Mode of action assessment for propylene dichloride as a human carcinogen. 2023

Jordan S Kozal, and Heather N Lynch, and Joanna Klapacz, and Rita S Schoeny, and Paul A Jean, and Andrew Maier
Stantec (ChemRisk), San Francisco, CA, 94104, USA. Electronic address: jordan.kozal@stantec.com.

As part of a systematic review of the non-cancer and cancer hazards of propylene dichloride (PDC), with a focus on potential carcinogenicity in workers following inhalation exposures, we determined that a mode of action (MOA)-centric framing of cancer effects was warranted. In our MOA analysis, we systematically reviewed the available mechanistic evidence for PDC-induced carcinogenesis, and we mapped biologically plausible MOA pathways and key events (KEs), as guided by the International Programme on Chemical Safety (IPCS)-MOA framework. For the identified pathways and KEs, biological concordance, essentiality of KEs, concordance of empirical observations among KEs, consistency, and analogy were evaluated. The results of this analysis indicate that multiple biologically plausible pathways may contribute to the cancer MOA for PDC, but that the relevant pathways vary by exposure route and level, tissue type, and species; further, more than one pathway may occur concurrently at high exposure levels. While several important data gaps exist, evidence from in vitro mechanistic studies, in vivo experimental animal studies, and ex vivo human tumor tissue analyses indicates that the predominant MOA pathway likely involves saturation of cytochrome p450 2E1 (CYP2E1)-glutathione (GSH) detoxification (molecular initiating event; MIE), accumulation of CYP2E1-oxidative metabolites, cytotoxicity, chronic tissue damage and inflammation, and ultimately tumor formation. Tumors may occur through several subsets of inflammatory KEs, including inflammation-induced aberrant expression of activation-induced cytidine deaminase (AID), which causes DNA strand breaks and mutations and can lead to tumors with a characteristic mutational signature found in occupational cholangiocarcinoma. Dose concordance analysis showed that low-dose mutagenicity (from any pathway) is not a driving MOA, and that prevention of target tissue damage and inflammation (associated with saturation of CYP2E1-GSH detoxification) is expected to also prevent the cascade of processes responsible for tumor formation.

UI MeSH Term Description Entries
D007249 Inflammation A pathological process characterized by injury or destruction of tissues caused by a variety of cytologic and chemical reactions. It is usually manifested by typical signs of pain, heat, redness, swelling, and loss of function. Innate Inflammatory Response,Inflammations,Inflammatory Response, Innate,Innate Inflammatory Responses
D011407 Propane A three carbon alkane with the formula H3CCH2CH3.
D002273 Carcinogens Substances that increase the risk of NEOPLASMS in humans or animals. Both genotoxic chemicals, which affect DNA directly, and nongenotoxic chemicals, which induce neoplasms by other mechanism, are included. Carcinogen,Oncogen,Oncogens,Tumor Initiator,Tumor Initiators,Tumor Promoter,Tumor Promoters,Initiator, Tumor,Initiators, Tumor,Promoter, Tumor,Promoters, Tumor
D004249 DNA Damage Injuries to DNA that introduce deviations from its normal, intact structure and which may, if left unrepaired, result in a MUTATION or a block of DNA REPLICATION. These deviations may be caused by physical or chemical agents and occur by natural or unnatural, introduced circumstances. They include the introduction of illegitimate bases during replication or by deamination or other modification of bases; the loss of a base from the DNA backbone leaving an abasic site; single-strand breaks; double strand breaks; and intrastrand (PYRIMIDINE DIMERS) or interstrand crosslinking. Damage can often be repaired (DNA REPAIR). If the damage is extensive, it can induce APOPTOSIS. DNA Injury,DNA Lesion,DNA Lesions,Genotoxic Stress,Stress, Genotoxic,Injury, DNA,DNA Injuries
D005978 Glutathione A tripeptide with many roles in cells. It conjugates to drugs to make them more soluble for excretion, is a cofactor for some enzymes, is involved in protein disulfide bond rearrangement and reduces peroxides. Reduced Glutathione,gamma-L-Glu-L-Cys-Gly,gamma-L-Glutamyl-L-Cysteinylglycine,Glutathione, Reduced,gamma L Glu L Cys Gly,gamma L Glutamyl L Cysteinylglycine
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D053858 Metabolic Networks and Pathways Complex sets of enzymatic reactions connected to each other via their product and substrate metabolites. Metabolic Networks,Metabolic Pathways,Metabolic Network,Metabolic Pathway,Network, Metabolic,Networks, Metabolic,Pathway, Metabolic,Pathways, Metabolic
D018281 Cholangiocarcinoma A malignant tumor arising from the epithelium of the BILE DUCTS. Cholangiocellular Carcinoma,Extrahepatic Cholangiocarcinoma,Intrahepatic Cholangiocarcinoma,Carcinoma, Cholangiocellular,Carcinomas, Cholangiocellular,Cholangiocarcinoma, Extrahepatic,Cholangiocarcinoma, Intrahepatic,Cholangiocarcinomas,Cholangiocarcinomas, Extrahepatic,Cholangiocarcinomas, Intrahepatic,Cholangiocellular Carcinomas,Extrahepatic Cholangiocarcinomas,Intrahepatic Cholangiocarcinomas
D019392 Cytochrome P-450 CYP2E1 An ethanol-inducible cytochrome P450 enzyme that metabolizes several precarcinogens, drugs, and solvents to reactive metabolites. Substrates include ETHANOL; INHALATION ANESTHETICS; BENZENE; ACETAMINOPHEN and other low molecular weight compounds. CYP2E1 has been used as an enzyme marker in the study of alcohol abuse. 4-Nitrophenol-2-Hydroxylase,CYP2E1,Dimethylnitrosamine N-Demethylase,CYP 2E1,CYP IIE1,CYPIIE1,Cytochrome P-450 (ALC),Cytochrome P-450 IIE1,Cytochrome P-450-J,Cytochrome P450 2E1,N-Nitrosodimethylamine Demethylase,4 Nitrophenol 2 Hydroxylase,Cytochrome P 450 CYP2E1,Cytochrome P 450 IIE1,Cytochrome P 450 J,Dimethylnitrosamine N Demethylase,N Nitrosodimethylamine Demethylase

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