THE EFFECT OF VITAMIN-E TOCOTRIENOLS FROM PALM OIL ON CHEMICALLY-INDUCED MAMMARY CARCINOGENESIS IN FEMALE RATS

In the DMBA induced rat mammary tumor model, palm oil appeared to be less tumourigenic than corn oil, soybean oil, beef tallow and lard. Palm oil is a rich source of tocotrienols which have been reported to have antitumour activity against certain types of transplantable murine tumors. Results of the present experiments showed that palm oil stripped of its vitamin E tocopherols and tocotrienols (EFPO) enhanced tumorigenesis compared to palm oil containing vitamin E. In view of this a second experiment was designed to determine whether addition of a tocotrienol rich fraction (TRF) of palm oil to corn oil was able to inhibit development of mammary tumors in the DMBA treated rat model. One hundred female Sprague Dawley rats at 50 days of age were treated with a single dose of 5 mg of DMBA. They were then divided into 5 groups and fed semi-synthetic diets containing 20% by weight (40 en%) of either corn oil (CO), refined bleached and deodorized palm oil (RBDPO), corn oil + 500 ppm TRF, corn oil + 1000 ppm TRF or CO + 135 ppm alpha-tocopherol. The experiment was terminated 5 months after DMBA treatment. The RBD palm oil group had the lowest tumor incidence, tumor count and tumors per rat compared to animals fed the CO diet. This suggests that CO has a greater tumor promoting effect than palm oil. Supplementation of TRF at 500 ppm to corn oil did not provide protection. However at the higher concentration of 1000 ppm of TRF, the corn oil fed animals had significantly greater median latency period, lower tumor incidence and tumor count than the corn oil fed group as well as the group supplemented with either 500 ppm of TRF or 135 ppm alpha-tocopherol. The results appear to indicate that supplementation of corn oil with adequate amounts of TRF may give some protection against the cancer promoting effect of corn oil. The results also suggest that the favourable effects observed on a palm oil diet maybe attributed to the presence of naturally occurring tocotrienols in palm oil.