Psychotropic drugs: evaluation of mutagenic effect

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Chromosomal aberrations induced by imipramine and desipramine in mouse

Imipramine (IMI) and desipramine (DES) are two drugs widely used for the treatment of depression as well as for other diseases. In the present study, we determined their capacity to induce chromosomal aberrations in mouse bone marrow cells. Three doses of each compound were tested and their results were compared with the frequency of chromosomal aberrations obtained in a control group as well as with a group treated with cyclophosphamide. Our results showed a significant increase in chromosome damage with the doses tested for each compound: 7, 20, and 60 mg/kg in the case of IMI, and 2, 20, and 60 mg/kg as regards DES. This last drug induced stronger chromosomal damage than IMI. Our results agree with previous studies regarding the induction of micronuclei and sister chromatid exchanges by the drugs in mouse and suggest caution with respect to their use in long-term treatments.

On the Mechanism of Hepatocarcinogenesis of Benzodiazepines: Evidence that Diazepam and Oxazepam are CYP2B Inducers in Rats, and both CYP2B and CYP4A Inducers in Mice

The aim of this study was to evaluate diazepam and oxazepam as cytochrome P450 inducers at doses previously shown to cause liver tumors in mice but not rats. In rats, diazepam and oxazepam induced CYP2B, and were as effective as phenobarbital despite lacking phenobarbital's tumor-promoting effect in rats. In mice, diazepam and oxazepam induced both CYP2B and CYP4A at dietary doses associated with liver tumor formation. It remains to be determined why diazepam and oxazepam induce CYP4A in mice but not rats and whether this difference accounts for the apparent species difference in the tumor-promoting activity of diazepam and oxazepam.

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.

DNA damage in children treated with imipramine for primary nocturnal enuresis

BACKGROUND

Despite the fact that primary nocturnal enuresis (PNE) is self-limited and pathologically benign, the emotional stress and inconvenience that it produces, warrants treatment. Imipramine is one of the widely used drugs in PNE treatment. Although some mutagenic effects were suggested in imipramine administration, this toxicity has never been investigated in enuretic patients. The aim of this study was to evaluate the association of exposure to imipramine with DNA damage.

METHODS

Thirty-five children treated with imipramine for at least 4.5 months who were in otherwise good health were accepted into the investigation. Twenty healthy sisters or brothers of the patients who did not use any long-term drugs were studied simultaneously as the control group. Comet assay was used to evaluate DNA damage.

RESULTS

Damaged (limited and extensive migrated) cells of the enuretic children who were taking imipramine were statically higher than that of the control group (P < 0.05) indicating a detectable DNA damaging effect of imipramine in human lymphocytes.

CONCLUSIONS

Our finding suggests that the difference in comet scores between two groups was induced by the imipramine treatment. The other possibility to be considered is the psychological stress of the children who were concerned by the symptoms and their parent's anxiety. As our preliminary data were based on a limited number of children, further research is needed considering the importance of this possible toxic effects which may be associated with mutagenicity.

Sister chromatid exchanges produced by imipramine and desipramine in mouse bone marrow cells treated in vivo

Imipramine and desipramine are two widely used tricyclic antidepressants which have shown conflicting results in regard to their in vitro genotoxic evaluation. The aim of this investigation was to determine the capacity of these compounds to induce in vivo sister-chromatid exchanges (SCEs) in mouse bone marrow cells. For each compound, the animals were organized in five groups constituted by five individuals. They were intraperitoneally (ip) administered with the test substances as follows: a negative control group treated with 0.4 ml of distilled water, a positive control group administered with cyclophosphamide (70 mg/kg), three groups treated with imipramine (7, 20 and 60 mg/kg), and three other groups treated with desipramine (2, 20 and 60 mg/kg). The general procedure included the subcutaneous implantation to each mouse of a 5-bromodesoxyuridine tablet (45 mg), and 1 h later, the administration of the chemicals involved. Twenty-one hours after the tablet implantation, the mice received colchicine, and 3 h later their femoral bone marrow was obtained in KCL, fixed, and stained with the Hoechst-Giemsa method. The results showed that both compounds were SCE inducers, starting from the second tested dose. The response of these compounds was dose-dependent, and showed that the highest tested dose increased about four times the SCE control level. The cellular proliferation kinetics was not affected by the chemicals, and the mitotic indexes were slightly diminished with the highest dose. These results indicate an in vivo genotoxic potential for both chemicals, and suggest that it is pertinent to follow their evaluation in other models.

Review of the genotoxic properties of chlorpromazine and related phenothiazines

Chlorpromazine and related phenothiazine drugs have been used in human and veterinary medications for more than 40 years, predominantly as psychotropic agents. Genotoxicity reports are in many cases of relatively antiquated test design. Overall there appears to be no genotoxic activity associated with these drugs when tested under standard conditions. Limited evidence for the potential to form mutagenic nitrosation products and some indication for the ability to modulate the genotoxic action of various mutagens have been presented in the literature. UV irradiation of chlorpromazine and other chlorinated derivatives produces reactive free radicals which possess DNA damaging properties. Induction of gene mutation and chromosomal aberrations have been observed in appropriately designed photomutagenesis experiments. Enhancement but also reduction of UV induced skin tumour formation by chlorpromazine have been found. The decisive factor for the discrepant actions has not been recognized. It is clearly advisable to avoid extensive UV exposure during therapy with these drugs.

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.

Structure-activity relationships of tricyclic antidepressants and related compounds in the wing somatic mutation and recombination test of Drosophila melanogaster

Four antidepressants and one neuroleptic drug were tested for genotoxicity using the somatic mutation and recombination test (SMART) in wing cells of Drosophila melanogaster. Three-day-old larvae trans-heterozygous for two linked recessive wing hair mutations (multiple wing hairs and flare) were fed the test compounds in water or solvents mixed with a standard dry food for 48 h. Wings of the emerging adult flies were scored for the presence of spots of mutant cells which can result from either somatic mutation or mitotic recombination. The tricyclic antidepressant clomipramine, which is closely related to imipramine (previously shown to be genotoxic in somatic cells of Drosophila), was clearly genotoxic at concentrations above 10 mM. The structurally related antidepressants lofepramine and mianserin were positive only at 100 mM which is the maximum tolerated dose. The antidepressant maprotiline and the antipsychotic chlorpromazine, which are distinguished from the other compounds by a 6-membered central ring instead of a 7-membered one, were not genotoxic in the same dose range. These results lend further support for the hypothesis that an N atom in the heterocyclic 7-membered ring of the tricyclic molecule is responsible for the genotoxic property of the compounds in Drosophila.

Cytogenetic effects of diazepam in peripheral lymphocytes of self-poisoned persons

The frequencies of chromosomal aberrations and of micronuclei were determined in lymphocyte cultures of 25 patients who attempted suicide with diazepam, 6-12 h, 72 h and 30 days after self-poisoning. These data were compared with those of healthy controls. The frequencies of numerical aberrations showed a significant increase immediately after self-poisoning. However, this effect could not be detected on the 3rd and 30th days after self-poisoning.

Genotoxicity evaluation of five tricyclic antidepressants in the wing somatic mutation and recombination test in Drosophila melanogaster

Five tricyclic antidepressants were tested for genotoxicity using the somatic mutation and recombination test (SMART) in wing cells of Drosophila melanogaster. Three-day-old larvae trans-heterozygous for 2 linked recessive wing hair mutants (multiple wing hairs and flare) were fed the test compounds in water mixed with a standard dry food for 48 h. Wings of the emerging adult flies were scored for the presence of spots of mutant cells which can be the consequence of either somatic mutation or mitotic recombination. Desipramine and imipramine were clearly genotoxic at concentrations above 1 mM whereas amitriptyline, nortriptyline and protriptyline were not genotoxic at concentrations up to 100 mM. This seems to implicate the nitrogen atom at position 5 in the 7-membered ring of the tricyclic molecule as being responsible for the genotoxic property of the compounds in Drosophila.

Genotoxicity evaluation of the tricyclic antidepressants amitriptyline and imipramine using human lymphocyte cultures

Two tricyclic antidepressants, amitriptyline and imipramine, were evaluated for their in vitro cytogenetic effects in human lymphocyte cultures. Peripheral blood cultures from three normal healthy donors were set up for 72 hr for each of the drugs. The drugs were added at the start (72-hr exposure), 24 hr (48-hr exposure), and 48 hr (24-hr exposure) after initiation of the cultures. The concentrations evaluated at each exposure time were 50, 250, 1,000, and 10,000 ng/ml for amitriptyline and 25, 500, and 5,000 ng/ml for imipramine. The first two concentrations correspond to the plasma levels of the respective drugs after therapeutic doses. All treatments for a donor were given at the same time. Untreated cultures served as controls for the baseline frequency of the parameters assayed. The parameters assayed were chromosome aberrations, mitotic index, and sister chromatid exchanges (SCEs). Amitriptyline was found to be nongenotoxic at plasma levels by all the parameters assayed. However, frequencies of chromosome aberrations and SCEs were significantly increased at concentrations 4 and 40 times the plasma level (1,000 and 10,000 ng/ml) although the actual increases was small. The mitotic index was not affected at any concentration. Through imipramine showed a significant increase in chromosome damage at the upper plasma level and at concentrations higher than that, SCE frequency was significantly increased only at concentration higher than the plasma level (5,000 ng/ml), the actual increase being small for both these parameters. The mitotic index was not affected at any concentration. These results suggest that amitriptyline may be a slightly safer drug than imipramine from a genetic point of view.