Chinese Hamster Lung Cells Research Articles

Chinese Hamster Lung Cell을 이용한 in vitro 소핵시험의 세포질 최적화 연구

Chinese Hamster Lung Cell을 이용한 in vitro 소핵시험의 세포질 최적화 연구

Construction and application of (Q)SAR models to predict chemical-induced in vitro chromosome aberrations

In drug development, genetic toxicology studies are conducted using in vitro and in vivo assays to identify potential mutagenic and clastogenic effects, as outlined in the International Council for Harmonisation (ICH) S2 regulatory guideline. (Quantitative) structure-activity relationship ((Q)SAR) models that predict assay outcomes can be used as an early screen to prioritize pharmaceutical candidates, or later during product development to evaluate safety when experimental data are unavailable or inconclusive. In the current study, two commercial QSAR platforms were used to build models for in vitro chromosomal aberrations in Chinese hamster lung (CHL) and Chinese hamster ovary (CHO) cells. Cross-validated CHL model predictive performance showed sensitivity of 80 and 82%, and negative predictivity of 75 and 76% based on 875 training set compounds. For CHO, sensitivity of 61 and 67% and negative predictivity of 68 and 74% was achieved based on 817 training set compounds. The predictive performance of structural alerts in a commercial expert rule-based SAR software was also investigated and showed positive predictivity of 48–100% for selected alerts. Case studies examining incorrectly-predicted compounds, non-DNA-reactive clastogens, and recently-approved pharmaceuticals are presented, exploring how an investigational approach using similarity searching and expert knowledge can improve upon individual (Q)SAR predictions of the clastogenicity of drugs.

In vitro and in vivo evaluation of the genotoxicity of Eriobotrya japonica leaf extract

Eriobotrya japonica leaf is included in the Chinese Pharmacopoeia, and is widely used as a medicinal material in traditional medicine. The present study investigated the potential genotoxic effects of E. japonica leaf extract (EJE) using three standard battery systems. Genotoxicity tests were conducted following the test guidelines of the Organisation for Economic Cooperation and Development (OECD) and Ministry of Food and Drug Safety (MFDS), with application of Good Laboratory Practice. The bacterial reverse mutation test was conducted using the pre-incubation method in the presence or absence of the metabolic activation system (S9 mixture). The in vitro chromosome aberration test was performed using cultured Chinese hamster lung cell line in the presence or absence of the S9 mixture. The in vivo micronucleus test was performed using ICR mice. The bacterial reverse mutation test with Salmonella typhimurium strains TA98, TA100, TA1535, and TA1537 and Escherichia coli strain WP2uvrA showed that EJE did not induce gene mutations at any dose level in all the strains tested. EJE also did not show any chromosomal aberrations in the in vitro chromosomal aberration test and in the in vivo micronucleus test. These results showed that EJE did not induce mutagenicity or clastogenicity in either in vitro or in vivo systems.

Genotoxicity and Embryotoxicity Study of Bicyclol Methyl Ether, Main Impurity in Bicyclol.

To assess the genotoxicity and embryotoxicity of bicyclol methyl ether (BME), the main impurity in bicyclol. Five concentrations of BME (0.5, 5, 50, 500 and 5000 μg/plate) were used in the Ames test to detect gene mutation. In the chromosome aberration test, Chinese hamster lung cells were used to detect chromosomal aberration of BME (15, 30, 60, 120 μg/mL) with or without S9 mixture. Embryotoxicity test was also conducted to determine any embryotoxicity of BME (7.5, 22.5, 67.5 μg/L) using zebrafish embryos. No significant differences were observed in the Ames test and the chromosome aberration test in the BME groups compared with the vehicle control group. The zebrafish embryos toxicity test also showed no embryo development toxicity of BME, including hatching rate, body length, pericardial area and yolk sac area. Bicyclol methyl ether has no genotoxicity in vitro and embryotoxicity in zebrafish embryos, and the impurity in bicyclol is qualified.

Potential role of mitochondrial damage and S9 mixture including metabolic enzymes in ZnO nanoparticles-induced oxidative stress and genotoxicity in Chinese hamster lung (CHL/IU) cells

The present study was designed to examine genotoxicity induced by 10–40 nm zinc oxide (ZnO) nanoparticles using the in vitro system. The frequency of micronuclei was significantly increased in a dose-dependent manner when cultured Chinese hamster lung (CHL/IU) cells were exposed to ZnO nanoparticles for 24, 48 and 72 h in the continuous treatment method. The maximal frequency of micronuclei was observed in exposure of CHL/IU cells to ZnO nanoparticles at a concentration of 125 μM. The frequency of micronuclei was profoundly enhanced when CHL/IU cells were exposed to ZnO nanoparticles in the presence vs. absence of S9 mixture including metabolic enzymes in the short-term treatment method, demonstrating an increase in the formation of micronuclei by S9 mixture. The maximal frequency of micronuclei was seen in exposure of CHL/IU cells to ZnO nanoparticles at a concentration of 140 μM. Similar results were obtained in chromosome aberrations, particularly structural aberrations. Surprisingly, administration of the superoxide radical scavenger, tempol, completely abolished an increase in the frequency of micronuclei in the presence or absence of S9 mixture, indicating a central role of superoxide radical in the formation of micronuclei. Indeed, reactive oxygen species (ROS) generation was elevated by simultaneous incubation of S9 mixture and ZnO nanoparticles and by exposure of CHL/IU cells to ZnO nanoparticles in the presence or absence of S9 mixture. An electron microscopic examination revealed mitochondrial damage in CHL/IU cells exposed to ZnO nanoparticles, indicating the participation of mitochondrial dysfunction in ROS generation in this setting. These observations suggest that ZnO nanoparticles evoke genotoxicity through superoxide radical-induced oxidative stress derived from mitochondrial damage in CHL/IU cells. S9 mixture appears to contribute to a further increase in genotoxicity through the generation of superoxide radical by metabolic activation of ZnO nanoparticles.

Simulation and experimental study on the mechanism of the chlorination of azithromycin

Azithromycin (AZI) has been listed as an emerging contaminant by the US EPA since 2009 because it is frequently detected in wastewater, surface water, and drinking water. In this paper, the chlorination of AZI in drinking water was simulated and studied. The results indicated that new compounds were generated in the chlorination of AZI. The byproducts were identified by liquid chromatography-quadrupole-time-of-flight mass spectrometry (LC-Q-TOF), and four of the byproducts were detected in real water samples. The kinetic studies demonstrated that the reaction rates of AZI chlorination were dependent on the initial concentration of free chlorine and the pH value. The potential toxicities of the byproducts were assessed by quantitative structure-activity relationship software and investigated by the viability of Chinese hamster lung (CHL), Jurkat T and Hep G2 cells.

Carbon dots-decorated Na2W4O13 composite with WO3 for highly efficient photocatalytic antibacterial activity

Photodisinfection by semiconductors has been proven to be an effective method for achieving antibacterial or antifungal activity. However, the toxicity of the nanomaterial to the environment and organisms is a major concern. Herein, a highly efficient and environmentally friendly photodisinfection material of a carbon dots (CDs) decorated Na2W4O13 composite with WO3 photocatalyst was fabricated via a facile hydrothermal-calcination approach. The TEM (transmission electron microscopy) images showed that CDs decorated the surface of the Na2W4O13 flakes. Compared with the samples without incorporated CDs, the as-synthesized composite of CDs/Na2W4O13/WO3 exhibited excellent antimicrobial activity against E. coli under visible light illumination. Electron spin resonance (ESR) spectroscopy and reactive species scavenging experiments revealed that the hydroxyl radicals and superoxide radical anions played the most important role in the photocatalytic bacterial inactivation. Furthermore, the cytotoxicity of the CDs/Na2W4O13/WO3 composite was evaluated by analyzing the viability of HepG2 and Chinese hamster lung (V79) cells using Cell Counting Kit-8 (CCK-8).

Initial hazard assessment of 4-benzylphenol, a structural analog of bisphenol F: Genotoxicity tests in vitro and a 28-day repeated-dose toxicity study in rats

4-Benzylphenol (CAS No. 101-53-1), a structural analog of bisphenol F, has estrogenic activity in vitro and in vivo, as is the case with bisphenol F. 4-Benzylphenol is used in plastics and during organic synthesis. Since its safety is largely unknown, we conducted toxicity tests as part of screening risk assessment in an existing chemical safety survey program. Based on results of the Ames test and the chromosomal aberration test using Chinese hamster lung cells (OECD TG 471 and 473), 4-benzylphenol was determined to be non-genotoxic in vitro. In a 28-day repeated-dose toxicity study, Crl:CD (SD) rats were administrated 4-benzylphenol by gavage at 0, 30, 150, or 750 mg/kg/day (OECD TG 407). Consequently, body weight was lower in males at 750 mg/kg/day. In the liver, relative organ weights were increased in both sexes at 750 mg/kg/day, and centrilobular hepatocellular hypertrophy was observed in males at 150 and 750 mg/kg/day. In the forestomach, hyperkeratosis and hyperplasia of squamous cells were observed in males at 150 and 750 mg/kg/day, and in females at 750 mg/kg/day. Based on these results, we identified the NOAEL for 4-benzylphenol as 30 mg/kg/day, with a hazard assessment value (D-value) of 0.05 mg/kg/day corresponding to hazard class 3.

Toxicological evaluation of 6′-sialyllactose (6'-SL) sodium salt

We performed a series of toxicity studies on the safety of 6′-sialyllactose (6′-SL) sodium salt as a food ingredient. 6′-SL sodium salt, up to a maximum dose of 5000 μg/plate, did not increase the number of revertant colonies in five strains of Salmonella typhimurium in the presence or absence of S9 metabolic activation. A chromosomal aberration assay (using Chinese hamster lung cells) found no clastogenic effects at any concentration of 6′-SL sodium salt in the presence or absence of S9 metabolic activation. An in vivo bone marrow micronucleus test in Kunming mice showed no clastogenic activities with 6′-SL sodium salt doses up to 2000 mg/kg body weight (bw). In an acute toxicity study, the mean lethal dose of 6′-SL sodium salt was greater than 20 g/kg bw in rats. In a 13-week subchronic toxicity investigation, no effects were found at doses up to 5.0 g/kg bw of 6′-SL sodium salt in food consumption, body weight, clinical signs, blood biochemistry and hematology, urinalysis, or ophthalmic and histological macroscopic examination of organs. The no-observed-adverse-effect level (NOAEL) was 5.0 g/kg bw/day in rats.

Genotoxicity evaluation of So-ochim-tang-gamibang (SOCG), a herbal medicine

BackgroundSo-ochim-tang-gamibang (SOCG) is a traditional Korean medicine frequently used for depression in the clinical field. In this study, we evaluated the potential genotoxicity of SOCG using three standard batteries of tests as part of a safety evaluation.MethodsSOCG was evaluated for potential genotoxic effects using the standard three tests recommended by the Ministry of Food and Drug Safety (MFDS) of Korea. These tests were the bacterial reverse mutation test (Ames test), in vitro mammalian chromosomal aberration test using Chinese hamster lung cells, and in vivo micronucleus test using ICR mice.ResultsThe Ames test with Salmonella typhimurium strains TA98, TA100, TA1535 and TA1537 and the Escherichia coli strain WP2uvrA(pKM101) showed that SOCG did not induce gene mutations at any dose level in all of the strains. SOCG did not induce any chromosomal aberrations in the in vitro chromosomal aberration test (for both the 6 and 24 h test) and the in vivo micronucleus test.ConclusionsBased on the results of these tests, it was concluded that SOCG does not exhibit any genotoxic risk under the experimental conditions of this study.

The genotoxicity of an aqueous extract of Gyejibokryeong-hwan

BackgroundGyejibokryeong-hwan (Guizhi Fuling Wan in China), a mixture of five herbal plants, is a well-known treatment for renal diseases including those associated with climacteric syndrome. However, the genotoxicity of Gyejibokryeong-hwan has not yet been well established.MethodsThe present study investigated that the genotoxicity of an aqueous extract of Gyejibokryeong-hwan (GJBRHE): an in vitro chromosomal aberration test using Chinese hamster lung cells, an in vitro bacterial reverse mutation assay (Ames test) with Salmonella typhimurium and Escherichia coli strains, and an in vivo micronucleus test using ICR mouse bone marrow.ResultsGJBRHE with or without the S9 mix showed no genotoxicity in the Ames test up to 5000 μg/plate or in the in vivo MN test up to 2000 mg/kg body weight. In contrast, the chromosomal aberration test showed that GJBRHE induced an increase in the number of chromosomal aberrations compared with the control after treatment for 6 h with 4200 μg/mL GJBRHE in the presence of the S9 mix and for 22 h with 800 μg/mL GJBRHE in the absence of the S9 mix.ConclusionsGJBRHE did not cause detectable genotoxic effects in the bacterial mutation test or the in vivo MN test, however genotoxic effect was detected in the in vitro chromosomal aberration assay. Our results suggest that GJBRHE may be associated with a low risk of carcinogenesis. Thus, further detailed experiments would be needed to clarify the compound responsible for inducing this genotoxicity of GJBRHE and to determine its mechanism.

Regulatory role of miR-18a to CCN2 by TGF-β1 signaling pathway in pulmonary injury induced by nano-SiO2.

This research is designed to investigate the regulatory effect of miR-18a to the target gene connective tissue growth factor (CTGF, or CCN2), by participating in TGF-β1 signaling pathway and explore the pathogenic mechanism of miR-18a in pulmonary injury induced by nano-SiO2 based on our early study. miR-18a and expression of TGF-β1 in Chinese hamster lung (CHL) fibroblasts cells stimulated by supernatants of NR8383 cells exposed to 40μg/ml nano-SiO2 for 24h demonstrated 1.58±0.22-fold and 1096.00±2.60pg/ml increase compared with blank control group analyzed by real-time quantitative PCR (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Expression increase of miR-18a and reduction of CCN2 mRNA expression levels and protein gray value ratio detected by Western blotting in CHL cells transfect miR-18a mimics for 48h. The reverse of CHL cell transfection miR-18a inhibit is also true. The result of miR-18a and CCN2 binding sites tested by luciferase reporter gene assay shows that the report relative fluorescence value of miR-18a mimics wild type on CCN2 is 0.50±0.02 with the control of mimics NC and mutant relative fluorescence report value 0.86±0.04 (P<0.05). Expression levels of miR-18a, CCN2 mRNA, and protein gray value ratio decreased in CHL cells treated by TGF-β1, respectively, and vice versa treated by TGF-β1corepressor. The results suggest that CCN2 is the target gene regulated by miR-18a and miR-18a participates in TGF-β1 signaling pathway by regulating the expression of CCN2 negatively through CCN2 3'UTR site, and thus may be involved in the development process of pulmonary injury.

Evaluation of genotoxicity and subchronic toxicity of standardized rose hip extract.

Rose hip is the fruit of the rose plant, which is widely used in food, cosmetics and as a traditional medicine. Therefore, rose hip is considered safe and has a sufficient history of consumption as food. However, few studies have reported on the safety of rose hip extracts in toxicological analyses. Thus, to evaluate the safety of rosehip polyphenol MJ (RHPMJ), an aqueous ethanol extract standardized with the trans-tiliroside content, we performed genotoxicity and 90-day repeated oral dose toxicity studies in compliance with the Organisation for Economic Co-operation and Development-Good Laboratory Practice. RHPMJ did not induce gene mutations in reverse mutation tests of Salmonella typhimurium TA98, TA100, TA1535, TA1537 and Escherichia coli WP2 uvrA strains and did not induce chromosomal aberrations in cultured Chinese hamster lung (CHL/IU) cells. Moreover, micronucleus tests using rat bone marrow showed RHPMJ had no micronucleus-inducing potential. Finally, 90-day repeated oral dose toxicity studies (100-1000 mg/kg) in male and female rats showed no treatment-related toxicity in rats. These data indicate that the RHPMJ had no genotoxicity and a no-observed-adverse-effect level greater than 1000 mg/kg in rats.

In vitro genotoxicity of asbestos substitutes induced by coupled stimulation of dissolved high-valence ions and oxide radicals.

The wide use of asbestos and its substitutes has given rise to studies on their possible harmful effects on human health and environment. However, their toxic effects remain unclear. The present study was aimed to disclose the coupled effects of dissolved high-valence ions and oxide radicals using the in vitro cytotoxicity and genotoxicity of chrysotile (CA), nano-SiO2 (NS), ceramic fiber (CF), glass fiber (GF), and rock wool (RW) on Chinese hamster lung cells V79. All samples induced cell mortality correlated well with the chemical SiO2 content of asbestos substitutes and the amount of dissolved Si. Alkali or alkaline earth metal elements relieved mortality of V79 cells; Al2O3 reinforced toxicity of materials. Asbestos substitutes generated lasting, increasing amount of acellular ·OH which formed at the fiber surface at sites with loose/unsaturated bonds, as well as by catalytic reaction through dissolved iron. Accumulated mechanical and radical stimulation induced the intracellular reactive oxygen species (ROS) elevation, morphology change, and deviating trans-membrane ion flux. The cellular ROS appeared as NS > GF > CF ≈ CA > RW, consistent with cell mortality rather than with acellular ·OH generation. Chromosomal and DNA lesions in V79 cells were not directly associated with the cellular ROS, while influenced by dissolved high-valence irons in the co-culture medium. In conclusion, ions from short-time dissolution of dust samples and the generation of extracellular ·OH presented combined effects in the elevation of intracellular ROS, which further synergistically induced cytotoxicity and genotoxicity.

Mechanisms of chromosomal aberrations induced by sesamin metabolites in Chinese hamster lung cells

Sesamin is a major lignan in sesame seeds and oil. We previously demonstrated that sesamin induces chromosomal aberrations (CA) in Chinese hamster lung (CHL/IU) cells in the presence of a metabolic activation system (S9 mix), although no genotoxicity was detected in vivo. To clarify the mechanism of CA induction by sesamin, we identified its principal active metabolite. A mono-catechol derivative, [2-(3,4-methylenedioxyphenyl)-6-(3,4-dihydroxyphenyl)-3,7-dioxabi-cyclo[3.3.0]octane (SC-1)], was previously identified in culture medium when sesamin was incubated with S9 mix. In the present study, we show that SC-1 induces CA in CHL/IU cells but not in human hepatoblastoma (HepG2) cells. SC-1 was unstable in culture medium. Addition of glutathione (GSH) to the incubation mixture decreased the rate of decomposition and also suppressed induction of CA in CHL/IU cells. These results indicate that SC-1 itself may not contribute to the induction of CA. Two GSH adducts of SC-1 were identified when SC-1 was incubated with GSH, suggesting that SC-1 was converted to the semiquinone/quinone form and then conjugated with GSH in the culture medium. Sodium sulfite (a quinone-responsive compound) also suppressed CA induction by SC-1. These findings strongly suggest that SC-1 is oxidized to semiquinone/quinone derivatives extracellularly in culture medium, that these derivatives are responsible for the induction of CA in CHL/IU cells, and therefore that the positive results obtained with sesamin in in vitro CA tests using CHL/IU cells may not be relevant to the assessment of in vivo activity.

Bacillus subtilis SN7이 생성한 조항균 물질의 유전독성학적 안정성평가

This study was carried out to perform genotoxicological safety evaluation of crude antifungal compounds produced by Bacillus subtilis SN7 (B. subtilis SN7) isolated from meju. Bacterial reverse mutation assay with Salmonella typhimurium TA98, TA100, TA1535, and TA1537 or Escherichia coli WP2uvrA in the presence and absence of the S9 metabolic activation system was carried out, and the crude antifungal compounds produced by B. subtilis SN7 showed no significant increase in the number of revertant colonies. In the chromosomal aberration tests using Chinese hamster lung (CHL) cells, sample treatment groups showed no increase in the frequency of chromosome aberrations compared to the negative control group. Furthermore, in the micronucleus formation test, the crude antifungal compounds showed no significance increase in the frequency of polychromatic erythrocytes with micronuclei. These results suggest that the crude antifungal compounds produced by B. subtilis SN7 isolated from meju showed no harmful genotoxic effects.

Genotoxicity evaluation of Hwanglyeonhaedok-tang, an herbal formula

Ethnopharmacological relevanceHwanglyeonhaedok-tang (Huanglianjiedu-tang, Orengedoku-to), a traditional herbal formula, is used for the treatment of inflammatory, gastrointestinal and cardiovascular diseases. PurposeThe purpose of this study was to evaluate the genotoxic potential of Hwanglyeonhaedok-tang water extract (HLHDT). MethodsA genotoxicity test was conducted using a bacterial reverse mutation test (Ames test), an in vitro chromosome aberration test using Chinese hamster lung cells, and an in vivo micronucleus test using ICR mouse bone marrow. ResultsIn the Ames test, which used different Salmonella typhimurium (S. typhimurium) and Escherichia coli (E. coli) strains, HLHDT did not increase the number of revertant colonies of S. typhimurium strains TA98, TA100 and TA1535 as well as E. coli strains with or without S9 mix. However, the number of revertant colonies with the S. typhimurium TA1537 strain and S9 mix increased in a dose-dependent manner. The chromosome aberration test showed that HLHDT did not increase the number of structural or numerical chromosome aberrations in a short-period test (6h) with S9 mix. By contrast, HLHDT significantly increased the number of structural chromosome aberrations in a short-period (6h) or continuous (22h) test without S9 mix. In the micronucleus test, no significant increase was observed in micronucleated polychromatic erythrocytes, and no significant decrease was observed in polychromatic to total erythrocytes. ConclusionsThese results indicate that HLHDT might be genotoxic, based on both the Ames and chromosome aberration tests. Therefore, further in vivo studies will be needed to define the mechanism of this genotoxicity.

Genotoxicity studies of substance-P by using short-term assay

Substance-P (SP) can function of mobilizing mesenchymal stem cells (MSCs) from the bone marrow to the circulation and exert anti-inflammatory effects by increasing anti-inflammatory M2-type macrophage and regulatory T cells in the circulation. The preclinical efficacy of SP was demonstrated in a variety of conditions including ischemia damages, but its safety was not assessed. In this study, we assessed the genotoxicity of SP by using in vitro bacterial reverse mutation assay, chromosomal aberration assay, and in vivo micronucleus test. The maximum test dose of SP was 250 μg/mL in a cell-based assay and 16.6 mg/kg for an in vivo test. Ames test revealed SP did not increase in the number of revertant colonies. An in vitro chromosomal aberration assay with Chinese hamster lung cells showed that SP was not clastogenic even at the maximum dose applied. In vivo micronucleus test also demonstrated that SP did not induce micronuclei formation in the bone marrow cells of male ICR mice. Taken together, our results suggest that SP is not mutagenic to bacterial cells. Moreover, SP does not cause chromosomal damage in mammalian cells either in vitro or in vivo.

The effect of particle size on the genotoxicity of gold nanoparticles.

Despite the increasing biomedical applications of gold nanoparticles (AuNPs), their toxicological effects need to be thoroughly understood. In the present study, the genotoxic potential of commercially available AuNPs with varying size (5, 20, and 50 nm) were assessed using a battery of in vitro and in vivo genotoxicity assays. In the comet assay, 20 and 50 nm AuNPs did not induce obvious DNA damage in HepG2 cells at the tested concentrations, whereas 5 nm NPs induced a dose-dependent increment in DNA damage after 24-h exposure. Furthermore, 5 nm AuNPs induced cell cycle arrest in G1 phase in response to DNA damage, and promoted the production of reactive oxygen species (ROS). In the chromosomal aberration test, AuNPs exposure did not increase in the frequency of chromosomal aberrations in Chinese hamster lung (CHL) cells. In the standard in vivo micronucleus test, no obvious increase in the frequency of micronucleus formation was found in mice after 4 day exposure of AuNPs. However, when the exposure period was extended to 14 days, 5 nm AuNPs presented significant clastogenic damage, with a dose-dependent increase of micronuclei frequencies. This finding suggests that particle size plays an important role in determining the genotoxicity of AuNPs. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 710-719, 2017.

In vitro chromosomal aberrations induced by various shapes of multi-walled carbon nanotubes (MWCNTs).

IARC has classified one type of multi-walled carbon nanotubes (MWCNTs), MWNT-7, as possibly carcinogenic to humans (Group 2B); however, other types of MWCNT were categorized as not classifiable as to their carcinogenicity to humans (Group 3). In vitro chromosomal aberration assays of MWNT-7 showed polyploid formation but not structural abnormalities. This study investigated the influence of the shape and size of MWCNT on in vitro induction of chromosomal aberrations. Microscopic analysis and viable cell counting were used to assay for chromosomal aberrations and cytotoxicity induced in a Chinese hamster lung cell line (CHL/IU) exposed to different MWCNTs. Using scanning electron microscopy, seven MWCNTs were classified into three types: straight fibrous, curved fibrous, and tangled. The straight fibrous MWCNTs were the strongest inducers of polyploidy and the most cytotoxic among the three types of MWCNTs. The curved fibrous MWCNTs induced more polyploidy than the tangled MWCNTs, and the cytotoxicity of both types seemed to be a reflection of their induction of polyploidy. None of the seven MWCNTs induced structural chromosomal aberrations. The non-clastogenicity of the MWCNTs indicates that the MWCNTs may not interact directly with DNA. Since the straight fibrous MWCNTs, which exhibit a structure similar to asbestos, were the strongest inducers of polyploidy, MWCNT shape may be an important factor in induction of polyploidy. We hypothesize that CHL/IU cells endocytosed MWCNTs and formed endosomes with shapes corresponding to those of the endocytosed MWCNTs, and that the long axis diameter of the endosome is important in the capability of MWCNTs to induce polyploidy.