Substance-dependent sex differences in the activation of benzylic alcohols to mutagens by hepatic sulfotransferases of the rat

Six primary and 10 secondary benzylic alcohols derived frompolycycic aromatic hydrocarbons were tested for mutagemcityin Salmonella typhimurium TA98 in the presence of varying amountsof hepatic cytosol from adult male and female rats and 3'-phosphoadenosine-5'-phospho-sulfate,the cofactor for sulfotransferases. With the exception of 1-(9-anthryl)ethanol,4H-cyclopenta[def] phenanthren-4-ol and 10-hydroxy-7,8,9,10-tetrahydrobenzo[a]all the benzylic alcohols were activated to mutagens. For 1-(1-pyrenyl)ethanol(1-HEP), 1-(2-pyrenyl)ethanol (2-HIEP), 6-hydroxymethylanthanthrene(6-HMAA), 2-hydroxymethylpyrene (2-HMP), 10H-indeno[1,2,7,7a-bcd]pyren-10-ol(OH-IP), 3-hydroxy-3,4-dihydrocyclopenta[cd]pyrene (3-OH-H₂-CPcdP)and 1-(6-benzo[a]pyrenl)ethanol (6-HEBP) this is the first observationof a mutagenic activity. The primary alcohols 1-hydroxymethylpyrene,2-HMP, 9-hydroxymethylanthracene, 7-hydroxymethyl-12-methylbenz[a]anthraceneand 6-hydroxymethylbenzo[a]pyrene as well as the secondary alcohols1-HEP and 3-OH-H₂ were more efficiently activated by hepaticcytosol from females than by preparations from males (2.6- to8-fold). A further compound, 6-HIEBP showed significant, butrelatively weak, effects in the presence of cytosol from females,whereas it was inactive in the presence of hepatic cytosol frommales. The reverse sex difference was observed in the activationof 4H-cyclopenta[def]chrysen-4-ol, the activity of cytosol frommales amounting to about four times that from females. Fourother compounds, 2-HEP, 7-hydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene6-HMAA and OH-IP, were activated with similar efficiency byhepatic cytosol from both sexes (< two-fold differences).The study indicates that different sulfotransferases are involvedin the bioactivation of benzylic alcohols, including forms preferentiallyexpressed in females as well as forms preferentially expressedin males, and that these enzymes qualitatively differ in theirsubstrate tolerance for benzylic alcohols.     

Dietary resistant starch type 3 prevents tumor induction by 1,2-dimethylhydrazine and alters proliferation, apoptosis and dedifferentiation in rat colon

Some epidemiological and experimental studies suggest that consumption of resistant starch is preventive against colon cancer. Resistant starch leads to a fermentation-mediated increase in the formation of short-chain fatty acids, with a particularly high butyrate fraction in large bowel. Butyrate is considered to be protective against colon cancer because it causes growth arrest and apoptosis and regulates expression of proteins involved in cellular dedifferentiation in various tumor cell lines in culture. We sought to investigate these processes under conditions of a carcinogenicity experiment in vivo. In the present study, 1,2-dimethylhydrazine-treated Sprague-Dawley rats were fed standard diet (n=12) or diet with 10% hydrothermally modified Novelose 330, a resistant starch type 3 (RS3), replacing digestible starch (n=8). After 20 weeks tumor number, epithelial proliferation, apoptosis, immunoreactivity of carcinogenesis-related proteins [protein kinase C-delta (PKC-delta), heat shock protein 25 (HSP25) and gastrointestinal glutathione peroxidase (GI-GPx)], as well as mucin properties were evaluated in proximal and distal colon in situ. No tumors developed under RS3 diet, compared to a tumor incidence of 0.6+/-0.6 (P<0.05) under the standard diet. RS3 decreased the number of proliferating cells, the length of the proliferation zone and the total length of the crypt in the distal colon, but not proximal colon, and enhanced apoptosis in both colonic segments. It induced PKC-delta and HSP25 expression, but inhibited GI-GPx expression in the epithelium of distal colon. RS3 increased the number of predominantly acidic mucin containing goblet cells in the distal colon, but had no effect on the goblet cell count. We conclude that hydrothermally treated RS3 prevented colon carcinogenesis, and that this effect was mediated by enhanced apoptosis of damaged cells accompanied by changes in parameters of dedifferentiation in colonic mucosa.     

Altered metabolic profile in the frontal cortex of PS2APP transgenic mice, monitored throughout their life span

The transgenic mouse line PS2APP (PS2N141I x APP(swe)) develops an age-related cognitive decline associated with severe amyloidosis, mimicking the pathophysiologic processes in Alzheimer disease (AD). In the quest for biomarkers to monitor, noninvasively, the progression of the disease, we used magnetic resonance imaging and 1H-spectroscopy to characterize PS2APP mice throughout their life span. Morphometric measurements revealed only small size differences to controls. The metabolic profile, however, showed clear indicators of hypometabolism with age in the PS2APP mice: both N-acetyl-aspartate and glutamate were significantly reduced in the older animals. These spectroscopic measures in vivo correlated well with the plaque load in the frontal cortex. A diagnostic test, based on these measures, reached 92% sensitivity and 82% specificity at age 20 months. These noninvasive biomarkers can be exploited in preclinical pharmaceutical research to cope with the high variability in transgenic animal models and to enhance the power of drug efficacy studies.     

Potent inhibition of estrogen sulfotransferase by hydroxylated metabolites of polyhalogenated aromatic hydrocarbons reveals alternative mechanism for estrogenic activity of endocrine disrupters

Polyhalogenated aromatic hydrocarbons (PHAHs), such as polychlorinated dibenzo-p-dioxins and dibenzofurans, polybrominated diphenylethers, and bisphenol A derivatives are persistent environmental pollutants, which are capable of interfering with reproductive and endocrine function in birds, fish, reptiles, and mammals. PHAHs exert estrogenic effects that may be mediated in part by their hydroxylated metabolites (PHAH-OHs), the mechanisms of which remain to be identified. PHAH-OHs show low affinity for the ER. Alternatively, they may exert their estrogenic effects by inhibiting E2 metabolism. As sulfation of E2 by estrogen sulfotransferase (SULT1E1) is an important pathway for E2 inactivation, inhibition of SULT1E1 may lead to an increased bioavailability of estrogens in tissues expressing this enzyme. Therefore, we studied the possible inhibition of human SULT1E1 by hydroxylated PHAH metabolites and the sulfation of the different compounds by SULT1E1. We found marked inhibition of SULT1E1 by various PHAH-OHs, in particular by compounds with two adjacent halogen substituents around the hydroxyl group that were effective at (sub)nanomolar concentrations. Depending on the structure, the inhibition is primarily competitive or noncompetitive. Most PHAH-OHs are also sulfated by SULT1E1. We also investigated the inhibitory effects of the various PHAH-OHs on E2 sulfation by human liver cytosol and found that the effects were strongly correlated with their inhibitions of recombinant SULT1E1 (r = 0.922). Based on these results, we hypothesize that hydroxylated PHAHs exert their estrogenic effects at least in part by inhibiting SULT1E1-catalyzed E2 sulfation.     

Biomarkers of exposure, effect, and susceptibility in workers exposed to nitrotoluenes.

Nitrotoluenes, such as 2-nitrotoluene, 2,4-dinitrotoluene (24DNT), and 26DNT, are carcinogenic in animal experiments. Humans are exposed to such chemicals in the workplace and in the environment. It is therefore important to develop methods to biomonitor people exposed to nitrotoluenes to prevent the potential harmful effects. For the present study, workers exposed to high levels of these chemicals were investigated. The external dose (air levels), the internal dose (urine metabolites), the biologically effective dose [hemoglobin (Hb) adducts and urine mutagenicity], and biological effects (chromosomal aberrations and health effects) were determined. Individual susceptibility was assessed by determining genetic polymorphisms of enzymes assumed to function in nitrotoluene metabolism, namely glutathione S-transferases (GSTM1, GSTT1, GSTP1), N-acetyltransferases (NAT1, NAT2), and sulfotransferases (SULT1A1, SULT1A2). The levels of urinary metabolites did not correlate with the air levels. The urinary mutagenicity levels determined in a subset of workers correlated with the levels of a benzylalcohol metabolite of DNT. The Hb-adducts correlated with the urine metabolites but not with the air levels. The frequency of chromosomal aberrations (gaps included) was increased (P < 0.05) in the exposed workers in comparison with a group of factory controls and correlated with the level of 24DNT Hb-adducts in young subjects (<31 years). The GSTM1-null genotype was significantly more prevalent in the controls than in the exposed group, which probably reflected an elevated susceptibility of the GSTM1-null genotype to adverse health effects of DNT exposure, such as nausea (odds ratio, 8.8; 95% confidence interval, 2.4-32.2). A statistically significant effect was seen for SULT1A2 genotype on a 24DNT Hb-adduct; GSTP1 genotype on a 2,4,6-trinitrotoluene Hb-adduct; and SULT1A1, SULT1A2, NAT1, GSTT1, and GSTP1 genotypes on chromosomal aberrations in the exposed workers.     

Components of total irradiation dose in Switzerland and their ranges

Summary The present knowledge about dose components in Switzerland and their ranges is reviewed. Considerable ranges are found for doses induced by radon decay-products and by cosmic and terrestrial radiation. Yearly doses from radon decay-products show average values between about 1 and 20 mSv in different communities and individual values up to about 150 mSv. The reliability of these average values is, however, limited, because radon concentrations have been measured up to now only in a small number of houses, and because corrections of the raw data are necessary, increasing the uncertainty of the results. Doses from terrestrial and cosmic radiation show locally variable values between about 0.5 and 1.5 mSv per year. These doses are mainly derived from outdoor measurements. Therefore, these results also are only of limited use in possible epidemiological applications.

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Dosis-Komponenten in der Schweiz und deren Schwankungsbreiten

Zusammenfassung Die Dosis-Komponenten in der Schweiz und deren Schwankungsbreiten sind aus heutiger Sicht zusammengestellt. Beachtliche Variationen zeigen sich bei den durch Radon-Folgeprodukte bewirkten Dosen und bei den Dosen infolge kosmischer und terrestrischer Strahlung. Die durch Radon-Zerfallsprodukte bewirkten mittleren Jahresdosen liegen in verschiedenen Schweizer Gemeinden zwischen ca. 1 und 20 mSv; für Einzelpersonen kommen Werte bis ca. 150 mSv vor. Die Zuverlässigkeit der Mittelwerte ist jedoch begrenzt, weil bis jetzt Radon-Konzentrationen nur in wenigen Häusern gemessen wurden und weil an den Messwerten Korrekturen vorgenommen werden müssen, was die Unsicherheit der Resultate erhöht. Die Dosen, die durch terrestrische und kosmische Strahlung verursacht werden, zeigen örtlich variable Werte zwischen ca. 0.5 und 1.5 mSv pro Jahr. Diese Dosiswerte wurden vorwiegend durch Messungen im Freien bestimmt. Deshalb können auch diese Resultate nur mit Einschränkungen in allfälligen epidemiologischen Studien verwendet werden.

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Contributions de la dose d'irradiation en Suisse et leur variabilité

Résumé Ce travail constitue une mise à jour des connaissances sur les contributions à la dose d'irradiation et leur variabilité en Suisse. Des variations considérables ont été mises en évidence pour les doses induites par les descendants du radon, le rayonnement cosmique et les composantes terrestres. Les doses annuelles occasionnées par les descendants du radon montrent des valeurs moyennes comprises entre 1 et 20 mSv dans les différentes communes suisses, des valeurs ponctuelles pouvant atteindre jusqu'à 150 mSv. La fiabilité de ces moyennes est limitée du fait du nombre encore restreint de maisons examinées et compte tenu d'une incertitude additionnelle des résultats impliquée par des corrections nécessaires au niveau des données brutes. Les doses dues à la radiation terrestre et cosmique mettent en évidence des variations locales s'échelonnant d'environ 0.5 à 1.5 mSv par an. Ces doses résultent principalement des mesures en plein air. C'est pourquoi l'exploitation de ces résultats pour des applications épidémiologiques s'avère également limitée.

     

Vitamin E activates gene expression via the pregnane X receptor

Tocopherols and tocotrienols are metabolized by side chain degradation via initial omega-oxidation and subsequent beta-oxidation. omega-Oxidation is performed by cytochrome P450 (CYP) enzymes which are often regulated by their substrates themselves. Results presented here show that all forms of Vitamin E are able to activate gene expression via the pregnane X receptor (PXR), a nuclear receptor regulating a variety of drug metabolizing enzymes. In HepG2 cells transfected with the human PXR and the chloramphenicol acetyl transferase (CAT) gene linked to two PXR responsive elements, CAT activity was most strongly induced by alpha- and gamma-tocotrienol followed by rifampicin, delta-, alpha- and gamma-tocopherol. The inductive efficacy was concentration-dependent; its specificity was underscored by a lower response when cotransfection with PXR was omitted. Up-regulation of endogenous CYP3A4 and CYP3A5 mRNA was obtained by gamma-tocotrienol, the most potent activator of PXR, with the same efficacy as with rifampicin. This points to a potential interference of individual forms of Vitamin E with the metabolism and efficacy of drugs.