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Biomedical subjects

Yan Zhang

Publications and source records attributed to Yan Zhang.

At least 433 records · Page 24Linked to original sources
PubMed2003

Circadian oscillator function in embryonic retina and retinal explant cultures.

Retinal circadian oscillators regulate many aspects of retinal function. Investigations of these oscillators and the biochemical cascades that entrain them would be greatly facilitated if experimental paradigms could be identified that permit long-term monitoring of retinal circadian oscillator function in vitro. The purpose of this study was to determine if chicken retinas maintained in explant culture conditions could serve in this capacity. Retinal circadian oscillator function was studied by monitoring iodopsin transcription under cyclic light, constant dark, and following reversal of the light cycle. Rhythms observed in the explant cultures were compared to those observed in retinas of embryos (in ovo) and post-hatch chickens. Robust iodopsin transcript rhythms were observed for up to 9 days in explant cultures maintained under cyclic light. These rhythms persisted for 48 h in constant darkness and the time course for re-entrainment of the rhythm to a reversed light/dark cycle was similar to that observed in post-hatch chicken retinas. These results show that circadian oscillators located within the retina play a key role in the regulation of iodopsin transcription in retinal explant cultures and in retinas of post-hatch chickens. Interestingly, our data show that iodopsin transcription in retinas of intact embryos is primarily, if not entirely, driven by light. These results show that the circadian oscillators driving iodopsin transcription in embryonic retinal explant cultures exhibit functional characteristics similar to those found in post-hatch chicken retina, supporting use of this paradigm in further studies of entrainment of these oscillators in retina.

Animals↗
PubMed2003

1-Acetyl-4'-ethyl-2a'-phenyl-2',2a',5',5a'-tetrahydrospiro[1H-indole-3,2'-oxeto[5,4-b]oxazol]-2(3H)-one and 1-acetyl-4',5a'-diphenyl-2',2a',5',5a'-tetrahydrospiro[1H-indole-3,2'-oxeto[5,4-b]oxazol]-2(3H)-one.

In the title compounds, C(21)H(18)N(2)O(4) and C(25)H(18)N(2)O(4), respectively, the five-membered ring of the indole system is almost planar. The oxetane and oxazole rings are individually planar. The orientations of the indole, oxetane, oxazole and phenyl moieties are conditioned by the sp(3) nature of the spiro-C atoms. In both compounds, the relative orientation of the indole and oxazole rings is opposite.

Journal Article↗
PubMed2003

A novel gene, RSD-3/HSD-3.1, encodes a meiotic-related protein expressed in rat and human testis.

The expression of stage-specific genes during spermatogenesis was determined by isolating two segments of rat seminiferous tubule at different stages of the germinal epithelium cycle delineated by transillumination-delineated microdissection, combined with differential display polymerase chain reaction to identify the differential transcripts formed. A total of 22 cDNAs were identified and accepted by GenBank as new expressed sequence tags. One of the expressed sequence tags was radiolabeled and used as a probe to screen a rat testis cDNA library. A novel full-length cDNA composed of 2228 bp, designated as RSD-3 (rat sperm DNA no.3, GenBank accession no. AF094609) was isolated and characterized. The reading frame encodes a polypeptide consisting of 526 amino acid residues, containing a number of DNA binding motifs and phosphorylation sites for PKC, CK-II, and p34cdc2. Northern blot of mRNA prepared from various tissues of adult rats showed that RSD-3 is expressed only in the testis. The initial expression of the RSD-3 gene was detected in the testis on the 30th postnatal day and attained adult level on the 60th postnatal day. Immunolocalization of RSD-3 in germ cells of rat testis showed that its expression is restricted to primary spermatocytes, undergoing meiosis division I. A human testis homologue of RSD-3 cDNA, designated as HSD-3.1 (GenBank accession no. AF144487) was isolated by screening the Human Testis Rapid-Screen arrayed cDNA library panels by RT-PCR. The exon-intron boundaries of HSD-3.1 gene were determined by aligning the cDNA sequence with the corresponding genome sequence. The cDNA consisted of 12 exons that span approximately 52.8 kb of the genome sequence and was mapped to chromosome 14q31.3.

Adult↗
PubMed2003

Ring-chain tautomerism in organic synthesis: synthesis of heterocyclic enamines from a novel and practical formal ring transformation reaction of lactones.

A novel approach to heterocyclic enamines has been developed from the formal ring transformation reaction of lactones. The synthesis comprises consecutive Reformatsky reaction of lactones and mesylation of the resulting mixture of ring-chain tautomers in a one-pot reaction, followed by cyclocondensation reaction with primary amines. The synthetic application of this method was demonstrated by a straightforward preparation of indolizidine compounds via N-(3-bromopropyl)-substituted enamine intermediates. The use of cheap and readily available materials and reagents under very mild conditions renders this formal ring transformation method practical and applicable in the preparation of various heterocyclic enamines that are the precursors for (poly)hydroxylated alkaloid derivatives.

Journal Article↗
PubMed2003

A novel pulsed-release system based on swelling and osmotic pumping mechanism.

A novel pulsed-release system based on bilayer coated tablets containing an osmotically active agent is presented. Hydroxypropylmethylcellulose (HPMC) and the mixture of Eudragit RS and RL were applied as the swelling layer and semipermeable outer coat, respectively. To examine the mechanism of drug release from this pulsed-release system, drug release behaviors were investigated under conditions of various osmotic pressures. Both lag time and release rate were dependent on the coating level and the osmotic pressure of the dissolution medium. The swelling of tablets and the dynamics of water uptake during the dissolution were investigated to further elucidate the mechanism of drug release. The osmotic active agent induces a continuous water influx resulting in a rapid expansion of the membrane. The subsequent formation of fractures leads to a fast drug release after an initial lag time. All the results obtained in the present study indicated that both diffusion and osmotic pumping effect were involved in drug release from the device, but the latter was more dominant.

Capsules↗
PubMed2003

[Detection of cell-free fetal DNA in the urine of pregnant women by nested polymerase chain reaction].

OBJECTIVE: To investigate the clinical feasibility of fetal sex determination by using nested polymerase chain reaction (PCR) to detect cell-free fetal DNA in the urine of pregnant women. METHODS: The urine specimens of 40 healthy predelivery women were centrifuged. The DNA in the specimens of supernatant was extracted by using of QIAamp Viral RNA Mini Kits. Nested PCR was used to specifically amplify the SRY gene, 300 bp in length, on Y chromosome in order to detect the fetal DNA from the women bearing male fetuses. One specimen of normal man's urine and one specimen of non-pregnant woman's urine were used as controls for each specimen from pregnant women. The results were confirmed by the sexes of neonates examined after birth. RESULTS: Amplified band of SRY was found in 6 specimens. Sex examination after delivery showed 21 male neonates and 19 female neonates. The positive rate of detection of SRY gene was 28.6% (6/21) and the false negative rate was 71.4%, and false positive rate was 0. Five out of the 6 cases with positive results showed positive 2 times and one out of the 6 cases only showed positive at the second time. CONCLUSION: There is cell-free fetal DNA in the urine of pregnant women. Nested PCR is useful in detection of fetal sex, however, still with a rather low positive rate.

DNA↗
PubMed2003

Bifunctional abietadiene synthase: mutual structural dependence of the active sites for protonation-initiated and ionization-initiated cyclizations.

Abietadiene synthase from grand fir catalyzes two sequential, mechanistically distinct cyclizations, of geranylgeranyl diphosphate and of copalyl diphosphate, in the formation of a mixture of abietadiene isomers as the committed step of diterpenoid resin acid biosynthesis. Each reaction is independently conducted at a separate active site residing in what were considered to be structurally distinct domains typical of terpene cyclases. Despite the presence of an unusual 250-residue N-terminal insertional element, a tandem pair of charged residues distal to the insertion was shown to form a functional part of the C-terminal active site. Because abietadiene synthase resembles the ancestral plant terpene cyclase, this observation suggests an early evolutionary origin of catalytically important positively charged residues at the N-terminus of enzymes of this general class. A series of N- and C-terminal truncations of this enzyme were constructed and characterized, both alone and as mixtures of adjacent polypeptide pairs, to assess the proposed domain architecture, the function of the insertional element, and the role of presumptive interdomain contacts. These studies indicated a requirement for the insertional element in functional folding and allowed definition of the minimum primary structure of N- and C-terminal active site peptides. Most importantly, the results showed that, although the two active sites of abietadiene synthase are catalytically independent, substantial contact between the two regions is essential for the functional competence of this enzyme. Thus, the two cyclization sites of abietadiene synthase cannot be dissected into catalytically distinct domains, and, therefore, abietadiene synthase is unlikely to have arisen by fusion of two previously independent genes.

Abies↗
PubMed2003

Peak early diastolic mitral annulus velocity by tissue Doppler imaging adds independent and incremental prognostic value.

OBJECTIVES: The aim of this study was to ascertain if left ventricular mitral annulus velocities measured by tissue Doppler imaging (TDI) are more powerful predictors of outcome compared with clinical data and standard Doppler-echocardiographic parameters. BACKGROUND: Tissue Doppler imaging of basal or mitral annulus velocities provides rapid assessment of ventricular long axis function. But it is not known if TDI-derived velocities in systole and diastole add incremental value and are superior to the standard Doppler-echocardiographic measurements as a predictor of outcome. METHODS: The study population consisted of 518 subjects, 353 with cardiac disease and 165 normal subjects who had full Doppler two-dimensional-echocardiographic studies with measurement of mitral inflow velocities in early and late diastole, E-wave deceleration time (DT), peak systolic mitral annular velocity (Sm) early and late diastolic mitral annular velocity (Em and Am) by TDI, early diastolic flow propagation velocity, and standard chamber dimensions. All subjects were followed up for two years. The end point was cardiac death. RESULTS: Tissue Doppler imaging mitral annulus systolic and diastolic velocities were all significantly lower in the non-survivors (all p < 0.05) as was DT (p = 0.024). In the Cox model the best predictors of mortality were Em, Sm, Am, left ventricular ejection fraction, left ventricular mass, and left atrial diameter in systole (LADs). By backward stepwise analysis Em and LADs were the strongest predictors. After forcing the TDI measurements into the covariate model with clinical and mitral DT <0.16 s, Em provided significant incremental value for predicting cardiac mortality (p = 0.004). CONCLUSIONS: Mitral annulus velocity measured by TDI in early diastole gives incremental predictive power for cardiac mortality compared to clinical data and standard echocardiographic measurements. This easily available measurement adds significant value in the clinical management of cardiac patients.

Adult↗
PubMed2003

[Effects of different pH values of fixatives and antigen retrieval buffers on immunohistochemical staining].

OBJECTIVE: To evaluate the influence of pH values of fixatives and antigen retrieval buffers on immunostains. METHODS: Samples of normal skin, gastric mucosa, uteri leiomyoma and breast carcinoma were fixed in buffered formalin with different pH values, namely 3.0, 5.0, 7.0, 8.0 and 10.0 to detect EMA, SMA, ER and CK (AE1/AE3) expression. Evinision two-step method was employed. Antigen retrieval was achieved by microwave using sodium citrate solution with pH 6.0, 7.0, 8.0 or pH 8.0 EDTA solution respectively. RESULTS: The number and intensity of positive cells varied due to different conditions. The change of positive cell's number is important for CK (AE1/AE3) expression, and the change of positive intensity is important for SMA and EMA expression. CONCLUSIONS: (1) The best results could be obtained by the use of 10% neutral or alkalescent buffered formalin. (2) Antigen retrieval effect is better in the solution of pH 7.0, 8.0 than in that of pH 6.0. EDTA(pH 8.0) appears better for skin. The best effect of Estrogen Receptor needs pH 8.0 sodium citrate solution. (3) The background could be easily induced by the fixative over pH 8.0. Antigen retrieval solution over pH 8.0 could result in detachment.

Buffers↗
PubMed2003

In vitro and in vivo models for assessing drug efflux transporter activity.

Determining the activity of drug efflux transport proteins has important implications in the identification of substrates and/or inhibitors of the various transport systems, as well as mechanistic determination of localization, and functional role of the transporters in absorption, distribution and elimination of compounds in the body. This review examines both in vitro and in vivo approaches used to determine drug efflux transporter activity, their applications, and advantages and potential limitations.

ATP-Binding Cassette Transporters↗
PubMed2003

Cloning and characterization of a novel UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase, pp-GalNAc-T14.

A novel member of the human UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase (pp-GalNAc-T) gene family was cloned and designated pp-GalNAc-T14. This type II membrane protein contains all motifs that are conserved in the pp-GalNAc-T family proteins and forms a subfamily with pp-GalNAc-T2 on the phylogenetic tree. Quantitative real time PCR analysis revealed significantly high expression of the pp-GalNAc-T14 transcript in kidney, although the transcripts were ubiquitously expressed in all tissues examined. Furthermore, the recombinant pp-GalNAc-T14 transferred GalNAc to a panel of mucin-derived peptide substrates such as Muc2, Muc5AC, Muc7, and Muc13 (-58). Our results provide evidence that pp-GalNAc-T14 is a new member of the pp-GalNAc-T family and suggest that pp-GalNAc-T14 may be involved in the O-glycosylation in kidney.

Amino Acid Sequence↗
PubMed2003

Measurement and modeling of human T cell kinetics.

The ability to measure, describe and interpret T cell kinetics is pivotal in understanding normal lymphocyte homeostasis and diseases that affect T cell numbers. Following in vivo labeling of dividing cells with 6,6-D(2)-glucose in eight healthy volunteers, peripheral blood T cells were sorted by CD4, CD8 and CD45 phenotype. Enrichment of deuterium in DNA was measured by gas chromatography-mass spectrometry. A novel model of T cell kinetics, allowing for heterogeneity within T cell pools, was used to analyze data on acquisition and loss of label and calculate proliferation and disappearance rates for each subpopulation. Proliferation rates for CD45RO(+)CD8(+) cells and CD45RO(+)CD4(+) cells were 5.1% and 2.7% /day, respectively (equivalent doubling times: 14 and 26 days). CD45RA(+)CD8(+) lymphocytes and CD45RA(+)CD4(+) lymphocytes had slower proliferation rates, 0.5% and 0.6% / day, respectively (doubling time about 4 months). Disappearance rates of labeled cells were similar for all cell types (7%-12% / day) and exceeded corresponding proliferation rates. This disparity may be understood conceptually in terms of either phenotypic heterogeneity (rapid versus slow turnover pools), or history (recently divided cells are more likely to die). The new kinetic model fits the data closely and avoids the need to postulate a large external source of lymphocytes to maintain equilibrium.

Adult↗
PubMed2003

Rapid turnover of T cells in acute infectious mononucleosis.

During acute infectious mononucleosis (AIM), large clones of Epstein-Barr virus-specific T lymphocytes are produced. To investigate the dynamics of clonal expansion, we measured cell proliferation during AIM using deuterated glucose to label DNA of dividing cells in vivo, analyzing cells according to CD4, CD8 and CD45 phenotype. The proportion of labeled CD8(+)CD45R0(+) T lymphocytes was dramatically increased in AIM subjects compared to controls (mean 17.5 versus 2.8%/day; p<0.005), indicating very rapid proliferation. Labeling was also increased in CD4(+)CD45R0(+) cells (7.1 versus 2.1%/day; p<0.01), but less so in CD45RA(+) cells. Mathematical modeling, accounting for death of labeled cells and changing pool sizes, gave estimated proliferation rates in CD8(+)CD45R0(+) cells of 11-130% of cells proliferating per day (mean 47%/day), equivalent to a doubling time of 1.5 days and an appearance rate in blood of about 5 x 10(9) cells/day (versus 7 x 10(7) cells/day in controls). Very rapid death rates were also observed amongst labeled cells (range 28-124, mean 57%/day),indicating very short survival times in the circulation. Thus, we have shown direct evidence for massive proliferation of CD8(+)CD45R0(+) T lymphocytes in AIM and demonstrated that rapid cell division continues concurrently with greatly accelerated rates of cell disappearance.

Acute Disease↗
PubMed2003

A single-strand conformation polymorphism method by capillary electrophoresis with laser-induced fluorescence for detection of the T1151A mutation in hMLH1 gene.

Mutation of hMLH1 gene plays an important role in human tumorigenesis. A highly sensitive single-strand conformation polymorphism (SSCP) method for detection of the T1151A mutation in exon 12 of the hMLH1 gene was for the first time developed employing laser-induced fluorescence capillary electrophoresis (LIF-CE). Effects of the concentration of linear polyacrylamide solution, running temperature, running voltage and the addition of glycerol on SSCP analysis were investigated, and the optimum separation conditions were defined. Thirty colorectal cancer patients and eight lung cancer patients were screened and the T1151A mutation was found in four of them. Based on CE-sequencing the mutation was further confirmed. To our knowledge, this is for the first time that the T1151A mutation is found in lung cancer. Our method is simple, rapid, and highly sensitive and is well suited to the analysis of large numbers of clinical samples.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Correlation between prostate cancer grade and vascularity on color doppler imaging: preliminary findings.

PURPOSE: We examined the relationship between the amount of prostate cancer-associated vascularity as seen on color Doppler imaging and the tumor grade. METHODS: Transrectal color Doppler imaging of the prostate was performed in 54 patients with prostate cancer. Color flow signal/total pixel ratios (SPRs) of selected images were calculated using the ratio of the number of pixels showing color Doppler signals to the total number of pixels within the lesion. All the patients underwent prostate biopsy guided by transrectal sonography. Gleason scores were determined from the biopsy specimens. RESULTS: Color Doppler signals were demonstrated in the lesions of 91% (49/54) of the patients. The mean SPRs of prostate cancers 3 cm or smaller and larger than 3 cm were 0.15 +/- 0.07 and 0.11 +/- 0.04 (+/- standard deviation), respectively (p < 0.05). The mean SPRs of well- (Gleason score of 2-4), moderately (Gleason 5-7), and poorly (Gleason 8-10) differentiated prostate cancers were 0.08 +/- 0.03, 0.12 +/- 0.06, and 0.17 +/- 0.11, respectively (r = 0.45; p < 0.01). CONCLUSIONS: The refinement of color Doppler equipment has improved the detection of color Doppler signals associated with prostate cancer. Our study shows a correlation between prostate cancer-associated vascularity as shown on color Doppler imaging and the tumor grade.

Biopsy↗
PubMed2003

Appropriate conditions or maximizing catalytic reduction efficiency of nitrate into nitrogen gas in groundwater.

This study focused on the appropriate catalyst preparation and operating conditions for maximizing catalytic reduction efficiency of nitrate into nitrogen gas from groundwater. Batch experiments were conducted with prepared Pd and/or Cu catalysts with hydrogen gas supplied under specific operating conditions. It has been found that Pd-Cu combined catalysts prepared at a mass ratio of 4:1 can maximize the nitrate reduction into nitrogen gas. With an increase in the quantity of the catalysts, both nitrite intermediates and ammonia can be kept at a low level. It has also been found that the catalytic activity is mainly affected by the mass ratio of hydrogen gas to nitrate nitrogen, and hydrogen gas gauge pressure. Appropriate operating values of H(2)/NO(3)-N ratio, hydrogen gas gauge pressure, pH, and initial nitrate concentration have been determined to be 44.6g H(2)/g N, 0.15 atm, 5.2 (-), 100 mg x L(-1) for maximizing the catalytic reduction of nitrate from groundwater.

Ammonia↗
PubMed2003

Preliminary studies on Alzheimer's disease using cDNA microarrays.

Alzheimer's disease (AD) is characterized by a progressive impairment of memory and intellectual functioning. The disease is a complex multi-factorial disease with the involvement of several possible genes. To study AD, a high-density cDNA array was developed to characterize the mRNA expression profile of 14160 genes. The preliminary results support the amyloid cascade hypothesis as the mechanism of the disease.

Alcohol Oxidoreductases↗