Pharmacological therapy in Parkinson's disease: focus on neuroprotection

Mechanistic Insights, Treatment Paradigms, and Clinical Progress in Neurological Disorders: Current and Future Prospects

Neurodegenerative diseases (NDs) are a major cause of disability and are related to brain development. The neurological signs of brain lesions can vary from mild clinical shortfalls to more delicate and severe neurological/behavioral symptoms and learning disabilities, which are progressive. In this paper, we have tried to summarize a collective view of various NDs and their possible therapeutic outcomes. These diseases often occur as a consequence of the misfolding of proteins post-translation, as well as the dysfunctional trafficking of proteins. In the treatment of neurological disorders, a challenging hurdle to cross regarding drug delivery is the blood-brain barrier (BBB). The BBB plays a unique role in maintaining the homeostasis of the central nervous system (CNS) by exchanging components between the circulations and shielding the brain from neurotoxic pathogens and detrimental compounds. Here, we outline the current knowledge about BBB deterioration in the evolving brain, its origin, and therapeutic interventions. Additionally, we summarize the physiological scenarios of the BBB and its role in various cerebrovascular diseases. Overall, this information provides a detailed account of BBB functioning and the development of relevant treatments for neurological disorders. This paper will definitely help readers working in the field of neurological scientific communities.

Glycolysis: The Next Big Breakthrough in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease characterized by the death of dopaminergic neurons. Its pathogenesis comprises defects in the physiological pathway of mitophagy and mutations in the genes involved in this process's regulatory mechanism. PD manifests itself with multiple motor and non-motor symptoms, and currently, there are multiple pharmacological treatments, and unconventional non-drug treatments available. The mainstay of Parkinson's disease treatment has centered around directly manipulating neural mechanisms to retain high dopamine levels, either by exogenous administration, increasing intrinsic production, or inhibiting the breakdown of dopamine. In this review, we highlight a new potential biochemical modality of treatment, treating PD through glycolysis. We highlight how terazosin (TZ), via PGK1, increases ATP levels and how enhanced glycolysis serves a neuroprotective role in PD, and compensates for damage caused by mitophagy. We also discuss the role of quercetin, a bioactive flavonoid, in preventing the development of PD, and reversing mitochondrial dysfunction but only so in diabetic patients. Thus, further research should be conducted on glycolysis as a protective target in PD that can serve to not just prevent, but also alleviate the non-dopaminergic signs and symptoms of PD.

Natural Molecules and Neuroprotection: Kynurenic Acid, Pantethine and α-Lipoic Acid

The incidence of neurodegenerative diseases has increased greatly worldwide due to the rise in life expectancy. In spite of notable development in the understanding of these disorders, there has been limited success in the development of neuroprotective agents that can slow the progression of the disease and prevent neuronal death. Some natural products and molecules are very promising neuroprotective agents because of their structural diversity and wide variety of biological activities. In addition to their neuroprotective effect, they are known for their antioxidant, anti-inflammatory and antiapoptotic effects and often serve as a starting point for drug discovery. In this review, the following natural molecules are discussed: firstly, kynurenic acid, the main neuroprotective agent formed via the kynurenine pathway of tryptophan metabolism, as it is known mainly for its role in glutamate excitotoxicity, secondly, the dietary supplement pantethine, that is many sided, well tolerated and safe, and the third molecule, α-lipoic acid is a universal antioxidant. As a conclusion, because of their beneficial properties, these molecules are potential candidates for neuroprotective therapies suitable in managing neurodegenerative diseases.

Nanodelivery of therapeutic agents in Parkinson's disease

Parkinson's disease (PD) as a motor disorder is pathologically featured by the loss of dopaminergic neurons of the substantia nigra compacta (SNc) and the consequent depletion of dopamine in the striatum. However, motor signs are detectable when the loss of dopaminergic striatal terminals exceeds to the dopaminergic neuronal degeneration in SN. Hence, recent evidences about the topological organization of the nigrostriatal system could provide novel insights about the progression of the neurodegenerative process as well as the correct application of the novel therapeutic strategies. Though dopaminergic drugs and different routes of administration have been proposed to treat PD, most of the effects are symptomatic with temporary effects resorting to invasive procedures to ameliorate the side effects. Since the blood-brain barrier (BBB) is the main obstacle for most of molecules to access to the brain, ongoing research is focused on halting the progression of PD through the use of those technologies that allow the effective delivery and diffusion of therapeutic molecules to the central nervous system for bypassing BBB and avoiding the side effects. In this context, nanotechnology is emerging as a promising tool for drug delivery. In fact, nanodelivery of restorative treatments in PD, such as gene therapy increased the effectiveness of neurotrophic factors for restoring the dopamine deficit and improving motor deficit in rodent models. Therefore, the present review is focused on the description and identification of the available nanotherapies developed in experimental models of PD which could suppose an important advance for controlled delivery of nanobioactive components into the brain and one more step for the clinical projection.

Identification of a Novel 1,4,8-Triazaphenanthrene Derivative as a Neuroprotectant for Dopamine Neurons Vulnerable in Parkinson's Disease

Parkinson's disease (PD) is a chronic degenerative disorder characterized by typical motor symptoms caused by the death of dopamine (DA) neurons in the midbrain and ensuing shortage of DA in the striatum, at the level of nerve terminals. No curative treatment is presently available for PD in clinical practice. In our search for neuroprotectants in PD, we generated new 1,4,8-triazaphenanthrenes by combining 6-endo-dig-cycloisomerization of propargylquinoxalines and Suzuki or Sonogashira cross-coupling reactions. Neuroprotection assessment of newly synthesized 1,4,8-triazaphenanthrenes in a PD cellular model resulted in the discovery of a new hit compound PPQ (5m). Neuroprotection by 5m was concentration-dependent and the result of a combined effect on intracellular calcium release channels and astroglial cells. Of interest, 5m also counteracted DA cell loss in a mouse model of PD, making this molecule a promising candidate for PD treatment.

New 6-Aminoquinoxaline Derivatives with Neuroprotective Effect on Dopaminergic Neurons in Cellular and Animal Parkinson Disease Models

Parkinson's disease (PD) is a neurodegenerative disorder of aging characterized by motor symptoms that result from the loss of midbrain dopamine neurons and the disruption of dopamine-mediated neurotransmission. There is currently no curative treatment for this disorder. To discover druggable neuroprotective compounds for dopamine neurons, we have designed and synthesized a second-generation of quinoxaline-derived molecules based on structure-activity relationship studies, which led previously to the discovery of our first neuroprotective brain penetrant hit compound MPAQ (5c). Neuroprotection assessment in PD cellular models of our newly synthesized quinoxaline-derived compounds has led to the selection of a better hit compound, PAQ (4c). Extensive in vitro characterization of 4c showed that its neuroprotective action is partially attributable to the activation of reticulum endoplasmic ryanodine receptor channels. Most interestingly, 4c was able to attenuate neurodegeneration in a mouse model of PD, making this compound an interesting drug candidate for the treatment of this disorder.

TAT-HSA-α-MSH fusion protein with extended half-life inhibits tumor necrosis factor-α in brain inflammation of mice

Neuroinflammation constitutes a principal process involved in the progression of various central nervous system (CNS) disorders, including Parkinson's disease, Alzheimer's disease, ischemic stroke, and traumatic brain injury. The safety and efficacy of potential neuroprotective therapeutic agents is controversial and limited. Alpha-melanocyte-stimulating hormone (α-MSH) as a tridecapeptide derived from pro-opiomelanocortin displays potent anti-inflammatory and protective effects with a wide therapeutic window in brain damage. However, it is difficult to deliver effective concentrations of α-MSH into brain tissue via nondirect application. Besides, the half-life of the tridecapeptide is only a few minutes. In the present study, we generated a novel TAT-HSA-α-MSH by genetically fusing α-MSH with N-terminus 11-amino acid protein transduction domain of the human immunodeficiency virus Tat protein (TAT) and human serum albumin (HSA), which showed favorable pharmacokinetic properties and can effectively cross the blood brain barrier (BBB). The findings showed that TAT-HSA-α-MSH significantly inhibits NF-κB activation in human glioma cells A172 and tumor necrosis factor-α (TNF-α) production in experimental brain inflammation. These results indicate that TAT-HSA-α-MSH may be a potential therapeutic agent for treating neuroinflammation which plays a fundamental role in CNS disorders.

Prevention of the degeneration of human dopaminergic neurons in an astrocyte co-culture system allowing endogenous drug metabolism

BACKGROUND AND PURPOSE

Few neuropharmacological model systems use human neurons. Moreover, available test systems rarely reflect functional roles of co-cultured glial cells. There is no human in vitro counterpart of the widely used 1-methyl-4-phenyl-tetrahydropyridine (MPTP) mouse model of Parkinson's disease

EXPERIMENTAL APPROACH

We generated such a model by growing an intricate network of human dopaminergic neurons on a dense layer of astrocytes. In these co-cultures, MPTP was metabolized to 1-methyl-4-phenyl-pyridinium (MPP(+) ) by the glial cells, and the toxic metabolite was taken up through the dopamine transporter into neurons. Cell viability was measured biochemically and by quantitative neurite imaging, siRNA techniques were also used.

KEY RESULTS

We initially characterized the activation of PARP. As in mouse models, MPTP exposure induced (poly-ADP-ribose) synthesis and neurodegeneration was blocked by PARP inhibitors. Several different putative neuroprotectants were then compared in mono-cultures and co-cultures. Rho kinase inhibitors worked in both models; CEP1347, ascorbic acid or a caspase inhibitor protected mono-cultures from MPP(+) toxicity, but did not protect co-cultures, when used alone or in combination. Application of GSSG prevented degeneration in co-cultures, but not in mono-cultures. The surprisingly different pharmacological profiles of the models suggest that the presence of glial cells, and the in situ generation of the toxic metabolite MPP(+) within the layered cultures played an important role in neuroprotection.

CONCLUSIONS AND IMPLICATIONS

Our new model system is a closer model of human brain tissue than conventional cultures. Its use for screening of candidate neuroprotectants may increase the predictiveness of a test battery.

Prediction of Metabolic Gene Biomarkers for Neurodegenerative Disease by an Integrated Network-Based Approach

Neurodegenerative diseases (NDs), such as Parkinson's disease (PD) and Huntington's disease (HD), have become more and more common among aged people worldwide. One hallmark of NDs is the presence of intracellular accumulation of specific pathogenic proteins that may result from abnormal function of metabolic processes. Previously, we have developed a computational method named Met-express that predicted key enzyme-coding genes in cancer development by integrating cancer gene coexpression network with the metabolic network. Here, we applied Met-express to predict key enzyme-coding genes in both PD and HD. Functional enrichment analysis and literature review of predicted genes suggested that there might be some common pathogenic metabolic pathways for PD and HD. We further found that the predicted genes had significant functional association with known disease genes, with some of them already documented as biomarkers or therapeutic targets for NDs. As such, the predicted metabolic genes may be of use as novel biomarkers not only for ND diagnosis but also for potential therapeutic treatments.

Astrocytic JWA expression is essential to dopaminergic neuron survival in the pathogenesis of Parkinson's disease

AIMS

To investigate the role of astrocytic JWA expression in dopaminergic (DA) neuron degeneration and in the pathogenesis of Parkinson's disease (PD).

METHODS

Conditional astrocytic JWA null (JWA∆2/∆2/GFAP-Cre) mice and U251 glioma cells were used to evaluate the effects of JWA gene on DA neuron degeneration. The oxidative stress-driven molecular events were determined in both in vivo and in vitro models.

RESULTS

Conditional astrocytic JWA knockout resulted in significant activation of astrocytes measured by increase in glial fibrillary acidic protein-positive cells (1.34×10(3)±74.5 vs. 8.44×10(3)±1.35×10(3), P<0.01) in mouse substantia nigra, accompanied by loss of DA neurons (1.03×10(4)±238 vs. 6.17×10(3)±392, P<0.001). Deficiency of JWA significantly aggravated reactive oxygen species (ROS) accumulation in substantia nigra compared with the wild-type mice. Increasing JWA expression in U251 glioma cells inhibited ROS with a concomitant increase in intracellular glutathione. Furthermore, suppression of IKKβ-nuclear factor (NF)-κB signaling pathway was shown to regulate JWA in a PD model.

CONCLUSIONS

The JWA gene exerts neuroprotective roles against DA neuronal degeneration via modulating intracellular redox status and NF-κB signaling pathway and is a potential treatment target for PD.

Study of the neuroprotective effects of memantine in patients with mild to moderate ischemic stroke

Ischemic stroke is amongst the top four causes of mortality and the leading cause of disability in the world. The aim of this study was to evaluate the efficacy of a high dose memantine on neurological function of patients with ischemic stroke. In a randomized, 2 armed, open-label study, patients with mild to moderate cerebral thromboembolic event (CTEE) who admitted to Imam Hossein Hospital, Tehran, Iran, during preceding 24 hours, entered the study. Patients allocated in two study groups of memantine (as add-on therapy) and control. All patients were managed based on the American Heart Association and American Stroke Association (AHA/ASA) guidelines. Patients in memantine group received conventional treatment plus memantine 20 mg TID. The National Institute of Health Stroke Scale (NIHSS) was determined and recorded daily. The primary objective was comparison of the changes in NIHSS in the study groups at day 1 and day 5 of intervention. Significance level of p<0.05 was considered for statistical analysis. Patients were randomly allocated in control (15 women and 14 men, age 70.78 ± 10.92 years) and memantine (16 women and 8 men, age 73.33 ± 9.35 years) groups. There were no significant differences in age and sex distribution of two study groups as well as in comorbidities and concurrent drugs. NIHSS changes were significantly different between control (1.24 ± 0.96) and memantine group (2.96 ± 0.1), (p < 0.0001). Our results reveal that memantine added to standard treatment of CTEE could result in a remarkable decrease in the NIHSS confirming improvement of the neurological function of the patients.

Oxidative stress is not involved in motion sickness in mice

AIMS

Some indirect evidences indicate a possible correlation between oxidative stress and motion sickness. The aim of this research was to investigate whether oxidative stress contributing to motion sickness in mice or not.

METHODS

We examined the mRNA levels of peroxiredoxin 6 (PRDX6), catalase, and enzyme superoxide dismutase 1 (SOD1); reactive oxygen species (ROS); and total antioxidant capacity and SOD activity in different brain regions after rotary stimulation. Mice motion sickness index was recorded after rotation when pretreated with paraquat, vitamin C, or vitamin E.

RESULTS

The ROS level and antioxidant capacity were both increased in cerebellum plus brainstem (CB) after rotation, a critical region determines motion sickness. However, manipulation of oxidants or antioxidants using pharmacological method in vivo had no influence on motion sickness index in mice.

CONCLUSION

Oxidative stress is not involved in the development of motion sickness in mice.

Targeting metabolic inflammation in Parkinson's disease: implications for prospective therapeutic strategies

1. Parkinson's disease (PD) is one of the most common neurodegenerative disorders and is characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Although the aetiology of PD has not been clarified as yet, it is believed that ageing, diet, diabetes and adiposity are associated with PD. 2. Type 2 diabetes and lipid abnormalities share multiple common pathophysiological mechanisms with PD. In particular, inflammation plays a critical role in the destruction of both pancreatic islet β-cells and dopaminergic neurons in the substantia nigra. Emerging evidence indicates that dysfunctions of energy metabolism evoke metabolic inflammation, which differs to the narrow concept of inflammation, participating in systemic pathological processes such as neurodegenerative disease and diabetes. 3. The brain is considered an immunologically privileged organ, free from immune reactions, because it is protected by the blood-brain barrier (BBB). However, studies have shown that there is gradual impairment of neurovascular function with ageing and in neurodegenerative disorders, resulting in abnormal states, including increased BBB permeability. Consequently, harmful elements that would not normally be able to cross the BBB, such as pro-inflammatory factors, reactive oxygen species and neurotoxins, infiltrate into the brain, triggering neural injury. 4. Currently, the drugs available for the treatment of PD only ameliorate the symptoms of the disease. Therapeutic strategies aimed at stopping or modifying disease progression are still being sought. Most recent studies suggest that both central and peripheral inflammation may be dysregulated in PD. Therefore, therapeutic strategies aimed at modulating systemic inflammatory reactions or energy metabolism may represent a goal in neuroprotection in PD.

Neuroprotection for stroke: current status and future perspectives

Neuroprotection aims to prevent salvageable neurons from dying. Despite showing efficacy in experimental stroke studies, the concept of neuroprotection has failed in clinical trials. Reasons for the translational difficulties include a lack of methodological agreement between preclinical and clinical studies and the heterogeneity of stroke in humans compared to homogeneous strokes in animal models. Even when the international recommendations for preclinical stroke research, the Stroke Academic Industry Roundtable (STAIR) criteria, were followed, we have still seen limited success in the clinic, examples being NXY-059 and haematopoietic growth factors which fulfilled nearly all the STAIR criteria. However, there are a number of neuroprotective treatments under investigation in clinical trials such as hypothermia and ebselen. Moreover, promising neuroprotective treatments based on a deeper understanding of the complex pathophysiology of ischemic stroke such as inhibitors of NADPH oxidases and PSD-95 are currently evaluated in preclinical studies. Further concepts to improve translation include the investigation of neuroprotectants in multicenter preclinical Phase III-type studies, improved animal models, and close alignment between clinical trial and preclinical methodologies. Future successful translation will require both new concepts for preclinical testing and innovative approaches based on mechanistic insights into the ischemic cascade.

Clinical utility of neuroprotective agents in neurodegenerative diseases: current status of drug development for Alzheimer's, Parkinson's and Huntington's diseases, and amyotrophic lateral sclerosis

INTRODUCTION

According to the definition of the Committee to Identify Neuroprotective Agents in Parkinson's Disease (CINAPS), "neuroprotection would be any intervention that favourably influences the disease process or underlying pathogenesis to produce enduring benefits for patients" [Meissner W, et al. Trends Pharmacol Sci 2004;25:249-253]. Preferably, neuroprotective agents should be used before or eventually during the prodromal phase of the diseases that could start decades before the appearance of symptoms. Although several symptomatic drugs are available, a disease-modifying agent is still elusive.

AREAS COVERED

The aim of the present review is to give an overview of neuroprotective agents being currently investigated for the treatment of AD, PD, HD and ALS in clinical phases.

EXPERT OPINION

Development of effective neuroprotective therapies resulting in clinically meaningful results is hampered by several factors in all research stages, both conceptual and methodological. Novel solutions might be offered by evaluation of new targets throughout clinical studies, therapies emerging from drug repositioning approaches, multi-target approaches and network pharmacology.

Adjunctive therapy in Parkinson's disease: the role of rasagiline

Parkinson's disease is the second most common neurodegenerative disorder, currently affecting 1.5 million people in the US. In this review, we describe the diagnostic and pathological features of Parkinson's disease, as well as its clinical course. We then review pharmacologic treatments for the disease, with a particular focus on therapies adjunctive to levodopa and specifically the role of rasagiline. We review the four pivotal rasagiline trials, and discuss rasagiline and its use as adjunctive therapy for Parkinson's disease. Finally, we discuss potential side effects, drug interactions, and other practical aspects concerning the use of rasagiline in Parkinson's disease.

Endogenous neuroprotection in chronic neurodegenerative disorders: with particular regard to the kynurenines

Parkinson's disease (PD) and Huntington's disease (HD) are progressive chronic neurodegenerative disorders that are accompanied by a considerable impairment of the motor functions. PD may develop for familial or sporadic reasons, whereas HD is based on a definite genetic mutation. Nevertheless, the pathological processes involve oxidative stress and glutamate excitotoxicity in both cases. A number of metabolic routes are affected in these disorders. The decrease in antioxidant capacity and alterations in the kynurenine pathway, the main pathway of the tryptophan metabolism, are features that deserve particular interest, because the changes in levels of neuroactive kynurenine pathway compounds appear to be strongly related to the oxidative stress and glutamate excitotoxicity involved in the disease pathogenesis. Increase of the antioxidant capacity and pharmacological manipulation of the kynurenine pathway are therefore promising therapeutic targets in these devastating disorders.

Kynurenines in Parkinson's disease: therapeutic perspectives

Parkinson's disease (PD) is a chronic progressive neurodegenerative disorder the pathomechanism of which is not yet fully known. With regard to the molecular mechanism of development of the disease, oxidative stress/mitochondrial impairment, glutamate excitotoxicity and neuroinflammation are certainly involved. Alterations in the kynurenine pathway, the main pathway of the tryptophan metabolism, can contribute to the complex pathomechanism. There are several possibilities for therapeutic intervention involving targeting of this altered metabolic route. The development of synthetic molecules that would shift the altered balance towards the achievement of neuroprotective effects would be of great promise for future clinical studies on PD.

Kynurenines, neurodegeneration and Alzheimer's disease

Alzheimer’s disease (AD) is one of the major causes of dementia. The pathogenesis of the disease is not entirely understood, but the amyloid β peptide (Aβ) and the formation of senile plaques seem to play pivotal roles. Oligomerization of the Aβ is thought to trigger a cascade of events, including oxidative stress, glutamate excitotoxicity and inflammation. The kynurenine (KYN) pathway is the major route for the metabolism of the essential amino acid tryptophan. Some of the metabolites of this pathway, such as 3-hydroxykynurenine and quinolinic acid, are known to have neurotoxic properties, whereas others, such as kynurenic acid, are putative neuroprotectants. Among other routes, the KYN pathway has been shown to be involved in AD pathogenesis, and connections to other known mechanisms have also been demonstrated. Oxidative stress, glutamate excitotoxicity and the neuroinflammation involved in AD pathogenesis have been revealed to be connected to the KYN pathway. Intervention at these key steps may serve as the aim of potential therapy.

Comparison of the antileukaemic activity of 5 aza-2-deoxycytidine and arabinofuranosyl-cytosine in rats with myelocytic leukaemia

Using a Brown Norway rat leukaemia model (BNML), which is a realistic model of human myelocytic leukaemia, we compared the antileukaemic activity, influence on cell cycle kinetics and effect on normal haematopoiesis of 5 aza-2-deoxycytidine (aza-dC) and arabinofuranosyl-cytosine (ara-C). The antileukaemic activity was evaluated by means of a survival study. For aza-dC a dose-response relationship was demonstrated for doses up to 50 mg kg-1 (3 times q 12 h); a higher dose resulted in only a slight increase in median survival time (MST). For ara-C a weak dose-response relationship was observed. At the maximum dose of aza-dC and ara-C tested, aza-dC induced a 10-day longer survival time than ara-C, which means 2 logs more of leukaemic cell kill for aza-dC. By means of flow cytometric analysis and a 3HTdR uptake study it was shown that aza-dC does not influence the cell cycle kinetics in the first 24 h after exposure, in contrast to ara-C which caused the characteristic G1/S blockage and synchronization. The influence of aza-dC and ara-C on normal haematopoiesis was evaluated with the CFU-S assay. The dose-response curve for CFU-S did not show a significant difference in stem cell cytotoxicity between aza-dC and ara-C. In the BNML model aza-dC is a much more effective antileukaemic agent than ara-C, while the toxic effect on normal haematopoiesis is comparable to that of ara-C.