Anticholinesterase Agents

Brian J. Piper, Ph.D., M.S.

Goals

• Synthesis & Breakdown of Acetylcholine• Therapeutics & Toxicology

Dietary Sources of Choline

http://lpi.oregonstate.edu/infocenter/othernuts/choline/

Biosynthesis of Acetylcholine

ACh: AcetylcholineAcCoA: acetyl coenzyme ACAT: choline acetyltransferase

Stahl (2008). Essential Psychopharmacology. p. 914.

Stahl (2008). Essential Psychopharmacology.

Anatomy of cholinergic pathways

• Nucleas basilis (Basal Forebrain): connections to frontal cortex, important for cognition

• Caudate-Putamen: important for motor functionMeyer & Quezner (2001). Psychopharmacology.

Acetylcholine (ACh) in PNS

ReceptorsN: NicotinicM: Muscarinic

Katzung et al. (2012). Basic & Clinical Pharmacology. p 80.

Acetylcholine Breakdown

BuChE: butyrylcholinesterase (pseudo), liver, plasmaVAChT: Vesicular Acetylcholine Transporter

See also Animation: Cholinergic Neuroeffector Junction

Stahl (2008). Essential Psychopharmacology. p. 915.

Acetycholinesterase (AChE) Gorge Structure

Acyl Pocket (AP): Pheylalanine 295 & 297

Choline Subsite (CS):Tryptophan 86Glutamic Acid 202Tyrosine 337

Catalytic Triad (CT):Glutamic Acid 334Histidine 447Serine 203 (phophorylation)

Bourne et al. (1995). Cell, 83, 493-506.

CT

CS

AP

Oneata Gorge, OR

Colombia River

Acetycholinesterase Gorge Structure

Acyl Pocket (AP):

Choline Subsite (CS):

Catalytic Triad (CT):

Peripheral (Rim) Binding Site (PBS):Tryptophan 286Tryptophan 124Tryptophan 72

Bourne et al. (1995). Cell, 83, 493-506.

CT

CS

AP

PBS

Physostigmine• Found in seed (Calabar bean) of African plant Physostigma

venenosum• Reversible acetylcholinesterase inhibitor• Ordeal Poison: accusation of demonic possession– Winner: vomited (or didn’t chew beans)– Loser: miosis, excessive salivation, decreased

bowel/bladder control, seizures, asphyxiation!• Used for glaucoma & belladonna overdose

Pronunciation: http://dictionary.reference.com/browse/Physostigmine?s=t

Sarin (GB)

• Colorless, odorless, liquid named after German scientists (Schrader, Ambros, Rudinger & Van der LINde) in 1938

• Used in Subway Sarin Incident of 1995 (killed 13, injured 50)

• Inhalation & skin absorption

Pesticides

• herbicides (plants), fungicides, pediculicides (lice), acaracide (ticks & mites), biocides (microorganisms), rodenticides

• Insecticides– Organophosphates (malathion): long-acting, irreversible,

phosphorylate active site– Carbamates: short-acting, reversible, carbamylation of active

site– “One-million people are poisoned by ACh-E inhibitor

insecticides and several hundred thousand die” (world-wide)

Gupta et al. (2012). Organophosphate and carbamate pesticides. In Reproductive Toxicology.

Organophosphate Pesticide (OP)

http://depts.washington.edu/opchild/acute.html

Chyka (2008). Clinicical toxicology. In Pharmacotherapy: A Pathophysiological Approach.

Antidote(s) to Acetycholinesterase Inhibitors

• Atropine: mACh antagonist• Diazepam: GABAA allosteric modulator, seizures• Reactivators: attach to inhibitor & separate inhibitor from

acetylcholinesterase (dephosphorylate)– Examples: pralidoxime (2-PAM), HI-6– Concern: not one reactivator for all AChE-Inhibitors

Bagjar (2010). Acta Medica, 53, 207-211.

Myasthenia Gravis• Autoimmune disorder caused by antibodies against nicotinic

Acetycholine receptors• Therapies include 1) neostigmine & pyridostigmine; 2)

immunosuppresive; 3) thymectomy

0:00 to 0:45 with Jade: http://www.youtube.com/watch?v=XdpW5RMp-T0

Ptosis (toe sis)

Alzheimer’s Disease (AD)

• Neurodegenerative disease• Nucleas basilis is one region affected early• AChE Inhibitors may provide some

symptomatic improvement– Tacrine: short acting, infrequently used– Donepezil: long acting, commonly used

Stahl (2008). Essential Psychopharmacology. p. 921.

Stahl (2008). Essential Psychopharmacology. p. 922.

Alzheimer’s Disease Assessment Scale: Cognitive

• Word Recall: memorize list of words for immediate recall

• Orientation: name, day of week, year, place• Praxis: copy geometric pattern• Word Recognition: get list (A), differentiate A

from other words (B)

Subtle Benefits for AD• Multi-site (23) randomized,

controlled trial (N=468/273) for 3 months.

• ADAS-Cognitive is clinician rated measure of memory, language, and movement (max score = 70).

• Adverse effect (sweating, ↑micturition) were 34% (placebo) versus 51% (Tacrine)

---------------------------------------

Farlow et al. (1992). JAMA, 268(18), 2523-2529.

Organophosphates & ADHD?

• Parents of nationally representative sample of children were interviewed for symptoms of Attention Deficit Hyperactivity Disorder (ADHD) using the Diagnostic Interview Schedule for Children (DISC)

• Child urine was analyzed for levels of organophospate metabolites (DEAP & DMAP)

• Odd’s Ratio: 1.0 events equal, <.5, >1.5 statistically sig

Bouchard et al. (2010). Pediatrics, 125(6), e1270-1277.

Refresher on Goodwin Terminology I (p. 185-194)

antiporter (p. 187): protein that moves two different molecules (e.g. ions) in opposite directions across a plasma membranesatellite cells (p. 189): small progenitor cells found in muscleplexus: intricate network (nerves or blood vessels)myenteric plexus (p. 189): plexus of unmyelinated fibers and postganglionic autonomic cell bodies found in the muscular coat of the esophagus, stomach, & intestines

miosis mydriasis

Refresher on Goodwin Terminology II (Chapter 10)

reversible enzyme inhibitors (p. 239): molecules that bind to enzymes weakly (non-covalent bonds)irreversible enzyme inhibitors (p. 239): molecules that bind to enzymes strongly with covalent bondsEdrophonium (p. 241): reversible acetylcholinesterase inhibitor, used to differentiate myashthenia gravis from a cholinergic crisisschistosomias (p. 245): disease caused by parasitic worm (Schistosoma), associated with unsanitary H2O

conjunctiva (p. 246): mucous membrane that covers eyeballachalasia (p. 246): inability of muscle to relaxatony (p. 246): lack of tone, muscular weaknessantidromic (p. 246): conduction of nerve impulse in the direction opposite of the usual one fasciculation (p. 246): small, localized, involuntary muscle contraction hypoxemia (p. 246): deficiency of oxygen in arterial bloodalkyl: carbon and hydrogenureter (p. 246): duct conveying urine from kidney to bladderalkoxy group (p. 249): alkyl group singly bonded to an oxygenstoichiometry (p. 249): branch of chemistry that deals with relative quantities of reactants & products in chemical reactionspesticide: substance intended for preventing, controlling, or destroying any pest including herbicides (plants), fungicides, pediculicides (lice), biocides (microorganism), & rodenticides dysuria (p. 250): painful urinationesters: chemical compounds consisting of a carbonyl (C=0) adjacent to an ether (R-O-R’)salutary (p. 246): favorable to or promoting health

Alzheimer’s Disease Assessment Scale: Cognitive

Schultz et al. (2001). Braz J of Med & Bio Res, 34, 1295-1302.