Renoprotective effect of contemporary blocking of angiotensin II and endothelin-1 in rats with membranous nephropathy

BACKGROUND

We previously showed that chronic administration of an angiotensin converting enzyme (ACE) inhibitor to rats with passive Heymann nephritis (PHN), a model of membranous nephropathy with proteinuria and increased renal synthesis of endothelin-1 (ET-1), reduces urinary proteins and partially limits the exaggerated ET-1 renal synthesis. Here we compared the effect of an ETA receptor antagonist and an ACE-inhibitor given as single therapies with a combination of the two drugs in uninephrectomized PHN rats.

METHODS

PHN was induced with a single i.v. injection of rabbit anti-Fx1A antibody in 40 male Sprague Dawley rats. To accelerate the onset of renal damage rats underwent uninephrectomy seven days later and were subsequently treated until eight months with the ETA receptor antagonist LU-135252 (50 mg/kg b.i.d. p.o.) or the ACE-inhibitor trandolapril (1 mg/kg in the drinking water) or the combination of the two drugs.

RESULTS

Either LU-135252 or trandolapril given alone prevented the increase in systolic blood pressure (SBP). Combined therapy was even more effective than single drugs. While LU-135252 and trandolapril reduced proteinuria by 23 to 25%, the drug combination resulted in 45% lowering of urinary proteins. Serum creatinine was significantly decreased by the combination, but not by the single drugs. Glomerulosclerosis and tubulointerstitial damage were more reduced by combined therapy than by LU-135252 or trandolapril alone.

CONCLUSIONS

These data suggest that contemporary blocking angiotensin II (Ang II) and ET-1 in an accelerated model of PHN had an additive renoprotective effect than single blocking Ang II or ET-1 and would represent a therapeutic advantage for renal disease patients who do not completely respond to ACE inhibitors.

Progressive glomerular injury in the MWF rat is predicted by inborn nephron deficit

It has been suggested that a reduced number of nephrons may predispose to systemic hypertension and glomerular injury. Compensatory hemodynamic changes, due to a low number of glomeruli, might be responsible for glomerular functional and structural changes. It is difficult to evaluate this hypothesis in humans because of limitations in estimating the number of nephrons in the living kidney. The aim of the present study was to estimate nephron number, single glomerular hemodynamics, and glomerular volume in male and female MWF rats, a strain that spontaneously develops systemic hypertension, proteinuria, and glomerulosclerosis. Male and female Wistar rats were used as controls. At 12 to 14 wk of age, male MWF rats developed proteinuria, whereas female MWF and Wistar rats showed normal urinary protein excretion rate. Glomerular number was significantly reduced in male and female MWF rats (13,690+/-1,489 and 12,855+/-1,781 gl/ kidney, respectively) compared with Wistar rats (26,955+/-2,171 and 27,166+/-1,754 gl/kidney, respectively). The mean number of nephrons per unit of body weight was also lower in MWF males (88+/-10) compared with MWF females (139+/-20) and compared with male and female Wistar animals (142+/-14 and 221+/-22 gl/g body wt). Whole-kidney hemodynamic parameters and the number of nephrons were used to calculate single-nephron filtration rate and plasma flow. Both measures were markedly elevated in male MWF rats relative to values obtained in the other three groups. Similarly, glomerular volume was significantly greater in MWF males than in other animals. These results suggest that an inborn deficit of nephrons may be responsible for spontaneous development of later-in-life hypertension and renal dysfunction. The data also indicate the need to investigate the role of this potential pathogenetic factor for human hypertension and kidney disease in humans.

The renoprotective properties of angiotensin-converting enzyme inhibitors in a chronic model of membranous nephropathy are solely due to the inhibition of angiotensin II: evidence based on comparative studies with a receptor antagonist

In several models of renal disease progression, angiotensin-converting enzyme (ACE) inhibitors reduced proteinuria and limited glomerulosclerosis, which suggested that reduction of renal angiotensin II (Ang II) activity is crucial for the preservation of glomerular structure and function. However, it cannot be ruled out that other hormonal systems, including inhibition of the bradykinin breakdown, also play a role. We compared the effects of chronic treatment with the ACE inhibitor lisinopril with those of a specific Ang II receptor antagonist, L-158,809, on proteinuria and renal injury in passive Heymann nephritis (PHN), a model of immune renal disease that closely resembles human membranous nephropathy, with long-lasting proteinuria followed by tubulointerstitial damage and glomerulosclerosis. Passive Heymann nephritis was induced with 0.5 mL/100 g of rabbit anti-Fx1A antibody in 24 male Sprague-Dawley rats. The animals were divided into three groups of eight rats each, and were given the following in the drinking water on a daily basis: lisinopril (40 mg/L), L-158,809 (50 mg/L), or no therapy. Treatment started at day 7 (proteinuria was already present) and lasted 12 months. Eight normal rats were used as controls. Untreated PHN rats developed hypertension, while rats with PHN given lisinopril or L-158,809 all had systolic blood pressure values even lower than those of normal rats. Urinary protein excretion progressively increased with time in untreated PHN rats, who developed tubulointerstitial damage and glomerulosclerosis. Both lisinopril and L-158,809 exhibited a potent antiproteinuric effect and preserved glomerular and tubular structural integrity at a similar extent. Renal gene expression of transforming growth factor-beta and extracellular matrix proteins was also effectively reduced by the two treatments. These results indicate that ACE inhibitors and Ang II receptor antagonists are equally effective in preventing renal injury in PHN and suggest that the renoprotective effects of ACE inhibitors in this model are solely due to inhibition of Ang II.