The effect of black cohosh extract and risedronate coadministration on bone health in an ovariectomized rat model

Preparations of black cohosh extract are sold as dietary supplements marketed to relieve the vasomotor symptoms of menopause, and some studies suggest it may protect against postmenopausal bone loss. Postmenopausal women are also frequently prescribed bisphosphonates, such as risedronate, to prevent osteoporotic bone loss. However, the pharmacodynamic interactions between these compounds when taken together is not known. To investigate possible interactions, 6-month-old, female Sprague-Dawley rats underwent bilateral ovariectomy or sham surgery and were treated for 24 weeks with either vehicle, ethinyl estradiol, risedronate, black cohosh extract or coadministration of risedronate and black cohosh extract, at low or high doses. Bone mineral density (BMD) of the femur, tibia, and lumbar vertebrae was then measured by dual-energy X-ray absorptiometry (DEXA) at weeks 0, 8, 16, and 24. A high dose of risedronate significantly increased BMD of the femur and vertebrae, while black cohosh extract had no significant effect on BMD individually and minimal effects upon coadministration with risedronate. Under these experimental conditions, black cohosh extract alone had no effect on BMD, nor did it negatively impact the BMD-enhancing properties of risedronate.

Lipidomic profiling of the hepatic esterified fatty acid composition in diet-induced nonalcoholic fatty liver disease in genetically diverse Collaborative Cross mice

Non-alcoholic fatty liver disease (NAFLD), one of the most common forms of chronic liver disease, is characterized by the excessive accumulation of lipid species in hepatocytes. Recent studies have indicated that in addition to the total lipid quantities, changes in lipid composition are a determining factor in hepatic lipotoxicity. Using ultra-high performance liquid chromatography coupled with electrospray tandem mass spectrometry, we analyzed the esterified fatty acid composition in 24 strains of male and female Collaborative Cross (CC) mice fed a high fat/high sucrose (HF/HS) diet for 12 weeks. Changes in lipid composition were found in all strains after the HF/HS diet, most notably characterized by increases in monounsaturated fatty acids (MUFA) and decreases in polyunsaturated fatty acids (PUFA). Similar changes in MUFA and PUFA were observed in a choline- and folate-deficient (CFD) mouse model of NAFLD, as well as in hepatocytes treated in vitro with free fatty acids. Analysis of fatty acid composition revealed that alterations were accompanied by an increase in the estimated activity of MUFA generating SCD1 enzyme and an estimated decrease in the activity of PUFA generating FADS1 and FADS2 enzymes. PUFA/MUFA ratios were inversely correlated with lipid accumulation in male and female CC mice fed the HF/HS diet and with morphological markers of hepatic injury in CFD diet-fed mouse model of NAFLD. These results demonstrate that different models of NAFLD are characterized by similar changes in the esterified fatty acid composition and that alterations in PUFA/MUFA ratios may serve as a diagnostic marker for NAFLD severity.

Effect of urinary pH upon the renal toxicity of melamine and cyanuric acid

In 2007, dietary exposure to "scrap melamine' resulted in the death of a large number of cats and dogs, which was attributed to the formation of melamine cyanurate crystals in their kidneys. In this study, we investigated if changes in urinary pH could diminish the renal toxicity associated with exposure to combinations of melamine and cyanuric acid. Female Sprague-Dawley rats were treated for three days with suspensions of melamine and cyanuric acid at doses that were expected to induce renal toxicity. Dosing was then discontinued and the rats were treated for seven days with drinking water solutions (i.e., ammonium chloride and sodium bicarbonate) that would alter urinary pH. The urinary pH of rats administered ammonium chloride drinking water decreased from pH 6.0-6.2 to pH 5.1-5.2. This was accompanied by a decrease in the incidence of melamine cyanurate crystals in the kidneys and a decrease in the incidence of renal lesions. These data suggest that acidification of urine may help overcome the renal toxicities associated with the formation of melamine cyanurate crystals in the kidney.

A rapid and highly sensitive UPLC-ESI-MS/MS method for the analysis of the fatty acid profile of edible vegetable oils

The analysis of the fatty acid profile of triglycerides has long played a central role in the evaluation and classification of edible vegetable oils. However, the range of analytical procedures available to evaluate these profiles remains limited and are typically based on transesterification of the triglyceride fatty acid residues to methyl esters, followed by capillary gas-liquid chromatography (GC) coupled with flame ionization or mass spectrometry detection. Although robust and long-proven, these analytical methods tend to entail long chromatographic runs and are relatively insensitive. In order to expand the range of available techniques for the analysis of the fatty acid profile of triglycerides in vegetable oils, we report herein a novel method based upon a rapid and straightforward transesterification of the triglycerides with dimethylaminoethanol under alkaline conditions, followed by a "dilute-and-shoot" analysis by ultra-performance liquid chromatography coupled with electrospray tandem mass spectrometry. The chromatographic analysis is accomplished in 1.5 min, affording a high throughput of samples compared to techniques based upon GC approaches. The method performance was assessed intra- and inter-day with 10 representative saturated and unsaturated fatty acids ranging from C₈ to C₁₈ and afforded fatty acid profile accuracies of 93-108% and imprecisions of only 0.3-2.0%. The limit of quantification of the method, estimated as the minimum amount of derivatized oil sample capable of affording less than 20% accuracy and precision error was determined to be approximately 0.5 pg on-column, making this new method potentially valuable for fields where high sensitivity, precision, and accuracy may be required, such as in toxicology studies, forensics, archeology, or art analysis.

Mutagenicity of acrylamide and glycidamide in human TP53 knock-in (Hupki) mouse embryo fibroblasts

Acrylamide is a suspected human carcinogen formed during high-temperature cooking of starch-rich foods. It is metabolised by cytochrome P450 2E1 to its reactive metabolite glycidamide, which forms pre-mutagenic DNA adducts. Using the human TP53 knock-in (Hupki) mouse embryo fibroblasts (HUFs) immortalisation assay (HIMA), acrylamide- and glycidamide-induced mutagenesis was studied in the tumour suppressor gene TP53. Selected immortalised HUF clones were also subjected to next-generation sequencing to determine mutations across the whole genome. The TP53-mutant frequency after glycidamide exposure (1.1 mM for 24 h, n = 198) was 9% compared with 0% in cultures treated with acrylamide [1.5 (n = 24) or 3 mM (n = 6) for 48 h] and untreated vehicle (water) controls (n = 36). Most glycidamide-induced mutations occurred at adenines with A > T/T > A and A > G/T > C mutations being the most common types. Mutations induced by glycidamide occurred at specific TP53 codons that have also been found to be mutated in human tumours (i.e., breast, ovary, colorectal, and lung) previously associated with acrylamide exposure. The spectrum of TP53 mutations was further reflected by the mutations detected by whole-genome sequencing (WGS) and a distinct WGS mutational signature was found in HUF clones treated with glycidamide that was again characterised by A > G/T > C and A > T/T > A mutations. The WGS mutational signature showed similarities with COSMIC mutational signatures SBS3 and 25 previously found in human tumours (e.g., breast and ovary), while the adenine component was similar to COSMIC SBS4 found mostly in smokers’ lung cancer. In contrast, in acrylamide-treated HUF clones, only culture-related background WGS mutational signatures were observed. In summary, the results of the present study suggest that glycidamide may be involved in the development of breast, ovarian, and lung cancer.

Pharmacokinetics of oseltamivir phosphate and oseltamivir carboxylate in non-pregnant and pregnant rhesus monkeys

Oseltamivir is an antiviral drug approved to treat influenza in humans. Although the dosing regimen of this drug is well established for non-pregnant patients, it is not clear if the significant physiological alterations associated with pregnancy affect the pharmacokinetics of oseltamivir and, thus, warrant different dosing regimens to assure efficacy. In this study, we investigated the suitability of rhesus macaques as an animal model for studying oseltamivir pharmacokinetics during all trimesters of pregnancy in comparison to pre-pregnant conditions. Specifically, we compared the pharmacokinetics of oseltamivir and its pharmacologically active metabolite oseltamivir carboxylate in rhesus monkeys after intravenous and nasogastric administration of 2.5 mg oseltamivir phosphate/kg body weight given prior to and during the first, second, and third trimesters of pregnancy. Pregnancy had only a modest effect upon the pharmacokinetic parameters of oseltamivir and oseltamivir carboxylate. Monkeys treated intravenously in the third trimester had a reduction in Vd and CL, compared to non-pregnant monkeys. These changes did not occur in the other two trimesters. Pregnant monkeys treated intravenously had 20-25% decrease in AUC_0-∞ of oseltamivir carboxylate and a corresponding increase in Vd and CL. Pregnant monkeys treated nasogastrically with oseltamivir phosphate demonstrated a pattern that recapitulated intravenous dosing. Taken together these data indicate that rhesus monkeys are an acceptable model for studying drug-pregnancy interactions.

Use of a physiologically-based pharmacokinetic model to explore the potential disparity in nicotine disposition between adult and adolescent nonhuman primates

The widespread use and high abuse liability of tobacco products has received considerable public health attention, in particular for youth, who are vulnerable to nicotine addiction. In this study, adult and adolescent squirrel monkeys were used to evaluate age-related metabolism and pharmacokinetics of nicotine after intravenous administration. A physiologically-based pharmacokinetic (PBPK) model was created to characterize the pharmacokinetic behaviors of nicotine and its metabolites, cotinine, trans-3'-hydroxycotinine (3'-OH cotinine), and trans-3'-hydroxycotinine glucuronide (3'-OH cotinine glucuronide) for both adult and adolescent squirrel monkeys. The PBPK nicotine model was first calibrated for adult squirrel monkeys utilizing in vitro nicotine metabolic data, plasma concentration-time profiles and cumulative urinary excretion data for nicotine and metabolites. Further model refinement was conducted when the calibrated adult model was scaled to the adolescents, because adolescents appeared to clear nicotine and cotinine more rapidly relative to adults. More specifically, the resultant model parameters representing systemic clearance of nicotine and cotinine for adolescent monkeys were approximately two- to three-fold of the adult values on a per body weight basis. The nonhuman primate PBPK model in general captured experimental observations that were used for both model calibration and evaluation, with acceptable performance metrics for precision and bias. The model also identified differences in nicotine pharmacokinetics between adolescent and adult nonhuman primates which might also be present in humans.

1-Formyl-7-hydroxy-6,7-dihydro-5 H-pyrrolizine (1-CHO-DHP): A Potential Proximate Carcinogenic Metabolite of Pyrrolizidine Alkaloids

Pyrrolizidine alkaloids (PAs) are phytochemicals present in more than 6000 plant species worldwide; about half of the PAs are hepatotoxic, genotoxic, and carcinogenic. Because of their wide exposure and carcinogenicity, the International Programme on Chemical Safety (IPCS) concluded that PAs are a threat to human health and safety. We recently determined that PA-induced liver tumor initiation is mediated by a set of four (±)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5 H-pyrrolizine (DHP)-DNA adducts and proposed that these DHP-DNA adducts are biomarkers of PA exposure and liver tumor initiation. To validate the generality of this metabolic activation pathway and DHP-DNA adducts as biomarkers, it is significant to identify reactive metabolites associated with this metabolic activation pathway. Segall et al. ( Segall et al. ( 1984 ) Drug Metab. Dispos. 12 , 68 - 71 ) previously reported that 1-formyl-7-hydroxy-6,7-dihydro-5 H-pyrrolizine (1-CHO-DHP) is generated from the metabolism of senecionine by mouse liver microsomes. In the present study, we examined the metabolism of seven hepatocarcinogenic PAs (senecionine, intermedine, retrorsine, riddelliine, DHR, heliotrine, and senkirkine) and one noncarcinogenic PA (platyphylline) by human, rat, and mouse liver microsomes. 1-CHO-DHP was identified as a common metabolite from the metabolism of these hepatotoxic PAs, but not from platyphylline. Incubation of 1-CHO-DHP with HepG2 and A549 cells produced the same set of DHP-DNA adducts, which were identified by both LC/MS MRM mode and selected ion monitoring analyses through comparison to synthetic standards. In the incubation medium of 1-CHO-DHP treated HepG2 cells, both DHP and 7-cysteine-DHP were formed, which were capable of binding to cellular DNA to produce DHP-DNA adducts. These results suggest that 1-CHO-DHP is a proximate DNA metabolite of genotoxic and carcinogenic PAs.

Simple and rapid quantification of brominated vegetable oil in commercial soft drinks by LC-MS

We report here a simple and rapid method for the quantification of brominated vegetable oil (BVO) in soft drinks based upon liquid chromatography-electrospray ionization mass spectrometry. Unlike previously reported methods, this novel method does not require hydrolysis, extraction or derivatization steps, but rather a simple "dilute and shoot" sample preparation. The quantification is conducted by mass spectrometry in selected ion recording mode and a single point standard addition procedure. The method was validated in the range of 5-25μg/mL BVO, encompassing the legal limit of 15μg/mL established by the US FDA for fruit-flavored beverages in the US market. The method was characterized by excellent intra- and inter-assay accuracy (97.3-103.4%) and very low imprecision [0.5-3.6% (RSD)]. The direct nature of the quantification, simplicity, and excellent statistical performance of this methodology constitute clear advantages in relation to previously published methods for the analysis of BVO in soft drinks.

Absorption and metabolism of triclosan after application to the skin of B6C3F1 mice

Triclosan is used as an antimicrobial agent in personal care products, household items, medical devices, and clinical settings. Humans can receive lifelong exposures to triclosan; however, data on the toxicity and carcinogenicity after topical application are lacking. This study determined the absorption, distribution, metabolism, and excretion of triclosan after application to the skin of B6C3F1 mice. [(14)C(U)]triclosan (10 or 100 mg triclosan/kg body weight) was administered topically to mice in two separate experiments: a vehicle selection experiment using propylene glycol, ethanol, and a generic cosmetic cream, and a toxicokinetic experiment. Mice were killed up to 72 h after triclosan administration, and excreta and tissues were analyzed for radioactivity. Ethanol had the best properties of the vehicles evaluated. Maximum absorption was obtained at approximately 12 h after dosing. Radioactivity appeared in the excreta and in all tissues examined, with the highest levels in the gall bladder and the lowest levels in the brain. Triclosan was metabolized to triclosan sulfate, triclosan glucuronide, 2,4-dichlorophenol, and hydroxytriclosan. The metabolite profile was tissue-dependent and the predominant route of excretion was fecal. The AUC(0-∞) and the Cmax of plasma and liver in females were greater than those in males. Slightly lower absorption was observed in mice with Elizabethan collars.

Characterization of water-soluble organic matter in urban aerosol by 1H-NMR spectroscopy

The functional and ¹³C isotopic compositions of water-soluble organic carbon (WSOC) in atmospheric aerosol were determined by nuclear magnetic resonance (¹H-NMR) and isotope ratio mass spectrometry (IRMS) in an urban location in the Southern Mississippi Valley. The origin of WSOC was resolved using the functional distribution of organic hydrogen, δ¹³C ratio, and positive matrix factorization (PMF). Three factors were retained based on NMR spectral bins loadings. Two factors (factors 1 and 3) demonstrated strong associations with the aliphatic region in the NMR spectra and levoglucosan resonances. Differences between the two factors included the abundance of the aromatic functional group for factor 1, indicating fresh emissions and, for factor 3, the presence of resonances attributed to secondary ammonium nitrate and low δ¹³C ratio values that are indicative of secondary organic aerosol. Factors 1 and 3 added 0.89 and 1.08 μgC m^-3, respectively, with the highest contribution in the summer and fall. Factor 2 retained resonances consistent with saccharides and was attributed to pollen particles. Its contribution to WSOC varied from 0.22 μgC m^-3 in winter to 1.04 μgC m^-3 in spring.

Metabolic activation of 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine and DNA adduct formation depends on p53: Studies in Trp53(+/+),Trp53(+/-) and Trp53(-/-) mice

The expression of the tumor suppressor p53 can influence the bioactivation of, and DNA damage induced by, the environmental carcinogen benzo[a]pyrene, indicating a role for p53 in its cytochrome P450 (CYP)-mediated biotransformation. The carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), which is formed during the cooking of food, is also metabolically activated by CYP enzymes, particularly CYP1A2. We investigated the potential role of p53 in PhIP metabolism in vivo by treating Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice with a single oral dose of 50 mg/kg body weight PhIP. N-(Deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP-C8-dG) levels in DNA, measured by liquid chromatography-tandem mass spectrometry, were significantly lower in liver, colon, forestomach and glandular stomach of Trp53(-/-) mice compared to Trp53(+/+) mice. Lower PhIP-DNA adduct levels in the livers of Trp53(-/-) mice correlated with lower Cyp1a2 enzyme activity (measured by methoxyresorufin-O-demethylase activity) in these animals. Interestingly, PhIP-DNA adduct levels were significantly higher in kidney and bladder of Trp53(-/-) mice compared to Trp53(+/+) mice, which was accompanied by higher sulfotransferase (Sult) 1a1 protein levels and increased Sult1a1 enzyme activity (measured by 2-naphthylsulfate formation from 2-naphthol) in kidneys of these animals. Our study demonstrates a role for p53 in the metabolism of PhIP in vivo, extending previous results on a novel role for p53 in xenobiotic metabolism. Our results also indicate that the impact of p53 on PhIP biotransformation is tissue-dependent and that in addition to Cyp1a enzymes, Sult1a1 can contribute to PhIP-DNA adduct formation.

Human Sulfotransferases Enhance the Cytotoxicity of Tolvaptan

Tolvaptan, a vasopressin receptor 2 antagonist used to treat hyponatremia, has recently been reported to be associated with liver injury. Sulfotransferases (SULTs) have been implicated as important detoxifying and/or activating enzymes for numerous xenobiotics, drugs, and endogenous compounds. To characterize better the role of SULTs in tolvaptan metabolism, HEK293 cells stably overexpressing 12 human SULTs were generated. Using these cell lines, the extent of tolvaptan sulfate formation was assessed by reversed-phase high-performance liquid chromatography through comparison to a synthetic standard. Of the 12 known human SULTs, no detectable sulfation of tolvaptan was observed with SULT1A1, SULT1A2, SULT1A3, SULT1C2, SULT1C4, SULT4A1, or SULT6B1. The affinity of individual SULT isozymes, as determined by Km analysis, was SULT1C3 >> SULT2A1 > SULT2B1 ∼ SULT1B1 > SULT1E1. The half inhibitory concentration of tolvaptan on cell growth in HEK293/SULT1C3 cells and HEK293/CYP3A4 & SULT1C3 cells was significantly lower than that in the corresponding HEK293/vector cells or HEK293/CYP3A4 & SULT vector cells. Moreover, exposing cells to tolvaptan in the presence of cyclosporine A, an inhibitor of the drug efflux transporters, significantly increased the intracellular levels of tolvaptan sulfate and decreased the cell viability in HEK293/SULT1C3 cells. These data indicate that sulfation increased the cytotoxicity of tolvaptan.

Effects of oral exposure to bisphenol A on gene expression and global genomic DNA methylation in the prostate, female mammary gland, and uterus of NCTR Sprague-Dawley rats

Bisphenol A (BPA), an industrial chemical used in the manufacture of polycarbonate and epoxy resins, binds to the nuclear estrogen receptor with an affinity 4-5 orders of magnitude lower than that of estradiol. We reported previously that "high BPA" [100,000 and 300,000 µg/kg body weight (bw)/day], but not "low BPA" (2.5-2700 µg/kg bw/day), induced clear adverse effects in NCTR Sprague-Dawley rats gavaged daily from gestation day 6 through postnatal day (PND) 90. The "high BPA" effects partially overlapped those of ethinyl estradiol (EE2, 0.5 and 5.0 µg/kg bw/day). To evaluate further the potential of "low BPA" to induce biological effects, here we assessed the global genomic DNA methylation and gene expression in the prostate and female mammary glands, tissues identified previously as potential targets of BPA, and uterus, a sensitive estrogen-responsive tissue. Both doses of EE2 modulated gene expression, including of known estrogen-responsive genes, and PND 4 global gene expression data showed a partial overlap of the "high BPA" effects with those of EE2. The "low BPA" doses modulated the expression of several genes; however, the absence of a dose response reduces the likelihood that these changes were causally linked to the treatment. These results are consistent with the toxicity outcomes.

Exceptionally long-term persistence of DNA adducts formed by carcinogenic aristolochic acid I in renal tissue from patients with aristolochic acid nephropathy

Aristolochic acid (AA) causes aristolochic acid nephropathy (AAN), first described in women in Belgium accidently prescribed Aristolochia fangchi in a slimming treatment, and also Balkan endemic nephropathy (BEN), through probable dietary contamination with Aristolochia clematitis seeds. Both nephropathies have a high risk of urothelial cancer, with AA being the causative agent. In tissues of AAN and BEN patients, a distinct DNA adduct, 7-(deoxyadenosin-N6-yl)-aristolactam I (dA-AAI), has been detected. DNA adducts can be removed through DNA repair, they can result in mutations through erroneous DNA replication or they can cause cell death. The dA-AAI adduct induces AT to TA transversions in the tumor-suppressor TP53 gene in experimental systems, matching TP53 mutations observed in urothelial tumors from AAN cancer cases. Using thin-layer chromatography 32P-postlabeling and mass spectrometric analysis we report the detection of dA-AAI in renal DNA from 11 Belgian AAN patients over 20 years after exposure to AA had ceased. Our results showed that dA-AAI is an established biomarker of AA exposure, and that this biomarker can be demonstrated to be persistent decades after a distinct AA exposure. Further, the persistence of dA-AAI adducts appears to be a critical determinant for the AA mutational fingerprint frequently found in oncogenes and tumor suppressor genes recently identified by whole genome sequencing of AA-associated urothelial tumors. The potential for exposure to AA worldwide is high; the unprecedented long-term persistence of dA-AAI provides a useful long-term biomarker of exposure and attests to the role of AA in human urothelial malignancy.

Toxicity evaluation of bisphenol A administered by gavage to Sprague Dawley rats from gestation day 6 through postnatal day 90

Bisphenol A (BPA) is a high production volume industrial chemical to which there is widespread human oral exposure. Guideline studies used to set regulatory limits detected adverse effects only at doses well above human exposures and established a no-observed-adverse-effect level (NOAEL) of 5 mg/kg body weight (bw)/day. However, many reported animal studies link BPA to potentially adverse effects on multiple organ systems at doses below the NOAEL. The primary goals of the subchronic study reported here were to identify adverse effects induced by orally (gavage) administered BPA below the NOAEL, to characterize the dose response for such effects and to determine doses for a subsequent chronic study. Sprague Dawley rat dams were dosed daily from gestation day 6 until the start of labor, and their pups were directly dosed from day 1 after birth to termination. The primary focus was on seven equally spaced BPA doses (2.5-2700 μg/kg bw/day). Also included were a naïve control, two doses of ethinyl estradiol (EE2) to demonstrate the estrogen responsiveness of the animal model, and two high BPA doses (100,000 and 300,000 μg/kg bw/day) expected from guideline studies to produce adverse effects. Clear adverse effects of BPA, including depressed gestational and postnatal body weight gain, effects on the ovary (increased cystic follicles, depleted corpora lutea, and antral follicles), and serum hormones (increased serum estradiol and prolactin and decreased progesterone), were observed only at the two high doses of BPA. BPA-induced effects partially overlapped those induced by EE2, consistent with the known weak estrogenic activity of BPA.

Modulation of intracellular iron metabolism by iron chelation affects chromatin remodeling proteins and corresponding epigenetic modifications in breast cancer cells and increases their sensitivity to chemotherapeutic agents

Iron plays a vital role in the normal functioning of cells via the regulation of essential cellular metabolic reactions, including several DNA and histone-modifying proteins. The metabolic status of iron and the regulation of epigenetic mechanisms are well-balanced and tightly controlled in normal cells; however, in cancer cells these processes are profoundly disturbed. Cancer-related abnormalities in iron metabolism have been corrected through the use of iron-chelating agents, which cause an inhibition of DNA synthesis, G₁-S phase arrest, an inhibition of epithelial-to-mesenchymal transition, and the activation of apoptosis. In the present study, we show that, in addition to these well-studied molecular mechanisms, the treatment of wild-type TP53 MCF-7 and mutant TP53 MDA-MB-231 human breast cancer cells with desferrioxamine (DFO), a model iron chelator, causes significant epigenetic alterations at the global and gene-specific levels. Specifically, DFO treatment decreased the protein levels of the histone H3 lysine 9 demethylase, Jumonji domain-containing protein 2A (JMJD2A), in the MCF-7 and MDA-MB-231 cells and down-regulated the levels of the histone H3 lysine 4 demethylase, lysine-specific demethylase 1 (LSD1), in the MDA-MB-231 cells. These changes were accompanied by alterations in corresponding metabolically sensitive histone marks. Additionally, we demonstrate that DFO treatment activates apoptotic programs in MCF-7 and MDA-MB-231 cancer cells and enhances their sensitivity to the chemotherapeutic agents, doxorubicin and cisplatin; however, the mechanisms underlying this activation differ. The induction of apoptosis in wild-type TP53 MCF-7 cells was p53-dependent, triggered mainly by the down-regulation of the JMJD2A histone demethylase, while in mutant TP53 MDA-MB-231 cells, the activation of the p53-independent apoptotic program was driven predominantly by the epigenetic up-regulation of p21.

Tumorigenicity of acrylamide and its metabolite glycidamide in the neonatal mouse bioassay

Acrylamide is a high-volume industrial chemical, a component of cigarette smoke, and a product formed in certain foods prepared at high temperatures. Previously, we compared the extent of DNA adduct formation and mutations in B6C3F(1) /Tk mice treated neonatally with acrylamide or glycidamide to obtain information concerning the mechanism of acrylamide genotoxicity. We have now examined the tumorigenicity of acrylamide and glycidamide in mice treated neonatally. Male B6C3F(1) mice were injected intraperitoneally on postnatal days 1, 8 and 15 with 0.0, 0.14 or 0.70 mmol acrylamide or glycidamide per kg body weight per day and the tumorigenicity was assessed after 1 year. Survival in each of the groups was >87%, there were no differences in body weights among the groups, and the only treatment-related neoplasms involved the liver. The incidence of combined hepatocellular adenoma or carcinoma was 3.8% in the control group, 8.3% in the 0.14 mmol acrylamide and glycidamide per kg body weight groups, 4.2% in the 0.70 mmol acrylamide per kg body weight group and 71.4% in the 0.70 mmol glycidamide per kg body weight group. Analysis of the hepatocellular tumors indicated that the increased incidence observed in mice administered 0.70 mmol glycidamide per kg body weight was associated with A → G and A → T mutations at codon 61 of H-ras. These results, combined with our previous data on DNA adduct formation and mutation induction, suggest that the carcinogenicity of acrylamide is dependent on its metabolism to glycidamide, a pathway that is deficient in neonatal mice.

Urinary biomarker detection of melamine- and cyanuric acid-induced kidney injury in rats

Oral coexposure of rats to melamine (MEL) and cyanuric acid (CYA) results in a dose-dependent increase in the formation of MEL-CYA crystals in the kidney. The aim of this study was to determine if urinary biomarkers of acute kidney injury could be used to noninvasively detect renal damage associated with crystal formation in the kidneys of MEL- and CYA-exposed rats. Urine was obtained on days 0 (predose), 2, 4, 14, and 28 from male and female Fischer 344 rats fed a diet supplemented with 0, 120, 180, or 240 ppm each of MEL and CYA. A number of urinary protein biomarkers (kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, osteopontin, albumin, alpha-GST, GST-Yb1, renal papillary antigen 1 [RPA-1], and clusterin) were measured using a multiplex assay system. The results showed that RPA-1 (distal tubule and collecting duct injury biomarker) was elevated on day 28 at the 120 ppm dose and higher in male rats and at the 180 ppm dose and higher in female rats; however, other urinary protein biomarkers were significantly elevated only at the 240 ppm dose. Significant elevation in blood urea nitrogen and serum creatinine levels, and severe renal damage evidenced by histopathology, were observed after 28 days of exposure to the highest dose, despite the fact that MEL-CYA crystals were observable at the 120 and 180 ppm doses. These data indicate that RPA-1 may serve as a noninvasive urinary biomarker for the detection and monitoring of obstructive nephropathy associated with MEL-CYA exposure.

Pharmacokinetics of melamine and cyanuric acid and their combinations in F344 rats

The intentional adulteration of pet food with melamine and cyanuric acid has been implicated in the kidney failure and death of a large number of cats and dogs in the United States. Although individually these compounds present low toxicity in a range of experimental animals, coexposure can lead to the formation of melamine cyanurate crystals in the nephrons and eventual kidney failure. Given this mode of action, a good understanding of the pharmacokinetic profiles of melamine and cyanuric acid and their combinations is essential to define properly the risk associated with different exposure scenarios. Previous studies have investigated the individual pharmacokinetic profiles of melamine and cyanuric acid. In this work, we report a comparison between the pharmacokinetic profiles of melamine and cyanuric acid administered individually, administered simultaneously as the individual compounds, and administered as a preformed melamine cyanurate complex. Although the oral coadministration of 1 mg/kg body weight of melamine and cyanuric acid did not alter significantly the pharmacokinetic profiles in relation to those determined upon individual oral administration of each compound, the administration of equal amounts of each triazine as the preformed melamine cyanurate complex significantly altered the pharmacokinetics, with reduced bioavailability of both compounds, lower observed maximum serum concentrations, delayed peak concentrations, and prolonged elimination half lives. These results indicate that in order to estimate properly the combined nephrotoxic potential of melamine and cyanuric acid, the experimental design of toxicological experiments and the evaluation of animal or human exposure scenarios should consider the detailed mode of exposure, with particular emphasis on any possible ex vivo formation of melamine cyanurate.

Effect of hepatic cytochrome P450 (P450) oxidoreductase deficiency on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-DNA adduct formation in P450 reductase conditional null mice

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), formed during the cooking of foods, induces colon cancer in rodents. PhIP is metabolically activated by cytochromes P450 (P450s). To evaluate the role of hepatic P450s in the bioactivation of PhIP, we used Reductase Conditional Null (RCN) mice, in which cytochrome P450 oxidoreductase (POR), the unique electron donor to P450s, can be specifically deleted in hepatocytes by pretreatment with 3-methylcholanthrene (3-MC), resulting in the loss of essentially all hepatic P450 function. RCN mice were treated orally with 50 mg/kg b.wt. PhIP daily for 5 days, with and without 3-MC pretreatment. PhIP-DNA adducts (i.e., N-(deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine [dG-C8-PhIP]), measured by liquid chromatography-tandem mass spectrometry, were highest in colon (1362 adducts/10(8) deoxynucleosides), whereas adduct levels in liver were ∼3.5-fold lower. Whereas no differences in PhIP-DNA adduct levels were found in livers with active POR versus inactivated POR, adduct levels were on average ∼2-fold lower in extrahepatic tissues of mice lacking hepatic POR. Hepatic microsomes from RCN mice with or without 3-MC pretreatment were also incubated with PhIP and DNA in vitro. PhIP-DNA adduct formation was ∼8-fold lower with hepatic microsomes from POR-inactivated mice than with those with active POR. Most of the hepatic microsomal activation of PhIP in vitro was attributable to CYP1A. Our results show that PhIP-DNA adduct formation in colon involves hepatic N-oxidation, circulation of activated metabolites via the bloodstream to extrahepatic tissues, and further activation, resulting in the formation of dG-C8-PhIP. Besides hepatic P450s, PhIP may be metabolically activated mainly by a non-P450 pathway in liver.

Gene expression of biomarkers of nephrotoxicity in F344 rats co-exposed to melamine and cyanuric acid for seven days

A number of studies have demonstrated that co-exposure to low levels of melamine and cyanuric acid elicits renal toxicity due to the formation of melamine cyanurate crystals in the kidney nephrons. In this work, we investigated if co-exposure of rats to these compounds leads to alterations in the expression of the genes encoding kidney injury molecule 1 (KIM-1), metallopeptidase inhibitor 1 (TIMP1), clusterin, osteopontin, and neutrophil gelatinase-associated lipocalin/lipocalin 2 (NGAL), which have been proposed as urinary biomarkers for nephrotoxicity. Six-week-old male and female F344 rats were fed ad libitum a diet fortified with 0 (control), 7, 23, 69, 229, or 694 ppm melamine and cyanuric acid (co-exposure groups), 1388 ppm melamine, or 1388 ppm cyanuric acid for seven days. Histopathology and clinical chemistry examination indicated marked toxicity only in the animals exposed to the two highest combined doses of melamine and cyanuric acid. Consistent with these observations, quantitative real-time polymerase chain reaction analysis of kidney tissue indicated increased expression of all genes analyzed relative to the control in both male and female rats fed daily with 229 or 694 ppm melamine and cyanuric acid. Exposure to lower levels of both compounds or to the individual compounds did not induce gene expression changes. These data indicate that quantifying the expression levels of the selected biomarker genes constitutes a useful endpoint to assess the combined toxicity of melamine and cyanuric acid in both male and female rats.

Dose-response assessment of nephrotoxicity from a 7-day combined exposure to melamine and cyanuric acid in F344 rats

The intentional adulteration of pet food with melamine and derivatives, including cyanuric acid, has been implicated in the kidney failure and death of a large number of cats and dogs in the United States. Although individually these compounds present low toxicity, coexposure can lead to the formation of melamine cyanurate crystals in the nephrons and eventual kidney failure. To determine the dose-response for nephrotoxicity upon coadministration of melamine and cyanuric acid, groups of male and female F344 rats (six animals per sex per group) were fed 0 (control), 7, 23, 69, 229, or 694 ppm of both melamine and cyanuric acid; 1388 ppm melamine; or 1388 ppm cyanuric acid in the diet for 7 days. No toxicity was observed in the rats exposed to the individual compounds, whereas anorexia and a statistically significant increase in blood urea nitrogen and serum creatinine levels was observed in the animals treated with 229 and 694 ppm melamine and cyanuric acid. The kidneys of these animals were grossly enlarged and pale yellow. Large numbers of crystalline structures deposited in the tubules were seen on sections in kidneys from all rats in these treatment groups. No significant changes were detected in the remaining treatment groups exposed to both melamine and cyanuric acid. In the melamine-only treatment group, 5 of 12 rats had scattered crystals present in renal tubules when examined by wet mount. These were not observed by histopathology. The observed adverse effect level (8.6 mg/kg bw [body weight]/day) and benchmark dose modeling data (8.4-10.9 mg/kg bw/day) determined in this study suggest that the tolerable daily intake values derived from studies conducted with melamine alone may underestimate the risk from coexposures to melamine and cyanuric acid.

Detection and quantitation of N-(deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine adducts in DNA using online column-switching liquid chromatography tandem mass spectrometry

The heterocyclic aromatic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is formed by the grilled cooking of certain foods such as meats, poultry and fish. PhIP has been shown to induce tumours in the colon, prostate and mammary glands of rats and is regarded as a potential human dietary carcinogen. PhIP is metabolically activated via cytochrome P450 mediated oxidation to an N-hydroxylamino-PhIP intermediate that is subsequently converted to an ester by N-acetyltransferases or sulfotransferases and undergoes heterolytic cleavage to produce a PhIP-nitrenium ion, which reacts with DNA to form the N-(deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP-C8-dG) adduct. Thus far, the detection and quantification of PhIP-DNA adducts has relied to a large extent on (32)P-postlabelling methodologies. In order to expand the array of available techniques for the detection and improved quantification of PhIP-C8-dG adducts in DNA we have developed an online column-switching liquid chromatography (LC)-electrospray ionization (ESI)-tandem mass spectrometry (MS/MS) selected reaction monitoring (SRM) method incorporating an isotopically [(13)C(10)]-labelled PhIP-C8-dG internal standard for the analysis of DNA enzymatically hydrolysed to 2'-deoxynucleosides. A dose-dependent increase was observed for PhIP-C8-dG adducts when salmon testis DNA was reacted with N-acetoxy-PhIP. Analysis of DNA samples isolated from colon tissue of mice treated by oral gavage daily for 5 days with 50 mg/kg body weight of PhIP resulted in the detection of an average level of 14.8+/-3.7 PhIP-C8-dG adducts per 10(6) 2'-deoxynucleosides. The method required 50 microg of hydrolysed animal DNA on column and the limit of detection for PhIP-C8-dG was 2.5 fmol (1.5 PhIP-C8-dG adducts per 10(8) 2'-deoxynucleosides). In summary, the LC-ESI-MS/MS SRM method provides for the rapid automation of the sample clean up and a reduction in matrix components that would otherwise interfere with the mass spectrometric analysis, with sufficient sensitivity and precision to analyse DNA adducts in animals exposed to PhIP.

Quantification of 3-nitrobenzanthrone-DNA adducts using online column-switching HPLC-electrospray tandem mass spectrometry

The aromatic nitroketone 3-nitrobenzanthrone (3-nitro-7H-benz[de]anthracen-7-one; 3-NBA) is an extremely potent mutagen and a suspected human carcinogen detected in the exhaust of diesel engines and in airborne particulate matter. 3-NBA is metabolically activated via reduction of the nitro group to the hydroxylamine (N-OH-3-ABA) to form covalent DNA adducts. Thus far, the detection and quantification of covalent 3-NBA-DNA adducts has relied solely on (32)P-postlabeling methodologies. In order to expand the range of available techniques for the detection and improved quantification of 3-NBA-DNA adducts, we have developed a method based upon online column-switching HPLC coupled to electrospray tandem mass spectrometry, with isotopic dilution of (15)N-labeled internal standards. This methodology was applied to the determination of three 3-NBA-derived adducts: 2-(2'-deoxyguanosin-N(2)-yl)-3-aminobenzanthrone (dG-N(2)-3-ABA), N-(2'-deoxyguanosin-8-yl)-3-aminobenzanthrone (dG-C8-N-3-ABA) and 2-(2'-deoxyguanosine-8-yl)-3-aminobenzanthrone (dG-C8-C2-3-ABA). Dose-dependent increases were observed for all three adducts when salmon testis DNA was reacted with N-acetoxy-3-aminobenzanthrone (N-AcO-3-ABA). dG-C8-C2-3-ABA was detected at much lower levels (overall 1%) than the other two adducts. DNA samples isolated from tissues of rats treated either intratracheally with 3-NBA or intraperitoneally with N-OH-3-ABA were analyzed by mass spectrometry, and the results compared to those obtained by (32)P-postlabeling. The method required 50 microg of hydrolyzed animal DNA on column and the limit of detection was 2.0 fmol for each adduct. dG-C8-C2-3-ABA was not observed in any of the samples providing confirmation that it is not formed in vivo. Linear regression analysis of the levels of dG-N(2)-3-ABA and dG-C8-N-3-ABA in the rat DNA showed a reasonable correlation between the two methods (R(2) = 0.88 and 0.93, respectively). In summary, the mass spectrometric method is a faster, more automated analytical approach that also provides structural confirmation of the adducts detected by (32)P-postlabeling, and it has sufficient sensitivity and precision to analyze DNA adducts in animals exposed to 3-NBA or its hydroxylamine metabolite.

Acrylamide formed at physiological temperature as a result of asparagine oxidation

Acrylamide is a probable human carcinogen that is neurotoxic to both humans and animals. It is known to be formed during cooking of foods at temperatures higher than 120 degrees C. The present study demonstrates that acrylamide can also be formed at physiological conditions (37 degrees C, pH 7.4) when asparagine is incubated in the presence of hydrogen peroxide (H(2)O(2)). The formation of acrylamide under these conditions is dependent on the incubation time and the concentration of H(2)O(2). Thus, the results raise the question of the possible endogenous formation of acrylamide in pathological conditions that are associated with long-term oxidative stress. Further studies are therefore warranted to clarify the possible endogenous formation of acrylamide and its significance in chronic conditions that are known to be associated with oxidative stress.

Mutagenic potential of nitrenium ions of nitrobenzanthrones: correlation between theory and experiment

The mutagenic activity of nine substituted nitrobenzanthrone (NBA) derivatives was recently established in the Ames assay and ranged from near inactivity to extremely high mutagenic activity (Takamura-Enya et al. 2006: Mutagenesis 21:399-404). Using thermochemical and molecular modeling techniques, the activation pathway of these NBA derivatives, namely 1-nitro-, 2-nitro-, 3-nitro-, 9-nitro-, 11-nitro-, 1,9-dinitro-, 3,9-dinitro-, 3,11-dinitro-, and 3,9,11-trinitrobenzanthrone, and the formation of the corresponding aryl-nitrenium ions, were investigated using density functional theory calculations. The calculated properties of the NBA derivatives were systematically compared with their bacterial mutagenic potency. Accommodation of the ligand substrates into the binding pocket of the bacterial nitroreductases was not sterically inhibited for the NBAs. Moreover, electron affinities, water elimination energies, esterification, and solvolysis energies did not reveal any possible links with the observed mutagenic potency of the NBAs. However, a strong negative linear correlation was found when the relative energies of the nitrenium ions of the mono and disubstituted NBAs were plotted against the logarithm of the mutagenic potency of the NBAs found in the different Salmonella typhimurium strains. Therefore, our data clearly indicate that the stability of the nitrenium ions is one critical determinant of the mutagenic potency of NBAs in Salmonella tester strains.

Effect of N,N-didesmethyltamoxifen upon DNA adduct formation by tamoxifen and alpha-hydroxytamoxifen

Tamoxifen undergoes sequential metabolism to N-desmethyltamoxifen and N,N-didesmethyltamoxifen. Whereas N-desmethyltamoxifen is a major metabolite in humans, nonhuman primates, and rats, appreciable concentrations of N,N-didesmethyltamoxifen are formed in humans and nonhuman primates but not in rats. This difference in the extent of N,N-didesmethyltamoxifen formation may be important because it has been proposed that N,N-didesmethyltamoxifen inhibits the cytochrome P450 (CYP)-catalyzed alpha-hydroxylation of tamoxifen and resultant tamoxifen-DNA adduct formation. To test this hypothesis directly, we compared the extent of tamoxifen-DNA adduct formation in rats co-administered 27micromol N,N-didesmethyltamoxifen per kg body weight and either 27micromol tamoxifen per kg body weight or 27micromol alpha-hydroxytamoxifen per kg body weight daily for 7days. Female Sprague-Dawley rats treated with N,N-didesmethyltamoxifen had a 44% decrease (p >0.05) in CYP 3A2 content (the CYP isoform responsible for tamoxifen alpha-hydroxylation), an 18% decrease (p =0.010) in CYP 3A activity, and higher blood levels of tamoxifen and N-desmethyltamoxifen compared to rats treated with solvent. Total tamoxifen-DNA adduct levels were 4.1-fold higher (p <0.001) in rats given alpha-hydroxytamoxifen as compared to tamoxifen. N,N-Didesmethyltamoxifen treatment caused a 1.2-fold increase in total tamoxifen-DNA adduct levels with both tamoxifen and alpha-hydroxytamoxifen, a difference that was not significant. These results indicate that, with this experimental model, N,N-didesmethyltamoxifen does not impair the metabolism of tamoxifen to a reactive electrophile.

Mutagenicity and DNA Adduct Formation by the Urban Air Pollutant 2-Nitrobenzanthrone

2-Nitrobenzanthrone (2-NBA) has recently been detected in ambient air particulate matter. Its isomer 3-nitrobenzanthrone (3-NBA) is a potent mutagen and suspected human carcinogen identified in diesel exhaust. The highest mutagenic activity of 2-NBA tested in Salmonella typhimurium was exhibited in strain TA1538-hSULT1A1 expressing human sulfotransferase (SULT) 1A1. 2-NBA also induced mutations in Chinese hamster lung V79 cells expressing human N-acetyltransferase 2 or SULT1A1, but no mutagenicity was observed in the parental cell line. DNA adduct formation in vitro was examined in different human cell lines by thin-layer chromatography (32)P-postlabeling. Whereas 3-NBA formed characteristic DNA adducts in lung A549, liver HepG2, colon HCT116, and breast MCF-7 cells, 2-NBA-derived DNA adducts were only observed in A549 and HepG2 cells, indicating differences in the bioactivation of each isomer. The pattern of 2-NBA-derived DNA adducts in both cell lines consisted of a cluster of up to five adducts. In HepG2 cells DNA binding by 2-NBA was up to 14-fold lower than by 3-NBA. DNA adduct formation of 2-NBA was also investigated in vivo in Wistar rats treated with a single dose of 2, 10, or 100 mg/kg body weight (bw). No DNA adduct formation was detected at doses of up to 10 mg/kg bw 2-NBA, even though 3-NBA induced DNA adducts at a dose of 2 mg/kg bw. Only after administration of one high dose of 100 mg/kg bw 2-NBA was a low level of DNA adduct formation detected, and then only in lung tissue. Density functional theory calculations for both NBAs revealed that the nitrenium ion of the 3-isomer is considerably more stable ( approximately 10 kcal/mol) than that of the 2-isomer, providing a possible explanation for the large differences in DNA adduct formation and mutagenicity between 2- and 3-NBA.

DNA adduct formation in the livers of female Sprague-Dawley rats treated with toremifene or alpha-hydroxytoremifene

Toremifene, an analogue of tamoxifen in which the ethyl side chain has been replaced with a 2-chloroethyl substituent, is used as a chemotherapeutic agent in postmenopausal women with advanced breast cancer. Toremifene is metabolized in a manner similar to that of tamoxifen, with alpha-hydroxytoremifene being a predominant metabolite in incubations in vitro. DNA adducts have been detected previously in liver DNA upon the administration of toremifene to rats; however, the identity of these adducts is unknown. In the present study, we have characterized the DNA adducts produced by alpha-hydroxytoremifene and have compared the extent of hepatic DNA adduct formation in rats administered toremifene, alpha-hydroxytoremifene, or tamoxifen. alpha-Hydroxytoremifene was synthesized, further activated by sulfation, and then reacted with salmon testis DNA. After enzymatic hydrolysis to deoxynucleosides, HPLC analysis indicated the formation of two major DNA adducts, which were characterized as (E)- and (Z)-alpha-(deoxyguanosin-N2-yl)toremifene on the basis of 1H NMR and mass spectral analyses. To assess the formation of toremifene DNA adducts in vivo, female Sprague-Dawley rats were treated intraperitoneally with toremifene, alpha-hydroxytoremifene, or tamoxifen. 32P-Postlabeling analyses of hepatic DNA from the tamoxifen-treated rats indicated three DNA adducts at a total level of 2,200 +/- 270 adducts/108 nucleotides. DNA adducts were not detected (<5 adducts/108 nucleotides) in the livers of rats treated with toremifene. Two DNA adducts, of which the major one coeluted with the 3',5'-bis-phosphate of (E)-alpha-(deoxyguanosin-N2-yl)toremifene, were present at a level of 57 +/- 12 adducts/108 nucleotides in hepatic DNA from rats administered alpha-hydroxytoremifene. The low level of hepatic DNA adduct formation observed with both toremifene and alpha-hydroxytoremifene, as compared to that with tamoxifen, may be due to the limited esterification of alpha-hydroxytoremifene and/or the poor reactivity of alpha-sulfoxytoremifene.

Cytogenetic Damage Induced by Acrylamide and Glycidamide in Mammalian Cells: Correlation with Specific Glycidamide-DNA Adducts

Acrylamide (AA) is a suspected human carcinogen generated in carbohydrate-rich foodstuffs upon heating. Glycidamide (GA), formed via epoxidation, presumably mediated by cytochrome P450 2E1, is thought to be the active metabolite playing a central role in AA genotoxicity. In this work we investigated DNA damage induced by AA and GA in mammalian cells, using V79 Chinese hamster cells. For this purpose, we evaluated two cytogenetic end points, chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs), as well as the levels of specific GA-DNA adducts, namely, N7-(2-carbamoyl-2-hydroxyethyl)guanine (N7-GA-Gua) and N3-(2-carbamoyl-2-hydroxyethyl)adenine (N3-GA-Ade) using high-performance liquid chromatography coupled with tandem mass spectrometry. GA was more cytotoxic and clastogenic than AA. Both AA and GA induced CAs (breaks and gaps) and decreased the mitotic index. GA induced SCEs in a dose-responsive manner; with AA, SCEs were increased at only the highest dose tested (2mM). A linear dose-response relationship was observed between the GA concentration and the levels of N7-GA-Gua. This adduct was detected for concentrations as low as 1 microM GA. N3-GA-Ade was also detected, but only at very high GA concentrations (>or= 250 microM). There was a very strong correlation between the levels of N7-GA-Gua in the GA- and AA-treated cells and the extent of SCE induction. Such correlation was not apparent for CAs. These data suggest that the induction of SCEs by AA is associated with the metabolism of AA to GA and subsequent formation of depurinating DNA adducts; however, other mechanisms must be involved in the induction of CAs.

DNA adducts derived from administration of acrylamide and glycidamide to mice and rats

Acrylamide (AA) is an important industrial chemical that is neurotoxic, mutagenic to somatic and germ cells, and carcinogenic in chronic rodent bioassays. Recent findings of AA in many common starchy foods have sparked renewed interest in determining toxic mechanisms and in understanding the cancer, neurotoxicity, and reproductive risks from typical human exposures. Dosing mice and rats with AA (50 mg/kg) led to presence of glycidamide (GA) in serum and tissues. Furthermore, GA-derived DNA adducts of adenine and guanine were formed in all tissues examined, including both target tissues identified in rodent carcinogenicity bioassays and in non-target tissues. Dosing rats and mice with an equimolar amount of GA typically produced higher levels of DNA adducts than observed with AA. Kinetics of DNA adduct formation and accumulation were measured following oral administration of a single dose of AA (50 mg/kg) or from repeat dosing (1 mg/kg/day), respectively. The formation of these DNA adducts is consistent with previously reported mutagenicity of AA and GA in vitro, which involved reaction of GA with adenine and guanine bases. These results provide strong support for a genotoxic mechanism of AA carcinogenicity in rodents. The kinetic/biomarker approaches described here may represent a meaningful way to extrapolate cancer risks to actual human exposures from food, which are much lower.

Inhibition of extrahepatic human cytochromes P450 1A1 and 1B1 by metabolism of isoflavones found in Trifolium pratense (red clover)

Biochanin A and formononetin are the predominant isoflavones in red clover. In a previous study (J. Agric. Food Chem. 2002, 50, 4783-4790), it was demonstrated that human liver microsomes converted biochanin A and formononetin to genistein and daidzein. This paper now shows CYP1B1-catalyzed O-demethylation of biochanin A and formononetin to produce genistein and daidzein, respectively, which inhibit CYP1B1. Recombinant human CYP1A1 or CYP1B1 was incubated with biochanin A or formononetin. CYP1A1 catalyzed isoflavone 4'-O-demethylation and hydroxylations with similar efficiency, whereas CYP1B1 favored 4'-O-demethylation over hydroxylations. Three of the biochanin A metabolites (5,7,3'-trihydroxy-4'-methoxyisoflavone, 5,7,8-trihydroxy-4'-methoxyisoflavone, and 5,6,7-trihydroxy-4'-methoxyisoflavone) were characterized by 1H NMR spectroscopy and mass spectrometry. Daidzein (Ki = 3.7 microM) exhibited competitive inhibition of CYP1B1 7-ethoxyresorufin O-deethylase activity, and genistein (Ki = 1.9 microM) exhibited mixed inhibition. Biochanin A and/or formononetin may exert anticarcinogenic effects directly by acting as competitive substrates for CYP1B1 or indirectly through their metabolites daidzein and genistein, which inhibit CYP1B1.

Analysis of tamoxifen-DNA adducts in endometrial explants by MS and 32P-postlabeling

The nonsteroidal antiestrogen tamoxifen increases the risk of endometrial cancer; however, the mechanism for the induction of these tumors is not known. Recently, Sharma et al. [Biochem. Biophys. Res. Commun. 307 (2003) 157], using high performance liquid chromatography (HPLC) with online postcolumn photochemical activation and fluorescence detection, reported the presence of (E)-alpha-(deoxyguanosin- N2-yl)tamoxifen in DNA from human endometrial explants incubated with tamoxifen. Inasmuch as the methodology used by these investigators does not allow unambiguous characterization of tamoxifen-DNA adducts, we have used two additional techniques (HPLC coupled with electrospray ionization tandem mass spectrometry and 32P-postlabeling analyses) to assay for the presence of tamoxifen-DNA adducts in the human endometrial explant DNA. Tamoxifen-DNA adducts were not detected by either method.

Electrospray ionization-tandem mass spectrometry and 32P-postlabeling analyses of tamoxifen-DNA adducts in humans

BACKGROUND

Although the nonsteroidal antiestrogen tamoxifen is used as an adjuvant chemotherapeutic agent to treat hormone-dependent breast cancer and as a chemopreventive agent in women with elevated risk of breast cancer, it has also been reported to increase the risk of endometrial cancer. Reports of low levels of tamoxifen-DNA adducts in human endometrial tissue have suggested that tamoxifen induces endometrial cancer by a genotoxic mechanism. However, these findings have been controversial. We used electrospray ionization-tandem mass spectrometry (ES-MS/MS) and 32P-postlabeling analyses to investigate the presence of tamoxifen-DNA adducts in human endometrial tissue.

METHODS

Endometrial DNA from eight tamoxifen-treated women and eight untreated women was hydrolyzed to nucleosides and assayed for (E)-alpha-(deoxyguanosin-N2-yl)-tamoxifen (dG-Tam) and (E)-alpha-(deoxyguanosin-N2-yl)-N-desmethyltamoxifen (dG-desMeTam), the two major tamoxifen-DNA adducts that have been reported to be present in humans and/or experimental animals treated with tamoxifen, using on-line sample preparation coupled with high-performance liquid chromatography (HPLC) and ES-MS/MS. The same DNA samples were assayed for the presence of dG-Tam and dG-desMeTam by (32)P-postlabeling methodology, using two different DNA digestion and labeling protocols, followed by both thin-layer chromatography and HPLC.

RESULTS

We did not detect either tamoxifen-DNA adduct by HPLC-ES-MS/MS analyses (limits of detection for dG-Tam and dG-desMeTam were two adducts per 10(9) nucleotides and two adducts per 10(8) nucleotides, respectively) or by 32P-postlabeling analyses (limit of detection for both adducts was one adduct per 10(9) nucleotides) in any of the endometrial DNA samples.

CONCLUSION

The initiation of endometrial cancer by tamoxifen is probably not due to a genotoxic mechanism involving the formation of dG-Tam or dG-desMeTam.

DNA adduct formation from acrylamide via conversion to glycidamide in adult and neonatal mice

Acrylamide (AA) is a high production volume chemical with many industrial uses; however, recent findings of ppm levels in starchy foods cooked at high temperature have refocused worldwide attention on the neurotoxicity, germ cell mutagenicity, and carcinogenicity of AA. Oxidative metabolism of AA to its epoxide metabolite, glycidamide (GA), has been observed in experimental animals and humans and may be associated with many of the toxic effects of AA exposure, including formation of N7-(2-carbamoyl-2-hydroxyethyl)guanine (N7-GA-Gua) in vivo. This paper describes the characterization of two new GA-derived DNA adducts formed in vitro, N3-(2-carbamoyl-2-hydroxyethyl)adenine (N3-GA-Ade) and N1-(2-carboxy-2-hydroxyethyl)-2'-deoxyadenosine. A sensitive method for quantification of N7-GA-Gua and N3-GA-Ade, based on LC with tandem mass spectrometry and isotope dilution, was developed and validated for use in measuring DNA adduct formation in selected tissues of adult and whole body DNA of 3 day old neonatal mice treated with AA and GA. In adult mice, DNA adduct formation was observed in liver, lung, and kidney with levels of N7-GA-Gua around 2000 adducts/10(8) nucleotides and N3-GA-Ade around 20 adducts/10(8) nucleotides. Adduct levels were modestly higher in adult mice dosed with GA as opposed to AA; however, treatment of neonatal mice with GA produced 5-7-fold higher whole body DNA adduct levels than with AA, presumably reflective of lower oxidative enzyme activity in newborn mice. DNA adduct formation from AA treatment in adult mice showed a supralinear dose-response relationship, consistent with saturation of oxidative metabolism at higher doses. These results increase our understanding of the mutagenic potential of GA and provide further evidence for a genotoxic mechanism in AA carcinogenesis.

Determination of acrylamide and glycidamide serum toxicokinetics in B6C3F1 mice using LC–ES/MS/MS

Acrylamide (AA) is a well-studied industrial toxicant; however, recent findings of AA at ppm levels in cooked starchy foods have refocused attention on the potential for neurotoxicity, germ cell mutagenicity, and carcinogenicity from AA. Oxidative metabolism of AA to glycidamide (GA) in experimental animals has previously been linked with many toxic effects of AA exposure. We report a new sensitive and selective analytical method, based on LC with electrospray tandem mass spectrometry, for the quantification of AA and GA in serum and its application to a preliminary toxicokinetic evaluation of AA and GA in adult B6C3F(1) mice following oral administration of AA.