Altered lung function in rats after subacute exposure to n-butyl isocyanate

Sensitivity of Zebrafish Embryogenesis to Risk of Fotemustine Exposure

Several anthropogenic products in wastewater are considered a threat to the aquatic environment. In addition to common industrial pollutants, levels of pharmaceuticals have been increasingly found in the environment in recent years, which may present a strong risk to the aquatic species that live there. The constant consumption of biologically active chemicals for human health has been matched by an increase in the leaking of these compounds in natural habitats over the last two decades. This study is aimed at evaluating the developmental toxicity of fotemustine in the ecological environment. Zebrafish embryos were exposed to doses of 25, 50 and 100 µg/mL from 4 h post-fertilization to 120 h. This study confirms that fotemustine exposure at 50 and 100 µg/mL affects the survival and hatching rate, morphology score and body length. Additionally, it significantly disturbs the antioxidant defense system and increases ROS in zebrafish larvae. From the molecular point of view, fotemustine exposure strongly induces apoptosis, endoplasmic reticulum stress (ERS) and the Wnt signaling pathway.

Ocular irritation from product of pesticide degradation among workers in a seed warehouse

Four workers at a seed supply warehouse in Chiba Prefecture, Japan, complained of ocular irritation on the job. Pesticide-coated seeds were stored in the warehouse but no significant amount of pesticide was detected in the air inside the warehouse. To identify the cause of the ocular irritation and to determine an appropriate solution to the problem, the authors used thermal desorption gas chromatography-mass spectrometry to analyze the profiles of volatile organic compounds (VOCs) in the air of the two warehouses at the site-warehouse A, where the four workers experienced ocular irritation, and warehouse B, where no workers experienced ocular irritation. Comparing the profiles of VOCs in these warehouses indicated that n-butyl isocyanate, a hydrolyzed product of the fungicide benomyl, was the cause of the workers' ocular irritation. n-Butyl isocyanate is known to be a contact irritant and if the benomyl-coated seeds were not properly dried before storage in the warehouse n-butyl isocyanate would have been produced. The results of the study suggest that more attention should be paid both to the pesticide itself and to the products of pesticide degradation. In this study, n-butyl isocyanate was identified as a product of pesticide degradation and a causative chemical affecting occupational health.

Assessment of chemicals for their potential to induce respiratory allergy in guinea pigs: A comparison of different routes of induction and confounding effects due to pulmonary hyperreactivity

Guinea pigs were sensitized either to selected low molecular weight chemicals known to induce respiratory allergy in humans, trimellitic anhydride (TMA), toluene diisocyanate (TDI), or diphenylmethane-4,4'-diisocyanate (MDI), or to ovalbumin (OA) as a positive control. In most instances, sensitization was induced either by repeated intradermal injections or by a single brief (15-min) high-concentration inhalation exposure. For TMA the repeated high dose intradermal injection regimen was compared with a single low dose intradermal injection regimen. Additionally, the effectiveness of the single 15-min induction protocol was compared with that of five consecutive inhalation exposures each of 3 hr/day. Animals were challenged 2-3 wk later by exposure to the substance used for induction, either as the free chemical or as a hapten-protein conjugate, and with increasing concentrations of acetylcholine (ACh). Challenge with the parental or conjugated hapten was used to assess compound-specific immediate-onset respiratory hyperreactivity, while ACh challenges were used to identify non-specific airway hyperreactivity. After intradermal sensitization with either MDI or TMA guinea pigs challenged with the corresponding hapten-protein conjugate showed a moderate incidence of immediate-type respiratory responses. However, the highest incidence of unequivocal allergic responses was evident from challenge with the hapten rather than with the protein conjugate, although these responses were only elicited with slightly irritant concentrations. After challenge with irritant concentrations of TDI, animals sensitized intradermally did not experience characteristic changes in respiratory patterns. On challenge with Ach and the TDI-protein conjugate these same animals showed an increased airway hyperresponsiveness although characteristic stereotypic breathing patterns, as observed in sensitized animals challenged with TMA, TMA-protein conjugate, or OA, were not detected. Comparison of the intradermal and inhalation induction regimens indicated that prior encounters with irritant haptens by inhalation reduces the concentration required to elicit airway hyperresponsiveness. This finding supports the conclusion that in animals sensitized and challenged by inhalation, irritant respiratory responses may be misconstrued as immediate-onset allergic responses. It appeared that the low dose single intradermal injection protocol is more effective in sensitizing guinea pigs than the high dose repeated injection protocol.

Acute nose-only inhalation exposure of rats to di- and triphosgene relative to phosgene

Groups of young adult Wistar rats were acutely exposed to trichloromethyl chloroformate (diphosgene) and bis(trichloromethyl) carbonate (triphosgene) vapor atmospheres using a directed-flow nose-only mode of exposure. The exposure duration used was 240 min. The median lethal concentration (LC50) of diphosgene and triphosgene was 13.9 and 41.5 mg/m3, respectively. Based on the molar exposure concentrations, the LC50s of phosgene (previously published), diphosgene, and triphosgene were 0.07, 0.07, and 0.14 mmol/m3, respectively. Although the principal toxic mode of action of the volatile diphosgene was similar to phosgene gas, the vapor phase of triphosgene appeared to be different to that of phosgene and diphosgene based on a more persistent occurrence of signs of respiratory distress and a biphasic onset of mortality. While all substances caused mortality within 1 day postexposure, triphosgene induced a second phase of mortality 11?14 days postexposure. The vapor saturation concentration of triphosgene at ambient temperature is ?100 times its LC50. In summary, triphosgene-induced lung injury patterns are different from that of phosgene and diphosgene. More research is needed to close the substantial data gaps of triphosgene.

Hypoxia-Induced Micronucleus Formation in Mice

The effect of hypoxia on micronucleus formation in mice was evaluated using special "shoebox" cages containing a silicone rubber membrane that effectively excludes the replacement of cage oxygen as it is spent by group-housed mice. In five separate trials using between 13 and 17 mice per cage, the oxygen level in the cage was reduced from the normal 21% to an average of 7.5% in 3-7 days. Compared to control animals, which exhibited a spontaneous micronuclei (MN) frequency of 0.08%, mice living under hypoxic conditions exhibited a statistically significant (p < or = 0.01) elevation in MN frequency of 0.15%. These findings may be relevant to in vivo studies in which drug or chemical treatment results in hypoactivity or complete sedation accompanied by varying degrees of hypoxia. It is proposed that structurally unexpected positive clastogenicity findings in animals exposed to these conditions may be due to hypoxia rather than to drug-DNA interaction. The likely mechanistic basis for this effect, decreased fidelity of cell division under conditions of elevated erythropoiesis, is discussed.

Comparative Analysis of Pulmonary Irritation by Measurements of Penh and Protein in Bronchoalveolar Lavage Fluid in Brown Norway Rats and Wistar Rats Exposed to Irritant Aerosols

The object of this study was to compare in two strain of rats (Brown Norway and Wistar) that were acutely exposed (1 x 6 hrs) to aerosols of polymeric methylenediphenyl-4,4'-diisocyanate (MDI), the relative sensitivity of the functional endpoint "enhanced pause (Penh)" with endpoints in bronchoalveolar lavage fluid (BALF) indicative of lower respiratory tract irritation. This approach included an analysis of both the concentration-response and the time-course of effects. Penh was measured repeatedly prior to (baseline) and during a stepped methacholine (MCh) bronchoprovocation challenge in barometric plethysmographic chambers on postexposure days 1, 3, and 7. Results show that total protein in BALF was a sensitive endpoint to probe early effects caused by exposure to irritant polyisocyanate aerosol. Baseline Penh increased in a concentration-dependent manner and paralleled closely the magnitude of increased BALF-protein on postexposure day 1. The time-course of changes in Penh complemented those of BALF-protein observed in previous studies. The incremental increase of Penh during a stepped MCh-challenge was attenuated with increasing baseline Penh values. In summary, these data show that the exposure to irritant concentrations of this aerosolized polyisocyanate caused a transient perturbation of the blood/air-barrier, which can suitably be probed by measurements of protein in BALF. Although Penh appears to parallel these changes, it displays substantially greater variability. The increase in Penh is apparently more related to changes in breathing patterns either caused by stimulation of receptors or changes in the mechanical properties of lung parenchyma. In regard to Penh and BALF-protein, both strains of rats were equally susceptible, although some endpoints displayed a higher variability in Brown Norway rats when compared to Wistar rats. This supports the conclusion that Wistar rats afford a higher diagnostic resolution than BN rats.

Toxic effects of carbendazim and n-butyl isocyanate, metabolites of the fungicide benomyl, on early development in the African clawed frog, Xenopus laevis

We investigated the toxic effects of carbendazim and n-butyl isocyanate (BIC), metabolites of the fungicide benomyl, on development in the African clawed frog, Xenopus laevis. To test the toxic effects, frog embryo teratogenesis assays using Xenopus were performed. Embryos were exposed to various concentrations of carbendazim (0-7 microM) and BIC (0-0.2 microM). LC(100) for carbendazim and BIC were 7 and 0.2 microM, respectively, and the corresponding LC(50), determined by probit analysis, were 5.606 and 0.135 microM. Exposure to carbendazim concentrations > or = 3 microM and BIC concentrations > or = 0.1 microM resulted in 10 different types of severe external malformation. Histological examinations revealed dysplasia of the brain, eyes, intestine, and somatic muscle, and swelling of the pronephric ducts. These phenomena were common in both test groups. The tissue-specific toxic effects were investigated with an animal cap assay. Neural tissues are normally induced at a high frequency by activin A, however, the induction of neural tissues was strongly inhibited by the addition of carbendazim. Conversely, the addition of BIC resulted in weak inhibition of neural tissues. Electron micrographs of animal cap explants revealed degeneration of cell junctions in the carbendazim-treated group, but not in the BIC-treated group. Numerous residual yolk platelets and mitochondrial degeneration were commonly observed in both test groups. The gene expression of cultivated animal cap explants was investigated by reverse transcriptase-polymerase chain reaction and revealed that expression of the neural-specific marker neural cell adhesion molecule was more strongly inhibited in the carbendazim-treated group than in the BIC-treated group.

Polyisocyanates in occupational environments: a critical review of exposure limits and metrics

BACKGROUND

Determination of polyisocyanates is important because they are a major contributor of exposure to the isocyanate functional group in many workplace environments and are capable of inducing sensitization and asthma. However, with multiple different measurement metrics in use, comparison of isocyanate exposure data between studies and development of occupational exposure limits (OELs) for polyisocyanates is difficult.

METHODS

An analysis of existing problems in the measurement and regulation of isocyanates is presented based on the published analytical, toxicological, and regulatory literature, and the authors' own analytical data and experience with isocyanates.

RESULTS

This analysis supports a need for standardization of isocyanate measurement metrics and provides a framework for the development of an OEL for polyisocyanates.

CONCLUSIONS

The total isocyanate group (microg NCO/m(3)) is recommended as the most feasible and practical metric (unit) by which to express polyisocyanate exposures for research, control, and regulatory purposes. The establishment of a comprehensive isocyanate OEL that simplifies the current agent-by-agent approach and expands coverage to polyisocyanates is also recommended.

Toxicity of fotemustine in rat hepatocytes and mechanism-based protection against it

Fotemustine is a relatively novel DNA-alkylating 2-chloroethyl-substituted N-nitrosourea (CENU) drug, clinically used for the treatment of disseminated malignant melanoma in different visceral and non-visceral tissues. Thrombocytopenia has been observed in patients treated with fotemustine and liver and renal toxicities as well. In this study, firstly the metabolism of fotemustine was investigated in vitro and secondly the undesired cytotoxicity of fotemustine as well as different ways of protection against it. In rat hepatocytes, chosen as a model system, fotemustine was shown to cause lactate dehydrogenase (LDH) leakage, glutathione (GSH) depletion, GSSG-formation and lipid peroxidation (LPO). A reactive metabolite, DEP-isocyanate, is most likely responsible for these undesired cytotoxic effects. Based on the observed cytotoxicity mechanisms, chemoprotection with several sulfhydryl-containing nucleophiles and antioxidants was investigated. The sulfhydryl nucleophiles; GSH, N-acetyl-L-cysteine (NAC) and glutathione isopropylester (GSH-IP) protected almost completely against fotemustine-induced LDH-leakage and LPO. NAC and GSH protected partly against fotemustine-induced GSH-depletion. The antioxidant, vitamin E protected completely against fotemustine-induced LPO, but only partly against fotemustine-induced LDH-leakage and not against GSH-depletion. Ebselen, a peroxidase-mimetic organoselenium compound, did not show protective effects against the cytotoxicity of fotemustine, possibly because GSH is required for the bioactivation of ebselen. It is concluded that co-administration of sulfhydryl nucleophiles, in particular NAC and GSH-IP, possibly in combination with antioxidants, such as vitamin E, are effective against the toxicity of fotemustine in vitro. It might, therefore, be worthwhile to investigate the cytoprotective potency of these agents against undesired toxicities of fotemustine in vivo as well.

Carbendazim and n-butylisocyanate: metabolites responsible for benomyl double action on cytochrome P450 in HepG2 cells

Changes in the cytochrome P450 monooxygenase system were investigated in HepG2 cells treated for 24 h with 1.25, 2.5, 5, 10 and 20 microg/ml of carbendazim (MBC) and n-butylisocyanate (BIC), the principal benomyl metabolites. The results show that n-butylisocyanate leads to a decrease in both ethoxyresorufin deethylase (P4501A1) (EROD) and ethoxycoumarin deethylase (P4502B) (ECOD), whereas MBC has no effect on EROD and increases ECOD. The decrease in ECOD and EROD activities after BIC treatment can be attributed to the detrimental action of this substance. The MBC-induced increase in ethoxycoumarin can be considered an enzyme-specific inductive phenomenon. This hypothesis was confirmed by Western immunoblot analysis and treatment with actinomycin D 8 x 10(-4) microM: the first showed an increase in P4502B isoenzyme content and the second evidence of a partial block of the increase in ECOD activity induced by MBC. Given these results, MBC and BIC seem to be the metabolites responsible for the double opposite action of their parent compound benomyl. Data deriving from an equimolar mixture of the two metabolites suggest that benomyl activity on some cytochrome P450 isoenzymes is the result of a balance between the action of the single metabolites (Radice et al., 1996).

Respiratory and other hazards of isocyanates

Isocyanates are increasingly being used for manufacturing polyurethane foam, elastomers, adhesives, paints, coatings, insecticides, and many other products. At present, they are regarded as one of the main causes of occupational asthma. The large number of workers who are exposed to these chemicals have a concentration-dependent risk of developing chronic airway disorders, especially bronchial asthma. Different pathophysiologic mechanisms are involved. Immunoglobulin E (IgE)-mediated sensitization and irritative effects have been clearly demonstrated in both exposed subjects and animals. Presumably, neural inflammation due to neuropeptide release of capsaicin-sensitive afferent nerves is crucial. We collected data on 1780 isocyanate workers who had been examined by our groups. Of them 1095 (including subjects from outpatient departments) had work-related symptoms, predominantly of the respiratory tract. Specific IgE antibodies were found in 14% of the 1095 subjects. The methacholine challenge test was shown to be an inadequate predictor of the results of inhalative isocyanate provocation tests in workers and in asthmatic controls. Isocyanate (toluene diisocyanate TDI) air concentrations of 10 ppb (0.07 mg/m3) and 20 ppb (0.14 mg/m3), respectively, did not cause significant bronchial obstruction in the majority of previously unexposed asthmatics with bronchial hyperreactivity. IgG-mediated allergic alveolitis, a rare disease among isocyanate workers, was found in approximately 1% of the symptomatic subjects. Experimental studies exhibit dose-dependent toxic effects and give evidence for tachykinin-mediated bronchial hyperreactivity after exposure to isocyanates. The clinical role of genotoxic effects of isocyanates and their by-products demonstrated here in vitro and in vivo has yet to be clarified.