Study of adrenal medullary tissue transplantation to striatum in parkinsonism

Dopaminergic Cell Replacement for Parkinson's Disease: Addressing the Intracranial Delivery Hurdle

Parkinson's disease (PD) is an increasingly prevalent neurological disorder, affecting more than 8.5 million individuals worldwide. α-Synucleinopathy in PD is considered to cause dopaminergic neuronal loss in the substantia nigra, resulting in characteristic motor dysfunction that is the target for current medical and surgical therapies. Standard treatment for PD has remained unchanged for several decades and does not alter disease progression. Furthermore, symptomatic therapies for PD are limited by issues surrounding long-term efficacy and side effects. Cell replacement therapy (CRT) presents an alternative approach that has the potential to restore striatal dopaminergic input and ameliorate debilitating motor symptoms in PD. Despite promising pre-clinical data, CRT has demonstrated mixed success clinically. Recent advances in graft biology have renewed interest in the field, resulting in several worldwide ongoing clinical trials. However, factors surrounding the effective neurosurgical delivery of cell grafts have remained under-studied, despite their significant potential to influence therapeutic outcomes. Here, we focus on the key neurosurgical factors to consider for the clinical translation of CRT. We review the instruments that have been used for cell graft delivery, highlighting current features and limitations, while discussing how future devices could address these challenges. Finally, we review other novel developments that may enhance graft accessibility, delivery, and efficacy. Challenges surrounding neurosurgical delivery may critically contribute to the success of CRT, so it is crucial that we address these issues to ensure that CRT does not falter at the final hurdle.

Regenerative Therapies for Parkinson's Disease: An Update

Parkinson's disease is the second most common neurodegenerative disorder. It is characterised by a typical movement disorder that occurs in part because of the selective degeneration of the dopaminergic neurons of the substantia nigra pars compacta. Current treatment for the motor disorder of Parkinson's disease consists of dopaminergic medications, but these come with significant adverse effects, themselves an important part of the clinical course of Parkinson's disease, particularly in advanced stages. Therefore, treatment is needed that can restore dopaminergic tone in the striatum in a physiological and targeted manner to avert these side effects. A number of potential regenerative treatments have been developed with a view to achieving this. Following decades of optimisation and development of stem-cell-based treatments and viral gene delivery, clinical trials are on the horizon. For these treatments to be widely useful, they must be clinically effective, cost efficient and safe, and a number of practical aspects regarding storage and delivery of treatment must be optimised. Many barriers have been overcome, and the field of regenerative medicine for Parkinson's disease is now increasingly focussed on how these treatments will be delivered, demonstrating the significant progress that has been made and the optimism surrounding these approaches.

Emerging Treatment Approaches for Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease, manifesting as a characteristic movement disorder with a number of additional non-motor features. The pathological hallmark of PD is the presence of intra-neuronal aggregates of α-synuclein (Lewy bodies). The movement disorder of PD occurs largely due to loss of dopaminergic neurons of the substantia nigra, resulting in striatal dopamine depletion. There are currently no proven disease modifying treatments for PD, with management options consisting mainly of dopaminergic drugs, and in a limited number of patients, deep brain stimulation. Long-term use of established dopaminergic therapies for PD results in significant adverse effects, and there is therefore a requirement to develop better means of restoring striatal dopamine, as well as treatments that are able to slow progression of the disease. A number of exciting treatments have yielded promising results in pre-clinical and early clinical trials, and it now seems likely that the landscape for the management of PD will change dramatically in the short to medium term future. Here, we discuss the promising regenerative cell-based and gene therapies, designed to treat the dopaminergic aspects of PD whilst limiting adverse effects, as well as novel approaches to reducing α-synuclein pathology.

Neural Repair Strategies for Parkinson's Disease: Insights from Primate Models

Nonhuman primate models of Parkinson's disease (PD) have been invaluable to our understanding of the human disease and in the advancement of novel therapies for its treatment. In this review, we attempt to give a brief overview of the animal models of PD currently used, with a more comprehensive focus on the advantages and disadvantages presented by their use in the nonhuman primate. In particular, discussion addresses the 6-hydroxydopamine (6-OHDA), 1-methyl-1,2,3,6-tetrahydopyridine (MPTP), rotenone, paraquat, and maneb parkinsonian models. Additionally, the role of primate PD models in the development of novel therapies, such as trophic factor delivery, grafting, and deep brain stimulation, are described. Finally, the contribution of primate PD models to our understanding of the etiology and pathology of human PD is discussed.

Cell therapies for Parkinson's disease: how far have we come?

Over the past three decades, significant progress has been made in the development of potential regenerative cell-based therapies for neurodegenerative disease, with most success being seen in Parkinson's disease. Cell-based therapies face many challenges including ethical considerations, potential for immune-mediated rejection with allogeneic and xenogeneic tissue, pathological spread of protein-related disease into the grafted tissue as well as the risk of graft overgrowth and tumorigenesis in stem cell-derived transplants. Preclinical trials have looked at many tissue types of which the most successful to date have been those using fetal ventral mesencephalon grafts, which led to clinical trials, which have shown that in some cases they can work very well. With important proof-of-concept derived from these studies, there is now much interest in how dopaminergic neurons derived from stem cell sources could be used to develop cell-based therapies suitable for clinical use, with clinical trials poised to enter the clinic in the next couple of years.

Cell-based therapies for Parkinson disease—past insights and future potential

Parkinson disease (PD) is characterized by loss of the A9 nigral neurons that provide dopaminergic innervation to the striatum. This discovery led to the successful instigation of dopaminergic drug treatments in the 1960s, although these drugs were soon recognized to lose some of their efficacy and generate their own adverse effects over time. Despite the fact that PD is now known to have extensive non-nigral pathology with a wide range of clinical features, dopaminergic drug therapies are still the mainstay of therapy, and work well for many years. Given the success of pharmacological dopamine replacement, pursuit of cell-based dopamine replacement strategies seemed to be the next logical step, and studies were initiated over 30 years ago to explore the possibility of dopaminergic cell transplantation. In this Review, we outline the history of this therapeutic approach to PD and highlight the lessons that we have learned en route. We discuss how the best clinical outcomes have been obtained with fetal ventral mesencephalic allografts, while acknowledging inconsistencies in the results owing to problems in trial design, patient selection, tissue preparation, and immunotherapy used post-grafting. We conclude by discussing the challenges of bringing the new generation of stem cell-derived dopamine cells to the clinic.

Adrenal medulla and Parkinson's disease

Parkinson's disease has been described as a multisystem disorder that includes alterations in the function of the autonomic nervous system. The activity of the adrenal medulla in this disease has not been thoroughly investigated. Previous reports are reviewed that demonstrate that the adrenal medullae of parkinsonian patients are compromised, having a decreased content of all catecholamines and several neuropeptides. An animal model was used to investigate whether the observations made in human patients were related to extended treatment with antiparkinsonian medications or were a natural concomitant of the disease. Administration of L-dopa and/or carbidopa to C57BL mice for 4-16 weeks had no significant effect on the level of any of the adrenal medullary catecholamines. Treatment with MPTP 4-16 weeks prior to sacrifice did not deplete adrenal medullary catecholamines in these animals, thus not fully mimicking Parkinson's disease in this animal model. The only significant effect was an interaction between group (MPTP or control) and treatment with antiparkinsonian medications; L-dopa, in the absence and presence of carbidopa, had opposite effects in the two groups. Based primarily on the lack of effect of antiparkinsonian medications on adrenal medullary catecholamines, it was concluded that the adrenal medullary depletion observed in human patients was a peripheral concomitant of Parkinson's disease.

The adrenal medulla and Parkinson's disease

This paper reviews the literature describing the condition of the adrenal medulla in Parkinson's disease. Parkinson's disease is a neurodegenerative disorder that is characterized primarily by the loss of dopaminergic neurons in the substantia nigra. Clinical observations have revealed that Parkinson's disease is also frequently accompanied by a variety of autonomic symptoms. The adrenal medulla is a major component of the autonomic nervous system. However, until recently this organ has not been of particular interest in Parkinson's disease. Early studies found histologic abnormalities in adrenal medullary cells, and several groups measured urinary and plasma catecholamines to determine general autonomic status. In the late 1980s adrenal medullary tissue was first transplanted to the caudate nucleus in an attempt to augment the decreased levels of dopamine, and thus treat the symptoms of Parkinson's disease. At this time the status of the adrenal medulla in this disease became clinically important. We measured the total catecholamine content of the parkinsonian adrenal medulla in tissue collected both at autopsy and in conjunction with adrenal-caudate transplants. Adrenal medullary catecholamines and several neuropeptides were severely depressed in parkinsonian glands. Thus, the adrenal medulla appears to be a target of the peripheral manifestations of Parkinson's disease.

Cerebral transplantation for Parkinson's disease: current progress and future prospects

Cerebral transplantation has received considerable attention from both the medical community and lay press as a potential treatment for Parkinson's disease. Animal models have demonstrated feasibility, although the experience in subhuman primates was very limited when the first human trials were initiated in the mid-1980s. The dramatic success reported for adrenal-to-brain transplantation in some initial trials could not be consistently replicated by other centers. Occasionally, however, patients benefited. Failure of the adrenal medullary graft to survive may have been a major factor in the poor outcomes. Recently, several US and European centers reported substantial clinical improvement after fetal dopaminergic mesencephalon was grafted into the striatum of patients with Parkinson's disease. Although many outcomes were impressive, in some cases the improvement was marginal; in no case was the condition completely reversed, and all but one patient still required levodopa therapy. Before this technique can be considered for routine use, further refinement is necessary, and many technical issues must be addressed. Certain animal studies have suggested that transplantation-related improvement may be derived from graft neurotrophic factors rather than from secretion of dopamine into the dopamine-depleted brain of patients with Parkinson's disease. Preliminary investigations in animals indicate that several other tissues, besides fetal mesencephalon, may also prove appropriate for grafting. Ultimately, advances in molecular biology may allow either transplantation of genetically engineered cells or direct modification of existing brain cells by transfection with viral vectors. The favorable preliminary experience with cerebral transplantation in patients with Parkinson's disease has resulted in the consideration of this strategy for other neurologic disorders.

The biology and behaviour of intracerebral adrenal transplants in animals and man

The catecholamine containing chromaffin cells of the adrenal medulla have recently been employed as intracerebral grafts in man and animals with lesions of the nigrostriatal dopaminergic system. This review outlines the basic biology of the chromaffin cell with reference to its efficacy as a source of dopamine in the grafted state. This is followed by an evaluation of the use of these grafts in experimentally lesioned animals and in patients with Parkinson's disease.

Neurotransplantation: a clinical update

The use of grafts to correct neurological disorders has great promise. The progress toward this goal, as it relates to Parkinson's disease, is briefly reviewed. Although there are a number of questions that remain unanswered, recent reports of improvement in parkinsonian symptoms are very encouraging. In order to successfully evaluate the clinical trials, multicenter and/or standardized reporting techniques will be required. Future studies will need to concentrate on improving the graft survival and ability of the graft to reinnervate the host. Eventually alternative tissues may alleviate the need for fetal tissue. The use of neurotrophic factors should prove an important adjuvant to the repair and restoration of lost neurological function. As this technology is applied to other neurological diseases, it will be important to evaluate the appropriateness of grafting through extensive animal model studies and to balance the potential benefits of such therapy against the degree of risk from surgery and the severity of the disease.

New aspects of neurotransplantation

We have examined the possibility of promoting axonal regeneration within lesioned neural tissue using grafted artificial gel matrices. Polymeric matrices which feature a three-dimensional crosslinked macromolecular network were implanted into preformed lesions of the central nervous system (CNS). The host response consisted of matrix invasion by glial elements and the deposition of newly synthesized extracellular molecules. This rearrangement of the brain scarring process into an organized cellular coating promoted axonal regeneration into the gels. Entrapment of embryonic neurons and embryonal carcinoma (EC)-derived neurons, within the gels, was performed to explore the possibility of using polymer brain implants as neural graft microcarriers. Our results suggest that this approach will be useful for the delivery of cells and the promotion of axonal elongation required for successful neurotransplantation.

A novel approach to neural transplantation in Parkinson's disease: use of polymer-encapsulated cell therapy

Transplantation of dopaminergic neurons derived from fetal or adrenal tissue into the striatum is a potentially useful treatment for Parkinson's disease (PD). Although initially promising, recent clinical studies using adrenal autografts have demonstrated limited efficacy. The use of human fetal cells, despite promising preliminary results, is complicated by tissue availability and ethical concerns. An attractive alternative is based on encapsulating dopamine-producing cells into polymer capsules prior to transplantation. Polymer capsules can be fabricated to surround the cells with a semi-permeable and immunoprotective barrier. The semi-permeable membrane allows nutrients to enter the capsule, so the encapsulated cells will survive and function, and dopamine and other low molecular weight constituents to diffuse out into the host tissue. Thus, the technique allows use of unmatched human tissue (allografts), or even animal tissue (xenografts) without immunosuppression of the recipient. Cell-loaded polymer capsules can also be retrieved if necessary or desired. The demonstration that striatal implants of encapsulated dopamine-producing cells promote behavioral recovery in rodent and primate models of PD further suggests that cellular encapsulation may be a useful strategy for ameliorating the behavioral consequences of PD.

Grafting of perfused adrenal medullary tissue into the caudate nucleus of patients with Parkinson's disease. Clinica Puerta de Hierro Neural Transplantation Group

The authors report results obtained in 20 severely affected patients with Parkinson's disease (Grade IV or V) who received an autotransplant of perfused adrenal medullary tissue. This study seems to indicate that these autoimplants can improve the parkinsonian symptomatology and induce amelioration in the patients' performance of routine activities. All the symptoms analyzed showed improvement, although it differed in intensity and time of onset. Moreover, this improvement was accompanied by a reduction in the daily intake of L-dopa, with discontinuance of dopamine agonists and amantadine. A number of medical complications were encountered, including three deaths, probably related to performing abdominal surgery in seriously affected parkinsonian patients who were unable to tolerate the discontinuance of their medication. The transient psychiatric disorders observed appeared to be related to the postoperative dose of L-dopa and/or anticholinergic agents administered, and diminished or disappeared when the doses were reduced. The reasons for improvement, which was bilateral, remain unknown, although one cause may be the surgical trauma (minicaudotomy) together with the implantation of adrenal medullary tissue, which may promote the sprouting of surviving dopaminergic fibers. Moreover, in this series, perfusion of adrenal medulla increased the capacity for revascularization of the tissue and may have reduced the damaging effects of warm ischemia on the cells. This, together with the existence of fenestrated vessels, could hypothetically have served as an access point for drugs, and if the implanted cells were viable, they might have served to store and manufacture different factors and/or transmitters. These results as well as those of other groups justify the development of a controlled international clinical trial.

Partial lesion of the substantia nigra: relation between extent of lesion and rotational behavior

Recent work, largely carried out in primate models of Parkinson's disease (PD), indicates that residual dopaminergic neurons in the midbrain and their axons to the nucleus accumbens and striatum can be stimulated to sprout collateral axons, reinnervate the striatum, and cause a behavioral recovery. We sought to create a partial lesion model of PD in the rat that would (i) mimic the pattern of cell loss in human patients in early stages of PD, and (ii) permit examination of experimental manipulations that promote sprouting of axons of the surviving dopaminergic cells in the midbrain. Rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta (SNpc) were tested weekly for rotational asymmetry following administration of apomorphine or amphetamine. After completion of behavioral testing, the animals were sacrificed and the brains immunolabeled for tyrosine hydroxylase (TH). Analysis of anatomical and behavioral data revealed a strong correlation between number of remaining TH-immunoreactive cells in the SNpc and the number of rotations induced by apomorphine. There was no significant correlation between number of remaining TH-immunoreactive nigral neurons and number of rotations induced by amphetamine. We also examined the relation between area in the denervated striatum with remaining TH-immunoreactive axons, number of TH-immunoreactive cells in the lesioned SNpc, and rotational behavior. As expected, there was a strong correlation between area innervated by TH-immunoreactive axons and number of remaining TH-immunoreactive neurons in the lesioned SNpc. Total extent of innervation was also correlated with number of apomorphine-induced rotations but not with number of amphetamine-induced rotations.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracerebral adrenal medulla grafts: a review

This review summarizes basic and clinical research on intracerebral adrenal medulla grafts, emphasizing potential applications to Parkinson's disease. Properties of intraventricular and intraparenchymal grafts are described, and cell survival and functional effects are compared. It is clear that adrenal medulla allografts survive poorly in the parenchyma of the corpus striatum and better in the lateral ventricle. Nerve growth factor (NGF) may improve the survival of adrenal medulla grafts. In the absence of added NGF even adrenal medulla grafts in the ventricle survive irregularly, and the factors required for graft survival in the ventricle are not well understood. In the 6-hydroxydopamine-lesioned rat model most evidence suggests, not surprisingly, that adrenal medulla grafts produce functional effects only when they survive. These effects may be related to production of catecholamines by the transplanted cells. In addition, adrenal medulla grafts may produce trophic effects on host brain. These effects are most evident in animals with MPTP-induced damage to dopaminergic systems and may be nonspecific, possibly related in part to the brain injury that is induced by graft implantation. Trophic effects may contribute to the functional effects of adrenal medulla grafts: For intraparenchymal grafts, trophic effects that do not require cell survival may contribute small functional changes, while additional behavioral effects may require substantial chromaffin cell survival. The evidence for direct dopamine-mediated effects as compared to trophic mechanisms of action for these grafts in animal models for Parkinson's disease is presented. Clinical studies of adrenal medulla grafts in human patients are examined and compared in detail. When inspected closely, the various clinical studies are in general agreement on most points, although there are differences in the degree of improvement found, both across different studies and individual patients. It is concluded that some beneficial clinical effects occur, with small to modest changes in most patients and substantial improvement in a minority of patients. There also seem to be larger or more consistent changes in durations of "on" and "off" times in L-dihydroxyphenylalanine-treated patients. There are substantial side effects, and it is not clear that the clinical changes are sufficient to justify performing adrenal medulla transplantation in human patients as a routine procedure.(ABSTRACT TRUNCATED AT 400 WORDS)

NGF-like trophic support from peripheral nerve for grafted rhesus adrenal chromaffin cells

Autopsy results on patients and corresponding studies in nonhuman primates have revealed that autografts of adrenal medulla into the striatum, used as a treatment for Parkinson's disease, do not survive well. Because adrenal chromaffin cell viability may be limited by the low levels of available nerve growth factor (NGF) in the striatum, the present study was conducted to determine if transected peripheral nerve segments could provide sufficient levels of NGF to enhance chromaffin cell survival in vitro and in vivo. Aged female rhesus monkeys, rendered hemiparkinsonian by the drug MPTP (n-methyl-4-phenyl-1,2,3,6 tetrahydropyridine), received autografts into the striatum using a stereotactic approach, of either sural nerve or adrenal medulla, or cografts of adrenal medulla and sural nerve (three animals in each group). Cell cultures were established from tissue not used in the grafts. Adrenal chromaffin cells either cocultured with sural nerve segments or exposed to exogenous NGF differentiated into a neuronal phenotype. Chromaffin cell survival, when cografted with sural nerve into the striatum, was enhanced four- to eightfold from between 8000 and 18,000 surviving cells in grafts of adrenal tissue only up to 67,000 surviving chromaffin cells in cografts. In grafts of adrenal tissue only, the implant site consisted of an inflammatory focus. Surviving chromaffin cells, which could be identified by both chromogranin A and tyrosine hydroxylase staining, retained their endocrine phenotype. Cografted chromaffin cells exhibited multipolar neuritic processes and numerous chromaffin granules, and were also immunoreactive for tyrosine hydroxylase and chromogranin A. Blood vessels within the graft were fenestrated, indicating that the blood-brain barrier was not intact. Additionally, cografted chromaffin cells were observed in a postsynaptic relationship with axon terminals from an undetermined but presumably a host origin.

Adrenal medullary transplantation into the brain for treatment of Parkinson's disease: clinical outcome and neurochemical studies

Transplantation of adrenal medulla into the caudate nucleus as treatment for Parkinson's disease was performed in eight patients. Although our previous 6-month follow-up revealed early modest improvement, an extension of that follow-up to 1 year disclosed no additional gains in any patient. At the end of 1 year, only one patient could be categorized as moderately improved; three patients were mildly improved, and four patients were unimproved. The rationale for transplanting adrenal medulla was to reestablish a physiologic source of dopamine to the striatum. We measured cerebrospinal fluid (CSF) and plasma catecholamines and metabolites before and after transplantation. Conjugated dopamine (the predominant form of dopamine found in the CSF) and homovanillic acid (the major dopamine metabolite) were modestly and inconsistently increased in the CSF. Conjugated and free epinephrine and norepinephrine, as well as 3-methoxy-4-hydroxyphenylglycol concentrations were not increased in CSF after graft placement, an indication that the adrenal chromaffin cells were no longer producing high levels of these nondopamine catecholamines and metabolites. CSF cortisol concentrations were not increased after transplantation, compared with values from controls, consistent with low numbers of functioning adrenal cortical cells contaminating the graft (or poor survival). Posttransplantation CSF did not induce a neurotrophic effect in cell cultures of 15-day embryonic rat dorsal root ganglion or PC12 (rat pheochromocytoma) cell lines. Survival of samples of patients' adrenal medullary tissue for 2 weeks in tissue culture attested to the viability of the graft at the time of transplantation. The relative concentrations of dopamine to epinephrine or norepinephrine increased in these cultured adrenal medullary cells, presumably because of loss of the glucocorticoid influence on catecholamine synthesis. A wide variety of factors could have contributed to our failure to replicate the earlier impressive results of adrenal-to-brain transplantation reported by others. Continued transplantation studies in animal models of parkinsonism are necessary for better elucidation of these factors.

Transplantation into the human brain: present status and future possibilities

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Adrenal medullary autografts into the basal ganglia of Cebus monkeys: injury-induced regeneration

Questions arising from recent clinical neural transplantation trials in Parkinson's disease have under-scored the necessity for a thorough experimental evaluation of the structural and functional consequences of this procedure. The present study investigated the neuroanatomical host reaction to intrastriatal implants in normal and 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP)-treated nonhuman primates. Nine monkeys (Cebus apella) received intrastriatal implants using either a stereotactic approach with a silver tissue carrier or an open microsurgical procedure. Seven of these animals received intrastriatal adrenal medullary autografts, while two received control implants consisting of the tissue carrier alone. One month following transplantation, the hosts' brains were evaluated via immunohistochemical and routine histologic methods. In both MPTP-treated and normal monkeys, enhanced ipsilateral expression of tyrosine hydroxylase-like immunoreactive (TH-IR) fibers in the caudate nucleus was observed, despite minimal survival of adrenal chromaffin cells in the implants. The intensity of this response was greatest adjacent to the implant site, but a clearly increased degree of ipsilateral striatal fiber staining also could be seen several millimeters from the graft. TH-IR fibers also were more dense and of thicker caliber throughout the nigrostriatal and mesolimbic pathways ipsilateral to the implant. Control stereotactic implants, consisting of a silver tissue carrier alone, produced a similar enhancement of immunoreactive fibers, suggesting an induction of TH-IR fibers by the parenchymal injury produced during surgical implantation. There are two major hypotheses proposed to explain why adrenal medullary grafts may promote functional recovery in human parkinsonism: (1) replacement of lost striatal neurotransmitter (dopamine) by the viable grafted tissue, or (2) induction of recovery of remaining host dopaminergic systems by the implantation procedure. Our current data appear to support the latter.