Submitted to: Meeting Proceedings
Publication Type: Proceedings
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 DIETS CONTAINING SOY PROTEIN ISOLATE (SPI) OR ISOFLAVONES ON GROWTH, PLASMA IGF1, CYP2C11 AND CYP4A1 IN RAT LIVER AT WEANING. 2003. CD-ROM. Prague, Czech Republic. 13th International Symposium on Cytochromes P450 Biochemistry and Biophysics. 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 appear to be associated with both the soy protein component itself and to phytochemicals bound to SPI+ such as the isoflavones genistein and daidzein. N = 8-10 male or female pups were weaned onto pelleted, semi-purifed diets containing either casein (CAS) or SPI+,beginning on post-natal d. 15 until sacrifice at post-natal d. 34. Other groups were fed SPI stripped of chemicals by ethanol washes (SPI-) or CAS diets supplemented with genistein or daidzein at a level of 1 mg/kg, similar to that found in soy. Body weight gain and serum concentrations of the growth factor, insulin-like growth factor 1 (IGF1) were measured. 16'-hydroxylation of the male sex steroid testosterone was measured as a marker activity for the rat male specific liver enzyme CYP2C11, expression of which is known to be dependent on the male pattern of growth hormone secretion. In addition, expression of another liver enzyme CYP4A1 involved in fatty acid degradation was measured. Feeding SPI+ or SPI- significantly reduced body weight gain in both male and female pups. This was accompanied by reductions in plasma IGF1 indicating a suppression or delay in development of the growth hormone axis in these animals. CYP2C11 mRNA and protein expression and testosterone 16'-hydroxylase were also significantly inhibited in male pups fed SPI+ or SPI-. Since food intake appeared unaltered, the growth effects of the soy diets may be due to reduced dietary energy bioavailability or a direct effect of soy protein on growth hormone secretion. No such effects were observed in pups fed CAS + gesistein or daidzein. Lauric acid 12-hydroxylase; CYP4A1 protein and mRNA expression were significantly inhibited in pups of both sex fed SPI+ but not SPI- or isoflavones suggesting a possible inhibition of fatty acid metabolism by non-isoflavone phytochemicals bound to SPI.
Technical Abstract: N = 8-10 male or female pups were weaned from rat dams onto diets containing either casein (CAS) or soy protein isolate (SPI+); SPI stripped of isoflavones (SPI-) or CAS plus the soy isoflavones genistein or daidzein at 1 mg/kg until sacrifice at post-natal d 34. Feeding SPI+ or SPI- reduced body weight and IGF1 in male pups (p < 0.05) while the isoflavones had no effect suggesting a suppression/delay in development of the GH/IGF1 axis in SPI fed animals. CYP2C11 mRNA and apoprotein expression and testosterone 16'-hydroxylase were also inhibited in male pups fed SPI+ and SPI- (p < 0.05). CYP4A1 apoprotein was reduced by 80% in pups of both sex fed SPI+ (p < 0.05) but not in pups fed SPI- or isoflavones suggesting a possible inhibition of peroxisomal proliferation in response to non-isoflavone phytochemical components of SPI.