Lack of genotoxicity of potassium iodate in the alkaline comet assay and in the cytokinesis-block micronucleus test. Comparison to potassium bromate

Protective Effects of Melatonin against Carcinogen-Induced Oxidative Damage in the Thyroid

Melatonin, primarily synthesized in the pineal gland, plays a crucial role in regulating circadian rhythms and possesses significant antioxidative properties. By neutralizing free radicals and reducing oxidative stress, melatonin emerges as a promising agent for the prevention and therapy of many different disorders, including cancer. This paper reviews the relationship between the thyroid gland and melatonin, presenting experimental evidence on the protective effects of this indoleamine against oxidative damage to macromolecules in thyroid tissue caused by documented carcinogens (as classified by the International Agency for Research on Cancer, IARC) or caused by potential carcinogens. Furthermore, the possible influence on cancer therapy in humans and the overall well-being of cancer patients are discussed. The article highlights melatonin's essential role in maintaining thyroid health and its contribution to management strategies in patients with thyroid cancer and other thyroid diseases.

Portulaca oleracea L. extract relieve mice liver fibrosis by inhibiting TLR-4/NF-κB, Bcl-2/Bax and TGF-β1/Smad2 signalling transduction

Portulaca oleracea L. are annual herb, which has various pharmacological effects including hepatoprotective property. However, the effect of Portulaca oleracea L. (POL-1) in mice with carbon tetrachloride (CCl4)-induced liver fibrosis and its mechanism of action have not been clarified. POL-1 ameliorated the CCl4-induced liver fibrosis in mice, as shown by decreased collagen deposition and the decreased expression of liver fibrosis marker collagen I and α-smooth muscle actin (α-SMA) mRNA. In addition, treatment with POL-1 suppressed the proliferation of activated human hepatic stellate cell line (LX-2). POL-1 inhibited the oxidative stress and inflammation in fibrotic livers of mice. Mechanistically, POL-1 inhibited the CCl4-induced expression of toll-like receptor-4 (TLR4), myeloid differentiation factor 88 (MyD88), nuclear factor kappa-B (NF-κBp65) p65, Bcl2-associated X (Bax), transforming growth factor-β1 (TGF-β1) and drosophila mothers against decapentaplegic 2 (Smad2) proteins, upregulated B-cell lymphoma -2 (Bcl-2) proteins in livers of mice. These findings suggested that POL-1 attenuated liver fibrosis.

New iodine-based electrochemical advanced oxidation system for water disinfection: Are disinfection by-products a concern?

A novel electrochemical Advanced Oxidation System (AOS) has been recently developed for water disinfection where iodide is used to generate active iodine species in-situ. However, the presence of iodide during water disinfection can lead to the formation of iodinated disinfection byproducts (I-DBPs), which have been shown to be more cyto- and genotoxic than their chlorinated and brominated analogs. In this study, the formation of DBPs was assessed in ultrapure water, river water and secondary wastewater effluents treated by the AOS. A comprehensive total organic halogen and target DBP analysis was used that included 25 unregulated DBPs, and the total organic halogen (TOX) quantified as total organic chlorine (TOCl), total organic bromine (TOBr), and total organic iodine (TOI). Ultrapure water disinfection only quantified iodoform (TIM) at a maximum concentration of 0.90 ± 0.05 µg/L. River water results show that TOI increase from 1.3 ± 0.3 µg/L before disinfection (t = 0) to a maximum of 3.5 ± 1.1 µg/L. TIM and bromodiiodomethane (BDIM) were the only targeted iodo-trihalomethanes (I-THMs) that were quantified with a maximum total I-THM concentration of 0.44 µg/L. Secondary wastewater effluent disinfection results show that TOI increased from 1.8 ± 0.3 µg/L (t = 0) to a maximum concentration of 35.3 ± 0.3 µg/L. Iodide and iodate were the main iodinated species exiting the AOS system with a iodine recovery of 94-101%. The results from this study show that the AOS formed low levels of iodinated DBPs in treated water sources that are comparable to the levels found in disinfected drinking water and wastewater.

Dose-response analysis of potassium bromate-induced toxicity in Allium cepa L. meristematic cells

In this study, the toxic effects of potassium bromate (KBrO₃) were tested on Allium cepa L. meristematic cells. In order to determine the toxic effect and dose relationship, KBrO₃ toxicity was investigated at doses of 25, 50, and 100 mg/L. The toxic effects were evaluated by using cytogenetic, biochemical, anatomical, and physiological parameters, and serious damages were observed depending on the dose. Significant reductions in germination percentage, weight gain, and radicle length were observed in all KBrO₃-treated groups compared with the control. Mitotic activity decreased in meristematic cells after KBrO₃ application. and mitotic index was decreased by 1.8 times in 100 mg/L KBrO₃-treated group compared with the control group. The frequencies of micronucleus and chromosomal abnormalities tested as cytogenetic parameters were significantly higher in the group treated with 100 mg/L KBrO₃ than those in the control group. Fragment and sticky chromosome were the most common types of chromosomal abnormalities. Lipid peroxidation measured in terms of MDA content increased with increasing doses of KBrO₃. The activities of catalase and superoxide dismutase as antioxidant enzymes were importantly changed in KBrO₃-treated groups. Anatomical changes such as cell deformation, substance accumulation, cell wall thickening, and flattened nucleus were determined after KBrO₃ application, and it was observed that these changes reached a maximum level at 100 mg/L dose of KBrO₃. As a result, KBrO₃ treatments were been found to cause physiological, biochemical, cytogenetic, and anatomically toxic effects in meristematic cells of A. cepa, a eukaryotic model organism. The versatile toxicity induced by KBrO₃ increased depending on the dose and reached a maximum level at 100 mg/L.

Underestimated risk from ozonation of wastewater containing bromide: Both organic byproducts and bromate contributed to the toxicity increase

Ozonation is widely used in wastewater treatment but the associated byproduct formation is a concern. When ozonation is used in the presence of bromide, bromate is generally considered as a major byproduct, and few studies have examined the toxicity of organic byproducts. This study was designed to investigate the cytotoxicity, genotoxicity and DNA/RNA oxidative damage to Chinese hamster ovary (CHO) cells of organic extracts from ozonated wastewater in the absence or presence of bromide. Ozonation effectively detoxified secondary effluents containing no bromide. However, ozonation significantly increased the cytotoxicity and genotoxicity of the effluents spiked with a bromide concentration as low as 100 μg/L, compared with the bromide-free effluent. When the bromide concentration in the effluent was increased to 2000 μg/L, ozonation resulted in 1.4-1.5 times the cytotoxicity and 1.5-5.0 times the genotoxicity of the non-ozonated secondary effluent. Besides, the oxidative stress (including reactive oxygen species and reactive nitrogen species) and DNA/RNA oxidative damage also became more severe and a high level of 8-hydroxy-(deoxy)guanosine was detected in the CHO cell nucleus in the presence of bromide. Cytotoxicity and genotoxicity were found to increase with the formation of total organic bromine (TOBr). When the CHO cells were exposed to both the organic byproducts and bromate formed from wastewater containing 500 and 2000 μg/L bromide, bromate significantly increased oxidative stress and DNA/RNA oxidative damage at relatively high concentration factors, suggesting both organic byproduct and bromate can contribute to toxicity increase. During ozonation of the effluent containing bromide, particular attention should be paid to the organic byproducts such as TOBr.

Induction and repair of DNA damage measured by the comet assay in human T lymphocytes separated by immunomagnetic cell sorting

The comet assay is widely used in human biomonitoring to measure DNA damage in whole blood or isolated peripheral blood mononuclear cells (PBMC) as a marker of exposure to genotoxic agents. Cytogenetic assays with phytohemagglutinin (PHA)-stimulated cultured T lymphocytes are also frequently performed in human biomonitoring. Cytogenetic effects (micronuclei, chromosome aberrations, sister chromatid exchanges) may be induced in vivo but also occur ex vivo during the cultivation of lymphocytes as a consequence of DNA damage present in lymphocytes at the time of sampling. To better understand whether DNA damage measured by the comet assay in PBMC is representative for DNA damage in T cells, we comparatively investigated DNA damage and its repair in PBMC and T cells obtained by immunomagnetic cell sorting. PBMC cultures and T cell cultures were exposed to mutagens with different modes of genotoxic action and DNA damage was measured by the comet assay after the end of a 2h exposure and after 18h post-incubation. The mutagens tested were methyl methanesulfonate (MMS), (±)-anti-B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE), 4-nitroquinoline-1-oxide (4NQO), styrene oxide and potassium bromate. MMS and potassium bromate were also tested by the modified comet assay with formamido pyrimidine glycosylase (FPG) protein. The results indicate that the mutagens tested induce DNA damage in PBMC and T cells in the same range of concentrations and removal of induced DNA lesions occurs to a comparable extent. Based on these results, we conclude that the comet assay with PBMC is suited to predict DNA damage and its removal in T cells.

Potassium iodide, but not potassium iodate, as a potential protective agent against oxidative damage to membrane lipids in porcine thyroid

Background

Fenton reaction (Fe²⁺+H₂O₂→Fe³⁺+^•OH+OH⁻) is of special significance in the thyroid gland, as both its substrates, i.e. H₂O₂ and Fe²⁺, are required for thyroid hormone synthesis. Also iodine, an essential element supplied by the diet, is indispensable for thyroid hormone synthesis. It is well known that iodine affects red-ox balance. One of the most frequently examined oxidative processes is lipid peroxidation (LPO), which results from oxidative damage to membrane lipids. Fenton reaction is used to experimentally induce lipid peroxidation. The aim of the study was to evaluate effects of iodine, used as potassium iodide (KI) or potassium iodate (KIO₃), on lipid peroxidation in porcine thyroid homogenates under basal conditions and in the presence of Fenton reaction substrates.

Methods

Porcine thyroid homogenates were incubated in the presence of either KI (0.00005 – 500 mM) or KIO₃ (0.00005 – 200 mM), without or with addition of FeSO₄ (30 μM) + H₂O₂ (0.5 mM). Concentration of malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA) was measured spectrophotometrically, as an index of lipid peroxidation.

Results

Potassium iodide, only when used in the highest concentrations (≥50 mM), increased lipid peroxidation in concentration-dependent manner. In the middle range of concentrations (5.0; 10; 25; 50 and 100 mM) KI reduced Fenton reaction-induced lipid peroxidation, with the strongest protective effect observed for the concentration of 25 mM. Potassium iodate increased lipid peroxidation in concentrations ≥2.5 mM. The damaging effect of KIO₃ increased gradually from the concentration of 2.5 mM to 10 mM. The strongest damaging effect was observed at the KIO₃ concentration of 10 mM, corresponding to physiological iodine concentration in the thyroid. Potassium iodate in concentrations of 5–200 mM enhanced Fenton reaction-induced lipid peroxidation with the strongest damaging effect found again for the concentration of 10 mM.

Conclusions

Potassium iodide, used in doses generally recommended in iodide prophylaxis, may prevent oxidative damage to membrane lipids in this gland. Toxic effects of iodide overload may result from its prooxidative action. Potassium iodate does not possess any direct beneficial effects on oxidative damage to membrane lipids in the thyroid, which constitutes an additional argument against its utility in iodine prophylaxis.

Dose-response analysis of bromate-induced DNA damage and mutagenicity is consistent with low-dose linear, nonthreshold processes

Mutagenic agents have long been inferred to act through low-dose linear, nonthreshold processes. However, there is debate about this assumption, with various studies interpreting datasets as showing thresholds for DNA damage and mutation. We have applied rigorous statistical analyses to investigate the shape of dose-response relationships for a series of in vitro and in vivo genotoxicity studies using potassium bromate (KBrO(3) ), a water ozonation byproduct that is bioactivated to a reactive species causing oxidative damage to DNA. We analyzed studies of KBrO(3) genotoxicity where no-effect/threshold levels were reported as well as other representative datasets. In all cases, the data were consistent with low-dose linear models. In the majority of cases, the data were fit either by a linear (straight line) model or a model which was linear at low doses and showed a saturation-like downward curvature at high doses. Other datasets with apparent upward curvature were still adequately represented by models that were linear at low dose. Sensitivity analysis of datasets showing upward curvature revealed that both low-dose linear and nonlinear models provide adequate fits. Additionally, a simple biochemical model of selected key processes in bromate-induced DNA damage was developed and illustrated a situation where response for early primary events suggested an apparent threshold while downstream events were linear. Overall, the statistical analyses of DNA damage and mutations induced by KBrO(3) are consistent with a low-dose linear response and do not provide convincing evidence for the presence of a threshold.

The indirect effect of radiation reduces the repair fidelity of NHEJ as verified in repair deficient CHO cell lines exposed to different radiation qualities and potassium bromate

The complexity of DNA lesions induced by ionizing radiation is mainly dependent on radiation quality, where the indirect action of radiation may contribute to different extent depending on the type of radiation under study. The effect of indirect action of radiation can be investigated by using agents that induce oxidative DNA damage or by applying free radical scavengers. The aim of this study was to investigate the role of the indirect effect of radiation for the repair fidelity of non-homologous end-joining (NHEJ), homologous recombination repair (HRR) and base excision repair (BER) when DNA damage of different complexity was induced by gamma radiation, alpha particles or from base damages (8-oxo-dG) induced by potassium bromate (KBrO(3)). CHO cells lines deficient in XRCC3 (HRR) irs1SF, XRCC7 (NHEJ) V3-3 and XRCC1 (BER) EM9 were irradiated in the absence or presence of the free radical scavenger dimethyl sulfoxide (DMSO). The endpoints investigated included rate of cell proliferation by the DRAG assay, clonogenic cell survival and the level of primary DNA damage by the comet assay. The results revealed that the indirect effect of low-LET radiation significantly reduced the repair fidelity of both NHEJ and HRR pathways. For high-LET radiation the indirect effect of radiation also significantly reduced the repair fidelity for the repair deficient cell lines. The results suggest further that the repair fidelity of the error prone NHEJ repair pathway is more impaired by the indirect effect of high-LET radiation relative to the other repair pathways studied. The response to bromate observed for the two DSB repair deficient cell lines strongly support earlier studies that bromate induces complex DNA damages. The significantly reduced repair fidelity of irs1SF and V3-3 suggests that NHEJ as well as HRR are needed for the repair, and that complex DSBs are formed after bromate exposure.

Cytotoxic and genotoxic effect in RTG-2 cell line exposed to selected biocides used in the disinfection of cooling towers

The cytotoxic and genotoxic effects induced by trichloroisocyanuric acid, Oxone, and sodium bromide, active principles included in formulations for cleaning and disinfection of cooling towers, were studied on RTG-2 cell line. Neutral red assay was used to determine the cellular viability. Toxicity ranking based on IC(50) values found that trichloroisocyanuric acid was the most cytotoxic biocide tested followed by Oxone, whereas sodium bromide resulted in a very low cytotoxicity. DNA damage has been evaluated on RTG-2 cultures by means of an in vitro assay based on the ability of PicoGreen fluorochrome to interact preferentially with dsDNA, and the results indicated that trichloroisocyanuric acid induced DNA strand breaks at concentrations above 1.2 mg/l, equivalent to 1/50-EC(50(48)), whereas exposures to Oxone and sodium bromide did not induce DNA damage at the maximal concentrations tested (1/10-EC(50(48))). These results confirm the suitability of this method for the screening of genotoxic effects of this type of aquatic pollutants, and we suggest their use in environmental risk assessment procedures.

The effects of boric acid on sister chromatid exchanges and chromosome aberrations in cultured human lymphocytes

The aim of this study was to determine the possible genotoxic effects of boric acid (BA) (E284), which is used as an antimicrobial agent in food, by using sister chromatid exchange (SCEs) and chromosome aberration (CAs) tests in human peripheral lymphocytes. The human lymphocytes were treated with 400, 600, 800, and 1000 mug/mL concentrations of BA dissolved in dimethyl sulfoxide (DMSO), for 24 h and 48 h treatment periods. BA did not increase the SCEs for all the concentrations and treatment periods when compared to control and solvent control (DMSO). BA induced structural and total CAs at all the tested concentrations for 24 and 48 h treatment periods. The induction of the total CAs was dose dependent for the 24 h treatment period. However, BA did not cause numerical CAs. BA showed a cytotoxic effect by decreasing the replication index (RI) and mitotic index (MI). BA decreased the MI in a dose-dependent manner for the 24 h treatment period.

Genotoxic effects of potassium bromate on human peripheral lymphocytes in vitro

The aim of this study was to investigate the genotoxic effects of potassium bromate, which is used as a bleaching agent in flour, on human peripheral blood lymphocytes in vitro by sister chromatid exchange (SCE), chromosomal aberrations (CA) and micronucleus (MN) tests, and also to determine whether it has any genotoxic potential for humans. Cells were treated with 400, 450, 500, 550 microg/ml concentrations of potassium bromate for 24 and 48 h. The SCE frequencies showed an increase after both treatment periods, however, the differences between the treated cells and the control groups were found to be statistically significant only for the 48-h treatment. In addition, potassium bromate statistically significantly induced CA after the 24-h and 48-h treatment periods. Strikingly, potassium bromate induced CA as much as the positive control, mitomycin-C (MMC). Furthermore, potassium bromate decreased both the cell proliferation index (PI) and the mitotic index (MI). Although micronucleus formation was induced by potassium bromate during the 24-h treatment period in a dose-dependent manner, only the doses 500 and 550 microg/ml yielded statistically significant results. In contrast, MN formation was significantly induced at all doses during the 48-h treatment period. These in vitro results provide important evidence about genotoxicity of potassium bromate on a human cell culture system.

Evaluation of the genotoxic potential of 3-monochloropropane-1,2-diol (3-MCPD) and its metabolites, glycidol and beta-chlorolactic acid, using the single cell gel/comet assay

3-monochloropropane-1,2-diol (3-MCPD) is a member of a group of chemicals known as chloropropanols. It is found in many foods and food ingredients as a result of food processing. 3-MCPD is regarded as a rat carcinogen known to induce Leydig-cell and mammary gland tumours in males and kidney tumours in both genders. The aim of our study was to clarify the possible involvement of genotoxic mechanisms in 3-MCPD induced carcinogenicity at the target organ level. For that purpose, we evaluated DNA damages in selected target (kidneys and testes) and non-target (blood leukocytes, liver and bone marrow) male rat organs by the in vivo alkaline single cell gel electrophoresis (comet) assay, 3 and 24 h after 3-MCPD oral administration to Sprague-Dawley and Fisher 344 adult rats. 3-MCPD may be metabolised to a genotoxic intermediate, glycidol, whereas the predominant urinary metabolite in rats following 3-MCPD administration is beta-chlorolactic acid. Therefore, we also studied the DNA damaging effects of 3-MCPD and its metabolites, glycidol and beta-chlorolactic acid, in the in vitro comet assay on CHO cells. Our results show the absence of genotoxic potential of 3-MCPD in vivo in the target as well as in the non-target organs. Glycidol, the epoxide metabolite, induced DNA damages in CHO cells. beta-Chlorolactic acid, the main metabolite of 3-MCPD in rats, was shown to be devoid of DNA-damaging effects in vitro in mammalian cells.

Study on the influence of potassium iodate on the metabolism of Escherichia coli by intrinsic fluorescence

Intrinsic fluorescence, in particular, has the advantage over the extrinsic fluorescence of an unperturbed environment during investigation, especially in complex systems such as biological cells and tissues. Potassium iodate may restrain bacteria growth as well as it acts as an additive in the salt. The influence of potassium iodate (KIO3) on the metabolism of Escherichia coli (E. coli) is investigated for the first time with the intrinsic fluorescence of tryptophan (Trp) and reduced nicotinamide adenine dinucleotide (NADH). We found that potassium iodate may restrain the growth of E. coli as a bacteriostatic agent. When the potassium iodate concentration was below 1.32 mmol/L, the intensity of tryptophan fluorescence decreased linearly whereas the NADH fluorescence did not change. When the KIO3 concentration was over 1.32 mmol/L, the fluorescence of tryptophan and NADH increased a little and their fluorescence intensity decreased when KIO3 was over 6.67 mmol/L. And the bacteria could not continue growing if the KIO3 was over 6.67 mmol/L.We could conclude that potassium iodate has great inhibiting effects on the growth of E. coli through the pathway of protein synthesis and respiratory chain.

Mutagenicity of bromate: Implications for cancer risk assessment

Bromate (BrO3-) is a rodent carcinogen that is formed as a drinking water ozone disinfection by-product and also used in some food and consumer products. Therefore, bromate is subject to assessment for its risk to humans. Because the selection of an appropriate model for conducting quantitative cancer risk assessment is based upon an understanding of the chemical's mode-of-action, it is necessary to determine whether the chemical is a mutagenic carcinogen. We present a review of the available information concerning the weight-of-the-evidence that bromate is a mutagenic carcinogen. The evidence indicates that bromate is mutagenic and that this activity is mediated by the formation of oxidative damage to the DNA, thus resulting in chromosomal damage. Not only does bromate induce genetic damage in vitro, it is also demonstrated to induce mutations in the kidney of exposed rats. This is significant because the rat kidney is one of the target tissues for tumor induction. While it is clear that bromate can cause damage in the target tissue, it is not clear whether bromate is a mutagenic carcinogen, that is, whether the observed tumors result from a mutagenic mode-of-action. Further research is needed to clarify bromate's mode-of-action. However, in the absence of additional information, it is reasonable, based on an extensive database, to assume that bromate induces tumors via oxidative damage that causes chromosomal breakage.

DNA damage in mice treated with sulfur dioxide by inhalation

Sulfur dioxide (SO2) is a ubiquitous air pollutant produced by the burning of fossil fuels. In this study, single-cell gel electrophoresis (the Comet assay) was used to evaluate the DNA damage produced by inhalation exposure of mice to SO2. Male and female mice were housed in exposure chambers and treated with 14.00 +/- 1.25, 28.00 +/- 1.98, 56.00 +/- 3.11, and 112.00 +/- 3.69 mg/m3 SO2 for 6 hr/day for 7 days, while control groups were exposed to filtered air. Comet assays were performed on blood lymphocytes and cells from the brain, lung, liver, spleen, kidney, intestine, and testicles of the animals. SO2 caused significant, dose-dependent increases in DNA damage, as measured by Olive tail moment, in all the cell types analyzed from both sexes of mice. The results indicate that inhalation exposure to SO2 damages the DNA of multiple organs in addition to the lung, and suggests that this damage could result in mutation, cancer, and other diseases related to DNA damage. Further work will be required to understand the ultimate toxicological significance of this damage. These data also suggest that detecting DNA damage in blood lymphocytes, using the Comet assay, may serve as a useful tool for evaluating the impact of pulmonary SO2 exposure in human biomonitoring studies.