Mutagenicity of pyrrolizidine alkaloids in the Salmonella/mammalian-microsome test

Transplacental micronucleus inducing ability of arecoline, a betel nut alkaloid, in mice

Arecoline, a major betel nut alkaloid, was tested for its effectiveness in inducing micronuclei in fetal mouse blood after transplacental exposure late in the gestation period. Positive results were obtained and a linear dose-response relationship was expressed when pregnant mice were treated with arecoline at dose levels of 20, 40 and 80 mg/kg and micronucleated polychromatic erythrocytes from fetal blood were subsequently analysed.

The SOS Chromotest, a colorimetric bacterial assay for genotoxins: validation study with 83 compounds

The SOS Chromotest is a simple bacterial colorimetric assay for genotoxicity. It is based on the measure of the induction of sfiA, a gene controlled by the general repressor of the SOS system in E. coli. Expression of sfiA is monitored by means of a gene fusion with lacZ, the structural gene for beta-galactosidase. We have examined 83 compounds of various chemical classes with the SOS Chromotest using a standard procedure. Comparison of the results with those obtained in the Mutatest (the Ames test) showed that most (90%) of the mutagenic compounds were also SOS inducers. For these compounds a quantitative correlation was observed between the mutagenic potency and the SOS-inducing potency (SOSIP). The case of the 10% remaining compounds giving conflicting results in the two tests is discussed. Sensitivity, specificity and accuracy for carcinogenicity prediction have been evaluated for the SOS Chromotest and the Mutatest using 73 chemicals for which carcinogenicity data were available. In spite of some differences, similar results were obtained in the two tests. The present data indicate that the SOS Chromotest has many practical advantages and may be used as a primary screening tool or as part of a battery of short-term tests for carcinogens.

Induction of SCEs by some pyrrolizidine alkaloids in V79 Chinese hamster cells co-cultured with chick embryo hepatocytes

Genotoxicity of heliotrine, monocrotaline, seneciphylline and senkirkine was studied with the sister-chromatid exchange assay in V79 Chinese hamster cells. Exposure to these pyrrolizidine alkaloids, in the presence of co-cultured primary chick embryo hepatocytes, resulted in a high induction of SCEs. It was also shown for heliotrine that co-cultivation with chick embryo hepatocytes resulted in a much higher response than addition of activated rat-liver homogenate to the test medium.

Enzymatic activation of chemicals to toxic metabolites

A variety of enzymes function in the oxygenation, oxidation-reduction, conjugation, and hydrolysis of drugs and other foreign chemicals. Often these enzymes detoxicate chemicals to prevent detrimental effects. In this review we will, however, concentrate on cases in which metabolism activates chemicals to reactive species which cause cellular damage. Particular attention will be given to mixed-function oxidases, which carry out a variety of oxygenations, as well as other reactions. (We will focus on cellular toxicity as opposed to initiation of tumorigenesis in this review.) In many cases, considerable circumstantial evidence exists linking these enzymes to enhanced toxicity of chemicals, although causal relationships have seldom been demonstrated. Further, in very few cases is the explicit cause of toxicity known. Modification of critical protein residues is suspected, although oxidative stress may also be involved in some cases. We discuss general aspects of mechanisms of toxic action, briefly list all cases in which metabolism is suspected to play a role in enhancing toxicity, and review a few examples in detail where substantial chemical and enzymatic information is available. The latter instances would involve knowledge of the enzymes involved, chemical evidence on the structures of the reactive metabolites, identification of adducts, and some inference into the biological processes which are effected to elicit toxicity. We consider, in this regard, vinyl halides (which have been a focus in our own laboratory), acetaminophen, pyrrolizidine alkaloids, and fluoroxene.

Mutagenic/carcinogenic hazards in a cold-rolling steel plant exposed to mineral oils: environmental monitoring phase

A survey was carried out in a cold-rolling steel plant exposed to mineral oils to study the mutagenic/carcinogenic hazards, following a coupled environmental/biological monitoring. The present paper deals only with the environmental phase by determining polycyclic aromatic hydrocarbons (PAH) and applying a mutagenicity test (Ames test), and includes the following steps: (a) work process and environment study; (b) sampling and analysing mineral oils before and after use (PAH determination and mutagenicity analysis); (c) sampling and analysing oil mist (TWA determination, PAH determination and mutagenicity analysis). The results showed that: (1) both unused and used (recycled) mineral oils contained only trace amounts of PAH and were not mutagenic; (2) the TWA concentrations of oil mists were lower than the TLV (less than 5 mg/m3); (3) oil mists contained only trace amounts of PAH and were not mutagenic. The authors suggest that these results could be due to the moderate temperature of the oil during the work process and that there is a relationship between low PAH content and absence of mutagenicity in the oils and air samples.

An evaluation of Salmonella (Ames) test data in the published literature: application of statistical procedures and analysis of mutagenic potency

We searched the published literature for Salmonella test data on some 450 chemicals. Only 137 of more than 400 articles containing original data satisfied minimum criteria for a quantitative analysis [1751 experiments, comprising data on 152 chemicals (Table 1)]. Many of these papers did not report basic information about the test protocol (Table 2). We used previously described statistical procedures (Bernstein et al., 1982) to estimate the initial slopes of the dose-response curves and corresponding standard errors. We also applied tests for significance and linear goodness-of-fit. We then used the results of these analyses to examine several issues: (1) Linearity of the low dose region of the dose-response curve. We found that the overwhelming majority of curves were linear, though ability to detect non-linearity of dose-response curves in the standard plate test is only limited. 7% of all experiments to which the goodness-of-fit test was applied were curves of increasing slope, and with a few possible exceptions, these were not obviously associated with any particular mutagens, even those generally considered to produce non-linear effects such as MNNG and EMS (Table 3). (2) Performance of the statistical test for significance. Results of the statistical test for significance of the dose-response were compared with author's opinions as to positivity. In almost all cases (94%) results of the statistical test and authors opinions were the same. In the examples of conflicting opinions, the reasons were: (a) the statistical test places more weight than do most authors on the presence of a linear dose-response; (b) most authors tend to require at least a 2-fold increase over the spontaneous background for 'significance', and (c) when the number of spontaneous revertants is small (e.g., TA1537), authors tend to require a larger increase in induced revertants than when the spontaneous background is large, whereas the statistical procedure makes no such distinction. These factors result in the statistical test tending to identify more experiments as positive than do authors, provided there is a linear dose-response, and authors tending to judge more experiments as positive when the dose-response is not linear. (3) Reproducibility. Among the 1751 experiments there were 122 data-sets (a total of 333 experiments) in which the same chemical was tested by two or more different laboratories under the same protocol. 21 of the 122 data-sets had some disagreement between experiments as to whether results were positive or negative (Table 4).(ABSTRACT TRUNCATED AT 400 WORDS)

Mutagenic activity of the pyrrolizidine alkaloids seneciphylline and senkirkine in Drosophila and their transfer into rat milk

Seneciphylline and senkirkine, two pyrrolizidine alkaloids that occur in animal feeds and medicinal herbs, respectively, have been tested for their ability to produce sex-linked recessive lethals in males of Drosophila melanogaster using the Basc test (3-day feeding method). Seneciphylline was found to be mutagenic at concentrations of 10(-5), 10(-4) and 10(-3)M, which produced 3.8% sex-linked recessive lethals (983 chromosomes tested). 9.0% (708) and 15.3% (327), respectively. Senkirkine (10(-5)M) produced 4.4% sex-linked recessive lethals (2541 chromosomes tested) against 0.17% (9081) in controls. Brood pattern analysis with senkirkine showed maximum sensitivity in the late spermatid stage of spermatogenesis, which agrees with evidence that pyrrolizidine alkaloids act as indirect mutagens. Flies fed with milk from lactating rats given an oral dose of 25 mg seneciphylline/kg showed 1.2% sex-linked recessive lethals (1477 chromosomes tested), against 0.3% (1533) in controls.

Influence of caffeine on arecoline-induced SCE in mouse bone-marrow cells in vivo

The effect of exposure of mice for 5, 10 and 15 days to arecoline or/and caffeine on the frequency of sister-chromatid exchanges (SCEs) in bone-marrow cells was evaluated by using the fluorescence plus Giemsa technique. There was a significant increase in the frequency of SCEs after exposure to either arecoline or caffeine. When these two alkaloids were given in combination, the SCE frequency-enhancing effect was additive. The implications of coffee/tea drinking and betel chewing on oral cancer are discussed.

Mutagenic effects of aqueous extracts of Symphytum officinale L. and of its alkaloidal fractions

Symphytum officinale L. (Boraginaceae) is a medicinal plant widely used in therapy. It roots, described in the Polish Pharmacopoeia as Radix symphyti, are recommended as expectorants, especially for children. Aqueous solutions of three alkaloid fractions obtained from infusions of Symphytum officinale L. root were tested for their antimitotic and mutagenic activity in meristematic cells of the lateral roots of Vicia faba L., var minor. Lasiocarpine, a proven carcinogen, served as a positive control. Mutagenic effects were induced by lasiocarpine, by the alkaloidal fraction I and by diluted infusions from Radix symphyti. Fraction III had only antimitotic effect. The biological activity of the tested solutions is discussed in relation to the relevant literature.

Mutagenicity of glutathione and cysteine in the Ames test

Postmitochondrial supernatant from rat liver and kidney homogenates transformed cysteine into a mutagen that reverted bacteria of the strain Salmonella typhimurium TA100 to histidine independence. Glutathione was also activated by kidney postmitochondrial supernatant but not by liver preparations. Hence, important endogenous compounds of mammals are positive in the most commonly used short-term test for carcinogenicity and mutagenicity. Glutathione is positive in the test even at concentrations found in mammalian tissues.

Revised methods for the Salmonella mutagenicity test

The methods for detecting carcinogens and mutagens with the Salmonella mutagenicity test were described previously (Ames et al., 1975b). The present paper is a revision of the methods. Two new tester strains, a frameshift strain (TA97) and a strain carrying an ochre mutation on a multicopy plasmid (TA102), are added to the standard tester set. TA97 replaces TA1537. TA1535 and TA1538 are removed from the recommended set but can be retained at the option of the investigator. TA98 and TA100 are retained. We discuss other special purpose strains and present some minor changes in procedure, principally in the growth, storage, and preservation of the tester strains. Two substitutions are made in diagnostic mutagens to eliminate MNNG and 9-aminoacridine. Some test modifications are discussed.

Mutagenicity screening of crude drugs with Bacillus subtilis rec-assay and Salmonella/microsome reversion assay

This paper describes the screening studies of 104 commercial crude drugs for mutagenicity by the rec-assay with Bacillus subtilis as well as the reversion assay with Ames strains TA98 and TA100 of Salmonella typhimurium. The rec-assays showed that 13 water extracts and 27 methanol extracts of the crude drugs were positive. The Ames assays with or without metabolic activation showed that 24 water extracts and 16 methanol extracts were mutagenic. In total, mutagenic activities were found in 45 samples among the 104 crude drugs tested.

Chromosome-breaking ability of arecoline, a major betel-nut alkaloid, in mouse bone-marrow cells in vivo

The chromosomal damaging properties of arecoline, a major betel-nut alkaloid were investigated in vivo after its administration to mice. Arecoline was injected in doses of 0.25, 0.5, 1 and 2 mg for 10, 20 and 30 days each. Significant numbers of aberrations were observed in the form of chromatid breaks, chromosome breaks, ring structure, multiple breaks and cells with pulverized chromosomal complements. The frequency of aberrations showed a dose-response relationship. So arecoline was concluded to have weak chromosome-damaging effects in vivo.

Toxicological procedures for assessing the carcinogenic potential of agricultural chemicals

Pesticides and other agricultural chemicals are now widely used throughout the world as a means of improving crop yields in order to meet the increasing demands being placed upon the global food supply. In Canada, the use of such chemicals is controlled through government regulations established jointly by the Department of Agriculture and the Department of National Health & Welfare. Such regulations require a detailed evaluation of the toxicological characteristics of the chemical prior to its being cleared for use. In this paper, procedures for assessing the carcinogenic potential of agricultural and other chemicals are discussed. Consideration is given to both the classical long-term in vivo carcinogen bioassay in rodent or other species and the more recently developed short-term in vitro tests based on genetic alterations in bacterial and other test systems.

Genotoxicity of pyrrolizidine alkaloids in the hepatocyte primary culture/DNA-repair test

The genotoxicity of 6 pyrrolizidine alkaloids and 2 related compounds was examined in the hepatocyte primary culture/DNA-repair test and compared to mutagenicity in a modified Salmonella/microsome test. All 6 pyrrolizidine alkaloids were positive in the DNA-repair test, and 4 of these are known to be carcinogenic. Of the 6 positive compounds, only 5 were mutagenic. Thus, the hepatocyte primary culture/DNA-repair test displays a comparable or better capacity than the bacterial mutagenesis test for detecting the genotoxic effects of this class of carcinogens.