Cell tracking technologies for acute ischemic brain injury

Accomplishments and challenges in stem cell imaging in vivo

Stem cell therapies have demonstrated promising preclinical results, but very few applications have reached the clinic owing to safety and efficacy concerns. Translation would benefit greatly if stem cell survival, distribution and function could be assessed in vivo post-transplantation, particularly in patients. Advances in molecular imaging have led to extraordinary progress, with several strategies being deployed to understand the fate of stem cells in vivo using magnetic resonance, scintigraphy, PET, ultrasound and optical imaging. Here, we review the recent advances, challenges and future perspectives and opportunities in stem cell tracking and functional assessment, as well as the advantages and challenges of each imaging approach.

Metallothionein I as a direct link between therapeutic hematopoietic stem/progenitor cells and cerebral protection in stroke

Stroke continues to be a leading cause of death and disability worldwide, yet effective treatments are lacking. Previous studies have indicated that stem-cell transplantation could be an effective treatment. However, little is known about the direct impact of transplanted cells on injured brain tissue. We wanted to help fill this knowledge gap and investigated effects of hematopoietic stem/progenitor cells (HSPCs) on the cerebral microcirculation after ischemia-reperfusion injury (I/RI). Treatment of HSPCs in I/RI for up to 2 wk after cerebral I/RI led to decreased mortality rate, decreased infarct volume, improved functional outcome, reduced microglial activation, and reduced cerebral leukocyte adhesion. Confocal microscopy and fluorescence-activated cell sorting analyses showed transplanted HSPCs emigrate preferentially into ischemic cortex brain parenchyma. We isolated migrated HSPCs from the brain; using RNA sequencing to investigate the transcriptome, we found metallothionein (MT, particularly MT-I) transcripts were dramatically up-regulated. Finally, to confirm the significance of MT, we exogenously administered MT-I after cerebral I/RI and found that it produced neuroprotection in a manner similar to HSPC treatment. These findings provide novel evidence that the mechanism through which HSPCs promote repair after stroke maybe via direct action of HSPC-derived MT-I and could therefore be exploited as a useful therapeutic strategy for stroke.-Smith, H. K., Omura, S., Vital, S. A., Becker, F., Senchenkova, E. Y., Kaur, G., Tsunoda, I., Peirce, S. M., Gavins, F. N. E. Metallothionein I as a direct link between therapeutic hematopoietic stem/progenitor cells and cerebral protection in stroke.

Tracking stem cells with superparamagnetic iron oxide nanoparticles: perspectives and considerations

Superparamagnetic iron oxide nanoparticles (SPIONs) have been used for diagnoses in biomedical applications, due to their unique properties and their apparent safety for humans. In general, SPIONs do not seem to produce cell damage, although their long-term in vivo effects continue to be investigated. The possibility of efficiently labeling cells with these magnetic nanoparticles has stimulated their use to noninvasively track cells by magnetic resonance imaging after transplantation. SPIONs are attracting increasing attention and are one of the preferred methods for cell labeling and tracking in preclinical and clinical studies. For clinical protocol approval of magnetic-labeled cell tracking, it is essential to expand our knowledge of the time course of SPIONs after cell incorporation and transplantation. This review focuses on the recent advances in tracking SPION-labeled stem cells, analyzing the possibilities and limitations of their use, not only focusing on myocardial infarction but also discussing other models.

Cell therapies administered in the chronic phase after stroke: a meta-analysis examining safety and efficacy

Aim: To assess the safety and efficacy of cell therapies for chronic stroke. Methodology: Five databases were searched for treatments administered >90 days post-stroke. Reporting quality, adherence to research guidelines, treatment safety (risk ratios/pooled incidence rates) and neurological/functional efficacy (Hedge’s g) were all evaluated. Results: Twenty-three studies examined 17 treatments. Reporting quality scores were medium to high, but adherence to recommended guidelines was lower. Three treatments resulted in serious adverse events; four improved outcomes more than standard care. However, many studies were under-powered and individual patients varied in their response to some treatments. Conclusion: Preliminary findings suggest that some cell therapies may be relatively safe and effective, but larger double-blinded placebo-controlled studies are needed to establish the long-term risks and benefits.

Erythropoietin Pretreatment of Transplanted Endothelial Colony-Forming Cells Enhances Recovery in a Cerebral Ischemia Model by Increasing Their Homing Ability: A SPECT/CT Study

Endothelial colony-forming cells (ECFCs) are promising candidates for cell therapy of ischemic diseases, as less than 10% of patients with an ischemic stroke are eligible for thrombolysis. We previously reported that erythropoietin priming of ECFCs increased their in vitro and in vivo angiogenic properties in mice with hindlimb ischemia. The present study used SPECT/CT to evaluate whether priming of ECFCs with erythropoietin could enhance their homing to the ischemic site after transient middle cerebral artery occlusion (MCAO) followed by reperfusion in rats and potentiate their protective or regenerative effect on blood-brain barrier (BBB) disruption, cerebral apoptosis, and cerebral blood flow (CBF).

METHODS

Rats underwent a 1-h MCAO followed by reperfusion and then 1 d after MCAO received an intravenous injection of either PBS (control, n = 10), PBS-primed ECFCs (ECFC_PBS, n = 13), or erythropoietin-primed ECFCs (ECFC_EPO, n = 10). ECFC homing and the effect on BBB disruption, cerebral apoptosis, and CBF were evaluated by SPECT/CT up to 14 d after MCAO. The results were expressed as median ± interquartile range for ipsilateral-to-contralateral ratio of the activity in middle cerebral artery-vascularized territories in each hemisphere. Histologic evaluation of neuronal survival and astrocytic proliferation was performed on day 14.

RESULTS

Erythropoietin priming increased homing of ECFCs to the ischemic hemisphere (ECFC_PBS, 111.0% ± 16.0%; ECFC_EPO, 146.5% ± 13.3%). BBB disruption was significantly reduced (control, 387% ± 153%; ECFC_PBS, 151% ± 46% [P < 0.05]; ECFC_EPO, 112% ± 9% [P < 0.001]) and correlated negatively with ECFC homing (Pearson r = -0.6930, P = 0.0002). Cerebral apoptosis was significantly reduced (control, 161% ± 10%; ECFC_PBS, 141% ± 9% [P < 0.05]; ECFC_EPO,118% ± 5% [P < 0.001]) and correlated negatively with ECFC homing (r = -0.7251, P < 0.0001). CBF was significantly restored with ECFCs and almost totally so with erythropoietin priming (control, 72% ± 2%; ECFC_PBS, 90% ± 4% [P < 0.01]; ECFC_EPO, 99% ± 4% [P < 0.001]) and correlated positively with ECFC homing (r = 0.7348, P < 0.0001). Immunoblocking against the CD146 receptor on ECFCs highlighted its notable role in ECFC homing with erythropoietin priming (ECFC_EPO, 147% ± 14%, n = 4; ECFC_EPO with antibody against CD146, 101% ± 12%, n = 4 [P < 0.05]).

CONCLUSION

Priming with erythropoietin before cell transplantation is an efficient strategy to amplify the migratory and engraftment capacities of ECFCs and their beneficial impact on BBB disruption, apoptosis, and CBF.

Safety and efficacy of cell therapies administered in the acute and subacute stages after stroke: a meta-analysis

AIMS

To evaluate the safety and efficacy of cell therapies administered acutely/sub-acutely after stroke.

METHODS

Five databases were searched for studies examining the safety/efficacy of cell therapies administered ≤90 days post-stroke. Reporting quality and adherence to research guidelines were evaluated. Safety and efficacy were assessed using risk ratios/pooled incidence rates and Hedge's g, respectively.

RESULTS

11 therapies (Nstudies= 28) were trialed: reporting quality was high, but adherence to guidelines low. Serious adverse events were observed following five treatments; six improved outcomes. There was a trend toward larger treatment effects in non-blinded studies, younger participants, and higher dosages.

CONCLUSION

Although a number of therapies appear effective, many studies did not control for normal recovery (standard-care). Long-term safety also needs to be established.

Bioluminescence imaging of transplanted human endothelial colony-forming cells in an ischemic mouse model

Ischemic strokes are devastating events responsible for high mortality and morbidity worldwide each year. Endothelial colony-forming cell (ECFC) therapy holds promise for stroke treatment; however, grafted ECFCs need to be monitored better understand their biological behavior in vivo, so as to evaluate their safety and successful delivery. The objectives of this study are to visualize the fate of infused human cord blood derived ECFCs via bioluminescence imaging (BLI) in an ischemic stroke mouse model and to determine the therapeutic effects of ECFC transplantation. ECFCs derived from human umbilical cord blood were infected with lentivirus carrying enhanced green fluorescent protein (eGFP) and firefly luciferase (Luc2) double fusion reporter gene. Labeled ECFCs were grafted into a photothrombotic ischemic stroke mouse model via intra-arterial injection though the left cardiac ventricle. The homing of infused cells and functional recovery of stroke mice were evaluated using BLI, neurological scoring, and immunohistochemistry. Significantly, BLI signals were highest in the brain on day 1 and decreased steadily until day 14. GFP-positive cells were also found surrounding infarct border zones in brain sections using immunohistochemical staining, suggesting that ECFCs properly homed to the ischemic brain tissue. Using a modified neurological severity score assay and histological analysis of brain slices with CD31 immunostaining in brain tissue, double cortin analysis, and the TdT-mediated dUTP nick end labeling (TUNEL) assay, we demonstrated functional restoration, improved angiogenesis, neurogenesis, and decreased apoptosis in ischemic mice after ECFC infusion. Collectively, our data support that ECFCs may be a promising therapeutic agent for stroke.

Current Challenges Facing the Translation of Brain Computer Interfaces from Preclinical Trials to Use in Human Patients

Current research in brain computer interface (BCI) technology is advancing beyond preclinical studies, with trials beginning in human patients. To date, these trials have been carried out with several different types of recording interfaces. The success of these devices has varied widely, but different factors such as the level of invasiveness, timescale of recorded information, and ability to maintain stable functionality of the device over a long period of time all must be considered in addition to accuracy in decoding intent when assessing the most practical type of device moving forward. Here, we discuss various approaches to BCIs, distinguishing between devices focusing on control of operations extrinsic to the subject (e.g., prosthetic limbs, computer cursors) and those focusing on control of operations intrinsic to the brain (e.g., using stimulation or external feedback), including closed-loop or adaptive devices. In this discussion, we consider the current challenges facing the translation of various types of BCI technology to eventual human application.

Optical coherence tomography-guided laser microsurgery for blood coagulation with continuous-wave laser diode

Blood coagulation is the clotting and subsequent dissolution of the clot following repair to the damaged tissue. However, inducing blood coagulation is difficult for some patients with homeostasis dysfunction or during surgery. In this study, we proposed a method to develop an integrated system that combines optical coherence tomography (OCT) and laser microsurgery for blood coagulation. Also, an algorithm for positioning of the treatment location from OCT images was developed. With OCT scanning, 2D/3D OCT images and angiography of tissue can be obtained simultaneously, enabling to noninvasively reconstruct the morphological and microvascular structures for real-time monitoring of changes in biological tissues during laser microsurgery. Instead of high-cost pulsed lasers, continuous-wave laser diodes (CW-LDs) with the central wavelengths of 450 nm and 532 nm are used for blood coagulation, corresponding to higher absorption coefficients of oxyhemoglobin and deoxyhemoglobin. Experimental results showed that the location of laser exposure can be accurately controlled with the proposed approach of imaging-based feedback positioning. Moreover, blood coagulation can be efficiently induced by CW-LDs and the coagulation process can be monitored in real-time with OCT. This technology enables to potentially provide accurate positioning for laser microsurgery and control the laser exposure to avoid extra damage by real-time OCT imaging.