Short-Term Administration of HIV Protease Inhibitor Saquinavir Improves Skull Bone Healing with Enhanced Osteoclastogenesis.

Abstract

Using immunomodulatory methods to address the challenging issue of craniofacial bone repair may be a potentially effective approach. The protease inhibitor saquinavir has been shown to inhibit the inflammatory response by targeting the toll-like receptor 4/myeloid differentiation primary response complex. Independently, inhibition of toll-like receptor 4 or myeloid differentiation primary response led to enhanced skull bone repair. Therefore, the authors aimed to investigate the effects of saquinavir on skull bone healing. The effects of saquinavir on skull bone healing were assessed by means of gene expression, histology, immunohistochemistry, and tomography in a mouse calvarial defect model. Subsequently, the role of saquinavir in cell viability, migration, and osteogenic and osteoclastogenic differentiation was also evaluated in vitro. One-week saquinavir administration improved skull bone healing based on micro-computed tomographic and histomorphometric analyses. Compared to the vehicle control, 1-week saquinavir treatment (1) enhanced osteoclast infiltration (tartrate-resistant acid phosphatase staining) at day 7, but not at days 14 and 28; (2) induced more CD206 + M2 macrophage infiltration, but not F4/80 + M0 macrophages at days 7, 14, and 28; and (3) elevated osteoclastogenic gene RANKL (quantitative polymerase chain reaction) expression and other osteogenic and cytokine expression. Furthermore, in vitro data showed that saquinavir administration did not influence MC3T3-E1 cell migration or mineralization, whereas higher concentrations of saquinavir inhibited cell viability. Saquinavir treatment also enhanced the osteoclastic differentiation of bone marrow-derived precursors, and partially reversed high-mobility group box 1-driven osteoclastogenesis inhibition and elevated proinflammatory cytokine expression. The improved skull bone repair following short-term saquinavir treatment may involve enhanced osteoclastogenesis and modulated inflammatory response following skull injury. The authors' work demonstrates improved skull bone healing by short-term application of saquinavir, a drug traditionally used in the treatment of acquired immunodeficiency syndrome. As such, saquinavir may be repurposed for skeletal repair.