Improvement of renal function with a selective thromboxane A₂ synthetase inhibitor, DP-1904, in lupus nephritis

Objective. To examine abnormalities of prostanoid metabolism in lupus nephritis, which may affect renal function, and the effects of 4 day dosing of a selective thromboxane A₂ (TXA₂) synthetase inhibitor, DP-1904, on prostanoid metabolism. Methods. Urinary levels of various prostanoids, thromboxane B₂ (TXB₂), 11-dehydro-TXB₂, 6-ketoprostaglandin F(1α), 2,3-dinor-6-keto-PGF(1α), and prostaglandin E₂ were determined. In a randomized crossover study, 8 patients with biopsy proven lupus nephritis were given 4 days' oral administration of DP-1904 (400 mg/day bid) or indomethacin (50 mg/day bid). The effects of DP-1904 on prostanoid metabolism were studied. Results. Urinary excretion of TXB₂, which reflects the renal production of TXA₂, was significantly increased in patients with lupus nephritis compared with non-renal systemic lupus erythematosus (SLE) (p < 0.05); enhanced production of TXA₂ was also estimated in patients with lupus nephritis. The urinary TXB₂/6-keto-PGF(1α) ratio was also increased in lupus nephritis compared with non-renal SLE (p < 0.01), indicating a prostanoid imbalance that may lead to impaired renal function and subsequent pathology. During administration of DP-1904, the urinary excretion of TXB₂ was significantly decreased after 1 to 2 days. An increase in creatinine clearance as a measure of renal function was observed. In contrast, during the administration of indomethacin, urinary excretion of both TXB₂ and 6-keto-PGF(1α) decreased and there were no significant changes in the urinary TXB₂/6-keto-PGF(1α) ratio or creatinine clearance. Hemodynamic changes were associated with a slight increase in sodium excretion, but with no change in arterial blood pressure. No side effects were elicited during the 4 days of treatments. Conclusion. The abnormal prostanoid metabolism observed in lupus nephritis could aggravate renal function, which was mediated hemodynamically, and the altered metabolism was reversible and at least partially corrected by a TXA₂ synthetase inhibitor, DP-1904.