Soybean implicated in goiter & also inhibits thyroid - NATIONAL LIBRARY OF MEDICINE

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Entrez-PubMedSoybean implicated in goiter & also inhibits thyroid -

NATIONAL LIBRARY OF MEDICINE

 

 

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http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?uid=9464451 & form=6 & db=m &

Dopt=b -

 

Anti-thyroid isoflavones from soybean: isolation, characterization, and

mechanisms of action.

 

Divi RL, Chang HC, Doerge DR.

 

National Center for Toxicological Research, Jefferson, AR 72079, USA.

 

The soybean has been implicated in diet-induced goiter by many studies. The

extensive consumption of soy products in infant formulas and in vegetarian

diets makes it essential to define the goitrogenic potential. In this

report, it was observed that an acidic methanolic extract of soybeans

contains compounds that inhibit thyroid peroxidase- (TPO) catalyzed

reactions essential to thyroid hormone synthesis. Analysis of the soybean

extract using HPLC, UV-VIS spectrophotometry, and LC-MS led to

identification of the isoflavones genistein and daidzein as major components

by direct comparison with authentic standard reference isoflavones. HPLC

fractionation and enzymatic assay of the soybean extract showed that the

components responsible for inhibition of TPO-catalyzed reactions coeluted

with daidzein and genistein. In the presence of iodide ion, genistein and

daidzein blocked TPO-catalyzed tyrosine iodination by acting as alternate

substrates, yielding mono-, di-, and triiodoisoflavones. Genistein also

inhibited thyroxine synthesis using iodinated casein or human goiter

thyroglobulin as substrates for the coupling reaction. Incubation of either

isoflavone with TPO in the presence of H2O2 caused irreversible inactivation

of the enzyme; however, the presence of iodide ion in the incubations

completely abolished the inactivation. The IC50 values for inhibition of

TPO-catalyzed reactions by genistein and daidzein were ca. 1-10 microM,

concentrations that approach the total isoflavone levels (ca. 1 microM)

previously measured in plasma from humans consuming soy products. Because

inhibition of thyroid hormone synthesis can induce goiter and thyroid

neoplasia in rodents, delineation of anti-thyroid mechanisms for soy

isoflavones may be important for extrapolating goitrogenic hazards

identified in chronic rodent bioassays to humans consuming soy products.

 

PMID: 9464451 [PubMed - indexed for MEDLINE]

 

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sparc-sun-solaris2.8 Nov 15 2001 10:41:10

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" Elaine " <mem121

<Undisclosed-Recipient:@usermail.com;>

Tuesday, February 19, 2002 2:48 PM

Soybean implicated in goiter & also inhibits thyroid -

NATIONAL LIBRARY OF MEDICINE

 

 

>

http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?uid=9464451 & form=6 & db=m & Dopt\

=b -

>

> Anti-thyroid isoflavones from soybean: isolation, characterization, and

> mechanisms of action.

 

Hi Elaine,

 

This soy / iodine interacting is well known and is more about not eating too

much soy without some iodine rich foods in

the meal, such as sea salmon.

 

Notice they talk about excessive soy consumption in a vegetarian diet (which can

be iodine deficient (due to lack of

meat) if they don't use iodine enriched salt)

========================

Good health & long life,

Greg Watson,

http://optimalhealth.cia.com.au