Characterization of the DNA adducts induced by aristolochic acids in oligonucleotides by electrospray ionization tandem mass spectrometry

Metabolic activation of carcinogenic aristolochic acids (AA) produces reactive aristolactam-nitrenium ion intermediates. Electrophilic attack of the aristolactam-nitrenium ion via its C7 position to the exocyclic amino group in the purine bases leads to the formation of DNA adducts. DNA-binding assays have demonstrated that carcinogens show site- and sequence-specificity and the biological consequence is defined by the nature of binding as well as their position in the genome. In this study, electrospray ionization tandem mass spectrometry was applied for the identification and position mapping of DNA adducts in oligonucleotides (ODNs). The developed method was successfully applied for the analysis of unmodified and AA-modified ODNs (5′-TTTATT- 3′, 5′-TTTGTT-3′ and 5′-TACATGTGT-3′). The observation of the modified bases (modified adenine and guanine) together with the complementary product ions ([an-B*n] -, w-) from the cleavage of the 3′ C-O bond adjacent to the modified base in MS/MS analyses readily enabled the identification of the AA-binding site in ODNs. Copyright © 2008 John Wiley & Sons, Ltd

Liquid chromatography/mass spectrometry for metabonomics investigation of the biochemical effects induced by aristolochic acid in rats: The use of information-dependent acquisition for biomarker identification

The toxic effects of oral administrations of nephrotoxic and carcinogenic aristolochic acid (AA) to male Sprague-Dawley rats were investigated by using high-performance liquid chromatography coupled with a quadrupole time-of-flight mass spectrometer. Analysis of the urine and plasma samples revealed distinct changes in the biochemical patterns in the AA-dosed rats. After peak finding and alignment, principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) were used for multivariate data analysis. Potential biomarkers were studied by high-resolution mass spectrometry (MS) and tandem mass spectrometry (MS/MS) analyses. The MS/ MS spectra of all endogenous metabolites satisfying the pre-defined criteria were acquired in a single information-dependent acquisition (IDA) analysis, demonstrating that IDA was an efficient approach for structural elucidation in metabonomic studies. Citric acid and a glucuronide-containing metabolite were observed as potential biomarkers in rat urine. A significant increase in plasma creatinine concentration was also observed in the AA-dosed rats, which indicated that AA induced an adverse effect on the renal clearance function. Copyright © 2008 John Wiley & Sons, Ltd

Apoptosis and expression of cytokines triggered by pyropheophorbide-a methyl ester-mediated photodynamic therapy in nasopharyngeal carcinoma cells

The photodynamic properties of pyropheophorbide-a methyl ester (MPPa), a semi-synthetic photosensitizer derived from chlorophyll a, were evaluated in a human nasopharyngeal carcinoma HONE-1 cell line. MPPa was non-toxic to the HONE-1. At the concentrations of 0.5-2 μM, MPPa-mediated a drug dose-dependent photocytotoxicity in the HONE-1 cells. Confocal microscopy revealed a subcellular localization of MPPa in mitochondria and the Golgi apparatus. MPPa PDT-induced apoptosis was associated with the collapse of mitochondrial membrane potential, release of cytochrome c, the up-regulation of endoplasmic reticulum (ER) stress proteins (calnexin, Grp 94 and Grp78), and the activation of caspases-3 and -9. The photocytotoxicity was reduced by the corresponding specific caspase inhibitors. MPPa PDT-treated HONE-1 cells also up-regulated the gene expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) and beta-chemokines (MIP-1β, MPIF-1, and MPIF-2). These results suggest that the MPPa may be developed as a chlorophyll-based photosensitizer for the treatment of nasopharyngeal carcinoma. © 2006 Elsevier B.V. All rights reserved