Role of fibrinogen in acute ischemic kidney injury

Fibrinolytic-deficiencies predispose hosts to septicemia from a catheter-associated UTI

Catheter-associated urinary tract infections (CAUTIs) are amongst the most common nosocomial infections worldwide and are difficult to treat partly due to development of multidrug-resistance from CAUTI-related pathogens. Importantly, CAUTI often leads to secondary bloodstream infections and death. A major challenge is to predict when patients will develop CAUTIs and which populations are at-risk for bloodstream infections. Catheter-induced inflammation promotes fibrinogen (Fg) and fibrin accumulation in the bladder which are exploited as a biofilm formation platform by CAUTI pathogens. Using our established mouse model of CAUTI, here we identified that host populations exhibiting either genetic or acquired fibrinolytic-deficiencies, inducing fibrin deposition in the catheterized bladder, are predisposed to severe CAUTI and septicemia by diverse uropathogens in mono- and poly-microbial infections. Furthermore, here we found that Enterococcus faecalis, a prevalent CAUTI pathogen, uses the secreted protease, SprE, to induce fibrin accumulation and create a niche ideal for growth, biofilm formation, and persistence during CAUTI.

DIA proteomics analysis reveals the mechanism of folic acid-induced acute kidney injury and the effects of icariin

The complexities of acute kidney injury (AKI), a multifaceted pathological occurrence, are not fully understood. At present, there is a lack of effective pharmaceutical treatments in clinical practice. Studies have shown that icariin has beneficial effects in models of acute kidney injury (AKI) caused by cisplatin and lipopolysaccharide (LPS). The aim is to explore the mechanisms that cause folic acid (FA)-induced AKI and examine the protective effects of icariin against this condition. To establish a mouse model of AKI, FA was administered via intraperitoneal injection. Icariin was used as the drug intervention. The model and the impact of drug intervention were assessed using measurements of renal function parameters, staining with hematoxylin and eosin, and Q-PCR. The analysis of protein expression changes in the control, model, and icariin treatment groups was conducted using proteomics. KEGG signaling pathway analysis indicates that differential expressed proteins are enriched in the component and coagulation cascades signaling pathway. Through protein-protein interaction network analysis, it was found that compared to the normal group, the expression of Fibrinogen and other proteins was significantly upregulated at the center of the protein interaction network in the model group. After drug treatment, the expression of these proteins was significantly downregulated. The validation experiment supports the above results. In conclusion, this study clarified the molecular mechanism of FA induced acute renal injury from the proteomics level, and provided target selection for AKI; At the same time, the mechanism of icariin in the treatment of AKI was analyzed from the proteomics level.

Pathophysiology of Red Blood Cell Trapping in Ischemic Acute Kidney Injury

Red blood cell (RBC) trapping describes the accumulation of RBCs in the microvasculature of the kidney outer medulla that occurs following ischemic acute kidney injury (AKI). Despite its prominence in human kidneys following AKI, as well as evidence from experimental models demonstrating that the severity of RBC trapping is directly correlated with renal recovery, to date, RBC trapping has not been a primary focus in understanding the pathogenesis of ischemic kidney injury. New evidence from rodent models suggests that RBC trapping is responsible for much of the tubular injury occurring in the initial hours after kidney reperfusion from ischemia. This early injury appears to result from RBC cytotoxicity and closely reflects the injury profile observed in human kidneys, including sloughing of the medullary tubules and the formation of heme casts in the distal tubules. In this review, we discuss what is currently known about RBC trapping. We conclude that RBC trapping is likely avoidable. The primary causes of RBC trapping are thought to include rheologic alterations, blood coagulation, tubular cell swelling, and increased vascular permeability; however, new data indicate that a mismatch in blood flow between the cortex and medulla where medullary perfusion is maintained during cortical ischemia is also likely critical. The mechanism(s) by which RBC trapping contributes to renal functional decline require more investigation. We propose a renewed focus on the mechanisms mediating RBC trapping, and RBC trapping-associated injury is likely to provide important knowledge for improving AKI outcomes. © 2024 American Physiological Society. Compr Physiol 14:5325-5343, 2024.

Recent Advances of Proteomics in Management of Acute Kidney Injury

Acute Kidney Injury (AKI) is currently recognized as a life-threatening disease, leading to an exponential increase in morbidity and mortality worldwide. At present, AKI is characterized by a significant increase in serum creatinine (SCr) levels, typically followed by a sudden drop in glomerulus filtration rate (GFR). Changes in urine output are usually associated with the renal inability to excrete urea and other nitrogenous waste products, causing extracellular volume and electrolyte imbalances. Several molecular mechanisms were proposed to be affiliated with AKI development and progression, ultimately involving renal epithelium tubular cell-cycle arrest, inflammation, mitochondrial dysfunction, the inability to recover and regenerate proximal tubules, and impaired endothelial function. Diagnosis and prognosis using state-of-the-art clinical markers are often late and provide poor outcomes at disease onset. Inappropriate clinical assessment is a strong disease contributor, actively driving progression towards end stage renal disease (ESRD). Proteins, as the main functional and structural unit of the cell, provide the opportunity to monitor the disease on a molecular level. Changes in the proteomic profiles are pivotal for the expression of molecular pathways and disease pathogenesis. Introduction of highly-sensitive and innovative technology enabled the discovery of novel biomarkers for improved risk stratification, better and more cost-effective medical care for the ill patients and advanced personalized medicine. In line with those strategies, this review provides and discusses the latest findings of proteomic-based biomarkers and their prospective clinical application for AKI management.

Proteomics reveals specific biological changes induced by the normothermic machine perfusion of donor kidneys with a significant up-regulation of Latexin

Renal normothermic machine perfusion (NMP) is an organ preservation method based on the circulation of a warm (35-37 °C) perfusion solution through the renal vasculature to deliver oxygen and nutrients. However, its biological effects on marginal kidneys are unclear. We therefore used mass spectrometry to determine the proteomic profile of kidney tissue and urine from eight organs reconditioned for 120 min using a Kidney Assist device. Biopsies were taken during the pre-implantation histological evaluation (T-1), at the start of back table preparation (T0), and after 60 and 120 min of perfusion (T60, T120). Urine samples were collected at T0 (urine produced in the first 15 min after the beginning of normothermic reperfusion), T30, T60 and T120. Multiple algorithms, support vector machine learning and partial least squares discriminant analysis were used to select the most discriminative proteins during NMP. Statistical analysis revealed the upregulation of 169 proteins and the downregulation of 196 during NMP. Machine learning algorithms identified the top 50 most discriminative proteins, five of which were concomitantly upregulated (LXN, ETFB, NUDT3, CYCS and UQCRC1) and six downregulated (CFHR3, C1S, CFI, KNG1, SERPINC1 and F9) in the kidney and urine after NMP. Latexin (LXN), an endogenous carboxypeptidase inhibitor, resulted the most-upregulated protein at T120, and this result was confirmed by ELISA. In addition, functional analysis revealed that the most strongly upregulated proteins were involved in the oxidative phosphorylation system and ATP synthesis, whereas the downregulated proteins represented the complement system and coagulation cascade. Our proteomic analysis demonstrated that even brief periods of NMP induce remarkable metabolic and biochemical changes in marginal organs, which supports the use of this promising technique in the clinic.

Prognostic value of fibrinogen to albumin ratios among critically ill patients with acute kidney injury

Fibrinogen to albumin ratios (FAR) have shown to be a promising prognostic factor for improving the predictive accuracy in various diseases. This study explores FAR's prognostic significance in critically ill patients with acute kidney injury (AKI). All clinical data were extracted from the Multiparameter Intelligent Monitoring in Intensive Care Database III version 1.4. All patients were divided into four groups based on FAR quartiles. The primary endpoint was in-hospital mortality. A generalized additive model was applied to explore a nonlinear association between FAR and in-hospital mortality. The Cox proportional hazards models were used to determine the association between FAR and in-hospital mortality. A total of 5001 eligible subjects were enrolled. Multivariate analysis demonstrated that higher FAR was an independent predictor of in-hospital mortality after adjusting for potential confounders (HR, 95% CI 1.23, 1.03-1.48, P = 0.025). A nonlinear relationship between FAR and in-hospital mortality was observed. FAR may serve as a potential prognostic biomarker in critically patients with AKI and higher FAR was associated with increased risk of in-hospital mortality among these patients.

The Therapeutic Potential of Anticoagulation in Organ Fibrosis

Fibrosis, also known as organ scarring, describes a pathological stiffening of organs or tissues caused by increased synthesis of extracellular matrix (ECM) components. In the past decades, mounting evidence has accumulated showing that the coagulation cascade is directly associated with fibrotic development. Recent findings suggest that, under inflammatory conditions, various cell types (e.g., immune cells) participate in the coagulation process causing pathological outcomes, including fibrosis. These findings highlighted the potential of anticoagulation therapy as a strategy in organ fibrosis. Indeed, preclinical and clinical studies demonstrated that the inhibition of blood coagulation is a potential intervention for the treatment of fibrosis across all major organs (e.g., lung, liver, heart, and kidney). In this review, we aim to summarize our current knowledge on the impact of components of coagulation cascade on fibrosis of various organs and provide an update on the current development of anticoagulation therapy for fibrosis.

Aggravation of fibrin deposition and microthrombus formation within the graft during kidney transplantation

In kidney transplantation, microthrombi and fibrin deposition may lead to local perfusion disorders and subsequently poor initial graft function. Microthrombi are often regarded as donor-derived. However, the incidence, time of development, and potential difference between living donor kidneys (LDK) and deceased donor kidneys(DDK), remains unclear. Two open-needle biopsies, taken at preimplantation and after reperfusion, were obtained from 17 LDK and 28 DDK transplanted between 2005 and 2008. Paraffin-embedded sections were immunohistochemically stained with anti-fibrinogen antibody. Fibrin deposition intensity in peritubular capillaries(PTC) and glomeruli was categorized as negative, weak, moderate or strong and the number of microthrombi/mm² was quantified. Reperfusion biopsies showed more fibrin deposition (20% to 100% moderate/strong, p < 0.001) and more microthrombi/mm² (0.97 ± 1.12 vs. 0.28 ± 0.53, p < 0.01) than preimplantation biopsies. In addition, more microthrombi/mm² (0.38 ± 0.61 vs. 0.09 ± 0.22, p = 0.02) and stronger fibrin intensity in glomeruli (28% vs. 0%, p < 0.01) and PTC (14% vs. 0%, p = 0.02) were observed in preimplantation DDK than LDK biopsies. After reperfusion, microthrombi/mm² were comparable (p = 0.23) for LDK (0.09 ± 0.22 to 0.76 ± 0.49, p = 0.03) and DDK (0.38 ± 0.61 to 0.90 ± 1.11, p = 0.07). Upon reperfusion, there is an aggravation of microthrombus formation and fibrin deposition within the graft. The prominent increase of microthrombi in LDK indicates that they are not merely donor-derived.

Urinary Exosomes Identify Inflammatory Pathways in Vancomycin Associated Acute Kidney Injury

Background: Vancomycin is commonly used as a first line therapy for gram positive organisms such as methicillin resistant Staphylococcusaureus. Vancomycin-induced acute kidney injury (V-AKI) has been reported in up to 43% of patients, especially in those with higher targeted trough concentrations. The precise mechanism of injury in humans remains elusive, with recent evidence directed towards proximal tubule cell apoptosis. In this study, we investigated the protein contents of urinary exosomes in patients with V-AKI to further elucidate biomarkers of mechanisms of injury and potential responses. Methods: Urine samples from patients with V-AKI who were enrolled in the DIRECT study and matched healthy controls from the UAB-UCSD O’Brien Center Biorepository were included in the analysis. Exosomes were extracted using solvent exclusion principle and polyethylene glycol induced precipitation. Protein identity and quantification was determined by label-free liquid chromatography mass spectrometry (LC/MS). The mean peak serum creatinine was 3.7 ± 1.4 mg/dL and time to kidney injury was 4.0 ± 3.0 days. At discharge, 90% of patients demonstrated partial recovery; 33% experienced full recovery by day 28. Proteomic analyses on five V-AKI and 7 control samples revealed 2009 proteins in all samples and 251 proteins significantly associated with V-AKI (Pi-score > 1). The top discriminatory proteins were complement C3, complement C4, galectin-3-binding protein, fibrinogen, alpha-2 macroglobulin, immunoglobulin heavy constant mu and serotransferrin. Conclusion: Urinary exosomes reveal up-regulation of inflammatory proteins after nephrotoxic injury in V-AKI. Further studies are necessary in a large patient sample to confirm these findings for elucidation of pathophysiologic mechanisms and validation of potential injury biomarkers.

The use of thromboelastography to assess post-operative changes in coagulation and predict graft function in renal transplantation

BACKGROUND

End stage renal disease (ESRD) is associated with elevated fibrinogen levels and fibrinolysis inhibition. However, there is a paucity of data on how renal transplantation impacts coagulation. we hypothesize that renal transplantation recipients with good functioning grafts will have improved fibrinolytic activity following surgery.

METHODS

Kidney recipients were analyzed pre-operatively and on post-operative day 1(POD1) using three different TEG assays with and without two concentration of tissue-plasminogen activator (t-PA). TEG indices and percent reduction in creatinine from pre-op to POD1 were measured, with >50% defining "good" graft function. Follow up was done at 6, 12, and 24 months.

RESULTS

Percent lysis(LY30) on POD1 the t-PA TEG was significantly correlated to change creatinine from pre-op to POD-1(p = 0.006). A LY30 ≥ 23% was associated with good early graft function, and lower creatinine at 24-months(p = 0.028) compared to recipients with low POD1 LY30.

CONCLUSIONS

Post-operative tPA-TEG LY30 is associated with favorable early and late outcomes in kidney transplant.

Predictive value of combining the level of fibrinogen and antithrombin III for contrast-induced nephropathy in coronary artery disease patients undergoing percutaneous coronary intervention

Contrast-induced nephropathy (CIN) is a common adverse event in the diagnosis and treatment of coronary intervention. The current study investigated the predictive effect of preoperative fibrinogen (FIB) combined with antithrombin III (AT-III) on CIN following percutaneous coronary intervention (PCI). A total of 394 patients who underwent PCI between October 2018 and May 2019 were selected for the present study. Pre-procedural FIB levels and AT-III activity were measured before PCI. CIN was defined as a 0.5 mg/dl or 25% increase in serum creatinine levels 48 to 72 h after exposure to a radiocontrast agent. Patients were classified into CIN and non-CIN groups. CIN occurred in 48 (12.2%) patients. The serum FIB levels were significantly higher in patients who developed CIN compared with those who did not develop CIN. In addition, AT-III levels ≤89.5% were associated with higher rates of CIN. Logistical regression analysis showed that high FIB, and low AT-III and albumin levels were high-risk factors associated with CIN. For FIB, the area under the receiver operating characteristic curve (AUC) for predicting CIN was 0.653. The optimal cut-off value was 3.48 g/l with a sensitivity of 45.8% and a specificity of 79.7% [95% confidence interval (CI): 0.603-0.701; P=0.0002)]. For AT-III, the AUC was 0.711, and the optimal cut-off value was 89.5%, with a sensitivity of 81.3% and specificity of 58.2% (95% CI: 0.659-0.758; P<0.0001). When combining FIB and AT-III, the AUC was 0.747. The optimal cut-off value was 0.090424, with a diagnostic sensitivity of 93.8% and specificity of 46.6% (95% CI: 0.697-0.792; P<0.0001). The results showed that FIB combined with AT-III resulted in improved predictive accuracy of CIN (FIB vs. AT-III, AUC=0.653 vs. 0.711, P=0.292; FIB vs. FIB + AT-III, AUC=0.653 vs. 0.747, P=0.012; AT-III vs. FIB + AT-III, AUC=0.711 vs. 0.747, P=0.138). Pre-procedural levels of FIB, AT-III and albumin were independently associated with an increased risk of CIN. Furthermore, the results suggested that the combination of FIB and AT-III was a better predictor of CIN after PCI.

Lysis of cold-storage-induced microvascular obstructions for ex vivo revitalization of marginal human kidneys

Thousands of kidneys from higher-risk donors are discarded annually because of the increased likelihood of complications posttransplant. Given the severe organ shortage, there is a critical need to improve utilization of these organs. To this end, normothermic machine perfusion (NMP) has emerged as a platform for ex vivo assessment and potential repair of marginal organs. In a recent study of 8 transplant-declined human kidneys on NMP, we discovered microvascular obstructions that impaired microvascular blood flow. However, the nature and physiologic impact of these lesions were unknown. Here, in a study of 39 human kidneys, we have identified that prolonged cold storage of human kidneys induces accumulation of fibrinogen within tubular epithelium. Restoration of normoxic conditions-either ex vivo during NMP or in vivo following transplant-triggered intravascular release of fibrinogen correlating with red blood cell aggregation and microvascular plugging. Combined delivery of plasminogen and tissue plasminogen activator during NMP lysed the plugs leading to a significant reduction in markers of renal injury, improvement in indicators of renal function, and improved delivery of vascular-targeted nanoparticles. Our study suggests a new mechanism of cold storage injury in marginal organs and provides a simple treatment with immediate translational potential.

Targeting of intragraft reactive oxygen species by APP-103, a novel polymer product, mitigates ischemia/reperfusion injury and promotes the survival of renal transplants

Inflammatory responses associated with ischemia/reperfusion injury (IRI) play a central role in alloimmunity and transplant outcomes. A key event driving these inflammatory responses is the burst of reactive oxygen species (ROS), with hydrogen peroxide (H₂ O₂ ) as the most abundant form that occurs as a result of surgical implantation of the donor organ. Here, we used a syngeneic rat renal transplant and IRI model to evaluate the therapeutic properties of APP-103, a polyoxalate-based copolymer molecule containing vanillyl alcohol (VA) that exhibits high sensitivity and specificity toward the production of H₂ O₂ . We show that APP-103 is safe, and that it effectively promotes kidney function following IRI and survival of renal transplants. APP-103 reduces tissue injury and IRI-associated inflammatory responses in models of both warm ischemia (kidney clamping) and prolonged cold ischemia (syngeneic renal transplant). Mechanistically, we demonstrate that APP-103 exerts protective effects by specifically targeting the production of ROS. Our data introduce APP-103 as a novel, nontoxic, and site-activating therapeutic approach that effectively ameliorates the consequences of IRI in solid organ transplantation.

The Acute Phase Response Is a Prominent Renal Proteome Change in Sepsis in Mice

(1) Background: Sepsis-induced acute kidney injury (AKI) is the most common form of acute kidney injury (AKI). We studied the temporal profile of the sepsis-induced renal proteome changes. (2) Methods: Male mice were injected intraperitoneally with bacterial lipopolysaccharide (LPS) or saline (control). Renal proteome was studied by LC-MS/MS (ProteomeXchange: PXD014664) at the early phase (EP, 1.5 and 6 h after 40 mg/kg LPS) and the late phase (LP, 24 and 48 h after 10 mg/kg LPS) of LPS-induced AKI. Renal mRNA expression of acute phase proteins (APP) was assessed by qPCR. (3) Results: Renal proteome change was milder in EP vs. LP. APPs dominated the proteome in LP (proteins upregulated at least 4-fold (APPs/all): EP, 1.5 h: 0/10, 6 h: 1/10; LP, 24 h: 22/47, 48 h: 17/44). Lipocalin-2, complement C3, fibrinogen, haptoglobin and hemopexin were the most upregulated APPs. Renal mRNA expression preceded the APP changes with peak effects at 24 h, and indicated renal production of the majority of APPs. (4) Conclusions: Gene expression analysis revealed local production of APPs that commenced a few hours post injection and peaked at 24 h. This is the first demonstration of a massive, complex and coordinated acute phase response of the kidney involving several proteins not identified previously.

C-reactive protein velocity and the risk of acute kidney injury among ST elevation myocardial infarction patients undergoing primary percutaneous intervention

BACKGROUND

Elevated C-reactive protein (CRP) was shown to be associated with an increased risk for acute kidney injury (AKI) in ST elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PCI), however, the optimal time frame to measure CRP for risk stratification is not known. We evaluated the relation between the change in CRP over time (CRP velocity-CRPv) and AKI among STEMI patients treated with primary PCI.

METHODS

We included 801 STEMI who presented between 2007 and 2017 and had their CRP measured with a wide range assay (wr-CRP) at least twice during the 24 h after admission. CRPv was defined as the change in wr-CRP concentration (mg/l) divided by the change in time (in h) between the two measurements. Patient's medical records were reviewed for occurrence of AKI.

RESULTS

Mean age was 62 ± 16 and 80% were males. Patients with AKI had significantly higher CRPv (1.47 versus 0.4 mg/l/h, p < 0.001). In a multivariate regression model CRPv was independently associated with AKI (OR 1.03, 95% CI 1.01-1.0 5, p = 0.001). On receiver operating characteristic (ROC) curve the optimal cutoff value of CRPv to predict AKI was measured as more than 0.8 mg/l/h, with 70% sensitivity and 65% specificity (AUC 0.712, 95% CI 0.64-0.78, p < 0.001).

CONCLUSION

CRPv might be an independent and rapidly measurable biomarker for AKI following primary PCI in STEMI patients.

Urinary fibrinogen is elevated in hospitalized patients undergoing angiography

OBJECTIVES

Previously, we found that urinary fibrinogen (Fg) levels were positively related to contrast-induced acute renal injury degree in mice. Reduction of fibrinogen in heterozygous mice can improve renal function. Here, we prospectively observed the variation in urinary Fg levels in patients undergoing angiography to determine the relationship between serum creatinine (Scr) and serum cystatin C (Cys C) levels.

METHODS

Serum Cys C and urinary Fg levels were evaluated by ELISA before and 2, 12, and 24 h after angiography in 115 enrolled inpatients. Scr was assessed before and 24 and 48 h after angiography. Data were analyzed using ANOVA or Kruskal-Wallis ANOVA and Spearman correlation.

RESULTS

Urinary Fg levels were elevated as early as 2 h after angiography and decreased thereafter before returning to baseline levels 24 h after angiography. Urinary Fg was correlated with the amount of contrast agent ( r = 0.24, p = 0.036) and the presence of diabetes and hypertension ( r = 0.31, r = 0.28, p < 0.05, respectively). Urinary Fg levels 2 h after angiography were positively related with Cys C at 12 and 24 h and Scr at 48 h after angiography ( r = 0.34, r = 0.51, r = 0.85, p < 0.05, respectively).

CONCLUSIONS

Our results showed that variations in urinary Fg levels are consistent with serum Cys C and Scr in patients undergoing angiography and that urinary Fg levels were the earliest parameter to become elevated. Urinary Fg should be investigated as a useful predictor for abnormal renal function after angiography.

Catheterization alters bladder ecology to potentiate Staphylococcus aureus infection of the urinary tract

Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging cause of catheter-associated urinary tract infection (CAUTI), which frequently progresses to more serious invasive infections. We adapted a mouse model of CAUTI to investigate how catheterization increases an individual's susceptibility to MRSA UTI. This analysis revealed that catheterization was required for MRSA to achieve high-level, persistent infection in the bladder. As shown previously, catheter placement induced an inflammatory response resulting in the release of the host protein fibrinogen (Fg), which coated the bladder and implant. Following infection, we showed that MRSA attached to the urothelium and implant in patterns that colocalized with deposited Fg. Furthermore, MRSA exacerbated the host inflammatory response to stimulate the additional release and accumulation of Fg in the urinary tract, which facilitated MRSA colonization. Consistent with this model, analysis of catheters from patients with S. aureus-positive cultures revealed colocalization of Fg, which was deposited on the catheter, with S. aureus Clumping Factors A and B (ClfA and ClfB) have been shown to contribute to MRSA-Fg interactions in other models of disease. We found that mutants in clfA had significantly greater Fg-binding defects than mutants in clfB in several in vitro assays. Paradoxically, only the ClfB^- strain was significantly attenuated in the CAUTI model. Together, these data suggest that catheterization alters the urinary tract environment to promote MRSA CAUTI pathogenesis by inducing the release of Fg, which the pathogen enhances to persist in the urinary tract despite the host's robust immune response.

Kidney Transplantation: Multiparametric Functional Magnetic Resonance Imaging for Assessment of Renal Allograft Pathophysiology in Mice

OBJECTIVES

The aims of this experimental study were to investigate renal allograft pathophysiology by multiparametric functional magnetic resonance imaging (MRI) and to directly correlate MRI parameters with renal histopathology in mouse models of allogenic and isogenic kidney transplantation (ktx).

MATERIALS AND METHODS

Allograft rejection was induced by transplantation of C57BL/6 (B6) donor kidneys into BALB/c recipients (allogenic ktx). B6 mice that received B6 kidneys served as controls (isogenic ktx). Three weeks after ktx, MRI was performed using a 7-T small-animal scanner. Flow sensitive alternating inversion recovery echoplanar imaging arterial spin labeling, multiecho turbo spin echo, and diffusion-weighted imaging sequences were acquired. Maps of renal perfusion, T2 and T1 relaxation times, and apparent diffusion coefficients were calculated. Histological changes in the kidney were evaluated according to Banff criteria. Renal cell infiltrates and fibrosis were quantified by immunohistochemistry. Differences between groups were assessed using the Mann-Whitney U test, and the correlation of MRI parameters with renal histopathology was determined by Spearman correlation analysis.

RESULTS

After allogenic, but not isogenic, ktx, animals developed acute allograft rejection. Allogenic grafts were infiltrated by macrophages and T-lymphocytes and exhibited marked renal fibrosis. Magnetic resonance imaging revealed stronger impairment of renal perfusion (56 ± 7 vs 293 ± 44 mL/[min × 100 g]; P < 0.01) and more pronounced increases in T2 (60.1 ± 2.0 vs 45.7 ± 1.2 milliseconds, P < 0.01) and T1 relaxation times (1938 ± 53 vs 1350 ± 27 milliseconds, P < 0.01) in allogenic than in isogenic kidneys. Apparent diffusion coefficient was reduced to 1.39 ± 0.14 × 10(-3) mm2/s in kidneys with an acute rejection and was 1.83 ± 0.05 × 10(-3) mm2/s in isogenic kidneys without rejection (P < 0.05). Magnetic resonance imaging parameters significantly correlated with the amount of cellular infiltration and renal fibrosis observed histologically.

CONCLUSIONS

Functional MRI allows detection of acute renal allograft rejection after allogenic ktx in mice. Functional MRI parameters correlate with cell infiltrates and fibrosis. Thus, MRI may be used noninvasively and longitudinally to investigate mechanisms of renal allograft rejection and evaluate novel therapeutic strategies in experimental studies.

Regardless of etiology, progressive renal disease causes ultrastructural and functional alterations of peritubular capillaries

Progressive renal diseases are associated with rarefaction of peritubular capillaries, but the ultrastructural and functional alterations of the microvasculature are not well described. To study this, we analyzed different time points during progressive kidney damage and fibrosis in 3 murine models of different disease etiologies. These models were unilateral ureteral obstruction, unilateral ischemia-reperfusion injury, and Col4a3-deficient mice, we analyzed ultrastructural alterations in patient biopsy specimens. Compared with kidneys of healthy mice, we found a significant and progressive reduction of peritubular capillaries in all models analyzed. Ultrastructurally, compared with the kidneys of control mice, focal widening of the subendothelial space and higher numbers of endothelial vacuoles and caveolae were found in fibrotic kidneys. Quantitative analysis showed that peritubular capillary endothelial cells in fibrotic kidneys had significantly and progressively reduced numbers of fenestrations and increased thickness of the cell soma and lamina densa of the capillary basement membrane. Similar ultrastructural changes were also observed in patient's kidney biopsy specimens. Compared with healthy murine kidneys, fibrotic kidneys had significantly increased extravasation of Evans blue dye in all 3 models. The extravasation could be visualized using 2-photon microscopy in real time in living animals and was mainly localized to capillary branching points. Finally, fibrotic kidneys in all models exhibited a significantly greater degree of interstitial deposition of fibrinogen. Thus, peritubular capillaries undergo significant ultrastructural and functional alterations during experimental progressive renal diseases, independent of the underlying injury. Analyses of these alterations could provide read-outs for the evaluation of therapeutic approaches targeting the renal microvasculature.

Role of Fibrin(ogen) in Progression of Liver Disease: Guilt by Association?

Strong experimental evidence indicates that components of the hemostatic system, including thrombin, exacerbate diverse features of experimental liver disease. Clinical studies have also begun to address this connection and some studies have suggested that anticoagulants can improve outcome in patients with liver disease. Among the evidence of coagulation cascade activation in models of liver injury and disease is the frequent observation of thrombin-driven hepatic fibrin(ogen) deposition. Indeed, hepatic fibrin(ogen) deposition has long been recognized as a consequence of hepatic injury. Although commonly inferred as pathologic due to protective effects of anticoagulants in mouse models, the role of fibrin(ogen) in acute liver injury and chronic liver disease may not be universally detrimental. The localization of hepatic fibrin(ogen) deposits within the liver is connected to the disease stimulus and in animal models of liver toxicity and chronic disease, fibrin(ogen) deposition may not always be synonymous with large vessel thrombosis. Here, we provide a balanced review of the experimental evidence supporting a direct connection between fibrin(ogen) and liver injury/disease pathogenesis, and suggest a path forward bridging experimental and clinical research to improve our knowledge on the nature and function of fibrin(ogen) in liver disease.

Niacin ameliorates kidney warm ischemia and reperfusion injury-induced ventricular dysfunction and oxidative stress and disturbance in mitochondrial metabolism in rats

OBJECTIVE

Kidney ischemia and reperfusion (I/R) injury-associated acute and chronic kidney injury often leads to cardiac dysfunction, which may involve depletion of intracellular NAD(+) (the oxidized form of the nicotinamide adenine dinucleotide coenzyme) and reduction in intracellular adenosine triphosphate (ATP) levels, resulting in mitochondrial dysfunction. We examined whether treatment with niacin, an antioxidant and a component of NAD+, protects cardiac function and improves myocardial mitochondrial metabolism during kidney I/R injury.

METHODS

Studies were performed in Sprague-Dawley male rats divided into sham-operated, kidney I/R, and niacin-treated kidney I/R groups. Niacin was administered 3 days before the ischemia through 7 days of reperfusion. Kidney ischemia was conducted by bilateral occlusion of renal pedicles for 45 minutes, followed by releasing the clamps and closing the abdominal incision. After 7 days of reperfusion, we measured the cardiac function using a simultaneous pressure-volume catheter, cardiac biomarker (troponin T; cTnT), and kidney injury marker (creatinine and blood urea nitrogen). Myocardial malondialdehyde level and peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α mRNA expression also were measured.

RESULTS

Kidney I/R injury impairs cardiac function, induces myocardial and kidney injury, and markedly increases myocardial PGC-1α mRNA expression, suggesting utilizing more free fatty acid for ATP production. Niacin treatment improved cardiac function, reduced oxidative stress, and sustained PGC-1α expression (P < .05).

CONCLUSIONS

Kidney I/R-associated cardiac dysfunction is likely associated with increases in myocardial lipid peroxidation and utilizing more free fatty acid for ATP production. Niacin improves mitochondrial metabolism and reduced myocardial oxidative stress.

The emerging role of coagulation proteases in kidney disease

A role of coagulation proteases in kidney disease beyond their function in normal haemostasis and thrombosis has long been suspected, and studies performed in the past 15 years have provided novel insights into the mechanisms involved. The expression of protease-activated receptors (PARs) in renal cells provides a molecular link between coagulation proteases and renal cell function and revitalizes research evaluating the role of haemostasis regulators in renal disease. Renal cell-specific expression and activity of coagulation proteases, their regulators and their receptors are dynamically altered during disease processes. Furthermore, renal inflammation and tissue remodelling are not only associated, but are causally linked with altered coagulation activation and protease-dependent signalling. Intriguingly, coagulation proteases signal through more than one receptor or induce formation of receptor complexes in a cell-specific manner, emphasizing context specificity. Understanding these cell-specific signalosomes and their regulation in kidney disease is crucial to unravelling the pathophysiological relevance of coagulation regulators in renal disease. In addition, the clinical availability of small molecule targeted anticoagulants as well as the development of PAR antagonists increases the need for in-depth knowledge of the mechanisms through which coagulation proteases might regulate renal physiology.

Inhibition of Thrombin-Activated Fibrinolysis Inhibitor Increases Survival in Experimental Kidney Fibrosis

Uncontrolled diabetes, inflammation, and hypertension are key contributors to progressive renal fibrosis and subsequent loss of renal function. Reduced fibrinolysis appears to be a feature of ESRD, but its contribution to the fibrotic program has not been extensively studied. Here, we show that in patients with CKD, the activity levels of serum thrombin-activated fibrinolysis inhibitor and plasmin strongly correlated with the degree of renal function impairment. We made similar observations in rats after subtotal nephrectomy and tested whether pharmacologic inhibition of thrombin-activated fibrinolysis inhibitor with UK-396082 could reduce renal fibrosis and improve renal function. Compared with untreated animals, UK-396082-treated animals had reduced glomerular and tubulointerstitial fibrosis after subtotal nephrectomy. Renal function, as measured by an increase in creatinine clearance, was maintained and the rate of increase in proteinuria was reduced in UK-396082-treated animals. Furthermore, cumulative survival improved from 16% to 80% with inhibition of thrombin-activated fibrinolysis inhibitor. Taken together, these data support the importance of the fibrinolytic axis in regulating renal fibrosis and point to a potentially important therapeutic role for suppression of thrombin-activated fibrinolysis inhibitor activity.

AKI Recovery Induced by Mesenchymal Stromal Cell-Derived Extracellular Vesicles Carrying MicroRNAs

Phenotypic changes induced by extracellular vesicles have been implicated in mesenchymal stromal cell-promoted recovery of AKI. MicroRNAs are potential candidates for cell reprogramming toward a proregenerative phenotype. The aim of this study was to evaluate whether microRNA deregulation inhibits the regenerative potential of mesenchymal stromal cells and derived extracellular vesicles in a model of glycerol-induced AKI in severe combined immunodeficient mice. We generated mesenchymal stromal cells depleted of Drosha to alter microRNA expression. Drosha-knockdown cells produced extracellular vesicles that did not differ from those of wild-type cells in quantity, surface molecule expression, and internalization within renal tubular epithelial cells. However, these vesicles showed global downregulation of microRNAs. Whereas wild-type mesenchymal stromal cells and derived vesicles administered intravenously induced morphologic and functional recovery in AKI, the Drosha-knockdown counterparts were ineffective. RNA sequencing analysis showed that kidney genes deregulated after injury were restored by treatment with mesenchymal stromal cells and derived vesicles but not with Drosha-knockdown cells and vesicles. Gene ontology analysis showed in AKI an association of downregulated genes with fatty acid metabolism and upregulated genes with inflammation, matrix-receptor interaction, and cell adhesion molecules. These alterations reverted after treatment with wild-type mesenchymal stromal cells and extracellular vesicles but not after treatment with the Drosha-knockdown counterparts. In conclusion, microRNA depletion in mesenchymal stromal cells and extracellular vesicles significantly reduced their intrinsic regenerative potential in AKI, suggesting a critical role of microRNAs in recovery after AKI.

High sensitive C-reactive protein and the risk of acute kidney injury among ST elevation myocardial infarction patients undergoing primary percutaneous intervention

BACKGROUND

Elevated periprocedural high sensitive C-reactive protein (hs-CRP) was shown to be associated with an increased risk for acute kidney injury (AKI) in non-myocardial infarction (MI) patients undergoing percutaneous coronary intervention (PCI), however, no information to date is present regarding its predicting role for AKI in MI patients. We evaluated whether admission serum hs-CRP levels may predict risk of AKI among ST elevation MI (STEMI) patients undergoing primary PCI.

METHODS

Five hundred and sixty-two patients that were admitted with STEMI and treated with primary PCI were included in the study. Serum hs-CRP levels were determined from blood samples taken prior to PCI. Patients' medical records were reviewed for occurrence of AKI, in-hospital complications and 30 days mortality.

RESULTS

Mean age was 62 ± 16 and 455 (80 %) were males. Patients were divided into two groups, according to their admission hs-CRP values: group 1: hs-CRP ≤9 mg/l (n = 394) and group 2: hs-CRP >9 mg/l (n = 168). Patients with hs-CRP >9 mg/l had significantly higher rate of AKI following PCI (17 vs. 6 %; p < 0.001), more in-hospital complications and higher30 -day mortality rate (11 vs. 1 %; p = 0.02). In a multivariable logistic regression model admission hs-CRP level >9 mg/l was an independent predictor for AKI (OR 2.7, 95 % CI: 1.39-5.29; p = 0.001) and a strong trend for 30 day mortality (OR 4.27, 95 % CI: 0.875-21.10; p = 0.07).

CONCLUSION

Admission serum hs-CRP level >9 mg/l is an independent predictor for AKI following primary PCI in STEMI patients.

Ischemia/reperfusion injury: effect of simultaneous inhibition of plasma cascade systems versus specific complement inhibition

Ischemia/reperfusion injury (IRI) may occur from ischemia due to thrombotic occlusion, trauma or surgical interventions, including transplantation, with subsequent reestablishment of circulation. Time-dependent molecular and structural changes result from the deprivation of blood and oxygen in the affected tissue during ischemia. Upon restoration of blood flow a multifaceted network of plasma cascades is activated, including the complement-, coagulation-, kinin-, and fibrinolytic system, which plays a major role in the reperfusion-triggered inflammatory process. The plasma cascade systems are therefore promising therapeutic targets for attenuation of IRI. Earlier studies showed beneficial effects through inhibition of the complement system using specific complement inhibitors. However, pivotal roles in IRI are also attributed to other cascades. This raises the question, whether drugs, such as C1 esterase inhibitor, which regulate more than one cascade at a time, have a higher therapeutic potential. The present review discusses different therapeutic approaches ranging from specific complement inhibition to simultaneous inhibition of plasma cascade systems for reduction of IRI, gives an overview of the plasma cascade systems in IRI as well as highlights recent findings in this field.