The Renin-Angiotensin system in Hypertension and Diabetes: from man to rodent and back

Abstract In addition to the systemic (endocrine) RAS, it is generally believed that the kidney has its own (paracrine) RAS, since it is capable of local angiotensin II synthesis, and all RAS components are expressed locally. Another source of RAS components in the kidney may be endocytotic uptake from the ultrafiltrate. It has been suggested that RAS components in urine reflect the activity of the intrarenal RAS independently from the systemic RAS. This implies that urinary RAS components can be used as a marker for the activity of the intrarenal RAS, or even as renal disease markers. Chapter 2 of this thesis gives an overview of studies on urinary RAS components as markers of the intrarenal RAS. In chapter 4 we conclude that variation in tubular reabsorption is sufficient to explain why urinary renin and albumin excretion do not correlate. In chapter 3 we compare a new renin ELISA with the classical ways of measuring renin, either immunoreactively or enzyme-kinetically. Our data suggest that the ELISA is less sensitive than the other two methods, and makes use of recombinant prorenin as a standard that has not been calibrated against the international standard. In chapters 5 and 6 we review recent studies on renal angiotensin-converting enzyme (ACE), and concluded that the evidence supporting a role for renal ACE in Angiotensin II- or NOS inhibition-induced hypertension is still incomplete. In chapter 7 we studied the combination of an angiotensin receptor blocker (ARB) with a neprilysin (NEP) inhibitor in hypertensive rats. This combination treatment is referred to as ‘ARNI’. We confirm that ARNI has an additional blood pressure lowering effect compared to ARB alone. However, when the dose of the NEP inhibitor was increased, this effect was annihilated, likely due to an increase in endothelin-1, accompanied by an increase in renal sodium-hydrogen exchanger 3 protein abundance, and an upregulation of constrictor vascular endothelin type B receptors. In chapter 8 we studied the effects of ARNI in diabetic, hypertensive rats. We found that ARNI reduced heart weight, and improved proteinuria and the development of focal segmental glomerulosclerosis more strongly than ARB alone. Blood pressure in ARB- and ARNI-treated animals was equal, which suggests that the observed effects occurred independently of blood pressure. Similar protective effects were found on diabetic retinopathy in these rats in chapter 9

From ARB to ARNI in Cardiovascular Control

Coexistence of hypertension, diabetes mellitus and chronic kidney disease synergistically aggravates the risk of cardiovascular and renal morbidity and mortality. These high-risk, multi-morbid patient populations benefit less from currently available anti-hypertensive treatment. Simultaneous angiotensin II type 1 receptor blockade and neprilysin inhibition (‘ARNI’) with valsartan/sacubitril (LCZ696) might potentiate the beneficial effects of renin-angiotensin-aldosterone inhibition by reinforcing its endogenous counterbalance, the natriuretic peptide system. This review discusses effects obtained with this approach in animals and humans. In animal models of hypertension, either alone or in combination with myocardial infarction or diabetes, ARNI consistently reduced heart weight and cardiac fibrosis in a blood pressure-independent manner. Additionally, LCZ696 treatment reduced proteinuria, focal segmental glomerulosclerosis and retinopathy, thus simultaneously demonstrating favourable effects on microvascular complications. These results were confirmed in patient populations. Besides blood pressure reductions in hypertensive patients and greatly improved (cardiovascular) mortality in heart failure patients, ventricular wall stress and albuminuria w

Urinary markers of intrarenal renin-angiotensin system activity in vivo

Recent interest focuses on urinary renin and angiotensinogen as markers of renal renin-angiotensin system activity. Before concluding that these components are independent markers, we need to exclude that their presence in urine, like that of albumin (a protein of comparable size), is due to (disturbed) glomerular filtration. This review critically discusses their filtration, reabsorption and local release. Given the close correlation between urinary angiotensinogen and albumin in human studies, it concludes that, in humans, urinary angiotensinogen is a filtration barrier damage marker with the same predictive power as urinary albumin. In contrast, in animals, tubular angiotensinogen release may occur, although tubulus-specific knockout studies do not support a functional role for such angiotensinogen. Urinary renin levels, relative to albumin, are >200-fold higher and unrelated to albumin. This may reflect release of renin from the urinary tract, but could also be attributed to activation of filtered, plasma-derived prorenin and/or incomplete tubular reabsorption

Beneficial effects of combined AT1 receptor/neprilysin inhibition (ARNI) versus AT1 receptor blockade alone in the diabetic eye

PURPOSE. Dysfunction of the renin-angiotensin system (RAS) contributes to pathogenesis of diabetic retinopathy (DR). Yet RAS blockers have only limited beneficial effects on progression of DR in clinical trials. The natriuretic peptide system offsets RAS, so that enhancing the activity of this system on top of RAS blockade might be beneficial. Neprilysin has an important role in the degradation of natriuretic peptides. Therefore, we hypothesize that dual angiotensin receptor-neprilysin inhibition (ARNI) may outperform angiotensin receptor blocker (ARB) in protection against DR. We tested this hypothesis in streptozotocininduced diabetic transgenic (mRen2)27 rats. METHODS. Adult male diabetic (mRen2)27 rats were followed for 5 or 12 weeks. Treatment with vehicle, irbesartan (ARB), or ARB combined with the neprilysin inhibitor thiorphan (irbesartan+thiorphan [ARNI]) occurred during the final 3 weeks. Retinal cell death, gliosis, and capillary loss were evaluated. Real-time polymerase chain reaction (RT-PCR) analyses were performed to quantify the retinal level of inflammatory cell markers. RESULTS. Both ARB-and ARNI-treated groups showed similarly reduced retinal apoptotic cell death, gliosis, and capillary loss compared to the vehicle-treated group in the 5-week study. Treatment with ARNI reduced the expression of inflammatory markers more than ARB treatment in the 5-week study. In the 12-week study, ARNI treatment showed significantly more reduction in apoptotic cell death (51% vs. 25% reduction), and capillary loss (68% vs. 43% reduction) than ARB treatment. CONCLUSIONS. Treatment with ARNI provides better protection against DR in diabetic (mRen2)27 transgenic rats, compared to ARB alone. This approach may be a promising treatment option for patients with DR

Effects of direct renin blockade on renal & systemic hemodynamics and on raas activity, in weight excess and hypertension: A randomized clinical trial

Aim: The combination of weight excess and hypertension significantly contributes to cardiovascular risk and progressive kidney damage. An unfavorable renal hemodynamic profile is thought to contribute to this increased risk and may be ameliorated by direct renin inhibition (DRI). The aim of this trial was to assess the effect of DRI on renal and systemic hemodynamics and on RAAS activity, in men with weight excess and hypertension. Methods: A randomized, double-blind, cross-over clinical trial to determine the effect of DRI (aliskiren 300 mg/day), with angiotensin converting enzyme inhibition (ACEi; ramipril 10 mg/day) as a positive control, on renal and systemic hemodynamics, and on RAAS activity (n = 15). Results: Mean (SEM) Glomerular filtration rate (101 (5) mL/min/1.73m2) remained unaffected by DRI or ACEi. Effective renal plasma flow (ERPF; 301 (14) mL/min/1.73m2) was increased in response to DRI (320 (14) mL/min/1.73m2, P = 0.012) and ACEi (317 (15) mL/min/1.73m2, P = 0.045). Filtration fraction (FF; 34 (0.8)%) was reduced by DRI only (32 (0.7)%, P = 0.044). Mean arterial pressure (109 (2) mmHg) was reduced by DRI (101 (2) mmHg, P = 0.008) and ACEi (103 (3) mmHg, P = 0.037). RAAS activity was reduced by DRI and ACEi. Albuminuria (20 [9±42] mg/d) was reduced by DRI only (12 [5±28] mg/d, P = 0.030). Conclusions: In men with weight excess and hypertension, DRI and ACEi improved renal and systemic hemodynamics. Both DRI and ACEi reduced RAAS activity. Thus, DRI provides effective treatment in weight excess and hypertension

Branched-chain amino acid requirements for enterally fed term neonates in the first month of life

Background: Knowledge of essential amino acid requirements in infants is important because excessive intake of protein can lead to increased long-term morbidity such as obesity. A deficient intake may lead to suboptimal growth and impaired neurodevelopment. The current recommended branched-chain amino acid requirements in infants aged 0-1 mo are based on the amino acid content of human milk. Objective: We quantified the requirements for isoleucine, leucine, and valine for term neonates by using the indicator amino acid oxidation method with [1-13C]phenylalanine as the indicator. Design: Fully enterally fed term infants received randomly graded amounts of isoleucine (5-216 mg · kg-1 · d-1), leucine (5-370 mg · kg -1 · d-1), or valine (5-236 mg · kg -1 · d-1) as part of an elemental formula. Data are expressed as means ± SDs. Results: Eighty-three Asian, term neonates (mean ± SD birth weight: 3.3 ± 0.4 kg; gestational age: 39.4 ± 1.3 wk) were studied at a postnatal age of 13 ± 5 d. Mean requirements for isoleucine, leucine, and valine (measured in boys only) were 105 mg · kg-1 · d-1 (r2 = 0.61, P < 0.001), 140 mg · kg-1 · d-1 (r 2 = 0.26, P < 0.01), and 110 mg · kg-1 · d-1 (r2 = 0.35, P = 0.001), respectively. Conclusions: Current human milk-based recommendations for isoleucine and valine in term infants aged 0-1 mo are correct. However, the current recommendation for leucine (166 mg · kg-1 · d-1) is higher than the mean requirement of 140 mg · kg-1 · d-1 that we determined in this study. This trial was registered at www.trialregister. nl as NTR1610

On the origin of urinary renin: A translational approach

Urinary angiotensinogen excretion parallels albumin excretion, which is not the case for renin, while renin's precursor, prorenin, is undetectable in urine. We hypothesized that renin and prorenin, given their smaller size, are filtered through the glomerulus in larger amounts than albumi