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The coronavirus disease 2019 (COVID-19) pandemic is associated with significant morbidity and mortality throughout the world, predominantly due to lung and cardiovascular injury. The virus responsible for COVID-19—severe acute respiratory syndrome coronavirus 2—gains entry into host cells via ACE2 (angiotensin-converting enzyme 2). ACE2 is a primary enzyme within the key counter-regulatory pathway of the renin-angiotensin system (RAS), which acts to oppose the actions of Ang (angiotensin) II by generating Ang-(1–7) to reduce inflammation and fibrosis and mitigate end organ damage. As COVID-19 spans multiple organ systems linked to the cardiovascular system, it is imperative to understand clearly how severe acute respiratory syndrome coronavirus 2 may affect the multifaceted RAS. In addition, recognition of the role of ACE2 and the RAS in COVID-19 has renewed interest in its role in the pathophysiology of cardiovascular disease in general. We provide researchers with a framework of best practices in basic and clinical research to interrogate the RAS using appropriate methodology, especially those who are relatively new to the field. This is crucial, as there are many limitations inherent in investigating the RAS in experimental models and in humans. We discuss sound methodological approaches to quantifying enzyme content and activity (ACE, ACE2), peptides (Ang II, Ang-[1–7]), and receptors (types 1 and 2 Ang II receptors, Mas receptor). Our goal is to ensure appropriate research methodology for investigations of the RAS in patients with severe acute respiratory syndrome coronavirus 2 and COVID-19 to ensure optimal rigor and reproducibility and appropriate interpretation of results from these investigations.

During the spread of the severe acute respiratory syndrome coronavirus-2, some reports of data still emerging and in need of full analysis indicate that certain groups of patients are at risk of COVID-19. This includes patients with hypertension, heart disease, diabetes mellitus, and clearly the elderly. Many of those patients are treated with renin-angiotensin system blockers. Because the ACE2 (angiotensin-converting enzyme 2) protein is the receptor that facilitates coronavirus entry into cells, the notion has been popularized that treatment with renin-angiotensin system blockers might increase the risk of developing a severe and fatal severe acute respiratory syndrome coronavirus-2 infection. The present article discusses this concept. ACE2 in its full-length form is a membrane-bound enzyme, whereas its shorter (soluble) form circulates in blood at very low levels. As a mono-carboxypeptidase, ACE2 contributes to the degradation of several substrates including angiotensins I and II. ACE (angiotensin-converting enzyme) inhibitors do not inhibit ACE2 because ACE and ACE2 are different enzymes. Although angiotensin II type 1 receptor blockers have been shown to upregulate ACE2 in experimental animals, the evidence is not always consistent and differs among the diverse angiotensin II type 1 receptor blockers and differing organs. Moreover, there are no data to support the notion that ACE inhibitor or angiotensin II type 1 receptor blocker administration facilitates coronavirus entry by increasing ACE2 expression in either animals or humans. Indeed, animal data support elevated ACE2 expression as conferring potential protective pulmonary and cardiovascular effects. In summary, based on the currently available evidence, treatment with renin-angiotensin system blockers should not be discontinued because of concerns with coronavirus infection.

Despite evidence of multiorgan tropism of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in patients with coronavirus disease 2019 (COVID-19), direct viral kidney invasion has been difficult to demonstrate. The question of whether SARS-CoV2 can directly infect the kidney is relevant to the understanding of pathogenesis of AKI and collapsing glomerulopathy in patients with COVID-19. Methodologies to document SARS-CoV-2 infection that have been used include immunohistochemistry, immunofluorescence, RT-PCR, in situ hybridization, and electron microscopy. In our review of studies to date, we found that SARS-CoV-2 in the kidneys of patients with COVID-19 was detected in 18 of 94 (19%) by immunohistochemistry, 71 of 144 (49%) by RT-PCR, and 11 of 84 (13%) by in situ hybridization. In a smaller number of patients with COVID-19 examined by immunofluorescence, SARS-CoV-2 was detected in 10 of 13 (77%). In total, in kidneys from 102 of 235 patients (43%), the presence of SARS-CoV-2 was suggested by at least one of the methods used. Despite these positive findings, caution is needed because many other studies have been negative for SARS-CoV-2 and it should be noted that when detected, it was only in kidneys obtained at autopsy. There is a clear need for studies from kidney biopsies, including those performed at early stages of the COVID-19–associated kidney disease. Development of tests to detect kidney viral infection in urine samples would be more practical as a noninvasive way to evaluate SARS-CoV-2 infection during the evolution of COVID-19–associated kidney disease.

Proximal renal tubular acidosis (RTA) is caused by a defect in bicarbonate (HCO3−) reabsorption in the kidney proximal convoluted tubule. It usually manifests as normal anion-gap metabolic acidosis due to HCO3− wastage. In a normal kidney, the thick ascending limb of Henle’s loop and more distal nephron segments reclaim all of the HCO3− not absorbed by the proximal tubule. Bicarbonate wastage seen in type II RTA indicates that the proximal tubular defect is severe enough to overwhelm the capacity for HCO3− reabsorption beyond the proximal tubule. Proximal RTA can occur as an isolated syndrome or with other impairments in proximal tubular functions under the spectrum of Fanconi syndrome. Fanconi syndrome, which is characterized by a defect in proximal tubular reabsorption of glucose, amino acids, uric acid, phosphate, and HCO3−, can occur due to inherited or acquired causes. Primary inherited Fanconi syndrome is caused by a mutation in the sodium-phosphate cotransporter (NaPi-II) in the proximal tubule. Recent studies have identified new causes of Fanconi syndrome due to mutations in the EHHADH and the HNF4A genes. Fanconi syndrome can also be one of many manifestations of various inherited systemic diseases, such as cystinosis. Many of the acquired causes of Fanconi syndrome with or without proximal RTA are drug-induced, with the list of causative agents increasing as newer drugs are introduced for clinical use, mainly in the oncology field.

Angiotensin-converting enzyme II (ACE2) is a homologue of angiotensin-converting enzyme discovered in 2000. From the initial discovery, it was recognized that the kidneys were organs very rich on ACE2. Subsequent studies demonstrated the precise localization of ACE2 within the kidney and the importance of this enzyme in the metabolism of Angiotensin II and the formation of Angiotensin 1–7. With the recognition early in 2020 of ACE2 being the main receptor of severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2), the interest in this protein has dramatically increased. In this review, we will focus on kidney ACE2; its localization, its alterations in hypertension, diabetes, the effect of ACE inhibitors and angiotensin type 1 receptor blockers (ARBs) on ACE2 and the potential use of ACE2 recombinant proteins therapeutically for kidney disease. We also describe the emerging kidney manifestations of COVID-19, namely the frequent development of acute kidney injury. The possibility that binding of SARS-CoV-2 to kidney ACE2 plays a role in the kidney manifestations is also briefly discussed.

Angiotensin converting enzyme 2 (ACE2) plays an important role in inflammation, which is attributable at least, in part, to the conversion of the pro‐inflammatory angiotensin (Ang) II peptide into angiotensin 1‐7 (Ang 1‐7), a peptide which opposes the actions of AngII. ACE2 and AngII are present in many tissues but information on the cornea is lacking. We observed that mice deficient in the Ace2 gene (Ace2−/−), developed a cloudy cornea phenotype as they aged. Haze occupied the central cornea, accompanied by corneal edema and neovascularization. In severe cases with marked chronic inflammation, a cell‐fate switch from a transparent corneal epithelium to a keratinized, stratified squamous, psoriasiform‐like epidermis was observed. The stroma contained a large number of CD11c, CD68, and CD3 positive cells. Corneal epithelial debridement experiments in young ACE2‐deficient mice showed normal appearing corneas, devoid of haze. We hypothesized, however, that these mice are “primed” for a corneal inflammatory response, which once initiated, would persist. In vitro studies reveal that interleukins (IL‐1a, IL‐1b), chemokines (CCL2, CXCL8), and TNF‐α, are all significantly elevated, resulting in a cytokine storm‐like phenotype. This phenotype could be partially rescued by treatment with the AngII type 1 receptor (AT1R) antagonist, losartan, suggesting that the observed effect was mediated by AngII acting on its main receptor. Since the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) utilizes human ACE2 as the receptor for entry with subsequent downregulation of ACE2, corneal inflammation in Ace2−/− mice may have a similar mechanism with that in COVID‐19 patients. Thus the Ace2−/− cornea, because of easy accessibility, may provide an attractive model to explore the molecular mechanisms, immunological changes, and treatment modalities in patients with COVID‐19.

Distal renal tubular acidosis (DRTA) is defined as hyperchloremic, non-anion gap metabolic acidosis with impaired urinary acid excretion in the presence of a normal or moderately reduced glomerular filtration rate. Failure in urinary acid excretion results from reduced H+ secretion by intercalated cells in the distal nephron. This results in decreased excretion of NH4 + and other acids collectively referred as titratable acids while urine pH is typically above 5.5 in the face of systemic acidosis. The clinical phenotype in patients with DRTA is characterized by stunted growth with bone abnormalities in children as well as nephrocalcinosis and nephrolithiasis that develop as the consequence of hypercalciuria, hypocitraturia, and relatively alkaline urine. Hypokalemia is a striking finding that accounts for muscle weakness and requires continued treatment together with alkali-based therapies. This review will focus on the mechanisms responsible for impaired acid excretion and urinary potassium wastage, the clinical features, and diagnostic approaches of hypokalemic DRTA, both inherited and acquired. Fil: Garramuño, Patricia. Universidad del Aconcagua. Facultad de Ciencias Médicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Medicina y Biología Experimental de Cuyo; Argentina Fil: Battle, Daniel. Northwestern University; Estados Unidos

In this commentary we emphasize the renoprotective effect of cyclic angiotensin-(1-7) described by Cassis et al. in a mouse model of diabetic kidney disease. The importance of the study is that this peptide was even more protective than the angiotensin-converting enzyme inhibitor lisinopril administered alone and that when the 2 componds were combined, the renoprotective action was additive.

The pathways implicated in diabetic kidney disease (DKD) are largely derived from animal models. To examine if alterations in renin-angiotensin system (RAS) in humans are concordant with those in rodent models, we measured concentration of angiotensinogen (AOG), cathepsin D (CTSD), angiotensin-converting enzyme (ACE), and ACE2 and enzymatic activities of ACE, ACE2, and aminopeptidase-A in FVB mice 13–20 wk after treatment with streptozotocin ( n = 9) or vehicle ( n = 15) and people with long-standing type 1 diabetes, with ( n = 37) or without ( n = 81) DKD. In streptozotocin-treated mice, urine AOG and CTSD were 10.4- and 3.0-fold higher than in controls, respectively ( P < 0.001). Enzymatic activities of ACE, ACE2, and APA were 6.2-, 3.2-, and 18.8-fold higher, respectively, in diabetic animals ( P < 0.001). Angiotensin II was 2.4-fold higher in diabetic animals ( P = 0.017). Compared with people without DKD, those with DKD had higher urine AOG (170 vs. 15 μg/g) and CTSD (147 vs. 31 μg/g). In people with DKD, urine ACE concentration was 1.8-fold higher (1.4 vs. 0.8 μg/g in those without DKD), while its enzymatic activity was 0.6-fold lower (1.0 vs. 1.6 × 109RFU/g in those without DKD). Lower ACE activity, but not ACE protein concentration, was associated with ACE inhibitor (ACEI) treatment. After adjustment for clinical covariates, AOG, CTSD, ACE concentration, and ACE activity remained associated with DKD. In conclusion, in mice with streptozotocin-induced diabetes and in humans with DKD, urine concentrations and enzymatic activities of several RAS components are concordantly increased, consistent with enhanced RAS activity and greater angiotensin II formation. ACEI use was associated with a specific reduction in urine ACE activity, not ACE protein concentration, suggesting that it may be a marker of exposure to this widely-used therapy.

Early recognition of acute kidney injury (AKI) is critical to prevent its associated complications as well as its progression to long term adverse outcomes like chronic kidney disease. A growing body of evidence from both laboratory and clinical studies suggests that inflammation is a key factor contributing to the progression of AKI regardless of the initiating event. Biomarkers of inflammation are therefore of interest in the evaluation of AKI pathogenesis and prognosis. There is evidence that the renin angiotensin aldosterone system is activated in AKI, which leads to an increase in angiotensin II (Ang II) formation within the kidney. Ang II activates pro-inflammatory and pro-fibrotic pathways that likely contribute to the progression of AKI. Angiotensinogen is the parent polypeptide from which angiotensin peptides are formed and its stability in urine makes it a more convenient marker of renin angiotensin system activity than direct measurement of Ang II in urine specimens, which would provide more direct information. The potential utility of urinary angiotensinogen as a biomarker of AKI is discussed in light of emerging data showing a strong predictive value of AKI progression, particularly in the setting of decompensated heart failure. The prognostic significance of urinary angiotensinogen as an AKI biomarker strongly suggests a role for renin–angiotensin system activation in modulating the severity of AKI and its outcomes.

Blockers of the renin-angiotensin system are effective in the treatment of experimental and clinical diabetic nephropathy. An approach different from blocking the formation or action of angiotensin II (1-8) that could also be effective involves fostering its degradation. Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that cleaves angiotensin II (1-8) to form angiotensin (1-7). Therefore, we examined the renal effects of murine recombinant ACE2 in mice with streptozotocin-induced diabetic nephropathy as well as that of amplification of circulating ACE2 using minicircle DNA delivery prior to induction of experimental diabetes. This delivery resulted in a long-term sustained and profound increase in serum ACE2 activity and enhanced ability to metabolize an acute angiotensin II (1-8) load. In mice with streptozotocin-induced diabetes pretreated with minicircle ACE2, ACE2 protein in plasma increased markedly and this was associated with a more than 100-fold increase in serum ACE2 activity. However, minicircle ACE2 did not result in changes in urinary ACE2 activity as compared to untreated diabetic mice. In both diabetic groups, glomerular filtration rate increased significantly and to the same extent as compared to non-diabetic controls. Albuminuria, glomerular mesangial expansion, glomerular cellularity, and glomerular size were all increased to a similar extent in minicircle ACE2-treated and untreated diabetic mice, as compared to non-diabetic controls. Recombinant mouse ACE2 given for 4 weeks by intraperitoneal daily injections in mice with streptozotocin-induced diabetic nephropathy also failed to improve albuminuria or kidney pathology. Thus, a profound augmentation of ACE2 confined to the circulation failed to ameliorate the glomerular lesions and hyperfiltration characteristic of early diabetic nephropathy. These findings emphasize the importance of targeting the kidney rather than the circulatory renin angiotensin system to combat diabetic nephropathy.

A 30-year-old man, who had moved to the United Kingdom from South Asia, was referred to the renal clinic with nephrotic syndrome. He had recently been diagnosed with systemic lupus erythematosus (SLE) after presenting to the rheumatology clinic with joint pain, skin rash, and pleuritic chest pain and fulfilling 8 of 17 SLICC (Systemic Lupus International Collaborating Clinics) diagnostic criteria.1 His immunology was in keeping with active SLE: his complement levels were low, and he had antibodies against double-stranded DNA and extractable nuclear antigens (Table S1A in the online-only Data Supplement). Our patient had heavy proteinuria (3.9 g/d) and a low serum albumin (25 g/L) in keeping with the nephrotic syndrome. Although his excretory renal function was normal, he had microhematuria (3+) on urinalysis. An urgent renal tract ultrasound with Doppler revealed that he had a preexistent renal vein thrombosis for which he was anticoagulated. In the absence of any serological evidence of antiphospholipid syndrome, this was attributed to his nephrotic syndrome. He went on to have a renal biopsy. This demonstrated classes III (focal proliferative) and V (membranous) lupus nephritis (Figure 1). Figure 1. Initial glomerular histology. A , Normal glomerulus. Single arrow: Normal capillary wall. This should be a similar thickness to the tubular epithelium (arrowhead). Double arrow: Normal mesangium. B , Classes III (focal proliferative) and V (membranous) lupus nephritis. Single arrow: Thickened capillary wall. Double arrow: Focal proliferation. At presentation, his blood pressure (BP) was 126/88 mm Hg in the absence of antihypertensive treatment. Although this lay within both UK and US recommended guidelines, …

Ogilvie's syndrome, or acute colonic pseudo-obstruction, is characterized by massive dilation of the colon without mechanical obstruction. Water and electrolytes often can be sequestered in the dilated intestinal loops resulting in profuse and watery diarrhea as well as hypokalemia. We report an anuric, end-stage renal disease (ESRD) patient undergoing peritoneal dialysis (PD) who developed acute colonic pseudo-obstruction causing a prolonged hospitalization. He also developed severe hypokalemia with a serum potassium (K+) as low as 2.4 mEq/L and required 180 - 240 mEq of potassium chloride per day for more than a month to correct it. While PD K+ losses often contribute to hypokalemia, the PD K+ loss was estimated to be only 39 mEq/day. Therefore, PD could only contribute modestly to the recalcitrant hypokalemia observed during the episode of pseudo-obstruction. It has been shown, however, that patients with colonic pseudo-obstruction have enhanced colonic K+ secretion. In addition, experimental studies in patients with chronic kidney disease (CKD) have demonstrated that colonic K+ excretion can be up to 3 times greater than in individuals with normal renal function. This increase may involve an upregulation of the large conductance K+ channel (maxi-K), also known as the BK channel, in the apical border of the colonocytes. We suggest that ESRD may have placed our patient at a greater risk of developing hypokalemia as his colon may have already adapted to secrete more K+. Clinicians should be aware of this extrarenal K+ wasting etiology in patients with colonic pseudo-obstruction, particularly in those with CKD where such a severe K+ deficit is not anticipated and, therefore, may inhibit more rigorous K+ replacement.

Prolylcarboxypeptidase (PRCP) is a carboxypeptidase that cleaves angiotensin II (AngII) forming Ang(1-7). The impact of genetic PRCP deficiency on AngII metabolism, blood pressure (BP), kidney histology, and cardiac phenotype was investigated in two lines of PRCP-deficient mice: KST302 derived in C57BL/6 background and GST090 derived in FVB/N background. The GST090 line had increased mean arterial pressure (MAP) (113.7 ± 2.07 vs. WT 105.0 ± 1.23 mmHg; p 0.01) and left ventricular hypertrophy (LVH) (ratio of diastolic left ventricular posterior wall dimension to left ventricular diameter 0.239 ± 0.0163 vs. WT 0.193 ± 0.0049; p 0.05). Mice in the KST302 line also had mild hypertension and LVH. Cardiac defects, increased glomerular size, and glomerular mesangial expansion were also observed. After infusion of AngII to mice in the KST302 line, both MAP and LVH increased, but the constitutive differences between the gene trap mice and controls were no longer observed. Plasma and cardiac AngII and Ang(1-7) were not significantly different between PRCP-deficient mice and controls. Thus, PRCP deficiency is associated with elevated blood pressure and cardiac alterations including LVH and cardiac defects independently of systemic or cardiac AngII and Ang(1-7). An ex vivo assay showed that recombinant PRCP, unlike recombinant ACE2, did not degrade AngII to form Ang(1-7) in plasma at pH 7.4. PRCP was localized in α-intercalated cells of the kidney collecting tubule. The low pH prevailing at this site and the acidic pH preference of PRCP suggest a role of this enzyme in regulating AngII degradation in the collecting tubule where this peptide increases sodium reabsorption and therfore BP. However, there are other potential mechanisms for increased BP in this model that need to be considered as well. PRCP converts AngII to Ang(1-7) but only at an acidic pH. Global PRCP deficiency causes heart and kidney alterations and a moderate rise in BP. PRCP is abundant in the kidney collecting tubules, where the prevailing pH is low. In collecting tubules, PRCP deficiency could result in impaired AngII degradation. Increased AngII at this nephron site stimulates Na reabsorption and increases BP.Prolylcarboxypeptidase (PRCP) converts AngII to Ang (1-7) but only at an acidic pH. Global PRCP deficiency causes heart and kidney alterations and a moderate rise in BP. PRCP is abundant in the kidney collecting tubules, where the prevailing pH is low. In collecting tubules, PRCP deficiency could result in impaired AngII degradation. Increased AngII at this nephron site stimulates Na reabsorption and increases BP.

We examined if urinary angiotensinogen (uAOG), a marker of intrarenal renin‐angiotensin system activity, antedates stage 3 chronic kidney disease (CKD) using samples from participants in the Diabetes Control and Complications Trial (DCCT) and later in the Epidemiology of Diabetes Intervention and Complications (EDIC) trial. In a nested case–control design, cases were matched at the outcome visit (eGFR less than 60, 21‐59 mL/min per 1.73 m2) on age, gender, and diabetes duration, with controls: eGFR (95, 75‐119, mL/min per 1.73 m2.) Additionally, in an exploratory analysis progressive renal decline (PRD), defined as eGFR loss >3.5 mL/min per 1.73m2/year, was evaluated using only data from EDIC because no progressions were observed during DCCT. At the EDIC visit, which antedated the GFR outcome visit by 2 years (range 1–7years) the median uAOG/creatinine was markedly higher in cases than in controls (13.9 vs. 3.8 ng/mg P = 0.003) whereas at the DCCT visit, which antedated the GFR outcome by 17 to 20 years it was not (2.75 vs. 3.16 ng/mg, respectively). The Odds Ratio for uAOG and CKD stage 3 development was significant after adjusting for eGFR, HbA1c, and systolic blood pressure 1.82 (1.00–3.29) but no longer significant when Albumin Excretion Ratio (AER) was included 1.21 (0.65–2.24).In the PRD analysis, uAOG/creatinine was sixfold higher in participants who experienced PRD than in those who did not (26 vs. 4.0 ng/mg, P = 0.003). The Odds Ratio for uAOG and PRD was significant after adjusting for eGFR, HbA1c, and systolic blood pressure 2.48 (1.46–4.22) but no longer significant when AER was included 1.32 (0.76–2.30). In people with type1 diabetes, a robust increase in uAOG antedates the development of stage 3 CKD but is not superior to AER in predicting this renal outcome. Increased uAOG moreover is associated with PRD, an index of progression to End Stage Kidney Disease (ESKD).

ACE2 is an enzyme with a molecular size of more than 100 kDa which produces Angiotensin (1-7) from Angiotensin II (1-8). Attempts to target kidney RAS using ACE2 to treat kidney disease are hampered by its large molecular size which precludes its glomerular filtration and subsequent tubular uptake. We tested two ACE2 truncates (1-605 and 1-619AA) that we generated through truncation from the C terminus. ACE2 enzyme activity measured using Mca-APK-Dnp substrate was as high for each of them as native rACE2 (1-740 AA). The two truncates had an apparent MW of ~70 kDa, as expected from the amino acid sequence, as shown by western blot. For radioimaging each purified truncate was labeled with 99m Tc to study kidney uptake. After i.v. injection of Tc99m -labeled rACE2, there was kidney cortex retention for Tc99m 1-605 [8.6±0.7% of whole body (WB) radioactivity] and for Tc99m 1-619 (4.2±2.1% WB) as compared to only trace retention after injection of native Tc99m -rACE2 1-740 (1.2±0.2% WB)(figure). When infused to mice with genetic ACE2 deficiency, a single i.v. injection of 1-619 resulted in detectable ACE2 activity in urine and kidneys (23.1±4.3 and 1.96±0.73 RFU/ug prot/hr, respectively). In addition, the kidneys of ACE2-nul mice infused with 1-619 studied ex vivo formed more Ang (1-7) from exogenous Ang II than those of uninfused animals (p We conclude that our novel ACE2 truncates undergo glomerular filtration which is associated with kidney uptake of enzymatically active protein that can enhance formation of Angiotensin 1-7 from Angiotensin II (1-8). These truncates may offer a potentially useful approach to target kidney RAS overactivity to combat kidney disease.

In patients with diabetic kidney disease (DKD), plasma renin activity is usually decreased, but there is limited information on urinary renin and its origin. Urinary renin was evaluated in samples from patients with longstanding type I diabetes mellitus and mice with streptozotocin-induced diabetes mellitus. Renin-reporter mouse model (Ren1d-Cre;mT/ mG) was made diabetic with streptozotocin to examine whether the distribution of cells of the renin lineage was altered in a chronic diabetic environment. Active renin was increased in urine samples from patients with DKD (n=36), compared with those without DKD (n=38; 3.2 versus 1.3 pg/mg creatinine; P

ACE2 is a monocarboxypeptidase which generates Angiotensin (1&ndash, 7) from Angiotensin II (1&ndash, 8). Attempts to target the kidney Renin Angiotensin System using native ACE2 to treat kidney disease are hampered by its large molecular size, 100 kDa, which precludes its glomerular filtration and subsequent tubular uptake. Here, we show that both urine and kidney lysates are capable of digesting native ACE2 into shorter proteins of ~60&ndash, 75 kDa and then demonstrate that they are enzymatically very active. We then truncated the native ACE2 by design from the C-terminus to generate two short recombinant (r)ACE2 variants (1-605 and 1-619AA). These two truncates have a molecular size of ~70 kDa, as expected from the amino acid sequence and as shown by Western blot. ACE2 enzyme activity, measured using a specific substrate, was higher than that of the native rACE2 (1-740 AA). When infused to mice with genetic ACE2 deficiency, a single i.v. injection of 1-619 resulted in detectable ACE2 activity in urine, whereas infusion of the native ACE2 did not. Moreover, ACE2 activity was recovered in harvested kidneys from ACE2-deficient mice infused with 1-619, but not in controls (23.1 &plusmn, 4.3 RFU/&micro, g creatinine/h and 1.96 &plusmn, 0.73 RFU/&micro, g protein/hr, respectively). In addition, the kidneys of ACE2-null mice infused with 1-619 studied ex vivo formed more Ang (1&ndash, 7) from exogenous Ang II than those infused with vehicle (AUC 8555 &plusmn, 1933 vs. 3439 &plusmn, 753 ng/mL, respectively, p &lt, 0.05) further demonstrating the functional effect of increasing kidney ACE2 activity after the infusion of our short ACE2 1-619 variant. We conclude that our novel short recombinant ACE2 variants undergo glomerular filtration, which is associated with kidney uptake of enzymatically active proteins that can enhance the formation of Ang (1&ndash, 7) from Ang II. These small ACE2 variants may offer a potentially useful approach to target kidney RAS overactivity to combat kidney injury.

In contrast to distal type I or classic renal tubular acidosis (RTA) that is associated with hypokalemia, hyperkalemic forms of RTA also occur usually in the setting of mild-to-moderate CKD. Two pathogenic types of hyperkalemic metabolic acidosis are frequently encountered in adults with underlying CKD. One type, which corresponds to some extent to the animal model of selective aldosterone deficiency (SAD) created experimentally by adrenalectomy and glucocorticoid replacement, is manifested in humans by low plasma and urinary aldosterone levels, reduced ammonium excretion, and preserved ability to lower urine pH below 5.5. This type of hyperkalemic RTA is also referred to as type IV RTA. It should be noted that the mere deficiency of aldosterone when glomerular filtration rate is completely normal only causes a modest decline in plasma bicarbonate which emphasizes the importance of reduced glomerular filtration rate in the development of the hyperchloremic metabolic acidosis associated with SAD. Another type of hyperkalemic RTA distinctive from SAD in which plasma aldosterone is not reduced is referred to as hyperkalemic distal renal tubular acidosis because urine pH cannot be reduced despite acidemia or after provocative tests aimed at increasing sodium-dependent distal acidification such as the administration of sodium sulfate or loop diuretics with or without concurrent mineralocorticoid administration. This type of hyperkalemic RTA (also referred to as voltage-dependent distal renal tubular acidosis) has been best described in patients with obstructive uropathy and resembles the impairment in both hydrogen ion and potassium secretion that are induced experimentally by urinary tract obstruction and when sodium transport in the cortical collecting tubule is blocked by amiloride.

Cyclophilins (Cyp) are peptidil-prolyl-isomerases and the intracellular receptors for the immunosuppressant Cyclosporine-A (CsA), which produces epithelial-mesenchymal-transition (EMT) and renal tubule-interstitial fibrosis. Since CsA inhibits Cyp enzymatic activity, we hypothesized that Cyp could be involved in EMT and fibrosis. Here, we demonstrate that CypB is a critical regulator of tubule epithelial cell plasticity on the basis that: i) CypB silencing caused epithelial differentiation in proximal tubule-derived HK-2 cells, ii) CypB silencing prevented TGFβ-induced EMT in HK-2, and iii) CypB knockdown mice exhibited reduced UUO-induced inflammation and kidney fibrosis. By contrast, silencing of CypA induces a more undifferentiated phenotype and favors TGFβ effects. EMT mediators Slug and Snail were up-regulated in CypA-silenced cells, while in CypB silencing, Slug, but not Snail, was down-regulated; thus, reinforcing the role of Slug in kidney fibrosis. CypA regulates Slug through its PPIase activity whereas CypB depends on its ER location, where interacts with calreticulin, a calcium modulator which is involved in TGFβ signaling. In conclusion, this work uncovers new roles for CypA and CypB in modulating proximal tubular cell plasticity.

RATIONALE & OBJECTIVE: Determining whether a change in estimated glomerular filtration rate (eGFR) or albuminuria is clinically significant requires knowledge of short-term within-person variability of the measurements, which few studies have addressed in the setting of chronic kidney disease. STUDY DESIGN: Cross-sectional study with multiple collections over less than 4 weeks. SETTING & PARTICIPANTS: Clinically stable outpatients with chronic kidney disease (N = 50; mean age, 56.8 years; median eGFR, 40 mL/min/1.73 m(2); median urinary albumin-creatinine ratio (UACR), 173 mg/g). EXPOSURE: Repeat measurements from serially collected samples across 3 study visits. OUTCOMES: Measurements of urine albumin concentration (UAC), UACR, and plasma creatinine, cystatin C, β(2)-microglobulin (B2M), and beta trace protein (BTP). ANALYTICAL APPROACH: We calculated within-person coefficients of variation (CV(w)) values and corresponding reference change positive and negative (RCV(pos) and RCV(neg)) values using log-transformed measurements. RESULTS: Median CV(w) (RCV(pos); RCV(neg)) values of filtration markers were 5.4% (+16%; –14%) for serum creatinine, 4.1% (+12%; –11%) for cystatin C, 7.4% (+23%; –18%) for BTP, and 5.6% (+17%; –14%) for B2M. Results for albuminuria were 33.2% (+145%; –59%) for first-morning UAC, 50.6% (+276%; –73%) for random spot UAC, 32.5% (+141%; –58%) for first-morning UACR, and 29.7% (124%; –55%) for random spot UACR. CV(w) values for filtration markers were comparable across the range of baseline eGFRs. CV(w) values for UAC and UACR were comparable across the range of baseline albuminuria values. LIMITATIONS: Small sample size limits the ability to detect differences in variability across markers. Participants were recruited and followed up in a clinical and not research setting, so some preanalytical factors could not be controlled. CONCLUSIONS: eGFR markers appear to have relatively low short-term within-person variability, whereas variability in albuminuria appears to be high, making it difficult to distinguish random variability from meaningful biologic changes.

Angiotensin-converting enzyme 2 (ACE2) is a carboxypeptidase that potently degrades angiotensin II to angiotensin 1-7. Previous studies showed that injection of the enzymatic ectodomain of recombinant ACE2 (rACE2) markedly increases circulatory levels of ACE2 activity, and effectively lowered blood pressure in angiotensin II-induced hypertension. However, due to the short plasma half-life of rACE2, its therapeutic potential for chronic use is limited. To circumvent this, we generated a chimeric fusion of rACE2 and the immunoglobulin fragment Fc segment to increase its plasma stability. This rACE2-Fc fusion protein retained full peptidase activity and exhibited greatly extended plasma half-life in mice, from less than two hours of the original rACE2, to over a week. A single 2.5 mg/kg injection of rACE2-Fc increased the overall angiotensin II-conversion activities in blood by up to 100-fold and enhanced blood pressure recovery from acute angiotensin II induced hypertension seven days after administration. To assess rACE2-Fc given weekly on cardiac protection, we performed studies in mice continuously infused with angiotensin II for 28 days and in a Renin transgenic mouse model of hypertension. The angiotensin II infused mice achieved sustained blood pressure control and reduced cardiac hypertrophy and fibrosis. In chronic hypertensive transgenic mice, weekly injections of rACE2-Fc effectively lowered plasma angiotensin II and blood pressure. Additionally, rACE2-Fc ameliorated albuminuria, and reduced kidney and cardiac fibrosis. Thus, our chimeric fusion strategy for rACE2-Fc is suitable for future development of new renin angiotensin system-based inhibition therapies.

Acid-base homeostasis by the kidney is maintained through proximal tubular reclamation of filtered bicarbonate and the excretion of the daily acid load by collecting duct type A intercalated cells. The impairment of either process results in renal tubular acidosis (RTA), a group of disorders characterized by a reduced net acid excretion and a persistent hyperchloremic, non–anion gap metabolic acidosis. The primary or hereditary forms of proximal (pRTA) and distal renal tubular acidosis (dRTA) have received increased attention because of advances in the understanding of the molecular mechanism, whereby mutations in the main proteins involved in acid-base transport result in either reduced bicarbonate reabsorption or reduced H+ secretion and impaired acid excretion. dRTA is characterized by reduced net acid excretion and an inability to lower urine pH despite severe acidemia (but minimal HCO3– wastage). pRTA (type 2), by contrast, is characterized by marked HCO3– wastage but preserved ability to lower urine pH when plasma HCO3– (and therefore filtered HCO3–) is below a certain threshold. In children with dRTA, growth retardation caused by chronic metabolic acidosis is the key manifestation but is fully reversible with appropriate alkali therapy if initiated early in life. A striking manifestation of many patients with dRTA is the development of severe hypokalemia that may cause muscle paralysis. In this review, we discuss these types of hereditary RTA and the mechanisms involved in the genesis of these inherited tubular disorders. This review contains 5 figures, 1 table, and 103 references. Key words: Proximal renal tubular acidosis (pRTA), Distal renal tubular acidosis (dRTA), Hyperchloremic, non–anion gap metabolic acidosis, Hypokalemia, Fractional HCO3– excretion, Urinary gap, Fanconi Syndrome.ATP6V1B1 and ATP6V0A4 gene mutations . Intercalated cells

Hypobicarbonatemia, or a reduced bicarbonate concentration in plasma, is a finding seen in 3 acid-base disorders: metabolic acidosis, chronic respiratory alkalosis and mixed metabolic acidosis and chronic respiratory alkalosis. Hypobicarbonatemia due to chronic respiratory alkalosis is often misdiagnosed as a metabolic acidosis and mistreated with the administration of alkali therapy. Proper diagnosis of the cause of hypobicarbonatemia requires integration of the laboratory values, arterial blood gas, and clinical history. The information derived from the urinary response to the prevailing acid-base disorder is useful to arrive at the correct diagnosis. We discuss the use of urine anion gap, as a surrogate marker of urine ammonium excretion, in the evaluation of a patient with low plasma bicarbonate concentration to differentiate between metabolic acidosis and chronic respiratory alkalosis. The interpretation and limitations of urine acid-base indexes at bedside (urine pH, urine bicarbonate, and urine anion gap) to evaluate urine acidification are discussed.

Angiotensin-converting enzyme-2 (ACE2) enhances the degradation of ANG II and its expression is altered in diabetic kidneys, but the regulation of this enzyme in the urine is unknown. Urinary ACE2 was studied in the db/db model of type 2 diabetes and stretozotocin (STZ)-induced type 1 diabetes during several physiological and pharmacological interventions. ACE2 activity in db/db mice was increased in the serum and to a much greater extent in the urine compared with db/m controls. Neither a specific ANG II blocker, telmisartan, nor an ACE inhibitor, captopril, altered the levels of urinary ACE2 in db/db or db/m control mice. High-salt diet (8%) increased whereas low-salt diet (0.1%) decreased urinary ACE2 activity in the urine of db/db mice. In STZ mice, urinary ACE2 was also increased, and insulin decreased it partly but significantly after several weeks of administration. The increase in urinary ACE2 activity in db/db mice reflected an increase in enzymatically active protein with two bands identified of molecular size at 110 and 75 kDa and was associated with an increase in kidney cortex ACE2 protein at 110 kDa but not at 75 kDa. ACE2 activity was increased in isolated tubular preparations but not in glomeruli from db/db mice. Administration of soluble recombinant ACE2 to db/m and db/db mice resulted in a marked increase in serum ACE2 activity, but no gain in ACE2 activity was detectable in the urine, further demonstrating that urinary ACE2 is of kidney origin. Increased urinary ACE2 was associated with more efficient degradation of exogenous ANG II (10−9 M) in urine from db/db compared with that from db/m mice. Urinary ACE2 could be a potential biomarker of increased metabolism of ANG II in diabetic kidney disease.

Proximal renal tubular acidosis (RTA) (Type II RTA) is characterized by a defect in the ability to reabsorb HCO(3) in the proximal tubule. This is usually manifested as bicarbonate wastage in the urine reflecting that the defect in proximal tubular transport is severe enough that the capacity for bicarbonate reabsorption in the thick ascending limb of Henle's loop and more distal nephron segments is overwhelmed. More subtle defects in proximal bicarbonate transport likely go clinically unrecognized owing to compensatory reabsorption of bicarbonate distally. Inherited proximal RTA is more commonly autosomal recessive and has been associated with mutations in the basolateral sodium-bicarbonate cotransporter (NBCe1). Mutations in this transporter lead to reduced activity and/or trafficking, thus disrupting the normal bicarbonate reabsorption process of the proximal tubules. As an isolated defect for bicarbonate transport, proximal RTA is rare and is more often associated with the Fanconi syndrome characterized by urinary wastage of solutes like phosphate, uric acid, glucose, amino acids, low-molecular-weight proteins as well as bicarbonate. A vast array of rare tubular disorders may cause proximal RTA but most commonly it is induced by drugs. With the exception of carbonic anhydrase inhibitors which cause isolated proximal RTA, drug-induced proximal RTA is associated with Fanconi syndrome. Drugs that have been recently recognized to cause severe proximal RTA with Fanconi syndrome include ifosfamide, valproic acid and various antiretrovirals such as Tenofovir particularly when given to human immunodeficiency virus patients receiving concomitantly protease inhibitors such as ritonavir or reverse transcriptase inhibitors such as didanosine.

A major challenge in early treatment of acute cardiorenal syndrome (CRS) is the lack of predictors for progression of AKI. We aim to investigate the utility of urinary angiotensinogen and other renal injury biomarkers in predicting AKI progression in CRS.In this prospective, multicenter study, we screened 732 adults who admitted for acute decompensated heart failure from September 2011 to December 2014, and evaluated whether renal injury biomarkers measured at time of AKI diagnosis can predict worsening of AKI. In 213 patients who developed Kidney Disease Improving Global Outcomes stage 1 or 2 AKI, six renal injury biomarkers, including urinary angiotensinogen (uAGT), urinary neutrophil gelatinase-associated lipocalin (uNGAL), plasma neutrophil gelatinase-associated lipocalin, urinary IL-18 (uIL-18), urinary kidney injury molecule-1, and urinary albumin-to-creatinine ratio, were measured at time of AKI diagnosis. The primary outcome was AKI progression defined by worsening of AKI stage (50 patients). The secondary outcome was AKI progression with subsequent death (18 patients).After multivariable adjustment, the highest tertile of three urinary biomarkers remained associated with AKI progression compared with the lowest tertile: uAGT (odds ratio [OR], 10.8; 95% confidence interval [95% CI], 3.4 to 34.7), uNGAL (OR, 4.7; 95% CI, 1.7 to 13.4), and uIL-18 (OR, 3.6; 95% CI, 1.4 to 9.5). uAGT was the best predictor for both primary and secondary outcomes with area under the receiver operating curve of 0.78 and 0.85. These three biomarkers improved risk reclassification compared with the clinical model alone, with uAGT performing the best (category-free net reclassification improvement for primary and secondary outcomes of 0.76 [95% CI, 0.46 to 1.06] and 0.93 [95% CI, 0.50 to 1.36]; P0.001). Excellent performance of uAGT was further confirmed with bootstrap internal validation.uAGT, uNGAL, and uIL-18 measured at time of AKI diagnosis improved risk stratification and identified CRS patients at highest risk of adverse outcomes.

The evaluation of metabolic acidosis requires an assessment of the kidneys response in terms of acid excretion and bicarbonate excretion. Because of bedside measurements of ammonium excretion and bicarbonate are often not available because clinical laboratories do not perform these tests routinely, surrogates like the urine anion gap were developed as an indirect measure of the ammonium excretion. Bicarbonate can be calculated based on the urine pH and PCO2 of the urine. The significance and limitations of the urine pH as an index of collecting tubule H+ secretion as discussed. Moreover, the use of provocative tests such as the furosemide test as a tool to assess sodium dependent collecting tubule H+ secretion is also discussed.

Evaluation of a presumed metabolic acidosis begins with the clinical history and assessment of potential causes of decreased plasma bicarbonate levels. Calculation of the plasma anion gap is the initial step in the evaluation of metabolic acidosis. The type of metabolic acidosis present can be initially approached by assessing whether plasma anion gap (AG) is normal or elevated and helps differentiate hyperchloremic metabolic acidosis (normal AG) from high AG metabolic acidosis. The relationship between the increase in the anion gap above normal ΔAG and the decrease in serum bicarbonate concentration below normal ΔHCO3 helps uncover the presence of a mixed acid–base disorders. Deviations from the presumed 1:1 ratio in this relationship that is present in a high AG metabolic acidosis can be used to diagnose complex mixed acid–base disorders.

The primary or hereditary forms of distal renal tubular acidosis (dRTA) have received increased attention because of advances in the understanding of the molecular mechanism, whereby mutations in the main proteins involved in acid-base transport result in impaired acid excretion. Dysfunction of intercalated cells in the collecting tubules accounts for all the known genetic causes of dRTA. These cells secrete protons into the tubular lumen through H(+)-ATPases functionally coupled to the basolateral anion exchanger 1 (AE1). The substrate for both transporters is provided by the catalytic activity of the cytosolic carbonic anhydrase II (CA II), an enzyme which is also present in the proximal tubular cells and osteoclasts. Mutations in ATP6V1B1, encoding the B-subtype unit of the apical H(+) ATPase, and ATP6V0A4, encoding the a-subtype unit, lead to the loss of function of the apical H(+) ATPase and are usually responsible for patients with autosomal recessive dRTA often associated with early or late sensorineural deafness. Mutations in the gene encoding the cytosolic CA II are associated with the autosomal recessive syndrome of osteopetrosis, mixed distal and proximal RTA and cerebral calcification. Mutations in the AE1, the gene that encodes the Cl(-)/HCO(3)(-) exchanger, usually present as dominant dRTA, but a recessive pattern has been recently described. Several studies have shown trafficking defects in the mutant protein rather than the lack of function as the major mechanism underlying the pathogenesis of dRTA from AE1 mutations.

Angiotensin-converting enzyme 2 (ACE2) degrades angiotensin II to angiotensin-(1–7) and is expressed in podocytes. Here we overexpressed ACE2 in podocytes in experimental diabetic nephropathy using transgenic methods where a nephrin promoter drove the expression of human ACE2. Glomeruli from these mice had significantly increased mRNA, protein, and activity of ACE2 compared to wild-type mice. Male mice were treated with streptozotocin to induce diabetes. After 16 weeks, there was no significant difference in plasma glucose levels between wild-type and transgenic diabetic mice. Urinary albumin was significantly increased in wild-type diabetic mice at 4 weeks, whereas albuminuria in transgenic diabetic mice did not differ from wild-type nondiabetic mice. However, this effect was transient and by 16 weeks both transgenic and nontransgenic diabetic mice had similar rates of proteinuria. Compared to wild-type diabetic mice, transgenic diabetic mice had an attenuated increase in mesangial area, decreased glomerular area, and a blunted decrease in nephrin expression. Podocyte numbers decreased in wild-type diabetic mice at 16 weeks, but were unaffected in transgenic diabetic mice. At 8 weeks, kidney cortical expression of transforming growth factor-β1 was significantly inhibited in transgenic diabetic mice as compared to wild-type diabetic mice. Thus, the podocyte-specific overexpression of human ACE2 transiently attenuates the development of diabetic nephropathy.

Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that degrades angiotensin II with high efficiency leading to the formation of angiotensin-(1–7). ACE2 within the kidneys is largely localized in tubular epithelial cells and in glomerular epithelial cells. Decreased glomerular expression of this enzyme coupled with increased expression of ACE has been described in diabetic kidney disease, both in mice and humans with type 2 diabetes. Moreover, both ACE2 genetic ablation and pharmacological ACE2 inhibition have been shown to increase albuminuria and promote glomerular injury. Studies using recombinant ACE2 have shown the ability of ACE2 to rapidly metabolize Ang II in vivo and form the basis for future studies to examine the potential of ACE2 amplification in the therapy of diabetic kidney disease and cardiovascular disease.

Page kidney refers to a clinical picture characterized by acute onset of hypertension due to external compression of the kidneys from hematoma, tumor, lymphocele, or urinoma. Hypertension is believed to result from renin-angiotensin-aldosterone activation triggered by renal hypoperfusion and microvascular ischemia. Renal failure, in addition to hypertension, may occur in the setting of a single functional kidney or a diseased contralateral kidney. We report a case of a patient who had a transplant kidney biopsy complicated by a subcapsular perinephric hematoma. The patient presented with an acute increase in blood pressure and a rapid rise in serum creatinine following a transplant kidney routine biopsy. He underwent emergent evacuation of the perinephric hematoma, with consequent decrease of his blood pressure and return of serum creatinine back to his baseline level. Early recognition and rapid intervention are needed in order to correct hypertension and reverse acute renal failure in Page kidney occurring in renal transplant recipients.

Background. Antagonists of relevant Gs protein-coupled and agonists of relevant Gi protein-coupled receptors lower renal cAMP and inhibit growth of renal cysts in animal models of human ARPKD (PCK rat) and/or ADPKD (Pkd2−/WS25 mouse). A calcium-sensing receptor (CaR) is expressed in various tubular segments and couples to Gq, thereby activating phospholipase Cγ, InsP3 generation and calcium mobilization from intracellular stores, and Gi proteins. By both mechanisms, CaR activation could lower intracellular cAMP and inhibit renal cyst growth. Methods. PCK rat and Pkd2−/WS25 mouse littermates were fed rodent chow without or with R-568, a type 2 calcimimetic, at a concentration of 0.05% or 0.1% between 3 and 10 or 16 weeks of age. Histomorphometric analysis was performed with Meta-Morph software. Western analysis and immunohistochemical staining were performed using antibodies for aquaporin-2, urea transporter UT-A1 and CaR. Northern blot hybridization was used to quantify the expression of vasopressin V2 receptor and aquaporin 2 mRNAs. Cyclic AMP was measured using an enzyme immunoassay kit. Results. R-568 had no effect on kidney weight, cyst volume, plasma BUN concentration or severity of the polycystic liver disease. A significant reduction in renal interstitial fibrosis was detected in PCK rats, but not in Pkd2−/WS25 mice. R-568 administration, as anticipated, resulted in hypocalcemia and hyperphosphatemia, and significant increases in urine output, osmolar clearance, and urinary excretions of sodium, potassium and calcium. Conclusions. CaR activation had no detectable effect on cystogenesis in models of autosomal recessive or dominant polycystic kidney disease. The lack of protective effect could be due to the absence of CaR in the outer medullary and cortical collecting ducts, the reduction in extracellular calcium and the unaffected levels of renal cAMP and renal expression of cAMP-dependent genes. A possible beneficial effect on interstitial fibrosis deserves further study at more advanced stages of the disease.

The renin-angiotensin system (RAS) plays a key role in the regulation of cardiovascular and renal function. Thus, RAS blockade with an angiotensin-converting enzyme (ACE) and/or angiotensin receptor blocker decreases blood pressure, cardiovascular events, and delays the progression of kidney disease. The discovery of ACE2, a homologue of ACE, capable of degrading angiotensin II to angiotensin 1-7, may offer new insights into the RAS. In this review we discuss the possible protective role of ACE2 in different organs, namely heart, lungs and kidneys. The role of this enzyme is inferred from recent studies performed using genetically manipulated mice that lack the ACE2 gene and also mice treated with pharmacological ACE2 inhibitors. These results suggest that ACE2 might be a new therapeutic target within the RAS.

Whereas angiotensin-converting enzyme promotes the formation of angiotensin II, angiotensin-converting enzyme 2 promotes the degradation of angiotensin II to angiotensin-(1-7). We review recent studies dealing with angiotensin-converting enzyme 2 in kidney disease and hypertension, and discuss the potential therapeutic benefit of increasing angiotensin-converting enzyme 2 activity in the treatment of these diseases.In glomeruli from diabetic mice, angiotensin-converting enzyme 2 expression is downregulated, and pharmacological inhibition of angiotensin-converting enzyme 2 leads to worsening of albuminuria, increased mesangial matrix deposition and fibronectin expression. The deletion of the angiotensin-converting enzyme 2 gene in mice leads to worsening of angiotensin II-induced hypertension and has also been shown to cause glomerulosclerosis in aging male mice.Angiotensin-converting enzyme 2 is a key enzyme in the renin-angiotensin system that favors the degradation of angiotensin I and angiotensin II. Angiotensin-converting enzyme 2 inhibition by pharmacological means and by genetic deletion worsens kidney disease in diabetic mice. Strategies geared to increasing angiotensin-converting enzyme 2 activity may provide a novel therapeutic target within the renin-angiotensin system by enhancing angiotensin II degradation that may complement the current approach of inhibiting angiotensin II formation and action. Amplifying angiotensin-converting enzyme 2 activity may have a potential therapeutic role for kidney disease and hypertension.

The discovery of angiotensin-converting enzyme (ACE) 2 adds a new level of complexity to the understanding of the renin-angiotensin system. The high catalytic efficiency of ACE2 for the generation of angiotensin (ANG)-1-7 from ANG II suggests an important role of ACE2 in preventing ANG II accumulation, while at the same time enhancing ANG-1-7 formation. ACE and ACE2 may have counterbalancing functions and a regulatory role in fine-tuning the rate at which ANG peptides are formed and degraded. By counterregulating the actions of ACE on ANG II formation, ACE2 may play a role in maintaining a balanced status of the renninangiotensin system. This review focuses on the function of ACE2 and its possible roles in kidney disease and hypertension. Studies using models of ACE2 ablation and the pharmacologic administration of an ACE2 inhibitor suggest that decreased ACE2 activity alone or in combination with increased ACE activity may play a role in both diseases.

Angiotensin converting enzyme 2 (ACE2) is localized to the glomerular epithelial cells. Since ACE2 promotes the degradation of angiotensin II, a decrease in ACE2 activity could lead to the development of glomerular injury. We gave a specific ACE2 inhibitor, MLN-4760, for 4 weeks to mice rendered diabetic with streptozotocin. The urinary albumin/creatinine ratio was increased along with expansion of the glomerular matrix in diabetic mice treated with the inhibitor compared to the vehicle-treated mice. Glomerular staining of ACE was increased in the diabetic group and was further significantly increased in the diabetic group treated with MLN-4760. In renal vessels, ACE expression was also increased in the diabetic mice and, again, further increased in those diabetic mice treated with the ACE2 inhibitor. Our study shows that chronic pharmacologic ACE2 inhibition worsens glomerular injury in streptozotocin-induced diabetic mice in association with increased ACE expression.

This study examines whether stabilization of the glomerular filtration rate (GFR) is possible in patients with advanced chronic kidney disease (CKD), managed in a CKD clinic. A cohort of 82 patients with stages 4 and 5 CKD was followed for a period of 2 years after initiation of erythropoietin for anemia to determine the GFR and the frequency of primary outcomes (dialysis, transplantation, or death). GFR, calculated by the abbreviated Modification of Diet in Renal Disease formula, was determined every 3 months. After 24 months, 35 subjects (43%) developed a primary outcome. Controlled for other risk factors, the risk of having a primary outcome increased 19.7% for every unit that the GFR decreased (95% confidence interval [CI], 11.9%-26.8%, P.001) and decreased 21.7% for every unit that the hemoglobin increased (95% CI, 0.5%-38.4%, P.001). Blacks had a 3.1 times higher risk (95% CI, 1.4-6.9, P = .006) of developing a primary outcome than other ethnicities. In subjects who did not develop primary outcomes (n = 47 or 57%), GFR remained unchanged (19.5 +/- 9.1 at the end of the study v 20.8 +/- 5.3 mL/min/1.73 m(2) at baseline, P = .16). The standardized mortality rate was 4.75 and 9.77 per 100 person-year for stages 4 and 5, respectively. We conclude that stabilization of GFR over a 2-year period can be achieved in many patients with advanced CKD treated with erythropoietin in a CKD clinic. Although the precise reason for the stabilization of GFR cannot be elucidated from this study, our data are "proof of concept" that CKD outcomes can be improved in a CKD clinic setting.

The possible occurrence of metabolic acidosis in patients with intestinal ileus is not well recognized. We describe a patient with acute alcohol-induced pancreatitis and a large transverse colon ileus in which plasma bicarbonate dropped rapidly in the absence of an increase in the plasma anion gap. The urinary anion gap and ammonium excretion were consistent with an appropriate renal response to metabolic acidosis and against the possibility of respiratory alkalosis. The cause of the falling plasma bicarbonate was ascribed to intestinal bicarbonate sequestration owing to the enhancement of chloride-bicarbonate exchange in a dilated paralyzed colon.

Pigment Epithelium Derived Factor (PEDF) encoded by SERPINF1 gene has potent anti-angiogenic and cytoprotective activities. It has been reported that PEDF protein levels are reduced in the kidneys of rodents with experimentally induced diabetes. However the effect of PEDF on blood pressure has not been elucidated. Here, we used SERPINF1 KO mice to examine the impact of PEDF deficiency on kidney pathology and blood pressure in the STZ-induced mouse model of diabetes. Twelve weeks after diabetes induction by STZ, SERPINF1 KO mice showed exacerbated glomerular damage with ~ 2-fold increase in mesangial matrix (2.8±0.14 vs. 1.2±0.14 arbitrary units, p Our data indicate that global PEDF deficiency intensifies glomerular injury in STZ-induced mouse model of diabetes. An important drawback of most murine models of diabetic kidney disease is the lack of hypertension, a known key factor that accelerates progression to CKD in humans. In contrast, we found that STZ-treated SERPINF1-/- mice become hypertensive. Together, our findings point to SERPINF1-/- mice as an attractive model to study diabetic kidney disease and hypertension in mice and suggest an important causative role of PEDF downregulation in glomerular pathology in diabetes.

See related article, pp 389–395 Left ventricular hypertrophy is the most common cardiac complication of hypertension. Although the initial adaptations associated with cardiac hypertrophy are compensatory, ultimately abnormal ventricular function including diastolic dysfunction (impaired relaxation) and often heart failure may develop.1 Activation of the renin–angiotensin system and its main effector peptide angiotensin II (Ang II), acting on the Ang II type 1 receptor, has been considered an important part of the cascade leading to left ventricular hypertrophy and cardiac fibrosis.1,2 Recent work, however, examining the effects of Ang II infusion using cardiomyocyte and vascular smooth muscle–specific Ang II type 1 receptor knockouts suggests that the hypertension-induced increase in afterload, rather than direct Ang II–Ang II type 1 receptor signaling in the heart, is the key factor that promotes hypertrophic responses.2 The renin–angiotensin system peptide Ang-(1–7), which is generated from Ang II by the action of carboxypeptidases, such as ACE2,3 exhibits actions that are mainly opposite to those of Ang II, including vasodilatory and antifibrotic effects.4 In this issue, Machado de Almeida et al5 report a series of interesting observations that suggest that in an Ang-(1–7) transgenic line, TGR(A1–7)3292, there is cardioprotection from deoxycorticosterone acetate (DOCA)–salt induced hypertension which is independent of blood pressure. The latter conclusion is not unexpected considering the strong evidence against an antihypertensive effect of Ang-(1–7): (1) acute infusions of supraphysiologic concentrations of this peptide do not lower blood pressure in mice,3 (2) a 4-week continuous infusion of Ang-(1–7) did not decrease blood pressure in DOCA-treated Sprague-Dawley (SD) rats,6 (3) acutely Ang-(1–7) does not attenuate the hypertensive effect of infused Ang II, and a blocker …

Background andobjectivesThecalcimimeticcinacalcet reduced therisk of death or cardiovascular (CV) events in older, but not younger, patients with moderate to severe secondary hyperparathyroidism (HPT) who were receiving hemodialysis. To determine whether the lower risk in younger patients might be due to lower baseline CV risk and more frequent use of cointerventions that reduce parathyroid hormone (kidney transplantation, parathyroidectomy, and commercial cinacalcet use), this study examined the effects of cinacalcet in older ($65 years, n=1005) and younger (,65 years, n=2878) patients. Design, setting, participants, & measurements Evaluation of Cinacalcet HCl Therapy to Lower Cardiovascular Events (EVOLVE) was a global, multicenter, randomized placebo-controlled trial in 3883 prevalent patients on hemodialysis, whose outcomes included death, major CV events, and development of severe unremitting HPT. The age subgroup analysis was prespecified. ResultsOlderpatients hadhigher baselineprevalenceof diabetesmellitusandCV comorbidity. Annualizedrates of kidney transplantation and parathyroidectomy were .3-fold higher in younger relative to older patients and were more frequent in patients randomized to placebo. In older patients, the adjusted relative hazard (95% confidence interval) for the primary composite (CV) end point (cinacalcet versus placebo) was 0.70 (0.60 to 0.81); in younger patients, the relative hazard was 0.97 (0.86 to 1.09). Corresponding adjusted relative hazards for mortality were 0.68 (0.51 to 0.81) and 0.99 (0.86 to 1.13). Reduction in the risk of severe unremitting HPT was similar in both groups. Conclusions In the EVOLVE trial, cinacalcet decreased the risk of death and of major CV events in older, but not younger, patients with moderate to severe HPT who were receiving hemodialysis. Effect modification by age may be partly explained by differences in underlying CV risk and differential application of cointerventions that reduce parathyroid hormone. Clin J Am Soc Nephrol 10: ccc–ccc, 2015. doi: 10.2215/CJN.07730814

It has been generally held that once glomerular filtration rate (GFR) falls below approximately 25ml/min, a relentless progression to end-stage renal disease (ESRD) inevitably ensues, regardless of the original cause of reduced function. There is a paucity of contemporary studies, however, addressing whether the rate of progression can be slowed down with contemporary and comprehensive renal care when chronic kidney disease (CKD) has progressed to stages 4 and 5 (GFR 2 ). In this review we argue that significant progress is being made already in retarding the progression of advanced CKD thereby delaying the initiation of renal replacement therapy. We propose that CKD clinics, by providing comprehensive management of CKD, will have a decisive role in preventing and delaying the progression to advanced CKD.

ACE-related carboxypeptidase (ACE2) may counterbalance the angiotensin (ANG) II–promoting effects of ACE in tissues where both enzymes are found. Alterations in renal ACE and ACE2 expression have been described in experimental models of diabetes, but ACE2 activity was not assessed in previous studies. We developed a microplate-based fluorometric method for the concurrent determination of ACE and ACE2 activity in tissue samples. Enzymatic activity (relative fluorescence unit [RFU] · μg protein−1 · h−1) was examined in ACE and ACE2 knockout mice and in two rodent models of diabetes, the db/db and streptozotocin (STZ)-induced diabetic mice. In kidney cortex, preparations consisting mainly of proximal tubules and cortical collecting tubules, ACE2 activity had a strong positive correlation with ACE2 protein expression (90-kDa band) in both knockout models and their respective wild-type littermates (r = 0.94, P < 0.01). ACE activity, likewise, had a strong positive correlation with renal cortex ACE protein expression (170-kDa band) (r = 0.838, P < 0.005). In renal cortex, ACE2 activity was increased in both models of diabetes (46.7 ± 4.4 vs. 22.0 ± 4.7 in db/db and db/m, respectively, P < 0.01, and 22.1 ± 2.8 vs. 13.1 ± 1.5 in STZ-induced diabetic versus untreated mice, respectively, P < 0.05). ACE2 mRNA levels in renal cortex from db/db and STZ-induced diabetic mice, by contrast, were not significantly different from their respective controls. In cardiac tissue, ACE2 activity was lower than in renal cortex, and there were no significant differences between diabetic and control mice (db/db 2.03 ± 0.23 vs. db/m 1.85 ± 0.10; STZ-induced diabetic 0.42 ± 0.04 vs. untreated 0.52 ± 0.07 mice). ACE2 activity in renal cortex correlated positively with ACE2 protein in db/db and db/m mice (r = 0.666, P < 0.005) as well as in STZ-induced diabetic and control mice (r = 0.621, P < 0.05) but not with ACE2 mRNA (r = −0.468 and r = −0.522, respectively). We conclude that in renal cortex from diabetic mice, ACE2 expression is increased at the posttranscriptional level. The availability of an assay for concurrent measurement of ACE and ACE2 activity should be helpful in the evaluation of kidney-specific alterations in the balance of these two carboxypeptidases, which are involved in the control of local ANG II formation and degradation.