Salt intake and non-ACE pathways for intrarenal angiotensin II generation in man

Mast Cell Chymase and Kidney Disease

A sizable part (~2%) of the human genome encodes for proteases. They are involved in many physiological processes, such as development, reproduction and inflammation, but also play a role in pathology. Mast cells (MC) contain a variety of MC specific proteases, the expression of which may differ between various MC subtypes. Amongst these proteases, chymase represents up to 25% of the total proteins in the MC and is released from cytoplasmic granules upon activation. Once secreted, it cleaves the targets in the local tissue environment, but may also act in lymph nodes infiltrated by MC, or systemically, when reaching the circulation during an inflammatory response. MC have been recognized as important components in the development of kidney disease. Based on this observation, MC chymase has gained interest following the discovery that it contributes to the angiotensin-converting enzyme’s independent generation of angiotensin II, an important inflammatory mediator in the development of kidney disease. Hence, progress regarding its role has been made based on studies using inhibitors but also on mice deficient in MC protease 4 (mMCP-4), the functional murine counterpart of human chymase. In this review, we discuss the role and actions of chymase in kidney disease. While initially believed to contribute to pathogenesis, the accumulated data favor a more subtle view, indicating that chymase may also have beneficial actions.

Urine RAS components in mice and people with type 1 diabetes and chronic kidney disease

The pathways implicated in diabetic kidney disease (DKD) are largely derived from animal models. To examine if alterations in renin-angiotensin system (RAS) in humans are concordant with those in rodent models, we measured concentration of angiotensinogen (AOG), cathepsin D (CTSD), angiotensin-converting enzyme (ACE), and ACE2 and enzymatic activities of ACE, ACE2, and aminopeptidase-A in FVB mice 13-20 wk after treatment with streptozotocin (n = 9) or vehicle (n = 15) and people with long-standing type 1 diabetes, with (n = 37) or without (n = 81) DKD. In streptozotocin-treated mice, urine AOG and CTSD were 10.4- and 3.0-fold higher than in controls, respectively (P < 0.001). Enzymatic activities of ACE, ACE2, and APA were 6.2-, 3.2-, and 18.8-fold higher, respectively, in diabetic animals (P < 0.001). Angiotensin II was 2.4-fold higher in diabetic animals (P = 0.017). Compared with people without DKD, those with DKD had higher urine AOG (170 vs. 15 μg/g) and CTSD (147 vs. 31 μg/g). In people with DKD, urine ACE concentration was 1.8-fold higher (1.4 vs. 0.8 μg/g in those without DKD), while its enzymatic activity was 0.6-fold lower (1.0 vs. 1.6 × 10⁹ RFU/g in those without DKD). Lower ACE activity, but not ACE protein concentration, was associated with ACE inhibitor (ACEI) treatment. After adjustment for clinical covariates, AOG, CTSD, ACE concentration, and ACE activity remained associated with DKD. In conclusion, in mice with streptozotocin-induced diabetes and in humans with DKD, urine concentrations and enzymatic activities of several RAS components are concordantly increased, consistent with enhanced RAS activity and greater angiotensin II formation. ACEI use was associated with a specific reduction in urine ACE activity, not ACE protein concentration, suggesting that it may be a marker of exposure to this widely-used therapy.

Renin inhibition ameliorates renal damage through prominent suppression of both angiotensin I and II in human renin angiotensinogen transgenic mice with high salt loading

BACKGROUND

The renin-angiotensin-aldosterone system (RAAS) plays pivotal roles in the pathogenesis of chronic kidney disease (CKD) progression. Aliskiren, a direct renin inhibitor, inhibits the rate-limiting step of the RAAS without any alternative pathway. It is proven to reduce albuminuria in CKD patients treated with angiotensin blockade. However, there are few reports which evaluate the advantage of aliskiren as the first-line drug against CKD progression in RAAS-activated hypertensive patients.

METHODS

Tsukuba hypertensive mice (THM), double transgenic mice carrying both the human renin and human angiotensinogen genes, were fed a high-salt diet and treated with hydraladine, ramipril and aliskiren for 10 weeks. Blood pressure and urinary albumin excretion were measured every 2 weeks during the experimental period. We evaluated renal histological changes and gene expression. Plasma angiotensin concentration was measured to evaluate the RAAS inhibitory effect.

RESULTS

High-salt-loaded THM showed severe hypertension and renal injury. All antihypertensive drugs suppressed blood pressure and prevented renal disease progression. RAAS blockade showed a higher renoprotective effect than hydraladine despite an equivalent blood pressure lowering effect. Aliskiren exhibited even stronger renoprotection than ramipril. Plasma angiotensin concentration was increased in THM fed both normal salt and high salt. Hydraladine did not alter the plasma angiotensin concentration. Ramipril significantly decreased angiotensin II concentration. Aliskiren treatment almost completely suppressed angiotensin I and resulted in lower angiotensin II concentration than ramipril treatment.

CONCLUSION

Aliskiren prevents renal disease progression by suppressing both angiotensin I and II in RAAS-activated pathology. Our data suggest the application of a renin inhibitor for preventing kidney disease progression in CKD patients.

Response to angiotensin-converting enzyme inhibition is selectively blunted by high sodium in angiotensin-converting enzyme DD genotype: evidence for gene-environment interaction in healthy volunteers

BACKGROUND

Renin-angiotensin-aldosterone system blockade is a cornerstone in cardiovascular protection. Angiotensin-converting enzyme (ACE)-DD genotype has been associated with resistance to angiotensin-converting enzyme inhibition (ACEi), but data are conflicting. As sodium intake modifies the effect of ACEi as well as the genotype-phenotype relationship, we hypothesize gene-environment interaction between sodium-status, the response to ACEi, and ACE genotype.

METHOD

Thirty-five male volunteers (26 ± 9 years; II n = 6, ID n = 18, DD n = 11) were studied during placebo and ACEi (double blind, enalapril 20 mg/day) on low [7 days 50 mmol Na/day (low salt)] and high [7 days 200 mmol Na/day (high salt)] sodium, with a washout of 6 weeks in-between. After each period mean arterial pressure (MAP) was measured before and during graded infusion of angiotensin II (Ang II).

RESULTS

During high salt, ACEi reduced MAP in II and ID, but not in DD [II: 88 (78-94) versus 76 (72-88); ID: 87 (84-91) versus 83 (79-87); both P < 0.05 and DD: 86 (82-96) versus 88 (80-90); ns, P < 0.05 between genotypes]. However, during low salt, ACEi reduced MAP in all genotype groups [II: 83 (78-89) versus 77 (72-83); ID: 88 (84-91) versus 82 (78-86); DD: 84 (80-91) versus 81 (75-85); all P < 0.05]. During high salt + ACEi, the Ang II response was blunted in DD, with an 18% rise in MAP during the highest dose versus 22 and 31% in ID and II (P < 0.05). Low salt annihilated these differences.

CONCLUSION

In healthy participants, the MAP response to ACEi is selectively blunted in DD genotype during high salt, accompanied by blunted sensitivity to Ang II. Low salt corrects both abnormalities. Further analysis of this gene-environment interaction in patients may contribute to strategies for improvement of individual treatment efficacy.

Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers and combined therapy in patients with micro- and macroalbuminuria and other cardiovascular risk factors: a systematic review of randomized controlled trials

BACKGROUND

A recent clinical trial showed harmful renal effects with the combined use of angiotensin-converting enzyme inhibitors (ACEI) and angiotensin-II receptor blockers (ARB) in people with diabetes or vascular disease. We examined the benefits and risks of these agents in people with albuminuria and one or more cardiovascular risk factors.

METHODS

MEDLINE, EMBASE and Renal Health Library were searched for trials comparing ACEI, ARB or their combination with placebo or with one another in people with albuminuria and one or more cardiovascular risk factor.

RESULTS

Eighty-five trials (21,708 patients) were included. There was no significant reduction in the risk of all-cause mortality or fatal cardiac-cerebrovascular outcomes with ACEI versus placebo, ARB versus placebo, ACEI versus ARB or with combined therapy with ACEI + ARB versus monotherapy. There was a significant reduction in the risk of nonfatal cardiovascular events with ACEI versus placebo but not with ARB versus placebo, ACEI versus ARB or with combined therapy with ACEI + ARB versus monotherapy. Development of end-stage kidney disease and progression of microalbuminuria to macroalbuminuria were reduced significantly with ACEI versus placebo and ARB versus placebo but not with combined therapy with ACEI + ARB versus monotherapy.

CONCLUSIONS

ACEI and ARB exert independent renal and nonfatal cardiovascular benefits while their effects on mortality and fatal cardiovascular disease are uncertain. There is a lack of evidence to support the use of combination therapy. A comparative clinical trial with ACE, ARB and its combination in people with albuminuria and a cardiovascular risk factor is warranted.

Agents in development for the treatment of diabetic nephropathy

BACKGROUND

Nephropathy is a major cause of morbidity and mortality in diabetic patients. Current treatments include optimization of glycemic and blood pressure control, but more innovative strategies are needed for the prevention and treatment of diabetic nephropathy.

OBJECTIVES

To review emerging therapies for diabetic nephropathy.

METHODS

This paper discusses the molecular mechanisms of diabetic nephropathy and the potential therapeutic interventions.

RESULTS/CONCLUSION

New therapies, including those targeting the accumulation of advanced glycation end products (AGEs) and reactive oxygen species (ROS) generation, are likely to feature in future treatment regimens. Other approaches that at this stage do not appear to be progressing include the glycosaminoglycan sulodexide and the protein kinase C-beta (PKC-beta) inhibitor, ruboxistaurin.

Racial differences in renal vascular response to angiotensin blockade with captopril or candesartan

OBJECTIVE

We compared the renal vascular response to captopril and candesartan among nondiabetic, normotensive black and white participants to explore angiotensin-converting enzyme-independent generation of angiotensin II.

METHODS

Thirteen black individuals and 10 white individuals in low-salt balance were given captopril and candesartan on sequential study days, and the renal plasma flow responses to these agents were measured.

RESULTS

Consistent with our prior observations, white individuals demonstrated a strong, significant correlation between responses to these drugs (r = 0.78, P = 0.008) and a significantly greater increase in the renal plasma flow in response to candesartan compared with captopril (104.2 +/- 26.8 versus 52.4 +/- 24.3 ml/min per 1.73 m; P = 0.03). In black participants, however, no correlation between responses to captopril and to candesartan was observed (r = 0.22, P = 0.47) and there was no difference in the renal plasma flow response between the two drugs (90.4 +/- 13.0 versus 80.4 +/- 15.3 ml/min per 1.73 m; P = 0.59). The difference in the response to the two drugs was significantly higher among white participants compared with black participants (P = 0.03).

CONCLUSION

We confirmed the contribution of an angiotensin-converting enzyme-independent pathway for angiotensin II generation in the kidneys of nondiabetic, normotensive white, but not black, individuals.

Combination Therapy With an Angiotensin Receptor Blocker and an ACE Inhibitor in Proteinuric Renal Disease: A Systematic Review of the Efficacy and Safety Data

Blockade of the renin-angiotensin system with either an angiotensin-converting enzyme (ACE) inhibitor or an angiotensin receptor blocker (ARB) was shown to decrease urinary protein excretion and slow the progression of both diabetic and nondiabetic proteinuric renal disease. The safety and efficacy of combined ACE-inhibitor and ARB therapy is not well established. We conducted a systematic review and meta-analysis of randomized trials evaluating the combination of an ACE inhibitor and an ARB in patients with chronic proteinuric renal disease. Twenty-one randomized controlled studies (n = 654 patients) were identified using MEDLINE, EMBASE, and Cochrane Central databases. Five trials had a parallel-group design and 16 trials used a crossover design. Combination therapy with an ACE inhibitor and an ARB resulted in a small, but significant, increase in serum potassium levels (weighted mean difference, 0.11 mEq/L [0.11 mmol/L]; 95% confidence interval [CI], 0.05 to 0.17) and a nonsignificant decrease in glomerular filtration rate (weighted mean difference, 1.4 mL/min [0.02 mL/s]; 95% CI, -2.6 to 0.2). Addition of an ARB resulted in a further decrease in proteinuria (weighted mean difference, 440 mg/d; 95% CI, 289 to 591) compared with an ACE inhibitor alone. This effect was observed in patients with diabetic (210 mg/d; 95% CI, 84 to 336) and nondiabetic (582 mg/d; 95% CI, 371 to 793) renal disease. In conclusion, the combination of ACE-inhibitor and ARB therapy in patients with chronic proteinuric renal disease is safe, without clinically meaningful changes in serum potassium levels or glomerular filtration rates. Combination therapy also was associated with a significant decrease in proteinuria, at least in the short term. Additional trials with longer follow-up are needed to determine whether the decrease in proteinuria will result in significant preservation of renal function.

ACE and non-ACE pathways in the renal vascular response to RAS interruption in type 1 diabetes mellitus

BACKGROUND

The enormous contribution of renin-angiotensin system (RAS) interruption with ACE (angiotensin-converting enzyme) inhibitors and angiotensin II receptor blockers (ARB) in the treatment of diabetic nephropathy has led to interest in the factors involved in angiotensin II (Ang II) generation. In normal subjects, RAS interruption using an ARB produced a 50% greater renal plasma flow (RPF) rise than with an ACE inhibitor, suggesting a substantial contribution of non-ACE pathways. Moreover, immunohistochemistry studies in kidneys of overtly proteinuric diabetic subjects showed up-regulation of chymase, an alternative Ang II-generating enzyme. Our aim was to determine the degree to which the non-ACE pathways contribute to RAS activation in type 1 diabetes mellitus (DM).

METHODS

Type 1 DM patients (N= 37, 14 M/23 F; age 31 +/- 2 years; DM duration 16 +/- 1.7 years; HbA1c 7.7.0 +/- 0.3%) were studied on a high-salt diet. They received captopril 25 mg po one day and candesartan 16 mg po the next day. RPF and glomerular filtration rate (GFR) were measured before and up to 4 hours after drug administration.

RESULTS

Both captopril and candesartan induced a significant rise in RPF (baseline vs. peak <0.0001 for both), and the rise was concordant for the 2 drugs (r= 0.77, P < 0.001). However, the RPF responses were not significantly different between the 2 drugs (captopril 72 +/- 11 mL/min/1.73 m(2), candesartan 75 +/- 12, P= 0.841).

CONCLUSION

In predominantly normoalbuminuric, normotensive type 1 DM, activation of the intrarenal RAS reflects a mechanism involving primarily the classic ACE pathway.

Effects of an angiotensin II receptor blocker, valsartan, on residual renal function in patients on CAPD

BACKGROUND

Both residual renal function and blood pressure (BP) control contribute to patient survival in patients receiving continuous ambulatory peritoneal dialysis (CAPD). It is unknown whether antihypertensive drugs affect residual renal function in addition to BP reduction.

METHODS

We examined the effects of an angiotensin II receptor blocker, valsartan, on residual renal function and total clearance (renal and peritoneal) in 34 Japanese CAPD patients from 3 months to 2 years after the start of dialysis therapy. Patients were randomly assigned to valsartan (n = 18; age, 63.5 +/- 3.7 years; 11 men, 7 women) or a control group (n = 16; age, 63.5 +/- 3.3 years; 10 men, 6 women). Conventional antihypertensive treatment was continued in all patients to achieve the target BP in both groups of 130/80 mm Hg or less, measured at home.

RESULTS

BP reduction was similar in the valsartan and control groups. Valsartan significantly slowed the progressive decline in both residual renal function (3.2 +/- 0.3 to 4.3 +/- 0.7 mL/min/1.73 m2) and total clearance (42.1 +/- 3.2 to 48.3 +/- 4.8 L/wk/1.73 m2) by dialysis in CAPD patients compared with controls (5.9 +/- 0.5 to 2.8 +/- 0.4 mL/min/1.73 m2; 47.1 +/- 4.8 to 31.4 +/- 5.2 L/wk/1.73 m2).

CONCLUSION

This study shows that in patients with hypertension starting CAPD therapy, valsartan slows the decline in residual renal function and contributes to maintenance of weekly creatinine clearance and Kt/V (fraction per dialysis), which are the major factors contributing to the mortality and morbidity of CAPD patients. This effect appears to be mostly a result of maintaining residual renal function.

Advances in the treatment of diabetic renal disease: focus on losartan

Diabetic nephropathy is the leading cause of end stage renal disease (ESRD), and given that treating this condition is a considerable economic burden, the prevention of ESRD is a major public health goal. The renin-angiotensin system (RAS) is aberrantly activated in patients with diabetes. Angiotensin II (AII), a downstream effector of the RAS, has haemodynamic and non-haemodynamic effects that contribute to the development and progression of nephropathy. For patients with type 2 diabetes mellitus (T2DM) and hypertension, an AII receptor blocker (AIIRB) is recommended as the first drug that should be used. This review will focus on the rationale for the use of losartan as a treatment for nephropathy associated with T2DM. In animal models of diabetes, losartan reduced proteinuria and conferred renal protection. In RENAAL (Reduction in Endpoints in Non-Insulin-Dependent Diabetes Mellitus with the Angiotensin II Antagonist Losartan), the first major randomised trial that investigated the benefit of losartan in patients with T2DM and nephropathy, losartan significantly reduced the risk of a doubling of serum creatinine and progression to ESRD, significantly lowered the levels of proteinuria and slowed the rate of decline in glomerular filtration rate. This review also discusses other clinical trials of losartan and other AIIRBs in T2DM, and considers alternative mechanisms by which losartan may be exerting its effects. The collective experience in treatment trials highlighted in this review indicate that losartan and other AIIRBs can reduce blood pressure and the progression of proteinuria in diabetic renal disease. However, losartan is thus far the only AIIRB that has been shown to reduce significantly the risk of ESRD and cardiovascular events in patients with T2DM. Its use in hypertensive patients with T2DM and nephropathy may play an important role in reducing the burden of ERSD.

High Dietary Sodium Blunts Effects of Angiotensin-converting Enzyme Inhibition on Vascular Angiotensin I–to–Angiotensin II Conversion in Rats

High sodium intake blunts the efficacy of angiotensin (Ang)-converting enzyme (ACE) inhibition (ACEi), but the underlying mechanism is incompletely characterized. High sodium has been reported to increase vascular expression and vascular activity of ACE. To investigate whether high-dietary sodium-induced effects on vascular conversion of Ang I might be involved in the sodium-induced blunting of the response to ACEi, the authors studied the vasoconstrictor responses to Ang I and Ang II of isolated aortic rings from healthy rats on low dietary sodium (LS: 0.05% NaCl) and high dietary sodium (HS: 2.0% NaCl) after 3 weeks of ACEi (lisinopril 75 mg/L) or vehicle (CON). Blood pressure was similar in LS and HS in CON, but HS blunted the blood pressure response to ACEi. Functional conversion of Ang I was assessed as the difference in dose-response curves to Ang I and Ang II in parallel aortic rings. Sodium intake did not affect the dose-response curves to Ang I and Ang II in CON. In the ACEi groups, a significant difference was present between the curves for Ang I and Ang II on LS (deltaEC50, 6.7 nM; range, 2.2-13 nM; P < 0.01) but not on HS (deltaEC50: 1.3 nM; range, 0.0-4.1 nM, median [interquartile range], NS). Thus, HS blunts the ACEi-induced reduction of functional vascular Ang I conversion compared with LS. Whether the blunted functional vascular conversion is causally related to the blunted blood pressure response remains to be elucidated.