Fracture Healing in Elderly Mice and the Effect of an Additional Severe Blood Loss: A Radiographic and Biomechanical Murine Study

Age-related exacerbation of lung damage after trauma is associated with increased expression of inflammasome components

Background

Trauma, a significant global cause of mortality and disability, often leads to fractures and hemorrhagic shock, initiating an exaggerated inflammatory response, which harms distant organs, particularly the lungs. Elderly individuals are more vulnerable to immune dysregulation post-trauma, leading to heightened organ damage, infections, and poor health outcomes. This study investigates the role of NF-κB and inflammasomes in lung damage among aged mice post-trauma.

Methods

Twelve male C57BL/6J mice underwent hemorrhagic shock and a femoral fracture (osteotomy) with external fixation (Fx) (trauma/hemorrhage, THFx), while another 12 underwent sham procedures. Mice from young (17-26 weeks) and aged (64-72 weeks) groups (n=6) were included. After 24h, lung injury was assessed by hematoxylin-eosin staining, prosurfactant protein C (SPC) levels, HMGB1, and Muc5ac qRT-PCR. Gene expression of Nlrp3 and Il-1β, and protein levels of IL-6 and IL-1β in lung tissue and bronchoalveolar lavage fluid were determined. Levels of lung-infiltrating polymorphonuclear leukocytes (PMNL) and activated caspase-3 expression to assess apoptosis, as well as NLRP3, ASC, and Gasdermin D (GSDMD) to assess the expression of inflammasome components were analyzed via immunostaining. To investigate the role of NF-κB signaling, protein expression of phosphorylated and non-phosphorylated p50 were determined by western blot.

Results

Muc5ac, and SPC as lung protective proteins, significantly declined in THFx versus sham. THFx-aged exhibited significantly lower SPC and higher HMGB1 levels versus THFx-young. THFx significantly increased activated caspase-3 versus both sham groups, and THFx-aged had significantly more caspase-3 positive cells versus THFx-young. IL-6 significantly increased in both sham and THFx-aged groups versus corresponding young groups. THFx significantly enhanced PMNL in both groups versus corresponding sham groups. This increase was further heightened in THFx-aged versus THFx-young. Expression of p50 and phosphorylated p50 increased in all aged groups, and THFx-induced p50 phosphorylation significantly increased in THFx-aged versus THFx-young. THFx increased the expression of inflammasome markers IL-1β, NLRP3, ASC and GSDMD versus sham, and aging further amplified these changes significantly.

Conclusion

This study's findings suggest that the aging process exacerbates the excessive inflammatory response and damage to the lung following trauma. The underlying mechanisms are associated with enhanced activation of NF-κB and increased expression of inflammasome components.

Advances in Fracture Healing Research

Despite a constant refinement of surgical techniques and bone fixation methods, up to 15% of fractures result in impaired healing or even develop a non-union [...].

Impact of age on liver damage, inflammation, and molecular signaling pathways in response to femoral fracture and hemorrhage

Background

Trauma causes disability and mortality globally, leading to fractures and hemorrhagic shock. This can trigger an irregular inflammatory response that damages remote organs, including liver. Aging increases the susceptibility to dysregulated immune responses following trauma, raising the risk of organ damage, infections, and higher morbidity and mortality in elderly patients. This study investigates how aging affects liver inflammation and damage post-trauma.

Methods

24 male C57BL/6J mice were randomly divided into four groups. Twelve young (17-26 weeks) and 12 aged (64-72 weeks) mice were included. Mice further underwent either hemorrhagic shock (trauma/hemorrhage, TH), and femoral fracture (osteotomy) with external fixation (Fx) (THFx, n=6) or sham procedures (n=6). After 24 hours, mice were sacrificed. Liver injury and apoptosis were evaluated using hematoxylin-eosin staining and activated caspase-3 immunostaining. CXCL1 and infiltrating polymorphonuclear leukocytes (PMNL) in the liver were assessed by immunostaining, and concentrations of CXCL1, TNF, IL-1β, and IL-10 in the liver tissue were determined by ELISA. Gene expression of Tnf, Cxcl1, Il-1β, and Cxcl2 in the liver tissue was determined by qRT-PCR. Finally, western blot was used to determine protein expression levels of IκBα, Akt, and their phosphorylated forms.

Results

THFx caused liver damage and increased presence of active caspase-3-positive cells compared to the corresponding sham group. THFx aged group had more severe liver injury than the young group. CXCL1 and PMNL levels were significantly higher in both aged groups, and THFx caused a greater increase in CXCL and PMNL levels in aged compared to the young group. Pro-inflammatory TNF and IL-1β levels were elevated in aged groups, further intensified by THFx. Anti-inflammatory IL-10 levels were lower in aged groups. Tnf and Cxcl1 gene expression was enhanced in the aged sham group. Phosphorylation ratio of IκBα was significantly increased in the aged sham group versus young sham group. THFx-induced IκBα phosphorylation in the young group was significantly reduced in the aged THFx group. Akt phosphorylation was significantly reduced in the THFx aged group compared to the THFx young group.

Conclusion

The findings indicate that aging may lead to increased vulnerability to liver injury and inflammation following trauma due to dysregulated immune responses.