Homo- and hetero-dimeric sesquiterpenoids with unprecedented skeletons and their co-occurring monomers from Vernonia solanifolia with anti-liver steatotic potential.

BACKGROUND: Sesquiterpenoids show potential as therapeutics against metabolic dysfunction-associated steatotic liver disease (MASLD). Vernonia solanifolia Benth. has been traditionally used to treat abdominal pain and enteritis. However, the anti-steatotic effect of V. solanifolia and its chemical principles have not been illustrated.

METHODS: The structures of new compounds were determined through extensive spectroscopic analysis including 1D/2D nuclear magnetic resonance (NMR), high-resolution electrospray ionization mass spectrometry, ultraviolet and infrared. Especially, the structure of compound 6 was further verified by single crystal X-ray diffraction, and the relative and absolute configurations of compounds 1-5 and 7-9 were resolved with the help from density-functional theory-NMR and time-dependent density-functional theory-electronic circular dichroism calculation. The lipid-lowering activity was evaluated on palmitic acid/oleic acid (P/O)-treated AML12 hepatocytes. The biological evaluation was performed using Nile Red staining, flow cytometry, commercial kits, and Western blotting.

RESULTS: Nine new sesquiterpenoid dimers and their co-occurring monomers (1-9) were identified from the leaves of V. solanifolia. A unique 10/5/6/5/7 pentacyclic ring system is exemplified in compounds 1 and 2. These compounds were constructed from a germacranolide and a 4,5-seco-guaianolide monomer through an unprecedented spiro cyclohexene ring. The first examples of germacrane-guaiane and guaiane-xanthane heterogeneous dimers are shown in compounds 3 and 4, respectively, which also possess a spiro cyclohexene ring linkage. A guaianolide dimer featuring a rare C-13/C-13' linkage is exhibited in compound 5. The plausible biosynthetic pathways for compounds 1 and 5 were proposed. The isolates were tested for their lipid-lowering effect on P/O-treated AML12 hepatocytes, and the results showed that compound 3 significantly reduced lipid content in hepatocytes by triggering the AMP-activated protein kinase/acetyl-CoA carboxylase/peroxisome proliferator-activated receptor γ coactivator-1α signaling pathway.

CONCLUSION: Five homo- and hetero-dimeric sesquiterpenoids with unprecedented skeletons were characterized from V. solanifolia, together with four new co-occurring monomers. It's the first time to report the lipid-lowering activity of sesquiterpenoids from this genus, which might be developed as lead compounds against MASLD.