Hues of risk: investigating genotoxicity and environmental impacts of azo textile dyes

The textile industry, with its extensive use of dyes and chemicals, stands out as a significant source of water pollution. Exposure to certain textile dyes, such as azo dyes and their breakdown products like aromatic amines, has been associated with health concerns like skin sensitization, allergic reactions, and even cancer in humans. Annually, the worldwide production of synthetic dyes approximates 7 × 107 tons, of which the textile industry accounts for over 10,000 tons. Inefficient dyeing procedures result in the discharge of 15-50% of azo dyes, which do not adequately bind to fibers, into wastewater. This review delves into the genotoxic impact of azo dyes, prevalent in the textile industry, on aquatic ecosystems and human health. Examining different families of textile dye which contain azo group in their structure such as Sudan I and Sudan III Sudan IV, Basic Red 51, Basic Violet 14, Disperse Yellow 7, Congo Red, Acid Red 26, and Acid Blue 113 reveals their carcinogenic potential, which may affect both industrial workers and aquatic life. Genotoxic and carcinogenic characteristics, chromosomal abnormalities, induced physiological and neurobehavioral changes, and disruptions to spermatogenesis are evident, underscoring the harmful effects of these dyes. The review calls for comprehensive investigations into the toxic profile of azo dyes, providing essential insights to safeguard the aquatic ecosystem and human well-being. The importance of effective effluent treatment systems is underscored to mitigate adverse impacts on agricultural lands, water resources, and the environment, particularly in regions heavily reliant on wastewater irrigation for food production.

Effects of dose and human N-acetyltransferase 1 genetic polymorphism in benzidine metabolism and genotoxicity

Benzidine undergoes N-acetylation and following CYP1A2-catalyzed N-hydroxylation undergoes O-acetylation catalyzed by N-acetyltransferase 1 (NAT1). Benzidine exposure is associated with urinary bladder cancer but the effect of NAT1 genetic polymorphism on individual risk remains unclear. We used Chinese hamster ovary (CHO) cells transfected with human CYP1A2 and NAT1*4 allele (reference) or NAT1*14B (variant) to investigate the effects of dose and NAT1 polymorphism on benzidine metabolism and genotoxicity. Rates of benzidine N-acetylation in vitro were higher in CHO cells transfected with NAT1*4 compared to NAT1*14B. CHO cells transfected with NAT1*14B exhibited greater N-acetylation rates in situ than cells transfected with NAT1*4 at low doses of benzidine expected with environmental exposures but not at higher doses. NAT1*14B exhibited over tenfold lower apparent KM which resulted in higher intrinsic clearance for benzidine N-acetylation compared to CHO cells transfected with NAT1*4. Benzidine-induced hypoxanthine phosphoribosyl transferase (HPRT) mutations were higher in CHO cells transfected with NAT1*14B than with NAT1*4 (p < 0.001). Benzidine caused concentration-dependent increase in γ-H2AX signal (indicative of DNA double-strand breaks) in CHO cells transfected with NAT1*4 or NAT1*14B. CHO cells transfected with NAT1*14B exhibited significantly higher level of DNA damage than with NAT1*4 (p < 0.0001). Benzidine-induced ROS did not differ significantly (p > 0.05) between CHO cells transfected with NAT1*4 or NAT1*14B except at 50 μM. Levels of benzidine-induced DNA damage and reactive oxygen species (ROS) showed strong dose-dependent correlation. Our findings support human studies associating NAT1*14B with increased incidence or severity of urinary bladder cancer in workers exposed to benzidine.

Chronic exposure to synthetic food colorant Allura Red AC promotes susceptibility to experimental colitis via intestinal serotonin in mice

Chemicals in food are widely used leading to significant human exposure. Allura Red AC (AR) is a highly common synthetic colorant; however, little is known about its impact on colitis. Here, we show chronic exposure of AR at a dose found in commonly consumed dietary products exacerbates experimental models of colitis in mice. While intermittent exposure is more akin to a typical human exposure, intermittent exposure to AR in mice for 12 weeks, does not influence susceptibility to colitis. However, exposure to AR during early life primes mice to heightened susceptibility to colitis. In addition, chronic exposure to AR induces mild colitis, which is associated with elevated colonic serotonin (5-hydroxytryptamine; 5-HT) levels and impairment of the epithelial barrier function via myosin light chain kinase (MLCK). Importantly, chronic exposure to AR does not influence colitis susceptibility in mice lacking tryptophan hydroxylase 1 (TPH1), the rate limiting enzyme for 5-HT biosynthesis. Cecal transfer of the perturbed gut microbiota by AR exposure worsens colitis severity in the recipient germ-free (GF) mice. Furthermore, chronic AR exposure elevates colonic 5-HT levels in naïve GF mice. Though it remains unknown whether AR has similar effects in humans, our study reveals that chronic long-term exposure to a common synthetic colorant promotes experimental colitis via colonic 5-HT in gut microbiota-dependent and -independent pathway in mice.

Melatonin reverses mitochondria dysfunction and oxidative stress-induced apoptosis of Sudan I-exposed mouse oocytes

Sudan I is one of the industry dyes and widely used in cosmetics, wax agent, solvent and textile. Sudan I has multiple toxicity such as carcinogenicity, mutagenicity, genotoxicity and oxidative damage. However, Sudan I has been illegally used as colorant in food products, triggering worldwide attention about food safety. Nevertheless, the toxicity of Sudan I on reproduction, particularly on oocyte maturation is still unclear. In the present study, using mouse in vivo models, we report the toxicity effects of Sudan I on mouse oocyte. The results reflect that Sudan I exposure disrupts spindle organization and chromosomes alignment as well as cortical actin distribution, thus leading to the failure of polar body extrusion. Based on the transcriptome results, it is found that the exposure of Sudan I leads to the change in expression of 764 genes. Moreover, it's further reflected that the damaging effects of Sudan I are mediated by the destruction of mitochondrial functions, which induces the accumulated ROS to stimulate oxidative stress-induced apoptosis. As an endogenous hormone, melatonin within the ovarian follicle plays function on improving oocyte quality and female reproduction by efficiently suppressing oxidative stress. Moreover, melatonin supplementation also improves oocyte quality and increases fertilization rate during in vitro culture. Consistent with these, we find that in vivo supplementation of melatonin efficaciously suppresses mitochondrial dysfunction and the accompanying apoptosis, thus reverses oocyte meiotic deteriorations. Collectively, our results prove the reproduction toxicity of Sudan I for the exposure of Sudan I reduces the oocyte quality, and demonstrate the protective effects of melatonin against Sudan I-induced meiotic deteriorations.

Fast, easy, cheap, robust and safe method of analysis of Sudan dyes in chilli pepper powder

Illicit use of Sudan dyes, a group of harmful and carcinogenic azo dyes, in the food industry has taken a surge in various parts of the world, especially in Africa. Their use in food as additives pose a dire health risk to consumers and have been banned by various food regulatory bodies worldwide. To help increase surveillance, various methods have been proposed for their analysis in literature. This study also sought to experiment and propose an alternative method for quick, easy, cheap, robust and ecologically safe analysis of Sudan dyes in chilli pepper powder and similar matrices. The optimized method used a 6.0 mL mixture of acetone:acetonitrile (1:5 v/v) solvent in a modified QuEChERs method for extraction of Sudan dyes I-IV. The simultaneous analysis of the dyes were achieved on Shimadzu prominence UFLC 20AD coupled with SPD 20AX UV detector operated at dual wavelength of 500 and 480 nm. A total of twenty four (24) chilli pepper powder samples from eight different vendors on the Ghana market were analysed using the optimized method. Quantitation of analytes were done using the external standard calibration method with determination coefficient, R² > 0.9999. The limit of detection (LOD) and limit of quantitation (LOQ) of the method were 0.02–0.04 mg/kg and 0.05–0.13 mg/kg respectively. A good recovery range between 85.3 – 121.2% were obtained for a spike level of 1.0 mg/kg in real samples. ANOVA analysis at 95% CL showed statistically no significant difference (p > 0.05) in the recoveries between samples and also between the individual compounds. The method experimented and proposed in this study is fast, easy, cheap, robust and ecologically safe, presenting an alternative method for routine analysis for increased rate of surveillance against the illicit use of Sudan dyes as food additives.

A Non-Cytotoxic Resin for Micro-Stereolithography for Cell Cultures of HUVECs

Three-dimensional (3D) printing of microfluidic devices continuously replaces conventional fabrication methods. A versatile tool for achieving microscopic feature sizes and short process times is micro-stereolithography (µSL). However, common resins for µSL lack biocompatibility and are cytotoxic. This work focuses on developing new photo-curable resins as a basis for µSL fabrication of polymer materials and surfaces for cell culture. Different acrylate- and methacrylate-based compositions are screened for material characteristics including wettability, surface roughness, and swelling behavior. For further understanding, the impact of photo-absorber and photo-initiator on the cytotoxicity of 3D-printed substrates is studied. Cell culture experiments with human umbilical vein endothelial cells (HUVECs) in standard polystyrene vessels are compared to 3D-printed parts made from our library of homemade resins. Among these, after optimizing material composition and post-processing, we identify selected mixtures of poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) methyl ethyl methacrylate (PEGMEMA) as most suitable to allow for fabricating cell culture platforms that retain both the viability and proliferation of HUVECs. Next, our PEGDA/PEGMEMA resins will be further optimized regarding minimal feature size and cell adhesion to fabricate microscopic (microfluidic) cell culture platforms, e.g., for studying vascularization of HUVECs in vitro.

Response of soil enzymes, functional bacterial groups, and microbial communities exposed to sudan I-IV

As an important type of typical synthetic azo dyes, the use of sudan I-IV dyes has been of concern worldwide because of their wide applications and illegal addition into various foodstuffs, potentially resulting in water and soil pollution and having adverse effects on human health and ecosystems. However, to date, little has been reported regarding the environmental levels of these dyes and the risks that they pose to human health and ecosystems. Understanding the responses of soil enzymes, functional groups of bacteria and microbial communities to sudan dyes is of great importance to reveal their effect on the soil environment. In this study, we performed a toxicological study on the specific and overall effects of sudan I-IV dyes on the activity of soil enzymes including catalase, urease, and alkaline phosphatase after a 2- and 7-day exposure, functional groups of soil bacteria including nitrogen-fixing, ammonia-oxidizing, and denitrifying bacteria on day 14, and the structure and diversity of soil microbial community compositions on day 30. The results showed that sudan I-IV affected the activity of the soil enzymes, the abundance of the bacterium functional groups, and the structure and diversity of microbial community compositions, and the effects varied by sudan dyes I-IV, the exposure concentration, and the exposure time.

A comparison of the genotoxicity of benzo[a]pyrene in four cell lines with differing metabolic capacity

Benzo[a]pyrene (B[a]P) is a known genotoxin and carcinogen, yet its genotoxic response at low level exposure has not been determined. This study was conducted to examine the interplay of dose and metabolic capacity on genotoxicity of B[a]P. Investigating and better understanding the biological significance of low level chemical exposures will help improve human health risk assessments. The genotoxic and mutagenic effects of B[a]P were investigated using human cell lines (AHH-1, MCL-5, TK6 and HepG2) with differential expression of the CYP450 enzymes CYP1A1, 1B1 and1A2 involved in B[a]P metabolism. MCL-5 and HepG2 cells showed detectable basal expression and activity of CYP1A1, 1B1 and 1A2 than AHH-1 which only show CYP1A1 basal expression and activity. TK6 cells showed negligible expression levels of all three CYP450 enzymes. In vitro micronucleus and HPRT assays were conducted to determine the effect of B[a]P on chromosome damage and point mutation induction. After 24h exposure, linear increases in micronucleus (MN) frequency were observed in all cell lines except TK6. After 4h exposure, only the metabolically competent cell lines MCL-5 and HepG2 showed MN induction (with a threshold concentration at 25.5μM from MCL-5 cells) indicating the importance of exposure time for genotoxicity. The HPRT assay also displayed linear increases in mutant frequency in MCL-5 cells, after 4h and 24h treatments. Mutation spectra analysis of MCL-5 and AHH-1 HPRT mutants revealed frequent B[a]P induced G to T transversion mutations (72% and 44% of induced mutations in MCL-5 and AHH-1 respectively). This study therefore demonstrates a key link between metabolic capability, B[a]P exposure time and genotoxicity.

Detoxification of azo dyes in the context of environmental processes

Azo dyes account for >70% of the global industrial demand (∼9 million tons). Owing to their genotoxic/carcinogenic potential, the annual disposal of ∼4,500,000 tons of dyes and/or degraded products is an environmental and socio-economic concern. In comparison to physico-chemical methods, microbe-mediated dye degradation is considered to be low-input, cost-effective and environmentally-safe. However, under different environmental conditions, interactions of chemically diverse dyes with metabolically diverse microbes produce metabolites of varying toxicity. In addition, majority of studies on microbial dye-degradation focus on decolorization with least attention towards detoxification. Therefore, the environmental significance of microbial dye detoxification research of past >3 decades is critically evaluated with reference to dye structure and the possible influence of microbial interactions in different environments. In the absence of ecosystem-based studies, the results of laboratory-based studies on dye degradation, metabolite production and their genotoxic impact on model organisms are used to predict the possible fate and consequences of azo dyes/metabolites in the environment. In such studies, the predominance of fewer numbers of toxicological assays that too at lower levels of biological organization (molecular/cellular/organismic) suggests its limited ecological significance. Based on critical evaluation of these studies the recommendations on inclusion of multilevel approach (assessment at multiple levels of biological organization), multispecies microcosm approach and native species approach in conjunction with identification of dye metabolites have been made for future studies. Such studies will bridge the gap between the fundamental knowledge on dye-microbe-environment interactions and its application to combat dye-induced environmental toxicity. Thus an environmental perspective on dye toxicity in the background of dye structure and effects of environmental processes has been developed. Based on past 3 decades of research on microbial dye detoxification, the current state of knowledge has been analyzed, environmental relevance of these studies was ascertained, research gaps in microbe-mediated azo dye detoxification have been identified and a research framework emphasizing a better understanding of complex interactions between dye-microbe and environmental processes has been proposed. It provides directions for undertaking environmentally sound microbial dye detoxification research.

Synergistic and Antagonistic Mutation Responses of Human MCL-5 Cells to Mixtures of Benzo[a]pyrene and 2-Amino-1-Methyl-6-Phenylimidazo[4,5-b]pyridine: Dose-Related Variation in the Joint Effects of Common Dietary Carcinogens

BACKGROUND

Chemical carcinogens such as benzo[a]pyrene (BaP) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) may contribute to the etiology of human diet-associated cancer. Individually, these compounds are genotoxic, but the consequences of exposure to mixtures of these chemicals have not been systematically examined.

OBJECTIVES

We determined the mutagenic response to mixtures of BaP and PhIP at concentrations relevant to human exposure (micromolar to subnanomolar).

METHODS

Human MCL-5 cells (metabolically competent) were exposed to BaP or PhIP individually or in mixtures. Mutagenicity was assessed at the thymidine kinase (TK) locus, CYP1A activity was determined by ethoxyresorufin-O-deethylase (EROD) activity and qRT-PCR, and cell cycle was measured by flow cytometry.

RESULTS

Mixtures of BaP and PhIP produced dose responses different from those of the individual chemicals; we observed remarkably increased mutant frequency (MF) at lower concentrations of the mixtures (not mutagenic individually), and decreased MF at higher concentrations of the mixtures, than the calculated predicted additive MF of the individual chemicals. EROD activity and CYP1A1 mRNA levels were correlated with TK MF, supporting involvement of the CYP1A family in mutation. Moreover, a cell cycle G2/M phase block was observed at high-dose combinations, consistent with DNA damage sensing and repair.

CONCLUSIONS

Mixtures of these genotoxic chemicals produced mutation responses that differed from those expected for the additive effects of the individual chemicals. The increase in MF for certain combinations of chemicals at low concentrations that were not genotoxic for the individual chemicals, as well as the nonmonotonic dose response, may be important for understanding the mutagenic potential of food and the etiology of diet-associated cancers.

CITATION

David R, Ebbels T, Gooderham N. 2016. Synergistic and antagonistic mutation responses of human MCL-5 cells to mixtures of benzo[a]pyrene and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine: dose-related variation in the joint effects of common dietary carcinogens. Environ Health Perspect 124:88-96; http://dx.doi.org/10.1289/ehp.1409557.

Empirical analysis of BMD metrics in genetic toxicology part I: in vitro analyses to provide robust potency rankings and support MOA determinations

Genetic toxicity testing has traditionally been used for hazard identification, with dichotomous classification of test results serving to identify genotoxic agents. However, the utility of genotoxicity data can be augmented by employing dose-response analysis and point of departure determination. Via interpolation from a fitted dose-response model, the benchmark dose (BMD) approach estimates the dose that elicits a specified (small) effect size. BMD metrics and their confidence intervals can be used for compound potency ranking within an endpoint, as well as potency comparisons across other factors such as cell line or exposure duration. A recently developed computational method, the BMD covariate approach, permits combined analysis of multiple dose-response data sets that are differentiated by covariates such as compound, cell type or exposure regime. The approach provides increased BMD precision for effective potency rankings across compounds and other covariates that pertain to a hypothesised mode of action (MOA). To illustrate these applications, the covariate approach was applied to the analysis of published in vitro micronucleus frequency dose-response data for ionising radiations, a set of aneugens, two mutagenic azo compounds and a topoisomerase II inhibitor. The ionising radiation results show that the precision of BMD estimates can be improved by employing the covariate method. The aneugen analysis provided potency groupings based on the BMD confidence intervals, and analyses of azo compound data from cells lines with differing metabolic capacity confirmed the influence of endogenous metabolism on genotoxic potency. This work, which is the first of a two-part series, shows that BMD-derived potency rankings can be employed to support MOA evaluations as well as facilitate read across to expedite chemical evaluations and regulatory decision-making. The follow-up (Part II) employs the combined covariate approach to analyse in vivo genetic toxicity dose-response data focussing on how improvements in BMD precision can impact the reduction and refinement of animal use in toxicological research.

Induced expression of cytochrome P450 1A and NAD(P)H:quinone oxidoreductase determined at mRNA, protein, and enzyme activity levels in rats exposed to the carcinogenic azo dye 1-phenylazo-2-naphthol (Sudan I)

Sudan I (1-phenylazo-2-hydroxynaphthol) is a suspected human carcinogen causing tumors in the livers and urinary bladders of rats, mice, and rabbits. Here, we investigated for the first time the influence of Sudan I exposure on the expression of several biotransformation enzymes in the livers, kidneys, and lungs of rats concomitantly at the mRNA and protein levels and assayed their enzymatic activities. We also studied its effect on the formation of Sudan I-derived DNA adducts in vitro. Sudan I increased the total amounts of cytochrome P450 (P450) in all organs tested. Western blots using antibodies raised against various P450s, NADPH:P450 reductase, and NAD(P)H:quinone oxidoreductase 1 (NQO1) showed that the expression of P450 1A1 and NQO1 was induced in the liver, kidney, and lung of rats treated with Sudan I. The higher protein levels correlated with increased enzyme activities of P450 1A1/2 and NQO1. Furthermore, 9.9-, 5.9-, and 2.8-fold increases in the formation of Sudan I oxidative metabolites catalyzed by microsomes isolated from the liver, kidney, and lung, respectively, of rats treated with Sudan I were found. The relative amounts of P450 1A and NQO1 mRNA, measured by real-time polymerase chain reaction (RT-PCR) analysis, demonstrated that Sudan I induced the expression of P450 1A1 and NQO1 mRNA in the liver, kidney, and lung, and of P450 1A2 mRNA in kidney and lung. Finally, microsomes isolated from livers, kidneys, and lungs of Sudan I exposed rats more effectively catalyzed the formation of Sudan I-DNA adducts than microsomes from organs of control rats. This was attributable to the higher P450 1A1 expression. Because P450 1A1 is playing a major role in the bioactivation of Sudan I in rat and human systems, its induction by Sudan I may have a profound effect on cancer risk by this azo dye. In addition, the induction of P450 1A1/2 and NQO1 enzymes can influence individual human susceptibility to other environmental carcinogens and have an effect on cancer risk.

Sudan dyes: are they dangerous for human health?

Azo and diazo compounds include Sudan dyes, which were widely used in industry. Although they are not permitted in food, they had been found contaminating different food products and their presence is investigated regularly (since 2003) in these products. Sudan III, as well as Sudan Black B, was included in different laboratory techniques for tissue ceroid and lipofucsin analysis and blood-cell staining. Also, Sudan Black B has been recently included in in vivo evaluations in human beings (through oral intake), and Sudan III is still allowed in cosmetics. These azo dyes were metabolized to possible carcinogenic colorless amines, both in the liver of mammalians and by the micro flora present in human skin and the gastrointestinal tract. Both human and laboratory animal cytochrome P450s (CYPs) were able to oxidize Sudan I, whereas Sudan III modified CYP activities. In vitro genotoxic effects were reported for Sudan I, and some DNA adducts formed through exposure to its metabolites were identified. Sudan I was also found to be carcinogenic in the rat, but not in the mouse. The aim of the present review is to put together the most relevant information concerning Sudan dye uses and toxicity to provide some tools for the identification of the risk they represent for human health.

Evaluation of impact of exposure of Sudan azo dyes and their metabolites on human intestinal bacteria

Sudan azo dyes are banned for food usage in most countries, but they are illegally used to maintain or enhance the color of food products due to low cost, bright staining, and wide availability of the dyes. In this report, we examined the toxic effects of these azo dyes and their potential reduction metabolites on 11 prevalent human intestinal bacterial strains. Among the tested bacteria, cell growth of 2, 3, 5, 5, and 1 strains was inhibited by Sudan I, II, III, IV, and Para Red, respectively. At the tested concentration of 100 μM, Sudan I and II inhibited growth of Clostridium perfringens and Lactobacillus rhamnosus with decrease of growth rates from 14 to 47%. Sudan II also affected growth of Enterococcus faecalis. Growth of Bifidobacterium catenulatum, C. perfringens, E. faecalis, Escherichia coli, and Peptostreptococcus magnus was affected by Sudan III and IV with decrease in growth rates from 11 to 67%. C. perfringens was the only strain in which growth was affected by Para Red with 47 and 26% growth decreases at 6 and 10 h, respectively. 1-Amino-2-naphthol, a common metabolite of the dyes, was capable of inhibiting growth of most of the tested bacteria with inhibition rates from 8 to 46%. However, the other metabolites of the dyes had no effect on growth of the bacterial strains. The dyes and their metabolites had less effect on cell viability than on cell growth of the tested bacterial strains. Clostridium indolis and Clostridium ramosum were the only two strains with about a 10 % decrease in cell viability in the presence of Sudan azo dyes. The present results suggested that Sudan azo dyes and their metabolites potentially affect the human intestinal bacterial ecology by selectively inhibiting some bacterial species, which may have an adverse effect on human health.