Toll-Like Receptor 4 Mediates Heme Induced Acute Lung Injury: Preclinical Study of Resatorvid in Sickle Cell Disease

Abstract 2113

Sickle cell disease (SCD) is characterized by multiple exacerbating events that cause intravascular hemolysis. Heme released into the circulation is scavenged by multiple plasma proteins and delivered to the liver for degradation. Our recent data indicate that this process is impaired in SCD resulting in excess protein-free plasma heme (PFPH) that triggers a lethal form of acute lung injury (ALI) in mice. In this study, we tested the hypothesis that toll-like receptor 4 (TLR4) mediates heme-induced ALI. Wild-type and two TLR4 mutant strains (B6.B10ScN-Tlr4^lps-del/JthJ and C3H/HeJ) were intravenously injected with a dose range of ferric heme (0–210 micromoles/kg) and respiratory function monitored using a pulse oximeter. Excess PFPH was associated with reductions in oxygen saturation (SpO₂) and breath rate in the wild-type mice but not in the TLR4 variants. Lungs of heme-treated wild-type mice were congested, edematous, hemorrhagic, and had thickened alveolar walls, while no histological abnormalities were found in the TLR4 variants. All heme-treated wild-type mice succumbed within 2 hours, while all TLR4 variants survived. Transgenic mice expressing exclusively human sickle hemoglobin (SS) were intravenously injected with a small molecule TLR4 inhibitor (resatorvid/TAK-242), or a lipid vehicle prior to induction of lung injury with heme (35 micromoles/kg). TAK-242 preserved lung function in the majority of SS mice that failed to scavenge excess PFPH, while both SpO2 and breath rate deteriorated in vehicle treated mice. The unique response to heme by TAK-242 and vehicle-treated SS mice was supported by histological analysis and survival (TAK-242; 76.9% vehicle; 23.5%, n=13–17; log-rank survival test, p<0.01). We provide the first evidence that the interaction between heme and TLR4 can be pathological, specifically causing a lethal form of ALI. Our data on TAK-242, a phase II drug, offers an attractive option to explore TLR4 inhibition as a novel therapeutic strategy to limit progression of acute chest syndrome.