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

Intracranial implantation of polymer-encapsulated PC-12 cells has been shown to improve motor behavioral performance in animal models of Parkinson's disease. The purpose of this blinded study was to examine whether such improvement is associated with the active uptake and metabolism of dopamine precursors by intracerebrally implanted polymer-encapsulated PC-12 cells. In an in vitro experiment we demonstrate that 3H-dopamine uptake by PC-12 cells was 108 fmol/min × 106 cells, and that this uptake can be specifically blocked 88% by the addition of 10 nM of nomifensine. In the in vivo experiments, polymer-encapsulated PC-12 cells were implanted in four MPTP-treated monkeys into the left deep parietal white matter (R1) or left striatum (R2-4). A fifth MPTP-treated monkey (R5) served as a control and received left striatal implants of empty capsules. 18F-Dopa Positron Emission Tomography (PET) imaging was performed on each monkey before and after implantation surgery by blinded investigators. PET images obtained 5-13 wk after implantation demonstrated well delineated focal areas of high 18F-dopa uptake in R1, R2, and R4. The focal area of high 18F-dopa uptake in R1 precisely coregistered on a brain magnetic resonance image to the site of implantation. R3 (in whom the polymer-encapsulated PC-12 cells demonstrated poor cell survival upon explantation) and R5 (empty capsules) failed to demonstrate any area of increased 18F-dopa uptake in their PET images. Histological examination of the host brain revealed no sprouting of dopaminergic nerve terminals around the implantation sites of the polymer-encapsulated PC-12 cells. These results indicate that the previously noted behavioral improvement after intrastriatal implantation of polymer encapsulated PC-12 cells is at least in part due to their highly specific uptake and metabolism of dopamine precursors. Furthermore, these data suggest that polymer-encapsulated PC-12 cells can store, reuptake, and functionally replenish dopamine and therefore, may be an effective treatment for Parkinson's disease.

Encapsulated PC 12 Cell Transplants into Hemiparkinsonian Monkeys: A Behavioral, Neuroanatomical, and Neurochemical Analysis

Four cynomolgus monkeys were trained on a hand reaching task and then rendered hemiparkinsonian with an intracarotid injection of n-methyl 4 phenyl 1,2,3,6, tetrahydropyridine (MPTP). Performance on this task with the limb contralateral to the MPTP injection was significantly impaired following the lesion. Three monkeys received implants of polymer-encapsulated containing PC12 cells into the caudate nucleus and putamen. One monkey received identical implants of empty capsules and served as a control. After a transient improvement, limb use in the control monkey dissipated and returned to post-MPTP disability. Two of the three PC12 cell grafted monkeys recovered performance on the hand reach task to near normal levels for up to 6.5 mo posttransplantation. Capsules retrieved from the monkeys who recovered limb function postimplantation contained numerous viable PC12 cells that continued to release levodopa, basal dopamine, and potassium evoked dopamine. In contrast, capsules retrieved from the PC12 cell-grafted monkey which did not recover limb use on the hand reach task contained few cells which secreted negligible or undetectable levels of levodopa and dopamine. Interestingly, functional disability was not reinstated following removal of the capsules. Neuroanatomical and neurochemical evaluation of the grafted striatum did not reveal a host-derived sprouting response of catecholaminergic or indolaminergic fibers. These data indicate that xenografts of PC12 cells can survive for up to 6.5 mo in nonimmunosuppressed monkeys when immunoisolated via polymer encapsulation. Moreover, these cells continue to secrete high levels of levodopa and dopamine and induce recovery of motor function in parkinsonian nonhuman primates.

Evaluation of Intracerebral Grafting of Dopamine-Secreting PC12 Cells into Allogeneic and Xenogeneic Brain

The PC12 pheochromocytoma tumor cell line is derived from a rat adrenal medullary tumor and secretes dopamine. We have previously reported that grafted microencapsulated PC12 cells using agarose and poly(styrene sulfonic acid) survived in the xenogeneic brain without immunosuppression. To investigate whether unencapsulated PC12 cells form a tumor and how they provoke immunological reaction, PC12 cell suspension was implanted into the striatum of Sprague-Dawley rat (allogeneic graft) or guinea pig (xenogeneic graft) and histological analysis using Nissl stain and immunocytochemical analysis using antityrosine hydroxylase (TH) antibody were performed 1, 2, and 4 wk after transplantation. Host animals were not immunosuppressed. PC12 cells formed a mass 1 and 2 wk after transplantation both in allogeneic and xenogeneic brain. These grafted PC12 cells were immunoreactive to anti-TH antibody. Four weeks after transplantation, however, grafted PC12 cells in the allogeneic brain were only found within the restricted area near the site of implantation. In the xenogeneic brain, only the trace of grafted PC12 cells were found around the site of implantation 4 wk after transplantation. In both allogeneic and xenogeneic animals, a number of lymphocytes were found in and around the grafts at all period investigated. These findings indicate that PC12 cells could survive in the allogeneic or xenogeneic brain for 2 wk and were ultimately rejected by immunological reaction by 4 wk after transplantation. Implantation of encapsulated PC12 cells in the allogeneic or xenogeneic brain is considered a safe and effective method for delivering dopamine into the brain because PC12 cells will not form a tumor in the long-term even if capsules are damaged in some reason.

Continued Presence of Intrastriatal but not Intraventricular Polymer-Encapsulated PC12 Cells is Required for Alleviation of Behavioral Deficits in Parkinsonian Rodents

To date, few studies have systematically evaluated the most appropriate location for grafting catechoiaminergic cells as a potential treatment for Parkinson's disease (PD). The following study was conducted to determine 1) if placement of catecholamine-secreting encapsulated PC12 cells into the lateral ventricle of 6-OHDA–treated rats is as effective as intrastriatal implants on reducing apomorphine-induced rotational behavior, and 2) to determine if the survival of encapsulated PC12 cells is differentially affected by the implant site. Polymer-encapsulated PC12 cells were implanted into either the striatum or lateral ventricle of unilateral 6-OHDA–lesioned rats. Animals were tested for apomorphine-induced rotations over a 6-wk period. Only those animals that received intrastriatal implants of encapsulated PC12 cells showed a reduction in rotation behavior. Moreover, removal of the devices from the striatum resulted in a return to preimplant rotation levels. Postexplant neurochemical analyses demonstrated that the potassium-evoked l-dopa device output increased in vivo while the potassium-evoked dopamine output from the devices decreased over time in vivo. The location of the implant significantly affected catecholamine output from the PC12 cell-loaded devices. The increase in potassium-evoked l-dopa output was greatest, as was the decrease in potassium-evoked dopamine output, from those devices implanted in the striatum. Basal output of dopamine and DOPAC was also significantly higher from devices explanted from the lateral ventricle. These results demonstrate that the continued presence of intrastriatal implants of encapsulated PC12 cells is required to maintain the behavioral effects in 6-OHDA–lesioned rats. In addition, the site of implantation appears to affect device output. These results provide additional support for intraparenchymal delivery of l-dopa and dopamine via polymer encapsulation as a possible treatment for PD.

Effective magnetic labeling of transplanted cells with HVJ-E for magnetic resonance imaging

Magnetic labeling of transplanted cells permits us to monitor their localization non-invasively using MRI. Since most transfection agents for magnetic labeling have the same cationic charge as Fe(3+), the efficiency may be reduced. The hemagglutinating virus-envelope has no charge and utilizes membrane fusion activity to deliver internalized materials. In this study, we investigated the feasibility of using the envelope to incorporate paramagnetic Fe(3+) particles into PC12 cells and astrocytes. The envelope effectively labeled both cells with Fe(3+), which showed significant decreases of signal intensity in T2-weighted MRI. Labeled cells transplanted into the rat striatum were clearly visualized by T2*-weighted MRI at a magnetic field of 2 T. The results indicate that the hemagglutinating virus-envelope is a powerful tool for magnetic labeling.

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.

Induction of orthotopic rat adrenomedullary neoplasia by intraadrenal pheochromocytoma cell transplantation

We aimed to establish a technically feasible, easily reproducible model of orthotopic adrenomedullary neoplasia. Male rats received adrenal injection of rat pheochromocytoma cells infected with the Escherichia coli gene for beta-galactosidase (lac Z). Each of 10 animals was perfused 7 or 24 days after tumor cell injection; 5 animals of each group were injected with cyclosporin. Animals without tumor cell injection served as controls. Tumor cells were identified and characterized in frozen sections by histochemical and immunohistochemical methods. Immunosuppressed animals had enlarged adrenals 7 days after tumor cell injection. In the rats without immunosuppression the adrenals seemed unaltered despite microscopic demonstration of tumor cells. After 24 days tumors had developed in all animals, weighing 50 times more than normal adrenals in animals with immunosuppression, and 9 times more in animals without immunosuppression. Intraadrenal catecholaminergic tumor cells could be identified by beta-galactosidase expression. No animal showed systemic spread. Generation of adrenomedullary neoplasia by intraadrenal pheochromocytoma cell transplantation is easily reproducible and technically feasible. This model allows simultaneous study of neoplastic and normal adrenal tissues (e.g., regarding their response to drugs intended for diagnostic and therapeutic purposes). The decreased tumor growth in animals without immunosuppression is presumably due to the high number of intraadrenal immunocompetent cells.

Dose control with cell lines used for encapsulated cell therapy

Cell therapy-use of cells to deliver active factors-is an emerging technique in treatment of neurodegenerative disease. Successful devices maintain cell viability and functionality over extended implant periods. Use of dividing cell lines to deliver therapeutic factors has been studied extensively. One emerging issue is the tendency of cells to continue proliferation within the intracapsular environment-potentially outstripping nutrient supply. This work presents a method of controlling proliferation and delivering therapeutic molecules within a dose range. The method entails encapsulation into a hollow fiber device of discrete numbers of cell-containing microcarriers. Proliferation control is attained by embedding cell-containing microcarriers in nonmitogenic hydrogels. PC-12 cells secreting L-dopa and dopamine was the model cell line tested. Feasibility of the method in controlling growth of normally rapidly dividing cells in the intracapsular environment was demonstrated in vitro and in vivo. Control nonmicrocarrier PC-12 cell devices had approximately fourfold greater expansion in cell number compared to experimental microcarrier-containing devices over 4 weeks in vitro and in vivo after implant into rat striatum. Ability to control dose released over a several-fold range was demonstrated with encapsulated PC-12 cells delivering neurotransmitters and C2C12 mouse myoblast cells delivering neurotrophic factors (CNTF).

Evaluation of reaction of primate brain to grafted PC12 cells

Intrastriatal implantation of polymer-encapsulated PC12 cells, which constitute a dopaminergic cell line derived from rat pheochromocytoma, has proved useful for ameliorating parkinsonian symptoms in several kinds of animals. In considering the clinical application of this technique, we should make sure that PC12 cells are rejected completely by the host immune system in case the capsule breaks. In the present study, unencapsulated PC12 cells were injected into the brain of Japanese monkeys (Macaca fuscata). Histological [hematoxylin-eosin (H&E), Nissl] and immunocytochemical [tyrosine hydroxylase (TH), and glial fibrillary acidic protein (GFAP)] analyses were performed 1, 2, 4, and 8 weeks after transplantation. Also, encapsulated PC12 cells were transplanted into the brain of another group of Japanese monkeys to investigate the host reaction to the capsule and to confirm that the encapsulated PC12 cells continue to survive in the host brain. H&E and GFAP staining were performed 2, 4, and 8 weeks after transplantation. L-DOPA and dopamine release from the explanted capsules was measured by high performance liquid chromatography. Magnetic resonance imaging was performed in both unencapsulated and encapsulated PC12 cell grafted groups. Although the xenografted unencapsulated cells formed a small cluster at 1 and 2 weeks after implantation, very few and no viable PC12 cells remained at 4 and 8 weeks, respectively. The reaction of the host towards the xenograft gradually decreased. Encapsulated PC12 cells retrieved from the host brain were found to release L-DOPA and dopamine continuously even 8 weeks after implantation. The host reaction to the PC12-loaded capsule was much weaker than that to the unencapsulated PC12 cells, and decreased with time. These results indicate that encapsulated PC12 cell transplantation is an effective and safe strategy for the treatment of Parkinson's disease.

Poly(vinyl alcohol) synthetic polymer foams as scaffolds for cell encapsulation

Poly(vinyl alcohol) (PVA) foams were used as scaffolds in hollow fiber membrane-based cell encapsulation devices. The surrounding permselective membrane serves as an immunoisolation barrier while allowing metabolites and other small molecules to be freely transported. The internal matrix defines the microenvironment for the encapsulated cells. PC12 cell-containing devices represent one possible strategy for safe transplantation of dopamine-secreting cells for the treatment of dopamine-deficient diseases such as Parkinson's disease. PC12 cells--a dopamine-secreting cell line--were encapsulated with PVA foam as a matrix material in the lumen of these hollow fibers. In this work, we demonstrate the presence of the PVA matrix increased the catecholamine secretion efficiency of the cells as compared to devices containing a chitosan matrix. Devices were implanted in vivo into rodent striatum and device output of catecholamines was measured preimplant and post-explant. Evoked stores of dopamine remained constant (preimplant vs explant) for devices encapsulated with the foam matrix and increased with devices encapsulated with chitosan matrix. Cell proliferation within devices was inhibited in the presence of the foam matrix. Cell viability and distribution was significantly improved with the inclusion of the foam matrix in both in vitro and in vivo studies. In comparison to chitosan--a typical matrix material for PC12 cells--addition of a foam-type matrix altered the encapsulated cell microenvironment and resulted in more efficient secretion of catecholamines and improved distribution within the device resulting in smaller necrotic regions and a lower rate of cell proliferation.

Somatic delivery of catecholamines in the striatum attenuate parkinsonian symptoms and widen the therapeutic window of oral sinemet in rats

Guidelines for clinical transplantation studies for Parkinson's disease emphasize that transplants should be considered as an adjunct to systemic L-DOPA, yet few preclinical studies have specifically assessed the potential of transplants as an adjunct to the clinical gold standard treatment. The objectives of the present study were to determine if encapsulated PC12 cells implanted in rats with severe unilateral dopamine depletions: (i) have a direct therapeutic effect on measures of parkinsonian symptoms; and/or (ii) increase the therapeutic window of oral sinemet in this model. Rats with severe unilateral dopamine depletions received striatal implants of encapsulated PC12 cells producing dopamine and L-DOPA. These rats were tested on a battery of behavioral measures of parkinsonian symptoms, at a range of doses of oral sinemet (0, 12, 24, and 36 mg/kg). Stereotypies/dyskinesias were also quantified after high doses of oral sinemet (36 and 50 mg/kg). The results confirm that parkinsonian symptoms can be quantified in rats with severe dopamine depletions, and the validity and clinical relevance of these measures are supported by the fact that the clinical gold standard treatment, oral sinemet, attenuates these parkinsonian symptoms. Somatic delivery of dopamine and L-DOPA, directly to the dopamine-depleted striatum, also attenuates parkinsonian symptoms. In fact, the magnitude of the therapeutic effect produced by continuous, site-specific, somatic delivery of dopamine and L-DOPA was larger than the effect produced by acute, systemic, oral sinemet. The beneficial effects of oral sinemet and striatal implants of catecholamine-producing devices were additive, but there were no adverse effects related to striatal catecholamine-producing devices, and these devices did not increase the adverse effects related to oral sinemet. Therefore, striatal implants of catecholamine-producing devices have direct therapeutic effects which are fairly robust, and they widen the therapeutic window of oral sinemet.

Preliminary report of polymer-encapsulated dopamine-secreting cell grafting into the brain

Polymer-encapsulated dopamine-secreting cell grafting is one of the most promising approaches for the treatment of Parkinson's disease. We microencapsulated dopamine secreting PC12 cells into agarose/poly(styrene sulfonic acid) complex and grafted them into the xenogeneic brain without immunosuppression. Dopamine secretion from the encapsulated cells was confirmed by high-performance liquid chromatography (HPLC) analysis before grafting. A large number of encapsulated PC12 cells survived in the brain 1 mo after transplantation and these cells were immunoreactive to tyrosine hydroxylase (TH) antibody, suggesting that these cells were secreting dopamine into the brain. There was no apparent immunological rejection or tumor formation. We concluded that microencapsulated PC12 cells survive in the xenogeneic brain without immunosuppression, and this grafting procedure is expected to be applied for the treatment of Parkinson's disease in the near future in combination with stereotaxic thalamotomy or pallidotomy.

Polyreactive autoimmune response induced by PC 12 cell grafts into rat striatum

In order to better characterize the autoantibodies induced by PC12 cells grafted into rat brain, we have tested sera from these animals by immunoblotting with several preparations, including phosphorylated and dephosphorylated neurofilaments, keratins, PC12 cells and proteins from various rat tissues, and by immunofluorescence of rat spinal cord neurons in culture. Sera from grafted rats reacted with several antigens present in all tissues tested and stained in cultured neurons not only NF but also cell bodies and membranous granular structures. These observations suggest either the polyreactivity of autoantibodies or the induction of a polyclonal B cell activation consecutive to the release of central nervous system antigens into the blood stream. These results are discussed with regard to the role of NF autoantibodies in neurodegenerative diseases.

Probing modifications of the neuronal cytoskeleton

The prominent death of central neurons in Alzheimer's and Parkinson's is reflected by changes in cell shape and by the formation of characteristic cytoskeletal inclusions (neurofibrillary tangles, Lewy bodies). This review focuses on the biology of neurofilaments and microtubule-associated proteins and identifies changes that can occur to these elements from basic and clinical research perspectives. Attention is directed at certain advances in neurobiology that have been especially integral to the identification of epitope domains, protein isoforms, and posttranslational (phosphorylation) events related to the composition, development, and structure of the common cytoskeletal modifications. Recently, a number of experimental strategies have emerged to simulate the aberrant changes in neurodegenerative disorders and gain insight into possible molecular events that contribute to alterations of the cytoskeleton. Descriptions of specific systems used to induce modifications are presented. In particular, unique neural transplantation methods in animals have been used to probe possible molecular and cellular conditions concerned with abnormal cytoskeletal changes in neurons.

Differential behaviour of PC12 cells grafted into rat hippocampus and striatum

To investigate the mechanisms involved in graft survival, a rat cell line (PC12) that differentiates into sympathetic-like neurons by exposure to trophic factors has been grafted into rat striatum and hippocampus, two structures which differ in their amounts of trophic factors. Our results show that grafted PC12 cells behave differently depending on the area of implantation; they display a differentiated morphology in the hippocampus and proliferate as a tumor in the striatum. A qualitatively similar immunological reaction occurs in both structures, characterized by the invasion of T and B lymphocytes, macrophage-like cells and by the expression of major histocompatibility complex class I and II antigens around the graft.

Growth of tumour cell lines in polymer capsules: ultrastructure of encapsulated PC12 cells

Recent studies indicate that polymer-encapsulated PC12 cells release sufficient amounts of dopamine to significantly alter behavioural paradigms in animals with unilateral lesions of dopaminergic midbrain neurons. Because cell fine structure provides a useful measure for assessment of storage function, exocytosis, metabolism, cell activity and cell viability, we examined the ultrastructure of PC12 cells grown in semi-permeable polymer capsules maintained in vitro or implanted into the forebrain of rats or guinea pigs. Encapsulated PC12 cells remained viable and continued to divide for the entire evaluation period of six months. Overall morphologies of encapsulated PC12 cells were similar in both environments and they resembled PC12 cells grown in monolayer cultures. In short-term cultures, encapsulated PC12 cells typically contained abundant quantities of chromaffin cell-like granules. The encapsulated cells had initially abundant microvilli on their surfaces which decline in frequency over time. After long-term enclosure for ten weeks or more, fewer secretory granules were detected in the cytoplasm of cells in capsules cultured in vitro and in brain-implanted capsules. Some cells in implanted capsules had long slender filipodia that were not present on PC12 cells in cultured capsules. The morphological changes of PC12 cells may correlate with altered growth conditions such as serum and oxygen concentrations, the presence or absence of growth factors in different environments, and with changes of cell interactions related to cell densities and build up of debris within the capsules over time. Since dopaminergic PC12 pheochromocytoma cells remain viable in semi-permeable polymer capsules for at least six months, such 'cell-capsules' could provide an alternative to dopamine-secreting embryonic neural grafts in dopamine replacement therapies.

Viral Kirsten ras infection differentiates PC12 cells and enhances their survival upon implantation into brain

Neuronal cells from established cell lines can offer a well-characterized source of cells for transplantation to the brain that is an alternative to fetal neurons. The infection of members of the PC12 cell line with a retrovirus containing ras-oncogene leads to their neuronal differentiation without the need of nerve growth factor (NGF). We find that neoplastic, naive PC12 cells grafted to the striatum of normal adult rats cause the transient formation of large hemorrhagic cavities and do not survive. After differentiation by infection with Kirsten-ras murine sarcoma virus, and transplantation to the opposite striatum of the same brain, PC12 cells survive for at least 8 weeks and emit neurites. These neuron-like cells and their neurites retain tyrosine hydroxylase and choline acetyl transferase, as detected immunohistochemically. Thus, ras-primed PC12 cells may serve as a continuous source for both cholinergic and adrenergic transmitters, in vivo, without the need of exogenous nerve growth factor.

Behavioral recovery following intrastriatal implantation of microencapsulated PC12 cells

The motor deficits associated with Parkinson's disease may be ameliorated by intrastriatal placement of dopamine-secreting cells in a polymer capsule. Water soluble polyelectrolytes were utilized for membrane encapsulation of dopamine-secreting PC12 cells. Membrane permeability studies revealed exclusion of radiolabeled 69,000 Da albumin, whereas 30,000 Da carbonic anhydrase was able to cross the membrane. No cytolytic activity was observed following incubation of the encapsulated PC12 cells with PC12 cell-directed antiserum and fresh complement. In vitro, dopamine release and the surface area of intact cells per microcapsule, reached a plateau at 4 weeks that was maintained for at least 12 weeks. Viable PC12 cells were observed in microcapsules implanted for 4 and 8 weeks in nonlesioned guinea pig striata. The behavioral effect of intrastriatal dopamine release from microencapsulated PC12 cells was evaluated in the 6-hydroxydopamine unilaterally lesioned rat model. From 1 to 4 weeks postimplantation a significant reduction in rotation behavior under apomorphine challenge was observed with PC12 cell-loaded microcapsules as compared to empty microcapsules. Tyrosine hydroxylase immunopositive PC12 cells were observed 4 weeks postimplantation in all animals exhibiting a reduction in turning behavior. Implantation of polymer-encapsulated cells may provide a means for long-term delivery of neurotransmitters and growth factors to the nervous system.