Clot-targeted magnetic hyperthermia permeabilizes blood clots to make them more susceptible to thrombolysis.

BACKGROUND: Thrombolysis is a frontline treatment for stroke, which involves the application of tissue plasminogen activator (tPA) to trigger endogenous clot-degradation pathways. However, it is only effective within 4.5 h of symptom onset because of clot contraction preventing tPA permeation into the clot. Magnetic hyperthermia (MH) mediated by tumor-targeted magnetic nanoparticles is used to treat cancer by using local heat generation to trigger apoptosis of cancer cells. OBJECTIVES: To develop clot-targeting magnetic nanoparticles to deliver MH to the surface of human blood clots, and to assess whether this can improve the efficacy of thrombolysis of contracted blood clots. METHODS: Clot-targeting magnetic nanoparticles were developed by functionalizing iron oxide nanoparticles with an antibody recognizing activated integrin αIIbß3 (PAC-1). The magnetic properties of the PAC-1-tagged magnetic nanoparticles were characterized and optimized to deliver clot-targeted MH. RESULTS: Clot-targeted MH increases the efficacy of tPA-mediated thrombolysis in contracted human blood clots, leading to a reduction in clot weight. MH increases the permeability of the clots to tPA, facilitating their breakdown. Scanning electron microscopy reveals that this effect is elicited through enhanced fibrin breakdown and triggering the disruption of red blood cells on the surface of the clot. Importantly, endothelial cells viability in a three-dimensional blood vessel model is unaffected by exposure to MH. CONCLUSIONS: This study demonstrates that clot-targeted MH can enhance the thrombolysis of contracted human blood clots and can be safely applied to enhance the timeframe in which thrombolysis is effective.

Iron stored in ferritin is chemically reduced in the presence of aggregating Aß(1-42).

Atypical low-oxidation-state iron phases in Alzheimer's disease (AD) pathology are implicated in disease pathogenesis, as they may promote elevated redox activity and convey toxicity. However, the origin of low-oxidation-state iron and the pathways responsible for its formation and evolution remain unresolved. Here we investigate the interaction of the AD peptide ß-amyloid (Aß) with the iron storage protein ferritin, to establish whether interactions between these two species are a potential source of low-oxidation-state iron in AD. Using X-ray spectromicroscopy and electron microscopy we found that the co-aggregation of Aß and ferritin resulted in the conversion of ferritin's inert ferric core into more reactive low-oxidation-states. Such findings strongly implicate Aß in the altered iron handling and increased oxidative stress observed in AD pathogenesis. These amyloid-associated iron phases have biomarker potential to assist with disease diagnosis and staging, and may act as targets for therapies designed to lower oxidative stress in AD tissue.

The potential of magnetic hyperthermia for triggering the differentiation of cancer cells.

Magnetic hyperthermia is a potential technique for cancer therapy that exploits heat generated by magnetic nanoparticles to kill cancerous cells. Many studies have shown that magnetic hyperthermia is effective at killing cancer cells both in vitro and in vivo, however little attention has been paid to the cellular functioning of the surviving cells. We report here new evidence demonstrating the onset of thermally triggered differentiation in osteosarcoma cancer cells that survive magnetic hyperthermia treatment. This raises the possibility that in addition to causing cell death, magnetic hyperthermia could induce surviving cancer cells to form more mature cell types and thereby inhibit their capacity to self-renew. Such processes could prove to be as important as cell death when considering magnetic hyperthermia for treating cancer.

Nanoscale synchrotron X-ray speciation of iron and calcium compounds in amyloid plaque cores from Alzheimer's disease subjects.

Altered metabolism of biometals in the brain is a key feature of Alzheimer's disease, and biometal interactions with amyloid-ß are linked to amyloid plaque formation. Iron-rich aggregates, including evidence for the mixed-valence iron oxide magnetite, are associated with amyloid plaques. To test the hypothesis that increased chemical reduction of iron, as observed in vitro in the presence of aggregating amyloid-ß, may occur at sites of amyloid plaque formation in the human brain, the nanoscale distribution and physicochemical states of biometals, particularly iron, were characterised in isolated amyloid plaque cores from human Alzheimer's disease cases using synchrotron X-ray spectromicroscopy. In situ X-ray magnetic circular dichroism revealed the presence of magnetite: a finding supported by ptychographic observation of an iron oxide crystal with the morphology of biogenic magnetite. The exceptional sensitivity and specificity of X-ray spectromicroscopy, combining chemical and magnetic probes, allowed enhanced differentiation of the iron oxides phases present. This facilitated the discovery and speciation of ferrous-rich phases and lower oxidation state phases resembling zero-valent iron as well as magnetite. Sequestered calcium was discovered in two distinct mineral forms suggesting a dynamic process of amyloid plaque calcification in vivo. The range of iron oxidation states present and the direct observation of biogenic magnetite provide unparalleled support for the hypothesis that chemical reduction of iron arises in conjunction with the formation of amyloid plaques. These new findings raise challenging questions about the relative impacts of amyloid-ß aggregation, plaque formation, and disrupted metal homeostasis on the oxidative burden observed in Alzheimer's disease.

Dynamical Magnetic Response of Iron Oxide Nanoparticles Inside Live Cells.

Magnetic nanoparticles exposed to alternating magnetic fields have shown a great potential acting as magnetic hyperthermia mediators for cancer treatment. However, a dramatic and unexplained reduction of the nanoparticle magnetic heating efficiency has been evidenced when nanoparticles are located inside cells or tissues. Recent studies suggest the enhancement of nanoparticle clustering and/or immobilization after interaction with cells as possible causes, although a quantitative description of the influence of biological matrices on the magnetic response of magnetic nanoparticles under AC magnetic fields is still lacking. Here, we studied the effect of cell internalization on the dynamical magnetic response of iron oxide nanoparticles (IONPs). AC magnetometry and magnetic susceptibility measurements of two magnetic core sizes (11 and 21 nm) underscored differences in the dynamical magnetic response following cell uptake with effects more pronounced for larger sizes. Two methodologies have been employed for experimentally determining the magnetic heat losses of magnetic nanoparticles inside live cells without risking their viability as well as the suitability of magnetic nanostructures for in vitro hyperthermia studies. Our experimental results-supported by theoretical calculations-reveal that the enhancement of intracellular IONP clustering mainly drives the cell internalization effects rather than intracellular IONP immobilization. Understanding the effects related to the nanoparticle transit into live cells on their magnetic response will allow the design of nanostructures containing magnetic nanoparticles whose dynamical magnetic response will remain invariable in any biological environments, allowing sustained and predictable in vivo heating efficiency.

Iron Biochemistry is Correlated with Amyloid Plaque Morphology in an Established Mouse Model of Alzheimer's Disease.

A signature characteristic of Alzheimer's disease (AD) is aggregation of amyloid-beta (Aß) fibrils in the brain. Nevertheless, the links between Aß and AD pathology remain incompletely understood. It has been proposed that neurotoxicity arising from aggregation of the Aß1-42 peptide can in part be explained by metal ion binding interactions. Using advanced X-ray microscopy techniques at sub-micron resolution, we investigated relationships between iron biochemistry and AD pathology in intact cortex from an established mouse model over-producing Aß. We found a direct correlation of amyloid plaque morphology with iron, and evidence for the formation of an iron-amyloid complex. We also show that iron biomineral deposits in the cortical tissue contain the mineral magnetite, and provide evidence that Aß-induced chemical reduction of iron could occur in vivo. Our observations point to the specific role of iron in amyloid deposition and AD pathology, and may impact development of iron-modifying therapeutics for AD.

The cellular magnetic response and biocompatibility of biogenic zinc- and cobalt-doped magnetite nanoparticles.

The magnetic moment and anisotropy of magnetite nanoparticles can be optimised by doping with transition metal cations, enabling their properties to be tuned for different biomedical applications. In this study, we assessed the suitability of bacterially synthesized zinc- and cobalt-doped magnetite nanoparticles for biomedical applications. To do this we measured cellular viability and activity in primary human bone marrow-derived mesenchymal stem cells and human osteosarcoma-derived cells. Using AC susceptibility we studied doping induced changes in the magnetic response of the nanoparticles both as stable aqueous suspensions and when associated with cells. Our findings show that the magnetic response of the particles was altered after cellular interaction with a reduction in their mobility. In particular, the strongest AC susceptibility signal measured in vitro was from cells containing high-moment zinc-doped particles, whilst no signal was observed in cells containing the high-anisotropy cobalt-doped particles. For both particle types we found that the moderate dopant levels required for optimum magnetic properties did not alter their cytotoxicity or affect osteogenic differentiation of the stem cells. Thus, despite the known cytotoxicity of cobalt and zinc ions, these results suggest that iron oxide nanoparticles can be doped to sufficiently tailor their magnetic properties without compromising cellular biocompatibility.

In situ measurement of magnetization relaxation of internalized nanoparticles in live cells.

Magnetization relaxation mechanisms strongly influence how magnetic nanoparticles respond to high-frequency fields in applications such as magnetic hyperthermia. The dominant mechanism depends on the mobility of the particles, which will be affected in turn by their microenvironment. In this study AC susceptometry was used to follow the in situ magnetic response of model systems of blocked and superparamagnetic nanoparticles, following their cellular internalization and subsequent release by freeze-thaw lysis. The AC susceptibility signal from internalized particles in live cells showed only Néel relaxation, consistent with measurements of immobilized nanoparticle suspensions. However, Brownian relaxation was restored after cell lysis, indicating that the immobilization effect was reversible and that nanoparticle integrity was maintained in the cells. The results presented demonstrate that cellular internalization can disable Brownian relaxation, which has significant implications for designing suitable nanoparticles for intracellular hyperthermia applications. Further to this, the results highlight the possibility that particles could be released in reusable form from degrading cells following hyperthermia treatment, and subsequently reabsorbed by viable cells.

Bacterially synthesized ferrite nanoparticles for magnetic hyperthermia applications.

Magnetic hyperthermia uses AC stimulation of magnetic nanoparticles to generate heat for cancer cell destruction. Whilst nanoparticles produced inside magnetotactic bacteria have shown amongst the highest reported heating to date, these particles are magnetically blocked so that strong heating occurs only for mobile particles, unless magnetic field parameters are far outside clinical limits. Here, nanoparticles extracellularly produced by the bacteria Geobacter sulfurreducens are investigated that contain Co or Zn dopants to tune the magnetic anisotropy, saturation magnetization and nanoparticle sizes, enabling heating within clinical field constraints. The heating mechanisms specific to either Co or Zn doping are determined from frequency dependent specific absorption rate (SAR) measurements and innovative AC susceptometry simulations that use a realistic model concerning clusters of polydisperse nanoparticles in suspension. Whilst both particle types undergo magnetization relaxation and show heating effects in water under low AC frequency and field, only Zn doped particles maintain relaxation combined with hysteresis losses even when immobilized. This magnetic heating process could prove important in the biological environment where nanoparticle mobility may not be possible. Obtained SARs are discussed regarding clinical conditions which, together with their enhanced MRI contrast, indicate that biogenic Zn doped particles are promising for combined diagnostics and cancer therapy.

Evidence of redox-active iron formation following aggregation of ferrihydrite and the Alzheimer's disease peptide ß-amyloid.

Recent work has demonstrated increased levels of redox-active iron biominerals in Alzheimer's disease (AD) tissue. However, the origin, nature, and role of iron in AD pathology remains unclear. Using X-ray absorption, X-ray microspectroscopy, and electron microscopy techniques, we examined interactions between the AD peptide ß-amyloid (Aß) and ferrihydrite, which is the ferric form taken when iron is stored in humans. We report that Aß is capable of reducing ferrihydrite to a pure iron(II) mineral where antiferromagnetically ordered Fe(2+) cations occupy two nonequivalent crystal symmetry sites. Examination of these iron(II) phases following air exposure revealed a material consistent with the iron(II)-rich mineral magnetite. These results demonstrate the capability of Aß to induce the redox-active biominerals reported in AD tissue from natural iron precursors. Such interactions between Aß and ferrihydrite shed light upon the processes of AD pathogenesis, while providing potential targets for future therapies.

Harnessing the extracellular bacterial production of nanoscale cobalt ferrite with exploitable magnetic properties.

Nanoscale ferrimagnetic particles have a diverse range of uses from directed cancer therapy and drug delivery systems to magnetic recording media and transducers. Such applications require the production of monodisperse nanoparticles with well-controlled size, composition, and magnetic properties. To fabricate these materials purely using synthetic methods is costly in both environmental and economical terms. However, metal-reducing microorganisms offer an untapped resource to produce these materials. Here, the Fe(III)-reducing bacterium Geobacter sulfurreducens is used to synthesize magnetic iron oxide nanoparticles. A combination of electron microscopy, soft X-ray spectroscopy, and magnetometry techniques was employed to show that this method of biosynthesis results in high yields of crystalline nanoparticles with a narrow size distribution and magnetic properties equal to the best chemically synthesized materials. In particular, it is demonstrated here that cobalt ferrite (CoFe(2)O(4)) nanoparticles with low temperature coercivity approaching 8 kOe and an effective anisotropy constant of ∼10(6) erg cm(-3) can be manufactured through this biotechnological route. The dramatic enhancement in the magnetic properties of the nanoparticles by the introduction of high quantities of Co into the spinel structure represents a significant advance over previous biomineralization studies in this area using magnetotactic bacteria. The successful production of nanoparticulate ferrites achieved in this study at high yields could open up the way for the scaled-up industrial manufacture of nanoparticles using environmentally benign methodologies.