Integrative Pharmacokinetic and Metabolomic Profiling of Polygonum capitatum Extract Reveals Renoprotective Mechanisms in a Rat Model of Acute Pyelonephritis

Polygonum capitatum (PC) is an ethnomedicine with reported antibacterial and anti-inflammatory activities and has been clinically used in urinary tract infection (UTI)-related disorders. However, its in vivo exposure characteristics and metabolically associated therapeutic mechanisms in acute pyelonephritis (AP) remain insufficiently understood. To address this issue, this study aimed to evaluate the therapeutic effects of PC in an Escherichia coli (E. coli)-induced rat model of AP and to explore constituents and metabolic pathways associated with its activity. Different PC extracts were screened for antibacterial and anti-inflammatory activities, and the 70% ethanol extract was selected for further study. Seven major compounds were quantified by HPLC. In AP rats, the pharmacokinetic profiles of these compounds in plasma and the renal cortex were analyzed by microdialysis-coupled HPLC-MS/MS. Pharmacodynamic evaluation included urinary bacterial load, urinalysis, renal function, inflammatory cytokines, and renal histopathology. Exploratory PK–PD analysis, untargeted renal metabolomics, and targeted metabolomics of the tryptophan–kynurenine (Trp–Kyn) pathway were also performed. The 70% ethanol extract of PC exhibited the strongest antibacterial and anti-inflammatory activities. The total content of seven active compounds was 3.85%, with gallic acid being the predominant compound (3.42%). Pharmacokinetic analysis revealed that gallic acid, protocatechuic acid, methyl gallate, and quercitrin achieved relatively high systemic exposure and renal distribution. In AP rats, the pharmacokinetic profiles of several compounds were altered, with increased plasma exposure of protocatechuic acid, vanillic acid, ethyl gallate, and syringic acid, while protocatechuic acid also showed higher exposure in the renal cortex. PC treatment reduced urinary bacterial load, improved renal function and urinalysis parameters, alleviated histopathological injury, and decreased inflammatory mediator levels, particularly in renal tissue. Exploratory PK–PD correlations were observed between several compounds and selected pharmacodynamic indicators. Metabolomic analysis suggested disturbances in glycerophospholipid metabolism and the Trp–Kyn pathway in AP rats, some of which were partially reversed after PC treatment. PC showed antibacterial and anti-inflammatory effects in AP rats. Gallic acid, protocatechuic acid, methyl gallate, and quercitrin may be candidate constituents associated with the therapeutic effects of PC, while modulation of glycerophospholipid metabolism and the Trp–Kyn pathway may be involved in its action against AP. These findings provide preclinical pharmacological evidence supporting the therapeutic potential of PC in AP.