Comprehensive toxicity study of safrole using a medium-term animal model with gpt delta rats

Safety of Nutmeg powder by oral exposure: Toxicity prediction and in vivo evaluation

Nutmeg (Myristica fragrans Houtt.) is widely cultivated in tropical regions and valued for its culinary and medicinal uses. However, its safety profile remains underexplored. This study aimed to evaluate the safety of nutmeg powder through in-silico toxicity predictions, acute oral toxicity, and a 13-week repeated-dose toxicity assessment. In the in-silico study, bioactive compounds identified via High-Performance Liquid Chromatography (HPLC) were analyzed for toxicity parameters using the ProTox II server. For acute toxicity, a single dose of nutmeg powder was administered to mice, with no mortality observed over 14 days, and an LD50 greater than 5000 mg/kg body weight was determined. In the sub-chronic toxicity study, rats received nutmeg powder at 1400 mg/kg and 3500 mg/kg (35 and 87.5 times the human therapeutic dosage, respectively) for 90 days. A 28-day recovery phase was included to assess delayed or reversible effects. The results indicate that a dose of 1400 mg/kg leads to liver damage and hemosiderin deposition in the spleen, while a dose of 3500 mg/kg causes liver and kidney damage, as well as hemosiderin deposition in the spleen. These findings highlight the potential toxicity of long-term nutmeg consumption and underscore the need for further research to ensure its safety in preclinical.

A 13-week comprehensive toxicity study with adductome analysis demonstrates the toxicity, genotoxicity, and carcinogenicity of the natural flavoring agent elemicin

Elemicin, an alkenylbenzene flavoring, exists naturally in foods, herbs, and spices. Some alkenylbenzenes are hepatotoxic and hepatocarcinogenic in rodents. However, few studies have examined the toxicology of elemicin. In the current study, we comprehensively evaluated the general toxicity, genotoxicity, and carcinogenicity of elemicin using gpt delta rats and DNA adductome analysis. Groups of 10 male F344 gpt delta rats were treated with elemicin by gavage at a dose of 0, 25, 100, or 400 mg/kg bw/day for 13 weeks. Liver weights were significantly increased with histopathological changes in groups receiving 100 mg/kg bw/day or more. Significant increases in serum hepatotoxic parameters were observed in the 400 mg/kg bw/day group. Based on the observed changes in liver weights, 18.6 mg/kg bw was identified as the low benchmark dose. Significant increases in the number and area of glutathione S-transferase placental form-positive foci and gpt mutant frequencies were apparent only in the 400 mg/kg/day group, although elemicin-specific DNA adducts were detected from the lowest dose, suggesting that elemicin exhibited hepatocarcinogenicity in rats only at higher doses. Because elemicin showed no mutagenicity at lower doses, there was an adequate safety margin between the acceptable daily intake and the estimated daily intake of elemicin.

A computational study on the biotransformation of alkenylbenzenes by a selection of CYPs: Reflections on their possible bioactivation

Alkenylbenzenes are aromatic compounds found in several vegetable foods that can cause genotoxicity upon bioactivation by members of the cytochrome P450 (CYP) family, forming 1'-hydroxy metabolites. These intermediates act as proximate carcinogens and can be further converted into reactive 1'-sulfooxy metabolites, which are the ultimate carcinogens responsible for genotoxicity. Safrole, a member of this class, has been banned as a food or feed additive in many countries based on its genotoxicity and carcinogenicity. However, it can still enter the food and feed chain. There is limited information about the toxicity of other alkenylbenzenes that may be present in safrole-containing foods, such as myristicin, apiole, and dillapiole. In vitro studies showed safrole as mainly bioactivated by CYP2A6 to form its proximate carcinogen, while for myristicin this is mainly done by CYP1A1. However, it is not known whether CYP1A1 and CYP2A6 can activate apiole and dillapiole. The present study uses an in silico pipeline to investigate this knowledge gap and determine whether CYP1A1 and CYP2A6 may play a role in the bioactivation of these alkenylbenzenes. The study found that the bioactivation of apiole and dillapiole by CYP1A1 and CYP2A6 is limited, possibly indicating that these compounds may have limited toxicity, while describing a possible role of CYP1A1 in the bioactivation of safrole. The study expands the current understanding of safrole toxicity and bioactivation and helps understand the mechanisms of CYPs involved in the bioactivation of alkenylbenzenes. This information is essential for a more informed analysis of alkenylbenzenes toxicity and risk assessment.

Comprehensive analysis of the general toxicity, genotoxicity, and carcinogenicity of 3-acetyl-2,5-dimethylfuran in male gpt delta rats

The safety of flavoring agents has been evaluated according to classification by chemical structure and using a decision tree approach. The genotoxic potential found in some flavoring agents has highlighted the importance of efficient toxicity studies. We performed a comprehensive toxicity analysis using reporter gene transgenic rats to assess the safety of 3-acetyl-2,5-dimethylfuran (ADF), a flavoring agent exhibiting genotoxic potential in silico and in vitro assays. Male F344 gpt delta rats were given 0, 30, or 300 mg/kg body weight/day ADF by gavage for 13 weeks. In serum biochemistry analyses, triglyceride, total cholesterol, phospholipid, and total protein levels and albumin/globulin ratios were significantly altered in the 30 and 300 mg/kg groups. Histopathologically, nasal cavity toxicity and hepatocellular hypertrophy were observed in the 300 mg/kg group. In the livers of 300 mg/kg group, a significant increase in gpt mutant frequencies were observed along with ADF-specific DNA adduct formation. The number and area of glutathione S-transferase placental form-positive foci were significantly increased in the same group. Thus, ADF affected nasal cavity, liver, and lipid metabolism and showed genotoxicity and possible carcinogenicity in the liver. Overall, our comprehensive toxicity study using gpt delta rats provided insights into the safety evaluation of ADF.

Toxicity, genotoxicity, and carcinogenicity of 2-methylfuran in a 90-day comprehensive toxicity study in gpt delta rats

2-Methylfuran (2-MF) exists naturally in foods and is used as a flavoring agent. Furan, the core structure of 2-MF, possesses hepatocarcinogenicity in rodents. Accumulation of toxicological information on furan derivatives is needed to elucidate their carcinogenic mode of action. In the current study, we examined the comprehensive toxicological studies of 2-MF using gpt delta rats. 2-MF was intragastrically administered to groups of 10 male and 10 female Sprague-Dawley gpt delta rats at a dose of 0, 1.2, 6, or 30 mg/kg/day for 13 weeks. Effects of 2-MF on the hepatobiliary system including an increase in serum alkaline phosphatase were observed in the 6 and 30 mg/kg groups, and cholangiofibrosis was found in the 30 mg/kg group. The no observed adverse effect level was set at 1.2 mg/kg/day for both sexes and 1.14 mg/kg/day was determined as the benchmark dose low. The acceptable daily intake was calculated to be 11.4 μg/kg/day. Increases in the number and areas of glutathione S-transferase placental form-positive foci in the 30 mg/kg group were apparent, suggesting the hepatocarcinogenicity of 2-MF in rats. By contrast, the lack of increase in in vivo mutagenicity in the liver implied that 2-MF hepatocarcinogenesis may not involve genotoxic mechanisms.

Myristicin and Elemicin: Potentially Toxic Alkenylbenzenes in Food

Alkenylbenzenes represent a group of naturally occurring substances that are synthesized as secondary metabolites in various plants, including nutmeg and basil. Many of the alkenylbenzene-containing plants are common spice plants and preparations thereof are used for flavoring purposes. However, many alkenylbenzenes are known toxicants. For example, safrole and methyleugenol were classified as genotoxic carcinogens based on extensive toxicological evidence. In contrast, reliable toxicological data, in particular regarding genotoxicity, carcinogenicity, and reproductive toxicity is missing for several other structurally closely related alkenylbenzenes, such as myristicin and elemicin. Moreover, existing data on the occurrence of these substances in various foods suffer from several limitations. Together, the existing data gaps regarding exposure and toxicity cause difficulty in evaluating health risks for humans. This review gives an overview on available occurrence data of myristicin, elemicin, and other selected alkenylbenzenes in certain foods. Moreover, the current knowledge on the toxicity of myristicin and elemicin in comparison to their structurally related and well-characterized derivatives safrole and methyleugenol, especially with respect to their genotoxic and carcinogenic potential, is discussed. Finally, this article focuses on existing data gaps regarding exposure and toxicity currently impeding the evaluation of adverse health effects potentially caused by myristicin and elemicin.

Dissecting dietary and semisynthetic volatile phenylpropenes: A compile of their distribution, food properties, health effects, metabolism and toxicities

Phenylpropenes represent a major subclass of plant volatiles, including eugenol, and (E)-anethole. They contribute to the flavor and aroma of many chief herbs and spices, to exert distinct notes in food, i.e., spicy anise- and clove-like to fruit. Asides from their culinary use, they appear to exert general health effects, whereas some effects are specific, e.g., eugenol being a natural local anesthetic. This review represents the most comprehensive overview of phenylpropenes with respect to their chemical structures, different health effects, and their food applications as flavor and food preservatives. Side effects and toxicities of these compounds represent the second main part of this review, as some were reported for certain metabolites generated inside the body. Several metabolic reactions mediating for phenylpropenes metabolism in rodents via cytochrome P450 (CYP450) and sulfotransferase (SULT) enzymes are presented being involved in their toxicities. Such effects can be lessened by influencing their pharmacokinetics through a matrix-derived combination effect via administration of herbal extracts containing SULT inhibitors, i.e., nevadensin in sweet basil. Moreover, structural modification of phenylpropanes appears to improve their effects and broaden their applications. Hence, such review capitalizing on phenylpropenes can help optimize their applications in nutraceuticals, cosmeceuticals, and food applications.

The genus Asarum: A review on phytochemistry, ethnopharmacology, toxicology and pharmacokinetics

ETHNOPHARMACOLOGICAL RELEVANCE

In essentially every quadrant of the globe, many species of genus Asarum are used as a common herbal medicine and appear in many formulas or Kampo. Crude drug from several medicinal plants of genus Asarum (MA) known as Asari Radix et Rhizoma (ARR) has been proven to have the functions of dispelling cold, relieving pain, and reducing phlegm according to Traditional Chinese Medicine (TCM) theory for thousands of years.

AIM OF THE STUDY

This article reviews the ethnopharmacology, phytochemistry, pharmacology, toxicology and metabolic kinetics related research of genus Asarum to evaluate its ethnopharmacology use and future opportunities for research.

MATERIALS AND METHODS

Information on relevant studies of the genus Asarum was gathered via the Internet using Baidu Scholar, Web of Science, Elsevier, ResearchGate, ACS, Pudmed and Chinese National Knowledge Infrastructure (CNKI). Additionally, information was also obtained from some local books, PhD, MS's dissertations and Pharmacopeias.

RESULTS

The genus Asarum has played an important role in herbal treatment. At present, more than 277 compounds have been isolated or identified from genus Asarum. Among them, volatile oil and lignans are the major active constituents and important chemotaxonomic markers. Modern pharmacological studies indicated that genus Asarum and its active compounds possess a wide range of pharmacological effects, especially analgesic, anti-inflammatory, neuroprotective, cardiovascular protection, antitussive, immunosuppressive, anti-tumor, and microbicidal activities.

CONCLUSIONS

Based on this review, therapeutic potential of genus Asarum has been demonstrated with the pharmacological effects on inflammation, CNS, respiratory regulation, cardiovascular diseases, cancer and microbial infection. The available literature showed that the major activities of the genus Asarum can be attributed to the active lignans and essential oils. Further in-depth studies on the aspects of the genus for mechanism of actions, metabolism, pharmacokinetics, toxicology, drug interactions, and clinical trials are still limited, thereby intensive research and assessments should be performed.

Study on the Composition and Physiological Activity of the Essential Oils and Extracts of Cinnamomum camphora Fruit

Supercritical carbon dioxide (SC-CO₂ ), hydrodistillation (HDO), ethanol extraction (EE), and petroleum ether extraction (PE) were used to extract the essential oil and extracts of Cinnamomum camphora fruit in this study. Gas chromatography-mass spectrometry was used to identify the volatile components of essential oils and extracts, and 63 compounds were identified. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assay and Ferric reducing ability of plasma (FRAP) assays and the inhibition experiment of bacteria and fungi (Staphylococcus aureus (S. aureus), Hay bacillus (H. bacillus), Escherichia coli (E. coli), Aspergillus niger (A. niger), Candida albicans (C. albicans)) showed these essential oils and extracts indicated antioxidant and antibacterial activities. S. aureus was the most sensitive to the essential oil (MIC=0.08 mg/ml). Combined with the Brine Shrimp Lethality Test (BSLT) experiment, HDO (LD₅₀ =68.21 μg/ml) was considered to have the most potential natural preservative. Subsequently, the inhibitory mechanism of HDO on bacteria and fungi was explored through extracellular conductivity and SEM, and the possibility of HDO to preserve the freshness of bananas was verified through banana shelf-life experiments. The results suggested these essential oils and extracts of Cinnamomum camphora fruit indicated effectively inhibit the growth of microorganisms on the surface of bananas, extend the shelf-life, and have the potential to become a natural antiseptic ingredient.

Lack of In Vivo Mutagenicity of Acetamide in a 13-Week Comprehensive Toxicity Study Using F344 gpt Delta Rats

Acetamide, a food contaminant, has been shown to induce hepatocellular tumors in rats. However, the mode of action underlying acetamide-induced hepatocarcinogenesis remains unclear. In the current study, we aimed to examine the possible involvement of in vivo mutagenicity in hepatocarcinogenesis of acetamide and evaluate its toxicological profile using a comprehensive medium-term toxicity study in gpt delta rats. Six-week-old male F344 gpt delta rats were given a basal diet containing 0%, 0.625%, 1.25%, or 2.5% acetamide for 13 weeks. In general toxicologic assessment, hepatotoxic parameters in serum, such as aspartate aminotransferase and alanine aminotransferase were significantly changed at the 1.25% group and higher. Histopathological examination of the liver revealed that various changes related to hepatic injury were observed at the 1.25% group and higher. Interestingly, Feulgen-positive cytoplasmic inclusion was frequently observed in hepatocytes in these groups. In the hematopoietic system, red blood cell parameters in plasma, such as mean corpuscular volume and mean corpuscular hemoglobin were significantly changed at the 1.25% group and higher, and decrease of erythroblast in the spleen was observed histopathologically in the 2.5% group. Thus, the no-observed-adverse-effect level of acetamide in this study was 0.625% (equivalent to 394 mg/kg body weight/day). In vivo mutation assays showed that acetamide induced no changes in gpt and red/gam gene mutant frequencies, even at the carcinogenic target site. In contrast, Ki67-positive hepatocytes were increased significantly at carcinogenic doses. Therefore, these results suggested that cell proliferation activity, but not mutagenicity, played crucial roles in acetamide-induced hepatocarcinogenesis in rats.

Background data of 2-year-old male and female F344 gpt delta rats

Although gpt delta rats, as reporter gene-transgenic rats, were originally developed for in vivo mutation assays, they have also been used to evaluate chemical carcinogenesis and comprehensive toxicity. Therefore, it is necessary to accumulate background data on carcinogenicity and general toxicity in gpt delta rats. Here, we investigated the background data of 110-week-old male and female F344 gpt delta rats and wild-type rats. There was no effect of reporter gene transfection on animal survival rates and body weights during the experiment. The relative weight of male gpt delta rat adrenals was significantly higher than that of wild-type rats, possibly due to the higher incidence of pheochromocytoma. There were no intergenotype differences in the incidence of nonneoplastic lesions in both sexes, including chronic progressive nephropathy and focus of cellular alteration in the liver, which had a higher incidence in both genotypes. Additionally, the significantly higher incidence of adrenal pheochromocytoma in male gpt delta rats than that in wild-type rats was likely incidental because of the lack of differences in the incidences of preneoplastic (male and female) and neoplastic (female) adrenal lesions in both genotypes. Other neoplastic lesions in both sexes showed no intergenotype differences in incidence rates, although large granular lymphocytic leukemia in the spleen and Leydig cell tumors in the testes of males showed higher incidence rates. Overall, there were no effects of reporter gene transfection on the spectrum of spontaneous lesions in F344 gpt delta rats, thus supporting their applicability in evaluating chemical toxicity and carcinogenicity.

Screening for Ames mutagenicity of food flavor chemicals by (quantitative) structure-activity relationship

Background

(Quantitative) Structure-Activity Relationship ((Q)SAR) is a promising approach to predict the potential adverse effects of chemicals based on their structure without performing toxicological studies. We evaluate the mutagenicity of food flavor chemicals by (Q) SAR tools, identify potentially mutagenic chemicals, and verify their mutagenicity by actual Ames test.

Results

The Ames mutagenicity of 3942 food flavor chemicals was predicted using two (Q)SAR) tools, DEREK Nexus and CASE Ultra. Three thousand five hundred seventy-five chemicals (91%) were judged to be negative in both (Q) SAR tools, and 75 chemicals (2%) were predicted to be positive in both (Q) SAR tools. When the Ames test was conducted on ten of these positive chemicals, nine showed positive results.

Conclusion

The (Q) SAR method can be used for screening the mutagenicity of food flavors.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41021-020-00171-1.

(+)-Erythro-Δ8'-7S,8R-Dihydroxy-3,3',5'-Trimethoxy-8-O-4'-Neolignan, an Anti-Acne Component in Degreasing Myristica fragrans Houtt

Acne is a common skin condition observed in adolescents. Nutmeg (Myristica fragrans Houtt) (MF) is a well-known traditional Chinese medicine; its major toxic components, safrole and myristicin, are rich in essential oils. Essential oils of MF (MFO) were extracted by hydrodistillation; the residue was extracted using 50% methanol (MFE-M). The minimum inhibitory concentration (MIC) of MFE-M against Cutibacterium acnes and Staphylococcus aureus was 0.64 mg. Four compounds were obtained from MFE-M: myristicin (1), (+)-erythro-Δ^8′-7S,8R- dihydroxy-3,3,5′-trimethoxy-8-O-4′-neolignan (2), (+)-erythro-Δ^8’-7-hydroxy-3,4,3’,5’-tetramethoxy 8-O-4-neolignan (3), and erythro-Δ^8′-7-acetoxy-3,4,3′,5′-tetramethoxy-8-O-4′-neolignan (4). Compound 2 exerted the strongest antimicrobial activity, with MICs of 6.25 and 3.12 μg/mL against C. acnes and S. aureus, respectively. Moreover, 2 inhibited NO, PGE₂, iNOS, and COX-2 levels in RAW 264.7 cells induced by LPS or heat-killed C. acnes; NO production at 50% inhibitory concentrations (IC₅₀) was 11.07 and 11.53 μg/mL, respectively. Myristicin and safrole content was higher in MFO than in MFE-M. MFO and MFE-M caused no skin irritation after a single topical application in Wistar rats. MFE-M, with low safrole and myristicin content, did not cause skin irritation and exhibited an anti-acne effect; moreover, 2 was identified as the active substance. Therefore, MFE-M could be employed to develop anti-acne compounds for use in cosmetics.

Furan Induced Characteristic Glutathione S-Transferase Placental Form-Positive Foci in Terms of Cell Kinetics and Gene Expression

Glutathione S-transferase placental form-positive (GST-P⁺) foci are markers of preneoplastic lesions in rat hepatocarcinogenesis. Our previous studies using reporter gene transgenic rats showed that furan, a hepatocarcinogen in rodents, rapidly induces the formation of GST-P⁺ foci after short exposure without reporter gene mutation. We hypothesized that GST-P⁺ foci induced by furan may have biological characteristics different from those induced by diethylnitrosamine (DEN), a genotoxic hepatocarcinogen. Accordingly, we compared the cell kinetics of GST-P⁺ foci after cessation of DEN treatment and performed comprehensive gene expression in DEN- or furan-induced GST-P⁺ foci. The number and area of DEN-induced GST-P⁺ foci were increased after cessation of treatment, whereas furan decreased these parameters. Size distribution analysis showed that large furan-induced GST-P⁺ foci disappeared after cessation of treatment. Hierarchical cluster analysis showed that all samples from GST-P⁺ foci induced by furan were separated from those induced by DEN. SOX9 expression was upregulated in furan-induced GST-P⁺ foci and was detected by immunohistochemistry in large furan-induced GST-P⁺ foci. Our results indicated that large furan-induced GST-P⁺ foci were quite different from DEN-induced GST-P⁺ foci at the molecular and cellular levels. And one of the properties of disappearing large GST-P⁺ foci were characterized by inclusion of hepatocytes expressing SOX9.

Traditional Herbal Medicine in Mesoamerica: Toward Its Evidence Base for Improving Universal Health Coverage

The quality of health care in Mesoamerica is influenced by its rich cultural diversity and characterized by social inequalities. Especially indigenous and rural communities confront diverse barriers to accessing formal health services, leading to often conflicting plurimedical systems. Fostering integrative medicine is a fundamental pillar for achieving universal health coverage (UHC) for marginalized populations. Recent developments toward health sovereignty in the region are concerned with assessing the role of traditional medicines, and particularly herbal medicines, to foster accessible and culturally pertinent healthcare provision models. In Mesoamerica, as in most regions of the world, a wealth of information on traditional and complementary medicine has been recorded. Yet these data are often scattered, making it difficult for policy makers to regulate and integrate traditionally used botanical products into primary health care. This critical review is based on a quantitative analysis of 28 survey papers focusing on the traditional use of botanical drugs in Mesoamerica used for the compilation of the "Mesoamerican Medicinal Plant Database" (MAMPDB), which includes a total of 12,537 use-records for 2188 plant taxa. Our approach presents a fundamental step toward UHC by presenting a pharmacological and toxicological review of the cross-culturally salient plant taxa and associated botanical drugs used in traditional medicine in Mesoamerica. Especially for native herbal drugs, data about safety and effectiveness are limited. Commonly used cross-culturally salient botanical drugs, which are considered safe but for which data on effectiveness is lacking constitute ideal candidates for treatment outcome studies.

Fabrication of functionalized magnetic microspheres based on monodispersed polystyrene for quantitation of allyl-benzodioxoles coupled with gas chromatography and mass spectrometry

Monodispersed magnetic microspheres were synthesized by the magnetization of the aminized polystyrene cores and the subsequent polymerization of allyl glycidyl ether, divinylbenzene and N-vinyl-2-pyrrolidone, which exhibited excellent monodispersity in aqueous solution and high efficiency for allyl-benzodioxoles extraction. Various techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR) and vibrating sample magnetometry (VSM) were employed to characterize the composites. Coupled with gas chromatography-mass spectrometry (GC-MS), a sensitive and simple magnetic solid phase extraction (MSPE) procedure based on the prepared microspheres was established for determination of allyl-benzodioxoles in cola-flavoured drinks. The factors affecting the extraction procedure, such as pH value, adsorbent amount, adsorption time, desorption solution and desorption time were optimized. The developed method was characterized by a high recovery (spiked at 5 μg L^-1, 25 μg L^-1 and 250 μg L^-1), a low detection limit (0.05 μg L^-1 for safrole and 0.08 μg L^-1 for myristicin), a good linearity (correlation coefficients higher than 0.9990 for both) and a satisfactory repeatability (relative standard deviation below 3.7% for both, n = 3). The approach proposed here was confirmed to be fast and reliable for quantitative analysis of allyl-benzodioxoles in cola samples, especially at a trace level.

Past, Present and Future Directions of gpt delta Rodent Gene Mutation Assays

Genotoxicity is a critical endpoint of toxicity to regulate environmental chemicals. Genotoxic chemicals are believed to have no thresholds for the action and impose genotoxic risk to humans even at very low doses. Therefore, genotoxic carcinogens, which induce tumors via genotoxic mechanisms, are regulated more strictly than non-genotoxic carcinogens, which induce tumors through non-genotoxic mechanisms such as hormonal effects, cell proliferation and cell toxicity. Although Ames bacterial mutagenicity assay is the gold standard to identify genotoxicity of chemicals, the genotoxicity should be further examined in rodents because Ames positive chemicals are not necessarily genotoxic in vivo. To better evaluate the genotoxicity of chemicals in a whole body system, gene mutation assays with gpt delta transgenic mice and rats have been developed. A feature of the assays is to detect point mutations and deletions by two distinct selection methods, ie, gpt and Spi- assays, respectively. The Spi- assay is unique in that it allows analyses of deletions and complex DNA rearrangements induced by double-strand breaks in DNA. Here, I describe the concept of gpt delta gene mutation assays and the application in food safety research, and discuss future perspectives of genotoxicity assays in vivo.

Modified Ames test using a strain expressing human sulfotransferase 1C2 to assess the mutagenicity of methyleugenol

Introduction

Several alkenylbenzenes, including methyleugenol (ME), are present in a wide range of botanicals and exhibit carcinogenic and mutagenic properties. Negative results are generally obtained for alkenylbenzenes in standard in vitro genotoxicity tests, including the Ames test. A lack of mutagenicity observed in such tests is thought to result from impaired metabolic activation of alkenylbenzenes via hydroxylation, with subsequent sulfoconjugation to its ultimate mutagenic or carcinogenic form. Although recent studies have reported the mutagenicity of hydroxylated ME metabolites in the Ames test using modified TA100 strains expressing human sulfotransferases (SULTs), to our knowledge, the detection of ME mutagenicity has not yet been reported.

Findings

Using strain TA100-hSULT1C2, which expresses human SULT1C2, we optimized the protein content of S9 Mix and the pre-incubation time required to promote metabolic activation in the Ames test. This procedure enabled us to obtain a positive response with ME.

Conclusions

We established Ames-test conditions enabling the detection of ME-induced mutagenicity, using a strain expressing human SULT1C2 in the presence of induced-rat S9 Mix. This simple approach will help assess the mutagenicity of other alkenylbenzenes and related chemicals.

Terpene constituents of the leaves of five Vietnamese species of Clausena (Rutaceae)

This article reports the compounds identified in the leaf oils of five Clauseana species growing in Vietnam. The hydrodistilled oils were analysed for their chemical constituents by using gas chromatography-flame ionisation detector and gas chromatography coupled with mass spectrometry. The major compounds identified in Clausena dentata (Willd.) M. Roem. were α-pinene (21.7%), sabinene (18.3%) and β-myrcene (14.3%). Clausena dimidiata Tanaka comprised mainly of safrole (56.9%) and α-terpinolene (22.1%). However, 1-menthone (70.6%) and β-phellandrene (13.0%) were the most abundant compounds of Clausena indica (Dalz.) Oliver. Sesquiterpene compounds represented mainly by β-caryophyllene (16.7%), spathulenol (11.9%) and bicyclogermacrene (7.5%) were the major constituents of Clausena excavata Burm. f., while those of Clausena engleri Tanaka include bicycloelemene (12.1%), bicyclogermacrene (11.0%) and (E)-nerolidol (6.6%). This is the first report on the chemical analysis of essential oils of C. dimidiata and C. engleri.

Lack of nrf2 results in progression of proliferative lesions to neoplasms induced by long-term exposure to non-genotoxic hepatocarcinogens involving oxidative stress

To explore the role of oxidative stress in chemical carcinogenesis driven by non-genotoxic mechanisms, nrf2-deficient (nrf2(-/-)) and nrf2-wild-type (nrf2(+/+)) mice were exposed to pentachlorophenol (PCP) at concentrations of 600 or 1200 ppm for 60 weeks, or piperonyl butoxide (PBO) at concentrations of 3000 or 6000 ppm in the diet for 52 weeks, respectively. Additional studies were performed to examine 8-hydroxydeoxyguanosine (8-OHdG) levels in liver DNA and hepatotoxicological parameters in serum following 8 weeks of exposure of each group to PBO at the same doses as in the long-term study. Exposure to 600 ppm PCP caused cholangiofibrosis (CF) only in nrf2(-/-) mice, while 1200 ppm PCP induced CF in both genotypes. Moreover, cholangiocarcinomas were found with significant incidence only in nrf2(-/-) mice treated with 1200 ppm PCP. Short-term exposure to 6000 ppm PBO caused significant elevation of 8-OHdG levels in both genotypes, while exposure to 3000 ppm caused a significant increase in 8-OHdG only in nrf2(-/-) mice. There were no inter-genotype changes in the incidences of regenerative hepatocellular hyperplasia (RHH) following long-term exposure to PBO. However, the incidence and multiplicity of hepatocellular adenomas, especially those observed in RHH, were much higher in nrf2-/- mice treated with 6000 ppm PBO than in nrf2+/+ mice treated with 6000 ppm PBO. Therefore, oxidative stress generated through PCP or PBO metabolism may promote the proliferation and progression of preneoplastic lesions to neoplasms.

Development of a Medium-term Animal Model Using gpt Delta Rats to Evaluate Chemical Carcinogenicity and Genotoxicity

In this study, the potential for development of an animal model (GPG46) capable of rapidly detecting chemical carcinogenicity and the underlying mechanisms of action were examined in gpt delta rats using a reporter gene assay to detect mutations and a medium-term rat liver bioassay to detect tumor promotion. The tentative protocol for the GPG46 model was developed based on the results of dose-response exposure to diethylnitrosamine (DEN) and treatment with phenobarbital over time following DEN administration. Briefly, gpt delta rats were exposed to various chemicals for 4 weeks, followed by a partial hepatectomy (PH) to collect samples for an in vivo mutation assay. The mutant frequencies (MFs) of the reporter genes were examined as an indication of tumor initiation. A single intraperitoneal (ip) injection of 10 mg/kg DEN was administered to rats 18 h after the PH to initiate hepatocytes. Tumor-promoting activity was evaluated based on the development of glutathione S-transferase placental form (GST-P)-positive foci at week 10. The genotoxic carcinogens 2-acetylaminofluorene (2-AAF), 2-amino-3-methylimidazo [4,5-f] quinolone (IQ) and safrole (SF), the non-genotoxic carcinogens piperonyl butoxide (PBO) and phenytoin (PHE), the non-carcinogen acetaminophen (APAP) and the genotoxic non-hepatocarcinogen aristolochic acid (AA) were tested to validate the GPG46 model. The validation results indicate that the GPG46 model could be a powerful tool in understanding chemical carcinogenesis and provide valuable information regarding human risk hazards.