Distribution of selenium in zebrafish larvae after exposure to organic and inorganic selenium forms

Abstract

Selenium is an essential micronutrient for many organisms, and in vertebrates has a variety of roles associated with protection from reactive oxygen species. Over the past two decades there have been conflicting reports upon human health benefits and detriments arising from consumption of selenium dietary supplements. Thus, early studies report a decrease in the incidence of certain types of cancer, whereas subsequent studies did not observe any anti-cancer effect, and adverse effects such as increased risks for type 2 diabetes have been reported. A possible contributing factor may be that different chemical forms of selenium were used in different studies. Using larval stage zebrafish (Danio rerio) as a model organism, we report a comparison of the toxicities and tissue selenium distributions of four different chemical forms of selenium. We find that the organic forms of selenium tested (Se-methyl-l-selenocysteine and l-selenomethionine) show considerably more toxicity than inorganic forms (selenite and selenate), and that this appears to be correlated with the level of bioaccumulation. Despite differences in concentrations, the tissue specific pattern of selenium accumulation was similar for the chemical forms tested; selenium was found to be highly concentrated in pigment (melanin) containing tissues especially for the organic selenium treatments, with lower concentrations in eye lens, yolk sac and heart. These results suggest that pigmented tissues might serve as a storage reservoir for selenium.

Zebrafish as a Model for Toxicological Perturbation of Yolk and Nutrition in the Early Embryo

“…Several studies have quantified xenobiotic bioaccumulation specifically in the yolk resulting from waterborne exposures to estradiol [42], selenium [43], graphene oxide [44], and hydrogen sulfide [45]. Uptake of these compounds could involve passive or active movement of the molecule across the yolk sac epithelium.…”

Health risk assessment of environmental selenium: Emerging evidence and challenges

“…2. However, this estimate may be still inadequate to protect human health from chronic selenium toxicity, and in addition it appears to apply only to organic selenium, and to selenomethionine in particular [whose toxicity has bene recently much better elucidated (63–65)].…”

A selenium species in cerebrospinal fluid predicts conversion to Alzheimer’s dementia in persons with mild cognitive impairment

“…Se exists in several chemical species with markedly different and even opposite biological properties [ 9 – 11 ]. In its selenocysteine-bound organic form, Se is an indispensable component in selenoprotein biosynthesis [ 7 , 12 ], while other organic species such as selenomethionine-bound Se [ 13 , 14 ] and the inorganic forms such as selenate or selenite [ 11 , 15 – 17 ] are also well recognized as powerful toxicants. Se exposure in the human mainly occurs through diet and in its organic forms, its major sources being meat and fish, cereals, eggs, and dairy products [ 18 , 19 ].…”