Differential sensitivity of Chinese hamster V79 and Chinese hamster ovary (CHO) cells in the in vitro micronucleus screening assay

Electronic cigarette liquids impair metabolic cooperation and alter proteomic profiles in V79 cells

Background

Although still considered a safer alternative to classical cigarettes, growing body of work points to harmful effects of electronic cigarettes (e-cigarettes) affecting a range of cellular processes. The biological effect of e-cigarettes needs to be investigated in more detail considering their widespread use.

Methods

In this study, we treated V79 lung fibroblasts with sub-cytotoxic concentration of e-cigarette liquids, with and without nicotine. Mutagenicity was evaluated by HPRT assay, genotoxicity by comet assay and the effect on cellular communication by metabolic cooperation assay. Additionally, comprehensive proteome analysis was performed via high resolution, parallel accumulation serial fragmentation-PASEF mass spectrometry.

Results

E-cigarette liquid concentration used in this study showed no mutagenic or genotoxic effect, however it negatively impacted metabolic cooperation between V79 cells. Both e-cigarette liquids induced significant depletion in total number of proteins and impairment of mitochondrial function in treated cells. The focal adhesion proteins were upregulated, which is in accordance with the results of metabolic cooperation assay. Increased presence of posttranslational modifications (PTMs), including carbonylation and direct oxidative modifications, was observed. Data are available via ProteomeXchange with identifier PXD032071.

Conclusions

Our study revealed impairment of metabolic cooperation as well as significant proteome and PTMs alterations in V79 cells treated with e-cigarette liquid warranting future studies on e-cigarettes health impact.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02102-w.

Acute Toxic and Genotoxic Effects of Aluminum and Manganese Using In Vitro Models

The objective of this study was to use the same concentrations of aluminum (Al) and manganese (Mn) detected previously in groundwater above those permitted by Brazilian law and assess their cytotoxic and genotoxic effects in hamster ovary cell lines and their mutagenic effects through the Salmonella microsome assay. Chinese hamster ovary (CHO) and CHO-XRS5 cells were treated with different concentrations of Al and Mn (0.2 to 2.0 mg/L and 0.1 to 3.0 mg/L, respectively). The Ames test was used to analyze the concentrations of Al and Mn ranging from 0.025 to 1.0 mg/L and 0.0125 to 1.5 mg/L, respectively. Both metals showed cytotoxic effects on both cell lines and two bacterial strains (TA98 and TA100). The genotoxic effects of the highest concentrations of Al and Mn in cell lines showed nuclear buds, micronuclei, and DNA damage; however, none of the concentrations showed a positive mutagenic response in the Ames test. This is one of the few studies to demonstrate the cytotoxic effects of Al and Mn through the Ames test. In addition, the metals caused genomic instability in cell lines. Therefore, this study may help hasten the review of established regulatory standards for human consumption of groundwater.

Usnic acid attenuates genomic instability in Chinese hamster ovary (CHO) cells as well as chemical-induced preneoplastic lesions in rat colon

Usnic acid (UA) is one of the pharmacologically most important compounds produced by several lichen species. To better understand the mechanism of action (MOA) of this important substance, this study examined the genotoxicity attributed to UA and its influence on mutagens with varying MOA using the micronucleus (MN) test in Chinese hamster ovary cells (CHO). Additional experiments were conducted to investigate the effect of UA on colon carcinogenesis in Wistar rats employing the aberrant crypt focus (ACF) assay. In vitro studies showed a significant increase in the frequency of MN in cultures treated with the highest UA concentration tested (87.13 µM). In contrast, UA concentrations of 10.89, 21.78, or 43.56 µM produced an approximate 60% reduction in chromosomal damage induced by doxorubicin, hydrogen peroxide, and etoposide, indicating an antigenotoxic effect. In the ACF assay, male Wistar rats treated with different UA doses (3.125, 12.5, or 50 mg/kg b.w.) and with the carcinogen 1,2-dimethylhydrazine exhibited a significantly lower incidence of neoplastic lesions in the colon than animals treated only with the carcinogen. Data suggest that the MOA responsible for the chemopreventive effect of UA may be related to interaction with DNA topoisomerase II and/or the antioxidant potential of the compound.

Diversity of cultivable fungal endophytes in Paullinia cupana (Mart.) Ducke and bioactivity of their secondary metabolites

Paullinia cupana is associated with a diverse community of pathogenic and endophytic microorganisms. We isolated and identified endophytic fungal communities from the roots and seeds of P. cupana genotypes susceptible and tolerant to anthracnose that grow in two sites of the Brazilian Amazonia forest. We assessed the antibacterial, antitumor and genotoxic activity in vitro of compounds isolated from the strains Trichoderma asperellum (1BDA) and Diaporthe phaseolorum (8S). In concert, we identified eight fungal species not previously reported as endophytes; some fungal species capable of inhibiting pathogen growth; and the production of antibiotics and compounds with bacteriostatic activity against Pseudomonas aeruginosa in both susceptible and multiresistant host strains. The plant genotype, geographic location and specially the organ influenced the composition of P. cupana endophytic fungal community. Together, our findings identify important functional roles of endophytic species found within the microbiome of P. cupana. This hypothesis requires experimental validation to propose management of this microbiome with the objective of promoting plant growth and protection.

Costunolide induces micronuclei formation, chromosomal aberrations, cytostasis, and mitochondrial-mediated apoptosis in Chinese hamster ovary cells

Costunolide (CE) is a sesquiterpene lactone well-known for its antihepatotoxic, antiulcer, and anticancer activities. The present study focused on the evaluation of the cytogenetic toxicity and cellular death-inducing potential of CE in CHO cells, an epithelial cell line derived from normal ovary cells of Chinese hamster. The cytotoxic effect denoting MTT assay has shown an IC₅₀ value of 7.56 μM CE, where 50% proliferation inhibition occurs. The oxidative stress caused by CE was confirmed based on GSH depletion induced cell death, conspicuously absent in N-acetylcysteine (GSH precursor) pretreated cells. The evaluation of genotoxic effects of CE using cytokinesis block micronucleus assay and chromosomal aberration test has shown prominent induction of binucleated micronucleated cells and aberrant metaphases bearing chromatid and chromosomal breaks, indicating CE's clastogenic and aneugenic potential. The apoptotic death in CE treated cells was confirmed by an increase in the number of cells in subG1 phase, exhibiting chromatin condensation and membranous phosphatidylserine translocation. The apoptosis induction follows mitochondrial mediation, evident from an increase in the BAX/Bcl-2 ratio, caspase-3/7 activity, and mitochondrial membrane permeability. CE also induces cytostasis in addition to apoptosis, substantiated by the reduced cytokinetic (replicative indices) and mitotic (mitotic indices and histone H3 Ser-10 phosphorylation) activities. Overall, the cellular GSH depletion and potential genotoxic effects by CE led the CHO cells to commit apoptosis and lowered cell division. The observed sensitivity of CHO cells doubts unintended adverse effects of CE on normal healthy cells, suggesting higher essentiality of further studies in order to establish its safety efficacy in therapeutic explorations.

Translational Safety Genetics

The emerging field of translational safety genetics is providing new opportunities to enhance drug discovery and development. Genetic variation in therapeutic drug targets, off-target interactors and relevant drug metabolism/disposition pathways can contribute to diverse drug pharmacologic and toxicologic responses between different animal species, strains and geographic origins. Recent advances in the sequencing of rodent, canine, nonhuman primate, and minipig genomes have dramatically improved the ability to select the most appropriate animal species for preclinical drug toxicity studies based on genotypic characterization of drug targets/pathways and drug metabolism and/or disposition, thus avoiding inconclusive or misleading animal studies, consistent with the principles of the 3Rs (replacement, reduction and refinement). The genetic background of individual animals should also be taken into consideration when interpreting phenotypic outcomes from toxicity studies and susceptibilities to spontaneous safety-relevant background findings.

Evaluation of the mutagenic potential and acute oral toxicity of standardized extract of Ocimum sanctum (OciBest™)

Ocimum sanctum L. (Lamiaceae) is found throughout India and in many parts of world. O. sanctum is used for the treatment of various health indications. In this lieu, it is of prime importance to investigate the safety aspects of the plant. Hence, the present study was conducted to investigate the possible genotoxic potential and acute oral toxicity of the extract of O. sanctum (OciBest™). The standard battery of in vitro genotoxicity tests, namely bacterial reverse mutation, chromosome aberration and micronucleus (MN) tests were employed to assess the possible mutagenic activity. The results showed that OciBest™ (7.9-2500.0 µg/mL) did not increase the number of histidine revertant colonies in Salmonella typhimurium strains (TA98 and TAMix) with and without exogenous metabolic activation (S9). OciBest™ (10.0-100.0 µg/mL) did not show structural chromosomal aberrations or increase in MN induction, with and without S9, at the tested dose range in both 4-h and 18-h exposure cell cultures. Thus, OciBest™ is not genotoxic in bacterial reverse mutation, chromosomal aberration and MN tests. In an acute oral toxicity test, rats were treated with 5 g/kg of OciBest™ and observed for signs of toxicity for 14 days and the results did not show any treatment-related toxic effects to Wistar rats.

Evaluation of differential representative values between Chinese hamster cells and human lymphocytes in mitomycin C-induced cytogenetic assays and caspase-3 activity

Chinese hamster ovary (CHO) cells, its lung fibroblasts (V79), and human lymphocytes are routinely used in in vitro cytogenetic assays, which include micronuclei (MN), sister chromatid exchange (SCE), and chromosome aberration (CA) assays. Mitomycin C (MMC), a DNA cross-link alkylating agent, is both an anticancer medicine and a carcinogen. To study the differential representative values of cell types in MMC-treated cytogenetic assays and its upstream factor, cysteine aspartic acid-specific protease (caspase)-3. Among the chosen cell types, lymphocytes expressed the highest sensitivity in all three MMC-induced assays, whereas CHO and V79 showed varied sensitivity in different assays. In MN assay, the sensitivity of CHO is higher than or equal to V79; in SCE assay, the sensitivity of CHO is the same as V79; and in CA assay, the sensitivity of CHO is higher than V79. In-depth analysis of CA revealed that in chromatid breaks and dicentrics formation, lymphocyte was the most sensitive of all and CHO was more sensitive than V79; and in acentrics and interchanges formation, lymphocyte was much more sensitive than the others. Furthermore, we found caspase-3 activity plays an important role in MMC-induced cytogenetic assays, with MMC-induced caspase-3 activity resulting in more sensitivity in lymphocytes than in CHO and V79. Based on these findings, lymphocyte will make a suitable predictive or representative control reference in cytogenetic assays and caspase-3 activity with its high specificity, positive predictive value, and sensitivity.

Aflatoxin genotoxicity is associated with a defective DNA damage response bypassing p53 activation

BACKGROUND

Hepatocellular carcinoma (HCC) is a leading cause of cancer deaths. Aflatoxins, which may play a causative role in 5-28% of HCCs worldwide, are activated in liver cells and induce principally G→T mutations, including the TP53 codon 249(G→T) hotspot mutation. The DNA damage checkpoint response acts as an antitumour mechanism against genotoxic agents, but its role in aflatoxin-induced DNA damage is unknown.

AIM

We studied the DNA damage checkpoint response of human cells to aflatoxin B1 (AFB1).

METHODS AND RESULTS

The treatment of HepG2 hepatoma cells with mutation-inducing doses (3-5 μmol/l) of AFB1 induced DNA adducts, 8-hydroxyguanine lesions and DNA strand breaks that lasted several days. Persistent phospho-H2AX and 53BP1 foci were also detected, but cell growth was not affected. AFB1-exposed HepG2 cells formed phospho-H2AX and 53BP1 foci, but failed to phosphorylate both Chk1 and Chk2. Huh7 hepatoma and HCT116 colorectal cancer cell lines also exhibited a similarly incomplete checkpoint response. p53 phosphorylation also failed, and AFB1-exposed cells did not show p53-dependent G1 arrest or a sustained G2/M arrest. These observations contrasted sharply with the fully functional DNA damage response of cells to Adriamycin. Cotreatment of cells with AFB1 did not inhibit p53 and p21(Cip1) accumulation induced by Adriamycin. Thus, the deficient checkpoint response to AFB1 was not due to an inhibitory effect, but could be explained by an inefficient activation.

CONCLUSION

Genotoxic doses of AFB1 induce an incomplete and inefficient checkpoint response in human cells. This defective response may contribute to the mutagenic and carcinogenic potencies of aflatoxins.

In vitro evaluation of the genotoxicity of a family of novel MeO-PEG-poly(D,L-lactic-co-glycolic acid)-PEG-OMe triblock copolymer and PLGA nanoparticles

Despite the booming development of nanoparticle materials for pharmaceutical applications, studies on their genotoxicity are few. In our previous efforts to develop an intravenous nanoparticle material, a family of novel monomethoxy(polyethylene glycol)-poly(D,L-lactic-co-glycolic acid)-monomethoxy (PELGE) polymers was synthesized. The cytotoxicity and genotoxicity of nine kinds of selected blank PELGE and PLGA (poly(D,L-lactic and glycolic acid)) nanoparticles were evaluated using methyl thiazolyl tetrazolium (MTT), micronucleus (MN) and sister chromatid exchange (SCE) assays with or without the addition of a metabolic activation system (S9 mix), using Chinese hamster ovary (CHO) cells. The cytotoxicity of nanoparticles exhibited a dose-dependent response, with a concentration of 5 mg ml(-1) being the turning point. The frequencies of MN observed in samples treated with various nanoparticles were not statistically different from those seen in the negative controls in the presence or absence of the S9 mix. Also, no cell cycle delay was observed. The numbers of SCE per cell observed in samples treated with five kinds of PELGE nanoparticles were significantly greater than those found in the negative controls with or without the S9 mix. The discrepancies found in the two assays suggest that the five kinds of nanoparticles may produce only a weakly clastogenic response.

In vitro safety evaluation and anticlastogenic effect of BacoMind on human lymphocytes

OBJECTIVE

BacoMind (BM) is a standardized extract of Bacopa monnieri, which belongs to the family Scrophulariaceae and is a creeping annual plant found throughout the Indian subcontinent. It has been used by Ayurvedic medicinal practitioners in India for almost 3000 years and is classified as a medharasayana, a substance which improves memory and intellect. With the widespread traditional use as well as scientific validation of Bacopa monnieri for nootropic activity, a bioactive-rich unique phytochemical composition-BacoMind was developed from B. monnieri for use as a cognition and memory enhancing agent. The present study aimed to investigate the in vitro toxicity of this formulation of BacoMind on human lymphocytes and to rule out its possible contribution to mutagenicity.

METHODS

In the present investigation the active ingredients present in BM were identified and quantified by high performance liquid chromatography (HPLC) and high performance thin-layer chromatography (HPTLC). Antioxidant and anticlastogenic properties of BM were studied in vitro with and without metabolic activation. Doses of BM were chosen on the basis of mitotic index (MI) and cytokinesis-block proliferation index (CBPI). Clastogenicity assays were performed at 31.2 microg/mL, 62.5 microg/mL, and 125 microg/mL, while the Salmonella reverse mutation assay (Ames test) was performed at doses of 61.72, 185.18, 555.55, 1666.67, and 5000.00 microg/plate.

RESULTS

HPLC and HPTLC analysis of BM revealed the presence of bacoside A3, bacopaside I, bacopaside II, jujubogenin isomer of bacopasaponin C, bacosine, luteolin, apigenin, bacosine, and beta-sitosterol D glucoside. BM demonstrated significant antioxidant activity. The number of chromosomal aberrations and the frequency of micronuclei induced by BM were not statistically significant up to a dose of 62.5 microg/mL. A subsequent dose of 125 microg/mL prior to metabolic activation induced mild clastogenicity, but it was found to be biologically insignificant as this effect was not seen post metabolic activation. BM also demonstrated a dose-dependent protection against the clastogens used in this study using the above tests for clastogenicity. Maximum protection was observed in presence of metabolic activation. Moreover, BM demonstrated no mutagenic effect on the tested strains, as observed in the Ames test.

CONCLUSION

BM protected human lymphocytes against various clastogens. BM also exhibited high antioxidant activity which might be responsible for the observed protective effects against the clastogens since the used clastogens are known to induce their clastogenic effects via production of oxidative radicals.

Marine toxin okadaic acid induces aneuploidy in CHO-K1 cells in presence of rat liver postmitochondrial fraction, revealed by cytokinesis-block micronucleus assay coupled to FISH

Okadaic acid (OA), a major polyether toxin involved in diarrhetic shellfish poisoning (DSP), is a potent tumor promoter in rodent skin and glandular stomach and a specific inhibitor of the serine/threonine protein phosphatases PP1 and PP2A. A previous study, which used the cytokinesis-block micronucleus (CBMN) assay in CHO-K1 cells, showed that OA induced chromosome damage in the presence of a rat liver metabolic activation system (S9). To support OA biotransformation by S9, the same test system was performed, and DNA damage induced by OA was measured with and without metabolic activation as well as in the presence of heat-inactivated S9 fraction. The results showed that only in the presence of active S9 did OA significantly increased the frequency of micronucleated binucleated (MNBN) cells. After a 4-h treatment a 2- to 5-fold increase of MNBN cells was observed at 30 nM and at 50 nM of OA. However, without S9 or in the presence of heat-inactivated S9, OA did not induce any chromosome damage. We concluded that OA can be metabolically activated in vitro into metabolites that are more genotoxic. The CBMN assay coupled with fluorescence in situ hybridization (FISH) using a DNA probe for centromere detection was performed to discriminate between clastogenic (chromosome breakage) and aneugenic (chromosome loss) effects. FISH analysis showed that OA metabolites increased in a dose-dependent manner in centromere positive micronuclei (CEN+): 60% of CEN+ at 30 nM and 75% of CEN+ at 50 nM of OA. The uptake of OA into CHO-K1 cells and the biotransformation of the toxin are discussed.

Heterologous expression of human cytochrome P450 2E1 in HepG2 cell line

AIM: Human cytochrome P-450 2E1 (CYP2E1) takes part in the biotransformation of ethanol, acetone, many small-molecule substrates and volatile anesthetics. CYP2E1 is involved in chemical activation of many carcinogens, procarcinogens, and toxicants. To assess the metabolic and toxicological characteristics of CYP2E1, we cloned CYP2E1 cDNA and established a HepG2 cell line stably expressing recombinant CYP 2E1.

METHODS: Human CYP2E1 cDNA was amplified with reverse transcription-polymerase chain reaction (RT-PCR) from total RNAs extracted from human liver and cloned into pGEM-T vector. The cDNA segment was identified by DNA sequencing and subcloned into a mammalian expression vector pREP9. A transgenic cell line was established by transfecting the recombinant plasmid of pREP9-CYP2E1 to HepG2 cells. The expression of CYP2E1 mRNA was validated by RT-PCR. The enzyme activity of CYP2E1 catalyzing oxidation of 4-nitrophenol in postmitochondrial supernate (S9) fraction of the cells was determined by spectrophotometry. The metabolic activation of HepG2-CYP2E1 cells was assayed by N-nitrosodiethylamine (NDEA) cytotoxicity and micronucleus test.

RESULTS: The cloned CYP2E1 cDNA segment was identical to that reported by Umeno et al (GenBank access No. J02843). HepG2-CYP2E1 cells expressed CYP2E1 mRNA and had 4-nitrophenol hydroxylase activity (0.162 ± 0.025 nmol·min^-1·mg^-1 S9 protein), which were undetectable in parent HepG2 cells. HepG2-CYP2E1 cells increased the cytotoxicity and micronucleus rate of NDEA in comparison with those of HepG2 cells.

CONCLUSION: The cDNA of human CYP2E1 can be successfully cloned, and a cell line, HepG2-CYP2E1, which can efficiently express mRNA and has CYP2E1 activity, is established. The cell line is useful for testing the cytotoxicity, mutagenicity and metabolism of xenobiotics, which may possibly be activated or metabolized by CYP2E1.

Effects of vitamins C and E on cytotoxicity induced by N-nitroso compounds, N-nitrosomorpholine and N-methyl-N'-nitro-N-nitrosoguanidine in Caco-2 and V79 cell lines

Since N-nitroso compounds as strong carcinogens are closely related to food and nutrition, the cytotoxic effects of N-nitrosomorpholine (NMOR) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and their reduction by vitamins C and E were investigated in hamster V79 cells and human colon carcinoma Caco-2 cells. Cytotoxicity was evaluated by the trypan blue exclusion technique in Caco-2 cells and by the plating efficiency assay in V79 cells. NMOR caused a dose-dependent decline of viable cells in both cell lines; MNNG induced a dose-dependent cytotoxic effect only in V79 cells. Pretreatment of cells with vitamin C and vitamin E significantly reduced the cytotoxicity of NMOR, however, both vitamins had not effect on cytotoxicity induced by MNNG. These results suggest that different N-nitroso compounds react differently with cellular macromolecules. Measurement of the level of NMOR-induced DNA strand breaks and alkali-labile sites in both cell types using the alkaline comet assay also indicates a protective effect of both vitamins against the genotoxic effects of NMOR.