Belinda J. Davis

Renoprotective effects of vasopeptidase inhibition in an experimental model of diabetic nephropathy

AimsAlthough ACE inhibitors slow progression of diabetic renal disease, the mortality and morbidity is still high. As other hormonal factors are involved, inhibition of vasopeptidases could further reduce progression. We studied dual inhibition of angiotensin converting enzyme and neutral endopeptidase in a model of progressive diabetic renal injury. The major endpoints were reductions in systemic blood pressure, albuminuria and renal structural injury.MethodsDiabetic spontaneously hypertensive rats were treated with the ACE inhibitor perindopril (mg·kg−1·day−1) or the vasopeptidase inhibitor omapatrilat at doses of 10 (oma10) and 40 (oma40) mg·kg−1·day−1 for 32 weeks. In vivo ACE and NEP inhibition was quantitated by in vitro autoradiography. Renal structural injury was assessed by measurement of the glomerulosclerotic (GS) index and tubulointerstitial area (TI). The expression of transforming growth factor β, β-inducible gene-h3 and nephrin were also quantitated.ResultsDespite a similar reduction in blood pressure by perindopril and oma10, greater attenuation of albuminuria was afforded by oma10, with a complete amelioration observed with oma40. Oma40 lead to a 33% reduction in renal NEP binding and this was associated with less albuminuria and prevention of GS, TI area and overexpression of TGFβ and βig-h3. Diabetes-associated reduction in nephrin expression was restored by both drugs.Conclusion/InterpretationThese findings suggest that other vasoactive mechanisms in addition to angiotensin II are important in the prevention of diabetic nephropathy, and that vasopeptidase inhibition might confer an advantage over blockade of the RAS alone in the treatment of diabetic renal disease.

Additive hypotensive and anti-albuminuric effects of angiotensin-converting enzyme inhibition and angiotensin receptor antagonism in diabetic spontaneously hypertensive rats.

Angiotensin II plays a pivotal role in the development of diabetic nephropathy, but it remains controversial as to the best approach to effectively block the actions of this hormone in the kidney. The aim of the present study was to explore the effects of long-term treatment (8 months) with a combination of an angiotensin type 1 (AT1) receptor antagonist, irbesartan (15 mg/kg per day), and an angiotensin-converting enzyme (ACE) inhibitor, captopril (100 mg/kg per day), in diabetic spontaneously hypertensive rats. Captopril treatment reduced blood pressure (163+/-3 mmHg versus diabetic 201+/-3 mmHg), but not albumin excretion rate (43.8x//1.3 mg/day versus diabetic 46.8x//1.4 mg/day). Irbesartan treatment was associated with a similar reduction in blood pressure (173+/-3 mmHg) to captopril, and albumin excretion rate was reduced (14x//1.5 mg/day). The combination of irbesartan and captopril induced further reductions in blood pressure (140+/-3 mmHg) and albumin excretion rates (4.0x//1.5 mg/day). Gene expression of transforming growth factor beta-1 was reduced by all treatments to a similar level as assessed by in situ hybridization. These results demonstrate the additive hypotensive and anti-albuminuric effects of an ACE inhibitor and an AT1 receptor, suggesting that combination therapy is an approach not only more effective at reducing blood pressure, but also at retarding the development of diabetic nephropathy.

Anti-atherosclerotic and renoprotective effects of combined angiotensin-converting enzyme and neutral endopeptidase inhibition in diabetic apolipoprotein E-knockout mice.

Objective To investigate the effects of the combined angiotensin-converting enzyme (ACE)/neutral endopeptidase (NEP) inhibitor omapatrilat on atherosclerosis and renal injury in a model of diabetes-associated accelerated atherosclerosis and renal injury. Design The study was performed using diabetic apolipoprotein E-knockout (apo E-KO) mice, a model combining hyperlipidemia and hyperglycemia, which leads to accelerated atherosclerosis and renal injury. Methods Diabetes was induced by the injection of streptozotocin in 6-week old apo E-KO mice. Diabetic animals received no treatment (n = 12) or treatment with the ACE/NEP inhibitor omapatrilat (30 mg/kg per day, via gavage, n = 12) or quinapril (10 mg/kg per day, in drinking water, n = 12) for 20 weeks. Non-diabetic apo E-KO mice (n = 12) served as controls. Results Omapatrilat reduced atherosclerosis and protected the mice from renal structural injury and albuminuria. The protective effects were associated with tissue inhibition of aortic and renal ACE and NEP as well as a significant reduction in blood pressure. Omapatrilat had similar anti-atherosclerotic effects compared with the ACE inhibitor quinapril in association with an almost complete inhibition of aortic ACE activity by both drugs. Omapatrilat conferred superior renoprotection in the diabetic apo E-KO mouse compared with quinapril in the context of greater renal ACE inhibition by omapatrilat than seen with quinapril, additional renal NEP inhibition and a modestly enhanced antihypertensive response. Conclusions These studies demonstrate the anti-atherosclerotic and renoprotective effects of omapatrilat in diabetic apo E-KO mice, a model of accelerated atherosclerosis and renal injury. These effects were observed in association with the local inhibition of ACE and NEP at the tissue level in the aorta and kidney. These results suggest that the anti-atherosclerotic effect conferred by omapatrilat treatment in the diabetic apo E-KO mouse is predominantly mediated by its capacity to inhibit local vascular ACE. By contrast, in the kidney, local renal ACE and NEP inhibition and the superior antihypertensive effect of omapatrilat all contribute to the renoprotective effect conferred by omapatrilat treatment in the diabetic apo E-KO mouse.

Combined inhibition of neutral endopeptidase with angiotensin converting enzyme or endothelin converting enzyme in experimental diabetes.

Objective The effects of combined inhibition of neutral endopeptidase (NEP) with either angiotensin-converting enzyme (ACE), or endothelin-converting enzyme (ECE) on blood pressure, urinary albumin excretion and heart weight were explored in experimental diabetes. Design Streptozotocin-induced diabetic Sprague–Dawley rats were treated with vehicle, the NEP/ACE inhibitor S 21402, the NEP/ECE inhibitor CGS 26303, the NEP inhibitor SCH 42495, the ACE inhibitor captopril or the endothelin receptor antagonist bosentan for 4 weeks. Methods Blood pressure was measured by tail-cuff method and radiotelemetry. Albuminuria, plasma renin activity and plasma atrial natriuretic peptide (ANP) were determined by radioimmunoassay. NEP binding was assessed by in vitro quantitative autoradiography. Metabolic and biochemistry parameters including food intake, 24-h urine volume, plasma glucose, glycated hemoglobin, glomerular filtration rate (GFR) and urinary sodium excretion were also determined. Results Mean blood pressure over the 4-week study period after commencement of treatment was reduced to a similar extent by a range of treatments including the ACE inhibitor, NEP/ACE inhibitor, endothelin receptor antagonist, NEP/ECE inhibitor, but not the NEP inhibitor, compared with vehicle-treated diabetic rats. Heart to body weight ratio in diabetic rats was only reduced by the NEP/ACE and the NEP/ECE inhibitor. Increased albuminuria in diabetic rats (1.1 ×/÷ 1.2 mg/day) was reduced by the NEP/ACE (0.6 ×/÷ 1.2 mg/day) and the NEP/ECE inhibitors (0.4 ×/÷ 1.2 mg/day). Renal NEP was reduced by the NEP/ACE inhibitor (35 ± 4%) or NEP/ECE inhibitor (38 ± 4%) as well as by the pure NEP inhibitor (27 ± 4%) compared with the untreated diabetic group. Other abnormal metabolic and biochemical parameters in diabetic rats were not influenced by any drug treatment. Conclusions Combined inhibition of NEP/ACE or NEP/ECE confers beneficial effects on blood pressure, albuminuria and heart to body weight ratio in experimental diabetes.