Oral Presentation ESA-SRB-ANZBMS 2024 in conjunction with ENSA

TNFα inhibition accelerates rebound bone loss following withdrawal of RANKL inhibition. (#183)

Victoria E Taylor 1 2 3 , Albert S Kim 3 4 , Caitlyn Massarotti 2 , Ariel Castro-Martinez 3 , Suraj Dhakal 3 , James Smith 3 , Peter Wong 2 , Jacqueline R Center 3 , Christian M Girgis 2 5 , Peter Croucher 3 4 , Ryan C Chai 3 4 , Michelle McDonald 3 4 6
  1. Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
  2. Faculty of Medicine and Health, The University of Sydney, Sydney, NSW, Australia
  3. Bone Biology, Cancer Plasticity and Dormancy Program, The Garvan Institute of Medical Research, Sydney, NSW, Australia
  4. School of Clinical Medicine, Faculty of Medicine and Health, UNSW, Sydney, NSW, Australia
  5. Department of Diabetes and Endocrinology, Westmead Hospital, Westmead, NSW, Australia
  6. Faculty of Medicine & Health, University of Sydney, Sydney, NSW, Australia

Denosumab withdrawal causes rapid bone mineral density (BMD) loss due to accelerated bone resorption driven by elevated RANKL levels which promote osteoclast formation. We hypothesized that inhibiting osteoclast formation through TNFα inhibition could prevent this rebound bone loss.

Seven-week-old female C57BL/6 mice received saline or osteoprotegerin (OPG:Fc 10mg/kg) twice weekly for 2 weeks, followed by withdrawal (OPG-W). One group received the TNFa inhibitor etanercept (ETN 5mg/kg) thrice weekly, concurrently and following OPG:Fc treatment (OPG-W+ETN) and one OPG-W group transitioned to ETN from week 2 (OPG-W/ETN)(Figure 1). BMD and serum TRAP5b were measured fortnightly to week 12, with femora analysed by MicroCT at weeks 2, 6, and 12. Single-cell RNAseq was performed on cells from the endosteum at week 2.

BMD increased by 8-17% at week 2 in OPG-W, OPG-W/ETN, and OPG-W+ETN groups (p<0.001). The OPG-W group reached peak BMD at week 10 (26% increase, p<0.0001) before declining to vehicle levels. OPG-W/ETN peaked above vehicle at week 5, declining to vehicle levels by week 8. OPG-W+ETN peaked at week 3, declining to vehicle levels by week 4. MicroCT analysis of trabecular bone parameters aligned with these BMD data. Serum TRAP was suppressed in all OPG-W groups by week 2 (p<0.001). TRAP levels returned to control in OPG-W by week 10, in OPG-W/ETN by week 5, and by week 3 had surpassed control in OPG-W+ETN (p<0.01). Preliminary scRNAseq analysis indicated an increase in chondrocytes in OPG-W and OPG-W+ETN groups compared to vehicle. Compared to OPG-W, OPG-W+ETN pre-osteoclasts showed downregulation of S100a9, a negative regulator of osteoclast formation.

Unexpectedly, TNFα inhibition accelerated osteoclast formation, leading to earlier BMD decline post-OPG-Fc withdrawal. Further analysis of scRNAseq data, serum RANKL, flow cytometry, and histology will provide additional mechanistic insight. These findings have implications for patients treated with both denosumab and etanercept for inflammatory arthritis.

 

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