Functional Improvement with Low-dose Dopaminergic Grafts in Hemiparkinsonian Rats

Influence of chronic L-DOPA treatment on immune response following allogeneic and xenogeneic graft in a rat model of Parkinson's disease

Although intrastriatal transplantation of fetal cells for the treatment of Parkinson's disease had shown encouraging results in initial open-label clinical trials, subsequent double-blind studies reported more debatable outcomes. These studies highlighted the need for greater preclinical analysis of the parameters that may influence the success of cell therapy. While much of this has focused on the cells and location of the transplants, few have attempted to replicate potentially critical patient centered factors. Of particular relevance is that patients will be under continued L-DOPA treatment prior to and following transplantation, and that typically the grafts will not be immunologically compatible with the host. The aim of this study was therefore to determine the effect of chronic L-DOPA administered during different phases of the transplantation process on the survival and function of grafts with differing degrees of immunological compatibility. To that end, unilaterally 6-OHDA lesioned rats received sham surgery, allogeneic or xenogeneic transplants, while being treated with L-DOPA before and/or after transplantation. Irrespective of the L-DOPA treatment, dopaminergic grafts improved function and reduced the onset of L-DOPA induced dyskinesia. Importantly, although L-DOPA administered post transplantation was found to have no detrimental effect on graft survival, it did significantly promote the immune response around xenogeneic transplants, despite the administration of immunosuppressive treatment (cyclosporine). This study is the first to systematically examine the effect of L-DOPA on graft tolerance, which is dependent on the donor-host compatibility. These findings emphasize the importance of using animal models that adequately represent the patient paradigm.

Embryonic stem cells derived neuron transplantation recovery in models of parkinsonism in relation to severity of the disorder in rats

6-Hydroxydopamine (6-OHDA)- and 1-methyl-4-phenylpyridinium (MPP(+))-induced hemi-parkinsonism was investigated in relation to the severity of the disorder in terms of behavioral disability and nigral neuronal loss and recovery regarding the number of stem cell-derived neurons transplanted in the striatum. Intra-median forebrain bundle infusion of the parkinsonian neurotoxins and intra-striatal transplantation of differentiated embryonic stem cells (ESCs) were carried out by rat brain stereotaxic surgery. The severity of the disease was determined using the number of amphetamine- or apomorphine-induced rotations, striatal dopamine levels as estimated by high-performance liquid chromatography (HPLC)-electrochemistry, and the number of surviving tyrosine hydroxylase immunoreactive dopaminergic neurons in the substantia nigra pars compacta. Rats that received unilateral infusion of 6-OHDA or MPP(+) responded with dose-dependent, unilateral bias in turning behavior when amphetamine or apomorphine was administered. Rotational asymmetry in both models correlated significantly well with the loss in the number of nigral dopaminergic neurons and striatal dopamine depletion. Transplantation of 2×10(5) differentiated murine ESCs revealed remarkably similar kinds of recovery in both animal models. The survival of the grafted dopaminergic cells in the striatum was better in animals with low-severity parkinsonism, but poor in the animals with severe parkinsonism. Amphetamine-induced rotational recovery correlated positively with an increasing number of cells transplanted in animals with uniform nigral neuronal lesion. These results suggest that disease severity is an important factor for determining the number of cells to be transplanted in parkinsonian rats for desirable recovery, which may be true in clinical conditions too.

Transplantation of GABAergic cells derived from bioreactor-expanded human neural precursor cells restores motor and cognitive behavioral deficits in a rodent model of Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder that is characterized by progressive dementia, choreiform involuntary movements, and emotional deterioration. Neuropathological features include the progressive degeneration of striatal γ-aminobutyric acid (GABA) neurons. New therapeutic approaches, such as the transplantation of human neural precursor cells (hNPCs) to replace damaged or degenerated cells, are currently being investigated. The aim of this study was to investigate the potential for utilizing telencephalic hNPCs expanded in suspension bioreactors for cell restorative therapy in a rodent model of HD. hNPCs were expanded in a hydrodynamically controlled and homogeneous environment under serum-free conditions. In vitro analysis revealed that the bioreactor-expanded telencephalic (BET)-hNPCs could be differentiated into a highly enriched population of GABAergic neurons. Behavioral assessments of unilateral striatal quinolinic acid-lesioned rodents revealed a significant improvement in motor and memory deficits following transplantation with GABAergic cells differentiated from BET-hNPCs. Immunohistochemical analysis revealed that transplanted BET-hNPCs retained a GABAergic neuronal phenotype without aberrant transdifferentiation or tumor formation, indicating that BET-hNPCs are a safe source of cells for transplantation. This preclinical study has important implications as the transplantation of GABAergic cells derived from predifferentiated BET-hNPCs may be a safe and feasible cell replacement strategy to promote behavioral recovery in HD.

Microtransplantation of Dopaminergic Cell Suspensions: Further Characterization and Optimization of Grafting Parameters

Intracerebral transplantation of dopaminergic (DA) cells is currently further explored as a potential restorative therapy for Parkinson's disease (PD). However, before they can be considered for a more widespread clinical use a number of critical issues have to be resolved, including an optimized transplantation protocol. This study has been performed in a rat 6-hydroxydopamine model of PD and is based on the microtransplantation approach. The results demonstrate a reduced survival (threefold) for a single cell suspension of E14 rat ventral mesencephalon compared to a fragment suspension when a metal cannula is used for implantation. However, fragment suspensions result in a more variable graft survival and ectopically placed cells along the implantation tract. When a glass capillary is used for implantation, the survival of the single cell suspension (so-called “micrograft”) improved by fourfold (vs. single cells/metal cannula) and is superior to the combination of the metal cannula and fragment suspension (+40%). The micrografts show a reduced variability in DA neuron survival as well as fewer ectopically placed cells. Moreover, the implantation time can significantly be reduced from 19 to 7 min in micrografted animals without a compromise in DA graft survival and functional behavioral outcome. Using the microtransplantation approach graft size can be tailored effectively by varying the density of the final cell suspension at least between 11,000 and 320,000 cells/μl, resulting in comparable survival of tyrosine hydroxylase (TH)-positive neurons in the range of 2–4%. With this approach no more than 100 surviving TH-positive neurons are necessary to produce functional effects in the amphetamine-induced rotation test. Interestingly, we found that DA micrografts into lesion striatum present 20% higher survival rates of TH neurons in comparison to the intact striatum. In summary, these results provide further evidence for the usefulness of the microtransplantation approach and allow for a more precise and tailored adaptation of the implantation parameters for further studies on DA, and possibly also other neural-, glial-, and stem cell-derived grafts.

Adjunctive use of the non-ionic surfactant Poloxamer 188 improves fetal dopaminergic cell survival and reinnervation in a neural transplantation strategy for Parkinson's disease

Although neural transplantation of fetal dopaminergic cells is a promising therapy for Parkinson's disease, poor transplanted cell survival limits its efficacy. In the present study it was hypothesized that the use of Poloxamer 188 (P188), a non-ionic surfactant, during cell preparation and transplantation may protect cells from associated mechanical injury and thus improve transplanted cell survival in a rat model of Parkinson's disease. Fetal rat dopaminergic tissue was dissociated in media with or without P188 and then cultured for 1 week or transplanted into the striatum of rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopaminergic pathway. Fetal dopaminergic cell survival and reinnervation of the host brain were examined using tyrosine hydroxylase immunohistochemistry and stereological quantification. The number of surviving tyrosine hydroxylase-immunoreactive cells in vitro and in vivo was significantly increased by 2.2-fold by incubating fetal dopaminergic cells with P188 during tissue dissociation. Furthermore, the striatal reinnervation in parkinsonian rats that received intrastriatal transplants of P188-exposed dopaminergic cells was significantly enhanced (1.8-fold increase) compared with rats that received non-P188-treated cells. In conclusion, P188 protects fetal dopaminergic cells from mechanical injury by increasing cell survival and enhances dopaminergic fibre outgrowth into the transplanted striatum. Use of P188 may thus be an important adjunct to improve the clinical efficacy of neural transplantation for Parkinson's disease.

Differential effects of glial cell line-derived neurotrophic factor on A9 and A10 dopamine neuron survival in vitro

Glial cell-line derived neurotrophic factor (GDNF) enhances dopamine (DA) cell survival and fiber outgrowth, and may be beneficial in enhancing cell restorative strategies for Parkinson's disease (PD). However, GDNF may have different roles for transplanted DA cell sub-types. The present in vitro study investigated the effect of GDNF on the survival of rat DA cells displaying a phenotype consistent with either the substantia nigra [A9 cells immunopositive for tyrosine hydroxylase (TH) and G-protein-gated inwardly rectifying potassium channel subunit 2 (GIRK2)] or with the ventral tegmental area [A10 cells immunopositive for TH and calbindin]. It was found that a single exposure of GDNF enhanced the number of DA cells of an A9 phenotype, without affecting DA cells of an A10 phenotype. Conversely, repeated GDNF exposure did not alter the survival of A9 phenotypic cells, but doubled the percentage of A10 cells. It was concluded that GDNF administration may affect dopaminergic cells differently depending on time and degree of GDNF exposure. For cell transplantation in PD, long-term GDNF administration may result in detrimental effects for transplanted A9 TH+ cells as this may introduce competition with A10 TH+ cells for survival and fiber outgrowth into the host striatum. These results may have important implications for clinical neural transplantation in PD.

The impact of graft size on the development of dyskinesia following intrastriatal grafting of embryonic dopamine neurons in the rat

Intrastriatal transplants of embryonic ventral mesencephalon can cause dyskinesia in patients with Parkinson's disease (PD). We assessed the impact of transplant size on the development of graft-induced dyskinesia. Rats with unilateral 6-hydroxydopamine lesions were primed to exhibit L-DOPA-induced dyskinesia. They were then intrastriatally grafted with different quantities of embryonic ventral mesencephalic tissue to give small and large grafts. Without drug treatment, discrete dyskinetic-like movements were observed in most rats with large grafts 2-6 weeks after transplantation, but disappeared later. Amphetamine evoked severe abnormal involuntary movements (AIMs) in grafted animals, which were more striking with large grafts. The AIMs coincided with contralateral rotation, but displayed a different temporal profile and pharmacological properties. Thus, selective dopamine uptake blockade elicited rotational behavior, whereas coadministration of both dopamine and serotonin uptake blockers was required to evoke significant orolingual and limb AIMs. In conclusion, robust and reproducible AIMs were evoked in rats with large grafts by blockade of monoamine reuptake. These AIMs may provide a new tool for assessing dyskinetic effects of neural grafting.