Geriatric Polytrauma-Cardiovascular and Immunologic Response in a Murine Two-Hit Model of Trauma

Cardiac alterations following experimental hip fracture - inflammaging as independent risk factor

Background

Cardiac injuries following trauma are associated with a worse clinical outcome. So-called trauma-induced secondary cardiac injuries have been recently described after experimental long bone fracture even in absence of direct heart damage. With the progressive aging of our society, the number of elderly trauma victims rises and therefore the incidence of hip fractures increases. Hip fractures were previously shown to be associated with adverse cardiac events in elderly individuals, which have mainly been attributed to pre-conditioned cardiac diseases. The aim of the present study was to investigate the effect of hip fractures on the heart in healthy young and middle-aged mice.

Materials and Methods

Young (12-week-old) and middle-aged (52-week-old) female C57BL/6 mice either received an intramedullary stabilized proximal femur fracture or sham treatment. The observation time points included 6 and 24 h. Systemic levels of pro-inflammatory mediators as well as local inflammation and alterations in myocardial structure, metabolism and calcium homeostasis in left ventricular tissue was analyzed following hip fracture by multiplex analysis, RT-qPCR and immunohistochemistry.

Results

After hip fracture young and middle-aged mice showed increased systemic IL-6 and KC levels, which were significantly elevated in the middle-aged animals. Furthermore, the middle-aged mice showed enhanced myocardial expression of HMGB1, TLR2/4, TNF, IL1β and NLRP3 as well as considerable alterations in the myocardial expression of glucose- and fatty acid transporters (HFABP, GLUT4), calcium homeostasis proteins (SERCA) and cardiac structure proteins (desmin, troponin I) compared to the young animals following hip fracture.

Conclusion

Young and middle-aged mice showed local myocardial alterations, which might predispose for the development of secondary cardiac injury following hip fracture. Age and the age-associated phenomenon of ‘inflammaging’ seemed to be an independent risk factor aggravating and accelerating cardiac alterations following hip fracture.

The Influence of Macrophage-Activating Lipopeptide 2 (MALP-2) on Local and Systemic Inflammatory Response in a Murine Two-Hit Model of Hemorrhagic Shock and Subsequent Sepsis

Pulmonary complications after severe trauma and sepsis remain to be the main cause for adverse outcome. MALP-2 has been described to exert beneficial effects on organ damage and the further course after isolated trauma and sepsis. However, the impact of MALP-2 on a clinically realistic two-hit scenario of trauma and subsequent sepsis remains unknown. We, therefore, investigated if the systemic inflammatory response and pulmonary immune response and damage are beneficially modulated by MALP-2 in a murine two-hit model. Blood pressure-controlled trauma-hemorrhage (TH) and cecal ligation and puncture (CLP) were induced in C57/BL6 mice. Mice were divided into 2 control groups (control 1: TH without CLP; control 2: TH and CLP) and 3 experimental groups treated with MALP-2 at different time points (ETH, end of TH; ECLP, end of CLP; and 6CLP 6 h after CLP). Survival rates were assessed over the observation period of 168 h after the induction of TH. Concentrations of plasma inflammatory cytokines and chemokines (TNF-α, IL-6, MIP-1α, IFN-γ, and IL-10) were assessed, and bacterial clearance of the lungs was determined. Furthermore, pulmonary MPO activity assay to evaluate the infiltration of polymorphonuclear neutrophils (PMN) and histological evaluation were performed. Survival rates were evaluated. Compared with control group 1, the level of TNF-α in the ECLP group showed a significant increase (ECLP, 2.27 pg./ml ± 1.39 vs. control 1: 0.16 pg./ml ± 0.11, p = 0.021). In contrast, levels of IFN-γ were significantly reduced in groups ETH and 6CLP compared with control group 1 (control 1: 8.92 pg./ml ± 4.38 vs. ETH: 1.77 pg./ml ± 4.34, p = 0.026 resp. vs. 6CLP: 1.83 pg./ml ± 4.49, p = 0.014). While systemic concentrations of inflammatory mediators were not affected by MALP-2 treatment, the lung tissue presented with significant alterations. Reduced MPO activity was lowest in group ECLP (ECLP 11,196.77 ± 547.81 vs. ETH 12,773.94 ± 1011.76; p = 0.023 resp. vs. 6CLP 13,155.19 ± 423.99, p = 0.016) in experimental groups. Also, histological damage after MALP-2 application was lowest in ECLP animals (ECLP 0.50 ± 0.08 vs. ETH 0.71 ± 0.05, p = 0.034 resp. vs. 6CLP 0.64 ± 0.08, p = 0.021). Furthermore, MALP-2 treatment was associated with a trend towards improved survival in the ECLP group (ECLP 83.3% vs. ETH 66.7 and 6CLP 58.3%, p > 0.05). Based on our results, MALP-2 might have beneficial effects on the clinical course after hemorrhage and sepsis by reducing pulmonary damage and PMN infiltration. This might also affect survival. According to our data, MALP-2 should be given at the earliest possible time point after the onset of sepsis. However, the optimal dosage and confirmation of our results in larger cohorts need to be the focus of further research.