Cadmium-induced microsatellite instability in the kidneys and leukocytes of C57BL/6J mice

Effects of Ecologically Relevant Concentrations of Cadmium on the Microbiota, Short-Chain Fatty Acids, and FFAR2 Expression in Zebrafish

Exposure to cadmium (Cd) can affect neurodevelopment and results in increased potential of developing neurodegenerative diseases during the early developmental stage of organisms, but the mechanisms through which exposure to environmentally relevant concentrations of Cd lead to developmental neurotoxicity remain unclear. Although we know that microbial community fixations overlap with the neurodevelopmental window during early development and that Cd-induced neurodevelopmental toxicity may be related to the disruption of microorganisms during early development, information on the effects of exposure to environmentally relevant Cd concentrations on gut microbiota disruption and neurodevelopment is scarce. Therefore, we established a model of zebrafish exposed to Cd (5 µg/L) to observe the changes in the gut microbiota, SCFAs, and free fatty acid receptor 2 (FFAR₂) in zebrafish larvae exposed to Cd for 7 days. Our results indicated that there were significant changes in the gut microbial composition due to the exposure to Cd in zebrafish larvae. At the genus level, there were decreases in the relative abundances of Phascolarctobacterium, Candidatus Saccharimonas, and Blautia in the Cd group. Our analysis revealed that the acetic acid concentration was decreased (p > 0.05) while the isobutyric acid concentration was increased (p < 0.05). Further correlation analysis indicated a positive correlation between the content of acetic acid and the relative abundances of Phascolarctobacterium and Candidatus Saccharimonas (R = 0.842, p < 0.01; R = 0.767, p < 0.01), and a negative correlation between that of isobutyric acid and the relative abundance of Blautia glucerasea (R = -0.673, p < 0.05). FFAR₂ needs to be activated by SCFAs to exert physiological effects, and acetic acid is its main ligand. The FFAR₂ expression and the acetic acid concentration were decreased in the Cd group. We speculate that FFAR₂ may be implicated in the regulatory mechanism of the gut-brain axis in Cd-induced neurodevelopmental toxicity.

Microsatellite Instability Assay as a Potential Approach to Evaluate Genotoxicity: Lead Exposure in a Nestling Passerine Bird at the Stage of Intensive Erythropoiesis

Although many avian studies have investigated the toxic effects of lead on important biochemical and physiological processes, organ and system function, and behavior, studies evaluating the specific genotoxic effects of exposure to lead are scarce. Nowadays, rapid technological advances can provide new molecular techniques in this regard. In this study, as a novel approach in bird studies, we used a panel of ten microsatellite loci to investigate the microsatellite instability (MSI) in response to experimental lead intoxication in a common hole-nesting species, the great tit Parus major. For this purpose, an experiment based on an intentional single supplementation of a lead (II) acetate trihydrate compound was conducted, with the use of two different doses, applied to randomly chosen great tit nestlings from randomly selected broods, being at the stage of intensive erythropoiesis. Although this preliminary study did not find any MSI in the seven microsatellite markers retained for the final comparison, it contributes to the examination of this molecular technique in field conditions as being potentially applicable in ecotoxicological bird studies. We believe that certain issues should be considered in finding an explanation for our result. First, the single doses of lead used in this study may have been too weak to induce genetic instability. Second, the panel of microsatellite markers studied may have been unsusceptible to lead genotoxicity in general. Third, the relatively short time interval (5 days) between the experimental procedure (lead exposure) and the sampling of post-exposure material (blood) for genetic analyses could have limited the effect of lead genotoxicity. Further analyzes are needed to verify these findings and to evaluate the scope of application of the MSI analysis in wild bird population studies.

GPX4 utilization by selenium is required to alleviate cadmium-induced ferroptosis and pyroptosis in sheep kidney

Cadmium (Cd), a persistent and harmful heavy metal in the environment, can accumulate in the kidneys and cause nephrotoxicity. Selenium (Se) is a beneficial natural element that alleviates the toxicity of Cd. To ascertain the relationship between the protective mechanism of Se against Cd nephrotoxicity and ferroptosis and pyroptosis, we randomly divided 48 sheep into four groups and treated them with Cd chloride and/or sodium selenite for 50 days. The data confirmed that Cd apparently resulted in impaired kidney histology and function, depletion of GSH and nicotinamide adenine dinucleotide phosphate contents and CAT and SOD activities, elevation of MDA level, as well as the reduction in selenoprotein mRNA (GPX1, GPX4, TXNRD1, SELP) levels and GPX4 protein level and immunofluorescence intensity. Meanwhile, Cd induced ferroptosis by causing iron overload, up-regulating PTGS2, NCOA4, TFR1, and LC3B mRNA levels and PTGS2 and LC3B-II/LC3B-I protein levels, reducing SLC7A11 and FTH1 mRNA and protein levels, and enhancing the immunofluorescence co-localization of FTH1/LC3B. Moreover, it was also found that Cd triggered pyroptosis, which was evidenced by the increase of NLRP3 immunohistochemical positive signal, GSDMD-N immunofluorescence intensity, IL-1β and IL-18 release and the levels of pyroptosis-related mRNA (NLRP3, ASC, Caspase-1, GSDMD, IL-1β and IL-18) and proteins (NLRP3, Caspase-1p20, GSDMD-N, IL-1β and IL-18). Notably, Se increased the expression level of GPX4 and the transcription factors TFAP2c and SP1, and ameliorated Cd-induced changes in aforementioned factors. In conclusion, GPX4 utilization by Se might be required to alleviate Cd-induced ferroptosis and pyroptosis in sheep kidney.

Hypomethylation of LINE-1 retrotransposons is associated with cadmium-induced testicular injury

Retrotransposons, as vital regulator of male fertility, are essential for spermatogenesis. Cadmium (Cd) is an environmental toxicant and endocrine disruptor, targeting the reproductive system. Growing evidence shows that Cd exposure can induce male infertility in mammals. In this study, we generated a male C57BL/6 J mice model with consecutive 35 days cadmium chloride (CdCl₂) in different concentrations of 0, 0.25, 0.5, 1.0, and 2.0 mg/kg. The results indicated that 1.0 and 2.0 mg/kg CdCl₂ significantly affected the body weight. Meanwhile, the highest dose group with 2.0 mg/kg CdCl₂ presented low fertility. Furthermore, the expression of retrotransposon mRNA was markedly increased in the higher doses group. We examined methylcytosine (mC) levels of the three active LINE-1 subfamilies TfI, A, and GfII in testis. Conclusively, Cd exposure probably undermines the male mice fertility by disrupting DNA methylation to regulate the retrotransposons. Further studies are required for identifying whether retrotransposon activation has any significant impacts on genome structure, stability, and expression in Cd-induced testicular injury, laying foundation for the treatment for male infertility.

Impact of age on N-methyl-N-nitrosourea induced microsatellite instability in young and old C57BL/6J mice

Age is an important factor in the evaluation of chemical toxicology. Chemical carcinogenic compounds can induce genomic mutations. However, few studies have been conducted on the association between genomic mutation frequency, such as microsatellite instability (MSI), and the age of mice treated with a nitrosourea mutagen. In the current work, we treated young (6 weeks) and old (10 months) mice with N-methyl-N-nitrosourea (MNU) for 4 months; the MSI frequency was then measured using polymerase chain reaction (PCR) and short tandem repeat (STR) scanning. The percentage of animals with MSI in the old group was significantly higher than that in the young group (100% and 75%). The frequency of MSI events was significantly different between the two groups as well (15.8% for old and 9.4% for young). The ratio of MSI loci displayed no obvious difference between the two groups. In addition, a few loci, including D15Mit5 and D8Mit14 exhibited the highest frequency of MSI events. Since specific loci showed increased MSI in the present study and a higher frequency in previous studies, these loci could be regarded as "hot spot". These results suggested that old mice would be more susceptible to this mutagen, and prone to accrue MSI. The hot spot microsatellite loci are potentially useful markers for genomic instability analysis.

The Dysbiosis of Gut Microbiota Caused by Low-Dose Cadmium Aggravate the Injury of Mice Liver through Increasing Intestinal Permeability

Cadmium (Cd), widely present in food and drinking water at low doses, can cause health risks. However, the mechanistic effects of long-term Cd exposure at low dose through dietary intake is poorly studied. The aim of this study is to elucidate whether the dysbiosis of gut microbiota caused by Cd at an environmental low dose can aggravate the injury of mice liver, and the possible mechanism is investigated. In order to explore the potential underlying mechanism, the analyses of the variation of gut microbiota composition, intestinal permeability, and hepatic transcriptome were conducted. Our results showed that gut microbiota was disturbed. The rise of intestinal permeability induced by the dysbiosis of gut microbiota resulted in more Cd ions accumulating in mice liver, but it could be restored partly through depleting gut microbiota by antibiotics cocktail. Transcriptomic analyses indicated that 162 genes were significantly differentially expressed including 59 up-regulated and 103 down-regulated in Cd treatment. These genes were involved in several important pathways. Our findings provide a better understanding about the health risks of cadmium in the environment.

Using pretreated chestnut endothelium to adsorb lead and cadmium ions from water

The nature chestnut endothelium, as waster source from chestnut (Castaneamollissima) has pigment effecting the process of adsorbing heavy metalions, and the decolorized endothelium has low adsorption capacity. In order to raise the adsorption capacity of heavy metal ions, the discolor endothelium was pretreated by acidic formaldehyde, cis-butenedioic acid and irradiation. Thermodynamic and kinetics model was fitted to the adsorption of Pb (II) and Cd(II) ions onto modified chestnut endothelium by cis-butenedioic acid. Three independent variables including pH, adsorption time and contact temperature were selected as affecting factors to Response Surface. The modified experiment results showed adsorption rate of Pb(II) and Cd(II) ions on the chestnut endothelium modified by 0.5 mol/L cis-butenedioic acid was higher than other modified methods. Thermodynamic and kinetics model was fitted with Langmuir and Pseudo-second-order kinetic model, respectively. 59.23 °C of the adsorption temperature, the 5.72 h of adsorption time and the 6.16 of pH are the optimized conditions of the adsorption rate of Pb²⁺ on modified chestnut endothelium. 55.93 °C of the adsorption temperature, the 4.43 h of adsorption time and the 6.06 of pH are the optimized adsorption conditions of Cd²⁺. Under the optimized condition, the experiment value of the adsorption of Pb²⁺ and Cd²⁺ was 99.76% and 98.90%, respectively, which are close to the predicted value. The FTIR indicated that C—O, O—H and C—H involved in the adsorption process of Pb²⁺ and Cd²⁺.

Linking arsenite- and cadmium-generated oxidative stress to microsatellite instability in vitro and in vivo

Mismatch repair (MMR) corrects replicative errors and minimizes DNA damage that occurs frequently in microsatellites. MMR deficiency is manifested as microsatellite instability (MSI), which contributes to hypermutability and cancer pathogenesis. Genomic instability, including MSI and chromosomal instability, appears to be responsible for the carcinogenesis of arsenic and cadmium, common contaminants in our environment. However, few studies have addressed arsenic- or cadmium-induced MSI, especially its potential link with arsenic- or cadmium-generated oxidative stress, due to the lack of quantifiable MSI assays and cost-effective animal models. Here, using a dual-fluorescent reporter, we demonstrate that sub-lethal doses of cadmium or arsenite, but not arsenate, increased the MSI frequency in human colorectal cancer cells. Arsenite- and cadmium-induced MSI occurred concomitantly with increased levels of reactive species and oxidative DNA damage, and with decreased levels of MMR proteins. However, N-acetyl-l-cysteine (NAC) suppressed arsenite- and cadmium-induced MSI and oxidative stress while restoring the levels of MMR proteins in the cells. Similarly, MSI was induced separately by arsenite and cadmium, and suppressed by NAC, in zebrafish in a fluorescinated PCR-based assay with newly-developed microsatellite markers and inter-segmental comparisons. Of five selected antioxidants examined, differential effects were exerted on the MSI induction and cytotoxicity of both arsenite and cadmium. Compared to MMR-proficient cells, MMR-deficient cells were more resistant to arsenic-mediated and cadmium-mediated cytotoxicity. Our findings demonstrate a novel linkage between arsenite-generated and cadmium-generated oxidative stress and MSI induction. Our findings also caution that antioxidants must be individually validated before being used for preventing arsenite- and cadmium-induced MSI that is associated with cancer development.

Sex-Dependent Effects of Cadmium Exposure in Early Life on Gut Microbiota and Fat Accumulation in Mice

BACKGROUND

Environmental cadmium, with a high average dietary intake, is a severe public health risk. However, the long-term health implications of environmental exposure to cadmium in different life stages remain unclear.

OBJECTIVES

We investigated the effects of early exposure to cadmium, at an environmentally relevant dosage, on adult metabolism and the mechanism of action.

METHODS

We established mouse models with low-dose cadmium (LDC) exposure in early life to examine the long-term metabolic consequences. Intestinal flora measurement by 16S rDNA sequencing, microbial ecological analyses, and fecal microbiota transplant was conducted to explore the potential underlying mechanisms.

RESULTS

Early LDC exposure (100 nM) led to fat accumulation in adult male mice. Hepatic genes profiling revealed that fatty acid and lipid metabolic processes were elevated. Gut microbiota were perturbed by LDC to cause diversity reduction and compositional alteration. Time-series studies indicated that the gut flora at early-life stages, especially at 8 weeks, were vulnerable to LDC and that an alteration during this period could contribute to the adult adiposity, even if the microbiota recovered later. The importance of intestinal bacteria in LDC-induced fat accumulation was further confirmed through microbiota transplantation and removal experiments. Moreover, the metabolic effects of LDC were observed only in male, but not female, mice.

CONCLUSIONS

An environmental dose of cadmium at early stages of life causes gut microbiota alterations, accelerates hepatic lipid metabolism, and leads to life-long metabolic consequences in a sex-dependent manner. These findings provide a better understanding of the health risk of cadmium in the environment. Citation: Ba Q, Li M, Chen P, Huang C, Duan X, Lu L, Li J, Chu R, Xie D, Song H, Wu Y, Ying H, Jia X, Wang H. 2017. Sex-dependent effects of cadmium exposure in early life on gut microbiota and fat accumulation in mice. Environ Health Perspect 125:437-446; http://dx.doi.org/10.1289/EHP360.

Cadmium Levels in Tissue and Plasma as a Risk Factor for Prostate Carcinoma: a Meta-Analysis

Cadmium is a heavy metal that has been suggested to be a carcinogen by evidence. A number of published studies have investigated the association between cadmium levels and prostate cancer, but the results were inconsistent. Thus, we conducted a meta-analysis to get a precise estimate of this subject. After a careful searching and screening, a total of 11 publications containing 14 separated studies were included. Based on a random-effect model, the pooled data showed that cadmium levels of prostate tissues (standard mean difference (SMD) = 3.17, 95 % confidence interval (CI) = 0.60-5.74, P < 0.05) and plasma (SMD = 4.07, 95 % CI = 2.01-6.13, P < 0.05) were significantly higher in prostate cancer patients than those in the healthy controls. No difference of hair and nail cadmium levels between the prostate cancer cases and the controls was found. The data suggested that cadmium exposure might exert an influence on the tumorigenesis of prostate tissues. Future investigations with large sample sizes are needed to verify the results.

Sublethal health effects in laboratory rodents from environmentally relevant exposures to oil sands contaminants

Increasing activity of oil sands extraction and processing in northern Alberta is marked by ongoing controversy about the nature and extent of associated environmental impacts. Bitumen contains a mixture of toxic chemicals, including metals and residual polycyclic aromatic hydrocarbons (PAHs), whose release into the environment poses a distinct risk to the surrounding environment, plus wildlife and human health. In the present study, the authors evaluated several subclinical biomarkers of exposure and effect to mixtures of metals (Pb, Cd, and Hg) and/or PAHs (3 alkylated forms) at environmentally relevant concentrations (100-fold and 10-fold higher than the maximum dissolved concentrations found in snow, to simulate a worst-case scenario), using laboratory mice as a model for future studies of small mammals in the wild. Both metals and alkyl-PAHs exposure were associated with 1) increased relative liver, kidney, and spleen size; 2) alterations in the homeostasis of the antioxidant vitamins A and E in liver; and 3) compromised glutathione redox status in testes, with results also indicating synergistic interactions from co-exposure. The combination of morphometric and oxidative stress biomarkers provide reliable and sensitive measures of the response to contaminant exposure in a mammalian model, suggesting associated physiological costs. Based on the present experimental study, the authors propose that wild small mammals will prove to be valuable sentinel species reflecting sublethal health effects from oil sands-related contaminants. The present study's results also present a basis for the interpretation of future field data.

Analysis of the relationship between microsatellite instability and thymic lymphoma induced by N-methyl-N-nitrosourea in C57BL/6J mice

Microsatellite instability (MSI) has been found to be closely associated with many types of human tumors and often shows strong correlations with specific tumor features. However, the relationship between MSI and tumors are still unclear. The aim of the present study is to explore the relationships between MSI, tumor formation under the mutagenic effects of N-methyl-N-nitrosourea (MNU). Mice were administered with either MNU (90 mg/kg) or PBS and DMSO (control) at the beginning of the 1st week of the experiment. Of the 31 mice that survived the entire experimental time course, 19 (61.3%) mice developed thymic lymphomas. In addition, 52.6% (10/19) of the tumors had metastasized to the liver. We detected MSI in MNU-treated mice using a panel of 42 mutation-sensitive loci. Nineteen loci (45.2%) in six organs showed 70 MSI events. Locus D8Mit14 showed enhanced MSI compared with the other examined loci. MSI frequency in thymus was higher than in other organs. Interestingly, there was no significant difference observed between the metastatic and non-metastatic livers. The MSI frequency (4.6%, 23/(42×12)) in the MNU-treated thymus that had never developed tumor was significantly higher than this in the thymus that had developed lymphoma (0.5%, 4/(42×19)) (p<0.0001). These results indicate that, although thymic tumorigenesis is associated with MSI, it occurs with higher frequency in these that have not developed tumors upon the MNU-treatment. Our study provides additional insights into the relationship between MSI occurrence and tumorigenesis.