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.

Human sulphotransferases are involved in the activation of aristolochic acids and are expressed in renal target tissue

Use of herbal preparations containing Aristolochia species has led to progressive nephropathy and urothelial cancer in humans. Analysis of DNA adducts formed in human target tissues and studies in animal models have pointed out a major role of the secondary plant metabolites, aristolochic acids, in these effects. Only a minority of the users of Aristolochia-containing products developed nephropathy and cancer, suggesting differences in individual susceptibility. Differences in metabolic activation and inactivation frequently affect the susceptibility towards chemicals. Others have shown that the activation of aristolochic acids to DNA-reactive and mutagenic metabolites requires reduction of their aryl nitro group. The biological activity of numerous nitro- and aminoarenes, after appropriate phase I metabolism, is strongly enhanced in the presence of acetyltransferases or sulphotransferases (SULTs). In the present study, we demonstrate that expression of human SULTs in bacterial and mammalian target cells reinforces the mutagenic activity of aristolochic acids. Using Salmonella typhimurium TA1538 as the recipient organism, we identified the expression of all 12 human SULT forms. SULT1A1 led to the strongest increase in the mutagenicity of aristolochic acids. Some activation was also observed with SULT1B1, but not with the remaining forms. The role of SULT1A1 in the activation of aristolochic acids was corroborated using S. typhimurium TA100- and Chinese hamster V79-derived target cells engineered for expression of human SULT1A1 when compared with control cells. Furthermore, pentachlorophenol, an inhibitor of SULT1A1, strongly reduced the mutagenic effect of aristolochic acids in V79-hCYP2E1-hSULT1A1 cells. Moreover, we demonstrate that SULT1A1 and SULT1B1 are expressed in human kidney using immunoblot analysis, but their levels are substantially lower than in liver. Finally, we discuss the possibility that reactive sulphuric acid conjugates produced in other tissues are transferred to kidney and ureter.

Chemical constituents of Piper betle Linn. (Piperaceae) roots

Column chromatography of the alcoholic extract of Piper betle roots furnished aristololactam A-II and a new phenyl propene, characterized as 4-allyl resorcinol, while the petroleum-ether extract yielded a diketosteroid, viz. stigmast-4-en-3,6-dione. All these compounds were characterized by spectroscopic means. Isolation of these compounds from this source is being reported here for the first time.

The binding of aristolochic acid I to the active site of human cytochromes P450 1A1 and 1A2 explains their potential to reductively activate this human carcinogen

Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, has been associated with the development of urothelial cancer in humans. Using the 32P-postlabeling assay we showed that AAI is activated by human recombinant cytochrome P450 (CYP) 1A1, CYP1A2 and NADPH:CYP reductase to species generating DNA adduct patterns reproducing those found in renal tissues from humans exposed to AA. 7-(Deoxyadenosin-N6-yl)aristolactam I, 7-(deoxyguanosin-N2-yl)aristolactam I and 7-(deoxyadenosin-N6-yl)aristolactam II were identified as AA-DNA adducts formed from AAI by the enzymes. The formation of these AA-derived DNA adducts indicates that all the human enzymes reduce the nitro group of AAI to the putative reactive cyclic nitrenium ion responsible for adduct formation. The concentrations of AAI required for its half-maximum DNA binding were 38, 65 and 126 microM AAI for reductive activation by human CYP1A2, CYP1A1 and NADPH:CYP reductase, respectively. CYP1A1 and 1A2 homology modeling followed by docking of AAI to the CYP1A1 and 1A2 active centers was utilized to explain the potential of these enzymes to reduce AAI. Models of human CYP1A1 and 1A2 were constructed on the basis of the crystallographic structure of truncated mammalian CYP enzymes, CYP2B4, 2C5, 2C8, 2C9 and 3A4. The in silico docking of AAI to the active sites of CYP1A1 and 1A2 indicates that AAI binds as an axial ligand of the heme iron and that the nitro group of AAI is in close vicinity to the heme iron of CYP1A2 in an orientation allowing the efficient reduction of this group observed experimentally. The orientation of AAI in the active centre of CYP1A1 however causes an interaction of the heme iron with both the nitro- and the carboxylic groups of AAI. This observation explains the lower reductive potential of CYP1A1 for AAI than CYP1A2, detected experimentally.

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-PK(1) 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 Ia 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.

[Study on three aristololatams from Piper wallichii]

OBJECTIVE

To study the chemical constituents from Piper wallichii.

METHODS

Three aristololatams were isolated and purified by chromatography with silica gel column and Sephadex LH-20 gel column, and the structures of the compounds were identified by spectral analysis.

RESULT

Three aristololatams were identified as cepharanone B, aristolactam A II and aristololatam A III a.

CONCLUSION

Three aristololatams were isolated from Piper wallichii for the first time.

[Key foundational science problem in experimental medicine study of Chinese materia medica: ascertainment of active and toxic constituents from Chinese materia medica]

The problem on study of the active and toxic constituents of Chinese materia medica is the core of the problems in the field of modern research of Chinese materia medica. But approved methods for ascertaining the active and toxic constituents in Chinese materia medica have not been developed yet and are in developing phases. In combination with the characteristics of Chinese materia medica in clinical use and the achievements of modern pharmaceutical research, series model may be a finer approach to make certain of the active and toxic constituents from Chinese materia medica, which includes the parent compound biotransformation by human intestinal bacteria to make biotransformation products, and the absorption and further biotransformation in intestinal wall, the metabolization in the liver, and the secretion by the kidney of the parent compounds and biotransformation products. This method is also an important research assignment in the field of experimental medicine study of Chinese materia medica.

Regio- and Stereoselective Synthesis of Isoindolin-1-ones via Electrophilic Cyclization

[reaction: see text] A variety of substituted isoindolin-1-ones are readily prepared in good to excellent yields under very mild reaction conditions by the reaction of o-(1-alkynyl)benzamides with ICl, I(2), and NBS. In a few cases, substituted isoquinolin-1-ones were obtained as the major product instead. This methodology accommodates various alkynyl amides and functional groups and has been successfully extended to heterocyclic starting materials. This chemistry has been successfully applied to the synthesis of a biologically interesting alkaloid, cepharanone B.

Naturally occurring aristolactams, aristolochic acids and dioxoaporphines and their biological activities

Aristolactams, having a phenanthrene chromophore are a small group of compounds mainly found in the Aristolochiaceae together with the aristolochic acids and 4,5-dioxoaporphines. In this report, these three important classes of natural products are reviewed and classified on the basis of their oxygenation pattern. In addition the biological activities of these compounds and their general chemistry are discussed.

A new aristolactam alkaloid and anti-platelet aggregation constituents from Piper taiwanense

A new alkaloid, piperolactam E, and fourteen known compounds have been isolated from the stem of Piper taiwanense. Bioassay-guided fractionation of the methanolic extract led to the isolation, from the chloroform-soluble part, of 4-allylcatechol, eugenol, trans-caffeic aldehyde, 2-hydroxy-1-methoxy-4 H-dibenzo[ de,g]quinoline-4,5-(6 H)-dione, piperolactam B, piperolactam C, and piperolactam E as the active principles of anti-platelet aggregation in vitro. The derived 1,2-diacetoxy-4-allyl-benzene and eugenol acetate exhibit stronger anti-platelet aggregation activities induced by arachidonic acid than 4-allylcatechol and eugenol, respectively.

An easy and rapid method to determine aristolochic acids I and II with high sensitivity

Aristolochic acid (AA), a natural component in some Chinese medicinal plants, is nephrotoxic and carcinogenic, and is involved in a specific type of renal fibrosis, called Chinese herbs nephropathy (CHN). In this paper, we report the electrochemistry of AA and a novel method to detect the species based on the electrochemical studies. The detection limit is estimated to be 1.0x10(-8) M with a linear range from 5.0x10(-8) M to 1.3x10(-6) M. Meanwhile, this method is applicable in detection in real samples, such as Caulis Aristolochiae Manshuriensis (CAM), Radix Aristolochiae (RA), Fructus Aristolochiae (FA) and Radix Stephaniae Tetrandrae (RST). The concentration of AA in the CAM sample was 3.50 +/- 0.12x10(-4) M. Consistent results have been obtained from both the electrochemical approach described here and the previously reported HPLC method.

Analysis of aristolochic acid in nine sources of Xixin, a traditional Chinese medicine, by liquid chromatography/atmospheric pressure chemical ionization/tandem mass spectrometry

Aristolochic acid I (AA-I), which is a known nephrotoxin, is found in a commonly used Chinese medicine, Xixin, that originates from nine Asarum species (Aristolochiaceae) found in China. A method has been developed using reversed-phase liquid chromatography coupled with atmospheric pressure chemical ionization (APCI) tandem mass spectrometry under the positive ion detection mode [LC/(+)APCI/MS/MS] to determine the amount of AA-I in Xixin. The limit of detection of AA-I, estimated by monitoring with LC/MS/MS, was at the low microg/l level. By applying this method to methanol extracts of nine Asarum species, the concentrations of AA-I were found to range from 3.3 ng/mg (Asarum sieboldii) to 3376.9 ng/mg (Asarum crispulatum).

Human cytosolic enzymes involved in the metabolic activation of carcinogenic aristolochic acid: evidence for reductive activation by human NAD(P)H:quinone oxidoreductase

Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, has been associated with the development of urothelial cancer in humans. Understanding which human enzymes are involved in AA metabolism is important in the assessment of an individual's susceptibility to this carcinogen. Using the 32P-postlabeling assay we examined the ability of enzymes of cytosolic samples from 10 different human livers and from one human kidney to activate the major component of the plant extract AA, 8-methoxy- 6-nitro-phenanthro-(3,4-d)-1,3-dioxolo-5-carboxylic acid (AAI), to metabolites forming adducts in DNA. Cytosolic fractions of both organs generated AAI-DNA adduct patterns reproducing those found in renal tissues from humans exposed to AA. 7-(Deoxyadenosin-N6-yl)aristolactam I, 7-(deoxyguanosin-N2-yl)aristolactam I and 7-(deoxyadenosin-N6-yl)aristolactam II, indicating a possible demethoxylation reaction of AAI, were identified as AA-DNA adducts formed from AAI by all human hepatic and renal cytosols. To define the role of human cytosolic reductases in the activation of AAI, we investigated the modulation of AAI-DNA adduct formation by cofactors or selective inhibitors of the NAD(P)H:quinone oxidoreductase (NQO1), xanthine oxidase (XO) and aldehyde oxidase. We also determined whether the activities of NQO1 and XO in different human hepatic cytosolic samples correlated with the levels of AAI-DNA adducts formed by the same cytosolic samples. Based on these studies, we attribute most of the activation of AA in human cytosols to NQO1, although a role of cytosolic XO cannot be ruled out. With purified NQO1 from rat liver and kidney and XO from buttermilk, the major role of NQO1 in the formation of AAI-DNA adducts was confirmed. The orientation of AAI in the active site of human NQO1 was predicted from molecular modeling based on published X-ray structures. The results demonstrate for the first time the potential of human NQO1 to activate AAI by nitroreduction.

Diterpene esters of aristolochic acids from Aristolochia pubescens

From the acetone and ethanol extracts of the tubercula of Aristolochia pubescens, two diterpene esters of aristolochic acids were isolated, together with 23 known compounds. The structures of the compounds were determined on the basis of spectroscopic analysis.

Molecular aspects on the interaction of aristololactam-beta-D-glucoside with H(L)-form deoxyribonucleic acid structures

Synthetic alternating GC-rich DNA polymers can adopt Hoogsteen base-paired structures (H(L)-form) under the influence of low pH and temperature. The interaction of aristololactam-beta-D-glucoside (ADG), a natural glucoside derivative of aristolochia group of alkaloids, with protonation-induced structures (H(L)-form) of poly(dG-dC).poly(dG-dC) and poly(dG-m(5)dC).poly(dG-m(5)dC) has been studied using different biophysical techniques. The binding of ADG to protonated DNA is characterized by typical hypochromism and bathochromism of the absorption spectrum of the alkaloid, quenching of steady state fluorescence intensity, decrease in quantum yield, increase in fluorescence polarization anisotropy values, increase in thermal transition temperature of polynucleotides following alkaloid binding and perturbation of circular dichroic spectrum of polynucleotides as a result of its interaction with the alkaloid. Scatchard analysis of the data indicates that ADG binds to protonated structures in a nonlinear noncooperative manner. The binding parameters determined from spectrophotometric titration data employing excluded site model indicate that protonated poly(dG-m(5)dC).poly(dG-m(5)dC) is more favorable for ADG binding than the corresponding nonmethylated analog. The binding of ADG to protonated structures renders a higher degree of stabilization against thermal denaturation compared to respective B-form-ADG interactions and induces a conformational switch to a bound altered form which is different from its interaction with B- and Z-form DNA structures. Thermodynamic parameters (Delta G degrees, Delta H degrees and Delta S degrees ) obtained by van't Hoff analysis of the data indicate that the binding of alkaloid to protonated structures is an exothermic process and the binding free energy arises primarily from a negative enthalpy change. Moreover, the binding leads to an increase in the contour length of protonated DNAs. These results suggest that ADG possibly binds to protonated DNAs by the mechanism of intercalation.

Determination of aristolochic acids by capillary electrophoresis

A method for the separation and quantification of aristolochic acids by capillary electrophoresis is described. Buffer solutions composed of sodium dihydrogen phosphate, sodium borate, and sodium dodecyl sulfate at pH 6.5-7 were found to be suitable for the separation of aristolochic acids, which can be well resolved in a few minutes. The separation and identification of six aristolochic acids contained in a commercial tincture called charrua, a traditional herbal medicine consisting of a hydroalcoholic extract of Aristolochia argentina, corroborate the usefulness of the method. The eventual toxic properties of the aristolochic acid containing charrua tincture are discussed.

Detection of aristolochic acid in Chinese phytomedicines and dietary supplements used as slimming regimens

Over the last 10 years, numerous cases of intoxications, leading for the most part to end-stage renal failure, have been reported after consumption of slimming regimens made of Chinese herbal preparations. These intoxications were associated with species of the Aristolochia genus, such as Aristolochia fangchi (Aristolochiaceae), known to contain very nephrotoxic and carcinogenic metabolites named aristolochic acids. Several commercial dietary supplements, teas and phytomedicines used as slimming regimens were analysed for their aristolochic acid I content. A preliminary detection of this toxic compound was made by thin-layer chromatography. The presence of aristolochic acid I in these preparations was confirmed by a HPLC/UV-DAD/MS analysis. A quantitative determination of aristolochic acid I was also achieved in the incriminated preparations using both UV and MS detection. Out of 42 analysed preparations, four were found to contain aristolochic acid I and two were suspected to contain aristolochic acid derivatives. Immediate removal of these products from the Swiss market was called for.

Antithrombin activity of some constituents from Origanum vulgare

Aristolochic acid I, aristolochic acid II, and D-(+)-raffinose were isolated from Origanum vulgare. Their inhibition of thrombin and activity against leukemia were evaluated. Aristolochic acid I and II have high inhibition of thrombin activity and were confirmed to possess activity against cancer.

An LC/DAD-UV/MS method for the rapid detection of aristolochic acid in plant preparations

A new method using direct on-line coupling between HPLC and UV-DAD/MS was developed for the rapid detection of aristolochic acid I in plant preparations. The use of both UV-DAD and MS detectors enables this method to be very selective. A ng range detection limit was determined for both UV and MS detections. A quantitative determination of aristolochic acid I in plant preparations was achieved using UV and MS detection. A thin layer chromatography assay was also developed for the preliminary detection of aristolochic acid I in complex mixtures.