Annotated References:
Investigating the Relationship Between Iodine and the Breast
Breastcancerchoices.org
Innovative Research and Patient Advocacy

PART 2:  WHAT ARE IODINE'S MECHANISMS OF ACTION? OBSERVATIONS AND
THEORIES

  • Iodine Treatment Found to Have an Effect on the Expression of
    Breast Cancer Genes

Editor's Note: Based upon studies finding that iodine deficiency increases breast cancer and
supplementing with iodine reverses the dysplastic changes, the objective of the 2006
microarray genes' analysis of iodine on breast cancer cells was to determine the specific
molecular pathways through which iodine exerts its protection of  breast tissue.  Of 19,000
genes tested,  1600 appeared to have some significance. All genes that were up- and down-
regulated were examined for common pathways, but none were found.  However, 65% were
involved in cellular components and 58% in physiologic processes.  This study supports the
hypothesis that iodine does effect gene expression in breast cancer cells, and the lack of a
common pathway may involve other uncharacterized genes.

Microarray Characterization of Iodine Metabolic Pathways in Breast Cancer
(Page 379)
by Eskin, Bernard; Stoddard H, Frederick; Brooks, Ari
Drexel University College of Medicine, Philadelphia, United States

Background: The metabolic iodine pathway critical to the thyroid is simulated in a wide range
of non-thyroidal tissues, including the female breast.  Iodine deficiency has been shown to
increase the incidence of breast carcinoma and iodine replacement reverses the dysplastic
changes that occur;  iodine protects breast tissue from malignant change.  Since the specific
molecular pathways through which iodine affects breast tissue is yet unknown, we are using
RNA profiling experiments to examine the effect of iodine treatment on gene expression in
breast cancer cells (MCF-7).
Experiment:  Human breast cancer MCF-7 cells were grown in medium containing either 0
(control), 0.1, or 1.0 uM of iodine for 24 hours.  RNA was isolated and subjected to microarray
analysis using arrays containing approximately 19,000 genes.  Comparisons were made
between the control and the two test conditions (either 0.1 or 1uM iodine).  Ratio of the
Medians (Rm) was used to compare signal intensities between groups.
Results:  Of the 19,000 genes, 1,600 demonstrated significant signal above background.  
Rm for the 1.0 uM condition ranged from 3.675 to 0.248 while the 0.1 uM condition ranged
from 1.774 to 0.46.  Out of these 1,600 genes, approximately 0.375% was up regulated (Rm
> 1.7) and 0.375% were down regulated (Rm < 0.5).  All genes that were up-or down-
regulated from the 1.0 uM array were analyzed for common pathways and cellular
processes.  No common pathways were identified;  however, 65% of the genes were found
to be involved in cellular components and 58% involved in physiologic processes.  Among
the down-regulated genes in the 1.0 uM condtion there was consistence between the 1.0 and
0.1 uM Rm.  This consistency was not apparent in the up-regulated genes.

Conclusion:  Our data supports the hypothesis that iodine effects gene expression in the
MCF-7 cell line.  Understanding alteration in genes expression in response to iodine may
provide insight into the breast iodine pathway responsible for iodine's protective effects on
the female breast. Although this study does not indicate a known common pathway, the
breast iodine pathway may involve yet uncharacterized genes.


  • Iodine's Three Ways of Action

Editor's Note: The authors below found three principal iodine actions: 1.  As an antioxidant by
exerting a competition with free radicals for membrane lipids, protein, and DNA to help
stabilize the cells. 2.  As inducers of antiproliferative and apoptotic mechanisms through the
formation of iodolactones. 3.  As a part of thyroid hormones.

J Mammary Gland Biol Neoplasia. 2005 Apr;10(2):189-96. Related Articles, Links  
Is iodine a gatekeeper of the integrity of the mammary gland?
by Aceves C, Anguiano B, Delgado G.
Instituto de Neurobiologia, Universidad Nacional Autonoma de Mexico, Juriquilla

This paper reviews evidence showing iodine as an antioxidant and antiproliferative agent
contributing to the integrity of normal mammary gland. Seaweed is an important dietary
component in Asian communities and a rich source of iodine in several chemical forms. The
high consumption of this element (25 times more than in Occident) has been associated
with the low incidence of benign and cancer breast disease in Japanese women. In animal
and human studies, molecular iodine (I(2)) supplementation exerts a suppressive effect on
the development and size of both benign and cancer neoplasias. This effect is accompanied
by a significant reduction in cellular lipoperoxidation. Iodine, in addition to its incorporation
into thyroid hormones, is bound into antiproliferative iodolipids in the thyroid called
iodolactones, which may also play a role in the proliferative control of mammary gland. We
propose that an I(2) supplement should be considered as an adjuvant in breast cancer
therapy.


  • Iodine as an Antioxidant

May 2006 Lab Study on Breast Cancer Cells Shows
Iodine Exhibits Antioxidant Activity Leading to Apoptosis

Editor's Note: In the Garcia-Solis study, cited in the Iodine and Breast Cancer section, iodine
treatment was shown to reduce the incidence of  chemically-induced tumors in rats.  Also,  the
study found that the progress of breast cancer and its effect may be related to the decrease in
the oxidative cell environment.  Specifically, there were lower levels of lipidperoxidation.  
Iodine may act as an antioxidant by competing with free radicals for membrane lipids,
proteins, and DNA to help stabilize the cells.

In the lab study below, iodine treatment induced changes in the bcl-2 family of genes,
leading to the activation and translocation of apoptosis-promoting Bax to the mitochondria
(where energy is created in the cells).  The subsequent release of apoptosis-inducing factor
from the mitochondria to the nucleus resulted in the destruction of the nucleus, which is cell
death.  This study found that iodine exhibits strong antioxidant acitivity and thiol depletion
seems to play an important role in iodine-induced apoptosis.

J Biol Chem. 2006 May 5
Molecular iodine induces caspase-independent apoptosis in human breast carcinoma
cells involving mitochondria-mediated pathway
by Shrivastava A, Tiwari M, Sinha RA, Kumar A, Balapure AK, Bajpai VK, Sharma R, Mitra K,
Tandon A, Godbole MM.
Sanjay Gandhi Postgraduate Institue of Medical Sciences, Lucknow, Uttar Pradesh 226014.

Molecular iodine (I(2)) is known to inhibit the induction and promotion of N-methyl-n-
nitrosourea-induced mammary carcinogenesis, regresses 7, 12-Dimethylbenz (a)-
anthracene-induced breast tumors in rat and has also shown beneficial effect in the
fibrocystic human breast disease. Cytotoxicity of iodine on cultured human breast cancer cell
lines viz. MCF-7, MDA-MB-231, MDA-MB-453, ZR-75-1 and T-47D is reported in this
communication. Iodine induces apoptosis in all the cell lines tested, except MDA-MB-231
shown by sub-G1 peak analysis using flow cytometry. Iodine inhibited proliferation of normal
human peripheral blood mononuclear cells, however did not induce apoptosis in these cells.
Iodine-induced apoptotic mechanism was studied in MCF-7 cells. DNA fragmentation
analysis confirmed internucleosomal DNA degradation. Terminal deoxynucleotidyl
transferase-dUTP nick end labeling established that iodine induces apoptosis in time and
dose- dependent manner in MCF-7 cells. Iodine-induced apoptosis is independent of
caspases. Iodine dissipates mitochondrial membrane potential, exhibits an antioxidant
activity and causes depletion in total cellular thiol content. Western blot results showed
decrease in Bcl-2 and upregulation of Bax. Immunofluorescence studies confirmed activation
and mitochondrial membrane localization of Bax. Ectopic Bcl-2 overexpression did not
rescue iodine-induced cell death. Iodine treatment induces translocation of Apoptosis
inducing factor from mitochondria to the nucleus. Treatment of N-acetyl-L-cysteine prior to
iodine exposure restored basal thiol content, ROS levels and completely inhibited nuclear
translocation of Apoptosis inducing factor and subsequently cell death, indicating that thiol
depletion may play an important role in iodine-induced cell death. These results demonstrate
that iodine treatment activates a caspase-independent and mitochondria-mediated apoptotic
pathway.

  • Formation of Iodolactones To Suppress Hyperplasia and Tumor Growth

Editor's Note:  Cann et al., in the article below, write about antiproliferative iodolactones.
"Antiproliferative iodolactones. This would explain the underlying mechanism for iodine-
induced suppression of mammary hyperplasia and tumor growth."  Cell membranes are
composed of lipids (fats).  Iodine can be incorporated into these lipids, forming iodolipids.
Iodolipids help to stabilize the lipids, help to normalize the cell cycle, and inhibit cellular
proliferation.  From the Shrivastrava study above, "Iodocompounds seem to act as mediators
of iodine function as an antioxidant."  Iodocompounds inhibit signal transduction pathways
induced by growth factors, such as epidermal growth factor  Perhaps iodine's antioxdant,
antiproliferative, apoptosis mechanisms are secondary to the formation of iodocompounds,
such as iodolactones.

The Journal of Clinical Endocrinology & Metabolism Vol. 84, No. 2 821
Copyright © 1999 by The Endocrine Society
Iodide Accumulation in Extrathyroidal Tissues
by Stephen A. Cann, Johannes P. van Netten and David W. Glover
Royal Jubilee Hospital University of Victoria Victoria, British Columbia, Canada V8R 1J8
Christiaan van Netten University of British Columbia Vancouver, British Columbia, Canada
V6T 1Z3

We read with interest the paper by Spitzweg et al. (1) on human sodium iodide symporter
(hNIS) gene expression in nonthyroidal tissues. The authors state that extrathyroidal tissues
are not able to organify accumulated iodide; however, there are exceptions to this rule. In
addition to thyroperoxidase, other peroxidases found in nonthyroidal tissues such as lacto-,
myelo-, and eosinophil peroxidase have been shown to efficiently organify iodide (2). In the
mammary gland, iodide is bound to tyrosyl residues of caseins and other milk proteins, and
this organification has been shown to correlate with peroxidase activity (3, 4). In addition,
there is evidence that iodoprotein formation may occur in inactive mammary tissue as well
(5). Thus, it is not unreasonable to assume that more extensive iodide organification may
occur in other tissues.

Although iodide uptake in nonthyroidal tissues does not appear to be influenced by TSH, a
number of other hormones are known to augment its accumulation. In mice, prolactin has
been shown to enhance mammary iodide uptake during pregnancy (6). In nonpregnant rats,
estradiol has been shown to significantly enhance mammary iodide accumulation (7).
Conversely, estradiol has been shown to inhibit, while progesterone enhances, iodide
uptake in the rat uterus and oviduct (8). Thus, a dynamic iodide balance may be maintained
in these nonthyroidal tissues depending on the hormonal milieu and dietary iodine levels.

What role might iodide play in these nonthyroidal tissues? In addition to its incorporation into
thyroid hormones, iodide is also bound, via thyroperoxidase, to various lipid molecules (9).
These iodolipids have been shown to influence a wide range of metabolic functions in the
thyroid, including inhibition of cellular proliferation (iodolactones) and reduction of H2O2
generation (iodoaldehydes) (9). Interestingly, -iodohexadecanal, a naturally occurring
iodoaldehyde, has been shown to inhibit adenylyl cyclase in kidney cortex and liver
membranes, in a fashion similar to its activity on thyroid cells (10). Such extrathyroidal activity
may also occur with the antiproliferative iodolactones. This would explain the underlying
mechanism for iodine-induced suppression of mammary hyperplasia (7) and tumor growth
(11) that has been observed in animal models. Furthermore, in tissues that secrete
inorganic iodide (i.e. stomach, salivary glands, cervix) (12), its accumulation through the hNIS
symporter and subsequent oxidation to hypoiodite may be an important aspect of mucosal
tissue defense (13). A wider physiological role for iodide needs to be explored; further
research into its accumulation, oxidation and organification, and functional activity in
nonthyroidal tissues should aid in elucidating these less well recognized functions.

From the conclusion of the 2004 Torremante Study:

"A source of nutrition which emphasizes seafood and, thereby, provides a source of
polyunsaturated fatty acids and iodine is a dietary basis for iodolactone formation.  This could
be the reason for the low incidence of breast cancer in Japan."

Dtsch Med Wochenschr. 2004 Mar 19;129(12):641-5.

Mastopathy, breast cancer and iodolactone
Torremante P.

Go to Iodine References Part 3