Biomedical subjects

W Pan

Publications and source records attributed to W Pan.

At least 37 records · Page 2Linked to original sources

PubMed2001

Sample size and power calculations with correlated binary data.

Correlated binary data are common in biomedical studies. Such data can be analyzed using Liang and Zeger's generalized estimating equations (GEE) approach. An attractive point of the GEE approach is that one can use a misspecified working correlation matrix, such as the working independence model (i.e., the identity matrix), and draw (asymptotically) valid statistical inference by using the so-called robust or sandwich variance estimator. In this article we derive some explicit formulas for sample size and power calculations under various common situations. The given formulas are based on using the robust variance estimator in GEE. We believe that these formulas will facilitate the practice in planning two-arm clinical trials with correlated binary outcome data.

Clinical Trials as Topic↗

PubMed2001

Low-density lipoprotein receptor-related protein-5 binds to Axin and regulates the canonical Wnt signaling pathway.

To understand how the Wnt coreceptor LRP-5 is involved in transducing the canonical Wnt signals, we identified Axin as a protein that interacts with the intracellular domain of LRP-5. LRP-5, when expressed in fibroblast cells, showed no effect on the canonical Wnt signaling pathway by itself, but acted synergistically with Wnt. In contrast, LRP-5 mutants lacking the extracellular domain functioned as constitutively active forms that bind Axin and that induce LEF-1 activation by destabilizing Axin and stabilizing beta-catenin. Addition of Wnt caused the translocation of Axin to the membrane and enhanced the interaction between Axin and LRP-5. In addition, the LRP-5 sequences involved in interactions with Axin are required for LEF-1 activation. Thus, we conclude that the binding of Axin to LRP-5 is an important part of the Wnt signal transduction pathway.

3T3 Cells↗

PubMed2001

Using frailties in the accelerated failure time model.

The accelerated failure time (AFT) model is an important alternative to the Cox proportional hazards model (PHM) in survival analysis. For multivariate failure time data we propose to use frailties to explicitly account for possible correlations (and heterogeneity) among failure times. An EM-like algorithm analogous to that in the frailty model for the Cox model is adapted. Through simulation it is shown that its performance compares favorably with that of the marginal independence approach. For illustration we reanalyze a real data set.

Algorithms↗

PubMed2001

A multiple imputation approach to linear regression with clustered censored data.

We extend Wei and Tanner's (1991) multiple imputation approach in semi-parametric linear regression for univariate censored data to clustered censored data. The main idea is to iterate the following two steps: 1) using the data augmentation to impute for censored failure times; 2) fitting a linear model with imputed complete data, which takes into consideration of clustering among failure times. In particular, we propose using the generalized estimating equations (GEE) or a linear mixed-effects model to implement the second step. Through simulation studies our proposal compares favorably to the independence approach (Lee et al., 1993), which ignores the within-cluster correlation in estimating the regression coefficient. Our proposal is easy to implement by using existing softwares.

Algorithms↗

PubMed2001

Adrenomedullin and the blood-brain barrier.

Adrenomedullin (ADM) is present both in the periphery and brain. In addition to its peripheral effects, this peptide can exert central effects such as decreasing food ingestion. We used multiple-time regression analysis to determine that labeled ADM can cross from blood to brain with an apparent influx constant (K(I)) of 5.83 +/- 1.44 x 10(-4) ml/g-min, much faster than that of albumin, the vascular control. HPLC showed that almost all of the injected 125I-ADM in the brain was intact, and capillary depletion showed that it could reach the parenchyma of the brain. However, more 125I-ADM was reversibly associated with the brain vasculature than we have seen with any other peptide tested by these methods. After intracerebroventricular injection, 125I-ADM exited the brain with the bulk reabsorption of cerebrospinal fluid at an efflux rate comparable to that of albumin. Although there was no blood-to-brain saturation, in situ brain perfusion of 125I-ADM in blood-free physiological buffer showed self-inhibition by excess unlabeled ADM. This, along with evidence of the lack of protein binding shown by capillary zone electrophoresis, indicated competition for the binding site of ADM at the BBB. The low lipophilicity of ADM determined by the octanol/buffer partition coefficient was also consistent with the prominent reversible association of ADM with the vasculature of the BBB. This suggests a function for ADM at the cerebral blood vessels, such as altering cerebral blood flow and perfusion, without disruption of the BBB.

Adrenomedullin↗

PubMed2001

Upregulation of the transport system for TNFalpha at the blood-brain barrier.

The transport system for the cytokine tumor necrosis factor-alpha (TNFalpha) at the blood-brain barrier (BBB) enables an enhanced yet saturable entry of TNFalpha from blood to the CNS. This review focuses on the selective upregulation of the transport system for TNFalpha at the BBB that is specific for type of pathology, region, and time. The upregulation is reflected by increased CNS tissue uptake of radiolabeled TNFalpha after iv injection in mice and by inhibition of this increase with excess non-radiolabeled TNFalpha. (1) Spinal cord injury (SCI): upregulation of TNFalpha uptake after thoracic transection is seen in the delayed phase of BBB disruption at the lumbar spinal cord. Thoracic SCI by compression, however, has a longer lasting impact on TNFalpha transport that involves thoracic and lumbar spinal cord, in contrast to the upregulation confined to the lumbar region in lumbar SCI by compression. Regardless, the uptake of TNFalpha by spinal cord does not parallel BBB disruption as measured by the leakage of radiolabeled albumin. (2) Experimental autoimmune encephalomyelitis (EAE): the increase in the differential permeability to TNFalpha is seen in all CNS regions (brain and cervical, thoracic, and lumbar spinal cord) and has a distinct time course and reversibility. Exogenous TNFalpha has biphasic effects in modulating functional scores. The BBB, a dynamically regulated barrier, is actively involved in disease processes.

Animals↗

PubMed2001

Genistein, daidzein and glycitein inhibit growth and DNA synthesis of aortic smooth muscle cells from stroke-prone spontaneously hypertensive rats.

Recent studies have reported that estrogen replacement therapy (ERT) reduces the risk of cardiovascular diseases in postmenopausal women. However, mechanisms responsible for this effect are not yet completely understood, and ERT is associated with carcinogenic side effects in women and feminizing effects in men. Because soybean isoflavones, a group of natural phytoestrogens, have only weak estrogenic activity and are not known to have side effects such as carcinogenesis and feminization, we evaluated the effects of genistein, daidzein and glycitein on the growth and DNA synthesis of aortic smooth muscle cells (SMC) from stroke-prone spontaneously hypertensive rats (SHRSP). SMC were cultured in dishes and proliferated on 10% dextran-coated charcoal/fetal bovine serum, and then treated with 0.1-30 micromol/L of genistein, daidzein or glycitein to investigate cell proliferation (cell number) and DNA synthesis (cell proliferation ELISA system), respectively. We also studied their effects on platelet-derived growth factor (PDGF)-BB (20 microg/L)-induced SMC proliferation. Soybean isoflavones inhibited proliferation and DNA synthesis of SMC from SHRSP in a concentration-dependent manner. Inhibition was significant at 3 micromol/L of genistein and 10 micromol/L of both daidzein and glycitein. For significant inhibition of PDGF-BB-induced SMC proliferation, concentrations as low as 0.1 micromol/L of each isoflavone were effective. These isoflavones, with their inhibitory effects on natural and PDGF-BB-induced SMC proliferation, may be useful in attenuatating such proliferation, a basic mechanism involved in atherosclerotic vascular change, thereby preventing atherosclerotic cardiovascular diseases.

Animals↗

PubMed2001

Akaike's information criterion in generalized estimating equations.

Correlated response data are common in biomedical studies. Regression analysis based on the generalized estimating equations (GEE) is an increasingly important method for such data. However, there seem to be few model-selection criteria available in GEE. The well-known Akaike Information Criterion (AIC) cannot be directly applied since AIC is based on maximum likelihood estimation while GEE is nonlikelihood based. We propose a modification to AIC, where the likelihood is replaced by the quasi-likelihood and a proper adjustment is made for the penalty term. Its performance is investigated through simulation studies. For illustration, the method is applied to a real data set.

Biometry↗

PubMed2001

Model selection in estimating equations.

Model selection is a necessary step in many practical regression analyses. But for methods based on estimating equations, such as the quasi-likelihood and generalized estimating equation (GEE) approaches, there seem to be few well-studied model selection techniques. In this article, we propose a new model selection criterion that minimizes the expected predictive bias (EPB) of estimating equations. A bootstrap smoothed cross-validation (BCV) estimate of EPB is presented and its performance is assessed via simulation for overdispersed generalized linear models. For illustration, the method is applied to a real data set taken from a study of the development of ewe embryos.

Bias↗

PubMed2001

A multiple imputation approach to regression analysis for doubly censored data with application to AIDS studies.

Sun, Liao, and Pagano (1999) proposed an interesting estimating equation approach to Cox regression with doubly censored data. Here we point out that a modification of their proposal leads to a multiple imputation approach, where the double censoring is reduced to single censoring by imputing for the censored initiating times. For each imputed data set one can take advantage of many existing techniques and software for singly censored data. Under the general framework of multiple imputation, the proposed method is simple to implement and can accommodate modeling issues such as model checking, which has not been adequately discussed previously in the literature for doubly censored data. Here we illustrate our method with an application to a formal goodness-of-fit test and a graphical check for the proportional hazards model for doubly censored data. We reanalyze a well-known AIDS data set.

Acquired Immunodeficiency Syndrome↗

PubMed2001

Effects of nutrients and serotonin 5-HT3 antagonism on symptoms evoked by distal gastric distension in humans.

Distal gastric distension may contribute to meal-related dyspeptic symptoms. This study's aims were to determine the effects of distinct nutrient classes on symptoms induced by distal gastric distension and their dependence on 5-hydroxytryptamine(3) (5-HT3) receptors. Nine healthy subjects rated pain, nausea, and bloating induced by isobaric distal gastric distensions (6-24 mmHg) during duodenal lipid, carbohydrate, protein, or saline perfusion after treatment with placebo or the 5-HT3 receptor antagonist granisetron (10 microg/kg iv). Distensions produced greater pain, nausea, and bloating with lipid at 1.5 kcal/min compared with saline (P < or = 0.02), primarily because of greater distal gastric volumes at each distending pressure. In contrast, carbohydrate and protein had no significant effect. At 3 kcal/min, lipid increased symptoms through a volume-independent as well as a volume-dependent effect. Granisetron did not affect symptom perception or gastric pressure-volume relationships. In conclusion, isobaric distal gastric distension produces more intense symptoms during duodenal lipid compared with saline perfusion. Symptom perception during distal gastric distension is unaffected by 5-HT3 receptor antagonism.

Adult↗

PubMed2001

Regulation of GH secretion in acromegaly: reproducibility of daily GH profiles and attenuated negative feedback by IGF-I.

GH hypersecretion is a hallmark of acromegaly. It is unknown whether the secretory activity of somatotroph adenoma is autonomous or is still governed by central or peripheral mechanisms. In this study we investigated whether GH secretion in acromegaly 1) has a reproducible circadian pattern and 2) is inhibited by exogenous IGF-I. Eleven patients with newly diagnosed acromegaly were studied in 2 protocols. In protocol 1, peripheral blood was sampled every 10 min for 48 h in 6 patients for the determination of concordance between 24-h GH profiles. There was no significant day to day variability in mean 24-h output. There was, however, a significant time effect, and the 24-h GH secretion pattern was maintained between days. In protocol 2, 5 patients were sampled for GH every 10 min twice, once during infusion of normal saline and once during iv infusion of recombinant human IGF-I (10 microg/kg x h). The recombinant human IGF-I infusion increased plasma IGF-I to approximately 230% of the baseline concentration. This resulted in GH suppression (4220 +/- 1950 vs. 3223 +/- 1472 microg/liter.min; P = 0.001), but did not alter GH secretion pattern. There were highly significant cross-correlations for 10 of the 11 of the subjects in the two protocols when the lag was 0 min. By harmonic analysis, nocturnal augmentation of GH was maintained, and maximum daily GH occurred at approximately 2300 h. These data demonstrate that the pattern of GH secretion in acromegaly is not random, but is highly preserved with 24-h periodicity. In addition, negative feedback regulation by IGF-I is preserved, although the degree of negative feedback is grossly attenuated. Thus, secretory activity of somatotroph adenomas is not autonomous or haphazard, but is still subject to both feedback and feedforward regulatory mechanisms.

Acromegaly↗

PubMed2001

Construction and identification of a single stranded cDNA clone containing full-length genome of hepatitis G virus.

AIM: To construct a single cDNA clone with full-length genome of hepatitis G virus (HGV) could be transcribed and expressed in vitro. METHODS: The 5 initial HGV cDNA fragments of Iw5, Iwq2, Iwh6, Iw3 and Iw3 used in this study were amplified from serum of a Japanese non A-E hepatitis patient. These fragments overlapped and covered the entire genome from 5'-end to 3'-end of HGV cDNA. Overlap extension PCR and ligation methods were used with 12 primers for the construction of a full-length genomic HGV cDNA clone from the subgenomic fragments. RESULTS: A single HGV cDNA clone (pHGVqz) was successfully constructed, physical mapping of the generated pHGVqz found identical to what we expected, and the sequence was deposited with the GenBank under the Accession number AF081782. The analysis of the full-length sequence, which was able to be in vitro transcribed and expressed, showed that this single clone contained 9373 nucleotides (encoding 2873 amino acids), and shared high homologies with other compared HGV isolates. CONCLUSION: A full-length genomic HGV cDNA clone is generated for the first of the kind in this study, it could be expressed and transcripted. This single cDNA clone is expected to be of importance in the investigation on replication and pathogenicity of HGV.

Blotting, Western↗

PubMed2001

Preparation and incorporation of probe-labeled apoA-I for fluorescence resonance energy transfer studies of rHDL.

Apolipoprotein A-I (apoA-I), the major constituent of HDL, plays an essential role in regulating cholesterol metabolism, acting as the physiological activator of lecithin: cholesterol acyltransferase, which converts cholesterol to cholesterol ester. Thiol-reactive fluorescent probes attached to cysteine-containing apoA-I mutants are currently being used to investigate the "LCAT active" conformation of lipid-bound apoA-I. Herein, we report new methodologies allowing rapid expression, fluorescent labeling, and recombinant HDL (rHDL) preparation for use in apoA-I in fluorescence resonance energy transfer (FRET) studies. Cysteine-containing mutant forms of human apoA-I were cloned into the pTYB12 vector containing a T7 promoter, a modified self-splicing protein element (intein), and a small affinity tag [chitin binding domain (CBD)]. The fusion proteins were expressed in Escherichia coli, isolated from cell lysates, and bound to a chitin-affinity column. Release of mature human apoA-I was initiated by the addition of DTT, which induced self-cleavage at the COOH terminus of the intein - CBD fusion protein. ApoA-I was further purified by Q-sepharose and then used for fluorescent probe labeling. Discoidal rHDL were then prepared with donor and/or acceptor labeled apoA-I and characterized with respect to their size, composition and ability to activate LCAT.

Apolipoprotein A-I↗

PubMed2001

[The effects of gut -- origin lipopolysaccharide translocation on the apoptosis of lymphocytes in scalded rats].

OBJECTIVE: To investigate the relationship between lymphocyte apoptosis in spleen and mesenteric lymph nodes (MLNs) and gut -- origin lipopolysaccharide (LPS) translocation after severe scalding in rats. METHODS: Wistar rats inflicted 30% TBSA III degree scalding were employed as the model. Serum LPS levels in portal vein and vena cava were determined by limulus amebocyte lysate (LAL) test. Apoptotic lymphocytes in paraffin -- embedded spleen and MLNs sections were detected with TdT -- mediated and dUTP nick end labeling (TUNEL) and peroxidase (POD) staining. The images were taken by cooldccd camera system, and the count and optical density (OD) value of apoptotic lymphocytes were analyzed with software Spot and Imagine proplus 4.10a (IPP4.10a). RESULTS: Serum LPS levels in portal vein and vena cava increased sharply in rats postburn (P < 0.01) and reached a peak value at 6 postburn hour (PBH). LPS level in portal vein was higher than that in vena cava (P < 0.01) in the period of 3 to 48 PBHs. The results of TUNEL -- POD staining and the count of apoptotic lymphocytes showed that the apoptotic cells were few in normal MLNs, but increased obviously postburn (P < 0.01), especially at 3 PBH. On the contrary, apoptotic lymphocytes were concentrated in spleen cortex before injury and decreased obviously postburn (P < 0.01), though a slight recovery was found after 24 PBH. Optical density of apoptotic lymphocytes was significantly reduced in spleen at 24 PBH, But the OD value of apoptotic lymphocytes in MLNs increased significantly within 48 PBHs when compared with that before injury (P < 0.01). CONCLUSION: Gut -- origin endotoxemia in rat could occur in early postburn period. The LPS translocation might induce lymphocyte apoptosis in MLNs. The decreased apoptotic lymphocytes in spleen implied abnormal immune function in spleen.

Animals↗

PubMed2001

[Dynamic monitoring of Ph positive cells during early post-transplant period in chronic granulocytic leukemia by interphase FISH].

OBJECTIVE: To assess the effectiveness of transplantation and observe the kinetics of residual leukemic cells during early post-transplantation period in chronic granulocytic leukemia (CGL). METHODS: Ten normal controls, seven untreated CGL patients and eleven CGL patients after allogeneic bone marrow transplantation (allo-BMT) or peripheral blood stem cell transplantation (PBSCT) were studied by interphase fluorescence in situ hybridization (I-FISH) with the FITC fluorescein labeled BCR probe. Conventional cytogenetic analysis (CCA) and reverse transcriptase-polymerase chain reaction (RT-PCR) were also employed. RESULTS: The normal cutoff was defined as less than 6.68% (x +/- 3s) from the analysis of normal controls. The reproduciblity of FISH method was confirmed by serial dilutions by mixing Ph positive cells and normal cells. Forty specimens from 11 CGL patients at 1 week to 6 years post-BMT were investigated after PBSCT and the results showed that (1) FISH and RT-PCR could accurately evaluate Ph (+) cells during early transplantation period (within one month), but RT-PCR was more sensitive in six months after BMT. (2) Residual Ph (+) cells tended to be linear decreasing with the time after transplantation and fell in normal range in most samples three months later. The mean time of normaligation was 57 days (20 to 170 days). (3) One case relapsed and received a second transplantation. FISH presented more precise data for predicting relapse as compared to CCA and RT-PCR. CONCLUSIONS: I-FISH as a useful tool can not only offer more precise assessment of residual leukemic cells compared with CCA and RT-PCR, but also provide dynamic monitoring during early post-BMT period to evaluate the transplantation outcome and predict relapse.

Adult↗

PubMed2001

[Identification of the genome of a picornavirus isolate using Random-PCR].

OBJECTIVE: To identify the genome of an enterovirus isolate (XJ90). METHODS: The double-stranded cDNA of isolated virus was synthesized with anchored-random primer and was amplified with anchor primer; the PCR products were cloned into pGEM-T vector for sequencing and analysis. RESULTS: Analysis on agarose gel electrophoresis of the Random-PCR products showed a typical smear; 11 randomly selected clones were all homologous to the members of enteroviruses and the homology rate over 80%; the 11 clones were distributed evenly along the whole genome and they assembled 4 contigs totally 2 261 bp long which covered 30% of the genome. The homology of the fourth contig and coxsackie virus B6 was 97.3% at amino acids level. The virus gene was specifically amplified with primers derived from the sequenced clones. CONCLUSIONS: The picornavirus isolate XJ90 is a member of enteroviruses.

Amino Acid Sequence↗

PubMed2001

[One stage otoplasty treatment for congenital malformations of the auricle and middle ear].

OBJECTIVE: To investigate the application of one stage otoplasty for congenital atresia of the external acoustic canal and malformations of the middle ear and the auricle. METHOD: Patients with the ear malformations were given surgical reconstruction of one stage otoplasty. The auricle was reconstructed with the rib which was encapsulated with the superthin temporal flap. According to the malformations of the middle ear in patients, I style tympanoplasty and III style tympanoplasty were carried out respectively. All patients were performed myringoplasty with temporal fascia and reconstructed the external acoustic canal with full thickness skin-grafting. RESULT: A long term follow-up (4-6 years) demonstrated that 11 ears were survival of which 8 ears figuration were ideal. The hearing improvement was observed in all patients. CONCLUSION: One stage otoplasty is effective for treatment of the congenital malformations of the external and middle ear.

Adult↗