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L Tian

Publications and source records attributed to L Tian.

At least 91 records · Page 5Linked to original sources
PubMed1998

Glucocorticoid regulation of calcium-activated potassium channels mediated by serine/threonine protein phosphatase.

Adrenal glucocorticoids exert powerful effects on cellular excitability in neuroendocrine cells and neurons, although the underlying mechanisms are poorly understood. In metabolically intact mouse anterior pituitary corticotrope (AtT20) cells glucocorticoid-induced proteins render large conductance calcium-activated potassium (BK) channels insensitive to inhibition by protein kinase A (PKA). In this study we have addressed whether this action of glucocorticoids is mediated via protein phosphatase activity at the level of single BK channels. In isolated inside-out patches from control AtT20 cells BK channels (125 pS) were inhibited by activation of closely associated PKA. Pretreatment (2 h) of cells with 1 microM dexamethasone before patch excision did not modify the intrinsic properties or expression levels of BK channel alpha-subunits in AtT20 cells. However, PKA-mediated inhibition of BK channel activity in isolated patches from steroid-treated cells was severely blunted. This effect of steroid was not observed using adenosine 5'-O-(3-thiotriphosphate) as phosphate donor or on exposure of the intracellular face of the patch with 10 nM of the protein phosphatase inhibitors okadaic acid or calyculin A but was mimicked by application of protein phosphatase 2A (PP2A) to the intracellular face of patches from control cells. Glucocorticoids did not modify total PP2A activity in AtT20 cells, suggesting that modified PP2A-like phosphatase activity closely associated with BK channels is required for glucocorticoid action.

Animals↗
PubMed1998

Leukocyte integrins and inflammation.

Leukocyte adhesion is of pivotal functional importance. Without adequate adhesion, T lymphocytes and natural killer cells are not cytotoxic, B cells cannot develop into antibody secreting plasma cells, leukocytes do not home into inflamed tissues and myeloid cells are not able to phagocytize or exhibit chemotactic responses. During evolution several leukocyte adhesion molecules have developed belonging to a few molecular families. Among these, the leukocyte-specific integrins (beta 2 integrins, CD11/CD18 molecules) are among the most important. Much progress has taken place during the past few years, and at present we have a considerable knowledge of their structure and function. Inflammation is critically dependent on integrin activity, and its regulation forms the topic of this short review.

Amino Acid Sequence↗
PubMed1998

Alterations of antioxidant enzymes and oxidative damage to macromolecules in different organs of rats during aging.

Oxygen free radicals have been hypothesized to play an important role in the aging process. To investigate the correlation between the oxidative stress and aging, we have determined the levels of oxidative protein damage and lipid peroxidation in the brain and liver, and activities of antioxidant enzymes in the brain, liver, heart, kidney, and serum from the Fisher 344 rats at ages of 1, 6, 12, 18, and 24 months. The results showed that the level of oxidative protein damage (measured as carbonyl content) in the brain and liver was significantly higher in older animals than in young animals. No statistical difference was observed in the lipid peroxidation of the liver and brain between young and old animals. The activities of antioxidant enzymes in most tissues displayed an age-dependent decline. Superoxide dismutases in the heart, kidney, and serum, glutathione peroxidase activities in the serum and kidney, and catalase activities in the brain, liver, and kidney, significantly decreased during aging. Cytochrome c oxidase, an enzyme involved in electron transport in mitochondria, initially increased, but subsequently decreased in the aged brain, whereas no significant alteration was observed in the liver mitochondrial antioxidant enzymes. The present studies suggest that the accumulation of oxidized proteins during aging is most likely to be linked with an age-related decline of antioxidant enzyme activities, whereas lipid peroxidation is less sensitive to predict the aging process.

Aging↗
PubMed1998

Dissociation of early glucocorticoid inhibition of ACTH secretion and glucose uptake in mouse AtT20 D16:16 corticotrophs.

Adrenal glucocorticoid hormones rapidly exert powerful effects on neurons, immune and neuroendocrine cells through induction of de novo protein synthesis. In this study, we investigated, using mouse clonal anterior pituitary AtT20 D16:16 corticotrophs, whether (i) glucocorticoids rapidly inhibit glucose transport and (ii) whether this inhibition of glucose transport is directly correlated with early inhibition of ACTH secretion. Glucose uptake in AtT20 D16:16 cells was Na+-independent because the Na+-independent glucose transport inhibitor phloretin (100 microM) completely inhibited specific 14C-deoxygluose (DoG) uptake and replacement of extracellular Na+ with N-methyl D-glucamine+ had no effect. Furthermore, the Na+-independent glucose transporters, GLUTs 1 and 3 were expressed in AtT20 D16:16 cells. The synthetic type II glucocorticoid receptor agonist dexamethasone, rapidly, within 2 h, inhibited DoG uptake into AtT20 D16:16 cells through a mechanism that was dependent on de novo mRNA synthesis. Glucocorticoid inhibition of glucose transport was not correlated with early inhibition of ACTH secretion because removal of glucose from the external medium had no effect on CRF-stimulated ACTH secretion or the efficacy of early glucocorticoid inhibition of ACTH release. Although the Na+-independent glucose transport inhibitor phloretin significantly inhibited CRF-stimulated ACTH release, this effect of phloretin was a result of its potent activation of large conductance calcium-activated potassium (BK) channels. These data suggest that different molecular pathways and/or glucocorticoid induced proteins underlie the mechanism(s) of early glucocorticoid inhibition of glucose uptake and ACTH release, respectively.

Adrenocorticotropic Hormone↗
PubMed1998

Tamoxifen reduces endogenous and UV light-induced oxidative damage to DNA, lipid and protein in vitro and in vivo.

We have investigated the effect of tamoxifen (TAM) on endogenous or ultraviolet radiation (UVR)-induced oxidative damage to macromolecules in vitro and in vivo. In a system containing calf thymus DNA exposed to a germicidal UV lamp, both TAM and 4-hydroxytamoxifen (4-OH-TAM) inhibited UVR-induced the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in DNA in a dose-dependent manner. At low concentrations, 4-OH-TAM quenched 8-OHdG more potently than TAM. However, the reduction of 8-OHdG by TAM and 4-OH-TAM became similar at a concentration of 10 microM. In contrast, ascorbic acid had the similar effect to TAM, whereas glutathione exhibited little effect on UVR-induced 8-OHdG. The order of quenching efficacy was: 4-OH-TAM > TAM approximately = ascorbic acid > glutathione. We have further determined the effect of TAM on endogenous 8-OHdG formation, lipid peroxidation, and protein oxidation in the skin of SENCAR mice. Topical application of 5 micromol TAM significantly reduced the level of 8-OHdG in mouse epidermis by approximately 27% (P < 0.05). Endogenous lipid peroxidation and protein oxidation, measured as malondialdehyde (MDA) and carbonyl groups, were also substantially reduced by topical TAM. Further study was conducted to evaluate the effect of TAM on UVR-induced 8-OHdG and MDA in skin of hairless mice. In mice subacutely exposed to low dose (3.4 kJ/m2 x six doses) and high dose (16.8 kJ/m2 x three doses) of UVB irradiation, TAM significantly blocked the formation of 8-OHdG in mouse epidermis by 57-81% and MDA by 37-65%, respectively. Our studies suggest that reduction of oxidative damages to biological macromolecules in vitro and in vivo may at least in part explain the anti-carcinogenic and chemopreventive actions of tamoxifen.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1998

The effects of different envelope patterns and uncertainty for the detection of a tone added to SAM complex tonal maskers.

Thresholds for the detection of a tone added in-phase to the carrier of a fully modulated SAM tone were measured. In some conditions the signal was added to a single SAM tone, and in other conditions the signal was added to the sum of three or more SAM tones. Level equalization ensured that the addition of the tonal signal did not lead to increases in energy. When multiple SAM tone maskers were used, a small number of reproducible maskers were tested, each masker being composed of SAM tones with a variety of relative modulator phases. The maskers were either fixed across intervals and trials, roved across trials but fixed across intervals, or randomly chosen across both intervals and trials. The frequency separation between the signal-centered and off-frequency SAM tones was also varied. For small signal-centered/off-frequency SAM tone frequency separations, a separation ratio of 1.3, thresholds in the fixed condition depend on the relative modulator phases, and a simple mixture model reasonably predicted thresholds in the roving condition based on thresholds in the fixed condition for two of the three observers. For signal-centered/off-frequency SAM tone frequency separation factor of 1.68, effects of relative modulator phases were not obtained. Thresholds in the target-alone condition were generally superior to thresholds measured with the comodulated masker. Comodulated thresholds were better than target-alone thresholds only when level equalization was not used, and so the addition of the signal led to increases in level.

Acoustic Stimulation↗
PubMed1998

Induction of Mn SOD in human monocytes without inflammatory cytokine production by a mutant endotoxin.

Endotoxin selectively induces monocyte Mn superoxide dismutase (SOD) without affecting levels of Cu,Zn SOD, catalase, or glutathione peroxidase. However, little is known about the structure-activity relationship and the mechanism by which endotoxin induces Mn SOD. In this study we demonstrated that a mutant Escherichia coli endotoxin lacking myristoyl fatty acid at the 3' R-3-hydroxymyristate position of the lipid A moiety retained its full capacity to coagulate Limulus amoebocyte lysate compared with the wild-type E. coli endotoxin and markedly stimulated the activation of human monocyte nuclear factor-kappaB and the induction of Mn SOD mRNA and enzyme activity. However, in contrast to the wild-type endotoxin, it failed to induce significant production of tumor necrosis factor-alpha and macrophage inflammatory protein-1alpha by monocytes and did not induce the phosphorylation and nuclear translocation of mitogen-activated protein kinase. These results suggest that 1) lipid A myristoyl fatty acid, although it is important for the induction of inflammatory cytokine production by human monocytes, is not necessary for the induction of Mn SOD, 2) endotoxin-mediated induction of Mn SOD and inflammatory cytokines are regulated, at least in part, through different signal transduction pathways, and 3) failure of the mutant endotoxin to induce tumor necrosis factor-alpha production is, at least in part, due to its inability to activate mitogen-activated protein kinase.

Chemokine CCL4↗
PubMed1998

Two quantitative methods for imaging samples in molecular biology.

In this paper, we introduce two autoradiography imaging systems from Packard Instrument Company, that provide unmatched speed, accuracy, sensitivity, and resolving power for radioisotopic imaging in biomedical research. The first system is a direct nuclear imaging system, which provides fast and accurate nuclear counting without intermediate steps. Data are displayed in real time so that counting, imaging and data analysis can be done all at the same time. The second system is a new storage phosphor system that was designed with a unique optical assembly which provides high resolution imaging. With various types of phosphor screens, one can optimize the performance of this storage phosphor system with any radiolabel and any appropriate sample size. With these two systems, quantitative radioisotopic imaging becomes not only faster and easier, but also more consistent and accurate, providing researchers with a higher standard in molecular biology imaging.

Animals↗
PubMed1998

[Allograft of frozen nerve in repairing sensory nerve defect].

To observe the effect of allogenic transplantation of deep frozen nerve in repairing sensory nerve defect, 22 patients who had received this type of treatment were followed up for 0.5-5 years. There were 18 males and 4 females in this group, and the average age was 28 years old. Thirty-six nerve defects including the common volar digital nerve, proper volar digital nerve were repaired by allograft of nerves stored at deep frozen (-80 degrees C). The storation period was ranged from 9 days to 1 years. The length of the nerves were 2 cm-12 cm. After follow-up for 3 years (ranged from 7 months-5 years), 23 cases of nerve allograft obtained excellent and good results (63.9%), 10 cases were fair (27.7%) and 3 cases were poor (8.3%). It was concluded that (1) frozen nerve is one of nice materials for repairing the nerve defect (< 5 cm); (2) the immunity of allogenenic nerve is weak; (3) the deep frozen storation can reduce the immunity of nerve; (4) the dimethyl sulfoxide can prevent the nerve tissue from injury by deep frozen; (5) the best temperature and period for deep frozen storation should be studied further.

Adolescent↗
PubMed1998

[Comparison of roxithromycin bioavailability of a conventional and a dispersible tablet formulation].

Following oral administrations of a single dose of 150 mg roxithromycin dispersible tablet (formulation A, a new formulation for clinical trial) and conventional tablet (formulation B, purchased from the market) to each of 10 healthy male volunteers in a randomized crossover design, the plasma levels of active drug at different times were determined by a microbial assay with Micrococcus luteus CMCC (B) 28001 and the plasma concentration-time profiles were obtained. The Tmax values of formulation A and B obtained were 1.7 +/- 0.9 and 3.7 +/- 1.6 h, the Cmax values were 4.97 +/- 1.17 and 2.04 +/- 1.26 micrograms.ml-1 and the AUC0-->infinity values were 62.2 +/- 11.9 and 35.0 +/- 16.9 micrograms.h.ml-1, respectively. Surprisingly, the relative bioavailability of formulation B was found to be only 59.8% +/- 32.6% (P < 0.01). The low bioavailability of the latter formulation was attributed to poor release of roxithromycin in the gastric site, which was proposed as a key factor to influence drug absorption. Other related factors were also discussed.

Adult↗
PubMed1997

Induction of tolerance toward rat cardiac allografts by treatment with allochimeric class I MHC antigen and FTY720.

BACKGROUND: The combination of FTY 720, a novel immunosuppressant, and allochimeric class I MHC proteins bearing donor-type amino acid (aa) epitope substitutions for host-type sequences induces tolerance of Wistar Furth (WF; RT1.Au) heart allografts in ACI (RT1.Aa) recipients. METHODS: Allochimeric alpha(1h)l58-80-RT1.Aa proteins were produced by substituting the allogeneic nucleotide sequence encoding 10 aa residues unique to the alpha1 helical (alpha1h) region of RT1.Al Lewis (Asp58, Arg62, Glu63, Gln65, Lys66, Gly69, Asn70, Asn73, Ser77, and Asn80) for native RT1.Aa residues. The RT1.Au and the RT1.Al haplotypes share four of these aa (Arg62, Glu63, Gln65, and Gly69). A baculovirus/Spodoptera frugiperda insect cell system was used to express the alpha(1h)l58-80-RT1.Aa proteins. RESULTS: The addition of a 3-day oral gavage of 0.05 mg/kg/day FTY720 to a single portal vein injection of 10 microg alpha(1h)l58-80-RT1.Aa protein induced permanent acceptance of WF heart allografts in 16 of 26 ACI recipients (>100 days); the alpha(1h)l58-80-RT1.Aa protein alone only modestly prolonged WF heart survival (13.8+/-0.8 days). The same tolerogenic protocol did not prolong the survival of third-party Brown Norway (RT1.An) heart allografts (14.3+/-2.5 days) compared with FTY720 alone (14.0+/-2.3 days; NS). Tolerant ACI recipients bearing primary WF heart allografts for more than 100 days accepted second WF hearts, but promptly rejected third-party Brown Norway heart grafts (9.3+/-1.5 days). The tolerant state was transferred to irradiated ACI rats (400 rad) with either purified T cells (4-10 x 10[7]) or serum (1-2 ml) from tolerant hosts, and was not broken by daily intraperitoneal injections of interleukin-2 (1000 U/day; 7 days). CONCLUSIONS: The combination of allochimeric protein with FTY720 induces transplantation tolerance, a state that may be associated with the appearance of donor-specific regulatory factors.

Animals↗
PubMed1997

Increased transcription of the regulatory subunit of gamma-glutamylcysteine synthetase in rat lung epithelial L2 cells exposed to oxidative stress or glutathione depletion.

gamma-Glutamylcysteine synthetase (GCS) is the initial and rate-limiting enzyme in the glutathione (GSH) de novo synthesis pathway. GCS is composed of a heavy (73-kDa) catalytic subunit and a light (30-kDa) regulatory subunit, which maintains the Km for glutamate near physiologic concentrations. Previous studies have shown that the steady-state mRNA level and gene transcription for the catalytic subunit increased in response to the redox-cycling quinone 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) in rat lung epithelial L2 cells (M. M. Shi, et al., 1994, J. Biol. Chem. 269,26512-26517). The ratio of the catalytic to regulatory subunit mRNAs varies among tissues, and the anticancer drug cisplatin appears to induce only the catalytic subunit, suggesting independent gene regulation of the two subunits. Nonetheless, the present study found that the steady-state mRNA level and the transcription rate of the GCS regulatory subunit also increased under DMNQ-induced oxidative stress. Changes in mRNA followed a pattern similar to that for the catalytic subunit. The mRNA levels of the two subunits of GCS also both increased above the baseline levels in cells treated with BSO, an inhibitor of GCS enzymatic activity. These data suggest that, under conditions of oxidative stress or glutathione depletion, the regulatory subunit is upregulated at the level of mRNA transcription. Along with the elevation of the catalytic subunit, this increase in GCS regulatory subunit transcription contributes to increases in GCS enzymatic activity and cellular GSH content.

Animals↗
PubMed1997

The neuronal glycoprotein telencephalin is a cellular ligand for the CD11a/CD18 leukocyte integrin.

Many leukocyte functions depend on interactions between the leukocyte-specific beta2 integrins CD11/CD18 and their ligands, the intercellular adhesion molecules (ICAMs). Telencephalin (TLN) is a novel member of the Ig superfamily expressed in the central nervous system. The NH2-terminal five Ig-like domains of TLN show the highest homology with the Ig domains of ICAM-1, ICAM-2, ICAM-3, and LW (ICAM-4), the known cellular ligands for CD11a/CD18. Here, we demonstrate that TLN interacts with CD11a/CD18. Peripheral blood T cells, Jurkat T cells, and B lymphoblastoid cells bound to immunopurified recombinant human TLN proteins. This adhesion was through CD11a/CD18 and was significantly inhibited by an Ab to CD11a/CD18. Reciprocally, TLN-transfected L cells also bound to purified CD11a/CD18. Recombinant TLN proteins comprising either the first five Ig domains (TLN(1-5)) or the entire extracellular portion (TLN(1-9)) showed binding to CD11a/CD18. We conclude that TLN is a novel neuronal cell adhesion molecule that may be important in integrin-mediated cell-cell interactions in the central nervous system, and that the CD11a/CD18-dependent recognition site of human TLN is located within the NH2-terminal five domains of this molecule.

Amino Acid Sequence↗
PubMed1997

Buthionine sulphoximine alone and in combination with melphalan (L-PAM) is highly cytotoxic for human neuroblastoma cell lines.

Buthionine sulphoximine (BSO) selectively inhibits glutathione (GSH) synthesis and may enhance the antineuroblastoma activity of melphalan (L-PAM). We determined the cytotoxicity of BSO (dose range 0-1000 microM) alone and in combination with L-PAM (dose range 0-0 microM) in a panel of 18 human neuroblastoma cell lines. BSO alone was highly cytotoxic with 16/18 neuroblastoma cell lines having IC90 values (range 2.1- > 1000 microM) below the clinically achievable steady-state plasma level of 500 microM BSO. Maximal cell killing correlated with GSH levels decreased to less than 10% baseline, and was partially reversed by the addition of exogenous anti-oxidants (GSH, vitamin E and ascorbate). Fluorocytometric analysis of DNA fragments by the Tunnel method detected 92% of a BSO sensitive cell line in apoptosis after a 48 h exposure to 500 microM BSO. The combination of L-PAM and BSO synergistically enhanced the cell killing of L-PAM alone by > 1-3 logs (combination index < 1). We conclude that BSO has significant single-agent cytotoxicity against neuroblastoma and enhances cell killing when combined with L-PAM.

Antineoplastic Agents↗
PubMed1997

Cytokine mRNA expression in tolerant heart allografts after immunosuppression with cyclosporine, sirolimus or brequinar.

We sought to examine the impact of the preferential activation of Th2 cells on the induction and maintenance of a tolerant state in heart allograft rat recipients treated with a short course of cyclosporine (CsA), sirolimus (SRL) or brequinar (BQR). A quantitative polymerase chain reaction (PCR) method was used to measure the levels of cytokine mRNAs, namely interferon (IFN)-gamma and interleukin (IL)-2 in T helper 1 (Th1) cells and IL-4, IL-5 and IL-10 in Th2 cells. Our main findings were that on day 5 postgrafting allografts from untreated recipients had increased levels of IFN-gamma (216 +/- 119 fg), IL-2 (449 +/- 75 fg), IL-4 (6.2 +/- 1.3 fg), IL-5 (34.8 +/- 9.3 fg) and IL-10 (1554 +/- 184 fg) mRNAs compared with normal hearts. CsA reduced the levels of IFN-gamma, IL-2, IL-5 and IL-10, but not IL-4, mRNAs. SRL did not affect the expression of cytokine mRNAs. BQR decreased the levels of IFN-gamma, IL-2 and IL-10, but not IL-5 or IL-4 mRNAs. Compared with grafts from untreated recipients, those from CsA- or BQR-treated tolerant hosts (day 100) displayed undetectable IL-2 mRNA levels, and reduced levels of IFN-gamma, IL-4 and IL-10 mRNAs. In fact, the patterns of cytokine mRNA expression in grafts from CsA- and BQR-treated tolerant hosts were similar to those of normal hearts. Grafts from SRL-treated tolerant hosts merely showed slightly increased Th2 cell activity. In conclusion the selective activation of Th2 cells is not absolutely required for induction or maintenance of tolerance.

Animals↗