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O Clément

Publications and source records attributed to O Clément.

At least 19 recordsLinked to original sources
PubMed2003

Analysis of the distribution of MRI contrast agents in the livers of small animals by means of complementary microscopies.

BACKGROUND: Magnetic resonance imaging (MRI) contrast agents contain magnetic molecules such as iron (Fe) or gadolinium (Gd) that are injected in vivo into rats or mice to study their distribution inside the liver. Fluorescent europium (Eu) can be used as a model of Gd to obtain comparable information of this distribution of corresponding contrast agents. In a similar approach, Fe can be attached to Texas Red and used as a model of ferumoxides and be detected by fluorescence. METHODS: To combine and compare the advantages of different microscopic imaging modes, characterization studies were carried out by means of a confocal laser scanning microscope (CLSM), a secondary ion mass spectrometric (SIMS) microscope, and an electron energy loss spectrometric (EELS) microscope. In the case of CLSM, the locations of fluorescent signals inside preparations were determined by factor analysis of biomedical image sequences (FAMIS) and selection of image sequences at emission. RESULTS: By CLSM and FAMIS, we distinguished chelated Eu and Texas Red attached to Fe. By SIMS microscopy, we distinguished Eu and Gd of chlorides and chelates and Fe of a ferumoxide. By EELS microscopy, we distinguished Eu and Gd of chlorides. CONCLUSIONS: Analysis of compounds inside correlative specimens by means of CLSM, SIMS, and EELS microscopes provided complementary results.

Animals↗
PubMed2001

Hepatocyte targeting with Gd-EOB-DTPA: potential application for gene therapy.

RATIONALE AND OBJECTIVES: To evaluate the suitability of the liver-specific MRI contrast agent Gd-EOB-DTPA as a nonviral vector for gene therapy of hepatocellular carcinoma. METHODS: Specific uptake of Gd-EOB-DTPA was quantified by relaxometry in rat cultured hepatocytes and the hepatoma cells HepG2 and Huh7. Nonviral vectors for gene transfer were synthesized by coupling Gd-EOB-DTPA to polyethyleneimine or polylysine as DNA condensing agents, and their efficiency was studied using beta-galactosidase (lacZ) as the reporter gene. RESULTS: Gd-EOB-DTPA was specifically taken up by rat cultured hepatocytes (4.32 vs. 1.08 mmol/L in nonhepatocyte control cells) but not by the hepatoma cells; this uptake was concentration-dependently inhibited by Bromsulphtalein. Polycation linkages were achieved with yields of 0.9 Gd-EOB-DTPA molecule per polyethyleneimine molecule and 10 Gd-EOB-DTPA molecules per polylysine molecule. Incubating the cells with plasmids containing lacZ reporter gene and polyethyleneimine-Gd-EOB-DTPA resulted in a few blue (transfected) cells, whereas no blue cells were observed on incubation with polylysine-Gd-EOB-DTPA. CONCLUSIONS: Gd-EOB-DTPA is taken up by normal hepatocytes but not by HepG2 and Huh7 cells, probably because of the lack of the organic anion transporter in these hepatoma cells. The Gd-EOB-DTPA polycation conjugates, such as polyethyleneimine-Gd-EOB-DTPA, could serve as transfer vectors of interest for gene targeting imagery at the early stage of hepatocarcinogenesis. However, the transfer efficiency of such conjugates is low and requires improvement.

Animals↗
PubMed2001

Early changes in liver perfusion caused by occult metastases in rats: detection with quantitative CT.

PURPOSE: To determine whether computed tomography (CT) can depict liver hemodynamic changes caused by occult hepatic micrometastases in rat. MATERIALS AND METHODS: Liver micrometastases (mean diameter, 500 micrometer +/- 300) were produced in seven BD IX rats by injecting 10(7) DHDK12 PROb colorectal carcinoma cells into the spleen. Macrometastases (mean diameter, 7 mm +/- 3) were produced in four other rats. Five normal rats were studied as controls. CT images were obtained every 300 msec for 30 seconds during the injection of 1 mL per kilogram of body weight of contrast medium. The time-attenuation curves of the aorta, portal vein, and liver were used to calculate liver perfusion with a deconvolution model designed for the dual blood supply. RESULTS: Micrometastases in an apparently normal liver caused a 34% decrease in portal blood flow and a 25% increase in the mean transit time for the blood to pass through the liver. These findings suggest increased resistance in the sinusoidal capillaries. Similar but greater changes were found in the macrometastases. CONCLUSION: Occult liver micrometastases in rats generate changes in liver perfusion that can be detected with CT.

Animals↗
PubMed2001

Confocal analysis of phosphatidylserine externalization with the use of biotinylated annexin V revealed with streptavidin-FITC, -europium, -phycoerythrin or -Texas Red in oxysterol-treated apoptotic cells.

OBJECTIVE: To analyze externalization of phosphatidylserine via annexin V on apoptotic cells by laser scanning confocal microscopy and factor analysis of biomedical image sequences (FAMIS). STUDY DESIGN: Streptavidin-fluorescein isothiocyanate (FITC), -europium (Eu), -phycoerythrin (PE) and -Texas Red (TR) were chosen to reveal the binding of biotinylated annexin V on apoptotic U937 human leukemic cells and ECV-304 human endothelial cells induced under treatment with 7-ketocholesterol or 7 beta-hydroxycholesterol. Excitation of each fluorochrome was obtained by selection of specific lines (351 + 364 nm, 488 nm) of the argon laser of a confocal microscope. Temporal and spectral series were performed to characterize each fluorochrome. FAMIS was applied to these series to estimate images corresponding to stains. RESULTS: Each fluorochrome was clearly distinguished, and images showed localization of phosphatidylserine, which was improved by image analysis. CONCLUSION: On apoptotic cells it is possible to analyze differences in the improved visualization of phosphatidylserine in series processed by FAMIS with the use of biotinylated annexin V revealed with streptavidin-FITC, -Eu, -PE or -TR.

Annexin A5↗
PubMed2001

Confocal image characterization of human papillomavirus DNA sequences revealed with Eu in HeLa cell nuclei stained with Hoechst 33342.

OBJECTIVE: To visualize and localize specific viral DNA sequences revealed with Eu by fluorescence in situ hybridization, confocal laser scanning microscopy (CLSM) and factor analysis of biomedical image sequences (FAMIS). STUDY DESIGN: Human papillomavirus DNA (HPV-DNA) was identified in HeLa cells with biotinylated DNA probes recognizing HPV-DNA types 16/18. DNA-DNA hybrids were revealed by a three-step immunohistochemical amplification procedure involving an antibiotin mouse monoclonal antibody, a biotinylated goat antimouse polyclonal antibody and streptavidin-Eu. Cell nuclei were counterstained with Hoechst 33342. Image sequences were obtained using a CLSM that made possible ultraviolet excitation. The location of fluorescent signals inside cellular preparations was determined by FAMIS and selection of filters at emission. Image sequences were summarized into a reduced number of images, or factor images, and curves, or factors. Factors estimate spectral or temporal patterns and depth emission profiles. Factor images correspond to spatial distributions of the different factors. RESULTS: We distinguished between Eu corresponding to HPV-DNA hybridization signals and nuclear staining by taking into account differences in their spectral and temporal patterns and (using their decay rates). CONCLUSION: FAMIS, together with CLSM and Eu, made possible the detection and characterization of viral papillomavirus DNA sequences in HeLa cells.

Base Sequence↗
PubMed2000

Confocal multilaser focusing and single-laser characterization of ultraviolet excitable stains of cellular preparations.

BACKGROUND: The aims of this study were (1) to realign cellular preparations when spots and structures are excited by different lasers of a confocal laser scanning microscope (multilaser studies); (2) to avoid the use of realigment methods by selecting fluorochromes that can be excited by only one laser (single-laser experiments). METHODS: In multilaser studies, we used propidium iodide fluorescent beads, as well as tetramethyl rhodamine isothiocyanate (TRITC), fluorescein isothiocyanate (FITC), and 4'-6 diamidino-2-phenylindole (DAPI)-stained human cancer lines. They were excited using HeNe, argon, and ultraviolet (UV) argon laser lines of a confocal laser scanning microscope. Single-laser experiments using UV excitation only were performed using europium as a model for magnetic resonance paramagnetic contrast agents. Nuclei of human cancer lines and tissue were counterstained by DAPI and cytoplasms were labeled with ELF-97 substrates. Factor analysis of medical images (FAMIS) and correlation methods were used to realign shifted images, focus images, and characterize each fluorochrome when necessary. RESULTS: In multilaser studies, superimposition of factor images corrected Z shifts and correlation methods provided X, Y correction values. In single-laser experiments, each fluorochrome was clearly distinguished in the group of fluorochromes. Estimated images in both studies showed colocalizations of structures. CONCLUSIONS: It is possible to characterize differences in the focus and alignment of fluorescent probes and to correct them. It is also possible to study colocalization of UV excitable fluorochromes (DAPI, ELF-97, europium) in cellular and tissular preparations via multilaser or single-laser experiments.

Europium↗
PubMed2000

Evaluation of HSV-tk gene therapy in a rat model of chemically induced hepatocellular carcinoma by intratumoral and intrahepatic artery routes.

Transfer of the herpes simplex virus-thymidine kinase (HSV-tk) gene followed by the administration of ganciclovir (GCV) into hepatocellular carcinoma (HCC)-derived cell lines either in vitro or transplanted into nude mice has been shown to provide a potential strategy for HSV-tk-based gene therapy of HCC. We report herein an analysis of the antitumoral efficacy of two recombinant adenoviruses (Ads), Ad.CMVtk and Ad.AFPtk, in a relevant model of multifocal hepatic lesions induced in rats by a potent alkylating chemical carcinogen, diethylnitrosamine. Two routes of administration of the Ad were studied: intratumoral and intrahepatic artery injections. Both recombinant Ads, Ad.CMVtk and Ad.AFPtk, express the HSV-tk gene under the control of the early enhancer/promoter cytomegalovirus and alpha-fetoprotein regulatory gene sequences, respectively. The antitumor response was assessed by magnetic resonance imaging and by autopsy and histological analysis following postmortem. Tumor growth cessation was demonstrated by magnetic resonance imaging in large tumor nodules of size 5-8 mm treated by intratumoral administration of 2x10(9) pfu Ad.CMVtk plus i.p. treatment with GCV. We also show an antitumor efficacy in small tumor nodules of size <3 mm treated with 2x10(9) pfu Ad.CMVtk plus GCV by the intrahepatic artery route, albeit associated with an adverse toxicity. In vivo targeting of the HSV-tk gene to diethylnitrosamine-induced HCC cells with the recombinant Ad.AFPtk suppresses the hepatic toxicity in the nontumoral liver. The lower antitumor response would argue for the use of multiple injections of such adenoviral constructs. These observations may lead to potential approaches for designing gene therapy destined for early treatment of dysplastic nodules or advanced HCC in cirrhosis.

Adenoviridae↗
PubMed2000

Distribution of iron oxide nanoparticles in rat lymph nodes studied using electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI).

Superparamagnetic iron nanoparticles have been developed as contrast agents for magnetic resonance lymphography. The kinetics of uptake of these particles has not yet been accurately determined. We have therefore monitored the distribution of individual iron particles (ferumoxtran, AMI-227, Sinerem) in rat lymph nodes 1.5, 3, 6, 12, and 24 hours after i.v. injection (two rats per time point). The ultrastructural distribution of the iron was determined by energy-filtered transmission electron microscopy (EFTEM). This method allows the identification of elements using element-specific energy-loss electrons. Iron was identified by the Fe-L(2,3) edge (EELS), and iron maps were obtained using iron-specific electrons for imaging (ESI). The background was calculated by simplex optimization (EELS) and by the two-window method (ESI). Ferumoxtran particles were regularly observed at the periphery of the lymph nodes but not in their centers. Isolated iron particles were seen extracellularly within lymph vessels and, 3 hours after injection, as small dots in phagocytic cells. Numerous dense clusters appeared within the cells at later times (6 and 12 hours after injection). These results suggest that the contrast agent moves rapidly across the capillary wall to the lymph and is then taken up by phagocytic cells. J. Magn. Reson. Imaging 2000;12:505-509.

Animals↗
PubMed2000

MR lymphography using iron oxide nanoparticles in rats: pharmacokinetics in the lymphatic system after intravenous injection.

The objective of the study was to quantify the kinetics of the superparamagnetic nanoparticle ferumoxtran (AMI 227, Sinerem(R), Combidex(R)) in the efferent lymph of the subdiaphragmatic lymph nodes and in various node groups of the rat to elucidate the uptake mechanism. The thoracic lymph duct was catheterized in 24 rats after an IV injection of 40 micromol Fe/kg ferumoxtran. Three rats were studied at several time points between 1.5 and 24 hours. At each time point, 0.3 ml of lymph were collected over 45 minutes. Lymph nodes were differentiated into five groups. The iron concentration in the samples and in plasma was measured by relaxometry at 0.47 T and atomic absorption spectrometry. Cytology was performed on the lymph. High concentrations of nanoparticles were found in the thoracic lymph soon after injection (90 minutes). No particle was found in the lymph cells, indicating that ferumoxtran was extracellular in the lymph fluid. The maximum concentration was reached later in all node groups, at 12 hours, and then plateaued. The transcapillary pathway and subsequent lymph drainage of the particles seem to play a major role in the delivery to the lymph nodes.

Animals↗
PubMed1999

The rete mirabile of the eel: a useful model for the study of transcapillary passage of MR contrast agents.

Our purpose was to study the capillary leakage of MR contrast media using a pure capillary model, the rete mirabile of the eel. The rete is a countercurrent-exchange organ composed of an arterial and a venous capillary system that can be catheterized and perfused. Substances are introduced at the arterial input by a constant infusion, and their steady-state concentrations are measured at the arterial and venous outputs. The capillary leakage of four MR contrast agents--Gd-DOTA(MW = 561 D), carboxymethyldextran-Gd-DTPA (MW = 38,900 D), albumin-Gd-DTPA (MW = 92,000 D), AMI-227 (400,000 D<MW<900,000 D)--was characterized by reference to radioactive tracers (3HHO, 22Na, 14C-sucrose, 125I-albumin) by two parameters. These parameters were the concentration ratio of the venous output over the arterial input [C(VOUT)(%)] and the permeability coefficient (P). The transcapillary pathway mechanisms for carboxymethyldextran-Gd-DTPA and albumin-Gd-DTPA were studied by electron microscopy. P values for Gd-DOTA (9.4+/-3.6 x 10(-7) cm/s) and albumin-Gd-DTPA (11.8+/-5.5 x 10(-7) cm/s) were close to P values for 14C-sucrose, while P values for carboxymethyldextran-Gd-DTPA (6.4+/-4.9 x 10(-7) cm/sec) were similar to P values for 125I-albumin. The lowest permeability was observed with AMI-227 (2.7+/-2 x 10(-7) cm/sec). Vesicular transport was demonstrated for carboxymethyldextran-Gd-DTPA and albumin-Gd-DTPA. The transcapillary passage of several MR contrast agents can be characterized with the rete mirabile model. Molecular weight is the major factor influencing transport.

Air Sacs↗
PubMed1999

Mechanisms of action of liver contrast agents: impact for clinical use.

New contrast agents for magnetic resonance imaging are continually being developed by pharmaceutical companies in order to better image the liver. These agents can be divided into hepatobiliary agents directed to the hepatocytes and nanoparticulate agents directed to the reticulo-endothelial system. After intravenous injection, all these agents concentrate in the liver and induce profound changes in signal intensity. Particulate agents induce predominantly a darkening of the liver parenchyma, while hepatobiliary agents induce a brightening. In both cases, liver-lesion conspicuity is enhanced, leading to a better visualization of the lesion. After a brief description of the principal characteristics of the agents, this paper will attempt to summarize the utility of these agents for the detection and characterization of focal liver disease.

Contrast Media↗
PubMed1998

Contrast agents in magnetic resonance imaging of the liver: present and future.

New contrast agents are being developed by drug companies to better image the liver magnetic resonance imaging (MRI). They can be divided into hepatobiliary agents (Gd-EOB-DTPA, Gd-BOPTA, Mangafodipir) and nanoparticulate agents directed to the reticulo-endothelial system (ferumoxides, SHU 555A). After intravenous injection, all these agents concentrate in the liver and induce profound signal changes. Particulate agents induce predominantly a darkening of the liver parenchyma, while hepatobiliary agents induce a brightening. In both cases, liver-lesion conspicuity is enhanced, leading to a better visualization of the lesion. After a description of the principal pharmacokinetic characteristics of the compounds, this review paper summarizes the utility of the agents in the detection and characterization of focal liver diseases.

Contrast Media↗
PubMed1998

Fat suppression techniques in MRI: an update.

Due to short relaxation times, fat has a high signal on magnetic resonance images (MRI). This high signal, easily recognized on MRI, may be useful to characterize a lesion. However, small amounts of lipids are more difficult to detect on conventional MRI. In addition, the high signal due to fat may be responsible for artifacts such as ghosting and chemical shift. Lastly, a contrast enhancing tumor may be hidden by the surrounding fat. These problems have prompted development of fat suppression techniques in MRI. Fat may be suppressed on the basis of its difference in resonance frequency with water by means of frequency selective pulses or phase contrast techniques, or on the basis of its short T1 relaxation time by means of inversion recovery sequences. Lastly, hybrid techniques combining several of these fat suppression techniques are also possible. The aim of this paper is to review the basic principles of all these fat suppression techniques and to exemplify their clinical use.

Adipose Tissue↗
PubMed1998

Enhanced in vivo adenovirus-mediated gene transfer to rat hepatocarcinomas by selective administration into the hepatic artery.

Adenovirus-mediated gene therapy of experimental hepatocarcinoma is hindered by low transduction efficacy in vivo. We evaluated the extent of gene expression following various routes of administration of recombinant adenovirus AdCMVlacZ in diethylnitrosamine-induced rat hepatocarcinoma. We first characterized the vascularization of diethylnitrosamine-induced hepatocarcinomas using a computerized tomography scanner approach. The efficacy of gene transfer was then evaluated by three routes of administration: intraportal, selective injection through the hepatic artery and direct injection into the tumor. Diethylnitrosamine-induced hepatocarcinomas had predominantly an arterial blood supply, 67% of the total liver blood supply. Compared with intraportal administration, arterial injection improved gene transfer into tumors whereas that to the non-tumor areas was diminished. In addition, this route of injection allowed the efficient transduction of dysplastic nodules. Diethylnitrosamine-induced hepatocarcinoma in rats is a relevant model for the study of human hepatocarcinoma due to its vascularization. Arterial infusion improved the ratio of transduced tumorous to nontumorous cells and allowed targeting of gene transfer to dysplastic nodules. This will be useful in the design of gene therapy for hepatocarcinoma.

Adenoviridae↗
PubMed1998

Liver imaging with ferumoxides (Feridex): fundamentals, controversies, and practical aspects.

Superparamagnetic nanoparticles (Feridex) have been recently made available to the radiological community as a contrast agent for MR imaging of the liver. This article reviews the principal physicochemical characteristics of this new compound, with an emphasis on the explanation of the contrast obtained (either positive or negative enhancement) that depends on the local concentration and the sequence used. The clinical use of Feridex is detailed, both for lesion detection and characterization. Finally, some guidelines for image optimization are given.

Contrast Media↗