An Evaluation of the Human Relevance of the Liver Tumors Observed in Female Mice Treated With Permethrin Based on Mode of Action

Abstract

In 2-year studies, the nongenotoxic pyrethroid insecticide permethrin produced hepatocellular tumors in CD-1 mice but not in Wistar rats. Recently, we demonstrated that the mode of action (MOA) for mouse liver tumor formation by permethrin involves activation of the peroxisome proliferator-activated receptor alpha (PPARα), resulting in a mitogenic effect. In the present study, the effects of permethrin and 2 major permethrin metabolites, namely 3-phenoxybenzoic acid and trans-dichlorochrysanthemic acid, on cytochrome P450 mRNA levels and cell proliferation (determined as replicative DNA synthesis) were evaluated in cultured CD-1 mouse, Wistar rat, and human hepatocytes. Permethrin and 3-phenoxybenzoic acid induced CYP4A mRNA levels in both mouse and human hepatocytes, with trans-dichlorochrysanthemic acid also increasing CYP4A mRNA levels in mouse hepatocytes. 3-Phenoxybenzoic acid induced CYP4A mRNA levels in rat hepatocytes, with trans-dichlorochrysanthemic acid increasing both CYP4A mRNA levels and replicative DNA synthesis. Permethrin, 3-phenoxybenzoic acid, and trans-dichlorochrysanthemic acid stimulated replicative DNA synthesis in mouse hepatocytes but not in human hepatocytes, demonstrating that human hepatocytes are refractory to the mitogenic effects of permethrin and these 2 metabolites. Thus, although some of the key (eg, PPARα activation) and associative (eg, CYP4A induction) events in the established MOA for permethrin-induced mouse liver tumor formation could occur in human hepatocytes at high doses of permethrin, 3-phenoxybenzoic acid, and/or trans-dichlorochrysanthemic acid, increased cell proliferation (an essential step in carcinogenesis by nongenotoxic PPARα activators) was not observed. These results provide additional evidence that the established MOA for permethrin-induced mouse liver tumor formation is not plausible for humans.

Critical evaluation of the human relevance of the mode of action for rodent liver tumor formation by activators of the constitutive androstane receptor (CAR)

“…In a study in marmosets, the PPARa activator clofibrate was shown not to produce liver tumors after 6.5 years of treatment, although this is less than the expected life-span of this species (Corton et al 2018). Several studies have demonstrated that rodent PPARa activators do not stimulate RDS in cultured human hepatocytes (Lake 2009;Corton et al 2014Corton et al , 2018Kondo et al 2020). In vivo studies with chimeric mice with human hepatocytes have demonstrated that the PPARa activator fenofibrate does not increase RDS in human hepatocytes and results in downregulation of pathways related to DNA synthesis (Tateno et al 2015;de la Rosa Rodriguez et al 2018) similar to the results with CAR activators in chimeric mice with human hepatocytes.…”

“…cytotoxicity, CYP enzyme induction, and RDS studies) as they can maintain functional activities for at least 24-72 h. Such cultures permit the medium-throughput screening of compounds and are thus useful for examining inter-species and inter-individual differences. While PB has been shown to stimulate RDS in cultured mouse and rat hepatocytes, many studies from a number of different laboratories have demonstrated that PB does not increase RDS in cultured human hepatocytes (Parzefall et al 1991;Hirose et al 2009;Yamada et al 2015;Okuda et al 2017a;Haines et al 2018b;Peffer et al 2018a;Wiemann et al 2019;Kondo et al 2020;Lake et al 2020;Strupp et al 2020). For example, in both published (Hirose et al 2009;Yamada et al 2015;Okuda et al 2017a;Kondo et al 2020) studies (five male and nine female donors), and unpublished studies (six male and three female donors) from our laboratory, overall PB was shown not to increase hepatocyte RDS in cultured primary human hepatocytes from a total of 23 human donors (11 males and 12 females) with ages ranging from 10 months to 80 years.…”

“…While PB has been shown to stimulate RDS in cultured mouse and rat hepatocytes, many studies from a number of different laboratories have demonstrated that PB does not increase RDS in cultured human hepatocytes (Parzefall et al 1991;Hirose et al 2009;Yamada et al 2015;Okuda et al 2017a;Haines et al 2018b;Peffer et al 2018a;Wiemann et al 2019;Kondo et al 2020;Lake et al 2020;Strupp et al 2020). For example, in both published (Hirose et al 2009;Yamada et al 2015;Okuda et al 2017a;Kondo et al 2020) studies (five male and nine female donors), and unpublished studies (six male and three female donors) from our laboratory, overall PB was shown not to increase hepatocyte RDS in cultured primary human hepatocytes from a total of 23 human donors (11 males and 12 females) with ages ranging from 10 months to 80 years. In addition to studies with PB, a number of other nongenotoxic rodent CAR activators, including benfluralin, metazachlor, metofluthrin, momfluorothrin, the natural pyrethrins, nitrapyrin, sedaxane, and TCPOBOP have also been shown not to increase RDS in cultured human hepatocytes (Hirose et al 2009;Osimitz and Lake 2009;Yamada et al 2015;Soldatow et al 2016;LaRocca et al 2017;Okuda et al 2017a;Peffer et al 2018a;Wiemann et al 2019;Lake et al 2020;Strupp et al 2020).…”

Application of humanized mice to toxicology studies: Evaluation of the human relevance of the mode of action for rodent liver tumor formation by activators of the constitutive androstane receptor (CAR)

“…As mentioned above, primary cultures of animal and human primary hepatocytes have been extensively used for in vitro testing (e.g., cytotoxicity, CYP enzyme induction, and RDS studies) as they can maintain functional activities for at least 24-72 h 6 . While PB has been shown to stimulate RDS in cultured mouse and rat hepatocytes, many studies from different laboratories have demonstrated that PB does not increase RDS in cultured human hepatocytes 20,[65][66][67][69][70][71][72][73][74] 84 .…”

Proteasomal and lysosomal degradation for specific and durable suppression of immunotherapeutic targets

“…Small molecule inhibitors have been used to control cellular protein levels through occupancy-driven pharmacology as the mode of action. However, this strategy only temporarily inhibits the functions of regulatory proteins 50 , 51 . Finding new models is essential to control cellular protein levels.…”