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Does iodide in the gastric mucosa have an ancient antioxidant role? 1998
Does iodide in the gastric mucosa have an ancient antioxidant role?
by Sebastiano Venturi and Marta Venturi, Pennabilli, Italy,
IDD Newsletter Volume 14 Number 4 November 1998

The thyroid is derived both embryogenetically and phylogenetically from the primitive gut. As such, we may consider thyroid cells to be primitive gastroenteric cells that during evolution migrated and specialized in iodide uptake, storage, and elaboration of iodinated compounds. The stomach and thyroid share an iodine concentrating ability and many morphological and functional features, such as apical microvilli, secretion of glycoproteins (thyroglobulin and mucin) and amino-acid hormones, the ability to digest and reabsorb, and the ability to form iodotyrosines by peroxidase activity (1).

However, the gastric iodide pump is phylogenetically more primitive than that of the thyroid, has a lower affinity for iodide, and does not respond to TSH.

What is the role of iodide in stomach pathophysiology? Iodide reduces H2O2 in normal thyroid hormonogenesis and defends cells
from lipid peroxidation in rats (2). In previous work (3) we have reported that iodine deficiency or excess might constitute a risk factor for stomach cancer and atrophic gastritis, both by regulating gastric response and by antagonizing the action of inhibitors such as nitrates, thiocyanates, and salt, well known risk factors for gastric carcinogenesis. Recently we have hypothesized that iodide might have an antioxidant role in more ancient organs, particularly in the stomach (4). In fact, three billion years ago, iodine-rich algae were the first living cells to produce oxygen, which was toxic at that time, in the terrestrial atmosphere. Therefore, algae cells required a protective antioxidant action, in which iodides might have a specific role.

The thyroid gland is phylogenetically a modern organ. It first appeared in a primitive chordate and evolved more recently in
mammals. T3 nuclear receptors are evolutionarily recent in comparison with those for T4. In fact, T4 is present in fibrous
exoskeletal tissues of invertebrates without any hormonal action. When primitive marine animals started to emerge from the iodine-rich sea and transferred to the iodine-deficient land, their terrestrial diet became iodine deficient and also harbored iodine competitors, such as nitrates, nitrites, thiocyanates and some glycosides.

From these considerations, we suggest that these animals learned to use T4 to transport antioxidant iodide into the cells, utilizing the remaining T3 for metamorphosis and thermogenesis, with new hormonal action made possible by the formation of modern T3 receptors.

References:
  1. Banerjee RK, Bose AK, Chakraborty TK, et al. (1985) Peroxidase-catalyzed iodotyrosine formation in dispersed cells of mouse extrathyroidal tissues. J Endocrinol 106:159-65.
  2. Katamine S, Hoshino N, Totsuka K, Suzuki M 1985 Effects of the long-term feeding of high-iodine eggs on lipid metabolism and thyroid function in rats. J Nutr Sci Vitaminol 31:339-53.
  3. Venturi S, Venturi A, Cimini D, Arduini C, Venturi M, Guidi A 1993 A new hypothesis: iodine and gastric cancer. Eur J Cancer Prevention 2:17-23.
  4. Venturi S, Guidi A, Venturi M 1996 I disordini extra-tiroideida carenza iodica. Qual it reale fabbisogno di iodio? Le Basi Razionali della Terapia 16:267-75.



Source: IDD Newsletter Volume 14 Number 4 November 1998 (Web.Archive.org)