Chromosome 11p15.5 regional imprinting: comparative analysis of KIP2 and H19 in human tissues and Wilms' tumors

The imprinted H19 gene is frequently inactivated in Wilms' tumors (WTs) either by chromosome 11p15.5 loss of heterozygosity (LOH) or by hypermethylation of the maternal allele and it is possible that there might be coordinate disruption of imprinting of multiple 11p15.5 genes in these tumors. To test this we have characterized total and allele- specific mRNA expression levels and DNA methylation of the 11p15.5 KIP2 gene in normal human tissues, WTs and embryonal rhabdomyosarcoma (RMS). Both KIP2 alleles are expressed but there is a bias with the maternal allele contributing 70-90% of mRNA. Tumors with LOH show moderate to marked reductions in KIP2 mRNA relative to control tissues and residual mRNA expression is from the imprinted paternal allele. Among WTs without LOH most cases with H19 inactivation also have reduced KIP2 expression and most cases with persistent H19 expression have high levels of KIP2 mRNA. In contrast to the extensive hypermethylation of the imprinted H19 allele, both KIP2 alleles are hypomethylated and WTs with biallelic H19 hypermethylation lack comparable hypermethylation of KIP2 DNA. 5-aza-2'-deoxycytidine (aza-C) increases H19 expression in RD RMS cells but does not activate KIP2 expression. These data indicate coordinately reduced expression of two linked paternally imprinted genes in most WTs and also suggest mechanistic differences in the maintenance of imprinting at these two loci.      

Data clustering and other archive retrieval strategies for teleradiology and picture archiving and communication systems

A key advantage in the conversion from film-based to digital radiology is the possibility of a long-term on line electronic archival of patient studies. The popular approach based on optical disk jukeboxes for the long-term archive and magnetic disk storage for data caching is not economically attractive because of the cost of both the jukebox and the medium. Strategies for extending the archival system design with a tape jukebox have been studied. The proposed strategy calls for the use of high-ratio lossy compression together with low-cost tape storage to make long-term on line archiving more affordable. An intelligent prefetching algorithm based on hospital information system and radiologic information system triggers, which in turn are augmented by manual case preparation, can effectively overcome the longer latency of ad hoc retrievals. This longer latency is caused by both system-level bottlenecks and the sequential access constraint of the tape drive. Strategies for image clustering and tape allocation by patient classification also enhance retrieval efficiency. This archival design using image compression, prefetching, and clustering could be implemented in many of the existing teleradiology and picture archiving and communication systems.     

Serratia marcescens bacteremia at a medical center in southern Taiwan: high prevalence of cefotaxime resistance.

Antimicrobial resistance of isolates and risk factors for mortality were retrospectively investigated in 71 adult patients with Serratia marcescens bacteremia. During the 4-year study period, 78 clinically significant episodes of S. marcescens bacteremia occurred in 71 patients. The mean age of the patients was 65 years (range, 25-86 years) with a male predominance (45 patients, 63%). Most of the bacteremic episodes were nosocomial (78%), and 34% were polymicrobial. The overall mortality rate within 2 weeks after the onset of bacteremia was 41%. The presence of malignancy and critical illness at initial presentation were independent risk factors for mortality. By disk susceptibility test, 72 isolates were resistant to cefotaxime (92%) but susceptible to ceftazidime (99%). All isolates were susceptible to meropenem. Among the 47 patients with monomicrobial S. marcescens bacteremia, the mortality rate within 5 days of onset in patients receiving appropriate empirical antimicrobial therapy was lower than that in patients receiving inappropriate therapy although this difference was not significant (14% vs 28%, p = 0.27). Among the patients with cefotaxime-resistant but ceftazidime-susceptible S. marcescens bacteremia treated with ceftazidime, 6 of 7 patients (86%) survived for more than 2 weeks, suggesting the potential effectiveness of ceftazidime in the treatment of cefotaxime-resistant Serratia infections. Further clinical studies are required to delineate the clinical role of ceftazidime therapy for infections caused by S. marcescens with this resistant phenotype.     

Monte Carlo dose verification for intensity-modulated arc therapy

Intensity-modulated arc therapy (IMAT), a technique which combines beam rotation and dynamic multileaf collimation, has been implemented in our clinic. Dosimetric errors can be created by the inability of the planning system to accurately account for the effects of tissue inhomogeneities and physical characteristics of the multileaf collimator (MLC). The objective of this study is to explore the use of Monte Carlo (MC) simulation for IMAT dose verification. The BEAM/DOSXYZ Monte Carlo system was implemented to perform dose verification for the IMAT treatment. The implementation includes the simulation of the linac head/MLC (Elekta SL20), the conversion of patient CT images and beam arrangement for 3D dose calculation, the calculation of gantry rotation and leaf motion by a series of static beams and the development of software to automate the entire MC process. The MC calculations were verified by measurements for conventional beam settings. The agreement was within 2%. The IMAT dose distributions generated by a commercial forward planning system (RenderPlan. Elekta) were compared with those calculated by the MC package. For the cases studied, discrepancies of over 10% were found between the MC and the RenderPlan dose calculations. These discrepancies were due in part to the inaccurate dose calculation of the RenderPlan system. The computation time for the IMAT MC calculation was in the range of 20-80 min on 15 Pentium-Ill computers. The MC method was also useful in verifying the beam apertures used in the IMAT treatments.     

Characterization of acrylic bone cement using dynamic mechanical analysis

Dynamic mechanical analysis (DMA) was used to characterize the properties of acrylic bone cement with the addition of tricalcium phosphate (TCP), hydroxyethyl methacrylate (HEMA), and ethylene glycol dimethacrylate (EGDMA). The glass transition temperature of acrylic bone cement is >100 degrees C; the cement has a flat modulus response near human body temperature. The height of the damping peak decreases and becomes broader with increasing TCP content. Thus, TCP is incompatibile with acrylic bone cement. When the frequency is changed from high to low, the damping peak shifts to low temperature. The shift in damping peak with frequency indicates that this relaxation is time-dependent. When acrylic bone cement contains TCP with HEMA and EGDMA, the incompatibility between acrylic bone cement and TCP can be ameliorated.     

Using a photon phase-space source for convolution/superposition dose calculations in radiation therapy

For a given linac design, the dosimetric characteristics of a photon beam are determined uniquely by the energy and radial distributions of the electron beam striking the x-ray target. However, in the usual commissioning of a beam from measured data, a large number of variables can be independently tuned, making it difficult to derive a unique and self-consistent beam model. For example, the measured dosimetric penumbra in water may be attributed in various proportions to the lateral secondary electron range, the focal spot size and the transmission through the tips of a non-divergent collimator; the head-scatter component in the tails of the transverse profiles may not be easy to resolve from phantom scatter and head leakage; and the head-scatter tails corresponding to a certain extra-focal source model may not agree self-consistently with in-air output factors measured on the central axis. To reduce the number of adjustable variables in beam modelling, we replace the focal and extra-focal sources with a single phase-space plane scored just above the highest adjustable collimator in a EGS/BEAM simulation of the linac. The phase-space plane is then used as photon source in a stochastic convolution/superposition dose engine. A photon sampled from the uncollimated phase-space plane is first propagated through an arbitrary collimator arrangement and then interacted in the simulation phantom. Energy deposition kernel rays are then randomly issued from the interaction points and dose is deposited along these rays. The electrons in the phase-space file are used to account for electron contamination. 6 MV and 18 MV photon beams from an Elekta SL linac are used as representative examples. Except for small corrections for monitor backscatter and collimator forward scatter for large field sizes (<0.5% with <20 x 20 cm2 field size), we found that the use of a single phase-space photon source provides accurate and self-consistent results for both relative and absolute dose calculations.     

Molecular modification of anticholinergics as probes for muscarinic receptors. 2. Amino esters of alpha-methyltropic acid

As a continuation of our goals to study molecular probes for muscarinic cholinergic receptors, a series of 3-substituted 2-methyl-2-phenylpropanoates with the general structure of C6H5C(CH2X)(CH3)COOCH2CH2NEt2 where X = OH, OTs, F, Cl, Br, I, and OAc were prepared and their antispasmodic activities examined on isolated rat ileum preparations. Structure-activity relationship studies with these compounds provide further evidence suggesting that binding of an aromatic moiety in a specific location within the hydrophobic region of the receptor is important for anticholinergic potency. A nucleophilic displacement of chloride by "naked" fluoride under mild conditions is also reported.     

Progression of mediastinal tuberculosis and superior vena caval obstruction demonstrated by gallium-67 citrate and radiocolloid liver scintigraphy

Most causes of superior vena caval (SVC) obstruction are caused by malignant mediastinal neoplasms, especially bronchogenic carcinoma. Less frequently SVC obstruction results from a non-malignant lesion such as mediastinal goiter or tuberculosis. We present a case of mediastinal tuberculosis which progressively enlarged as shown in consecutive Ga-67 citrate studies. As a result, SVC obstruction developed, exhibited by radionuclide SV Cavagram, and demonstrated "hot" spots in the radiocolloid scans.     

Necessity of ascorbic acid in the radioligand binding assay for [3H]5-hydroxytryptamine

Evidence is presented to suggest that ascorbic acid is required in the radioligand binding assay for [3H]5-hydroxytryptamine ([3H]5-HT, [3H]serotonin). In the absence of ascorbic acid, oxidation of [3H]5-HT occurred if the radioligand solution was left on ice for 1 or 3 hr. The oxidative products were detectable by thin-layer chromatography. They increased the binding significantly, although there was only slight oxidation (less than 1%) of the [3H]5-HT. When ascorbic acid was not used in the radioligand binding assay for [3H]5-HT, even though [3H]5-HT was prepared immediately before incubating with the membranes from the cortex of the rat, the binding also increased. The increased binding of [3H]5-HT had a low affinity (Kd = 14 nM) and high B max (1180 fmol/mg protein), compared to that in the presence of ascorbic acid (Kd = 5 nM; B max = 210 fmol/mg protein). However, the increased binding was not receptor-related because the additional radioactivity was not displaceable by excess of unlabelled 5-HT (10 microM) or d-LSD (d-lysergic acid iethylamide) and anomalous "specific binding" occurred in boiled membranes from cortex, in which the binding sites for 5-HT were destroyed. These results suggest that oxidation of [3H]5-HT may occur during the incubation with membranes and that ascorbic acid is therefore required as an antioxidant.