Torjus Skajaa

Aarhus University, Aarhus, Central Jutland, Denmark

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Publications (18)91.95 Total impact

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    ABSTRACT: Lipid coated nanocrystal assemblies are among the most extensively investigated nanoparticle platforms for biomedical imaging and therapeutic purposes. However, very few efforts have been addressed to the lipid coating exchange dynamics in such systems, which is key to our understanding of the nanoparticles' coating stability and their interactions with the environment. Here, we apply the Förster resonance energy transfer (FRET) from quantum dot (QD) core to Cy5.5 dye labeled lipids at the surface to monitor the lipid exchange dynamics in situ and to study its dependence on concentration, temperature and solvent. A kinetic model is developed to describe the experimental data, allowing the rate constants and the activation energy for lipid exchange to be determined. The activation energy for lipid exchange on QD micelles is 155 kJ/mol in saline environment and 130 kJ/mol in pure water. The findings presented here provide basic knowledge on these self-assembled structures and contribute to understanding their performance and to further design of nanomedicine.
    Small 12/2013; · 7.82 Impact Factor
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    ABSTRACT: Lipoproteins are natural nanoparticles composed of phospholipids and apolipoproteins that transport lipids throughout the body. As key effectors of lipid homeostasis, the functions of lipoproteins have been demonstrated to be crucial during the development of cardiovascular diseases. Therefore various strategies have been used to study their biology and detect them in vivo. A recent approach has been the production of lipoprotein biomimetic particles loaded with diagnostically active nanocrystals in their core. These include, but are not limited to: quantum dots, iron oxide or gold nanocrystals. Inclusion of these nanocrystals enables the utilization of lipoproteins as probes for a variety of imaging modalities (computed tomography, magnetic resonance imaging, fluorescence) while preserving their biological activity. Furthermore as some lipoproteins naturally accumulate in atherosclerotic plaque or specific tumor tissues, nanocrystal core lipoprotein biomimetics have been developed as contrast agents for early diagnosis of these diseases.
    Current Cardiovascular Imaging Reports 02/2013; 6(1):45-54.
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    ABSTRACT: There are many liver diseases that could be treated with delivery of therapeutics such as DNA, proteins, or small molecules. Nanoparticles are often proposed as delivery vectors for such therapeutics; however, achieving nanoparticle accumulations in the therapeutically relevant hepatocytes is challenging. In order to address this issue, we have synthesized polymer coated, fluorescent iron oxide nanoparticles that bind and deliver DNA, as well as produce contrast for magnetic resonance imaging (MRI), fluorescence imaging, and transmission electron microscopy (TEM). The composition of the coating can be varied in a facile manner to increase the quantity of poly(ethylene glycol) (PEG) from 0% to 5%, 10%, or 25%, with the aim of reducing opsonization but maintaining DNA binding. We investigated the effect of the nanoparticle coating on DNA binding, cell uptake, cell transfection, and opsonization in vitro. Furthermore, we exploited MRI, fluorescence imaging, and TEM to investigate the distribution of the different formulations in the liver of mice. While MRI and fluorescence imaging showed that each formulation was heavily taken up in the liver at 24 h, the 10% PEG formulation was taken up by the therapeutically relevant hepatocytes more extensively than either the 0% PEG or the 5% PEG, indicating its potential for delivery of therapeutics to the liver.
    Bioconjugate Chemistry 03/2011; 22(3):353-61. · 4.58 Impact Factor
  • Torjus Skajaa
    Acta Obstetricia Et Gynecologica Scandinavica 01/2011; 40(1):68 - 76. · 1.85 Impact Factor
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    ABSTRACT: The study of lipoproteins, natural nanoparticles comprised of lipids and apolipoproteins that transport fats throughout the body, is of key importance to better understand, treat, and prevent cardiovascular disease. In the current study, we have developed a lipoprotein-based nanoparticle that consists of a quantum dot (QD) core and Cy5.5 labeled lipidic coating. The methodology allows judicious tuning of the QD/Cy5.5 ratio, which enabled us to optimize Förster resonance energy transfer (FRET) between the QD core and the Cy5.5-labeled coating. This phenomenon allowed us to study lipoprotein-lipoprotein interactions, lipid exchange dynamics, and the influence of apolipoproteins on these processes. Moreover, we were able to study HDL-cell interactions and exploit FRET to visualize HDL association with live macrophage cells.
    Nano Letters 11/2010; · 13.03 Impact Factor
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    ABSTRACT: Apoptosis and macrophage burden are believed to correlate with atherosclerotic plaque vulnerability and are therefore considered important diagnostic and therapeutic targets for atherosclerosis. These cell types are characterized by the exposure of phosphatidylserine (PS) at their surface. In the present study, we developed and applied a small micellar fluorescent annexin A5-functionalized nanoparticle for noninvasive magnetic resonance imaging (MRI) of PS exposing cells in atherosclerotic lesions. Annexin A5-mediated target-specificity was confirmed with ellipsometry and in vitro binding to apoptotic Jurkat cells. In vivo T(1)-weighted MRI of the abdominal aorta in atherosclerotic ApoE(-/-) mice revealed enhanced uptake of the annexin A5-micelles as compared to control-micelles, which was corroborated with ex vivo near-infrared fluorescence images of excised whole aortas. Confocal laser scanning microscopy (CLSM) demonstrated that the targeted agent was associated with macrophages and apoptotic cells, whereas the nonspecific control agent showed no clear uptake by such cells. In conclusion, the annexin A5-conjugated bimodal micelles displayed potential for noninvasive assessment of cell types that are considered to significantly contribute to plaque instability and therefore may be of great value in the assessment of atherosclerotic lesion phenotype.
    Bioconjugate Chemistry 10/2010; 21(10):1794-803. · 4.58 Impact Factor
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    ABSTRACT: Lipoproteins are a family of plasma nanoparticles responsible for the transportation of lipids throughout the body. High-density lipoprotein (HDL), the smallest of the lipoprotein family, measures 7-13 nm in diameter and consists of a cholesteryl ester and triglyceride core that is covered with a monolayer of phospholipids and apolipoproteins. We have developed an iron oxide core HDL nanoparticle (FeO-HDL), which has a lipid based fluorophore incorporated in the phospholipid layer. This nanoparticle provides contrast for optical imaging, magnetic resonance imaging (MRI) and transmission electron microscopy (TEM). Consequently, FeO-HDL can be visualized on the anatomical, cellular and sub-cellular level. In the current study we show that the biophysical features of FeO-HDL closely resemble those of native HDL and that FeO-HDL possess the ability to mimic HDL characteristics both in vitro as well as in vivo. We demonstrate that FeO-HDL can be applied to image HDL interactions and to investigate disease settings where HDL plays a key function. More generally, we have demonstrated a multimodal approach to study the behavior of biomaterials in vitro as well as in vivo. The approach allowed us to study nanoparticle dynamics in circulation, as well as nanoparticle targeting and uptake by tissues and cells of interest. Moreover, we were able to qualitatively assess nanoparticle excretion, critical for translating nanotechnologies to the clinic.
    Biomaterials 10/2010; 32(1):206-13. · 8.31 Impact Factor
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    ABSTRACT: To investigate the potential of spectral computed tomography (CT) (popularly referred to as multicolor CT), used in combination with a gold high-density lipoprotein nanoparticle contrast agent (Au-HDL), for characterization of macrophage burden, calcification, and stenosis of atherosclerotic plaques. The local animal care committee approved all animal experiments. A preclinical spectral CT system in which incident x-rays are divided into six different energy bins was used for multicolor imaging. Au-HDL, an iodine-based contrast agent, and calcium phosphate were imaged in a variety of phantoms. Apolipoprotein E knockout (apo E-KO) mice were used as the model for atherosclerosis. Gold nanoparticles targeted to atherosclerosis (Au-HDL) were intravenously injected at a dose of 500 mg per kilogram of body weight. Iodine-based contrast material was injected 24 hours later, after which the mice were imaged. Wild-type mice were used as controls. Macrophage targeting by Au-HDL was further evaluated by using transmission electron microscopy and confocal microscopy of aorta sections. Multicolor CT enabled differentiation of Au-HDL, iodine-based contrast material, and calcium phosphate in the phantoms. Accumulations of Au-HDL were detected in the aortas of the apo E-KO mice, while the iodine-based contrast agent and the calcium-rich tissue could also be detected and thus facilitated visualization of the vasculature and bones (skeleton), respectively, during a single scanning examination. Microscopy revealed Au-HDL to be primarily localized in the macrophages on the aorta sections; hence, the multicolor CT images provided information about the macrophage burden. Spectral CT used with carefully chosen contrast agents may yield valuable information about atherosclerotic plaque composition.
    Radiology 09/2010; 256(3):774-82. · 6.34 Impact Factor
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    ABSTRACT: An important challenge in medical diagnostics is to design all-in-one contrast agents that can be detected with multiple techniques such as magnetic resonance imaging (MRI), X-ray computed tomography (CT), positron emission tomography (PET), single photon emission tomography (SPECT) or fluorescence imaging (FI). Although many dual labeled agents have been proposed, mainly for combined MRI/FI, constructs for three imaging modalities are scarce. Here gold/silica nanoparticles with a poly(ethylene glycol), paramagnetic and fluorescent lipid coating were synthesized, characterized and applied as trimodal contrast agents to allow for nanoparticle-enhanced imaging of macrophage cells in vitro via MRI, CT and FI, and mice livers in vivo via MRI and CT. This agent can be a useful tool in a multitude of applications, including cell tracking and target-specific molecular imaging, and is a step in the direction of truly multi-modal imaging.
    Contrast Media & Molecular Imaging 01/2010; 5(4):231-6. · 2.87 Impact Factor
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    ABSTRACT: 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.
    Wiley Interdisciplinary Reviews Nanomedicine and Nanobiotechnology 01/2010; 2(2):138-50. · 5.68 Impact Factor
  • Contrast Media & Molecular Imaging 11/2009; 4(6):293-294. · 2.87 Impact Factor
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    ABSTRACT: Lipoproteins, natural nanoparticles, have a well-recognized biological role and are highly suitable as a platform for delivering imaging agents. The ease with which both the exterior and interior of the particles can be modified permits the creation of multifunctional nanoparticles for imaging as well as the delivery of therapeutics. Importantly, their endogenous nature may make them biocompatible and biodegradable and allows them to avoid the recognition of the reticuloendothelial system. In particular, high-density lipoproteins (HDL) are of interest, because of their small size they can easily cross the endothelium and penetrate the underlying tissue. We summarize here the progress in establishing HDL as a vector for delivering a variety of diagnostically active materials to vulnerable atherosclerotic plaques in mouse models of atherosclerosis. By loading various types of image-enhancing compounds into either the core or surface of HDL, they can be visualized by different imaging modalities (MRI, CT, optical). By rerouting of HDL away from plaque macrophages, imaging of biological processes in diseases besides atherosclerosis may also be achieved.
    Arteriosclerosis Thrombosis and Vascular Biology 10/2009; 30(2):169-76. · 6.34 Impact Factor
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    ABSTRACT: Nanoemulsions are increasingly investigated for the delivery of hydrophobic drugs to improve their bioavailability or make their administration possible. In the current study, oil-in-water emulsions with three different mean diameters (30, 60, and 95 nm) were developed as a new multimodality nanoparticle platform for tumor targeting and imaging. To that aim, hydrophobically coated iron oxide particles were included in the soybean oil core of the nanoemulsions to enable their detection with magnetic resonance imaging (MRI), while the conjugation of a near infrared fluorophore allowed optical imaging. The accumulation of this novel nanocomposite in subcutaneous human tumors in nude mice was demonstrated with MRI and fluorescence imaging in vivo, and with Perl's staining of histological tumor sections ex vivo.
    Biomaterials 09/2009; 30(36):6947-54. · 8.31 Impact Factor
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    ABSTRACT: Contrast-enhanced MRI of atherosclerosis can provide valuable additional information on a patient's disease state. As a result of the interactions of HDL with atherosclerotic plaque and the flexibility of its reconstitution, it is a versatile candidate for the delivery of contrast-generating materials to this pathogenic lesion. We herein discuss the reports of HDL modified with gadolinium to act as an MRI contrast agent for atherosclerosis. Furthermore, HDL has been modified with fluorophores and nanocrystals, allowing it to act as a contrast agent for fluorescent imaging techniques and for computed tomography. Such modified HDL has been found to be macrophage specific, and, therefore, can provide macrophage density information via noninvasive MRI. As such, modified HDL is currently a valuable contrast agent for probing preclinical atherosclerosis. Future developments may allow the application of this particle to further diseases and pathological or physiological processes in both preclinical models as well as in patients.
    Clinical lipidology. 08/2009; 4(4):493-500.
  • Torjus Skajaa
    Acta Obstetricia et Gynecologica Scandinavica. 07/2009; 40(1).
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    ABSTRACT: Nanoparticles have become more and more prevalent in reports of novel contrast agents, especially for molecular imaging, the detection of cellular processes. The advantages of nanoparticles include their potency to generate contrast, the ease of integrating multiple properties, lengthy circulation times, and the possibility to include high payloads. As the chemistry of nanoparticles has improved over the past years, more sophisticated examples of nano-sized contrast agents have been reported, such as paramagnetic, macrophage targeted quantum dots or alpha(v)beta(3)-targeted, MRI visible microemulsions that also carry a drug to suppress angiogenesis. The use of these particles is producing greater knowledge of disease processes and the effects of therapy. Along with their excellent properties, nanoparticles may produce significant toxicity, which must be minimized for (clinical) application. In this review we discuss the different factors that are considered when designing a nanoparticle probe and highlight some of the most advanced examples.
    Arteriosclerosis Thrombosis and Vascular Biology 01/2009; 29(7):992-1000. · 6.34 Impact Factor
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    ABSTRACT: High density lipoprotein (HDL) is an important natural nanoparticle that may be modified for biomedical imaging purposes. Here we developed a novel technique to create unique multimodality HDL mimicking nanoparticles by incorporation of gold, iron oxide, or quantum dot nanocrystals for computed tomography, magnetic resonance, and fluorescence imaging, respectively. By including additional labels in the corona of the particles, they were made multifunctional. The characteristics of these nanoparticles, as well as their in vitro and in vivo behavior, revealed that they closely mimic native HDL.
    Nano Letters 11/2008; 8(11):3715-23. · 13.03 Impact Factor
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    ABSTRACT: Introduction Cardiovascular disease is one of the most prevalent causes of mortality in the world and adverse cardiovascular events are most commonly linked to rupture of atherosclerotic plaques. Macrophages have been identified as intimately linked to the progression of atherosclerosis 1 and thus the ability to non-invasively image this cell type would be advantageous. High density lipoprotein (HDL) is naturally targeted to atherosclerotic plaques and we have previously modified the phospholipid coating of HDL to act as an MRI contrast agent. 2 In this report we will discuss a new generation of HDL-based contrast agent where the cholesterol ester/triglyceride core has also been modified via substitution for inorganic nanoparticles, such as gold for CT/MRI, iron oxide for MRI or quantum dots for MRI/optical imaging (Figure 1). These particles allow the multimodal imaging of macrophages. We present here the synthesis and characterization of the particles and, as an example, the results of incubation of the gold HDL with macrophages analyzed by MRI, CT, confocal microscopy and TEM. Materials and Methods The synthesis was achieved for each particle in a similar fashion, where the phospholipids and inorganic nanoparticles, i.e. gold, iron oxide, quantum dots, were co-dissolved in a chloroform-methanol solvent mixture. This solution was slowly added to hot buffer, forming the encapsulated particles. ApoA-I was included in the phospholipid layer via incubation. Purification was achieved via centrifugation, filtration and washing. Lipid only coated particles were also formed as controls. These nanoparticles were characterized via TEM, ICP-MS, relaxometry, CT imaging, phosphorous and protein quantification. The gold HDL was incubated with J774A.1 macrophages for ½ 1, 2, 4, 7 and 12 hours. HeLa cells were also incubated with the agent to verify specificity, for 2 and 4 hrs. Relevant commercially available contrast agents, Omnipaque and Magnevist were used as controls. The cells were collected as a loose pellet and analyzed using different imaging methods. T1-weighted imaging and T1-mapping were done on a 9.4 T MRI scanner. and CT images of the cell pellets were acquired on a Siemens Somatom Emotion 6. The cellular localization of the gold HDL was established using confocal laser scanning microscopy and TEM. For the former method, the nuclei were stained with DAPI and for the latter method the cells were fixed in glutaraldehyde and stained with osmium tetraoxide and uranyl acetate. Results and Discussion The synthesis and purification of the particles resulted in individually dispersed particles (Figure 2A). The relaxivities of the gold particle were found to be r1=13.1 (mMs) -1 and r2=16.8 (mMs) -1 , comparable to values found for quantum dots (another inorganic particle) in a similar phospholipid coating. 3 Protein analysis showed that the apoA-I readily adsorbed onto the particle.

Publication Stats

467 Citations
91.95 Total Impact Points

Institutions

  • 2013
    • Aarhus University
      • Department of Clinical Medicine
      Aarhus, Central Jutland, Denmark
  • 2009–2013
    • Mount Sinai School of Medicine
      • Department of Radiology
      Manhattan, NY, United States
  • 2009–2011
    • Aarhus University Hospital
      • Department of Surgery
      Aarhus, Central Jutland, Denmark