Renoprotective and blood pressure-lowering effect of dietary soy protein via protein kinase C βII inhibition in a rat model of metabolic syndrome

Abstract

We studied whether substitution of soy protein for casein can improve insulin sensitivity, lower blood pressure (BP), and inhibit protein kinase C βII (PKCβII) activation in kidney in an acquired model of metabolic syndrome. Adult male rats were fed 4 different diets: (i) starch (60%) and casein (20%) (CCD), (ii) fructose (60%) and casein (20%) (FCD), (iii) fructose (60%) and soy protein (20%) (FSD), and (iv) starch (60%) and soy protein (20%) (CSD). Renal function parameters, BP, pressor mechanisms, PKCβII expression, oxidative stress, and renal histology were evaluated after 60 days. FCD rats displayed insulin resistance and significant changes in body weight, kidney weight, urine volume, plasma and urine electrolytes accompanied by significant changes in renal function parameters compared with CCD rats. Elevated BP, plasma angiotensin-converting enzyme (ACE) activity, renal oxidative stress, and reduced nitrite (NO) and kallikrein activity were observed. Western blot analysis revealed enhanced renal expression of membrane-associated PKCβII in the FCD group. Histology showed fatty infiltration and thickening of glomeruli while urinary protein profile revealed a 5-fold increase in albumin. Substitution of soy protein for casein improved insulin sensitivity, lowered BP and PKCβII activation and restored renal function. Antioxidant action, inhibitory effect on ACE and PKCβII activation, and increased availability of kinins and NO could be contributing mechanisms for the benefits of dietary soy protein.