An investigation of micronucleus and mutation induction by oxazepam in mammalian cells

[Genotoxicity of psychotropic drugs in experimental and clinical studies]

The analysis of experimental data on the study of the genotoxic activity of psychotropic drugs published over the past 25 years has been carried out. It has been shown that the information describing the genotoxicity of psychotropic drugs is characterized by fragmentation, contradictions, and the conditions for their experimental production often do not meet modern requirements. Conclusions about the presence or absence of genotoxic properties can be made only for 9.6% 94 examined drugs. The need for a large-scale systematic reassessment of the genotoxicity of psychotropic drugs, especially drugs of the first generation, on the basis of modern methodology, including studies of mutagen-modifying activity, has been proven. The expediency of monitoring the genotoxic status of patients receiving psychotropic drugs is emphasized, which should contribute to an adequate assessment of the genotoxic risk of their use and objectification of approaches when choosing a drug for the safe therapy. The urgency of conducting research to determine the role of primary DNA damage in the pathogenesis of mental illnesses has been substantiated.

Potential contribution of benzodiazepine abuse in the development of a bladder sarcomatoid carcinoma: A case report

Invasive urothelial carcinoma has a propensity for disparate differentiation and presentation of morphological variants. Sarcomatoid carcinoma (SaC) of the bladder is an extremely uncommon and aggressive variant of bladder cancer. An accurate diagnosis for this variant is necessary, but at times difficult. Immunohistochemistry can increase the diagnostic accuracy for SaC. The therapeutic approaches currently adopted for the treatment of SaC are similar to those used for the urothelial variant: Surgery, chemotherapy and radiation therapy. To date, however, there exists no standard treatment due to the lack of knowledge regarding the pathogenesis of SaC. Future research is required to focus on this rare histological tumor subtype in order to identify more effective treatment strategies. The present study reported an unusual case of bladder SaC in a woman aged 48 years, who was a non-smoker with a long history of benzodiazepine abuse. Although saving the patient's life was a priority, it was also essential to consider her subsequent quality of life. For that reason, the patient underwent a cystectomy with orthotopic neobladder reconstruction using ileum, followed by chemotherapy. At the 7 month follow-up, the patient was still alive, in complete remission and had normal bladder function. The present case report shows the potential contribution of benzodiazepine abuse in the development of a bladder sarcomatoid carcinoma, a rare variant of BC, whose early detection and accurate diagnosis are key to attaining satisfactory treatment outcomes and a favorable prognosis for patients.

Is long-term use of benzodiazepine a risk for cancer?

The carcinogenicity of benzodiazepines (BZDs) is still unclear. We aimed to assess whether long-term benzodiazepines use is risk for cancer.We conducted a longitudinal population-based case-control study by using 12 years from Taiwan National Health Insurance database and investigated the association between BZDs use and cancer risk of people aged over 20 years. During the study period, 42,500 cases diagnosed with cancer were identified and analyzed for BZDs use. For each case, six eligible controls matched for age, sex, and the index date (ie, free of any cancer in the date of case diagnosis) by using propensity score. For appropriate risk estimation, we observed the outcomes according to their length of exposure (LOE) and defined daily dose (DDD). To mimic bias, we adjusted with potential confounding factors such as medications and comorbid diseases which could influence for cancer risk during the study period. The data was analyzed by using Cox proportional hazard regression and conditional logistic regression.The finding unveils benzodiazepines use into safe and unsafe groups for their carcinogenicity. The use of diazepam (HR, 0.96; 95%CI, 0.92-1.00), chlorodizepoxide (HR, 0.98; 95%CI, 0.92-1.04), medazepam (HR, 1.01; 95%CI, 0.84-1.21), nitrazepam (HR, 1.06; 95%CI, 0.98-1.14), oxazepam (HR, 1.05; 95%CI, 0.94-1.17) found safer among BZDs. However, clonazepam (HR, 1.15; 95%CI, 1.09-1.22) were associated with a higher risk for cancers. Moreover, specific cancer risk among BZDs use was observed significantly increased 98% for brain, 25% for colorectal, and 10% for lung, as compared with non-BZDs use.Diazepam, chlordiazepoxide, medazepam, nitrazepam, and oxazepam are safe among BZDs use for cancer risk. Our findings could help physicians to select safer BZDs and provide an evidence on the carcinogenic effect of benzodiazepines use by considering the LOE and DDD for further research.

ECVAM retrospective validation of in vitro micronucleus test (MNT)

In the past decade several studies comparing the in vitro chromosome aberration test (CAT) and the in vitro micronucleus test (MNT) were performed. A high correlation was observed in each of the studies (>85%); however, no formal validation for the micronucleus in vitro assay had been carried out. Therefore, a working group was established by the European Centre for the Validation of Alternative Methods (ECVAM) to perform a retrospective validation of the existing data, in order to evaluate the validity of the in vitro MNT on the basis of the modular validation approach. The primary focus of this retrospective validation was on the evaluation of the potential of the in vitro MNT as alternative to the standard in vitro CAT. The working group evaluated, in a first step, the available published data and came to the conclusion that two studies [German ring trial, von der Hude, W., Kalweit, S., Engelhardt, G. et al. (2000) In-vitro micronucleus assay with Chinese hamster V79 cells: results of a collaborative study with 26 chemicals. Mutat. Res., 468, 137–163, and SFTG International Collaborative Study, Lorge, E., Thybaud, V., Aardema, M., Oliver, J., Wataka, A., Lorenzon, G. and Marzin, D. (2006) SFTG International Collaborative Study on in-vitro micronucleus test I. General conditions and overall conclusions of the study. Mutat. Res., 607, 13–36] met the criteria for a retrospective validation according to the criteria previously defined by the working group. These two studies were evaluated in depth (including the reanalysis of raw data) and provided the information required for assessing the reliability (reproducibility) of the test. For the assessment of the concordance between the in vitro MNT and the in vitro CAT, additional published data were considered. Based on this retrospective validation, the ECVAM Validation Management Team concluded that the in vitro MNT is reliable and relevant and can therefore be used as an alternative method to the in vitro CAT. Following peer review, these conclusions were formally endorsed by the ECVAM Scientific Advisory Committee.

Evaluation of the ability of a battery of three in vitro genotoxicity tests to discriminate rodent carcinogens and non-carcinogens I. Sensitivity, specificity and relative predictivity

The performance of a battery of three of the most commonly used in vitro genotoxicity tests--Ames+mouse lymphoma assay (MLA)+in vitro micronucleus (MN) or chromosomal aberrations (CA) test--has been evaluated for its ability to discriminate rodent carcinogens and non-carcinogens, from a large database of over 700 chemicals compiled from the CPDB ("Gold"), NTP, IARC and other publications. We re-evaluated many (113 MLA and 30 CA) previously published genotoxicity results in order to categorise the performance of these assays using the response categories we established. The sensitivity of the three-test battery was high. Of the 553 carcinogens for which there were valid genotoxicity data, 93% of the rodent carcinogens evaluated in at least one assay gave positive results in at least one of the three tests. Combinations of two and three test systems had greater sensitivity than individual tests resulting in sensitivities of around 90% or more, depending on test combination. Only 19 carcinogens (out of 206 tested in all three tests, considering CA and MN as alternatives) gave consistently negative results in a full three-test battery. Most were either carcinogenic via a non-genotoxic mechanism (liver enzyme inducers, peroxisome proliferators, hormonal carcinogens) considered not necessarily relevant for humans, or were extremely weak (presumed) genotoxic carcinogens (e.g. N-nitrosodiphenylamine). Two carcinogens (5-chloro-o-toluidine, 1,1,2,2-tetrachloroethane) may have a genotoxic element to their carcinogenicity and may have been expected to produce positive results somewhere in the battery. We identified 183 chemicals that were non-carcinogenic after testing in both male and female rats and mice. There were genotoxicity data on 177 of these. The specificity of the Ames test was reasonable (73.9%), but all mammalian cell tests had very low specificity (i.e. below 45%), and this declined to extremely low levels in combinations of two and three test systems. When all three tests were performed, 75-95% of non-carcinogens gave positive (i.e. false positive) results in at least one test in the battery. The extremely low specificity highlights the importance of understanding the mechanism by which genotoxicity may be induced (whether it is relevant for the whole animal or human) and using weight of evidence approaches to assess the carcinogenic risk from a positive genotoxicity signal. It also highlights deficiencies in the current prediction from and understanding of such in vitro results for the in vivo situation. It may even signal the need for either a reassessment of the conditions and criteria for positive results (cytotoxicity, solubility, etc.) or the development and use of a completely new set of in vitro tests (e.g. mutation in transgenic cell lines, systems with inherent metabolic activity avoiding the use of S9, measurement of genetic changes in more cancer-relevant genes or hotspots of genes, etc.). It was very difficult to assess the performance of the in vitro MN test, particularly in combination with other assays, because the published database for this assay is relatively small at this time. The specificity values for the in vitro MN assay may improve if data from a larger proportion of the known non-carcinogens becomes available, and a larger published database of results with the MN assay is urgently needed if this test is to be appreciated for regulatory use. However, specificity levels of <50% will still be unacceptable. Despite these issues, by adopting a relative predictivity (RP) measure (ratio of real:false results), it was possible to establish that positive results in all three tests indicate the chemical is greater than three times more likely to be a rodent carcinogen than a non-carcinogen. Likewise, negative results in all three tests indicate the chemical is greater than two times more likely to be a rodent non-carcinogen than a carcinogen. This RP measure is considered a useful tool for industry to assess the likelihood of a chemical possessing carcinogenic potential from batteries of positive or negative results.

Comparison of the mutant frequencies and mutation spectra of three non-genotoxic carcinogens, oxazepam, phenobarbital, and Wyeth 14,643, at the lambdacII locus in Big Blue transgenic mice

Oxazepam (OX), a widely used benzodiazepine anxiolytic, phenobarbital (PHE), a drug used for convulsive disorders, and Wyeth 14,643 (WY; [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid), a hypolipidemic agent, are all hepatocarcinogenic in B6C3F1 mice. They have been classified as "non-genotoxic" carcinogens since they are non-DNA reactive in in vitro assays and are either negative or weakly positive in Salmonella typhimurium (Ames assay). Male B6C3F1 Big Blue(R) transgenic mice were fed 2500 ppm of OX or PHE or 500 ppm of WY in their diet, while a control group of mice received diet alone for 180 days. The mutant frequency (MF) of cII in the control mice, after correction for clonality, was 6.2 +/- 2.8 x 10(-5). The MF values for mice fed OX, PHE, and WY were 10.0 +/- 3.6 x 10(-5) (P < 0.05), 7.9 +/- 1.3 x 10(-5) (P = 0.1) and 17.4 +/- 4.2 x 10(-5) (P < 0.01), respectively. The mutation spectrum (MS) at cII from the PHE-fed mice was significantly different (P < 0.05) from that of the control mice even though the MF was not, whereas the MS spectra of mice fed OX (P = 0.4) and WY (P = 0.7) were not significantly different. The PHE-derived spectrum differed from the spontaneous spectrum in the lower occurrence of G:C>C:G transversions (17 vs 1.6%) and the higher incidence of A:T>T:A transversions (3.4 vs 9.5%). Prior to correction for clonal expansion, each treated group exhibited a high incidence of frameshift mutations at the homopolymeric run of guanines at bp 179-184 (OX 21%, PHE 21%, WY 16% of the total mutations); this was not the case with the control group (6%). Even after clonal correction, more than 10% of the mutations were frameshifts in the treated mice, while 5% were frameshifts in the control mice. Despite this hypersensitive region of the gene, our findings suggest that the cII locus is less sensitive than the lacI locus to mutation induction by non-DNA reactive carcinogens.

Induction of micronuclei in Syrian hamster embryo cells: comparison to results in the SHE cell transformation assay for National Toxicology Program test chemicals

Sixteen chemicals currently being tested in National Toxicology Program (NTP) carcinogenicity studies were evaluated in the Syrian hamster embryo (SHE) cell in vitro micronucleus assay. Results from these studies were compared to the results from the SHE cell transformation assay for the same chemicals The overall concordance between induction of micronuclei and transformation of SHE cells was 56%, which is far lower that the 93% concordance between these two tests reported previously by Fritzenschaf et al. (1993; Mutation Res. 319, 47-53). The difference between our results appears to be due to differences in the types of chemicals in the two studies. Overall, there is good agreement between the SHE cell micronucleus and transformation assays for mutagenic chemicals, but, as our study highlights, the SHE cell transformation assay has the added utility of detecting nonmutagenic carcinogens. The utility of a multi-endpoint assessment in SHE cells for carcinogen screening is discussed.

Genetic toxicology of four commonly used benzodiazepines: a review

Benzodiazepines are a group of drugs which have been extensively used for their activities as an anti-anxiety, sedative, muscle relaxant and anti-convulsant. Benzodiazepines at present are the most commonly prescribed drugs. Some of these drugs are teratogenic and also carcinogenic in experimental animals. The wide human exposure to this group of drugs throughout the world is of great concern for human health. In the present review, we have attempted to evaluate and update the mutagenic and genotoxic effects of four of the most commonly used benzodiazepines, i.e., chlordiazepoxide (CDZ), diazepam (DZ), nitrazepam (NZ) and oxazepam (OZ) based on available literature.

Oxidative biotransformation of oxazepam to reactive and nonreactive products in rat, mouse and human microsomes

1. The oxidative metabolism of oxazepam by human, B6C3F1 mouse and F344 rat microsomes was examined. The major metabolite in all three species was 6-chloro-4-phenyl-2(1H)-quinazolinecarboxylic acid (CPQ-carboxylic acid). In addition, rat microsomes produced 4'-hydroxyoxazepam and oxazepam-dihydrodiol in NADPH-containing incubations. 2. Covalent protein adducts were increased by the addition of NADPH to rat and mouse microsomes but not human microsomes. The magnitude of adduct formation was rats > mice > humans. 3. Formation of oxazepam-dihydrodiol was reduced by the addition of cyclohexene oxide and GSH to the incubations. Two additional metabolites were produced under these conditions. One of these was tentatively identified as a GSH conjugate. Covalent adduct formation was unaffected by GSH or cyclohexene oxide. 4. These results suggest that adduct formation occurred via an unknown reactive product rather than via oxazepam-epoxide, and that the relative rates of oxidative metabolism in vitro parallel that in vivo for the three species examined.

In situ and suspension protocols for chemically-induced mutation at the tk locus in L5178Y MOLY cells: dose response and colony size distribution

We used EMS up to concentrations of 0.25 microliters/ml (292 micrograms/ml) to induce mutations at the tk locus in L5178Y MOLY cells, measured the cellular response by the in situ mutation assay protocol and compared these results to those obtained in a concomitant suspension assay. EMS induced mutagenic responses with both protocols. The mutant fraction for the solvent control was 89 mutants per million viable colonies for the suspension protocol and 426 mutations per million viable cells plated for the in situ protocol. These numbers increase to 447 and 2073 respectively, with 0.25 microliter/ml EMS treatment. Sizing curves indicated that the in situ protocol detected a greater proportion of smaller colonies than did the suspension protocol. Not only were the number of small colonies greater than large colonies in the in situ protocol, but their rate of increase was also slightly higher than that of the large colonies. The in situ protocol also reduces the time and cost of experimentally performing the assay compared to the suspension protocol. In this paper we compare the use of the suspension and in situ protocols to measure chemically-induced mutations and demonstrate that the latter method detects a larger fraction of induced mutations at the tk locus in L5178Y MOLY cells.