title: Additive effects of a cholinesterase inhibitor and a histamine inverse agonist on scopolamine deficits in humans.
abstract: BACKGROUND
  Enhancement of histaminergic neurotransmission or histaminergic plus cholinergic neurotransmission may represent novel strategies for improving cognition in Alzheimer's disease.
  
  
  OBJECTIVE
  To evaluate the effects of a novel histamine H3 receptor inverse agonist (MK-3134), an acetylcholinesterase inhibitor (donepezil), and their combination in attenuating the cognitive impairment associated with scopolamine.
  
  
  METHODS
  Thirty-one subjects were randomized, and 28 completed this double-blind, placebo-controlled, five-period crossover study. Cognition was assessed using the Groton Maze Learning Task (GMLT) as the primary outcome measure. The two primary hypotheses were that donepezil 10 mg and MK-3134 25 mg, respectively, would attenuate scopolamine (0.5 mg)-induced impairment as measured by the GMLT over the first 12 h after scopolamine administration (AUC(1-12)  (h)). A secondary hypothesis was that the combination of donepezil and MK-3134 would attenuate scopolamine-induced cognitive impairment to a greater extent than either agent alone as measured by the GMLT AUC(1-12 h).
  
  
  RESULTS
  The primary and secondary hypotheses were not met. Upon examining the time course of the scopolamine effects (an exploratory objective), peak effects were generally observed around 2 h after scopolamine administration. Administration of MK-3134 or donepezil improved performance on the GMLT at the 2-h time point, rather than AUC(1-12 h), compared with scopolamine alone. Moreover, it appeared that the combination of MK-3134 and donepezil blunted the scopolamine effect to a greater extent than either drug alone.
  
  
  CONCLUSIONS
  Exploratory analyses provide evidence for cognitive improvement through inverse agonism of the H3 histamine receptor and for cooperation between human cholinergic and histaminergic neurotransmitter systems. (ClinicalTrials.gov trial registration number: NCT01181310).
authors.affiliation: Merck Sharp & Dohme Corp, Whitehouse Station, NJ, USA. cho.william@gene.com
authors.forename: William
authors.initials: W
authors.lastname: Cho
authors.forename: Paul
authors.initials: P
authors.lastname: Maruff
authors.forename: John
authors.initials: J
authors.lastname: Connell
authors.forename: Cindy
authors.initials: C
authors.lastname: Gargano
authors.forename: Nicole
authors.initials: N
authors.lastname: Calder
authors.forename: Scott
authors.initials: S
authors.lastname: Doran
authors.forename: Sabrina
authors.initials: S
authors.lastname: Fox-Bosetti
authors.forename: Aizza
authors.initials: A
authors.lastname: Hassan
authors.forename: John
authors.initials: J
authors.lastname: Renger
authors.forename: Gary
authors.initials: G
authors.lastname: Herman
authors.forename: Christopher
authors.initials: C
authors.lastname: Lines
authors.forename: Ajay
authors.initials: A
authors.lastname: Verma
mesh_terms: D000328:Adult; D019540:Area Under Curve; D018680:Cholinergic Antagonists / Q000009:adverse effects; D002800:Cholinesterase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D003071:Cognition / Q000187:drug effects*; D018592:Cross-Over Studies; D000077265:Donepezil; D004311:Double-Blind Method; D054314:Drug Inverse Agonism; D004359:Drug Therapy, Combination; D017442:Histamine Agonists / Q000008:administration & dosage / Q000494:pharmacology; D006801:Humans; D007189:Indans / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D010880:Piperidines / Q000008:administration & dosage / Q000494:pharmacology*; D018100:Receptors, Histamine H3 / Q000187:drug effects / Q000378:metabolism; D012601:Scopolamine / Q000009:adverse effects*; D055815:Young Adult
chemical_list: D018680:Cholinergic Antagonists; D002800:Cholinesterase Inhibitors; D017442:Histamine Agonists; D007189:Indans; D010880:Piperidines; D018100:Receptors, Histamine H3; D000077265:Donepezil; D012601:Scopolamine