Scaling the Andean Shilajit: A Novel Neuroprotective Agent for Alzheimer's Disease.

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder without a cure, despite the enormous number of investigations and therapeutic approaches. AD is a consequence of microglial responses to "damage signals", such as aggregated tau oligomers, which trigger a neuro-inflammatory reaction, promoting the misfolding of cytoskeleton structure. Since AD is the most prevalent cause of dementia in the elderly (>60 years old), new treatments are essential to improve the well-being of affected subjects. The pharmaceutical industry has not developed new drugs with efficacy for controlling AD. In this context, major attention has been given to nutraceuticals and novel bioactive compounds, such as molecules from the Andean Shilajit (AnSh), obtained from the Andes of Chile. Primary cultures of rat hippocampal neurons and mouse neuroblastoma cells were evaluated to examine the functional and neuroprotective role of different AnSh fractions. Our findings show that AnSh fractions increase the number and length of neuronal processes at a differential dose. All fractions were viable in neurons. The AnSh fractions inhibit tau self-aggregation after 10 days of treatment. Finally, we identified two candidate molecules in M3 fractions assayed by UPLC/MS. Our research points to a novel AnSh-derived fraction that is helpful in AD. Intensive work toward elucidation of the molecular mechanisms is being carried out. AnSh is an alternative for AD treatment or as a coadjuvant for an effective treatment.

Inflammation: A Major Target for Compounds to Control Alzheimer's Disease.

Several hypotheses have been postulated to explain how Alzheimer's disease is triggered, but none of them provide a unified view of its pathogenesis. The dominant hypothesis based on build-ups of the amyloid-ß peptide has been around for longer than three decades; however, up to today, numerous clinical trials based on the amyloid postulates have been attempted, but all of them have failed. Clearly, the revisited tau hypothesis provides a better explanation of the clinical observations of patients, but it needs to integrate the cumulative observations on the onset of this disease. In this context, the neuroimmuno modulation theory, based on the involvement of inflammatory events in the central nervous system, accounts for all these observations. In this review we intend to emphasize the idea that neuroinflammation is a main target for the search of new therapeutic strategies to control Alzheimer's disease. Beyond mono-targeting approaches using synthetic drugs that control only specific pathophysiological events, emerging therapeutics views based on multi targeting compounds appear to provide a new pathway for Alzheimer's disease treatment.

Biomarkers for Alzheimer's Disease.

Alzheimer´s disease (AD) and related forms of dementia are increasingly affecting the aging population throughout the world, at an alarming rate. The World Alzheimer´s Report indicates a prevalence of 46.8 million people affected by AD worldwide. As population ages, this number is projected to triple by 2050 unless effective interventions are developed and implemented. Urgent efforts are required for an early detection of this disease. The ultimate goal is the identification of viable targets for the development of molecular markers and validation of their use for early diagnosis of AD that may improve treatment and the disease outcome in patients. The diagnosis of AD has been difficult to resolve since approaches for early and accurate detection and follow-up of AD patients at the clinical level have been reported only recently. Some proposed AD biomarkers include the detection of pathophysiological processes in the brain in vivo with new imaging techniques and novel PET ligands, and the determination of pathogenic proteins in cerebrospinal fluid showing anomalous levels of hyperphosphorylated tau and low Aß peptide. These biomarkers have been increasingly accepted by AD diagnostic criteria and are important tools for the design of clinical trials, but difficulties in accessibility to costly and invasive procedures have not been completely addressed in clinical settings. New biomarkers are currently being developed to allow determinations of multiple pathological processes including neuroinflammation, synaptic dysfunction, metabolic impairment, protein aggregation and neurodegeneration. Highly specific and sensitive blood biomarkers, using less-invasive procedures to detect AD, are derived from the discoveries of peripheric tau oligomers and amyloid variants in human plasma and platelets. We have also developed a blood tau biomarker that correlates with a cognitive decline and also with neuroimaging determinations of brain atrophy.

Molecules of the quinoline family block tau self-aggregation: implications toward a therapeutic approach for Alzheimer's disease.

The neurofibrillary tangles (NFTs) generated by self-aggregation of anomalous forms of tau represent a neuropathological hallmark of Alzheimer's disease (AD). These lesions begin to form long before the clinical manifestation of AD, and its severity is correlated with cognitive impairment in patients. We focused on the search for molecules that interact with aggregated tau of the Alzheimer's type and that may block its aggregation before the formation of NFTs. We show that molecules from a family of quinolines interact specifically with oligomeric forms of tau, inhibiting their assembly into AD filaments. The quinolines 2-(4-methylphenyl)-6-methyl quinoline (THQ-4S) and 2-(4-aminophenyl)-6-methylquinoline (THQ-55) inhibited in vitro aggregation of heparin-induced polymers of purified brain tau and aggregates of human recombinant tau. They also interact with paired helical filaments (PHFs) purified from AD postmortem brains. In vitro studies indicated a significantly lower inhibitory effect of amyloid-ß42 on the aggregation, suggesting that tau aggregates are specific targets for quinoline interactions. These compounds showed highly lipophilic properties as corroborated with the analysis of total polar surface areas, and evaluation of their molecular properties. Moreover, these quinolines exhibit physical chemical properties similar to drugs able to penetrate the human brain blood barrier. Docking studies based on tau modeling, as a structural approach to the analysis of the interaction of tau-binding ligands, indicated that a C-terminal tau moiety, involved in the formation of PHFs, seems to be a site for binding of quinolines. Studies suggest the potential clinical use of these quinolines and of their derivatives to inhibit tau aggregation and possible therapeutic routes for AD.

Insulin resistance and Alzheimer's disease: molecular links & clinical implications.

Hyperinsulinemia as well as type II diabetes mellitus are among the risk factors for Alzheimer's disease (AD). However, the molecular and cellular basis that link insulin resistance disorders and diabetes with AD are far from clear. Here, we discuss the potential molecular mechanisms that may explain the participation of these metabolic disorders in the pathogenesis of AD. The human brain uses glucose as a primary fuel; insulin secreted by the pancreas cross the blood-brain barrier (BBB), reaching neurons and glial cells, and exerts a region-specific effect on glucose metabolism. Glucose homeostasis is critical for energy generation, neuronal maintenance, neurogenesis, neurotransmitter regulation, cell survival and synaptic plasticity. It also plays a key role in cognitive function. In an insulin resistance condition, there is a reduced sensitivity to insulin resulting in hyperinsulinemia; this condition persists for several years before becoming full-blown diabetes. Toxic levels of insulin negatively influence neuronal function and survival, and elevation of peripheral insulin concentration acutely increases its cerebrospinal fluid (CSF) concentration. Peripheral hyperinsulinemia correlates with an abnormal removal of the amyloid beta peptide (Abeta) and an increase of tau hyperphosphorylation as a result of augmented cdk5 and GSK3beta activities. This leads to cellular cascades that trigger a neurodegenerative phenotype and decline in cognitive function. Chronic peripheral hyperinsulinemia results in a reduction of insulin transport across the BBB and a reduced insulin signaling in brain, altering all of insulin's actions, including its anti-apoptotic effect. However, the increase in brain insulin levels resulting from its peripheral administration at optimal doses has shown a cognition-enhancing effect in patient with AD. Some drugs utilized in type II diabetes mellitus reduce cognitive impairment associated with AD. The link between insulin resistance and neurodegeneration and AD, and the possible therapeutic targets in preventing the insulin-resistance disorders are analyzed.