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ARS Home » Southeast Area » Little Rock, Arkansas » Arkansas Children's Nutrition Center » Research » Publications at this Location » Publication #149279
Title: EFFECTS OF WEANING TO DIETS CONTAINING SOY PROTEIN ISOLATE (SPI) OR ISOFLAVONES ON GROWTH, PLASMA IGF1 AND EXPRESSION OF CYP2C11 AND CYP4A1 IN RAT LIVER

Author
item RONIS, MARTIN - UAMS
item REEVES, MISTY - ACNC
item HARDY, HOLLY - ACNC
item BADEAUX, JAMIE - ACNC
item DAHL, CHRIS - ACNC
item HARRISON, DAVID - ACNC
item HALEY, RANI - ACNC
item HUMPHREY, LANDON - ACNC
item FERGUSON, MATTHEW - ACNC
item BADGER, THOMAS - UAMS

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/15/2003
Publication Date: 6/30/2003
Citation: RONIS, M.J., REEVES, M.N., HARDY, H., BADEAUX, J., DAHL, C., HARRISON, D., HALEY, R., HUMPHREY, L., FERGUSON, M., BADGER, T.M. EFFECTS OF WEANING TO DIETS CONTAINING SOY PROTEIN ISOLATE (SPI) OR ISOFLAVONES ON GROWTH, PLASMA IGF1 AND EXPRESSION OF CYP2C11 AND CYP4A1 IN RAT LIVER. Chemicke Listy. 2003. v. 97. p. S109-S110. Abstract No. MP62.

Interpretive Summary: Soy protein isolate (SPI+) is fed to over 1 million children each year in the U.S. as part of soy-infant formula. Soy has been shown to have a number of health beneficial effects including reductions in cholesterol and has been suggested to increase lean body mass. The health effects have appear to be associated with both the soy protein component itself and to isoflavone chemicals bound to SPI+. In the current study we fed groups of pregnant female Sprague-Dawley rats diets made with casein as the sole protein source throughout pregnancy and lactation. The offspring were weaned onto diets made with either casein (CAS) or SPI+ at age 21 days and sacrificed at age 34 days. Other groups were fed SPI stripped of phytochemicals (SPI-) or CAS diets supplemented with the soy-isoflavones genistein or daidzein. All rats grew well through the study, but rats fed SPI diets had lower body weight gains and reduced plasma insulin-like growth factor (IGF-1). Since IGF-1 is regulated by growth hormone (GH), SPI may regulate the GH system. Male and female rats have different patterns of GH production, and the pattern of GH is important in regulating a protein called CYP2C11. CYP2C11 was found to be lower in SPI-fed rats. In addition, these studies suggested that the protein and not the isoflavones were responsible for these effects. A protein involved in fatty acid degradation, CYP4A1, was reduced in rats fed SPI diets with isoflavones, but not in rats fed SPI diets without isoflavones. These results suggest that soy proteins and/or their phytochemicals can regulate important hormones and proteins that may be serve significant roles in disease prevention. Future studies will explore these effects and will determine the factors in soy responsible and the mechanisms underlying these effects.

Technical Abstract: Soy protein isolate (SPI+) is fed to over 1 million children each year in the U.S. as part of soy-infant formula. Soy has been shown to have a number of health beneficial effects including reductions in cholesterol (1) and has been suggested to increase lean body mass (2,3). The health effects have appear to be associated with both the soy protein component itself and to isoflavone phytoestrogens bound to SPI+ (1). In the current study we fed groups of time-impregnated female Sprague-Dawley rats pelleted AIN-93G diets with casein as the sole protein source ad libitum from gestational day 4 until their pups weaned at post-natal day 21. Litters were culled to 5 male and 5 female pups and N = 8-10 male or female pups were weaned onto amino acid matched, pelleted, diets containing either casein (CAS) or SPI+, ad libitum beginning on post-natal day 15 until sacrifice at post-natal day 34. Other groups were fed SPI stripped of phytochemicals by ethanol washes (SPI-) or CAS diets supplemented with the soy-isoflavones genistein or daidzein at a level of 1 mg/kg Body weight gain and serum IGF-1 concentrations were measured. CYP2C11-dependent testosterone 16'-hydroxylase was measured in liver microsomes from male pups, CYP2C11 apoprotein was quantified by Western blot and CYP2C11 mRNA by real time RT-PCR. In addition, CYP4A1 apoprotein and mRNA were measured in male and female pups and microsomal CYP4A1-dependent lauric acid 12-hydroxylase was assessed. Offspring fed SPI+ or SPI- had lower body weight gains in both male and female pups (p < 0.05). This was accompanied by reductions in plasma IGF-1 indicating a suppression or delay in development of the GH/IGF1 axis in these animals. CYP2C11 mRNA and apoprotein expression and testosterone 16'-hydroxylase were also inhibited in male pups fed SPI+ or SPI- (p < 0.05). Since food intake was not measured it is unclear if this effect was due to reduced intake, reduced dietary energy availability or a direct effect of SPI on GH secretion. No such effects were observed in pups fed CAS + gesistein or daidzein. Lauric acid 12-hydroxylase; CYP4A1 apoprotein and mRNA expression were inhibited (p < 0.05) in pups of both sex fed SPI+ but not SPI- or isoflavones suggesting a possible inhibition of peroxisomal proliferation response by non-isoflavone phytochemical components bound to SPI.