N-acetylcysteine ameliorates acute kidney injury but not glomerular hemorrhage in an animal model of warfarin-related nephropathy

Role of mitochondria in reno-cardiac diseases: A study of bioenergetics, biogenesis, and GSH signaling in disease transition

Acute kidney injury (AKI) and chronic kidney disease (CKD) are global health burdens with rising prevalence. Their bidirectional relationship with cardiovascular dysfunction, manifesting as cardio-renal syndromes (CRS) types 3 and 4, underscores the interconnectedness and interdependence of these vital organ systems. Both the kidney and the heart are critically reliant on mitochondrial function. This organelle is currently recognized as a hub in signaling pathways, with emphasis on the redox regulation mediated by glutathione (GSH). Mitochondrial dysfunction, including impaired bioenergetics, redox, and biogenesis pathways, are central to the progression of AKI to CKD and the development of CRS type 3 and 4. This review delves into the metabolic reprogramming and mitochondrial redox signaling and biogenesis alterations in AKI, CKD, and CRS. We examine the pathophysiological mechanisms involving GSH redox signaling and the AMP-activated protein kinase (AMPK)-sirtuin (SIRT)1/3-peroxisome proliferator-activated receptor-gamma coactivator (PGC-1α) axis in these conditions. Additionally, we explore the therapeutic potential of GSH synthesis inducers in mitigating these mitochondrial dysfunctions, as well as their effects on inflammation and the progression of CKD and CRS types 3 and 4.

N-acetylcysteine in Kidney Disease: Molecular Mechanisms, Pharmacokinetics, and Clinical Effectiveness

N-acetylcysteine (NAC) has shown beneficial effects in both acute kidney disease and chronic kidney disease (CKD) in preclinical and clinical studies. Different dosage and administration forms of NAC have specific pharmacokinetic properties that determine the temporal pattern of plasma concentrations of NAC and its active metabolites. Especially in acute situations with short-term NAC administration, appropriate NAC and glutathione (GSH) plasma concentrations should be timely ensured. For oral dosage forms, bioavailability needs to be established for the respective NAC formulation. Kidney function influences NAC pharmacokinetics, including a reduction of NAC clearance in advanced CKD. In addition, mechanisms of action underlying beneficial NAC effects depend on kidney function as well as comorbidities, both involving GSH deficiency, alterations in nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent signaling, oxidative stress, mitochondrial dysfunction, and disturbed mitochondrial bioenergetics. This also applies to nonrenal NAC mechanisms. The timing of preventive NAC administration in relation to potential injury is important. NAC administration seems most effective either preceding, or preceding and paralleling conditions that induce tissue damage. Furthermore, studies suggest that very high concentrations of NAC should be avoided because they could exert reductive stress. Delayed administration of NAC might interfere with endogenous repair mechanisms. In conclusion, studies on NAC treatment regimens need to account for both NAC pharmacokinetics and NAC molecular effects. Kidney function of the patient population and pathomechanisms of the kidney disease should guide rational NAC trial design. A targeted trial approach and biomarker-guided protocols could pave the way for the use of NAC in precision medicine.

Role of plasminogen activated inhibitor-1 in the pathogenesis of anticoagulant related nephropathy

Anticoagulant related nephropathy (ARN) is the result of glomerular hemorrhage in patients on systemic anticoagulation therapy or underlying coagulopathy. Red blood cells (RBC) that passed through the glomerular filtration barrier form RBC casts in the tubules, increase oxidative stress and result in acute tubular necrosis (ATN). The mechanisms of ARN still not completely discovered. Plasminogen activator inhibitor-1 (PAI-1) plays a significant role in the maintenance of coagulation homeostasis. We developed an animal model to study ARN in 5/6 nephrectomy (5/6NE) rats. The aim of this study was to elucidate the role of PAI-1 in the ARN pathogenesis. 5/6NE rats were treated per os with warfarin (0.75 mg/kg/day) or dabigatran (150 mg/kg/day) alone or in combination with PAI-1 antagonist TM5441 (2.5, 5.0 and 10 mg/kg/day). TM5441 in a dose dependent manner ameliorated anticoagulant-induced increase in serum creatinine in 5/6NE rats. Anticoagulant-associated increase in hematuria was no affected by TM5441. The levels of reactive oxygen species (ROS) in the kidneys were in a dose-dependent manner decreased in 5/6NE rats treated with an anticoagulant and TM5441. Our data demonstrates that PAI-1 may reduce ARN by decreasing ROS in the kidneys. Glomerular hemorrhage is not affected by anti-PAI-1 treatment. These findings indicate that while symptoms of ARN can be reduced by PAI-1 inhibition, the main pathogenesis of ARN - glomerular hemorrhage - cannot be prevented.

Toxicology of chemical biocides: Anticoagulant rodenticides - Beyond hemostasis disturbance

The use of anticoagulant rodenticides (ARs) is one of the most commonly employed management methods for pest rodents. ARs compete with vitamin K (VK) required for the synthesis of blood clotting factors in the liver, resulting in inhibition of blood coagulation and often animal death due to hemorrhage. Besides rodents (target species), ARs may affect non-target animal species and humans. Out of hemostasis disturbance, the effects of ARs may be related to the inhibition of proteins that require VK for their synthesis but are not involved in the coagulation process, to their direct cytotoxicity, and their pro-oxidant/proinflammatory activity. A survey of the cellular and molecular mechanisms of these sublethal/asymptomatic AR effects is given in this review. Data from field, clinical, and experimental studies are presented. Knowledge of these mechanisms might improve hazard characterization and identification of potential ecotoxicological risks associated with ARs, contributing to a safer use of these chemicals.

N-acetylcysteine ameliorates hematuria-associated tubulointerstitial injury in 5/6 nephrectomy mice

Chronic kidney disease (CKD) is characterized by increased interstitial fibrosis and tubular atrophy (IFTA) in the kidney. Chronic hematuria is a hallmark of several human kidney diseases and often is seen in patients on anticoagulation therapy. We had previously demonstrated that chronic hematuria associated with warfarin increases IFTA in 5/6 nephrectomy (5/6NE) rats, and such treatment increases reactive oxygen species (ROS) in the kidney. The goal of this study was to evaluate the effects of the antioxidant N-acetylcysteine (NAC) on the progression of IFTA in 5/6NE mice. 5/6NE C57BL/6 and 5/6NE 129S1/SvImJ mice were treated with warfarin alone or with warfarin and NAC for 23 weeks. Serum creatinine (SCr), hematuria, blood pressure (BP), and ROSs in the kidney were measured; kidney morphology was evaluated. Warfarin doses were titrated to achieve prothrombin time (PT) increase to the levels seen with therapeutic human doses. Warfarin treatment resulted in an increased SCr, systolic BP, hematuria, expression of TGF-ß and ROS in the kidney in both mouse strains. Tumor necrosis factor alpha (TNF-ɑ) levels in the serum were increased in 5/6NE mice treated with warfarin. IFTA was increased as compared with control 5/6NE mice, and this increase in IFTA was more prominent in 129S1/SvImJ than in C57BL/6 mice. NAC ameliorated the warfarin-associated increase in SCr and BP but not hematuria. IFTA, TGF-ß, and ROS in the kidney as well as TNF-ɑ levels in the serum were reduced in mice treated with NAC and warfarin as compared to mice treated with warfarin alone. NAC mitigates the increase in SCr and IFTA in mice with chronic hematuria by reducing oxidative stress in the kidney. This data open novel possibilities for treatments in CKD patients.

Research Letter: Is the 129S1/SvImJ Mouse Strain More Suitable to Study Anticoagulant-Related Nephropathy Than the C57BL/6 Strain?

Background

We have previously demonstrated that excessive anticoagulation with warfarin or dabigatran may result in acute kidney injury with red blood cell (RBC) tubular casts in some patients with chronic kidney disease, and this condition was named anticoagulant-related nephropathy (ARN). 5/6 nephrectomy (5/6NE) rats treated with warfarin or dabigatran reproduce the main pathologic features of human ARN. We had reported that 5/6NE C57BL/6 mice only partially develop ARN with increased serum creatinine and hematuria but no RBC tubular casts in the kidney.

Objectives

The aim of this study was to investigate whether ARN can develop in 5/6NE 129S1/SvImJ mice.

Methods

5/6NE was performed in 129S1/SvImJ mice. Three weeks after 5/6NE, mice were treated with warfarin (1.0 and 1.5 mg/kg/day) or vehicle for 7 days. Serum creatinine, hematuria, and prothrombin time (PT) were monitored daily. Renal morphology was evaluated at the end of the studies.

Results

Treatment with warfarin resulted in PT elevation 2 to 3 folds from baseline (1.0 mg/kg/day warfarin) and 4 to 5 folds from baseline (1.5 mg/kg/day warfarin) by day 7. Serum creatinine and hematuria elevated by day 7 in a dose-dependent manner. Histologically, 2 of 8 (25%) 5/6NE mice had RBCs in the tubules, and there was acute tubular epithelial cell injury in all warfarin-treated 5/6NE 129S1/SvImJ mice.

Conclusions

Our findings suggest that 129S1/SvImJ mouse strain is a more suitable murine model to study ARN than C57BL/6 mouse strain.

Acute kidney injury from presumptive intramural ureteral hemorrhage secondary to diphacinone rodenticide exposure in a dog

OBJECTIVE

To describe the clinical features and outcome of a dog with anticoagulant rodenticide (diphacinone) exposure, which was subsequently diagnosed with a coagulopathy characterized by hemoperitoneum, and presumptive ureteral wall hemorrhage contributing to acute kidney injury (AKI).

CASE SUMMARY

A 4-year-old, female neutered Australian Cattle Dog was evaluated for an acute onset of lethargy, decreased appetite, and a mild right thoracic limb lameness. Radiographs and point of care ultrasound demonstrated retroperitoneal and peritoneal effusion. Diagnostic abdominocentesis confirmed hemorrhagic effusion. Complete blood count, biochemistry, and coagulation profile showed a regenerative anemia (PCV 32%), thrombocytopenia (platelets 96 × 10⁹ /L [96 × 10³ /µl]), azotemia (BUN 38.9 mmol/L [109 mg/dl], creatinine 512.8 µmol/L [5.8 mg/dl]), and coagulopathy (prothrombin time >100 s, activated partial thromboplastin time >42.3 s). The client reported access to anticoagulant rodenticide up to 72 hours prior to presentation. Ultrasonographic examination revealed bilateral pyelectasia and hydroureter with thickened distal ureteral walls at the level of the ureteral-vesicular junctions. The ultrasonographic conclusion was presumptive intramural ureteral hemorrhage resulting in ureteral obstruction. The patient was diagnosed with AKI with likely prerenal, renal, and postrenal components. Treatment included vitamin K and frozen plasma transfusion. The patient recovered fully and was discharged 3 days after presentation. Two days after discharge, the patient had improvement in azotemia (BUN 10.7 mmol/L [30 mg/dl], creatinine 176.6 µmol/L [2.0 mg/dl]). Gas chromatography-mass spectrometry confirmed presence of diphacinone in the blood. Repeat ultrasound and biochemistry 60 and 210 days, respectively, after discharge showed resolution of ureteral wall thickening, hydroureter, pyelectasia, and recovery of kidney parameters.

NEW OR UNIQUE INFORMATION

Although nephropathies secondary to anticoagulant therapy have been described in people, the authors believe this is the first report of diphacinone anticoagulant rodenticide exposure contributing to an AKI secondary to obstruction from ureteral wall hemorrhage in the veterinary literature.

Vitamin K antagonist-associated microscopic hematuria

BACKGROUND

Vitamin K antagonists (VKA) are the most widely used anticoagulants for the prevention of thrombotic events. Several renal adverse effects have been associated with the use of VKA. The main aim of our study was to explore the association between international normalized ratio (INR) levels and microscopic hematuria in patients with VKA.

METHODS

We performed a cross-sectional study of patients treated with VKA that attended the outpatient clinic for routine INR control. A simple urinalysis was performed on the day of the INR control and the precise number of red cells in the urine sediment was quantified. Demographic data, kidney function tests, comorbidities, anticoagulant dose and concomitant treatment were registered.

RESULTS

A total of 337 patients were included with median INR levels of 2.6 (IQR 2.1-3.3). 11.9% of the patients presented microscopic hematuria (≥14 RBCs/µl). There was a significant correlation between INR levels and the number of red blood cells in the urine sediment (r = 0.201, p = 0.024). In the univariate analysis, microscopic hematuria was associated with having an INR >3.5 (19% vs. 10.2%, p = 0.046), bacteriuria (15.2% vs. 3.6%, p = 0.015), leukocyturia (14.8% vs. 6.6%, p =  0.026), hypertension (16.2% vs. 9.5%, p = 0.053), and the use of renin-angiotensin system (RAS) blockers (6.9% vs. 17.2%, p = 0.004). Multivariate logistic regression showed an association between microscopic hematuria and RAS blockade (OR 0.38, CI 95% 0.163-0.886, p = 0.025), independent from INR levels, hypertension, leukocyturia or bacteriuria.

CONCLUSIONS

INR overdose was significantly associated with the presence of microscopic hematuria. RAS blockade is an independent protective factor for the presence of microscopic hematuria in anticoagulated patients.

Role of protease-activated receptor-1 (PAR-1) in the glomerular filtration barrier integrity

Protease-activated receptors (PAR) play an important role in the regulation of cellular function by the coagulation system, and they are activated by thrombin. PAR-1 is expressed in both endothelial cells and podocytes in the kidney. The role of PAR1 in the maintenance of the glomerular filtration barrier is not clear. Anticoagulant-related nephropathy (ARN) is a kidney disease with glomerular hematuria and red blood cell tubular casts. We validated 5/6 nephrectomy (5/6NE) in rats as a model of ARN and had demonstrated that direct thrombin inhibitor (dabigatran) induces ARN. The aim of this study was to investigate the role of PAR-1 in the ARN pathogenesis. 5/6NE rats were treated with dabigatran (150 mg/kg/day), PAR-1 inhibitor SCH79797 (1 and 3 mg/kg/day) and PAR-1 agonist TFLLR-NH2 (0.25 and 0.50 µmol/kg/day) for 7 days. Serum creatinine and hematuria were assessed daily. Kidney morphology was evaluated at the end of the study. In 5/6NE rats treated with either dabigatran or combination with a PAR-1 modulator, there was an elevation in serum creatinine, glomerular hematuria, red blood casts in the tubules, and acute tubular epithelial cell injury. Interestingly, both PAR-1 modulators in a dose-depended manner had similar effects on the serum creatinine levels and hematuria as those of dabigatran. Dabigatran-induced increase in the systolic blood pressure was not affected by PAR-1 modulators. In conclusion, the normal function of PAR-1 is crucial to maintain the glomerular filtration barrier integrity. Either activation or blockage of PAR-1 leads to glomerular hematuria and subsequent acute tubular epithelial cell injury.

Vitamin K1 inhibits ferroptosis and counteracts a detrimental effect of phenprocoumon in experimental acute kidney injury

Ferroptosis, a type of iron-dependent programmed cell death distinct from apoptosis, necroptosis, and other types of cell death, is characterized by lipid peroxidation, reactive oxygen species production, and mitochondrial dysfunction. Accumulating evidence has highlighted vital roles for ferroptosis in multiple diseases, including acute kidney injury. Therefore, ferroptosis has become a major focus for translational research. However, despite its involvement in pathological conditions, there are no pharmacologic inhibitors of ferroptosis in clinical use. In the context of drug repurposing, a strategy for identifying new uses for approved drugs outside the original medical application, we discovered that vitamin K1 is an efficient inhibitor of ferroptosis. Our findings are strengthened by the fact that the vitamin K antagonist phenprocoumon significantly exacerbated ferroptotic cell death in vitro and also massively worsened the course of acute kidney injury in vivo, which is of utmost clinical importance. We therefore assign vitamin K1 a novel role in preventing ferroptotic cell death in acute tubular necrosis during acute kidney injury. Since the safety, tolerability, pharmacokinetics, and pharmacodynamics of vitamin K1 formulations are well documented, this drug is primed for clinical application, and provides a new strategy for pharmacological control of ferroptosis and diseases associated with this mode of cell death.

[A new approach to combat the sepsis including COVID-19 by accelerating detoxification of hemolysis-related DAMPs]

Sepsis is one of the leading cause of death worldwide. Recently, several studies suggested that free-hemoglobin and heme derived from hemolysis are important factors which may be associated with severity of septic patients including COVID-19. In other words, hemolysis-derived products enhance the inflammatory responses as damage-associated molecular patterns (DAMPs) in both intravascular and extravascular space. In addition, hemoglobin has vasoconstrictive activity by depleting nitric oxide, whereas heme or Fe²⁺ produce reactive oxygen species (ROS) through Fenton reaction leading to tissue injury. At present, we have no therapeutic options against sepsis-related hemolysis in clinical settings, however, there might be two therapeutic strategies in this regard. One is supplemental therapy of depleted scavenging proteins such as haptoglobin and hemopexin, the other is activation of the internal scavenging system including macrophage-CD163 pathway. These novel targets against sepsis are also critical for the next pandemic. In this review, we summarize the current issues regarding sepsis-related hemolysis including COVID-19, as well as for future perspectives.

Chronic Hematuria Increases Chronic Kidney Injury and Epithelial-Mesenchymal Transition in 5/6 Nephrectomy Rats

Chronic kidney disease (CKD) is a common outcome of many kidney diseases. Interstitial fibrosis and tubular atrophy (IFTA) is a histologic hallmark of CKD. Hematuria is a common symptom in many human kidney diseases. Free hemoglobin may affect tubular epithelial cells by generating reactive oxygen species (ROS). Epithelial–mesenchymal transition (EMT) of the tubular epithelial cells has been shown to play an important role in the IFTA development. The aim of this study was to determine the effects of chronic hematuria on the CKD progression in 5/6 nephrectomy (5/6NE) rat model of CKD. 5/6 NE rats were treated with oral warfarin (0.5 mg/kg/day) or vehicle (control). The animals were monitored for 26 weeks, while prothrombin time (PT), serum creatinine (SCr), and hematuria were measured weekly. Staining for iron, trichrome, and EMT (vimentin, E-cadherin, smooth muscle actin) markers was performed on the remnant kidneys. ROS were detected in the kidneys by protein carbonyl assay and immunohistochemistry for heme oxygenase 1 (HMOX1), at the end of the study. Apoptosis was detected by TUNEL assay. Warfarin treatment resulted in a PT increase 1.5–2.5 times from control and an increase in hematuria and SCr. Histologically, warfarin-treated animals had more iron-positive tubular epithelial cells and increased IFTA as compared to control (42.9 ± 17% vs. 18.3 ± 2.6%). ROS were increased in the kidney in warfarin-treated rats. The number of tubules that show evidence of EMT was significantly higher in warfarin-treated 5/6NE as compared to control 5/6NE rats. The number of apoptotic tubular epithelial cells was higher in warfarin-treated 5/6 NE rats. Chronic hematuria results in increased iron-positive tubular epithelial cells, EMT, apoptosis, and more prominent IFTA in CKD rats. Our data suggest an important role of chronic hematuria in the progression of CKD.

Porcine models of acute kidney injury

Pigs represent a potentially attractive model for medical research. Similar body size and physiological patterns of kidney injury that more closely mimic those described in humans make larger animals attractive for experimentation. Using larger animals, including pigs, to investigate the pathogenesis of acute kidney injury (AKI) also serves as an experimental bridge, narrowing the gap between clinical disease and preclinical discoveries. This article compares the advantages and disadvantages of large versus small AKI animal models and provides a comprehensive overview of the development and application of porcine models of AKI induced by clinically relevant insults, including ischemia-reperfusion, sepsis, and nephrotoxin exposure. The primary focus of this review is to evaluate the use of pigs for AKI studies by current investigators, including areas where more information is needed.

Anticoagulant Related Nephropathy Only Partially Develops in C57BL/6 Mice: Hematuria Is Not Accompanied by Red Blood Cell Casts in the Kidney

Anticoagulant-related nephropathy (ARN) may develop in patients that are on anticoagulation therapy. Rats with 5/6 nephrectomy treated with different anticoagulants showed acute kidney injury (AKI) and red blood cell (RBC) casts in the tubules similar to ARN in humans. The aim of the current study was to investigate the feasibility of inducing ARN in mice. C57BL/6 5/6 nephrectomy mice were treated with warfarin and dabigatran 3 weeks after ablative surgery for 7 days. Two doses of each anticoagulant were used. All anticoagulants resulted in serum creatinine and hematuria increase. Mortality was 63% in 5.0 mg/kg/day of warfarin but only 13% in 2.5 mg/kg/day of warfarin or in 400 mg/kg/day of dabigatran and 0% in 200 mg/kg/day of dabigatran. In spite of increasing hematuria, RBC tubular casts were not seen in mice treated with any anticoagulant. The 5/6 nephrectomy murine model in C57BL/6 mice only partially reproduced ARN in terms of increasing serum creatinine and hematuria, but there were no RBC tubular casts in the remnant kidney.

Red-Colored Urine in the Cardiac Surgical Patient-Diagnosis, Causes, and Management

Red-colored urine occurring in the intraoperative and early postoperative periods after cardiac surgery is often a cause for concern. This observation may be a result of hematuria from pathology within the urinary tract, anticoagulant-related nephropathy, drug-induced acute interstitial nephropathy, excretion of heme pigment-containing proteins, such as myoglobin and hemoglobin, and hemolysis occurring during extracorporeal circulation. Within the kidneys, heme-containing compounds result in pigment nephropathy, which is a significant contributory factor to cardiac surgery-associated acute kidney injury. Concerted efforts to reduce red blood cell damage during cardiopulmonary bypass, together with early recognition of the at-risk patient and the institution of prompt therapeutic intervention, may improve outcomes. This review addresses the diagnosis, causes, and management of red-discolored urine occurring during and after cardiac surgery.

Dabigatran-induced anticoagulant-related nephropathy with undiagnosed IgA nephropathy in a patient with normal baseline renal function

Occasionally, over-anticoagulation with warfarin induces acute kidney injury (AKI) characterized by glomerular hemorrhage with tubular obstruction by red blood cell casts, which is widely acknowledged as warfarin-related nephropathy. Owing to extensive use of direct oral anticoagulants, similar AKI cases have been reported among patients treated with dabigatran. Dabigatran is primarily excreted by the kidneys; thus, renal impairment is one of the risk factors for dabigatran-induced bleeding complications. Nevertheless, risk factors for dabigatran-induced anticoagulant-related nephropathy (ARN) remain partially clarified. Here, we report a histologically established case of dabigatran-induced ARN with undiagnosed IgA nephropathy in a patient with normal baseline renal function. In addition, we summarize previously published cases of biopsy-proven, dabigatran-related ARN. A 67-year-old female with normal preexisting renal function developed macrohematuria and AKI. She had been treated with dabigatran for deep vein thrombosis. A renal biopsy diagnosed ARN with inactive IgA nephropathy. After dabigatran withdrawal, her macrohematuria and renal function improved. This report demonstrates that ARN could occur in patients with normal baseline renal function. Our case and prior reports suggest that IgA nephropathy could be a risk factor for dabigatran-induced ARN.

The Bile Sequestrant Cholestyramine Increases Survival in a Rabbit Model of Brodifacoum Poisoning

Patients exposed to long acting anticoagulant rodenticides (LAARs) are typically administered large amounts of oral vitamin K1 (VK1) to counteract life-threatening anticoagulant effects. Although VK1 treatment effectively prevents mortality, additional methods are needed to reduce the long duration of VK1 treatment which can last for months at high expense. We developed a model of brodifacoum (BDF) poisoning, one of the most potent LAARs, in adult male New Zealand White (NZW) rabbits. The LD50 for oral BDF was determined to be 192 μg/kg, similar to that calculated for adult rats. However, in contrast to rats, NZW rabbits exhibited severe internal hemorrhage including in the brain, symptoms which mimic what occurs in cases of human poisoning. Similar to warfarin, BDF and other LAARs undergo enterohepatic recirculation which contributes to their long half-lives. We therefore tested effects of cholestyramine (CSA), an FDA-approved bile sequestrant, on BDF-induced mortality. When given daily (0.67 g/kg, oral) starting the day of BDF administration, CSA reduced mortality from 67% to 11%. At the same CSA prevented the increase in clotting time, and reduced the decrease in core body temperature due to BDF. Given its excellent safety record and that it is approved for children older than 6 years, these findings suggest CSA could be considered as an adjunct to VK1 for treatment of LAAR poisoning.

Mechanisms of haemolysis-induced kidney injury

Intravascular haemolysis is a fundamental feature of chronic hereditary and acquired haemolytic anaemias, including those associated with haemoglobinopathies, complement disorders and infectious diseases such as malaria. Destabilization of red blood cells (RBCs) within the vasculature results in systemic inflammation, vasomotor dysfunction, thrombophilia and proliferative vasculopathy. The haemoprotein scavengers haptoglobin and haemopexin act to limit circulating levels of free haemoglobin, haem and iron - potentially toxic species that are released from injured RBCs. However, these adaptive defence systems can fail owing to ongoing intravascular disintegration of RBCs. Induction of the haem-degrading enzyme haem oxygenase 1 (HO1) - and potentially HO2 - represents a response to, and endogenous defence against, large amounts of cellular haem; however, this system can also become saturated. A frequent adverse consequence of massive and/or chronic haemolysis is kidney injury, which contributes to the morbidity and mortality of chronic haemolytic diseases. Intravascular destruction of RBCs and the resulting accumulation of haemoproteins can induce kidney injury via a number of mechanisms, including oxidative stress and cytotoxicity pathways, through the formation of intratubular casts and through direct as well as indirect proinflammatory effects, the latter via the activation of neutrophils and monocytes. Understanding of the detailed pathophysiology of haemolysis-induced kidney injury offers opportunities for the design and implementation of new therapeutic strategies to counteract the unfavourable and potentially fatal effects of haemolysis on the kidney.

Glomerular Hematuria: Cause or Consequence of Renal Inflammation?

Glomerular hematuria is a cardinal symptom of renal disease. Glomerular hematuria may be classified as microhematuria or macrohematuria according to the number of red blood cells in urine. Recent evidence suggests a pathological role of persistent glomerular microhematuria in the progression of renal disease. Moreover, gross hematuria, or macrohematuria, promotes acute kidney injury (AKI), with subsequent impairment of renal function in a high proportion of patients. In this pathological context, hemoglobin, heme, or iron released from red blood cells in the urinary space may cause direct tubular cell injury, oxidative stress, pro-inflammatory cytokine production, and further monocyte/macrophage recruitment. The aim of this manuscript is to review the role of glomerular hematuria in kidney injury, the role of inflammation as cause and consequence of glomerular hematuria, and to discuss novel therapies to combat hematuria.

Anticoagulant-Related Nephropathy in Kidney Biopsy: A Single-Center Report of 41 Cases

Rationale & Objective

In 2009, the first case of acute kidney injury and occlusive red blood cell (RBC) tubular casts associated with a high international normalized ratio in a patient receiving warfarin was identified. This entity, named warfarin-related nephropathy, was later renamed anticoagulant-related nephropathy (ARN) after similar cases with other anticoagulants were described. We provide our 10-year experience with ARN based on a single-center kidney biopsy laboratory.

Study Design

The kidney pathology database at the Ohio State University Wexner Medical Center (OSUWMC) was searched for native kidney biopsy cases consistent with ARN. Clinical data were obtained from patient medical records.

Setting & Participants

Native kidney biopsies evaluated between January 1, 2009, and December 31, 2017 at OSUWMC.

Results

Among 8,636 native kidney biopsies reviewed at the OSUWMC, there were 41 (0.5%) patients for whom deterioration in kidney function could not be explained by kidney biopsy findings alone if anticoagulation was not considered. There were 63% men and 95% were white; average age was 62 ± 14 years. Most were on warfarin therapy (N = 28), although cases were also attributed to direct-acting anticoagulants (N = 2), antiplatelet medications (N = 1), heparin or enoxaparin (N = 4), and disseminated intravascular coagulopathy (N = 6). Morphologically, there was acute tubular necrosis and RBC casts. The majority of biopsies had an underlying glomerular disease and many patients had positive serologic test results. In all these cases, the severity of kidney failure, RBC tubular casts, and hematuria were disproportionate to glomerular morphologic changes.

Limitations

Selection bias in the decision to perform a kidney biopsy.

Conclusions

ARN is an uncommon diagnosis in kidney pathology practice, but it should be considered when the number of RBC tubular casts is disproportionate to the severity of glomerular changes in a kidney biopsy in patients either receiving anticoagulation therapy or who presented with acute coagulopathy. Our data suggest that anticoagulation aggravates underlying glomerular diseases rather than directly affecting the glomerular filtration barrier.

Anticoagulant-related nephropathy: systematic review and meta-analysis

Background

The aim of this study was to report the prevalence and mortality associated with anticoagulant-related nephropathy (ARN) through a systematic review of the literature.

Methods

Electronic searches were conducted in the Medline and EMBASE databases, and manual searches were performed in the reference lists of the identified studies. The studies were selected by two independent researchers, first by evaluating the titles and abstracts and then by reading the complete texts of the identified studies. Case series, cross-sectional studies, cohort studies and case–control studies reporting the prevalence and factors associated with ARN were selected. The methodological quality was assessed using the Newcastle–Ottawa scale. Meta-analyses of the prevalence of ARN and 5-year mortality using the random effects model were performed when possible. Heterogeneity was assessed using the I² statistic.

Results

Five studies were included. Prevalence of ARN ranged from 19% to 63% among the four included cohort studies. Meta-analysis of these resulted in high heterogeneity [I² 96%, summary effect 31%; 95% confidence interval (CI) 22–42%]. Subgroup meta-analysis yielded an ARN prevalence of 20% among studies that included patients with fewer comorbidities (I² 12%; 95% CI 19–22%). In a direct comparison, meta-analysis of the 5-year mortality rate between anticoagulated patients who had experienced ARN and anticoagulated patients without ARN, patients with ARN were 91% more likely to die (risk ratio = 1.91; 95% CI 1.22–3; I² 87%). Risk factors for ARN that were reported in the literature included initial excessive anticoagulation, chronic kidney disease, age, diabetes, hypertension, cardiovascular disease and heart failure.

Conclusions

ARN studies are scarce and heterogeneous, and present significant methodological limitations. The high prevalence of ARN reported herein suggests that this entity is underdiagnosed in clinical practice. Mortality in patients with ARN seems to be high compared with patients without this condition in observational studies.

Dabigatran-Induced Acute Interstitial Nephritis: An Important Complication of Newer Oral Anticoagulation Agents

Acute kidney injury (AKI) due to an acute interstitial nephritis (AIN) is common and can lead to increased morbidity and mortality. Medications such as antibiotics, nonsteroidal anti-inflammatory drugs (NSAIDs), proton pump inhibitors (PPI) and rifampin are common offending agents. Anticoagulant-associated AIN is more frequently reported with the use of warfarin; however, only few case reports have reported an association with the use of novel oral anticoagulants (NOACs). Herein, we report the case of a 59-year-old male who developed AKI after initiating dabigatran for the treatment of atrial fibrillation. Laboratory data demonstrated elevated blood urea nitrogen (BUN) of 115 mg/dL (baseline = 35 mg/dL) and serum creatinine (Cr) of 5.06 mg/dL (baseline = 1.3 mg/dL). Urinalysis revealed eosinophiluria. Renal biopsy disclosed diffuse tubulointerstitial nephritis and eosinophils and confirmed the diagnosis of AIN. At 1 week, renal function improved (BUN/Cr = 53/2.73 mg/dL) with steroid therapy and discontinuation of dabigatran. With an increasing use of NOACs, it is important to monitor renal function to diagnose AIN in a timely fashion. Early diagnosis and prompt treatment can mitigate serious renal damage induced by dabigatran.

Effects of warfarin on biological processes other than haemostasis: A review

Warfarin is the world's most widely used anticoagulant drug. Its anticoagulant activity is based on the inhibition of the vitamin K-dependent (VKD) step in the complete synthesis of a number of blood coagulation factors that are required for normal blood coagulation. Warfarin also affects synthesis of VKD proteins not related to haemostasis including those involved in bone growth and vascular calcification. Antithrombotic activity of warfarin is considered responsible for some aspects of its anti-tumour activity of warfarin. Some aspects of activities against tumours seem not to be related to haemostasis and included effects of warfarin on non-haemostatic VKD proteins as well as those not related to VKD proteins. Inflammatory/immunomodulatory effects of warfarin indicate much broader potential of action of this drug both in physiological and pathological processes. This review provides an overview of the published data dealing with the effects of warfarin on biological processes other than haemostasis.

Anticoagulant-related nephropathy in a patient with IgA nephropathy

Anticoagulant-related nephropathy is a type of acute kidney injury caused by overcoagulation. We describe a case of an 84-year-old man with arterial hypertension, coronary heart disease and atrial fibrillation treated with acenocoumarol, who presented with haematoproteinuria and acute kidney injury during a phase of excessive anticoagulation. In addition to IgA nephropathy, renal biopsy also revealed acute tubular necrosis, red blood cell casts and positive iron staining in tubular cells. After this acute episode, renal function improved and proteinuria decreased below the nephrotic range.

Warfarin-related nephropathy induced by three different vitamin K antagonists: analysis of 13 biopsy-proven cases

Background: Acute kidney injury (AKI) with renal tubular obstruction by red blood cell casts (RBCC) has been described in patients treated with warfarin and is known as warfarin-related nephropathy (WRN).

Methods: To determine whether other vitamin K antagonists (VKA) cause WRN, we retrospectively collected and analyzed the clinical and histological data of 13 patients treated with different VKA (seven with fluindione, four with warfarin and two with acenocoumarol) in seven French hospitals.

Results: They all developed gross hematuria following overanticoagulation complicated by severe AKI (median serum creatinine concentration = 693 μmol/L). Histological analysis of the kidney biopsies highlighted the presence of intratubular RBCC and acute tubular necrosis in all patients and of an underlying kidney disease in 12 patients. WRN was suspected in patients treated with warfarin; however, the initial diagnosis was incorrect in six of the nine patients treated with other VKA. Nine patients progressed to chronic kidney disease, one fully recovered renal function, two died and one still needs dialysis.

Conclusions: This is the first report of AKI caused by fluindione. In agreement with the recent publication on AKI in two patients treated with dabigatran, we suggest that the term ‘anticoagulant-related nephropathy’ is more appropriate than WRN. Gross hematuria in patients with an underlying kidney disease and treated with VKA requires rapid control of the international normalized ratio and renal function monitoring.

Strain differences in intestinal toxicity of warfarin in rats

Intestinal hemorrhage characterizes effectiveness of warfarin (WF) as rodenticide and is among adverse effects of therapy in humans. Having in mind genetic variations in the effectiveness of WF in wild rats and in the doses required for therapeutic effect, strain differences in the intestinal toxicity of oral warfarin in rats were examined in this study. High WF dose (3.5mg/l) led to mortality in Albino Oxford (AO) rats, with no lethality in Dark Agouti (DA) rats. Higher values of prothrombin time were noted at low WF dose (0.35mg/l) in the former strain. Leukocyte infiltration in intestine noted at this dose in both strains was associated with oxidative injury and more pronounced anti-oxidative response in AO rats. Suppression of mesenteric lymph node cell proliferation and IFN-γ and IL-10 production in AO rats and lack of these effects in DA rats, represent different strategies to protect vulnerable intestine from harmful immune responses.

The emerging threat of superwarfarins: history, detection, mechanisms, and countermeasures

Superwarfarins were developed following the emergence of warfarin resistance in rodents. Compared to warfarin, superwarfarins have much longer half-lives and stronger affinity to vitamin K epoxide reductase and therefore can cause death in warfarin-resistant rodents. By the mid-1970s, the superwarfarins brodifacoum and difenacoum were the most widely used rodenticides throughout the world. Unfortunately, increased use was accompanied by a rise in accidental poisonings, reaching >16,000 per year in the United States. Risk of exposure has become a concern since large quantities, up to hundreds of kilograms of rodent bait, are applied by aerial dispersion over regions with rodent infestations. Reports of intentional use of superwarfarins in civilian and military scenarios raise the specter of larger incidents or mass casualties. Unlike warfarin overdose, for which 1-2 days of treatment with vitamin K is effective, treatment of superwarfarin poisoning with vitamin K is limited by extremely high cost and can require daily treatment for a year or longer. Furthermore, superwarfarins have actions that are independent of their anticoagulant effects, including both vitamin K-dependent and -independent effects, which are not mitigated by vitamin K therapy. In this review, we summarize superwarfarin development, biology and pathophysiology, their threat as weapons, and possible therapeutic approaches.

Intestinal toxicity of oral warfarin intake in rats

Though warfarin is extensively used in the prevention and treatment of thromboembolic processes in humans, adverse effects of warfarin therapy have been recognized. Intestinal hemorrhage is one of the hazards of anticoagulant therapy, but the mechanisms of warfarin toxicity are virtually unknown. In this work, the effects of 30 days oral warfarin (0.35 mg/l and 3.5 mg/l) intake on rat's gut were examined. Both doses resulted in prolongation of prothrombin time. Systemic effects of higher warfarin dose (increases in plasma AST, proteinuria, hematuria, changes in peripheral blood hematological parameters) were seen. Warfarin intake resulted in histologically evident tissue damage, leukocyte infiltration and intestinal inflammation [increases in myeloperoxidase activity, malondialdehyde content, superoxide dismutase and catalase activity, proinflammatory cytokine (IFN-γ, IL-17) concentrations in intestinal homogenates]. In contrast, suppression of gut-draining mesenteric lymph node (MLN) cell activity [proliferation responsiveness, production of IFN-γ and IL-17 to T lymphocyte mitogen Concanavalin A stimulation] was noted. Inhibition of regulatory cytokine IL-10 production by MLN cells, suggests commitment of MLN to the suppression of all inflammatory activities and creation of the microenvironment which is non-permissive for induction of potentially harmful immune response. These novel findings indicate the need of staying alert for (adverse) effects of warfarin therapy.

The Complex Relationship of Extracorporeal Membrane Oxygenation and Acute Kidney Injury: Causation or Association?

Extracorporeal membrane oxygenation (ECMO) is a modified cardiopulmonary bypass (CPB) circuit capable of providing prolonged cardiorespiratory support. Recent advancement in ECMO technology has resulted in increased utilisation and clinical application. It can be used as a bridge-to-recovery, bridge-to-bridge, bridge-to-transplant, or bridge-to-decision. ECMO can restitute physiology in critically ill patients, which may minimise the risk of progressive multiorgan dysfunction. Alternatively, iatrogenic complications of ECMO clearly contribute to worse outcomes. These factors affect the risk : benefit ratio of ECMO which ultimately influence commencement/timing of ECMO. The complex interplay of pre-ECMO, ECMO, and post-ECMO pathophysiological processes are responsible for the substantial increased incidence of ECMO-associated acute kidney injury (EAKI). The development of EAKI significantly contributes to morbidity and mortality; however, there is a lack of evidence defining a potential benefit or causative link between ECMO and AKI. This area warrants investigation as further research will delineate the mechanisms involved and subsequent strategies to minimise the risk of EAKI. This review summarizes the current literature of ECMO and AKI, considers the possible benefits and risks of ECMO on renal function, outlines the related pathophysiology, highlights relevant investigative tools, and ultimately suggests an approach for future research into this under investigated area of critical care.

Oral anticoagulants and risk of nephropathy

Anticoagulant-related nephropathy, a recently recognized entity, manifests as unexplained acute kidney injury in the setting of excessive anticoagulation with oral agents. Histologic findings in warfarin-related nephropathy include glomerular hemorrhage and renal tubular obstruction by red blood cells. Affected patients are at increased risk of mortality as well as irreversible kidney injury. Patients with chronic kidney disease are particularly vulnerable to this complication. Similar case reports of anticoagulant-related nephropathy have been linked to the more novel oral anticoagulant, dabigatran. Anticoagulant-related nephropathy has been successfully reproduced in rat models. These animal models shed light on the pathogenesis of the disease including the potential role of direct thrombin and protease-activated receptor-1 inhibition. Warfarin and dabigatran also cause an increase in systolic blood pressure in rats, a risk factor for developing nephropathy. This article reviews the current evidence for anticoagulant-related nephropathy and provides data for the suggested possible mechanisms underlying this adverse effect.

Cisplatin-Induced Non-Oliguric Acute Kidney Injury in a Pediatric Experimental Animal Model in Piglets

Objective

To design an experimental pediatric animal model of acute kidney injury induced by cisplatin.

Methods

Prospective comparative observational animal study in two different phases. Acute kidney injury was induced using three different doses of cisplatin (2, 3 and 5 mg/kg). The development of nephrotoxicity was assessed 2 to 4 days after cisplatin administration by estimating biochemical parameters, diuresis and renal morphology. Analytical values and renal morphology were compared between 15 piglets treated with cisplatin 3 mg/kg and 15 control piglets in the second phase of the study.

Results

41 piglets were studied. The dose of 3 mg/kg administered 48 hours before the experience induced a significant increase in serum creatinine and urea without an increase in potassium levels.

Piglets treated with cisplatin 3 mg/kg had significantly higher values of creatinine, urea, phosphate and amylase, less diuresis and lower values of potassium, sodium and bicarbonate than control piglets. Histological findings showed evidence of a dose-dependent increase in renal damage.

Conclusions

a dose of 3 mg/kg of cisplatin induces a significant alteration in renal function 48 hours after its administration, so it can be used as a pediatric animal model of non-oliguric acute kidney injury.

Warfarin related nephropathy: a case report and review of the literature

Background

Warfarin related nephropathy is one of the potential complications of warfarin therapy. Despite the well described histological entity, the clinical course and approach to warfarin related nephropathy in patients requiring life-long anticoagulation is however not well described in the literature.

Case presentation

We report the clinical course of a 56 years old Chinese lady who presented with over anti-coagulation and acute kidney injury while on warfarin therapy for permanent atrial fibrillation and mechanical valve replacement. Renal biopsy was performed as the acute kidney injury was persistent despite normalization of the International Normalized Ratio and the diagnosis of warfarin related nephropathy was made. Temporary interruption of anti-coagulation, in combination with oral N-acetylcysteine resulted in subsequent stabilization of renal function.

Conclusion

The diagnosis of warfarin induced nephropathy should be considered in patients presenting with unexplained acute kidney injury and over anti-coagulation. Awareness of this clinical entity is important for clinician managing anti-coagulation therapy and renal function should be monitored regularly in patients who are on warfarin therapy.

Transdermal toxicity of topically applied anticoagulant rodenticide warfarin in rats

Occupational/accidental exposure data have showed hemorrhage as a result of transdermal exposure to warfarin, however, other effects are not known. In the present study, the impact of epicutaneous application of 10 μg or 100 μg of warfarin (three times, once a day) on peripheral blood polymorphonuclear (PMN) and mononuclear cells (PBMC) was examined in rats. Both doses resulted in prolongation of prothrombin time and changes in hematologic parameters. Increases in PMN intracellular myeloperoxidase (MPO) activity were seen at higher warfarin dose and both doses resulted in higher percentages of granular CD11b(+) cells. In contrast, a decrease in PMN TNF and IL-6 production (ELISA) and gene expression (RT-PCR) was observed. Epicutaneous application of warfarin resulted in decreased numbers of PBMC, higher numbers of mononuclear CD11b(+) cells, but without effect on PMBC cytokine production. The data obtained showed differential effects of transdermal exposure to warfarin depending on leukocyte type and activity.

Dabigatran-Related Nephropathy in a Patient with Undiagnosed IgA Nephropathy

Dabigatran is a direct thrombin inhibitor used as an alternative to warfarin for long term anticoagulation. Warfarin-related nephropathy is an increasingly recognized entity, but recent evidence suggests that dabigatran can cause a WRN-like syndrome. We describe a case of a biopsy-proven anticoagulant nephropathy related to dabigatran in a patient with IgA nephropathy and propose that, despite the base glomerular disease, acute kidney injury was due to tubular obstruction by red blood cells and heme-associated tubular injury, and through a mechanism involving inhibition of anticoagulation cascade and barrier abnormalities caused by molecular mechanisms.

Brodifacoum induces early hemoglobinuria and late hematuria in rats: novel rapid biomarkers of poisoning

INTRODUCTION

Brodifacoum (BDF) is a superwarfarin that is used primarily as a rodenticide. There have been increasing numbers of reports of human cases of accidental or intentional BDF ingestion with high mortality rate. Its broad availability and high lethality suggest that BDF should be considered a potential chemical threat. Currently, there is no biomarker for early detection of BDF ingestion in humans; patients typically present with severe coagulopathy. Since we demonstrated earlier that warfarin can induce acute kidney injury with hematuria, we tested whether BDF would also lead to change in urinary biomarkers.

MATERIAL AND METHODS

BDF was administered to Sprague Dawley rats via oral gavage. N-acetylcysteine (NAC) was given per os in drinking water 24 h prior to BDF. Urinalysis was performed at different times after BDF administration. Anticoagulation and serum creatinine levels were analyzed in the blood.

RESULTS

We observed that within a few hours the animals developed BDF-dose-dependent transient hemoglobinuria, which ceased within 24 h. This was accompanied by a transient decrease in hematocrit, gross hemolysis and an increase in free hemoglobin in the serum. At later times, animals developed true hematuria with red blood cells in the urine, which was associated with BDF anticoagulation. NAC prevented early hemoglobinuria, but not late hematuria associated with BDF.

CONCLUSIONS

We propose that transient early hemoglobinuria (associated with oxidative stress) with consecutive late hematuria (associated with anticoagulation) are novel biomarkers of BDF poisoning, and they can be used in clinical setting or in mass casualty with BDF to identify poisoned patients.

Oral warfarin and the thrombin inhibitor dabigatran increase blood pressure in rats: hidden danger of anticoagulants?

BACKGROUND

Hypertension is a common comorbidity in patients with chronic kidney disease (CKD). We reported earlier that oral anticoagulants, including warfarin and dabigatran, may induce acute kidney injury. No effects of oral anticoagulants on blood pressure (BP) have been previously reported. The aim of this study was to examine in detail the relationship of anticoagulant therapy and BP in rats.

METHODS

Sham-operated and 5/6 nephrectomy rats were treated with different doses of oral anticoagulants (warfarin and dabigatran), superoxide scavenger N-acetylcysteine (NAC), vitamin K, and protease activated receptor 1 (PAR-1) inhibitor SCH79797. BP was measured by a tail cuff daily.

RESULTS

Warfarin and dabigatran both increased systolic BP in sham-operated and 5/6 nephrectomy rats in a dose-dependent manner. SCH79797 also increased systolic BP in a dose-dependent manner. Vitamin K prevented warfarin-induced increase in BP but did not affect BP when administered alone. NAC delayed the warfarin-associated increase in BP. Warfarin effects on BP were similar in 5/6 nephrectomy rats with different CKD stages.

CONCLUSIONS

Both warfarin and dabigatran increase systolic BP in rats. The mechanism of this effect is not clear, but our data suggest that it is related to decreased thrombin activity associated with anticoagulant treatment. The superoxide scavenger NAC delayed, but did not prevent, warfarin-induced hypertension.

Anticoagulants and acute kidney injury: clinical and pathology considerations

We have recently identified a new clinical syndrome in patients receiving warfarin for anticoagulation therapy. This syndrome has been named warfarin-related nephropathy (WRN), and patients with chronic kidney disease (CKD) appear to be particularly susceptible. WRN is defined as an acute increase in international normalized ratio (INR) to >3.0, followed by evidence of acute kidney injury (AKI) within 1 week of the INR increase. AKI was defined as a sustained increase in serum creatinine of greater than or equal to 0.3 mg/dL. The AKI cannot be explained by any other factors, and the kidney biopsy demonstrates extensive glomerular hemorrhage with tubular obstruction by red blood cells (RBCs). Beyond AKI, WRN is a significant risk factor for mortality within the first 2 months of diagnosis and it accelerates the progression of CKD. We demonstrated that 5/6 nephrectomy in rats is a suitable experimental model to study WRN. Animals treated with warfarin showed an increase in serum creatinine and morphologic findings in the kidney similar to those in humans with WRN. Our recent evidence suggests that novel oral anticoagulants may induce AKI. Diagnosis of WRN may be challenging for a renal pathologist. A few cases with suspected WRN and pathologic considerations are described.

The central role of renal microcirculatory dysfunction in the pathogenesis of acute kidney injury

Acute kidney injury (AKI) is a rapidly developing condition often associated with critical illness, with a high degree of morbidity and mortality, whose pathophysiology is ill understood. Recent investigations have identified the dysfunction of the renal microcirculation and its cellular and subcellular constituents as being central to the etiology of AKI. Injury is caused by inflammatory activation involving endothelial leucocyte interactions in combination with dysregulation of the homeostatis between oxygen, nitric oxide, and reactive oxygen species. Effective therapies expected to resolve AKI will have to control inflammation and restore this homeostasis. In order to apply and guide these therapies effectively, diagnostic tools aimed at physiological biomarkers of AKI for monitoring renal microcirculatory function in advance of changes in pharmacological biomarkers associated with structural damage of the kidney will need to be developed.