Pollen of Brassica campestris L. ameliorates hyperuricemic and obstructive nephropathy by targeting the β-catenin/TCF4-ferroptosis pathway

Ethnopharmacological relevance The pollen of Brassica campestris L. (BCP, syn. Brassica rapa L. subsp. oleifera (DC.) Metzg.), included in the Chinese Pharmacopoeia as a licensed patent medicine (Pule'an tablets), is used clinically for kidney-qi deficiency-related lower urinary tract symptoms in chronic prostatitis and benign prostatic hyperplasia. Prostatic obstruction is a common cause of obstructive uropathy that may progress to renal fibrosis. However, the renoprotective effects and the underlying mechanism remain to be fully elucidated. Aim of the study To study the renoprotective effects, the active fraction, the effective components of BCP and the underlying mechanisms. Materials and methods Mouse models of hyperuricemic nephropathy (HN) and unilateral ureteral obstruction (UUO) were established to evaluate the renoprotective effects of BCP. Transcriptomics and liquid chromatography-mass spectrometry were applied to explore potential mechanisms and intrarenal constituents. Erastin- and uric acid (UA)-induced HK-2 cells were employed to validate the cytoprotective effects of the potential active compounds, whose binding capability with direct target was confirmed by CETSA/SPR. Results BCP dose-dependently reduced UA levels and reversed the protein expression of UA-producing enzymes and renal transporters (for reabsorption and excretion) in HN mice. Additionally, BCP improved renal injury and fibrosis in HN mice and UUO mice by reducing UA and direct renoprotection, in which the flavonoids of BCP played a crucial role. Meanwhile, BCP alleviated renal fibrosis by inhibiting the β-catenin/TCF4-ferroptosis axis, which was achieved mainly by its bioactive components, kaempferol and kaempferol-3-glucuronide (K-3-G), in HK-2 cells. Furthermore, kaempferol and K-3-G were demonstrated to directly bind with β-catenin, block the transcriptional activation of β-catenin, and subsequently suppress ferroptosis. Conclusions BCP and its major bioactive compounds, kaempferol and K-3-G, exert nephroprotective effects by inhibiting the β-catenin/TCF4-ferroptosis axis.