Renin-angiotensin system blockade is renoprotective in immune complex-mediated glomerulonephritis

Abstract

Blockade of the renin-angiotensin system is renoprotective in a variety of chronic nephropathies, but the direct effect of such treatment in active, immune complex-mediated glomerulonephritis is unknown. This study investigated the short- and long-term effects of an angiotensin-converting enzyme inhibitor (enalapril) and an angiotensin II type 1 receptor blocker (losartan) in thymic stromal lymphopoietin transgenic (TSLPtg) mice, which develop mixed cryoglobulinemia and severe cryoglobulinemia-associated membranoproliferative glomerulonephritis. Enalapril and losartan each reduced hypertension, proteinuria, glomerular extracellular matrix deposition, and mesangial cell activation in TSLPtg mice. These renoprotective effects were not observed with hydralazine treatment, despite a similar antihypertensive effect. Treatment with enalapril or losartan also decreased renal plasminogen activator inhibitor-1 in TSLPtg mice, assessed by immunohistochemistry and quantitative real-time reverse transcriptase-PCR. None of the treatments affected immune complex deposition or macrophage infiltration. Overall, enalapril- and losartan-treated TSLPtg mice survived significantly longer than untreated TSLPtg mice. These studies demonstrate that angiotensin blockade may provide renoprotective benefits, independent of its BP-lowering effect, in the treatment of active immune complex-mediated glomerulonephritis.

Figure 1.

Representative photographs of glomeruli with hematoxylin and eosin (A through E), silver methenamine (F through J), and type IV collagen (K through O) immunohistochemistry staining of 8-wk groups of untreated WT (A, F, and K) and TSLPtg mice (B, G, and L), and hydralazine-treated (C, H, and M), enalapril-treated (D, I, and N), or losartan-treated (E, J, and O) TSLPtg mice. Magnification, ×400.

Figure 2.

Morphometric analysis of glomerular silver staining matrix and type IV collagen immunohistochemistry staining in untreated and hydralazine-, enalapril-, or losartan-treated WT and TSLPtg mice of female 4- and 8-wk and male 12- and 24-wk groups. Data are means ± SEM (n = 4 to 6 in each group). ***P < 0.001, **P < 0.01, *P < 0.05 versus matched untreated TSLPtg control.

Figure 3.

Kidney PAI-1 mRNA expression was reduced by enalapril and losartan treatment as assessed by quantitative real-time RT-PCR. The fold change of the expression level of PAI-1 gene in TSLPtg mice compared with WT mice was normalized to the endogenous housekeeping gene glyceraldehyde-3-phosphate dehydrogenase. Data are fold change (means ± SEM) of PAI-1 mRNA expression relative to WT control (n = 4 in WT control and n = 6 in untreated and treated TSLPtg groups). ⁺⁺P < 0.01, ⁺P < 0.05 versus matched WT control; *P < 0.05 versus matched untreated TSLPtg control.

Figure 4.

Representative photographs of glomerular PAI-1 immunohistochemistry staining of female 8-wk groups (A through D) and male 24-wk groups (E through H) of untreated WT (A and E), untreated TSLPtg (B and F), and enalapril-treated (C and G) and losartan-treated (D and H) TSLPtg mice. Magnification, ×400.

Figure 5.

Morphometric measurements of glomerular PAI-1 protein expression of female 8-wk groups and male 24-wk groups. Untreated TSLPtg control mice have markedly increased glomerular PAI-1 protein expression in both 8-wk females and 24-wk males compared with WT mice of the same age. Enalapril and losartan treatment decreased glomerular PAI-1 expression in TSLPtg mice. Data are means ± SEM (n = 4 in WT control, n = 5 in untreated and treated TSLPtg groups). ⁺⁺⁺P < 0.001, ⁺⁺P < 0.01 versus WT control; **P < 0.01 versus untreated TSLPtg control.

Figure 6.

Kidney immunofluorescence study of untreated and hydralazine-, enalapril-, or losartan-treated TSLPtg mice. Photos are representative glomerular immunofluorescence staining of deposited IgG (A through D) and complement C3 (E through H) of female 8-wk groups of untreated TSLPtg mice (A and E) and hydralazine-treated (B and F), enalapril-treated (C and G), and losartan-treated (D and H) TSLPtg mice. Magnification, ×400.

Figure 7.

(A and B) Proteinuria of 4- and 8-wk females of untreated WT and TSLPtg mice and hydralazine-, enalapril-, or losartan-treated TSLPtg mice (A), and 24-wk males of untreated WT and TSLPtg mice and enalapril- or losartan-treated TSLPtg mice (B). Proteinuria was measured as urine albumin (μg)-creatinine (mg) ratio. Untreated TSLPtg mice have marked increased urine albumin excretion compared with WT mice. The proteinuria level of hydralazine-treated TSLPtg mice is similar to that of untreated TSLPtg mice. Proteinuria was significantly decreased in enalapril- or losartan-treated TSLPtg mice. Data are means ± SEM (n = 4 to 6 per group). *P < 0.05 versus matched untreated TSLPtg control; ⁺⁺P < 0.01 versus WT control.

Figure 8.

Time course of systolic BP in untreated and hydralazine-, enalapril- or losartan-treated wild type and TSLP transgenic mice. BP of each mouse at each time point is the mean of 6 to 10 measurements. Every group had 4 to 6 mice. Data are mean ± SEM (mmHg). ***P < 0.001; **P < 0.01; *P < 0.05 hydralazine-, enalapril- or losartan-treated TSLPtg mice versus matched untreated TSLPtg control.

Figure 9.

Survival curves of 24-wk male TSLPtg and WT mouse groups. At the start point, all groups had 12 male mice. Treatment groups started enalapril or losartan treatment at 3 wk of age and continued for 24 wk. Seven of 12 untreated TSLPtg mice died in this duration, whereas one of 12 enalapril-treated TSLPtg mice and two of 12 losartan-treated TSLPtg mice died in this duration, suggesting enalapril and losartan treatment markedly improved survival in TSLPtg mice. They did not show an impact on survival of WT mice in this time frame.

Figure 10.

Representative lung sections with hematoxylin and eosin staining of 8-wk female groups of untreated WT and TSLPtg mice, and hydralazine-, enalapril-, or losartan-treated TSLPtg mice. Magnification, ×100.