Stress endurance mediates the healthspan-promoting effect of two newly described iridoid glycosides from Verbascum nigrum ssp. abietinum in Caenorhabditis elegans

BACKGROUND: Natural products are emerging as promising options for promoting health and managing age-related diseases. Iridoid glycosides, a diverse class of monoterpenoids, exert multiple beneficial effects and are of significant interest in pharmaceutical research. They are abundant in Scrophulariaceae, particularly in the genus Verbascum L. (mulleins). However, the infraspecific taxon V. nigrum ssp. abietinum (Borbas) I.K. Ferguson, native to the Balkan Peninsula, has not been previously investigated regarding chemical composition or healthspan-modulating potential. PURPOSE: This study aimed to isolate and characterize the main secondary metabolites of V. nigrum ssp. abietinum and to evaluate the effects of iridoid glycosides on age-related physiological changes and stress tolerance in Caenorhabditis elegans. We focused on two newly isolated sinuatol derivatives (1 and 2) and their influence on conserved molecular networks regulating stress response and aging. METHODS: Following isolation and identification of compounds 1 and 2, phenotypic analyses were conducted to assess toxicity, lifespan, physiology, and stress resistance. Basal metabolism and molecular mechanisms were further examined. RESULTS: Methanol extract of aerial parts of V. nigrum ssp. abietinum yielded two previously undescribed iridoid glycosides (1 and 2) along with twelve known constituents. Both compounds upregulated sek-1/p38 (MAPK) and sqst-1/p62 (SQSTM1), indicating enhanced autophagy and stress response. Additionally, sgk-1/SGK-1, hsf-1/HSF1, and tcer-1/TCERG1 were consistently overexpressed, suggesting improved oxidative stress defense, heat shock response, and transcriptional regulation. Notably, the selective upregulation of hsp-16.1 and hsp-16.2 upon supplementation with compound 1 suggests a stereospecific interaction with the HSP network, potentially linked to the positional arrangement of the caffeoyl moiety. CONCLUSION: This study provides the first evidence that iridoid glycosides 1 and 2 from V. nigrum ssp. abietinum promote C. elegans healthspan by enhancing stress response through modulation of genes related to autophagy and inflammation.