Dissolvable microneedles loaded with denosumab alleviate knee osteoarthritis in rodent and canine models by inhibiting macrophage senescence

Rationale: Osteoarthritis (OA) lacks disease-modifying therapies. Although systemic denosumab delays OA progression, it causes uneven drug distribution and off-target effects, whereas intra-articular injections are invasive and risk joint infection. We aimed to develop a minimally invasive microneedle platform that delivers denosumab locally to achieve therapeutic efficacy comparable to intra-articular injection while avoiding systemic exposure. Methods: A dissolvable denosumab-loaded microneedle array (MNs@De) was fabricated for transcutaneous intra-articular delivery. OA was induced in rodents and Beagle dogs; animals were treated with MNs@De, systemic denosumab, intra-articular denosumab, or vehicle. Synovial inflammation, cartilage erosion, and pain were evaluated histologically and behaviorally. Single-cell RNA sequencing and immunofluorescence were performed to assess macrophage senescence and chondrocyte metabolism. Secretion of pro-inflammatory and catabolic factors was quantified in vitro using senescent macrophage-chondrocyte co-cultures. Results: MNs@De delivered denosumab effectively into joints, significantly reducing synovial inflammation, cartilage erosion, and pain compared with systemic administration and achieving outcomes comparable to intra-articular injection. Single-cell profiling revealed that denosumab markedly decreased senescent macrophage abundance within synovial tissue. Mechanistically, denosumab inhibited senescent macrophage-derived pro-inflammatory and catabolic factor release, thereby shifting chondrocytes from catabolic to anabolic states. Conclusions: Targeting senescent macrophages via MNs@De attenuates OA progression without requiring intra-articular injections or increasing systemic drug exposure. Microneedle-mediated denosumab delivery offers a minimally invasive, localized therapeutic strategy for OA.