mRNA in a series of 86 tissues from excised primary rectal cancers. In each case, accompanying normal mucosa was collected for comparison. RESULTS: Among the 86 rectal cancer tissues, 48 cases showed PPARdelta overexpression: 39 tumours gave an expression level 1.5-5 times, five tumours 10-20 times, and four tumours more than 20 times relative to normal mucosa. However, the general level of PPARdelta mRNA in rectal cancer tissues is not statistically different from normal mucosa. CONCLUSIONS: The expression of PPARdelta gene in rectal cancers is not statistically different from normal mucosa.

Biomarkers, Tumor↗
PubMed2005

Deterministic weak localization in periodic structures.

In some perfect periodic structures classical motion exhibits deterministic diffusion. For such systems we present the weak localization theory. As a manifestation for the velocity autocorrelation function a universal power law decay is predicted to appear at four Ehrenfest times. This deterministic weak localization is robust against weak quenched disorders, which may be confirmed by coherent backscattering measurements of periodic photonic crystals.

Journal Article↗
PubMed2004

Weak dynamical localization in periodically kicked cold atomic gases.

Quantum kicked rotor was recently realized in experiments with cold atomic gases and standing optical waves. As predicted, it exhibits dynamical localization in the momentum space. Here we consider the weak-localization regime concentrating on the Ehrenfest time scale. The latter accounts for the spread time of a minimal wave packet and is proportional to the logarithm of the Planck constant. We show that the onset of the dynamical localization is essentially delayed by four Ehrenfest times, and give quantitative predictions suitable for an experimental verification.

Journal Article↗
PubMed2001

Role of phosphatidylinositide 3-kinase in brain-derived neurotrophic factor-induced DARPP-32 expression in medium size spiny neurons in vitro.

Brain-derived neurotrophic factor (BDNF) regulates several properties of striatal dopaminoceptive medium-sized spiny neurons (MSNs) in vivo and in vitro, including expression levels of DARPP-32 (dopamine and cyclic adenosine 3',5'-monophosphate-regulated phosphoprotein, 32 kDa). DARPP-32 is expressed in 96% of the MSNs, and is a key modulator of dopamine actions. We investigated the intracellular signal transduction pathways activated by BDNF in MSNs and via which BDNF induces DARPP-32 expression. We found that phosphorylation of the cyclic AMP response element binding protein (CREB) is only transiently increased following stimulation of MSNs by BDNF, whereas increased phosphorylation of the extracellular signal regulated kinases 1 and 2 (Erk1/2) and Akt is sustained for longer than 4 h. Treatment of cultures with inhibitors of mitogen-activated protein kinase kinase (MEK) or phosphatidylinositide 3-kinase (PI3K) showed that the majority of the BDNF-induced increase in DARPP-32 requires the PI3K pathway. We also found that inhibition of PI3K reduces BDNF-induced Erk phosphorylation, indicating that cross-talk between these pathways may play a prominent role in MSNs.

Animals↗
PubMed2001

Chelation of hypocrellin B with zinc ions with electron paramagnetic resonance (EPR) evidence of the photodynamic activity of the resulting chelate.

Hypocrellin B (HB), a perylenequinone derivative, is an efficient phototherapeutic agent. The chelation of HB with Zinc ions (Zn2+) results in a metal chelate (Zn-HB) which exhibits considerable absorption (lambda max = 612 nm) in the phototherapeutic window. The structure of this chelate has been characterized by UV-Vis, IR and mass spectra. The redox potentials of the Zn-HB chelate were Eox = +1.1 V (vs. SCE) and Ere = -0.7 V (vs. SCE) as measured using the circle volt curve. The quantum yield of singlet oxygen generated by the Zn-HB chelate was 0.86, which both the electron spin trap (EPR) method and the chemical trap method show to be about 0.1 higher than that of its parent compound HB. In irradiated oxygen-saturated solutions of Zn-HB chelate, superoxide radical anions and hydroxyl radicals were detected by EPR spectroscopy using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trapping agent.

Chelating Agents↗
PubMed2001

Photobleaching of hypocrellin B and its butylamino-substituted derivative in solutions.

The photobleaching of hypocrellin B (HB) and its derivative butylamino-substituted hypocrellin B (BAHB), both of which are potent sensitizers for photodynamic therapy (PDT), were investigated by studies of absorption spectra and quenching experiments and by the determination of photoproducts. Control experiments indicated that the sensitizer, oxygen and light were essential for the photobleaching of HB and BAHB, which suggested that it was a photodynamic process, e.g. the photobleaching processes of both HB and BAHB were mainly self-sensitized photooxidations. The illumination of HB with visible light in oxygenated nonpolar solvents generated singlet oxygen efficiently [phi(1O2) = 0.76] which in turn attacked the sensitizer HB with the subsequent formation of an endoperoxide product. The endoperoxide of HB is unstable at room temperature and undergoes loss of singlet oxygen with regeneration of the parent HB. The singlet oxygen released from the endoperoxide of HB was detected with chemical trapping experiments. The quenching experiments indicated that in increasingly polar solvents the superoxide anion mechanism (type I) as well as the singlet oxygen mechanism (type II) contributed to the photobleaching of HB. The introduction of the electron-donating butylamino group not only enhanced the yield of the superoxide anion generation but also altered the position of attack in the BAHB molecule by the activated oxygen species. No endoperoxide product was observed, and no singlet oxygen released from the photobleaching process of BAHB was detected. The photobleaching process of BAHB was more complex. Both the singlet oxygen and superoxide anion mechanism played important roles in the photobleaching of BAHB in all organic solvent used here, even in aerobic nonpolar solvents such as CHCl3.

Electron Transport↗
PubMed2000

Simian-human immunodeficiency virus-associated nephropathy in macaques.

A number of chimeric simian-human immunodeficiency virus (SHIV) viruses containing tat, rev, vpu, and env from HIV-1 (strain HXBc2) in a genetic background of simian immunodeficiency virus (SIV(mac)239) have been derived from the parental nonpathogenic SHIV-4 virus. In this article we examine the renal pathology associated with the derivation of these pathogenic SHIV strains. The first of the pathogenic SHIVs, SHIV(KU-1), is associated with rapid CD4(+) T cell loss and opportunistic infections associated with AIDS, but only one of four infected pigtail macaques examined has developed significant renal pathology. The renal pathology in this macaque consists of a diffuse increase in matrix in the core of each lobule with collapsed glomerular capillries, which is similar to the renal changes reported in HIVAN. Passage of this virus into rhesus macaques yielded SHIV(KU-2), which results in renal pathology in three of four inoculated rhesus macaques in which <10% of the glomeruli are involved. A molecular clone of SHIV(KU-2) was derived (SHIV(KU-2MC4)) that causes neurologic and renal pathology with more than 60% of the glomeruli involved and results in uremic level BUN concentrations. These results indicate that SHIV(KU-2MC4) causes severe significant glomerular pathology and should permit a detailed analysis of the molecular determinants associated with the development of SHIV-associated glomerulosclerosis in rhesus macaques.

AIDS-Associated Nephropathy↗
PubMed2000

Imaging membrane protein helical wheels.

Resonance patterns have been observed in 2D solid-state NMR spectra of the transmembrane segment of M2 protein from Influenza A virus in oriented samples reflecting the helical wheel of this alpha-helix. The center of this pattern uniquely defines the helical tilt with respect to the bilayer normal without a need for resonance assignments. The distribution of resonances from amino acid specific labels around the "PISA wheel" defines the rotational orientation of the helix and yields preliminary site-specific assignments. With assignments high-resolution structural detail, such as differences in tilt and rotational orientation along the helical axis leading to an assessment of helical coiling, can be obtained.

Influenza A virus↗
PubMed2000

Enhancement of primary and secondary cellular immune responses against human immunodeficiency virus type 1 gag by using DNA expression vectors that target Gag antigen to the secretory pathway.

In this study, we have investigated the influence of antigen targeting after DNA vaccination upon the induction of cellular immune responses against human immunodeficiency virus type 1 (HIV-1) Gag. In addition to the standard version of HIV-1 Gag, we constructed Gag expression vectors that encode a secreted (Sc-Gag) and a cytoplasmic (Cy-Gag) Gag molecule. Although all three HIV-1 Gag expression vectors induced detectable humoral and cellular immune responses, after intramuscular injection the DNA vector encoding the Sc-Gag generated the highest primary cytotoxic T-lymphocyte (CTL) and T-helper responses. Mice immunized with one of the HIV-1 Gag DNA vectors (but not with the control vector pcDNA3. 1) developed a protective immune response against infection with recombinant vaccinia virus expressing HIV-1 Gag, and this response persisted for 125 days. The magnitude of the protection correlated with the levels of Gag-specific ex vivo CTL activity and the number of CD8(+) T cells producing gamma interferon. The DNA vector encoding the Sc-Gag induced higher levels of protection and greater secondary CTL responses than did the DNA vector encoding Cy-Gag.

AIDS Vaccines↗
PubMed2000

[Mycorrhizal research on nitrogen-fixing plants].

Advances in mycorrhizal research on nitrogen-fixing plants were introduced. The universality of mycorrhizal formation in nitrogen fixing plants, the reciprocal promotion effect of symbiosis, and the application prospect of mycorrhizal techniques under stressed conditions were summarized and reviewed. The mechanism of enhancing nitrogen fixation of N-fixing plants by mycorrhizal fungi in symbiosis was preliminary discussed.

Fungi↗
PubMed2000

[Determination of cinnamaldehyde in Guizhi by HPLC].

OBJECTIVE: To establish a HPLC method for the determination of cinnamaldehyde in Guizhi. METHOD: Cinnamaldehyde was separated by a Kromasil C18 column (4.6 mm x 200 mm) with a mobile phase of acetonitrile-0.1% phosphoric acid solution(48:52) and an UV detection wavelength of 285 nm. RESULT: The calibration curve was linear in the range of 0.004-0.02 microliter.ml-1, with a correlation coefficient of 0.9996. The average recovery was 100.7%(n = 5), and RSD 0.3%(n = 6). CONCLUSION: The method is simple and accurate.

Acrolein↗
PubMed1999

Derivation and biological characterization of a molecular clone of SHIV(KU-2) that causes AIDS, neurological disease, and renal disease in rhesus macaques.

Previously, we described the derivation of a pathogenic strain of simian-human immunodeficiency virus (SHIV(KU-2)) consisting of the tat, rev, vpu, and env genes of HIV-1 (strain HXB2) in a genetic background of SIV(mac)239 that causes AIDS and productive infection of the CNS in rhesus macaques (Macca mulatta) (Raghavan et al., 1997, Brain Pathol. 7, 851-861). We report here on the characterization of a molecular clone of SHIV(KU-2), designated SHIV(KU-2MC4), that caused CD4(+) T cell loss as well as neurological and renal disease in macaques. DNA sequence analysis of selected SIV regions of SHIV(KU-2MC4) revealed 10 nucleotide changes in the LTR, whereas Gag, Vif, Vpr, Vpx, and Nef had 1, 1, 1, 2, and 13 predicted amino acid substitutions, respectively, compared to SIV(mac)239. DNA sequence analysis of HIV-1 derived regions of SHIV(KU-2MC4) revealed 2, 1, 2, and 18 predicted amino acid substitutions in the Tat, Rev, Vpu, and Env proteins, respectively, when compared to SHIV-4. Unlike the parental SHIV-4, which is not tropic for macrophages, SHIV(KU-2MC4) replicated efficiently in macrophage cultures as determined by p27 assays. However, despite the numerous changes in the Env protein and newly acquired tropism for macrophages, SHIV(KU-2MC4), like the parental SHIV-4, used CXCR4 exclusively as its coreceptor for entry into susceptible cells. Inoculation of SHIV(KU-2MC4) into two rhesus macaques resulted in severe infection in which the numbers of circulating CD4(+) T cells in the blood declined rapidly by 2 weeks postinoculation and virus producing cells in the peripheral blood mononuclear cells were identified throughout the course of infection. At the time of euthanasia (20 and 22 weeks), both macaques had lost a significant amount of weight and had no circulating CD4(+) T cells. In addition, one macaque developed intension tremors and uncoordinated movements. Virological examination of tissues at necropsy revealed active virus replication in both lymphoid and nonlymphoid tissues such as the lung and brain. Histological examination revealed that the induced immunodeficiency was associated with lymphoid depletion of the lymph nodes and spleen, opportunistic infections, lentiviral encephalitis, and severe glomerulosclerosis of the kidney. This molecular clone will serve as the basis for analyzing the molecular determinants through which SHIV(KU-2) causes severe CD4(+) T cell loss, neurological disease, and SHIV nephropathy in rhesus macaques.

AIDS Dementia Complex↗
PubMed1999

Modulating dipoles for structure-function correlations in the gramicidin A channel.

Dipoles of the tryptophan indole side chains have a direct impact on ion conductance in the gramicidin channel. Here, fluorination of the indoles (both 5- and 6-fluoro) is used to manipulate both the orientations and the magnitudes of the dipoles. The orientations and positions with respect to the channel axis were determined using (2)H solid state NMR of uniformly aligned lipid bilayer preparations. By exchange of the remaining four protons in the indole ring for deuterium, comparison could be made to d(5)-indole spectra that have previously been recorded for each of the four indoles of gramicidin A. After making the assignments which were aided by the observation of (19)F-(2)H dipolar interactions, we found that fluorination caused only minor changes in side chain conformation. With the high-resolution structural characterization of the fluorinated indoles in position 11, 13, and 15, the electrostatic interactions with a cation at the channel and bilayer center can be predicted and the influence of the modified dipoles on ion conductance estimated. The importance of the long-range electrostatic interaction was recently documented with the observation of alpha-helical dipoles oriented toward the bilayer center on the ion conductance pathway for the Streptomyces K(+) channel. We present direct measurements of the orientation of gramicidin channel F-Trp positions for use in analysis of dipole effects on channel permeation.

Bacillus↗
PubMed1999

Developmental expression of urine concentration-associated genes and their altered expression in murine infantile-type polycystic kidney disease.

Currently, there is little understanding of what factors regulate the development of urine concentrating capability in normal or polycystic kidney. The present study examined the developmental expression of genes associated with urine concentration in developing mice, including C57BL/6J-cpk/cpk mice with autosomal recessive-infantile (AR) polycystic kidney disease (PKD). Concentration of urine requires: 1) medullary collecting ducts (CD) located within a hypertonic interstitium, 2) CD cell expression of functional arginine vasopressin V2 receptors (AVP-V2R), and 3) the presence of appropriate CD water channels (aquaporins, AQP 2 and 3). An increase in urine osmolarity, normally seen between 1 and 3 weeks of age, was absent in cpk cystic mice. Aldose reductase mRNA expression (a gene upregulated by medullary hyperosmolarity) increased in normal mice, but remained low in the cystic kidney, suggesting the absence of a hypertonic medullary interstitium. AVP-V2R, AQP2, and AQP3 mRNA expression normally increase between 7 and 14 days. However, all were dramatically overexpressed even at 7 days of age in the cpk kidney in vivo, but decreased in vitro. Activation of the AVP-V2 receptor stimulates the production of cAMP, a substance known to promote cyst enlargement. To determine if CD cAMP, generated from increased AVP-V2Rs, was accelerating the PKD, cystic mice and their normal littermates were treated with OPC31260, a relatively specific AVP-V2R antagonist. OPC31260 treatment of cystic mice led to an amelioration of the cystic enlargement and azotemia. Treatment also decreased renal AQP2 mRNA but increased AVP-V2R and AQP3 mRNA expression in vivo. AVP upregulates the expression of AVP-V2R, AQP2, and AQP3 mRNAs in vitro. Renal EGF, known to inhibit AVP-V2R activity, downregulates AVP-V2R mRNA in vitro. Brief in vivo EGF treatment, known to decrease PKD in cpk mice, led to increased expression of AVP-V2R, AQP2, and AQP3 mRNAs at 2 weeks in both normal and cystic mice but no change was evident at 3 weeks of age. In conclusion, the development of urinary concentration ability correlates with the development of an increased medullary osmotic gradient which is diminished in murine ARPKD. However, CD genes associated with this process are overexpressed in vivo but underexpressed in vitro in the cystic kidney. The overexpression and/or overactivity of the AVP-V2R appears to contribute to the progression of PKD since an AVP-V2R antagonist inhibits cystic renal enlargement in the cpk mouse.

Aldehyde Reductase↗
PubMed1999

Time correlation of momentum in a collisionless plasma due to large fluctuations.

The present paper shows that in one-dimensional collisionless plasma, due to large fluctuation, the time correlation of momentum asymptotically behaves inverse quadratically with time. The long-time tail correlation is closely related to nonlinear Landau damping [M.B. Isichenko, Phys. Rev. Lett. 78, 2369 (1997)]. Furthermore, it reveals the possible relationship between fluctuation and dispersion. The result indicates that the long-time tail correlation can also occur in a reversibly dispersive system, where the previous theories are invalid. A by-product proves that it may be efficient to investigate the dispersive features of collisionless plasma in view of time correlation.

Journal Article↗