Isorhamnetin Alleviates Renal Fibrosis by Inducing Endogenous Hydrogen Sulfide and Regulating Thiol-Based Redox State in Obstructed Kidneys

Isorhamnetin (ISO) is an active flavonoid compound mainly isolated from the fruits of Hippophae rhamnoides L. and the leaves of Ginkgo biloba L. Previous studies have revealed the antifibrotic action of ISO in the liver and lungs, although its potential protective effects against renal fibrosis and the underlying mechanisms are still poorly understood. Given that many actions of ISO could be similarly attained by hydrogen sulfide (H₂S), we speculated that ISO may work through the induction of endogenous H₂S. To test the hypothesis, we established the unilateral ureteral obstruction (UUO) renal fibrosis rat model and transforming growth factor-β1(TGF-β1)-induced fibrosis in cultured renal tubular cells. ISO treatment inhibited epithelial–mesenchymal transition (EMT) formation, decreased extracellular matrix (ECM) deposition, and relieved renal fibrosis. Further analysis revealed that ISO stimulated the expression of the H₂S-synthesizing enzyme cystathionine lyase (CSE) and cystathionine beta-synthase (CBS), and promoted H₂S production in vivo and in vitro. The elevated H₂S attenuated oxidative stress and elevated the thiol level. It induced Keap1 sulfhydration, disrupted Keap1-Nrf2 interaction, and promoted the entry of Nrf2 into the nucleus. Finally, we found that circulating H₂S mainly derived from the liver, and not the kidney. Collectively, our study revealed that ISO alleviated renal fibrosis by inducing endogenous H₂S and regulating Keap1-Nrf2 interaction through sulfhydration of Keap1. Endogenous H₂S could be an important mediator underlying the pharmacological actions of ISO. Due to the multifunctional properties of H₂S, the H₂S-inducing nature of ISO could be exploited to treat various diseases.