A novel sesquiterpene acid and an alkaloid from leaves of the Eastern Nigeria mistletoe, Loranthus micranthus with potent immunostimulatory activity on C57BL6 mice splenocytes and CD69 molecule

Abstract

Context: The Eastern Nigeria mistletoe, Loranthus micranthus Linn. (Loranthaceae), is used in the treatment of severaldiseases including immune-modifying diseases and thus there is a need to identify the immunoactive constituents. Objective: This research isolated and characterized the immunoactive constituents in the Eastern Nigeria mistletoe. Materials and methods: Bioassay-guided fractionation was employed in the isolation and purification of the constituents. The characterized compounds were screened for immunostimulatory activities on isolated C57BL/6 mice splenocytes and early activation marker, CD69 at concentrations of 10, 25, and 100 µg/mL using flow cytometry techniques and compared to lipopolysaccharide (LPS; 10 µg/mL) and concanavalin A (ConA; 2 µg/mL) as standards. Results: Two compounds, a novel sesquiterpene, 2, 3-dimethoxy-benzo [a, b] cyclopentenyl-3′,3′,5′-trimethyl pyran4-carboxylic acid (1), and a known alkaloid, lupinine (2) were isolated and characterized. The compounds (25 µg/ mL) showed statistically significantly (p<0.05) stimulatory activity on the splenocytes with values of 56.34±0.26% and 69.84±0.19%, respectively, compared to 7.58±0.42% recorded for the unstimulated control. Similarly, the CD69 expression assay showed immunostimulation with statistically significant values (p<0.05) of 2.31±0.07% and 2.71±0.03%, respectively, compared to 1.69±0.05% recorded for the non stimulated control. Discussion: These data suggest that the isolated compounds possess immunomodifying abilities. In addition, the activation of the CD69 molecule is possibly one of its mechanisms of action. Conclusion: These compounds may be responsible in part, for the immunostimulatory activities already established for the Eastern Nigeria mistletoes.