Rathanam Boopathy

Aryl acylamidase activity on acetylcholinesterase is high during early chicken brain development.

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are known to exhibit aryl acylamidase activities (here called AAAAChE and AAABChE, respectively), which have been suggested to be involved in developmental and pathological processes. We here have investigated the developmental profiles of both AAAAChE and AAABChE activities along with their AChE and BChE activities from embryonic days E3 to hatching (E21) in Triton-extracted homogenates from chicken embryonic brains. AAAAChE follows continuously an increase that is typical for AChE expression itself, whereas AAABChE was relatively high before E10 to then become negligible toward hatching. Sucrose gradient centrifugation of both homogenized and immunopurified samples from E6–E18 brains showed that all globular forms (G1, G2, G4) of AChE present AAAAChE activity. Interestingly, the ratio of AAAAChE to AChE is highest at E6, and here again higher on G1/G2- over the G4-form. Noticeably, the sensitivity of AAAAChE toward the specific AChE inhibitor BW284c51 at all stages is higher than that of AChE itself. These data of high ratios of AAA associated at young stages with cholinesterases strongly indicate a role of AAA in early brain development.

A direct method to visualise the aryl acylamidase activity on cholinesterases in polyacrylamide gels

BackgroundIn vertebrates, two types of cholinesterases exist, acetylcholinesterase and butyrylcholinesterase. The function of acetylcholinesterase is to hydrolyse acetylcholine, thereby terminating the neurotransmission at cholinergic synapse, while the precise physiological function of butyrylcholinesterase has not been identified. The presence of cholinesterases in tissues that are not cholinergically innervated indicate that cholinesterases may have functions unrelated to neurotransmission. Furthermore, cholinesterases display a genuine aryl acylamidase activity apart from their predominant acylcholine hydrolase activity. The physiological significance of this aryl acylamidase activity is also not known. The study on the aryl acylamidase has been, in part hampered by the lack of a specific method to visualise this activity. We have developed a method to visualise the aryl acylamidase activity on cholinesterase in polyacrylamide gels.ResultsThe o-nitroaniline liberated from o-nitroacetanilide by the action of aryl acylamidase activity on cholinesterases, in the presence of nitrous acid formed a diazonium compound. This compound gave an azo dye complex with N-(1-napthyl)-ethylenediamine, which appeared as purple bands in polyacrylamide gels. Treating the stained gels with trichloroacetic acid followed by Tris-HCl buffer helped in fixation of the stain in the gels. By using specific inhibitors for acetylcholinesterase and butyrylcholinesterase, respectively, differential staining for the aryl acylamidase activities on butyrylcholinesterase and acetylcholinesterase in a sample containing both these enzymes has been demonstrated. A linear relationship between the intensity of colour developed and activity of the enzyme was obtained.ConclusionsA novel method to visualise the aryl acylamidase activity on cholinesterases in polyacrylamide gels has been developed.

Adaptability to hypobaric hypoxia is facilitated through mitochondrial bioenergetics: an in vivo study

High‐altitude pulmonary oedema (HAPE) experienced under high‐altitude conditions is attributed to mitochondrial redox distress. Hence, hypobaric hypoxia (HH)‐induced alteration in expression of mitochondrial biogenesis and dynamics genes was determined in rat lung. Further, such alteration was correlated with expression of mitochondrial DNA (mtDNA)‐encoded oxidative phosphorylation (mtOXPHOS) genes. The prophylactic effect of dexamethasone (DEX) in counteracting the HH‐induced mitochondrial distress was used as control to understand adaptation to high‐altitude exposure.

Why calcium channel blockers could be an elite choice in the treatment of Alzheimer’s disease: a comprehensive review of evidences

Abstract The universality and vitality of calcium ions are implicit from its diverse physiological functions, from regulation of enzymes to synaptic plasticity and memory. However, overloading of these ions could result in life-threatening degenerative disorders. Calcium channels, which are involved in the transport of calcium ions, are targeted and blocked to prevent its overload, favoring vascular relaxation. Besides this primary action, calcium channel blockers (CCBs) also genuinely exhibit cognitive-enhancing abilities and reduce the risk of dementia, especially of Alzheimer’s type. Alzheimer’s disease (AD) is triggered by the disruption of calcium homeostasis, which underlies the observed progressive cognitive decline that occurs in this neurodegenerative disorder. Fortunately, CCB is expected to offer neuroprotection and additionally demonstrate antiamyloid, antitau, antiphospholipase, antiplatelet, antioxidant, and anti-inflammatory activity, a solitary solution to all the subcellular physiological complications that are observed in AD. Therefore, the aim of this review was to unearth the prospective of CCB against cognitive frailty with a sole purpose of elucidating CCB as cognitive enhancers, which could find its use as a drug in prevention or treatment of AD.

The aryl acylamidase activity is much more sensitive to Alzheimer drugs than the esterase activity of acetylcholinesterase in chicken embryonic brain

The appearance of cholinergic trait often precedes synaptogenesis, indicating the involvement of cholinesterase proteins in nervous system development, particularly so acetylcholinesterase (AChE). In addition to AChEs acclaimed esterase activity, its lesser known non-cholinergic functions have gained much attention, because of AChE protein expression in areas other than cholinergic innervations; one such function could be exerted by its associated aryl acylamidase (AAA) activity. In this study, an attempt has been made in profiling esterase and AAA activities of AChE at different developmental stages of the chick embryo, e.g. at embryonic day 6 (E6), E9, E12, E15 and E18. AAA activity showed a correlated expression with esterase activity at all stages, but the relative ratios of AAA to esterase activity were higher at younger stages. The inhibition of AAA activity was shown to be more sensitive towards Huperzine, Donepezil whereas inhibition of esterase activity was sensitive to Tacrine and DFP. Remarkably, the major Alzheimer drugs- Huperzine and Donepezil, much more strongly inhibited AAA activity of AChE at younger developmental stages whose IC50 values are 0.01 muM and 0.1 muM respectively. In the case of BW284c51, inhibition was more pronounced at older stages and IC50 value was 0.1 muM. Since in Alzheimers disease (AD), embryonic forms of AChE have been reported to reappear, a possible role of AAA activity in the pathogenesis of AD should be considered.

Altered mitochondrial biogenesis and its fusion gene expression is involved in the high-altitude adaptation of rat lung

Intermittent hypobaric hypoxia-induced preconditioning (IHH-PC) of rat favored the adaption of lungs to severe HH conditions, possibly through stabilization of mitochondrial function. This is based on the data generated on regulatory coordination of nuclear DNA-encoded mitochondrial biogenesis; dynamics, and mitochondrial DNA (mtDNA)-encoded oxidative phosphorylation (mtOXPHOS) genes expression. At 16th day after start of IHH-PC (equivalent to 5000m, 6h/d, 2w of treatment), rats were exposed to severe HH stimulation at 9142m for 6h. The IHH-PC significantly counteracted the HH-induced effect of increased lung: water content; tissue damage; and oxidant injury. Further, IHH-PC significantly increased the mitochondrial number, mtDNA content and mtOXPHOS complex activity in the lung tissues. This observation is due to an increased expression of genes involved in mitochondrial biogenesis (PGC-1α, ERRα, NRF1, NRF2 and TFAM), fusion (Mfn1 and Mfn2) and mtOXPHOS. Thus, the regulatory pathway formed by PGC-1α/ERRα/Mfn2 axes is required for the mitochondrial adaptation provoked by IHH-PC regimen to counteract subsequent HH stress.

Interaction of metal chelators with different molecular forms of acetylcholinesterase and its significance in Alzheimer's disease treatment

The peripheral anionic site (PAS) of acetylcholinesterase (AChE) is involved in amyloid beta (Aβ) peptides aggregation of Alzheimers disease (AD). AChE exhibits an aryl acylamidase (AAA) activity along with the well known esterase activity. Numerous studies have reported the beneficiary effect of metal chelators in AD treatment. Hence, a comparative study on the effect of metal chelators on both the esterase and AAA activity of AChE globular (G4 and G1) molecular forms was performed. The inhibitory effect of 1,10‐phenanthroline was high towards AChE esterase activity. The corresponding IC50 values for esterase activity of G4 and G1‐form was 190 µM and 770 µM and for AAA activity it was 270 µM and 2.74 mM, respectively. Kinetic studies on both forms of AChE show that 1,10‐phenanthroline inhibits esterase in competitive and AAA activity in non‐competitive manner. Protection studies further revealed that the nature of 1,10‐phenanthroline inhibition on AChE is through its direct binding to protein rather than its metal chelation property. Molecular docking studies shows orientation of 1,10‐phenathroline in the PAS through hydrophobic interactions with the PAS residues (Trp286, Tyr124 and Tyr341) and hydrogen bonding with Phe295. Further molecular dynamics simulation of “hAChE‐1,10‐phenanthroline” complex revealed that both hydrogen and hydrophobic interaction contribute equally for 1,10‐phenanthroline binding to hAChE. Such an interaction of 1,10‐phenanthroline on PAS may hinder “AChE‐Aβ peptide” complex formation. Hence, 1,10‐phenanthroline can act as a lead molecule for developing drug(s) against AD ailment with dual functions namely, anti‐cholinesterase and anti‐amyloid aggregation potency in a single chemical entity. Proteins 2013. Proteins 2013; 81:1179–1191.

Understanding the molecular mechanism of aryl acylamidase activity of acetylcholinesterase – An in silico study

Acetylcholinesterase (AChE) exhibits two different activities, namely esterase and aryl acylamidase (AAA). Unlike esterase, AAA activity of AChE is inhibited by the active site inhibitors while remaining unaffected by the peripheral anionic site inhibitors. This differential inhibitory pattern of active and peripheral anionic site inhibitors on the AAA activity remains unanswered. To answer this, we investigated the mechanism of binding and trafficking of AAA substrates using in silico tools. Molecular docking of serotonin and AAA substrates (o-nitroacetanilide, and o-nitrotrifluoroacetanilide,) onto AChE shows that these compounds bind at the side door of AChE. Thus, we conceived that the AAA substrates prefer the side door to reach the active site for their catalysis. Further, steered molecular dynamics simulations show that the force required for binding and trafficking of the AAA substrate through the side door is comparatively lesser than their dissociation (900kJ/mol/nm). Among the two substrates, o-nitrotrifluoroacetanilide required lesser force (380kJ/mol/nm) than o-nitroacetanilide the (550kJ/mol/nm) for its binding, thus validating o-nitrotrifluoroacetanilide as a better substrate. With these observations, we resolve that the AAA activity of AChE is mediated through its side door. Therefore, binding of PAS inhibitors at the main door of AChE remain ineffective against AAA activity.

The allele frequency of T920C mutation in butyrylcholinesterase gene is high in an Indian population.

The genetic variants of butyrylcholinesterase (BChE) are the cause of concern in individuals experiencing prolonged apnea on administration of muscle relaxants. In an Indian community called Vysya, a variant (L307P; T920C) was associated with imperceptible plasma BChE. Since BChE has several pharmacological significances in humans, the identification of its variants having altered activity is very important. Previous studies for identifying the mutants in a population were based only on its functional attributes (phenotypic characters) such as esterase activity, dibucaine number and fluoride number. Generally phenotyping method is not considered as the accurate methodology till date though it might be used as a primary screening tool. Molecular biology provides a better technique in identifying these variants. Our aim was to screen this particular community living in South India for the heterozygosity of T920C mutation by phenotypic and genotypic analysis and to find the reliability between the two methods. We analysed 266 individuals for the heterozygosity of T920C. Based on BChE phenotypes, we found that 95% of the individuals are heterozygous. Real-time PCR based genotyping revealed that 96% of individuals are heterozygous. The allele frequency for the mutant allele C was 0.52 which confirmed that the genetic pool of this allele is much higher in Vysya. Also, we observed that genotyping correlates 97% with the phenotype in our study. Further, both phenotype and genotype of age matched other ethnic group do not show any preponderance to this mutation authenticating the vulnerability of Vysyas to this mutation is dominant.

A New Role for the Nonpathogenic Nonsynonymous Single-Nucleotide Polymorphisms of Acetylcholinesterase in the Treatment of Alzheimer's Disease: A Computational Study

Single-nucleotide polymorphisms (SNPs) are implicated in the complexity of understanding the genetics of diseases and their therapeutics. Here we have attempted to determine the impact of nonsynonymous SNPs (nsSNPs) on structure, dynamics, and ligand-binding properties of the human acetylcholinesterase (hAChE) protein, which has been targeted in the treatment of Alzheimers disease. Of the reported 153 SNPs, 4 nsSNPs, namely, A415G, P104A, V302E, and Y119H, were prioritized to be functionally unfavorable by SIFT and PolyPhen algorithms. Molecular dynamics simulation revealed these nsSNP forms to be structurally stable, and they are also considered functionally active as they lie away from the catalytic triad. However, the aromatic amino acids lining the active-site gorge exhibited altered degrees of side chain dihedral angles. Such conformational alterations were evaluated for their ability to interfere with binding of hAChE inhibitors. The inhibitors (donepezil, galantamine, rivastigmine, and tacrine) were oriented differently in comparison to the native because of the steric hindrance offered by the altered dihedral angles. Interestingly, huperzine A alone exhibited higher efficiency in its binding to the AChE and retained similar orientation irrespective of the polymorphisms since the orientation of Asp74 involved in its binding and trafficking remained unaltered in all protein forms. Therefore, we conclude that nsSNPs confer changes to the dynamicity of proteins, which in turn affects their ligand-binding properties rather than their stability. Considering the diverse polymorphic nature of hAChE, while contemplating any structure-based drug design, the common, nonpathogenic nsSNPs should be considered for the utmost efficacy of drugs.