Conjugated linoleic acid (CLA) inhibits osteoclast formation from human CD14+ monocytes

Conjugated linoleic acid (CLA) has variable effects on bone mass, which may be due to different amounts of 9 cis ,11 trans (9,11) and 10 trans ,12 cis (10,12) isomers in commercial CLA preparations. We previously showed that 9,11 CLA increases mineralized bone nodule formation from human osteoblast‐like cells. Osteoblastic bone formation is tightly coupled with osteoclastic bone resorption, and an imbalance favouring resorption leads to bone loss. Mixed CLA isomers decrease osteoclast differentiation from murine monocytes in vitro , and decrease osteoclast function in mice. However, the effects of CLA on human osteoclastic cells is not known. The purpose of this study was to determine the effects of individual CLA isomers on osteoclast differentiation from human CD14 + monocytes. Cells were seeded in osteoclast differentiation media at a density of 3x10 5 cells/cm 2 , and treated with 0–100 μM 9,11 or 10,12 CLA for two weeks. Osteoclast differentiation was determined by the number of tartrate‐resistant acid phosphatase (TRAP) + multinucleated (≥3 nuclei) cells. Our results show that 50–100 μM 9,11 CLA decreases the number of TRAP + multinucleated cells by 60–82% (P<0.01), but 10,12 CLA does not. These results demonstrate that 9,11 CLA inhibits osteoclast formation from human CD14 + monocytes, and suggest that this isomer may prevent bone resorption in humans. (Supported by a grant from the Dairy Farmers of Canada)