Tea is one of the most widely consumed beverages in the world. The popularity of tea has increased with reports of potential health benefits against such chronic diseases as cardiovascular disease and cancer (1
), notwithstanding recent findings to the contrary for gastric cancer among the Japanese (5
). The health benefits of tea have been attributed in large part to the high levels of catechins and related polyphenols, operating via one or more of the following mechanisms: 1) induction of various enzyme activities involved in drug metabolism and carcinogen activation/detoxification, 2) inhibition of the activated metabolites of carcinogens and mutagens, 3) scavenging of reactive oxygen species and nitric oxide, 4) modification of signal transduction pathways, and 5) alterations in cell cycle check points and apoptosis (reviewed in Refs. 1
). Through these various mechanisms, tea has demonstrated excellent chemoprotective properties in animal models of skin, lung, esophageal, and gastrointestinal cancers (6
). Included among these investigations of the inhibitory properties of tea are several reports that focused on protection against the mutagenic and carcinogenic effects of heterocyclic amines (9
Heterocyclic amines are potent mutagens created during the cooking of meat and fish (13
). Some heterocyclic amines, such as 2-amino-3-methylimidazo[4,5-f
]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b
]pyridine (PhIP), induce tumors of the colon in experimental animals, and for this reason, they have been used as model compounds for the study of events that occur during colon carcinogenesis (14
). We reported in previous studies using the Fischer 344 (F344) rat (9
) that green and black teas protected against IQ-induced aberrant crypt foci (ACF), which are putative preneoplastic lesions in the colon (15
). Because green tea was more effective than black tea, it was suggested that the degree of protection against IQ-induced ACF might be related to the extent of tea processing.
Tea processing and manufacturing practices influence the types of tea commonly consumed. Green tea, which is most popular in Japan and China, is produced when the leaves of Camellia sinensis
are subjected to withering and then are pan-fried/steamed, rolled, shaped, and dried. When tea is pan-fried or steamed, polyphenol oxidases in the leaf become inactive, which prevents compounds such as epigallocatechin-3-gallate (EGCG) from undergoing oligomerization (oxidation) to more complex polyphenols, such as theaflavins and thearubigins (17
). However, if the leaves are deliberately crushed or broken to facilitate oxidation of EGCG and other polyphenols, a darker color is produced and unique flavor characteristics associated with black and oolong teas are generated. White tea is the least processed type of tea, in that, unlike other teas, it is simply steamed and dried without a prior withering stage.
Because catechins are converted to more complex polyphenols with extent of tea processing and green tea was more effective than black tea in inhibiting IQ-induced ACF (9
), we hypothesized that white tea also might exhibit chemopreventive properties against heterocyclic amines. Indeed, in preliminary studies in vitro, four white tea varieties (Silver Needle, Flowery Pekoe, Mutan White, and Exotica China White) exhibited strong antimutagenic activity in the Salmonella
assay, and the most effective of these teas, Exotica China White, was significantly more potent than Premium Green (“Dragonwell Special grade”) tea against several heterocyclic amines, including PhIP (18
). Therefore, we have sought to determine whether white tea would protect against PhIP-induced ACF in the rat and, if so, to provide data on the possible inhibitory mechanism(s).