Gut Dysbiosis in Experimental Kidney Disease: A Meta-Analysis of Rodent Repository Data.

SIGNIFICANCE STATEMENT: Alterations in gut microbiota contribute to the pathophysiology of a diverse range of diseases, leading to suggestions that chronic uremia may cause intestinal dysbiosis that contributes to the pathophysiology of CKD. Various small, single-cohort rodent studies have supported this hypothesis. In this meta-analysis of publicly available repository data from studies of models of kidney disease in rodents, cohort variation far outweighed any effect of experimental kidney disease on the gut microbiota. No reproducible changes in animals with kidney disease were seen across all cohorts, although a few trends observed in most experiments may be attributable to kidney disease. The findings suggest that rodent studies do not provide evidence for the existence of "uremic dysbiosis" and that single-cohort studies are unsuitable for producing generalizable results in microbiome research. BACKGROUND: Rodent studies have popularized the notion that uremia may induce pathological changes in the gut microbiota that contribute to kidney disease progression. Although single-cohort rodent studies have yielded insights into host-microbiota relationships in various disease processes, their relevance is limited by cohort and other effects. We previously reported finding metabolomic evidence that batch-to-batch variations in the microbiome of experimental animals are significant confounders in an experimental study. METHODS: To attempt to identify common microbial signatures that transcend batch variability and that may be attributed to the effect of kidney disease, we downloaded all data describing the molecular characterization of the gut microbiota in rodents with and without experimental kidney disease from two online repositories comprising 127 rodents across ten experimental cohorts. We reanalyzed these data using the DADA2 and Phyloseq packages in R, a statistical computing and graphics system, and analyzed data both in a combined dataset of all samples and at the level of individual experimental cohorts. RESULTS: Cohort effects accounted for 69% of total sample variance ( P <0.001), substantially outweighing the effect of kidney disease (1.9% of variance, P =0.026). We found no universal trends in microbial population dynamics in animals with kidney disease, but observed some differences (increased alpha diversity, a measure of within-sample bacterial diversity; relative decreases in Lachnospiraceae and Lactobacillus ; and increases in some Clostridia and opportunistic taxa) in many cohorts that might represent effects of kidney disease on the gut microbiota . CONCLUSIONS: These findings suggest that current evidence that kidney disease causes reproducible patterns of dysbiosis is inadequate. We advocate meta-analysis of repository data as a way of identifying broad themes that transcend experimental variation.

Persistent colonization of exit site is associated with modality failure in peritoneal dialysis.

Exit-site infections (ESIs) increase the risk of developing peritoneal dialysis (PD) peritonitis and PD technique failure. There are no clear guidelines on how to monitor exit site (ES) after ESI with Staphylococcus aureus or Pseudomonas. We report on a 1-year observational study of 23 patients who developed an ESI with one of these serious pathogens. After completing initial antibiotic treatment, swabs were taken every month for 3 months. Primary treatment cure occurred in 19/23 (83%). Colonization of ES after primary cure occurred in 8/19 (42%) patients. In the eight colonized patients, five had subsequent PD technique failure due to infections. By contrast, during an average follow-up period of 7.2 months, none of the 11 patients who were proven noncolonized developed PD technique failure from infections; HR (colonized vs. noncolonized) = 10.89, 95% CI 2.6-45.43, p < 0.05. In conclusion, colonization significantly increased the risk of catheter loss. Increased surveillance and aggressive treatment may ameliorate this risk.

Treating Posttransplant Anemia With Erythropoietin Improves Quality of Life but Does Not Affect Progression of Chronic Kidney Disease.

OBJECTIVES: Posttransplant anemia affects 30% to 45% of kidney transplant recipients and is associated with increased morbidity. However, there is lack of evidence about safe hemoglobin levels after erythropoietin treatment. Studies are needed to better understand the potential benefits and risks, as well as to define safe target hemoglobin ranges in these patients. MATERIALS AND METHODS: In this single-center exploratory, open-label randomized controlled trial, kidney trans-plant recipients with anemia 3 months posttransplant were either treated with epoetin beta to a hemoglobin target level of 11.5 to 13.5 g/dL (n = 28) or given no treatment (n = 27). Treatment effects on graft function and health quality of life were assessed. RESULTS: After 2 years, hemoglobin concentrations were significantly higher in the epoetin beta treatment group than in the no treatment group (12.3 ± 0.18 vs 9.99 ± 0.22 g/dL; P < .0001). Estimated glomerular filtration rate, calculated by Modified Diet in Renal Disease 7, declined by 1.7 mL/min (interquartile range, -6 to 4.24) in the epoetin treatment group and by 4.16 mL/min (interquartile range, -12.42 to 2.78) in the no treatment group (P = .32). Rate of progression, determined by estimated glomerular filtration rate slope, was not significantly different between groups (-0.09 ± 0.1 vs -0.12 ± 0.15 mL/min for treated vs not treated; P = .78). Moreover, we observed no significant differences in proteinuria and blood pressure. Treated patients had greater improvements in the vitality and mental health domains of the Medical Outcomes Short Form Health Survey quality of life scores. CONCLUSIONS: Treatment of anemia in kidney transplant recipients to a hemoglobin level of 11.5 to 13.5 g/dL with erythropoietin improves some quality of life scores. The treatment was safe and not associated with adverse outcomes. There were no changes in rate of decline of graft function.

Annexin A1 attenuates microvascular complications through restoration of Akt signalling in a murine model of type 1 diabetes.

AIMS/HYPOTHESIS: Microvascular complications in the heart and kidney are strongly associated with an overall rise in inflammation. Annexin A1 (ANXA1) is an endogenous anti-inflammatory molecule that limits and resolves inflammation. In this study, we have used a bedside to bench approach to investigate: (1) ANXA1 levels in individuals with type 1 diabetes; (2) the role of endogenous ANXA1 in nephropathy and cardiomyopathy in experimental type 1 diabetes; and (3) whether treatment with human recombinant ANXA1 attenuates nephropathy and cardiomyopathy in a murine model of type 1 diabetes. METHODS: ANXA1 was measured in plasma from individuals with type 1 diabetes with or without nephropathy and healthy donors. Experimental type 1 diabetes was induced in mice by injection of streptozotocin (STZ; 45 mg/kg i.v. per day for 5 consecutive days) in C57BL/6 or Anxa1 -/- mice. Diabetic mice were treated with human recombinant (hr)ANXA1 (1 µg, 100 µl, 50 mmol/l HEPES; 140 mmol/l NaCl; pH 7.4, i.p.) or vehicle (100 µl, 50 mmol/l HEPES; 140 mmol/l NaCl; pH 7.4, i.p.). RESULTS: Plasma levels of ANXA1 were elevated in individuals with type 1 diabetes with/without nephropathy compared with healthy individuals (66.0 ± 4.2/64.0 ± 4 ng/ml vs 35.9 ± 2.3 ng/ml; p < 0.05). Compared with diabetic wild-type (WT) mice, diabetic Anxa1 -/- mice exhibited a worse diabetic phenotype and developed more severe cardiac (ejection fraction; 76.1 ± 1.6% vs 49.9 ± 0.9%) and renal dysfunction (proteinuria; 89.3 ± 5.0 µg/mg vs 113.3 ± 5.5 µg/mg). Mechanistically, compared with non-diabetic WT mice, the degree of the phosphorylation of mitogen-activated protein kinases (MAPKs) p38, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) was significantly higher in non-diabetic Anxa1 -/- mice in both the heart and kidney, and was further enhanced after STZ-induced type 1 diabetes. Prophylactic treatment with hrANXA1 (weeks 1-13) attenuated both cardiac (ejection fraction; 54.0 ± 1.6% vs 72.4 ± 1.0%) and renal (proteinuria; 89.3 ± 5.0 µg/mg vs 53.1 ± 3.4 µg/mg) dysfunction associated with STZ-induced diabetes, while therapeutic administration of hrANXA1 (weeks 8-13), after significant cardiac and renal dysfunction had already developed, halted the further functional decline in cardiac and renal function seen in diabetic mice administered vehicle. In addition, administration of hrANXA1 attenuated the increase in phosphorylation of p38, JNK and ERK, and restored phosphorylation of Akt in diabetic mice. CONCLUSIONS/INTERPRETATION: Overall, these results demonstrate that ANXA1 plasma levels are elevated in individuals with type 1 diabetes independent of a significant impairment in renal function. Furthermore, in mouse models with STZ-induced type 1 diabetes, ANXA1 protects against cardiac and renal dysfunction by returning MAPK signalling to baseline and activating pro-survival pathways (Akt). We propose ANXA1 to be a potential therapeutic option for the control of comorbidities in type 1 diabetes.

Ischemic conditioning in solid organ transplantation: is it worth giving your right arm for?

PURPOSE OF REVIEW: Ischemia reperfusion injury (IRI) is an inevitable complication in solid organ transplantation. Limiting this injury can increase patient and graft survival and can decrease complications associated with transplantation. We provide an extensive literature review analyzing the available evidence for ischemic conditioning in solid organ transplantation, including kidney, liver, heart, and lung. RECENT FINDINGS: Ischemic conditioning strategies are a group of interventions, characterized by episodes of ischemia and reperfusion to an organ which confirm tissue protection. Arguably, transplantation is the ideal setting to use this novel strategy due to the predictable timing and duration of the ischemic insult. Liver transplantation has provided us with the most number of clinical trials, followed by kidney transplantation. Most of these trials have been negative but the methodology has been variable, making comparison difficult. SUMMARY: Despite the promising results seen in animal models, translating these results in clinical trials has proved to be difficult. The promising effects of ischemic conditioning are present in some trials with weaker positive signals existing in other trials. We believe that tailoring trials to allow better comparison will provide positive results in the future.

Inhibition of IκB Kinase at 24 Hours After Acute Kidney Injury Improves Recovery of Renal Function and Attenuates Fibrosis.

BACKGROUND: Acute kidney injury (AKI) is a major risk factor for the development of chronic kidney disease. Nuclear factor-κB is a nuclear transcription factor activated post-ischemia, responsible for the transcription of proinflammatory proteins. The role of nuclear factor-κB in the renal fibrosis post-AKI is unknown. METHODS AND RESULTS: We used a rat model of AKI caused by unilateral nephrectomy plus contralateral ischemia (30 minutes) and reperfusion injury (up to 28 days) to show impairment of renal function (peak: 24 hours), activation of nuclear factor-κB (peak: 48 hours), and fibrosis (28 days). In humans, AKI is diagnosed by a rise in serum creatinine. We have discovered that the IκB kinase inhibitor IKK16 (even when given at peak serum creatinine) still improved functional and structural recovery and reduced myofibroblast formation, macrophage infiltration, transforming growth factor-ß expression, and Smad2/3 phosphorylation. AKI resulted in fibrosis within 28 days (Sirius red staining, expression of fibronectin), which was abolished by IKK16. To confirm the efficacy of IKK16 in a more severe model of fibrosis, animals were subject to 14 days of unilateral ureteral obstruction, resulting in tubulointerstitial fibrosis, myofibroblast formation, and macrophage infiltration, all of which were attenuated by IKK16. CONCLUSIONS: Inhibition of IκB kinase at peak creatinine improves functional recovery, reduces further injury, and prevents fibrosis.

Glucolipotoxicity initiates pancreatic ß-cell death through TNFR5/CD40-mediated STAT1 and NF-κB activation.

Type 2 diabetes is a chronic metabolic disorder, where failure to maintain normal glucose homoeostasis is associated with, and exacerbated by, obesity and the concomitant-elevated free fatty acid concentrations typically found in these patients. Hyperglycaemia and hyperlipidaemia together contribute to a decline in insulin-producing ß-cell mass through activation of the transcription factors nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and signal transducer and activator of transcription (STAT)-1. There are however a large number of molecules potentially able to modulate NF-κB and STAT1 activity, and the mechanism(s) by which glucolipotoxicity initially induces NF-κB and STAT1 activation is currently poorly defined. Using high-density microarray analysis of the ß-cell transcritptome, we have identified those genes and proteins most sensitive to glucose and fatty acid environment. Our data show that of those potentially able to activate STAT1 or NF-κB pathways, tumour necrosis factor receptor (TNFR)-5 is the most highly upregulated by glucolipotoxicity. Importantly, our data also show that the physiological ligand for TNFR5, CD40L, elicits NF-κB activity in ß-cells, whereas selective knockdown of TNFR5 ameliorates glucolipotoxic induction of STAT1 expression and NF-κB activity. This data indicate for the first time that TNFR5 signalling has a major role in triggering glucolipotoxic islet cell death.

Erythropoietin attenuates acute kidney dysfunction in murine experimental sepsis by activation of the ß-common receptor.

The ß-common receptor (ßcR) plays a pivotal role in the nonhematopoietic tissue-protective effects of erythropoietin (EPO). Here we determined whether EPO reduces the acute kidney injury (AKI) caused by sepsis and whether this effect is mediated by the ßcR. In young (2 months old) C57BL/6 wild-type and ßcR knockout mice, lipopolysaccharide caused a significant increase in serum urea and creatinine, hence AKI. This AKI was not associated with any overt morphological alterations in the kidney and was attenuated by EPO given 1 h after lipopolysaccharide in wild-type but not in ßcR knockout mice. In the kidneys of endotoxemic wild-type mice, EPO enhanced the phosphorylation of Akt, glycogen synthase kinase-3ß, and endothelial nitric oxide synthase, and inhibited the activation of nuclear factor-κB. All these effects of EPO were lost in ßcR knockout mice. Since sepsis is more severe in older animals or patients, we tested whether EPO was renoprotective in 8-month-old wild-type and ßcR knockout mice that underwent cecal ligation and puncture. These older mice developed AKI at 24 h, which was attenuated by EPO treatment 1 h post cecal ligation and puncture in wild-type mice but not in ßcR knockout mice. Thus, activation of the ßcR by EPO is essential for the observed reduction in AKI in either endotoxemic young mice or older mice with polymicrobial sepsis, and for the activation of well-known signaling pathways by EPO.

Erythropoietin attenuates cardiac dysfunction in experimental sepsis in mice via activation of the ß-common receptor.

There is limited evidence that the tissue-protective effects of erythropoietin are mediated by a heterocomplex of the erythropoietin receptor and the ß-common receptor ('tissue-protective receptor'), which is pharmacologically distinct from the 'classical' erythropoietin receptor homodimer that is responsible for erythropoiesis. However, the role of the ß-common receptor and/or erythropoietin in sepsis-induced cardiac dysfunction (a well known, serious complication of sepsis) is unknown. Here we report for the first time that the ß-common receptor is essential for the improvements in the impaired systolic contractility afforded by erythropoietin in experimental sepsis. Cardiac function was assessed in vivo (echocardiography) and ex vivo (Langendorff-perfused heart) in wild-type and ß-common receptor knockout mice, that were subjected to lipopolysaccharide (9 mg/kg body weight; young mice) for 16-18 hours or cecal ligation and puncture (aged mice) for 24 hours. Mice received erythropoietin (1000 IU/kg body weight) 1 hour after lipopolysaccharide or cecal ligation and puncture. Erythropoietin reduced the impaired systolic contractility (in vivo and ex vivo) caused by endotoxemia or sepsis in young as well as old wild-type mice in a ß-common-receptor-dependent fashion. Activation by erythropoietin of the ß-common receptor also resulted in the activation of well-known survival pathways (Akt and endothelial nitric oxide synthase) and inhibition of pro-inflammatory pathways (glycogen synthase kinase-3ß, nuclear factor-κB and interleukin-1ß). All the above pleiotropic effects of erythropoietin were lost in ß-common receptor knockout mice. Erythropoietin attenuates the impaired systolic contractility associated with sepsis by activation of the ß-common receptor, which, in turn, results in activation of survival pathways and inhibition of inflammation.

Reversal of the deleterious effects of chronic dietary HFCS-55 intake by PPAR-δ agonism correlates with impaired NLRP3 inflammasome activation.

Although high-fructose corn syrup (HFCS-55) is the major sweetener in foods and soft-drinks, its potential role in the pathophysiology of diabetes and obesity ("diabesity") remains unclear. Peroxisome-proliferator activated receptor (PPAR)-δ agonists have never been tested in models of sugar-induced metabolic abnormalities. This study was designed to evaluate (i) the metabolic and renal consequences of HFCS-55 administration (15% wt/vol in drinking water) for 30 weeks on male C57Bl6/J mice and (ii) the effects of the selective PPAR-δ agonist GW0742 (1 mg/kg/day for 16 weeks) in this condition. HFCS-55 caused (i) hyperlipidemia, (ii) insulin resistance, and (iii) renal injury/inflammation. In the liver, HFCS-55 enhanced the expression of fructokinase resulting in hyperuricemia and caused abnormalities in known insulin-driven signaling events. In the kidney, HFCS-55 enhanced the expression of the NLRP3 (nucleotide-binding domain and leucine-rich-repeat-protein 3) inflammasome complex, resulting in caspase-1 activation and interleukin-1ß production. All of the above effects of HFCS-55 were attenuated by the specific PPAR-δ agonist GW0742. Thus, we demonstrate for the first time that the specific PPAR-δ agonist GW0742 attenuates the metabolic abnormalities and the renal dysfunction/inflammation caused by chronic HFCS-55 exposure by preventing upregulation of fructokinase (liver) and activation of the NLRP3 inflammasome (kidney).

Mild chronic kidney disease is an independent predictor of long-term mortality after emergency angiography and primary percutaneous intervention in patients with ST-elevation myocardial infarction.

OBJECTIVE: Moderate renal impairment (RI) with a glomerular filtration rate (GFR) <60 ml/min/1.73 m2 is known to predict survival. The authors investigated whether mild RI with an estimated GFR of 60-89 ml/min/1.73 m2 independently predicts survival in a contemporary population with ST segment elevation myocardial infarction (STEMI). DESIGN: This is a single-centre, observational, retrospective cohort study. Patients 601 patients with STEMI who underwent emergency catheter laboratory admission met the inclusion criteria for this study. METHODS: Estimated glomerular filtration rate (eGFR) was obtained by the Modified Diet in Renal Disease equation, and preprocedure renal function was subdivided into chronic kidney disease stages. Univariate and multivariate Cox regression analyses were performed to assess which of 17 patient or procedural variables were independent risk factors for death. RESULTS: Longitudinal data were collated for 576 patients (96.3%). Median follow-up time was 2.6 years. 30-day and long-term death rates were 5.7% and 12.5%, respectively. Following multivariable analysis, mild RI with an eGFR of 60-89 ml/min/1.73 m2 was a strong independent predictor of death, compared with an eGFR ≥90 ml/min/1.73 m2 (HR 2.79, 95% CI 1.98 to 3.92, p<0.001), and increasing chronic kidney disease stage was a strong predictor of death after both 30 days and long-term follow-up. An eGFR of 60-89 ml/min/1.73 m2 had a greater independent effect on short- and long-term mortality than the presence of diabetes mellitus (HR 2.0, 95% CI 1.2 to 3.33). CONCLUSION: Mild RI (eGFR=60-89 ml/min/1.73 m2) on admission is strongly predictive of short- and long-term mortality in patients with STEMI admitted to the catheter laboratory. A redefined threshold of clinically significant impairment is now required (GFR<90 ml/min/1.73 m2).

Metformin suppresses hepatic gluconeogenesis through induction of SIRT1 and GCN5.

Abnormal elevation of hepatic gluconeogenesis is central to the onset of hyperglycaemia in patients with type 2 diabetes mellitus (T2DM). Metformin corrects hyperglycaemia through inhibition of gluconeogenesis, but its mechanism of action is yet to be fully described. SIRT1 and GCN5 (listed as KAT2A in the MGI Database) have recently been identified as regulators of gluconeogenic gene expression through modulation of levels and activity of the coactivators cAMP-response element binding protein-regulated transcription coactivator 2 (TORC2 or CRTC2 as listed in the MGI Database) and peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC1alpha or PPARGC1A as listed in the MGI Database). We report that in db/db mice, metformin (250 mg/kg per day; 7 days) increases hepatic levels of GCN5 protein and mRNA compared with the untreated db/db mice, as well as increases levels of SIRT1 protein and activity relative to controls and untreated db/db mice. These changes were associated with reduced TORC2 protein level and decreased gene expression and activation of the PGC1alpha gene target phosphoenolpyruvate carboxykinase, and lower plasma glucose and insulin. Inhibition of SIRT1 partially blocked the effects of metformin on gluconeogenesis. SIRT1 was increased through an AMP-activated protein kinase-mediated increase in gene expression of nicotinamide phosphoribosyltransferase, the rate-limiting enzyme of the salvage pathway for NAD(+). Moreover, levels of GCN5 were dramatically reduced in db/db mice compared with the controls. This indicates that loss of GCN5-mediated inhibition of gluconeogenesis appears to constitute a major mechanism for the onset of abnormally elevated hepatic glucose production in db/db mice. In conclusion, induction of GCN5 and SIRT1 potentially represents a critical mechanism of action of metformin. In addition, these data identify induction of hepatic GCN5 as a potential therapeutic strategy for treatment of T2DM.

Comparison of the relation between renal impairment, angiographic coronary artery disease, and long-term mortality in women versus men.

Mild to moderate renal impairment has recently been associated with increased cardiovascular mortality. However, gender differences in the association of mild to moderate renal impairment with the presence of angiographic coronary artery disease and long-term mortality remain unknown. We examined a prospective cohort of consecutive patients who underwent coronary angiography from the ACRE study in the Royal Hospitals Trust (London, United Kingdom) with referral from 5 contiguous health authorities. Among 1,609 patients (465 women) who had angiographic and serum creatinine measurements at baseline, renal impairment at modification of diet in renal disease glomerular filtration rates of 45 to 59, 30 to 44, and <30 ml/min/1.73 m(2) was more common in women than in men and was significantly associated with the presence of angiographic coronary artery disease in women but not in men. At each level of glomerular filtration rate, multivariate adjusted hazard ratios of 7-year all-cause mortality for women compared with men were higher: 2.64 (95% confidence intervals [CI] 1.21 to 5.73) versus 1.34 (95% CI 0.995 to 1.79); 2.62 (95% CI 1.12 to 16.12) versus 2.35 (95% CI 1.60 to 3.43); and 10.42 (95% CI 3.97 to 27.39) versus 4.77 (95% CI 2.95 to 7.70), respectively. Similar patterns were observed in cardiovascular and coronary deaths. In conclusion, mild to moderate renal impairment may be a marker for unmeasured proatherogenic factors for women only, and women may bear a greater mortality burden that is attributable to renal impairment compared with men. Gender may influence the prognostic effect of renal impairment in coronary disease.

Angiotensin-converting enzyme gene polymorphism and erythropoietin requirement.

OBJECTIVES: To study the effect of angiotensin-converting enzyme (ACE) polymorphisms II, ID, and DD on erythropoietin (EPO) requirement in patients on continuous ambulatory peritoneal dialysis (CAPD) therapy. DESIGN: Retrospective observational study. SETTING: CAPD Unit, Royal London/St. Bartholomews Hospital, London, UK. PATIENTS: 46 patients on the transplant waiting list (age 20-70 years), on CAPD therapy for an average of 28 months, seen consecutively over a period of 3 months in the outpatients department. MAIN OUTCOME MEASURES: Primary end point: EPO dose requirement in different ACE genotypes. Secondary end points: C-reactive protein, ferritin, parathyroid hormone, Kt/V, duration of dialysis, folate, cause of renal failure, and whether or not patients were on ACE inhibitor therapy. RESULTS: There was a statistically significant difference (p < 0.05) in EPO requirement in the II/ID group compared to the DD group. The mean +/- standard error of EPO for the II/ID group was 144 +/- 15 U/kg/week, and for the DD group, 87 +/- 9 U/kg/week. The difference in EPO requirement could not be explained by age, C-reactive protein, ferritin, parathyroid hormone, Kt/V, duration of dialysis, folate, cause of renal failure, or whether or not patients were on ACE inhibitor therapy. CONCLUSION: In CAPD patients, ACE genotype has predictive value when determining the EPO dosage, as the III/ID genotype may be associated with a suboptimal response.