Osteoarthritis is a heterogeneous and multifactorial disease characterized by the progressive loss of hyaline articular cartilage. Recently, therapies that utilize autologous chondrocytes have been pursued, but the use of a patient’s own articular cartilage cells is quite limited. In pathological conditions where the body is unable to repair or regenerate tissue on its own, stem cell based therapeutic strategies have shown great promise. In particular, bone marrow derived mesenchymal stem cells (MSCs), a subset of adult stem cells, have demonstrated the ability to differentiate into a variety of cell lineages, including osteoblasts, adipocytes, chondrocytes, and myoblasts. Based on the ability to isolate these cells from patients, culture them ex vivo, and transplant them back into the body, adult stem cells are currently under investigation for their therapeutic potential in treating osteoarthritis.
The development of non-invasive imaging for assessing cell and tissue co-localizaton, cell migration, proliferation and therapeutic response will be critical for the success of future stem cell therapies. However, there are major challenges in the monitoring of these cells once administered in vivo. In order to visualize and track transplanted stem cells with MR imaging, cells have to be labeled with MR contrast agents. Initial cell labeling techniques have been hampered by a limited concentration of internalized contrast agents with subsequent limited sensitivity of MR to depict the labeled cells. In addition, the interaction between contrast agent-cell-scaffold becomes important in this case. New and improved methods need to be developed for efficient tracking of labeled cells, and ultimately the delivery and regenerative potential must be evaluated. In order to visualize and track transplanted stem cells with MR imaging, we propose the use of Micrometer-sized iron oxide (MPIO) particles as magnetic resonance contrast agents to track the fate of stem-cells non-invasively.
Statement of Benefit to California:
This proposal has significant benefit for the advancement of science, education, national and global visibility and economy for the state of California, (CA).
Research and Scientific Benefit:
The use of mesenchymal stem cells in regenerative medicine, is particularly important, as MSCs can be used for producing a wide variety of cell types and used to replace their dysfunctional counterparts in living humans. The key obstacle to stem cell therapy is the inability to track the cells and their fate through the body, non-invasively. This study will create novel non-invasive magnetic resonance imaging for monitoring the success of MSC transplantation for cartilage repair. This work will lead to novel therapeutic applications in tissue engineering and studies will potentially alleviate the cost of care in CA.
Training and Talent Development:
This proposal, with chemists, biologists, clinicians, and bioengineers focusing on non-invasive imaging for tracking stem cells, epitomizes an inter-disciplinary effort. This research as planned will include participation from graduate students, medical students, and post-doctoral researchers from multiple departments at UC San Francisco (UCSF). This will provide unique hands-on training, supplementing text-book teaching, and motivating a diverse and large number of individuals in CA, and lead to future funding from diverse sources.
National and Global Standing:
CA has taken leadership and is one of the few states investing resources in Stem Cell research. The science proposed here would potentially bring investments from institutions in other states. The technology transfer potential from researchers in institutions in states not as progressive as CA, represents a new paradigm with significant financial gains for the future. The diversity and outreach efforts of the team and the institutions are well known and will lead to rapid dissemination of the science and research to the public.
Financial benefit is the common denominator for all of the above aspects. The rapid progress in inter-disciplinary science, the impact of the research on cartilage tissue engineering, the intellectual property potential, the enhanced national and international standing will all lead to economic benefits for CA.
Methods for tracking stem cell migration and engraftment are critical for monitoring cell-based therapies. In this proposal the investigators plan to combine cartilage differentiation of mesenchymal stem cells (MSC) with scaffold technology and with iron particle labeling to develop cartilage for in vivo implantation to treat cartilage defects, combined with the ability for non-invasive imaging. Studies are proposed to assess the uptake of micrometer-sized iron oxide (MPIO) particles in MSC combined with standard differentiation methods (kit-based). The influence of the particles on cartilage differentiation will be assessed. In addition, a number of scaffolds will be evaluated to determine their ability to support and enhance cartilage differentiation. Finally, studies will be performed on in vivo grafts of scaffolds containing labeled stem cells to evaluate their persistence in vivo using magnetic resonance imaging (MRI). Development of methods aimed at cartilage repair using MSC are important in view of the aging population and increasing incidence of osteoarthritis (OA).
The investigators will combine expertise in cartilage differentiation from MSC with scaffold technology and magnetic particle labeling to generate grafts that can be implanted in injured cartilage surfaces allowing non-invasive imaging of the graft. MSC can be induced to become cartilage but reviewers identified major problems with this approach. The efficiency of this process decreases significantly with ex vivo expansion of MSC, decreases when MSC are harvested from older individuals, and importantly, the cartilage tissue generated is not the needed functional articular cartilage suitable for restoration of cartilage surface. So the important issues go well beyond survival of transplanted cells to their ability to integrate in the cartilage properly, which is not addressed well in the proposal. In terms of novelty, the methods to induce cartilage differentiation are standard (kit-based), not novel. The combination with scaffold technology is not sufficiently focused on generating improved MSC-derived articular cartilage. The studies evaluating incorporation of magnetic particles in MSC are also not particularly novel and will likely confirm published data. Reviewers felt that evaluation of the effects of particle labels on cartilage differentiation could yield useful information, but overall were not enthusiastic about the proposal.
Several additional concerns were raised. The principal investigator proposes to use hydrogels to encapsulate rabbit MSCs (presumably bone marrow-derived) to induce chondrogenic differentiation. The analyses proposed will be performed on a limited number of constructs. Furthermore, the hydrogel that will be used is based on a material that is not widely used for these kinds of studies, thus the reviewers were expecting some justification for this choice of material. There was some concern that generalizations from one material to the other would not hold. Also, the cells will be labeled with MPIO particles, which are described as non-toxic, but convincing data to support this claim was lacking. Reviewers pointed to an increasing body of literature showing that particulates this size do cause changes in cell responses of osteoblasts. Reviewers felt it was risky to just assume that each cell would contain only one microparticle.
The second part of the study, to test the MPIO particles after placement of cell scaffolds in a rabbit model of OA also raised some concerns. The goal is to show that the particles will allow visualization by MRI. Because the OA model is very challenging, and though OA is the long-term target of the technology, a standard osteochondral defect model might have facilitated answers to many of the questions. Overall, reviewers were of the opinion that sufficient experiments to address the many variables were not proposed.
Despite the experience of the team, reviewers found the application difficult to read, especially because the important parameters to be measured were not well highlighted, and the feasibility issues were given insufficient detail. Preliminary data were not extensive and alternative approaches were not addressed.
The investigators are well-established researchers in their respective fields, and work in an excellent environment for this kind of research. They bring together expertise in bioengineering, scaffold design, radiology and orthopedics, and cell biology, but are scattered geographically, which may make logistics difficult.