<p>Iodine is considered an essential nutrient as lack can cause
severe metabolic and neurological issues in adults, with the added consequence
of permanent developmental damage in children and infants. However, excessive
iodine intake can result in similar symptoms, with a wide variance in adverse
health outcomes. The safe range of iodine intake may be relatively low, with
some studies suggesting the possibility of a high frequency of subclinical
cases of iodine poisoning going unnoticed or misdiagnosed. </p>
<p>In this study, the zebrafish model was tested as an
integrative whole animal model to demonstrate behavioral, morphological, and
genetic responses to overt and subclinical iodine poisoning in developing
humans. Zebrafish embryos were treated with sodium iodide (NaI) immediately
after fertilization. Survivability was monitored every 24 hours until 120 hours
post fertilization (hpf). Concentrations with no statistical significance on
survival, plus the smallest dose of significant lethality were then examined
using behavioral analysis at 120 hpf to compare both overt and subclinical
outcomes. Morphology measurements of body length, head length, head width,
brain length, swim bladder volume, jaw length, and ventral dissension were also
recorded at 120 hpf. Gene expression of <i>slc5a5</i>,
<i>tpo</i>, and <i>tshba</i> at 72 hpf was also measured using quantitative PCR (qPCR). </p>
<p>A significant decrease in survival rates were observed at 24
hpf for 25, 37.5, and 50 mM NaI treatments (p<0.0001). Morphological
measurements taken at 120 hpf showed a significant increase in body length,
head length, head width, jaw length, and swim bladder volume in the 10 mM NaI
treatment group (p<0.0001) and a significant decrease in body length, head
length, jaw length, and swim bladder volume in the 25 mM treatment group
(p<0.0001). A ventral distension also developed near the location of the
thyroid gland exclusively in the 25 mM group. </p>
<p>Behavioral analysis showed significant increases in movement
for both the 10 mM and 25 mM treatment groups during dark phases (p<0.0001).
The 25 mM treatment group had an increase in movement during dark phases for
standard well environments (p<0.0001), but this did not hold true for larger
well environments, instead trending towards a non-significant decrease
(p>0.05). The 10 mM group had a significant decrease during the first light
phase in standard wells (p=0.002), with a significant increase in the second
light phase for large wells (p=0.005). There were no significant changes in the
expression of selected genes associated with the thyroid pathway (<i>slc5a5</i>, <i>tpo</i>, or <i>tshba</i>) across all
treatment groups (p>0.05). </p><p><br></p>
<p>Overall, the results suggest zebrafish larvae exhibit both
overt and subclinical symptoms of excess iodine intake. Future studies are
needed to determine internalization, biodistribution, clearance, and further characterization
of adverse outcomes along the thyroid pathway for additional exploration into
subclinical thyrotoxicosis due to excess iodine intake. Researchers should
express caution with time points, as the Wolff-Chaikoff effect may influence
exposure windows in zebrafish. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/13363370 |
| Date | 14 December 2020 |
| Creators | Brian A Sumprer (9757382) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY-NC-SA 4.0 |
| Relation | https://figshare.com/articles/thesis/Developmental_Toxicity_of_Sodium_Iodide_Using_the_Zebrafish_Model/13363370 |
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