Cholinergic agents such as nicotine, muscarine, and pilocarpine act by mimicking acetylcholine at nicotinic and muscarinic sites. Acetylcholinesterase inhibitors such as neostigmine, pyridostigmine, and organophosphates promote the accumulation of acetylcholine by irreversibly or reversibly inhibiting the enzyme. These agents are used therapeutically for conditions like glaucoma but produce toxic effects in high doses by overstimulating cholinergic receptors. Pralidoxime can reactivate phosphorylated acetylcholinesterase and reverse some effects of organophosphate poisoning.

1. Cholinergic Agents

2. Cholinergic Agents Alkaloids Nicotine Lobeline Arecoline Muscarine Pilocarpine Synthetic Agents Dimethylphenylpiperazinium-(DMPP) Oxotremorine Methacholine Bethanechol Carbachol Cevimeline

6. Structure of Acetylcholine and its Derivatives Acetylcholine Methacholine Bethanechol Carbachol

10. Agents That Inhibit Acetylcholinesterase

11. Acetylcholinesterase (True Cholinesterase)

15. Butyrylcholinesterase (Plasma esterase, pseudocholinesterase, serum esterase, BuChE, PseudoChE)

18. Active Site of Acetylcholinesterase

19. Interaction of AChE and Acetylcholine

21. Acetylation of AChE and Release of Choline

22. Hydroxyl Group of Water Attacks the Carbonyl Group of Acetylated-AChE to Liberate AChE

23. Carbamyl Inhibitors of AChE

28. Neostigmine Carbamylates Acetylcholinesterase

29. Slow Hydrolysis of Carbamylated-AChE and Enzyme Liberation

30. Organophosphate Inhibitors of Acetylcholinesterase

35. Diisopropylflurophosphate (DFP) is a Substrate for AChE

36. The Extremely Slow Hydrolysis of Phosphorylated-AChE New enzyme synthesis is required for recovery of enzyme function

37. Various “States” of Acetylcholinesterase Clockwise: free AChE, acetylated AChE, carbamylated AChE, phosphorylated AChE

38. Acetylated-AChE Is Very Rapdily Hydrolyzed AChE + Acetylcholine  AChE-acetylated + choline AChE-acetylated + H 2 O  AChE + acetate Hydrolysis of AChE-acetylated is rapid, in the order of microseconds P

39. Carbamylated-AChE Is Hydrolyzed Slowly AChE + Carbamyl inhibitor  AChE-carbamylated + noncarbamylated metabolite AChE-carbamylated + H 2 O  AChE + carbamic acid derivative Hydrolysis of the AChE-carbamylated is slow, in the order of hours. The carbamylated enzyme is reversibly inhibited, and recovery of function is in the order of hours Enzyme after phosphorylation by neostigmine

40. Phosphorlylated-AChE Is Hydrolyzed Extremely Slowly AChE + organophosphate inhibitor  AChE-phosphorylated + nonphosphorylated metabolite AChE-phosphorylated + H 2 O  AChE + phosphorylated derivative Hydrolysis of the AChE-phosphorylated is extremely slow, in the order of days. The phosphorylated enzyme is considered to be irreversibly inhibited, and recovery of function is in the order of days. Pralidoxime, a reactivating agent, may be adminstered to a subject before the enzyme has “aged.” Enzyme after phosphorylation by DFP

41. AGING OF ACETYLCHOLINESTERASE

42. Loss of An Alkyl Group From Phosphorylated AChE “Ages” the Enzyme AChE, phosphorylated and inhibited by DFP “ Aged” AChE

43. “ Aging” of Phosphorylated- AChE

44. Cholinesterase Reactivation

46. Pralidoxime Reacts Chemically with Phosphorylated-AChE The oxime group makes a nucleophilic attack upon the phosphorus atom

47. Oxime Phosphonate and Regenerated AChE

50. Edrophonium

51. Edrophonium is a Short Acting Inhibitor that Binds to the Ionic Site but Not to the Esteratic Site of AChE

52. Pharmacology of Acetylcholinesterase Inhibition

53. Inhibition of Acetylcholinesterase Produces Stimulation of All Cholinergic Sites

58. Determining Proper Dose of AChE Inhibitor

60. Organophosphate Inhibitors of AChE

62. Organophosphate Inhibitors - 2 Diisopropylfluorophosphate (DFP) Soman Sarin Tabun

63. Echothiophate Therapeutic use - local application to the eye for wide angle glaucoma

64. Conversion of Parathion to Paraoxon

65. Conversion of Malathion to Malaoxon

66. Malathion Is Hydrolyzed by Plasma Carboxylases in Birds and Mammals but Not Insects

72. NERVE AGENT VX Chemical name: O-ETHYL-S-(2-DIISOPROPYLAMINOMETHYL)METHYL-PHOSHONOTHIOLATE Trade name: PHOSPHONOTHIOIC ACID NERVE AGENT VX

73. NERVE AGENT VX Chemical name: O-ETHYL-S-(2-DIISOPROPYLAMINOMETHYL)METHYL-PHOSHONOTHIOLATE Trade name: PHOSPHONOTHIOIC ACID

76. Use of Pyridostigmine During the Gulf War