Evolution of the Secondary Metabolites in Invasive Plant Species Chromolaena odorata for the Defense and Allelopathic Functions

Chromolaena odorata (L.) R.M. King & H. Robinson is native to tropical America, and has naturalized in many other countries in tropical Asia, Austria, and West Africa. The species often forms dense thickets and reduces the native species diversity and population in the invasive ranges. The species is also considered as a noxious weed in agriculture fields, and listed in the 100 of the world's worst invasive alien species. The characteristics of its life-history such as the seed production rate, growth pattern, and adaptative ability to the environmental conditions may contribute to the invasiveness of the species. Possible evidence of the defense capacity against the natural enemy, and the allelopathic potential against the competitive plant species for C. odorata has been accumulated in the literature over three decades. The extracts, residues, and/or rhizosphere soil of C. odorata increased the mortality of various insects and parasitic nematodes, and decreased their population. The extracts, residues, and/or rhizosphere soil of C. odorata also inhibited the germination and growth of several plant species including the indigenous plant species in the invasive ranges of C. odorata. Toxic substances, pyrrolizidine alkaloids were found in the leaves and flowers of C. odorata. These pyrrolizidine alkaloids may work as the defense agents against the natural enemies. Several potential allelochemicals such as flavonoids, phenolic acids, and terpenoids were also found in the plant extracts of C. odorata. Some of these compounds may work as allelopathic agents of C. odorata and inhibit the germination and growth of the competitive plant species. These characteristics of C. odorata for the defense function against their natural enemies such as insects and parasitic nematodes, and allelopathic potential against the competitive native plant species may contribute to the invasiveness and naturalization of C. odorata in the new habitats as invasive plant species. However, it is necessary to determine the concentration of these allelochemicals in the neighboring environment of C. odorata such as the rhizosphere soil since allelochemicals are able to work only when they are released into the neighboring environment. It is the first review article focusing on the defense function and allelopathy of C. odorata.

Activity of mangosteen xanthones and teleocidin a-2 in death receptor expression enhancement and tumor necrosis factor related apoptosis-inducing ligand assays

A screening study using a luciferase assay to identify natural products that enhance death receptor 5 (DR5) expression was carried out, and bioassay-guided fractionation of two organisms, the pericarp of Garcinia mangostana (mangosteen) and actinomycete CKK609 strain, led to the isolation of eight xanthone derivatives (1-8) and teleocidin A-2 (9). Among them, compounds 1, 2, and 5, isolated from G. mangostana, and 9, from the actinomycete, showed potent DR5 promoter activity. Furthermore, we revealed that combined treatment with gartanin (5) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) showed a potentiation effect in sensitizing TRAIL-resistant human gastric adenocarcinoma (AGS) cells. Thus, the present results suggested that 5 has the ability to overcome TRAIL resistance via the up-regulation of DR5 and may be an effective sensitizer of TRAIL-resistant cells.

Death receptor 5 promoter-enhancing compounds isolated from Catimbium speciosum and their enhancement effect on TRAIL-induced apoptosis

The TRAIL/death-receptor signaling pathway has been considered a promising target for selective cancer therapy, although some malignant tumors exhibit TRAIL resistance. We previously found that isoflavonoid enhanced TRAIL-induced apoptosis in TRAIL-resistant cells, which is achieved through up-regulation of death receptor 5 (DR5). In our screening program targeting DR5 promoter enhancement activity, activity-guided fractionations of the extract of Catimbium speciosum led to the isolation of six compounds. Of the isolates, cardamomin (6), the most potent compound, enhanced the expressions of DR5 and DR4 and decreased the Bcl-xL level in TRAIL-resistant DLD1 cells. The combination of 6 and TRAIL synergistically enhanced TRAIL-induced apoptosis against TRAIL-resistant cells upon the activation of caspase-8, 9, and 3. In addition, enhancement of apoptosis by 6 was inhibited by human recombinant DR5/Fc and DR4/Fc chimera proteins, TRAIL-neutralizing fusion proteins, indicating that 6 sensitize TRAIL-resistant cells to TRAIL through the induction of DR5 and DR4. Also, up-regulation of DR5 by 6 paralleled that of CCAAT/enhancer-binding protein-homologous protein (CHOP).