Striatal tissue transplantation in non-human primates

Neural Mechanisms of High-Level Vision

The last three decades have seen major strides in our understanding of neural mechanisms of high-level vision, or visual cognition of the world around us. Vision has also served as a model system for the study of brain function. Several broad insights, as yet incomplete, have recently emerged. First, visual perception is best understood not as an end unto itself, but as a sensory process that subserves the animal's behavioral goal at hand. Visual perception is likely to be simply a side effect that reflects the readout of visual information processing that leads to behavior. Second, the brain is essentially a probabilistic computational system that produces behaviors by collectively evaluating, not necessarily consciously or always optimally, the available information about the outside world received from the senses, the behavioral goals, prior knowledge about the world, and possible risks and benefits of a given behavior. Vision plays a prominent role in the overall functioning of the brain providing the lion's share of information about the outside world. Third, the visual system does not function in isolation, but rather interacts actively and reciprocally with other brain systems, including other sensory faculties. Finally, various regions of the visual system process information not in a strict hierarchical manner, but as parts of various dynamic brain-wide networks, collectively referred to as the "connectome." Thus, a full understanding of vision will ultimately entail understanding, in granular, quantitative detail, various aspects of dynamic brain networks that use visual sensory information to produce behavior under real-world conditions. © 2017 American Physiological Society. Compr Physiol 8:903-953, 2018.

Therapeutic effects of stem cells in rodent models of Huntington's disease: Review and electrophysiological findings

The principal symptoms of Huntington's disease (HD), chorea, cognitive deficits, and psychiatric symptoms are associated with the massive loss of striatal and cortical projection neurons. As current drug therapies only partially alleviate symptoms, finding alternative treatments has become peremptory. Cell replacement using stem cells is a rapidly expanding field that offers such an alternative. In this review, we examine recent studies that use mesenchymal cells, as well as pluripotent, cell-derived products in animal models of HD. Additionally, we provide further electrophysiological characterization of a human neural stem cell line, ESI-017, which has already demonstrated disease-modifying properties in two mouse models of HD. Overall, the field of regenerative medicine represents a viable and promising avenue for the treatment of neurodegenerative disorders including HD.

Rehabilitation training in neural restitution

Over the last decade, neural transplantation has emerged as one of the more promising, albeit highly experimental, potential therapeutics in neurodegenerative disease. Preclinical studies in rat lesion models of Huntington's disease (HD) and Parkinson's disease (PD) have shown that transplanted precursor neuronal tissue from a fetus into the lesioned striatum can survive, integrate, and reconnect circuitry. Importantly, specific training on behavioral tasks that target striatal function is required to encourage functional integration of the graft to the host tissue. Indeed, "learning to use the graft" is a concept recently adopted in preclinical studies to account for unpredicted profiles of recovery posttransplantation and is an emerging strategy for improving graft functionality. Clinical transplant studies in HD and PD have resulted in mixed outcomes. Small sample sizes and nonstandardized experimental procedures from trial to trial may explain some of this variability. However, it is becoming increasingly apparent that simply replacing the lost neurons may not be sufficient to ensure the optimal graft effects. The knowledge gained from preclinical grafting and training studies suggests that lifestyle factors, including physical activity and specific cognitive and/or motor training, may be required to drive the functional integration of grafted cells and to facilitate the development of compensatory neural networks. The clear implications of preclinical studies are that physical activity and cognitive training strategies are likely to be crucial components of clinical cell replacement therapies in the future. In this chapter, we evaluate the role of general activity in mediating the physical ability of cells to survive, sprout, and extend processes following transplantation in the adult mammalian brain, and we consider the impact of general and specific activity at the behavioral level on functional integration at the cellular and physiological level. We then highlight specific research questions related to timing, intensity, and specificity of training in preclinical models and synthesize the current state of knowledge in clinical populations to inform the development of a strategy for neural transplantation rehabilitation training.

Mitochondrial cofactors in experimental Huntington's disease: behavioral, biochemical and histological evaluation

The present study was carried out to evaluate the beneficial effect of mitochondrial cofactors; alpha-lipoic acid (ALA) and acetyl-l-carnitine (ALCAR) in 3-nitropropionic acid (3-NP) induced experimental model of Huntington's disease (HD). HD was developed by administering sub-chronic doses of 3-NP, intraperitoneally, twice daily for 17 days. The animals were assessed for their behavioral performance in terms of motor (spontaneous locomotor activity, narrow beam walk test, footprint analysis and rotarod test) and cognitive (elevated plus maze and T-maze tests) functions. 3-NP treated animals showed impairment in motor coordination such as decreased stride length, increased distance between inner toes, and increased gait angle. Increased transfer latency on elevated plus maze and T-maze tasks revealed cognition deficits in 3-NP treated animals. Increased lipid peroxidation and concomitant decrease in thiol levels were also observed. 3-NP administration also induced histopathological changes in terms of enhanced striatal lesion volume, presence of pyknotic nuclei and astrogliosis. However, combined supplementation with ALA+ALCAR to 3-NP administered animals for 21 days was able to efficiently improve behavioral deficits, attenuate oxidative stress and histological changes, suggesting a putative role of these two supplements if given together in ameliorating 3-NP induced impairments and thus could be engaged in managing HD.

Stem cell-based therapy for Huntington's disease

Huntington's disease (HD) is a late-onset neurodegenerative disease characterized by a progressive loss of medium spiny neurons in the basal ganglia. The development of stem cell-based therapies for HD aims to replace lost neurons and/or to prevent cell death. This review will discuss pre-clinical studies which have utilized stem or progenitor cells for transplantation therapy using HD animal models. In several studies, neural stem and progenitor cells used as allotransplants and xenografts have been shown to be capable of surviving transplantation and differentiating into mature GABAergic neurons, resulting in behavioral improvements. Beneficial effects have also been reported for transplantation of stem cells derived from non-neural tissue, for example, mesenchymal- and adipose-derived stem cells, which have mainly been attributed to their secretion of growth and neurotrophic factors. Finally, we review studies using stem cells genetically engineered to over-express defined neurotrophic factors. While these studies prove the potential of stem cells for transplantation therapy in HD, it also becomes clear that technical and ethical issues regarding the availability of stem cells must be solved before human trials can be conducted.

Injectable hydrogels for central nervous system therapy

Diseases and injuries of the central nervous system (CNS) including those in the brain, spinal cord and retina are devastating because the CNS has limited intrinsic regenerative capacity and currently available therapies are unable to provide significant functional recovery. Several promising therapies have been identified with the goal of restoring at least some of this lost function and include neuroprotective agents to stop or slow cellular degeneration, neurotrophic factors to stimulate cellular growth, neutralizing molecules to overcome the inhibitory environment at the site of injury, and stem cell transplant strategies to replace lost tissue. The delivery of these therapies to the CNS is a challenge because the blood-brain barrier limits the diffusion of molecules into the brain by traditional oral or intravenous routes. Injectable hydrogels have the capacity to overcome the challenges associated with drug delivery to the CNS, by providing a minimally invasive, localized, void-filling platform for therapeutic use. Small molecule or protein drugs can be distributed throughout the hydrogel which then acts as a depot for their sustained release at the injury site. For cell delivery, the hydrogel can reduce cell aggregation and provide an adhesive matrix for improved cell survival and integration. Additionally, by choosing a biodegradable or bioresorbable hydrogel material, the system will eventually be eliminated from the body. This review discusses both natural and synthetic injectable hydrogel materials that have been used for drug or cell delivery to the CNS including hyaluronan, methylcellulose, chitosan, poly(N-isopropylacrylamide) and Matrigel.

Clinical trials of neural transplantation in Huntington's disease

Clinical neural transplantation in Huntington's disease has moved forward as a series of small studies, which have provided some preliminary proof of principle that neural transplantation can provide benefit. However, to date, such benefits have not been robust, and there are a number of important issues that need to be addressed. These include defining the optimum donor tissue conditions and host characteristics in order to produce reliable benefit in transplant recipients, and whether, and for how long, immunosuppression is needed. Further clinical studies will be required to address these, and other issues, in order to better understand the processes leading to a properly functioning neural graft. Such studies will pave the way for future clinical trials of renewable donor sources, in particular, stem cell-derived neuronal progenitor grafts.

Overview of the marmoset as a model in nonclinical development of pharmaceutical products

Callithrix jacchus (common marmoset) is one of the more primitive non-human primate species and is used widely in fundamental biology, pharmacology and toxicology studies. Marmosets breed well in captivity with good reproductive efficiencies and their sexual maturity is reached within 18 months of age allowing for rapid expansion of colonies and early availability of sexually mature animals permitting an earlier assessment of product candidates in the adult. Their relatively small size allows a reduction in material requirements leading to a reduction in development time and cost. Fewer animals are also required due to their ability to be used in both pharmacology and toxicology (nonclinical) studies. These factors, alongside a better understanding of their optimal nutrient and welfare requirements over recent years, facilitate the generation of a more cohesive and robust dataset. With the growth of biotechnology-derived pharmaceuticals, non-human primate use has, by necessity, also increased; nevertheless, there is also a growing public call for minimizing their use. Utilizing, the more primitive marmoset species may provide the optimal compromise and once the scientific rationale has been carefully considered and their use justified, there are several advantages to using the marmoset as a model in nonclinical development of pharmaceutical products.

Stem cell biology in traumatic brain injury: effects of injury and strategies for repair

Approximately 350,000 individuals in the US are affected annually by severe and moderate traumatic brain injuries (TBI) that may result in long-term disability. This rate of injury has produced approximately 3.3 million disabled survivors in the US alone. There is currently no specific treatment available for TBI other than supportive care, but aggressive prehospital resuscitation, rapid triage, and intensive care have reduced mortality rates. With the recent demonstration that neurogenesis occurs in all mammals (including man) throughout adult life, albeit at a low rate, the concept of replacing neurons lost after TBI is now becoming a reality. Experimental rodent models have shown that neurogenesis is accelerated after TBI, especially in juveniles. Two approaches have been followed in these rodent models to test possible therapeutic approaches that could enhance neuronal replacement in humans after TBI. The first has been to define and quantify the phenomenon of de novo hippocampal and cortical neurogenesis after TBI and find ways to enhance this (for example by exogenous trophic factor administration). A second approach has been the transplantation of different types of neural progenitor cells after TBI. In this review the authors discuss some of the processes that follow after acute TBI including the changes in the brain microenvironment and the role of trophic factor dynamics with regard to the effects on endogenous neurogenesis and gliagenesis. The authors also discuss strategies to clinically harness the factors influencing these processes and repair strategies using exogenous neural progenitor cell transplantation. Each strategy is discussed with an emphasis on highlighting the progress and limiting factors relevant to the development of clinical trials of cellular replacement therapy for severe TBI in humans.

Gene and cell delivery to the degenerated striatum: status of preclinical efforts in primate models

Significant progress has been achieved in developing restorative neurosurgical strategies for movement disorders on the basis of preclinical gene and cell therapy experiments in primates. Because of the unique similarities between human and primate anatomy and physiology, experiments in primate models are the critical step in translating these innovative neurosurgical treatment concepts into successful human applications. To clarify progress toward this goal, we have examined recent preclinical data regarding the delivery of gene and cell therapy to the lesioned primate striatum. Improved behavioral outcomes after in vivo gene transduction, achieved by brain delivery of adeno-associated vectors, have resulted in the initiation of ongoing clinical trials. Cell transplantation experiments are transitioning from the grafting of fetal tissue, which has met with mixed clinical success, to the grafting of expanded neural stem cells, for which preliminary results in primates are encouraging. Careful attention to the surgical delivery parameters for these agents in primate studies, along with the ability to realistically model imaging and behavioral outcomes in these animals, is essential for optimizing the restoration of function for patients. The authors review data obtained from primate models that form the basis for ongoing clinical trials to consider how new preclinical models should be developed to answer questions that arise from experimental clinical data.

Developing cell transplantation for temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is presumed to develop progressively as a consequence of synaptic reorganization and neuronal loss, although the exact etiology of seizure development is unknown. Nearly 30% of patients with MTLE have disabling seizures despite pharmacological treatment, and the majority of these patients are recommended for resection. The authors review cell transplantation as an alternative approach to the treatment of epilepsy. Recent work in animal models shows that grafted neuronal precursors that differentiate into inhibitory interneurons can increase the level of local inhibition. Grafts of these inhibitory neurons could help restore equilibrium in MTLE. Developing a sound transplantation strategy involves careful consideration of the etiology of MTLE and the expected functional role of transplanted cells. These issues are reviewed, with a focus on those factors most likely to influence clinically applicable results.

Time processing in Huntington's disease: a group-control study

BACKGROUND

"Timing" processes are mediated via a disturbed neuronal network including the basal ganglia. Brain structures important for "timing" are also discussed to be critical for the deterioration of movements in Huntington's disease (HD). Changes in "timing processes" are found in HD, but no study has varied the degree of motor demands in timing functions in parallel in HD. It may be hypothesized that timing functions may be deteriorated to a different extent in motor and non-motor timing, because in motor timing the underlying brain structures may be more demanding than in non-motor timing.

METHODOLOGY/PRINCIPLE FINDINGS

WE ASSESSED TIMING IN TWO DIFFERENT EXPERIMENTS: a time-estimation (TE) and a time-discrimination (TD) task. The demand on motor functions is high in the TE-task and low in the TD-task. Furthermore, general motor ability was assessed at different complexity levels. A presymptomatic (pHD), a symptomatic (HD) and a control group were investigated. We found a decline in timing functions when demands on the motor system were high (TE-task), in HD and even in pHD, compared to controls. In non-motor timing (TD task) and in the assessment of general motor ability, performance in the pHD-group was comparable to the controls and better than in the symptomatic group. Performance in both timing tasks was related to the duration until the estimated age of onset in pHDs.

CONCLUSIONS/SIGNIFICANCE

The study shows a selective deterioration of time-estimation processes in symptomatic and even presymptomatic Huntington's disease. Time-discrimination processes were not affected in both patient groups. The relation of timing performance to the duration until the estimated age of onset in pHD is of clinical importance.

Evidence for hemispheric specialization in the marmoset (Callithrix penicillata) based on lateralization of behavioral/neurochemical correlations

A correlative study between behavioral, neurochemical and hormonal measures was conducted on male black tufted-ear marmoset monkeys (Callithrix penicillata). Behavioral analysis was performed in order to examine the effects of confrontation with a natural predator (taxidermized oncilla cat, Felis tigrina). The subjects were subjected to four trials without predator, six confrontation trials with predator present, and four trials with the predator removed. Handedness was analyzed by the frequency with which they performed scratching, grooming and hanging behaviors with the left or right hands. The animals' brains were subjected to ex vivo neurochemical analysis of several structures from both hemispheres. The content of monoamines, acetycholine and metabolites were analyzed by HPLC-ED. Plasma levels of cortisol and adrenocorticotrophic hormone (ACTH) were analyzed by chemoluminescence immunoassay. Testosterone plasma concentration was determined by radioimmunoassay. Higher levels of dopamine and acetylcholine were detected in the right caudate/putamen, in comparison to the left. For the remaining areas, similar levels were observed in both hemispheres. A hand preference between and within the behaviors scored was not detected. However, correlative analyses revealed complex interactions between the behavioral and neurochemical measures, particularly in the left hemisphere. Lateralized correlations were found in relation to brain site, type of behavior, neurochemical parameter and treatment condition, thus providing evidence for functional brain asymmetries in this species. Interhemispheric comparisons of neurochemical/behavioral correlations appear to be a promising approach towards delineating hemispheric specialization of functions in this, and perhaps, other species.

Pharmaceutical, cellular and genetic therapies for Huntington's disease

HD (Huntington's disease) is a devastating neurodegenerative disorder caused by a polyglutamine expansion in the gene encoding the huntingtin protein. Presently, there is no known cure for HD and existing symptomatic treatments are limited. However, recent advances have identified multiple pathological mechanisms involved in HD, some of which have now become the focus of therapeutic intervention. In this review, we consider progress made towards developing safe and effective pharmaceutical-, cell- and genetic-based therapies, and discuss the extent to which some of these therapies have been successfully translated into clinical trials. These new prospects offer hope for delaying and possibly halting this debilitating disease.

Topography of cortico-striatal connections in man: anatomical evidence for parallel organization

Tracing studies in non-human primates support the existence of several parallel neuronal circuits involving cerebral cortex, basal ganglia and thalamus. Distinct functional loops were proposed to underlie multiple aspects of normal and pathological behaviour in man. We present here the first anatomical evidence for separate corticostriatal systems in humans. Neural connections of the sensorimotor and prefrontal cortex to the striatum were studied in one human brain using the Nauta method for anterogradely degenerating axons. Axons originating from a lesion in the left sensorimotor cortex, including the face area, were found to terminate in the superolateral part of the ipsilateral putamen, forming a narrow band in its posterior part. Inside the band, the distribution of degenerating axons was inhomogeneous; high-density clusters of approximately 2.5 mm in diameter were separated by regions with less dense cortical projections. Axons originating from a small lesion in the fundus of the right superior frontal sulcus were found in the upper part of the ipsilateral caudate nucleus. The existence of discrete and anatomically segregated terminal patches originating from distinct cortical regions suggests parallel organization of cortico-striatal connections in man.

Neural transplantation in patients with Huntington's disease

The gene for Huntington's disease was identified in 1993 as being a CAG repeat expansion in exon 1 of a gene now known as huntingtin on chromosome 4. Although many of the downstream effects of this mutant gene were identified in the subsequent years, a more detailed understanding of these events will be necessary in order to design specific interventions to interfere with the disease process and slow disease progression. In parallel, a number of groups have been investigating alternative approaches to treatment of Huntington's disease, including cell and tissue transplantation. As the brunt of cell dysfunction and loss is borne by the striatum, at least in the early to mid-stages of disease, the goal is to identify methods for replacing lost cells with fetal neuroblasts that can develop, integrate into the host circuitry and thereby restore lost function. Clinical studies in which primary fetal neuroblasts were transplanted into the brains of patients with advanced Parkinson's disease have demonstrated benefit when the transplant methodology closely follows the biological principles established in animal experiments. On the basis of demonstrated benefit following striatal cell transplantation in animal models of Huntington's disease, a small number of studies have now commenced in patients with Huntington's disease. To date, these clinical studies have demonstrated the feasibility and safety of transplantation in this condition, but it will require several more years yet before the efficacy of the procedure can be confidently established.

Unilateral transplantation of human primary fetal tissue in four patients with Huntington's disease: NEST-UK safety report ISRCTN no 36485475

OBJECTIVES

Huntington's disease (HD) is an inherited autosomal dominant condition in which there is a CAG repeat expansion in the huntingtin gene of 36 or more. Patients display progressive motor, cognitive, and behavioural deterioration associated with progressive cell loss and atrophy in the striatum. Currently there are no disease modifying treatments and current symptomatic treatments are only partially effective in the early to moderate stages. Neural transplantation is effective in animal models of HD and offers a potential strategy for brain repair in patients. The authors report a safety study of unilateral transplantation of human fetal striatal tissue into the striatum of four patients with HD.

SUBJECTS AND METHODS

Stereotaxic placements of cell suspensions of human fetal ganglionic eminence were made unilaterally into the striatum of four patients with early to moderate HD. All patients received immunotherapy with cyclosporin A, azathioprine, and prednisolone for at least six months postoperatively. Patients were assessed for safety of the procedure using magnetic resonance imaging (MRI), regular recording of serum biochemistry and haematology to monitor immunotherapy, and clinical assessment according to the Core Assessment Protocol For Intrastriatal Transplantation in HD (CAPIT-HD).

RESULTS

During the six month post-transplantation period, the only adverse events related to the procedure were associated with the immunotherapy. MRI demonstrated tissue at the site of implantation, but there was no sign of tissue overgrowth. Furthermore, there was no evidence that the procedure accelerated the course of the disease.

CONCLUSIONS

Unilateral transplantation of human fetal striatal tissue in patients with HD is safe and feasible. Assessment of efficacy will require longer follow up in a larger number of patients.