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Enigma of the function of iodide in primitive algae and in animal extrathyroidal organs: is it an ancient antioxidant?
Enigma of the function of iodide in primitive algae and in animal extrathyroidal organs: is it an ancient antioxidant?

Letter to the Editor

Dear Sir,
in relation to the functional role of inorganic iodide in metabolism of algal and animal cells, we have hypothesized, in previous (1) and recent works (2)(3) that iodide might have a (phylogenetically and evolutionistically) ancient antioxidant role in extrathyroidal iodide-concentrating cells.

Into these cells iodide may act as an electron donor in the presence of H2O2 and peroxidase, and the remaining iodine readily iodinates the tyrosine (and more slowly, the histidine (4)(5) or some protein and lipid), and so, neutralizes its own high oxidant power (3). In fact, three billion years ago, Algae, which contain a high amount of iodine, were the first living cells to produce oxygen, toxic at that time, in terrestrial atmosphere. So, algae cells required a protective antioxidant action in which iodides might have had a specific role.

Now this hypothesis of the antioxidant role of iodide is experimentally confirmed in Algae by a recent study carried out by Kupper et al. (6).

We believe that this work, which convalidates our hypothesis, may constitute a fundamental experimental milestone in the study of the extrathyroidal nonhormonal action of iodine-iodide in biology and physiology of the cells.

Several extrathyroidal organs in animals, many of which share the same gene expression of sodium-iodide symporter of thyroidal iodide-pump (7), particularly stomach mucosa and lactanting mammary gland, but also salivary glands, thymus, epidermis, choroid plexus, articular and arterial sistems, have a iodide-concentrating ability without showing any hormonal or biological action (8), and so, Algae, Porifera, Anthozoa (9) and several marine Invertebrates. In human organism extrathyroidal nonhormonal inorganic iodide is about 50-80% of the total amount of iodine and its role is not known. Besides, direct uptake of inorganic iodine by tumor shows experimentally a suppressive effect on DMBA-induced breast tumors growth in the rat (10). The antioxidant action of iodide may give a satisfactory explanation of the function of this trace-element and might be a very important knowledge for preventive purpose.

We should point out that extrathyroidal action of iodide might be an important new area for investigation.

REFERENCES

  1. Venturi S et al (1993) A new hypothesis: iodine and gastric cancer. European Journal of Cancer Prevention. 2 :17-23
  2. Venturi S & Venturi M (1998) Does iodine in the gastric mucosa have an ancient antioxidant role? IDD-Newsletter 14, 4 :61-2
  3. Venturi S & Venturi M (1999). Iodide, thyroid and stomach carcinogenesis: evolutionary story of a primitive antioxidant? European Journal of Endocrinology 140, 4 :371-2
  4. Li CH (1945) J Am Chem Soc 67 :1065
  5. Mayberry WE & Hockert TJ (1970). Endocrinology 86 :225..
  6. Kupper FC, Schweigert N, Ar Gall E, Legendre J-M, Vilter H & Kloareg B (1998). Iodine uptake in Laminariales involves extracellular, haloperoxidase-mediated oxidation of iodide. PLANCTA 207 :163-171
  7. Spitzweg C, Joba W, Eisenmenger W & Heufelder AE (1998). Analysis of human sodium iodide symporter gene expression in extrathyroidal tissues and cloning of its complementary deoxyribonucleic acid from salivary gland, mammary gland, and gastric mucosa. J Clin Endocrinol Metab 83, 5 :1746-51
  8. Venturi S, Guidi A & Venturi M (1996). I disordini extra-tiroidei da carenza iodica. Qual è il reale fabbisogno di iodio? Le Basi Razionali della Terapia 16 :267-75
  9. Roche J (1952) Biochimie comparée des scléroprotéines iodées des Anthozoaires et des Spongiaires. Experientia 8 :45-56
  10. Funahashi H, Imai T, Tanaka Y, Tobinaga J, Wada M, Morita T & al. (1996) Suppressive effect of iodine on DMBA-induced breast tumor growth in the rat. J Surg Oncol 61, 3 :209-13