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Biomedical subjects

S Chen

Publications and source records attributed to S Chen.

At least 397 records · Page 22Linked to original sources
PubMed2000

Diabetes-induced myocardial structural changes: role of endothelin-1 and its receptors.

Several metabolic abnormalities may be triggered secondary to hyperglycemia in diabetes. Some of these abnormalities may alter expression of vasoactive factors in the target organs of diabetic complications. We investigated alterations of endothelin-1 (ET-1) and its receptors, ET(A) and ET(B), and associated structural changes in the myocardium of streptozotocin-induced diabetic rats after 6 months of hyperglycemia. We further assessed the preventive effects of an ET-receptor antagonist bosentan on these changes. Compared to the non-diabetic, age- and sex-matched control animals, diabetic rats showed hyperglycemia, glucosuria, reduced body weight gain and elevated glycated Hb levels. Measurement of ET-1, ET(A) and ET(B) mRNAs by semiquantitative RT-PCR showed significantly increased mRNA levels in the hearts of diabetic rats. Treatment with bosentan failed to reduce ET-1 or ET(B) mRNA expression in diabetes, however ET(A) mRNA expression was reduced. Immunocytochemically, ET-1 was detected in the cardiomyocytes, endothelium and smooth muscle cells of the larger blood vessels and was increased in diabetes. Autoradiographic localization of ET-1 receptors, using (125)I-ET-1, showed increased binding in the endothelium and myocardium of diabetic animals. Histologically, focal fibrous scarring with apoptotic cardiomyocytes, consistent with changes secondary to microvascular occlusion, was only present in the diabetic rats. In keeping with focal fibrosis, myocardium from diabetic rats further showed significantly increased mRNA expression of two extracellular matrix protein transcripts, fibronectin and collagen alpha 1(IV) which were completely prevented by treatment with bosentan. These data suggest that hyperglycemia-induced upregulation of the ET-system in the heart may be important in the pathogenesis of cardiac involvement in diabetes.

Animals↗
PubMed2000

Metabolism of dauricine and identification of its main metabolites.

To study the metabolism of dauricine in vivo and in vitro and identify the structure of its main metabolites, urine of rats after drug administration as the samples of dauricine metabolism in vivo was studied. Rat liver S9 fraction was prepared and the oxygenation metabolism system reconstituted to perform phase I reaction of dauricine in vitro. TLC, HPLC-DAD and MS were used to analyze and identify dauricine and its main phase I metabolites in the samples. The results showed that besides the untransformed dauricine, in the urine samples there was little product of X' which had the same features of TLC, HPLC-DAD and MS as those of N-desmethyl dauricine (N-ddau). Part of dauricine could be transformed to a main metabolite X after incubating with S9 fraction in appropriate conditions. The molecular ion peak of X was m/z 611. The full scan MS2 spectrum of m/z 611 peak from S9 sample were m/z 580, m/z 566, m/z 552, m/z 206, which were same as those of N-ddau. Liver is the major organ for dauricine metabolism and part of dauricine is biotransformed by liver. The major metabolite is considered to be N-ddau.

Alkaloids↗
PubMed2000

A sensitive HPLC technique for the quantitation of dauricine.

To establish the determination method of dauricine (Dau) concentration in rats' blood and other biological samples, a reverse-phase HPLC method was adopted. Under the given condition, dauricine could be well separated. The retention time (tR) of Dau and its internal standard, daurisoline were 9.2 and 6.1 respectively. The detection limit was 10(-2) mg/ml. The absolute recoveries of all kinds of samples were above 70%, and the relative ones were over 85%. A good liner relationship has been obtained over the entire range of 0.030 to 3.000 mg/L in blood samples and 0.050 to 5.000 mg/L in other tissue samples. The intraday and interday coefficients of variation were below 10%. The results showed that the method can be used for detecting Dau in all kinds of biological samples.

Alkaloids↗
PubMed2000

Apoptotic germ-cell death and testicular damage in experimental diabetes: prevention by endothelin antagonism.

This paper explores the role of endothelins (ETs) in diabetes-induced testicular damage by investigating, in a temporal manner, testes from streptozotocin (STZ)-induced diabetic rats. Testicular and epididymal weights and testicular morphology were assessed. Cell death was evaluated by light microscopy using conventional staining and morphology, and by apoptotic cell staining using the Terminal deoxynucleotidyl transferase-mediated dUTP Nick End-Labeling (TUNEL) technique. Expression of endothelin-1 (ET-1) mRNA was evaluated by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) method. Furthermore, effects of a mixed ETA and ETB receptor antagonist, bosentan, were studied. Testicular weights did not show any change at 1 month of follow-up, but were decreased after 6 months of diabetes. However, epididymal weights were significantly decreased at the end of both time periods in the diabetic rats. Morphological evaluations of the testes from diabetic rats showed a reduction in seminiferous tubular diameter, an increase in the number of empty testicular tubules and an increase in vascular density. Furthermore, degenerated germ cells and TUNEL-positive cells were significantly higher in diabetic rats than in control animals. The changes in diabetic animals were associated with increased ET-1 mRNA expression and were prevented by bosentan treatment. Administration of bosentan prevented decreased testicular weights, reduced seminiferous tubule diameters, increased vascular densities and incidences of degenerated and apoptotic germ cells and empty tubules in diabetic rats at the long-term follow-up. These results demonstrated that an ET-1 mediated pathway might be involved in testicular injury and germ-cell apoptosis in diabetes.

Animals↗
PubMed2000

Induction of metallothionein synthesis with preservation of testicular function in rats following long term renal transplantation.

Metallothionein (MT), as an acute phase or stress-response protein and free radical scavenger, is related to inflammation and cellular protection from oxidative damage. In order to evaluate long-term testicular damage and the role of MT following renal transplant, nine allogenic (Fisher 344 --> Lewis) and seven isogenic (Lewis --> Lewis) renal transplants were performed and the recipient rats were followed for 140 days when allografts develop chronic transplant rejection. Testicular weight, light microscopic morphology, and lactate dehydrogenase-X enzyme activity were assessed. Testicular MT was determined by Cd-heme assay, and was localized immunocytochemically using a polyclonal rabbit antibody. No differences in testis weight, morphology, or LDH-X enzyme activity were found between allograft and isograft recipients. Testicular MT level was significantly increased in the testis of allograft recipients. Testicular zinc (Zn) and copper (Cu) levels, but not iron (Fe) level, were significantly higher in testis with allograft kidney than that with isograft kidney. In addition, Cu/Zn ratio was also significantly high in the allograft group. However, the MT level did not show any significant correlation either with Cu and Zn alone or with Cu/Zn and Fe/Zn ratios. These data suggest that allogenic stimuli may induce MT synthesis in the recipient testis. The increased MT level in an allograft may offer a protective action from oxidative damage in the testis.

Animals↗
PubMed2000

Surface antigen expression and complement susceptibility of differentiated neuroblastoma clones.

Human neuroblastoma cell lines typically consist of heterogenous subpopulations of cells that are morphologically and biochemically distinct. The cell types are characterized as neuroblastic (N-type), substrate-adherent Schwann-like (S-type), or intermediate (I). These cell types can undergo spontaneous or induced transdifferentiation in vitro. We investigated the complement sensitivity of different neuroblastoma cell lines and of matched sets of cloned N- and S-type neuroblastoma cell lines. Human neuroblastoma cell lines that consisted predominantly of a neuroblastic phenotype were shown to be significantly more susceptible to human complement-mediated lysis than cell lines of other cancer types. Complement sensitivity of neuroblastoma cell lines was correlated with low levels of CD59, decay-accelerating factor, and membrane cofactor protein expression. We found that cloned S-type neuroblastoma cells were much more resistant to complement-mediated lysis than cloned N-type cells. The increased complement resistance of S-type cells was shown to be due to increased expression of membrane-bound complement inhibitors. CD59 was the single most important protein in providing S-type cells with protection from complement lysis. S-type cells were also found to express lower levels of GD2, a target antigen for a complement activating monoclonal antibody currently in clinical trials for neuroblastoma immunotherapy. The ability of S-type cells to evade complement, and the ability of S-type cells to differentiate into the more tumorigenic N-type cells, may represent a mechanism of tumor survival and regrowth, a phenomenon often observed with this cancer.

Antibodies, Blocking↗
PubMed2000

Resonant frequency method for the measurement and uncertainty analysis of acoustic and elastic properties

A resonant frequency method is proposed to determine the bar speed and the Poisson's ratio of a rod several meters long of the kind often used for manufacturing power sonic transducers and mechanical horns in mass production. This method is shown to be robust in a field test and with high resolution for estimation of the bar speed. The uncertainty (standard deviation/average) for the bar speed and the Poisson's ratio can be reduced by appropriately selecting the mode number pairs and increasing the mode number. In this study, the uncertainties of the bar speed and Poisson's ratio are less than 0.043% and 2.9%, respectively. The resonant frequency method is verified by comparing the dilatational wave speeds calculated by elastic theory with those from experiments, the difference between them being less than 0.17%.

Journal Article↗
PubMed2000

The use of PLS algorithms and quantum chemical parameters derived from PM3 hamiltonian in QSPR studies on direct photolysis quantum yields of substituted aromatic halides.

The Partial Least-Squares (PLS) method was used to further study Quantitative Structure-Property Relationship (QSPR) for photohydrolysis quantum yields of selected aromatic halides. The cluster of substituted bromobenzenes and iodobenzenes was further grouped into two clusters, substituted bromobenzenes and substituted iodobenzenes, for which QSPRs were obtained, respectively. The QSPRs obtained by PLS are more significant than those obtained in previous studies. The studies showed that only when the compounds belonging to different groups are studies separately, inherent relationships between molecular properties and their structure characteristics can be revealed. It can be generally concluded that the photohydrolysis quantum yields of the substituted aromatic halides are dependent on the overall characters of the molecules, the characters of the carbon-halogen bonds to be broken in the photolysis, and the character of the halogen atoms to be replaced in the photolysis. Electronegativity has great relevance to the photohydrolysis processes of the compounds. Substituted aromatic halides with large average molecular polarizability and molecular weight values tend to have low photolysis quantum yields.

Algorithms↗
PubMed2000

Structure-function studies of DT-diaphorase (NQO1) and NRH: quinone oxidoreductase (NQO2).

DT-diaphorase, also referred to as NQO1 or NAD(P)H: quinone acceptor oxidoreductase, is a flavoprotein that catalyzes the two-electron reduction of quinones and quinonoid compounds to hydroquinones, using either NADH or NADPH as the electron donor. NRH (dihydronicotinamide riboside): quinone oxidoreductase, also referred to as NQO2, has a high nucleotide sequence identity to DT-diaphorase and is considered to be an isozyme of DT-diaphorase. These enzymes transfer two electrons to a quinone, resulting in the formation of a hydroquinone product without the accumulation of a dissociated semiquinone. Steady and rapid-reaction kinetic experiments have been performed to determine the reaction mechanism of DT-diaphorase. Furthermore, chimeric and site-directed mutagenesis experiments have been performed to determine the molecular basis of the catalytic differences between the two isozymes and to identify the critical amino acid residues that interact with various inhibitors of the enzymes. In addition, functional studies of a natural occurring mutant Pro-187 to Ser (P187S) have been carried out. Results obtained from these investigations are summarized and discussed.

Amino Acid Sequence↗
PubMed2000

Characterization of the 16S rRNA gene V2 region and the rrn operons of Gardnerella vaginalis.

Ribosomal RNA (rRNA) gene polymorphism was apparent when Gardnerella vaginalis DNA restriction profiles were hybridized with nonradioactively labeled total rRNA isolated from this bacterium. In contrast, use of a polymerase chain reaction (PCR)-based 16S rRNA gene V2 region resulted in a 118-bp V2-PCR amplicon that was specific and common in all 30 tested G. vaginalis isolates. In addition to providing a G. vaginalis-specific fingerprint, when the V2-PCR amplicon along with total rRNA were utilized as probes, a partial rRNA gene restriction map could be constructed. G. vaginalis contains two rrn operons with an EcoRI fragment of 1.6 kb common to both.

DNA Fingerprinting↗
PubMed2000

Photodynamic action of amino substituted hypocrellins: EPR studies on the photogenerations of active oxygen and free radical species.

A novel method has been employed to prepare 2-butylamino-2-demethoxy hypocrellin A (BADMHA) and 2-butylamino-2-demethoxy hypocrellin B (BADMHB). Both compounds exhibit stronger absorption at the phototherapeutic window (600-900 nm). The spin trapping and spin counteraction studies have shown that they are both efficient generators of the active oxygen (1O2, O2*-) in the aerobic condition. Under the anaerobic condition they generate non-oxygen free radical (semiquinone radical anion), and the active oxygen mechanism of photosensitization can be converted into non-oxygen free radical mechanism with the depletion of oxygen. The quantum yields of 1O2 generation of BADMHA and BADMHB are 0.46 and 0.44, respectively. Both are lower than those of their parent compounds HA and HB. But the productions of superoxide anion are enhanced significantly compared with HA and HB, indicating they are both favorable Type I phototherapeutic agents.

Cyclic N-Oxides↗
PubMed2000

Mechanisms of molecular recognition in the pikromycin polyketide synthase.

BACKGROUND: Modular polyketide synthases (PKSs) produce a wide range of medically significant compounds. In the case of the pikromycin PKS of Streptomyces venezuelae, four separate polypeptides (PikAI-PikAIV), comprising a total of one loading domain and six extension modules, generate the 14-membered ring macrolactone narbonolide. The polypeptide PikAIV contains a thioesterase (TE) domain and is responsible for catalyzing both the last elongation step with methylmalonyl CoA, and subsequent release of the final polyketide chain elongation intermediate from the PKS. Under certain growth conditions this polypeptide is synthesized from an alternative translational start site, giving rise to an N-terminal truncated form of PikAIV, containing only half of the ketosynthase (KS(6)) domain. The truncated form of PikAIV is unable to catalyze the final elongation step, but is able to cleave a polyketide chain from the preceding module on PikAIII (ACP(5)), giving rise to the 12-membered ring product 10-deoxymethynolide. RESULTS: S. venezuelae mutants expressing hybrid PikAIV polypeptides containing acyl carrier protein (ACP) and malonyl CoA specific acyltransferase (AT) domains from the rapamycin PKS were unable to catalyze production of 12- or 14-membered ring macrolactone products. Plasmid-based expression of a hybrid PikAIV containing the native KS(6) and TE domains, however, restored production of both narbonolide and 10-deoxymethynolide in the S. venezuelae AX912 mutant that generates a TE-deleted form of PikAIV. Use of alternative KS domains or deletion of the KS(6) domain within the hybrid PikAIV resulted in loss of both products. Plasmid-based expression of a TE domain of PikAIV as a separate polypeptide in the AX912 mutant resulted in greater than 50% restoration of 10-deoxymethynolide, but not in mutants expressing a hybrid PikAIV bearing an unnatural AT domain. Mutants expressing hybrid PikAIV polypeptides containing the natural AT(6) domains and different ACP domains efficiently produced polyketide products, but with a significantly higher 10-deoxymethynolide/narbonolide ratio than observed with native PikAIV. CONCLUSIONS: Dimerization of KS(6) modules allows in vivo formation of a PKS heterodimer using PikAIV polypeptides containing different AT and ACP domains. In such heterodimers, the TE domain and the AT(6) domain responsible for formation of the narbonolide product are located on different polypeptide chains. The AT(6) domain of PikAIV plays an important role in facilitating TE-catalyzed chain termination (10-deoxymethynolide formation) at the proceeding module in PikAIII. The pikromycin PKS can tolerate the presence of multiple forms (active and inactive) of PikAIV, and decreased efficiency of elongation by PikAIV can result in increased levels of 10-deoxymethynolide. These results provide new insight into functional molecular interactions and interdomain recognition in modular PKSs.

Anti-Bacterial Agents↗
PubMed2000

Improving the quality of care through routine teleradiology consultation.

RATIONALE AND OBJECTIVES: The hypotheses of this study were as follows: (a) University subspecialty radiologists can provide consultations effectively to general radiologists as part of routine clinical operations; (b) these consultations will improve the quality of the final radiologic report; and (c) the consultations will improve the care process and may save money, as well. MATERIALS AND METHODS: For 2,012 consecutive computed tomographic or magnetic resonance (MR) imaging studies, the initial interpretations provided by radiology generalists were subsequently reviewed by specialists, with a final consensus report available. "Truth" was established by final consensus reports. To control for potential bias, 150 adult MR imaging and 250 pediatric radiologic studies were interpreted initially by specialists and then by generalists. Again, truth was established by final consensus reports. RESULTS: There was disagreement between generalist and specialist radiologist interpretations in 427 (21.2%) of the cases reviewed. These disagreements were stratified further by independent specialists, who graded them as important, very important, or unimportant. Differences were considered important or very important in 99% of the cases reviewed. CONCLUSION: Consultations by subspecialty radiologists improved the quality of the radiology reports studied and, at least in some cases, improved the process of care by eliminating unnecessary procedures or suggesting more specific follow-up examinations. The consultation services can be provided cost-effectively from the payer's perspective and may save additional costs when unnecessary procedures can be eliminated.

Humans↗
PubMed2000

Structural basis of pore formation by cholesterol-binding toxins.

In this paper we describe reconstructions by electron cryo-microscopy of two oligomeric states of the pore-forming toxin pneumolysin. The results are interpreted by the fitting of atomic models of separated domains to the 3-dimensional electron density maps, revealing two steps in the mechanism of pore formation by the family of cholesterol-binding toxins. We briefly describe the observation of the toxin pore in model membranes and contrast the apparent mechanism of pneumolysin with that of other pore-forming toxins.

Bacterial Proteins↗
PubMed2000

Evidence of hydroxyl-ion deficiency in bone apatites: an inelastic neutron-scattering study.

The novelty of very large neutron-scattering intensity from the nuclear-spin incoherence in hydrogen has permitted the determination of atomic motion of hydrogen in synthetic hydroxyapatite and in deproteinated isolated apatite crystals of bovine and rat bone without the interference of vibrational modes from other structural units. From an inelastic neutron-scattering experiment, we found no sharp excitations characteristic of the vibrational mode and stretch vibrations of OH ions around 80 and 450 meV (645 and 3630 cm(-1)), respectively, in the isolated, deproteinated crystals of bone apatites; such salient features were clearly seen in micron- and nanometer-size crystals of pure hydroxyapatite powders. Thus, the data provide additional definitive evidence for the lack of OH(-) ions in the crystals of bone apatite. Weak features at 160-180 and 376 meV, which are clearly observed in the apatite crystals of rat bone and possibly in adult mature bovine bone, but to a much lesser degree, but not in the synthetic hydroxyapatite, are assigned to the deformation and stretch modes of OH ions belonging to HPO(4)-like species.

Animals↗
PubMed2000

Characterization of novel glutathione adducts of a non-nucleoside reverse transcriptase inhibitor, (S)-6-chloro-4-(cyclopropylethynyl)-4-(trifluoromethyl)-3, 4-dihydro-2(1H)-quinazolinone (DPC 961), in rats. Possible formation of an oxirene metabolic intermediate from a disubstituted alkyne.

The postulated formation of oxirene-derived metabolites from rats treated with a disubstituted alkyne, (S)-6-chloro-4-(cyclopropylethynyl)-4-(trifluoromethyl)-3, 4-dihydro-2(1H)-quinazolinone (DPC 961), is described. The reactivity of this postulated oxirene intermediate led to the formation of novel glutathione adducts whose structures were confirmed by LC/MS and by two-dimensional NMR experiments. These metabolites were either excreted in rat bile or degraded to mercapturic acid conjugates and eliminated in urine. To demonstrate the oxidation of the triple bond, an analogue of DPC 961 was synthesized, whereby the two carbons of the alkyne moiety were replaced with (13)C stable isotope labels. Rats were orally administered [(13)C]DPC 961 and glutathione adducts isolated from bile. The presence of an oxygen atom on one of the (13)C labels of the alkyne was demonstrated unequivocally by NMR experiments. Administration of (14)C-labeled DPC 961 showed that biliary elimination was the major route of excretion with the 8-OH glucuronide conjugate (M1) accounting for greater than 90% of the eliminated radioactivity. On the basis of radiochemical profiling, the glutathione-derived metabolites were minor in comparison to the glucuronide conjugate. Studies with cDNA-expressed rat enzymes, polyclonal antibodies, and chemical inhibitors pointed to the involvement of P450 3A1 and P450 1A2 in the formation of the postulated oxirene intermediate. The proposed mechanism shown in Scheme 1 begins with P450-catalyzed formation of an oxirene, rearrangement to a reactive cyclobutenyl ketone, and a 1,4-Michael addition with endogenous glutathione to produce two isomeric adducts, GS-1 and GS-2. The glutathione adducts were subsequently catabolized via the mercapturic acid pathway to cysteinylglycine, cysteine, and N-acetylcysteine adducts. The transient existence of the alpha,beta-unsaturated cyclobutenyl ketone was demonstrated by incubating the glutathione adduct in the presence of N-acetylcysteine and monitoring the formation of N-acetylcysteine adducts by LC/MS. Epimerization of GS-1 to GS-2 was also observed when N-acetylcysteine was omitted from the incubation.

Animals↗
PubMed2000

Alpha 1E subunit of the R-type calcium channel is associated with myelinogenesis.

During myelinogenesis, we found an exceedingly strong, transient expression of the alpha(1E) gene for the R-type voltage-gated calcium channel in CNS white matter. This immunoreactivity appeared in glial cells along specific pathways of the brainstem, cerebellum, and telencephalon. The reactivity followed a wave that progressed from the brainstem at P5, to the cerebellar peduncles by P8, the arbor vitae by P14, and the granular layer by P17. The reactivity-peaked about 3-4 days later and decreased gradually to become negligible in all areas before adulthood. Ultrastructural analysis confirmed that alpha(1E) immunoreactivity was located in oligodendroglial somata, their projections, paranodal wraps and loose myelin sheaths. There was a distinct association of the channel protein reactivity on oligodendroglial membranes in contact with the axon. We propose that glial projections, contacting axons, sense axonal firing through small K(+) currents and open the high voltage R-type calcium channels to signal myelination.

Aging↗