Detection and quantitation of dG-AAI and dA-AAI adducts by 32P-postlabeling methods in urothelium and exfoliated cells in urine of rats treated with aristolochic acid I

Aristolochic acid-containing Chinese herbal medicine and upper urinary tract urothelial carcinoma in Taiwan: a narrative review

PURPOSE

The high incidence of upper urinary tract urothelial carcinoma (UTUC) in Taiwan is largely due to exposure to aristolochic acid (AA), a principal component of Aristolochia-based herbal medicines. Here we systematically review the molecular epidemiology, clinical presentation and biomarkers associated with AA-induced UTUC.

METHODS

This is a narrative review. Medline, Embase, and Web of Science were searched from inception to December 31, 2021. Studies evaluating the association, detection, and clinical characteristics of AA and UTUC were included.

RESULTS

A nationwide database revealed 39% of the Taiwanese population had been exposed to AA-containing herbs between 1997 and 2003. Epidemiological reports revealed AA posed a significantly higher hazard for renal failure and UTUC in herbalists and the general population who ingested AA-containing herbs. The presence of aristolactam-DNA adducts and a distinctive signature mutation, A:T to T:A transversions, located predominantly on the non-transcribed DNA strand, with a strong preference for deoxyadenosine in a consensus sequence (CAG), was observed in many UTUC patients. Clinically, AA-related UTUC patients were characterized by a younger age, female gender, impaired renal function and recurrence of contralateral UTUC. To date, there are no preventive measures, except prophylactic nephrectomy, for subjects at risk of AA nephropathy or AA-related UTUC.

CONCLUSION

AA exposure via Aristolochia-based herbal medicines is a problem throughout Taiwan, resulting in a high incidence of UTUC. Aristolactam-DNA adducts and a distinctive signature mutation, A:T to T:A transversions, can be used as biomarkers to identify AA-related UTUC. AA-related UTUC is associated with a high recurrence rate of contralateral UTUC.

Synergistic Interaction of Polycyclic Aromatic Hydrocarbons, Phthalate Esters, or Phenol on DNA Adduct Formation by Aristolochic Acid I: Insights into the Etiology of Balkan Endemic Nephropathy

Balkan endemic nephropathy (BEN) is a multifactorial environmental disease, with chronic exposure to aristolochic acids (AAs) through AA-contaminated food being one of the major etiological mechanisms. However, the bulk of previous research has only focused on investigating the possible roles of individual pollutants in disease development and the etiological mechanism of BEN remains controversial. In this study, we investigated the exposure concentration and duration dependence of coexposure to phthalate esters and lignite coal-derived phenol and polycyclic aromatic hydrocarbons (PAHs) on the metabolism and DNA adduct formation of aristolochic acid I (AAI). Results showed that both the metabolic activation and DNA adduct formation of AAI in cultured human kidney cells were affected by their coexposure to the above-mentioned environmental pollutants. Furthermore, our results suggest that chemicals leached from lignite coal likely played a role by triggering AA-activating enzymes to produce more of the promutagenic DNA adducts, thus further elevating the nephrotoxicity and carcinogenicity of AAs and increasing the risk of BEN. It is believed that the results of this study provide a better understanding of the etiological mechanism of BEN and offer insights into methods and policies to lower the risk of this devastating disease.

In Vivo Metabolism of Aristolochic Acid I and II in Rats Is Influenced by Their Coexposure

The plant extract aristolochic acid (AA), containing aristolochic acid I (AAI) and II (AAII) as major components, causes aristolochic acid nephropathy and Balkan endemic nephropathy, unique renal diseases associated with upper urothelial cancer. Differences in the metabolic activation and detoxification of AAI and AAII and their effects on the metabolism of AAI/AAII mixture in the plant extract might be of great importance for an individual's susceptibility in the development of AA-mediated nephropathies and malignancies. Here, we investigated in vivo metabolism of AAI and AAII after ip administration to Wistar rats as individual compounds and as AAI/AAII mixture using high performance liquid chromatography/electrospray ionization mass spectrometry. Experimental findings were supported by theoretical calculations using density functional theory. We found that exposure to AAI/AAII mixture affected the generation of their oxidative and reductive metabolites formed during Phase I biotransformation and excreted in rat urine. Several Phase II metabolites of AAI and AAII found in the urine of exposed rats were also analyzed. Our results indicate that AAI is more efficiently metabolized in rats in vivo than AAII. Whereas AAI is predominantly oxidized during in vivo metabolism, its reduction is the minor metabolic pathway. In contrast, AAII is mainly metabolized by reduction. The oxidative reaction only occurs if aristolactam II, the major reductive metabolite of AAII, is enzymatically hydroxylated, forming aristolactam Ia. In AAI/AAII mixture, the metabolism of AAI and AAII is influenced by the presence of both AAs. For instance, the reductive metabolism of AAI is increased in the presence of AAII while the presence of AAI decreased the reductive metabolism of AAII. These results suggest that increased bioactivation of AAI in the presence of AAII also leads to increased AAI genotoxicity, which may critically impact AAI-mediated carcinogenesis. Future studies are needed to explain the underlying mechanism(s) for this phenomenon.

DNA adducts: Formation, biological effects, and new biospecimens for mass spectrometric measurements in humans

Hazardous chemicals in the environment and diet or their electrophilic metabolites can form adducts with genomic DNA, which can lead to mutations and the initiation of cancer. In addition, reactive intermediates can be generated in the body through oxidative stress and damage the genome. The identification and measurement of DNA adducts are required for understanding exposure and the causal role of a genotoxic chemical in cancer risk. Over the past three decades, 32 P-postlabeling, immunoassays, gas chromatography/mass spectrometry, and liquid chromatography/mass spectrometry (LC/MS) methods have been established to assess exposures to chemicals through measurements of DNA adducts. It is now possible to measure some DNA adducts in human biopsy samples, by LC/MS, with as little as several milligrams of tissue. In this review article, we highlight the formation and biological effects of DNA adducts, and highlight our advances in human biomonitoring by mass spectrometric analysis of formalin-fixed paraffin-embedded tissues, untapped biospecimens for carcinogen DNA adduct biomarker research.

Quantification of aristolochic acid-RNA adducts in the urine of aristolochic acid-treated rats by liquid chromatography-tandem mass spectrometry

Balkan endemic nephropathy (BEN) is a peculiar renal disease affecting thousands of farmers living in the suburban areas of the Balkan countries. Emerging evidence suggested that BEN is an environmental disease caused by chronic food poisoning with aristolochic acid (AA). We have developed a sensitive liquid chromatography-tandem mass spectrometry method to detect urinary RNA-AA adducts. Results revealed high levels of RNA-AA adducts in the urine samples collected from AA-treated rats. To the best of our knowledge, this study is the first to report on the detection of urinary RNA-AA adducts. Compared with previous studies that quantified DNA-AA adducts, this method is more sensitive and user-friendly.

New Approaches for Biomonitoring Exposure to the Human Carcinogen Aristolochic Acid

Aristolochic acids (AA) are found in all Aristolochia herbaceous plants, many of which have been used worldwide for medicinal purposes for centuries. AA are causal agents of the chronic kidney disease entity termed aristolochic acid nephropathy (AAN) and potent upper urinary tract carcinogens in humans. AAN and upper urinary tract cancers are endemic in rural areas of Croatia and other Balkan countries where exposure to AA occurs through the ingestion of home-baked bread contaminated with Aristolochia seeds. In Asia, exposure to AA occurs through usage of traditional Chinese medicinal herbs containing Aristolochia. Despite warnings from regulatory agencies, traditional Chinese herbs containing AA continue to be used world-wide. In this review, we highlight novel approaches to quantify exposure to AA, by analysis of aristolactam (AL) DNA adducts, employing ultraperformance liquid chromatography-electrospray ionization/multistage mass spectrometry (UPLC-ESI/MSⁿ). DNA adducts are a measure of internal exposure to AA and serve as an important end point for cross-species extrapolation of toxicity data and human risk assessment. The level of sensitivity of UPLC-ESI/MSⁿ surpasses the limits of detection of AL-DNA adducts obtained by ³²P-postlabeling techniques, the most widely employed methods for detecting putative DNA adducts in humans. AL-DNA adducts can be measured by UPLC-ESI/MS³, not only in fresh frozen renal tissue, but also in formalin-fixed, paraffin-embedded (FFPE) samples, an underutilized biospecimen for assessing chemical exposures, and in exfoliated urinary cells, a non-invasive approach. The frequent detection of AL DNA adducts in renal tissues, combined with the characteristic mutational spectrum induced by AA in TP53 and other genes provides compelling data for a role of AA in upper urothelial tract cancer.

Noninvasive measurement of aristolochic acid-DNA adducts in urine samples from aristolochic acid-treated rats by liquid chromatography coupled tandem mass spectrometry: evidence for DNA repair by nucleotide-excision repair mechanisms

Nephrotoxic aristolochic acids (AAs) form covalently bonded DNA adducts upon metabolic activation. In this work, a non-invasive approach to detect AAs exposure by quantifying urinary excreted DNA-AA adducts is presented. The developed method entails solid-phase extraction (SPE) enrichment of the urine-excreted DNA-AAs adducts, addition of internal standard, and quantification by liquid chromatography coupled tandem mass spectrometric (LC-MS/MS) analysis. Quantitative analysis revealed 7-(deoxyadenosine-N(6)-yl)-aristolactam II and 7-(deoxyguanosine-N(2)-yl)-aristolactam I that were previously detected as major DNA-AA adducts in different organs of AA-dosed rats, were detected as the major urine excreted adducts. Lower levels of 7-(deoxyadenosine-N(6)-yl)-aristolactam I and 7-(deoxyguanosine-N(2)-yl)-aristolactam II were also detected in the collected urine samples. The identities of the detected urinary DNA-AA adducts were confirmed by comparing chromatographic retention time with synthetic standards, by high-accuracy MS, and MS/MS analyses. LC-MS/MS analysis of the urine samples collected from the AAs-dosed rats demonstrated a time-dependent decrease in the urinary adduct levels, indicating the urinary DNA-AA adduct levels were reflective of the tissue adduct levels. It is expected that the developed approach of detecting urinary DNA-AA adducts will facilitate further carcinogenesis investigations of AAs.

Mechanisms of chemical carcinogenesis in the kidneys

Chemical carcinogens are substances which induce malignant tumours, increase their incidence or decrease the time taken for tumour formation. Often, exposure to chemical carcinogens results in tissue specific patterns of tumorigenicity. The very same anatomical, biochemical and physiological specialisations which permit the kidney to perform its vital roles in maintaining tissue homeostasis may in fact increase the risk of carcinogen exposure and contribute to the organ specific carcinogenicity observed with numerous kidney carcinogens. This review will address the numerous mechanisms which play a role in the concentration, bioactivation, and uptake of substances from both the urine and blood which significantly increase the risk of cancer in the kidney.

Quantitative determination of aristolochic acid-derived DNA adducts in rats using 32P-postlabeling/polyacrylamide gel electrophoresis analysis

Aristolochic acids (AA) are nephrotoxic and carcinogenic nitroaromatic compounds produced by the Aristolochiaceae family of plants. Ingestion of these phytotoxins by humans results in a syndrome known as AA nephropathy, characterized by renal tubulointerstitial fibrosis and upper urothelial cancer. After activation by cellular enzymes, AA I and II react with DNA to form covalent adducts and as such represent potential biomarkers for studies of AA toxicity. Using site-specifically modified oligodeoxynucleotides as standards, we have developed a method for quantifying 7-(deoxyadenosin-N(6)-yl) aristolactam-DNA or 7-(deoxyguanosin-N(2)-yl) aristolactam-DNA adducts in tissues of Wistar rats using an assay in which (32)P-postlabeling techniques are coupled with nondenaturing polyacrylamide gel electrophoresis. The limit of detection with this technique is five adducts in 10(9) nucleotides for a 5-microg DNA sample. In contrast to previous reports, we find that the levels of AA adducts in renal tissues of Wistar rats treated p.o. with AA for 1 week with 5 mg/kg/day of AA I or AA II were much higher than that in the forestomach. Highest adduct levels were observed in rats treated with AA II, suggesting that this compound may be more genotoxic than AA I. Treatment of rats with aristolactam I, an end-product of AA I metabolism, resulted in a much lower level of adduction. This study establishes the feasibility of using AA-DNA adducts as intermediate biomarkers of exposure in studies of AA nephropathy and its associated urothelial cancer.

Genotoxicity in the rodent urinary bladder

Elucidation of the mechanisms by which a chemical may induce urinary bladder tumours in rodents can be expected to provide insight into the relative risk from that agent. The methodologies for exploring whether tumour induction may be a response to direct genotoxic effect of the compound have been successfully applied to the bladders of both mice and rats. Thus, with experimental approaches that utilize adduct detection through the use of immunochemical and postlabelling techniques, unscheduled DNA synthesis and mutagenicity as studied with transgenic animals it is possible to obtain fundamental information on the genotoxic potential of carcinogens in the target bladder. Application of these experimental approaches to carcinogens for which the mechanisms of action are not known should permit assessment of the likelihood that genotoxic or non-genotoxic mechanisms are involved in the tumour induction process. Moreover, such studies may provide knowledge of the molecular pathways that are involved in the action of genotoxic agents, thus enabling judgements to be made as to whether humans are subject to tumour induction by the chemical.