Salvinorin A, an Active Component of the Hallucinogenic Sage Salvia divinorum Is a Highly Efficacious -Opioid Receptor Agonist: Structural and Functional Considerations

The diterpene salvinorin A from Salvia divinorum has recently been reported to be a high-affinity and selective -opioid receptor agonist (Roth et al., 2002). Salvinorin A and selected derivatives were found to be potent and efficacious agonists in several measures of agonist activity using cloned human -opioid receptors expressed in human embryonic kidney-293 cells. Thus, salvinorin A, salvinorinyl-2-propionate, and salvinorinyl2-heptanoate were found to be either full (salvinorin A) or partial (2-propionate, 2-heptanoate) agonists for inhibition of forskolinstimulated cAMP production. Additional studies of agonist potency and efficacy of salvinorin A, performed by cotransfecting either the chimeric G proteins Gaq-i5 or the universal G protein Ga16 and quantification of agonist-evoked intracellular calcium mobilization, affirmed that salvinorin A was a potent and effective -opioid agonist. Results from structure-function studies suggested that the nature of the substituent at the 2-position of salvinorin A was critical for -opioid receptor binding and activation. Because issues of receptor reserve complicate estimates of agonist efficacy and potency, we also examined the agonist actions of salvinorin A by measuring potassium conductance through G protein-gated K channels coexpressed in Xenopus oocytes, a system in which receptor reserve is minimal. Salvinorin A was found to be a full agonist, being significantly more efficacious than (trans)-3,4-dichloro-N-methyl-N[2-(1-pyrrolidinyl)-cyclohexyl] benzeneacetamide methanesulfonate hydrate (U50488) or (trans)-3,4-dichloro-N-methyl-N[2-(1-pyrrolidinyl)-cyclohexyl] benzeneacetamide methanesulfonate hydrate (U69593) (two standard -opioid agonists) and similar in efficacy to dynorphin A (the naturally occurring peptide ligand for -opioid receptors). Salvinorin A thus represents the first known naturally occurring non-nitrogenous full agonist at -opioid receptors. Salvia divinorum, a member of the Lamiaceae family, has been used by the Mazatec Indians of northeastern Oaxaca, Mexico, primarily for its psychoactive effects (Wasson, 1962, 1963) for many hundreds of years (for reviews, see Valdes et al., 1983; Sheffler and Roth, 2003). The active ingredient of S. divinorum is salvinorin A, a non-nitrogenous neoclerodane diterpene that represents the most potent naturally occurring hallucinogen known (Valdes et al., 1984; Siebert, 1994). Salvinorin A induces an intense, short-lived hallucinogenic experience qualitatively distinct from that induced by the classical hallucinogens lysergic acid diethylamide, psilocybin, and mescaline (Siebert, 1994). Both S. divinorum and salvinorin A have been used recreationally for their hallucinogenic properties (Giroud et al., 2000). Intriguingly, an anecdotal case report has suggested that S. divinorum may have antidepressant properties as well (Hanes, 2001). Quite recently, we discovered that salvinorin A has high affinity and selectivity for the cloned -opioid receptor (KOR) and suggested, based on limited functional studies, that salvinorin A was a KOR agonist (Roth et al., 2002). We now present a detailed report on the agonist properties of salvinorin A and selected derivatives. We discovered that salvinorin A is an extraordinarily efficacious and potent -opioid The work was supported by U.S. Public Health Service Grant RO1 DA04123 from National Institute on Drug Abuse (to C.C.) and by the National Institute of Mental Health Psychoactive Drug Screening Program and KO2MH01366 and RO1DA017204 (to B.L.R.). Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. DOI: 10.1124/jpet.103.059394. ABBREVIATIONS: KOR, -opioid receptor; hKOR, human -opioid receptor; nor-BNI, nor-binaltorphimine; U50488, (trans)-3,4-dichloro-Nmethyl-N-[2-(1-pyrrolidinyl)-cyclohexyl] benzeneacetamide methane-sulfonate hydrate; U69593, ( )-(5 ,7 ,8 )-N-methyl-N-[7-(1-pyrrolidinyl)-1oxaspiro[4.5]dec-8-yl]-benzeneacetamide. 0022-3565/04/3083-1197–1203$20.00 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 308, No. 3 Copyright © 2004 by The American Society for Pharmacology and Experimental Therapeutics 59394/1130181 JPET 308:1197–1203, 2004 Printed in U.S.A.