Interactions of odorants with olfactory receptors and receptor neurons match the perceptual dynamics observed for woody and fruity odorant mixtures.

The present study aimed to create a direct bridge between observations on peripheral and central responses to odorant mixtures and their components. Three experiments were performed using mixtures of fruity (isoamyl acetate; ISO) and woody (whiskey lactone; WL) odorants known to contribute to some of the major notes in Burgundy red wine. These experiments consisted of (i) calcium imaging of human embryonic kidney cells (HEK293T) transfected with olfactory receptors (ORs); (ii) single-unit electrophysiological recordings from olfactory receptor neurons (ORNs) and analyses of electro-olfactogram (EOG) responses in the rat nose in vivo; and (iii) psychophysical measurements of the perceived intensity of the mixtures as rated by human subjects. The calcium imaging and electrophysiological results revealed that ISO and WL can act simultaneously on single ORs or ORNs and confirm that receptor responses to mixtures are not the result of a simple sum of the effects of the individual mixture compounds. The addition of WL to ISO principally suppressed the ORN activation induced by ISO alone and was found to enhance this activation in a subset of cases. In the human studies, the addition of high concentrations of WL to ISO decreased the perceived intensity of the ISO. In contrast, the addition of low concentrations of WL enhanced the perceived intensity of the fruity note (ISO) in this mixture, as it enhanced EOG responses in ORNs. Thus, both OR and ORN responses to ISO + WL mixtures faithfully reflected perceptual response changes, so the odour mixture information is set up after the peripheral stage of the olfactory system.

Protective effects of garlic sulfur compounds against DNA damage induced by direct- and indirect-acting genotoxic agents in HepG2 cells.

The aim of this study was to assess the antigenotoxic activity of several garlic organosulfur compounds (OSC) in the human hepatoma cell line HepG2, using comet assay. The OSC selected were allicin (DADSO), diallyl sulfide (DAS), diallyl disulfide (DADS), S-allyl cysteine (SAC) and allyl mercaptan (AM). To explore their potential mechanisms of action, two approaches were performed: (i) a pre-treatment protocol which allowed study of the possible modulation of drug metabolism enzymes by OSC before treatment of the cells with the genotoxic agent; (ii) a co-treatment protocol by which the ability of OSC to scavenge direct-acting compounds was assessed. Preliminary studies showed that, over the concentration range tested (5-100 microM), the studied OSC neither affected cell viability nor induced DNA damage by themselves. In the pre-treatment protocol, aflatoxin B1 genotoxicity was significantly reduced by all the OSC tested except AM. DADS was the most efficient OSC in reducing benzo(a)pyrene genotoxicity. SAC and AM significantly decreased DNA breaks in HepG2 cells treated with dimethylnitrosamine. Additionally, all the OSC studied were shown to decrease the genotoxicity of the direct-acting compounds, hydrogen peroxide and methyl methanesulfonate. This study demonstrated that garlic OSC displayed antigenotoxic activity in human metabolically competent cells.

Post-initiation modulating effects of allyl sulfides in rat hepatocarcinogenesis.

Effects of administration of diallyl sulfide (DAS) and diallyl disulfide (DADS) on the promotion stage of hepatocarcinogenesis were investigated in rats using the Ito model. They were compared with those of phenobarbital (PB), a well-known liver promoter in rats. Initiation was induced by a single dose of N-nitrosodiethylamine (NDEA) and 3 weeks later, a partial hepatectomy was conducted. Two weeks after the NDEA injection, rats received either 0.05% allyl sulfides, PB or both in their diet for 8 weeks. Feeding with DAS increased the number of liver preneoplastic foci by 63% with respect to the untreated group. However, rats fed DAS showed a lower foci development than rats fed PB. The DADS group did not differ from control group for any of the measured morphometric parameters. Simultaneous administration of DADS with PB partially reduced the promotional activity of PB whereas DAS co-treatment did not modify PB properties. These findings confirm that DAS can act as a promoter in rat liver but exerts no co-promoting effect. Conversely, DADS was found to have promotion-inhibiting ability, suggesting that DADS has greater value than DAS as a chemopreventive agent.

Antimutagenic activity of organosulfur compounds from Allium is associated with phase II enzyme induction.

In a previous study, we showed that naturally occurring organosulfur compounds (OSCs) from garlic and onion modulated the activation of carcinogen via the alteration of cytochromes P450. The present study was undertaken to determine the incidence of the in vivo induction of phase II enzymes by individual OSCs on the genotoxicity of several carcinogens. Diallyl sulfide (DAS), diallyl disulfide (DADS), dipropyl sulfide (DPS) and dipropyl disulfide (DPDS), were administered by gavage (1mmol/kg) to male SPF Wistar rats for 4 consecutive days. The effects of treatments on phase II enzymes and on the genotoxicity of carcinogens were evaluated with hepatic cytosols and microsomes from OSCs-treated rats. DADS strongly increased all the phase II enzymes activities examined, i.e. total glutathione S-transferase (GST) activity, mu GST activity, quinone reductase (QR) activity and epoxide hydrolase (EH) activity. In addition, DADS strongly increased the protein level of rGSTP1. QR activity, total and mu GST activities were also increased by DAS and DPDS whereas DPS increased only mu GST activity and QR activity. To assess the repercussions of these inductions on the genotoxicity of carcinogens, the effects of cytosols or microsomes from OSCs-treated rats on the mutagenicity of (+)-anti-7beta,8alpha-dihydroxy-9alpha,10alpha-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE), styrene oxide (SO) and 4-nitroquinoline 1-oxide (4-NQO) were measured in the Ames test. DADS showed a very effective antimutagenic activity against BPDE, SO and 4-NQO. DAS reduced the mutagenicity of BPDE and SO. In contrast, DPS and DPDS showed little efficient antimutagenic activity since they only reduced the mutagenicity of BPDE and 4-NQO, respectively. Interestingly, DADS appeared to be as effective as ethoxyquin, a model inducer of phase II enzymes, in both inducing phase II enzymes and inhibiting the mutagenicity of carcinogens. This study demonstrated that the antimutagenic activities of OSCs against several ultimate carcinogens were closely related to their ability to induce phase II enzymes.

Type i interferons potently enhance humoral immunity and can promote isotype switching by stimulating dendritic cells in vivo.

Type I interferons (IFN-I) are rapidly induced following infection and play a key role in nonspecific inhibition of virus replication. Here we have investigated the effects of IFN-I on the generation of antigen-specific antibody responses. The data show that IFN-I potently enhance the primary antibody response to a soluble protein, stimulating the production of all subclasses of IgG, and induce long-lived antibody production and immunological memory. In addition, endogenous production of IFN-I was shown to be essential for the adjuvant activity of CFA. Finally, IFN-I enhanced the antibody response and induced isotype switching when dendritic cells were the only cell type responding to IFN-I. The data reveal the potent adjuvant activity of IFN-I and their important role in linking innate and adaptive immunity.

Organosulfur compounds from Allium and the chemoprevention of cancer.

Allium vegetables and their associated organosulfur constituents are extensively studied for their chemopreventive potential against cancer. This article overviews their anticarcinogenic and antigenotoxic properties. Epidemiological studies (mostly case-control studies) provide strong evidence that Allium vegetable consumption reduces the incidence of gastric and colon cancer while the association between Allium vegetable consumption and other cancers is less convincing. Furthermore, many experimental studies have demonstrated that organosulfur compounds and Allium extracts have inhibitory effects on carcinogenesis in animals. These inhibitory effects are supported by many diverse mechanisms, including inhibition of carcinogen formation, modulation of carcinogen metabolism, inhibition of mutagenesis and genotoxicity, inhibition of cell proliferation and increase of apoptosis, inhibition of angiogenesis, and immune system enhancement. Before such constituents or extracts can be used in chemopreventive trials, it is important to verify their lack of toxicity and to investigate further their precise mechanisms of action throughout the whole process of carcinogenesis.

Mechanisms involved in the chemoprevention of flavonoids.

Flavonoids, widespread in edible plants, have been studied extensively for their anticarcinogenic properties. However, only few studies have been done with these constituents being administered by the dietary route. In our research, the effects of feeding rats with flavone, flavanone, tangeretin, and quercetin were investigated on two steps of aflatoxin B1 (AFB1)-induced hepatocarcinogenesis (initiation and promotion). Nonpolar flavonoids such as flavone, flavanone and tangeretin administered through the initiation period, decreased the number of -gamma-glutamyl transpeptidase-preneoplastic foci. In the same conditions of administration, quercetin, a polyhydroxylated flavonoid, showed no protective effect. Moreover, feeding rats with flavanone during the phenobarbital-induced promotion step significantly reduced the areas of placental glutathione S-transferase preneoplastic foci. Quercetin, flavone, and tangeretin, administered in the same conditions, caused no significant effect. Therefore flavanone act as an anti-initiator as well as an anti-promotor. Several mechanisms were involved in the anti-initiating effects of flavone, flavanone, and tangeretin: enhancement of enzymes involved in the detoxication of AFB1 (glutathione S-transferase, UDP-glucuronyl transferase), increase of the formation of AFB1-glutathione conjugates and inhibition of the binding of AFB1 to DNA. Although the relevance of these data to the human situation remains to be demonstrated, they confirm that several flavonoids administered by the dietary route possess promising chemoprotective effects.

Liver subcellular fractions from rats treated by organosulfur compounds from Allium modulate mutagen activation.

The effects of in vivo administration of naturally occurring organosulfur compounds (OSCs) from Allium species were studied on the activation of several mutagens. Male SPF Wistar rats were given p.o. one of either diallyl sulfide (DAS), diallyl disulfide (DADS), dipropyl sulfide (DPS) or dipropyl disulfide (DPDS) during 4 consecutive days and the ability of hepatic S9 and microsomes from treated rats to activate benzo[a]pyrene (BaP), cyclophosphamide (CP), dimethylnitrosamine (DMN), N-nitrosopiperidine (N-PiP) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was determined in the Ames test. Administration of DAS, DPS and DPDS resulted in a significant increase of the activation of BaP, CP, N-PiP and PhIP mediated by S9 and microsomes while DADS treatment only increased the mutagenicity of PhIP. In contrast, S9 from DADS-treated rats significantly inhibited the mutagenicity of N-PiP and BaP. DAS, DADS and DPS strongly inhibited DMN mutagenicity while DPDS enhanced it. To understand the mechanisms underlying these effects, the modifications of the activities of specific isozymes of CYP involved in the activation of these mutagens were studied. DAS, DPS and DPDS strongly enhanced pentoxyresorufin O-dealkylase (PROD) activity related to CYP2B and slightly increased ethoxyresorufin O-deethylase (EROD) and methoxyresorufin O-demethylase (MROD) activities related to CYP1A family. DADS exerted the same effects than other OSCs but to a lesser extent. p-Nitrophenol hydroxylase (PNPH) activity related to CYP2E1 was inhibited by DAS and DADS, whereas DPDS significantly increased this activity. Hence, the effects of OSCs on the mutagenicity of several genotoxic compounds are mediated by modification (enhancement or inhibition) of specific CYP involved in their activation.

In vivo elimination of viral superantigen-activated CD4+ T cells: apoptosis occurs at a distance from the activation site.

Local injection of mouse mammary tumor virus (MMTV) induces a local immune response, with activation of viral superantigen (vSAG)-specific T cell subsets followed by their clonal deletion. We investigated the fate of vSAG-reactive T cells following footpad injection of MMTV(SW) to mice. Activated T cells accumulated in draining lymph nodes. However, we demonstrated that apoptosis did not occur at the activation site, on the contrary of what has been shown after bacterial SAG activation. Although activated T cells were already shown to have the capacity to migrate to the gut, the fate of gut homing cells remains unclear. We demonstrate that the number of vSAG-specific T cells activated in the periphery was increasing in the follicles of gut-associated lymphoid organs, together with the number of apoptotic cell clusters. These results strongly suggested that gut-associated lymphoid tissue was the specific graveyard for apoptotic vSAG-activated CD4 T cells.

Modulation of phase II enzymes by organosulfur compounds from allium vegetables in rat tissues.

The naturally occurring organosulfur compounds (OSCs) diallyl sulfide (DAS), diallyl disulfide (DADS), dipropyl sulfide (DPS), and dipropyl disulfide (DPDS) were studied with respect to their effects on hepatic, intestinal, renal, and pulmonary phase II drug metabolizing enzymes, i.e., glutathione S-transferase (GST), microsomal epoxide hydrolase (mEH), quinone reductase (QR), and UDP-glucuronosyltransferase (UGT). OSCs were administered po to male SPF Wistar rats. In addition to assays of total enzyme activity, the ability of OSCs to modify the levels of mEH and rGSTA1/A2, A3/A5, M1, M2, and P1 was assessed by Western blotting. Remarkably, DADS significantly increased all Phase II enzyme activities, except the pulmonary mEH. It was noteworthy that only DADS induced QR activity. DAS, DPS, and DPDS induced mEH, GST, and UGT activities in the liver. Interestingly, DAS, DPS, and DPDS significantly decreased renal GST activity. In the same manner, DAS, DPS, and DPDS decreased rGSTA1/A2 and A3/A5 levels in the kidney. Conversely, all OSCs were able to induce GST of alpha and mu classes in the liver. In the intestine, DADS and DAS increased rGSTA1/A2, M2, and P1, while rGSTA3/A5 and M2 were only increased by DADS. In addition, DADS induced rGSTP1 dramatically in the four tissues analyzed. DADS also increased the mEH levels in the liver, intestine, and kidney, while DAS and DPS moderately induced mEH level in the liver. This study brings additional insights into the effects of OSCs on Phase II enzymes and suggests that DADS could be a promising chemopreventive agent considering its pleiotropic capacity of induction.

Dietary carotenoids inhibit aflatoxin B1-induced liver preneoplastic foci and DNA damage in the rat: role of the modulation of aflatoxin B1 metabolism.

To study the effects of carotenoids on the initiation of liver carcinogenesis by aflatoxin B1 (AFB1), male weanling rats were fed beta-carotene, beta-apo-8'-carotenal, canthaxanthin, astaxanthin or lycopene (300 mg/kg diet), or an excess of vitamin A (21000 RE/kg diet), or were injected i.p. with 3-methylcholanthrene (3-MC) (6 x 20 mg/kg body wt) before and during i.p. treatment with AFB1 (2 x 1 mg/kg body wt). The rats were later submitted to 2-acetylaminofluorene treatment and partial hepatectomy, and placental glutathione S-transferase-positive liver foci were detected and quantified. The in vivo effects of carotenoids or of 3-MC on AFB1-induced liver DNA damage were evaluated using different endpoints: liver DNA single-strand breaks (SSB) induced by AFB1, and in vivo binding of [3H]AFB1 to liver DNA and plasma albumin. Finally, the modulation of AFB1 metabolism by carotenoids or by 3-MC was investigated in vitro by incubating [14C]AFB1 with liver microsomes from rats that had been fed with carotenoids or treated by 3-MC, and the metabolites formed by HPLC were analyzed. In contrast to lycopene or to an excess of vitamin A, both of which had no effect, beta-carotene, beta-apo-8'carotenal, astaxanthin and canthaxanthin, as well as 3-MC, were very efficient in reducing the number and the size of liver preneoplastic foci. In a similar way as 3-MC, the P4501A-inducer carotenoids, beta-apo-8'-carotenal astaxanthin and canthaxanthin, decreased in vivo AFB1-induced DNA SSB and the binding of AFB1 to liver DNA and plasma albumin, and increased in vitro AFB1 metabolism to aflatoxin M1, a less genotoxic metabolite. It is concluded that these carotenoids exert their protective effect through the deviation of AFB1 metabolism towards detoxication pathways. In contrast, beta-carotene did not protect hepatic DNA from AFB1-induced alterations, and caused only minor changes of AFB1 metabolism: seemingly, its protective effect against the initiation of liver preneoplastic foci by AFB1 is mediated by other mechanisms.

In vivo antigenotoxic effects of dietary allyl sulfides in the rat.

The effects of dietary administration of diallyl sulfide (DAS), diallyl disulfide (DADS) and allyl mercaptan (AM) on the genotoxicity of different chemicals were studied in two experimental systems: (i) measurement of hepatic DNA single-strand breaks induced in rats by aflatoxin B1 (AFB1), N-nitrosodimethylamine (NDMA) or methylnitrosourea (MNU); (ii) mutagenicity of AFB1 or NDMA on Salmonella typhimurium TA100 using hepatic S9 from rats fed allyl sulfides as the activation system. All compounds strongly reduced hepatic DNA breaks induced by AFB1 and NDMA but did not modify the genotoxicity of MNU. In the Ames test, the mutagenicity of NDMA was strongly inhibited by hepatic S9 from rats fed either compound. The mutagenicity of AFB1 was also reduced but to a lesser extent. Such effects are likely related to the modulation of drug-metabolizing enzymes which play a key role in metabolic activation as well as detoxication of NDMA and AFB1.

Modulation of aflatoxin B1 carcinogenicity, genotoxicity and metabolism in rat liver by dietary carotenoids: evidence for a protective effect of CYP1A inducers.

The effects of several carotenoids of vitamin A and of 3-methylcholanthrene have been tested on the initiation of hepatocarcinogenesis by aflatoxin B1, using the sequential protocol of Solt and Farber. AFB1-induced DNA single-strand breaks and AFB1-metabolism were also assessed. The P4501A inducer carotenoids (canthaxanthin, astaxanthin, beta-apo-8'-carotenal) and 3-methylcholanthrene reduce the carcinogenicity of AFB1, divert AFB1-metabolism into the less genotoxic aflatoxin M1 and reduce AFB1-induced DNA single-strand breaks: we conclude that these carotenoids exert their protective effect through the deviation of AFB1 metabolism towards detoxification pathways. beta-Carotene decreased AFB1 carcinogenicity but did not alter its metabolism, probably acting by other mechanisms.

Modification of hepatic drug-metabolizing enzymes in rats treated with alkyl sulfides.

Natural compounds which elevate detoxification enzymes and/or reduce activating enzymes could be considered as good candidates to protect against cancer. In this work, we studied the modulation of hepatic drug-metabolizing enzymes in rats treated with dimethyl sulfide (DMS), dimethyl disulfide (DMDS), methylpropyl disulfide (MPDS), dipropyl sulfide (DPS), dipropyl disulfide (DPDS) and diallyl disulfide (DADS) issued from Allium species. Compounds containing methyl groups had little or no effect. Compounds with two propyl groups or two allyl groups provoked a pleiotropic response on drug-metabolizing enzymes. DPS, DPDS and DADS induced ethoxyresorufin O-deethylase, methoxyresorufin O-demethylase and mostly pentoxyresorufin O-depentylase and decreased nitrosodimethylamine N-demethylase and erythromycin N-demethylase. These modifications of enzyme activities were accompanied by an increase of CYP 2B1,2 and a decrease of CYP 2E1, evidenced by immunoblotting. The same treatments stimulated some phase II enzyme activities such as glutathione transferase and UDP-glucuronyl transferases. This pattern of induction and/or inhibition of drug metabolizing enzymes was qualitatively similar to that elicited by the enzyme inducer, phenobarbital. The magnitude of the effects produced by DPDS was smaller than those produced by DADS and DPS. Our results suggest a possible protective effect of alkyl sulfides as well as diallyl disulfide, on the first step of carcinogenesis via the modulation of enzymes involved in carcinogen metabolism.

In vivo T cell response to viral superantigen. Selective migration rather than proliferation.

Superantigens induce T cell activation and proliferation in vitro, and some also induce cell activation in vivo. MMTV(SW) is an infectious mouse mammary tumor virus (MMTV) encoding a superantigen with the same Vbeta specificity as MIs-1a (Mtv-7), which induces a strong local response in vivo. injection of MMTV(SW) into mouse footpads leads to accumulation of superantigen-reactive T cells (Vbeta6+CD4+) and B cells in the draining lymph nodes (LN). We investigated the kinetics of this cell accumulation by measuring cell activation (blastogenesis, CD25 and CD69 expression), cell migration (using syngenic FITC-labeled CD4+ cells and L-selectin detection), and cell proliferation (using in vivo labeling with bromodeoxyuridine). Specific T cells selectively migrated to the draining LN. Accumulating Vbeta6+CD4+ T cells were large CD69+ cells, but remained CD25 negative and showed down-regulated L-selectin expression. Their DNA synthesis rate, studied by pulse labeling and continuous administration of bromodeoxyuridine, was increased, but remained too low to explain the draining LN hyperplasia. These data show that the local T cell response to MMTV(SW) mainly consists of selective migration followed by local activation of reactive T cells, and that cell proliferation is only a minor component of the response. By contrast, the optimal dose of staphylococcal enterotoxin B that, nevertheless, leads to a lower reactive T cell accumulation in the draining LN induces a very high proliferation rate.

Lack of tumor-promoting effects of flavonoids: studies on rat liver preneoplastic foci and on in vivo and in vitro gap junctional intercellular communication.

Possible tumor-promoting activity of four flavonoids, quercetin (QC), tangeretin (TG), flavone (FO), and flavanone (FN), was examined in a rat liver short-term carcinogenesis assay as well as with in vivo and in vitro assays of inhibition of gap junctional intercellular communication (GJIC). Rat hepatocarcinogenesis was induced by aflatoxin B1 treatment followed by a selection phase (2-acetylaminofluorene treatment and partial hepatectomy), then treatment with or without test chemicals (in vivo studies of antipromotion were not performed). Using glutathione S-transferase placental form (GST-P)-positive foci, we compared the effects of flavonoids (at 1,000 ppm in the diet) with the effects of phenobarbital (PB) on the occurrence of liver preneoplastic lesions. In addition, we studied the effects of flavonoids on GJIC in the livers derived from these experiments and in two types of cultured cells. No significant difference in the number and area of GST-P-positive foci was found after one or three months of treatment between any flavonoid group and control group. In the positive control group, PB markedly increased the numbers and areas of preneoplastic lesions at three months. Whereas PB also decreased by 60% the average size of lucifer yellow dye spread in slices of liver parenchyma free of preneoplastic lesions among the different flavonoids, only TG decreased the dye transfer in vivo: by 30% at one month and 50% at three months. With the dye transfer assay applied to a rat liver epithelial cell line (REL) and the Chinese hamster V79 metabolic cooperation assay, none of the tested flavonoids (< or = 25 microM) inhibited GJIC. Conversely, protective properties were seen for some of the compounds in antipromotion in vitro studies, because TG and FN enhanced the dye transfer in REL cells and FO, TG, and QC partly prevented the inhibition of metabolic cooperation by 12-O-tetradecanoylphorbol-13-acetate. Thus, taken together, our results suggest that QC, FO, and FN do not show tumor-promoting activity. Concerning TG, some discrepancies in the in vivo data are observed. Some of them (GJIC inhibition in liver slices) are probably more relevant to promotion of hepatocarcinogenesis.

Neonatal impaired response to viral superantigen encoded by MMTV(SW) and Mtv-7.

MMTV(SW) is an exogenous mouse mammary tumor virus that codes for a superantigen sharing the same V beta specificity as Mtv-7 (Mis-1a). Neonatal mice infected by suckling-infected milk show a deletion of the CD4+ V beta 6+ T cell subset within 8 weeks. In contrast, adult mice infected by injection of the virus in the footpad have a much faster deletion, which occurs within 2 weeks. In the present work, we investigated possible mechanisms for the different kinetics of deletion in the adult and newborn mice. To find out if the route of infection could be responsible for this discrepancy, we infected 5-day-old and adult mice by injection in the footpad. Our results demonstrate that the route of infection is not responsible for the delayed kinetics of reactive T cell deletion since newborn mice injected with the virus show similar kinetics to neonates infected by maternal milk. To exclude differences in viral spreading between the two models, we used a PCR assay to detect proviral DNA. Spreading of the virus was shown to occur at a similar rate or even more rapidly in neonates than in adults. We also compared the activation induced by MMTV(SW) or Mis-1a spleen cells in the draining lymph node in neonatal and adult mice and showed that a poor local activation is induced in neonates compared with adults. In vitro, neonatal T cell reactivity to anti-V beta 6 antibody was also impaired. Thus, the delay in clonal deletion could be linked to impaired expression, presentation and/or response to the viral superantigen. Our results suggest that the initial response to MMTV(SW) could be of importance for the kinetics of reactive T cell deletion.

Differential effects of dietary diallyl sulfide and diallyl disulfide on rat intestinal and hepatic drug-metabolizing enzymes.

The chemopreventive properties of allyl sulfides on carcinogenesis may be related to the modulation of drug-metabolizing enzymes involved in carcinogen activation or detoxication. In order to investigate the effects of diallyl sulfide (DAS) and diallyl disulfide (DADS) on intestinal and hepatic drug-metabolizing enzymes, rats were fed a diet containing 0.2% of either allyl sulfide. The DADS enhanced intestinal epoxide hydrolase (EH) and cytochrome P-450 (P-450) 2B1/2 protein levels and the activities of pentoxy- and benzyl-oxyresorufin O-dealkylases, arylhydrocarbon hydroxylase, microsomal epoxide hydrolase, p-nitrophenol UDP-glucuronyl transferase and glutathione S-transferase, and decreased nitrosodimethylamine demethylase activity. In liver, DADS produced similar effects and, in addition, increased P-450 1A1/2 protein level and phenoxazone metabolizing activities (ethoxy- and methoxyresorufin O-dealkylases), p-hydroxybiphenyl UDP-glucuronyl transferase, and decreased P-450 2E1 level. The DAS enhanced only EH activity in the small intestine and induced P-450 2B1/2 and epoxide hydrolase protein levels. In liver, DAS produced similar effects as DADS. The different effects of DAS on intestinal drug-metabolizing enzymes, compared to liver, could be ascribed to less metabolism of this compound in small intestine. It is also suggested that DAS and DADS may not yield the same metabolites and therefore would have different effects on intestinal drug-metabolizing enzymes.

Inhibition of microsome-mediated binding of benzo[a]pyrene to DNA by flavonoids either in vitro or after dietary administration to rats.

The in vitro and in vivo effects of selected natural flavonoids (flavone, flavanone, tangeretin, quercetin, chrysin) on the microsome-catalysed binding of [3H]benzo[a]pyrene to calf thymus DNA were investigated and compared with those of two synthetic flavonoids, 7,8-benzoflavone and 5,6-benzoflavone. In vitro addition of these flavonoids (0.1 mM) to an incubation system containing hepatic microsomes prepared from Aroclor 1254-pretreated rats strongly inhibited BaP-DNA adduct formation (72-89%). The incubation of BaP with hepatic microsomes prepared from animals fed 0.3% quercetin, tangeretin and 7,8-benzoflavone for 2 weeks also resulted in less effective binding of BaP metabolites to added DNA, than with microsomes from untreated rats. Other tested compounds, chrysin, flavone, flavanone and 5,6-benzoflavone showed no or little effect. The influence of flavonoid pretreatment on hepatic microsomal enzymes involved in BaP metabolism has also been examined. Aryl hydrocarbon hydroxylase activity was moderately increased (1.5-1.8-fold) in microsomes prepared from rats fed flavone, tangeretin, 7,8-benzoflavone and 5,6-benzo-flavone. Epoxide hydrolase activity was enhanced by 7,8-benzoflavone (1,6-fold), and by flavone and flavanone (5-fold). These results confirm that flavonoids, in vitro, are potent inhibitors of carcinogen-DNA binding. Oral administration of 0.3% flavonoids alters the properties of liver microsomes, resulting in the decreased ability of BaP metabolites to bind DNA.