Toward the chemical ecology of medicinal plant use in chimpanzees: The case ofVernonia amygdalina,a plant used by wild chimpanzees possibly for parasite-related diseases

The bitter and related constituents have been isolated fromVernonia amygdalina (Compositae), a plant ingested by wild chimpanzees possibly suffering from parasite-related diseases in the Mahale Mountains National Park, Tanzania. Isolated from the plant were four known sesquiterpene lactones, seven new steroid glucosides, and two aglycones of the glucosides. The sesquiterpene lactones showed significant in vitro antischistosomal, plasmodicidal, and leishmanicidal activities. Antischistosomal activity was also found for the major steroid glucoside, vernonioside B₁. A trend in the glucosides to show significant antischistosomal, plasmodicidal, and amebicidal activities when the sugar moiety was removed, was observed. Vernodalin, judged as the most significant constituent for antiparasitic activities in vitro, was tested for in vivo antischistosomal effect. It was, however, highly toxic to the cercaria-infected mouse. Chimpanzees have been only rarely observed to ingest anything but the pith of the young stem. The occurrence of vernonioside B₁ and its aglycone vernoniol B₁, the major constituents among the steroid-related constituents, were detected at significant levels in the pith. However, vernodalin was abundant only in the leaves and bark. Thus, chimpanzees at Mahale were hypothesized to control parasite-related diseases by ingesting the young pith of this tree containing steroid-related constituents.