Effect of GDNF-releasing biodegradable microspheres on the function and the survival of intrastriatal fetal ventral mesencephalic cell grafts

Mouse Embryonic Stem Cells Expressing GDNF Show Enhanced Dopaminergic Differentiation and Promote Behavioral Recovery After Grafting in Parkinsonian Rats

Parkinson's disease (PD) is characterized by the progressive loss of midbrain dopaminergic neurons (DaNs) of the substantia nigra pars compacta and the decrease of dopamine in the brain. Grafting DaN differentiated from embryonic stem cells (ESCs) has been proposed as an alternative therapy for current pharmacological treatments. Intrastriatal grafting of such DaNs differentiated from mouse or human ESCs improves motor performance, restores DA release, and suppresses dopamine receptor super-sensitivity. However, a low percentage of grafted neurons survive in the brain. Glial cell line-derived neurotrophic factor (GDNF) is a strong survival factor for DaNs. GDNF has proved to be neurotrophic for DaNs in vitro and in vivo, and induces axonal sprouting and maturation. Here, we engineered mouse ESCs to constitutively produce human GDNF, to analyze DaN differentiation and the possible neuroprotection by transgenic GDNF after toxic challenges in vitro, or after grafting differentiated DaNs into the striatum of Parkinsonian rats. GDNF overexpression throughout in vitro differentiation of mouse ESCs increases the proportion of midbrain DaNs. These transgenic cells were less sensitive than control cells to 6-hydroxydopamine in vitro. After grafting control or GDNF transgenic DaNs in hemi-Parkinsonian rats, we observed significant recoveries in both pharmacological and non-pharmacological behavioral tests, as well as increased striatal DA release, indicating that DaNs are functional in the brain. The graft volume, the number of surviving neurons, the number of DaNs present in the striatum, and the proportion of DaNs in the grafts were significantly higher in rats transplanted with GDNF-expressing cells, when compared to control cells. Interestingly, no morphological alterations in the brain of rats were found after grafting of GDNF-expressing cells. This approach is novel, because previous works have use co-grafting of DaNs with other cell types that express GDNF, or viral transduction in the host tissue before or after grafting of DaNs. In conclusion, GDNF production by mouse ESCs contributes to enhanced midbrain differentiation and permits a higher number of surviving DaNs after a 6-hydroxydopamine challenge in vitro, as well as post-grafting in the lesioned striatum. These GDNF-expressing ESCs can be useful to improve neuronal survival after transplantation.

Neurotrophic Factors in Parkinson's Disease: Clinical Trials, Open Challenges and Nanoparticle-Mediated Delivery to the Brain

Neurotrophic factors (NTFs) are small secreted proteins that support the development, maturation and survival of neurons. NTFs injected into the brain rescue and regenerate certain neuronal populations lost in neurodegenerative diseases, demonstrating the potential of NTFs to cure the diseases rather than simply alleviating the symptoms. NTFs (as the vast majority of molecules) do not pass through the blood-brain barrier (BBB) and therefore, are delivered directly into the brain of patients using costly and risky intracranial surgery. The delivery efficacy and poor diffusion of some NTFs inside the brain are considered the major problems behind their modest effects in clinical trials. Thus, there is a great need for NTFs to be delivered systemically thereby avoiding intracranial surgery. Nanoparticles (NPs), particles with the size dimensions of 1-100 nm, can be used to stabilize NTFs and facilitate their transport through the BBB. Several studies have shown that NTFs can be loaded into or attached onto NPs, administered systemically and transported to the brain. To improve the NP-mediated NTF delivery through the BBB, the surface of NPs can be functionalized with specific ligands such as transferrin, insulin, lactoferrin, apolipoproteins, antibodies or short peptides that will be recognized and internalized by the respective receptors on brain endothelial cells. In this review, we elaborate on the most suitable NTF delivery methods and envision "ideal" NTF for Parkinson's disease (PD) and clinical trial thereof. We shortly summarize clinical trials of four NTFs, glial cell line-derived neurotrophic factor (GDNF), neurturin (NRTN), platelet-derived growth factor (PDGF-BB), and cerebral dopamine neurotrophic factor (CDNF), that were tested in PD patients, focusing mainly on GDNF and CDNF. We summarize current possibilities of NP-mediated delivery of NTFs to the brain and discuss whether NPs have impact in improving the properties of NTFs and delivery across the BBB. Emerging delivery approaches and future directions of NTF-based nanomedicine are also discussed.

Simultaneous Transplantation of Fetal Ventral Mesencephalic Tissue and Encapsulated Genetically Modified Cells Releasing GDNF in a Hemi-Parkinsonian Rat Model of Parkinson's Disease

Transplantation of fetal ventral mesencephalic (VM) neurons for Parkinson’s disease (PD) is limited by poor survival and suboptimal integration of grafted tissue into the host brain. In a 6-hydroxydopamine rat model of PD, we investigated the feasibility of simultaneous transplantation of rat fetal VM tissue and polymer-encapsulated C2C12 myoblasts genetically modified to produce glial cell line–derived neurotrophic factor (GDNF) or mock-transfected myoblasts on graft function. Amphetamine-induced rotations were assessed prior to transplantation and 2, 4, 6 and 9 wk posttransplantation. We found that rats grafted with VM transplants and GDNF capsules showed a significant functional recovery 4 wk after implantation. In contrast, rats from the VM transplant and mock-capsule group did not improve at any time point analyzed. Moreover, we detected a significantly higher number of tyrosine hydroxylase immunoreactive (TH-ir) cells per graft (2-fold), a tendency for a larger graft volume and an overall higher TH-ir fiber outgrowth into the host brain (1.7-fold) in the group with VM transplants and GDNF capsules as compared to the VM transplant and mock-capsule group. Most prominent was the TH-ir fiber outgrowth toward the capsule (9-fold). Grafting of GDNF-pretreated VM transplants in combination with the implantation of GDNF capsules resulted in a tendency for a higher TH-ir fiber outgrowth into the host brain (1.7-fold) as compared to the group transplanted with untreated VM transplants and GDNF capsules. No differences between groups were observed for the number of surviving TH-ir neurons or graft volume. In conclusion, our findings demonstrate that simultaneous transplantation of fetal VM tissue and encapsulated GDNF-releasing cells is feasible and support the graft survival and function. Pretreatment of donor tissue with GDNF may offer a way to further improve cell transplantation approaches for PD.

Tackling Cell Transplantation Anoikis: An Injectable, Shape Memory Cryogel Microcarrier Platform Material for Stem Cell and Neuronal Cell Growth

Highly macroporous semisynthetic cryogel microcarriers can be synthesized for culturing stem cells and neuronal type cells. Growth factors loaded to heparin-containing microcarriers show near zero-order release kinetics and cell-loaded microcarriers can be injected through a fine gauge cannula without negative effect on the cells. These carriers can be applied for cell transplantation applications.

From molecular to nanotechnology strategies for delivery of neurotrophins: emphasis on brain-derived neurotrophic factor (BDNF)

Neurodegenerative diseases represent a major public health problem, but beneficial clinical treatment with neurotrophic factors has not been established yet. The therapeutic use of neurotrophins has been restrained by their instability and rapid degradation in biological medium. A variety of strategies has been proposed for the administration of these leading therapeutic candidates, which are essential for the development, survival and function of human neurons. In this review, we describe the existing approaches for delivery of brain-derived neurotrophic factor (BDNF), which is the most abundant neurotrophin in the mammalian central nervous system (CNS). Biomimetic peptides of BDNF have emerged as a promising therapy against neurodegenerative disorders. Polymer-based carriers have provided sustained neurotrophin delivery, whereas lipid-based particles have contributed also to potentiation of the BDNF action. Nanotechnology offers new possibilities for the design of vehicles for neuroprotection and neuroregeneration. Recent developments in nanoscale carriers for encapsulation and transport of BDNF are highlighted.

Neurotrophic factors and neurodegenerative diseases: a delivery issue

Neurotrophic factors (NTFs) represent one of the most stimulating challenge in neurodegenerative diseases, due to their potential in neurorestoring and neuroprotection. Despite the large number of proofs-of-concept and evidences of their activity, most of the clinical trials, mainly regarding Parkinson's disease and Alzheimer's disease, demonstrated several failures of the therapeutic intervention. A large number of researches were conducted on this hot topic of neuroscience, clearly evidencing the advantages of NTF approach, but evidencing the major limitations in its application. The inability in crossing the blood-brain barrier and the lack of selectivity actually represent some of the most highlighted limits of NTFs-based therapy. In this review, beside an overview of NTF activity versus the main neuropathological disorders, a summary of the most relevant approaches, from invasive to noninvasive strategies, applied for improving NTF delivery to the central nervous systems is critically considered and evaluated.

The administration of BDNF and GDNF to the brain via PLGA microparticles patterned within a degradable PEG-based hydrogel: Protein distribution and the glial response

Tailored delivery of neurotrophic factors (NFs) is a critical challenge that continues to inhibit strategies for guidance of axonal growth in vivo. Of particular importance is the ability to recreate innervation of distant brain regions by transplant tissue, for instance rebuilding the nigrostriatal track, one focus in Parkinson's disease research. Many strategies have utilized polymer drug delivery to target NF release in space and time, but combinatorial approaches are needed to deliver multiple NFs at relevant therapeutic times and locations without toxic side effects. Here we engineered a paradigm of PLGA microparticles entrapped within a degradable PEG-based hydrogel device to locally release two different types of NFs with two different release profiles. Hydrogel/microparticle devices were developed and analyzed for their ability to release GDNF in the caudal area of the brain, near the substantia nigra, or BDNF in the rostral area, near the striatum. The devices delivered their respective NFs in a region localized to within 100 μm of the bridge, but not exclusively to the targeted rostral or caudal ends. BDNF was slowly released over a 56-day period, whereas a bolus of GDNF was released around 28 days. The timed delivery of NFs from implanted devices significantly reduced the microglial response relative to sham surgeries. Given the coordinated drug delivery ability and reduced localized inflammatory response, this multifaceted PEG hydrogel/PLGA microparticle strategy may be a useful tool for further development in combining tissue engineering and drug delivery, and recreating the nigrostriatal track.

Recombinant human NGF-loaded microspheres promote survival of basal forebrain cholinergic neurons and improve memory impairments of spatial learning in the rat model of Alzheimer's disease with fimbria-fornix lesion

Neurotrophic factors are used for the experimental treatment of neurological disorders, such as Alzheimer's disease. However, delivery of the neurotrophic factors into the brain remains a big challenge. Recombinant human nerve growth factor (NGF)-loaded microspheres were fabricated and characterized in vitro and in vivo in our previous study. The present study was to assess the therapeutic benefit of rhNGF-loaded microspheres in treating the rat model of Alzheimer's disease with fimbria-fornix lesion. Recombinant human NGF-loaded microspheres were implanted into the basal forebrain of the rats with fimbria-fornix lesion. Four weeks after implantation in the basal forebrain, immunohistochemical analysis showed that rhNGF-loaded microspheres had a significant effect on the survival of axotomized cholinergic neurons in the medial septum (MS) and vertical diagonal branch (VDB) (p<0.05). Y-maze tests showed rhNGF-loaded microspheres can significantly improve the ability of spatial learning and memory of the rats with fimbria-fornix lesion (p<0.05). These results indicate that rhNGF-loaded microspheres are an effective means for the treatment of Alzheimer's disease.

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.