Tocotrienols, a form of vitamin E, could stop the spread of cancer cells, explaining the inconsistent results of previous studies and drawing attention to this least studied form of the vitamin.
There are eight forms of vitamin E: four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta). Alpha-tocopherol is the form found in most supplements, while gamma-tocopherol is the most common form in the American diet, and dl-alpha tocopherol is the synthetic form found in cheap supplements.
While the majority of research on vitamin E has focused on alpha-tocopherols, studies into tocotrienols account for less than one per cent of all research into vitamin E.
In a new in vitro study, published in 2006 in Biochemical and Biophysical Research Communications, Japanese researchers studied the effects of all eight forms of vitamin E on the inhibition of mammalian DNA polymerase, the enzyme that assists DNA replication.
“The four tocopherols did not influence the activities of mammalian polymerases at all. On the other hand, the alpha- and delta-tocotrienols inhibited polymerase lambda activity,” reported lead author Yoshiyuki Mizushina from Kobe-Gakuin University.
The researchers reported that the inhibition of the polymerase enzyme was dose-dependent, with a dose of 18.4 micromoles needed to achieve 50 per cent inhibition.
The spread of cancer cells (cell proliferation) was also considered by the research team. Again, the alpha- and delta-tocotrienols inhibited the spread of cells, while the tocopherols had no effect.
The significance of these results, taken together, is the indication that angiogenesis (the growth of new blood vessels) is inhibited by this form of vitamin E. Also by stopping cell proliferation, the spread of the cancer to other parts of the body is hindered, a process called metastasis.
“These results led us to hypothesise that the inhibition of tumour growth by vitamin E in part by its polymerase lambda inhibitory activity and antioangiogenic activity,” said Mizushina.
“Since angiogenesis is essential for tumour growth, its strong inhibition by tocotrienols but not tocopherols, could very well provide us with a safe dietary means to prevent a cancer from becoming metastatic,” said Leong.
The researchers also showed that these vitamin E tocotrienols inhibited the proliferation and formation of tubes by bovine aortic endothelial cells, with delta-tocotrienol having the greatest effect. “The isomer’s structure might be an important factor in the inhibition of pol lambda,” suggested Y. Mizushina and colleagues at the Kobe Gakuin University.
What is interesting is that the regular tocopherols (alpha, beta, gamma and delta-tocopherol) do not influence the activities of mammalian polymerase and angiogenesis at all, suggesting that the three double bonds in the unsaturated side chain of tocotrienols play an important factor in the inhibition of polymerase lambda.
“Since angiogenesis is essential for tumour growth, its strong inhibition by tocotrienols but not tocopherols, could very well provide us with a safe dietary means to prevent a cancer from becoming metastatic,” says WH Leong, Vice President for Carotech Inc, the largest producer of full spectrum palm tocotrienol complex in the world.
Biochemical and Biophysical Research Communication, 2006 (339), 949-955.