Polymer-encapsulated PC-12 cells demonstrate high-affinity uptake of dopamine in vitro and 18F-Dopa uptake and metabolism after intracerebral implantation in nonhuman primates

PC 12 Pheochromocytoma Cell Response to Super High Frequency Terahertz Radiation from Synchrotron Source

High frequency (HF) electromagnetic fields (EMFs) have been widely used in many wireless communication devices, yet within the terahertz (THz) range, their effects on biological systems are poorly understood. In this study, electromagnetic radiation in the range of 0.3–19.5 × 10¹² Hz, generated using a synchrotron light source, was used to investigate the response of PC 12 neuron-like pheochromocytoma cells to THz irradiation. The PC 12 cells remained viable and physiologically healthy, as confirmed by a panel of biological assays; however, exposure to THz radiation for 10 min at 25.2 ± 0.4 °C was sufficient to induce a temporary increase in their cell membrane permeability. High-resolution transmission electron microscopy (TEM) confirmed cell membrane permeabilization via visualisation of the translocation of silica nanospheres (d = 23.5 ± 0.2 nm) and their clusters (d = 63 nm) into the PC 12 cells. Analysis of scanning electron microscopy (SEM) micrographs revealed the formation of atypically large (up to 1 µm) blebs on the surface of PC 12 cells when exposed to THz radiation. Long-term analysis showed no substantial differences in metabolic activity between the PC 12 cells exposed to THz radiation and untreated cells; however, a higher population of the THz-treated PC 12 cells responded to the nerve growth factor (NGF) by extending longer neurites (up to 0–20 µm) compared to the untreated PC12 cells (up to 20 µm). These findings present implications for the development of nanoparticle-mediated drug delivery and gene therapy strategies since THz irradiation can promote nanoparticle uptake by cells without causing apoptosis, necrosis or physiological damage, as well as provide a deeper fundamental insight into the biological effects of environmental exposure of cells to electromagnetic radiation of super high frequencies.

Encapsulated cell therapy for neurodegenerative diseases: from promise to product

Delivering therapeutic molecules, including trophic factor proteins, across the blood brain barrier to the brain parenchyma to treat chronic neurodegenerative diseases remains one of the great challenges in biology. To be effective, delivery needs to occur in a long-term and stable manner at sufficient quantities directly to the target region in a manner that is selective but yet covers enough of the target site to be efficacious. One promising approach uses cellular implants that produce and deliver therapeutic molecules directly to the brain region of interest. Implanted cells can be precisely positioned into the desired region and can be protected from host immunological attack by encapsulating them and by surrounding them within an immunoisolatory, semipermeable capsule. In this approach, cells are enclosed within a semiporous capsule with a perm selective membrane barrier that admits oxygen and required nutrients and releases bioactive cell secretions while restricting passage of larger cytotoxic agents from the host immune defense system. Recent advances in human cell line development have increased the levels of secreted therapeutic molecules from encapsulated cells, and membrane extrusion techniques have led to the first ever clinical demonstrations of long-term survival and function of encapsulated cells in the brain parenchyma. As such, cell encapsulation is capable of providing a targeted, continuous, de novo synthesized source of very high levels of therapeutic molecules that can be distributed over significant portions of the brain.

PHBV microspheres as neural tissue engineering scaffold support neuronal cell growth and axon-dendrite polarization

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) microspheres, with properties such as slower degradation and more efficient drug delivery properties, have important benefits for neural tissue engineering. Our previous studies have shown PHBV microspheres to improve cell growth and differentiation. This study aimed to investigate if PHBV microspheres would support neurons to extend these benefits to neural tissue engineering. PHBV microspheres' suitability as neural tissue engineering scaffolds was investigated using PC12 cells, cortical neurons (CNs), and neural progenitor cells (NPCs) to cover a variety of neuronal types for different applications. Microspheres were fabricated using an emulsion-solvent-evaporation technique. DNA quantification, cell viability assays, and immunofluorescent staining were carried out. PC12 cultures on PHBV microspheres showed growth trends comparable to two-dimensional controls. This was further verified by staining for cell spreading. Also, CNs expressed components of the signaling pathway on PHBV microspheres, and had greater axon-dendrite segregation (4.1 times for axon stains and 2.3 times for dendrite stains) than on coverslips. NPCs were also found to differentiate into neurons on the microspheres. Overall, the results indicate that PHBV microspheres, as scaffolds for neural tissue engineering, supported a variety of neuronal cell types and promoted greater axon-dendrite segregation.

The interhemispheric connections of the striatum: Implications for Parkinson's disease and drug-induced dyskinesias

Parkinson's disease (PD) is characterized by loss of nigrostriatal neurons and depletion of dopamine. This pathological feature leads to alterations to basal ganglia circuitry and subsequent motor disability. Pharmacological dopamine replacement therapy with medications such as levodopa ameliorates the symptoms of PD but can lead to motor complications known as drug-induced dyskinesias. We have recently shown that clinically hemiparkinsonian rhesus monkeys do not develop levodopa-induced dyskinesias despite chronic intermittent exposure and significant unilateral loss of nigrostriatal neurons and dopamine. It is currently unclear what mechanisms prevent the onset of dyskinesias in these animals. Based on our study and results from previous lesioning studies in both the rat and monkey models of PD, we hypothesize that one potential mechanism that may prevent the genesis of dyskinesias in these animals is interhemispheric neuromodulation. Two potential interhemispheric connections that may modulate dyskinesias are the interhemispheric nigrostriatal and corticostriatal pathways. Few investigators have examined the interhemispheric nigrostriatal and corticostriatal connections and the functional role they may play in drug-induced dyskinesias in PD. Therefore, in the following review, we assess the neuroanatomical, electrophysiological and behavioral properties of these interhemispheric connections. Future studies evaluating these interhemispheric striatal pathways and the pathophysiological changes that occur to these pathways in the dyskinetic state are warranted to further develop treatments that prevent or mitigate drug-induced dyskinesias in PD.

Dyskinesias do not develop after chronic intermittent levodopa therapy in clinically hemiparkinsonian rhesus monkeys

The stable 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced hemiparkinsonian (HP) rhesus monkey model of Parkinson's disease (PD) has been frequently used to test preclinical experimental therapeutics targeted to treat patients with advanced PD who suffer from motor fluctuations and drug-induced dyskinesias. We retrospectively analyzed data from 17 stable HP rhesus monkeys treated long-term with chronic intermittent dosing of levodopa (LD) in an attempt to induce choreoathetoid and dystonic dyskinesias. Rhesus monkeys in stable HP state for greater than 6 months as confirmed by multiple blinded behavioral ratings and (18)F-dopa Positron Emission Tomography (PET) were treated with optimal doses of LD to provide maximal amelioration of unilateral clinical parkinsonism without any adverse effects. Thereafter, each animal was given chronic intermittent daily challenge with doses of LD up to 700 mg/day orally or with 300 mg/kg/day parenteral injections. LD treatments failed to induce choreoathetoid and dystonic dyskinesias in these animals despite chronic intermittent high dose administration. These results suggest that the stable strictly unilateral HP rhesus monkey model of PD may not be a suitable animal model to test experimental therapeutics targeted against dyskinesias, and that bilateral parkinsonian rhesus models that readily demonstrate drug-induced dyskinesias and clinically relevant motor fluctuations are more appropriate for preclinical experimental testing of therapies designed to treat patients with advanced PD.

A water extract of Mucuna pruriens provides long-term amelioration of parkinsonism with reduced risk for dyskinesias

Dopaminergic anti-parkinsonian medications, such as levodopa (LD) cause drug-induced dyskinesias (DID) in majority of patients with Parkinson's disease (PD). Mucuna pruriens, a legume extensively used in Ayurveda to treat PD, is reputed to provide anti-parkinsonian benefits without inducing DID. We compared the behavioral effects of chronic parenteral administration of a water extract of M. pruriens seed powder (MPE) alone without any additives, MPE combined with the peripheral dopa-decarboxylase inhibitor (DDCI) benserazide (MPE+BZ), LD+BZ and LD alone without BZ in the hemiparkinsonian rat model of PD. A battery of behavioral tests assessed by blinded investigators served as outcome measures in these randomized trials. In experiment 1, animals that received LD+BZ or MPE+BZ at high (6mg/kg) and medium (4mg/kg) equivalent doses demonstrated significant alleviation of parkinsonism, but, developed severe dose-dependent DID. LD+BZ at low doses (2mg/kg) did not provide significant alleviation of parkinsonism. In contrast, MPE+BZ at an equivalent low dose significantly ameliorated parkinsonism. In experiment 2, MPE without any additives (12mg/kg and 20mg/kg LD equivalent dose) alleviated parkinsonism with significantly less DID compared to LD+BZ or MPE+BZ. In experiment 3, MPE without additives administered chronically provided long-term anti-parkinsonian benefits without causing DID. In experiment 4, MPE alone provided significantly more behavioral benefit when compared to the equivalent dose of synthetic LD alone without BZ. In experiment 5, MPE alone reduced the severity of DID in animals initially primed with LD+BZ. These findings suggest that M. pruriens contains water-soluble ingredients that either have an intrinsic DDCI-like activity or mitigate the need for an add-on DDCI to ameliorate parkinsonism. These unique long-term anti-parkinsonian effects of a parenterally administered water extract of M. pruriens seed powder may provide a platform for future drug discoveries and novel treatment strategies in PD.

MRI guidance improves accuracy of stereotaxic targeting for cell transplantation in parkinsonian monkeys

Accuracy of targeting is critical for the success of cell transplantation in the central nervous system. We compared the accuracy of conventional atlas-guided stereotaxis to magnetic resonance imaging (MRI)-guided stereotaxic targeting in various basal ganglia nuclei in parkinsonian monkeys. 28 monkeys underwent unilateral striatal transplantation. High-resolution 3D MR images of the brain were used in 15 monkeys fitted with a MRI-compatible stereotaxic frame for target localization. This was immediately followed by cranial surgery with the frame "in situ". 13 additional monkeys underwent stereotaxic atlas-guided cranial surgery for placement of cell transplants. Following extensive behavioral testing and microelectrode recordings, all animals were perfused. The brains were sectioned coronally and stained to determine the morphology of needle tracts as an accuracy measure of stereotaxic placements. MRI-guided stereotaxy was completely accurate in 80% as compared to 38.5% in atlas-guided stereotaxis. The chance of missing a target completely was as high as 38.5% in atlas-guided stereotaxis, which was reduced to 6.67% when MRI was used for guidance. Targeting error occurred mostly in the anterior caudate and posterior putamen as against better accuracy in the anterior putamen. These results suggest that accuracy of stereotaxic unilateral cranial targeting into the putamen and the caudate in monkeys can be improved with high-resolution 3D MR imaging.

Treatment of neurodegenerative diseases with neural cell transplantation

Neural cell transplantation is an emerging therapy that may provide an effective treatment for neurodegenerative disorders. The most extensive work with neural transplants has been carried out for Parkinson's and Huntington's diseases. However, intensive efforts are also being made for the treatment of other neurological indications, such as spinal cord repair, stroke, epilepsy, multiple sclerosis (MS), Alzheimer's disease and amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease), to name just a few. The major barrier for the successful application of cells as therapeutics is achieving long-term survival and function. The CNS has proven to be ideal for transplantation, in part because immune rejection is attenuated in the CNS compared to peripheral locations. However, some form of immunosuppression is desirable for optimal allograft survival and required for xenograft survival. This review will focus on the challenges of restoring function to something as intricate as the CNS and on the limitations imposed by this complexity on any cellular therapeutic.

Complications of a trophic xenotransplant approach in parkinsonian monkeys

Various restorative cell transplantation strategies have been investigated to substitute for lost dopamine (DA) neurons or to enhance DA synthesis in Parkinson's disease. Intracerebral implantation of engineered cells encapsulated in a semipermeable polymer membrane constitutes one way to deliver bioactive substances unable to cross the blood-brain barrier while avoiding the need for long-term immunosuppression. Glial cell line-derived neurotrophic factor (GDNF) has shown trophic effects on DA neurons but effective and sustained delivery within the brain parenchyma remains problematic. The long-term efficacy and late complications of a xenotransplant approach utilizing GDNF-expressing encapsulated baby hamster kidney (BHK) cells were examined. Each of five MPTP-lesioned parkinsonian cynomolgus monkeys received five devices containing active or inert cells grafted bilaterally in the striatum in a two-stage procedure 9 months apart and animals were sacrificed 4 months later for analyses. No definite motor benefit was observed, DA levels were comparable between GDNF- and control cell-implanted striata, and tyrosine hydroxylase (TH) immunoreactivity in the substantia nigra showed no consistent recovery. Cell viability and GDNF synthesis in the explanted devices were negligible. The brain tissue surrounding all implants showed an intense immune reaction with prominent "foreign body" inflammatory infiltrates. Membrane biophysics, the cell type used, and the extended period of time the devices remained in situ may have contributed to the negative outcome and should be addressed in future investigations using this approach.

Human neural stem cell transplantation in the MPTP-lesioned mouse

Human neural stem cells have exhibited a remarkable versatility to respond to environmental signals. Their characterization in models of neurotoxic injury may provide insight into human disease treatment paradigms. This study investigates the survival and migration of transplanted human stem cells and tyrosine hydroxylase immunoreactivity in the parkinsonian 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned mouse model, using antisera recognizing human nuclear protein (hNuc) and tyrosine hydroxylase (TH). Our results indicate long-term (up to 90 days) survival of human stem cell xenograft in the MPTP-lesioned mouse and the presence of hNuc-immunoreactive cells at sites distal to the transplant core. Few TH-positive cells are identified in the striatum by immunoperoxidase staining and using immunofluorescent double labeling, infrequent TH-immunoreactive, transplanted cells are identified.

Stereotactic transplantation of a dopamine-producing capsule into the striatum for treatment of Parkinson disease: a preclinical primate study

OBJECT

The PC12 cells are well known for their ability to secrete dopamine and levodopa. In multiple animal mode encapsulated PC12 cells have been shown to ameliorate parkinsonian symptoms when transplanted into the striatum; technique is expected to be effective clinically as well. The present study was performed using nonhuman primates to ensure that the transplantation of encapsulated PC12 cells is likely to be both safe and effective in human clinical trials.

METHODS

Unencapsulated or encapsulated PC12 cells were implanted into the brains of Japanese monkeys (Macaca fuscata). Histological and immunocytochemical analyses were performed 1, 2, 4, and 8 weeks posttransplantation on the unencapsulated cells and 2, 4, and 8 weeks after transplantation on the encapsulated cells. The survival of the PC12 cells inside the capsule was determined by measuring the amounts of dopamine and levodopa released from the capsules a removal from the striatum. Magnetic resonance imaging was performed in both unencapsulated and encapsulated PC12 cell-grafted groups. Due to the immunological reaction of the host brain no unencapsulated PC12 cells remained in the grafted area 8 weeks after transplantation. On the contrary, encapsulated PC12 cells retrieved from the host brain continued to release dopamine and levodopa even 8 weeks after implantation. The host's reaction to the PC12-loaded capsule was much weaker than that to the unencapsulated PC12 cells.

CONCLUSIONS

These results suggest that the transplantation of encapsulated PC12 cells could be a safe and effective treatment modality for Parkinson disease in human patients.

Antiparkinsonian and behavioral effects of inactivation of the substantia nigra pars reticulata in hemiparkinsonian primates

Altered activity in one of the output nuclei of the basal ganglia, the internal segment of the globus pallidus, is known to play an important role in the generation of parkinsonism. These inactivation studies tested the hypothesis that altered activity in the second major output nucleus of the basal ganglia, the substantia nigra pars reticulata (SNr), also contributes to parkinsonian motor signs. To this end, three rhesus monkeys were rendered hemiparkinsonian by intracarotid injections of MPTP. The animals then received intra-SNr injections of the GABA(A) receptor agonist muscimol to inactivate small portions of the SNr. Before and after these injections, parkinsonian motor signs were evaluated with a battery of behavioral observation methods. Injections into the centrolateral SNr reduced contralateral limb akinesia and bradykinesia in two animals. By contrast, medial injections induced generalized activation, contralateral turning, and saccadic eye movements in all animals. Injections in the most lateral and posterior portions of the nucleus had no effects. Two of the animals also received ibotenic acid lesions of the SNr, followed by a series of similar observations. These injections induced improvements in limb akinesia, postural improvements, and turning. The experiments suggest that the anterolateral "motor" territory of the SNr is involved in the development of appendicular parkinsonian motor signs.

Cell delivery to the central nervous system

A dysfunctional central nervous system (CNS) resulting from neurological disorders and diseases impacts all of humanity. The outcome presents a staggering health care issue with a tremendous potential for developing interventive therapies. The delivery of therapeutic molecules to the CNS has been hampered by the presence of the blood-brain barrier (BBB). To circumvent this barrier, putative therapeutic molecules have been delivered to the CNS by such methods as pumps/osmotic pumps, osmotic opening of the BBB, sustained polymer release systems and cell delivery via site-specific transplantation of cells. This review presents an overview of some of the CNS delivery technologies with special emphasis on transplantation of cells with and without the use of polymer encapsulation technology.

Cellular transplants as sources for therapeutic agents

Soluble factors normally produced by cells of the human body are of increasing importance as potential therapeutic agents. Although considerable progress has been made in understanding the etiology and pathogenesis of disease, in developing animal models and newer experimental therapeutics, few discoveries have been translated into clinically effective ways of delivering the multiple therapeutic agents obtained from living mammalian cells. This review examines the use of transplanted cells as alternatives to conventional delivery systems to deliver a variety of protein based therapeutic agents. The chapter begins with a set of questions to establish the complexity and challenges of this form of drug delivery. The following section focuses the discussion on our understanding of genetic engineering, tissue engineering, and some areas of developmental biology as they relate to the development of this nascent field. Much of the discussion has a neuro/endocrine emphasis. The chapter ends by listing the basic ingredients needed to push the use of transplanted cells toward medical practice and some general comments about future developments.