Aristolochic Acid-Induced Genotoxicity and Toxicogenomic Changes in Rodents

Abstract

Aristolochic acid (AA) is a group of structurally related nitrophenanthrene carboxylic acids found in many plants that are widely used by many cultures as traditional herbal medicines. AA is a causative agent for Chinese herbs nephropathy, a term replaced later by AA nephropathy. Evidence indicates that AA is nephrotoxic, genotoxic, and carcinogenic in humans; and it also induces tumors in the forestomach, kidney, renal pelvis, urinary bladder, and lung of rats and mice. Therefore, plants containing AA have been classified as carcinogenic to humans (Group 1) by the International Agency for Research on Cancer. In our laboratories, we have conducted a series of genotoxicity and toxicogenomic studies in the rats exposed to AA of 0.1-10 mg/kg for 12 weeks. Our results demonstrated that AA treatments induced DNA adducts and mutations in the kidney, liver, and spleen of rats, as well as significant alteration of gene expression in both its target and nontarget tissues. AA treatments altered mutagenesis- or carcinogenesis-related microRNA expression in rat kidney and resulted in significant changes in protein expression profiling. We also applied benchmark dose (BMD) modeling to the 3-month AA-induced genotoxicity data. The obtained BMDL₁₀ (the lower 95% confidence interval of the BMD₁₀ that is a 10% increase over the background level) for AA-induced mutations in the kidney of rats was about 7 μg/kg body weight per day. This review constitutes an overview of our investigations on AA-induced genotoxicity and toxicogenomic changes including gene expression, microRNA expression, and proteomics; and presents updated information focused on AA-induced genotoxicity in rodents.

Keywords: Aristolochic acid; benchmark dose; genotoxicity; mutation; toxicogenomics.

Figure 1:

Bioactivation and detoxification of aristolochic acid I by metabolic enzymes. UGT: uridine 5’-diphospho-glucuronosyltransferase, SULT: sulfotransferase, NAT: N-acetyltransferase. The question mark (?) indicates that the role of sulfotransferase in the bioactivation of aristolochic acid is controversial

Figure 2:

Total DNA adduct levels in the kidney, liver, and spleen of Big Blue rats treated with aristolochic acid at different doses (0.1, 1.0, and 10.0 mg/kg body weight) for 12 weeks. All DNA adducts (dA-AAI, dG-AAI, and dA-AAII) were detected by the nuclease P1 enrichment version of the ³²P-postlabeling assay. The kidney and liver data are from Mei et al.^[35] while the spleen data are from McDaniel et al.^[37] All data represent the mean value of groups of 6 rats. The part of DNA adducts under 700/10⁸ nucleotides has been enlarged in the inset graph

Figure 3:

The cII mutant frequencies in the kidney, liver, and spleen of Big Blue rats treated with aristolochic acid at different doses (0.1, 1.0, and 10.0 mg/kg body weight) for 12 weeks. The data represent the mean value for groups of 6 rats. The kidney data are from Chen et al.,^[36] while the liver and spleen data are from Mei et al.^[35] and McDaniel et al.,^[37] respectively. *Indicating a significant difference from the concurrent control group

Figure 4:

The summary of independent mutations in the cII gene of the kidney, liver, and spleen from control and 10 mg/kg aristolochic acid-treated rats. The kidney data are from Chen et al.,^[36] while the liver and spleen data are from Mei et al.^[35] and McDaniel et al.,^[37] respectively. There are statistically significant differences between the mutation spectra in the control and AA-treated rats for each tissue. The group of “others” includes tandem base substitution and complex mutation

Figure 5:

Correlations between H‑Ras codon 61 CTA mutant fraction and DNA adducts (black lines) or cII mutant frequencies (red lines) in the Kidney (a) and liver (b) from control and 10 mg/kg aristolochic acid‑treated rats. H‑Ras data are from Wang et al.,^[38] while total DNA adduct levels and cII mutant frequencies are from Figures 2 and 3. Open dot: H-Ras mutant fraction vs. cII mutant frequency, Close dot: H-Ras mutant fraction vs. DNA adducts

Figure 6:

Comparison of benchmark dose values for the cII mutant frequencies and H-Ras mutant fractions induced by aristolochic acid. The benchmark dose values producing a 10%, 50%, and 100% increase over the background level were calculated using Benchmark dose software package. The bars indicate the calculated lower and upper 95% confidence interval (BMDL and BMDU) of each value. Black bar, BMD₁₀; red bar, BMD₅₀; and blue bar, BMD₁₀₀