Gallic acid, a major component of Toona sinensis leaf extracts, contains a ROS-mediated anti-cancer activity in human prostate cancer cells
Introduction
Prostate cancer (PCA) is the most frequently diagnosed malignancy in elderly males and the second leading cause of cancer-related deaths in the United States [1]. It has also become a major malignancy in many Asian countries in the past two decades [2]. Scientists are putting more efforts on identifying novel botanicals that can selectively target tumor cells growth without affecting normal cells [3], [4]. With regard to PCA chemoprevention, natural botanicals and dietary substances are gaining more attention and have the potential to become a major resource of the cancer chemo-preventive agents [4], [5].
One major biochemical change in cancer cells after treatment with anti-cancer agents is the increase in reactive oxygen species (ROS) generation which is often considered as a cancer-promoting factor [6], [7], [8]. Studies have demonstrated that high levels of ROS can cause cellular damage [9], [10], [11], [12], [13] and play an important role in mediating apoptosis [14], [15]. Interestingly, ROS has been demonstrated to selectively kill cancer cells [8], [16], [17]. For instance, Hileman et al. show that ROS generated by 2-methoxyestradiol (2-ME) preferentially kill human leukemia cells without exhibiting significant cytotoxicity to normal lymphocytes [18]. Trachootham et al. demonstrate that elevated ROS levels by β-phenylethyl isothiocyanate (PEITC) can be exploited to selectively kill malignant cells. In contrast, normal cells can better tolerate oxidative insults owing to their low basal ROS output and normal metabolic regulation [8]. This biochemical difference between normal and cancer cells may constitute a basis for modulating cellular ROS as a strategy to selectively kill cancer cells.
Toona sinensis Roem. (Meliaceae; T. sinensis), a species of arbor widely distributed in Asia, has been used as a nutritious food for a long time and the leaves cooked with eggs is a very popular vegetarian dish in Taiwan. The edible leaves were employed as an oriental medicine for treatment of enteritis, dysentery and dermatitis with no significant side effects [19]. Recently, various biological activities of T. sinensis leaf extracts have been reported, including anti-cancer [20], [21], anti-inflammation [22], anti-diabetes [23], [24], antioxidant [13], [25], inhibiting Leydig cell steroidogenesis [26], and improving the dynamic activity of human sperm [27]. In a previous study in which the D-7000 HPLC System was applied, we reported that the specific fraction, TSL2, of the T. sinensis leaf extracts contains the most significant anti-cancer activity [21, also see Materials and Methods]. In this study, we report that gallic acid (3,4,5-trihydroxybenzoic acid, GA) is the major bioactive compound isolated from TSL2 fraction of T. sinensis leaf extracts and contains an anti-cancer activity, at least partly through the ROS-mediated pathway, in human prostate cancer cells.
Section snippets
Isolation of gallic acid from T. sinensis leaf extracts
The leaves used in this preparation were obtained from T. sinensis Roem. grown in Tuku (Yunlin County, Taiwan) and were picked and washed briskly with water. To investigate the potential effect against cancer cells, five different extraction fractions (TSL1, TSL2, TSL3, TSL4 and TSL5) were collected from the leaves of T. sinensis. The methods for the fractionation of leaf extracts of T. sinensis were described previously [21].
The TSL2 extracts were dissolved in a mobile phase consisting of
Purification of gallic acid from the TSL2 fraction of T. sinensis leaf extracts that contains the most significant anti-cancer activity
In our previous study, TSL2 fraction of T. sinensis leaf extracts contains the most significant anti-cancer activity [21]. In this study, we determined to identify the pure compounds with anti-cancer activity from TSL fraction (please see Section 2 for the detailed procedures). Gallic acid, the natural phenolic component purified from the TSL2 extracts, was identified and collected for further studies (Fig. 1).
Cytotoxicity of T. sinensis extracts on various cancer cell lines
To investigate the potential effect against cancer cells, there were five different
Discussion
Gallic acid, a polyhydroxyphenolic compound, is one of the major bioactive compounds isolated and purified from T. sinensis. It is widely distributed in various plants and fruits, such as gallnuts, sumac, oak bark, green tea, apple-peels, grapes, strawberries, pineapples, bananas, lemons and in red and white wine [39], [40], [41]. Various pharmacological activities of GA have been reported, including anti-cancer [22] and antioxidant [14]. Studies have also demonstrated that GA selectively
Acknowledgements
We thank Professors Lih-Min Tsai (E-DA Hospital, Taiwan), Lih-Ching Chang (I-Shou University, Taiwan), Lih-Wen Fang (I-Shou University, Taiwan), Catherine Hernon (E-DA Hospital, Taiwan) for critical reading of the manuscript. This work was supported by the grants from Department of Health, Taiwan, ROC to S.-S.F. Y. (DOH92-TD-1004 and DOH93-TD-1015) and an intramural grant from E-DA Hospital to C.-C. C. (EDAHP97024).
References (68)
Prostate cancer chemoprevention: current status and future prospects
Toxicol. Appl. Pharmacol.
(2007)Reactive oxygen species in cancer cells: live by the sword, die by the sword
Cancer Cell
(2006)- et al.
Selective killing of ncogenically transformed cells through a ROS mediated mechanism by β-phenylethyl isothiocyanate
Cancer Cell
(2006) - et al.
ROS stress in cancer cells and therapeutic implications
Drug Resist. Update
(2004) - et al.
Free radical, metals and antioxidants in oxidative stress-induce cancer
Chem. Biol. Interact.
(2006) - et al.
Antioxidant activities of Toona Sinensis leaves extracts using different antioxidant models
Food Chem. Toxicol.
(2008) - et al.
Direct effect of ceramide on the mitochondrial electron transport chain leads to generation of reactive oxygen species. Role of mitochondrial glutathione
J. Biol. Chem.
(1997) - et al.
Genipin-induced apoptosis in hepatoma cells is mediated by reactive oxygen species/c-Jun NH2-terminal kinase-dependent activation of mitochondrial pathway
Biochem. Pharmacol.
(2005) - et al.
The fractionated Toona sinensis leaf extract induces apoptosis of human ovarian cancer cells and inhibits tumor growth in a murine xenograft model
Gynecol. Oncol.
(2006) - et al.
Toona sinensis extracts induces apoptosis via reactive oxygen species in human premyelocytic leukemia cells
Food Chem. Toxicol.
(2006)