Glomerular Capillary Pressure Research Articles

Association between plasma aldosterone concentration and intraglomerular hemodynamics in primary aldosteronism.

In primary aldosteronism (PA), aldosterone could affect glomerular hemodynamics by elevating renal vascular resistance and glomerular capillary pressure. However, the relationship between plasma aldosterone concentrations (PAC) and glomerular hemodynamics including efferent arteriolar resistance (Re), afferent arteriolar resistance (Ra) in humans is still unclear. The aim of this study was to investigate the relationships of PAC with intraglomerular hemodynamic parameters in patients with PA. An observational study of glomerular hemodynamics was performed using simultaneous measurements of plasma clearance of para-aminohippurate and inulin (Cin; glomerular filtration rate (GFR)) in 17 patients with PA. Kidney function was evaluated by Cin, estimated GFR based on serum creatine (eGFRcre) and serum cystatin C (eGFRcys) and creatine clearance (Ccr). Intraglomerular hemodynamic parameters, including Re, Ra, and intraglomerular hydrostatic pressure (Pglo) were calculated using Gomez's formulae. In the 17 PA cases, PAC was significantly correlated with Cin (rho=0.752, p=0.001) and eGFRcys (rho=0.567, p=0.018), but was not correlated witheGFRcreand Ccr. PAC was also significantly correlated with Pglo, Re, and urinary protein/day (rho=0.775, p=0.0004, rho=0.625, p=0.009, and rho=0.625, p=0.007, respectively). Multivariable regression analysis showed that PAC was significantly associated with Cin and Re. In comparing aldosterone producing adenoma (APA) and non-APA cases, Cin was significantly elevated in APA (p=0.037), whereas eGFRcre, eGFRcys, and Ccr were not. Re tended to be higher in APA (p=0.064). These results suggest high aldosterone cause glomerular hyperfiltration by constricting Re. Cin, but not eGFRcre and Ccr, may be useful for evaluating kidney function in PA.

Preliminary Exploration of Potential Active Ingredients and Molecular Mechanisms of Yanggan Yishui Granules for Treating Hypertensive Nephropathy Using UPLC-Q-TOF/MS Coupled with Network Pharmacology and Molecular Docking Strategy.

Hypertensive nephropathy (HN) is a prevalent complication of hypertension and stands as the second primary reason for end-stage renal disease. Research in clinical settings has revealed that Yanggan Yishui Granule (YGYSG) has significant therapeutic effects on HN. However, the material basis and action mechanisms of YGYSG against HN remain unclear. Consequently, this study utilized a comprehensive method integrating ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS), network pharmacology, and molecular docking to delineate the active ingredients and potential therapeutic mechanisms of YGYSG for treating HN. Firstly, sixty distinct components were recognized in total as potential active ingredients in YGYSG by UPLC-Q-TOF/MS. Subsequently, the mechanisms of YGYSG against HN were revealed for the first time using network pharmacology. 23 ingredients played key roles in the complete network and were the key active ingredients, which could affect the renin-angiotensin system, fluid shear stress and atherosclerosis, HIF-1 signaling pathway, and AGE-RAGE signaling pathway in diabetic complications by regulating 29 key targets such as TNF, IL6, ALB, EGFR, ACE, and MMP2. YGYSG could treat HN through the suppression of inflammatory response and oxidative stress, attenuating the proliferation of renal vascular smooth muscle cells, lessening glomerular capillary systolic pressure, and ameliorating renal dysfunction and vascular damage through the aforementioned targets and pathways. Molecular docking results revealed that most key active ingredients exhibited a high affinity for binding to the key targets. This study pioneers in clarifying the bioactive compounds and molecular mechanisms of YGYSG against HN and offers scientific reference into the clinical application.

Unraveling a Novel Mechanism of Altered Glomerular Hemodynamics in Pre-diabetic Obesity

Background: In pre-diabetic obesity, disrupted glomerular autoregulation leads to increased glomerular capillary pressure and renal blood flow, causing potential barotrauma-induced glomerular damage. A decrease in Afferent arteriole ( Af-Art) resistance causes higher glomerular capillary pressure but the underlying mechanism behind this, specifically in pre-diabetic obesity, remains unclear. Hyperinsulinemia is common in pre-diabetic obesity, but its role in reducing Af-Art resistance in the kidneys is unknown. Kidney blood flow is auto-regulated by vasoconstriction via tubuloglomerular feedback (TGF) and vasodilation through the Distal convoluted tubule-2/connecting tubule (DCT-2/CNT) mechanism. Our earlier studies indicate increased Af-Art dilation in pre-diabetic obese rats through the DCT-2/CNT mechanism without affecting TGF. This DCT-2/CNT induced Af-Art dilation requires initiation from epithelial sodium channels (ENaC) present at this tubular segment and interestingly insulin is a known ENaC activator. Hypothesis: We hypothesize that in the context of pre-diabetic obesity, hyperinsulinemia contributes to an increase in renal cortical blood flow (CBF) by increasing DCT-2/CNT-induced Af-Art dilation, subsequently leading to glomerular injury. Methods: We assessed the effects of insulin on Af-Art dilation by perfusing juxtaposed DCT-2/CNT segments with insulin in normal rabbits. Contribution of DCT-2/CNT induced Af-Art dilation was measured by co-administration of the ENaC blocker benzamil. To study hyperinsulinemia's role in an in-vivo setting without altering blood glucose levels, we used a hyperinsulinemic-euglycemic (HI-EUG) clamp in obese rats with intravenous (IV) glucose and insulin infusions. Renal CBF and blood pressure were monitored using a laser Doppler probe and femoral artery catheter, respectively, both with and without benzamil administration (400 μg/kg, IV). To evaluate insulin's potential role in causation of renal damage, we infused insulin directly into one kidney of lean rats for 6 weeks via a renal sub-capsular catheter, with the contralateral kidney serving as control. Glomerular basement membrane (GBM) thickness, a marker of renal damage, was measured via electron microscopy. Untargeted lipidomic analysis of the renal cortex was performed to identify potential renal damage pathways in insulin infused kidneys. Results: Insulin perfusion in rabbits' DCT-2/CNT potentiated the dilation of adherent Af-Art compared to control infusions with artificial tubular fluid. ENaC inhibition reversed the insulin-induced Af-Art dilation, confirming that insulin increases Af-Art dilation through the ENaC-initiated DCT-2/CNT mechanism. In obese rats, insulin delivery using a HI-EUG clamp resulted in a significant 20.8±4.9% increase in CBF, which was negated by the administration of the ENaC blocker benzamil, indicating the potential involvement of DCT-2/CNT-mediated vasodilation. Neither the HI-EUG clamp nor benzamil infusion affected blood pressure. Additionally, continuous direct insulin infusion into the kidneys of lean rats led to an increase in glomerular basement membrane (GBM) thickness and ceramide accumulation in the renal cortex, both indicative of renal damage. Conclusion: Our study demonstrates that insulin directly augments DCT-2/CNT-mediated Af-Art dilation and increases renal cortical blood flow in obese rats. Chronic renal insulin infusion led to structural changes and damage markers in the kidney, independent of blood glucose and blood pressure levels. Henry Ford Health System Internal Funding. Pilot and Feasibility grant from southeast center for integrated metabolomics. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effect of SGLT2 and dual SGLT1/2 Inhibition on the Development of Salt-induced Hypertension

In recent years, sodium-glucose co-transporter inhibitors (SGLT2i) have become the new mainstay in treating diabetes mellitus and, lately, cardiovascular diseases. Large clinical trials have shown remarkable benefits of SGLT2i on renal and cardiovascular outcomes. SGLT2i have been reported to slow the progression of chronic kidney disease by reducing hyperfiltration and glomerular capillary pressure, kidney hypertrophy, and albuminuria. Recently, the dual SGLT1/2 inhibitor sotagliflozin (Sota) was approved by the FDA for the treatment of heart failure independent of ejection fraction. However, despite these promising outcomes, the effects of SGLTi, particularly in salt-sensitive hypertension, requires further investigation. The main goal of this study was to define the effects of SGLT inhibition on the development of salt-induced hypertension and characterize potential contributing mechanisms. In our recent studies, we showed that SGLTi dapagliflozin (Dapa) caused an increase of diuresis in 8-weeks old male and female Dahl SS rats when fed a high salt (HS, 4% NaCl for 3 weeks) diet. Additionally, Dapa increased glucose and Na+ excretion. Chronic Dapa treatment also resulted in inhibition of the development of hypertension. Interestingly, male rats had no changes in kidney damage, whereas in females Dapa attenuated kidney fibrosis. To define potential molecular mechanisms involved in the beneficial effects of SGLT2i, we performed additional analyses of tissues collected from SS rats on a HS diet treated with either vehicle or Dapa. Transcriptomics analyses revealed that in the kidney cortex, top biological functions affected by SGLT2 inhibition were related to lipid and amino acid metabolism, molecular transport, as well as cell function. Preliminary studies were performed to test lipid mediators in the kidney cortex of male Dahl SS rats fed 3 weeks with HS diet and treated with Dapa. We found that several tested bioactive lipids, specifically pro-inflammatory mediators, were elevated in Dahl SS rats following HS diet, and these increased levels were completely blocked in Dapa-treated rats. Dual SGLT1/2 inhibition by Sota (30 mg/kg/day in food, n=6 rats/group) resulted in rapid attenuation of salt-induced hypertension. Starting from day 5 of HS challenge, MAP of vehicle-treated Dahl SS male rats was significantly higher compared to Sota-treated rats (~33 mmHg MAP difference on day 21), whichout differences in heart rate. In response to Sota treatment, SS rats had ~1.6-fold greater diuresis (at day 21: vehicle 37±2 vs. treated 61±6 ml/day) and glucosuria (values?). Further studies are ongoing to define the effects on GFR, kidney, and heart damage, and the potential resulting mechanisms. Our preliminary data indicate that dual SGLT1/2 inhibition with Sota had a significant impact on salt-induced hypertension in the Dahl SS rats. Further research will provide a more comprehensive understanding of the mechanisms. This research was supported by National Institutes of Health grant R35 HL135749 (to AS). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Glomerular Hemodynamics During Recovery from Renal Ischemia-Reperfusion Injury Addressed with Micropuncture in Rats

Objective: To establish the physical basis for low GFR in ischemic renal injury (IR) and determine whether abnormalities in GFR determinants persist after renal recovery. Method: IR was generated in male and female Wistar Froemter rats by clamping both renal pedicles for 60 minutes. Controls had same surgery without pedicle clamp. Glomerular hemodynamics were assessed by renal micropuncture (MP) after 1 day, 1 week, or 4 weeks. Single nephron GFR (SNGFR) was paired with tubular stop-flow (PSF) and free-flow pressure (PFF) in each nephron. Afferent Starling pressure (EFPa) is PSF-PFF. Glomerular capillary pressure (PGC) was computed from PSF, PFF and plasma oncotic pressure. ANOVA factors included IR, sex, time point and date of experiment (nested). Inter-nephron heterogeneity was extracted from normalized root-square difference between each data point and the mean for that animal. (total n=349 nephrons, 47 rats). Results: [Formula: see text] Summary and conclusion: The physical cause of low GFR in IR was low EFPa, which resulted from low PGC with normal PFF in all animals except 1. The injured kidney manifest elevated inter-nephron variability for all variables. Mean values for SNGFR and intra-renal pressures returned to normal in the “recovered” kidney, but variability between nephrons did not return to normal. Female rats had lower baseline SNGFR and PGC than males but the hemodynamic patterns during IR and renal recovery were not differentiable by sex (excluding one female outlier with high PFF). Despite “normal” GFR and PGC, the “recovered” kidney is not a “normal” kidney. NIH NIDDK R01 132690. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Glomerular Hyperfiltration and Th17 Responses Promote Glomerulosclerosis Following Nephron Loss

Objective: Chronic kidney disease (CKD) affects 37 million Americans resulting in $87 billion healthcare cost annually. Impaired renal autoregulation in obesity, diabetes and hypertension causes elevated glomerular capillary pressure and whole-kidney hyperfiltration, leading to progressive glomerulosclerosis and CKD. In advanced CKD with less than 50% functional nephron mass, single-nephron hyperfiltration causes further nephron loss, ultimately leading to hypofiltration and end-state kidney disease. Increased renal perfusion pressure directly drives T cell infiltration to the kidney. We and others have shown that T helper (Th) 17 cells promote vascular stiffening in hypertension and renal interstitial fibrosis after ischemia-reperfusion injury, but their roles in glomerulosclerosis and CKD are poorly understood. We hypothesized that glomerular hypertension and hyperfiltration promote renal fibrosis through Th17-mediated immune responses. Methods: We investigated the causal roles of glomerular hyperfiltration and Th17 responses in a mouse CKD model induced by reduced kidney mass (RKM), which involved right kidney nephrectomy and partial renal artery ligation in the left kidney such that the functional renal mass is reduced by ~ 5/6. Male 129/S6 mice received sham or RKM surgery at 8 weeks of age, and blood pressure (BP, by radiotelemetry), glomerular filtration rate (GFR, by transcutaneous FITC-sinistrin) and serum/urine CKD markers were assessed at baseline (BL) and week 1, 2, 3, 4, 8, and 12 post-surgery. Results: BP and GFR of RKM mice were identical to sham controls at BL (n=4-6). Immediately after the RKM procedure, GFR dropped to 22% of BL, consistent with the extent of renal mass ablation. BP increased by 29 mmHg first week after 5/6 ablation (144 ± 8 vs BL 112 ± 2 mmHg, p<0.05, 2-way ANOVA), exposing the remnant nephrons to increased renal perfusion pressure. Serum creatinine, blood urea nitrogen and urinary albumin were significantly elevated by week 2. BP and CKD markers remained elevated through week 12 in the 5/6 ablation mice. The GFR of ablated mice gradually increased to 38% of BL at day 3, 57% at week 1 and 68% at week 2, suggesting that systemic hypertension and impaired renal autoregulation may have caused substantial single-nephron hyperfiltration in the remnant kidney mass. GFR plateaued at ~ 70% of BL in week 3-4 then declined to 48% at week 8-12 when glomerular, interstitial, and microvascular fibrosis developed as evidence by Periodic Acid Schiff and Picro Sirius Red staining. Supporting a causal role of hemodynamic derangements in CKD progression, calcium channel blocker amlodipine, a potent vasodilator, dose dependently (5-10 mg/kg/day, n=7-9) exacerbated glomerular hyperfiltration, glomerulosclerosis and mortality despite marked BP-lowering effects. Importantly, the adaptive increase of GFR in the first 2 weeks post 5/6 ablation was accompanied by significant increase of renal Th17 cells, which not only preceded the infiltration of CD11b+ myeloid cells, F4/80+ monocyte/macrophages and T regulatory cells, but also the glomerulosclerosis and GFR decline in week 8. Conclusions: Our data suggest that glomerular hyperfiltration causes progressive nephron loss and kidney fibrosis, at least in part, through Th17-mediated renal inflammation. To further establish causality, ongoing studies will assess if Th17 blockade ameliorates glomerulosclerosis and retard CKD progression. Funding: This work was supported by NIDDK R01 DK094907, R01 DK113632, R01 DK128677 to THL, and K01 DK126972 to JW. JW is also supported by an American Heart Association Second Century Early Faculty Independence Award (23SCEFIA1148464), a University of Rochester Environmental Health Science Center pilot award (Prime sponsor: NIEHS P30ES001247), and a University of Rochester Program for Advanced Immune Bioimaging Pilot Award (Prime Sponsor: NIAID P01AI102851). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

How can inhibition of glucose and sodium transport in the early proximal tubule protect the cardiorenal system?

What mechanisms can link the inhibition of SGLT2-mediated Na+-coupled glucose reabsorption in early proximal tubules to kidney and heart protection in patients with and without type 2 diabetes? Due to physical and functional coupling of SGLT2 to other sodium and metabolite transporters in the early proximal tubule (including NHE3, URAT1), inhibitors of SGLT2 (SGLT2i) reduce reabsorption not only of glucose, inducing osmotic diuresis, but of other metabolites plus of a larger amount of sodium than expected based on SGLT2 inhibition alone, thereby reducing volume retention, hypertension, and hyperuricemia. Metabolic adaptations to SGLT2i include a fasting-like response, with enhanced lipolysis and formation of ketone bodies that serve as additional fuel for kidneys and heart. Making use of the physiology of tubulo-glomerular communication, SGLT2i functionally lower glomerular capillary pressure and filtration rate, thereby reducing physical stress on the glomerular filtration barrier, tubular exposure to albumin and nephrotoxic compounds, and the oxygen demand for reabsorbing the filtered load. Together with reduced gluco-toxicity in the early proximal tubule and better distribution of transport work along the nephron, SGLT2i can preserve tubular integrity and transport function and, thereby, GFR in the long-term. By shifting transport downstream, SGLT2 inhibitors may simulate systemic hypoxia at the oxygen sensors in the deep cortex/outer medulla, which stimulates erythropoiesis and, together with osmotic diuresis, enhances hematocrit and thereby improves oxygen delivery to all organs. The described SGLT2-dependent effects may be complemented by off-target effects of SGLT2i on the heart itself and on the microbiome formation of cardiovascular-effective uremic toxins.

Glomerular hyperfiltration as a therapeutic target for CKD.

The global burden of chronic kidney disease (CKD) is high and increasing. Early diagnosis and intervention are key to improve outcomes. Single nephron glomerular hyperfiltration is an early pathophysiologic manifestation of CKD that may result in absolute glomerular hyperfiltration, i.e. a high glomerular filtration rate (GFR) or be associated with normal or low GFR because of nephron loss (relative glomerular hyperfiltration). Even though compensatory glomerular hyperfiltration may contribute to maintain kidney function after loss of kidney mass, the associated increased glomerular capillary pressure and glomerular and podocyte size drive podocyte loss, albuminuria and proximal tubular overload, contributing to CKD progression. In this regard, all kidney protective drugs in clinical use so far, from renin-angiotensin system blockers to mineralocorticoid receptor blockers to sodium-glucose cotransporter-2 inhibitors to tolvaptan, induced an early dip in glomerular filtration that is thought to represent reversal of hyperfiltration. As glomerular hyperfiltration may be present early in the course of kidney disease, its recognition may provide an effective intervention window that may predates current criteria based on high albuminuria or loss of GFR. Nevertheless, there is no diagnostic method with high sensitivity and specificity to identify single nephron glomerular hyperfiltration, except when it leads to obvious absolute glomerular hyperfiltration, as observed in the early stages of diabetic kidney disease when nephron mass is still preserved. We now review the concept of glomerular hyperfiltration as an indicator of CKD risk, including definitions, challenges in diagnosis and evaluation, underlying pathophysiological mechanisms, potential therapeutic approaches and unanswered questions.

Advanced optical imaging reveals preferred spatial orientation of podocyte processes along the axis of glomerular capillaries

Mammalian kidneys filter enormous volumes of water and small solutes, a filtration driven by the hydrostatic pressure in glomerular capillaries, which is considerably higher than in most other tissues. Interdigitating cellular processes of podocytes form the slits for fluid filtration connected by the membrane-like slit diaphragm cell junction containing a mechanosensitive ion channel complex and allow filtration while counteracting hydrostatic pressure. Several previous publications speculated that podocyte processes may display a preferable orientation on glomerular capillaries instead of a random distribution. However, for decades, the controversy over spatially oriented filtration slits could not be resolved due to technical limitations of imaging technologies. Here, we used advanced high-resolution, three-dimensional microscopy with high data throughput to assess spatial orientation of podocyte processes and filtration slits quantitatively. Filtration-slit-generating secondary processes preferentially align along the capillaries' longitudinal axis while primary processes are preferably perpendicular to the longitudinal direction. This preferential orientation required maturation in development of the mice but was lost in mice with kidney disease due to treatment with nephrotoxic serum or with underlying heterologous mutations in the podocyte foot process protein podocin. Thus, the observation that podocytes maintain a preferred spatial orientation of their processes on glomerular capillaries goes well in line with the role of podocyte foot processes as mechanical buttresses to counteract mechanical forces resulting from pressurized capillaries. Future studies are needed to establish how podocytes establish and maintain their orientation and why orientation is lost under pathological conditions.

Role of Alström syndrome 1 in the regulation of glomerular hemodynamics.

Inactivating mutations in the ALMS1 gene in humans cause Alström syndrome, characterized by the early onset of obesity, insulin resistance, and renal dysfunction. However, the role of ALMS1 in renal function and hemodynamics is unclear. We previously found that ALMS1 is expressed in thick ascending limbs, where it binds and decreases Na+-K+-2Cl- cotransporter activity. We hypothesized that ALMS1 is expressed in macula densa cells and that its deletion enhances tubuloglomerular feedback (TGF) and reduces glomerular filtration rate (GFR) in rats. To test this, homozygous ALMS1 knockout (KO) and littermate wild-type Dahl salt-sensitive rats were studied. TGF sensitivity was higher in ALMS1 KO rats as measured by in vivo renal micropuncture. Using confocal microscopy, we confirmed immunolabeling of ALMS1 in macula densa cells (nitric oxide synthase 1 positive), supporting a role for ALMS1 in TGF regulation. Baseline glomerular capillary pressure was higher in ALMS1 KO rats, as was mean arterial pressure. Renal interstitial hydrostatic pressure was lower in ALMS1 KO rats, which is linked to increased Na+ reabsorption and hypertension. GFR was reduced in ALMS1 KO rats. Seven-week-old ALMS1 KO rats were not proteinuric, but proteinuria was present in 18- to 22-wk-old ALMS1 KO rats. The glomerulosclerosis index was higher in 18-wk-old ALMS1 KO rats. In conclusion, ALMS1 is involved in the control of glomerular hemodynamics in part by enhancing TGF sensitivity, and this may contribute to decreased GFR. Increased TGF sensitivity, enhanced glomerular capillary pressure, and hypertension may lead to glomerular damage in ALMS1 KO rats. These are the first data supporting the role of ALMS1 in TGF and glomerular hemodynamics.NEW & NOTEWORTHY ALMS1 is a novel protein involved in regulating tubuloglomerular feedback (TGF) sensitivity, glomerular capillary pressure, and blood pressure, and its dysfunction may reduce renal function and cause glomerular damage.

Evaluation of Renoprotective Effect of Lipoic Acid and Bosentan Against Diclofenac-Induced Acute Renal Failure

Acute renal failure also known as acute kidney injury (AKI) is a complex health condition related to significant morbidity and mortality. In hospitalized patients, around 19-33 percent of AKI episodes are linked to drug induced nephrotoxicity. Although considered safe, NSAIDs such as diclofenac have gained special attention over the past few years due to the potential risk of renal injury. The direct effect of diclofenac-induced renal injury depends on targeting the mitochondria in kidney tissue, and formation of reactive oxygen species (ROS) resulting in oxidative stress. Secondly, diclofenac inhibit renal prostaglandin production, limiting renal afferent arteriole vasodilation, increasing afferent resistance; thus decreasing the glomerular capillary pressure below normal values and glomerular filtration rate will decrease resulting in AKI. Alpha-Lipoic acid (ALA) has beneficial effects in prevention or relief of symptoms of oxidative stress- related diseases, as it acts as antioxidant and anti-inflammatory micronutrient. Bosentan is a competitive antagonist with dual endothelin-1 receptors, as renal vascular ET-1 system is upregulated under many pathophysiological situations. In present study, we investigated the effect of lipoic acid and bosentan in diclofenac induced acute renal failure in male rats.
 We observed that diclofenac increased serum levels of urea, creatinine, malondialdehyde, KIM-1, TGFβ1 and fibronectin significantly (p>0.05) in the induction group compared to control group. While, SOD significantly (p>0.05) reduced in the induction group compared to control group. Both of lipoic acid and bosentan alone didn’t significantly protect against diclofenac induced AKI. However, the combination group showed a significant protection against AKI. Pearson correlation analysis showed a significant positive correlation between (urea and KIM-1) and between (creatinine and KIM-1) (r2=0.792 and r2=0.677 respectively). Furthermore, there was a significant positive correlation between fibronectin and urea (r2= 0.498, p>0.01) and fibronectin and creatinine (r2=0.356, p>0.05). Interestingly, KIM-1 showed a significant positive correlation with fibronectin (r2=0.536, p>0.01).
 ROC curve test was performed for KIM-1 and fibronectin biomarkers. The AUC for KIM-1 was 0.986 and for fibronectin was 0.829. We concluded that combination therapy of lipoic acid and bosentan showed a significant protective effect against diclofenac-induced AKI. In addition, fibronectin could be a promising biomarker for detection and diagnosis of acute kidney injury.
 Key words: Diclofenac, oxidative stress, alpha- lipoic acid, endothelin-1, bosentan

Renoprotective effects of GLP-1 receptor agonists and SGLT-2 inhibitors-is hemodynamics the key point?

Two novel treatments for diabetic kidney disease have emerged after decades with little progression. Both agents were developed for improved glycemic control in patients with type-2 diabetes. However, large clinical trials showed renoprotective effects beyond their ability to lower plasma glucose levels, body weight, and blood pressure. How this renal protection occurs is unknown. We will discuss their physiological effects, with special focus on the renal effects. We discuss how these drugs affect the function of the diabetic and nondiabetic kidneys to elucidate mechanisms by which the renoprotection could arise. Diabetic kidney disease affects the glomerular capillaries, which are usually protected by the renal autoregulatory mechanisms, the myogenic response, and the tubuloglomerular feedback mechanism. Animal models with reduced renal autoregulatory capacity develop chronic kidney disease. Despite different cellular targets, both drugs are suspected to affect renal hemodynamics through changes in the renal autoregulatory mechanisms. The glucagon-like peptide-1 receptor agonists (GLP-1RAs) exert a direct vasodilatory effect on the afferent arteriole (AA) positioned just before the glomerulus. Paradoxically, this effect is expected to increase glomerular capillary pressure, causing glomerular injury. In contrast, the sodium-glucose transporter-2 inhibitors (SGLT2i) are believed to activate the tubuloglomerular feedback mechanism to elicit vasoconstriction of the afferent arteriole. Because of their opposing effects on the renal afferent arterioles, it appears unlikely that their renoprotective effects can be explained by common effects of renal hemodynamics, but both drugs appear to add protection to the kidney beyond what can be obtained with classical treatment targeted at lowering blood glucose levels and blood pressure.

Relaxin mechanistic effects on renal hemodynamics and natriuresis: a mathematical modeling approach

Relaxin (RLX) is a hormone that stimulates renal vasodilation during early pregnancy. Recombinant RLX may have potential as a treatment for heart failure and chronic kidney disease, but its application has been limited in part due to uncertainties about its mechanism of action, and particularly its effect on glomerular capillary hydrostatic pressure (P gc ) and fluid status. The objective of this study was to couple mathematical modeling with experimental observations of the renal hemodynamic and natriuretic response to RLX, in order to quantitatively describe the mechanistic effects of relaxin on the kidney, and to predict its effect on clinically difficult-to-measure variables such as P gc . Utilizing a previously developed mathematical model of kidney function and hemodynamics, we began by hypothesizing a minimum set of RLX mechanisms (afferent/efferent vasodilation), fitting the available hemodynamic/natriuretic response in two previously published rat studies (GFR, renal plasma flow (RPF), mean arterial pressure (MAP), sodium and water excretion), and adding additional RLX mechanisms to the model only when the minimal set could not explain available data. We found that changes in renal vascular resistances alone were sufficient to reproduce observed changes in RPF, but insufficient to explain other data features. Experimental studies reported much larger increases in sodium excretion relative to water excretion with RLX, and this effect could only be reproduced if an effect of RLX on the osmotic setpoint for vasopressin release was included in the model – a mechanism that has previously been reported in ovariectomized rats treated with RLX. A small effect of RLX on heart rate was necessary to produce observed changes in MAP.In addition, the single experimental study in which P gc has been measured with RLX reported a rise in GFR but fall in P gc , and this difference could not be explained mathematically by relative afferent/efferent dilation or by downstream shifting of the filtration equilibrium with increased RPF; it could only be reproduced mathematically if RLX was assumed to large positive effect on glomerular membrane permeability. However, the magnitude of this effect is difficult to justify physiologically. Thus, while the model can be forced to fit this limited data, further study is needed to understand whether and how RLX might have such large permeability effects.The fitted model was then able to make predictions consistent with observed renal responses in human subjects, and these effects were better predicted when the RLX effect on permeability was excluded, further suggesting that this effect may not be real. In these simulations, RLX had no net effect on P gc . In conclusion, while some uncertainty remains, this analysis suggests that RLX acts primarily by dilating the afferent and efferent arterioles and shifting the osmotic setpoint for vasopressin release. AstraZeneca and Eli Lilly This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

S-41-5: NEW INSIGHTS INTO THE OPTIMAL ANTIHYPERTENSIVE THERAPY IN CKD PATIENTS

Chronic kidney disease (CKD) is defined as continuous existence of reduced renal function, estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73m2, and/or proteinuria including microalbuminuria. CKD patients are not only prone to progress to renal failure but also at high risk for developing cardiovascular diseases (CVD) as the concept of cardio-renal syndrome is assumed. As the cause of CKD, diabetic kidney disease and nephrosclerosis are dominating and their progression is promoted by aging and lifestyle-related diseases (LSD) such as hypertension and diabetes. Therefore, in order to maximally prevent renal failure and CVD in CKD patients, aggressive intervention achieving strict control of LSD starting at its earliest stage is important. Renal function is generally evaluated by eGFR, however, the fundamental aspect of renal function is renal blood flow or renal plasma flow (RPF), and the decrease of RPF is compensated by the increase in filtration fraction yielding the maintenance of GFR value. Accordingly, if eGFR is less than 60, it should be recognized that the extent of renal injury is not mild but moderate or worse. However, the measurement of RPF requires laborious and invasive procedure. Albuminuria may reflect the increase in glomerular capillary pressure (glomerular hypertension) elicited by reduced nephron number but the urinary albumin excretion is highly variable and is not necessarily parallel to the degree of renal injury. Among LSD, hypertension plays a pivotal role as the risk factor for renal failure and CVD, and the strict blood pressure control targeting < 130/80mmHg is recommended in the guidelines. As antihypertensive agents, renin-angiotensin system inhibitors such as ARB and ACE inhibitors are preferred because of dilating the efferent arterioles resulting in the alleviation of glomerular hypertension and the reduction in albuminuria. Calcium channel blockers have advantage in preserving RPF and GFR by dilating the afferent arterioles. In addition, recent randomized controlled trials have demonstrated that sodium-glucose cotransporter 2 inhibitors retard the GFR decrease in diabetic and non-diabetic CKD patients. Angiotensin receptor neprilysin inhibitor, now used for hypertension, has also been shown to reduce the risks of GFR decrease and worsening of renal function in heart failure patients. Nonsteroidal mineralocorticoid receptor antagonists are expected to provide renoprotective effects such as albuminuria reduction with affordable risk of hyperkalemia. Thus, in future strategy of antihypertensive therapy for CKD aiming maximum renal and cardiovascular protection, practical evaluation of renal injuries at early stages and incorporation of drugs with new evidence are the key issues.

JS-HR-12: BASIC RESEARCH: ELUCIDATION OF “MOSAIC” PATHOGENESIS OF HYPERTENSION

Basic research plays critical roles in elucidating the “mosaic” pathogenesis of hypertension and developing its treatment. In the field of brain and autonomic nervous system, Chen et al. demonstrated that mild cold exposure elicits autonomic dysregulation, such as increased sympathetic activity and decreased baroreflex sensitivity, and poor sleep quality, causing blood pressure (BP) elevation in normotensive rats. This finding may have critical implications for the cardiovascular event occurrence with low ambient temperature. Domingos-Souza et al. showed that the ability of baroreflex activation to modulate hemodynamics and induce lasting vascular adaptation is critically dependent on the electrical parameters and duration of carotid sinus stimulation in spontaneously hypertensive rats (SHRs), proposing a rationale for improving baroreflex activation therapy in humans. In the kidney, Kasacka et al. showed that activity of Wnt/β-catenin pathway is increased in SHRs and 2K1C hypertensive rats, while it is inhibited in DOCA-salt rats. Intrarenal renin-angiotensin system (RAS) is involved in BP regulation. In renal damage with an impaired glomerular filtration barrier, liver-derived angiotensinogen filtered through damaged glomeruli regulates intrarenal RAS activity. Matsuyama et al. further showed that the glomerular filtration of liver-derived angiotensinogen depending on glomerular capillary pressure causes circadian rhythm of the intrarenal RAS. Otsuki et al. revealed that TWIST1, a transcription factor regulating mesodermal embryogenesis, transcriptionally upregulates complement 3, which has been demonstrated to activate intrarenal RAS, in the glomerular mesangial cells from SHRs. The RAS in the vascular system also contributes to BP regulation. Soring nexins (SNXs) are cellular sorting proteins and can regulate the expression and function of G protein-coupled receptors (GPCRs). Liu C et al. demonstrated that SNX1 knockout mice exhibit hypertension through vasoconstriction mediated by increased expression of GPCR AT1R within the arteries. Liu X et al. found that sirtuin 6 (SIRT6) expression is downregulated in the aortae of aged rats and showed that SIRT6 knockdown enhances angiotensin II-induced vascular adventitial aging by activating NF-κB pathway in vitro studies. The studies investigating extracellular vesicles (EVs) and gut microbiota have been increased. Ochiai-Homma et al. showed that pendrin in urinary EVs can be a useful biomarker for diagnosis and treatment of primary aldosteronism. Wu et al. demonstrated that captopril has the potential to rebalance the dysbiotic gut microbiota of DOCA-salt hypertensive rats. Several reports indicate the potential treatment for hypertension and the associated organ damages: rivaroxaban in cardiac hypertrophy; nebivolol, maximakinin, and Pinggan-Qianyang in hypertension; and melatonin and crocin in gestational hypertension.

S-27-1: THE ROLE OF KIDNEY IN BLOOD PRESSURE REGULATION

The kidney plays important roles in homeostasis of body fluid and electrolyte balances as well as blood pressure (BP) regulation. For these, two functions are required. One is a stable and huge (150L/day) amount of glomerular filtration rate (GFR) in the face of large variations of BP and dairy salt intake, and the other is pressure natriuresis. Even if BP changed acutely, glomerular capillary pressure of each nephron is maintained relatively stale by myogenic response and tubuloglomerular feedback (TGF). When salt intake is changed, GFR is maintained by exquisitely precise and elegant interplays among the rein-angiotensin-aldosterone (RAA) system, TGF and connecting TGF (cTGF). The cTGF is a recently discovered intrinsic mechanism controlling glomerular hemodynamics. The pressure natriuresis plays a crucial role in the maintenance of body fluid volume, and its site of action is renal medulla. Blood supply to renal medulla is governed by descending vasa recta, the efferent arteriole of the juxtaglomerulus. In outer medulla, thick ascending limb of juxtamedullary nephron makes direct contact with descending vasa recta. Studies indicate that nitric oxide and oxidative stress produced by this tubular segment affect vascular tone of descending vasa recta, a phenomenon called tubulo-vascular crosstalk. The tubule-vascular crosstalk is implicated to play an important role in oxygen metabolism in such conditions as heart failure and high salt intake. In this presentation, I will discuss above mentioned mechanisms that control renal hemodynamics, sodium balances and BP.

Abstract 100: Effects Of Upregulation Of Cyp4a In Dahl Salt-sensitive Rats And Ko Of Cyp4a2 And 4a3 In Ss.5 Bn Rats On The Development Of Hypertension And Renal Injury

Mutations in CYP4F2 (rs2108622) and CYP4A11 (rs1126742) that inhibit the production of 20-HETE have been linked to hypertension in human genetic studies. We confirmed that these same variants are associated with hypertension and cognitive dysfunction in 4,286 elderly subjects in the Atherosclerosis Risk in Communities Neurocognitive Study . These studies establish that mutations in CYP enzymes that reduce 20-HETE promote hypertension, but the mechanisms remain controversial since 20-HETE has both pro- and antihypertensive actions. To address this question, we identified a homologous genetic deficiency in the formation of 20-HETE in Dahl S (SS) rats and created SS.5 BN consomic and CYP4A transgenic SS rats to restore CYP4A expression and 20-HETE production, and CYP4A2 and CYP4A3 KO rats on the rescued SS.5 BN background. Mean arterial pressure (MAP), renal and cerebral blood flow, proteinuria, and renal injury were compared in SS versus SS.5 BN and CYP4A transgenic SS rats and in SS.5 BN versus CYP4A2 and CYP4A3 KO rats. MAP increased from 117±2 to 158±5 mmHg (n=34) in SS rats fed a high salt (HS) diet for 3 weeks. Proteinuria rose from 50±4 to 403±30 mg/day. MAP increased less, from 108 + 5 to 133 + 5 mmHg (n=7) in CYP4A1 transgenic SS rats and from 109 + 2 to 132 + 2 mmHg (n=23) in SS.5 BN rats. Proteinuria (141±15 and 169±11 mg/day), glomerular injury, and renal fibrosis were all significantly reduced in the CYP4A transgenic and SS.5 BN rats compared to SS rats. KO of CYP4A2 had no effect on MAP (134 + 2 mmHg, n=23) or proteinuria (248 + 23 mg/day) relative to SS.5 BN rats fed an HS diet for 3 weeks. In contrast, MAP and proteinuria were elevated to 148 + 3 mmHg and 350 + 23 mg/day in CYP4A3 KO rats (n=23). The myogenic response of renal and cerebral arteries and autoregulation of RBF and CBF were impaired in SS and CYP4A3 KO rats but were intact in CYP4A transgenic SS rats, SS.5 BN and CYP4A2 KO rats. These findings indicate that a deficiency in the formation of 20-HETE that impairs the myogenic response of renal and cerebral arteries, autoregulation of RBF and CBF, and increases glomerular capillary pressure, promotes the development of hypertension, proteinuria, and renal injury in genetically susceptible individuals and SS rats.

Ion channels and channelopathies in glomeruli.

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.

The role of TRPC6 calcium channels and P2 purinergic receptors in podocyte mechanical and metabolic sensing.

Podocyte calcium (Ca2+) signaling plays important roles in the (patho)physiology of the glomerular filtration barrier. Overactivation of podocyte transient receptor potential canonical (TRPC) channels including TRPC6 and purinergic signaling via P2 receptors that are known mechanosensors can increase podocyte intracellular Ca2+ levels ([Ca2+]i) and cause cell injury, proteinuria and glomerular disease including in diabetes. However, important mechanistic details of the trigger and activation of these pathways in vivo in the intact glomerular environment are lacking. Here we show direct visual evidence that podocytes can sense mechanical overload (increased glomerular capillary pressure) and metabolic alterations (increased plasma glucose) via TRPC6 and purinergic receptors including P2Y2. Multiphoton microscopy of podocyte [Ca2+]i was performed in vivo using wild-type and TRPC6 or P2Y2 knockout (KO) mice expressing the calcium reporter GCaMP3/5 only in podocytes and in vitro using freshly dissected microperfused glomeruli. Single-nephron intra-glomerular capillary pressure elevations induced by obstructing the efferent arteriole lumen with laser-induced microthrombus in vivo and by a micropipette in vitro triggered >2-fold increases in podocyte [Ca2+]i. These responses were blocked in TRPC6 and P2Y2 KO mice. Acute elevations of plasma glucose caused >4-fold increases in podocyte [Ca2+]i that were abolished by pharmacological inhibition of TRPC6 or P2 receptors using SAR7334 or suramin treatment, respectively. This study established the role of Ca2+ signaling via TRPC6 channels and P2 receptors in mechanical and metabolic sensing of podocytes in vivo, which are promising therapeutic targets in conditions with high intra-glomerular capillary pressure and plasma glucose, such as diabetic and hypertensive nephropathy.

Decreased tubuloglomerular feedback response in high-fat diet-induced obesity.

Obesity increases the risk of renal damage, but the mechanisms are not clear. Normally, kidneys autoregulate to keep the glomerular capillary pressure (PGC), renal blood flow, and glomerular filtration rate in a steady state. However, in obesity, higher PGC, renal blood flow, and glomerular filtration rate are noted. Together, these may lead to glomerular damage. PGC is controlled mainly by afferent arteriole resistance, which, in turn, is regulated by tubuloglomerular feedback (TGF), a vasoconstrictor mechanism. High fat-induced obesity causes renal damage, and this may be related to increased PGC. However, there are no studies as to whether high-fat diet (HFD)-induced obesity affects TGF. We hypothesized that TGF would be attenuated in obesity caused by HFD feeding (60% fat) in Sprague-Dawley rats. Sprague-Dawley rats fed a normal-fat diet (NFD; 12% fat) served as the control. We studied 4 and 16 wk of HFD feeding using in vivo renal micropuncture of individual rat nephrons. We did not observe significant differences in body weight, TGF response, and mean arterial pressure at 4 wk of HFD feeding, but after 16 wk of HFD, rats were heavier and hypertensive. The maximal TGF response was smaller in HFD-fed rats than in NFD-fed rats, indicating an attenuation of TGF in HFD-induced obesity. Baseline PGC was higher in HFD-fed rats than in NFD-fed rats and was associated with higher glomerulosclerosis. We conclude that attenuated TGF and higher PGC along with hypertension in HFD-fed obese Sprague-Dawley rats could explain the higher propensity of glomerular damage observed in obesity.NEW & NOTEWORTHY Reduced tubuloglomerular feedback, higher glomerular capillary pressure, and hypertension in combination may explain the higher glomerular damage observed in high-fat diet-induced obesity.