Plants produce a wide variety of secondary metabolites, including compounds with biological activities that could be used for the treatment of human diseases. In the present study, we examined the putative production of bioactive molecules in the legume plant Lotus japonicus, which engages into symbiotic relationships with beneficial soil microorganisms. To monitor the production of secondary metabolites when the plant develops beneficial symbiotic relationships, we performed single and double inoculations with arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing Rhizobium bacteria. Plant extracts from non-inoculated and inoculated plants were chemically characterized and tested for anti-proliferative, apoptotic, and anti-inflammatory effects on human HEK-293 cells. Both shoot and root extracts from non-inoculated and inoculated plants significantly reduced the HEK-293 cell viability; however, a stronger effect was observed when the root extracts were tested. Shoot and root extracts from Rhizobium-inoculated plants and shoot extracts from AMF-inoculated plants showed apoptotic effects on human cells. Moreover, both shoot and root extracts from AMF-inoculated plants significantly reduced TNFα-induced NF-κB transcriptional activity, denoting anti-inflammatory activity. These results suggest that symbiotic L. japonicus plants are enriched with metabolites that have interesting biological activities and could be further explored for putative future use in the pharmaceutical sector.
Keywords: Lotus japonicus; Rhizobium; anti-inflammatory activity; apoptosis; arbuscular mycorrhizal fungi; cell viability; plant extracts; symbiosis.