MALP-2 (Helmholtz Zentrum fur Infektionsforschung)

Tendon injuries are accounted for up to 50% of musculoskeletal injuries and often result in poor outcomes. Inflammation is a major hallmark of tendon regeneration. Therefore, we analyzed in this study whether the topical application of the pro-inflammatory mediator macrophage-activating lipoprotein (MALP)-2 improves the healing of partial tendon injuries. C57BL/6 mice underwent a partial tenotomy of the flexor digitorum longus tendon of the left hind limb, which was treated with a solution containing either 0.5 µg MALP-2 or vehicle (control). Repetitive gait analyses were performed prior to the surgical intervention as well as postoperatively on days 1, 3, 7, 14 and 36. The structural stability of the tendons was biomechanically tested on day 7 and 36. In addition, Western blot analyses were performed on isolated tendons that were treated in vitro with MALP-2 or vehicle. In both groups, partial tenotomy resulted in a pathological gait pattern during the initial postoperative phase. On day 7, the gait pattern normalized in vehicle-treated animals, but not in MALP-2-treated mice. Moreover, the tendons of MALP-2-treated mice exhibited a significantly reduced biomechanical stiffness after 7 and 36 days when compared to controls. Western blot analyses revealed a significantly higher expression of heme oxygenase (HO)-1 and lower expression of cyclin D in MALP-2-treated tendons. These findings indicate that MALP-2 delays the healing of injured tendons most likely due to increased intracellular stress and suppressed cell proliferation in this naturally bradytrophic tissue. Hence, the application of MALP-2 cannot be recommended for the treatment of tendon injuries.

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.