Acrylamide: its metabolism, developmental and reproductive effects, genotoxicity, and carcinogenicity

Monomeric acrylamide is an important industrial chemical primarily used in the production of polymers and copolymers. It is also used for producing grouts and soil stabilizers. Acrylamide's neurotoxic properties have been well documented. This review will focus on pertinent information concerning other, non-neurotoxic, effects observed after exposure to acrylamide, including: its genotoxic, carcinogenic, reproductive, and developmental effects. It will also cover its absorption, metabolism, and distribution. The data show that acrylamide is capable of inducing genotoxic, carcinogenic, developmental, and reproductive effects in tested organisms. Thus, acrylamide may pose more than a neurotoxic health hazard to exposed humans. Acrylamide is a small organic molecule with very high water solubility. These properties probably facilitate its rapid absorption and distribution throughout the body. After absorption, acrylamide is rapidly metabolized, primarily by glutathione conjugation, and the majority of applied material is excreted within 24 h. Preferential bioconcentration of acrylamide and/or its metabolites is not observed although it appears to persist in tests and skin. Acrylamide can bind to DNA, presumably via a Michael addition-type reaction, which has implications for its genotoxic and carcinogenic potential. The available evidence suggests that acrylamide does not produce detectable gene mutations, but that the major concern for its genotoxicity is its clastogenic activity. This clastogenic activity has been observed in germinal tissues which suggest the possible heritability of acrylamide-induced DNA alterations. Since there is 'sufficient evidence' of carcinogenicity in experimental animals as outlined under the U.S. EPA proposed guidelines for carcinogen risk assessment, acrylamide should be categorized as a 'B2' carcinogen and therefore be considered a 'probable human carcinogen.' The very limited human epidemiological data do not provide sufficient evidence to enable one to judge the actual carcinogenic risk to humans. Acrylamide is able to cross the placenta, reach significant concentrations in the conceptus and produce direct developmental and post-natal effects in rodent offspring. It appears that acrylamide may produce neurotoxic effects in neonates from exposures not overtly toxic to the mothers. Acrylamide has an adverse effect on reproduction as evidenced by dominant lethal effects, degeneration of testicular epithelial tissue, and sperm-head abnormalities.     

Synergy between systemic toxicity and genotoxicity: relevance to human cancer risk

The health risk manager and policy analyst must frequently make recommendations based upon incomplete toxicity data. This is a situation which is encountered in the evaluation of human carcinogenic risks as animal cancer bioassay results are often not available. In this study, in order to assess the relevance of other possible indicators of carcinogenic risks, we used the "chemical diversity approach" to estimate the magnitude of the human carcinogenic risk based upon Salmonella mutagenicity and systemic toxicity data of the "universe of chemicals" to which humans have the potential to be exposed. Analyses of the properties of 10,000 agents representative of the "universe of chemicals" suggest that chemicals that have genotoxic potentials as well as exhibiting greater systemic toxicity are more likely to be carcinogens than non-genotoxicants or agents that exhibit lesser toxicity. Since "genotoxic" carcinogenicity is a hallmark of recognized human carcinogens, these findings are relevant to human cancer risk assessment.     

A review of the genotoxicity of ethylbenzene

Ethylbenzene is an important industrial chemical that has recently been classified as a possible human carcinogen (IARC class 2B). It induces tumours in rats and mice, but neither the relevance of these tumours to humans nor their mechanism of induction is clear. Considering the carcinogenic potential of ethylbenzene, it is of interest to determine whether there is sufficient data to characterize its mode of action as either genotoxic or non-genotoxic. A review of the currently available genotoxicity data is assessed. Ethylbenzene is not a bacterial mutagen, does not induce gene conversion or mutations in yeast and does not induce sister chromatid exchanges in CHO cells. Ethylbenzene is not clastogenic in CHO or rat liver cell lines but was reported to induce micronuclei in SHE cells in vitro. No evidence for genotoxicity has been seen in humans exposed to relatively high levels of ethylbenzene. Mouse lymphoma gene mutation studies produced a mixed series of responses that have proved difficult to interpret. An increase in morphological transformation of SHE cells was also found. Results from a more relevant series of in vivo genotoxicity studies, including acute and sub-chronic micronucleus tests and the mouse liver UDS assay, indicate a lack of in vivo genotoxic activity. The composite set of results from both in vitro and in vivo tests known to assess direct damage to DNA have been predominantly negative in the absence of excessive toxicity. The available data from the standard battery of genotoxicity assays do not support a genotoxic mechanism for ethylbenzene-induced kidney, liver or lung tumors in rats and mice.     

Review of the genotoxicity of ozone.

Ozone is a powerful oxidant, reactive to biomolecules. In aqueous solution it decomposes to give hydrogen peroxide, superoxide and hydroxy radicals which can take part in secondary reactions. Ozone is a disinfectant that inactivates both viruses and bacteria. Although other reactions are primarily responsible for the inactivation, cellular DNA is also damaged. Ozone is genotoxic to microorganisms, plants and cell cultures in vitro. The results from in vivo cytogenetic studies with laboratory animals after inhalation exposure are contradictory. Chromosome aberrations in lymphocytes, but not SCEs, have been demonstrated in Chinese hamsters but not in mice. Chromatid deletions were induced in pulmonary macrophages in rats. No cytogenetic effects have been reported for bone marrow cells or spermatocytes. The few experimental and epidemiological studies with human subjects do not allow a conclusion on the cytogenetic effects of ozone in lymphocytes in humans. No life-long cancer studies have been performed with ozone. However, after 4 and 6 months of inhalation exposure, lung adenomas were induced in strain A/J mice, but not in Swiss-Webster mice.     

Use of in vivo genetic toxicity data for risk assessment

Mutagenicity studies have been used to identify specific agents as potential carconogens or other human health hazards; however, they have been used minimally for risk assessment or in determining permissible levels of human exposure. The poor predictive value of in vitro mutagenesis tests for carcinogenic activity and a lack of mechanistic understanding of the roles of mutagens in the induction of specific cancers have made these tests unattractive for the purpose of risk assessment. However, the limited resources available for carcinogen testing and large number of chemicals which need to be evaluated necessitate the incorporation of more efficient methods into the evaluation process. In vivo genetic toxicity testing can be recommended for this purpose because in vivo assays incorporate the metabolic activation pathways that are relevant to humans. We propose the use of a multiple end-point in vivo comprehensive testing protocol (CTP) using rodents. Studies using sub-acute exposure to low levels of test agents by routes consistent with human exposure can be a useful adjunct to methods currently used to provide data for risk assessment. Evaluations can include metabolic and pharmacokinetic endpoints, in addition to genetic toxicity studies, in order to provide a comprehensive examination of the mechanism of toxicity of the agent. A parallelogram approach can be used to estimate effects in non-accessible human tissues by using data from accessible human tissues and analogous tissues in animals. A categorical risk assessment procedure can be used which would consider, in order of priority, genetic damage in man, genetic damage in animals that is highly relevant to disease outcome (mutation, chromosome damage), and data from animals that is of less certain relevance to disease. Action levels of environmental exposure would be determined based on the lowest observed effect levels or the highest observed no effect levels, using sub-acute low level exposure studies in rodents. As an example, the known genotoxic effects of benzene exposure at low levels in man and animals are discussed. The lowest observed genotoxic effects were observed at about 1–10 parts per million for man and 0.04–0.1 parts per million in subacute animal studies. If genetic toxicity is to achieve a prominent role in evaluating carcinogens and characterizing germ-cell mutagens, minimal testing requirements must be established to ascertain the risk associated with environmental mutagen exposure. The use of the in vivo approach described here should provide the information needed to meet this goal. In addition, it should allow truly epigenetic or non-genotoxic carcinogens to be distinguished from the genotoxic carcinogens that are not detected by in vitro methods.     

Interpretation of the biological relevance of genotoxicity test results: the importance of thresholds

Despite recent improvements in genotoxicity protocols, we have observed an increase in the occurrence of positive results, particularly in chromosomal aberration tests in vitro, yet very few of these are accompanied by positive responses in vivo. Thus, the positive results may not be biologically relevant either for rodents or humans in vivo, but how should we determine "biological relevance"? Chemicals that produce thresholded dose-responses may well not pose a genotoxic risk at low (relevant to human) exposures, but thresholds should not just be "seen"; there must be an explanation and understanding of the underlying mechanism. In addition to extremes of pH, ionic strength and osmolality, as have been identified previously, such mechanisms include indirect genotoxicity resulting from interaction with non-DNA targets, chemicals/metabolites which are inherently genotoxic but which, at low concentrations, are effectively conjugated and unable to form adducts, and production of specific metabolites under in vitro conditions that are not formed in rodents or humans in vivo. If such thresholded mechanisms can be identified at exposures which are well in excess of expected human exposure, then there may be a strong argument that the positive results are not biologically relevant.     

In vitro genotoxicity of rocuronium bromide in human peripheral lymphocytes

Rocuronium bromide (RB), an aminosteroid type neuromuscular blocking agent, acts by reducing or inhibiting the depolarising effect of acetylcholine on the terminal disc of the muscle cell. To our knowledge, there is no adequate information on the genotoxic effects of RB, up to now. In the present study, possible genotoxic effects of RB have been determined by means of sister chromatid exchange (SCE), chromosome aberration (CA) and micronucleus (MN) analyses in human peripheral blood lymphocytes. The human peripheral blood lymphocytes were exposed to three different concentrations of RB (60, 80 and 100 μg/mL) for 24- and 48-h. In this study, RB increased the frequency of CAs, however, did not increase the frequency of SCEs. RB did not decrease the proliferation index (PI) and mitotic index (MI). Accordingly, RB increased the frequency of micronucleus (MN) but did not decrease the nuclear division index (NDI). Findings from this study suggest that rocuronium bromide is clastogenic but not cytotoxic to cultured human peripheral blood lymphocytes.     

Review of the genotoxicity of styrene in humans

Styrene (CAS No. 100-42-5) is an important industrial chemical for which positive results have been reported in in vitro and in vivo genotoxicity assays. Styrene-exposed workers have been studied extensively over two decades for the induction of various types of genotoxic effects. The outcomes of these studies have been conflicting, and where positive responses have been reported, it has proved difficult to demonstrate clear relationships between levels of damage reported and exposure levels. In this review, we have assessed studies addressing mutagenicity (chromosome aberrations, micronuclei and gene mutations) and other endpoints (sister chromatid exchanges, DNA breaks and DNA adducts) using criteria derived from the IPCS guidelines for the conduct of human biomonitoring studies. Based on the re-evaluated outcomes, the data are not convincing that styrene induces gene mutations. The evidence for induction of clastogenicity in occupationally exposed workers is less clear, with a predominant lack of induction of micronuclei in different studies, but conflicting responses in chromosome aberration assays. The results of numerous studies on sister chromatid exchanges do not provide evidence of a clear positive response, despite these being induced in animals exposed to styrene at high concentrations. However, there is evidence that both DNA adducts and DNA single strand breaks are induced in styrene workers. These types of damage are considered indicative of exposure of the target cells and interaction with cellular DNA but do not necessarily result in heritable changes. There is evidence that the metabolism of styrene in humans is affected by genetic polymorphisms of metabolizing genes and that these polymorphisms affect the outcome of in vitro mutagenicity studies on styrene. Therefore, studies that have addressed the potential of this factor to affect in vivo responses were considered. To date, there are no consistent relationships between genetic polymorphisms and induction of genotoxicity by styrene in humans, but further work is warranted on larger samples. The analyses of individual studies, together with a consideration of dose-response relationships and the lack of a common profile of positive responses for the various endpoints in different studies, provide no clear evidence that styrene exposure in workers results in detectable levels of mutagenic damage. However, evidence of exposure to genotoxic metabolites is demonstrated by the formation of DNA adducts and strand breaks.     

High-specificity and high-sensitivity genotoxicity assessment in a human cell line: validation of the GreenScreen HC GADD45a-GFP genotoxicity assay

The battery of genetic toxicity tests required by most regulatory authorities includes both bacterial and mammalian cell assays and identifies practically all genotoxic carcinogens. However, the relatively high specificity of the Salmonella mutagenicity assay (Ames test) is offset by the low specificity of the established mammalian cell assays, which leads to difficulties in the interpretation of the biological relevance of results. This paper describes a new high-throughput assay that links the regulation of the human GADD45a gene to the production of Green Fluorescent Protein (GFP). A study of 75 well-characterised genotoxic and non-genotoxic compounds with diverse mechanisms of DNA-damage induction (including aneugens) reveals that the assay responds positively to all classes of genotoxic damage with both high specificity and high sensitivity. The current micro-well assay format does not include metabolic activation, but a separate low-throughput protocol demonstrates a successful proof-of-principle for an S9 metabolic activation assay with the model pro-mutagen cyclophosphamide. The test should be of value both as a tool in the selection of candidate compounds for further development, where additional data may be required because of conflicting information from the in vitro test battery, or in product development areas where the use of animals is to be discontinued. As a microplate assay however, it has the qualities of high throughput and low compound use that will facilitate its application in early screening for genotoxic liability.     

Chromosome aberrations in Chinese hamster and human cells: a comparison using compounds with various genotoxicity profiles

Chromosome aberrations (Cabs) can be induced in vitro by non-DNA damaging compounds, often associated with cytotoxicity and DNA synthesis inhibition, and under conditions that would not be relevant in vivo. Such misleading positive results are reported both in Chinese hamster cell lines and in human peripheral blood lymphocytes (HL). We assessed the response of HL to compounds with varied genetic toxicity profiles, all of which induced Cabs in CHO cells Seven of 10 compounds were negative or equivocal in HL. Results in purified lymphocytes for four verified that the difference was not due to the presence of blood in cultures. Two compounds that were weakly positive in the Ames test and one that induced DNA adducts were negative or equivocal in the HL assay; their overall mutagenic potential in vivo is not clear. Of four Ames-negative compounds, three of which inhibited DNA synthesis in CHO cells, three were negative and one was equivocal in the HL assay. A potent Cab inducer, which also induced micronuclei in vivo (but was negative in the Ames test) was clearly positive in the HL assay. Two compounds were clearly positive in HL only when the mitotic indices (MI) were below 50% of control. These are genotoxic in other assays but our evidence suggests that Cab induction is related more to toxicity than to primary DNA damage. For this limited set of 10 compounds, HL were more likely than CHO cells to give negative or equivocal results. It is likely that more stringent checkpoint controls in human cells prevent damaged cells reaching mitosis, and may also influence the reported greater sensitivity to induction of aneuploidy and polyploidy of normal rodent compared with human cells. In the studies reported here, two strong inducers of polyploidy in CHO cells gave weaker increases in HL. Human lymphocytes have disadvantages as a routine screening assay (finding donors, known individual variability, increased time required and the inadequacy of the MI as a toxicity measure), but may be useful in follow-up testing to assess weight of evidence about genotoxic risk to humans, for compounds that are positive in the Chinese hamster cell Cabs assays.     

In vitro and in vivo genotoxicity of radiofrequency fields

There has been growing concern about the possibility of adverse health effects resulting from exposure to radiofrequency radiations (RFR), such as those emitted by wireless communication devices. Since the introduction of mobile phones many studies have been conducted regarding alleged health effects but there is still some uncertainty and no definitive conclusions have been reached so far. Although thermal effects are well understood they are not of great concern as they are unlikely to result from the typical low-level RFR exposures. Concern rests essentially with the possibility that RFR-exposure may induce non-thermal and/or long-term health effects such as an increased cancer risk. Consequently, possible genetic effects have often been studied but with mixed results. In this paper we review the data on alleged RFR-induced genetic effects from in vitro and in vivo investigations as well as from human cytogenetic biomonitoring surveys. Attention is also paid to combined exposures of RFR with chemical or physical agents. Again, however, no entirely consistent picture emerges. Many of the positive studies may well be due to thermal exposures, but a few studies suggest that biological effects can be seen at low levels of exposure. Overall, however, the evidence for low-level genotoxic effects is very weak.     

Toxicokinetics and toxicodynamics of ochratoxin A, an update

Ochratoxin A (OTA) is a mycotoxin produced by fungi of two genera: Penicillium and Aspergillus. OTA has been shown to be nephrotoxic, hepatotoxic, teratogenic and immunotoxic to several species of animals and to cause kidney and liver tumours in mice and rats. Because of differences in the physiology of animal species, wide variations are seen in the toxicokinetic patterns of absorption, distribution and elimination of the toxin. Biotransformation of OTA has not been entirely elucidated. At present, data regarding OTA metabolism are controversial. Several metabolites have been characterized in vitro and/or in vivo, whereas other metabolites remain to be characterized. Several major mechanisms have been shown as involved in the toxicity of OTA: inhibition of protein synthesis, promotion of membrane peroxidation, disruption of calcium homeostasis, inhibition of mitochondrial respiration and DNA damage. The contribution of metabolites in OTA genotoxicity and carcinogenicity is still unclear. The genotoxic status of OTA is still controversial because contradictory results were obtained in various microbial and mammalian tests, notably regarding the formation of DNA adducts. More recent studies are focused on the OTA ability to disturb cellular signalling and regulation, to modulate physiological signals and thereby to influence cells viability and proliferation. The present paper offers an update on these different issues. In addition since humans and animals are likely to be simultaneously exposed to several mycotoxins, especially through their diet, the little information available on the combined effects of OTA and other mycotoxins has also been reviewed.     

Differential effect of cyclosporine A on respiratory burst by several types of human leukocytic cells.

The effect of cyclosporine on PMA-stimulated superoxide production has been studied on human alveolar macrophages, human neutrophils, cytoplasts and Epstein-Barr-virus-transformed B lymphocytes. Cyclosporine inhibits superoxide production in alveolar macrophages but not in neutrophils and cytoplasts. The respiratory burst of B-lymphocytes was scarcely inhibited by cyclosporine. The activity of NADPH oxidase from macrophages and neutrophils was not directly affected by cyclosporine. These data are considered in relation with the proposed mechanism for cyclosporine action and the stimulation of the respiratory burst.     

The genotoxicity of selenium

Selenium at nutritional levels has been shown to have numerous anticarcinogenic or preventative effects against carcinogen-induced breast, colon, liver and skin cancer in animals. Many of these anticarcinogenic effects have been summarized. In addition, numerous mutagenic and antimutagenic effects of selenium compounds have been reported. Some of the selenium compounds frequently tested for mutagenicity are listed in Table 1. Because of the numerous reported anticarcinogenic and preventative effects of selenium, many individuals are supplementing their diets with amounts of selenium that are greater than the recommended daily requirement. Selenium is also used widely in industrial products such as selenium rectifiers, photoelectric batteries, alloys and paints. Because selenium at higher levels is known to be toxic, there should be a greater understanding about its genotoxic as well as its beneficial effect. The object of this review is to summarize experimental evidence both for the antimutagenic and the mutagenic effect of selenium.     

Antitumor activity of a new platinum(II) complex with low nephrotoxicity and genotoxicity

Cisplatin is an important antineoplastic agent, but dose-limiting nephrotoxicity and the occurrence of cellular resistance prevent its potential efficacy. Moreover, cisplatin is known to be carcinogenic and genotoxic in mammalian cells and this feature is of a special interest due to the risk of inducing secondary malignancies. There is a great interest in developing new platinum agents that have broad spectrum of antitumor activity and reduced toxicity. We have recently synthesized a novel platinum(II) coordination complex containing a pyridine nucleus and a dithiocarbamate moiety as ligands, [Pt(ESDT)(Py)Cl], in order to obtain an agent with more favorable therapeutic indices than cisplatin. In this study, the new platinum(II) complex was tested for its cytotoxicity, by MTT assay, on various human cancer cell lines also including different cisplatin-resistant cells endowed with different mechanisms of resistance. On human peripheral blood lymphocytes we evaluated the genotoxic potential of [Pt(ESDT)(Py)Cl] via micronuclei and SCE detection. We also performed in vivo experiments with the purpose of investigating the antitumor and nephrotoxic effects of the new platinum(II) complex. The antitumor activity was studied in ascitic or solid Ehrlich carcinoma bearing mice while nephrotoxicity was monitored in male Wistar rats by means of histopathological findings of renal specimens and of biochemical investigation on urinary parameters (GS and NAG activities and of TUP excretion) of urine samples. The results reported here indicate that [Pt(ESDT)(Py)Cl] showed a remarkable in vitro antitumor activity (with IC50 values about twofold as low as those of cisplatin), moreover, it markedly circumvented the acquired cisplatin resistance in selected human cancer cells. The analysis of the cytogenetic damage in normal cells clearly attested that the new dithiocarbamate complex, tested at equitoxic concentrations, is less genotoxic than cisplatin. Chemotherapy in Ehrlich carcinoma bearing mice with [Pt(ESDT)(Py)Cl] was significantly better tolerated than that with cisplatin. Against the ascitic tumor, [Pt(ESDT)(Py)Cl], showed an activity noticeably higher than that of cisplatin in increasing the life span of treated animals (% T/C = 190 and 129, respectively). In solid-tumor-bearing mice, [Pt(ESDT)(Py)Cl] induced a tumor size reduction very close to that observed with the reference compound. Finally, our findings obtained from the nephrotoxicity studies demonstrated [Pt(ESDT)(Py)Cl] was not nephrotoxic, contrary to cisplatin which caused a notorious acute proximal tubular damage. In summary, [Pt(ESDT)(Py)Cl] may be considered as a new platinum(II) complex with remarkable antitumor activity and low nephrotoxicity and genotoxicity compared with cisplatin.     

Evaluation of the genotoxic potential of the natural neurotoxin Tetrodotoxin (TTX) in a battery of in vitro and in vivo genotoxicity assays

The genotoxic potential of the natural neurotoxin Tetrodotoxin (TTX) was evaluated in a battery of in vitro and in vivo genotoxicity assays. These comprised a bacterial reverse-mutation assay (Ames test), an in vitro human lymphocyte chromosome-aberration assay, an in vivo mouse bone-marrow micronucleus assay and an in vivo rat-liver UDS assay. Maximum test concentrations in in vitro assays were determined by the TTX limit of solubility in the formulation vehicle (0.02% acetic acid solution). In the Ames test, TTX was tested at concentrations of up to 200 microg/plate. In the chromosome-aberration assay human lymphocytes were exposed to TTX at concentrations of up to 50 microg/ml for 3 and 20 h in the absence of S9, and for 3h in the presence of S9. For the in vivo assays, maximum tested dose levels were determined by the acute lethal toxicity of TTX after subcutaneous administration. In the mouse micronucleus assay TTX dose levels of 2, 4 and 8 microg/kg were administered to male and female animals, and bone-marrow samples taken 24 and 48 h (high-dose animals only) after administration. In the UDS assay, male rats were given TTX on two occasions with a 14-h interval at dose levels of 2.4 and 8 microg/kg, the last dose being administered 2h before liver perfusion and hepatocyte culturing. Relevant vehicle and positive control cultures and animals were included in all assays. TTX was clearly shown to lack in vitro or in vivo genotoxic activity in the assays conducted in this study. The results suggest that administration of TTX as a therapeutic analgesic agent would not pose a genotoxic risk to patients.     

Evaluation of the cytotoxicity, cytostaticity and genotoxicity of argentatins A and B from Parthenium argentatum (Gray)

Argentatins A and B are abundant triterpenes present in Parthenium argentatum. Both compounds have shown cytotoxic properties on K562, MCF-7, PC-3, HCT-15 and U251 human cancer cell lines. Furthermore the cytotoxic, cytostatic and genotoxic effects of the argentatins on proliferating lymphocytes were evaluated using cytokinesis-block micronucleus test. Argentatin A had no cytostatic properties, but it was cytotoxic for proliferating lymphocytes at a concentration of 25 microM (P < 0.005). On the other hand, argentatin B showed significant cytostatic effects (P < 0.001) at concentrations of 5 to 25 microM and it did not show cytotoxic effects at the same concentrations. Neither argentatin showed genotoxic effects in terms of micronucleus frequency in human lymphocytes. According to these results the argentatins are not able to cause injury on DNA by clastogenic or aneugenic mechanisms.     

Cyclosporine A, an in vitro calmodulin antagonist, induces nuclear lobulations in human T cell lymphocytes and monocytes

Cyclosporine A is a noncytotoxic, natural, 11 amino acid cyclic peptide used clinically as an immunosuppressant to prevent organ rejection after transplantation. Cyclosporine A is an in vitro calmodulin antagonist. At the low concentrations required to inhibit calmodulin-dependent phosphodiesterase in vitro, cyclosporine A causes a dramatic alteration in the nuclear morphology of 23% of human peripheral blood mononuclear leukocytes in vitro without loss of viability. The shape of the nucleus changes from ovoid to a distinctive, radially splayed lobulated structure. The changes occur in a dose-dependent manner in 60 min at 37 degrees C. Specific monoclonal antibodies to human leukocytes identify the cells susceptible to nuclear lobulation by cyclosporine A as OKT4 antigen-positive T cell lymphocytes and monocytes. The lobulated nuclei are 2N as determined by flow cytometric measurement of ethidium bromide fluorescence of DNA. The cyclosporine A-induced lobulation of T cell nuclei requires both physiologic temperature and metabolic energy. Although structurally different than cyclosporine A, the calmodulin antagonists R24571 and W-7 [N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide] also produce T cell nuclear lobulations that are indistinguishable from the nuclear lobulations caused by cyclosporine A. These data indicate that nonmitotic structural elements that govern normal nuclear morphology in a subset of mononuclear leukocytes appear to require a calmodulin-mediated process. Cyclosporine A may be a useful noncytotoxic inhibitor of calmodulin-dependent systems that influence nuclear structure and function.     

Prevalence of genotoxic chemicals among animal and human carcinogens evaluated in the IARC Monograph series.

To determine whether genotoxic and non-genotoxic carcinogens contribute similarly to the cancer burden in humans, an analysis was performed on agents that were evaluated in Supplements 6 and 7 to the IARC Monographs for their carcinogenic effects in humans and animals and for the activity in short-term genotoxicity tests. The prevalence of genotoxic carcinogens on four groups of agents, consisting of established human carcinogens (group 1, n = 30), probable human carcinogens (group 2A, n = 37), possible human carcinogens (group 2B, n = 113) and on agents with limited evidence of carcinogenicity in animals (a subset of group 3, n = 149) was determined. A high prevalence in the order of 80 to 90% of genotoxic carcinogens was found in each of the groups 1, 2A and 2B, which were also shown to be multi-species/multi-tissues carcinogens. The distribution of carcinogenic potency in rodents did not reveal any specific characteristic of the human carcinogens in group 1 that would differentiate them from agents in groups 2A, 2B and 3. The results of this analysis indicate that (a) an agent with unknown carcinogenic potential showing sufficient evidence of activity in in vitro/in vivo genotoxicity assays (involving as endpoints DNA damage and chromosomal/mutational damage) may represent a hazard to humans; and b) an agent showing lack of activity in this spectrum of genotoxicity assays should undergo evaluation for carcinogenicity by rodent bioassay, in view of the present lack of validated short-term tests for non-genotoxic carcinogens. Overall, this analysis implies that genotoxic carcinogens add more to the cancer burden in man than non-genotoxic carcinogens. Thus, identification of such genotoxic carcinogens and subsequent lowering of exposure will remain the main goal for primary cancer prevention in man.