Dose-response formation of N7-(3-benzo[1,3]dioxol-5-yl-2-hydroxypropyl)guanine in liver and urine correlates with micronucleated reticulocyte frequencies in mice administered safrole oxide

Safrole oxide (SAFO), a metabolite of naturally occurring hepatocarcinogen safrole, is implicated in causing DNA adduct formation. Our previous study first detected the most abundant SAFO-induced DNA adduct, N7-(3-benzo[1,3] dioxol-5-yl-2-hydroxypropyl)guanine (N7γ-SAFO-G), in mouse urine using a well-developed isotope-dilution high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (ID-HPLC-ESI-MS/MS) method. This study further elucidated the genotoxic mode of action of SAFO in mice treated with SAFO 30, 60, 90, or 120 mg/kg for 28 days. The ID-HPLC-ESI-MS/MS method detected N7γ-SAFO-G with excellent sensitivity and specificity in mouse liver and urine of SAFO-treated mice. Our data provide the first direct evidence of SAFO-DNA adduct formation in rodent tissues. N7γ-SAFO-G levels in liver were significantly increased by SAFO 120 mg/kg compared with SAFO 30 mg/kg, suggesting rapid spontaneous or enzymatic depurination of N7γ-SAFO-G in tissue DNA. Urinary N7γ-SAFO-G exhibited a sublinear dose response. Moreover, the micronucleated peripheral reticulocyte frequencies increased dose-dependently and significantly correlated with N7γ-SAFO-G levels in liver (r = 0.8647; p < 0.0001) and urine (r = 0.846; p < 0.0001). Our study suggests that safrole-mediated genotoxicity may be caused partly by its metabolic activation to SAFO and that urinary N7γ-SAFO-G may serve as a chemically-specific cancer risk biomarker for safrole exposure.

Betel quid containing safrole enhances metabolic activation of tobacco specific 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)

Cigarette smoking (CS) and betel quid (BQ) chewing are two known risk factors that have synergistic potential for the enhancing the development of oral squamous cell carcinoma (OSCC) in Taiwan. Most mutagens and carcinogens are metabolically activated by cytochrome P450 (CYP450) to exert their mutagenicity or carcinogenicity. Previous studies have shown that metabolic activation of the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), by CYP2A6 activity determines NNK-induced carcinogenesis. In addition, safrole affects cytochrome P450 activity in rodents. However, the effect of BQ safrole on the metabolism of tobacco-specific NNK and its carcinogenicity remains elusive. This study demonstrates that safrole (1 mg/kg/d) induced CYP2A6 activity, reduced urinary 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) levels, and increased NNK-induced DNA damage, including N7-methylguanine, 8-OH-deoxyguanosine and DNA strand breaks in a Syrian golden hamster model. Furthermore, altered NNK metabolism and increased NNK-induced DNA damage were also observed in healthy subjects with CS and BQ chewing histories compared to healthy subjects with CS histories. In conclusion, BQ containing safrole induced tobacco-specific NNK metabolic activation, resulting in higher NNK-induced genotoxicity. This study provides valuable insight into the synergistic mechanisms of CS- and BQ-induced OSCC.

Safrole induced cytotoxicity, DNA damage, and apoptosis in macrophages via reactive oxygen species generation and Akt phosphorylation

Safrole is a natural compound categorized as a group 2B carcinogen extracted from betel quid chewing, which is a common practice of psychoactive habits integrated into social and cultural ceremonies among serveral million people, especially in Southern or Southeastern Asia. Safrole is one of the major risk compunds for development of oral squamous cell carcinoma and hepatocellular carcinoma via DNA adduction. In innate immunity, macrophages are the predominant cells for non-specific first line defense against pathogens in oral tissue. Up to now, there is no evidence to implicate the potential toxicological effect of safrole on macrophages. In this study, we found safrole induced the generation of reactive oxygen species (ROS) and myeloperoxidase (MPO) in RAW264.7 macrophages in a concentration-dependent manner. Furthermore, cytotoxicity, DNA damage, and apoptosis were caused by safrole in a concentration-dependent manner. While the activation of antioxidative enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx) was reduced, the phosphorylation of Akt was induced by safrole in a concentration-dependent manner. These results indicated that the induction of cytotoxicity, DNA damage, and apoptosis in macrophages by safrole was through generation of ROS and inhibition of antioxidative enzymes possibly via Akt phosphorylation.

In vivo genotoxicity of estragole in male F344 rats

Estragole, a naturally occurring constituent of various herbs and spices, is a rodent liver carcinogen which requires bio-activation. To further understand the mechanisms underlying its carcinogenicity, genotoxicity was assessed in F344 rats using the comet, micronucleus (MN), and DNA adduct assays together with histopathological analysis. Oxidative damage was measured using human 8-oxoguanine-DNA-N-glycosylase (hOGG1) and EndonucleaseIII (EndoIII)-modified comet assays. Results with estragole were compared with the structurally related genotoxic carcinogen, safrole. Groups of seven-week-old male F344 rats received corn oil or corn oil containing 300, 600, or 1,000 mg/kg bw estragole and 125, 250, or 450 mg/kg bw safrole by gavage at 0, 24, and 45 hr and terminated at 48 hr. Estragole-induced dose-dependent increases in DNA damage following EndoIII or hOGG1 digestion and without enzyme treatment in liver, the cancer target organ. No DNA damage was detected in stomach, the non-target tissue for cancer. No elevation of MN was observed in reticulocytes sampled from peripheral blood. Comet assays, both without digestion or with either EndoIII or hOGG1 digestion, also detected DNA damage in the liver of safrole-dosed rats. No DNA damage was detected in stomach, nor was MN elevated in peripheral blood following dosing with safrole suggesting that, as far both safrole and estragole, oxidative damage may contribute to genotoxicity. Taken together, these results implicate multiple mechanisms of estragole genotoxicity. DNA damage arises from chemical-specific interaction and is also mediated by oxidative species.

Safrole-2',3'-oxide induces atherosclerotic plaque vulnerability in apolipoprotein E-knockout mice

Safrole-2',3'-oxide (SFO) is the major electrophilic metabolite of safrole (4-allyl-1, 2-methylenedioxybenzene), a natural plant constituent found in essential oils of numerous edible herbs and spices and in food containing these herbs, such as pesto sauce, cola beverages and bologna sausages. The effects of SFO in mammalian systems, especially the cardiovascular system, are little known. Disruption of vulnerable atherosclerotic plaques in atherosclerosis, a chronic inflammatory disease, is the main cause of cardiovascular events. In this study, we investigated SFO-induced atherosclerotic plaque vulnerability (possibility of rupture) in apolipoprotein E-knockout (apoE(-/-)) mice. Lipid area in vessel wall reached 59.8% in high dose SFO (SFO-HD) treated group, which is only 31.2% in control group. SFO treatment changed the lesion composition to an unstable phenotype, increased the number of apoptotic cells in plaque and the endothelium in plaques was damaged after SFO treatment. Furthermore, compared with control groups, the plaque endothelium level of p75(NTR) was 3-fold increased and the liver level of p75(NTR) was 17.4-fold increased by SFO-HD. Meanwhile, the serum level of KC (a functional homolog of IL-8 and the main proinflammatory alpha chemokine in mice) in apoE(-/-) mice was up to 357pg/ml in SFO-HD treated group. Thus, SFO contributes to the instability of atherosclerotic plaque in apoE(-/-) mice through activating p75(NTR) and IL-8 and cell apoptosis in plaque.

Toxicological actions of plant-derived and anthropogenic methylenedioxyphenyl-substituted chemicals in mammals and insects

The methylenedioxyphenyl (MDP) substituent is a structural feature present in many plant chemicals that deter foraging by predatory insects and herbivores. With increasing use of herbal extracts in alternative medicine, human exposure to MDP-derived plant chemicals may also be significant. Early studies found that most MDP agents themselves possess relatively low intrinsic toxicity, but strongly influence the actions of other xenobiotics in mammals and insects by modulating cytochrome P-450 (CYP)-dependent biotransformation. Thus, after exposure to MDP chemicals an initial phase of CYP inhibition is followed by a sustained phase of CYP induction. In insects CYP inhibition by MDP agents underlies their use as pesticide synergists, but analogous inhibition of mammalian CYP impairs the clearance of drugs and foreign compounds. Conversely, induction of mammalian CYP by MDP agents increases xenobiotic oxidation capacity. Exposure of insects to MDP-containing synergists in the environment, in the absence of coadministered pesticides, may also enhance xenobiotic detoxication. Finally, although most MDP agents are well tolerated, several, typified by safrole, aristolochic acid, and MDP-kavalactones, are associated with significant toxicities, including the risk of hepatotoxicity or tumorigenesis. Thus, the presence of MDP-substituted chemicals in the environment may produce a range of direct and indirect toxicities in target and nontarget species.

Safrole-Induced Ca2+Mobilization and Cytotoxicity in Human PC3 Prostate Cancer Cells

The effect of the carcinogen safrole on intracellular Ca2+ mobilization and on viability of human PC3 prostate cancer cells was examined. Cytosolic free Ca2+ levels ([Ca2+]i) were measured by using fura-2 as a probe. Safrole at concentrations above 10 microM increased [Ca2+]i in a concentration-dependent manner with an EC50 value of 350 microM. The Ca2+ signal was reduced by more than half after removing extracellular Ca2+ but was unaffected by nifedipine, nicardipine, nimodipine, diltiazem, or verapamil. In Ca2+-free medium, after treatment with 650 microM safrole, 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor) failed to release Ca2+. Neither inhibition of phospholipase C with U73122 nor modulation of protein kinase C activity affected safrole-induced Ca2+ release. Overnight incubation with 0.65-65 microM safrole did not affect cell viability, but incubation with 325-625 microM safrole decreased viability. Collectively, the data suggest that in PC3 cells, safrole induced a [Ca2+]i increase by causing Ca2+ release from the endoplasmic reticulum in a phospholipase C- and protein kinase C-independent fashion, and by inducing Ca2+ influx. Safrole can decrease cell viability in a concentration-dependent manner.

Elevated expression of NF-kappaB in oral submucous fibrosis--evidence for NF-kappaB induction by safrole in human buccal mucosal fibroblasts

Nuclear factor-kappa B (NF-kappaB) is considered to be important in many inflammatory and immune responses. The aim of this study was to compare NF-kappaB expression in normal human buccal mucosa and oral submucous fibrosis (OSF) specimens and further explore the potential mechanism that may lead to induction of NF-kappaB expression. Seventeen OSF and six normal buccal mucosa specimens were examined by immunohistochemistry. Primary human buccal mucosal fibroblasts (BMFs) were established and challenged with safrole, a major polyphenolic compound in the influorescence of Piper betel, by cytotoxicity and western blot assays. Furthermore, glutathione precursor N-acetyl-L-cysteine (NAC), extracellular signal-regulated protein kinase (ERK) inhibitor PD98059, cyclooxygenase-2 (COX-2) inhibitor NS-398, dexamethasone, and cyclosporin A were added to find the possible mechanism. NF-kappaB expression was significantly higher in OSF specimens and expressed mainly by fibroblasts, endothelial cells, and inflammatory cells. Safrole was cytotoxic to BMFs in a dose-dependent manner (p<0.05). Western blot demonstrated highly elevated NF-kappaB protein expression in BMFs stimulated by safrole (p<0.05). In addition, pretreatment with pharmacological agents markedly inhibited the safrole induced-NF-kappaB expression (p<0.05). The result suggests that chewing areca quid may activate NF-kappaB expression that may be involved in the pathogenesis of OSF. NF-kappaB expression induced by safrole in fibroblasts may be mediated by ERK activation and COX-2 signal transduction pathway.

Safrole-induced cellular Ca2+ increases and death in human osteosarcoma cells

The effect of the carcinogen safrole on intracellular Ca2+ movement has not been explored in osteoblast-like cells. This study examined whether safrole could alter Ca2+ handling and viability in MG63 human osteosarcoma cells. Cytosolic free Ca2+ levels ([Ca2+]i) in populations of cells were measured using fura-2 as a fluorescent Ca2+ probe. Safrole at concentrations above 130 microM increased [Ca2+]i in a concentration-dependent manner with an EC50 value of 450 microM. The Ca2+ signal was reduced by 30% by removing extracellular Ca2+. Addition of Ca2+ after safrole had depleted intracellular Ca2+ induced Ca2+ influx, suggesting that safrole caused Ca2+ entry. In Ca2+-free medium, after pretreatment with 650 microM safrole, 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor) failed to release more Ca2+; and pretreatment with thapsigargin inhibited most of the safrole-induced [Ca2+]i increases. Inhibition of phospholipase C with U73122 did not affect safrole-induced Ca2+ release; whereas activation of protein kinase C with phorbol ester enhanced safrole-induced [Ca2+]i increase. Trypan exclusion assays revealed that incubation with 65 microM safrole for 30 min did not kill cells, but incubation with 650 microM safrole for 10-30 min nearly killed all cells. Flow cytometry demonstrated that safrole evoked apoptosis in a concentration-dependent manner. Safrole-induced cytotoxicity was not reversed by chelation of Ca2+ with BAPTA. Collectively, the data suggest that in MG63 cells, safrole induced a [Ca2+]i increase by causing Ca2+ release mainly from the endoplasmic reticulum in a phospholipase C-independent manner. The safrole response involved Ca2+ influx and is modulated by protein kinase C. Furthermore, safrole can cause apoptosis in a Ca2+-independent manner.

Inhibition of human cytochrome P450 enzymes by the natural hepatotoxin safrole

The hepatotoxin, safrole is a methylenedioxy phenyl compound, found in sassafras oil and certain other essential oils. Recombinant cytochrome P450 (CYP, P450) and human liver microsomes were studied to investigate the selective inhibitory effects of safrole on human P450 enzymes and the mechanisms of action. Using Escherichia coli-expressed human P450, our results demonstrated that safrole was a non-selective inhibitor of CYP1A2, CYP2A6, CYP2D6, CYP2E1, and CYP3A4 in the IC(50) order CYP2E1 < CYP1A2 < CYP2A6 < CYP3A4 < CYP2D6. Safrole strongly inhibited CYP1A2, CYP2A6, and CYP2E1 activities with IC(50) values less than 20 microM. Safrole caused competitive, non-competitive, and non-competitive inhibition of CYP1A2, CYP2A6 and CYP2E1 activities, respectively. The inhibitor constants were in the order CYP1A2 < CYP2E1 < CYP2A6. In human liver microsomes, 50 microM safrole strongly inhibited 7-ethoxyresorufin O-deethylation, coumarin hydroxylation, and chlorzoxazone hydroxylation activities. These results revealed that safrole was a potent inhibitor of human CYP1A2, CYP2A6, and CYP2E1. With relatively less potency, CYP2D6 and CYP3A4 were also inhibited.

Genotoxic effects of eugenol, isoeugenol and safrole in the wing spot test of Drosophila melanogaster

In the present study, the phenolic compounds eugenol, isoeugenol and safrole were investigated for genotoxicity in the wing spot test of Drosophila melanogaster. The Drosophila wing somatic mutation and recombination test (SMART) provides a rapid means to evaluate agents able to induce gene mutations and chromosome aberrations, as well as rearrangements related to mitotic recombination. We applied the SMART in its standard version with normal bioactivation and in its variant with increased cytochrome P450-dependent biotransformation capacity. Eugenol and safrole produced a positive recombinagenic response only in the improved assay, which was related to a high CYP450-dependent activation capacity. This suggests, as previously reported, the involvement of this family of enzymes in the activation of eugenol and safrole rather than in its detoxification. On the contrary, isoeugenol was clearly non-genotoxic at the same millimolar concentrations as used for eugenol in both the crosses. The responsiveness of SMART assays to recombinagenic compounds, as well as the reactive metabolites from eugenol and safrole were considered responsible for the genotoxicity observed.

Safrole–DNA adducts in tissues from esophageal cancer patients: clues to areca-related esophageal carcinogenesis

Epidemiological studies have demonstrated that areca quid chewing can be an independent risk factor for developing esophageal cancer. However, no studies are available to elucidate the mechanisms of how areca induces carcinogenesis in the esophagus. Since the areca nut in Taiwan contains a high concentration of safrole, a well-known carcinogenic agent, we analyzed safrole-DNA adducts by the 32P-postlabelling method in tissue specimens from esophageal cancer patients. In total, we evaluated 47 patients with esophageal cancer (16 areca chewers and 31 non-chewers) who underwent esophagectomy at the National Taiwan University Hospital between 1996 and 2002. Of the individuals with a history of habitual areca chewing (14 cigarette smokers and two non-smokers), one of the tumor tissue samples and five of the normal esophageal mucosa samples were positive for safrole-DNA adducts. All patients positive for safrole-DNA adducts were also cigarette smokers. Such adducts could not be found in patients who did not chew areca, irrespective of their habits of alcohol consumption or cigarette smoking (p<0.001, comparing the areca chewers with non-chewers). The genotoxicity of safrole was also tested in vitro in three esophageal cell lines and four cultures of primary esophageal keratinocytes. In two of the esophageal keratinocyte cultures, adduct formation was increased by treatment with safrole after induction of cytochrome P450 by 3-methyl-cholanthrene. This paper provides the first observation of how areca induces esophageal carcinogenesis, i.e., through the genotoxicity of safrole, a component of the areca juice.

Inhibition of sulfotransferase affecting in vivo genotoxicity and DNA adducts induced by safrole in rat liver

The effect of pretreatment with pentachlorophenol (PCP), a known inhibitor of sulfotransferases, on the induction of chromosomal aberrations, sister chromatid exchanges (SCEs), replicative DNA synthesis (RDS), and the formation of DNA adducts was studied in the liver of rats treated with safrole (1-allyl-3,4-methylenedioxy-benzene). Rats were given a single oral dose (1,000 mg/kg body weight) or 5 repeated doses (500 mg/kg body weight) of safrole, with or without intraperitoneal pretreatment with PCP (10 mg/kg body weight). Hepatocytes were isolated 24 hr after administration of safrole and allowed to proliferate in Williams' medium E supplemented with epidermal growth factor to test for chromosomal aberrations and SCEs. For examination of RDS, hepatocytes were incubated in Williams' medium E containing 5-bromo-2'-deoxyuridine. Safrole-DNA adducts were detected by a nuclease P1-enhanced 32P-postlabeling assay. A single dose of safrole induced significant SCEs and RDS, while chromosomal aberrations were induced by 5 repeated doses. Two major and 2 minor DNA adducts were detected by both a single dose and 5 repeated doses. PCP significantly decreased safrole-induced cytogenetic effects and RDS, and caused a decrease in DNA adducts formed by safrole. These results suggest that safrole is capable of inducing SCEs, chromosomal aberrations, and RDS in the rat liver in vivo and that these effects may be induced by the sulfuric acid ester metabolite that can bind DNA.

Analysis of cytogenetic effects and DNA adduct formation induced by safrole in Chinese hamster lung cells

Safrole (1-allyl-3,4-methylenedioxybenzene) was tested for its ability to induce sister chromatid exchanges (SCEs) and chromosomal aberrations (CAs) and to form DNA adducts in Chinese hamster lung (CHL) cells, in order to investigate the relationship between cytogenetic effects and DNA adduct formation under the same treatment conditions. The cells were treated with 0.025-0.2 mg/ml safrole in the presence or absence of rat liver postmitochondrial supernatant fraction (S9). Safrole induced significant SCEs and CAs dose-dependently in the presence of S9. SCEs ranged in number from 15.6 to 21.1 SCEs/cell and CAs were observed in 4-37% of cells. Using the 32P-postlabeling assay, two major and two minor safrole-DNA adducts were detected in DNA digests obtained from CHL cells in the presence of S9. The levels of total DNA adducts ranged from 1.3 to 22.8 adducts/10(7) nucleotides. The two major adducts were shown to be guanine derivatives since these adducts comigrated on polyethylenimine plates with the adducts produced by the reaction of safrole with 2'-deoxyguanosine 3'-monophosphate. A correlation was seen between DNA adducts and SCEs or CAs. Neither induction of SCEs and CAs nor formation of DNA adducts was observed in the absence of S9. These findings suggest that SCEs and CAs induced by safrole result from covalent DNA modification metabolically activated by S9 in cultured cells.

Safrole-induced oxidative damage in the liver of Sprague-Dawley rats

Safrole is a weak hepatocarcinogen, and its carcinogenic effect has been linked to the formation of stable safrole DNA adducts. In this study, we tested whether safrole also induces oxidative damages in Sprague-Dawley rats. By single i.p. injection, safrole dose-dependently induced the formation of hepatic lipid hydroperoxides (LHP) and 8-hydroxy-2'-deoxyguanosine (8-OH-dG). The safrole-induced LHP reached peak level on day 3 and gradually returned to the basal level on day 15. On the other hand, 8-OH-dG levels from the similarly treated rats peaked on day 5 and returned to basal level on day 15. Safrole also dose-dependently induced serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities. We also examined the protective effect of vitamin E, deferoxamine and N-acetylcysteine against the safrole-induced oxidative damage. N-Acetylcysteine, the precursor of glutathione, exerted the greatest protective effect among the three antioxidants tested. In contrast, buthionine sulfoximine, the glutathione synthesis inhibitor, enhanced the safrole-induced oxidative damage, as evidenced by the elevation of LHP and 8-OH-dG levels on day 3 (P<0.05). These findings demonstrate that safrole treatment induces oxidative damage in rat hepatic tissue, and glutathione plays an important protective role. This oxidative damage may be involved in the hepatocarcinogenic effect of safrole.

The reproductive toxicity of molinate and metabolites to the male rat: effects on testosterone and sperm morphology

Molinate causes an impairment in reproductive capability in the male rat. Administration of molinate to rats (40 mg/kg/day for 7 days) caused a distinctive sperm lesion. At higher doses of molinate (140 mg/kg for 7 days) this lesion was accompanied by morphological changes to the testis that were consistent with a delayed release of the late spermatids to the seminiferous tubular lumen, a process controlled by the release of testosterone. In accordance with this, molinate (>/=40 mg/kg) caused a marked decrease in the concentration of circulating and testicular testosterone. The Leydig cells of the testis appear to be the primary target site in that radiolabel from [3H]molinate specifically localized within this cell type. In addition, esterase activity in the Leydig cells was inhibited following molinate administration. In vitro, molinate is a poor inhibitor of esterase activity, whereas molinate sulfoxide, a major metabolite of molinate in rats, and molinate sulfone were shown to be potent inhibitors of this process, suggesting that metabolic activation of molinate is required in vivo. Molinate sulfoxide (>/=10 mg/kg) caused an identical sperm lesion to that of molinate and markedly decreased plasma and testicular testosterone concentration. These effects were not seen with the molinate metabolites 4-hydroxymolinate (10 mg/kg), molinate sulfone (10 mg/kg), and hexamethyleneimine (10 mg/kg). Since the sperm lesion is a secondary event caused by a disruption of spermatogenesis, this would imply that the testis lesion and the reproductive impairment are also a consequence of molinate sulfur oxidation.

Testicular toxicity of molinate in the rat: metabolic activation via sulfoxidation

Molinate is a thiocarbamate herbicide widely used in rice culture. Studies conducted for regulatory purposes have indicated that molinate exposure causes male reproductive damage in rats. The present study describes the testicular lesion after administration of single doses of molinate. The hypothesis that a metabolite of molinate is responsible for testicular toxicity was also investigated. Testicular damage was evaluated histopathologically in Sprague-Dawley rats 48 h and 1, 2, and 3 weeks after administration of molinate (100-400 mg/kg i.p.). No testicular damage was seen at any time point at the 100 mg/kg dose level. Damage was first seen 1 week after 200 mg/kg and 48 h after 400 mg/kg. The lesion was characterized by Sertoli cell vacuolation, failed spermiation, and phagocytosis of spermatids particularly evident at Stages X and XI. With increasing time, damage progressed until disorganization of the seminiferous epithelium was extensive, multinucleated giant cells were numerous, and neither spermatozoa nor late step spermatids were present. At 3 weeks after administration of the two higher-dose levels, germ cells in the seminiferous tubules were almost completely absent. Administration of the sulfoxide metabolite of molinate (200 mg/kg i.p.) caused testicular damage similar in severity to that seen at the 400 mg/kg dose level for the parent compound, indicating that it was more potent as a testicular toxicant. In vitro metabolism studies using liver and testis microsomes found that the major metabolite in both preparations was molinate sulfoxide. Testis microsomes produced only slightly less sulfoxide when compared with liver microsomes. Molinate was also metabolized via ring hydroxylation to form small amounts of hydroxymolinate. The amount of hydroxymolinate was substantially less in testis microsomes. Overall, these data indicate that sulfoxidation of molinate plays a role in molinat-induced testicular toxicity. Moreover, molinate is metabolized readily by both liver and testis microsomal enzymes, suggesting that the molinate toxic metabolite could be formed in the testis in close proximity to its site of action.

In vivo genotoxicity and DNA adduct levels in the liver of rats treated with safrole

The induction of chromosome aberrations, sister chromatid exchanges (SCEs), and the formation of DNA adducts was studied in hepatocytes of F344 rats exposed in vivo to safrole. Hepatocytes were isolated 24 h after a single dose of safrole or five repeated doses (once a day) by gastric intubation and allowed to proliferate in Williams' medium E supplemented with epidermal growth factor. Cells were fixed after 48 h in culture. Safrole-DNA adducts were detected by a nuclease P1-enhanced 32P-post-labeling assay in isolated hepatocytes from the rats. While a single dose was not sufficient to induce detectable levels of chromosome aberrations at the time of assay, five repeated doses induced these changes with a maximum frequency of 13.4%, compared with the control value of 1.8%. Both a single dose and five repeated doses induced significant SCEs, to a maximum frequency of 0.81 SCEs per chromosome, while the control value was 0.59 SCEs per chromosome. Two major and two minor DNA adducts were detected after treatment with either a single dose or five repeated doses. The maximum amount of total DNA adducts was 89.8 DNA adducts/10(7) nucleotides. These results show that safrole is a genotoxic carcinogen in the rat liver in vivo and suggest that the cytogenetic effects of this compound may result from covalent DNA modification in the rat liver. This in vivo cytogenetic assay should provide a useful means of evaluation of the genotoxicity of hepatocarcinogens.

Cytogenetic effects of piperonyl butoxide and safrole in CHO-K1 cells

Recently, hepatocarcinogenicity in rats and mice was reported with regard to the methylenedioxyphenyl compound, piperonyl butoxide (PB), which is used as a synergist for pyrethrins and related insecticides. Induction of sister-chromatid exchanges (SCEs) and chromosomal aberrations (CAs) due to PB were investigated using CHO-K1 cells with or without rat liver S9 fraction (S9); at the same time, the effects of safrole (SF), a methylenedioxyphenyl compound and a weak hepatocarcinogen, were also examined. PB (0.25 and 0.3 mM) and SF (0.8 mM) caused a slight but significant increase in SCEs followed by a cell-cycle delay in the 3-h treatment without S9. In the presence of S9 (4.5%), the cytotoxicity of PB or SF was weakened greatly or slightly, the top dose capable of cell division was raised to 0.6 mM (2-fold) or 1 mM, respectively. PB with S9 induced SCE at doses of 0.4 and 0.5 mM, and caused endoreduplications (ERDs, 7%) at a dose of 0.6 mM, while SF caused a dose-related significant increase in SCE at all doses used (0.4-1 mM) with S9. Genotoxicity of the metabolites of PB or SF was cleared by changing the dose of S9 (1.5-9%) while holding the dose of each chemical constant. In the case of SF (0.6 mM), induction of SCE, ERD and cell-cycle delay intensified almost in a dose-effect relationship, and CAs and a high level of ERD (14%) were caused by a 9% dose of S9. The concentration of unchanged SF in the incubated medium was certainly in inverse proportion to the dose of S9. This strongly suggests that the metabolites of SF are genotoxic. In the case of PB (0.3 mM), no positive responses were produced in the cultures, even with a high level of S9, though the amount of unchanged PB left in the incubated medium was very slight. This indicates that the metabolites of PB may not be genotoxic. In conclusion, PB and SF are possible to somewhat induce SCE at high dose(s) in the absence of S9, and the genotoxic effects of SF are more intensified in the presence of S9 than in its absence, while PB is probably no genotoxic in the presence of sufficient metabolic activation.

Genotoxic evaluation of ten carcinogens in the Drosophila melanogaster wing spot test

To provide further background data on the wing spot somatic mutation and recombination assay, 10 selected carcinogens (acetamide, acrylamide, benzo(a)pyrene, cyclophosphamide, diethylstilbestrol, 4-nitroquinoline N-oxide, propyleneimine, safrole, thiourea, and o-toluidine) were tested in this assay. 72-h-old third-instar larvae, trans-heterozygous for 2 recessive wing cell markers: multiple wing hairs (mwh) and flare3 (flr3) were fed with 3 concentrations of each carcinogen during the rest of their development until pupation, and the genotoxic effects were measured as significant increases in the appearance of visible mutant hair clones on the adult wing blade. Our results show that 6 of the carcinogens tested produce significant increases in wing spot frequency, at least at one of the concentrations assayed. Benzo(a)pyrene, diethylstilbestrol, safrole and thiourea were the compounds that did not increase the incidence of mutant clones.

32P-postlabeling analysis of adducts formed between DNA and safrole 2',3'-epoxide: absence of adduct formation in vivo

We have used the 32P-postlabeling technique to examine the binding of safrole 2',3'-oxide to DNA. At least 8 covalent adducts are formed when calf thymus DNA is incubated with this oxygenated metabolite of safrole in vitro. However, no corresponding adducts are formed with liver DNA when whole animals are exposed to safrole 2',3'-oxide, or safrole itself. Although safrole 2',3'-oxide is readily formed in vivo, and is sufficiently reactive to covalently bind to DNA, it is probably not a factor in the in vivo genotoxicity of safrole. We also demonstrate that adducts with similar mobility to the major safrole 2',3'-oxide-DNA adduct are formed in vitro between safrole 2',3'-oxide and deoxyguanosine, and also between its chemical analogs allylbenzene 2',3'-oxide or estragole 2',3'-oxide and DNA.

Evidence that 4-allyl-o-quinones spontaneously rearrange to their more electrophilic quinone methides: potential bioactivation mechanism for the hepatocarcinogen safrole

Several naturally occurring aromatic ethers, of which safrole [1-allyl-3,4-(methylenedioxy)-benzene] is one example, are hepatocarcinogens. One bioactivation pathway previously proposed for safrole involves hydroxylation of the benzyl carbon, conjugation with sulfate, and then alkylation of DNA with displacement of the sulfate group [Miller, J.A., and Miller, E.C. (1983) Br. J. Cancer 48, 1-15]. The fact that safrole is O-dealkylated to the corresponding catechol (hydroxychavicol, 1-allyl-3,4-dihydroxybenzene) indicates that quinoid formation is also possible and may contribute to the genotoxic and/or cytotoxic activity of this compound. In the present investigation we selectively oxidized hydroxychavicol to the corresponding o-quinone (HC-quinone, 4-allyl-3,5-cyclohexadiene-1,2-dione) or p-quinone methide (HC-QM, 2-hydroxy-4-allylidene-2,5-cyclohexadien-1-one) and trapped these reactive electrophiles with glutathione (GSH). The GSH adducts were fully characterized by UV, NMR, and mass spectrometry. Microsomal incubations with safrole or hydroxychavicol in the presence of glutathione produced only o-quinone glutathione conjugates. However, if the trapping agent (GSH) was added after an initial incubation of 10 min, both o-quinone and p-quinone methide GSH conjugates were observed. The first-order rate constant of isomerization was estimated from the decrease in HC-quinone GSH adducts to be 1.9 x 10(-3) s-1 (t1/2 = 9 min). Kinetic studies showed that while HC-QM reacts rapidly with water, the model o-quinone (4-tert-butyl-3,5-cyclohexadiene-1,2-dione), which cannot isomerize to a quinone methide, was remarkably resistant to hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the yeast DEL assay with 10 compounds selected by the International Program on Chemical Safety for the evaluation of short-term tests for carcinogens

The Saccharomyces cerevisiae DEL assay detects a wide variety of nonmutagenic carcinogens (Schiestl et al. (1989) Carcinogenesis, 10, 1445-1455). This study shows the effect on DEL recombination of 8 carcinogenic compounds (o-toluidine, hexamethylphosphoramide, safrole, acrylonitrile, benzene, diethylhexylphthalate, phenobarbital and diethylstilbestrol) and 2 noncarcinogenic compounds (caprolactam and benzoin). These chemicals have been selected by the Program on Chemical Safety for the evaluation of short-term tests for carcinogens, because sufficient carcinogenicity data for these compounds exist, and because they are difficult to detect with the Salmonella assay. 5 of 8 carcinogens reproducibly gave a strong positive response and the noncarcinogen benzoin was negative. Thus, 60% of the chemicals tested in this study have been correctly identified with the DEL assay compared to only 20% with the Salmonella assay.

Both physiological and pharmacological levels of melatonin reduce DNA adduct formation induced by the carcinogen safrole

Hepatic DNA adduct formation induced by the chemical carcinogen, safrole, was suppressed by both endogenous pineal melatonin release and by the exogenous administration of melatonin to rats. DNA damage after administration of of melatonin to rats. DNA damage after administration of 100 mg/kg safrole (i.p.) was measured by the P1 enhanced 32P-postlabeling analysis method. The RAL (relative adduct labeling) x 10(7) of carcinogen modified DNA in the liver of untreated controls and in safrole treated animals killed during the day, at night, after pinealectomy and pinealectomy plus melatonin injection (0.15 mg/kg x 4 or a total of 0.6 mg/kg) was 0, 12.6 +/- 0.75, 10.9 +/- 0.72, 13.6 +/- 1.12 and 5.7 +/- 0.53 respectively. For the same groups of animals, circulating melatonin levels at the termination of the study were 31 +/- 3, 29 +/- 2, 276 +/- 31, 24 +/- 1 and 13,950 +/- 1016 pg/ml serum respectively. The higher the melatonin concentration in the serum the lower was DNA adduct formation in the rat liver. Thus, high nocturnal levels of melatonin were protective against safrole-induced DNA damage. These findings indicate that the functional pineal gland plays an important role in oncostatic actions of carcinogens such as safrole. At physiological levels, melatonin seemed to prevent especially the formation of what was referred to as the N1 DNA adduct. Melatonin's ability to suppress DNA adduct formation may relate to its inhibitory effect on a mixed function oxidase, cytochrome p-450, and on the recently identified hydroxyl radical scavenging capacity of the indole. The oncostatic action of melatonin is also suggested by its nuclear accumulation and DNA stabilization characteristics. At pharmacological levels melatonin is extremely potent in preventing DNA modification induced by the chemical carcinogen, safrole.

Structure-genotoxicity relationships of allylbenzenes and propenylbenzenes: a quantum chemical study

Quantum mechanical calculations at the semiempirical level (AM1 method) were conducted for estragole (1), methyleugenol (2), safrole (3), alpha-asarone (4), beta-asarone (5), elemicin (6), allylbenzene (7), eugenol (8), trans-anethole (9), isosafrole (10), and myristicin (11), and the results compared with the known genotoxicity of 1-6 and the absence of genotoxicity of 7-11 (unscheduled DNA synthesis assay). The various compounds showed no significant differences in the relative stability of the radical species formed as intermediates in C-sp3 hydroxylation (delta HR(radical)) and in the corresponding enthalpy of activation (delta H++). In contrast, the carbonium ions of the genotoxic congeners 1-6 were shown to be comparatively more stable than those of the inactive compounds 7-11, with the exception of eugenol (8). The inactivity of this compound could be due to a very rapid stabilization of the carbonium ion by deprotonation to form a quinone methide, as suggested by quantum chemical calculations. The relative stability of the carbonium ion thus appears to be one of the key factors in the genotoxicity of allylbenzenes and propenylbenzenes.

Altered fidelity of a nucleic acid modifying enzyme, T4 polynucleotide kinase, by safrole-induced DNA damage

Mouse liver DNA adducted with metabolites of the spice constituent safrole (1-allyl-3,4-methylenedioxybenzene), when analyzed via the bisphosphate version of the 32P-postlabeling assay, exhibits two major adducts, which had been previously identified as N2-(trans-isosafrol-3'-yl)2'-deoxyguanosine 3',5'-bisphosphate (adduct 1) and N2-(safrol-1'-yl)2'-deoxyguanosine 3',5'-bisphosphate (adduct 2). However, analysis of the same DNA preparation by the dinucleotide/monophosphate version of the assay gave two additional spots on PEI-cellulose TLC whose nature was clarified in the present study. Several enzymes (T4 polynucleotide kinase, nuclease P1, venom phosphodiesterase and spleen phosphodiesterase) were utilized to hydrolyze these compounds, and the products co-chromatographed on PEI-cellulose thin layers with radiolabeled and non-radioactive nucleotides of known structure. The additional spots were found to be adducted dinucleotides carrying 32P-label at both the 5'- and 3'-hydroxyls. T4 polynucleotide kinase-catalyzed 3'-phosphorylation was highly specific in that only dinucleoside monophosphate derivatives of adduct 1, with an unmodified purine in the 3'-position, were susceptible to both 5'- and 3'-phosphorylation by the enzyme. Thus, the structures of the two additional 32P-labeled safrole derivatives were pX1pAp and pX1pGp where X1 denotes N2-(trans-isosafrol-3'-yl)2'-deoxyguanosine. The official name of T4 polynucleotide kinase, ATP:5'-dephosphopolynucleotide 5'-phosphotransferase (EC 2.7.1.78), denotes the specific action of this enzyme as a 5'-phosphokinase. Although the enzyme has 3'-phosphatase activity at acidic pH, no 3'-kinase reaction has been previously reported. Possible implications for chemical carcinogenesis of the finding that carcinogen-DNA adducts can specifically alter the fidelity of protein-nucleotide interactions are discussed.

Formation and persistence of safrole-DNA adducts over a 10,000-fold dose range in mouse liver

The spice constituent safrole (1-allyl-3,4-methylenedioxybenzene) and related allylbenzenes form DNA adducts and are rodent carcinogens. This study examined both dose and time dependence of hepatic safrole-DNA adduct formation over a 10,000-fold dose range up to 30 days after single administration. Female CD-1 mice were treated with safrole i.p. at 0.001, 0.01, 0.1, 1.0, and 10.0 mg/mouse in 0.2 ml tricaprylin or with vehicle alone. Liver DNA was analyzed at 0.5, 1, 2, 3, 7, 15 and 30 days via the dinucleotide/monophosphate version of the 32P-postlabeling assay. An approximately 10-fold increase in total safrole adduct levels with each successive 10-fold increase in dose was observed, giving relative adduct labeling (RAL) values of 10(-9)-10(-5). Each dose elicited identical kinetics of adduct formation, showing peak levels at 2 days and only slight decreases thereafter. The time course of adduct persistence was independent of the dose (0.01-10 mg/mouse). An in vitro experiment established that the assay responded in strictly linear fashion to adduct concentration over a 10,000-fold range, and thus was suitable for in vivo dosimetry. DNA synthesis, as measured by [3H]thymidine incorporation, was enhanced only for the 10.0 mg dose at 2, 3 and 7 days. These results indicate a linear response of safrole-DNA adduct formation and persistence in mouse liver following administration of minute (0.001 mg/mouse) to high (10.0 mg/mouse) doses of the carcinogen.

Induction of three histochemically distinct populations of hepatic foci in C57BL/6J mice

Although expression of the enzyme gamma-glutamyl transpeptidase (GGT) is the most common phenotypic marker of preneoplastic foci in the livers of carcinogen-treated rats, it is not generally expressed in mouse liver tumors or hepatic foci. However, several carcinogens, including safrole and ortho-azoaminotoluene (OAT), have been reported to induce GGT-positive foci in mice. We asked whether safrole and OAT induce GGT expression in preneoplastic foci or if these compounds select for a distinct set of lesions that can be identified by their GGT-positive phenotype. We treated 12-day-old male and female C57BL/6J mice with N,N-diethylnitrosamine (DEN) (0.20 mumol/g body wt) to initiate hepatocarcinogenesis. From 6 to 24 weeks of age, during the promotion phase of hepatocarcinogenesis, groups of mice were treated with 3,4,5,3',4',5'-hexabromobiphenyl (HBB), safrole or OAT. Additional groups of female mice were ovariectomized at 6 weeks of age with or without subsequent chronic treatment with testosterone. All the animals were killed at 24 weeks of age and serial liver sections were stained for glucose-6-phosphatase (G6Pase) or GGT. Both testosterone and HBB were strong promoters of the development of G6Pase-deficient foci. No GGT-positive foci were observed in animals treated with these agents or with DEN alone. In mice fed safrole or OAT during the promotion period, female mice developed more G6Pase-deficient foci than male mice, and GGT-positive foci were observed. Analysis of serial sections revealed that the G6Pase-deficient foci and the GGT-positive foci were independent populations. The relative number of these two classes of foci varied according to the treatment regimen. In females fed safrole, 7% of the foci in the liver were GGT-positive while in female mice fed OAT, 45% were GGT-positive. In all groups of mice in which we observed GGT-positive foci and in ovariectomized female mice, we noted a third independent population of foci which demonstrated significantly increased expression of G6Pase relative to surrounding normal liver. These data indicate that different treatments during the promotion stage of hepatocarcinogenesis in the mouse may give rise to distinct populations of preneoplastic lesions. Further studies of the molecular events giving rise to these distinct lesions will provide insights into the multiple pathways that result in hepatocarcinogenesis.

Flavor constituents in cola drinks induce hepatic DNA adducts in adult and fetal mice

Mice given one of several widely consumed cola drinks in place of drinking water for up to 8 weeks developed significant levels of covalent liver DNA adducts in a time dependent manner, as measured by 32P-postlabeling. These adducts were not detected in mice given tap water or one of 3 non-cola beverages. Adducts chromatographically identical to those induced by cola drinks were detected in mice treated with extracts of nutmeg or mace, spices from the nutmeg tree (Myristica fragrans Houttuyn), or with myristicin (1-allyl-5-methoxy-3,4-methylenedioxybenzene), the major spice constituent of nutmeg. In addition, small amounts of adducts derived from the hepatocarcinogen safrole (1-allyl-3,4-methylenedioxybenzene), a minor constituent of nutmeg, were observed. Liver DNA adducts were also detected in fetal liver when pregnant mice were intubated with myristicin. Possible implications of these findings for human health are discussed.

Carcinogenicity testing of some constituents of black pepper (Piper nigrum)

In mice, injection of safrole, tannic acid or methylcholanthrene (MCA) during the preweaning period induced tumors in different organs. Safrole and tannic acid (constituents of black pepper) were weak carcinogens when compared with MCA which was used as a carcinogenic control substance. Force feeding of d-limonene (one of the pepper terpenoids) for a long time to the mice which were injected with any of the above 3 substances reduced their carcinogenic activity, while force feeding of piperine (one of black pepper alkaloids) was ineffective.

A comparison of DNA adduct formation in white blood cells and internal organs of mice exposed to benzo[a]pyrene, dibenzo[c,g]carbazole, safrole and cigarette smoke condensate

Measurement of tissue/cell DNA adducts represents a suitable monitor of carcinogen exposure because the majority of chemical mutagens/carcinogens react with DNA, forming covalent adducts, a key event in the initiation of chemical carcinogenesis. Investigations of DNA-adduct formation in vivo in white blood cells (WBC) versus target tissues, i.e. internal organs for most carcinogens, is expected to yield useful information about the suitability of WBC for biomonitoring and risk assessment. For this purpose, female ICR mice were given 0.4 mmole/kg benzo[a]pyrene (BP), 0.045 mmole/kg dibenzo[c,g]carbazole (DBC) or 2.47 mmole/kg safrole by oral gavage or 4 daily doses (equivalent to 3 cigarettes) of cigarette-smoke condensate (CSC) by topical application. At 24 h after dosing, DNA adducts were detected by a nuclease P1-enhanced 32P-postlabeling assay [M.V. Reddy and K. Randerath, Carcinogenesis, 7 (1986) 1543] in WBC and internal tissues treated with individual carcinogens, while CSC treatment elicited aromatic adducts in most tissues but not in WBC. Adduct patterns of WBC DNA were qualitatively similar to those of internal organs, but adduct amounts varied. BP, a systemic carcinogen, bound nearly as much to WBC DNA as to target-tissue DNA samples; whereas the liver carcinogens, DBC and safrole, bound to WBC DNA considerably less (22- and 51-fold, respectively) compared with liver DNA. The number of adducts in 10(7) nucleotides of WBC, liver, lung, kidney and spleen DNA, respectively, were: 2, 5, 3, 2 and 3 with BP; 6, 131, 6, 14 and 4 with DBC; 5, 238, 3, 5 and 0.6 with safrole. For CSC, these values were 0, 1 and 0.02 in WBC, lung and spleen, respectively. Our results show that carcinogen binding to WBC DNA does not reflect binding to target-tissue DNA in a quantitative sense for the carcinogens studied except for BP, and that WBC are not suitable surrogates for monitoring CSC exposure by DNA-adduct measurement after topical application. The CSC data in mice was consistent with the previous findings in humans that smokers' tissues but not WBC show smoking-related bulky/aromatic DNA adducts, as measured by 32P-postlabeling.

Mutational specificities of 1'-acetoxysafrole, N-benzoyloxy-N-methyl-4-aminoazobenzene, and ethyl methanesulfonate in human cells

We have used an oriP-tk shuttle vector to determine the types of mutations induced in human cells by ethyl methanesulfonate (EMS), 1'-acetoxysafrole (AcOS), and N-benzoyloxy-N-methyl-4-aminoazobenzene (BzOMAB). Plasmid DNA was treated in vitro with mutagen and electroporated into human lymphoblastoid cells. After replication of the vector in human cells, plasmids were analyzed for mutations in the herpes simplex virus type 1 thymidine kinase gene. Ethyl methanesulfonate induced predominantly GC----AT transition mutations. Treatment of the shuttle vector with AcOS induced 5 of the 6 possible base substitution mutations, including GC----AT (32%) and AT----GC (14%) transition mutations, GC----TA (9%), GC----CG (18%), and AT----TA (14%) transversion mutations, as well as a low frequency (9%) of -1 frameshift mutations at GC base pairs. Replication in human cells of DNA modified with BzOMAB yielded a significant increase (17-fold) in the frequency of deletion mutations relative to solvent-treated DNA. A majority (94%) of the point mutations induced by BzOMAB occurred at GC base pairs and were predominantly GC----AT transitions (33%) and -1 frameshift (22%) mutations, with the remainder consisting mainly of transversions at GC base pairs (28%). The broad spectrum of base substitution mutations observed for AcOS and BzOMAB may indicate the frequent insertion of a variety of bases during replicative bypass of aralkylated bases in human cells.

Inhibition by pentachlorophenol of the initiating and promoting activities of 1'-hydroxysafrole for the formation of enzyme-altered foci and tumors in rat liver

The hepatocarcinogen 1'-hydroxysafrole (HOS) exhibited weak initiating activity and strong promoting activity for the induction of enzyme-altered foci and tumors in rat liver. Thus, administration of a single dose of HOS to rats 18 h after a 70% hepatectomy, followed by administration of phenobarbital (PB) in the diet for 6 months, induced a low, but statistically significant, number of foci of enzyme-altered cells. This treatment did not result in gross liver tumors, even when the PB treatment was continued for 16 months. Large numbers of enzyme-altered foci developed when HOS was administered in the diet at levels of 0.05-0.25% to rats previously administered a single dose of N,N-diethylnitrosamine (DEN) 24 h after a 70% hepatectomy. Similarly, rats given a single dose of DEN 24 h after a partial hepatectomy and then fed 0.10 or 0.25% of HOS in the diet for 10 months developed a high incidence of hepatocellular carcinomas. In the absence of pretreatment with DEN, dietary administration for at least 4 months of 0.10 or 0.25% of HOS induced significant numbers of enzyme-altered foci; these data and liver tumor induction by continuous feeding of HOS, in the absence of pretreatment with DEN, provide additional evidence for an initiating, as well as a promoting, activity of HOS in rat liver. Concurrent administration of the hepatic sulfotransferase inhibitor pentachlorophenol with HOS in each of the above assays almost completely inhibited the initiating and promoting activities of HOS for the formation of enzyme-altered foci and tumors; these data strongly suggest that both the initiating and promoting activities are mediated by the sulfuric acid ester, 1'-sulfooxysafrole. HOS also exhibited initiating activity in adult mouse liver. Thus, dietary administration of 0.25% of HOS for only 1 month, followed by administration of the hepatic tumor promoter 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene resulted in a high incidence and multiplicity of hepatomas by 10 months. In the absence of the promoter, administration of HOS for only 1 month induced no hepatomas; 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene alone induced only a low incidence. In mice not given the promoter, continuous administration of HOS for 3-6 months was required for hepatoma development by 16 months.

Interaction of piperine with rat liver microsomes

Pretreatment of adult male albino rats with piperine did not induce cytochrome P-450 whereas safrole did cause such induction. Piperine and safrole interacted with different forms of cytochrome P-450 as indicated by their in vivo effect on drug metabolising enzymes and mixed function oxidases and electrophoretic patterns. Incubation of piperine or safrole with dithionite- or NADPH-reduced microsomes from untreated rats resulted in a modified type II difference spectrum with an absorption maximum at 427 nm and a trough at 408 nm.

Apurinic/apyrimidinic site induction in supercoiled DNA and mutagenesis in Salmonella typhimurium TA100 by 1'-acetoxysafrole and related electrophilic alkenylbenzene derivatives

The abilities of seven electrophilic alkenylbenzene derivatives related to 1'-acetoxysafrole to induce apurinic/apyrimidinic (AP) sites in supercoiled SV40 DNA were quantitated by gel electrophoresis after neutral thermal hydrolysis of DNA adducts with unstable N-glycosidic bonds and putrescine/Mg2+ ion-enhanced cleavage of the adjacent phosphodiester linkages. A 20-fold range in AP site production was observed for this series of closely related electrophiles. Analysis of SV40 DNA modified with [2',3'-3H]-1'-acetoxysafrole indicated that approximately 14% of the total safrole-DNA adducts generated AP sites under the conditions used. Neutral thermal hydrolysis of the modified DNA released a product with the same h.p.l.c. retention time as N7-(isosafrol-3'-yl)guanine. The mutagenic potencies in Salmonella typhimurium strain TA100 of these seven electrophilic alkenylbenzene derivatives covered a 75-fold range (from 0.1 to 7.7 revertants/nmol). Although the mutagenic activities of these electrophiles generally correlated well with the hepatocarcinogenic activities of the parent 1'- or 3'-hydroxy derivatives on administration to preweanling male mice, the mutagenic and carcinogenic activities did not correlate with the abilities to induce AP sites.

32P-postlabeling assay in mice of transplacental DNA damage induced by the environmental carcinogens safrole, 4-aminobiphenyl, and benzo(a)pyrene

Transplacental exposure of fetuses to carcinogens is known to induce tumors in the offspring, often with a high incidence and short latency. While covalent adduction of DNA appears to be essential for tumor initiation, little is known about the binding of carcinogens to the DNA of fetal tissues. A sensitive 32P-postlabeling method enabled us to study the binding of the environmental carcinogens safrole (600 mumol/kg p.o.), 4-aminobiphenyl (800 mumol/kg), and benzo(a)pyrene (200 mumol/kg) to the DNA of various maternal and fetal tissues after administration of test carcinogens to pregnant ICR mice on day 18 of gestation. The results show that these carcinogens bound to the DNA of maternal and fetal liver, lung, kidney, heart, brain, intestine, skin, maternal uterus, and placenta, with organ-specific quantitative and qualitative differences. It was possible for the first time to analyze DNA adduct patterns in minute amounts of tissue, for example those available from fetal heart. The covalent binding index (mumol adducted nucleotides per mol of DNA nucleotides/mumol carcinogen administered per g body weight) 24 h after safrole treatment was estimated for the different organs and ranged from 0.1 to 247 and 0.1 to 5.8 for maternal and fetal DNA, respectively. Covalent binding index values of 0.2 to 13 and 0.1 to 0.3 for maternal and fetal DNA, respectively, were found for 4-aminobiphenyl. Benzo(a)pyrene treatment yielded covalent binding index values of 0.6 to 6.5 and 0.3 to 0.7 for maternal and fetal DNA, respectively. In both maternal and fetal tissues, safrole exhibited preferential binding to liver DNA. 4-Aminobiphenyl bound preferentially to DNA of maternal liver and kidney but showed no preference among fetal tissues. Benzo(a)pyrene exhibited weak tissue preference in both maternal and fetal organs. For all of the compounds studied, the fetal adduct levels were generally lower than the corresponding maternal adduct levels, especially when the level of maternal adduction was high. The major finding was that several carcinogens of diverse structure or their metabolites readily crossed the placenta and gave rise to DNA adducts in fetal organs. The resulting DNA damage in rapidly proliferating tissues may play a critical role in transplacental carcinogenesis.

Strong evidence from studies with brachymorphic mice and pentachlorophenol that 1'-sulfoöxysafrole is the major ultimate electrophilic and carcinogenic metabolite of 1'-hydroxysafrole in mouse liver

The role of sulfation of 1'-hydroxysafrole in the formation of hepatic macromolecular adducts and in hepatic tumor formation in mice given 1'-hydroxysafrole was investigated by the use of: (a) mice treated with the specific sulfotransferase inhibitor pentachlorophenol; and (b) brachymorphic mice, which are characterized by a deficiency in the hepatic synthesis of 3'-phosphoadenosine 5'-phosphosulfate. Cytosolic sulfotransferase activity for 1'-hydroxysafrole in both mouse and rat liver was significantly inhibited by 10 microM pentachlorophenol, usually by greater than 90%. Prior administration of nontoxic amounts of pentachlorophenol, either in the diet of adult female CD-1 mice or by i.p. injection of 12-day-old male C57BL/6 X C3H F1 (hereafter called B6C3F1) mice, resulted in an 85% decrease in the level of adducts formed from 1'-hydroxysafrole in hepatic DNA and RNA as compared to those of non-pentachlorophenol-treated animals. Likewise, the chronic administration of a nontoxic level of pentachlorophenol in the diet of adult female CD-1 mice strongly inhibited hepatic tumor induction by long-term dietary administration of either safrole or 1'-hydroxysafrole. Initiation of hepatic tumors by a single i.p. injection of 1'-hydroxysafrole to 12-day-old male B6C3F1 mice was strongly inhibited by prior treatment with pentachlorophenol. Under these conditions, the hepatocarcinogenicity of diethylnitrosamine was not inhibited by pentachlorophenol. Supplementation with adenosine triphosphate and sulfate of hepatic cytosols from adult female or 12-day-old brachymorphic progeny of a B6C3 background outbred to B6C3F1 mice (B6C3F2), of either sex, resulted in 5- to 10-fold less binding of 1'-hydroxysafrole to added RNA than when cytosols from phenotypically normal B6C3F2 mice were used. On administration of [3H]-1'-hydroxysafrole to adult female or 12-day-old brachymorphic B6C3F2 mice of either sex, the levels of hepatic DNA and RNA adducts were 7- to 12-fold lower than those obtained in phenotypically normal B6C3F2 mice of the same age and sex. Brachymorphic mice were also much less responsive than their phenotypically normal littermates to the induction of liver tumors by 1'-hydroxysafrole; lower incidences were observed both when the carcinogen was fed chronically to adult females and when it was administered to males only prior to weaning. Thus, all of these data strongly support the conclusion that 1'-sulfoöxysafrole is the major ultimate electrophilic and tumor-initiating metabolite of 1'-hydroxysafrole.

Effects of dihydrosafrole on cytochromes P-450 and drug oxidation in hepatic microsomes from control and induced rats

Changes in cytochromes P-450, aminopyrine N-demethylase (APDM), aromatic hydrocarbon (benzo[a]pyrene) hydroxylase (AHH), and type III spectral complex formation were measured in hepatic microsomes of control, phenobarbital (PB)-, and beta-naphthoflavone (beta NF)-induced rats after a single dose of dihydrosafrole (4-n-propyl-1,2-methylenedioxybenzene, DHS). Time profiles of changes in these microsomal parameters were complex and showed that APDM activities and cytochrome P-450 levels decreased immediately after treatment and were associated with concurrent increases in the intensity of the type III methylenedioxyphenyl (MDP) metabolite/cytochrome P-450 spectral complex. In noninduced rats, both APDM activity and cytochrome P-450 levels returned to control levels between 12 and 24 hr after treatment with DHS and subsequently increased above control levels. In PB- and beta NF-induced animals, the inhibitory phases were more prolonged and activity never returned to levels higher than the corresponding controls. AHH activity was increased substantially (two- to three-fold) in all cases after DHS administration. Although displacement of the MDP metabolite/cytochrome P-450 complex with 2-methylbenzimidazole generally led to a marked restoration of cytochrome P-450 levels and partially reversed the inhibition of APDM, it had little or no effect on AHH activities.

Alkali-sensitive sites in DNA from human cells treated with ultraviolet light, 1'-acetoxysafrole or 1'-acetoxyestragole

The formation and repair of alkali-labile sites in the DNA of human cells treated with 254 nm u.v. light, 1'-acetoxyestragole (1'-AcO-E) or 1'-acetoxysafrole (1'-AcO-S) have been studied. DNA was analysed by sedimentation in alkaline sucrose gradients after the cells had been layered on the gradients in lysis solution for 15 h (long lysis) or for only 0.75 h (short lysis). With the long lysis technique, a dose of 20 J/m2 resulted in 0.2-0.4 strand breaks/10(8) daltons while treatment of cells with 0.5 mM 1'-AcO-E or 1'-AcO-S caused 0.1-0.3 strand breaks/10(8) daltons. In excision repair proficient T98G cells, one third to two thirds of these strand breaks disappeared upon 4 h incubation after exposure to each of the three agents. In excision repair deficient xeroderma pigmentosum fibroblasts (XPA), the alkali-labile sites produced by 1'-AcO-E or 1'-AcO-S were still repaired, although those resulting from u.v.-irradiation were not. Similar characteristics were observed after the short lysis period. The sedimentation velocities of nucleoids, prepared from treated XPA cells, in neutral sucrose gradients containing ethidium bromide, did not reveal the presence of overt strand breaks in the DNA, suggesting that the lesions were of a type in which the sugar-phosphate backbone was intact but sensitive to hydrolysis by alkali. The contribution of this type of damage to the total DNA damage produced by the agents was estimated to be less than 1% for u.v., and less than 2.5% for 1'-AcO-E and 1'-AcO-S.

Repair replication characteristics of human cells exposed to 1'-acetoxysafrole or 1'-acetoxyestragole

The response of cultured human cells to treatment with 1'-acetoxysafrole (1'-AcO-S) and 1'-acetoxyestragole (1'-AcO-E), which are electrophilic and mutagenic, has been examined. Fifty percent survival of T98G cells followed exposure to 0.2 mM 1'-AcO-E. Fifty percent inhibition of DNA synthesis rate occurred after exposure to 0.3-0.5 mM of either compound. DNA repair replication in treated cells was measured by the combined 5-bromodeoxyuridine density and radioisotope labelling method. Detectable levels of repair over a 4 h time period appeared following exposure to 0.1 mM or higher concentrations of either compound. However, the maximum level of repair in 1'-AcO-S-treated cells was only 15% of the value seen after a saturating dose of u.v. (254 nm), and that for 1'-AcO-E was only 10% of the u.v. maximum. The time course for repair was similar for u.v. and 1'-AcO-S up to at least 11 h after treatment. Normal human fibroblasts (GM38) exhibited a similar ability to that of T98G cells for repair of 1'-AcO-S-induced damage. Even SV40-transformed fibroblasts from a xeroderma pigmentosum patient (complementation group A) exhibited a low but significant amount of repair after treatment with 0.5 mM 1'-AcO-S. The repair patch size distribution in T98G cells treated wih 1'-AcO-S or 1'-AcO-E was 19-23 nucleotides, -70% of the value obtained by the density-labelling method in u.v.-irradiated human cells.

Biology of hepatocellular neoplasia in the mouse. III. Electron microscopy of safrole-induced hepatocellular adenomas and hepatocellular carcinomas

A systematic, ultrastructural analysis wsa performed on safrole-induced hepatocellular adenomas and hepatocellular carcinoma(s) (HPC) in BALB/c mice. Adenomas were heterogeneous in cell composition containing dark-staining basophilic cells, pale-staining acidophilic cells, clear cells, and lipid-laden cells. Darkly staining cells resembled fetal hepatocytes. They had large nuclei with irregular borders and limited diversity of organelles. Rough endoplasmic reticulum was prominent and seen as parallel cisternae in single or double tracts often in association with mitochondria. Pale-staining cells contained abundant smooth endoplasmic reticulum. Other organelles were often displaced to the perinuclear or peripheral region of the cell. The clear cells resembled dark-staining or pale-staining cells but also containing large areas of glycogen deposition. Lipid-laden cells contained numerous, multisized lipid droplets in the cytoplasm. HPC contained cell types similar to those of the adenoma. In addition, they contained many anaplastic cells. These resembled hepatocytes but contained several other alterations. The most striking was an apparent increase in the number of altered mitochondria. The cytoplasm was often fluid with enlarged mitochondria with dense or pale matrices. The cristae were few and had altered configurations. Also, an apparent increase was seen in the number of microbodies. These were often clustered in one region of the cytoplasm. An increase in microbodies was also noted in other cell types of hepatocellular carcinomas. The results of this study demonstrated similarities in the cell types of the adenomas and HPC. This study also demonstrated differences, with the anaplastic cell being common only to the carcinoma. Due to the similarity of cell types, the adenoma should be considered a possible site of HPC development.

Biology of hepatocellular neoplasia in the mouse. I. Histogenesis of safrole-induced hepatocellular carcinoma

A sequential, histologic analysis of the livers of male BALB/c mice chronically fed the hepatocarcinogen safrole (4,000 ppm) was performed at 2, 4, 8, 16, 24, 36, 52, and 75 weeks. The transplantability of selected lesions to syngeneic hosts was also assessed. Histopathologic liver alterations at 2, 4, 8, and 16 weeks induced hypertrophy of centrolobular hepatocytes, oval cell proliferation, fatty change in periportal hepatocytes, including basophilic, acidophilic, and clear cell, were noted. At 36 and 52 weeks, hepatocellular adenomas occurred in 4 of 10 and 7 of 10 mice, respectively. At 75 weeks they occurred in 5 of 5 mice. Adenomas were larger than a lobule in diameter compressed the adjacent parenchyma, and distorted the hepatic architecture. Individual adenomas were composed of a mixture of basophilic, acidophilic, clear, and lipid-laden cells, arranged in disorganized cords, one to three cells in thickness. None of the 10 adenomas tested grew upon subcutaneous transplantation into syngeneic hosts. Hepatocellular carcinomas (HPC) developed in 2 of 10 safrole-exposed mice at 52 weeks and 3 of 5 mice at 75 weeks. These lesions were large, multilobed and, unlike adenomas, seemed to invade adjacent parenchyma. The HPC were heterogeneous in cell composition. Their architecture was disorganized with trabeculae of 1-10 or more cells in thickness. No central veins or portal tracts were seen. All HPC proliferated when transplanted into syngeneic hosts. The results of this study demonstrated a sequential development of altered hepatocyte populations leading to HPC in safrole-treated mice. The transplantability of HPC indicated their malignant nature.

Biology of hepatocellular neoplasia in the mouse. II. Sequential enzyme histochemical analysis of BALB/c mouse liver during safrole-induced carcinogenesis

Sequential alterations in enzyme histochemical profiles and reaction of hepatocytes to rapid iron overload were examined in male BALB/c mice during chronic, safrole exposure. At 24 weeks after initiation of safrole treatment, foci of enzyme-altered hepatocytes were noted. These foci were composed of cells showing a decrease in reactivity for glucose-6-phosphatase (Glc-6-Pase) and succinate dehydrogenase (SDH) and an increase for gamma-glutamyl transpeptidase (gamma-Glu-T). In control, iron-loaded mice, the livers were intensely siderotic. In safrole-exposed, iron-loaded mice, foci of iron-negative hepatocytes, varying from a few cells to a lobule in diameter, were initially noted at 24 weeks. Both enzyme-altered and iron-negative foci occurred in the livers of exposed mice at all time periods after 24 weeks. After 36, 52, and 75 weeks of safrole treatment, hepatocellular adenomas were noted with altered enzyme histochemical profiles. Hepatocytes from adenomas were characterized by a decreased staining for Glc-6-pase and SDH and increased staining for gamma-Glu-T and glucose-6-phosphate dehydrogenase (Glc-6-PD). In addition, a few nodules showed a decrease in staining for 5'nucleotidase. In iron-loaded mice, hepatocytes of adenomas showed a decreased to negative reaction for iron when the surrounding parenchyma was siderotic. Hepatocellular carcinomas (HPC) occurred in livers of mice exposed to safrole for 52-75 weeks. The cells of HPC displayed similar enzyme histochemical reactions as cells of adenomas. They were decreased for Glc-6-Pase and SDH activity and increased for gamma-Glu-T and Glc-6-PD. In iron-loaded mice, the HPC cells were negative for stainable iron. Foci, adenomas, and HPC displayed some variability in enzyme histochemical reactions. Variability existed between lesions as well as between cells of the same lesion.