Modulation of Cytosolic Phospholipase A2 as a Potential Therapeutic Strategy for Alzheimer's Disease

Background

Alzheimer's disease (AD) is a neurodegenerative disorder lacking any curative treatment up to now. Indeed, actual medication given to the patients alleviates only symptoms. The cytosolic phospholipase A2 (cPLA2-IVA) appears as a pivotal player situated at the center of pathological pathways leading to AD and its inhibition could be a promising therapeutic approach.

Objective

A cPLA2-IVA inhibiting peptide was identified in the present work, aiming to develop an original therapeutic strategy.

Methods

We targeted the cPLA2-IVA using the phage display technology. The hit peptide PLP25 was first validated in vitro (arachidonic acid dosage [AA], cPLA2-IVA cellular translocation) before being tested in vivo. We evaluated spatial memory using the Barnes maze, amyloid deposits by MRI and immunohistochemistry (IHC), and other important biomarkers such as the cPLA2-IVA itself, the NMDA receptor, AβPP and tau by IHC after i.v. injection in APP/PS1 mice.

Results

Showing a high affinity for the C2 domain of this enzyme, the peptide PLP25 exhibited an inhibitory effect on cPLA2-IVA activity by blocking its binding to its substrate, resulting in a decreased release of AA. Coupled to a vector peptide (LRPep2) in order to optimize brain access, we showed an improvement of cognitive abilities of APP/PS1 mice, which also exhibited a decreased number of amyloid plaques, a restored expression of cPLA2-IVA, and a favorable effect on NMDA receptor expression and tau protein phosphorylation.

Conclusions

cPLA2-IVA inhibition through PLP25 peptide could be a promising therapeutic strategy for AD.

Molecular and cellular biology of PCSK9: impact on glucose homeostasis

Proprotein convertase substilisin/kexin 9 (PCSK9) inhibitors (PCSK9i) revolutionised the lipid-lowering therapy. However, a risk of type 2 diabetes mellitus (T2DM) is evoked under PCSK9i therapy. In this review, we summarise the current knowledge on the link of PCSK9 with T2DM. A significant correlation was found between PCSK9 and insulin, homeostasis model assessment (HOMA) of insulin resistance and glycated haemoglobin. PCSK9 is also involved in inflammation. PCSK9 loss-of-function variants increased T2DM risk by altering insulin secretion. Local pancreatic low PCSK9 regulates β-cell LDLR expression which in turn promotes intracellular cholesterol accumulation and hampers insulin secretion. Nevertheless, the association of PCSK9 loss-of-function variants and T2DM is inconsistent. InsLeu and R46L polymorphisms were associated with T2DM, low HOMA for β-cell function and impaired fasting glucose, while the C679X polymorphism was associated with low fasting glucose in Black South African people. Hence, we assume that the impact of these variants on glucose homeostasis may vary depending on the genetic background of the studied populations and the type of effect caused by those genetic variants on the PCSK9 protein. Accordingly, these factors should be considered when choosing a genetic variant of PCSK9 to assess the impact of long-term use of PCSK9i on glucose homeostasis.

Novel Polymeric Micelles-Coated Magnetic Nanoparticles for In Vivo Bioimaging of Liver: Toxicological Profile and Contrast Enhancement

Magnetic nanoparticles are intensively studied for magnetic resonance imaging (MRI) as contrast agents but yet there remained some gaps regarding their toxicity potential and clinical implications of their biodistribution in organs. This study presents the effects induced by magnetite nanoparticles encapsulated in polymeric micelles (MNP-DSPE-PEG) on biochemical markers, metabolic functions, and MRI signal in CD1 mice liver. Three groups of animals, one control and the other ones injected with a suspension of five, respectively, 15 mg Fe/kg bw nanoparticles, were monitored up to 14 days. The results indicated the presence of MNP-DSPE-PEG in the liver in the first two days of the experiment. The most significant biochemical changes also occurred in the first 3 days after exposure when the most severe histological changes were observed. The change of the MRI signal intensity on the T2-weighted images and increased transverse relaxation rates R2 in the liver were observed after the first minutes from the nanoparticle administration. The study shows that the alterations of biomarkers level resulting from exposure to MNP-DSPE-PEG are restored in time in mice liver. This was associated with a significant contrast on T2-weighted images and made us conclude that these nanoparticles might be potential candidates for use as a contrast agent in liver medical imaging.

Comparative study of the visual system of two psammophilic lizards (Scincus scincus &Eumeces schneideri)

Sand deserts are common biotopes on the earth's surface. Some specialized vertebrate species have colonized these ecological habitats by living buried in the sand. Among these so called psammophilic species are the Scincidae sand dune living species Scincus scincus and Eumeces schneideri. These two skinks share a relatively similar behavioral ecology by living buried in sand, almost all the time for S. scincus and at least for some part of the day for E. schneideri. The visual system of these two lizards was investigated by histological, immunohistochemical, Magnetic Resonance Imaging (MRI) and morphometric techniques. Both skink species exhibit a retina lacking fovea, composed predominantly of cones presenting two types of oil droplets (pale blue-green and colorless). Both species possess a subset of rod like-photoreceptors (about 1 rod for 30 cones) evidenced by anti-rhodopsin immunoreactivity. A ratio 1:1-1:2 between ganglion cells and photoreceptors points to a linear connection (photoreceptors/bipolar neurons/ganglion cells) in the retina and indicates that both skinks more likely possess good visual acuity, even in the peripheral retina. The MRI analysis revealed differences between the species concerning the eye structures, with a more spherical eye shape for S. scincus, as well as a more flattened lens. The relative lens diameter of both species seems to correspond to a rather photopic pattern. Beside the fact that S. scincus and E. schneideri have different lifestyles, their visual capacities seem similar, and, generally speaking, these two psammophilic species theoretically exhibit visual capacities not far away from non-fossorial species.

Molecular Imaging of Galectin-1 Expression as a Biomarker of Papillary Thyroid Cancer by Using Peptide-Functionalized Imaging Probes

Thyroid cancers are the most frequent endocrine cancers and their incidence is increasing worldwide. Thyroid nodules occur in over 19–68% of the population, but only 7–15% of them are diagnosed as malignant. Diagnosis relies on a fine needle aspiration biopsy, which is often inconclusive and about 90% of thyroidectomies are performed for benign lesions. Galectin-1 has been proposed as a confident biomarker for the discrimination of malignant from benign nodules. We previously identified by phage display two peptides (P1 and P7) targeting galectin-1, with the goal of developing imaging probes for non-invasive diagnosis of thyroid cancer. The peptides were coupled to ultra-small superparamagnetic particles of iron oxide (USPIO) or to a near-infrared dye (CF770) for non-invasive detection of galectin-1 expression in a mouse model of papillary thyroid cancer (PTC, as the most frequent one) by magnetic resonance imaging and fluorescence lifetime imaging. The imaging probes functionalized with the two peptides presented comparable image enhancement characteristics. However, those coupled to P7 were more favorable, and showed decreased retention by the liver and spleen (known for their galectin-1 expression) and high sensitivity (75%) and specificity (100%) of PTC detection, which confirm the aptitude of this peptide to discriminate human malignant from benign nodules (80% sensitivity, 100% specificity) previously observed by immunohistochemistry.

Modulation of adiponectin receptors AdipoR1 and AdipoR2 by phage display-derived peptides in in vitro and in vivo models

Type 2 diabetes (T2D) is often linked to metabolic syndrome, which assembles various risk factors related to obesity. Plasma levels of adiponectin are decreased in T2D and obese subjects. Aiming to develop a peptide able to bind adiponectin receptors and modulate their signalling pathways, a 12-amino acid sequence homologous in AdipoR1/R2 has been targeted by phage display with a linear 12-mer peptide library. The selected peptide P17 recognises AdipoR1/R2 expressed by skeletal muscle, liver and pancreatic islets. In HepaRG and C2C12 cells, P17 induced the activation of AMPK (AMPKα-pT172) and the expression of succinate dehydrogenase and glucokinase; no cytotoxic effects were observed on HepaRG cells. In db/db mice, P17 promoted body weight and glycaemia stabilisation, decreased plasma triglycerides to the range of healthy mice and increased adiponectin (in high fat-fed mice) and insulin (in chow-fed mice) levels. It restored to the range of healthy mice the tissue levels and subcellular distribution of AdipoR1/R2, AMPKα-pT172 and PPARα-pS12. In liver, P17 reduced steatosis and apoptosis. The docking of P17 to AdipoR is reminiscent of the binding mechanism of adiponectin. To conclude, we have developed an AdipoR1/AdipoR2-targeted peptide that modulates adiponectin signalling pathways and has therapeutic relevance for T2D and obesity associated pathologies.

Toward a new and noninvasive diagnostic method of papillary thyroid cancer by using peptide vectorized contrast agents targeted to galectin-1

The incidence of papillary thyroid cancer has increased these last decades due to a better detection. High prevalence of nodules combined with the low incidence of thyroid cancers constitutes an important diagnostic challenge. We propose to develop an alternative diagnostic method to reduce the number of useless and painful thyroidectomies using a vectorized contrast agent for magnetic resonance imaging. Galectin-1 (gal-1), a protein overexpressed in well-differentiated thyroid cancer, has been targeted with a randomized linear 12-mer peptide library using the phage display technique. Selected peptides have been conjugated to ultrasmall superparamagnetic particles of iron oxide (USPIO). Peptides and their corresponding contrast agents have been tested in vitro for their specific binding and toxicity. Two peptides (P1 and P7) were selected according to their affinity toward gal-1. Their binding has been revealed by immunohistochemistry on human thyroid cancer biopsies, and they were co-localized with gal-1 by immunofluorescence on TPC-1 cell line. Both peptides induce a decrease in TPC-1 cells' adhesion to gal-1 immobilized on culture plates. After coupling to USPIO, the peptides preserved their affinity toward gal-1. Their specific binding has been corroborated by co-localization with gal-1 expressed by TPC-1 cells and by their ability to compete with anti-gal-1 antibody. The peptides and their USPIO derivatives produce no toxicity in HepaRG cells as determined by MTT assay. The vectorized contrast agents are potential imaging probes for thyroid cancer diagnosis. Moreover, the two gal-1-targeted peptides prevent cancer cell adhesion by interacting with the carbohydrate-recognition domain of gal-1.

Early detection of colonic dysplasia by magnetic resonance molecular imaging with a contrast agent raised against the colon cancer marker MUC5AC

Human gastric mucin MUC5AC is secreted in the colonic mucus of cancer patients and is a specific marker of precancerous lesions called aberrant crypt foci. Using MUC5AC as a specific marker can improve sensitivity in the detection of early colorectal cancer. Here we demonstrated that the accumulation of MUC5AC in xenograft and mouse stomach can be detected by magnetic resonance imaging (MRI). We used ultrasmall particles of iron oxide (USPIOs) conjugated with disulfide constrained heptapeptide that were identified using a screening phage display. To accomplish this, we employed positive selection of the phage display library on MUC5AC purified from fresh human colonic adenomas in combination with negative selection of the phage library on purified human MUC2, which is predominantly found in normal colorectal tissues. This conjugate was tested on human colorectal cancer cell lines that were either able or unable to secrete MUC5AC, both in vitro and in vivo. MUC5AC-USPIO contrast agent and USPIOs alone were not detected in cell lines unable to secrete MUC5AC. A combination of MRI and microscopy studies was performed to detect a specific accumulation of the contrast agent in vivo. Thus, the MUC5AC contrast agent enabled non-invasive detection of precancerous lesions and colorectal cancer, highlighting its potential use in diagnostics, in the early detection of colorectal cancer recurrences after treatment and in mechanistic studies implicating MUC5AC. Copyright © 2016 John Wiley & Sons, Ltd.

Development of a peptide-functionalized imaging nanoprobe for the targeting of (FXYD2)γa as a highly specific biomarker of pancreatic beta cells

Diabetes is characterized by a progressive decline of the pancreatic beta cell mass (BCM), which is responsible for insufficient insulin secretion and hyperglycaemia. There are currently no reliable methods to measure non-invasively the BCM in diabetic patients. Our work describes a phage display-derived peptide (P88) that is highly specific to (FXYD2)γa expressed by human beta cells and is proposed as a molecular vector for the development of functionalized imaging probes. P88 does not bind to the exocrine pancreas and is able to detect down to ~156 human pancreatic islets/mm(3) in vitro after conjugation to ultra-small particles of iron oxide (USPIO), as proven by the R2 measured on MR images. For in vivo evaluation, MRI studies were carried out on nude mice bearing Capan-2 tumours that also express (FXYD2)γa. A strong negative contrast was obtained subsequent to the injection of USPIO-P88, but not in negative controls. On human histological sections, USPIO-P88 seems to be specific to pancreatic beta cells, but not to duodenum, stomach or kidney tissues. USPIO-P88 thus represents a novel and promising tool for monitoring pancreatic BCM in diabetic patients. The quantitative correlation between BCM and R2 remains to be demonstrated in vivo, but the T2 mapping and the black pixel estimation after USPIO-P88 injection could provide important information for the future pancreatic BCM evaluation by MRI.

Cell "vision": complementary factor of protein corona in nanotoxicology

Engineered nanoparticles are increasingly being considered for use as biosensors, imaging agents and drug delivery vehicles. Their versatility in design and applications make them an attractive proposition for new biological and biomedical approaches. Despite the remarkable speed of development in nanoscience, relatively little is known about the interaction of nanoscale objects with living systems. In a biological fluid, proteins associate with nanoparticles, and the amount and the presentation of the proteins on their surface could lead to a different in vivo response than an uncoated particle. Here, in addition to protein adsorption, we are going to introduce concept of cell "vision", which would be recognized as another crucial factor that should be considered for the safe design of any type of nanoparticles that will be used in specific biomedical applications. The impact of exactly the same nanoparticles on various cells is significantly different and could not be assumed for other cells; the possible mechanisms that justify this cellular response relate to the numerous detoxification strategies that any particular cell can utilize in response to nanoparticles. The uptake and defence mechanism could be considerably different according to the cell type. Thus, what the cell "sees", when it is faced with nanoparticles, is most likely dependent on the cell type.

Development of a Magnetic Resonance Imaging Protocol for the Characterization of Atherosclerotic Plaque by Using Vascular Cell Adhesion Molecule-1 and Apoptosis-Targeted Ultrasmall Superparamagnetic Iron Oxide Derivatives

Objective—

Acute ischemic events are often caused by the disruption of lipid-rich plaques, which are frequently not angiographically visible. Vascular cell adhesion molecule-1 and apoptotic cell-targeted peptides studied during our previous work were conjugated to ultrasmall superparamagnetic iron oxide (USPIO) (USPIO-R832 for vascular cell adhesion molecule-1 targeting; USPIO-R826 for apoptosis targeting) and assessed by magnetic resonance imaging.

Methods and Results—

Apolipoprotein E knockout mice were injected with 0.1 mmol Fe/kg body weight and were imaged on a 4.7-T Bruker magnetic resonance imaging until 24 hours after contrast agent administration. Aortic samples were then harvested and examined by histochemistry, and the magnetic resonance images and histological micrographs were analyzed with ImageJ software. The plaques enhanced by USPIO-R832 contained macrophages concentrated in the cap and a large necrotic core, whereas USPIO-R826 produced a negative enhancement of plaques rich in macrophages and neutral fats concentrated inside the plaque. Both USPIO derivatives colocalized with their target on histological sections and were able to detect plaques with a vulnerable morphology, but each one is detecting a specific environment.

Conclusion—

Our vascular cell adhesion molecule-1 and apoptotic cell targeted USPIO derivatives seem to be highly promising tools for atherosclerosis imaging contributing to the detection of vulnerable plaques. They are able to attain their target in low doses and as fast as 30 minutes after administration.

Design and evaluation of a 6-mer amyloid-beta protein derived phage display library for molecular targeting of amyloid plaques in Alzheimer's disease: Comparison with two cyclic heptapeptides derived from a randomized phage display library

Amyloid plaques are the main molecular hallmark of Alzheimer's disease. Specific carriers are needed for molecular imaging and for specific drug delivery. In order to identify new low molecular weight amyloid plaque-specific ligands, the phage display technology was used to design short peptides that bind specifically to amyloid-beta protein, which is the principal component of amyloid plaques. For this purpose, a phage display library was designed from the amino acid sequence of amyloid-beta 1-42. Then, the diversity was increased by soft oligonucleotide-directed mutagenesis. This library was screened against amyloid-beta 1-42 and several phage clones were isolated. Their genomes were sequenced to identify the displayed peptides and their dissociation constants for amyloid-beta 1-42 binding were evaluated by ELISA. The two best peptides, which are derived from the C-terminus hydrophobic domain of amyloid-beta 1-42 that forms a beta-strand in amyloid fibers, were synthesized and biotinylated. After confirming their binding affinity for amyloid-beta 1-42 by ELISA, the specific interaction with amyloid plaques was validated by immunohistochemistry on brain sections harvested from a mouse model of Alzheimer's disease. The thioflavin T aggregation assay has furthermore shown that our peptides are able to inhibit the amyloid fiber formation. They are not toxic for neurons, and some of them are able to cross the blood-brain barrier after grafting to a magnetic resonance imaging contrast agent. To conclude, these peptides have high potential for molecular targeting of amyloid plaques, either as carriers of molecular imaging and therapeutic compounds or as amyloid fiber disrupting agents.

In vitro biomedical applications of functionalized iron oxide nanoparticles, including those not related to magnetic properties

Superparamagnetic iron oxide nanoparticles (SPION) are very promising contrast media, especially for molecular imaging, due to their superior NMR efficacy. They even have wider biomedical applications such as in drug and gene delivery, tissue engineering and bioseparation, or as sensitive biological nanosensors. By coupling them to affinity ligands, SPION can bind to drugs, proteins, enzymes, antibodies or nucleotides. For in vitro biomedical applications, the detection of molecular interaction is possible by using a diversity of systems capable of sensing the magnetic properties of these materials. The goal of the present work was to develop and validate various in vitro biomedical applications of ultrasmall superparamagnetic particles of iron oxide (USPIO), including some that are not related to their magnetic properties. USPIO coated with dextran, starch or bisphosphonate exposing carboxylate groups were synthesized and some of them were functionalized by conjugating various biomolecules, such as biotin, streptavidin and apoptosis, or VCAM-1 specific peptides. The in vitro biomedical applications assessed in the present work included: (1) the relaxometric measurement of antibody concentration, cell receptor expression, molecular interaction, and enzymatic activity in aqueous suspensions; (2) MRI visualization of cells and detection of molecular interaction in an ELISA system; (3) ELISA applications of USPIO derivatives; and (4) detection of specific biomolecules by histochemistry. Our results confirm that rapid and simple in vitro detection of a diversity of functionalized SPION with relevance in medicine is possible by the existing NMR techniques and by chemical staining reactions. The protocols can be applied to minimally prepared biological samples (e.g. whole blood, blood plasma or serum, cell suspensions, biopsies, histological preparations, etc.), and often do not need complicated systems of signal amplification. The use of SPION labeled compounds could furthermore contribute to cost reductions in the diagnosis and in patient care.

Synthesis and characterization of new low-molecular-weight lysine-conjugated Gd-DTPA contrast agents

Various blood pool contrast agents (CAs), characterized by intravascular distribution, have been developed to assist contrast enhanced magnetic resonance angiography (MRA). Among these CAs, the DTPA derivatives conjugated to synthetic polypeptides, such as polylysine, represent attractive candidates for blood pool imaging. However, due to the presence of charged residues located on their backbone, these agents are retained in the kidneys and this compromises their long blood half-life. In order to overcome this major drawback of the polylysine compounds, two new low-molecular-weight CAs were synthesized in the present work by conjugating four or six 1-p-isothiocyanatobenzyl-DTPA moieties to tri- or penta-Lys peptides [(Gd-DTPA)(4) Lys(3) and (Gd-DTPA)(6) Lys(5)], respectively. All the -NH(2) groups of Lys were thus blocked by covalent conjugation to DTPA. The stability and relaxometric properties of these compounds, as well as their pharmacokinetic and biodistribution characteristics, were then evaluated. The half-life in blood of these new polylysine derivatives, as determined in rats, is twofold longer than that of Gd-DTPA. The compounds could thus be optimal blood pool markers for MRA, which typically uses fast acquisition times. The absence of positive molecular charge did not limit their retention in kidneys 2 h after administration. On the other hand, (Gd-DTPA)(4) Lys(3) is retained in kidneys to a lesser extent than (Gd-DTPA)(6) Lys(5) . Their moderate retention in blood and their higher stability and relaxivity in comparison with Gd-DTPA highlight these polylysine derivatives as optimal compared with previously developed polylysine compounds.

Peptidic targeting of phosphatidylserine for the MRI detection of apoptosis in atherosclerotic plaques

Molecular and cellular imaging of atherosclerosis has garnered more interest at the beginning of the 21st century, with aims to image in vivo biological properties of plaque lesions. Apoptosis seems an attractive target for the diagnosis of vulnerable atherosclerotic plaques prone to a thrombotic event. The aim of the present work was to screen for apoptosis peptide binders by phage display with the final purpose to detect apoptotic cells in atherosclerotic plaques by magnetic resonance imaging (MRI). A phosphatidylserine-specific peptide identified by phage display was thus used to design an MRI contrast agent (CA), which was evaluated as a potential in vivo reporter of apoptotic cells. A library of linear 6-mer random peptides was screened in vitro against immobilized phosphatidylserine. Phage DNA was isolated and sequenced, and the affinity of peptides for phosphatidylserine was evaluated by enzyme-linked immunosorbent assay. The phosphatidylserine-specific peptide and its scrambled homologue were attached to a linker and conjugated to DTPA-isothiocyanate. The products were purified by dialysis and by column chromatography and complexed with gadolinium chloride. After their evaluation using apoptotic cells and a mouse model of liver apoptosis, the phosphatidylserine-targeted CA was used to image atherosclerotic lesions on ApoE(-/-) transgenic mice. Apoptotic cells were detected on liver and aorta specimens by the immunostaining of phosphatidylserine and of active caspase-3. Sequencing of the phage genome highlighted nine different peptides. Their alignment with amino acid sequences of relevant proteins revealed a frequent homology with Ca2+ channels, reminiscent of the function of annexins. Alignment with molecules involved in apoptosis provides a direct correlation between peptide selection and utility. The in vivo MRI studies performed at 4.7 T provide proof of concept that apoptosis-related pathologies could be diagnosed by MRI with a low molecular weight paramagnetic agent. The new CA could have real potential in the diagnosis and therapy monitoring of atherosclerotic disease and of other apoptosis-associated pathologies, such as cancer, ischemia, chronic inflammation, autoimmune disorders, transplant rejection, neurodegenerative disorders, and diabetes mellitus. The phage display-derived peptide could also play a potential therapeutic role through anticoagulant activity by mimicking the role of annexin V, the endogenous ligand of phosphatidylserine.

Molecular imaging of alpha v beta3 integrin expression in atherosclerotic plaques with a mimetic of RGD peptide grafted to Gd-DTPA

AIMS

The integrin alpha v beta3 is highly expressed in atherosclerotic plaques by medial and intimal smooth muscle cells and by endothelial cells of angiogenic microvessels. In this study, we have assessed non-invasive molecular magnetic resonance imaging (MRI) of plaque-associated alpha v beta3 integrin expression on transgenic ApoE-/- mice with a low molecular weight peptidomimetic of Arg-Gly-Asp (mimRGD) grafted to gadolinium diethylenetriaminepentaacetate (Gd-DTPA-g-mimRGD). The analogous compound Eu-DTPA-g-mimRGD was employed for an in vivo competition experiment and to confirm the molecular targeting. The specific interaction of mimRGD conjugated to Gd-DTPA or to 99mTc-DTPA with alpha v beta3 integrin was furthermore confirmed on Jurkat T lymphocytes.

METHODS AND RESULTS

The mimRGD was synthesized and conjugated to DTPA. DTPA-g-mimRGD was complexed with GdCl3.6H2O, EuCl3.6H2O, or with [99mTc(CO)3(H2O)3]+. MRI evaluation was performed on a 4.7 T Bruker imaging system. Blood pharmacokinetics of Gd-DTPA-g-mimRGD were assessed in Wistar rats and in c57bl/6j mice. The presence of angiogenic blood vessels and the expression of alpha v beta3 integrin were confirmed in aorta specimens by immunohistochemistry. Gd-DTPA-g-mimRGD produced a strong enhancement of the external structures of the aortic wall and of the more profound layers (possibly tunica media and intima). The aortic lumen seemed to be restrained and distorted. Pre-injection of Eu-DTPA-g-mimRGD diminished the Gd-DTPA-g-mimRGD binding to atherosclerotic plaque and confirmed the specific molecular targeting. A slower blood clearance was observed for Gd-DTPA-g-mimRGD, as indicated by a prolonged elimination half-life and a diminished total clearance.

CONCLUSION

The new compound is potentially useful for the diagnosis of vulnerable atherosclerotic plaques and of other pathologies characterized by alpha v beta3 integrin expression, such as cancer and inflammation. The delayed blood clearance, the significant enhancement of the signal-to-noise ratio, and the low immunogenicity of the mimetic molecule highlight its potential for an industrial and clinical implementation.

Contrast agents: magnetic resonance

Even though the intrinsic magnetic resonance imaging (MRI) contrast is much more flexible than in other clinical imaging techniques, the diagnosis of several pathologies requires the involvement of contrast agents (CAs) that can enhance the difference between normal and diseased tissues by modifying their intrinsic parameters. MR CAs are indirect agents because they do not become visible by themselves as opposed to other imaging modalities. The signal enhancement produced by MRI CAs (i.e., the efficiency of the CAs) depends on their longitudinal (r1) and transverse (r2) relaxivity (expressed in s(-1) mmol(-1) 1), which is defined as the increase of the nuclear relaxation rate (the reciprocal of the relaxation time) of water protons produced by 1 mmol per liter of CA. Paramagnetic CAs (most of them complexes of gadolinium) are frequently used in clinics as extracellular, hepatobiliary or blood pool agents. Low molecular weight paramagnetic CAs have similar effects on R1 and R2, but the predominant effect at low doses is that of T1 shortening (and R1 enhancement). Thus, organs taking up such agents will become bright in a T1-weighted MRI sequence; these CAs are thus called positive contrast media. The CAs known as negative agents influence signal intensity mainly by shortening T2* and T2, which produces the darkening of the contrast-enhanced tissue. These CAs are generally composed of superparamagnetic nanoparticles, consisting of iron oxides (magnetite, Fe3O4, maghemite, gammaFe2O3, or other ferrites). Iron oxide nanoparticles are taken up by the monocyte-macrophage system, which explains their potential application as MRI markers of inflammatory and degenerative disorders. Most of the contemporary MRI CAs approved for clinical applications are non-specific for a particular pathology and report exclusively on the anatomy and the physiological status of various organs. A new generation of MRI CAs is progressively emerging in the current context of molecular imaging, agents that are designed to detect with a high specificity the cellular and molecular hallmarks of various pathologies.

From Phage Display to Magnetophage, a New Tool for Magnetic Resonance Molecular Imaging

Phage display, an extremely promising technology in the context of molecular imaging, allows for the selection of peptides interacting with virtually any target from a heterogeneous mixture of bacteriophages. In this work, we propose the concept of magnetophages, obtained by covalent coupling of ultrasmall particles of iron oxide (USPIO) to the proteins of the phage wall. To validate magnetophages as a magnetic resonance imaging contrast agent (MRI), we have used as a prototype the clone E3 because of its specific affinity for phosphatidylserine, a marker of apoptosis. Enzyme-linked immunosorbent assay showed that E3 magnetophages incubated with phosphatidylserine retained the properties of the nonmagnetically labeled phages. The usefulness of magnetophages as an MRI contrast agent was estimated by incubation with phosphatidylcholine and phosphatidylserine or with apoptotic and control cells. Under these conditions, E3 magnetophages allow the discrimination of phosphatidylserine from phosphatidylcholine and of apoptotic cells from control ones. Injected in vivo, magnetophages are rapidly cleared from the blood stream and internalized by the phagocytic cells of the liver. To abrogate this problem, USPIO were pegylated to obtain stealthy E3-PEG-magnetophages, invisible to phagocytic cells, which were successfully targeted to apoptotic liver. If this feature demonstrated for E3 magnetophages can be extrapolated to other phage display selected entities, magnetophages become an original system which allows validation of the candidate binding peptides before their synthesis is considered. The concept of the magnetophage could be extended to other imaging modalities by replacing USPIO with an adequate reporter (i.e., radiolabeled phages).

A glycosylated complex of gadolinium, a new potential contrast agent for magnetic resonance angiography?

A new low-molecular weight dendrimer-like MRI contrast agent (Gd-D1) has been synthesized and characterized in vitro by proton and oxygen-17 relaxometry. Its pharmacokinetic parameters and biodistribution patterns were evaluated on rats. Its in vitro and in vivo properties, that is, the longitudinal relaxivity (defined as the increase of the water proton longitudinal relaxation rate induced by one millimole per liter of Gd-D1) equal to 5.6s(-1)mM(-1) at 20 MHz and 310 K, the elimination half-time equal to 85 min, and its low accumulation in liver and spleen, underline its potential as a blood-pool MRI contrast agent.

Synthesis, characterization, and pharmacokinetic evaluation of a potential MRI contrast agent containing two paramagnetic centers with albumin binding affinity

A dinuclear gadolinium(III) complex of an amphiphilic chelating ligand, containing two diethylenetriamine-N,N,N',N'',N''-pentaacetate (DTPA) moieties bridged by a bisindole derivative with three methoxy groups, has been synthesized and evaluated as a potential magnetic resonance imaging (MRI) contrast agent. Nuclear magnetic relaxation dispersion (NMRD) measurements indicate that at 20 MHz and 37 degrees C the dinuclear gadolinium(III) complex has a much higher relaxivity than [Gd(DTPA)] (6.8 vs 3.9 s(-1) mmol(-1)). The higher relaxivity of the dinuclear gadolinium(III) complex can be related to its reduced motion and larger rotational correlation time relative to [Gd(DTPA)]. In the presence of human serum albumin (HSA) the relaxivity value of the noncovalently bound dinuclear complex increases to 15.2 s(-1) per mmol of Gd3+, due to its relatively strong interaction with this protein. The fitted value of the binding constant to HSA (Ka) was found to be 10(4) M(-1). Because of its interaction with HSA, the dinuclear complex exhibits a longer elimination half-life from the plasma, and a better confinement to the vascular space compared to the commercially available [Gd(DTPA)] contrast agent. Transmetalation of the dinuclear gadolinium(III) complex by zinc(II) has been investigated. Biodistribution studies suggest that the complex is excreted by the renal pathway, and possibly by the hepatobiliary route. In vivo studies indicated that half of the normal dose of the gadolinium(III) complex enhanced the contrast in hepatic tissues around 40 % more effectively than [Gd(DTPA)]. The dinuclear gadolinium(III) complex was tested as a potential necrosis avid contrast agent (NACA), but despite the binding to HSA, it did not exhibit necrosis avidity, implying that binding to albumin is not a key parameter for necrosis-targeting properties.

C-MALISA (cellular magnetic-linked immunosorbent assay), a new application of cellular ELISA for MRI

A modified cellular ELISA (enzyme-linked immunosorbent assay), named cellular magnetic-linked immunosorbent assay (C-MALISA), has been developed as an application of magnetic resonance imaging (MRI) for in vitro clinical diagnosis. To validate the method, three contrast agents targeted to integrins were synthesized by grafting to USPIO (ultrasmall particles of iron oxide): (a) the CS1 (connecting segment-1) fragment of fibronectin (FN) (USPIO-g-FN); (b) the peptide GRGD (USPIO-g-GRGD); (c) a non-peptidic RGD mimetic (USPIO-g-mimRGD). Jurkat cells and rat mononuclear cells were stimulated to activate their integrins. After cell fixation on ELISA plates, incubation with the contrast agents, rinsing, and digestion in 5N HCl, the samples were analyzed by MRI. Paramagnetic relaxation rate enhancements (delta R2) were measured on images. Delta R2 was converted in values of iron concentration based on a calibration curve. The apparent dissociation constants (K(d)*) of the three contrast agents were estimated based on the MRI measurement of delta R2. K(d)* of 1.22 x 10(-7) M, of 7.00 x 10(-8) M, and of 1.13 x 10(-8) M were found respectively for USPIO-g-FN, USPIO-g-GRGD, and USPIO-g-mimGRG. The MRI confirmed a statistically significant difference (p < 0.01, p < 0.05) between the stimulated cells incubated with integrin-targeted compounds with respect to the controls (i.e., non-stimulated cells and stimulated cells incubated with non-specific USPIO). The integrin specificity of the three compounds was confirmed by the pre-incubation with GRGD (for USPIO-g-mimRGD and USPIO-g-GRGD) or FN (for USPIO-g-FN).

Ferritin-induced relaxation in tissues: an in vitro study

PURPOSE

To study in vitro the proton relaxation induced in tissues by ferritin, the iron-storing protein of mammals.

MATERIALS AND METHODS

Nuclear magnetic relaxation dispersion (NMRD) profiles of liver and spleen from control and iron-overloaded mice are compared with NMRD profiles of ferritin and Fercayl-a ferritin-like akaganeite particle-in aqueous solutions or in 1% agarose gel.

RESULTS

The relaxation of water protons induced by ferritin and Fercayl in 1% agarose gel is comparable with the relaxation of aqueous solutions of the same compounds, but slower than the relaxation of liver and spleen. The gel is not a good model of tissues containing ferritin. The longitudinal NMRD profiles of control and iron-overloaded liver and spleen are almost identical: ferritin accumulation has only a slight effect on longitudinal relaxation. The transverse NMRD profiles of liver and spleen tissues are linear, but the slope of the linear regression is larger for iron-loaded organs than for control ones, which is a consequence of a higher ferritin concentration in the former. However, the correlation between the slope of the transverse NMRD profiles and the iron concentration is not very good, probably because transverse relaxation is modified by the clustering of ferritin in cells.

CONCLUSION

It could be difficult to develop a general technique for the accurate quantification of ferritin-bound iron by nuclear magnetic resonance or magnetic resonance imaging.

Magnetic resonance imaging of inflammation with a specific selectin-targeted contrast agent

E-selectin-targeted contrast enhancement of blood vessels in inflamed tissues was investigated with a new contrast agent, Gd-DTPA-B(sLe(x))A, which was recently obtained by grafting a synthetic mimetic of sialyl-Lewis(x), an E-selectin ligand, onto Gd-DTPA. The pharmacokinetics, biodistribution, and potential to image inflammation by MRI of this E-selectin-targeted contrast agent were evaluated. The inhibition (by 15-34%) produced by Gd-DTPA-B(sLe(x))A on Sialyl Le(x)-PAA-biotin binding to E-selectin confirmed the specific interaction of the new contrast agent with this adhesion molecule. Gd-DTPA-B(sLe(x))A was tested at a dose of 0.1 mmol/kg b.w. on mice and rats in a fulminant hepatitis model induced by the co-administration of D-galactosamine and E. coli lipopolysaccharide. A significant and prolonged contrast enhancement between blood vessels and liver parenchyma was obtained in pathological conditions, which attests to the specificity of the agent for E-selectin. The prolonged vascular residence (48.9 min in hepatitis vs. 29.8 min in healthy animals), as evidenced by the pharmacokinetic characterization, suggests that Gd-DTPA-B(sLe(x))A interacts with the specific receptors expressed during inflammation. The biodistribution of the compound indicates its retention in inflamed liver by both specific mechanisms and nonspecific accumulation due to the necrotic lesions. The same mechanisms are invoked to account for its retention in the spleen.

Development of new glucosylated derivatives of gadolinium diethylenetriaminepentaacetic for magnetic resonance angiography

RATIONALE AND OBJECTIVES

A possible approach for the extension of the vascular residence time of contrast agents relies on the renal reabsorption mechanisms of some molecules such as glucose. In this study, various small-molecular-weight glucosyl derivatives of gadolinium diethylenetriaminepentaacetic (Gd-DTPA) were synthesized and their vascular half-life was studied.

METHODS

Several Gd-DTPA-bisamides carrying glucosyl groups bound by different linkers were prepared. The pharmacokinetics and biodistribution of these compounds were determined on Wistar rats.

RESULTS

The sugar moieties linked to Gd-DTPA efficiently reduce the renal excretion of some derivatives. The interaction with renal carrier has not been clearly demonstrated, nor was any interaction observed with blood components.

CONCLUSIONS

Two of the new glucosylated derivatives of Gd-DTPA (Cd-DTPA-BC2-beta-cellobionA 2 and Gd-DTPA-BC4-beta-glucosylA 7) can be proposed as blood-pool MR contrast agents, considering their vascular remanence.

Activity of glutathione-s-transferase, gammaglutamiltransferase and catalase in the erythrocytic membrane in arterial hypertension

Our clinical-biological study has been performed in patients with various clinical forms of arterial hypertension (AHT), as well as with sequelae-type complications from stroke that had occurred during the evolution of the disease. We performed biological determinations of the activity of four erythrocytic enzymes: glutathione-s-transferase (GST), catalase, gamma-glutamyltransferase (GGT), and lactate dehydrogenase (LDH). The results point to the existence of individual values and also of important differences depending on the presence of arterial hypertension complications. We found a moderate but significant increase of erythrocytic GGT in hypertensive patients compared to healthy controls. Erythrocytic GST and LDH were decreased in patients vs controls. The results of the enzymatic, erythrocyitc activities of GST, GGT, catalase and LDH can also be correlated with the parameters of erythrocyitc membrane permeability and with the thiolic groups, fibrinogen and ionic calcium concentration. The data described in this paper suggest the possible involvement of the disturbances mentioned above in the etiopathogeny of AHT.

Spin-spin relaxation times in myocardial hypertrophy induced by endocrine agents in rat

Magnetic resonance techniques afford a significant advantage for noninvasive diagnosis of cardiovascular pathology. The purpose of our present study was to assay the proton nuclear magnetic resonance (1H-NMR) sensitivity in the differential diagnosis of certain endocrine cardiovascular complications. In this context, we investigated the water state and content in the hypertrophied myocardium. Male and female Wistar rats were treated with different hormones (hydrocortisone acetate, testosterone, estradiol, thyroid hormones) in combination with isoproterenol (a synthetic catecholamine that induces myocardial ischemia and hypertrophy). The animals were sacrificed after 20 days of treatment and samples of integral myocardium and left ventricular myocardium were analyzed on a 1H-NMR AREMI spectrometer (0.6 T; proton resonance at 25 MHz). The estimation of T2 was made by Carr Purcell-Meiboom-Gill pulse sequence. The data were fitted to a bi-exponential curve, yielding short (T21) values for bound water and long (T22) values for free water. In order to evaluate the myocardial hypertrophy, the following ratios were calculated: integral myocardium to body weight; left ventricle to body weight; left ventricle to integral myocardium. The first two ratios were also calculated for dried tissue, in order to estimate its contribution to myocardial hypertrophy. Our findings demonstrate that myocardial hypertrophy is associated with a decrease of T22, as a consequence of the increase in the dried component (i.e. proteins) of the tissue, while the total tissue water (H2Ot%), measured by gravimetry) was not significantly modified. Nevertheless, it is reasonable that the increase in the protein content would be proportional with the increase in H2Ot%. The decrease of T21 seems to be proportional with the level of left ventricle hypertrophy in female groups. The 1H-NMR measurements were much sensitive for the differential diagnosis of myocardial hypertrophy in the case of left ventricle.

Research on red cell membrane permeability in arterial hypertension

Arterial hypertension, including the elucidation of hypertension pathogenic mechanisms involving elements in the composition of the blood, continues to represent a topical research area. Recent work, such as nuclear magnetic resonance studies looking into red cell permeability, illustrates the presence of modifications of red cell permeability to water (RCPW) related to the stage of arterial hypertension. The identification of a significant increase of RCPW compared to that present in the population with normal arterial pressure values can be useful both in early diagnosis and in warning about a possible predisposition for this condition. At the same time, the dynamic investigation of protonic relaxation time of both intra- and extra-erythrocytic water, the assessment of proton exchange time across the red cell and the calculation of permeability to water enable one not only to diagnose arterial hypertension but also to ascertain the evolution of the disease, its complications and the effectiveness of anti-hypertensive medication. Our studies have also proven the existence of a correlation between the values of systolic arterial pressure and red cell permeability to water. The curve describing the interdependence of the two values has the shape of a bell, in the case of males. The peak of the curve is reached for a systolic pressure of 160 mmHg and gets below the values of the control group in the case of systolic pressures above 200 mmHg. The RCPW test can also be considered a valuable indicator in evaluating the risk of stroke in hypertensive patients. In the chronic therapy of arterial hypertension with various types of anti-hypertensive drugs, one can note differences in the RCPW values related to the effectiveness of the respective medication, to the clinical form and stage of the disease, the sex of the patient as well as to the existence of cerebro-vascular complications.