Inhibition of endothelial cell prostaglandin H synthase gene expression by naproxen

Naproxen is a potent anti-inflammatory drug whose action is attributed to inhibition of prostaglandin biosynthesis. In view of our recent discovery that aspirin and sodium salicylate are capable of reducing cellular levels of prostaglandin H (PGH) synthase mRNA, we have evaluated the effect of naproxen on PGH synthase protein and mRNA levels in cultured human umbilical vein endothelial cells (HUVEC). PGH synthase mRNA levels were quantified by a competitive polymerase chain reaction (PCR) assay; protein was assessed by Western blotting. Naproxen decreased the PGH synthase protein level in HUVEC in a concentration-dependent manner. It abolished entirely the 70 kDa PGH synthase subunit at 5 micrograms/ml. It appears more effective in blocking interleukin-1 inducible PGH synthase levels. Naproxen also inhibited the synthase mRNA level in a concentration-dependent manner; levels were reduced by 33% at 5 micrograms/ml and 60% at 30 micrograms/ml naproxen. These results indicate that naproxen, like the salicylates, inhibits PGH synthase levels in cultured endothelial cells either by inhibiting transcription of the PGH synthase gene or by destabilizing its messenger RNA.