Selenium is an essential micronutrient for humans, and seafood is one of the major selenium source in Japan. Recent studies show that the tissues of tuna and other predatory fish contain high levels of the selenium-containing imidazole compound, 2-selenyl-Nα, Nα, Nα-trimethyl-L-histidine (selenoneine). A substantial proportion of the total amount of selenium is present as selenoneine in the muscles of ocean fish. Selenoneine contains an imidazole ring with a unique selenoketone group and has an antioxidant activity in vitro and in vivo. The dietary intake of selenoneine through fish consumption is thought to be important for enhancing selenium redox functions in tissues and cells. In addition, selenoneine accelerated the excretion and demethylation of methylmercury through the formation of secretory extracellular lysosomal vesicles via the specific organic cation/carnitine transporter-1 (OCTN1). Dietary intake of selenoneine might decrease the formation of hydroxyl and other radicals and accelerate the excretion of heavy metals, and thereby inhibit carcinogenesis, lifestyle chronic diseases, and aging.
