The Induction of COX-2 and DDH by Areca Quid Components and It's Role in Oral Carcinogenesis
| Autor: | Deh-Wei Tang, 湯德瑋 |
|---|---|
| Rok vydání: | 2004 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 92 Elevated expression of cyclooxygenase (COX)-2, a rate-limiting enzyme in the conversion of arachidonic acid to prostaglandin (PG) biosynthesis, has been demonstrated in several human cancers including squamous cell carcinoma of the head and neck. Oral squamous cell carcinoma (OSCC) is an important malignancy in Taiwan, which is highly associated with areca quid (AQ) use. Whether COX-2 is up-regulated in AQ related OSCC is unknown, and the potential of AQ ingredient to induce COX-2 expression has not been studied. COX-2 expression was analyzed by immunohistochemistry, in situ hybridization and reverse transcription-PCR in paired OSCC and adjacent normal tissues. The COX-2 mRNA and protein induction potential of AQ components, such as hydroxychavicol (HC) were quantitatively analyzed by real-time RT-PCR and Western blot analysis in cultured human normal oral keratinocytes and fibroblasts The cytotoxicity and PGE2 production as modulated by betel ingredient was assayed by ELISA assay. Using immunohistochemistry, the COX-2 expression was found to be significantly higher (P < 0.05) in OSCC as compared with their adjacent normal tissue (n = 27). The level of COX-2 mRNA was remarkably elevated in 63% (12 / 19) OSCC carcinomas compared with adjacent normal tissues (n = 11). Using in situ hybridization, the COX-2 mRNA was found to have higher expression in cytoplasm of cancer cells. HC, the unique AQ component in locally chewed AQ, induced COX-2 mRNA and protein expression dose- and time-dependently in oral keratinocytes. These results suggest the early involvement of COX-2 in AQ induced oral cancer carcinogenesis. AQ chewing and smoking have synergistic potential in the development of OSCC. It has been shown that COX-2 was expressed in OSCC and HC induced COX-2 expression. COX-2 is involved in benzo[a]pyrene (B[a]P) metabolism. This study investigated whether HC modulates B[a]P-mediated genotoxicity through COX-2 induction. Pretreatment of HC, with known elevated COX-2 expression, did not increase B[a]P-DNA adduct, instead, it significantly reduced B[a]P-DNA adduct levels. This is demonstrated by 32P-postlabeling analysis (P < 0.05). However, this treatment resulted in higher cytotoxicity and HPRT gene mutation frequency (P < 0.05). Western blot analysis showed that the expression of dihydrodiol dehydrogenase (DDH) was also increased. DDH has been shown to divert B[a]P-diol to B[a]P-7,8-quinone, which resulted in the generation of reactive oxygen species. Using flow cytometry, I showed that the production of 8-oxoguanine was increased following the treatment (P < 0.001). Overall, the results suggest that HC induced DDH is more important than site-by-site up-regulation of COX-2 in B[a]P-induced cytotoxicity and HPRT gene mutation. Furthermore, DDH mediated oxidative DNA damage and not B[a]P adduct formation may be involved in the B[a]P-induced toxic effects. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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