9-Month observational Dia-Vacc study of vaccine type influence on SARS-CoV-2 immunity in dialysis and kidney transplant patients

BACKGROUND

SARS-CoV-2mRNA vaccination related seroconversion rates are reduced in dialysis and kidney transplant patients.

METHODS

We evaluated nine months follow up data in our observational Dia-Vacc study exploring specific cellular (interferon-γ release assay) or/and humoral immune responses after 2x SARS-CoV-2mRNA vaccination in 880 participants including healthy medical personnel (125-MP), dialysis patients (595-DP), kidney transplant recipients (111-KTR), and apheresis patients (49-AP) with positive seroconversion (de novo IgA or IgG antibody positivity by ELISA) after eight weeks.

FINDINGS

Nine months after first vaccination, receptor binding domain (RBD) antibodies were still positive in 90 % of MP, 86 % of AP, but only 55 %/48 % of DP/KTR, respectively. Seroconversion remained positive in 100 % of AP and 99·2 % of MP, but 86 %/81 % of DP/KTR, respectively. Compared to MP, DP but not KTR or AP were at risk for a strong RBD decline, while KTR kept lowest RBD values over time. By multivariate analysis, BNT162b2mRNA versus 1273-mRNA vaccine type was an independent risk factor for a strong decline of RBD antibodies. Within the DP group, only time on dialysis was another (inverse) risk factor for the DP group. Compared to humoral immunity, T-cell immunity decline was less prominent.

INTERPRETATION

While seroconverted KTR reach lowest RBD values over time, DP are at specific risk for a strong decline of RBD antibodies after successful SARS-CoV-2mRNA vaccination, which also depends on the vaccine type being used. Therefore, booster vaccinations for DP should be considered earlier compared to normal population.

Risk of strong antibody decline in dialysis and transplant patients after SARS-CoV-2mRNA vaccination: Six months data from the observational Dia-Vacc study

Background

Vulnerable dialysis and kidney transplant patients show impaired seroconversion rates compared to medical personnel eight weeks after SARS-CoV-2mRNA vaccination.

Methods

We evaluated six months follow up data in our observational Dia-Vacc study exploring specific cellular (interferon-γ release assay) or/and humoral immune responses after 2x SARS-CoV-2mRNA vaccination in 1205 participants including medical personnel (125 MP), dialysis patients (970 DP) and kidney transplant recipients (110 KTR) with seroconversion (de novo IgA or IgG antibody positivity by ELISA) after eight weeks.

Findings

Six months after vaccination, seroconversion remained positive in 98% of MP, but 91%/87% of DP/KTR (p = 0·005), respectively. Receptor binding domain-IgG (RBD-IgG) antibodies were positive in 98% of MP, but only 68%/57% of DP/KTR (p < 0·001), respectively. Compared to MP, DP and KTR were at risk for a strong IgG or RBD-IgG decline (p < 0·001). Within the DP but not KTR group male gender, peritoneal dialysis, short time on dialysis, BNT162b2mRNA vaccine, immunosuppressive drug use and diabetes mellitus were independent risk factors for a strong decline of IgG or RBD antibodies. The percentage of cellular immunity decline was similar in all groups.

Interpretation

Both vulnerable DP and KTR groups are at risk for a strong decline for IgG and RBD antibodies. In KTR, antibody titres peak at a markedly lower level and accelerated antibody decline is mixed with a delayed/increasing IgG, RBD-IgG, or cellular immune response in a 16% fraction of patients. In both populations, immune monitoring should be used for early timing of additional booster vaccinations.

Funding

This study was funded by the Else Kröner Fresenius Stiftung, Bad Homburg v. d. H., grant number Fördervertrag EKFS 2021_EKSE.27.

Humoral and cellular immunity to SARS-CoV-2 vaccination in renal transplant versus dialysis patients: A prospective, multicenter observational study using mRNA-1273 or BNT162b2 mRNA vaccine

Background

Dialysis and kidney transplant patients are vulnerable populations for COVID-19 related disease and mortality.

Methods

We conducted a prospective study exploring the eight week time course of specific cellular (interferon-γ release assay and flow cytometry) or/and humoral immune responses (ELISA) to SARS-CoV-2 boost vaccination in more than 3100 participants including medical personnel, dialysis patients and kidney transplant recipients using mRNA vaccines BNT162b2 or mRNA-1273.

Results

SARS-CoV-2-vaccination induced seroconversion efficacy in dialysis patients was similar to medical personnel (> 95%), but markedly impaired in kidney transplant recipients (42%). T-cellular immunity largely mimicked humoral results. Major risk factors of seroconversion failure were immunosuppressive drug number and type (belatacept, MMF-MPA, calcineurin-inhibitors) as well as vaccine type (BNT162b2 mRNA). Seroconversion rates induced by mRNA-1273 compared to BNT162b2 vaccine were 97% to 88% (p < 0.001) in dialysis and 49% to 26% in transplant patients, respectively. Specific IgG directed against the new binding domain of the spike protein (RDB) were significantly higher in dialysis patients vaccinated by mRNA-1273 (95%) compared to BNT162b2 (85%, p < 0.001). Vaccination appeared safe and highly effective demonstrating an almost complete lack of symptomatic COVID-19 disease after boost vaccination as well as ceased disease incidences during third pandemic wave in dialysis patients.

Conclusion

Dialysis patients exhibit a remarkably high seroconversion rate of 95% after boost vaccination, while humoral response is impaired in the majority of transplant recipients. Immunosuppressive drug number and type as well as vaccine type (BNT162b2) are major determinants of seroconversion failure in both dialysis and transplant patients suggesting immune monitoring and adaption of vaccination protocols.

Podocyte Density and Albuminuria in Aging Diabetic Ins2± Mice with or Without Adenosine A1 Receptor Signaling

Aim of Study

To investigate podocyte density in aging diabetic Ins2± and Ins2±, A1AR-/- mouse models in C57Bl/6 background.

Methods

Ins2± mice and especially Ins2±, adenosine A1 receptor knockout mice (Ins2±, A1AR-/-) are mouse models with a phenotype of diabetic nephropathy. Aged mice (at ~40 weeks) were assessed for glomerular filtration barrier function by measuring albuminuria, glomerular filtration, glomerular damage by electron microscopy, and podocyte numbers by Wilms Tumor protein (WT-1) staining.

Results

Compared to healthy wild-type mice, both diabetic mouse models developed diabetic nephropathy, including hyperfiltration (p<0.01) and albuminuria (p<0.05). Typical diabetic structural glomerular and podocyte damage was visualized by electron microscopy. Podocyte count per glomerular area (podocyte density) was significantly decreased in both diabetic mouse models (p<0.01). In contrast, no significant correlation was detected between albuminuria and absolute podocyte count per glomerulus.

Conclusion

The amount of albuminuria as marker of diabetic nephropathy does not correlate with the podocytes density; however, a relative podocyte deficiency became evident with an increase in glomerular area in the diabetic animals, suggesting a relative podocytopenia.

Renal replacement therapy intensity for acute kidney injury and recovery to dialysis independence: a systematic review and individual patient data meta-analysis

Background

There is no consensus whether higher intensity dose renal replacement therapy (RRT) compared with standard intensity RRT has survival benefit and achieves better renal recovery in acute kidney injury (AKI).

Methods

In an individual patient data meta-analysis, we merged individual patient data from randomized controlled trials (RCTs) comparing high with standard intensity RRT in intensive care unit patients with severe AKI. The primary outcome was all-cause mortality. The secondary outcome was renal recovery assessed as the proportion of patients who were RRT dependent at key trial endpoints and by time to the end of RRT dependence.

Results

Of the eight prospective RCTs assessing different RRT intensities, seven contributed individual patient data (n = 3682) to the analysis. Mortality was similar between the two groups at 28 days [769/1884 (40.8%) and 744/1798 (41.4%), respectively; P = 0.40] after randomization. However, more participants assigned to higher intensity therapy remained RRT dependent at the most common key study point of 28 days [e.g. 292/983 (29.7%) versus 235/943 (24.9%); relative risk 1.15 (95% confidence interval 1.00-1.33); P = 0.05]. Time to cessation of RRT through 28 days was longer in patients receiving higher intensity RRT (log-rank test P = 0.02) and when continuous renal replacement therapy was used as the initial modality of RRT (log-rank test P = 0.03).

Conclusions

In severe AKI patients, higher intensity RRT does not affect mortality but appears to delay renal recovery.

Trial Registration

Australian New Zealand Clinical Trials Registry (ANZCTR) identifier ACTRN12615000394549 (https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?ACTRN=12615000394549).

The effect of A1 adenosine receptor in diabetic megalin loss with caspase-1/IL18 signaling

PURPOSE

In our previous study, exacerbation of albuminuria was observed in A1 adenosine receptor knockout (A1AR^-/-) mice with diabetic nephropathy (DN), but the mechanism was unclear. Here, we investigated the relationship of megalin loss and albuminuria, to identify the protective effect of A1AR in megalin loss associated albuminuria by inhibiting pyroptosis-related caspase-1/IL-18 signaling of DN.

METHODS

We successfully collected DN patients' samples and built diabetes mice models induced by streptozotocin. Megalin, cubilin, and A1AR expression were detected in kidney tissue samples from DN patients and mice through immunohistochemical and immunofluorescent staining. A1AR, caspase-1, interleukin-18 (IL-18) expression were analyzed using Western blotting in wild-type and A1AR ^-/- mice. Human renal proximal tubular epithelial cells (PTC) were cultured with high glucose to observe the effect of A1AR agonist and antagonist on caspase-1/IL-18 and megalin injury.

RESULTS

The loss of megalin, co-localized with A1AR at PTC, was associated with the level of albuminuria in diabetic patients and mice. The injury of megalin-cubilin was accompanied with the A1AR upregulation (1.30±0.1 vs 0.98±0.2, P=0.042), the caspase-1 (1.33±0.1 vs 1.0±0.2, P=0.036), and IL-18 (1.26±0.2 vs 0.96±0.2, P=0.026) signaling activation in mice with DN. More severe pathological injury, 24 hrs urine albumin excretion (170.8±4.1 μg/d vs 132.0±2.9 μg/d vs 17.9±2.8 μg/d, P<0.001) and megalin-cubilin loss were observed in A1AR ^-/- DN mice with more pronounced caspase-1 (1.52±0.03 vs 1.20±0.01, P=0.017) and IL-18 (1.42±0.02 vs 1.21±0.02, P=0.018) secretion. High glucose could stimulate the secretion of caspase-1 (1.72 times, P≤0.01) and IL-18 (1.64 times, P≤0.01), which was abolished by A1AR agonist and aggravated by A1AR antagonist.

CONCLUSION

A1AR played a protective role in proximal tubular megalin loss associated albuminuria by inhibiting the pyroptosis-related caspase-1/IL-18 signaling in DN.

The Circular RNA ciRs-126 Predicts Survival in Critically Ill Patients With Acute Kidney Injury

Introduction

Circular RNAs (circRNAs) have recently been described as novel noncoding regulators of gene expression. They might have an impact on microRNA expression by their sponging activity. The detectability in blood of these RNA transcripts has been demonstrated in patients with cancer and cardiovascular disease. We tested the hypothesis that circulating circRNAs in blood of critically ill patients with acute kidney injury (AKI) at inception of renal replacement therapy may also be dysregulated and associated with patient survival.

Methods

We performed a global circRNA expression analysis using RNA isolated from blood of patients with AKI as well as controls. This global screen revealed several dysregulated circRNAs in patients with AKI. Most highly increased circRNA-array−based transcripts as well as expression of the circRNA target miR-126-5p were confirmed in blood of 109 patients with AKI, 30 age-matched healthy controls, 25 critically ill non-AKI patients, and 20 patients on maintenance hemodialysis by quantitative real-time polymerase chain reaction.

Results

Circulating concentrations of 3 novel circRNAs were amplified in blood of patients with AKI and in controls. Circular RNA sponge of miR-126 (or ciRs-126) was most highly altered compared to healthy controls and disease controls (fold change of 52.1). ciRs-126 was shown to bioinformatically sponge miR-126-5p, which was found to be highly suppressed in AKI patients and hypoxic endothelial cells. Cox regression and Kaplan−Meier curve analysis revealed ciRs-126 as an independent predictor of 28-day survival (P < 0.01).

Conclusion

Circulating concentrations of circRNAs in patients with AKI are detectable. ciRs-126 may potentially sponge miR-126-5p and acts as a predictor of mortality in this patient cohort.

Health status, renal function, and quality of life after multiorgan failure and acute kidney injury requiring renal replacement therapy

Background

Critically ill patients with acute kidney injury (AKI) in need of renal replacement therapy (RRT) may have a protracted and often incomplete rehabilitation. Their long-term outcome has rarely been investigated.

Study design

Survivors of the HANnover Dialysis OUTcome (HANDOUT) study were evaluated after 5 years for survival, health status, renal function, and quality of life (QoL). The HANDOUT study had examinded mortality and renal recovery of patients with AKI receiving either standard extendend or intensified dialysis after multi organ failure.

Results

One hundred fifty-six former HANDOUT participants were analyzed. In-hospital mortality was 56.4%. Five-year survival after AKI/RRT was 40.1% (86.5% if discharged from hospital). Main causes of death were cardiovascular complications and sepsis. A total of 19 survivors presented to the outpatient department of our clinic and had good renal recovery (mean estimated glomerular filtration rate 72.5±30 mL/min/1.73 m²; mean proteinuria 89±84 mg/d). One person required maintenance dialysis. Seventy-nine percent of the patients had a pathological kidney sonomorphology. The Charlson comorbidity score was 2.2±1.4 and adjusted for age 3.3±2.1 years. Numbers of comorbid conditions averaged 2.38±1.72 per patient (heart failure [52%] > chronic kidney disease/myocardial infarction [each 29%]). Median 36-item short form health survey (SF-36™) index was 0.657 (0.69 physical health/0.66 mental health). Quality-adjusted life-years after 5 years were 3.365.

Conclusion

Mortality after severe AKI is higher than short-term prospective studies show, and morbidity is significant. Kidney recovery as well as general health remains incomplete. Reduction of QoL is minor, and social rehabilitation is very good. Affectivity is heterogeneous, but most patients experience emotional well-being. In summary, AKI in critically ill patients leads to incomplete rehabilitation but acceptable QoL after 5 years.

Circulating long noncoding RNATapSaki is a predictor of mortality in critically ill patients with acute kidney injury

BACKGROUND

Long noncoding RNAs (lncRNAs) are novel intracellular noncoding ribonucleotides regulating gene expression. Intriguingly, these RNA transcripts are detectable and stable in the blood of patients with cancer and cardiovascular disease. We tested whether circulating lncRNAs in plasma of critically ill patients with acute kidney injury (AKI) at inception of renal replacement therapy were deregulated and might predict survival.

METHODS

We performed a global lncRNA expression analysis using RNA isolated from plasma of patients with AKI, healthy controls, and ischemic disease controls. This global screen revealed several deregulated lncRNAs in plasma samples of patients with AKI. lncRNA-array-based alterations were confirmed in kidney biopsies of patients as well as in plasma of 109 patients with AKI, 30 age-matched healthy controls, and 30 disease controls by quantitative real-time PCR.

RESULTS

Circulating concentrations of the novel intronic antisense lncRNA TrAnscript Predicting Survival in AKI (TapSAKI) (P < 0.0001) were detectable in kidney biopsies and upregulated in plasma of patients with AKI. Cox regression and Kaplan-Meier curve analysis revealed TapSAKI as an independent predictor of 28-day survival (P < 0.01). TapSAKI was enriched in tubular epithelial cells subjected to ATP depletion (P = 0.03).

CONCLUSIONS

The alteration of circulating concentrations of lncRNAs in patients with AKI supports TapSAKI as a predictor of mortality in this patient cohort.

Adipokines and central control in adenosine A1 receptor dependent glucose metabolism

Adenosine A1 receptor-deficient mice develop a phenotype of insulin resistance and grow fat. Participating pathophysiological pathways are not understood in detail yet, as discussed in our recent manuscript. This commentary further explores possible pathophysiological mechanisms with emphasis on the roles of the adipokines resistin, retinol-binding protein 4, adiponectin and the function of the gastric hormone ghrelin in adenosine mediated central regulation of energy balance. The postulate of an important function of ghrelin/A1AR axis provides a good hypothetical basis for further investigations to clarify the mechanism of A1AR-dependent metabolic homeostasis.

Impaired glucose tolerance in the absence of adenosine A1 receptor signaling

OBJECTIVE

The role of adenosine (ADO) in the regulation of glucose homeostasis is not clear. In the current study, we used A1-ADO receptor (A1AR)-deficient mice to investigate the role of ADO/A1AR signaling for glucose homeostasis.

RESEARCH DESIGN AND METHODS

After weaning, A1AR(-/-) and wild-type mice received either a standard diet (12 kcal% fat) or high-fat diet (HFD; 45 kcal% fat). Body weight, fasting plasma glucose, plasma insulin, and intraperitoneal glucose tolerance tests were performed in 8-week-old mice and again after 12-20 weeks of subsequent observation. Body composition was quantified by magnetic resonance imaging and epididymal fat-pad weights. Glucose metabolism was investigated by hyperinsulinemic-euglycemic clamp studies. To describe pathophysiological mechanisms, adipokines and Akt phosphorylation were measured.

RESULTS

A1AR(-/-) mice were significantly heavier than wild-type mice because of an increased fat mass. Fasting plasma glucose and insulin were significantly higher in A1AR(-/-) mice after weaning and remained higher in adulthood. An intraperitoneal glucose challenge disclosed a significantly slower glucose clearance in A1AR(-/-) mice. An HFD enhanced this phenotype in A1AR(-/-) mice and unmasked a dysfunctional insulin secretory mechanism. Insulin sensitivity was significantly impaired in A1AR(-/-) mice on the standard diet shortly after weaning. Clamp studies detected a significant decrease of net glucose uptake in A1AR(-/-) mice and a reduced glucose uptake in muscle and white adipose tissue. Effects were not triggered by leptin deficiency but involved a decreased Akt phosphorylation.

CONCLUSIONS

ADO/A1AR signaling contributes importantly to insulin-controlled glucose homeostasis and insulin sensitivity in C57BL/6 mice and is involved in the metabolic regulation of adipose tissue.

Circulating miR-210 predicts survival in critically ill patients with acute kidney injury

BACKGROUND AND OBJECTIVES

MicroRNAs (miRNAs) are small ribonucleotides regulating gene expression. MicroRNAs are present in the blood in a remarkably stable form. We tested whether circulating miRNAs in the plasma of critically ill patients with acute kidney injury (AKI) at the inception of renal replacement therapy are deregulated and may predict survival.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We profiled miRNAs using RNA isolated from the plasma of patients with AKI and healthy controls. The results were validated in 77 patients with acute kidney injury, 30 age-matched healthy controls, and 18 critically ill patients with acute myocardial infarction by quantitative real-time PCR.

RESULTS

Circulating levels of miR-16 and miR-320 were downregulated in the plasma of kidney injury AKI patients, whereas miR-210 was upregulated compared with healthy controls (all P < 0.0001) and disease controls (miR-210 and miR-16: P < 0.0001; miR-320: P = 0.03). Cox regression (P < 0.05) and Kaplan-Meier curve analysis (P = 0.03) revealed miR-210 as an independent and powerful predictor of 28-day survival.

CONCLUSIONS

Circulating miRNAs are altered in patients with kidney injury AKI. MiR-210 predicts mortality in this patient cohort and may serve as a novel biomarker AKI reflecting pathophysiological changes on a cellular level.

Renal failure in mice with Gsalpha deletion in juxtaglomerular cells

BACKGROUND

Mice with deletion of Gsalpha in renin-producing cells (RC/FF mice) have been shown to have greatly reduced renin production and lack of responsiveness of renin secretion to acute stimuli. In addition, young RC/FF mice are hypotensive and have a vasopressin-resistant concentrating defect. In the present study we have determined the long-term effect on renal function, blood pressure, and renal pathology in this low renin and diuretic mouse model.

METHODS AND RESULTS

Urine osmolarity of RC/FF mice was decreased in all age groups. GFR measured at 7, 14 and 20 weeks of age declined progressively. Single nephron GFR similarly declined while fractional proximal fluid absorption was maintained. Expression levels of extracellular matrix proteins (collagen I, IV and fibronectin) and alpha-smooth muscle actin were increased in kidneys of RC/FF mice at 20 weeks, and this was accompanied by focal segmental glomerulosclerosis and periglomerular interstitial fibrosis. RC/FF mice showed a progressive reduction of body weight, an increase in urine albumin excretion, and an increase of blood pressure with aging.

CONCLUSION

A chronic reduction of renin production in mice may be a risk factor in its own right, and does not protect renal function against the profibrotic influence of a chronically elevated urine flow.

Vitamin C transporter Slc23a1 links renal reabsorption, vitamin C tissue accumulation, and perinatal survival in mice

Levels of the necessary nutrient vitamin C (ascorbate) are tightly regulated by intestinal absorption, tissue accumulation, and renal reabsorption and excretion. Ascorbate levels are controlled in part by regulation of transport through at least 2 sodium-dependent transporters: Slc23a1 and Slc23a2 (also known as Svct1 and Svct2, respectively). Previous work indicates that Slc23a2 is essential for viability in mice, but the roles of Slc23a1 for viability and in adult physiology have not been determined. To investigate the contributions of Slc23a1 to plasma and tissue ascorbate concentrations in vivo, we generated Slc23a1-/- mice. Compared with wild-type mice, Slc23a1-/- mice increased ascorbate fractional excretion up to 18-fold. Hepatic portal ascorbate accumulation was nearly abolished, whereas intestinal absorption was marginally affected. Both heterozygous and knockout pups born to Slc23a1-/- dams exhibited approximately 45% perinatal mortality, and this was associated with lower plasma ascorbate concentrations in dams and pups. Perinatal mortality of Slc23a1-/- pups born to Slc23a1-/- dams was prevented by ascorbate supplementation during pregnancy. Taken together, these data indicate that ascorbate provided by the dam influenced perinatal survival. Although Slc23a1-/- mice lost as much as 70% of their ascorbate body stores in urine daily, we observed an unanticipated compensatory increase in ascorbate synthesis. These findings indicate a key role for Slc23a1 in renal ascorbate absorption and perinatal survival and reveal regulation of vitamin C biosynthesis in mice.

Serum neutrophil gelatinase-associated lipocalin at inception of renal replacement therapy predicts survival in critically ill patients with acute kidney injury

INTRODUCTION

Neutrophil gelatinase-associated lipocalin (NGAL) is a promising novel biomarker that correlates with the severity and outcome of acute kidney injury (AKI). However, its prognostic utility during the late course of AKI, especially in patients that require renal replacement therapy (RRT) remains unknown. The aim of this study was to evaluate the predictive value of serum NGAL in patients with established AKI at inception of RRT in the intensive care unit (ICU).

METHODS

Serum NGAL (ELISA methodology) was measured in 109 critically ill patients with AKI at inception of RRT in 7 ICUs of a tertiary care university hospital. The primary outcome studied was 28-day mortality. Secondary outcome measures were ICU length of stay, ventilator-free days, and renal recovery at day 28.

RESULTS

There was a significant difference in serum NGAL between healthy subjects (median [interquartile range] 39.0 [37.5-42.75] ng/mL), critically ill patients with systemic inflammatory response syndrome (SIRS) (297 [184-490] ng/mL), and critically ill patients with sepsis (708 [365-1301] ng/mL; P < 0.0001), respectively. Multiple linear regression showed that NGAL levels were independently related to the severity of AKI and the extent of systemic inflammation. NGAL levels were higher in non-survivors (430 [303-942] ng/mL) compared to survivors (298 [159-506] ng/mL; P = 0.004). Consistently, Cox proportional hazards regression analysis identified NGAL as a strong independent predictor for 28-day survival (hazard ratio 1.6 (95% confidence interval [CI] 1.15 - 2.23), P = 0.005).

CONCLUSIONS

This is the first prospective evaluation of serum NGAL as an outcome-specific biomarker in critically ill patients at initiation of RRT. The results from this study indicate that serum NGAL is as an independent predictor of 28-day mortality in ICU patients with dialysis-dependent AKI.

Major contribution of tubular secretion to creatinine clearance in mice

This study was performed to quantify the fraction of excreted creatinine not attributable to creatinine filtration for accurately determining the glomerular filtration rate in mice. To measure this we compared creatinine filtration with the simultaneous measurement of inulin clearance using both single-bolus fluorescein isothiocyanate (FITC)-inulin elimination kinetics and standard FITC-inulin infusion. During anesthesia, creatinine filtration was found to be systematically higher than inulin clearance in both male and female C57BL/6J mice. The secretion fraction was significantly less in female mice. Administration of either cimetidine or para-aminohippuric acid, competitors of organic cation and anion transport respectively, significantly reduced the secretion fraction in male and female mice and both significantly increased the plasma creatinine level. Creatinine secretion in both genders was not mediated by the organic cation transporters OCT1 or OCT 2 since secretion fraction levels were identical in FVB wild-type and OCT1/2 knockout mice. Thus, secretion accounts for about 50 and 35% of excreted creatinine in male and female mice, respectively. Increasing plasma creatinine threefold by infusion further increased the secretion fraction. Renal organic anion transporter 1 mRNA expression was higher in male than in female mice, reflecting the gender difference in creatinine secretion. Hence we show that there is a major secretory contribution to creatinine excretion mediated through the organic anion transport system. This feature adds to problems associated with measuring endogenous creatinine filtration in mice.

Angiopoietin-2 in patients requiring renal replacement therapy in the ICU: relation to acute kidney injury, multiple organ dysfunction syndrome and outcome

PURPOSE

Endothelial activation has emerged as an early event in the pathogenesis of microcirculatory dysfunction, capillary leakage and multi-organ dysfunction syndrome (MODS). Angiopoietin-2 (Ang-2), a circulating antagonistic ligand of the endothelial-specific Tie2 receptor, has been identified as a non-redundant gatekeeper of endothelial activation. On the basis of our previous report demonstrating release of Ang-2 in endotoxemia and sepsis, we aimed to study the utility of Ang-2 to serve as an outcome-specific biomarker in patients requiring renal replacement therapy (RRT) in the intensive care unit (ICU).

METHODS

We measured circulating Ang-2 by ELISA in 117 critically ill patients with AKI at inception of RRT in the ICU. Mortality, length of stay and renal recovery were prospectively assessed during a study period of 28 days after the inception of RRT.

RESULTS

Circulating Ang-2 levels were significantly higher in AKI patients with RIFLE category-Injury or -Failure, compared to patients with RIFLE category-Risk. Elevated levels of circulating Ang-2 correlated with impaired oxygenation, low mean arterial pressure, vasopressor dose and the sequential organ failure assessment (SOFA) score. Ang-2 concentrations were significantly higher in non-survivors than in survivors at day 0 and day 14 after initiation of RRT. Multivariate Cox regression and decision tree analyses confirmed a strong independent prognostic impact of elevated Ang-2 as a predictor of 28-day survival.

CONCLUSIONS

The results from this study indicate that circulating Ang-2 is as a strong and independent predictor of mortality in ICU patients with dialysis-dependent AKI.

The Hannover Dialysis Outcome study: comparison of standard versus intensified extended dialysis for treatment of patients with acute kidney injury in the intensive care unit

BACKGROUND

Increasing the dose of renal replacement therapy has been shown to improve survival in critically ill patients with acute kidney injury (AKI) in several smaller European trials. However, a very recent large multicentre trial in the USA could not detect an effect of dose of renal replacement therapy on mortality. Based on those studies, it is not known whether a further increase in dialysis dose above and beyond the currently employed doses would improve survival in patients with AKI. We therefore aimed to assess mortality and renal recovery of patients with AKI receiving either standard (SED) or intensified extended dialysis (IED) therapy in the intensive care unit.

METHODS

A prospective randomized parallel group study was conducted in seven intensive care units of a tertiary university hospital. Pre-existing chronic kidney disease was an exclusion criterion. A total of 156 patients (570 screened) with AKI requiring renal replacement therapy were randomly assigned to receive standard dialysis [dosed to maintain plasma urea levels between 120 and 150 mg/dL (20-25 mmol/L)] or intensified dialysis [dosed to maintain plasma urea levels <90 mg/dL (<15 mmol/L)]. Outcome measures were survival at Day 14 (primary) and survival and renal recovery at Day 28 (secondary) after initiation of renal replacement therapy.

RESULTS

Treatment intensity differed significantly (P < 0.01 for plasma urea and administered dose). No differences between intensified and standard treatment were seen for survival by Day 14 (70.4% versus 70.7%) or Day 28 (55.6% versus 61.3%), or for renal recovery amongst the survivors by Day 28 (60.0% versus 63.0%).

CONCLUSIONS

Although this study cannot deliver a definitive answer, it suggests that increasing the dose of extended dialysis above the currently recommended dose might neither reduce mortality nor improve renal recovery in critically ill patients, mainly septic patients, with AKI.

Excess circulating angiopoietin-2 is a strong predictor of mortality in critically ill medical patients

Introduction

The endothelial specific angiopoietin (Ang)-Tie2 ligand-receptor system has been identified as a non-redundant mediator of endothelial activation in experimental sepsis. Binding of circulating Ang-1 to the Tie2 receptor protects the vasculature from inflammation and leakage, whereas binding of Ang-2 antagonises Tie2 signalling and disrupts endothelial barrier function. Here, we examine whether circulating Ang-1 and/or Ang-2 independently predict mortality in a cohort of critically ill medical patients.

Methods

Circulating vascular endothelial growth factor (VEGF), Ang-1 and Ang-2 were prospectively measured in sera from 29 healthy controls and 43 medical ICU patients by immunoradiometric assay (IRMA) and ELISA, respectively. Survival after 30 days was the primary outcome studied.

Results

Median serum Ang-2 concentrations were increasingly higher across the following groups: healthy controls, patients without sepsis, patients with sepsis and patients with septic shock. In contrast, Ang-1 and VEGF concentrations were significantly lower in all patient groups compared with healthy controls. Ang-2 correlated with partial pressure of oxygen in arterial blood (PaO₂)/fraction of inspired oxygen (FiO₂), tissue hypoxia, Sequential Organ Failure Assessment (SOFA) and Physiology and Chronic Health Evaluation II (APACHE II) score. Multivariate Cox regression analyses confirmed a strong independent prognostic impact of high Ang-2 as a novel marker of 30-day survival.

Conclusions

A marked imbalance of the Ang-Tie system in favour of Ang-2 is present in critically ill medical patients. Our findings highlight the independent prognostic impact of circulating Ang-2 in critical illness. Ang-2 may be used as a readily available powerful predictor of outcome and may open new perspectives to individualise treatment in the ICU.

Dense-core vesicle proteins IA-2 and IA-2{beta} affect renin synthesis and secretion through the {beta}-adrenergic pathway

IA-2 and IA-2beta, major autoantigens in type 1 diabetes, are transmembrane proteins in dense-core vesicles, and their expression influences the secretion of hormones and neurotransmitters. The present experiments were performed to examine whether IA-2 and IA-2beta modulate the release of renin from dense-core vesicles of juxtaglomerular granular cells in the kidney. Plasma renin concentration (PRC; ng angiotensin I.ml(-1).h(-1)) was significantly reduced in mice with null mutations in IA-2, IA-2beta, or both IA-2 and IA-2beta compared with wild-type mice (876 +/- 113, 962 +/- 130, and 596 +/- 82 vs. 1,367 +/- 93; P < 0.01, P < 0.02, and P < 0.001). Renin mRNA levels were reduced to 26.4 +/- 5.1, 39 +/- 5.4, and 35.3 +/- 5.5% of wild-type in IA-2-/-, IA-2beta-/-, and IA-2/IA-2beta-/- mice. Plasma aldosterone levels were not significantly different among genotypes. The regulation of PRC by furosemide and salt intake, and of aldosterone by salt intake, was maintained in all genotypes. IA-2 and IA-2beta expression did not colocalize with renin but showed overlapping immunoreactivity with tyrosine hydroxylase. While propranolol reduced PRC in wild-type mice, it had no effect on PRC in IA-2/ IA-2beta-/- mice. Renal tyrosine hydroxylase mRNA and immunoreactivity were reduced in IA-2/IA-2beta-/- mice as was the urinary excretion of catecholamines. We conclude that IA-2 and IA-2beta are required to maintain normal levels of renin expression and renin release, most likely by permitting normal rates of catecholamine release from sympathetic nerve terminals.

Salt sensitivity of blood pressure in NKCC1-deficient mice

NKCC1 is a widely expressed isoform of the Na-2Cl-K cotransporter that mediates several direct and indirect vascular effects and regulates expression and release of renin. In this study, we used NKCC1-deficient (NKCC1-/-) and wild-type (WT) mice to assess day/night differences of blood pressure (BP), locomotor activity, and renin release and to study the effects of high (8%) or low (0.03%) dietary NaCl intake on BP, activity, and the renin/aldosterone system. On a standard diet, 24-h mean arterial blood pressure (MAP) and heart rate determined by radiotelemetry, and their day/night differences, were not different in NKCC1-/- and WT mice. Spontaneous and wheel-running activities in the active night phase were lower in NKCC1-/- than WT mice. In NKCC1-/- mice on a high-NaCl diet, MAP increased by 10 mmHg in the night without changes in heart rate. In contrast, there was no salt-dependent blood pressure change in WT mice. MAP reductions by hydralazine (1 mg/kg) or isoproterenol (10 microg/mouse) were significantly greater in NKCC1-/- than WT mice. Plasma renin (PRC; ng ANG I.ml(-1).h(-1)) and aldosterone (aldo; pg/ml) concentrations were higher in NKCC1-/- than WT mice (PRC: 3,745+/-377 vs. 1,245+/-364; aldo: 763+/-136 vs. 327+/-98). Hyperreninism and hyperaldosteronism were found in NKCC1-/- mice during both day and night. High Na suppressed PRC and aldosterone in both NKCC1-/- and WT mice, whereas a low-Na diet increased PRC and aldosterone in WT but not NKCC1-/- mice. We conclude that 24-h MAP and MAP circadian rhythms do not differ between NKCC1-/- and WT mice on a standard diet, probably reflecting a balance between anti- and prohypertensive factors, but that blood pressure of NKCC1-/- mice is more sensitive to increases and decreases of Na intake.

Lack of A1 adenosine receptors augments diabetic hyperfiltration and glomerular injury

Intraglomerular hypertension and glomerular hyperfiltration likely contribute to the pathogenesis of diabetic nephropathy, and tubuloglomerular feedback (TGF) has been suggested to play a role in diabetic hyperfiltration. A1 adenosine receptor (A1AR) null mice lack a TGF response, so this model was used to investigate the contribution of TGF to hyperfiltration in diabetic Ins2(+/-) Akita mice. TGF responses in Ins2(+/-) A1AR(-/-) double mutants were abolished, whereas they were attenuated in Ins2(+/-) mice. GFR, assessed at 14, 24, and 33 wk, was approximately 30% higher in Ins2(+/-) than in wild-type (WT) mice and increased further in Ins2(+/-) A1AR(-/-) mutants (P < 0.01 versus both WT and Ins2(+/-) mice at all ages). Histologic evidence of glomerular injury and urinary albumin excretion were more pronounced in double-mutant than single-mutant or WT mice. In summary, the marked elevation of GFR in diabetic mice that lack a TGF response indicates that TGF is not required to cause hyperfiltration in the Akita model of diabetes. Rather, an A1AR-dependent mechanism, possibly TGF, limits the degree of diabetic hyperfiltration and nephropathy.

Tubuloglomerular feedback and renin secretion in NTPDase1/CD39-deficient mice

Studies in mice with null mutations of adenosine 1 receptor or ecto-5'-nucleotidase genes suggest a critical role of adenosine and its precursor 5'-AMP in tubulovascular signaling. To assess whether the source of juxtaglomerular nucleotides can be traced back to ATP dephosphorylation, experiments were performed in mice with a deficiency in NTPDase1/CD39, an ecto-ATPase catalyzing the formation of AMP from ATP and ADP. Urine osmolarity and glomerular filtration rate (GFR) were indistinguishable between NTPDase1/CD39(-/-) and wild-type (WT) mice. Maximum tubuloglomerular feedback (TGF) responses, as determined by proximal tubular stop flow pressure measurements, were reduced in NTPDase1/CD39(-/-) mice compared with controls (4.2 +/- 0.9 vs. 10.5 +/- 1.2 mmHg, respectively; P = 0.0002). Residual TGF responses gradually diminished after repeated changes in tubular perfusion flow averaging 2.9 +/- 0.9 (on response) and 3.5 +/- 1.1 (off response) mmHg after the second and 2.2 +/- 0.5 (on response) and 1.5 +/- 0.8 (off response) mmHg after the third challenge, whereas no fading of TGF responsiveness was observed in WT mice. Macula densa-dependent and pressure-dependent inhibition of renin secretion, as assessed by acute salt loading and phenylephrine injection, respectively, were intact in NTPDase1/CD39-deficient mice. In summary, NTPDase1/CD39-deficient mice showed a markedly compromised TGF regulation of GFR. These data support the concept of an extracellular dephosphorylation cascade during tubular-vascular signal transmission in the juxtaglomerular apparatus that is initiated by a regulated release of ATP from macula densa cells and results in adenosine-mediated afferent arteriole constriction.

Regulation of Renin Secretion and Expression in Mice Deficient in β1- and β2-Adrenergic Receptors

The present experiments were performed in beta1/beta2-adrenergic receptor-deficient mice (beta1/beta2ADR(-/-)) to assess the role of beta-adrenergic receptors in basal and regulated renin expression and release. On a control diet, plasma renin concentration (in ng angiotensin I per mL per hour), determined in tail vein blood, was significantly lower in beta1/beta2ADR(-/-) than in wild-type (WT) mice (222+/-65 versus 1456+/-335; P<0.01). Renin content and mRNA were 77% and 65+/-5% of WT. Plasma aldosterone (in picograms per mL) was also significantly reduced (420+/-36 in beta1/beta2ADR(-/-) versus 692+/-59 in WT). A low-salt diet (0.03%) for 1 week increased plasma renin concentration significantly in both beta1/beta2ADR(-/-) and WT mice (to 733+/-54 and 2789+/-555), whereas a high-salt diet (8%) suppressed it in both genotypes (to 85+/-24 in beta1/beta2ADR(-/-) and to 676+/-213 in WT). The absolute magnitude of salt-induced changes of plasma renin concentration was markedly greater in WT mice. Acute stimulation of renin release by furosemide, quinaprilat, captopril, or candesartan caused significant increases of plasma renin concentration in both beta1/beta2ADR(-/-) and WT mice, but again the absolute changes were greater in WT mice. We conclude that maintenance of normal levels of renin synthesis and release requires tonic beta-adrenergic receptor activation. In the chronic absence of beta-adrenergic receptor input, the size of the releasable renin pool decreases with a concomitant reduction in the magnitude of the plasma renin concentration changes caused by variations of salt intake or acute stimulation with furosemide, angiotensin-converting enzyme, or angiotensin type 1 receptor inhibition, but regulatory responsiveness is nonetheless maintained.

Renal function in mice with targeted disruption of the A isoform of the Na-K-2Cl co-transporter

Three different full-length splice isoforms of the Na-K-2Cl co-transporter (NKCC2/BSC1) are expressed along the thick ascending limb of Henle (TAL), designated NKCC2A, NKCC2B, and NKCC2F. NKCC2F is expressed in the medullary, NKCC2B mainly in the cortical, and NKCC2A in medullary and cortical portions of the TAL. NKCC2B and NKCC2A were shown to be coexpressed in the macula densa (MD) segment of the mouse TAL. The functional consequences of the existence of three different isoforms of NKCC2 are unclear. For studying the specific role of NKCC2A in kidney function, NKCC2A-/- mice were generated by homologous recombination. NKCC2A-/- mice were viable and showed no gross abnormalities. Ambient urine osmolarity was reduced significantly in NKCC2A-/- compared with wild-type mice, but water deprivation elevated urine osmolarity to similar levels in both genotypes. Baseline plasma renin concentration and the effects of a high- and a low-salt diet on plasma renin concentration were similar in NKCC2A+/+ and -/- mice. However, suppression of renin secretion by acute intravenous saline loading (5% of body weight), a measure of MD-dependent inhibition of renin secretion, was reduced markedly in NKCC2A-/- mice compared with wild-type mice. Cl and water absorption along microperfused loops of Henle of NKCC2A-/- mice were unchanged at normal flow rates but significantly reduced at supranormal flow. Tubuloglomerular feedback function curve as determined by stop flow pressure measurements was left-shifted in NKCC2A-/- compared with wild-type mice, with maximum responses being significantly diminished. In summary, NKCC2A activity seems to be required for MD salt sensing in the high Cl concentration range. Coexpression of both high- and low-affinity isoforms of NKCC2 may permit transport and Cl-dependent tubuloglomerular feedback regulation to occur over a wider Cl concentration range.

Regulation of renin in mice with Cre recombinase-mediated deletion of G protein Gsα in juxtaglomerular cells

By crossing mice with expression of Cre recombinase under control of the endogenous renin promoter (Sequeira Lopez ML, Pentz ES, Nomasa T, Smithies O, Gomez RA. Dev Cell 6: 719–728, 2004) with mice in which exon 1 of the Gnas gene was flanked by loxP sites (Chen M, Gavrilova O, Liu J, Xie T, Deng C, Nguyen AT, Nackers LM, Lorenzo J, Shen L, Weinstein LS. Proc Natl Acad Sci USA), we generated animals with preferential and nearly complete excision of Gsα in juxtaglomerular granular (JG) cells. Compared with wild-type animals, mice with conditional Gsα deficiency had markedly reduced basal levels of renin expression and very low plasma renin concentrations. Furthermore, the acute release responses to furosemide, hydralazine, and isoproterenol were virtually abolished. Consistent with a state of primary renin depletion, Gsα-deficient mice had reduced arterial blood pressure, reduced levels of aldosterone, and a low glomerular filtration rate. Renin content and renin secretion of JG cells in primary culture were drastically reduced, and the stimulatory response to the addition of PGE2or isoproterenol was eliminated. Unexpectedly, Gsα recombination was also observed in the renal medulla, and this was associated with a vasopressin-resistant concentrating defect. Our study shows that Cre recombinase under control of the renin promoter can be used for the excision of floxed targets from JG cells. We conclude that Gsα-mediated signal transduction is essential and nonredundant in the control of renin synthesis and release.