Jon Dobson

Magnetic micro- and nano-particle-based targeting for drug and gene delivery.

The use of magnetic micro- and nano-particles as carriers for in vivo targeting of therapeutic compounds was first proposed over 25 years ago. Since then, a variety of animal studies have demonstrated the efficacy of the technique, however, only a handful of Phase I/II clinical trials have taken place. While the theoretical underpinnings have been lacking, recent advances in mathematical modeling of magnetic targeting, as well as the development of novel magnetic nanoparticle carriers and implantable magnets, show promise in progressing this technology from the laboratory to the clinic.

Iron: The Redox-active Center of Oxidative Stress in Alzheimer Disease

Although iron is essential in maintaining the function of the central nervous system, it is a potent source of reactive oxygen species. Excessive iron accumulation occurs in many neurodegenerative diseases including Alzheimer disease (AD), Parkinson’s disease, and Creutzfeldt-Jakob disease, raising the possibility that oxidative stress is intimately involved in the neurodegenerative process. AD in particular is associated with accumulation of numerous markers of oxidative stress; moreover, oxidative stress has been shown to precede hallmark neuropathological lesions early in the disease process, and such lesions, once present, further accumulate iron, among other markers of oxidative stress. In this review, we discuss the role of iron in the progression of AD.

Development of Superparamagnetic Iron Oxide Nanoparticles (SPIONS) for Translation to Clinical Applications

Superparamagnetic iron oxide nanoparticles (SPIONs) have attract a great deal of interest in biomedical research and clinical applications over the past decades. Taking advantage the fact that SPIONs only exhibit magnetic properties in the presence of an applied magnetic field, they have been used in both in vitro magnetic separation and in vivo applications such as hyperthermia (HT), magnetic drug targeting (MDT), magnetic resonance imaging (MRI), gene delivery (GD) and nanomedicine. Successful applications of SPIONs rely on precise control of the particles shape, size, and size distribution and several synthetic routes for preparing SPIONs have been explored. Tailored surface properties specifically designed for cell targeting are often required, although the generic strategy involves creating biocompatible polymeric or non-polymeric coating and subsequent conjugation of bioactive molecules. In this review article, synthetic routes, surface modification and functionaliztion of SPIONs, as well as the major biomedical applications are summarized, with emphasis on in vivo applications.

Three-Dimensional Tomographic Imaging and Characterization of Iron Compounds within Alzheimer's Plaque Core Material

Although it has been known for over 50 years that abnormal concentrations of iron are associated with virtually all neurodegenerative diseases, including Alzheimers disease, its origin, nature and role have remained a mystery. Here, we use high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray (EDX) spectroscopy and electron energy-loss spectroscopy (EELS), electron tomography, and electron diffraction to image and characterize iron-rich plaque core material - a hallmark of Alzheimers disease pathology - in three dimensions. In these cores, we unequivocally identify biogenic magnetite and/or maghemite as the dominant iron compound. Our results provide an indication that abnormal iron biomineralization processes are likely occurring within the plaque or the surrounding diseased tissue and may play a role in aberrant peptide aggregation. The size distribution of the magnetite cores implies formation from a ferritin precursor, implicating a malfunction of the primary iron storage protein in the brain.

Development of magnetic particle techniques for long-term culture of bone cells with intermittent mechanical activation

Magnetic particles were coated with RGD and adhered to primary human osteoblasts. During a 21-day culture, the osteoblasts plus adhered magnetic particles underwent a daily exposure to a time-varying magnetic field via a permanent NdFeB magnet, thus applying a direct mechanical stress to the cells (Bmax approximately 60 mT). After 21 days, preliminary results show that the cells plus magnetic particles were viable and had proliferated. A von-kossa stain showed mineralized bone matrix produced at 21 days in the experimental group whereas the control groups showed no mineralized matrix production. Real-time reverse transcription-polymerase chain reaction at 21 days showed an upregulation of osteopontin from the experimental group in comparison to the control group of cells with adhered particles and no magnet applied. These preliminary results indicate that adherence of RGD-coated 4.5 microm ferromagnetic particles to primary human osteoblasts does not initiate cell necrosis up to 21 days in vitro. Also, mechanical stimulation of human osteoblasts by magnetic particle technology appears to have an influence on osteoblastic activity.

Mapping and characterization of iron compounds in Alzheimer's tissue

Understanding the management of iron in the brain is of great importance in the study of neurodegeneration, where regional iron overload is frequently evident. A variety of approaches have been employed, from quantifying iron in various anatomical structures, to identifying genetic risk factors related to iron metabolism, and exploring chelation approaches to tackle iron overload in neurodegenerative disease. However, the ease with which iron can change valence state ensures that it is present in vivo in a wide variety of forms, both soluble and insoluble. Here, we review recent developments in approaches to locate and identify iron compounds in neurodegenerative tissue. In addition to complementary techniques that allow us to quantify and identify iron compounds using magnetometry, extraction, and electron microscopy, we are utilizing a powerful combined mapping/characterization approach with synchrotron X-rays. This has enabled the location and characterization of iron accumulations containing magnetite and ferritin in human Alzheimers disease (AD) brain tissue sections in situ at micron-resolution. It is hoped that such approaches will contribute to our understanding of the role of unusual iron accumulations in disease pathogenesis, and optimise the potential to use brain iron as a clinical biomarker for early detection and diagnosis.

Investigation of age-related variations in biogenic magnetite levels in the human hippocampus.

The magnetic properties of human hippocampal tissue from 23 subjects (15 epilepsy patients and eight cadavers with no neuropathology) were analysed and tissue concentrations of magnetic material were calculated. The biogenic iron oxide magnetite (Fe3O4) is the dominant source of magnetisation in the tissue. Analysis of the group as a whole revealed no significant trend towards either increasing or decreasing magnetite concentration with age. Separate analysis of male and female subjects, however, reveals a trend towards increasing magnetite concentration with age in males. This trend is not seen in females and may have implications for iron metabolism and neurological disorders associated with disruptions in normal iron homeostasis.

The influence of static magnetic fields on mechanosensitive ion channel activity in artificial liposomes

The influence of static magnetic fields (SMFs) on the activity of recombinant mechanosensitive ion channels (the bacterial mechanosensitive ion channel of large conductance—MscL) following reconstitution into artificial liposomes has been investigated. Preliminary findings suggest that exposure to 80-mT SMFs does not induce spontaneous MscL activation in the absence of mechanical stimulation. However, SMFs do appear to influence the open probability and single channel kinetics of MscL exposed to negative pipette pressure. Typical responses include an overall reduction in channel activity or an increased likelihood of channels becoming “trapped open” in sub-conducting states following exposure to SMFs. There is a delay in the onset of this effect and it is maintained throughout exposure. Generally, channel activity showed slow or limited recovery following removal of the magnetic field and responses to the magnetic were often reduced or abolished upon subsequent exposures. Pre-exposure of the liposomes to SMFs resulted in reduced sensitivity of MscL to negative pipette pressure, with higher pressures required to activate the channels. Although the mechanisms of this effect are not clear, our initial observations appear to support previous work showing that the effects of SMFs on ion channels may be mediated by changes in membrane properties due to anisotropic diamagnetism of lipid molecules.

Superconducting quantum interference device measurements of dilute magnetic materials in biological samples

Superconducting quantum interference device (SQUID) magnetometers are very high precision instruments: for example, the Quantum Design MPMS-7 instrument capable of measuring an absolute magnetization of ≈10−7to10−11emu (10−10to10−14Am2), corresponding to better than ≈1ng of magnetite, Fe3O4. However, in biological samples, such precision is rarely achieved. In the presence of ≈100mg of biological tissue there is a diamagnetic contribution of ≈−9×10−9emu∕Oe so that at 10kOe the measurement of 1ng of magnetite in 100mg of tissue has its precision reduced by a factor of 10, with a loss in accuracy of a factor of 2.5. The extra volume of the biological material also reduces accuracy, typically by ≈25%. We describe here a measurement protocol that increases the obtainable precision and improves accuracy by a factor of 5, and which limits the sample volume effects to ≈2%–3%. This then allows accurate measurement of magnetic biominerals in a biological/diamagnetic matrix. Details on how to prepare, mount, and accurately measure dilute magnetic samples are given. The improvement in data quality comes at the cost of extended measurement periods and slightly increased helium consumption.Superconducting quantum interference device (SQUID) magnetometers are very high precision instruments: for example, the Quantum Design MPMS-7 instrument capable of measuring an absolute magnetization of ≈10−7to10−11emu (10−10to10−14Am2), corresponding to better than ≈1ng of magnetite, Fe3O4. However, in biological samples, such precision is rarely achieved. In the presence of ≈100mg of biological tissue there is a diamagnetic contribution of ≈−9×10−9emu∕Oe so that at 10kOe the measurement of 1ng of magnetite in 100mg of tissue has its precision reduced by a factor of 10, with a loss in accuracy of a factor of 2.5. The extra volume of the biological material also reduces accuracy, typically by ≈25%. We describe here a measurement protocol that increases the obtainable precision and improves accuracy by a factor of 5, and which limits the sample volume effects to ≈2%–3%. This then allows accurate measurement of magnetic biominerals in a biological/diamagnetic matrix. Details on how to prepare, mount, and ac...

Use of magnetic particles to apply mechanical forces for bone tissue engineering purposes

It is possible to influence osteoblast activity by the application of mechanical forces. There is potential in using these forces for tissue engineering applications in that cell matrix production may be upregulated, resulting in a functional tissue engineered construct created in a shorter culture time. We have been developing a novel technique for applying mechanical forces directly to the cell with the use of magnetic particles. Particles attached to the cell membrane can be manipulated using an external magnetic field thus applying forces in the piconewton range. We have previously demonstrated that primary human osteoblasts respond to this type of stimulus by upregulating bone related gene expression and producing mineralized matrix at early time points. In this paper we discuss the optimization of this technique by presenting data on the effects of this type of force on osteoblast proliferation, phagocytosis and also the potential use of this technique in developing 3D tissue engineered constructs.