Inflachromene attenuates monocrotaline-induced pulmonary arterial hypertension by suppressing the HMGB1-TLR4/RAGE-NF-κB signaling pathway.

Pulmonary arterial hypertension (PAH) is a debilitating and fatal cardiovascular disorder marked by progressive deterioration of pulmonary arterial function, mainly due to structural remodeling. This pathological remodeling is predominantly driven by prolonged inflammatory activity together with dysregulated proliferation of pulmonary arterial smooth muscle cells (PASMCs). Inflachromene (ICM) is a recently characterized small molecule with targeted inhibitory effects on high-mobility group box 1 (HMGB1), demonstrating anti-inflammatory and antiproliferative activities. However, how ICM affects remodeling of the pulmonary vasculature during PAH progression has yet to be explored. In this study, we examined whether ICM could suppress PAH-associated pulmonary vascular remodeling and further explored the potential mechanisms contributing to its action. We first investigated ICM's capacity to inhibit HMGB1 in PASMCs under hypoxic exposure. Subsequently, 36 Sprague-Dawley rats (male; 4-6 weeks of age) were randomly assigned to a control group (n = 10), an MCT group (n = 13), and an MCT + ICM group (n = 13). The PAH model was established by a single intraperitoneal injection of monocrotaline (MCT, 60 mg/kg). Rats in the MCT + ICM group received ICM (1.40 mg/kg/day) for 28 consecutive days starting on the first day of model induction. At the end of the experiment, mean pulmonary arterial pressure (mPAP) and right ventricular systolic pressure (RVSP) were measured by right heart catheterization under isoflurane anesthesia. In vitro, ICM significantly reduced hypoxia-induced overexpression of HMGB1 in PASMCs. In vivo, ICM treatment improved the overall physical condition of the rats, with survival rates of 53.8% in the MCT group and 84.6% in the MCT + ICM group. Animals that died were excluded from all subsequent analyses. The data showed that ICM attenuated the MCT-induced increases in mPAP and RVSP, while also reducing pulmonary arteriole wall thickness and collagen volume fraction. Furthermore, following ICM intervention, a marked suppression of α-smooth muscle actin (α-SMA) and proliferation markers (Ki-67, PCNA, and c-Myc) was observed in the pulmonary arteries. ICM also led to reduced inflammatory cytokine levels in lung tissue and peripheral circulation, specifically IL-1β, IL-6, TNF-α, and TGF-β1. Further mechanistic studies revealed that ICM downregulated TLR4, RAGE, and phosphorylated p65 (p-p65) protein levels by inhibiting HMGB1 release in lung tissue. Collectively, this study is the first to demonstrate that ICM, as a small-molecule agent with the potential to inhibit pulmonary vascular remodeling in PAH, exerts protective effects by suppressing the HMGB1-TLR4/RAGE-NF-κB signaling pathway and the inflammation it mediates.