Migration, fate and in vivo imaging of adult stem cells in the CNS

Advanced Nanotechnology Approaches as Emerging Tools in Cellular-Based Technologies

Stem cells are valuable tools in regenerative medicine because they can generate a wide variety of cell types and tissues that can be used to treat or replace damaged tissues and organs. However, challenges related to the application of stem cells in the scope of regenerative medicine have urged scientists to utilize nanomedicine as a prerequisite to circumvent some of these hurdles. Nanomedicine plays a crucial role in this process and manipulates surface biology, the fate of stem cells, and biomaterials. Many attempts have been made to modify cellular behavior and improve their regenerative ability using nano-based strategies. Notably, nanotechnology applications in regenerative medicine and cellular therapies are controversial because of ethical and legal considerations. Therefore, this review describes nanotechnology in cell-based applications and focuses on newly proposed nano-based approaches. Cutting-edge strategies to engineer biological tissues and the ethical, legal, and social considerations of nanotechnology in regenerative nanomedicine applications are also discussed.

Iron Oxide Nanoparticles in Regenerative Medicine and Tissue Engineering

In recent years, many promising nanotechnological approaches to biomedical research have been developed in order to increase implementation of regenerative medicine and tissue engineering in clinical practice. In the meantime, the use of nanomaterials for the regeneration of diseased or injured tissues is considered advantageous in most areas of medicine. In particular, for the treatment of cardiovascular, osteochondral and neurological defects, but also for the recovery of functions of other organs such as kidney, liver, pancreas, bladder, urethra and for wound healing, nanomaterials are increasingly being developed that serve as scaffolds, mimic the extracellular matrix and promote adhesion or differentiation of cells. This review focuses on the latest developments in regenerative medicine, in which iron oxide nanoparticles (IONPs) play a crucial role for tissue engineering and cell therapy. IONPs are not only enabling the use of non-invasive observation methods to monitor the therapy, but can also accelerate and enhance regeneration, either thanks to their inherent magnetic properties or by functionalization with bioactive or therapeutic compounds, such as drugs, enzymes and growth factors. In addition, the presence of magnetic fields can direct IONP-labeled cells specifically to the site of action or induce cell differentiation into a specific cell type through mechanotransduction.

Options for imaging cellular therapeutics in vivo: a multi-stakeholder perspective

Cell-based therapies have been making great advances toward clinical reality. Despite the increase in trial activity, few therapies have successfully navigated late-phase clinical trials and received market authorization. One possible explanation for this is that additional tools and technologies to enable their development have only recently become available. To support the safety evaluation of cell therapies, the Health and Environmental Sciences Institute Cell Therapy-Tracking, Circulation and Safety Committee, a multisector collaborative committee, polled the attendees of the 2017 International Society for Cell & Gene Therapy conference in London, UK, to understand the gaps and needs that cell therapy developers have encountered regarding safety evaluations in vivo. The goal of the survey was to collect information to inform stakeholders of areas of interest that can help ensure the safe use of cellular therapeutics in the clinic. This review is a response to the cellular imaging interests of those respondents. The authors offer a brief overview of available technologies and then highlight the areas of interest from the survey by describing how imaging technologies can meet those needs. The areas of interest include imaging of cells over time, sensitivity of imaging modalities, ability to quantify cells, imaging cellular survival and differentiation and safety concerns around adding imaging agents to cellular therapy protocols. The Health and Environmental Sciences Institute Cell Therapy-Tracking, Circulation and Safety Committee believes that the ability to understand therapeutic cell fate is vital for determining and understanding cell therapy efficacy and safety and offers this review to aid in those needs. An aim of this article is to share the available imaging technologies with the cell therapy community to demonstrate how these technologies can accomplish unmet needs throughout the translational process and strengthen the understanding of cellular therapeutics.

Assessment of proliferation, migration and differentiation potentials of bone marrow mesenchymal stem cells labeling with silica-coated and amine-modified superparamagnetic iron oxide nanoparticles

Superparamagnetic iron oxide nanoparticles have been widely used for cell labeling in preclinical and clinical studies, to improve labeling efficiency, particle conjugation and surface modifications are developed, but some modified SPIONs exert side-effect on physiological activity of cells, which cannot be served as ideal cell tracker. In this study, amine-modified silica-coated SPIO (SPIO@SiO₂-NH₂, SPIO@S-N) nanoparticles were used to label bone marrow derived mesenchymal stem cells (BM-MSCs), then the stem cell potentials were evaluated. It was found BM-MSCs could be efficiently labeled by SPIO@S-N nanoparticles. After labeling, the BM-MSCs viability kept well and the migration ability increased, but the osteogenesis and adipogenesis potentials were not impaired. In steroid associated osteonecrosis (SAON) bone defect model, stem cell implantation was performed by injection of SPIO@S-N labeled BM-MSCs into marrow cavity locally, it was found the SPIO positive cells homed to the periphery of defect region in control group, but were recruited to the defect region in poly lactic-coglycolic acid/tricalcium phosphate (PLGA/TCP) scaffold implantation group. In conclusion, SPIO@S-N nanoparticles promoted migration while retained proliferation and differentiation ability of BM-MSCs, implying this kind of nanoparticles could be served not only an ideal tracking marker but also an accelerator for stem cell homing during tissue repair.

Application of Nanotechnology in Targeting of Cancer Stem Cells: A Review

Cancer is increasingly apparent as a systems-level, network happening. The central tendency of malignant alteration can be described as a two-phase procedure, where an initial increase of network plasticity is followed by reducing plasticity at late stages of tumor improvement. Cancer stem cells (CSCs) are cancer cells that take characteristics associated with normal stem cells. Cancer therapy has been based on the concept that most of the cancer cells have a similar ability to separate metastasise and kill the host. In this review, we addressed the use of nanotechnology in the treatment of cancer stem cells.

Grafted Neural Stem Cells Show Lesion-Specific Migration in Radiation-Injured Rat Brains

Neural stem cells (NSCs) exhibit preferential homing toward some types of brain lesion, but their migratory property during radiation brain injury (RBI) remains unexplored. Here, we use the superparamagnetic iron oxide (SPIO)-labeled magnetic resonance imaging (MRI) technology to determine the migration of transplanted NSCs in two partial RBI models in real time, created by administering 30–55 Gy of radiation to the right or posterior half of the adult rat brain. SPIO-labeled NSCs were stereotactically grafted into the uninjured side one week after RBI. The migration of SPIO-labeled NSCs in live radiation-injured brains was traced by MRI for up to 28 days after engraftment and quantified for their moving distances and speeds. A high labeling efficiency (>90%) was achieved by incubating NSCs with 100 μg ml⁻¹ of SPIO for 12–24 hours. Upon stereotactic transplantation into the healthy side of the brain, SPIO-labeled NSCs were distinctively detected as hypointense signals on T2-weighted images (T2WI), showed sustained survival for up to 4 weeks, and exhibited directional migration to the radiation-injured side of the brain with a speed of 86–127 μm per day. The moving kinetics of grafted NSCs displayed no difference in brains receiving a high (55 Gy) vs. moderate (45 Gy) dose of radiation, but was slower in the right RBI model than in the posterior RBI model. This study shows that NSCs can be effectively labeled by SPIO and traced in vivo by MRI, and that grafted NSCs exhibit directional migration toward RBI sites in a route-dependent but radiation dose-independent manner.

Neural stem cells (NSCs) exhibit preferential homing toward some types of brain lesion, but their migratory property during radiation brain injury (RBI) remains unexplored.

A Look into Stem Cell Therapy: Exploring the Options for Treatment of Ischemic Stroke

Neural stem cells (NSCs) offer a potential therapeutic benefit in the recovery from ischemic stroke. Understanding the role of endogenous neural stem and progenitor cells under normal physiological conditions aids in analyzing their effects after ischemic injury, including their impact on functional recovery and neurogenesis at the site of injury. Recent animal studies have utilized unique subsets of exogenous and endogenous stem cells as well as preconditioning with pharmacologic agents to better understand the best situation for stem cell proliferation, migration, and differentiation. These stem cell therapies provide a promising effect on stimulation of endogenous neurogenesis, neuroprotection, anti-inflammatory effects, and improved cell survival rates. Clinical trials performed using various stem cell types show promising results to their safety and effectiveness on reducing the effects of ischemic stroke in humans. Another important aspect of stem cell therapy discussed in this review is tracking endogenous and exogenous NSCs with magnetic resonance imaging. This review explores the pathophysiology of NSCs on ischemic stroke, stem cell therapy studies and their effects on neurogenesis, the most recent clinical trials, and techniques to track and monitor the progress of endogenous and exogenous stem cells.

In-vitro Labelling of Ovine Adipose-Derived Mesenchymal Stem Cells (oADMSCs) and Tracking Using MRI Technique

To understand the mechanisms standing behind a successful stem cell-based therapy, the monitoring of transplanted cell’s migration, homing as well as the engraftment efficiency and functional capability in-vivo has become a critical issue. The present study was designed to track the labelled oADMSCs in-vitro and its visualization through MRI technique. oADMSCs from passage 4 (P-4) to passage 6 (P-6) were labelled with superparamagnetic iron oxide (SPIO) conjugated with rhodamine (Molday Ion Rhodamine-B - MIRB) at the concentration of 25μg Fe/ml in DMEM. Internalized MIRB was observed under fluorescent microscope after 72 hrs of incubation. Labelled oADMSCs showed Prussian Blue positive reaction demonstrating the iron uptake of the cells. The viability of the MIRB-labelled oADMSCs ranged between 98-99 per cent and Trypan blue exclusion test showed no significant difference in viability between labelled and unlabelled oADMSCs. MR signal in control group of cells was similar to that of water. MR signals or fluorescence in MIRB-labelled cells decreased with increasing concentrations of iron. The T2 weighted images of MIRB-labelled oADMSCs increased with increasing concentrations of SPIOs. The MIRB was found to be nontoxic, and did not affect proliferation capacity in-vitro.

Behaviour of adipose-derived canine mesenchymal stem cells after superparamagnetic iron oxide nanoparticles labelling for magnetic resonance imaging

BACKGROUND

Therapy with mesenchymal stem cells (MSCs) has been reported to provide beneficial effects in the treatment of neurological and orthopaedic disorders in dogs. The exact mechanism of action is poorly understood. Magnetic resonance imaging (MRI) gives the opportunity to observe MSCs after clinical administration. To visualise MSCs with the help of MRI, labelling with an MRI contrast agent is necessary. However, it must be clarified whether there is any negative influence on cell function and viability after labelling prior to clinical administration.

RESULTS

For the purpose of the study, seven samples with canine adipose-derived stem cells were incubated with superparamagnetic iron oxide nanoparticles (SPIO: 319.2 μg/mL Fe) for 24 h. The internalisation of the iron particles occurred via endocytosis. SPIO particles were localized as free clusters in the cytoplasm or within lysosomes depending on the time of investigation. The efficiency of the labelling was investigated using Prussian blue staining and MACS assay. After 3 weeks the percentage of SPIO labelled canine stem cells decreased. Phalloidin staining showed no negative effect on the cytoskeleton. Labelled cells underwent osteogenic and adipogenic differentiation. Chondrogenic differentiation occurred to a lesser extent compared with a control sample. MTT-Test and wound healing assay showed no influence of labelling on the proliferation. The duration of SPIO labelling was assessed using a 1 Tesla clinical MRI scanner and T2 weighted turbo spin echo and T2 weighted gradient echo MRI sequences 1, 2 and 3 weeks after labelling. The hypointensity caused by SPIO lasted for 3 weeks in both sequences.

CONCLUSIONS

An Endorem labelling concentration of 319.2 μg/mL Fe (448 μg/mL SPIO) had no adverse effects on the viability of canine ASCs. Therefore, this contrast agent could be used as a model for iron oxide labelling agents. However, the tracking ability in vivo has to be evaluated in further studies.

Nanoparticle Technologies in the Spinal Cord

Nanoparticles are increasingly being studied within experimental models of spinal cord injury (SCI). They are used to image cells and tissue, move cells to specific regions of the spinal cord, and deliver therapeutic agents locally. The focus of this article is to provide a brief overview of the different types of nanoparticles being studied for spinal cord applications and present data showing the capability of nanoparticles to deliver the chondroitinase ABC (chABC) enzyme locally following acute SCI in rats. Nanoparticles releasing chABC helped promote axonal regeneration following injury, and the nanoparticles also protected the enzyme from rapid degradation. In summary, nanoparticles are viable materials for diagnostic or therapeutic applications within experimental models of SCI and have potential for future clinical use.

Hydrogels for central nervous system therapeutic strategies

The central nervous system shows a limited regenerative capacity, and injuries or diseases, such as those in the spinal, brain and retina, are a great problem since current therapies seem to be unable to achieve good results in terms of significant functional recovery. Different promising therapies have been suggested, the aim being to restore at least some of the lost functions. The current review deals with the use of hydrogels in developing advanced devices for central nervous system therapeutic strategies. Several approaches, involving cell-based therapy, delivery of bioactive molecules and nanoparticle-based drug delivery, will be first reviewed. Finally, some examples of injectable hydrogels for the delivery of bioactive molecules in central nervous system will be reported, and the key features as well as the basic principles in designing multifunctional devices will be described.

Improved biocompatibility and efficient labeling of neural stem cells with poly(L-lysine)-coated maghemite nanoparticles

BACKGROUND

Cell tracking is a powerful tool to understand cellular migration, dynamics, homing and function of stem cell transplants. Nanoparticles represent possible stem cell tracers, but they differ in cellular uptake and side effects. Their properties can be modified by coating with different biocompatible polymers. To test if a coating polymer, poly(L-lysine), can improve the biocompatibility of nanoparticles applied to neural stem cells, poly(L-lysine)-coated maghemite nanoparticles were prepared and characterized. We evaluated their cellular uptake, the mechanism of internalization, cytotoxicity, viability and proliferation of neural stem cells, and compared them to the commercially available dextran-coated nanomag(®)-D-spio nanoparticles.

RESULTS

Light microscopy of Prussian blue staining revealed a concentration-dependent intracellular uptake of iron oxide in neural stem cells. The methyl thiazolyl tetrazolium assay and the calcein acetoxymethyl ester/propidium iodide assay demonstrated that poly(L-lysine)-coated maghemite nanoparticles scored better than nanomag(®)-D-spio in cell labeling efficiency, viability and proliferation of neural stem cells. Cytochalasine D blocked the cellular uptake of nanoparticles indicating an actin-dependent process, such as macropinocytosis, to be the internalization mechanism for both nanoparticle types. Finally, immunocytochemistry analysis of neural stem cells after treatment with poly(L-lysine)-coated maghemite and nanomag(®)-D-spio nanoparticles showed that they preserve their identity as neural stem cells and their potential to differentiate into all three major neural cell types (neurons, astrocytes and oligodendrocytes).

CONCLUSION

Improved biocompatibility and efficient cell labeling makes poly(L-lysine)-coated maghemite nanoparticles appropriate candidates for future neural stem cell in vivo tracking studies.

Monitoring/Imaging and Regenerative Agents for Enhancing Tissue Engineering Characterization and Therapies

The past three decades have seen numerous advances in tissue engineering and regenerative medicine (TERM) therapies. However, despite the successes there is still much to be done before TERM therapies become commonplace in clinic. One of the main obstacles is the lack of knowledge regarding complex tissue engineering processes. Imaging strategies, in conjunction with exogenous contrast agents, can aid in this endeavor by assessing in vivo therapeutic progress. The ability to uncover real-time treatment progress will help shed light on the complex tissue engineering processes and lead to development of improved, adaptive treatments. More importantly, the utilized exogenous contrast agents can double as therapeutic agents. Proper use of these Monitoring/Imaging and Regenerative Agents (MIRAs) can help increase TERM therapy successes and allow for clinical translation. While other fields have exploited similar particles for combining diagnostics and therapy, MIRA research is still in its beginning stages with much of the current research being focused on imaging or therapeutic applications, separately. Advancing MIRA research will have numerous impacts on achieving clinical translations of TERM therapies. Therefore, it is our goal to highlight current MIRA progress and suggest future research that can lead to effective TERM treatments.

Antioxidant and anti-inflammatory effects of intravenously injected adipose derived mesenchymal stem cells in dogs with acute spinal cord injury

Introduction

Mesenchymal stem cells can potentially be used in therapy for spinal cord injury (SCI). Methylprednisolone sodium succinate (MPSS) has been used as a scavenging agent in acute SCI treatment, but its use no longer recommended. This study aimed to identify ways to reduce the usage and risk of high doses of glucocorticoid steroids, and determine whether AD-MSCs could be used as an early alternative treatment modality for acute SCI.

Methods

Sixteen adult beagle dogs with SCI were assigned to four treatment groups: control, MPSS, AD-MSCs, and AD-MSCs + MPSS. Additionally, one dog was used to evaluate the distribution of AD-MSCs in the body after injection. AD-MSCs (1 × 10⁷ cells) were injected intravenously once a day for 3 days beginning at 6 hours post-SCI. MPSS was also injected intravenously according to the standard protocol for acute SCI. A revised Tarlov scale was used to evaluate hindlimb functional recovery. The levels of markers for oxidative metabolism (3-nitrotyrosine, 4-hydroxynonenal, and protein carbonyl) and inflammation (cyclooxygenase-2, interleukin-6, and tumor necrosis factor-α) were also measured.

Results

At 7 days post-treatment, hindlimb movement had improved in the AD-MSCs and AD-MSCs + MPSS groups; however, subjects in the groups treated with MPSS exhibited gastrointestinal hemorrhages. Hematoxylin and eosin staining revealed fewer hemorrhages and lesser microglial infiltration in the AD-MSCs group. The green fluorescent protein-expressing AD-MSCs were clearly detected in the lung, spleen, and injured spinal cord; however, these cells were not detected in the liver and un-injured spinal cord. Levels of 3-nitrotyrosine were decreased in the MPSS and AD-MSCs + MPSS groups; 4-hydroxynenonal and cyclooxygenase-2 levels were decreased in all treatment groups; and interleukin-6, tumor necrosis factor-α, and phosphorylated-signal transducer and activator transcription 3 levels were decreased in the AD-MSCs and AD-MSCs + MPSS groups.

Conclusion

Our results suggest that early intravenous injection of AD-MSCs after acute SCI may prevent further damage through enhancement of antioxidative and anti-inflammatory mechanisms, without inducing adverse effects. Additionally, this treatment could also be used as an alternative intravenous treatment modality for acute SCI.

g-force induced giant efficiency of nanoparticles internalization into living cells

Nanotechnology plays an increasingly important role in the biomedical arena. Iron oxide nanoparticles (IONPs)-labelled cells is one of the most promising approaches for a fast and reliable evaluation of grafted cells in both preclinical studies and clinical trials. Current procedures to label living cells with IONPs are based on direct incubation or physical approaches based on magnetic or electrical fields, which always display very low cellular uptake efficiencies. Here we show that centrifugation-mediated internalization (CMI) promotes a high uptake of IONPs in glioblastoma tumour cells, just in a few minutes, and via clathrin-independent endocytosis pathway. CMI results in controllable cellular uptake efficiencies at least three orders of magnitude larger than current procedures. Similar trends are found in human mesenchymal stem cells, thereby demonstrating the general feasibility of the methodology, which is easily transferable to any laboratory with great potential for the development of improved biomedical applications.

An effective strategy of magnetic stem cell delivery for spinal cord injury therapy

Spinal cord injury (SCI) is a condition that results in significant mortality and morbidity. Treatment of SCI utilizing stem cell transplantation represents a promising therapy. However, current conventional treatments are limited by inefficient delivery strategies of cells into the injured tissue. In this study, we designed a magnetic system and used it to accumulate stem cells labelled with superparamagnetic iron oxide nanoparticles (SPION) at a specific site of a SCI lesion. The loading of stem cells with engineered SPIONs that guarantees sufficient attractive magnetic forces was achieved. Further, the magnetic system allowed rapid guidance of the SPION-labelled cells precisely to the lesion location. Histological analysis of cell distribution throughout the cerebrospinal channel showed a good correlation with the calculated distribution of magnetic forces exerted onto the transplanted cells. The results suggest that focused targeting and fast delivery of stem cells can be achieved using the proposed non-invasive magnetic system. With future implementation the proposed targeting and delivery strategy bears advantages for the treatment of disease requiring fast stem cell transplantation.

Nanoparticle labeling of bone marrow-derived rat mesenchymal stem cells: their use in differentiation and tracking

Mesenchymal stem cells (MSCs) are promising candidates for cellular therapies due to their ability to migrate to damaged tissue without inducing immune reaction. Many techniques have been developed to trace MSCs and their differentiation efficacy; however, all of these methods have limitations. Conjugated polymer based water-dispersible nanoparticles (CPN) represent a new class of probes because they offer high brightness, improved photostability, high fluorescent quantum yield, and noncytotoxicity comparing to conventional dyes and quantum dots. We aimed to use this tool for tracing MSCs' fate in vitro and in vivo. MSC marker expression, survival, and differentiation capacity were assessed upon CPN treatment. Our results showed that after CPN labeling, MSC markers did not change and significant number of cells were found to be viable as revealed by MTT. Fluorescent signals were retained for 3 weeks after they were differentiated into osteocytes, adipocytes, and chondrocytes in vitro. We also showed that the labeled MSCs migrated to the site of injury and retained their labels in an in vivo liver regeneration model. The utilization of nanoparticle could be a promising tool for the tracking of MSCs in vivo and in vitro and therefore can be a useful tool to understand differentiation and homing mechanisms of MSCs.

Seeing stem cells at work in vivo

Stem cell based-therapies are novel therapeutic strategies that hold key for developing new treatments for diseases conditions with very few or no cures. Although there has been an increase in the number of clinical trials involving stem cell-based therapies in the last few years, the long-term risks and benefits of these therapies are still unknown. Detailed in vivo studies are needed to monitor the fate of transplanted cells, including their distribution, differentiation, and longevity over time. Advancements in non-invasive cellular imaging techniques to track engrafted cells in real-time present a powerful tool for determining the efficacy of stem cell-based therapies. In this review, we describe the latest approaches to stem cell labeling and tracking using different imaging modalities.

Rapid synthesis of water-dispersible superparamagnetic iron oxide nanoparticles by a microwave-assisted route for safe labeling of endothelial progenitor cells

We synthesize highly crystalline citrate-coated iron oxide superparamagnetic nanoparticles that are stable and readily dispersible in water by an extremely fast microwave-assisted route and investigate the uptake of magnetic nanoparticles by endothelial cells. Nanoparticles form large aggregates when added to complete endothelial cell medium. The size of the aggregates was controlled by adjusting the ionic strength of the medium. The internalization of nanoparticles into endothelial cells was then investigated by transmission electron microscopy, magnetometry and chemical analysis, together with cell viability assays. Interestingly, a sevenfold more efficient uptake was found for systems with larger nanoparticle aggregates, which also showed significantly higher magnetic resonance imaging effectiveness without compromising cell viability and functionality. We are thus presenting an example of a straightforward microwave synthesis of citrate-coated iron oxide nanoparticles for safe endothelial progenitor cell labeling and good magnetic resonance cell imaging with potential application for magnetic cell guidance and in vivo cell tracking.

Regenerative medicine for the treatment of spinal cord injury: more than just promises?

Spinal cord injury triggers a complex set of events that lead to tissue healing without the restoration of normal function due to the poor regenerative capacity of the spinal cord. Nevertheless, current knowledge about the intrinsic regenerative ability of central nervous system axons, when in a supportive environment, has made the prospect of treating spinal cord injury a reality. Among the range of strategies under investigation, cell-based therapies offer the most promising results, due to the multifactorial roles that these cells can fulfil. However, the best cell source is still a matter of debate, as are clinical issues that include the optimal cell dose as well as the timing and route of administration. In this context, the role of biomaterials is gaining importance. These can not only act as vehicles for the administered cells but also, in the case of chronic lesions, can be used to fill the permanent cyst, thus creating a more favourable and conducive environment for axonal regeneration in addition to serving as local delivery systems of therapeutic agents to improve the regenerative milieu. Some of the candidate molecules for the future are discussed in view of the knowledge derived from studying the mechanisms that facilitate the intrinsic regenerative capacity of central nervous system neurons. The future challenge for the multidisciplinary teams working in the field is to translate the knowledge acquired in basic research into effective combinatorial therapies to be applied in the clinic.

Hydrogel-based nanocomposites and mesenchymal stem cells: a promising synergistic strategy for neurodegenerative disorders therapy

Hydrogel-based materials are widely employed in the biomedical field. With regard to central nervous system (CNS) neurodegenerative disorders, the design of injectable nanocomposite hydrogels for in situ drug or cell release represents an interesting and minimally invasive solution that might play a key role in the development of successful treatments. In particular, biocompatible and biodegradable hydrogels can be designed as specific injectable tools and loaded with nanoparticles (NPs), to improve and to tailor their viscoelastic properties upon injection and release profile. An intriguing application is hydrogel loading with mesenchymal stem cells (MSCs) that are a very promising therapeutic tool for neurodegenerative or traumatic disorders of the CNS. This multidisciplinary review will focus on the basic concepts to design acellular and cell-loaded materials with specific and tunable rheological and functional properties. The use of hydrogel-based nanocomposites and mesenchymal stem cells as a synergistic strategy for nervous tissue applications will be then discussed.

Imaging challenges in biomaterials and tissue engineering

Biomaterials are employed in the fields of tissue engineering and regenerative medicine (TERM) in order to enhance the regeneration or replacement of tissue function and/or structure. The unique environments resulting from the presence of biomaterials, cells, and tissues result in distinct challenges in regards to monitoring and assessing the results of these interventions. Imaging technologies for three-dimensional (3D) analysis have been identified as a strategic priority in TERM research. Traditionally, histological and immunohistochemical techniques have been used to evaluate engineered tissues. However, these methods do not allow for an accurate volume assessment, are invasive, and do not provide information on functional status. Imaging techniques are needed that enable non-destructive, longitudinal, quantitative, and three-dimensional analysis of TERM strategies. This review focuses on evaluating the application of available imaging modalities for assessment of biomaterials and tissue in TERM applications. Included is a discussion of limitations of these techniques and identification of areas for further development.

Human conditionally immortalized neural stem cells improve locomotor function after spinal cord injury in the rat

Introduction

A growing number of studies have highlighted the potential of stem cell and more-differentiated neural cell transplantation as intriguing therapeutic approaches for neural repair after spinal cord injury (SCI).

Methods

A conditionally immortalized neural stem cell line derived from human fetal spinal cord tissue (SPC-01) was used to treat a balloon-induced SCI. SPC-01 cells were implanted into the lesion 1 week after SCI. To determine the feasibility of tracking transplanted stem cells, a portion of the SPC-01 cells was labeled with poly-L-lysine-coated superparamagnetic iron-oxide nanoparticles, and the animals grafted with labeled cells underwent magnetic resonance imaging. Functional recovery was evaluated by using the BBB and plantar tests, and lesion morphology, endogenous axonal sprouting and graft survival, and differentiation were analyzed. Quantitative polymerase chain reaction (qPCR) was used to evaluate the effect of transplanted SPC-01 cells on endogenous regenerative processes.

Results

Transplanted animals displayed significant motor and sensory improvement 2 months after SCI, when the cells robustly survived in the lesion and partially filled the lesion cavity. qPCR revealed the increased expression of rat and human neurotrophin and motor neuron genes. The grafted cells were immunohistologically positive for glial fibrillary acidic protein (GFAP); however, we found 25% of the cells to be positive for Nkx6.1, an early motor neuron marker. Spared white matter and the robust sprouting of growth-associated protein 43 (GAP43)⁺ axons were found in the host tissue. Four months after SCI, the grafted cells matured into Islet2⁺ and choline acetyltransferase (ChAT)⁺ neurons, and the graft was grown through with endogenous neurons. Grafted cells labeled with poly-L-lysine-coated superparamagnetic nanoparticles before transplantation were detected in the lesion on T₂-weighted images as hypointense spots that correlated with histologic staining for iron and the human mitochondrial marker MTCO2.

Conclusions

The transplantation of SPC-01 cells produced significant early functional improvement after SCI, suggesting an early neurotrophic action associated with long-term restoration of the host tissue, making the cells a promising candidate for future cell therapy in patients with SCI.

Baculovirus as an ideal radionuclide reporter gene vector: a new strategy for monitoring the fate of human stem cells in vivo

PURPOSE

Radionuclide reporter gene imaging holds promise for non-invasive monitoring of transplanted stem cells. Thus, the feasibility of utilizing recombinant baculoviruses carrying the sodium iodide symporter (NIS) reporter gene in monitoring stem cell therapy by radionuclide imaging was explored in this study.

METHODS

Recombinant baculoviruses carrying NIS and green fluorescent protein (GFP) reporter genes (Bac-NIS and Bac-GFP) were constructed and used to infect human induced pluripotent stem cells (hiPSCs), human embryonic stem cells (hESCs) and human umbilical cord blood mesenchymal stem cells (hUCB-MSCs). Infection efficiency, total fluorescence intensity and duration of transgene expression were determined by flow cytometry. Cytotoxicity/proliferative effects of baculovirus on hUCB-MSCs were assessed using CCK-8 assays. ¹²⁵I uptake and perchlorate inhibition assays were performed on Bac-NIS-infected hUCB-MSCs. Radionuclide imaging of mice transplanted with Bac-NIS-infected hUCB-MSCs was performed by NanoSPECT/CT imaging.

RESULTS

Infection efficiencies of recombinant baculovirus in hESCs, hiPSCs and hUCB-MSCs increased with increasing MOIs (27.3%, 35.8% and 95.6%, respectively, at MOI = 800). Almost no cytotoxicity and only slight effects on hUCB-MSCs proliferation were observed. Obvious GFP expression (40.6%) remained at 8 days post-infection. The radioiodide was functionally accumulated by NIS gene products and specifically inhibited by perchlorate (ClO₄⁻). Radioiodide uptake, peaking at 30 min and gradually decreasing over time, significantly correlated with hUCB-MSCs cell number (R² = 0.994). Finally, radionuclide imaging showed Bac-NIS-infected hUCB-MSCs effectively accumulated radioiodide in vivo, which gradually weakened over time.

CONCLUSION

Baculovirus as transgenic vector of radionuclide reporter gene imaging technology is a promising strategy for monitoring stem cell transplantation therapy.

Stem cells in regenerative medicine

BACKGROUND

A number of cardiovascular, neurological, musculoskeletal and other diseases have a limited capacity for repair and only a modest progress has been made in treatment of brain diseases. The discovery of stem cells has opened new possibilities for the treatment of these maladies, and cell therapy now stands at the cutting-edge of modern regenerative medicine and tissue engineering. Experimental data and the first clinical trials employing stem cells have shown their broad therapeutic potential and have brought hope to patients suffering from devastating pathologies of different organs and systems.

AIMS

Here, we briefly review the main achievements and trends in cell-based therapy, with an emphasis on the main types of stem cells: embryonic, mesenchymal stromal and induced pluripotent cells.

DISCUSSION

Many questions regarding the application of stem cells remain unanswered, particularly tumorigenicity, immune rejection and danger of gene manipulation. Currently, only MSC seems to be safe and might be considered to be a leading candidate for human application to treat pathologies that affect the cardiovascular, neurological and musculoskeletal systems.

Stem cells in regenerative medicine

BACKGROUND

A number of cardiovascular, neurological, musculoskeletal and other diseases have a limited capacity for repair and only a modest progress has been made in treatment of brain diseases. The discovery of stem cells has opened new possibilities for the treatment of these maladies, and cell therapy now stands at the cutting-edge of modern regenerative medicine and tissue engineering. Experimental data and the first clinical trials employing stem cells have shown their broad therapeutic potential and have brought hope to patients suffering from devastating pathologies of different organs and systems.

AIMS

Here, we briefly review the main achievements and trends in cell-based therapy, with an emphasis on the main types of stem cells: embryonic, mesenchymal stromal and induced pluripotent cells.

DISCUSSION

Many questions regarding the application of stem cells remain unanswered, particularly tumorigenicity, immune rejection and danger of gene manipulation. Currently, only MSC seems to be safe and might be considered to be a leading candidate for human application to treat pathologies that affect the cardiovascular, neurological and musculoskeletal systems.

Glia: an emerging target for neurological disease therapy

Therapeutic strategies using stem cells for treating neurological diseases are receiving more attention as the scientific community appreciates cell-autonomous contributions to several diseases of the central nervous system. The transplantation of stem cells from various sources is now being employed for both neuronal and glial replacement. This review provides an assessment of glial contributions to some of the central nervous system diseases and the advancements in cellular replacement approaches. The rationale for glial replacement in individual diseases and the potential hurdles for cell-replacement strategies are also emphasized. The significant progress in the field of stem cell biology with the advent of tools such as induced pluripotent stem cells and imaging techniques holds promise for the clinical application of cell therapeutics.

Nano-regenerative medicine towards clinical outcome of stem cell and tissue engineering in humans

Nanotechnology is a fast growing area of research that aims to create nanomaterials or nanostructures development in stem cell and tissue-based therapies. Concepts and discoveries from the fields of bio nano research provide exciting opportunities of using stem cells for regeneration of tissues and organs. The application of nanotechnology to stem-cell biology would be able to address the challenges of disease therapeutics. This review covers the potential of nanotechnology approaches towards regenerative medicine. Furthermore, it focuses on current aspects of stem- and tissue-cell engineering. The magnetic nanoparticles-based applications in stem-cell research open new frontiers in cell and tissue engineering.

Stem cell therapy for neonatal brain injury: perspectives and challenges

Cerebral palsy is a major health problem caused by brain damage during pregnancy, delivery, or the immediate postnatal period. Perinatal stroke, intraventricular hemorrhage, and asphyxia are the most common causes of neonatal brain damage. Periventricular white matter damage (periventricular leukomalacia) is the predominant form in premature infants and the most common antecedent of cerebral palsy. Stem cell treatment has proven effective in restoring injured organs and tissues in animal models. The potential of stem cells for self-renewal and differentiation translates into substantial neuroprotection and neuroregeneration in the animal brain, with minimal risks of rejection and side effects. Stem cell treatments described to date have used neural stem cells, embryonic stem cells, mesenchymal stem cells, umbilical cord stem cells, and induced pluripotent stem cells. Most of these treatments are still experimental. In this review, we focus on the efficacy of stem cell therapy in animal models of cerebral palsy, and discuss potential implications for current and future clinical trials.

Harnessing the therapeutic potential of mesenchymal stem cells in multiple sclerosis

Phase I clinical trials exploring the use of autologous mesenchymal stem cell (MSC) therapy for the treatment of multiple sclerosis (MS) have begun in a number of centers across the world. MS is a complex and chronic immune-mediated and neurodegenerative disease influenced by genetic susceptibility and environmental risk factors. The ideal treatment for MS would involve both attenuation of detrimental inflammatory responses, and induction of a degree of tissue protection/regeneration within the CNS. Preclinical studies have demonstrated that both human-derived and murine-derived MSCs are able to improve outcomes in the animal model of MS, experimental autoimmune encephalomyelitis. How MSCs ameliorate experimental autoimmune encephalomyelitis is being intensely investigated. One of the major mechanisms of action of MSC therapy is to inhibit various components of the immune system that contribute to tissue destruction. Emerging evidence now supports the idea that MSCs can access the CNS where they can provide protection against tissue damage, and may facilitate tissue regeneration through the production of growth factors. The prospect of cell-based therapy using MSCs has several advantages, including the relative ease with which they can be extracted from autologous bone marrow or adipose tissue and expanded in vitro to reach the purity and numbers required for transplantation, and the fact that MSC therapy has already been used in other human disease settings, such as graft-versus-host and cardiac disease, with initial reports indicating a good safety profile. This article will focus on the theoretical and practical issues relevant to considerations of MSC therapy in the context of MS.

Dilemmas in the reliable estimation of the in-vitro cell viability in magnetic nanoparticle engineering: which tests and what protocols?

Magnetic nanoparticles [MNPs] made from iron oxides have many applications in biomedicine. Full understanding of the interactions between MNPs and mammalian cells is a critical issue for their applications. In this study, MNPs were coated with poly(ethylenimine) [MNP-PEI] and poly(ethylene glycol) [MNP-PEI-PEG] to provide a subtle difference in their surface charge and their cytotoxicity which were analysed by three standard cell viability assays: 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium [MTS], CellTiter-Blue and CellTiter-Glo (Promega, Southampton, UK) in SH-SY5Y and RAW 264.7 cells The data were validated by traditional trypan blue exclusion. In comparison to trypan blue manual counting, the MTS and Titer-Blue assays appeared to have consistently overestimated the viability. The Titer-Glo also experienced a small overestimation. We hypothesise that interactions were occurring between the assay systems and the nanoparticles, resulting in incorrect cell viability evaluation. To further understand the cytotoxic effect of the nanoparticles on these cells, reactive oxygen species production, lipid peroxidation and cell membrane integrity were investigated. After pegylation, the MNP-PEI-PEG possessed a lower positive surface charge and exhibited much improved biocompatibility compared to MNP-PEI, as demonstrated not only by a higher cell viability, but also by a markedly reduced oxidative stress and cell membrane damage. These findings highlight the importance of assay selection and of dissection of different cellular responses in in-vitro characterisation of nanostructures.

Labeling stem cells with superparamagnetic iron oxide nanoparticles: analysis of the labeling efficacy by microscopy and magnetic resonance imaging

Stem cell therapy has emerged as a potential therapeutic option for cell death-related heart diseases. Application of non-invasive cell tracking approaches is necessary to determine tissue distribution and lifetime of stem cells following their injection and will likely provide knowledge about poorly understood stem cells mechanisms of tissue repair. Magnetic resonance imaging (MRI) is a potentially excellent tool for high-resolution visualization of the fate of cells after transplantation and for evaluation of therapeutic strategies. The application of MRI for in vivo cell tracking requires contrast agents to achieve efficient cell labeling without causing any toxic cellular effects or eliciting any other side effects. For these reasons clinically approved contrast agents (e.g., ferumoxides) and incorporation facilitators (e.g., protamine) are currently the preferred materials for cell labeling and tracking. Here we describe how to use superparamagnetic iron oxide nanoparticles to label cells and to monitor cell fate in several disease models.

Labeling human embryonic stem-cell-derived cardiomyocytes for tracking with MR imaging

BACKGROUND

Human embryonic stem cells (hESC) can generate cardiomyocytes (CM), which offer promising treatments for cardiomyopathies in children. However, challenges for clinical translation result from loss of transplanted cell from target sites and high cell death. An imaging technique that noninvasively and repetitively monitors transplanted hESC-CM could guide improvements in transplantation techniques and advance therapies.

OBJECTIVE

To develop a clinically applicable labeling technique for hESC-CM with FDA-approved superparamagnetic iron oxide nanoparticles (SPIO) by examining labeling before and after CM differentiation.

MATERIALS AND METHODS

Triplicates of hESC were labeled by simple incubation with 50 μg/ml of ferumoxides before or after differentiation into CM, then imaged on a 7T MR scanner using a T2-weighted multi-echo spin-echo sequence. Viability, iron uptake and T2-relaxation times were compared between groups using t-tests.

RESULTS

hESC-CM labeled before differentiation demonstrated significant MR effects, iron uptake and preserved function. hESC-CM labeled after differentiation showed no significant iron uptake or change in MR signal (P < 0.05). Morphology, differentiation and viability were consistent between experimental groups.

CONCLUSION

hESC-CM should be labeled prior to CM differentiation to achieve a significant MR signal. This technique permits monitoring delivery and engraftment of hESC-CM for potential advancements of stem cell-based therapies in the reconstitution of damaged myocardium.

MRI stem cell tracking for therapy in experimental cerebral ischemia

Magnetic resonance has an established role in investigations on the evolution of stroke and the assessment of therapeutic strategies in experimental animals. Here we show that the technique has also an important place for the study of stem cell-mediated regenerative therapies after stroke. We review the literature by bridging from the methodological aspects of stem cell labeling via grafting and monitoring of cell dynamics after implantation into the brain all the way to MRI's role in analyzing the stem cell-mediated functional improvement. Thus, we have aimed at a view combining the focus on the monitoring of the cell activities with the aspect of lesion evolution while including also the essence of a potential functional improvement by the implantation of stem cells following stroke.

The use of cellular magnetic resonance imaging to track the fate of iron-labeled multipotent stromal cells after direct transplantation in a mouse model of spinal cord injury

PURPOSE

The objective of this study was to track the fate of iron-labeled, multipotent stromal cells (MSC) after their direct transplantation into mice with spinal cord injuries using magnetic resonance imaging (MRI).

PROCEDURES

Mice with spinal cord injuries received a direct transplant of (1) live MSC labeled with micron-sized iron oxide particles (MPIO); (2) dead, MPIO-labeled MSC; (3) unlabeled MSC; or (4) free MPIO and were imaged at 3 T for 6 weeks after transplantation.

RESULTS

Live, iron-labeled MSC appeared as a well-defined region of signal loss in the mouse spinal cord at the site of transplant. However, the MR appearance of dead, iron-labeled MSC and free iron particles was similar and persisted for the 6 weeks of the study.

CONCLUSIONS

Iron-labeled stem cells can be detected and monitored in vivo after direct transplantation into the injured spinal cord of mice. However, the fate of the iron label is not clear. Our investigation indicates that caution should be taken when interpreting MR images after direct transplantation of iron-labeled cells.

Early Immunomodulation by Intravenously Transplanted Mesenchymal Stem Cells Promotes Functional Recovery in Spinal Cord Injured Rats

Although intravenous administration of mesenchymal stem cells (MSCs) can enhance functional recovery after spinal cord injury (SCI), the underlying mechanisms have to be elucidated. In this study, we explored the mechanisms for functional recovery in SCI rats after intravenous transplantation of MSCs derived from human umbilical cord blood. Sprague-Dawley rats were randomly assigned to receive either MSCs (1 × 10(6) cells/0.5 ml) or PBS into the tail vein immediately after SCI. They were then evaluated by the Basso-Beattie-Bresnahan (BBB) locomotor rating scale weekly for 8 weeks and by somatosensory evoked potentials (SSEPs) 8 weeks after transplantation. MSC-treated rats showed a modest but significant improvement in BBB scores and latencies of SSEPs, compared with PBS controls. When human-specific Alu element was measured in the spinal cord, it was detected only 1 h after transplantation, suggesting transient engraftment of MSCs. Inflammatory cytokines were also determined using RT-PCR or Western blot in spinal cord extracts. In MSC-treated rats, the level of proinflammatory cytokine IL-1β was decreased, but that of anti-inflammatory cytokine IL-10 was increased. MSCs also immediately suppressed IL-6 at 1 h posttransplantation. However, the response of IL-6, which has an immunoregulatory role, was increased 1-3 days after transplantation. In addition, we quantified microglia/macrophage stained with Iba-1 around the damaged spinal cord using immunohistochemistry. A proportion of activated microglia and macrophages in total Iba-1(+) cells was significantly decreased in MSC-treated rats, compared with PBS controls. These results suggest that early immunomodulation by intravenously transplanted MSCs is a potential underlying mechanism for functional recovery after SCI.

Identification of chemoattractive factors involved in the migration of bone marrow-derived mesenchymal stem cells to brain lesions caused by prions

Bone marrow-derived mesenchymal stem cells (MSCs) have been reported to migrate to brain lesions of neurodegenerative diseases; however, the precise mechanisms by which MSCs migrate remain to be elucidated. In this study, we carried out an in vitro migration assay to investigate the chemoattractive factors for MSCs in the brains of prion-infected mice. The migration of immortalized human MSCs (hMSCs) was reduced by their pretreatment with antibodies against the chemokine receptors, CCR3, CCR5, CXCR3, and CXCR4 and by pretreatment of brain extracts of prion-infected mice with antibodies against the corresponding ligands, suggesting the involvement of these receptors, and their ligands in the migration of hMSCs. In agreement with the results of an in vitro migration assay, hMSCs in the corpus callosum, which are considered to be migrating from the transplanted area toward brain lesions of prion-infected mice, expressed CCR3, CCR5, CXCR3, and CXCR4. The combined in vitro and in vivo analyses suggest that CCR3, CCR5, CXCR3, and CXCR4, and their corresponding ligands are involved in the migration of hMSCs to the brain lesions caused by prion propagation. In addition, hMSCs that had migrated to the right hippocampus of prion-infected mice expressed CCR1, CX3CR1, and CXCR4, implying the involvement of these chemokine receptors in hMSC functions after chemotactic migration. Further elucidation of the mechanisms that underlie the migration of MSCs may provide useful information regarding application of MSCs to the treatment of prion diseases.

Polyamidoamine dendrimer-conjugated quantum dots for efficient labeling of primary cultured mesenchymal stem cells

Monitoring of cells in vivo after transplantation could supply important information for determining the efficacy of stem cell therapy. The use of quantum dots (QDs) has several advantages for in vivo imaging, such as remarkable resistance to photo bleaching, high fluorescence efficiency, and size-tunable emission. After they are taken up by cells via endocytosis, QDs lose their fluorescence intensity in endosomes/lysosomes at low pH because the intensity cannot survive under acidic conditions. Moreover, the amount of QD uptake by mesenchymal stem cells (MSCs) is extremely small. Therefore, for effective labeling of MSCs and long observation of MSCs labeled by QDs in vivo, it is essential both to increase cellular uptake of QDs and to promote endosomal escape into the cytosol. The polyamidoamine (PAMAM) dendrimer had plenty of cationic charge, which promoted cellular uptake though electrostatic interactions, and a "buffering capacity," which enhanced endosomal escape into the cytosol. In this study, QDs were modified with PAMAM dendrimer for the efficient labeling of MSCs by QDs. The uptake efficiency and cytosolic distribution of QDs in primary cultured MSCs were increased by the modification of the PAMAM dendrimer. The fluorescence intensity in MSCs labeled by PAMAM dendrimer-conjugated QDs lasted for a longer time in harvested culture plates or in cell-transplanted mice than that in MSCs labeled by non-conjugated QDs.

Ambidextrous magnetic nanovectors for synchronous gene transfection and labeling of human MSCs

The synchronization of gene expression and cell trafficking in transfected stem cells is crucial for augmentation of stem cell functions (differentiation and neurotropic factor secretion) and real time in vivo monitoring. We report a magnetic nanoparticle-based gene delivery system that can ensure simultaneous gene delivery and in vivo cell trafficking by high resolution MR imaging. The polar aprotic solvent soluble MnFe₂O₄ nanoparticles were enveloped using cationic polymers (branched polyethyleneimine, PEI) by the solvent shifting method for a gene loading. Using our magnetic nanovector system (PEI-coated MnFe₂O₄ nanoparticles), thus, we synchronized stem cell migration and its gene expression in a rat stroke model.

Optimized labeling of bone marrow mesenchymal cells with superparamagnetic iron oxide nanoparticles and in vivo visualization by magnetic resonance imaging

BACKGROUND

Stem cell therapy has emerged as a promising addition to traditional treatments for a number of diseases. However, harnessing the therapeutic potential of stem cells requires an understanding of their fate in vivo. Non-invasive cell tracking can provide knowledge about mechanisms responsible for functional improvement of host tissue. Superparamagnetic iron oxide nanoparticles (SPIONs) have been used to label and visualize various cell types with magnetic resonance imaging (MRI). In this study we performed experiments designed to investigate the biological properties, including proliferation, viability and differentiation capacity of mesenchymal cells (MSCs) labeled with clinically approved SPIONs.

RESULTS

Rat and mouse MSCs were isolated, cultured, and incubated with dextran-covered SPIONs (ferumoxide) alone or with poly-L-lysine (PLL) or protamine chlorhydrate for 4 or 24 hrs. Labeling efficiency was evaluated by dextran immunocytochemistry and MRI. Cell proliferation and viability were evaluated in vitro with Ki67 immunocytochemistry and live/dead assays. Ferumoxide-labeled MSCs could be induced to differentiate to adipocytes, osteocytes and chondrocytes. We analyzed ferumoxide retention in MSCs with or without mitomycin C pretreatment. Approximately 95% MSCs were labeled when incubated with ferumoxide for 4 or 24 hrs in the presence of PLL or protamine, whereas labeling of MSCs incubated with ferumoxide alone was poor. Proliferative capacity was maintained in MSCs incubated with ferumoxide and PLL for 4 hrs, however, after 24 hrs it was reduced. MSCs incubated with ferumoxide and protamine were efficiently visualized by MRI; they maintained proliferation and viability for up to 7 days and remained competent to differentiate. After 21 days MSCs pretreated with mitomycin C still showed a large number of ferumoxide-labeled cells.

CONCLUSIONS

The efficient and long lasting uptake and retention of SPIONs by MSCs using a protocol employing ferumoxide and protamine may be applicable to patients, since both ferumoxides and protamine are approved for human use.

HPMA-RGD hydrogels seeded with mesenchymal stem cells improve functional outcome in chronic spinal cord injury

Chronic spinal cord injury (SCI) is characterized by tissue loss and a stable functional deficit. While several experimental therapies have proven to be partly successful for the treatment of acute SCI, treatment of chronic SCI is still challenging. We studied whether we can bridge a chronic spinal cord lesion by implantation of our newly developed hydrogel based on 2-hydroxypropyl methacrylamide, either alone or seeded with mesenchymal stem cells (MSCs), and whether this treatment leads to functional improvement. A balloon-induced compression lesion was performed in adult 2-month-old male Wistar rats. Five weeks after injury, HPMA-RGD hydrogels [N-(2-hydroxypropyl)-methacrylamide with attached amino acid sequences--Arg-Gly-Asp] were implanted into the lesion, either with or without seeded MSCs. Animals with chronic SCI served as controls. The animals were behaviorally tested using the Basso–Beattie-Breshnahan (BBB) (motor) and plantar (sensory) tests once a week for 6 months. Behavioral analysis showed a statistically significant improvement in rats with combined treatment, hydrogel and MSCs, compared with the control group (P < 0.05). Although a tendency toward improvement was found in rats treated with hydrogel only, this was not significant. Subsequently, the animals were sacrificed 6 months after SCI, and the spinal cord lesions evaluated histologically. The combined therapy (hydrogel with MSCs) prevented tissue atrophy (P < 0.05), and the hydrogels were infiltrated with axons myelinated with Schwann cells. Blood vessels and astrocytes also grew inside the implant. MSCs were present in the hydrogels even 5 months after implantation. We conclude that 5 weeks after injury, HPMA-RGD hydrogels seeded with MSCs can successfully bridge a spinal cord cavity and provide a scaffold for tissue regeneration. This treatment leads to functional improvement even in chronic SCI.

Experimental reconstruction of the injured spinal cord

Injury to the spinal cord, with its pathological sequelae, results in a permanent neurological deficit. With currently available tools at hand, there is very little that clinicians can do to treat such a condition with the view of helping patients with spinal cord injury (SCI). On the other hand, in the last 20 years experimental research has brought new insights into the pathophysiology of spinal cord injury; we can divide the time course into 3 phases: primary injury (the time of traumatic impact and the period immediately afterwards), the secondary phase (cell death, inflammation, ischemia), and the chronic phase (scarring, demyelination, cyst formation). Increased knowledge about the pathophysiology of SCI can stimulate the development of new therapeutic modalities and approaches, which may be feasible in the future in clinical practice. Some of the most promising experimental therapies include: neurotrophic factors, enzymes and antibodies against inhibitory molecules (such as Nogo), activated macrophages, stem cells and bridging scaffolds. Their common goal is to reconstitute the damaged tissue in order to recover the lost function. In the current review, we focus on some of the recent developments in experimental SCI research.

Superparamagnetic iron oxide nanoparticles (SPIONs): development, surface modification and applications in chemotherapy

At present, nanoparticles are used for various biomedical applications where they facilitate laboratory diagnostics and therapeutics. More specifically for drug delivery purposes, the use of nanoparticles is attracting increasing attention due to their unique capabilities and their negligible side effects not only in cancer therapy but also in the treatment of other ailments. Among all types of nanoparticles, biocompatible superparamagnetic iron oxide nanoparticles (SPIONs) with proper surface architecture and conjugated targeting ligands/proteins have attracted a great deal of attention for drug delivery applications. This review covers recent advances in the development of SPIONs together with their possibilities and limitations from fabrication to application in drug delivery. In addition, the state-of-the-art synthetic routes and surface modification of desired SPIONs for drug delivery purposes are described.

Long-term magnetic resonance imaging of stem cells in neonatal ischemic injury

OBJECTIVE

Quantitative magnetic resonance imaging (MRI) can serially and noninvasively assess the degree of injury in rat pup models of hypoxic ischemic injury (HII). It can also noninvasively monitor stem cell migration following iron oxide prelabeling. Reports have shown that neural stem cells (NSCs) may help mediate neuroprotection or stimulate neuroreparative responses in adult and neonatal models of ischemic injury. We investigated the ability of high-field MRI to monitor and noninvasively quantify the migration, proliferation, and location of iron oxide-labeled NSCs over very long time periods (58 weeks) in real time while contemporaneously correlating this activity with the evolving severity and extent of neural damage.

METHODS

Labeled clonal murine NSCs (mNSCs) were implanted 3 days after unilateral HII in 10-day-old rat pups into the contralateral striatum or ventricle. We developed methods for objectively quantifying key aspects of dynamic NSC behavior (eg, viability; extent, and speed of migration; degree of proliferation; extent of integration into host parenchyma). MRI images were validated with histological and immunohistochemical assessments.

RESULTS

mNSCs rapidly migrated (100 μm/day) to the lesion site. Chains of migrating NSCs were observed in the corpus callosum. In pups subjected to HII, though not in intact control animals, we observed a 273% increase in the MR-derived volume of mNSCs 4 weeks after implantation (correlating with the known proliferative behavior of endogenous and exogenous NSCs) that slowly declined over the 58-week time course, with no adverse consequences. Large numbers of now quiescent mNSCs remained at the site of injury, many retaining their iron oxide label.

INTERPRETATION

Our studies demonstrate that MRI can simultaneously monitor evolving neonatal cerebral injury as well as NSC migration and location. Most importantly, it can noninvasively monitor proliferation dynamically for prolonged time periods. To be able to pursue clinical trials in newborns using stem cell therapies it is axiomatic that safety be insured through the long-term real time monitoring of cell fate and activity, particularly with regard to observing unanticipated risks to the developing brain. This study supports the feasibility of reliably using MRI for this purpose.

Concise review: Nanoparticles and cellular carriers-allies in cancer imaging and cellular gene therapy?

Ineffective treatment and poor patient management continue to plague the arena of clinical oncology. The crucial issues include inadequate treatment efficacy due to ineffective targeting of cancer deposits, systemic toxicities, suboptimal cancer detection and disease monitoring. This has led to the quest for clinically relevant, innovative multifaceted solutions such as development of targeted and traceable therapies. Mesenchymal stem cells (MSCs) have the intrinsic ability to "home" to growing tumors and are hypoimmunogenic. Therefore, these can be used as (a) "Trojan Horses" to deliver gene therapy directly into the tumors and (b) carriers of nanoparticles to allow cell tracking and simultaneous cancer detection. The camouflage of MSC carriers can potentially tackle the issues of safety, vector, and/or transgene immunogenicity as well as nanoparticle clearance and toxicity. The versatility of the nanotechnology platform could allow cellular tracking using single or multimodal imaging modalities. Toward that end, noninvasive magnetic resonance imaging (MRI) is fast becoming a clinical favorite, though there is scope for improvement in its accuracy and sensitivity. In that, use of superparamagnetic iron-oxide nanoparticles (SPION) as MRI contrast enhancers may be the best option for tracking therapeutic MSC. The prospects and consequences of synergistic approaches using MSC carriers, gene therapy, and SPION in developing cancer diagnostics and therapeutics are discussed.