Activation of the renin-angiotensin system in anti-glomerular basement membrane antibody-induced glomerulonephritis

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

An essential role of angiotensin II receptor type 1a in recipient kidney, not in transplanted peripheral blood leukocytes, in progressive immune-mediated renal injury

Despite an intensive effort of elucidating the pathogenic role of angiotensin II (AII) in immune-mediated renal injury, the precise mechanisms are poorly understood. In the present study, we examined the site of AII action, peripheral blood leukocytes or resident renal cells, in immune-mediated renal injury using AII type 1a receptor (AT1a)-deficient homozygous (AT1a -/-) mice and wild-type (AT1a +/+) mice. The AT1a -/- mice showed delayed-type hypersensitivity similar to that of the AT1a +/+ mice, suggesting that the lack of AT1a does not impair a Th1-type cellular immune response of peripheral blood leukocytes involved in immune-mediated renal injury. We then generated the radiation bone marrow chimera mice, WA and AW, which have transplanted peripheral blood leukocytes from the AT1a +/+ and AT1a -/- mice into the AT1a -/- and AT1a +/+ mice, respectively. As controls, WW and AA, the AT1a +/+ and AT1a -/- mice given bone marrow cells from the AT1a +/+ and AT1a -/- mice, respectively, were generated. Seven days after induction of antiglomerular basement membrane nephritis, glomerulosclerosis observed in the WW mice was markedly ameliorated in the WA mice, but not in the AW mice. In addition, the recruitment of monocytes/macrophages and the expressions of monocyte chemoattractant protein-1 and intercellular adhesion molecule-1 in the glomeruli of the AW and WW mice was evident, but such significant phenotypes were not seen in the WA and AA mice, showing a marked amelioration of renal injury dependent on the host AT1a genotype. These results demonstrate an essential role of AT1a in intrinsic renal cells for progressive immune-mediated renal injury and indicate a beneficial effect of blocking the renin-angiotensin system in the treatment of such diseases.

Prevention of renal damage by angiotensin II blockade, accompanied by increased renal hepatocyte growth factor in experimental hypertensive rats

Hepatocyte growth factor (HGF) is a unique growth factor that has many protective functions against renal damage. Our previous study demonstrated that HGF stimulated the growth of endothelial and epithelial cells without the replication of mesangial cells. Moreover, angiotensin (Ang) II significantly decreased local HGF production in mesangial cells. Therefore, we examined the effects of Ang II blockade on renal HGF expression and renal damage in experimental hypertensive rats. An angiotensin-converting enzyme inhibitor (cilazapril; 10 mg. kg(-1). d(-1)), an Ang II type 1 receptor antagonist (E-4177; 30 mg. kg(-1). d(-1)), hydralazine (8 mg. kg(-1). d(-1)), and vehicle were administered to 16-week-old stroke-prone spontaneously hypertensive rats (SHR-SP) for 3 weeks. Renal damage was evaluated with a computer analysis system, and renal HGF mRNA was measured by Northern blot analysis. Blood pressure of SHR-SP was significantly decreased by all drug treatments compared with vehicle. Moreover, cilazapril, E-4177, and hydralazine significantly decreased the thickening and necrosis of blood vessels compared with vehicle. Similarly, degeneration and necrosis of glomeruli were also markedly improved by cilazapril and E-4177 (P<0.01). We next examined the effects of Ang II blockade on renal HGF expression in SHR-SP. Renal HGF mRNA was markedly decreased in SHR-SP compared with Wistar-Kyoto rats, although Ang II blockade by cilazapril and E-4177 but not hydralazine significantly increased renal HGF mRNA in SHR-SP. Ang II blockade significantly increased renal HGF (a protective growth factor for tubular epithelial cells); thus, we examined tubular histological appearance. Degeneration and necrosis of tubules were significantly improved by cilazapril and E-4177 treatment (P<0.01). In addition, cell infiltration into the glomeruli and hemorrhage were also significantly reduced in SHR-SP treated with cilazapril or E-4177. The present data demonstrated the prevention of renal damage by Ang II blockade in SHR-SP, which was accompanied by a significant increase in renal HGF mRNA. Given the strong mitogenic activity and antiapoptotic actions of HGF on endothelial and epithelial cells, we believe that increased local HGF production by the blockade of Ang II may improve renal function in hypertension.

Angiotensin II type I receptor antagonist suppresses proteinuria and glomerular lesions in experimental nephritis

Angiotensin-converting enzyme inhibitors exert a beneficial effect on nephritis. We investigated the effects of KD3-671, an angiotensin AT1 receptor antagonist (2-propyl-8-oxo-1-[(2'-(H-tetrazole-5-yl)biphenyl-4-yl)methyl]-4,5,6,7-t etrahydro-cycloheptimidazole), on anti-glomerular basement membrane antibody-associated nephritis in rats. Untreated nephritic rats had massive proteinuria, glomerular lesions including crescent formation, a significant augmentation of proliferating cell nuclear antigen-positive cells, alpha-smooth muscle actin-positive cells, and the increase in deposition of proteoglycan, fibronectin and desmin in the glomeruli. Administration of KD3-671 to nephritic rats prevented the development of intense proteinuria, glomerular alterations and the increase in plasma urea nitrogen. KD3-671 suppressed the deposition of matrix protein and the expression of alpha-smooth muscle actin and desmin in the nephritic glomeruli. Captopril, an angiotensin-converting enzyme inhibitor, suppressed urinary protein excretion and the expression of desmin in the nephritic glomeruli, but not other parameters. These results suggest that KD3-671 may be a useful medicine against glomerulonephritis and glomerulosclerosis.

Angiotensin II plays a pathogenic role in immune-mediated renal injury in mice

Several lines of evidence show the importance of angiotensin II (AII) in renal injuries, especially when hemodynamic abnormalities are involved. To elucidate the role of AII in immune-mediated renal injury, we studied anti-glomerular basement membrane (GBM) nephritis in AII type 1a receptor (AT1a)-deficient homozygous (AT1a-/-) and wild-type (AT1a+/+) mice. A transient activation of the renin-angiotensin system (RAS) was observed in both groups of mice at around day 1. A renal expression of monocyte chemoattractant protein-1 (MCP-1) was transiently induced at six hours in both groups, which was then downregulated at day 1. In the AT1a+/+ mice, after RAS activation, the glomerular expression of MCP-1 was exacerbated at days 7 and 14. Thereafter, severe proteinuria developed, and the renal expressions of transforming growth factor-beta1 (TGF-beta1) and collagen type I increased, resulting in severe glomerulosclerosis and interstitial fibrosis. In contrast, glomerular expression of MCP-1, proteinuria, and tissue damage were markedly ameliorated in the AT1a-/- mice. Because this amelioration is likely due to the lack of AT1a, we can conclude that AII action, mediated by AT1a, plays a pathogenic role in anti-GBM nephritis, in which AII may contribute to the exacerbation of glomerular MCP-1 expression. These results suggest the involvement of AII in immune-mediated renal injuries.

Extrarenal resistance to atrial natriuretic peptide in rats with experimental nephrotic syndrome

Nephrotic syndrome is associated with resistance to the renal actions of atrial natriuretic peptide (ANP). We performed experiments in anesthetized, acutely nephrectomized rats 21-28 days after injection of adriamycin (7-8 mg/kg i.v.) or 9-14 days after injection of anti-Fx1A antiserum (5 ml/kg i.p.) (passive Heymann nephritis; PHN) to test whether extrarenal resistance also occurred. Proteinuria was significantly elevated in both models compared with controls before study. ANP infusion (1 microgram.kg-1.min-1) caused arterial pressure to decrease similarly in control rats, adriamycin-treated rats, and rats with PHN (by 8.2 +/- 1.0, 9.4 +/- 2.3, and 9.0 +/- 2.0%, respectively; all P < 0.05 vs. both baseline and vehicle-infused control rats). In control rats, hematocrit increased progressively to a maximal value 9.5 +/- 0.9% over baseline as a result of the infusion, an increase corresponding to a reduction in plasma volume of 16.1 +/- 0.9%. The ANP-induced increase in hematocrit was preserved in adriamycin-treated rats (9.2 +/- 1.3%) but was markedly blunted in rats with PHN (2.4 +/- 1.3%; P < 0.0001 vs. ANP infusion in control rats). ANP infusion increased plasma ANP levels to the same extent in the three groups, whereas plasma guanosine 3',5'-cyclic monophosphate was significantly lower in rats with PHN compared with both control and adriamycin-treated rats. Infusion of a subpressor dose of angiotensin II (ANG II, 2.5 ng.kg-1.min-1) fully restored the ANP-induced increase in hematocrit in rats with PHN. This study demonstrates that 1) the hemoconcentrating and hypotensive actions of ANP are preserved in adriamycin-treated rats, 2) the effect of ANP on hematocrit and fluid distribution is blunted in rats with PHN while its hypotensive action is preserved, and 3) low-level ANG II infusion normalizes the hemoconcentrating effect of exogenously infused ANP in rats with PHN. Thus deficient ANG II generation in rats with PHN, but not adriamycin nephrosis, may contribute to extrarenal ANP resistance.