Erratum: "Diversity Outbred Mice Identify Population-Based Exposure Thresholds and Genetic Factors that Influence Benzene-Induced Genotoxicity".

[This corrects the article DOI: http://dx.doi.org/10.1289/ehp.1408202.].

Chemical Reactivity and Respiratory Toxicity of the α-Diketone Flavoring Agents: 2,3-Butanedione, 2,3-Pentanedione, and 2,3-Hexanedione.

Occupational exposure to 2,3-butanedione (BD) vapors has been associated with severe respiratory disease leading to the use of potentially toxic substitutes. We compared the reactivity and respiratory toxicity of BD with that of two structurally related substitutes, 2,3-pentanedione (PD) and 2,3-hexanedione (HD). Chemical reactivity of the diketones with an arginine substrate decreased with increasing chain length (BD > PD > HD). Animals were evaluated the morning after a 2-week exposure to 0, 100, 150, or 200 ppm BD, PD, or HD (postexposure) or 2 weeks later (recovery). Bronchial fibrosis was observed in 5/5 BD and 5/5 PD rats at 200 ppm and in 4/6 BD and 6/6 PD rats at 150 ppm in the postexposure groups. Following recovery, bronchial fibrosis was observed in all surviving rats exposed to 200 ppm BD (5/5) or PD (3/3) and in 2/10 BD and 7/9 PD rats exposed to 150 ppm. Bronchial fibrosis was observed only in 2/12 HD-exposed rats in the 200 ppm postexposure group. Patchy interstitial fibrosis affected lungs of recovery groups exposed to 200 ppm PD (3/3) or BD (1/5) and to 150 ppm PD (4/9) or BD (7/10) and correlated with pulmonary function deficits. BD and PD were more reactive and produced more bronchial fibrosis than HD.

Diversity Outbred Mice Identify Population-Based Exposure Thresholds and Genetic Factors that Influence Benzene-Induced Genotoxicity.

BACKGROUND: Inhalation of benzene at levels below the current exposure limit values leads to hematotoxicity in occupationally exposed workers. OBJECTIVE: We sought to evaluate Diversity Outbred (DO) mice as a tool for exposure threshold assessment and to identify genetic factors that influence benzene-induced genotoxicity. METHODS: We exposed male DO mice to benzene (0, 1, 10, or 100 ppm; 75 mice/exposure group) via inhalation for 28 days (6 hr/day for 5 days/week). The study was repeated using two independent cohorts of 300 animals each. We measured micronuclei frequency in reticulocytes from peripheral blood and bone marrow and applied benchmark concentration modeling to estimate exposure thresholds. We genotyped the mice and performed linkage analysis. RESULTS: We observed a dose-dependent increase in benzene-induced chromosomal damage and estimated a benchmark concentration limit of 0.205 ppm benzene using DO mice. This estimate is an order of magnitude below the value estimated using B6C3F1 mice. We identified a locus on Chr 10 (31.87 Mb) that contained a pair of overexpressed sulfotransferases that were inversely correlated with genotoxicity. CONCLUSIONS: The genetically diverse DO mice provided a reproducible response to benzene exposure. The DO mice display interindividual variation in toxicity response and, as such, may more accurately reflect the range of response that is observed in human populations. Studies using DO mice can localize genetic associations with high precision. The identification of sulfotransferases as candidate genes suggests that DO mice may provide additional insight into benzene-induced genotoxicity.

Macrophage solubilization and cytotoxicity of indium-containing particles as in vitro correlates to pulmonary toxicity in vivo.

Macrophage-solubilized indium-containing particles (ICPs) were previously shown in vitro to be cytotoxic. In this study, we compared macrophage solubilization and cytotoxicity of indium phosphide (InP) and indium-tin oxide (ITO) with similar particle diameters (∼ 1.5 µm) and then determined if relative differences in these in vitro parameters correlated with pulmonary toxicity in vivo. RAW 264.7 macrophages were treated with InP or ITO particles and cytotoxicity was assayed at 24 h. Ionic indium was measured in 24 h culture supernatants. Macrophage cytotoxicity and particle solubilization in vitro were much greater for InP compared with ITO. To correlate changes in vivo, B6C3F1 mice were treated with InP or ITO by oropharyngeal aspiration. On Days 14 and 28, bronchoalveolar lavage (BAL) and pleural lavage (PL) fluids were collected and assayed for total leukocytes. Cell differentials, lactate dehydrogenase activity, and protein levels were also measured in BAL. All lavage parameters were greatly increased in mice treated with InP compared with ITO. These data suggest that macrophage solubilization and cytotoxicity of some ICPs in vitro are capable of predicting pulmonary toxicity in vivo. In addition, these differences in toxicity were observed despite the two particulate compounds containing similar amounts of indium suggesting that solubilization, not total indium content, better reflects the toxic potential of some ICPs. Soluble InCl3 was shown to be more cytotoxic than InP to macrophages and lung epithelial cells in vitro further suggesting that ionic indium is the primary cytotoxic component of InP.

Bronchial and bronchiolar fibrosis in rats exposed to 2,3-pentanedione vapors: implications for bronchiolitis obliterans in humans.

2,3-Pentanedione (PD) is a component of artificial butter flavorings. The use of PD is increasing since diacetyl, a major butter flavorant, was associated with bronchiolitis obliterans (BO) in workers and has been removed from many products. Because the toxicity of inhaled PD is unknown, these studies were conducted to characterize the toxicity of inhaled PD across a range of concentrations in rodents. Male and female Wistar-Han rats and B6C3F1 mice were exposed to 0, 50, 100, or 200 ppm PD 6 h/d, 5 d/wk for up to 2 wk. Bronchoalveolar lavage fluid (BALF) was collected after 1, 3, 5, and 10 exposures, and histopathology was evaluated after 12 exposures. MCP-1, MCP-3, CRP, FGF-9, fibrinogen, and OSM were increased 2- to 9-fold in BALF of rats exposed for 5 and 10 days to 200 ppm. In mice, only fibrinogen was increased after 5 exposures to 200 ppm. The epithelium lining the respiratory tract was the site of toxicity in all mice and rats exposed to 200 ppm. Significantly, PD also caused both intraluminal and intramural fibrotic airway lesions in rats. The histopathological and biological changes observed in rats raise concerns that PD inhalation may cause BO in exposed humans.

Pleural effects of indium phosphide in B6C3F1 mice: nonfibrous particulate induced pleural fibrosis.

The mechanism(s) by which chronic inhalation of indium phosphide (InP) particles causes pleural fibrosis is not known. Few studies of InP pleural toxicity have been conducted because of the challenges in conducting particulate inhalation exposures, and because the pleural lesions developed slowly over the 2-year inhalation study. The authors investigated whether InP (1 mg/kg) administered by a single oropharyngeal aspiration would cause pleural fibrosis in male B6C3F1 mice. By 28 days after treatment, protein and lactate dehydrogenase (LDH) were significantly increased in bronchoalveolar lavage fluid (BALF), but were unchanged in pleural lavage fluid (PLF). A pronounced pleural effusion characterized by significant increases in cytokines and a 3.7-fold increase in cell number was detected 28 days after InP treatment. Aspiration of soluble InCl(3) caused a similar delayed pleural effusion; however, other soluble metals, insoluble particles, and fibers did not. The effusion caused by InP was accompanied by areas of pleural thickening and inflammation at day 28, and by pleural fibrosis at day 98. Aspiration of InP produced pleural fibrosis that was histologically similar to lesions caused by chronic inhalation exposure, and in a shorter time period. This oropharyngeal aspiration model was used to provide an initial characterization of the progression of pleural lesions caused by InP.

Gestational mercury vapor exposure and diet contribute to mercury accumulation in neonatal rats.

Exposure of pregnant Long-Evans rats to elemental mercury (Hg0) vapor resulted in a significant accumulation of Hg in tissues of neonates. Because elevated Hg in neonatal tissues may adversely affect growth and development, we were interested in how rapidly Hg was eliminated from neonatal tissues. Pregnant rats were exposed to 1, 2, or 4 mg Hg0 vapor/m3 or air (controls) for 2 hr/day from gestation day 6 (GD6) through GD15. Neonatal brain, liver, and kidney were analyzed for total Hg at various times between birth and postnatal day 90 (PND90). Milk was analyzed for Hg between birth and weaning (PND21). Before weaning, the Hg levels in neonatal tissues were proportional to maternal exposure concentrations and were highest in kidney followed by liver and then brain. There was no elimination of Hg between birth and weaning, indicating that neonates were exposed continuously to elevated levels of Hg during postpartum growth and development. Consumption of milk from exposed dams resulted in a slight increase in kidney Hg concentration during this period. Unexpectedly, neonatal Hg accumulation increased rapidly after weaning. Increased Hg was measured in both control and exposed neonates and was attributed to consumption of NIH-07 diet containing trace levels of Hg. By PND90, tissue Hg levels equilibrated at concentrations similar to those in unexposed adult Long-Evans rats fed the same diet. These data indicate that dietary exposure to trace amounts of Hg can result in a significantly greater accumulation of Hg in neonates than gestational exposure to high concentrations of Hg0 vapor.