Addition: Effects of Iodine and Selenium on Mitochondrial Damage of Renal Cells in Mice Induced by Fluoride

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Effects of Iodine and Selenium on Mitochondrial Damage of Renal Cells in Mice Induced by Fluoride

Authors
Zhang Zigu, Xu Xiaolu, Shen Xiuyin, Hu Yuxian
(College of Life and Environmental Sciences, Zhejiang Normal University, Jinhua, Zhejiang 321004, China)

Published in the Journal of Zhejiang Normal University (Natural Science Edition), Vol. 25, No. 4, November 2002.

Abstract
This paper aimed to study the effects of iodine and selenium on the impairments of mitochondria induced by fluoride in renal cells of mice. It observed the morphological changes of mitochondria in renal cells of mice containing high concentrations of fluoride or different concentrations of iodine and selenium using the JEM-1200EX transmission electron microscope. The results showed that membrane systems of mitochondria in renal cells of mice were damaged in the groups treated with fluoride or a combination of high iodine and fluoride, while they were almost intact in the groups treated with low iodine and high fluoride, general iodine and high fluoride, and high iodine and fluoride combined with selenium. The results suggest that a certain amount of iodine has an antagonistic effect on fluoride-induced mitochondrial damage in renal cells of mice, but excessive iodine has a synergistic toxic effect. A certain amount of selenium also has an antagonistic effect on mitochondrial damage induced by high iodine and fluoride.

Keywords: iodine; selenium; fluorosis; mice; mitochondria

Introduction
Endemic fluorosis is a systemic chronic disease, with the kidneys being the primary organs for fluoride excretion in animals and humans, and also one of the major target organs for fluorosis. The mechanism of fluoride-induced soft tissue damage remains unclear, but lipid peroxidation is widely considered one of the mechanisms of fluoride toxicity. Iodine and selenium are essential trace elements for the human body, and certain doses of selenium have been reported to counteract lipid peroxidation in the body. However, the relationship between iodine and lipid peroxidation has not been extensively studied. This study aims to observe the ultrastructure of mitochondria in renal cells of mice and explore the effects of different doses of iodine and combined use of iodine and selenium on fluoride-induced mitochondrial damage in renal cells of mice. The goal is to provide morphological evidence for the application of trace elements in the prevention and treatment of fluorosis.

Materials and Methods
Experimental Animals
Male Kunming mice that had just been weaned were provided by the Experimental Animal Breeding Center of the Zhejiang Province Pharmaceutical Inspection Institute, Jinhua, China.

Grouping of Experimental Animals
KI, NaF, and Na2SeO3 were dissolved in distilled water to prepare solutions with the concentrations shown in Table 1. A total of 180 mice were randomly divided into 6 groups, with 30 mice in each group. The control group was given distilled water; one group was exposed to high fluoride (F); three groups were exposed to combinations of iodine and fluoride at low (I-L + F), medium (I-M + F), and high iodine concentrations (I-H + F); and one group was exposed to high iodine, high fluoride, and selenium (I-H + F + Se). The exposure period was 8 weeks, during which the experimental animals had free access to standard feed.

Table 1: Grouping of Experimental Animals

Group Iodine Concentration (mg/L) Fluoride Concentration (mg/L) Selenium Concentration (mg/L)
Control 0 0 0
High Fluoride (F) 0 50 0
Low Iodine + F 0.03 50 0
Medium Iodine + F 0.1 50 0
High Iodine + F 0.5 50 0
High Iodine + F + Se 0.5 50 0.5
Observation of Mitochondrial Ultrastructure in Renal Cells
Four mice were randomly selected from each group. After sacrifice, a 1 mm³ block of kidney tissue was quickly collected and fixed in 5% glutaraldehyde solution. Ultrathin sections were prepared using conventional methods, and the mitochondrial structure within renal cells was observed and photographed using the JEM-1200EX transmission electron microscope. The changes in the double-layer membrane and cristae structures of mitochondria in renal cells were compared across the groups.

Results
Control Group: The double-layer membrane and cristae structures of mitochondria in renal cells were clear and distinct (see Figure 1).
High Fluoride Group: The double-layer membrane and cristae structures of mitochondria were blurred (see Figure 2).
Low Iodine + F Group: The double-layer membrane and cristae structures of mitochondria were relatively clear (see Figure 3).
Medium Iodine + F Group: The double-layer membrane and cristae structures of mitochondria were relatively clear (see Figure 4).
High Iodine + F Group: The double-layer membrane and cristae structures of mitochondria were blurred (see Figure 5).
High Iodine + F + Se Group: The double-layer membrane and cristae structures of mitochondria were clear and distinct (see Figure 6).
Figures:

Figure 1: Control Group (x20,000)
Figure 2: High Fluoride Group (x20,000)
Figure 3: Low Iodine + F Group (x20,000)
Figure 4: Medium Iodine + F Group (x20,000)
Figure 5: High Iodine + F Group (x20,000)
Figure 6: High Iodine + F + Se Group (x20,000)
These results indicate that high fluoride exposure causes significant damage to the mitochondrial membrane system in renal cells of mice, while an appropriate dose of iodine can antagonize this damage. However, when iodine levels are excessive, it can have a synergistic toxic effect with fluoride. Adding a certain amount of selenium can also antagonize the damage to the mitochondrial membrane system in renal cells caused by high iodine and fluoride.

Discussion
Most researchers believe that the damage caused by fluoride to soft tissues is related to the enhancement of lipid peroxidation induced by fluoride, which leads to damage in various parts of the body, especially the membrane system. This study shows that high fluoride can indeed cause damage to the mitochondrial membrane system. Fluoride is a highly reactive element, and previous studies have indicated that excessive fluoride intake can directly attack oxygen, interfering with oxygen metabolism and leading to an increase in oxygen free radicals. Fluoride may also affect trace elements that constitute antioxidant enzymes, resulting in a decrease in antioxidant enzyme activity and an increase in oxygen free radicals, thereby damaging biological membranes. Mitochondria, being the primary membrane structure within cells and a target of free radical damage, are therefore prone to damage when the body ingests excessive fluoride over a long period. Mitochondria, which contain various enzyme systems and are crucial for maintaining cellular life activities, can suffer functional impairments when their structure is damaged.

This study indicates that the main morphological changes in fluoride-induced mitochondrial damage in renal cells include blurred mitochondrial double-layer membranes and cristae structures. Iodine is an essential trace element for the human body, but studies have shown that in areas with high fluoride levels, high iodine can exacerbate the symptoms of fluorosis. This study also suggests that excessive doses of iodine and high doses of fluoride can have a synergistic toxic effect. Just as low iodine or iodine deficiency can cause conditions such as cretinism, excessive iodine intake can lead to hyperthyroidism and apoptosis of thyroid cells, as well as reduced activity of antioxidant enzymes like SOD. Excessive apoptosis of thyroid cells can damage thyroid structure and function, affecting the secretion of thyroxine, which is a key hormone regulating the growth and development of various organs in the body, and ultimately impacting the structure and function of multiple organs.

However, an appropriate dose of iodine can promote the growth and development of thyroid cells, maintaining normal thyroxine secretion, and thereby ameliorating the structural damage to mitochondria in renal cells induced by high fluoride. Selenium, being an important component of glutathione peroxidase (GSH-PX), can enhance GSH-PX activity, reduce lipid peroxides, stabilize biological membranes, and thus counteract the lipid peroxidation caused by fluoride. Experiments have confirmed that selenium compounds can inhibit free radical damage. Therefore, an appropriate dose of selenium can reverse the pathological changes in the ultrastructure of mitochondria in renal cells caused by high fluoride and high iodine.

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