Characterization of serum levels of testosterone and corticosterone in a blast and amputation rat model of heterotopic ossification

Downregulation of TGF-β1 in fibro-adipogenic progenitors initiates muscle ectopic mineralization

In previous studies, we have demonstrated that stress response-induced high glucocorticoid levels could be the underlying cause of traumatic heterotopic ossification (HO), and we have developed a glucocorticoid-induced ectopic mineralization (EM) mouse model by systemic administration of a high dose of dexamethasone (DEX) to animals with muscle injury induced by cardiotoxin injection. In this model, dystrophic calcification (DC) developed into HO in a cell autonomous manner. However, it is not clear how DC is formed after DEX treatment. Therefore, in this study, we aimed to explore how glucocorticoids initiate muscle EM at a cellular and molecular level. We showed that DEX treatment inhibited inflammatory cell infiltration into injured muscle but inflammatory cytokine production in the muscle was significantly increased, suggesting that other non-inflammatory muscle cell types may regulate the inflammatory response and the muscle repair process. Accompanying this phenotype, transforming growth factor β1 (TGF-β1) expression in fibro-adipogenic progenitors (FAPs) was greatly downregulated. Since TGF-β1 is a strong immune suppressor and FAP's regulatory role has a large impact on muscle repair, we hypothesized that downregulation of TGF-β1 in FAPs after DEX treatment resulted in this hyperinflammatory state and subsequent failed muscle repair and EM formation. To test our hypothesis, we utilized a transgenic mouse model to specifically knockout Tgfb1 gene in PDGFRα-positive FAPs to investigate if the transgenic mice could recapitulate the phenotype that was induced by DEX treatment. Our results showed that the transgenic mice completely phenocopied this hyperinflammatory state and spontaneously developed EM following muscle injury. On the contrary, therapeutics that enhanced TGF-β1 signaling in FAPs inhibited the inflammatory response and attenuated muscle EM. In summary, these results indicate that FAPs-derived TGF-β1 is a key molecule in regulating muscle inflammatory response and subsequent EM, and that glucocorticoids exert their effect via downregulating TGF-β1 in FAPs.

The development of a mouse model to investigate the formation of heterotopic ossification

BACKGROUND

Muscle injury and concomitant bone injury are important drivers to induce heterotopic ossification (HO). However, the related roles of muscle and concomitant bone injury in HO formation are still unclear. This study aims to develop a mouse model through the combination of hindlimb amputation (Am) and cardiotoxin (CTX) injection to investigate the mechanism of HO formation.

METHOD

The mice were randomly divided into Am group (Am of right hindlimb, n = 12), CTX group (CTX injection in the calf muscle of left hindlimb, n = 12) and Am + CTX group (the combination of Am of right hindlimb and CTX injection of left hindlimb, n = 18). MicroCT was used to evaluate the incidence of HO. Histology was used to investigate the progression of HO.

RESULTS

The MicroCT showed that only Am or CTX injection failed to induce HO while the combination of Am and CTX injection successfully induced HO. The incidence of HO was significant in Am + CTX group on day 7 (0% vs 0% vs 83.3%, p = 0.001) and day 14 (0% vs 0% vs 83.3%, p = 0.048). HO was located on the left hindlimb where CTX was injected. Moreover, the bone volume and bone density on day 14 were higher than those on day 7 in Am + CTX group. Histology revealed the evidence of calcification and expression of osteogenic markers in calcification sites in Am + CTX group.

CONCLUSION

In summary, the combination of Am and CTX injection could successfully induce dystrophic calcification/HO, which occurs in the location of muscle injury.

Genetic, biochemical and histopathological evaluations of thymoquinone on male reproduction system damaged by paclitaxel in Wistar rats

This study was aimed to evaluate therapeutic effects of thymoquinone on male reproductive damages induced by paclitaxel. Forty-eight male rats were divided; control, paclitaxel (4 mg/kg), paclitaxel + thymoquinone (1.25, 2.5 and 5 mg/kg) and thymoquinone (1.25, 2.5 and 5 mg/kg). Paclitaxel and thymoquinone were administrated intraperitoneally for 4 and 14 days respectively. Then, the testes were removed for H&E staining, sperm parameters and apoptotic genes expression assessments. Serum levels of nitric oxide, total antioxidant capacity and testosterone were evaluated, and sperm DNA fragmentation was assessed. Paclitaxel significantly (p < .05) increased nitric oxide, decreased total antioxidant capacity and reduced testosterone levels than control group. Sperm motility, viability and count were significantly (p < .05) reduced in paclitaxel group than control. Co-administration of thymoquinone + paclitaxel caused decreased levels of nitric oxide and increased total antioxidant capacity, testosterone levels and reproductive parameters than paclitaxel group significantly (p < .05). Paclitaxel significantly (p < .05) increased caspase-3 and p-53 and decreased Bcl-2 genes expression than control. Sperm DNA fragmentation index was also increased significantly (p < .05) in paclitaxel group than control, and this value was decreased in whole doses of paclitaxel + thymoquinone groups than paclitaxel. Thymoquinone can alleviate the side effects of paclitaxel on the male reproductive system.

Development of a rodent high-energy blast injury model for investigating conditions associated with traumatic amputations

AIMS

In recent conflicts, most injuries to the limbs are due to blasts resulting in a large number of lower limb amputations. These lead to heterotopic ossification (HO), phantom limb pain (PLP), and functional deficit. The mechanism of blast loading produces a combined fracture and amputation. Therefore, to study these conditions, in vivo models that replicate this combined effect are required. The aim of this study is to develop a preclinical model of blast-induced lower limb amputation.

METHODS

Cadaveric Sprague-Dawley rats' left hindlimbs were exposed to blast waves of 7 to 13 bar burst pressures and 7.76 ms to 12.68 ms positive duration using a shock tube. Radiographs and dissection were used to identify the injuries.

RESULTS

Higher burst pressures of 13 and 12 bar caused multiple fractures at the hip, and the right and left limbs. Lowering the pressure to 10 bar eliminated hip fractures; however, the remaining fractures were not isolated to the left limb. Further reducing the pressure to 9 bar resulted in the desired isolated fracture of the left tibia with a dramatic reduction in the fractures to other sites.

CONCLUSION

In this paper, a rodent blast injury model has been developed in the hindlimb of cadaveric rats that combines the blast and fracture in one insult, necessitating amputation. Experimental setup with 9 bar burst pressure and 9.13 ms positive duration created a fracture at the tibia with total reduction in non-targeted fractures, rendering 9 bar burst pressure suitable for translation to a survivable model to investigate blast injury-associated diseases. Cite this article: Bone Joint Res 2021;10(3):166-172.

A review of the biomarkers and in vivo models for the diagnosis and treatment of heterotopic ossification following blast and trauma-induced injuries

Heterotopic ossification (HO) is the process of de novo bone formation in non-osseous tissues. HO can occur following trauma and burns and over 60% of military personnel with blast-associated amputations develop HO. This rate is far higher than in other trauma-induced HO development. This suggests that the blast effect itself is a major contributing factor, but the pathway triggering HO following blast injury specifically is not yet fully identified. Also, because of the difficulty of studying the disease using clinical data, the only sources remain the relevant in vivo models. The aim of this paper is first to review the key biomarkers and signalling pathways identified in trauma and blast induced HO in order to summarize the molecular mechanisms underlying HO development, and second to review the blast injury in vivo models developed. The literature derived from trauma-induced HO suggests that inflammatory cytokines play a key role directing different progenitor cells to transform into an osteogenic class contributing to the development of the disease. This highlights the importance of identifying the downstream biomarkers under specific signalling pathways which might trigger similar stimuli in blast to those of trauma induced formation of ectopic bone in the tissues surrounding the site of the injury. The lack of information in the literature regarding the exact biomarkers leading to blast associated HO is hampering the design of specific therapeutics. The majority of existing blast injury in vivo models do not fully replicate the combat scenario in terms of blast, fracture and amputation; these three usually happen in one insult. Hence, this paper highlights the need to replicate the full effect of the blast in preclinical models to better understand the mechanism of blast induced HO development and to enable the design of a specific therapeutic to supress the formation of ectopic bone.