Cholinergic nicotinic systems in Alzheimer's disease: prospects for pharmacological intervention

Novel donepezil-tacrine hybrid (TAHB3) induces neurodifferentiation, neuroprotective effects, and activates the PI3K/AKT pathway on PC12 cells

Background

Alzheimer's disease (AD) is a neurodegenerative disease characterized by the impairment of cognitive functions and neuronal loss. AD has no cure; current treatments like acetylcholinesterase inhibitors (AChEI) alleviate symptoms but do not halt disease progression.

Objective

We aimed to evaluate the effects and mechanisms of two novel AChEI hybrid compounds (TAHB3 and TA8Amino), regarding cytotoxicity, neuroprotection and neurodifferentiation in PC12 cells.

Methods

The effects of TAHB3 and TA8Amino on neurodifferentiation were analyzed on PC12 cells which were treated with AChEI compounds for seven days, following morphological, and quantitative analyses to calculate the differentiation percentages, neurite length, and protein expression. Regarding cytotoxicity and neuroprotection assays, PC12 cells were differentiated into mature neurons, then treated with TAHB3 or TA8Amino, following a posttreatment with H2O2 (an inducer of oxidative damage); the analyses were performed using the XTT assay and flow cytometry.

Results

The hybrid compound TAHB3 induced differentiation of PC12 cells, but TA8Amino did not cause the same effect. Both compounds did not show cytotoxic effects to PC12 cells and did not change the cell cycle progression, nor induce cell death. Only TAHB3 showed neuroprotective potential against induced-oxidative damage, and TAHB3 increased the levels of p-AKT, suggesting its action through the activation of the PI3K/AKT pathway.

Conclusions

Our results showed that TAHB3 can induce neurodifferentiation, besides a neuroprotective activity, indicating the potential of AChEI hybrid compounds as novel candidates to be explored for the establishment of novel therapeutic strategies for patients with AD.

Nicotinic acetylcholine receptors in chemotherapeutic drugs resistance: An emerging targeting candidate

There is no definitive cure for cancer, and most of the current chemotherapy drugs have limited effects due to the development of drug resistance and toxicity at high doses. Therefore, there is an ongoing need for identifying the causes of chemotherapeutic resistance, and it will be possible to develop innovative treatment approaches based on these novel targeting candidates. Cigarette smoking is known to be one of the main causes of resistance to chemotherapeutic agents. Nicotine as a component of cigarette smoke is an exogenous activator of nicotinic acetylcholine receptors (nAChRs). It can inhibit apoptosis, increase cell proliferation and cell survival, reducing the cytotoxic effects of chemotherapy drugs and cause a reduced therapeutic response. Recent studies have demonstrated that nAChRs and their downstream signaling pathways have considerable implications in different cancer's initiation, progression, and chemoresistance. In some previous studies, nAChRs have been targeted to obtain better efficacies for chemotherapeutics. Besides, nAChRs-based therapies have been used in combination with chemotherapy drugs to reduce the side effects. This strategy requires lower doses of chemotherapy drugs compared to the conditions that must be used alone. Here, we discussed the experimental and clinical studies that show the nAChRs involvement in response to chemotherapy agents. Also, controversies relating to the effects of nAChR on chemotherapy-induced apoptosis are in our focus in this review article. Delineating the complex influences of nAChRs would be of great interest in establishing new effective chemotherapy regimens.

Growth factor treatment to overcome Alzheimer's dysfunctional signaling

The number of people suffering from Alzheimer's disease (AD) will increase as the world population ages, creating a huge socio-economic burden. The three pathophysiological hallmarks of AD are the cholinergic system dysfunction, the β-amyloid peptide deposition and the Tau protein hyperphosphorylation. Current treatments have only transient effects and each tends to concentrate on a single pathophysiological aspect of AD. This review first provides an overall view of AD in terms of its pathophysiological symptoms and signaling dysfunction. We then examine the therapeutic potential of growth factors (GFs) by showing how they can overcome the dysfunctional cell signaling that occurs in AD. Finally, we discuss new alternatives to GFs that help overcome the problem of brain uptake, such as small peptides, with evidence from some of our unpublished data on human neuronal cell line.

Cholinomimetic agents and neurocognitive impairment following head injury: a systematic review

PRIMARY OBJECTIVE

There has been increasing interest in the role of cholinomimetic agents in the long-term management of cognitive impairment following traumatic brain injury. This paper aims to assess the evidence accumulated thus far.

METHODS

Studies are identified by searching MEDLINE, EMBASE and PsychINFO, contacting experts and pharmaceutical companies and hand searching bibliographies. All study designs are included.

MAIN OUTCOME AND RESULTS

This study identified 25 papers that studied cholinesterase inhibitors, physostigmine and choline in mild-to-severe traumatic brain injury. The outcome with cholinesterase inhibitors and choline is suggestive but not conclusive while physostigmine appears of little benefit. A lack of rigorous studies and a plethora of outcome measures preclude drawing definitive conclusions. Further randomized controlled trials are urgently required.

Differential neuroimmune markers to the onset of Alzheimer's disease neurodegeneration and dementia: Autoantibodies to Aβ(25–35) oligomers, S100b and neurotransmitters

Alzheimer's disease (AD) autoimmunity is a focus for dementia prevention. Generated autoantibodies against major etiopathogenic molecular targets as neuroimmune markers of dementia were measured by ELISA in patient sera. Biphasic antibody levels to Abeta((25-35)) oligomers, S100b and DA were detected during distinctly diagnosed dementia stages. Abeta((25-35)) oligomer autoimmune responses reflected mild to moderate AD dementia, while those to S100b, DA and the S100b concentrations, matched moderate to severe dementia progression. 5-HT antibodies increased during mild dementia and plateaued thereafter. This autoimmunity pattern may be used as a differential biomarker profile in designing AD therapeutic strategies involving early vaccination.

Pharmacological characterization of DM232 (unifiram) and DM235 (sunifiram), new potent cognition enhancers

DM232 (unifiram) and DM235 (sunifiram) are potent cognition-enhancers, which are four order of magnitude more potent than piracetam. These compounds, although not showing affinity in binding studies for the most important central receptors or channels, are able to prevent amnesia induced by modulation of several neurotransmission systems. These compounds are able to increase the release of acetylcholine from rat cerebral cortex, and, as far as unifiram is concerned, to increase the amplitude of fEPSP in rat hippocampal slices. In vitro experiments, performed on hippocampal slices, also supported the hypothesis of a role of the AMPA receptors for the cognition-enhancing properties of unifiram and sunifiram.

The airway cholinergic system: physiology and pharmacology

The present review summarizes the current knowledge of the cholinergic systems in the airways with special emphasis on the role of acetylcholine both as neurotransmitter in ganglia and postganglionic parasympathetic nerves and as non-neuronal paracrine mediator. The different cholinoceptors, various nicotinic and muscarinic receptors, as well as their signalling mechanisms are presented. The complex ganglionic and prejunctional mechanisms controlling the release of acetylcholine are explained, and it is discussed whether changes in transmitter release could be involved in airway dysfunctions. The effects of acetylcholine on different target cells, smooth muscles, nerves, surface epithelial and secretory cells as well as mast cells are described in detail, including the receptor subtypes involved in signal transmission.