Current Status of Short-Term Tests for Evaluation of Genotoxicity, Mutagenicity, and Carcinogenicity of Environmental Chemicals and NCEs

q-RASTR modelling for prediction of diverse toxic chemicals towards T. pyriformis

A series of diverse organic compounds impose serious detrimental effects on the health of living organisms and the environment. Determination of the structural aspects of compounds that impart toxicity and evaluation of the same is crucial before public usage. The present study aims to determine the structural characteristics of compounds for Tetrahymena pyriformis toxicity using the q-RASTR (Quantitative Read Across Structure-Toxicity Relationship) model. It was developed using RASTR and 2-D descriptors for a dataset of 1792 compounds with defined endpoint (pIGC50) against a model organism, T. pyriformis. For the current study, the whole dataset was divided based on activity/property into the training and test sets, and the q-RASTR model was developed employing six descriptors (three latent variables) having r2, Q2F1 and Q2 values of 0.739, 0.767, and 0.735, respectively. The generated model was thoroughly validated using internationally recognized internal and external validation criteria to assess the model's dependability and predictability. It was highlighted that high molecular weight, aromatic hydroxyls, nitrogen, double bonds, and hydrophobicity increase the toxicity of organic compounds. The current study demonstrates the applicability of the RASTR algorithm in QSTR model development for the prediction of toxic chemicals (pIGC50) towards T. pyriformis.

Antagonistic Skin Toxicity of Co-Exposure to Physical Sunscreen Ingredients Zinc Oxide and Titanium Dioxide Nanoparticles

Being the main components of physical sunscreens, zinc oxide nanoparticles (ZnO NPs) and titanium dioxide nanoparticles (TiO₂ NPs) are often used together in different brands of sunscreen products with different proportions. With the broad use of cosmetics containing these nanoparticles (NPs), concerns regarding their joint skin toxicity are becoming more and more prominent. In this study, the co-exposure of these two NPs in human-derived keratinocytes (HaCaT) and the in vitro reconstructed human epidermis (RHE) model EpiSkin was performed to verify their joint skin effect. The results showed that ZnO NPs significantly inhibited cell proliferation and caused deoxyribonucleic acid (DNA) damage in a dose-dependent manner to HaCaT cells, which could be rescued with co-exposure to TiO₂ NPs. Further mechanism studies revealed that TiO₂ NPs restricted the cellular uptake of both aggregated ZnO NPs and non-aggregated ZnO NPs and meanwhile decreased the dissociation of Zn²⁺ from ZnO NPs. The reduced intracellular Zn²⁺ ultimately made TiO₂ NPs perform an antagonistic effect on the cytotoxicity caused by ZnO NPs. Furthermore, these joint skin effects induced by NP mixtures were validated on the epidermal model EpiSkin. Taken together, the results of the current research contribute new insights for understanding the dermal toxicity produced by co-exposure of different NPs and provide a valuable reference for the development of formulas for the secure application of ZnO NPs and TiO₂ NPs in sunscreen products.

Inhibitory effect of purple rice husk extract on AFB1-induced micronucleus formation in rat liver through modulation of xenobiotic metabolizing enzymes

Background

Rice husk, a waste material produced during milling, contains numerous phytochemicals that may be sources of cancer chemopreventive agents. Various biological activities of white and colored rice husk have been reported. However, there are few comparative studies of the cancer chemopreventive effects of white and colored rice husk.

Methods

This study investigated the cancer chemopreventive activities of two different colors of rice husk using in vitro and in vivo models. A bacterial mutation assay using Salmonella typhimurium strains TA98 and TA100 was performed; enzyme induction activity in murine hepatoma cells was measured, and a liver micronucleus test was performed in male Wistar rats.

Results

The white rice husk (WRHE) and purple rice husk (PRHE) extracts were not mutagenic in Salmonella typhimurium TA98 or TA100 in the presence or absence of metabolic activation. However, the extracts exhibited antimutagenicity against aflatoxin B₁ (AFB₁) and 2-amino-3,4 dimethylimidazo[4,5-f]quinolone (MeIQ) in a Salmonella mutation assay. The extracts also induced anticarcinogenic enzyme activity in a murine Hepa1c1c7 hepatoma cell line. Interestingly, PRHE but not WRHE exhibited antigenotoxicity in the rat liver micronucleus test. PRHE significantly decreased the number of micronucleated hepatocytes in AFB₁-initiated rats. PRHE contained higher amounts of phenolic compounds and vitamin E than WRHE in both tocopherols and tocotrienols as well as polyphenol such as cyanidin-3-glucoside, protocatechuic acid and vanillic acid. Furthermore, PRHE increased CYP1A1 and 1A2 activities while decreasing CYP3A2 activity in the livers of AFB₁-treated rats. PRHE also enhanced various detoxifying enzyme activities, including glutathione S-transferase, NAD(P)H quinone oxidoreductase and heme oxygenase.

Conclusions

PRHE showed potent cancer chemopreventive activity in a rat liver micronucleus assay through modulation of phase I and II xenobiotic metabolizing enzymes involved in AFB₁ metabolism. Vitamin E and phenolic compounds may be candidate antimutagens in purple rice husk.

Electronic supplementary material

The online version of this article (10.1186/s12906-019-2647-9) contains supplementary material, which is available to authorized users.

ZnO nanoparticles-associated mitochondrial stress-induced apoptosis and G2/M arrest in HaCaT cells: a mechanistic approach

Zinc oxide nanoparticles (ZnO NPs) with their wide range of consumer applications in day-to-day life received great attention to evaluate their effects in humans. This study has been attempted to elucidate the DNA damage response mechanism in a dermal model exposed to ZnO NPs through Ataxia Telangiectasia Mutated (ATM)-mediated ChK1-dependent G2/M arrest. Further, viability parameters and mechanism involved in the cell death with special reference to the consequences arising due to DNA damage were explored. Our study showed that ZnO NPs at concentrations 5 and 10 µg/ml induced significant cytotoxic effect in skin cell line. Moreover, the results confirmed generation of reactive oxygen species (ROS) induces the cell death by genotoxic insult, leading to mitochondrial membrane depolarisation and cell cycle arrest. Subsequently, ZnO NPs treatment created DNA damage as confirmed via Comet assay (increase in olive tail moment), micronucleus assay (increase in micronucleus formation), double-strand breaks (increase in ATM and Ataxia Telangiectasia and Rad3 related (ATR) expression), DNA fragmentation and cell cycle (G2/M arrest) studies. Finally, marker proteins analysis concluded the mechanistic approach by demonstrating the key marker expressions HMOX1 and HSP60 (for oxidative stress), cytochrome c, APAF1, BAX, Caspase 9, Caspase 3 and decrease in BCL2 (for activating apoptotic pathway), pATM, ATR and γH2AX (for double-strand breaks), DNA-PK (involved in DNA repair) and decrease in cell cycle regulators. In together, our data revealed the mechanism of ROS generation that triggers apoptosis and DNA damage in HaCaT cell lines exposed to ZnO NPs.

Formulation of vitamin D encapsulated cinnamon oil nanoemulsion: Its potential anti-cancerous activity in human alveolar carcinoma cells

Cinnamon oil is used for medicinal purpose since ancient time because of its antioxidant activity. Oil-in-water nanoemulsion (NE) of cinnamon oil was formulated using cinnamon oil, nonionic surfactant Tween 80 and water by ultrasonication technique. Phase diagram was constructed to investigate the influence of oil, water and surfactant concentration. Vitamin D encapsulated cinnamon oil NE was fabricated by wash out method followed by ultrasonication in similar fashion. The hydrodynamic size of cinnamon oil NE and vitamin D encapsulated cinnamon oil NE was observed as 40.52 and 48.96 nm in complete DMEM F12 media respectively. We focused on the cytotoxic and genotoxic responses of NEs in A549 cells in concentration dependent manner. We observed that both NEs induce DNA damage along with corresponding increase in micronucleus frequency that is evident from the comet and CBMN assay. Both the NEs arrested the cell cycle progression in G0/G1 phase, showed increased expression of Bax, capase-3 and caspase-9 and decrease expression of BcL2 proteins along with significant (p < 0.05) increase in apoptotic cell population and loss of mitochondrial membrane potential. NEs were also evaluated for bactericidal efficacy against E. coli. Thus, both NEs have cytotoxic, genotoxic and antibacterial potential and hence can also be used in food industry with cinnamon oil as carrier for lipophilic nutraceutical like vitamin D.

The lower alkyl methacrylates: Genotoxic profile of non-carcinogenic compounds

All of the lower alkyl methacrylates are high production chemicals with potential for human exposure. The genotoxicity of seven mono-functional alkyl esters of methacrylic acid, i.e. methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, n-, i- and t-butyl methacrylate and 2 ethyl hexyl methacrylate, as well as methacrylic acid itself, the acyl component common to all, is reviewed and compared with the lack of carcinogenicity of methyl methacrylate, the representative member of the series so evaluated. Also reviewed are the similarity of structure, chemical and biological reactivity, metabolism and common metabolic products of this group of compounds which allows a category approach for assessing genotoxicity. As a class, the lower alkyl methacrylates are universally negative for gene mutations in prokaryotes but do exhibit high dose clastogenicity in mammalian cells in vitro. There is no convincing evidence that these compounds induce genotoxic effects in vivo in either sub-mammalian or mammalian species. This dichotomy of effects can be explained by the potential genotoxic intermediates generated in vitro. This genotoxic profile of the lower alkyl methacrylates is consistent with the lack of carcinogenicity of methyl methacrylate.

8-Azapurines as isosteric purine fluorescent probes for nucleic acid and enzymatic research

The 8-azapurines, and their 7-deaza and 9-deaza congeners, represent a unique class of isosteric (isomorphic) analogues of the natural purines, frequently capable of substituting for the latter in many biochemical processes. Particularly interesting is their propensity to exhibit pH-dependent room-temperature fluorescence in aqueous medium, and in non-polar media. We herein review the physico-chemical properties of this class of compounds, with particular emphasis on the fluorescence emission properties of their neutral and/or ionic species, which has led to their widespread use as fluorescent probes in enzymology, including enzymes involved in purine metabolism, agonists/antagonists of adenosine receptors, mechanisms of catalytic RNAs, RNA editing, etc. They are also exceptionally useful fluorescent probes for analytical and clinical applications in crude cell homogenates.

High-throughput in vivo genotoxicity testing: an automated readout system for the somatic mutation and recombination test (SMART)

Genotoxicity testing is an important component of toxicity assessment. As illustrated by the European registration, evaluation, authorization, and restriction of chemicals (REACH) directive, it concerns all the chemicals used in industry. The commonly used in vivo mammalian tests appear to be ill adapted to tackle the large compound sets involved, due to throughput, cost, and ethical issues. The somatic mutation and recombination test (SMART) represents a more scalable alternative, since it uses Drosophila, which develops faster and requires less infrastructure. Despite these advantages, the manual scoring of the hairs on Drosophila wings required for the SMART limits its usage. To overcome this limitation, we have developed an automated SMART readout. It consists of automated imaging, followed by an image analysis pipeline that measures individual wing genotoxicity scores. Finally, we have developed a wing score-based dose-dependency approach that can provide genotoxicity profiles. We have validated our method using 6 compounds, obtaining profiles almost identical to those obtained from manual measures, even for low-genotoxicity compounds such as urethane. The automated SMART, with its faster and more reliable readout, fulfills the need for a high-throughput in vivo test. The flexible imaging strategy we describe and the analysis tools we provide should facilitate the optimization and dissemination of our methods.

TiO2 nanoparticles induce DNA double strand breaks and cell cycle arrest in human alveolar cells

TiO2 nanoparticles (NPs) have the second highest global annual production (∼3000 tons) among the metal-containing NPs. These NPs are used as photocatalysts for bacterial disinfection, and in various other consumer products including sunscreen, food packaging, therapeutics, biosensors, surface cleaning agents, and others. Humans are exposed to these NPs during synthesis (laboratory), manufacture (industry), and use (consumer products, devices, medicines, etc.), as well as through environmental exposures (disposal). Hence, there is great concern regarding the health effects caused by exposure to NPs and, in particular, to TiO2 NPs. In the present study, the genotoxic potential of TiO2 NPs in A549 cells was examined, focusing on their potential to induce ROS, different types of DNA damage, and cell cycle arrest. We show that TiO2 NPs can induce DNA damage and a corresponding increase in micronucleus frequency, as evident from the comet and cytokinesis-block micronucleus assays. We demonstrate that DNA damage may be attributed to increased oxidative stress and ROS generation. Furthermore, genomic and proteomic analyses showed increased expression of ATM, P53, and CdC-2 and decreased expression of ATR, H2AX, and Cyclin B1 in A549 cells, suggesting induction of DNA double strand breaks. The occurrence of double strand breaks was correlated with cell cycle arrest in G2/M phase. Overall, the results indicate the potential for genotoxicity following exposure to these TiO2 NPs, suggesting that use should be carefully monitored.

Green tea infusion improves cyclophosphamide-induced damage on male mice reproductive system

Green tea presents catechins as its major components and it has a potential antioxidant activity. Cyclophosmamide (CP) is an antineoplastic and immunosuppressive agent, known to reduce fertility. In the present study, we evaluated the effect of green tea infusion on cyclophosphamide-induced damage in male mice reproductive system. Mice received green tea infusion (250 mg/kg) or vehicle by gavage for 14 days. Saline or CP were injected intraperitoneally at a single dose (100 mg/kg) at the 14th day. Animals were euthanized 24 h after CP administration and testes and epididymis were removed for biochemical analysis and sperm evaluation. Catechins concentration in green tea infusion was evaluated by HPLC. CP increased lipid peroxidation, DNA damage and superoxide dismutase activity whereas sperm concentration, glutathione peroxidase (GPx), glutathione S-transferase (GST) and 17β-hydroxysteroid (17β-HSD) dehydrogenase activities were reduced in both tissues tested. Catalase activity and protein carbonyl levels were changed only in testes, after CP administration. Green tea pre-treatment reduced significantly lipid peroxidation, protein carbonylation, DNA damage and restored GPx and GST activity in testes. In epididymis, therapy significantly increased sperm concentration and restored GPx and 17β-HSD activity. Green tea improves CP-induced damage on reproductive system, probably due to their high catechins content.

Assessment of genotoxic potential of hridayarnava rasa (a herbo-mineralo-metallic ayurvedic formulation) using chromosomal aberration and sperm abnormality assays

OBJECTIVES

Herbo-mineral formulations are being successfully used in therapeutics since centuries. But recently, they came under the scanner for their metallic contents especially the presence of heavy metals. Hence it is the need of the hour to assess and establish the safety of these formulations through toxicity studies. In line with the various toxicity studies that are being carried out, Government of India expressed the need for conducting genotoxicity studies of different metal- or mineral-based drugs. Till date very few Ayurvedic herbo-mineral formulations have been studied for their genotoxic potential. The present study is aimed to evaluate the genotoxic potential of Hridayarnava Rasa.

MATERIALS AND METHODS

It was prepared as per classical guidelines and administered to Swiss albino mice for 14 consecutive days. Chromosomal aberration and sperm abnormality assay were done to evaluate the genotoxic potential of the test drugs. Cyclophosphamide (CP) was taken as positive group and results were compared.

RESULTS

All treated groups exhibited significant body weight gain in comparison to CP group. Results revealed no structural deformity in the above parameters in comparison to the CP-treated group.

CONCLUSION

Reported data showed that both tested samples of Hridayarnava Rasa does not possess genotoxic potential under the experimental conditions and can be safely used.

γ-Oryzanol protects against acute cadmium-induced oxidative damage in mice testes

Cadmium is a non-essential heavy metal that is present at low levels mainly in food and water and also in cigar smoke. The present study evaluated the testicular damage caused by acute cadmium exposure and verified the protective role of γ-oryzanol (ORY). Mice were administrated with a single dose of 2.5mg/kg of CdCl2, and then treated with ORY (50mM in canola oil, 5mL/kg). Testes were removed after 24h and tested for lipid peroxidation (TBARS), protein carbonylation, DNA breakage, ascorbic acid, cadmium and non-proteic thiols contents, and for the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST) and δ-aminolevulic acid dehydratase (δ-ALA-D). Cadmium presented a significant alteration in all parameters, except GPx and CAT activities. Therapy reduced in a slight degree cadmium concentration in testes (around 23%). ORY restored SOD and GST activities as well as TBARS production to the control levels. Furthermore, ORY partially recovered δ-ALA-D activity inhibited by cadmium. This study provides the first evidence on the therapeutic properties of ORY in protecting against cadmium-induced testicular toxicity.

Repeated vitrification/warming of human sperm gives better results than repeated slow programmable freezing

In this study, we compared the effects of repeated freezing/thawing of human sperm by our in-house method of rapid freezing with slow programmable freezing. Sperm samples from 11 normozoospermic subjects were processed through density gradients and divided into three aliquots: non-frozen, rapid freezing and slow programmable freezing. Sperm in the rapid freezing group had better motility and viability than those in the slow freezing group (P<0.01) after the first, second and third cycles of freezing/thawing, but there was no difference in morphology. In the second experiment, rapid freezing was repeated three times in 20 subjects. The samples from each thawing cycle were evaluated for DNA fragmentation using the alkaline comet assay. DNA fragmentation began to increase considerably after the second cycle of freezing/thawing, but to a level that was not clinically important. In the third experiment, rapid freezing was done repeatedly in 10 subjects, until no motile sperm were observed after thawing. The median number of repeated freezing/thawing that yielded no motile sperm was seven (range: 5-8, mean: 6.8). In conclusion, we demonstrated that repeated freezing/thawing of processed semen using our rapid freezing method gave better results than standard slow programmable freezing. This method can help maximize the usage of precious cryopreserved sperm samples in assisted reproduction technology.

Random Forest Prediction of Mutagenicity from Empirical Physicochemical Descriptors

Fast-to-calculate empirical physicochemical descriptors were investigated for their ability to predict mutagenicity (positive or negative Ames test) from the molecular structure. Fast methods are highly desired for the screening of large libraries of compounds. Global molecular descriptors and MOLMAP descriptors of bond properties were used to train random forests. Error percentages as low as 15% and 16% were achieved for an external test set with 472 compounds and for the training set with 4083 structures, respectively. High sensitivity and specificity were observed. Random forests were able to associate meaningful probabilities to the predictions and to explain the predictions in terms of similarities between query structures and compounds in the training set.