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

Abstract

Fracture healing is a well-orchestrated and coordinated process and begins with the inflammatory stage involving the infiltration of immune cells and the release of cytokines, including tumour necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and interleukin-10 (IL-10). Low-magnitude high-frequency vibration (LMHFV) stimulation is effective in promoting fracture healing. The study hypothesis was that the innate immune response was impaired in osteoporotic fracture and LMHFV could positively modulate it. 9-month-old ovariectomy (OVX)-induced osteoporotic rats were randomised into sham (SHAM), OVX control (OVX), OVX-vibration (OVX-VT) or OVX vibration plus administration of COX-2 specific non-steroid anti-inflammatory drugs (OVX-VT-NSAID). LMHFV (35 Hz, 0.3 ×g) was given 20 min/d and 5 d/week to the treatment groups. Healing and innate immune response were evaluated by weekly radiographs, endpoint micro-computed tomography (µCT), enzyme-linked immunosorbent assay (ELISA) and histomorphometry at weeks 1, 2, 4 and 8 post-treatment.Results showed that OVX slightly elevated systemic inflammation but impaired the innate immune response locally at the fracture site, with significantly lower expressions of TNF-α and IL-6 but higher IL-10 expression during the early stage of healing. LMHFV was effective in accelerating the delayed fracture healing in OVX bones by partly restoring the impaired innate immune response at the fracture site, accompanied by promoted progression of macrophage polarisation from M1 (pro-inflammatory) to M2 (anti-inflammatory) phenotype. In conclusion, vibration treatment could positively modulate the impaired innate immune response and promote macrophage polarisation in osteoporotic-fracture healing.

Influence of Low-Magnitude High-Frequency Vibration on Bone Cells and Bone Regeneration

“…Chow et al investigated whether LMHFV influences the early inflammatory response after fracture in osteoporotic rats, because in estrogen-deficient, osteoporotic animal models, the innate immune response after fracture was shown to be altered (Chow et al, 2019). However, there is no clear consensus on whether the inflammation is lower (Chow et al, 2019) or rather increased (Haffner-Luntzer et al, 2017;Fischer et al, 2018). Chow et al (2019) found that LMHFV induced a phenotype switch from pro-inflammatory M1 to pro-regenerative M2 macrophages.…”

“…However, there is no clear consensus on whether the inflammation is lower (Chow et al, 2019) or rather increased (Haffner-Luntzer et al, 2017;Fischer et al, 2018). Chow et al (2019) found that LMHFV induced a phenotype switch from pro-inflammatory M1 to pro-regenerative M2 macrophages. M2 macrophages were previously demonstrated to promote osteogenic differentiation of progenitor cells (Zhang et al, 2017); therefore, this could represent a mechanism by which LMHFV might influence the fracture healing outcome.…”

Inflammatory response in postmenopausal osteoporotic fracture healing

“…Chow et al 38 revealed that TNF-α level at the fracture callus by immunohistochemistry (IHC) was significantly lower compared to SHAM rats at week 1 post-fracture, while the serum level of TNF-α by enzyme-linked immunosorbent assay (ELISA) test was significantly higher in OVX rats at weeks 1 and 2. 38 Wang F et al 39 showed that the serum level of TNF-α by ELISA test was significantly higher in OVX mice at day 5 compared to SHAM mice but no significant difference was found at day 3 post-fracture. The level of TNF-α in serum by ELISA test was also found to be significantly higher in OVX rats at week 5 and week 6 by Zhang et al 40 and Wang J et al, 41 respectively.…”

“…Four out of seven preclinical studies included the proinflammatory cytokine IL-6, which stimulates angiogenesis 42 and MSCs to differentiate towards the osteoblast lineage 43 and modulates osteoblast and osteoclast activities. 44 Chow et al 38 demonstrated that IL-6 level at the fracture callus by IHC was significantly lower in OVX rats compared to SHAM rats at week 1 post-fracture. Significantly lower serum level of IL-6 was detected by ELISA test in OVX rats at week 8.…”

“…Significantly lower serum level of IL-6 was detected by ELISA test in OVX rats at week 8. 38 Fischer et al 34 showed that IL-6 level at the fracture callus by ELISA test was significantly higher compared to SHAM mice on day 3 post-fracture, while no significance was detected in plasma IL-6 level by multiplex cytokine assay at six hours and days 1, 2, and 3 after fracture. Haffner-Luntzer et al 35 reported that IL-6 expression by immunostaining was increased in periosteal callus in OVX mice compared to SHAM mice on day 3 post-fracture.…”