Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: 2/15/2005
Publication Date: 3/4/2005
Citation: Ronis, M.J., Chen, Y., Badger, T.M. 2005. Effects of soy protein isolate (spi) and dietary isoflavones on cholesterol metabolism and transport in weanling rats. The FASEB Journal. 19(5):A997.
Interpretive Summary: The FDA granted a health claim for soy protein. The claim was based upon data that demonstrated a reduction of serum cholesterol in people and monkeys who consumed 25 g/day of soy protein. However, the mechanisms by which soy reduced the cholesterol have not been found. The results from the current study suggest that the mechanisms involve the transport and metabolism of cholesterol. The components of soy protein responsible for these effects are unknown and the topic of future research.
Technical Abstract: Consumption of soy products has been shown to effectively lower cholesterol in clinical trials and is the basis for the heart health campaign for soy approved by the FDA. However, the molecular mechanisms underlying this effect are unclear. In the current study, we fed rats AIN-93G diets made with casein (CAS) from gestational day 4 until weaning and then continued some pups on CAS or weaned other (N=8-10 males and females/group) onto AIN-93G diets where the protein source was soy protein isolate (SPI+), SPI stripped of phytochemiclas (SPI-) or CAS substituted with 200mg/kg of the soy isoflavones genistein or diadzein. On post natal day 34, livers were collected. Hepatic cholesterol 7-alpha-hydroxylase (CYP7A1) mRNA expression was assessed by real time RT-PCR. In addition, hepatic expression of mRNAs coding for the major cholesterol transporters ABCA1, ABCG5 and ABCG8 were accessed. Consumption of SPI+, SPI- and isoflavones all increased CYP7A1 mRNA expression in the liver 2-5-fold (p<0.05). However, while SPI+ consumption increased all three hepatic ABC transporter mRNAs (P<0.05); feeding SPI- or the purified isoflavones resulted in no increase. CYP7A1 and the ABC cholesterol/sterol transporters are known to be coordinately regulated via orphan nuclear receptors including LXR. SPI+ may contain phytochemicals and peptides in addition to isoflavones which are orally active orphan receptor agonist/antagonists resulting in hypocholesterolemic and anti-atherosclerotic properties.