Laboratory of Health Science, Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Kyoto 606-8522, Japan.
Curr Pharm Biotechnol. 2012 Jan;13(1):156-64. doi: 10.2174/138920112798868656.
Vitamin E is well known as an antioxidant, with 8 natural isoforms, such as α-, bgr;-, γ- and δ-tocopherols and α-, β-, gamma;- and δ-tocotrienols. It has been suggested that both tocopherols and tocotrienols have anti-tumor effects due to the antioxidant effect. The results of several studies have indicated that the tocotrienols may have a stronger bioactivity than the tocopherols. Both types have shown antiproliferative, proapoptotic and cyclooxygenase-2- inhibiting effects in in vitro studies. Several animal studies have demonstrated that vitamin E has cancer-preventing effects. However, clinical trials have not shown similar results for the cancer prevention effect of tocopherol. Although the Linxian Trials demonstrated that the supplementation of β-carotene, α-tocopherol and selenium reduced cancer risk, the beneficial effects of α- tocopherol on prostate cancer disappeared after several years in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. Vitamin E, especially tocotrienols, seems to be a potent agent for cancer prevention, however no large-scale clinical trial on the cancer prevention effect of tocotrienols has been conducted yet. Therefore it is expected that clinical trials overcoming the lower bioavailability of tocotrienols will be conducted, and it is urgently needed to assess the safety and the efficacy of the administration of the tocotrienols as a part of a cancer prevention regimen.
维生素 E 作为一种抗氧化剂而广为人知，它有 8 种天然同分异构体，如 α-、βγ-、δ-生育酚和 α-、β-、γ-、δ-生育三烯酚。由于抗氧化作用，有人认为生育酚和生育三烯酚都具有抗肿瘤作用。多项研究结果表明，生育三烯酚的生物活性可能比生育酚更强。这两种类型在体外研究中均显示出抗增殖、促凋亡和环氧化酶-2 抑制作用。几项动物研究表明，维生素 E 具有预防癌症的作用。然而，临床试验并未显示出tocopherol 在预防癌症方面的类似效果。虽然林县试验表明，β-胡萝卜素、α-生育酚和硒的补充降低了癌症风险，但在α-生育酚、β-胡萝卜素癌症预防研究中，几年后α-生育酚对前列腺癌的有益作用消失了。维生素 E，尤其是生育三烯酚，似乎是一种有效的癌症预防剂，但是目前尚未进行大规模的tocotrienol 预防癌症的临床试验。因此，预计将开展克服tocotrienol 生物利用度较低的临床试验，迫切需要评估tocotrienol 作为癌症预防方案一部分的安全性和疗效。
