Cytochrome P450 CYP2E1, but not nicotinamide adenine dinucleotide phosphate oxidase, is required for ethanol-induced oxidative DNA damage in rodent liver

Abstract

The occurrence of malignant tumors of the upper gastrointestinal tract and liver is, based largely on epidemiological evidence, causally related to the consumption of ethanol. It is widely recognized that oxidants play a key role in alcohol-induced liver injury; however, it is unclear how oxidants may be involved in DNA damage. We asked whether nicotinamide adenine dinucleotide phosphate oxidase, cytochrome P450 CYP2E1, or both are responsible for the production of DNA damage. The rodent Tsukamoto-French model of intragastric ethanol infusion was used. Wistar rats, Cyp2e1-, p47 phox -null, and hCyp2e1 transgenic mice were used. The abundance of oxidative DNA adducts, mutagenic apurinic/apyrimidinic sites, and expression of base excision DNA repair genes was determined. In rats and wild-type mice, ethanol treatment for 4 weeks led to an increase in oxidative DNA damage and induction of expression of the base excision DNA repair genes that are known to remove oxidative DNA lesions. No increase in either of the endpoints was observed in ethanol-treated Cyp2e1-null mice, whereas the magnitude of response in p47 phox -null mice and transgenic hCyp2e1 was identical to that in wild types. The increase in expression of DNA repair genes was completely abolished by treatment with the P450 inhibitor 1-aminobenzotriazole. In conclusion, the data support the hypothesis that oxidative stress to DNA is induced in liver by ethanol. Furthermore, although it was shown that nicotinamide adenine dinucleotide phosphate oxidase-derived oxidants are critical for the development of ethanol-induced liver injury, CYP2E1 is required for the induction of oxidative stress to DNA, and thus may play a key role in ethanol-associated hepatocarcinogenesis. (HEPATOLOGY 2005;41: 336-344.)

Ethanol-induced cytochrome P4502E1 causes carcinogenic etheno-DNA lesions in alcoholic liver disease

“…26 In line with these data, there were fewer oxidized DNA products in CYP2E1 knockout compared with wild-type mice after challenge with ethanol, and CYP2E1-null or 1-aminobenzotriazole-treated mice were completely protected from ethanol-induced DNA damage. 14 The fact that CYP2E1-null mice also developed liver injury was attributed to compensatory mechanisms, including the induction of CYP4A isozymes. 27,28 However, the role of CYP4A10 and CYP4A14 in the generation of LPO products and ROS has been controversially discussed 29 ; Bradford et al 14 did not find increased oxidative DNA damage in CYP2E1-null mice despite elevated CYP4A enzyme levels.…”

“…14 The fact that CYP2E1-null mice also developed liver injury was attributed to compensatory mechanisms, including the induction of CYP4A isozymes. 27,28 However, the role of CYP4A10 and CYP4A14 in the generation of LPO products and ROS has been controversially discussed 29 ; Bradford et al 14 did not find increased oxidative DNA damage in CYP2E1-null mice despite elevated CYP4A enzyme levels.…”

“…12 Inhibition of CYP2E1 by chlormethiazole (CMZ), a specific CYP2E1 inhibitor, improved alcoholic liver disease (ALD) as shown in the Tsukamoto-French rat model. 13 An increase of oxidative DNA adducts and of mutagenic apurinic and apyrimidinic DNA sites were found in wild-type mice chronically fed ethanol, but not in mice knocked out for functional CYP2E1, 14 further highlighting the importance of CYP2E1 in the generation of DNA damage after ethanol ingestion.…”

CYP2E1 and oxidative liver injury by alcohol

“…The induction and the DNA damage induced by ethanol was the same in wild type mice and NADPH oxidase deficient mice. The authors concluded that CYP2E1 but not NADPH oxidase is required for the ethanol induction of oxidative stress to DNA and thus CYP2E1 may play a key role in ethanolassociated hepatocarcinogenesis (139). On the other hand, as mentioned above, studies by Thurman and colleagues suggests that CYP2E1 may not play a role in alcohol-induced liver injury (135).…”

“…They concluded that CYP2E1 induction by chronic ethanol treatment was responsible for the decrease in proteasome activity and accumulation of oxidized proteins in the liver. In a very interesting study, Bradford et al (139) found that ethanol treatment for four weeks led to an increase in oxidative DNA damage and induction of expression of basic excision DNA repair genes in wild type mice but not in CYP2E1 knockout mice. The increase in DNA repair genes in wild type mice was abolished by treatment with a P450 inhibitor.…”