The inflammatory phase of fracture healing is influenced by oestrogen status in mice

Abstract

BackgroundFracture healing is known to be delayed in postmenopausal, osteoporotic females under oestrogen-deficient conditions. Confirming this, experimental studies demonstrated impaired callus formation in ovariectomised animals. Oestrogen-deficiency is known to affect the immune system and the inflammatory response during wound healing. Because a balanced immune response is required for proper bone healing, we were interested to ascertain whether the early immune response after facture is affected by oestrogen depletion.MethodsTo address the above question, female mice received either a bilateral ovariectomy (OVX) or were sham-operated, and femur osteotomy was performed 8 weeks after OVX/sham operation. The effects of OVX on the presence of immune cells and pro-inflammatory cytokines were evaluated by flow cytometry and immunohistochemistry of the fracture calli on days 1 and 3 after fracture.ResultsOne day after fracture, immune cell numbers and populations in the fracture haematoma did not differ between OVX- and sham-mice. However, on day 3 after fracture, OVX-mice displayed significantly greater numbers of neutrophils. Local expression of the oestrogen-responsive and pro-inflammatory cytokine midkine (Mdk) and interleukin-6 (IL-6) expression in the fracture callus were increased in OVX-mice on day 3 after fracture compared with sham-mice, indicating that both factors might be involved in the increased presence of neutrophils. Confirming this, Mdk-antibody treatment decreased the number of neutrophils in the fracture callus and reduced local IL-6 expression in OVX-mice.ConclusionsThese data indicate that oestrogen-deficiency influences the early inflammatory phase after fracture. This may contribute to delayed fracture healing after oestrogen depletion.

Vibration treatment modulates macrophage polarisation and enhances early inflammatory response in oestrogen-deficient osteoporotic-fracture healing

“…The local inflammatory response to injury is lowered in OVX animal models (Khan and Ansar Ahmed, 2015). However, there are other studies demonstrating that oestrogen-deficiency increases the early inflammatory response after fracture, as shown by an increased number of neutrophils and expression of pro-inflammatory cytokines, midkine and IL-6 in the fracture callus in oestrogen-deficient mice Haffner-Luntzer et al, 2017). This provides further evidence of the altered inflammatory response after injury under oestrogen deficiency.…”

“…6a, 7a). Indeed, the level of inflammatory response can also be evaluated by the presence of innate immune cells, including neutrophils (Kovtun et al, 2016), lymphocytes (Haffner-Luntzer et al, 2017), macrophages (Schlundt et al, 2018) and T and B cells (Konnecke et al, 2014). These cells are present at the fracture site at various levels following a specific sequential order during the healing process.…”

Review of Animal Models of Comorbidities in Fracture‐Healing Research

“…Limitations of this animal model are that the total bone mineral density (BMD) loss is less than in human patients, that bone loss after OVX varies greatly between different mouse strains and that OVX does not completely mimic the kinetic and the underlying cause of natural menopause. During bone healing, OVX mice display delayed fracture bridging, callus maturation, disturbed immune response, and reduced angiogenesis as well as diminished mechano‐responsiveness similar to osteoporotic patients, demonstrating the translational relevance of this animal model. One drawback is that most fracture healing studies using OVX mice are conducted in a diaphyseal fracture setup .…”

“…The treatment and healing of osteoporotic fractures is often associated with orthopaedic complications. These can result from implant anchorage problems in the fragile bone and/or from the disturbed healing capacity of the bone tissue itself . There is need for suitable animal models to test newly developed implants and biomaterials on the one hand and on the other hand to better understand the poor bone healing capacity and delayed fracture healing on a cellular and molecular level .…”

Analysis of low-dose estrogen on callus BMD as measured by pQCT in postmenopausal women

“…Conversely, estrogen treatment of mice with bone fractures led to enhanced healing, i.e. the chondrocyte areas were larger, callus mineralization was increased, and the neocortex was thicker when compared to untreated control animals [4,8,9,[11][12][13][14]. Furthermore, estrogen treatment also led to bene cial effects on the biomechanical properties of the bones [4].…”