Mapping the kidney distribution of Huangkui capsule-derived components in diabetic nephropathy treatment: a mass spectrometry imaging and metabolomics approach nominates quercetin and its conjugates as bioactive candidates

The Huangkui capsule (HKC) demonstrates significant efficacy against diabetic nephropathy (DN), yet its bioactive components that exert effects within the target organ, the kidney, have remained poorly characterized. This study aimed to elucidate the renal in situ effective constituents of HKC by integrating multimodal mass spectrometry analyses. A spontaneous DN model was established using db/db mice. Physiological parameters, biochemical indices, and histopathological assessments confirmed the model’s success and the therapeutic effects of HKC intervention. Serum pharmacochemistry based on UPLC-Q-TOF-MS/MS characterized 24 absorbed components. Among them, quercetin, isoquercetin, and their metabolites exhibited the strongest correlation with pharmacodynamic indicators. Crucially, matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-TOF-MSI) directly visualized and identified these quercetin-derived conjugates, particularly quercetin glucuronide, within kidney tissues, suggesting their potential as primary in situ bioactive candidates. This study is the first to spatially resolve the kidney distribution of HKC’s active constituents, providing a scientific basis for understanding its mechanism of action and advancing quality control protocols. Graphical