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Biomedical subjects

L Tan

Publications and source records attributed to L Tan.

At least 19 recordsLinked to original sources
PubMed2000

Extracellular protein kinase A as a cancer biomarker: its expression by tumor cells and reversal by a myristate-lacking Calpha and RIIbeta subunit overexpression.

Overexpression of cAMP-dependent protein kinase (PKA) type I isozyme is associated with cell proliferation and neoplastic transformation. The presence of PKA on the external surface of LS-174T human colon carcinoma cells has been shown. Here, we show that cancer cells of various cell types excrete PKA into the conditioned medium. This extracellular PKA (ECPKA) is present in active, free catalytic subunit (C subunit) form, and its activity is specifically inhibited by PKA inhibitory protein, PKI. Overexpression of the Calpha or RIalpha subunit gene of PKA in an expression vector, which up-regulates intracellular PKA type I, markedly up-regulates ECPKA expression. In contrast, overexpression of the RIIbeta subunit, which eliminates PKA type I, up-regulates PKA type II, and reverts the transformed phenotype, down-regulates ECPKA. A mutation in the Calpha gene that prevents myristylation allows the intracellular PKA up-regulation but blocks the ECPKA increase, suggesting that the NH(2)-terminal myristyl group of Calpha is required for the ECPKA expression. In serum of cancer patients, the ECPKA expression is up-regulated 10-fold as compared with normal serum. These results indicate that the ECPKA expression is an ordered cellular response of a living cell to actively exclude excess intracellular PKA molecules from the cell. This phenomenon is up-regulated in tumor cells and has an inverse relationship with the hormone dependency of breast cancer. Thus, the extracellular PKA may serve as a potential diagnostic and prognostic marker for cancer.

3T3 Cells↗
PubMed2000

Poor correspondence between predicted and experimental binding of peptides to class I MHC molecules.

Naturally processed peptides presented by class I major histocompatibility complex (MHC) molecules display a characteristic allele specific motif of two or more essential amino acid side chains, the so-called peptide anchor residues, in the context of an 8-10 amino acid long peptide. Knowledge of the peptide binding motif of individual class I MHC molecules permits the selection of potential peptide antigens from proteins of infectious organisms that could induce protective T-cell-mediated immunity. Several methods have been developed for the prediction of potential class I MHC binding peptides. One is based on a simple scanning for the presence of primary peptide anchor residues in the sequence of interest. A more sophisticated technology is the utilization of predictive computer algorithms. Here, we have analyzed the experimental binding of 84 peptides selected on the basis of the presence of peptide binding motifs for individual class I MHC molecules. The actual binding was compared with the results obtained when analyzing the same peptides by two well-known, publicly available computer algorithms. We conclude that there is no strong correlation between actual and predicted binding when using predictive computer algorithms. Furthermore, we found a high number of false-negatives when using a predictive algorithm compared to simple scanning for the presence of primary anchor residues. We conclude that the peptide binding assay remains an important step in the identification of cytotoxic T lymphocyte (CTL) epitopes which can not be substituted by predictive algorithms.

Algorithms↗
PubMed2000

Integrin expression by primary and immortalized human chondrocytes: evidence of a differential role for alpha1beta1 and alpha2beta1 integrins in mediating chondrocyte adhesion to types II and VI collagen.

OBJECTIVE: Chondrocytes have been shown to express beta1-containing integrins both in vitro and in situ, but their role in regulating chondrocyte function is poorly understood. The objective of this study was to determine how the relative expression of different integrins may be modulated in relation to the differentiated state and proliferative capacity of the chondrocyte. DESIGN: Integrin expression by four different cell lines of human chondrocytes immortalized with Simian virus 40 large T-antigen (SV40-TAg) was studied and compared to primary chondrocytes. Differences in alpha1 and alpha2 integrin subunit expression were utilized to further study the role of these integrins in mediating adhesion to types II and VI collagen. RESULTS: The overall cell-surface levels of beta1-containing integrins were higher on all four immortalized cell lines which expressed over 10-fold higher levels of alpha2 and alpha3 integrin subunits compared to primary cells. However, primary cells expressed higher levels of the alpha1 integrin subunit which was not expressed by T/C28a4 cells and expressed at variable and lower levels in the other lines. Levels of the alpha3 integrin subunit were significantly greater on the highly proliferative juvenile costal chondrocyte lines (T/C-28a4, C-2812, and C-20a4) compared to primary articular chondrocytes and tsT/AC-62 cells which were derived from adult articular chondrocytes. Expression of alpha5 was similar among primary cells and cell lines except on C-20/A4 cells which had an average of over 4-fold higher levels. None of the primary or immortalized chondrocytes tested expressed significant levels of alpha4. Cell adhesion assays revealed that both alpha1beta1 and alpha2beta1 could serve as chondrocyte adhesion receptors for types II and VI collagen. In cell lines expressing both integrins, alpha1beta1 was the preferential receptor for type VI collagen while alpha2beta1 was the preferential receptor for type II collagen. Rather than inhibiting adhesion, incubation with the alpha3 blocking antibody P1B5 increased adhesion of C-28/12 cells to both fibronectin and type II collagen by 67% and 100% respectively. CONCLUSIONS: Immortalization with SV40-TAg results in altered integrin expression by chondrocytes. Changes in the relative levels of alpha1, alpha2, and alpha3 subunits may significantly alter the manner in which chondrocytes interact with types II and VI collagen in the extracellular matrix.

Adult↗
PubMed2000

Twelve year outcomes following bacterial meningitis: further evidence for persisting effects.

AIM: To determine whether intellectual and cognitive impairments observed seven years following early childhood bacterial meningitis persist into adolescence. METHODS: Blinded neuropsychological, auditory, and behaviour assessments were conducted in 109 (69%) subjects from an original cohort of 158 children, seven and 12 years after their meningitis, and in 96 controls. RESULTS: Meningitis subjects remained at greater risk than controls for any disability (odds ratio OR 4.7, confidence interval 2.2 to 9.6). Those with acute neurological complications had more sequelae than children with uncomplicated meningitis or controls (47% v 30% v 11.5% respectively; p < 0.001). Differences in intellectual, academic, and high level cognitive function between subjects and controls were maintained at the seven and 12 year assessments. In contrast, lower order skills improved, while behaviour scores deteriorated significantly (p = 0.033). CONCLUSIONS: Many of the deficits identified at the seven year follow up persist 12 years after an episode of bacterial meningitis.

Adolescent↗
PubMed2000

Abdominal coarctation and Alagille syndrome.

Structural cardiac defects such as peripheral pulmonary stenosis are well-described in Alagille syndrome (AS), which is transmitted in an autosomal dominant inheritance. The genetic defect, with incomplete penetrance and variable expression, is localized to the short arm of chromosome 20. Abdominal coarctation is an uncommon congenital anomaly, with a spectrum of symptoms that may range from hypertension, intermittent claudication to abdominal pain. The association of abdominal coarctation with AS is rarely described. We report such a patient who also had aberrations of the visceral vascular supply involving the celiac, splenic, and superior mesenteric arteries. The indications to treat the coarctation, and in the context of a patient with AS, in whom liver transplantation may be contemplated at some stage, merit discussion.

Alagille Syndrome↗
PubMed1999

The Drosophila CPEB homolog, orb, is required for oskar protein expression in oocytes.

The establishment of polarity axes in the Drosophila egg and embryo depends upon the localization and on-site expression of maternal mRNAs. The critical step in the targeting of posterior determinants is the localization of oskar (osk) mRNA to the pole and its on-site translation. Osk protein then recruits other posterior group gene products involved in the formation of pole plasm and in the localization and regulation of the posterior determinant, nanos. Here we have investigated the role of the Drosophila CPEB homolog, the orb gene, in the osk mRNA localization pathway. We demonstrate that the expression of Osk protein is dependent upon the orb gene. In strong orb mutants, Osk protein expression is undetectable, while in the hypomorphic mutant, orb(mel), little or no on-site expression of Osk protein at the posterior pole is observed. The defects in Osk protein accumulation in orb mutant ovaries are correlated with a reduction in the length of the osk poly(A) tails. We show that osk mRNA is in immunoprecipitable complexes with Orb protein in ovaries and that the osk 3' UTR can be UV cross-linked to Orb protein in ovarian extracts. These data suggest that Orb is required to activate the translation of osk mRNA and at that this may be accomplished by a mechanism similar to that used by the Xenopus CPEB protein to control translation of "masked" mRNAs.

3' Untranslated Regions↗
PubMed1999

Identification and characterization of endothelial glycoprotein Ib using viper venom proteins modulating cell adhesion.

The expression and function of a glycoprotein Ib (GPIb) complex on human umbilical vein endothelial cells (HUVECs) is still a matter of controversy. We characterized HUVEC GPIb using viper venom proteins: alboaggregins A and B, echicetin, botrocetin, and echistatin. Echicetin is an antagonist, and alboaggregins act as agonists of the platelet GPIb complex. Botrocetin is a venom protein that alters von Willebrand factor (vWF) conformation and increases its binding affinity for the GPIb complex. Echistatin is a disintegrin that blocks alphavbeta3. Echistatin, but not echicetin, inhibited the adhesion to vWF of Chinese hamster ovary (CHO) cells transfected with alphavbeta3. We found the following: (1) Binding of monoclonal antibodies against GPIbalpha to HUVECs was moderately increased after stimulation with cytokines and phorbol ester. Echicetin demonstrated an inhibitory effect. (2) Both echicetin and echistatin, an alphavbeta3 antagonist, inhibited the adhesion of HUVECs to immobilized vWF in a dose-dependent manner. The inhibitory effect was additive when both proteins were used together. (3) Botrocetin potentiated the adhesion of HUVECs to vWF, and this effect was completely abolished by echicetin, but not by echistatin. (4) CHO cells expressing GPIbalphabeta/IX adhered to vWF (in the presence of botrocetin) and to alboaggregins; GPIbalpha was required for this reaction. Echicetin, but not echistatin, inhibited the adhesion of cells transfected with GPIbalphabeta/IX to immobilized vWF. (5) HUVECs adhered strongly to immobilized vWF and alboaggregins with extensive spreading, which was inhibited by LJ1b1, a monoclonal antibody against GPIb. The purified alphavbeta3 receptor did not interact with the alboaggregins, thereby excluding the contribution of alphavbeta3 in inducing HUVEC spreading on alboaggregins. In conclusion, our data confirm the presence of a functional GPIb complex expressed on HUVECs in low density. This complex may mediate HUVEC adhesion and spreading on immobilized vWF and alboaggregins.

Animals↗
PubMed1999

Microfabricated filters for microfluidic analytical systems.

Solvent and reagent filters were micromachined into quartz wafers using deep reactive ion etching to create a network of intersecting 1.5 x 10 microns channels. When placed at the bottom of reservoirs with a side exit, this channel network behaved as a lateral percolation filter composed of an array of cubelike structures one layer deep. Flow through these filters was driven by electroosmotic flow (EOF). Silanol groups at the walls of channels in the network provided the requisite charge to trigger EOF when voltage was applied laterally to the filter. Adsorption of cationic proteins in this silanol-rich matrix was controlled by the application of a polyacrylamide coating prepared by bonding N-hydroxysuccinimide (NHS)-activated poly(acrylic acid) to (gamma-aminopropyl)silane-derivatized filters. Subsequent reaction of residual NHS groups in the coating with 2-(2-aminoethoxy)ethanol provided channels of low charge density and adsorptivity. These lateral percolation filters were shown to be efficacious in filtering solvents containing a variety of particulate materials, ranging from dust to cells.

Adsorption↗
PubMed1999

Saikosaponins from roots of Bupleurum scorzonerifolium.

Saikosaponin u and saikosaponin v, were isolated from the roots of Bupleurum scorzonerifolium and these saponins were identified as 3-O-[beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl- (1-->3)-beta-D-fucopyranosyl]-3 beta,16 alpha,23,28-tetrahydroxy-olean- 11,13(18)-dien-30-oic acid-30-O-[pentito(1-->1)-beta-D-glucopyranosyl-(6-->)] ester and 3-O-[beta-D-glucopyranosyl-(1-->3)-beta-D-fucopyranosyl]-3 beta,16 alpha,23,28-tetrahydroxy-olean-11,13(18)-dien-30-oic acid-30-O-[pentito(1-->1)-beta-D-glucopyranosyl(6-->)] ester, respectively.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1999

Role of screening chest computed tomography in patients with advanced head and neck cancer.

OBJECTIVE: The presence of pulmonary metastases significantly alters the treatment of patients with head and neck cancers. Currently, a chest radiograph (CXR) is used as a screening examination, although a chest CT (CCT) can detect smaller lesions. The aim of this study was to evaluate the benefit of CCT as a screening tool in patients with newly diagnosed advanced head and neck cancers. METHOD: New patients with stage III and IV head and neck squamous cell carcinomas were enrolled in this prospective study from August 1994 to December 1995. Twenty-five patients underwent CXR ($71) and CCT ($597) within 2 weeks of diagnosis of the index cancer. RESULTS: In 20 patients neither the CXR nor the CCT showed any evidence of pulmonary malignancy. Two patients had normal CXRs but possible metastases on CCT. Both the pulmonary lesions resolved on follow-up evaluation. Two patients had suspicious lesions on CXR, 1 of whom had a normal CCT. The second patient underwent CT-guided biopsy which was negative for malignancy. Both the CXR and CCT of the final patient, who had a bronchogenic carcinoma, were suspicious. CONCLUSION: In 2 patients CCT detected suspicious lesions missed on CXR, although neither revealed malignancy. Three patients with suspicious CXRs would have had CCTs anyway. Thus 22 of 25 CCTs done at the additional cost of $13,314 did not add to the sensitivity of the screening for pulmonary metastasis or second lung primary.

Adult↗
PubMed1999

Diffuse alveolar damage in BCGosis: a rare complication of intravesical bacillus Calmette-Guérin therapy for transitional cell carcinoma.

Intravesical administration of bacillus Calmette-Guérin is a relatively simple procedure used in the treatment of superficial transitional cell carcinoma of the urinary bladder. It is usually well tolerated with few major side effects. In rare instances, systemic complications can result in death. The usual autopsy finding is that of caseating and non-caseating granulomata in the affected organ. We report the second case of BCGosis in which granulomata together with acute and organising phase diffuse alveolar damage were found in the lungs.

Aged↗
PubMed1999

Biomechanics of A-to-T flap design.

OBJECTIVES/HYPOTHESIS: The objective of this study was to determine the vertical height, horizontal incision width, and extent of undermining that correlated with the lowest closure tension. STUDY DESIGN: Prospective, cadaver study. METHODS: Forty "A-to-T" flaps were made on the torso and lower extremities of fresh cadavers. Ten flaps each were designed at heights of three, four, and five defect radii. Closing tensions were measured for each of these flaps initially, followed by serial base extensions. Based on the information from these first flaps, 10 additional flaps were made at the optimal height and base extensions. These flaps were then serially undermined and tension measurements taken. RESULTS: Our results suggest that making the vertical height of the "A" twice the height of the defect yields a significant decrease in tension of closure when compared with a vertical height one and a half times the defect (P < .01), while increasing the height to two and a half times the defect height provides only a minimal further reduction in closure tension. Extending the base (horizontal) incision one defect diameter in each direction offers the greatest reduction in closing tension. Undermining up to three times the diameter of the defect offers progressive improvement in the tension of closure, while further undermining confers little additional benefit. CONCLUSIONS: Our findings indicate that the ideal A-to-T flap is designed to be twice the height of the original defect, with base extensions one defect diameter in each direction, and undermined to three times the diameter of the defect.

Biomechanical Phenomena↗
PubMed1999

An integrated theory of the no-reflow phenomenon and the beneficial effect of vascular washout on no-reflow.

OBJECTIVES: No-reflow is failure of perfusion in free tissue transfer despite adequate arterial inflow. The objectives of this study were to construct a theory of interactive mechanisms of the no-reflow phenomenon and to determine whether preischemic vascular washout could increase flap ischemia tolerance. STUDY DESIGN: The evidence for the role of various mechanisms in the development of no-reflow is reviewed, and an integrated network proposed. A rat-groin free flap model is used to test preischemic vascular washout with normal saline, heparinized normal saline, lactated Ringer's solution, Tis-U-Sol, and Viaspan. METHODS: The mean ischemia tolerance of this flap without any therapeutic intervention was first determined, using 22 animals. An additional 50 animals were used to compare with the control group the ischemia tolerance of flaps washed out with the above fluids before their ischemic period. RESULTS: The critical ischemia time 50 (time after which half of the flaps are expected to survive and half, die) of the untreated flap is 23.4 hours in this model (P<.05). Flaps washed out with normal saline or lactated Ringer's solution have significantly worse ischemia tolerance (P<.0001). Flaps washed out with Tis-U-Sol or Viaspan behave similarly to the control group (P>.57). Flaps receiving preischemic washout with heparinized normal saline (4,000 units/L) had a significantly better outcome than the control group (P<.027). CONCLUSIONS: Preischemic washout with normal saline, lactated Ringer's solution, or heparinized Tis-U-Sol is detrimental for flap survival after ischemia, Tis-U-Sol- and Viaspan-treated flaps do have ischemia tolerance similar to the control group, and flaps washed out with heparinized normal saline have a survival advantage in this model.

Animals↗
PubMed1999

Interobserver variability in the measurement of internal carotid stenosis.

OBJECTIVE: To assess interobserver variability in the measurement of carotid stenoses from digital subtraction angiograms displayed in different ways (nonmagnified or magnified, white or black arteries); and to compare human readers with computer-generated densitometric measurements of vessel stenosis. METHODS: Digital subtraction angiograms of 20 proximal internal carotid artery stenoses were laser printed in the following ways: (1) Nonmagnified white artery on a black background; (2) Magnified white artery on a black background; (3) Nonmagnified black artery on a white background; (4) Magnified black artery on a white background. This resulted in 80 images of internal carotid artery stenoses. These stenoses were independently measured by 4 radiologists using the North American Symptomatic Carotid Endarterectomy Trial method. A computer-generated densitometric measurement of the black nonmagnified images was also obtained. RESULTS: The most reliable stenosis measurements were obtained from the nonmagnified black and white artery images. The interobserver variability in the measurement of internal carotid stenoses using these images was quite small. Variability increased with the use of magnification. The computer-generated stenosis measurements were consistently much higher than those of the radiologists. CONCLUSION: There was significant variability in measurements made from magnified images and between human readers and computer-generated measurements. This has great clinical significance. Readers of digital angiographic images must determine the most reliable, reproducible images generated by their equipment, as these measurements significantly affect treatment of patients with symptomatic internal carotid artery stenosis.

Absorptiometry, Photon↗
PubMed1999

Treatment of delayed partial bronchial rupture with expandable metallic stent.

Traumatic bronchial rupture is a rare entity. The severity of the trauma often causes lethal injury to other thoracic organs. The incidence in patients with blunt chest trauma admitted to the hospital ranges from 1.5% to 3%. As a rule, early diagnosis and surgical treatment are important to facilitate successful repair of the disruption. We describe an unusual case of bronchial rupture which was diagnosed 15 days after blunt chest trauma and was treated by bronchial stenting. The success of this case involving the left main bronchial rupture provides a feasible alternative to the repair of partial airway disruption and greatly reduces the morbidity.

Adult↗