Oral toxicity of 1,2-dichloropropane: acute, short-term, and long-term studies in rats

Systematic review of the human health hazards of propylene dichloride

Propylene dichloride (PDC) is a chlorinated substance used primarily as an intermediate in basic organic chemical manufacturing. The United States Environmental Protection Agency (EPA) is currently evaluating PDC as a high-priority substance under the Toxic Substances Control Act (TSCA). We conducted a systematic review of the non-cancer and cancer hazards of PDC using the EPA TSCA and Integrated Risk Information System (IRIS) frameworks. We identified 12 epidemiological, 16 toxicokinetic, 34 experimental animal, and 49 mechanistic studies. Point-of-contact respiratory effects are the most sensitive non-cancer effects after inhalation exposure, and PDC is neither a reproductive nor a developmental toxicant. PDC is not mutagenic in vivo, and while in vitro evidence is mixed, DNA strand breaks consistently occur. Nasal tumors in rats and lung tumors in mice occurred after lifetime high-level inhalation exposure. Cholangiocarcinoma (CCA) was observed in Japanese print workers exposed to high concentrations of PDC. However, co-exposures, as well as liver parasites, hepatitis, and other risk factors, may also have contributed. The cancer mode of action (MOA) analysis revealed that PDC may act through multiple biological pathways occurring sequentially and/or simultaneously, although chronic tissue damage and inflammation likely dominate. Critically, health benchmarks protective of non-cancer effects are expected to protect against cancer in humans.

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-1β 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.

1,2-Dichloropropane (1,2-DCP)-Induced Angiogenesis in Dermatitis

1,2-Dichloropropane (1,2-DCP) has been used as an industrial solvent and a chemical intermediate, as well as in soil fumigants. Human exposure may occur during its production and industrial use. The target organs of 1,2-DCP are the eyes, respiratory system, liver, kidneys, central nervous system, and skin. Repeated or prolonged contact may cause skin sensitization. In this study, 1,2-DCP was dissolved in corn oil at 0, 2.73, 5.75, and 8.75 mL/kg. The skin of mice treated with 1,2-DCP was investigated using western blotting, hematoxylin and eosin staining, and immunohistochemistry. 1,2-DCP was applied to the dorsal skin and both ears of C57BL/6J mice. The thickness of ears and the epidermis increased significantly following treatment, and the appearance of blood vessels was observed in the dorsal skin. Additionally, the expression of vascular endothelial growth factor, which is tightly associated with neovascularization, increased significantly. The levels of protein kinase-B (PKB), phosphorylated PKB, mammalian target of rapamycin (mTOR), and phosphorylated mTOR, all of which are key components of the phosphoinositide 3-kinase/PKB/mTOR signaling pathway, were also enhanced. Taken together, 1,2-DCP induced angiogenesis in dermatitis through the PI3K/PKB/mTOR pathway in the skin.

Acute inhalation co-exposure to 1,2-dichloropropane and dichloromethane cause liver damage by inhibiting mitochondrial respiration and defense ability in mice

1,2-Dichloropropane (1,2-DCP) is used as an industrial solvent, insecticide fumigant and household dry cleaning product. Carcinogenicity caused by long-term exposure to 1,2-DCP is well established. However, the possible liver damage and related toxic mechanisms associated with acute inhalation exposure to 1,2-DCP are rarely reported. In this study, we investigated the effects of individual and combined exposure to 1,2-DCP and dichloromethane (DCM) on mice liver. The results showed that 1,2-DCP significantly caused liver necrosis, possibly due to 1,2-DCP-induced inhibition of the mitochondrial respiratory chain complex I-IV activities, resulting in mitochondrial dysfunction and extreme ATP consumption. Moreover, 1,2-DCP also decreased mitochondrial defense ability by inhibiting the mitochondrial glutathione S-transferase 1 (MGST1) activity, further aggravating liver damage. Additionally, we found that DCM co-exposure potentially enhanced 1,2-DCP toxicity. Our findings suggest that inhibition of mitochondrial function and MGST1 activity play critical roles in modulating 1,2-DCP-induced liver damage. Furthermore, our results contribute to study the new mechanism of mitochondria-dominated signaling pathways underlying liver injury induced by 1,2-DCP and DCM.

Lack of in vivo mutagenicity of 1,2-dichloropropane and dichloromethane in the livers of gpt delta rats administered singly or in combination

1,2-Dichloropropane (1,2-DCP) and dichloromethane (DCM) are possible causative agents associated with the development of cholangiocarcinoma in employees working in printing plant in Osaka, Japan. However, few reports have demonstrated an association between these agents and cholangiocarcinoma in rodent carcinogenicity studies. Moreover, the combined effects of these compounds have not been fully elucidated. In the present study, we evaluated the in vivo mutagenicity of 1,2-DCP and DCM, alone or combined, in the livers of gpt delta rats. Six-week-old male F344 gpt delta rats were treated with 1,2-DCP, DCM or 1,2-DCP + DCM by oral administration for 4 weeks at the dose (200 mg kg^-1 body weight 1,2-DCP and 500 mg kg^-1 body weight DCM) used in the carcinogenesis study performed by the National Toxicology Program. In vivo mutagenicity was analyzed by gpt mutation/Spi^- assays in the livers of rats. In addition, gene and protein expression of CYP2E1 and GSTT1, the major enzymes responsible for the genotoxic effects of 1,2-DCP and DCM, were analyzed by quantitative polymerase chain reaction and western blotting. Gpt and Spi^- mutation frequencies were not increased by 1,2-DCP and/or DCM in any group. Additionally, there were no significant changes in the gene and protein expression of CYP2E1 and GSTT1 in any group. These results indicated that 1,2-DCP, DCM and 1,2-DCP + DCM had no significant impact on mutagenicity in the livers of gpt delta rats under our experimental conditions. Copyright © 2016 John Wiley & Sons, Ltd.

The Subacute and Subchronic Oral Toxicity of 1,3-Dichloropropane in the Rat

1,3-Dichloropropane (DCP) was administered by gavage for 14 and 90 days to male and female Sprague-Dawley-derived rats (10/sex/group). In the 14-day study using dose levels of 200, 600, and 1800 mg/kg/day, all high-dose group animals died, and none died in the other two treatment groups. Other signs associated with treatment in high-dose animals included languid behavior, salivation (also seen in middose group animals), dyspnea, and prostration. No differences were found between animals in the low-dose or middose groups compared to the control animals for body weight, food consumption, hematology, and gross postmortem and histopathology data. Total protein and albumin blood levels were increased for low-dose and middose females, and middose females, respectively. The clinical chemistry findings appeared to be treatment-related, since they were accompanied by significantly increased liver weights (absolute and relative; both sexes of middose animals) and kidney weights (absolute and relative; middose males). The dose levels used in the 90-day study, chosen on the results of the 14-day study, were 50, 200, and 800 mg/kg/day. All animals survived to termination. Males in the high-dose group exhibited a significant decrease in body weight, whereas females in this group exhibited urine-stained fur. No treatment-related effects were found in food consumption or hematology data. Alkaline phosphatase, alanine aminotransferase (males only), albumin, and total protein for high-dose group animals were increased. These findings were accompanied by increases in liver weight for low-dose (females only), middose, and high-dose animals and kidney weights for middose and high-dose group animals. Microscopic evaluations revealed centrilobular hepatocellular hypertrophy for the high-dose group animals and an exacerbation of chronic progressive nephropathy for middose (males only) and high-dose animals.

Cytochrome P450 2E1 is responsible for the initiation of 1,2-dichloropropane-induced liver damage

1,2-Dichloropropane (1,2-DCP), a solvent, which is the main component of the cleaner used in the offset printing companies in Japan, is suspected to be the causative agent of bile duct cancer, which has been recently reported at high incidence in those offset printing workplaces. While there are some reports about the acute toxicity of 1,2-DCP, no information about its metabolism related to toxicity in animals is available. As part of our efforts toward clarifying the role of 1,2-DCP in the development of cancer, we studied the metabolic pathways and the hepatotoxic effect of 1,2-DCP in mice with or without cytochrome P450 2E1 (CYP2E1) activity. In an in vitro reaction system containing liver homogenate, 1,2-DCP was only metabolized by liver tissue of wild-type mice but not by that of cyp2e1-null mice. Furthermore, the kinetics of the solvent in mice revealed a great difference between the two genotypes; 1,2-DCP administration resulted in dose-dependent hepatic damage, as shown biochemically and pathologically, but this effect was only observed in wild-type mice. The nuclear factor κB p52 pathway was involved in the liver response to 1,2-DCP. Our results clearly indicate that the oxidative metabolism of 1,2-DCP in mice is exclusively catalyzed by CYP2E1, and this step is indispensable for the manifestation of the hepatotoxic effect of the solvent.

A proposal for calculating the no-observed-adverse-effect level (NOAEL) for organic compounds responsible for liver toxicity based on their physicochemical properties

OBJECTIVES

Both environmental and occupational exposure limits are based on the no-observed-adverse-effect level (NOAEL), lowest-observed-adverse-effect level (LOAEL) or benchmark dose (BMD) deriving from epidemiological and experimental studies. The aim of this study is to investigate to what extent the NOAEL values for organic compounds responsible for liver toxicity calculated based on their physicochemical properties could be used for calculating occupational exposure limits.

MATERIAL AND METHODS

The distribution coefficients from air to the liver (log K(liver)) were calculated according to the Abraham solvation equation. NOAEL and LOAEL values for early effects in the liver were obtained from the literature data. The descriptors for Abraham's equation were found for 59 compounds, which were divided into 2 groups: "non-reactive" (alcohols, ketones, esters, ethers, aromatic and aliphatic hydrocarbons, amides) and "possibly reactive" (aldehydes, allyl compounds, amines, benzyl halides, halogenated hydrocarbons, acrylates).

RESULTS

The correlation coefficients between log-log K and log NOAEL for non-reactive and reactive compounds amounted to r = -0.8123 and r = -0.8045, respectively, and were statistically significant. It appears that the Abraham equation could be used to predict the NOAEL values for compounds lacking information concerning their liver toxicity.

CONCLUSIONS

In view of the tendency to limit animal testing procedures, the method proposed in this paper can improve the practice of setting exposure guidelines for the unstudied compounds.

Inhalation carcinogenicity and toxicity of 1,2-dichloropropane in rats

The toxicity and carcinogenicity of 1,2-dichloropropane (DCP) were examined by inhalation exposure of male and female F344 rats to DCP for either 13 wk or 2 years. In the 13-wk study, the DCP concentrations used were 125, 250, 500, 1000, or 2000 ppm (v/v), and in the 2-year study the DCP concentrations were 80, 200, or 500 ppm (v/v). Thirteen-week exposure to DCP induced hyperplasia in the respiratory epithelium and atrophy of the olfactory epithelium at 125 ppm and above. At the higher levels of exposure, hemolytic anemia and lesions of liver and adrenal gland were observed. Two-year exposure to DCP significantly increased incidences of papilloma in the nasal cavity of male and female rats exposed to 500 ppm DCP. In addition, three cases of esthesioneuroepithelioma were observed in the DCP-exposed male rats. Total nasal tumors increased in a concentration-dependent manner. Hyperplasia of the transitional epithelium and squamous cell hyperplasia, both of which were morphologically different from the hyperplasia of the respiratory epithelium observed in the 13-wk exposure study, occurred in a concentration-dependent manner; these lesions are considered to be preneoplastic lesions. Atrophy of the olfactory epithelium, inflammation of the respiratory epithelium, and squamous cell metaplasia were also seen in the 2-year study. These results demonstrate that DCP is a nasal carcinogen in rats. Lifetime cancer risks for humans exposed to DCP in the ambient air and work environment were quantitatively estimated, using both nonthreshold and threshold approaches, with the data obtained from the 2-year study.

A Toxicogenomic Approach Revealed Hepatic Gene Expression Changes Mechanistically Linked to Drug-Induced Hemolytic Anemia

A variety of pharmaceutical compounds causes hemolytic anemia as a significant adverse effect and this toxicity restricts the clinical utility of these drugs. In this study, we applied microarray technology to investigate hepatic gene expression changes associated with drug-induced hemolytic anemia and to identify potential biomarker genes for this hematotoxicity. We treated female Sprague-Dawley rats with two hemolytic anemia-inducing compounds: phenylhydrazine and phenacetin. Hepatic gene expression profiles were obtained using a whole-genome oligonucleotide microarray with pooled RNA samples from individual rats within each dose group and analyzed in comparison with hepatic histopathology, hematology, and blood chemistry data. We identified a small subset of genes that were commonly deregulated in all the severe hemolytic conditions, some of which were considered to be involved in hepatic events characteristic of hemolytic anemia, such as hemoglobin biosynthesis, heme metabolism, and phagocytosis. Among them, we selected six upregulated genes as putative biomarkers, and their expression changes from microarray measurements were confirmed by quantitative real-time PCR using RNAs from individual animals. They were Alas2, beta-glo, Eraf, Hmox1, Lgals3, and Rhced. Expression patterns of all these genes showed high negative and positive correlation against erythrocyte counts and total bilirubin levels in circulation, respectively, suggesting that these genes may be the potential biomarkers for hemolytic anemia. These findings indicate that drug-induced hemolytic anemia may be detected based on hepatic changes in the expression of a subset of genes that are mechanistically linked to the hematotoxicity.

Mammalian toxicity of 1,3-dichloropropene

DCP has been utilized as a soil fumigant for more than 45 yr for the control for parasitic plant nematodes. Injected into soil before planting of crops, the instability of DCP in soil and water and its volatility dictate the principal route of human exposure that may occur, inhalation. Extensive data have been accumulated on the toxicity and metabolism of DCP. DCP is moderately toxic via oral or inhalation exposure, is irritating to the skin and eyes, and has potential to produce skin sensitization. It is rapidly and extensively metabolized. It has a half-life in the blood of rats and humans of only 3-7 min and < 10 min, respectively. Rats and mice excrete approximately 80% of even relatively high oral dosages within 24 hr, primarily as breakdown products of a glutathione conjugate or as carbon dioxide. These products reflect the primary routes of metabolism of DCP, via GSH-conjugative and hydrolytic pathways. An additional pathway based upon the epoxidation of DCP has also been proposed, but this does not appear to occur to any toxicologically significant degree in the presence of normally occurring GSTs. Direct evidence of the latter pathway is only been obtained at dosages of DCP in excess of the reported LD50. Humans also appear to rapidly metabolize DCP and excrete its metabolites. Subchronic toxicity studies of relatively pure DCP in rats and mice via oral or inhalation routes have resulted in portal-of-entry tissue effects that reflect the irritant properties of this chemical to nasal and gastric mucosa. At higher exposure levels in mice, however, toxicity was also identified in a remote tissue, the urinary bladder. Toxicity in dogs ingesting DCP was limited to the formation of a regenerative hypochromic, microcytic anemia. No teratological or reproductive effects were observed in rats or rabbits inhaling DCP vapors. Nonneoplastic changes from chronic dosing of DCP were generally similar to those observed in subchronic studies. Somewhat variable responses, however, have been observed for neoplastic effects, depending on the DCP formulation, route, and species used. Inhalation of a recent formulation increased the benign tumor incidence in the lungs of male mice (only) while ingestion of similar test material by rats and mice resulted in a low incidence of benign liver tumors in rats (only). In contrast, an older formulation containing Epi as a stabilizing agent administered to rats and mice via bolus oral dosing induced a number of malignant or benign tumors: in the forestomach and liver in rats and the forestomach, lung, and urinary bladder in mice. An equally complicated database has accumulated for DCP in vitro and in vivo genotoxicity testing. Genotoxicity has been reported in in vitro assays; however, confounding factors such as low-purity formulations, use of a genotoxic stabilizer, or generation of reactive impurities during attempts to purify test material have complicated interpretation. DCP appears to lack direct DNA reactivity, and a general trend toward decreasing activity with increasing complexity of the assay system and the presence of GST is evident. The weight-of-evidence evaluation of the genotoxicity data base suggests a lack of genotoxicity in vivo. Clearly definable treatment-related effects of DCP suggesting a plausible nongenotoxic mechanism of tumorigenic action, for example, enhanced cell proliferation, have not been in evidence in target tissues of treated animals. Thus, the specific mode of tumorigenesis of DCP in test animals remains to be elucidated but appears to involve a non-DNA-reactive mechanism. In conclusion, DCP-based soil fumigants have maintained an important role in agricultural despite the structural similarity of DCP to known genotoxic carcinogens and its own activity in in vitro genotoxicity assays. This role results from a combination of its use on soils before the planting of crops, its limited environmental half-life, rapid metabolism by animals via GSH conjugation and catabolism to CO2, lack of genotoxicity in in vivo assays, and an extensive toxicological database in animals, including several oncogenicity bioassays. These data, when combined with occupational and environmental exposure information, have provided a scientifically sound basis for the continued safe use of DCP-containing products.

The use of hematological effects in the development of minimal risk levels

The Agency for Toxic Substances and Disease Registry (ATSDR) derives minimal risk levels (MRLs) to assist in evaluating risk of adverse health effects in individuals exposed to hazardous substances. MRLs are derived from published values identifying no-observed-adverse-effect levels (NOAELs) or lowest-observed-adverse-effect levels (LOAELs) in animal or human studies. The most sensitive end points are used. To date, 4 inhalation MRLs and 13 oral MRLs have been derived from hematological end points for 12 substances. This paper provides a brief overview of the hematological system, examples of hematological end points, and the MRL for substances with hematological end points.

Recovery of biochemical changes induced by 1,2-dichloro propane in rat liver and kidney

1. Biochemical changes in male, Wistar rats, treated with different doses of 1,2-dichloropropane (50-500 mg kg-1 body weight), were investigated at the end of a 4-week treatment and after a 4-week recovery period. 2. The behaviour of Phase I and Phase II metabolic steps and of the angiotensin converting enzyme activity of the renal proximal tubule brush border were determined. 3. Phase II is more affected by the solvent than Phase I metabolism, and liver metabolism is more affected than the kidney. 4. Angiotensin converting enzyme activity from the proximal tubule brush border appears to be the most sensitive parameter of kidney involvement during treatment. 5. After a 4-week recovery period all the metabolic indices together with angiotensin converting enzyme activity have returned to normal. Only liver reduced glutathione content shows a slight, but significant, increase for the highest dose (500 mg kg-1 body weight). 6. The results show that the biochemical changes induced in liver and kidney by 1,2-dichloropropane are reversible.

Disposition and metabolism of [14C]1,2-dichloropropane following oral and inhalation exposure in Fischer 344 rats

The objective of this study was to compare the disposition and metabolism of [14C]1,2-dichloropropane [( 14C]DCP) following oral and inhalation exposure since these two routes are of interest with regards to occupational and accidental exposure. [14C]DCP was administered orally to groups of four rats of each sex as a single dose of 1 or 100 mg/kg and as a multiple 1 mg/kg nonradiolabeled dose for 7 days followed by a single 1 mg [14C]DCP/kg dose on day 8. In addition, four rats of each sex were exposed to [14C]DCP vapors for a 6-h period in a head-only inhalation chamber at target concentrations of 5, 50 and 100 ppm. [14C]DCP was readily absorbed, metabolized and excreted after oral or inhalation exposure. For all treatment groups the principal routes of elimination were via the urine (37-65%) and expired air (18-40%). The tissues, carcass, feces and cage wash contained less than 11, 9.7 and 3.8% of the dose, respectively. The major urinary metabolites, as a group, from the oral and inhalation exposures were identified as three N-acetylcysteine conjugates of DCP, N-acetyl-S-(2-hydroxypropyl)-L-cysteine, N-acetyl-S-(2-oxopropyl)-L-cysteine and N-acetyl-S-(1-carboxyethyl)-L-cysteine. The majority (61-87%) of the expired volatile organic material was found to be parent DCP in all samples analyzed. Increasing the dose/concentration of [14C]DCP resulted in an increase in the amount of exhaled [14C]-volatile organics. The peak DCP blood concentrations (inhalation exposure) were not proportional to dose, indicating a dose-dependency in the blood clearance of DCP. Nonetheless, upon termination of exposure, DCP was rapidly eliminated from the blood. In all treatment groups, following oral and inhalation exposure the majority of the radioactivity was eliminated by 24 h postdosing and no differences were noted between sexes. Therefore, it can be concluded that in the rat the pharmacokinetics and metabolism of [14C]DCP are similar regardless of route of exposure or sex.