Context-dependent Activities of Mitrephorone Link Lipid Redirection, Anti-inflammatory Action, and Ferroptosis...

Liver diseases are driven by aberrant metabolism, involve necrotic cell death, particularly ferroptosis, and progress with low-grade inflammation. Rationally designed small molecules that simultaneously target these processes are lacking. Here, we investigated mitrephorone B, an ent-trachylobane diterpenoid from the Bornean shrub Mitrephora glabra, accessible by total synthesis, as a potential hepatoprotective agent in vitro.

We tested mitrephorone B and four derivatives in human HepaRG hepatocytes, primary peripheral blood mononuclear cells (PBMCs), polarized monocyte-derived macrophages, and lipid-driven in vitro disease models. Quantitative lipidomics, cell viability and membrane integrity assays, overexpression studies, immunodetection, molecular probes, expression analysis, and cell-free activity assays were used to assess effects on programmed cell death, lipid mediator biosynthesis, cytokine expression, and alternations of the cellular lipidome.

Mitrephorone B reduced pro-inflammatory cytokine expression in PBMCs independently of nuclear factor-κB signaling, inhibited phospholipid peroxidation, and suppressed ferroptosis in hepatocytes, associated with altered triglyceride fatty acid composition in PBMCs. It lowered cholesteryl ester levels in PBMCs and cocultures with hepatocytes and suppressed pro-inflammatory leukotriene production by antagonizing 5-lipoxygenase-activating protein. Over time, mitrephorone B limited the capacity of PBMCs to generate pro-inflammatory lipid mediators while modestly promoting the formation of epoxyeicosatrienoic acids, known to counteract inflammation and cell death. In an immunocompetent in vitro model of lipid-induced hepatotoxicity, it improved metabolic activity and reduced triglyceride content. Structurally, the 9-oxo group was essential for effective 5-lipoxygenase-activating protein antagonism, while the 10-oxo group contributed to cytokine suppression. Anti-ferroptotic activity was largely preserved across derivatives, whereas small structural modifications fine-tuned lipidome effects.

Mitrephorone B displays a unique activity profile, redirecting neutral lipid accumulation, suppressing ferroptosis, and inhibiting inflammation. These properties highlight its potential as a candidate lead structure for treating necroinflammatory liver diseases associated with aberrant lipid metabolism, including metabolic dysfunction-associated steatotic liver disease, steatohepatitis, cirrhosis, and hepatocellular carcinoma.