Cancer-preventive activities of tocopherols and tocotrienols

The cancer-preventive activity of vitamin E has been studied. Whereas some epidemiological studies have suggested a protective effect of vitamin E against cancer formation, many large-scale intervention studies with alpha-tocopherol (usually large doses) have not demonstrated a cancer-preventive effect. Studies on alpha-tocopherol in animal models also have not demonstrated robust cancer prevention effects. One possible explanation for the lack of demonstrable cancer-preventive effects is that high doses of alpha-tocopherol decrease the blood and tissue levels of delta-tocopherols. It has been suggested that gamma-tocopherol, due to its strong anti-inflammatory and other activities, may be the more effective form of vitamin E in cancer prevention. Our recent results have demonstrated that a gamma-tocopherol-rich mixture of tocopherols inhibits colon, prostate, mammary and lung tumorigenesis in animal models, suggesting that this mixture may have a high potential for applications in the prevention of human cancer. In this review, we discuss biochemical properties of tocopherols, results of possible cancer-preventive effects in humans and animal models and possible mechanisms involved in the inhibition of carcinogenesis. Based on this information, we propose that a gamma-tocopherol-rich mixture of tocopherols is a very promising cancer-preventive agent and warrants extensive future research.

Tocotrienol distribution in foods: estimation of daily tocotrienol intake of Japanese population

Tocotrienol (T3) is an unsaturated form of natural vitamin E that has been focused on because of its potential health benefits (i.e., antioxidative, antihypercholesterolemic, and antiangiogenic effects). The presence of T3 in some plant sources (e.g., rice bran and palm oil) is known, but its distribution in other edible sources and its daily intake remain unclear. In this study, we aimed at clarifying the distribution of T3 in various food sources and estimating the daily T3 intake of Japanese population. T3 contents of 242 food items and 64 meal items were measured by using normal-phase HPLC with fluorescence detection. As for the results, T3 contents were nondetectable to 12 mg T3/kg wet wt of food items, and nondetectable to 1.3 mg T3/item of processed (cooked) meal. Accordingly, the daily intake of T3 was estimated as 1.9-2.1 mg T3/day/person. The estimated daily intake of T3 appears rather low compared with the intake of tocopherol (8-10 mg/day/person as reported in the Japanese National Nutrition Survey), and additional T3 is important for its therapeutic aspects.

Simultaneous induction of non-neoplastic and neoplastic lesions with highly proliferative hepatocytes following dietary exposure of rats to tocotrienol for 2 years

It was recently shown that 1-year chronic exposure of rats to tocotrienol (TT) induced highly proliferative liver lesions, nodular hepatocellular hyperplasia (NHH), and independently increased the number of glutathione S-transferase placental form (GST-P)-positive hepatocytes. Focusing attention on the pathological intrinsic property of NHH, a 104-week carcinogenicity study was performed in male and female Wistar Hannover rats given TT at concentrations of 0, 0.4 or 2% in the diet. The high-dose level was adjusted to 1% in both sexes from week 51 because the survival rate of the high-dose males dropped to 42% by week 50. At necropsy, multiple cyst-like nodules were observed, as in the chronic study, but were further enlarged in size, which consequently formed a protuberant surface with a partly pedunculated shape in the liver at the high dose in both sexes. Unlike the chronic study, NHH was not always accompanied by spongiosis, and instead angiectasis was prominent in some nodules. However, several findings in the affected hepatocytes such as minimal atypia, no GST-P immunoreactivity and heterogeneous proliferation, implied that NHH did not harbor neoplastic characteristics from increased exposure despite sustained high cell proliferation. On the other hand, in the high-dose females, the incidence of hepatocellular adenomas was significantly higher than in the control. There was no TT treatment-related tumor induction in any other organs besides the liver. Thus, the overall data clearly suggested that NHH is successively enlarged by further long-term exposure to TT, but does not become neoplastic. In contrast, TT induces low levels of hepatocellular adenomas in female rats.

Cross-fertilization for enhancing tocotrienol biosynthesis in rice plants and QTL analysis of their F2 progenies

As rice bran tocotrienol (T3) has been known to have a wide range of physiological functions (e.g., antiangiogenesis), we aimed at developing a T3-rich rice variety for nutraceutical purposes. T3 content in more than 250 kinds of rice bran samples were investigated, and Milyang23 was found as the best variety rich in T3. The variety was therefore chosen for cross-fertilization with Koshihikari. Among obtained F(2) progenies, some of them became improved in T3 content (up to 2-fold of reference Koshihikari). QTL analysis of the F(2) progenies revealed five putative loci corresponding to T3 biosynthesis, in which the main loci were located near a marker RM3827 on chromosome 6. The results show that cross-breeding is effective in improving rice bran T3 and provides more genetic understanding on T3 biosynthesis in rice plants.