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Biomedical subjects

E Choi

Publications and source records attributed to E Choi.

At least 37 records · Page 2Linked to original sources
PubMed2002

Optimization of nitrogen removal from piggery waste by nitrite nitrification.

The piggery waste characteristics greatly vary with types of manure collections and the amount of water used. If solids are separated well, the waste strength will be greatly reduced resulting in lower TCOD/TKN ratio of 4 (average). If solids are separated by a mechanical scraper, some solids will remain and the waste strength will be increased with a TCOD/TKN ratio of 7. This study was conducted to find an optimum operating condition for nitrogen removal with these two ratios. Nitrite nitrification was targeted because it could be a short cut process for savings in oxygen for nitrification and carbon requirements for denitrification. The study results indicated that nitrogen loading rate and pH were the most important factors to be considered for stable nitrite nitrification. The applicable nitrogen loads were estimated to be 0.3 to 2.0 kgTKN/oxic m3/d for high TCOD/TKN ratio without pH control. With higher pH > 8, NO2N/NOxN ratios in oxic stages even with lower nitrogen loads were increased. The SBR with low TCOD/TKN ratio less than 4 required additional alkalinity. For a complete denitrification, the influent TCOD/TKN ratio must exceed 6 with oxic/total reactor volume ratio of 0.5. Nitrite nitrification and denitrification could save about 35% in tank volume and 50% in carbon requirement, respectively. However, 9.5% oxygen saving could be expected during the operation with low TCOD/TKN ratio. The elevated temperature due to the heat released from COD removal also enhanced microbial activities for nitrification and denitrification as well as ammonia stripping. However, careful attention must be provided for the reactor temperature not to inhibit the nitrification process.

Agriculture↗
PubMed2002

Strategy for nitrogen removal from piggery waste.

This study was conducted with an influent containing about 20% solids, obtainable from scraper type separation resulting in about 40 g/L TCOD and 5.5 g/L TKN, to find an optimum operating condition for nitrogen removal. Both laboratory scale reactors and a full scale treatment plant removed 80 to 90% nitrogen by biological means up to 35 degrees C with 10% by ammonia stripping. The full scale plant however was operated at 35 to 45 degrees C, and at 45 degrees C, 30% nitrogen was removed by biological means, 50% by ammonia stripping, 14% by chemical coagulation and 6% by activated carbon adsorption, respectively. Struvite formation could not be observed at 30 degrees C or higher. Nitrite nitrification and denitrification could save about 35% in tank volume and 50% in carbon requirements at 25 degrees C, respectively. For a complete denitrification with a proper temperature, the influent TCOD/TKN ratio must exceed 6 with oxic/total reactor volume ratio of 0.5. The influent TCOD level or organic load should be lower so as not to increase the reactor temperature above 35 degrees C and avoid nitrification inhibition. The estimated optimum nitrogen loading rates were 0.15 for summer and 0.23 kg TKN/m3/d for winter, respectively. With a cooling facility, the nitrogen loads could be increased to 0.35 kg TKN/m3/d equivalent to an organic loading rate of 2.5 kg COD/m3/d.

Adsorption↗
PubMed2002

The nomographic design approach to recycled water reatment by the nitritation process.

The side-stream generated recycled water in the wastewater treatment plants is characterized as high in both nitrogen concentration and fluctuation of load. Thus, the design approach for recycle water management became an important part of the biological nutrient removal system design. The application of nitrogen removal from recycled water using the nitritation process has recently been increased due to economical reasons associated with an effective carbon allocation as well as the minimization of aeration cost. The concept of nitritation reactor design related to an inhibition of nitrite oxidizer has not been fully practiced in reality because of the limited field experiences. In this paper, a new approach has been proposed to determine reactor size and oxygen requirement in nitritation process design. The SRT-based design approach has been examined based on a series of laboratory experiments.

Bioreactors↗
PubMed2001

Tripartite structure of Saccharomyces cerevisiae Dna2 helicase/endonuclease.

In order to gain insights into the structural basis of the multifunctional Dna2 enzyme involved in Okazaki fragment processing, we performed biochemical, biophysical and genetic studies to dissect the domain structure of Dna2. Proteolytic digestion of Dna2 using subtilisin produced a 127 kDa polypeptide that lacked the 45 kDa N-terminal region of Dna2. Further digestion generated two subtilisin-resistant core fragments of approximately equal size, 58 and 60 kDa. Surprisingly, digestion resulted in a significant (3- to 8-fold) increase in both ATPase and endonuclease activities compared to the intact enzyme. However, cells with a mutant DNA2 allele lacking the corresponding N-terminal region were severely impaired in growth, being unable to grow at 37 degrees C, indicating that the N-terminal region contains a domain critical for a cellular function(s) of Dna2. Analyses of the hydrodynamic properties of and in vivo complex formation by wild-type and/or mutant Dna2 lacking the N-terminal 45 kDa domain revealed that Dna2 is active as the monomer and thus the defect in the mutant Dna2 protein is not due to its inability to multimerize. In addition, we found that the N-terminal 45 kDa domain interacts physically with a central region located between the two catalytic domains. Our results suggest that the N-terminal 45 kDa domain of Dna2 plays a critical role in regulation of the enzymatic activities of Dna2 by serving as a site for intra- and intermolecular interactions essential for optimal function of Dna2 in Okazaki fragment processing. The possible mode of regulation of Dna2 is discussed based upon our recent finding that replication protein A interacts functionally and physically with Dna2 during Okazaki fragment processing.

Adenosine Triphosphatases↗
PubMed2001

Inhibitory effect of YC-1 on the hypoxic induction of erythropoietin and vascular endothelial growth factor in Hep3B cells.

YC-1 is a newly developed agent that inhibits platelet aggregation and vascular contraction. Although its effects are independent of nitric oxide (NO), it mimics some of the biological actions of NO. For example, it stimulates soluble guanylate cyclase (sGC) and increases intracellular cGMP concentration. Here, we tested the possibility that YC-1 inhibits hypoxia-inducible factor (HIF)-1-mediated hypoxic responses, as does NO. Hep3B cells were used during the course of this work to observe hypoxic induction of erythropoietin (EPO) and vascular endothelial growth factor (VEGF), and the effects of YC-1 were compared with those of a NO donor, sodium nitropurruside (SNP). In hypoxic cells, YC-1 blocked the induction of EPO and VEGF mRNAs, and inhibited the DNA-binding activity of HIF-1. It suppressed the hypoxic accumulation of HIF-1alpha, but not its mRNA level. It also reduced HIF-1alpha accumulation induced by cobalt and desferrioxamine. Treatment with antioxidants did not recover the HIF-1alpha suppressed by YC-1. We examined whether these effects of YC-1 are related to the sGC/cGMP signal transduction system. Two sGC inhibitors examined failed to block the effects of YC-1, and 8-bromo-cGMP did not mimic actions of YC-1. The effects of YC-1 on the hypoxic responses were comparable with those of SNP. These results suggest that YC-1 and SNP suppressed the hypoxic responses by post-translationally inhibiting HIF-1alpha accumulation. The YC-1 effect may be linked with the metal-related oxygen sensing pathway, and is not due to the stimulation of sGC. This observation implies that the inhibitory effects of YC-1 on hypoxic responses can be developed to suppress EPO-overproduction by tumor cells and tumor angiogenesis.

Cell Hypoxia↗
PubMed2001

The alterations of N-Methyl-D-aspartate receptor expressions and oxidative DNA damage in the CA1 area at the early time after ischemia-reperfusion insult.

Delayed neuronal death in the CA1 of the hippocampus following global ischemia has been evoked by both the activation of N-methyl-D-aspartate receptor (NR) and the generate reactive oxygen species in the neurons. In the present study, we investigated whether oxidative DNA damages may be correlated with NR subunits (NR1 and NR2A/B) expression following ischemia insults in vivo. Thirty minutes after ischemia-reperfusion, the intensities of both NR and 8-hydroxy-2'-deoxyguanosine (8-OHdG) immunoreactivities were markedly increased in neurons of CA1. However, NR2A/B and 8-OHdG immunoreactivities were enhanced in CA1 over 24 h after ischemia although NR1 immunoreactivity was decreased. These results suggest that oxidative stress and excitotoxicity in the CA1 may simultaneously trigger neuronal damages at early time after ischemia, and free radical damage including oxidative DNA damage may eventually promote the delayed neuronal death in this region.

Animals↗
PubMed2001

NUR and our relationship in BNR processes with sewage at different temperatures and its design application.

Denitrification is known as an essential part of a biological nutrient removal (BNR) process to remove nitrogen and it also affects phosphorus removal. However, an accurate prediction of nitrogen removal is extremely difficult because there are too many factors involved. This study was conducted to find a relationship between nitrate uptake rate (NUR) and carbonaceous oxygen uptake rate (OUR) and develop a simple method to predict applicable NUR for the design of various BNR processes. Sewage was subdivided into soluble and particulate organic fractions. NUR/OUR ratios were measured by respirometer with these organic fractions and the test sludges grown at various BNR processes and temperatures. NUR/OUR ratios were varied with the types of organic fractions of sewage and temperature. The NURs predicted from the NUR/OUR ratios and computed OUR based on the total tank volume of anoxic and oxic stages with the influent sewage characteristics were very much comparable with the observed NURs from various BNR processes.

Nitrogen↗
PubMed2001

Sildenafil citrate effectively reverses sexual dysfunction induced by three-dimensional conformal radiation therapy.

OBJECTIVES: We evaluated the response of sildenafil citrate in patients with prostate cancer treated with three-dimensional conformal radiation therapy (3DCRT) whose sexual function (SF) was known prior to therapy initiation. METHODS: From March 1996 to April 1999, 24 men with median age of 68 years (range 51 to 77) had 3DCRT for localized prostate cancer (median prescribed dose to the planning target volume of 70.2 Gy). These men started taking sildenafil for relief of sexual dysfunction at a median time of 1 year after completing 3DCRT. We used the self-administered O'Leary Brief Sexual Function Inventory to evaluate in series SF and overall satisfaction at three time points. These points were (a) before initiation of all therapies (3DCRT or hormonal treatment [HT]) for prostate cancer, (b) before starting sildenafil (50 mg or 100 mg) but after completion of all therapies, and (c) at least 2 months afterward. Rates of SF were based on the number of men responding to a given question. We tested for significance of these two interventions to change SF by applying the Wilcoxon sign rank test. RESULTS: Prior to all treatments, 20 (87%) of 23 men were sexually potent, with 8 (36%) of 22 fully potent (little or no difficulty for penetration at intercourse). After 3DCRT with or without HT and prior to sildenafil use, 13 (65%) of the 20 potent patients remained potent, with only 2 (11%) of 19 being fully potent. The use of sildenafil citrate resulted in 21 (91%) of 23 men being potent, with 7 (30%) being fully potent. In 16 men responding to the satisfaction question, 10 (63%) and 12 (75%) were mixed to very satisfied with their sex life before 3DCRT with or without HT and after sildenafil citrate use, respectively. This response corresponded to potency and satisfaction scores significantly decreasing and subsequently increasing on average by one unit after 3DCRT and sildenafil citrate use, respectively (P <0.05). CONCLUSIONS: In men receiving 3DCRT for prostate cancer, these data indicate that sildenafil citrate is effective for restoring SF and associated satisfaction back to baseline before treatment.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2001

Polymorphisms in inflammatory cytokines and Fcgamma receptors in childhood chronic immune thrombocytopenic purpura: a pilot study.

Inflammatory cytokines and low-affinity Fcgamma receptor (FcgammaR) polymorphisms were investigated in 37 children with chronic immune thrombocytopenic purpura (cITP) and 218 controls. Genotype analysis included common variants in the regulatory regions of cytokines, TNF, LTA, IL1RN, IL1A, IL1B, IL4, IL6 and IL10, and structural variants of the low affinity FcgammaRs, FCGR2A, FCGR3A and FCGR3B. Associations were observed for TNF (P = 0.0032), LTA (P = 0.019), FCGR3A (P = 0.038) and FCGR3B (P = 0.0034). Two combinations of genotypes (TNF and FCGR3A; P = 0.0003, and LTA and FCGR3B; P = 0.011) were significantly associated with cITP. These results provide preliminary evidence that variant genotypes of FcgammaRs and cytokines contribute to cITP pathogenesis.

Case-Control Studies↗
PubMed2001

A new HIF-1 alpha variant induced by zinc ion suppresses HIF-1-mediated hypoxic responses.

The expressions of hypoxia-inducible genes are upregulated by hypoxia-inducible factor 1 (HIF-1), which is a heterodimer of HIF-1alpha and HIF-1beta/ARNT (aryl hydrocarbon receptor nuclear transporter). Under hypoxic conditions, HIF-1alpha becomes stabilized and both HIF-1alpha and ARNT are translocated into the nucleus and codimerized, binding to the HIF-1 consensus sequence and transactivating hypoxia-inducible genes. Other than hypoxia, cobalt and nickel, which can substitute for iron in the ferroprotein, induce the stabilization of HIF-1alpha and the activation of HIF-1. We found previously that, although zinc, another example of a metal substitute for iron, stabilized HIF-1alpha, it suppressed the formation of HIF-1 by blocking the nuclear translocation of ARNT. Here, we identify a new spliced variant of human HIF-1alpha that is induced by zinc. The isoform lacks the 12th exon, which produced a frame-shift and gave a shorter form of HIF-1alpha (557 amino acids), designated HIF-1alphaZ (HIF-1alpha induced by Zn). This moiety was found to inhibit HIF-1 activity and reduce mRNA expressions of the hypoxia-inducible genes. It blocked the nuclear translocation of ARNT but not that of endogenous HIF-1alpha, and was associated with ARNT in the cytosol. These results suggest that HIF-1alphaZ functions as a dominant-negative isoform of HIF-1 by sequestering ARNT in the cytosol. In addition, the generation of HIF-1alphaZ seems to be responsible for the inhibitory effects of the zinc ion on HIF-1-mediated hypoxic responses, because the expressed HIF-1alphaZ behaved in the same manner as zinc in terms of inhibited HIF-1 activity and ARNT translocation.

Active Transport, Cell Nucleus↗
PubMed2001

Phosphorus removal from SBR with controlled denitrification for weak sewage.

Most SBRs operating for weak sewage have a tendency of poor removal of phosphorus due to NO3N inhibition. To minimize this inhibition, NO3N storage was utilized in this study. With influent BOD 100 mg/L and VFA 30 mg/L, a total of the maximum removable nitrogen and phosphorus was about 25 mg/L with 8 hr cycle. With this storage, VFA utilized for phosphorus removal could be maximized. The effluent nitrogen and phosphorus levels were generally 11 and 1 mg/L, respectively.

Bioreactors↗
PubMed2001

Extracellular polymeric substances in relation to nutrient removal from a sequencing batch biofilm reactor.

Experimental investigations were performed to determine the possibility of simultaneous biological nitrogen and phosphorus removal during various biofilm processes in conjunction with biofilm characterisation, especially extracellular polymeric substance (EPS). Since biologial nitrogen removal requires an alternating exposure of anaerobic-anoxic-oxic conditions in the bulk liquid that surrounds the biofilm growth media, a sequencing batch reactor (SBR)-type operation was used. Various materials including expanded clay, polystyrene, polyurethane, and acrylic materials were used as the biofilm growth support medium. Simultaneous nitrogen and phosphorus removal was possible with SBR, but it was postulated that nutrient removal efficiencies varied with film thickness. Thinner biofilm promoted nitrification and phosphorus removal, but thicker biofilm enhanced denitrification and reduced phosphorus removal. EPS contents were similar regardless of support media types or biofilm configuration, but EPS contents gradually increased as the film growth continued after backwashing. EPS contents were increased with increased nitrogen removal, but it was difficult to define its relation with phosphorus removal. In addition, suspended solids removal was correlated well with the EPS content in the biofilms.

Biofilms↗
PubMed2000

Molecular cloning and characterization of a protein tyrosine phosphatase enriched in testis, a putative murine homologue of human PTPMEG.

Protein tyrosine phosphorylation is regulated by protein tyrosine kinase and protein tyrosine phosphatase activities. These two counteracting proteins are implicated in cell growth and transformation. Using polymerase chain reaction with degenerate primers, we have identified a novel mouse protein tyrosine phosphatase (PTP). This cDNA contains a single open reading frame of the predicted 926 amino acids. Those predicted amino acids showed significant identity with human megakaryocyte protein-tyrosine phosphatase by 91% in nucleotide sequences and 94% in amino acid sequences. We have identified that expression of this PTP is highly enriched in the testis in mouse and human and has been termed here as a 'testis-enriched phosphatase' (TEP). Northern analysis detected two mRNA species of 3.7 and 3.2kb for this PTP in mouse testis and the expression of TEP is regulated during development. The recombinant phosphatase domain possesses protein tyrosine phosphatase activity when expressed in Escherichia coli. Immunohistochemical analysis of the cellular localization of TEP on mouse testis sections showed that this PTP is specifically expressed in spermatocytes and spermatids within seminiferous tubules, suggesting an important role in spermatogenesis.

Amino Acid Sequence↗
PubMed2000

Zinc induces the accumulation of hypoxia-inducible factor (HIF)-1alpha, but inhibits the nuclear translocation of HIF-1beta, causing HIF-1 inactivation.

The replacement of heme iron by cobalt or nickel in a putative oxygen sensor is supposed to reduce oxygen binding to the heme protein, resulting in HIF-1 activation and erythropoietin (EPO) induction. According to this hypothesis, zinc might be another example of a transition metal which is capable of stimulating EPO production. By substituting for heme iron, zinc protoporphyrin IX is produced, which has a known low oxygen affinity. However, it has been reported that zinc fails to induce EPO in normoxia, and that it suppresses EPO production in hypoxic cells. This unexpected effect of zinc on EPO production is not understood. In this study, we found that zinc induced the accumulation and nuclear translocation of hypoxia-inducible factor (HIF)-1alpha but inhibited the nuclear translocation of HIF-1beta, which inactivated HIF-1 and suppressed EPO mRNA induction in hypoxic cells.

Biological Transport↗
PubMed2000

"Malgun" (clear) cell change of gastric epithelium in chronic Helicobacter pylori gastritis.

To characterize the Helicobacter pylori gastritis-associated epithelial change, we analyzed 251 randomly selected gastric biopsies. The "malgun" (clear) cell change of the gastric epithelium was noted in 229 biopsies (91.2%). Malgun cells were characterized by large, pale nuclei with a euchromatin pattern, enlarged nucleoli, and clear cytoplasm. In the proliferative zone, individual malgun cells and small clusters were often in close contact with infiltrating neutrophils, suggesting that they had developed individually in the background of acute foveolitis. Mitotic figures of malgun cells were not infrequent, including atypical ones. In the surface epithelium, most malgun cells were in clusters that were often large enough to occupy wide epithelial segments. With Warthin-Starry triple staining, they were distinguished by the absence of silver impregnation, while other cells showed staining of the heterochromatin. They displayed prominent immunostaining for low molecular weight cytokeratin (No. 8). Most malgun cells were PCNA-positive in both surface and proliferative zones, whereas Ki67-positive cells were found only in the proliferative zone. It was suggested that a population of malgun cells, which were positive for PCNA only, were in the process of active DNA repair. The malgun cell change may represent a "cellular pattern of activation" in a population which had significant DNA damage, but somehow escaped the detection by the apoptosis system. The notion of "damage at the genetic level" was supported by the observation that these cells remained at least for 8 weeks after eradication of the H. pylori infection.

Adult↗