Hyaluronan of Different Molecular Weights Exerts Distinct Therapeutic Effects on Bleomycin-Induced Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a fatal inflammatory lung disorder with few effective treatments. Hyaluronan (HA), a major extracellular matrix component, exhibits diverse biological activities depending on its molecular weight. This study aimed to evaluate the therapeutic potential of HA of various molecular weights in a rat model of ARDS. ARDS was induced in rats via the intratracheal instillation of 5 mg of bleomycin. Seven days later, when ARDS symptoms developed, low (LHA), medium (MHA), high (HHA), and mixed (MIX HA) hyaluronan were intratracheally administered seven times from Days 7 to 28. On Day 7, arterial oxygen saturation (SpO₂) and the partial pressure of oxygen (PaO₂) decreased, carbon dioxide levels increased, the respiratory rate increased, and extensive lung cell infiltration was observed, confirming successful ARDS induction. LHA and MIX HA improved the SpO₂ and PaO₂, and the latter increased lung and alveolar volume, reduced infiltration, and normalized breathing. All HA types attenuated collagen deposition and M1 macrophage activity, while MIX HA enhanced M2 polarization and upregulated MMP-2, MMP-9, and TLR-4. LHA increased VEGF and EGF expression. These findings demonstrate that different-weight HAs provide partial ARDS protection via distinct mechanisms. MIX HA shows synergistic effects, restoring and improving lung structure and function, respectively, representing a promising ARDS therapy.