Biomedical subjects

S Yan

Publications and source records attributed to S Yan.

At least 19 recordsLinked to original sources

PubMed2006

Polyhydroxyalkanoates (PHA) production using wastewater as carbon source and activated sludge as microorganisms.

Activated sludge from different full-scale wastewater treatment plants (municipal, pulp and paper industry, starch manufacturing and cheese manufacturing wastewaters) was used as a source of microorganisms to produce biodegradable plastics in shake flask experiments. Acetate, glucose and different wastewaters were used as carbon sources. Pulp and paper wastewater sludge was found to accumulate maximum concentration (43% of dry weight of suspended solids) of polyhydroxy alkanoates (PHA) with acetate as carbon source. Among the different wastewaters tested as a source of carbon, pulp and paper industry and starch industry wastewaters were found to be the best source of carbon while employing pulp and paper activated sludge for maximum accumulation of PHA. High concentration of volatile fatty acids in these wastewaters was the probable reason.

Acetates↗

PubMed2005

Infliximab improves health related quality of life and physical function in patients with psoriatic arthritis.

OBJECTIVES: To evaluate the effect of infliximab on health related quality of life (HRQoL) and physical function in patients with active psoriatic arthritis (PsA) in the IMPACT 2 trial. METHODS: 200 patients with PsA unresponsive to conventional treatment were randomised to intravenous infusions of infliximab 5 mg/kg or placebo at weeks 0, 2, 6, 14, and 22; patients with inadequate response entered early escape at week 16. HRQoL was assessed using the Short Form-36 (SF-36) at weeks 0, 14, and 24. Functional disability was assessed using the Health Assessment Questionnaire (HAQ) at every visit through week 24. Associations between changes in quality of life (SF-36) and articular (American College of Rheumatology (ACR)) and dermatological (Psoriasis Area and Severity Index (PASI)) responses were examined. RESULTS: Mean percentage improvement from baseline in HAQ was 48.6% in the infliximab group compared with worsening of 18.4% in the placebo group at week 14 (p < 0.001). Furthermore, 58.6% and 19.4% of infliximab and placebo treated patients, respectively, achieved a clinically meaningful improvement in HAQ (that is, > or = 0.3 unit decrease) at week 14 (p < 0.001). Increases in physical and mental component summary (PCS and MCS) scores and all eight scales of the SF-36 in the infliximab group were greater than those in the placebo group at week 14 (p < or = 0.001). These benefits were sustained through week 24. Patients achieving ACR20 and PASI75 responses had the greatest improvements in PCS and MCS scores. CONCLUSIONS: In patients with PsA, infliximab 5 mg/kg significantly improved HRQoL and physical function compared with placebo through 24 weeks.

Adult↗

PubMed2004

Deferred versus prophylactic therapy with gancyclovir for cytomegalovirus in allograft liver transplantation.

OBJECTIVE: The aim of this study was to assess the efficacy of deferred versus prophylactic therapy with gancyclovir to prevent cytomegalovirus (CMV) infection or disease in liver transplantation recipients, and to alter the timing of infection or the incidences of acute rejection, chronic rejection, or death. METHODS: We retrospectively studied 89 consecutive liver transplant recipients with a minimum of 1 year follow-up. CMV early antigen detection (pp65) was performed weekly for the first 2 months and thereafter monthly for an additional 10 months. Forty-one recipients were administered prophylactic treatment and (48 recipients) deferred therapy for positive antigenemia. RESULTS: During the first year after transplantation, CMV infection or disease developed in 61% or 12.2% of those treated with prophylactic therapy and 54.1% or 31.3% of those treated with deferred therapy (P = 0.51 or P = 0.032, respectively). The mean time to CMV disease in the prophylactic group was 161 +/- 33 days compared with 82 +/- 27 days for the deferred therapy arm (P < 0.001). Subgroup analysis based on CMV serological status also showed prophylactic treatment significantly diminished CMV disease in the CMV IgG antibody negative group. No patients died in the prophylactic group, and one died in the deferred group (P = 0.54). The incidence of acute rejection episodes was 34% in the prophylactic and 46% in the deferred group (P = 0.26). Chronic rejection was observed in two recipients in the prophylactic group versus one recipient in the deferred arm (P = 0.35). CONCLUSION: Compared with deferred therapy prophylactic therapy with gancyclovir decreased CMV disease and delayed the onset of CMV disease after liver transplantation.

Adult↗

PubMed2002

Phase III randomized trial of droloxifene and tamoxifen as first-line endocrine treatment of ER/PgR-positive advanced breast cancer.

PURPOSE: This trial was designed to demonstrate equivalence between droloxifene 40 mg/d and tamoxifen 20 mg/d as first-line treatment in pre- and post-menopausal women with ER+ and/or PgR+ advanced breast cancer based on time to disease progression and tumor response. MATERIALS AND METHODS: One thousand three hundred fifty four women with measurable disease, previously untreated by hormonal or chemotherapy for advanced or recurrent breast cancer, were enrolled by 179 institutions in 35 countries. Patients were stratified at baseline for menopausal status. Patients receiving adjuvant hormonal therapy within I year were excluded. All patients gave written informed consent, were randomized to 40mg droloxifene or 20 mg tamoxifen daily as single-agent therapy and underwent tumor assessment every 3 months. A central committee reviewed digitized images for all cases of tumor progression or objective response. RESULTS: The hazard ratio (droloxifene/tamoxifen) for the primary endpoint, time to disease progression, was 1.287 favoring tamoxifen (95% C.I.: 1.114-1.487; p <.001). The objective response rate (CR+PR) was 22.4% for droloxifene and 28.6% for tamoxifen (p = .02). Tamoxifen was superior to droloxifene overall, among both pre- and postmenopausal patients and among patients < or =65 years; there was no difference among women >65 years. The hazard ratio for all-cause mortality was 0.871 (95% C.I.: 0.672-1.129; p = .29), favoring droloxifene but not statistically significant. CONCLUSIONS: Droloxifene was significantly less effective than tamoxifen overall and particularly among women under 65 years. Tamoxifen and droloxifene were both less effective in pre-menopausal women with receptor-positive disease compared to post-menopausal women. Further clinical development of droloxifene was stopped.

Age Factors↗

PubMed2001

[Monitoring and intervention of infant mortality rate and fetal and infant mortality rate in Beijing, 1992-2000].

OBJECTIVE: To monitor the changing trend of infant mortality rate (IMR) and fetal and infant mortality rate (FIM) in Beijing and to develop proper measures to decrease these two rates. METHODS: Dynamic series analysis was used to analyze the monitoring data of 590,833 cases of live birth, 5,835 cases of infant death, and 10,499 cases of stillbirth in Beijing during 1992-2000. The interventional measures in different phases were analyzed too. RESULTS: The IMR and FIMR in Beijing were 12.42% and 19.43% respectively in 1992 and were reduced to 6.84% and 15.79% respectively in 2000. The IMR and FIMR were declining significantly during the periods of 1992-1994, 1995-1997, and 1998-2001 (P < 0.01). The decrease of IMR by 48% was more remarkable than that of FIMR by 19%. The IMR I rural areas was higher than that in urban area. Pneumonia dropped from the position of the first death cause for infants to the fourth cause and congenital heart disease became the first cause. CONCLUSION: FIMR helps more comprehensively evaluate the effect of maternal and child health care. Monitoring and intervention of congenital heart diseases is very important.

Cause of Death↗

PubMed2001

Conformationally constrained analogues of diacylglycerol. 18. The incorporation of a hydroxamate moiety into diacylglycerol-lactones reduces lipophilicity and helps discriminate between sn-1 and sn-2 binding modes to protein kinase C (PK-C). Implications for isozyme specificity.

An approach to reduce the log P in a series of diacylglycerol (DAG)-lactones known for their high binding affinity for protein kinase C (PK-C) is presented. Branched alkyl groups with reduced lipophilicity were selected and combined with the replacement of the ester or lactone oxygens by NH or NOH groups. Compound 6a with an isosteric N-hydroxyl amide arm represents the most potent and least lipophilic DAG analogue known to date.

4-Butyrolactone↗

PubMed2001

Genomic organization and functional characterization of the Leishmania major Friedlin ribosomal RNA gene locus.

The sequence and gene organization of the ribosomal RNA (rRNA) genes of Leishmania major Friedlin (LmjF) were determined. Interestingly, the rDNA repeat unit contained a duplicated 526 bp fragment at the 3' end of the unit with two copies of the LSUepsilon rRNA gene. Our results suggested the presence of only approximately 24 copies of the rRNA unit per diploid genome in LmjF. Repetitive elements (IGSRE) of 63 bp occurred in the intergenic spacer (IGS) between the LSUepsilon and the SSU rRNA genes. Among the different rDNA units, the region containing the IGSRE fluctuated in length from approximately 1.3 to approximately 18 kb. The transcription initiation site (TIS) of the rRNA unit was localized by primer extension to 1043 bp upstream of the SSU gene and 184 bp downstream of the IGSRE. Sequence comparison among several species of Leishmania showed a high degree of conservation around the TIS. Moreover, the IGSRE also showed considerable similarity between Leishmania species. In transient transfection assays, a fragment containing the TIS directed a 164- to 178-fold increase in luciferase activity over the no-insert control, indicating the presence of a promoter within this 391 bp fragment. The LmjF promoter region was also functional in other species of Leishmania. Nuclear run-on analyses demonstrated that only the rRNA-coding strand is transcribed, downstream of this RNA polymerase I (pol I) promoter. These experiments also suggested that transcription terminates upstream of the IGSRE.

Animals↗

PubMed2001

SbF(5)-mediated reactions of oxafluorodiazirines.

[reaction: see text] The reaction of benzyloxyfluorodiazirine (3) with SbF(5) in benzene gives PhCH(2)OCF, which undergoes SbF(5)-mediated fragmentation to PhCH(2)(+), CO, and SbF(6)(-); the benzyl cation alkylates benzene to yield diphenylmethane. Phenoxyfluorodiazirine (4) reacts with SbF(5) in benzene to give PhOCF and (ultimately) triphenylmethane by a pathway that avoids fragmentation.

Antimony↗

PubMed2001

Stereochemical, structural, and thermodynamic origins of stability differences between stereoisomeric benzo[a]pyrene diol epoxide deoxyadenosine adducts in a DNA mutational hot spot sequence.

Benzo[a]pyrene (BP), a prototype polycyclic aromatic hydrocarbon (PAH), can be metabolically activated to the enantiomeric benzo[a]pyrene diol epoxides (BPDEs), (+)-(7R,8S,9S,10R)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene and the (-)-(7S,8R,9R,10S) enantiomer. These can react with adenine residues in DNA, to produce the stereoisomeric 10S (+)- and 10R (-)-trans-anti-[BP]-N(6)-dA adducts. High-resolution NMR solution studies indicate that in DNA duplexes the 10R (-) adduct is intercalated on the 5'-side of the modified adenine, while the 10S (+) adduct is disordered, exhibits multiple adduct conformations, and is positioned on the 3'-side of the modified adenine. Duplexes containing the 10S (+) adduct positioned at A within codon 61 of the human N-ras sequence CAA are thermodynamically less stable and more easily excised by human DNA repair enzymes than those containing the 10R (-) adduct. However, the molecular origins of these differences are not understood and represent a fascinating opportunity for elucidating structure-function relationships. We have carried out a computational investigation to uncover the structural and thermodynamic origins of these effects in the 11-mer duplex sequence d(CGGACAAGAAG).d(CTTCTTGTCCG) by performing a 2-ns molecular dynamics simulation using NMR solution structures as the basis for the starting models. Then, we applied the MM-PBSA (molecular mechanics Poisson-Boltzmann surface area) method to compute free energy differences between the stereoisomeric adducts. The 10R (-) isomer is more stable by approximately 13 kcal/mol, of which approximately 10 kcal/mol is enthalpic, which agrees quite well with their observed differences in thermodynamic stability. The lower stability of the 10S (+) adduct is due to diminished stacking by the BP moiety in the intercalation pocket, more helix unwinding, and a diminished quality of Watson-Crick base pairing. The latter stems from conformational heterogeneity involving a syn-anti equilibrium of the glycosidic bond in the modified adenine residue. The lower stability and conformational heterogeneity of the 10S (+) adduct may play a role in its enhanced susceptibility to nucleotide excision repair.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed2001

Seroprevalence of Borna disease virus in domestic animals in Xinjiang, China.

To investigate the animals infected with Borna disease virus (BDV) in Xinjiang, China, we examined for BDV antibodies in the sera from groups of 20 horses, sheep and cattle, and from 165 wild rodents (18 species) by ELISA and immunoblot. The serological study disclosed the presence of antibodies to both BDV-p24 and -p40 in the horses (20%) and sheep (25%), whereas no apparent positive reaction was detected either in cattle or rodents. The results suggested that BDV is prevalent in horses and sheep in the district investigated.

Animals↗

PubMed2001

An optimized protein kinase C activating diacylglycerol combining high binding affinity (Ki) with reduced lipophilicity (log P).

A small, focused combinatorial library encompassing all possible permutations of acyl branched alkyl chains-small and large, saturated and unsaturated-was generated from the active diacylglycerol enantiomer (S-DAG) to help identify the analogue with the highest binding affinity (lowest Ki) for protein kinase C (PK-C) combined with the minimum lipophilicity (log P). The selected ligand (3B) activated PK-C more effectively than sn-1,2-dioctanoylglycerol (diC8) despite being 1.4 log units more hydrophilic. Compound 3B indeed represents the most potent, hydrophilic DAG ligand to date. With the help of a green fluorescent protein (GFP)-tagged PK-Calpha, 3B was able to translocate the full length protein to the membrane with an optimal dose of 100 microM in CHO-K1 cells, while diC8 failed to achieve translocation even at doses 3-fold higher. Molecular modeling of 3B into an empty C1b domain of PK-Cdelta clearly showed the existence of a preferred binding orientation. In addition, molecular dynamic simulations suggest that binding discrimination could result from a favorable van der Waals (VDW) interaction between the large, branched sn-1 acyl group of 3B and the aromatic rings of Trp252 (PK-Cdelta) or Tyr252 (PK-Calpha). The DAG analogue of 3B in which the acyl groups are reversed (2C) showed a decrease in binding affinity reflecting the capacity of PK-C to effectively discriminate between alternative orientations of the acyl chains.

Animals↗

PubMed2001

Class I major histocompatibility complex anchor substitutions alter the conformation of T cell receptor contacts.

An immunogenic peptide (GP2) derived from HER-2/neu binds to HLA-A2.1 very poorly. Some altered-peptide ligands (APL) of GP2 have increased binding affinity and generate improved cytotoxic T lymphocyte recognition of GP2-presenting tumor cells, but most do not. Increases in binding affinity of single-substitution APL are not additive in double-substitution APL. A common first assumption about peptide binding to class I major histocompatibility complex is that each residue binds independently. In addition, immunologists interested in immunotherapy frequently assume that anchor substitutions do not affect T cell receptor contact residues. However, the crystal structures of two GP2 APL show that the central residues change position depending on the identity of the anchor residue(s). Thus, it is clear that subtle changes in the identity of anchor residues may have significant effects on the positions of the T cell receptor contact residues.

Amino Acid Sequence↗

PubMed2001

Dynamic realization of transport phenomenon in finite system.

Exploring the Fokker-Planck or Langevin type transport equation from the underlying dynamics, we study by exploiting the numerical simulations whether or not one may expect dissipative motions in a Hamilton system with finite degrees of freedom without introducing any statistical concept. It will be shown that the macro-level transport phenomenon in a finite system can be dynamically established from the underlying Hamilton system, and the nonlinear coupling between two subsystems is decisive for generating the transport phenomenon.

Journal Article↗

PubMed2001

Tetracycline regulated gene expression in Leishmania donovani.

The prokaryotic tetracycline-responsive repressor/operator system has proven to be useful for studying the function of essential genes and the expression of toxic gene products in a number of organisms, including Trypanosoma brucei. We report here the adaptation of this system for use in Leishmania. The inducible promoter construct contains a bleomycin resistance-luciferase fusion (BLE-LUC) gene driven by an rRNA promoter with two copies of the TetO sequence inserted two nucleotides upstream of the transcriptional start site. This construct showed regulation of BLE-LUC expression by two orders of magnitude when targeted into the rDNA locus in the reverse orientation relative to transcription of the rRNA genes in a Leishmania donovani cell line expressing TETR. The luciferase expression level in the absence of tetracycline was approximately 50-fold lower than that in the tubulin locus (where it is transcribed by pol II), while the expression level in the presence of tetracycline was approximately five-fold higher than that from the tubulin locus. There was no linear relationship between the level of TETR expression and the regulation, and changing of positions of operator did not increase regulation.

Animals↗

PubMed2001

Modulation of cyclin D1 and its signaling components by the phorbol ester TPA and the tyrosine phosphatase inhibitor vanadate.

The mechanism by which 12-O-tetradecanoylphorbol-13-acetate (TPA) triggers cell-cycle progression at G1 phase in mouse embryonic fibroblast C3H 10T1/2 cells was examined. TPA treatment resulted in a temporary induction of cyclin D1 peaking at 9 h post stimulation. PD98059 (10 microM), the specific inhibitor of MAPK kinase, completely blocked TPA-stimulated cyclin D1 induction and DNA synthesis, confirming that MAPK activation plays an essential role in TPA-stimulated cell-cycle progression. Although both PKCalpha and PKCepsilon are expressed in C3H 10T1/2 cells, inhibitor studies suggest that PKCepsilon activation is required for the activation of MEK/MAPK signal transduction cascade. p70s6K, an important kinase involved in the regulation of protein synthesis and cell-cycle progression, has been reported to be activated through a PKC-dependent pathway (TPA-activatable) in addition to a PI3K-dependent pathway. Here, we demonstrate for the first time that TPA-stimulated MAPK activation is essential for the phosphorylation of several key residues involved in the activation of p70s6K, namely, thr389, thr421, and ser424. Vanadate, the tyrosine phosphatase inhibitor, triggered a sustained elevation of the level of active MAPK. However, corresponding to a rapid loss of cyclin D1 protein, vanadate treatment resulted in a significant shut out of 3H-thymidine incorporation into DNA regardless of TPA cotreatment. Vanadate treatment also led to the increase of active MEK, increased phosphorylation of p70s6K at thr389, thr421, and ser424 yet without activation of PKB. These data suggest that vanadate can selectively perturb the activation of signaling components which raises the interesting issue as to how vanadate downregulates the cyclin D1 level.

Animals↗

PubMed2001

The Leishmania genome project: new insights into gene organization and function.

The sequencing of Leishmania major Friedlin chromosome 1 (Chr1), Chr3, and Chr4 has been completed. and several other chromosomes are well underway. The complete genome sequence should be available by 2003. Over 1,000 full-length new genes have been identified, with the majority (approximately 75%) having unknown function. Many of these may be Leishmania (or kinetoplastid) specific. Most interestingly, the genes are organized into large (> 100-500 kb) polycistronic clusters of adjacent genes on the same DNA strand. Chr1 contains two such clusters organized in a "divergent" manner, i.e., the mRNAs for the two sets of genes are both transcribed towards the telomeres. Nuclear run-on analysis suggests that transcription is initiated in both directions within the "divergent" region. Chr3 and Chr4 contain two "convergent" clusters, with a single "divergent" gene at one telomere of Chr3. Sequence analysis of several genes from the LD1 region of Chr35 indicates a high degree of sequence conservation between L. major and L. donovani/L. infantum within protein-coding open reading frames (ORFs), with a lower degree of conservation within the non-coding regions. Immunization of mice with recombinant antigen from two of these genes, BTI (formerly ORFG) and ORFF, results in significant reduction in parasite burden following Leishmania challenge. Recombinant ORFF antigen shows promise as a serodiagnostic. We have also developed a tetracycline-regulated promoter system, which allows us to modulate gene expression in Leishmania.

Animals↗

PubMed2001

Prediction of presence and absence of two- and three-amino-acid sequences of human monoamine oxidase from its amino acid composition according to the random mechanism.

Three probabilistic procedures are used to analyse the human monoamine oxidase B (MAO-B). (1) Each kind of two-, three- and multi-amino-acid sequences is counted along MAO-B from one terminal to the other and their frequencies and probabilities are calculated. (2) The amino-acid sequences in MAO-B are compared with the theoretical amino-acid sequences and the present or absent theoretical amino-acid sequences in MAO-B are determined. (3) The random principle is used to predict the frequencies of presence and absence of amino-acid sequences in MAO-B from its amino acid composition and the comparison is made between predicted and counted frequencies. The results show the random principle can predict the presence of 99 two-amino-acid sequences in MAO-B and the absence of 38 and 7506 kinds of theoretical two- and three-amino-acid sequences from MAO-B.

Amino Acid Sequence↗

PubMed2001

Cyclohexene ring and Fjord region twist inversion in stereoisomeric DNA adducts of enantiomeric benzo[c]phenanthrene diol epoxides.

The sterically hindered, nonplanar fjord region polycyclic aromatic hydrocarbons (PAHs) have been of great interest because of the exceptionally high mutagenic and tumorigenic activity of certain of their metabolically activated diol epoxides. Benzo[c]phenanthrene (B[c]Ph), a representative fjord region PAH, is metabolically activated to a pair of enantiomers, 1S,2R,3R,4S-3,4-dihydroxy-1,2-epoxy-1,2,3,4-tetrahydrobenzo[c]phenanthrene, (+)-anti-B[c]PhDE, and the corresponding 1R,2S,3S,4R enantiomer, (-)-anti-B[c]PhDE. Both of these can bind covalently to the amino group of purines in DNA via trans addition. In the present work we carry out an extensive computational investigation of the 1R(+) and 1S(-)-trans-anti-B[c]Ph adducts to the base guanine, with the goal of delineating the conformational possibilities for the fjord region and the adjacent cyclohexene-type benzylic ring and their relevance to DNA duplexes. We created 10 369 starting structures for each adduct and minimized the energy using AMBER 5.0. A limited set of conformational families is computed, in which the R isomer structures are near mirror images of the S isomer. The benzylic rings are essentially all half-chair-type. Cyclohexene-type ring inversion as well as fjord region twist inversion are possible for each isomer and are correlated. DNA duplexes modified by fjord region adducts select conformers from the allowed families that optimize stacking interactions, which contributes to the stability of the carcinogen-intercalated DNA duplex structures [Cosman et al. (1993) Biochemistry 32, 12488-12497; Cosman et al. (1995) Biochemistry 34, 1295-1307; Suri et al. (1999) J. Mol. Biol. 292, 289-307; Lin et al. (2001) J. Mol. Biol. 306, 1059-1080]. In turn, this stability could contribute to the resistance to repair by the human nucleotide excision system observed in fjord region adducts [Buterin et al. (2000) Cancer Res. 60, 1849-1856].

Cyclohexanes↗