Preservation of fetal ventral mesencephalic cells by cool storage: in-vitro viability and TH-positive neuron survival after microtransplantation to the striatum

Past, present, and future of cell replacement therapy for parkinson's disease: a novel emphasis on host immune responses

Parkinson's disease (PD) stands as the second most common neurodegenerative disorder after Alzheimer's disease, and its prevalence continues to rise with the aging global population. Central to the pathophysiology of PD is the specific degeneration of midbrain dopamine neurons (mDANs) in the substantia nigra. Consequently, cell replacement therapy (CRT) has emerged as a promising treatment approach, initially supported by various open-label clinical studies employing fetal ventral mesencephalic (fVM) cells. Despite the initial favorable results, fVM cell therapy has intrinsic and logistical limitations that hinder its transition to a standard treatment for PD. Recent efforts in the field of cell therapy have shifted its focus towards the utilization of human pluripotent stem cells, including human embryonic stem cells and induced pluripotent stem cells, to surmount existing challenges. However, regardless of the transplantable cell sources (e.g., xenogeneic, allogeneic, or autologous), the poor and variable survival of implanted dopamine cells remains a major obstacle. Emerging evidence highlights the pivotal role of host immune responses following transplantation in influencing the survival of implanted mDANs, underscoring an important area for further research. In this comprehensive review, building upon insights derived from previous fVM transplantation studies, we delve into the functional ramifications of host immune responses on the survival and efficacy of grafted dopamine cells. Furthermore, we explore potential strategic approaches to modulate the host immune response, ultimately aiming for optimal outcomes in future clinical applications of CRT for PD.

Critical points for optimizing long-term culture and neural differentiation capacity of rodent and human neural stem cells to facilitate translation into clinical settings

Despite several decades of research on the nature and functional properties of neural stem cells, which brought great advances in regenerative medicine, there is still a plethora of ambiguous protocols and interpretations linked to their applications. Here, we present a whole spectrum of protocol elements that should be standardized in order to obtain viable cell cultures and facilitate their translation into clinical settings. Additionally, this review also presents outstanding limitations and possible problems to be encountered when dealing with protocol optimization. Most importantly, we also outline the critical points that should be considered before starting any experiments utilizing neural stem cells or interpreting their results.

Dual origins of the Northwest Chinese Kyrgyz: the admixture of Bronze age Siberian and Medieval Niru'un Mongolian Y chromosomes

The Kyrgyz are a trans-border ethnic group, mainly living in Kyrgyzstan. Previous genetic investigations of Central Asian populations have repeatedly investigated the Central Asian Kyrgyz. However, from the standpoint of human evolution and genetic diversity, Northwest Chinese Kyrgyz is one of the more poorly studied populations. In this study, we analyzed the non-recombining portion of the Y-chromosome from 298 male Kyrgyz samples from Xinjiang Uygur Autonomous Region in northwestern China, using a high-resolution analysis of 108 biallelic markers and 17 or 24 STRs. First, via a Y-SNP-based PCA plot, Northwest Chinese Kyrgyz tended to cluster with other Kyrgyz population and are located in the West Asian and Central Asian group. Second, we found that the Northwest Chinese Kyrgyz display a high proportion of Y-lineage R1a1a1b2a2a-Z2125, related to Bronze Age Siberian, and followed by Y-lineage C2b1a3a1-F3796, related to Medieval Niru'un Mongols, such as Uissun tribe from Kazakhs. In these two dominant lineages, two unique recent descent clusters have been detected via NETWORK analysis, respectively, but they have nearly the same TMRCA ages (about 13th-14th centuries). This finding once again shows that the expansions of Mongol Empire had a striking effect on the Central Asian gene pool.

Winter is coming: the future of cryopreservation

The preservative effects of low temperature on biological materials have been long recognised, and cryopreservation is now widely used in biomedicine, including in organ transplantation, regenerative medicine and drug discovery. The lack of organs for transplantation constitutes a major medical challenge, stemming largely from the inability to preserve donated organs until a suitable recipient is found. Here, we review the latest cryopreservation methods and applications. We describe the main challenges-scaling up to large volumes and complex tissues, preventing ice formation and mitigating cryoprotectant toxicity-discuss advantages and disadvantages of current methods and outline prospects for the future of the field.

The Effect of Hypothermic and Cryogenic Preservation on Engineered Neural Tissue

This study explored different approaches to preserve engineered neural tissue (EngNT), a stabilized, cellular collagen hydrogel containing columns of aligned Schwann cells for nervous system repair. The ability to preserve EngNT without disrupting cellular and extracellular components and structures is important for clinical translation and commercialization. Stabilized cellular gels and EngNT constructs were preserved under various conditions and cell survival assessed using live/dead microscopy and metabolic assay. Optimal survival was recorded in hypothermic (4°C) conditions for 2–3 days using Hibernate^®-A media and, for longer-term cryogenic storage (liquid nitrogen), using a mixture of 60% Dulbecco's modified Eagle's medium, 30% fetal bovine serum, and 10% dimethyl sulfoxide. Functionality and structure of preserved EngNT were assessed in coculture with dorsal root ganglion neurons, which indicated that alignment of Schwann cells and the ability of EngNT to support and guide neuronal regeneration were not disrupted. The identification of conditions that preserve EngNT will inform development of storage and transport methodologies to support clinical and commercial translation of this technology and other therapies based on cellular hydrogels.

A Comparative Study of Preparation Techniques for Improving the Viability of Striatal Grafts Using Vital Stains, in Vitro Cultures, and in Vivo Grafts

Cell suspension grafts from embryonic striatal primordia placed into the adult rat striatum survive well and are able to alleviate a number of behavioral deficits caused by excitotoxic lesions to this structure. However, neither the anatomical connectivity between the graft and host nor the functional recovery elicited by the grafts is completely restored. One way in which the survival and function of embryonic striatal grafts may be enhanced is by the improvement of techniques for the preparation of the cell suspension prior to implantation, an issue that has been addressed only to a limited extent. We have evaluated a number of parameters during the preparation procedure, looking at the effects on cell survival over the first 24 h from preparation using vital dyes and the numbers of surviving neurons in vitro, after 4 days in culture, in addition to graft survival and function in vivo. Factors influencing cell survival include the type of trypsinization procedure and the age of donor tissues used for suspension preparation. The presence of DNase has no effect on cell viability but aids the dissociation of the tissue to form single cells. These results have important implications for the use of embryonic striatal grafts in animal models of Huntington's disease, and in any future clinical application of this research.

Electrophysiological Characterization of eGFP-Labeled Intrastriatal Dopamine Grafts

Substitution of degenerated dopaminergic (DA) neurons by intrastriatally transplanted ventral mesencephalon (VM)-derived progenitor cells has been shown to improve motor functions in parkinsonian patients and animal models, whereas investigations of electrophysiological properties of the grafted DA neurons have been rarely performed. Here we show electrophysiological properties of grafted VM progenitor cells at different time intervals up to 12 weeks after transplantation measured in acute brain slices using eGFP-Flag transfection to identify the graft. We were able to classify typical DA neurons according to the biphasic progression (voltage "sag") to hyperpolarizing current injections. Two types of DA-like neurons were classified. Whereas type 1 neurons were characterized by delayed action potentials after hyperpolarization and irregular spontaneous firing, type 2 neurons displayed burst firing after hyperpolarization, spontaneous bursts, and regular firing. Comparison to identified DA neurons in vitro indicates a high integration of the intrastriatally grafted neurons, since in vitro cultures displayed regular firing spontaneously, whereas grafted identified DA neurons showed irregular firing. Additionally, type 1 and type 2 neurons exhibited a slight increase in the spontaneous firing frequency over time intervals after grafting, which might reflect a progressive integration of the grafted DA neurons. Our results provide evidence of the differentiation of grafted VM progenitor cells into mature integrated DA neurons, which are shown to replace the missing DA neurons functionally early after grafting.

A novel strategy for intrastriatal dopaminergic cell transplantation: sequential "nest" grafting influences survival and behavioral recovery in a rat model of Parkinson's disease

Neural transplantation in experimental parkinsonism (PD) is limited by poor survival of grafted embryonic dopaminergic (DA) cells. In this proof-of-principle study we hypothesized that a first regular initial graft may create a "dopaminergic" environment similar to the perinatal substantia nigra and consequently stimulate a subsequent graft. Therefore, we grafted ventral mesencephalic neurons sequentially at different time intervals into the same target localization. Rats with a unilateral lesion of the dopamine neurons produced by injections of 6-hydroxydopamine (6-OHDA) received E14 ventral mesencephalon derived grafts into the DA-depleted striatum. In the control group we grafted all 6 deposits on the first day (d0). The other 4 groups received four graft deposits distributed over 2 implantation tracts followed by a second engraftment injected into the same site 3, 6, 14 and 21 days later. Quantitative assessment of the survival of tyrosine hydroxylase-immunoreactive neurons and graft volume revealed best results for those DA grafts implanted 6 days after the first one. In the present study, a model of short-interval sequential transplantation into the same target-site, so called "nest" grafts were established in the 6-OHDA rat model of PD which might become a useful tool to further elucidate the close neurotrophic and neurotopic interactions between the immediate graft vicinity and the cell suspension graft. In addition, we could show that the optimal milieu was established around the sixth day after the initial transplantation. This may also help to further optimize current transplantation strategies to restore the DA system in patients with PD.

Nigral grafts in animal models of Parkinson's disease. Is recovery beyond motor function possible?

Parkinson's disease (PD) has long been considered predominantly to be a "movement disorder," and it is only relatively recently that nonmotor symptoms of PD have been recognized to be a major concern to patients. Consequently, there has been surprisingly little investigation into the feasibility of utilizing cell replacement therapies to ameliorate any of the nonmotor dysfunctions of PD. In this chapter, we identify nonmotor impairments associated predominately with dopaminergic dysmodulation, evaluate the few emerging studies that have identified a role for dopamine and nigral transplantation in nonmotor performance, and consider a number of outstanding questions and considerations dominating the field of nigral transplantation today. Preliminary results obtained from rodent models of PD, despite being limited in number, give clear indications of graft effects on striatal processing beyond the simple activation of motor output and promise a major, exciting, and fruitful new avenue of research for the next decade. We can now consider the prospect of rewriting the opportunities for treating patients, with new stem cell sources to be complemented by new targets for therapeutic benefit.

Cell transplantation and gene therapy in Parkinson's disease

Parkinson's disease is a progressive neurodegenerative disorder affecting, in part, dopaminergic motor neurons of the ventral midbrain and their terminal projections that course to the striatum. Symptomatic strategies focused on dopamine replacement have proven effective at remediating some motor symptoms during the course of disease but ultimately fail to deliver long-term disease modification and lose effectiveness due to the emergence of side effects. Several strategies have been experimentally tested as alternatives for Parkinson's disease, including direct cell replacement and gene transfer through viral vectors. Cellular transplantation of dopamine-secreting cells was hypothesized as a substitute for pharmacotherapy to directly provide dopamine, whereas gene therapy has primarily focused on restoration of dopamine synthesis or neuroprotection and restoration of spared host dopaminergic circuitry through trophic factors as a means to enhance sustained controlled dopamine transmission. This seems now to have been verified in numerous studies in rodents and nonhuman primates, which have shown that grafts of fetal dopamine neurons or gene transfer through viral vector delivery can lead to improvements in biochemical and behavioral indices of dopamine deficiency. However, in clinical studies, the improvements in parkinsonism have been rather modest and variable and have been plagued by graft-induced dyskinesias. New developments in stem-cell transplantation and induced patient-derived cells have opened the doors for the advancement of cell-based therapeutics. In addition, viral-vector-derived therapies have been developed preclinically with excellent safety and efficacy profiles, showing promise in clinical trials thus far. Further progress and optimization of these therapies will be necessary to ensure safety and efficacy before widespread clinical use is deemed appropriate.

Isolation and culture of ventral mesencephalic precursor cells and dopaminergic neurons from rodent brains

The ability to isolate ventral midbrain (VM) precursor cells and neurons provides a powerful means to characterize their differentiation properties and to study their potential for restoring dopamine (DA) neurons degenerated in Parkinson's disease (PD). Preparation and maintenance of DA VM in primary culture involves a number of critical steps to yield healthy cells and appropriate data. Here, we offer a detailed description of protocols to consistently prepare VM DA cultures from rat and mouse embryonic fetal-stage midbrain. We also present methods for organotypic culture of midbrain tissue, for differentiation as aggregate cultures, and for adherent culture systems of DA differentiation and maturation, followed by a synopsis of relevant analytical read-out options. Isolation and culture of rodent VM precursor cells and DA neurons can be exploited for studies of DA lineage development, of neuroprotection, and of cell therapeutic approaches in animal models of PD.

Principles and practical issues for cryopreservation of nerve cells

Nerve cells isolated from the brain have a number of research and clinical applications, not the least of which is their transplantation to patients with Parkinson's disease. Neural primary and precursor cells of several areas of the brain are potential candidates for transplantation and research. However, supply of suitable tissue is one of the major problems associated with the widespread application of such techniques. The ability to store such tissue for prolonged periods would greatly alleviate this problem. Cryopreservation allows indefinite storage, provided the storage temperature is sufficiently low. Whilst many of the potentially usable cell types have been shown to be capable of surviving cryopreservation to some degree, survival post-thaw needs to be considerably improved. Cryopreservation techniques applied to date are mostly crude and often adopted from those used for unrelated cell types. Studies involving cryopreservation of primary neural cells and stem cells are reviewed, the basic principles of cryopreservation explained and suggestions made for improvements to the low temperature storage of these cells.

Induction dopamine releasing cells from mouse embryonic stem cells and their long-term culture

Cell transplantation therapy using dopaminergic neurons derived from embryonic stem (ES) cells for the treatment of Parkinson's disease has been proposed as one of the major applications for stem cell-based therapy. However, the low collection efficiency of neurons from a culture dish and the rejection of cells after transplantation are expected to limit their future clinical applications. To overcome these problems, we examined the induction of neurogenesis of ES cells under free-floating conditions and microencapsulation of the obtained cell aggregates into an agarose hydrogel. Cell aggregates from ES cells were cultured in various media under the free-floating condition. Immunohistochemical staining for tyrosine hydroxylase (TH) and RT-PCR analyses for TH and Nurr1 showed that dopaminergic neurons were induced in ES cell aggregates cultured in a 1:2 mixture of conditioned medium of PA6 stromal cells and Glasgow minimum essential medium (GMEM) after 16 days in culture. The cell aggregates could be collected and were encased within agarose microcapsules without loss of dopaminergic neurons. The cell aggregates with/without microencapsulation were maintained in CM/GMEM for an additional period. KCl stimulation assays were done at day 23, 30, 37, 44, 51, and 58 to examine dopamine release. Dopamine release abilities were well maintained during 58 days of observation. Amounts of dopamine release from encapsulated cell aggregates were slightly higher than those of unencapsulated cell aggregates from day 16 to 58. Although efficacy for immunoisolation of the agarose microcapsules still remains for future in vivo studies, microencapsulation did not adversely affect viability and functions of the dopamine releasing ES cell progeny.

Development of A9/A10 dopamine neurons during the second and third trimesters in the African green monkey

Disruption in the development of dopamine-containing neurons has been postulated to underlie several CNS disorders. However, there have been no quantitative studies on the normal development of primate dopamine neurons. Thus, the fetal maturation of primate midbrain dopamine neurons was examined to establish changes that occur in the A9/A10 groups during the second and third trimesters. Eleven fetal African green monkey midbrains were immunostained for tyrosine hydroxylase (TH-ir) as a marker for dopamine neurons and quantified using stereological techniques (nucleator method). The number and size of defined dopamine neurons and the volume occupied by A9/A10 neurons increased in near linear fashion throughout the term. The estimated number of defined dopamine neurons in each hemisphere rose from approximately 50,000 at embryonic day (E) 70 to 225,000 at birth (E165), similar to the adult population. The size and the area occupied by them at birth were, however, well below the estimated adult levels. Additionally, the younger fetal midbrains had far less diversity in dopamine cell volumes compared with older fetuses and adult brains. Until midway through gestation (E81), clusters of apparently immature midbrain TH-ir cells were observed, but could not be counted. Even though the majority of cells destined to become dopamine neurons are generated in the first trimester, phenotypical maturation of A9 and A10 cell bodies continues steadily throughout gestation and extends well into the postnatal period. These data have relevance to transplantation studies that employ fetal dopaminergic grafts, and to disorders hypothesized to result from damage to developing midbrain dopamine neurons.

Long-term hibernation of human fetal striatal tissue does not adversely affect its differentiation in vitro or graft survival: implications for clinical trials in Huntington's disease

Transplantation of human fetal CNS tissue is a promising therapy for neurodegenerative conditions such as Huntington's disease (HD), but its widespread adoption is limited by restricted tissue availability. One method of overcoming this problem would be to store the tissue in hibernation medium, an approach that we reported previously for human fetal striatal tissue stored for up to 24 h. We now demonstrate the feasibility of storing such tissue for up to 8 days in hibernation medium. When either fresh or 8-day hibernated striatal cells were cultured under standard conditions for 4 days, the proportion of DARPP-32-positive neurons did not differ significantly, although the total number of cells was significantly less from tissue that had been hibernated. Six weeks after transplantation into cyclosporin A-immunosuppressed unilateral quinolinic acid-lesioned rats, there was no significant difference between fresh and hibernated grafts, both in terms of graft volume and extent of striatal phenotypic markers. This study therefore clearly demonstrates that hibernation of human fetal striatal tissue for up to 8 days is not deleterious to its differentiation in culture or survival following transplantation, and is therefore an appropriate method of storage for this tissue.

Glial cell line-derived neurotrophic factor-supplemented hibernation of fetal ventral mesencephalic neurons for transplantation in Parkinson disease: long-term storage

OBJECT

Transplantation of fetal dopaminergic tissue is being investigated in animal models and clinical trials for its potential as a treatment for advanced Parkinson disease. At the same time, the availability of fetal tissue is limited, making its storage time prior to transplantation a key practical issue. Although it results in a smaller percentage of surviving cells. a longer storage time enables fetal tissue obtained over several days to be pooled for transplantation in a recipient. Glial cell line-derived neurotrophic factor (GDNF) has been shown to improve survival of human dopaminergic tissue that has been stored prior to transplantation. The objective of this study was to evaluate the effects on fetal dopaminergic tissue of GDNF-supplemented hibernation for extended periods of 6 to 15 days.

METHODS

The ventral mesencephalon (VM) was harvested in a total of 27 14-day-old rat fetuses, and three VMs were cultured immediately (fresh control group). The remaining 24 VMs were divided sagittally along the midline to yield 48 equal pieces of hemimesencephalon. Twenty-four pieces were stored with GDNF-supplemented hibernation medium for 6, 9, 12, or 15 days, and the 24 "partner" hemimesencephalon pieces were stored in control hibernation medium for the same periods of time. Tissue was cultured for 48 hours and processed for tyrosine hydroxylase (TH) immunoreactivity and double-stained with cresyl violet. Cell counts for all cultures and the percentage of TH-immunoreactive cells were obtained. The percentage of TH-immunoreactive cells for the fresh control group was 6.3 +/- 0.5%. The percentage of TH-immunoreactive cells in cultures derived from tissue stored in GDNF-supplemented medium was significantly increased at 6 and 9 days posthibernation compared with the fresh control group and the "partner" groups stored in hibernation medium only. No significant increase in the percentage of TH-immunoreactive cells was observed in the 12- and 15-day groups.

CONCLUSIONS

In this study the authors have demonstrated that fetal dopaminergic tissue can be safely stored for up to 9 days in GDNF-supplemented hibernation medium. Furthermore, the percentage of TH-immunoreactive cells is significantly increased after 6 and 9 days of storage in this medium, improving the yield of TH-immunoreactive cells prior to transplantation. These observations have practical clinical implications for collecting fetal dopaminergic cells and improving their survival after transplantation.

Glial cell line-derived neurotrophic factor-supplemented hibernation of fetal ventral mesencephalic neurons for transplantation in Parkinson disease: long-term storage

OBJECT

Investigation of fetal dopaminergic tissue transplantation is being conducted in animal models and clinical trials as a potential treatment for advanced Parkinson disease (PD). Because the availability of fetal tissue is limited, however, the duration of its storage prior to transplantation is a key practical issue. Longer storage times may enable fetal tissue obtained over several days to be pooled together for transplantation in a recipient. Glial cell line-derived neurotrophic factor (GDNF) has been shown to improve survival of stored human dopaminergic tissue prior to transplantation. The objective of this study was to evaluate GDNF-supplemented hibernation of fetal dopaminergic tissue for extended periods of 6 to 15 days.

METHODS

A total of 27 rat ventral mesencephalons (VMs) were obtained in gestation Day 14 rat fetuses, and three were cultured immediately (fresh-culture control group). The remaining 24 VMs were divided sagittally along the midline to form 48 equal pieces of hemimesencephalons. Twenty-four pieces were stored with GDNF-supplemented hibernation medium for 6, 9, 12, or 15 days, and the 24 "partner" hemimesencephalons were stored in control hibernation medium for the same periods of time. Tissue was cultured for 48 hours and processed for tyrosine hydroxylase (TH) immunoreactivity and cresyl violet. Cell counts for all cultures and percentage of TH-immunoreactive cells were obtained. The percentage of TH-positive cells for the fresh control group was 6.3 +/- 0.5%; that measured in cultures derived from tissue hibernated in GDNF-supplemented medium was significantly increased at 6 and 9 days posthibernation compared with the fresh-culture control group and the partner groups stored in hibernation medium only. No significant increase in percentage of TH-immunoreactive cells was observed in the 12- and 15-day hibernation groups.

CONCLUSIONS

In summary the authors found that fetal dopaminergic tissue can safely be stored up to 9 days in GDNF-supplemented hibernation medium. Furthermore the percentage of TH-immunoreactive cells is significantly increased after 6 and 9 days of storage in this medium, improving the yield of TH-positive cells prior to transplantation. These observations may have important clinical implications for collecting fetal dopaminergic cells and improving their survival after transplantation.

Comparison of fresh and cryopreserved porcine ventral mesencephalon cells transplanted in A rat model of Parkinson's disease

To evaluate whether cryopreservation of porcine ventral mesencephalon cells influences graft survival and function in vivo, we have transplanted either freshly prepared or cryopreserved cells into the striatum of 6-hydroxydopamine-lesioned rats. A single cell suspension of porcine ventral mesencephalon cells from the same isolation either was stored at 4 degrees C and transplanted the next day or was cryopreserved for 4 weeks in liquid nitrogen vapor. The cryopreserved cells were then rapidly thawed, rinsed, and transplanted in the same manner as the fresh cells, with the same dose of viable cells. All animals received daily injections of cyclosporin A to prevent xenograft rejection. To monitor graft function, amphetamine-induced rotation was measured every 3 weeks between 6 and 15 weeks posttransplantation. After sacrifice at 15 weeks posttransplantation, histological methods were used to compare fresh cell and cryopreserved cell transplants with respect to graft survival, differentiation and integration, and host immune response. Cryopreserved cells were found to be either equivalent or in some cases superior to fresh cells with respect to rotational correction, graft survival, graft volume, numbers of graft-derived dopaminergic neurons, and host immune responses. In conclusion, the results indicate that it is feasible to cryopreserve porcine ventral mesencephalon cells for long-term storage of cells prior to transplantation in an animal model of Parkinson's disease.

Prospects for the treatment of Parkinson's disease using neurotrophic factors

Parkinson's disease (PD) is a debilitating neurodegenerative condition that is characterised by a progressive loss of dopaminergic neurones of the substantia nigra pars compacta (SNpc) and the presence of alpha-synuclein cytoplasmic inclusions (Lewy bodies). Cardinal symptoms include tremor, bradykinesia, and rigidity, although cognitive and autonomic disturbances are not uncommon. Pharmacological treatment targeting the dopaminergic network is relatively effective at ameliorating these symptoms, especially in the early stages of the disease, but none of these therapies are curative and they generate their own problems. As dopaminergic neuronal death in PD occurs in a gradual manner, it is amenable to treatments that can either protect remaining dopaminergic neurones or prevent death of those neurones that have begun to die. Use of neurotrophic factors is a potential candidate, as various factors have been shown to increase dopaminergic neuronal survival in culture and promote survival and axonal growth in animal models of PD. Glial cell line-derived neurotrophic factor (GDNF) is currently the most effective substance that has been intensively studied and shown to have a specific 'dopaminotrophic' effect. This review will therefore focus on studies that have investigated GDNF and discuss the potential for neurotrophic factor treatment in PD.

Influence of time in culture and BDNF pretreatment on survival and function of grafted embryonic rat ventral mesencephalon in the 6-OHDA rat model of Parkinson's disease

Embryonic midbrain can be maintained as free-floating roller tube cultures prior to grafting in experimental Parkinson's disease. We examined the influence of pregrafting culture time and pretreatment with brain-derived neurotrophic factor on graft survival and function. Cultures were prepared from solid pieces of embryonic (E14) rat ventral mesencephalon and maintained 4, 8, or 12 days in vitro with or without brain-derived neurotrophic factor (100 ng/ml) and grafted into the striatum of 6-hydroxydopamine-lesioned rats. Graft survival and function were evaluated by amphetamine-induced rotation behavior, number of tyrosine hydroxylase-immunoreactive neurons, striatal reinnervation, and graft volume. Rats receiving untreated tissue cultured for 4 or 8 days displayed no differences in graft quality, while grafts from 12-day-old cultures contained significantly fewer (P < 0.05) tyrosine hydroxylase-immunoreactive neurons (340 +/- 97, 267 +/- 92, and 62 +/- 19) and displayed a lower survival rate (9.6 +/- 2.7, 7.9 +/- 2.7, and 2.6 +/- 0.8% for 4, 8, and 12 days in vitro, respectively). Only rats grafted with 4- and 8-day-old cultures recovered significantly (P < 0.05) from lesion-induced rotations (69.4 +/- 18.6, 70.3 +/- 13.9, and 23.2 +/- 12.1% for 4, 8, and 12 days in vitro, respectively). Striatal reinnervation decreased with increasing culture time (P < 0.05). Pretreatment of the cultures with brain-derived neurotrophic factor affected only graft-induced fiber reinnervation, which was reduced even after short culture times. We therefore suggest that a storage period of 8 days is well suited to maintain embryonic rat ventral mesencephalon with the free-floating roller tube culture technique prior to transplantation. BDNF pretreatment as a new strategy to improve graft survival and function, however, was not effective.

Hibernated human fetal striatal tissue: successful transplantation in a rat model of Huntington's disease

The use of fresh human fetal tissue in neural transplantation presents considerable logistical difficulties and limits the clinical applicability of this promising therapy. This study compared the survival of human fetal striatal tissue that had been stored for 24 h in a defined hibernation medium with that of fresh human fetal striatal tissue following xenotransplantation in a rat model of Huntington's disease (HD). Six to 7 weeks postgrafting, there was no significant difference between fresh and hibernated grafts in volume or in various striatal phenotypic markers, although there was a trend towards decreased graft volume. We conclude that short-term hibernation of this tissue is without significant adverse effects on the survival of grafted human fetal striatal tissue. This has important implications for the practical implementation of clinical neural transplant programs in HD.

Grafting of nigral tissue hibernated with tirilazad mesylate and glial cell line-derived neurotrophic factor

Transplantation of embryonic ventral mesencephalon is a potential therapy for patients with Parkinson's disease. As only around 5-10% of embryonic dopaminergic neurons survive grafting into the adult striatum, it is considered necessary to use multiple donor embryos. To increase the survival of the grafted dopaminergic neurons, the clinical transplantation program in Lund currently employs the lipid peroxidation inhibitor, tirilazad mesylate, in all solutions used during tissue storage, preparation, and transplantation. However, the difficulty in obtaining a sufficient number of donor embryos still remains an important limiting factor for the clinical application of neural transplantation. In many clinical transplantation programs, it would be a great advantage if human nigral donor tissue could be stored for at least 1 week. This study was performed in order to investigate whether storage of embryonic tissue at 4 degrees C for 8 days can be applied clinically without creating a need to increase the number of donors. We compared the survival of freshly grafted rat nigral tissue, prepared according to the clinical protocol, with tissue transplanted after hibernation. Thus, in all groups tirilazad mesylate was omnipresent. One group of rats was implanted with fresh tissue and three groups with hibernated tissue with or without addition of glial cell line-derived neurotrophic factor (GDNF) in the hibernation medium and/or the final cell suspension. Earlier studies have suggested that GDNF improves the survival of hibernated nigral transplants. We found no statistically significant difference between the groups regarding graft survival after 3 weeks. However, there was a nonsignificant trend for fewer surviving dopaminergic neurons in grafts from hibernated tissue compared to fresh controls. Furthermore, we show that the addition of GDNF to the hibernation medium and/or to the final cell suspension does not significantly increase the survival of the dopaminergic neurons.

Improving the survival of grafted dopaminergic neurons: a review over current approaches

Neural transplantation is developing into a therapeutic alternative in Parkinson's disease. A major limiting factor is that only 3-20% of grafted dopamine neurons survive the procedure. Recent advances regarding how and when the neurons die indicate that events preceding actual tissue implantation and during the first week thereafter are crucial, and that apoptosis plays a pivotal role. Triggers that may initiate neuronal death in grafts include donor tissue hypoxia and hypoglycemia, mechanical trauma, free radicals, growth factor deprivation, and excessive extracellular concentrations of excitatory amino acids in the host brain. Four distinct phases during grafting that can involve cell death have been identified: retrieval of the embryo; dissection and preparation of the donor tissue; implantation procedure followed by the immediate period after graft injection; and later stages of graft maturation. During these phases, cell death processes involving free radicals and caspase activation (leading to apoptosis) may be triggered, possibly involving an increase in intracellular calcium. We review different approaches that reduce cell death and increase survival of grafted neurons, typically by a factor of 2-4. For example, changes in transplantation procedure such as improved media and implantation technique can be beneficial. Calcium channel antagonists such as nimodipine and flunarizine improve nigral graft survival. Agents that counteract oxidative stress and its consequences, such as superoxide dismutase overexpression, and lazaroids can significantly increase the survival of transplanted dopamine neurons. Also, the inhibition of apoptosis by a caspase inhibitor has marked positive effects. Finally, basic fibroblast growth factor and members of the transforming growth factor-beta superfamily, such as glial cell line-derived neurotrophic factor, significantly improve the outcome of nigral transplants. These recent advances provide hope for improved survival of transplanted neurons in patients with Parkinson's disease, reducing the need for human embryonic donor tissue and increasing the likelihood of a successful outcome.

Rat fetal ventral mesencephalon grown as solid tissue cultures: influence of culture time and BDNF treatment on dopamine neuron survival and function

Free-floating roller tube (FFRT) cultures of fetal rat and human nigral tissue are a means for tissue storage prior to grafting in experimental Parkinson's disease. In the present study, FFRT cultures prepared from embryonic-day-14 rat ventral mesencephalon were maintained for 4, 8, 12, or 16 days in vitro (DIV) in the presence or absence (controls) of BDNF [100 ng/ml]. The dopamine content in the culture medium, analyzed by HPLC, was significantly higher (4-5 fold) in the BDNF group at DIV 8 and DIV 12 compared to the corresponding control levels (40 pg/ml). The number of tyrosine hydroxylase immunoreactive neurons was significantly higher for BDNF treated cultures (2729+/-300) at DIV 8, as compared to controls (1679+/-217). At DIV 12, the culture volume was significantly increased by BDNF (1.05+/-0.12 vs. 0.71+/-0.04 mm3). Similar results were obtained for total protein. Western blot analysis demonstrated increasing signals for GFAP with increasing time in culture, but levels for control and BDNF treated cultures did not differ at any time-point investigated. In conclusion, it is suggested that the time window for effective storage of dopaminergic tissue prior to grafting can be extended by using the FFRT culture technique and that the in vitro storage may be further prolonged by treatment with BDNF.

Glial cell line-derived neurotrophic factor improves intrastriatal graft survival of stored dopaminergic cells

Glial cell line-derived neurotrophic factor, the newest member of the transforming growth factor-beta superfamily, has been shown to promote the survival and differentiation of dopaminergic neurons in the ventral mesencephalon. Glial cell line-derived neurotrophic factor has been implicated in both the in vitro and in vivo recovery of mesencephalic dopaminergic cells challenged with the neurotoxins 1-methyl-4-phenylpyridinium and 6-hydroxydopamine. Previous studies have shown increased survival of intrastriatally transplanted dopaminergic cells when followed by infusion of neurotrophic factors such as basic fibroblast growth factor, brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor. However, the effects of glial cell line-derived neurotrophic factor co-administered with dopaminergic cells prior to implantation in the host striatum have not been studied. In the present study, the hypothesis was that treating fetal ventral mesencephalic tissue containing the dopaminergic substantia nigra with glial cell line-derived neurotrophic factor either during storage or at the time of transplantation, would enhance grafted dopaminergic cell survival and functional reinnervation of the host striatum in the unilaterally 6-hydroxydopamine-lesioned rat. To test this hypothesis, two experiments were performed. In the first experimental group (n = 7), fetal ventral mesencephalons from embryonic day 14 rats were maintained in hibernation medium containing glial cell line-derived neurotrophic factor (1 migrogram/ml) at 4 degrees C for six days prior to dissociation and stereotactic implantation into the host striatum: the control group (n = 5) received tissue hibernated without glial cell line-derived neurotrophic factor. The second experimental group (n = 8) received fresh fetal ventral mesencephalic tissue treated with glial cell line-derived neurotrophic factor (0.2 microgram/microliter) while the control group (n = 5) received the fresh graft with no glial cell line-derived neurotrophic factor. Transplantation success was assessed by behavioural analysis (rotometry) and tyrosine hydroxylase immunohistochemistry. Cell counts of tyrosine hydoxylase-stained sections revealed a statistically significant increase in tyrosine hydroxylase-positive neurons in grafts exposed to glial cell line-derived neurotrophic factor during hibernation as compared to control grafts. In addition, there was a statistically significant enhancement of fibre density in the glial cell line-derived neurotrophic factor hibernation graft group as compared to the glial cell line-derived neurotrophic factor fresh graft group. Behavioural analysis three weeks post-grafting exhibited a statistically significant decrease in amphetamine-induced rotations in animals transplanted with glial cell line-derived neurotrophic factor grafts as compared to control grafts. These findings suggest that storing dopaminergic cells in a glial cell line-derived neurotrophic factor-containing medium prior to transplantation increases graft survival, graft derived fibre outgrowth, and behavioural recovery in the adult host. This observation has potential implications for enhancing the efficacy of neural transplantation in the treatment of Parkinson's disease.

Characteristics of human fetal spinal cord grafts in the adult rat spinal cord: influences of lesion and grafting conditions

The present study evaluated the growth potential and differentiation of human fetal spinal cord (FSC) tissue in the injured adult rat spinal cord under different lesion and grafting conditions. Donor tissue at 6-9 weeks of gestational age was obtained through elective abortions and transplanted either immediately into acute resection (solid grafts) or into chronic contusion (suspension and solid grafts) lesions (i.e., 14-40 days after injury) in the thoracic spinal cord. The xenografts were then examined either histologically in plastic sections or immunocytochemically 1-3 months postgrafting. Intraspinal grafts in acute lesions demonstrated an 83% survival rate and developed as well-circumscribed nodules that were predominantly composed of immature astrocytes. Solid-piece grafts in chronic contusion lesions exhibited a 92% survival rate and also developed as nodular masses. These grafts, however, contained many immature neurons 2 months postgrafting. Suspension grafts in chronic contusion lesions had an 85% survival rate and expanded in a nonrestrictive, diffuse pattern. These transplants demonstrated large neuronally rich areas of neural parenchyma. Extensive neuritic outgrowth could also be seen extending from these grafts into the surrounding host spinal cord. These findings show that human FSC tissue reliably survives and differentiates in both acute and chronic lesions. However, both the lesion environment and the grafting techniques can greatly influence the pattern of differentiation and degree of host-graft integration achieved.

Morphometric characteristics of cryopreserved mesencephalic dopamine neurons in culture

Blocks of embryonic rat mesencephalon were freeze-stored for 1-2 years in liquid nitrogen at -196 degrees C with 7.5% dimethyl sulfoxide (DMSO) as cryoprotectant. After thawing, pooled mesencephalic tissues were mechanically dissociated. The cells, plated at two different densities (4.10[5] and 2.10[5]/cm2) were cultured in a serum-supplemented medium for at least 2 weeks before immunocytochemical staining with highly specific antidopamine (DA) antibodies. The cryopreserved DA-immunoreactive (IR) neurons were compared, by means of computerized morphometry, to the fresh ones plated at the same densities. A separate analysis of the dendritic and axonal morphometric parameters revealed that the cryopreserved DA-IR cells, whatever the experimental conditions, had significantly larger dendritic fields and, less significantly, larger axonal fields than their fresh counterparts. A principal component analysis, mainly based on the dendritic morphometric parameters, allowed to individualize only two populations (cryopreserved and fresh) among the four groups studied. These findings underline the role of dendrites as potential sites of release and/or re-uptake of dopamine and their possible implications in functionally effective cryopreserved nigral grafts.

The lazaroid U-83836E improves the survival of rat embryonic mesencephalic tissue stored at 4 degrees C and subsequently used for cultures or intracerebral transplantation

We assessed the effects of addition of the lazaroid U-83836E to a preservation medium on the survival of rat dopamine neurons stored before culturing or intracerebral transplantation. Embryonic ventral mesencephalic tissue was preserved at 4 degrees C for 8 days with or without the addition of 0.3 mu M of U-83836E to a chemically defined "hibernation" medium. Freshly dissected mesencephalic tissue was used in control groups. For culture experiments, the mesencephalic tissue was dissociated and grown in serum-containing medium. Following 24-48 h in vitro, the number of dopamine neurons in cultures derived from tissue hibernated without the lazaroid was 40% of fresh control, compared with 67% of control in cultures prepared from tissue stored in the presence of U-83836E. When mesencephalic tissue was transplanted to the dopamine-depleted striatum of hemiparkinsonian rats following 8 days storage at 4 degrees C in a medium without U-83836E, the mean number of surviving dopamine neurons in the grafts was significantly reduced to 40% of control. In contrast, grafts of tissue which had been hibernated in U-83836E-containing medium contained as many dopamine neurons as transplants of freshly dissected tissue. High yields of surviving grafted dopamine neurons were correlated to a significantly faster onset of functional recovery of amphetamine-induced motor asymmetry. We conclude that the storage period for rat mesencephalic tissue can be prolonged up to 8 days when using lazaroid-supplemented hibernation medium. As lazaroids have undergone clinical safety testing, the application of lazaroids for tissue storage in clinical transplantation trials can be envisaged.