Ganoderic acid A alleviates acute lung injury in mice by inhibiting ferroptosis via upregulating NLRP3

Technical Summary: Ganoderic Acid A Alleviates Acute Lung Injury via NLRP3-Mediated Ferroptosis Inhibition

Problem Statement
Acute lung injury (ALI) is a severe clinical condition with a mortality rate of 30–60%, characterized by diffuse alveolar damage, hypoxemia, and uncontrolled pulmonary inflammation. Current clinical treatments lack targeted therapies, necessitating the identification of new therapeutic agents. Recent evidence suggests that ferroptosis—an iron-dependent form of regulated cell death driven by lipid peroxidation and the failure of antioxidant defenses (specifically the GSH-GPX4 system)—plays a critical role in ALI pathogenesis. While Ganoderma lucidum and its active component, Ganoderic acid A (GAA), are known for anti-inflammatory and antioxidant properties, their specific mechanism regarding ferroptosis in ALI and the role of the NLRP3 inflammasome in this context remain unclear.

Methodology
The study employed a dual approach using in vitro and in vivo models to investigate the therapeutic potential of GAA:

• In Vitro Models: Human bronchial epithelial cells (16HBE) were treated with lipopolysaccharide (LPS) to induce inflammation and ferroptosis. Cells were pre-treated with varying concentrations of GAA.
• Genetic Manipulation: A CRISPR/Cas9-based approach was used to construct an NLRP3-knockout (NLRP3-KO) 16HBE cell line to verify the dependency of GAA's effects on NLRP3.
• In Vivo Models: An LPS-induced ALI mouse model (C57BL/6) was established. Mice were divided into five groups: Control, LPS, LPS+GAA, LPS+MCC950 (NLRP3 inhibitor), and LPS+GAA+MCC950. GAA was administered intragastrically, and LPS was injected intratracheally to induce injury.
• Assays:
  • Cell Viability & ROS: CCK-8 assays and flow cytometry for ROS detection.
  • Ferroptosis Markers: Quantification of Fe²⁺, GSH, MDA, and GPX4 activity using commercial kits.
  • Inflammatory Cytokines: ELISA for TNF-α and IL-1β.
  • Molecular Analysis: qRT-PCR and Western blotting to assess mRNA and protein levels of Nrf2, GPX4, SLC7A11, NLRP3, TNF-α, and IL-1β.
  • Histology: H&E staining for lung injury scoring and immunohistochemistry (IHC) for GPX4 and NLRP3 expression.
  • Pharmacological Intervention: The specific NLRP3 inhibitor MCC950 was used in vivo to block NLRP3 activity and observe the impact on GAA's efficacy.

Key Results

1. LPS Induces Ferroptosis: LPS treatment in 16HBE cells and mouse lung tissue significantly increased ROS, Fe²⁺, and MDA levels while decreasing GSH content and GPX4 activity. This was accompanied by the downregulation of the Nrf2/GPX4/SLC7A11 pathway and upregulation of inflammatory cytokines.
2. GAA Protects Against Ferroptosis and Inflammation: GAA treatment significantly reversed LPS-induced cell death, restored GSH levels, reduced MDA and ROS, and increased GPX4 activity. It also suppressed the release of TNF-α and IL-1β.
3. Ferroptosis Mediates Inflammation: Treatment with the ferroptosis inhibitor Liproxstatin-1 (Lip-1) mimicked the protective effects of GAA, confirming that ferroptosis is a key driver of LPS-induced inflammation in this model.
4. Paradoxical Role of NLRP3: Contrary to the general understanding that NLRP3 inhibition reduces inflammation, GAA treatment upregulated NLRP3 expression (both mRNA and protein).
5. NLRP3 Dependency: In NLRP3-KO cells, the protective effects of GAA were significantly compromised. GAA failed to upregulate GPX4, Nrf2, and SLC7A11 or suppress inflammatory cytokines in the absence of NLRP3.
6. In Vivo Confirmation: In mice, GAA alleviated lung tissue damage, reduced inflammatory infiltration, and restored ferroptosis markers. Crucially, the administration of the NLRP3 inhibitor MCC950 abolished the protective effects of GAA, confirming that GAA requires NLRP3 upregulation to inhibit ferroptosis and alleviate ALI.

Key Contributions

• Mechanistic Insight: The study identifies a novel mechanism where GAA alleviates ALI by inhibiting ferroptosis through the upregulation of the NLRP3 inflammasome, rather than its inhibition.
• Pathway Elucidation: It establishes a specific signaling axis where GAA activates NLRP3, which subsequently activates the Nrf2/GPX4/SLC7A11 pathway to combat oxidative stress and lipid peroxidation.
• Therapeutic Candidate: It validates GAA as a promising therapeutic candidate for ALI, offering a potential alternative to current treatments with high mortality rates.

Significance and Claims
The authors claim that this study provides innovative evidence that GAA exerts anti-inflammatory and anti-ferroptotic effects in ALI by activating the NLRP3 inflammasome. This finding challenges the conventional view that NLRP3 activation is solely detrimental in inflammatory diseases, suggesting a context-dependent protective role where NLRP3 activation facilitates the clearance of damage and inhibits ferroptosis. The study concludes that GAA is a viable candidate for ALI treatment, though the precise molecular mechanism linking NLRP3 activation to ferroptosis inhibition requires further investigation. The authors emphasize that their findings highlight a complex crosstalk between Nrf2 and NLRP3 in the context of ferroptosis.