Adrenal chromaffin cells on microcarriers exhibit enhanced long-term functional effects when implanted into the mammalian brain

The potential of biomaterials for central nervous system cellular repair

The central nervous system (CNS) can be injured or damaged through a variety of insults including traumatic injury, stroke, and neurodegenerative or demyelinating diseases, including Alzheimer's disease, Parkinson's disease and multiple sclerosis. Existing pharmacological and other therapeutics strategies are limited in their ability to repair or regenerate damaged CNS tissue meaning there are significant unmet clinical needs facing patients suffering CNS damage and/or degeneration. Through a variety of mechanisms including neuronal replacement, secretion of therapeutic factors, and stimulation of host brain plasticity, cell-based repair offers a potential mechanism to repair and heal the damaged CNS. However, over the decades of its evolution as a therapeutic strategy, cell-based CNS repair has faced significant hurdles that have prevented its translation to widespread clinical practice. In recent years, advances in cell technologies combined with advances in biomaterial-based regenerative medicine and tissue engineering have meant there is very real potential for many of these hurdles to be overcome. This review will provide an overview of the main CNS conditions that lend themselves to cellular repair and will then outline the potential of biomaterial-based approaches for improving the outcome of cellular repair in these conditions.

Striatal Xenotransplantation of Human Retinal Pigment Epithelial Cells Attached to Microcarriers in Hemiparkinsonian Rats Ameliorates Behavioral Deficits without Provoking a Host Immune Response

Attachment of donor cells to microcarriers has been reported to make them more tolerable for transplantation into the brain. Human retinal pigment epithelial (hRPE) cells have been previously reported to contain enzymes for the production of dopa. Therefore, we examined the host immune response and behavioral effects of xenotransplantation of hRPE cells attached to microcarriers (hRPE-M) into the striatum of unilateral dopamine-depleted rats. Thirty-four adult rats were lesioned with 6-OHDA injections into the medial forebrain bundle on the right side. After 5 weeks of testing for apomorphine-induced rotations (AIR), animals were randomized for right striatal surgery into the following four groups: hRPE-M (group 1), hRPE alone (group 2), microcarriers alone (group 3), or needle tract alone (group 4). Following surgery, animals were tested for AIR every 4 weeks for a period of 12–18 weeks and thereafter euthanized. There was a significant reduction in AIR scores posttransplantation in all groups of animals in the initial observation points at 4 weeks and 8 weeks. However, there was a gradual return to baseline scores in groups 2, 3, and 4 animals at 12 weeks and at 18 weeks only group 1 animals had statistically significant (p = 0.001, repeated measures ANOVA, means comparison, predetermined contrasts) reduction in AIR scores. Brain tissue from representative animals from each group was cut into 30-μm coronal sections, stained for cresyl violet, tyrosine hydroxylase (TH), and markers for host immune activation. Sections through the striatum from group 1 animals revealed microcarriers with attached cells resembling RPE cells. No evidence of transplanted hRPE cells could be detected in sections from group 2 animals while those from groups 3 and 4 animals showed microcarriers and a needle tract alone, respectively. There was no host TH-immunoreactive sprouting response in the striatum in any of the groups and the host immune response was minimal. These results suggest that intrastriatal hRPE-M xenotransplantation into rats is well tolerated without systemic immunosuppression and that such transplants may provide behavioral benefit for parkinsonism.

In Vivo Evaluation of Pharmacologically Active Microcarriers Releasing Nerve Growth Factor and Conveying PC12 Cells

Cell therapy will probably become a major therapeutic strategy in the coming years. Nevertheless, few cells survive transplantation when employed as a treatment for neuronal disorders. To address this problem, we have developed a new tool, the pharmacologically active microcarriers (PAM). PAM are biocompatible and biodegradable microparticles coated with cell adhesion molecules, conveying cells on their surface and presenting a controlled delivery of growth factor. Thus, the combined effect of growth factor and coating influences the transported cells by promoting their survival and differentiation and favoring their integration in the host tissue after their complete degradation. Furthermore, the released factor may also influence the microenvironment. In this study, we evaluated their efficacy using nerve growth factor (NGF)-releasing PAM and PC12 cells, in a Parkinson's disease paradigm. After implantation of NGF-releasing or unloaded PAM conveying PC12 cells, or PC12 cells alone, we studied cell survival, differentiation, and apoptosis, as well as behavior of the treated rats. We observed that the NGF-releasing PAM coated with two synthetic peptides (poly-D-lysine and fibronectin-like) induced PC12 cell differentiation and reduced cell death and proliferation. Moreover, the animals receiving this implant presented an improved amphetamine-induced rotational behavior. These findings indicate that PAM could be a promising strategy for cell therapy of neurological diseases and could be employed in other situations with fetal cell transplants or with stem cells.

Microcarrier Enhanced Survival of Human and Rat Fetal Ventral Mesencephalon Cells Implanted in the Rat Striatum

The transplantation of tissue containing dopamine-producing cells into the mammalian central nervous system is an emerging treatment for Parkinson's disease, despite relatively poor survival of implanted tissue. Recent evidence has suggested that Cytodex microcarriers enhance the survival of dopaminergic rat chromaffin cells transplanted into the rat striatum in the absence of immunosuppression. The current study was undertaken to evaluate the survival of rat and human fetal ventral mesencephalic neurons (VM) implanted alone or after attachment to microcarriers in the striatum of rats without immunosuppression. Rat fetal VM neurons demonstrated enhanced survival in the rat striatum when transplanted on microcarriers, compared to their transplantation alone during the 3-mo period examined in the present study. Transplants of human fetal VM neurons on microcarriers also survived remarkably well in the rat striatum without systemic immunosuppression. In contrast, human fetal VM cells transplanted alone into the rat striatum did not survive without systemic immunosuppression. There was no evidence of TH fiber sprouting in the vicinity of any transplant site. These data indicated that Cytodex microcarriers provide enhanced survival of both rat allograft and human xenograft fetal mesencephalic cells in the rat striatum without the necessity of systemic immunosuppression, perhaps by inducing a unique neuron–glia environment.

Stem cell therapies for ischemic stroke: current animal models, clinical trials and biomaterials

We report the facilitation of stem cell therapy in stroke by tissue engineering and applications of biomaterials.

Carriers in cell-based therapies for neurological disorders

There is a pressing need for long-term neuroprotective and neuroregenerative therapies to promote full function recovery of injuries in the human nervous system resulting from trauma, stroke or degenerative diseases. Although cell-based therapies are promising in supporting repair and regeneration, direct introduction to the injury site is plagued by problems such as low transplanted cell survival rate, limited graft integration, immunorejection, and tumor formation. Neural tissue engineering offers an integrative and multifaceted approach to tackle these complex neurological disorders. Synergistic therapeutic effects can be obtained from combining customized biomaterial scaffolds with cell-based therapies. Current scaffold-facilitated cell transplantation strategies aim to achieve structural and functional rescue via offering a three-dimensional permissive and instructive environment for sustainable neuroactive factor production for prolonged periods and/or cell replacement at the target site. In this review, we intend to highlight important considerations in biomaterial selection and to review major biodegradable or non-biodegradable scaffolds used for cell transplantation to the central and peripheral nervous system in preclinical and clinical trials. Expanded knowledge in biomaterial properties and their prolonged interaction with transplanted and host cells have greatly expanded the possibilities for designing suitable carrier systems and the potential of cell therapies in the nervous system.

Functional Cells Cultured on Microcarriers for Use in Regenerative Medicine Research

Microcarriers have been successfully used for many years for growing anchorage-dependent cells and as a means of delivering cells for tissue repair. When cultured on microcarriers, the number of anchorage-dependent cells, including primary cells, can easily be scaled up and controlled to generate the quantities of cells necessary for therapeutic applications. Recently, stem cell technology has been recognized as a powerful tool in regenerative medicine, but adequate numbers of stem cells that retain their differentiation potential are still difficult to obtain. For anchorage-dependent stem cells, however, microcarrier-based suspension culture using various types of microcarriers has proven to be a good alternative for effective ex vivo expansion. In this article, we review studies reporting the expansion, differentiation, or transplantation of functional anchorage-dependent cells that were expanded with the microcarrier culture system. Thus, the implementation of technological advances in biodegradable microcarriers, the bead-to-bead transfer process, and appropriate stem cell media may soon foster the ability to produce the numbers of stem cells necessary for cell-based therapies and/or tissue engineering.

Retinal pigment epithelial cells secrete neurotrophic factors and synthesize dopamine: possible contribution to therapeutic effects of RPE cell transplantation in Parkinson's disease

BACKGROUND

New strategies for the treatment of Parkinson's disease (PD) are shifted from dopamine (DA) replacement to regeneration or restoration of the nigro-striatal system. A cell therapy using human retinal pigment epithelial (RPE) cells as substitution for degenerated dopaminergic (DAergic) neurons has been developed and showed promising prospect in clinical treatment of PD, but the exact mechanism underlying this therapy is not fully elucidated. In the present study, we investigated whether the beneficial effects of this therapy are related to the trophic properties of RPE cells and their ability to synthesize DA.

METHODS

We evaluated the protective effects of conditioned medium (CM) from cultured RPE cells on the DAergic cells against 6-hydroxydopamine (6-OHDA)- and rotenone-induced neurotoxicity and determined the levels of glial cell derived neurotrophic factor (GDNF) and brain derived neurotrophic factor (BDNF) released by RPE cells. We also measured the DA synthesis and release. Finally we transplanted microcarriers-RPE cells into 6-OHDA lesioned rats and observed the improvement in apomorphine-induced rotations (AIR).

RESULTS

We report here: (1) CM from RPE cells can secret trophic factors GDNF and BDNF, and protect DAergic neurons against the 6-OHDA- and rotenone-induced cell injury; (2) cultured RPE cells express L-dopa decarboxylase (DDC) and synthesize DA; (3) RPE cells attached to microcarriers can survive in the host striatum and improve the AIR in 6-OHDA-lesioned animal model of PD; (4) GDNF and BDNF levels are found significantly higher in the RPE cell-grafted tissues.

CONCLUSION

These findings indicate the RPE cells have the ability to secret GDNF and BDNF, and synthesize DA, which probably contribute to the therapeutic effects of RPE cell transplantation in PD.

Spheramine for treatment of Parkinson's disease

Spheramine (Bayer Schering Pharma AG, Berlin, Germany) is currently being tested as a new approach for the treatment of Parkinson's disease (PD). It consists of an active component of cultured human retinal pigment epithelial (hRPE) cells, attached to an excipient part of cross-linked porcine gelatin microcarrriers. Spheramine is administered by stereotactic implantation into the striatum of PD patients and the use of immunosuppression is not required. Current pharmacologic therapies of PD are oriented to the administration of dopaminergic medications. Human RPE cells produce levodopa, and this constitutes the rationale to use Spheramine for the treatment of PD. The preclinical development of Spheramine included extensive biologic, pharmacologic, and toxicologic studies in vitro and in animal models of PD. The first clinical trial in humans evaluated the safety and efficacy of Spheramine implanted in the postcommissural putamen contralateral to the most affected side in six patients with advanced PD. This open-label study demonstrated good tolerability and showed sustained motor clinical improvement. A phase II double-blind, randomized, multicenter, placebo-controlled (sham surgery) study is underway to evaluate safety, tolerability, and efficacy of Spheramine implanted bilaterally into the postcommissural putamen of patients with advanced PD. Spheramine represents a treatment approach with the potential of supplying a more continuous delivery of levodopa to the striatum in advanced PD than can be achieved with oral therapy alone.

Human retinal pigment epithelial cell implants ameliorate motor deficits in two rat models of Parkinson disease

Intrastriatal transplantation of gelatin microcarrier-attached human retinal pigment epithelial cells (hRPE-GM) may represent an alternative source for cell therapy in Parkinson disease (PD). The use of human retinal pigment epithelial (hRPE) cells in PD relies on the capacity of these cells to produce l-dopa as an intermediate product in the eumelanin synthesis pathway. We investigated the behavioral effects of hRPE-GM implants on forelimb use asymmetries and hindlimb motor deficits in unilateral and bilateral 6-hydroxydopamine (6-OHDA) rat models of PD. We report that intrastriatal unilateral implantation of hRPE-GM in rats with 6-OHDA nigrostriatal lesions produce an amelioration of the contralateral forelimb disuse and the contralateral hindlimb deficits. These results further support the possibility that implantation of cultured hRPE cells may be a promising therapeutic option for patients with PD.

Pharmacologically active microcarriers releasing glial cell line – derived neurotrophic factor: Survival and differentiation of embryonic dopaminergic neurons after grafting in hemiparkinsonian rats

To improve the outcome of foetal dopaminergic cell transplantation for the treatment of Parkinson's disease, pharmacologically active microcarriers (PAM) were developed. PAM are able to convey cells on their surface and release a growth factor to improve cell survival, differentiation and integration after brain implantation. Lysozyme-releasing PAM were first produced and characterized. They served as a model system for the development of glial cell line-derived neurotrophic factor (GDNF)-releasing PAM conveying foetal ventral mesencephalic (FVM) cells. The effects of the intrastriatal implantation of this system were studied in hemiparkinsonian rats during a 6-week period. This study reports on the degradation of coated and non-coated PAM and the release of lysozyme and of biologically active GDNF for 42 days. Unloaded and GDNF-loaded PAM conveying FVM cells allowed a high improvement of the grafted cell survival and of fibre outgrowth, when compared to the cells transplanted alone. The animals receiving the PAM showed an earlier improvement in amphetamine-induced rotational behaviour compared to animals receiving FVM cells only; behaviour that appears to be more regular and stable with the GDNF-releasing PAM. The use of PAM to convey foetal cells is thus an efficient strategy for cell therapy in neurodegenerative diseases, as it allows improvement of cell survival and fibre outgrowth inducing a rapid recovery of behaviour using only low amounts of cells.

Pharmacologically active microcarriers: a tool for cell therapy

To overcome certain problems encountered in cell therapy, particularly cell survival, lack of cell differentiation and integration in the host tissue, we developed pharmacologically active microcarriers (PAM). These biodegradable particles made with poly(D,L-lactic-co-glycolic acid) (PLGA) and coated with adhesion molecules may serve as a support for cell culture and may be used as cell carriers presenting a controlled delivery of active protein. They can thus support the survival and differentiation of the transported cells as well as their microenvironment. To develop this tool, nerve growth factor (NGF)-releasing PAM, conveying PC12 cells, were produced and characterized. Indeed, these cells have the ability to differentiate into sympathetic-like neurons after adhering to a substrate, in the presence of NGF, and can then release large amounts of dopamine. Certain parameters such as the size of the microcarriers, the conditions enabling the coating of the microparticles and the subsequent adhesion of cells were thus studied to produce optimized PAM.

Stereotaxic intrastriatal implantation of human retinal pigment epithelial (hRPE) cells attached to gelatin microcarriers: a potential new cell therapy for Parkinson's disease

Human retinal pigment epithelial (hRPE) cells are dopaminergic support cells in the neural retina. Stereotaxic intrastriatal implantation of hRPE cells attached to gelatin microcarriers (Spheramine) in rodent and non-human primate models of Parkinson's disease (PD) produces long term amelioration of motor and behavioral deficits, with histological and PET evidence of cell survival without immunosuppression. Long-term safety in cynomologous monkeys has also been demonstrated. Six H&Y stage III/IV PD patients were enrolled in a one-year, open-label, single center study to evaluate the safety and efficacy of Spheramine (approximately 325,000 cells) implanted in the most affected post-commissural putamen. All patients tolerated the implantation of Spheramine well and demonstrated improvement. At 6, 9, and 12 months post-operatively, the mean UPDRS-Motor score "off", the primary outcome measure, improved 33%, (n = 6), 42% (n = 6), and 48% (n = 3), respectively. No "off-state" dyskinesias have been observed. Based on these preliminary results, Spheramine appears to show promise in treating late stage PD patients.