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Gustafson DH, Hawkins RP, Boberg EW, Bricker E, Pingree S, Chan CL. The use and impact of a computer-based support system for people living with AIDS and HIV infection. PROCEEDINGS. SYMPOSIUM ON COMPUTER APPLICATIONS IN MEDICAL CARE 1994:604-8. [PMID: 7949999 PMCID: PMC2247754] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
CHESS (the Comprehensive Health Enhancement Support System) is an interactive, computer-based system to support people facing AIDS/HIV Infection and other health-related crises or concerns. CHESS provides information, referral to service providers, support in making tough decisions and networking to experts and others facing the same concerns. CHESS is designed to improve access to health and human services for people who would otherwise face psychological, social, economic or geographic barriers to receiving services. CHESS has been evaluated in a random-assignment study with over 200 men and women living with AIDS and HIV infection. When CHESS was placed in subjects' homes for 3-6 months, use of CHESS was extremely heavy, with the average subject using CHESS 138 times for 39 hours. Compared with a control group which did not receive CHESS, subjects who used CHESS reported significantly higher quality of life in several dimensions, including social support and cognitive functioning. Users also reported significant reductions in some types of health care costs, especially inpatient services (hospitalizations). All segments of the study population used and benefited from CHESS, including women, minorities and those subjects with lower levels of education. Thus, CHESS appears to be an effective means of delivering education and support to the diverse populations which are affected by AIDS and HIV infection.
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Chan CL, Landick R. Dissection of the his leader pause site by base substitution reveals a multipartite signal that includes a pause RNA hairpin. J Mol Biol 1993; 233:25-42. [PMID: 8377190 DOI: 10.1006/jmbi.1993.1482] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
A key feature of transcriptional attenuation in some amino acid biosynthetic operons is a transcriptional pause that occurs immediately after synthesis of the first leader transcript secondary structure. Both RNA secondary structure and downstream DNA sequence are important for pausing at these sites; however, the precise RNA structures involved and the relative contribution of other RNA and DNA bases to pausing are unknown. We studied the effects of base substitutions upstream from the his leader pause site (immediately prior to addition of G103) to determine how nucleic acid sequences and RNA structure contribute to pausing. By testing compensatory base substitutions, we found that pausing depended in part on an RNA secondary structure containing a five base-pair stem and eight nucleotide loop, which we call the his pause RNA hairpin. The his pause hairpin forms 11 nucleotides upstream from the paused transcript 3' end and thus corresponds to only the upper portion of the larger his A:B leader transcript secondary structure. Some base substitutions in the ten nucleotides between the pause hairpin and the 3' end of the transcript increased pausing, whereas others decreased pausing. However, compensatory substitutions that restored pairing of these bases in the lower portion of the A:B secondary structure did not alter these effects. Changing the 3'-terminal nucleotide of the transcript (U102) altered both the position and strength of pausing. Thus, in addition to the downstream DNA sequence, three distinct segments of nucleic acid upstream from the nucleotide-addition site in the transcription complex contribute to pausing in different ways: the pause RNA hairpin, the 3'-proximal region of transcript or DNA template, and the 3'-terminal nucleotide. We suggest that electrostatic interaction between the pause hairpin and RNA polymerase, rather than disruption of an RNA:DNA heteroduplex, delays elongation at the his leader pause site.
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Ratnam SS, Devendra S, Marshall B, Anandkumar C, Wong YC, Goh HH, Bongso TA, Chan CL, Kumar J, Ng SC. Stimulation regimens in Assisted Reproductive Technology (ART) programme: experience in the University Hospital, Singapore. ANNALS OF THE ACADEMY OF MEDICINE, SINGAPORE 1993; 22:351-4. [PMID: 8373118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Ovarian stimulation is critical to the success of patients in Assisted Reproductive Technology (ART) programmes. We compared two stimulation regimes retrospectively for ART in the NUH programme. These were the 2:1 and the GnRHa-FSH/hMG regimes. The former was our first-line regime while the latter was used for cycles where there was a prior endogenous LH surge, previous poor response, or an elevated LH level between days three to five of the cycle. All cycles in our ART programme in 1991 were studied, except those for special research procedures, e.g. micro-insemination sperm transfer (MIST) cycles, a total of 241 cycles. Cancellation rates were 14.4% (21 of 146 cycles) and 37.3% (19 of 51 cycles) for the 2:1 and GnRHa-FSH/hMG regimes respectively (p > 0.001). For the 2:1 regime, the majority of cancellations were due to ovulation prior to the oocyte recovery (42.9%; nine of 21 cycles). However, for the GnRHa-FSH/hMG regime, almost all the cancellations were due to poor response (84.2%; 16 of 19 cycles). Fertilisation rates were lower for the 2:1 regime (for both IVF-ER and IVF-TET, where sperm quality was poorer) compared to the GnRHa-FSH/hMG (55.0 and 66.6% respectively; p < 0.001). Pregnancy rates were higher for the 2:1 regime when IVF-ER and IVF-TET were used (16.4% and 23.3% respectively per oocyte recovery, versus 9.8% and 18.8% respectively for the GnRHa-FSH/hMG regime).
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Chan CL, Wu Z, Ciardelli T, Eastman A, Bresnick E. Kinetic and DNA-binding properties of recombinant human O6-methylguanine-DNA methyltransferase. Arch Biochem Biophys 1993; 300:193-200. [PMID: 8424652 DOI: 10.1006/abbi.1993.1027] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
O6-Methylguanine-DNA methyltransferase (MGMT) is a DNA repair protein that plays an important role in chemotherapy, mutagenesis, and carcinogenesis. Recombinant human MGMT was isolated from an Escherichia coli high performance expression system and purified to homogeneity. The kinetic and DNA-binding properties of the recombinant human MGMT were studied. The purified human MGMT reacted stoichiometrically with methylated DNA under second-order rate kinetics. The rate constant with normal methylated DNA was 1 x 10(9) M-1 min-1 at 37 degrees C. The binding to DNA was the rate determining step in the repair process. Approximately eight base pairs of the DNA substrate were covered by the human MGMT protein. The affinity constant for interaction of DNA to MGMT was approximately 4.7 x 10(5) M-1. The binding to methylated DNA was also examined; the binding affinity to methylated DNA was two times higher than that to unmodified DNA. The interaction with DNA induced a conformational change in the human MGMT protein as monitored by circular dichroism and fluorescence analysis. A similar conformational change was induced by both methylated and unmodified DNA.
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80
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Chan CL, Katsaggelos AK, Sahakian AV. Image sequence filtering in quantum-limited noise with applications to low-dose fluoroscopy. IEEE TRANSACTIONS ON MEDICAL IMAGING 1993; 12:610-621. [PMID: 18218455 DOI: 10.1109/42.241890] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Clinical angiography requires hundreds of X-ray images, putting the patients and particularly the medical staff at risk. Dosage reduction involves an inevitable sacrifice in image quality. In this work, the latter problem is addressed by first modeling the signal-dependent, Poisson-distributed noise that arises as a result of this dosage reduction. The commonly utilized noise model for single images is shown to be obtainable from the new model. Stochastic temporal filtering techniques are proposed to enhance clinical fluoroscopy sequences corrupted by quantum mottle. The temporal versions of these filters as developed here are more suitable for filtering image sequences, as correlations along the time axis can be utilized. For these dynamic sequences, the problem of displacement field estimation is treated in conjunction with the filtering stage to ensure that the temporal correlations are taken along the direction of motion to prevent object blur.
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Abstract
In this paper, the boundary element method (BEM) approach is applied to solve the Pennes (1948) bioheat equation. The objective is to develop the BEM formulation and demonstrate its feasibility. The basic BEM formulations for the transient and steady-state cases are first presented. To demonstrate the usefulness of the BEM approach, numerical solutions for 2-D steady-state problems are obtained and compared to analytical solutions. Further, the BEM formulation is applied to model a conjugate problem for an artery imbedded in a perfused heated tissue. Analytical solution is possible when the conduction in the x-direction is negligible. The BEM and analytical results have very good agreement.
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82
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Chan CL, Devendra S. Oocyte and embryo donation. ANNALS OF THE ACADEMY OF MEDICINE, SINGAPORE 1992; 21:545-53. [PMID: 1309125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Oocyte and embryo donation, first reported in humans in 1983 has helped patients who do not possess functional ovarian tissues or whose oocyte cannot be used for fertilisation, to conceive. Though it is the female counterpart as the donor insemination in the male, it imposes quite different bioethical issues. The article is a review of the oocyte and embryo donation programme in general, with special discussion on regimes of Cyclic Steroid Replacement Therapy, the recruitment of oocyte donors, bioethical issues, and future applications of oocyte donation in medicine.
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Marshall BM, Ng SC, Chan CL, Ratnam SS. Adoption in utero is the wrong term. BMJ (CLINICAL RESEARCH ED.) 1992; 304:1384. [PMID: 1611360 PMCID: PMC1882021 DOI: 10.1136/bmj.304.6838.1384-a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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84
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Chan CL, Wu Z, Eastman A, Bresnick E. Irradiation-induced expression of O6-methylguanine-DNA methyltransferase in mammalian cells. Cancer Res 1992; 52:1804-9. [PMID: 1372530] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/25/2023]
Abstract
O6-Methylguanine-DNA methyltransferase (MGMT) is a DNA repair protein which plays an important role in chemotherapy, mutagenesis, and carcinogenesis. The specific activity of MGMT in female rat liver can be induced by approximately 20-fold by treatment of the rats with gamma-irradiation. Maximum response occurred 48 h after 15 Gy irradiation. MGMT levels in male rats were induced by only 3-fold. MGMT activity was also induced by irradiation of rat hepatoma H4IIE cells with a 3-fold increase noted after treatment with 3 Gy. Northern analysis and nuclear run-on assays indicated that the induction of MGMT was regulated at the transcriptional level. The radiation-mediated increase in MGMT was blocked by H7, a protein kinase inhibitor, but not by H89, an inhibitor of protein kinase A. Hydroxyl radicals may play a role in the induction mechanism since dimethyl sulfoxide, a radical scavenger, blocked the radiation-mediated increase in MGMT. MGMT activity was also increased by treatment of the cells with H2O2, in accordance with the involvement of activated oxygen species in the induction of MGMT. Finally, the addition of cycloheximide, an inhibitor of protein synthesis, prior to but not after irradiation, abolished the increase in MGMT activity.
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85
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Wu ZN, Chan CL, Eastman A, Bresnick E. Expression of human O6-methylguanine-DNA methyltransferase in a DNA excision repair-deficient Chinese hamster ovary cell line and its response to certain alkylating agents. Cancer Res 1992; 52:32-5. [PMID: 1727384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A plasmid has been constructed in which the expression of human O6-methylguanine-DNA methyltransferase (MGMT) complementary DNA is driven by the Rous sarcoma virus promoter sequence. We had previously shown that transfection of this plasmid into Chinese hamster ovary (CHO) cells results in the expression of MGMT and in increased cellular resistance to N-methyl-N'-nitro-N-nitrosoguanidine and 1-(2-chloroethyl)-1-nitrosourea (CNU) but not N-nitroso-N-ethylurea (ENU). In the present study, the Rous sarcoma virus promoter-MGMT was transfected into DNA excision repair-deficient CHO UV41 cells to investigate the phenotype associated with MGMT expression in the absence of DNA excision repair. Both the UV41/MGMT and CHO/MGMT cells expressed similar levels of MGMT and exhibited a similar increased resistance to N-methyl-N'-nitro-N-nitrosoguanidine. The UV41 cells were 20-fold more sensitive to CNU than the wild-type CHO cells. Expression of MGMT increased the resistance to CNU about 6-fold in both cell lines, but the difference between the two cell lines attributable to the excision repair defect still persisted. The UV41 cells were 2- to 3-fold more sensitive than the wild-type CHO cells to the monofunctional alkylating agents 1-(2-hydroxyethyl)-1-nitrosourea and ENU, but the MGMT phenotype did not alter sensitivity. This suggests that alkylation at the O6 position of guanine has no role in cytotoxicity of ethylating agents and that monofunctional DNA damage has little role in the cytotoxicity of CNU. Since MGMT can prevent the formation of G-C interstrand cross-links formed by CNU, other excision repair-sensitive DNA adducts must play a major role in the sensitivity of UV41 cells to this bifunctional alkylating agent. These results suggest that DNA intrastrand cross-links may be major contributors to the cytotoxicity of CNU.
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McKee SP, Schor CM, Steinman SB, Wilson N, Koch GG, Davis SM, Hsu-Winges C, Day SH, Chan CL, Movshon JA. The classification of amblyopia on the basis of visual and oculomotor performance. TRANSACTIONS OF THE AMERICAN OPHTHALMOLOGICAL SOCIETY 1992; 90:123-44; discussion 145-8. [PMID: 1494815 PMCID: PMC1298430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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87
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Chan CL, Wigley CB, Wyse J, Berry M. Immunocytochemical analysis of glial cells in the hypomyelinated optic nerve of the BW mutant rat. JOURNAL OF NEUROCYTOLOGY 1991; 20:732-45. [PMID: 1720450 DOI: 10.1007/bf01187847] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The Browman-Wyse (BW) rat is a mutant with structural defects of the visual system, including a failure of the proximal (retinal) end of the optic nerve to myelinate. This latter abnormality is correlated with an absence of CAII+ oligodendrocytes, but we have previously shown that astrocytes are normally distributed, as judged by morphological characteristics of GFAP+ cells in vivo. We have further examined in vitro the immunohistochemical characteristics of macroglia isolated from the BW optic nerve, either as cell suspensions or after 4 days in culture. Cell cultures derived from the hypomyelinated proximal segment of BW optic nerves contained very few 0-2A progenitor cells (from which oligodendrocytes and cells with the GFAP+/A2B5+ phenotype develop), whereas over 90% of the glia were Schwann cells. A proportion of these few 0-2A progenitor cells differentiated normally after 4 days in vitro into both progeny phenotypes in appropriate media. Accordingly, we conclude that the myelination deficiency in the BW optic nerve could be explained as a failure of 0-2A progenitor cells to populate fully the proximal extremity of the nerve during development. Since most glia isolated from adult optic nerves did not adhere to the culture substrate, we analysed the phenotypes of freshly isolated cells in suspension. Comparing optic nerves of normal adult rats with those of BW mutants, a significantly higher fraction of the GFAP+ cells reacted with A2B5 in cell suspensions of the latter. The double-labelled cells which are present in abnormally high numbers may be the differentiated progeny of 0-2A progenitors in the hypomyelinated segment of nerve. One explanation for these findings is that Schwann cells within the BW nerve induce the differentiation of 0-2A progenitor cells to the GFAP+/A2B5+ phenotype. We investigated this possibility using conditioned medium from cultured Schwann cells which increased tenfold the frequency of GFAP+/A2B5+ cells in normal neonatal rat optic nerve cultures. Oligodendrocyte numbers showed a concomitant decline with increasing concentration of Schwann cell conditioned medium. Hypomyelination in the BW rat optic nerve may therefore arise because Schwann cells, present in the proximal segment of the nerve, not only impede the migration of 0-2A progenitor cells but also release a factor which induces those 0-2A progenitor cells which arrive in the proximal segment of the nerve to differentiate into GFAP+ cells at a critical stage in oligodendrocyte development.
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Grisham JD, Bowman MC, Owyang LA, Chan CL. Vergence orthoptics: validity and persistence of the training effect. Optom Vis Sci 1991; 68:441-51. [PMID: 1891195 DOI: 10.1097/00006324-199106000-00005] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The validity and permanence of orthoptic treatment for vergence deficiencies requires investigation due to the subjective nature of determining success in most clinical cases, i.e., the amelioration of symptoms and increases in vergence ranges. The relation between Risley prism vergences, a subjective measure, and vergence tracking rate, an objective index, is investigated. The course of orthoptics progress is compared in cases of clinical vergence dysfunction. Vergence-deficient control subjects showed no significant change in either index. However, trained subjects demonstrated rapid increases in both indices. The persistence of the training effect was monitored for up to 9 months. No regression was observed in subjects who met all release criteria, but one subject who chose to terminate therapy early showed a slow regression in tracking rate and recurrence of symptoms. These data support the validity of vergence training and increase the plausibility of previous clinical reports of orthoptics success.
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89
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Wu Z, Chan CL, Eastman A, Bresnick E. Expression of human O6-methylguanine-DNA methyltransferase in Chinese hamster ovary cells and restoration of cellular resistance to certain N-nitroso compounds. Mol Carcinog 1991; 4:482-8. [PMID: 1793486 DOI: 10.1002/mc.2940040612] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have constructed a plasmid in which the expression of human O6-methylguanine-DNA methyltransferase (MGMT) cDNA is driven by the Rous sarcoma virus promoter sequence. Transfection of this plasmid into Chinese hamster ovary (CHO) cells results in expression of MGMT and in cellular resistance to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and 1-(2-chloroethyl)-1-nitrosourea (CNU), but not to N-nitroso-N-ethylurea. The specific activity of MGMT in transfected CHO cells correlated well with their resistance to MNNG and CNU. Southern analysis showed that the plasmid had been integrated into the CHO cell genome. Western analysis of extracts from transfected CHO cells using an antibody against a peptide corresponding to the carboxyl-terminal end of the human MGMT protein demonstrated a single band with a molecular size of 24-25 kDa; no such band was observed in extracts from wild-type CHO cells. These transfected cells may therefore be used to study the role of MGMT in the repair of alkylating DNA lesions and to determine its importance in carcinogenesis as well as in chemotherapy.
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90
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Ng SC, Bongso TA, Chan CL, Hagglund L, Devendra S, Soon SB, Ratnam SS. Future of assisted reproductive technologies. ANNALS OF THE ACADEMY OF MEDICINE, SINGAPORE 1990; 19:841-4. [PMID: 2130751] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Within a decade, from the birth of Louise Brown in 1978, there has been tremendous advances in the field of assisted reproduction. These advances are the collective result of techniques known as Assisted Reproductive Technologies (ART). ART is defined as techniques in which the oocyte is handled in-vitro before replacement either as oocytes or embryos. The techniques in ART include in-vitro fertilisation and embryo replacement (IVF-ER), gamete intra-fallopian transfer (GIFT), tubal embryo (TET), donor oocytes and embryos, and freezing of embryos and oocytes. The most recent has been assisting fertilisation by micro-manipulation, including zonal procedures and micro-insemination, e.g. micro-insemination sperm transfer (MIST). There has also been many ethical issues in ART, and little advance in the "take home" baby rate. There is now major interest in co-culture of embryos with ampullary, endometrial and fibroblast mono-layers, to improve the quality of these embryos before their return into the mother. Because of the public's interest in ART, its usefulness has been "oversold". In time to come, ART may be limited to patients who really need it.
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Chan CL, Wigley CB, Berry M. Oligodendrocyte-type 2 astrocyte (O-2A) progenitor cells from neonatal and adult rat optic nerve differ in their responsiveness to platelet-derived growth factor. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1990; 55:275-82. [PMID: 2253328 DOI: 10.1016/0165-3806(90)90209-h] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
We have investigated, in vitro, the mitogenic responsiveness to platelet-derived growth factor (PDGF) of oligodendrocyte-type 2 astrocyte (O-2A) progenitor cells isolated from adult rat optic nerve and their differentiation into oligodendrocytes. Progenitor cells from adult optic nerves differentiate into oligodendrocytes in a limiting concentration of foetal calf serum more slowly than in cultures of neonatal cells. Nevertheless, differentiation of oligodendrocytes from progenitors is nearly complete by 6 days in vitro, with 50% expressing galactocerebroside by 4-5 days. In these experiments, adult optic nerve cells were grown in medium containing PDGF, a potent mitogen for neonatal O-2A progenitor cells, and yet the decline in numbers of O-2A progenitor cells matches the rise in oligodendrocyte numbers. We suggest that this is because adult O-2A progenitor cells differ from their neonatal counterparts and do not show the same proliferative response in the presence of exogenous PDGF. We tested this hypothesis by a quantitative autoradiographic analysis of tritiated thymidine-labelled nuclei, comparing percentages of labelled adult and neonatal O-2A lineage glial cells in low-serum medium, in the presence of absence of PDGF, with their response to a monolayer of neonatal rat cortical type 1 astrocytes or astrocyte-conditioned medium. Whereas, adult O-2A progenitors responded to astrocyte monolayers and to conditioned medium from astrocyte cultures, there was no dose-dependent response to PDGF-BB over a wide range of concentrations. Antibodies to human PDGF neutralise the growth-promoting activity of astrocyte-conditioned medium for neonatal O-2A cells but do not neutralise astrocyte-conditioned medium stimulation of adult O-2A progenitor cells. This indicates that the principal astrocyte-derived growth factor(s) for adult O-2A progenitor cells is unlikely to be PDGF.
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92
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Chan CL, Wu Z, Eastman A, Bresnick E. Induction and purification of O6-methylguanine-DNA-methyltransferase from rat liver. Carcinogenesis 1990; 11:1217-21. [PMID: 2197015 DOI: 10.1093/carcin/11.7.1217] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
O6-Methylguanine-DNA-methyltransferase (OMMT) is a DNA repair protein that plays an important role in chemotherapy, mutagenesis and carcinogenesis. The sp. act. of OMMT in rat liver can be induced by approximately 12- to 20-fold by treatment of the rats with ionizing radiation. The effects of dose and time were investigated in this study. We have found that OMMT sp. act. can be increased, although to a lower extent, in kidney, spleen and brain in addition to liver. However, the sp. act. of OMMT in lung was reduced by irradiation. OMMT has been purified from the livers of irradiated rats by solubilization in high-salt-containing buffer, ammonium sulfate precipitation and a series of column chromatographic steps, including phenyl-Sepharose, heparin-agarose, double-stranded DNA-cellulose and FPLC. A 3000-fold enrichment of OMMT was achieved from the induced liver preparations. However, with regard to the sp. act. of this protein in normal rat liver, the fold purification was approximately 35,000. After methylation, OMMT during the course of its action exhibited a mol. wt of 28 kd under SDS-PAGE conditions.
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93
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Shiu W, Dewar G, Leung N, Leung WT, Chan M, Tao M, Lui C, Chan CL, Lau WY, Metreweli C. Hepatocellular carcinoma in Hong Kong: clinical study on 340 cases. Oncology 1990; 47:241-5. [PMID: 2160632 DOI: 10.1159/000226823] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Three hundred and forty cases of hepatocellular carcinoma in Hong Kong were studied for their clinical features, and various factors were analysed for their prognostic values. The clinical presentation was often vague and rather non-specific and a majority of patients were presented late and often unresectable. The overall median survival was 8 weeks. The Karnofsky performance scale and bilirubin level were the most important prognostic factors. The treated group survived longer than the untreated group.
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Chan CL, Landick R. The Salmonella typhimurium his operon leader region contains an RNA hairpin-dependent transcription pause site. Mechanistic implications of the effect on pausing of altered RNA hairpins. J Biol Chem 1989; 264:20796-804. [PMID: 2479649] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The Salmonella typhimurium his leader region contains a well documented transcription attenuator. We report here the results of in vitro transcription studies that characterized a transcription pause site in the his leader region. The pause occurred after synthesis of the first his leader secondary structure (A:B) and immediately preceding addition of G103 to the nascent transcript. RNA polymerase pausing at this site would allow a ribosome synthesizing the his leader peptide to release the paused polymerase and synchronize transcription and translation of the his leader region. The half-life of transcription complexes paused in the his leader was enhanced by NusA, but not guanosine 5'-diphosphate 3'-diphosphate. Nuclease digestion and RNA modeling studies were consistent with a compact three-dimensional structure for the his pause RNA. The half-life of the his leader paused transcription complex was decreased greatly on altered templates in which the C71-G93 base pair was disrupted but was unchanged when the C65-G100 base pair was disrupted. This result is consistent with a model for the structure of paused transcription complexes in which a portion of the RNA:DNA elongation heteroduplex is retained.
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95
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Chan CL, Ratnam SS. Management of unexplained infertility. Singapore Med J 1989; 30:584-9. [PMID: 2699677] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Unexplained or idiopathic infertility means no cause can be found to account for the infertility. This depends on the enthusiasm to look for the subtle causes like luteal phase defect (LPD), luteinizing unruptured follicle syndrome (LUFS), abnormal prolactin secretion, psychogenic, environmental, nutritional and immunological factors. Sometimes, these subclinical conditions can be corrected. Failing to identify these treatable conditions, various empirical treatments, laboratory manipulation or assisted reproductive techniques (ART) can be attempted to achieve conception.
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96
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Chan CL, Arulkumaran S, Wong YC, Ratnam SS. Importance of antenatal karyotyping in the management of a case with vestigial radii. Singapore Med J 1989; 30:213-4. [PMID: 2692184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
An uncommon presentation of vestigial radii in a Trisomy E fetus was detected prenatally with ultrasound scanning. Appropriate counselling and obstetric management were thus carried out avoiding an unnecessary caesarean section. The importance of identifying high risk pregnancy and prenatal diagnosis by a qualified personnel cannot be overstressed.
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Wong PC, Ng SC, Hamilton MP, Chan CL, Bongso TA, Ratnam SS. Birth from replacement of frozen-thawed embryos after failure of gamete intra-fallopian transfer: a successful pregnancy case. ASIA-OCEANIA JOURNAL OF OBSTETRICS AND GYNAECOLOGY 1989; 15:7-10. [PMID: 2735844 DOI: 10.1111/j.1447-0756.1989.tb00143.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The patient was 8 years subfertile and had failed other forms of treatment when she was enrolled in the GIFT program. Of the total of 16 oocytes recovered 4 were transferred and the remaining 12 inseminated with her husband's sperm. Four resulting embryos were frozen. When she did not conceive, the 4 embryos were thawed 3 months later and replaced into her. She conceived and recently delivered a pair of twins. The protocol will be discussed in detail. Cryopreservation of embryos therefore may increase the patient's chance of pregnancy in a GIFT program.
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98
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Wong PC, Wong YC, Anandakumar C, Hamilton MP, Chan CL, Ng SC, Bongso TA, Ratnam SS. Ultrasound directed oocyte recovery in an IVF program. ASIA-OCEANIA JOURNAL OF OBSTETRICS AND GYNAECOLOGY 1988; 14:433-5. [PMID: 2977092 DOI: 10.1111/j.1447-0756.1988.tb00129.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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99
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Ng SC, Bongso A, Ratnam SS, Sathananthan H, Chan CL, Wong PC, Hagglund L, Anandakumar C, Wong YC, Goh VH. Pregnancy after transfer of sperm under zona. Lancet 1988; 2:790. [PMID: 2901626 DOI: 10.1016/s0140-6736(88)92433-6] [Citation(s) in RCA: 145] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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100
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Wong PC, Chan CL, Hamilton MP, Ng SC, Bongso A, Wong YC, Anadakumar C, Goh V, Ratnam SS. Gamete intrafallopian transfer (GIFT): an alternate method of conception in couples with unexplained infertility, endometriosis and oligo-asthenospermia. ANNALS OF THE ACADEMY OF MEDICINE, SINGAPORE 1988; 17:247-50. [PMID: 3044262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
138 treatment cycles of GIFT were carried out in couples with mainly unexplained infertility, endometriosis and male factor. The overall pregnancy rate was 24.6%, abortion 29.2%, multiple pregnancy 20.6% and ectopic pregnancy 0%. Four oocytes seem to be the optimal number of oocytes to be transferred. Patients with male factor infertility fared the worse in comparison with the other groups. Successful in-vitro fertilization of excess eggs did not correlate with a positive outcome of the GIFT procedure.
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