Attenuating Effect Of Soy Protein As Compared With Casein On Glomerular Injury In Spontaneous Hypercholesterolemic Male Imai Rats

Soy protein has hypocholesterolemic and oestrogenic properties. Because the renoprotective effect of both lipid-lowering agents and oestrogen has been reported, we investigated whether soy protein has an ability to attenuate glomerular injury in male Imai rats in which hypercholesterolemia, focal and segmental glomerulosclerosis (FSGS) and renal insufficiency occur spontaneously. Twenty male Imai rats were randomly divided into two groups and fed diets containing 20.0 g/100 g of either casein or soy protein. Each group was fed freely one of the respective test diets from when they were 8-26 weeks of age. Bodyweight, urinary protein, serum constituents and systolic blood pressure was investigated every 4 or 8 weeks from when rats were 10 weeks through to 26 weeks of age. At 26 weeks of age, rats were studied morphologically. Soy protein-fed animals consumed larger amounts of diet and showed higher urinary urea excretion and a more rapid weight gain than the control casein diet-fed animals. No significant differences were seen in blood pressure between the two groups. The soy protein diet did not influence absolute kidney or heart weight, but significantly reduced those organs to bodyweight ratios. Soy protein diet resulted in less proteinuria, less hyperlipidemia, less hypoalbuminemia, less renal functional impairment, less glomerular hypertrophy, and less renal histological damage as compared with the control casein diet. The soy protein diet tended to affect serum sex-hormone levels with a trend toward lower levels of both testosterone and estradiol. The present study showed a beneficial effect of soy protein diet on glomerular disease in a spontaneous FSGS model, although the mechanisms remain to be determined.