Correlation analysis of secondary metabolites, metal elements, and anti-BSA denaturation activity in different parts of Rhododendron tomentosum from China.

BACKGROUND: Rhododendron tomentosum (also known as Ledum palustre L.) is a traditional medicinal plant, yet the accumulation patterns of secondary metabolites and the distribution of metal elements across its different parts (roots, old branches, young branches, branches and leaves, leaves, flowers, and fruits) remain largely unclear. METHODS: UPLC-MS, HPLC, ICP-MS, and chemometric tools were employed to analyze the secondary metabolites (predominantly flavonoids) and the contents of Al, Fe, Cu, Mg, K, Ca, Mn, and Zn in different parts of Chinese R. tomentosum. The anti-inflammatory activity was evaluated by the inhibition rate against bovine serum albumin (BSA) denaturation. RESULTS: Three coumarin compounds-the glycosides aesculin and fraxin, and their aglycone fraxetin-were present in all parts. Aesculin and fraxin were abundant in young branches, old branches, and roots. Hyperoside, guaijaverin, isoquercitrin, and avicularin were mainly distributed in leaves and young branches. Quercitrin was abundant in flowers, followed by fruits, with the highest levels observed in samples rich in reproductive organs. The contents of Al and Fe were relatively high in roots, whereas the levels of Mg, K, Ca, and Mn were relatively low in roots and old branches. Correlation analysis revealed that Al and Fe showed significant positive correlations with coumarins (aesculin and fraxin), while Al exhibited significant negative correlations with flavonoid glycosides (hyperoside, guaijaverin, isoquercitrin, avicularin, and quercitrin). Mg, K, Ca, and Mn were significantly negatively correlated with coumarins but significantly positively correlated with flavonoid glycosides. Cu was present at relatively low levels and showed significant negative correlations with aesculin and fraxin. Significant positive correlations were also observed between Al and Fe, Al and Zn, and Fe and Zn, as well as among Mn, Mg, K, and Ca. K was positively correlated with Cu, and Mn was positively correlated with Zn. Conversely, Mg was negatively correlated with Al, and K was negatively correlated with both Al and Fe. Inhibition rates of roots, old branches, and young branches were lower than those of branches and leaves, leaves, fruits, and flowers. Flowers and fruits exhibited high inhibition rates. The inhibition rate was negatively correlated with aesculin and fraxin, and positively correlated with hyperoside, guaijaverin, isoquercitrin, avicularin, and quercitrin. CONCLUSION: This study provides new insights into the intrinsic relationships among "DNA molecular identification - different parts - chemical composition - function" in Chinese R. tomentosum, facilitating its artificial cultivation, selective breeding, and comprehensive utilization. Specifically, the findings suggest that: (1) R. tomentosum may serve as a candidate woody species for studying the co-accumulation of coumarins with Al/Fe under acidic soil conditions, although this hypothesis requires experimental validation; (2) Al and Fe are highly co-accumulated and may synergistically influence secondary metabolite accumulation in different parts together with Mg and K, also warranting further testing; (3) Hyperoside, avicularin, guaijaverin, isoquercitrin, and quercitrin may be the major potential anti-BSA denaturation components based on correlation and in vitro activity assays; and (4) Combining DNA barcoding (ITS sequences) and flavonoid profiling may help distinguish broad-leaved and fine-leaved types of Chinese Ledum species, pending further verification.