5/6 Nephrectomy as a Validated Rat Model Mimicking Human Warfarin-Related Nephropathy

Abstract

Background/Aims: We previously reported that patients with chronic kidney disease (CKD) receiving warfarin therapy and whose international normalized ratio increases to >3.0 may develop acute kidney injury (AKI) as a result of glomerular hemorrhage and formation of obstructive red blood cell (RBC) casts. We named this condition warfarin-related nephropathy (WRN). We also previously reported that acute excessive anticoagulation with brodifacoum (superwarfarin) induces AKI in 5/6 nephrectomy (5/6NE) rats. Limitations of the brodifacoum model precluded a careful assessment of dose-response relationships. Methods: Warfarin treatment was used in 5/6NE. Results: Herein we report that warfarin treatment of 5/6NE rats resulted in a dose-dependent increase in serum creatinine (SC). The increase in SC following warfarin treatment was greater at 3 and 19 weeks after the ablative surgery, than that observed 8 weeks after the ablative surgery. The SC increase was correlated with the prothrombin time increase. Morphologically, 5/6NE, but not control rats, had acute tubular injury with RBC and RBC casts in the tubules. Treatment with vitamin K prevented SC increase and morphologic changes in the kidney associated with warfarin treatment. A single episode of WRN did not affect the progression of CKD in 5/6NE. Conclusion: (1) The 5/6NE model of CKD is an appropriate animal model to study the pathogenesis of WRN. (2) The pharmacokinetics of warfarin is better suited to the study of WRN than that of brodifacoum. (3) The more advanced stages of 5/6NE are more susceptible to WRN than the earlier stages. (4) Vitamin K treatment prevents WRN.

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

“…We used 5/6 nephrectomy rats 3 wk after the ablative surgery for these studies. Earlier we reported that the changes in serum creatinine and kidney morphology associated with anticoagulation were more prominent in 5/6 nephrectomy rats at 3 wk than at 9 and 19 wk after the ablative surgery (31).…”

“…The 5/6 nephrectomy surgery was performed under a ketamine/xylazine (6.0 mg/0.77 mg/100 g) anesthesia by a nephrectomy of the right kidney and resection of twothirds of the left kidney (31,41). Animals were allowed to recover from the surgery for 3 wk before the start of warfarin treatment.. Warfarin and NAC were given per os in drinking water in the concentrations described below.…”

“…We used a "surrogate" INR (sINR) by comparing PT after and before treatment with warfarin, as described previously (31,41). The average PT in 100 rats (50 control and 50 5/6 nephrectomy rats) was used as the normal PT time (21.44 s).…”

“…We documented this association in both humans (5-7) and animal models (31,41). We named this condition warfarin-related nephropathy (WRN).…”

“…On this basis, it has been assumed that the tubular obstruction was the principle mechanism of the AKI in WRN. It was recognized, however, that in both patients and animals with WRN and severe reductions in glomerular filtration rate (GFR), only a small percentage of the tubular cross sections in any given slide showed complete obstruction by RBC casts (7,31). To explain the discrepancy between the degree of tubular obstruction and the degree of GFR decrease, it was assumed that the degree of tubular obstruction shown in any given slide represented only the "tip of the iceberg" of obstructed tubules.…”