Intrarenal renin-angiotensin system

Ameliorative effect of mussel-derived ACE inhibitory peptides on spontaneous hypertension rats

PURPOSE

The purpose of this study was to prepare the novel mussel-derived ACE inhibitory peptides (MEPs) by enzymatic hydrolysis of Mytilus edulis and investigate their antihypertensive effects in vivo.

METHODS

After assessing the stability of MEPs in vitro, we investigated the effect of MEPs on hypertension using spontaneously hypertensive rats (SHRs). Subsequently, MEPs were purified and identified by ultrafiltration, gel filtration chromatography and liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

Our study demonstrated that MEPs could keep stable ACE inhibitory activity after treatment with heat, acid, alkali, metal ions and simulated gastrointestinal digestive fluid. Additionally, the animal experiments showed that both short-term and long-term treatment with MEPs resulted in a significant reduction in systolic and diastolic blood pressure in SHRs. Mechanistically, the results suggested that MEPs could reduce vascular remodeling, regulate renin-angiotensin system (RAS), and inhibit kidney and myocardial fibrosis. Finally, we isolated and identified five peptides from MEPs, with the peptide Ile-Leu-Thr-Glu-Arg showed the highest ACE inhibition rate.

CONCLUSION

Our findings demonstrate the potential use of MEPs as active components in functional foods designed to lower blood pressure.

Hypertensive Nephropathy: Unveiling the Possible Involvement of Hemichannels and Pannexons

Hypertension is one of the most common risk factors for developing chronic cardiovascular diseases, including hypertensive nephropathy. Within the glomerulus, hypertension causes damage and activation of mesangial cells (MCs), eliciting the production of large amounts of vasoactive and proinflammatory agents. Accordingly, the activation of AT1 receptors by the vasoactive molecule angiotensin II (AngII) contributes to the pathogenesis of renal damage, which is mediated mostly by the dysfunction of intracellular Ca²⁺ ([Ca²⁺]_i) signaling. Similarly, inflammation entails complex processes, where [Ca²⁺]_i also play crucial roles. Deregulation of this second messenger increases cell damage and promotes fibrosis, reduces renal blood flow, and impairs the glomerular filtration barrier. In vertebrates, [Ca²⁺]_i signaling depends, in part, on the activity of two families of large-pore channels: hemichannels and pannexons. Interestingly, the opening of these channels depends on [Ca²⁺]_i signaling. In this review, we propose that the opening of channels formed by connexins and/or pannexins mediated by AngII induces the ATP release to the extracellular media, with the subsequent activation of purinergic receptors. This process could elicit Ca²⁺ overload and constitute a feed-forward mechanism, leading to kidney damage.

High Salt Enhances Reactive Oxygen Species and Angiotensin II Contractions of Glomerular Afferent Arterioles From Mice With Reduced Renal Mass

High salt, Ang II (angiotensin II), and reactive oxygen species enhance progression of chronic kidney disease. We tested the hypothesis that a high salt intake generates specific reactive oxygen species to enhance Ang II contractions of afferent arterioles from mice with reduced renal mass (RRM). C57BL/6 mice were subjected to surgical RRM or sham operations and received 6% or 0.4% NaCl salt diet for 3 months. Ang II contractions were measured in perfused afferent arterioles and superoxide (O2-) and hydrogen peroxide (H2O2) by fluorescence microscopy. RRM enhanced the afferent arteriolar gene expression for p47phox and neutrophil oxidase (NOX) 2 and high salt intake in RRM mice enhanced gene expression for angiotensin type 1 receptors, POLDIP2 and NOX4 and reduced catalase. High salt in mice with RRM enhanced arteriolar O2- and H2O2 generation and maximal contractions to Ang II (10-6 mol/L) that were dependent on O2- because they were prevented by gene deletion of p47phox and on H2O2 because they were prevented by transgenic smooth muscle cell expression of catalase (tgCAT-SMC) and POLDIP2 gene deletion. Three months of tempol normalized arteriolar reactive oxygen species and Ang II contractions. However, arteriolar contractions to lower concentrations of Ang II (10-8 to 10-11 mol/L) were paradoxically inhibited by H2O2 and POLDIP2. In conclusion, both O2- from p47phox/NOX2 and H2O2 from NOX4/POLDIP2 enhance maximal arteriolar Ang II contractions from RRM mice during high salt, but H2O2 and NOX4/POLDIP2 reduce the sensitivity to lower concentrations of Ang II by >100-fold. Tempol prevents all of these changes in function.

Isolation, purification and molecular mechanism of a peanut protein-derived ACE-inhibitory peptide

Although a number of bioactive peptides are capable of angiotensin I-converting enzyme (ACE) inhibitory effects, little is known regarding the mechanism of peanut peptides using molecular simulation. The aim of this study was to obtain ACE inhibiting peptide from peanut protein and provide insight on the molecular mechanism of its ACE inhibiting action. Peanut peptides having ACE inhibitory activity were isolated through enzymatic hydrolysis and ultrafiltration. Further chromatographic fractionation was conducted to isolate a more potent peanut peptide and its antihypertensive activity was analyzed through in vitro ACE inhibitory tests and in vivo animal experiments. MALDI-TOF/TOF-MS was used to identify its amino acid sequence. Mechanism of ACE inhibition of P8 was analyzed using molecular docking and molecular dynamics simulation. A peanut peptide (P8) having Lys-Leu-Tyr-Met-Arg-Pro amino acid sequence was obtained which had the highest ACE inhibiting activity of 85.77% (half maximal inhibitory concentration (IC50): 0.0052 mg/ml). This peanut peptide is a competitive inhibitor and show significant short term (12 h) and long term (28 days) antihypertensive activity. Dynamic tests illustrated that P8 can be successfully docked into the active pocket of ACE and can be combined with several amino acid residues. Hydrogen bond, electrostatic bond and Pi-bond were found to be the three main interaction contributing to the structural stability of ACE-peptide complex. In addition, zinc atom could form metal-carboxylic coordination bond with Tyr, Met residues of P8, resulting into its high ACE inhibiting activity. Our finding indicated that the peanut peptide (P8) having a Lys-Leu-Tyr-Met-Arg-Pro amino acid sequence can be a promising candidate for functional foods and prescription drug aimed at control of hypertension.

Modeling of the renal kinetics of the AT1 receptor specific PET radioligand [11C]KR31173

Purpose. The radioligand [¹¹C]KR31173 has been introduced for PET imaging of the angiotensin II subtype 1 receptor (AT1R). The purpose of the present project was to employ and validate a compartmental model for quantification of the kinetics of this radioligand in a porcine model of renal ischemia followed by reperfusion (IR). Procedures. Ten domestic pigs were included in the study: five controls and five experimental animals with IR of the left kidney. To achieve IR, acute ischemia was created with a balloon inserted into the left renal artery and inflated for 60 minutes. Reperfusion was achieved by deflation and removal of the balloon. Blood chemistries, urine specific gravity and PH values, and circulating hormones of the renin angiotensin system were measured and PET imaging was performed one week after IR. Cortical time-activity curves obtained from a 90 min [¹¹C]KR31173 dynamic PET study were processed with a compartmental model that included two tissue compartments connected in parallel. Radioligand binding quantified by radioligand retention (80 min value to maximum value ratio) was compared to the binding parameters derived from the compartmental model. A binding ratio was calculated as DVR = DV_S/DV_NS, where DV_S and DV_NS represented the distribution volumes of specific binding and nonspecific binding. Receptor binding was also determined by autoradiography in vitro. Results. Correlations between rate constants and binding parameters derived by the convolution and deconvolution curve fittings were significant (r > 0.9). Also significant was the correlation between the retention parameter derived from the tissue activity curve (Y_ret) and the retention parameter derived from the impulse response function (f_ret). Furthermore, significant correlations were found between these two retention parameters and DVR. Measurements with PET showed no significant changes in the radioligand binding parameters caused by IR, and these in vivo findings were confirmed by autoradiography performed in vitro. Conclusions. Correlations between various binding parameters support the concept of the parallel connectivity compartmental model. If an arterial input function cannot be obtained, simple radioligand retention may be adequate for estimation of in vivo radioligand binding.

Albumin overload activates intrarenal renin-angiotensin system through protein kinase C and NADPH oxidase-dependent pathway

OBJECTIVE

Inappropriate activation of the intrarenal renin-angiotensin system (RAS) plays an important role in the pathogenesis of hypertension and renal injury. However, the underlying mechanisms remain elusive. Proteinuria has been shown to elicit the renal activation of RAS. The present study was performed to test the intracellular signal pathway involved in albumin-triggered activation of RAS.

DESIGN AND METHODS

NRK52E cells, a rat renal proximal tubular cell line, were incubated with increased levels of albumin. The rat model of protein overload was established in female Wistar-Kyoto rats that were subjected to unilateral nephrectomy followed by daily intraperitoneal injection of BSA at various doses (0.5, 1.0, and 5.0 g/kg) or combination with intragastric administration of apocynin (100 mg/kg per day), an inhibitor of NADPH oxidase.

RESULTS

Exposure of the cells to high levels of albumin activated the RAS through the endocytic receptors megalin and cubilin. High levels of albumin triggered the production of intracellular reactive oxygen species by a protein kinase C (PKC)-NADPH oxidase-dependent pathway and this, in turn, led to activation of nuclear factor-κB (NF-κB) and activation protein-1 (AP-1). Inhibition of PKC or NADPH oxidase abolished albumin-induced activation of RAS. In a protein overload rat model, activation of RAS in renal proximal tubular cells was significantly increased, coincident with activation of PKC, NADPH oxidase, NF-κB, and AP-1. Chronic inhibition of NADPH oxidase by apocynin largely ameliorated intrarenal activation of RAS.

CONCLUSION

Exposure of renal tubular epithelial cells with high levels of albumin triggers activation of RAS via a PKC-NADPH oxidase-dependent pathway.

Long-term exercise attenuates blood pressure responsiveness and modulates kidney angiotensin II signalling and urinary sodium excretion in SHR

Observations have been made regarding the effects of long-term exercise training on blood pressure, renal sodium handling and renal renin-angiotensin-aldosterone (RAS) intracellular pathways in conscious, trained Okamoto-Aoki spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKy) normotensive rats, compared with appropriate age-matched sedentary SHR and WKy. To evaluate the influence of exercise training on renal function and RAS, receptors and intracellular angiotensin II (AngII) pathway compounds were used respectively, and lithium clearance and western blot methods were utilised. The current study demonstrated that increased blood pressure in SHR was blunted and significantly reduced by long-term swim training between the ages of 6 and 16 weeks. Additionally, the investigators observed an increased fractional urinary sodium excretion in trained SHR (SHR(T)) rats, compared with sedentary SHR (SHR(S)), despite a significantly decreased creatinine clearance (C(Cr)). Furthermore, immunoblotting analysis demonstrated a decreased expression of AT1(R) in the entire kidney of T(SHR) rats, compared with S(SHR). Conversely, the expression of the AT2(R), in both sedentary and trained SHR, was unchanged. The present study may indicate that, in the kidney, long-term exercise exerts a modulating effect on AngII receptor expression. In fact, the present study indicates an association of increasing natriuresis, reciprocal changes in renal AngII receptors and intracellular pathway proteins with the fall in blood pressure levels observed in T(SHR) rats compared with age-matched S(SHR) rats.

A computational model of the circulating renin-angiotensin system and blood pressure regulation

The renin-angiotensin system (RAS) is critical in sodium and blood pressure (BP) regulation, and in cardiovascular-renal (CVR) diseases and therapeutics. As a contribution to SAPHIR project, we present a realistic computer model of renin production and circulating RAS, integrated into Guyton's circulatory model (GCM). Juxtaglomerular apparatus, JGA, and Plasma modules were implemented in C ++/M2SL (Multi-formalism Multi-resolution Simulation Library) for fusion with GCM. Matlab optimization toolboxes were used for parameter identification. In JGA, renin production and granular cells recruitment (GCR) are controlled by perfusion pressure (PP), macula densa (MD), angiotensin II (Ang II), and renal sympathetic activity (RSNA). In Plasma, renin and ACE (angiotensin-converting enzyme) activities are integrated to yield Ang I and II. Model vs. data deviation is given as normalized root mean squared error (nRMSE; n points).

IDENTIFICATION

JGA and Plasma parameters were identified against selected experimental data. After fusion with GCM: (1) GCR parameters were identified against Laragh's PRA-natriuresis nomogram; (2) Renin production parameters were identified against two sets of data ([renin] transients vs. ACE or renin inhibition). Finally, GCR parameters were re-identified vs. Laragh's nomogram (nRMSE 8%, n = 9).

VALIDATION

(1) model BP, PRA and [Ang II] are within reported ranges, and respond physiologically to sodium intake; (2) short-term Ang II infusion induces reported rise in BP and PRA. The modeled circulating RAS, in interaction with an integrated CVR, exhibits a realistic response to BP control maneuvers. This construction will allow for modelling hypertensive and CVR patients, including salt-sensitivity, polymorphisms, and pharmacotherapeutics.

Plasma renin responses to mental stress and carotid intima-media thickness in black Africans: the SABPA study

The renin-angiotensin-aldosterone system can be activated by sympathetic nervous input and is thought to have an important role in the prevalence of hypertension and cardiovascular risk in black Africans. We examined (1) the association between plasma renin responses to mental stress and a marker of sub-clinical atherosclerosis; and (2) associations between resting renin and 24-h ambulatory blood pressure. Participants were 143 urbanized black African men and women (43.1 ± 7.7 years) drawn from a study of Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA). After an overnight fast, participants completed the Stroop mental stress task. Blood samples were drawn during baseline and 10 min after the task to assess the concentration of active renin in plasma. Blood pressure assessments included continuous Finometer measures during the stress testing and 24-h ambulatory monitoring. Carotid intima-media thickness (CIMT) was measured using high-resolution ultrasound. Approximately 50% of the sample responded to the task with an increase in renin concentration. Multiple linear regression analysis revealed an association between the renin stress response and CIMT (β = 0.024, 95% confidence interval, 0.004-0.043), after adjustment for conventional risk factors, blood pressure stress responses and basal levels of renin activity (R(2) for model = 0.37). In addition, resting renin was inversely associated with ambulatory blood pressure. In summary, heightened release of renin during a laboratory mental stressor was associated with a marker of sub-clinical atherosclerosis; thus, it may be a potential mechanism in explaining the increased burden of cardiovascular disease in urbanized black Africans.