Search PubMed⌕ Search

Biomedical subjects

K Clarke

Publications and source records attributed to K Clarke.

At least 19 recordsLinked to original sources
PubMed2002

Electromagnetic characterisation of MR RF coils using the transmission-line modelling method.

The Transmission-Line Modelling (TLM) method is applied to the electromagnetic characterisation of RF coils and samples for magnetic resonance imaging MRI. Theoretical verification was performed using a simple surface coil. Experimental verification was performed using Alderman-Grant and birdcage coils constructed for use on a 7 T micro-imaging system. The modelling method enabled electromagnetic characteristics of frequency response, electromagnetic field generation, energy stored and power loss to be determined. From these parameters, coil resonant modes, B1 field profiles, voltages, currents, quality factor (Q), pi/2 pulse length, and the equivalent lumped-element circuit components of resistance, inductance and capacitance were calculated. Equations are presented that enable a comprehensive electromagnetic characterisation of the RF coil and sample to be achieved based on the results of the TLM simulations. The use of the TLM method is extended to include the design of safe arbitrary multi-nuclear pulse sequences such that the specific absorption rate (SAR) of tissue, and RF coil component safety limits are not exceeded.

Algorithms↗
PubMed2001

Metabolic profiling of genetic disorders: a multitissue (1)H nuclear magnetic resonance spectroscopic and pattern recognition study into dystrophic tissue.

A principal problem in understanding the functional genomics of a pathology is the wide-reaching biochemical effects that occur when the expression of a given protein is altered. To complement the information available to bioinformatics through genomic and proteomic approaches, a novel method of providing metabolite profiles for a disease is suggested, using pattern recognition coupled with (1)H NMR spectroscopy. Using this technique the mdx mouse, a model of Duchenne muscular dystrophy (DMD) was examined. Dystrophic tissue had distinct metabolic profiles not only for cardiac and other muscle tissues, but also in the cerebral cortex and cerebellum, where the role of dystrophin is still controversial. These metabolic ratios were expressed crudely as biomarker ratios to demonstrate the effectiveness of the approach at separating dystrophic from control tissue (cardiac (taurine/creatine): mdx = 2.08 +/- 0.04, control 1.55 +/- 0.04, P < 0.005; cortex (phosphocholine/taurine): mdx = 1.28 +/- 0.12, control = 0.83 +/- 0.05, P < 0.01; cerebellum (glutamate/creatine): mdx = 0.49 +/- 0.03, control = 0.34 +/- 0.03, P < 0.01). This technique produced new metabolic biomarkers for following disease progression but also demonstrated that many metabolic pathways are perturbed in dystrophic tissue.

Animals↗
PubMed2001

Specific localization, gamma camera imaging, and intracellular trafficking of radiolabelled chimeric anti-G(D3) ganglioside monoclonal antibody KM871 in SK-MEL-28 melanoma xenografts.

The chimeric monoclonal antibody KM871, directed against the G(D3) antigen, is under evaluation for its potential to target melanoma. To facilitate the in vivo evaluation of biodistribution properties and measurement of pharmacokinetics, KM871 was radiolabeled with (125)I via tyrosine residues and with (111)In via the bifunctional metal ion chelator C-functionalized trans-cyclohexyl diethylenetriaminepentaacetic acid (CHX-A"-DTPA) to lysine residues. Using antigen-positive SK-MEL-28 melanoma cells, immunoreactivities of 42 and 40% cell binding were obtained, respectively, for the two radioconjugates. Binding was enhanced in the presence of added unlabeled antibody. A humanized A33 antibody was similarly labeled with the two isotopes and used as a control. To determine and compare in vivo biodistribution characteristics of KM871 radiolabeled with (111)In or (125)I, mixtures of the radioconjugates were injected i.v. into BALB/c nude mice bearing G(D3)-positive-SK-MEL-28 melanoma xenografts. Gamma camera images were acquired; groups of five mice were sacrificed at various time intervals, and tumors, blood, and tissues were analyzed. (111)In-labeled CHX-A"-DTPA-KM871 showed a maximum tumor uptake of 41.9 +/- 7.0% injected dose/g at 72 h with prolonged retention over a 15-day period. The tumor:blood ratio was 3:1 by 72 h, and higher ratios were observed at later time points. No abnormal accumulation of (111)In-labeled conjugate was found in normal tissues. In contrast, there was little accumulation of (125)I-labeled KM871 in the same tumors. The specificity of antibody localization was confirmed by the low tumor uptake values for radiolabeled control antibody. Gamma camera imaging demonstrated excellent uptake of (111)In-labeled CHX-A"-DTPA-KM871 in the xenografts. Chromatographic analyses of xenograft cytosolic extracts demonstrated tumor internalization and catabolism of radiolabeled KM871 with the formation of small molecular weight metabolites. Laser scanning confocal microscopy demonstrated that the majority of intracellular KM871 is localized to lysosomes. Despite the catabolism of the radioconjugate, a dose-dependent increase in KM871 tumor localization was shown through immunohistochemical examination of xenograft biopsies. This study demonstrates for the first time the in vivo localization of a radiolabeled anti-G(D3) monoclonal antibody to G(D3)-expressing xenografts using gamma camera scanning techniques and tumor cell internalization of KM871 tagged with a green fluorescent dye, Alexa Fluor 488, through confocal microscopy. KM871 has potential for targeting tumors in patients with melanoma.

Animals↗
PubMed2001

Mutant epidermal growth factor receptor enhances induction of vascular endothelial growth factor by hypoxia and insulin-like growth factor-1 via a PI3 kinase dependent pathway.

Over-expression of truncated epidermal growth factor receptor (EGFR) occurs in a variety of malignancies including glioblastoma multiforme, breast and lung cancer. The truncation deletes an extracellular domain and results in constitutive activation of the receptor. NIH3T3 cells were transfected with full length or truncated human EGFR and differences in growth rates in vivo and in vitro analysed. A growth advantage was seen for cells expressing mutant receptor compared to full length EGFR in vivo only. Administration of an anti-mutant EGFR antibody to mice transiently reduced the growth rates of mutant tumours, confirming that the mutant receptor itself was important in this enhanced tumorigenicity. This showed that stimuli present in vivo and not in vitro may be contributing to growth. We therefore analysed the regulation of the angiogenic factor vascular endothelial growth factor (VEGF). Although levels of secreted VEGF did not differ significantly between wild-type and mutant EGFR cell lines when grown in vitro under normoxic conditions, following exposure to 0.1% hypoxia levels of VEGF produced by mutant cells increased 3.5-6.6 fold compared to 2 or less for full length EGFR cells. The fold induction was influenced by experimental conditions, including cell confluence and percentage of fetal bovine serum, but was consistently higher for mutant cell lines. The increase in VEGF under hypoxic conditions was blocked by the addition of PI3 kinase inhibitors, indicating that the latter pathway is important in the hypoxic stress response. Basal levels were not affected. Addition of insulin-like growth factor-1 also increased levels of VEGF under normoxic conditions in the mutant cells and no further increase was seen when added to cells exposed to 0.1% oxygen, indicating that levels of VEGF were already maximally stimulated. These results show that the mutant EGFR interacts with other growth factors and hypoxia to regulate VEGF via a PI3 kinase pathway, and suggests a specific role for anti-mutant EGFR antibodies and PI3 kinase inhibitors as therapy of this specific tumour target.

3T3 Cells↗
PubMed2001

Clinical activity of trastuzumab and vinorelbine in women with HER2-overexpressing metastatic breast cancer.

PURPOSE: To determine the response rate and toxicity profile of trastuzumab administered concurrently with weekly vinorelbine in women with HER2-overexpressing advanced breast cancer. PATIENTS AND METHODS: Forty women with HER2-positive (+3 by immunohistochemistry, n = 30; +2 or positive, n = 10) breast cancer were enrolled onto a study of trastuzumab (4 mg/kg x 1, 2 mg/kg weekly thereafter) and vinorelbine (25 mg/m2 weekly, with dose adjusted each week for neutrophil count). Eighty-two percent of women had received prior chemotherapy as part of adjuvant (30%), metastatic (25%), or both (28%) treatment, including substantial portions of patients who had previously received either anthracyclines (20%), taxanes (15%), or both types (38%) of chemotherapy. RESULTS: Responses were observed in 30 of 40 patients (overall response rate, 75%, conditional corrected 95% confidence interval, 57% to 89%). The response rate was 84% in patients treated with trastuzumab and vinorelbine as first-line therapy for metastatic disease, and 80% among HER2 +3 positive patients. High response rates were also seen in women treated with second- or third-line therapy, and among patients previously treated with anthracyclines and/or taxanes. Combination therapy was feasible; patients received concurrent trastuzumab and vinorelbine in 93% of treatment weeks. Neutropenia was the only grade 4 toxicity. No patients had symptomatic heart failure. Grade 2 cardiac toxicity was observed in three patients. Prior cumulative doxorubicin dose in excess of 240 mg/m2 and borderline pre-existing cardiac function were associated with grade 2 cardiac toxicity. CONCLUSION: Trastuzumab in combination with vinorelbine is highly active in women with HER2-overexpressing advanced breast cancer and is well tolerated.

Adult↗
PubMed2001

Spatial working memory deficit in unilateral neglect.

Based on the similarity of brain areas lesioned in neglect and those activated by spatial working memory (WM) tasks in normals, we hypothesized that neglect may involve spatial WM impairments. A left neglect patient with right inferior frontal and basal ganglia damage performed cancellation tasks, making either highly visible marks (to provide a reminder of visited items), or invisible marks (so only spatial WM could represent cancelled items). Invisible marks led to repeated cancellations for targets that differed only in location, but not for targets with memorable unique identities, suggesting a deficit of spatial WM, with non-spatial WM spared. Neglect was greater for cancellation with invisible marks, consistent with a role for deficient spatial WM in cancellation deficits, but contrary to account solely in terms of attention capture by salient visible marks made in ipsilesional space.

Attention↗
PubMed2001

Reaching with a tool extends visual-tactile interactions into far space: evidence from cross-modal extinction.

Several recent studies have shown cross-modal visual-tactile extinction in patients with right hemisphere lesions. In the present case, patient BV, a visual stimulus close to the right hand extinguished awareness of a touch on the left hand that would otherwise have been felt. Such extinction was reduced if the right visual stimulus was placed more distant from the patient's hand in the radial plane. However, when the patient held sticks in both hands, so that a far right visual stimulus was now at the end of the "tool" in his right hand, cross-modal extinction from this far stimulus increased. This effect depended on the patient holding a stick that reached to the position of the far visual stimulus; a similar large stick, but not connected with the patient's hand and laying passively on the right, had no effect. Wielding the stick induced a re-mapping of space, so that the far light became treated as near (and reachable by) the hand, thus modifying the spatial nature of cross-modal extinction. This may relate to the properties of multimodal neurons as found in the monkey intraparietal sulcus.

Aged↗
PubMed2001

Recombinant canine IL-13 receptor alpha2-Fc fusion protein inhibits canine allergen-specific-IgE production in vitro by peripheral blood mononuclear cells from allergic dogs.

Human IL-13, like IL-4, is involved in the regulation of B-cell development, IgE synthesis and allergic responses. However, because IL-13 does not affect either murine Ig class switching or IgE production in vitro, the use of murine models to study the role of IL-13 in IgE-mediated diseases has been limited. In this communication, we report that recombinant protein of canine IL-13 (rcaIL-13) stimulates production of allergen-specific-IgE in vitro by peripheral blood mononuclear cells (PBMC) from flea allergen-sensitized dogs, and that this stimulation activity is specifically inhibited by recombinant protein of canine IL-13Ralpha2 and Fc fragment of canine IgG heavy chain (rcaIL-13Ralpha2-Fc). The data suggest that the regulatory effects of IL-13 on IgE production in canine PBMC are similar to those reported in humans. Thus, canine IL-13 may be a central mediator of allergic diseases in dogs, and allergic dogs may be excellent models for research on IgE-mediated diseases in humans.

Amino Acid Sequence↗
PubMed2001

Development of chronic colitis is dependent on the cytokine MIF.

The cytokine macrophage-migration inhibitory factor (MIF) is secreted by a number of cell types upon induction by lipopolysaccharide (LPS). Because colitis is dependent on interplay between the mucosal immune system and intestinal bacteria, we investigated the role of MIF in experimental colitis. MIF-deficient mice failed to develop disease, but reconstitution of MIF-deficient mice with wild-type innate immune cells restored colitis. In addition, established colitis could be treated with anti-MIF immunoglobulins. Thus, murine colitis is dependent on continuous MIF production by the innate immune system. Because we found increased plasma MIF concentrations in patients with Crohn's disease, these data suggested that MIF is a new target for intervention in Crohn's disease.

Adoptive Transfer↗
PubMed2001

Free fatty acids, but not ketone bodies, protect diabetic rat hearts during low-flow ischemia.

To determine whether the effects of fatty acids on the diabetic heart during ischemia involve altered glycolytic ATP and proton production, we measured energetics and intracellular pH (pH(i)) by using (31)P NMR spectroscopy plus [2-(3)H]glucose uptake in isolated rat hearts. Hearts from 7-wk streptozotocin diabetic and control rats, perfused with buffer containing 11 mM glucose, with or without 1.2 mM palmitate or the ketone bodies, 4 mM beta-hydroxybutyrate plus 1 mM acetoacetate, were subjected to 32 min of low-flow (0.3 ml x g wet wt(-1) x min(-1)) ischemia, followed by 32 min of reperfusion. In control rat hearts, neither palmitate nor ketone bodies altered the recovery of contractile function. Diabetic rat hearts perfused with glucose alone or with ketone bodies, had functional recoveries 50% lower than those of the control hearts, but palmitate restored recovery to control levels. In a parallel group with the functional recoveries, palmitate prevented the 54% faster loss of ATP in the diabetic, glucose-perfused rat hearts during ischemia, but had no effect on the rate of ATP depletion in control hearts. Palmitate decreased total glucose uptake in control rat hearts during low-flow ischemia, from 106 +/- 17 to 52 +/- 12 micromol/g wet wt, but did not alter the total glucose uptake in the diabetic rat hearts, which was 42 +/- 5 micromol/g wet wt. Recovery of contractile function was unrelated to pH(i) during ischemia; the glucose-perfused control and palmitate-perfused diabetic hearts had end-ischemic pH(i) values that were significantly different at 6.36 +/- 0.04 and 6.60 +/- 0.02, respectively, but had similar functional recoveries, whereas the glucose-perfused diabetic hearts had significantly lower functional recoveries, but their pH(i) was 6.49 +/- 0.04. We conclude that fatty acids, but not ketone bodies, protect the diabetic heart by decreasing ATP depletion, with neither having detrimental effects on the normal rat heart during low-flow ischemia.

Animals↗
PubMed2001

Increased uncoupling proteins and decreased efficiency in palmitate-perfused hyperthyroid rat heart.

The physiological role of mitochondrial uncoupling proteins (UCPs) in heart and skeletal muscle is unknown, as is whether mitochondrial uncoupling of oxidative phosphorylation by fatty acids occurs in vivo. In this study, we found that UCP2 and UCP3 protein content, determined using Western blotting, was increased by 32 and 48%, respectively, in hyperthyroid rat heart mitochondria. Oligomycin-insensitive respiration rate, a measure of mitochondrial uncoupling, was increased in all mitochondria in the presence of palmitate: 36% in controls and 71 and 100% with 0.8 and 0.9 mM palmitate, respectively, in hyperthyroid rat heart mitochondria. In the isolated working heart, 0.4 mM palmitate significantly lowered cardiac output by 36% and cardiac efficiency by 38% in the hyperthyroid rat heart. Thus increased mitochondrial UCPs in the hyperthyroid rat heart were associated with increased uncoupling and decreased myocardial efficiency in the presence of palmitate. In conclusion, a physiological effect of UCPs on fatty acid oxidation has been found in heart at the mitochondrial and whole organ level.

Animals↗
PubMed2000

Magnetic resonance spectroscopy evidence of abnormal cardiac energetics in Xp21 muscular dystrophy.

OBJECTIVES: Our aim was to measure the cardiac phosphocreatine to adenosine triphosphate ratio (PCr/ATP) noninvasively in patients and carriers of Xp21 muscular dystrophy and to correlate the results with left ventricular (LV) function as measured by echocardiography. BACKGROUND: Duchenne and Becker muscular dystrophy (the Xp21 dystrophies) are associated with the absence or altered expression of dystrophin in cardiac and skeletal muscles. They are frequently complicated by cardiac hypertrophy and dilated cardiomyopathy. The main role of dystrophin is believed to be structural, but it may also be involved in signaling processes. Defects in energy metabolism have been found in skeletal muscle in patients with Xp21 muscular dystrophy. We therefore hypothesized that a defect in energy metabolism may be part of the mechanism leading to the cardiomyopathy of Xp21 muscular dystrophy. METHODS: Thirteen men with Becker muscular dystrophy, 10 female carriers and 23 control subjects were studied using phosphorus-31 magnetic resonance spectroscopy and echocardiography. RESULTS: The PCr/ATP was significantly reduced in patients (1.55+/-0.37) and carriers (1.37+/-0.25) as compared with control subjects (2.44+/-0.33; p<0.0001 for both groups). The PCr/ATP did not correlate with LV ejection fraction or mass index. CONCLUSIONS: Altered expression of dystrophin leads to a reduction in the PCr/ATP. Since this reduction did not correlate with indexes of left ventricular function, this raises the possibility of a direct link between altered dystrophin expression and the development of cardiomyopathy in such patients.

Adenosine Triphosphate↗
PubMed2000

Vision and touch through the looking glass in a case of crossmodal extinction.

When observing ourselves in a mirror, we see our body and adjacent objects (e.g. a comb or razor) projecting the image of distant objects. Are these recoded by the brain as reflecting stimuli in peripersonal space? To address this, we exploited the neuropsychological phenomenon of crossmodal, visual-tactile extinction, as shown by patient BV following right-hemisphere stroke. In such crossmodal extinction, a right visual event impairs the perception of a simultaneous left tactile event. In BV, the right visual stimulus (an LED flash) induced more extinction of touch on the contralesional left hand when presented near the ipsilesional right hand, than when distant from it. This agrees with previous data in patients and monkeys showing that visual-tactile interactions are strongest within peripersonal space. Crucially, we also found that an ipsilesional flash produced more extinction when observed as the distant mirror-reflection of an LED that lay close to the ipsilesional hand, rather than as a distant LED flash projecting an equivalent visual image directly. This suggests that in BV, seeing his own hand via a mirror activates a representation of peripersonal space around that hand, not of the extrapersonal space suggested by the distant visual image in the mirror. We discuss the possible neural basis of interpreting mirror reflections.

Aged↗
PubMed2000

In vivo biodistribution of a humanized anti-Lewis Y monoclonal antibody (hu3S193) in MCF-7 xenografted BALB/c nude mice.

The biodistribution characteristics of a humanized anti-Lewis(y) antibody (hu3S193) radiolabeled to three radioisotopes, 125I, 111In, and 90Y, were examined in a BALB/c nude mouse xenograft model of breast cancer. The immunoreactivity of both 125I- and 111In-bound hu3S193 exceeded 50% and was 20% for 90Y. In vivo, labeled antibody was shown by gamma camera imaging and immunohistochemical and autoradiographic techniques to localize to Lewis(y)-expressing breast xenografts with minimal normal tissue uptake. Maximal radioisotope uptake peaked at 48 h for all three isotopes; however, the percentage of injected dose/gram and tumor retention were greater for 111In- and 90Y-bound antibody than for 125I-bound antibody. Although immunoreactivity of 111In- and 125I-labeled hu3S193 in serum was stable over a 5-day period, the amount of unlabeled 111In in serum was lower than 125I, which together with higher tumor uptake indicates better retention of 111In-labeled hu3S193 and catabolites within the tumor cells. Superior tumor uptake and retention of 111In-labeled hu3S193 and similar blood clearance compared with 125I-labeled hu3S193, suggest that radiometals are the preferred radioisotope for this antibody-antigen system. Humanized 3S193 is a promising new construct for the targeting and potential therapy of Lewis(y)-expressing tumors.

Adenocarcinoma↗
PubMed2000

Construction, production, and characterization of humanized anti-Lewis Y monoclonal antibody 3S193 for targeted immunotherapy of solid tumors.

The Lewis Y (Ley) antigen is a blood group-related antigen that is expressed in a high proportion of epithelial cancers (including breast, colon, ovary, and lung cancer) and is an attractive target for monoclonal antibody-directed therapy. The murine monoclonal 3S193 (IgG3) was generated in BALB/c mice by immunization with Ley-expressing cells of the MCF-7 breast carcinoma cell-line. The murine 3S193 showed high specificity for Ley in ELISA tests with synthetic Ley and Ley-containing glycoproteins and glycolipids and also reacted strongly in rosetting assays and cytotoxic tests with Ley-expressing cells. We generated a humanized form of the murine 3S193 antibody by linking cDNA sequences encoding the variable region of murine 3S913 with frameworks of the human KOL heavy chain and REI K chain. The genes for the humanized 3S193 monoclonal antibody IgG1 were transfected into mouse myeloma NS0 cells and cloned for the establishment of high antibody-producing colonies. Humanized 3S193 antibody was subsequently produced through in vitro culture and under good manufacturing practice conditions using hollow-fiber bioreactors. The purified humanized 3S193 (hu3S193) was subsequently characterized and validated for use in preliminary immunotherapy investigations. hu3S193 reacted specifically with Ley antigen, with similar avidity to the murine form. hu3S193 demonstrated potent immune effector function, with higher antibody-dependent cell-mediated cytotoxicity than its murine counterpart and potent complement-dependent cytotoxicity (ED50, 1.0 microg/ml). The in vivo immunotherapeutic potential of hu3S193 was assessed in a human breast xenograft model using MCF-7, Ley-positive cells. Six i.v. doses of up to 1 mg of hu3S193 were administered to animals bearing established tumors (120-130 mm3) with no significant effect on tumor growth. In contrast, in an MCF-7 xenograft preventive model, a 1-mg hu3S193 dosage schedule was able to significantly slow tumor growth compared with placebo and isotype-matched control IgG1 antibody. hu3S193 has promise for immunotherapy of Ley-positive tumors and is currently entering Phase I clinical trials.

Amino Acid Sequence↗