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| Scrutinizing the evidence for breast cancer procedures and treatments |
| References: What is the background of iodine and breast disease risk? What are iodines's mechanisms of action? |
| Breast Cancer Choices reviews the peer reviewed literature |
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DISEASE RISK?
Editor's Note: The author below found that from 1990-1993, the US had 22.3 deaths per 100,000 women of breast cancer, placing them in 45th place in the world, while in Japan, where they have high dietary iodine, there were 6.6 deaths per 100,000, placing them in 13th place (Cancer Statistics, 1997). These findings tally with the study below finding that the low intake of dietary iodine, found due to geographical differences, leads to a risk of breast, endometrial, and ovarian cancer. Lancet. 1976 Apr 24;1(7965):890-1. Dietary Iodine and Risk of Breast, Endometrial, and Ovarian Cancer by Stadel BV Geographic differences in the rates of breast, endometrial, and ovarian cancer appear to be inversely correlated with dietary iodine intake. Endocrinological considerations suggest that a low dietary iodine intake may produce a state of increased effective gonadotrophin stimulation, which in turn may produce a hyperoestrogenic state characterised by relatively high production of oestrone and oestradiol and a relatively low oestriol to oestrone plus oestradiol ratio. This altered endocrine state may increase the risk of breast, endometrial, and ovarian cancer. Increasing dietary iodine intake may reduce the risk of these cancers.
Editor's Note: The author below found iodine-deficient breasts show changes in RNA/DNA ratios, estrogen receptor proteins, and cytosol iodine levels. Iodine is a necessary element for breast tissue growth and development. Adv Exp Med Biol. 1977,91:293-304 Iodine and mammary cancer. by Eskin BA. From laboratory studies presented, iodine appears to be a requisite for the normalcy of breast tissue in higher vertebrates. When lacking, the parenchyma in rodents and humans show atypia, dysplasia, and even neoplasia. Iodine- deficient breast tissues are also more susceptible to carcinogen action and promote lesions earlier and in greater profusion. Metabolically, iodine-deficient breasts show changes in RNA/DNA ratios, estrogen receptor proteins, and cytosol iodine levels. Clinically, radionuclide studies have shown that breast atypia and malignancy have increased radioactive iodine uptakes. Imaging of the breasts in high-risk women has localized breast tumors. The potential use of breast iodine determination to determine estrogen dependence of breast cancer has been considered and the role of iodide therapy discussed. In conclusion, iodine appears to be a compulsory element for the breast tissue growth and development. It presents great potential for its use in research directed toward the prevention, diagnosis, and treatment of breast cancer.
Editor's Note: The 2005 study below found that ovarian estrogen production increases during an iodine-deficient state, while changes in the estrogen receptors in iodine-deficient breasts make them more sensitive to circulating estrogens (Eskin above). A diet low in iodine can lead to a hyperestrogen state with high estrone and estradiol and a low estriol to estrone ratio that can lead to cancer (Stadel above). Domest Anim Endocrinol. 2005 Jul;29(1):97-103. Epub 2005 Apr 7. Ovarian iodide uptake and triiodothyronine generation in follicular fluid. The enigma of the thyroid ovary interaction. by Slebodzinski AB. Polish Academy of Sciences, ul. Promienista 166A/34, 60-157 Poznan, Poland. Since 1928, the iodine concentration in the ovary has been known to be higher than in every other organs except the thyroid. The ovarian iodide uptake varies with sexual activities, is enhanced by estrogens and a hypothyroid state and blocked by goitrogens. The recent discovery of a sodium iodide symporter (NIS) in ovaries has offered a possible mechanism for ovarian iodide uptake and other functional similarities to its thyroid counterpart. Nevertheless, the physiological significance of ovarian iodine uptake and accumulation remains unknown. The presence of thyroid hormones (TH) in follicular fluid (FF) has been established recently. Our preliminary studies on TH in FF (1996-1998) in rabbits, pigs, horses showed that the concentration of T4 is generally lower than that in serum and that for T3 is within the normal range or higher. A positive correlation exists between the T4 levels in FF and serum but not between the corresponding T3 levels. These studies revealed, for the first time, the presence of the ovarian 5'-monodeiodinase system in FF capable of generating T3 (ovary-born T3) by outer ring deiodination of T4. In mares, seasonal polyestrus, ovarian 5'-monodeiodinase (MD) activity and FF T3 levels have been found to be higher during the ovulatory period than in the anovulatory one. The exact physiological significance of this system generating T3 and coexisting with isoforms of TH receptors in granulosa cells has not been elucidated. A direct role of T3 for the early follicular development, differentiation and for the steroidogenic capability of granulosa cells, although strongly suggested by data obtained from in vitro studies, has to be elucidated.
Editor's Note: The authors below found that blocking dietary iodine and imposing a chemical blockade of iodine in female rats, from the midreproductive to perimenopausal years, progressively caused human-like fibrocystic disease in the rats. The older 52-week-old rats exhibited atypical lobules, papillomas, sclerosing adenosis, calcifications, and lobular dysplasia. Arch Pathol Lab Med. 1979 Nov;103(12):631-4. Age-related changes resembling fibrocystic disease in iodine-blocked rat breasts by Krouse TB, Eskin BA, Mobini J. It has been reported that dietary restriction and chemical blockade of iodine causes histopathologic changes in peripubertal female rat breasts. This study extended the age range to include midreproductive life and perimenopausal rats; there is a wider spectrum of structural alterations that are associated with the older breast, with sodium perchlorate as the blocking agent. In 16-week- old rats, breasts showed general increased parenchymal activity and growth, regressing after removal of the block. In 42-week-old rats, breasts showed noticeable calcospherite deposition, intralobular fibrosis, and cystic changes resembling human fibrocystic disease. In 52-week-old rats, breasts exhibited atypical lobules cytologically, papillomatosis, sclerosing adenosis, calcifications, and a lobular transformation of a histologically dysplastic type. It is the older rat that experiments will more closely parallel the human condition.
Editor's Note: The authors below observed that for iodine-deficient rats that manifest atypical breast and thyroid tissues, supplementing with iodine helped with the breast and iodide helped with the thyroid. Biol Trace Elem Res. 1995.Jul;49(1):9-19 Different tissue responses for iodine and iodide in rat thyroid and mammary glands by Eskin BA, Grotkowski CE, Connolly CP, Ghent WR. Department of Obstetrics and Gynecology, Medical College of Pennsylvania, Philadelphia 19129, USA. This research describes the effects of short-term elemental iodine (I2) and iodide (I-) replacement on thyroid glands and mammary glands of iodine- deficient (ID) Sprague-Dawley female rats. Iodine deficiency causes atypical tissue and physiologic changes in both glands. Tissue histopathology and the endocrine metabolic parameters, such as serum TT4, tissue and body weights, and vaginal smears, are compared. A moderate reduction in thyroid size from the ID control (IDC) was noted with both I- and I2, whereas serum total thyroxine approached the normal control with both I- and I2, but was lower in IDC. Thyroid gland IDC hyperplasia was reduced modestly with I2, but eliminated with I-. Lobular hyperplasia of the mammary glands decreased with I2 and increased with I- when compared with the IDC; extraductal secretions remained the same as IDC with I2, but increased with I-; and periductal fibrosis was markedly reduced with I2, but remained severe with I-. Thus, orally administered I2 or I- in trace doses with similar iodine availability caused different histopathological and endocrine patterns in thyroid and mammary glands of ID rats. The significance of this is that replacement therapy with various forms of iodine are tissue-specific.
Editor's Note: As cited above, for iodine-deficient rats, iodine was more beneficial than iodide for the mammary gland. Similarly, for humans with fibrocystics breasts, the patients incurred more benefits from supplementing with iodine rather than iodide. The benefits included a reduction in breast size and remission of disease symptoms. Can J Surg.1993 Oct;36(5):453-60. Iodine replacement in fibrocystic disease of the breast. by Ghent WR, Eskin BA, Low DA, Hill LP. Department of Surgery, Queen's University, Hotel Dieu Hospital, Kingston, Ont. OBJECTIVE: To determine the response of patients with fibrocystic breast disease to iodine replacement therapy. DESIGN: Review of three clinical studies beginning in 1975: an uncontrolled study with sodium iodide and protein-bound iodide; a prospective, control, crossover study from iodide to molecular iodine; and a prospective, control, double-blind study with molecular iodine. SETTING: University affiliated breast-treatment clinics. PATIENTS: Study 1: 233 volunteers received sodium iodide for 2 years and 588 received protein-bound iodide for 5 years. Study 2: the treatment of 145 patients from study 1 treated with protein-bound iodide for several months who still had symptoms was switched to molecular iodine 0.08 mg/kg; 108 volunteers were treated initially with molecular iodine. Study 3: 23 patients received molecular iodine, 0.07 to 0.09 mg/kg body weight; 33 received an aqueous mixture of brown vegetable dye and quinine. The numbers in study 2 increased over the review period so that 1365 volunteers were being treated with molecular iodine by 1989. INTERVENTIONS: All patients in study 3 had pre- and post- treatment mammography and measurement of serum triiodothyronine, thyroxine and thyroid-stimulating hormone levels. MAIN OUTCOME MEASURES: Subjective evaluation--freedom from pain--and objective evaluation--resolution of fibrosis. RESULTS: Study 1: 70% of subjects treated with sodium iodide had clinical improvement in their breast disease, but the rate of side effects was high; 40% of patients treated with protein-bound iodide had clinical improvement. Study 2: 74% of patients in the crossover series had clinical improvement, and objective improvement was noted in 72% of those who received molecular iodine initially. Study 3: in the treatment group 65% had subjective and objective improvement; in the control group there was a subjective placebo effect in 33% and an objective deterioration of 3%. CONCLUSIONS: The fibrocystic breast reacts differently to sodium iodide, protein-bound iodide and molecular iodine. Molecular iodine is nonthytropic and was the most beneficial.
Editor's Note: The author below found patients with breast pain associated with fibrocystic disease experienced iodine-dependent symptom relief after taking iodine. Of patients taking 1.5 mg., 3.0 mg., or 6.0 mg. a day of iodine for six months for breast pain associated with fibrocystic disease, more than 50% of patients taking 6.0 mg. for six months reported less pain. After five months, physician assessment of reduction in pain, tenderness and nodularity was seen in the women taking 3.0 mg. and 6.0 mg. of iodine a day - but not in the women taking just 1.5 mg. a day. The Breast Journal, Volume 10, Number 4, 2004 328-336 The Effect of Supraphysiologic Levels of iodine on Patients with Cyclic Mastalgia by Jack H. Kessler, Ph.D. A randomized, double-blind, placebo-controlled, multicenter clinical trial was conducted with 111 otherwise healthy euthyroid women wiht a history of breast pain. Patients had to document moderate or severe breast pain by recording a score> 5 on a visual analog scale (VAS) of pain for > 6 days per cycle and had to present with fibrosis involving at least 25% of both breast surfaces. Subjects could not be effectively treated wiht more conservative measures such as local heat or nonprescription analgesics. There was not a stastically significant difference in the dropout rate for patients on placebo (11.8%), 1.5 mg/day (31.3%), 3.0 mg/day (18.4%), or 6.0 mg/day (25%) of molecular idodine for 6 months. Physicians assessed breast pain, tenderness, and nodularity each cycle. A statistically significant improvement (p<0.01) associated with dose was observed in the Lewin overall pain scale for all treated groups compared to placebo. Reductions in all three physician assessments were observed in patients after 5 months of therapy in the 3.0 mg/day (7/28; 25%) and 6.0 mg/day (15/27; 18.5%) treatment groups, but not the 1.5 mg/day or placebo group. Patients recorded statistically significant decreases in pain by month 3 in the 3.0 and 6.0 mg/day treatment groups, but not the 1.5 mg/day or placebo group; more than 50% of the 6.0 mg/day treatment group recorded a clinically significant reduction in overall pain. All doses were associated with an acceptable safety profile. No dose-related increase in any adverse event was observed.
Editor's Note: The authors below found 94% of patients taking tablets of brown sea alga containing iodine, chlorophyll and Omega-3 fats for three months experienced pain relief and breast cyst regression. Vopr Onkol. 2005;51(2):236-41. Investigation of the drug "Mamoclam" for the treatment of patients with fibroadenomatosis of the breast by Bezpalov VG, Barash NIu, Ivanova OA, Semenov II, Aleksandrov VA, Semiglazov VF. The clinical trial of a new drug "mamoclam" was carried out in patients with benign breast disease. The drug contains omega-3 polyunsaturated fatty acids, iodine and chlorophyll derivatives and is produced from the brown sea alga laminaria. The study involved 33 patients (mean age 42.5 +/- 1.1 yrs). Two tablets were administered thrice a day for three months. Examination included clinical evaluation of symptoms of mastopathy and dysalgomenorrhea, breast sonography and mammography. Therapeutic response presented as reduced mastalgia, premenopausal syndrome, dysmenorrhea and algomenorrhea, breast cyst regression as well as attenuated pain associated with benign breast disease and palpation. Positive response was reported in 94%. The drug should be recommended for benign breast disease treatment.
Editor's Note: In the 2005 Mayo Clinic study below, benign breast disease , most specifically, the category of the benign breast lesion, was found to be an important factor in the subsequent development of breast cancer. Benign breast lesions, biopsied in over 9,000 women, were classified as either nonproliferative, proliferative without atypia, and atypical hyperplasia, and these biopsied women were followed for a median of 15 years to see if they developed breast cancer. All of the women had an increased risk of breast cancer that persisted for at least 25 years after the biopsy. "One form of benign breast disease, atypical hyperplasia, or atypia, is characterized by abnormal cell growth and can be precancerous. Women with this condition have a four times greater risk of developing breast breast cancer." Of the 235 women with atypia (out of the over 9,000 biopsies studied), 41 went on to develop breast cancer in 15-20 years. (Abstract No. 2353, AACR presentation, April 2006.) N Engl J Med. 2005 Jul 21;353(3):229-37. Benign breast disease and the risk of breast cancer by Hartmann LC, Sellers TA, Frost MH, Lingle WL, Degnim AC, Ghosh K, Vierkant RA, Maloney SD, Pankratz VS, Hillman DW, Suman VJ, Johnson J, Blake C, Tlsty T, Vachon CM, Melton LJ 3rd, Visscher DW. Division of Medical Oncology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA. BACKGROUND: Benign breast disease is an important risk factor for breast cancer. We studied a large group of women with benign breast disease to obtain reliable estimates of this risk. METHODS: We identified all women who received a diagnosis of benign breast disease at the Mayo Clinic between 1967 and 1991. Breast-cancer events were obtained from medical records and questionnaires. To estimate relative risks, we compared the number of observed breast cancers with the number expected on the basis of the rates of breast cancer in the Iowa Surveillance, Epidemiology, and End Results registry. RESULTS: We followed 9087 women for a median of 15 years. The histologic findings were nonproliferative lesions in 67 percent of women, proliferative lesions without atypia in 30 percent, and atypical hyperplasia in 4 percent. To date, 707 breast cancers have developed. The relative risk of breast cancer for the cohort was 1.56 (95 percent confidence interval, 1.45 to 1.68), and this increased risk persisted for at least 25 years after biopsy. The relative risk associated with atypia was 4.24 (95 percent confidence interval, 3.26 to 5.41), as compared with a relative risk of 1.88 (95 percent confidence interval, 1.66 to 2.12) for proliferative changes without atypia and of 1.27 (95 percent confidence interval, 1.15 to 1.41) for nonproliferative lesions. The strength of the family history of breast cancer, available for 4808 women, was a risk factor that was independent of histologic findings. No increased risk was found among women with no family history and nonproliferative findings. In the first 10 years after the initial biopsy, an excess of cancers occurred in the same breast, especially in women with atypia. CONCLUSIONS: Risk factors for breast cancer after the diagnosis of benign breast disease include the histologic classification of a benign breast lesion and a family history of breast cancer. |
OBSERVATIONS AND THEORIES
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.
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.
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.
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. |
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