Amino acids and SGLT2 inhibitors (SGLT2i) have recently been reported to attenuate the risk of hypoxic acute kidney injury (AKI), determined by changes in estimated glomerular filtration rate (GFR) following cardiac surgery and interventions with radiocontrast media, respectively. Yet, strategies to prevent or treat hypoxic AKI by the intensification of GFR, such as the administration of amino acids, in fact may predispose to intensified renal hypoxia and potential injury through enhanced tubular transport activity. Likewise, SGLT2i may intensify medullary hypoxia by translocating oxygen consumption for tubular transport from proximal to distal nephron segments. The outer medulla is particularly susceptible to hypoxic AKI, since intense regional oxygen consumption is barely met by a limited local blood supply, as reflected by low ambient oxygenation under normal conditions. In fact, declining GFR during AKI to large extent attenuates medullary hypoxia by the reduction of solute delivery for reabsorption in the distal nephron. Therefore, as outlined in this review, despite encouraging clinical outcomes, the safety, regarding renal parenchymal integrity, of enhancing GFR with amino acid infusion or by translocation of tubular transport to distal nephron segments by SGLT2i, administered to prevent AKI, should be assured, possibly by the determination of biomarkers of renal injury. Changes in renal oxygen expenditure, particularly within the hypoxic medulla should be considered in designing therapeutic interventions, conceivably with efforts aimed at reducing, rather than enhancing medullary tubular transport.

ACE2, serving as a receptor to SARS-CoV-2, is a key player in RAAS. Consequent ACE2 depletion disrupts the balance between the Ang II/ AT1R and Ang (1-7)/MasR arms of the angiotensin system, promoting intense inflammation. A crosstalk existing between the angiotensin system and ACE2/spike proteins may affect the infection severity, with potential therapeutic implications. Evaluating such potential interactions and their relevance to the severity of COVID-19, which is directly affected by ACE2 abundance or indirectly by RAAS axis dysregulation. The intensity of SARS-CoV-2 infection was assessed using a cell-to-cell fusion assay and AT1R activation was assessed using AT1R-Tango approach. We demonstrate the critical function of ACE2 in mitigating AT1R activation, which is disrupted following SARS-CoV-2 infection. Moreover, we show that the spike protein indirectly intensifies AT1R activation. Beyond its established role in activating MasR, Ang1-7 was found to function as a biased agonist for AT1R, without altering ACE2 levels or affecting SARS-CoV-2 entry. In contrast, AVE0991, a MasR agonist, was observed to increase ACE2 levels and enhance SARS-CoV-2 infection. Angiotensin receptor blockers (ARBs) effectively inhibited AT1R activity and had minimal impact on viral entry. Our data supports the likelihood that AT1R blockers (ARBs) may be effective in managing COVID-19 since they inhibit AT1R activation and its deleterious subsequent effects, with no impact on SARS-CoV-2 entry. By contrast, MasR and its agonist AVE0991, by increasing ACE2 levels, may restore RAAS physiological balance, but facilitate host cell invasion by SARS-CoV-2.

Angiotensin converting enzyme 2 (ACE2), a component of the renin-angiotensin aldosterone system (RAAS), is the main receptor for SARS-CoV-2 entry into human cells. The occurrence of long-term symptoms post-COVID 19 infection (Long COVID, LC) is an important public health issue with an unclear etiological mechanism. We aimed to determine whether LC was associated with long-term RAAS disruption. We recruited a cohort of healthcare workers (HCWs) from Ziv Medical Center in Safed, Israel, who were uninfected and unvaccinated at baseline, and who later became infected with SARS-CoV-2. We measured serum circulating levels of four RAAS components (ACE, ACE2, Ang1-7 and AngII) using commercially available ELISA assays at three time points, using serum samples regularly collected from consenting hospital workers during the COVID-19 pandemic: pre-infection, 3–6 months post-infection, and a year post-infection. Post-serum collection we determined LC status using an online survey based on self-reported, LC-compatible symptoms not explained by alternative diagnoses. We excluded participants with conditions or medications interfering with the RAAS (e.g. hypertension, chronic kidney disease, antihypertensives, antidiuretics). At each time point we compared the levels of each of the four RAAS components between those infected and reporting LC and those infected not reporting LC using Mann Whitney U tests and Wilcoxon signed-rank tests, corrected for multiple testing. We included 38 LC positive and 38 LC negative participants. Age/gender distribution was similar in both groups. No statistically significant differences in any of the four RAAS markers were observed between LC cases and controls at either 3–6 months or 12 months post-infection in our study sample. No evidence was detected within the limits of the study design and sample size to conclude that long-term disruption of RAAS is a significant contributor to LC pathophysiology. Not applicable.

Alveolar active sodium transport is essential for clearing edema from airspaces, in a process known as alveolar fluid clearance (AFC). Although it has been reported that atrial natriuretic peptide (ANP) attenuates AFC, little is known about the underlying molecular effects of natriuretic peptides (NPs). Therefore, we examined the contribution of NPs to AFC and their effects as mediators of active sodium transport. By using the isolated liquid-filled lungs model, we investigated the effects of NPs on AFC. The expression of NPs, Na+, K+-ATPase, and Na+ channels was assessed in alveolar epithelial cells. Congestive heart failure (CHF) was induced by using the aortocaval fistula model. ANP and brain NP (BNP) significantly reduced AFC rate from 0.49 ± 0.02 mL/h in sham rats to 0.26 ± 0.013 and 0.19 ± 0.005 in ANP and BNP-treated groups, respectively. These effects were mediated by downregulating the active Na+ transport components in the alveolar epithelium while enhancing the ubiquitination and degradation of αENaC in the lungs, as reflected by increased levels of Nedd4-2. In addition, AFC was reduced in compensated CHF rats treated with ANP, while in decompensated CHF, ANP partially restored AFC. In conclusion, NPs regulate AFC in health and CHF. This research could help optimize pharmacological treatments for severe CHF.

Fluid administration is the mainstay intervention effective in the prevention of radiocontrast-associated nephropathy (CAN) in high-risk patients. Vigorous hydration shortens intratubular solute transit-time and reduces tubular intraluminal concentration of contrast media (CM), decreasing exposure of tubular cells to CM and reducing renal parenchymal retention of the nephrotoxin. Lowered plasma and urine viscosity might also improve vasa recta flow and renal interstitial pressure, improving compromised renal parenchymal microcirculation and oxygenation. Herein we emphasize the overlooked plausible role of down-regulation of tubular transport, generated by vigorous hydration in the mitigation of medullary hypoxia and hypoxic medullary damage generated in CAN. Volume expansion triggers natriuretic peptides that improve renal parenchymal oxygenation and may attenuate hypoxic renal injury. Furthermore, enhanced large-volume hydration protocols used for high-risk patients undergoing coronary interventions or transcatheter aortic valve implantation include the administration of furosemide. Loop diuretics block oxygen consumption in medullary thick ascending limbs, improve medullary oxygenation and prevent outer medullary injury in experimental CAN. Thus, fluids are likely not the sole issue, and restoration of medullary oxygenation is critical in attenuating the risk of CAN by large volume hydration protocols for high-risk patients.

Acute kidney injury (AKI) is a serious health concern with high morbidity and high mortality worldwide. Recently, sexual dimorphism has become increasingly recognized as a factor influencing the severity of the disease. This study explores the gender-specific renoprotective pathways in αMUPA transgenic mice subjected to AKI. αMUPA transgenic male and female mice were subjected to ischemia–reperfusion (I/R)-AKI in the presence or absence of orchiectomy, oophorectomy, and L-NAME administration. Blood samples and kidneys were harvested 48 h following AKI for the biomarkers of kidney function, renal injury, inflammatory response and intracellular pathway sensing of or responding to AKI. Our findings show differing responses to AKI, where female αMUPA mice were remarkably protected against AKI as compared with males, as was evident by the lower SCr and BUN, normal renal histologically and attenuated expression of NGAL and KIM-1. Moreover, αMUPA females did not show a significant change in the renal inflammatory and fibrotic markers following AKI as compared with wild-type (WT) mice and αMUPA males. Interestingly, oophorectomized females eliminated the observed resistance to renal injury, highlighting the central protective role of estrogen. Correspondingly, orchiectomy in αMUPA males mitigated their sensitivity to renal damage, thereby emphasizing the devastating effects of testosterone. Additionally, treatment with L-NAME proved to have significant deleterious impacts on the renal protective mediators, thereby underscoring the involvement of eNOS. In conclusion, gender-specific differences in the response to AKI in αMUPA mice include multifaceted and keen interactions between the sex hormones and key biochemical mediators (such as estrogen, testosterone and eNOS). These novel findings shed light on the renoprotective pathways and mechanisms, which may pave the way for development of therapeutic interventions.

Acute pancreatitis (AP) is a common gastrointestinal disease with high morbidity and mortality rate. Unfortunately, neither the etiology nor the pathophysiology of AP are fully understood and causal treatment options are not available. Recently we demonstrated that heparanase (Hpa) is adversely involved in the pathogenesis of AP and inhibition of this enzyme ameliorates the manifestation of the disease. Moreover, a pioneer study demonstrated that Aspirin has partial inhibitory effect on Hpa. Another compound, which possesses a mild pancreato-protective effect against AP, is Trehalose, a common disaccharide. We hypothesized that combination of Aspirin, Trehalose, PG545 (Pixatimod) and SST0001 (Roneparstat), specific inhibitors of Hpa, may exert pancreato-protective effect better than each drug alone. Thus, the current study examines the pancreato-protective effects of Aspirin, Trehalose, PG545 and SST0001 in experimental model of AP induced by cerulein in wild-type (WT) and Hpa over-expressing (Hpa-Tg) mice. Cerulein-induced AP in WT mice was associated with significant rises in the serum levels of lipase (X4) and amylase (X3) with enhancement of pancreatic edema index, inflammatory response, and autophagy. Responses to cerulein were all more profound in Hpa-Tg mice versus WT mice, evident by X7 and X5 folds increase in lipase and amylase levels, respectively. Treatment with Aspirin or Trehalose alone and even more so in combination with PG545 or SST0001 were highly effective, restoring the serum level of lipase back to the basal level. Importantly, a novel newly synthesized compound termed Aspirlose effectively ameliorated the pathogenesis of AP as a single agent. Collectively, the results strongly indicate that targeting Hpa by using anti-Hpa drug combinations constitute a novel therapy for this common orphan disease.

Metabolic dysfunction-associated steatotic liver disease (MASLD) affects one-third of the global population. Understanding the metabolic pathways involved can provide insights into disease progression and treatment. Untargeted metabolomics of livers from mice with early-stage steatosis uncovered decreased methylated metabolites, suggesting altered one-carbon metabolism. The levels of glycine, a central component of one-carbon metabolism, were lower in mice with hepatic steatosis, consistent with clinical evidence. Stable-isotope tracing demonstrated that increased serine synthesis from glycine via reverse serine hydroxymethyltransferase (SHMT) is the underlying cause for decreased glycine in steatotic livers. Consequently, limited glycine availability in steatotic livers impaired glutathione synthesis under acetaminophen-induced oxidative stress, enhancing acute hepatotoxicity. Glycine supplementation or hepatocyte-specific ablation of the mitochondrial SHMT2 isoform in mice with hepatic steatosis mitigated acetaminophen-induced hepatotoxicity by supporting de novo glutathione synthesis. Thus, early metabolic changes in MASLD that limit glycine availability sensitize mice to xenobiotics even at the reversible stage of this disease.

Gaucher disease (GD) has a high carrier rate among Ashkenazi Jews.The most common disease-causing variant in this population N370S, is also prevalent pan-ethnically. This has led to speculations of some protective effect for carriers of this variant. During the recent COVID-19 pandemic, GD patients reportedly had a surprisingly low infection rate and mild symptoms considering their disease status. As SARS-CoV-2 gains entry into the cell via membrane-bound angiotensin-converting enzyme 2 (ACE2), we speculated that differences in levels of soluble ACE2 in GD patients could contribute to this protective state. While ACE is known to be elevated in GD, to our knowledge, ACE2 levels have not been explored.We measured serum and macrophage-bound levels of ACE and ACE2 by ELISA and western blot, respectively, in GD patients and age- and sex-matched controls. Our results reveal a significant elevation of both serum and macrophage-bound ACE and ACE2 in GD patients compared to healthy controls. This elevation appears to be mitigated by GD treatment. Moreover, the most robust ACE2 elevation was observed in N370S homozygotes, and was not effected by treatment.Since coronaviruses use the ACE2 receptor as a gateway for host cell entry, we speculate that elevated circulating ACE2 may serve as a decoy. This might explain the observed mild infections in GD patients during the COVID-19 pandemic.

Abstract The central role of natriuretic peptides (NPs) in the complex cardio‐renal integrated physiology and organ failure has been revealed over the last four decades. Atrial natriuretic peptide (ANP), the oldest representative of the NPs family, is produced through conversion of proANP to the mature peptide by corin, a trans‐membrane protease localized to the cardiac myocyte membrane. Similarly, brain natriuretic peptide (BNP) is generated by furin, which cleaves proBNP to BNP in myocytes. Though the components of NPs system, their synthesis and target organs are well established, understanding their role in the interplay between the heart and the kidney is steadily evolving. In this context, Feldman et al. (New England Journal of Medicine, 389, 1685) recently described patients with hypertension, cardiomyopathy, atrial arrhythmia and left atrial fibrosis, associated with a homozygous loss‐of‐function variant of the gene encoding corin (Cor−/−). Notably, reduced baseline urinary electrolyte and creatinine excretion have been observed in one of the studied patients. This renal excretory functional impairment could be attributed to the lack of cardiac‐derived ANP in these patients, as implied by Feldman et al. Yet, in this mini‐review we suggest that this aberrant renal manifestation may principally stem from lack of local ANP production at renal tissue, as corin is normally expressed in proximal tubules, Henle's loop and collecting ducts, with locally produced ANP provoking Na+ and water exertion. Collectively, it seems that beside the classic well‐established cardio‐renal axis, the renal NPs system functions as local endocrine machinery in the regulation of sodium excretion.

Background/Objectives: The incidence of acute kidney injury (AKI) has been steadily increasing. Despite its high prevalence, there is no pathogenetically rational therapy for AKI. This deficiency stems from the poor understanding of the pathogenesis of AKI. Renal ischemia/hypoxia is one of the leading causes of clinical AKI. This study investigates whether αMUPA mice, overexpressing the urokinase plasminogen activator (uPA) gene are protected against ischemic AKI, thus unraveling a potential renal damage treatment target. Methods: We utilized an in vivo model of I/R-induced AKI in αMUPA mice and in vitro experiments of uPA-treated HEK-293 cells. We evaluated renal injury markers, histological changes, mRNA expression of inflammatory, apoptotic, and autophagy markers, as compared with wild-type animals. Results: the αMUPA mice exhibited less renal injury post-AKI, as was evident by lower SCr, BUN, and renal NGAL and KIM-1 along attenuated adverse histological alterations. Notably, the αMUPA mice exhibited decreased levels pro-inflammatory, fibrotic, apoptotic, and autophagy markers like TGF-β, IL-6, STAT3, IKB, MAPK, Caspase-3, and LC3. By contrast, ACE-2, p-eNOS, and PGC1α were higher in the kidneys of the αMUPA mice. In vitro results of the uPA-treated HEK-293 cells mirrored the in vivo findings. Conclusions: These results indicate that uPA modulates key pathways involved in AKI, offering potential therapeutic targets for mitigating renal damage.

The use of SGLT2 inhibitors (SGLT2is) has been found in large clinical studies to slow the progression of chronic kidney disease (CKD) and to lower the risk of acute kidney injury (AKI). Recent reports suggest that SGLT2is may also reduce the likelihood of developing radiocontrast-associated nephropathy (CAN) following contrast-enhanced imaging and intravascular interventions. This review underscores potential pitfalls and confounders in these studies and calls for caution in adopting their conclusions regarding the safety and renoprotective potency of SGLT2is, in particular in patients at high risk, with advanced CKD and hemodynamic instability undergoing coronary intervention. This caution is particularly warranted since both SGLT2is and contrast media intensify medullary hypoxia in the already hypoxic diabetic kidney and their combination may lead to medullary hypoxic damage, a principal component of CAN. Further studies are needed to evaluate this dispute, particularly in patients at high risk, and to reveal whether SGLT2is indeed provide renal protection or are hazardous during contrast-enhanced imaging and vascular interventions.

Despite the high prevalence of acute kidney injury (AKI), the therapeutic approaches for AKI are disappointing. This deficiency stems from the poor understanding of the pathogenesis of AKI. Recent studies demonstrate that αMUPA, alpha murine urokinase-type plasminogen activator (uPA) transgenic mice, display a cardioprotective pathway following myocardial ischemia. We hypothesize that these mice also possess protective renal pathways. Male and female αMUPA mice and their wild type were subjected to 30 min of bilateral ischemic AKI. Blood samples and kidneys were harvested 48 h following AKI for biomarkers of kidney function, renal injury, inflammatory response, and intracellular pathways sensing or responding to AKI. αMUPA mice, especially females, exhibited attenuated renal damage in response to AKI, as was evident from lower SCr and BUN, normal renal histology, and attenuated expression of NGAL and KIM-1. Notably, αMUPA females did not show a significant change in renal inflammatory and fibrotic markers following AKI as compared with wild-type (WT) mice and αMUPA males. Moreover, αMUPA female mice exhibited the lowest levels of renal apoptotic and autophagy markers during normal conditions and following AKI. αMUPA mice, especially the females, showed remarkable expression of PGC1α and eNOS following AKI. Furthermore, MUPA mice showed a significant elevation in renal leptin expression before and following AKI. Pretreatment of αMUPA with leptin-neutralizing antibodies prior to AKI abolished their resistance to AKI. Collectively, the kidneys of αMUPA mice, especially those of females, are less susceptible to ischemic I/R injury compared to WT mice, and this is due to nephroprotective actions mediated by the upregulation of leptin, eNOS, ACE2, and PGC1α along with impaired inflammatory, fibrotic, and autophagy processes.

BACKGROUND:Concern exists regarding the renal safety of blocking the renin-angiotensin system (RAS) during acute illness, especially in the presence of volume depletion and hemodynamic instability. METHODS:We explored the impact of loop diuretics and RAS blockers on the likelihood of developing acute kidney injury (AKI) or acute kidney functional recovery (AKR) among inpatients. Adjusted odds ratio for AKI, AKR and mortality was calculated, using logistic regression models, with subgroup analysis for patients with estimated glomerular filtration rate (eGFR) <30 ml/min/1.73 m2, corrected for blood pressure measurements. RESULTS:53,289 patients were included. RAS blockade was associated with reduced adjusted odds ratio for both AKI (0.76, CI 0.70-0.83) AKR (0.55, 0.52-0.58), and mortality within 30 days (0.44, 0.41-0.48), whereas loop diuretics were associated with increased risk of AKI (3.75, 3.42-4.12) and mortality (1.71, 1.58-1.85) and reduced AKR (0.71, 0.66-0.75). Comparable impact of RAS blockers and loop diuretics on renal outcomes and death was found among 6,069 patients with eGFR < 30 ml/min/1.73m2. RAS inhibition and diuretics tended to increase the adjusted odds ratios for AKI and to reduce the likelihood of AKR in hypotensive patients. CONCLUSIONS:Reduced blood pressure, RAS blockers and diuretics affect the odds of developing AKI or AKR among inpatients, suggesting possible disruption in renal functional reserve (RFR). As long as blood pressure is maintained, RAS inhibition seems to be safe and renoprotective in this population, irrespective of kidney function upon admission, and is associated with reduced mortality.

The introduction of gliflozins in the management of type 2 diabetes mellitus leads to a better control of hyperglycemia, obesity, hypertension, dyslipidemia, and fluid retention. Most importantly, it also improves renal survival and reduces major cardiovascular events and mortality. Gliflozins were also found to induce erythropoietin (EPO) synthesis, leading to reticulocytosis and erythropoiesis. The mechanism(s) by which gliflozins induce erythropoiesis is a matter of debate. Although the canonical pathway of triggering EPO synthesis is through renal tissue hypoxia, it has been suggested that improved renal oxygenation may facilitate EPO synthesis via non-canonical routes. The latter proposes that the recovery of peritubular interstitial fibroblasts producing erythropoietin (EPO) is responsible for enhanced erythropoiesis. According to this hypothesis, enhanced glucose/sodium re-uptake by proximal tubules in uncontrolled diabetes generates cortical hypoxia, with injury to these cells. Once transport workload declines with the use of SGLT2i, they recover and regain their capacity to produce EPO. In this short communication, we argue that this hypothesis may be wrong and propose that gliflozins likely induce EPO through the documented intensification of renal hypoxia at the corticomedullary junction, related to the translocation of tubular transport from cortical segments to medullary thick ascending limbs. We propose that gliflozins, through intensified hypoxia in this region, trigger local EPO synthesis in peritubular interstitial cells via the canonical pathway of blocking HIF-prolyl hydroxylases (that initiate HIF alpha degradation), with the consequent stabilization of HIF-2 signal and an apocrinic induction of EPO in these same cells.

Congestive heart failure (CHF) is often associated with impaired kidney function. Over- activation of the renin–angiotensin–aldosterone system (RAAS) contributes to avid salt/water retention and cardiac hypertrophy in CHF. While the deleterious effects of angiotensin II (Ang II) in CHF are well established, the biological actions of angiotensin 1-7 (Ang 1-7) are not fully characterized. In this study, we assessed the acute effects of Ang 1-7 (0.3, 3, 30 and 300 ng/kg/min, IV) on urinary flow (UF), urinary Na+ excretion (UNaV), glomerular filtration rate (GFR) and renal plasma flow )RPF) in rats with CHF induced by the placement of aortocaval fistula. Additionally, the chronic effects of Ang 1-7 (24 µg/kg/h, via intra-peritoneally implanted osmotic minipumps) on kidney function, cardiac hypertrophy and neurohormonal status were studied. Acute infusion of either Ang 1-7 or its agonist, AVE 0991, into sham controls, but not CHF rats, increased UF, UNaV, GFR, RPF and urinary cGMP. In the chronic protocols, untreated CHF rats displayed lower cumulative UF and UNaV than their sham controls. Chronic administration of Ang 1-7 and AVE 0991 exerted significant diuretic, natriuretic and kaliuretic effects in CHF rats, but not in sham controls. Serum creatinine and aldosterone levels were significantly higher in vehicle-treated CHF rats as compared with controls. Treatment with Ang 1-7 and AVE 0991 reduced these parameters to comparable levels observed in sham controls. Notably, chronic administration of Ang 1-7 to CHF rats reduced cardiac hypertrophy. In conclusion, Ang 1-7 exerts beneficial renal and cardiac effects in rats with CHF. Thus, we postulate that ACE2/Ang 1-7 axis represents a compensatory response to over-activity of ACE/AngII/AT1R system characterizing CHF and suggest that Ang 1-7 may be a potential therapeutic agent in this disease state.

Recent studies using propensity score matching have clearly indicated that contrast nephropathy following computed tomography occurs in hospitalized patients with advanced chronic kidney disease (eGFR < 30 ml/min/1.73 m(2)) and that this iatrogenic complication is likely underestimated because of concomitant renal functional recovery, unrelated to the imaging procedure. These findings should be considered regarding contrast-enhanced studies in such patients.