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

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.

Nano to micro delivery systems: targeting angiogenesis in brain tumors

Treating brain tumors using inhibitors of angiogenesis is extensively researched and tested in clinical trials. Although anti-angiogenic treatment holds a great potential for treating primary and secondary brain tumors, no clinical treatment is currently approved for brain tumor patients. One of the main hurdles in treating brain tumors is the blood brain barrier - a protective barrier of the brain, which prevents drugs from entering the brain parenchyma. As most therapeutics are excluded from the brain there is an urgent need to develop delivery platforms which will bypass such hurdles and enable the delivery of anti-angiogenic drugs into the tumor bed. Such delivery systems should be able to control release the drug or a combination of drugs at a therapeutic level for the desired time. In this mini-review we will discuss the latest improvements in nano and micro drug delivery platforms that were designed to deliver inhibitors of angiogenesis to the brain.

An intermittent, controlled-rate, slow progressive degeneration model of Parkinson's disease: antiparkinson effects of Sinemet and protective effects of methylphenidate

The causes of nigrostriatal neuron degeneration in Parkinson's disease (PD) are not known, but it has been suggested that exogenous or endogenous factors or neurotoxins may play a role. The degree of vulnerability to neurotoxins or other potential mediators of nigral dopamine cell death is thought to be important in understanding Parkinson's disease. In most animal models, the rate of terminal degeneration and corresponding functional impairment is too rapid to investigate effectively either cell vulnerability or the potential benefits of some neuroprotective treatments. In the present study, a new model of Parkinson's disease is described that might help in addressing the issue of nigral cell vulnerability and to evaluate interventions with clinical potential. 6-Hydroxydopamine (6-OHDA) was infused in escalating, intrastriatal doses over several weeks. Control animals received multiple infusions of vehicle at the same volume. Behavioral testing was carried out between each infusion, including forelimb-use and somatosensory function. A symptomatic threshold was established for each animal, indicating the amount of neurotoxin required to induce a stable deficit. Oral administration of L-DOPA (Sinemet) ameliorated limb-use asymmetries acutely. An immunocytochemical assay for tyrosine hydroxylase, a dopamine cell marker, revealed a partial loss of immunoreactive cells in the substantia nigra. Animals that were co-administered methylphenidate (MPH), a dopamine transport inhibitor, along with the 6-OHDA were spared from the behavioral and neurochemical effects of 6-OHDA, despite receiving more than twice as much neurotoxin as controls. These data suggest that establishing a symptomatic threshold preclinically may help researchers evaluate potential treatments and model individual and group resistance to nigrostriatal insults.

Long-lasting functional disabilities in middle-aged rats with small cerebral infarcts

Recommendations from experts and recently established guidelines on how to improve the face and predictive validity of animal models of stroke have stressed the importance of using older animals and long-term behavioral-functional endpoints rather than relying almost exclusively on acute measures of infarct volume in young animals. The objective of the present study was to determine whether we could produce occlusions in older rats with an acceptable mortality rate and then detect reliable, long-lasting functional deficits. A reversible intraluminar suture middle cerebral artery occlusion (MCAO) procedure was used to produce small infarcts in middle-aged rats. This resulted in an acceptable mortality rate, and robust disabilities were detected in functional assays, although the degree of total tissue loss measured 90 d after MCAO was quite modest. Infarcted animals were functionally impaired relative to sham control animals even 90 d after the occlusions, and when animals were subgrouped based on amount of tissue loss, MCAO animals with only 4% tissue loss exhibited enduring neurological-behavioral impairments relative to sham-operated controls, and the functional impairments in the group with the largest infarcts (20% tissue loss) were more severe than the functional impairments in the rats with 4% tissue loss. These results suggest that this model, using reversible MCAO to produce small infarcts and long-lasting functional-behavioral deficits in older rats, may represent an advance in the relatively higher-throughput modeling of stroke and its recovery in rodents and may be useful in the development and characterization of future stroke therapies.

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.

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.

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.

Incomplete nigrostriatal dopaminergic cell loss and partial reductions in striatal dopamine produce akinesia, rigidity, tremor and cognitive deficits in middle-aged rats

The present study was conducted to determine if the full array of parkinsonian symptoms could be detected in rats with nigrostriatal cell loss and striatal dopamine depletions similar to levels reported in the clinical setting, and to determine if older rats exhibit more robust parkinsonian deficits than younger rats. Young (2 months old) and middle-aged (12 months old) rats received bilateral striatal infusions of 6-OHDA, over the next 3 months they were assessed with a battery of behavioral tests, and then dopaminergic nigrostriatal cells and striatal dopamine and DOPAC levels were quantified. The results of the present study suggest that: (1) the full array of parkinsonian symptoms (i.e. akinesia, rigidity, tremor and visuospatial cognitive deficits) can be quantified in rats with incomplete nigrostriatal dopaminergic cell loss and partial reductions in striatal dopamine levels (2) parkinsonian symptoms were more evident in middle-aged rats with 6-OHDA infusions, and (3) there was evidence of substantial neuroplasticity in the older rats, but regardless of the age of the animal, endogenous compensatory mechanisms were unable to maintain striatal dopamine levels after rapid, lesion-induced nigrostriatal cell loss. These results suggest that using older rats with nigrostriatal dopaminergic cell loss and reductions in striatal dopamine levels similar to those in the clinical condition, and measuring behavioral deficits analogous to parkinsonian symptoms, might increase the predictive validity of pre-clinical rodent models.

Therapeutic Potential of a Polymer-Encapsulated L-Dopa and Dopamine-Producing Cell Line in Rodent and Primate Models of Parkinson's Disease

Encapsulation of cells within polymer membranes prior to transplantation provides a novel means of achieving continuous, site-specific delivery of therapeutic molecules to the CNS. The use of encapsulated dopamine-secreting cells that can be transplanted directly into the striatum has particular appeal for the treatment of Parkinson's disease. This article provides a brief and timely review of the progress that has been made over the past decade using encapsulated PC12 cells as a means of delivering dopamine and l-DOPA to the striatum in rodent and primate models of Parkinson's disease. The polymer membranes are well tolerated and biocompatible. Encapsulated PC12 cells survive in vivo for up to 6 mo, they release dopamine into the surrounding host striatum, and they clearly improve behavioral function in both dopamine-depleted rodents and primates. Although these results are promising, fundamental issues remain concerning the extent of dopamine diffusion from the polymer membranes and the number of devices needed for behavioral improvement, and the duration and consistency of cell viability and device output. Nevertheless, this technology appears to be a promising means of avoiding many of the practical, societal, and ethical issues that have been associated with other transplantation approaches.