Selenium Preferentially Accumulates in the Eye Lens Following Embryonic Exposure: A Confocal X-ray Fluorescence Imaging Study

Abstract

Maternal transfer of elevated selenium (Se) to offspring is an important route of Se exposure for fish in the natural environment. However, there is a lack of information on the tissue specific spatial distribution and speciation of Se in the early developmental stages of fish, which provide important information about Se toxicokinetics. The effect of maternal transfer of Se was studied by feeding adult zebrafish a Se-elevated or a control diet followed by collection of larvae from both groups. Novel confocal synchrotron-based techniques were used to investigate Se within intact preserved larvae. Confocal X-ray fluorescence imaging was used to compare Se distributions within specific planes of an intact larva from each of the two groups. The elevated Se treatment showed substantially higher Se levels than the control; Se preferentially accumulated to highest levels in the eye lens, with lower levels in the retina, yolk and other tissues. Confocal X-ray absorption spectroscopy was used to determine that the speciation of Se within the eye lens of the intact larva was a selenomethionine-like species. Preferential accumulation of Se in the eye lens may suggest a direct cause-and-effect relationship between exposure to elevated Se and Se-induced ocular impairments reported previously. This study illustrates the effectiveness of confocal X-ray fluorescence methods for investigating trace element distribution and speciation in intact biological specimens.

Interaction of mercury and selenium in the larval stage zebrafish vertebrate model

“…Figure 5 shows a section taken through the eye and brain of a zebrafish larva treated with 2 μM HgCl 2 . In this case the eye lens contains large quantities of selenium, which we have previously observed using confocal methods in selenium supplemented fish, 19 but with the rest of the section showing selenium levels that are more typical of those observed in the trunk section. In particular, pigmented areas of the retina show high relative selenium levels, consistent with those observed in the pigmented areas of the trunk section.…”

Parental dietary seleno-L-methionine exposure and resultant offspring developmental toxicity

“…The function of selenoproteins and the antioxidant properties of excess Se in postnatal mammalian ocular physiology are known to cause oxidative damage via redox cycling and result in cataracts (Flohe, 2005). In situ hybridization (ISH) has been used to localize specific selenoprotein expression in retina of developing zebrafish (Thisse et al, 2003), and confocal X-ray fluorescence imaging of zebrafish offspring of dietary SeMet exposed mothers showed accumulation of Se in the eyes of hatchlings (Choudhury et al, 2015). The highest concentrations appeared in the lens-core followed by the lens-epithelium, and these investigators regarded sulfur-substitution as the mechanism in lens proteins, as opposed to the oft-studied oxidative stress mechanism, and suggested that the eye may be an ideal site to test mechanisms of toxicity (Choudhury et al, 2015).…”

“…In situ hybridization (ISH) has been used to localize specific selenoprotein expression in retina of developing zebrafish (Thisse et al, 2003), and confocal X-ray fluorescence imaging of zebrafish offspring of dietary SeMet exposed mothers showed accumulation of Se in the eyes of hatchlings (Choudhury et al, 2015). The highest concentrations appeared in the lens-core followed by the lens-epithelium, and these investigators regarded sulfur-substitution as the mechanism in lens proteins, as opposed to the oft-studied oxidative stress mechanism, and suggested that the eye may be an ideal site to test mechanisms of toxicity (Choudhury et al, 2015). Taken together, even minor ocular impairments in fish could be expected to have direct effects on behavior and survival including visual attraction to food, migration within the water column, and detection of predators (Guthrie, 1986).…”

Stabilization of mercury in sediment by using biochars under reducing conditions

“…CXMFI provides compositional and structural information from precise locations on the surface of, and within, intact particles, with greater spatial precision than can be obtained using conventional micro x-ray fluorescence (µ-XRF) methods [18]. Limited applications of CXMFI are reported for natural materials; examples include the characterization of Se accumulation in fish eye lens [19]; W, Pt, and Fe in particles embedded in a mineralogical matrix [20]; K, Ca, and Fe in rice grains [21]; and U-Th-Pb for dating of geological materials [22].…”