Challenges and promises in the development of neurotrophic factor-based therapies for Parkinson's disease

Current Treatments and New, Tentative Therapies for Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative pathology, the origin of which is associated with the death of neuronal cells involved in the production of dopamine. The prevalence of PD has increased exponentially. The aim of this review was to describe the novel treatments for PD that are currently under investigation and study and the possible therapeutic targets. The pathophysiology of this disease is based on the formation of alpha-synuclein folds that generate Lewy bodies, which are cytotoxic and reduce dopamine levels. Most pharmacological treatments for PD target alpha-synuclein to reduce the symptoms. These include treatments aimed at reducing the accumulation of alpha-synuclein (epigallocatechin), reducing its clearance via immunotherapy, inhibiting LRRK2, and upregulating cerebrosidase (ambroxol). Parkinson’s disease continues to be a pathology of unknown origin that generates a significant social cost for the patients who suffer from it. Although there is still no definitive cure for this disease at present, there are numerous treatments available aimed at reducing the symptomatology of PD in addition to other therapeutic alternatives that are still under investigation. However, the therapeutic approach to this pathology should include a combination of pharmacological and non-pharmacological strategies to maximise outcomes and improve symptomatological control in these patients. It is therefore necessary to delve deeper into the pathophysiology of the disease in order to improve these treatments and therefore the quality of life of the patients.

BDNF-modified human umbilical cord mesenchymal stem cells-derived dopaminergic-like neurons improve rotation behavior of Parkinson's disease rats through neuroprotection and anti-neuroinflammation

Parkinson's disease (PD) is a neurodegenerative disease still without any cure. Brain-derived neurotrophic factor (BDNF) has shown therapeutic potential in PD, which is limited by its short half-life and inability to penetrate the blood-brain barrier. Stem cells not only present migration, differentiation and neurotrophy characteristics, but also can be used as delivery vectors for BDNF. This study aimed to investigate the therapeutic effects and possible mechanisms of BDNF-modified human umbilical cord mesenchymal stem cells (hUC-MSCs)-derived dopaminergic (DAergic)-like neurons in the PD rats. Results showed that transplantation of BDNF-modified hUC-MSCs-derived DAergic-like neurons improved the apomorphine induced rotation behavior of PD rats, increased the dopamine concentration and the expression of glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule-1 (Iba-1) in the striatum, promoted the expression of tyrosine hydroxylase (TH), nuclear receptor-related factor 1 (Nurr1), pituitary homeobox 3 (Pitx3), BDNF, tyrosine kinase B (TrkB), phosphatidylinositol-3-hydroxykinase (PI3K), phosphorylated protein kinase B (p-Akt), heat shock protein 60 (Hsp60), toll-like receptor 4 (TLR4) and myeloid differentiation factor 88 (MyD88) and inhibited the neural apoptosis in the substantia nigra (SN) and striatum. Results suggest that BDNF-modified hUC-MSCs-derived DAergic-like neurons improve the rotation of PD rats might through neuroprotection and anti-neuroinflammation by regulating the BDNF-TrkB-PI3K/Akt and Hsp60-TLR4/MyD88 signaling pathways, respectively.

Advances in treatment of neurodegenerative diseases: Perspectives for combination of stem cells with neurotrophic factors

Neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis, are a group of incurable neurological disorders, characterized by the chronic progressive loss of different neuronal subtypes. However, despite its increasing prevalence among the ever-increasing aging population, little progress has been made in the coincident immense efforts towards development of therapeutic agents. Research interest has recently turned towards stem cells including stem cells-derived exosomes, neurotrophic factors, and their combination as potential therapeutic agents in neurodegenerative diseases. In this review, we summarize the progress in therapeutic strategies based on stem cells combined with neurotrophic factors and mesenchymal stem cells-derived exosomes for neurodegenerative diseases, with an emphasis on the combination therapy.

Overview of Therapeutic Drugs and Methods for the Treatment of Parkinson's Disease

Parkinson's Disease (PD) is a neurodegenerative disease involving degeneration of dopaminergic neurons of the nigrostriatal pathways. Over the past decades, most of the medications for the treatment of PD patients have been used to modulate dopamine concentrations in the basal ganglia. This includes levodopa and its inhibitory metabolizing enzymes. In addition to modulating dopamine concentrations in the brain, there are D2-like dopamine receptor agonists that mimic the action of dopamine to compensate for the deficit in dopamine found in PD patients. Muscarinic antagonists' drugs are used rarely due to some side effects. Monoamine oxidase inhibitors are among the first in line, and are considered popular drugs that reduce the metabolism of dopamine in PD patients. Furthermore, we discussed in this review the existence of certain glutamate receptor antagonists for the treatment of PD. Alternatively, we further discussed the potential therapeutic role of adenosine (2A) receptor antagonists, such as tozadenant and istradefylline in the treatment of PD. We also discussed the important role of serotonin1A receptor agonist, adrenergic autoreceptors (α2) antagonists and calcium channel blockers in the treatment of PD. Finally, neurotrophic factors, such as glial cell line-derived neurotrophic growth factor and brain-derived neurotrophic factor are considered the primary factors for neuroprotection in PD.

Amyotrophic Lateral Sclerosis (ALS) and Adenosine Receptors

In the present review we discuss the potential involvement of adenosinergic signaling, in particular the role of adenosine receptors, in amyotrophic lateral sclerosis (ALS). Though the literature on this topic is not abundant, the information so far available on adenosine receptors in animal models of ALS highlights the interest to continue to explore the role of these receptors in this neurodegenerative disease. Indeed, all motor neurons affected in ALS are responsive to adenosine receptor ligands but interestingly, there are alterations in pre-symptomatic or early symptomatic stages that mirror those in advanced disease stages. Information starts to emerge pointing toward a beneficial role of A_2A receptors (A_2AR), most probably at early disease states, and a detrimental role of caffeine, in clear contrast with what occurs in other neurodegenerative diseases. However, some evidence also exists on a beneficial action of A_2AR antagonists. It may happen that there are time windows where A_2AR prove beneficial and others where their blockade is required. Furthermore, the same changes may not occur simultaneously at the different synapses. In line with this, it is not fully understood if ALS is a dying back disease or if it propagates in a centrifugal way. It thus seems crucial to understand how motor neuron dysfunction occurs, how adenosine receptors are involved in those dysfunctions and whether the early changes in purinergic signaling are compensatory or triggers for the disease. Getting this information is crucial before starting the design of purinergic based strategies to halt or delay disease progression.

An ortho-Iminoquinone Compound Reacts with Lysine Inhibiting Aggregation while Remodeling Mature Amyloid Fibrils

Protein aggregation is a hallmark of several neurodegenerative diseases, including Alzheimer's and Parkinson's diseases. It has been shown that lysine residues play a key role in the formation of these aggregates. Thus, the ability to disrupt aggregate formation by covalently modifying lysine residues could lead to the discovery of therapeutically relevant antiamyloidogenesis compounds. Herein, we demonstrate that an ortho-iminoquinone (IQ) can be utilized to inhibit amyloid aggregation. Using alpha-synuclein and Aβ_1-40 as model amyloidogenic proteins, we observed that IQ was able to react with lysine residues and reduce amyloid aggregation. We also observed that IQ reacted with free amines within the amyloid fibrils preventing their dissociation and seeding capacity.

Cerebral Dopamine Neurotrophic Factor: A Potential Therapeutic Agent for Parkinson's Disease

The application of neurotrophic factors (NTFs) is a promising therapeutic strategy for neurodegenerative disorders such as Parkinson's disease (PD). Many NTFs have been reported to enhance the survival, regeneration, and differentiation of neurons and to induce synaptic plasticity. However, because of their potential side-effects and low efficacy after clinical administration, more potent treatments for neurodegenerative disorders are being sought. Cerebral dopamine neurotrophic factor (CDNF), a newly-identified NTF homologous to mesencephalic astrocyte-derived NTF, is structurally and functionally different from other NTFs, providing new hope especially for PD patients. In various animal models of PD, CDNF is efficient in protecting and repairing dopaminergic neurons, and it inhibits endoplasmic reticulum stress, neuroinflammation, and apoptosis. Recent progress in all facets of CDNF research has enabled researchers to better understand its beneficial effects in the treatment of PD.

FTY720-derivatives do not induce FTY720-like lymphopenia

FTY720 is an immunosuppressive multiple sclerosis (MS) drug that stimulates the expression of neuroprotective brain-derived-neurotrophic-factor (BDNF). In vivo preclinical data suggest that FTY720 could be beneficial for treating Parkinson’s patients, though its immunosuppressive effects might limit its efficacy. Two novel FTY720-derivatives, FTY720-C2 and FTY720-Mitoxy, also stimulate BDNF expression and enter brain like FTY720 but are not phosphorylated, suggesting they will not produce FTY720-like immunosuppression. Using FTY720 as a positive control, we measured low and high dose FTY720-derivatives, which did not stimulate FTY720-like lymphopenia or immunosuppressive signaling. These findings support the further preclinical assessment of the derivatives as potential novel Parkinson’s therapies.

Bile Acids in Neurodegenerative Disorders

Bile acids, a structurally related group of molecules derived from cholesterol, have a long history as therapeutic agents in medicine, from treatment for primarily ocular diseases in ancient Chinese medicine to modern day use as approved drugs for certain liver diseases. Despite evidence supporting a neuroprotective role in a diverse spectrum of age-related neurodegenerative disorders, including several small pilot clinical trials, little is known about their molecular mechanisms or their physiological roles in the nervous system. We review the data reported for their use as treatments for neurodegenerative diseases and their underlying molecular basis. While data from cellular and animal models and clinical trials support potential efficacy to treat a variety of neurodegenerative disorders, the relevant bile acids, their origin, and the precise molecular mechanism(s) by which they confer neuroprotection are not known delaying translation to the clinical setting.

Protection of cultured dopamine neurons from MPP(+) requires a combination of neurotrophic factors

Parkinson's disease is a progressive neurodegenerative disorder, caused in part by the loss of dopamine (DA) neurons in the substantia nigra (SN). Neurotrophic factors have been shown to increase the basal survival of DA neurons in vitro, as well as to protect the neurons from some toxins under certain in vitro conditions and in animal models. Although these factors have often been tested individually, they have rarely been studied in combinations. We therefore examined the effect of such combinations after acute exposure to the toxin 1-methyl-4-phenylpyridinium (MPP(+) ) using dissociated postnatal rat midbrain cultures isolated from SN and ventral tegmental area (VTA). We found that significant loss of DA neurons in the SN occurred with an LC50 of between 1 and 10 μm, whereas the LC50 of DA neurons from the VTA was approximately 1000-fold higher. We did not observe neuroprotection against MPP(+) by individual exposure to glial cell-line derived neurotrophic factor (GDNF), brain derived neurotrophic factor (BDNF), transforming growth factor beta (TGFβ), basic fibroblast growth factor (FGF-2) or growth/differentiation factor 5 (GDF5) at concentrations of 100 or 500 ng/mL. Combinations of two, three or four neurotrophic factors were also ineffective. However, when the SN cultures were exposed to a combination of all five neurotrophic factors, each at a concentration of 100 ng/mL, we observed a 30% increase in DA neuron survival in the presence of 10 and 500 μm MPP(+) . These results may be relevant to the use of neurotrophic factors as therapeutic treatments for Parkinson's disease.

An update on potential therapeutic strategies for Parkinson's disease based on pathogenic mechanisms

INTRODUCTION

Parkinson's disease is a common neurodegenerative disorder mainly caused by the loss of nigral dopaminergic neurons, of which the pathogenesis remains essentially unknown. Current therapeutic strategies help manage signs and symptoms but have no effect in disease modification. Over the past several decades, scientists have devoted a lot of effort to clarifying the pathological mechanism and searching for new targets for Parkinson's disease treatment.

AREAS COVERED

Treatment of Parkinson's disease. Expert Commentary: Illustrated in this review are newly found discoveries and evidence that contribute to the understanding of Parkinson's disease pathogenic mechanism. Also discussed are potential therapeutic strategies that are being studied, including disease-modifying and genetically mediated small molecule compounds, cell- and gene-based therapeutic strategies, immunization strategies and anti-diabetic therapy, which may be very promising therapeutic methods in the future.

Implantation of autologous peripheral nerve grafts into the substantia nigra of subjects with idiopathic Parkinson's disease treated with bilateral STN DBS: a report of safety and feasibility

OBJECTIVE One avenue of intense efforts to treat Parkinson's disease (PD) involves the delivery of neurotrophic factors to restore dopaminergic cell function. A source of neurotrophic factors that could be used is the Schwann cell from the peripheral nervous system. The authors have begun an open-label safety study to examine the safety and feasibility of implanting an autologous peripheral nerve graft into the substantia nigra of PD patients undergoing deep brain stimulation (DBS) surgery. METHODS Multistage DBS surgery targeting the subthalamic nucleus was performed using standard procedures in 8 study participants. After the DBS leads were implanted, a section of sural nerve containing Schwann cells was excised and unilaterally delivered into the area of the substantia nigra. Adverse events were continuously monitored. RESULTS Eight of 8 participants were implanted with DBS systems and grafts. Adverse event profiles were comparable to those of standard DBS surgery. Postoperative MR images did not reveal edema, hemorrhage, or significant signal changes in the graft target region. Three participants reported a patch of numbness on the outside of the foot below the sural nerve harvest site. CONCLUSIONS Based on the safety outcome of the procedure, targeted peripheral nerve graft delivery to the substantia nigra at the time of DBS surgery is feasible and may provide a means to deliver neurorestorative therapy. Clinical trial registration no.: NCT01833364 ( clinicaltrials.gov ).

Gene Transfer of Brain-derived Neurotrophic Factor (BDNF) Prevents Neurodegeneration Triggered by FXN Deficiency

Friedreich's ataxia is a predominantly neurodegenerative disease caused by recessive mutations that produce a deficiency of frataxin (FXN). Here, we have used a herpesviral amplicon vector carrying a gene encoding for brain-derived neurotrophic factor (BDNF) to drive its overexpression in neuronal cells and test for its effect on FXN-deficient neurons both in culture and in the mouse cerebellum in vivo. Gene transfer of BDNF to primary cultures of mouse neurons prevents the apoptosis which is triggered by the knockdown of FXN gene expression. This neuroprotective effect of BDNF is also observed in vivo in a viral vector-based knockdown mouse cerebellar model. The injection of a lentiviral vector carrying a minigene encoding for a FXN-specific short hairpin ribonucleic acid (shRNA) into the mouse cerebellar cortex triggers a FXN deficit which is accompanied by significant apoptosis of granule neurons as well as loss of calbindin in Purkinje cells. These pathological changes are accompanied by a loss of motor coordination of mice as assayed by the rota-rod test. Coinjection of a herpesviral vector encoding for BDNF efficiently prevents both the development of cerebellar neuropathology and the ataxic phenotype. These data demonstrate the potential therapeutic usefulness of neurotrophins like BDNF to protect FXN-deficient neurons from degeneration.

BDNF levels are increased by aminoindan and rasagiline in a double lesion model of Parkinson׳s disease

The anti-Parkinsonian drug rasagiline is a selective, irreversible inhibitor of monoamine oxidase and is used in the treatment of Parkinson׳s disease (PD). Its postulated neuroprotective effects may be attributed to MAO inhibition, or to its propargylamine moiety. The major metabolite of rasagiline, aminoindan, has shown promising neuroprotective properties in vitro but there is a paucity of studies investigating in vivo effects of this compound. Therefore, we examined neuroprotective effects of rasagiline and its metabolite aminoindan in a double lesion model of PD. Male Fisher 344 rats received i.p. injections of the noradrenergic neurotoxin DSP-4 and intra-striatal stereotaxic microinjections of the dopamine neurotoxin 6-OHDA. Saline, rasagiline or aminoindan (3mg/kg/day s.c.) were delivered via Alzet minipumps for 4 weeks. Rats were then tested for spontaneous locomotion and a novel object recognition task. Following behavioral testing, brain tissue was processed for ELISA measurements of growth factors and immunohistochemistry. Double-lesioned rats treated with rasagiline or aminoindan had reduced behavioral deficits, both in motor and cognitive tasks compared to saline-treated double-lesioned rats. BDNF levels were significantly increased in the hippocampus and striatum of the rasagiline- and aminoindan-lesioned groups compared to the saline-treated lesioned group. Double-lesioned rats treated with rasagiline or aminoindan exhibited a sparing in the mitochondrial marker Hsp60, suggesting mitochondrial involvement in neuroprotection. Tyrosine hydroxylase (TH) immunohistochemistry revealed a sparing of TH-immunoreactive terminals in double-lesioned rats treated with rasagiline or aminoindan in the striatum, hippocampus, and substantia nigra. These data provide evidence of neuroprotection by aminoindan and rasagiline via their ability to enhance BDNF levels.

Intranasal insulin protects against substantia nigra dopaminergic neuronal loss and alleviates motor deficits induced by 6-OHDA in rats

Protection of substantia nigra (SN) dopaminergic (DA) neurons by neurotrophic factors (NTFs) is one of the promising strategies in Parkinson's disease (PD) therapy. A major clinical challenge for NTF-based therapy is that NTFs need to be delivered into the brain via invasive means, which often shows limited delivery efficiency. The nose to brain pathway is a non-invasive brain drug delivery approach developed in recent years. Of particular interest is the finding that intranasal insulin improves cognitive functions in Alzheimer's patients. In vitro, insulin has been shown to protect neurons against various insults. Therefore, the current study was designed to test whether intranasal insulin could afford neuroprotection in the 6-hydroxydopamine (6-OHDA)-based rat PD model. 6-OHDA was injected into the right side of striatum to induce a progressive DA neuronal lesion in the ipsilateral SN pars compact (SNc). Recombinant human insulin was applied intranasally to rats starting from 24h post lesion, once per day, for 2 weeks. A battery of motor behavioral tests was conducted on day 8 and 15. The number of DA neurons in the SNc was estimated by stereological counting. Our results showed that 6-OHDA injection led to significant motor deficits and 53% of DA neuron loss in the ipsilateral side of injection. Treatment with insulin significantly ameliorated 6-OHDA-induced motor impairments, as shown by improved locomotor activity, tapered/ledged beam-walking performance, vibrissa-elicited forelimb-placing, initial steps, as well as methamphetamine-induced rotational behavior. Consistent with behavioral improvements, insulin treatment provided a potent protection of DA neurons in the SNc against 6-OHDA neurotoxicity, as shown by a 74.8% increase in tyrosine hydroxylase (TH)-positive neurons compared to the vehicle group. Intranasal insulin treatment did not affect body weight and blood glucose levels. In conclusion, our study showed that intranasal insulin provided strong neuroprotection in the 6-OHDA rat PD model, suggesting that insulin signaling may be a novel therapeutic target in broad neurodegenerative disorders.

Purine nucleosides in neuroregeneration and neuroprotection

In the present review, we stress the importance of the purine nucleosides, adenosine and guanosine, in protecting the nervous system, both centrally and peripherally, via activation of their receptors and intracellular signalling mechanisms. A most novel part of the review focus on the mechanisms of neuronal regeneration that are targeted by nucleosides, including a recently identified action of adenosine on axonal growth and microtubule dynamics. Discussion on the role of the purine nucleosides transversally with the most established neurotrophic factors, e.g. brain derived neurotrophic factor (BDNF), glial derived neurotrophic factor (GDNF), is also focused considering the intimate relationship between some adenosine receptors, as is the case of the A2A receptors, and receptors for neurotrophins. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Advances in Neurotrophic Factor and Cell-Based Therapies for Parkinson's Disease: A Mini-Review

Parkinson's disease (PD) affects an estimated 7-10 million people worldwide and remains without definitive or disease-modifying treatment. There have been many recent developments in cell-based therapy (CBT) to replace lost circuitry and provide chronic biological sources of therapeutic agents to the PD-affected brain. Early neural transplantation studies underscored the challenges of immune compatibility, graft integration and the need for renewable, autologous graft sources. Neurotrophic factors (NTFs) offer a potential class of cytoprotective pharmacotherapeutics that may complement dopamine (DA) replacement and CBT strategies in PD. Chronic NTF delivery may be an integral goal of CBT, with grafts consisting of autologous drug-producing (e.g., DA, NTF) cells that are capable of integration and function in the host brain. In this mini-review, we outline the past experience and recent advances in NTF technology and CBT as promising and integrated approaches for the treatment of PD.

Alpha-synuclein as a pathological link between chronic traumatic brain injury and Parkinson's disease

The long-term consequences of traumatic brain injury (TBI) are closely associated with the development of histopathological deficits. Notably, TBI may predispose long-term survivors to age-related neurodegenerative diseases, such as Parkinson's disease (PD), which is characterized by a gradual degeneration of the nigrostriatal dopaminergic neurons. However, preclinical studies on the pathophysiological changes in substantia nigra (SN) after chronic TBI are lacking. In the present in vivo study, we examined the pathological link between PD-associated dopaminergic neuronal loss and chronic TBI. Sixty days post-TBI, rats were euthanized and brain tissues harvested. Immunostaining was performed using tyrosine hydroxylase (TH), an enzyme required for the synthesis of dopamine in neurons, α-synuclein, a presynaptic protein that plays a role in synaptic vesicle recycling, and major histocompatibility complex II (MHCII), a protein found in antigen presenting cells such as inflammatory microglia cells, all key players in PD pathology. Unbiased stereology analyses revealed significant decrease of TH-positive expression in the surviving dopaminergic neurons of the SN pars compacta (SNpc) relative to sham control. In parallel, increased α-synuclein accumulation was detected in the ipsilateral SN compared to the contralateral SN in TBI animals or sham control. In addition, exacerbation of MHCII+ cells was recognized in the SN and cerebral peduncle ipsilateral to injury relative to contralateral side and sham control. These results suggest α-synuclein as a pathological link between chronic effects of TBI and PD symptoms as evidenced by significant overexpression and abnormal accumulation of α-synuclein in inflammation-infiltrated SN of rats exposed to chronic TBI. J. Cell. Physiol. 230: 1024–1032, 2015. © 2014 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Brain-derived neurotrophic factor mediates neuroprotection against Aβ-induced toxicity through a mechanism independent on adenosine 2A receptor activation

Brain-derived neurotrophic factor (BDNF) promotes neuronal survival through TrkB-FL activation. The activation of adenosine A2A receptors (A2AR) is essential for most of BDNF-mediated synaptic actions, such as synaptic plasticity, transmission and neurotransmitter release. We now aimed at evaluating the A2AR influence upon BDNF-mediated neuroprotection against Aβ25-35 toxicity in cultured neurons. Results showed that BDNF increases cell survival and reduces the caspase-3 and calpain activation induced by amyloid-β (Aβ) peptide, in a mechanism probably dependent on PLCγ pathway. This BDNF-mediated neuroprotection is not affected by A2AR activation or inhibition. Moreover neither activation nor inhibition of A2AR, per se, significantly influenced Aβ-induced neuronal death on calpain-mediated cleavage of TrkB induced by Aβ. In conclusion, these results suggest that, in opposition to the fast synaptic actions of BDNF, the neuroprotective actions of this neurotrophin against a strong Aβ insult do not require the activation of A2AR.

Neuromodulation and metamodulation by adenosine: Impact and subtleties upon synaptic plasticity regulation

Synaptic plasticity mechanisms, i.e. the sequence of events that underlies persistent changes in synaptic strength as a consequence of transient alteration in neuronal firing, are greatly influenced by the 'chemical atmosphere' of the synapses, that is to say by the presence of molecules at the synaptic cleft able to fine-tune the activity of other molecules more directly related to plasticity. One of those fine tuners is adenosine, known for a long time as an ubiquitous neuromodulator and metamodulator and recognized early as influencing synaptic plasticity. In this review we will refer to the mechanisms that adenosine can use to affect plasticity, emphasizing aspects of the neurobiology of adenosine relevant to its ability to control synaptic functioning. This article is part of a Special Issue entitled Brain and Memory.