Tannins and catechin gallate mediate the vasorelaxant effect of Arbutus unedo on the rat isolated aorta

Abstract

This study examined the vascular effect of Arbutus leaves (aqueous extract) and described the isolation of several fractions responsible for their vasorelaxant activity. The aqueous extract (AE) of leaves was tested on rat aortic rings precontracted with 0.1 microm noradrenaline. At 10(-2) g/L, AE produced an endothelium dependent relaxation of 66% +/- 5%, (n = 8). The leaves of Arbutus were then extracted successively with different solvents and the methanol extract was the most active. When tannins (primarily condensed tannins) were precipitated from the methanol extract, they showed a strong vasorelaxant activity (87% +/- 4%, n = 5), whereas the elimination of tannins in the methanol extract reduced significantly its vasorelaxant activity (42% +/- 8%, n = 8, p < 0.005). The methanol extract was further separated semi-preparatively by reversed-phase HPLC. Four fractions (Fr2, Fr3, Fr4 and Fr6) were the most active and produced 88% +/- 2% (n = 5), 75% +/- 6% (n = 5), 76% +/- 3% (n = 7) and 77% +/- 3% (n = 10) relaxation, respectively. These four fractions mainly correspond to polyphenol compounds. Analysis of Fr6 indicated that this fraction contained catechin gallate. In conclusion, the vasorelaxant activity of Arbutus is likely to be due to polyphenol compounds, primarily condensed tannins and catechin gallate.

Papuabalanols A and B, New Tannins from Balanophora papuana

“…7,12) Some hydrolysable tannins such as 1,2,6-tri-O-galloyl-b-D-glucose, 2,3-(S)-hexahydroxy diphenoyl (HHDP)-D-glucose, and pedunculagin inhibit tyrosinase activity in B16 melanoma cells 13,14) as well as vasorelaxant effect on rat aorta. 15,16) Preliminary experiments revealed that the ethyl acetate extract of B. papuana showed anti-tyrosinase activity using mushroom tyrosinase (inhibition rate, 78% at 100 mg/ml; 60% at 50 mg/ml). Papuabalanol B (2) showed inhibition of tyrosinase dose-dependently (IC 50 23.3 mM), but papuabalanol A (1) and pinoresinol (3) did not show any inhibition (IC 50 Ͼ100 mM) as shown in Table 2.…”

Morphological, chemical and pharmacological characterization of selected plant species of genus Arbutus L., Bruckenthalia Rchb., Calluna Salisb. i Erica L. (Ericaceae)

“…Iz listova su izolovani: glikozidi flavonola -kvercetina i kemferola (kvercitrin, izokvercitrin, hiperozid, rutin, avikularin, afzelin i juglanin) (58,60,61), fenolni glikozidi (arbutin i piceozid) (53), triterpeni (lupeol i ursolna i betulinska kiselina) (53), iridoidni glikozidi (monotropein, monotropein metilestar, unedid, unedozid, stilberikozid i genipozid) (53,60), tanini (epikatehin, katehin, katehin galat i galna kiselina) (63,64), lipidi i vitamin E (do 0,01328%) (63,65).…”

“…Oba ekstrakta odlažu razvoj hipertenzije, dok ventrikularnu hipertrofiju redukuje samo ekstrakt korena (koren je bogatiji taninima, dok su listovi bogatiji flavonoidima). Hronična primena zaustavlja razvoj hipertenzije, poboljšava kardiovaskularne i renalne funkcije u NO deficijentnoj hipertenziji (54,61,64,74).…”

“…Ovakvi rezultati dokaznih reakcija za tanine su u skladu sa prethodnim ispitivanjima ovih biljnih vrsta: za vrstu Arbutus unedo se navodi prisustvo i katehinskih i galnih (63,64), a za vrste Calluna vulgaris i Erica arborea samo katehinskih tanina (34,49). U drogi Uvae ursi folium dominiraju galni tanini (18,171), ali se navodi i prisustvo katehinskih tanina (34).…”

“…Ekstrakti listova i korena vrste Arbutus unedo ispoljavaju snažan endotel-zavisni vazorelaksantni efekat, koji uključuje aktivaciju endotelijalne NO sintaze i cGMP sintaze (61,64). Pored poznate uloge u vazorelaksaciji, NO je važan medijator relaksacije i glatkih mišića GIT-a (151).…”