Endothelial dysfunction promotes the transition from compensatory renal hypertrophy to kidney injury after unilateral nephrectomy in mice

Age and Pre-operative HbA1c levels affect renal function compensation in living kidney donors

OBJECTIVES

About 90% of Japanese kidney transplantations are conducted from living donors, and their safety and the maintenance of their renal function are critical. This study aims to identify factors that affect the compensation of renal function in living kidney donors after donor nephrectomy.

METHOD

In a retrospective cohort study, we reviewed data from 120 patients who underwent nephrectomy as living kidney transplant donors in our department from 2012 to 2021. Univariable and multivariable linear regression analyses were performed for donor factors affecting renal function after donor nephrectomy.

RESULT

The multivariable linear regression model revealed that the donor's age (p = 0.025), preoperative estimated Glomerular Filtration Rate (eGFR) (p < 0.001), and hemoglobin A1c (HbA1c) (p = 0.043) were independent risk factors for eGFR at six months after nephrectomy. The eGFR deterioration was more strongly associated with age in females than in males, whereas higher HbA1c values were more strongly associated with eGFR deterioration in males. Higher donor age and higher HbA1c each enhance the deterioration of eGFR six months after living donor nephrectomy. The data suggest that old age in especially female donors and preoperative higher HbA1c in male donors have a harmful impact on their renal function compensation.

Insights into the Regulation of GFR by the Keap1-Nrf2 Pathway

Key Points

Kelch-like erythroid cell-derived protein with CNC homology (ECH)-associated protein 1-NF (erythroid-derived 2)–like 2 pathway increases GFR without an appreciable increase in intraglomerular pressure. Kelch-like ECH-associated protein 1-NF (erythroid-derived 2)–like 2 pathway regulates GFR through changes in filtration area by modulating calcium dynamics and contractility in glomerular cells.

Background

Literature data suggest that the activation of the Kelch-like ECH-associated protein 1 (Keap1)-NF (erythroid-derived 2)–like 2 (Nrf2) pathway increases GFR in patients with type 2 diabetes and CKD. However, the mechanisms whereby the Keap1-Nrf2 pathway regulates GFR are unknown.

Methods

Various renal physiological parameters were assessed in C57BL/6 mice (wild-type), Nrf2 -deficient mice, and Nrf2 -activated Keap1- knockdown mice. In addition, these parameters were assessed after the administration of receptor targeting agent (RTA) dh404 (CDDO‐dhTFEA), an Nrf2 activator.

Results

Pharmacologic and genetic Keap1 -Nrf2 activation increased renal blood flow (P < 0.05), glomerular volume (P < 0.05), and GFR (P < 0.05) but did not alter the afferent-to-efferent arteriolar diameter ratio or glomerular permeability. Calcium influx into the podocytes through transient receptor potential canonical (TRPC) channels in response to H2O2 was suppressed by Keap1-Nrf2 activation and TRPCs inhibition. Treatment with a TRPC6 and TRPC5 inhibitors increased single-nephron GFR in wild-type mice.

Conclusions

In conclusion, the Keap1-Nrf2 pathway regulates GFR through changes in ultrafiltration by modulating redox-sensitive intracellular calcium signaling and cellular contractility, mediated through TRPC activity, in glomerular cells, particularly the podocytes.

Divergent roles of angiotensin II upon the immediate and sustained increases of renal blood flow following unilateral nephrectomy

Although the molecular and functional responses related to renal compensatory hypertrophy after unilateral nephrectomy (UNX) has been well described, many aspects of these events remain unclear. One question is how the remaining kidney senses the absence of the contralateral organ, and another is what the role of the renin-angiotensin system is in these responses. Both acute anesthetized and chronic unanesthetized experiments were performed using the angiotensin II type 1 receptor blocker losartan and the renin inhibitor aliskiren to determine the contribution of the renin-angiotensin system to immediate changes and losartan for chronic changes of renal blood flow (RBF) and the associated hypertrophic events in male Sprague-Dawley rats. Chronic experiments used implanted RBF probes and arterial catheters for continuous data collection, and the glomerular filtration rate was determined by noninvasive transcutaneous FITC-sinistrin measurements. The results of the acute experiments found that RBF increased nearly 25% (4.6 ± 0.5 to 5.6 ± 0.6 mL/min/g kidney wt) during the first 15 min following UNX and that this response was abolished by losartan (6.7 ± 0.7 to 7.0 ± 0.7 mL/min/g kidney wt) or aliskiren (5.8 ± 0.4 to 6.0 ± 0.4 mL/min/g kidney wt) treatment. Thereafter, RBF increased progressively over 7 days, and kidney weight increased by 19% of pre-UNX values. When normalized to kidney weight determined at day 7 after UNX, RBF was not significantly different from pre-UNX levels. Semiquantification of CD31-positive capillaries revealed increases of the glomeruli and peritubular capillaries that paralleled the kidney hypertrophy. None of these chronic changes was inhibited by losartan treatment, indicating that neither the compensatory structural nor the RBF changes were angiotensin II type 1 receptor dependent.NEW & NOTEWORTHY This study found that the immediate increases of renal blood flow (RBF) following unilateral nephrectomy (UNX) are a consequence of reduced angiotensin II type 1 (AT1) receptor stimulation. The continuous monitoring of RBF and intermittent measurement of glomerular filtration rate (GFR) in conscious rats during the 1-wk period of rapid hypertrophy following UNX provided unique insights into the regulation of RBF and GFR when faced with increased metabolic loads. It was found that neither kidney hypertrophy nor the associated increase of capillaries was an AT1-dependent phenomenon.

Functional adaptation after kidney tissue removal in patients is associated with increased plasma atrial natriuretic peptide concentration

BACKGROUND

Following nephrectomy, the remaining kidney tissue adapts by an increase in GFR. In rats, hyperfiltration can be transferred by plasma. We examined whether natriuretic peptides (ANP, BNP) increase in plasma proportionally with kidney mass reduction and, if so, whether the increase relates to an increase in GFR.

METHODS

Patients (n = 54) undergoing partial or total unilateral nephrectomy at two Danish centers were followed for one year in an observational study. Glomerular filtration rate was measured before, 3, and 12 months after surgery. Natriuretic propeptides (proANP and proBNP) and aldosterone were measured in plasma before and at 24 hours, five days, 21 days, three months, and 12 months. Cyclic GMP was determined in urine.

RESULTS

There was no baseline difference in GFR between total- and partial nephrectomy (90.1 mL/min ±14.6 vs. 82.9±18, p = 0.16). Single-kidney GFR increased after 3 and 12 months (12.0 and 11.9 ml/min/1.73m2, +23.3%). There was no change in measured GFR 3 and 12 months after partial nephrectomy. ProANP and proBNP increased 3-fold 24h after surgery and returned to baseline after five days. The magnitude of acute proANP and proBNP increases did not relate to kidney mass removed. ProANP, not proBNP, increased 12 months after nephrectomy. Plasma aldosterone and urine cGMP did not change. Urine albumin/creatine ratio increased transiently after partial nephrectomy. Blood pressure was similar between groups.

CONCLUSION

ANP and BNP increase acutely in plasma with no relation to degree of kidney tissue ablation. After 1year, only unilateral nephrectomy patients display increased plasma ANP which could support adaptation.

Evaluation of Neutrophil Dynamics Change by Protective Effect of Tadalafil After Renal Ischemia/Reperfusion Using In Vivo Real-time Imaging

BACKGROUND

Neutrophils play a major role in ischemia/reperfusion injury (IRI) in renal transplantation and acute kidney injury. However, it has been difficult to observe changes in neutrophil dynamics over time in living mice kidney. We investigate neutrophil dynamics in IRI in living mice using novel in vivo multiphoton microscope imaging techniques and characterize the renoprotective effects of a selective phosphodiesterase (PDE) 5 inhibitor, tadalafil.

METHODS

Wild-type (WT) and eNOS knockout (eNOS-KO) mice, a model of endothelial dysfunction, were used to establish in vivo real-time imaging in living mouse kidneys. Neutrophils were labeled green with Ly-6G monoclonal antibody, and plasma flow was labeled red with bovine serum albumin. Tadalafil was administered orally 1 h before surgery. Both kidney pedicles were reperfused after 37° warm ischemia for 45 min.

RESULTS

Our novel approach revealed that neutrophils were trapped in glomerulus within a few minutes after reperfusion. They gradually increased over time and Infiltrated neutrophils were observed in the tubular lumen and peritubular capillary. The neutrophils were clearly visualized rolling on peritubular capillary plexus at 3 μm/min. The administration of tadalafil significantly reduced neutrophil influx into the glomerulus in both WT and eNOS-KO mice. Reduced neutrophil infiltration in tadalafil groups, which was confirmed by flow cytometry, resulted in histopathologically decreased tubular injury. The expression of VCAM-1 and KIM-1 was partially prevented by tadalafil.

CONCLUSIONS

Use of a novel technique contributed to elucidation of neutrophil dynamics after reperfusion. Tadalafil has a potential for inhibiting neutrophil infiltration in renal IRI.Supplemental Visual Abstract; http://links.lww.com/TP/C223.

Antihypertensive Effects of Gynura divaricata (L.) DC in Rats with Renovascular Hypertension

Gynura divaricata (L.) DC (Compositae) (GD) could be found in various parts of Asia. It has been used as a traditional medicine to treat diabetes, high blood pressure, and other diseases, but its effects have not yet been scientifically confirmed. Therefore, we aimed at determining whether GD could affect renal function regulation, blood pressure, and the renin-angiotensin-aldosterone system (RAAS). Cardio-renal syndrome (CRS) is a disease caused by the interaction between the kidney and the cardiovascular system, where the acute or chronic dysfunction in one organ might induce acute or chronic dysfunction of the other. This study investigated whether GD could improve cardio-renal mutual in CRS type 4 model animals, two-kidney one-clip (2K1C) renal hypertensive rats. The experiments were performed on the following six experimental groups: control rats (CONT); 2K1C rats (negative control); OMT (Olmetec, 10 mg/kg/day)-treated 2K1C rats (positive control); and 2K1C rats treated with GD extracts in three different doses (50, 100, and 200 mg/kg/day) for three weeks by oral intake. Each group consisted of 10 rats. We measured the systolic blood pressure weekly using the tail-cuff method. Urine was also individually collected from the metabolic cage to investigate the effect of GD on the kidney function, monitoring urine volume, electrolyte, osmotic pressure, and creatinine levels from the collected urine. We observed that kidney weight and urine volume, which would both display typically increased values in non-treated 2K1C animals, significantly decreased following the GD treatment (###p < 0.001 vs. 2K1C). Osmolality and electrolytes were measured in the urine to determine how renal excretory function, which is reduced in 2K1C rats, could be affected. We found that the GD treatment improved renal excretory function. Moreover, using periodic acid-Schiff staining, we confirmed that the GD treatment significantly reduced fibrosis, which is typically increased in 2K1C rats. Thus, we confirmed that the GD treatment improved kidney function in 2K1C rats. Meanwhile, we conducted blood pressure and vascular relaxation studies to determine if the GD treatment could improve cardiovascular function in 2K1C rats. The heart weight percentages of the left atrium and ventricle were significantly lower in GD-treated 2K1C rats than in non-treated 2K1C rats. These results showed that GD treatment reduced cardiac hypertrophy in 2K1C rats. Furthermore, the acetylcholine-, sodium nitroprusside-, and atrial natriuretic peptide-mediated reduction of vasodilation in 2K1C rat aortic rings was also ameliorated by GD treatment (GD 200 mg/kg/day; p < 0.01, p < 0.05, and p < 0.05 vs. 2K1C for vasodilation percentage in case of each compound). The mRNA expression in the 2K1C rat heart tissue showed that the GD treatment reduced brain-type natriuretic peptide and troponin T levels (p < 0.001 and p < 0.001 vs. 2K1C). In conclusion, this study showed that GD improved the cardiovascular and renal dysfunction observed in an innovative hypertension model, highlighting the potential of GD as a therapeutic agent for hypertension. These findings indicate that GD shows beneficial effects against high blood pressure by modulating the RAAS in the cardio-renal syndrome. Thus, it should be considered an effective traditional medicine in hypertension treatment.

Physiology and Pathophysiology of Compensatory Adaptations of a Solitary Functioning Kidney

Children born with a solitary functioning kidney (SFK) have an increased risk of hypertension and kidney disease from early in adulthood. In response to a reduction in kidney mass, the remaining kidney undergoes compensatory kidney growth. This is associated with both an increase in size of the kidney tubules and the glomeruli and an increase in single nephron glomerular filtration rate (SNGFR). The compensatory hypertrophy and increase in filtration at the level of the individual nephron results in normalization of total glomerular filtration rate (GFR). However, over time these same compensatory mechanisms may contribute to kidney injury and hypertension. Indeed, approximately 50% of children born with a SFK develop hypertension by the age of 18 and 20–40% require dialysis by the age of 30. The mechanisms that result in kidney injury are only partly understood, and early biomarkers that distinguish those at an elevated risk of kidney injury are needed. This review will outline the compensatory adaptations to a SFK, and outline how these adaptations may contribute to kidney injury and hypertension later in life. These will be based largely on the mechanisms we have identified from our studies in an ovine model of SFK, that implicate the renal nitric oxide system, the renin angiotensin system and the renal nerves to kidney disease and hypertension associated with SFK. This discussion will also evaluate current, and speculate on next generation, prognostic factors that may predict those children at a higher risk of future kidney disease and hypertension.

Corin plays a protective role via upregulating MAPK and downregulating eNOS in diabetic nephropathy endothelial dysfunction

Diabetic nephropathy (DN) is one of the leading causes of mortality in diabetic patients, but its pathogenesis is unclear. We aimed to study the role of the pro-ANP convertase Corin in the pathogenesis of DN. Corin and ANP expression in DN rat kidneys and high-glucose-treated HK-2 cells was analyzed by real-time PCR, western blotting, and immunohistochemical staining. The effect of Corin-siRNA or ANP-siRNA HK-2 cells on EA.hy926 cell migration was determined by scratch-wound healing assay. The expression of mitogen-activated protein kinase (MAPK) and endothelial NO synthase (eNOS) in EA.hy926 cells treated with conditioned medium from Corin-siRNA- or ANP-siRNA-transfected HK-2 cells was determined by western blotting. We found a significant reduction in Corin and ANP expression in DN rat kidneys. These results were recapitulated in HK-2 cells treated with high glucose. EA.hy926 cells treated with conditioned medium from Corin-deficient HK-2 cells had inhibited migration, increased MAPK activity, and decreased eNOS activity. Similar effects were observed with ANP-siRNA transfection. Finally, adding ANP to the Corin-deficient HK-2 conditioned medium rescued the above defects, indicating that Corin mediates its effects through ANP. In conclusion, Corin plays a renoprotective role through pro-ANP processing, and defects in Corin cause endothelial dysfunction through MAPK and eNOS signaling in DN.

Compensatory renal hypertrophy following nephrectomy: When and how?

Following surgical removal of one kidney, the other enlarges and increases its function. The mechanism for the sensing of this change and the growth is incompletely understood but begins within days and compensatory renal hypertrophy (CRH) is the dominant contributor to the growth. In many individuals undergoing nephrectomy for cancer or kidney donation this produces a substantial and helpful increase in renal function. Two main mechanisms have been proposed, one in which increased activity by the remaining kidney leads to hypertrophy, the second in which there is release of a kidney specific factor in response to a unilateral nephrectomy that initiates CRH. Whilst multiple growth factors and pathways such as the mTORC pathway have been implicated in experimental studies, their roles and the precise mechanism of CRH are not defined. Unrestrained hypoxia inducible factor activation in renal cancer promotes growth and may play an important role in driving CRH.

Metabolic reprogramming by the S-nitroso-CoA reductase system protects against kidney injury

Endothelial nitric oxide synthase (eNOS) is protective against kidney injury, but the molecular mechanisms of this protection are poorly understood^1,2. Nitric oxide-based cellular signalling is generally mediated by protein S-nitrosylation, the oxidative modification of Cys residues to form S-nitrosothiols (SNOs). S-nitrosylation regulates proteins in all functional classes, and is controlled by enzymatic machinery that includes S-nitrosylases and denitrosylases, which add and remove SNO from proteins, respectively^3,4. In Saccharomyces cerevisiae, the classic metabolic intermediate co-enzyme A (CoA) serves as an endogenous source of SNOs through its conjugation with nitric oxide to form S-nitroso-CoA (SNO-CoA), and S-nitrosylation of proteins by SNO-CoA is governed by its cognate denitrosylase, SNO-CoA reductase (SCoR)⁵. Mammals possess a functional homologue of yeast SCoR, an aldo-keto reductase family member (AKR1A1)⁵ with an unknown physiological role. Here we report that the SNO-CoA-AKR1A1 system is highly expressed in renal proximal tubules, where it transduces the activity of eNOS in reprogramming intermediary metabolism, thereby protecting kidneys against acute kidney injury. Specifically, deletion of Akr1a1 in mice to reduce SCoR activity increased protein S-nitrosylation, protected against acute kidney injury and improved survival, whereas this protection was lost when Enos (also known as Nos3) was also deleted. Metabolic profiling coupled with unbiased mass spectrometry-based SNO-protein identification revealed that protection by the SNO-CoA-SCoR system is mediated by inhibitory S-nitrosylation of pyruvate kinase M2 (PKM2) through a novel locus of regulation, thereby balancing fuel utilization (through glycolysis) with redox protection (through the pentose phosphate shunt). Targeted deletion of PKM2 from mouse proximal tubules recapitulated precisely the protective and mechanistic effects of S-nitrosylation in Akr1a1^-/- mice, whereas Cys-mutant PKM2, which is refractory to S-nitrosylation, negated SNO-CoA bioactivity. Our results identify a physiological function of the SNO-CoA-SCoR system in mammals, describe new regulation of renal metabolism and of PKM2 in differentiated tissues, and offer a novel perspective on kidney injury with therapeutic implications.

The eNOS-NO pathway attenuates kidney dysfunction via suppression of inflammasome activation in aldosterone-induced renal injury model mice

Hypertension causes vascular complications, such as stroke, cardiovascular disease, and chronic kidney disease (CKD). The relationship between endothelial dysfunction and progression of kidney disease is well known. However, the relationship between the eNOS-NO pathway and chronic inflammation, which is a common pathway for the progression of kidney disease, remains unexplored. We performed in vivo experiments to determine the role of the eNOS-NO pathway by using eNOS-deficient mice in a hypertensive kidney disease model. All mice were unilateral nephrectomized (Nx). One week after Nx, the mice were randomly divided into two groups: the aldosterone infusion groups and the vehicle groups. All mice also received a 1% NaCl solution instead of drinking water. The aldosterone infusion groups were treated with hydralazine to correct blood pressure differences. After four weeks of drug administration, all mice were euthanized, and blood and kidney tissue samples were collected. In the results, NLRP3 inflammasome activation was elevated in the kidneys of the eNOS-deficient mice, and tubulointerstitial fibrosis was accelerated. Suppression of inflammasome activation by knocking out ASC prevented tubulointerstitial injury in the eNOS knockout mice, indicating that the eNOS-NO pathway is involved in the development of kidney dysfunction through acceleration of NLRP3 inflammasome in macrophages. We revealed that endothelial function, particularly the eNOS-NO pathway, attenuates the progression of renal tubulointerstitial injury via suppression of inflammasome activation. Clinically, patients who develop vascular endothelial dysfunction have lifestyle diseases, such as hypertension or diabetes, and are known to be at risk for CKD. Our study suggests that the eNOS-NO pathway could be a therapeutic target for the treatment of chronic kidney disease associated with endothelial dysfunction.

The Impact of the Nitric Oxide (NO)/Soluble Guanylyl Cyclase (sGC) Signaling Cascade on Kidney Health and Disease: A Preclinical Perspective

Chronic Kidney Disease (CKD) is a highly prevalent disease with a substantial medical need for new and more efficacious treatments. The Nitric Oxide (NO), soluble guanylyl cyclase (sGC), cyclic guanosine monophosphate (cGMP) signaling cascade regulates various kidney functions. cGMP directly influences renal blood flow, renin secretion, glomerular function, and tubular exchange processes. Downregulation of NO/sGC/cGMP signaling results in severe kidney pathologies such as CKD. Therefore, treatment strategies aiming to maintain or increase cGMP might have beneficial effects for the treatment of progressive kidney diseases. Within this article, we review the NO/sGC/cGMP signaling cascade and its major pharmacological intervention sites. We specifically focus on the currently known effects of cGMP on kidney function parameters. Finally, we summarize the preclinical evidence for kidney protective effects of NO-donors, PDE inhibitors, sGC stimulators, and sGC activators.

Dietary methionine restriction modulates renal response and attenuates kidney injury in mice

Methionine restriction (MR) extends the lifespan across several species, such as rodents, fruit flies, roundworms, and yeast. MR studies have been conducted on various rodent organs, such as liver, adipose tissue, heart, bones, and skeletal muscle, to elucidate its benefits to the healthspan; however, studies of the direct effect of MR on kidneys are lacking. To investigate the renal effects of MR, we used young and aged unilateral nephrectomized and 5/6 nephrectomized (5/6Nx) mice. Our studies indicated that MR mice experienced polydipsia and polyuria compared with control-fed counterparts. Urine albumin, creatinine, albumin-to-creatinine ratio, sulfur amino acids, and electrolytes were reduced in MR mice. Kidneys of MR mice up-regulated genes that are involved in ion transport, such as Aqp2, Scnn1a, and Slc6a19, which indicated a response to maintain osmotic balance. In addition, we identified renoprotective biomarkers that are affected by MR, such as clusterin and cystatin C. Of importance, MR attenuated kidney injury in 5/6Nx mice by down-regulating inflammation and fibrosis mechanisms. Thus, our studies in mice show the important role of kidneys during MR in maintaining osmotic homeostasis. Moreover, our studies also show that the MR diet delays the progression of kidney disease.-Cooke, D., Ouattara, A., Ables, G. P. Dietary methionine restriction modulates renal response and attenuates kidney injury in mice.

Dual Therapeutic Effects of an Albumin-Based Nitric Oxide Donor on 2 Experimental Models of Chronic Kidney Disease

Chronic kidney disease (CKD) is accompanied by a variety of complications, typically renal anemia and kidney fibrosis. Accordingly, it is desirable to develop the novel therapeutics that can treat these CKD conditions. Since nitric oxide (NO) has multiple functions including hypoxia inducible factor stabilizing, anti-inflammatory, anti-oxidative, and anti-apoptoic activities, the use of NO for the CKD therapy has attracted considerable interest. Here, we evaluate the therapeutic impacts of S-nitrosated human serum albumin (SNO-HSA), a long-lasting NO donor, on 2 animal models of CKD. SNO-HSA increased the expression of erythropoietin (EPO), VEGF, and eNOS by stabilizing hypoxia inducible factor-1α in HepG2 and HK-2 cells. SNO-HSA increased hematopoiesis in both healthy and renal anemia rats, suggesting the promotion of EPO production. In unilateral ureteral obstruction-treated mice, SNO-HSA ameliorated kidney fibrosis by suppressing the accumulation of renal extracellular matrix. SNO-HSA also inhibited unilateral ureteral obstruction-induced α-smooth muscle actin increase and E-cadherin decrease, suggesting that SNO-HSA might suppress the accumulation of myofibroblasts, an important factor of fibrosis. SNO-HSA also inhibited the elevations of fibrosis factors, such as transforming growth factor-β, interleukin-6, and oxidative stress, while it increased EPO production, an anti-fibrosis factor. In conclusion, SNO-HSA has the potential to function as a dual therapeutics for renal anemia and kidney fibrosis.

Infiltration of M1, but not M2, macrophages is impaired after unilateral ureter obstruction in Nrf2-deficient mice

Chronic inflammation can be a major driver of the failure of a variety of organs, including chronic kidney disease (CKD). The NLR family pyrin domain-containing 3 (NLRP3) inflammasome has been shown to play a pivotal role in inflammation in a mouse kidney disease model. Nuclear factor erythroid 2-related factor 2 (Nrf2), the master transcription factor for anti-oxidant responses, has also been implicated in inflammasome activation under physiological conditions. However, the mechanism underlying inflammasome activation in CKD remains elusive. Here, we show that the loss of Nrf2 suppresses fibrosis and inflammation in a unilateral ureter obstruction (UUO) model of CKD in mice. We consistently observed decreased expression of inflammation-related genes NLRP3 and IL-1β in Nrf2-deficient kidneys after UUO. Increased infiltration of M1, but not M2, macrophages appears to mediate the suppression of UUO-induced CKD symptoms. Furthermore, we found that activation of the NLRP3 inflammasome is attenuated in Nrf2-deficient bone marrow–derived macrophages. These results demonstrate that Nrf2-related inflammasome activation can promote CKD symptoms via infiltration of M1 macrophages. Thus, we have identified the Nrf2 pathway as a promising therapeutic target for CKD.

Distant effects of unilateral renal ischemia/reperfusion on contralateral kidney but not lung in rats: the roles of ROS and iNOS

Acute kidney injury is usually associated with distant organ dysfunction. The roles of inducible nitric oxide synthase (iNOS) and reactive oxygen species (ROS) in this phenomenon were investigated following 2 h unilateral renal ischemia and 24 h reperfusion. There were 3 groups of rats subjected to either unilateral ischemia/reperfusion (UIR group), unilateral nephrectomy (UNX group), or sham operation. Two further groups were given α-tocopherol and aminoguanidine with UIR (treated-UIR group) and UNX (treated-UNX group). Plasma nitrite/nitrate and malondialdehyde were elevated only in the UIR group. Creatinine clearance and blood flow increased in non-ischemic kidney of the UIR, but not to the same extent as remnant kidney of the UNX group, while they had equal compensatory rises in absolute Na(+) and K(+) excretion and urine flow. Non-ischemic kidney of the treated-UIR group, but not remnant kidney of the treated-UNX group, showed more elevation in blood flow, whereas both kidneys had reductions in absolute Na(+) excretion and urine flow. Respiratory functional variable were not different between all groups. Therefore, 2 h unilateral renal ischemia and 24 h reperfusion did not affect lung but had distant effects on contralateral kidney partly mediated by ROS and NO-derived from iNOS to dampen compensatory increases in renal hemodynamics and to decrease tubular reabsorption.

Short-term prognosis of living-donor kidney transplantation from hypertensive donors with high-normal albuminuria

BACKGROUND

High-normal albuminuria (HNA) is an independent predictor of cardiovascular risk in the general population. Although hypertensive donor (HTD) candidates with HNA were considered acceptable donors by the Amsterdam Forum 2004, the transplant prognosis of HTDs with HNA has not been determined. Therefore, we investigated the transplant prognosis of HTDs with HNA.

METHODS

We retrospectively analyzed 52 adult living-donor kidney transplants performed at Kagawa University Hospital. HNA was defined as albuminuria of 15 to 30 mg/g Cr. Changes in kidney function of donors and recipients were assessed up to 2 years after transplantation.

RESULTS

Overall, 38 donors were normotensive and 14 were hypertensive. Nine of 14 HTDs exhibited HNA before donation. More HTDs with HNA had arteriosclerotic vasculopathy or glomerulosclerosis than did normotensive donors (NTDs). Hypertension and the degree of albuminuria did not affect the donors' posttransplantation kidney function. The risk of discompensatory changes in kidney function after donation was significantly higher in HTDs with HNA than in NTDs (odds ratio, 10.5; 95% confidence interval, 1.51-72.9; P=0.02). In multivariate analysis, the coexistence of hypertension and HNA was not significantly associated with discompensatory changes after donation (adjusted odds ratio, 6.04; 95% confidence interval, 0.19-192; P=0.31). Recipients of HTDs with HNA had similar allograft survival rates but lower allograft function compared with recipients of NTDs.

CONCLUSIONS

Although further studies are needed to confirm our results, the short-term prognosis of living-donor kidney transplantation was similar between HTDs with HNA and NTDs.

Direct sGC activation bypasses NO scavenging reactions of intravascular free oxy-hemoglobin and limits vasoconstriction

AIMS

Hemoglobin-based oxygen carriers (HBOC) provide a potential alternative to red blood cell (RBC) transfusion. Their clinical application has been limited by adverse effects, in large part thought to be mediated by the intravascular scavenging of the vasodilator nitric oxide (NO) by cell-free plasma oxy-hemoglobin. Free hemoglobin may also cause endothelial dysfunction and platelet activation in hemolytic diseases and after transfusion of aged stored RBCs. The new soluble guanylate cyclase (sGC) stimulator Bay 41-8543 and sGC activator Bay 60-2770 directly modulate sGC, independent of NO bioavailability, providing a potential therapeutic mechanism to bypass hemoglobin-mediated NO inactivation.

RESULTS

Infusions of human hemoglobin solutions and the HBOC Oxyglobin into rats produced a severe hypertensive response, even at low plasma heme concentrations approaching 10 μM. These reactions were only observed for ferrous oxy-hemoglobin and not analogs that do not rapidly scavenge NO. Infusions of L-NG-Nitroarginine methyl ester (L-NAME), a competitive NO synthase inhibitor, after hemoglobin infusion did not produce additive vasoconstriction, suggesting that vasoconstriction is related to scavenging of vascular NO. Open-chest hemodynamic studies confirmed that hypertension occurred secondary to direct effects on increasing vascular resistance, with limited negative cardiac inotropic effects. Intravascular hemoglobin reduced the vasodilatory potency of sodium nitroprusside (SNP) and sildenafil, but had no effect on vasodilatation by direct NO-independent activation of sGC by BAY 41-8543 and BAY 60-2770.

INNOVATION AND CONCLUSION

These data suggest that both sGC stimulators and sGC activators could be used to restore cyclic guanosine monophosphate-dependent vasodilation in conditions where cell-free plasma hemoglobin is sufficient to inhibit endogenous NO signaling.

Nitric oxide in afferent arterioles after uninephrectomy depends on extracellular l-arginine

Uninephrectomy (UNX) causes hyperperfusion of the contralateral remaining kidney via increased nitric oxide (NO) synthesis. Although the exact mechanism remains largely unknown, we hypothesize that this would be localized to the afferent arteriole and that it depends on cellular uptake of l-arginine. The experiments were performed in rats 2 days (early) or 6 wk (late) after UNX and compared with controls (Sham) to study acute and chronic effects on NO metabolism. Renal blood flow was increased after UNX (21 ± 2 ml·min−1·kg−1 in sham, 30 ± 3 in early, and 26 ± 1 in late, P < 0.05). NO inhibition with Nω-nitro-l-arginine methyl ester hydrochloride (l-NAME) caused a greater increase in renal vascular resistance in early UNX compared with Sham and late UNX (138 ± 24 vs. 88 ± 10, and 84 ± 7%, P < 0.01). The lower limit of autoregulation was increased both in early and late UNX compared with Sham ( P < 0.05). l-NAME did not affect the ANG II-induced contraction of isolated afferent arterioles (AA) from Sham. AA from early UNX displayed a more pronounced contraction in response to l-NAME (−57 ± 7 vs. −16 ± 7%, P < 0.05) and in the absence of l-arginine (−41 ± 4%, P < 0.05) compared with both late UNX and Sham. mRNA expression of endothelial NO synthase was reduced, whereas protein expression was unchanged. Cationic amino acid transporter-1 and -2 mRNA was increased, while protein was unaffected in isolated preglomerular resistance vessels. In conclusion, NO-dependent hyperperfusion of the remaining kidney in early UNX is associated with increased NO release from the afferent arteriole, which is highly dependent on extracellular l-arginine availability.