Separation of Selenium Species in Japanese Littleneck Clam ‘Asari’ (Ruditapes philippinarum) and In Vitro Assessment of Their Bioavailability
ABSTRACT
Elemental selenium, an essential element for humans and animals is totally
obtained from foods and used for the synthesis of selenoproteins, such
as glutathione peroxidases (GPx). Fish and shellfish are selenium-rich
foodstuffs, and are the major dietary source of selenium for the Japanese
population. However, the chemical structure and bioavailability of selenium
species from seafood materials have hardly been elucidated. The Japanese
littleneck clam (Asari) is the most popular consumed seawater bivalve in
Japan. In this study, the selenium species in Asari were separated and
assessed as a nutritional selenium source using cultured cells. The selenium
content in the lyophilized Asari edible meat was 4.34±0.49 μg/g. The selenium
extraction rate into water was 17−24% (1.07±0.14 μg/g-dry Asari). Based
on the results that selenium in the Asari water-extract was mostly retained
on both cationic Q Sepharose and anionic SP Sepharose columns, the selenium
species in the Asari water-extract appeared to possess an amphoteric character.
Selenium in the Asari water-extract mostly passed through a membrane with
the molecular mass cutoff of 5000. After lyophilization, the resulting
filtrate was subjected to in vitro assessment of the selenium bioavailability.
HepG2 and HeLa cells were cultured in a basal medium containing the filtrate.
The selenium content and GPx activity of the HepG2 cells increased with
the increasing selenium content in the medium and incubation time, which
suggested that the selenium species in the Asari water-extract were utilized
for the synthesis of the GPxs. Overall, these results demonstrated that
Asari contains nutritionally effective selenium species.