Effect of combining an ACE inhibitor and an angiotensin II receptor blocker on plasma and kidney tissue angiotensin II levels

TGF-β1 Induced by High Glucose is Controlled by Angiotensin-Converting Enzyme Inhibitor and Angiotensin II Receptor Blocker on Cultured Human Peritoneal Mesothelial Cells

Background

Loss of peritoneal function is a major complication associated with long-term peritoneal dialysis. Observed changes include loss and degeneration of the mesothelium, submesothelial thickening, alterations in the structure and number of blood vessels, and reduplication of the vascular basement membrane. Exposure to high glucose concentrations in peritoneal dialysis solutions is known to cause injury to cultured human peritoneal mesothelial cells (HPMC) as a result of overexpression of transforming growth factor beta 1 (TGF-β1). Previous studies have demonstrated that angiotensin II (AII) increases expression of TGF-β1 in a number of different cell types; although this has not been demonstrated in HPMC.

Objective

To clarify possible mechanisms involved in peritoneal fibrosis, we investigated whether HPMC expressed AII-forming pathway mRNA and whether increases in AII induced by high glucose contribute to the production of TGF-β1. We also examined the effects of the angiotensin-converting enzyme inhibitor (ACEI) perindoprilat and the AII receptor blocker (ARB) candesartan on expression of TGF-β1 and proliferation of HPMC.

Methods

Expression of mRNA for the AII-forming pathway and TGF-β1 in HPMC was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative RT-PCR. Levels of AII and TGF-β1 following 48 hours of incubation of the cells in a range of glucose concentrations were measured by enzyme immunoassay and enzyme linked immunosorbent assay respectively. The effect of glucose on cell proliferation was examined using the water-soluble tetrazolium salt WST-1 and [3H]-thymidine uptake. We also investigated the effect of ACEI and ARB on the expression of TGF-β1 and the proliferation of HPMC incubated at high glucose for 48 hours.

Results

AII-forming pathway mRNA was detected in HPMC, with expression of angiotensinogen, angiotensin-converting enzyme (ACE), AII type 1 receptor, and TGF-β1 mRNA increasing following exposure to glucose according to glucose concentration. High glucose was also shown to increase the production of AII and TGF-β1 and decrease the proliferation of HPMC. In contrast, we found that both the ACEI and the ARB attenuated the increase in TGF-β1 production and reduced cell proliferation caused by exposure to high glucose. These effects were greater with a combination of the two drugs.

Conclusion

The present study provides evidence that ( 1 ) HPMC express mRNA for the AII-forming pathway; ( 2 ) ACEI and ARB inhibit the TGF-β1 production induced by high glucose; ( 3 ) the AII-forming pathway is one mechanism by which high glucose causes production of TGF-β1. In addition to having antihypertensive and renal-protective effects, combination therapy with an ACEI and an ARB may also be effective in preventing loss of peritoneal function and decreasing peritoneal fibrosis.

Time Course Changes in Urinary Angiotensinogen and Circulating N-Terminal Pro-B-Type Natriuretic Peptide in Patients Hospitalized with Acute Heart Failure

Objective Home care is important in patients with heart failure (HF) in order to maintain their quality of life. A biomarker that can be measured noninvasively is needed to optimize the home care of patients with HF. Urinary angiotensinogen (uAGT) is an indicator of the intrarenal renin-angiotensin system activity, which may be augmented in HF. We hypothesized that uAGT might be a urinary biomarker in HF. Methods We measured uAGT by an enzyme-linked immunosorbent assay and uAGT normalized by urinary creatinine (uCr)-designated uAGT/uCr-at admission and discharge in 45 patients hospitalized for HF. Results We found that both uAGT/uCr [median (interquartile range): 65.5 (17.1-127.7) μg/g Cr at admission; 12.1 (6.0-37.0) μg/g Cr at discharge; p<0.01] and N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels [5,422 (2,280-9,907) pg/mL at admission; 903 (510-1,729) pg/mL at discharge; p<0.01] significantly decreased between admission and discharge along with an improvement in patient's clinical status [New York Heart Association scores: 3 (3-4) at admission; 1 (1-1) at discharge; p<0.01]. The generalized least squares model revealed that the time course changes in uAGT/uCr also correlated with those in NT-proBNP levels between admission and readmission in five patients readmitted for HF. Conclusion The results indicated that the time course changes in uAGT/uCr correlated with those in the NT-proBNP levels in patients with HF who showed a clinical improvement. Further investigation and development of a kit for the rapid measurement of uAGT are needed to evaluate the clinical utility of uAGT as a biomarker in HF.

Relationship between intrarenal renin-angiotensin activity and re-hospitalization in patients with heart failure with reduced ejection fraction

OBJECTIVE

Heart failure (HF) is a clinical syndrome resulting from structural or functional damages. Although clinical trials have shown that the plasma renin-angiotensin system (RAS) activation decreases HF functional status and increases hospitalization for HF patients, the effect of intrarenal RAS activity is still unknown. In this study, we investigated the relationship between the New York Heart Association (NYHA) class, duration, and number of hospitalizations in the previous year and urinary angiotensinogen (UAGT) in patients with HF with reduced ejection fraction (HFrEF).

METHODS

This study included 85 patients who had an ejection fraction of <40% and were receiving optimal medical treatment. Among these, 22 were excluded from the study for various reasons. Demographically and biochemically, the remaining 63 patients were compared according to the NYHA functional classes and re-hospitalization status.

RESULTS

When the groups were compared in terms of N-terminal pro-B-type natriuretic peptide (NT-proBNP), UAGT, and high-sensitivity C-reactive protein (Hs-CRP), it was found that these parameters were significantly higher in patients who were hospitalized more than two times in the previous year [p<0.001; p=0.007; p<0.001, respectively]. There was a significant correlation between number of hospitalizations and NT-proBNP (r=0.507, p<0.001), Hs-CRP (r=0.511, p<0.001), hemoglobin (r=-0.419, p=0.001), serum sodium (r=-0.26, p=0.04), and systolic blood pressure (r=-0.283, p=0.02). When the independence of multiple correlations was assessed using multiple linear regression analysis, NT-proBNP, Hs-CRP, and hemoglobin levels were independent predictors of re-hospitalization, but this was not the same for UAGT.

CONCLUSION

Although UAGT levels are high in patients with poor NYHA functional class and repeated hospitalizations, this marker is not valuable for predicting repeated hospitalization in patients with HFrEF.

Effect of candesartan and lisinopril alone and in combination on blood pressure and microalbuminuria

Background

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blocking drugs (ARB) block the effect of angiotensin II by different mechanisms. It has been suggested that combined therapy may be more effective at reducing blood pressure (BP) than higher doses of either drug.

Methods

Twenty-three elderly patients with systolic hypertension completed a double-blind crossover study comparing placebo, candesartan (C) 16 mg, C32 mg, lisinopril (L) 20 mg, L40 mg and C16 mg + L20 mg. Treatment periods were one month and ambulatory BP measurements were performed at the end of each period. The effects on albumin excretion in eight patients with microalbuminuria were determined.

Results

All treatments lowered BP. The falls in systolic and diastolic BP with C16, C32, L20 and L40 were similar. Plasma renin rose to a similar extent. A plateau effect was reached with C16 and L20. Systolic BP on the combination of C16 + L20 was lower than on each monotherapy (C16, 3.8 mmHg [p=0.002]; C32, 6.4 [0.0003]; L20, 2.9 [0.05]; L40, 3.3 [0.003]). The additional fall in BP with the combination appeared to be due to recruitment of non-responders, rather than to an additive effect in most patients. All treatments reduced microalbuminuria to a similar extent. The combination was well tolerated and there was no deterioration in renal function.

Conclusion

When patients are on a plateau dose of an ACE inhibitor or an ARB, addition of the other drug class has a small but significant incremental effect on BP in the overall group. However, some patients respond better to one drug class than to the other and this may explain the results. This study lends no support to the use of these two drugs in combination to treat hypertension.

RGS4 inhibits angiotensin II signaling and macrophage localization during renal reperfusion injury independent of vasospasm

Vascular inflammation is a major contributor to the severity of acute kidney injury. In the context of vasospasm-independent reperfusion injury we studied the potential anti-inflammatory role of the Gα-related RGS protein, RGS4. Transgenic RGS4 mice were resistant to 25 minute injury, although post-ischemic renal arteriolar diameter was equal to the wild type early after injury. A 10 minute unilateral injury was performed to study reperfusion without vasospasm. Eighteen hours after injury blood flow was decreased in the inner cortex of wild type mice with preservation of tubular architecture. Angiotensin II levels in the kidneys of wild type and transgenic mice were elevated in a sub-vasoconstrictive range 12 and 18 hours after injury. Angiotensin II stimulated pre-glomerular vascular smooth muscle cells (VSMC) to secrete the macrophage chemoattractant, RANTES; a process decreased by angiotensin II R2 (AT2) inhibition. However, RANTES increased when RGS4 expression was suppressed implicating Gα protein activation in an AT2-RGS4-dependent pathway. RGS4 function, specific to VSMC, was tested in a conditional VSMC-specific RGS4 knockout showing high macrophage density by T2 MRI compared to transgenic and non-transgenic mice after the 10 minute injury. Arteriolar diameter of this knockout was unchanged at successive time points after injury. Thus, RGS4 expression, specific to renal VSMC, inhibits angiotensin II-mediated cytokine signaling and macrophage recruitment during reperfusion, distinct from vasomotor regulation.

Diabetic kidney disease; review of the current knowledge

Diabetes is the most common cause of chronic kidney disease (CKD) and end-stage renal disease (ESRD) in most parts of the world. 20 to 30% of diabetic patient have diabetic nephropathy in type 1 and type 2. Hyperglycemia is the key of nephropathy creation. Hyperglycemia also by production of toxic materials, advanced glycosylated end product (AGE), increased activity of aldose reductase has some role. Some metabolites of arachidonic acid, hemodynamic derangements and genetic factors have also some role. Although diabetic nephropathy is most common cause of nephropathy in these patients, but diabetic patients are also prone to other urinary tract and renal parenchymal disease and should not be confused with renal failure due to diabetic nephropathy. The principle of treatment of diabetic nephropathy is based on tight control of hyperglycemia, tight control of blood pressure and glomerular pressure, control of dyslipidemia, restriction of protein intake and smoking withdrawal.

Angiotensin 1-7 and Mas decrease thrombosis in Bdkrb2-/- mice by increasing NO and prostacyclin to reduce platelet spreading and glycoprotein VI activation

Bradykinin B2 receptor-deleted mice (Bdkrb2(-/-)) have delayed carotid artery thrombosis times and prolonged tail bleeding time resulting from elevated angiotensin II (AngII) and angiotensin receptor 2 (AT2R) producing increased plasma nitric oxide (NO) and prostacyclin. Bdkrb2(-/-) also have elevated plasma angiotensin-(1-7) and messenger RNA and protein for its receptor Mas. Blockade of Mas with its antagonist A-779 in Bdkrb2(-/-) shortens thrombosis times (58 ± 4 minutes to 38 ± 4 minutes) and bleeding times (170 ± 13 seconds to 88 ± 8 seconds) and lowers plasma nitrate (22 ± 4 μM to 15 ± 5 μM), and 6-keto-PGF1α (259 ± 103 pg/mL to 132 ± 58 pg/mL). Bdkrb2(-/-) platelets express increased NO, guanosine 3',5'-cyclic monophosphate, and cyclic adenosine monophosphate with reduced spreading on collagen, collagen peptide GFOGER, or fibrinogen. In vivo A-779 or combined L-NAME and nimesulide treatment corrects it. Bdkrb2(-/-) platelets have reduced collagen-related peptide-induced integrin α2bβ3 activation and P-selectin expression that are partially corrected by in vivo A-779, nimesulide, or L-NAME. Bone marrow transplantations show that the platelet phenotype and thrombosis time depends on the host rather than donor bone marrow progenitors. Transplantation of wild-type bone marrow into Bdkrb2(-/-) hosts produces platelets with a spreading defect and delayed thrombosis times. In Bdkrb2(-/-), combined AT2R and Mas overexpression produce elevated plasma prostacyclin and NO leading to acquired platelet function defects and thrombosis delay.

A reduction of unilateral ureteral obstruction-induced renal fibrosis by a therapy combining valsartan with aliskiren

The protective effect of combination therapy with valsartan and aliskiren against renal fibrosis remains to be defined. This study was undertaken to examine the protective effects of the combination of valsartan and aliskiren against renal fibrosis induced by unilateral ureteral obstruction (UUO). Combination therapy with valsartan (15 mg·kg(-1)·day(-1)) and aliskiren (10 mg·kg(-1)·day(-1)), valsartan monotherapy (30 mg·kg(-1)·day(-1)), and aliskiren monotherapy (20 mg·kg(-1)·day(-1)) all significantly ameliorated the increase in blood urea nitrogen and the degree of hydronephrosis determined by the increase in weight and length of the obstructed kidney. The dose titration study and blood pressure measurement confirmed that the combination therapy provided a greater benefit independent of the vasodilatory effect. There were no significant changes in serum levels of creatinine, sodium, and potassium in UUO rats and any treatment groups. Combination therapy also attenuated UUO-related increases in the scores of tubular dilatation, interstitial volume, interstitial collagen deposition, α-smooth muscle actin, the activation of ERK 1/2, the infiltration of monocytes/macrophages, the mRNA expression of snail-1, and transforming growth factor-β1 to a greater extent compared with aliskiren or valsartan used alone. The mRNA expression of renin and the (pro)renin receptor significantly increased after UUO. Combination therapy and monotherapy of valsartan and aliskiren had a comparable enhancing effect on the mRNA expression of renin, whereas all these treatments did not affect the expression of the (pro)renin receptor. In conclusion, a direct renin inhibitor in conjunction with an angiotensin II receptor blocker exerts increased renal protection against renal fibrosis and inflammation during obstruction over either agent alone.

Long-term antiproteinuric effect of dual renin-angiotensin system blockade

We evaluated the long-term changes on overt proteinuria induced by dual blockade of the renin-angiotensin system (RAS). Dual blockade was produced by adding an angiotensin II receptor blocker (ARB) to treatment with maximal recommended doses of an angiotensin converting enzyme (ACE) inhibitor in proteinuric patients. A total of 28 patients (19 men and 9 women) with proteinuria higher than 1 g/24 h were enrolled in this trial of treatment with the ARB candesartan (from 4 up to 32 mg daily) added to existing treatment with an ACE inhibitor. At 6, 12, 24, and 36 months, we evaluated proteinuria in 24-h urinary collections, office blood pressure (BP), plasmatic creatinine (Cr), serum potassium (K), and 24 h urine collection creatinine clearance (CrC). During monoblockade of the RAS by ACE inhibitor treatment, albuminuria was 2.94 +/- 1.92 mg/24 h; BP was 137/76 mmHg; K+ was 4.8 +/- 0.5 mmol/l, Cr was 1.76 +/- 0.67 mg/dL, and CrC was 62 +/- 31.9 mL/min. After 6 months, dual blockade of the RAS albuminuria was 2.18 +/- 2.29 mg/24 h (P < 0.01 vs. baseline) and BP was 133/75 mmHg (not significant). At 36 months, albuminuria was 2.21 +/- 2.20 mg/24 h (P < 0.05 vs. baseline); BP was 133/73 mmHg (not significant). CrC was not changed along the follow up. A small increment of Cr was detected at 24 months (2.11 +/- 1.06 mg/mL, P < 0.05). The antiproteinuric effect of dual renin-angiotensin system blockade combining candesartan and ACE inhibitors remain after 36 months without losing its initial effect. Blood pressure changes seem not to explain this long-term antiproteinuric effect.

Low-dose dual blockade of the renin–angiotensin system improves tubular status in non-diabetic proteinuric patients

OBJECTIVE

Treatment with agents that inhibit the renin-angiotensin system is commonly regarded as a gold standard renoprotective strategy in patients with chronic kidney diseases. For maximum antiproteinuric effect, the dose titration of these agents is recommended. This therapeutic strategy is not used for proteinuric patients who are not able to receive high doses of angiotensin-converting enzyme inhibitor or angiotensin II receptor antagonists.

MATERIAL AND METHODS

In patients with primary glomerulonephritis (n=24), a randomized, triple-treatment, triple-period, cross-over study was performed to compare the effects of combined therapy with benazepril 5 mg and losartan 25 mg and monotherapy with either agent alone at a two-fold higher dose on the extent of tubular injury as assessed by alpha1-microglobulin (alpha1-m) excretion and the plasma level of transforming growth factor-beta1 (TGF-beta1).

RESULTS

Combination therapy significantly reduced alpha1-m excretion compared to either agent used alone: 178.29+/-27.36 to 99.63+/-13.03 mg/g creatinine for losartan + benazepril vs 178.29+/-27.36 to 161.59+/-23.22 mg/g creatinine for benazepril alone (p<0.05; ANOVA) and 178.29+/-27.36 to 99.63+/-13.03 mg/g creatinine for losartan + benazepril vs 178.29+/-27.36 to 173.45+/-27.69 mg/g creatinine for losartan alone (p<0.05; ANOVA). There was a significant correlation between change in alpha1-m excretion and reduction in proteinuria (r=0.704; p=0.023). There were no differences in TGF-beta1 level between the studied treatments. Systemic blood pressure reduction did not differ among the therapies.

CONCLUSIONS

Combination therapy with angiotensin-converting enzyme inhibitor and angiotensin II subtype 1 receptor antagonists at very small doses may be superior to monotherapy with these agents at higher doses as far as tubular injury is concerned. We speculate that such a therapeutic strategy may be a useful approach for patients who are known not to be capable of receiving optimal renoprotective doses of these regimens.

Treatments of Hemodynamic Maladjustment and Oxidative Stress Prevent Renal Disease Progression in Chronically Severe Glomerulonephritides

Hemodynamic maladjustment is a unique observation in chronically severe glomerulonephritides. It is characterized by a markedly elevated efferent arteriolar resistance (RE), an elevated intraglomerular hydrostatic pressure (PG) and a markedly decreased renal plasma flow (RPF), and peritubular capillary flow (PTCF). A correction of such hemodynamic maladjustment can be accomplished by administering a combination of vasodilators (angiotensin receptor antagonist, angiotensin converting enzyme inhibitor, and calcium channel blocker) in 14 chronic glomerulonephritides with severe renal function impairment (mean serum creatinine 3.6 + 1.3 mg/dL). Doses titration aim for maximal renal perfusion effect (increased RPF, PTCF) or maximal renal function improvement (increased CCr, reduced FE Mg) usually higher than needed for maximal blood pressure reduction. Evidence of oxidative stress is also corrected with high doses of vitamins C and E. After a mean period of treatment for 13.5 months, improvements in CCr (pre R(x) 22 +/- 10 vs. post R(x) 32 +/- 13 mL/min/1.73 m2), and FE Mg (pre R(x) 11.9 +/- 4% vs. post R(x) 10 +/- 3%) were observed in conjunction with the improvement in intrarenal hemodynamics namely RPF (pre R(x) 201 +/- 71 vs. post R(x) 288 +/- 99 mL/min/1.73 m2), PTCF (pre R(x) 161 +/- 57 vs. post R(x) 242 +/- 90 mL/ min/1.73 m2), PG (pre R(x) 56.7 +/- 0.5 vs. post R(x) 51 +/- 0.1 mm Hg), and RE (pre R(x) 12085 +/- 6503 vs. post R(x) 6550 +/- 1872 dyne.s.cm(-5)).

Hemodynamic Maladjustment and Disease Progression in Nephrosis with FSGS

Idiopathic nephrotic syndrome (NS) associated with focal segmental glomerulosclerosis (FSGS) and severe renal function impairment is usually refractory to the conventional treatment and progresses to end-stage renal disease. Herein, we reported 10 patients with NS-FSGS who had initially had CCr 34 +/- 12 mL/min/1.73 m2 (normal 120 mL/min/1.73 m2), FE Mg 7.8 +/- 2.6% (normal 2.2%), 24-h urinary protein 3.1 g (normal <200 mg) and been followed up for over 10 years. The initial intrarenal hemodynamic study revealed a marked elevation of efferent arteriolar resistance (RE 17289 +/- 8636 dyne x s x cm(-5); normal 3000 dyne x s x cm(-5)), intraglomerular hypertension (PG 57 +/- 1 mm Hg; normal 52 mm Hg), hyperfiltration (FF 0.24; normal 0.2), marked reductions in GFR 35 +/- 17 mL/min/1.73 m2, renal plasma flow (RPF 159 +/- 61 mL/min/1.73 m2; normal 600 mL/min/1.73 m2) and peritubular capillary flow (PTCF 123 +/- 57 mL/min/1.73 m2; normal 480 mL/min/1.73 m2). Such a hemodynamic alteration indicated a hemodynamic maladjustment with a preferential constriction at RE. Treatment consists of multidrugs, namely angiotensin converting enzyme inhibitor, calcium channel blocker, antiplatelet and anticoagulant, with or without angiotensin II receptor antagonist. Following the treatment, correction of hemodynamic maladjustment has been achieved which is characterized by reductions in RE 6046 +/- 2191 dyne x s x cm(-5), PG 52 +/- mm Hg, FF 0.19 +/- 0.1 and increments in RPF 341 +/- 118 mL/min/1.73 m2, PTCF 280 +/- 106 mL/min/1.73 m2 and GFR 64 +/- 17 mL/min/1.73 m2. Coinciding with hemodynamic improvement, there has been a steadily increased creatinine clearance and improvement in FE Mg 4.3 +/- 2.6% and suppression of proteinuria 0.29 +/- 0.4 g/24 h after the period of follow-up of greater than 10 years.

ACE-inhibitor, AT1-receptor-antagonist, or both? A clinical pharmacologist's perspective after publication of the results of ONTARGET

Clinical Pharmacology is commonly accepted to be a bridging discipline between basic science observations and clinical practice. Today, it should be a major task of the clinical pharmacologist in academia to provide support in the interpretation of preclinical and clinical study data, to develop evidence-based treatment guidelines and to serve as drug expert supporting all disciplines of clinical medicine with specific pharmacological and therapeutic knowledge. The results of the ONTARGET-trial confront both researchers and clinicians with the unexpected truth that AT(1)-receptor-blockade with an angiotensin-receptor-blocker (ARB) does not seem to have superior therapeutic benefit compared with an ACE-inhibitor (ACE-I) at reducing fatal and nonfatal cardiovascular events. The combination of the two drugs was associated with more adverse events without an increase in benefit. Therefore, the crucial question 'ACE-I, ARB, or both?' requires a new and critical appraisal depending on the medical indication for which these renin-angiotensin-system (RAS)-inhibitors are used: In a population of high-risk patients suffering from cardiovascular disease or diabetes mellitus, the evidence to favor an ARB over an ACE-I is still limited after ONTARGET and because of the higher costs for ARBs one can rather support the old therapeutic advice that ARBs are equally effective as ACE-Is and therefore therapeutic alternatives for patients with ACE-I intolerance. With respect to a very moderate additive BP-lowering effect of dual therapy with an ACE-I and an ARB seen in metaanalysis which was not even clearly attributable to dual RAS-inhibition and the increased adverse event rate in the combination treatment group of ONTARGET, this regimen seems not to be recommendable for the treatment of hypertension. Dual-RAS-blockade using an ACE-I-ARB-combination is an effective therapy to treat proteinuria and might be of therapeutic benefit especially in diabetic patients without concomitant diseases. There may be a therapeutic rationale to prefer ARBs over ACE-Is in well-selected patients with congestive heart failure (CHF) because a considerable amount of angiotensin II (Ang II) is produced independent of angiotensin-conversion-enzyme (ACE) in the failing heart and is therapeutically unaffected by ACE-I treatment. The results of the Val-HeFt and the CHARM-added-study revealed additive effects of an ARB on heart failure related morbidity and mortality when added to existing therapy with an ACE-I suggesting a role for ACE-I-ARB-combination treatment in well selected heart failure patients. Independent of the medical indication for its use, the concept of dual RAS-blockade with an ARB-ACE-I-combination should clinically be used with caution and a close monitoring of potassium levels and kidney function. Although the results of ONTARGET revealed equity of ramipril and telmisartan at reducing fatal and nonfatal cardiovascular events, we should not forget that pharmacologically not all ARBs are the same and the question if the study results of ONTARGET with telmisartan are transferable to the complete class of ARBs still merits further investigation.

Involvement of prolylcarboxypeptidase in the effect of rutaecarpine on the regression of mesenteric artery hypertrophy in renovascular hypertensive rats

1. Previous studies indicate that rutaecarpine blocks increases in blood pressure and inhibits vascular hypertrophy in experimentally hypertensive rats. The aim of the present study was to determine whether the effects of rutaecarpine are related to activation of prolylcarboxypeptidase (PRCP). 2. Renovascular hypertensive rats (Goldblatt two-kidney, one-clip (2K1C)) were developed using male Sprague-Dawley rats. Chronic treatment with rutaecarpine (10 or 40 mg/kg per day) or losartan (20 mg/kg per day) for 4 weeks to the hypertensive rats caused a sustained dose-dependent attenuation of increases in blood pressure, increased lumen diameter and decreased media thickness, which was accompanied by a similar reduction in the media cross-sectional area : lumen area ratio in mesenteric arteries compared with untreated hypertensive rats. 3. Angiotensin (Ang) II expression was significantly increased in mesenteric arteries of hypertensive rats compared with sham-operated rats. No significant differences in plasma AngII levels were observed between untreated hypertensive and sham-operated rats. Hypertensive rats treated with high-dose rutaecarpine had significantly decreased Ang II levels in both the plasma and mesenteric arteries. 4. Expression of PRCP protein or kallikrein mRNA was significantly inhibited in the right kidneys and mesenteric arteries of hypertensive rats. However, expression of PRCP protein and kallikrein mRNA was significantly increased after treatment with rutaecarpine or losartan (20 mg/kg per day). 5. The data suggest that the repression of increases in systolic blood pressure and reversal of mesenteric artery remodelling by rutaecarpine may be related to increased expression of PRCP in the circulation and small arteries in 2K1C hypertensive rats.

The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease

In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.

Combination Angiotensin-Converting Enzyme Inhibitor and Angiotensin Receptor Blocker Therapy: Its Role in Clinical Practice

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers are commonly prescribed for the management of hypertension. In addition, each of these drug classes has been shown to be effective in the treatment of congestive heart failure, proteinuric chronic kidney disease, and most recently the high-cardiac-risk profile patient. The individual success of each of these drug classes has fueled the theory that given together, the overall biologic effect of both would surpass that of either given alone. The foundation of this premise, although biologically plausible, has yet to be proven in a compelling enough fashion to support the everyday use of these two drug classes in combination. Additional clarifying studies are required to establish whether specific patient subsets exist that might benefit from such combination therapy.

Combination ACE Inhibitor and Angiotensin Receptor Blocker Therapy-Future Considerations

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers are regularly prescribed for the management of hypertension. Each of these drug classes has also been shown to provide survival benefits for patients with heart failure, proteinuric chronic kidney disease, and/or a high cardiac risk profile. The individual gains seen with each of these drug classes have led to speculation that their combination might offer additive if not synergistic outcome benefits. The foundation of this hypothesis, although biologically possible, has thus far not been sufficiently well proven to support the everyday use of these 2 drug classes in combination. Additional outcomes trials, which are currently proceeding to their conclusion, may provide the necessary proof to support an expanded use of these 2 drug classes in combination.

Mesangial hypercellularity predicts antiproteinuric response to dual blockade of RAS in primary glomerulonephritis

The greater antiproteinuric efficacy of converting enzyme inhibitor and angiotensin II receptor blocker combination (CEI+ARB), versus monotherapy with either drug, is not a consistent finding. We evaluated the clinicopathologic predictors of response to CEI+ARB in 43 patients with primary glomerulonephritis (GN), never treated with immunosuppressive drugs, and with persistent proteinuria after CEI alone. Main histological lesions were analyzed by obtaining on 557 glomeruli and 165 arteries formal score of mesangial cellularity, glomerulosclerosis, tubulointerstitial damage, mononuclear cell infiltration, arteriosclerosis, and arteriolar hyalinosis. Duration of CEI and CEI+ARB therapy was similar (4.7+/-2.4 and 5.0+/-1.5 months). Proteinuria (g/day) decreased from 3.5+/-2.9 to 2.4+/-2.3 after CEI, and to 1.5+/-1.3 after CEI+ARB (P<0.0001). Reduction of proteinuria after CEI+ARB was greater in proliferative versus non-proliferative GN (-63.3+/-23.4 versus 42.4+/-23.7%, respectively; P=0.006). When patients were categorized in responders and non-responders to CEI+ARB, no difference between the two groups was detected in any demographic or clinical variable, whereas histology showed in responders a greater prevalence of proliferative GN (71.4 versus 31.8%, P=0.009) and higher score of mesangial cellularity (1.76+/-0.53 versus 1.20+/-0.22, P<0.0001). At multiple regression analysis (r(2)=0.476, P=0.001), response to CEI+ARB resulted independently related only to mesangial cellularity (P<0.0001). In conclusion, the best independent predictor of antiproteinuric efficacy of CEI+ARB in patients with primary GN is the degree of mesangial cellularity. This finding supports the experimental evidence that high angiotensin II contributes to proliferation of mesangial cells.

Dual blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers in chronic kidney disease

Despite the renoprotective effects of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs), many patients with chronic kidney disease develop end-stage kidney disease. Combination treatment with an ACEI and an ARB is a recently introduced approach to obtain more complete blockade of the renin-angiotensin system, based on the different mechanisms of action of the two classes of drug. To assess the shortcomings of single treatment with ACEIs and ARBs, and the potential benefits of combination treatment, we reviewed the experimental and clinical evidence suggesting that combination treatment offers more complete blockade of the renin-angiotensin system and identified areas in which further research is necessary to confirm the benefits of combination treatment. The available data suggest that combination treatment with an ACEI and an ARB has a greater renoprotective effect than either drug alone. In addition, more recent data have shown that combination treatment is more potent in suppressing renal fibrosis, and is well tolerated in patients with advanced chronic kidney disease. Clinical trials with rigorous endpoints are needed to further establish the benefits of combination treatment in renal protection.

Preventing end-stage renal disease in diabetic patients - dual blockade of the renin-angiotensin system (Part II)

Diabetic nephropathy is a major cause of diabetes related morbidity and mortality. The first part of the current review was published in the last issue of this journal and discussed the important role of the renin-angiotensin system (RAS) in diabetic nephropathy and the genetic influence on development of endstage renal disease (ESRD) in diabetic patients. This second part of the review focus on the potential improvement of the current treatment strategy to slow down the loss of kidney function using dual blockade of the RAS with both ACE-inhibitors (ACE-I) and angiotensin II receptor blockers (ARBs). Substantial evidence from short-term studies using surrogate endpoints indicates a beneficial impact of dual blockade of the RAS, not obtainable with single agent blockade alone, both in diabetic and non-diabetic renal disease. This conclusion has been confirmed and extended in a longterm trial with regard to prevention of ESRD in non-diabetic renal disease. Results indicate that dual blockade of the RAS may further slow down, but not arrest progressive loss of renal function. However, studies defining the optimal dose of ACE-I / ARBs without additional adverse effects are essential to ensure relevant comparison with dual blockade therapy. Trials using primary renal endpoints in diabetic nephropathy are still needed, and will finally establish the role of dual blockade of the RAS in a clinical setting.

Beneficial effect of lisinopril plus telmisartan in patients with type 2 diabetes, microalbuminuria and hypertension

Angiotensin-converting enzyme (ACE) inhibitors have favourable effects on hypertension and diabetic nephropathy, but persistent use may result in incomplete blockade of the renin-angiotensin system. Long-term effects of dual blockade using the ACE inhibitor lisinopril and the long-acting angiotensin II receptor blocker (ARB) telmisartan on blood pressure and albumin excretion rate (AER) were evaluated. Patients with type 2 diabetes mellitus, hypertension (systolic blood pressure [SBP] >or=140 mmHg or diastolic blood pressure [DBP] >or=90 mmHg) and microalbuminuria (AER 30-300 mg/24h) received 20mg of lisinopril or 80 mg of telmisartan once a day for 24 weeks. Patients were then randomised to continuing treatment with the respective monotherapy or with lisinopril plus telmisartan for a further 28 weeks. Significant (P<0.001) declines in SBP (11.1 mmHg versus 10.0 mmHg), DBP (5.6 mmHg versus 5.3 mmHg) and AER (98 mg/24 h versus 80 mg/24 h) were achieved with lisinopril (n=95) or telmisartan (n=97), respectively, after 24 weeks. Subsequent treatment with lisinopril plus telmisartan for 28 weeks resulted in further significant reductions (P<0.001) in SBP, DBP and AER compared with either monotherapy. All treatments were well tolerated. Lisinopril plus telmisartan thus provides superior blood pressure and AER control than either monotherapy. We conclude that use of dual blockade may provide a new approach to prevention of diabetic nephropathy in patients with type 2 diabetes, hypertension and microalbuminuria.

Effect of low-dose dual blockade of renin-angiotensin system on urinary TGF-beta in type 2 diabetic patients with advanced kidney disease

BACKGROUND

We evaluated the renoprotective effects of dual blockade of renin-angiotensin system (RAS) by using a low-dose combination of ACE inhibiter and angiotensin II receptor blocker in type 2 diabetic patients with advanced kidney disease. The amount of proteinuria and the urinary levels of bioassayable TGF-beta1 were used as surrogate markers of renal injury and sclerosis.

METHODS

We performed a prospective double-blinded randomized crossover trial consisting of three 16-week treatment periods with ramipril alone (10 mg/day), candesartan alone (16 mg/day), and ramipril (5 mg/day) plus candesartan (8 mg/day) combination therapy. Twenty-one type 2 diabetic patients with overt nephropathy with a 24 h urinary protein excretion rate (UPER) of > 1.0 g/24 h and creatinine clearance (Ccr) of 30 to 59 ml/min/1.73 m2 completed the entire study.

RESULTS

Subjects consisted of 10 female and 11 male patients with a mean age of 49 +/- 8 years and duration of diabetes ranging from 4 to 13 years. At baseline, 24-h blood pressures (BPs) were 133 +/- 6/81 +/- 7 mmHg, Ccr 40.6 +/- 4.1 ml/min/1.73 m2, 24-h UPER 4.1 +/- 1.9 g/24 h, and urinary TGF-beta1 level 28.4 +/- 16.1 pg/mg creatinine (cr). Although there was no comparable change in BP and plasma/urinary biochemical parameters, 24-h UPER was significantly reduced by the combination therapy (2.9 +/- 1.4 g/24 h) compared with that of ramipril (3.5 +/- 1.8 g/24 h) and of candesartan (3.3 +/- 2.0 g/24 h) single therapy (P < 0.05). Urinary TGF-beta1 level was reduced in all three therapies compared with that of the control (28.4 +/- 16.1 pg/mg cr) (P < 0.05). However, the combination therapy showed the most significant change (combination 19.6 +/- 10.6 pg/mg cr; ramipril 24.7 +/- 13.3 pg/mg cr; candesartan; 23.4 +/- 11.7 pg/mg cr). No significant or irreversible adverse effect was observed in the 21 patients who completed the entire study.

CONCLUSIONS

The dual blockade of RAS with low-dose ramipril plus candesartan was found to be safe and offered additive benefits with respect to reducing proteinuria and urinary TGF-beta1 excretion in diabetic patients with advanced kidney disease. These benefits were evident as compared with single ramipril and candesartan therapies at doses two-fold greater. Further study on the dose-titration is mandatory in terms of safety and especially for maximizing renoprotection in this patient population.

Systematic Review of Combined Angiotensin-Converting Enzyme Inhibition and Angiotensin Receptor Blockade in Hypertension

Some evidence suggests that long-term angiotensin-converting enzyme (ACE) inhibition may become less effective, thereby increasing angiotensin II levels, which could be inhibited by the addition of an angiotensin receptor blocker. We conducted a meta-analysis of randomized trials with searches of MEDLINE, EMBASE, and Cochrane databases. Overall, the combination of an ACE inhibitor and an angiotensin receptor blocker reduced ambulatory blood pressure by 4.7/3.0 mm Hg (95% confidence interval [CI], 2.9 to 6.5/1.6 to 4.3) compared with ACE inhibitor monotherapy and 3.8/2.9 mm Hg (2.4 to 5.3/0.4 to 5.4) compared with angiotensin receptor blocker monotherapy. Clinic blood pressure was reduced by 3.8/2.7 mm Hg (0.9 to 6.7/0.8 to 4.6) and 3.7/2.3 mm Hg (0.4 to 6.9/0.2 to 4.4) compared with ACE inhibitor and angiotensin receptor blocker, respectively. However, the majority of these studies used submaximal doses or once-daily dosing of shorter-acting ACE inhibitors and, when a larger dose of shorter-acting ACE inhibitor was given or a longer-acting ACE inhibitor was used, there was generally no additive effect of the angiotensin receptor blocker on blood pressure. Proteinuria was reduced by the combination compared with ACE inhibitor and angiotensin receptor blocker monotherapy, an effect that was independent of blood pressure in several studies, suggesting that the combination could have benefits in proteinuric nephropathies. None of the studies was of sufficient size and duration to determine whether there may be safety concerns. In conclusion, although there is a small additive effect on blood pressure with an ACE inhibitor-angiotensin receptor blocker combination, the routine use of this combination in uncomplicated hypertension is not recommended until more carefully controlled studies are performed.

Temporal adaptation of tubuloglomerular feedback: effects of COX-2

BACKGROUND

Reductions in proximal reabsorption cause increases in delivery of sodium chloride to the macula densa (MD), which activates the tubuloglomerular feedback (TGF) mechanism and reduces glomerular filtration rate. TGF undergoes temporal adaptation, permitting filtration rate to rise in spite of elevated MD delivery of NaCl. Inhibitors of nitric oxide synthase I (NOS I) prevent TGF adaptation, but angiotensin-converting enzyme inhibitors have no effect. COX-2 activity moves in parallel with changes in NOS I and intrarenal renin. We examined the impact of COX-2 inhibition on TGF temporal adaptation and effects of inhibition of COX-2 and NOS I on plasma and kidney angiotensin II (Ang II).

METHODS

Kidney blood flow (RBF) and glomerular filtration rate (GFR) were measured before and during benzolamide (BNZ) infusion in control Wistar rats and rats concurrently receiving COX-2 inhibitors. Plasma and kidney angiotensin II content was evaluated by radioimmunoassay in control rats, rats after 60 minutes of BNZ, and during COX-2 and NOS-1 inhibition after BNZ.

RESULTS

BNZ reduced both RBF and GFR in all groups. During BNZ, RBF and GFR returned to normal control values within 60 minutes. COX-2 inhibitors totally prevented TGF adaptation. Plasma and kidney Ang II did not change after BNZ, and NOS I and COX-2 inhibitors had no effect on plasma or intrarenal Ang II.

CONCLUSION

Within 1 hour after BNZ, rats undergo TGF temporal adaptation. Administration of COX-2 inhibitors prevented TGF temporal adaptation, identical to the effect of NOS I inhibition. Changes in intrarenal Ang II cannot explain this prevention of TGF temporal adaptation.

Glomerular endothelial dysfunction in chronic kidney disease

A dysfunctioning glomerular endothelium was demonstrated in chronic kidney disease (CKD) patients by means of in vitro endothelial cell cytotoxicity test and of in vivo intrarenal hemodynamic study. An enhanced endothelial cell cytotoxicity in CKD patients was 26.5 +/- 12% as compared to 0.4 +/- 1% of control. An altered intrarenal hemodynamics revealed 1) a reduction in renal plasma flow, 190 +/- 67 mL/min/1.73 m2 versus control 595 +/- 45 mL/min/1.73 m2, and in peritubular capillary flow, 149 +/- 55 mL/min/1.73 m2 versus control 479 +/- 46 mL/min/1.73 m2, 2) an elevated intraglomerular hydrostatic pressure, 55 +/- 2 mmHg versus control 51 mmHg, elevated afferent arteriolar resistance, 13184 dyne x s x cm(-5) versus control 2443 +/- 154 dyne x s x cm(5), and elevated efferent arteriolar resistance, 13591 +/- 7591 dyne x s x cm(-5) versus control 3062 +/- 177 dyne x s x cm(-5). Both enhanced endothelial cell cytotoxicity and altered intrarenal hemodynamics reflect glomerular endothelial dysfunction which is likely responsible for the renal disease progression in CKD.

Combination therapy with ACE inhibitors and angiotensin II receptor blockers to halt progression of chronic renal disease: Pathophysiology and indications

It is no a secret that we are confronted by an alarmingly increasing number of patients with progressive renal disease. There is ample evidence for the notion that angiotensin II (Ang II) is a major culprit in progression. The vasopeptide Ang II turned out to have also multiple nonhemodynamic pathophysiologic actions on the kidney, including proinflammatory and profibrogenic effects. Diverse complex Ang II generating systems have been identified, including specifically local tissue-specific renin-angiotensin systems (RAS). For example, proximal tubular cells have all components required for a functional RAS capable of synthesizing Ang II. On the other hand, Ang II is not the only effector of the RAS and other peptides generated by the RAS influence renal function and structure as well. Moreover, the discoveries that Ang II can be generated by enzymes other than angiotensin-converting enzyme (ACE) and that Ang II and other RAS derived peptides bind to various receptors with different functional consequences have further added to the complexity of this system. Several major clinical trials have clearly shown that ACE inhibitor treatment slows the progression of renal diseases, including in diabetic nephropathy. Well-controlled studies demonstrated that this effect is in part independent of blood pressure control. More recently, with Ang II type 1 receptor (AT(1)) receptor antagonists a similarly protective effect on renal function was seen in patients with type 2 diabetes. Neither ACE inhibitor treatment nor AT(1) receptor blockade completely abrogate progression of renal disease. A recently introduced novel therapeutic approach is combination treatment comprising both ACE inhibitor and AT(1) receptor antagonists. The rationale for this approach is based on several considerations. Small-scale clinical studies, mainly of crossover design, documented that combination therapy is more potent in reducing proteinuria in patients with different chronic renal diseases. Blood pressure as an important confounder was, however, significantly lower in the majority of this studies in the combination treatment arms compared to the respective monotherapies. In a recent prospective study Japanese authors avoided this confounder and demonstrated that combination therapy reduced hard end-points (end stage renal failure or doubling of serum creatinine concentration) by 50% compared to the respective monotherapies. This effect could not be explained by a more pronounced reduction of blood pressure in the combination therapy group. Although these results are encouraging, administration of combination therapy should be reserved currently to special high risk groups. Further studies are necessary to confirm these promising results. It is possible that combination therapy may increase the risk of hyperkalemia, particularly when with coadministered with medications such as nonsteroidal anti-inflammatory drugs (NSAIDs) or spironolactone. In our opinion patients with proteinuria >1 g/day despite optimal blood pressure control under RAS-blocking monotherapy are a high-risk group which will presumably benefit from combination therapy.

Diabetic nephropathy: the proteinuria hypothesis

BACKGROUND/AIMS

Proteinuria, nearly a universal finding in progressive kidney disease, has been the subject of frequent recent analyses in the renal literature. Proteinuria is a hallmark of diabetic nephropathy: microalbuminuria is the principal early predictor for progression of diabetic glomerulopathy, and proteinuria may be viewed as a measure of the severity and promoter of progression of nephropathy.

METHODS

This article critically reviews for the first time the full scope of diabetic proteinuria--complex molecular mechanisms, natural history, and analysis of treatment trials--in order to address the validity of 'the proteinuria hypothesis', i.e., that diabetic proteinuria is a modifiable determinant of renal progression. This hypothesis is analyzed in detail, including recent studies on the primary therapy of diabetic nephropathy, renin-angiotensin blockade.

RESULTS

As fully developed, this hypothesis consists of three postulates: that higher amounts of proteinuria predict progressive loss of function, that proteinuria reduction correlates with slowing progression, and that proteinuria is a surrogate endpoint for clinical trials. The latter postulate has not before been adequately linked to growing information about the first two postulates as they apply to diabetic kidney disease.

CONCLUSION

While diabetic nephropathy is a disease model for the potential use of proteinuria as a surrogate marker for renal progression, this shift in perspective will require prospective data from additional clinical trials, particularly of non-renin-angiotensin blocking drugs, to be complete.

Renin-angiotensin system blockade prevents the increase in plasma transforming growth factor beta 1, and reduces proteinuria and kidney hypertrophy in the streptozotocin-diabetic rat

INTRODUCTION

Combination therapy with angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) is used to improve renal outcome achieved by monotherapy in diabetic patients. In addition, interference with the renin-angiotensin system (RAS) reduced expression and excretion of transforming growth factor beta 1 (TGF-beta 1) in diabetic nephropathy. The aim of this study was to investigate the effects of interrupting the RAS by ACE inhibitor (ACE-I) or ARB monotherapy or by combination therapy on proteinuria, kidney hypertrophy and plasma TGF-beta 1 in diabetic rats.

MATERIALS AND METHODS

Forty-one male Wistar rats were allocated to five groups: 1 = control rats, 2 = diabetic rats (streptozotocin [STZ] 55 mg/kg), 3 = diabetic rats as above receiving enalapril (20 mg/kg/day), 4 = diabetic rats receiving losartan (80 mg/kg/day), 5 = diabetic rats receiving both losartan and enalapril. The study lasted 60 days.

RESULTS

Urinary protein excretion, kidney weight, serum ACE activity and plasma TGF-beta1 increased significantly in untreated diabetic rats compared with controls. Administration of losartan, enalapril, or both for 60 days prevented these changes. Furthermore, combined therapy for 30 days normalised urinary protein excretion, while monotherapy did not. Losartan inhibited serum ACE activity both in vivo and in vitro. Plasma TGF-beta 1 levels were positively correlated with blood glucose levels (r=0.4059) and with urinary protein excretion (r=0.3558).

CONCLUSIONS

Combination therapy with losartan and enalapril was more effective than monotherapy with either drug in achieving an early antiproteinuric response. Long-term treatment with losartan was as effective as the combined treatment, possibly due to a dual inhibitory effect on the RAS. The antiproteinuric effect may be related, in part, to reduced TGF-beta 1.

Renin Inhibition: What Are the Therapeutic Opportunities?

Blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers has become a crucial element in cardiovascular and renal medicine. This review evaluates the potential of renin inhibition as an adjunct to therapies that depend on renin system interruption.

Diuretic and Enhanced Sodium Restriction Results in Improved Antiproteinuric Response to RAS Blocking Agents

Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and diuretics may exert synergistic antiproteinuric effects. Eighteen patients with a proteinuria >1 g/24 h after 6 mo of treatment with ramipril at 5 mg/d were assigned to receive in random order ramipril at 10 mg/d, valsartan at 160 mg/d, or combined ramipril at 5 mg/d and valsartan at 80 mg/d in addition to their antihypertensive treatment. The treatment periods lasted 4 wk and were separated by a 4-wk washout with ramipril at 5 mg/d. At the end of this crossover sequence, patients received combined ramipril at 5 mg/d, valsartan at 80 mg/d, and an increased furosemide dosage for an additional 4-wk period. The primary end point was the urinary protein/creatinine ratio for two 24-h urine collections at the end of each treatment period. No significant differences were noted between the study end points of the ramipril 10, valsartan 160, and combined ramipril 5 and valsartan 80 treatment groups. However, the urinary protein/creatinine ratio was lower with combined ramipril 5 and valsartan 80-increased furosemide dosage than with valsartan 160 and combined ramipril 5 and valsartan 80, with a similar tendency compared with ramipril 10. Combined ramipril 5 and valsartan 80-increased furosemide dosage decreased systolic home BP and increased serum creatinine but did not significantly increase the number of symptomatic hypotension cases compared with the other three treatments. Thus, in patients with severe proteinuria and hypertension, a cautious increase in diuretic dosage in addition to combined angiotensin-converting enzyme inhibitors and angiotensin receptor blockers decreases proteinuria and BP but may expose the patient to prerenal failure.

Why are angiotensin concentrations so high in the kidney?

PURPOSE OF REVIEW

Recent studies have reported that intrarenal angiotensin II content and angiotensin II concentrations in the proximal tubular fluid and renal interstitial fluid are much greater than the circulating angiotensin II levels. These high intrarenal angiotensin II levels are responsible for regulating renal hemodynamics and tubular transport.

RECENT FINDINGS

Intrarenal angiotensin II levels have been assessed from total tissue contents as well as renal interstitial fluid and proximal tubular fluid concentrations. Total tissue contents expressed per gram of tissue weight are greater than plasma angiotensin II concentrations; tubular fluid concentrations and renal interstitial fluid concentrations are even greater in the range of 3-10 pmoles/ml. In hypertensive states, there is also an increased intracellular accumulation of angiotensin II mediated by angiotensin type 1 receptor-dependent endocytosis. The high intrarenal angiotensin II levels are also caused by the presence of angiotensinogen messenger RNA and protein in the proximal tubule cells. Furthermore, there is positive amplification by which increases in circulating angiotensin II stimulate increased production and secretion of angiotensinogen, which is also manifested as an increased urinary excretion rate.

SUMMARY

The ability of the kidney to generate high intratubular and interstitial concentrations allows the kidney to regulate intrarenal levels in accord with the homeostatic needs for the regulation of renal hemodynamics and tubular reabsorption and the regulation of sodium balance. When inappropriately stimulated, high intrarenal angiotensin II levels contribute to excessive salt and water retention, the development of hypertension, and long-term proliferative effects leading to renal injury.

Compelling drug indications in diabetic and nondiabetic nephropathy

To halt progression of renal disease, the combination of several interventional strategies is recommended. The most important components comprise lowering of systolic blood pressure to approximately 120 mm Hg; providing pharmacologic blockade of the renin-angiotensin system by angiotensin-converting enzyme inhibitors or angiotensin receptor blockers; and reducing proteinuria to rates of less than 1 g/d.

Angiotensin receptor blockers in diabetic nephropathy: renal and cardiovascular end points

The activity of the renin-angiotensin-aldosterone system (RAAS) is elevated both in the circulation and in the renal tissue of diabetic and nondiabetic nephropathies. The increased RAAS activity plays an important role in the hemodynamic and nonhemodynamic pathogenetic mechanisms involved in kidney disease. Previous studies have demonstrated that albuminuria is not only a marker of glomerular lesions, but also a progression promoter, and finally a powerful predictor of the long-term beneficial effect of blood pressure-lowering therapy. Randomized crossover and parallel blind studies in patients with diabetic nephropathy have demonstrated that angiotensin II receptor blockers (ARB) induce favorable changes in systemic blood pressure, renal hemodynamics, and proteinuria similar to those induced by angiotensin-converting enzyme (ACE) inhibition. Studies have revealed the optimal renoprotective dose for some ARBs; however, additional dose titration studies are urgently needed to obtain the maximum benefit of this valuable new class of compounds. The combination of ARB and ACE inhibition is well tolerated and even more effective than monotherapy in reducing systemic blood pressure and albuminuria in diabetic nephropathy. In addition, dual RAAS blockade is safe and well tolerated. Impaired autoregulation of glomerular filtration rate (GFR); demonstrated with some blood pressure-lowering agents implies disturbances in the downstream transmission of the systemic blood pressure into the glomerulus, leading to capillary hypertension or hypotension depending of the level of blood pressure. ARB does not interfere with GFR autoregulation in hypertensive diabetic patients. In contrast to previous observational studies with ACE inhibition, long-term treatment with ARB has similar beneficial renoprotective effect on progression of diabetic kidney disease in hypertensive diabetic patients with ACE II and DD genotypes. ARB can prevent/delay development of diabetic nephropathy independently of its beneficial blood pressure-lowering effect in patients with type 2 diabetes and microalbuminuria. Recently, two landmark studies led to the following conclusion: "Losartan and Irbesartan conferred significant renal benefit in patients with type 2 diabetes and nephropathy. This protection is independent of the reduction in blood pressure it causes. The ARB is generally safe and well tolerated." A recent metaanalysis indicates that ARBs reduce cardiovascular events mainly because of reduction in first hospitalization for congestive heart failure in hypertensive type 2 diabetic patients with albuminuria. The studies mentioned here suggest that ARB represents a beneficial treatment of hypertension and proteinuria in incipient and overt diabetic nephropathy.

Low-dose dual blockade of the renin-angiotensin system in patients with primary glomerulonephritis

BACKGROUND

Treatment with agents interfering with the renin-angiotensin system retards the progressive course of proteinuric chronic renal disease. However, because of unwanted effects associated with such therapy, some patients cannot be treated with these drugs at all or may be administered only very small doses. To find an optimal nephroprotective strategy for these patients, we compared antiproteinuric effects of combination therapy with an angiotensin-converting enzyme inhibitor and angiotensin II type 1 receptor antagonist in very small doses with treatment with either agent alone at greater, but not maximal, doses. We compared the concomitant use of benazepril, 5 mg, and losartan, 25 mg, and monotherapy with these agents in doses 2-fold greater.

METHODS

This is a randomized, open, crossover study of 3 treatments in 3 periods of 4 months each. Twenty-four patients with primary glomerulonephritis and nonnephrotic proteinuria, recognized previously as not able to be administered high doses of drugs from these classes, completed the protocol.

RESULTS

Combined therapy decreased 24-hour proteinuria (-45.54% versus baseline) more effectively than either losartan (-28.17%; analysis of variance, P < 0.01) or benazepril (-20.19%; analysis of variance, P < 0.001) alone. Subgroup analysis showed that antiproteinuric effects of combination therapy, as well as losartan or benazepril alone, were significantly greater in patients with basal proteinuria greater than 2 g/24 h than in those with proteinuria less than this value (P < 0.001, P < 0.01, and P < 0.05, respectively). All therapies significantly decreased blood pressure (BP) compared with baseline, but there were no differences between treatments in BP changes.

CONCLUSION

The study shows that combination therapy with very small doses of losartan and benazepril was more effective in reducing proteinuria than greater doses of either agent in monotherapy, and this greater antiproteinuric efficacy was independent of changes in BP.

How high should an ACE inhibitor or angiotensin receptor blocker be dosed in patients with diabetic nephropathy?

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs), two drug classes that effectively block the actions of the renin-angiotensin system (RAS), have unique capabilities as antihypertensive agents. Recent landmark clinical trials have demonstrated their important roles as primary therapy for the prevention of renal disease in diabetes. The optimal dosage of these RAS blockers required to slow the progression of renal disease or impair the development of cardiovascular risk is not known. However, data from many studies strongly support the use of the higher doses of ACE inhibitors or ARBs to reduce proteinuria. All studies of kidney disease progression demonstrate benefit on slowing only when blood pressure is reduced when using higher doses. In order to accrue the optimum benefit from ACE inhibitors and ARBs, the dose-response relationship for diabetic renal disease will have to be determined. The best strategy, ie, supramaximal doses of ACE inhibitors or ARBs or combining them, is still a matter of debate but may be resolved soon by results of ongoing studies.

Renoprotective effects of adding angiotensin II receptor blocker to maximal recommended doses of ACE inhibitor in diabetic nephropathy: a randomized double-blind crossover trial

OBJECTIVE

We evaluated the renoprotective effects as reflected by short-term changes in albuminuria of dual blockade of the renin-angiotensin system (RAS) by adding an angiotensin II receptor blocker (ARB) to treatment with maximal recommended doses of an ACE inhibitor (ACEI) in patients with type 2 diabetes and nephropathy.

RESEARCH DESIGN AND METHODS

A total of 20 patients (17 men and 3 women) with type 2 diabetes along with hypertension and nephropathy were enrolled in this double-blind, randomized, two-period, crossover trial of 8 weeks of treatment with the ARB candesartan 16 mg daily and placebo added in random order to existing treatment with lisinopril/enalapril 40 mg daily or captopril 150 mg daily. At the end of each treatment period, we evaluated albuminuria in three 24-h urinary collections by turbidimetry, 24-h ambulatory blood pressure (ABP) using the Takeda-TM2420, and glomerular filtration rate (GFR) by the (51)Cr-EDTA plasma-clearance technique.

RESULTS

During monoblockade of the RAS by ACEI treatment, albuminuria was 706 (349-1,219) mg/24 h [geometric mean (IQR)]; 24-h ABP was 138 +/- 3/72 +/- 2 mmHg (mean +/- SE); and GFR was 77 +/- 6 ml x min(-1) x 1.73 m(-2) (mean +/- SE). During dual blockade of the RAS by addition of candesartan 16 mg daily, there was a mean (95% CI) reduction in albuminuria of 28 (17-38) compared with ACEI alone (P < 0.001). There was a modest reduction in systolic/diastolic 24-h ABP of 3/2 mmHg (-2 to 8 systolic, -2 to 5 diastolic; NS). Changes in albuminuria did not correlate to changes in ABP. Addition of candesartan 16 mg daily induced a small, insignificant decrease in GFR of 4 (-1 to 9) ml x min(-1) x 1.73 m(-2).

CONCLUSIONS

Dual blockade of the RAS provides superior short-term renoprotection independent of systemic blood pressure changes in comparison with maximally recommended doses of ACEI in patients with type 2 diabetes as well as nephropathy.

Dual blockade of the renin-angiotensin system versus maximal recommended dose of ACE inhibition in diabetic nephropathy

BACKGROUND

Albuminuria and hypertension are predictors of poor renal and cardiovascular outcome in diabetic patients. We tested whether dual blockade of the renin-angiotensin system (RAS) with both an angiotensin-converting enzyme (ACE) inhibitor and an angiotensin II receptor blocker (ARB) is superior to maximal recommended dose of ACE inhibitor in type 1 diabetic patients with diabetic nephropathy (DN).

METHODS

We performed a randomized, double-blind, crossover trial with 8 weeks treatment with placebo and irbesartan 300 mg (once daily), added on top of enalapril 40 mg (once daily). We included 24 type 1 patients with DN. At the end of each treatment period, albuminuria, 24-hour blood pressure, and glomerular filtration rate (GFR) were measured.

RESULTS

Values on ACE inhibitors + placebo were: albuminuria [mean (95% CI)], 519 (342 to 789) mg/24 hours; blood pressure [mean (SEM)], 131 (3)/74 (1) mm Hg, and GFR [mean (SEM)], 65 (5) mL/min/1.73 m2. Dual blockade of the RAS induced a reduction in albuminuria [mean (95% CI)] of 25% (15, 34) (P < 0.001), a reduction in systolic blood pressure of 8 mm Hg (4, 12) (P = 0.002), and a reduction of 4 mm Hg (2, 7) (P = 0.003) in diastolic blood pressure. GFR and plasma potassium remained unchanged during both treatment regimes. Dual blockade was safe and well tolerated.

CONCLUSION

Dual blockade of the RAS is superior to maximal recommended dose of ACE inhibitors with regard to lowering of albuminuria and blood pressure in type 1 patients with DN. Long-term trials are needed to further establish the role of dual blockade of the RAS in renal and cardiovascular protection.

Outcome studies in diabetic nephropathy

Outcome studies in diabetic nephropathy have focused on strategies to prevent progression of diabetic nephropathy, the leading cause of ESRD in the United States. Once diabetics develop overt nephropathy, prognosis is poor. Risk factors for diabetic nephropathy are discussed, and include hyperglycemia, hypertension, angiotensin II, proteinuria, dyslipidemia, smoking, and anemia. Major outcomes as well as outcome studies in diabetic nephropathy for patients with microalbuminuria and macroalbuminuria are reviewed. Furthermore, the role of therapy with angiotensin converting enzyme inhibitors, angiotensin II receptor blockers, calcium channel blockers, and mineralocorticoid receptor antagonists as well as selected combination therapy are discussed. Recommendations for therapy with ace inhibitors and angiotensin II receptor blockers are made based on this evidence.