Study of the role of leukotriene B4 in abnormal function of human subchondral osteoarthritis osteoblasts: Effects of cyclooxygenase and/or 5‐lipoxygenase inhibition

Abstract Objective To compare the effect of licofelone, NS‐398 (an inhibitor of cyclooxygenase 2 [COX‐2]), and BayX‐1005 (an inhibitor of 5‐lipoxygenase activating protein) on the production of leukotriene B 4 (LTB 4 ) and prostaglandin E 2 (PGE 2 ), and on cell biomarkers by human osteoarthritis (OA) subchondral osteoblasts. Methods Primary in vitro osteoblasts were prepared from subchondral bone specimens obtained from OA patients and autopsy subjects. LTB 4 and PGE 2 levels were measured by enzyme‐linked immunosorbent assay in conditioned media of osteoblasts incubated in the presence or absence of licofelone, NS‐398, or BayX‐1005. The effect of these drugs or of the addition of LTB 4 on alkaline phosphatase (AP) activity and osteocalcin release by OA and normal osteoblasts was determined. The presence of LTB 4 receptors in normal and OA osteoblasts was evaluated by Western blot analysis. Results OA osteoblasts produced variable levels of PGE 2 and LTB 4 compared with normal osteoblasts. Licofelone, at the maximal dose used, inhibited production of PGE 2 and LTB 4 by OA osteoblasts by a mean ± SEM of 61.2 ± 6.4% and 67.0 ± 7.6%, respectively. NS‐398 reduced PGE 2 production by 75.8 ± 5.3%. BayX‐1005 inhibited LTB 4 production in OA osteoblasts by 38.7 ± 14.5% and marginally affected PGE 2 levels (reduction of 14.8 ± 5.3%). Licofelone dose‐dependently stimulated 1,25‐dihydroxyvitamin D‐induced AP activity while inhibiting osteocalcin release. BayX‐1005 partly reproduced these effects, but NS‐398 failed to affect them. LTB 4 dose‐dependently inhibited AP activity in OA osteoblasts, while its effect on osteocalcin depended on endogenous LTB 4 levels in these cells. In normal osteoblasts, LTB 4 dose‐dependently stimulated osteocalcin, whereas it failed to influence AP. LTB 4 receptors BLT1 and BLT2 were present in normal and OA osteoblasts. Conclusion Licofelone inhibits the production of PGE 2 and LTB 4 . Selective effects of licofelone on AP and osteocalcin occur via its role on LTB 4 production. Because LTB 4 can modify cell biomarkers in OA and normal osteoblasts, our results suggest licofelone could modify abnormal bone remodeling in OA.