Neuroprotection and neurodegenerative diseases: from biology to clinical practice

Salidroside protects PC-12 cells against amyloid β-induced apoptosis by activation of the ERK1/2 and AKT signaling pathways

Alzheimer’s disease (AD) is one of the most frequent diseases in elderly people and causes high mortality. Its incidence is increasing annually and no effective therapeutic treatment currently exists. In the present study, salidroside, a major active ingredient of Rhodiola rosea, was able to protect PC-12 cells from the toxicity and apoptosis induced by AD inducer amyloid (A)β_1--42. Salidroside significantly protected PC-12 cells by inhibiting Aβ_1-42-induced cytotoxicity and mitochondria-mediated endogenous caspase apoptotic pathways. Mechanistic studies demonstrated that salidroside significantly activated the extracellular signal regulated kinase (ERK)1/2 and protein kinase B (AKT) signaling pathways. This observation was further confirmed using the ERK1/2 inhibitor PD98059 and the AKT inhibitor LY294002, which demonstrated that salidroside promoted PC-12 cell survival and proliferation by activating the ERK1/2 and AKT signaling pathways. Salidroside is a therapeutic candidate for the treatment of AD and provides a basis for further drug development.

Nonhuman Primate Models of Neurodegenerative Disorders

Alzheimer's (AD), Huntington's (HD), and Parkinson's (PD) disease are age-related neurodegenerative disorders characterized by progressive neuronal cell death. Although each disease has particular pathologies and symptoms, accumulated evidence points to similar mechanisms of neurodegeneration, including inflammation, oxidative stress, and protein aggregation. A significant body of research is ongoing to understand how these pathways affect each other and what ultimately triggers the onset of the disease. Experiments in nonhuman primates (NHPs) account for only 5% of all research in animals. Yet the impact of NHP studies for clinical translation is much greater, especially for neurodegenerative disorders, as NHPs have a complex cognitive and motor functions and highly developed neuroanatomy. New NHP models are emerging to better understand pathology and improve the platform in which to test novel therapies. The goal of this report is to review NHP models of AD, HD, and PD in the context of the current understanding of these diseases and their contribution to the development of novel therapies.

Signaling by growth/differentiation factor 5 through the bone morphogenetic protein receptor type IB protects neurons against kainic acid-induced neurodegeneration

Growth/differentiation factor-5 (GDF-5), a member of the transforming growth factor-beta (TGF-β) superfamily, has been shown to protect rat dopaminergic neurons against insult both in embryonic neuronal culture and in Parkinson's disease models. However, whether GDF-5 exerts neuroprotective effects in hippocampal neurons is unclear. Here, we show that both mRNA levels and protein levels of GDF-5 are decreased in the mouse hippocampus upon kainic acid (KA) treatment. KA induced dramatic neuronal loss specifically in the cornu ammonis 1 (CA1) and CA3 areas of the mouse hippocampus, while intracerebral infusion of GDF-5 prevented this neuronal loss. The neuroprotective effects of GDF-5 were recapitulated by constitutively active bone morphogenetic protein type IB receptor (BMPRIB-CA) and could be blocked by BMPRI kinase inhibitor LDN-193189. Furthermore, the neuroprotective effects of GDF-5 were mediated through the prevention of apoptosis, which was indicated by terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) staining and reduced cleaved caspase 3 expression level. Thus, we conclude that GDF-5 protects hippocampal neurons against KA-induced neurodegeneration by signaling through BMPRIB, suggesting a therapeutic potential for GDF-5 in neurodegenerative diseases.

Guanosine and its role in neuropathologies

Guanosine is a purine nucleoside thought to have neuroprotective properties. It is released in the brain under physiological conditions and even more during pathological events, reducing neuroinflammation, oxidative stress, and excitotoxicity, as well as exerting trophic effects in neuronal and glial cells. In agreement, guanosine was shown to be protective in several in vitro and/or in vivo experimental models of central nervous system (CNS) diseases including ischemic stroke, Alzheimer's disease, Parkinson's disease, spinal cord injury, nociception, and depression. The mechanisms underlying the neurobiological properties of guanosine seem to involve the activation of several intracellular signaling pathways and a close interaction with the adenosinergic system, with a consequent stimulation of neuroprotective and regenerative processes in the CNS. Within this context, the present review will provide an overview of the current literature on the effects of guanosine in the CNS. The elucidation of the complex signaling events underlying the biochemical and cellular effects of this nucleoside may further establish guanosine as a potential therapeutic target for the treatment of several neuropathologies.

Mediterranean diet and cognitive function: the SUN project

OBJECTIVE

Our aim was to evaluate the association between adherence to the Mediterranean Diet (MedDiet) and cognitive function in 823 participants (62 ± 6 years at baseline) from a Spanish prospective cohort (SUN project).

METHOD

A validated 136-item food frequency questionnaire was used to assess the adherence to the MedDiet at baseline. The 10-point (0 to 9) MedDiet Score was used to categorize adherence to MedDiet. Cognitive function was assessed twice at follow-up with a mean follow-up time between exposure and outcome assessment of 6 and 8y using the Telephone Interview of Cognitive Status-modified (TICS-m, range 0 to 54 points). ANCOVA models were used to assess the association between adherence to the MedDiet and cognitive decline.

RESULTS

In the multivariable-adjusted analysis of 2-year changes, a higher cognitive decline was observed among participants with low or moderate baseline adherence to the MedDiet than among those with better adherence (adjusted difference = -0.56 points in TICS-m, 95% CI = -0.99 to -0.13).

CONCLUSION

A higher adherence to the MedDiet might be associated with better cognitive function. However, observed differences were of small magnitude and further studies are needed to confirm this finding.

Neuroprotection targeting ischemic penumbra and beyond for the treatment of ischemic stroke

Neuroprotection to attenuate or block the ischemic cascade and salvage neuronal damage has been extensively explored for the treatment of ischemic stroke. In the last two decades, neuroprotective strategy has been evolving from targeting a signal pathway in neurons to protecting all neurovascular components and improving cell-cell and cell-extracellular matrix interaction that ultimately benefits the brain recovery after ischemic stroke. The progression from potentially reversible to irreversible injury in the ischemic penumbra has provided the opportunity to develop therapies to attenuate the ischemic stroke damage. Thus, the ischemic penumbra has been the main target for the current neuroprotective intervention. However, despite our increasing knowledge of the physiologic, mechanistic, and imaging characterizations of the ischemic penumbra, no effective neuroprotective therapy has been found so far for the treatment of ischemic stroke. The current acute neuroprotective approach focusing on the damaging mechanisms at the ischemic penumbra is greatly limited by the rapid evolution of the deleterious cascades in the ischemic penumbra. Neuroprotective intervention attempts to promote endogenous repairing in the transition zone of the penumbra for the therapeutic purposes may overcome the unrealistic therapeutic windows under the current neuroprotective strategy. In addition, increasing evidence has indicated ischemic stroke could induce long-lasing cellular and hemodynamic changes beyond the ischemic territory. It is unclear whether and how the global responses induced by the ischemic cascade contribute to the progression of cognitive impairment after ischemic stroke. The prolonged pathophysiological cascades induced by ischemic stroke beyond the ischemic penumbra might provide novel therapeutic opportunities for the neuroprotective intervention, which could prevent or slow down the progression of vascular dementia after ischemic stroke.

Challenges to demonstrating disease-modifying effects in Alzheimer's disease clinical trials

Progress in understanding the molecular biology of Alzheimer's disease (AD) has provided a number of plausible therapeutic targets for disease-modifying interventions. To advance these agents toward eventual US Food and Drug Administration (FDA) approval and incorporation into clinical practice by physicians and acceptance by patients and caregivers it is necessary to reach consensus on the meaning of disease modification and on what information is needed to provide a compelling factual basis for distinguishing disease modification from symptomatic treatment effects. Disease modification requires that the intervention have an impact of underlying pathology and pathophysiology of AD; disease course modification, illness modification or disability sparing are alternate terminologies that could be applied to symptomatic agents that do not affect the underlying neurobiology of AD. A variety of trial designs have been proposed to provide information supporting disease modification including change from baseline designs, survival type designs, staggered start designs, and staggered withdrawal designs. Each of these has shortcomings, and by themselves trial designs are not likely to provide sufficient information to conclusively prove that disease modification has occurred. Incorporation of a biomarker into clinical trials will support the claim for disease modification. Such a surrogate marker ideally should respond to the intervention, predict the clinical response to the intervention, and be compellingly related to the neurobiology of AD in the pathway affected by the intervention. A third axis of information supportive of disease modification is derived from observation of the effect of treatment in animal models of AD. The triad of a clinical outcome consistent with disease modification, support from a surrogate marker incorporated into the clinical trial, and basic science information indicating the effect of the therapy on a model of AD would combine to make a convincing case for disease modification.

Olive oil and cognition: results from the three-city study

BACKGROUND

Olive oil is a major component of the Mediterranean diet suggested to be beneficial to counteract Alzheimer's disease.

AIM OF THE STUDY

Our objective was to examine the association between olive oil use, cognitive deficit and cognitive decline in a large elderly population.

METHODS

We followed 6,947 subjects with a brief baseline food frequency questionnaire and repeated cognitive tests. Olive oil intake was categorized as none (22.7%), moderate (use for cooking or dressing, 39.9%) and intensive (use for both cooking and dressing, 37.4%). Associations between olive oil and cognitive outcomes were examined taking into account socio-economic factors, health behaviors, health measures and other dietary intakes.

RESULTS

Participants with moderate or intensive use of olive oil compared to those who never used olive oil showed lower odds of cognitive deficit for verbal fluency and visual memory. For cognitive decline during the 4-year follow-up, the association with intensive use was significant for visual memory (adjusted OR = 0.83, 95% CI: 0.69-0.99) but not for verbal fluency (OR = 0.85, 95% CI: 0.70-1.03) in multivariate analysis.

CONCLUSIONS

This olive oil-cognition association needs to be confirmed by further studies. However, our findings already shed light on the potential importance of olive oil in the Mediterranean diet and on its beneficial effects on health.

Contributions of non-human primates to neuroscience research

Non-human primates have a small but important role in basic and translational biomedical research, owing to similarities with human beings in physiology, cognitive capabilities, neuroanatomy, social complexity, reproduction, and development. Although non-human primates have contributed to many areas of biomedical research, we review here their unique contributions to work in neuroscience, and focus on four domains: Alzheimer's disease, neuroAIDS, Parkinson's disease, and stress. Our discussion includes, for example, the role of non-human primates in development of new treatments (eg, stem cells, gene transfer) before phase I clinical trials in patients; basic research on disease pathogenesis; and understanding neurobehavioural outcomes resulting from genotype-environment interactions.

Disease-modifying drugs and Parkinson's disease

Symptomatic medications, l-Dopa and dopaminergic agents, remain the only clinically pertinent pharmacological treatment proven effective and available for the large population of patients with Parkinson's disease. The challenge for the pharmaceutical industry is to develop disease-modifying drugs which could arrest, delay or at least oppose the progression of the specific pathogenic processes underlying Parkinson's disease. The purpose of this review, based on recent biological and genetic data to be validated with appropriate animal models, was to re-examine the putative neuroprotective agents in Parkinson's disease and discuss the development of new strategies with the ultimate goal of demonstrating neurocytoprotective activity in this neurodegenerative disease. Since guidelines for research on neurocytoprotective drugs remain to be written, innovation will be the key to success of future clinical trials. It is reasonable to expect that future advances in our understanding of the pathogenic processes of Parkinson's disease will open the way to new perspectives for the treatment of other neurodegenerative diseases.

Molecular and cellular immune mediators of neuroprotection

Our view of the immune privileged status of the brain has dramatically changed during the past two decades. Even though systemic immune stimuli have the ability to activate different populations of neurons, cells of monocytic lineage also have access to the neuronal tissue and populate it as microglia. Although such a phenomenon is limited in intact brains, it is greatly increased during neurodegenerative processes associated with innate immunity and the release of pro-inflammatory molecules by either resident microglia or those derived from the bone marrow stem cells. The role of these events is currently a matter of great debate and controversy, especially as it relates to brain protection, repair, or further injury. In recent years, accumulating data have supported the notion that when immune molecules are timely released by microglia, they limit neuronal injury in the presence of pathogens and toxic agents, help clear debris from degenerated cells, and restore the cerebral environment for repair. It has been shown that alteration of the natural innate immune response by microglia has direct consequences in exacerbating the damages following acute injury to neurons. This article presents and discusses these data, supporting a powerful neuroprotective role for microglia and their innate immune reactions in response to pathogens and central nervous system insults.

Cannabinoids and neuroprotection in basal ganglia disorders

Cannabinoids have been proposed as clinically promising neuroprotective molecules, as they are capable to reduce excitotoxicity, calcium influx, and oxidative injury. They are also able to decrease inflammation by acting on glial processes that regulate neuronal survival and to restore blood supply to injured area by reducing the vasoconstriction produced by several endothelium-derived factors. Through one or more of these processes, cannabinoids may provide neuroprotection in different neurodegenerative disorders including Parkinson's disease and Huntington's chorea, two chronic diseases that are originated as a consequence of the degeneration of specific nuclei of basal ganglia, resulting in a deterioration of the control of movement. Both diseases have been still scarcely explored at the clinical level for a possible application of cannabinoids to delay the progressive degeneration of the basal ganglia. However, the preclinical evidence seems to be solid and promising. There are two key mechanisms involved in the neuroprotection by cannabinoids in experimental models of these two disorders: first, a cannabinoid receptor-independent mechanism aimed at producing a decrease in the oxidative injury and second, an induction/upregulation of cannabinoid CB2 receptors, mainly in reactive microglia, that is capable to regulate the influence of these glial cells on neuronal homeostasis. Considering the relevance of these preclinical data and the lack of efficient neuroprotective strategies in both disorders, we urge the development of further studies that allow that the promising expectatives generated for these molecules progress from the present preclinical evidence till a real clinical application.

Treatment of the mild cognitive impairment (MCI)

According to Evidence-Based-Medicine, any proposal for the rationale treatment of mild cognitive impairment (MCI) must be based on the results of double-blind, randomized clinical trials (RCTs). However, since MCI at the present time does not constitute a homogeneous clinical syndrome, it is still inappropriate to propose a specific drug treatment. Moreover, RCTs assessing the therapeutic value of acetylcholinesterase-inhibitors (AChEIs) are negative either trying to improve symptoms (memory performance) or preventing the conversion from MCI to real Alzheimer's Disease (AD). The same negative results were obtained with drugs targeting some systems considered as the early steps of the pathophysiological cascade leading to dementia: non-steroidal anti-inflammatory compounds (rofecoxib), sex steroid hormones (testosterone, estrogens), or antioxidants (tocopherol). Either MCI is considered as the very early phase of development of AD (and then the treatments will aim at preventively antagonizing the hallmarks of the disease) or MCI is a new entity (and then the drugs will target the associated neurochemical disturbances such as tau protein or soluble Abeta oligomers); MCI could also be considered as a monosymptomatic syndrome (amnesia) leading to the development of pure pro-mnestic drugs. These three hypotheses will be presented on the basis of the neurobiology and the pharmacology, and examples of potentially active candidates will be discussed.

Impaired cognition and attention in adults: pharmacological management strategies

Cognitive psychology has provided clinicians with specific tools for analyzing the processes of cognition (memory, language) and executive functions (attention-concentration, abstract reasoning, planning). Neuropsychology, coupled with the neurosciences (including neuroimaging techniques), has authenticated the existence of early disorders affecting the "superior or intellectual" functions of the human brain. The prevalence of cognitive and attention disorders is high in adults because all the diseases implicating the central nervous system are associated with cognitive correlates of variable intensity depending on the disease process and the age of the patient. In some pathologies, cognitive impairment can be a leading symptom such as in schizophrenia, posttraumatic stress disorder or an emblematic stigmata as in dementia including Alzheimer's disease. Paradoxically, public health authorities have only recognized as medications for improving cognitive symptoms those with proven efficacy in the symptomatic treatment of patients with Alzheimer's disease; the other cognitive impairments are relegated to the orphanage of syndromes and symptoms dispossessed of medication. The purpose of this review is to promote a true "pharmacology of cognition" based on the recent knowledge in neurosciences. Data from adult human beings, mainly concerning memory, language, and attention processes, will be reported. "Drug therapeutic strategies" for improving cognition (except for memory function) are currently rather scarce, but promising perspectives for a new neurobiological approach to cognitive pharmacology will be highlighted.