Tag Archives: toxicology

Fluoride a Risk Factor for Renal Tubular Damage

Usuda K, Ueno T,Ito Y, Dote T, Yokoyama H, Kono K, Tamaki J. Risk Assessment Study of Fluoride Salts: Probability-Impact Matrix of Renal and Hepatic Toxicity Markers. Biological Trace Element Research 2016 Sep; Vol. 173 (1), pp. 154-60.

The present risk assessment study of fluoride salts was conducted by oral administration of three different doses of sodium and potassium fluorides (NaF, KF) and zinc fluoride tetrahydrate (ZnF2 •4H2O) to male Wistar rats. The rats were divided into control and nine experimental groups, to which oral injections of 0.5 mL distilled water and 0.5 mL of fluoride solutions, respectively, were given. The dosage of fluoride compounds was adjusted to contain 2.1 mg (low-dose group, LG), 4.3 mg (mid-dose group, MG), and 5.4 mg fluoride per 200 g rat body weight (high-dose group, HG) corresponding to 5, 10, and 12.5 % of LD50 values for NaF. The 24-h urine volume, N-acetyl-β-D-glucosaminidase (NAG) and creatinine clearance (Ccr) were measured as markers of possible acute renal impact. The levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were determined in serum samples as markers of acute hepatic impact. The levels of serum and urinary fluoride were determined to evaluate fluoride bioavailability. The results reveal that higher doses of NaF, KF, and ZnF2 induced renal damage as indicated by higher urinary NAG (p < 0.05 with ≥90th percentile of control). High doses of ZnF2 also induced a significant Ccr decrease (p < 0.05 with ≤10th percentile of control). Low doses of NaF and mid-doses of ZnF2 induced polyuria (p < 0.05 with ≥90th percentile of control) while medium doses of NaF and low doses of KF also induced liver damage, as indicated by a high level of AST (p < 0.05 with ≥90th percentile of control). These findings suggest that oral administration of fluoride is a potential, dose-dependent risk factor of renal tubular damage.

Chromium 6 Not Mutagenic in its Mode of Action

Thompson CM, Young RR, Suh M, Dinesdurage HR, Elbekai RH, Harris MA, Rohr AC, Proctor DM. Assessment of the mutagenic potential of cr(VI) in the oral mucosa of big blue® transgenic f344 rats. Environ Mol Mutagen. 2015 May 22. doi: 10.1002/em.21952.

Exposure to high concentrations of hexavalent chromium [Cr(VI)] in drinking water was associated with an increased incidence of oral tumors in F344 rats in a 2-year cancer bioassay conducted by the National Toxicology Program. These tumors primarily occurred at 180 ppm Cr(VI) and appeared to originate from the gingival mucosa surrounding the upper molar teeth. To investigate whether these tumors could have resulted from a mutagenic mode of action (MOA), a transgenic mutation assay based on OECD Test Guideline 488 was conducted in Big Blue® TgF344 rats. The mutagenic oral carcinogen 4-nitroquinoline-1-oxide (4-NQO) served as a positive control. Mutant frequency was measured in the inner gingiva with adjacent palate, and outer gingiva with adjacent buccal tissue. Exposure to 10 ppm 4-NQO in drinking water for 28 days increased mutant frequency in the cII transgene significantly, from 39.1 ± 7.5 × 10-6 to 688 ± 250 × 10-6 in the gingival/buccal region, and from 49.8 ± 17.8 × 10-6 to 1818 ± 362 × 10-6 in the gingival/palate region. Exposure to 180 ppm Cr(VI) in drinking water for 28 days did not significantly increase the mutant frequency in the gingival/buccal (44.4 ± 25.4 × 10-6 ) or the gingival/palate (57.8 ± 9.1 × 10-6 ) regions relative to controls. These data indicate that high (∼180,000 times expected human exposure), tumorigenic concentrations of Cr(VI) did not significantly increase mutations in the gingival epithelium, and suggest that Cr(VI) does not act by a mutagenic MOA in the rat oral cavity.

Review of the Health Effects of Oral Exposure to Arsenic

Ulrike Schuhmacher-Wolz, Hermann H. Dieter, Dominik Klein, Klaus Schneider. Oral exposure to inorganic arsenic: evaluation of its carcinogenic and non-carcinogenic effects. Critical Reviews in Toxicology. Apr2009, Vol. 39 Issue 4, p271-298.

Inorganic arsenic, which is extensively metabolised in humans into even more toxic methylated arsenicals, is a potent carcinogen, causing tumours of the skin, lung, urinary bladder, and other organs. It also induces a number of non-cancer effects. Consumption of drinking water highly contaminated by arsenic causes serious health problems in some countries in southeastern Asia, and arsenic poses problems for drinking-water safety worldwide. Existing risk assessments are based on epidemiological studies from regions with high exposure concentrations (in the mg/L range). It is a matter of debate whether these findings are useful at predicting arsenic-induced effects at low concentrations. In recent years numerous epidemiological studies on cancer and non-cancer effects of inorganic arsenic have been published. This work aims at reviewing recent toxicological and epidemiological data on inorganic arsenic with emphasis on effects at low exposure concentrations. Information obtained from epidemiological studies is supplemented with mechanistic data from in vitro and in vivo studies. Various modes of action for arsenic carcinogenicity are discussed. The information gathered was used to evaluate the reliability of existing cancer-risk assessments and to improve current assessments of non-cancer health effects. A tolerable daily dose, based on epidemiological studies on arsenic-induced skin disorders, is presented.

Click here for paper (fee).

Toxicogenomics as a Tool in Human Risk Assessment of BaP

Moffat I, Chepelev NL, Labib S, Bourdon-Lacombe J, Kuo B, Buick JK, Lemieux F, Williams A, Halappanavar S, Malik AI, Luijten M, Aubrecht J, Hyduke DR, Fornace AJ Jr, Swartz CD, Recio L, Yauk CL. Comparison of toxicogenomics and traditional approaches to inform mode of action and points of departure in human health risk assessment of benzo[a]pyrene in drinking water. Critical Reviews in Toxicology. 2015 Jan;45(1):1-43. doi: 10.3109/10408444.2014.973934.

Toxicogenomics is proposed to be a useful tool in human health risk assessment. However, a systematic comparison of traditional risk assessment approaches with those applying toxicogenomics has never been done. We conducted a case study to evaluate the utility of toxicogenomics in the risk assessment of benzo[a]pyrene (BaP), a well-studied carcinogen, for drinking water exposures. Our study was intended to compare methodologies, not to evaluate drinking water safety. We compared traditional (RA1), genomics-informed (RA2) and genomics-only (RA3) approaches. RA2 and RA3 applied toxicogenomics data from human cell cultures and mice exposed to BaP to determine if these data could provide insight into BaP’s mode of action (MOA) and derive tissue-specific points of departure (POD). Our global gene expression analysis supported that BaP is genotoxic in mice and allowed the development of a detailed MOA. Toxicogenomics analysis in human lymphoblastoid TK6 cells demonstrated a high degree of consistency in perturbed pathways with animal tissues. Quantitatively, the PODs for traditional and transcriptional approaches were similar (liver 1.2 vs. 1.0 mg/kg-bw/day; lungs 0.8 vs. 3.7 mg/kg-bw/day; forestomach 0.5 vs. 7.4 mg/kg-bw/day). RA3, which applied toxicogenomics in the absence of apical toxicology data, demonstrates that this approach provides useful information in data-poor situations. Overall, our study supports the use of toxicogenomics as a relatively fast and cost-effective tool for hazard identification, preliminary evaluation of potential carcinogens, and carcinogenic potency, in addition to identifying current limitations and practical questions for future work.

Click here for paper (fee).

Proteomic Analysis of Liver in Rats Chronically Exposed to Fluoride

Pereira HA, Leite Ade L, Charone S, Lobo JG, Cestari TM, Peres-Buzalaf C, Buzalaf MA. Proteomic analysis of liver in rats chronically exposed to fluoride. Plos One [PLoS One] 2013 Sep 17; Vol. 8 (9), pp. e75343.

Fluoride (F) is a potent anti-cariogenic element, but when ingestion is excessive, systemic toxicity may be observed. This can occur as acute or chronic responses, depending on both the amount of F and the time of exposure. The present study identified the profile of protein expression possibly associated with F-induced chronic hepatotoxicity. Weanling male Wistar rats (three-weeks old) were divided into three groups and treated with drinking water containing 0, 5 or 50 mg/L F for 60 days (n=6/group). At this time point, serum and livers were collected for F analysis, which was done using the ion-sensitive electrode, after hexamethyldisiloxane-facilitated diffusion. Livers were also submitted to histological and proteomic analyses (2D-PAGE followed by LC-MS/MS). Western blotting was done for confirmation of the proteomic data A dose-response was observed in serum F levels. In the livers, F levels were significantly increased in the 50 mg/L F group compared to groups treated with 0 and 5 mg/L F. Liver morphometric analysis did not reveal alterations in the cellular structures and lipid droplets were present in all groups. Proteomic quantitative intensity analysis detected 33, 44, and 29 spots differentially expressed in the comparisons between control vs. 5 mg/L F, control vs. 50 mg/L F, and 5 mg/L vs. 50 mg/L F, respectively. From these, 92 proteins were successfully identified. In addition, 18, 1, and 5 protein spots were shown to be exclusive in control, 5, and 50 mg/L F, respectively. Most of proteins were related to metabolic process and pronounced alterations were seen for the high-F level group. In F-treated rats, changes in the apolipoprotein E (ApoE) and GRP-78 expression may account for the F-induced toxicity in the liver. This can contribute to understanding the molecular mechanisms underlying hepatoxicity induced by F, by indicating key-proteins that should be better addressed in future studies.

Click here for paper (Open Access).

Chronic Fluorosis Associated with Learning Deficits, Memory Loss?

Dong YT, Wang Y, Wei N, Zhang QF, Guan ZZ. Deficit in learning and memory of rats with chronic fluorosis correlates with the decreased expressions of M1 and M3 muscarinic acetylcholine receptors. Archives of Toxicology 2014 Nov 23.

To reveal the molecular mechanism of deficit in learning and memory induced by chronic fluorosis, the expression of muscarinic acetylcholine receptors (mAChRs) and oxidative stress were investigated. Sixty Sprague-Dawley (SD) rats were divided randomly into two groups (30 cases in each), i.e., the control group (<0.5 ppm fluoride in drinking water) and the fluoride group (50 ppm fluoride) for 10 months of treatment. The pups born from SD mothers with or without chronic fluorosis were selected at postnatal days 1, 7, 14, 21 and 28 for experiments (10 for each age). Spatial learning and memory were evaluated by Morris water maze test. The expressions of M1 and M3 mAChRs at the protein and mRNA levels were determined by Western blotting and real-time PCR, respectively. In addition, the contents of ·OH, H2O2, O2 ·- and malondialdehyde (MDA), and activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in brains were quantitated by biochemical methods. Our results showed that as compared to controls, the abilities of learning and memory were declined in the adult rats and the offspring rats of postnatal day 28 in the fluoride groups; the expressions of both M1 and M3 mAChRs were significantly reduced at protein and mRNA levels; and the levels of ·OH, H2O2, O2 ·- and MDA were significantly increased, while the activities of SOD and GSH-Px decreased. Interestingly, the decreased protein levels of M1 and M3 mAChRs were significantly correlated with the deficits of learning and memory and high level of oxidative stress induced by chronic fluorosis. Our results suggest that the mechanism for the deficits in learning and memory of rats with chronic fluorosis may be associated with the decreased expressions of M1 and M3 in mAChRs, in which the changes in the receptors might be the result of the high level of oxidative stress occurring in the disease.

“Genome Profiling-based Mutation Assay” Method Proposed for Drinking Water

An interesting approach. But it is premature to conclude that this technique is epidemiologically important. Additional work is needed to validate non-accepted methods and this technique is no different. Further, measuring the generic “mutagenicity” of water is not new and the findings were to be expected. A more sensitive assay may or may not be relevant or useful. To be useful the method results and interpretation must be relevant to human exposure and health risk to specific contaminants. In this case attribution is made to THMs but this may have been premature as there are other differences in water quality between tap water and bottled water. Such a technique may be useful for identifying the more mutagenic contaminants. (As was done in the past for MX.)

Kumari P, Kamiseki M, Biyani M, Suzuki M, Nemoto N, Aita T, Nishigaki K. Detection of ultra-low levels of DNA changes by drinking water: epidemiologically important finding. Journal of biochemistry. 2014 Nov 17. pii: mvu072.

The safety of drinking water is essential to our health. In this context, the mutagenicity of water needs to be checked strictly. However, from the methodological limit, the lower concentration (less than ppm) of mutagenicity could not be detected, though there have been of interest in the effect of less concentration mutagens. Here we describe a highly sensitive mutation assay that detects mutagens at the ppb level, termed GPMA (Genome Profiling-based Mutation Assay). This consists of two steps; i) E. coli culture in the medium with/without mutagens and ii) Genome profiling (GP) method (an integrated method of random PCR, temperature gradient gel electrophoresis (TGGE), and computer-aided normalization). Owing to high sensitivity of this method, very low concentration of mutagens in tap water could be directly detected without introducing burdensome concentration processes, enabling rapid measurement of low concentration samples. Less expectedly, all of the tap waters tested (22 samples) were shown to be significantly mutagenic while mineral waters were not. Resultantly, this paper informs two facts that the GPMA method is competent to measure the mutagenicity of waters directly and the experimental results supported the former reports that the city tap waters contain very low level of mutagenicity reagent trihalomethanes.

Click here for paper (fee).