Toxicological evaluation of aristolochic acid II following single and repeated oral administration over a 24-week period

Background: Aristolochic acid II (AAII), a major nephrotoxic and carcinogenic component of aristolochic acids (AAs), has been less studied compared with its well-characterized analog, aristolochic acid I (AAI). Although AAs are known to induce carcinogenesis via DNA adduct formation, the toxicity mechanisms, environmental prevalence, and long-term health impacts of AAII remain poorly understood. Objective: This study aimed to systematically evaluate AAII’s acute and chronic toxicity, carcinogenic mechanisms, and environmental exposure patterns using integrated murine models and phytochemical analyses to clarify its toxicological profile and associated health risks. Methods: C57BL/6J mice were used in the following experiments: (1) determination of AAII content in 3 commonly used Aristolochia medicinal materials via liquid chromatography-mass spectrometry/mass spectrometry; (2) acute toxicity testing with single doses of 10, 20, or 40 mg/kg; and (3) chronic exposure with 1 or 10 mg/kg administered every other day for 24 weeks, followed by 21 to 40 weeks of postexposure monitoring. Histopathological examination, whole-exome sequencing, biochemical assays, and micronucleus tests were performed to assess multi-organ damage, tumorigenesis, genomic mutation signatures, and direct clastogenicity. Phytochemical analyses were used to evaluate environmental distribution. Results: (1) A single 40 mg/kg dose of AAII induced dose-dependent renal tubular degeneration without hepatotoxicity; (2) the 10 mg/kg group showed significant mortality (20%), tumor incidence (33.3%, primarily forestomach and bladder transitional cell carcinomas), persistent renal interstitial fibrosis, and subclinical hepatic injury. Chronic exposure to 1 mg/kg still induced 13.3% mortality and 15.5% tumor incidence over a 64-week period; (3) whole-exome sequencing revealed a predominance of C>T mutations and pathway enrichment in chemical carcinogenesis and cytochrome P450-mediated metabolism, indicating reactive metabolite-driven mechanisms distinct from classical AA-DNA adducts; and (4) no histopathological changes were observed in nontarget organs (brain, heart, and testes), and micronucleus assays confirmed the absence of direct clastogenicity. Conclusion: This study highlights the delayed carcinogenic risks of low-dose chronic AAII exposure and emphasizes the need to update regulatory frameworks to ensure the safe use of aristolochiaceae-containing herbal products.