| ObjectivesOxidative stress has been one of the underlying mechanisms of iodide excess induced thyroid disease. Nuclear factor E2-related factor 2(Nrf2) is an important transcription factor, which plays a crucial role in regulating the expressions of some antioxidant enzymes, such as Sulfiredoxin(Srx) and Peroxiredoxin 3(Prx 3). Nrf2 is released from the Nrf2-Keap1 complex by oxidative stress. Nrf2 is transferred from cytosol to nucleus and activates the expressions of target antioxidant proteins. By studying the effect of short-term iodide excess on Nrf2-Keap 1 pathway and the expressions of Srx and Prx 3, we aim to figure out the effect of short-term iodide excess on oxidative stress-antioxidant defense in the thyroid MethodsWistar rats were used to set up short-term(7, 14 and 28 days) iodide excess model: Wistar rats, 10-12 weeks, 280-300 g, randomly divided into normal iodide(NI) intake groups, 10 times high iodide(10 HI) intake groups and 100 times high iodide(100 HI) intake groups. The daily iodide intake was 7.5 μg/d, 75 μg/d and 750 μg/d by feeding with different concentrations of potassium iodide(KI) solution and normal diet for 7, 14 and 28 days respectively. The body weight and the weight of the dissected thyroid gland were measured, and the relative ratio of thyroid weight/body weight was calculated. Urinary iodine concentration was measured by ammonium persulfate digestion arsenic cerium catalytic spectrophotometry. Serum thyroid hormone levels(T3, T4, FT3, FT4 and TSH) were measured by competitive immune method of direct chemiluminescence technology. Mitochondrial superoxide production was measured by flow cytometry using a mitochondrial superoxide indicator(MitoSOX Red). Western blot was used to detect the changes of protein level of Nrf2, Keap 1, Srx and Prx 3. Fluorescence staining was used to detected the expressions of Nrf2 and Srx. Results 1. The ratio of thyroid weight/body weight: body weight, thyroid weight and the ratio of thyroid weight/body weight were not significantly altered when the iodide intake was NI, 10 HI and 100 HI across Days 7, 14 and 28(p > 0.05). 2. Urinary iodine concentrations: at all the different time periods, there was a significant increase in urinary iodine concentrations in 10 HI and 100 HI when compared to the NI group(p < 0.05). The urinary concentration of 10 HI group on Days 7, 14 and 28 was approximately 10 times of NI group, whereas it was merely 60-80 times for 100 HI group. 3. Serum thyroid hormone levels: there were no significant alterations in serum thyroid hormone(T3, T4, FT3, FT4, TSH) levels and the ratio T3/T4 following the intake of NI, 10 HI and 100 HI on Days 7, 14 and 28(p > 0.05). 4. Mitochondrial superoxide production: on Days 7, 14 and 28, when compared to the NI group and 10 HI group, there was a significant increase in mitochondrial superoxide production for the 100 HI group(p < 0.05). In the 100 HI group, compared to Day 7 and Day 14, there were a significant increase in mitochondrial superoxide production on Day 28(p < 0.05). 5. Western blot: on Days 7, 14 and 28, when compared to the NI group, there were no significant alterations in expressions of Nrf2, Keap 1, Srx and Prx 3 in 10 HI group, however, the expressions of Nrf2, Srx and Prx 3 were significantly increased(p < 0.05) while Keap 1 was notably decreased in 100 HI group(p < 0.05). 6. Immunofluorescence staining: much stronger positive staining of Nrf2 could be detected in the nuclear on Days 7, 14 and 28 in the 100 HI group. Conclusion 1. There is still a part of the iodide accumulation in 100 HI group of Wistar rats. It maybe the underlying mechanism of oxidative stress investigated by 100 HI. 2. Although short-term iodide excess may increase the production of mitochondrial superoxide, expressions of Srx and Prx 3 were increased by activating Nrf2-Keap 1 pathway, which indicated that excessive iodide accumulated in the body may trigger the oxidative stress- antioxidant defense in the thyroid to maintain the normal thyroid function. |
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