Tobacco cembranoids block behavioral sensitization to nicotine and inhibitneuronal acetylcholine receptor function

Cembranoids are cyclic diterpenoids found in tobacco and in marine inverteb rates. The present study established that tobacco cembranoids inhibit behav ioral sensitization to nicotine in rats and block several types of nicotine acetylcholine receptors (AChRs). 1) At the behavioral level, rat locomotor activity induced by nicotine was significantly increased after seven daily nicotine injections. This sensitization to nicotine was blocked by mecamyl amine (1 mg/kg) and by the cembranoids eunicin, eupalmerin acetate (EUAC), and (4R)-2,7,11-cembratriene-4-6-diol (4R), each at 6 mg/kg. None of these compounds modified locomotor activity of nonsensitized rats. 2) In cells ex pressing human AChRs, cembranoids blocked carbamoylcholine-induced Rb-86(+) flux with IC50 in the low micromolar range. The cell lines used were the S H-EP1-h alpha4 beta2 cell line heterologously expressing human alpha4 beta2 -AChR, the SH-SY5Y neuroblastoma line naturally expressing human ganglionic alpha3 beta4-AChR, and the TE671/RD cell line naturally expressing embryon ic muscle alpha1 beta1 gamma delta -AChR. The tobacco cembranoids tested we re 4R and its diastereoisomer 4S, and marine cembranoids tested were EUAC a nd 12,13-bisepieupalmerin. 3) At the molecular level, tobacco (4R and 4S) a nd marine (EUAC) cembranoids blocked binding of the noncompetitive inhibito r [H-3]tenocyclidine to AChR from Torpedo californica electric organ. IC,, values were in the submicromolar to low-micromolar range, with 4R displayin g an order of magnitude higher potency than its diastereoisomer, 4S. (C) 20 01Wiley-Liss, Inc.