Critical Role of Neprilysin in Kidney Angiotensin Metabolism.

RATIONALE: Kidney homeostasis is critically determined by the coordinated activity of the renin-angiotensin system (RAS), including the balanced synthesis of its main effector peptides Ang (angiotensin) II and Ang (1-7). The condition of enzymatic overproduction of Ang II relative to Ang (1-7) is termed RAS dysregulation and leads to cellular signals, which promote hypertension and organ damage, and ultimately progressive kidney failure. ACE2 (angiotensin-converting enzyme 2) and NEP (neprilysin) induce the alternative, and potentially reno-protective axis by enhancing Ang (1-7) production. However, their individual contribution to baseline RAS balance and whether their activities change in chronic kidney disease (CKD) has not yet been elucidated. OBJECTIVE: To examine whether NEP-mediated Ang (1-7) generation exceeds Ang II formation in the healthy kidney compared with diseased kidney. METHODS AND RESULTS: In this exploratory study, we used liquid chromatography-tandem mass spectrometry to measure Ang II and Ang (1-7) synthesis rates of ACE, chymase and NEP, ACE2, PEP (prolyl-endopeptidase), PCP (prolyl-carboxypeptidase) in kidney biopsy homogenates in 11 healthy living kidney donors, and 12 patients with CKD. The spatial expression of RAS enzymes was determined by immunohistochemistry. Healthy kidneys showed higher NEP-mediated Ang (1-7) synthesis than Ang II formation, thus displaying a strong preference towards the reno-protective alternative RAS axis. In contrast, in CKD kidneys higher levels of Ang II were recorded, which originated from mast cell chymase activity. CONCLUSIONS: Ang (1-7) is the dominant RAS peptide in healthy human kidneys with NEP rather than ACE2 being essential for its generation. Severe RAS dysregulation is present in CKD dictated by high chymase-mediated Ang II formation. Kidney RAS enzyme analysis might lead to novel therapeutic approaches for CKD.

Combined sodium glucose co-transporter-2 inhibitor and angiotensin-converting enzyme inhibition upregulates the renin-angiotensin system in chronic kidney disease with type 2 diabetes: Results of a randomized, double-blind, placebo-controlled exploratory trial.

AIM: Sodium glucose co-transporter-2 inhibitors (SGLT-2i) improve cardiorenal outcomes in patients with chronic kidney disease (CKD), with and without type 2 diabetes. The molecular mechanisms underlying these pleiotropic effects remain unclear, yet it is speculated that SGLT-2i elicit a neurohormonal modulation resulting in renin-angiotensin system (RAS) activation. We hypothesized that combined SGLT-2 and angiotensin-converting enzyme inhibition (ACEi) favours RAS regulation towards the beneficial angiotensin-(1-7)-driven axis. MATERIALS AND METHODS: This randomized controlled prospective study investigated the effect of 12 weeks treatment with the SGLT-2i empagliflozin on top of ACEi on the molecular RAS dynamics in 24 diabetic and 24 non-diabetic patients with CKD. Systemic RAS peptides were quantified by mass spectrometry. RESULTS: In patients with type 2 diabetes, combined SGLT-2i and ACEi significantly upregulated plasma renin activity [pre-treatment median and interquartile range 298.0 (43.0-672.0) pmol/L versus post-treatment 577.0 (95.0-1543.0) pmol/L; p = .037] and angiotensin I levels [pre-treatment 289.0 (42.0-668.0) pmol/L versus post-treatment 573.0 (93.0-1522.0) pmol/L; p = .037], together with a significant increase of angiotensin-(1-7) levels [pre-treatment 14.0 (2.1-19.0) pmol/L versus post-treatment 32.0 (5.7-99.0) pmol/L; p = .012]. Empagliflozin treatment resulted in a 1.5 to 2-fold increase in main RAS peptides in patients with diabetes compared with placebo. No significant effect of empagliflozin on top of ACEi on RAS peptides was found in patients with CKD without diabetes. CONCLUSION: A distinct RAS modulation by SGLT-2i occurs in diabetic kidney disease reflected by enhancement of the beneficial angiotensin-(1-7) providing a molecular background for this renoprotective therapeutic approach.

HDL Cholesterol Efflux Does Not Predict Cardiovascular Risk in Hemodialysis Patients.

The cardioprotective effect of HDL is thought to be largely determined by its cholesterol efflux capacity, which was shown to inversely correlate with atherosclerotic cardiovascular disease in populations with normal kidney function. Patients with ESRD suffer an exceptionally high cardiovascular risk not fully explained by traditional risk factors. Here, in a post hoc analysis in 1147 patients with type 2 diabetes mellitus on hemodialysis who participated in the German Diabetes Dialysis Study (4D Study), we investigated whether the HDL cholesterol efflux capacity is predictive for cardiovascular risk. Efflux capacity was quantified by incubating human macrophage foam cells with apoB-depleted serum. During a median follow-up of 4.1 years, 423 patients reached the combined primary end point (composite of cardiac death, nonfatal myocardial infarction, and stroke), 410 patients experienced cardiac events, and 561 patients died. Notably, in Cox regression analyses, we found no association of efflux capacity with the combined primary end point (hazard ratio [HR], 0.96; 95% confidence interval [95% CI], 0.88 to 1.06; P=0.42), cardiac events (HR, 0.92; 95% CI, 0.83 to 1.02; P=0.11), or all-cause mortality (HR, 0.96; 95% CI, 0.88 to 1.05; P=0.39). In conclusion, HDL cholesterol efflux capacity is not a prognostic cardiovascular risk marker in this cohort of patients with diabetes on hemodialysis.

Ig-like transcript 4 as a cellular receptor for soluble complement fragment C4d.

Complement regulation leads to the generation of complement split products (CSPs) such as complement component (C)4d, a marker for disease activity in autoimmune syndromes or antibody-mediated allograft rejection. However, the physiologic role of C4d has been unknown. By screening murine thymoma BW5147 cells expressing a cDNA library generated from human monocyte-derived dendritic cells with recombinant human C4d, we identified Ig-like transcript (ILT)4 and ILT5v2 as cellular receptors for C4d. Both receptors, expressed on monocytes, macrophages, and dendritic cells, also interacted with the CSPs C3d, C4b, C3b, and iC3b. However, C4d did not bind to classic complement receptors (CRs). Interaction between cell surface-resident ILT4 and soluble monomeric C4d resulted in endocytosis of C4d. Surprisingly, binding of soluble ILT4 to C4d covalently immobilized to a cellular surface following classic complement activation could not be detected. Remarkably, C4d immobilized to a solid phaseviaits intrinsic thioester conferred a dose-dependent inhibition of TNF-α and IL-6 secretion in monocytes activatedviaFc-cross-linking of up to 50% as compared to baseline. Similarly, C4d conferred an attenuation of intracellular Ca(2+)flux in monocytes activatedviaFc-cross-linking. In conclusion, ILT4 represents a scavenger-type endocytotic CR for soluble monomeric C4d, whereas attenuation of monocyte activation by physiologically oriented C4d on a surface appears to be dependent on a yet to be identified C4d receptor.-Hofer, J., Forster, F., Isenman, D. E., Wahrmann, M., Leitner, J., Hölzl, M. A., Kovarik, J. K., Stockinger, H., Böhmig, G. A., Steinberger, P., Zlabinger, G. J. Ig-like transcript 4 as a cellular receptor for soluble complement fragment C4d.

Heart Failure with Preserved and Reduced Ejection Fraction in Hemodialysis Patients: Prevalence, Disease Prediction and Prognosis.

BACKGROUND/AIMS: Heart failure (HF) is a main cause of mortality of hemodialysis (HD) patients. While HF with reduced ejection fraction (HFrEF) is known to only affect a minority of patients, little is known about the prevalence, associations with clinical characteristics and prognosis of HF with preserved ejection fraction (HFpEF). METHODS: We included 105 maintenance HD patients from the Medical University of Vienna into this prospective single-center cohort study and determined the prevalence of HFpEF (per the 2013 criteria of the European Society of Cardiology) and HFrEF (EF <45%), using standardized post-HD transthoracic echocardiography. We also assessed clinical, laboratory and volume status parameters (by bioimpedance spectroscopy). These parameters served to calculate prediction models for both disease entities, while clinical outcomes (frequency of cardiovascular hospitalizations and/or cardiac death) were assessed prospectively over 27±4 months of follow-up. RESULTS: All but 4 patients (96%) had evidence of diastolic dysfunction. 70% of the entire cohort fulfilled HF criteria (81% HFpEF, 19% HFrEF). Age, female sex, body mass index, blood pressure and dialysis vintage were predictive of HFpEF (sensitivity 86%, specificity 63%; AUC 0.87), while age, female sex, NT pro-BNP, history of coronary artery disease and atrial fibrillation were predictive of HFrEF (sensitivity 85%, specificity 90%; AUC 0.95). Compared to patients without HF, those with HFpEF and HFrEF had a higher risk of hospitalization for cardiovascular reason and/or cardiac death (adjusted HR 4.31, 95% CI 0.46-40.03; adjusted HR 3.24, 95% CI 1.08-9.75, respectively). CONCLUSION: Diastolic dysfunction and HFpEF are highly prevalent in HD patients while HFrEF only affects a minority. Distinct patient-specific characteristics predict diagnosis of either entity with good accuracy.

Restoration of renal function does not correct impairment of uremic HDL properties.

Cardiovascular disease remains the leading cause of death in renal transplant recipients, but the underlying causative mechanisms for this important problem remain elusive. Recent work has indicated that qualitative alterations of HDL affect its functional and compositional properties in ESRD. Here, we systematically analyzed HDL from stable renal transplant recipients, according to graft function, and from patients with ESRD to determine whether structural and functional properties of HDL remain dysfunctional after renal transplantation. Cholesterol acceptor capacity and antioxidative activity, representing two key cardioprotective mechanisms of HDL, were profoundly suppressed in kidney transplant recipients independent of graft function and were comparable with levels in patients with ESRD. Using a mass spectroscopy approach, we identified specific remodeling of transplant HDL with highly enriched proteins, including α-1 microglobulin/bikunin precursor, pigment epithelium-derived factor, surfactant protein B, and serum amyloid A. In conclusion, this study demonstrates that HDL from kidney recipients is uniquely altered at the molecular and functional levels, indicating a direct pathologic role of HDL that could contribute to the substantial cardiovascular risk in the transplant population.

Resveratrol enhances TNF-α production in human monocytes upon bacterial stimulation.

BACKGROUND: Resveratrol is a key component of red wine that has been reported to have anti-carcinogenic and anti-aging properties. Additional studies conducted in vitro and in animal models suggested anti-inflammatory properties. However, data from primary human immune cells and in vivo studies are limited. METHODS: A pilot study was performed including 10 healthy volunteers. Plasma cytokine levels were measured over 48h after oral application of 5g resveratrol. To verify the in vivo findings, cytokine release and gene expression in human peripheral blood mononuclear cells (PBMC) and/or monocytes was assessed after treatment with resveratrol or its metabolites and stimulation with several toll-like receptor (TLR)-agonists. Additionally, the impact on intracellular signaling pathways was analyzed using a reporter cell line and Western blotting. RESULTS: Resveratrol treated individuals showed a significant increase in tumor necrosis factor-α (TNF-α) levels 24h after treatment compared to baseline. Studies using human PBMC or isolated monocytes confirmed potentiation of TNF-α production with different TLR agonists, while interleukin (IL)-10 was inhibited. Moreover, we observed significantly enhanced nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NF-κB) activation using a reporter cell line and found increased phosphorylation of p105, which is indicative of alternative NF-κB pathway activation. GENERAL SIGNIFICANCE: By administering resveratrol to healthy humans and utilizing primary immune cells we were able to detect TNF-α enhancing properties of the agent. In parallel, we found enhanced alternative NF-κB activation. We report on a novel pro-inflammatory property of resveratrol which has to be considered in concepts of its biologic activity.

Molecular regulation of the renin-angiotensin system in haemodialysis patients.

BACKGROUND: Blockade of the renin-angiotensin system (RAS) exerts beneficial effects in patients with mild-to-moderate chronic kidney disease, yet evidence suggesting a similar benefit in haemodialysis (HD) patients is not available. Furthermore, knowledge of the effects of RAS blockade on systemic RAS components in HD patients is limited. Analysis of the quantity and dynamics of all known peripheral constituents of the RAS may yield important pathomechanistic information of a widespread therapeutic measure in HD patients. METHODS: Fifty-two HD patients from the following groups were analysed cross-sectionally: patients without RAS blockade (n = 16), angiotensin-converting enzyme inhibitor (ACEi) users (n = 8), angiotensin receptor blocker (ARB) users (n = 11), patients on ACEi plus ARB (dual blockade, n = 8) and anephric patients (n = 9). Ten healthy volunteers served as controls. Angiotensin metabolites were quantified by mass spectrometry. RESULTS: In general, HD patients showed a broad variability of RAS activity. Patients without RAS blockade displayed angiotensin metabolite patterns similar to healthy controls. ACEi therapy increased plasma Ang 1-10 and Ang 1-7 concentrations, whereas ARB treatment increased both Ang 1-8 and Ang 1-5, while suppressing Ang 1-7 to minimal levels. Dual RAS blockade resulted in high levels of Ang 1-10 and suppressed levels of other angiotensins. Anephric patients were completely devoid of detectable levels of circulating angiotensins. CONCLUSION: In HD patients, the activity status of the systemic RAS is highly distorted with the emergence of crucial angiotensin metabolites upon distinct RAS blockade. The characterization of molecular RAS patterns associated with specific RAS interfering therapies may help to individualize future clinical studies and therapies.

Eicosanoid modulation by the short-chain fatty acid n-butyrate in human monocytes.

n-Butyrate deriving from bacterial fermentation in the mammalian intestine is a key determinant in gastrointestinal homeostasis. We examined the effects of this short-chain fatty acid and Toll-like receptor 2 (TLR) and TLR4 engagement on inflammatory/immunity-associated genes, cyclo-oxygenases (COXs), prostaglandins (PGs) and leukotrienes (LTs) in human monocytes. Before RNA isolation, freshly isolated human monocytes were co-incubated for different time-points with 1 mm n-butyrate alone or in combination with bacterial stimuli. Based on a knowledge-driven approach, a signature of 180 immunity/inflammation-associated genes was picked and real-time PCR analysis was performed. Pathway analysis was carried out using a web-based database analysing program. Based on these gene expression studies the findings were evaluated at the protein/mediator level by Western blot analysis, FACS and ELISA. Following co-incubation with n-butyrate and lipopolysaccharide, key enzymes of the eicosanoid pathway, like PTGS2 (COX-2), TXS, ALOX5, LTA4H and LTC4S, were significantly up-regulated compared with stimulation with lipopolysaccharide alone. Furthermore, release of the lipid mediators PGE(2), 15d-PGJ(2), LTB(4) and thromboxane B(2) was increased by n-butyrate. Regarding signalling, n-butyrate had no additional effect on mitogen-activated protein kinase and interfered differently with early and late phases of nuclear factor-κB signalling. Our results suggest that among many other mediators of eicosanoid signalling n-butyrate massively induces PGE(2) production by increasing the expression of PTGS2 (COX-2) in monocytes following TLR4 and TLR2 activation and induces secretion of LTB(4) and thromboxane B(2). This underscores the role of n-butyrate as a crucial mediator of gut-specific immunity.

Fluid overload in hemodialysis patients: a cross-sectional study to determine its association with cardiac biomarkers and nutritional status.

BACKGROUND: Chronic fluid overload is associated with higher mortality in dialysis patients; however, the link with cardiovascular morbidity has not formally been established and may be influenced by subclinical inflammation. We hypothesized that a relationship exists between fluid overload and [i] cardiovascular laboratory parameter as well as between fluid overload and [ii] inflammatory laboratory parameters. In addition, we aimed to confirm whether volume status correlates with nutritional status. METHODS: We recorded baseline characteristics of 244 hemodialysis patients at three hemodialysis facilities in Vienna (Austria) and determined associations with volume measurements using the body composition monitor (Fresenius/Germany). In one facility comprising 126 patients, we further analyzed cardiovascular, inflammatory and nutritional parameters. RESULTS: We detected predialysis fluid overload (FO) in 39% of all patients (n = 95) with FO defined as ≥15% of extracellular water (ECW). In this subgroup, the absolute FO was 4.4 +/-1.5 L or 22.9 ± 4.8% of ECW. A sub-analysis of patients from one center showed that FO was negatively associated with body mass index (r = -0.371; p = <0.001), while serum albumin was significantly lower in fluid overloaded patients (p = 0.001). FO was positively associated with D-Dimer (r = 0.316; p = 0.001), troponin T (r = 0.325; p < 0.001), and N-terminal pro-B-type natriuretic peptide (r = 0.436; p < 0.001), but not with investigated inflammatory parameters. CONCLUSIONS: Fluid overload in HD patients was found to be lower in patients with high body mass index, indicating that dry weight was inadequately prescribed and/or difficult to achieve in overweight patients. The association with parameters of cardiovascular compromise and/or damage suggests that fluid overload is a biomarker for cardiovascular risk. Future studies should determine if this applies to patients prior to end-stage renal disease.

Abdominal Aortic Aneurysm Detection in Bioelectrical Impedance Cardiovascular Screenings-A Pilot Study.

Screening and diagnosing abdominal aortic aneurysms (AAA) are currently dependent on imaging studies such as ultrasound or computed tomography angiography. All imaging studies offer distinct advantages but also suffer from inherent limitations such as examiner dependency or ionizing radiation. Bioelectrical impedance analysis has previously been investigated with respect to its use in the detection of several cardiovascular and renal pathologies. The present pilot study assessed the feasibility of AAA detection based on bioimpedance analysis. In this single-center exploratory pilot study, measurements were conducted among three different cohorts: patients with AAA, end-stage renal disease patients without AAA, and healthy controls. The device used in the study, CombynECG, is an open-market accessible device for segmental bioelectrical impedance analysis. The data was preprocessed and used to train four different machine learning models on a randomized training sample (80% of the full dataset). Each model was then evaluated on a test set (20% of the full dataset). The total sample included 22 patients with AAA, 16 chronic kidney disease patients, and 23 healthy controls. All four models showed strong predictive performance in the test partitions. Specificity ranged from 71.4 to 100%, while sensitivity ranged from 66.7 to 100%. The best-performing model had 100% accuracy for classification when applied to the test sample. Additionally, an exploratory analysis to approximate the maximum AAA diameter was conducted. An association analysis revealed several impedance parameters that might possess predictive ability with respect to aneurysm size. AAA detection via bioelectrical impedance analysis is technically feasible and appears to be a promising technology for large-scale clinical studies and routine clinical screening assessments.

A multi-omics based anti-inflammatory immune signature characterizes long COVID-19 syndrome.

To investigate long COVID-19 syndrome (LCS) pathophysiology, we performed an exploratory study with blood plasma derived from three groups: 1) healthy vaccinated individuals without SARS-CoV-2 exposure; 2) asymptomatic recovered patients at least three months after SARS-CoV-2 infection and; 3) symptomatic patients at least 3 months after SARS-CoV-2 infection with chronic fatigue syndrome or similar symptoms, here designated as patients with long COVID-19 syndrome (LCS). Multiplex cytokine profiling indicated slightly elevated pro-inflammatory cytokine levels in recovered individuals in contrast to patients with LCS. Plasma proteomics demonstrated low levels of acute phase proteins and macrophage-derived secreted proteins in LCS. High levels of anti-inflammatory oxylipins including omega-3 fatty acids in LCS were detected by eicosadomics, whereas targeted metabolic profiling indicated high levels of anti-inflammatory osmolytes taurine and hypaphorine, but low amino acid and triglyceride levels and deregulated acylcarnitines. A model considering alternatively polarized macrophages as a major contributor to these molecular alterations is presented.

The zymogen granule protein 2 (GP2) binds to scavenger receptor expressed on endothelial cells I (SREC-I).

The pancreatic zymogen granule membrane protein (GP2) is expressed by pancreatic acinar cells and M cells of the ileum. GP2 is the closest related homologue of the urine resident Tamm-Horsfall protein (THP). Recently, it was shown that THP is a ligand of various scavenger receptors (SRs). Therefore, we were interested, if GP2 has similar properties. cDNA of different SRs was stably transfected into a murine thymoma cell line. GP2 was recombinantly expressed, purified and biotinylated. Binding or uptake of GP2 by transfected cells or monocyte-derived dendritic cells (moDCs) was analyzed by flow-cytometry. GP2 is a binding partner of the scavenger receptor expressed on endothelial cells I (SREC-I) but not of SR-AI and SR-BI. The dissociation constant (K(d)) of GP2 binding to SREC-I is 41.3nM. SREC transfected cells are able to internalize GP2. moDCs express SREC-I and also bind and internalize GP2. Inhibition of SREC-I on moDCs with anti-SREC-I antibodies does not result in a decreased GP2 binding. Interaction of GP2 with SREC-I and uptake might have profound effects in antigen clearance and mediation of the immune response. In addition to SREC-I other presently unknown receptors for GP2 on DCs might be involved in this process.

Impaired anti-inflammatory efficacy of n-butyrate in patients with IBD.

BACKGROUND: The intestinal mucosa of patients with inflammatory bowel diseases (IBD) characteristically shows a high degree of inflammation when compared to healthy subjects. This appears to be attributable to an imbalance in local reactivity of inflammatory cells. In the present study, we tested the hypothesis that immune cells from patients with IBD are less sensitive to anti-inflammatory agents in the gut as exemplified by the short-chain fatty acid (SCFA) n-butyrate. MATERIAL AND METHODS: Peripheral blood mononuclear cells (PBMC) of patients with IBD (22 Crohn`s Disease, CD; 9 Ulcerative Colitis, UC) and 20 healthy individuals were stimulated through TLR-4 and TLR-2 engagement, respectively, and the anti-inflammatory activity of n-butyrate (0·06-1 mM) on cytokine production (IL-1ß, IL-10, IL-12/23p40, TNF-α) was assessed. Inhibition curves were generated, and effective doses (ED20-ED80) were determined. RESULTS: Hyperresponsiveness to TLR-2 activation reflected by increased IL-12/23p40 and TNF-α production was observed in patients with IBD. To inhibit the release of IL-12/23p40 from PBMC after activation via TLR2-agonists, higher concentrations of n-butyrate were required in patients with IBD , when compared to healthy subjects. With regard to TLR-4 activation, PBMC from patients with IBD and controls were equally responsive to the immunoregulatory effects of n-butyrate. Further analysis revealed that the impaired sensitivity of PBMC to the anti-inflammatory action of n-butyrate was independent from hyperreactivity of immunocompetent cells. CONCLUSIONS: Impaired sensitivity to the inhibitory action of n-butyrate in IBD may constitute a determinant in the pathogenesis of these inflammatory diseases.

Effect of Mineralocorticoid Receptor Antagonism and ACE Inhibition on Angiotensin Profiles in Diabetic Kidney Disease: An Exploratory Study.

BACKGROUND: Renin-angiotensin-aldosterone system (RAAS) blockade with angiotensin-converting enzyme inhibitors (ACEi) or angiotensin receptor blockers (ARB) is the cornerstone of antihypertensive treatment in patients with chronic kidney disease (CKD) and diabetes mellitus. Mineralocorticoid receptor antagonists (MRA) on top of conventional RAAS blockade confer cardio- and renoprotective effects. Yet, the detailed effects of this therapeutic approach on key RAAS effectors have not been elucidated to date. METHODS: In this exploratory placebo-controlled study, 15 patients with CKD stages 2-3 and albuminuria due to diabetic kidney disease (DKD) were randomized to receive the MRA eplerenone or placebo in addition to ACEi therapy. Employing mass-spectrometry, we quantified plasma angiotensin levels [Ang I, Ang II, Ang-(1-7), Ang-(1-5), Ang III, Ang IV], renin and aldosterone in patients before and after 8 weeks of MRA treatment. RESULTS: While blood pressure and kidney function were similar in the placebo and eplerenone treatment group during the study period, distinct differences in RAAS regulation occurred: eplerenone treatment resulted in an increase in plasma renin activity, Ang I and aldosterone concentrations, indicating global RAAS activation. In addition, eplerenone on top of ACEi profoundly upregulated the alternative RAAS effector Ang-(1-7). CONCLUSIONS: Combined eplerenone and ACEi therapy increases Ang-(1-7) levels in patients with CKD indicating a unique nephroprotective RAAS pattern with considerable therapeutic implications.

Adaptive physiological water conservation explains hypertension and muscle catabolism in experimental chronic renal failure.

AIM: We have reported earlier that a high salt intake triggered an aestivation-like natriuretic-ureotelic body water conservation response that lowered muscle mass and increased blood pressure. Here, we tested the hypothesis that a similar adaptive water conservation response occurs in experimental chronic renal failure. METHODS: In four subsequent experiments in Sprague Dawley rats, we used surgical 5/6 renal mass reduction (5/6 Nx) to induce chronic renal failure. We studied solute and water excretion in 24-hour metabolic cage experiments, chronic blood pressure by radiotelemetry, chronic metabolic adjustment in liver and skeletal muscle by metabolomics and selected enzyme activity measurements, body Na+ , K+ and water by dry ashing, and acute transepidermal water loss in conjunction with skin blood flow and intra-arterial blood pressure. RESULTS: 5/6 Nx rats were polyuric, because their kidneys could not sufficiently concentrate the urine. Physiological adaptation to this renal water loss included mobilization of nitrogen and energy from muscle for organic osmolyte production, elevated norepinephrine and copeptin levels with reduced skin blood flow, which by means of compensation reduced their transepidermal water loss. This complex physiologic-metabolic adjustment across multiple organs allowed the rats to stabilize their body water content despite persisting renal water loss, albeit at the expense of hypertension and catabolic mobilization of muscle protein. CONCLUSION: Physiological adaptation to body water loss, termed aestivation, is an evolutionary conserved survival strategy and an under-studied research area in medical physiology, which besides hypertension and muscle mass loss in chronic renal failure may explain many otherwise unexplainable phenomena in medicine.

Identification of Immune Activation Markers in the Early Onset of COVID-19 Infection.

This study aimed to determine the specific cytokine profile in peripheral blood during the early onset of COVID-19 infection. This was a cross-sectional exploratory, single center study. A total of 55 plasma samples were studied. Serum samples of adults showing symptoms of COVID-19 infection who were tested positive for SARS-CoV-2 infection (CoV+, n=18) at the COVID-19 outpatient clinic of the Medical University of Vienna were screened for immune activation markers by Luminex technology. Additionally, age and gender-matched serum samples of patients displaying COVID-19 associated symptoms, but tested negative for SARS-CoV-2 (CoV-, n=16) as well as healthy controls (HC, n=21) were analyzed. COVID-19 positive (CoV+) patients showed a specific upregulation of BLC (141; 74-189 pg/mL), SCD30 (273; 207-576 pg/mL), MCP-2 (18; 12-30 pg/mL) and IP-10 (37; 23-96 pg/mL), compared to patients with COVID19-like symptoms but negative PCR test (CoV-), BLC (61; 22-100 pg/mL), sCD30L (161; 120-210 pg/mL), MCP-2 (8; 5-12 pg/mL) and IP-10 (9; 6-12 pg/mL) and healthy controls (HC) (BLC 22; 11-36 pg/mL, sCD30 74; 39-108 pg/mL, MCP-2 6; 3-9. pg/mL, IP-10 = 8; 5-13). The markers APRIL, sIL-2R, IL7, MIF, MIP-1b, SCF, SDF-1a, sTNF-RII were elevated in both CoV+ and CoV- patient groups compared to healthy controls. HGF, MDC and VEGF-A were elevated in CoV- but not CoV+ compared to healthy controls. BLC, sCD30, MCP-2 and IP-10 are specifically induced during early stages of COVID-19 infection and might constitute attractive targets for early diagnosis and treatment of this disease.

Intrarenal Renin-Angiotensin-System Dysregulation after Kidney Transplantation.

Angiotensin-converting enzyme inhibitors (ACEis) are beneficial in patients with chronic kidney disease (CKD). Yet, their clinical effects after kidney transplantation (KTx) remain ambiguous and local renin-angiotensin system (RAS) regulation including the 'classical' and 'alternative' RAS has not been studied so far. Here, we investigated both systemic and kidney allograft-specific intrarenal RAS using tandem mass-spectrometry in KTx recipients with or without established ACEi therapy (n = 48). Transplant patients were grouped into early (<2 years), intermediate (2-12 years) or late periods after KTx (>12 years). Patients on ACEi displayed lower angiotensin (Ang) II plasma levels (P < 0.01) and higher levels of Ang I (P < 0.05) and Ang-(1-7) (P < 0.05) compared to those without ACEi independent of graft vintage. Substantial intrarenal Ang II synthesis was observed regardless of ACEi therapy. Further, we detected maximal allograft Ang II synthesis in the late transplant vintage group (P < 0.005) likely as a consequence of increased allograft chymase activity (P < 0.005). Finally, we could identify neprilysin (NEP) as the central enzyme of 'alternative RAS' metabolism in kidney allografts. In summary, a progressive increase of chymase-dependent Ang II synthesis reveals a transplant-specific distortion of RAS regulation after KTx with considerable pathogenic and therapeutic implications.