Published in Cancer Detection and Prevention 2002; 26(6).

Modification of lung cancer susceptibility by green tea extract as measured by the comet assay

Huifeng Zhang, MDa, Margaret R. Spitz, MD, MPHa, Gail E. Tomlinson, MD, PhDb, Matthew B. Schabath, MSa, John D. Minna, MDb, Xifeng Wu, MD, PhDa

aDepartment of Epidemiology, The University of Texas M.D. Anderson Cancer Center, Box 189, 1515 Holcombe Blvd, Houston, TX 77030, USA, bDepartment of Pediatrics, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA

Green tea is widely consumed throughout the world and is known to possess various beneficial properties that may affect carcinogen metabolism, free radical scavenging, or formation of DNA adducts. Therefore, it is plausible that green tea extract may modify BPDE-induced DNA damage. In this report, we utilized the comet assay to (1) evaluate BPDE-induced DNA damage as a potential marker of cancer susceptibility and (2) assess the ability of green tea to modify BPDE-induced DNA damage. DNA damage in individual comet cells was quantified by (1) visually measuring the proportion of cells exhibiting migration versus those without and (2) the length of damaged DNA migration (comet tail). We detected a dose-response between BDPE concentration and mean comet tail length in EBV-immortalized lymphoblastiod (lymphoid) cell lines. As the concentration of BPDE increased from 0.5 to 3 M, the length of the mean comet tail length increased proportionally in the 3590P (derived from a healthy subject) and 3640P (derived from a patient with head and neck cancer) cell lines. In separate experiments using lymphoid cells from 21 lung cancer cases and 12 healthy subjects, the mean comet tail length was significantly higher in the lung cancer cases (80 .19 ± 15.55) versus the healthy subjects (59.94 ± 14.23) (P < 0.01). Similar findings were observed when analyzing the mean percentage of comet induced cells (84 .57 ± 8.85 and 69.04 ± 12.50, respectively) (P < 0.01). When green tea extract was added in conjunction with BPDE, there was a notable reduction of the mean comet tail length (13 .29 ± 0.97) as compared to BPDE treatment alone (80 .19 ± 15.55) (P < 0.01) in lung cancer cases. When the green tea extract was added in conjugation with BPDE (13 .29 ± 0.97), the levels of DNA damage returned near baseline but there was a borderline statistically significant difference (12 .74 ± 0.63) (P = 0.035). These data suggest the modification of lung cancer susceptibility by the green tea extract. Similar results were observed for the percentage of induced comet cells and the statistical trends were similar for the 12 healthy subjects. This preliminary study demonstrated that the detection of BPDE-induced DNA damage via the comet assay may be a useful biologic marker of lung cancer susceptibility. The differential effects in BPDE-induced DNA damage between lung cancer cases and healthy subjects suggests predisposed cancer susceptibility to lung cancer risk. This reports also demonstrated the chemopreventive effects of green tea extract on BPDE-induced DNA damage. These observations provide further support for the application of the comet assay in a molecular epidemiologic study.

KEY WORDS: Molecular epidemiology, DNA damage, Chemoprevention, Single cell gel electrophoresis.