Magnetic quaternary ammonium polymer bearing porous agarose for selective extraction of Aristolochic acids in the plasma

Aristolochic acids (AAs) naturally occurring in the herbal genus Aristolochia are associated with a high risk of kidney failure, multiple tumors and cancers. However, approaches with high selectivity and rapidity for measuring AAs in biological samples are still inadequate. Inspired by the mechanism of AAs-induced nephrotoxicity, we designed a hybrid magnetic polymer-porous agarose (denoted as MNs@SiO2M@DNV-A), mimicking the effect of basic and aromatic residues of organic anion transporter 1 (OAT1) for efficient enriching aristolochic acid I (AA I) and aristolochic acid II (AA II) in the plasma. The monomers of vinylbenzyl trimethylammonium chloride (VBTAC), N-vinyl-2-pyrrolidinone (NVP) and divinylbenzene (DVB) were employed to construct the polymer layer, which provided a selective adsorption for AAs by multiple interactions. The porous agarose shell contributed to remove interfering proteins in the plasma samples. A magnetic solid-phase extraction (MSPE) based on the proposed composite enhanced the selectivity toward AA I and AA II in the plasma samples. In combination of HPLC analysis, the proposed method was proved to be applicable to fast and specific quantification of AAs in blood samples, which was characterized by a good linearity, high sensitivity, acceptable recovery, excellent repeatability and satisfactory reusability.

Screening DNA Damage in the Rat Kidney and Liver by Untargeted DNA Adductomics

Air pollution, tobacco smoke, and red meat are associated with renal cell cancer (RCC) risk in the United States and Western Europe; however, the chemicals that form DNA adducts and initiate RCC are mainly unknown. Aristolochia herbaceous plants are used for medicinal purposes in Asia and worldwide. They are a significant risk factor for upper tract urothelial carcinoma (UTUC) and RCC to a lesser extent. The aristolochic acid (AA) 8-methoxy-6-nitrophenanthro-[3,4-d]-1,3-dioxolo-5-carboxylic acid (AA-I), a component of Aristolochia herbs, contributes to UTUC in Asian cohorts and in Croatia, where AA-I exposure occurs from ingesting contaminated wheat flour. The DNA adduct of AA-I, 7-(2'-deoxyadenosin-N6-yl)-aristolactam I, is often detected in patients with UTUC, and its characteristic A:T-to-T:A mutational signature occurs in oncogenes and tumor suppressor genes in AA-associated UTUC. Identifying DNA adducts in the renal parenchyma and pelvis caused by other chemicals is crucial to gaining insights into unknown RCC and UTUC etiologies. We employed untargeted screening with wide-selected ion monitoring tandem mass spectrometry (wide-SIM/MS2) with nanoflow liquid chromatography/Orbitrap mass spectrometry to detect DNA adducts formed in rat kidneys and liver from a mixture of 13 environmental, tobacco, and dietary carcinogens that may contribute to RCC. Twenty DNA adducts were detected. DNA adducts of 3-nitrobenzanthrone (3-NBA), an atmospheric pollutant, and AA-I were the most abundant. The nitrophenanthrene moieties of 3-NBA and AA-I undergo reduction to their N-hydroxy intermediates to form 2'-deoxyguanosine (dG) and 2'-deoxyadenosine (dA) adducts. We also discovered a 2'-deoxycytidine AA-I adduct and dA and dG adducts of 10-methoxy-6-nitro-phenanthro-[3,4-d]-1,3-dioxolo-5-carboxylic acid (AA-III), an AA-I isomer and minor component of the herbal extract assayed, signifying AA-III is a potent kidney DNA-damaging agent. The roles of AA-III, other nitrophenanthrenes, and nitroarenes in renal DNA damage and human RCC warrant further study. Wide-SIM/MS2 is a powerful scanning technology in DNA adduct discovery and cancer etiology characterization.

Computational Analysis of Naturally Occurring Aristolochic Acid Analogues and Their Biological Sources

Aristolochic acids are known for nephrotoxicity, and implicated in multiple cancer types such as hepatocellular carcinomas demonstrated by recent studies. Natural products that are analogues to aristolochic acids have been constantly isolated from organisms; a larger chemical space of these compounds and a wider coverage of biological sources should be determined in consideration of the potential hazard of aristolochic acid analogues and the wide distribution of their biological sources in the nature. Therefore, we carried out an in silico research of naturally occurring aristolochic acid analogues and their biological sources, as a supplement to existing studies. The result shows a chemical space of 238 naturally occurring aristolochic acid analogues that are present in 175 species of biological sources including 44 traditional medicines. With the computational estimation for toxicity and the implication in hazard assessment of a biological source with the presence of aristolochic acid analogues, we propose that additional awareness should be raised to the public for avoidance of toxic species, especially those that are used as herbal medicines and easily accessible.

Berberine-Based Heterogeneous Linear Supramolecules Neutralized the Acute Nephrotoxicity of Aristolochic Acid by the Self-Assembly Strategy

Aristolochic acid (AA) has been reported to cause a series of health problems, including aristolochic acid nephropathy and liver cancer. However, AA-containing herbs are highly safe in combination with berberine (Ber)-containing herbs in traditional medicine, suggesting the possible neutralizing effect of Ber on the toxicity of AA. In the present study, in vivo systematic toxicological experiments performed in zebrafish and mice showed that the supramolecule self-assembly formed by Ber and AA significantly reduced the toxicity of AA and attenuated AA-induced acute kidney injury. Ber and AA can self-assemble into linear heterogenous supramolecules (A-B) via electrostatic attraction and π-π stacking, with the hydrophobic groups outside and the hydrophilic groups inside during the drug combination practice. This self-assembly strategy may block the toxic site of AA and hinder its metabolism. Meanwhile, A-B linear supramolecules did not disrupt the homeostasis of gut microflora as AA did. RNA-sequence analysis, immunostaining, and western blot of the mice kidney also showed that A-B supramolecules almost abolished the acute nephrotoxicity of AA in the activation of the immune system and tumorigenesis-related pathways.

Rapid characterization and pharmacokinetic study of aristolochic acid analogues using ion mobility mass spectrometry

Aristolochic acid analogues (AAAs), naturally existing in herbal Aristolochia and Asarum genera, were once widely used in traditional pharmacopeias because of their anti-inflammatory properties, but lately they were identified as potential nephrotoxins and mutagens. A method for rapid characterization of AAAs in serum was developed using ion mobility spectrometry coupled with mass spectrometry (IMS-MS). Five AAAs, containing four aristolochic acids and one aristolactam, were separated and identified within milliseconds. AAAs were separated in gas phase based on the difference of their ion mobility (K0), and then identified based on their K0 values, m/z, and product ions from MS/MS. Quantitative analysis of AAAs was performed using an internal standard with a satisfactory sensitivity. Limits of detection (signal-to-noise = 3) and quantification (signal-to-noise = 10) were 1-5 ng/mL and 3-8 ng/mL, respectively. The method was validated and successfully applied to the pharmacokinetics study of AAAs in rats, offering a promising way for fast screening and evaluation of AAAs in biological samples.

Method for Biomonitoring DNA Adducts in Exfoliated Urinary Cells by Mass Spectrometry

Tobacco smoking contributes to about 50% of the bladder-cancer (BC) cases in the United States. Some aromatic amines in tobacco smoke are bladder carcinogens; however, other causal agents of BC are uncertain. Exfoliated urinary cells (EUCs) are a promising noninvasive biospecimen to screen for DNA adducts of chemicals that damage the bladder genome, although the analysis of DNA adducts in EUCs is technically challenging because of the low number of EUCs and limiting quantity of cellular DNA. Moreover, EUCs and their DNA adducts must remain viable during the time of collection and storage of urine to develop robust screening methods. We employed RT4 cells, a well-differentiated transitional epithelial bladder cell line, as a cell-model system in urine to investigate cell viability and the chemical stability of DNA adducts of two prototypical bladder carcinogens: 4-aminobiphenyl (4-ABP), an aromatic amine found in tobacco smoke, and aristolochic acid I (AA-I), a nitrophenanthrene found in Aristolochia herbaceous plants used for medicinal purposes worldwide. The cell viability of RT4 cells pretreated with 4-ABP or AA-I in urine exceeded 80%, and the major DNA adducts of 4-ABP and AA-I, quantified by liquid chromatography-mass spectrometry, were stable for 24 h. Thereafter, we successfully screened EUCs of mice treated with AA-I to measure DNA adducts of AA-I, which were still detected 25 days following treatment with the carcinogen. EUCs are promising biospecimens that can be employed for the screening of DNA adducts of environmental and dietary genotoxicants that may contribute to the development of BC.

Aristolic Acid Derivatives from the Bark of Antidesma ghaesembilla

Antidesma ghaesembilla is an important medicinal and food plant in many Asian countries. Ten substances could be isolated from the dichloromethane and methanol extract: sitostenone (3), daucosterol (4), chavibetol (5), asperphenamate (6), protocatechuic acid (7), vanillic acid-4-O-β-D-glucoside (8), 1-O-β-D-glucopyranosyl-3-O-methyl-phloroglucinol (9), and aristolic acid II-8-O-β-D-glucoside (10), and two new aristolic acid derivatives, 10-amino-5,7-dimethoxy-aristolic acid II (= 6-amino-9,11-dimethoxyphenanthro[3,4-d]-1,3-dioxole-5-carboxylic acid; 1) and 5,7-dimethoxy-aristolochic acid II (= 9,11-dimethoxy-6-nitrophenantro[3,4-d]-1,3-dioxole-5-carboxylic acid; 2). Exposure to humans of some of these compounds is associated with a severe disease today known as aristolochic acid nephropathy. Therefore, the traditional usage of this plant has to be reconsidered carefully.

Interference-free spectrofluorometric quantification of aristolochic acid I and aristololactam I in five Chinese herbal medicines using chemical derivatization enhancement and second-order calibration methods

A rapid interference-free spectrofluorometric method combined with the excitation-emission matrix fluorescence and the second-order calibration methods based on the alternating penalty trilinear decomposition (APTLD) and the self-weighted alternating trilinear decomposition (SWATLD) algorithms, was proposed for the simultaneous determination of nephrotoxic aristolochic acid I (AA-I) and aristololactam I (AL-I) in five Chinese herbal medicines. The method was based on a chemical derivatization that converts the non-fluorescent AA-I to high-fluorescent AL-I, achieving a high sensitive and simultaneous quantification of the analytes. The variables of the derivatization reaction that conducted by using zinc powder in acetose methanol aqueous solution, were studied and optimized for best quantification results of AA-I and AL-I. The satisfactory results of AA-I and AL-I for the spiked recovery assay were achieved with average recoveries in the range of 100.4-103.8% and RMSEPs <0.78ngmL^-1, which validate the accuracy and reliability of the proposed method. The contents of AA-I and AL-I in five herbal medicines obtained from the proposed method were also in good accordance with those of the validated LC-MS/MS method. In light of high sensitive fluorescence detection, the limits of detection (LODs) of AA-I and AL-I for the proposed method compare favorably with that of the LC-MS/MS method, with the LODs <0.35 and 0.29ngmL^-1, respectively. The proposed strategy based on the APTLD and SWATLD algorithms by virtue of the "second-order advantage", can be considered as an attractive and green alternative for the quantification of AA-I and AL-I in complex herbal medicine matrices without any prior separations and clear-up processes.

An Integrated View of Aristolochic Acid Nephropathy: Update of the Literature

The term “aristolochic acid nephropathy” (AAN) is used to include any form of toxic interstitial nephropathy that is caused either by ingestion of plants containing aristolochic acids (AA) as part of traditional phytotherapies (formerly known as “Chinese herbs nephropathy”), or by the environmental contaminants in food (Balkan endemic nephropathy). It is frequently associated with urothelial malignancies. Although products containing AA have been banned in most of countries, AAN cases remain regularly reported all over the world. Moreover, AAN incidence is probably highly underestimated given the presence of AA in traditional herbal remedies worldwide and the weak awareness of the disease. During these two past decades, animal models for AAN have been developed to investigate underlying molecular and cellular mechanisms involved in AAN pathogenesis. Indeed, a more-in-depth understanding of these processes is essential to develop therapeutic strategies aimed to reduce the global and underestimated burden of this disease. In this regard, our purpose was to build a broad overview of what is currently known about AAN. To achieve this goal, we aimed to summarize the latest data available about underlying pathophysiological mechanisms leading to AAN development with a particular emphasis on the imbalance between vasoactive factors as well as a focus on the vascular events often not considered in AAN.

LC-MS- and (1)H NMR-Based Metabolomic Analysis and in Vitro Toxicological Assessment of 43 Aristolochia Species

Species of Aristolochia are used as herbal medicines worldwide. They cause aristolochic acid nephropathy (AAN), a devastating disease associated with kidney failure and renal cancer. Aristolochic acids I and II (1 and 2) are considered to be responsible for these nephrotoxic and carcinogenic effects. A wide range of other aristolochic acid analogues (AAAs) exist, and their implication in AAN may have been overlooked. An LC-MS- and (1)H NMR-based metabolomic analysis was carried out on 43 medicinally used Aristolochia species. The cytotoxicity and genotoxicity of 28 Aristolochia extracts were measured in human kidney (HK-2) cells. Compounds 1 and 2 were found to be the most common AAAs. However, AA IV (3), aristolactam I (4), and aristolactam BI (5) were also widespread. No correlation was found between the amounts of 1 or 2 and extract cytotoxicity against HK-2 cells. The genotoxicity and cytotoxicity of the extracts could be linked to their contents of 5, AA D (8), and AA IIIa (10). These results undermine the assumption that 1 and 2 are exclusively responsible for the toxicity of Aristolochia species. Other analogues are likely to contribute to their toxicity and need to be considered as nephrotoxic agents. These findings facilitate understanding of the nephrotoxic mechanisms of Aristolochia and have significance for the regulation of herbal medicines.

A Mechanism of O-Demethylation of Aristolochic Acid I by Cytochromes P450 and Their Contributions to This Reaction in Human and Rat Livers: Experimental and Theoretical Approaches

Aristolochic acid I (AAI) is a plant alkaloid causing aristolochic acid nephropathy, Balkan endemic nephropathy and their associated urothelial malignancies. AAI is detoxified by cytochrome P450 (CYP)-mediated O-demethylation to 8-hydroxyaristolochic acid I (aristolochic acid Ia, AAIa). We previously investigated the efficiencies of human and rat CYPs in the presence of two other components of the mixed-functions-oxidase system, NADPH:CYP oxidoreductase and cytochrome b₅, to oxidize AAI. Human and rat CYP1A are the major enzymes oxidizing AAI. Other CYPs such as CYP2C, 3A4, 2D6, 2E1, and 1B1, also form AAIa, but with much lower efficiency than CYP1A. Based on velocities of AAIa formation by examined CYPs and their expression levels in human and rat livers, here we determined the contributions of individual CYPs to AAI oxidation in these organs. Human CYP1A2 followed by CYP2C9, 3A4 and 1A1 were the major enzymes contributing to AAI oxidation in human liver, while CYP2C and 1A were most important in rat liver. We employed flexible in silico docking methods to explain the differences in AAI oxidation in the liver by human CYP1A1, 1A2, 2C9, and 3A4, the enzymes that all O-demethylate AAI, but with different effectiveness. We found that the binding orientations of the methoxy group of AAI in binding centers of the CYP enzymes and the energies of AAI binding to the CYP active sites dictate the efficiency of AAI oxidation. Our results indicate that utilization of experimental and theoretical methods is an appropriate study design to examine the CYP-catalyzed reaction mechanisms of AAI oxidation and contributions of human hepatic CYPs to this metabolism.

Temporal Variation of Aristolochia chilensis Aristolochic Acids during Spring

In this communication, we report the springtime variation of the composition of aristolochic acids (AAs) in Aristolochia chilensis leaves and stems. The dominant AA in the leaves of all samples, which were collected between October and December, was AA-I (1), and its concentration varied between 212.6 ± 3.8 and 145.6 ± 1.2 mg/kg and decreased linearly. This decrease occurred in parallel with the increase in AA-Ia (5) concentration from 15.9 ± 0.8 mg/kg at the beginning of October to 96.8 ± 7.8 mg/kg in mid-December. Both acids are enzymatically related by methylation-demethylation reactions. Other AAs also showed important variations: AA-II (2) significantly increased in concentration, reaching a maximum in the first two weeks of November and subsequently decreasing in mid-December to approximately the October levels. The principal component in the AA mixture of the stems was also AA-I (1); similar to AA-II (2), its concentration increased beginning in October, peaked in the second week of November and subsequently decreased. The concentrations of AA-IIIa (6) and AA-IVa (7) in the leaves and stems varied throughout the study period, but no clear pattern was identified. Based on the variation of AAs in A. chilensis leaves and stems during the study period, the reduced contents of non-phenolic AAs and increased concentrations of phenolic AAs are likely associated with a decrease in this plant’s toxicity during the spring.

Mass Spectrometric and Spectrofluorometric Studies of the Interaction of Aristolochic Acids with Proteins

Aristolochic acid (AA) is a potent carcinogen and nephrotoxin and is associated with the development of "Chinese herb nephropathy" and Balkan endemic nephropathy. Despite decades of research, the specific mechanism of the observed nephrotoxicity has remained elusive and the potential effects on proteins due to the observed toxicity of AA are not well-understood. To better understand the pharmacotoxicological features of AA, we investigated the non-covalent interactions of AA with proteins. The protein-binding properties of AA with bovine serum albumin (BSA) and lysozyme were characterized using spectrofluorometric and mass spectrometric (MS) techniques. Moreover, the protein-AA complexes were clearly identified by high-resolution MS analyses. To the best of our knowledge, this is the first direct evidence of non-covalently bound protein-AA complexes. An analysis of the spectrofluorometric data by a modified Stern-Volmer plot model also revealed that both aristolochic acid I (AAI) and aristolochic acid II (AAII) were bound to BSA and lysozyme in 1:1 stoichiometries. A significantly stronger protein binding property was observed in AAII than in AAI as evidenced by the spectrofluorometric and MS analyses, which may explain the observed higher mutagenicity of AAII.

Structural Basis for the Inhibition of a Phospholipase A2-Like Toxin by Caffeic and Aristolochic Acids

One of the main challenges in toxicology today is to develop therapeutic alternatives for the treatment of snake venom injuries that are not efficiently neutralized by conventional serum therapy. Venom phospholipases A2 (PLA2s) and PLA2-like proteins play a fundamental role in skeletal muscle necrosis, which can result in permanent sequelae and disability. This leads to economic and social problems, especially in developing countries. In this work, we performed structural and functional studies with Piratoxin-I, a Lys49-PLA2 from Bothropspirajai venom, complexed with two compounds present in several plants used in folk medicine against snakebites. These ligands partially neutralized the myotoxic activity of PrTX-I towards binding on the two independent sites of interaction between Lys49-PLA2 and muscle membrane. Our results corroborate the previously proposed mechanism of action of PLA2s-like and provide insights for the design of structure-based inhibitors that could prevent the permanent injuries caused by these proteins in snakebite victims.

Mechanisms of enzyme-catalyzed reduction of two carcinogenic nitro-aromatics, 3-nitrobenzanthrone and aristolochic acid I: Experimental and theoretical approaches

This review summarizes the results found in studies investigating the enzymatic activation of two genotoxic nitro-aromatics, an environmental pollutant and carcinogen 3-nitrobenzanthrone (3-NBA) and a natural plant nephrotoxin and carcinogen aristolochic acid I (AAI), to reactive species forming covalent DNA adducts. Experimental and theoretical approaches determined the reasons why human

NAD(P)H

quinone oxidoreductase (NQO1) and cytochromes P450 (CYP) 1A1 and 1A2 have the potential to reductively activate both nitro-aromatics. The results also contributed to the elucidation of the molecular mechanisms of these reactions. The contribution of conjugation enzymes such as N,O-acetyltransferases (NATs) and sulfotransferases (SULTs) to the activation of 3-NBA and AAI was also examined. The results indicated differences in the abilities of 3-NBA and AAI metabolites to be further activated by these conjugation enzymes. The formation of DNA adducts generated by both carcinogens during their reductive activation by the NOQ1 and CYP1A1/2 enzymes was investigated with pure enzymes, enzymes present in subcellular cytosolic and microsomal fractions, selective inhibitors, and animal models (including knock-out and humanized animals). For the theoretical approaches, flexible in silico docking methods as well as ab initio calculations were employed. The results summarized in this review demonstrate that a combination of experimental and theoretical approaches is a useful tool to study the enzyme-mediated reaction mechanisms of 3-NBA and AAI reduction.

Spectroscopic and quantum chemical study of an alkaloid aristolochic acid I

Aristolochic acids (AAs) (Aristolochiaceae) are used in the traditional Chinese herb medicine. We have presented the geometry optimization, electrostatic potential surface, frontier orbital energy gap and vibrational wavenumbers of aristolochic acid I (AA I) using ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method employing 6-311G(d,p) basis set. A complete vibrational assignment has been done on the basis of calculations on monomer and dimer of AA I. The UV-vis absorption spectrum has been recorded in ethanol solvent and compared with the calculated one in the gas phase as well as in solvent environment (integral-equation formalism polarizable continuum model; IEF-PCM) using TD-DFT/6-31G basis set. A short outline of the NBO analysis segment with their structural meaning has been presented. The variation of thermodynamic properties with temperature was calculated theoretically and the thermal response of the compound has been recorded with the help of differential scanning calorimetry (DSC) in N2 environment.

Conversion of aristolochic acid I into aristolic acid by reaction with cysteine and glutathione: biological implications

Aristolochic acid I (AA-I), naturally occurring in Aristolochia plants, is a potent nephrotoxin and carcinogen. Here we report that AA-I suffers hydrogenolysis with loss of the nitro group by reaction with cysteine or glutathione to give aristolic acid. Since the reaction can proceed in aqueous solutions at pH 7.0 and 37 °C, it is inferred that it may also occur in biological systems and contribute to the nephrotoxic effects induced by AA-I.

Human formalin-fixed paraffin-embedded tissues: an untapped specimen for biomonitoring of carcinogen DNA adducts by mass spectrometry

DNA adducts represent internal dosimeters to measure exposure to environmental and endogenous genotoxicants. Unfortunately, in molecular epidemiologic studies, measurements of DNA adducts often are precluded by the unavailability of fresh tissue. In contrast, formalin-fixed paraffin embedded (FFPE) tissues frequently are accessible for biomarker discovery. We report here that DNA adducts of aristolochic acids (AAs) can be measured in FFPE tissues at a level of sensitivity comparable to freshly frozen tissue. AAs are nephrotoxic and carcinogenic compounds found in Aristolochia herbaceous plants, many of which have been used worldwide for medicinal purposes. AAs are implicated in the etiology of aristolochic acid nephropathy and upper urinary tract carcinoma. 8-Methoxy-6-nitrophenanthro-[3,4-d]-1,3-dioxole-5-carboxylic acid (AA-I) is a component of Aristolochia herbs and a potent human urothelial carcinogen. AA-I reacts with DNA to form the aristolactam (AL-I)-DNA adduct 7-(deoxyadenosin-N(6)-yl) aristolactam I (dA-AL-I). We established a method to quantitatively retrieve dA-AL-I from FFPE tissue. Adducts were measured, using ultraperformance liquid chromatography/mass spectrometry, in liver and kidney tissues of mice exposed to AA-I, at doses ranging from 0.001 to 1 mg/kg body weight. dA-AL-I was then measured in 10-μm thick tissue-sections of FFPE kidney from patients with upper urinary tract cancers; the values were comparable to those observed in fresh frozen samples. The limit of quantification of dA-AL-I was 3 adducts per 10(9) DNA bases per 2.5 μg of DNA. The ability to retrospectively analyze FFPE tissues for DNA adducts may provide clues to the origin of human cancers for which an environmental cause is suspected.

[Effect of honey-toasting on the constituents and contents of aristolochic acid analogues in aristolochiae fructus]

OBJECTIVE

To evaluate the degree of de-toxification of Aristolochiae Fructus by honey-toasting technology from chemical viewpoint.

METHODS

The contents of aristolochic acid analogues (AAs) in Aristolochiae Fructus and its honey-toasted product were determined by HPLC, and the degree of de-toxification was evaluated comprehensively.

RESULTS

After honey-toasted, the contents of AAs decreased to varying degrees, and some new compounds were found.

CONCLUSION

The constituents and contents of Aristolochiae Fructus change after honey-toasted, which indicate honey-toasting can reduce the toxicity of Aristolochiae Fructus.

Aristoxazole analogues. Conversion of 8-nitro-1-naphthoic acid to 2-methylnaphtho[1,2-d]oxazole-9-carboxylic acid: comments on the chemical mechanism of formation of DNA adducts by the aristolochic acids

2-Methylnaphtho[1,2-d]oxazole-9-carboxylic acid was obtained by reduction of 8-nitro-1-naphthoic acid with zinc-acetic acid. This naphthoxazole is a condensation product between an 8-nitro-1-naphthoic acid reduction intermediate and acetic acid and is a lower homologue of aristoxazole, a similar condensation product of aristolochic acid I with acetic acid that was previously reported. Both oxazoles are believed to arise via a common nitrenium/carbocation ion mechanism that is likely related to that which leads to aristolochic acid-DNA-adducts.

Lack of recognition by global-genome nucleotide excision repair accounts for the high mutagenicity and persistence of aristolactam-DNA adducts

Exposure to aristolochic acid (AA), a component of Aristolochia plants used in herbal remedies, is associated with chronic kidney disease and urothelial carcinomas of the upper urinary tract. Following metabolic activation, AA reacts with dA and dG residues in DNA to form aristolactam (AL)-DNA adducts. These mutagenic lesions generate a unique TP53 mutation spectrum, dominated by A:T to T:A transversions with mutations at dA residues located almost exclusively on the non-transcribed strand. We determined the level of AL-dA adducts in human fibroblasts treated with AA to determine if this marked strand bias could be accounted for by selective resistance to global-genome nucleotide excision repair (GG-NER). AL-dA adduct levels were elevated in cells deficient in GG-NER and transcription-coupled NER, but not in XPC cell lines lacking GG-NER only. In vitro, plasmids containing a single AL-dA adduct were resistant to the early recognition and incision steps of NER. Additionally, the NER damage sensor, XPC-RAD23B, failed to specifically bind to AL-DNA adducts. However, placing AL-dA in mismatched sequences promotes XPC-RAD23B binding and renders this adduct susceptible to NER, suggesting that specific structural features of this adduct prevent processing by NER. We conclude that AL-dA adducts are not recognized by GG-NER, explaining their high mutagenicity and persistence in target tissues.

Discovery of GABA(A) receptor modulator aristolactone in a commercial sample of the Chinese herbal drug "Chaihu" (Bupleurum chinense roots) unravels adulteration by nephrotoxic Aristolochia manshuriensis roots

In a two-microelectrode voltage clamp assay using Xenopus laevis oocytes, a petroleum ether extract prepared from a commercial sample of the traditional Chinese herbal drug labelled as " Chaihu" (Bupleurum chinense DC. roots) enhanced the I(GABA) by 156 % ± 22 % when tested at 100 µg/mL. By means of HPLC-based activity profiling combined with high-resolution LC-MS and microprobe NMR, the germacranolide aristolactone was identified as one of the main active compounds (EC₅₀ 56.02 µM ± 5.09 µM). However, aristolactone has been previously reported only from the genus Aristolochia (Aristolochiaceae), suggesting a possible adulteration. With the aid of a validated HPTLC protocol for detection of aristolochic acids and with reference samples, the commercial sample was confirmed to be a mixture of Aristolochia manshuriensis root and Bupleurum chinense root. This finding was corroborated by macroscopic inspection of the drug. This case of adulteration with a highly nephrotoxic drug raises concerns about adequate quality control of TCM drugs commercialized in Europe.

A new aristolactam-type alkaloid from the roots of Aristolochia fangchi

Phytochemical investigation of 85% ethanol extracts from the roots of Aristolochia fangchi yielded a new aristolactam derivative named 6-methoxyl aristolactam I N-β-glucoside (1), together with four known compounds, aristolactam IVa (2), aristolactam I-β-D-glucoside (3), aristolactam I (4), and aristolactam-N-β-D-glucoside (5). Their structures were elucidated by spectral analysis. The cytotoxicity of the isolated compounds was also determined.

Theoretical investigation of differences in nitroreduction of aristolochic acid I by cytochromes P450 1A1, 1A2 and 1B1

OBJECTIVES

The herbal drug aristolochic acid (AA) derived from Aristolochia species has been shown to be the cause of aristolochic acid nephropathy (AAN), Balkan endemic nephropathy (BEN) and their urothelial malignancies. One of the common features of AAN and BEN is that not all individuals exposed to AA suffer from nephropathy and tumor development. One cause for these different responses may be individual differences in the activities of the enzymes catalyzing the biotransformation of AA. Thus, the identification of enzymes principally involved in the metabolism of AAI, the major toxic component of AA, and detailed knowledge of their catalytic specificities is of major importance. Human cytochrome P450 (CYP) 1A1 and 1A2 enzymes were found to be responsible for the AAI reductive activation to form AAI-DNA adducts, while its structurally related analogue, CYP1B1 is almost without such activity. However, knowledge of the differences in mechanistic details of CYP1A1-, 1A2-, and 1B1- mediated reduction is still lacking. Therefore, this feature is the aim of the present study.

METHODS

Molecular modeling capable of evaluating interactions of AAI with the active site of human CYP1A1, 1A2 and 1B1 under the reductive conditions was used. In silico docking, employing soft-soft (flexible) docking procedure was used to study the interactions of AAI with the active sites of these human enzymes.

RESULTS

The predicted binding free energies and distances between an AAI ligand and a heme cofactor are similar for all CYPs evaluated. AAI also binds to the active sites of CYP1A1, 1A2 and 1B1 in similar orientations. The carboxylic group of AAI is in the binding position situated directly above heme iron. This ligand orientation is in CYP1A1/1A2 further stabilized by two hydrogen bonds; one between an oxygen atom of the AAI nitro-group and the hydroxyl group of Ser122/Thr124; and the second bond between an oxygen atom of dioxolane ring of AAI and the hydroxyl group of Thr497/Thr498. For the CYP1B1:AAI complex, however, any hydrogen bonding of the nitro-group of AAI is prevented as Ser122/Thr124 residues are in CYP1B1 protein replaced by hydrophobic residue Ala133.

CONCLUSION

The experimental observations indicate that CYP1B1 is more than 10× less efficient in reductive activation of AAI than CYP1A2. The docking simulation however predicts the binding pose and binding energy of AAI in the CYP1B1 pocket to be analogous to that found in CYP1A1/2. We believe that the hydroxyl group of S122/T124 residue, with its polar hydrogen placed close to the nitro group of the substrate (AAI), is mechanistically important, for example it could provide a proton required for the stepwise reduction process. The absence of a suitable proton donor in the AAI-CYP1B1 binary complex could be the key difference, as the nitro group is in this complex surrounded only by the hydrophobic residues with potential hydrogen donors not closer than 5 Å.

Targeting RNA by small molecules: comparative structural and thermodynamic aspects of aristololactam-β-D-glucoside and daunomycin binding to tRNA(phe)

BACKGROUND

Interaction of aristololactam-β-D-glucoside and daunomycin with tRNA(phe) was investigated using various biophysical techniques.

METHODOLOGY/PRINCIPAL FINDINGS

Absorption and fluorescence studies revealed that both the compounds bind tRNA(phe) non-cooperatively. The binding of daunomycin was about one order of magnitude higher than that of aristololactam-β-D-glucoside. Stronger binding of the former was also inferred from fluorescence quenching data, quantum efficiency values and circular dichroic results. Results from isothermal titration calorimetry experiments suggested that the binding of both compounds was predominantly entropy driven with a smaller but favorable enthalpy term that increased with temperature. A large favorable electrostatic contribution to the binding of daunomycin to tRNA(phe) was revealed from salt dependence data and the dissection of the free energy values. The electrostatic component to the free energy change for aristololactam-β-D-glucoside-tRNA(phe) interaction was smaller than that of daunomycin. This was also inferred from the slope of log K versus [Na(+)] plots. Both compounds enhanced the thermal stability of tRNA(phe). The small heat capacity changes of -47 and -99 cal/mol K, respectively, observed for aristololactam-β-D-glucoside and daunomycin, and the observed enthalpy-entropy compensation phenomenon confirmed the involvement of multiple weak noncovalent interactions. Molecular aspects of the interaction have been revealed.

CONCLUSIONS/SIGNIFICANCE

This study presents the structural and energetic aspects of the binding of aristololactam-β-D-glucoside and daunomycin to tRNA(phe).

The human carcinogen aristolochic acid i is activated to form DNA adducts by human NAD(P)H:quinone oxidoreductase without the contribution of acetyltransferases or sulfotransferases

Ingestion of aristolochic acid (AA) is associated with development of urothelial tumors linked with AA nephropathy and is implicated in the development of Balkan endemic nephropathy-associated urothelial tumors. We investigated the efficiency of human NAD(P)H:quinone oxidoreductase (NQO1) to activate aristolochic acid I (AAI) and used in silico docking, using soft-soft (flexible) docking procedure, to study the interactions of AAI with the active site of human NQO1. AAI binds to the active site of NQO1 indicating that the binding orientation allows for direct hydride transfer (i.e., two electron reductions) to the nitro group of AAI. NQO1 activated AAI, generating DNA adduct patterns reproducing those found in urothelial tissues from humans exposed to AA. Because reduced aromatic nitro-compounds are often further activated by sulfotransferases (SULTs) or N,O-acetlytransferases (NATs), their roles in AAI activation were investigated. Our results indicate that phase II reactions do not play a major role in AAI bioactivation; neither native enzymes present in human hepatic or renal cytosols nor human SULT1A1, -1A2, -1A3, -1E, or -2A nor NAT1 or NAT2 further enhanced DNA adduct formation by AAI. Instead under the in vitro conditions used, DNA adducts arise by enzymatic reduction of AAI through the formation of a cyclic hydroxamic acid (N-hydroxyaristolactam I) favored by the carboxy group in peri position to the nitro group without additional conjugation. These results emphasize the major importance of NQO1 in the metabolic activation of AAI and provide the first evidence that initial nitroreduction is the rate limiting step in AAI activation.

Quality control of traditional chinese medicine by monoclonal antibody method

In a previous study, we reported the preparation, characterization, variation, specificity, and sensitivity of an anti-aristolochic acid-II (AA-II) monoclonal antibody. The preparation procedure was as follows. AA-II conjugated with bovine serum albumin was used as an antigen for immunizing BALB/c mice. Splenocytes isolated from the immunized mice were fused with an aminopterin-sensitive mouse myeloma cell line to produce hybridoma cells secreting a mono-clonal antibody (MAb) against AA-II. The selected MAb was subsequently cloned. Hapten number, isotype, and an esti-mated dissociation constant (KD) of the secreted MAb were determined. This MAb was used to establish an ELISA method. The linear range was 0.19-13 µg/ml. Anti-AA-II MAb showed extremely high specificity for AA-II, low cross-reactivity (CR) against other AAs or aristololactam-I, and negligible CR (<0.5%) toward other natural compounds with different chemical structures. This study describes the successful application of the ELISA method using anti-AA-II MAb to determine AA-II concentration in several crude drugs derived from Aristolochia species. The highest AA-II concentration (2.82 µg/mg) was observed in the stem of A. manshuriensis, followed by that in the fruit of A. contorta (0.81 µg/mg). In case of A. indica, AA-II concentration in the root was higher than that in the aerial parts. These data indicated that the established ELISA method can be used for the quality control of crude drugs derived from Aristolochia plants.

Interaction of aristololactam-β-D-glucoside and daunomycin with poly(A): spectroscopic and calorimetric studies

The binding of two sugar containing antibiotics viz. aristololactam-β-D-glucoside and daunomycin with single and double stranded poly(A) was investigated by spectroscopic and calorimetric studies. The binding affinity of daunomycin to ss poly(A) was of the order of 10⁶ M⁻¹ and that to ds poly(A) was of the order of 10⁵ M⁻¹. Aristololactam-β-D-glucoside showed a relatively weaker binding with an affinity of the order of 10⁴ M⁻¹ with both the conformations of poly(A). Fluorescence studies showed maximum quenching for daunomycin-ss poly(A) complexes. The binding constants calculated from fluorescence spectroscopy were in good agreement with that obtained from UV spectroscopy. Moderate perturbation of circular dichroic spectra of both the conformations of poly(A) in presence of these molecules with concomitant formation of prominent extrinsic CD bands in the 300-450 nm region further revealed the association. Isothermal titration calorimetry results showed an overall entropy driven binding in all the four systems though the entropy change was maximum in daunomycin-ss poly(A) binding. The binding affinity was also maximum for daunomycin-ss poly(A) and varied as daunomycin-ds poly(A) > aristololactam-β-D-glucoside-ds poly(A) > aristololactam-β-D-glucoside-ss poly(A). A 1:1 binding stoichiometry was observed in all the cases, as confirmed by Job plot analysis, indicating the interaction to consist of a single binding mode. Ferrocyanide quenching studies showed good stacking interaction in all cases but was best for daunomycin-ss poly(A) interaction. No self-structure formation was observed in poly(A) with both daunomycin and aristololactam-β-D-glucoside suggesting the hindrance of the sugar moiety for such structural organization.

[A new aristolochic acid derivative from Asarum himalaicum]

To study the chemical constituents of Asarum himalaicum, fifteen compounds were isolated from a 70% ethanol extract by using a combination of various chromatographic techniques including column chromatography over silica gel, Sephadex LH-20, and semi-preparative HPLC. By spectroscopic techniques including 1H NMR, 13C NMR, and HR-ESI-MS, these compounds were identified as 4-demethoxyaristolochic acid BII (1), aristolochic acid I (2), aristolochic acid Ia (3), 7-hydroxyaristolochic acid I (4), aristolochic acid IV (5), aristolic acid II (6), debilic acid (7), aristololactam I (8), 9-hydroxyaristololactam I (9), 7-methoxyaristololactam IV (10), (2S)-narigenin-5, 7-di-O-beta-D-pyranosylglucoside (11), 4-hydroxybenzoic acid (12), 3, 4-dihydroxybenzoic acid (13), 4-hydroxycinnamic acid (14), and beta-sitosterol (15). All of these compounds (1-15) were obtained from A. himalaicum for the first time. Among them, 1 was identified as a new compound, and compounds 3-6, 9, 12-14 were isolated from Asarum genus for the first time. Since the kidney toxicity of aristolochic acids and aristololactams has been reported, the result of this investigation suggests that it should be cautioned to use A. himalaicum as a medicine.

Comparison of activation of aristolochic acid I and II with NADPH:quinone oxidoreductase, sulphotransferases and N-acetyltranferases

OBJECTIVES

Ingestion of aristolochic acid (AA) is associated with development of urothelial tumors linked with aristolochic acid nephropathy, and is implicated in the development of Balkan endemic nephropathy-associated urothelial tumors. Aristolochic acid I (AAI), the major toxic component of AA, is more toxic than its demethoxylated derivate AAII. A different enzymatic conversion of both carcinogens might be one of the reasons explaining this feature. Therefore, the present study has been designed to compare efficiency of human NAD(P)H:quinone oxidoreductase (NQO1) and phase II enzymes such as sulfotransferases (SULTs) and N,O-acetyltransferases (NATs) to activate AAI and AAII in vitro. In addition, to investigate the molecular mechanisms of AAI and AAII reduction by human NQO1, molecular modeling was used to compare interactions of AAI and AAII with the active site of this enzyme.

METHODS

DNA adduct formation by AAI and AAII was investigated by the nuclease P1 version of the 32P-postlabeling method. In silico docking, employing soft-soft (flexible) docking procedure, was used to study the interactions of AAI and AAII with the active site of human NQO1.

RESULTS

Human NQO1 activated AAI and AAII, generating DNA adduct patterns reproducing those found in several species including human exposed to these compounds. These results demonstrate that NQO1 is capable of reducing both AAs to reactive species binding to DNA. However, concentrations required for half-maximum DNA binding mediated by NQO1 were higher for AAII (158 µM) than for AAI (17 µM). One of the reasons causing this phenomenon is a lower efficiency of NQO1 to reduce AAII than AAI we found in this work; although both AAI and AAII are bound with similar binding affinities to the NQO1 active site, the binding orientation of AAII in the active site of NQO1 does not favor the effective reduction of its nitro group. Because reduced nitro-aromatics are often further activated by SULTs or NATs, their roles in AAI and AAII activation were investigated. Our results indicate that phase II reactions do not stimulate the bioactivation of AAs; neither enzymes present in human hepatic cytosols nor human SULT1A1, 1A2, 1A3, 1E, or 2A nor NAT1 or NAT2 further enhanced DNA adduct formation by AAs. In contrast, human SULT1A1, 1A2 and 1A3 as well as NAT1 and NAT2 enzymes even inhibited NQO1-mediated bioactivation of AAII. Therefore, under the in vitro conditions used, DNA adducts arise by enzymatic reduction of AAs through the formation of N-hydroxyaristolactams that are spontaneously decomposed to the reactive species forming DNA adducts.

CONCLUSION

The results found in this study emphasize the importance of NQO1 in the metabolic activation of AAI and AAII and provide the evidence that initial nitroreduction is the rate limiting step in their activation. This enzyme is more effective in activation of AAI relative to AAII, which might contribute to its lower binding to DNA found both in vitro and in vivo, Moreover, inhibition effects of conjugation reactions on AAII activation might further contribute to its decreased capability of forming DNA adducts and its lower toxicity comparing with AAI.

Identification of a reduction product of aristolochic acid: implications for the metabolic activation of carcinogenic aristolochic acid

Aristolochic acids are nephrotoxic and carcinogenic natural products that have been implicated both in endemic nephropathy in the Balkan region and in ailments caused by ingestion of herbal remedies. Aristolochic acids are metabolized to active intermediates that bind to DNA. In this study, reduction of aristolochic acid I with zinc in acetic acid afforded a new product that was characterized as 9-methoxy-7-methyl-2H-1,3-oxazolo[5',4'-10,9]phenanthro[3,4-d]-1,3-dioxolane-5-carboxylic acid, designated as aristoxazole, along with the expected aristolactam I. This new compound is a condensation product of aristolochic acid and acetic acid that may be related to the aristolochic acid-DNA adducts. The proposed mechanism of formation of aristoxazole involves nucleophilic attack of acetic acid on the nitrenium ion of aristolochic acid I. On the basis of these studies, a route to the metabolic activation of aristolochic acids and formation of adducts with DNA in in vitro systems is proposed and discussed.

[Studies on the chemical constituents from the fruit of Aristolochia debilis]

OBJECTIVE

To study the chemical constituents of the fruit of Aristolochia debilis.

METHODS

The compounds were isolated by chromatographic techniqcue and crystal methods, the structures were elucidated by spectrum analysis.

RESULTS

8 compounds were isolated from the dry fruit of Aristolochia debilis which were aristolochic acid I (1), aristolochic acid II (2), aristolochic acid III (3), aristolochic acid III a(4), aristolochic acid VII a (5), aristolactam I (6), aristolactam II (7) and aristolactam III a (8).

CONCLUSION

Compounds 1-8 are isolated from the fruit of Aristolochia debilis for the first time.

p53 mutations as fingerprints for aristolochic acid: an environmental carcinogen in endemic (Balkan) nephropathy

The activation of protooncogenes and inactivation of tumor suppressor genes are considered to be the main molecular events in the multistep process of carcinogenesis. Mutations of the TP53 tumor suppressor gene have been found in nearly all tumor types and are estimated to contribute to more than 50% of all cancers. Most mutations lead to the synthesis of highly stable, inactive proteins that accumulate in the nucleus of cancer cells. Among the 393 codons of the human p53 gene, 222 are targets of 698 different types of mutations. Alterations of codons 175, 248, 273 and 282 correspond to 19% of all mutations and are considered general hot spot mutations. Dietary exposure to aristolochic acid (AA), an established nephrotoxin and human carcinogen found in all Aristolochia species was shown to be the causative agent of aristolochic acid nephropathy (previously called Chinese herbs nephropathy). This syndrome is characterized by proximal tubular damage, renal interstitial fibrosis, slow progression to the end stage renal disease and a high prevalence of upper urinary tract urothelial carcinoma (otherwise a highly unusual location). AA preferentially binds to purines in DNA and is associated with a high frequency of A-->T transversions in the p53 gene. Rats treated with AA develop A:T-->T:A mutations in codon 61. The pathological and clinical features of endemic (Balkan) nephropathy closely resemble those associated with aristolochic acid nephropathy except for the slower progression to end stage renal disease and longer cumulative period before the appearance of urothelial cancer. Recently, we reported the presence of AA-DNA adducts in renal cortex and A-->T p53 mutations in tumor tissue of patients from Croatia and Bosnia with endemic nephropathy. These data support the hypothesis that dietary exposure to AA is a major risk factor for endemic (Balkan) nephropathy.

Improved preparation and identification of aristolochic acid-DNA adducts by solid-phase extraction with liquid chromatography-tandem mass spectrometry

Aristolochic acid (AA) is a known nephrotoxin and potential carcinogen, which can form covalent DNA adducts after metabolic activation in vivo and in vitro. A simple method for preparation and characterization of aristolochic acid-DNA adducts was developed. Four AA-adducts were synthesized by a direct reaction of AAI/AAII with 2'-deoxynucleosides. The reaction mixture was first cleaned-up and pre-concentrated using solid phase extraction (SPE), and further purified by a reversed-phase high performance liquid chromatography (HPLC). By the application of developed SPE procedure, matrices and byproducts in reaction mixture could be greatly reduced and adducts of high purity (more than 94% as indicated by HPLC) were obtained. The purified AA-DNA adducts were identified and characterized with liquid-electrospray ionization-quadrupole-time of flight-mass spectrometry (LC-ESI-Q-TOF-MS/MS) and LC-Diode array detector-fluorescence (LC-DAD-FL) analysis. This work provides a robust tool for possible large-scale preparation of AA-DNA adduct standards, which can promote the further studies on carcinogenic and mutagenic mechanism of aristolochic acids.

Quantification of aristolochic acid-derived DNA adducts in rat kidney and liver by using liquid chromatography-electrospray ionization mass spectrometry

Aristolochic acid (AA), derived from the herbal genus Aristolochia and Asarum, has recently been shown to be associated with the development of nephropathy. Upon enzyme activation, AA is metabolized to the aristolactam-nitrenium ion intermediate, which reacts with the exocyclic amino group of the DNA bases via an electrophilic attack at its C7 position, leading to the formation of the corresponding DNA adducts. The AA-DNA adducts are believed to be associated with the nephrotoxic and carcinogenic effects of AA. In this study, liquid chromatography coupled with electrospray ionization mass spectrometry (LC-MS) was used to identify and quantify the AA-DNA adducts isolated from the kidney and liver tissues of the AA-dosed rats. The deoxycytidine adduct of AA (dC-AA) and the deoxyadenosine-AA adduct (dA-AA) were detected and quantified in the tissues of rats with one single oral dose (5mg or 30mg AA/kg body weight). The deoxyguanosine adduct (dG-AA), however, was detected only in the kidney of rats that were dosed at 30mg AA/kg body weight for three consecutive days. The amount of AA-DNA adducts found in the rats correlated well with the dosage.

[Synthesis and mass spectrometric analysis of aristolochic acid-deoxyguanosine adducts]

To synthesize aristolochic acid (AA)-2'-deoxyguanosine 5'-monophosphate (dGp) adducts in vitro and develop a novel method for the characterization of the adducts using multiple mass spectrometric techniques. AA was incubated with dGp in vitro using either enzymatic activation (by xanthine oxidase) or chemical activation (by zinc) to synthesize AA-dGp adducts, and the reaction conditions were optimized. Crude extracts were analyzed by techniques of liquid chromatography-electrospray ionization/tandem mass spectrometry (LC-MS/MS) and high accuracy mass data and isotope pattern of super high resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICRMS). The quasi-molecular ion peaks of the AA-dGp adducts were obtained in the negative ion mode. Analysis by electrospray ionization/tandem mass spectrometry (ESI-MS/MS) provided useful structural information about AA-dGp adducts. AA can bind covalently to the exocyclic amino group of deoxyguanosine to form AA-dGp adducts. MS analysis is a powerful tool to detect and identify AA-dGp adducts simply, rapidly and accurately.

Metabolic activation of carcinogenic aristolochic acid, a risk factor for Balkan endemic nephropathy

Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, is associated with tumor development in patients suffering from Chinese herbs nephropathy (now termed aristolochic acid nephropathy, AAN) and may also be a cause for the development of a similar type of nephropathy, the Balkan endemic nephropathy (BEN). Major DNA adducts [7-(deoxyadenosin-N6-yl)-aristolactam and 7-(deoxyguanosin-N2-yl)aristolactam] formed from AA after reductive metabolic activation were found in renal tissues of patients with both diseases. Understanding which human enzymes are involved in AA activation and/or detoxication is important in the assessment of an individual's susceptibility to this plant carcinogen. This paper reviews major hepatic and renal enzymes responsible for AA-DNA adduct formation in humans. Phase I biotransformation enzymes play a crucial role in the metabolic activation of AA to species forming DNA adducts, while a role of phase II enzymes in this process is questionable. Most of the activation of AA in human hepatic microsomes is mediated by cytochrome P450 (CYP) 1A2 and, to a lower extent, by CYP1A1; NADPH:CYP reductase plays a minor role. In human renal microsomes NADPH:CYP reductase is more effective in AA activation. Prostaglandin H synthase (cyclooxygenase, COX) is another enzyme activating AA in human renal microsomes. Among the cytosolic reductases, NAD(P)H:quinone oxidoreductase (NQO1) is the most efficient in the activation of AA in human liver and kidney. Studies with purified enzymes confirmed the importance of CYPs, NADPH:CYP reductase, COX and NQO1 in the AA activation. The orientation of AA in the active sites of human CYP1A1, -1A2 and NQO1 was predicted from molecular modeling and explains the strong reductive potential of these enzymes for AA detected experimentally. We hypothesized that inter-individual variations in expressions and activities of enzymes activating AA may be one of the causes responsible for the different susceptibilities to this carcinogen reflected in the development of AA-induced nephropathies and associated urothelial cancer.

Online concentration of aristolochic acid I and II in Chinese medicine preparations by micellar electrokinetic chromatography

In this study, an online concentration method in micellar electrokinetic chromatography (MEKC) applying field-enhanced sample injection (FESI) mode was developed for the detection of aristolochic acids (AAs) in Chinese medicine preparations. AA-I and AA-II were baseline separated with high separation efficiency, and 100-fold enhancement of the detection sensitivity was achieved compared with those obtained from normal capillary zone electrophoresis (CZE) or simple MEKC method. The proposed method was successfully applied for the determination of AAs in Chinese medicine preparations.

A sensitivity enhanced high-performance liquid chromatography fluorescence method for the detection of nephrotoxic and carcinogenic aristolochic acid in herbal medicines

A new, sensitive and selective HPLC method with fluorescence detector (HPLC-FLD) for the determination of nephrotoxic and carcinogenic aristolochic acid (AA) in herbal medicines by using pre-column derivatization with zinc powder in acetic acid is presented. Variables governing the derivatization reaction, such as the amount of zinc powder and acetic acid, as well as the derivatization time were studied and optimized. An extended linear dynamic range over three orders of magnitude was observed for AA-I and AA-II (R(2)>0.9998). Method accuracy at low, medium and high spiked AA levels determined by the percentage mean deviation was below 4.4% and 7.2% for AA-I and AA-II, respectively. The detection limits of 0.39 ng/mL (AA-I) and 0.52 ng/mL (AA-II) were 2 orders of magnitude lower than those obtained from HPLC-MS or CE-ECD analyses, 3-4 orders of magnitude lower than those from HPLC-UV or CE-UV methods. The developed method has been applied for the determination of AA in herbal medicines. Among the tested samples, Guanmutong had the highest AA concentration (2607.0 microg/g AA-I, 711.2 microg/g AA-II). Comparison studies between HPLC-FLD and HPLC-MS/MS demonstrated that the two methods gave similar quantitative results for the selected herb samples.

Aristolochic acid and the etiology of endemic (Balkan) nephropathy

Endemic (Balkan) nephropathy (EN), a devastating renal disease affecting men and women living in rural areas of Bosnia, Bulgaria, Croatia, Romania, and Serbia, is characterized by its insidious onset, invariable progression to chronic renal failure and a strong association with transitional cell (urothelial) carcinoma of the upper urinary tract. Significant epidemiologic features of EN include its focal occurrence in certain villages and a familial, but not inherited, pattern of disease. Our experiments test the hypothesis that chronic dietary poisoning by aristolochic acid is responsible for EN and its associated urothelial cancer. Using (32)P-postlabeling/PAGE and authentic standards, we identified dA-aristolactam (AL) and dG-AL DNA adducts in the renal cortex of patients with EN but not in patients with other chronic renal diseases. In addition, urothelial cancer tissue was obtained from residents of endemic villages with upper urinary tract malignancies. The AmpliChip p53 microarray was then used to sequence exons 2-11 of the p53 gene where we identified 19 base substitutions. Mutations at A:T pairs accounted for 89% of all p53 mutations, with 78% of these being A:T --> T:A transversions. Our experimental results, namely, that (i) DNA adducts derived from aristolochic acid (AA) are present in renal tissues of patients with documented EN, (ii) these adducts can be detected in transitional cell cancers, and (iii) A:T --> T:A transversions dominate the p53 mutational spectrum in the upper urinary tract malignancies found in this population lead to the conclusion that dietary exposure to AA is a significant risk factor for EN and its attendant transitional cell cancer.

Enforcement of the ban on aristolochic acids in Chinese traditional herbal preparations on the Dutch market

In traditional Chinese medicine several Aristolochia species are used. Aristolochia spp. contain a mixture of aristolochic acids (AAs), mainly AA I and AA II which are nephrotoxicants and carcinogens. After AA-related nephropathy (AAN) and urothelial cancer were described in female patients in Belgium following intake of AA-contaminated herbal preparations, herbs with AAs were prohibited worldwide. Confusing nomenclature can cause AA contamination of certain Chinese traditional herbal preparations (THPs). Here we report the results of investigations by the Dutch Food and Consumer Product Safety Authority (VWA) into the presence of AAs in THPs sampled on the Dutch market using a liquid-chromatography--mass spectrometry method. Between 2002 and 2006 we sampled 190 Chinese THPs using recent information on Chinese THPs potentially containing AAs. AA I was found in 25 samples up to a concentration of 1,676 mg/kg. AA II was also found in 13 of these samples up to 444 mg/kg. All 25 positive samples including Mu Tong, Fang Ji, Tian Xian Teng and Xi Xin were part of a group of 68 THPs identified as possibly containing AAs. In a worst-case scenario, use of a sample of Mu Tong with the highest AA content over a 7-day period would result in the same intake levels of AAs which significantly raised the cancer risk in the Belgian AAN cases. Our results show that contaminated THPs still can be found on the market following worldwide publicity. Therefore, it can be concluded that testing of possibly AA-contaminated THPs is still essential.

[Amides from the stems of Uvaria kweichowensis]

Uvaria kweichowensis is a folk nongovernmental herb used to treat cure inflammation and tumour in the Southwest area of China. During the course of our investigation for antitumour agents from the stems of Uvaria kweichowensis, six amides were obtained by means of solvent extraction, chromatography on silica gel and Sephadex LH-20 repeatedly. And their structures were identified as uvariadiamide (1), cepharanone (2), aristololactam A II (3), enterocarpam II (4), aristololactam A Ia (5), and 4,5-dioxodehydroasimilobine (6) on the basis of chemical methods and spectral analyses (EI-MS, 1H NMR, 13C NMR). Among them, compound 1 is a new compound; the other compounds were obtained from this plant for the first time.

Liquid chromatography-tandem mass spectrometry analysis of the DNA adducts of aristolochic acids

Electrophilic attack of aristolactam-nitrenium ion by the C7 position to the exocyclic amino group in the DNA bases led to the formation of the major adducts. In this study, liquid chromatography coupled with electrospray ionization tandem mass spectrometry was applied to the study of DNA adducts of aristolochic acid (AA). When DNA (bases and CT-DNA) was incubated with AA, dG-AAI, dG-AAII, dA-AAI, dA-AAII, dC-AAI, and dC-AAII were detected and characterized. The dC adducts of AA were identified for the first time. The soft ionization technology allowed detection of the intact DNA adducts. High-resolution MS and MS-MS capabilities of a quadrupole time-of-flight mass spectrometer were shown to be efficient for DNA adducts analysis. DNA-AA adducts showed characteristic fragmentation patterns in MS-MS analysis. The dissociative loss of 116 Da from the DNA-AA adducts, which resulted from internal hydrogen transfer and cleavage at the C-N glycosidic bond, provided a characteristic fragment for the structural elucidation.

Characterization and determination of six aristolochic acids and three aristololactams in medicinal plants and their preparations by high-performance liquid chromatography-photodiode array detection/electrospray ionization mass spectrometry

Aristolochic acid derivatives (AAs) and aristolactam derivatives (ALs) have been characterized by electrospray ionization mass spectrometry, and their fragmentation pathways are proposed. ALs exhibit a single ionization product [M+H]+, whereas AAs show multiple ionization products. By optimizing the chromatographic separation and mass spectrometric parameters, the precursor ions of the derivatives with the best responses were found, and the sensitivities in the determination of the nine derivatives were improved. Based on the investigation of ionization behaviour, a HPLC-DAD/ESI-MS (high-performance liquid chromatography-photodiode array detection/electrospray ionization mass spectrometry) method has been developed for simultaneous analysis of nine derivatives, i.e., AA I, AA II, AA C, AA D, 7-OH AA I, aristolic acid I, AL AII, AL IIIa and AL IVa, in nine medicinal herbs and two preparations. The method appears to be suitable for safety assurance and quality control of commercially available samples with good selectivity and suitable sensitivity.

Molecular aspects on the interaction of protoberberine, benzophenanthridine, and aristolochia group of alkaloids with nucleic acid structures and biological perspectives

Alkaloids occupy an important position in chemistry and pharmacology. Among the various alkaloids, berberine and coralyne of the protoberberine group, sanguinarine of the benzophenanthridine group, and aristololactam-beta-d-glucoside of the aristolochia group have potential to form molecular complexes with nucleic acid structures and have attracted recent attention for their prospective clinical and pharmacological utility. This review highlights (i) the physicochemical properties of these alkaloids under various environmental conditions, (ii) the structure and functional aspects of various forms of deoxyribonucleic acid (DNA) (B-form, Z-form, H(L)-form, protonated form, and triple helical form) and ribonucleic acid (RNA) (A-form, protonated form, and triple helical form), and (iii) the interaction of these alkaloids with various polymorphic DNA and RNA structures reported by several research groups employing various analytical techniques like absorbance, fluorescence, circular dichroism, and NMR spectroscopy; electrospray ionization mass spectrometry, thermal melting, viscosity, and DNase footprinting as well as molecular modeling and thermodynamic studies to provide detailed binding mechanism at the molecular level for structure-activity relationship. Nucleic acids binding properties of these alkaloids are interpreted in relation to their biological activity.

NMR-based metabonomic study on the subacute toxicity of aristolochic acid in rats

The subacute toxicity of aristolochic acid (AA) was investigated by (1)H NMR spectroscopic and pattern recognition (PR)-based metabonomic methods. Model toxins were used to enable comparisons of the urinary profiles from rats treated with known toxicants and AA at various time intervals. Urinary (1)H NMR spectra were data-processed and analyzed by pattern recognition method. The result of visual comparison of the spectra showed that AA caused a renal proximal tubular and papillary lesion and a slight hepatic impair. Pattern recognition analysis indicated that the renal proximal tubule lesion was the main damage induced by AA, and the renal toxicity induced by AA was a progressive course with the accumulation of dosage by monitoring the toxicological processes from onset, development and part-recovery. These results were also supported by the conventional clinical biochemical parameters.

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.

[Research on the interaction of aristolochic acid and bovine serum albumin]

The interaction between aristolochic acid and bovine serum albumin (BSA) under physiological conditions was investigated by fluorescence quenching methods. The results indicate that there is a strong interaction between aristolochic acid and BSA, and the distances between the binding location and tryptophan residue is 2.8 nm. The binding location of aristolochic acid in BSA is in subdomain III A. In addition, the effects of aristolochic acid on the protein second structure were studied using CD and FTIR techniques. The results of CD proved that the alpha-helix contents of BSA decreased from 43.5% to 36.7% after binding with aristolochic acid.

New aristolochic acid, aristololactam and renal cytotoxic constituents from the stem and leaves of Aristolochia contorta

Two novel phenanthrene derivatives, aristololactam IVa (1) and 9-hydroxy aristolochic acid I (2) were isolated from the stem and leaves of Anstolochia contorta Bunge, together with 17 known compounds (3-19). The structures of these compounds were determined by spectroscopic analysis. The phenanthrenes obtained were tested for cytotoxicity against renal proximal tubular epithelial cell line (HK-2). Aristololactam IVa and 7-methoxy aristololactam IV were found to have strong cytotoxic activity against HK-2 cells with a potency similar to or even stronger than those of aristolochic acid I and aristololactam I.