Sustained behavioral recovery from unilateral nigrostriatal damage produced by the controlled release of dopamine from a silicone polymer pellet placed into the denervated striatum

The problems of delivering neuroactive molecules to the CNS

At present, the aetiologies of many neurological and neurodegenerative diseases are unknown. However, emergence of a better understanding of these diseases, at both cellular and molecular levels, opens up the possibility of replacement therapies. The presence of the blood-brain barrier complicates the delivery of molecules to the central nervous system. Numerous attempts have been made to bypass this barrier either by delivering the drugs directly into the brain or by transplanting cells to produce the missing molecules in situ. This review explores several methods for delivering bioactive molecules into the CNS, including the use of permeabilizers, osmotic pumps, slow polymer release systems and transplantation of cells with or without the use of the encapsulation technology.

Aggregation enhances catecholamine secretion in cultured cells

Transplanted cells and tissues have potential uses in the treatment of genetic, geriatric, and metabolic disorders, but optimal conditions for transplantation are not yet known. In this report, PC12 cells were aggregated in rotary and microgravity culture, using serum-free or serum-supplemented medium, and using a multifunctional polymer-peptide aggregation factor. Aggregates and single cells were then encapsulated and cultured within agarose gels, and the dopamine secretion in response to a depolarization buffer was measured using high-performance liquid chromatography combined with electrochemical detection (HPLC-ECD). On a per-cell basis, aggregated cells secreted higher levels of dopamine than did single cells. The size of the aggregates was also a factor in catecholamine secretion; dopamine release from the larger aggregates formed in rotary culture was observed to increase at a faster rate, then achieve a plateau level at an earlier time than did the smaller aggregates. Cells aggregated in microgravity culture exhibited a markedly different behavior, lacking the rapid rise in dopamine secretion characteristic of the rotary-aggregates cells: on a per-cell basis, the dopamine secretion remained at a level corresponding to the plateau level expressed by the rotary-aggregates cells. Dopamine secretion in aggregates may be enhanced by the increase in number of cell-cell contacts, as occurs during high-density culture of PC12 cells. These results provide further evidence that cell-cell contact regulates the behavior of differentiated cells, and therefore is important in tissue engineering.

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.

Development of microspheres for neurological disorders: from basics to clinical applications

Drug delivery to the central nervous system remains a challenging area of investigation for both basic and clinical neuroscientists. Numerous drugs are generally excluded from blood to brain transfer due to the negligible permeability of the brain capillary endothelial wall, which makes up the blood brain barrier in vivo. For several years, we have explored the potential applications of the microencapsulation of therapeutic agents to provide local controlled drug release in the central nervous system. Due to their size, these microparticles can be easily implanted by stereotaxy in discreet, precise and functional areas of the brain without damaging the surrounding tissue. This type of implantation avoids the inconvenient insertion of large implants by open surgery and can be repeated if necessary. We have established the compatibility of poly(lactide-co-glycolide) microspheres with brain tissues. Presently, the most developed applications concern Neurology and Neuro-oncology, with local delivery of neurotrophic factors and antimitotic drugs into neurodegenerative lesions and brain tumours, respectively. The drugs that had been encapsulated by our group included nerve growth factor (NGF), 5-fluorouracil (5-FU), idoxuridine and BCNU. Preclinical studies have been performed with each drug. Studies with NGF are reported as an example. A phase I/II clinical trial has been carried out in patients with newly diagnosed glioblastomas to assess the potentialities of 5-FU-loaded microspheres when intracranially implanted.

Repair of the damaged brain. The Alfred Meyer Memorial Lecture 1998

Over the last decade, neural transplantation has progressed from being an experimental technique for studying regeneration and plasticity in the brain to clinical trials of reconstructive surgery in human neurodegenerative disease. Whereas clear evidence is only available at present for the viability of this technique in Parkinson's disease, applications to several other diseases, including Huntington's disease, multiple sclerosis, spinal cord injury, and chronic pain are currently under active consideration. It is clear that the techniques of transplantation can be functionally viable under certain well-defined biological circumstances, but significant problems remain in the availability of suitable donor tissues and defining the optimal conditions for reliable survival of the implanted cells. If we are to obtain improved reliability of the present techniques or identify suitable alternatives, we need a better understanding of the conditions for the survival and integration of grafts into the host brain, and the mechanisms by which they influence host function. In this review I consider the nature of the structural reconstruction required to achieve repair in animal models of Parkinson's and Huntington's diseases, contrasting the replacement of deficient neurochemicals within the striatum in the former case, and the need for reconstruction of input and output connections of the striatal circuitry in the latter.

Prospects for new restorative and neuroprotective treatments in Parkinson's disease

The degeneration of forebrain dopamine systems in Parkinson's disease has been an effective target for pharmaceutical research over the past four decades. However, although dopamine replacement may alleviate the symptoms of the disease, it does not halt the underlying neuronal degeneration. The past decade has seen major advances in identifying discrete genetic and molecular causes of parkinsonism and mapping the events involved in nigral cell death. This new understanding of the pathogenesis of the disease now offers novel prospects for therapy based on targeted neuroprotection of vulnerable neurons and effective strategies for their replacement.

Biocompatibility of poly (DL-lactide-co-glycolide) microspheres implanted into the brain

The delivery of therapeutic molecules to the brain has been limited in part due to the presence of the blood-brain barrier. One potential solution is the implantation of biodegradable polymers with sustained release of drugs. Poly (DL-lactide-co-glycolide) (PLG) is a bioerodible polymer with a long and successful history of use as a suture material. More recently, PLG has been investigated for localized and sustained delivery of molecules into both peripheral sites and the brain. Despite its well-defined safety profile for parenteral applications, little information exists concerning the safety of PLG when implanted into the brain. To further characterize the biocompatibility of PLG in the brain, we examined the gliotic response following implants of PLG into the brains of rats. As a control, each animal received an injection of the suspension medium into the contralateral hemisphere. Following implantation, PLG was well tolerated. GFAP-positive astrocytes were observed throughout the cerebral cortex and striatum on both the implanted and control sides, with the reaction being greatest within the heavily myelinated fiber tracts of the corpus callosum. Quantitative analyses revealed that this reaction occurred within 1 h postsurgery, reached its peak at 1 week following surgery, and then decreased markedly by 1 month postsurgery. A minimal gliotic reaction was still present 1 year postsurgery but was localized to the needle tract. No differences in GFAP reactivity were seen between the polymer-implanted and control sides at any time point. Histological analysis determined that the majority of the PLG disappeared between 1 and 4 weeks. A set of parallel studies in which PLG samples were retrieved from the brain at various time points corroborated these findings and determined that the majority of PLG degraded within 2 weeks following implantation. Together, these results demonstrate that PLG is well tolerated following implantation into the CNS and that the astrocytic response to PLG is largely a consequence of the mechanical trauma that occurs during surgery. The biocompatibility of PLG implanted into the CNS provides further support for its use in a wide range of new therapeutic applications for sustained and localized drug delivery to the brain.

Dopamine secretion by PC12 cells microencapsulated in a hydroxyethyl methacrylate--methyl methacrylate copolymer

A rat pheochromocytoma cell line (PC12) was encapsulated in a water-insoluble hydroxyethyl methacrylate-methyl methacrylate copolymer by interfacial precipitation from a polyethylene glycol 200 solution into phosphate-buffered saline. The resulting capsules (660 +/- 44 microns in diameter; 84 +/- 27 microns wall thickness) contained viable PC12 cells in a spheroidal arrangement, much like tumour spheroids, the latter grown on surfaces unsuitable for cell attachment. In these spheroids, the viable cells formed a band approximately 100 microns thick, surrounding an inner core of necrotic cells. A similar arrangement was seen 14, 28 and 42 days after encapsulation, with capsules maintained in an in vitro tissue culture environment; the annular ring was roughly constant in size, although the packing density appeared to increase over the 6 week observation period. During the first 4 weeks, when measurements were made the encapsulated cells converted a tetrazolium dye (MTT) into an insoluble formazan product, in a time-after-encapsulation-dependent manner. This indicated that PC12 cells retained viability despite encapsulation and an ability to increase (at least in part) their metabolic capacity, presumably by a combination of proliferation and altered cellular activity. The encapsulated PC12 cells also secreted dopamine when incubated in a high potassium release medium but not in a low potassium, conventional tissue culture medium (RPMI 1640). Consistent with the MTT results, the amount of dopamine released was also dependent on the time after encapsulation, as well as the cell density at the time of encapsulation.

Parkinson's disease, trophic factors, and adrenal medullary chromaffin cell grafting: basic and clinical studies

Neural transplantation is one of the promising approaches for the treatment of Parkinson's disease. Although the strategy of using adrenal medulla as donor tissue, rather than fetal nigra tissue, started as an alternative method, recent experimental studies demonstrated the efficacy of adrenal medulla grafting as a neurotrophic source. Many methods to increase the survival of grafted chromaffin cells have been developed, some of which have already been applied clinically with encouraging results. This review summarizes the advancements of adrenal medulla grafting in basic and clinical studies. Special attention is focused on the relationship with neurotrophic factors and how we can enhance the survival of grafted chromaffin cells.

Distribution of drugs following controlled delivery to the brain interstitium

Intracranial controlled release polymers have been used for drug delivery to the brain, bypassing the blood brain barrier (BBB). By understanding the rates and patterns of transport in the local tissues, it is possible to design delivery systems that provide the optimal spatial and temporal pattern of chemotherapy within the intracranial space. This paper reviews the kinetics of drug release from polymeric controlled release implants, and describes the fate of drug molecules following release into the brain interstitium. Potential improvements in drug delivery based on the understanding of the mechanisms of drug release, transport and elimination are discussed.

Mucociliary activity and histopathology of sinus mucosa in experimental maxillary sinusitis: a comparison of systemic administration of antibiotic and antibiotic delivery by polylactic acid polymer

To evaluate the efficacy of antibiotic delivered by polyactic acid (PLA) polymer in sinusitis, we induced maxillary sinusitis in 32 New Zealand white rabbits by occluding the sinus ostium and inoculating the sinus cavity with Streptococcus pneumoniae. The rabbits were divided into three groups consisting of group 1 (control group, 8 rabbits), which was treated only by reopening the ostium; group 2, which was treated by both reopening the ostium and injecting ampicillin intramuscularly (40 mg/kg/day in three divided doses, 12 rabbits); and group 3 (12 rabbits) in which a piece of PLA-polymer ampicillin (0.326 mg) sheet (1.5 x 1.5 cm) was placed within the sinus after re-establishing ostial patency. The light microscopic findings such as epithelial ulceration, loss of cilia, infiltration of inflammatory cells, and edema were less pronounced in group 2 and minimal in group 3. The electron microscopic findings such as swelling of mitochondria and endoplasmic reticulum and protruded cytoplasm were severest in the control group, followed by groups 2 and 3. The mucociliary transport speed measured at the medial wall of the maxillary sinus was highest in group 3. The results of this study suggest that treatment with PLA-polymer ampicillin may have a better efficacy in maxillary sinusitis than that with systemic administration of ampicillin.

Update on cellular transplantation into the CNS as a novel therapy for chronic pain

The transplantation of cells that secrete neuroactive substances with analgesic properties into the CNS is a novel method that challenges current approaches in treating chronic pain. This review covers pre-clinical and clinical studies from both allogeneic and xenogeneic sources. One cell source that has been utilized successfully is the adrenal chromaffin cell, since such cells constitutively release catecholamines, opioid peptides, and neurotrophic factors; release can be augmented with nicotine. Other graft sources include AtT-20 and B-16 cell lines which release enkephalins and catecholamines, respectively. For grafting in rodents, adrenal medullary tissue pieces are transplanted to the subarachnoid space. Chromaffin cell transplants can decrease pain sensitivity in normal rats using standard acute pain tests (paw-pinch, hot-plate, and tail-flick). In addition, transplants can restore normal pain thresholds in rodent models of chronic pain (formalin, adjuvant-induced arthritis, and sciatic-nerve tie) which closely similate the pathologies of human chronic pain conditions. Xenografts have been studied due to concerns that future application for human pain may be limited by donor availability. Despite immune privileges of the CNS, xenografts require at least short-term immunosuppression to obtain a viable graft. Cell encapsulation is one method of sustaining a xenograft (in rat and human hosts) while circumventing the need for immunosuppression. Clinical studies have been initiated for terminal cancer patients with promising results as assessed by markedly reduced narcotic intake, visual analog scale ratings, and increased CSF levels of catecholamines and met-enkephalin.

Application of polylactic acid polymer in the treatment of acute maxillary sinusitis in rabbits

To evaluate the therapeutic effects of topical antibiotic delivered by polylactic acid (PLA) polymer on paranasal sinusitis, we induced maxillary sinusitis in 32 New Zealand white rabbits by obstructing the maxillary sinus ostium and inoculating the sinus cavity with Streptococcus pneumoniae. The rabbits were divided into three groups: a control group (group 1) treated only by reopening the ostium, a group (group 2) treated by both reopening the ostium and injecting ampicillin (40 mg/kg/day), and a group (group 3) in which ampicillin in the PLA carrier (0.326 mg) was placed within the sinus after ostial patency was reestablished. The number of colony forming units (CFU) was lowest in group 3, followed by groups 2 and 1. Ampicillin concentration in the maxillary sinus secretion of group 3 was significantly higher than in group 2. The results suggest that treatment with PLA-ampicillin polymer may maintain high therapeutic concentrations of ampicillin in maxillary sinus secretion.

Functional repair of striatal systems by neural transplants: evidence for circuit reconstruction

Intrastriatal grafts of nigral and adrenal tissues have been found to be effective in alleviating many of the simple motor and sensorimotor deficits associated with lesions of the nigrostriatal dopamine system. However, the mechanisms by which such grafts exert their effects may be less specific than originally conceived, and both pharmacological and trophic actions play an essential role. Damage to intrinsic cortico-striatal circuits are unlikely to prove similarly amenable to such diffuse mechanisms of repair. Nevertheless, striatal grafts have been found to alleviate cognitive and motor deficits after excitotoxic lesions of the neostriatum. Accumulating evidence suggests that in this particular case many aspects of functional recovery may indeed be attributable to the striatal grafts providing an effective functional reconstruction of damaged neuronal circuits within the host brain.

Behavioural consequences of neural transplantation

Neural grafts can reverse many functional deficits associated with brain damage, whether of traumatic, toxic, neurodegenerative or genetic origin. In some model systems recovery can be partial or complete; whereas in others the grafts have limited effects or may actually cause further dysfunction. In order to devise rational and effective transplantation strategies it is necessary to understand the mechanisms by which grafts exert their functional effects. Several alternatives have been proposed, and these include non-specific consequences of surgery, acute diffuse neurotrophic and growth mechanisms, chronic diffuse release of deficient neurochemicals, bridging tissues for host regeneration, diffuse reinnervation of the host brain, and reciprocal graft-host reconnection. These alternative mechanisms are not necessarily exclusive in any particular situation, and all have been seen to apply in different model systems.

Modulated drug release using iontophoresis through heterogeneous cation-exchange membranes. 2. Influence of cation-exchanger content on membrane resistance and characteristic times

An implantable drug delivery method using iontophoresis through cation-selective membranes was further developed. Heterogeneous cation-exchange membranes (HCMs) were prepared by mixing conductive sulfonated polystyrene beads into a nonconductive silicone rubber matrix. The membrane resistivity and lag time to steady-state transport of two salts, (+/-)-phenylpropanolamine hydrochloride (PPA) and NaCl, were evaluated during constant current iontophoresis at 37 degrees C as a function of the resin content in the HCMs. A continuous decline in membrane resistivity was observed as fractional resin content (l) was increased over the entire usable region (l = 0.29-0.52), a characteristic that could be described by a percolation scaling law (for an infinite lattice, 3-D geometry). Morphological analysis of the membranes before and after swelling strongly suggested that the conducting clusters of resin beads form during the swelling period prior to use. The response time to steady-state transport of PPA into NaCl during a 40 microA constant current (0.27 cm2) was found to increase with increasing l, but not without decreasing the permselectivity of the HCMs for the drug cation. The lag time effect could be explained in terms of an increasing number of fixed charge groups in the membrane available for transport (mfcA), which was derived from a macroscopic mass balance model. The values of mfcA were also found to be related to the characteristic time of diffusion in a homogeneous transport projection of the HCM (or an effective medium), an essential parameter for future non-steady-state simulations. The characteristic time of diffusion was found to be invariant with changing resin content, suggesting that the membranes are fairly nontortuous (ca. seven beads thick). By assuming that the thickness of the HCM approaches the thickness of its homogeneous projection, an expression was derived to predict lag time to steady-state PPA transport requiring resistance measurements only (provided that the resin capacity is known). There was excellent agreement between the theoretical and experimental lag time to steady-state transport of PPA (r = 0.96, p < 0.001), further implicating the role of membrane resistance in the bi-ionic system. These modeling approaches have already found utility in iontophoretic implant design for prevention of cardiac arrhythmias and may be valuable in future non-steady-state analysis to further develop on-line detection-implant response technology.

Fate and biocompatibility of three types of microspheres implanted into the brain

The implantation of polymer devices in the brain that release neuroactive drugs locally and in a controlled manner is gaining increasing interest. The fates and tissue reactions of poly(epsilon-caprolactone), ethylcellulose, and polystyrene microspheres, prepared by the solvent evaporation method, radiosterilized by gamma-irradiation, and stereotactically implanted in rat brain have been studied by routine staining and immunohistochemistry. During the first few days after implantation, a nonspecific astrocytic brain tissue reaction was observed along with a macrophagous-microglial cell reaction typically found following any damage in the central nervous system, except in the presence of certain foreign body giant cells. Nine months into the experiment, microspheres appeared to be engulfed by histiocytic cells. The microsphere cluster was surrounded by a sheath composed of collagen and astrocytic cells. No necrosis was observed, suggesting the absence of toxicity. In some animals, however, an hydrocephalus developed as a result of obstruction of the medial ventricle by some microspheres.

Seizure suppression in kindling epilepsy by intracerebral implants of GABA- but not by noradrenaline-releasing polymer matrices

Gamma-aminobutyric acid (GABA)-releasing polymer matrices were implanted bilaterally, immediately dorsal to the substantia nigra, in rats previously kindled in the amygdala. Two days after implantation, rats with GABA-releasing matrices exhibited only focal limbic seizures in response to electrical stimulation, whereas animals with control matrices devoid of GABA had generalized convulsions. GABA release from the polymer matrices was high during the first days after implantation, as demonstrated both in vitro and, using microdialysis, in vivo. The anticonvulsant effect was no longer observed at 7 and 14 days at which time GABA release was found to be low. In a parallel experiment, polymer matrices containing noradrenaline (NA) were implanted bilaterally into the hippocampus of rats with extensive forebrain NA depletion induced by an intraventricular 6-hydroxydopamine injection. No effect on the development of hippocampal kindling was observed, despite extracellular NA levels exceeding those of rats with intrahippocampal locus coeruleus grafts that have previously been shown to retard kindling rate. The results indicate that GABA-releasing implants located in the substantia nigra region can suppress seizure generalization in epilepsy, even in the absence of synapse formation and integration with the host brain. In contrast, the failure of NA-releasing polymer matrices to retard the development of seizures in NA-depleted rats suggests that such an effect can only be exerted by grafts acting through a well-regulated, synaptic release of NA.

Catecholamine-containing biodegradable microsphere implants as a novel approach in the treatment of CNS neurodegenerative disease. A review of experimental studies in DA-lesioned rats

Biodegradable controlled-release microsphere systems made with the biocompatible biodegradable polyester excipient poly(DL-lactide-co-glycolide) constitute an exciting new technology for drug delivery to the central nervous system (CNS). Implantable controlled-release microspheres containing dopamine (DA) or norepinephrine (NE) provide a novel means to compare DA- or NE -induced restitution of function in unilateral 6-hydroxydopamine lesioned rats. A suspension of 3 microL of DA- or NE-containing microspheres or empty microspheres was implanted in 2 sites of the DA denervated striatum of rats previously unilaterally lesioned with 6-hydroxydopamine. Contralateral-rotational behavior induced by apomorphine was used as an index of lesion success and, following implantation of the microspheres, also as an index of functional recovery. Interestingly, both DA- and NE-microsphere-implanted rats displayed a 30-50% reduction in the number of apomorphine-induced rotations up to 8 wk postimplantation. Rats implanted with empty microspheres did not demonstrate significant changes in contralateral rotational behavior. Behavioral studies following implantation of a mixture of DA and NE microspheres revealed an 80% decrease in the number of apomorphine induced rotations up to 4 wk. On conclusion of the studies, immunocytochemical examination revealed growth of DA and tyrosine hydroxylase immunoreactive fibers in the striatum of DA and NE microsphere-implanted rats. Functional behavior appeared to correlate with the degree of fiber growth. Preliminary electron microscopic studies showed signs of axonal sprouting in the vicinity of the implanted microspheres. No growth was noted in rats implanted with empty microspheres. This report reviews the abilities of both microencapsulated NE and DA to assure functional recovery and to promote DA fiber (re)growth in parkinsonian rats. This novel means to deliver these substances to the central nervous system could be of therapeutic usefulness in Parkinson's disease.

Drug targeting into the central nervous system by stereotactic implantation of biodegradable microspheres

Controlled drug release in the central nervous system through an implantable polymeric vector has been developed in recent years. For this purpose, different polymeric devices composed primarily of synthetic biocompatible and biodegradable polymers have been investigated. The first polymeric devices developed were macroscopic implants (monolithic devices), which required open surgery for implantation. Microencapsulation methods, however, allow the production of microparticles or nanoparticles loaded with neuroactive drugs. Because of their size, these micro- or nanoparticles may be easily implanted by stereotaxy in discrete, precise, and functional areas of the brain without causing damage to the surrounding tissue. Presently, this method is most frequently applied in the fields of neuro-oncology and neurodegenerative diseases, but neurologically, the potential applications of drug targeting by stereotactic implantation of drug-loaded particles are legion.

Biodegradation and brain tissue reaction to poly(D,L-lactide-co-glycolide) microspheres

The therapeutic application of neuroactive molecules in neuroscience is limited, due to the problems posed by the administration of these drugs (peripheral metabolism, systemic effect and passage of the blood-brain barrier). One solution is the implantation in the brain of biodegradable polymer devices with controlled release of a neuroactive drug. The biodegradation and tissue reaction of the copolymer poly(D,L-lactide-co-glycolide) microspheres prepared by the solvent evaporation method, radiosterilized and stereotactically implanted in the rat brain were studied by routine staining, immunohistochemistry and transmission electronic microscopy. The brain tissue reaction observed was a non-specific astrocytic proliferation and a macrophagous-microglial cell reaction, typically found following damage to the central nervous system. Some foreign-body giant cells were observed and the inflammatory and macrophagous reaction decreased dramatically after 1 month and almost ended after 2 months when the microspheres were totally biodegraded. The copolymer poly(D,L-lactide-co-glycolide) microspheres may be considered biocompatible to the brain tissue.

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

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

Grafts in the treatment of Parkinson's disease: animal models

Long-term treatment of parkinsonian patients with L-DOPA leads to a loss of efficacy over time and the appearance of important side effects such as dyskinesias. Grafts of chromaffin cells of the adrenal medulla or fetal ventral mesencephalic neurons bring behavioral improvement in animal models of Parkinson's disease. These improvements are likely to be related to the secretion of dopamine by the grafted cells and/or to the reinnervation of the host tissue. In addition, a leak in the blood-brain barrier may allow peripheral catecholamines to gain access to the brain. Lack of clear effects of grafts in parkinsonian patients may be due to their poor survival in the human brain. Improvement of grafting techniques as well as the addition of neurotrophic factors to grafts may help increase their survival and improve behavioral effects. Recently, genetic techniques have allowed the creation of genetically modified cell lines which can produce L-DOPA and these cells may be grafted in the brain. Interestingly, these cell lines may be encapsulated in permselective membranes which can protect them from immunological rejection and avoid the uncontrolled cell growth of these mitotically active cells. Grafting techniques seem to be an interesting alternative to treat parkinsonian patients. Improvement of grafting procedures may help increase survival of grafts and thus enhance behavioral improvements. Moreover, genetic modification of well-known tumor cell lines or patient's own cells such as astrocytes may help avoid the low availability as well as ethical and immunological problems linked to the use of fetal human tissue.

Dopaminergic transplants in experimental parkinsonism: cellular mechanisms of graft-induced functional recovery

The ability of intrastriatal grafts of fetal mesencephalic dopamine neurons to ameliorate the symptoms of experimental and clinical parkinsonism has raised the question of the mechanisms underlying the transplant-induced functional effects. Recent studies have taken advantage of quantitative cytochemical and in situ hybridization techniques to study functional graft-host interactions at the cellular level in the rat Parkinson model. The results provide evidence that behaviorally functional grafts restore dopaminergic neurotransmission and normalize dopamine receptor function in the denervated striatum, and that these effects are likely to depend on both synaptic and extrasynaptic mechanisms.

Dopamine fiber growth induction by implantation of synthetic dopamine-containing microspheres in rats with experimental hemi-parkinsonism

Injectable local drug delivery formulations-so-called microspheres have recently been developed, in which drugs are microencapsulated within biocompatible and biodegradable copolymer excipients like poly[DL-lactide-co-glycolide]. In view of its potential therapeutical usefulness, we have studied the microsphere methodology as a means to substitute for experimentally induced subnormal levels of endogenous dopamine (DA). Administration of 6-hydroxydopamine (6-OH-DA) unilaterally in the medial forebrain bundle of rats results in an up-regulation of postsynaptic receptors in the denervated striatum, functionally manifested as contralateral rotational behavior after apomorphine. DA microspheres were implanted in the denervated striatum. The majority of the rats displayed an attenuation of the contralateral rotational behavior induced by apomorphine up to 8 wk postimplantation. Immunocytochemical observations unexpectedly demonstrated growth of DA and tyrosine hydroxylase immunoreactive fibers in the denervated striatum. Interestingly, there was an apparent correlation between functional recovery and the degree of growth of DA fibers. The present results suggest that implantation of DA microspheres may promote DA fiber growth and extended recovery of surviving DA neurons, and, therefore, could be of therapeutic usefulness in Parkinson's disease.

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

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

Changes in blood-brain barrier permeability are associated with behavioral and neurochemical indices of recovery following intraventricular adrenal medulla grafts in an animal model of Parkinson's disease

Intraventricular adrenal medulla grafts were found to produce dissociable effects on rotational behavior induced by amphetamine and apomorphine in rats with unilateral striatal dopamine depletions. Some animals showed a decrease in the behavioral response to apomorphine, some showed a decrease to amphetamine, and some showed a decrease to both amphetamine and apomorphine. Using in vivo microdialysis, the experiments reported demonstrate that in animals with decreased rotational behavior, assessed with either amphetamine or apomorphine, there was an increase in the permeability of the blood-brain barrier to dopamine. The increased blood-brain barrier permeability was visually confirmed with horseradish peroxidase. The extent of the blood-brain barrier disruption, however, was greater in animals with a decreased response to amphetamine. Animals that exhibited decreased amphetamine-induced turning after adrenal medulla grafts also had a greater amphetamine-stimulated increase in striatal dopamine and greater extracellular striatal dihydroxyphenylacetic acid concentrations compared to controls and animals with a graft-induced decrease in the response to apomorphine. We conclude that more than one mechanism is involved in mediating the behavioral effects of adrenal medulla grafts.

Regional changes of striatal dopamine receptors following denervation by 6-hydroxydopamine and fetal mesencephalic grafts in the rat

Young adult female rats received a 6-hydroxydopamine lesion in the left substantia nigra and, 3 weeks later, some of them were grafted with a cell suspension from the ventral mesencephalon of rat embryos (14-15 days old). Six months after transplantation, some grafted rats, following injection of amphetamine, had switched to turning only toward the intact side (type 1), whereas others turned toward the intact side only during the first half of the test (type 2). Levels of dopamine, dihydroxyphenylacetic acid and homovanillic acid were, respectively, 2%, 15% and 35% of the intact side in the denervated striatum of 6-hydroxydopamine rats. Dopamine concentrations were restored to 13% and 10% of the intact side in the grafted striatum of type 1 and type 2 animals, respectively. Levels of homovanillic acid were unchanged following grafts whereas those of dihydroxyphenylacetic acid increased by 209% and 247% in the grafted striatum of type 1 and type 2 animals, respectively. The ratios of dihydroxyphenylacetic acid/dopamine as well as homovanillic acid/dopamine were low in the intact striatum whereas they increased in the denervated striatum with or without graft. The tyrosine hydroxylase immunoreactivity decreased by about 80% in the denervated striatum of 6-hydroxydopamine rats. In type 1 rats, tyrosine hydroxylase immunoreactivity revealed that the graft was localized in the dorsomedial part of the denervated striatum, whereas in type 2 animals, it was also in the medial striatum but it overlapped the dorsal and ventral parts of it equally. D1 as well as D2 dopamine receptors were measured throughout the striatum (9.0-7.6 rostral-caudal coordinates), by autoradiography, using [3H]SCH 23390 (D1 antagonist) and [3H]spiperone (D2 antagonist) binding. Supersensitive D2 receptors were normalized in the dorso- and ventromedial parts of the grafted striatum. D2 receptor density was higher in type 2 than in type 1 rats, more specifically at 8.6-8.2 rostral-caudal coordinates, where the graft was. D1 receptor supersensitivity was modest compared to D2 receptors in the striatum of 6-hydroxydopamine rats and decreased following grafts. DA receptors changes in the striatum, following fetal mesencephalic grafts, may explain the behavioral recovery seen in grafted rats.

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.

Brain grafts and Parkinson's disease

In animal models, grafts derived from several different tissues, principally fetal substantia nigra and adrenal medulla from young adults, have been found to be effective in alleviating some of the manifestations of lesions of the substantia nigra. It has been suggested that these grafts function by diffusely secreting dopamine, by exerting trophic effects on the host brain, or by producing a new innervation of the host corpus striatum. Evidence for each of these modes of action is briefly reviewed. Several brain tissue transplantation techniques have been described. Each of these techniques has significant limitations in animal models. The significance of these limitations for human application is described, and possibilities for improving the efficacy of brain tissue transplantation in animal models and for human application are discussed.

Intracerebral adrenal medulla grafts: a review

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