Effects of the cyclooxygenase-2 inhibitor NS-398 on thromboxane and leukotriene synthesis in rat peritoneal cells.

Objective: Inhibition of inducible cyclooxygenase (COX)-2 has been suggested to offer therapeutic advantages without some side effects associated with the inhibition of constitutive COX activity. These side effects encompass asthmatic responses that can be induced by analgesic/ antiphlogistic drugs and are possibly related to increased leukotriene (LT) biosynthesis. We have therefore investigated whether or not the selective COX-2 inhibitor NS-398, similar to indomethacin, stimulates leukotriene (LT) biosynthesis in rat peritoneal cells.

Methods: Three hours after rats had received intraperitoneal injections of bacterial lipopolysaccharide (LPS) or saline, cells were obtained by peritoneal lavage. Northern blot analysis confirmed induction of COX-2 mRNA by LPS treatment. For determination of eicosanoid biosynthesis, peritoneal cells were incubated in the presence of various concentrations of test compounds for 60 min. The supernatants were used for radioimmunological determination of immunoreactive eicosanoids.

Results: In cells from LPS treated rats, but not in controls, NS-398 (10-300nM) reduced the amount of TXB2-like immunoreactivity (IR) in the supernatants, the maximum effect being a 25% inhibition. At these concentrations, there was no detectable effect of NS-398 on the amount of LTB4-IR or LTC4-IR in the supernatants. At higher concentrations (1-10 microM), NS-398 caused further inhibition of TXB2 synthesis, an effect that was observed also in non-LPS treated preparations. A significant increase of LTB4-IR was caused by 3-10 microM NS-398. Indomethacin (3-100 nM) reduced the amount of TXB2-IR, and at >10 nM increased the amount of LTB4- and LTC4-IR in the supernatant.

Conclusions: The results show that concentrations of NS-398 that selectively inhibited COX-2 activity, produced no detectable increase in LT biosynthesis, thus raising the possibility that COX-2 inhibitors are less likely than non-selective COX inhibitors to produce LT- related side effects.