Role of glomerular filtration rate-modifying drugs in the development of anticoagulant-related nephropathy

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.

Dabigatran-related Nephropathy Complicated by Tubulointerstitial Nephritis in a Patient with a Normal Renal Function and Undiagnosed IgA Nephropathy

A 69-year-old woman was referred to our hospital because of an acute kidney injury with macroscopic hematuria. She had been taking dabigatran for atrial flutter for six years. Based on the typical histological findings of her kidney biopsy and her history of dabigatran use with prolonged activated partial thromboplastin time, she was diagnosed with dabigatran-related nephropathy complicated by tubulointerstitial nephritis with IgA nephropathy. After prednisolone therapy, the renal function improved. Direct-acting oral anticoagulants, including dabigatran, may cause anticoagulant-related nephropathy similar to warfarin, even in patients with a normal renal function. Tubulointerstitial nephritis may coexist with dabigatran-related nephropathy, and prednisolone therapy should be considered in such cases. IgA nephropathy has been reported as a background disease, and caution should be exercised when encountering it.

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.

IgA nephropathy is the most common underlying disease in patients with anticoagulant-related nephropathy

Introduction

Anticoagulant-related nephropathy (ARN) is a relatively novel recognized entity characterized by hematuria-associated acute kidney injury (AKI) in the context of overanticoagulation. Preexisting or underlying kidney disease seems to be a predisposing factor; however, few studies have described histologic findings in patients with ARN. We aimed to evaluate underlying kidney pathology in patients on oral anticoagulation who presented an episode of AKI with hematuria in whom a kidney biopsy was performed.

Methods

Retrospective observational multicenter case study in patients treated with oral anticoagulants who developed macroscopic or intense hematuria followed by AKI. Only patients with available kidney biopsy specimens were included. Histologic findings and clinical data throughout follow-up were analyzed.

Results

A total of 26 patients were included with a median age of 75 years (62–80) and a follow-up period of 10.1 months. Of the patients, 80% were male, and most cases (92%) were on anticoagulation with vitamin K antagonists (VKAs). At admission, median serum creatinine (SCr) level was 4.2 mg/dl (2.8–8.2), median international normalized ratio (INR) 2.4 (1.5–3.4), and 11 patients (42%) required acute dialysis during hospitalization. Kidney biopsy results revealed that all patients except 1 had an underlying nephropathy: IgA nephropathy (IgAN) in 19, probable IgAN in 1, diabetic nephropathy in 3, nephrosclerosis in 1, and idiopathic nodular glomerulosclerosis in 1. At 12 weeks after discharge, only 6 subjects (24%) attained complete kidney recovery whereas 7 (28%) remained on chronic dialysis.

Conclusion

IgAN was the most common underlying kidney disease in our biopsy-proven series of ARN, in which a significant percentage of patients did not achieve kidney function recovery.

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.

Role of glomerular filtration rate-modifying drugs in the development of anticoagulant-related nephropathy

Introduction

Anticoagulant‐related nephropathy (ARN), that was described in humans first as warfarin‐related nephropathy, is characterized by acute kidney injury and red blood cell (RBC) tubular casts in the kidney. 5/6 nephrectomy (5/7NE) rats treated with warfarin or dabigatran show changes in kidney function and morphology that are similar to human disease. The role of glomerular filtration rate (GFR) in the pathogenesis of ARN is not clear. The aim of these studies was to elucidate the role of GFR in the pathogenesis of dabigatran‐induced ARN in 5/6NE rats.

Methods

5/6NE rats were treated per os with 150 mg/kg/day dabigatran alone or with drugs that lower (enalapril, 1.5 mg/kg/day) or increase (albuterol, 4.0 mg/kg/day) GFR for 7 days. Changes in coagulation and kidney function were recorded daily. Kidney morphology was evaluated on day 7 after the treatment.

Results

Dabigatran resulted in activated partial thromboplastin time increase that was not affected by GFR‐modifying drugs. Blood pressure was significantly lower in 5/6NE rats treated with enalapril and dabigatran as compared to dabigatran alone. The GFR was decreased by 35% in enalapril/dabigatran‐ and increased by 26% in albuterol/dabigatran‐treated animals. There were no changes in serum creatinine, hematuria or urinary kidney injury molecule (KIM‐1) levels when GFR‐modifying drugs were added to dabigatran. All dabigatran‐treated animals had RBC casts in the kidney regardless of the GFR modification.

Conclusions

GFR does not play a significant role in the dabigatran‐induced acute kidney injury in 5/6 nephrectomy model in rats. Based in these data, modification of GFR in patients with ARN is not warranted.