Selective Cyclooxygenase-2 Inhibitor Suppresses Renal Thromboxane Production but Not Proliferative Lesions in the MRL/lpr Murine Model of Lupus Nephritis

Introduction: Proliferative lupus nephritis (LN) is marked by increased renal thromboxane (TX) A(2) production. Targeting the TXA(2) receptor or TXA(2) synthase effectively improves renal function in humans with LN and improves glomerular pathology in murine LN. This study was designed to address the following hypotheses: (1) TXA(2) production in the MRL/MpJ-Tnfrsf6(lpr)/J (MRL/lpr) model of proliferative LN is cyclooxygenase (COX)-2 dependent and (2) COX2 inhibitor therapy improves glomerular filtration rate (GFR), proteinuria, markers of innate immune response and glomerular pathology. Methods: Twenty female MRL/lpr and 20 BALB/cJ mice were divided into 2 equal treatment groups: (1) SC-236, a moderately selective COX2 inhibitor or (2) vehicle. After treatment from the age of 10 to 20 weeks, the effectiveness of inhibition of TXA(2) was determined by measuring urine TXB2. Response endpoints measured at the age of 20 weeks were renal function (GFR), proteinuria, urine nitrate + nitrite (NOx) and glomerular histopathology. Results: SC-236 therapy reduced surrogate markers of renal TXA(2) production during early, active glomerulonephritis. When this pharmacodynamic endpoint was reached, therapy improved GFR. Parallel reductions in markers of the innate immune response (urine NOx) during therapy were observed. However, the beneficial effect of SC-236 therapy on GFR was only transient, and renal histopathology was not improved in late disease. Conclusions: These data demonstrate that renal TXA(2) production is COX2 dependent in murine LN and suggest that NO production is directly or indirectly COX2 dependent. However, COX2 inhibitor therapy in this model failed to improve renal pathology, making COX2 inhibition a less attractive approach for treating LN.