Genotoxic activity of a technical toxaphene mixture and its photodegradation products in SOS genotoxicity tests

Toxaphene (CAS No. 800-35-2) is a complex mixture of several hundred components that was used worldwide primarily as an agricultural pesticide with insecticide effects in the second half of the 20th century. In vitro investigations of the genotoxicity and mutagenicity of toxaphene were generally described in the literature, but they provided somewhat equivocal results. We re-evaluated the genotoxicity of technical toxaphene in two prokaryotic systems. The SOS Chromotest showed high sensitivity to toxaphene: three concentrations (40, 20 and 10 mg/l) were clearly positive and the dose–response effect was evident. In the umuC assay, a dose-dependent increase in genotoxic activity was observed at toxaphene concentrations from 2.5 to 40.0 mg/l, but these results were found to be not significant. The genotoxicity of toxaphene and its photodegradation products after UV-irradiation (3–6–9 h) at concentrations ranging from 7.5 to 60.0 mg/l was also examined in this study. An irradiated solution of technical toxaphene after 3 h showed no significant evidence of bacterial growth inhibition. However, exposure of Salmonella to 6 h UV-irradiated toxaphene showed a toxic effect compared with the negative control. After 9 h irradiation, a decrease of bacterial growth was observed. Activity of β-galactosidase in the presence of a toxaphene solution was significantly increased after 6 and 9 h irradiation, reaching values that were 2.4- and 3.1-fold higher, respectively, than the control, which exceeded the criteria of significant genotoxicity. These results show that while technical toxaphene is a weak, direct-acting mutagen in some bacterial tests, a dose-dependent toxicity and genotoxicity of its photoproducts could be conclusively demonstrated by the umuC test.     

Selecting arthropod biological control agents against arthropod pests: Can the science be improved to decrease the risk of releasing ineffective agents?

With greater emphasis being placed on management of the risks attached to natural enemy releases for biocontrol programs and the need to justify research budgets, the efficient selection of effective natural enemies is increasingly important. Historically there has been little agreement regarding how or whether this can be accomplished. Recent studies have demonstrated that there is good correspondence between insect host-finding behavior and attack rates in well-designed laboratory studies and their performance of this behavior in the field. Success in measuring efficacy of candidate agents remains somewhat of an art due to the multitude of factors influencing efficacy, but will be improved by attention to: (1) characterization of natural enemy candidates using morphological taxonomy or genetic markers at the onset of a program, (2) climatic matching candidate agents when possible, and (3) evaluations in semi-field or field cage conditions following quarantine evaluations whenever possible before proceeding with widespread releases. The application of these principles is discussed in regard to US biocontrol programs for Bemisia tabaci (Gennadius), Lygus spp., and Aphis glycines Matsumura. Proper project planning and interdisciplinary cooperation will enhance the chances for a successful project.     

Apoptosis may contribute to false-positive results in the in vitro micronucleus test performed in extreme osmolality, ionic strength and pH conditions

Conditions in which clastogens produce positive responses have been increasingly challenged, and several situations have been described in which clastogenic responses would be considered not to be relevant. For example, extreme culture conditions lead to high variations of pH, osmolality or ionic strength. Apoptosis is induced in extreme culture conditions and contributes to false-positive results in the in vitro micronucleus test performed with CTLL-2 cells. These cells can enter apoptosis when exposed to apoptosis stimuli or after IL-2 deprivation, whereas the CTLL-2 Bcl2 cell line is protected from apoptosis due to the over-expression of the apoptosis inhibitor Bcl2 in bcl2-transfected CTLL-2 cells. The two cell lines were treated in extreme culture conditions of either pH or osmolality or were submitted to high ionic strength. The apoptosis level was measured in parallel with the in vitro micronucleus test using the annexin V-FITC method. Data obtained in the two cell lines suggested that apoptosis caused by extreme culture condition induces the formation of micronucleated cells, which leads to false-positive results in the in vitro micronucleus test.     

It’s the first bites that count: Survival of first‐instar monarchs on milkweeds

Mortality of first instars is generally very high, but variable, and is caused by many factors, including physical and chemical plant characters, weather and natural enemies. Here, a summary of detailed field‐based studies of the early‐stage survival of a specialist lepidopteran herbivore is presented. First‐instar larvae of the monarch butterfly, Danaus plexippus, a milkweed specialist, generally grew faster and survived better on leaves when latex flow was reduced by partial severance of the leaf petiole. The outcome depended on milkweed species, and was related to the amount of latex produced, as well as other plant characters, such as leaf hairs, microclimate and concentration of secondary metabolites. Even for a so‐called ‘milkweed specialist’, larval performance and survival appears to be related to the concentration of cardenolides produced by the plants (a potential chemical defence against herbivory). This case study of monarchs and milkweeds highlights the need for field‐based experiments to assess the effect of plant characters on the usually poor survival of early instar phytophagous insects. Few similar studies concerning the performance and survival of first‐instar, eucalypt‐specific herbivores have been conducted, but this type of study is considered essential based on the findings obtained using D. plexippus.     

鱼微核试验筛检水体诱变物的应用与研究

对五种试验污染物的遗传毒性采用鱼微核试验技术进行了筛检,试验结果表明鱼微核试验用作筛检诱变物的遗传毒性有效的,对监测水体的质量也具有潜在的价值;同时,对国内外学将各种各样的技术应用到鱼微核式试验进行了总结,概述了微核形成的机理;在此基础上,提出应用鱼微核试验筛检水体诱变物时应注意的问题。     

念珠伪角毛虫小核体功能初步研究

为了研究念珠伪角毛虫的小核是否具有及具有怎样的体功能,采用显微切割手术去小核并建立无小核细胞系。经蛋白银染色鉴定,无小核细胞系群体中大多数细胞的形态结构存在缺陷：口围带的部分小膜缺损或排列紊乱,大核的数目和形态也不正常。这表明,念珠伪角毛虫的小核对于保持口围带结构的完整性以及大核的数目和形态结构的稳定性起着明确的作用。     

Cytogenetic monitoring of industrial radiographers using the micronucleus assay

Industrial radiography is the process of using either gamma-emitting radionuclide sources or X-ray machines to examine the safety of industrial materials. Industrial radiographers are among the radiation workers who receive the highest individual occupational radiation doses. To assess occupationally induced chromosomal damage, we performed the cytokinesis-block micronucleus (CBMN) assay in peripheral lymphocytes of 29 male industrial radiographers, exposed to ionizing radiation for 12.8 years±11.2, in comparison with 24 gender-, age-, and smoking habits-matched controls. The CBMN assay was combined with fluorescent in situ hybridization with a pan-centromeric DNA probe in 17 exposed subjects and 17 controls randomized from the initial populations. The mean cumulative equivalent dose, recorded by film dosimeters, was 67.2 mSv±49.8 over the past 5 years. The mean micronucleated binucleated cell rate (MCR) was significantly higher in the industrial radiographers than in the controls (10.7‰±5.2 versus 6.6‰±3.1, P=0.009); this difference was due to a significantly higher frequency of centromere-negative micronuclei (C−MN) in exposed subjects than in controls (8.5‰±4.9 versus 2.2‰±1.6, P<0.001). The two populations did not significantly differ in centromere-positive micronuclei (C+MN) frequency. These findings demonstrate a clastogenic effect in lymphocytes of industrial radiographers. MCR significantly positively correlated with age in the two groups. After correction for the age effect, MCR did not correlate with duration of occupational exposure. No correlation between radiation doses and MCR, C−MN, and C+MN frequencies was observed. In addition to physical dosimetry records, the enhanced chromosomal damage in lymphocytes of industrial radiographers emphasizes the importance of radiation safety programs.     

Genotoxic ability of cadmium, chromium and nickel salts studied by kinetochore staining in the cytokinesis-blocked micronucleus assay

The aneugenic and clastogenic ability of cadmium chloride(II), cadmium sulfate(II), nickel chloride(II), nickel sulfate(II), chromium chloride(III) and potassium dichromate(IV) have been evaluated through kinetochore-stained micronucleus test. Traditional genotoxicity assays evaluate DNA damage, gene mutations and chromosome breakage. However, these tests are not adequate to detect aneugenic agents that do not act directly on DNA. Staining kinetochores in the cytokinesis-blocked micronucleus assay is a useful way to discriminate between clastogens and aneuploidogens and may allow a rapid identification of aneuploidy-inducing environmental compounds.Human diploid fibroblasts (MRC-5) were employed. All compounds increased micronuclei frequency in a statistically significant way. However, increases in kinetochore-positive micronuclei frequencies were higher than in kinetochore-negative ones. The present work demonstrates the genotoxic ability of the cadmium and chromium salts studied. Aneugenic as well as clastogenic ability could be observed with this assay. Nickel salts, as it was expected because of their known weak mutagenicity, showed lower genotoxic effects than the other metal salts studied. As the test employed only allows the detection of malsegregation, it is proposed that this mechanism is at least one of those by which the tested metal salts induced aneuploidy. On the other hand, visualization of kinetochores in all experiments suggests that the compounds studied did not act by damaging these structures.     

Binding of colchicine and lumicolchicine to components in plant extracts

Irradiation of dilute, aqueous solutions of colchicine and of colcemid by long wavelength UV resulted, in each case, in a mixture of three major lumi-products whose relative concentrations depended upon the degree of UV exposure. Components in plant extracts, after concentration by ammonium sulphate precipitation, bound the drugs and their lumi-derivatives. Consideration of the different ratios of colchicine- to lumicolchicine-binding activity in different fractions of a plant extract, and after various enzymatic and temperature treatments of the plant preparations, suggest the involvement of different binding sites for the various forms of the alkaloid.     

Novel naftopidil derivatives containing methyl phenylacetate and their blocking effects on α1D/1A-adrenoreceptor subtypes

α₁-Adrenoceptor (α₁-AR) antagonists are considered to be the most effective monotherapy agents for lower urinary tract symptoms associated with benign prostatic hyperplasia (LUTS/BPH). In this study, we synthesized compounds 2–17, which are novel piperazine derivatives that contain methyl phenylacetate. We then evaluated the vasodilatory activities of these compounds. Among them, we found that compounds 2, 7, 12, which contain 2-OCH₃, 2-CH₃ or 2, 5-CH₃, respectively, exhibited potent α₁-blocking activity similar to protype drug naftopidil (1). The antagonistic effects of 2, 7, and 12 on the (?)-noradrenaline-induced contractile response of isolated rat prostatic vas deferens (α_1A), spleen (α_1B) and thoracic aorta (α_1D) were further characterized to assess the sub receptor selectivity. Compared with naftopidil (1) and terazosin, compound 12 showed the most desirable α_1D/1A subtype selectivity, especially improved α_1A subtype selectivity, and the ratios pA₂ (α_1D)/pA₂ (α_1B) and pA₂ (α_1A)/pA₂ (α_1B) were 17.0- and 19.5-fold, respectively, indicating less cardiovascular side effects when used to treat LUTS/BPH. Finally, we investigated the chiral pharmacology of 12. We found, however, that the activity of enantiomers (R)-12 and (S)-12 are not significantly different from that of rac-12.