Surface-cleaned black phosphorus nanosheets chelate iron and rebalance the ferroptosis-immune axis in acute kidney injury.

RATIONALE: Nanomaterials have been explored for acute kidney injury (AKI) therapy because of their ability to scavenge reactive oxygen species (ROS) and reduce oxidative stress. Black phosphorus nanosheets (BPNSs) show renoprotective potential, but spontaneous surface oxidation may weaken their redox activity and therapeutic efficacy. It remains unclear whether surface engineering can improve the biological activity of BPNSs and modulate ferroptosis and immune activation during AKI. METHODS: Surface-cleaned BPNSs (sc-BPNSs) were prepared by hydrogen reduction and characterized. Fluorescence-labeled sc-BPNSs were used to examine biodistribution, and therapeutic efficacy was evaluated in mice with AKI. In vitro, mouse renal tubular epithelial cells (mRTECs) were subjected to hypoxia/reoxygenation (H/R). Ferroptosis and iron homeostasis were assessed using biochemical, histological, and imaging assays. RNA sequencing was performed in mRTECs and macrophages to identify pathways affected by sc-BPNSs. A tubular epithelial cell-macrophage co-culture model was used to examine intercellular crosstalk after injury. RESULTS: Hydrogen reduction produced sc-BPNSs with reduced surface oxidation, stronger antioxidant activity, and improved renal accumulation. After intravenous administration, sc-BPNSs preferentially accumulated in injured kidneys, reduced ROS accumulation and lipid peroxidation, alleviated tubular injury, and improved renal function. Transcriptomic analysis showed that sc-BPNSs affected pathways related to oxidative stress, iron metabolism, and immune regulation. Mechanistically, sc-BPNSs restored iron homeostasis by sequestering labile iron and regulating transferrin receptor 1/2 (TFR1/TFR2) and ferroportin (FPN1), thereby suppressing ferroptosis in vitro and in vivo. sc-BPNSs also inhibited Ras-MAPK signaling, reduced M1 macrophage activation, and increased M2-associated marker expression. In the co-culture model, sc-BPNSs attenuated the ferroptotic and inflammatory crosstalk between injured tubular epithelial cells and macrophages. CONCLUSIONS: sc-BPNSs protect against AKI by reducing oxidative stress, restoring iron homeostasis, suppressing ferroptosis, and modulating macrophage activation. These findings suggest that surface-cleaned BPNSs may provide a therapeutic approach for AKI by targeting both tubular ferroptosis and inflammatory amplification.