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Biomedical subjects

C H Koh

Publications and source records attributed to C H Koh.

13 recordsLinked to original sources
PubMed2000

Influences of dietary uptake and reactive sulfides on metal bioavailability from aquatic sediments.

Understanding how animals are exposed to the large repository of metal pollutants in aquatic sediments is complicated and is important in regulatory decisions. Experiments with four types of invertebrates showed that feeding behavior and dietary uptake control bioaccumulation of cadmium, silver, nickel, and zinc. Metal concentrations in animal tissue correlated with metal concentrations extracted from sediments, but not with metal in porewater, across a range of reactive sulfide concentrations, from 0.5 to 30 micromoles per gram. These results contradict the notion that metal bioavailability in sediments is controlled by geochemical equilibration of metals between porewater and reactive sulfides, a proposed basis for regulatory criteria for metals.

Animals↗
PubMed2000

The differentiation-specific factor CDP/Cut represses transcription and replication of human papillomaviruses through a conserved silencing element.

The life cycles of human papillomaviruses (HPVs) are intimately linked to the differentiation program of infected stratified epithelia, with both viral gene expression and replication being maintained at low levels in undifferentiated basal cells and increased upon host cell differentiation. We recently identified, in HPV-16, a negative regulatory element between the epithelial-cell-specific enhancer and the E6 promoter that is capable of silencing E6 promoter activity, and we termed this element a papillomavirus silencing motif (PSM) and the unknown cellular factor that bound to it PSM binding protein (PSM-BP). Here we show that the homologous genomic segments of six other distantly related genital HPV types contain a PSM that binds PSM-BP and is capable of repressing transcription. Conservation of the PSM suggests that it is indispensable for the HPV life cycle. Purification, electrophoretic mobility shift assay experiments, and the use of specific antibodies proved that the cellular factor PSM-BP is identical to a previously described transcriptional repressor, the CCAAT displacement protein (CDP), also referred to as the human Cut protein (Cut). CDP/Cut repression of HPV-16 may stem from the modification of specifically positioned nucleosomes, as suggested by transcriptional stimulation under the influence of the histone deacetylase inhibitor trichostatin A. CDP/Cut is an important developmental regulator in several different tissues. It was recently shown that CDP/Cut is expressed in basal epithelial cells but not in differentiated primary keratinocytes. This suggests the possibility that repression by PSM couples HPV transcription to the stratification of epithelia. In each of the studied HPV types, the two CDP/Cut binding sites of PSM overlap with the known or presumed binding sites of the replication initiator protein E1. Transfection of CDP/Cut expression vectors into cells that support HPV-16 or HPV-31 replication leads to the elimination of viral episomes. Similarly, two PSM-like motifs overlapping the E1 binding site of bovine papillomavirus type 1 bind CDP/Cut, and CDP/Cut overexpression reduces the copy number of episomally replicating BPV-1 genomes in mouse fibroblasts. CDP/Cut appears to be a master regulator of HPV transcription and replication during epithelial differentiation, and PSMs are important cis-responsive targets of this repressor.

Animals↗
PubMed1999

Assessment of metal pollution in Onsan Bay, Korea using Asian periwinkle Littorina brevicula as a biomonitor.

Cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn) concentrations in the marine gastropod, Littorina brevicula Philippi, were determined to assess the metal pollution in Onsan Bay, Korea. Samples of L. brevicula employed as a biomonitor and seawater were collected from 12 to 20 stations of Onsan Bay in November 1997, respectively. Dissolved metal concentrations in surface seawater were highest at the station near Onsan Non-ferrous Industrial Complex: 1.15 micrograms l-1 for Cd, 2.49 micrograms l-1 for Pb, 3.75 micrograms l-1 for Cu and 23.98 micrograms l-1 for Zn. These values were 1-2 orders higher than those shown at outer regions of the Bay. Metal concentrations in the soft body of periwinkles were highly variable at different sampling locations: 0.48-27.11 micrograms g-1 for Cd, 1.41-24.91 micrograms g-1 for Pb, 57-664 micrograms g-1 for Cu and 83-246 micrograms g-1 for Zn. The values from stations near the industrial complex were higher than those expected from relationships between body sizes and metal body burdens in periwinkles collected from the whole Korean coast. Spatial distribution of metal concentrations in the periwinkle and seawater indicated that Onsan industrial complex near the Bay is the input source of these metals. Especially, Cd and Pb concentrations in the periwinkle and seawater were distinctly decreased with distance from the Onsan industrial complex. Non-essential metals such as Cd and Pb in the periwinkle showed a strong correlation with dissolved metal concentrations in seawater. Conversely, essential Cu and Zn in the periwinkle were hardly explained by those in seawater, except at the most contaminated sites.

Animals↗
PubMed1999

Laparoscopic microsurgical tubal anastomosis.

The authors explored the feasibility of performing true microsurgery through the laparoscope in 1990. The first laparoscopic microsurgical tubal anastomosis was performed in February 1992. Operative laparoscopy will continue to expand as technical feasibility continues to improve, driven by both hardware advances and increased surgical dexterity. Laparoscopic microsurgery will introduce a new dimension to reproductive surgery and over time, will replace laparotomy for microsurgery.

Anastomosis, Surgical↗
PubMed1999

Laparoscopic microsurgery: current and future status.

The successful introduction of microsuturing and microinstruments for operative laparoscopy has allowed the convergence of laparoscopy and traditional microsurgery, resulting in the evolution of the 'new microsurgery'. This more dynamic approach overcomes the limitations of open microsurgery by providing continuous magnification and the benefits of a closed environment, making laparoscopy a complete surgical tool. The test model for microsurgery is tubal anastomosis, which is very dependent on operative technique to attain well-established pregnancy rates. Our cumulative pregnancy results for laparoscopic microsurgical tubal anastomosis of 76% at 12 months, 70% at 9 months, 67% at 6 months and 44% at 3 months, compares favorably to the best results achieved by traditional open microsurgery. With this validation the technique is now employed as a complete solution for all tubal surgery. The ability to effect microsurgical repair of the ureter, bladder, bowel and vessels has expanded the surgical repertoire, allowing radical excision of deep endometriosis, severe enterolysis, and adhesiolysis.

Anastomosis, Surgical↗
PubMed1998

A new technique and system for simplifying total laparoscopic hysterectomy.

Because total laparoscopic hysterectomy (TLH) is technically challenging, laparoscopic-assisted vaginal hysterectomy is often the operation of choice, even in patients in whom it may not be successful. To encourage greater performance of TLH, I developed a technique and instrumentation that should enable gynecologists to do the operation successfully more often. The system consists of a pneumo-occluder and a cup, combined with a uterine manipulator. The cup, which is both visible and palpable, is placed over the cervix to delineate vaginal fornices, thus ensuring safe desiccation and avoiding ureteral dissection. Acceptable operating times allow TLH to be combined with other procedures, including excision of endometriosis, colposuspension, and enterocele repair.

Equipment Design↗
PubMed1998

A novel YY1-independent silencer represses the activity of the human papillomavirus type 16 enhancer.

Regulation of the human papillomavirus type 16 (HPV-16) E6 promoter is a complex process in which transcriptional repression as well as activation plays an important role. Here, we identify a negative regulatory element that in the context of a continuous long control region fragment overcomes the activation of the HPV-16 enhancer. This silencing element, which we have termed a PSM (papillomavirus silencing motif), consists of two copies of the sequence 5'-TAYAATAAT-3' that overlap the origin of replication. Each copy of this 9-bp sequence binds the same unknown cellular factor, which we refer to as PSM-BP (PSM binding protein). Both copies of the binding sequence are required for transcriptional repression, and we provide evidence that suggests that this particular organization results in the stabilization of a PSM-BP dimer. The silencing motif, while functioning in either orientation, showed a positional requirement between the enhancer and the promoter. Experiments with both a heterologous enhancer and a promoter also demonstrated a general ability of this element to function as a transcriptional silencer in non-HPV systems. Our findings provide an important addition to our understanding of HPV-16 gene regulation and an interesting model for the study of transcriptional repression.

Base Sequence↗
PubMed1998

Vinorelbine induces apoptosis and caspase-3 (CPP32) expression in leukemia and lymphoma cells: a comparison with vincristine.

Vinorelbine (NVB) is a novel vinca alkaloid FDA approved for use in some advanced carcinomas. However, its role in non-Hodgkin's lymphoma (NHL) is still not well defined. NVB is an antimicrotubule agent, but as yet, it is not known whether it induces apoptosis. By flow cytometry using nuclear staining (propidium iodide) and annexin V, we demonstrated that NVB and vincristine (VCR) induced both mitotic arrest and apoptosis in leukemia and lymphoma cells, in a drug exposure time dependent manner. Cell cycle kinetics in 3 different cell lines varied during vinca alkaloid treatment. The annexin V method showed that apoptosis, as opposed to necrosis, was the dominant mode of cell kill of chemosensitive leukemia and lymphoma cells. Phosphatidylserine expression on the cell surface was detectable as a hallmark of apoptosis at earlier drug exposure when compared to conventional flow cytometry with PI staining. By Western blot analysis, we demonstrated that CPP32 or caspase-3, a critical apoptosis inducer, and its active subunits p20 and p11 were upregulated in chemo- and apoptosis-sensitive lymphoma and leukemia cells treated with NVB. Our data contributes to the emerging hypothesis suggesting that widely divergent exogenous stimuli and chemotherapeutic agents can effect apoptosis in cancer cells via different pathways involving the caspases. We believe that vinorelbine may be a potentially important drug in the treatment of NHL in the future.

Annexin A5↗
PubMed1995

A ring-shaped lateral meniscus.

Ring-shaped lateral meniscus has not previously been reported. We report a case of ring-shaped lateral meniscus with ruptured anterior cruciate ligament.

Adult↗
PubMed1987

Chronic myeloid leukemia presenting as a gynecological emergency.

An unusual case of chronic myeloid leukemia presenting to the gynecological unit as a case of septic abortion is presented. Though history and clinical examination suggested the possibility of double pathology of septic abortion and chronic myeloid leukemia, histology of the products removed from the uterus showed it to be leukemic deposits. The diagnosis of leukemia was confirmed by marrow aspiration (trephine biopsy). Careful clinical examination and systematic investigation helped in diagnosing the pathology and to treat her appropriately.

Abortion, Septic↗
PubMed1987

Augmentation of labour--mode of delivery related to cervimetric progress.

This study was designed to investigate the possible benefits, in terms of obstetric and neonatal outcome, of a prolonged augmentation period with oxytocin in patients with dysfunctional first stage of labour. The majority of patients (65.5% of nulliparas and 83.8% of multiparas) responded with satisfactory progress within the first 4 hours of augmentation and the Caesarean section rate was low in this group (1.3%). In those with unsatisfactory progress during the first 4 hours of augmentation a further 4 hour period of augmentation resulted in vaginal delivery for 50.7% of nulliparas with primary dysfunctional labour and 33.3% of those with secondary arrest in labour. Corresponding figures for multiparas were 41.7% and 25.0%, respectively. The neonatal outcome was uniformly good. It is concluded that the management protocol presented for augmentation of labour seems to be a safe procedure and might reduce the rising Caesarean section rate for dystocia.

Female↗
PubMedDate not supplied

Wet decontamination-induced stratum corneum hydration--effects on the skin barrier function to diethylmalonate.

Decontamination of chemical agents from the skin uses both dry and wet decontamination processes. Recent studies have shown that wet decontamination frequently results in stratum corneum hydration. To evaluate the hydration effect of wet decontamination on the skin barrier function and hence on the decontamination efficiency, a series of comparative studies were carried out on human skin contaminated with the nerve agent simulant diethylmalonate, using decontamination media having different salinity and surfactants. The results showed that, compared to non-decontaminated skin, remnant diethylmalonate on decontaminated skin penetrated at an accelerated rate in the immediate 2 h following decontamination. This transient enhancement effect, ranging from 20 to 98%, was depended on the nature of the decontamination media used and was more obvious in skin samples that were decontaminated 1 h postexposure. All decontamination media exhibited this effect, with the greatest enhancement observed in the following order: anionic surfactant > cationic surfactant > non-ionic surfactant > deionized water > 0.9% saline > 9% saline.

Aged↗