The role of preterm birth in stress-induced sodium excretion in young adults

BACKGROUND

Early-life programming due to prematurity and very low birth weight (VLBW, <1500 g) is believed to contribute to development of hypertension, but the mechanisms remain unclear. Experimental data suggest that altered pressure natriuresis (increased renal perfusion pressure promoting sodium excretion) may be a contributing mechanism. We hypothesize that young adults born preterm will have a blunted pressure natriuresis response to mental stress compared with those born term.

METHODS

In this prospective cohort study of 190 individuals aged 18-23 years, 156 born preterm with VLBW and 34 controls born term with birth weight at least 2500 g, we measured urine sodium/creatinine before and after a mental stress test and continuous blood pressure before and during the stress test. Participants were stratified into groups by the trajectory at which mean arterial pressure (MAP) increased following the test. The group with the lowest MAP trajectory was the reference group. We used generalized linear models to assess poststress urine sodium/creatinine relative to the change in MAP trajectory and assessed the difference between groups by preterm birth status.

RESULTS

Participants' mean age was 19.8 years and 57% were women. Change in urine sodium/creatinine per unit increase in MAP when comparing middle trajectory group against the reference group was greater in those born preterm [β 5.4%, 95% confidence interval (95% CI) -11.4 to 5.3] than those born term (β 38.5%, 95% CI -0.04 to 92.0), interaction term P = 0.002.

CONCLUSION

We observed that, as blood pressure increased following mental stress, young adults born preterm exhibited decreased sodium excretion relative to term-born individuals.

Dysfunction of the renin-angiotensin-aldosterone system in human septic shock

Sepsis and septic shock are global healthcare problems associated with mortality rates of up to 40% despite optimal standard-of-care therapy and constitute the primary cause of death in intensive care units worldwide. Circulating biomarkers of septic shock severity may represent a clinically relevant approach to individualize those patients at risk for worse outcomes early in the course of the disease, which may facilitate early and more precise interventions to improve the clinical course. However, currently used septic shock biomarkers, including lactate, may be non-specific and have variable impact on prognosis and/or disease management. Activation of the renin-angiotensin-aldosterone system (RAAS) is likely an early event in septic shock, and studies suggest that an elevated level of renin, the early and committed step in the RAAS cascade, is a better predictor of worse outcomes in septic shock, including mortality, than the current standard-of-care measure of lactate. Despite a robust increase in renin, other elements of the RAAS, including endogenous levels of Ang II, may fail to sufficiently increase to maintain blood pressure, tissue perfusion, and protective immune responses in septic shock patients. We review the current clinical literature regarding the dysfunction of the RAAS in septic shock and potential therapeutic approaches to improve clinical outcomes.

ACE inhibitors and angiotensin receptor blockers differentially alter the response to angiotensin II treatment in vasodilatory shock

BACKGROUND

Angiotensin-converting enzyme inhibitor (ACEi) and angiotensin receptor blockers (ARB) medications are widely prescribed. We sought to assess how pre-admission use of these medications might impact the response to angiotensin-II treatment during vasodilatory shock.

METHODS

In a post-hoc subgroup analysis of the randomized, placebo-controlled, Angiotensin Therapy for High Output Shock (ATHOS-3) trial, we compared patients with chronic angiotensin-converting enzyme inhibitor (ACEi) use, and patients with angiotensin receptor blocker (ARB) use, to patients without exposure to either ACEi or ARB. The primary outcome was mean arterial pressure after 1-h of treatment. Additional clinical outcomes included mean arterial pressure and norepinephrine equivalent dose requirements over time, and study-drug dose over time. Biological outcomes included baseline RAS biomarkers (renin, angiotensin-I, angiotensin-II, and angiotensin-I/angiotensin-II ratio), and the change in renin from 0 to 3 h.

RESULTS

We included n = 321 patients, of whom, 270 were ACEi and ARB-unexposed, 29 were ACEi-exposed and 22 ARB-exposed. In ACEi/ARB-unexposed patients, angiotensin-treated patients, compared to placebo, had higher hour-1 mean arterial pressure (9.1 mmHg [95% CI 7.6-10.1], p < 0.0001), lower norepinephrine equivalent dose over 48-h (p = 0.0037), and lower study-drug dose over 48-h (p < 0.0001). ACEi-exposed patients treated with angiotensin-II showed similarly higher hour-1 mean arterial pressure compared to ACEi/ARB-unexposed (difference in treatment-effect: - 2.2 mmHg [95% CI - 7.0-2.6], pinteraction = 0.38), but a greater reduction in norepinephrine equivalent dose (pinteraction = 0.0031) and study-drug dose (pinteraction < 0.0001) over 48-h. In contrast, ARB-exposed patients showed an attenuated effect of angiotensin-II on hour-1 mean arterial pressure versus ACEi/ARB-unexposed (difference in treatment-effect: - 6.0 mmHg [95% CI - 11.5 to - 0.6], pinteraction = 0.0299), norepinephrine equivalent dose (pinteraction < 0.0001), and study-drug dose (pinteraction = 0.0008). Baseline renin levels and angiotensin-I/angiotensin-II ratios were highest in ACEi-exposed patients. Finally, angiotensin-II treatment reduced hour-3 renin in ACEi/ARB-unexposed and ACEi-exposed patients but not in ARB-exposed patients.

CONCLUSIONS

In vasodilatory shock patients, the cardiovascular and biological RAS response to angiotensin-II differed based upon prior exposure to ACEi and ARB medications. ACEi-exposure was associated with increased angiotensin II responsiveness, whereas ARB-exposure was associated with decreased responsiveness. These findings have clinical implications for patient selection and dosage of angiotensin II in vasodilatory shock. Trial Registration ClinicalTrials.Gov Identifier: NCT02338843 (Registered January 14th 2015).

Association of Active Renin Content With Mortality in Critically Ill Patients: A Post hoc Analysis of the Vitamin C, Thiamine, and Steroids in Sepsis (VICTAS) Trial

OBJECTIVE

Sepsis is a leading cause of mortality. Predicting outcomes is challenging and few biomarkers perform well. Defects in the renin-angiotensin system (RAS) can predict clinical outcomes in sepsis and may outperform traditional biomarkers. We postulated that RAS dysfunction (elevated active renin, angiotensin 1-7 [Ang-(1-7)], and angiotensin-converting enzyme 2 (ACE2) activity with depressed Ang-II and ACE activity) would be associated with mortality in a cohort of septic patients.

DESIGN

Post hoc analysis of patients enrolled in the Vitamin C, Thiamine, and Steroids in Sepsis (VICTAS) randomized controlled trial.

SETTING

Forty-three hospitals across the United States.

PATIENTS

Biorepository samples of 103 patients.

INTERVENTIONS

We analyzed day 0 (within 24 hr of respiratory failure, septic shock, or both) and day 3 samples ( n = 103 and 95, respectively) for assessment of the RAS. The association of RAS values with 30-day mortality was determined using Cox proportional hazards regression with multivariable adjustments for age, sex, VICTAS treatment arm, systolic blood pressure, Sequential Organ Failure Assessment Score, and vasopressor use.

MEASUREMENTS AND MAIN RESULTS

High baseline active renin values were associated with higher 30-day mortality when dichotomized to the median of 188.7 pg/mL (hazard ratio [HR] = 2.84 [95% CI, 1.10-7.33], p = 0.031) or stratified into quartiles (Q1 = ref, HR Q2 = 2.01 [0.37-11.04], HR Q3 = 3.22 [0.64-16.28], HR Q4 = 5.58 [1.18-26.32], p for linear trend = 0.023). A 1- sd (593.6 pg/mL) increase in renin from day 0 to day 3 was associated with increased mortality (HR = 3.75 [95% CI, 1.94-7.22], p < 0.001), and patients whose renin decreased had improved survival compared with those whose renin increased (HR 0.22 [95% CI, 0.08-0.60], p = 0.003). Ang-(1-7), ACE2 activity, Ang-II and ACE activity did not show this association. Mortality was attenuated in patients with renin over the median on day 0 who received the VICTAS intervention, but not on day 3 ( p interaction 0.020 and 0.137, respectively). There were no additional consistent patterns of mortality on the RAS from the VICTAS intervention.

CONCLUSIONS

Baseline serum active renin levels were strongly associated with mortality in critically ill patients with sepsis. Furthermore, a greater relative activation in circulating renin from day 0 to day 3 was associated with a higher risk of death.

Renin-Angiotensin System and Sex Differences in COVID-19: A Critical Assessment

The current epidemic of corona virus disease (COVID-19) has resulted in an immense health burden that became the third leading cause of death and potentially contributed to a decline in life expectancy in the United States. The severe acute respiratory syndrome-related coronavirus-2 binds to the surface-bound peptidase angiotensin-converting enzyme 2 (ACE2, EC 3.4.17.23) leading to tissue infection and viral replication. ACE2 is an important enzymatic component of the renin-angiotensin system (RAS) expressed in the lung and other organs. The peptidase regulates the levels of the peptide hormones Ang II and Ang-(1-7), which have distinct and opposing actions to one another, as well as other cardiovascular peptides. A potential consequence of severe acute respiratory syndrome-related coronavirus-2 infection is reduced ACE2 activity by internalization of the viral-ACE2 complex and subsequent activation of the RAS (higher ratio of Ang II:Ang-[1-7]) that may exacerbate the acute inflammatory events in COVID-19 patients and possibly contribute to the effects of long COVID-19. Moreover, COVID-19 patients present with an array of autoantibodies to various components of the RAS including the peptide Ang II, the enzyme ACE2, and the AT1 AT2 and Mas receptors. Greater disease severity is also evident in male COVID-19 patients, which may reflect underlying sex differences in the regulation of the 2 distinct functional arms of the RAS. The current review provides a critical evaluation of the evidence for an activated RAS in COVID-19 subjects and whether this system contributes to the greater severity of severe acute respiratory syndrome-related coronavirus-2 infection in males as compared with females.

Discrete Correlation Summation Clustering Reveals Differential Regulation of Liver Metabolism by Thrombospondin-1 in Low-Fat and High-Fat Diet-Fed Mice

Thrombospondin-1 (TSP1) is a matricellular protein with many important roles in mediating carcinogenesis, fibrosis, leukocyte recruitment, and metabolism. We have previously shown a role of diet in the absence of TSP1 in liver metabolism in the context of a colorectal cancer model. However, the metabolic implications of TSP1 regulation by diet in the liver metabolism are currently understudied. Therefore Discrete correlation summation (DCS) was used to re-interrogate data and determine the metabolic alterations of TSP1 deficiency in the liver, providing new insights into the role of TSP1 in liver injury and the progression of liver pathologies such as nonalcoholic fatty liver disease (NAFLD). DCS analysis provides a straightforward approach to rank covariance and data clustering when analyzing complex data sets. Using this approach, our previous liver metabolite data was re-analyzed by comparing wild-type (WT) and Thrombospondin-1 null (Thbs1-/-) mice, identifying changes driven by genotype and diet. Principal component analysis showed clustering of animals by genotype regardless of diet, indicating that TSP1 deficiency alters metabolite handling in the liver. High-fat diet consumption significantly altered over 150 metabolites in the Thbs1-/- livers versus approximately 90 in the wild-type livers, most involved in amino acid metabolism. The absence of Thbs1 differentially regulated tryptophan and tricarboxylic acid cycle metabolites implicated in the progression of NAFLD. Overall, the lack of Thbs1 caused a significant shift in liver metabolism with potential implications for liver injury and the progression of NAFLD.

Abstract P103: Apelin And Elabela Attenuate The Pro-inflammatory Response In Hypoxic HTR-8/SVneo Trophoblastic Cells

Preeclampsia is a significant pregnancy complication characterized by de novo hypertension, proteinuria, and further organ dysfunction. We previously demonstrated both cardio- and renoprotective effects by systemic activation of apelin receptor system (APJ) in preeclampsia. Although the APJ ligands apelin and elabela stimulate trophoblast cell proliferation and migration, the cellular mechanisms underlying these actions are not well understood, particularly in response to hypoxia. To examine the response of the APJ system to cellular hypoxia in human trophoblasts, HTR-8/SVneo trophoblastic cells were treated with cobalt chloride (CoCl 2: 200 μM, 24 hours) to induce hypoxic conditions. The cellular mRNA responses for sFlt-1 variants, VEGF, PLGF, IL-6, and IL-1β were determined by RT-qPCR for control and apelin- or elabela-treated cells with or without CoCl 2 . The presence of APJ mRNA was confirmed in HTR-8/SVneo cells. Hypoxia increased apelin content approximately 2-fold in both the cell lysate (723 ± 52 vs. 1216 ± 20 ng/mg protein, n=6, p<0.01) and the conditioned media (49 ± 5 vs. 102 ± 9 ng/ml, n=6, p<0.01). Elabela content also increased in the media of hypoxic cells (0.11 ± 0.01 vs. 0.14 ± 0.01 ng/ml, n=6, p<0.05), although elabela levels were 100-fold lower than apelin. Hypoxia upregulated hsFlt-1-i13 (2.6 fold), hsFlt-1-e15a (2.9 fold), VEGF (3.7 fold), PLGF (1.3 fold), and IL-6 (3.5 fold) mRNA levels. Treatment with (Pyr-1)-apelin-13, a stable APJ ligand (0.1 μM), decreased VEGF (1.2 fold; n=3, p<0.05) and IL-6 (1.4 fold, n=3, p<0.05) mRNA levels in cells exposed to COCl 2 , but had no effect in normoxic cells. Similarly, elabela (0.1 μM) downregulated VEGF (1.1 fold; n=3, p<0.05) and IL-6 (1.2 fold; n=3, p<0.05). We found no difference in sFlt-1 variants, PLGF, or IL-1β mRNAs following treatment of hypoxic cells with either peptide. We conclude that cobalt-induced hypoxia markedly increases various indices of inflammation, as well as stimulates the endogenous apelin and elabela systems in the HTR-8/SVneo cells. Furthermore, local activation of these peptidergic systems may be a compensatory response of the trophoblast cells to hypoxia as exogenous apelin and elabela treatment effectively ameliorate the hypoxia-induced pro-inflammatory milieu.

Abstract P252: Differential Expression Of ACE2, Neprilysin And ACE In Extracellular Vesicles Isolated From Human Urine

The Ang II convertase ACE2 is present in urine and may correlate with various renal pathologies. We reported functional ACE2 in urinary exosomes and now extend our studies to distinguish exosomes (EXOs) and microvesicles (MVs) containing ACE2, as well as neprilysin (NEP) and ACE. EXO purification was modified by an intermediate centrifugation step (20k xg, 60 mins) to pellet MVs followed by 100k xg to pellet EXOs. The MV, EXO, and 100k supernatant (soluble, SOL) fractions were assessed for ACE2 activity with MCA-APK-DNP, and NEP and ACE activities with MCA-RPPGFSAFK-Dnp with selective inhibitors. Peptidase activities were expressed as relative fluorescent units (RFU x10 6 /min/mL), and data are means ± SEM (*P<0.05; **P<0.01, N=4). Morning collections from male subjects [51 to 65 years of age, non-smokers] were collected, treated with Cibacron blue to bind albumin, 0.2 μM filtration, and 100 kDa Amicon concentration prior to high speed and ultracentrifugation steps. ACE2 activity was >3-fold higher in the EXO versus the MV fractions with minor activity in the SOL fraction. In contrast, NEP activity was highest in the MV fraction [~2-fold > EXO] while endopeptidase activity was barely detectable in the SOL fraction. ACE activity was similar in MVs and EXOs, but NEP activity was 40-fold higher than ACE in both the MV and EXO fractions. Differential centrifugation of the 100-kDa urine concentrate reveals a unique profile of ACE2, NEP and ACE expression in MVs and EXOs. The functional significance of these peptidase activities in different vesicular populations is currently unknown; however, their origin may reflect the distinct regulation and release of ACE2 and NEP/ACE in urinary vesicles.

Abstract P253: Delta And Omicron Variants Of SARS-Cov-2 Do Not Stimulate ACE2 Conversion Of Ang II To Ang-(1-7)

The Spike domain of SARS-COV-2 binds ACE2 and induces peptidase internalization removing a key regulatory site within the renin-angiotensin system that may exacerbate the effects of SARS-COV-2. However, a recent study finds that an early Beta variant (D614G) of the SARS-COV-2 Spike protein and its receptor-binding domain (RBD) markedly stimulated ACE2 activity using fluorescent substrates. The more dominant forms of SARS-COV-2 include the Delta and Omicron variants and we determined whether these new variants activate ACE2. Delta (B.1.617.1) and Omicron (B.1.1.529) RBDs, and Beta Spike (B1.351) were incubated with human soluble ACE2 for 10 mins at 37°C followed by Ang II [2 μM] and 125I-Ang II [0.5 nM] for up to 20 mins, and the Ang-(1-7)/Ang II ratio quantified by HPLC-γ detection. Ang-(1-7)/Ang II increased linearly over time and doubled with 10 ng of ACE2 (*P<0.01 vs 5 ng; N=4); however, the Delta or Omicron RBD proteins (1 μM) failed to stimulate ACE2 activity at any time point (A). Varying concentrations of the Delta or Omicron RBDs, as well as Spike protein also failed to stimulate ACE2 activity (5 ng), although 200 nM Omicron RBD was inhibitory (B). The newer Spike variants may not activate ACE2; however, the Spike D614G variant also failed to activate ACE2, which questions whether SARS-COV-2 enhances ACE2 activity to metabolize Ang II. We conclude that Delta and Omicron variants do not stimulate the metabolism of Ang II to Ang-(1-7). Moreover, alterations in circulating ACE2 activity in COVID-19 patients likely reflect changes in protein content through shedding of the peptidase, although the interaction of ACE2 autoantibodies to influence peptidase activity is also possible.

Abstract P250: Targeting The Thrombospondin-CD47 Axis Attenuates Blood Pressure And Renal Injury In Female Hypertensive (mRen2)27 Rats

Alterations in the extracellular matrix (ECM) can influence vascular stiffness and compromise organ function contributing to hypertension. A key component of the ECM is the type I integral membrane receptor CD47 that regulates the ECM by binding to the matricellular protein thrombospondin-1(TSP1). Increased circulating levels of TSP1 and CD47 activation are associated with cardiac and renal pathologies. Thus, the objective of the current study determined the efficacy of targeting CD47 with an anti-sense morpholinos to reduce blood pressure and renal injury in 20-week old hypertensive (mRen2)27 female rats. The CD47 morpholino (Morph) or the missense probe (Control) were dissolved in sterile PBS and administered by tail vein injection twice weekly for 6 weeks. Systolic blood pressures (SBPs) were monitored in conscious rats by a tail cuff auscultation and expression of RAS components assessed by RT-qPCR; all data are means ± SEM with n=8-10 per group. Prior to treatment, the baseline SBPs did not differ between the Control and Morph groups [196 ± 5 vs.197 ± 4 mmHg; p=0.87]. However, as early as one week of treatment, the CD47 Morph group exhibited a significant reduction in SBPs compared to the Control transgenics [185 ± 5 vs. 204 ± 3 mmHg; p<0.01]. At the end of the 6 week treatment period, SBPs remained significantly lower in the CD47 Morph group compared to the Controls [185 ± 4 vs.199 ± 3 mmHg; p<0.02]. In addition, CD47 blockade was associated with reduced proteinuria in the CD47 Morph compared to Controls [7 ± 1 vs. 26 ± 7 mg protein/24 hr excretion; p<0.05]. Regarding the mechanism of CD47 blockade to reduce blood pressure and proteinuria, mRNA analysis revealed lower renal renin mRNA levels in the CD47 Morph versus the Control group [0.54 ± 0.11 vs.1.04 ± 0.11; p<0.01]. Moreover, CD47 Morph treatment significantly reduced the mRNA levels of renal ACE [0.78 ± 0.13 vs.1.05 ± 0.14; p<0.05] and the renal AT1A receptor [0.74 ± 0.07 vs.1.05 ± 0.12; p<0.05], however, renal angiotensinogen mRNA levels were not different among the CD47 Morph and Controls [1.04.± 0.10 vs. 1.16 ± 0.20, p=0.83]. We conclude that silencing CD47 attenuates hypertension and renal injury in the female (mRen2)27 potentially by reducing expression of the renin-ACE-AT1 receptor axis within the kidney.

Angiotensinogen uptake and stimulation of oxidative stress in human pigment retinal epithelial cells

We previously reported that isolated proximal tubules (PT) internalize the precursor protein angiotensinogen and that the ¹²⁵Iodine-labeled protein accumulated in the nuclear and mitochondrial fractions of the PT cells; however, whether internalization of angiotensinogen occurs in non-renal epithelial cells is unknown. Therefore, the present study assessed the cellular uptake of ¹²⁵I-angiotensinogen in human retinal pigment ARPE-19 epithelial cells, a widely utilized cell model for the assessment of retinal injury, inflammation and oxidative stress. ARPE-19 cells, maintained in serum-free media to remove extracellular sources of bovine serum angiotensinogen and renin, were incubated with ¹²⁵Iodine-angiotensinogen at 37 °C and revealed the time-dependent uptake of angiotensinogen over 24 h. In contrast, incubation with labelled Ang II, Ang-(1-7) or Ang I revealed minimal cellular uptake. Subcellular fractionation following a 4-hour uptake of ¹²⁵I-angiotensinogen revealed that the majority of the labeled protein localized to the nuclear fraction with lower accumulation in the mitochondrial and cytosolic fractions. Finally, we show that addition of angiotensinogen (2 nM) to the ARPE-19 cells increased oxidative stress as assessed by DCF fluorescence that was blocked by pretreatment of the cells with either the NADPH oxidase 1/4 inhibitor GKT137831, apocynin or atorvastatin, but not the AT₁ receptor antagonist losartan. In contrast, treatment of the cells with Angiotensin II at an equivalent dose to angiotensinogen failed to stimulate oxidative stress. We conclude that human retinal pigment cells internalize angiotensinogen to elicit an increase in oxidative stress through a pathway that appears distinct from the Ang II-AT₁ receptor axis.

Abstract MP36: Human Urinary Exosomes Contain Functional ACE2

The Ang II convertase and SARS-COV-2 co-receptor ACE2 is highly expressed on proximal tubules within the kidney. ACE2 is also present in urine and reportedly correlates with various renal pathologies that may reflect enhanced shedding of the peptidase through activation of ADAMs. Indeed, 95 kDa ACE2 is typically detected in urine consistent with a shorter, soluble form of the peptidase; however, the full-length, membrane-bound form of ACE2 (120 kDa) is also evident in urine which is difficult to reconcile with ACE2 shedding. To account for these isoforms, we evaluated ACE2 expression in exosomes isolated from human urine. Morning collections from males [50 to 64 years of age, non-smokers] were immediately processed for exosome isolation by cibacron blue binding of albumin followed by 0.2 μmicron filtration to remove microvesicles and apoptotic bodies, Amicon 100 kDa concentration, and ultracentrifugation (UC) to pellet exosomes. Analysis of the UC pellet fraction revealed the exosomal markers ALIX, CD63 and HSP70, as well as the proximal tubule peptidases neprilysin (NEP) and ACE2. Exosomal ACE2 content was 45 ± 11 ng/mL (mean ± SEM; N=5) by ELISA and exosomal activity hydrolyzed Ang II to Ang-(1-7) that was abolished by the ACE2 inhibitor MLN4760. Fluorescent nanotracking analysis (f-NTA) with Alexa Fluor antibodies and CellMask Deep Red membrane stain (CMDR) demonstrate a similar density of ACE2+ and NEP+ exosomes that were ~50% of total urinary exosomes (*P<0.05 vs. CD63+, N=3) while particle sizes were comparable and in the expected range of exosomes (100-150 nm). We conclude that human urinary exosomes express functional ACE2 which may originate from proximal tubule release.

A pilot study to assess the circulating renin-angiotensin system in COVID-19 acute respiratory failure

The renin-angiotensin system (RAS) is fundamental to COVID-19 pathobiology, due to the interaction between the SARS-CoV-2 virus and the angiotensin-converting enzyme 2 (ACE2) coreceptor for cellular entry. The prevailing hypothesis is that SARS-CoV-2-ACE2 interactions lead to an imbalance of the RAS, favoring proinflammatory angiotensin II (ANG II)-related signaling at the expense of the anti-inflammatory ANG-(1-7)-mediated alternative pathway. Indeed, multiple clinical trials targeting this pathway in COVID-19 are underway. Therefore, precise measurement of circulating RAS components is critical to understand the interplay of the RAS on COVID-19 outcomes. Multiple challenges exist in measuring the RAS in COVID-19, including improper patient controls, ex vivo degradation and low concentrations of angiotensins, and unvalidated laboratory assays. Here, we conducted a prospective pilot study to enroll 33 patients with moderate and severe COVID-19 and physiologically matched COVID-19-negative controls to quantify the circulating RAS. Our enrollment strategy led to physiological matching of COVID-19-negative and COVID-19-positive moderate hypoxic respiratory failure cohorts, in contrast to the severe COVID-19 cohort, which had increased severity of illness, prolonged intensive care unit (ICU) stay, and increased mortality. Circulating ANG II and ANG-(1-7) levels were measured in the low picomolar (pM) range. We found no significant differences in circulating RAS peptides or peptidases between these three cohorts. The combined moderate and severe COVID-19-positive cohorts demonstrated a mild reduction in ACE activity compared with COVID-19-negative controls (2.2 ± 0.9 × 105 vs. 2.9 ± 0.8 × 105 RFU/mL, P = 0.03). These methods may be useful in designing larger studies to physiologically match patients and quantify the RAS in COVID-19 RAS augmenting clinical trials.

Phase I Study of Muscadine Grape Extract for Patients With Advanced Cancer

OBJECTIVE

Preclinical studies with muscadine grape extract (MGE) show antitumor activity and decreased systemic inflammation. This phase I study (NCT02583269) assessed safety and tolerability of a proprietary MGE preparation in patients with advanced solid tumors.

METHODS

Patients with metastatic or unresectable cancers who were progressing on standard therapies were assigned to MGE in a standard 3+3 design. Five dose levels were tested (320 to 1600 mg total phenolics/d). Safety and maximum-tolerated dose were assessed after 4 weeks. Patients were evaluated for response at 8 weeks and continued on MGE if clinically stable. Secondary outcomes were response, survival, adherence, fatigue, and quality of life (QOL).

RESULTS

In total, 23 patients (lung, n=7; gastrointestinal, n=7; genitourinary, n=6; other, n=3) received MGE capsules by mouth twice daily. The cohort [median age 72 years, 48% Eastern Cooperative Oncology Group (ECOG) 2] was heavily pretreated. After 4 weeks on MGE, possibly attributable adverse events grade 2 or higher were fatigue (n=1), decreased lymphocyte count (n=1), and constipation (n=2), including 1 dose-limiting toxicity for grade 3 constipation. Maximum-tolerated dose was not reached. No partial responses were observed. Median time on therapy was 8 weeks, with 29% of patients treated beyond 16 weeks and a median overall survival of 7.2 months. QOL and fatigue levels were stable from baseline to 8 weeks. Higher MGE dose was correlated with improvement in self-reported physical well-being QOL at 8 weeks (r=0.6; P=0.04).

CONCLUSIONS

MGE is safe and well-tolerated in heavily pretreated and older cancer patients.  The potential anticancer properties and the effects of MGE on physical well-being and QOL metrics will be evaluated in future studies.

Diet, obesity, and the gut microbiome as determinants modulating metabolic outcomes in a non-human primate model

BACKGROUND

The objective of this study was to increase understanding of the complex interactions between diet, obesity, and the gut microbiome of adult female non-human primates (NHPs). Subjects consumed either a Western (n=15) or Mediterranean (n=14) diet designed to represent human dietary patterns for 31 months. Body composition was determined using CT, fecal samples were collected, and shotgun metagenomic sequencing was performed. Gut microbiome results were grouped by diet and adiposity.

RESULTS

Diet was the main contributor to gut microbiome bacterial diversity. Adiposity within each diet was associated with subtle shifts in the proportional abundance of several taxa. Mediterranean diet-fed NHPs with lower body fat had a greater proportion of Lactobacillus animalis than their higher body fat counterparts. Higher body fat Western diet-fed NHPs had more Ruminococcus champaneliensis and less Bacteroides uniformis than their low body fat counterparts. Western diet-fed NHPs had significantly higher levels of Prevotella copri than Mediterranean diet NHPs. Western diet-fed subjects were stratified by P. copri abundance (P. copri^HIGH versus P. copri^LOW), which was not associated with adiposity. Overall, Western diet-fed animals in the P. copri^HIGH group showed greater proportional abundance of B. ovatus, B. faecis, P. stercorea, P. brevis, and Faecalibacterium prausnitzii than those in the Western P. copri^LOW group. Western diet P. copri^LOW subjects had a greater proportion of Eubacterium siraeum. E. siraeum negatively correlated with P. copri proportional abundance regardless of dietary consumption. In the Western diet group, Shannon diversity was significantly higher in P. copri^LOW when compared to P. copri^HIGH subjects. Furthermore, gut E. siraeum abundance positively correlated with HDL plasma cholesterol indicating that those in the P. copri^LOW population may represent a more metabolically healthy population. Untargeted metabolomics on urine and plasma from Western diet-fed P. copri^HIGH and P. copri^LOW subjects suggest early kidney dysfunction in Western diet-fed P. copri^HIGH subjects.

CONCLUSIONS

In summary, the data indicate diet to be the major influencer of gut bacterial diversity. However, diet and adiposity must be considered together when analyzing changes in abundance of specific bacterial taxa. Interestingly, P. copri appears to mediate metabolic dysfunction in Western diet-fed NHPs. Video abstract.

Evidence that angiotensin II does not directly stimulate the MD2-TLR4 innate inflammatory pathway

The renin-angiotensin system (RAS) plays a critical role in the regulation of blood pressure. Inappropriate activation of the RAS, particularly stimulation of the ACE-Ang II-AT₁ receptor axis is a key factor in hypertension and AT₁R antagonists (ARBs) are first line therapies in the treatment of cardiovascular disease (CVD). Accumulating evidence suggests that the Ang II-AT₁R axis may stimulate both innate and adaptive immune systems. Indeed, recent studies suggest that Ang II stimulates inflammatory events in an AT₁R-independent manner by binding the MD2 accessory protein of the TLR4 complex in renal NRK-52E cells. Direct Ang II stimulation of the TLR4 complex is clinically relevant as ARBs increase circulating Ang II levels. Thus, the current study further investigated Ang II stimulation of the TLR4 pathway to release of the pro-inflammatory cytokine CCL2 under identical conditions to the TLR4 ligands LPS and palmitate in the NRK-52E cells. Although LPS (1 ng/mL) and palmitate (100 μM) stimulated CCL2 release 20-fold, Ang II (0.1-10 μM) failed to induce CCL2 release. Both the LPS and palmitate CCL2 responses were abolished by the TLR4 inhibitor Tak242 and significantly reduced by the MD2 inhibitor L48H37. Ang II (1 μM) had no additive effects on LPS (1 ng/mL) or palmitate (100 μM), and the ARB candesartan failed to attenuate CCL2 release to either agent alone. Ang II also failed to induce the release of the putative TLR4 ligand HMBG1. These studies failed to confirm that Ang II directly stimulates the MD2-TLR4 complex to induce cytokine release in NRK-52E cells.

Abstract P053: Enhanced Exercise Capacity By Muscadine Grape Extract Treatment Is Only Evident In Older Hypertensive Female Rats And Is Independent Of Blood Pressure

Physical performance and systolic blood pressure (SBP) during aging in normotensive female Sprague-Dawley (SD) and hypertensive (mRen2)27 transgenic rats were assessed following long-term treatment with a Muscadine Grape Extract (MGE, Piedmont Research and Development Corp). MGE was administered at a dose of 0.2 mg/mL in the drinking water starting at 14 weeks (wks) of age with an endpoint at 70 wks of age (total time of treatment of 56 wks). At 20-, 40- and 70-wks of age, physical performance (exercise capacity in seconds and workload in grams - meters) was determined using a treadmill at a velocity of 17 cm/second with a 5% incline. SBP was determined by tail-cuff plethysmography in trained rats. There were no significant differences in physical performance between SD and (mRen2)27 female rats at any age despite the higher SBP in the (mRen2)27 rats at all ages. Long-term treatment with MGE had no significant effect on physical performance or SBP in SD rats at any age. In contrast, MGE treatment markedly increased exercise capacity (40 wks: 1615 ± 166 vs 4943 ± 442 seconds, p<0.01, n = 4-9; 70 wks: 2520 ± 374 vs 4117 ± 245 seconds, p<0.01, n = 4-8) and workload (40 wks: 4579 ± 490 vs 14730 ± 1353 grams - meters, p<0.01, n = 4-9; 70 wks: 8338 ± 1340 vs 13659 ± 933 grams - meters, p<0.01, n = 4-8) at the later ages in female (mRen2)27 rats, while there was no effect on SBP (20 wks: 167 ± 4 vs 173 ± 4 mm Hg, n = 4-6; 40 wks: 177 ± 8 vs 170 ± 7 mm Hg, n = 6-7; 70 wks:154 ± 6 vs 172 ± 6 mm Hg, n = 5) at any age. These data suggest that MGE treatment is effective in improving physical performance only in hypertensive female rats and may be independent of changes in blood pressure. The benefit of MGE in the older hypertensive female may reflect reductions in vascular stiffness and oxidative stress. Support: Chronic Disease Research Fund, Hypertension & Vascular Research Center

Abstract P129: Angiotensin II Does Not Directly Stimulate The TLR4-MD2-MyD88 Inflammatory Pathway

Current evidence suggests that the deleterious actions of Angiotensin II (Ang II) reflect activation of both innate and adaptive inflammatory pathways. Indeed, recent studies find that Ang II stimulates the TLR-4 signaling cascade to promote cytokine release and renal injury by directly binding to the TLR4 accessory protein MD2 to induce TLR-4 dimerization and internalization that is independent of the AT 1 receptor (AT 1 R). Moreover, knockdown of TLR4 or MD2 attenuates renal injury and expression of pro-inflammatory cytokines in a chronic Ang II infusion model and in rat proximal tubule NRK-52e cells treated with Ang II. In the present study, we evaluated the proposed Ang II-TLR4-MD2 pathway in the NRK-52e cells regarding the stimulation of the chemokine MCP-1 (CCL2) and activation of the TLR4-MyD88 complex. NRK-52e cells, maintained in antibiotic-free media, were transferred to serum-free media prior to stimulation with the TLR4 agonists LPS and palmitate or Ang II for 24 hrs; reported data are the means ± SEM, n=4. The NRK-52e cells were sensitive to a low dose of LPS (1 ng/ml) stimulating CCL2 release 20-fold [Basal: 24.3 ± 1.0 pg/ml vs. 504 ± 30.4 pg/ml, p<0.001]. The LPS induced release of CCL2 was abolished by the specific TLR4 inhibitor Tak-242 [TAK: 23.9 ± 1.3 pg/ml] and was significantly reduced by the MD2 inhibitor L48H37 [135 ± 24.2 pg/ml]. Palmitate [100 μM] also stimulated CCL2 release [482 ± 21.0 pg/ml; p<0.001] that was abolished by TAK [32.3 ± 6.3 pg/ml]. The overall effects are consistent with previously reported responses to LPS and palmitate in these cells, as well as TLR4 protein expression and TAK inhibition. However, Ang II treatment over a dose range of 0.1 to 10 μM for 24 hrs failed to elicit CCL2 release [24.3 ± 1.0, 22.6 ± 0.5, and 27.6 ± 2.3 pg/ml, respectively; P>0.1 vs. Basal]. Ang II [1 μM] also failed to augment the CCL2 response to LPS [496 ± 6.5 pg/ml] or palmitate [511 ± 35.0 pg/ml]. Finally, pre-treatment of the NRK-52e cells with the AT 1 R antagonist candesartan [5 μM] failed to attenuate CCL2 release to LPS [512 ± 21 pg/ml]. We conclude that Ang II does not directly stimulate the TLR4-MD2 complex to induce CCL2 and that the inflammatory events associated with Ang II in vivo may reflect the release of other factors (LPS, AGEs, HMGB1) that serve as TLR-4 agonists.

Lower urinary α-Klotho is associated with lower angiotensin-(1-7) and higher blood pressure in young adults born preterm with very low birthweight

Early-life factors including preterm birth and VLBW increase the risk of hypertension, but the mechanisms remain poorly understood. Reductions in the anti-aging protein α-klotho are associated with hypertension, possibly due to angiotensin (Ang) II activation, but the mechanisms are incompletely understood and clinical evidence is lacking. The association of α-klotho with the alternative Ang-(1-7) pathway, which counteracts Ang II to lower BP, is undescribed. We hypothesized that lower urinary α-klotho is associated with higher BP and lower urinary Ang-(1-7) in preterm-born VLBW young adults. In a cross-sectional analysis of data from a prospective cohort of 141 preterm-born VLBW young adults, we assessed the associations among urinary α-klotho/creatinine, Ang II/creatinine, Ang-(1-7)/creatinine, Ang II/Ang-(1-7), and BP using generalized linear models adjusted for age and hypertensive pregnancy and conducted a sensitivity analysis in 32 term-born young adults. Among those born preterm, lower α-klotho/creatinine was associated with higher systolic BP (adjusted β (aβ): -2.58 mm Hg, 95% CI -4.99 to -0.17), lower Ang-(1-7)/creatinine (ln aβ: 0.1, 0.04-0.16), and higher Ang II/Ang-(1-7) (ln aβ: -0.14, -0.21 to -0.07). In term-born participants, α-klotho/creatinine was inversely associated with Ang II/creatinine (ln aβ: -0.15, -0.27 to -0.03) and Ang II/Ang-(1-7) (ln aβ: -0.15, -0.27 to -0.03). In preterm-born young adults with VLBW, lower urinary α-klotho/creatinine was associated with higher SBP, lower urinary Ang-(1-7)/creatinine, and higher urinary Ang II/Ang-(1-7). Reduced renal α-klotho expression could lead to renal Ang-(1-7) suppression as a novel mechanism for the development of hypertension among individuals born preterm with VLBW.

COVID-19, ACE2, and the cardiovascular consequences

The novel SARS coronavirus SARS-CoV-2 pandemic may be particularly deleterious to patients with underlying cardiovascular disease (CVD). The mechanism for SARS-CoV-2 infection is the requisite binding of the virus to the membrane-bound form of angiotensin-converting enzyme 2 (ACE2) and internalization of the complex by the host cell. Recognition that ACE2 is the coreceptor for the coronavirus has prompted new therapeutic approaches to block the enzyme or reduce its expression to prevent the cellular entry and SARS-CoV-2 infection in tissues that express ACE2 including lung, heart, kidney, brain, and gut. ACE2, however, is a key enzymatic component of the renin-angiotensin-aldosterone system (RAAS); ACE2 degrades ANG II, a peptide with multiple actions that promote CVD, and generates Ang-(1-7), which antagonizes the effects of ANG II. Moreover, experimental evidence suggests that RAAS blockade by ACE inhibitors, ANG II type 1 receptor antagonists, and mineralocorticoid antagonists, as well as statins, enhance ACE2 which, in part, contributes to the benefit of these regimens. In lieu of the fact that many older patients with hypertension or other CVDs are routinely treated with RAAS blockers and statins, new clinical concerns have developed regarding whether these patients are at greater risk for SARS-CoV-2 infection, whether RAAS and statin therapy should be discontinued, and the potential consequences of RAAS blockade to COVID-19-related pathologies such as acute and chronic respiratory disease. The current perspective critically examines the evidence for ACE2 regulation by RAAS blockade and statins, the cardiovascular benefits of ACE2, and whether ACE2 blockade is a viable approach to attenuate COVID-19.

Association of circulating uric acid and angiotensin-(1-7) in relation to higher blood pressure in adolescents and the influence of preterm birth

Elevated serum uric acid increases the risk of hypertension, and individuals born preterm have higher blood pressure (BP) and uric acid, but the mechanisms remain unclear. Preclinical studies demonstrate uric acid increases BP via increased renin-angiotensin system (RAS) expression, especially angiotensin (Ang) II, but the association of uric acid with Ang-(1–7) is unknown. Ang-(1–7), an alternative RAS product, counteracts Ang II by stimulating sodium excretion, vasodilation, and nitric oxide, thus contributing to lower BP. Plasma Ang-(1–7) is lower in preterm-born adolescents. We hypothesized uric acid is associated with a higher ratio of Ang II to Ang-(1–7) in plasma, especially in preterm-born adolescents. We measured BP, serum uric acid, and plasma RAS components in a cross-sectional analysis of 163 14-year-olds (120 preterm, 43 term). We estimated the associations between uric acid and the RAS using generalized linear models adjusted for sex, obesity, sodium intake, and fat intake, stratified by birth status. Uric acid was positively associated with Ang II/Ang-(1–7) (adjusted β (aβ): 0.88 mg/dl, 95% CI 0.17 to 1.58), plasma renin activity (aβ: 0.32 mg/dl, 95% CI 0.07 to 0.56), and aldosterone (aβ: 1.26 mg/dl, 95% CI 0.18 to 2.35), and inversely with Ang-(1–7) (aβ: −1.11 mg/dl, 95% CI −2.39 to 0.18); preterm birth did not modify these associations. Higher Ang II/Ang-(1–7) was associated with higher uric acid in adolescents. As preterm birth is associated with higher BP and uric acid, but lower Ang-(1–7), the imbalance between uric acid and Ang-(1–7) may be an important mechanism for the development of hypertension.

Cardiorenal Syndrome and Heart Failure-Challenges and Opportunities

Cardiorenal syndromes (CRS) describe concomitant bidirectional dysfunction of the heart and kidneys in which 1 organ initiates, perpetuates, and/or accelerates decline of the other. CRS are common in heart failure and universally portend worsened prognosis. Despite this heavy disease burden, the appropriate diagnosis and classification of CRS remains problematic. In addition to the hemodynamic drivers of decreased renal perfusion and increased renal vein pressure, induction of the renin-angiotensin-aldosterone system, stimulation of the sympathetic nervous system, disruption of balance between nitric oxide and reactive oxygen species, and inflammation are implicated in the pathogenesis of CRS. Medical therapy of heart failure including renin-angiotensin-aldosterone system inhibition and β-adrenergic blockade can blunt these deleterious processes. Renovascular disease can accelerate the progression of CRS. Volume overload and diuretic resistance are common and complicate the management of CRS. In heart failure and CRS being treated with diuretics, worsening creatinine is not associated with worsened outcome if clinical decongestion is achieved. Adjunctive therapy is often required in the management of volume overload in CRS, but evidence for these therapies is limited. Anemia and iron deficiency are importantly associated with CRS and might amplify decline of cardiac and renal function. End-stage cardiac and/or renal disease represents an especially poor prognosis with limited therapeutic options. Overall, worsening renal function is associated with significantly increased mortality. Despite progress in the area of CRS, there are still multiple pathophysiological and clinical aspects of CRS that need further research to eventually develop effective therapeutic options.

Abstract 129: The Microbiome Product Urolithin a Abrogates the Tgf-β Egfr Pai-1 Pathway by Inhibiting Egfr Activation and Expression

Introduction: Ellagitanins are highly abundant in various foods including fruits, nuts and wines, and particularly high in commercial muscadine grape-derived supplements. The microbiome metabolizes ellagitanins to urolithins. Urolithin A (UA), the final product of the microbiome processing pathway may contribute to the cardioprotective effects of ellagitanins; however, the cellular signaling mechanisms of UA are unclear. Since the TGFβ-PAI-1 pathway contributes to fibrosis, cellular senescence and progressive kidney injury, we evaluated the effects of UA on TGFβ-induced stimulation of PAI-1 in rat renal proximal tubule cells (rPTCs - NRK52E). We hypothesize that UA may be an endogenous anti-fibrotic compound that attenuates the TGFβ-PAI-1 response.

Results: TGFβ (5 ng/ml) treatment markedly increased PAI-1 levels 10-fold [43.9 ± 0.7 vs 3.5 ± 0.3 ng/ml; P<0.001, n=3] in the rPTCs at 24 hrs. The TGFβ receptor (TGFβR) kinase (ALK5) inhibitor SB525334 or UA abolished the increase in PAI-1 to TGFβ [SB: 1.3 ± 0.3; UA: 2.0 ± 0.4 ng/ml; P<0.001, n=3]; UA exhibits an IC50 of 3.1 μM to abrogate the TGFβ-PAI-1 response. Since the TGFβ pathway may transactivate the EGFR, treatment with the EGFR kinase inhibitors AG1478 (AG, 1 μM) and Lapatinib (LAP, 1 μM) also abrogated the PAI-1 response to TGFβ [AG: 3.3 ± 0.4; LAP: 6.2 ± 1.4 ng/ml; P<0.001, n=3]. Addition of EGF alone increased PAI-1 to a similar extent as TGFβ [46.6 ± 2.7 ng/ml; P<0.001, n=3], and treatment with UA or AG abolished the EGF-PAI-1 response [2.4 ± 0.1 and 1.3 ± 0.1 ng/ml, respectively; P<0.001, n=3]. Given the dependence on EGFR signaling for PAI-1, we determined whether UA directly attenuates EGFR stimulation. Indeed, UA treatment inhibited peak EGFR phosphorylation to EGF at 5 mins [10 μM: 67 ± 4%; 50 μM: 71 ± 5%; P<0.05, n=3], and reduced total EGFR expression at 24 hrs [10 μM: 27 ± 11%; 50 μM: 66 ± 7%; P<0.05, n=6]. UA was devoid of cytotoxic effects (LDH release).

Conclusion: The present study is the first to establish that UA abrogates the TGFβ-EGFR-PAI-1 pathway via the inhibition of EGFR stimulation and expression. Moreover, the potency of UA to attenuate PAI-1 is comparable to its physiological levels. The microbiome product UA may convey anti-fibrotic actions within the kidney by targeting the EGFR system.

Central ANG-(1-7) infusion improves blood pressure regulation in antenatal betamethasone-exposed sheep and reveals sex-dependent effects on oxidative stress

Fetal exposure to betamethasone (BMX) as a consequence of glucocorticoid administration to women threatening premature delivery may lead to long-term deleterious effects on the cardiovascular system and dysregulation of blood pressure in exposed adults. Indeed, adult offspring of BMX sheep exhibit increased mean arterial pressure (MAP) and attenuated baroreflex sensitivity (BRS) that are associated with lower medullary and cerebrospinal fluid (CSF) angiotensin-(1-7) [(ANG-(1-7)] content. Thus we determined the effects of ANG-(1-7) supplementation in the CSF on MAP, BRS, blood pressure (BPV) and heart rate variability (HRV) in conscious animals. The peptide or artificial CSF (aCSF) was infused continuously into the lateral ventricle (intracerebroventricular) of 4-mo-old male and female BMX sheep for 2 wk. Analysis of data from males and females combined revealed that intracerebroventricular ANG-(1-7) significantly lowered MAP and heart rate and improved BRS as compared with baseline; intracerebroventricular aCSF did not change these indexes. Similar patterns were observed for altered hemodynamics and autonomic function produced by intracerebroventricular ANG-(1-7) in both sexes. Oxidative stress and MAP kinase (MAPK) activation were lower in tissues from the dorsomedial medulla (DMM) of ANG-(1-7)-treated males but were unchanged in the treated females, when assessed at the end of the treatment period. We conclude that in the face of ANG-(1-7) deficiency in CSF and medullary tissue in BMX sheep intracerebroventricular supplementation of ANG-(1-7) lowers MAP and restores the impaired autonomic function to a similar degree in both males and females; however, the attenuation of MAPK and oxidative stress within the DMM was evident only in males. NEW & NOTEWORTHY We demonstrate that intracerebroventricular angiotensin-(1-7) [(ANG-(1-7)] treatment for 2 wk in antenatal betamethasone-exposed sheep provides beneficial effects on blood pressure and autonomic function. The physiological improvements are accompanied by an attenuation of oxidative stress in males but not females. The finding that ANG-(1-7) supplementation lowers blood pressure and restores the impaired autonomic function in a model of fetal programming previously shown to exhibit a deficiency in cerebrospinal fluid and brain tissue illustrates the potential for new therapeutic strategies for reducing cardiovascular dysfunction arising from prenatal events.

Obesity is Associated with Higher Blood Pressure and Higher Levels of Angiotensin II but Lower Angiotensin-(1-7) in Adolescents Born Preterm

OBJECTIVES

To evaluate if obesity is associated with increased angiotensin II (Ang II) and decreased angiotensin-(1-7) or Ang-(1-7) in the circulation and urine among adolescents born prematurely.

STUDY DESIGN

In a cross-sectional analysis of 175 14-year-olds born preterm with very low birth weight, we quantified plasma and urinary Ang II and Ang-(1-7) and compared their levels between subjects with overweight/obesity (body mass index ≥85th percentile, n = 61) and those with body mass index <85th percentile (n = 114) using generalized linear models, adjusted for race and antenatal corticosteroid exposure.

RESULTS

Overweight/obesity was associated with higher systolic blood pressure and a greater proportion with high blood pressure. After adjustment for confounders, overweight/obesity was associated with an elevated ratio of plasma Ang II to Ang-(1-7) (β: 0.57, 95% CI 0.23-0.91) and higher Ang II (β: 0.21 pmol/L, 95% CI 0.03-0.39) but lower Ang-(1-7) (β: -0.37 pmol/L, 95% CI -0.7 to -0.04). Overweight/obesity was associated with a higher ratio of urinary Ang II to Ang-(1-7) (β: 0.21, 95% CI -0.02 to 0.44), an effect that approached statistical significance.

CONCLUSIONS

Among preterm-born adolescents, overweight/obesity was associated with increased Ang II but reduced Ang-(1-7) in the circulation and the kidney as well as higher blood pressure. Obesity may compound the increased risk of hypertension and cardiovascular disease in individuals born prematurely by further augmenting the prematurity-associated imbalance in the renin-angiotensin system.

Fetal programming and the angiotensin-(1-7) axis: a review of the experimental and clinical data

Hypertension is the primary risk factor for cardiovascular disease that constitutes a serious worldwide health concern and a significant healthcare burden. As the majority of hypertension has an unknown etiology, considerable research efforts in both experimental models and human cohorts has focused on the premise that alterations in the fetal and perinatal environment are key factors in the development of hypertension in children and adults. The exact mechanisms of how fetal programming events increase the risk of hypertension and cardiovascular disease are not fully elaborated; however, the focus on alterations in the biochemical components and functional aspects of the renin-angiotensin (Ang) system (RAS) has predominated, particularly activation of the Ang-converting enzyme (ACE)-Ang II-Ang type 1 receptor (AT1R) axis. The emerging view of alternative pathways within the RAS that may functionally antagonize the Ang II axis raise the possibility that programming events also target the non-classical components of the RAS as an additional mechanism contributing to the development and progression of hypertension. In the current review, we evaluate the potential role of the ACE2-Ang-(1-7)-Mas receptor (MasR) axis of the RAS in fetal programming events and cardiovascular and renal dysfunction. Specifically, the review examines the impact of fetal programming on the Ang-(1-7) axis within the circulation, kidney, and brain such that the loss of Ang-(1-7) expression or tone, contributes to the chronic dysregulation of blood pressure (BP) and cardiometabolic disease in the offspring, as well as the influence of sex on potential programming of this pathway.

Renal function and blood pressure are altered in adolescents born preterm

BACKGROUND

Preterm birth increases the risk of hypertension and kidney disease. However, it is unclear when changes in blood pressure (BP) and renal function become apparent and what role obesity and sex play. We hypothesized adolescents born preterm have higher BP and worse kidney function compared to term in an obesity- and sex-dependent manner.

METHODS

Cross-sectional analysis of 14-year-olds born preterm with very low birth weight (n = 96) compared to term (n = 43). We used generalized linear models to estimate the associations among preterm birth and BP, estimated glomerular filtration rate (eGFR), and ln (x) urinary albumin-to-creatinine ratio (ACR), stratified by overweight/obesity (OWO, body mass index (BMI) ≥ 85th percentile) and sex.

RESULTS

Compared to term, preterm-born adolescents had higher systolic blood pressure (SBP) and diastolic blood pressure (DBP) (adjusted β (aβ) 3.5 mmHg, 95% CI - 0.1 to 7.2 and 3.6 mmHg, 95% CI 0.1 to 7.0), lower eGFR (β - 8.2 mL/min/1.73 m², 95% CI - 15.9 to - 0.4), and higher ACR (aβ 0.34, 95% CI - 0.04 to 0.72). OWO modified the preterm-term difference in DBP (BMI < 85th percentile aβ 5.0 mmHg, 95% CI 0.7 to 9.2 vs. OWO 0.2 mmHg, 95% CI - 5.3 to 5.6) and ACR (OWO aβ 0.72, 95% CI 0.15 to 1.29 vs. BMI < 85th percentile 0.17, 95% CI - 0.31 to 0.65). Sex modified the preterm-term ACR difference (female aβ 0.52, 95% CI 0.001 to 1.04 vs. male 0.18, 95% CI - 0.36 to 0.72).

CONCLUSIONS

Prematurity was associated with higher BP and reduced renal function that were detectable in adolescence. OWO and sex may modify the strength of these relationships.

Abstract P306: Preterm Birth is Associated with Increased Blood Pressure and Increased Urinary Angiotensinogen in Young Adults

Introduction: Cardiovascular disease (CVD) is the leading cause of mortality and hypertension (HTN) is a major risk factor for CVD. Preterm birth is an emerging risk factor for both CVD and HTN, but the underlying mechanisms are poorly described. The renin-angiotensin system (RAS) plays a key role in HTN and CVD, and adolescents born preterm have higher blood pressure (BP) with a shift in the balance of the classical and alternative pathways of the RAS exhibited as increased angiotensin II and reduced angiotensin-(1-7) as compared to term-born adolescents. Although numerous factors influence the expression of angiotensins, the precursor protein angiotensinogen in the kidney is implicated in the development of HTN and CVD and may contribute to higher angiotensin II. As the status of renal angiotensinogen in individuals born preterm is unknown, we hypothesized that urinary angiotensinogen is increased in young adults born preterm as compared to their term-born peers.

Methods: We compared urinary excretion of angiotensinogen corrected for urine creatinine and systolic and diastolic BP in 142 young adults (mean age 19.9 years) born preterm with very low birth weight (<1500 g) to 32 young adults born term using Wilcoxon Rank-Sum test and t-test. We used generalized linear models to compare the ln(x) urinary angiotensinogen between the preterm and term groups adjusted for the potentially confounding factors race, maternal hypertensive pregnancy, and maternal smoking during pregnancy.

Results: Compared to term, subjects born preterm had higher median urinary angiotensinogen (0.02 μg/g, IQR 0.01 to 0.04 vs. 0.01 μg/g, IQR 0.004 to 0.01, p < 0.001) and higher mean systolic BP (111 mmHg, SD 11 vs. 106 mmHg, SD 10, p = 0.03). On crude and adjusted analyses urinary angiotensinogen was associated positively with preterm birth (crude β : 0.82, 95% CI 0.47 to 1.16; adjusted β : 0.79, 95% CI 0.39 to 1.18).

Discussion: In addition to higher BP, young adults born preterm demonstrated increased urinary angiotensinogen as compared to their term-born peers. Preterm birth may induce programming of the renal RAS leading to higher angiotensinogen and a higher angiotensin-to-angiotensin-(1-7) ratio, potentially contributing to the increased risk of HTN in individuals born preterm.

Abstract P245: The Angiotensin-(1-7) Agonist AVE0991 Attenuates Angiotensinogen Release from Human Proximal Epithelial Cells

A local renin-angiotensin system (RAS) is evident within the renal proximal tubules and overexpression of the precursor angiotensinogen targeted to the tubules increases blood pressure and promotes renal injury. Tubular angiotensinogen is enhanced by the Ang II-AT1 receptor axis, oxidative stress and pro-inflammatory cytokines (IL-6, TGFβ), as well as hyperglycemic conditions. Stimulation of angiotensinogen by the Ang II-AT1 receptor pathway constitutes a positive-feedback loop that may promote a sustained increase in blood pressure and renal damage. Mediators that promote angiotensinogen also attenuate the expression of the ACE2-Ang-(1-7) axis. Downregulation of the Ang-(1-7) axis and its associated signaling pathways may contribute to greater expression of angiotensinogen within the kidney. To examine this potential pathway, we assessed the chronic effects of the Ang-(1-7) agonist AVE0991 on angiotensinogen release in human HK-2 proximal epithelial cells maintained under mild hyperglycemic conditions. HK-2 cells were placed in serum-free media and then treated with varying doses of the AVE0991 agonist (0.1 nM to 1 uM) for up to 48 hours. Human angiotensinogen was quantified in the cell media by ELISA with a sensitivity of 30 picogram (pg). Basal release of angiotensinogen at 48 hrs was 1.47 ± 0.28 ng/ml (n=4). Addition of 0.1 nM AVE0991 attenuated angiotensinogen release by 23 ± 4%, p<0.05 with a maximal inhibitory effect of 48 ± 9%, p<0.05 [n=3]. AVE0991 at the maximal dose had no detrimental effect on cell viability. The NOS inhibitor LNAME (100 uM) failed to block the inhibitory effect of AVE0991 and LNAME alone did not influence release. Addition of the AT2R agonist C21 (1 uM) had no effect on angiotensinogen release. The Ang-(1-7) receptor antagonist [D-Pro 7 ]-Ang-(1-7) blocked the inhibitory effects of AVE0991; however, [D-Ala 7 -Ang-(1-7)(A779), losartan, PD123319 or the kinin B2 receptor HOE140 had no effect. We conclude that the Ang-(1-7) axis may exert negative feedback on the tubular angiotensin system and that the renoprotective effects of AVE0991 may reflect attenuation of angiotensinogen release. Furthermore, the inhibitory actions of AVE0091 on the tubular release of angiotensinogen appear to be independent of the NOS-NO pathway.

Abstract 135: Impaired Autonomic Function in Young Adults Born Preterm With Very Low Birth Weight is Associated With Elevated Serum Uric Acid Levels

Preterm birth increases the risk of cardiometabolic disease. We showed that prematurity induces programming effects that lead to elevated blood pressure (BP), higher serum uric acid, and impaired autonomic control characterized by reduced heart rate variability (HRV), baroreflex sensitivity (BRS), and elevated ratio of low frequency to high frequency power (LF/HF), a marker of sympathovagal balance. However, the relationships among these factors in subjects born preterm are undefined. Since uric acid has been shown to correlate with HRV in adult hypertensive subjects, we hypothesized that higher uric acid is associated with impaired autonomic function in subjects born preterm.

Methods: A cohort of 131 young adults born preterm was compared to a cohort of 26 born term (19.6 years). Serum uric acid was measured. BP and ECG were recorded continuously for analysis of autonomic function reflected in HRV and BRS. We used generalized linear models to estimate the association between uric acid and measures of HRV and BRS, adjusting for race, age at follow up, and BMI. The potential interaction between uric acid and preterm birth was tested by introducing an interaction term and, if suggestive of an interaction (p ≤ 0.1), estimates were calculated within strata (preterm & term).

Results: Compared to term, preterm participants had higher serum uric acid levels (5.2 mg/dL, IQR: 4.2, 6.2 vs 4.8 mg/dL, IQR: 3.9, 6.0) and lower HRV as measured by standard deviation of normal to normal RR intervals (71 ms, IQR: 54, 97 vs 80 ms, IQR: 55, 101). Across term and preterm groups combined, uric acid was inversely associated with BRS measured as HF alpha ( β : -0.12, 95% CI -0.20 to -0.03, p for interaction = 0.06). Assessment of interaction showed this association was significant in preterms only ( β : -0.15, 95% CI -0.24 to -0.06 vs 0.07, -0.17 to 0.30). Uric acid was positively associated with LF/HF ( β : 0.13, 95% CI 0.01 to 0.25, p for interaction=0.01).

Conclusions: Young adults born preterm had dampened parasympathetic control of heart rate and BP, and higher serum uric acid was associated with sympathovagal imbalance. The data suggest that alterations of uric acid metabolism associated with preterm birth may increase the risk of early cardiovascular disease in part by impairing autonomic control

Therapeutic Approaches to the Alternative Angiotensin-(1-7) Axis of the Renin-Angiotensin System

Cardiovascular disease remains the leading cause of death for both men and women in the United States despite the recent advances in drug development, changes in lifestyle and screening protocols. A key target in the treatment of cardiovascular disease and hypertension is the renin-angiotensinsystem (RAS), a circulating and tissue system involved in the regulation of blood pressure, fluid balance and cellular injury. Pharmacologic approaches have traditionally focused on the Ang II-AT1receptor axis of the RAS to prevent the generation of Ang II with angiotensin converting enzyme inhibitors (ACEI) or to block the binding of Ang II to the AT1 receptor (AT1R) with selective antagonists (ARBs).

Abstract P411: Angiotensin-(1-7) Preserves Mitochondrial Function in Doxorubicin-exposed Renal Epithelial Cells

We recently identified components of an Angiotensin-(1-7) system (Ang7) within mitochondria (Mito) of the renal cortex, as well as angiotensinogen uptake and trafficking to the Mito and nucleus in proximal tubules. Although activation of the Ang II-AT1 receptor (AT1R) axis is deleterious to the Mito, the functional role of Ang7 is unknown. Thus, we evaluated the effects of Ang7 and its agonist AVE0991 (AVE) to attenuate doxorubicin (DOX)-induced Mito toxicity. NRK-52 renal epithelial cells were exposed to DOX (10 μM, 24 hours) and either saline, Ang7 (100 nM), AVE (100 nM), the MasR antagonist A779 (10 μM) or LNAME (1 mM). Mito function in NRK cells was evaluated by a Seahorse XF-96 analyzer; the OCR data were expressed as the mean ± SD. Both Ang7 and AVE attenuated the decline in Mito function by DOX exposure (Fig_A); the calculated maximal respiration (MR) rates for Ang7 and AVE treated DOX cells were similar to control cells without DOX [25.5 ± 4.4 and 26.7 ± 7.8 vs. 33.9 ± 11.4 pmol/min; p>0.05]. Preservation of Mito function by Ang7 and AVE in DOX cells was reversed by the A779 antagonist (Fig_B). Ang7 stimulation of the nitric oxide synthase (NOS)-NO pathway is a key signaling event in various cell types; however, the NOS inhibitor LNAME failed to block the Ang7 response in DOX exposed cells [MR: 32.2 ± 7.6 pmol/min; Fig_B]. DOX also increased phospho-ERK1/2 over 10-fold [1.12 ±. 0.27 vs. 0.08 ± 0.03], but Ang7 did not attenuate the MAPK response [1.19 ±. 0.34]. We conclude that Ang7 preserves mitochondrial function following DOX exposure in tubular epithelial cells. Moreover, the protective effect of the Ang7-MasR axis does not apparently reflect the contribution of the NOS-NO or MAPK pathways.

Abstract P123: Obesity and Alterations in Renal Function in Adolescents Born Preterm With Very Low Birth Weight

Background: Survival of children born preterm has improved dramatically, but prematurity and low birth weight may increase the risk of renal disease. Children born preterm have a lower glomerular filtration rate (GFR) and higher blood pressure (BP) compared to term peers, but compounding risk factors for renal disease among children born preterm remain poorly characterized. Indeed, patient factors such as obesity may influence the development of kidney disease. Thus, we hypothesize that obesity is associated with decreased renal function in adolescents born preterm with very low birth weight.

Methods: We measured systolic and diastolic BP, serum creatinine, and urine albumin at age 14 years in 124 adolescents born preterm with very low birth weight (mean birth weight 1056 g). We calculated the GFR by the Schwartz equation and the albumin-to-creatinine ratio (ACR) on morning urine samples. We used generalized linear models to estimate the association between obesity [body mass index (BMI) ≥95 th %ile for age and sex, n= 27] and renal function, adjusting for race, sex, maternal smoking during pregnancy, and birth weight z-score.

Results: Obesity was associated with higher systolic BP ( p =0.03). Compared to adolescents with BMI <95 th %ile, those with obesity had lower GFR ( β : -14.68 mL/min/1.73 m 2 , 95% CI -26.8 to -2.55). Adjustment for covariates attenuated this relationship ( β : -10.05 mL/min/1.73 m 2 , -21.12 to 1.03). Adolescents with obesity had a higher serum creatinine, but this did not reach statistical significance ( β : 0.05 mg/dL, -0.01 to 0.11). There was no difference in the ACR ( β : -0.05, -0.13 to 0.02).

Conclusions: Obese adolescents born preterm with very low birth weight exhibit higher systolic BP and lower GFR compared to those with BMI <95 th %ile, though the statistical significance of the relationship with GFR weakened after adjustment for possible confounders. Importantly, sex was a significant confounder that may influence the relationship between GFR and obesity, as female adolescents had significantly lower GFR than male adolescents. While obesity should be avoided, other factors should be considered that may contribute to worse renal function in adolescents born preterm with very low birth weight.

Abstract P190: Long-term Intake of Muscadine Grape Extract Markedly Improves Exercise Capacity in Older Female (mRen2)27 Hypertensive Rats

Muscadine grapes ( Vitis rotundifolia ) contain significant levels of polyphenols and their antioxidant capacity may have cardiovascular benefit. We determined the cardiovascular effects of a water soluble muscadine grape extract (MGE) from Piedmont Research & Development Corporation (PRDC, Winston-Salem, NC) that we confirmed has a high content of epicatechin, gallic acid, ellagic acid and procyanidin B2. We hypothesize that this soluble MGE with a potentially high phenolic bioavailability exhibits cardioprotective actions. The effect of long-term MGE intake on blood pressure, cardiac function and exercise tolerance was established in female and male hemizygous (mRen2)27 [mRen2] transgenic rats, an Ang II-AT 1 R-dependent model of hypertension. The mRen2 were administered MGE (8 mg of total phenolics/mL) in the drinking water for 26 weeks (7 female; 7 male); control rats (9 female; 11 male) were given water only. At 40 weeks of age, exercise tolerance was assessed by treadmill (10.2 m x min -1 , 5% inclination). The MGE-treated female mRen2 exhibited a >300% improvement in workload ( W: g X m ) as compared to the untreated group [14551 ± 1313 vs. 4498 ± 481; p<0.01]. MGE intake also extended the time to fatigue (TTF) by 300% in females (4943 ± 443 vs.1615 ± 166 sec; p<0.01). In contrast, chronic intake of MGE had no effect on either exercise workload or TTF in the male mRen2. MGE intake did not alter systolic blood pressure in females (162 ± 3 vs. 166 ± 6 mm Hg, p>0.05) and males (165 ± 5 vs. 160 ± 3 mm Hg) nor alter body weight in either group [females: 334 ± 7 g vs. 339 ± 8 g; males: 613 ± 12 g vs. 590 ± 6 g). Echocardiographic analyses revealed that although the female mRen2 exhibited a higher ejection fraction [73.4±5.1 vs. 42.3±4.5%, n=4-5, p<0.05] and a higher fractional shortening [44.2±4.2 vs. 22.1±2.7%, n=4-5, p<0.05] as compared to males, MGE treatment did not improve these indices in either group. We conclude that the marked improvement in exercise capacity in older adult hypertensive females by chronic MGE intake is not accompanied by augmented cardiac performance, perhaps reflecting the lack of an effect on blood pressure. Thus, it is possible that MGE may directly impact the skeletal muscle to improve exercise in the hypertensive mRen2 females, but not the males.

Abstract P428: Internalization of Angiotensinogen is Coupled to Oxidative Stress in Human Retinal Epithelial Cells

We previously reported that isolated proximal tubules internalize angiotensinogen (Aogen); labeled Aogen accumulated in the nuclear and mitochondrial fractions and was associated with increased oxidative stress. Aogen internalization in non-renal epithelial cell types is unknown, thus, we assessed Aogen uptake in human retinal ARP-19 cells. Cells, maintained in serum-free media to remove extracellular sources of Aogen and renin were exposed to 125I-Aogen at 37°C and washed in HCl-glycine to dissociate any membrane-bound label. Subcellular fractionation revealed that the majority of the labeled Aogen localized to the nucleus with a lower accumulation in the mitochondrial and cytosolic fractions [42.0 ± 0.2% vs. 12.0 ± 0.2% and 5.2 ± 0.2%, respectively, p<0.01; n=3]. The rate of Aogen internalization in the retinal cells was 244 ± 15 fmol/hr/mg [n=3]; however, the cellular uptake of 125I-labeled Ang II, Ang I or Ang 7 was not evident [< 1 fmol/hr/mg]. Cells were then exposed to a low concentration of Aogen [200 pM] for 60 mins and oxidative stress assessed. As shown in the figure, Aogen elicited a marked increase in oxidative stress [*P<0.01 vs. control(CON); n=4-5 all groups] that was abolished by Apocynin (APO). Atorvastatin (ATV) also blocked the Aogen response, but did not attenuate Aogen uptake. Ang II (AII, 200 pM) had no effect and the AT1R antagonist losartan (LOS, 10 μM) failed to block Aogen uptake or its response. Finally, the dynamin inhibitor dynasore (DYN) blocked internalization and abolished the Aogen response. We conclude that human retinal cells internalize Aogen through a pathway distinct from the Ang II-AT1R axis to elicit an acute increase in oxidative stress.

Abstract 145: Central Angiotensin-(1-7) Treatment Attenuates ERK 1/2 Expression and Oxidative Stress in the Dorsal Medulla of Betamethasone-Exposed Sheep That Associates With Improved Blood Pressure and Baroreflex Sensitivity

Fetal exposure to betamethasone (BMX) that is routinely administered to women threatening premature delivery may lead to deleterious long-term effects on the central cardiovascular system. In the adult offspring of BMX-exposed sheep, we demonstrate increased mean arterial pressure (MAP) and attenuated baroreflex sensitivity (BRS). These responses are associated with dysregulation of the brain renin-angiotensin system (RAS) reflecting lower medullary expression of Angiotensin-(1-7) [Ang-(1-7)] and its beneficial actions. Moreover, mitogen activated protein kinase (MAPK), a key signaling cascade implicated in cardiovascular dysfunction and stimulation of oxidative stress is increased in the brain dorsomedial medulla (DMM). We hypothesize that loss of Ang-(1-7) tone with BMX is an underlying mechanism for the programming effects to increase MAPK and oxidative stress. Thus, we examined whether intracerebroventricular treatment with Ang-(1-7) that lowers MAP and improves BRS will impact MAPK signaling and downstream generation of reactive oxygen species (ROS). MAPK activation as detected by the ratio of phospho-ERK 1/2 to total ERK densities was significantly reduced by >80% in the Ang-(1-7)-treated BMX sheep as compared to the CSF-treated BMX controls (0.20 ± 0.07 vs 1.04 ± 0.31; p = 0.01, N=4/group). Ang-(1-7) treatment was associated with lower expression of two indices of ROS including 4-HNE (0.23 ± 0.03 vs. 0.31 ± 0.03 p = 0.03) and protein carbonyl content (9.95 ± 0.69 vs 15.94 ± 3.49; p = 0.07). Finally, regression analysis revealed that phospho-ERK 1/2 expression positively correlated with ROS (4-HNE) (r = 0.816; p = 0.01). The 4-HNE content also trended positively with MAP (r = 0.659, p = 0.08), but exhibited a negative correlation with BRS (r = -0.831; p = 0.01). We conclude that reduced central Ang-(1-7) tone may contribute to the chronic dysregulation of the MAPK and ROS signaling pathways within the DMM following BMX exposure. Moreover, Ang-(1-7) may constitute a potential therapeutic approach to improve autonomic dysfunction by attenuating both MAPK and ROS pathways. HD 047584.

Abstract 051: Influence of Sex and Obesity on the Effect of Preterm Birth on the Renin-angiotensin System in Adolescents

Background: Preterm birth increases the risk of cardiovascular disease, but the underlying mechanisms are not known. Prematurity may induce programming effects that differentially influence the renin-angiotensin (Ang) system (RAS), particularly suppression of the beneficial Ang-(1-7) axis. Patient factors such as sex and obesity may influence the degree of RAS programming. Therefore, we hypothesize that preterm birth is associated with alterations in the RAS in adolescence in a sex and adiposity-dependent manner.

Methods: We evaluated a cohort of 175 adolescents born preterm and 51 term controls at age 14 years. We recorded systolic and diastolic BP z-scores, measured Ang II and Ang-(1-7) levels in plasma and urine, and calculated the peptide ratios. We applied generalized linear models to estimate the association between preterm birth and the RAS, adjusting for race, socioeconomic status, and maternal hypertension and smoking; the models were stratified by sex and overweight/obesity (body mass index ≥85 th %ile for age and sex).

Results: Mean systolic and diastolic BP z-scores were higher among those born preterm ( p <0.001 and p =0.03, respectively). Relative to term birth, preterm birth was associated with an increased plasma ratio of Ang II to Ang-(1-7) ( β : 4.42, 95% CI 1.52 to 7.32), decreased Ang II ( β : -5.16 pmol/L, -10.28 to -0.04), decreased Ang-(1-7) ( β : -5.38 pmol/L, -8.66 to -2.09), and a decreased urinary ratio of Ang II to Ang-(1-7) ( β : -0.13, -0.26 to -0.003). In stratified analyses, female sex ( β : -7.14 pmol/L, -11.03 to -3.24) and overweight/obesity ( β : -8.21 pmol/L, -12.51 to -3.91) were associated with greater reductions in plasma Ang-(1-7). Overweight/obesity was associated with a greater increase in the ratio of plasma Ang II to Ang-(1-7) ( β : +6.13, 0.58 to 11.68).

Conclusions: Circulating Ang-(1-7) was lower relative to Ang II in adolescents born preterm. This suggests fetal RAS programming may contribute to the increased risk of cardiovascular disease in those born preterm. We note an important influence of sex in that the decrease in Ang-(1-7) is intensified in girls. Moreover, obesity may confer a second physiologic insult through a higher Ang II/Ang-(1-7) that exacerbates the risk of cardiovascular disease, including hypertension.

Angiotensin-(1-7)-dependent vasorelaxation of the renal artery exhibits unique angiotensin and bradykinin receptor selectivity

Angiotensin-(1-7) [Ang-(1-7)] exhibits blood pressure lowering actions, inhibits cell growth, and reduces tissue inflammation and fibrosis which may functionally antagonize an activated Ang II-AT₁ receptor axis. Since the vascular actions of Ang-(1-7) and the associated receptor/signaling pathways vary in different vascular beds, the current study established the vasorelaxant properties of the heptapeptide in the renal artery of male Wistar male rats. Ang-(1-7) produced an endothelium-dependent vasodilator relaxation of isolated renal artery segments pre-contracted by a sub-maximal concentration of phenylephrine (PE) (3×10^-7M). Ang-(1-7) induced vasodilation of the rat renal artery with an ED₅₀ of 3±1nM and a maximal response of 42±5% (N=10). The two antagonists (10^-5M each) for the AT₇/Mas receptor (MasR) [D-Pro⁷]-Ang-(1-7) and [D-Ala⁷]-Ang-(1-7) significantly reduced the maximal response to 12±1% and 18±3%, respectively. Surprisingly, the AT₂R receptor antagonist PD123319, the AT₁R antagonist losartan and B₂R antagonist HOE140 (10^-6M each) also significantly reduced Ang-(1-7)-induced relaxation to 12±2%, 22±3% and 14±7%, respectively. Removal of the endothelium or addition of the soluble guanylate cyclase (sGC) inhibitor ODQ (10^-5M) essentially abolished the vasorelaxant response to Ang-(1-7) (10±4% and 10±2%, P <0.05). Finally, the NOS inhibitor LNAME (10^-4M) reduced the response to 13±2% (p<0.05), but the cyclooxygenase inhibitor indomethacin failed to block the Ang-(1-7) response. We conclude that Ang-(1-7) exhibits potent vasorelaxant actions in the isolated renal artery that are dependent on an intact endothelium and the apparent stimulation of a NO-sGC pathway. Moreover, Ang-(1-7)-dependent vasorelaxation was sensitive to antagonists against the AT₇/Mas, AT₁, AT₂ and B₂ receptor subtypes.

Antenatal betamethasone attenuates the angiotensin-(1-7)-Mas receptor-nitric oxide axis in isolated proximal tubule cells

We previously reported a sex-specific effect of antenatal treatment with betamethasone (Beta) on sodium (Na⁺) excretion in adult sheep whereby treated males but not females had an attenuated natriuretic response to angiotensin-(1-7) [Ang-(1-7)]. The present study determined the Na⁺ uptake and nitric oxide (NO) response to low-dose Ang-(1-7) (1 pM) in renal proximal tubule cells (RPTC) from adult male and female sheep antenatally exposed to Beta or vehicle. Data were expressed as percentage of basal uptake or area under the curve for Na⁺ or percentage of control for NO. Male Beta RPTC exhibited greater Na⁺ uptake than male vehicle cells (433 ± 28 vs. 330 ± 26%; P < 0.05); however, Beta exposure had no effect on Na⁺ uptake in the female cells (255 ± 16 vs. 255 ± 14%; P > 0.05). Ang-(1-7) significantly inhibited Na⁺ uptake in RPTC from vehicle male (214 ± 11%) and from both vehicle (190 ± 14%) and Beta (209 ± 11%) females but failed to attenuate Na⁺ uptake in Beta male cells. Beta exposure also abolished stimulation of NO by Ang-(1-7) in male but not female RPTC. Both the Na⁺ and NO responses to Ang-(1-7) were blocked by Mas receptor antagonist d-Ala⁷-Ang-(1-7). We conclude that the tubular Ang-(1-7)-Mas-NO pathway is attenuated in males and not females by antenatal Beta exposure. Moreover, since primary cultures of RPTC retain both the sex and Beta-induced phenotype of the adult kidney in vivo they appear to be an appropriate cell model to examine the effects of fetal programming on Na⁺ handling by the renal tubules.

Angiotensinogen import in isolated proximal tubules: evidence for mitochondrial trafficking and uptake

The renal proximal tubules are a key functional component of the kidney and express the angiotensin precursor angiotensinogen; however, it is unclear the extent that tubular angiotensinogen reflects local synthesis or internalization. Therefore, the current study established the extent to which angiotensinogen is internalized by proximal tubules and the intracellular distribution. Proximal tubules were isolated from the kidney cortex of male sheep by enzymatic digestion and a discontinuous Percoll gradient. Tubules were incubated with radiolabeled ¹²⁵I-angiotensinogen for 2 h at 37°C in serum/phenol-free DMEM/F12 media. Approximately 10% of exogenous ¹²⁵I-angiotensinogen was internalized by sheep tubules. Subcellular fractionation revealed that 21 ± 4% of the internalized ¹²⁵I-angiotensinogen associated with the mitochondrial fraction with additional labeling evident in the nucleus (60 ± 7%), endoplasmic reticulum (4 ± 0.5%), and cytosol (15 ± 4%; n = 4). Subsequent studies determined whether mitochondria directly internalized ¹²⁵I-angiotensinogen using isolated mitochondria from renal cortex and human HK-2 proximal tubule cells. Sheep cortical and HK-2 mitochondria internalized ¹²⁵I-angiotensinogen at a comparable rate of (33 ± 9 vs. 21 ± 10 pmol·min^-1·mg protein^-1; n = 3). Lastly, unlabeled angiotensinogen (100 nM) competed for ¹²⁵I-angiotensinogen uptake to a greater extent than human albumin in HK-2 mitochondria (60 ± 2 vs. 16 ± 13%; P < 0.05, n = 3). Collectively, our data demonstrate angiotensinogen import and subsequent trafficking to the mitochondria in proximal tubules. We conclude that this pathway may constitute a source of the angiotensinogen precursor for the mitochondrial expression of angiotensin peptides.