Determination of protective effect of low molecular weight heparin (LMWH) on lipopolysaccharide (LPS)-induced acute lung injury via complement system inhibition: effect alveolo-capillary membrane

Enoxaparin sodium (ENX) is a low-molecular-weight heparin (LMWH) commonly used after malignancy surgeries, in the prophylaxis of venous thromboembolism associated with organ failure and in severe infections. Besides its effectiveness, it inhibits the complement protein cascade through its proximal steps. For this reason, we preferred to use this agent as a classical and lectin pathway inhibitor in our study. In the lipopolysaccharide (LPS)-induced acute lung injury (ALI) model, we aimed to reveal the role of complement blockade in the pathogenesis by examining the dynamics of changes in the local and systemic levels of some cytokines and complements, as well as their correlation with histopathological changes in tissue. The experiment included 46 male Wistar Albino rats, which were randomly divided into four groups: Sham (SHM), ENX, ENX+LPS, and LPS. The rats were administered 5 mg/kg LPS intratracheally, immediately followed by 2 mg/kg LMWH administered subcutaneously. Six hours after LPS administration, bronchoalveolar lavage fluid (BALF) samples were collected, and sacrification was performed to obtain serum and tissue samples. TNF-α, IL-8, C3, and C2 levels in the samples obtained from BALF and serum were analyzed using the ELISA method. Tissue samples were evaluated for histopathological changes through histochemical (H&E, Masson Trichrome, PAS) and immunohistochemical (TNF-α and CC-16) staining. Significant differences were detected between the groups in local parameters (BALF, histopathology). While no significant difference was observed in systemic parameters (serum), significant correlations were observed between the parameters. In the LPS group, the histopathological damage score was significantly higher compared to the SHM, ENX, and ENX+LPS groups. ENX's prevention of alveolo-capillary membrane damage has also confined inflammation to the interstitial area. While C3 significantly correlated with the damage, no correlation was observed with C2. In the ENX group, TNF-α and IL-8 were more strongly correlated with the damage, whereas in the LPS group, C3 showed a more significant correlation. This situation indicates that although the complement system was partially blocked by ENX administration, our findings indicate that inflammation continued via alternative pathways and TNF-α/IL-8. Accordingly, complement system products have played a more dominant role compared to cellular cytokines. In this context, it is suggested that the cytokine storm, which leads to the poor prognosis of ALI, can be inhibited through the complement system. In conclusion, we suggest that ENX plays a protective role in the alveolo-capillary membrane, we believe that prolonging the duration of the LPS procedure could provide a clearer understanding of its connection to the cytokine storm, the complement system, and pathogenesis.