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Biomedical subjects

R J Ott

Publications and source records attributed to R J Ott.

At least 19 recordsLinked to original sources
PubMed1992

Nucleoside transport in brush border membrane vesicles from human kidney.

The goal of this study was to elucidate the mechanisms of nucleoside transport in the brush border membrane of the human kidney. [3H]Uridine was transported into brush border membrane vesicles (BBMV) from human kidney via Na(+)-independent and Na(+)-dependent processes. The Na(+)-dependent transport was saturable (Km = 4.76 +/- 0.39 microM; Vmax = 6.42 +/- 0.17 pmol/mg proteins per s) and was trans-stimulated by unlabeled uridine. Structural analogs of uridine (100 microM), 2'-deoxyuridine (2-dU) and dideoxyuridine (ddU), significantly inhibited Na(+)-uridine uptake into BBMV. Previous studies have suggested that Na(+)-nucleoside co-transport occurs via two major systems (Vijayalakshmi et al. (1988) J. Biol. Chem. 263, 19419-19423). One system (cit) is generally pyrimidine-selective; thymidine serves as a model substrate. The other system (cif) is generally purine-selective; formycin B serves as a model substrate. Uridine and adenosine are substrates of both systems. Thymidine and cytidine (100 microM), but not formycin B (100 microM) inhibited Na(+)-uridine uptake. In addition, [3H]thymidine exhibited an Na(+)-driven overshoot phenomenon whereas [3H]formycin B did not. Na(+)-thymidine uptake was inhibited by (100 microM) adenosine, uridine, guanosine, but not by formycin B and inosine. Further studies demonstrated that guanosine trans-stimulated thymidine uptake suggesting that guanosine and thymidine share a common transporter in the human renal BBMV. A different pattern was identified in BBMV from the rabbit kidney where both [3H]thymidine and [3H]formycin B as well as [3H]uridine exhibited a transient Na(+)-driven overshoot phenomenon. Collectively, these data suggest that in rabbit renal BBMV both cif and cit systems are present whereas in human renal BBMV, there appears to be a single concentrative Na(+)-nucleoside cotransport system that interacts with uridine, cytidine, thymidine, adenosine and guanosine but not with formycin B and inosine. The system is similar to the previously described cit system except that guanosine is also a substrate.

Animals↗
PubMed1992

Inhibition of N-linked glycosylation affects organic cation transport across the brush border membrane of opossum kidney (OK) cells.

Many organic cations are transported across the apical membrane of the proximal tubule by specific saturable mechanisms. The goal of this study was to determine if the transporter for tetraethylammonium (TEA) in the brush border membrane of an established opossum kidney (OK) cell line is glycosylated and to elucidate the function of this glycosylation. The uptake of TEA was determined in OK cell monolayers treated with tunicamycin (TM), a compound that prevents synthesis of the core oligosaccharide precursor molecules. TM exposure significantly decreased the incorporation of [3H]mannose in OK cell proteins and significantly reduced TEA uptake in a time and a concentration dependent manner. No effect of TM exposure on cellular protein synthesis, DNA content, cell viability, or on [3H]proline uptake was observed. The transport of TEA in control cells was characterized by a Km of 26.9 +/- 16.4 microM and a Vmax of 378 +/- 39 pmol/mg of protein/min. TM treatment (1 microgram/ml for 21 h) significantly increased the Km by over 4-fold to 111.5 +/- 18.4 microM while not affecting the Vmax. The apparent KI values of other organic cations known to interact with this transport system were also significantly increased by TM exposure. Estimated KI values of N1-methylnicotinamide, cimetidine, and mepiperphenidol increased by 6-fold, 4-fold, and 2-fold, respectively, after exposure of OK cells to TM. An increased KI for protons was also observed. Additional inhibitors of the N-linked glycosylation pathway, castanospermine, deoxynojirimycin, and deoxymannojirimycin significantly decreased TEA transport, whereas swainsonine had no effect. Our results suggest that the organic cation transporter is glycosylated. The N-linked oligosaccharide side chain appears to be of the hybrid type, and it either directly or indirectly affects the binding site of the transporter for both organic cations and protons. This is the first report describing the importance of glycosylation in the function of the organic cation transporter in the apical membrane of OK cells.

Animals↗
PubMed1992

Development of a high performance zinc-62/copper-62 radionuclide generator for positron emission tomography.

Clinical utilisation of positron emission tomography could be enhanced by the availability of short-lived radionuclides derived from generator systems. The zinc-62/copper-62 combination is one such system which could be used as a source for a number of copper-62 radiopharmaceuticals. We have developed and optimised a high activity (5.6 GBq, 150 mCi) zinc-62/copper-62 generator to provide 62Cu in a form that is suitable for direct labelling of pyruvaldehyde-bis-(N4-methylthiosemicarbazone)-copper(II), Cu(PTSM). The distribution coefficients of Zn(II) and Cu(II) between anion-exchange resin and various hydrochloric acid/organic solvent mixtures were measured. Based on these measurements a generator eluent of 0.3 M HCl/40% ethanol provided 62Cu in greater than 90% yield in a 3-ml volume. A very low 62Zn breakthrough of less than 3 x 10(-7)% was achieved. Copper-PTSM was successfully labelled with the no-carrier-added 62Cu eluent directly from the generator with 94% radiochemical yield.

Copper↗
PubMed1992

Quantitative analysis of a reconstruction method for fully three-dimensional PET.

The major advantage of positron emission tomography (PET) using large area planar detectors over scintillator-based commercial ring systems is the potentially larger (by a factor of two or three) axial field-of-view (FOV). However, to achieve the space invariance of the point spread function necessary for Fourier filtering a polar angle rejection criterion is applied to the data during backprojection resulting in a trade-off between FOV size and sensitivity. A new algorithm due to Defrise and co-workers developed for list-mode data overcomes this problem with a solution involving the division of the image into several subregions. A comparison between the existing backprojection-then-filter algorithm and the new method (with three subregions) has been made using both simulated and real data collected from the MUP-PET positron camera. Signal-to-noise analysis reveals that improvements of up to a factor of 1.4 are possible resulting from an increased data usage of up to a factor of 2.5 depending on the axial extent of the imaged object. Quantitation is also improved.

Algorithms↗
PubMed1992

Monte Carlo modelling of the performance of a rotating slit-collimator for improved planar gamma-camera imaging.

Planar imaging with a gamma camera is currently limited by the performance of the collimator. Spatial resolution and sensitivity trade off against each other; it is not possible with conventional parallel-hole collimation to have high geometric sensitivity and at the same time excellent spatial resolution unless field-of-view is sacrificed by using fan- or cone-beam collimators. We propose a rotating slit-collimator which collects one-dimensional projections from which the planar image may be reconstructed by the theory of computed tomography. The performance of such a collimator is modelled by Monte Carlo methods and images are reconstructed by a convolution and backprojection technique. The performance is compared with that of a conventional parallel-hole collimator and it is shown that higher spatial resolution with increased sensitivity is possible with the slit-collimator. For a point source a spatial resolution of some 6 mm at a distance of 100 mm from the collimator with a x7 sensitivity compared with a parallel-hole collimator was achieved. Applications to bone scintigraphy are modelled and an improved performance in hot-spot imaging is demonstrated. The expected performance in cold-spot imaging is analytically investigated. The slit-collimator is not expected to improve cold-spot imaging. Practical design considerations are discussed.

Equipment Design↗
PubMed1992

Treatment planning for 131I-mIBG radiotherapy of neural crest tumours using 124I-mIBG positron emission tomography.

Patients designated to receive 131I-meta-iodobenzylguanadine (mIBG) for the treatment of neural crest tumours have been scanned with 124I-mIBG using the MUP-PET positron camera. Uptake was detected in tumour sites in lung, liver and abdomen. The tomographic images produced have allowed estimates to be made of the concentration of mIBG in both tumour and normal tissue. From these data it is possible to predict the radiation doses that would be achieved using therapy levels (up to 11 GBq) of 131I-mIBG. The levels of tumour uptake are between 0.5 and 2.0 kBq/g indicating that the radiation doses to tumour would be in the range 3 Gy to 7.5 Gy.

3-Iodobenzylguanidine↗
PubMed1992

c-erbB2 protein overexpression in breast cancer as a target for PET using iodine-124-labeled monoclonal antibodies.

ICR 12, one of a panel of rat monoclonal antibodies recognizing the external domain of the human c-erb B2 proto-oncogene product, (Styles, 1990) was chosen as a candidate for radiolabeling with 124I for positron emission tomography of selected patients with breast cancer. By using N-bromosuccinimide (NBS), optimal labeling conditions were established using 125I. The labeling efficiency was determined using instant thin-layer chromatography (ITLC) and gel filtration (HPLC). The antibody was then labeled with the positron emitter 124I, and a labeling efficiency of 96% and immunoreactivity of 80%-90% was obtained. The product was stable, with less than 5% of the radiolabel being eluted after six days storage in plasma at 37 degrees C. Immunolocalization studies were performed in athymic mice bearing human breast carcinoma xenografts overexpressing the c-erb B2 gene product using as controls 125I labeled isotype-matched rat antibody, and antigen-negative tumors. Good uptake of 124I-labeled ICR12 was obtained in c-erb B2 expressing tumors (up to 12% injected dose per gram at intervals up to 120 hr), with localization indices of 3.4-6.2. Tumor xenografts of 6 mm diameter were successfully imaged with high resolution at 24, 48 and 120 hr using the RMH/ICR MUP-PET camera. We suggest that 124I-labeled ICR12 is a suitable agent to image and quantify immunolocalization in patients whose tumors overexpress the c-erb B2 proto-oncogene product.

Animals↗
PubMed1991

Transport of organic cations by a renal epithelial cell line (OK).

The goal of this study was to determine the mechanisms involved in the transport of the organic cation, tetraethylammonium (TEA), across the apical membrane of OK cells. [14C]TEA accumulated in OK cell monolayers reaching equilibrium in 2 h. The uptake of [14C]TEA at equilibrium was dependent upon temperature and was inhibited by sodium azide and by various organic cations, including N1-methylnicotinamide (NMN), mepiperphenidol, and cimetidine but not by the organic anion, p-aminohippuric acid. The initial uptake of [14C]TEA was characterized by a saturable process. The mean +/- S.D. Km was 27.8 +/- 2.6 microM and the Vmax was 414 +/- 26.5 pmol/mg protein/min. Both an accelerated efflux and influx of [14C]TEA in the presence of a trans-gradient of unlabeled TEA and NMN was observed, whereas a deaccelerated influx and efflux was observed in the presence of a trans-gradient of mepiperphenidol. The mechanism of interaction between NMN and TEA was examined. NMN significantly increased the apparent Km (mean +/- S.D.) of TEA to 82.8 +/- 16.4 microM (p less than 0.001), whereas the Vmax (mean +/- S.D.) was only slightly affected (478 +/- 72 pmol/mg protein/min) suggesting a competitive inhibition. The stimulatory effect of trans-gradients of NMN on TEA transport was due to an increase in the Vmax of TEA suggesting that NMN trans-stimulates TEA transport by increasing the turnover rate of the exchanger. In the presence of an inwardly directed proton gradient, the efflux at 30 s of [14C]TEA from the OK cell monolayers was significantly accelerated (p less than 0.05). Studies with the pH-sensitive fluorescent probe, 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, suggested that TEA could drive the countertransport of protons. In apical membrane vesicles prepared from OK cells, the uptake of [3H]NMN exhibited an apparent "overshoot phenomenon" in the presence of an initial outwardly directed proton gradient. Protons competitively inhibited TEA uptake suggesting that the proton/organic cation and the organic cation/organic cation self exchange mechanism are the same mechanism. This is the first report describing both TEA self-exchange and proton/TEA exchange in the apical membrane of a continuous cell line. OK cells are an excellent model for the study of organic cation transport across the apical membrane.

Animals↗
PubMed1991

Measurements of blood-brain barrier permeability in patients undergoing radiotherapy and chemotherapy for primary cerebral lymphoma.

Positron emission tomography (PET) has been used to measure changes in regional blood-brain barrier (BBB) permeability in patients with primary cerebral lymphoma undergoing radiotherapy and chemotherapy. The method employed is to measure the rate of wash-out of a radioactive tracer (68Ga-EDTA) from blood into brain tissue using time-sequence PET imaging. Preliminary studies carried out on patients with more common primary cerebral tumours show that time-activity data are reproducible to approximately 10%. Measurements made in 2 patients with primary cerebral lymphoma treated with initial chemotherapy showed significant changes in permeability in the region of the tumour. Within 5 weeks of the start of treatment, permeability values reached the levels of normal brain. No changes in BBB permeability in normal brain were seen immediately after radiotherapy.

Adult↗
PubMed1991

Organic cation transport in human renal brush-border membrane vesicles.

The renal proximal tubule is responsible for the active elimination of organic cations. Studies in brush-border membrane vesicles (BBMV) suggest that active organic cation transport is mediated by an organic cation-proton antiporter. The goals of this study were to determine whether this transporter is expressed in human kidney and to elucidate its characteristics. Transport of the organic cations N1-[3H]methylnicotinamide (NMN) and [14C]tetraethylammonium (TEA) was determined by rapid filtration in BBMV of donor human kidneys. The uptake of NMN and TEA was driven against a concentration gradient by an outwardly directed proton gradient. NMN uptake was inhibited by the organic cations TEA, NMN, quinine, and cimetidine, but was not affected by p-aminohippuric acid, cephalexin, and polyamines. The electroneutral transport of NMN was characterized by a Km of 0.44 +/- 0.07 mM and a Vmax of 24.4 +/- 15.2 pmol.mg protein-1.s-1. The rate of proton efflux from BBMV increased in the presence of an inwardly directed TEA gradient. Preloading BBMV with NMN or TEA trans-stimulated the initial rate of uptake of TEA. Therefore the human proximal tubule expresses an organic cation-proton antiporter in the brush-border membrane. The antiporter is similar to that described in other mammalian species but shows some differences in its transport characteristics.

Adult↗
PubMed1990

An evaluation of 99mTc-HMPAO uptake in cerebral gliomas--a comparison with X-ray CT.

Nineteen patients with biopsy-proven cerebral gliomas were studied with 99mTc-HMPAO single photon emission tomography (SPECT) imaging and X-ray computed tomography (CT). The uptake of 99mTc-HMPAO was correlated with tumour size and morphology as shown by X-ray CT, and overall patient survival. It appears that uptake of 99mTc-HMPAO is associated with larger, ill-defined tumours and was an adverse factor in patient survival. In those tumours with normal or increased uptake, 99mTc-HMPAO imaging is useful in distinguishing the tumour margin from surrounding oedema.

Brain Neoplasms↗
PubMed1990

Thyroid imaging using positron emission tomography--a comparison with ultrasound imaging and conventional scintigraphy in thyrotoxicosis.

Forty-six comparative studies were performed on 41 patients with hyperthyroidism. Clinically these comprised two groups: those with Graves' disease, and those with multinodular goitre. All patients underwent an ultrasound examination and positron emission tomography (PET) using 124I, then gamma camera pinhole imaging following their 131I therapy administration. Although the 131I pinhole imaging was not performed for diagnostic purposes, there was good correlation (78% agreement) between it and 124I PET in determining relative lobe size. Hence either imaging modality could be used as an indicator of the relative radiation dose delivered to each thyroid lobe at a macroscopic level. In terms of gland morphology the PET images corresponded well to the high resolution ultrasound images (78% agreement), unlike the pinhole images which correlated poorly (only 28% agreement). The results showed that PET imaging gives better anatomical and physiological detail than 131I pinhole imaging. In 77% of cases where the pinhole image showed a uniform distribution of radioisotope, the improved spatial resolution of the PET images revealed non-homogeneous distribution indicating a non-uniform distribution of radiation dose. Since all dosimetry calculations are based on the assumption of uniform distribution of radioiodine, this non-uniformity could possibly have important consequences in the outcome of radioiodine therapy in thyrotoxicosis.

Adult↗
PubMed1989

Image quantification with a large area multiwire proportional chamber positron camera (MUP-PET).

A large area multi wire proportional chamber positron camera system is under evaluation for clinical Nuclear Medicine investigation using isotopes both from the house generators (68Ga) and from remote cyclotrons (18F, 124I, 64Cu and 81Rb). Images are reconstructed using a fully three dimensional (3D) algorithm and exhibit equal resolution in all three orthogonal directions. The axial field of view of 15 cm is large enough to allow coverage of the whole brain. This paper discusses the performance of the MUP-PET system with particular emphasis on quantification and the development of an attenuation correction scheme for a large area detector system. The distribution of scattered and accidental events is investigated and observed to contribute a fairly uniform background to the image. Dead time correction factors are calculated from an analytical expression obtained by considering the various sources of dead time present in the system. Following correction for attenuation, accidentals, scattered events and dead time, reconstructed phantom images show a strong linear correlation (r = 0.998) between count density and regional isotope concentration. The extension of the methods to clinical studies is discussed.

Image Processing, Computer-Assisted↗
PubMed1989

Radiation dose assessment in radioiodine therapy. 2. Practical implementation using quantitative scanning and PET, with initial results on thyroid carcinoma.

We have designed special high-resolution, low-sensitivity collimators for a dual-headed whole-body scanner for imaging and quantifying therapy levels of iodine-131. In addition, we have used positron emission tomography (PET) with a low-cost large-area PET camera to achieve improved accuracy in the estimate to tumor mass. The physical performance of these two imaging systems is described. In order to illustrate the practical implementation of these systems for the assessment of radiation dose to normal and tumour tissue during radioiodine therapy, three clinical examples are reported, and a summary of the initial clinical results obtained from 16 patients with carcinoma of the thyroid is presented. The dose to normal thyroid remnants for patients undergoing ablation ranged from 16 to 400 Gy, while the dose to involved neck nodes ranged from 2.5 to 33 Gy for patients undergoing post-ablation radioiodine therapy. In one patient with distant metastasis in the spine, a dose of 100 Gy was achieved. The techniques described in this paper can be used to determine if sufficient activity can be accumulated in tumours to provide a therapeutic effect while minimising irradiation of normal tissues by avoiding administrations which do not provide tumouricidal radiation doses.

Carcinoma↗