Structure activity relationships of aristolochic acid analogues: Toxicity in cultured renal epithelial cells

Background. Aristolochia species are nephrotoxic and carcinogenic. Recent studies showed that aristolochic acid (AA) could induce acute renal failure and tubular lesions in several species and available evidences demonstrate the unequivocal role of AA in so called Chinese herbs nephropathy. Methods. A series of AA derivatives isolated from Aristolochia spp. were analyzed for their nephrotoxic potential using the neutral red dye exclusion assay in cultures of LLC-PK1 cells. The structural relationships between AA I and its analogues were compared with their cytotoxic effects to predict structural determinants for AA toxicity. Further, caspase-3 assay was performed on toxic compounds to determine if caspases, the enzymes that play a critical role in apoptosis are involved in AA-induced cytotoxicity. Results. AA I was found to be most toxic followed by AA II, AA VIIIa, and AA la in decreasing levels of toxicity. The other compounds, nitrophenanthrene carboxylic acid analogues of AA I, aristolactams, and other derivatives did not exhibit considerable toxicity. The results showed significant relationships between cytotoxicity of AA compounds and the localization of functional groups in their structure. Analogues containing hydroxyl groups diminished cytotoxicity. The demethylated analogues of AA I are markedly less active. The negative impact on cytotoxicity was found on nitroreduction of AA I. AA induced caspase activation was also observed. Conclusion. These cytotoxic data suggest that the nitro and methoxy groups are critical determinants of nephrotoxicologic potency of AA.