Biomedical subjects

S Chen

Publications and source records attributed to S Chen.

At least 91 records · Page 5Linked to original sources

PubMed2005

Studies into using manure in a biorefinery concept.

Animal manure is an underutilized biomass resource containing a large amount of organic carbon that is often wasted with the existing manure disposal practices. A research project funded by the US Department of Energy explored the feasibility of using manure via the sugar platform in a biorefinery, converting the carbon from fiber to biochemicals. The results showed that (1) fiber was the major component of manure dry material making up approx 50%, 40%, and 36% of the dry dairy, swine, and poultry manure material, respectively; within dairy manure, more than 56% of the dry matter was in particles larger than 1.680 mm; (2) in addition to being a carbon source, manure could provide a variety of nutrient for fungi T. reesei and A. phoenicis to produce cellulase; (3) the hemicellulose component in the manure fiber could be readily converted to sugar through acid hydrolysis; while concentrated acid decrystallization treatment was most effective in manure cellulose hydrolysis; (4) purification and separation was necessary for further chemical conversion of the manure hydrolysate to polyols through hydrogenation; and (5) the manure utilization strategy studied in this work is currently not profitable.

Agriculture↗

PubMed2005

Mechanism of inhibition of cytochrome P450 C21 enzyme activity by autoantibodies from patients with Addison's disease.

OBJECTIVE: To study possible mechanisms for the inhibition of cytochrome P450 C21 (steroid 21-hydroxylase) enzyme activity by P450 C21 autoantibodies (Abs) in vitro. DESIGN: Two possible mechanisms for the inhibition of P450 C21 enzyme activity by P450 C21 Abs were studied: (a) conformational changes in the P450 C21 molecule induced by Ab binding and (b) the effects of Ab binding to P450 C21 on the electron transfer from the nicotinamide adenine dinucleotide phosphate reduced (NADPH) cytochrome P450 reductase (CPR) to P450 C21. METHODS: The effect of P450 C21 Ab binding on the conformation of recombinant P450 C21 in yeast microsomes was studied using an analysis of the dithionite-reduced CO difference spectra. The effect of P450 C21 Abs on electron transfer was assessed by analysis of reduction of P450 C21 in the microsomes in the presence of CO after addition of NADPH. RESULTS: Our studies confirmed the inhibiting effect of P450 C21 Abs on P450 C21 enzyme activity. Binding of the Abs did not induce significant change in the P450 C21 peak at 450nm (native form) and did not produce a detectable peak at 420 nm (denatured form) in the dithionite-reduced CO difference spectra. This indicated that conformation of P450 C21 around the heme was not altered compared with the native structure. However, incubation of the P450 C21 in yeast microsomes with P450 C21 Ab inhibited the fast phase electron transfer from the CPR to P450 C21. CONCLUSIONS: Our observations suggested that the mechanism by which P450 C21 Abs inhibit P450 C21 enzyme activity most likely involves inhibition of the interaction between the CPR and P450 C21.

Addison Disease↗

PubMed2005

MRI-guided focused ultrasound treatment of uterine fibroids.

Magnetic resonance imaging-guided focused ultrasound (MRI-FUS) is a minimally invasive alternative to surgical and less invasive treatments for uterine fibroids. Early results from small sample studies indicate that the procedure may provide short-term symptom relief with advantages such as shorter recovery time. Few occurrences of major adverse events are reported. Little information is available on the costs or comparisons with other treatments. Long-term studies of larger patient groups are needed to provide further reliable evidence on the safety of this procedure, as well as its clinical and cost-effectiveness.

Catheter Ablation↗

PubMed2004

The HPLC resolution of N-2,4-dinitrophenylated amino acids and peptides stereoisomers on naphthylethylcarbamate-beta-cyclodextrin bonded phase using the acetonitrile-based mobile phase: evidence for the chiral recognition pattern.

A facile method of enantioresolving a variety of alpha-amino acids and peptides on naphthylethylcarbamate-beta-cyclodextrin bonded phases (i.e., SN- and RN-beta-CDs) under the elution of acetonitrile-based mobile phase makes use of 2,4-dinitrofluorobenzene (DNFB) as the tagging reagent, which undergoes nucleophilic substitution by the free amino group in alkaline medium to give a N-2,4-dinitrophenyl (DNP) derivative. The resolution is better obtained on RN-beta-CD phase and fails to reproduce on the intact beta-cyclodextrin bonded phase under the same chromatographic conditions, which strongly suggests that the observed resolution should be due to the interaction of analyte with naphthylethylcarbamate moiety, not with the residual secondary hydroxyl groups on the beta-cyclodextrin.

Acetonitriles↗

PubMed2004

Proton source size measurements in the eA-->e'ppX reaction.

Two-proton correlations at small relative momentum q were studied in the eA(3He,4He,C,Fe)-->e(')ppX reaction at E(0)=4.46 GeV using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small q was found to be in accordance with theoretical expectations. Sizes of the emission region were extracted, and proved to be dependent on A and on the proton momentum. The size of the two-proton emission region for He was measured in eA reactions for the first time.

Journal Article↗

PubMed2004

Improved measurement of the K+-->pi+nunu; branching ratio.

An additional event near the upper kinematic limit for K+-->pi(+)nunu; has been observed by experiment E949 at Brookhaven National Laboratory. Combining previously reported and new data, the branching ratio is B(K+-->pi(+)nunu;)=(1.47(+1.30)(-0.89))x10(-10) based on three events observed in the pion momentum region 211<P<229 MeV/c. At the measured central value of the branching ratio, the additional event had a signal-to-background ratio of 0.9.

Journal Article↗

PubMed2004

Two-nucleon momentum distributions measured in 3He(e,e'pp)n.

We have measured the 3He(e,e'pp)n reaction at 2.2 GeV over a wide kinematic range. The kinetic energy distribution for "fast" nucleons (p>250 MeV/c) peaks where two nucleons each have 20% or less, and the third nucleon has most of the transferred energy. These fast pp and pn pairs are back to back with little momentum along the three-momentum transfer, indicating that they are spectators. Calculations by Sargsian and by Laget also indicate that we have measured distorted two-nucleon momentum distributions by striking one nucleon and detecting the spectator correlated pair.

Journal Article↗

PubMed2004

Observation of an exotic baryon with S=+1 in photoproduction from the proton.

The reaction gamma p-->pi(+)K(-)K(+)n was studied at Jefferson Laboratory using a tagged photon beam with an energy range of 3-5.47 GeV. A narrow baryon state with strangeness S=+1 and mass M=1555+/-10 MeV/c(2) was observed in the nK(+) invariant mass spectrum. The peak's width is consistent with the CLAS resolution (FWHM=26 MeV/c(2)), and its statistical significance is (7.8+/-1.0)sigma. A baryon with positive strangeness has exotic structure and cannot be described in the framework of the naive constituent quark model. The mass of the observed state is consistent with the mass predicted by the chiral soliton model for the Theta(+) baryon. In addition, the pK(+) invariant mass distribution was analyzed in the reaction gamma p-->K(-)K(+)p with high statistics in search of doubly charged exotic baryon states. No resonance structures were found in this spectrum.

Journal Article↗

PubMed2004

Re-institution of good metabolic control in diabetic rats and activation of caspase-3 and nuclear transcriptional factor (NF-kappaB) in the retina.

Hyperglycemia is one of the major underlying factors in the development of retinopathy in diabetes. Retinal microvascular cells undergo accelerated apoptosis before other histopathological changes are detectable in diabetes. We examined the effect of re-institution of good metabolic control (GC) on the activation of retinal apoptosis executor enzyme, caspase-3, and nuclear transcriptional factor NF-kB. In streptozotocin diabetic rats, two or six months of poor metabolic control (PC) with glycated hemoglobin >11.0% was followed by seven additional months of GC (glycated hemoglobin <5.5%). Caspase-3 activity in retina was measured by the cleavage of its substrate, the expression of active 17 kD subunit, and cleavage of poly(ADP ribosyl) polymerase. NF-kB activation was determined by electrophoretic shift assay and by western blots for P65 subunit. Caspase-3 activity in diabetic rats kept in PC for 13 months was 175% that in normal rats. Re-institution of GC after two months of PC partially normalized the hyperglycemia-induced activation of caspase-3 (to 140% of normal values) while re-institution of GC after six months of PC had no significant effect on the activation of caspase-3 NF-kB activity was 2.5-fold higher in diabetic rats kept in PC than in normal rats. Re-institution of GC after 2 months of PC partially reversed this increase (X-fold over normal), but GC after 6 months of PC had no effect. Initiation of GC soon after induction of diabetes in rats prevented activation of retinal caspase-3 and NF-kB. These results suggest that the process of activation of apoptosis execution enzyme and NF-kB in retina that starts before appearance of histopathological changes is not easily reversed by re-institution of GC. Characterization of the abnormalities responsible for the resistance of retinopathy to halt after re-institution of GC will help identify potential therapies for inhibition of progression of diabetic retinopathy.

Animals↗

PubMed2004

The involvement of microsomal oxidases in pyrethroid resistance in Helicoverpa armigera from Asia.

Five contemporary strains of the bollworm Helicoverpa armigera Hübner from China, Pakistan and India, all with high resistance to pyrethroids, were compared with a standard susceptible strain that originated from the Cote D'Ivoire in the 1970s ('SCD'). Two of the Chinese strains ('YGF' and 'YGFP') were derived by laboratory selection from a third, field collected strain ('YG'). The strain 'YG' exhibited 7-, 14- and 21-fold resistance to fenvalerate, cypermethrin and deltamethrin, respectively. After selection with fenvalerate for 14 generations ('YGF'), this increased to 1690-, 540- and 73-fold. Selection with a mixture of fenvalerate and piperonyl butoxide (PBO) for 14 generations ('YGFP') resulted in resistance ratios of 2510, 2920 and 286. The synergistic ratios to fenvalerate that resulted from pre-treatment of PBO were 5-, 462- and 12-fold in YG, YGF and YGFP strains, respectively. Resistance ratios for a Pakistani strain (PAK) were 2320-, 4100- and 223-fold to fenvalerate, cypermethrin and deltamethrin, respectively. The synergistic ratio of PBO to these pyrethroids was 450-, 950- and 11-fold. The strong synergism of pyrethroids by PBO implied that an oxidative metabolism could be involved in pyrethroid resistance in these resistant strains. The activities of cytochrome P450 monooxygenases from midguts of final instar larvae to p-nitroanisole (PNOD), ethoxycoumarin (ECOD), methoxyresorufin (MROD) significantly increased in all the resistant strains when compared with the susceptible strain. This further implies that cytochrome P450 monooxygenases are involved in pyrethroid resistance in Asian H. armigera. Comparative in vitro studies of the metabolism of 14C-deltamethrin by midgut microsomes of the resistant PAK and susceptible SCD strains showed that the resistant strain had a much greater capacity than the susceptible strain for the metabolic degradation of deltamethrin. This enhanced metabolic degradation occurred in the presence of NADPH which suggested an oxidative detoxification. In the resistant strains, minor increases in glutathione S-transferase activity (to the substrates CDNB and DCNB), and esterase activity (to the substrate alpha-naphthyl acetate) further suggested that, of the putative metabolic mechanisms, oxidases are the most important. This study provides the first evidence that cytochrome P450 monooxygenases are a major metabolic mechanism responsible for pyrethroid resistance in H. armigera from Asia.

Animals↗

PubMed2004

Invulnerability of retinal ganglion cells to NMDA excitotoxicity.

NMDA excitotoxicity has been proposed to mediate the death of retinal ganglion cells (RGCs) in glaucoma and ischemia. Here, we reexamine the effects of glutamate and NMDA on rat RGCs in vitro and in situ. We show that highly purified RGCs express NR1 and NR2 receptor subunits by Western blotting and immunostaining, and functional NMDA receptor channels by whole-cell patch-clamp recording. Nevertheless, high concentrations of glutamate or NMDA failed to induce the death of purified RGCs, even after prolonged exposure for 24 h. RGCs co-cultured together with ephrins, astrocytes, or mixed retinal cells were similarly invulnerable to glutamate and NMDA, though their NMDA currents were 4-fold larger. In contrast, even a short exposure to glutamate or NMDA induced the rapid and profound excitotoxic death of most hippocampal neurons in culture. To determine whether RGCs in an intact retina are vulnerable to excitotoxicity, we retrogradely labeled RGCs in vivo using fluorogold and exposed acutely isolated intact retinas to high concentrations of glutamate or NMDA. This produced a substantial and rapid loss of amacrine cells; however, RGCs were not affected. Nonetheless, RGCs expressed NMDA currents in situ that were larger than those reported for amacrine cells. Interestingly, the NMDA receptors expressed by RGCs were extrasynaptically localized both in vitro and in situ. These results indicate that RGCs in vitro and in situ are relatively invulnerable to glutamate and NMDA excitotoxicity compared to amacrine cells, and indicate that important, as yet unidentified, determinants downstream of NMDA receptors control vulnerability to excitotoxicity.

Amacrine Cells↗

PubMed2004

The influence of brain death on liver in rats.

OBJECTIVE: Donor brain death produces functional and morphological changes in peripheral organs. We examined the influence of brain death on liver function. METHODS: Fifty rats were randomly divided into three groups: controls (C), sham-operated (E1), and brain-dead (E2). All rats underwent tracheotomy with assisted respiration. The sera of rats at 1 and 3 hours after brain death were tested for the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), hyaluronic acid (HA), and endothelin-1 (ET-1). At the end of assisted respiration, liver samples were collected for ultrastructural observation. RESULTS: At 1 and 3 hours, the levels of ALT, AST, HA, and ET-1 in group E2 were significantly higher than those in groups C and E1 (P < .05). The levels of ALT, AST, HA, and ET1 at 3 hours were significantly higher than those at 1 hour (P < .05). Under the electronic microscope, Kupffer cells were activated, sinusoidal endothelial cells (SEC) denuded, fenestration widened, and hepatocytes under the SEC exposed in group E2. In group C and E1, Kupffer cells were not obviously activated and SEC were almost intact. CONCLUSIONS: Brain death damages hepatocytes and nonparenchymal cells in rat. Endothelin-1 and Kupffer cells play an important role in the process. The clearance of hyaluronic acid may provide reliable index to judge SEC function after brain death.

Alanine Transaminase↗

PubMed2004

The role of ischemic preconditioning in rat liver graft.

OBJECTIVE: The objective of this study was to investigate the protective effects of different modes of ischemic preconditioning (IPC) on an ischemia/reperfusion (I/R) injury in rat liver graft. METHODS: A total of 192 Wistar rats were randomly allocated into 4 groups, each including 48 rats: control group (C), experimental group 1 (E(1)), experimental group 2 (E(2)), and experimental group 3 (E(3)). IPC was not performed in group C. Among the animals in the experimental groups, IPC was performed by blocking blood flow by the portal vein and the hepatic artery followed by reperfusion by removal of the clamp before donor liver resection: Group E(1), 5-minute ischemia and 10-minute reperfusion; Group E(2), 5-minute ischemia and 5-minute reperfusion and immediately the same procedure; and Group E(3), 10-minute ischemia and 15-minute reperfusion. Liver transplantations were performed 4 hours after IPC. At 0.5 hour, 2 hours, 6 hours, and 24 hours after portal vein reperfusion recipient blood and graft samples were obtained to determine the levels of ALT, AST, TNF-alpha, and apoptosis index (AI). RESULTS: At 0.5 hour and 2 hours after portal vein reperfusion, serum tumor necrosis factor (TNF)-alpha in the experimental groups (E(1), E(2), and E(3)) was significantly lower than in the control group (P < .05). The values in group E(2) were significantly lower than those in groups E(1) and E(3) (P < .05). At 24 hours serum TNF-alpha in group E(2) was significantly lower than groups C, E(1), and E(3) (P < .05). At 2 hours and 6 hours, AI values in experimental groups (E(1), E(2), and E(3)) were significantly lower than in group C (P < .05). AI in group E(2) was significantly lower than that in groups E(1) and E(3) (P < .05). At 24 hours, AI values among experimental groups (E(1), E(2), and E(3)) were significantly lower than that in the control group (P < .05). CONCLUSION: IPC may attenuate liver graft injury by decreasing apoptosis of hepatocytes and production of TNF-alpha. The method of IPC with 5-minute ischemia and 5-minute reperfusion followed immediately by another cycle of the same procedure was a better way to protect a liver graft from I/R injury.

Alanine Transaminase↗

PubMed2004

Prolongation of skin allograft survival by combined feeding of donor spleen cells and cyclosporine in mice.

BACKGROUND: Oral immune tolerance is a method for inducing donor-specific immunotolerance and prolonging graft survival. OBJECTIVES: We studied the effect of feeding donor spleen cells in combination with cyclosporine (CsA) on skin allograft survival in mice. METHODS: Tail skins from BALB/c (H-2d) female mice were transplanted onto C57BL/6 (H-2b) female mice. The animals were divided into four groups, each with eight mice: group I, untreated controls; group II, treated with spleen cells; group III, treated with CsA; and group IV, treated with spleen cells and CsA. All grafts were inspected daily. Rejection was diagnosed when the graft loss was >80% to 90%. The immune responses of C57BL/6 toward donor mice were examined by delayed-type hypersensitivity (DTH). RESULTS: Survival times of allogeneic skin grafts in groups I, II, III, and IV were 9.9 +/- 0.6, 13.1 +/- 0.6, 14.7 +/- 0.9, and 20.0 +/- 0.7 days, respectively. When compared with group I, the survival times of groups II, III, and IV were prolonged significantly (P < .01). The survival time for group IV was prolonged significantly compared with groups II and III (P < .01). The DTH responses of group IV were decreased significantly in contrast to groups II and III (P < .01). CONCLUSIONS: Feeding donor spleen cells prolonged the survival of skin allografts in mice; combination with CsA led to further prolongation of skin allograft survival.

Animals↗

PubMed2004

Allogeneic T-cell apoptosis induced by interleukin-10-modified dendritic cells: a mechanism of prolongation of intestine allograft survival?

BACKGROUND: Genetic modification of donor dendritic cells (DC) is a potential therapy for allograft rejection. We hypothesized that in vitro interleukin-10 (IL)-10-transfected DC (DC-IL-10) may induce allogeneic T-cell apoptosis, resulting in prolonged allograft survival rat small intestine. METHODS: Myeloid DC from Wistar-Furth rats (RT-1u) were propagated with rrGM-CSFand rrIL-4,then genetically modified to express the hIL-10 gene. Secretion of IL-10 was quantitated by enzyme-linked immunosorbent assay (ELISA). Allogeneic T cells from Lewis (LEW; RT-1(l)) at proliferative responses were determined by MTT assay in primary mixed leukocyte reactions. We then used a combination of DNA agarose gel electrophoresis, acridine orange staining, and Annexin V/propridium iodide assays to examine apoptosis of allogeneic T cells exposed to DC-IL-10. Then 5 x 10(6) donor-derived DC-IL-10 or untransduced DC were injected intravenously 7 days before small intestine transplantation (WF-->LEW). RESULTS: DC-IL-10 showed pronounced impairment of T-cell allostimulatory activity. Apoptotic T cells were detected in the DC-IL-10 group. Flow cytometry counting at 72 hours showed 45.1% apoptotic T cells in response to DC-IL-10, whereas the untransduced group did not undergo significant apoptosis (P < .01). DC-IL-10 pretreated recipients showed moderate prolongation of allograft survival compared with controls (20.7 +/- 6.0 days vs 7.5 +/- 2.2 days, P < .01). CONCLUSIONS: DC-IL-10 induced allogeneic T-cell hyporesponsiveness in vitro, possibly due to apoptosis. DC-IL-10 pretreated recipients displayed prolonged intestinal allograft survival rates.

Animals↗

PubMed2004

The study of new SLA classical molecules in inbreeding Chinese Wuzhishan pig.

UNLABELLED: The pig may be used as an alternative organ donor source in the future. The Wuzhishan miniature pig (WZSP) is a Chinese inbred mini pig with the highest inbreeding coefficient and has been used in many biologic experiments. We studied the classical MHC molecules of WZSP to confirm its pure gene background and to provide information for xenotransplantation. METHODS: The classical class I (P1 and P14) and class II (DQA, DQB, DRA, and DRB) molecules were studied using RT-PCR. The products were cloned into a pGEM-T vector, respectively, sequenced and compared with related data for homology analysis. RESULTS: WZSP is highly homologous (>90%) with NIH miniature swine for class I and class II molecules amino acids in alpha-3 domain responsible for the binding of human T-cell CD8 were largely conserved; only two critical residues were altered. The critical residues of class I molecules recognized by human natural killer (NK) cells were completely different from humans. Furthermore, new class II molecules were homologous (>70%) with the Chinese south population in amino acids. The amino acids for binding to human CD4 were identical in DRB and showed only two differences in DRA. CONCLUSIONS: WZSP bears new alleles in porcine MHC-relevant loci. We might alter residues of class I molecules to avoid killing by human NK cells. The striking similarities of DRB would make WZSP less likely in compatible in xeno-rejection. We can also alter the two residues of the DRA sequence to make WZSP a better model for xenotransplant research in China.

Animals↗

PubMed2004

A study of HLA-G1 protection of porcine endothelial cells against human NK cell cytotoxicity.

UNLABELLED: Human natural killer (NK) cells, which can directly lyse porcine endothelial cells, play an important role in xenotransplantation. HLA-G is a nonclassical major histocompatibility complex (MHC) class I molecules that has been implicated in protecting susceptible target cells from lysis by NK cells. The objective was to study the effect of protecting porcine endothelial cells transfected with HLA-G1 from human NK cell lysis. METHODS: The recombinant expression vector pcDNA3-HLA-G1 was transfected into primary cultured porcine aortic endothelial cells (PAECs) by lipofection. Surface expression of HLA-G1 in transected PAECs was confirmed by an immunofluoresence technique. Peripheral blood mononuclear cells (PBMC) and NK cell line (NK92) were used as NK effects cells with pcDNA3-HLA-G1-transfected PAECs as targets in a MTT method using pcDNA3 transfection as a negative control. RESULTS: Expression of HLA-G1 on PAECs conferred significant protection against NK-mediated lysis. The rate of NK92 cytotoxicity was reduced to 41.5% +/- 14.0% from 75.3% +/- 10.5% in the control group (P < .01). Similarly the rate of the PBMC cytotoxicity among different donors (n = 7) was reduced to 45.4% +/- 12.1% in contrast to 74.6% +/- 11.2% in the control group (P < .05). CONCLUSIONS: HLA-G1 molecules can directly protect xenogeneic PAECs against attack by human NK cells. These results indicate that the expression of HLA-G1 on the porcine cell surface may provide a new approach to overcome NK-mediated immunity to xenografts.

Animals↗

PubMed2004

Prolonged heart allograft survival resulted from donor-specific T-cell sequestering and removal by selective splenectomy in mice.

INTRODUCTION: Selective splenectomy when donor antigen-specific activated T cells are sequestered in the recipient spleen may prolong allograft survival because of removal of all of these T cells. OBJECTIVES: We investigated the effect on cardiac allograft survival in mice by means of removal of activated specific T cells by splenectomy. METHODS: Donor (Balb/c) spleen cells were injected into primed allogeneic recipients (C57BL/6). Selective recipient splenectomy and donor-type cervical heart grafting in Balb/c to C57BL/6 from mice were examined at 0, 24, 48, and 72 hours after donor spleen cell infusion. RESULTS: Control C57BL/6 mice rejected Balb/c heart grafts at 6.86 +/- 0.19 days. Delayed heart grafting plus splenectomy at 24 or 48 hours after donor-type spleen cell infusion significantly prolonged heart allograft survival (24 hours: 15.86 +/- 3.44 days, P < .001; 48 hours: 21.71 +/- 5.22 days, P < .001, respectively). However, 72-hour delayed heart grafting plus splenectomy failed to prevent acute rejection (72 hours: 9.57 +/- 2.51 days, P > .01). Immunohistochemistry showed, at 24 to 48 hours after donor antigen infusion, the recipient spleens characterized by an obvious increase in CD4+ CD8+ T cells in periateriolar lymphoid sheaths, marginal zones, and red pulp compared with the 72-hour group. CONCLUSIONS: Transient accumulation of donor-specific activated T cells in the spleen of recipients provide an opportunity to remove all of these T cells by a surgical procedure. As the largest immune organ the spleen is the main place where T cells are activated and regenerated. At 24 or 48 hours when donor-specific T cells were sequestered in the spleen after donor antigen stimulation, selective recipient splenectomy was able to remove the T cells and prolong was allograft survival. Refinement of this protocol may eventually warrant clinical application.

Animals↗