Cancer preventive effect of Thai rat-tailed radish (Raphanus sativus L. var. caudatus Alef)
Introduction
Raphanus sativus L. var. caudatus Alef belongs to the family Brassicaceae. The Thai vernacular name is Khi Hood (Thai rat-tailed radish in English and Hatsuka daikon in Japanese). It is an annual (or sometimes biennial) 30–90 cm tall vegetable, commonly found in Northern Thailand. Propagation is from seeds. Thai rat-tailed radish is available in Thailand during the cool, dry season between November and February. Thai rat-tailed radish produces edible inflorescences and siliquas, which are eaten when young as a side dish or cooked in a mixed vegetable curry.
Previous research revealed that the seed of Thai rat-tailed radish comprised sulforaphene, sulforaphane and other isothiocyanates (Songsak & Lockwood, 2002). There are, however, no reports on its composition or the biological activity in humans of the extracts of the edible parts.
Epidemiological studies of several cancers have revealed an inverse association between a diet of vegetables and morbidity and mortality (Feskanich et al., 2000, Larsson et al., 2006, Michaud et al., 1999, Voorrips et al., 2000). Cruciferae (Brassicaceae) are popular vegetables globally and their consumption reduces the risk for many types of cancer (Higdon et al., 2007, Verhoeven et al., 1996). Thus, several research groups have focused their resources on finding the bioactive compounds from this family as a source of potential chemopreventive agents. Due to the unique sulphur-containing compounds of the Cruciferae family—responsible for their pungent aroma and spicy (or bitter) taste (Drewnowski & Gomez-carneros, 2000)—glucosinolates have undergone considerable investigation for their anticancer potential. Glucosinolates—a class of secondary metabolites present primarily in Cruciferates, do not, however, possess direct biological activity. Their hydrolysis products, especially indole and isothiocyanate catalyzed by myrosinase activation, possess biological activity including putative anticancer attributes (Holst & Williamson, 2004).
When carcinogenesis exceeds apoptosis, the malignant phenotype (s) perpetuate. Thus, targeting apoptosis pathways in premalignant cells is the most effective method of cancer prevention (Sun, Hail, & Lotan, 2004). To substantiate the value of Thai rat-tailed radish as a chemopreventive resource, we investigated its chemopreventive potential by determining its ability to decrease cancer cell viability. The anticancer mechanisms were evaluated; particularly whether it was via apoptosis induction. The compositional analysis by GC–MS for any isothiocyanate in Thai rat-tailed radish was performed in order to identify which phytochemicals might be attributed to the anticancer activity. R. sativus contains several classes of compounds that might support the enhancement of anticancer action through multiple pathways: this study, therefore, tested the extract from a cultivar of caudatus Alef (Thai rat-tailed radish). The edible tissues, inflorescence and unripe fruit, were analyzed for any known cancer preventive effect that could arise with dietary intake. Finally, the apoptosis activity of the plant extract was observed for its value as a marker for sources of potential chemopreventives.
Section snippets
Materials
The D,L-Sulforaphane standard was purchased from Calbiochem (EMD, Darmstadt, Germany). The L-sulforaphene standard was purchased from Enzo Life Science (NY, USA). The dichloromethane (Fisher scientific, Loughborough, UK) was analytical grade. The acetonitrile was HPLC grade (RCI labscan, Bangkok, Thailand). The mitomycin C was clinical grade and kindly provided by the Melatonin Research group, Khon Kaen University, Khon Kaen, Thailand.
Plant extraction
The Thai rat-tailed radish was cultivated in Phayao province
Cytotoxicity
Due to the diversity of the chemical constituents in the cruciferous extract, the cancer preventive effect needed to be tested for cytotoxicity using the MTT assay. The results are presented as the half maximal inhibitory concentration (IC50) (Table 1) for which Thai rat-tailed radish (Khi Hood) induced HCT116 cell death. The extract from the pods and flowers of the Thai rat-tailed radish had the greatest cytotoxicity against the HCT116 cell line (IC50 = 9.42 ± 0.46 μg/ml) and can be classified as
Conclusion
Thai Rat-tailed radish extract possesses a high cytotoxicity and its extract induced cancer cell death via apoptosis. The GC–MS profile revealed the presence of two isothiocyanate compounds sulforaphane and sulforaphene—in the Thai rat-tailed radish extract, with known high cytotoxicity and apoptosis induction against the HCT116 cell line. This is the first report of the cancer preventive effect via apoptosis induction of Thai rat-tailed radish extract against this colon cancer cell line. Our
Acknowledgments
This work was supported by the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission, through the Food and Functional Food Research Cluster and Research and Development of Herbal Nutraceutics Subcluster of Khon Kaen University (F-2553-M-11 and NRU541051). The authors thank Mr. Bryan Roderick Hamman and Mrs. Janice Loewen-Hamman for assistance with the English-language presentation.
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