Physiological and neurobehavioral effects of cholinesterase inhibition in healthy adults

Positive association of acetylcholinesterase (AChE) with the neutrophil-to-lymphocyte ratio and HbA1c, and a negative association with hydrogen sulfide (H2S) levels among healthy African Americans, and H2S-inhibition and high-glucose-upregulation of AChE in cultured THP-1 human monocytes

The incidence of Alzheimer's disease (AD) is higher in people over the age of 65 and in African Americans (AA). Elevated acetylcholinesterase (AChE) activity has been considered a major player in the onset of AD symptoms. As a result, many FDA-approved AD drugs target AChE inhibition to treat AD patients. Hydrogen sulfide (H2S) is a signaling molecule known to downregulate oxidative stress and inflammation. The neutrophil-to-lymphocyte ratio (NLR) in the blood is widely used as a biomarker to monitor inflammation and immunity. This study examined the hypothesis that plasma AChE levels have a negative association with H2S levels and that a positive association exists between levels of NLR, HbA1c, and ROS with the AChE in the peripheral blood. The fasting blood sample was taken from 114 African Americans who had provided written informed consent approved by the IRB. The effect of H2S and high-glucose treatment on AChE activity levels was also investigated in THP-1 human monocytes. There was a significant negative relationship between AChE and the levels of H2S (r = -0.41, p = 0.001); a positive association between the levels of AChE with age (r = 0.26, p = 0.03), NLR (r = 0.23, p = 0.04), ROS (r = 0.23, p = 0.04) and HbA1c levels (r = 0.24, p = 0.04), in AA subjects. No correlation was seen between blood levels of AChE and acetylcholine (ACh). Blood creatinine had a negative correlation (r = -0.23, p = 0.04) with ACh levels. There was a significant effect of H2S on AChE inhibition and of high glucose in upregulating AChE activity in cultured monocytes. This study suggests hyperglycemia and lower H2S status can contribute to an increase in the AChE activity levels. Future clinical studies are needed to examine the potential benefits of supplementation with hydrogen sulfide pro-drugs/compounds in reducing the AChE and the cognitive dysfunctions associated with AD.

A Synopsis of Multitarget Potential Therapeutic Effects of Huperzine A in Diverse Pathologies-Emphasis on Alzheimer's Disease Pathogenesis

Numerous challenges are confronted when it comes to the recognition of therapeutic agents for treating complex neurodegenerative diseases like Alzheimer's disease (AD). The perplexing pathogenicity of AD embodies cholinergic dysfunction, amyloid beta (Aβ) aggregation, neurofibrillary tangle formation, neuroinflammation, mitochondrial disruption along with vicious production of reactive oxygen species (ROS) generating oxidative stress. In this frame of reference, drugs with multi target components could prove more advantageous to counter complex pathological mechanisms that are responsible for AD progression. For as much as, medicinal plant based pharmaco-therapies are emerging as potential candidates for AD treatment keeping the efficacy and safety parameters in terms of toxicity and side effects into consideration. Huperzine A (Hup A) is a purified alkaloid compound extracted from a club moss called Huperzia serrata. Several studies have reported both cholinergic and non-cholinergic effects of this compound on AD with significant neuroprotective properties. The present review convenes cumulative demonstrations of neuroprotection provided by Hup A in in vitro, in vivo, and human studies in various pathologies. The underlying molecular mechanisms of its actions have also been discussed. However, more profound evidence would certainly promote the therapeutic implementation of this drug thus furnishing decisive insights into AD therapeutics and various other pathologies along with preventive and curative management.

Pharmacological Neuroenhancement: Current Aspects of Categorization, Epidemiology, Pharmacology, Drug Development, Ethics, and Future Perspectives

Recent pharmacoepidemiologic studies suggest that pharmacological neuroenhancement (pNE) and mood enhancement are globally expanding phenomena with distinctly different regional characteristics. Sociocultural and regulatory aspects, as well as health policies, play a central role in addition to medical care and prescription practices. The users mainly display self-involved motivations related to cognitive enhancement, emotional stability, and adaptivity. Natural stimulants, as well as drugs, represent substance abuse groups. The latter comprise purines, methylxanthines, phenylethylamines, modafinil, nootropics, antidepressants but also benzodiazepines, β-adrenoceptor antagonists, and cannabis. Predominant pharmacodynamic target structures of these substances are the noradrenergic/dopaminergic and cholinergic receptor/transporter systems. Further targets comprise adenosine, serotonin, and glutamate receptors. Meta-analyses of randomized-controlled studies in healthy individuals show no or very limited verifiability of positive effects of pNE on attention, vigilance, learning, and memory. Only some members of the substance abuse groups, i.e., phenylethylamines and modafinil, display positive effects on attention and vigilance that are comparable to caffeinated drinks. However, the development of new antidementia drugs will increase the availability and the potential abuse of pNE. Social education, restrictive regulatory measures, and consistent medical prescription practices are essential to restrict the phenomenon of neuroenhancement with its social, medical, and ethical implications. This review provides a comprehensive overview of the highly dynamic field of pharmacological neuroenhancement and elaborates the dramatic challenges for the medical, sociocultural, and ethical fundaments of society.

Oral Pretreatment with Galantamine Effectively Mitigates the Acute Toxicity of a Supralethal Dose of Soman in Cynomolgus Monkeys Posttreated with Conventional Antidotes

Earlier reports suggested that galantamine, a drug approved to treat mild-to-moderate Alzheimer's disease (AD), and other centrally acting reversible acetylcholinesterase (AChE) inhibitors can serve as adjunct pretreatments against poisoning by organophosphorus compounds, including the nerve agent soman. The present study was designed to determine whether pretreatment with a clinically relevant oral dose of galantamine HBr mitigates the acute toxicity of 4.0×LD₅₀ soman (15.08 µg/kg) in Macaca fascicularis posttreated intramuscularly with the conventional antidotes atropine (0.4 mg/kg), 2-pyridine aldoxime methyl chloride (30 mg/kg), and midazolam (0.32 mg/kg). The pharmacokinetic profile and maximal degree of blood AChE inhibition (∼25%-40%) revealed that the oral doses of 1.5 and 3.0 mg/kg galantamine HBr in these nonhuman primates (NHPs) translate to human-equivalent doses that are within the range used for AD treatment. Subsequent experiments demonstrated that 100% of NHPs pretreated with either dose of galantamine, challenged with soman, and posttreated with conventional antidotes survived 24 hours. By contrast, given the same posttreatments, 0% and 40% of the NHPs pretreated, respectively, with vehicle and pyridostigmine bromide (1.2 mg/kg, oral), a peripherally acting reversible AChE inhibitor approved as pretreatment for military personnel at risk of exposure to soman, survived 24 hours after the challenge. In addition, soman caused extensive neurodegeneration in the hippocampi of saline- or pyridostigmine-pretreated NHPs, but not in the hippocampi of galantamine-pretreated animals. To our knowledge, this is the first study to demonstrate the effectiveness of clinically relevant oral doses of galantamine to prevent the acute toxicity of supralethal doses of soman in NHPs. SIGNIFICANCE STATEMENT: This is the first study to demonstrate that a clinically relevant oral dose of galantamine effectively prevents lethality and neuropathology induced by a supralethal dose of the nerve agent soman in Cynomolgus monkeys posttreated with conventional antidotes. These findings are of major significance for the continued development of galantamine as an adjunct pretreatment against nerve agent poisoning.

Evidence for positive allosteric modulation of cognitive-enhancing effects of nicotine in healthy human subjects

RATIONALE

Cognitive benefits of nicotinic acetylcholine receptor (nAChR) agonists are well established but have generally been of small magnitude and uncertain clinical significance. A way of raising the effect size may be to facilitate agonist-induced responses by co-administering a nAChR positive allosteric modulator (PAM).

OBJECTIVE

The aim was to test whether galantamine, a PAM at several nAChR subtypes, can potentiate the cognitive-enhancing effects of nicotine.

METHODS

Twenty-six adult never-smokers were treated, in a double-blind counterbalanced sequence, with nicotine (7 mg/24 h, transdermally) and galantamine (4 mg, p.o.) combined, nicotine alone, galantamine alone, and double placebo. A low dose of galantamine was chosen to minimize acetylcholinesterase inhibition, which was verified in blood assays. In each condition, participants were tested with three cognitive tasks.

RESULTS

Nicotine significantly improved reaction time (RT) and signal detection in a visuospatial attention task and the Rapid Visual Information Processing Task. Galantamine did not modulate these effects. A trend toward RT reduction by galantamine correlated with acetylcholinesterase inhibition. In a change detection task, there were no effects of nicotine or galantamine alone on accuracy or RT. However, both drugs combined acted synergistically to reduce RT. This effect was not associated with acetylcholinesterase inhibition.

CONCLUSIONS

A pattern consistent with allosteric potentiation of nicotine effects by galantamine was observed on one of six performance measures. This may reflect specific nAChR subtype involvement, or additional pharmacological actions of galantamine may have overshadowed similar interactions on other measures. The finding suggests that allosteric potentiation of nAChR agonist-induced cognitive benefits is possible in principle.

[Doping for the brain]

The enhancement of physical and cognitive abilities (i. e. concentration, vigilance, memory) has always been desirable for humans. The term pharmacological neuroenhancement refers to the use of legal or nonprescription psychoactive substances by healthy subjects with the intention of cognitive enhancement. To give the most prominent example, caffeine serves worldwide as a natural stimulant. Brain doping, however, specifies the use of illegal substances or prescription drugs beyond approval with the purpose of cognitive enhancement. Only amphetamines, methylphenidate and modafinil have significant effects on attentiveness, concentration and alertness, whereas other substances, such as anti-dementia drugs or anti-depressants failed to demonstrate cognitive enhancement in healthy subjects.

Cholinergic modulation of the hippocampal region and memory function

Acetylcholine (ACh) plays an important role in memory function and has been implicated in aging-related dementia, in which the impairment of hippocampus-dependent learning strongly manifests. Cholinergic neurons densely innervate the hippocampus, mediating the formation of episodic as well as semantic memory. Here, we will review recent findings on acetylcholine's modulation of memory function, with a particular focus on hippocampus-dependent learning, and the circuits involved. In addition, we will discuss the complexity of ACh actions in memory function to better understand the physiological role of ACh in memory. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

A randomized, double-blind, placebo controlled, parallel group, efficacy study of alpha BRAIN® administered orally

OBJECTIVE

Alpha BRAIN® is a nootropic supplement that purports to enhance cognitive functioning in healthy adults. The goal of this study was to investigate the efficacy of this self-described cognitive enhancing nootropic on cognitive functioning in a group of healthy adults by utilizing a randomized, double blind, placebo-controlled design.

METHODS

A total of 63-treatment naïve individuals between 18 and 35 years of age completed the randomized, double-blind, placebo controlled trial. All participants completed a 2-week placebo run in before receiving active product, Alpha BRAIN® or new placebo, for 6 weeks. Participants undertook a battery of neuropsychological tests at randomization and at study completion. Primary outcome measures included a battery of neuropsychological tests and measures of sleep.

RESULTS

Compared with placebo, Alpha BRAIN® significantly improved on tasks of delayed verbal recall and executive functioning. Results also indicated significant time-by-group interaction in delayed verbal recall for the Alpha BRAIN® group.

CONCLUSIONS

The use of Alpha BRAIN® for 6 weeks significantly improved recent verbal memory when compared with controls, in a group of healthy adults. While the outcome of the study is encouraging, this is the first randomized controlled trial of Alpha BRAIN®, and the results merit further study.