Chemical structure-related mechanisms underlying in vivo genotoxicity induced by nitrofurantoin and its constituent moieties in gpt delta rats

A simplified modification to rapidly determine the residues of nitrofurans and their metabolites in aquatic animals by HPLC triple quadrupole mass spectrometry

A simplified method is described for reducing the analysis time of nitrofurans (NFs) and nitrofuran metabolites (NFMs) in the aquatic animals. Most existing HPLC-MS/MS methods are intended only for NFMs and are based on their fast metabolic transformations. We optimized a method for simultaneously detecting major NFs and their metabolites, including nitrovin (NV) that imply use of an optimized buffer solution. The novel method was validated by six different aquatic animal matrices (loach, catfish, shrimp, lobster, scallop, and eel) spiked with the analytes at 0.5, 1.0, and 2.0 μg kg^-1. Recovery rates and %RSDs (relative standard deviations) of 82-97% and 1-8% were observed for NFMs, respectively, with values of 70-96% and 1-8% obtained for furazolidone, furaltadone, nitrofurazone, nitrofurantoin, and NV, respectively. Linearity was observed in the 0.1-20 μg L^-1 range, with correlation coefficients greater than 0.99 recorded for all compounds. The developed method is sensitive, accurate, easier to use, and faster than previous methods when applied to real samples. To the best of our knowledge, this is the first method that can simultaneously determine NFs and their metabolites, as well as NV, using a single-step extraction process.

Nitrofurantoin-Microbial Degradation and Interactions with Environmental Bacterial Strains

The continuous exposure of living organisms and microorganisms to antibiotics that have increasingly been found in various environmental compartments may be perilous. One group of antibacterial agents that have an environmental impact that has been very scarcely studied is nitrofuran derivatives. Their representative is nitrofurantoin (NFT)-a synthetic, broad-spectrum antibiotic that is often overdosed. The main aims of the study were to: (a) isolate and characterize new microbial strains that are able to grow in the presence of NFT, (b) investigate the ability of isolates to decompose NFT, and (c) study the impact of NFT on microbial cell properties. As a result, five microbial species were isolated. A 24-h contact of bacteria with NFT provoked modifications in microbial cell properties. The greatest differences were observed in Sphingobacterium thalpophilum P3d, in which a decrease in both total and inner membrane permeability (from 86.7% to 48.3% and from 0.49 to 0.42 µM min^-1) as well as an increase in cell surface hydrophobicity (from 28.3% to 39.7%) were observed. Nitrofurantoin removal by selected microbial cultures ranged from 50% to 90% in 28 days, depending on the bacterial strain. Although the isolates were able to decompose the pharmaceutical, its presence significantly affected the bacterial cells. Hence, the environmental impact of NFT should be investigated to a greater extent.

Extrapolation of in vitro structural alerts for mutagenicity to the in vivo endpoint

As part of the hazard and risk assessment of chemicals in man, it is important to assess the ability of a chemical to induce mutations in vivo. Because of the commonalities in the molecular initiating event, mutagenicity in vitro can correlate well to the in vivo endpoint for certain compound classes; however, the difficulty lies in identifying when this correlation holds true. In silico alerts for in vitro mutagenicity may therefore be used as the basis for alerts for mutagenicity in vivo where an expert assessment is carried out to establish the relevance of the correlation. Taking this into account, a data set of publicly available transgenic rodent gene mutation assay data, provided by the National Institute of Health Sciences of Japan, was processed in the expert system Derek Nexus against the in vitro mutagenicity endpoint. The resulting predictivity was expertly reviewed to assess the validity of the observed correlations in activity and mechanism of action between the two endpoints to identify suitable in vitro alerts for extension to the in vivo endpoint. In total, 20 alerts were extended to predict in vivo mutagenicity, which has significantly improved the coverage of this endpoint in Derek Nexus against the data set provided. Updating the Derek Nexus knowledge base in this way led to an increase in sensitivity for this data set against this endpoint from 9% to 66% while maintaining a good specificity of 89%.

Risk of Cancer after Lower Urinary Tract Infection: A Population-Based Cohort Study

To investigate the association among lower urinary tract infection (UTI), the type and timing of antibiotic usage, and the subsequent risk of developing cancers, especially genitourinary cancers (GUC), in Taiwan. This retrospective population-based cohort study was conducted using 2009–2013 data from the Longitudinal Health Insurance Database. This study enrolled patients who were diagnosed with a UTI between 2010 and 2012. A 1:2 propensity score-matched control population without UTI served as the control group. Multivariate analysis with a multiple Cox regression model was applied to analyze the data. A total of 38,084 patients with UTI were included in the study group, and 76,168 participants without UTI were included in the control group. The result showed a higher hazard ratio of any cancer in both sexes with UTI (for males, adjusted hazard ratio (aHR) = 1.32; 95% confidence interval (CI) = 1.12–1.54; for females, aHR = 1.21; 95% CI = 1.08–1.35). Patients with UTI had a higher probability of developing new GUC than those without UTI. Moreover, the genital organs, kidney, and urinary bladder of men were significantly more affected than those of women with prior UTI. Furthermore, antibiotic treatment for more than 7 days associated the incidence of bladder cancer in men (7–13 days, aHR = 1.23, 95% CI = 0.50–3.02; >14 days, aHR = 2.73, CI = 1.32–5.64). In conclusion, UTI is significantly related to GUC and may serve as an early sign of GUC, especially in the male genital organs, prostate, kidney, and urinary bladder. During UTI treatment, physicians should cautiously prescribe antibiotics to patients.

Role of oxidative stress in the chemical structure-related genotoxicity of nitrofurantoin in Nrf2-deficient gpt delta mice

Despite its antimicrobial activity, nitrofurantoin (NFT) is a renal carcinogen in rats. Oxidative stress induced by reduction of the nitro group of NFT may contribute to its genotoxicity. This is supported by our recent results indicating that the structure of the nitrofuran plays a key role in NFT-induced genotoxicity, and oxidative DNA damage is involved in renal carcinogenesis. Nuclear factor erythroid 2-related factor 2 (NRF2) regulates cellular responses to oxidative stress. To clarify the role of oxidative stress in the chemical structure-related genotoxic mechanism of NFT, we performed reporter gene mutation assays for NFT and 5-nitro-2-furaldehyde (NFA) using Nrf2-proficient and Nrf2-deficient gpt delta mice. NFT administration for 13 weeks resulted in a significant increase in 8-hydroxydeoxyguanosine (8-OHdG; a marker of oxidative stress) and gpt mutant frequency only in the kidneys of Nrf2-/- mice. The mutation spectrum, characterized by increased substitutions at guanine bases, suggested that oxidative stress is involved in NFT-induced genotoxicity. However, NFA did not increase the mutation frequency in the kidneys, despite the increased 8-OHdG in NFA-treated Nrf2-/- mice. Thus, it is unlikely that oxidative stress is involved in the genotoxic mechanism of NFA. These results imply that nitro reduction plays a key role in the genotoxicity of NFT, but the lack of a role of oxidative stress in the genotoxicity of NFA indicates a potential role of side chain interactions in oxidative stress caused by nitro reduction. These findings provide a basis for the development of safe nitrofurans.

Mechanisms of oxidative stress-induced in vivo mutagenicity by potassium bromate and nitrofurantoin

Oxidative stress is well known as a key factor of chemical carcinogenesis. However, the actual role of oxidative stress in carcinogenesis, such as oxidative stress-related in vivo mutagenicity, remains unclear. It has been reported that 8-hydroxydeoxyguanosine (8-OHdG), an oxidized DNA lesion, might contribute to chemical carcinogenesis. Potassium bromate (KBrO3) and nitrofurantoin (NFT) are known as renal carcinogens in rats. Our previous studies showed an increase in mutant frequencies accompanied by an increased level of 8-OHdG in the kidneys of rodents following KBrO3 or NFT exposure. Furthermore, KBrO3 and NFT induced different types of gene mutations. Thus, in the present study, we performed reporter gene mutation assays and 8-OHdG measurements following KBrO3 or NFT exposure using Nrf2-proficient and Nrf2-deficient mice to clarify the relationship between KBrO3- or NFT-induced oxidative stress and subsequent genotoxicity. Administration of 1,500 ppm of KBrO3 in drinking water resulted in an increase in deletion mutations accompanied by an increase in 8-OHdG level, and administration of 2,500 ppm of NFT in diet induced an increase in guanine base substitution mutations without elevation of the 8-OHdG level in Nrf2-deficient mice. These results demonstrated that the formation of 8-OHdG, which resulted from the oxidizing potential of KBrO3, was directly involved in the increase in deletion mutations, although factors related to oxidative stress other than 8-OHdG might be crucial for NFT-induced guanine base substitution mutations. The present study provides new insight into oxidative stress-related in vivo mutagenicity.

Phototransformation of 5-nitro-2-furaldehyde in aqueous solution. A laser flash photolysis and product analysis study

Laser flash photolysis of 5-nitro-2-furaldehyde (NFA) in solution shows a short-lived transient absorption with λ_max = 475 ± 5 nm, which is relatively insensitive to solvent polarity and is assigned to the lowest triplet state of NFA (³NFA*). In water, the ³NFA* absorption decays to a long-lived absorption, the study of which, at different times after the end of the laser pulse, reveals it to be due to a furyloxyl radical (λ_max ≈ 375 nm) and to the radical anion NFA˙^- (λ_max ≈ 400 nm). These radicals were produced independently to confirm the assignment. The lifetime of ³NFA* depends both on the solvent and the ground-state concentration of NFA. An (n, π*) nature is attributed to ³NFA* on the basis of the propensity of ³NFA* to abstract a hydrogen-atom from the solvent. Kinetic evidence for triplet excimer formation was obtained from the self-quenching of ³NFA* in solvents where the triplet decay is slower. The effect of acidity on the triplet lifetime is discussed with respect to an electron-transfer self-quenching mechanism, assisted by the triplet excimer which is proposed to dissociate into radical ions. Chromatographic and spectroscopic analysis of the photolysed aqueous solution of NFA enabled the identification of 5-hydroxymethylene-2(5H)-furanone, nitrite ion and an unknown substance as the major photoproducts. Conclusive evidence is presented that the observed 5-hydroxymethylene-2(5H)-furanone is formed from the furyloxyl radical. It is shown that the unknown substance can also be obtained from both the photoreduction of NFA in propan-2-ol and chemical reduction of NFA by Fe(s) in water (along with 5-amino-2-furaldehyde). Based on ¹H- and ¹³C-NMR (with 2-D HMQC) and vibrational absorption spectroscopy, a tentative structure is proposed for the substance of t_R 3.69 minutes obtained as a photoreduction product of NFA in water. Inorganic anions are shown to be one-electron oxidised by ³NFA* (as indicated by the observation of both the radical anion of NFA and the inorganic radical) with second-order rate constants being dependent on E of the inorganic radical. The implications of the results from complete quenching of ³NFA* by inorganic anions, and subsequent product analysis, for the phototransformation mechanism of NFA in water are discussed.

Disruption of spindle checkpoint function in rats following 28 days of repeated administration of renal carcinogens

We previously reported that 28-day exposure to hepatocarcinogens that facilitate cell proliferation specifically alters the expression of G1/S checkpoint-related genes and proteins, induces aberrant early expression of ubiquitin D (UBD) at the G2 phase, and increases apoptosis in the rat liver, indicating G1/S and spindle checkpoint dysfunction. The present study aimed to determine the time of onset of carcinogen-specific cell-cycle disruption after repeated administration of renal carcinogens for up to 28 days. Rats were orally administered the renal carcinogens nitrofurantoin (NFT), 1-amino-2,4-dibromoantraquinone (ADAQ), and 1,2,3-trichloropropane (TCP) or the non-carcinogenic renal toxicants 1-chloro-2-propanol, triamterene, and carboxin for 3, 7 or 28 days. Both immunohistochemical single-molecule analysis and real-time RT-PCR analysis revealed that carcinogen-specific expression changes were not observed after 28 days of administration. However, the renal carcinogens ADAQ and TCP specifically reduced the number of cells expressing phosphorylated-histone H3 at Ser10 in both UBD(+) cells and proliferating cells, suggestive of insufficient UBD expression at the M phase and early transition of proliferating cells from the M phase, without increasing apoptosis, after 28 days of administration. In contrast, NFT, which has marginal carcinogenic potential, did not induce such cellular responses. These results suggest that it may take 28 days to induce spindle checkpoint dysfunction by renal carcinogens; however, induction of apoptosis may not be essential. Thus, induction of spindle checkpoint dysfunction may be dependent on carcinogenic potential of carcinogen examined, and marginal carcinogens may not exert sufficient responses even after 28 days of administration.