Antinociceptive anti-inflammatory effect of monotropein isolated from the root of Morinda officinalis

The root of Morinda officinalis (Rubiaceae) is used to treat rheumatoid arthritis and impotence in the traditional Oriental medicine. To identify the antinociceptive anti-inflammatory components of this crude drug, we adopted an activity-directed fractionation approach. The active fraction of the BuOH extract of M. officinalis root was subjected to silica gel and ODS column chromatography to yield two diterpenes, compounds 1 and 2 and these were identified as monotropein and deacetylasperulosidic acid, respectively. The iridoid glycoside, monotropein, was tested for its anti-inflammatory antinociceptive effects using hot plate- and writhing antinociceptive assays and by using carrageenan-induced anti-inflammatory assays in mice and rats. Pretreatment with monotropein (at 20, 30 mg/kg/d, p.o.) significantly reduced stretching episodes and prolonged action time in mice. It also significantly reduced acute paw edema by carrageenan in rats. These results indicate that monotropein contributes to the antinociceptive and anti-inflammatory action of Morinda officinalis root.