Please cite this article in press as: Dongmo, A.B., et al., Tetra-acetylajugasterone a new constituent of Vitex cienkowskii with vasorelaxant activity. Phytomedicine (2014), http://dx.doi.org/10.1016/j.phymed.2014.02.009 ARTICLE IN PRESS G Model PHYMED-51611; No. of Pages 6 Phytomedicine xxx (2014) xxx–xxx Contents lists available at ScienceDirect Phytomedicine jou rn al homepage: www.elsevier.de/phymed Tetra-acetylajugasterone a new constituent of Vitex cienkowskii with vasorelaxant activity Alain Bertrand Dongmo a,∗ , Pepin Alango Nkeng-Efouet b , Krishna Prasad Devkota c , Jörg W. Wegener d , Norbert Sewald e , Hildebert Wagner f , Wolfgang Vierling d a Department of Animal Biology, Faculty of Science, University of Douala, P.O. Box 24157, Douala, Cameroon b Department of Chemistry, University of Dschang, P.O. Box 371, Dschang, Cameroon c Institute of Forestry, Tribhuvan University, Pokhara Campus, P.O. Box 43, Pokhara, Nepal d Institute of Pharmacology and Toxicology, Technical University of Munich, Biedersteiner Str. 29, 80802 Munich, Germany e Chemistry Department, Organic and Bioorganic Chemistry, Bielefeld University, P.O. Box 100131, 33501 Bielefeld, Germany f Institute of Pharmaceutical Biology, Butenandt Str. 5 - 13 B, 81377 Munich, Germany a r t i c l e i n f o Article history: Received 22 October 2013 Received in revised form 16 January 2014 Accepted 24 February 2014 Keywords: Vitex cienkowskii Tetra-acetylajugasterone C Aortic smooth muscle Relaxation Nitric oxide cGMP cGKI a b s t r a c t Tetra-acetylajugasterone C (TAAC) was found to be one of the naturally occurring compounds of the Cameroonian medicinal plant Vitex cienkowskii which is responsible for a vasorelaxant activity of an extract of this plant. The evaluation of the underlying mechanisms for the relaxing effect of TAAC was determined using aortic rings of rats and mice. TAAC produced a concentration-dependent relaxation in rat artery rings pre-contracted with 1 M noradrenaline (IC 50 : 8.40 M) or 60 mM KCl (IC 50 : 36.30 M). The nitric oxide synthase inhibitor l-NAME (100 M) and the soluble guanylate cyclase inhibitor ODQ (10 M) significantly attenuated the vasodilatory effect of TAAC. TAAC also exerted a relaxing effect in aorta of wild-type mice (cGKI +/+ ; IC 50 = 13.04 M) but a weaker effect in aorta of mice lacking cGMP- dependent protein kinase I (cGKI -/- ; IC 50 = 36.12 M). The involvement of calcium channels was studied in rings pre-incubated in calcium-free buffer and primed with 1 M noradrenaline prior to addition of calcium to elicit contraction. TAAC (100 M) completely inhibited the resulting calcium-induced vaso- constriction. The same concentration of TAAC showed a stronger effect on the tonic than on the phasic component of noradrenaline-induced contraction. This study shows that TAAC, a newly detected con- stituent of Vitex cienkowskii contributes to the relaxing effect of an extract of the plant. The effect is partially mediated by the involvement of the NO/cGMP pathway of the smooth muscle but additionally inhibition of calcium influx into the cell may play a role. © 2014 Elsevier GmbH. All rights reserved. Introduction The genus Vitex belonging to the family of Verbenaceae includes approximately 250 known species of trees and shrubs within trop- ical and sub-tropical regions, although few species may be found in temperate zones (Correa, 1926; Arbonnier, 2004). V. cienkowskii Kotschy & Peyritsch is a deciduous tree, prescribed by Cameroo- nian traditional healers as one of the most popular plants widely Abbreviations: cGK(I), cGMP-dependent protein kinase (I); (e)NOS, (endothe- lial) nitric oxide synthase; l-NAME, N-nitro-l-arginine methyl ester; MMEvc, methylene chloride-methanol (1:1) extract of V. cienkowskii; NA, noradrenaline; NO, nitric oxide; ODQ, 1-H-[1,2,4]-oxadiazolo-[4,3a]-quinoxalin-1-one; ROC, receptor- operated ion channels; TAAC, tetra-acetylajugasterone C; TRP, transreceptor potential; VOC, voltage-operated ion channels. ∗ Corresponding author. Tel.: +237 76491950. E-mail addresses: alainberd@yahoo.fr, adongmo@hotmail.com (A.B. Dongmo). used in many disorders including cardiovascular diseases such as hypertension (Nkeng-Efouet, 1987). Hypertension is a major risk factor for stroke, myocardial infarc- tion as well as heart and kidney failure worldwide and also in Cameroon. The prevalence of hypertension in Cameroon is esti- mated to be about 19.1% in urban areas and 15.4% in rural areas (Fourcade et al., 2007). For populations with poor economic resources herbal drugs as tea were widely used like V. Cienkowskii which possessed multi- valent pharmacological activities (Arbonnier, 2004). V. cienkowskii is one of the plants used in Cameroon to cure cardiovascular disorders such as hypertension. Thus, pharmacological valida- tion of medicinal plants for antihypertensive effects or evaluation of ethnomedical treatment methods could have great bene- fit. Initial chemical characterization studies on V. cienkowskii have been carried out and led to the identification and isolation of a http://dx.doi.org/10.1016/j.phymed.2014.02.009 0944-7113/© 2014 Elsevier GmbH. All rights reserved.