Add-on aliskiren elicits stronger renoprotection than high-dose valsartan in type 2 diabetic KKAy mice that do not respond to low-dose valsartan

Abstract

We hypothesized that aliskiren provides renoprotection in diabetic animals that did not receive sufficient renoprotection by AT1-receptor antagonist treatment. Type 2 diabetic KKAy mice were treated with group 1: vehicle or group 2: valsartan (15 mg/kg per day) from 12 to 16 weeks of age. The mice were subsequently divided into 4 groups and treated with the following combinations of drugs for another 6 weeks: 1: group 1 kept receiving vehicle, 2: group 2 continuously received 15 mg/kg per day of valsartan (Val-Val15), 3: group 2 received 50 mg/kg per day of valsartan (Val-Val50), 4: group 2 continuously received 15 mg/kg per day of valsartan with 25 mg/kg per day of aliskiren (Val-Val+Ali). Aliskiren exerted significant anti-albuminuric effects, whereas valsartan failed to ameliorate the albuminuria in the first four weeks. Surprisingly, the increasing dosage of valsartan in the Val-Val50 group showed non-significant tendencies to attenuate the albuminuria compared with vehicle infusion. Val-Val+Ali significantly suppressed the development of albuminuria and podocyte injury. Val-Val50 and Val-Val+Ali showed similar suppression of angiotensin II contents in the kidney of KKAy mice. In conclusion, the anti-albuminuric effect that was observed in the type 2 diabetic mice showing no anti-albuminuric effect by valsartan can be attributed to the add-on aliskiren.

Fig. 1

Renal angiotensin II (AngII) contents. The vehicle-treated mice show a greater AngII content in the kidney than C57BL mice. Val-Val15 tends to suppress the renal AngII level in type 2 diabetic KKAy mice, but the effect is not significant. Both Val-Val50 and Val-Val+Ali normalize the accumulation of AngII in the kidney. *P < 0.05 vs. C57BL mice, #P < 0.05 vs. vehicle group. Val-Val15: 15 mg/kg per day of valsartan for 10 weeks, Val-Val50: treatment with 15 mg/kg per day of valsartan for the first 4 weeks and treatment with 50 mg/kg per day of valsartan from weeks 4 to 10, Val-Val+Ali: treatment with 15 mg/kg per day of valsartan for 10 weeks and additional treatment with 25 mg/kg per day of aliskiren from weeks 4 to 10.

Fig. 2

Urinary albumin excretion/creatinine ratios (UACRs). The vehicle-treated mice show more urinary albumin excretion than C57BL mice. Both low (Val-Val15) and high (Val-Val50) dosages of valsartan do not attenuate the albuminuria. In contrast, combined treatment with aliskiren and a low dosage of valsartan (Val-Val+Ali) shows dramatic inhibition of albuminuria. Aliskiren treatment started from week 0 (Ali-mono and Ali-Ali+Val) showed strong anti-albuminuric effects and maintained albuminuria at normal value throughout the experimental period. *P < 0.05 vs. C57BL mice, #P < 0.05 vs. vehicle group, n.s.: not significant. Val-Val15: 15 mg/kg per day of valsartan for 10 weeks, Val-Val50: treatment with 15 mg/kg per day of valsartan for the first 4 weeks and treatment with 50 mg/kg per day of valsartan from weeks 4 to 10, Val-Val+Ali: treatment with 15 mg/kg per day of valsartan for 10 weeks and additional treatment with 25 mg/kg per day of aliskiren from weeks 4 to 10, Ali-mono: 25 mg/kg per day of aliskiren for 10 weeks, Ali-Ali+Val: treatment with 25 mg/kg per day of aliskiren for 10 weeks and additional treatment with 15 mg/kg per day of valsartan from weeks 4 to 10.

Fig. 3

Desmin immunostaining. Podocyte injury revealed by desmin (dark staining) is increased in the vehicle-treated mice compared with C57BL mice. All the drug treatment groups, including Val-Val15, Val-Val50, and Val-Val+Ali, show significant decreases in the desmin-positive areas in the glomeruli. Val-Val+Ali tends to show stronger inhibition of the positive areas than Val-Val15 and Val-Val50. *P < 0.05 vs. C57BL mice, #P < 0.05 vs. vehicle group. Val-Val15: 15 mg/kg per day of valsartan for 10 weeks, Val-Val50: treatment with 15 mg/kg per day of valsartan for the first 4 weeks and treatment with 50 mg/kg per day of valsartan from weeks 4 to 10, Val-Val+Ali: treatment with 15 mg/kg per day of valsartan for 10 weeks and additional treatment with 25 mg/kg per day of aliskiren from weeks 4 to 10.

Fig. 4

Senescence-associated β galactosidase (SABG) staining and renal p21 mRNA expression. The SABG-positive areas (dark staining) are significantly greater in the tubular cells in the vehicle-treated mice than in C57BL mice. Val-Val50 show a comparable reduction in the SABG-positive area to the vehicle group. The SABG-positive areas are almost abolished in Val-Val+Ali. The p21 mRNA expression is significantly increased in the kidney of the vehicle group. The increase in p21 mRNA expression is not inhibited by Val-Val15 and Val-Val50. On the other hand, Val-Val+Ali shows almost normalized p21 mRNA expression in the kidney. *P < 0.05 vs. C57BL mice, #P < 0.05 vs. vehicle group. Val-Val15: 15 mg/kg per day of valsartan for 10 weeks, Val-Val50: treatment with 15 mg/kg per day of valsartan for the first 4 weeks and treatment with 50 mg/kg per day of valsartan from weeks 4 to 10, Val-Val+Ali: treatment with 15 mg/kg per day of valsartan for 10 weeks and additional treatment with 25 mg/kg per day of aliskiren from weeks 4 to 10.