High-Protein Diet-Induced Glomerular Hyperfiltration Is Dependent on Neuronal Nitric Oxide Synthase β in the Macula Densa via Tubuloglomerular Feedback Response

SGLT2 Inhibitors and Kidney Protection: Mechanisms Beyond Tubuloglomerular Feedback

Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce the risk for kidney failure and are a key component of guideline-directed therapy for CKD. While SGLT2 inhibitors' ability to activate tubuloglomerular feedback and reduce hyperfiltration-mediated kidney injury is considered to be the central mechanism for kidney protection, recent data from experimental studies raise questions on the primacy of this mechanism. This review examines SGLT2 inhibitors' role in tubuloglomerular feedback and summarizes emerging evidence on following of SGLT2 inhibitors' other putative mechanisms for kidney protection: optimization of kidney's energy substrate utilization and delivery, regulation of autophagy and maintenance of cellular homeostasis, attenuation of sympathetic hyperactivity, and improvement in vascular health and microvascular function. It is imperative to examine the effect of SGLT2 inhibition on these different physiologic processes to help our understanding of mechanisms underpinning kidney protection with this important class of drugs.

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.

Reno- and cardioprotective molecular mechanisms of SGLT2 inhibitors beyond glycemic control: from bedside to bench

Large placebo-controlled clinical trials have shown that sodium-glucose cotransporter-2 inhibitors (SGLT2i) delay the deterioration of renal function and reduce cardiovascular events in a glucose-independent manner, thereby ultimately reducing mortality in patients with chronic kidney disease (CKD) and/or heart failure. These existing clinical data stimulated preclinical studies aiming to understand the observed clinical effects. In animal models, it was shown that the beneficial effect of SGLT2i on the tubuloglomerular feedback (TGF) improves glomerular pressure and reduces tubular workload by improving renal hemodynamics, which appears to be dependent on salt intake. High salt intake might blunt the SGLT2i effects on the TGF. Beyond the salt-dependent effects of SGLT2i on renal hemodynamics, SGLT2i inhibited several key aspects of macrophage-mediated renal inflammation and fibrosis, including inhibiting the differentiation of monocytes to macrophages, promoting the polarization of macrophages from a proinflammatory M1 phenotype to an anti-inflammatory M2 phenotype, and suppressing the activation of inflammasomes and major proinflammatory factors. As macrophages are also important cells mediating atherosclerosis and myocardial remodeling after injury, the inhibitory effects of SGLT2i on macrophage differentiation and inflammatory responses may also play a role in stabilizing atherosclerotic plaques and ameliorating myocardial inflammation and fibrosis. Recent studies suggest that SGLT2i may also act directly on the Na+/H+ exchanger and Late-INa in cardiomyocytes thus reducing Na+ and Ca2+ overload-mediated myocardial damage. In addition, the renal-cardioprotective mechanisms of SGLT2i include systemic effects on the sympathetic nervous system, blood volume, salt excretion, and energy metabolism.

Protein restriction in adults with chronic kidney disease, with or without diabetes: Integrated Diabetes and Endocrine Academy (IDEA) consensus statement for Indian patients

BACKGROUND AND AIMS

Most guidelines recommend protein restriction in adults with chronic kidney disease (CKD), with or without diabetes. However, advising protein restriction for every person with CKD is controversial. We aim to arrive at a consensus on this topic, especially among Indian adults with CKD.

METHODS

A systematic literature search in the PubMed electronic database was undertaken using specific keywords and MeSH terms until May 1, 2022. All the retrieved literature was circulated and rigorously deliberated upon by the panel members.

RESULTS

Seventeen meta-analyses that evaluated the outcomes of protein restriction in adults with CKD, with or without diabetes, met our inclusion criteria and were analyzed. A low-protein diet (LPD) in people with stages 3-5 of CKD (who are not on haemodialysis [HD]) reduces the severity of uremic symptoms and the rate of decline in glomerular filtration rate, leading to a delay in dialysis initiation. However, LPD in patients on maintenance HD may not be desirable because HD-induced protein catabolism may lead to protein-energy malnutrition. Since the average protein intake among Indians is much lower than recommended, this must be taken into consideration before recommending LPD for all Indian adults with CKD, particularly those on maintenance HD.

CONCLUSION

It is essential to assess the nutritional status of people with CKD, particularly in countries like India where average daily protein intake is poor, before recommending guideline-directed protein restriction. The prescribed diet, including the quantity and quality of proteins, should be tailored to the person's habits, tastes, and needs.

Novel insights in classic versus relative glomerular hyperfiltration and implications on pharmacotherapy

PURPOSE OF REVIEW

Glomerular filtration rate (GFR) assessment and its estimation (eGFR) is a long-lasting challenge in medicine and public health. Current eGFR formulae are indexed for standardized body surface area (BSA) of 1.73 m2, ignoring persons and populations wherein the ratio of BSA or metabolic rate to nephron number might be different, due to increased BSA, increased metabolic rate or reduced nephron number. These equations are based on creatinine, cystatin C or a combination of the two, which adds another confounder to eGFR assessment. Unusually high GFR values, also known as renal hyperfiltration, have not been well defined under these equations.

RECENT FINDINGS

Special conditions such as solitary kidney in kidney donors, high dietary protein intake, obesity and diabetes are often associated with renal hyperfiltration and amenable to errors in GFR estimation. In all hyperfiltration types, there is an increased intraglomerular pressure that can be physiologic, but its persistence over time is detrimental to glomerulus leading to progressive glomerular damage and renal fibrosis. Hyperfiltration might be underdiagnosed due to BSA standardization embedded in the formula. Hence, timely intervention is delayed. Reducing intraglomerular pressure in diabetes can be achieved by SGLT2 inhibitors or low protein diet to reverse the glomerulopathy process.

SUMMARY

Accurate identification of glomerular hyperfiltration as a pre-CKD condition needs accurate estimation of GFR in the above normal range should establish a threshold for timely intervention.

Effects of Thai native chicken breast meat consumption on serum uric acid level, biochemical parameters, and antioxidant activities in rats

This study aimed to evaluate the effect of a high protein diet comprising breast meat from commercial broiler (BR), Thai native (PD), and commercial broiler × Thai native crossbred (KKU-ONE) chicken on serum uric acid, biochemical parameters, and antioxidant activities in rats. Male Sprague–Dawley rats were divided into four groups. The control group received a standard chow diet, and the other three groups were fed a high protein diet (70% standard diet + 30% BR, PD, or KKU-ONE chicken breast) for five weeks. The PD- and KKU-ONE-fed rats had lower plasma total cholesterol and triglyceride levels than the control rats. A decrease in HDL-c was also observed in rats fed a diet containing BR. Liver weight, liver enzyme, plasma ALP, xanthine oxidase activity, serum uric acid, creatinine, superoxide production, and plasma malondialdehyde levels increased in BR-fed rats. The findings of this study might provide evidence to support the use of Thai native and Thai native crossbred chicken breast meat as functional foods.

Glomerular hyperfiltration

Circulating blood is filtered across the glomerular barrier to form an ultrafiltrate of plasma in the Bowman's space. The volume of glomerular filtration adjusted by time is defined as the glomerular filtration rate (GFR), and the total GFR is the sum of all single-nephron GFRs. Thus, when the single-nephron GFR is increased in the context of a normal number of functioning nephrons, single glomerular hyperfiltration results in 'absolute' hyperfiltration in the kidney. 'Absolute' hyperfiltration can occur in healthy people after high protein intake, during pregnancy and in patients with diabetes, obesity or autosomal-dominant polycystic kidney disease. When the number of functioning nephrons is reduced, single-nephron glomerular hyperfiltration can result in a GFR that is within or below the normal range. This 'relative' hyperfiltration can occur in patients with a congenitally reduced nephron number or with an acquired reduction in nephron mass consequent to surgery or kidney disease. Improved understanding of the mechanisms that underlie 'absolute' and 'relative' glomerular hyperfiltration in different clinical settings, and of whether and how the single-nephron haemodynamic and related biomechanical forces that underlie glomerular hyperfiltration promote glomerular injury, will pave the way toward the development of novel therapeutic interventions that attenuate glomerular hyperfiltration and potentially prevent or limit consequent progressive kidney injury and loss of function.

Reducing ischemic kidney injury through application of a synchronization modulation electric field to maintain Na+/K+-ATPase functions

Renal ischemia-reperfusion injury is an important contributor to the development of delayed graft function after transplantation, which is associated with higher rejection rates and poorer long-term outcomes. One of the earliest impairments during ischemia is Na⁺/K⁺-ATPase (Na/K pump) dysfunction due to insufficient ATP supply, resulting in subsequent cellular damage. Therefore, strategies that preserve ATP or maintain Na/K pump function may limit the extent of renal injury during ischemia-reperfusion. Here, we applied a synchronization modulation electric field to activate Na/K pumps, thereby maintaining cellular functions under ATP-insufficient conditions. We tested the effectiveness of this technique in two models of ischemic renal injury: an in situ renal ischemia-reperfusion injury model (predominantly warm ischemia) and a kidney transplantation model (predominantly cold ischemia). Application of the synchronization modulation electric field to a renal ischemia-reperfusion injury mouse model preserved Na/K pump activity, thereby reducing kidney injury, as reflected by 40% lower plasma creatinine (1.17 ± 0.03 mg/dl) in the electric field-treated group as compared to the untreated control group (1.89 ± 0.06 mg/dl). In a mouse kidney transplantation model, renal graft function was improved by more than 50% with the application of the synchronization modulation electric field according to glomerular filtration rate measurements (85.40 ± 12.18 μl/min in the untreated group versus 142.80 ± 11.65 μl/min in the electric field-treated group). This technique for preserving Na/K pump function may have therapeutic potential not only for ischemic kidney injury but also for other diseases associated with Na/K pump dysfunction due to inadequate ATP supply.

Functional Reserve of the Kidney

An exploration of the normal limits of physiologic responses and how these responses are lost when the kidney is injured rarely occurs in clinical practice. However, the differences between "resting" and "stressed" responses identify an adaptive reactiveness that is diminished before baseline function is impaired. This functional reserve is important in the evaluation of prognosis and progression of kidney disease. Here, we discuss stress tests that examine protein-induced hyperfiltration, proximal tubular secretion, urea-selective concentration defects, and acid retention. We discuss diseases in which these tests have been used to diagnose subclinical injury. The study and follow-up of abnormal functional reserve may add considerable understanding to the natural history of CKD.

Update on Pathogenesis of Glomerular Hyperfiltration in Early Diabetic Kidney Disease

In the existing stages of diabetic kidney disease (DKD), the first stage of DKD is called the preclinical stage, characterized by glomerular hyperfiltration, an abnormally elevated glomerular filtration rate. Glomerular hyperfiltration is an independent risk factor for accelerated deterioration of renal function and progression of nephropathy, which is associated with a high risk for metabolic and cardiovascular disease. It is imperative to understand hyperfiltration and identify potential treatments to delay DKD progress. This paper summarizes the current mechanisms of hyperfiltration in early DKD. We pay close attention to the effect of glucose reabsorption mediated by sodium-glucose cotransporters and renal growth on hyperfiltration in DKD patients, as well as the mechanisms of nitric oxide and adenosine actions on renal afferent arterioles via tubuloglomerular feedback. Furthermore, we also focus on the contribution of the atrial natriuretic peptide, cyclooxygenase, renin-angiotensin-aldosterone system, and endothelin on hyperfiltration. Proposing potential treatments based on these mechanisms may offer new therapeutic opportunities to reduce the renal burden in this population.

Revisiting glomerular hyperfiltration and examining the concept of high dietary protein-related nephropathy in athletes and bodybuilders

PURPOSE OF REVIEW

High-protein diets (HPDs) are popular but their consequences for kidney health, especially among athletes and bodybuilders who typically maintain a high protein intake for a long time, have not been investigated. This review focused on recent studies of the association of HPD with long-term kidney health and the concept of high dietary protein-related nephropathy.

RECENT FINDINGS

Several long-term observational studies including large populations have reinforced the notion that HPDs are associated with a rapid decline of kidney function. An increase in renal blood flow and glomerular hyperfiltration caused by vasodilation, and increased levels of endocrine and paracrine factors (glucagon, IGF-1, prostanoids, and nitric oxide), facilitates the excretion of protein-derived nitrogenous waste. Inhibition of tubule-glomerular feedback and increased proximal tubular Na+ reabsorption after a HPD augment glomerular hyperfiltration and may trigger synthesis of proinflammatory cytokines and receptor for advanced glycation end-products (RAGE). Focal segmental glomerulosclerosis reported in association with anabolic steroid may indeed be a HPD nephropathy given that HPD results in progressive glomerulosclerosis, especially in remnant glomeruli or in diabetic kidney disease but can happen in any high-risk situation, such as solitary kidney and polycystic kidneys.

SUMMARY

HPD among athletes and bodybuilders in an extreme way across a long-term period may pose a risk to renal health including high incidence of HPD nephropathy.

Knockout of Macula Densa Neuronal Nitric Oxide Synthase Increases Blood Pressure in db/db Mice

[Figure: see text].

Macula Densa NOS1β Modulates Renal Hemodynamics and Blood Pressure during Pregnancy: Role in Gestational Hypertension

BACKGROUND

Regulation of renal hemodynamics and BP via tubuloglomerular feedback (TGF) may be an important adaptive mechanism during pregnancy. Because the β-splice variant of nitric oxide synthase 1 (NOS1β) in the macula densa is a primary modulator of TGF, we evaluated its role in normal pregnancy and gestational hypertension in a mouse model. We hypothesized that pregnancy upregulates NOS1β in the macula densa, thus blunting TGF, allowing the GFR to increase and BP to decrease.

METHODS

We used sophisticated techniques, including microperfusion of juxtaglomerular apparatus in vitro, micropuncture of renal tubules in vivo, clearance kinetics of plasma FITC-sinistrin, and radiotelemetry BP monitoring, to determine the effects of normal pregnancy or reduced uterine perfusion pressure (RUPP) on macula densa NOS1β/NO levels, TGF responsiveness, GFR, and BP in wild-type and macula densa-specific NOS1 knockout (MD-NOS1KO) mice.

RESULTS

Macula densa NOS1β was upregulated during pregnancy, resulting in blunted TGF, increased GFR, and decreased BP. These pregnancy-induced changes in TGF and GFR were largely diminished, with a significant rise in BP, in MD-NOS1KO mice. In addition, RUPP resulted in a downregulation in macula densa NOS1β, enhanced TGF, decreased GFR, and hypertension. The superimposition of RUPP into MD-NOS1KO mice only caused a modest further alteration in TGF and its associated changes in GFR and BP. Finally, in African green monkeys, renal cortical NOS1β expression increased in normotensive pregnancies, but decreased in spontaneous gestational hypertensive pregnancies.

CONCLUSIONS

Macula densa NOS1β plays a critical role in the control of renal hemodynamics and BP during pregnancy.

Gut microbiota dependent trimethylamine N-oxide aggravates angiotensin II-induced hypertension

Gut microbiota produce Trimethylamine N-oxide (TMAO) by metabolizing dietary phosphatidylcholine, choline, l-carnitine and betaine. TMAO is implicated in the pathogenesis of chronic kidney disease (CKD), diabetes, obesity and atherosclerosis. We test, whether TMAO augments angiotensin II (Ang II)-induced vasoconstriction and hence promotes Ang II-induced hypertension. Plasma TMAO levels were indeed elevated in hypertensive patients, thus the potential pathways by which TMAO mediates these effects were explored. Ang II (400 ng/kg⁻¹min⁻¹) was chronically infused for 14 days via osmotic minipumps in C57Bl/6 mice. TMAO (1%) or antibiotics were given via drinking water. Vasoconstriction of renal afferent arterioles and mesenteric arteries were assessed by microperfusion and wire myograph, respectively. In Ang II-induced hypertensive mice, TMAO elevated systolic blood pressure and caused vasoconstriction, which was alleviated by antibiotics. TMAO enhanced the Ang II-induced acute pressor responses (12.2 ± 1.9 versus 20.6 ± 1.4 mmHg; P < 0.05) and vasoconstriction (32.3 ± 2.6 versus 55.9 ± 7.0%, P < 0.001). Ang II-induced intracellular Ca²⁺ release in afferent arterioles (147 ± 7 versus 234 ± 26%; P < 0.001) and mouse vascular smooth muscle cells (VSMC, 123 ± 3 versus 157 ± 9%; P < 0.001) increased by TMAO treatment. Preincubation of VSMC with TMAO activated the PERK/ROS/CaMKII/PLCβ3 pathway. Pharmacological inhibition of PERK, ROS, CaMKII and PLCβ3 impaired the effect of TMAO on Ca²⁺ release. Thus, TMAO facilitates Ang II-induced vasoconstriction, thereby promoting Ang II-induced hypertension, which involves the PERK/ROS/CaMKII/PLCβ3 axis.

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Orally administered TMAO aggravates Ang II-induced hypertension. Antibiotics alleviate Ang II-induced hypertension by reducing TMAO generation.

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High concentrations of TMAO constrict afferent arterioles and mesenteric arteries and increase blood pressure.

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Low concentrations of TMAO enhance Ang II-induced vasoconstriction and acute pressor response via activating PERK/ROS/CaMKII/PLCβ3/Ca²⁺ pathway.

Current Concepts of Pediatric Acute Kidney Injury-Are We Ready to Translate Them into Everyday Practice?

Pediatric acute kidney injury (AKI) is a major cause of morbidity and mortality in children undergoing interventional procedures. The review summarizes current classifications of AKI and acute kidney disease (AKD), as well as systematizes the knowledge on pathophysiology of kidney injury, with a special focus on renal functional reserve and tubuloglomerular feedback. The aim of this review is also to show the state-of-the-art in methods assessing risk and prognosis by discussing the potential role of risk stratification strategies, taking into account both glomerular function and clinical settings conditioned by fluid overload, urine output, or drug nephrotoxicity. The last task is to suggest careful assessment of eGFR as a surrogate marker of renal functional reserve and implementation of point-of-care testing, available in the case of biomarkers like NGAL and [IGFBP-7] × [TIMP-2] product, into everyday practice in patients at risk of AKI due to planned invasive procedures or treatment.

DHHC21 deficiency attenuates renal dysfunction during septic injury

Renal dysfunction is one of the most common complications of septic injury. One critical contributor to septic injury-induced renal dysfunction is renal vascular dysfunction. Protein palmitoylation serves as a novel regulator of vascular function. Here, we examined whether palmitoyl acyltransferase (PAT)-DHHC21 contributes to septic injury-induced renal dysfunction through regulating renal hemodynamics. Multispectral optoacoustic imaging showed that cecal ligation and puncture (CLP)-induced septic injury caused impaired renal excretion, which was improved in DHHC21 functional deficient (Zdhhc21^dep/dep) mice. DHHC21 deficiency attenuated CLP-induced renal pathology, characterized by tissue structural damage and circulating injury markers. Importantly, DHHC21 loss-of-function led to better-preserved renal perfusion and oxygen saturation after CLP. The CLP-caused reduction in renal blood flow was also ameliorated in Zdhhc21^dep/dep mice. Next, CLP promoted the palmitoylation of vascular α1-adrenergic receptor (α1AR) and the activation of its downstream effector ERK, which were blunted in Zdhhc21^dep/dep mice. Vasoreactivity analysis revealed that renal arteries from Zdhhc21^dep/dep mice displayed reduced constriction response to α1AR agonist phenylephrine compared to those from wild-type mice. Consistently, inhibiting PATs with 2-bromopalmitate caused a blunted vasoconstriction response to phenylephrine in small arteries isolated from human kidneys. Therefore, DHHC21 contributes to impaired renal perfusion and function during septic injury via promoting α1AR palmitoylation-associated vasoconstriction.

Microvascular dysfunction and kidney disease: Challenges and opportunities?

Kidneys are highly vascular organs that despite their relatively small size receive 20% of the cardiac output. The highly intricate, delicately organized structure of renal microcirculation is essential to enable renal function and glomerular filtration rate through the local modulation of renal blood flow and intraglomerular pressure. Not surprisingly, the dysregulation of blood flow within the microvessels (abnormal vasoreactivity), fibrosis driven by disordered vascular-renal cross talk, or the loss of renal microvasculature (rarefaction) is associated with kidney disease. In addition, kidney disease can cause microcirculatory dysfunction in distant organs such as the heart and brain, mediated by mechanisms that remain to be elucidated. The objective of this review is to highlight the role of renal microvasculature in kidney disease. The overview will outline the impetus to study renal microvasculature, the bidirectional relationship between kidney disease and microvascular dysfunction, the key pathways driving microvascular diseases such as vasoreactivity, the cell dynamics coordinating fibrosis, and vessel rarefaction. Finally, we will also briefly highlight new therapies targeting the renal microvasculature to improve renal function.

The Impact of Allogeneic Hematopoietic Stem Cell Transplantation on Kidney Function in Children-A Single Center Experience

Background: Knowledge about the impact of allogeneic hematopoietic stem cell transplantation (alloHSCT) on renal function in children is still limited. Objectives: The aim of the study was to evaluate kidney function in children undergoing alloHSCT, with special focus on differences between patients transplanted due to oncological and non-oncological indications. Materials and Methods: The data of 135 children undergoing alloHSCT were analyzed retrospectively. The serum creatinine and estimated glomerular filtration rate (eGFR) values were estimated before transplantation at 24 h; 1, 2, 3, 4 and 8 weeks; and 3 and 6 months after alloHSCT. Then, acute kidney injury (AKI) incidence was assessed. Results: Oncological children presented with higher eGFR values and more frequent hyperfiltration rates than non-oncological children before alloHSCT and until the 4th week after transplantation. The eGFR levels rose significantly after alloHSCT, returned to pre-transplant records after 2–3 weeks, and decreased gradually until the 6th month. AKI incidence was comparable in oncological and non-oncological patients. Conclusions: Children undergoing alloHSCT due to oncological and non-oncological reasons demonstrate the same risk of AKI, but oncological patients may be more prone to sustained renal injury. Serum creatinine and eGFR seem to be insufficient tools to assess kidney function in the early post-alloHSCT period, when hyperfiltration prevails, yet they reveal significant differences in long-term observation.

Knockout of γ-Adducin Promotes NG-Nitro-L-Arginine-Methyl-Ester-Induced Hypertensive Renal Injury

Previous studies identified a region on chromosome 1 associated with N^G-nitro-L-arginine methyl ester (L-NAME) hypertension-induced renal disease in fawn-hooded hypertensive (FHH) rats. This region contains a mutant γ-adducin (Add3) gene that impairs renal blood flow (RBF) autoregulation, but its contribution to renal injury is unknown. The present study evaluated the hypothesis that knockout (KO) of Add3 impairs the renal vasoconstrictor response to the blockade of nitric oxide synthase and enhances hypertension-induced renal injury after chronic administration of L-NAME plus a high-salt diet. The acute hemodynamic effect of L-NAME and its chronic effects on hypertension and renal injury were compared in FHH 1^{Brown Norway} (FHH 1^BN) congenic rats (WT) expressing wild-type Add3 gene versus FHH 1^BN Add3 KO rats. RBF was well autoregulated in WT rats but impaired in Add3 KO rats. Acute administration of L-NAME (10 mg/kg) raised mean arterial pressure (MAP) similarly in both strains, but RBF and glomerular filtration rate (GFR) fell by 38% in WT versus 15% in Add3 KO rats. MAP increased similarly in both strains after chronic administration of L-NAME and a high-salt diet; however, proteinuria and renal injury were greater in Add3 KO rats than in WT rats. Surprisingly, RBF, GFR, and glomerular capillary pressure were 41%, 82%, and 13% higher in L-NAME-treated Add3 KO rats than in WT rats. Hypertensive Add3 KO rats exhibited greater loss of podocytes and glomerular nephrin expression and increased interstitial fibrosis than in WT rats. These findings indicate that loss of ADD3 promotes L-NAME-induced renal injury by altering renal hemodynamics and enhancing the transmission of pressure to glomeruli. SIGNIFICANCE STATEMENT: A mutation in the γ-adducin (Add3) gene in fawn-hooded hypertensive rats that impairs autoregulation of renal blood flow is in a region of rat chromosome 1 homologous to a locus on human chromosome 10 associated with diabetic nephropathy. The present results indicate that loss of ADD3 enhanced N^G-nitro-L-arginine methyl ester-induced hypertensive renal injury by altering the transmission of pressure to the glomerulus.

A new mechanism for the sex differences in angiotensin II-induced hypertension: the role of macula densa NOS1β-mediated tubuloglomerular feedback

Females are protected against the development of angiotensin II (ANG II)-induced hypertension compared with males, but the mechanisms have not been completely elucidated. In the present study, we hypothesized that the effect of ANG II on the macula densa nitric oxide (NO) synthase 1β (NOS1β)-mediated tubuloglomerular feedback (TGF) mechanism is different between males and females, thereby contributing to the sexual dimorphism of ANG II-induced hypertension. We used microperfusion, micropuncture, clearance of FITC-inulin, and radio telemetry to examine the sex differences in the changes of macula densa NOS1β expression and activity, TGF response, natriuresis, and blood pressure (BP) after a 2-wk ANG II infusion in wild-type and macula densa-specific NOS1 knockout mice. In wild-type mice, ANG II induced higher expression of macula densa NOS1β, greater NO generation by the macula densa, and a lower TGF response in vitro and in vivo in females than in males; the increases of glomerular filtration rate, urine flow rate, and Na⁺ excretion in response to an acute volume expansion were significantly greater and the BP responses to ANG II were significantly less in females than in males. In contrast, these sex differences in the effects of ANG II on TGF, natriuretic response, and BP were largely diminished in knockout mice. In addition, tissue culture of human kidney biopsies (renal cortex) with ANG II resulted in a greater increase in NOS1β expression in females than in males. In conclusion, macula densa NOS1β-mediated TGF is a novel and important mechanism for the sex differences in ANG II-induced hypertension.

Dietary Protein Intake and Single-Nephron Glomerular Filtration Rate

High protein intake can increase glomerular filtration rate (GFR) in response to excretory overload, which may exacerbate the progression of kidney disease. However, the direct association between glomerular hemodynamic response at the single-nephron level and dietary protein intake has not been fully elucidated in humans. In the present study, we evaluated nutritional indices associated with single-nephron GFR (SNGFR) calculated based on corrected creatinine clearance (SNGFR_Cr). We retrospectively identified 43 living kidney donors who underwent enhanced computed tomography and kidney biopsy at the time of donation at Jikei University Hospital in Tokyo from 2007 to 2018. Total nephron number was estimated with imaging-derived cortical volume and morphometry-derived glomerular density. SNGFR_Cr was calculated by dividing the corrected creatinine clearance by the number of non-sclerosed glomeruli (Nglom_NSG). The mean (± standard deviation) Nglom_NSG/kidney and SNGFR_Cr were 685,000 ± 242,000 and 61.0 ± 23.9 nL/min, respectively. SNGFR_Cr was directly associated with estimated protein intake/ideal body weight (p = 0.005) but not with body mass index, mean arterial pressure, albumin, or sodium intake. These findings indicate that greater protein intake may increase SNGFR and lead to glomerular hyperfiltration.

A two-stage bilateral ischemia-reperfusion injury-induced AKI to CKD transition model in mice

Acute kidney injury (AKI) significantly increases the risk of development of chronic kidney disease (CKD). Recently, our laboratory generated a mouse model with the typical phenotypes of AKI to CKD transition in the unilateral kidney. However, AKI, CKD, and even the transition from AKI to CKD usually occur bilaterally rather than unilaterally in patients. Therefore, in the present study, we further modified the strategy and developed a new model of CKD transitioned from bilateral ischemia-reperfusion injury (IRI) in C57BL/6 mice. In this new model, unilateral severe IRI was performed in one kidney while the contralateral kidney was kept intact to maintain animal survival; then, following 14 days of recovery, when the renal function of the injured kidney restored above the survival threshold, the contralateral intact kidney was subjected to a similar IRI. Animals of these two-stage bilateral IRI models with pedicle clamping of 21 and 24 min at a body temperature of 37°C exhibited incomplete recovery from AKI and subsequent development of CKD with characteristics of progressive decline in glomerular filtration rate, increases in plasma creatinine, worsening of proteinuria, and deleterious histopathological changes, including interstitial fibrosis and glomerulosclerosis, in both kidneys. In conclusion, a new bilateral AKI to CKD transition animal model with a typical phenotype of CKD was generated in C57BL/6 mice.