Well-defined, multifunctional nanostructures of a paramagnetic lipid and a lipopeptide for macrophage imaging

Conformational Changes in High-Density Lipoprotein Nanoparticles Induced by High Payloads of Paramagnetic Lipids

High-density lipoprotein (HDL) nanoparticles doped with gadolinium lipids can be used as magnetic resonance imaging diagnostic agents for atherosclerosis. In this study, HDL nanoparticles with different molar fractions of gadolinium lipids (0 < x_Gd-lipids < 0.33) were prepared, and the MR relaxivity values (r1 and r2) for all compositions were measured. Both r1 and r2 parameters reached a maximal value at a molar fraction of approximately x_Gd-lipids = 0.2. Higher payloads of gadolinium did not significantly increase relaxivity values but induced changes in the structure of HDL, increasing the size of the particles from d_H = 8.2 ± 1.6 to 51.7 ± 7.3 nm. High payloads of gadolinium lipids trigger conformational changes in HDL, with potential effects on the in vivo behavior of the nanoparticles.

{Dy(α-fur)3}n: from double relaxation single-ion magnet behavior to 3D ordering

The synthesis and magnetostructural properties of a new low-dimensional magnetic system based on α-furoate ligands, {[Dy(α-C4H3OCOO)(μ-(α-C4H3OCOO))2(H2O)3]}n, abbreviated {Dy(α-fur)3}n, are reported. X-ray diffraction experiments results evidence the presence of two different Dy coordination environment types differing only in the position of one of the furoate ligands. The crystallographic structure is formed by polymeric chains along the c-axis, each composed of just one Dy type, coupled within the bc-plane with chains of the same Dy type. These planes, each of them containing only one Dy type, are randomly stacked along the a-axis. The magnetic behaviour was studied by magnetization, static and dynamic susceptibility, heat capacity measurements and ab initio simulations. The directions of the easy axes of magnetization, gyromagnetic values and energy level structures of the two Dy types were obtained from ab initio calculations. {Dy(α-fur)3}n exhibits slow magnetic relaxation dynamics below 10 K. The two Dy types with different coordination environments behave as single-ion magnets, with different thermal activation energies of 80.5(6) K and 32.4(5) K, until they reach, upon cooling, a quantum tunneling (QT) regime. Magnetic diluted samples, substituting Dy by Y, {Y(x)Dy(1-x)(α-fur)3}n, were prepared to study the effect of intercluster interactions. Decreasing the Dy interaction by dilution by 90-95% leaves the activation energy unchanged, but shifts the transition to the QT regime to lower temperatures. At T = 2.4 K the tunneling time constant has been shown to decrease weakly with the field in the x = 0 case, and more strongly for x = 0.9. As the external field increases, quantum tunneling is quenched and a new slow relaxation appears that is identified at high fields as caused by a direct relaxation process. As the temperature is decreased, interchain AF coupling becomes effective and gives rise to the occurrence of an antiferromagnetic 3D order transition at T(N) = 0.66 K. From all the evidence, it is concluded that within each bc-plane Dy ions arrange in chains along the c-direction, having weak uncompensated ferromagnetic spin-canted intrachain coupling and antiferromagnetic interchain coupling.

Hydrothermally synthesized PEGylated calcium phosphate nanoparticles incorporating Gd-DTPA for contrast enhanced MRI diagnosis of solid tumors

Organic-inorganic hybrid nanoparticles with calcium phosphate (CaP) core and PEGylated shell were developed to incorporate magnetic resonance imaging (MRI) contrast agent diethylenetriaminepentaacetic acid gadolinium (III) (Gd-DTPA) for noninvasive diagnosis of solid tumors. A two-step preparation method was applied to elaborate hybrid nanoparticles with a z-average hydrodynamic diameter about 80nm, neutral surface ξ-potential and high colloidal stability in physiological environments by self-assembly of poly(ethylene glycol)-b-poly(aspartic acid) block copolymer, Gd-DTPA, and CaP in aqueous solution, followed with hydrothermal treatment. Incorporation into the hybrid nanoparticles allowed Gd-DTPA to show significant enhanced retention ratio in blood circulation, leading to high accumulation in tumor positions due to enhanced permeability and retention (EPR) effect. Moreover, Gd-DTPA revealed above 6 times increase of relaxivity in the nanoparticle system compared to free form, and eventually, selective and elevated contrast enhancements in the tumor positions were observed. These results indicate the high potential of Gd-DTPA-loaded PEGylated CaP nanoparticles as a novel contrast agent for noninvasive cancer diagnosis.

Sugar/gadolinium-loaded gold nanoparticles for labelling and imaging cells by magnetic resonance imaging

Targeted magnetic resonance imaging (MRI) probes for selective cell labelling and tracking are highly desired. We here present biocompatible sugar-coated paramagnetic Gd-based gold nanoparticles (Gd-GNPs) and test them as MRI T₁ reporters in different cellular lines at a high magnetic field (11.7 T). With an average number of 20 Gd atoms per nanoparticle, Gd-GNPs show relaxivity values r₁ ranging from 7 to 18 mM^-1 s^-1 at 1.41 T. The multivalent presentation of carbohydrates on the Gd-GNPs enhances the avidity of sugars for carbohydrate-binding receptors at the cell surface and increases the local concentration of the probes. A large reduction in longitudinal relaxation times T₁ is achieved with both fixed cells and live cells. Differences in cellular labelling are obtained by changing the type of sugar on the gold surface, indicating that simple monosaccharides and disaccharides are able to modulate the cellular uptake. These results stress the benefits of using sugars to produce nanoparticles for cellular labelling. To the best of our knowledge this is the first report on labelling and imaging cells with Gd-based gold nanoparticles which use simple sugars as receptor reporters.

Gd-DTPA-loaded polymer-metal complex micelles with high relaxivity for MR cancer imaging

Nanodevices for magnetic resonance imaging of cancer were self-assembled to core-shell micellar structures by metal complex formation of K(2)PtCl(6) with diethylenetriaminepentaacetic acid gadolinium (III) dihydrogen (Gd-DTPA), a T(1)-contrast agent, and poly(ethylene glycol)-b-poly{N-[N'-(2-aminoethyl)-2-aminoethyl]aspartamide} (PEG-b-PAsp(DET)) copolymer in aqueous solution. Gd-DTPA-loaded polymeric micelles (Gd-DTPA/m) showed a hydrodynamic diameter of 45 nm and a core size of 22 nm. Confining Gd-DTPA inside the core of the micelles increased the relaxivity of Gd-DTPA more than 13 times (48 mM(-1) s(-1)). In physiological conditions Gd-DTPA/m sustainedly released Gd-DTPA, while the Pt(IV) complexes remain bound to the polymer. Gd-DTPA/m extended the circulation time in plasma and augmented the tumor accumulation of Gd-DTPA leading to successful contrast enhancement of solid tumors. μ-Synchrotron radiation-X-ray fluorescence results confirmed that Gd-DTPA was delivered to the tumor site by the micelles. Our study provides a facile strategy for incorporating contrast agents, dyes and bioactive molecules into nanodevices for developing safe and efficient drug carriers for clinical application.

1H chemical shift magnetic resonance imaging probes with high sensitivity for multiplex imaging

Proton-based chemical shift imaging probes were encapsulated inside nano-carriers to increase the sensivitity of the reporters. Co-encapsulation with a relaxation agent results in improved sensitivity and suppresses background signals. Simultaneous imaging of different chemical shift reporters allows multiplexed detection.

Hybrid magnetic nanostructures (MNS) for magnetic resonance imaging applications

The development of MRI contrast agents has experienced its version of the gilded age over the past decade, thanks largely to the rapid advances in nanotechnology. In addition to progress in single mode contrast agents, which ushered in unprecedented R(1) or R(2) sensitivities, there has also been a boon in the development of agents covering more than one mode of detection. These include T(1)-PET, T(2)-PET T(1)-optical, T(2)-optical, T(1)-T(2) agents and many others. In this review, we describe four areas which we feel have experienced particular growth due to nanotechnology, specifically T(2) magnetic nanostructure development, T(1)/T(2)-optical dual mode agents, and most recently the T(1)-T(2) hybrid imaging systems. In each of these systems, we describe applications including in vitro, in vivo usage and assay development. In all, while the benefits and drawbacks of most MRI contrast agents depend on the application at hand, the recent development in multimodal nanohybrids may curtail the shortcomings of single mode agents in diagnostic and clinical settings by synergistically incorporating functionality. It is hoped that as nanotechnology advances over the next decade, it will produce agents with increased diagnostics and assay relevant capabilities in streamlined packages that can meaningfully improve patient care and prognostics. In this review article, we focus on T(2) materials, its surface functionalization and coupling with optical and/or T(1) agents.

Multimodality and nanoparticles in medical imaging

A number of medical imaging techniques are used heavily in the provision of spatially resolved information on disease and physiological status and accordingly play a critical role in clinical diagnostics and subsequent treatment. Though, for most imaging modes, contrast is potentially enhanced through the use of contrast agents or improved hardware or imaging protocols, no single methodology provides, in isolation, a detailed mapping of anatomy, disease markers or physiological status. In recent years, the concept of complementing the strengths of one imaging modality with those of another has come to the fore and been further bolstered by the development of fused instruments such as PET/CT and PET/MRI stations. Coupled with the continual development in imaging hardware has been a surge in reports of contrast agents bearing multiple functionality, potentially providing not only a powerful and highly sensitised means of co-localising physiological/disease status and anatomy, but also the tracking and delineation of multiple markers and indeed subsequent or simultaneous highly localized therapy ("theragnostics").

Cell delivery of therapeutic nanoparticles

Nanomedicine seeks to manufacture drugs and other biologically relevant molecules that are packaged into nanoscale systems for improved delivery. This includes known drugs, proteins, enzymes, and antibodies that have limited clinical efficacy based on delivery, circulating half-lives, or toxicity profiles. The <100 nm nanoscale physical properties afford them a unique biologic potential for biomedical applications. Hence they are attractive systems for treatment of cancer, heart and lung, blood, inflammatory, and infectious diseases. Proposed clinical applications include tissue regeneration, cochlear and retinal implants, cartilage and joint repair, skin regeneration, antimicrobial therapy, correction of metabolic disorders, and targeted drug delivery to diseased sites including the central nervous system. The potential for cell and immune side effects has necessitated new methods for determining formulation toxicities. To realize the potential of nanomedicine from the bench to the patient bedside, our laboratories have embarked on developing cell-based carriage of drug nanoparticles to improve clinical outcomes in infectious and degenerative diseases. The past half decade has seen the development and use of cells of mononuclear phagocyte lineage, including dendritic cells, monocytes, and macrophages, as Trojan horses for carriage of anti-inflammatory and anti-infective medicines. The promise of this new technology and the perils in translating it for clinical use are developed and discussed in this chapter.

Large relaxivity enhancement of paramagnetic lipid nanoparticles by restricting the local motions of the Gd(III) chelates

A Gd(III)-DOTA-like complex bearing two aliphatic chains on adjacent acetic arms was designed, synthesized, and compared with its analogous monofunctionalized complex. A 1/T(1) NMR relaxometric study of the two amphiphilic complexes incorporated into micelles and liposomes showed an unprecedented relaxivity enhancement for the complex with two lipophilic side arms. This remarkable result, which is attributed to a favorable water exchange rate and increased rigidity of the system resulting from limiting of the local motion of the gadolinium center, represents an important advance in the development of highly efficient nanosystems for MRI applications.

Multifunctional imaging nanoprobes

Multifunctional imaging nanoprobes have proven to be of great value in the research of pathological processes, as well as the assessment of the delivery, fate, and therapeutic potential of encapsulated drugs. Moreover, such probes may potentially support therapy schemes by the exploitation of their own physical properties, e.g., through thermal ablation. This review will present four classes of nanoparticulate imaging probes used in this area: multifunctional probes (1) that can be tracked with at least three different and complementary imaging techniques, (2) that carry a drug and have bimodal imaging properties, (3) that are employed for nucleic acid delivery and imaging, and (4) imaging probes with capabilities that can be used for thermal ablation. We will highlight several examples where the suitable combination of different (bio)materials like polymers, inorganic nanocrystals, fluorophores, proteins/peptides, and lipids can be tailored to manufacture multifunctional probes to accomplish nanomaterials of each of the aforementioned classes. Moreover, it will be demonstrated how multimodality imaging approaches improve our understanding of in vivo nanoparticle behavior and efficacy at different levels, ranging from the subcellular level to the whole body.