Fetal rat anemia from flumioxazin, an N-phenylimide herbicide, is caused by suppression of heme synthesis resulting from inhibition of protoporphyrinogen oxidase (PPO). A series of studies to investigate the effects of flumioxazin have revealed that developmental toxicity is caused in rats but not in rabbits, and the adverse effects are not likely to occur in humans. In this study, as a final weight-of-evidence approach for assessing the human safety of flumioxazin, we compared the toxic potential of inhibition of heme synthesis leading to anemia between human and rat embryonic erythroid cells, which were degenerated as the target of flumioxazin in the rat developmental toxicity. To obtain embryonic erythroid cells, we established respective differentiation methods for embryonic erythroid cells from both human and rat pluripotent stem cells. Derived human and rat embryonic erythroid cells were treated with flumioxazin or dihydroartemisinin (DHA), an anti-malarial drug that causes reduction of embryonic erythroid cells and leads to anemia without species differences. In the human embryonic erythroid cells, DHA inhibited cell proliferation and heme synthesis, whereas there were no effects on heme content or cell proliferation with flumioxazin. In the rat embryonic erythroid cells, however, a dose-related reduction in heme synthesis occurred with treatment of flumioxazin and of DHA. These results confirmed that flumioxazin has no effect on heme synthesis in human embryonic erythroid cells. The present data were in accordance with the results of previous studies and demonstrated that there are no concerns in humans regarding the developmental toxicity of flumioxazin observed in rats.
Methidathion [3-(dimethoxyphosphinothioylsulfanylmethyl)-5-methoxy-1,3,4-thiadiazol-2-one; hereinafter DMTP], one of the most widely used organophosphorus pesticides, has been detected in some clinical cases of accidental exposure and suicide in Japan. It has been reported that DMTP concentration is decreased in blood. In this study, it is difficult to recover DMTP in the free form because DMTP is bound to human serum albumin (HSA). We detected DMTP adducts in HSA by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q/TOF-MS). The mass spectra showed that DMTP was preferably bound to the lysine (K), tyrosine (Y), and cysteinylproline (CP) residues of HSA. The concentrations of K-adduct, DMTP-Y-adduct and DMTP-CP-adduct were increased in vitro in a dose-dependent fashion when DMTP concentration was lower than the lethal dose. Furthermore, the DMTP-Y-adduct and DMTP-CP-adduct were also detected in post-mortem blood of an autopsied subject who died by intentional DMTP ingestion. The results suggested that the DMTP-Y-adduct and DMTP-CP-adduct could be used as a biomarker of DMTP poisoning, and the decrease concentration of DMTP in blood after death could be determined on the basis of the concentration of the DMTP-CP-adduct in blood.
A patient who survived acute paraquat (PQ) poisoning for more than 5 years was followed up in the emergency room. The patient had recurrent coughing and wheezing one month after discharge. Re-examination of chest CT showed increased dual lung texture. Spirometry suggested severe ventilatory dysfunction while bronchial dilation test was positive. The serum IgE level was significantly high. It is considered that patients with acute PQ poisoning may develop asthma in the long term.
The effect of nanoparticle type, shape, as well as primary and secondary particle size on toxicity remains poorly characterized. In this study, suspensions of nickel oxide (NiO) nanoparticles with the same primary particle size (< 50 nm) but different secondary particle sizes were prepared, and their cytotoxicity was investigated. A planetary ball mill wet nanopulverizer with zirconium milling balls of decreasing sizes (φ: 0.5, 0.1, and 0.05 mm) yielded NiO nanoparticles of decreasing mean particle size (310.4 ± 6.7, 172.0 ± 2.8, and 102.0 ± 0.5 nm). Stock solutions were diluted to various concentrations in 10% heat-inactivated fetal bovine serum containing minimum essential medium, and shown to have the same primary particle size, but different secondary particle sizes. Tests with A549 cells revealed that cytotoxicity increased with increasing secondary particle size: milling ball diameter φ 0.05 mm (IC50: 148 μg/mL) < φ 0.1 mm (IC50: 83.5 μg/mL) < φ 0.5 mm (IC50: 33.4 μg/mL). Uptake experiments indicated that the intracellular amount of Ni increased with increasing secondary particle size. In summary, the present findings show that differences in secondary particle size affected the cytotoxicity of NiO suspensions, which could be ascribed at least in part to differences in the amount of NiO taken up by the cells.
Detailed in vitro studies on the effects of perfluorooctanoic acid (PFOA) have demonstrated that activation of peroxisome proliferator-activated receptor α (PPARα) is a key process by which PFOA affects the malignancy of estrogen receptor α (ERα)-positive breast cancer cells. However, there is very little information on the PPARα-regulated genes responsible for the effects of PFOA in ERα-negative breast cancer cell malignancy. We recently demonstrated that fatty acid 2-hydroxylase (FA2H) stimulates the migration of ERα-negative human MDA-MB-231 cells, and PPARα is a key factor for the induction of FA2H in these cells. However, evidence for the relationship between PFOA exposure and PPARα-FA2H axis-driven migration has not been obtained. Here we analyzed the effects of PFOA on PPARα transcription and FA2H expression in relation to MDA-MB-231 cell migration. We found that simultaneously with stimulated migration, PFOA upregulated FA2H and activated the transcription of PPARα. FA2H-selective siRNA, but not siRNA control, clearly dampened PFOA-mediated cell migration. There is an inhibitory interaction between PPARα and PPARβ/δ (i.e., PPARβ/δ can suppress PPARα-mediated transcription) in MDA-MB-231 cells, but even in the presence of PPARβ/δ expression, PFOA appeared to free PPARα to upregulate FA2H. Collectively, our findings show that i) PFOA activates PPARα-mediated transcription, ii) PFOA stimulates migration dependent on FA2H expression, and iii) mechanistically, PFOA relieves PPARβ/δ suppression of PPARα activity to upregulate FA2H in MDA-MB-231 cells.