Effects of combination PPARγ agonist and angiotensin receptor blocker on glomerulosclerosis

Abstract

We previously observed that high-dose angiotensin receptor blocker (ARB) can induce regression of existing glomerulosclerosis. We also found that proliferator-activated recepto-γ (PPARγ) agonist can attenuate glomerulosclerosis in a nondiabetic model of kidney disease, with specific protection of podocytes. We now assessed effects of combination therapy with ARB and pioglitazone on established glomerulosclerosis. Sprague-Dawley male rats underwent 5/6 nephrectomy (5/6 Nx) at week 0 and renal biopsy at week 8. Rats were randomized to groups with equal starting moderate glomerulosclerosis, and treated with ARB, PPARγ agonist (pioglitazone), combination or vehicle from weeks 8 to 12. Body weight, systolic blood pressure (SBP), and urinary protein (UP) were measured at intervals. In rats with established sclerosis, SBP, UP, and GS were equal in all groups at week 8 before treatment by study design. Untreated control rats had hypertension, decreased GFR, and progressive proteinuria and glomerulosclerosis at week 12. Only combination therapy significantly ameliorated hypertension and proteinuria. ARB alone or pioglitazone alone had only numerically lower SBP and UP than vehicle at week 12. Both pioglitazone alone and combination had significantly less decline in GFR than vehicle. Combination-induced regression of glomerulosclerosis in more rats from weeks 8 to 12 than ARB or pioglitazone alone. In parallel, combination treatment reduced plasminogen activator inhibitor-1 expression and macrophage infiltration, and preserved podocytes compared with vehicle. These results were linked to increased AT2 receptor and Mas1 mRNA in the combination group. PPARγ agonists in combination with ARB augment regression of glomerulosclerosis, with downregulation of injurious RAAS components vs PPARγ alone, with increased anti-fibrotic/healing RAAS components, enhanced podocyte preservation, and decreased inflammation and profibrotic mechanisms.

Figure 1

Combination therapy decreased SBP and proteinuria more than monotherapy. (a) Only combination therapy significantly decreased SBP. (b) Combination therapy, but not ARB or Pio alone, prevented increase of proteinuria from weeks 8 to 12. ARB, angiotensin receptor blocker; SBP, systolic blood pressure.

Figure 2

Both PPARγ agonist and combination treatment protected renal function. Serum creatinine (a) increased and Ccr (b) decreased from weeks 8 to 12 in all groups. Pio preserved Ccr, but only combination treatment prevented both the increase of Scr and decrease of Ccr. Ccr, creatinine clearance.

Figure 3

Combination therapy prevented the progression of glomerulosclerosis. Compared with the vehicle 5/6 Nx group, PPARγ agonist (Pio) and ARB alone ameliorated glomerulosclerosis (a; PAS staining, ˟200), but combination therapy markedly reduced the extent of glomerulosclerosis at week 12. (b) Regression, defined as reduction of sclerosis from biopsy in the same rat (Bx, circles) to autopsy (Ax, squares), occurred in 5/7 rats in the Combination group, compared with 2/6 in ARB and 1/7 each in vehicle and PPARγ groups. (c) ARB, angiotensin receptor blocker; PPARγ, proliferator-activated receptor-γ.

Figure 4

Combination therapy reduced PAI-1 expression. Both ARB and PPARγ agonist (Pio) alone showed a trend to reduce kidney cortical PAI-1 protein expression, while combination therapy showed significantly less PAI-1 expression when compared with vehicle. ARB, angiotensin receptor blocker; PPARγ, proliferator-activated receptor-γ.

Figure 5

Combination therapy reduced inflammation and preserved differentiated podocytes. (a) Macrophages, stained by ED1, were increased in glomeruli of vehicle at week 12. Treatment with PPARγ agonist did not significantly decrease infiltrating glomerular macrophages. There was a remarkable decrease in macrophage infiltration in the combination group. (b) At week 8, before treatment, WT1-positive cell density, a marker of differentiated podocytes, was similarly decreased in fall our groups compared with normal kidney. At week 12, vehicle, ARB and Pio groups had further reduced WT1 density (*P<0.05 compared with week 8), while combination therapy preserved WT1-positive cell. ARB, angiotensin receptor blocker; PPARγ, proliferator-activated receptor-γ.

Figure 6

Interactions of PPARγ agonists and ARB. (a) PPARγ agonist and combination treatment-activated PPARγ in the kidney, while ARB alone did not significantly increase PPARγ activity. (b) PPARγ agonists induced renin, but reduced ACE mRNA expressions. Combination treatment significantly increased AT₂R and Mas1 mRNA expressions, while either therapy alone had no effect compared with vehicle. ACE, angiotensin I converting enzyme; ARB, angiotensin receptor blocker; PPARγ, proliferator-activated receptor γ.