Dietary soy protein isolate and isoflavones modulate hepatic thyroid hormone receptors in rats.
Thyroid hormone receptors (TRs) are regulators of many genes involved in cholesterol and lipid metabolism. The purpose of this study was to examine the effect of soy protein isolate (SPI) and isoflavones on hepatic TRs in rats. In Expt. 1, Sprague-Dawley rats were fed diets containing either casein or alcohol-washed SPI with or without isoflavone supplementation (5-1250 mg/kg diet) for 70, 190, and 310 d. The offspring (F1) were fed the same diets as their parents (F0). In Expt. 2, Sprague-Dawley rats were fed diets containing casein or casein plus isoflavones (50-400 mg/kg diet) for 120 d. The mRNA and protein contents of the hepatic TRs were measured by semiquantitative RT-PCR and Western blot, respectively. TRalpha1, TRalpha2, and TRbeta2 contents were not affected by SPI. However, the content of the 52-kDa TRbeta1 protein, the major isoform present in the liver, was markedly increased by dietary SPI in both sexes of F0 and F1 compared with casein. The supplemental isoflavones had no effect on TRbeta1, whereas the high doses of isoflavones (250 and 1250 mg/kg diet) reduced the hepatic TRalpha1 protein content in F1 male rats on d 28. SPI had no effect on total T3 and T4 levels. However, higher dose of supplemental isoflavones markedly increased T4 level in female rats. Overall, this study demonstrates for the first time that SPI upregulates hepatic TRbeta1 expression, and that isoflavones reduce the hepatic TRalpha1 level in young male rats. The SPI-induced TRbeta1 may play a role in mediating the hypocholesterolemic and lipid-lowering actions of soy protein.
Xiao
Chao Wu
CW
Nutrition Research Division, Food Directorate, Health Products and Food Branch, Health Canada, Ottawa, ON, Canada K1A 0L2. chaowu_xiao@hc-sc.gc.ac.
L'Abbé
Mary R
MR
Gilani
G Sarwar
GS
Cooke
Gerard M
GM
Curran
Ivan H
IH
Papademetriou
Suzanne A
SA
D000818:Animals; D015153:Blotting, Western; D001835:Body Weight; D002364:Caseins / Q000494:pharmacology; D004044:Dietary Proteins / Q000494:pharmacology; D004435:Eating; D005260:Female; D007529:Isoflavones / Q000494:pharmacology*; D008099:Liver / Q000033:anatomy & histology / Q000737:chemistry* / Q000187:drug effects*; D008297:Male; D009929:Organ Size; D020033:Protein Isoforms / Q000032:analysis / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D011988:Receptors, Thyroid Hormone / Q000032:analysis* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D030262:Soybean Proteins / Q000494:pharmacology*; D037021:Thyroid Hormone Receptors alpha / Q000032:analysis / Q000235:genetics; D037042:Thyroid Hormone Receptors beta / Q000032:analysis / Q000235:genetics; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D002364:Caseins; D004044:Dietary Proteins; D007529:Isoflavones; D020033:Protein Isoforms; D012333:RNA, Messenger; D011988:Receptors, Thyroid Hormone; D030262:Soybean Proteins; D037021:Thyroid Hormone Receptors alpha; D037042:Thyroid Hormone Receptors beta; D014284:Triiodothyronine; D013974:Thyroxine