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Genotoxicity, toxicity, and carcinogenicity of the antihistamine methapyrilene
Abstract:
The antihistamine methapyrilene hydrochloride (MP) has been shown to be a potent hepatocarcinogen in rats, but not in hamsters or guinea pigs. This finding is in contrast to the relative nongenotoxicity of this compound. MP has been evaluated for genotoxicity in a wide variety of short-term tests and has generally demonstrated little genotoxic activity. One exception to this is the mouse lymphoma L5178Y mutagenesis assay, in which MP produced a very significant increase in small colony mutants with concomitant chromosomal damage in these cells. MP also induced positive responses in several cell transformation assays. One potentially very significant effect of MP is that it induces a large increase in hepatic cell proliferation coupled with mitochondrial proliferation in the livers of treated animals. This effect is discussed as a possible mechanism of liver tumor induction in rats.
Insights
The antihistamine methapyrilene hydrochloride (MP) is a potent liver carcinogen in rats, despite showing little genotoxicity. MP induces significant hepatic cell and mitochondrial proliferation, a potential mechanism for liver tumor induction.
Area of Science:
- Toxicology
- Hepatocarcinogenesis
- Genotoxicity
Background:
- Methapyrilene hydrochloride (MP), an antihistamine, is a known potent hepatocarcinogen in rats.
- MP exhibits relative nongenotoxicity across various short-term tests.
- Species-specific differences in MP hepatocarcinogenicity exist, with rats being susceptible while hamsters and guinea pigs are not.
Purpose of the Study:
- To investigate the mechanisms underlying methapyrilene hydrochloride-induced hepatocarcinogenesis in rats.
- To evaluate the genotoxic potential of MP and its correlation with carcinogenicity.
- To explore the role of hepatic cell proliferation in MP-induced liver tumors.
Main Methods:
- Evaluation of MP genotoxicity using a wide range of short-term assays.
- Assessment of MP's effect in the mouse lymphoma L5178Y mutagenesis assay.
- Analysis of cell transformation assays.
- Examination of hepatic cell proliferation and mitochondrial proliferation in MP-treated rats.
Main Results:
- MP demonstrated minimal genotoxic activity in most assays, with a notable exception in the mouse lymphoma assay, showing increased mutants and chromosomal damage.
- MP induced positive responses in cell transformation assays.
- A significant increase in hepatic cell proliferation and mitochondrial proliferation was observed in the livers of MP-treated rats.
Conclusions:
- The hepatocarcinogenicity of MP in rats may not be directly linked to genotoxicity.
- MP induces significant hepatic cell proliferation and mitochondrial proliferation, suggesting these as potential mechanisms for liver tumor induction.
- Further research is warranted to elucidate the precise pathways of MP-induced hepatocarcinogenesis.