A paradigm for single nucleotide polymorphism analysis: The case of the acetylcholinesterase gene

Acetylcholinesterase Activity Measurement and Clinical Features of Delirium

AIMS

Cholinergic deficiency is commonly implicated in the pathophysiology of delirium. We aimed to investigate the relationship between directly measured serum acetylcholinesterase (AChE) activity and (1) clinical features of delirium and (2) outcomes among older hospital patients with delirium.

METHODS

Hospitalised patients with delirium were recruited, and delirium motor subtype, severity and duration of delirium were measured. Serum AChE activity was measured using a colorimetric assay.

RESULTS

The mean AChE activity for the whole sample was 2.46 μmol/μL/min (standard deviation 1.75). Higher AChE activity was associated with increased likelihood of hypoactive delirium rather than the hyperactive or mixed subtype (odds ratio 1.98, 95% confidence interval 1.10-3.59).

CONCLUSION

Higher AChE activity was associated with hypoactive delirium but did not predict outcomes. Simple enhancement of cholinergic neurotransmission may not be sufficient to treat delirium.

Personalized genetics of the cholinergic blockade of neuroinflammation

Acetylcholine signaling is essential for cognitive functioning and blocks inflammation. To maintain homeostasis, cholinergic signaling is subjected to multi‐leveled and bidirectional regulation by both proteins and non‐coding microRNAs (‘CholinomiRs’). CholinomiRs coordinate the cognitive and inflammatory aspects of cholinergic signaling by targeting major cholinergic transcripts including the acetylcholine hydrolyzing enzyme acetylcholinesterase (AChE). Notably, AChE inhibitors are the only currently approved line of treatment for Alzheimer's disease patients. Since cholinergic signaling blocks neuroinflammation which is inherent to Alzheimer's disease, genomic changes modifying AChE's properties and its susceptibility to inhibitors and/or to CholinomiRs regulation may affect the levels and properties of inflammasome components such as NLRP3. This calls for genomic‐based medicine approaches based on genotyping of both coding and non‐coding single nucleotide polymorphisms (SNPs) in the genes involved in cholinergic signaling. An example is a SNP in a recognition element for the primate‐specific microRNA‐608 within the 3′ untranslated region of the AChE transcript. Carriers of the minor allele of that SNP present massively elevated brain AChE levels, increased trait anxiety and inflammation, accompanied by perturbed CholinomiR‐608 regulatory networks and elevated prefrontal activity under exposure to stressful insults. Several additional SNPs in the AChE and other cholinergic genes await further studies, and might likewise involve different CholinomiRs and pathways including those modulating the initiation and progression of neurodegenerative diseases. CholinomiRs regulation of the cholinergic system thus merits in‐depth interrogation and is likely to lead to personalized medicine approaches for achieving better homeostasis in health and disease.

This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

A selective and sensitive near-infrared fluorescent probe for acetylcholinesterase imaging

HupNIR2 is the first NIR fluorescent probe for acetylcholinesterase imaging in tissues. This probe penetrates easily and deeply into the tissue, and directly labels AChE.

Competing targets of microRNA-608 affect anxiety and hypertension

MicroRNAs (miRNAs) can repress multiple targets, but how a single de-balanced interaction affects others remained unclear. We found that changing a single miRNA-target interaction can simultaneously affect multiple other miRNA-target interactions and modify physiological phenotype. We show that miR-608 targets acetylcholinesterase (AChE) and demonstrate weakened miR-608 interaction with the rs17228616 AChE allele having a single-nucleotide polymorphism (SNP) in the 3'-untranslated region (3'UTR). In cultured cells, this weakened interaction potentiated miR-608-mediated suppression of other targets, including CDC42 and interleukin-6 (IL6). Postmortem human cortices homozygote for the minor rs17228616 allele showed AChE elevation and CDC42/IL6 decreases compared with major allele homozygotes. Additionally, minor allele heterozygote and homozygote subjects showed reduced cortisol and elevated blood pressure, predicting risk of anxiety and hypertension. Parallel suppression of the conserved brain CDC42 activity by intracerebroventricular ML141 injection caused acute anxiety in mice. We demonstrate that SNPs in miRNA-binding regions could cause expanded downstream effects changing important biological pathways.

Cholinergic involvement and manipulation approaches in multiple system disorders

Within the autonomic system, acetylcholine signaling contributes simultaneously and interactively to cognitive, behavioral, muscle and immune functions. Therefore, manipulating cholinergic parameters such as the activities of the acetylcholine hydrolyzing enzymes in body fluids or the corresponding transcript levels in blood leukocytes can change the global status of the autonomic system in treated individuals. Specifically, cholinesterase activities are subject to rapid and effective changes. The enzyme activity baseline increases with age and body mass index and depends on gender and ethnic origin. Also, the corresponding DNA (for detecting mutations) and RNA (for measuring specific mRNA transcripts) of cholinergic genes present individual variability. In leukocytes, acetylcholine inhibits the production of pro-inflammatory cytokines, suggesting relevance of cholinergic parameters to both the basal levels and to disease-induced inflammation. Inversely, acetylcholine levels increase under various stress stimuli, inducing changes in autonomic system molecules (e.g., pro-inflammatory cytokines) which can penetrate the brain; therefore, manipulating these levels can also effect brain reactions, mainly of anxiety, depression and pain. Additionally, neurodegenerative diseases often involve exacerbated inflammation, depression and anxiety, providing a focus interest group for cholinergic manipulations. In Alzheimer's disease, the systemic cholinergic impairments reflect premature death of cholinergic neurons. The decline of cholinesterases in the serum of Parkinson's disease and post- stroke patients, discovery of the relevant microRNAs and the growing range of use of anticholinesterase medications all call for critical re-inspection of established and novel approaches for manipulating cholinergic parameters.

Why has butyrylcholinesterase been retained? Structural and functional diversification in a duplicated gene

While acetylcholinesterase (EC 3.1.1.7) has a clearly defined role in neurotransmission, the functions of its sister enzyme butyrylcholinesterase (EC 3.1.1.8) are more obscure. Numerous mutations, many inactivating, are observed in the human butyrylcholinesterase gene, and the butyrylcholinesterase knockout mouse has an essentially normal phenotype, suggesting that the enzyme may be redundant. Yet the gene has survived for many millions of years since the duplication of an ancestral acetylcholinesterase early in vertebrate evolution. In this paper, we ask the questions: why has butyrylcholinesterase been retained, and why are inactivating mutations apparently tolerated? Butyrylcholinesterase has diverged both structurally and in terms of tissue and cellular expression patterns from acetylcholinesterase. Butyrylcholinesterase-like activity and enzymes have arisen a number of times in the animal kingdom, suggesting the usefulness of such enzymes. Analysis of the published literature suggests that butyrylcholinesterase has specific roles in detoxification as well as in neurotransmission, both in the brain, where it appears to control certain areas and functions, and in the neuromuscular junction, where its function appears to complement that of acetylcholinesterase. An analysis of the mutations in human butyrylcholinesterase and their relation to the enzyme's structure is shown. In conclusion, it appears that the structure of butyrylcholinesterase's catalytic apparatus is a compromise between the apparently conflicting selective demands of a more generalised detoxifier and the necessity for maintaining high catalytic efficiency. It is also possible that the tolerance of mutation in human butyrylcholinesterase is a consequence of the detoxification function. Butyrylcholinesterase appears to be a good example of a gene that has survived by subfunctionalisation.

Different sensitivities of rat skeletal muscles and brain to novel anti-cholinesterase agents, alkylammonium derivatives of 6-methyluracil (ADEMS)

BACKGROUND AND PURPOSE

The rat respiratory muscle diaphragm has markedly lower sensitivity than the locomotor muscle extensor digitorum longus (EDL) to the new acetylcholinesterase (AChE) inhibitors, alkylammonium derivatives of 6-methyluracil (ADEMS). This study evaluated several possible reasons for differing sensitivity between the diaphragm and limb muscles and between the muscles and the brain.

EXPERIMENTAL APPROACH

Increased amplitude and prolonged decay time of miniature endplate currents were used to assess anti-cholinesterase activity in muscles. In hippocampal slices, induction of synchronous network activity was used to follow cholinesterase inhibition. The inhibitor sensitivities of purified AChE from the EDL and brain were also estimated.

KEY RESULTS

The intermuscular difference in sensitivity to ADEMS is partly explained caused by a higher level of mRNA and activity of 1,3-bis[5(diethyl-o-nitrobenzylammonium)pentyl]-6-methyluracildibromide (C-547)-resistant BuChE in the diaphragm. Moreover, diaphragm AChE was more than 20 times less sensitive to C-547 than that from the EDL. Sensitivity of the EDL to C-547 dramatically decreased after treadmill exercises that increased the amount of PRiMA AChE(G4), but not ColQ AChE(A12) molecular forms. The A12 form present in muscles appeared more sensitive to C-547. The main form of AChE in brain, PRiMA AChE(G4), was apparently less sensitive because brain cholinesterase activity was almost three orders of magnitude more resistant to C-547 than that of the EDL.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that ADEMS compounds could be used for the selective inhibition of AChEs and as potential therapeutic tools.

Implication de la pharmacogénétique dans les traitements des cancers colorectaux

SCOPE

Clinical implications associated with polymorphisms in drug-metabolizing genes involved in the chemotherapy of colorectal cancers (5-flurorouracil, oxaliplatin and irinotecan) are reviewed.

CURRENT SITUATION AND SALIENT POINTS

Treatments of colorectal cancers have been greatly improved last years but patients respond differently to identical medication. Genetic polymorphisms are one of the major causes of these individual responses to drugs associated with sometimes severe adverse effects. Pharmacogenetics is based on all polymorphisms that determine genetic human diversity associated with variable response to anticancer drugs.

PERSPECTIVES

Morbidity and mortality related to toxicity or inefficacy of these drugs could be reduced by analyzing the pharmacogenetic profile of patients before treatment. Results should be integrated in protocols for monitoring and assessment the dosage of drugs.

Rationale for diagnosing deficiency of ChEs and for applying exogenous HuChEs to the treatment of diseases

Recent evidence strongly demonstrates that acetylcholine (ACh) is not only involved in the function of the central and peripheral nervous systems, including the parasympathetic and somatic systems, but also acts as a ubiquitous cell signaling molecule or cytotransmitter, and as a hormone with paracrine, juxtacrine and autocrine properties. This active molecule exerts versatile and potent functions primarily through its specific nicotinic and muscarinic receptors (nAChRs and mAChRs, respectively). These functions modulate numerous biomechanisms, including cell growth, survival, proliferation and differentiation, cell-cell contact, cell cycle, locomotion, electrical activity, immune function, apoptosis, organization of the cytoskeleton, trophic functions, secretion, adhesion, resorption, and stress-response-regulation. By nature, the precise ACh levels and responses from receptors must be controlled and regulated by its degrading enzymes, the cholinesterases (ChEs), namely, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Once ChEs become critically deficient in quality and quantity, ACh signaling will be uncontrollably aberrant and persistent. An in-depth account of the fundamental roles of ChEs, comprising their diverse soluble and membrane-bound forms, in maintaining the functional equilibrium of ACh in the macro and microenvironment has been undertaken. This work also covers ACh receptors, signaling pathways, other interdependent and interrelated substances, functional processes, role of ChEs as first-line gatekeepers and defenses for the architecture of cells, tissues and organisms, physically, chemically, and structurally. The mechanisms of many diseases ranging from the acute cholinergic crisis to the chronic degenerative and hypergenerative disorders such as Alzheimer's disease, cancers, atopic dermatitis, may involve a deficiency of ChEs or imbalance between ACh and ChEs, initially or consequentially. It is therefore essential to ascertain a ChE deficiency, or an imbalance between ACh and ChEs, in tissues and body fluids in order for conducting clinical diagnosis, prevention and treatment. An argument is put forward on the rationale of applying exogenous human ChEs to reverse enzymatic deficiency and correct the imbalance between ACh and ChEs, to repair the affected receptors and protect against their further loss in the body, and consequently to alleviate the signs and symptoms of diseases. Evidence is adduced for the safety and efficacy of ChEs treatment.

Mutations in Olfactory Signal Transduction Genes Are Not a Major Cause of Human Congenital General Anosmia

Anosmia affects the western world population, mostly the elderly, reaching to 5% in subjects over the age of 45 years and strongly lowering their quality of life. A smaller minority (about 0.01%) is born without a sense of smell, afflicted with congenital general anosmia (CGA). No causative genes for human CGA have been identified yet, except for some syndromic cases such as Kallman syndrome. In mice, however, deletion of any of the 3 main olfactory transduction components (guanidine triphosphate binding protein, adenylyl cyclase, and the cyclic adenosine monophosphate-gated channel) causes profound reduction of physiological responses to odorants. In an attempt to identify human CGA-related mutations, we performed whole-genome linkage analysis in affected families, but no significant linkage signals were observed, probably due to the small size of families analyzed. We further carried out direct mutation screening in the 3 main olfactory transduction genes in 64 unrelated anosmic individuals. No potentially causative mutations were identified, indicating that transduction gene variations underlie human CGA rarely and that mutations in other genes have to be identified. The screened genes were found to be under purifying selection, suggesting that they play a crucial functional role not only in olfaction but also potentially in additional pathways.