Walsh R

References (14)

Title : Enzyme-linked DNA dendrimer nanosensors for acetylcholine - Walsh_2015_Sci.Rep_5_14832
Author(s) : Walsh R , Morales JM , Skipwith CG , Ruckh TT , Clark HA
Ref : Sci Rep , 5 :14832 , 2015
Abstract : It is currently difficult to measure small dynamics of molecules in the brain with high spatial and temporal resolution while connecting them to the bigger picture of brain function. A step towards understanding the underlying neural networks of the brain is the ability to sense discrete changes of acetylcholine within a synapse. Here we show an efficient method for generating acetylcholine-detecting nanosensors based on DNA dendrimer scaffolds that incorporate butyrylcholinesterase and fluorescein in a nanoscale arrangement. These nanosensors are selective for acetylcholine and reversibly respond to levels of acetylcholine in the neurophysiological range. This DNA dendrimer architecture has the potential to overcome current obstacles to sensing in the synaptic environment, including the nanoscale size constraints of the synapse and the ability to quantify the spatio-temporal fluctuations of neurotransmitter release. By combining the control of nanosensor architecture with the strategic placement of fluorescent reporters and enzymes, this novel nanosensor platform can facilitate the development of new selective imaging tools for neuroscience.
ESTHER : Walsh_2015_Sci.Rep_5_14832
PubMedSearch : Walsh_2015_Sci.Rep_5_14832
PubMedID: 26442999

Title : Synergistic inhibition of butyrylcholinesterase by galantamine and citalopram - Walsh_2011_Biochim.Biophys.Acta_1810_1230
Author(s) : Walsh R , Rockwood K , Martin E , Darvesh S
Ref : Biochimica & Biophysica Acta , 1810 :1230 , 2011
Abstract : BACKGROUND: Many persons with Alzheimer's disease (AD) treated with galantamine appear to receive additional cognitive benefit from citalopram. Both drugs inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). These enzymes co-regulate acetylcholine catabolism. In AD brain, AChE is diminished while BuChE is not, suggesting BuChE inhibition may be important in raising acetylcholine levels. BuChE is subject to activation at high acetylcholine levels reached at the synaptic cleft. The present study explores one way combining galantamine and citalopram could be beneficial in AD. METHODS: Spectrophotometric studies of BuChE catalysis in the absence or presence of galantamine or citalopram or both, were performed using the Ellman method. Data analysis involved expansion of our previous equation describing BuChE catalysis. RESULTS: Galantamine almost completely inhibited BuChE at low substrate concentrations (V(S)=43.6 muM/min; V(S(gal))=0.34 muM/min) without influencing the substrate-activated form of the enzyme (V(SS)=64.0 muM/min;V(SS(gal))=62.3 muM/min). Conversely, citalopram inhibited both un-activated (V(S)=43.6 muM/min; V(S(cit))=10.2 muM/min) and substrate-activated (V(SS)=64.0 muM/min; V(SS(cit))=47.3 muM/min) forms of BuChE. Combined galantamine and citalopram increased inhibition of un-activated BuChE (V(S)=43.6 muM/min; V(S(gal)(cit))=2.73 muM/min) and substrate-activated form (V(SS)=64.0 muM/min; V(SS(gal)(cit))=42.2 muM/min). CONCLUSION: Citalopram and galantamine produce a combined inhibition of BuChE that is considered to be synergistic. GENERAL SIGNIFICANCE: Clinical benefit from combined galantamine and citalopram may be related to a synergistic inhibition of BuChE, facilitating cholinergic neurotransmission. This emphasizes the importance of further study into use of drug combinations in AD treatment.
ESTHER : Walsh_2011_Biochim.Biophys.Acta_1810_1230
PubMedSearch : Walsh_2011_Biochim.Biophys.Acta_1810_1230
PubMedID: 21872646

Title : Potentially procholinergic effects of medications commonly used in older adults - Rockwood_2011_Am.J.Geriatr.Pharmacother_9_80
Author(s) : Rockwood K , Walsh R , Martin E , Darvesh S
Ref : Am J Geriatr Pharmacother , 9 :80 , 2011
Abstract : BACKGROUND: Older adults are susceptible to a variety of illnesses, many of which can be treated with medications that may need to be used for the long term. Considerable attention has been paid to drugs that, in addition to their intended function, may have an anticholinergic effect that results in undesirable side effects, including impairment in cognition. Cholinesterase inhibitors are used as procholinergic drugs to improve cognitive dysfunction in Alzheimer's disease. We hypothesized that some of the drugs commonly used by older adults might, in addition to their intended function, also have procholinergic effects by virtue of inhibiting cholinesterases. OBJECTIVE: To determine the potential procholinergic nature of some of the commonly used drugs by examining their cholinesterase inhibiting properties. METHODS: The Ellman spectrophotometric method was used with human acetylcholinesterase and butyrylcholinesterase, in the absence and presence of increasing concentrations of each test drug. To compare inhibition potencies, from enzyme kinetic data, we determined half maximal inhibitory concentration (IC(50) values) for each cholinesterase by each drug. RESULTS: Of the 28 drugs examined, over half (17/28) inhibited one or both of the human cholinesterases. The inhibition potencies were often within 1 to 2 orders of magnitude of reversible cholinesterase inhibitors currently used to treat Alzheimer's disease. These included trazodone, quetiapine, risperidone, indapamide, and perindopril. CONCLUSIONS: Many drugs used by older adults for other reasons have potentially clinically relevant procholinergic effects. The effect of cumulative cholinesterase inhibition merits clinical evaluation.
ESTHER : Rockwood_2011_Am.J.Geriatr.Pharmacother_9_80
PubMedSearch : Rockwood_2011_Am.J.Geriatr.Pharmacother_9_80
PubMedID: 21459311

Title : Differential binding of phenothiazine urea derivatives to wild-type human cholinesterases and butyrylcholinesterase mutants - Darvesh_2010_Bioorg.Med.Chem_18_2232
Author(s) : Darvesh S , Pottie IR , Darvesh KV , McDonald RS , Walsh R , Conrad S , Penwell A , Mataija D , Martin E
Ref : Bioorganic & Medicinal Chemistry , 18 :2232 , 2010
Abstract : A series of N-10 urea derivatives of phenothiazine was synthesized and each compound was evaluated for its ability to inhibit human cholinesterases. Most were specific inhibitors of BuChE. However, the potent inhibitory effects on both cholinesterases of one sub-class, the cationic aminoureas, provide an additional binding mechanism to cholinesterases for these compounds. The comparative effects of aminoureas on wild-type BuChE and several BuChE mutants indicate a binding process involving salt linkage with the aspartate of the cholinesterase peripheral anionic site. The effect of such compounds on cholinesterase activity at high substrate concentration supports ionic interaction of aminoureas at the peripheral anionic site.
ESTHER : Darvesh_2010_Bioorg.Med.Chem_18_2232
PubMedSearch : Darvesh_2010_Bioorg.Med.Chem_18_2232
PubMedID: 20181484

Title : Carbamates with differential mechanism of inhibition toward acetylcholinesterase and butyrylcholinesterase - Darvesh_2008_J.Med.Chem_51_4200
Author(s) : Darvesh S , Darvesh KV , McDonald RS , Mataija D , Walsh R , Mothana S , Lockridge O , Martin E
Ref : Journal of Medicinal Chemistry , 51 :4200 , 2008
Abstract : Most carbamates are pseudoirreversible inhibitors of cholinesterases. Phenothiazine carbamates exhibit this inhibition of acetylcholinesterase but produce reversible inhibition of butyrylcholinesterase, suggesting that they do not form a covalent bond with the catalytic serine. This atypical inhibition is attributable to pi-pi interaction of the phenothiazine moiety with F329 and Y332 in butyrylcholinesterase. These residues are in a helical segment, referred to here as the E-helix because it contains E325 of the catalytic triad. The involvement of the E-helix in phenothiazine carbamate reversible inhibition of butyrylcholinesterase is confirmed using mutants of this enzyme at A328, F329, or Y332 that show typical pseudoirreversible inhibition. Thus, in addition to various domains of the butyrylcholinesterase active site gorge, such as the peripheral anionic site and the pi-cationic site of the Omega-loop, the E-helix represents a domain that could be exploited for development of specific inhibitors to treat dementias.
ESTHER : Darvesh_2008_J.Med.Chem_51_4200
PubMedSearch : Darvesh_2008_J.Med.Chem_51_4200
PubMedID: 18570368

Title : A versatile equation to describe reversible enzyme inhibition and activation kinetics: modeling beta-galactosidase and butyrylcholinesterase - Walsh_2007_Biochim.Biophys.Acta_1770_733
Author(s) : Walsh R , Martin E , Darvesh S
Ref : Biochimica & Biophysica Acta , 1770 :733 , 2007
Abstract : Current treatments for Alzheimer's disease involve inhibiting cholinesterases. Conversely, cholinesterase stimulation may be deleterious. Homocysteine is a known risk factor for Alzheimer's and vascular diseases and its active metabolite, homocysteine thiolactone, stimulates butyrylcholinesterase. Considering the opposing effects on butyrylcholinesterase of homocysteine thiolactone and cholinesterase inhibitors, understanding how these molecules alter this enzyme may provide new insights in the management of dementia. Butyrylcholinesterase does not strictly adhere to Michaelis-Menten parameters since, at higher substrate concentrations, enzyme activation occurs. The substrate activation equation for butyrylcholinesterase does not describe the effects of inhibitors or non-substrate activators. To address this, global data fitting was used to generate a flexible equation based on Michaelis-Menten principles. This methodology was first tested to model complexities encountered in inhibition by imidazole of beta-galactosidase, an enzyme that obeys Michaelis-Menten kinetics. The resulting equation was sufficiently flexible to permit expansion for modeling activation or inhibition of butyrylcholinesterase, while accounting for substrate activation of this enzyme. This versatile equation suggests that both the inhibitor and non-substrate activator examined here have little effect on the substrate-activated form of butyrylcholinesterase. Given that butyrylcholinesterase inhibition can antagonize stimulation of this enzyme by homocysteine thiolactone, cholinesterase inhibition may have a role in treating Alzheimer and vascular diseases related to hyperhomocysteinemia.
ESTHER : Walsh_2007_Biochim.Biophys.Acta_1770_733
PubMedSearch : Walsh_2007_Biochim.Biophys.Acta_1770_733
PubMedID: 17307293

Title : Selective reversible inhibition of human butyrylcholinesterase by aryl amide derivatives of phenothiazine - Darvesh_2007_Bioorg.Med.Chem_15_6367
Author(s) : Darvesh S , McDonald RS , Darvesh KV , Mataija D , Conrad S , Gomez G , Walsh R , Martin E
Ref : Bioorganic & Medicinal Chemistry , 15 :6367 , 2007
Abstract : Evidence suggests that specific inhibition of butyrylcholinesterase may be an appropriate focus for the development of more effective drugs to treat dementias such as Alzheimer's disease. Butyrylcholinesterase is a co-regulator of cholinergic neurotransmission and its activity is increased in Alzheimer's disease, and is associated with all neuropathological lesions in this disease. Some selective butyrylcholinesterase inhibitors have already been reported to increase acetylcholine levels and to reduce the formation of abnormal amyloid found in Alzheimer's disease. Synthesized N-(10)-aryl and N-(10)-alkylaryl amides of phenothiazine are specific inhibitors of butyrylcholinesterase. In some cases, inhibition constants in the nanomolar range are achieved. Enzyme specificity and inhibitor potency of these molecules can be related to molecular volumes, steric and electronic factors. Computed logP values indicate high potential for these compounds to cross the blood-brain barrier. Use of such butyrylcholinesterase inhibitors could provide direct evidence for the importance of this enzyme in the normal nervous system and in Alzheimer's disease.
ESTHER : Darvesh_2007_Bioorg.Med.Chem_15_6367
PubMedSearch : Darvesh_2007_Bioorg.Med.Chem_15_6367
PubMedID: 17681768

Title : Homocysteine thiolactone and human cholinesterases - Darvesh_2007_Cell.Mol.Neurobiol_27_33
Author(s) : Darvesh S , Walsh R , Martin E
Ref : Cellular Molecular Neurobiology , 27 :33 , 2007
Abstract : 1. The cholinergic system is important in cognition and behavior as well as in the function of the cerebral vasculature. 2. Hyperhomocysteinemia is a risk factor for development of both dementia and cerebrovascular disease. 3. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) are serine hydrolase enzymes that catalyze the hydrolysis of the neurotransmitter acetylcholine, a key process in the regulation of the cholinergic system. 4. It has been hypothesized that the deleterious effects of elevated homocysteine may, in part, be due to its actions on cholinesterases. 5. To further test this hypothesis, homocysteine and a number of its metabolites and analogues were examined for effects on the activity of human cholinesterases. 6. Homocysteine itself did not have any measurable effect on the activity of these enzymes. 7. Homocysteine thiolactone, the cyclic metabolite of homocysteine, slowly and irreversibly inhibited the activity of human AChE. 8. Conversely, this metabolite and some of its analogues significantly enhanced the activity of human BuChE. 9. Structure-activity studies indicated that the unprotonated amino group of homocysteine thiolactone and related compounds represents the essential feature for activation of BuChE, whereas the thioester linkage appears to be responsible for the slow AChE inactivation. 10. It is concluded that hyperhomocysteinemia may exert its adverse effects, in part, through the metabolite of homocysteine, homocysteine thiolactone, which is capable of altering the activity of human cholinesterases, the most pronounced effect being BuChE activation.
ESTHER : Darvesh_2007_Cell.Mol.Neurobiol_27_33
PubMedSearch : Darvesh_2007_Cell.Mol.Neurobiol_27_33
PubMedID: 16955366

Title : On the active site for hydrolysis of aryl amides and choline esters by human cholinesterases - Darvesh_2006_Bioorg.Med.Chem_14_4586
Author(s) : Darvesh S , McDonald RS , Darvesh KV , Mataija D , Mothana S , Cook H , Carneiro KM , Richard N , Walsh R , Martin E
Ref : Bioorganic & Medicinal Chemistry , 14 :4586 , 2006
Abstract : Cholinesterases, in addition to their well-known esterase action, also show an aryl acylamidase (AAA) activity whereby they catalyze the hydrolysis of amides of certain aromatic amines. The biological function of this catalysis is not known. Furthermore, it is not known whether the esterase catalytic site is involved in the AAA activity of cholinesterases. It has been speculated that the AAA activity, especially that of butyrylcholinesterase (BuChE), may be important in the development of the nervous system and in pathological processes such as formation of neuritic plaques in Alzheimer's disease (AD). The substrate generally used to study the AAA activity of cholinesterases is N-(2-nitrophenyl)acetamide. However, use of this substrate requires high concentrations of enzyme and substrate, and prolonged periods of incubation at elevated temperature. As a consequence, difficulties in performing kinetic analysis of AAA activity associated with cholinesterases have hampered understanding this activity. Because of its potential biological importance, we sought to develop a more efficient and specific substrate for use in studying the AAA activity associated with BuChE, and for exploring the catalytic site for this hydrolysis. Here, we describe the structure-activity relationships for hydrolysis of anilides by cholinesterases. These studies led to a substrate, N-(2-nitrophenyl)trifluoroacetamide, that was hydrolyzed several orders of magnitude faster than N-(2-nitrophenyl)acetamide by cholinesterases. Also, larger N-(2-nitrophenyl)alkylamides were found to be more rapidly hydrolyzed by BuChE than N-(2-nitrophenyl)acetamide and, in addition, were more specific for hydrolysis by BuChE. Thus, N-(2-nitrophenyl)alkylamides with six to eight carbon atoms in the acyl group represent suitable specific substrates to investigate further the function of the AAA activity of BuChE. Based on the substrate structure-activity relationships and kinetic studies, the hydrolysis of anilides and esters of choline appears to utilize the same catalytic site in BuChE.
ESTHER : Darvesh_2006_Bioorg.Med.Chem_14_4586
PubMedSearch : Darvesh_2006_Bioorg.Med.Chem_14_4586
PubMedID: 16504521

Title : Structure-activity relationships for inhibition of human cholinesterases by alkyl amide phenothiazine derivatives - Darvesh_2005_Bioorg.Med.Chem_13_211
Author(s) : Darvesh S , McDonald RS , Penwell A , Conrad S , Darvesh KV , Mataija D , Gomez G , Caines A , Walsh R , Martin E
Ref : Bioorganic & Medicinal Chemistry , 13 :211 , 2005
Abstract : Several lines of evidence indicate that inhibition of butyrylcholinesterase (BuChE) is important in the treatment of certain dementias. Further testing of this concept requires inhibitors that are both BuChE-selective and robust. N-alkyl derivatives (2, 3, 4) of phenothiazine (1) have previously been found to inhibit only BuChE in a mechanism involving pi-pi interaction between the phenothiazine tricyclic ring system and aromatic residues in the active site gorge. To explore features of phenothiazines that affect the selectivity and potency of BuChE inhibition, a series of N-carbonyl derivatives (5-25) was synthesized and examined for the ability to inhibit cholinesterases. Some of the synthesized derivatives also inhibited AChE through a different mechanism involving carbonyl interaction within the active site gorge. Binding of these derivatives takes place within the gorge, since this inhibition disappears when the molecular volume of the derivative exceeds the estimated active site gorge volume of this enzyme. In contrast, BuChE, with a much larger active site gorge, exhibited inhibition that increased directly with the molecular volumes of the derivatives. This study describes two distinct mechanisms for binding phenothiazine amide derivatives to BuChE and AChE. Molecular volume was found to be an important parameter for BuChE-specific inhibition.
ESTHER : Darvesh_2005_Bioorg.Med.Chem_13_211
PubMedSearch : Darvesh_2005_Bioorg.Med.Chem_13_211
PubMedID: 15582466

Title : Differential effects of lipid-lowering agents on human cholinesterases - Darvesh_2004_Clin.Biochem_37_42
Author(s) : Darvesh S , Martin E , Walsh R , Rockwood K
Ref : Clinical Biochemistry , 37 :42 , 2004
Abstract : OBJECTIVES: Epidemiologic reports indicate that lipid-lowering agents (LLAs) protect against dementia. We hypothesized that LLAs might affect cholinergic systems. The effects of LLAs on the activity of cholinesterases were examined. DESIGN AND
METHODS: Odds ratios and relative risks were calculated from clinical studies of LLAs and dementia and compared with their impacts on human cholinesterases. Representative LLAs were examined for their effects on the activity of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) using Ellman's assay.
RESULTS: Epidemiological studies, but not clinical trials, showed lower odds of dementia in patients taking "statins". Comparison of LLAs indicated that "statins" most consistently produced apparent protection. Individual "statins" showed differential cholinesterase inhibition. Lovastatin and simvastatin significantly inhibited butyrylcholinesterase, while mevastatin, pravastatin and the "non-statins" did not. None of the LLAs inhibited acetylcholinesterase.
CONCLUSIONS: Some "statins" inhibit butyrylcholinesterase. This inhibition suggests a possible means whereby "statins" could protect against dementia.
ESTHER : Darvesh_2004_Clin.Biochem_37_42
PubMedSearch : Darvesh_2004_Clin.Biochem_37_42
PubMedID: 14675561

Title : Inhibition of human cholinesterases by drugs used to treat Alzheimer disease - Darvesh_2003_Alzheimer.Dis.Assoc.Disord_17_117
Author(s) : Darvesh S , Walsh R , Kumar R , Caines A , Roberts S , Magee D , Rockwood K , Martin E
Ref : Alzheimer Disease & Associated Disorders , 17 :117 , 2003
Abstract : Current approaches to the treatment of cognitive and behavioral symptoms of Alzheimer disease emphasize the use of cholinesterase inhibitors. The kinetic effects of the cholinesterase inhibitors donepezil, galantamine, metrifonate, physostigmine, rivastigmine, and tetrahydroaminoacridine were examined with respect to their action on the esterase and aryl acylamidase activities of human acetylcholinesterase (AChE) and human butyrylcholinesterase (BuChE). Each of these drugs inhibited both AChE and BuChE, but to different degrees. Inhibition of BuChE by these compounds was approximately the same, or better, when acetylthiocholine, the analog of the neurotransmitter acetylcholine, was used as the substrate, instead of butyrylthiocholine. In addition, for these drugs, the inhibition of aryl acylamidase activity paralleled that observed for inhibition of esterase activity of AChE and BuChE. Given that drugs that are currently in use for the treatment of Alzheimer disease inhibit both AChE and BuChE, the development of drugs targeted toward the exclusive inhibition of one or the other cholinesterase may be important for understanding the relative importance of inhibition of BuChE and AChE in the treatment of this disease.
ESTHER : Darvesh_2003_Alzheimer.Dis.Assoc.Disord_17_117
PubMedSearch : Darvesh_2003_Alzheimer.Dis.Assoc.Disord_17_117
PubMedID: 12794390

Title : Enantiomer effects of huperzine A on the aryl acylamidase activity of human cholinesterases - Darvesh_2003_Cell.Mol.Neurobiol_23_93
Author(s) : Darvesh S , Walsh R , Martin E
Ref : Cellular Molecular Neurobiology , 23 :93 , 2003
Abstract : 1. Acetylcholinesterase (AChE, EC and butyrylcholinesterase (BuChE, EC are serine hydrolase enzymes that catalyze the hydrolysis of acetylcholine. 2. (-) Huperzine A is an inhibitor of AChE and is being considered for the treatment of Alzheimer's disease. 3. In addition to esterase activity, AChE and BuChE have intrinsic aryl acylamidase activity. 4. The function of aryl acylamidase is unknown but has been speculated to be important in Alzheimer pathology. 5. Kinetic effects of (-) huperzine A and (+/-) huperzine A on the aryl acylamidase activity of human cholinesterases were examined. 6. (-) Huperzine A inhibited the aryl acylamidase activities of both AChE and BuChE. 7. (+/-) Huperzine A inhibited this function in AChE but stimulated BuChE aryl acylamidase suggesting that the (+) enantiomer is a powerful activator of this enzyme activity. 8. The two huperzine enantiomers may prove to be useful tools to examine the function of aryl acylamidase activity, including its role in Alzheimer pathology.
ESTHER : Darvesh_2003_Cell.Mol.Neurobiol_23_93
PubMedSearch : Darvesh_2003_Cell.Mol.Neurobiol_23_93
PubMedID: 12701885

Title : Butyrylcholinesterase-Mediated enhancement of the enzymatic activity of trypsin - Darvesh_2001_Cell.Mol.Neurobiol_21_285
Author(s) : Darvesh S , Kumar R , Roberts S , Walsh R , Martin E
Ref : Cellular Molecular Neurobiology , 21 :285 , 2001
Abstract : 1. Acetylcholinesterase (AChE, EC and butyrylcholinesterase (BuChE, EC are enzymes that catalyze the hydrolysis of esters of choline. 2. Both AChE and BuChE have been shown to copurify with peptidases. 3. BuChE has also been shown to copurify with other proteins such as transferrin, with which it forms a stable complex. In addition, BuChE is found in association with beta-amyloid protein in Alzheimer brain tissues. 4. Since BuChE copurifies with peptidases, we hypothesized that BuChE interacts with these enzymes and that this association had an influence on their catalytic activities. One of the peptidases that copurifies with cholinesterases has specificity similar to trypsin, hence, this enzyme was used as a model to test this hypothesis. 5. Purified BuChE causes a concentration-dependent enhancement of the catalytic activity of trypsin while trypsin does not influence the catalytic activity of BuChE. 6. We suggest that, in addition to its esterase activity, BuChE may assume a regulatory role by interacting with other proteins.
ESTHER : Darvesh_2001_Cell.Mol.Neurobiol_21_285
PubMedSearch : Darvesh_2001_Cell.Mol.Neurobiol_21_285
PubMedID: 11569538