Toshihiro Kawamoto

Expression of cytochrome P450 in tumor tissues and its association with cancer development.

CYPs (cytochrome P450s) catalyze the conversion of numerous numbers of xenobiotics including carcinogens and drugs. CYPs can be involved in metabolic pathways of activation of procarcinogens and/or inactivation of carcinogens during the tumorigenic processes. Recently, increasing number of cancer tissues as well as normal tissues have been found to express a variety of CYPs. The local expression of CYPs in tumors appears to be very important for the management of cancers since CYPs expressed in tumors may be involved in activation and/or inactivation of anticancer drugs. The expression of CYPs in tumors may also convert endogenous substrates to metabolites that facilitate cancer development. In this review, we summarize the association of CYP expression in cancer tissues with carcinogenesis and cancer treatment.

TISSUE-DISTRIBUTION OF ALDEHYDE DEHYDROGENASE 2 AND EFFECTS OF THE ALDH2 GENE- DISRUPTION ON THE EXPRESSION OF ENZYMES INVOLVED IN ALCOHOL METABOLISM

In alcohol metabolism, acetaldehyde, a highly reactive intermediate that may cause cellular and DNA damages, is converted to acetate by mitochondrial aldehyde dehydrogenase ALDH2. Although the majority of ingested alcohol is eliminated in the liver, the first-pass metabolism of ethanol in the upper digestive tract is also important for prevention and management of ethanol-related gastrointestinal diseases. However, the tissue-distribution of Aldh2 in mice has been poorly investigated. In this study, therefore, we investigated the tissue-distribution of Aldh2 as well as Aldh1, Cyp1a1, Cyp2e1, and Cyp4b1 in wild type and Aldh2-null mice by immuno-histochemical analysis. The human liver and esophageal tissues were also examined. In mice, the Aldh2 protein was detected in the liver, lung, heart, kidney, testis, esophagus, stomach, colon, and pancreas, suggesting that the tissue-distribution of Aldh2 in mice is similar to that in humans. Therefore, Aldh2-null mice may be useful model animals for the investigation of alcohol metabolism and related diseases. Compared with the wild type, the expression level of Cyp2e1 was increased in the liver from Aldh2-null mice based on Western blot analysis, whereas the levels of Aldh1, Cyp1a1, and Cyp4b1 were indistinguishable. This observation suggests that a metabolite(s) of Aldh2 might down-regulate the expression of Cyp2e1 gene.

Identification of cytochrome P450 isoforms involved in 1-hydroxylation of pyrene

Urinary 1-hydroxypyrene (1-OHP) has been used as a biomarker for environmental polyaromatic hydrocarbon (PAH) exposure. However, it is known that there is an interindividual variability in metabolism of pyrene to 1-OHP depending on the activities of the metabolizing enzymes, especially cytochrome P450s (CYPs). In this study, we investigated the 1-hydroxylation of pyrene by 10 forms of cDNA-expressed human P450s in order to identify the principal isoforms of P450s that are involved in the major metabolic pathway of pyrene. The pyrene 1-hydroxylation activity was found to be the highest in CYP1A1 at both 0.5 and 50microM of pyrene, followed by CYP1B1 and 1A2, whereas other enzymes, including CYP2A6, 2C8, 2C9*1, 2C19, 2D6, 2E1, 3A4, and control microsomes, showed very low or undetectable rates of 1-hydroxylation. In conclusion, CYP1A1, 1B1, and 1A2 are major metabolizing enzymes in 1-hydroxylation of pyrene in vitro. This suggests that the individual difference of these enzymes must be included in epidemiological studies to evaluate PAH exposure using urinary 1-OHP.

Variation in the distribution of trace elements in hepatoma.

There are many reports of reduction of zinc level and rise of copper level in serum of patients with liver disease. However, there are a few reports that compare the trace elements in tumor tissues and nontumor tissues of the liver with hepatoma.We studied trace element distribution in tumor tissues and nontumor tissues of liver with hepatoma and compared them with data from normal liver tissues. Zinc (Zn), copper (Cu), selenium (Se), cadmium (Cd), mercury (Hg), and iron (Fe) were chosen as the trace elements to be observed.We observed falls of Zn, Cd, and Hg levels in tumor tissues and the rise of Cu level as a result of this investigation. Zn, Cd, and Hg levels in tumor tissues were significantly lower than those in nontumor tissues and Zn, Cd, and Hg levels in nontumor tissues were significantly lower than in normal liver tissues. This tendency was clearer for Cd and Hg than for Zn. Although the distribution of Cu was not significant, a distribution contrary to that of Zn was shown.These findings indicate that the distribution of Zn, Cd, and Hg can serve as supportive evidence that could be useful as a tumor marker. Selenium showed almost the same accumulation tendency among tumor tissues, nontumor tissues, and normal livers. Although correlation was observed among most metals in the normal liver, there was almost no correlation in tumor tissues.

Immunohistochemical evaluation of cytochrome P450 (CYP) and p53 in breast cancer.

In breast cancer, cytochrome P450 (CYP) metabolizes both endogenous substrates (i.e. estradiol) and exogenous substrates (i.e. anticancer drugs), which is associated not only with tumor development and progression but also with efficacy of cancer treatment. Therefore, we examined the expression of CYPs (CYP2A6, CYP1B1 and CYP3A) and p53 in specimens from 34 Japanese patients with breast cancer by immunohistochemistry. The expression of CYP3A was not detected in the 34 cases. CYP2A6 was detected only in one specimen (2.9%). Twenty-eight specimens (82.4%) showed positive signals for CYP1B1 expression. Eight of 34 (23.5%) were positive for p53 expression. Positive rate of CYP1B1 in stage I disease (100%) was statistically higher than that in stage II - IV disease (70.0%). Positive rate of p53 was 21.4% (6/28) in CYP1B1-positive cases and 33.3% (2/6) in CYP1B1-negative cases. There was no significant relationship between CYP1B1 expression and p53 expression. In conclusion, the expression of CYP3A in breast cancer may be less frequent in Japanese population although the expression of CYP3A has been reported in 20% of breast cancer in Caucasian, suggesting that the CYP3A expression in breast cancer may be dependent on ethnic groups. Since CYP3A is involved in the conversion of tamoxifen to its metabolites, the variation of the CYP3A expression in breast cancer tissues among ethnic groups might cause differences in the efficacy of tamoxifen.