Background: Dietary soy protein compared with casein retards disease progression in a gender-specific manner in the pcy mouse. In this model of polycystic kidney disease (PKD), kidney insulin-like growth factor-I (IGF-I) levels are elevated. The present study examined the gender-specific effects of soy protein feeding on disease and IGF-I in Han:SPRD-cy rats.
Methods: Normal (+/+) and affected (cy/+) weanling male and female Han:SPRD-cy rats were given either casein- or soy protein-based diets for six weeks. Renal size, water content, cyst size and IGF-I, serum creatinine, urea and IGF-I, and creatinine clearance were determined.
Results: Soy protein-fed cy/+ animals had lower kidney weight, water content and cyst size, lower serum urea and creatinine, and higher creatinine clearance. In cy/+ females, dietary soy protein resulted in normalized serum creatinine and creatinine clearance. Kidney IGF-I levels (ng/kidney) were 32 to 76% higher in cy/+ compared with +/+ groups (P < 0.001). Soy protein feeding resulted in lower kidney IGF-I in cy/+ males (1123 vs. 1496 ng/kidney, P < 0.001) and cy/+ females (816 vs. 943 ng/kidney, P < 0.05). In males, soy protein feeding resulted in lower serum IGF-I concentrations in +/+ (1439 vs. 1708 ng/mL, P < 0.05) and in cy/+ (1483 vs. 2073 ng/mL, P < 0.001) animals.
Conclusions: Dietary soy protein compared with casein delays the progression of disease in male and female Han:SPRD-cy rats. Overall, IGF-I was lower in +/+ animals, in females, and in animals consuming the soy protein diet, supporting a role for IGF-I in the pathogenesis of disease in the Han:SPRD-cy rat and an ameliorating role for dietary soy protein.