Anticarcinogenic activity of natural and synthetic carotenoids

Vitamin A deficiency has been known as a risk factor for various cancers, such as stomach cancer. Because long-term administration of vitamin A is practically difficult due to its hepatic toxicity, vitamin A analogs have been developed and applied for cancer prevention in clinical trials. Provitamin A carotenoids, which are widely distributed in vegetables and fruits, are also important nutritional factors as the source of vitamin A. These help to maintain our healthy condition, including risk reduction of cancer development. We should also pay attention to natural carotenoids other than provitamin A carotenoids, some of which were proved to have very potent anticarcinogenic activity. For example, lycopene is a very potent suppressor for liver cancer development. In the case of phytoene, the concept of “bio-chemoprevention,” which means biotechnology-assisted method for cancer chemoprevention, may be applicable. In fact, establishment of mammalian cells producing phytoene was succeeded by the introduction of crtB gene, which encodes phytoene synthase, and these cells were proved to acquire the resistance against carcinogenesis. Antioxidative phytoene-containing animal foods may be classified as a novel type of functional food, which has the preventive activity against carcinogenesis, as well as the ability to reduce the accumulation of oxidative damage, which is hazardous for human health.