PubMed Health⌕ Search

Biomedical subjects

S C Leung

Publications and source records attributed to S C Leung.

13 recordsLinked to original sources
PubMed2001

Subfrontal schwannoma masquerading as meningioma.

Intracranial schwannomas not associated with cranial nerves are rare and seldom encountered in the subfrontal region. We report a case of subfrontal schwannoma in a 21-year-old man who presented with seizures. Radiological features resembled an olfactory groove meningioma. The histological diagnosis of schwannoma was confirmed by immunohistochemical staining with S-100 and electron microscopy. We advocate the use of immunohistochemistry and electron microscopy as adjuncts to conventional light microscopy in differentiating schwannomas from meningiomas. Surgery remains the main therapeutic modality and complete excision is associated with cure.

Adult↗
PubMed1997

Classification of user expertise level by neural networks.

A neural network approach to low-level user modeling is described, in the context of text editing tasks using the Jove editor. Knowledge of a user's expertise is extracted automatically, based on their interaction with Jove over a two week period. A MLP classifier which uses rprop learning and incorporates output data fuzzification is developed to classify users into one of five expertise levels. Classification into the correct level is achieved in around 80% of the cases, with misclassification being restricted to adjacent classes. The neurofuzzy system is seen to outperform not only the binary classifier of Beale [1989], but also production rule and inductive expert systems developed especially for comparison purposes in this study.

Artificial Intelligence↗
PubMed1997

Muscle fatigue monitoring using wavelet decomposition of surface EMG.

Monitoring the local muscle fatigue in maximum voluntary isometric contraction is successful using median frequency and mean power frequency of the surface EMG. However, it has very limited success in maximum voluntary dynamic contraction. We showed that the relaxation electromechanical delay was a reliable fatigue indicator during the maximum voluntary isokinetic concentric contraction. In this paper, we use wavelet decomposition to generate fatigue indicators including contraction delay (WCD), relaxation delay (WRD), and the power ratio related to high frequency and low frequency regions (HF/LF) of the power spectrum of surface electromyogram (SEMG). Eight subjects were asked to perform right knee isokinetic contractions at two angular velocities (120 and 240 degrees/sec). Total work (TW), knee angle, and four channels of quadriceps SEMGs were sampled simultaneously. The results indicate that the initial slopes of WCD and WRD increase and are correlated with TW significantly, the initial slope of HF/LF declines and is correlated with TW significantly, and the WRD is more stable than the WCD. It concludes that wavelet decomposition enhances the features of surface EMG, and that power ratio (HF/LF) and contraction and relaxation delays obtained with the EMG wavelet decomposition can be used to monitor the muscle fatigue during the maximum voluntary isokinetic concentric contraction.

Electromyography↗
PubMed1989

Evaluation of neutralizing antibodies in patients treated with recombinant interferon-beta ser.

Patients receiving recombinant interferon-beta ser (rIFN-beta ser) for cancer and viral diseases were evaluated for formation of antibodies with IFN-neutralizing activity. The assay for serum neutralizing activity measures the ability of the sample to neutralize the antiviral activity of rIFN-beta ser. Neutralizing antibody incidence was route dependent. Of 335 patients treated intravenously, 3 were positive, representing an incidence of 0.9%. The remaining 13 antibody-positive patients had been treated subcutaneously, representing an incidence of 9.6% (13/136). In general, peak titers for neutralizing activity were low to moderate; 15 of the 16 patients (94%) had titers between 100 and 2,000 neutralizing units/ml. The incidence of neutralizing antibodies was higher in patients who had been under study for longer periods of time. Mean time of onset of neutralizing activity for the 16 positive patients was about 5 months. Because length of time on study appeared to be a possible predisposing factor for development of neutralizing antibodies, we recalculated the incidence of this activity for all patients on study for 5 months or longer (90 i.v., 71 s.c.). All of the 16 neutralizing-positive patients were on study for more than 150 days, whereas the remaining 87 in the i.v. group and 58 in the s.c. group were negative. Thus, a longer time on study appears to increase incidence, but in only a portion of subjects treated. No adverse clinical effects could be directly associated with neutralizing antibodies.

Antibodies↗
PubMed1987

Parathyroid hormonelike protein from human renal carcinoma cells. Structural and functional homology with parathyroid hormone.

A variety of solid tumors secrete proteins that are immunochemically distinct from parathyroid hormone (PTH) but activate PTH-responsive adenylate cyclase. Such PTH-like proteins have been proposed as mediators of the hypercalcemia and hypophosphatemia frequently associated with malignancies. We purified to apparent homogeneity a PTH-like protein with a molecular weight of 6,000, that is produced by human renal carcinoma cells. The amino-terminal sequence of the PTH-like protein and that of human PTH were found to display at least five identities in the first 13 positions. The purified protein bound to PTH receptors, activated adenylate cyclase in renal plasma membranes, and stimulated cAMP formation in rat osteosarcoma cells. The PTH-like protein reproduced two additional effects of PTH, stimulation of bone resorption in fetal rat limb bone cultures and inhibition of phosphate uptake in cultured opossum kidney cells. These properties are consistent with a role for PTH-like proteins as mediators of the syndrome of malignancy-associated hypercalcemia.

Carcinoma, Renal Cell↗
PubMed1987

Parathyroid hormone-like adenylate cyclase-stimulating activity from a human carcinoma is associated with bone-resorbing activity.

We found previously that a human renal carcinoma cell line derived from a hypercalcemic patient induces humoral hypercalcemia when grown as allografts in the nude mouse and secretes a protein that activates adenylate cyclase via the PTH receptor. The purpose of this study was to examine the conditioned medium of this cell line for bone-resorbing activity in vitro. Processed conditioned medium produced dose-dependent stimulation of bone resorption in cultured fetal rat limb bone explants. Two PTH antagonists were used to assess the PTH receptor dependence of this bone-resorbing activity. Neither [8Nle,18Nle,34Tyr]bovine (b) PTH-(3-34) amide nor [34Tyr]bPTH-(7-34)amide inhibited bone resorption or limb bone cAMP accumulation induced by either processed conditioned medium or equivalent concentrations of bPTH-(1-34). As an alternate means to assess whether this tumor-derived PTH-like protein had intrinsic bone-resorbing activity, the latter was measured during partial purification of PTH-like adenylate cyclase-stimulating activity (ACSA) from conditioned medium by consecutive gel filtration and reverse phase HPLC. The bone-resorbing activity in conditioned medium could not be resolved from PTH-like ACSA by these two separation techniques, indicating that the activities may be intrinsic to the same protein. These results are consistent with the view that a tumor-derived protein with PTH-like ACSA and bone-resorbing activity may be responsible for hypercalcemia in vivo.

Adenocarcinoma↗
PubMed1986

Pathogenesis of hypercalcemia in nude mice bearing a human renal carcinoma.

When grown as sc tumors in the nude (nu/nu) mouse, cells of the established human renal carcinoma cell line 786-0 produce hypercalcemia; this has an apparent humoral basis because it is reversed by resection of the primary tumor. We have investigated the pathogenesis of hypercalcemia in this model. Tumor-bearing mice were hypercalcemic (13.4 +/- 0.9 vs. 9.52 +/- 0.13 mg/dl in control mice) and hypophosphatemic (10.0 +/- 0.8 vs. 13.8 +/- 1.5 mg/dl in control mice; all values are mean +/- SEM). The serum concentration of 1,25-dihydroxyvitamin D was increased in tumor-bearing animals (70.0 +/- 9.3 vs. 43.8 +/- 4.8 pg/ml in control animals). Urinary excretion of cAMP was similar in control (33.7 +/- 1.4 nmol/mg creatinine) and tumor-bearing mice (38.2 +/- 4.7 nmol/mg creatinine). However, in the latter, the acute response of urinary cAMP to PTH was blunted. Although intestinal calcium transport in everted duodenal sacs in vitro was increased in tumor-bearing mice, hypercalcemia was unaffected by feeding the animals for 8 days a diet containing less than 0.02% calcium. Hence, absorption of dietary calcium did not play a significant role in maintenance of hypercalcemia. In hypercalcemic animals, the calcium content of the humerus was decreased (2.95 +/- 0.08 vs. 3.29 +/- 0.13 mg in controls; P less than 0.05). Quantitative histomorphometric analysis of the distal femoral metaphysis disclosed a significant reduction in trabecular bone volume in tumor-bearing mice (12.0 +/- 1.1% vs. 16.1 +/- 1.1% in controls; P less than 0.02). A strong trend for increased osteoclast surface and number was observed, suggesting that bone resorption was increased. Osteoblast surface and number were also somewhat increased, as was the rate of mineral apposition (2.55 +/- 0.14 vs. 1.91 +/- 0.04 micron/day in controls; P less than 0.01). Thus, the decrease in trabecular bone volume was associated with high turnover of bone, with an apparent net increase in bone resorption. We conclude that hypercalcemia in the nude mouse bearing human renal carcinoma cells is associated with increased bone resorption, high bone turnover, hypophosphatemia, and increased serum levels of 1,25-dihydroxyvitamin D.

Adenocarcinoma↗
PubMed1985

Activation of the parathyroid hormone receptor-adenylate cyclase system in osteosarcoma cells by a human renal carcinoma factor.

Human renal carcinoma cell line 786-0 elaborates a protein that is structurally and immunochemically distinct from parathyroid hormone (PTH) and that activates renal cortical adenylate cyclase via an interaction with the PTH receptor. Because of the high frequency of excessive bone resorption and resultant hypercalcemia in patients with malignant disease we evaluated the ability of this 786-0 cell factor to reproduce PTH action in bone-derived cells. The 786-0 factor as well as bovine PTH (BPTH) (1-34) and prostaglandin E1 produced marked increases in cyclic adenosine 3':5'-monophosphate (cAMP) accumulation in the clonal rat osteosarcoma cell line UMR-106. A competitive antagonist of PTH action, [norleucine8, norleucine18, tyrosine34] BPTH(3-34)amide, blocked the cAMP stimulation produced by 786-0 factor and BPTH(1-34) but not that produced by prostaglandin E1. In the presence of forskolin (0.1 microM) UMR-106 cells were extremely sensitive to 786-0 factor, showing significant increases in cAMP production at a concentration 10-fold less than that required to activate adenylate cyclase in renal membranes. In contrast UMR-106 cells were less sensitive to BPTH(1-34) than were renal membranes. This preferential increase in sensitivity to 786-0 factor was not seen in membranes prepared from UMR-106 cells suggesting the importance of cytosolic components. Six additional human genitourinary carcinoma cell lines were found to produce factors that increased cAMP levels in UMR-106 cells. We conclude that 786-0 factor is a potent activator of the PTH receptor-adenylate cyclase system in these bone-derived cells. These findings are consistent with the view that cancer-associated hypercalcemia may frequently be attributable to tumor secretion of proteins (such as 786-0 factor) that are distinct from PTH but are capable of activating skeletal PTH receptors.

Adenylyl Cyclases↗
PubMedDate not supplied

The identification of credit card encoders by hierarchical cluster analysis of the jitters of magnetic stripes.

The relative bit density variation graphs of 207 specimen credit cards processed by 12 encoding machines were examined first visually, and then classified by means of hierarchical cluster analysis. Twenty-nine credit cards being treated as 'questioned' samples were tested by way of cluster analysis against 'controls' derived from known encoders. It was found that hierarchical cluster analysis provided a high accuracy of identification with all 29 'questioned' samples classified correctly. On the other hand, although visual comparison of jitter graphs was less discriminating, it was nevertheless capable of giving a reasonably accurate result.

Cluster Analysis↗