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Biomedical subjects

L Yuan

Publications and source records attributed to L Yuan.

At least 19 recordsLinked to original sources
PubMed2002

Involvement of the mt1 melatonin receptor in human breast cancer.

Two putative melatonin receptors have been described including the cell surface G-protein-linked receptors, mt1 and MT2, and the nuclear retinoic orphan receptor alpha (RORalpha). The mt1 receptor, but not the MT2 receptor, is expressed in human breast tumor cell lines, and melatonin-induced growth suppression can be mimicked by the mt1 and MT2 agonist, AMMTC, and blocked by the antagonist, CBPT. RORalpha receptors are also expressed in MCF-7 breast cancer cells and the putative RORalpha agonist CPG-52608 inhibits MCF-7 cell growth but with a very different dose-response than melatonin. Finally, melatonin and AMMTC, but not CPG-52608, can repress RORalpha transcriptional activity in MCF-7 cells.

Breast Neoplasms↗
PubMed2002

Effects of ionization in single-bubble sonoluminescence.

We studied the effects of ionization in a sonoluminescing (SL) bubble within the hydrodynamic framework. The thermodynamic variables and the degrees of ionization inside the bubble throughout an oscillation cycle are obtained by solving the hydrodynamic equations assuming spherical symmetry. Several models are used to compute the emitted radiation, which are then compared with experimental data. Numerical results show that shock waves are absent in the stable SL regime, and compressional waves are already strong enough to produce moderate temperature and ionization. The degrees of ionization at the bubble center are found to be within 7% to 30%, and Ar+ is the only dominant ion. Moreover, an opacity-corrected blackbody radiation model gives the peak power, pulse widths, and spectra that agree very well with the experimental data.

Journal Article↗
PubMed2002

Hypernuclear fine structure in (9)(lambda)Be.

With a germanium detector array (Hyperball), we observed two gamma-ray peaks corresponding to the two transitions (5/2(+)-->1/2(+) and 3/2(+)-->1/2(+)) in the (9)(Lambda)Be hypernucleus which was produced by the 9Be(K-,pi(-)) reaction. The energies of the gamma rays are 3029 +/- 2 +/- 1 keV and 3060 +/- 2 +/- 1 keV. The energy difference was measured to be 31.4(+2.5)(-3.6) keV, which indicates a very small Lambda-spin-dependent spin-orbit force between a Lambda and a nucleon. This is the smallest level splitting by far ever measured in a hypernucleus.

Journal Article↗
PubMed2002

Melatonin inhibits estrogen receptor transactivation and cAMP levels in breast cancer cells.

We have previously demonstrated that the pineal hormone, melatonin, can inhibit the growth of estrogen receptor-alpha (ERalpha)-positive breast cancer cells and suppress ERalpha gene transcription. To investigate the relationship between the estrogen response pathway and melatonin's growth inhibition, ERalpha-positive MCF-7 human breast cancer cells were transiently transfected with an estrogen response element (ERE) luciferase reporter construct and then treated with melatonin (10(-9)-10(-6) M) for 30 min followed by 10(-9) M 17-beta-estradiol (E2) or treated with each compound alone. Melatonin pre-treatment significantly reduced E2-induced ERalpha transactivation and ERalpha-ERE binding activity. We also conducted experiments to determine if melatonin modulates cAMP levels in MCF-7 cells. Melatonin inhibited the forskolin-induced and E2-induced elevation of cAMP levels by 57 and 45%, respectively. These data indicate that melatonin can act as a biological modifier to affect ERalpha transcriptional activity by regulating signal transduction pathways which impinge on the ERalpha and by altering E2-mediated ERalpha transactivation and ERalpha DNA binding activity.

Adjuvants, Immunologic↗
PubMed2002

Tumor prevention by 9-cis-retinoic acid in the N-nitroso-N-methylurea model of mammary carcinogenesis is potentiated by the pineal hormone melatonin.

Our laboratory has demonstrated that treatment of MCF-7 breast cancer cells with melatonin (Mlt) followed 24h later with physiological concentrations of all-trans retinoic acid (atRA) results in apoptosis. These studies were extended into trials using the N-nitroso-N-methylurea (NMU)-induced rat mammary tumor model. Initial studies conducted by feeding the animals 9-cis-retinoic acid (9cRA in the chow) and administering melatonin by subcutaneous injection in the late afternoon demonstrated that the combination of Mlt and 9cRA was able to significantly prevent tumor development, and that the combination was more efficacious that either Mlt or 9cRA alone. In this report, we conducted studies to determine if lower doses of 9cRA could be used in combination with Mlt while still maintaining anti-tumor activity and if the route of administration of 9cRA (bolus (gavage) v.s. chronic (chow) routes) affected its interaction with Mlt. The studies presented here demonstrate that significantly reduced doses of 9cRA can be used in combination with Mlt while maintaining anti-tumor efficacy. Furthermore, our studies demonstrate that 9cRA is equally effective when it is administered chronically (chow) or as a bolus (gavage). These data demonstrate that the combined use of Mlt and 9cRA produces additive or synergistic effects, which are more efficacious than 9cRA alone. This combination of Mlt and 9cRA could be a potentially useful clinical treatment regimen for breast cancer since it allows the use of lower doses of retinoic acid, thus, avoiding the toxic side effects associated with the use of high dose retinoids.

Administration, Oral↗
PubMed2002

[The human alpha(2A)-AR gene and the genotype of site -1296 and the susceptibility to motion sickness].

The gene sequences of alpha(2A)-adrenergic receptor(alpha(2A)-AR) in 39 Chinese and 1 Englishman showed 13 differences of g or c insertion or deletion in its regulation region, coding region and 3' untranslated region, compared with that reported in GenBank. The gene sequences from all the samples respectively were identical except for 2 single nucleotide polymorphisms, including the sequence of sense and antisense strand sequenced. It was found that: (1) the frequency of gg genotype in Chinese and Japanese, who are high susceptible to motion sickness, were 5.8 and 7.8 fold higher than that in Englishmen; (2) g allele frequencies in Chinese and Japanese were higher than latter ( P 0.01 ); (3) gg genotype frequency in population susceptible to motion sickness was 1.6 fold higher than that in population unsusceptible to motion sickness, and g allele frequency was higher than latter ( P 0.01 ). All the populations were in Hardy-Weinberg equilibrium. The results suggested that gg genotype and g allele at site -1296 in alpha(2A)-AR gene could associate with the susceptibility to motion sickness.

Asian People↗
PubMed2001

Longitudinal electroproduction of charged pions from (1)H, (2)H, and (3)He.

Separated longitudinal and transverse cross sections for charged pion electroproduction from (1)H, (2)H, and (3)He were measured at Q(2) = 0.4 (GeV/c)(2) for two values of the invariant mass, W = 1.15 GeV and W = 1.60 GeV, in a search for a mass dependence which would signal the effect of nuclear pions. This is the first such study that includes recoil momenta significantly above the Fermi surface. The longitudinal cross section, if dominated by the pion-pole process, should be sensitive to nuclear pion currents. Comparisons of the longitudinal cross section target ratios to a quasifree calculation reveal a significant suppression in (3)He at W = 1.60 GeV. The W = 1.15 GeV results are consistent with simple estimates of the effect of nuclear pion currents, but are also consistent with pure quasifree production.

Journal Article↗
PubMed2001

Production of (4)(double Lambda)H hypernuclei.

An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.

Journal Article↗
PubMed2001

Measurement of the high energy two-body deuteron photodisintegration differential cross section.

The first measurements of the d(gamma,p)n differential cross section at forward angles and photon energies above 4 GeV were performed at the Thomas Jefferson National Accelerator Facility (JLab). The results indicate evidence of an angular dependent scaling threshold. Results at straight theta(cm) = 37 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 4 GeV, while those at 70 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 1.5 GeV.

Journal Article↗
PubMed2001

Chemoprevention of NMU-induced rat mammary carcinoma with the combination of melatonin and 9-cis-retinoic acid.

In experimental trials using the N-nitroso-N-methylurea (NMU)-induced rat mammary tumor model, a significant decrease in tumor incidence (to 5%) was observed in rats treated with melatonin and 9-cis-retinoic acid (9 cRA) compared to controls (55%). Although 9cRA alone decreased tumor incidence to 26%, this response did not reach statistical significance. Tumor incidence was significantly inhibited to 20% in the animals that received melatonin and 9cRA on alternating days. Latency to tumor onset was prolonged in animals receiving either of the combination treatments compared with controls, and tumor multiplicity was also significantly decreased.

Adenocarcinoma↗
PubMed2001

Role of gas density in the stability of single-bubble sonoluminescence.

Recent full hydrodynamic simulations of a sonoluminescing bubble interior have shown that the bubble content is compressed to a very dense state during the violent collapse. In this paper, we numerically studied the shape stability of a radially oscillating gas bubble by using Hilgenfeldt et al. theoretical model with corrections taking into account the gas density effect. Our results show that gas density variations not only significantly suppress the Rayleigh-Taylor instability, but also enhance the threshold of the parametric instability under sonoluminescence conditions.

Journal Article↗
PubMed2001

Activated microglia in the human glaucomatous optic nerve head.

To investigate the distribution and potential participation of microglia, the resident defense cells of the central nervous system, in the optic nerve head (ONH) in glaucoma, histological paraffin sections of optic nerves from normal and glaucoma patients with mild to advanced nerve damage were studied using double labeling immunohistofluorescence. A monoclonal antibody for HLA-DR, indicating activated microglia, was colocalized with antibodies for functional proteins. In normal ONHs, microglia do not contain TGF-beta2, COX-2, or TNF-alpha and are not positive for PCNA; however, in glaucomatous ONHs, microglia contain abundant TGF-beta2, TNF-alpha, and PCNA. In glaucomatous eyes, a few microglia are usually positive for COX-2. In normal ONHs, there are rarely microglia containing TGF-beta1, NOS-2, TSP, TIMP-2, and CD68, but, in glaucomatous tissue, a few microglia are positive from the prelaminar to the postlaminar regions. MMP-1, MMP-2, MMP-3, and MMP-14 are constitutively present in the perivascular microglia in normal ONHs and appear to be more abundant in glaucomatous tissue. COX-1, TNF-R1, TIMP-1, and c-fms are constitutively present in normal tissues and appear to be increased in microglia in the glaucomatous ONHs. HSP27 is not present in microglia. In glaucomatous ONHs, microglia become activated and phagocytic and produce cytokines, mediators, and enzymes that can alter the extracellular matrix. Our findings suggest that activated microglia may participate in stabilizing the tissue early in the disease process, but, as the severity of the glaucomatous damage increases, the activities of microglia may have detrimental consequences for the pathological course of glaucomatous optic neuropathy.

Aged↗
PubMed2001

Transcriptional repression of RORalpha activity in human breast cancer cells by melatonin.

Melatonin has repeatedly been shown to inhibit the proliferation of MCF-7 human breast cancer cells. Previous reports suggest that the actions of melatonin can be mediated either through G-protein coupled membrane receptors or via retinoid orphan receptors (RORalphas). In this study, we demonstrated the expression of RORalpha2, 3, and 4 transcripts in MCF-7 cells. These cells exhibited a high basal level of RORalpha transcriptional activity, which was further stimulated by serum. In the presence of serum, RORalpha transactivation and DNA-binding activity was repressed by melatonin even though melatonin had no effect on RORalpha protein levels. We found that RORalpha transcriptional activity in MCF-7 cells was regulated by modulators of the Ca2+/CaM signaling pathway. Given that melatonin has been reported to modulate the Ca2+/CaM signaling pathway in other tissues, our data indicate that melatonin may affect RORalpha transcriptional activity, expression of RORalpha regulated genes, and even breast cancer cell proliferation via modulation of the Ca2+/CaM signaling pathway.

Antioxidants↗
PubMed2001

Observation of spin-orbit splitting in lambda single-particle states.

The spin-orbit splitting of Lambda single-particle states in (13)(Lambda)C was measured. The 13C(K-,pi(-))(13)(Lambda)C reaction was used to excite both the 1/2(-) and 3/2(-) states simultaneously, which have predominantly 12C(0(+)) x p(Lambda) configuration. gamma rays from the states to the ground state were measured in coincidence with the pi(-)'s, by which ls splitting was found to be 152+/-54(stat)+/-36(syst) keV. The value is 20-30 times smaller than exhibited by the ls splitting in the nuclear shell model. This value gives us new insight into the YN interaction.

Journal Article↗
PubMed2001

Selective expression of angiopoietin 1 and 2 in mesenchymal cells surrounding veins and arteries of the avian embryo.

The expression of angiopoietin1 and 2 (ang1 and 2) and their receptor tie-2 was studied in avian embryos using in situ hybridization. Ang1 was transcribed in the mesenchymal cells surrounding venous endothelium expressing tie-2. By contrast, ang2 was transcribed around arteries in which the endothelium down-regulated tie-2 mRNA. The aorta and large arteries of the heart outflow tract were never surrounded by ang2 positive cells and maintained tie-2 expression.

Angiopoietin-1↗
PubMed2001

Short-term immunoglobulin A B-cell memory resides in intestinal lymphoid tissues but not in bone marrow of gnotobiotic pigs inoculated with Wa human rotavirus.

Immunological memory is important for protecting the host from reinfection. To investigate the development and sites of residence of intestinal memory B cells, and their role in protective immunity to reinfection with an enteric virus, we assessed the association between memory B cell and antibody-secreting cell (ASC) responses and protection using a gnotobiotic pig model for human rotavirus (HRV) infection and diarrhoea. The isotypes, quantities and tissue distribution of rotavirus-specific memory B cells and ASC were evaluated prechallenge (28 and 83 postinoculation days [PID]) and postchallenge (7 postchallenge days [PCD]), using enzyme-linked immunospot (ELISPOT) assay, in gnotobiotic pigs inoculated once with virulent or three times with attenuated HRV and challenged at PID 28 with the corresponding virulent HRV. Complete protection against HRV shedding and diarrhoea was associated with significantly higher numbers of immunoglobulin A (IgA) and immunoglobulin G (IgG) memory B cells and ASC in the ileum of virulent HRV-inoculated pigs at challenge. In contrast, pigs inoculated with attenuated HRV had lower numbers of IgA and IgG memory B cells and ASC in intestinal lymphoid tissues, but higher numbers in the spleen. The bone marrow had the lowest mean numbers of IgA and IgG memory B cells and ASC prechallenge in both groups of HRV-inoculated pigs. Therefore, bone marrow was not a site for IgA and IgG rotavirus-specific antibody production or for memory B cells after inoculation with live rotavirus, from 28 PID up to at least 83 PID. The effect of in vitro antigen dose was examined and it was determined to play an important role in the development of ASC from memory B cells for the different tissues examined.

Animals↗
PubMed2001

Is equity being sacrificed? Willingness and ability to pay for schistosomiasis control in China.

Decentralization of the health care system in China has led to an increasing need for income generation at all operational levels, both for curative services and for public health programmes. In general, people have accepted the costs of curative services, although the impact of charges on health-seeking behaviour has yet to be assessed. Public health programmes present particular problems in terms of revenue generation, however, because of the less direct impact of these activities on individual health and well-being. In this paper, we report the results of a cross-sectional study of willingness and ability to pay for schistosomiasis control. Questionnaires were administered to household heads of six representative villages in the Dongting Lake Region of Hunan Province, China. A total of 628 valid questionnaires were analyzed. The yearly mean household expenditure on schistosomiasis diagnosis and treatment was RMB 59.50 +/- 146.04 Yuan (US$1 = 8 RMB Yuan), accounting for 0.94% of the total yearly household income. Most household heads (514, 82%) thought schistosomiasis was the greatest health threat in their communities, but only 30.9% of them were willing to pay for screening, diagnosis and treatment of the infection. On the other hand, 72.3% of the respondents were willing to undertake volunteer work for control.

Adult↗