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S C Lo

Publications and source records attributed to S C Lo.

At least 37 records · Page 2Linked to original sources
PubMed1998

High-frequency DNA rearrangements in the chromosomes of clinically isolated Mycoplasma fermentans.

Mycoplasma fermentans is currently being examined as an agent potentially associated with human disease. Several strains of M. fermentans were isolated from patients with respiratory tract disease and AIDS. Two of these clinical strains, M64 and SK6, were triple-filter-cloned and designated as the parental clones in this study. Genomic DNA of randomly picked subclones in four and five subsequent generations passed from the parental M64 and SK6 clones were analyzed by using a radiolabeled M. fermentans-specific insertion sequence (IS)-like element as the probe. The hybridization patterns of DNA restriction fragments revealed high frequencies of chromosomal changes accompanied with excision or new insertion of the IS-like element in M. fermentans chromosome. The findings indicate M. fermentans has an effective mechanism(s) to produce a rapid gene rearrangement that may be mediated by one or more copies of the IS-like element.

Blotting, Southern↗
PubMed1998

Porcine pyridoxal kinase c-DNA cloning, expression and confirmation of its primary sequence.

Porcine brain pyridoxal kinase has been cloned. A 1.2 kilo-based cDNA with a 966-base pair open reading frame was determined from a porcine brain cortex cDNA library using PCR technique. The DNA sequence was shown to encode a protein of 322 amino acid residues with a molecular mass of 35.4 kDa. The amino acid sequence deduced from the nucleotide sequence of the cDNA was shown to match the partial primary sequence of pyridoxal kinase. Expression of the cloned cDNA in E. coli has produced a protein which displays both pyridoxal kinase activity and immunoreactivity with monoclonal antibodies raised against natural enzyme from porcine brain. With respect to the physical properties, it is shown that the recombinant protein exhibits identical kinetic parameters with the pure enzyme from porcine brain. Although the primary sequence of porcine pyridoxal kinase has been shown to share 87% homology with the human enzyme, we have shown that the porcine enzyme carries an extra peptide of ten amino acid residues at the N-terminal domain.

Amino Acid Sequence↗
PubMed1998

Partially folded conformations of inositol monophosphatase endowed with catalytic activity.

The stability of porcine brain inositol monophosphatase in the presence of increasing concentrations of urea was investigated at pH 7.5. Exposure of the enzyme to 8 M urea brings about the dissociation of the dimeric species of 58 kDa into monomeric forms as revealed by gel filtration chromatography. Unfolding of the protein by 8 M urea results in a decrease of the ellipticity at 220 nm (20%) together with a perturbation of the near-UV circular dichroism spectrum. Urea-treated inositol monophosphatase binds Co2+ ions with a dissociation constant of 3.3 microM. The enzyme is catalytically competent when assayed with 4-nitrophenyl-phosphate in the presence of the activating ion Co2+ at pH 7.5 in 8 M urea. The apparent activation constant for Co2+ is 2.5 mM. It is postulated that partially folded conformations of monomeric species preserve their catalytic function because the affinity of Co2+ ions for the metal coordination center of the protein is not perturbed by exposure to 8 M urea.

Animals↗
PubMed1998

Reduction of light-induced anthocyanin accumulation in inoculated sorghum mesocotyls. Implications for a compensatory role in the defense response.

Sorghum (Sorghum bicolor L. Moench) accumulates the anthocyanin cyanidin 3-dimalonyl glucoside in etiolated mesocotyls in response to light. Inoculation with the nonpathogenic fungus Cochliobolus heterostrophus drastically reduced the light-induced accumulation of anthocyanin by repressing the transcription of the anthocyanin biosynthesis genes encoding flavanone 3-hydroxylase, dihydroflavonol 4-reductase, and anthocyanidin synthase. In contrast to these repression effects, fungal inoculation resulted in the synthesis of the four known 3-deoxyanthocyanidin phytoalexins and a corresponding activation of genes encoding the key branch-point enzymes in the phenylpropanoid pathway, phenylalanine ammonia-lyase and chalcone synthase. In addition, a gene encoding the pathogenesis-related protein PR-10 was strongly induced in response to inoculation. The accumulation of phytoalexins leveled off by 48 h after inoculation and was accompanied by a more rapid increase in the rate of anthocyanin accumulation. The results suggest that the plant represses less essential metabolic activities such as anthocyanin synthesis as a means of compensating for the immediate biochemical and physiological needs for the defense response.

Acyltransferases↗
PubMed1998

Absence of mycoplasmal gene in malignant mammalian cells transformed by chronic persistent infection of mycoplasmas.

Chronic persistent infections by mycoplasmas induced malignant transformation of C3H mouse embryo cells that normally had never been reported to undergo spontaneous transformation. This mycoplasma-mediated oncogenic process had a long latency (more than 7 weeks of continuous mycoplasmal infection) and showed a multistage progression characterized by reversibility (at least up to 11 weeks of mycoplasmal infection) and irreversibility of malignant properties upon removal of the mycoplasma from culture. Further prolonged infections (18 weeks) by Mycoplasma fermentans or M. penetrans resulted in permanent transformation of these C3H cells that no longer required the continued presence of the transformation-inducing mycoplasmas in cultures to retain their malignant properties. Previous studies of viral oncogenesis revealed that virus-transformed cells always had viral gene(s) present. Integration of viral gene(s) apparently played an important role in the process of oncogenesis. In this study, we examined if the continued presence of any mycoplasmal gene(s) in mammalian cells, in whatever form, was also crucial in causing malignant cell transformation. Representational difference analysis (RDA) was a recently developed powerful technique to compare differences between two complex genomes. In the RDA system, subtractive and kinetic enrichment was used to purify and isolate restriction endonuclease gene fragment(s) of mycoplasmal origin, presumably present only in mycoplasma-transformed C3H cells, but not in nonmycoplasma-exposed control C3H cells. After three rounds of subtractive hybridization following PCR enrichment for each of three different restriction enzymes DNA digests, no gene fragment of mycoplasmal origin was amplified or identified in the permanently transformed C3H cells. Differing from tumorigenesis in animal cells induced by most oncogenic viruses or in plant cells induced by Agrobacteria, mycoplasmas evidently did not cause malignant transformation by integrating their gene(s) into the mammalian cell genome.

Animals↗
PubMed1997

Fractal modeling and segmentation for the enhancement of microcalcifications in digital mammograms.

The objective of this research is to model the mammographic parenchymal, ductal patterns and enhance the microcalcifications using deterministic fractal approach. According to the theory of deterministic fractal geometry, images can be modeled by deterministic fractal objects which are attractors of sets of two-dimensional (2-D) affine transformations. The iterated functions systems and the collage theorem are the mathematical foundations of fractal image modeling. In this paper, a methodology based on fractal image modeling is developed to analyze and model breast background structures. We show that general mammographic parenchymal and ductal patterns can be well modeled by a set of parameters of affine transformations. Therefore, microcalcifications can be enhanced by taking the difference between the original image and the modeled image. Our results are compared with those of the partial wavelet reconstruction and morphological operation approaches. The results demonstrate that the fractal modeling method is an effective way to enhance microcalcifications. It may also be able to improve the detection and classification of microcalcifications in a computer-aided diagnosis system.

Algorithms↗
PubMed1997

Mycoplasma genitalium infection and host antibody immune response in patients infected by HIV, patients attending STD clinics and in healthy blood donors.

Prevalence of Mycoplasma genitalium in humans is still not clear. We have developed a sensitive and specific serological assay for M. genitalium using lipid-associated membrane proteins (LAMPs) as antigens. Antibodies to LAMPs from M. genitalium showed little cross-reactivity to LAMPs from antigenically similar M. pneumoniae. For validity testing, urines from 104 patients were tested by PCR for M. genitalium. All 15 PCR+ patients had M. genitalium-LAMPs antibodies. Moreover, none of 64 antibody-negative patients were PCR+. Serological study of 1800 patients of various diseased groups and healthy blood donors showed M. genitalium was primarily a sexually transmitted microbe that infected patients with AIDS (44.0%), intravenous drugs users with or without HIV infection (42.5%), and also HIV- patients attending STD clinics (42.6%). Only 5.5% HIV- healthy blood donors and 1.3% HIV+ hemophiliacs tested positive. M. genitalium has been associated with acute non-gonococcal urethritis in male patients. However, many sexually active men and women appear to be chronically infected or colonized by the microbe without apparent clinical symptoms and may continue to transmit the organism through sexual contacts.

Antibodies, Bacterial↗
PubMed1997

High-level expression of H-ras and c-myc oncogenes in mycoplasma-mediated malignant cell transformation.

C3H mouse embryo cells, which normally have low inherent spontaneous transformation, underwent malignant transformation while chronically infected with Mycoplasma fermentans or Mycoplasma penetrans. This mycoplasma-mediated oncogenic process had long latency (more than 7 weeks of persistent mycoplasmal infection) and showed multistage progression characterized by reversibility and irreversibility of malignant properties upon removal of M. fermentans from culture. Marked expression of H-ras and c-myc mRNA, but not N-myc, src, N-ras, or p53 mRNA, was found in the mycoplasma-transformed C3H cells that exhibited characteristic malignant properties of morphological changes and uncontrolled cell growth. However, at least up to the eleventh week of persistent mycoplasma infection, the marked expression of H-ras or c-myc mRNA in C3H cells depended on continued presence of the mycoplasma in culture. H-ras or c-myc mRNA rapidly declined to the undetectable low levels of nontransformed parental C3H cells, and all malignant properties of the once-fully-transformed C3H cells quickly reversed, if M. fermentans was eradicated from culture. In comparison, infection with M. penetrans for 7 or 11 weeks also induced a high level of H-ras, but not c-myc, mRNA expression in C3H cells. Despite having prominent amount of steady-state H-ras mRNA, these M. penetrans-infected C3H cells did not show any sign of malignant transformation. Thus, marked expression of H-ras gene alone was not sufficient to effect transformation in C3H cells. Interestingly, after a further prolonged (18 weeks) infection with either M. fermentans or M. penetrans, C3H cells revealed prominent chromosomal changes, expressed constitutively (with or without the presence of the transforming mycoplasmas) at high levels of both H-ras and c-myc mRNA and became permanently transformed. These cells were able to form tumors in animals.

Animals↗
PubMed1997

In vitro evaluation of the effects of transportation and storage on platelet concentrates.

Platelets may be activated and become acidic during transportation and storage, resulting in poor post-transfusion platelet survival and recovery. In this study, we evaluated the current local shipment protocol for platelet concentrates and the storage technique used at the National Taiwan University Hospital. Platelet concentrates were transported routinely in cardboard boxes at ambient temperature. They were then stored in an agitator at 20 degrees C to 24 degrees C in the blood bank. We measured changes in beta-thromboglobulin, pH, platelet distribution width (PDW) and platelet counts before and after shipment and storage. The level of beta-thromboglobulin reflects platelet activation and was determined by enzyme immunoassay. The beta-thromboglobulin levels and platelet counts were not significantly different after transportation and during the storage period but there were significant changes in pH and PDW after storage (p < 0.001). Regression study showed that the prestorage platelet counts and pH were strongly associated with the pH at the end of storage (r = -0.71, r = 0.75 respectively). We concluded that the current shipment technique has no adverse effect on the in vitro characteristics of platelets, and the prestorage pH and platelet count could be used as predictors for the pH at end of storage. The data indicate that it is important to measure the prestorage pH and platelet count to set up an optimal storage strategy.

Blood Platelets↗
PubMed1996

Image compression in digital mammography: effects on computerized detection of subtle microcalcifications.

Our previous receiver operating characteristic (ROC) study indicated that the detection accuracy of microcalcifications by radiologists is significantly reduced if mammograms are digitized at 0.1 mm x 0.1 mm. Our recent study also showed that detection accuracy by computer decreases as the pixel size increases from 0.035 mm x 0.035 mm. It is evident that very large matrix sizes have to be used for digitizing mammograms in order to preserve the information in the image. Efficient compression techniques will be needed to facilitate communication and archiving of digital mammograms. In this study, we evaluated two compression techniques: full frame discrete cosine transform (DCT) with entropy coding and Laplacian pyramid hierarchical coding (LPHC). The dependence of their efficiency on the compression parameters was investigated. The techniques were compared in terms of the trade-off between the bit rate and the detection accuracy of subtle microcalcifications by an automated detection algorithm. The mean-square errors in the reconstructed images were determined and the visual quality of the error images was examined. It was found that with the LPHC method, the highest compression ratio achieved without a significant degradation in the detectability was 3.6:1. The full frame DCT method with entropy coding provided a higher compression efficiency of 9.6:1 at comparable detection accuracy. The mean-square errors did not correlate with the detection accuracy of the microcalcifications. This study demonstrated the importance of determining the quality of the decompressed images by the specific requirements of the task for which the decompressed images are to be used. Further investigation is needed for selection of optimal compression technique for digital mammograms.

Breast Diseases↗
PubMed1995

Mycoplasmas and oncogenesis: persistent infection and multistage malignant transformation.

Oncogenic potential of human mycoplasmas was studied using cultured mouse embryo cells, C3H/10T1/2 (C3H). Mycoplasma fermentans and Mycoplasma penetrans, mycoplasmas found in unusually high frequencies among patients with AIDS, were examined. Instead of acute transformation, a multistage process in promotion and progression of malignant cell transformation with long latency was noted; after 6 passages (1 wk per passage) of persistent infection with M. fermentans, C3H cells exhibited phenotypic changes with malignant characteristics that became progressively more prominent with further prolonged infection. Up to at least the 11th passage, all malignant changes were reversible if mycoplasmas were eradicated by antibiotic treatment. Further persistent infection with the mycoplasmas until 18 passages resulted in an irreversible form of transformation that included the ability to form tumors in animals and high soft agar cloning efficiency. Whereas chromosomal loss and translocational changes in C3H cells infected by either mycoplasma during the reversible stage were not prominent, the onset of the irreversible phase of transformation coincided with such karyotypic alteration. Genetic instability--i.e., prominent chromosomal alteration of permanently transformed cells--was most likely caused by mutation of a gene(s) responsible for fidelity of DNA replication or repair. Once induced, chromosomal alterations continued to accumulate both in cultured cells and in animals without the continued presence of the transforming microbes. Mycoplasma-mediated multistage oncogenesis exhibited here shares many characteristics found in the development of human cancer.

AIDS-Related Opportunistic Infections↗
PubMed1995

Classification of microcalcifications in radiographs of pathologic specimens for the diagnosis of breast cancer.

RATIONALE AND OBJECTIVES: Early detection of breast cancer depends on accurate classification of microcalcifications. We have developed a computer vision system that has the potential to classify microcalcifications objectively and consistently to aid radiologists in diagnosing breast cancer. METHODS: A convolution neural network (CNN) was used to classify benign and malignant microcalcifications in radiographs of pathologic specimens. Digital images were acquired by digitizing radiographs at a high resolution of 21 microns x 21 microns. RESULTS: Eighty regions of interest selected from digitized radiographs of pathologic specimens were used for training and testing of the neural network system. The CNN achieved an Az value (area under the receiver operating characteristic curve) of 0.90 in classifying clusters of microcalcifications associated with benign and malignant processes. CONCLUSION: Classification of microcalcifications in pathologic specimens for diagnosis of breast cancer was achieved at a high level in our computer vision system, which consists of high-resolution digitization of mammograms and a CNN.

Breast Neoplasms↗
PubMed1995

Computer-aided detection of mammographic microcalcifications: pattern recognition with an artificial neural network.

We are developing a computer program for automated detection of clustered microcalcifications on mammograms. In this study, we investigated the effectiveness of a signal classifier based on a convolution neural network (CNN) approach for improvement of the accuracy of the detection program. Fifty-two mammograms with clustered microcalcifications were selected from patient files. The clusters on the mammograms were ranked by experienced mammographers and divided into an obvious group, an average group, and a subtle group. The average and subtle groups were combined and randomly divided into two sets, each of which was used as training or test set alternately. The obvious group served as an additional independent test set. Regions of interest (ROIs) containing potential individual microcalcifications were first located on each mammogram by the automated detection program. The ROIs from one set of the mammograms were used to train CNNs of different configurations with a back-propagation method. The generalization capability of the trained CNNs was then examined by their accuracy of classifying the ROIs from the other set and from the obvious group. The classification accuracy of the CNNs for the ROIs was evaluated by receiver operating characteristic (ROC) analysis. It was found that CNNs of many different configurations can reach approximately the same performance level, with the area under the ROC curve (Az) of 0.9. We incorporated a trained CNN into the detection program and evaluated the improvement of the detection accuracy by the CNN using free response ROC analysis. Our results indicated that, over a wide range of true-positive (TP) cluster detection rate, the CNN classifier could reduce the number of false-positive (FP) clusters per image by more than 70%. For the obvious cases, at a TP rate of 100%, the FP rate reduced from 0.35 cluster per image to 0.1 cluster per image. For the average and subtle cases, the detection accuracy improved from a TP rate of 87% at an FP rate of four clusters per image to a TP rate of 90% at an FP rate of 1.5 clusters per image.

Automation↗
PubMed1995

In vitro antibiotic susceptibility testing of clinical isolates of Mycoplasma penetrans from patients with AIDS.

In vitro susceptibilities of Mycoplasma penetrans were determined. MICs and MBCs were determined. The MICs at which 50% of the isolates are inhibited (micrograms per milliliter) for broth dilution testing were as follows: azithromycin, 0.039; chloramphenicol, 0.625; ciprofloxacin, 0.156; clindamycin, 0.078; doxycycline, 0.312; erythromycin, 0.312; gentamicin. > 10; levofloxacin, 0.078; lincomycin, 0.625; streptomycin, > 10; and tetracycline, 1.25. Bactericidal activity was significant only for ciprofloxacin (MBC at which 50% of the isolates are killed, 0.312 microgram/ml) and levofloxacin (MBC at which 50% of the isolates are killed, 0.312 microgram/ml).

AIDS-Related Opportunistic Infections↗
PubMed1994

Development of a continuous coupled enzymatic assay for myo-inositol monophosphatase.

Myo-inositol monophosphatase, an enzyme purified from brain tissues, catalyses the dephosphorylation of myo-inositol 1-phosphate. This enzyme has become the subject of intense research interest since myo-inositol is needed for the resynthesis of phosphatidylinositol in cell membranes. Since phosphate contamination has always been a problem for the assay of this enzyme activity, we have developed a coupled enzymatic assay for detecting the activity of the phosphatase with no interference by the presence of phosphate. The assay is based on the measurement of inositol release after dephosphorylation and subsequent conversion of inositol into scyllo-inosose by a second enzyme, inositol dehydrogenase from Enterobacter aerogenes. Since the second reaction requires the presence of beta-NAD+, the activity of the dephosphorylation reaction can be monitored continuously by the increase of absorbance at 340 nm spectrophotometrically.

Animals↗
PubMed1994

Induced mouse spleen B-cell proliferation and secretion of immunoglobulin by lipid-associated membrane proteins of Mycoplasma fermentans incognitus and Mycoplasma penetrans.

Mycoplasmas have been implicated as a possible cofactor in AIDS pathogenesis. Mycoplasma fermentans and M. penetrans infect human immunodeficiency virus-positive patients at a significantly higher frequency than non-human immunodeficiency virus-infected control subjects. Various mycoplasmal membrane preparations are known to affect the functions of immune cells both in vitro and in vivo. A group of lipid-associated membrane proteins (LAMPs) extracted by Triton X-114 from mycoplasmas are major antigenic targets of human host antibody responses. In this study, LAMPs prepared from both M. fermentans and M. penetrans nonspecifically stimulated spleen cells of CBA/CaH mice to proliferate. LAMPs were also stimulatory to spleen cells from athymic mice. On the other hand, enriched splenic T cells from CBA/CaH mice with or without accessory cells responded poorly. Thus, the mitogenic effect of mycoplasmal LAMPs appeared mainly on B cells. High levels of immunoglobulin (Ig) M and low but detectable amounts of IgG were found in the supernatant of LAMP-treated splenic cell culture. M. penetrans LAMPs had a much more potent effect on murine spleen cells than did M. fermentans incognitus LAMPs in inducing both B-cell proliferation and Ig secretion. In conclusion, the mycoplasmal LAMPs contained an active component(s) with T-independent B-cell mitogenic effect.

Animals↗