Glycnsisitin A: A promising bicyclic peptide against heart failure that facilitates TFRC-mediated uptake of iron in cardiomyocytes

Zhigancao decoction is a traditional prescription for treating irregular pulse and palpitations in China. As the monarch drug of Zhigancao decoction, the bioactive molecules of licorice against heart diseases remain elusive. We established the HRESIMS-guided method leading to the isolation of three novel bicyclic peptides, glycnsisitins A-C (1-3), with distinctive C-C and C-O-C side-chain-to-side-chain linkages from the roots of Glycyrrhiza uralensis (Licorice). Glycnsisitin A demonstrated stronger cardioprotective activity than glycnsisitins B and C in an in vitro model of doxorubicin (DOX)-induced cardiomyocyte injury. Glycnsisitin A treatment not only reduced the mortality of heart failure (HF) mice in a dose-dependent manner but also significantly attenuated DOX-induced cardiac dysfunction and myocardial fibrosis. Gene set enrichment analysis (GSEA) of the differentially expressed genes indicated that the cardioprotective effect of glycnsisitin A was mainly attributed to its ability to maintain iron homeostasis in the myocardium. Mechanistically, glycnsisitin A interacted with transferrin and facilitated its binding to the transferrin receptor (TFRC), which caused increased uptake of iron in cardiomyocytes. These findings highlight the key role of bicyclic peptides as bioactive molecules of Zhigancao decoction for the treatment of HF, and glycnsisitin A constitutes a promising therapeutic agent for the treatment of HF.