title: (R,S)-Ketamine metabolites (R,S)-norketamine and (2S,6S)-hydroxynorketamine increase the mammalian target of rapamycin function.
abstract: BACKGROUND
  Subanesthetic doses of (R,S)-ketamine are used in the treatment of neuropathic pain and depression. In the rat, the antidepressant effects of (R,S)-ketamine are associated with increased activity and function of mammalian target of rapamycin (mTOR); however, (R,S)-ketamine is extensively metabolized and the contribution of its metabolites to increased mTOR signaling is unknown.
  
  
  METHODS
  Rats (n = 3 per time point) were given (R,S)-ketamine, (R,S)-norketamine, and (2S,6S)-hydroxynorketamine and their effect on the mTOR pathway determined after 20, 30, and 60 min. PC-12 pheochromocytoma cells (n = 3 per experiment) were treated with escalating concentrations of each compound and the impact on the mTOR pathway was determined.
  
  
  RESULTS
  The phosphorylation of mTOR and its downstream targets was significantly increased in rat prefrontal cortex tissue by more than ~2.5-, ~25-, and ~2-fold, respectively, in response to a 60-min postadministration of (R,S)-ketamine, (R,S)-norketamine, and (2S,6S)-hydroxynorketamine (P < 0.05, ANOVA analysis). In PC-12 pheochromocytoma cells, the test compounds activated the mTOR pathway in a concentration-dependent manner, which resulted in a significantly higher expression of serine racemase with ~2-fold increases at 0.05 nM (2S,6S)-hydroxynorketamine, 10 nM (R,S)-norketamine, and 1,000 nM (R,S)-ketamine. The potency of the effect reflected antagonistic activity of the test compounds at the α7-nicotinic acetylcholine receptor.
  
  
  CONCLUSIONS
  The data demonstrate that (R,S)-norketamine and (2S,6S)-hydroxynorketamine have potent pharmacological activity both in vitro and in vivo and contribute to the molecular effects produced by subanesthetic doses of (R,S)-ketamine. The results suggest that the determination of the mechanisms underlying the antidepressant and analgesic effects of (R,S)-ketamine requires a full study of the parent compound and its metabolites.
authors.affiliation: From the Laboratory of Clinical Investigation (R.K.P., N.S.S., M.K., R.M., M.S., I.W.W.) and Translational Gerontology Branch (M.B.), National Institute on Aging, National Institutes of Health, Baltimore, Maryland; SRI Biosciences, SRI International, Menlo Park, California (C.E.G., K.O.); and Department of Anesthesiology, Cooper Medical School of Rowan University, Camden, New Jersey (M.C.T., I.W.W.).
authors.forename: Rajib K
authors.initials: RK
authors.lastname: Paul
authors.forename: Nagendra S
authors.initials: NS
authors.lastname: Singh
authors.forename: Mohammed
authors.initials: M
authors.lastname: Khadeer
authors.forename: Ruin
authors.initials: R
authors.lastname: Moaddel
authors.forename: Mitesh
authors.initials: M
authors.lastname: Sanghvi
authors.forename: Carol E
authors.initials: CE
authors.lastname: Green
authors.forename: Kathleen
authors.initials: K
authors.lastname: O'Loughlin
authors.forename: Marc C
authors.initials: MC
authors.lastname: Torjman
authors.forename: Michel
authors.initials: M
authors.lastname: Bernier
authors.forename: Irving W
authors.initials: IW
authors.lastname: Wainer
mesh_terms: D000157:Aconitine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D007649:Ketamine / Q000031:analogs & derivatives* / Q000032:analysis / Q000493:pharmacokinetics / Q000494:pharmacology; D008297:Male; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D016716:PC12 Cells; D010766:Phosphorylation; D017397:Prefrontal Cortex / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000187:drug effects*
chemical_list: D018691:Excitatory Amino Acid Antagonists; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; C054634:methyllycaconitine; D007649:Ketamine; D009538:Nicotine; C050654:6-hydroxynorketamine; D058570:TOR Serine-Threonine Kinases; D000157:Aconitine; C033419:norketamine