Effect of long-term administration of arsenic (III) and bromine with and without selenium and iodine supplementation on the element level in the thyroid of rat

Dana Kotyzová,Martin Mihaljevič,Eystein Glattre,Vladislav Eybl

doi:10.5507/bp.2005.052

Abstract

The aim of this study was to evaluate the influence of arsenic and bromine exposure with or without iodine and selenium supplementation on the element level in the thyroid of rats. Four major groups of Wistar female rats were fed with respective diets: group A - standard diet, group B - iodine rich diet (10 mg I/kg food), group C - selenium rich diet (1 mg Se/kg) and group D - iodine and selenium rich diet (as in group B and C). Each group was divided into four subgroups per 7 animals each receiving either NaAsO(2) ip (6.5 mg.kg(-1) twice a week for two weeks and 3.25 mg.kg(-1) for six weeks) or KBr in drinking water (58.8 mg.l(-1)) for 8 weeks or combined administration of both substances. Remaining subgroup served as controls. After 8 weeks thyroid glands were analyzed by ICP-MS for As, Br, Se, and I content. The exposition of rat to arsenic or bromine causes the accumulation of these elements in the thyroid gland ( approximately 18 ppm of As, approximately 90 ppm of Br) and significantly affects iodine and selenium concentration in the thyroid. In iodine and/or selenium supplemented rats the bromine intake into the thyroid was lowered to approximately 50% of the level in unsupplemented animals. Also selenium thyroid level elevated due to KBr administration was lowered by iodine supplementation in the diet. The accumulation of arsenic in the thyroid was not influenced by selenium or iodine supplementation; however, As(III) administration increased iodine thyroid level and suppressed selenium thyroid level in selenium or iodine supplemented group of animals.

Highlights

An increased incidence of thyroid cancer has been reported especially in the female population of the United States[1,2], in most other affluent countries (Scandinavia, Israel)[3] and as well in the Czech Republic[4]
Other dietary substances may be present in seawater, and subsequently taken up by fish and seafood, that interact with iodine metabolism or may be carcinogenic to the thyroid without any relation to iodine metabolism[15]
The administration of selenium-rich diet (1.25 mg/kg food) for 8 weeks resulted in a decrease of weight gain compared to animals fed standard diet (Table 1) and could reflect some slight toxic effect of selenium supplementation at this level

Summary

Introduction

An increased incidence of thyroid cancer has been reported especially in the female population of the United States[1,2], in most other affluent countries (Scandinavia, Israel)[3] and as well in the Czech Republic[4]. Clinical and experimental studies, both the dietary deficiency and excess of iodine have been associated with increased risk of thyroid carcinomas[5,6,7,8]. In this connection, the effect of salt water fish and shellfish consumption as a measure of iodine exposure has been discussed[9,10,11]. Its increasing use in both, industry and agriculture introduces bromine into the alimentary chain in ever-growing quantities Another sea-water bound element is carcinogenic metalloid arsenic; its interaction with selenium has been known for more than half a century[16]

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Conclusion