Just wanted to stress the importance of I2 intake for those that are dealing with FBD, PCOS, any hormonally-driven cystic/pre-cancerous or cancerous condition. I2 is utilized by the body in a different way that KI is, it's uptake is different, and it performs different functions. I could attempt to paraphrase here for you, but I won't. Lots of links for you to peruse, I don't pretend to understand all of the technical jargon. Read and learn.

The most bang for your buck, re: I2, is Lugol's solution.


http://www.thyroidscience.com/cases/Derry.Iodine.Regen.6.7.08.pdf


Lugol’s Solution

Lugol’s solution is made of 5% free Iodine and
10% potassium Iodide in water. Free iodine (elemental
iodine) is only slightly soluble in water, but 200
years ago Henri Lugol, a Paris physician, discovered
that Potassium Iodide increased free iodine’s solubility
in water. Three chemical iodine species exist in
Lugol’s solutions: free elemental iodine, triiodide,
and iodide. [11][12][13] Free iodine reacts with water to
make Lugol’s solution brown, triiodide’s weaker yellow
color is not visible, and iodide is colorless.

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http://www.biomedexperts.com/Abstract.bme/15922087/Inhibition_of_N-methyl-N-n...


Inhibition of N-methyl-N-nitrosourea-induced mammary carcinogenesis by molecular iodine (I2) but not by iodide (I-) treatment Evidence that I2 prevents cancer promotion

We analyzed the effect of molecular iodine (I2), potassium iodide (KI) and a subclinical concentration of thyroxine (T4) on the induction and promotion of mammary cancer induced by N-methyl-N-nitrosourea. Virgin Sprague-Dawley rats received short or continuous treatment. Continuous I2 treated rats exhibited a strong and persistent reduction in mammary cancer incidence (30%) compared to controls (72.7%). Interruption of short or long term treatments resulted in a higher incidence in mammary cancer compared to the control groups. The protective effect of I2 was correlated with the highest expression of the I-/Cl- transporter pendrin and with the lowest levels of lipoperoxidation expression in mammary glands. Triiodothyronine serum levels and Na+/I- symporter, lactoperoxidase, or p53 expression did not show any changes. In conclusion continuous I2 treatment has a potent antineoplastic effect on the progression of mammary cancer and its effect may be related to a decrease in the oxidative cell environment.


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http://www.medsci.org/v05p0189.htm


Iodine Alters Gene Expression in the MCF7 Breast Cancer Cell Line: Evidence for an Anti-Estrogen Effect of Iodine

The high rate of breast disease in women with thyroid abnormalities (both dietary and clinical) suggests a correlation between thyroid and breast physiology [1-3]. In addition, women with breast cancer have larger thyroid volumes then controls [2]. Multiple studies suggest that abnormalities in iodine metabolism are the likely link [4-7]. Additionally, the impact of iodine therapy for the maintenance of healthy breast tissue has been reported in both animal [4-7] and clinical studies [8, 9] yet the mechanisms responsible remain unclear.

Iodide (I-) uptake is observed in approximately 80% of breast cancers as well as fibrocystic breast disease and lactating breasts; however, quantitatively, no significant iodide uptake is reported in normal, non-lactating breast tissue [10]. Clinical trials have demonstrated that women with cyclic mastalgia [9] or fibrocystic disease [8] can have symptomatic relief from treatment with molecular iodine (I2). Iodine deficiency, either dietary or pharmacologic, can lead to breast atypia and increased incidence of malignancy in animal models [11]. Furthermore, iodine treatment can reverse dysplasia which results from iodine deficiency [5]. Rat models using N-methyl-N-nitrosourea (NMU) and dimethyl-benz[a]anthracene (DMBA) to induce dysplasia and eventually carcinogenesis have shown that the presence of molecular iodine in the animal's diet can prevent tumor formation; yet, when iodine is removed from the diet, these animals develop tumors at rates comparable to those of control animals [5, 7]. These data suggest that iodine diminishes early cancer progression through an inhibitory effect on cancer initiating cells.

Evidence indicates that the impact of iodine treatment on breast tissue is independent of thyroid function. For example, iodine deficient rats given the thyroid hormone thyroxine (T4) did not achieve reduced tumor growth following NMU treatment suggesting that the effect of iodine on tumor growth is independent of the thyroid gland or thyroid hormone [7]. Additionally, Eskin et al and others have reported that administration of molecular iodine has a greater impact on tumor growth than the equivalent dose of iodide [5-9]. Since the thyroid primarily utilizes iodide as opposed to iodine [5], this data supports the hypothesis that iodine is not acting through the thyroid.

In addition to differences in the metabolism of iodine, the mechanisms of iodine and iodide uptake appear to differ. While iodide uptake is essentially via the Sodium-Iodide Symporter (NIS) in the thyroid, data suggests that iodine uptake in the breast may be NIS-independent, possibly through a facilitated diffusion system [12]. Together this data indicates that the effect of iodine on breast cancer progression is in part independent of thyroid function and suggests that iodine's protective effect on breast cancer progression is elicited through its direct interactions with breast cancer cells.

One proposed mechanism by which iodine may influence breast physiology and cancer progression is through an interaction with estrogen pathways. Qualitative changes in the estrogen receptor have been found in the breasts of iodine deficient rats compared to normal euthyroid animals suggesting that the iodine pathway may augment the synthesis of the estrogen receptor α (ERα) [13]. Furthermore, when estrogen-responsive and estrogen-independent tumors were transplanted into mice, estrogen-responsive tumors had higher radioactive iodine uptakes than estrogen-independent transplants [14]. Additionally, iodine deficiency induced atypia is worsened by estrogen addition [15]. Together, this data supports the hypothesis that an interaction exists between iodine and estrogen within the breast [16]. However, the precise molecular mechanisms responsible for this interaction remain unknown. We hypothesize that iodine effects breast physiology though an interaction with the estrogen pathway.

To test our hypothesis, we analyzed the effects of Lugol's iodine solution (5% I2, 10% KI) on global gene expression in the estrogen responsive MCF-7 breast cancer cell line. Analysis of the gene expression profile was used to evaluate potential mechanisms of action of iodine.

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http://journal.shouxi.net/html/qikan/jcyxyswyxgc/swwlxzz/200672817/wzjh/20080...


Iodine is essential to maintaining the normalcy of the thyroid and the breast. An iodine-deficient state renders the rat thyroid and the breast susceptible to physiological changes and leads to atypia, dysplasia, and hyperplasia (1). The results of iodine replacement therapy in the iodine-deficient rat model shows that different forms of iodine have different tissue responses; iodide (I-) is found to restore the normal morphology and physiology of the thyroid gland, whereas molecular iodine (I2) results in a decrease of rat breast hyperplasia and perilobular/ductal fibrosis (2). The beneficial effect of molecular iodine has also been documented in the human fibrocystic breast condition and in cyclic mastalgia (3, 4). Iodine, in conjunction with medroxy progesterone acetate (5), and an iodine-rich seaweed "wakame" diet (6) are shown to regress 7,12-dimethylbenz(a)anthracene-induced rat breast tumors, and this effect has been corroborated by high tumor tissue iodine content (5, 6) and induction of apoptosis at the tumor site (6). Iodide excess is known to induce apoptosis in the thyroid cells in vitro (7) and also in sodium iodide symporter and thyroperoxidase stably transfected non-small cell lung carcinoma cells (8). Earlier studies show that sodium iodide symporter facilitates iodide transport, and thyroperoxidase oxidizes iodide (I-) to iodine (I2), which is important for its organification (9). Propyl-thiouracil, an inhibitor of peroxidase, completely abolishes the cell death-inducing effect of iodide in thyroid cells, establishing I2 as the mediator of apoptosis (7). The enhanced expression of sodium iodide symporter in human breast cancer tissue has been reported; however, its significance is unknown (9, 10). In addition to this, non-lactating breast tissue is known to be peroxidase-poor (11) and does not provide milieu conducive for iodide organification. On the other hand, molecular iodine is a highly reactive species and can be utilized without involvement of sodium iodide symporter and peroxidase activity (12).

Studies performed in the cell-free system show that iodine exposure to mitochondria isolated from breast tumor tissue causes swelling, organification of the mitochondrial proteins, and release of apoptogenic effectors from mitochondria that cause nuclear fragmentation (13). The mechanism of iodine action in breast cancer cells has not been studied to date. This led us to investigate the anti-proliferative and cytotoxic effects of iodine on breast cancer cells, which can be mediated through apoptosis.

Apoptosis is a physiological cell suicide program critical to development and tissue homeostasis. The caspases, a family of intracellular cysteine proteases, are the central executioners of apoptosis. Effector caspases, such as caspase-3 and -7, are activated by initiator caspases, such as caspase-9, through proteolytic cleavage. Once activated, effector caspases are responsible for the digestion of a diverse array of structural and regulatory proteins, resulting in an apoptotic phenotype (14). During apoptosis, divergent cellular stresses, such as DNA damage, heat shock, oxidative stress, withdrawal of growth factor, etc., also converge on mitochondria. Decrease in the mitochondrial transmembrane potential and altered cellular redox state are the early changes in mitochondria-mediated apoptosis (15). Mitochondrial intermembrane space contains several proteins that can either induce apoptosis involving caspases (e.g. cytochrome c), the secondary mitochondrial activator of caspases (Smac) and HtrA2/Omi or execute a caspase-independent apoptotic death program through apoptosis-inducing factor (AIF)3 and endonuclease G (16-22). The Bcl-2 family of proteins, with both anti-apoptotic as well as pro-apoptotic members, is implicated in the regulation of mitochondria-mediated apoptosis. Two of the anti-apoptotic members, namely Bcl-2 and Bcl-xL, confer resistance to apoptosis induced by a number of stimuli, whereas the other homologues Bid, Bax, Bak, and BH-3 domain-only proteins promote apoptosis (23, 24).

This study elucidates the detailed mechanism of molecular iodine-induced apoptosis in human breast cancer cells. Iodine treatment induces changes in members of Bcl-2 family proteins and leads to the activation and translocation of Bax to mitochondria. The release of AIF from mitochondria executes nuclear fragmentation in a caspase-independent manner. The results show that iodine exhibits strong antioxidant activity, and thiol depletion seems to play an important role in iodine-induced apoptosis.

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http://www.jbc.org/cgi/content/abstract/281/28/19762


Molecular Iodine Induces Caspase-independent Apoptosis in Human Breast Carcinoma Cells Involving the Mitochondria-mediated Pathway*
Ashutosh Shrivastava{ddagger}1, Meenakshi Tiwari{ddagger}, Rohit A. Sinha{ddagger}, Ashok Kumar{ddagger}, Anil K. Balapure§, Virendra K. Bajpai¶, Ramesh Sharma§, Kalyan Mitra¶, Ashwani Tandon{ddagger}, and Madan M. Godbole{ddagger}2

From the {ddagger}Department of Endocrinology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, §National Laboratory Animal Cell Culture and ¶Electron Microscopy Unit, Central Drug Research Institute, Lucknow 226 014, India

Molecular iodine (I2) is known to inhibit the induction and promotion of N-methyl-n-nitrosourea-induced mammary carcinogenesis, to regress 7,12-dimethylbenz(a)anthracene-induced breast tumors in rat, and has also been shown to have beneficial effects in fibrocystic human breast disease. Cytotoxicity of iodine on cultured human breast cancer cell lines, namely MCF-7, MDA-MB-231, MDA-MB-453, ZR-75-1, and T-47D, is reported in this communication. Iodine induced apoptosis in all of 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, it did not induce apoptosis in these cells. The iodine-induced apoptotic mechanism was studied in MCF-7 cells. DNA fragmentation analysis confirmed internucleosomal DNA degradation. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling established that iodine induced apoptosis in a time- and dose-dependent manner in MCF-7 cells. Iodine-induced apoptosis was independent of caspases. Iodine dissipated mitochondrial membrane potential, exhibited antioxidant activity, and caused depletion in total cellular thiol content. Western blot results showed a decrease in Bcl-2 and up-regulation of Bax. Immunofluorescence studies confirmed the activation and mitochondrial membrane localization of Bax. Ectopic Bcl-2 overexpression did not rescue iodine-induced cell death. Iodine treatment induces the translocation of apoptosis-inducing factor from mitochondria to the nucleus, and 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.

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http://tinyurl.com/kn4b67



This study analyzes the uptake and antiproliferative effect of two different chemical forms of iodine, iodide (I-) and molecular iodine (I2), in MCF-7 cells, which are inducible for the Na+/I- symporter (NIS) and positive for pendrin (PDS). The mouse fibroblast cell line NIH3T3 was used as control. Our results show that in MCF-7 cells, I- uptake is sustained and dependent on NIS, whereas I2 uptake is transient with a maximal peak at 10 min and a final retention of 10% of total uptake. In contrast, no I- was taken up by NIH3T3 cells, and although I2 was captured with the same time pattern as in MCF-7 cells, its uptake was significantly lower, and it was not retained within the cell. The uptake of I2 is independent of NIS, PDS, Na+, and energy, but it is saturable and dependent on protein synthesis, suggesting a facilitated diffusion system. Radioiodine was incorporated into protein and lipid fractions only with I2 treatment. The administration of non-radiolabeled I2 and 6-iodo-5-hydroxy-8,11,14-eicosatrienoic acid (6-iodolactone, an iodinated arachidonic acid), but not KI, significantly inhibited proliferation of MCF-7 cells. Proliferation of NIH3T3 cells was not inhibited by 20 µM I2. In conclusion, these results demonstrate that I2 uptake does not depend on NIS or PDS; they suggest that in mammary cancer cells, I2 is taken up by a facilitated diffusion system and then covalently bound to lipids or proteins that, in turn, inhibit proliferation.

All vertebrates concentrate iodide (I-) in the thyroid gland for thyroid hormone (TH) synthesis (Carrasco 2000, Pisarev & Gartner 2000). The mechanism of I- uptake involves active and passive transport systems present in several organs, including thyroid and mammary glands (Carrasco 2000, Soleimani et al. 2001, Rillema & Hill 2003a, Gillan et al. 2004). The active transport is mediated by Na+/I- symporter (NIS), which is a transmembrane glycoprotein that transports I- against its concentration gradient and is perchlorate (KClO4) sensitive (Eskandari et al. 1997, Carrasco 2000). In lactating animals, NIS actively transports I- from the maternal plasma to the alveolar epithelial cells of the mammary gland (Tazebay et al. 2000). In the human breast cancer cell line MCF-7, retinoic acid (RA) treatment increases NIS mRNA, NIS protein, and iodide uptake (Kogai et al. 2000). Pendrin (PDS) is a facilitated diffusion transporter that is sensitive to disulfonic-2,2'-stilbene-4,4'-diisotiocianic acid (DIDS). PDS is also involved in I-uptake and has been described in thyroid and mammary gland as well as in immortalized cell lines such as normal rat thyroid FRTL-5 (Royaux et al. 2000) and in several human breast cancer cell lines (Shennan 2001, Rillema & Hill 2003b, García-Solís et al. 2005a,b).

With regard to I2 uptake, studies in brown algae show that I- uptake is dependent on oxidation, i.e. the I- in seawater is oxidized to I2 or hypoiodous acid (HIO) by exohaloperoxidases and then penetrates into algal cells by means of a facilitated diffusion system (Küpper et al. 1998). Thyroid cancer cells transfected with the exoenzyme thyroperoxidase (TPO) or with both NIS and TPO (NIS/TPO) incorporate 125I-into proteins, but cells transfected only with NIS do not. Moreover, in the presence of specific inhibitors of NIS or TPO, uptake and protein organification of 125I- is strictly dependent on TPO but not on NIS (Wenzel et al. 2003). These studies suggest that 125I- is oxidized by TPO but does not use NIS to enter in the cell. Recent studies in our laboratory have shown that normal rat mammary glands and tumors take up I2 even in presence of KClO4 or furosamide, suggesting that I2 uptake does not depend on NIS or PDS respectively (García-Solís et al. 2005a,b). Several studies support the idea that the biological effect of I- is mediated by iodinated derivatives, for example, I- supplementation of cultured thyrocytes inhibits cell proliferation and induces apoptosis, effects shown only if TPO activity is present. Moreover, Vitale et al.(2000) showed that if TPO activity is blocked with 6-n-propyl-2-thiouracil (PTU), the apoptotic I- effect is eliminated. In addition, in lung cancer cells transfected with NIS or NIS/TPO, the apoptotic effect is induced only in NIS/TPO transfected cells treated with I- (Zhang et al. 2003). These data indicated that I- must be oxidized in order to have a cytotoxic effect. In thyroid, this effect is mediated by iodinated arachidonic acid (AA) derivatives called: 6-iodo-5-hydroxy-8,11,14-eicosatrienoic acid or 6-iodolactone (6-IL) and/or by iodohexadecanal (Dugrillon et al. 1990, Pisarev et al. 1994, Langer et al. 2003). In mammary gland, iodine deficiency is involved in dysplasias (Eskin et al. 1995, Aceves et al. 2005), which are reversible with I2 but not with I- administration (Eskin et al. 1995). Recent data generated in our laboratory showed that continuous treatment with I2, but not with I-, has a potent antineoplasic effect on tumoral progression in N-methyl-N-nitrosourea-treated virgin rats (García-Solís et al. 2005a,b). The lack of I- effect has been explained by the fact that lactoperoxidase, the enzyme that oxidizes I- and covalently binds it to the milk protein, casein, is expressed in mammary gland only when this tissue is lactating (Strum 1978, Shah et al. 1986). In agreement with our findings, Shrivastava et al.(2006) reported that I2 treatment causes apoptosis in several human breast cancer cell lines but not in normal human peripheral blood lymphocytes. They showed the involvement of apoptosis-inducing factor (AIF) from mitochondria, which caused nuclear fragmentation independent of caspases. However, neither the I2-uptake mechanism nor iodolipid formation has been investigated in mammary cells...



...The present work shows for first time that the capture of I2 occurs by a mechanism different from the transport of I-. Previous studies have demonstrated that NIS and PDS transporters are involved in I- uptake in both thyroid and mammary glands (Carrasco 2000, Rillema & Hill 2003a). In the present study, only RA-treated MCF-7 cells showed NIS mRNA expression and I- uptake, confirming that iodide internalization requires NIS (Kogai et al. 2000). Our findings show that in MCF-7 cells, with or without RA (NIS+ or NIS- respectively), I2 uptake is five times greater than I- and has a peak within 5 and 15 min, suggesting that I2 uptake does not require the NIS transporter. The NIH3T3 cells showed a similar pattern of I2 uptake, but its capture was significantly lower. MCF-7 cells also express the PDS transporter, which is DIDS sensitive (Royaux et al. 2000, Rillema & Hill 2003b). Neither KClO4 nor DIDS inhibited I2 uptake in NIS+ MCF-7 cells, demonstrating that NIS and PDS do not participate in I2 uptake. Our results suggest that I2 uptake is mediated by a common facilitated transporter in mammary and non-mammary cells; however, in NIH3T3 cells the I2 uptake is reduced, and I2 not retained within the cell.

Our results show the existence of a distinct uptake system for I2 that is saturable (>5 µM) and has a high affinity (Km of 0.91 µM) and high velocity (Vmax of 1.13 pmol/min per 104 cells), contrasting with the low affinity and high velocity of I-uptake in NIS+MCF-7 cells (Km of 21.9 µM and Vmax of 2.17 pmol/min per 104 cells; Kogai et al. 2000). In addition, I2 uptake is dependent on protein synthesis, but it is independent of ATP and Na+/K+-ATPase. These characteristics were reported by Rillema & Hill (2003b) for I- uptake by PDS, the DIDS-sensitive transporter. However, I2 uptake by MCF-7 cells was not inhibited with DIDS. I2 uptake followed Michaelis-Menten kinetics, but ATP and Na+/K+-ATPase were not required, suggesting a facilitated diffusion mechanism, according to the definition by Lobban et al.(1985). I2 uptake showed similar characteristics in brown algae, where it was shown that after oxidation of I- to I2 or HIO by haloperoxidases, oxidized iodine is captured by a facilitated diffusion system (Küpper et al. 1998).

Several studies have reported that I- needed to be oxidized by peroxidases, such as thyro-, myelo-, eosinophil-, and lactoperoxidases, and these, in turn, induced cytotoxic effects (Strum 1978, Boeynaems & Hubbard 1980, Turk et al. 1983, Ekholm & Bjorkman 1997). A specific species of oxidized iodine has not yet been identified, but several candidates exist, such as I+ (iodinium), I0 (iodine free radical), IO- (hypoiodite), HIO, and I2 (Smyth 2003). Our results of organification in mammary cells show iodination of proteins with low-molecular weight. In lactating mammary gland, iodine is incorporated into the milk protein, casein (Strum 1978, Shah et al. 1986), which is expressed by MCF-7 cells (Constantinou et al. 1998). It is possible that the lack of casein expression in mouse fibroblast cells explains why I2 is not retained within these cells. In mammary cells, we show that protein iodination took place in the presence of PTU, indicating that I2 organification does not require peroxidase activity. This result is consistent with previous studies showing that I2 generates thyroxine (T4) in the absence of peroxidase (Thrall et al. 1992). In contrast, I- treatment did not generate iodinated proteins, which can be explained by the absence of peroxidase activity in MCF-7 cells (Kogai et al. 2000). Although we found radioactivity in the lipid fraction from I- treated cells, when we analyzed it by TLC and autoradiography no iodinated spots were identified. Thus, the 125I- we found in the lipid fraction might reflect a non-covalent interaction. It has been shown that I- can bind to the lipid bilayer surface (Langner & Hui 1991). In contrast, lipids from cells treated with I2 showed a migration similar to the 6-IL standard, suggesting that I2 treatment could generate this type of iodolactone. In the thyroid gland, the antiproliferative and/or apoptotic effect of I- treatment is mediated by iodinated arachidonic acid derivatives such as 6-IL or iodohexadecanal (Dugrillon et al. 1990, Pisarev et al. 1994, Langer et al. 2003). In vivo iodolipid formation in mammary gland treated with I2 has not been investigated. Data generated in our laboratory showed a reduction in mammary tumors without changes in thyroid status (García-Solís et al. 2005a,b), suggesting a specific I2 effect only in tumoral tissue in rats. Several studies have reported elevated prostaglandin levels in breast cancer but not in normal mammary gland (Tan et al. 1974, Bennett et al. 1977, Rolland et al. 1980). Prostaglandins are produced from AA by the enzyme cyclooxygenase, indicating the presence of high levels of AA in breast tumors. It is possible that these high levels of AA, and the iodolipids formed from them, may explain the specific effect of I2 in tumoral cells. This hypothesis is being explored in our laboratory.

We also examined the effects of non-radioactive KI, I2, or 6-IL, and we found that I2 and 6-IL treatments inhibited the proliferation rate of mammary cells in a dose-dependent manner at 72 h. When we analyzed the time dependence, I2 and 6-IL treatments inhibited proliferation within 24 h, but the mechanism of this inhibition has not been studied. In thyroid gland, iodine treatment arrested the cell cycle at the GO/G1 and G2/M phases (Tramontano et al. 1989, Smerdely et al. 1993). Other studies have shown an apoptotic effect induced by iodine excess in cultured thyrocytes. This effect did not involve changes in the antitumor protein p53 and did not require expression of apoptosis-related proteins, such as Bax, Bcl2, or Bcl XL (Vitale et al. 2000). With regard to the mammary gland, several authors have proposed that iodine deficiency alters the structure and function of human and rat mammary cells, and that I2 is more effective than I- in diminishing ductal hyperplasia and perilobular fibrosis (Ghent et al. 1993, Eskin et al. 1995). Studies in our laboratory have shown that chronic administration of I2 but not I- has a potent antineoplasic effect at the promotional level of mammary cancer and does not involve changes in the expression of p53 (García-Solís et al. 2005a,b). In addition to this, a recent report showed that the I2 effect in human breast cancer cell lines involves the activation and translocation of Bax from mitochondria, allowing the release and translocation of AIF to the nucleus, where it brings about nuclear fragmentation independent of caspases (Shrivastava et al. 2006). In the present study, we show that I2 treatment diminishes cell proliferation and is accompanied by iodination of lipids and proteins. We propose that the peroxisome proliferator-activated receptor (PPAR), a ligand-dependent transcription factor, can participate in the antiproliferative I2 effect. It is noteworthy that polyunsaturated fatty acids, including linoleic acid, eicosanoids, and AA (6-IL precursor), are endogenous PPAR ligands (Kliewer et al. 1997). PPAR ligands are involved in the regulation of cellular differentiation, cell cycle control, and apoptosis unrelated to p53 (Rosen & Spiegelman 2001, Shen & Brown 2003). Our results show that I2 treatment has an antiproliferative effect on MCF-7 cells, and they suggest the formation of 6-IL, which may mediate this effect; however, more detailed investigations are needed to elucidate the molecular mechanism of the actions of iodine derivatives in proliferation and/or apoptosis.

Taken together, these results demonstrate that I2 uptake does not require NIS or PDS transporters and suggest that I2 is taken up by a facilitated diffusion system and is subsequently bound to proteins or lipids that inhibit cell proliferation.

Finally, our findings both in vivo (García-Solís et al. 2005a) and in vitro (present work), as well the recent report of Shrivastava et al.(2006) showing that the antiproliferative effect of I2 treatment is exerted only in tumoral cells, lead us to propose that I2 treatment should be tested in clinical trials as an adjuvant of breast cancer therapy.

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