Antinociceptive and anti-inflammatory activities of leaf extracts from Annona tomentosa R.E.Fr.

Annona tomentosa R.E.Fr is a species not endemic to Brazil that belongs to the phytogeographic areas of the Amazon, Cerrado and Pantanal. Popularly known as "araticum rasteiro" or "araticum de moita", A. tomentosa is edible and tea made from the leaves has been used as an anti-inflammatory by native communities. There is no scientific evidence for these uses of A. tomentosa, especially those related to the control of pain and inflammation. For this reason, in the present study we evaluated the antinociceptive and anti-inflammatory activities of partitions from the methanolic extract of A. tomentosa leaves (A. tomentosa leaf methanolic extract (ATFM) in hexane partition: ATFM-H; ATFM in dichloromethane partition: ATFM-D; ATFM in ethyl acetate partition: ATFM-Ac; ATFM in butanol partition: ATFM-B) in mice.

The antinociceptive effects of leaf extracts from A. tomentosa were evaluated by abdominal writhing and tail-flick tests, while the anti-inflammatory effects were evaluated by paw oedema and air-pouch tests. The locomotor activity was evaluated with the open-field test. Furthermore, we evaluated the possible action mechanism of A. tomentosa, using naloxone, nitro-L-arginine methyl ester, glibenclamide, atropine, naltrindole and norbinaltorphimine in tail-flick tests. The productions of tumor necrosis factor α (TNF-α) and interleukin (IL)-1β were also evaluated.

The chromatographic fractionation of the partitions of the methanolic extract from the leaves of A. tomentosa revealed the presence of diterpenes, flavonoids, and steroids compounds. From the analysis of the hexane partition kaurenoic acid was identified as the major component. ATFM-H and ATFM-D had a significant antinociceptive effect in acute pain models in mice. The ATFM-H showed central antinociceptive effect from the involvement of the δ opioid receptors, without causing alterations in the locomotor activity of the mice, while ATFM-D was effective in decreasing paw oedema and TNF-α and IL-1β production.

These results demonstrate that leaf extracts from A. tomentosa present antinociceptive and anti-inflammatory effects that can to be used in relieving algesic and inflammatory conditions.