Inhibition of Lipopolysaccharide-Induced Prostaglandin E 2 Production and Inflammation by the Na + /H + Exchanger Inhibitors

We analyzed the effects of the Na + /H + exchanger (NHE) inhibitor 3,5-diamino-6-chloro- N -(diaminomethylidene)pyrazine-2-carboxamide hydrochloride (amiloride) and its analogs 5-( N, N -dimethyl)-amiloride (DMA) and 5-( N -ethyl- N- isopropyl)-amiloride (EIPA) on the lipopolysaccharide (LPS)-induced production of prostaglandin (PG) E 2 in vitro and in vivo. In the mouse macrophage-like cell line RAW 264, these inhibitors suppressed the LPS (1 μg/ml)-induced production of PGE 2 at 8 h in a concentration-dependent manner. They also reduced the LPS-induced release of arachidonic acid from membrane phospholipids at 4 h and the LPS-induced increase in the level of cyclooxygenase (COX)-2 protein at 6 h, but not the level of COX-2 mRNA at 3 h. The LPS-induced phosphorylation of mitogen-activated protein kinases and degradation of inhibitor of κB-α were not inhibited by these drugs. In an air pouch-type LPS-induced inflammation model in mice 30 mg/kg amiloride and 10 mg/kg EIPA as well as the COX inhibitor indomethacin (10 mg/kg), significantly reduced the level of PGE 2 in the pouch fluid at 8 h and the vascular permeability from 4 to 8 h. The accumulation of pouch fluid and leukocytes in the pouch fluid at 8 h was significantly inhibited by amiloride and EIPA but not by indomethacin. These findings suggested that the NHE inhibitors suppress the production of PGE 2 through inhibiting the release of arachidonic acid and the increase in COX-2 protein levels and thus induce anti-inflammatory activity.