Identification of a Novel Selenium-containing Compound, Selenoneine, as the Predominant Chemical Form of Organic Selenium in the Blood of Bluefin Tuna

Abstract

A novel selenium-containing compound having a selenium atom in the imidazole ring, 2-selenyl-N ␣ ,N ␣ ,N ␣ -trimethyl-Lhistidine, 3-(2-hydroseleno-1H-imidazol-5-yl)-2-(trimethylammonio)propanoate, was identified from the blood and other tissues of the bluefin tuna, Thunnus orientalis. The seleniumcontaining compound was purified from the tuna blood in several chromatographic steps. High resolution mass spectrometry and nuclear magnetic resonance spectroscopy showed that the exact mass of the [M؉H] ؉ ion of the compound was 533.0562 and the molecular formula was C 18 H 29 N 6 O 4 Se 2 . Its gross structure was assigned as the oxidized dimeric form of an ergothioneine selenium analog in which the sulfur of ergothioneine is replaced by selenium. Therefore, we named this novel seleniumcontaining compound "selenoneine." By speciation analysis of organic selenium compounds using liquid chromatography inductively coupled plasma mass spectrometry, selenoneine was found widely distributed in various tissues of the tuna, with the highest concentration in blood; mackerel blood contained similar levels. Selenoneine was measurable at 2-4 orders of magnitude lower concentration in a limited set of tissues from squid, tilapia, pig, and chicken. Quantitatively, selenoneine is the predominant form of organic selenium in tuna tissues.

Purification and characterization of glutathione peroxidase 1 in the red muscle of Pacific bluefin tuna Thunnus orientalis

“…GPx1 was detected by immunostaining with anti-GPx1 antibody, and enolase was detected as an internal control by Coomassie Brilliant Blue R-250 staining mechanisms of these two GPx1 isozymes in fish in response to selenium exposure. GPx1 is a major selenoprotein, and selenoneine is a low molecular weight compound that acts as a strong free radical scavenger in the red muscle of bluefin tuna [20][21][22]. These two organic selenium species may be important members of the redox cycle in a variety of physiological and nutritional processes in fish muscle [20,21].…”

“…The dietary intake of selenoneine through the consumption of fish may be important in free radical detoxification mechanisms. In addition, GPx1 has been identified as a major selenoprotein in tuna muscle [20][21][22]. Our recent study showed that selenoneine is incorporated into human and fish cells by the organic cation/carnitine transporter OCTN1 where it mediates methylmercury detoxification (Yamashita et al, submitted).…”

“…Recently, a novel selenium-containing compound, selenoneine, was identified as the major form of organic selenium in the muscle and other tissues of tuna [20][21][22]. This compound has a unique selenoketone structure and a strong antioxidant capacity.…”

Comparison of selenoneine found in marine organisms with selenite in the interaction with mercury compounds in vitro

“…MT is another detoxifi cation factor because it actually sequesters iHg. It has reported that selenoneine shows the antioxidant activity in vitro (Yamashita and Yamashita, 2010). Recently, methylated selenoneine was detected in human urine (Klein et al, 2011).…”

“…Recently, a novel selenometabolite, selenoneine (2-selenyl-N,N,N-trimethyl-L-histidine), was identified in bluefin tuna and other fish species (Yamashita and Yamashita, 2010). It is also reported that sea turtles accumulate Se in their livers in spite of the low hepatic Hg concentration, and the major portion of Se in the liver exists as selenoneine (Anan et al, 2011).…”