Tobacco cembranoids block behavioral sensitization to nicotine and inhibit neuronal acetylcholine receptor function

Cembranoids are cyclic diterpenoids found in tobacco and in marine invertebrates. The present study established that tobacco cembranoids inhibit behavioral 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 mecamylamine (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 non-sensitized rats. 2) In cells expressing human AChRs, cembranoids blocked carbamoylcholine-induced ⁸⁶Rb⁺ flux with IC₅₀ in the low micromolar range. The cell lines used were the SH-EP1-hα4β2 cell line heterologously expressing human α4β2-AChR, the SH-SY5Y neuroblastoma line naturally expressing human ganglionic α3β4-AChR, and the TE671/RD cell line naturally expressing embryonic muscle α1β1γδ-AChR. The tobacco cembranoids tested were 4R and its diastereoisomer 4S, and marine cembranoids tested were EUAC and 12,13-bisepieupalmerin. 3) At the molecular level, tobacco (4R and 4S) and marine (EUAC) cembranoids blocked binding of the noncompetitive inhibitor [³H]tenocyclidine to AChR from Torpedo californica electric organ. IC₅₀ values were in the submicromolar to low-micromolar range, with 4R displaying an order of magnitude higher potency than its diastereoisomer, 4S.