Evaluation of glomerular hemodynamic changes by sodium-glucose-transporter 2 inhibition in type 2 diabetic rats using in vivo imaging.

The mechanisms responsible for glomerular hemodynamic regulation with sodium-glucose co-transporter 2 (SGLT2) inhibitors in kidney disease due to type 2 diabetes remain unclear. Therefore, we investigated changes in glomerular hemodynamic function using an animal model of type 2 diabetes, treated with an SGLT2 inhibitor alone or in combination with a renin-angiotensin-aldosterone system inhibitor using male Zucker lean (ZL) and Zucker diabetic fatty (ZDF) rats. Afferent and efferent arteriolar diameter and single-nephron glomerular filtration rate (SNGFR) were evaluated in ZDF rats measured at 0, 30, 60, 90, and 120 minutes after the administration of a SGLT2 inhibitor (luseogliflozin). Additionally, we assessed these changes under the administration of the adenosine A1 receptor (A1aR) antagonist (8-cyclopentyl-1,3-dipropylxanthine), along with coadministration of luseogliflozin and an angiotensin II receptor blocker (ARB), telmisartan. ZDF rats had significantly increased SNGFR, and afferent and efferent arteriolar diameters compared to ZL rats, indicating glomerular hyperfiltration. Administration of luseogliflozin significantly reduced afferent vasodilatation and glomerular hyperfiltration, with no impact on efferent arteriolar diameter. Urinary adenosine levels were increased significantly in the SGLT2 inhibitor group compared to the vehicle group. A1aR antagonism blocked the effect of luseogliflozin on kidney function. Co-administration of the SGLT2 inhibitor and ARB decreased the abnormal expansion of glomerular afferent arterioles, whereas the efferent arteriolar diameter was not affected. Thus, regulation of afferent arteriolar vascular tone via the A1aR pathway is associated with glomerular hyperfiltration in type 2 diabetic kidney disease.

Prostanoid receptors in hyperfiltration-mediated glomerular injury: Novel agonists and antagonists reveal opposing roles for EP2 and EP4 receptors.

Increased fluid-flow shear stress (FFSS) contributes to hyperfiltration-induced podocyte and glomerular injury resulting in progression of chronic kidney disease (CKD). We reported that increased FFSS in vitro and in vivo upregulates PGE2 receptor EP2 (but not EP4 expression), COX2-PGE2 -EP2 axis, and EP2-linked Akt-GSK3ß-ß-catenin signaling pathway in podocytes. To understand and use the disparities between PGE2 receptors, specific agonists, and antagonists of EP2 and EP4 were used to assess phosphorylation of Akt, GSK3ß and ß-catenin in podocytes using Western blotting, glomerular filtration barrier function using in vitro albumin permeability (Palb ) assay, and mitigation of hyperfiltration-induced injury in unilaterally nephrectomized (UNX) mice at 1 and 6 months. Results show an increase in Palb by PGE2 , EP2 agonist (EP2AGO ) and EP4 antagonist (EP4ANT ), but not by EP2 antagonist (EP2ANT ) or EP4 agonist (EP4AGO ). Pretreatment with EP2ANT blocked the effect of PGE2 or EP2AGO on Palb . Modulation of EP2 and EP4 also induced opposite effects on phosphorylation of Akt and ß-Catenin. Individual agonists or antagonists of EP2 or EP4 did not induce significant improvement in albuminuria in UNX mice. However, treatment with a combination EP2ANT + EP4AGO for 1 or 6 months caused a robust decrease in albuminuria. EP2ANT + EP4AGO combination did not impact adaptive hypertrophy or increased serum creatinine. Observed differences between expression of EP2 and EP4 on the glomerular barrier highlight these receptors as potential targets for intervention. Safe and effective mitigating effect of EP2ANT + EP4AGO presents a novel opportunity to delay the progression of hyperfiltration-associated CKD as seen in transplant donors.

Influence of carnosine and carnosinase-1 on diabetes-induced afferent arteriole vasodilation: implications for glomerular hemodynamics.

Dysregulation in glomerular hemodynamics favors hyperfiltration in diabetic kidney disease (DKD). Although carnosine supplementation ameliorates features of DKD, its effect on glomerular vasoregulation is not known. We assessed the influence of carnosine and carnosinase-1 (CN1) on afferent glomerular arteriole vasodilation and its association with glomerular size, hypertrophy, and nephrin expression in diabetic BTBRob/ob mice. Two cohorts of mice including appropriate controls were studied: i.e., diabetic mice that received oral carnosine supplementation (cohort 1) and human (h)CN1 transgenic (TG) diabetic mice (cohort 2). The lumen area ratio (LAR) of the afferent arterioles and glomerular parameters were measured by conventional histology. Three-dimensional analysis using a tissue clearing strategy was also used. In both cohorts, LAR was significantly larger in diabetic BTBRob/ob versus nondiabetic BTBRwt/ob mice (0.41 ± 0.05 vs. 0.26 ± 0.07, P < 0.0001 and 0.42 ± 0.06 vs. 0.29 ± 0.04, P < 0.0001) and associated with glomerular size (cohort 1: r = 0.55, P = 0.001 and cohort 2: r = 0.89, P < 0.0001). LAR was partially normalized by oral carnosine supplementation (0.34 ± 0.05 vs. 0.41 ± 0.05, P = 0.004) but did not differ between hCN1 TG and wild-type BTBRob/ob mice. In hCN1 TG mice, serum CN1 concentrations correlated with LAR (r = 0.90, P = 0.006). Diabetic mice displayed decreased nephrin expression and increased glomerular hypertrophy. This was not significantly different in hCN1 TG BTBRob/ob mice (P = 0.06 and P = 0.08, respectively). In conclusion, carnosine and CN1 may affect intraglomerular pressure in an opposing manner through the regulation of afferent arteriolar tone. This study corroborates previous findings on the role of carnosine in the progression of DKD.NEW & NOTEWORTHY Dysregulation in glomerular hemodynamics favors hyperfiltration in diabetic kidney disease (DKD). Although carnosine supplementation ameliorates features of DKD, its effect on glomerular vasoregulation is not known. We assessed the influence of carnosine and carnosinase-1 (CN1) on afferent glomerular arteriole vasodilation and its association with glomerular size, hypertrophy, and nephrin expression in diabetic BTBRob/ob mice. Our results provide evidence that carnosine feeding and CN1 overexpression likely affect intraglomerular pressure through vasoregulation of the afferent arteriole.

Genetically increased angiotensin I-converting enzyme alters peripheral and renal vascular reactivity to angiotensin II and bradykinin in mice.

Angiotensin I-converting enzyme (ACE) levels in humans are under strong genetic influence. Genetic variation in ACE has been linked to risk for and progression of cardiovascular and renal diseases. Causality has been documented in genetically modified mice, but the mechanisms underlying causality are not completely elucidated. To further document the vascular and renal consequences of a moderate genetic increase in ACE synthesis, we studied genetically modified mice carrying three copies of the ACE gene (three-copy mice) and littermate wild-type animals (two-copy mice). We investigated peripheral and renal vascular reactivity to angiotensin II and bradykinin in vivo by measuring blood pressure and renal blood flow after intravenous administration and also reactivity of isolated glomerular arterioles by following intracellular Ca2+ mobilization. Carrying three copies of the ACE gene potentiated the systemic and renal vascular responses to angiotensin II over the whole range of peptide concentration tested. Consistently, the response of isolated glomerular afferent arterioles to angiotensin II was enhanced in three-copy mice. In these mice, signaling pathways triggered by endothelial activation by bradykinin or carbachol in glomerular arterioles were also altered. Although the nitric oxide (NO) synthase (NOS)/NO pathway was not functional in arterioles of two-copy mice, in muscular efferent arterioles of three-copy mice NOS3 gene expression was induced and NO mediated the effect of bradykinin or carbachol. These data document new and unexpected vascular consequences of a genetic increase in ACE synthesis. Enhanced vasoconstrictor effect of angiotensin II may contribute to the risk for cardiovascular and renal diseases linked to genetically high ACE levels. NEW & NOTEWORTHY A moderate genetic increase in angiotensin I-converting enzyme (ACE) in mice similar to the effect of the ACE gene D allele in humans unexpectedly potentiates the systemic and renal vasoconstrictor responses to angiotensin II. It also alters the endothelial signaling pathways triggered by bradykinin or carbachol in glomerular efferent arterioles.

Influence of sex on hyperfiltration in patients with uncomplicated type 1 diabetes.

The aim of this analysis was to examine sex-based differences in renal segmental resistances in healthy controls (HCs) and patients with type 1 diabetes (T1D). We hypothesized that hyperfiltration-an early hemodynamic abnormality associated with diabetic nephropathy-would disproportionately affect women with T1D, thereby attenuating protection against the development of renal complications. Glomerular hemodynamic parameters were evaluated in HC (n = 30) and in normotensive, normoalbuminuric patients with T1D and either baseline normofiltration [n = 36, T1D-N, glomerular filtration rate (GFR) 90-134 ml·min-1·1.73 m2] or hyperfiltration (n = 32, T1D-H, GFR ≥ 135 ml·min-1·1.73 m2) during euglycemic conditions (4-6 mmol/l). Gomez's equations were used to derive efferent (RE) and afferent (RA) arteriolar resistances, glomerular hydrostatic pressure (PGLO) from inulin (GFR) and paraaminohippurate [effective renal plasma flow (ERPF)] clearances, plasma protein and estimated ultrafiltration coefficients (KFG). Female patients with T1D with hyperfiltration (T1D-H) had higher RE (1,985 ± 487 vs. 1,381 ± 296 dyne·sec-1·cm-5, P < 0.001) and filtration fraction (FF, 0.20 ± 0.047 vs. 0.16 ± 0.03 P < 0.05) and lower ERPF (876 ± 245 vs. 1,111 ± 298 134 ml·min-1·1.73 m2P < 0.05) compared with male T1D-H patients. Overall, T1D-H patients had higher PGLO and lower RA vs. HC subjects, although there were no sex-based differences. In conclusion, female T1D-H patients had higher RE and FF and lower ERPF than their male counterparts with no associated sex differences in RA Prospective intervention studies should consider sex as a modifier of renal hemodynamic responses to renal protective therapies.

Physiopathological implications of P2X1 and P2X7 receptors in regulation of glomerular hemodynamics in angiotensin II-induced hypertension.

Deleterious effects of purinergic P2X1 and P2X7 receptors (P2XRs) in ANG II-dependent hypertension include increased renal vascular resistance, and impaired autoregulation and pressure natriuresis. However, their specific effects on the determinants of glomerular hemodynamics remain incompletely delineated. To investigate the P2XR contributions to altered glomerular hemodynamics in hypertension, the effects of acute blockade of P2X1R, P2X7R, and P2X4R with NF449, A438079, and PSB12054, respectively, were evaluated in ANG II-infused rats (435 ng·kg-1·min-1). P2X1R or P2X7R blockade reduced afferent (6.85 ± 1.05 vs. 2.37 ± 0.20 dyn·s-1·cm-5) and efferent (2.85 ± 0.38 vs. 0.99 ± 0.07 dyn·s-1·cm-5) arteriolar resistances, leading to increases in glomerular plasma flow (75.82 ± 5.58 vs. 206.7 ± 16.38 nl/min), ultrafiltration coefficient (0.0198 ± 0.0024 vs. 0.0512 ± 0.0046 nl·min-1·mmHg-1), and single-nephron glomerular filtration rate (22.73 ± 2.02 vs. 51.56 ± 3.87 nl/min) to near normal values. Blockade of P2X4R did not elicit effects in hypertensive rats. In normotensive sham-operated rats, only the P2X1R antagonist caused an increase plasma flow and single-nephron glomerular filtration rate, whereas the P2X4R antagonist induced glomerular vasoconstriction that was consistent with evidence that P2X4R stimulation increases release of nitric oxide from endothelial cells. Mean arterial pressure remained unchanged in both hypertensive and normotensive groups. Western blot analysis showed overexpression of P2X1R, P2X7R, and P2X4R proteins in hypertensive rats. Whereas it has been generally assumed that the altered glomerular vascular resistances in ANG II hypertension are due to AT1 receptor-mediated vasoconstriction, these data indicate a predominant P2X1R and P2X7R control of glomerular hemodynamics in ANG II hypertension.

Cyclooxygenase-2, prostaglandin E2, and prostanoid receptor EP2 in fluid flow shear stress-mediated injury in the solitary kidney.

Hyperfiltration subjects podocytes to increased tensile stress and fluid flow shear stress (FFSS). We showed a 1.5- to 2.0-fold increase in FFSS in uninephrectomized animals and altered podocyte actin cytoskeleton and increased synthesis of prostaglandin E2 (PGE2) following in vitro application of FFSS. We hypothesized that increased FFSS mediates cellular changes through specific receptors of PGE2. Presently, we studied the effect of FFSS on cultured podocytes and decapsulated isolated glomeruli in vitro, and on solitary kidney in uninephrectomized sv129 mice. In cultured podocytes, FFSS resulted in increased gene and protein expression of cyclooxygenase (COX)-2 but not COX-1, prostanoid receptor EP2 but not EP4, and increased synthesis and secretion of PGE2, which were effectively blocked by indomethacin. Next, we developed a special flow chamber for applying FFSS to isolated glomeruli to determine its effect on an intact glomerular filtration barrier by measuring change in albumin permeability (Palb) in vitro. FFSS caused an increase in Palb that was blocked by indomethacin (P < 0.001). Finally, we show that unilateral nephrectomy in sv129 mice resulted in glomerular hypertrophy (P = 0.006), increased glomerular expression of COX-2 (P < 0.001) and EP2 (P = 0.039), and increased urinary albumin excretion (P = 0.001). Activation of the COX-2-PGE2-EP2 axis appears to be a specific response to FFSS in podocytes and provides a mechanistic basis for alteration in podocyte structure and the glomerular filtration barrier, leading to albuminuria in hyperfiltration-mediated kidney injury. The COX-2-PGE2-EP2 axis is a potential target for developing specific interventions to ameliorate the effects of hyperfiltration-mediated kidney injury in the progression of chronic kidney disease.

Renal Sodium Avidity in Heart Failure.

BACKGROUND: Increased renal sodium avidity is a hallmark feature of the heart failure syndrome. SUMMARY: Increased renal sodium avidity refers to the inability of the kidneys to elicit potent natriuresis in response to sodium loading. This eventually causes congestion, which is a major contributor to hospital admissions and mortality in heart failure. KEY MESSAGES: Important novel concepts such as the renal tamponade hypothesis, accelerated nephron loss, and the role of hypochloremia, the sympathetic nervous system, inflammation, the lymphatic system, and interstitial sodium buffers are involved in the pathophysiology of renal sodium avidity. A good understanding of these concepts is crucially important with respect to treatment recommendations regarding dietary sodium restriction, fluid restriction, rapid up-titration of guideline-directed medical therapies, combination diuretic therapy, natriuresis-guided diuretic therapy, use of hypertonic saline, and ultrafiltration.

Role of Heart Rate Variability in Association Between Glomerular Hyperfiltration and All-Cause Mortality.

Background Glomerular hyperfiltration (GHF) is paradoxically associated with increased cardiovascular events in healthy individuals, but the pathogenesis remains unclear. We aim to investigate whether GHF is associated with mortality and whether decreased heart rate variability (HRV) is associated with GHF. Methods and Results We retrospectively analyzed 1615 participants (aged 66.1±17.3 years, 61.9% men) without prior cardiovascular events. The glomerular filtration rate was estimated using the Chronic Kidney Disease Epidemiology Collaboration equation. GHF was defined as glomerular filtration rate >the 95th percentile after stratification for age and sex, whereas normal filtration was defined as the 25th to 75th percentiles. HRV indexes, including time domain, frequency domain, and sample entropy, were measured using 24-hour ambulatory electrocardiography. Clinical outcomes were defined as all-cause mortality at 2 years. During a mean follow-up of 16.5±8.2 months, there were 117 deaths (7.2%). GHF was associated with a higher risk of death (hazard ratio and 95% CIs, 1.97 [1.15-3.37]). Reduced HRV indexes, including time domain, frequency domain, and sample entropy (odds ratio and 95% CIs, 0.79 [0.70-0.89]) were all independently associated with the presence of GHF after accounting for age, sex, mean heart rate, morbidities, and medications. In subgroup analysis, reduced HRV was more predictive of GHF in the young than the elderly. Mediation analysis revealed a significant mediation effect between HRV and GHF in addition to their respective detrimental effects on survival. Conclusions Reduced HRV was independently associated with the presence of GHF. Autonomic dysfunction may be involved in the pathogenesis of adverse outcomes of GHF in individuals without prior cardiovascular events.

Transcription Factor ß-Catenin Plays a Key Role in Fluid Flow Shear Stress-Mediated Glomerular Injury in Solitary Kidney.

Increased fluid flow shear stress (FFSS) in solitary kidney alters podocyte function in vivo. FFSS-treated cultured podocytes show upregulated AKT-GSK3ß-ß-catenin signaling. The present study was undertaken to confirm (i) the activation of ß-catenin signaling in podocytes in vivo using unilaterally nephrectomized (UNX) TOPGAL mice with the ß-galactosidase reporter gene for ß-catenin activation, (ii) ß-catenin translocation in FFSS-treated mouse podocytes, and (iii) ß-catenin signaling using publicly available data from UNX mice. The UNX of TOPGAL mice resulted in glomerular hypertrophy and increased the mesangial matrix consistent with hemodynamic adaptation. Uninephrectomized TOPGAL mice showed an increased ß-galactosidase expression at 4 weeks but not at 12 weeks, as assessed using immunofluorescence microscopy (p < 0.001 at 4 weeks; p = 0.16 at 12 weeks) and X-gal staining (p = 0.008 at 4 weeks; p = 0.65 at 12 weeks). Immunofluorescence microscopy showed a significant increase in phospho-ß-catenin (Ser552, p = 0.005) at 4 weeks but not at 12 weeks (p = 0.935) following UNX, and the levels of phospho-ß-catenin (Ser675) did not change. In vitro FFSS caused a sustained increase in the nuclear translocation of phospho-ß-catenin (Ser552) but not phospho-ß-catenin (Ser675) in podocytes. The bioinformatic analysis of the GEO dataset, #GSE53996, also identified ß-catenin as a key upstream regulator. We conclude that transcription factor ß-catenin mediates FFSS-induced podocyte (glomerular) injury in solitary kidney.

The Renal Arterial Resistance Index Predicts Worsening Renal Function in Chronic Heart Failure Patients.

BACKGROUND/AIM: The renal arterial resistance index (RRI) is a Doppler measure, which reflects abnormalities in the renal blood flow. The aim of this study was to verify the value of RRI as a predictor of worsening renal function (WRF) in a group of chronic heart failure (CHF) outpatients. METHODS: We enrolled 266 patients in stable clinical conditions and on conventional therapy. Peak systolic velocity and end diastolic velocity of a segmental renal artery were obtained by pulsed Doppler flow, and RRI was calculated. Creatinine serum levels were evaluated at baseline and at 1 year, and the changes were used to assess WRF occurrence. RESULTS: During follow-up, 34 (13%) patients showed WRF. RRI was associated with WRF at univariate (OR: 1.13; 95% CI: 1.07-1.20) as well as at a forward stepwise multivariate logistic regression analysis (OR: 1.09; 95% CI: 1.03-1.16; p = 0.005) including the other univariate predictors. CONCLUSIONS: Quantification of arterial renal perfusion provides a new parameter that independently predicts the WRF in CHF outpatients. Its possible role in current clinical practice to better define the risk of cardiorenal syndrome progression is strengthened.