Renal autoregulation and passive pressure-flow relationships in diabetes and hypertension

Association between CYP4A11 and EPHX2 genetic polymorphisms and chronic kidney disease progression in hypertensive patients

BACKGROUND

There are evidence indicating that some metabolites of arachidonic acid produced by cytochromes P450 (CYP) and epoxide hydroxylase (EPHX2), such as hydroxyeicosatetraenoic acids (HETEs), epoxyeicosatrienoic acids (EETs) or dihydroxyeicosatrienoic acids (DHETEs), play an important role in blood pressure regulation and they could contribute to the development of hypertension (HT) and kidney damage. Therefore, the main aim of the study was to evaluate whether the genetic polymorphisms of CYP2C8, CYP2C9, CYP2J2, CYP4F2, CYP4F11 and EPHX2, responsible for the formation of HETEs, EETs and DHETEs, are related to the progression of impaired renal function in a group of patients with hypertension.

METHODS

151HT patients from a hospital nephrology service were included in the study. Additionally, a group of 87 normotensive subjects were involved in the study as control group. For HT patients, a general biochemistry analysis, estimated glomerular filtration rate and genotyping for different CYPs and EPHX2 variant alleles was performed.

RESULTS

CYP4A11 rs3890011, rs9332982 and EPHX2 rs41507953 polymorphisms, according to the dominant model, presented a high risk of impaired kidney function, with odds ratios (OR) of 2.07 (1.00-4.32; P=0.049) 3.02 (1.11-8.23; P=0.030) and 3.59 (1.37-9.41; P=0.009), respectively, and the EPHX2 rs1042032 polymorphism a greater risk according to the recessive model (OR=6.23; 95% CI=1.50-25.95; P=0.007). However, no significant differences in allele frequencies between HT patients and in normotensive subjects for any of the SNP analysed. In addition, the patients with diagnosis of dyslipidemia (n=90) presented higher frequencies of EPHX2 K55R (rs41507953) and *35A>G (rs1042032) variants than patients without dyslipidemia, 4% vs. 14% (P=0.005) and 16 vs. 27% (P=0.02), respectively.

CONCLUSIONS

In this study has been found higher odds of impaired renal function progression associated with rs3890011 and rs9332982 (CYP4A11) and rs41507953 and rs1042032 (EPHX2) polymorphisms, which may serve as biomarkers for improve clinical interventions aimed at avoiding or delaying, in chronic kidney disease patients, progress to end-stage kidney disease needing dialysis or kidney transplant.

Hyaluronan Inhibition as a Therapeutic Target for Diabetic Kidney Disease: What Is Next?

Diabetic kidney disease (DKD) is the leading cause of CKD and ESKD in the United States and worldwide. Pharmacotherapy and lifestyle modifications for glycemia, dyslipidemia, and BP control have shown success in slowing the progression of DKD. Traditional treatments, such as angiotensin-converting enzyme inhibitors or angiotensin receptor blockers and more recently the use of sodium-glucose cotransporter 2 inhibitors, nonsteroidal selective mineralocorticoid receptor antagonists, such as finerenone, and glucagon-like peptide 1 receptor agonists, have led to added benefits on various outcomes. However, significant residual risk for DKD progression remains despite the current standard-of-care approaches. Arteriolar hyalinosis (AH) is among the key findings seen on kidney biopsies of patients with DKD. It results from the excessive accumulation of hyaluronan (HA) in the arterioles. AH has not been targeted specifically by any of the therapeutic methods currently being used. We discuss in this manuscript the potential use of a selective therapy targeting AH and the increased total renal HA deposits using a HA synthesis inhibitor in DKD.

Association of intraoperative hypotension and postoperative acute kidney injury after adrenalectomy for pheochromocytoma: a retrospective cohort analysis

BACKGROUND

Perioperative acute kidney injury (AKI) has been one of the leading causes of morbidity and mortality for surgical patients. Pheochromocytoma is a rare, catecholamine-secreting neuroendocrine neoplasm characterized by typical long-term hypertension that needs surgical resection. Our objective was to determine whether intraoperative mean arterial pressures (MAPs) less than 65 mmHg are associated with postoperative AKI after elective adrenalectomy in patients with pheochromocytoma.

METHODS

We performed a retrospective review of patients undergoing adrenalectomy for pheochromocytoma between 1991 and 2019 at Peking Union Medical College Hospital, Beijing, China. Two intraoperative phases, before and after tumor resection, were recognized based on distinctly different hemodynamic characteristics. The authors evaluated the association between AKI and each blood pressure exposure in these two phases. The association between the time spent under different absolute and relative MAP thresholds and AKI was then evaluated adjusting for potential confounding variables.

RESULTS

We enrolled 560 cases with 48 patients who developed AKI postoperatively. The baseline and intraoperative characteristics were similar in both groups. Though time-weighted average MAP was not associated with postoperative AKI during the whole operation (OR 1.38; 95% CI, 0.95-2.00; P = 0.087) and before tumor resection phase (OR 0.83; 95% CI, 0.65-1.05; P = 0.12), both time-weighted MAP and time-weighted percentage changes from baseline were strongly associated with postoperative AKI after tumor resection, with OR 3.50, 95% CI (2.25, 5.46) and 2.03, 95% CI (1.56, 2.66) in the univariable logistic analysis respectively, and with OR 2.36, 95% CI (1.46, 3.80) and 1.63, 95% CI (1.23, 2.17) after adjusting sex, surgical type (open vs. laparoscopic) and estimated blood loss in the multiple logistic analysis. At any thresholds of MAP less than 85, 80, 75, 70, and 65 mmHg, prolonged exposure was associated with increased odds of AKI.

CONCLUSIONS

We found a significant association between hypotension and postoperative AKI in patients with pheochromocytoma undergoing adrenalectomy in the period after tumor resection. Optimizing hemodynamics, especially blood pressure after the adrenal vessel ligation and tumor is resected, is crucial for the prevention of postoperative AKI in patient with pheochromocytoma, which could be different from general populations.

Membrane estrogen receptor alpha (ERα) participates in flow-mediated dilation in a ligand-independent manner

Estrogen receptor alpha (ERα) activation by estrogens prevents atheroma through its nuclear action, whereas plasma membrane-located ERα accelerates endothelial healing. The genetic deficiency of ERα was associated with a reduction in flow-mediated dilation (FMD) in one man. Here, we evaluated ex vivo the role of ERα on FMD of resistance arteries. FMD, but not agonist (acetylcholine, insulin)-mediated dilation, was reduced in male and female mice lacking ERα (Esr1-/- mice) compared to wild-type mice and was not dependent on the presence of estrogens. In C451A-ERα mice lacking membrane ERα, not in mice lacking AF2-dependent nuclear ERα actions, FMD was reduced, and restored by antioxidant treatments. Compared to wild-type mice, isolated perfused kidneys of C451A-ERα mice revealed a decreased flow-mediated nitrate production and an increased H₂O₂ production. Thus, endothelial membrane ERα promotes NO bioavailability through inhibition of oxidative stress and thereby participates in FMD in a ligand-independent manner.

Glucagon-like peptide-1 receptors in the kidney: impact on renal autoregulation

Glucagon-like peptide-1 (GLP-1) and strategies based on this blood sugar-reducing and appetite-suppressing hormone are used to treat obesity and type 2 diabetes. However, the GLP-1 receptor (GLP-1R) is also present in the kidney, where it influences renal function. The effect of GLP-1 on the kidney varies between humans and rodents. The effect of GLP-1 on kidney function also seems to vary depending on its concentration and the physiological or pathological state of the kidney. In studies with rodents or humans, acute infusion of pharmacological doses of GLP-1 stimulates natriuresis and diuresis. However, the effect on the renal vasculature is less clear. In rodents, GLP-1 infusion increases renal plasma flow and glomerular filtration rate, suggesting renal vasodilation. In humans, only a subset of the study participants exhibits increased renal plasma flow and glomerular filtration rate. Differential status of kidney function and changes in renal vascular resistance of the preglomerular arterioles may account for the different responses of the human study participants. Because renal function in patients with type 2 diabetes is already at risk or compromised, understanding the effects of GLP-1R activation on kidney function in these patients is particularly important. This review examines the distribution of GLP-1R in the kidney and the effects elicited by GLP-1 or GLP-1R agonists. By integrating results from acute and chronic studies in healthy individuals and patients with type 2 diabetes along with those from rodent studies, we provide insight into how GLP-1R activation affects renal function and autoregulation.

Impact of individualized target mean arterial pressure for septic shock resuscitation on the incidence of acute kidney injury: a retrospective cohort study

BACKGROUND

To examine the relationship between delta mean arterial pressure (ΔMAP; MAP change between pre-admission minus post-resuscitation) and acute kidney injury (AKI) among patients with septic shock. In this retrospective, single-center cohort study of adult patients pre-admission MAP is defined as the median MAP recorded from 365 to 7 days before admission. Post-resuscitation MAP was median MAP during the 7th hour after initiating resuscitation.

RESULTS

In our cohort (N = 233; 55% male), the median (interquartile range [IQR]) age was 71 (58-81) years and the median (IQR) acute physiology, age, chronic health evaluation (APACHE) III score was 81 (66-97). Although those in the lowest ΔMAP quartile (-24.5 to 3.9 mmHg) had no demographic differences compared with the rest of the cohort, the odds ratio for AKI was 0.26 (95% CI 0.11-0.57) after adjustment for other known AKI risk factors. Among patients with a history of hypertension, the lowest quartile had an odds ratio for AKI of 0.12 (95% CI 0.04-0.37) after adjusting for risk factors for AKI in this cohort.

CONCLUSIONS

The incidence of AKI was lowest among those whose post-resuscitation MAP was closest to or higher than their pre-admission MAP. Further study regarding the effect of targeting the pre-admission MAP for post-resuscitation on the incidence of AKI is warranted.

Angiotensin II control of regional haemodynamics in rats with aortocaval fistula

NEW FINDINGS

What is the central question of this study? Hyperdynamic circulation because of arteriovenous fistula results in reduction of blood flow to organs but is a model of low circulatory resistance with activated renin-angiotensin system. The aim was to determine contributions of different subtypes of angiotensin II receptors to regional blood flow and vascular conductance in a hyperdynamic circulatory state. What is the main finding and its importance? The renin-angiotensin system plays a pivotal role in control of regional blood flow in animals with arteriovenous fistula and makes a major contribution to the maintenance of normal arterial blood pressure. In this hyperdynamic circulatory state model, angiotensin II type 1 receptors predominated in regulating regional haemodynamics. Regional perfusion is reduced and the renin-angiotensin system activated in rats with aortocaval fistula. The effects of captopril (angiotensin-converting enzyme inhibitor), losartan (angiotensin II type 1 receptor antagonist) and PD 123319 (angiotensin II type 2 receptor antagonist) on regional blood flow and vascular conductance were assessed in rats with aortocaval fistula and sham-operated rats. Control of blood flow and vascular conductance by angiotensin II was evaluated by serial bolus injections of captopril, losartan and PD 123319 in anaesthetized rats. In rats with fistula, PD 123319 significantly decreased, whereas captopril and losartan increased, mesenteric blood flow. The decrease in mesenteric blood flow induced by PD 123319 was significantly greater in rats with fistula compared with sham operation. Captopril and PD 123319 significantly decreased renal blood flow compared with losartan, which increased it. In sham-operated rats, captopril and losartan significantly increased, whereas PD 123319 decreased, mesenteric and renal conductance. In rats with fistula, captopril and losartan significantly increased, whereas PD 123319 decreased, mesenteric conductance. The significant increase produced by losartan on mesenteric conductance was greater in rats with fistula compared with sham operation. PD 123319 produced a significantly greater decrease in renal conductance of rats with aortocaval fistula compared with sham-operated rats. Captopril, losartan and PD 123319 did not significantly affect perfusion in the hindquarter in rats with fistula or sham-operated. The renin-angiotensin system is more active in the control of regional haemodynamics in rats with aortocaval fistula and acts as a mechanism of maintaining normal arterial blood pressure in these animals. In rats with fistula, angiotensin II type 1 receptors predominate in regulating regional haemodynamics.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Contrast-enhanced ultrasonography to evaluate changes in renal cortical microcirculation induced by noradrenaline: a pilot study

Introduction

We used contrast-enhanced ultrasound (CEUS) to estimate the effect of an increase in mean arterial pressure (MAP) induced by noradrenaline infusion on renal microvascular cortical perfusion in critically ill patients.

Methods

Twelve patients requiring a noradrenaline infusion to maintain a MAP more than 60 mmHg within 48 hours of intensive care unit admission were included in the study. Renal CEUS scans with destruction-replenishment sequences and Sonovue® (Bracco, Milano Italy) as a contrast agent, were performed at baseline (MAP 60 to 65 mmHg) and after a noradrenaline-induced increase in MAP to 80 to 85 mmHg.

Results

There was no adverse effect associated with ultrasound contrast agent administration or increase in noradrenaline infusion rate. Adequate images were obtained in all patients at all study times. To reach the higher MAP target, median noradrenaline infusion rate was increased from 10 to 14 μg/min.

Noradrenaline-induced increases in MAP were not associated with a significant change in overall CEUS derived mean perfusion indices (median perfusion index 3056 (interquartile range: 2438 to 6771) arbitrary units (a.u.) at baseline versus 4101 (3067 to 5981) a.u. after MAP increase, P = 0.38). At individual level, however, we observed important heterogeneity in responses (range -51% to +97% changes from baseline).

Conclusions

A noradrenaline-induced increase in MAP was not associated with an overall increase in renal cortical perfusion as estimated by CEUS. However, at individual level, such response was heterogeneous and unpredictable suggesting great variability in pressure responsiveness within a cohort with a similar clinical phenotype.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0653-3) contains supplementary material, which is available to authorized users.

Intrarenal transfer of an intracellular fluorescent fusion of angiotensin II selectively in proximal tubules increases blood pressure in rats and mice

The present study tested the hypothesis that intrarenal adenoviral transfer of an intracellular cyan fluorescent fusion of angiotensin II (ECFP/ANG II) selectively in proximal tubules of the kidney increases blood pressure by activating AT(1) (AT(1a)) receptors. Intrarenal transfer of ECFP/ANG II was induced in the superficial cortex of rat and mouse kidneys, and the sodium and glucose cotransporter 2 (sglt2) promoter was used to drive ECFP/ANG II expression selectively in proximal tubules. Intrarenal transfer of ECFP/ANG II induced a time-dependent, proximal tubule-selective expression of ECFP/ANG II in the cortex, which peaked at 2 wk and was sustained for 4 wk. ECFP/ANG II expression was low in the glomeruli and the entire medulla and was absent in the contralateral kidney or extrarenal tissues. At its peak of expression in proximal tubules at day 14, ANG II was increased by twofold in the kidney (P < 0.01) and more than threefold in proximal tubules (P < 0.01), but remained unchanged in plasma or urine. Systolic blood pressure was increased in ECFP/ANG II-transferred rats by 28 ± 6 mmHg (P < 0.01), whereas fractional sodium excretion was decreased by 20% (P < 0.01) and fractional lithium excretion was reduced by 24% (P < 0.01). These effects were blocked by losartan and prevented in AT(1a) knockout mice. Transfer of a scrambled ECFP/ANG IIc had no effects on blood pressure, kidney, and proximal tubule ANG II, or sodium excretion. These results provide evidence that proximal tubule-selective transfer of an intracellular ANG II fusion protein increases blood pressure by activating AT(1a) receptors and increasing sodium reabsorption in proximal tubules.