Might iodide have in Gastric Mucosa an ancient antioxidant role ? Why
the primitive Thyroxine
(T4) is transformed in Triiodothyroxine (T3), the real active hormone
of modern Vertebrates ?
Dear sir :
the thyroid gland is, embryogenetically and phylogenetically, derived
from primitive gut , and we
may consider the thyroid cells such as primitive gastroenteric cells,
which , during evolution , are
migrated and specialized in intake of iodides, and in storage and
elaboration of iodine compounds.
Stomach and thyroid share iodine-concentranting ability and many
morphological and functional
similarities such as apical microvilli , secretion of glycoproteins
(thyroglobulin and mucin) and
amino-acid hormones, the digesting and readsorbing ability and lastly,
similar ability to form
iodotyrosines by peroxidase activity (1). But gastric iodide-pump,
phylogenetically more primitive
than the thyroidal one, has lower affinity for iodide and not respond
to, more recent, TSH.
Which is the role of iodide in physiopathology of the stomach?
Iodides reduce, by peroxidase, the oxygen of H2O2 in normal thyroid
hormonogenesis and , are able
to defend 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 gastric
cancer and atrophic gastritis
both by regulating gastric trophism and by antagonizing ( in thyroid
and in gastric mucosa ) the
action of those iodine-inhibitors such as nitrates, thiocyanates and
salt , well-known risk-factors for
gastric carcinogegesis. Recently (4) , we have hypothesized that
iodide might have a
( phylogenetically primitive) antioxidant role in more ancient organs
, particularly in the stomach.
In fact , three billion years ago, Algae, which contain the highest
level 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 a specific
role.
The thyroid gland is, phylogenetically , a modern organ , and its
function started and was
improved from primitive Chordates to more recent Mammalia . Recent are
the T3-nuclear-receptors
in comparison with primitive T4 . In fact thyroxine is present in
fibrous exoskeletal tissues of the
lowest animals ( Invertebrates ) without any hormonal action .
When the primitive marine-animals started to emerge from the sea
, rich of iodine, and
transfered in iodine-deficient mainland, its terrestrial diet became
deficient of iodine and rich of
iodine-competitors ( nitrates, nitrites, thiocyanates, some glycosides,
etc.) .
So, we believe that these animals learned to use the
not-competitivized T4 , to transport into the
cells antioxidant-iodide , utilizing the remaining T3 for metamorphosis
and thermogenesis , with a
new hormonal action by formation of the modern T3-receptors .
Yours sincerely
Sebastiano Venturi & Marta Venturi
via Tre Genghe, 2
Servizio di Igiene e Sanità Pubblica
USL n.1 - Reg. Marche
61016 - PENNABILLI (Italy)
E-Mail: venturis at nf.infotel.it
REFERENCES
1) Banerjee RK, Bose AK, Chakraborty TK,et al. (1985)
Peroxidase-catalysed iodotyrosine formation
in dispersed cells of mouse extrathyroidal tissues. J Endocrinol
,106:2, 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. Europ J Cancer Prevention 2:17-23
4) Venturi S, Guidi A, Venturi M (1996) I disordini extra-tiroidei da
carenza iodica. Qual é il reale
fabbisogno di iodio ? Le Basi Razionali della Terapia. 16: 267-75
