Aminothiazoles Inhibit RANKL- and LPS-mediated Osteoclastogenesis and PGE2 Production in RAW 264.7 Cells

Periodontitis is characterized by chronic inflammation and osteoclast-mediated bone loss regulated by the receptor activator of nuclear factor-κB (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG). The aim of this study was to investigate the effect of aminothiazoles targeting prostaglandin E synthase-1 (mPGES-1) on RANKL- and lipopolysaccharide (LPS)-mediated osteoclastogenesis and prostaglandin E2 (PGE2 ) production in vitro using the osteoclast precursor RAW 264.7 cells. RAW 264.7 cells were treated with RANKL or LPS alone or in combination with the aminothiazoles 4-([4-(2-naphthyl)-1,3-thiazol-2-yl]amino)phenol (TH-848) or 4-(3-fluoro-4-methoxyphenyl)-N-(4-phenoxyphenyl)-1,3-thiazol-2-amine (TH-644). Aminothiazoles significantly decreased the number of multinucleated tartrate-resistant acid phosphatase (TRAP)-positive osteoclast-like cells in cultures of RANKL- and LPS-stimulated RAW 264.7 cells, as well as reduced the production of PGE2 in culture supernatants. LPS-treatment induced mPGES-1 mRNA expression at 16 hrs and the subsequent PGE2 production at 72 hrs. Conversely, RANKL did not affect PGE2 secretion but markedly reduced mPGES-1 at mRNA level. Furthermore, mRNA expression of TRAP and cathepsin K (CTSK) was reduced by aminothiazoles in RAW 264.7 cells activated by LPS, whereas RANK, OPG or tumour necrosis factor α mRNA expression was not significantly affected. In RANKL-activated RAW 264.7 cells, TH-848 and TH-644 down-regulated CTSK but not TRAP mRNA expression. Moreover, the inhibitory effect of aminothiazoles on PGE2 production was also confirmed in LPS-stimulated human peripheral blood mononuclear cell cultures. In conclusion, the aminothiazoles reduced both LPS- and RANKL-mediated osteoclastogenesis and PGE2 production in RAW 264.7 cells, suggesting these compounds as potential inhibitors for treatment of chronic inflammatory bone resorption, such as periodontitis.