Biomedical subjects

John W Chen

Publications and source records attributed to John W Chen.

8 recordsLinked to original sources

PubMed2006

A paramagnetic contrast agent with myeloperoxidase-sensing properties.

Myeloperoxidase (MPO) is an essential component of inflammatory response in norm and pathology. With an ultimate goal of non-invasive imaging of MPO we used a gadolinium-chelating bis(5-hydroxytrytamide) derivative of diethylenetetraamine pentaacetic acid (L1-Gd3+ salt) as a paramagnetic sensor of enzymatic activity. We tested whether L1-Gd3+ is active in reducing the oxidized form of myeloperoxidase, generated as a result of hydrogen peroxide reduction by the enzyme. We expected that upon activation by MPO/H2O2 L1-Gd3+ would not only oligomerise but also bind to other macromolecules present in the media and that the overall process will give rise to a net T1-weighted MRI signal increase.

Contrast Media↗

PubMed2006

Metabolic biotinylation of cell surface receptors for in vivo imaging.

We have developed a versatile, potent technique for imaging cells in culture and in vivo by expressing a metabolically biotinylated cell-surface receptor and visualizing it with labeled streptavidin moieties. The recombinant reporter protein, which incorporates a biotin acceptor peptide (BAP) between an N-terminal signal sequence and a transmembrane domain, (BAP-TM) was efficiently biotinylated by endogenous biotin ligase in mammalian cells with the biotin displayed on the cell surface. Tumors expressing the BAP-TM have high sensitivity for magnetic resonance and fluorescence tomographic imaging in vivo after intravascular injection of streptavidin conjugated to magnetic nanoparticles or fluorochromes, respectively. Moreover, streptavidin-horseradish peroxidase conjugates in conjunction with a peroxidase-sensitive gadolinium agent further increased and prolonged the magnetic resonance signal. This BAP-TM allows noninvasive real-time imaging of any cell type transduced to express this reporter protein in culture or in vivo.

Base Sequence↗

PubMed2006

Imaging of myeloperoxidase in mice by using novel amplifiable paramagnetic substrates.

PURPOSE: To evaluate whether contrast agents for molecular magnetic resonance (MR) imaging can demonstrate the in vivo activity of myeloperoxidase, an enzyme that is secreted by stimulated polymorphonuclear leukocytes, monocytes, and macrophages during inflammation. MATERIALS AND METHODS: Animal experiments were approved by the animal care committee. Protocols for the procurement and use of human blood were approved by the institutional review board. Informed consent was obtained from each donor, and HIPAA guidelines were followed for humans. Two paramagnetic myeloperoxidase substrates--that is, gadolinium-5-hydroxytryptamide-tetraazacyclododecane tetraacetic acid (Gd-5-HT-DOTA) and Gd-bis-5-HT-diethylenetriaminepentaacetic acid (Gd-bis-5-HT-DTPA)--were synthesized. Indium 111-labeled bis-5-HT-DTPA was used to determine biodistribution and target localization. A total of 22 mice were used in three models. In the first model, human myeloperoxidase was embedded in a basement membrane matrix gel and was injected intramuscularly. In the second model, lipopolysaccharide (LPS) from Escherichia coli was embedded in a basement membrane matrix gel and was injected intramuscularly to induce endogenous myeloperoxidase secretion. In the third model, LPS was injected intramuscularly to induce myositis. Statistical significance was calculated for contrast-to-noise ratio (CNR) curves by using the Kolmogorov-Smirnov test. RESULTS: After the administration of Gd-bis-5-HT-DTPA, strong MR signal enhancement (up to 2.5-fold increase in CNR, P < .001) was observed in vivo for implants that contained human myeloperoxidase. In the LPS-induced myositis model, a smaller visible difference was seen (1.3-fold increase in CNR, P < .001), which was consistent with the fact that endogenous mouse myeloperoxidase is only about 10%-20% as active as human myeloperoxidase. Prolonged contrast material enhancement was observed in the myeloperoxidase-containing areas that were injected with Gd-5-HT-DOTA or Gd-bis-5-HT-DTPA but was not observed in areas that were injected with Gd-DTPA or Gd-dopamine-DOTA (P < .05). Single photon emission computed tomography combined with computed tomography was used to confirm the increased retention of contrast agents at sites that contained human myeloperoxidase, and the results of biodistribution studies demonstrated a more than fourfold increase radiotracer accumulation at these sites. CONCLUSION: Human and mouse myeloperoxidase activity in myeloperoxidase implants and inflamed tissues can be visualized and reported in vivo by using myeloperoxidase-sensitive "smart" molecular imaging probes.

Animals↗

PubMed2005

DTPA-bisamide-based MR sensor agents for peroxidase imaging.

[reaction: see text] The synthesis and some properties of two novel DTPA-bisamides are reported. These derivatives were designed as enzyme-activated contrast agents (CA) for magnetic resonance imaging. Both derivatives bear tyramido or 5-hydroxytryptamido groups that could be oligomerized in situ in the presence of peroxidase/H(2)O(2) pair resulting in a net increase in longitudinal (R1) relaxivity.

Contrast Media↗

PubMed2005

Vulnerable plaque imaging.

The concept of vulnerable plaque is well established with increasing evidence from clinical and basic research. The paradigm has shifted from focusing exclusively on the hemodynamic effects of plaque (ie, resulting lumenal stenosis alone as a predictor of stroke risk) to assessment of the structure and composition of plaque (eg, denuded endothelium with inflammatory elements as a nidus for platelet-fibrin clumping). It is increasingly evident that methods to detect and characterize vulnerable plaque must be developed and optimized. Although MR imaging, CT, and ultrasound provide data regarding single lesions, future investigations relying heavily on nuclear medicine techniques may offer functional assessment of the entire cardiovascular system.

Arteriosclerosis↗

PubMed2004

Human myeloperoxidase: a potential target for molecular MR imaging in atherosclerosis.

Plaque rupture in atherosclerotic disease is the major cause of morbidity and correlates well with myeloperoxidase (MPO) secretion by activated neutrophils and macrophages in humans. We hypothesized that paramagnetic electron donor compounds that rapidly oxidize and polymerize in the presence of MPO could be designed to enable imaging of local MPO activity levels in arterial segments at risk. Several potential substrates for MPO were synthesized and tested. One lead compound consisting of a covalent conjugate of GdDOTA and serotonin (3-(2-aminoethyl)-5-hydroxyindole) was efficiently polymerized in the presence of human neutrophil MPO resulting in a 70-100% increase in proton relaxivity. As a result, we were able to demonstrate MPO activity in enzyme solutions and in a model tissue-like system. These studies suggest that activatable paramagnetic MR imaging agents can be used to directly image MPO activity.

Arteriosclerosis↗

PubMedDate not supplied

Myeloperoxidase activity imaging using (67)Ga labeled substrate.

PURPOSE: The aim of the study is to assess the feasibility of imaging specific activity of myeloperoxidase (MPO), a leukocyte enzyme with important roles in inflammation and atherosclerosis, by single photon emission computed tomography (SPECT) using a novel (67)Ga-labeled radiotracer obtained by conjugating desferrioxamine (DF) and hydroxyindolyl acetic acid in vivo. MATERIALS AND METHODS: A reducing substrate of MPO (I) was synthesized by reacting commercially available DF with 2-(5-hydroxy-1H-indol-3-yl) acetic acid in the presence of a coupling agent [dicyclohexyl carbodiimide (DCC)]. The chelating unit was labeled with (67)Ga, and its interaction with MPO was characterized using MALDI-TOF and UV-vis. Mice with Matrigel implants containing human MPO were used to model diseased tissues rich in MPO. Three hours after the injection of (67)Ga-I, SPECT/computed tomography (CT) imaging was performed on a high-resolution Gamma Medica X-SPECT system. Biodistribution studies were performed six hours after the injection of the radiotracer. RESULTS: The feasibility of compound I oligomerization in the presence of MPO and MPO-mediated cross-linking with proteins was initially confirmed in vitro. In vivo, a 2.7-fold increase in target-to-muscle ratio could be measured in MPO-containing Matrigel implants in mice. Biodistribution experiments demonstrated a 60% increase of radioactivity in MPO-containing vs. control (contralateral) Matrigel implants. CONCLUSION: (67)Ga-I can be used to image MPO activity in a model system. The accumulation mechanism is based on a differential pharmacokinetics because of the size increase resulting from (67)Ga-I interaction with the target enzyme.

Animals↗

PubMedDate not supplied

Endothelins induce gallbladder contraction independent of elevated blood pressure in vivo in the Australian possum.

Endothelin levels are elevated in shock, sepsis, and cholestatic jaundice, and an effect on biliary motility may be postulated. The aim of this study was to determine whether (1) endothelin-1 and endothelin-3 induce gallbladder contraction in vivo, (2) the response is caused by changes in blood pressure, and (3) the response is nerve mediated. Gallbladder pressure and blood pressure were measured in 38 anesthetized possums. Endothelin-1 or endothelin-3 (5 to 200 pmol/kg) was administered by close intra-arterial injection. Tetrodotoxin (9 microg/kg) or the mixed endothelin antagonist tezosentan was infused at a rate of 10 or 100 nmol/kg/min (close intra-arterial injection). Maximum changes in gallbladder pressure (% of carbachol-induced contraction) and blood pressure (mm Hg) were determined. Statistical analysis was carried out by means of repeated-measures analysis of variance and Kruskal-Wallis test. Both endothelin-1 and endothelin-3 induced dose-dependent increases in gallbladder pressure and blood pressure (P < 0.05), which were unaffected by pretreatment with tetrodotoxin. The endothelin-1-induced gallbladder pressure but not blood pressure was reduced by the higher dose of tezosentan (P < 0.03). The lower dose of tezosentan also produced a decrease in the endothelin-3-induced gallbladder pressure (P < 0.02) but not in blood pressure, whereas the higher dose reduced the blood pressure with no further reduction in gallbladder pressure (P < 0.05). Endothelins increase gallbladder motility in vivo, acting directly on the smooth muscle and independent of changes in blood pressure.

Anesthetics, Local↗