Factory site analysis of respirable fibers generated during the process of cutting and grinding of carbon fibers-reinforced plastics.

OBJECTIVES: Carbon fibers are used in a variety of industrial applications, based on their lightweight and high stiffness properties. There is little information on the characteristics and exposure levels of debris generated during the factory processing of carbon fibers or their composites. This study revisits the general assumption that carbon fibers or their debris released during composite processing are considered safe for human health. METHODS: The present interventional study was conducted at a factory located in Japan, and involved on-site collection of debris generated during the industrial processing of polyacrylonitrile (PAN)-based carbon-fiber-reinforced plastic (CFRP). The debris were collected before being exhausted locally from around different factory machines and examined morphologically and quantitatively by scanning electron microscopy. The levels of exposure to respirable carbon fibers at different areas of the factory were also quantified. RESULTS: The collected debris mainly contained the original carbon fibers broken transversely at the fiber's major axis. However, carbon fiber fragments morphologically compatible with the WHO definition of respirable fibers (length: > 5 µm, width: < 3 µm, length/width ratio: > 3:1) were also found. The concentrations of respirable fibers at the six examined factory areas under standard working conditions in the same factory were below the standard limit of 10 fibers/L, specified for asbestos dust-generating facilities under the Air Pollution Control Law in Japan. CONCLUSIONS: Our study identified potentially dangerous respirable fibers with high aspect ratio, which was generated during the processing of PAN-based CFRP. Regular risk assessment of carbon fiber debris is necessary to ensure work environment safety.

Role of Macrophages in Cytotoxicity, Reactive Oxygen Species Production and DNA Damage in 1,2-Dichloropropane-Exposed Human Cholangiocytes In Vitro.

1,2-Dichloropropane (1,2-DCP), a synthetic chlorinated organic compound, was extensively used in the past in offset color proof-printing. In 2014, the International Agency for Research on Cancer (IARC) reclassified 1,2-DCP from its initial Group 3 to Group 1. Prior to the reclassification, cholangiocarcinoma was diagnosed in a group of workers exposed to 1,2 -DCP in an offset color proof-printing company in Japan. In comparison with other forms of cholangiocarcinoma, 1,2-DCP-induced cholangiocarcinoma was of early onset and accompanied by extensive pre-cancerous lesions in large bile ducts. However, the mechanism of 1,2-DCP-induced cholangiocarcinoma is poorly understood. Inflammatory cell proliferation was observed in various sites of the bile duct in the noncancerous hepatic tissues of the 1,2-DCP-induced cholangiocarcinoma. The aim of this study was to enhance our understanding of the mechanism of 1,2-DCP-related cholangiocarcinogenesis. We applied an in vitro system to investigate the effects of 1,2-DCP, using MMNK-1 cholangiocytes cultured alone or with THP-1 macrophages. The cultured cells were exposed to 1,2-DCP at 0, 0.1, 0.2, 0.4, and 0.8 mM for 24 h, and then assessed for cell proliferation, cell cytotoxicity, DNA damage, and ROS production. Exposure to 1,2-DCP increased proliferation of MMNK-1 cholangiocytes cultured alone, but not those cultured with macrophages. 1,2-DCP also increased LDH cytotoxicity, DNA damage, and ROS production in MMNK-1 cholangiocytes co-cultured with macrophages but not those cultured alone. 1,2-DCP increased TNFα and IL-1ß protein expression in macrophages. The results highlight the role of macrophages in enhancing the effects of 1,2-DCP on cytotoxicity, ROS production, and DNA damage in cholangiocytes.

Nrf2 Activation Attenuates Acrylamide-Induced Neuropathy in Mice.

Acrylamide is a well characterized neurotoxicant known to cause neuropathy and encephalopathy in humans and experimental animals. To investigate the role of nuclear factor erythroid 2-related factor 2 (Nrf2) in acrylamide-induced neuropathy, male C57Bl/6JJcl adult mice were exposed to acrylamide at 0, 200 or 300 ppm in drinking water and co-administered with subcutaneous injections of sulforaphane, a known activator of the Nrf2 signaling pathway at 0 or 25 mg/kg body weight daily for 4 weeks. Assessments for neurotoxicity, hepatotoxicity, oxidative stress as well as messenger RNA-expression analysis for Nrf2-antioxidant and pro-inflammatory cytokine genes were conducted. Relative to mice exposed only to acrylamide, co-administration of sulforaphane protected against acrylamide-induced neurotoxic effects such as increase in landing foot spread or decrease in density of noradrenergic axons as well as hepatic necrosis and hemorrhage. Moreover, co-administration of sulforaphane enhanced acrylamide-induced mRNA upregulation of Nrf2 and its downstream antioxidant proteins and suppressed acrylamide-induced mRNA upregulation of tumor necrosis factor alpha (TNF-α) and inducible nitric oxide synthase (iNOS) in the cerebral cortex. The results demonstrate that activation of the Nrf2 signaling pathway by co-treatment of sulforaphane provides protection against acrylamide-induced neurotoxicity through suppression of oxidative stress and inflammation. Nrf2 remains an important target for the strategic prevention of acrylamide-induced neurotoxicity.

Genetic ablation of Nrf2 exacerbates neurotoxic effects of acrylamide in mice.

Acrylamide (ACR), a recognized neurotoxicant in humans and experimental animals, is widely used in industry and in food generated through Maillard reaction. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulator of the cellular defense system and activates antioxidants and cytoprotective genes. The exact roles of Nrf2 in environmental electrophile-induced neurotoxicity is poorly understood. The aim of this study was to determine the roles of Nrf2 in ACR-induced neurotoxicity including degeneration of monoaminergic axons and sensorimotor dysfunction. Male 10-week-old C57BL/6JJcl Nrf2-knockout mice and wild type (WT) counterparts were each divided into four groups of 12 and provided with drinking water containing acrylamide at 0, 67, 110 or 200 ppm for four weeks. The effects of acrylamide were examined by landing foot spread test, immunohistochemistry for noradrenaline (NA) and serotonin (5-HT)-containing axons and Iba1-positive microglia in the prefrontal cortex as well as quantitative real-time polymerase chain reaction (qRT-PCR) on antioxidant, proinflammatory and anti-inflammatory genes in the prefrontal cortex. Relative to the wild type, exposure of Nrf2-knockout mice to acrylamide increased hindlimb splay length, microglial area and process length as well as decreasing the density of NA and 5-HT-immunoreactive axons to a greater extent. Moreover, deletion of Nrf2 gene suppressed acrylamide-induced mRNA upregulation of Nrf2-antioxidants, NAD(P): quinone oxidoreductase 1 (NQO1), superoxide dismutase-1 (SOD-1) and heme oxygenase-1 (HO-1) as well as anti-inflammatory markers such as, arginase-1 (Arg1), found in the inflammatory zone-1 (Fizz1), chitinase-like 3 (Chi3l3), interleukin-4 receptor alpha (IL-4Rα), cluster of differentiation  206 (CD206) and transforming growth factor beta-1 (TGFß1) while enhancing acrylamide-induced upregulation of pro-inflammatory cytokines, interleukin-1 beta (IL-1ß), tumor necrosis-alpha (TNF-α) and inducible nitric oxide synthase (iNOS) in the prefrontal cortex. The results demonstrate susceptibility of mice lacking the Nrf2 gene to acrylamide-induced neurotoxicity and neuroinflammation with the activation of microglia. Moreover, the results suggest the role of Nrf2 not only in induction of antioxidant gene expression, but also in suppression of proinflammatory cytokine gene expression.

Proteomic analysis of liver proteins of mice exposed to 1,2-dichloropropane.

1,2-Dichloropropane (1,2-DCP) is recognized as the causative agent for cholangiocarcinoma among offset color proof-printing workers in Japan. The aim of the present study was to characterize the molecular mechanisms of 1,2-DCP-induced hepatotoxic effects by proteomic analysis. We analyzed quantitatively the differential expression of proteins in the mouse liver and investigated the role of P450 in mediating the effects of 1,2-DCP. Male C57BL/6JJcl mice were exposed to 0, 50, 250, or 1250 ppm 1,2-DCP and treated with either 1-aminobenzotriazole (1-ABT), a nonselective P450 inhibitor, or saline, for 8 h/day for 4 weeks. Two-dimensional difference in gel electrophoresis (2D-DIGE) combined with matrix-assisted laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF/TOF/MS) was used to detect and identify proteins affected by the treatment. PANTHER overrepresentation test on the identified proteins was conducted. 2D-DIGE detected 61 spots with significantly different intensity between 0 and 250 ppm 1,2-DCP groups. Among them, 25 spots were identified by MALDI-TOF/TOF/MS. Linear regression analysis showed significant trend with 1,2-DCP level in 17 proteins in mice co-treated with 1-ABT. 1-ABT mitigated the differential expression of these proteins. The gene ontology enrichment analysis showed overrepresentation of proteins functionally related to nickel cation binding, carboxylic ester hydrolase activity, and catalytic activity. The results demonstrated that exposure to 1,2-DCP altered the expression of proteins related with catalytic and carboxylic ester hydrolase activities, and that such effect was mediated by P450 enzymatic activity.