Biomedical subjects

H Yee

Publications and source records attributed to H Yee.

At least 37 records · Page 2Linked to original sources

PubMed2000

A microfluidic system for high-speed reproducible DNA sizing and quantitation.

Microfabrication technology was used to develop a system consisting of disposable glass chips containing etched channels, reagents including polymer matrix and size standards, computer-controlled instrumentation for performing electrophoretic separations and fluorescence detection of double-stranded DNA, and software for automated data analysis. System performance was validated for separation and quantitation reproducibility using samples varying in amount and size of DNA fragments, buffer composition, and salt concentrations. Several applications of the microfluidic system for DNA analysis have been demonstrated, such as of polymerase chain reaction (PCR) products, sizing of plasmid digests, and detection of point mutations by restriction fragment length polymorphism (RFLP) mapping.

Animals↗

PubMed2000

Infrared spectroscopy of human cells and tissue. VIII. Strategies for analysis of infrared tissue mapping data and applications to liver tissue.

Experimental and computational methods of infrared microspectroscopy (IRI-MSP) and infrared spectral mapping (ISM) are presented. These methods are subsequently applied to the analysis of cirrhotic liver tissue. The sensitivity of infrared spectral mapping toward spectral changes caused by disease will be demonstrated. In addition, the excellent agreement between ISM data and histopathological information will be discussed.

Humans↗

PubMed2000

Topical hepatic hypothermia attenuates pulmonary injury after hepatic ischemia and reperfusion.

BACKGROUND: Prolonged periods of hepatic ischemia are associated with hepatocellular injury and distant organ dysfunction in experimental models. Neutrophils (PMN) and tumor necrosis factor (TNF)-alpha have been implicated, mostly because of their local deleterious effects on the hepatocyte after hepatic ischemia and reperfusion (I/R) injury. We hypothesize that topical hepatic hypothermia (THH) reduces ischemia and reperfusion-induced hepatic necrosis, PMN infiltration, TNF-alpha release, and consequent acute pulmonary injury. STUDY DESIGN: Sprague-Dawley rats (250 to 300g) were evenly divided into three groups: 90 minutes of normothermic (37 degrees C) partial hepatic ischemia (normothermic I/R), 90 minutes of hypothermic (25 degrees C) partial hepatic ischemia (hypothermic I/R), and sham laparotomy (without ischemia). There were six animals in each experimental group per time point unless otherwise specified. Hepatic necrosis and PMN infiltration were evaluated and scored on hematoxylin and eosin-stained liver specimens 12 hours after reperfusion. Serum TNF-alpha levels were determined by ELISA at 0 minutes, 15 minutes, 30 minutes, 1 hour, and 12 hours postreperfusion. Pulmonary PMN infiltration and vascular permeability were measured by myeloperoxidase activity and Evans blue dye extravasation, respectively, to quantitate pulmonary injury 12 hours after reperfusion. RESULTS: Normothermic I/R results in a significant increase in TNF-alpha at 15 and 30 minutes (p < 0.005), PMN infiltration (p < 0.001), and hepatic necrosis (p < 0.001), compared with sham. Institution of THH reduced peak serum TNF-alpha levels by 54% at 15 minutes (p < 0.005) and by 73% at 30 minutes (p < 0.001) postreperfusion compared with normothermic I/R. Similarly, hepatic PMN infiltration and necrosis at 12 hours were reduced by 60% (p < 0.05) and 47% (p < 0.05), respectively. Myeloperoxidase activity and Evans blue extravasation (measures of acute lung injury) were reduced by 42% and 39%, respectively, with institution of THH compared with animals undergoing normothermic I/R (p < 0.001). CONCLUSIONS: These results demonstrate that THH protects the liver from ischemia and reperfusion-induced necrosis and PMN infiltration. In addition, THH reduces the serum levels of TNF-alpha and associated pulmonary injury. These data suggest that the ischemic liver is a potential source of inflammatory mediators associated with hepatic ischemia and reperfusion-induced pulmonary injury.

Analysis of Variance↗

PubMed2000

Vascular apoptosis and involution in gliomas precede neovascularization: a novel concept for glioma growth and angiogenesis.

Vascular changes in gliomas were analyzed by implanting fluorescent-labeled glioma 261 cells in the brains of 28 mice. Seven animals were killed each week for 4 weeks. We investigated the expression of angiopoietin-2 (Ang-2) by in situ hybridization and compared it with the distribution of apoptotic cells identified by DNA strand breaks (using the terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphate nick end labeling [TUNEL] method) and transmission electron microscopy (TEM). As early as 1 week after implantation, tumor cells accumulated around vessels, which expressed Ang-2 and were TUNEL negative. TEM showed tumor cells adjacent to the vascular cells "lifting up" the normal astrocytic feet processes away from the endothelial cells and disrupting normal pericytic cuffing. After 2 weeks the number of perivascular glioma cells had increased. No increase in the number of blood vessels was detected at this time. Vascular cells remained positive for Ang-2 and rare ones were TUNEL positive. TEM showed closely packed proliferating perivascular tumor cells. After 3 weeks, there was vascular involution with scant zones of tumor necrosis. Ang-2 was still detected in vascular cells, but now numerous vascular cells were TUNEL positive. In addition, TEM showed apoptotic vascular cells. After 4 weeks, there were extensive areas of tumor necrosis with pseudopalisading and adjacent angiogenesis. Ang-2 was detected in vascular cells at the edge of the tumors in the invaded brain and in vessels surrounded by tumor cells. At both 3 and 4 weeks, most of the TUNEL-positive tumor cells lacked morphological features characteristic of apoptosis and displayed features consistent with necrotic cell death as determined by TEM. Only rare tumor cells appeared truly apoptotic. In contrast, the TUNEL-positive endothelial cells and pericytes were round and shrunken, with condensed nuclear chromatin by TEM, suggesting that vascular cells were undergoing an apoptotic cell death. These results suggest that vascular cell apoptosis and involution preceded tumor necrosis and that angiogenesis is a later event in tumor progression in experimental gliomas. Moreover, Ang-2 is detected prior to the onset of apoptosis in vascular cells and could be linked to vascular involution.

Angiopoietin-2↗

PubMed2000

Preferential inactivation of the p53 tumor suppressor pathway and lack of EGFR amplification distinguish de novo high grade pediatric astrocytomas from de novo adult astrocytomas.

Classification of high grade astrocytomas of children into genetic subtypes similar to the adult remains to be defined. Here we report an extensive characterization of 29 high grade pediatric astrocytomas, 7 WHO grade III and 22 WHO grade IV, for genetic alterations frequently observed in high grade adult astrocytomas occurring in either the p53/MDM2/p14ARF or Rb/CDK4/p16INK4a tumor suppressor pathways. In addition, we have assessed the contribution of EGFR overexpression and amplification and LOH for chromosome 10, two genetic alterations commonly associated with the development of de novo adult glioblastoma for their roles in the development of de novo astrocytomas of childhood. Our results suggest two major differences in the genetic pathway(s) leading to the formation of de novo high grade astrocytomas in children compared with those of the adult. Our findings show preferential inactivation of the p53 tumor suppressor pathway in >95% of pediatric astrocytomas versus inactivation of the Rb tumor suppressor pathway in <25% of the same tumors. In addition, de novo high grade pediatric astrocytomas lack amplification of the EGFR gene compared with EGFR amplification in one-third of adult glioblastomas. Since drug treatments and gene therapy strategies exploit specific genetic alterations in tumor cells, our findings have important implications for the future development of treatments for high grade pediatric astrocytomas.

Adolescent↗

PubMed2000

Response and determinants of sensitivity to paclitaxel in human non-small cell lung cancer tumors heterotransplanted in nude mice.

The lack of tumor models that can reliably predict for response to anticancer agents remains a major deficiency in the field of experimental cancer therapy. Although heterotransplants of certain human solid tumors can be successfully grown in nude mice, they have never been appropriately explored for prediction of in vivo chemosensitivity to anticancer agents. We determined the tumor response rate and studied the influence of several biological and molecular tumor parameters on the in vivo sensitivity to paclitaxel in a series of heterotransplanted human non-small cell lung cancer (NSCLC) tumors. One hundred consecutive resected NSCLC tumors were heterotransplanted s.c. in nude mice. The in vivo sensitivity to i.v. paclitaxel (60 mg/kg every 3 weeks) was studied in 34 successfully grown heterotransplants. Treatment started when the tumors reached a size of 5 mm in diameter, and strict standard clinical criteria (>50% shrinkage in tumor weight or cross-sectional surface) were used to define tumor response. Baseline multidrug resistance protein (MRP), Her-2/neu, and epidermal growth factor receptor (EGFR) expression, and pre- and posttherapy bax and bcl-2 expression were determined by Western blot analysis. p53 status was determined by sequencing. The overall take rate was 46% (95% confidence interval, 36-56%) and was significantly higher (P < 0.05) for squamous carcinoma tumors (75%) than for adenocarcinoma tumors (30%) and bronchoalveolar tumors (23%). The heterotransplants were morphologically very similar to the original tumors. The response rate to paclitaxel was 21% (95% confidence interval, 9-38%). Baseline tumor parameters associated with response were no Her-2/neu expression (none of the responding tumors expressed Her-2/neu versus 48% of the nonresponding tumors, P = 0.05) and baseline bcl-2 expression (all responding tumors expressed bcl-2 versus only 43% of the nonresponding tumors, P = 0.02). There was a trend toward a higher response rate in bax-positive tumors, and MRP- and EGFR-negative tumors, but it was not statistically significant. The response was independent of baseline p53 status and baseline mitotic index. Responding tumors had a higher bax/bcl-2 ratio 24 h after therapy, but the difference was only marginally significant (2.8 for responding tumors versus 1.1 for nonresponding tumors, P = 0.07). The extent of mitotic arrest at 24 h after therapy was not associated with response. Human NSCLC heterotransplants are morphologically identical to the original tumors and have a response rate to paclitaxel that is equivalent to that reported in Phase II studies in patients with advanced NSCLC treated with single-agent paclitaxel. NSCLC heterotransplants deserve to be explored to evaluate new agents for lung cancer and to predict clinical response on an individual basis in selected groups of patients.

ATP-Binding Cassette Transporters↗

PubMed1999

The canals of Hering and hepatic stem cells in humans.

Small, extraportal, hepatic parenchymal cells, positive for biliary-type cytokeratins, may represent hepatic stem cells, canals of Hering (CoH), and/or ductal plate remnants. We evaluated these cells 3 dimensionally in normal human liver and massive necrosis. Tissues from normal human livers and from 1 liver with acetaminophen-induced massive necrosis were serially sectioned, immunostained for cytokeratin 19 (CK19), and sequentially photographed. Images were examined to determine 3-dimensional relationships among CK19-positive cells. Immunostains for other hepatocyte and progenitor cell markers were examined. In normal livers, intraparenchymal CK19-positive cells lined up as linear arrays in sequential levels. One hundred of 106 (94.3%) defined, complete arrays within levels examined, most having 1 terminus at a bile duct, the other in the lobule, beyond the limiting plate. In massive necrosis, there were 767 individual CK19-positive cells or clusters around a single portal tract, 747 (97.4%) of which were spatially related forming arborizing networks connected to the interlobular bile duct by single tributaries. C-kit was positive in normal CoH. CK19 co-expressed with HepPar1, c-kit, and alpha-fetoprotein (AFP) in parenchymal cells in massive necrosis. Small, extraportal, biliary-type parenchymal cells represent cross-sections of the CoH that radiate from the portal tract, usually extending past the limiting plate into the proximate third of the hepatic lobule. The 3-dimensional structure of ductular reactions in massive necrosis suggests that these reactions are proliferations of the cells lining the CoH. Therefore, the CoH consist of, or harbor, facultative hepatic stem cells in humans.

Acetaminophen↗

PubMed1999

A novel treatment of patients with chronic hepatitis C.

OBJECTIVES: Interferon alpha-2b therapy for Chronic Hepatitis C patients has been unsatisfactory. Recombinant Granulocyte Macrophage Colony-Stimulating Factor has been shown to have anti-viral effects in vivo and in vitro via cytokines release. Recently its effects on chronic hepatitis B and possibly chronic hepatitis C were reported. We, decided to conduct a pilot study to evaluate the anti-viral effects of recombinant human GM-CSF mono-therapy in patients with chronic hepatitis C and to assess its side effects. METHODS: A total of 10 patients (male/female: 5/5) (age: 34-60, mean: 45) seen in our center between 2/95 to 2/96 were randomly selected to receive recombinant human Granulocyte Macrophage Colony-Stimulating-Factor at 125 ug/m2 subcutaneously daily for two weeks followed by three times weekly for another 8 weeks. Biochemical (ALT) and viral (HCV-RNA) responses were measured prior to treatment and at weeks four and eight. Side effects were recorded. RESULTS: Six out of the ten patients treated had significant viral reduction but none became negative. Eight out the ten patients treated showed biochemical improvement and three out of the eight had normalized liver enzymes. Age, sex, stage of the disease did not influence the response but there seems to be a tendency for patients with higher pre-treatment viral level to respond virally. Side effects are minimal and well-tolerated. CONCLUSION: Recombinant human Granulocyte Macrophage Colony-Stimulating-Factor in the dose used has anti-viral effects in the majority of the chronic hepatitis C patients studied. Side effects are minimal and well tolerated. Further study with higher doses and longer duration is needed to prove its clinical efficacy in treating patients with chronic hepatitis C.

Adult↗

PubMed1998

Infrared spectroscopy of human tissue. I. Differentiation and maturation of epithelial cells in the human cervix.

Infrared spectral results for the different epithelial layers of human cervical squamous tissue are reported. The layers, representing different cellular maturation stages, exhibit quite different spectral patterns. Thus, infrared spectroscopy presents a powerful tool to monitor cell maturation and differentiation. Furthermore, a detailed understanding of the spectra of the individual layers of tissue permit a proper interpretation of the state of health of cells exfoliated from such tissue. Part II of this series describes the use of the spectral information presented here to interpret the infrared spectra of exfoliated cells.

Cell Differentiation↗

PubMed1998

Infrared spectroscopy of human tissue. IV. Detection of dysplastic and neoplastic changes of human cervical tissue via infrared microscopy.

Infrared absorption spectra of formalin-fixed, paraffin-embedded human cervical tissue are reported for normal, dysplastic and neoplastic samples. The spectral differences found in this study between these states of the tissues are far less than those observed for single cells by us and others. Nevertheless, we find a direct correspondence between spectral data from tissue sections, obtained from biopsies, and individual exfoliated cells, typically obtained during a pap procedure. We also find that spectra due to dysplastic samples fall about halfway between the spectral features of normal and cancerous samples.

Carcinoma, Squamous Cell↗

PubMed1995

Occult cocaine and opiate exposure in children and associated physical findings.

We determined the prevalence of cocaine and opiate exposure and the association of exposure with objective physical findings in children presenting to an urban pediatric emergency department. The study included 942 children between one and 60 months of age who required urinalysis for investigation of their chief complaint. Anonymously and without informed consent, urine was screened for benzoylecgonine (BE) and opiates, using an enzyme multiplied immunoassay technique (EMIT) with sensitivity of 50 ng/ml. EMIT-positive samples were rescreened using a fluorescence polarization immunoassay (FPIA). Specimens positive by both EMIT and FPIA were confirmed by gas chromatography/mass spectrometry (GC/MS) if sufficient quantity of urine was available. BE was identified in 41 (4.4%) and opiates in 46 (4.9%) patients by both EMIT and FPIA. The presence of BE or opiate was confirmed by GC/MS in all 34 cases where sufficient urine was available. The age- and sex-adjusted systolic and diastolic blood pressure percentiles were greater, and head circumference and weight percentiles were lower in BE-positive patients compared to those with negative drug screens. There were no associations between opiate exposure and any of these variables. We conclude that occult postnatal cocaine exposure is associated with measurable physical and physiologic differences.

Blood Pressure↗

PubMed1994

Transvaginal sonographic characterization combined with cytologic evaluation in the diagnosis of ovarian and adnexal cysts.

A transvaginal sonographic (TVS) scoring system using morphologic features has been developed at our institution to maximize discrimination between benign and malignant ovarian and adnexal cysts. Low (4-7) or intermediate (8-9) scores have been found to correlate with benignity, hence TVS-guided or laparoscopically directed needle aspiration of low-scoring lesions may safely be performed. High-scoring lesions (10-14) are often malignant, therefore in situ needle aspiration of such lesions is not recommended. The aim of our study was to correlate the results of TVS characterization of ovarian and adnexal cysts with the aspiration cytologic evaluation. Twenty-three of the 43 cysts studied were aspirated in situ from the patient; 20 were aspirated from resected surgical specimens. Thirty-six benign cysts had TVS scores ranging from 4 to 12, with a median score of 7. All 25 cysts that were benign by TVS and/or histology were also cytologically benign as well as an additional 11 cysts that were not resected (TVS scores: 4 to 9). Seven cytologically and histologically malignant cysts had high TVS scores (TVS scores 10-14; median = 12). The combination of TVS and needle aspiration cytology is valuable, particularly in the diagnosis of cysts having low or intermediate TVS scores and benign cytology. Aspiration of cysts or masses with high TVS scores is not recommended. This combined evaluation may allow a more limited surgical approach, such as operative laparoscopy, or, in some cases, obviate the need for operative treatment altogether.

Adnexal Diseases↗

PubMed1993

Adaptation of the meconium drug test for mass screening.

For purposes of mass drug screening, the procedure for analysis of meconium for drugs was modified into a one-step extraction and analysis by enzyme immunoassay. The accuracy of this modified method was tested by comparing the results of simultaneous analysis of 61 meconium samples for cocaine opiate and cannabinoid metabolites by both the original and the modified methods. In 61 samples analyzed, opiate was detected in 8 (13%) samples by the original method and in 9 (15%) by the modified method; cocaine was detected in 39 (64%) samples by the original method and in 39 (64%) by the modified method. The concordance between the negative and positive results of the modified versus the original methods was 98% and 100%, respectively, for opiate and 95% and 98%, respectively, for cocaine. Only one sample was positive for cannabinoid. Thus a comparison of positive results for cannabinoid was not done; however, all the negative results obtained by the modified method were confirmed by the original method. The clinical experience of mass meconium drug testing using the modified method in 1991 is also reported. In four centers tested (total tests = 4409), the prevalence of presence of drug was consistent with the high- or low-risk status of the population. This simplified, rapid procedure can be performed in most clinical laboratories. This adaptation has made the meconium drug test feasible for large-scale clinical and research use.

Cannabinoids↗

PubMed1993

Implantable cardioverter defibrillator electrogram recognition with a multilayer perceptron.

With the continuing development of new pacing and shock modalities, implantable cardioverter defibrillators must be able to recognize an increasingly wider range of arrhythmias so that therapy is delivered in an optimal way. Current rate-based systems can no longer meet this need. It is, therefore, necessary to develop new techniques that consider waveform morphology in addition to heart rate. Any developments, however, must be compatible with the strict power and space constraints imposed by implantable devices. Artificial neural networks offer a potentially viable way of meeting these objectives. In this article an artificial neural network based approach to the classification of arrhythmias from the ventricular intracardiac electrogram is described. It performs its classification on a set of easily extracted features that characterize waveform morphology and heart rate. Simulations showed that the artificial neural network performed better than a rate-based scheme similar to those used in some commercial devices.

Algorithms↗

PubMed1992

Community education on stroke.

A programme of community education on stroke in Micronesia is based on the use of brightly illustrated posters with a limited content of written material in the native languages. This approach has been favourably received by the people.

Audiovisual Aids↗

PubMed1991

Occult cocaine exposure in children.

We determined the prevalence of cocaine and cannabinoid exposure among young children presenting to an urban pediatric emergency department without signs or symptoms suggestive of the exposure. The study included 460 children between 1 and 60 months of age in whom urinalysis was required for investigation of routine pediatric complaints. Anonymously and without informed consent, an aliquot of urine was screened for cocaine metabolite (benzoylecgonine) and 11- or delta-9-tetrahydrocannabinol-9 carboxylic acid with the enzyme multiplied immunoassay technique. Positive specimens were rescreened with a radioimmunoassay and confirmed with gas chromatography/mass spectrometry, if a sufficient quantity of urine was available. Benzoylecgonine was identified in 25 patients (5.4%) by both screening techniques. Enough urine was available for confirmatory testing in eight patients, and all eight urine specimens contained benzoylecgonine. Neither 11- nor delta-9-tetrahydrocannabinol-9 carboxylic acid was detected in any patient. We documented the magnitude of the problem of occult passive cocaine exposure in young children living in an urban environment. Such exposure has serious implications for the assessment of outcomes in postnatal follow-up studies of prenatally exposed children as well as potential risks to children living in household environments where occult cocaine exposure occurs.

Adult↗

PubMed1984

Cardiac abnormalities in the thalassaemia syndromes.

Cardiac complications are the leading cause of death in patients with the thalassaemia syndromes. The cardiac abnormalities may be the result of chronic anaemia or iron overload. The cardiac status was evaluated in 30 patients with thalassaemia to determine whether the structural and functional changes could be related to the degree of anaemia or to other factors suggesting iron overload. Clinical, radiological, electrocardiographic and echocardiographic methods were employed. The study provided evidence that cardiac abnormalities were due to undertransfusion. Echocardiography provides a reliable, noninvasive means of assessing cardiac abnormalities in patients with thalassaemia.

Adolescent↗

PubMed1983

Profile of phospholipids in amniotic fluid to assess fetal lung maturity in high-risk pregnancy.

In assessing fetal lung maturity, an amniotic fluid profile, consisting of a total phospholipid (as phosphorus) (TPP) and total lecithin (LT) concentration, has been shown to yield a predictive accuracy of 97.5% with a false-negative rate of 2.4%. The LT had a range of specificity of 93% to 99%, whereas the one for the TPP was 88% to 96%. The cut-off values were 0.14 mg P/dl and 3.5 mg lecithin/dl of amniotic fluid. The analytical variables for laboratory tests for measuring amniotic fluid phospholipids led to the development of the quantitative tests used for this study. The proposed profile appears to offer the clinician an excellent means of judging how to manage the high-risk pregnancy.

Amniocentesis↗