The effects and mechanisms of benazepril and losartan on glomerular podocyte autophagy in aged spontaneously hypertensive rats

Abstract

Objective To examine the effects of benazepril and losartan on glomerular podocyte autophagy in aged spontaneously hypertensive rats (SHRs) and investigate the underlying mechanisms of renal-protective effects of angiotensin-converting enzyme inhibitors (ACEI)/angiotensin receptor blockers (ARB). Methods Wistar-Kyoto rats (WKYs) were used as the normal control (NORM) group (2 ml physiological saline per day). SHRs were randomly divided into 4 groups: the CTRL group (2 ml physiological saline per day), the ACEI group (10 mg·kg-1·d-1), the ARB group (30 mg·kg-1·d-1) and the combined group (10 mg·kg-1·d-1 benazepril and 30 mg·kg-1·d-1), with six 18-month-old male rats in each group. The experiments were conducted during a 4-month period. Blood pressure was monitored regularly. At the end of the experiments, we measured the levels of urine protein, urine creatinine, serum creatinine (SCR), blood urea nitrogen (BUN), and serum and renal cortex angiotensin Ⅱ (AngII). Ultrastructural changes in the kidney were examined under light and transmission electron microscopy. The expressions of nephrin, LC3BII, Atg5 and p62 in the glomerulus were analyzed by Western blot analysis. Results After treatment, the blood pressure and the urine albumin/creatinine ratio of the four SHR groups were still significantly higher than those of the NORM group, but the blood pressure and the urine albumin/creatinine ratio of the ARB group and the combined group were significantly lower than those of the CTRL group (all P 0.05); The level of serum AngII of the combined group was significantly higher than that of the CTRL group 〔CTRL (0.08±0.00) μg/L, Combined (0.12±0.01) μg/L, P<0.05〕; The levels of cortex AngII of the four SHR groups were significantly lower than those of the NORM group, while the level of cortex AngII of the ARB group was significantly higher than that of the CTRL group (all P<0.05); Renal ultrastructural examination revealed shrunken glomeruli, fused or effaced epithelial cell foot processes, and focal atrophy of renal tubules in the four SHR groups. These pathological changes were more serious in the CTRL group but less so in the combined group. There were significantly more autophagosomes in the NORM group and the combined group than in the CTRL group (P<0.05). Compared with the NORM group, the expressions of nephrin, LC3BII, Atg5 and p62 in the CTRL group were suppressed significantly (P<0.05). The expressions of nephrin, LC3BII and Atg5 in the ACEI group and the expressions of nephrin, LC3BII, Atg5 and p62 in the ARB group and the combined group were higher than in the CTRL group (P<0.05). Conclusions ACEI/ARB can decrease the autophagic activity of glomerular podocytes. The renal-protective effects of ACEI/ARB may be mediated by glomerular podocyte autophagy, which is induced by AngII. Key words: Hypertension; Podocytes; Autophagy; Angiotensin-converting enzyme inhibitor; Angiotensin receptor antagonist