Iridoids from the edible flowers of Rhododendron pachypodum: structural elucidation and healthspan related bioactivities in Caenorhabditis elegans

Rhododendron pachypodum flowers are traditionally consumed by ethnic minorities in Yunnan as seasonal edible flowers, yet their bioactive iridoid constituents and associated biological activities remain underexplored. This study characterized the iridoid constituents and evaluated in vivo bioactivities relevant to healthspan. Nine iridoids were isolated from the flowers, including seven previously undescribed analogues (1-7) and two known compounds (8-9). The structures of these compounds were determined based on 1D/2D NMR spectroscopic data and HRMS data, while absolute configurations were assigned by comparing experimental ECD spectra with TD-DFT-calculated spectra. The in vivo effects of compounds 5 and 8 were assessed in Caenorhabditis elegans, including lifespan, pharyngeal pumping, locomotion, and survival under oxidative and heat stress, as well as early brood size and body size. Both compounds significantly extended lifespan across multiple doses (up to 30.8% for compound 8 and 30.4% for compound 5), and the effects exceeded those of the positive control β-nicotinamide mononucleotide (NMN, 25.4%; all P < 0.001). They also improved pharyngeal pumping and locomotion and enhanced survival under oxidative stress (up to 41.1% for compound 8; P < 0.001). Compound 5 additionally increased heat-stress tolerance and stimulated early brood size, whereas compound 8 exerted stronger effects on body size. This work integrates rigorous phytochemical characterization with in vivo functional evaluation and supports further mechanistic and safety evaluations.